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TEXT-BOOK 


OF 


ANATOMY 


EDITED  BY 


D.  J.  CUNNINGHAM,  F.R.S. 

M.D.    fEDIN.    ET    DUEL.),   D.SC,    LL.D.    (gLASG.    ET   ST.    AND.),    D.C.L.    (OXON.) 
PROFESSOR    OF    ANATOMY,    UNIVERSITY    OF    EDINBURGH 


ILLUSTRATED    WITH    936    WOOD    ENGRAVINGS    FROM    ORIGINAL 
DRAWINGS,    406    OF  WHICH    ARE    PRINTED    IN    COLORS 


THIRD  EDITION 


NEW  YORK 
WILLIAM  WOOD  AND  COMPANY 

MDCCCCIX 


TO 

5ir  SHilUam  ^Turner,  M,€M. 

K.R.S.,     M.B.,     LL.D.,     D.C.L.,     D.SC, 

IX    RECOGNITION    OF 

HIS     EMINENCE     AS     AN     ANATOMIST 

AND     HIS     INFLUENCE     AS     A     TEACHER 

THIS    VOLUME 

IS     DEDICATED 

BY     THOSE     OF     HIS     FORMER     PUPILS     AND     ASSISTANTS 

WHO     HAVE     CONTRIBUTED 

TO     ITS     PAGES 


PRINTED    FOR    HEXRY   FKOWDE,    OXFORD    CXIVERSITV    PRESS,    AND   HODDER   &    STOCGHTON, 
WARWICK    SQUARE,    E.C.,    BY    R.    &    R.    CLARK,    LTD.,    EDINBURGH. 


All  rights  resen-ed 


PREFACE    TO    THE    THIRD    EDITION. 


The  very  gratifying  reception  which  this  work  continues  to  receive,  not  only  in  this 
country  but  abroad,  has  necessitated  the  production  of  a  third  edition. 

Tlie  co-operation  of  the  Authors  of  the  sections  on  the  Bony  Skeleton  and  the 
Muscular  System  has  therefore  been  obtained,  and  the  Editor  has  received  every 
assistance  in  carrying  out  all  the  suggestions  made  by  him  with  the  view  of  im- 
proving the  work  in  many  ways. 

The  section  on  Osteology  has  been  mainly  re-written,  and  many  useful  illustra- 
tions have  been  added  by  the  Author,  while  the  addition  of  illustrations  in  several 
colours  throughout  the  section  will,  it  is  hoped,  largely  add  to  its  usefulness  to 
students.  The  interesting  notes  on  the  architecture  of  Bone,  the  variations  in  the 
Skeleton,  Craniology,  and  the  Morphology  of  the  Limbs,  are  now  brought  together 
in  appendices  to  the  section,  and  it  is  hoped  that  this  will  prove  a  convenience  to 
the  student. 

The  section  on  the  Muscular  System  has  been  very  largely  altered,  the  text 
has  been  freely  revised,  but  the  chief  change  will  be  found  in  the  illustrations. 

The  greater  number  of  the  old  figures  have  now  been  replaced  with  illustra- 
tions of  new  dissections  modelled  on  a  different  plan.  The  majority  of  these  new 
illustrations  have  been  prepared  in  the  Anatomical  Department  of  the  University 
of  Edinburgh,  under  my  own  personal  supervision,  but  those  of  the  lower  limbs, 
head,  and  neck,  have  been  carried  out  under  the  supervision  of  the  author. 
Professor  A.  M.  Paterson.  In  these  illustrations  the  Editor  has  again  had  the 
advantage  of  Mr.  J.  T.  Murray's  assistance,  and  it  will,  doubtless,  be  admitted  that 
he  shows  all  his  accustomed  vigour  and  power  of  anatomical  delineation  in  carry- 
ing out  the  work.  The  new  figures  represent  a  great  deal  of  labour  on  every  side 
and  the  Editor  trusts  that  the  result  will  justify  him. 

The  question  of  anatomical  terminology  would  appear  at  the  present  time  to  be 
a  difficult  one.  Of  late  strong  attempts  have  been  made  to  discard  the  old  British 
terminology,  and  to  adopt,  in  its  entirety,  the  B.N.A.  nomenclature.  It  will  be 
remembered  that  the  Editor  was  one  of  the  original  members  of  the  B.N.A.  Com- 
mission, and  has  naturally  been  desirous  from  the  first  to  replace  the  old  by  the 
new  nomenclature  where  possible.  In  this  connection  he  feels  compelled  to 
emphasise  the  fact  that  in  the  first  edition  of  this  work  the  B.N.A.  terms  were 
introduced,  in  all  cases  of  difference,  in  brackets ;  thus  the  present  work  has  been 
from  the  beginning  the  first  Text-book  written  in  the  English  language  which 
recognised  the  Basle  nomenclature. 

At  the  same  time,  it  is  the  Editor's  deliberate  opinion  that  no  terminology, 
however  superior  or  desirable  it  may  be,  can  ever  be  forced  either  on  teachers  or 
pupils,  and  that  it  can  only  be  a  matter  of  gradual  growth.     Again  it  cannot  be 


PEEFACE.  V 

too  fully  recognised  that  the  labours  of  the  Basle  Commission  were  conducted,  not 
to  ensure  the  adoption  of  a  Latin  terminology  in  every  country,  but  rather  a 
uniform  system  of  nomenclature,  and  the  abolition  of  many  different  terms. 

As  a  result  of  long  thought  and  some  experience,  the  Editor  has  been  forced  to 
regard  the  adoption  of  a  rigid  framework  of  terminology  as  by  no  means  an  un- 
qualified advantage,  and  he  cannot  doubt  for  a  moment  that,  at  any  rate  in  those 
departments  of  anatomy  where  growth  of  knowledge  is  more  amply  evident,  any 
such  limitation  may  act  even  as  a  stumbling-block. 

So  far  as  the  Editor  is  aware  the  B.N. A.  nomenclature  has  not  as  yet  been 
entirely  adopted  among  the  English-speaking  races.  He  recognises,  however,  that 
more  may  be  done  to  assure  its  adoption,  without  imposing  undue  burdens  on  the 
student  of  the  present  day.  For  these  reasons,  in  the  re-written  sections  which 
comprise  the  ground -work  of  the  subject,  all  old  nomenclature  which  could  be 
altered  without  undue  confusion  has  been  so  arranged  that  in  most  cases,  while 
the  older  terminology  has  been  given,  all  alternative  nomenclature  has  been 
abolished.  In  many  instances  (as,  for  example,  the  bones  of  the  Carpus  or  Tarsus) 
the  step  has  been  boldly  taken.  Eeferences  have  been  given  as  footnotes  in  the  case 
of  Vessels,  Nerves,  or  other  Structures  where  alteration  in  name  occurs. 

In  relative  terms  the  terms  "  Medial "  and  "  Lateral "  have  been  employed 
throughout  instead  of  "  Inner  "  and  "  Outer." 

Through  illness  the  Editor  has  not  been  able  to  undertake  the  full  work  of 
revision,  and  he  owes  a  deep  debt  of  gratitude  for  the  help  given  him  by  Mr.  J. 
Keogh  Murphy,  F.E.C.S.,  throughout  the  work. 

At  his  suggestion  the  Publishers  have  prepared  a  Glossary  of  the  terms  adopted 
by  the  Basle  Commission  to  show  the  student  at  a  glance  the  essential  differences. 
For  the  whole  he  would  wish  to  acknowledge  the  indebtedness  of  anatomists 
throughout  the  world  to  Professor  His  and  his  colleagues  on  the  Commission. 

A  new  and  exhaustive  Index  has  been  prepared  for  the  present  edition  by  the 
Editor's  own  demonstrators  in  the  University  of  Edinburgh,  to  whom  he  tenders 
his  grateful  thanks. 


18  Grosvenor  Crescent,  Edinburgh, 
June  1909. 


(This  edition  of  the  Text-book  is  the  last  work  that  Professor  Cunningham 
undertook ;  in  spite  of  failing  health  he  laboured  up  to  the  end  at  the  plan  and 
revision  of  the  new  edition,  and  the  above  Preface  was  drafted  a  few  days  only 
before  he  died  on  23rd  June.) 


PREFACE    TO    THE    SECOND    EDITION. 


The  gratifying  reception  given  to  the  Text-look  of  Anatomy,  not  only  in  this 
country  but  also  in  America,  has  rendered  it  necessary  to  prepare  a  new  edition. 
In  carrying  out  this  work  the  whole  book  has  been  carefully  revised,  and  a  large 
number  of  new  illustrations  have  been  added. 

The  sections  in  which  the  chief  changes  and  additions  have  been  made  are 
those  upon  Embryology,  the  Joints,  the  Muscles,  the  Brain  and  Spinal  Cord,  the 
Genito- Urinary  Organs,  the  Lymphatics,  and  Applied  Anatomy.  By  pruning 
down  in  various  directions,  it  has  been  found  possible  to  incorporate  a  considerable 
amount  of  new  matter  in  these  and  other  sections  without  materially  increasing 
the  bulk  of  the  book. 

The  lamented  death  of  Professor  Birmingham  was  felt  by  all  the  contributors 
to  be  not  only  a  personal  loss,  but  one  which  materially  affected  an  important 
section  of  the  book.  Although  in  very  bad  health,  Professor  Birmingham  was 
desirous  to  undertake  his  share  of  the  work,  and  he  had  the  sheets  on  the 
Digestive  System  in  his  possession  for  this  purpose  when  he  died.  There  was 
probably  no  part  of  the  book  which  required  less  revision  than  his,  and  the 
Editor  has  taken  upon  himself  the  duty  of  making  the  alterations  which  seemed 
essential.  In  doing  this  he  has  been  careful  to  avoid  unnecessary  changes  and  to 
preserve  throughout  the  original  character  of  the  article. 

In  the  section  upon  the  Muscular  System,  a  series  of  illustrations  has  been 
added  in  which  the  areas  of  muscle  attachment  are  delineated  upon  the  bones.  Eor 
the  preparation  of  the  specimens,  and  for  assistance  in  the  mapping  out  of  these 
areas,  the  Editor  is  indebted  to  Dr.  E.  B.  Jamieson.  Those  who  have  attempted 
work  of  this  kind  will  appreciate  the  amount  of  labour  and  judgment  entailed,  as 
it  is  only  by  taking  the  average  condition  in  many  specimens,  and  by  the  close 
study  of  the  bones  selected  for  the  delineations,  that  a  sufficiently  accurate 
result  can  be  attained. 

With  the  exception  of  the  figures  which  have  been  added  to  the  sections  of 
the  book  dealing  with  Embryology,  Osteology,  and  the  Genito-Urinary  Organs, 
the  many  new  illustrations  which  appear  in  this  edition  have  been  prepared  in 
the  Anatomical  Department  of  the  University  of  Edinburgh.  In  carrying  out  this 
work,  the  Editor  has  again  had  the  good  fortune  to  secure  the  co-operation  of  Mr. 
J.  T.  Murray,  an  artist  whose  ability  in  the  rendering  of  anatomical  subjects  is 
recognised  on  all  hands.  Wherever  it  was  felt  that  colour  would  increase  the 
artistic  effect  or  the  general  usefulness  of  an  illustration,  it  has  been  freely 
employed,  both  in  the  case  of  the  old  and  of  the  new  figures. 

The  Editor  cannot  conclude  this  preface  to  the  second  edition  of  the  Text-book 
without  expressing  his  grateful  acknowledgment  of  the  assistance  which  has  been 
so  freely  extended  to  him  by  his  fellow-contributors  at  every  stage  of  the  work. 
He  has  also  to  thank  many  readers  of  the  first  edition  for  calling  his  attention  to 
typographical  errors  and  other  imperfections  which  had  escaped  his  notice  in 
passing  the  sheets  through  the  press. 

18  Grosvenor  Crescent,  Edinburgh, 
August  1905. 

vi 


PREFACE  TO  THE  FIRST  EDITION. 


The  form  which  this  book  has  taken  expresses  the  desire  of  those  who  have 
contributed  the  various  sections  to  produce  something  which  they  might  dedicate 
to  their  former  teacher  and  master,  Sir  William  Turner.  With  one  exception, 
all  the  contributors  have  studied  under  Sir  William  Turner,  and  all  but  two 
have  for  longer  or  shorter  periods  acted  as  his  Assistants.  Bound  together  by  this 
common  tie,  and  animated  by  affection  and  reverence  for  their  great  master,  they 
have  sought  to  produce  a  book  worthy  of  him  whose  teaching  it  so  largely  reflects, 
and  if  this  object  has  not  been  attained  it  is  not  for  want  of  will,  but  of  power,  on 
the  part  of  the  writers. 

In  the  preparation  of  a  work  such  as  this  it  is  no  easy  matter  to  prevent  over- 
lapping of  the  different  articles  and  to  keep  the  various  sections  in  harmony  with 
each  other.  Yet  in  this  direction  it  is  believed  that  a  fair  amount  of  success  has 
been  attained.  Differences  of  opinion  on  particular  points  were  bound  to  arise, 
but  the  Editor  found  in  those  concerned  the  greatest  readiness  to  come  to  a  mutual 
understanding,  and  he  is  deeply  grateful  to  his  colleagues  for  the  manner  in  which 
they  endeavoured  to  lighten  his  work  and  assist  him  in  his  task.  Of  course  when 
totally  different  views  were  held  by  two  authors  on  a  matter  which  had  to  be  dealt 
with  in  two  sections,  no  serious  attempt  was  made  to  urge  these  writers  to  qualify 
their  statements  so  as  to  produce  an  apparent  agreement.  It  was  felt  that  if  this 
were  done  the  individuality  of  the  author,  which  forms  a  characteristic  feature  of 
each  article  as  it  stands,  would  thereby  be  damaged ;  and  further,  it  was  believed 
that  the  same  question  discussed  from  two  different  points  of  view  could  not  fail 
to  be  of  advantage  to  the  reader.  At  the  same  time  it  is  right  to  state  that  the 
places  in  which  a  divergence  of  opinion  appears  are  very  few,  and  taking  into 
account  that  nine  writers  have  co-operated  with  the  Editor,  a  remarkable  degree 
of  harmony  in  the  treatment  of  the  different  sections  has  been  obtained. 

The  recent  introduction  of  Formalin  as  a  hardening  and  preserving  reagent 
imposed  an  especially  arduous  duty  upon  those  writers  who  had  undertaken  the 
chapters  dealing  with  the  thoracic  and  abdominal  viscera.  The  possibilities  for 
establishing  a  more  accurate  topography  and  of  improving  our  conception  of  the 
forms  assumed  by  the  viscera  under  different  conditions  have  by  this  means  been 
greatly  extended  ;  and  in  preparing  the  sections  which  treat  of  these  organs  the 
writers  have  taken  full  advantage  of  the  new  method.  Much,  therefore,  which 
appears  in  this  book  on  the  topographical  relations  of  the  viscera  departs  con- 
siderably from  the  older  and  more  conventional  descriptions  hitherto  in  vogue. 

The  arrangement  of  the  matter  treated  in  the  following  pages  is  very  much 
the  same  as  that  adopted  in  the  various  courses  of  lectures  delivered  in  the  schools 
from  which  the  different  sections  of  the  work  have  emanated.      The  first  chapter  is 

vii 


viii  PEEFACE. 

devoted  to  the  general  principles  and  elementary  facts  of  Embryology.  Then 
follow,  in  an  order  best  suited  for  the  student,  the  chapters  dealing  with  the 
various  systems  of  organs ;  whilst  the  last  seventy-five  pages  are  used  for  the 
purpose  of  applying  the  information  conveyed  in  the  preceding  part  of  the  book 
to  the  practice  of  medicine  and  surgery.  Each  chapter  is  more  or  less  complete 
in  itself,  although  an  effort  has  been  made  to  weld  them  all  into  one  consistent 
whole. 

The  numerous  illustrations  which  appear  in  the  text  are  all  new  in  the  sense 
that  in  no  case  has  an  old  drawing  or  an  old  block  been  used.  Further,  the  vast 
majority  of  the  illustrations  are  new  in  the  sense  that  they  are  original.  The 
very  few  that  are  not  have  been  taken  from  monographs  dealing  with  the  subjects 
so  illustrated,  and  in  every  case  the  source  from  which  these  have  been  obtained 
is  acknowledged  in  the  text.  The  drawings  for  each  section  were  prepared  under 
the  personal  supervision  of  its  author,  and,  with  the  exception  of  the  figures  in 
two  chapters,  they  are  the  work  of  Mr.  J.  T.  Murray.  This  talented  artist  has 
devoted  much  time  to  the  undertaking,  and  the  reader  can  judge  for  himself  the 
success  which  has  attended  his  efforts.  The  Editor  cannot  suf&ciently  express  his 
indebtedness  to  Mr.  Murray  for  the  great  technical  skill  and  the  patience  which  he 
brought  to  bear  upon  this  extremely  trying  and  difficult  work.  The  chapter  on 
Osteology  has  been  illustrated  by  Mr.  W.  C.  Stevens  ;  that  upon  Embryology  by 
the  authors  themselves ;  whilst  the  microscopical  drawings  in  the  section  on  the 
Brain  and  Cord  were  executed  by  Mr.  Wm.  Cathie.  It  is  also  necessary  to  mention 
that  the  coloured  outlines  representing  the  attachments  of  the  muscles  on  the 
figures  of  the  bones  were  mapped  in  by  Professor  A.  M.  Paterson. 

The  Editor  has  to  thank  his  former  Assistant,  Professor  A.  F.  Dixon  of  Cardiff, 
for  much  help  in  the  correction  of  the  proofs. 


Teinity  College,  Dublin, 
June  1902. 


LIST    OF    CONTRIBUTORS 


AMBROSE  BIRMINGHAM,  M.D.,  F.R.C.S.I., 

Formerly  Professor  of  Anatomy,  Catholic  University  School  of  Medicine,  Duljlin. 
{Tlu  Digestive  System.) 

D.  J.  CUNNINGHAM,  M.D.,   F.R.S., 

Professor  of  Anatomy,  University  of  Edinburgh. 

(The  Brain  and  Spinal  Cord,  The  Respiratory  System,  The  Ductless  Glands.) 

A.  FRANCIS  DIXON,  M.B.,  D.Sc.  (Dubl.), 

Professor  of  Anatomy,  Trinity  College,  Dublin. 
{The  Urinogenital  System.) 

DAVID  HEPBURN,  M.D.,  F.R.S.E., 

Professor  of  Anatomy,  University  College,  Cardiff. 

(Arthrology.) 

ROBERT  HOWDEN,  M.A.,  M.B., 

Professor  of  Anatomy,  University  of  Durham. 
(The  Organs  of  Sense  and  the  Integument.) 

A.  M.  PATERSON,  M.D., 

Professor  of  Anatomy,  University  of  Liverpool. 

(Myology,  The  Spinal  and  Cranial  Nerves,  Tfie  Sympathetic  Nervous  System.) 

ARTHUR  ROBINSON,  M.D., 

Professor  of  Anatomy,  University  of  Birmingham. 

(General  Embryology,  The  Vascular  System.) 

HAROLD  J.  STILES,  M.B.,  F.R.C.S.  Ed., 

Surgeon  to  the  Royal  Hospital  for  Sick  Children,  Edinburgh. 

(Surface  and  Surgical  Anatomy.) 

ARTHUR  THOMSON,  M.A.,  M.B., 

Professor  of  Human  Anatomy,  University  of  Oxford. 
(Osteology.) 

A.  H.  YOUNG,  M.B.,  F.R.C.S., 

till  recently  Professor  of  Anatomy,  Victoria  University,  Manchester. 
(General  Embryology,  The  Vascular  System.) 


The  New  Index  is  the  work  of  Dr.  E.  B.  Jamieson,  M.D.  Ed.,  Mr.  T.  B.  Johnston,  M.B.,  Ch.B., 
and  Mr.  R.  B.  Thomson,  M.B.,  Ch.B.,  Demonstrators  of  Anatomy  in  the  University  of 
Edinburgh. 


CONTENTS. 


INTEODUCTION. 
GENERAL  EMBEYOLOGY. 


The  Animal  Cell 

PAGE 

8 

Mouth  and  Nose 

PAGE 

38 

Eeproduction  of  Cells 

9 

External   Ear,  Tympanic    Cavity,  and 

The  Ovum 

10 

Eustachian  Tube    .... 

43 

Its  Structure      .... 

10 

Hind-gut,  Anal  Passage,  and  Post-anal 

Its  Maturation  .... 

12 

Gut 

45 

The  Spermatozoon  .... 

14 

The  Limbs 

46 

Fertilisation  of  the  Ovum 

16 

Nutrition    and    Protection  of  Embryo 

Segmentation  of  Ovum 

17 

during  Intrauterine  Existence 

47 

Formation  of  Blastodermic  Vesicle 

18 

Festal  Membranes  and  Appendages 

48 

Ectoderm  and  Entoderm   . 

19 

Yolk-Sac 

48 

Embryonic  Area 

19 

Amnion     ...... 

48 

Neural  Groove  and  Tube  . 

21 

Body-Stalk 

50 

Formation  of  Notochord    . 

24 

Allantois   ...... 

51 

Formation  of  Ccelom 

24 

Umbilical  Cord          .... 

51 

Mesodermic  Somites  . 

26 

Chorion 

52 

Folding  off  of  the  Embryo 

26 

The  Placenta 

52 

The  Embryo 

28 

Primitive  Vascular  System  and  Foetal 

Primitive  Alimentary  Canal  . 

32 

Circulation 

60 

Pharynx  and  Stomatodseum      . 

34 

External  Features  of  Human  Embryo 

Visceral  Clefts  and  Arches 

35 

at  dijBferent  periods 

65 

OSTEOLOGY. 


The  Skeleton 

69 

The  Lacrimal  Bones 

.       131 

Composition  of  Bone 

70 

The  Vomer     . 

.       131 

Structure  of  Bone 

71 

Nasal  Bones 

132 

Ossification  and  Growth  of  Bones 

73 

Wormian  Bones 

.       133 

The  Vertebral  Column    . 

75 

Bones  of  the  Face    . 

.       133 

A  Typical  Vertebra 

76 

Maxillae     .         .         .         . 

.       133 

Cervical  Vertebrae     . 

78 

Palate  Bones     . 

.       138 

Thoracic  Vertebrse    . 

81 

Zygomatic  Bones 

140 

Lumbar  Vertebrae     . 

83 

Mandible  .         .         .         . 

.       142 

False  or  Fixed  Vertebrae 

84 

The  Hyoid  Bone    . 

.       145 

Sacrum      .         .         .         ... 

84 

The  Skull  as  a  whole 

.       146 

Coccyx 

87 

Norma  Frontalis 

.•      146 

The  Verteljral  Column  as  a  whole 

88 

Norma  Lateralis 

151 

The  Cartilaginous  Verteljral  Column 

90 

Norma  Occipitalis     . 

.       157 

Ossification  of  tlie  Vertel»r;e  . 

92 

Norma  Verticalis 

158 

The  Stenium 

94 

Norma  Basalis  . 

159 

Tlie  Ribs 

97 

The  Skull  in  Section 

.         .       166 

The  Costal  Cartilages 

100 

Up])er  Surface  of  tlie  B 

ase  of  the 

The  Thorax  as  a  whole  . 

101 

Skull      . 

166 

The  Bones  of  the  Skull  . 

103 

Medial  Sagittal  Section  ol 

the  Skull        170 

Frontal  Bone     .... 

103 

Nasal  Fossa? 

.       170 

Paiietal  Bones  .... 

106 

Nasal  Septum   . 

.       172 

Occipital  Bone  .... 

108 

Air-sinuses  in  connexion  a 

villi  Nasal 

Temporal  Bones 

112 

Fosste 

172 

Sphenoid  Bone. 

Ethmoid  Bone  .... 

121 

Coronal  Sections 

.       173 

127 

Horizontal  Section  of  the 

Skull        .       179 

Inferior  Turbinated  Bones 

130 

Sexual  Differences  in  Skull 

.       180 

CONTENTS. 

xi 

PAOB 

PAGE 

Differences  due  to  Age     . 

181 

Tarsus 

238 

Bones  of  Upper  Extremity 

181 

Talus  or  Astragalus   . 

238 

Clavicle 

181 

Calcaneus  . 

243 

Scapula 

183 

Navicular  Bone 

245 

Humerus 

188 

Cuneiform  Bones 

245 

Ulna 

194 

Cuboid  Bone 

247 

Radius 

198 

The  Tarsus  as  a  whole 

248 

Carpal  Bones      .... 

201 

Metatarsal  Bones 

249 

Carpus  as  a  whole 

206 

Phalanges  . 

251 

Metacarpal  Bones 

207 

Sesamoid  Bones 

253 

Phalangeal  Bones 

210 

Appendix — 

Sesamoid  Bones 

212 

Architecture    of   the    Bones   of   tht 

Bones  of  the  Lower  Limb 

212 

Skeleton          .... 

i 

Pelvic  Girdle  and  Lower  Extremity 

212 

Variations  in  the  Skeleton 

vi 

Innominate  Bone 

212 

Serial  Homologies  of  the  Vertebrae 

xiii 

Pelvis 

219 

Measurements  and  Indices  inPhysica 

L 

Femur 

223 

Anthropology         .         . 

XV 

Patella 

229 

Developmentof  the  Chondro-crauiun 

Tibia 

230 

and  Morphology  of  the  Skull 

XX 

Fibula 

234 

Morphology  of  the  Limbs 

xxiii 

THE   AETICULATIONS   OR   JOINTS. 


Arthrology 

Spiarthroses      .... 

Movable  Joints .... 

Structures    which    enter    into     th 
Formation  of  Joints 

Different    Kinds    of    Movement    at 
Joints     . 

Development  of  Joints 

Morphology  of  Ligaments 
Ligaments  of  the  Vertebral  Column  and 
Skull 

Articulation  of  Atlas  with  Axis 

Articulation  of  Spine  with  Cranium 
Temporo-mandibular  Joint    . 
Cranial    Ligaments   not    directly  asso 

ciated  with  Articulations 
Joints  of  Thorax 

Costo-central  Joints  . 

Costo-transverse  Joints 

Articulations  between  the  Ribs  and 
their  Cartilages 

Interchondral  Joints 

Costo-sternal  Joints  . 

Sternal  Articulations 
Articulations  of  the  Superior  Extremity 
Articulations  of  the  Clavicle 

Sterno-clavicular  Joint 


255   j 

255  I 

256  i 

257  I 

259  j 
259  I 
261    ! 

261 
265 
266 
267 

269 
269 
269 
270 

271 
271 
271 
272 
273 
273 
273 


Acromio  -  clavicular      or      Scapulo 

clavicular  Joint 

274 

Ligaments  of  Scapula 

.       275 

Shoulder-joint         .... 

276 

Elbow-joint 

279 

Radio-ulnar  Joints 

281 

Radio-carpal  Joint 

283 

Carjjal  Joints           .... 

284 

Intermetacarpal  Joints    . 

287 

Carpo-metacarjjal  Joints 

287 

Metacarpo-phalangeal  Joints 

288 

Interphalangeal  Joints    . 

288 

Articulations  and  Ligaments  of  Pelvis 

289 

Lumbo-sacral  Joints 

289 

Sacro-iliac  Joint        .         .         .         . 

290 

Symphysis  Pubis     .... 

292 

Articulations  of  Lower  Extremity 

293 

Hip-joint 

293 

Knee-joint          .... 

297 

Tibio-fibular  Joints    . 

304 

Joints  of  Foot     .... 

306 

Ankle-joint        .... 

306 

Intertarsal  Joints 

308 

Tarso-metatarsal  Joints 

313 

Intermetatarsal  Joints 

314 

Metatarso-phalangeal  Joints 

314 

Interphalangeal  Joints 

314 

THE  MUSCULAR  SYSTEM. 


The  Muscular  System     . 

Fascite     ...... 

Description  of  the  Muscles 

Appendicular  Muscles    . 

Fasci*  and  Superficial  Muscles  of  the 

Back 

Fascise     ...... 

The  Superficial  Muscles  of  the  Back 
The  Fasciae  and  Muscles  of  the  Pectoral 

Region  ..... 

Fasciae     ...... 

Muscles  of  the  Pectoral  Region 
Fasciae  and  Muscles  of  the  Shoulder 


317 
318 
319 
319 

319 
319 
319 

322 
322 
323 
327 


Muscles 

Fasciae  and  Muscles  of  the  Arm 
Fasciae  and  Muscles  of  the  Forearm  and 

Hand 

Fasciae 

The  Muscles  of  the  Front  and  Media 

Aspect  of  the  Forearm  . 
Superficial  Muscles 
Intermediate  Layer 
Deep  Layer     ..... 
Short  Muscles  of  the  Hand     . 
Muscles  of  the  Thumb    . 
Muscles  of  the  Little  Finger  . 


327 
332 

336 
336 

338 
338 
341 
341 
343 
343 
345 


Xll 


CONTENTS. 


Tlie  Interosseous  Muscles 
The  Muscles  on  tlie  Back  of  tlie  Forearm 
Superficial  Muscles  . 
Deep  Muscles    . 
The  Lower  Limb    . 
Fascife  and  Muscles  of   the  Thigh  and 

Buttock 

Fasciag 

Muscles  of  the  Thigh  and  Buttock 
The  Muscles  of  the^Front  of  the  Thigh 
The  Muscles  on  the  Medial  Side  of  the 

Thigh 

The  Muscles  of  the  Buttock   . 

The  Muscles  on  the  Back  of  the  Thigh 

The  Hamstring  Muscles 

The  Fasciae  and  Muscles  of  the  Leg  and 

Foot 

Fascice    ...... 

The  Muscles  of  the  Leg  and  Foot  . 
The  Muscles  on  the  Front  of  the  Leg  and 

Dor-sum  of  the  Foot 
The  Muscles  on  the  Lateral  Side  of  the  Leg 
The  Muscles  on  the  Back  of  the  Leg 
The  Muscles  in  the  Sole  of  the  Foot 
Axial  Muscles  .... 

The  Fascife  and  Muscles  of  the  Back 
The  Fasciae  of  the  Back  . 
The  Muscles  of  the  Back 
First  Group     . 
Second  Group 
Third  Group  . 


PAGE 

346 
347 
348 
349 
353 

353 

353 
356 

356 

361 
364 
368 
368 

371 
371 
373 

373 
375 
376 

380 
385 
385 
385 
386 
386 
387 
389 


Fourth  Group 

The  Fasciae  and  Muscles  of  the  Head 

and  Neck       .... 

Fasciae     ...... 

The  Muscles  of  the  Head 

Superficial  Muscles 

The  Muscles  of  the  Scalp 

The  Muscles  of  the  Face 

The  Fascias  and  Muscles  of  the  Orbit 

Muscles  of  Mastication    . 

The  Muscles  of  the  Neck 

The  Muscles  of  the  Hyoid  Bone 

The  Muscles  of  the  Tongue     . 

The  Muscles  of  the  Pharynx  . 

The  Muscles  of  the  Soft  Palate 

Deep  Lateral  and  Praevertebral  Muscles 

of  the  Neck   .         .  '      . 
The  Muscles  of  the  Thorax     . 
Muscles  of  Eespiration   . 
Fasciae  and  Muscles  of  the  Abdominal 

WaU 

Fasciae    ...... 

The  Muscles  of  the  Abdominal  Wall 
Fasciae  and   Muscles   of  the   Periiieum 

and  Pelvis       .... 
Fasciae  of  the  Perineum . 
The  Muscles  of  the  Perineum 
The  Fasciae  of  the  Pelvis 
Muscles  of  the  Pelvis 
The  Development  and   MorjDhology  of 

the  Skeletal  Muscles 


PAGE 

391 

394 
394 
395 
395 
395 
397 
399 
401 
404 
405 
408 
410 
412 

413 
415 
415 

419 
420 
421 

430 
430 
431 
433 

438 

439 


THE  NEEVOUS  SYSTEM. 


Cerebrospinal  Nervous  System 
Nerve-fibres  ..... 
Nerve-cells  ..... 
Neuroglia        ..... 

Spinal  Cord 

Internal  Structure  of  Sj)inal  Cord 
Characters  presented  by  Cord  in  its 

Different  Eegions  . 
Component  Parts  of  Gray  Matter  of 

Spinal  Cord   .... 
Component  Parts  of  the  White  Matter 

of  the  Sjjinal  Cord 
Development  of  Spinal  Cord     . 
Brain  or  Encephalon  . 

General  Outline  of  Development  of 

Brain 

Parts  of  Encephalon  derived  from  the 
Hind-brain     .... 
Medulla  Oblongata  or  Bulb 
Pons  Varolii       .... 
Internal  Structure  of  Medulla  . 
Internal  Structure  of  Pons  A^'arolii 

Cerebellum 

Minute   Structure    of    a    Cerebellar 

Folium 

Deep    Connexions    of    Cranial    Nerves 

attached  to  Medulla  and  Pons 
Development    of    Parts    derived    from 

Ilhombencephalon  . 
Mesencephalon         .... 

Internal  Structure  of  Mesencephalon 

Deep  Origin  of  Cranial  Nerves  which 

arise  within  the  Mesencephalon     . 

Development  of  Mesencephalon 

Fore-brain       ...... 

Parts  derived  from  the  Diencephalon 


443 
444 
445 
451 
452 
456 

460 

461 

465 
471 

474 

476 

481 
481 
486 
489 
499 
505 

512 

514 

526 
531 
533 

540 
542 
542 
542 


Optic  Thalamus 

Subthalamic  Tegmental  Region 

Pineal  Body 

Trigonum  Habenulae 

Corpora  Mammillaria 

Pituitary  Body  . 

Third  Ventricle 

Cerebral  Connexions  of  Optic  Tract 
Parts  derived  from  the  Telencephalon 

Cerebral  Hemisj)heres 

Olfactory  Lobe  .... 

Corpus  Callosum,  Septum  Lucidum 
and  Fornix     .... 

Lateral  Ventricle 

Basal   Ganglia    of    Cerebral   Hemi 
sphere 

Intimate  Structure  of  Cerebral  Hemi 
sphere 

Cerebral  Cortex 

Olfactory  Tract  and  Bulb  . 

White  Medullary  Centre  of  Cerebral 
Hemisjjhere    . 

Develoj^ment  of  Parts  derived  from 
Fore-brain       .... 

Weight  of  Brain 
Meninges  of  Brain  and  Spinal  Cord 

Dura  Mater        .... 

Arachnoidea       .... 

Pia  Mater 

Spinal  Nerves      .... 
Posterior  Primary  Divisions  of  Spinal 

Nerves   . 
Cervical  Nerves 
Thoracic  Nerves 
Lumbar  Nerves 
Sacral  and  Coccygeal  Nerves 


542 
546 
547 
547 
548 
549 
550 
551 
553 
553 
569 

570 
573 

579 

584 
584 
587 

588 

594 
597 
597 
597 
600 
603 
607 

610 
611 
613 
613 
613 


CONTENTS. 


xiu 


Morphology    of    Posterior    Primary 

Divisions        .         .         .         .         . 

Anterior  Primary   Divisions   of  Spinal 

Nerves  ..... 
Cervical  Nerves  .... 
Cervical  Plexus       .... 

Phrenic  Nerve  .... 

Morphology  of  Cervical  Ple.\us 
Brachial  Plexus      .... 

Branches  of  Brachial  Plexus 

Anterior  Thoracic  Nerves 

Musculo-cutaneous  Nerve 

Median  Nerve    .... 

Uhiar  Nerve       .... 

Internal  Cutaneous  Nerve 

Lesser  Internal  Cutaneous  Nerve 

Circumflex  Nerve 

Musculo-spiral  Nerve 

Eadial  Nerve     .... 

Posterior  Interosseous  Nerve     . 

Subscapular  Nerves   . 
Thoracic  Nerves       .... 
Lumbo-sacral  Plexus 
Lumbar  Plexus        .... 

Obturator  Nerve 

Anterior  Crural  Nerve 
Sacral  or  Sciatic  Plexus 

Great  Sciatic  Nerve  . 

Nerves    of    Distribution    from    the 
Sacral  Plexus 

Peroneal  Nerve  .... 

Anterior  Tibial  Nerve 

Musculo-cutaneous  Nerve  . 

Tibial  Nerve      .... 

Internal  Plantar  Nerve 

External  Plantar  Nerve     . 


614 

615 
617 
617 
621 
622 
622 
624 
626 
627 
627 
629 
631 
632 
632 
632 
634 
634 
635 
635 
639 
641 
643 
645 
647 
648 

649 
650 
651 
651 
652 
654 
654 


Pudendal  Plexus     .... 
Pudic  Nerve      .... 
Development  of  Spinal  Nerves 
Morphology  of  Limb-plexuses 
Distribution  of  Spinal  Nerves  to  Muscles 

and  Skin  of  Limbs 
Variations  in  Position  of  Limb-plexuses 
Significance  of  Limb-plexuses 
Cranial  Nerves  .... 
First  or  Olfactory  Nerve  . 
Second  or  Optic  Nerve 
Third  or  Oculo-motor  Nerve     . 
Fourth  or  Trochlear  Nerve 
Fifth,  Trigeminal  or  Trifacial  Nerve 
Sixth  or  Abducent  Nerve 
Seventh  or  Facial  Nerve  . 
Eighth  or  Auditory  Nerve 
Ninth  or  Glosso-pharyngeal  Nerve 
Tenth  or  Pneumogastric  Nerve 
Thoracic  Plexuses    .... 
Eleventh  or  Spinal  Accessory  Nerve 
Twelfth  or  Hypoglossal  Nerve  . 
Development  of  Cranial  Nerves 
Morphology  of  Cranial  Nerves 
Sympathetic  Nervous  System     . 
Cervical  Part  of  Sympathetic  Cord 
Superior  Cervical  Ganglion 
Middle  Cervical  Ganglion 
Inferior  Cervical  Ganglion 
Thoracic  Part  of  Sympathetic  Coi-d 
Lumbar  Part  of  Sympathetic  Cord 
Sacral  Part  of  Gangliated  Cord 
Sympathetic  Plexuses     . 

Solar  and  Pelvic  Plexuses 
Development  of  Sympathetic  System 
Morphology  of  Sympathetic  System 


PAOB 

655 

658 
660 
662 

665 
673 

674 
674 
675 
675 
676 
677 
678 
686 
686 
688 
689 
690 
693 
695 
696 
698 
700 
703 
706 
706 
708 
708 
708 
710 
711 
712 
712 
715 
716 


THE  OEGANS  OF  SENSE  AND  THE  INTEGUMENT. 


Nose 

717 

Pinna         

.       743 

Cartilages  of  Nose     . 

717 

External  Auditory  Meatus 

746 

Nasal  Fosste   ..... 

719 

Middle  Ear  or  Tympanic  Cavity    . 

748 

Eye 

723 

Mastoid  Antrum  and  Mastoid  A 

Lir- 

Eyeball 

724 

cells        ..... 

.        752 

Sclera 

725 

Eustachian  Tube 

.        753 

Cornea    

726 

Tympanic  Ossicles     . 

754 

Vascular  and  Pigmented  Tunic 

727 

Internal  Ear  ..... 

.       759 

Retina 

731 

Osseous  Labyrinth  .... 

.       759 

Refracting  Media  of  Eyeball  . 

735 

Membranous  Labyrinth . 

.       762 

Eyelids 

738 

Development  of  Labyrinth 

.       769 

Lacrimal  Apparatus 

740 

Organs  op  Taste  .... 

770 

Development  of  Eye 

741 

Skin  or  Integument     . 

.       772 

Ear 

743 

Appendages  of  Skin 

.       775 

External  Ear 

743 

Development  of  Skin  and  its  Appenda 

ges       778 

THE  VASCULAE  SYSTEM. 


Structure  of  Blood-vesse 

s 

780 

Heart     .... 

783 

Chambers  of  Heart 

786 

Structure  of  the  Heart 

791 

Pericardium    . 

793 

Arteries 

795 

Pulmonary  Artery  . 

795 

Systemic  Arteries   . 

797 

Aorta 

797 

Thoracic  Aorta 

797 

Abdominal  Aorta    . 

798 

Branches  of  Ascending  Aorta  .         .  800 

Coronary  Ai-teries      ....  800 

Branches  of  Arch  of  Aorta      .         .         .  800 

Innominate  Artery  ....  801 

Arteries  of  Head  and  Neck     .         .         .  801 

Common  Carotid  Arteries       .         .         .  801 

External  Carotid  Artery         .         .         .  803 

Branches  of  External  Carotid  Artery  804 

Internal  Carotid  Artery  .         .         .  813 

Branches  of  Internal  Carotid  Artery  814 

Vertebral  Artery       .         .         .         .  818 


XIV 


CONTENTS. 


Arteries  of  Upper  Extremity 
Subclavian  Arteries        ... 

Branclies  of  Subclavian  Artery 
Axillarj^  Artery       .... 

Brandies  of  Axillary  Artery 
Brachial  Artery       .... 

Brandies  of  Brachial  Artery 

Radial  Ai-tery    .... 

Ulnar  Artery     .... 

Arterial  Ai'ches  of  Wrist  and  Hand 
Branches  of  Descending  Thoracic  Aorta 

Parietal     Branches     of    Descending 
Thoracic  Aorta       .         .         .         . 

Visceral    Brandies     of    Descending 
Thoracic  Aorta 
Branches  of  Abdominal  Aorta 

Parietal     Branches    of    Abdominal 
Aorta 

Common  Iliac  Arteries      .         .    ' 

Paired  Visceral  Branches  of  Abdomi 
nal  Aorta        .... 

Unpaired  or  Single  Visceral  Branches 
of  Abdominal  Aorta 
Internal  Iliac  Artery 

Branches  of  Posterior  Division 

Branches  of  Anterior  Division  of  In 
ternal  Iliac  Artery 

Visceral  Branches 

Parietal  Branches  of  Anterior  Divi- 
sion of  Internal  Iliac 
Arteries  of  Lower  Extremity 
External  Iliac  Artery 
Femoral  Artery 
Popliteal  Artery 

Posterior  Tibial  Artery 

Plantar  Arteries 

Anterior  Tibial  Artery 

Veixs 

Pulmonary  Veins    . 
Systemic  Veins 
Coronary  Sinus  and  Veins  of  Heart 
Superior   Vena    Cava    and    its    Tribu 
taries      ..... 

Azygos  Veins     .... 

Innominate  Veins 
Veins  of  Head  and  Neck 

Veins  of  Scalj)   .... 

Veins  of  Orbit,  Nose,  and  Pterygo 
maxillary  Region  . 
Venous  Sinuses  and  Veins  of  Cranium 
and  of  its  Contents 

Dijjloic  and  Meningeal  Veins    . 

Veins  of  Brain  .... 

Blood  Sinuses  of  Cranium 

Spinal  Veins      .... 
Veins  of  Upper  Extremity 

Deep  Veins  of  Upper  Extremity 

Axillary  Vein    .... 

Suj^erficial  Veins  of  U2)2Jer   Extre 
inity 


PAGE 

821 
821 
823 
827 
828 
830 
831 
831 
834 
835 
837 

837 

838 
839 

839 
841 

842 

843 
848 
850 

851 
851 

852 
856 
856 
858 
863 
864 
865 
867 
870 
870 
870 
871 

871 
872 
873 
875 
879 

879 


881 
883 
887 


PAGE 

Inferior  Vena  Cava  and  its  Tributaries  892 

Iliac  Veins 895 

Veins  of  Lower  Extremity      .         .         .  897 
Deep  Veins  of  Lower  Extremity       .  897 
Superficial  Veins   of  Lower   Extre- 
mity        900 

Portal  System 901 

Mesenteric  and  Splenic  Veins   .         .  903 

Lymph  Vascular  System         .         .         .  904 

Terminal  Lymph  Vessels        .         .         .  906 
Lymphatic  Vessels  and  Glands  of  Head 

and  Neck 909 

Lymphatic  Glands  and  Vessels  of  Upper 

Extremity 913 

Lymphatic  Glands  and  Vessels  of  Lower 

Extremity 916 

Lymphatic  Glands  and  Vessels  of  Ab- 
domen and  Pelvis  .        .         .         .  918 
Lymphatic     Glands     and     Lymphatic 

Vessels  of  Thorax  ....  923 
Development    of    Blood    Vascular 

System 925 

Pericardium,  the  Primitive  Aortse, 

and  Heart 925 

Development  of  Heart,  of  first  part 
of     Aorta,     and     of     Pulmonary 

Artery 928 

Division  of  Heart  into  its  different 
Chambers,  and  Division  of  Aortic 

Bulb 929 

Aortic  Arches — Formation  of  Chief 

Arteries 932 

Primitive  Dorsal  Aortse — Formation 

of  Descending  Aorta       .         .         .  933 

Branches  of  Primitive  Dorsal  Aortse  933 

Arteries  of  Limbs      .         .         .         .  933 

Development  of  Veins     .         .         .         .  934 

Veins  of  Limbs 938 

Pulmonary  Veins       ....  938 
Morphology  of  Vascular  System      .  938 
Segmental  Arteries  and  their  Ana- 
stomoses            939 

Aorta,  Pulmonary  Artery,  and  other 

Chief  Stem  Vessels         .         .         .942 

Limb  Arteries    .....  943 

Morphology  of  Veins  .         .         .  943 

Abnormalities  of  Vascular  System  .  946 

Abnormalities  of  Heart  ....  946 

Abnormalities  of  Arteries       .         .         .  947 

Branches  of  Aorta      ....  947 

Arteries  of  Head  and  Neck        .         .  950 

Arteries  of  Upper  Limb    .         .         .951 

Iliac  Arteries  and  their  Branches     .  952 

Arteries  of  Lower  Limb     .         .         .  953 

Abnormalities  of  Veins  ....  954 

Superior  Vena  Cava ....  954 

Veins  of  Upper  Extremity        .         .  955 

Inferior  Vena  Cava   ....  955 

Veins  of  Lower  Extremity         .         .  955 

Abnormalities  of  Lymphatics  .         .  955 


THE   RESPIEATOKY   SYSTEM. 


Organs  of  Respiration  and  Voice    .         .  957 
Larynx  or  Organ  of  Voice       .         .         .957 

Caitiiages  of  Larynx       ....  958 
Joints,  Ligaments,  and   Membranes   of 

Larynx 961 

Interior  of  Larynx 964 

Laryngeal  Muscles 968 

Trachea 972 


Bronchi 

Thoracic  Cavity 
Pleural  Memljranes 
Mediastinal  or  Intei'pleural  Space 
Lungs 

Root  of  Lung 

Structure  of  Lung 
Develoj)ment  of  Respiratory  Apparatus 


975 
976 

977 
982 
983 
989 
990 
992 


CONTENTS. 


XV 


THE   DIGESTIVE   SYSTEM. 


Mouth 

Palate  and  Isthmus  Faucium 
Tongue    ...... 

Glands     

Salivary  Glands        ... 

Development    of    Salivary    Glands 
Palate,  and  Tongue 
Teeth 

Permanent  Teeth 

Milk  Teeth        .... 

Structure  of  Teeth     ... 

Develojjment  of  Teeth 

Morphology  of  Teeth 
Pharynx  ...... 

Development  of  Pharynx  and  Tonsil 
CEsophagus      

Development  of  CEsophagus 
Abdominal  Cavity  .... 

Subdivision  of  Abdominal  Cavity 
Peritoneum      ..... 
Stomach  ...... 


PAOK 

995 

998 

1000 

1007 

1009 

1013 
1014 
1016 

1022 
1023 
1025 
1029 
1029 
1037 
1038 
1042 
1043 
1045 
1048 
1050 


Structure  of  Stomach 

PAOE 

.     1058 

Intestines 

.     1060 

Structure  of  Intestines 

.     1061 

Small  Intestine 

.     1064 

Duodenum       .... 

.     1065 

Jejunum  and  Ileum 

.     1071 

Large  Intestine 

.      1074 

Ciecum  and  Appendix    . 

.     1076 

Colon       ..... 

.     1082 

Kectum   ..... 

.     1087 

Anal  Canal      .... 

.     1091 

Peritoneum      .... 

.     1097 

Development  of  Intestinal   Cana 

,  and 

Peritoneum    . 

.     1105 

Liver       ..... 

.     1108 

Gail-Bladder  and  Bile  Passages 

.     1118 

Vessels  of  Liver 

.     1120 

Structure  of  Liver     . 

.     1121 

Development  of  Liver 

.     1122 

Pancreas.         .... 

.     1124 

Development  of  Pancreas  . 

.     1129 

THE   UEINOGENITAL  SYSTEM. 


Urinary  Organs  . 

Kidneys 

Bladder  ..... 

Urethra  .... 

Male  Reproductive  Organs 

Testis      . 

Vas  Deferens  . 

Descent  of  Testis     . 

Spermatic  Cord 

Scrotum . 

Penis 

Prostate  . 


1130 
1130 
1144 
1157 
1159 
1159 
1162 
1167 
1168 
1169 
1170 
1173 


Cowper's  Glands     .... 

Male  Urethra  .... 

Female  Reproductive  Organs   . 
Ovary      ...... 

Fallopian  Tubes      .... 

Uterus     ...... 

Vagina     ...... 

Female  External  Genital  Organs    . 

Glands  of  Bartholin  . 
Development  of  Urinogenital  Organs 
Mammary  Glands   .... 

Development  of  Mammae 


1176 
1177 
1181 
1182 
1185 
1187 
1192 
1195 
1198 
1198 
1207 
1209 


THE   DUCTLESS   GLANDS. 


Spleen     . 

Suprarenal  Capsules 
Thyreoid  Body 


1210 
1213 

1216 


Parathyreoids    . 
Thymus  Gland 
Carotid  and  Coccygeal  Bodies 


1218 
1218 
1220 


SUKFACE   AND   SUKGICAL  ANATOMY. 


Head  and  Neck 

Cranium 

Face  . 

Neck 
Thorax  . 

Lungs 

Heart  and  Great  Vessels 
Abdomen 

Anterior  Abdominal  Wall 

Abdominal  Cavity 
Male  Perineum 
Prostate  . 
Female  Pelvis 
Back 


1222 
1222 
1236 
1246 
1253 
1255 
1262 
1264 
1264 
1267 
1277 
1278 
1282 
1284 


Upper  Extremity  . 

Shoulder  . 

Axilla 

Upper  Arm 

Elbow 

Forearm  and  Hand 
Lower  Extremity   . 

Buttock 

Back  of  the  Thigh 

Popliteal  Space. 

Front  of  Thigh . 

Knee . 

Leg    . 

Foot  and  Ankle 


1291 
1291 
1293 
1295 
1296 
1298 
1302 
1302 
1303 
1305 
1305 
1307 
1308 
1310 


INDEX 1313 


LIST    OF    ILLUSTRATIONS. 


GENEEAL  EMBRYOLOGY. 


FIG. 
1. 

2. 
3. 
4. 
5. 


9. 
10. 

11. 

12. 

13. 

14. 

15. 
16. 

17. 
18. 

19. 

20. 
21. 

22. 


23. 

24. 

25. 
26. 
27. 

28. 


29. 


Horizontal  Section  through  Trunk  at 
Level  of  First  Lumbar  Vertebra  . 

Diagram  of  an  Animal  Cell 

Cell-Division 

The  Ovum  and  its  Coverings    . 

Maturation  of  the  Ovum  :  Extrusion 
of  the  "Polar  Bodies". 

Diagram  illustrating  the  Maturation 
of  the  Ovum         .... 

Diagram  illustrating  the  Process  of 
Cell-Division  resulting  in  the 
Formation  of  Spermatids  which 
are  afterwards  modified  into  Sper- 
matozoa        ..... 

Human  Spermatozoa 

Structure  of  a  Human  Spermatozoon 

Fertilisation  of  the  Ovum 

Segmentation  of  the  Fertilised  Ovum 
in  the  Rabbit        .... 

Conversion  of  the  Morula  to  the 
Blastula        ..... 

Surface  View  of  the  Blastodermic 
Vesicle 

The  Upper  Pole  of  the  Blastodermic 
Vesicle ...... 

Transverse  Section  of  a  Ferret  Embryo 

Transverse  Section  of  a  Ferret 
Embiyo 

Surface  Areas  of  the  Blastoderm 

Sections  showing  the  different  Areas 
of  the  Blastodermic  Vesicle 

Extension  of  Mesoderm  and  Forma- 
tion of  Ccelom       .... 

Surface  View  of  an  Early  Embryo   . 

Early  Stages  in  the  Folding-oflf  of  the 
Embryo 

The  Relative  Positions  of  the 
Blastodermic  Layers  in  the  Body 
of  the  Embryo  when  the  "  Fold- 
ing-off "  is  completed 

Transverse  Section  of  a  Ferret 
Embryo 

Further  Differentiation  of  the  Meso- 
derm    ...... 

Coronal  Section  of  a  Rat  Embryo     . 

Tiansverse  Section  of  a  Rat  Embryo 

Diagram  of  a  Developing  Ovum,  .seen 
in  Longitudinal  Section 

Diagram  representing  the  Condition 
of  the  Alimentaiy  Canal  in  a 
Human  Emljryo  about  fifteen 
days  old  (modified  from  His) 

Further  Development  of  the  Aliment- 
ary Canal,  as  seen  in  a  Human 
Embryo  about  five  weeks  old 


PAGE 
4 

8 

9 

11 

FIG. 

30. 
31. 

12 

32. 

13 

33. 

34. 

14 
15 
15 
16 

35. 
36. 
37. 

17 

18 

38. 

19 

39. 

20 
20 

40. 

21 
23 

41. 

24 

42. 

25 
25 

43. 

27 

44. 

45. 

28 

46. 

29 

47. 

29 
30 
31 

48. 
49. 

32 

50. 
51. 

33 

52 

34 

Stages  in  the  Formation  of  the 
Tongue  and  Upper  Aperture  of 
the  Larynx  in  the  Human  Embryo 
(after  His) 

Head  of  Human  Embryo  (four  views  ; 
two  after  His)       .... 

Head  of  Human  Embryo  (four  views ; 
two  after  His)       .... 

Head  of  Human  Embryo  (two  views  ; 
one  after  His)        .... 

Vertical  Section  through  Head  of 
Rat  Embryo  .... 

Transverse  Section  through  the  Head 
of  a  Rat  Embryo 

Figures,  modified  from  His,  illustrat- 
ing the  Formation  of  the  Pinna  . 

Diagrams  showing  the  Separation  of 
the  Cloacal  Part  of  the  Hind-gut 
into  Geni to  -  urinary  Tract  and 
Rectum 

Transverse  Sections  of  the  Uterus 
and  Developing  Ovum  of  a  Ferret 

Very  young  Human  Ovum  almost 
immediately  after  its  entrance 
into  the  Decidua  .... 

Relation  of  the  young  Human  Ovum 
to  the  Decidua      .... 

Further  Stage  of  Development  of  the 
Human  Ovum  and  its  Relation  to 
the  Decidual  Tissues    . 

Completion  of  the  Decidua  Capsu- 
laris,  etc 

Enlargement  of  the  Blood  Sinuses  in 
the  Maternal  Part  of  the  Placenta 
and  the  Closure  of  the  Amnion    . 

Fcetal  Ectoderm  surrounding  the 
Maternal  Blood  Sinuses,  etc. 

Further  Growth  of  the  Placental 
Sinuses  and  Villi,  etc. 

Later  Stage  in  the  Development  of 
the  Placenta  .... 

Development  of  Blood -Vessels  in  the 
Vascular  Area  of  the  Rat 

The  Primitive  Blood-Vessels  of  the 
Embryo 

Blood  -  Vessels  of  a  Mammalian 
Embryo  after  the  Formation  of 
the   Heart 

Diagram  of  the  Foetal  Circulation    . 

Human  Embryo  at  the  end  of  the 
12th,  13th,  and  14th  days  of  De- 
velopment (after  His)  . 

Human  Embrvo  at  the  21st,  23rd, 
and  27th  days  of  Development 
(after  His) 


36 
39 

40 
41 
42 
43 

44 

46 
49 

53 
53 

54 
54 

55 
55 
56 
58 
61 
62 


63 

64 


65 
66 


LIST  OF  ILLUSTEATIONS. 


xvii 


53.  Human  Embryo  at  the  29th  and  32nd 
days  of  Development  (after  His)  . 

64.  Human  Foetus  at  the  sixth  week  of 
Development  (after  His) 


55.  Human  Fojtus  six  and  a  half  weeks 
67  old  (after  His)       ....         67 

'   56.  Human    Foetus    eight    and    a    half 
67  weeks  old  (after  His)    ...         68 


OSTEOLOGY. 


57  a.  Fifth  Thoracic  Vertebra  from  the 

Right  Side 77 

51  h.  Fifth  Thoracic  Vertebra  from  Above         77 

58.  Fourth  Cervical  Vertebra,  (A)  from 

Above,  (B)  from  the  Eight  Side .         78 

59.  Tlie  Atlas  from  Above  ...  79 
60  a.  Axis  from  Behind  and  Above  .  80 
60  b.  Axis  from  the  Left  Side         .         .         80 

61.  First,  Ninth,  Tenth,  Eleventh,  and 

Twelfth  Thoracic  Vertebrte  from 

the  Left  Side      ....         82 

62.  Third  Lumbar  Vertebra,  (A)   from 

Above,  and  (B)  from  the  Left  Side         83 

63.  The  Sacrum  (anterior  view)      .         .         85 

64.  The  Sacrum  (posterior  view)    .         .         86 

65.  The  Coccyx 87 

66.  Vertebral  Column  from  the  Left  Side         89 

67.  Vertebral     Column    as    seen    from 

Behind 90 

68.  The  Development  of  the  Membranous 

Basis  of  a  Vertebra     .         .         .         91 
69  a.  Ossification  of  Vertebrae  .         .         92 

69  b.  Ossification  of  Vertebrae  .         .         93 

70.  Ossification  of  the  Sacrum         .         .         94 

71.  The  Sternum  (anterior  view)     .         .         95 

72.  Ossification  of  the  Sternum       .         .         96 

73.  Fifth     Right    Rib     as    seen     from 

Below 98 

74.  Fifth     Right    Rib     as    seen     from 

Behind 99 

75.  First   and    Second    Right    Ribs   as 

seen  from  Above  ...         99 

76.  The  Thorax  as  seen  from  the  Front .       100 

77.  The  Thorax  as  seen  from  the  Right 

Side 101 

78.  The  Frontal  Bone  (anterior  view)     .       104 

79.  The  Frontal  Bone  as  seen  from  Below       105 

80.  Ossification  of  the  Frontal  Bone        .       106 

81.  The  Right  Parietal  Bone  (jiarietal 

surface) 106 

82.  The  Right  Parietal  Bone  (cerebral 

surface)       .....       107 

83.  The  Occipital  Bone  as  seen  from  Below       110 

84.  Occipital  Bone  (cerebral  surface)       .       Ill 

85.  Ossification  of  the  Occipital  Bone     .       112 

86.  The  Right  Temporal  Bone  seen  from 

the  Parietal  Side         .         .         .114 

87.  The  Right  Temporal  Bone  (cerebral 

aspect) 115 

88.  The  Right  Temporal  Bone  seen  from 

Below 117 

89.  A  Preparation  to  show  the  Position 

and  Relations  of  the  Mastoid 
Antrum 118 

90  a.  Vertical  Transverse  Section  through 
the  Left  Temporal  Bone  (anterior 
half  of  sectioia)    .         .         .         .119 

90  b.  Vertical  Transverse  Section  through 
the  Left  Temporal  Bone  (pos- 
terior half  of  section)  .         .       119 

90  c.  Horizontal  Section  through  the 
Left  Temporal  Bone  (lower  half 
of  section) 120 


97. 


98. 


99. 

100 


101. 


91.  The  Parietal  and  Cerebral  Surfaces 

of  the  Right  Temporal  Bone  at 
Birth 121 

92.  The  Sphenoid  seen  from  Behind     .       122 

93.  The  Sphenoid  seen  from  the  Fi'ont       122 

94.  Ossification  of  the  Sphenoid   .         .       126 

95.  The  Ethmoid  seen  from  Behind      .       127 

96.  The  Ethmoid  seen  from  the  Right 

Side 128 

Section  showing  the  Nasal  Aspect  of 
the   Left   Lateral    Mass   of  the 

Ethmoid 128 

Showing   the   Articulation   of  the 

Inferior  Turbinated  Bone  with 

the  Ethmoid       .         .         .         .129 

The  Ethmoid  seen  from  Above       .       129 

Right    Inferior  Turbinated    Bone, 

(A)  Medial  Surface,  (B)  Lateral 

Surface 130 

The  Right  Lacrimal  Bone       .         .       131 

102.  The  Vomer  seen   from  the  Right 

Side 132 

103.  The  Vomer  at  Birth        .         .         .132 

104.  The  Right  Nasal  Bone,  (A)  Lateral 

Side,  (B)  Medial  Side  .         .       133 

105  a.  The  Right  Maxilla  (lateral  aspect)       134 
105  6.  The  Right  Maxilla  (medial  aspect)       134 

106.  Ossification  of  the  Maxilla      .         .       137 

107.  The  Right  Palate  Bone,  (A) from  the 

Lateral  Side,  (B)  from  the  Medial 

Side 138 

108.  The  Right  Palate  Bone  from  Behind       139 

109.  The    Right    Zygomatic   Bone,  (A) 

Lateral  Side,  (B)  Medial  Side    .       141 

110.  Medial  Surface  of  the  Zygomatic 

Bone  at  Birth  ....  141 
Ilia.  The  Mandible  from  the  Left  Side  142 
1116.  Medial  Side  of  the  Right  Half  of 

the  Mandible      ....       143 

112.  The  Mandible  at  Birth,  (A)  from 

Above,  (B)  Lateral  Side,  (C) 
Medial  Side        ....       144 

113.  The  Hyoid  Bone  as  seen  from  the 

Front 145 

Norma  Frontalis  of  the  Skull         .       148 
Norma  Lateralis  of  the  Skull  .       152 

Coronal      Section      through      the 
Spheno  -  maxillary      (Pterygo  - 
palatine)  Fossa  of  the  Right  Side       157 
Norma  Basalis  of  the  Skull    .         .       160 
Base  of  the  Skull  seen  from  Above       167 

1 19.  Medial  Aspect  of  Left  Half  of  Skull 

sagittally  divided        .         .         .       171 

120.  Nasal  Septum  seen  from  the  Left 

Side 173 

121.  Part   of  the   Frontal,   Nasal,   and 

Maxillary  Bones  removed  in 
order  to  disj^lay  the  relation  of 
the  various  cavities  exposed        .       174 

122.  Coronal  Section  passing  inferiorly 

through  the  interval  between 
the  First  and  Second  Molar 
Teeth 175 


114 
115, 
116 


117 

118 


LIST  OF  ILLUSTKATIONS. 


FIG.  PAGE 

123.  Coronal   Section   passing    througli 

tlie  Splieno-maxillaiy  Fossa       .       176 

124.  Coronal  Sectionof  the  Skull  passing 

through  the  Glenoid  Fossa  just 
behind  the  Articular  Eminence        177 

125.  Anterior  Surface  of  the  Section  of 

the   Skull  immediately  behind 

the  preceding  Section         .         .       178 

126.  Vertical  Section  through  the  Skull 

immediately  in  front  of  the  Root 

of  the  Styloid  Process         .         .       179 

127.  Horizontal  Section  of  the  Skull  a 

little    below   the   level    of    the 
Inferior  Orbital  Margin     .         .       180 
128  a.  The    Right    Clavicle    seen   from 

Above 181 

128  b.  The  Upper  Surface  of  the  Right 

Clavicle   with    Muscle   Attach- 
ments niajDj^ed  out      .         .         .       182 

129  a.  The   Right    Clavicle    seen   from 

Below 182 

129  b.  The  Under  Surface  of  the  Right 

Clavicle     with     the     Muscular 

Attachments  majjjJed  out  .  .  182 
130.  Ossification  of  the  Clavicle  .  .  183 
131  a.  The  Right    Scapula    seen    from 

Behind 184 

131  b.  The  Dorsum  of  the  Right  Scapula 

^vith  the  Muscular  Attachments 
majjped  out         .         .         .         .185 

132  a.  The  Right  Scapula  seen  from  the 

Front 186 

132  b.  Ventral   Aspect     of   the     Right 
Scapula  with  Muscular  Attach- 
ments map23ed  out      .         .         .186 
133.  Ossification  of  the  Scapula      .         .       188 
134  a.  Anterior    View     of    the     Right 

Humerus 189 

134  b.  The  Anterior  Aspect  of  the  Right 

Humerus  Avith  Muscular  Attach- 
ments majDped  out       .         .         .189 

135  a.  Posterior     View    of    the    Right 

Humerus 190 

135  b.  Posterior  Asjsect  of  the  Right 
Humerus  with  Attachments 
of  Muscles  mapped  out        .         .       191 

136.  The  Head  of  the  Right  Humerus 

seen  from  Above  .         .         .         .192 

137.  The  Lower  Extremity  of  the  Right 

Humerus  seen  from  Below   .         .       192 

138.  The    Lower    End    of    the    Right 

Humerus  seen  from  the  Lateral 

Side 192 

139.  Ossification  of  the  Humerus    .         .       193 

140.  The  Right  Ulna  viewed  from  the 

Lateral  Side 194 

141  a.  The  Right  Radius  and  Ulna  seen 

from  the  Front    ....       195 
141  b.  Anterior  Aspect  of  Bones  of  the 
Forearm  with  Muscular  Attach- 
ments mapped  out      .         .         .       196 
142.  The  Ossification  of  tlie  Ulna  .         .       197 
143  a.  Tlie  Radius  and  Ulna  seen  from 

Behind 198 

143  b.  Posterior  Aspect  of  Bones  of  Rigli  t 
Forearm   witli   Attachments   of 
Muscles  mapped  out  .         .         .        199 
144.  The  Ossification  of  the  Radius        .       201 
145  a.  The  Bones  of  tlie  Right  Wrist  and 

Hand  seen  from  the  Front  .         .       201 
145  b.   Palmar  Aspect   of   Bones  of   the 
Right  Carpus  and  Metacarpus 


with  Muscular  Attachments 
majDped  out         .... 

145  c.  Dorsal  Aspect  of  Bones  of  the 
Right  Carpus  and  Metacarpus 
with  Muscular  Attachments 
maj)2)ed  out         .... 

145  fZ.  Tlie  Bones  of  the  Right  Wrist 
and  Hand  seen  from  Behind 

146.  The  Right  Navicular  Bone     . 

147.  The  Right  Os  Lunatum  . 

148.  The  Right  Os  Triquetrum      . 

149.  The  Right  Pisiform  Bone 

150.  The     Right     Large     Multangular 

Bone     ...... 

151.  The     Right     Small     Multangular 

Bone  ...... 

152.  The  Right  Capitate  Bone 

153.  The  Right  Os  Hamatum 

154.  Radiograph  of  the  Hand  at  Birth . 

155.  The  First  Right  Metacarpal  Bone  . 
156  a.  The  Second  Right  Metacarjaal  Bone 
156  b.  The  Third  Right  Metacarpal  Bone 
156  c.  The  Fourth  Right  Metacarpal  Bone 
156  d.  The  Fifth  Right  Metacarpal  Bone 

157.  The  Phalanges  of  the  Fingers 

158.  Radiographs  of  Foetal  Hands . 

159  a.  The  Right  Innominate  Bone  seen 
from  the  Lateral  Side 

159  b.  Lateral  Aspect  of  the  Right  In- 
nominate Bone  with  the  Attach- 
ments of  the  Muscles  mapped  out 

160.  The  Right  Innominate  Bone  (medial 

aspect) 

161.  Muscle-Attachments  to  the  Lateral 

Surface  of  the  Pubis  and  Ischium 

162.  Ossification     of    the     Innominate 

Bone 

163  a.  The  Male  Pelvis  seen  from  the  Front 

163  b.  The  Female  Pelvis  seen  from  the 

Front 

164  a.  The  Right  Femur  seen  from  the 

Front  

164  b.  Front  Aspect  of  Upper  Portion  of 

the  Right  Femur  with  Attach- 
ments of  Muscles  mapped  out    . 

165  a.  The  Right  Femur  seen  from  Behind 
165  b.  Posterior    Aspect   of   the   Upj)er 

Portion  of  the  Right  Femur  with 
Attachments  of  Muscles  mapped 

out 

165  c.  Posterior  View  of  the  Upper  End 
of  the  Right  Femur  . 

166.  Posterior  Aspect  of  Lower  Portion 

of  the  Right  Femur  with  Attach- 
ments of  Muscles  mapped  out     . 

167.  Lower   End  of  the   Right   Femur 

(lateral  side) 

168.  Lower   End  of  the  Right  Femur 

seen  from  Below 

169.  Ossification  of  the  Femur 

170.  The  Right  Patella  .... 

171.  The  Upper  Surface  of  the  Superior 

Extremity  of  the  Right  Tibia    . 

172  a.  The  Right  Tibia  and  Fibula  seen 
from  the  Front  .... 

172  6.  Front  Aspect  of  the  Upper  Portion 
of  the  Bones  of  the  Right  Leg 
with  Attachments  of  Muscles 
mapped  out         .... 

173.  Ossification  of  the  Tibia 

174  a.  The  Right  Tibia  and  Fibula  seen 
from  Behind         .... 


202 


202 

203 
204 
204 
205 
205 

205 

206 
206 
207 
207 
208 
208 
209 
209 
209 
211 
211 

213 


224 

215 

217 

219 
220 

220 

223 


223 
224 


225 


225 


227 

227 

228 
229 
230 

230 

231 


232 
234 

235 


LIST  OF  ILLUSTKATIONS. 


XIX 


175. 

176. 
177. 

178  ( 


j-IG.  PAGE  FIG. 

174  b.  Posterior  Aspect  of  the  Bones  of  186 

the  Right  Leg  Avith  Attachments 

of  Muscles  mapped  out  .  .  235  186 
Right  Fibula  seen  from  the  Medial 

Side 236       187. 

Ossification  of  the  Fibula  .  .  238  188. 
Bones  of  the  Right  Foot  seen  from  189 

Above 239       189 

.  Bones   of  the   Right    Foot    seen  190. 

from  Below         ....  240 

178  b.  Plantar  Aspect  of  the  Left  Tarsus  191. 

and   Metatarsus    with    Attach- 
ments of  Muscles  mapped  out     .       241 

179  ((.  The  Right  Talus,  (A)  Upper  Sur-  I   192. 

face,  (B)  Under  Surface      .         .       242   '    193. 

179  6.  The  Right  Talus,  (C)  from  Lateral  194. 

Side,  (D)  from  Medial  Side         .       242       195. 

180  rt.  The    Right  Calcaneus,  (A)  from 

Above,  (B)  from  Below       .         .       243       196. 
180  b.  The  Right  Calcaneus,  (C)  from  the 

Lateral    Side,    (D)     from      the  197. 

Medial  Side         ....       244 
The  Right  Navicular  Bone     .        .       245       198. 
Anterior  Yiew  of  the  three  Cunei- 
form    Bones     of     the      Right  199. 

Foot 246 

The  Right  First  Cuneiform  Bone  200. 

(medial  side)       ....       246 
The  Right  First  Cuneiform  Bone  201 

(lateral  side)        ....       246 
185  a.  The    Right    Second    Cuneiform 

(medial  side)       ....       246      202 
The     Right    Second    Cuneiform 

(lateral  side)        ....       246 


181. 
182. 


183. 


184. 


185  6. 


a.  The  Right  Third  Cuneiform 
(medial  side)       .... 

b.  The  Right  Third  Cuneiform 
(lateral  side)        .... 

The  Right  Cuboid  Bone . 
Radiographs  of  the  Fcetal  Foot 

a.  Radiograph  of  the  Hand  at  Birth 

b.  Radiograph  of  the  Foot  at  Birth  . 
.  The  First  Metatarsal  Bone  of  the 

Right  Foot 

.  View  of  the  Bases  and  Shafts  of  the 
Second,  Third,  and  Fourth  Meta- 
tarsal Bones  of  the  Right  Foot  . 

The  Fifth  Right  Metatarsal  Bone  . 

The  Phalanges  of  the  Toes     . 

Radiographs  of  the  Fcetal  Foot 

Dissection  showing  the  Calcar 
Femorale     ..... 

Section  through  Head  and  Neck  of 
Femur  to  show  Calcar  Femorale 

Diagram  to  illustrate  the  Homolo- 
gous parts  of  the  Vertebrae 

Diagram  to  illustrate  the  chief 
points  used  in  Craniometry 

View  of  the  Chondro-cranium  of 
a  Human  Foetus  5  cm.  in  length 

Diagram  to  illustrate  the  Homolo- 
gies of  the  Bones  of  the  Limbs     . 

Diagram  to  illustrate  the  Homolo- 
gous parts  of  the  Scapula  and 
Ilium,  according  to  Flower 

Diagram  to  illustrate  the  Homolo- 
gous Parts  of  the  Scapula  and 
Ilium  according  to  Humphry    . 


247 

247 
248 
248 
249 
249 

250 


250 
251 
252 

252 

iv 

iv 

xiv 

xvi 

xxi 

xxiv 


THE  AETICULATIONS   OR  JOINTS. 


203.  Vertical  Section  through  a  Suture . 

204.  Section     through     the     Occipito- 

sphenoid  Synchondrosis 

205.  Sutura  Serrata         .... 

206.  Diagram  of  a  Diarthrodial  Joint    . 

207.  Diagram  of  a  Diarthrodial  Joint     . 

208.  Medial  Section  through  a  portion  of 

the  Lumbar  part  of  the  Spine 

209.  Anterior  Common  Ligament  of  the 

Vertebral  Column,  and  the  Costo- 
vertebral Joints  as  seen  from  Front 

210.  Posterior  Common  Ligament  of  the 

Vertebral  Column 

211.  Ligamenta  Subflava 

212.  Medial  Section  through  the  Occi- 

pito-atloid  and  Atlo-axoid  Joints 

213.  Dissection    from    Behind    of    the 

Ligaments  connecting  the  Occipi- 
tal Bone,  the  Atlas,  and  the  Axis 
with  each  other    .... 

214.  Temporo-mandibular  Joint     . 

215.  Section   through   Temporo-mandi- 

bular Joint 

216.  Internal  Lateral  Ligament  of  the 

Temporo-maxillary  Joint     . 

217.  Sterno-clavicular  and  Costo-sternal 

Joints   ...... 

218.  Capsule  of  the  Shoulder-Joint  and 

Coraco-acromial  Ligament   . 

219.  Capsular    Ligament    of   Shoulder- 

Joint  cut  across  and  Humerus 
removed        ..... 

220.  Vertical     Section      through      the 

Shoulder-Joint     .... 


255 

256 
256 
257 

258 

262 


262 

263 
264 

265 


221. 
222. 
223. 


224. 
225. 


226. 
227. 

228. 


266 

267 

229. 

230. 

268 

231. 

268 

232. 

272 

233. 

276 

234. 

235. 

277 

236. 

278 

237 

Anterior  View  of  Elbow-Joint 

Elbow-Joint  (inner  aspect) 

Vertical  Section  through  the 
Trochlear  part  of  the  Elbow- 
Joint  ..... 

Orbicular  Ligament  of  the  Radius . 

Carpal  Articular  Surface  of  the 
Radius,  and  Triangular  Fibro- 
Cartilage  of  the  Wrist 

Ligaments  on  Anterior  Aspect  of 
Radio-carpal,  Carpal,  and  Carpo- 
metacarpal Joints 

Coronal  Section  through  the  Radio- 
carpal, Carpal,  Carpo-metacarpal, 
and  Intermetacarpal  Joints  to 
show  Joint  Cavities  and  Inter- 
osseous Ligaments  (diagram  - 
matic) 

Metacarpo-phalangeal  and  Inter- 
phalangeal  Joints 

Coronal  Section  of  Pelvis 

Posterior  View  of  the  Pelvic  Liga- 
ments and  of  the  Hip-Joint 

Dissection  of  the  Hip-Joint    . 

Dissection  of  the  Hip-Joint  from  the 
Front    

Dissection  of  the  Knee-Joint  from 
the  Front     ..... 

The  Knee-Joint  (posterior  view)     . 

The  Knee- Jointopened  from  behind 
by  the  removal  of  the  Posterior 
Ligament      ..... 

Upper  End  of  Tibia  .  .  . 
,  Ankle- Joint  dissected  from  Behind 


279 

280 


281 

282 


282 
284 

286 

288 
290 

291 
294 


296 


298 
299 


301 
302 
305 


XX 


LIST  OF  ILLUSTEATIONS. 


238.  Articular   Surfaces   of   Tibia    and 

Fibula  wliicli  are  opposed  to  tlie 
Astragalus 

239.  Ankle  and  Tarsal  Joints  from  the 

Tibial  Aspect        .... 

240.  Ligaments  on  the  Outer  Aspect  of 


PAGE      I      FIG. 


306 


307 


241. 


242. 


the  Ankle  -  Joint  and  on  the 
Dorsum  of  the  Tarsus  . 

The  Composite  Articular  Socket  for 
the  Head  of  the  Astragalus . 

Plantar  Aspect  of  Tarsal  and  Tarso- 
metatarsal Joints .... 


THE  MUSCULAE   SYSTEM. 


243. 


245. 


246. 


247. 


251. 
252. 

253. 

254. 


Muscle-Attachments  to  the  Eight  274. 

Clavicle  (upper  surface)  .  .  320 
244.  Superficial   Muscles   of    the   Back  275. 

and  Vertebro-scapular  Muscles  .  321 
Muscle-Attachments  to  the  Right  276. 

Scapula  (posterior  surface)  .  .       322 

Muscle-Attachments  to  the  Front  of  277. 

the  Sternum  .  .  .  .323 
The  Muscles  of  the  Front  of  the  Chest     324 

248.  Muscle-Attachments  to  the  Right  278. 

Clavicle  (under  surface)        .         .       325 

249.  The  Left  Serratus  Anterior  (Ser-  279. 

ratus  Magnus)  Muscle .         .         .       326 

250.  Muscle-Attachments  to  the  Right 
Scapula  (anterior  aspect)      .         .       326       280. 

Left  Scapular  Muscles  and  Tricejjs  328 
Muscles  of  Posterior  Wall  of  Left 

Axilla  and  Front  of  the  Arm  .  329 
Muscle-Attachments  to  the  Front  281. 

of  the  Right  Humerus  .         .       330 

Muscle-Attachments  to  the  Right 

Scajiula  (posterior  surface)  .         .       330      282. 

255.  Superficial  Muscles  on  the  Front  of 

the  Right  Arm  and  Forearm        .       333 

256.  The   Muscles  on   the  Back  of  the  283. 

Left  Arm,  Forearm,  and  Hand  .  333 
257  a.  Muscle-Attachments  to  the  Front  284. 

of  the  Right  Humerus        .         .       334 
Muscle-Attachments  to  the  Back  285. 

of  the  Right  Humerus        .         .       334 
The  Left  Palmar  Fascia  .         .         .336      286. 
Superficial   Muscles   and   Tendons 

in  the  Palm  of  the  Left  Hand  .  337 
Section  Across  the  Forearm  in  the  287. 

Middle  Third       ....       339      288. 
The  Superficial  Muscles  of  the  Left 
Forearm 340      289. 

262.  Deeper  Muscles  of  the  Left  Forearm       340 

263.  The  Tendons  attached  to  the  Index- 

Finger  341       290. 

264.  Muscle-Attachments  to  the  Right 

Radius  and  Ulna  (anterior  aspect)      342 

265.  Deepest  Muscles  in  the  Front  of  the  291. 

Left  Forearm        .         .         ...       343 
The  Palmar  Muscles,  Right  Side    .       344      292. 
Muscle-Attachments  to  the  Palmar 

Aspect  of  the  Right  Carpus  and 

Metacarpus 345      293. 

The    Right    Palmar    Interosseous 

Muscles 346      294. 

Muscle-Attachments  to  the  Dorsal  295. 

Aspect  of  tlie  Right  Metacarpus  .  346 
Dorsal  Interosseous  Muscles  of  the  296. 

Right  Hand  (seenfrom  the  palmar 

aspect) 347       297. 

Muscle -Attachments  to  the  Right 

Radius      and      Ulna     (jjosterior 

aspects) 349       298. 

272.  The  Superficial  Muscles  of  the  Back  299. 

of  the  Left  Forearm      .         .         .       350 

273.  Deep  Muscles  on  the  Back  of  the  300. 

Left  Forearm        ....       350 


257  6. 

258. 
259. 

260. 

261. 


266 

267, 


268. 
269. 


270. 


27  L 


Superficial  Anatomy  of  the  Left 
Groin   ...... 

The  Dissection  of  the  Left  Inguinal 
Canal   ...... 

The  Muscles  on  the  Front  of  the 
Right  Thigh         .... 

Muscle  -  Attachments  to  the  An- 
terior Surface  of  the  Upper  Part 
of  the  Left  Femur 

Transverse  Section  of  the  Thigh 
(Hunter's  Canal)  .... 

Muscle-Attachments  to  the  Medial 
side  of  the  Upper  Part  of  the 
Left  Tibia 

View  of  the  Posterior  Abdominal 
Wall,  to  show  the  Muscles  and  the 
Nerves  of  the  Lumbo- sacral 
Plexus 

Muscle- Attachments  to  the  Posterior 
Aspect  of  the  Upper  Part  of  the 
Left  Femur 

Muscle -Attachments  to  the  Outer 
Surface  of  the  Right  Pubis  and 
Ischium        ..... 

Scheme  of  the  Course  and  Distribu- 
tion of  the  Right  Obturator  Nerve 

Deep  Muscles  on  the  Back  of  the 
Right  Thigh        .... 

Muscle -Attachments  to  the  Right 
Dorsum  Iliiand  Tuber  Ischiadicum 

Muscle-Attachments  to  the  Posterior 
Aspect  of  the  Upper  Part  of  the 
Left  Femur  ..... 

The  Right  GlutseusMaximus  Muscle 

The  Muscles  and  Nerves  of  the 
Right  Buttock      .... 

Muscle-Attachments  to  the  Upper 
Aspect  of  the  Greater  Trochanter 
of  the  Left  Femur 

Muscle-Attachments  to  the  Right 
Dorsum  Ilii  and  Tuber  Ischii 
(Ischiadicum)        .... 

The  Muscles  on  the  Back  of  the 
Right  Thigh         .... 

Muscle-Attachments  to  the  Medial 
Side  of  the  Upper  Part  of  the 
Right  Tibia ..... 

Coronal  Section  through  the  Left 
Ankle- Joint,  Talus,  and  Calcaneus 

The  Left  Plantar  Fascia 

Muscle-Attachments  to  Left  Tarsus 
and  Metatarsus  (plantar  aspect)  . 

Muscles  of  the  Front  of  the  Right 
Leg  and  Dorsum  of  the  Right  Foot 

The  Insertions  of  the  Tibialis 
Posterior  and  Peronteus  Longus 
in  the  Sole  of  the  Left  Foot 

The  Right  Soleus  Muscle 

The  Deep  Muscles  on  the  Back  of 
the  Right  Leg       .         .         .         . 

Muscle- Attachments  to  the  Posterior 
Surface  of  the  Right  Tibia  . 


308 
309 
310 


354 
355 
357 

358 
358 

359 

360 

361 

362 
363 
364 
365 


366 
366 

367 


367 

368 
369 

369 

372 
373 

374 

375 

376 
376 

377 

377 


LIST  OF  ILLUSTEATIONS. 


XXI 


FIG.  PAfiE 

301.  The   Muscles   of   the    Right   Foot 

(second  layer)        ....       378 

302.  Muscle-Attachments  to  Left  Tarsus 

and  Metatarsus  (jjlantar  asjiect)   .       380 

303.  The    Superficial    Muscles    of    the 

Right  Foot 381 

304.  The  Deep  Muscles  of  the  Sole  of 

the  Right  Foot     ....       382 

305.  Interosseous  Muscles  of  the  Right 

Foot 383 

306.  Transvei-se    Section    through    the 

Abdomen,  opposite  the  Second 
Lumbar  Vertebra  .         .         .       385 

307.  Schematic    Representation  of    the 

parts  of  the  Left  Sacro-sjiinalis 
(Erector  Spinae)  Muscle        .         .       386 

308.  Scheme  of  Muscular -Attachments 

to  the  Transverse  Processes  of  the 
Cervical  Vertebrae        .         .         .       387 

309.  The  Deep  Muscles  of  the  Back       .       388 

310.  The  Suboccipital  Triangle  of  the 

Left  Side 390 

311.  Muscle-Attachments  to  the  Sacrum       390 

312.  Muscle-Attachments  to  the  Occipi- 

tal Bone  (parietal  surface)    .         .       391 

313.  Transverse  Section  in  the  Cervical 

Region 394 

314.  The  Muscles  of  the  Face  and  Scalp       396 

315.  Transverse  Vertical  Section  through 

the  Left  Orbit  behind  the  Eye- 
ball to  show  the  arrangement  of 
Muscles 399 

316.  The  Muscles  of  the  Right   Orbit 

(from  above)         ....       400 

317.  The  Muscles  of  the  Right   Orbit 

(from  without)      ....       400 

318.  Schematic   Representation  of    the 

Nerves  which  traverse  the  Cavity 

of  the  Right  Orbit  .  .  .401 
319  a.  Muscle-Attachments  to  the  Lateral 

Aspect  of  the  Lower  Jaw  .  .  402 
319  h.  Muscle  -  Attachments      on       the 

Medial  Side  of  the  Lower  Jaw     .       402 

320.  Muscles  of  Mastication  (superficial 

view) 403 

321.  The  Right  Temporal  Muscle  .         .       403 

322.  The  Pterygoid  Muscles  of  the  Right 

Side 404 

323.  Muscle -Attachments  to  the  Occipi- 

tal Bone  (parietal  surface)    .         .       405 

324.  The  Muscles   of  the   Tongue   and 

Hyoid  Bone  (right  side)       .         .       406 

325.  The  Muscles  of  the  Side  of  the  Neck 

(anterior  and  posterior  triangles)        407 

326.  Muscle  -  Attachments       on        the 

Medial  Side  of  the  Lower  Jaw     .       408 

327.  Transverse       and       Longitudinal 

Vertical  Sections  through  the 
Tongue 408 

328.  Posterior  View  of  the  Pharynx  and 

Constrictor  Muscles      .         .         .       411 


FIO. 

329. 


330. 


331. 


332. 


335. 
336. 


337  a. 
337  h. 

338. 


Lateral  View  of  the  Wall  of  the 
Pharynx 412 

Muscle-Attachments  to  the  Upper 
Surface  of  tlie  First  Rib  and  the 
Lateral  Surface  of  the  Second  Rib       413 

The  Prsevertebral  Muscles  of  the 
Neck 414 

Sclieme  of  Muscular-Attachments 
to  Cervical  Vertebrae   .         .         .414 

333.  Muscle-Attachments  to  the  Occipi- 

tal Bone  (inferior  surface)    .         .       415 

334.  The  Muscles  of  the  Right  Thoracic 

Wall 416 

The  Diaphragm  (from  below)  .       417 

View  of  the  Posterior  Abdominal 
Wall,  to  show  the  Muscles  and 
the  Nerves  of  the  Lumbo-sacral 

Plexus 418 

Superficial  Anatomy  of  the  Groin       420 
The  Dissection   of  the  Inguinal 

Canal 421 

Transverse  Section  through  the 
Abdomen 422 

339.  The  Left  Obliquus  Externus  Ab- 

dominis        .....       423 

340.  The  Right  Obliquus  Internus  Ab- 

dominis        .....       424 
341  a.  The  Left  Inguinal  Canal  on  Re- 
flection of  the  External  Oblique       425 
341  h.  The  Dissection  of  the    Inguinal 

Canal 426 

342.  Deep  Dissection  of  the  Abdominal 

Wall 427 

343.  Sheath   of  the  Rectus  Abdominis 

Muscle 428 

View  of  the  Posterior  Abdominal 
Wall  to  show  the  Muscles  and  the 
Nerves  of  the  Lumbo  -  sacral 
Plexus 429 

The   Muscles   and   Nerves   of   the 
Male  Perineum     .         .         .         .431 
346.  The  Muscles  of  the  Female  Peri- 
neum (after  Peter  Thompson)      .       432 

The  Triangular  Ligament  of  the 
Perineum,  and  the  Termination 
of  the  Pudic  Nerve       .         .         .       433 

Relations  of  the  Pelvic  Fascia  to 
the  Rectum  and  Prostate     .         .       435 

Relations  of  the  Pelvic  Fascia  to 
the  Rectum  and  Prostate  (medial 
section) 436 

Relations  of  the  Pelvic  Fascia  to 
the  Rectum,  Urethra,  and  Vagina 
(medial  section)  ....  437 
351.  Fascial  and  Muscular  Wall  of  the 
Pelvis  after  removal  of  i:)art  of 
the  Left  Innominate  Bone  .         .       439 

Scheme  to  illustrate  the  disj^osition 
of  the  Myotomes  in  the  Embryo 
in  relation  to  the  Head,  Trunk, 
and  Limbs 440 


344. 


345. 


34 


348. 


349. 


350. 


352. 


THE  NEEVOUS  SYSTEM. 


353.  Nerve-Fibre   from    a   Frog    (after 

V.  Kolliker) 

354.  Three  Nerve-Cells  from    the  An- 

terior Horn  of  Gray  Matter  of  the 
Human  Spinal  Cord    . 

355.  Two  Multipolar  Nerve-Cells  . 


444 


445 
446 


356.  Nerve-Cell  from  Cerebellum  (Pro- 

fessor Symington)         .         .         .       446 

357.  Transverse    Section    through    the 

early   Neiu-al   Tube    (Alfred    H. 
Young) 447 

358.  Developmental  Stages  exhibited  by 


LIST  OF  ILLUSTEATIONS. 


a  Pyramidal  Cell  of  the  Brain 
(after  Ramon  j  Cajal)  .         .         .       447 

359.  Diagi-am  of  the  Connexion  estab- 

lished by  a  Ganglionic  and  a 
Motor  Neuron  (Eam6n  j  Cajal)  .       449 

360.  Three  Stages  in  the  development 

of  a  Cell  from  a  Spinal  Ganglion       449 

361.  Nerve-Cells  as  depicted  by  Bethe  .       450 

362.  Section  through  the  Central  Canal 

of  the  Sjjinal  Cord  of  a  Human 
Embryo  (after  v.  Lenhossek)         .       451 

363.  Human  Foetus  in  the  third  month 

of  Development,  with  the  Brain 
and  Spinal  Cord  exposed  from 
behind 452 

364.  The    Conns    Medullaris    and    the 

Filuni  Terminale  exposed  within 

the  Spinal  Canal ....       453 

365.  The  Roots  of  Origin  of  the  Seventh 

Dorsal  Nerve        ....       453 

366.  Section  through  the  Conus  Medul- 

laris and  the  Cauda  Equina  as 

they  lie  in  the  Sjsinal  Canal        .       453 

367.  Diagram  of  the  Spinal  Cord  as  seen 

from  behind  ....       455 

368.  Transverse    Section    through    the 

Upper  Part  of  the  Cervical  Region 

of  the  Cord  of  an  Orang       .         .       456 

369.  Section  through  each  of  the  Four 

Regions  of  the  Cord      .         .         .       458 

370.  Section  through  the  Fifth  Cervical 

Segment  of  the  Cord    .         .         .462 

371.  Section  through  the  eighth  Dorsal 

Segment  of  the  Spinal  Cord        .       463 

372.  Section  through  the  Third  Lumbar 

Segment  of  the  Spinal  Cord  to 
show  the  grouping  of  the  Motor 
Cells 463 

373.  Section   through    the    first   Sacral 

Segment  of  the  Spinal  Cord         .       464 

374.  Transverse    Section    through    the 

White  Matter  of  the  Cord   .         .       465 

375.  Diagram  to  show  the  Arrangement 

of  the  Fibres  of  the  Posterior 
Nerve -Roots  in  the  Posterior 
Columns  of  the  Cord    .         .         .       467 

376.  Diagram   to  show  the  manner  in 

which  the  Fibres  of  the  Posterior 
Nerve-Roots  enter  and  ascend  in 
the  Posterior  Column  of  the  Cord 
(from  Edinger)      .... 

377.  Diagrammatic  Representation  of  a 

Transver.se  Section  through  the 
SpinaJ4&ord  .... 

378.  Schema    of   a   Transverse   Section 

through  the  Early  Neural  Tube 
(Young)         ..... 

379.  Three  Stages  in  the  Develoi^ment 

of  the  Spinal  Cord  (His) 

380.  The  Base  of  the  Brain  with  Cranial 

Nerves  attached   .... 

381.  Schema  showing  the  Connexions  of 

the  several  parts  of  the  Brain 

382.  Two   Stages   in   the  Development 

of  the  Human  Brain  (after  His)  . 

383.  Two   Cross    Sections  through   the 

Fore-Brain 

384.  The  Brain  of  a  Human  Embryo  in 

tlie  Fifth  Week  (after  His)  . 

385.  Profile   View   of    the   Brain    of   a 

Human  Embryo  of  Ten  Weeks 
(His) .479 


402. 

403. 

467 

404. 

469 

405. 

471 

472 

406. 

474 

476 

407. 

477 
477 
478 

408. 
409. 
410. 

FIQ.  PAGE 

386.  Diagrams  to  illustrate  the  Alar  and 

Basal  Laminae  .         ,         .       480 

387.  Front  View  of  the  Medulla,  Pons, 

and  Mesencei^halon  of  a  full-time 
Human  Foetus      .         .         .         .481 

388.  Back  View  of  the  Medulla,  Pons, 

and  Mesencephalon  of  a  full-time 
Human  Foetus      ....       482 

389.  Diagram  of  the  Decussation  of  the 

Pyramids  (modified  from  van 
Gehuchten) 483 

390.  Lateral  View  of  the  Medulla,  Pons, 

and  Mesencephalon  of  a  full-time 
Human  Foetus      ....       484 

391.  Floor  of  the  Fourth  Ventricle         .       487 

392.  Section  through  the  Lower  End  of 

the  Medulla  Oblongata  of  a  Chim- 
panzee to  show  the  Decussation 
of  the  Pyramids  ....       489 

393.  Transverse  Section  through  Lower 

End  of  the  Medulla  of  a  full-time 
Foetus 491 

394.  Section  through  the  Closed  Part  of 

Human  Medulla  immediately 
above  the  Decussation  of  the 
Pyramids 492 

395.  Section  through  the  Lower  Part  of 

the  Medulla  of  the  Orang     .         .       492 

396.  Transverse    Section    through    the 

Closed  Part  of  a  Foetal  Medulla  .       493 

397.  Transverse    Section    through    the 

Human  Medulla  in  the  Lower 
Olivary  Region     ....       493 

398.  Transverse    Section    through    the 

Middle  of  the  Olivary  Region  of 

the  Human  Medulla     .         .         .       495 

399.  Inferior  Olivary  Nucleus  as  recon- 

structed and  figured  by  Miss 
Florence  R.  Sabin         .         .         .       495 

400.  Diagram  which  shows  in  part  the 

Fibres  which  enter  into  the 
Constitution  of  the  Restiform 
Body 496 

401.  Section  through  the  Junction  be- 

tween the  Cord  and  Medulla  of 

the  Orang 496 

Diagram  of  the  Cerebello-olivary 
Fibres 497 

Section  through  the  Lower  Part  of 
the  Human  Pons  Varolii  imme- 
diately above  the  Medulla    .         .       500 

Diagram  to  show  Connexions  of  the 
Direct  Cerebellar  and  the  Olivo- 
cerebellar Tracts  .         .         .         .501 

Transverse  Section  through  the 
Pons  Varolii  at  the  Level  of  the 
Nuclei  of  the  Trigeminal  Nerve 
(Orang) 503 

Section  through  the  Upper  Part  of 
the  Pons  Varolii  of  the  Orang, 
above  the  Level  of  the  Trigeminal 
Nuclei 504 

Two  Sections  through  the  Tegmen- 
tum of  the  Pons  at  its  Upper 
Part,  close  to  the  Mesencephalon       605 

Upper  Surface  of  the  Cerebellum  .       505 

Lower  Surface  of  the  Cerebellum   .       508 

Sagittal  Section  through  the  Left 
Lateral  Hemisphere  of  the  Cere- 
bellum   509 

411.  From   a   Dissection  by  Dr.  E.  B. 
Jamieson,  showing  Corpus  Den- 


LIST  OF  ILLUSTEATIONS. 


XXlll 


tatum  and  Superior  Cerebellar 
Peduncle,  etc 509 

412.  IVIedial  Section  through  the  Corpus 

Callosuni,  the  Mesencephalon,  the 
Pons,  Medulla,  and  Cerebellum    .       512 

413.  Transverse  Section  through  a  Cere- 

bellar Folium  (after  Kolliker)      .       513 

414.  Section  through  the  Moleculai-  and 

Granular  Layers  in  the  Long 
Axis  of  a  Cerebellar  Folium 
(after  Kolliker)    .         .         .  .514 

415.  Diagram  of  the  Spinal  Origin  of 

the  Spinal  Accessory  Nerve  (after 
Bruce)  ...... 

416.  Section  through  the  Upper  Part  of 

the  Cervical  Kegiorf  of  the  Cord 
(Orang)  .         .         ... 

417.  Diagram  showing  the  Brain  Con- 

nexions of  the  Vagus,  Glosso- 
pharyngeal, Auditory,  Facial, 
Abducent,  and  Trigeminal  Nerves 

418.  Central  Connexions  of  the  Cochlear 

and  Vestibular  Divisions  of  the 
Auditory  Nerve    .... 

419.  Section  through  the  Pons  Varolii  of 

the  Orang 

420.  Diagram  of  the  Intrapontine  Course 

pursued  by  the  Facial  Nerve 

421.  Section  through  the  Pons  Varolii 

of  the  Orang  at  the  Level  of  the 
Nuclei  of  the  Trigeminal  Nerve 

422.  Three  Stages  in'  the  Development 

of  the  Medulla  Oblongata  (His — 
slightly  modified) 

423.  Drawings  to  illustrate  the  Develop- 

ment of  the  Cerebellum  (from 
Kuithan)       ..... 

424.  Brain   of   an   Embryo   of    Eleven 

Weeks 

425.  Sections    through    Cerebellum    of 

Human  Foetus      .... 

426.  Under  Surface  of  the  Cerebellum  of 

a  Human  Foetus  .... 

427.  Cerebellum  of  a  Human  Foetus 

428.  Diagram  of  the  Roots  of  the  Oj^tic 

Nerve 

429.  Transverse    Section    through    the 

Upper  Part  of  the  Mesencephalon 

430.  Transverse    Section    through     the 

Human  Mesencephalon  at  the 
Level  of  the  Inferior  Quadri- 
geminal  Body       .... 

431.  Transverse    Section    through    the 

Human  Mesencephalon  at  the 
Level  of  the  Superior  Quadri- 
geminal  Body       ....       536 

432.  Section  tlirough  the  Inferior  Quadri- 

geminal  Body  and  the  Tegmentum 
of  the  Mesencephalon  below  the 
Level  of  the  Nucleus  of  the  Fourth 
Nerve  in  the  Orang      .         .         .       537 

433.  Section  through  the  Inferior  Quad- 

rigeminal  Body  and  the  Tegmen- 
tum of  the  Mesencephalon    .         .       538 

434.  Diagram  of  the  Connexions  of  the 

Posterior  Longitudinal  Bundle 
(after  Held— modified)  .         .       538 

435.  Diagram  of  the  Connexions  of  the 

Medial  FiUet  and  also  of  certain 

of  the  Thalamo-Cortical  Fibres    .       539 

436.  Section  through  the  Inferior  Quad- 

rigeminal    Body    and    the    Teg- 


437. 


438. 
439. 
440. 

441. 


516 

442. 
443. 

516 

444. 

445. 

518 

446. 

520 
522 
523 

447. 
448. 
449. 
450. 

525 

451 

527 

452. 

529 

453. 
454 

529 

455. 

530 

456 

530 
530 

532 

457. 
458 
459. 

533 

460. 

535 

461 
462 

463. 

464. 

465. 
466. 
467. 
468. 
469. 


mentum  of  the  Mesencephalon 
(Orang) 540 

Section  through  the  Inferior  Quad- 
rigeminal  Body  and  the  Tegmen- 
tum of  the  Mesencephalon  (Orang)       541 

Tlie  Two  Optic  Thalami  .         .       543 

Schema 546 

Coronal  Section  through  the  Cere- 
brum of  an  Orang         .         .         .       547 

Medial  Section  through  the  Pituitary 
Region  in  a  Cliild  of  Twelve 
Months  old 549 

Medial  Section  through  the  Pituitary 
Region  in  the  Adult     .         .         .       549 

Medial  Section  through  the  Corpus 
Callosum,  Diencephalon,  etc.         .       550 

Ca.^  of  the  Ventricles  of  the  Brain 
(from  Retzius)        .         .         .         .551 

Diagram  of  the  Central  Connexions 
of  the  Optic  Nerve  and  Optic  Tract       552 

Gyri  and  Sulci  on  the  Outer  Surface 
of  the  Cerebral  Hemisphere  .       555 

Three  Stages  in  the  Development  of 
the  Insula  and  the  Insular  Opercula     557 

Development  of  the  Opercula  which 
cover  the  Insula   ....       557 

Fissure  of  Rolando  fully  ojjened 
up 558 

Left  Cerebral  Hemisphere  from  a 
Foetus 559 

The  Gyri  and  Sulci  on  the  Medial 
Aspect  ofthe  Cerebral  Hemisphere       559 

Gyri  and  Sulci  on  the  Tentorial 
and  Orbital  Aspects  of  the  Cerebral 
Hemispheres 562 

Intraparietal  Sulcus  fully  opened  up       564 

Internal  Parieto-occipital  and  the 
Calcarine  Fissures  fully  opened  up       565 

Development  of  the  Parieto-occi- 
pital and  the  Calcarine  Fissures  .       566 

Coronal  Section  through  the  Left 
Side  of  the  Cerebrum,  Mesen- 
cephalon, and  Pons  (Chimpanzee)       569 

The  Cor^jus  CaUosum      .         .         .570 

Profile  View  of  the  Fornix      .         .       572 

Cast  of  the  Ventricular  System  of 
the  Brain  (after  Retzius)      .         .       574 

Coronal  Section  through  the  Frontal 
Lobes  and  the  Anterior  Horns  of 
the  Lateral  Ventricles  .         .         .       574 

Dissection  to  show  the  Fornix  and 
Lateral  Ventricles         .         .         .575 

Coronal  Section  through  the 
Posterior  Horns  of  the  Lateral 
Ventricles 576 

Dissection  to  show  the  Fornix  and 
the  Posterior  and  Descending 
Cornua  of  the  Lateral  Ventricle 
of  the  Left  Side    ....       677 

Dissection  to  show  the  Posterior 
and  Descending  Cornua  of  the 
Lateral  Ventricle  .         .         .       578 

Horizontal  Section  through  the 
Right  Cerebral  Hemisphere         .       579 

Coronal  Section  through  the  Cere- 
bral Hemispheres         .         .         .       580 

Coronal  Section  through  the  Cere- 
brum    ......       581 

Coronal  Section  through  the  Left 
Side  of  the  Cerebrum  of  an  Orang       582 

Diagram  to  illustrate  Minute 
Structure  of  the  Cerebral  Cortex        586 


XXIV 


LIST  OF  ILLUSTEATIONS. 


FIO. 

470.  Diagram  of  tlie  Minute  Structure 

of  the  Olfactory  Bulb  . 

471.  Two  Coronal  Sections  through  the 

Cerebral  Hemispheres  of  an  Orang 

472.  Diagram  of  the  Leading  Association 

Bundles ofthe  Cerebral  Hemisphere 

473.  Coronal  Section  through  the  Left 

Side  of  the  Cerebrum,  Mesen- 
cephalon and  Pons  (Chimpanzee) 

474.  Diagrams  to  show  Flechsig's  Sensory 

and  Association  Areas  on  the  sur- 
face of  the  Cerebral  Hemisphere 

475.  Two  Drawings  of  the  Embryonic 

Brain  (by  His)      .... 

476.  Two  Drawings  by  His  illustrating  the 

Development  ofthe  Human  Brain 

477.  Sagittal  Section  through  the  Skull 

478.  Diagram  to  show  the  Eelations  of 

the  Membranes  of  the  Brain  to 
the  Cranial  Wall,  etc.  . 

479.  Membranes  of  the  Spinal  Cord,  and 

the  Mode  of  Origin  of  the  Spinal 
Nerves 

480.  Medial  Section  through  the  Cranial 

Vault  in  the  Frontal  Eegion 

481.  Dissection  to  show  the  Velum  In- 

terpositum    ..... 

482.  Diagrammatic      Coronal      Section 

through  the  Optic  Thalami 

483.  Membranes  of  the  Spinal  Cord,  and 

the  Mode  of  Origin  of  the  Spinal 
Nerves  ..... 

484.  Scheme  of  the  Arrangement  of  the 

Membranes  of  the  Spinal  Cord 
and  the  Roots  of  the  Spinal  Nerves 

485.  Diagrammatic    Representation    of 

the  Origin  of  the  Spinal  Nerves  . 

486.  Scheme   of  the  Distribution  of  a 

Typical  Spinal  Nerve  . 

487.  Distribution  of  Cutaneous  Nerves 

on  the  Back  of  the  Trunk    . 

488.  Posterior  Cervical  Plexus 

489.  Distribution  of  Cutaneous  Nerves 

on  the  Front  of  the  Trunk  . 

490.  The  Cervical  Plexus 

491.  Distribution  of  Cutaneous  Nerves 

to  the  Head  and  Neck 

492.  The  Triangles  of  the  Neck      . 

493.  Muscles   of  the   Hyoid   Bone   and 

Styloid  Process,  and  the  Extrinsic 
Muscles  of  the  Tongue,  with  their 
Nerves 

494.  Nerves  of  the  Brachial  Plexus 

495.  Diagram  of  the  Origin  and  Distri- 

bution of  the  Nerves  to  the 
Pectoral  Muscles  .... 

496.  The  Posterior  Wall  of  the  Axilla 

and  the  Front  of  the  Arm    . 

497.  The     Distribution    of    Cutaneous 

Nerves  on  the  Front  of  the  Arm 
and  Hand 

498.  The    Distribution     of     Cutaneous 

Nerves  on  the  Back  of  the  Arm 
and  Hand 

499.  Deltoid  Region  and  Back  of  Arm  . 

500.  Diagrammatic    Representation    of 

the  Brandies  of  the  Musculo- 
spiral  Nerve  .... 

501.  The  Muscles   of  the  Back  of  the 

Forearm 

502.  Scheme   of  the   Distribution   of  a 

Typical  Spinal  Nerve  . 


587 


589 


590 


592 


593 

595 

596 
598 


601 


602 


603 


604 


605 


605 


607 
608 
609 

611 

612 

615 
616 

618 
619 


620 
623 


625 


626 


628 


630 
631 


633 


634 


636 


FIO. 

503.  The     Distribution    of    Cutaneous 

Nerves  on  the  Front  of  the  Trunk 

504.  Nerves  of  the  L;imbo-sacral  Plexus 

505.  View  of  the  Posterior  Abdominal 

Wall,  to  show  the  Muscles  and  the 
Nerves  of  the  Lumbo-Sacral  Plexiis 

506.  Scheme  of  the  Course  and  Distri- 

bution of  the  Obturator  Nerve     . 

507.  Distribution  of  Cutaneous  Nerves 

on  the  Front  of  the  Lower  Limb  . 

508.  Distribution  of  Cutaneous  Nerves 

on  the  Dorsum  of  the  Foot  . 

509.  Distribution  of  Cutaneous  Nerves 

on  the  Back  of  the  Lower  Limb  . 

510.  Scheme    of    Distribution     of    the 

Plantar  Nerves     ....       654 

511.  Nerves  of  the  Lumbo-sacral  Plexus       656 

512.  The    Muscles   and   Nerves   of  the 

Male  Perineum     ....       658 

513.  The   Triangular   Ligament  of  the 

Perineum 659 

514.  Scheme  of  the  Innervation  of  the 

Hinder  Portion  of  the  Trunk  and 

of  the  Perineum    ....       660 

515.  Development  of  the  Spinal  Nerves       661 

516.  Scheme  ofthe  Segmental  Distribu- 

tion of  the  Muscular  Nerves  of  the 
Upper  and  Lower  Limbs     .         .       671 

517.  View  of  the  Under  Surface  of  the 

Brain 675 

518.  Innervation  of  the  Nasal  Cavity    .       676 

519.  Diagram  of  the  Central  Connexions 

of  the  Optic  Nerve  and  Optic  Tract       676 

520.  Relations  of  Structures  in  the  Cav- 

ernous Sinus  and  Sphenoidal 
Fissure 677 

521.  Dorsal  Surface  of  the  Mid-Brain     .       677 

522.  The  Base  of  the  Skull     .         .         .678 

523.  Distribution  of  Sensory  Nerves  to 

the  Head  and  Neck      .         .         .679 

524.  Scheme  of  the  Distribution  of  the 

Ophthalmic  Nerve        .         .         .       680 

525.  Schematic   Representation   of    the 

Nerves  which  traverse  the  Cavity 

of  the  Orbit 681 

526.  Scheme,  of  the  Course  and  Distri- 

bution of  the  Superior  Maxillary 
Nerve 682 

527.  Scheme  of  the  Distribution  of  the 

Inferior  Maxillary  Nerve     .         .       684 

528.  The  Facial  Nerve  with  its  Branches 

and  Communications  in  the  Aque- 
duct of  Fallopius  ....       687 

529.  Distribution  of  Facial  Nerve  out- 

side the  Skull,  and  Communica- 
tions with  Trigeminal  Nerve  on 
the  Face 688 

530.  Scheme  of  the  Origin  and  Distribu- 

tion of  the  Auditory  Nerve .         .       689 

531.  Scheme  of  the  Distribution  of  the 

Glosso-pharyngeal  Nerve     .         .       690 

532.  The  Distribution  of  the  Pneumo- 

gastric  Nerve         ....       691 

533.  The   Constitution   of  the    Cardiac 

Plexuses 694 

534.  The  Distribution  of  the  Pneumo- 

gastric  Nerve        ....       695 

535.  Scheme  of  the  Origin,  Connexions, 

and  Distribution  of  the  Spinal 
Accessory  Nerve  ....       696 

536.  The  Muscles  of  the  Hyoid  Bone  and 

Styloid  Process,  and  the  Extrinsic 


LIST  OF  ILLUSTKATIONS. 


XXV 


Muscles  of  the  Tongue  with  their 
Nerves 

537.  Comparison  of  Origins  of  Nerve- 

Roots  from  Spinal  Cord  and  Hind- 
Brain  (after  His)  .... 

538.  Scheme  to  illustrate  the  Disposition 

of  the  Myotonies  in  the  Embryo  in 
relation  to  the  Head,  Trunk,  and 
Limbs 

539.  Scheme  to  illustrate  the  Embryo- 

logical  Arrangement  of  the  Cranial 
Nerves 

540.  Scheme  of  the  Constitution  of  tlie 

White  Ramus  Communicans  of 
the  Sympathetic  .... 

541.  Scheme   of  the    Constitution   and 

Connexions  of  the  Gangliated 
Cord  of  the  Sympathetic 


PAGE 

697 

700 

702 
703 

704 
705 


FIO.  PAGE 

542.  The    Distribution     of    the     Sym- 

pathetic Gangliated  Cord  in  the 
Neck 707 

543.  The   Constitution    of  the    Cardiac 

Plexuses 708 

544.  The    Arrangement    of    the    Sym- 

jmthetic  System   in  the  Thorax, 
Abdomen,  and  Pelvis    .         .         .       709 

545.  The  Lumbar  Portion  of  the  Sym- 

pathetic   Gangliated    Cord    and 
Lumbar  Plexus     .         .         .         .       711 

546.  The    Arrangement    of    the    Sym- 

pathetic  System  in  the  Thorax, 
Abdomen,  and  Pelvis   .         .         .       713 

547.  The    Development    of    the    Sym- 

pathetic Gangliated  Cord     .         .       715 

548.  Section   through   the  Sympathetic 

Gangliated  Cord  of  an  Embryo    .       716 


THE  OKGANS  OF  SENSE  AND  THE  INTEGUMENT. 


549.  Lateral  View  of  Nasal  Septum 

550.  Profile  View  of  the  Bony  and  Carti- 

laginous Skeleton  of  the  Nose 

551.  Front  View  of  the  Bony  and  Carti- 

laginous Skeleton  of  the  Nose 

552.  Cartilages  of  Nose  from  Below 

553.  Coronal     Section    through    Nasal 

Fossfe  ;  Anterior  Half  of  Section 
viewed  from  Behind     . 

554.  Section  through   Nose   of  Kitten, 

showing   position   of    Jacobson's 
Organ 

555.  View  of  the  Outer  Wall  of  the  Nose 

556.  Section     through      the     Olfactory 

Mucous  Membrane 

557.  Olfactory  and  Supporting  Cells 

558.  Diagram  of  a  Horizontal   Section 

through  Left  Eyeball  and  Optic 
Nerve 

559.  Vertical  Section  of  Cornea 

560.  Vertical   Section  of  Chorioid  and 

Inner  Part  of  Sclera 

561.  Diagram  of  the  Circulation  in  the 

Eye  (Leber) 

562.  Section  through  Ciliary  Region  of 

Eyeball 

563.  Blood-Vessels  of  Iris  and  Anterior 

Part  of  Chorioid  (Arnold)     . 

564.  Diagrammatic      Section     of     the 

Human    Retina   (modified    from 
Schultze) 

565.  Perpendicular    Sections   of    ]\Iam- 

malian  Retina  (Cajal)  . 

566.  Cone    and    two     Rods     from    the 

Human  Retina      .         .         . 

567.  Pigmented  Epithelium  ofj  Human 

Retina  .        .         .        •  J      • 

568.  Section   through   Outer   Layers  of 

Retina  .         .         .         •  I      • 

569.  Blood-Vessels  of  the  Retina    . 

570.  Canal     of     Petit    distenfled     and 

viewed  from  the  Front  [ 

571.  Lens  hardened   in   Fornialiu    and 

dissected  to  show  its  (Joncentric 
Laminse        .         .         .1       .        . 

572.  Diagrammatic    Represedtatidn    of 

the   Radii   Lentis  of  flie   Fcetal 
Lens      •••/•. 

573.  Section  through  the  Eqifctor  of  the 

Lens      .         .         .        I         . 


718 

574. 

719 

575. 

719 

576. 

720 

577. 

720 

578. 

579. 

721 

580. 

721 

58L 

722 

582. 

722 

583. 

584. 

724 

726 

585. 

586. 

727 

587. 

728 

588. 

729 

589. 

590. 

730 

591. 

592. 

732 

593. 

733 

594. 

733 

595. 

734 

734 

596. 

735 

736 

597. 

598. 

736 

599. 

600. 

737 

601. 

737 

Vertical    Section    through   Upper 

Eyelid 738 

Sections  through   Portions  of  the 

Heads  of  Foetal  Rabbits  .  .  741 
Optic  Cup  and  Lens  viewed  from 

Behind  and  Below  .  .  .  742 
Diagrammatic  View  of  the  Organ 

of  Hearing  .....  744 
View    of    Outer   Surface    of    Left 

Pinna 744 

Outer  Surface  of  Cartilage  of  Pinna  745 
Inner  Surface  of  Cartilage  of  Pinna  745 
Vertical  Transverse  Section  of  Right 

Ear 747 

Horizontal  Section  through  Right 

Ear 747 

Section  through  Left  Temporal  Bone  749 
Left  Membrana  Tympani  and  Re- 

cessus  Epitympanicus  .  .  .  749 
Left  Tympanic  Membrane  .  .  751 
Transverse  Section  of  the  Cartilag- 
inous Part  of  the  Eustachian  Tube  753 
Tympanic  Ossicles  of  Left  Ear  .  755 
Left  Membrana  Tympani  and  Chain 

of  Tympanic  Ossicles    .         .         .       755 
Left  Bony  Labyrinth       .         .         .       759 
Interior  of  Left  Bony  Labyrinth     .       759 
Section  of  Bony  Cochlea         .         .       761 
Diagrammatic    Representation    of 
the  Different  Parts  of  the  Mem- 
branous Labyrinth        .         .         .       762 
Transverse  Section  of  Human  Semi- 
circular Canal  (Riidinger)     .         .       763 
Section  across  the  Ductus  Cochlearis 

(Retzius) 764 

Transverse  Section  through  Outer 

Wall      of     Ductus      Cochlearis 

(Schwalbe)    ....  765 

Transverse  Section  of  Corti's  Organ 

from  the  Central  Coil  of  Cochlea 

(Retzius) 766 

Membranous  Labyrinth  of  a  Five 

Months'  Foetus  (Retzius)  .  .  768 
Part  of  Cochlear  Nerve  (Henle)  .  768 
Sections  through  the  Region  of  the 

Hind-Brain  of  Foetal  Rabbits       .       769 
Left  Labyrinth  of  Human  Embryo       770 
Section    through    Papilla    Vallata 
(A)  of  Human  Tongue  and  (B)  of 
Rabbit 770 


LIST  OF  ILLUSTRATIONS. 


602.  Three-quarter    Surface    View   and 

Vertical  Section  of  Taste  Bud 
from  the  Pajjilla  Foliata  of  a 
Eabbit 771 

603.  Isolated    Cells  from   Taste  Bud  of 

Eabbit  (Engelmann)     .         .         .771 

604.  Vertical  Section  of  the  Skin   .         .       772 


605.  Vertical  Section  of  E]Didermis  and 

Pai^illse  of  Corium        .         .         .773 

606.  Tactile  Corpuscles  ....       775 

607.  Transverse  Section  of  a  Nail  .         .       776 

608.  Longitudinal  Section  through  Eoot 

of  Nail 776 

609.  Transverse  Section  of  Haif  Follicle 

witli  Contained  Hair    .         .         .777 


THE  VASCULAR  SYSTEM. 


610.  Structure  of  Blood- Vessels 

611.  Transverse    Section  through  Wall 

of  a  Large  Artery 

612.  Transverse  Section  of  the  Wall  of  a 

Vein      ...... 

613.  The  Base  and  Inferior  Surface  of  the 

Heart 

614.  The  Antero-superior  Surface  of  the 

Heart 

615.  The    Eelation    of    the    Heart    to 

the  Anterior  Wall  of  the  Thorax 

616.  The  Cavities  of  the  Eight  Auricle 

and  Eight  Ventricle  of  the  Heart 

617.  The  Bases  of  the  Ventricles  of  the 

Heart 

618.  The   Eelations   of  the   Heart  and 

the  Auriculo-ventricular,  Aortic, 
and  Pulmonary  Orifices  to  the 
Anterior  Thoracic  Wall 

619.  Posterior  Wall  of  the  Pericardium 

after  Eemoval  of  the  Heart . 

620.  The  Pulmonary  Arteries  and  Veins 

and  their  Eelations 

621.  The     Abdominal    Aorta    and    its 

Branches 

622.  TheCarotidand  Subclavian  Arteries 

and  their  Branches 

623.  The    External    Carotid,     Internal 

Maxillary,  and  Meningeal  Ar- 
teries   ...... 

624.  The  Carotid,  Subclavian,  and  Verte- 

bral Arteries  and  their  Main 
Branches 

625.  Distribution      of      the      Cerebral 

Arteries  on  the  Medial,  Tentorial, 
and  Inferior  Surfaces  of  the  Cere- 
bral Hemispheres 

626.  Distribution  of  Cerebral  Arteries  on 

the  Outer  Surface  of  the  Cerebrum 

627.  The  Arteries  of  the  Base  of  the  Brain 

628.  Dissection    of    the    Back    of    the 

Shoulder  and  Ui^per  Arm    . 

629.  The     Axillary     Artery     and     its 

Branches  and  Eelations 

630.  The     Bi-acliial     Artery     and     its 

Branches 

631.  Superficial  Dissection  of  the  Front 

of  the  Forearm  and  Hand    . 

632.  Deep   Dissection   of  the   Front  of 

the  Forearm  and  Hand 

633.  The  Posterior  Interosseous  Artery 

and  the  Second  Part  of  the  Eadial 
Artery,  with  tlieir  Branches 

634.  The    Abdominal    Aorta     and    its 

Branches 

635.  The  Coeliac  Axis  and  its  Branches 

636.  The  Superior  Mesenteric  Artery  and 

its  Branches  .... 

637.  The  Internal  Iliac  Artery  and  its 

Branches  in  the  Female 


781 

638. 

781 

639. 

782 

640. 

784 

641. 

785 

642. 

786 

643. 

787 

644. 

788 

645. 

646. 

789 

647. 

794 

648. 

796 
799 

649. 
650. 

803 

651. 

810 

652. 

813 

653. 

654. 

815 

816 
819 

655. 
656. 
657. 

824 

658. 

827 
830 
832 
833 

659. 
660. 

661. 

662. 

835 

840 
844 

846 

849 


663. 

664. 
665. 


The  Perineal  Distribution  of  the  In- 
ternal Pudic  Artery  in  the  Male  .       853 

The  Arteries  of  the  Buttock  and  the 
Back  of  the  Thigh  and  Knee       .       855 

The  Iliac  Arteries  and  Veins  in  the 
Female 857 

The  Femoral  Artery  and  its 
Branches       .....       858 

The  Femoral  Vessels  in  Scarpa's 
Triangle 860 

The  Arteries  of  the  Buttock  and 
the  Back  of  the  Thigh  and  Knee  .       862 

The  Popliteal  and  Posterior  Tibial 
Arteries  and  their  Branches         .       864 

The  Plantar  Arteries  and  their 
Branches 866 

The  Anterior  Tibial  Artery  and  its 
Branches 867 

The  Dorsalis  Pedis  Artery  and  its 
Branches       .....       869 

Superficial  Veins  of  the  Head  and 
Neck 878 

The  Veins  of  the  Diploe         .         .       881 

Dissection  of  the  Head  and  Neck, 
showing  the  Cranial  Blood  Sinuses 
and  the  Upper  Part  of  the  Internal 
Jugular  Vein        ....       884 

Basal  Blood  Sinuses  of  the  Dura 
Mater 885 

Superficial  Veins  on  the  Dorsum 
of  the  Hand  and  Digits        .         .       889 

Superficial  Veins  on  the  Flexor 
Aspect  of  the  Upper  Extremity  .       890 

Superficial  Veins  at  the  Bend  of 
the  Elbow 891 

The  Inferior  Vena  Cava  and  its 
Tributaries 893 

The  Femoral  Vessels  in  Scarpa's 
Triangle 898 

The  Internal  or  Long  Saphenous 
Vein  and  its  Tributaries       .         .       899 

Tlie  External  or  Short  Saphenous 
Vein  and  its  Tribiitaries       .         .       901 

The  Portal  Vein  and  its  Tributaries       902 

The  Thoracic  Duct  and  its  Tribu- 
taries     907 

Lymjjhatic  Vessels  and  Glands  of 
the  Head  and  Neck      .         .         .       910 

Superficial  Lymphatic  Vessels  of 
the  Trunk,  and  the  Lymphatic 
Glands  and  Vessels  Superficial  and 
Deep  of  the  Limbs        .         .         .       912 

Superficial  Lymphatics  of  the  Digits 
and  of  tlie  Dorsal  Aspect  of  the 
Hand    .  \ 915 

Deep  Lymj'iihatic  Glands  and  Vessels 
of  tlie  Th  prax  and  Abdomen        .       919 

Diagram  of  the  Primitive  Vascular 
System  b«fore  the  Formation  of 
the  Heart 926 


LIST  OF  ILLUSTKATIONS. 


xxvn 


TIO. 

666.  Diagram  of  the  Primitive  Blood- 

vessels after  the  Formation  of 
the  Heart     ..... 

667.  Diagram  of  the  Primitive  Blood- 

vessels after  the  Formation  of 
the  Heart,  but  before  its  Sub- 
division by  Septa  into  Auricles 
and  Ventricles      .... 

668.  Development  of  the  Heart 

669.  Development  of  the  Heart  and  the 

Main  Arteries       .... 

670.  Diagram    of    the    Course    of    the 

Foetal  Circulation 

671.  Development  of  the  Venous  System 

(Stage  I.) 

672.  Development  of  the  Venoiis  System 

(Stage  II.) 935 

673.  Development  of  the  Venous  System 

(Stage  III.) 936 

674.  Develojjment  of  the  Venous  System 

(Stage  IV.) 937 


92"; 


927 
928 

930 

931 

934 


675.  Diagram   of    the   Cejihalic   Aortic 

Arches,  and  of  the  Segmental  and 
Intersegmental  Arteries  in  the 
Eegion  in  front  of  the  Umbilicus       939 

676.  Diagram  of  the  Caudal  Aortic  Arch, 

and  of  the  Segmental  and  Inter- 
segmental Arteries  in  the  Region 
behind  the  Umbilicus  .         .         .       939 

677.  Diagram  showing  the  Arrangement 

and  Communications  of  the  Seg- 
mental and  Intersegmental  Ar- 
teries at  an  Early  Stage  of  De- 
velopment      940 

Diagram  of  the  Segmental  and 
Intersegmental  Arteries  at  a 
Later  Period  of  Development 
than  in  Fig.  677   .         .         .         .941 

Diagram  showing  the  Arrangement 
and  Communications  of  the  Seg- 
mental Arteries  in  the  Region  of 
the  Cephalic  Aortic  Arches .         .       941 


678. 


679. 


THE   KESPIEATOEY   SYSTEM. 


680.  The     Cartilages     and     Ligaments 

of  the  Larynx  viewed  from  the 
Front    ...... 

681.  Profile  View  of  the  Cartilages  and 

Ligaments  of  the  Larynx 

682.  Cartilages  and  Ligaments  of  Larynx 

from  Behind         .         .         .         . 

683.  Dissection  to  show  the  Lateral  Part 

of  the  Crico-thyreoid  Membrane  . 

684.  Superior  Aperture  of  Larynx 

685.  Coronal  Section  through  Larynx    . 

686.  Mesial  Section  through  LarjTix 

687.  Diagram  of  Rima  Glottidis     . 

688.  Specimen   showing    a    Great 

tension   of    the    Saccule   of 
Larynx  .... 

689.  The  Crico-thyreoid  Muscle     . 

690.  Dissection  of  the   Muscles  in 

Lateral  Wall  of  the  Larynx 

691.  Dissection  of  the  Muscles  on  the 

Posterior  Aspect  of  the  Lar}Tix    . 

692.  Cavitv  of  the  Larvnx 

693.  The  Trachea  and  Bronchi 

694.  Transverse    Sections    through    the 

Trachea  and  its  Immediate  Sur- 
roundings       


Ex- 

the 


the 


959 

959 

960 

963 
964 
965 
966 
966 


967 

968 

969 

970 
972 
973 


974 


695.  Diagram  showing  Arrangement  of 

Pleural  Sacs  ....       977 

696.  Dissection  of  a  Subject  hardened  by 

Formalin-Injection,  to  show  the 
Relations  of  the  two  Pleural  Sacs       978 

697.  Lateral  View  of  the  Right  Pleural 

Sac  in  a  Subject  hardened  by 
Formalin-Injection       .         .         .       979 

698.  Left    Pleural    Sac    in    a    Subject 

hardened  by  Formalin-Injection .       980 

699.  Dissection  of  the  Pleural  Sacs  from 

Behind 981 

700.  Dissection  of  Thorax  and  Root  of 

the  Neck  from  the  Front  to  show 
the  Relations  of  the  Lungs,  Peri- 
cardium, and  Thymus  Gland        .       984 

701.  Mediastinal   Surfaces    of   the    two 

Lungs  of  a  Subject  hardened  by 
Formalin-Injection       .         .         .       985 

702.  Outer  or  Costal  Surfaces  of  the  two 

Lungs 986 

703.  Sagittal     Section     through     Left 

Shoulder  and  Left  Lung       .         .       987 

704.  Sagittal  Section  through  the  Left 

Shoulder,    Lung,    and    Apex    of 

the  Heart 988 


THE   DIGESTIVE   SYSTEM. 


705.  General    View    of    the    Digestive 

System  ...... 

706.  Coronal  Section  through  the  Closed 

Mouth 

707.  Open  Mouth  showing  Palate  and 

Tonsils 

708.  Sagittal   Section   through    Mouth, 

Tongue,   Larjnix,    Pharj-nx,   and 
Nasal  Cavity         .... 

709.  Horizontal  Section  through  Mouth 

and  Pharynx  at  the  Level  of  the 
Tonsils 

710.  The  Anterior  Wall  of  the  Pharynx 

with  its  Orifices,  seen  from  Behind 

711.  The  Papilla3  of  the  Tongue     . 

712.  Open  Mouth  with  Tongue  raised. 


994 


996 


999 


1001 


1002 

1003 
1004 


and  the  Sublingual  and  A2:)ical 
Glands  exposed     ....     1005 

713.  Sections     through      the      Tongue 

(Krause) ;  and  Lymphoid  Follicle 
from  Back  Part  of  Tongiie  (Mac- 
alister) 1006 

714.  Section  of  a  Serous  Gland  and  a 

Mucous  Gland  (Bohm  and  v. 
Davidoff) 1008 

715.  Horizontal  Section  through  Mouth 

and  Pharynx  at  the  Level  of  the 
Tonsils 1009 

716.  The    Salivary   Glands    and    their 

Ducts 1010 

717.  Teeth  of  a  Child  over  seven  years 

old  (modified  from  Testut)    .         .     1014 


XXVlll 


LIST  OF  ILLUSTKATIONS. 


FIG.  PAGE 

718.  Vertical  Section  of  Canine  Tootli   .     1015 

719.  The  Permanent  Teeth  of  the  Right 

Side,  Outer  or  Labial  Aspect        .     1017 

720.  The  Permanent  Teeth  of  the  Right 

Side,  Inner  or  Lingual  Aspect     .  1018 

721.  Tlie  Upper  Permanent  Teeth  .  1018 

722.  The  Lower  Permanent  Teeth  .  1020 

723.  Horizontal  Sections  through  both 

the  Upper  and  Lower  Jaws  to 
show  the  Roots  of  the  Teeth         .     1021 

724.  To  show  the  Relation  of  the  Upper 

to  the  Lower  Teeth  when  the 
Mouth  is  Closed   ....     1022 

725.  The  Milk  Teeth  of  the  Left  Side    .     1023 

726.  Vertical  Section  of  Canine  Tooth   .     1024 

727.  Diagram  to  illustrate  the  Develoj)- 

ment  of  a  Dermal  Tooth  in  the 
Shark 1025 

728.  Diagram  to  illustrate  DevelojDment 

of  a  Tooth 1026 

729.  The  Anterior  Wall  of  the  Pharynx 

with  its  Orifices,  seen  from  Behind     1030 

730.  Sagittal    Section   through   Mouth, 

Tongue,  Larynx,  Pharynx,  and 
Nasal  Cavity         ....     1031 

731.  The  Naso-Pharynx  from  the  Front     1032 

732.  Open  Mouth   showing  Palate  and 

Tonsils 1034 

733.  Horizontal  Section  through  Mouth 

and  Pharynx  at  the  Level  of  the 
Tonsils 1035 

734.  Diagram  to  show  the  Course  of  the 

CEsophagus 1038 

735.  Tracings  from  Frozen  Sections  to 

show  the  Relations  of  the  Oeso- 
phagus   1039 

736.  Dissection  to  show  the  Arrangement 

of  the  Muscular  Fibres  on  the 
Back  of  the  Q^lsopliagus  and 
Pharynx 1041 

737.  The  Lower  Part  of  the  Pharynx  and 

the  Upper  Part  of  the  Qllsophagus  1042 

738.  Structure  of  the  CEsophagus   .         .  1042 

739.  The  Abdominal  Viscera  in  situ       .  1044 

740.  The  Front  of  the  Body   .         .         .  1046 

741.  Diagrammatic    Medial    Section  of 

Female  Body        ....     1048 

742.  Diagrammatic  Transverse  Sections 

of  Abdomen 1049 

743.  Moderately  distended  Stomach        .     1050 

744.  The  Abdominal  Viscera  after  the 

Removal  of  the  Jejunum  and 
Ileum 1051 

745.  The  Stomach  Chamberand  Stomach 

Bed 1053 

746.  The   Viscera   and    Vessels   on   the 

Posterior  Abdominal  Wall  .         .     1054 

747.  Longitudinal  Section  through  the 

Pyloric  Canal  and  Commence- 
ment of  the  Duodenum  in  a  New- 
bom  Child 1056 

748.  Abdomen  of  Female,  showing  Dis- 

placements resulting  from  Tight 
Lacing 1057 

749.  Section  through  Wall  of  Stomach, 

Cardiac  Portion  (slightly  modi- 
fied from  Stijhr)    ....     1058 

750.  The  Three  Layers  of  the  Muscular 

Coat  of  the  Stomach     .         .         .     1059 

751.  Diagram    to    show    Formation    of 

Pylorus 1060 

752.  The  Mucous  Membrane  of  Stomach     1060 


FIG.  PAGE 

753.  A  Portion  of  Small  Intestine,  with 

Mesentery  and  Vessels  .        .         .     1061 

754.  Diagram  to  show  the  Structure  of 

the    Small  and   Large    Intestine 

and  the  Duodenum       .         .         .     1062 

755.  Valvules  Conniventes      .         .         .     1063 

756.  Peyer's  Patch  and  Solitary  Glands 

from  Intestine  of  Child         .         .     1064 

757.  The   Viscera   and   Vessels   on    the 

Posterior  Abdominal  Wall  .         .     1066 

758.  The   Peritoneal    Relations   of    the 

Duodenum,  Pancreas,  Spleen, 
Kidneys,  etc 1067 

759.  The  Duodenal  Fossse  and  Folds      .     1069 

760.  The  Bile  Papilla  in  the  Interior  of 

the  Duodenum      ....     1069 

761.  The  Abdominal  Viscera  after  the  Re- 

moval of  the  Jejunum  and  Ileum  1071 

762.  Large  Intestine        ....  1074 

763.  Caecum  showing  Ileo-csecal  Valve  .  1076 

764.  Three  Forms  of  Ileo-csecal  Valve    .  1077 

765.  Diagrammatic  Section  through  the 

Junction  of  Ileum  with  Caecum, 
to  show  the  Formation  of  the 
Ileo-caecal  Valve  ....     1078 

766.  The  Blood-Supply  of  the  Csecum 

and  Vermiform  Appendix    .         .     1079 

767.  Structure    of  the  Vermiform  Ap- 

pendix   1080 

768.  The  Cascal  Folds  and  Fossae    .         .     1081 

769.  The  Abdominal  Viscera  after  the  Re- 

moval of  the  Jejunum  and  Ileum  1084 

770.  The  Iliac  and  Pelvic  Colons    .         .  1085 

771.  The  Rectum  from  Behind       .        .  1087 

772.  Distended  Rectum  in  situ        .        .  1088 

773.  The    Peritoneum    of    the    Pelvic 

Cavity 1090 

774.  Diagram  of  Rectum         .         .         .     1093 

775.  The  Interior  of  the  Anal  Canal  and 

Lower  Part  of  Rectum  .         .     1094 

776.  The  Anal  Canal  and  Lower  Part  of 

Rectum  in  the  Foetus  .        .         .     1094 

777.  Diagrammatic    Medial    Section   of 

Female  Body        ....     1098 

778.  The  Peritoneum  of  the  Pelvic  Cavity     1100 

779.  Diagrammatic  Transverse  Sections 

of  Abdomen  ....     1101 

780.  The    Peritoneal    Relations    of  the 

Duodenum,  Pancreas,  Spleen, 
Kidneys,  etc.         ....     1103 

781.  Two    Diagrams    to    illustrate   the 

Development  of  the  Intestinal 
Canal 1106 

782.  Two   Diagrams    to    illustrate    the 

Development  of  the  Mesenteries  .     1107 

783.  Diagrams  to  illustrate  the  Develop- 

ment of  the  Great  Omentum  (after 

Hertwig) 1107 

784.  The  Abdominal  Viscera  in  situ       .  1109 

785.  The  Liver  from  the  Front       .         .  1111 

786.  The  Liver  from  Below  and  Behind  1112 

787.  The     Abdominal     and     Thoracic 

Viscera  of  a  Five  Months'  Foetus .     1117 

788.  Structures  between  the  Layers  of 

the  Lesser  Omentum    .         .         .1119 

789.  Diagram    showing    the    Bile    and 

Pancreatic  Ducts  piercing  the 
Wall  of  the  Duodenum  obliqixely     1120 

790.  Liver  of  a  Pig  injected  from  the 

Hepatic  Vein  by  T.  A.  Carter      .     1122 

791 .  Diagrams  illustrating  the  Structure 

of  Liver 1122 


LIST  OF  ILLUSTEATIONS. 


Flo. 

792. 


793. 


Diagram  illustrating  the  Arrange- 
ment of  the  Blood-Vessels  and  of 
the  Hepatic  Cells  and  Bile  Ducts 
within  a  Lobule  of  the  Liver       .     1123 

Two  Diagrams  to  illustrate  the 
Development  of  the  Intestinal 
Canal 1123 


794.  The   Viscera  and   Vessels   on   the 

Posterior  Abdominal  Wall  .         .     1125 

795.  The   Peritoneal    Relations   of   the 

Duodenum,     Pancreas,      Spleen, 
Kidneys,  etc.         ....     1126 

796.  The  Pancreas  and  Duodenum  from 

Behind 1128 


THE    UEINOGENITAL   SYSTEM. 


797.  Dissection  to  show  the  Position  and 

Relationships  of  the  Kidneys 

798.  Transverse    Section    through    the 

Abdomen  at  the  Level  of  the 
Second  Lumbar  Vertebra     . 

799.  The  Posterior  Relationships  of  the 

Kidneys 

800.  The  Kidneys  viewed  from  Behind  . 

801.  Right  Kidney  and  Duodenum 

802.  Left    Kidney,    the    Pancreas,    the 

Spleen,  and  the  Descending 
Colon 

803.  The    Kidneys   and    Great    Vessels 

viewed  from  the  Front 

804.  Longitudinal  Section  through  the 

Kidney 

805.  Section  through  a  Portion  of  the 

Kidney 

806.  Diagrammatic    Representation    of 

the  Structures  forming  a  Kidney 
Lobe 

807.  Longitudinal  Section  of  the  Kidney 

ojjening  up  the  Kidney  Sinus 

808.  Medial  Section  of  an  Adult  Male 

Pelvis 

809.  Medial  Section  through  the  Male 

Pelvis 

810.  Medial  Section  of  the  Male  Pelvis  . 

811.  Under  Aspect  of  the  Empty  Male 

Bladder         

812.  The  Bladder,  Prostate,  and  Seminal 

Vesicles,  viewed  from  Below 

813.  The  Bladder,  Prostate,  and  Seminal 

Vesicle,  from  the  Outer  Side 

814.  The   Bladder   and   the   Structures 

traversed  by  the  Urethra  in  the 
Male 

815.  Lateral  Aspect  of  Bladder  contain- 

ing Ten  Ounces  of  Fluid 

816.  View  looking  into  the  Pelvis  from 

Above  and  somewhat  Behind 

817.  View  of  the  Interior  of  the  Bladder 

in  the  Region  of  the  Urethral 
Orifice 

818.  Medial  Section  of  the  Pelvis  in  an 

Adult  Female       .... 

819.  The  Bladder  of  a  Newly-born  Male 

Child 

820.  Medial  Section  through  the  Pelvis 

of  Newly-born  Child    . 

821.  View  looking  from  Above  into  the 

Pelvis  and  Lower  Part  of  the 
Abdominal  Cavity  in  a  Fcstus  of 
about  the  Seventh  Month    . 

822.  View  looking  into  the  Male  Pelvis 

seen  from  Above  and  somewhat 
Behind 

823.  Medial  Section  of  the  Pelvis  in  an 

Adult  Male 

824.  Medial  Section  through  the  Female 

Pelvis 


1131 


1132 


1133 

1134 

828 

1135 

829 

1135 

830. 

1136 

831. 

1137 

832. 

1138 

833. 

1139 

834. 

1141 

1142 

835. 

1145 

1146 

836. 

1147 

1147 

837. 

1148 

838. 

1149 

839. 

1150 

1150 

840. 

841. 

1151 

842. 

1152 

843. 

1152 

844. 

1153 

845. 

846. 

1154 

847. 

1154 

1155 

848. 

1158 

825. 
826. 

827. 


The  Right  Testis  and  Epididymis  .     1159 

Right  Testis  within  Tunica 
Vaginalis 1160 

Transverse  Section  of  Testis  and 
Epididymis  and  of  Spermatic 
Cord  below  External  Al)dominal 
Ring 1161 

Diagram  to  illustrate  the  Structure 
of  the  Testis  and  Eijididymis       .     1162 

The  Peritoneum  of  the  Pelvic 
Cavity 1163 

Horizontal  Section  through  the 
Rectum  and  Bladder    .         .         .     1164 

View  of  the  Base  of  the  Bladder, 
Prostate,  Seminal  Vesicles,  and 
Vasa  Deferentia  from  Behind      .     1165 

The  Bladder,  Prostate,  and  Seminal 
Vesicle  viewed  from  the  Side       .     1166 

The  Seminal  Vesicle  and  the 
Ampulla  of  Vas  Deferens     .         .     1166 

View  looking  from  Above  into  the 
Pelvis  and  Lower  Part  of  the 
Abdominal  Cavity  in  a  Foetus  of 
about  the  Seventh  Month    .         .     1167 

Diagram  to  illustrate  the  Descent 
of  the  Testis  and  the  manner  in 
which  the  Tunica  Vaginalis  is 
derived 1168 

Transverse  Sections  of  Testis  and 
Epididymis  and  of  Spermatic 
Cord  below  External  Abdominal 
Ring 1169 

Deep  Dissection  of  the  Inguinal 
Region 1169 

Dissection  to  illustrate  the  Com- 
ponent Parts  of  the  Penis    .         .     1171 

A  Longitudinal  Section  of  the 
Terminal  Portion  of  the  Penis, 
and  a  Transverse  Section  through 
the  Body  of  the  Organ         .         .1172 

Bladder,  Prostate,  and  Seminal 
Vesicles,  from  the  Outer  Side      .     1173 

Prostate,  Bladder,  and  Seminal 
Vesicles,  seen  from  Below    .         .     1174 

Transverse  Section  through  the 
Prostate 1175 

Transverse  Section  through  the 
Prostate 1176 

The  Bladder  and  the  Structures 
traversed  by  the  Urethra     .         .     1177 

Medial  Section  of  an  Adult  Male 
Pelvis 1178 

The  Prostatic,  Membranous,  and 
the  Upper  Portion  of  the  Spongv 
Urethra        .         .         .         .       '.1178 

A  Longitudinal  Section  of  the  Ter- 
minal Portion  of  the  Penis,  and  a 
Transverse  Section  through  the 
Body  of  the  Organ        .         .         .1180 

Medial  Section  through  the  Female 
Pelvis 1181 


XXX 


LIST  OF  ILLUSTEATIONS. 


FIO.  PAGE 

849.  Side  Wall  of  tlie  Female  Pelvis      .     1183 

850.  The  Uterus  and  Broad  Ligament, 

and  Diagrammatic  Representa- 
tion of  the  Uterine  Cavity  .         .     1183 

Graafian  Follicle     ....     1185 

The  Uterus  and  Broad  Ligament, 
and  Diagrammatic  Representa- 
tion of  the  Uterine  Cavity  .         .     1188 

Medial  Section  of  the  Pelvis  in  an 
Adult  Female       .         .         .         .1193 

Tlie  Vagina,  the  Base  of  the  Bladder, 
and  the  Recto-vaginal  Pouch  of 
Peritoneum  ....     1194 

Female  External  Genital  Organs    .     1196 

Dissection  of  the  Female  External 
Genital  Organs     .         .         .         .1197 

Dissection  of  Female  Perineum  to 
show  the  Clitoris,  the  Bulb  of 
the  Vestibule,  and  Bartholin's 
Glands 1198 


851 

852 


853. 


854. 


855. 
856. 

857. 


FIG. 

858.  Development     of     the      Bladder, 

Ureter,  and  Kidney 

859.  Transverse    Section    through    the 

Body  of  a  Fowl  Embryo 

860.  Diagram  to  illustrate  the  manner 

in  which,  the  Ureter,  the  Vas 
Deferens,  and  the  Bladder  arise  in 
the  Embryo 

861.  Diagrammatic  Representation  and 

Comparison  of  the  manner  in 
which  the  Urinogenital  Passages 
arise  in  the  two  Sexes  . 

862.  Transverse    Section    through    the 

Body  of  a  Rat  Embryo 

863.  Development     of     the     External 

Genital  Organs     .... 

864.  External  Genital  Organs  in  a  Male 

Embryo 

865.  Dissection  of  the  Mammary  Gland 

866.  Section  through  a  Mammary  Gland 


1199 
1200 

1201 

1202 

1203 

1205 

1206 
1207 
1208 


THE  DUCTLESS   GLANDS. 


867.  Dissection  of  the  Spleen,  Liver,  and 

Kidneys  from  Behind  . 

868.  The  Spleen 

869.  Anterior   Surfaces    of    Suprarenal 

Capsules       ..... 

870.  Posterior   Surfaces   of    Suprarenal 

Cai^sules 

871.  Transverse    Section    through    the 

Suprarenal   Capsule   of  a   New- 
born Child  in  situ 

872.  Dissection   of  the   Thyreoid  Body 


1211 
1212 

1214 

1214 


1215 


and  of  the  Parts  in  immediate  re- 
lation to  it   . 

873.  Thymus  Gland  ina  Full-time  Foetus 

hardened  by  Formalin-Injection. 

874.  Dissection    to    show  the    Thymus 

Gland  in  an  Adult  Female  . 

875.  Deep  Surface  of  Thymus  Gland 

876.  Section  through  Carotid  Body 

877.  Schema  of  the  relation  presented 

by  the  Carotid  Gland  and  its  ac- 
cessory Outlying  Parts  to  Branches 
of  Middle  Sacral  Artery 


1216 

1218 

1219 
1220 
1221 


•1221 


SURFACE  AND  SUEGICAL  ANATOMY. 


the 


tlie 


878.  Diagrammatic  Representation  of  a 
Coronal  Section  through  the 
Scalp,  Cranium,  Meninges,  and 
Cortex  Cerebri      .... 

Cranio-cerebral  Topography  . 

Scheme  showing  Relative  Topo- 
graphy of  the  Chief  Subdivi- 
sions of  the  Motor  Area  (adapted 
from  Griinbaum  and  Sherring- 
ton)         

Cranio-cerebral  Topography  . 

View  of  the   Outer    Wall   of 
Middle  Ear 

Left  Tympanic  Membrane 

View   of  tlie    Inner   Wall   of 
Middle  Ear  .... 

Section  through  Left  Temporal 
Bone,  showing  Outer  Wall  of 
Tympanic  Cavity,  etc.  . 

886.  Section  through  Petrous  Portion  of 

Temporal  Bone  of  Adult 

887.  Frontal  Sinuses  of  average  dimen- 

sions,   with    a    Medial    Sei^tum 
(Logan  Turner)      .... 

888.  A  Large  Right  Frontal  Sinus  with 

Septum  oblique  to  the  Left 
(Logan  Turner)  .... 
Right  Frontal  Sinus  of  very  large 
dimensions;  Left  Sinus  unopened 
(Logan  Turner)     .... 


879, 
880, 


881. 
882. 

883. 
884. 

885. 


889. 


1223 
1226 


1227 
1228 

1230 
1230 

1231 


1231 
1232 

1234 

1234 

1235 


890.  Vertical  Coronal  Section  through 

the  Nose  and  Frontal  Sinuses      .     1236 

891.  Head   of   Human    Embryo    about 

29  days  old 1240 

892.  Coronal  Section  through  the  Face  of 

a  Human  Embryo  at  the  Seventh 
Week 1241 

893.  From  a  Photograph  showingDouble 

Complete    Hare -Lip    and    Cleft 
Palate 1241 

894.  Shows  Arrangement  of  Bones   in 

Double  Cleft  Palate     .         .         .     1242 

895.  Coronal  Section  through  the  Tongue 

and    Submaxillary  Region   in  a 
Plane  behind  the  Molar  Teeth     .     1243 

896.  Open  Mouth  with  Tongue  raised 

and  the  Sublingual  and  Apical 
Glands  exposed     ....     1243 

897.  Horizontal  Section  through  Mouth 

and  Pharynx  at  the  Level  of  the 
Tonsils 1245 

898.  Anterior    Aspect     of     Neck     and 

Shoulders 1247 

899.  Dissection  of  the  Front  of  the  Neck     1248 

900.  Lateral  Aspect  of  Neck  .        .         .1250 

901.  Anterior  Aspect  of  Trunk,  showing 

Surface  Topography  of  Viscera    .     1254 

902.  Dissection  of  a  Subject  to  show  the 

relations  of  the  two  Pleural  Sacs 
viewed  from  the  Front         .         .     1256 


LIST  OF  ILLUSTKATIONS. 


FIG. 

903. 

904. 
905. 

906. 


907. 

908. 
909. 
910. 
911.. 
912. 
913. 

914. 

915. 
916. 

917. 

918. 
919. 


Anterior  Aspect  of  Trunk,  sliowing 
Surface  Tojiography  of  Viscera    .     1257 

Lateral  Viewof  the  Right  Pleural  Sac     1258 

Dissection  of  the  Pleural  Sacs  from 
Behind 1259 

Dissection  from  Behind  to  show  the 
relation  of  the  two  Pleural  Sacs  to 
the  Kidneys  ....     1260 

Posterior  Aspect  of  Trunk,  showing 
Surface  Topography  of  Viscera    .     1261 

I  Relations  of  the  Cavities  and  Valves 
-  of  the  Heart  to  Anterior  Wall  of 
I    Thorax 1263 

The  Groin 1265 

Anterior  Aspect  of  Trunk,  showing 

Surface  Topography  of  Viscera  .  1268 
Lateral  Aspect  of  Trunk,  showing 

Surface  Topography  of  Viscera  .  1269 
The  Ctecal  Folds  and  Fosste  .  .  1273 
The  Blood-Supply  of  the  Csecum 

and  Vermiform  Appendix  .  .  1274 
Anterior  Aspect  of  Trunk,  showing 

Surface  Topography  of  Viscera  .  1275 
Dissection  of  the  Perineum  .  .  1277 
Tlie  Interior  of  the  Anal  Canal  and 

Lower  Part  of  Rectum  .         .         .     1280 


*"I0-  PAOE 

920.  The  Rectum  from  Behind       .         .1282 

921.  Dissection  of  the  Spleen,  Liver,  and 

Kidneys  from  Behind  .         .         .     1286 

922.  Posterior  Aspect  of  Trunk,  show- 

ing     Surface      Topogi'aphy      of 
Viscera 1287 

923.  Dissection  of  the  Left  Hypochon- 

driuni 1288 

924.  Axilla,  Inner  Aspect  of  Upper  Arm 

and  Elbow 1294 

925.  Extensor  Aspect  of  Upper  Limb     .     1295 

926.  Transverse    Section    through    the 

Bend  of  the  Elbow       .         .         .1297 

927.  Bend  of  Elbow,  Front  of  Forearm, 

and  Palm  of  Hand        .         .         .  1298 

928.  Palm  of  Hand  ....  1299 

929.  Dorsal  Aspect  of  Hand    .         .         .  1300 

930.  Section  through  Thigh  at  the  Level 

of  the  Upper  Part  of  Hunter's 
Canal 1303 

931.  Section  through  the  Thigh  immedi- 

ately above  the  Patella         .  .  1304 

932.  The  Thigh  and  Groin     .         .  .  1305 

933.  Anterior  Aspect  of  Knee         .  .  1307 

934.  Outer  Aspect  of  Knee  and  Leg  .  1309 

935.  Outer  Aspect  of  Foot  and  Ankle  .  1310 

936.  Inner  Aspect  of  Foot  and  Ankle  .  1311 


GLOSSARY    OF 
ANATOMICAL    TERMINOLOGY. 

Introduction. 

The  question  of  the  introduction  of  the  B.N. A.  (Basle  Nomina  Anatomica)  into  English 
Text-Books  is  discussed  in  the  Editor's  Preface,  but  it  may  be  of  interest  to  add  a  few 
words  here  as  to  the  origin  and  objects  of  this  nomenclature.  The  Terminology  of  Anatomy 
has  been  for  many  years  in  a  chaotic  condition.  This  fact  has  long  been  recognised  not 
only  by  anatomists,  but  by  teachers  and  students  of  other  branches  of  medical  and  allied 
sciences.  The  Anatomical  World  must  ever  remain  indebted  to  Professor  W.  His  of 
Leipzig  and  his  distinguished  countrymen  for  their  energy  and  perseverance  in  initiating 
successfully  the  gigantic  task  of  forming  an  international  Anatomical  Nomenclature, 
otherwise  known  as  the  "B.N. A."  (Basle  Nomina  Anatomica). 

Historical. 

The  first  step  towards  the  revision  of  anatomical  nomenclature  with  the  view  of  making 
it  internationally  uniform  was  taken  by  Professor  W.  His,  who  introduced  the  subject  at 
the  meeting  of  the  Anatomical  Society  at  Leipzig  in  1887.  Professor  His  admitted  that 
he  owed  the  conception  to  the  example  given  in  Henle's  work  on  Anatomy.  The  matter 
was  taken  up  and  as  a  result  an  International  Commission  was  formed  in  1891,  con- 
sisting of  von  Bardeleben,  Henle,  Hertwig,  His,  Kolliker  (as  President),  Kollmann, 
Kliptter,  Leboucq,  Merkel,  von  Mikalkovics,  Romiti,  Schwalbe,  Toldt,  Waldeyer,  Duval, 
and  Testut ;  and  as  representatives  of  the  English-speaking  Anatomists  :  the  dis- 
tinguished Editor  of  the  present  work — Professor  Cunningham,  Professor  Thane,  and  Sir 
William  Turner,  to  whom  this  volume  is  dedicated  by  the  Editor  and  the  contributors. 
For  this  Commission  Professor  W.  Krause  of  Berlin  acted  as  Editor.  From  the  very 
constitution  of  the  Committee  it  will  be  seen  that  its  success  was  assured ;  it  only 
remained  to  go  through  the  work — "  periculosse  plenum  opus  alese." 

The  Method  of  the  Commission. 

As  a  basis  for  comparison  anatomical  names  were  taken  as  they  appeared  in 
Gegenbauer's  Text-Book  of  Human  Anatomy,  which  was  at  that  time  the  most  recent 
text-book  ;  to  these  the  various  synonyms  which  had  appeared  from  time  to  time  were 
appended,  and  the  individual  members  of  the  Commission  were  asked  to  record  their 
choice  of  each  name.  After  many  alterations  in  arrangement,  and  after  six  years' 
strenuous  work,  the  result  of  their  labours  was  presented  by  the  Commission  to  a  meeting 
of  the  Anatomical  Society  in  Basle  in  1895,  and  there  adopted — hence  the  name. 

The  Objects  held  in  View  by  the  Commission. 

These  are  of  the  greatest  importance,  and  their  excellence  must  be  admitted  by  all. 
They  may  be  given  in  the  words  of  the  Editor,  Professor  Krause  : — 

1.  Every  part  of  the  body  shall  have  one  single  Latin  name  only  ;  there  shall  be  no 

synonyms  separated  by  a  "  sive  "  or  "  seu  "  as  in  most  text-books.     Each  nation 
using  the  Latin  names  can  translate  them  in  the  way  that  seems  best  to  it. 

2.  The  name  shall  be  short  and  distinctive  and  should  recall  some  point  of  description 

or  distinctive  charactei*. 

3.  No  part  of  the  body  shall  have  an  unnecessarily  long  Latin  name. 

4.  No  two  parts  of  the  body  shall  have  the  same  name  unless  they  are  truly  homologous 

parts. 

xxxiii 


XXXIV 


GLOSSAEY. 


5.  The  names  given  shall  be  consistent  with  Latin  grammar  and  orthography. 

6.  Names  of  observers   shall,   as   far   as   possible,   be   removed  from  anatomical  terms 

except  where  they  actually  mark  historical  observation. 

7.  In  the  whole  work  the  Commission  shall  endeavour  to  be  as  conservative  as  possible. 

8.  The  same  names  shall  be  used  for  arteries,  veins,  and  nerves,  where  they  run  together 

— at  least  where  possible ;  e.g.  femoral  artery  and  femoral  nerve  (anterior  crural). 

9.  The  same  names  shall   be   given   to  foramina  and   to  the  vessels  or  other  structures 

which  pass  through  them. 

10.  Adjectives    shall,    as    far    as    possible,   be    used    as    opposites — Scf.    profundus    and 

superficialis. 

11.  Ligaments  shall  be  named  according  to  their  attachments,  the  final  part  of  the  name 

indicating  the  proximal  attachment  {i.e.  sacro-iliac,  not  ilio-sacral). 

12.  There  shall  be  no  hybrid  names. 

It  might  at  first  sight  appear  that  all  these  conditions  were  easy  to  fulfil ;  such  a 
conclusion,  howeA'er,  would  be  far  from  the  truth.  The  laboiirs  of  the  Commission 
occupied  a  space  of  no  less  than  six  years,  and  even  at  their  conclusion  many  names 
remained  which  could  not  be  brought  into  harmony  with  the  conditions  laid  down ;  in 
retaining  these,  many  of  the  above  conditions  were  violated  at  times ;  in  all  such  cases, 
however,  there  were  strong  grounds  for  retaining  the  old  nomenclature.  For  these  and 
other  details  in  connection  with  the  International  Nomenclature  we  would  refer  those 
interested  to  the  original  papers  by  Professors  Krause  and  His ;  Die  anatomische  Nomen- 
clatur  by  Professor  W.  Krause,  Leipzig,  George  Thieme  and  Co.,  1893;  and  Die  anatomische 
Nomendatur  by  Wilhelm  His,  Leipzig,  von  Vert  and  Co.,  1895. 

In  conclusion,  we  wish  to  emphasise  the  fact  that  the  Latin  names  are  the  essential 
and  international.  Each  country  may,  does,  and  will  continue,  no  doubt,  to  translate 
these  names  as  seems  best  to  it. 

In  the  form  of  a  Glossary  we  append  a  list  of  the  B.N. A.  terms  which  differ  in  any 
important  detail  from  those  originally  used  in  this  work  or  from  the  terms  in  common 
use  in  the  English  language. 

It  is  our  hope  that  the  student  may  readily  find  in  the  Glossary  any  name  he  may 
require  at  once,  and  if  the  name  is  not  to  be  found  in  the  Glossary  he  may  rest  assured 
that  it  has  not  been  altered. 

THE   BONY   SKELETON. 


Or.D  Tbrminoloqy. 

Vertebrae 

Incomplete   facet  for 

head  of  rib,  upper 
lucoiajilete   facet  for 

head  of  rib,  lower 
Facet   for    transverse 

process 
Pedicle 
(This  word  is  retained 

in  use,  the  Latin  term 
being  unwieldy) 

Atlas 

Facet   for  odontoid 
process 
Axis 

Odontoid  process 
Sternum 
Gladiolus 
Eusiform  process 
Supra-sternal  notch 


B.N.A.  Terminology. 

Fovea  costalis  superior 

Fovea  costalis  inferior 

Fovea    costalis    trans- 

versalis 
Radix  arcus  vertebrae 


Fovea  dentis 

Epistropheus 

Dens 

Corpus  sterni 
Xipiioid  process 
Incisura  jugularis 


Bones  of  Skull. 


Frontal 

Nasal  spine 
Lateral    angulaiy 
])rocess 
(Use  retained) 
Internal  surface 
External  surface 
Parietal 

Temporal  ridges 


Si)ina  frontalis 
Processus  zygomaticus 

Cerebral  surface 
Parietal  surface 

Temporal  lines 


Old  Terminology. 

Groove    for    lateral 
sinus 

Occipital 

Anterior    condyloid 

foramen 
Posterior  condyloid 

foramen 
Supeiior  longitudinal 

groove 

Sphenoid 

Pterygoid  ridge 
Optic  groove 
Ethmoidal  crest 
Spinous  process 
Internal     pterygoid 

process 
Pjxternal    pterygoid 

l)rocess 
Vidian  canal 

Pterygo  -  palatine 
canal 

Temporal  Bone 

A(jueduct    of   Fal- 

lopius 
Hiatus  Fallojiii 
Vaginal    process    of 

tympanic  bone 
Digastric  fossa 


B.N.A.  Terminology. 
Sulcus  transversus 


Canalis  hypoglossi 
Canalis  condjdoideus 
Sulcus  sagittalis 


Ci'ista  infratemporalis 

Sulcus  chiasmatis 

Crista  sphenoidalis 

Spina  angularis 

Lamina  niedialis  pro- 
cessus pterygoidei 

Lamina  lateralis  pro- 
cessus pterygoidei 

Canalis  pterygo  id  eus 
[Vidii] 

Canalis  i)haryiigeus 


Canalis  facialis  [Fal- 

lopii] 
Hiatus  canalis  facialis 
Vagina  processus  sty- 

loidei 
Incisura  mastoidea 


GLOSSARY. 


XXXV 


Old  Terminology. 

Glaserian  fissure 
(Still  retained) 

Glenoid  cavity 
(Still  retained) 

Ethmoid 

Lateral  mass 

Os  plaiiuin 

Lacrimal  Bone 

Haiuular  process 
Lacrimal  crest 

Nasal  Bone 

Groove    for    nasal 
nerve 

Maxilla 

Facial   or  external 

surface 
Antrum  of  Higlimore 
Nasal  process 
]\Ialar  process 

Malar  Bone 

Zygomatic  process 
Frontal  process 

Temporo-malar  canal 

Malar  foramen 

Mandible 

Genial    tubercle    or 

spine 
External  oblique  line 
Internal  oblique  line 
Sigmoid  notch 
Inferior  dental  fora- 
men 
Inferior  dental  canal 


B.N. A.  Tekminology. 
Fissura  petrotympanica 

Fissura  mandibularis 


Labyrinthus  etlimoiil- 

alis 
Lamina  papyracea 

Hamulus  lacrimalis 
Crista  lacrimalis  pon- 
terior 

Sulcus  etlimoidalis 


Facies  anterior 

Sinus  maxillaris 
Processus  frontalis 
Processus  zygomaticus 

Os  zygomaticum 

Processus  temporalis 
Processus  fronto-sphen- 

oidalis 
Foramen  zygomatico- 

orbitale 
Foramen   zygomatico- 

faciale 

Spina  mentalis 

Linea  ohliqua 
Linea  myloliyoidea 
Incisura  mandibularis 
Foramen  mandibulare 

Canalis  mandibulie 


The  Skull  as  a  Whole. 


Wormian  bones 
Pacchionian  depressions 

Spheno-maxillary  fossa 
Posterior  palatine  canal 

Foramen     lacerum 

medium 
Posterior  nares 


Ossa  suturaruin 
Foveohe    granulares 

(Pacchioni) 
Fossa  pterygo-palatina 
Canalis  pterygo-palat- 

inus 
Foramen  lacerum 

Choanse 


Upper  Extremity. 


Clavicle 

Impression  for  conoid 
ligament 

Impression  for  rhom- 
boid ligament 

Scapula 

Anterior  or  lateral 

angle 
Superior  angle 

Humerus 

Bicipital  groove 

External  lip 

Internal  lip 
Internal  surface 
External  surface 


Tuberositas  coracoidea 
Tubei'ositas  costalis 

Margo  lateralis 
Margo  medialis 

Sulcus  intertubercularis 
Crista  tuberculi  majoris 
Crista  tuberculi  niinoris 
Facies  anterior  medialis 
Facies  anterior  lateralis 


Old  Terminology. 

Musculo-spiral  groove 
Capitellum 
Intei'iial  condyle 
Lateral  condyle 

Ulna 

Greater    sigmoid 

cavity 
Lesser  sigmoid  cavity 

Radius 

Bicipital  tuberosity 
Sigmoid  cavity 

Carpus 
Scaphoid 
Semilunar 
Cuneiform 
Trapezium 

Trapezoid 

Os  magnum 
Unciform 


B.N. A.  Terminology. 

Sulcus  nervi  radialis 
Cajiitulum 

Epicondylus  medialis 
Epicondylus  lateralis 

Incisura  semilunaris 
Incisura  radialis 

Tuberositas  radii 
Incisura  ulnaris 

Navicular 
Os  lunatum 
Os  triquetrum 
Os    multangulum 

majus 
Os    multangulum 

minus 
Os  capitatum 
Os  hamatum 


Lower  Extremity, 

Innominate  Bone 

Inferior  curved  line 
Superior  curved  line 
Spine  of  the  ischium 
Great  sacro-sciatic 

notch 
Lesser  sacro-sciatic 

notch 
Spine  of  pubis 
Descending  ramus  of 

pubis 

Pelvis 

False  pelvis 
True  pelvis 
Pelvic  inlet 


Linea  glirtrea  anterior 
Linea  glutfea  posterior 
Spina  ischiadica 
Incisura    ischiadica 

major 
Incisura    ischiadica 

minor 
Tuberculum  pubicum 
Ramus  inferior  pubis 


Pelvic  outlet 

Femur 

Digital  fossa 
Spiral  line 
Intertrochanteric  line 

Inner  tuberosity 
Outer  tuberosity 

Tibia 

Internal  tuberosity 
External  tuberosity 
Spine 

Tubercle 

Bones  of  the  Foot 
Astragalus 
Os  calcis 

Tuberosity  of 
Inner 

Outer 

Inner  cuneiform 
Middle  cuneiform 

Outer  cuneiform 


Pelvis  major 
Pelvis  minor 
Apertura  pelvis  minoris 

suijerior 
Apertura  pelvis  minoris 

inferior 

Fossa  trochanterica 
Linea  intertrochanterica 
Crista     intertrochan- 
terica 
Epicondylus  medialis 
Epicondylus  lateralis 

Condylus  medialis 
Condylus  lateralis 
Eminentia  intercondy- 

loidea 
Tuberositas  tibife 


Talus 

Calcaneus 

Tuber  calcauei 

Processus  medialis  tuber 
calcanei 

Processus  lateralis  tuber 
calcanei 

Os  cuneiforme  primum 

Os  cuneiforme  secun- 
dum 

Os  cuneiforme  tertium 


XXXVl 


GLOSSAKY. 


SYNDESMOLOGY. 


Old  Terminology. 

Posterior  occipito- axial 
ligament 

Joint  between  the  atlas 
and  the  axis 

Odontoid  ligament 

Suspensorj'  ligament 

External  lateral  liga- 
ment of  the  jaw 

Internal  lateral  liga- 
ment of  the  jaw 

Khomboid  ligament 

Accessory  ligament  of 
the  shoulder -joint 

Superior  radio  -  irlnar 
joint 

Internal  lateral  liga- 
ment of  elbow-joint 

External  lateral  liga- 
ment 

Orbicular  ligament 

Oblique  ligament  of  the 
superior  radio  -  ulnar 
joint 

Inferior  radio  -  ulnar 
joint 

Anterior  ligament  of  the 
radio-carpal  joint 

Posterior  ligament  of 
the  radio  -  carpal 
joint 


B.N. A.   Terminology. 
Membrana  tectoria 

Articulatio  atlauto-epis- 

trophica 
Lig.  alaria 
Lig.  apicis  dentis 
Lig.    temporo-iuandibu- 

lare 
Lig.     spheno-mandibu- 

lare 
Lig.  costo-elaviculare 
Lig.  coraco-humerale 

Articulatio  radio-ulnaris 

proximalis 
Lig.  collaterale  ulnare 

Lig.  collaterale  radiale 

Lig.  annulare  radii 
Chorda  obliqua 


Articulatio  radio-ulnaris 
distalis 

Lig.  radio-carpeum  vo- 
lare 

Lig.  radio-carpeum  dor- 
sale 


Old  Terminology. 

Palmar  ligaments  of  the 
metacarpo  -  phalan  - 
geal  joints 

Transverse  metacarpal 
ligament 

Lateral  phalangeal  liga- 
ments 

Great  sacro-sciatic  liga- 
ment 

Small  sacro-sciatic  liga- 
ment 

Posterior  ligament  of 
knee-joint 

Arcuate  popliteal  liga- 
ment 

External  semilunar  car- 
tilage 

Internal  semilunar  car- 
tilage 

Superior  tibio  -  fibular 
articulation 

Inferior  tibio  -  fibular 
articulation 

Superior  astragalo-sca- 
phoid  ligament 

Superior  calcaneo  -  sca- 
phoid ligament 

Internal  calcaneo-cuboid 
ligament 


B.N. A.  Terminology. 
Lig.  accessoria  volaria 

Lig.  capitulorum  (oss. 
metacarpalium)  trans- 
versa 

Lig.  collateralia 

Lig.  sacro-tuberosum 
Lig.  sacro-spinosum 

Lig.      popliteum     obli- 

quum 
Lig.    popliteum    arcua- 

tum 
Meniscus  lateralis 

Meniscus  medialis 

Articulatio  tibiofibularis 

Syndesmosis     tibiofibu- 
laris 
Lig.  talo-naviculare 

Pars     calcaneo  -  navicu- 

laris 
Pars  calcaneo-cuboidea 


NEUROLOGY. 


Spinal  Cord. 

Clark's  column  Nucleus  dorsalis 

Dorsal    part    of   spinal       Pars  thoracalis 
cord 

Paramedian  furrow  Sulcus  intermedins  pos- 

terior 

Direct  pyramidal  tract         Fasciculus  cerebro-spin- 
alis  anterior 

Crossed  pyramidal  tract       Fasciculus  cerebro-spin- 
alis  lateralis 

Direct  cerebellar  tract  Fasciculus       cerebello  - 

spinalis 

Gower's  tract  Fasciculus  antero-later- 

alis  supcrficialis 

Brain. 

Cerebello-olivary  fibres         Fibne  eerebello-olivares 


Corpus  Trapezoid  es 
Posterior  crescentic  lo- 
bule 
Postero-infeiior  lobule 

Great  horizontal  fissure 

Crus  cerebri 

Iter  e  tertio  ad  ipiartuni 

ventriculum 
Foranicn  of  Monro 

Sulcus  of  Monro 
Middle  commissure 
Bundle  of  Vicq  d'Azyr 

Pars  basilaris 


Cori)US  Trapezoideum 
Lobulus  semilunaris  su- 
perior 
Lobulus  semilunaris  in- 
ferior 
Sulcus  horizontalis  cerc- 

belli 
Pcdunculus  cerebri 
Aqueductus  cerebri 

Foramen  interventricu- 

lare 
Sulcus  hypothahimicus 
Massa  intermedia 
Fasciculus       thalanio- 

mammillaris 
Pars  opercularis 


Fissure  of  Sylvius 
First  temporal  gyrus 

Second  temporal  gyrus 
Third  temporal  gyrus 

Fissure  of  Rolando 
Parallel  sulcus 

Second  temporal  sulcus 

Occipito -temporal    sul- 
cus 
Occipito-temporal    con- 
volution 
Intraparietal  sulcus 
Callosal  sulcus 
Calloso-niarginal  fissure 
Dentate  fissure 
Callosal  convolution 
Ticnia  semicircularis 
'i'rigonum  ventriculi 
Jlippocampus  major 
Pes  liippocam[)i 

Gyrus  dcntatus 

Lenticular  nucleus 

Anterior  limb  (of  inter- 
nal capsule) 

Posterior  limb  (of  inter- 
nal cap.sule) 

0[)tic  radiation 


Fissura  cerebri  lateralis 

Gyrus  temporalis  su- 
perior 

Gyrus  temporalis  medius 

Gyrus  temporalis  in- 
ferior 

Sulcus  centralis 

Sulcus  temporalis  su- 
perior 

Sulcus  temporalis  me- 
dius 

Sulcus  temporalis  in- 
ferior 

Gyrus  fusiforniis 

Sulcus  inter[)arietalis 

Sulcus  corporis  callosi 

Sulcus  cinguli 

Fissura  hippocampi 

Gyrus  cinguli 

Stria  tcnuinalis 

Trigonum  collaterale 

Hippocampus 

Digitationes  hippo  - 
campi 

Fascia  dentata  hippo- 
campi 

Nucleus  lentiformis 

Pars  frontalis  capsulfe 
internae 

Pars  occipitalis  capsulae 
internas 

Radiatio  occipito-thal- 
amica 


GLOSSAKY 


XXXVll 


Membranes  of  Brain. 


Old  Terminology. 
Cistenia  magna 

Cisterna  basalis 

Pacchionian  bodies 


Cranial 

Superior    maxillarj' 

nerve 
Inferior  maxillary  nerve 
Great  superficial  petro- 
sal nerve 
Deep  petrosal  nerve 
Lenticular  ganglion 
External  palatine  nerve 
Pars    intermedia  of 

Wrisberg 
Auditory  nerve 
.Jugular  ganglion 
Recurrent  laryngeal 

nerve 
Ganglion  of  root 
Ganglion  of  trunk 

Plexus  gulii? 

Accessory     portion     of 
spinal  accessory  nerve 
Spinal  portion 


B.N.  A.    TEHMINOLOdV. 

Cisterna       cerebello- 

niedullaris 
Cisterna    interpeduncu- 

laris 
Granulationes  araclinoi- 

deales 

Nerves. 

N.  maxillaris 

N.  niandibularis 

N.  petrosus  superlicialis 

major 
N.  petrosus  profundus 
G.  ciliare 

N.  palatinus  niedius 
N.  intermedins 

N.  acusticus 
G.  sujierius 
N.  recurrens 

Ganglion  jugulare 
Ganglion  nodcEum 

r  Plexus     oesopliageus 

I      anterior 
"j  Plexus     cesophageus 

I     posterior 
Ramus  internus 

Ramus  externus 


Posterior  primary  divi- 
sions 
Superficial  cervical  nerve 
Suprasternal  nerves 

Supraclavicular  nerves 

Supra-acromial  nerves 

Nerve  to  the  rhomboids 
Cutaneous  branch  of  the 
musculo-  cutaneous 
nerve 
Nerve  of  Bell 
Long  subscapular  nerve 
Lesser  internal  cutane- 
ous nerve 


Spinal  Nerves. 

Rami  posteriores 


N.  cutaneus  colli 

Nn.      supraclaviculares 

anteriores 
Nn.      supraclaviculares 

niedii 
Nn.      siipraclaviculares 

posteriores 
N.  dorsalis  scapulte 
N.  cutaneus  antibrachii 

lateralis 

N.  thoracalis  longus 
N.  thoraco-dorsalis 
N.      cutaneus      brachii 
medialis 


Or,n  Tkuminology. 
I  nteriKil  cutaneous  nerve 

Anterior  branch 
Internal  branch 
Circumflex  nerve 
Anterior  interosseous 
Palmar       cutaneous 
branch  of  the  median 
nerve 
Collateral  palmar  digi- 
tal branches  of  median 
nerve 
Dorsal  cutaneous  branch 

of  ulnar  nerve 
Palmar       cutaneous 
branch  of  ulnar  nerve 
Musculo-sj)iral  nerve 
Upper  external  cutane- 
ous  branch   of   mus- 
culo-spiral  nerve 
LoAver  external  cutane- 
ous  branch   of   mus- 
culo-si)iral  nerve 
Radial  nerve 
Posterior      interosseous 

nerve 
Dorsal  digital  nerves 
I  n  tercosto- h  umeral 

nerve 
Iliac  branch  of  ilio-hypo- 

gastric  nerve 
Hypogastric  branch    of 
ilio-hy}»ogastric  nerve 
Genito-crural  nerve 
Crural  branch  of  genito- 
crural  nerve 
Genital  branch  of  genito- 
crural  nerve 
External  cutaneous 

nerve 
Anterior  crural  nerve 
Long  saphenous  nerve 
Patellar  branch  of  long 

saphenous  nerve 
Great  sciatic  nerve 
External  popliteal  nerve 
Musculo  -  cutaneous 

nerve 
Anterior  tibial  nerve 
Internal  ]»opliteal  nerve 
Short  saphenous  nerve 
Pudic  nerve 


B.N. A.  Terminology. 

N.  cutaneus  antibrachii 

medialis 
Ramus  volaris 
Rannis  ulnaris 
N.  axillaris 
N.  interosseus  volai'is 
Ramus      palmaris      N. 

median! 

Nn.     digitales     volares 
proprii 

Ramus  dorsalis  manus 

Ramus     cutaneus     iial- 

maris 
N.  radialis 
N.      cutaneus      brachii 

posterior 

N.  cutaneus  antibrachii 
dorsalis 

Ramus  superficialis 
N.  interosseus  dorsalis 

Nn.  digitales  dorsales 
Nn.    intercosto-brachi- 

ales 
Ramus      cutaneus 

lateralis 
Ramus     cutaneus     an- 
terior 
N.  genito-femoralis 
N.  lumbo-ingninalis 

N.  spermaticus  externus 

N.  cutaneus  femoris  la- 
teralis 
N.  femoral  is 
N.  saphenus 
R.  infrapatellaris 

N.  ischiadicus 
N.  peronseus  communis 
N.     peronseus     superfi- 
cialis 
N.  peroniTeus  profundus 
N.  tibialis 
N.  suralis 
N.  pudendus 


MYOLOGY. 


Muscles  of  the  Back. 
Superficial. 

Levator  angulae  scapulfe       Levator  scapulre 

Muscles  of  the  Chest. 


Serratus  magnus 


Serratus  anterior 


Muscles  of  Upper  Extremity. 


Biceps 

Bicipital  fascia 

Brachialis  anticus 

Triceps 

Inner  head 
Outer  head 


Biceps  brachii 
Lacertus  tibrosus 
Brachialis 
Triceps  brachii 
Caput  mediale 
Caput  laterale 


Pronator  radii  teres 
Coronoid  head 
Supinator  longus 
Supinator  brevis 
Extensor  car})!  radialis 

longior 
Extensor  carpi  radialis 

brevior 
Extensor  indicis 

Extensor  minimi  digiti 

Extensor     ossis     meta- 

carpi  pollicis 
Abductor  pollicis 


Pronator  teres 
Caput  ulnare 
Brachio-radialis 
M.  supinator 
Extensor  carpi  radialis 

longus 
Extensor  carpi  radialis 

brevis 
Extensor    indicis     pro- 

prius 
Extensor    digiti    quinti 

proprius 
Abductor  pollicis  longus 

Abductor  pollicis  brevis 


XXXVlll 


GLOSSAEY. 


Old  Terminology.  B.N. A.  Terminology. 

Extensor    primi    inter-  Extensor  pollieis  brevis 

nodii  pollieis 

Extensor  secundi  inter-  Extensor  pollieis  longus 

nodii  pollieis 

Anterior   annular    liga-  Lig.  carpi  transversuni 

ment 

Posterior  annular   liga-  Lig.  carpi  dorsale 

ment 

Muscles  of  Lower  Extremity. 


Tensor  fascia?  femoris 
Hunter's  canal 

Scarpa's  triangle 

Crui'al  canal 
Crural  ring 
Quadriceps — 

Vastus  externus 

Crureus 

Internus 
SuLcrureus 
Tibialis  anticus 
Tendo  Achillis 
Tibialis  posticus 
Accessorius 

Upper  annular  ligament 
Internal   annular    liga- 
ment 
Lower  annular  ligament 


Tensor  fascite  latae 
Canalis    adductorius 

(Hunteri) 
Trigonum      femorale 

(fossa  ScarpEE  major) 
Canalis  femoralis 
Annulus  femoralis 

Vastus  lateralis 
A''astus  intermedins 
Vastus  medialis 
M.  articularis  genu 
Tibialis  anterior 
Tendo  calcaneus 
Tibialis  posterior 
Quadratus  jJantge 
Lig.  transversuni  cruris 
Lig.  laciniatum 

Lig.  cruciatum  cruris 


Axial  Muscles. 
Muscles  of  the  Back. 


Serratus    posticus 

superior 
Serratus  posticus  in- 
ferior 
Splenius  colli 
Erector  spinse 
Ilio-costalis — 

Sacro-lumbalis 

Accessorius 

Cervicalis  ascendens 
Longissimus — 

Dorsi 

Transversalis  cervicis 

Trachelo-mastoid 
Spinalis — 

Dorsi 

Colli 

Caj)itis 
Semispinalis — 

Dorsi 

Colli 

Complexus 
Multifidus  spinae 


Serratus    posterior 

superior 
Serratus  posterior  in- 
ferior 
Splenius  cervicis 
M.  sacro-spinalis 
Ilio-costalis — 

Lumborum 

Dorsi 

Cervicis 
Longissimus — 

Dorsi 

Cervicis 

Capitis 
Spinalis — 

Dorsi 

Cervicis 

Capitis 
Semispinalis — 

Dorsi 

Cervicis 

Capitis 
Multifidus 


Muscles  of  Head  and  Neck. 


Platysma  inyoidcs 
Occipito-frontalis 
Epicranial  aponeurosis 
Attrahens  aurein 
Retrahens  aurem 
Attollens  aurem 
Orbicularis  palpebrarum 
Tensor  tarsi 

Pyramidalis  nasi 
Compressor  naris 
Dilatores  naris 


Platysma 
M.  eiiicranius 
Galea  aj  ion  euro  tica 
M.  auricularis  anterior 
M.  auricularis  posterior 
M.  auricularis  suijerioi' 
Orbicularis  oculi 
Orbicularis  -  pars    lacri- 

malis 
M.  }jroeerus 
M.  nasalis 
Pars  alaris 


Old  Terminology. 

Depressor  alaj  nasi 
Depressor  anguli  oris 
Quadratus  labii  superi- 
oris — 

Z3^gomaticus  minor 
;_  Levator  labii  superi- 

" .,  oris 

Lev^r  labii  superi- 
oris  alfeque  nasi 
Zygomaticus  major 
Levator  anguli  oris 
Depressor  labii  inferioris 


B.N. A.  Terminology 
Depressor  septi 
M.  triangularis 


Caput  zygomaticum 
Caput  infraorbitale 

Caput  angulare 

M.  zygomaticus 
M.  caninus 

M.   quadratus  labii   in- 
ferioris 
M.  mentalis 


Depi-essor  menti 

Muscles  and  Fascia  of  the  Orhit. 

Capsule  of  Tenon  Fascia  bulbi 


Palpebral  ligaments 
Rectus  externus 
Rectus  internus 


Septum  orbitale 
Rectus  lateralis 
Rectus  medialis 


Muscles  of  the  Tongue. 


Genio-hyo-glossus 
Superior  lingualis 

Inferior  lingualis 

Transverse  fibres 
Vertical  fibres 


Genio-glossus 
M.  longitudinalis 

superior 
M.  longitudinalis 

inferior 
M.  transversus  linguae 
M.  verticalis  linguae 


Muscles  of  the  Pharynx. 

Palato-iaharyngeus  Pharyngo-palatinus 

Azygos-uvulse  M.  uvulae 

Levator  palati  Lerator  veli  palatini 

Tensor  jjalati  •  Tensor  veli  palatini 
Palato-glossus  M.  glosso-palatinus 

Deep  Lateral  Muscles  of  Neck. 


Scalenus  anticus 
Scalenus  posticus 
Rectus    capitis    anticus 

major 
Rectus    capitis    anticus 

minor 

Muscles  of  Thorax, 


Scalenus  anterior 
Scalenus  jjosterior 
Longus  capitis 

Rectus  capitis  anterior 


Triangularis  sterni 
Diaphragm,  lumbar 
part — 
Internal  arcuate  liga- 
ment 


Ligamentum  arcu- 
atum  internum 

Ligamentum  arcu- 
atum  externum 


M.  transversus  thoracis 


Cms  mediale 

Crus  intermedium 

Crus  lateral  e 

Arcus  lumbo-costalis 

medialis  (Halleri) 
Arcus   lumbo-costalis 

lateralis  (Halleri) 


Muscles  of  the  Abdomen. 

Poupart's  ligament 


Gimbernat's  ligament 

Intercolumnar  fi))res 
Triangular  fascia 

External  abdominal  ring 

Internal  pillar 
External  pillar 


Ligamentum    inguinale 

Pouparti 
Ligamentum      lacunare 

(Gimbernati) 
FibrsB  intercrurales 
Ligamentum    inguinale 

rcdexum  (Collesi) 
Annulus  inguiualis  sub- 

cutaneus 
Crus  superius 
Crus  inferius 


GLOSSAKY. 


XXXIX 


Old  Teiiminology. 
Conjoined  tendon 

Transversalis  muscle 

Fold  of  Douglas 

Internal  abdominal  rinj 

Hesselbach's  liijament 


B.N. A.   Tkuminology. 

Falx    aponeurotica    in- 
guinalis 

M.   transversns  abdom- 
inis 

Linea     semicircularis 
(I)ouglasi) 

Annulns  inguinalis  ab- 
dominalis 

Ligamentum  interfoveo- 
lare  (Hesselbachi) 


Perineum. 


Ol.l)    TKKMINOUKiY. 

Traiisversus  perinei 

Compressor  urethrae 

Triangular  ligament 
Deep  layer  of  triangular 

ligament 
White  line  of  pelvis 


B.N. A.  Tekminology. 
Transversns    perinei 

superficialis 
M.    sjihincter    uretlirfe 

membranaceae 
Diaphragma  urogenitale 
Fascia    diaphragmatis 

iirogenitalis  superior 
Arcus    tendineus    m. 

levatoris  ani 


SPLANCHNOLOGY. 


Digestive  Apparatus. 


Anterior  palatine  arch 
Posterior  palatine  arch 

Gland  of  Nuhn 
Wharton's  duct 
Circumvallate  papilhie 
Pharyngeal     recess     of 

Rosenmiiller 
Pharyngeal  aponeurosis 
Valvulae  conniventes 
Crypts  of  Lieberkuhn 
Ileo-crecal  valve 
Columns  of  Morgagni 
Valves  of  Houston 
Valve  of  Heister 


Arcus  glosso-palatinus 
Arcus     pharyngo  -  pala- 

tinus 
Gl.  lingualis  anterior 
Ductus  submaxillaris 
PapilliE  vallatje 
Recessus  i)haryngeus 

Tela  submucosa 
Plicfe  circulares 
Gl.  intestinales 
Valvula  coli 
Columnae  rectales 
Pliciie  transversales  recti 
Valvula  spiralis 


Respiratory  Apparatus. 


Adam's  apple 
Superior  thyroid  notch 

Aryteno  -  epiglottidean 
muscle 

Internal  thy ro  -  ary- 
tenoid muscle 

Thyro- epiglottidean 
muscle 

Laryngeal  sac 


Prominentia  laryngea 
Incisura  thyreoidea  su- 
perior 
M.  ary-epiglotticus 

M.  vocalis 

M.  thyreo-epiglottieus 

Appendix     ventriculi 
laryngis 


True  vocal  cord 
False  vocal  cord 
Superior       thyro  -  ary  - 

tenoid  ligament 
Inferior        thyro  -  ary  - 

tenoid  ligament 
Glottis  vera 
Glottis  spuria 


Plica  vocalis 
Plica  ventricularis 
Ligamentum    ventricu- 

lare 
Ligamentum  vocale 

Glottis 

Rima  vestibuli 


Urogenital  Apparatus. 


Malpighian  corpuscles 
Organ  of  Giraldes 
Hydatid  of  Morgagni 

Vas  deferens 
Glands  of  Littre 
Graaliau  follicles 

Discus  proligerus 
Fallo]>ian  tube 
Hydatids  of  Morgagni 
Gartner's  duct 


Parovarium 


Lesser  peritoneal  sac 
Foramen  of  Winslow 
Costo-colic  ligament 
Douglas'  pouch 


Corpuscula  renis 
Paradidymis 
Appendix  testis 
Ductus  deferens 
Gl.  urethrales 
Folliculi    oophori    vesi- 

culosi 
Cumulus  oophorus 
Tuba  uterina 
Appendices  vesiculosi 
Ductus  epoophori  longi- 

tudinalis 
Epoophoron 


Peritoneum. 

Bursa  omentalis 
Foramen  epiploicum 
Lig.  phrenico-colicum 
Excavatio  recto-uterina 
(cavum  Douglasi) 


ANGIOLOGY. 


Heart. 


Auricle 

Auricular  appendix 
Notch  at  ai)ex  of  heart 
Columufe  carnepe 
Intervenous  tubercle  of 
Lower 


Atrium 

Auricula  cordis 
Incisura  cordis 
Trabeculae  caruepe 
Tuberculum   interveno - 
sum 


Arteries. 


Sinuses  of  Valsalva 
Innominate  artery 
Ranine  artery 
Facial  artery 
Inferior  dental  artery 
Small  meningeal  artery 

Buccal  artery 
Posterior  dental  artery 

Anterior  superior  dental 
arteries 


Sinus  aortse 

A.  anonyma 

A.  profunila  lingufe 

A.  maxillaris  externa 

A.  alveolaris  inferior 

Ramus    meningeus    ac- 

cessorius 
A.  buccinatoria 
A.    alveolaris     superior 

postei'ior 
Aa.  alveolares  superiores 

anteriores 


Anterior  chorioidal  ar-       A.  chorioidea 
tery 

Auditory  artery 

Transverse  arteries 
(branches  of  Basilar 
artery) 

Arteria  comes  nervi 
phrenici 

Anterior  intercostal  ar- 
teries 

Thyreoid  axis 


Suprascapular  artery 
Superior  intercostal  ar- 
tery 
Superior     intercostal 

proper 
Transversalis  colli 
Superior  thoracic  artery 
Long  thoracic  artery 
Dorsalis  scapulae 
Superior  profunda 


A.  auditiva  interna 
Rami  ad  pontem 

A.  pericardiaco-phrenica 

Rami  intercostales 

Truncus      thyreo-cervi- 

calis 
A.  transvei'sa  scapulte 
Truncus  costo-cervicalis 

A.  intercostalis  suprema 

A.  transversa  colli 
A.  thoracalis  suprema 
A.  thoracalis  lateralis 
A.  circumflexa  scapulae 
A.  2^1'ofunda  brachii 


xl 


GLOSS  AEY. 


Old  Terminology. 

Articular  branch  of  su- 
perior profunda 
Inferior  profunda 

Anastomotica  magna 

Anterior  radial  carpal 
Posterior  radial  carpal 
Dorsal  interosseous   ar- 
teries 
Kadialis  indicis 

Deep  palmar  arch 
Posterior      interosseous 

artery 
Posterior      interosseous 

recurrent  artery 
Anterior       interosseous 

artery 
Posterior  ulnar  carjial 
Anterior  ulnar  carpal 
Superficial  palmar  arch 

Palmar  digital  arteries 

Collateral     digital     ar- 
teries 
Rami  intestini  tenuis 
iliddle  capsular  artery 
Internal  iliac  artery 
Deep  epigastric  artery 
Cremasteric  artery 
Superficial  and  deep  ex- 
ternal pudic  arteries 
Internal   circumflex  ar- 
tery 
External  circumflex  ar- 
tery 
Anastomotica  magna 
Superior    external  arti- 
cular artery 
Inferior    external    arti- 
cular artery 
Superior    internal    arti- 
cular artery 
Inferior    internal    arti- 
cular ai'tery 
Azygos  articular  artery 


B.N. A.  Terminology. 
A.  collateralis  radialis 

A.    collateralis    ulnaris 

superior 
A.    collateralis    ulnaris 

inferior 
Ramus  carpeus  volaris 
Ramus  carpeus  dorsalis 
Aa.  metacarpeae  dorsales 

A.  volaris  indicis  radi- 
alis 
Arcus  volaris  profundus 
A.  interossea  dorsalis 

A.  interossea  recurrens 

A.  interossea  volaris 

Ramus  carpeus  dorsalis 
Ramus  carpeus  volaris 
Arcus  volaris  superfici- 

alis 
Aa.     digitales     volares 

communes 
Aa.      digitales     volares 

proprise 
Aa.  ilefe 

A.  suprarenalis  media 
A.  hypogastrica 
A.  epigastrica  inferior 
A.  spermatica  externa 
Aa.  pudendse  externa 

A.  circumflexa  femoris 
medialis 

A.  circumflexa  femoris 
lateralis 

A.  genu  suprema 

A.  genu  sujierior  later- 
alis 

A.  genu  inferior  lateralis 

A.    genu    superior    me- 
dialis 
A.  genu  inferior  medialis 

A.  genu  media 


Old  Terminology. 

External  malleolar  ar- 
tery 

Internal  malleolar  ar- 
teiy 

Anterior  peroneal  artery 

Posteri  or  peroneal  artery 

Internal  malleolar  ar- 
tery 

External  calcaneal!  ar- 
tery 

Internal  calcanean  ar- 
tery 

Internal  plantar  artery 

External  plantar  artery 

Digital  branches 

Collateral  digital 
branches 


B.N. A.  Terminology. 

A.    malleolaris  anterior 

lateralis 
A.   malleolaris   anterior 

medialis 
Ramus  perforans 
A.  malleolaris  posterior 

lateralis 
A.  malleolaris  posterior 

medialis 
Rami  calcanei  laterales 

Rami  calcanei  mediales 

A.  plantai'is  medialis 
A.  plantaris  lateralis 
Aa.  metatarsaj  plantares 
Aa.  digitales  plantares 


Veins. 


Great  cardiac  vein 
Oblique  vein  of  Marshall 
Vestigial   fold   of   Mar- 
shall 
Veins  of  Thebesius 
Lateral  sinus 
Torcular  Herophili 
Basilar  sinus 
Superior      longitudinal 

sinus 
Inferior        longitudinal 

sinus 
Veins  of  Galen 
Vena  magna  Galeni 
Vein  of  the  corpus  stria- 
tum 
Basilar  vein 
Suprascapular  vein 
Vena  azygos  major 
Vena  azygos  minor  in- 
ferior 
Vena  azygos  minor  su- 
perior 
Internal  saphenous  vein 
External  saphenous  vein 


V.  cordis  magna 

V.  obliqua  atrii  sinistri 

Lig.  V.  cavaj  sinistra 

Vv.  cordis  minimte 
Sinus  transversus 
Confluens  sinuum 
Plexus  basilaris 
Sinus  sagittalis  sui^erior 

Sinus  sagittalis  inferior 

V.  cerebri  internae 
V.  cerebri  magna 
V.  terminalis 

V.  basalis 

V.  transversa  scajjulre 

V.  azygos 

V.  hemiazygos 

V.     hemiazygos     acces- 

soria 
V.  saphena  magna 
V.  saphena  parva 


Lymphatics. 

Receptaculum  chyli  Cisterna  chyli 


TEXT-BOOK    OF    ANATOMY. 


INTRODUCTION. 

Anatomy  is  a  comprehensive  term,  which  includes  several  closely  related  branches 
of  study.  Primarily  it  is  employed  to  indicate  the  study  of  the  several  parts 
which  build  up  the  body,  and  the  relationship  which  these  present  to  each  other. 
But  during  the  period  of  its  existence  the  individual  exhibits  many  structural 
changes :  its  structure  is  not  the  same  at  all  stages  of  its  life.  The  ovum  or 
starting-point  of  every  individual  is  very  different  from  the  finished  organism  as 
represented  by  the  adult,  and  the  series  of  changes  through  which  the  organism 
passes  until  its  structure  is  perfected  and  full  growth  is  attained  constitute  the 
study  of  development.  The  general  term  "  development "  includes  not  only  the 
various  and  striking  structural  changes  which  occur  during  the  intrauterine  life  of 
the  individual,  to  the  study  of  which  the  term  embryology  is  more  specially  applied, 
but  also  many  growth  processes  which  occur  after  birth,  such  as  the  later  stages  in 
the  ossification  and  growth  of  the  bones,  the  eruption  of  the  two  series  of  teeth,  the 
adjustment  of  the  vascular  system  to  its  new  requirements,  etc.  The  actual  obser- 
vation of  the  processes  by  which  the  parts  of  the  body  are  gradually  formed,  and  of 
the  structural  arrangements  by  means  of  which  a  temporary  connexion  is  estab- 
lished between  the  ovum  and  the  mother,  through  which  an  interchange  of 
nutritive  and  other  matters  between  the  two  takes  place,  renders  embryology  one 
of  the  most  interesting  of  all  the  departments  of  anatomy.  The  term  ontogeny  is 
also  used  to  denote  the  development  of  the  individual.  There  is,  however,  another 
form  of  development,  slower,  but  just  as  certain  in  its  processes,  which  affects  not 
only  the  individual,  but  every  member  of  the  animal  group  collectively  to  which  it 
belongs.  The  theory  of  descent  or  evolution  leads  us  to  believe  that  between  man 
of  the  present  day  and  his  remote  ancestors  there  is  a  wide  structural  gap,  which, 
if  the  geological  record  were  perfect,  would  be  seen  to  be  completely  occupied  by 
long-lost  intermediate  forms.  In  the  process  of  evolution,  therefore,  structural 
changes  have  gradually  taken  place  which  have  modified  the  entire  race.  A  more 
or  less  close  or  remote  blood-relationship  links  together  all  the  members  of  the 
animal  kingdom.  These  evolutionary  phases  constitute  the  ancestral  history  or 
phylogeny  of  the  individual.  Ontogeny  and  phylogeny  are  intertwined  in  a 
remarkable  manner,  and  present  certain  extraordinary  relationships.  In  other 
words,  the  ancestral  evolutionary  development  appears  to  be  so  stamped  upon  an 
individual  that  it  repeats  certain  of  the  phylogenetic  stages  with  more  or  less 
clearness  during  the  process  of  its  own  individual  development.  Thus  at  an  early 
period  in  the  embryology  of  man  we  recognise  evanescent  gill-slits  comparable  with 
those  of  a  fish,  whilst  a  study  of  the  development  of  his  heart  shows  that  it  passes 
1 


2  TEXT-BOOK  OF  ANATOMY. 

through  transitory  structural  conditions  in  many  respects  similar  to  the  permanent 
condition  of  the  heart  in  certain  of  the  lower  animals.  It  is  in  connexion  with 
this  that  the  phrase  has  arisen  that  every  animal  in  its  individual  development  or 
ontogeny  climbs  up  its  own  genealogical  tree — a  saying  which,  taking  it  even  in 
the  broadest  sense,  is  only  partially  true. 

The  higher  conceptions  of  anatomy,  which  are  obtained  by  taking  a  general 
survey  of  the  structural  aspects  of  the  entire  animal  kingdom,  constitute  morphology. 
The  morphologist  investigates  the  laws  of  form  and  structure,  and  in  his  generalisa- 
tions he  gives  attention  to  detail  only  in  so  far  as  this  is  necessary  for  the  proper 
establishment  of  his  views.  The  knowledge  of  anatomy  which  is  required  by  the 
student  of  medicine  is  different.  It  is  essentially  one  of  detail,  and  often  details 
important  from  the  practical  and  utilitarian  points  of  view  have  little  or  no 
morphological  value.  This  want  of  balance  in  the  interest  attached  to  anatomical 
facts,  according  to  the  aspect  from  which  they  are  examined,  so  far  from  being 
unfortunate,  affords  the  teacher  the  means  of  making  the  study  of  anatomy  at  once 
fascinating  and  attractive.  Almost  every  fact  which  is  brought  under  the  notice 
of  the  student  can  be  accompanied  by  a  morphological  or  a  practical  application. 
This  it  is  that  lightens  a  study  which,  presented  to  the  student  of  medicine  in  any 
other  way,  would  be  at  once  dry  and  tedious. 

Certain  terms  employed  in  morphology  require  early  and  definite  explanation. 
These  are  homology,  serial  homology,  and  homoplasy.     The  same  organ  repeated  in 
two  different  animals  is  said  to  present  a  case  of  homology.     But  this  morphological 
identity  between  these   two  organs  must  be  proved  beyond  dispute  before   the 
homology  between  them  can  be  allowed.     In  deciding  this  identity  the  great  and 
essential  test  is  that  the  two  organs  in  question  should  have  a  similar  develop- 
mental origin.     Thus  the  fore-limb  of  a  quadruped  is  homologous  with  the  upper 
limb  of  man ;  the  puny  collar-bone  of  a  tiger,  the  fibrous  thread  which  is  the  only 
representative  of  this  bone  in  the  horse,  and  the  strongly  marked  clavicle  of  the 
ape  or  man,  are  aU,  strictly  speaking,  homologous  with  each  other.     Homologous 
oro'ans   in   different   animals   usually  present   a   similar   position   and   a   similar 
structure,  but  not  invariably  so.     It  is  not  uncommon  for  a  muscle  to  wander 
somewhat  from  its  original  position,  and  many  cases  could  be  quoted  in  which 
parts  have  become  completely  transformed  in  structure,  either  from  disuse  or  for 
the  purpose  of  meeting  some  special  demand  in  the  animal  economy.     In  the  study 
of  the  muscles  and  ligaments  instances  of  this  will  be  brought  under  the  notice  of 
the  reader.     Identity  or  correspondence  in  the  function  performed  by  two  organs 
in  two  different  animals  is  not  taken  into  consideration  in  deciding  questions  of 
homology.     The  gills  of  a  fish  and  the  lungs  of  a  higher  vertebrate  perform  very 
much  the  same  physiological  office,  and  yet  they  are  not  homologous.     The  term 
analogy  is  often  used  to  express  functional  correspondence  of  this  kind.     Often 
orcrans  which  perform  totally  different    functions  are  yet  perfectly  homologous. 
Thus  the  wing  of  a  bat  or  the  wing  of  a  bird,  both  of  which  are  subservient  to 
flight,  are  homologous  with  the  upper  limb  of  man,  the  office  of  which  is  the 
different  one  of  prehension. 

In  the  construction  of  vertebrates  and  certain  other  animal  groups  a  series  of 
similar  parts  are  repeated  along  a  longitudinal  axis,  one  after  the  other.  Thus  the 
series  of  vertebra?  which  build  up  the  backbone,  the  series  of  ribs  which  gird  round 
either  side  of  the  chest,  the  series  of  intercostal  muscles  which  fill  up  the  intervals 
between  the  ribs,  the  series  of  nerves  which  arise  from  the  brain  and  spinal  cord, 
are  all  examples  of  this.  An  animal  exhibiting  such  a  condition  of  parts  is  said  to 
present  the  segmental  type  of  organisation,  and  in  the  early  stages  of  development 
this  segmentation  is  much  more  strongly  marked,  and  is  to  be  seen  in  parts  which 


INTEODUCTION.  3 

subsequently  lose  all  trace  of  such  a  subdivision.  The  parts  thus  repeated  are  said 
to  be  serially  homologous.  But  there  are  other  instances  of  serial  homology  besides 
those  which  are  manifestly  produced  by  segmentation.  The  upper  limb  is  serially 
homologous  with  the  lower  limb :  each  is  composed  of  parts  which,  to  a  large 
extent,  are  repeated  in  the  other,  and  the  correct  adjustment  of  this  comparison 
between  the  several  parts  of  the  upper  and  lower  limbs  constitutes  one  of  the  most 
difficult  and  yet  interesting  problems  of  morphology. 

Homoplasy  is  a  term  which  has  been  introduced  to  express  a  form  of  corre- 
spondence between  organs  in  different  animals  which  cannot  be  included  under 
the  term  homology.  Two  animal  groups,  which  originally  have  sprung  from  the 
same  stem-form,  may  independently  develop  a  similar  structural  character  which  is 
altogether  absent  in  the  ancestor  common  to  both.  Thus  the  common  ancestor  of 
man  and  the  carnivora  in  all  probability  possessed  a  smooth  brain,  and  yet  the 
human  brain  and  the  carnivore  brain  are  both  richly  convoluted.  Not  only  this, 
but  certain  anatomists  seek  to  reconcile  the  convolutionary  pattern  of  the  one  with 
the  convolutionary  pattern  of  the  other.  What  correspondence  there  is  does  not, 
in  every  instance,  constitute  a  case  of  homology,  because  there  is  not  in  every  case 
a  community  of  origin.  Correspondence  of  this  kind  is  included  under  the  term 
"  homoplasy."  Another  example  is  afforded  by  the  heart  of  the  mammal  and  that 
of  the  bird.  In  both  of  these  groups  the  ventricular  portion  of  the  heart  consists 
of  a  right  and  a  left  chamber,  and  yet  the  ventricular  septum  in  the  one  is  not 
homologous  with  the  corresponding  septum  in  the  other,  because  the  common 
ancestor  from  which  both  have  sprung  possessed  a  heart  with  a  single  ventricular 
cavity,  and  the  double-chambered  condition  has  been  a  subsequent  and  independent 
development  in  the  two  groups. 

Systematic  Anatomy. — The  human  body  is  composed  of  a  combination  of 
several  systems  of  organs,  and  the  several  parts  of  each  system  not  only  present  a 
certain  similarity  in  structure,  but  also  fulfil  special  functions.     Thus  we  have — 

1.  The  skeletal  system,  composed  of  the  bones  and  certain  cartilaginous  and 
membranous  parts  associated  with  them,  the  study  of  which  is  known  as  osteology. 

2.  The  articulatory  system,  which  includes  the  joints  or  articulations,  the  study 
of  which  is  termed  arbhrology. 

3.  The  muscular  system,  comprising  the  muscles,  the  study  of  which  constitutes 
myology. 

4.  The  nervous  system,  in  which  are  included  the  brain,  the  spinal  cord,  the 
spinal  and  cranial  ganglia,  the  sympathetic  ganglia,  and  the  various  nerves 
proceeding  from  and  entering  these.  The  study  of  these  parts  is  expressed  by  the 
term  neurology.     In  this  system  the  organs  of  sense  may  also  be  included. 

5.  The  vascular  and  lymphatic  system,  including  the  heart,  blood-vessels,  the 
lymphatic  vessels,  and  the  lymphatic  glands.  Angeiology  is  the  term  applied  to  the 
study  of  this  system. 

6.  The  respiratory  system,  in  which  we  place  the  lungs,  windpipe,  and  larynx. 

7.  The  digestive  system,  which  consists  of  the  alimentary  canal  and  its  associated 
glands,  and  parts  such  as  the  tongue,  teeth,  liver,  pancreas,  etc. 

8.  The  urogenital  system,  composed  of  the  urinary  organs  and  the  reproductive 
organs — the  latter  difiering  in  the  two  sexes. 

The  term  splanchnology  denotes  the  study  of  the  organs  included  in  the 
respiratory,  digestive,  and  genito-urinary  systems. 

9.  The  integumentary  system,  consisting  of  the  skin,  nails,  hair,  etc. 

These  numerous  organs  which  form  the  various  systems  are  themselves  built  up 
of  tissues,  the  ultimate  elements  of  which  can  only  be  studied  by  the  aid  of  the 


4  TEXT-BOOK  OF  ANATOMY. 

microscope.  The  study  of  these  elements  and  the  manner  in  which  they  are 
grouped  together  to  form  the  various  tissues  of  the  body  forms  an  important  branch 
of  anatomy,  which  is  termed  histology. 

The  structure  of  the  human  body  may  be  studied  in  two  different  ways.  The 
several  parts  may  be  considered  with  reference  to  their  relative  positions,  either  as 
they  are  met  with  in  the  course  of  an  ordinary  dissection,  or  as  they  are  seen  on 
the  surface  of  a  section  through  the  body.  This  is  the  topographical  method.  On 
the  other  hand,  the  several  systems  of  organs  may  be  treated  separately  and  in 
sequence.  This  constitutes  the  systematic  method,  and  it  is  the  plan  which  is 
adhered  to  in  this  treatise. 

Descriptive  Terms. — Anatomy  is  a  descriptive  science  founded  on  observation, 
and  in  order  that  precision  and  accuracy  may  be  attained  it  is  absolutely  necessary 
that  we  should  be  provided  with  a  series  of  well-defined  descriptive  terms.  It  must 
be  clearly  understood  that  all  descriptions  are  framed  on  the  supposition  that  the 
body  is  in  the  erect  position,  with  the  arms  by  the  side,  and  the  hands  held  so  that 


Fig.  1. — Horizontal  Section  through  the  Trunk  at  the  Level  of  the  First  Lumbar  Vertebra. 

the  palms  look  forwards  and  the  thumbs  outwards.  An  imaginary  plane  of 
section,  passing  longitudinally  through  the  body  so  as  to  divide  it  accurately  into  a 
right  and  left  half,  is  called  the  medial  plane.  Fig.  1  (M.P.).  When  the  right  and 
left  halves  of  the  body  are  studied  it  will  be  found  that  both  are  to  a  large  extent 
formed  of  similar  parts.  The  right  and  left  limbs  are  alike ;  the  right  and  left 
halves  of  the  brain  are  the  same ;  there  are  a  right  and  left  kidney  and  a  right 
and  left  lung,  and  so  on.  So  far  tlie  organs  are  said  to  be  symmetrically  arranged. 
But  still  a  large  amount  of  asymmetry  may  be  observed.  Thus  the  chief  bulk  of 
the  liver  lies  to  the  right  side  of  the  medial  plane,  and  the  spleen  is  an  organ 
which  belongs  wholly  to  the  left  half  of  the  body.  Indeed,  it  is  well  to  state  that 
perfect  symmetry  never  does  exist.  There  always  will  be,  and  always  must  be,  a 
certain  want  of  balance  between  symmetrically  placed  parts  of  the  body.  Thus 
the  right  upper  limb  is,  as  a  rule,  constructed  upon  a  heavier  and  more  massive 
plan  than  the  left,  and  even  in  those  organs  where  the  symmetry  appears  most 
perfect,  as  for  instance  the  brain  and  spinal  cord,  it  only  requires  a  closer  study  to 
reveal  many  points  of  difference  between  the  right  and  left  halves.  The  line 
on  the  front  of  the  body  along  which  the  medial  plane  reaches  the  surface  is 


INTEODUCTION.  5 

termed  the  anterior  median  line  ;  whilst  the  corresponding  line  behind  is  called  the 
posterior  median  line. 

It  is  convenient  to  employ  other  terms  to  indicate  other  imaginary  planes  of 
section  through  the  body.  The  term  sagittal  is,  therefore,  used  to  denote  any  plane 
which  cuts  through  the  body  along  a  path  which  is  parallel  to  the  medial  plane 
(S  S') ;  and  the  term  coronal  or  frontal  is  given  to  any  vertical  plane  which  passes 
through  the  body  in  a  path  which  cuts  the  medial  plane  at  right  angles  (C  C). 
The  term  horizontal  as  applied  to  a  plane  of  section  requires  no  explanation. 

Any  structure  which  lies  nearer  to  the  medial  plane  than  another  is  said  to  be 
medial  or  internal  to  it ;  and  any  structure  placed  further  from  the  medial  plane 
than  another  is  said  to  lie  lateral  or  external  to  it.  Thus  in  Fig.  1,  A  is  lateral  to 
B ;  whilst  B  is  medial  to  A. 

The  terms  anterior  and  ventral  are  synonymous,  and  are  used  to  indicate  a 
structure  (D)  which  lies  nearer  to  the  front  or  ventral  surface  of  the  body  than 
another  structure  (E)  which  is  placed  nearer  to  the  back  or  dorsal  surface  of  the 
body,  and  which  is  thus  said  to  be  posterior  or  dorsal.  In  some  respects  it  would 
be  well  to  discard  the  terms  "  anterior  "  and  "  posterior  "  in  favour  of  "  ventral  " 
and  "  dorsal,"  seeing  that  the  former  are  only  applicable  to  man  in  the  erect 
attitude,  and  cannot  be  applied  to  an  animal  in  the  prone  or  quadrupedal  position. 
They  have,  however,  become  so  deeply  ingrained  into  the  descriptive  language  of 
the  human  anatomist  that  it  would  hardly  be  advisable  at  the  present  moment  to 
adopt  this  course  throughout.  A  similar  objection  may  be  raised  to  the  terms 
superior  and  inferior,  which  are  employed  to  indicate  the  relative  levels  at  which 
two  structures  lie  with  reference  to  the  upper  and  lower  ends  of  the  body.  The 
equivalent  terms  of  cephalic  and  preaxial  are,  therefore,  frequently  used  in  place  of 
"  superior,"  and  caudal  and  postaxial  in  place  of  "  inferior." 

The  terms  proximal  and  distal  should  only  be  applied  in  the  description  of  the 
limbs.  They  denote  relative  nearness  to  or  distance  from  the  trunk.  Thus  the 
hand  is  distal  to  the  fore-arm,  whilst  the  upper  arm  or  brachium  is  proximal  to  the 
fore-arm. 


GENERAL    EMBRYOLOGY. 

By  Alfeed  H.  Young  and  Arthur  Kobinson. 

Although  Llie  tissues  and  organs  of  the  body  when  fully  formed  differ  greatly 
not  only  in  respect  of  their  functional  characteristics,  but  also  with  regard  to  their 
structural  features,  they  are  developed  from  cell  elements  so  similar  in  appear- 
ance at  first  that  they  cannot  be  distinguished  from  one  another.  They  are  all 
the  offspring  of  parent  cells — the  female  cell  or  ovum,  and  the  male  cell  or 
spermatozoon.  Developmental  processes  apparently  take  place  in  the  female  cell 
alone,  but  they  cannot  occur  unless  tlie  essential  elements  of  a  sperm  or  male  cell 
previously  unite  with  it. 

Like  all  animal  cells,  the  ovum  is  a  mass  of  protoplasm  (cytoplasm)  containing 
a  nucleus.  In  many  cells  the  cytoplasm  or  cell  body  is  itself  enclosed  by  an  ex- 
ternal investing  membrane,  the  cell  wall,  and  such  a  membrane  is  present  in  the 
ovum.  Speaking  generally,  animal  cells  are  minute  structures,  those  of  the 
human  body  rarely  attaining  a  diameter  of  more  than  about  '083  mm.,  but  they 
vary  somewhat  in  size,  they  assume  different  forms,  and  they  acquire  characteristic 
peculiarities  associated  with  their  positions  and  functions ;  thus,  whilst  the  majority 
of  the  constituent  cells  of  an  individual  form  the  various  tissues  and  organs  of  the 
body,  others  are  reproductive  or  germinal  cells. 

Ova  are  simply  specialised  cells  modified  and  adapted  for  the  purpose  of  repro- 
duction and  the  continuance  of  the  species.  They  are  enclosed,  and  partially  or 
entirely  matured,  in  the  ovaries,  or  female  generative  glands,  in  the  cell-lined 
spaces  known  as  Graafian  follicles. 

When  an  ovum  has  reached  a  certain  stage  of  development  it  is  discharged  from 
the  ovary,  and  passing  along  the  oviduct  or  Fallopian  tube  it  eventually  reaches 
the  cavity  of  the  uterus.  Though  mature  and  capable  of  being  fertilised  it  may 
not  be  impregnated,  in  which  case  it  does  not  remain  in  the  uterus,  but  is  cast  out 
from  .that  organ.  If,  however,  it  becomes  fertilised,  l»y  union  with  the  male 
germinal  element,  it  is  retained  in  the  uterus,  and  develops  into  an  embryo  which 
possesses  all  the  characteristic  features  of  the  species  to  which  it  belongs  and  most 
of  the  special  peculiarities  of  its  parents. 

When  the  embryo,  or  the  foetus  as  it  is  termed  after  it  has  assumed  definite 
form,  is  capable  of  independent  existence,  its  intrauterine  life  terminates,  and 
it  is  separated  from  the  rest  of  the  ovum  and  is  born.  The  development  of  the 
individual,  however,  is  not  complete,  nor  does  it  become  complete  until  the  new 
being  reaches  the  adult  condition. 

The  term  embryology  is  sometimes  used  to  include  the  consideration  of  all  the 
developmental  changes  and  processes  which  take  place  in  the  ovum  from  the  begin- 
ning up  to  the  final  adult  stage.  It  is  more  convenient,  however,  to  restrict  its 
application  to  the  study  of  those  changes  which  take  place  during  the  development 
and  growth  of  the  organism  before  the  fcetus  is  separated  from  the  rest  of  the 
ovum,  or,  in  other  words,  during  its  intrauterine  existence. 

Briefly  epitomised,  the  sequence  of  changes  is  as  follows  : — Impregnation  of  the 
mature  ovum  is  followed  by  segmentation  or  cleavage.  By  a  series  of  successive 
divisions  the  egg-cell  is  divided  into  two,  four,  eight,  and  ultimately  into  a  large 

7 


8 


GENEEAL  EMBEYOLOGY. 


number  of  cells,  and  so  is  transformed  into  a  multicellular  mass,  the  morula.  The 
majority  of  the  "  segmentation  masses  "  or  cells,  or  blastomeres,  as  they  are  termed, 
are  differentiated  into  tissue  elements,  but  a  certain  number  retain  the  characters 
of  the  original  germ-cells  and  become  ova  or  sperm-cells,  which  form  the  "  points 
of  departure "  of  succeeding  generations.  Every  germ-cell  is  derived,  therefore, 
"  by  a  continuous  and  unbroken  series  of  cell-divisions "  which  have  extended 
through  the  past  from  the  most  primitive  ancestor,  and  it  forms  a  point  from 
which,  under  ordinary  circumstances,  all  future  generations  will  commence.  It  is 
in  this  sense  that  the  changes  through  which  a  living  being  passes  in  the  course 
of  its  life  "may,  in  their  completest  form,  be  considered  as  constituting  a  morpho- 
logical cycle,  beginning  with  the  ovum  and  ending  with  the  ovum  again." 

To  follow  these  changes  it  is  necessary  that  the  characters  and  capabilities  of 
the  constructive  elements  should  be  clearly  understood.  The  animal  cell,  which 
plays  an  all-important  part  in  the  life-history  of  the  individual,  and  the  modified 
germ-cells  must  be  carefully  studied,  and  as  far  as  possible  the  exact  nature  of 
their  constituent  parts  ascertained. 

The  phenomena  of  impregnation  and  segmentation,  and  the  subsequent  develop- 
mental processes  and  morphological  changes  which  result  in  the  formation  of  the 
embryo,  and,  finally,  the  arrangements  for  the  nutrition  and  protection  of  the  ovum 
during  its  intrauterine  existence,  will  then  be  considered. 


THE   ANIMAL   CELL. 


Nucleolus 


Nucleus 


Nuclear  ^ 
membrane 


Spongioplasm 
(cyto-reticulum) 


Hyaloplasm 


Attraction  sphere 


Ceutrosome 


Cells  are  the  structural  units  of  the  body.  Each  cell  has  an  individual  life- 
history  within  the  tissue  or  organ  to  which  it  belongs,  it  is  produced  by  a  pre- 
existing cell,  it  develops  and  grows,  is  modified  by  circumstances,  reproduces  other 
cells  similar  to  itself,  or  it  dies. 

A  cell  possesses  a  body  and  a  nucleus.  An  external  investing  membrane 
or  cell  waU  may  or  may  not  be  differentiated. 

The  cell  body  consists  of  proto- 
plasm— an  unstable,  highly  complex 
organic  substance,  the  constitution 
of  which  is  approximately  repre- 
sented by  the  formula  C^QH^QQK^gO^Q. 
It  is  colourless,  semi-fluid,  viscous, 
insoluble  in  water,  capable  of 
osmosis,  and  it  is  contractile  and 
irritable.  In  the  living  condition 
it  always  contains  a  certain  amount 
of  water  and  various  inorganic 
matters.  It  is  to  be  observed,  how- 
ever, that  there  are  many  varieties 
of  protoplasm,  differing  somewhat  in  nature  and  qualities. 

The  protoplasm  of  the  cell  body  is  called  cytoplasm.  Under  low  powers  of  the 
microscope  it  is  homogeneous  or  slightly  granular,  but  with  higher  magnification, 
and  especially  after  the  application  of  staining  agents,  it  is  possible  to  distinguish — 

(1)  A  highly  refractile,  elastic,  and  extensile  network — the  cyto-reticulum  or 

spongioplasm — the  meshes  of  which  are  filled  with 

(2)  A  clear,  semi-fluid  substance — the  cytolymph  or  hyaloplasm. 

The  fibres  of  the  reticulum  present  some  few  minute  rounded  bodies  of  doubtful 
nature,  which  are  termed  microsomes. 

The  nucleus  is  a  spherical  vesicle  embedded  in  the  cell  body.  It  is  surrounded 
by  a  distinct  nuclear  membrane,  and  usually  contains  nucleoli. 

It  consists  of  modified  protoplasm,  which  is  termed  karyoplasm,  the  precise  rela- 
tion of  which  to  the  cytoplasm  is  not  clear.  Structurally  it  resembles  cytoplasm  in 
that  it  presents  a  fine  reticulum,  the  fibres  of  which  seem  to  be  continuous  with 
the  cyto-reticulum  through  the  nuclear  membrane,  whilst  its  meshes  are  occupied 
by  nuclear  juice. 


Fig.  2.— Diagram  of  an  Animal  Cell. 


THE  ANIMAL  CELL.  9 

The  reticulum  forms  a  line  network  composed  of  linin  fibres  (achromatic 
substance).  There  is  also  a  coarser  network,  more  readily  stainable,  consisting  of 
chromatin,  granular  portions  of  which  may  also  be  embedded  in  the  linin.  Instead 
of  forming  a  coarse  network  the  chromatin  may  be  arranged  in  the  form  of  a  con- 
voluted cord,  or  as  a  number  of  separate  filaments,  and  in  certain  cases  it  constitutes 
a  series  of  loops  from  which  secondary  branches  are  projected,  the  apices  of  the 
loops  being  grouped  together  at  one  pole  of  the  nucleus  round  a  clear  area  known 
as  the  "  polar  field." 

The  nuclear  membrane  consists  of  both  chromatin  and  linin. 

Nucleoli  are  of  two  kinds,  true  and  false.  A  true  nucleolus  is  a  small,  refractile 
particle,  of  spherical  outline,  embedded  in  the  reticulum.  It  stains  deeply,  and  is 
said  to  consist  of  a  special  modification  of  the  karyoplasm  which  is  called  pyrenin. 
False  nucleoli  are  simply  the  nodes  of  the  chromatin  reticulum. 

The  nucleus  is  capable  of  motion ;  it  has  been  seen  to  alter  its  shape  in 
the  living  cell,  and  it  undoubtedly  plays  an  active  part  in  the  process  of  cell 
reproduction. 

In  addition  to  the  nucleus  many  cells  contain  one  or  more  small  rounded  bodies 
called  centrosomes.  The  centrosomes  are  modified  portions  of  the  protoplasm,  and 
they  lie,  as  a  rule,  in  a  modified,  clear-looking  area  of  the  cytoplasm,  which  is 
known  as  the  attraction  sphere.  This  is  generally  situated  close  to  the  nucleus, 
and  from  its  surface  a  number  of  fine  radiating  lines  project  into  the  adjacent 
cytoplasm. 

Centrosomes  become  very  evident  when  reproduction  commences,  but  are  not 
so  distinct  at  other  times. 

The  attraction  sphere  also  becomes  more  evident  when  cell-division  commences, 
and  the  radii  which  project  from  it,  as  well  as  the  contained  centrosome,  appear  to 
play  important  parts  in  the  reproductive  process. 

Reproduction  of  Cells. — Cell  division  or  reproduction  may  take  place  either — 

1.  By  direct  division — amitosis  ; 

2.  By  indirect  division— mitosis  or  karyokinesis. 

In  the  amitotic  or  direct  form  of  division  the  nucleus,  and  then  the  cell  body, 
are  equatorially  constricted,  the  constrictions  deepen  until  both  are  completely 
divided,  and  so  two  daughter  cells  are  produced.     Apparently  the  attraction  sphere 


Fig.  3. — Cell  Division. 

Huccessive  stages  of  mitosis  or  karyokinesis  (diagrammatic,  modified  from  Heuneguy).  A,  B,  C,  D,  and  E 
illustrate  the  phenomena  of  the  prophase  ;  F  those  of  the  metaphase  ;  G  and  H  those  of  the  anajihase  ; 
J,  K,  and  L  those  of  the  telophase. 

and  centrosome  play  some  part  in  this  process,  but  whether  their  influence  is 
initiative  or  directive  is  unknown. 

Mitosis,  the  process  of  indirect  division,  is  by  far  the  most  common  mode  of 


10  GENERAL  EMBRYOLOGY. 

cell-division.  It  is  a  complex  process,  and  the  phenomena  observable  during  its 
progress  are  classified  into  four  groups :  (1)  the  j^Tophase,  (2)  the  metaphase,  (3)  the 
anaphase,  and  (4)  the  telophase. 

The  phenomena  of  the  prophase  commence  with  the  division  of  the  centrosome 
and  attraction  sphere  into  two  parts  which  travel  to  opposite  poles  of  the  nucleus. 
At  the  same  time  the  reticulum  of  the  nucleus  disappears,  and  in  its  place  a  con- 
voluted cord  of  chromatin,  the  skein  or  spirem,  is  formed  (Fig.  3,  A,  B,  and  C) ; 
this  is  afterwards  broken  up  into  a  number  of  segments  which  may  be  mere  rods, 
but  which  more  frequently  have  the  form  of  V-shaped  loops  (Fig.  3,  D).  The 
nucleoli  disappear,  and  some  of  the  filaments  which  radiate  from  the  newly-formed 
attraction  spheres  seem  to  penetrate  the  nuclear  membrane  at  the  poles  of  the 
nucleus.  The  nuclear  membrane  subsequently  disappears,  and  the  filaments 
passing  from  the  attraction  spheres  into  the  nucleus  form  two  cones,  the  bases  of 
which  meet  at  the  equator  of  the  nucleus,  where  they  fuse  together,  forming  an 
achromatic  spindle  which  extends  between  the  two  attraction  spheres  (Fig.  3,  E). 

The  loops,  or  rods,  of  chromatin  are  gradually  grouped  at  the  equator  of  the 
spindle,  each  rod,  or  chromosome,  being  apparently  connected  with  one  of  the 
achromatic  fibrils ;  and  the  prophase  is  completed. 

In  the  metaphase  each  chromosome  is  split  longitudinally  into  two  halves — 
daughter  chromosomes — which  separate  from  one  another ;  the  separation  com- 
mences at  the  apex  of  each  V-shaped  chromosome,  which  appears  to  be  attached  to 
an  achromatic  fibril  (Fig.  3,  F). 

In  the  anapihase  the  daughter  chromosomes  pass  to  the  opposite  poles  of  the 
spindle.  It  is  suggested  that  this  movement  is  brought  about  by  the  contraction 
of  the  spindle  fibrils,  but  this  is  doubtful,  though  it  is  noteworthy  that  in  some 
cases  fine  achromatic  fibrils  connecting  the  separated  daughter  chromosomes  are 
present  (Fig.  3,  G  and  H).  Slightly  before,  or  simultaneously  with,  the  completion 
of  the  anaphase  the  cell  body  is  equatorial  ly  constricted. 

During  the  telophase  the  constriction  deepens  and  the  cell  is  divided  into  two 
daughter  cells.  Whilst  this  division  is  taking  place  the  daughter  chromosomes, 
which  are  grouped  in  the  neighbourhood  of  each  attraction  sphere  at  opposite  ends 
of  the  spindle,  unite  into  a  convoluted  cord,  round  which  a  nuclear  membrane  is 
formed,  whilst  the  cord  is  converted  into  a  reticulum,  and  nucleoli  appear  (Fig.  3, 
J,  K,  L).  Therefore  when  the  separation  of  the  daughter  cells  is  completed,  at  the 
end  of  the  telophase,  each  possesses  all  the  characteristic  features  of  the  mother  cell. 

Reproductive  Cells. — The  germinal  elements,  the  union  of  which  is  essential 
to  the  formation  of  a  new  being,  are  the  ovum  or  female  element,  and  the  sperma- 
tozoon or  male  element. 

THE  OVUM. 

Structurally  an  ovum  presents  all  the  characteristic  features  of  a  typical  cell. 
It  is  peculiar  because  of  the  large  size  of  the  nucleus  and  nucleolus  and  in  the 
possession  of  two  investing  membranes,  an  inner  one,  tlie  vitelline  membrane, 
which  corresponds  to  tlie  cell  wall,  and  an  outer  one,  the  oolemma  or  zona  pellucida. 
Moreover,  the  nucleus  always  occupies  an  excentric  position  in  the  cytoplasm,  and 
the  cell  body  contains  nutritive  material  in  the  form  of  yolk  granules. 

The  constituent  parts  of  an  ovum  have  received  distinctive  names,  however ; 
thus  the  cell  body  is  known  as  the  yolk  or  vitellus,  the  nucleus  is  termed  the 
germinal  vesicle,  and  the  true  nucleolus  is  called  the  germinal  spot. 

Vitellus  or  Yolk. — The  body  of  the  ovum,  consisting  as  in  an  ordinary  cell  of 
cytoplasm  resolvable  into  reticulum  and  cytolymph,  contains  also  numerous  granules 
of  small  but  varying  size  called  yolk  granules.  These  are  highly  retractile,  fatty, 
and  albuminoid  bodies  containing  phosphorus  and  mineral  salts ;  collectively  they 
constitute  the  deutoplasm  or  nutritive  yolk,  in  contradistinction  to  the  cytoplasm  or 
formative  yolk. 

Xutritive  or  food  yolk  plays  an  important  part  in  development.  In  some 
animals  it  is  the  only  means  of  support  for  the  embryo  in  the  early  stages  of 
development ;  in  most  mammals,  on  the  other  hand,  the  embryo  is  supplied  almost 
from  the  first  with  food  not  from  the  egg  itself,  but  directly  from  the  mother 


THE  OVUM. 


11 


through  the  placenta.     The  amount  of  deutoplasm  present  in  the  ova  of  different 
animals  therefore  varies  greatly. 

Ova  in  which  there  is  no  deutoplasm  are  spoken  of  as  alecithal.     Such  ova,  if 
they  exist,  are  very  rare  ;  most  of  those  usually  classed  under  this  head  undoubtedly 
contain  a  certain  amount  of  deutoplasm  granules  scattered  throughout  the  cyto- 
plasm, and  are  better  described   by  the  . 
term  oligolecithal.     The  size  of  an  ovum 
is  determined  by  the  amount  of  food  yolk 
present,  and  all  oligolecithal  ova  are  small; 
the  human  ovum,  which  may  be  taken  as 
a  type  of  the  class,  is  about  '2  mm.,  or 
T^^tli  of  an  inch  in  diameter. 

As  the  deutoplasm  is  increased  m 
amount  the  ovum  is^  increased  in  size. 
The  deutoplasm  also  tends  to  accumulate 
in  certain  situations ;  if  the  accumulation 
is  at  one  extremity  of  the  cell  the  ovum 
is  described  as  telolecithal ;  such  ova  are 
naturally  divisible  into  two  areas  or  poles, 
a  cytoplasmic  or  formative  pole,  and  a 
deutoplasmic  or  nutritive  pole. 

In  eutelolecithal  ova  the  deutoplasm 
almost  entirely  displaces  the  cytoplasm 
from  one  pole,  as  in  the  egg  of  the  fowl, 
in  which  the  cytoplasm  is  represented  b}' 
a  disc  spread  over  one  pole  of  a  large 
deutoplasmic  mass.  In  many  of  the 
arthropoda  the  deutoplasm  accumulates  at 
the  centre  of  the  ovum,  which  is  there- 
fore termed  centrolecithal. 

The  germinal  vesicle  or  nucleus  of 

the  human  ovum  is   about  "05  mm.  or   ; 

diameter  of  the  whole  ovum.  It  lies  excentrically  in  the  yolk,  and  has  the  usual 
characters  of  a  cell  nucleus,  i.e.  it  possesses  a  nuclear  membrane  within  which  is 
the  karyoplasm,  divisible  into  reticulum  or  nucleoplasm,  and  nuclear  juice.  The 
nucleoplasm  consists  of  chromatin  and  achromatic  filjres  (linin),  and  the  nuclear 
juice  contains  one  or  more  spherical  and  highly  refractile  true  nucleoli  or  geruunal 
spots ;  the  nodes  of  the  reticulum  constitute  false  nucleoli. 

In  addition  to  the  nucleus,  the  vitelhis,  at  certain  periods,  also  contains  a  structure 
known  as  the  vitelline  body,  body  of  Balbiani,  or  accessory  nucleus.  It  is  readily  seen 
in  young  ova  lying  near  the  nucleus.  It  contains  one  or  more  centrosomes,  and  probably 
represents  an  attraction  sphere. 

Vitelline  Membrane.  —  The  viteUine  membrane  is  simply  the  peripheral 
portion  of  the  vitellus,  modified  and  transformed  into  a  fine  structureless  envelope 
which  covers  the  outer  surface  of  the  yolk.  It  is  usually  closely  appUed  to  the 
inner  aspect  of  the  outer  membrane,  the  zona  pellucida,  and  is  best  seen  in  the 
dead  ovum  and  after  treatment  by  reagents.  It  is  therefore  thought  by  some  to 
be  merely  a  condensation  of  the  outer  part  of  the  vitellus  produced  by  the  action  of 
the  reacrents.  There  is  evidence,  however,  to  show  that  it  is  present  in  the  normal 
living  ovum. 

Zona  Pellucida  or  Oolemma.— This  membrane  is  thick,  tough,  and  refractile. 
It  serves  as  a  protective  covering  for  the  ovum,  and  persists  for  a  considerable 
time  after  fertilisation,  only  disappearing  when  the  ovum  becomes  attached  to 
the  uterus.  It  is  perforated  by  numerous  fine  canals,  which  give  to  the  broad  clear 
membrane  a  finely  striated  appearance,  from  which  circumstance  it  has  been  called 
the  "  zona  striata."  The  zona  pellucida  is  not  formed  by  the  ovum,  but  is  secreted 
by  the  cells  of  the  Graafian  follicle  in  which  the  ovum  lies ;  it  is  consequently 
regarded  as  a  secondary  membrane,  and  is  altogether  different  from  the  vitelline 


Pn;.  4. — The  Ovum  and  its  Cuverings 
( Diagrammatic). 

The  corona  radiata,  which  completely  surroimds  the 
ovum,  is  only  represented  in  the  lower  part  of 
the  figure. 

5.  Vitellus  or  Yolk, 
(i.  (ierniinal  vesicle  (nucleus). 
GenniuHl  spot  (nucleolus). 


1.  Corona  radiata 

2.  Granular  layer 

3.  Vitelline  menil)ran 


4.  Zona  pcUuciila  ((joleiiiina).  S.  Nuclear  membrane. 

L^th  of  an  inch  in  diameter,  i.e.  \  the 


12 


GENEKAL  EMBEYOLOGY. 


membrane.  The  perforations  in  the  zona  serve  for  the  passage  of  nutritive 
material  to  the  ovum. 

When  the  ovum  leaves  the  Graafian  follicle  it  is  surrounded  by  several  layers 
of  cells,  the  innermost  of  which  are  columnar.  They  are  derived  from  the  cells  of 
the  follicle,  and  collectively  constitute  the  corona  radiata  ;  the  cells  gradually 
diminish  in  size,  and  ultimately  disappear.  Their  function  is  unknown,  but 
between  them  and  the  zona  pellucida  there  is  a  layer  of  granular  matter,  probably 
formed  by  the  cells  of  the  corona  radiata,  which  rapidly  swells  up  when  the  ovum 
is  liberated  from  the  follicle,  and  forms  a  gelatinous  elastic  layer  called  the  albumen  ; 
this  increases  in  thickness  as  the  ovum  passes  along  the  oviduct,  and  persists  for 
some  time  after  it  enters  the  uterine  cavity.  The  function  of  the  albumen  has  not 
been  definitely  ascertained ;  it  may  act  merely  as  a  protective  covering  against 
undue  pressure,  possibly  it  may  be  nutritive,  whilst  in  the  dog  it  apparently  helps 
to  fix  the  ovum  to  the  wall  of  the  uterus.  It  has  not  been  found  in  all  mammalian 
ova,  and  it  has  not  been  seen  round  the  human  ovum ;  still  it  may  be  present,  for 
human  ova  at  the  stage  when  it  might  be  expected  to  develop  have  not  yet  been 
observed. 

Special  Characters  of  the  Ovum. — The  ovum  as  it  lies  in  the  Graafian 
follicle  presents  no  obvious  structural  modifications  when  compared  with  an 
ordinary  animal  cell,  but  undoubtedly  differs  greatly  in  its  capabilities  and  life 
history.  Unlike  an  ordinary  cell,  it  has  no  inherent  power  of  division  into  two 
equal  parts,  but  before  it  is  capable  of  fertilisation  it  twice  undergoes  unequal 
division  during  the  period  of  ripening  or  maturation ;  again,  its  history  is  different 
from  that  of  ordinary  tissue  cells,  though  it  corresponds  closely  with  that  of  the 
male  germinal  elements  or  spermatozoa. 

Maturation  of  the  Ovum. — As  it  lies  in  the  Graafian  follicle  before  matura- 


FiG.  5. 


IJ  E  !■' 

-The  Matukation  of  thk  Ovum:    Extrusion  of  the  "Polar  i:ioDiE.s  "  (Diagrammatic). 


A,  An  ovum  at  the  commeucement  of  the  process  ;  B,  After  the  formation  of  the  .spindle.  The  chromosomes 
are  gathered  at  the  equator  of  the  spindle.  C,  One  apex  of  the  spindle  has  projected  into  a  bud  on  the 
surface,  and  half  of  the  divide<l  dyads  have  passed  to  each  ]wle  ;  D,  The  separation  of  the  first  polar 
body  ;  E,  The  commencement  of  the  second  polar  body  ;  Y,  The  completion  of  the  second  polar  body. 

tion  commences,  the  ovum  is,  strictly  speaking,  an  oocyte  of  the  first  order,  derived 
by  a  process  of  cell -division  and  growth  from  a  primitive  germinal  cell  which 
became  embedded  in  the  ovary.  The  more  direct  descendants  of  this  primitive 
germ  cell  are  called  oogonia,  and  from  them  oocytes  of  the  first  order  are  developed. 


THE  OVUM.  13 

The  oocyte  of  the  first  order  is  at  first  small,  but  as  the  Graafian  follicle  in  which 
it  lies  grows  the  oocyte  also  increases  in  size,  and  either  before  or  immediately 
after  its  extrusion  from  the  follicle  it  undergoes  the  changes  which  constitute 
maturation  or  preparation  for  fertilisation ;  in  other  words,  it  divides  twice  into 
unequal  parts  by  a  modified  process  of  mitotic  division. 

It  is  a  well-known  fact  that  all  animal  cells  contain  in  their  nuclei  a  definite 
number  of  chromosomes,  the  number  varying  in  different  groups  of  animals,  but 
being  constant  in  any  given  species,  and  both  the  primitive  germ  cells  and  the 
oogonia  descended  from  them  contain  the  same  number  of  chromosomes  as 
ordinary  tissue  cells.  But  when  the  oocyte  of  the  first  order  begins  to  prepare  for 
the  first  division  during  the  process  of  maturation,  it  is  seen  that  the  number  of 
chromosomes  it  contains  is  only  half  that  of  the  ordinary  tissue  cells.  Moreover, 
the  chromosomes  are  not  slender  V-shaped  loops,  but  short,  thick  rods  in  rings  or 
groups  of  four  granules,  and  if  they  are  rod-like  they  do  not  he  in  the  prophase  with 
their  long  axes  at  an  angle  with  the  achromatic  spindle,  as  in  ordinary  mitosis,  but 
parallel  with  the  filaments  of  the  spindle.  During  the  metaphase  the  chromosomes 
do  not  split  longitudinally  as  in  ordinary  mitosis,  but  transversely.     This  modifica- 


Oof-yte  of  1st  onlpr 


Oocyte  of  2nd  orrlpr 


1st  polar  body 


Descendant  of  Descendant  of 

1st  polar  body  1st  jiolar  body 


ilatiire  ovum 


Fig.  6. — Diagram  illustrating  the  Maturation  of  the  Ovum.     It  must  be  remembered  that  in  some 
cases  only  one  polar  body  is  formed,  and  in  others  the  first  polar  body  does  not  divide  into  two  parts. 

tion  of  ordinary  or  homotype  mitosis  is  known  as  heterotype  mitosis ;  it  takes  place 
not  only  in  oocytes  of  the  first  order  at  the  commencement  of  maturation,  but  also 
in  the  cells  of  malignant  tumours,  and  its  exact  signification  is  not  understood. 
If  we  imagine  that  the  nuclei  of  the  tissue  cells  of  the  animal  with  which  we  are 
deahng  contain  six  chromosomes  each,  then  at  the  commencement  of  the  first 
maturation  division  of  the  oocyte  only  three  chromosomes  will  be  seen  on  the 
spindle  which  forms.  The  spindle  at  its  appearance  is  parallel  with  one  surface 
of  the  ovum,  but  it  gradually  rotates  till  it  stands  at  right  angles  to  the  surface 
upon  which  it  impinges,  pushing  a  small  part  of  the  cytoplasm  before  it  in  the 
form  of  a  small  bud  (Fig.  5,  B  and  C).  In  the  anaphase  the  chromosomes  divide 
transversely,  and  three  half  chromosomes  pass  to  the  inner  end  of  the  spindle  and 
three  to  the  outer  end,  that  is,  into  the  bud-like  projection.  When  the  telophase 
is  completed  the  oocyte  of  the  first  order  is  divided  into  a  small  part,  the  first  polar 
body,  and  a  larger  part,  the  oocyte  of  the  second  order,  and  each  contains  three 
chromosomes  (Fig.  5,  D).  Almost  immediately  the  heterotype  division  is  followed  in 
the  oocyte  of  the  second  order  by  a  homotype  division,  no  resting  stage  interven- 
ing. A  new  spindle  appears,  the  three  chromosomes  radiate  from  its  equator 
in    the    usual   way,   and    they   divide   longitudinally.      Three   of    the    daughter 


14  GENEE.AL  EMBKYOLOGY. 

chromosomes  pass  to  tlie  inner  end  of  the  spindle  and  three  to  the  outer,  which 
projects  into  a  second  pohir  bud.  Division  now  occurs,  and  the  oocyte  of  the 
second  order  divides  into  the  mature  ovum  and  the  second  polar  body,  each  of  which 
contains  three  chromosomes  in  its  nucleus  (Fig.  5,  E  and  F).  Thus  at  the  end  of 
maturation  there  lie  within  the  zona  pellucida  the  mature  ovum  and  two  polar 
bodies,  and  the  nucleus  of  the  mature  ovum,  or  female  pronucleus  as  it  is  called, 
contains  half  the  number  of  chromosomes  which  were  present  in  the  primitive 
germ  cell.^ 

THE   SPEKMATOZOON". 

Spermatozoa  are  modified  cells  produced  in  the  testicles  or  male  generative 
glands.  They  are  formed  from  the  spermatogonia  or  sperm  mother  cells  which  are 
derived  from  the  primitive  germ  cells  of  the  testicle,  and  which  ultimately  produce 
the  spermatocytes  of  the  first  order  (Fig.  7),  the  latter  constituting  the  immediate 
point  of  departure  in  the  production  of  a  spermatozoon,  and  corresponding  therefore 
with  the  ovum  or  oocyte  of  the  first  order  immediately  before  its  maturation 
commences.  The  daughter  cells  of  the  spermatocytes  of  the  first  order  are 
spermatocytes  of  the  second  order,  and  their  descendants  the  spermatids  are  the 
granddaughter  cells  of  the  spermatocytes  of  the  first  order.  The  spermatids 
become  closely  associated  with  special  sustentacular  or  nurse  cells,  and  during  this 
association  are  converted  into  spermatozoa. 

Each  spermatid  is  a  cell  possessing  a  cell  body,  a  nucleus,  two  centrosomes,  and 
a  structure  known  as  an  idiosome.     The  latter  is  believed  by  some  authorities  to 


Spprmatocytc  of  1st  order 


Si)firiiiatid  Spcniiat.iil  Siicrmaliil  SpcniiatiJ 


Fk;.  7.— Diagram  tllu-stratint.  thi:  Process  of  CEt.L-l)ivisioN  hesultixo  in  the  Formation  ok 
Spermatids  which  ake  afterwards  modified  into  Spermatozoa. 

represent  the  attraction  sphere,  whilst  others  look  upon  it  as  a  special  modification 
of  the  protoplasm  only  established  during  the  process  of  mitosis,  and 'distinct  from 
the  attraction  sphere.  However  this  may  be,  the  nucleus  of  the  spermatid  becomes 
the  head  of  the  spermatozoon  (Fig.  9).  The  idiosome  forms  the  head  cap,  a  tail 
filament  grows  out  from  the  region  of  the  centrosomes,  and  the  body  of  the 
spermatid  forms  part  if  not  all  of  the  neck,  body,  tail,  and  end  piece  of  the 
spermatozoon.  The  centrosomes  become  embedded  in  the  neck,  one  at  its  cephalic 
and  the  other  at  its  caudal  end.  The  axial  filament  is  closely  connected  with 
the  posterior  centrosome,  which  has  possibly  united  with  the  cytoplasm  in  its 
formation. 

'  In  the  mouse,  an<l  probahly  also  in  some  other  mammals,  only  one  polar  body  is  formed  in  many  cases. 


THE  SPEEMATOZOON. 


15 


Head 


Body      — 


\eckT3i 


Body  J  I 


There  is  no  doubt  that  the  mature  ovum  and  the  spermatozoon,  so  far  as  their 
development  is  concerned,  are  very  similar.  Each  is  derived  from  a  primitive 
germ  cell,  which  becomes  embedded  in  the  generative  gland.  From  the  primitive 
germ  cell  in  the  one  case  oogonia  are  formed  and  in  the  other  spermatogonia,  and 
from  the  oogonia  and  spermatogonia  respectively  oocytes  and  spermatocytes  of  the 
first  order  are  derived.  The  oocyte  of  the  first  order  divides  by  heterotype  mitosis 
into  an  oocyte  of  the  second  order  and  the  first  polar  body,  and  the  spermatocyte 
of  the  first  order  divides,  also  by  heterotype  mitosis,  into  two  spermatocytes  of  the 
second  order.  By  a  second  and  homotype  mitosis  the  oocyte  of  the  second  order 
divides  into  a  mature  ovum  and  a  second  polar  body,  and  the  spermatocyte  of  the 
second  order  divides  into  two  spermatids.  Thus  the  final  result  of  the  division  of 
the  spermatocyte  of  the  first  order  is  the  formation  of  four  granddaughter  cells  or 
spermatids,  each  of  which  contains  half  the  number  of  chromatic  particles  present 
in  the  primitive  germ  cell,  whilst  the  final  result  of  the  division  of  the  oocyte  of 
the  first  order  is  the  production  in  some  cases  of  only  three  granddaughter 
cells,  the  mature  ovum  and  two  polar  bodies,  but  in  many  cases  the  first 
polar  body  divides  in  the  homotype  manner  simultaneously  with  tlie  division 
of  the  oocyte  of  the  second  order,  and  thus  the  final  result  of  the  division 
of  the  oocyte  is  four  granddaughter  cells,  the  mature  ovum  and  three  polar 
bodies,  each  containing  half  the  number  of  chromosomes  present  in  the  primitive 
germ  cell.  There  are,  however,  two  differences  of  importance  between  the  male 
and  the  female  elements.  The 
final  result  of  the  division  of  the 
female  element  is  one  mature 
ovum  immediately  capable  of 
fertilisation  and  further  develop- 
ment, and  two  or  three  polar 
bodies  which  are  incapable  of 
further  development  and  which 
ultimately  disappear.  On  the 
other  hand,  the  result  of  the 
division  of  the  male  element  is 
the  production  of  four  equal 
parts,  the  spermatids,  each  of 
which  undergoes  further  modi- 
fication, and  is  transformed  into 
a  spermatozoon  capable  of  fertil- 
ising a  mature  ovum. 

A  spermatozoon,  like  an 
ovum,  is  a  nucleated  mass  of 
cytoplasm,  but  it  presents  strik- 
ing modifications  in  structure. 
It  is  very  small,  and  possesses  a 
head,  a  neck,  a  body,  a  tail,  and 
In  addition  it  is  provided  with 
a  head  cap  which  covers  more  than  the  anterior  half 
of  the  head  (Fig.  9).  This  cap  is  modified  over  the  apex 
of  the  head  into  a  sharp  cutting  edge,  by  means  of  which 
the  spermatozoon,  driven  forward  by  the  movement  of  the 
tail,  pierces  its  way  through  the  oolemma  of  the  ovum. 

In  the  short  neck  are  an  anterior  and  a  posterior 
centrosome  separated  by  an  intermediate  disc,  and  from 
the  posterior  centrosome  an  axial  filament  extends 
through  the  body  and  tail,  and  terminates  posteriorly  as 
the  end  piece.  The  axial  filament  is  surrounded  by  a 
sheath  which  is  thicker  in  the  body  than  in  the  tail.  Outside  the  sheath  of  the 
axial  filament,  in  the  body,  is  a  spiral  sheath,  and  this  is  enclosed  by  a  sheath  of 
punctiform  substance,  the  mitochondrial  sheath,  which  rests  at  the  lower  end  of 
the  body  on  an  annulus  or  terminal  disc. 


Head  cap 


Aiit.  centrosome 
Post,  centrosome 

Axial  fibre 

.  Spiral  sheath 
Mitochondrial 
sheath 
Jermiiial  disc 


-End  piece- 


FlG.  8 


Human  Spermatozoa 

(after  Retzius). 

A,  Side  view  ;  B,  Front  view. 

an  end  piece  (Fig.  8). 


Axial  fibre 


Sheath  of  axial 
fibre 


End  piece 


Fig.  9. — Structure  of  a  Human 
Spermatozoon  (after  Meeves). 


16 


GENEEAL  EMBEYOLOGY. 


A  transverse  striation  of  the  head,  a  spiral  filament,  a  spiral  sheath  associated 
with  the  body  and  tail,  and  a  terminal  spear  connected  with  the  head  have  been 
described  by  Bardleben  and  others,  but  apparently  they  do  not  exist  normally  as 
parts  of  the  human  spermatozoon. 

The  head  of  the  spermatozoon  is  ovoid  and  laterally  compressed,  so  that  when 
viewed  from  the  side  it  appears  pointed;  it  is  about  4-5  /z  long,  2-5  /x  broad,  and 
1-5  fM  thick.  The  body  is  somewhat  longer  than  the  head,  and  the  tail  is  six  times 
as  long  as  the  body,  therefore  the  total  length  of  the  spermatozoon  is  about  one- 
fifth  of  the  diameter  of  the  ovum. 


FEETILISATION  OF  THE  OVUM  AND  THE  EESULTS  THAT  ENSUE. 

Fertilisation. — The  mature  ovum  is  fertilised  by  a  spermatozoon.  The  two 
generative  elements  meet,  and  fertilisation  takes  place  as  a  rule  in  the  upper 
part  of  the  Fallopian  tube.  The  spermatozoon  penetrates  the  zona  pellucida  of 
the  ovum,  cutting  through  it  by  means  of  the  sharp  edge  of  its  head  cap.  At  the 
same  time  a  conical  projection,  the  cone  of  attraction,  appears  on  the  surface  of 
the  ovum,  within   the  zona  pellucida,  directly  beneath  the  point  at  which   the 


MP 


Fro.  10. — Fertilisation  of  the  Ovum  (Diagrammatic). 
A,  The  entrance  of  the  spermatozoon  and  the  formation  of  the  cone  of  attraction  ;  B,  The  appearance  of  the 
centrosome  ;  C,  The  approachment  of  the  male  and  female  pronuclei  ;  D,  The  first  segmentation  nncleus. 


C.      Centrosome. 

CA.   Cone  of  attraction. 


PP.    Female  pronucleus. 
MP.   Main  pronucleus. 


P.      Polar  body. 

S\.  SsRinentation  nucleus. 


spermatozoon  is  entering.  The  head,  and  probably  a  portion  of  the  body  of  the 
spermatozoon,  plunge  into  the  cone  of  attraction  ;  the  remainder  of  the  body  and  the 
tail  are  cast  off  and  disappear.  The  portion  of  the  spermatozoon  which  enters  the 
cytoplasm  of  the  ovum  is  converted  into  a  nucleus,  the  male  pronucleus,  which  is 
accompanied  by  its  attraction  sphere  and  centrosome.  When  the  male  pronucleus 
is  distinctly  formed  the  granules  of  the  cytoplasm  in  its  neighbourhood  begin  to 
radiate  around  it,  as  if  under  its  influence,  and  the  pronucleus  itself  travels 
inwards. 

As  the  male  pronucleus  approaches  the  female  pronucleus  the  latter  shows 


FEKTILISATION  OF  THE  OVUM. 


17 


sigus  of  activity,  it  undergoes  changes  of  form,  and  moves  to  meet  the  male 
pronucleus.  For  a  time  the  two  pronuclei  lie  in  juxtaposition,  and  ultimately  they 
fuse  together,  forming  the  first  segmentation  nucleus. 

The  first  segmentation  nucleus  is  accompanied  by  two  centrosomes  which  lie  at 
its  opposite  poles,  and  are  the  products  of  the  male  centrosome  which  divides  as 
the  pronuclei  fuse. 

The  fertilised  ovum,  the  product  of  the  fusion  of  the  mature  ovum  and  the 
spermatozoon,  contains  in  its  nucleus,  the  first  segmentation  nucleus,  the  same 
number  of  chromosomes  as  the  primitive  ovum  or  the  sperm-mother  cell,  but  the 
chromosomes  of  the  segmentation  nucleus  are  derived  partly  from  a  male  and 
partly  from  a  female  individual. 

According  to  some  authorities,  both  the  male  and  female  pronuclei  are  accompanied  by 
centrosomes,  and  at  the  moment  of  union  of  the  pronuclei  each  centrosome  divides ;  thus  four 
half-centrosomes  are  formed,  two  male  and  two  female.  From  the  four  half-centrosomes  two  new 
centrosomes  are  formed  Ijy  the  union  of  half  a  male  centrosome  with  half  a  female  centrosome. 
If  this  view  be  correct,  each  of  the  two  centrosomes  which  accompany  the  first  segmentation 
nucleus  contains  both  male  and  female  elements. 

Segmentation. — Segmentation  is  the  division  of  the  fertilised  ovum  (oosperm) 
into  a  number  of  cells.  These  cells  are  afterwards  arranged  in  layers — the  gerniinal 
layers  or  layers  of  the  blastoderm  ;  ultimately  they  are  differentiated  into  the  tissue 
elements  of  the  body. 


A  B  c 

Fig.  11. — Segmentation  of  the  Fertilised  Ovum  in  the  Rabbit. 

Formation  of  blastomeres  aud  morula  (Diagi-ammatic). 

A,  Division  into  two  segments  ;  B,  Division  into  four  segments  ;  C,  Morula  ; 

P,  Polar  bodies. 

All  the  phenomena  of  segmentation  have  not  been  observed  in  the  human  ovum, 
and  it  is  to  be  understood  that  the  following  description  is  based  chieiiy  upon  the 
conditions  met  with  in  rodents,  more  especially  in  the  rabbit,  an  animal  well 
adapted  for  the  study  of  these  phenomena. 

After  a  period  of  quiescence,  which  succeeds  the  fusion  of  the  male  and  female 
pronuclei,  a  period  of  activity  supervenes,  during  which  repeated  divisions  of  the 
impregnated  ovum  result  in  the  production  of  a  solid  mass  of  cells  called  a  morula. 
The  divisions  are  mitotic,  and  all  the  phenomena  associated  with  mitosis  are  readily 
observable  in  properly  prepared  specimens. 

The  planes  which  separate  the  several  segments  of  the  divided  ovum  in  its 
various  stages  are  termed  the  "  planes  of  segmentation,"  aud  in  some  animals  the 
first  plane  by  which  the  ovum  is  divided  into  the  first  two  daughter  cells  coincides 
with  the  future  mid-axial  or  mesial  plane  of  the  body,  the  descendants  of  the  cell 
lying  to  the  right  of  it  being  developed  into  the  right  half  of  the  body,  and  those 
of  the  cell  to  the  left  into  the  left  half.  There  is  no  proof,  however,  that  this 
occurs  in  mammals ;  all  that  is  definitely  known  is  that  the  first  division  separates 
the  ovum  into  two  parts  of  unequal  size  but  of  similar  colour  and  structure. 

The  second  plane  of  segmentation  is  at  right  angles  to  the  first,  and  it  separates 
the  two  daughter  cells  into  four  granddaughter  cells,  of  which,  in  some  cases,  two 
may  be  larger  and  two  smaller.  The  subsequent  divisions  occur  irregularly,  and 
they  result  in  the  formation  of  numerous  cells  (blastomeres)  which  apparently  only 
differ  in  size  in  the  rabbit,  but  which  also  differ  in  appearance  in  many  mammals. 
They  are  mixed  together  so  irregularly  that  it  is  impossible  to  distinguish   the 


18 


GENEEAL  EMBEYOLOGY. 


Fig.  12. — Convehsion  of  the  Morula  to 

THE  Blastdla. 

Formation  of  blastodermic  vesicle  and 

membrane. 

A,  Appearance  of  segmentation  cavity  and 
attachment  of  inner  cell  mass  to  ectoderm 
at  upper  pole  of  ovum  ;  B',  Extension  and 
flattening  of  inner  cell  mass  as  it  occurs  in 
)-abh»it  and  some  other  mammals  ;  B',  Ex- 
tension of  entoderm  as  it  occurs  in  insec- 
tivora,  monkeys,  apes,  and  man  ;  C,  Com- 
pletion of  bilaminar  blastodermic  vesicle. 
BC,  Blastodermic  cavity  ;  EC,  Ectoderm  ; 
EE,  Embryonic  ectoderm  ;  EN,  Entoderm  ; 
I,  Inner  cell  mass ;  8C,  Segmentation 
cavity  ;  ZP,  Zona  pellucida. 


descendants  of  one  daughter  cell  from  those  of 
the  other,  and  in  this,  the  morula  stage,  there 
is  frequently  no  indication  of  any  separation 
of  the  cells  into  layers.  In  the  meantime  the 
polar  bodies  have  disappeared. 

The  next  phenomenon  of  importance  is  the 
appearance  of  a  cavity — the  segmentation  cavity 
— in  the  morula  ;  the  ovum  assumes  a  vesicular 
character,  and  is  now  termed  a  blastula.  Simul- 
taneously with  the  appearance  of  the  cavity 
the  cells  of  the  morula  are  arranged  in  two  groups 
— an  outer  and  an  inner.  The  cells  of  the  outer 
group  form  a  layer,  the  primitive  ectoderm  or 
epiblast ;  those  of  the  inner  group  remain  massed 
together  and  constitute  the  inner  cell  mass.  The 
two  groups  are  in  contact  at  one  pole  of  the 
ovum,  and  it  is  in  this  region  that  the  embryo 
develops  (Fig.  12,  A). 

In  the  rabbit  and  in  some  other  mammals 
the  outer  cells  of  the  inner  mass  at  the  embryonic 
pole  of  the  ovum  blend  with  the  superjacent 
primitive  ectoderm  (Eauber's  cells)  to  form  the 
embryonic  ectoderm.  This  is  merely  a  modi- 
fication of  the  more  general  plan,  by  which  the 
inner  cell  mass  becomes  the  inner  layer  of  the 
now  vesicular  ovum,  but  the  conversion  of  the 
inner  mass  into  the  entoderm  may  take  place 
in  two  different  ways. 

(1)  In  the  rabbit  and  in  many  other  mam- 
mals the  inner  mass  gradually  flattens  out  till 
its  cells  form  a  layer  at  the  embryonic  pole, 
and  the  wall  of  the  vesicular  ovum,  which  is  now 
called  a  blastodermic  vesicle,  is  partly  unilaminar 
and  partly  bilaminar  (B^,  Eig.  12).  Gradually, 
however,  the  margins  of  the  entodermal  layer 
extend,  and  ultimately  the  cavity  of  the  vesicle 
is  surrounded  by  two  complete  layers,  ectoderm 
and  entoderm. 

In  the  hedgehog,  in  monkeys,  apes,  and  the 
human  subject,  a  cavity  appears  in  the  inner 
cell  mass  (B-,  Fig.  12),  and  the  cells  around  it 
assume  a  laminar  character,  constituting  the  en- 
toderm, which  is  separated  from  the  ectoderm, 
except  in  the  embryonic  area,  by  the  original 
cavity  of  the  blastodermic  vesicle. 

In  the  case  of  the  hedgehog  the  cavity 
in  the  entoderm  expands  until  the  entoderm  is 
forced  into  contact  with  the  ectoderm,  and  a 
condition  is  attained  similar  to  that  met  with 
in  the  rabbit  (C,  Fig.  12),  but  in  monkeys,  apes, 
and  the  human  subject  the  expansion  of  the 
entoderm  cavity  is  not  so  great,  and  the  entoderm 
does  not  attain  contact  with  the  ectoderm 
except  in  the  embryonic  area. 

In  amphioxus  and  many  of  the  in  vertebra  ta  the 
results  of  the  segmentation  are  not  quite  the  same 
as  in  mammals,  for  at  a  very  early  period,  without 
the  definite  formation  of  a  morulamass,  the  segmenta- 
tion cells  arrange  themselves  in  a  layer  round  a  central 


THE  EMBEYONIC  AEEA. 


19 


cavity  and  form  a  complete  unilaminar  blastoderm.  In  these  cases  the  bilaminar  condition 
is  produced  by  the  invagination  of  a  portion  of  the  wall  of  the  vesicle.  The  opening  at 
which  the  invagination  occurs  is  called  the  blastopore.  The  cavity  enclosed  by  the 
invagiuated  cells  is  the  archenteron,  or  primitive  alimentary  cavity  or  gastrula  cavity. 
Except  at  the  blastopore  the  cavity  is  surrounded  by  two  layers  of  cells,  an  outer  the 
ectoderm,  and  an  inner  the  entoderm,  and  the  animal  at  this  period  of  its  development  is 
a  gastrula.  In  the  mammal  the  cells  which  become  invaginated  in  amphioxus  to  form 
the  entoderm  are  enclosed  in  the  interior  of  the  morula  mass  at  a  very  early  period  of  the 
segmentation,  before  the  vesicular  condition  is  attained,  but  eventually,  as  already  pointed 
out,  they  form  a  layer  inside  the  ectoderm  and  they  enclose  a  cavity,  the  blastodermic 
cavity,  which  is  homologous  with  the  archenteron  or  gastrula  cavity  of  the  lower  forms, 
but  the  cavity  is  closed  and  the  blastopore  is  not  obvious.  In  amphioxus,  however,  the 
blastopore  becomes  elongated  antero-posteriorly,  and  along  the  margins  a  third  layer,  the 
mesoderm,  grows  out  between  the  two  primitive  layers.  In  the  mammal,  on  the  other 
hand,  after  the  entoderm  and  ectoderm  are  definitely  established,  a  linear  streak,  called 
the  primitive  streak,  to  which  further  reference  will  be  made,  appears  on  the  surface  of 
the  ovum ;  this  becomes  perforated  at  its  anterior  end,  and  from  its  margins  and  mesoderm 
extends  outwards ;  clearly,  therefore,  it  represents  the  blastopore  of  amphioxus  though 
an  actual  perforation  is  only  present  for  a  short  time,  and  the  mammalian  ovum  at  this 
period  may  be  looked  upon  as  a  gastrula. 

The  ectoderm  and  entoderm  together  constitute  the  blastoderm  or  blastodermic 
membrane,  which  is  bilaminar,  and  the  vesicle  of  which  they  form  the  wall  is  no 
longer  spoken  of  as  the  blastula,  but  as  the  blastodermic  vesicle. 

Structure  of  the  Ectoderm  and  Entoderm. — The  cells  of  the  ectoderm  are  at 
first  irregular  in  size  and  shape,  and  their  outlines  are  indistinct ;  but  after  a  short 
time  the  ectoderm  cells  at  one  pole  of  the  blastodermic  vesicle  become  cubical  or 
slightly  columnar,  whilst  the  remaining  cells  of  the  outer  layer  are  flattened  and 
have  irregular  outlines. 
The  columnar  cells 
form  the  ectoderm  of 
the  embryo,  and  the 
flattened  cells  are  util- 
ised in  the  formation  of 
nutritive  and  protec- 
tive structures  known 
as  the  placenta  and 
foetal  membranes. 

The  cells  of  the  en- 
toderm are  also,  at  first, 
very  irregular  in  shape 
and  size,  but  after- 
wards, as  they  are 
spread  out  into  a  layer,  ^ 
they  become  more  or 
less  rounded,  and  they 
anastomose  together  by 
filamentous  processes. 
At  a  still  later  period  they  are  transformed  into  polygonal  plates  which  appear 
spindle-shaped  in  section  (Fig.  12). 

Embryonic  Area.  ■ —  When  the  upper  pole  of  the  bilaminar  blastodermic 
vesicle  is  examined  in  surface  view  from  above,  a  dark,  somewhat  opaque  circular 
area  is  visible ;  this  is  known  as  the  embryonic  area.  It  is  coextensive  with  the 
columnar  portion  of  the  ectoderm.  Very  soon  after  it  appears  the  embryonic  area 
becomes  ovoid ;  the  small  end  of  the  ovoid  area  is  posterior,  that  is,  it  lies  in  the 
region  which  is  afterwards  converted  into  the  posterior  part  of  the  embryo.  At 
the  hinder  end  of  the  ovoid  area  a  still  darker  patch  of  triangular  form  is  developed  ; 
this  soon  becomes  crescentic,  and  is  the  first  indication  of  the  primitive  streak  and 
of  the  formation  of  a  third  blastodermic  layer  termed  the  mesoderm  or  mesoblast. 

The  primitive  streak  consists  of  thickened  ectoderm  which  is  seen  in  transverse 
sections  projecting  downwards,  and  resting  upon  the  entoderm  in  the  form  of  a  ridge. 


Mesoderm 


Fig.  13. — Surface  Vikw  of  the  Blastodermic  Vesicle. 

Showing  the  embryonic  area  and  the  commencement  of  the  mesoderm. 

Before  the  appearance  of  the  primitive  streak  —  the  embryonic  area  is 
circuhar  in  form  and  bilaminar  tliroughout  ;  B,  After  the  appearance  of 
tlie  primitive  streak.  The  posterior  end  of  the  primitive  streak  shows 
a  crescentic  thickening,  which  indicates  the  commencement  of  the  meso- 
derm or  middle  layer  of  the  blastodermic  membrane. 


20 


GENERAL  EMBRYOLOGY. 


From  the  sides  and  the  posterior  extremity  of  the  ectodermal  ridge  a  lamina  of 
cells  projects  outwards,  and  gradually  insinuates  itself  between  the  ectoderm  and 
the  entoderm  over  the  whole  area  of  the  vesicle,  except  in  certain  regions  to  be 
afterwards  described.  This  lamina  is  the  rudiment  of  the  mesoderm.  With  the 
formation  of  the  mesoderm  the  blastodermic  membrane  becomes  trilaminar. 


Embryonic  area 


Nenral  groove 


Notochord 

Entoderm 

Embryonic  area 
I 

,  Primitive  groove 

, Ectoderm 


Fig.  14. — The  Upper  Pole  of  the  Blastodermic  Vesicle. 

Showing  the  embryonic  area,  the  primitive  streak  with  the  extension  of  the  mesoderm  from  its  sides  and 
posterior  end,  and  the  commencement  of  the  neural  groove. 

A,  Surface  view  (diagrammatic)  ;  B  and  C,  Transverse  sections  through  the  blastoderm  of  the  ferret  at  the 
stage  represented  in  A  and  along  the  lines  b  and  c  respectively. 

The  majority  of  the  cells  of  the  mesoderm  are  derived  from  those  of  the 
primitive  streak,  but  it  is  said  that  cells  from  the  entoderm  also  take  part  in  its 
formation.  Young  mesodermal  cells  are  round  or  ovoid,  and  some  give  off  numerous 
processes.  In  later  stages  they  may  assume  various  shapes,  and  many  closely 
resemble  the  cells  of  the  ectoderm  or  those  of  the  entoderm. 

As  the  blastodermic  vesicle  grows,  the  embryonic  or  germinal  area  becomes 
pyriform  and  increases  in  length,  principally  in  the  posterior  part  of  its  extent 
where  the  primitive  streak  is  situated ;  at  the  same  time  the  streak  lengthens  and 


GO      SB 


BO   -V 

[SoP 

'  <5-.  %,S ."S-r-^^-^rra_  SpM  \ 


Fi(j.  15. — Transverse  Section  of  a  Ferret  Embryo. 

Showing  neural  groove  before  the  separation  of  the  paraxial  from  the  lateral  mesoderm. 

€.      Ccelom.  GC.  Germinal  cell.  PM.   Paraxial  mesoderm.  SoM.  Somatic  mesoderm. 

EC.   Ectoderm.  N.     Notochord.  SB.    Spongioblast.  SoP.  Somatopleui'e. 

EN.  Entoderm.  NG.  Neural  groove.  SG.    Spinal  ganglion.  SpM.  Splanchnic  mesoderm. 

SpP.  Splanchnopleure. 

becomes  more  linear.  For  a  short  time  a  groove,  thte  primitive  groove,  appears  on 
the  surface  of  the  streak.  It  is  deepest  in  front,  where  in  some  mammals,  includ- 
ing man,  a  small  transitory  perforation  is  formed,  the  neurenteric  canal. 

A  second  broader  and  sliallower  groove  then  appears  in  the  embryonic  area 
immediately  in  front  of  the  primitive  streak  ;  this  is  the  neural  groove,  the  rudiment 
of  the  nervous  system.  The  neural  groove,  its  bounding  folds,  and  the  nervous 
system  subsequently  developed  from  them  are  formed  entirely  of  ectodermal  elements, 
which  at  first  are  continuous  with  those  forming  the  outer  layer  of  the  embryo. 
The  posterior  end  of  the  neural  groove  embraces  the  anterior  end  of  the  primitive 
streak  and  groove,  and  at  this  period  the  neurenteric  canal  forms  a  communication 


THE  NEUEAL  OE  MEDULLAEY  GEOOVE. 


21 


between  the  interior  of  the  ovum  and  the  bottom  of  the  neural  groove,  which 
latter  afterwards  becomes  the  closed  canal  of  the  central  nervous  system.  In  some 
vertebrates  the  neurenteric  canal  persists  for  a  considerable  period,  and  upon  the 
development  of  the  alimentary  canal  it  constitutes  a  communicating  channel 
between  it  and  the  cavity  of  the  neural  tube. 

As  the  neural  groove  grows  backwards  the  anterior  part  of  the  primitive  streak 
is  absorbed,  and  although  the  posterior  part  continues  to  grow,  the  primitive  streak 
as  a  whole  diminishes  in  length ;  ultimately  the  greater  part  of  the  primitive 
streak  disappears,  but  a  portion  is  recognisable  for  a  considerable  time  extending 
from  the  base  of  the  tail,  a  transitory  structure  in  the  human  embryo,  to  the 
ventral  wall  of  the  body.  This  portion  forms  the  posterior  boundary  of  the 
primitive  alimentary  canal ;  it  remains  bilaminar,  and  is  called  the  cloacal 
membrane. 

The  primitive  streak  is  of  great  morjjliological  importance  ;  recent  researches  have  shown 
that  from  it  and  the  cells  in  its  neighbourhood  the  greater  jiart  of  the  body  of  the  embryo, 
with  the  exception  of  the  anterior  part  of  the  head  and  heart  region,  is  developed.  It  possibly 
represents  the  mouth  of  a  remote  (pre-vertebrate)  ancestor,  the  fused  lips  of  which  formed  the 
body  of  a  primitive  vertebrate  animal.  The  aperture  of  this  mouth  is  still  represented  in  lower 
vertebrates  by  an  oj)ening  known  as  the  blastopore.  The  neurenteric  canal  is  the  only  represen- 
tative of  the  opening  in  the  hximan  subject. 

The  neural  or  medullary  groove  is  bounded  laterally  by  medullary  folds 
which  are  continuous  in  front  of  the  groove,  but  separate    behind  where    they 


PS 


so     GC 


SB     NO     cc 


SoP- 


SpP— 


.^< 


=x  r 


SpP 


IMC  N  PA 

Fig.  16. — Transverse  Section  of  Ferret  Embryo. 

Showing  the  closure  of  the  neural  groove,  the  formation  of  the  neural  crest,  the  outgrowth  of  the  spinal 
ganglia,  the  commencement  of  the  separation  of  the  paraxial  mesoderm  from  the  lateral  plates,  and  the 
differentiation  of  the  intermediate  cell  mass. 


C.      Coelom.  GC.     Germinal  cell.  PA.  Primitive  aorta. 

CC.   Central  canal.      IMC.  Intermediate  cell  mass.       PS.  Mesodermic  somite. 
EC.   Ectoderm.  N.        Notochord.  SB.  Spongioblast. 

EN.  Entoderm.  NC.     Neural  crest.  SC.  Spinal  cord. 

SpP.  Splanchnopleure 


SG.  Spinal  ganglion. 

SoM.  Somatic  mesoderm. 

SoP.  Somatopleure. 

SpM.  Splanchnic  mesoderm. 


embrace  the  anterior  end  of  the  primitive  streak.  The  neural  groove  increases 
in  length  both  in  front  and  behind.  The  backward  increase  takes  place  at  the 
expense  of  the  primitive  streak,  whilst  the  anterior  increase  is  due  to  the  rapid 
growth  of  the  anterior  part  of  the  embryonic  area ;  at  the  same  time,  not  because 
of,  though  coincident  with,  an  increase  of  the  mesoderm  which  has  grown  beneath 
them,  the  medullary  folds  are  gradually  elevated,  and  their  apices  bending  inwards 
unite  together  over  the  neural  groove,  which  is  thvis  converted  into  a  tube  or  canal 
— the  neural  tube.  The  medullary  folds  unite,  in  the  iirst  place,  in  the  region 
which  afterwards  becomes  the  neck ;  and  subsequently  they  unite  progressively, 
forwards  and  backwards. 

Along  the  line  of  union  the  neural  tube  is  connected,  for  a  time,  with  the 
surface  ectoderm  by  a  ridge  of  cells,  the  neural  crest.  The  crest  soon  separates 
from  the  surface,  but  it  remains  connected  with  the  neural  tube,  and  is  utilised  in 
the  formation  of  the  cranial  and  spinal  nerve  ganglia,  the  sympathetic  ganglia,  the 
carotid  and  coccygeal  bodies,  and  the  medullary  parts  of  the  suprarenal  bodies, 
whilst  the  walls  of  the  neural  tube  are  converted  into  the  nervous  and  sustentacular 
tissue  elements  of  the  whole  of  the  central  nervous  system  (brain  and  spinal  cord). 


22  GENERAL  EMBRYOLOGY. 

Before  the  tube  is  closed  the  neural  groove  is  dilated  at  each  end  (see  Fig.  20). 
The  posterior  dilatation  is  single ;  it  constitutes  the  rhomboidal  sinus,  which  under 
ordinary  circumstances  soon  disappears.  Anteriorly,  numerous  dilatations  are 
distinguishable  at  first.  The  exact  number  of  these  dilatations  (neuro meres)  is 
said  to  be  eleven.  As  the  tube  closes  they  resolve  themselves  into  three  distinct 
vesicles  termed  the  primary  cerebral  vesicles.  These  constitute  the  rudiments  of  the 
fore-  mid-  and  hind-brains,  and  their  respective  ventricular  cavities.  The  remainder 
of  the  cavity  of  the  tube  becomes  the  central  canal  of  the  spinal  cord. 

After  the  separation  of  the  neural  crest  from  the  surface  -the  mesoderm  com- 
pletely surrounds  the  whole  of  the  neural  tube,  and  from  it  are  formed  the 
membranes  of  the  brain  and  spinal  cord  and  their  skeletal  environments. 

The  ectodermal  cells  which  form  the  wall  of  the  primitive  neural  tube  are  ill- 
defined,  but  they  soon  differentiate  into  two  sets,  spongioblasts  and  germinal  cells. 
The  spongioblasts  are  the  more  numerous,  they  are  columnar  in  form,  and  all 
extend  from  an  internal  limiting  membrane  which  is  developed  round  the  periphery 
of  the  central  canal  to  an  external  limiting  membrane  which  forms  the  outer 
limit  of  the  neural  tube.  There  is  frequently  considerable  difficulty  in  recognising 
their  columnar  character,  even  in  the  early  stages,  partly  because  their  nuclei  do 
not  all  lie  at  the  same  level,  and  partly  because  they  are  so  closely  opposed.  The 
spongioblasts  are  converted  into  the  sustentacular  tissue,  or  myelospongium,  of  the 
brain  and  spinal  cord,  but  all  do  not  undergo  precisely  the  same  transformations. 
The  inner  portions  of  those  spongioblasts  whose  nuclei  lie  near  the  central  canal 
retain  a  columnar  form,  and  cilia  grow  from  their  free  surfaces  into  the  lumen  of  the 
canal;  in  other  words,  they  are  converted  into  the  ciliated  epithelium  of  the  central 
canal,  but  the  outer  portions  of  the  same  cells  are  transformed  into  fibrillar  processes 
which  terminate  externally  by  fusing  with  the  external  limiting  membrane.  The 
remaining  spongioblasts  entirely  lose  their  columnar  form,  they  become  much 
branched,  and  their  branches  interlace  with  the  fibrillar  processes  of  the  ciliated 
epithelial  cells,  and  with  similar  branches  of  neighbouring  cells,  forming  the 
reticular  sustentacular  tissue  or  myelospongium ;  the  external  limiting  membrane 
is  produced  by  the  close  interweaving  of  the  peripheral  myelospongial  fibrils. 

The  germinal  cells  are  spherical  in  outline,  and  contain  clear  protoplasm  and 
darkly-staining  nuclei.  They  lie  between  the  inner  ends  of  the  spongioblasts  close 
to  the  central  canal  where,  at  the  fourth  or  fifth  week,  they  form  an  irregular  layer, 
and  it  is  believed  that  they  very  soon  give  rise  to  a  new  generation  of  cells,  the 
neuroblasts,  or  young  nerve-cells — at  all  events  neuroblasts  appear  as  the  germinal 
cells  disappear.  Each  neuroblast  rapidly  becomes  pyriform  by  the  outgrowth  of  an 
axial  process  or  axon,  which  projects  from  its  outer  end  towards  the  periphery  of 
the  tube. 

Shortly  after  their  formation  the  neuroblasts  migrate  outwards,  and  ultimately 
those  of  the  cord  are  arranged  in  longer  or  shorter  columns  in  the  myelospongium, 
whilst  those  of  the  brain  are  grouped  together  in  definite  areas  to  form  the 
cerebral  nuclei. 

Each  neuroblast  as  it  develops  gives  off  many  processes,  which  vary  in  length 
and  thickness.  The  first  formed  of  these  is  the  axial  process  or  axon  already 
referred  to.  It  carries  impulses  from  the  cell,  gives  off  lateral  branches,  and 
terminates  either  in  association  with  a  special  end-organ  or  by  ramifying  amidst 
other  nerve-processes  or  round  a  nerve-cell  of  the  central  or  peripheral  nervous 
system.  The  remaining  processes  of  the  neuroblast  are  called  dendrites  or 
protoplasmic  processes.  They  are  usually  shorter  and  more  branched  than  the 
axon,  and  they  carry  impulses  to  the  cell.  The  whole  system  of  cell  body,  axon 
and  dendrites  into  which  a  neuroblast  develops  is  termed  a  neuron. 

Every  neuron  is  probably  a  separate  and  distinct  entity.  Its  processes  neither 
anastomose  together  nor  with  the  processes  of  other  neurons.  They  lie,  however, 
in  close  contiguity  with  either  the  body  or  processes  of  other  neurons,  or  with 
special  end -organs,  and  it  is  possible  for  impulses  to  pass  from  one  neuron  to 
another  althoiigli  there  is  no  structural  continuity  between  them. 

Extension  of  the  Mesoderm  and  Division  of  the  Blastodermic  Membrane 
tino  Areas. — It  has  already  been  jxjinted  out  that  when  the  primitive  streak  first 


EXTENSION  OF  THE  MESODEKM. 


23 


Proaniniotic 
area 


Xotochordal 
area 


appears  it  consists  of  a  thickened  ridge  of  ectoderm  situated  in  the  posterior  part 
of  the  embryonic  area  and  resting  upon  the  entoderm.  The  anterior  end  of  the 
ridge  soon  fuses  with  the  entoderm  beneath  it,  and  from  its  sides  and  posterior 
extremity  a  lamelUform  outgrowth,  the  mesoderm,  is  projected  between  the 
ectoderm  and  eatoderm.  At  its  commencement  the  mesoderm  is  an  outgrowth 
from  the  primitive  streak,  but  during  its  subsequent  extension  it  is  probably  added 
to  by  cells  proliferated  from  the  entoderm. 

As  it  extends  the  mesoderm  forms  a  semilunar  sheet  of  cells,  the  concavity  of 
the  semilune  being  turned  forwards,  whilst  the  convexity  is  gradually  projected 
beyond  the  margins  of  the  embryonic  area.  The  cornua  of  the  semilunar  sheet 
grow  forwards  on  either  side  of,  and  at  some  little  distance  from  the  middle  line, 
immediately  beneath  the  medullary  folds.  Each  cornu  on  reaching  the  anterior 
end  of  the  embryonic  area  bifurcates,  and  the  resulting  processes  unite  with  their 
fellows  of  the  opposite  side. 

At  the  same  time  the  mesoderm  grows  from  its  convex  margin,  and  extends 
over  the  rest  of  the  ovum  as  a  continuous  sheet.  But  even  when  the  extension  is 
completed,  in  the  majority 
of  mammals,  three  areas  on 
the  upper  aspect  of  the 
ovum  remain  devoid  of 
mesoderm,  and  consist  only 
of  ectoderm  and  entoderm. 

The  largest  of  these  areas 
lies  directly  in  front  of 
the  embryonic  region.  In 
many  mammals  it  is  folded 
upwards  and  backwards  in 
front  of  the  head  of  the 
embryo,  when  this  becooies 
distinguishable,  and  it  takes 
part  in  the  formation  of 
one  of  the  protecting  foetal 
membranes,  viz.  the  amnion ; 
it  is  therefore  called  the 
proamnion,  and  the  area 
from  which  it  is  developed 
constitutes  the  proamniotic  area.  Probably  it  is  not  present  in  the  human  blasto- 
derm, or  if  it  exists  it  is  very  transitory. 

The  second  of  the  areas  into  which  the  mesoderm  does  not  extend  lies  in  the 
embryonic  region.  It  is  separated  from  the  proamniotic  area  by  a  bar  of  mesoderm 
in  w'hich  the  pericardial  cavity  afterwards  appears.  The  anterior  part  of  tliis 
second  area  is  situated  in  front  of  the  neural  groove,  and  as,  at  a  later  period,  it 
forms  a  septum  between  the  primitive  mouth  and  the  pharynx,  it  may  be  termed 
the  bucco-pharyngeal  area.  The  posterior  part  of  the  area  forms  the  floor  of  the 
medullary  groove,  and  as  the  notochord  is  formed  from  its  entodermal  layer  we 
have  named  it  the  notochordal  area. 

The  third  area  corresponds  to  the  posterior  part  of  the  primitive  streak.  It 
extends  from  the  base  of  the  tail  towards  the  umbilicus,  forming  the  cloacal  mem- 
brane, which  itself  forms  the  posterior  boundary  of  the  primitive  alimentary  canal. 
It  is  eventually  perforated  by  the  genito-urinary  and  anal  apertures. 

Except  in  the  areas  just  described,  the  blastodermic  membrane  is  trilaminar,  and 
at  ;an  early  period  it  is  possible  to  distinguish  the  regions  in  which  the  heart  and 
pericardium,  the  amnion,  and  the  placental  and  non-placental  parts  of  the  chorion 
are  subsequently  developed.  These  regions  form  fairly  well-defined  areas,  to  the 
relative  positions  of  which  reference  may  now  be  made. 

The  anterior  part  of  the  embryonic  area  in  front  of  the  bucco-pharyngeal  area 
is  the  region  in  which  the  pericardium  and  heart  are  developed,  and  it  may  therefore 
be  termed  the  pericardial  area. 

The  blastodermic    membrane    immediately    surrounding    the    embryonic  area. 


Cliorionic 
area 


Surface  Areas  of  the  Blastoderm. 


24 


GENEEAL  EMBEYOLOGY. 


including  the  proamniotic  part  in  those  animals  in  which  it  exists,  is  the  amniotic 
area,  and  this  is  bounded  externally  by  a  band  of  elevated  and  thickened  ectoderm 
which  indicates  the  placental  area.  The  latter,  together  with  the  blastoderm  over 
the  rest  of  the  ovum,  forms  the  chorionic  area,  which  is  separable,  therefore,  into 
placental  and  non-placental  portions. 

These  areas  are  further  referred  to  in  the  description  of  the  folding  off  of  the 
embryo  and  the  formation  of  the  fcetal  membranes  and  placenta. 

Formation  of  the  Notochord. — The  notochord  is  the  primitive  skeletal  axis  of 
the  embryo.  When  differentiated  it  forms  a  rod  which  intervenes  between  the 
ectodermal  neural  tube  and  the  entoderm  of  the  primitive  alimentary  canal.  It  is 
developed  from  the  entoderm  beneath  the  neural  groove  in  the  notochordal  area. 
A  linear  strip  of  entoderm  thickens  and  then  separates  as  a  solid  rod  of  cells,  the 
continuity  of  the  entodermal  layer  being  restored  beneath  it.  When  it  is  completed 
the  notochord  extends  from  a  point  immediately  behind  the  primitive  fore-brain,  and 

Embryonic  area 


Placental  area 


Chorionic  area 


Placental  area 


Chorionic  area 


Fig.  18. — Sections  showing  the  diffeeent  Areas  of  the  Blastodermic  Vesicle  (Diagrammatic). 

I.   Transverse  section  ;  II.  Longitudinal  section. 

EC.  Ectoderm.  M.  Mesoderm.  N.  Notochordal  thickening. 


EN.  Entoderm. 


NG.  Nenral  groove. 


beneath  the  anterior  end  of  the  mid-brain,  to  the  anterior  end  of  the  primitive  streak, 
and  in  later  stages,  as  the  skeleton  is  formed,  the  notochord  can  be  traced  from  the 
post-sphenoid  section  of  the  base  of  the  skull,  which  is  situated  beneatli  the  mid-brain, 
to  the  tip  of  the  coccyx. 

The  seyjaration  of  the  notochord  from  the  entoderm  commences  in  the  cervical 
region,  and  extends  forwards  and  backwards.  The  anterior  extremity  is  the  last  part 
to  be  detached,  the  separation  occurring  shortly  after  the  perforation  and  disappear- 
ance of  the  bucco-pharyngeal  membrane. 

The  cellular  notochord  develops  a  cuticular  sheath  ;  it  is  subsequently  surrounded 
by  mesoderm  which  separates  it  both  from  the  neural  tube  and  the  entoderm, 
and  which  is  ultimately  transformed  into  the  vertebrte  and  their  ligaments,  the 
intervertebral  discs,  the  basi-sphenoid  and  basi- occipital  parts  of  the  skull,  and  the 
membranes  of  the  brain  and  cord. 

As  the  surrounding  mesoderm  is  differentiated  the  notochord  ])econies  nodulated ; 
the  thickened  portions  are  situated  in  the  regions  of  the  intervertebral  discs,  and 
the  intermediate  constricted  portions  in  the  regions  of  the  vertebral  bodies.  The 
vertebral  portions  gradually  disappear,  and  the  intervertebral  parts  are  converted 
into  a  kind  of  mucoid  tissue,  the  pulp  of  the  intervertebral  discs. 

Formation  of  the  Coelom. — In  all  animals  in  which  the  entoderm  and  ectoderm 


FORMATION  OF  THE  CCELOM. 


25 


lie  in  close  relation  with   each  other  over  the  whole  surface   of  the  ovum,  the 


Fig.  19. — Extension  of  Mesoderm  and  Formation  of  C'celom  (Diagramiuatic). 

A.  Mesoderm  spreading  from  the  sides  of  the  ectodermal  primitive  streak,  and  extending  between  the  ectoderm 

and  entoderm.     B.  Further  extension  of  the  mesoderm   and   appearance  of  ccelomic  cleft-like  spaces. 

C.  Complete  delamination  of  the  mesoderm  and  formation  of  coelom. 

BC.  Blastodermic  cavity.  C.  Coelom.  EC.  Ectoderm.  EN.  Entoderm.  M.   Mesoderm. 

P.   Primitive  Streak.  SoP.  Somatopleure.  SpP.  Splanchnoplenre. 


mesoderm  as  it  extends  from 
this  exists  the  blastoderm  is 
trilaminar,  but  in  monkeys, 
apes,  and  the  human  subject, 
as  the  ectoderm  and  entoderm 
are  separated  from  each  other 
by  the  segmentation  cavity 
(Fig.  12,  B-),  the  mesoderm  al- 
most from  its  commencement 
extends  in  two  layers,  one  the 
splanchnic  on  the  entoderm, 
and  the  other  the  somatic  on 
the  inner  surface  of  the  ecto- 
derm. In  other  mammals 
before  the  extending  meso- 
derm entirely  separates  the 
ectoderm  from  the  entoderm, 
a  cavity  is  formed  in  it  by 
the  union  of  a  series  of  cleft- 
like spaces  which  appear  near 
the  margin  of  the  embryonic 
area  and  rapidly  fuse  together, 
forming  the  ccelom  or  body 
cavity.  Thus  in  the  majority 
of  mammals  the  ccelom  is 
formed  by  the  cleavage  of  the 


the  primitive  streak  forms  a  single  layer,  and  where 


Proamniotie 
area 


Hhoiiiboidal 
sinus 


Paraxial  iiieso- 
denn  (not  yet 
segmented) 


Fig.  20. — Surface  View  of  an  Early  Embryo  (Diagrammatic). 

Showing  the  neural  groove,  dilated  in  the  head  region  but  still  un- 
closed, and  the  first  protovertebral  somites.  The  margins  of  Ithe 
crelomic  space  are  indicated  by  dotted  lines. 


mesoderm,  but  in  the  higher  forms  it  represents  the  segmentation   cavity    which 
has  become  surrounded  by  two  extending  layers  of  mesoderm.     In  those  animals 


26  GENERAL  EMBRYOLOGY. 

in  which  it  appears  by  cleavage  of  the  mesoderm,  it  extends  towards  both  poles 
of  the  ovum,  but  in  the  higher  forms  only  towards  the  embryonic  pole,  and  in 
both  groups  its  extension  in  the  embryonic  area  is  arrested  before  it  quite 
reaches  the  side  of  the  notochord  and  the  mesial  plane  of  the  primitive  streak.  It 
extends  across  the  pericardial  area,  however,  and  forms  the  rudiment  of  the 
pericardial  cavity,  which  appears  as  a  transverse  tubular  passage  continuous  on 
each  side  with  the  general  body  cavity.  The  outer  or  parietal  layer  of  the 
mesoderm  becomes  more  or  less  closely  attached  to  the  ectoderm,  and  with  it 
forms  the  somatopleure,  whilst  the  inner  or  visceral  layer  is  similarly  associated 
with  the  entoderm  to  form  the  splanclmopleure. 

"\\1ien  the  ccelom  is  fully  formed  the  blastoderm  contains  two  cavities,  one,  the 
ccelom  or  body  cavity,  situated  between  the  two  layers  of  the  mesoderm,  and  the 
other  the  cavity  of  the  blastodermic  vesicle,  usually  called  the  vitelline  cavity,  which 
lies  inside  the  entoderm. 

Mesodermic  or  Protovertebral  Somites. — During  the  formation  of  the  ccelom 
the  undivided  mesoderm  at  each  side  of  the  notochord  thickens,  principally  by  a 
dorsal  upgrowth  which  is  coincident  with  the  uprising  of  the  ectodermal  medullary 
folds  which  bound  the  neural  groove.  There  are  thus  formed  two  thickened  bars  of 
mesodermal  tissue,  one  on  each  side  of  the  neural  tube,  and  they  together  constitute 
the  paraxial  mesoderm  (Fig.  15) ;  the  more  laterally  situated  portions  of  the  mesoderm 
are  known  as  the  lateral  plates. 

The  paraxial  mesoderm  is  soon  divided,  except  in  the  head  region,  by  a  number 
of  transverse  clefts  into  a  series  of  cubical  masses  termed  the  mesodermic  somites. 
These  are  at  first  partially,  and  afterwards  more  completely  separated  from  the 
lateral  plates  by  longitudinal  grooves.  After  the  longitudinal  grooves  are  formed, 
the  mesodermic  somites  of  each  side  are  connected  with  the  lateral  mesoderm  by  a 
somewhat  contracted  strand  of  cells,  the  intermediate  cell  mass  (Fig.  16).  This 
strand  is  represented  in  lower  vertebrates  by  a  series  of  separate  cords  of  cells, 
the  stalks  of  the  somites,  each  somite  possessing  one  stalk. 

The  separation  of  the  paraxial  mesoderm  from  the  lateral  plates  and  the 
segmentation  of  the  former  into  somites  extends  forwards  to  the  region  of  the  hind 
brain,  where  the  first  protovertebral  somite  is  formed.  In  front  of  this  the 
mesoderm,  in  mammals  at  least,  does  not  become  segmented. 

The  cavity  of  the  ccelom  may  extend  into  the  paraxial  mesoderm  before  it  is 
segmented  into  protovertebral  somites,  or  it  may  stop  just  outside  the  limits  of  the 
paraxial  mesoderm.  In  the  former  case  each  somite,  when  separated  from  the 
lateral  plate,  contains  a  cavity,  and  the  intermediate  cell  mass  is  also  hollow  for  a 
time.  In  the  latter  case  the  protovertebral  somites  and  the  intermediate  cell  masses 
are  solid ;  at  a  later  period,  however,  a  cavity  which  contains  a  few  spherical  cells 
appears  temporarily  in  each  somite. 

Folding  Off  of  the  Embryo  from  the  Blastodermic  Vesicle. — Although  so 
many  rudiments  of  the  embryo  become  distinguishable  at  an  early  period  in  its 
development  (the  embryonic  area,  the  primitive  streak  and  groove,  the  neural 
groove,  the  notochord,  and  the  protovertebral  somites),  the  body  of  the  embryo  does 
not  assume  its  characteristic  form  until  it  becomes  raised  and  folded  off  from  the 
general  surface  of  the  blastodermic  vesicle. 

The  main  cause  of  the  folding  off  of  the  embryo  from  the  surface  of  the  vesicle 
is  the  more  rapid  growth  of  the  embryonic  area  as  contrasted  with  the  slower  growth 
and  expansion  of  the  remainder  of  the  wall  of  the  vesicle ;  and  the  moulding  of  the 
increasing  embryonic  area  into  the  form  of  the  embryo  is  due  to  differences  in  the 
rate  of  growth  of  the  various  parts  of  the  area  itself. 

The  manner  in  which  the  area  is  folded,  and  the  changes  in  the  relative 
positions  of  its  various  parts  which  necessarily  result,  will  be  easily  understood  by 
reference  to  Figs.  21  and  27. 

The  embryonic  area  at  an  early  period  increases  rapidly,  especially  in  length. 
Its  margins,  however,  appear  to  remain  comparatively  fixed,  and  hence  as  the  area 
increases  it  must  fold  upon  itself.  It  becomes  more  convex  externally,  and  is 
raised  slightly  aljove  the  general  surface,  but  at  the  same  time  it  apparently  sinks 
into  the  interior  of  the  ovum,  and  the  amnion  folds  close  over  it. 


FOLDING  OFF  OF  THE  EMBEYO. 


27 


The  antero-posterior  growth  is  greater  than  the  lateral ;  consequently  the 
folding  of  the  embryonic  area  is  most  marked  in  front  and  behind.  Anterior  and 
posterior,  or  cephalic  and  caudal  folds  are  formed,  which  indicate  the  head  and 
tail  extremities  of  the  embryo.  Similarly,  lateral  folds  define  the  lateral  limits  of 
the  body. 

When  the  body  of  the  embryo  thus  becomes  folded  off  it  contains  a  portion  of 
the  blastodermic  cavity  and  of  the  coelom ;  the  former  is  the  primitive  alimentary 
canal,  and  tha  latter  is  the  rudiment  of  the  pericardial,  pleural,  and  peritoneal 
cavities. 

The  communication  between   the   pleuro-peritoneal  and  the   extra-emljryonic 


SoM 


SoM 


Fig.  21. — Early  Stages  in  the  Folding  Off  of  the  Embryo  (Diagrammatic). 

I.  Longitudinal  section  of  a  developing  ovum.     The  folding  oflF  of  the  embryo  lias  commenced,  and  the  head  fold, 

bending  down  in  front,  has  invagiuated  the  amniotic  area.  The  tail  fold  is  partly  formed,  and  the 
primitive  alimentary  canal,  closed  in  front,  communicates  freely  with  the  j-olk-sac  by  a  wide  umbilical 
aperture. 

II.  Transverse  section  of  a  developing  ovum  showing  the  commencement  of  the  "folding  off."     The  thickened 

embryonic  area  is  convex  externally,  and  it  already  appears  to  sink  below  the  surface  of  the  ovum. 

III.  Transverse    section  showing    the    "folding    off"  more    advanced.     The  changes    seen  in   II.    are   more 

marked,  and  by  apparent  constriction  at  the  junction  of  the  embryonic  area  with  the  rest  of  the 
blastodermic  vesicle  the  embryo  is  still  further  nipped  off,  and  distinct  lateral  folds  are  formed. 

The  division  of  the  cavity  of  the  blastodermic  vesicle  into  that  of  the  primitive  alimentary  canal  and  that  of 
the  yolk-sac  is  shown  in  all  the  figures. 

The  amniotic  area,  directed  upwards  and  inwards  in  II.,  forms  with  the  placental  area  the  amniotic  fold,  and 
in  III.  the  amniotic  folds  of  opposite  sides  are  approaching  one  another  over  the  back  of  the  embryo  to 
enclose  the  cavity  of  the  amnion.  The  relative  positions  of  the  different  areas  of  the  blastoderm  are 
correspondingly  modified. 

PA.      Placental  area.  SpM.  Splanchnic  mesoderm. 

PAC.   Primitive  alimentary  canal.    YS.     Yolk-sac. 
SoM.   Somatic  mesoderm.  V.       Villi. 


AA.   Amnion  fold. 

EC. 

Ectoderm. 

C.      Coelom. 

EN. 

Entoderm. 

EA.   Embryonic  area. 

N. 

Notochord. 

portion  of  the  coelom  is  obviously  bounded  by  the  margins  of  the  embryonic  area, 
which  constitutes  the  limits  of  the  umbilical  orifice. 

The  margins  of  the  embryonic  area  retain  approximately  their  original  positions, 
and  in  its  further  growth  the  embryo  extends  beyond  them  in  all  directions. 


28 


GENEEAL  EMBEYOLOGY. 


THE  EMBEYO. 

The  embryo,  now  easily  distinguishable  from  the  rest  of  the  ovum,  is  already 
sufficiently  developed  to  give  some  indication  of  the  general  plan  of  its  organisation, 
and  of  the  ultimate  relation  and  fate  of  the  three  layers  of  the  blastoderm  which 
enter  into  its  constitution.  There  are  as  yet  no  limbs,  but  the  general  contour  of 
the  head  and  body  are  defined.  It  possesses  a  notochord,  afterwards  replaced  by 
the  permanent  vertebral  column,  which  constitutes  a  longitudinal  central  axis. 
On  the  dorsal  aspect  of  the  notochord  the  neural  groove  is  closing  to  form  the 
neural  canal,  or  primitive  cerebro-spinal  nervous  system,  whilst  on  its  ventral  side 
a  portion  of  the  blastodermic  cavity  is  being  included  as  a  primitive  tubular 
alimentary  canal,  which  freely  communicates  with  the  remainder  of  the  blastodermic 
cavity  now  called  the  cavity  of  the  yolk-sac. 

The  formation  of  the  mesodermic  somites  has  commenced,  and  this  is  the  first 

indication  of  that  segmenta- 
tion which  is  such  a  char- 
acteristic feature  in  the 
structure  of  the  vertebrate 
body. 

The  general  relations  of 
the  three  layers  of  the  blas- 
toderm remain  unaltered. 
Thus,  externally,  there  is  a 
layer  of  ectoderm  forming  the 
surface  of  the  body ;  inter- 
nally, a  layer  of  entoderm 
lining  the  primitive  aliment- 

FiG.  22.— The  Relative  Positions  of  the  Blastodermic  Layers  ary  canal ;  and  between  them 
IN  THE  Body  of  the  Embryo  when  the  "Folding  Off"  is  is  the  mesoderm  enclosing 
completed  (Diagrammatic).  ^J^g  COelom. 

I.   Transverse  section  through  the  umbilical  aperture.  The        SUrfclce       ectoderm 

forms  the  epithelial  ele- 
ments^ of  the  skin  and  its 
appendages,  and  of  the  glands 
which  open  on  it.  Thus  the 
hairs  and  hair-follicles,  the  nails,  the  enamel  of  the  teeth,  the  epithelium  of  the 
sebaceous  glands,  of  the  sweat  glands,  and  of  the  mammary  glands  are  all  ectodermal. 
The  epithelium  of  the  conjunctivse  and  of  the  lachrymal  glands  is  also  derived 
from  ectoderm.  The  roof  of  the  mouth,  the  inner  surfaces  of  the  cheeks,  the  nasal 
passages  and  their  associated  cavities,  together  with  the  adjacent  part  of  the  pharynx 
and  the  anterior  lobe  of  the  pituitary  body,  as  well  as  the  external  auditory  canal 
and  the  outer  layer  of  the  tympanic  membrane,  are  all  developed  from  the  surface, 
and  their  epithelium,  with  that  of  their  glands,  is  ectodermal  in  origin.  The 
epithelium  of  the  sense  organs,  except  that  of  taste  (the  tongue),  is  derived  from 
ectoderm ;  the  auditory  and  olfactory  epithelial  elements,  and  those  of  the  lens 
and  cornea,  are  from  surface  ectoderm ;  whilst  the  epithelial  elements  of  the  retina 
are  from  neural  ectoderm. 

The  neural  ectoderm  is  removed  from  the  surface  to  form  the  neural  tube  and 
neural  crest,  from  which  the  cells  and  fibres  of  the  whole  of  the  nervous  systeni,^ 

'  The  term  "Epithelium"  is  applied  to  tissues  consisting  of  cells  which  are  united  with  one  another 
V)y  means  of  a  small  amount  of  intercellular  substance. 

The  cells  constituting  epithelium  are  always  arranged  in  one  or  more  layers  ;  they  cover  free  surfaces 
and  line  the  various  cavities  of  the  body,  including  the  vascular  and  lymphatic  systems  ;  they  also  form 
the  active  elements  in  secretory  glands  and  line  their  ducts.  Epithelium  is  always  non-vascular,  and  the 
cells  receive  their  nourishment  from  blood-vessels  which  are  in  their  vicinity.  Epithelial  cells  are 
modified  in  accordance  with  the  particular  functions  they  are  called  upon  to  serve,  and  they  present  many 
variations  in  shape,  size,  and  structure,  e.'j.  the  neuro-epithelial  cells  of  the  central  nervous  system  and  of 
the  peripheral  sense  organs  differ  considerably  from  the  more  ordinary  epithelial  type ;  but  they  are 
simply  more  specialised,  and  therefore  more  modified. 

^  It  seems  possible  that  this  statement  may,  before  long,  require  modification,  for  evidence  is  being 
brought  forward  to  show  that  some  portions  of  the  system  are  developed  from  peripherally  situated 
ectodermal  cells. 


II.   Similar  section  in  front  of  or  behind  the  umbilicu, 

AC.  Alimentary  canal.  EN.  Entoderm.  N.  Notochord. 

EC.  Ectoderm.  M.     Mesoderm.  SC.  Spinal  cord 

VI.  Vitello-intestinal  duct  and  umbilical  aperture. 


THE  EMBKYO. 


29 


both  central  and  peripheral,  and  the  sustentacular  tissue  of  the  brain  and  spinal 


SoP 


SpP- 


Fio.  23. — Thansverse  Section  ok  a  Ferret  Embryo, 
Showing  further  differentiation  of  the  mesoderm. 


CC.   Central  caual. 

CL.  Cutaneous  lamella  of  proto- 

vertebral  somite. 
CO.  Coeloni. 
EC.   Ectoderm. 
EN.  Entoderm. 
GC.  Germinal  cell. 


ML.    Muscular  layer  of  mesoder- 
mic  somite. 
N.    Notochord. 
NC.   Neural  crest. 
PA.    Primitive  aorta. 
PS.    Mesodermic  somite. 
SB.    Spongioblast. 

SpP.    Splanchnopleiire. 


SC.     Spinal  cord. 

SG.     Spinal  ganglion. 

SL.     Scleratogenous  layer  of  pro- 

tovertebral  somite. 
SoM.  Somatic  mesoderm. 
SoP.    Somatopleure. 
SpM.  Splanchnic  mesoderm. 


AMC 


Proto- 
vertebral^ 
soiiii 


to- 
lite  I 


Cutaneous 
lamella 
Muscle 
plate 

Sclerato- 
enous 
layer 


cord,  are  developed.  The  neural  ectoderm  also  furnishes  the  epithelial  elements  of 
the  retinae,  the  pineal  gland,  and  of  the  posterior  lobe  of  the  pituitary  body.  It 
forms  a  large 
part  of  the  vitre- 
ous humour  of 
the  eye,  and  con- 
tributes to  the 
formation  of  the 
carotid,  coccy- 
geal and  supra- 
renal bodies. 

The  entoderm 
lines  the  alimen- 
tary canal  and 
the  spaces  and 
glands  which 
open  into  it,  ex- 
cept the  upper 
parts  of  the 
mouth  and  phar- 
ynx  and  the 
terminal  portion 
of  the  rectum ; 
thus  the  epi- 
thelium of  the 
Eustachian  tube 

and         tvmiDanic    Transverse   section   of  a  rat  embryo,  showing  the  transformation  of  the  cells  of  the 

cavity,  the 
trachea,  the 
bronchi,  the  air- 
vesicles  of  the 
lungs,  the  gall- 
bladder,      the 

urinary  bladder,  and  part  of  the  urethra  is  entodermal.     It  forms  the  epithelial 
constituents  of  the  taste  buds  or  organs  of  taste,  the  liver  and  the  pancreas,  the 


Somatopleure 


Splanchuopleure 


Fig.  24. — Further  Differentiation  of  the  Mesoderm. 


scleratogenous  layer  of  a  protovertebral  somite  and  their    extension  round  the 
notochord  and  spinal  cord. 


AM. 
AMC. 
C. 
E.C. 


Amnion. 
Amnion  cavity. 
Cffilom. 
Ectoderm. 


N.        Notochord.  SC.      Spinal  cord. 

PA.      Primitive  aorta.  SG.      Spinal  ganglion. 

PAC.  Primitive  alimentary        SoM.  Somatic  mesoderm. 

caual.  SpM.  Splanchnic  mesoderm. 

YD.   Vitello-intestinal  duct. 


50 


GENEEAL  EMBKYOLOGY. 


epithelium  lining  the  vesicles  of  the  thyroid  body  and  the  cell  nests  of  the  thymus 
gland. 

From  the  mesoderm  all  the  remaining  structures  which  intervene  between  the 
surface  ectoderm  and  the  entodermal  lining  of  the  primitive  alimentary  tube  are 
formed. 

Mesodermic  Somites  and  the  Lateral  Plates. — Each  mesodermal  somite 
consists  of  numerous  cells  arranged  radially  round  a  central  cavity — the  myelocode ; 
this  latter,  however,  quickly  disappears. 

The  cells  of  the  somites  are  gradually  grouped  into  three  sets,  two  to  the  inner 
and  lower  side  of  the  cavity,  and  one  to  its  upper  and  outer  side.  The  two  groups 
on  the  lower  and  inner  side  are  an  outer,  next  the  cavity,  the  muscle  plate,  and  an 
inner,  the  scleratogenous  layer.  The  group  on  the  upper  and  outer  side  of  the 
ca^^ty  is  the  sub-epithelial  or  cutaneous  lamella. 

Scleratogenous    Layer.  —  The   cells    of    this   layer   proliferate   rapidly   and 

migrate  inwards,  surrounding  the 


i;t>S^ 


m^-. 


Scleratogenous 

layer" 


Muscle  plate 


'Blood-vessel 


_   „Spinal  cord 


Ectoderm 


— Coronal  Section  of  a  Rat  Embryo. 


Showing  the  relationship  of  the  extending  scleratogenous  tissue 
to  the  spinal  cord  and  to  the  muscle  plates. 


notochord,  and  passing  both  be- 
neath the  neural  tube  and  up- 
wards along  its  lateral  walls  to 
its  dorsal  aspect ;  they  intermingle 
above  and  below  with  the  cells  of 
the  corresponding  layer  of  the 
opposite  side,  and  in  front  and 
behind  with  the  cells  of  the  sclerato- 
genous layers  of  adjacent  somites. 
In  this  way  the  neural  tube  and 
the  notochord  are  gradually  en- 
veloped by  a  continuous  sheath 
of  mesodermal  tissue,  which  forms 
the  membranous  vertebral  column. 
This  is  perforated  at  regular  in- 
tervals by  the  nerve-roots  issuing 
from  the  spinal  cord  and  brain, 
and  by  the  vessels  of  supply  to 
those  structures.  From  its  sub- 
stance the  vertebrae  and  ligaments, 
the  greater  part  of  the  interverte- 
bral discs,  and  the  investing  mem- 
branes of  the  brain  and  cord  are 
afterwards  developed. 

Muscle    Plates.  —  The   cells 
of   the   muscle   plate   layer   lose 


their  original  epithelial-like  characters;  they  elongate  antero-posteriorly,  become 
spindle-shaped  and  striated,  and  they  give  rise  to  the  striped  muscles  of  the  body. 
For  a  long  time  the  fibres  developed  from  each  muscle  plate  remain  localised  and 
quite  distinct  from  the  fibres  developed  from  neighbouring  segments ;  the  masses 
they  form  are  called  myotomes.  After  a  time,  however,  the  fibres  of  neighbouring 
myotomes  are  more  or  less  intermingled,  and  in  the  adult,  except  in  certain  situa- 
tions, the  intermyotomic  intervals  are  no  longer  recognisable. 

The  main  portions  of  the  myotomes  are  converted  into  the  muscle  masses 
situated  in  the  dorsal  part  of  the  body  wall,  that  is,  into  the  erectores  spinse 
and  their  main  subdivisions,  and  the  other  muscles  which  occupy  the  vertebral 
grooves. 

In  the  lower  vertebrates  the  ventral  ends  of  the  myotomes  descend  in  the 
somatojjleure  almost  to  the  mid- ventral  line,  and  are  transformed  into  the  muscles 
of  the  ventro-lateral  walls  of  the  body.  A  similar  descent  of  the  ventral  ends  of 
the  myotomes  into  the  lateral  walls  of  the  body  has  not  been  proved  in  the  highest 
vertebrates.  In  mammals,  including  man,  the  ventral  ends  of  the  myotomes  only 
descend  for  a  short  distance  in  the  somatopleure,  and  then  all  trace  of  their  char- 
acteristic structure  is  lost.     It  is  presumed,  however,  that  cells  budded  off  from  the 


THE  EMBEYO. 


31 


myotomes  descend  to  a  lower  level,  and  that  they  take  part  in  the  formation  of  the 
ventro-lateral  muscles. 

In  lower  vertebrates  bud-like  projections  pass  from  the  myotomes  in  the 
thoracic  and  peMc  regions  into  the  limb  rudiments,  and  from  these  the  muscles  of 
the  limbs  are  developed.  In  the  highest  vertebrates  distinct  buds  from  the  myo- 
tomes have  not  been  observed,  but  it  is  said  that  outgrowths  of  ceUs  pass  from  the 
myotomes  into  the  limb  buds,  where  they  proliferate  and  form  the  limb-muscles. 
The  occurrence  of  these  outgrowths  into  the  limbs,  like  the  descent  of  the  lower 
ends  of  the  myotomes  into  the  ventral  part  of  the  body-wall,  has  not  been  jjroved 
in  mammals;  possibly  it  occurs,  but  if  not,  the  ventral  and  limb-muscles  of 
mammals  must  be  develijped  from  the  somatopleural  mesoderm. 

Cutaneous    Lamellae  of  the  Mesodennic   Somites. — The  cells  which  form 


Hind-btain 


Auditory  ganglion 
, Rudiment  of  otic  vesicle 


Paraxial  meso<lerm 


SpMl 

First  cephalic  aortic  arch 

SpMz 


Fig.  26. — -Trajs'sverse  SECTioy  of  a  Rat  Embryo. 

Showing  the  relation  of  the  paraxial  mesoderm  of  the  head  to  the  lateral  plates,  the  commencement  of  the 
formation  of  the  otic  vesicles  and  hyomandibular  clefts,  and  the  relation  of  the  primitive  heart  to  the 
pericardium  and  fore-gut. 

EC.  Ectoderm.  SoM.  Somatic  mesoderm.  SpM.  Splanchnic  mesoderm. 


the  outer  and  dorsal  walls  of  the  cavities  of  the  mesodermal  somites  retain  their 
epithelial-like  characters  for  a  longer  period  than  those  of  other  portions  of  the 
somites,  and  at  the  borders  of  the  lamellae  they  pass  by  gradual  transition  into 
the  cells  of  the  muscle  plates.  After  a  time  they  undergo  histological  differentia- 
tion, and  they  are  utilised  in  the  formation  of  the  subcutaneous  tissues  and  fasciae 
on  the  dorsal  aspect  of  the  body,  and  outgrowths,  which  descend  with  the  offsets  of 
the  muscle  plates,  enter  into  the  formation  of  the  ventro-lateral  walls  of  the  body. 

Mesodennic  Somites  of  the  Head.  —  It  has  aheady  been  pointed  out  (p.  26)  that 
protovertebral  somites  are  not  recognisable  in  mammals  further  forwards  than  the  occipital 
region  ;  but,  from  the  evidence  obtained  by  examination  of  lower  vertebrates,  it  is  believed  that 
originally  nine  somites  were  present  in  the  cephalic  region.  From  the  first,  second,  and  third  of 
these,  muscle  plates  form  which  are  developed  into  the  muscles  of  the  eyeballs.  If  any  muscle 
plates  are  formed  in  connexion  with  the  foiu-th,  fifth,  and  sixth  somites  they  disappear,  leaving 
no  traces,  and  the  muscles  developed  from  the  remaining  cephalic  somites  are  those  of  the  tongue 
and  those  connecting  the  head  with  the  shoulder  girdle. 

Lateral  Plates. — At  an  early  stage,  before  its  separation  from  the  paraxial 
mesoderm,  each  lateral  plate  is  di\"ided  into  an  outer  or  somatic  and  an  inner  or 
splanchnic  layer.  The  somatic  layer  is  concerned  with  the  formation  of  the 
parietal  layers  of  the  pleural  and  peritoneal  membranes,  and  with  the  development 


32 


GENEEAL  EMBEYOLOaY. 


of  the  couuective  tissues,  fasciae,  and  vessels  of  the  ventro-lateral  walls  of  the  body  ; 
and  in  mammals,  apparently,  it  also  gives  origin  to  the  ventro-lateral  body  muscles 
and  the  muscles  of  the  limbs.  The  splanchnic  portions  of  the  lateral  plates  form 
the  fascia?,  the  connective  tissues,  the  smooth  muscles  of  the  walls  of  the  ahmentary 
canal,  the  heart  and  great  blood-vessels,  the  visceral  layers  of  the  pleural  and 
peritoneal  membranes,  the  spleen,  and  the  germinal  epithelium,  which  becomes 
transformed  into  the  mother  cells  of  the  ova  and  spermatozoa. 

In  the  cephalic  region,  in  higher  vertebrates,  lateral  plates  are  not  recognisable, 
except  so  far  as  they  may  be  represented  by  the  walls  of  the  pericardium ;  but  in 
some  lower  vertebrates  lateral  plates  can  be  distinguished,  corresponding  in  number 
with  the  cephalic  somites,  and  it  has  been  asserted  that  the  muscles  of  the  face 
and  the  muscles  of  mastication  are  developed  from  the  lateral  plates  associated 
with  the  second  and  third  cephalic  somites.  The  subject,  however,  is  one  which  is 
still  obscure,  and  requires  further  investigation  before  any  very  positive  conclusion 
can  be  arrived  at. 

Intermediate  Cell  Mass. — As  already  mentioned,  the  lateral  plates  and  the 
mesodermic  somites  are  connected  by  the  intermediate  cell  masses,  which  are 
intimately  associated  with  the  development  of  the  ducts  and  tubules  of  the  genital 
and  urinary  organs  in  man  and  other  mammals.  On  each  side  the  mass  soon 
separates  from  the  mesodermic  somites,  and  is  transformed  by  rapid  proliferation 
of  its  cells  into  an  elongated  body,  the  Wolffian  body  or  primitive  kidney,  which 
projects  downwards  into  the  dorsal  angle  of  the  body  cavity.  In  early  stages  it 
extends  from  the  fifth  somite  of  the  body,  backwards  to  its  posterior  end,  but  is 
most  clearly  differentiated  in  the  middle  portion.  The  Wolffian  duct  and  tubules 
and  the  MilUerian  duct  are  developed  in  connexion  with  it;  after  the  second  month 
of  intrauterine  life  it  degenerates,  and  is  replaced  by  the  permanent  kidney,  which 
is  formed  dorsal  to  its  posterior  extremity. 


THE  DEVELOPMENT  OF  THE  PEIMITIVE  ALIMENTAEY  CANAL. 

When  the  cephalic,  caudal,  and  lateral  folds  are  established,  and  the  general 
outline  of  the  embryo  is  clearly  defined,  its  dorsal  and  lateral  surfaces  and  its 


Sijiiial  cord 


Notocliord 


Mid-brain 
Aiiiiiiotic  fold 
Placental  area 


Rhomboidal  sinus 

Primitive  streak 

Cloacal  membrane 


Placental  area 


SpM      SoM 
Bucco-)>haryngeal  niembrane 
Fk;.  27. — Diagram  ok  a  Developing  Ovum,  seen  in  Longitudinal  Section. 
The  folding  off  of  the  embryo  has  commenced,  and  the  downward  bend  of  the  head  fold  in  front  lias  invagi- 
nated  the  amniotic  area.     The  tail  fold  i.s  partly  formed,  and  the  primitive  alimentary  canal,  closed  in 
front  by  the  Imcco-pharyngeal  membrane  and  behind  V;y  the  cloacal  membrane,  i.s  distinguishable  ;  it 
communicates  freely  with  the  yolk  sac  by  a  wide  umbilical  aperture. 

C.     Ccelom.  EN.  Entoderm.  SoM.  Somatic  mesoderm. 

EC.  Ectoderm.  M.     Mesoderm.  SpM.  Splanchnic  mesoderm. 

anterior  and  posterior  extremities  are  easily  recognisable,  and,  as  the  embryo  is 
folded  off  from  the  surface  of  the  blastodermic  vesicle,  a  portion  of  the  blastodermic 
cavity  is  enclosed  within  it ;  this  is  the  primitive  alimentary  canal.  It  is  simply 
an  incomplete  tubular  cavity,  situated  beneath  the  notochord,  which  is  bounded  in 


THE  PEIMITIVE  ALIMENTARY  CANAL. 


o3 


otic  vesicle 


front  by  the  head  fold,  l^ehind  bv  the  tail  fold,  and  laterally  by  the  lateral  folds, 
but  is  widely  open  telow  and  continuous  \s"ith  the  cayity  of  the  yolk-sac. 

As  the  head  of  the  embryo  grows  more  rapidly  than  any  other  part,  the  head 
fold  is  more  marked  than  the  other  folds,  and  with  its  formation  the  pericardial 
area  is  bent  round  until  it  Ijecomes  yentral  in  position,  its  original  upper  and  lower 
surfaces  being  reyersed  (Fig.  27}.  It  is  owing  to  this  change  of  relatiye  position 
that  the  yentral  wall  of  the  alimentary  canal  is  completed  in  front,  and  it  is 
obyious  that  its  anterior  limit,  corresponds  to  the  bucco-pharyngeal  area  of  the 
blastoderm.  The  part  of  the  blastodermic  cavity  enclosed  in  the  head  fold  con- 
stitutes the  fore-gnt. 

The  tail  fold  at  this  period  is  smaU,  but  it  limits  the  primitive  gut  behind. 

The  yentral  closing  of  the  posterior  end  of  the  primitive  alimentary  canal  to 
form  a  Mnd-gut  is  produced, 
as  in  the  case  of  the  fore-gut, 
by  tending  of  the  embryonic 
area.  This  takes  place  in  the 
region  of  the  tail  fold;  but 
the  posterior  part  of  the  em- 
bryonic area  retains  for  a  con- 
siderable time  it?  original 
position,  and  forms  a  connect- 
ing stalk,  termed  the  body- 
stalk,  between  the  embryo 
and  the  chorionic  area  of  the 
blastoderm.  Ultimately,  how- 
ever, this  terminal  section  of 
the  eml>ryonic  area  is  re- 
versed in  position,  its  posterior 
end  being  carried  forwards  till 
it  forms  the  posterior  boundary 
of  the  umbihcal  orifice,  and  the 
yentral  wall  of  the  hind-gut  is 
thus  completed. 

The  rest  of  the  primitive 
alimentary  canal  constitutes 
the  mid -gut.  It  remains  for 
some  time  in  free  communica- 
tion with  the  cavity  of  the 
yolk-sac,  and  this  communica- 
tion between  the  alimentary 
canal  and  the  yolk-sac  at  a 
later  stage  forms  a  tubular 
passage,  the  vitello  -  intestinal 
duct. 

The  entoderm  forms  the 
lining  epithelium  of  the  ali- 
mentary canal.,  but  this  is 
invested  by  the  splanchnic  layer  of  the  mesoderm,  which  is  separated  from  the 
somatopleure  or  body  wall  by  the  coelom  or  body  cavity.  As  the  splanchnic 
mesoderm  passes  on  each  side  to  its  continuity  with  the  somatic  mesoderm  it  forms 
a  fold,  by  which  the  gut  is  suspended  from  the  under  surface  of  the  primitive 
vertebral  column  ;  this  fold  is  the  mesentery. 

"When  the  diaphragm  is  formed  at  a  later  period  it  separates  the  thorax  from 
the  abdomen,  and  divides  the  ci.'elom  into  pleural  and  peritoneal  portions. 

The  primitive  alimentary  canal  is  almost  a  straight  tube,  bhnd  at  both  its 
extremities,  and  communicating  only  with  the  cavity  of  the  yolk-sac.  As  yet  there 
is  no  mouth  and  no  anal  passage  or  aperture.  The  simple  tubular  canal  is  divisible 
into  fore-gut,  mid-gut,  and  hind-gut,  parts  which  are  conveniently  associated 
developmentally  with  definite  portions  of  the  fully-formed  alimentary  canal. 
o 


Yolk-sac 


Cloacal  membraue         Body  stalk 
Fig.  2S. — Diagram   represkxtisc.   the   Cosditios   of   the  Ali- 

MEXTART    CaXAL    IX    A    HCJIAX    EMBRYO    ABOUT    FlFTEEM    DaTS 

Old  (modified  from  His). 
The  visceral  clefts  are  formed,  and  the  subtlivisions  of  the  fore-gut, 
together  with  the  rudiments  of  the  bronchi  and  liver,  are  distinct. 


34 


GENEEAL  EMBRYOLOGY. 


Thus  the  fore-gut  is  converted  into  the  pharynx,  cesophagus,  stomach,  and  the 
, greater  part  of  the  duodenum ;  whilst  from  the  mid-gut  and  the  hind-gut  the  rest 
of  the  small  intestine  (jejunum  and  ileum),  and  the  whole  length  of  the  large 
intestine  (cfecum,  colon,  and  rectum),  are  formed.  There  is  no  sharp  limit  between 
the  mid-gut  and  the  hind-gut,  or  between  the  portions  of  the  intestinal  canal 
which  develop  from  them. 

Diverticular  outgrowths  from  the  entoderm  of  the  primitive  alimentary  canal 
form  the  rudiments  of  the  intestinal  glands,  including  the  liver  and  pancreas  ;  of  the 
respu'atory  apparatus ;  and  of  the  thyroid  and  thymus  glands.  Details  of  the 
formation  of  these  structures  are  given  in  the  special  description  of  the  develop- 
ment of  the  system  to  which  each  belongs. 


Fig.  29. — Further  Development  of  the  Alimentary  Canal,  as  seen  in  a  Human  Embryo 
ABOUT  Five  Weeks  Old  (Diagrammatic). 

The  tongue  is  well  formed,  the  trachea  and  ojsophagus  are  separated,  the  bronchi  have  comnieiiced  to  branch  ; 
the  duodenal  curve  is  well  formed,  and  the  CEecum  has  appeared  in  the  loop  of  the  mid-gut.  The 
cloaca  is  partially  separated  into  genito-urinary  and  rectal  portions. 


1.  Hind-brain. 

2.  Mouth. 

3.  Tongue. 

4.  Pericardium. 

5.  Pharynx. 

6.  Heart. 


7.  Trachea. 

8.  (Esophagus. 

9.  Lung. 

10.  Liver. 

11.  Bile  duct. 

12.  Stomach. 


13.  Pancreas. 

14.  Small  intestine. 

15.  C'secum. 

16.  Intestinal  loop. 

17.  Large  intestine. 

18.  Notochord. 


19.  Vertebra. 

20.  Spinal  cord. 

21.  Bladder. 

22.  Wolffian  duct. 

23.  Kidney. 

24.  Ureter. 


25.  Rectum. 

26.  ProetodiEum. 

27.  Allantoic  diverticulum. 

28.  Vitello-intestiual  duct. 

29.  Fore-brain. 

30.  Mid-brain. 


Except  with  respect  to  the  anterior  part  of  the  fore-gut,  the  changes  in  shape 
and  position  which  the  originally  simple  alimentary  tube  undergoes  during  its 
conversion  into  its  final  or  adult  form  are  described  in  the  account  of  the 
development  of  the  digestive  organs ;  Ijut  the  development  of  the  pharynx  and  the 
structures  associated  with  it,  and  the  formation  of  the  mouth  and  anus,  may 
be  considered  now. 

Development  of  the  Pharynx  and  Stomatodseum. — The  development  of  the 
anterior  x^art  of  the  fore-gut  into  the  pharynx  and  the  floor  of  the  mouth  is  so  inti- 
mately associated  with  the  formation  of  a  primitive  mouth,  the  stomatodseum,  that 
the  two  must  to  a  certain  extent  be  considered  simultaneously. 

The  stomatodaeum  first  ajjpears  as  a  depression  between  the  head  and  the  peri- 


VISCERAL  CLEFTS  AND  VISCERAL  ARCHES.  35 

cardial  region.  It  is  produced  by  the  downward  growth  of  the  fore-part  of  the 
head  in  front  and  the  bulging  forward  of  the  pericardium  behind,  and  it  is  separated* 
from  the  anterior  end  of  the  fore-gut  by  the  bilaminar  bucco-pharyngeal  membrane. 
When  the  stomatodreum  first  appears  it  is  not  enclosed  laterally ;  but  at  a  later 
period  side  boundaries  are  formed,  and  the  space  is  developed  into  the  upper  part 
of  the  mouth  and  the  nasal  cavities. 

The  fore-gut,  a  relatively  wide  space,  continuous  posteriorly  with  the  mid-gut, 
is  at  first  closed  anteriorly  by  the  bucco-pharyngeal  membrane,  which  separates 
it  from  the  stomatodaeum.  About  the  fifteenth  day,  in  the  human  embryo,  the  bucco- 
pharyngeal membrane  disappears,  the  fore -gut  is  then  thrown  into  continuity 
with  the  stomatodseal  space,  and  the  anterior  opening  of  the  alimentary  canal 
is  formed. 

As  development  proceeds  the  cavity  of  the  fore-gut  is  gradually  compressed 
dorso-ventrally  until  its  transverse  section  assumes  a  triangular  outline ;  but  in 
the  earliest  stages  there  are  no  indications  of  the  various  organs  which  are  ulti- 
mately developed  from  its  walls.  After  a  short  interval,  however,  two  elevations 
appear  in  its  ventral  wall.  The  anterior  of  these  is  a  rounded  elevation,  termed 
the  tuberculum  impar.  It  is  situated  directly  behind  the  lower  ends  of  two  raised 
bars  or  arches,  called  the  mandibular  arches,  which  are  growing  down  into  the  floor 
of  the  fore-gut  from  the  anterior  parts  of  its  lateral  walls.  The  tuberculum  impar 
is  the  rudiment  of  the  anterior  two-thirds  of  the  tongue,  which  is  thus  formed  in 
the  floor  of  the  entodermal  portion  of  the  alimentary  canal.  The  more  posterior 
elevation,  termed  the  furcula,  is  a  curved  ridge,  which  bounds  a  mesial  longitudinal 
depression.  It  is  separated  from  the  lateral  walls  of  the  fore-gut  and  from  the 
tuberculum  impar  by  a  groove,  the  sinus  arcuatus.  The  anterior  part  of  the  furcula 
is  transformed  into  the  epiglottis  and  the  margins  of  the  upper  aperture  of  the 
larynx  ;  the  median  depression  becomes  the  cavity  of  the  larynx  and  of  the  trachea, 
and  from  its  posterior  end  hollow  outgrowths  extend  and  form  the  rudiments  of  the 
epithelial  lining  of  the  bronchi  and  lungs.  Still  more  posteriorly,  behind  the  region 
of  the  furcula,  a  dilatation  of  the  fore-gvit  is  formed,  which  projects  forwards  and 
downwards  towards  the  pericardium.     This  is  the  first  indication  of  the  stomach. 

Visceral  Clefts  and  Visceral  Arches. — In  the  lateral  wall  of  the  anterior  part 
of  the  fore-gut,  on  each  side,  four  incomplete  and  more  or  less  transverse  clefts,  the 
visceral  clefts,  appear.  They  are  due  to  outward  linear  pouchings  of  the  entoderm, 
and  corresponding,  but  less  marked,  inward  depressions  of  the  ectoderm.  The 
anterior  cleft  is  the  best  marked,  and  the  rest  diminish  in  size  from  before  back- 
wards. At  the  bottoms  of  the  clefts  the  ectoderm  and  the  entoderm  are  in  contact, 
but  the  thin  membranes  thus  formed,  which  intervene  between  the  cavity  of  the 
fore-gut  and  the  exterior,  are  only  exceptionally  and  abnormally  perforated  in  the 
human  subject,  though  in  lower  vertebrates  they  invariably  disappear,  and  the 
pharyngeal  or  anterior  part  of  the  fore-gut  is  thrown  into  continuity,  laterally, 
with  the  exterior  by  a  number  of  narrow  slits,  the  gill  slits,  which  are  used  for 
respiratory  purposes.  In  man  and  other  mammals,  however,  the  floors  of  the 
second,  third,  and  fourth  clefts  are  utilised  in  the  formation  of  the  sides  of  the 
neck ;  that  of  the  first  cleft  is  transformed  into  the  tympanic  membrane,  which 
separates  the  external  auditory  meatus  from  the  cavity  of  the  tympanum. 

In  the  further  consideration  of  the  fate  of  the  visceral  clefts,  it  must  be  borne 
in  mind  that  each  consists  of  an  inner  or  entodermal  portion  and  an  outer  or  ecto- 
dermal portion.  The  inner  part  of  the  first  cleft  is  converted  into  the  tympanum 
and  the  Eustachian  tube,  and  the  outer  part  becomes  the  external  auditory  meatus. 
No  traces  of  the  outer  part  of  the  second  cleft  are  left,  but  a  portion  of  the  inner 
part  can  be  recognised  as  a  slight  depression  above  the  tonsil  in  the  lateral  wall  of 
the  pharynx  and  in  a  recess,  the  fossa  of  Rosenmuller,  behind  the  pharyngeal  end  of 
the  Eustachian  tube.  Both  the  outer  and  inner  portions  of  the  third  and  fourth 
clefts  disappear,  but  from  their  inner  parts  diverticula  are  given  off  which  form 
the  rudiments  of  the  thymus  and  the  lateral  lobes  of  the  thyroid  body.  The 
diverticula  from  which  the  thymus  is  developed  are  derived  from  the  third  clefts, 
whilst  each  lateral  lobe  of  the  thyroid  body,  in  the  majority  of  mammals,  is  formed 
by  a  diverticulum  from  the  fourth  cleft,  but  in  some  mammals  the  lateral  lobes  are 


36 


GENEKAL  EMBEYOLOGY. 


derived  from  the  median  diverticulum,  and  the  outgrowths  from  the  posterior  parts 
of  the  fourth  clefts  constitute  the  post-branchial  bodies. 

The  margins  of  the  visceral  clefts  are  thickened  Ijy  the  growth  of  the  mesoderm 
between  the  entodermal  and  ectodermal  layers,  and  they  are  moulded  into  a  series 
of  five  rounded  bars,  the  visceral  arches,  of  which  the  fifth  is  not  recognisable 
externally,  though  it  is  easily  seen  internally.  The  dorsal  extremities  of  the  arches 
terminate  at  the  sides  of  the  head  below  the  level  of  the  neural  tube,  and  in  the 
early  stages  the  ventral  ends  rest  upon  the  pericardial  region.  When  the  neck  is 
formed,  it  grows  forwards  from  the  pericardial  region  and  carries  with  it  the  lower 
ends  of  the  visceral  arches,  which  henceforth  terminate  in  its  ventral  wall.  As  the 
visceral  arches  are  carried  forwards  the  head  is  strongly  curved  towards  the  ventral 
aspect,  and  the  lower  ends  of  the  visceral  arches  are  pushed  backwards  over  each 

other     till     the 
^  fourth    is    over- 

lapped by  the 
third,  and  the 
third  by  the 
second. 

The  first  arch 
is  the  mandi- 
bular, the  second 
the  hyoid,  the 
third  the  thyro- 
hyoid; the  fourth 
and  fifth  have  no 
special  designa- 
tions. Each  arch 
is  covered — ex- 
ternally by  ecto- 
derm, internally 
by  entoderm,  and 
its  core  is  formed 
of  mesoderm,  in 
which  there  is 
developed  a  bar 
of  cartilage  and 
a    blood  -  vessel 


Fig.  30. — Stages  in  the  Formation  of  the  Tongue  and  Uppek  Aperture  of  the 
Larynx  in  the  Human  Embryo  (after  His). 

Embryo  14  days  old.     II.  Embryo  23  days  old.     III.   Embryo  28  to  30  days  old. 
Embryo  2  months  old. 

Cojlom.  G.  Glottis. 

Epiglottis.  HA.  Sinus  arcuatus. 

Furcula.  T.  Tongue. 

Foramen  crecum.  TI.  Tuberculum  impar. 


Visceral 
arches. 


IV. 

C. 
E. 
F. 
FC. 


called  a  cephalic 
aortic  arch. 

At  first  each 
arch  is  limited  to 
the  side  wall  of 
the  fore-gut ;  but 
after  a  time  it  is 

prolonged  into  the  ventral  wall,  encroaching,  with  the  exception  of  the  first,  upon 
the  sinus  arcuatus. 

The  first,  or  mandibular  arch,  is  ibrmed  between  the  first  visceral  cleft  and  the 
bucco-pharyngeal  membrane.  As  it  develops  it  forms  the  lateral  and  lower 
boundaries  of  the  stomatodseal  space,  and  it  grows  downwards  till  it  meets  its 
fellow  of  the  opposite  side  in  the  ventral  middle  line,  immediately  in  front  of  the 
tuberculum  impar.  The  greater  part  of  this  arch  is  converted  into  the  lower  jaw 
and  the  soft  tissues  which  invest  it.  From  its  upper  part  a  process  grows  forwards, 
the  maxillary  process,  from  which  the  upper  lateral  part  of  the  face,  between  the 
orbit  and  the  mouth,  is  developed,  and  in  which  the  superior  maxillary,  the  malar, 
and  the  palate  bones,  and  possibly  the  internal  pterygoid  plate  also,  are  developed 
and  ossified. 

From  the  posterior  border  of  the  outer  aspect  of  the  mandibular  arch  the  tragus 
and  a  portion  of  the  helix  of  the  pinna  of  the  external  ear  are  formed.  The  carti- 
laginous bar  in  its  interior  is  known  as  Meckel's  cartilage.     It  forms  the  primitive 


VENTEAL  WALL  OF  THE  FOEE-GUT.  37 

skeleton  of  the  arch.  Its  upper  and  lower  extremities  are  ossified  and  remain  in 
the  adult,  the  former  as  the  malleus,  and  possibly  the  incus,  and  the  latter  as  the 
symphysial  part  of  the  lower  jaw.  Tlie  remainder  of  the  cartilaginous  bar  dis- 
appears, but  the  hbrous  membrane  which  surrounds  the  lower  section  of  the  inter- 
mediate part  is  ossified  and  converted  into  the  main  part  of  the  lower  jaw,  whilst 
that  round  the  upper  section  of  the  intermediate  portion  persists  as  the  spheno- 
mandibular  hgameut.  The  blood-vessel  developed  in  the  mandibular  arch  is,  for 
the  main  part,  a  transitory  structure,  but  its  ventral  section  is  converted  into  the 
internal  maxillary,  superficial  temporal,  facial  and  lingual  arteries. 

The  second  and  third  arches  are  continued  downwards  into  the  floor  of  the 
pharyngeal  portion  of  the  fore-gut.  There,  converging,  they  insinuate  themselves 
between  the  tuberculum  impar  and  the  furcula,  across  the  anterior  part  of  the  sinus 
arcuatus,  and  uniting  together  form  a  transverse  bar.  This  rapidly  changes  into  a 
semilunar  ridge  which  first  embraces,  and  afterwards  fuses  with  the  posterior  part 
of  the  tuberculum  impar,  and  it  forms  the  posterior  third  of  the  tongue. 

The  second  arch  takes  part  in  the  formation  of  the  side  and  anterior  part  of  the 
neck.  From  its  anterior  border  externally  a  part  of  the  helix,  the  antihelix,  the 
antitragus,  and  the  lobule  of  the  pinna  of  the  external  ear  are  developed.  The 
lower  and  upper  portions  of  its  cartilaginous  bar — the  hyoid  bar — are  ossified : 
the  lower  portion  forms  part  of  the  body  and  the  small  cornu  of  the  hyoid  bone  on 
its  own  side,  and  the  upper  portion  is  converted  into  the  intra-  and  extra- temporal 
sections  of  the  styloid  process  (the  tympano-hyal  and  stylo-hyal  portions  of  the 
styloid  process  of  the  temporal  bone).  The  fibrous  tissue  of  the  intermediate  imrt 
of  the  hyoidean  bar  persists  in  the  adult  as  the  stylo-hyoid  ligament.  The  blood- 
vessel of  the  hyoid  arch,  the  second  cephalic  aortic  arch,  almost  entirely  disappears, 
but  from  its  ventral  extremity  the  ascending  pharyngeal,  occipital,  and  posterior 
auricular  arteries  are  probably  developed. 

The  third  visceral  arch  forms  part  of  the  neck  posterior  to  the  region  of  the 
second  arch,  and,  as  already  pointed  out,  its  lower  end  takes  part  in  the  formation 
of  the  posterior  part  of  the  tongue.  The  upper  and  middle  parts  of  its  cartilaginous 
bar  disappear,  but  the  lower  part  persists,  and  is  converted  into  the  posterior  part 
of  the  body  and  the  great  cornu  of  the  hyoid  bone  on  its  own  side.  Its  blood- 
vessel, the  third  cephalic  aortic  arch,  becomes  the  lower  part  of  the  stem  of  the 
internal  carotid  artery. 

The  fourth  and  fifth  visceral  arches  also  enter  into  the  formation  of  the  neck, 
but  their  exact  limits  in  the  adult  cannot  be  defined.  Of  the  upper  sections  of  their 
cartilaginous  bars  no  trace  remains  in  the  adult,  but  their  lower  portions  are 
believed  to  enter  into  the  formation  of  the  thyroid  cartilage  of  the  larynx.  The 
blood-vessel  of  the  fourth  arch  on  the  right  side  becomes  part  of  the  right  sub- 
clavian artery,  that  on  the  left  side  is  converted  into  the  arch  of  the  aorta.  The 
vessels  of  the  fifth  arches  form  portions  of  the  pulmonary  arteries,  and  that  on  the 
left  side  forms  also  the  ductus  arteriosus. 

Further  Development  of  the  Ventral  Wall  of  the  Fore-gut  in  the  Region 
of  the  Furcula. — The  sinus  arcuatus  which  surrounds  the  furcula  disappears  to  a 
great  extent  as  development  proceeds,  but  certain  parts  of  it  remain  and  are  recog- 
nisable in  the  adult.  The  anterior  portion  immediately  in  front  of  the  furcula  is 
divided  into  two  parts  as  the  lower  ends  of  the  second  and  third  arches  of  the  two 
sides  converge  and  fuse  in  the  ventral  wall  of  the  pharyngeal  portion  of  the 
fore-gut ;  the  middle  portion  of  the  sinus,  in  front  of  the  transverse  bar  formed  by 
this  fusion,  persists  in  the  adult  as  the  foramen  caecum  of  the  tongue,  and  at  a  very 
early  period  a  diverticulum  grows  backwards  from  it  in  the  floor  of  the  pharynx, 
dorsal  to  the  cartilage  bars  which  form  the  hyoid  bone,  but  ventral  to  the  rudi- 
ments of  the  thyroid  cartilage.  This  diverticulum  is  the  thyro-glossal  duct.  As 
soon  as  it  reaches  the  level  of  the  fourth  visceral  clefts  it  enlarges,  unites  with  the 
diverticula  from  those  clefts  which  form  the  lateral  lobes  of  the  thyroid  body,  and 
is  itself  converted  into  the  isthmus  of  the  thyroid,  its  pyramidal  process  and  the 
thyro-glossal  duct  or  the  fibrous  cord  into  which  that  duct  becomes  converted  in 
the  adult.  Occasionally  the  thyro-glossal  duct  is  not  wholly  transformed  into  a 
fibrous  cord,  but  portions  of  it  remain  in  the  form  of  isolated  vesicles,  hned  with 


38  GENERAL  EMBEYOLOGY. 

columnar  or  cubical  epithelium,  or  as  cords  of  cells,  and  these  occasionally  undergo 
abnormal  development,  forming  tumours  at  the  base  of  the  tongue  or  in  the  upper 
part  of  the  neck. 

The  portion  of  the  sinus  arcuatus  which  lies  behind  the  conjoined  lower 
extremities  of  the  second  and  third  arches  of  opposite  sides,  and  in  front  of  the 
farcula,  persists  in  a  modified  form  in  the  adult,  and  is  recognisable  as  glosso- 
epiglottidean  pouches  or  valleculce  at  the  base  of  the  tongue. 

The  furcula  and  the  groove  in  the  ventral  wall  of  the  fore-gut,  which  it  embraces 
antero-laterallj,  are  both  of  considerable  importance.  The  anterior  part  of  the 
furcula  is  situated  in  the  ventral  wall  of  the  pharyngeal  portion  of  the  fore-gut,  but 
its  backward  prolongations  and  the  furrow  between  them  lie  in  what  may  be 
termed  the  intermediate  part  of  the  fore-gut,  that  is,  in  that  part  of  the  fore-gut 
which  intervenes  between  the  pharyngeal  and  stomach  regions.  Gradually  the 
furrow  deepens,  and  its  posterior  extremity  dilates  on  each  side.  Afterwards  the 
margins  of  the  furrow  coalesce  from  behind  forwards,  and  in  this  manner  the 
cavity  of  the  furrow  is  separated  from  the  fore-gut,  its  walls  are  converted  into  the 
trachea  and  the  lower  part  of  the  larynx,  whilst  the  diverticula  which  are  projected 
from  its  posterior  end  form  the  rudiments  of  the  bronchi.  The  fusion  of  the 
margin  of  the  furrow  ceases  a  short  distance  behind  its  anterior  extremity,  which 
latter  persists  as  the  superior  aperture  of  the  larynx.  The  anterior  part  of  the 
furcula,  which  bounds  this  aperture  in  front,  becomes  the  epiglottis,  and  its  lateral 
extensions,  which  form  the  margins  of  the  aperture,  are  converted  into  the  aryteno- 
epiglottidean  folds  in  the  substance  of  which  the  arytenoid  cartilages  and  the 
cartilages  of  Santorini  and  Wrisberg  (cuneiform  cartilages)  are  formed. 

DEVELOPMENT   OF   THE   MOUTH   AND   THE   NOSE. 

The  nose  is  formed  entirely  from  the  stomatodseum.  The  mouth  has  a  double 
origin  ;  the  roof  and  fore-part,  including  the  teeth,  are  developed  from  the  stomato- 
dceum,  whilst  the  floor  and  the  tongue  are  developed  from  the  pharyngeal  portion  of 
the  fore-gut. 

It  has  already  been  pointed  out  (p.  34)  that  the  stomatodccal  depression  lies 
between  the  anterior  part  of  the  head  {i.e.  the  tissues  forming  the  base  of  the 
primary  fore-brain)  and  the  pericardial  region,  and  that  it  is  separated  posteriorly 
from  the  fore-gut  by  the  bucco-pharyngeal  membrane.  At  first  it  has  no  distinct 
lateral  boundaries,  but  subsequently  the  mandibular  arches,  which  are  developed  at 
the  sides  of  the  bucco-pharyngeal  membrane,  project  forward  beyond  the  membrane 
and  form  lateral  limits  of  the  depression.  If  the  stomatodseal  space  is  examined 
from  the  front  at  this  period  the  following  boundaries  are  recognisable  : — Above  and 
in  front  is  the  projecting  anterior  part  of  the  head  which  is  termed  the  fronto-nasal 
process,  laterally  are  the  mandibular  arches,  and  below  and  posteriorly  is  the  anterior 
part  of  the  pericardial  region.  After  a  short  time  the  lower  ends  of  the  mandibular 
arches  meet  in  front  of  the  pericardial  region,  and,  fusing  together,  form  the 
posterior  or  lower  margin  of  the  aperture ;  simultaneously  the  lateral  boundaries  of 
the  space  are  still  further  completed  by  the  forward  growth  of  a  nodular  projection, 
the  maxillary  process,  from  the  upper  end  of  each  mandibular  arch.  About  the 
fifteenth  day  the  bucco-pharyngeal  membrane  disappears,  and  the  stomatodseal  space 
and  pharynx  are  thenceforth  continuous.  No  trace  of  the  bucco-pharyngeal  mem- 
brane is  recognisable  in  the  adult,  but  its  position  may  be  represented  by  an 
imaginary  plane  extending  from  the  anterior  parb  of  the  basi-sphenoid  above  to  the 
base  of  the  alveolar  process  of  the  lower  jaw,  on  its  lingual  surface,  below. 

Whilst  the  boundaries  of  the  stomatodajal  space  are  being  defined,  two  oval 
depressions,  lined  with  thickened  epithelium,  appear  in  its  upper  boundary  on  the 
lower  and  anterior  surfaces  of  the  fronto-nasal  process ;  these  are  the  olfactory  pits 
or  depressions.  A  portion  of  the  epithelium  of  their  walls  is  separated  off  and  takes 
part  in  the  formation  of  the  olfactory  bulbs,  whilst  the  remainder  is  transformed 
into  the  olfactory  epithelium,  from  which  the  olfactory  nerve-fibres  grow  inwards 
to  the  olfactory  bulbs.  As  the  olfactory  pits  deepen  they  grow  backwards  into  the 
roof  of  the  stomatodseal  space,  and  at  the  same  time  they  separate  the  lower  portion 


THE  MOUTH  AND  NOSE. 


39 


of  the  fronto-nasal  process  into  three  parts,  constituting  a  median  and  two  lateral 
nasal  processes.  At  each  lateral  angle  of  the  median  nasal  process  a  spheroidal 
elevation,  the  globular  process,  appears.  The  part  of  the  median  nasal  process 
which  intervenes  between  the  two  globular  processes  is  divided  into  two  areas,  an 
upper  triangular  and  a  lower  quadrilateral,  by  the  appearance  of  a  transverse  ridge, 
which  is  afterwards  moulded  into  the  tip  of  the  nose.  The  upper  triangular  area 
becomes  the  dorsum  of  the  nose,  and  the  lower  quadrilateral  area  forms  the 
columella,  i.e.    the  lower  and  anterior  part  of  the  septum  between  the   anterior 


Mesencephalon 


Maxillary 
Eye  process      Mandibular  arch 


Prosencephalon 


Olfactory 
pit 


Prosencephalon 


Mesial  nasal 
process 


Stomatodceum. 


Fig.  31. 

I.  Side  view  of  the  head  of  human  embryo  about  27  days  old,  showiug  the  olfactory  pit  and  the  visceral  arches 

aud  clefts  (from  His). 

II.  Transverse  section  through  the  head  of  an  emliryo,  showiug  the  relation  of  the  olfactory  pits  to  the  fore- 

brain  and  to  the  roof  of  the  stomatodajal  space. 

III.  Head  of  human  embryo  about  29  days  old,  showing  the  division  of  the  lower  part  of  the  mesial  frontal 

process  into  the  two  globular  processes,  the  intervention  of  the  olfactory  pits  between  the  mesial 
and  lateral  nasal  processes,  and  the  approximation  of  the  maxillary  and  lateral  nasal  processes,  which, 
however,  are  separated  by  the  oculo-nasal  sulcus  (from  His). 

IV.  Transverse  section  of  head  of  embryo,  showiug  the  deepening  of  the  olfactory  pits  and  their  relation  to  the 

hemisphere  vesicles  of  the  fore-brain. 

nasal  apertures.  The  globular  processes  are  utilised  in  the  formation  of  the  philtrum 
or  middle  part  of  the  upper  lip,  and  the  lateral  nasal  processes  form  the  alse  of 
the  nose  or  lateral  boundaries  of  the  anterior  nasal  apertures.  As  the  olfactory  pits 
deepen  and  grow  backwards  into  the  roof  of  the  stomatod^eum  the  maxillary  pro- 
cesses grow  forwards  from  the  lateral  boundaries  of  that  space,  that  is  from  the 
upper  ends  of  the  mandibular  arches,  and  pass  beneath  the  eyes,  which  now  form 
distinct  prominences  on  the  sides  of  the  head.  The  upper  borders  of  the  maxillary 
processes  come  into  contact  with  the  lateral  nasal  processes  from  which  they  are 
temporarily  separated  by  grooves,  the  oculo-nasal  sulci.  These  latter  pass  from  the 
depressions  round  the  eyeballs,  the  rudimentary  conjunctival  sacs,  to  the  margins 
of  the  nasal  pits.     The  anterior  extremities  of  the  maxillary  processes  impinge 


40 


GENEEAL  EMBEYOLOGY. 


upon  the  globular  processes,  and  ultimately  their  upper  borders  and  anterior  ex- 
tremities fuse  with  the  lateral  nasal  and  globular  processes,  completing  the  lower 
boundaries  of  the  anterior  nasal  orifices  and  the  lateral  parts  of  the  primitive 
upper  lip.  At  the  same  time  the  oculo-nasal  sulci  are  converted  first  into  solid 
cords  of  cells,  and  afterwards  into  the  lachrymal  sacs  and  the  nasal  ducts,  which 
henceforth  constitute  the  channels  of  communication  between  the  conjunctival 
sacs  and  the  nose. 

The  result  of  the  ingrowth  of  the  maxillary  processes  and  their  fusion  with  the 


Cerebral  liemisi)he!es 


Olfactory  pit 


Globular  proces-- 


Maxillary  process 


Pituitary 
depression 


Aiit.  nasal  orifice      "^ 

Globular  process 
Maxillary  proces'- 


Lower  jaw 


Olfactory  pit 

Maxillary  process 

Globular  process 
Moutli 


Cerebral 
hemisphere 


Nasal  cavity 

Jacobson's  organ 

Globular  process 
Maxillary  process 

Lower  jaw 


Mouth 


Fig.  32. 

I.  Portiou  of  the  head  and  neck  of  a  human  embryo  32  days  old.     The  fioor  of  the  month  and  pharynx  and 

the  ventral  part  of  the  anterior  portion  of  the  body  have  been  removed.  By  the  approximation  of  the 
globular  and  maxillary  processes  the  boundaries  of  the  anterior  nares  are  almost  complete,  but  the 
olfactory  pits  still  open  in  the  whole  of  their  lengths  into  the  roof  of  the  mouth  (from  His). 

II.  Transverse  section  of  the  head  oi  an  embryo,   showing  the  close  apposition  of  the  globular  and  maxillary 

processes. 

III.  Head  of  human  embryo  about  2  months  old,  showing  the  union  of  the  globular  processes  and  their  fusion 

with  the  maxillary  processes.     The  anterior  nasal  apertures  are  now  completely  defined  (from  His). 

IV.  Transverse  section  of  the  head  of  an  embryo,  showing  tlie  fusion  of  the  maxillary  processes   with  the 

globular  processes,  and  the  separation  anteriorly  of  the  nose  from  the  mouth. 

lateral  nasal  and  globular  processes  is  the  division  of  the  large  orifice  which  led  into 
the  stomatodccal  space  into  three  parts — a  large  lower,  and  two  smaller  upper  aper- 
tures. The  lower  opening  is  the  aperture  of  the  mouth ;  it  is  bounded  below  by 
the  united  mandibular  arches,  and  above  by  the  fused  mesial  nasal  and  maxillary 
processes.  The  smaller  upper  openings  are  the  anterior  nares,  which  on  their  first 
Ibrmation  are  merely  foramina  of  communication  between  the  exterior  and  the 
upper  part  of  the  stomatod^eal  sjjace ;  the  latter  is  not  yet  separated  into  nasal  and 
oral  chambers. 

Formation  of  the  Palate  and  the  Separation  of  the  Nasal  and  Buccal 
Cavities. — This  separation  is  effected  by  the  formation  of  the  palate,  which  is 
developed  to   a  slight  extent   by  the  backward  growth  of  the  globular  processes 


FOKMATION  OF  THE  PALATE. 


41 


along  the  roof  of  the  space  as  a  pair  of  ridges,  termed  the  nasal  laminae,  which  fuse 
together  to  form  a  small  anterior  portion  of  the  palate,  viz.  the  intermaxillary  pro- 
cess, in  which  the  intermaxillary  parts  of  the  superior  maxilhe  are  formed.  The 
remaining  and  greater  part  of  the  palate  is  formed  by  two  ledge-like  ingrowths, 
one  from  the  inner  surface  of  each  maxillary  process,  which  meet  and  fuse  anteriorly 
with  the  intermaxillary  process,  and  behind  this  with  each  other.  In  these  pro- 
jections the  palatal  processes  of  the  superior  maxillae  and  the  horizontal  plates  of 
the  palate  bones  are  formed,  and  by  their  fusion  the  upper  part  of  the  stomatodieal 
space  is  separated  off  from  the  remainder  as  a  common  nasal  chamber  which  com- 
municates in  front  with  the  exterior  by  the  anterior  narial  orifices,  and  behind 
with  the  pharyngeal  portion  of  the  fore-gut  by  the  choanal  apertures  or  posterior 
nares.  The  lower  part  of  the  stomatodteal  space  and  the  front  part  of  the  fore-gut 
together  form  the  mouth  or  buccal  cavity ;  this  opens  anteriorly  by  a  transverse 
aperture,  the  boundaries  of  which  have  already  been  described,  and  posteriorly  it  is 
in  direct  continuity  w^ith  the  pharynx. 

The  division  of  the  common  nasal  chamber  into  two  parts  commences  before  its 
separation  from  the  mouth  is  completed,  and  it  is  brought  about  by  the  development 


Anterior  nasal  orifice 


Etlimo-vomerine  plate 
Xasal  cavity 


Palatal 
process 


Pituitary  depression 
Fig, 


Mediel's  cartilage 


I.  Portion  of  the  head  of  a  human  embryo  about  2^  months  old  (His).     The  lips  are  separated  from  the  gums, 

and  the  line  of  the  common  dental  germ  is  visible  in  the  latter.     The  palatal  processes  are  growing 
inwards  from  the  maxillary  processes. 

II.  Transverse  section  of  the  head  of  an  embryo  after  the  fusion  of  the  palatal  processes  of  the  maxillary  pro- 

cesses with  the  nasal  septum,  which  grows  backwards  from  the  fused  globular  processes. 

of  a  septum  which  is  continuous  anteriorly  with  the  fused  nasal  laminte,  and  which 
grows  downwards  and  backwards  from  the  mesial  part  of  the  under  aspect  of  the 
fronto-nasal  process.  This  septum  fuses  below  with  the  conjoined  margins  of  the 
palatal  ledges  of  the  maxillary  processes,  and  a  vertical  plate  of  cartilage  soon 
develops  in  its  interior,  which  is  continuous  above  with  the  cartilaginous  base  of  the 
cranium  (basi-cranial  axis).  A  portion  of  this  septal  cartilage  remains  in  the  adult 
as  the  septal  cartilage  of  the  nose,  and  the  remainder  is  more  or  less  completely 
replaced  by  the  vertical  plate  of  the  ethmoid  bone  and  by  the  vomer.  The  lateral 
wall  of  each  nasal  chamber  is  formed,  in'  the  lower  part  of  its  extent,  by  the 
maxillary  process  of  the  mandibular  arch,  in  which  the  superior  maxillary,  malar, 
and  palate  bones,  and  possibly  the  internal  pterygoid  plate,  are  developed,  and  in 
the  upper  part  by  the  outer  boundary  of  the  original  nasal  pit,  which  now  forms 
only  the  upper  part  of  the  nasal  cavity.  In  this  upper  section  of  the  outer  wall 
an  outgrowth  of  the  basi-cranial  axis  projects  downwards,  and  is  developed  into 
the  lateral  mass  of  the  ethmoid  bone ;  probably  it  also  takes  part  in  the  formation 
of  the  inferior  turbinal  bone. 

The  fusion  of  the  three  segments  of  the  palate  commences  anteriorly  at  the 
eighth  week  by  the  union  of  the  maxillary  and  globular  processes ;  it  passes  back- 
wards and  is  completed  by  the  fusion  of  the  posterior  parts  of  the  palatal  ledges  of 
the  maxillary  processes  about  the  tenth  week.  To  the  non-completion  of  this 
fusion  the  various  cases  of  hare-Hp  and  cleft  palate  are  due. 

Organ  of  Jacobson. — The  organs  of  Jacobsou  are  rudimentary  structures  in  man. 


4:2 


G ENSEAL  EMBKYOLOGY. 


They  lie  in  the  lower  and  anterior  part  of  the  nasal  septum,  one  upon  each  side. 
They  are  developed  as  small  diverticula  which  grow  backwards  and  upwards  in  the 
substance  of  the  septum,  and  their  points  of  commencement  are  situated  immediately 
above  the  intermaxillary  segment  of  the  palate.  Each  diverticulum  is  partially  sur- 
rounded, on  its  inner  side,  by  a  cartilaginous  capsule,  it  ends  blindly  behind,  and  it  opens 
anteriorly  close  to  the  floor  of  the  nose  in  the  region  of  Stenson's  foramen — a  small 
aperture  left  between  the  premaxillary  and  maxillary  sections  of  the  bony  palate. 


TH 


Pituitary  Body. — The  pituitary  body  is  formed  partly  from  the  floor  of  the 
first  primary  cerebral  vesicle,  and  partly  from  the  roof  of  the  stomatodseal  space. 
The  stomatodfeal  portion  appears  as  a  small  pouch,  Eathke's  pouch,  which  grows 
upwards  into  the  base  of  the  head  immediately  in  front  of  the  dorsal  margin 
of  the  bucco-pharyngeal  membrane  and  the  anterior  end  of  the  notochord,  and 

behind  the  fore-brain.  It  is  lined  by 
ectoderm,  and  soon  becomes  a  conical 
vesicle  which  lies  beneath  the  base  of 
the  fore-brain.  Its  orifice  of  communica- 
tion with  the  stomatodseal  space  is  gradu- 
ally constricted  until  the  lumen  dis- 
appears, and  then  for  a  time  the  vesicle 
is  connected  with  the  surface  by  a  solid 
cord  of  ectodermal  cells.  This  also  dis- 
appears, and  the  vesicle  is  embedded  in 
the  base  of  the  head  in  a  region  above 
and  between  those  parts  of  the  basal 
axis  which  afterwards  are  transformed 
into  the  basi-  and  pre-sphenoid  elements 
of  the  sphenoid  bone. 

During  the  period  of  its  formation 
and  separation  the  ingrowth  from  the 
stomatodseum  comes  into  relation  pos- 
teriorly with  a  small  diverticulum  from 
the  floor  of  the  fore-brain,  which  dilates 
at  its  lower  end  to  form  the  posterior 
or  cerebral  lobe  of  the  pituitary  body, 
whilst  its  upper  part  remains  as  the 
Showing  the  formation  of  the  two  parts  of  the  pituitary  jnfundibulum,  the  Connecting  stalk  be- 

body  (diagrammatic).  '=' 


Fig.  34. 


-Vertical  Section  through  Head  of 
Rat  Embryo. 


(Ectoderm  is  represented  in  black,  entoderm  in  blue, 
and  mesoderm  in  red.) 


At. 
Ax 
B. 


Atlas. 

Axis. 

Cartilaginous    basi- 
cranial  axis. 

Heart. 

HB.    Hind-brain. 

.MB.  Mid-brain. 

Part  of  nasal  cavity. 


H 


N. 


P.     Pineal  body. 

PR.  Cerebral  hemisphere. 


body. 
SG.  Spinal  ganglion. 
T.     Tongue. 


Th.  Tlialameiicci^halon. 


tween  the  pituitary  body  and  the  floor 
of  the  third  ventricle  of  the  brain.  The 
anterior  or  stomatodeeal  lobe  of  the 
pituitary  body  is  much  larger  than  the 
Pfi.  Cerebral  part  of  pituit-  posterior  lobe,  which  it  surrounds  and 
Pt2.  Buccli'part'of  pituitary  conceals  both  in  front  and  at  the  sides. 

It  is  evident  that  in  the  early  stages 
the  pituitary  body  consists  of  two  ecto- 
dermal vesicles,  the  cavity  of  the  pos- 
terior vesicle  is  continuous  with  the 
cerebral  tube,  and  that  of  the  anterior  vesicle  with  the  cavity  of  the  primitive 
mouth.  The  cavity  of  the  posterior  vesicle  is  generally  obliterated,  and  though 
nervous  structures  are  for  a  time  developed  in  its  walls  they  entirely  disappear  in 
man  and  are  replaced  by  vascular  connective  tissue.  Occasionally  a  small  part  of 
tlie  cavity  remains  as  a  minute  vesicle  lined  with  columnar  ciliated  epithelium. 

The  cavity  of  the  anterior  vesicle  persists,  it  sends  out  numerous  diverticula, 
and  is  gradually  converted  into  a  number  of  tubular  spaces,  lined  with  cubical  or 
columnar  cells,  united  together  by  vascular  connective  tissue  which  has  grown 
amidst  the  tubules  from  the  surrounding  mesoderm. 


THE  EXTERNAL  EAR  AND  EUSTACHIAN  TUBE. 


43 


THE  EXTERNAL  EAR,  THE  TYMPANIC  CAVITY,  AND  THE 
EUSTACHIAN  TUBE. 

The  external  ear,  the  tympanic  cavity,  and  the  Eustachian  tube  are  all  developed 
from  the  first  visceral  cleft  and  its  boundaries.  The  cleft  lies  between  the 
mandibular  (first)  and  the  hyoid  (second)  visceral  arch  in  the  side  wall  of  the 
pharyngeal  portion  of  the  fore-gut,  and,  before  a  neck  is  developed,  it  extends  from 
just  ventral  to  the  otic  vesicle,  which  lies  at  the  side  of  the  hind-brain,  above,  to 
the  pericardial  region  below.  The  membrane  which  lies  at  the  bottom  of  the  cleft 
consists  in  the  early  stages  of  ectoderm  and  entoderm,  but  in  a  short  time  a  thin 
layer  of  mesoderm  grows  between  the  two  primary  layers,  and  the  trilaminar  septum 
is  ultimately  converted   into  hb 

the  tympanic  membrane  which 
separates  the  external  from 
the  middle  ear. 

The  differentiation  of  the 
outer  part  of  the  cleft  is  initi- 
ated by  the  appearance  of  six 
tubercles  round  its  margins, 
which  are  afterwards  trans- 
formed into  the  several  parts 
of  the  pinna. 

Two  tubercles  are  formed 
anteriorly  on  the  mandibular 
arch,  one  at  the  dorsal  end  of 
the  cleft  and  three  posteriorly 
on  the  hyoid  arch.  The  two 
tubercles  on  the  mandibular 
arch  are  a  small  lower,  the 
tuberculum  tragicum,  and  a 
larger  upper,  the  tuberculum 
anterius  helicis.  The  tubercle 
at  the  upper  end  of  the  cleft 
is  the  tuberculum  intermedium 
helicis.  The  upper  tubercle 
on  the  hyoid  arch  is  the  tuber- 
culum anthelicis,  the  middle  is 
the  tuberculum  antitragicum, 
and  the  lowest  is  the  tuber- 
culum lobulare.  Shortly  after  the  appearance  of  the  tubercles  a  process,  the  caudal 
process,  grows  backwards  and  downwards,  from  the  posterior  part  of  the  tuberculum 
intermedium  helicis,  behind  the  tuberculum  anthelicis  and  the  tuberculum  anti- 
tragicum to  the  tuberculum  lobulare,  with  which  it  fuses.  The  tuberculum  tragicum 
remains  more  or  less  distinct,  and  it  forms  the  prominence  called  the  tragus  which 
lies  in  front  of  the  concha  and  external  auditory  meatus. 

The  two  tubercles  of  the  helix  and  the  caudal  process  unite  to  form  the  helix 
or  marginal  portion  of  the  pinna ;  this  terminates  below  in  the  lobule  which  is 
developed  from  the  tuberculum  lobulare.  The  tuberculum  anthelicis  and  the 
tuberculum  antitragicum  are  the  rudiments  respectively  of  the  antihelix  and  the 
antitragus,  and  the  latter  unites  below  the  lower  part  of  the  cleft  with  the  rudiment 
of  the  tragus,  forming  the  lower  boundary  of  the  outer  part  of  the  external  meatus. 
It  should  be  noted  that  in  the  early  stages  the  tuberculum  anterius  helicis  lies  in 
front  of  the  outer  part  of  the  first  visceral  cleft,  but  it  does  not  retain  this  position 
in  the  later  stages  during  which  the  cleft  is  relatively  reduced  in  size,  and  when 
development  is  completed  and  the  outer  part  of  the  cleft  is  transformed  into  the 
external  auditory  meatus  the  commencement  of  the  helix,  which  is  developed  from 
the  tuberculum  anterius  helicis,  is  situated  just  above  the  outer  extremity  of  the 
external  meatus. 


Fig.  35. 


-Transverse  Section  throdgh  the  Head 
OF  A  Rat  Embryo. 


Showing  the  rudiments  of  the  three  parts  of  the  ear  and  their 
relation  to  the  hyo-mandibular  cleft. 


BV.  Blood-vessels. 

C.       Cochlea. 

EM.  Ext.  auditory  meatus. 

ET.    Eustachian  tube. 

HB.  Hind-brain. 

HM.  Hyo-mandibular  cleft. 


N.  Notochord. 

OV.  Otic  vesicle. 

P.  Pharynx. 

RL.  Recessus  labyrinthii. 

SC.  Semicircular  canal. 

T.  Tympanum. 


44 


GENEKAL  EMBEYOLOaY. 


The  outer  part  of  the  cleft  is  moulded  into  the  external  auditory  passage.  It 
remains  relatively  shallow  and  devoid  of  bony  boundaries  till  after  birth,  but  in 
the  subcutaneous  tissue  round  the  lower  margin  of  the  tympanic  membrane  an 
incomplete  ring  of  bone  is  formed  during  the  third  month,  and  at  an  earlier  period, 
above  the  upper  part  of  that  membrane,  the  rudiment  of  the  squamous  loart  of  the 
temporal  bone  appears.  To  the  outer  side  of  the  tympanic  ring  in  the  subcutaneous 
tissue  of  the  pinna  and  the  outer  part  of  the  external  auditory  passage  three  pieces 
of  cartilage  appear,  and  they  afterwards  join  to  form  the  cartilage  of  the  pinna  and 
the  external  auditory  meatus. 

After  birth  the  external  meatus  is  deepened  by  the  outgrowth  of  the  tympanic 
ring  below  and  of  the  squamous  part  of  the  temporal  bone  above,  together  with  a 

coincident  in- 
crease of  the  outer 
part  of  the  canal. 
The  tympanic 
cavity  and  the 
Eustachian  tube 
are  both  formed 
from  the  inner 
part  of  the  first 
visceral  cleft,  and 
consequently  they 
are  both  lined  by 
entoderm. 

The  tympanic 
cavity  is  developed 
from  the  dorsal  or 
upper  end  of  this 
portion  of  the  cleft, 
and  it  is  prolonged 
upwards  on  the 
outer  side  of  the 
otic  vesicle  which 
simultaneously 
descends  in  the 
tissuesof  the  head. 
Thus  the  upper 
end  of  the  inner 
portion  of  the  cleft, 
which  is  somewhat 
dilated,  comes  to 
lie  between  the 
otic  vesicle,  which 
is  developed  into  the  internal  ear  on  the  inner  side,  and  the  tympanic  membrane 
which  separates  it  from  the  external  auditory  meatus  on  the  outer  side,  and  it 
remains  in  the  adult  as  a  laterally  compressed  space,  the  tympanic  cavity,  which 
is  continuous  through  the  Eustachian  tube  with  the  upper  part  of  the  pharynx.  In 
the  mesoderm  round  the  inner,  upper,  and  back  part  of  the  cavity  the  petrous  part  of 
the  temporal  bone  is  developed  and  ossified,  and  in  the  lower  and  anterior  part  the 
tympanic  ossification  extends  outwards  during  the  formation  of  the  tympanic  plate. 

The  upper  part  of  the  tympanic  space  is  prolonged  backwards  between  the  ossifying 
petrous  and  squamous  parts  of  the  temporal  bone,  where  it  forms  a  recess  known  in  the 
adult  as  the  mastoid  antrum,  from  which  at  a  later  period  diverticula  are  projected  into 
the  mastoid  portion  of  the  temporal  bone,  forming  the  mastoid  air  cells. 

The  lower  portion  of  the  inner  part  of  the  cleft  is  moved  obliquely  forwards. 
As  development  proceeds  it  is  contracted  and  carried  downwards  and  forwards  in 
front  of  the  developing  otic  vesicle.  It  is  the  rudiment  of  the  Eustachian  tube, 
and,  as  the  septum  which  separates  the  nasal  chambers  from  the  mouth  is  formed. 


Fig.  36.- 


HM 


-FiGUUKS,    MODIFIED   FROM    HiS,    ILLUSTRATING   THE  FORMATION    OF 

THE  Pinna. 


1.  Tuberculuiu  tragicum  =  Tragus. 

2.  ,,  anterius  helicis  \ 

3.  ,,  intermedium  helicis  p 

4.  Cauda  helicis  j 

5.  Tuberculum  anthelicis  =  Antihelix. 


6.  Tuberculum    antitragicum  =  Anti- 

tragus. 

7.  Tuberculum  lobulare  =  Lobule. 
HM.  Hj'o-mandibular  cleft. 

OV.    Otic  vesicle. 


THE  HIND-aUT  AND  ANAL  PASSAGE.  45 

itsilower  end  attains  a  position  just  behind  and  at  the  side  of  the  posterior  narial 
orifice  in  the  upper  and  lateral  part  of  the  pharynx.  Apparently,  therefore,  the 
lower  end  of  the  Eustachian  tube  has  a  much  higher  position  than  that  originally 
occupied  by  the  lower  end  of  the  cleft  from  which  it  is  formed,  for  it  will  be 
rememljered  that  the  lower  end  of  the  first  visceral  cleft  is  situated,  in  the  early 
stages,  at  the  side  of  the  tuberculum  impar  from  which  the  anterior  two-thirds  of 
the  tongue  is  formed.  This  alteration  in  relative  position  is  due,  however,  not  to 
elevation  of  the  lower  end  of  the  first  visceral  cleft  during  its  transformation  into 
the  Eustachian  passage,  l3ut  to  the  enormous  downgrowth  of  the  mandibular  arches, 
which  carry  with  them  the  tongue,  as  they  enlarge  to  form  the  lower  jaw. 

THE  HIND-GUT,  THE  ANAL  PASSAGE,  AND  THE  POST-ANAL 

OE  TAIL-GUT. 

By  the  formation  of  the  mouth  the  primitive  alimentary  canal  opens  anteriorly  ; 
it  remains  closed  posteriorly  until  a  later  date,  when  the  anal  passage  and  orifice 
are  developed. 

The  posterior  end  of  the  hind-gut  which  is  enclosed  in  the  tail-fold  is  termed 
the  cloaca.  The  cloaca  is  dilated,  and,  assuming  a  conical  form,  receives  the 
terminations  of  the  genito-urinary  ducts.  It  is  bounded  postero-inferiorly  by  the 
cloacal  membrane  which  extends  from  the  root  of  the  tail  to  the  body  stalk  by  which 
the  embryo  is  attached  to  the  chorion.  The  cloacal  membrane  is  modified  from  the 
posterior  part  of  the  primitive  streak ;  this  remains  on  the  surface  of  the  body  after 
the  anterior  part  has  been  separated  and  enclosed  during  the  completion  of  the 
posterior  part  of  the  neural  canal,  and  it  forms  a  septum  between  the  cavity  of  the 
cloaca  and  the  exterior.  It  consists  at  first  of  ectoderm  and  entoderm  alone,  and 
it  is  only  at  its  lower  and  anterior  part  that  it  is  subsequently  invaded  to  a  slight 
extent  by  mesoderm. 

During  the  second  month  of  intrauterine  Life  the  cloaca  is  divided  into  a  ventral 
or  genito-urinary,  and  a  dorsal  or  rectal  section,  by  the  formation  and  fusion  of 
lateral  folds,  which  gradually  unite,  from  before  backwards,  till  finally  the  posterior 
end  of  the  septum  approaches  and  fuses  with  the  cloacal  membrane,  and  the 
rectum  is  separated  from  the  genito-urinary  chaml^er.  Before  this  separation 
is  completed  an  eminence  appears  in  the  region  of  the  anterior  part  of  the 
cloacal  membrane  at  the  junction  of  the  ventral  surface  with  the  posterior 
extremity  of  the  body,  i.e.  in  that  part  which  afterwards  becomes  the  region  of  the 
symphysis  pubis.  This  eminence  is  the  genital  eminence,  and  from  it  are  formed 
the  penis  in  the  male  and  the  clitoris  in  the  female.  The  genital  eminence  is 
surrounded  by  an  oval  fold  of  skin,  genital  fold,  which  extends  from  the  front  of 
the  eminence  to  the  root  of  the  tail  and  encloses  a  shallow  fossa,  the  cloacal  fossa, 
at  the  bottom  of  which  is  the  cloacal  membrane.  The  posterior  part  of  the  cloacal 
fossa  is  afterwards  separated  from  the  anterior  part  by  a  transverse  fold,  the  perineal 
fold,  which  crosses  the  external  surface  of  the  cloacal  membrane  in  a  position  which 
corresponds  internally  J  with  that  occupied  by  the  lower  end  of  the  septum  separating 
the  genito-urinary  from  the  rectal  portions  of  the  cloacal.  The  posterior  part  of 
the  cloacal  fossa,  ]jehind  the  transverse  fold,  is  the  proctodeeal  depression  or 
proctodaeum ;  at  first  its  long  axis  lies  transversely,  afterwards  it  assumes  a 
triangular  and  then  a  circular  form,  the  sphincter  ani  muscle  develops  in  its  walls, 
and  it  is  transformed  into  the  greater  part,  if  not  the  whole,  of  the  anal  canal  of 
the  adult.  It  is  separated  from  the  rectum  by  the  posterior  part  of  the  cloacal 
membrane,  but  when  that  disappears,  at  a  date  which  has  not  yet  been  definitely 
ascertained,  but  probably  about  the  third  month,  the  anal  passage  forms  the  canal 
by  which  the  rectum  communicates  with  the  exterior  of  the  body. 
The  orifices  of  the  alimentary  canal  are  thus  completed. 

The  Post-anal  or  Tail-Gut. — When  the  hind-gut  is  first  enclosed  there  is  no  tail, 
but  a  rudimentary  tail  is  subsequently  developed  as  an  outgrowth  from  the  dorsal  end  of 
the  tail-fold,  i.e.  from  the  posterior  extremity  of  the  body  of  the  embryo.  As  the  tail  is 
formed,  a  narrow  tube,  which  communicates  in  front  with  the  hind-gut,  is  developed 
within  it.     This  is  called  the  post-anal  or  tail-gut.     As  a   rule  it  only  exists  for  a   short 


46 


GENEEAL  EMBRYOLOGY. 


time,  disappearing  from  before  backwards  about  the  period  when  cartilage  begins  to  be 
formed  in  the  body  and  limbs,  and  before  the  cloaca  is  divided  into  its  rectal  and  genito- 
urinary portions.  In  the  few  cases  in  which  it  persists 
it  retains  its  continuity  with  the  rectum,  which  is 
formed  from  the  dorsal  part  of  the  cloaca. 

The  tail-gut  appears  in  the  human  subject  when 
the  embryo  is  3  mm.  long,  and  the  rudimentary  tail  is 
just  visible  as  a  small  nodule.  When  the  embryo 
attains  the  length  of  4-8  mm.  the  anterior  part  of 
the  tail-gut  begins  to  degenerate,  its  cavity  disappears, 
and  it  is  converted  into  a  solid  cord  of  cells  which  is 
still  attached  in  front  to  the  hind-gut.  In  embryos 
11-5  mm.  long,  when  the  tail  has  been  enclosed  in  the 
posterior  part  of  the  body,  the  connexion  of  the  tail- 
gut  with  the  hind -gut  is  lost,  and  the  tail -gut  is 
represented  by  a  small  vesicle  with  a  short  cord  of 
degenerating  cells  attached  to  its  anterior  part. 

In  larger  embryos  the  tail-gut  entirely  disappears. 
When,  as  in  the  human  subject,  the  rudimentary  tail  is 
eventually  embedded  in  the  posterior  end  of  the  body, 
any  rudiments  of  the  tail -gut  which  persist  will  be 
found  in  this  situation ;  it  is  stated  that  such  rudi- 
ments occasionally  develop  into  tumour  formations. 
In  mammals  with  free  tails,  rudiments  of  the  tail-gut 
may  be  met  with  in  any  part  of  the  tail,  and  apparently 
the  anterior  portion  occasionally  persists  and  maintains 
its  connexion  with  the  rectum,  from  which  it  extends 
backwards  as  a  narrow  and  blind  diverticulum. 

THE   LIMBS. 

Though  the  body  of  the  embryo  begins  to  assume 
definite  form  as  soon  as  it  is  folded  and  nipped  off 
from  the  rest  of  the  ovum,  it  does  not  present  any 
distinguishable  human   characteristics    until    the 
anterior  and  posterior  limbs  are  formed.     There  are 
no   traces  of   these  before  the  third  week  of  in- 
trauterine life  when  two  longitudinal  ridges,  the 
_.  Wolffian  ridges,  are  developed,  one  on  each  lateral 
tioii'of  the  cioacai  part  "of  tiie  hind- surfacc  of   the   body,  just   external    to  the  outer 
gut    into    genito- urinary    tract    and  margins  of  the  mesodcrmic  somitcs,  and  opposite 

the  line  of  the  intermediate  cell  mass.     The  rudi- 
ments of  the  fore-  and  hind -limbs  are  discernible, 
vs.'  vtsicuin"mi-  almost  from  the  first,  as  slight  prominences  of  the 
WT.  w"^]!"-   ,    .  Wolffian  ridg-es,  and  in  the  fourth  week  they  project 

WD.  Wolffian  cluct.  -,  -,       ^  t         •  t  t  •  i         i     • 

as  bud-like  outgrowths  m  the  thoracic  and  pelvic 
regions  respectively.  The  development  of  the  fore-limb  or  arm  is  throughout 
slightly  in  advance  of  that  of  the  hind-limb  or  leg.  At  the  fourth  week  each 
limb-bud  is  a  flattened  semilunar  projection,  as  long  as  it  is  broad,  with  a  dorsal 
and  a  ventral  surface  and  an  anterior  or  preaxial,  and  a  posterior  or  postaxial 
border.  As  growth  proceeds  the  elongating  limb-buds  are  bent  ventrally,  and  in 
the  fifth  week  two  transverse  furrows,  on  the  ventral  aspect  of  each,  indicate  the 
positions  of  the  joints  and  the  division  of  each  limb  into  three  segments — distal, 
middle,  and  proximal — representing  the  hand,  fore-arm,  and  arm  in  the  upper  limb, 
and  the  foot,  leg,  and  thigh  in  the  lower  limb.  The  terminal  or  distal  segments 
are  broad,  flat  x^lates  with  rounded  margins,  but  each  is  soon  divided  into  a  some- 
what enlarged  basal  part,  and  a  thinner  and  more  flattened  marginal  part.  It  is 
where  these  two  parts  are  continuous  that  the  rudiments  of  the  digits  appear. 
They  become  distinguishable  about  the  end  of  the  fifth  week  as  small  lobes  which 
gradually  extend  outwards.  In  the  fore-limb  the  fingers  project  beyond  the  margin 
of  the  hand-segments  in  the  sixth  week,  but  the  toes  do  not  reach  the  margins  of 


CM 


Fig.  37. — Diagrams  showing  the  separa- 


rectum. 


A.  Allantoic  stalk. 

B.  Bladder. 

C.  Cloaca. 

CM.  Cloacal  membrane 
K.      Kidney. 
R.      Rectum. 


U. 
Ur. 


Ureter. 
Uretlira. 


THE  LIMBS.  47 

the  foot  till  the  early  part  of  the  seventh  week.  The  nails  appear  at  the  third 
month,  and  reach  the  ends  of  the  digits  at  the  sixth  month. 

In  the  primary  position  of  the  limljs  the  elbow  and  the  knee  appear  alike  to  be 
directed  outwards,  but  this  is  soon  altered.  At  the  end  of  the  sixth  week  each 
limb  undergoes  a  partial  rotation,  the  direction  of  which  is  different  in  the  fore-  and 
hind-limbs  respectively.  In  the  former  the  elbow  is  turned  backwards,  the  ventral 
surface  therefore  becomes  anterior,  and  the  preaxial  (thumb)  margin  is  directed 
outwards ;  in  the  hind-hmb  the  knee  is  turned  forwards,  and  the  ventral  surface  of 
the  limb  becomes  posterior,  whilst  the  preaxial  (great  toe)  margin  is  directed 
inwards  ;  thus  in  the  adult  the  anterior  surface  and  outer  border  of  the  upper 
extremity  correspond  with  the  posterior  surface  and  inner  border  of  the  lower 
extremity,  whilst  obviously  the  posterior  surface  and  inner  border  of  the  former 
are  homologous  with  the  anterior  surface  and  outer  border  of  the  latter. 

Each  limb-bud  may  be  regarded  as  an  extension  from  a  definite  number  of  the 
segments  of  the  body ;  it  contains  a  core  of  mesoderm,  and  the  anterior  or  ventral 
primary  divisions  of  the  corresponding  spinal  nerve  segments  are  apparently 
prolonged  into  it. 

The  central  part  of  the  mesoderm,  except  in  the  regions  of  the  joints  where 
cavities  appear,  is  condensed  and  then  converted  first  into  cartilage,  and  afterwards 
into  bone.  The  proximal  part  of  the  bony  skeleton  of  each  liml),  the  limb  girdle, 
is  not,  however,  developed  in  the  limb-bud,  but  in  the  body-wall  at  its  base.  The 
more  superficially  situated  mesoderm  is  transformed  into  muscles  and  subcutaneous 
tissues,  the  extensor  muscles  appearing  on  the  dorsal  and  the  flexor  muscles  on  the 
ventral  aspect. 

As  the  nerve  trunks  pass  into  the  free  portion  of  the  limb  they  bifurcate,  the 
branches  passing  respectively  to  the  dorsal  or  extensor  aspect  of  the  limb,  and  to 
the  ventral  or  flexor  aspect. 

Apparently  in  mammals  the  whole  of  the  mesodermal  core  of  each  limb-bud  is 
formed  from  the  somatic  mesoderm  of  the  lateral  plates.  If  this  is  the  case  the 
muscles  of  the  limbs  differ  in  origin  from  those  of  the  back,  for  the  latter  are 
developed  from  the  muscle  plates  of  the  protovertebral  somites.  In  lower  verte- 
brates (cartilaginous  fishes)  buds  are  given  off  to  the  limbs  from  the  muscle  plates 
and  cutaneous  lamellee  in  the  thoracic  and  pelvic  regions,  and  as  the  muscle  plates 
pass  downwards  in  the  somatopleure  towards  the  ventral  aspect  of  the  body,  these 
buds  grow  outwards  into  the  limb-rudiments  and  develop  into  the  muscles  of  the 
limbs.  Presumably  this  is  the  more  primitive  arrangement,  and  that  met  with  in 
man  and  other  mammals  is  secondary,  and  it  is  stated  that  although  no  distinct 
buds  from  the  muscle  plates  pass  into  the  limbs  of  mammals,  nevertheless  the 
limb-muscles  are  formed  by  cells,  proliferated  from  the  muscle  plates,  which  have 
migrated  into  the  somatopleural  mesoderm  of  the  limbs. 


THE  NUTKITION   AND   PROTECTION   OF   THE   EMBRYO 
DURING   ITS   INTRAUTERINE   EXISTENCE. 

The  impregnated  ovum  during  its  passage  down  the  Fallopian  tube,  and  for  a 
brief  period  also  after  it  enters  the  uterus,  lives  either  on  the  yolk  granules  (deuto- 
plasm)  embedded  in  its  own  cytoplasm,  or  upon  material  absorbed  from  the  fluids 
by  which  it  is  surrounded.  The  human  ovum  is  very  small,  and  consequently  it  is 
almost  from  the  first  dependent  for  its  nutrition  upon  sources  of  supply  outside 
itself.  The  urgent  necessity  for  adequate  arrangements  whereby  this  may  be 
effected  leads  to  that  early  establishment  of  an  intimate  vascular  connexion 
between  the  embryo  and  the  mother  which  is  so  characteristic  a  feature  in  the 
development  of  the  human  ovum.  At  the  end  of  the  second  week,  after  fertilisa- 
tion of  the  ovum,  the  embryo  is  separated  by  a  slight  constriction  from  the  rest  of 
the  blastodermic  vesicle,  and  already  a  primitive  heart  and  rudimentary  blood- 
vessels are  distinguishable. 

The  development  of  the  vascular  system,  and  the  establishment  of  the  fcetal 


48  GENERAL  EMBRYOLOGY. 

circulation,  however,  cannot  well  be  understood  until  the  formation  and  structural 
features  of  the  group  of  closely  associated  extra-embrj^onic  organs  or  appendages 
have  been  considered. 

This  group  includes  the  yolk-sac,  the  chorion,  the  amnion,  the  allantois,  and 
the  placenta. 

THE   ECETAL   MEMBRANES   AND   APPENDAGES. 

Yolk-Sac  or  Umbilical  Vesicle. — That  portion  of  the  blastodermic  cavity 
and  its  wall  which  is  not  included  in  the  body  of  the  embryo  to  form  the  primitive 
alimentary  canal  constitutes  the  umbilical  vesicle  or  yolk-sac.  Its  walls,  like  its 
cavity,  are  continuous  with  the  corresponding  parts  of  the  intestine,  and  their 
structural  features  are  identical,  there  being  an  inner  layer  of  entodermal  cells  and 
an  outer  layer  which  is  formed  by  the  splanchnic  layer  of  the  mesoderm. 

In  the  human  embryo  the  yolk-sac  is  a  small  flask-like  body,  suspended  from 
the  ventral  wall  of  the  alimentary  canal  by  a  hollow  stalk,  the  vitello-intestinal 
duct,  which  passes  through  the  umbilical  orifice.  It  lies  in  the  extra-embryonic 
continuation  of  the  body-cavity  (ccelom),  and  is  filled  with  fluid.  Possibly  the 
contents  of  the  yolk-sac  are  utilised  in  the  nutrition  of  the  embryo  in  its  earliest 
stages,  and  the  first  rudiments  of  the  blood  vascular  system,  viz.  blood  corpuscles 
and  vessels,  appear  in  its  walls.  In  the  human  embryo,  however,  it  is  of  little 
nutritional  importance  ;  it  soon  atrophies  and  almost  entirely  disappears,  but  leaves 
traces  of  its  existence  in  the  umbilical  cord. 

Amnion. — The  amnion  is  a  protective  sac  which  surrounds  the  embryo.  It 
is  formed,  after  the  development  of  the  coelom,  from  the  amniotic  area  of  the 
blastoderm,  and  its  wall  is  continuous,  at  the  margins  of  the  umbilical  orifice,  with 
the  body-wall  of  the  embryo.  Both  walls  consist  of  a  layer  of  ectoderm  and  a 
layer  of  somatic  mesoderm,  but  whilst  in  the  body-wall  the  ectoderm  is  external 
and  the  mesoderm  internal,  the  relative  positions  of  the  layers  are  reversed  in  the 
amnion,  the  mesoderm  being  external  and  the  ectoderm  internal. 

The  cavity  enclosed  between  the  amnion  and  the  embryo,  the  amniotic  cavity, 
is  filled  with  fluid,  the  amniotic  fluid,  in  which  the  embryo  floats.  The  amniotic 
cavity  is  quite  shut  off  for  some  time  from  all  the  neighbouring  spaces,  but  after 
the  disappearance  of  the  bucco-pharyngeal  and  cloacal  membranes  it  communicates, 
both  anteriorly  and  posteriorly,  with  the  alimentary  canal  of  the  embryo. 

The  development  of  the  amnion  in  mammals  is  closely  associated  with  the 
attachment  of  the  ovum  to  the  uterine  wall  and  with  the  subsequent  formation  of 
the  placenta.  Thus  in  the  carnivora,  before  the  coelom  is  formed,  the  ectoderm  in 
the  chorionic  area  becomes  attached  to  the  uterine  tissues  by  small  villous  out- 
grow"ths  which  invade  the  uterine  mucous  membrane.  This  attachment  is  most 
complete  in  the  placental  region,  that  is,  around  the  margins  of  the  amniotic  area. 
As  the  embryo  is  folded  off  from  the  blastoderm  and  the  coelom  develops,  both  the 
embryo  and  the  amniotic  area  remain  quite  free  from  the  uterine  tissues,  indeed,  it 
may  be  said  that,  at  this  period,  the  embryo  is  suspended  from  the  margins  of  the 
placental  area  hj  the  amniotic  membrane. 

As  development  proceeds  the  amniotic  area  increases  in  extent  by  interstitial 
growth,  and  thereupon  the  emljryo,  the  membrane  which  suspends  it  being  relaxed, 
sinks  more  and  more  into  the  interior  of  the  ovum,  or,  to  be  more  precise,  into  the 
coelomic  space,  which,  in  the  meantime,  has  considerably  increased.  At  the  same 
time  the  growth  of  the  placental  area  causes  all  parts  of  its  inner  margin  to  converge, 
and  as  the  inner  margins  of  the  placental  area  are  continuous  with  the  outer 
margins  of  tlie  amniotic  membrane,  the  amnion  is  gradually  carried  over  the  dorsal 
surface  of  the  embryo  till  its  margins  meet  and  fuse.  After  the  fusion  of  its 
margins  the  amnion  separates  entirely  from  the  chorionic  area,  henceforth 
known  as  the  chorion,  and  forms  a  closed  sac  which  completely  surrounds 
the  embryo. 

On  reference  to  Figs.  21  and  27  it  will  be  seen  that  as  the  wall  of  the  blasto- 
dermic vesicle  is  carried  inwards  over  the  dorsal  surface  of  the  embryo  it  is  folded  ; 
the  outer  part  of  the  fold  consists  of  the  chorionic  portion,  and  the  inner  part  of  the 


THE  FCETAL  MEMBEANES  AND  APPENDAGES. 


49 


amniotic  portion  of  the  blastoderm.  The  fold  is  called  the  amnion  fold  ;  it  is  quite 
continuous  round  the  whole  margin  of  the  embryo,  but  some  parts  of  it  are  more 
advanced  than  others,  or  in  other  words  the  convergence  of  the  inner  margin 
of  the  placental  area  of  the  blastoderm  over  the  dorsal  surface  of  the  embryo  does 
not  take  place  at  the  same  rate  or  to  the  same  extent  in  all  parts.  For  convenience 
of  description  it  is  usual  to  divide  the  amnion  fold  into  four  parts — the  cephalic,  the 
caudal,  and  the  two  lateral  amnion  folds  ;  these,  however,  are  all  continuous  with 
one  another. 

The  inner  part  of  the 
fold,  which  is  formed  from 
the  amniotic  area,  is 
termed  the  true  amnion, 
and  the  outer  part,  formed 
from  the  chorionic  area, 
the  false  amnion.  The 
latter  term  is,  however, 
synonymous  with  chorion, 
and  as  it  is  misleading,  it 
should  be  avoided. 

As  the  amnion  is 
formed  from  the  amniotic 
area  of  the  blastoderm 
after  the  extension  of  the 
coelom,  it  must  consist,  as 
previously  mentioned,  of 
ectoderm  and  somatic 
mesoderm, 'and  as  the  sur- 
face of  the  amniotic  area 

reversed    during    the 


18 

formation  of  the  amnion 
folds,  it  is  obvious  that  in 
the  fully-formed  amnion 
the  ectodermal  layer  is 
internal  and  the  somatic 
mesoderm  external. 

In  the  case  of  the 
human  ovum  the  phe- 
nomena of  amnion  forma- 
tion are  probably  practi- 
cally similar,  except  that 
the  ovum  develops  not  in 
the  cavity  of  the  uterus, 
but  in  the  substance  of 
the  mucous  membrane  into 
which  it  has  penetrated. 
It  is  therefore  surrounded 
by  the  mucous  membrane 
on    all    sides,    and     the 

chorionic  part  of  the  surface  of  the  ovum  is  closely  attached  to  the  surrounding 
tissue,  but  the  amniotic  and  embryonic  areas  are  free.  If  this  is  the  case  the  process 
of  amnion  folding  can  take  place  in  the  human  ovum  exactly  as  in  the  ovum  of  a 
carnivorous  animal,  the  inner  margin  of  the  chorionic  area  growing  inwards  over 
the  amniotic  and  embryonic  areas,  the  only  difference  being  that  the  process  takes 
place  in  a  cavity  in  the  mucous  membrane  and  not  on  its  surface.  This  conclusion 
is  supported  by  Spec's  observations  on  human  ova  and  by  those  of  Selenka  on  the 
ova  of  monkeys  and  apes,  but  it  is,  however,  possible  that,  as  in  some  rodents  and 
insectivora,  the  amnion  cavity  appears  in  a  mass  of  ectoderm  which  lies  at  the 
embryonic  pole  of  the  ovum,  the  mass  being  cleft  by  the  appearance  of  the  cavity 
into  embryonic  and  amniotic  sections.  The  two  parts  are  then  continuous  at  the 
4 


-Transverse  Sections  of  the  Uterus  and  Developing 
Ovum  of  a  Ferret. 

Showing  the  formation  and  closure  of  the  amnion  folds,  the  completion  of 
the  amnion,  and  the  coincident  ingrowth  of  the  inner  margins  of  the 
placental  area  of  the  blastoderm. 

Amnion.  EN.  Entoderm. 

Amnion  fold.     M.      Muscular  wall 


A. 
AF. 

C. 

Ch. 

EC. 


Ccelom. 
Chorion. 
Ectoderm . 


NG. 
PV. 


of  uterus. 
Neural  groove. 
Placental  villus 


SC. 
SS. 
SoM. 


Stratum  compactum. 
Stratum  spongiosum. 
Somatic  mesoderm. 


Sp.M.   Splanchnic  mesoderm. 
UL.        Unchanged     layer    of 
uterine  mucosa. 


50  GENEEAL  EMBEYOLOGY. 

margin  of  the  embryonic  area,  and  the  mesoderm    growing  round  the  amniotic 
ectoderm  separates  it  from  the  chorionic  ectoderm. 

After  the  amnion  is  completed  its  cavity  is  distended  with  fluid.  As  it  expands 
it  gradually  obliterates  the  extra-embryonic  part  of  the  coelomic  cavity,  and  finally 
its  outer  surface,  of  somatic  mesoderm,  comes  into  contact  and  fuses  with  the  somatic 
mesoderm  on  the  inner  surface  of  the  chorion.  At  this  period  the  cavities  in  the 
ovum  are  the  amniotic  cavity,  the  remains  of  the  yolk-sac,  and  those  portions  of  the 
original  blastodermic  and  ccelomic  spaces  which  have  been  included  in  the  embryo. 
In  the  human  ovum,  when  the  amnion  folds  unite  and  the  true  amnion  separates 
from  the  chorion,  the  embryo  and  its  enclosing  amnion  would  be  free  within  the 
cavity  of  the  chorion,  or  extra-embryonic  coelom,  were  it  not  that  a  very  short  cord 
of  somatic  mesoderm  and  ectoderm,  the  body-stalk,  connects  the  posterior  end  of  the 
embryo  with  the  somatic  mesoderm  on  the  inner  surface  of  the  chorion. 

Body-Stalk. — To  thoroughly  understand  how  this  union  is  effected  in  the 
human  ovum,  and  to  comprehend  the  nature  of  the  body-stalk,  it  is  necessary  to 
refer  to  some  striking  peculiarities  which  are  to  be  observed  in  the  earlier  stages 
in  the  development  of  the  human  embryo.  When  segmentation  is  completed,  and 
the  morula  is  converted  into  a  blastula  by  the  appearance  of  a  cavity  in  its  interior, 
the  human  ovum  consists  of  an  outer  layer,  the  ectoderm,  and  an  inner  cell-mass 
(Figs.  12  and  39).  The  latter,  however,  which  is  attached  to  a  small  area  of  the 
ectoderm,  does  not,  as  in  many  mammals,  extend  itself  by  migration  round  the  inner 
surface  of  that  layer,  and  so  transform  the  unilaminar  into  a  bilaminar  blastoderm 
and  convert  the  cavity  of  the  blastula  into  the  blastodermic  cavity.  The  sequence 
of  events  is  different :  a  cavity  or  space  appears  in  the  inner  cell-mass  itself  (Figs. 
41,  42,  and  44),  and  this  expanding  rapidly,  is  ultimately  converted  into  the  yolk- 
sac  and  the  alimentary  canal  of  the  embryo ;  it  corresponds,  therefore,  with  the 
blastodermic  cavity  of  other  mammals. 

Thus  the  entoderm,  though  derived  from  the  inner  cell-mass,  never  lines  the 
inner  surface  of  the  ectoderm  except  in  the  embryonic  area,  for  soon  after  the 
appearance  of  the  cavity  of  the  inner  cell-mass  the  mesoderm  grows  rapidly  from 
the  primitive  streak  and  extends,  not  in  a  single  layer,  as  in  the  majority  of 
mammals,  but  as  two  layers,  one  over  the  outer  surface  of  the  entoderm,  the 
splanchnic  layer,  and  the  other,  the  somatic  layer,  over  the  inner  surface  of  the 
ectoderm.  The  cavity  of  the  blastula  is  thus  ultimately  enclosed  between  the 
somatic  and  splanchnic  layers  of  the  mesoderm,  and  so  becomes  converted  into  the 
coelomic  space  (Fig.  42). 

As  the  mesoderm  extends,  the  several  areas  of  the  blastoderm  are  differentiated 
as  in  other  mammals,  but  the  embryonic  and  amniotic  areas  remain  of  relatively 
small  size.  The  separation  of  the  amnion  from  the  chorion  is  effected  at  a  very 
early  period,  Ijefore  the  folding  off  of  the  embryo  has  commenced,  but  the  somatic 
mesoderm  growing  from  the  posterior  end  of  the  embryonic  area  still  retains  its 
connexion  with  the  similar  layer  on  the  inner  surface  of  the  chorion,  and  it  forms 
a  short,  and  for  a  time  a  ])road  stalk  which  unites  the  embryo,  and  consequently 
the  amnion  and  the  blastodermic  cavity,  with  which  the  embryo  is  connected,  to  the 
chorion  (Fig.  42).  In  addition  to  forming  a  bond  of  union  between  the  embryo 
and  the  chorion  the  mesodermal  stalk  conducts  blood-vessels  from  the  embryo  to 
the  chorion,  and  more  especially  to  its  placental  part. 

At  an  early  period  a  pouch -like  diverticulum  projects  from  the  posterior  part 
of  the  entodermal  sac.  This  is  the  allantoic  diverticulum ;  it  lies  beneath  the 
posterior  part  of  the  embryonic  area,  and  the  area  is  curved  upon  itself  so  that  its 
convexity  looks  towards  the  entodermal  sac,  and  its  concavity  towards  the  amnion. 

After  the  embryonic  area  has  increased  in  extent,  and  when  the  folding  off  of 
the  eml^ryo  has  commenced,  the  anterior  end  of  the  area  and  the  posterior  end  of 
the  primitive  streak  remain  relatively  stationary  as  in  other  mammals,  the  cephalic 
and  caudal  folds  appear,  and  the  curvature  of  the  greater  part  of  the  area  is 
reversed,  but  the  most  posterior  part  retains  its  original  position,  lying  for  a  time 
parallel  with  the  caudal  fold  ;  afterwards,  however,  it  assumes  a  more  horizontal 
position.  This  posterior  section  of  the  embryonic  area  contains  the  diverticular 
process  of  the  entodermal  sac  wliich  is  called  the  allantois ;  it  also  contains  the 


THE  ALLANTOIS  AND  UMBILICAL  COED.  51 

blood-vessels,  allantoic  arteries  and  veins,  which  pass  between  the  embryo  and  the 
placenta.  It  is  in  relation  at  first  with  the  amnion,  it  appears  to  be  entirely 
behind  the  embryo,  and  it  is  called  the  "  body-stalk."  At  a  later  period, 
when  the  stalk  of  mesoderm — the  allantoic  stalk — which  connects  it  with  the 
inner  surface  of  the  chorion  is  elongated,  this  part  of  the  embryonic  area  is 
reversed  in  position,  its  anterior  end  is  carried  forwards  till  it  forms  the  posterior 
boundary  of  the  umbilical  orifice,  and  the  area  in  question  forms  the  ventral  wall 
of  the  Ijody  from  the  umbilical  to  the  genital  region. 

Allantois. — The  allantois  plays  an  important  part  in  the  formation  of  the 
placenta.  It  consists  of  two  portions,  an  entodermic  diverticulum  Irom  the  ^■entral 
wall  of  the  cloacal  part  of  the  hind-gut,  and  a  mesodermal  covering.  The  ento- 
dermic diverticulum  appears  in  the  human  subject,  before  the  hind-gut  is  defined, 
as  a  hollow  blind  protrusion  from  the  blastodermic  cavity  ;  it  extends  behind  the 
primitive  streak  into  the  mesoderm  of  the  body-stalk,  but  as  the  folding  off  of  the 
embryo  proceeds,  and  the  body-stalk  is  carried  forward  into  the  ventral  wall  of  the 
embryo,  the  position  of  the  diverticulum  is  altered,  and  ultimately,  when  the 
folding  off  is  completed,  it  springs  from  the  ventral  part  of  the  cloaca,  runs  forward 
to  the  umbilical  orifice,  and  passing  through  it,  projects  for  a  short  distance  still 
invested  with  the  mesodermal  covering  primarily  obtained  from  the  body-stalk. 
The  ventral  part  of  the  cloaca  is  afterwards  converted  into  the  bladder,  while  the 
rectum  is  formed  from  the  dorsal  part. 

The  mesodermal  sheath  which  surrounds  the  entodermic  diverticulum  extends 
beyond  it  to  the  inner  surface  of  the  chorion  ;  the  part  which  extends  beyond  the 
diverticulum  is  at  first  extremely  short,  indeed  it  is  only  recognisable  as  a  layer  of 
mesoderm  uniting  the  body-stalk  and  chorion,  but  as  development  proceeds  and 
the  body-stalk  is  folded  forward  to  form  the  ventral  wall  of  the  body  of  the  embryo, 
posterior  to  the  umbilicus,  this  portion  of  the  mesoderm  is  elongated,  and  it  forms 
the  allantoic  stalk  by  which  the  embryo  retains  its  connexion  with  the  chorion, 
and  along  which  pass  the  allantoic  or  umbilical  arteries  to,  and  the  corresponding 
veins  from,  the  chorionic  villi. 

After  the  separation  of  the  cloaca  into  bladder  and  rectum,  that  portion  of  the 
allantois  which  lies  in  the  body  of  the  embryo,  between  the  apex  of  the  bladder 
and  the  umbilical  orifice,  is  gradually  converted  into  a  fibrous  cord,  the  urachus. 
The  entodermal  diverticulum  disappears,  and  after  birth,  when  the  placental  circu- 
lation ceases,  the  umbilical  arteries  are  transformed  into  fine  fibrous  strands.  The 
remainder  of  the  allantois  which  lies  outside  the  body  of  the  embryo,  and  which 
takes  part  in  the  formation  of  the  umbilical  cord  and  placenta,  is  separated  from 
the  embryo  at  birth. 

Umbilical  Cord. — The  umbilical  cord  is  essentially  a  mesodermal  structure 
which  connects  the  embryo  with  the  placenta,  serving  as  a  passage  for  the  allantoic 
vessels  to  and  from  the  fcetal  portion  of  the  latter  organ.  It  replaces,  functionally, 
the  body-stalk  and  the  allantoic  stalk,  which  were  earlier  provisions  for  the  same 
purpose,  and  it  is  formed  by  the  fusion  of  the  allantoic  stalk  with  part  of  the 
vitello-intestinal  duct  and  the  remains  of  the  yolk-sac. 

The  vitello-intestinal  duct  is  at  first  a  relatively  wide  channel  which  connects 
the  primitive  gut  with  the  yolk-sac ;  it  passes  through  the  imibilical  orifice.  In 
later  stages,  as  the  body-stalk  is  swung  round  into  the  ventral  wall  of  the  body, 
the  allantoic  stalk,  which  projects  from  the  end  of  the  body-stalk,  is  brought  into 
close  relation  with  the  distal  end  of  the  vitello-intestinal  duct  and  the  remains  of 
the  yolk-sac ;  the  mesodermal  constituents  of  the  three  structures  then  fuse 
together,  and  the  whole  is  surrounded  by  the  expanding  amnion.  In  this  way  the 
umbilical  cord  is  formed.  It  includes,  therefore,  the  allantoic  stalk  and  its  blood- 
vessels, together  with  the  remains  of  the  yolk-sac  and  its  stalk,  the  vitello-intestinal 
duct,  all  of  which  are  invested  and  bound  together  by  the  amnion. 

The  mesodermal  core  of  the  cord  forms  a  fibro-mucoid  tissue  known  as 
"  Wharton's  jelly,"  which  consists  of  stellate  and  irregular  cells  embedded  in  a 
gelatinous  matrix.  The  blood-vessels  of  the  cord  are  situated  in  the  core,  and 
include  two  allantoic  or  umbilical  arteries  which  run  spirally  round  a  single 
umbilical  vein.     The  terminal  portion  of  the  allantoic  diverticulum  projects  into 


52  GENEEAL  EMBEYOLOaY. 

the  embryonic  end  of  the  cord,  and  at  first  a  loop  of  intestine  protrudes   into  it  for 
a  short  distance ;  the  gut,  however,  soon  recedes  into  the  abdominal  cavity. 

The  umbihcal  cord,  which  extends  from  the  umbilical  orifice  to  the  centre  of  the 
placenta,  is  at  first  short  and  straight.  As  the  amnion  expands  the  length  of  the 
umbilical  cord  increases  until,  at  the  time  of  birth  it  measures,  on  an  average, 
about  20  inches.  This  increase  in  the  length  of  the  cord  allows  the  foetus  to  float 
freely  in  the  amniotic  fluid,  and  prevents  traction  on  the  placenta. 

After  the  middle  of  the  second  month  the  umbilical  cord  is  twisted  spirally, 
usually  from  right  to  left.  It  is  suggested  that  this  is  due  either  to  the  great 
elongation  of  the  allantoic  arteries  or  to  muscular  movements  of  the  foetus,  and  it 
involves  a  rotation  of  the  foetus  in  the  amniotic  fluid. 

Chorion. — The  chorionic  area,  by  far  the  largest  of  the  areas  into  which 
the  blastoderm  is  divisible,  lies  external  to  the  amniotic  area.  In  most  mammals 
it  consists  at  first  of  ectoderm  and  entoderm,  but  after  the  extension  and  cleavage 
of  the  mesoderm  has  taken  place,  it  is  formed  by  ectoderm  and  somatic  mesoderm. 
In  man,  however,  it  consists  in  the  earliest  stages  of  ectoderm  alone,  but  on  the 
formation  and  extension  of  the  mesoderm  it  also  acquires  an  inner  layer  of  somatic 
mesoderm.     In  all  cases,  therefore,  it  eventually  consists  of  the  same  two  layers. 

The  ectoderm  of  the  chorionic  area  which  immediately  surrounds  the  amniotic 
area  thickens  to  form  the  annular  placental  area,  and  in  this  way  the  chorionic  area 
becomes  divisible  into  placental  and  non-placental  regions. 

When  the  blastodermic  vesicle  enters  the  uterus  numerous  ectodermal  villous 
processes  grow  from  the  surface  of  the  chorionic  area,  both  in  its  placental  and  non- 
placental  parts,  and  attach  themselves  to  the  uterine  mucous  membrane.  As 
already  pointed  out  in  the  description  of  the  formation  of  the  amnion,  the  embryonic 
and  amniotic  areas  do  not  become  attached  to  the  uterus,  but  remain  free  from  it, 
whilst  by  the  approximation  and  fusion  of  its  inner  margins,  the  rapidly  growing 
ring-like  placental  area  is  converted  into  a  disc  which  intervenes  between  the 
amnion  and  the  uterine  wall. 

The  chorionic  area  after  the  separation  of  the  amnion  is  known  as  the  chorion 
or  chorionic  membrane. 

The  chorion  forms  the  outer  wall  of  a  vesicle,  the  chorionic  vesicle,  which  is  the 
modified  remains  of  the  blastodermic  vesicle,  and  which  contains  the  embryo,  the 
yolk-sac,  the  amnion,  and  the  allantois.  It  consists  of  an  outer  layer  of  ectoderm 
and  an  inner  layer  of  somatic  mesoderm. 

The  cavity  of  the  chorion  is  the  extra-embryonic  portion  of  the  ccelom.  Eor  a 
time  it  remains  distinct,  and  is  traversed  by  the  allantoic  stalk  which  unites  the 
embryo  to  the  inner  or  mesodermal  layer  of  the  placental  area.  The  cavity  is 
ultimately  obliterated  by  the  growth  of  the  amnion,  the  latter  sac  expanding 
rapidly  till  its  outer  surface  is  in  contact  and  intimately  blended  with  the  inner 
surface  of  the  chorion. 

Chorionic  Villi.  —  The  villous  processes  which  begin  to  grow  from  the 
surface  of  the  chorionic  area  before  it  is  separated  from  the  amnion  continue  to 
develop  after  the  separation  of  the  two  membranes  is  completed.  They  penetrate 
the  surrounding  uterine  tissues.  At  first  each  consists  of  ectoderm  only,  but  a 
core  of  vascular  mesoderm  is  soon  acquired.  The  villi  increase  in  size  and  in  com- 
plexity also,  but  ultimately  only  those  in  the  placental  area  persist  and  continue 
to  grow  ;  the  remainder  atrophy  and  disappear. 

Thus  the  placental  region  of  the  chorion  eventually  constitutes  the  main  bond  of 
union  between  the  ovum  and  the  mother,  and  it  forms  the  foetal  part  of  the  placenta. 

THE  PLACENTA. 

The  placenta  is  the  organ  of  foetal  nutrition  and  respiration. 

In  it  the  blood-vessels  of  the  foetus  and  those  of  the  uterus  are  brought  into 
such  close  relationship  with  one  another  that  free  interchanges  readily  take  place 
between  the  blood  of  the  mother  and  that  of  the  fcetus.  In  the  simplest  form  of 
placenta  the  foetal  villi  are  merely  embedded  in  the  maternal  mucous  membrane, 
and  the  relationship  between  foetal  and  maternal  blood  is  not  very  close.     In  other 


THE  PLACENTA. 


53 


forms,  e.(j.  ihe  huinau  placenta,  the  relation  of  fcetal  to  maternal  blood  is  much 
more  intimate  ;  this  involves  marked  complications  in  the  elements  of  the  placenta, 
and  its  strvicture  becomes  correspondingly  more  complex.  In  all  forms,  however, 
the  placenta  consists  of  fcetal  and  maternal  portions. 

Before  the  impregnated  ovum  reaches  the  uterine  cavity  the  mucous  membrane  of 
the  uterus  undergoes  certain  changes  in  preparation  for  its  reception  and  reten- 


Decidua.basalis 


Dilated  part\ 
l  Unrhaiiged  part 


liirlianged  layer 

Stratum  siioiigiosuiii  i  uterine 

.Stratum  compactuin  /'""f^o^a 


Ectoilf'rmal  villus  enclosing 
jiaee  containing  maternal 

blood 


mass  (Entoderm) 


Gland- 


Unchanged 
Dilated 


Fig.  39. — Diagram  reineseiitiug  a  very  young  human  ovum  almost  immediately  after  its  entrance  into  the 
decidua,  and  whilst  the  place  of  its  entrance  is  still  covered  with  a  plug  of  tibrin.  The  ectoderm  has 
already  proliferated  and  embraced  spaces  which  contain  maternal  bloo<l  and  are  continuous  with  the 
maternal  blood-vessels. 

tion,  and  the  modified  mucous  membrane  is  known  as  the  uterine  decidua.  These 
changes  are,  for  the  most  part,  hypertrophic  ;  the  vascularity  of  the  mucous  mem- 
brane is  increased  mainly  by  the  dilatation  of  its  veins  and  capillaries,  the  tubular 
uterine    glands     become 

1  ,      1      •  1  1  Decidua  hasalis 

elongated,  irreo-ular,  and 
tortuous,  and  they  dilate 
both  at  their  orifices  and 
in  the  deeper  part  of  the 
mucous  membrane ;  at  the 
same  time  the  inter - 
glandular  connective  tis- 
sue proliferates,  and  as  a 
result  the  decidua  is 
thicker,  softer,  and  more 
spongy  than  the  unaltered 
mucous  membrane. 

After  the  developing 
ovum  enters  the  uterus 
it  comes  into  contact 
with  the  decidua,  into 
which  it  forces  its  way 
destroying  the  surface 
epithelium,  and  destroy- 
ing, or  pushing  aside,  the 
superficial  portions  of  the 
glands.  In  this  way  it 
becomes   embedded    in    the  vascular  interglandular  tissue 


Unchanged  layer  \  jytpvine 

-^-*""i  spongiosum  '.       ,™.l 

^     °  /  mucosa 

atuni  comiiactuni ) 
Blood-vessel 


Ectoilermal  villus 


Inner  cell-mass 
(Entoderm) 


Decidua  vera 


Px,;.  40. — DiAcHAM,  showing  the  relation  of  the  young  human  ovum  to 
the  decidua. 

The  ectoderm  is  distinct  from  the  inner  cell-mass,  but  as  yet  there  is  no 
entodermal  cavity  in  the  latter. 


The  orifice  which  it 
makes  in  the  superficial  surface  of  the  decidua  is  plugged,  for  a  time,  by  a  mass  of 
fibrin,  but  all  traces  of  the  aperture  which  the  fibrin  closes  eventually  disappear 
and  the  ovum  is  entirely  encapsuled  in  the  decidua,  which  again  presents  an 
unbroken  surface  towards  the  uterine  cavity. 
4a 


54 


GENEEAL  EMBEYOLOGY. 


Pecidua  basalis 


Unchanged  layer 

Stratum  spongiosum 
Stratum  coiiipactum 

Placental  vilhi 


Primitive  streak 
Mesoderm 


Placental  \-illus 


Cavity  whicl 
becomes  ccelom 


Decidua  vera 


Decidua  vera 


Fig 


Immediately  after  tl:e  ovum  becomes  embedded  the  superficial  ectoderm  cells  of 
its  surface  proliferate  rapidly  and  form  numerous  branching  processes  or  villi  which 
invade  the  surrounding  decidua,  destroying  its  cells  and  gradually  enclosing  the 

maternal     blood     spaces 

Jlaternal  vessel  witll      wMcll      they     COmC 

into  relation.  After  a 
time  the  maternal  tissues 
which  at  first  surrounded 
the  maternal  blood  spaces 
entirely  disappear,  and 
from  this  period  onwards 
the  maternal  blood  circu- 
lates in  the  spaces  in  the 
foetal  ectoderm.  After  a 
time  the  proliferation  of 
the  ectodermal  villi  be- 
comes most  marked  im- 
mediately around  the 
margin  of  the  amniotic 
area  of  the  ovum,  and 
thus  a  placental  area  of 
the  chorion  is  differ- 
entiated. In  the  mean- 
time the  expanding  ovum 
has  forced  the  decidua  on 
its  superficial  surface  to- 
wards the  cavity  of  the 

uterus,  and  at  this  period  three  areas  of  the  decidua  can  be  distinguished.     The 

part   outside   the  ovum,    that  is   between  the   ovum   and    the  muscular  wall  of 

the  uterus,  is  known 

as  the  decidua  basalis  ;  Ty„„>„„„..i  lo,,.,.        Decidnp.  basaiis 

the  part  pushed  into 
the  cavity  of  the 
uterus  around  the 
growing  ovum  is  the 
decidua  capsularis ;  and 
the  remainder  of  the 
decidua  is  the  decidua 
vera. 

The  decidua  cap- 
sularis is  not  formed, 
as  was  formerly  be- 
lieved, by  folds  of  the 
decidua  which  have 
grown  up  and  sur- 
rounded an  ovum 
merely  attached  to 
the  surface  of  the 
decidua  basalis.  On 
the  contrary  it  is 
merely  the  superficial 
part  of  that  portion 
of    the   decidua   into 


41. — Diagram,  sliowing  a  further  stage  of  developnient  of  the  human 
ovum  and  its  relation  to  the  decidual  tissues.  The  entoderuial  cavity 
or  yolk-sac  has  appeared  in  the  inner  cell -mass,  and  the  mesoderm 
has  commenced  to  extend  from  the  primitive  streak  in  two  layers, 
splanchnic  on  the  yolk-sac  and  somatic  on  the  ectoderm. 


Unchanged  layer 
Stratum  spongiosum 
Stratum  compactu 


Placental  villus 


Maternal  \'essel 


Body-stalk 


Coelom 


Ectoderm 

Somatic 

mesoderm 

Entoderm 

Splanchnic 

mesoderm 


Decidua  vera 


Decidua  vera 


Fig. 


42. — Diagram,  showing  the  completion  of  the  decidua  capsularis,  the 
enlargement  of  the  maternal  blood-vessels  in  the  stratum  compactum  of 
the  decidua  basalLs,  the  increase  of  the  placental  villi,  the  formation  of 
the  amnion  folds,  and  the  appearance  of  the  allantoic  diverticulum. 

which  the  ovum  has  penetrated,  theretbre  it  may  contain  glands  or  the  remains  of 
glands  which  open  on  its  superficial  surface  into  the  uterine  cavity,  but  no  glands 
open  on  its  inner  surface. 

The  decidua  basalis  lies  in  contact  with  the  placental  area  of  the  chorion,  i.e. 
the  foetal  part  of  the  placenta,  and  it  forms  the  maternal  part  of  the  organ.  In 
the  fully  developed  human  placenta,  the  fcetal  and  maternal  tissues  of  which  it 


THE  PLACENTA. 


55 


Unchanged  layer 
Stratum  spongiosum 
Stratum  compactum 


Amnion 

Matprnal  blood-vessel 

Fuetal  ectoderm  villus, 
enclosing  space  filled 
witli  maternal  blood 


Allantoic 
diverticulum 

Ectoderm 

Somatic 
mesoderm 
Splanchnic  mesoderm 
Entoderm 


Decidua 


Decidua  vera 


DiAGEAM,  showing  enlargement  of  the  blood  sinuses  in  the  maternal 
part  of  the  placenta  and  the  closnre  of  the  amnion. 


is  formed  are  so  intimately  mingled  and  blended  together  that  it  is  impossible 
to  say  where  one  ends  and  the  other  begins.  By  a  careful  study,  however,  of  a 
series  of  placentae  of  different  ages  a  fairly  clear  and  satisfactory  idea  of  the  part 
})layed  by  the  maternal 
and  the  fcetal  elements 
respectively,  as  well  as 
of  their  relations  to  each 
other,  may  be  obtained. 
The  structural  char- 
acters of  the  completed 
organ  will  be  best  under- 
stood if  the  two  con- 
stituent parts  are  first 
considered  separately. 

Fcetal  Part  of 
the  Placenta.  —  The 
villi  of  the  placental 
portion  of  the  chorion 
invade  and  penetrate 
the  decidua  basalis, 
whilst  the  villi  of  the 
non-placental  chorionic 
area  of  the  ovum  enter 
the  decidua  capsularis. 
As  previously  ex- 
plained, in  connexion  fig.  43 
with  the  formation  both 
of  the  amnion  and  of 

the  chorion,  the    annular  placental    area   is  converted   into   a  circular  disc.     It 
consists,  like  the  rest  of  the  chorion,  of  ectoderm  and  mesoderm,  and  it  contains 

ramificationsof  the 
allantoic  vessels ; 
but  the  ectoderm 
is  thickened  and 
increased,  its  villi 
are  larger  than 
those  of  the  non- 
placental  region 
of  the  chorion,  and 
it  is  directly  con- 
nected with  the 
allantoic  stalk. 
The  early  villi 

■  i.entary  canal  g^j,g      merely      CCtO- 

Yoik-sac  dermal  buds  which 
penetrate  the  sur- 
rounding decidual 
tissues,  destroying 
and  replacing  the 
uterine  elements. 
These  villi  grow 
and  branch,  and 
their  Vjranches  an- 
astomose together 

Fig.  44. — Diagram,  showing  the  fcetal  ectoderm  surrounding  the  maternal  blood  Surrounding  the 
sinuses,  the  commencement  of  secondary  fcetal  villi  which  project  into  the  ])lood  SpaceS  of  the 
sinuses,  and  the  disappearance  of  the  superficial  portions  of  the  glands.  i      •  i  i  •    i, 

decidua  which  are 
in  the  immediate  neighbourhood  of  the  ovum.  As  development  proceeds  every 
ectodermal  villus  is   penetrated   Ijy   an    outgrowth    of   the   subjacent   mesoderm 


Decidua  basalis 


Unchanged  layer 


Placental v 


Maternal  blood  sinus 
Maternal  vessel 


Placental  villus 

Allantoic  stalk 


Foetal  villus 


Allantoic 
diverticulum 
Primitive  ali- 


Ectoderm 
Somatic  mesoderm 
Splanchnic  mesoderm 
Entoderm 


Decidua  vera 


56 


GENEEAL  EAIBEYOLOGY. 


Decidua  basalis 


Unchanged  layer 

Stratum 
spongiosum 

Stratum 
compactuin 


Maternal  blood  sinus 


Foetal  villus 


Body-.stalk 


which  carries  branches  of  thf  allantoic  vessels,  and  so  the  villi  become  vascularised 
with  foetal  blood.  ¥ov  some  time  all  the  vilH,  placental  and  non-placental,  grow  and 
absorb  nutriment  from  the  maternal  tissues,  probably  utihsing  as  food  the  tissues 
which  they  destroy  and  replace :  but  when  the  decidua  capsularis  is  thinned  by 
the  expansion  of  the  growing  ovum,  the  vilh  of  the  non-placental  region  which 
have  penetrated  it  are  no  longer  able  to  obtain  nutrient  matter,  and  they  con- 
sequently atrophy  and  disappear.  The  placental  vilh,  on  the  contrary,  continue  to 
increase  ;  they  grow  in  size  and  become  more  complex,  and  secondary  branches 
growing  i'rom  them  project  into  the  maternal  blood  spaces  which  they  have 
surrounded  and  float  in  the  maternal  blood.     When  the  formation  of  the  placenta 

is  completed,  its 
foetal  part  consists 
of  vilh,  each  of 
which  possesses  an 
external  covering 
of  two  layers  of 
ectodermal  cells 
and  a  vascular 
mesodermal  core ; 
the  villi  project 
into  the  interior 
of  large  blood 
spaces  which  are 
surrounded  more 
dnertfcuium  01'  Isss  Completely 
by  foetal  ectoderm, 
and  they  are  bathed 
by  maternal  bloo 
from  which  they  ol 
tain  the  materiaJ 
necessary  for  the 
nutrition  and 
growth  of  the  em- 
bryo, and  into 
which  they  trans- 
mit the  effete  ex- 
cretory matters 
from  the  embryo. 

Maternal 
Part  of  the  Pla- 
centa    and     the 

Changes  in  the  Decidua. — The  occurrence  of  further  changes  in  the  decidua,  after 
the  developing  ovum  enters  the  uterus,  is  dependent  upon  the  retention  of  the 
ovum  in  the  substance  of  the  decidua.  These  changes  only  occur,  therefore,  in 
what  may  be  termed  the  decidua  of  pregnancy.  They  are  intimately  associated 
with  and  essential  to  the  development  of  the  maternal  part  of  the  placenta,  and 
a  more  detailed  and  complete  account  of  the  decidua  and  the  modifications  of  its 
several  yjarts  is  therefore  necessary. 

The  decidua  is  formed  by  the  mucous  membrane  of  the  uterus,  which  is  a  hollow, 
thick- walled  muscular  organ,  situated  in  the  pelvic  cavity.  The  mucous  membrane 
contains  numerous  tubular  glands  embedded  in  an  interglandular  tissue  formed  of 
round  and  irregular  cells.  The  uterine  glands  are  lined  by  a  columnar  or  cubical 
epithelium,  and  they  open  into  the  cavity  of  the  uterus  on  a  surface  which  is  also 
covered  by  columnar  cells.  The  whole  of  the  mucous  membrane  is  plentifully 
supplied  with  blood-vessels  which  pass  into  it  from  the  surrounding  muscular 
walls,  and  it  is  transformed  into  the  decidua  by  proliferation  and  hypertrophy  of 
all  its  parts.  The  interglandular  tissue  increases  in  amount  and  its  blood-vessels 
dilate,  especially  near  the  surface  of  the  membrane :  but  the  most  striking  of  the 
early   changes   occur   in    the   glands — they   become   longer,  more  tortuous,  their 


Yolk-sac 


Cceloi 


Somatic 
mesodenn 

Splanclinie 
mesoderni 


Entoderm 
Decidua  caijsularis 


Decidua  vera 


Fio.  45. — Diagram,  showing  further  growth  of  the  placental  .sinuses  and  villi  ;  the 
fusion  of  the  decidua  capsularis  with  the  decidua  vera,  and  the  obliteratiou  of 
the  uterine  cavity. 


THE  PLACENTA.  57 

apertures  enlarge  and  assume  a  funnel-like  appearance,  and  they  dilate  a  short 
distance  from  their  terminations  into  large  irregular  spaces.  The  increase  of 
the  interglandular  tissue  is  most  marked  in  the  intervals  between  the  dilated 
portions  of  the  glands  and  their  apertures,  and  when  all  the  changes  are  fully- 
established  it  is  possible  to  recognise  three  layers  of  the  decidual  tissue.  (1)  A 
sviperficial  relatively  thick  layer  in  which  the  interglandular  tissue  preponderates, 
the  stratum  compactum ;  (2)  A  layer  formed  principally  by  the  dilated  portions 
of  the  glands,  the  stratum  spongiosum ;  and  (3)  a  thin  deep  part  of  the  membrane 
which  contains  the  outer  extremities  of  the  glands  which  are  practically  unchanged, 
the  unchanged  layer. 

The  decidua  capsularis  differs  from  the  other  portions  of  the  decidua  in  that 
it  represents  only  the  superficial  portion  of  the  other  parts  of  the  decidua,  and 
therefore  contains  no  spongy  layer  or  deep  unchanged  layer.  This  is  obviously  the 
case,  for  after  the  ovum  has  penetrated  through  the  surface  epithelium  it  becomes 
embedded  in  the  stratum  compactum  of  that  portion  of  the  decidua  which  it  has 
invaded,  and  consequently  the  portion  of  the  stratum  which  closes  over  it  cannot 
contain  more  than  the  outer  parts  of  some  of  the  uterine  glands  with  their  orifices 
and  the  intervening  interglandular  tissue. 

The  changes  which  occur  in  the  decidua  capsularis  are  due,  first,  to  its 
connexion  with  and  invasion  by  the  chorionic  villi;  and,  secondly,  to  the  pressure 
exerted  upon  it  by  the  enlarging  ovum.  The  former  influence  is  brought  to  bear 
whilst  the  decidua  is  still  increasing ;  the  latter  after  it  has  reached  its  full 
development. 

The  changes  which  result  from  its  union  with  the  chorion  are  the  destruction 
and  absorption  of  some  of  the  interglandular  tissue ;  they  are  due  to  the  activity 
of  the  ectodermic  cells  of  the  chorion,  which  attack  and  invade  the  uterine  tissues. 

The  changes  due  to  pressure  exerted  by  the  enlarging  ovum  are  diminution  of 
vascularity,  disappearance  of  the  lumina  of  such  portions  of  the  glands  as  remain  in 
the  decidua  capsularis,  and  the  removal  of  their  epithelium,  together  with  the  co- 
incident atrophy  of  the  fatal  villi  which  have  penetrated  this  portion  of  the  placental 
decidua.  All  these  changes  result  in  the  reduction  of  the  decidua  capsularis  to  a 
thin  membrane  in  which  no  traces  of  the  original  structure  are  recognisable,  in  the 
fusion  of  the  altered  decidua  capsularis  with  the  decidua  vera,  and  the  consequent 
obliteration  of  the  uterine  cavity. 

After  the  fifth  month  the  decidua  vera  also  undergoes  atrophic  changes,  but  they 
do  not  proceed  so  far  as  in  the  decidua  capsularis ;  nevertheless  the  stratum  com- 
pactum is  greatly  reduced,  the  superficial  epithelium  and  the  superficial  parts  of 
the  glands  entirely  disappear  from  it,  the  interglandular  tissue  becomes  less 
vascular,  and  it  diminishes  very  considerably  in  thickness.  The  epithelium  dis- 
appears from  the  spaces  in  the  spongy  layer,  and  the  spaces  themselves  are 
flattened  out  into  long  slit -like  clefts,  in  which  condition  they  remain  till 
the  period  of  pregnancy  is  completed.  The  decidua  vera  is  thus  reduced  to  the 
condition  of  a  relatively  thin  membrane,  and  its  inner  surface  is  fused  with 
the  remains  of  the  decidua  capsularis. 

Decidua  Basalts. — This  portion  of  the  decidua  is  constituted  by  the  deeper 
part  of  the  stratum  compactum  in  which  the  ovum  is  embedded  together  with 
the  more  externally  situated  spongy  and  unchanged  layers,  and,  apart  from  the 
changes  due  to  the  invasion  of  the  foetal  villi,  the  most  important  transformations 
in  this  part  of  the  decidua  occur  in  the  stratum  compactum.  The  alterations  in 
the  spongy  layer  are  similar  to  those  which  occur  in  the  same  layer  of  the  decidua 
vera,  viz.  the  lining  epithelium  disappears  and  the  spaces  are  flattened  out  into  a 
layer  of  cleft-like  slits. 

In  the  stratum  compactum,  however,  much  more  striking  changes  occur ;  all 
traces  of  the  glands  disappear,  Imt  the  blood-vessels  become  greatly  dilated,  and, 
consequently,  the  layer  increases  considerably  in  thickness.  The  small  blood-vessels 
which  lie  in  the  immediate  neighbourhood  of  the  ovum  become  converted  into 
enormous  blood  sinuses,  but  in  the  deeper  part  of  the  stratum  a  thin  layer,  which 
lies  next  the  stratum  spongiosum,  remains  relatively  unchanged ;  this  deeper  part 
is  called  the  basal  layer,  and  through  it  the  blood-vessels  pass  to  and  from  the 


58 


GENEEAL  EMBRYOLOGY 


blood  sinuses  in  the  more  superficial  portion  of  the  membrane.  When  it 
is  completed,  therefore,  the  maternal  portion  of  the  placenta,  which  is  the 
transformed  decidua  basalis,  no  longer  consists  of  the  stratum  compactum,  the 
stratum  spongiosum,  and  the  unchanged  layer,  but  it  is  formed  from  within 
outwards  of — (1)  a  layer  of  blood  sinuses,  (2)  the  basal  layer,  (3)  the  modified 
spongy  layer,  and  (4)  the  unchanged  layer.  The  difference  between  the  decidua 
basalis  and  the  maternal  part  of  the  placenta  may  be  tabulated  as  follows : — 


Decidua  basalis. 

Deep  part  of  stratum  compactum 

Stratum  spongiosum 
Unchanged  layer 


Maternal  placenta. 

Layer  of  blood  sinuses. 
Basal  layer. 

Modified  stratum  spongiosum. 
Unchanged  layer. 


Placenta 


Unchanged  layer 

stratum 
■sponglo■^um 

Stratnra 


Placental  \  illus 


It  must  not  be  forgotten,  however,  that  whilst  the  changes  which  result  in  the 
formtvtion  of  the  maternal  placenta  out  of  the  decidua  basalis  are  taking  place  the 
stratum  compactum  has  been  invaded  by  the  placental  villi. 

The  first  result  of  this  invasion  is  the  destruction  of  much  of  the  decidual  tissue  by 

the  ectoderm  of 
the  foetal  villi. 
Gradually  the  ec- 
toderm of  the  villi, 
always  in  advance 
of  the  main  body, 
reaches  and  sur- 
rounds the  dilated 
decidual  vessels, 
destroys  the  in- 
tervening tissues, 
and  ultimately  re- 
places the  endo- 
thelial walls  of  the 
vessels,  which  by 
this  time  have 
dilated  into  enor- 
mous spaces.  Into 
these  spaces  the 
ramifications  of 
the  villi  project, 
and,  as  the  endo- 
thelial walls  are 
destroyed,  they  lie 
directly  within 
the  cavities  of  the 
spaces,  and  are 
surrounded  on  all 
sides  by  maternal 
blood.  The  most 
peculiar  feature  of 
this  part  of  the 
placenta,  when 
fully  developed,  is 
that  the  whole  of 
the  maternal  por- 
tion of  it,  except 
the      blood,     has 

been  removed  and  replaced  hj  fcetal  tissues,  so  that,  although  the  maternal 
blood  continues  to  circulate  in  the  same  spaces  wliich  it  has  occupied  from  the 
first,  viz.  the  blood  sinuses  in  the  more  superficial  part  of  the  stratum  compactum  of 
the"  maternal  decidua,  yet  the  walls  of  these  spaces  have  been  replaced  more  or  less 


Yolk-sac 


Peri- 
cardium 


decidua  cap- 
s  and  decidua 


Fused  mesoderm  of 
amnion  and  cliorion 


Fig.  46. — Diagha.m.  Later  stage  in  the  developmeut  of  the  placenta,  showing  the 
relations  of  the  fcetal  villi  to  the  placental  sinuses,  the  fusion  of  the  amnion  with 
the  inner  surface  of  the  chorion,  and  the  thinning  of  tlie  fused  deciduic  (cap- 
sularis  and  vera). 


THE  PLACENTA.  59 

completely  by  fcetal  ectoderm,  and,  consequently,  the  spaces  now  lie  in  the  midst  of 
the  foetal  tissues. 

The  invasion  of  the  maternal  by  the  foetal  part  of  the  placenta  proceeds  as  far 
as  the  basal  layer,  and  in  this  region  the  foetal  ectoderm  is  directly  continuous  with 
the  walls  of  the  maternal  blood-vessels  at  the  points  where  they  enter  the  sinuses. 

Although  the  invasion  of  the  decidua  basalis  is  so  complete,  some  portions  of 
the  maternal  tissues  persist ;  thus  the  basal  layer  and  many  strands  of  the  stratum 
compactum  escape  destruction.  The  latter  extend  from  the  basal  layer  to  the  outer 
surface  of  the  chorion,  and  they  are  eventually  converted  into  fibrous  strands,  which 
divide  the  superficial  part  of  the  completed  placenta  into  lobular  areas. 

The  completed  placenta  consists,  therefore,  of  closely  intermingled  and  fused 
foetal  and  maternal  tissues,  through  which  both  the  fcetal  and  maternal  blood 
streams  circulate.  It  is  well  adapted,  on  account  of  its  peculiarities  of  structure,  to 
fulfil  the  nutritive  and  respiratory  requirements  of  the  embryo.  The  fcetal  blood 
stream  which  flows  through  the  placental  villi  and  the  maternal  blood  stream  in 
the  placental  sinuses  are  only  separated  irom  each  other  by  two  layers  of  fcetal 
ectodermal  epithelium  and  a  small  amount  of  foetal  mesoderm,  the  latter  being 
practically  reduced  to  the  single  layer  of  endothelial  cells  which  form  the  walls  of 
the  fcetal  vessels.  Through  these  layers,  by  osmosis,  and  possibly  by  secretion, 
materials  are  passed  ijoth  from  mother  to  embryo  and  from  embryo  to  mother,  the 
placenta  ser\dng  not  only  for  purposes  of  nutrition  and  respiration,  but  also  as  an 
excretory  organ. 

Whilst  tlie  placenta  is  attaining  its  full  development  the  amnion  is  expanding, 
and  finally  its  outer  surface  fuses  with  the  inner  surface  of  the  chorion,  consequently, 
the  innermost  portion  of  the  placenta  is  provided  with  a  covering  of  amnion. 

The  full-time  placenta  is  a  discoid  mass  about  20  or  25  inches  (50  to  60  cm.)  in 
circumference  and  1\  in  thickness  at  its  centre  ;  it  is  much  thinner,  however, 
at  its  margins,  where  it  is  continuous  with  the  membranes  formed  by  the  fused 
chorion,  decidua  vera,  and  decidua  capsularis.  Its  weight  is  about  one  pound,  and 
it  consists  from  within  outwards  of  the  following  layers  : — 


Fcetal 


,        .  f   Ectoderm. 

Amnion     .  .  .  .  .  •       i   at      ^ 

(   Mesoderm. 

Allantois  with  foetal  vessels  .  .  .  Mesoderm. 

I    Mesoderm. 


Chorion 


Ectoderm. 


Layer  of  maternal  blood  sinuses  and  remains  of  the  intergiandular 
tissue  of  the  stratum  compactum. 
Maternal  -{    Basal  la^^er. 

Modifiecl  spongy  layer. 
Unchanged  layer. 

When  the  period  of  intrauterine  life  is  completed  the  muscular  walls  of  the 
uterus  contract  and  the  lower  orifice  of  the  uterine  cavity  is  dilated,  the  fused 
chorion  and  amnion,  which  close  the  upper  part  of  the  orifice,  rupture  and  the 
amniotic  fluid  escapes,  the  foetus  is  then  expelled,  but  it  remains  attached  to  the 
placenta  by  the  umbilical  cord.  The  cord  is  divided  artificially,  and  after  a  short 
period  the  placenta  and  membranes  are  expelled.  The  membranes  attached  to  the 
placenta  consist  of  the  fused  amnion,  chorion,  decidua  capsularis,  and  also  the 
decidua  vera  internal  to  the  altered  spongy  layer ;  therefore  both  the  placenta  and 
the  membranes  consist  of  maternal  and  fcetal  tissues.  Before  the  placenta  and 
membranes  are  expelled  the  uterine  decidua  is  separated  into  two  parts  by  a 
cleavage  which  takes  place  in  the  modified  stratum  spongiosum.  The  inner  portion 
which  inclucies  the  placenta  and  membranes  is  cast  off.  The  outer  portion  remains 
in  the  uterus ;  it  consists  almost  entirely  of  the  deep  unchanged  layer  of  the 
decidua,  and  from  it  the  uterine  mucous  membrane  is  reconstructed. 


CO  GENERAL  EMBRYOLOGY. 

THE    PRIMITIVE    VASCULAR   SYSTEM   AND    THE   FffiTAL 

CIRCULATION. 

It  has  already  been  said  that  the  ovum  during  its  passage  down  the  Fallopian 
tube  lives  either  on  its  own  yolk  particles  or  upon  substances  absorbed  from  the 
tiuids  by  which  it  is  surrounded.  For  a  time  after  it  enters  the  uterus  its  nutrition 
must  be  provided  for  in  a  similar  manner,  but  as  soon  as  the  chorionic  villi  are 
formed  it  is  probable  that  the  ectodermal  cells,  of  which  in  the  earliest  stages  they 
entirely  consist,  and  which  cover  their  surfaces  in  the  later  stages,  actually  eat  up 
the  decidual  tissues  which  they  invade  and  use  them  for  food.  This  source  of 
nutrition,  however,  is  only  sufficient  for  the  short  period  during  which  the  ovum 
remains  relatively  small,  and  substances  absorbed  through  the  surface  cells  can  be 
readily  transmitted  to  all  its  parts. 

In  addition  to  the  solid  decidual  tissues  devoured  by  the  ectodermal  cells  it  is 
evident  that  fluids  from  the  mother  are  also  absorbed,  for  the  yolk-sac  and  coelom 
enlarge  and  are  filled  with  fluid.  The  only  sources  from  which  this  can  have  been 
derived  are  the  uterine  glands  or  the  blood  and  lymph  vessels  of  the  decidua. 

In  all  probability  the  fluids  absorbed  into  the  ovum  contain  nutritive  material, 
and  so  long  as  the  embryo  is  constituted  by  the  thin  layers  of  the  early  blastoderm 
sufficient  food  material  can  easily  be  absorbed.  When,  however,  the  various  parts 
of  the  embryo  increase  in  thickness  and  become  moulded  into  the  form  of  organs 
they  are  no  longer  in  such  intimate  relation  with  the  surrounding  nutritive  fluids, 
whilst,  further,  as  their  development  progresses  they  require  a  greater  amount  of 
food  and  oxygen  than  they  can  obtain  from  these  fluids.  There  is,  therefore,  an 
imperative  necessity  for  a  further  supply  of  nutritive  material  by  which  their  re- 
quirements may  be  satisfied,  failing  which,  development  must  cease  and  death  ensue. 

To  meet  this  necessity  the  vascular  system  is  formed.  It  is  essentially  an 
irrigation  system  consisting  of  a  propulsive  organ,  the  heart,  and  of  tubular 
vessels,  the  blood-vessels,  all  of  which  contain  blood.  The  heart  propels  the  blood 
through  the  blood-vessels  to  all  parts  of  the  embryo,  but  the  blood  which  is  at  first 
formed  from  the  mesoderm  of  the  ovum  must,  at  least  so  far  as  its  fluid  part  is 
concerned,  be  supplemented  largely  from  maternal  sources.  It  is  necessary,  there- 
fore, that  the  foetal  blood-vessels  be  brought  into  close  relation  with  the  maternal 
blood-vessels  at  an  early  period.  It  is  for  this  purpose,  amongst  others,  that  the 
large  blood  sinuses  are  formed  in  the  maternal  portion  of  the  placenta,  and  that 
they  are  surrounded  and  invaded  by  the  fcetal  villi,  carrying  in  their  interior 
branches  of  the  foetal  blood-vessels,  and  as  previously  shown,  the  foetal  blood- 
vessels in  the  placenta  are  only  separated  from  the  maternal  blood  in  the  sinuses 
by  their  own  thin  mesodermal  walls,  and  by  one  or  two  layers  of  ectodermal  cells. 
When  the  placenta  is  fully  formed  fluids  can  readily  pass  from  the  maternal  to 
the  f(etal  vessels,  and  there  can  be  no  doubt  that  both  food  and  oxygen  pass  from 
the  maternal  blood  to  the  foetal  blood  through  and  by  the  agency  of  the  .intervening 
cells,  whilst  at  the  same  time  the  waste  products  which  are  formed  in  the  embryo 
pass  outwards  to  the  maternal  blood. 

Ob\T.ously,  however,  a  system  of  vessels  filled  with  fluid  would  be  of  little  use 
in  the  general  economy  unless  there  were  some  means  by  which  the  fluid  could  be 
kept  in  constant  movement.  In  the  first  instance  this  is  accomplished  by  rhythmical 
contractions  of  the  vessel  walls,  but  in  a  short  time  portions  of  the  two  primitive 
stem-vessels  which  appear  in  the  embryo  are  modified  into  a  single  propulsive 
organ,  the  heart,  which  forces  the  fluid,  or  blood,  in  a  definite  direction  both 
through  the  body  of  the  embryo,  along  the  body-stalk  or  umbilical  cord,  accord- 
ing to  the  age  of  the  embryo,  and  through  the  vessels  in  the  placental  villi. 

We  have  now  to  consider  how  the  blood-vessels  and  blood  are  formed. 

Where,  or  how,  the  first  blood-vessels  appear  in  the  human  subject  is  not 
definitely  known,  but  in  other  mammals  they  are  first  seen  outside  the  body  of 
the  embryo  in  the  wall  of  the  yolk-sac.  The  outer  layer  of  the  wall  of  the  yolk- 
sac  consists  of  splanchnic  mesoderm,  and  in  that  part  of  this  layer  which  lies 
nearest  the  j>rimitive  alimentary  canal  a  large   num})er  of  the  cells  proliferate 


PEIMITIVE  VASCULAR  SYSTEM  AND  FGETAL  CIRCULATION.     61 


rapidly  and,   fusing    together,    form   multi-nucleated   masses   of  protoplasm,  the 
"  blood  islands  "  of  I'ander. 

Soon  after  their  appearance  the  blood  islands  anastomose  together  by  means  of 
nucleated  processes  which  they  throw  out  on  all  sides,  and  thus  a  nucleated  proto- 
plasmic reticulum  is  formed  in  the  substance  of  the  splanchnic  mesoderm.  The 
region  in  which  this  occurs  is  known  as  the  vascular  area.  The  solid  nucleated 
reticulum  is  soon  converted  into  a  system  of  anastomosing  canals,  the  primitive 
blood-vessels,  by  the  ap- 
pearance within  it  of  ^.^'Y^^iM^rvrTT'raTAC:,,,,,  ^ 
numerous   vacuoles  w'hich                   ^v^/r^-avv^r-'A.^sieii^aurss^irsKr.j^fv'*      ^.^t 

soon  fuse  together,  whilst 
at  the  same  time  the  nu- 
cleated protoplasm  is  trans- 
formed into  cells.  The  cells 
which  lie  nearest  the  in- 
terior separate  from  each 
other  and  form  the  primi- 
tive blood -corpuscles, 
whilst  those  situated  ex- 
ternally remain  connected 
by  their  margins  and  form 
the  endothelial  walls  of  the 
embryonic  vessels.  The 
fluid  which  fills  these  first- 
formed  vessels  in  the  vas- 
cular area  is  probably  de- 
rived either  from  thecoelom 
or  from  the  yolk-sac. 

The  primitive  blood - 
corpuscles  are  nucleated 
cells  of  a  reddish  colour ; 
white  or  colourless  blood- 
corpuscles  appear  later,  and 
it  is  statecl  that  those 
first  formed  are  developed 
in  the  thymus  gland. 

Nucleated  red  cor- 
puscles persist  and  increase 
in  number  till  the  end  of 
the  second  month  of  in- 
trauterine life ;  they  are 
then  gradually  replaced  by 
non-nucleated  red  corpus- 
cles. The  majority  of  the 
nucleated  red  corpuscles  disappear  long  before  birth,  but  a  few  can  usually  be  found 
in  the  blood  of  the  new-born  child.  There  is  some  doubt  about  their  ultimate  fate, 
but  it  is  generally  believed  that  their  nuclei  disappear,  and  that  they  are  converted 
into  non-nucleated  corpuscles. 

Directly  after  the  appearance  of  the  blood  islands  in  the  vascular  area  of  the 
yolk-sac,  and  just  as  the  folding  off  of  the  embryo  commences,  two  short  tubular 
vessels  appear  in  the  splanchnic  layer  of  the  pericardial  mesoderm.  These  vessels 
at  once  extend  forwards  and  outwards  into  the  extra-embryonic  region  where  they 
become  .connected  with  the  vessels  of  the  vascular  area ;  they  also  extend  back- 
wards in  the  body  of  the  embryo  beneath  the  protovertebral  somites.  In  the 
majority  of  mammals  they  at  first  terminate  behind,  as  in  front,  on  the  wall  of  the 
yolk-sac,  but  after  a  time  the  main  stems  appear  to  be  continued  along  the  allantoic 
stalk  to  the  placenta,  whilst  they  give  off  branches  to  the  yolk-sac.  It  is  probable 
that  in  the  human  embryo  also,  though  this  has  not  apparently  been  actually 
observed,  these  main  stem  vessels,  the  primitive  aortse,  end  at  first  on  the  wall  of 


BV2 


Fig.  47. — Development  of  Blood-Vessels  in  the  Yasculae  Area  op 
THE  Rat. 

I.  Entoderm  and  splaiichuic  mesoderm. 
II.  Proliferation    of   cells  of   mesoderm  and  formation   of    "blood 
islands." 
III.  Commencing  differentiation  of  islands  to  form  blood-vessels  and 
blood-corpuscles. 


IV.  Completed  vessels. 
BC  Blood-corpuscles. 
BI   Blood  islands. 
BVj  Blood  islands  being  trans- 
formed into  blood-vessels. 


BVo  Blood-vessels. 


EN  Entoderm. 
M  Mesoderm. 


62 


GENEEAL  EMBEYOLOGY. 


the  yolk-sac,  but  on  the  fourteenth  day  of  intrauterine  life,  before  the  heart  is 
formed,  the  two  primitive  stem  vessels  pass  backwards  along  the  body-stalk  to  the 
chorion,  their  terminal  branches  entering  the  chorionic  villi.  As  they  pass  back- 
wards the  primitive  aortiie  give  off  branches  to  the  wall  of  the  yolk-sac.  Thus,  at 
this  period  the  vascular  system  of  the  human  embryo  consists  of  two  longitudinal 
vessels  which  run  parallel  vsdth  each  other,  one  on  each  side  of  the  middle  line, 
throughout  the  whole  length  of  the  embryo.  They  communicate  anteriorly  with 
the  vessels  on  the  yolk-sac,  and  terminate  posteriorly  in  the  chorion.  When  the 
circulation  commences  the  blood  flows  from  the  anterior  part  of  the  vascular  area 
into  the  anterior  ends  of  the  primitive  aortse,  and  passes  backwards  through  the 
embryo.  Some  of  it  is  returned  to  the  vascular  area  by  the  branches  which  are 
given  off  to  the  walls  of  the  yolk-sac ;  but  the  greater  part  is  carried  to  the 
chorion,  whence  it  returns  by  venous  channels,  the  allantoic  veins,  which  have 
been  developed  in  the  meantime,  to  the  anterior  ends  of  the  primitive  aortse. 

As  the  cephalic  and  caudal  folds  are  developed  the  anterior  and  posterior  parts 
of  the  primitive  aortse  are  carried  into  the  ventral  wall  of  the  body  of  the  embryo, 

and  thus  each  primitive  vessel  is  divisible  into 
three  parts :  (1)  a  dorsal  part,  the  primitive 
dorsal  aorta,  which  extends  from  the  dorsal  end 
of  the  mandibular  arch  to  the  cloaca,  and  runs 
beneath  the  protovertebral  somites;  (2)  an 
anterior  ventral  part,  situated  in  the  dorsal 
wall  of  the  pericardium  and  extending  from 
the  umbilicus  to  the  ventral  end  of  the  man- 
dibular arch ;  and  (3)  a  posterior  ventral  part, 
which  at  first  runs  in  the  ventral  wall  at  the 
side  of  the  cloaca,  and  then  turns  backwards  in 
the  body -stalk  to  the  placenta,  but  afterwards, 
when  the  posterior  part  of  the  ventral  wall  of 
the  body  is  completed,  it  extends  forwards  from 
the  pelvic  region  to  the  umbilical  orifice,  through 
which  it  passes  to  the  umbilical  cord. 

The  three  sections  are  united  together  by  two 
arches — an  anterior  arch,  the  first  cephalic  aortic 
arch,  which  passes  through  the  mandibular  arch, 
and  a  posterior  arch,  the  caudal  arch,  which  lies 
at  the  side  of  the  cloaca. 

In  a  short  time  four  additional  communica- 
tions are  formed  between  the  anterior  ventral  and 
the  dorsal  part  of  each  primitive  aorta;  they  are  the  second,  third,  fourth,  and 
fifth  cephalic  aortic  arches,  each  of  which  lies  in  the  substance  of  the  corresponding 
visceral  arch. 

As  soon  as  the  last  cephaUc  aortic  arch  is  developed  the  rudiments  of  the  main 
vessels  of  the  embryo  are  established  ;  and  by  a  series  of  transformations,  for  a  full 
account  of  which  the  chapter  which  deals  with  the  Vascular  System  must  be 
consulted,  there  are  formed  from  the  vessels  which  have  been  mentioned  the  heart, 
the  aorta,  the  main  vessels  of  the  head  and  neck,  the  pulmonary  artery  and  its 
primary  branches,  the  common  and  internal  iliac  arteries,  and  the  hypogastric  arteries. 
The  blood  distributed  by  the  various  arteries  is  returned  to  the  heart  by  vessels 
called  veins,  which  are  developed  in  the  substance  of  the  mesoderm  in  the  same 
manner  as  the  arteries.  From  the  yolk-sac  the  blood  returns  by  the  vitelline 
veins ;  from  the  alimentary  canal  and  its  appendages,  through  the  portal  and  hepatic 
veins ;  from  the  head  and  neck,  by  the  jugular  veins  and  the  superior  vena  cava ; 
and  from  the  body  and  lower  limbs,  first  by  the  cardinal  veins,  and  afterwards  by 
the  inferior  vena  cava  and  the  azygos  veins. 

The  heart  is  formed  by  the  fusion  of  portions  of  the  anterior  ventral  sections  of 
the  primitive  aorta  behind  the  origins  of  the  cephalic  aortic  arches,  and,  therefore, 
it  is  primitively  a  bilateral  organ.  Subsequently  it  possesses  for  a  time  a  single 
chamber,  but  this  is  afterwards  divided.     During  the  greater  part  of  foetal  life  the 


Poster  or 

ventral  aorta 

Primitive 

caudal  arch 
Hypogastric 
artery 

.Chorionic 
vessels 

3. — The  Primitive  Blood- Vessels 
OF  THE  Embryo. 


PEIMITIVE  VASCULAR  SYSTEM  AND  ECETAL  CIRCULATION.     63 


heart,  as  in  the  adult,  possesses  four  chambers— two  auricles  or  upper  chambers,  and 
two  ventricles  or  lower  chambers,  right  and  left.  The  two  auricles  communicate 
with  the  corresponding  ventricles  through  auriculo- ventricular  apertures,  and  with 
each  other  through  a  foramen,  the  foramen  ovale,  in  the  septum  between  them. 

In  the  adult  the  blood  enters  the  right  auricle  by  the  superior  and  inferior 
venae  cavse  and  the  coronary  sinus ;  from  the  right  auricle  it  passes  into  the  right 
ventricle,  by  which  it  is  propelled  through  the  pulmonary  arteries  and  lungs ;  re- 
turning to  the  heart  by  the  pulmonary  veins  it  passes  into  the  left  auricle,  and 
then  into  the  left  ventricle,  by  the  contraction  of  which  it  is  forced  into  the 
systemic  aorta.  From  the  aorta,  by  various  branches,  it  traverses  the  organs  and 
tissues  of  the  body,  and  is  returned  again  to  the  right  auricle. 

The  course  of  the  fcetal  circulation  differs  from  that  of  the  adult ;  the  blood 
passes  out  of  the  body  into  the  placenta,  to  be  oxygenated  and  p\irified,  the  lungs 
of  the  fcetus  remaining  functionless  until  the  time  of  birth.  Very  little  of  the 
blood  which  is  ejected  from  the  right  ventricle  at  every  contraction  of  that 
chamber  reaches  the  lungs ;  the  greater  part  is  transferred  from  the  pulmonary 


Caudal  arches 


Dorsal  aortiv 


7th  pair  of 
segmental  arteries 


Vertebral 
arteries 

1st  pair  of 
segmental  arteries 


Umbilical  vein 
Splanchnic  arteries 

Hypogastric  artery 


1st  cephalic  aortic  arch 
2nd  cephalic  aortic  arch 
3rd  cephalic  aortic  arch 
4th  cephalic  aortic  arch 
yth  cephalic  aortic  arch 
Aortic  bulb 


Sinus  Vf*nosus 
Vitelline  vein 

Fig.  49. — Diagram  of  the  Blood-Vessels  of  a  Mammalian  Embryo  after  the  formation  of  the  Heart. 

artery  to  the  aorta  by  an  anastomosing  channel,  the  ductus  arteriosus,  which 
disappears  after  the  pulmonary  circulation  is  established. 

During  the  later  months  of  foetal  life,  blood  enters  the  right  auricle  by  the 
superior  and  inferior  vense  cavte  and  through  the  coronary  sinus ;  only  a  small 
amount  of  blood,  viz.  that  returning  from  the  walls  of  the  heart,  enters  the  right 
auricle  through  the  coronary  sinus.  The  blood  poured  into  the  right  auricle  by 
the  superior  vena  cava  is  returned  from  the  head,  neck,  upper  extremities,  and  the 
thoracic  walls ;  passing  from  the  auricle  by  the  right  auriculo-ventricular  opening 
it  enters  the  right  ventricle ;  from  the  right  ventricle  it  is  forced  into  the 
pulmonary  artery,  and  a  small  part  of  it  traverses  the  lungs  and  returns  to  the 
left  auricle  by  the  pulmonary  veins ;  the  main  part,  however,  is  conducted  by  the 
ductus  arteriosus  into  the  aorta  at  a  point  beyond  where  the  main  vessel  of  supply 
to  the  left  upper  extremity,  the  left  subclavian  artery,  rises. 

The  blood  which  enters  the  right  auricle  by  the  inferior  vena  cava  is  mixed ;  it 
consists  partly  of  purified  blood  from  the  placenta,  and  partly  of  impure  blood 
returning  from  the  abdomen  and  lower  extremities.  The  blood  from  the  placenta 
is  returned  to  the  embryo  by  the  umbihcal  vein.  From  the  umbilical  vein  it  passes 
along  a  channel  called  the  ductus  venosus,  which  terminates  in  the  upper  part  of  the 
inferior  vena  cava.  The  mixed  blood  from  the  inferior  vena  cava  passes  through 
the  right  auricle,  traverses  the  foramen  ovale  in  the  interauricular  septum,  and 


64 


GENEEAL  EMBEYOLOGY. 


enters  the  left  auricle ;  from  the  left  auricle  it  is  transferred  to  the  left  ventricle 
through  the  left  auriculo-ventricular  opening,  and  the  left  ventricle  ejects  it  into 
the  aorta.  From  the  first  part  of  the  aorta  some  of  the  blood  passes  into  the 
vessels  which  supply  the  head  and  neck  and  upper  extremities,  the  remainder 


Internal  jugular  vein 
External  jugular  vein 

Right  vertebral  artery- 
Right  subclavian  artery 
Right  subclavian  vein 
Innominate  veins 
Pulmonary  artery 
Superior  vena  cava 
Vena  azygos  major 
Right  auricle 

Right  ventricle 

Hepatic  vein 

Inferior  vena  cava 

Intercostal  veins 


1st  cephalic 
aortic  arch 

Internal  carotid  artery 


2ncl  cephalic 
aortic  arch 


External  carotid  artery 

3rd  cephalic 

aortic  arch 

Vertebral  artery 

Subclavian  artery 

4th  cephalic  aortic  arch 

Superior  intercostal  vein 

5th  cephalic  aortic  arch 

Pulmonary  artery 
Vena  azygos  minor  superior 
Left  auricle 


Vena  azygos  minor  inferior 
Ductus  venosus 


Atrophied  cardinal  vein j,     /| 

Portal  vein 


Renal  vein 
Lumbar  vein 

Common  iliac  artery 
External  iliac  artery 
Internal  iliac  artery 


Aorta 

Atrophied  cardinal  vein 


Placenta 


Hypogastric  arteries 


Middle  sacial  vein 

Fig.  50. — Diagram  of  the  Fcetal  Circulation. 

mixes  'with  the  blood  conveyed  to  the  aorta  by  the  ductus  arteriosus,  and  the 
blood,  thus  further  mixed,  is  in  part  distributed  to  the  walls  of  the  thorax  and 
abdomen  to  the  abdominal  viscera  and  to  the  lower  extremities,  and  in  part  it 
passes  to  the  placenta. 

Before  birth,  therefore,  there  is  no  pure  arterial  or  fully  oxygenated  blood  in 
the  arteries  of  the  fretus.  The  blood  entering  the  heart  by  the  superior  vena  cava 
is  venous  blood  from  the  head,  neck,  upper  extremities,  and  thorax  ;  that  entering 
by  the  inferior  vena  cava  is  mixed  blood,  consisting  of  venous  blood  from  the  lower 


PEIMITIVE  VASCULAK  SYSTEM  AND  FO^.TAL  CIECULATION.      65 

part  of  the  body  and  the  lower  extremities,  and  arterial  blood  from  the  placenta. 
The  two  streams  do  not  mix  in  the  right  auricle,  but  the  mixed  or  more  arterial 
stream  passes  directly  through  the  right  into  the  left  auricle,  thence  into  the  left 
ventricle,  and  from  the  left  ventricle  into  the  aorta  or  main  systemic  vessel,  which 
conveys  it  to  all  parts  of  the  body.  The  different  parts  of  the  body  do  not,  however, 
receive  equally  oxygenated  blood,  for  the  venous  stream  which  enters  the  right 
auricle  by  the  superior  vena  cava,  passes  througli  that  cavity  into  the  right  ventricle  ; 
by  the  right  ventricle  it  is  forced  into  the  pulmonary  artery,  from  which  some  small 
part  passes  into  the  lungs,  and  so  back  to  the  left  auricle  by  the  pulmonary  veins, 
but  by  far  the  greater  part  is  carried  by  the  ductus  arteriosus  to  the  aorta,  which  it 
enters  beyond  the  origins  of  the  vessels  which  supply  the  head,  neck,  and  upper 
extremities ;  therefore  the  blood  in  the  lower  part  of  the  aorta,  which  is  distributed 
to  the  abdomen,  the  abdominal  viscera  including  the  liver,  the  lower  limbs,  and  the 
placenta,  is  much  more  mixed  or  impure  (less  oxygenated)  than  that  which  is  dis- 
tributed to  the  head,  neck,  and  upper  extremities  from  the  upper  part  of  the  aorta. 


SUMMARY   OF   THE   EXTERNAL   FEATURES   OF   THE   HUMAN 
EMBRYO   AT   DIFFERENT   PERIODS   OF   DEVELOPMENT. 

First  week. — The  phenomena  of  fertilisation  and  segmentation  have  not  been 
observed  in  the  human  ovum,  but  there  is  no  reason  to  believe  that  they  differ  in  any 
essential  respect  from  those  met  with  in  the  ova  of  other  mammals.  Fertilisation  probably 
occurs  in  the  upper  jjart  of  the  Fallopian  tube,  and  segmentation  is  completed  in  the 
lower  part  of  the  same  canal  by  the  sixth  or  eighth  day,  when,  presumably,  the  ovum 
becomes  a  morula,  and  passes,  either  as  such  or  as  a  blastula,  into  the  cavity  of  the  uterus. 

Second  week. — At  the  twelfth  day  the  ovum  is  embedded  in  the  uterine  wall ; 
it  is  a  lenticular  vesicle, 
which  measures  5'5  mm. 
(i  of  an  inch)  in  length  and 
3"3  mm.  (^  of  an  inch)  in 
breadth.  Its  upper  and 
lower  surfaces  are  smooth 
and  convex,  the  latter 
being  somewhat  flatter 
than  the  former,  and  it  is 
surrounded  equatorially 
by  a  broad  band  of  villi, 
some  of  which  are  slightly 
branched.  The  wall  of 
the  vesicle  and  the  villous 
processes  which  project 
from  it  consist  of  ecto- 
dermal cells,  and  in  the 
embryonic  area,  wliich  is  clearly  marked  on  the  upper  surface,  there  is  an  inner  layer 
of  granular  nucleated  corpuscles. 

By  the  end  of  the  twelfth  or  the  beginning  of  the  thirteenth  day  the  length  of  the 
ovum  has  increased  to  6  mm.  {\  inch),  and  its  breadth  to  4 -.5  mm.  (^V  inch).  The  embryonic 
area  is  no  longer  on  the  surface  of  the  ovum,  for  the  amnion  folds  have  closed.  The  yolk- 
sac  is  formed,  and  the  rudiment  of  the  allantoic  duct  projects  backwards  from  the  upper 
and  posterior  part  of  the  embryonic  area.  Mesoderm  has  formed,  and  it  has  extended 
round  the  yolk-sac  and  over  the  inner  surface  of  the  chorion.  The  embryonic  area,  with 
the  yolk-sac  and  the  amnion,  are  enclosed  within  the  blastoderm,  but  they  remain 
attached  to  the  inner  surface  of  the  chorion  by  a  relatively  thick  stalk  of  ectodermal  and 
mesodermal  tissue,  the  body-stalk,  which  is  subsequently  replaced  by  the  umbilical  coid. 
The  outer  surface  of  the  ovum,  which  now  consists  entirely  of  chorion,  is  covered  with 
small  villi  into  some  of  which  mesodermal  cores  are  projecting. 

Obviously  the  ovum  of  the  latter  part  of  the  twelfth  day  differs  considerably  from 
that  of  the  earlier  part  of  the  same  day,  but  the  transitional  stages  which  intervene 
between  the  two  have  not  yet  been  observed.  Probably,  however,  the  inner  granular 
layer  of  cells  in  the  embryonic  area,  which  represent  the  entoderm,  increase  and  form  a 
solid  mass  in  which  a  cavity  soon  appears.  Directly  after  the  foimation  of  the  cavity  in 
the  entoderm  the  primitive  streak  appears,  and  the  mesoderm,  growing  from  it,  rapidly 
5 


A. 


AM 


A  B 

Fig.  51. 

Human  embryo  at  the  end  of  the  12th  day  of  development  ;  B.  At  the 
end  of  the  13th  day  of  development  ;  C.  At  the  end  of  the  14th  day  of 
development.      (After  His.) 

.  Amnion  ;  AS.  Allantoic  stalk  ;  BS.  Body-stalk  ;  CV.  Chorionic  villi  on 
a  segment  of  the  chorion  ;  E.  Embryo  ;  H.  Head  of  embryo  ;  PR.  Peri- 
cardial region  ;  SS.  Stomatodieal  depression  ;  YS.   Yolk-sac. 


66 


GENERAL  EMBRYOLOGY. 


covers  the  entodermal  sac  and  spreads  over  the  inner  surface  of  the  chorionic  area.  At 
the  same  time  tlie  amniotic  folds  form  and  separate  from  the  chorion,  but  this  separation  is 
not  efiected  till  the  mesoderm,  extending  backwards  from  the  posterior  end  of  the  embryonic 
area,  has  reached  and  becomes  connected  with  the  inner  surface  of  the  chorion.  Consequently, 
when  the  amniotic  folds  fuse  together  and  separate  from  the  remainder  of  the  blastoderm, 
the  embryonic  area  with  the  yolk-sac  and  amnion  still  remain  attached  to  the  inner 
surface  of  the  chorion. 

Dnring  the  thirteenth  day  the  embryonic  area  is  elevated,  the  cephalic  and  caudal 
folds  are  developed,  and  the  pericardial  region  becomes  prominent  between  the  head 
extremity  of  tlie  embryo  and  the  upper  and  anterior  part  of  the  yolk-sac.  The  neural 
groove  and  the  neural  folds  appear ;  the  posterior  ends  of  the  folds  embrace  the  anterior 
extremity  of  the  primitive  streak  on  which  the  primitive  groove  is  formed.  At  the 
anterior  end  of  the  primitive  groove  a  neurenteric  canal  appears,  forming  a  communication 
between  the  neural  groove  and  the  posterior  end  of  the  primitive  alimentary  canal 

On  the  fourteenth  day  the  embryo  is  more  distinctly  separated  from  the  yolk-sac  ;  the 
head  increases  considerably  in  size,  and  its  anterior  part  is  bent  downwards.  The  posterior 
part  of  the  neural  canal  is  completed,  except  at  the  extreme  end,  by  the  meeting  and  fusion 
of  the  neural  folds,  but  it  is  still  open  anteriorly,  where  traces  of  the  cerebral  vesicles  are 
present.  The  two  halves  of  the  heart  fuse  together  ;  the  single  tube  thus  formed  is 
slightly  bent  upon  itself,  and  its  outline  is  visible  from  the  exterior.  The  pericardial 
region  increases  in  size,  and  a  distinct  stomatodfeal  space  appears  between  it  and  the 
anterior  part  of  the  head.  The  outlines  of  fourteen  protovertebral  somites  are  visible  on 
the  outer  surface  of  the  body. 


HA 


HL 


D 


D. 


AS. 


E  F 

Fig.  52. 

Human  embryo  at  tlie  21st  day  of  development  ;  E.    At  the  23rd  day  nf  development  ; 
F.  At  the  27th  day  of  development.     (After  His.) 

Allantoic  stalk  ;  BS.  Body-stalk  ;  CV.  Chorionic  villi  on  a  segment  of  the  chorion  ;  EY.  Eye  ;  FL.  Fore- 
limb  ;  H.  Head;  HA.  Hyoid  arch  ;  HL.  Hind-limb;  MA.  Mandibular  arch  ;  MB.  Mid-brain;  MP. 
Maxillary  process  ;  OP.  Olfactory  pit  ;  OV.  Otic  vesicle  ;  PR.  Pericardial  region  ;  PS.  Protovertebral 
somite  ;  SS.  Stomatodseal  space  ;  U(J.  Umbilical  cord  ;  VC.  Visceral  cleft ;  WR.  Wolffian  ridge  ;  YS. 
Yolk-sac. 

Third  week. — On  the  fifteenth  day  the  auditory  pits  and  two  visceral  clefts 
appear.  Tlie  head  and  pci-icavflial  region  enlarge,  and  the  stomatodasal  space,  which 
increases  simultaneously,  becomes  more  defined  laterally  by  tlie  forward  growth  of  the 
maxillary  processes. 

]>y  the  end  of  the  third  week  Wolffian  ridges  appear  below  the  ventral  ends  of  the 
])rotovertebral  somites ;  they  are  most  marked  in  the  thoracic  and  pelvic  regions,  where 
bud-like  projections  form  the  rudiments  of  the  limbs.  Four  visceral  clefts  are  visible,  and 
there  is  ;i  distinct  tail. 

Fourth  week.  —  The  embryo  is  curved  upon  itself,  and  its  outline  is  almost 
circular.  'I'he  visceral  arches  begin  to  overlap  each  other.  The  rudiments  of  the  external 
ear  are  just  visible  as  small  nodules.     The  limb  rudiments  are  flat,  oval  buds. 

Fifth  week. — The  curvature  is  diminished,  and  tlie  head  and  neck  form  about 
half  the  embryo.  Tlie  eye  is  recognisable  externally.  The  nose  begins  to  grow  forwards, 
but  it  is  still  broad  and  flat,  and  the  nostrils  are  widely  apart.  The  nodular  elements  of 
the  external  ear  fuse  together.  The  segments  of  the  limbs  are  defined,  but  the  digits  do 
not  project  beyond  the  ends  of  the  limb-buds.  The  genital  tubercle,  the  rudiment  of  the 
external  generative  organs,  is  formed. 

Sixth  week. — During  the  sixth  week  the  increase  in  size  is  less  rapid  than  in 
previous  stages,  but  the  embryo  begins  to  assume  a  more  distinctly  human  form.     The 


HUMAN  EMBRYO  AT  DIFFERENT  STAGES. 


67 


liead  remains  relatively  large  and  it  is  bent  at  right  angles  to  the  body.     Tlie  neck  is 
l)etter  defined  and  appears  as  a  constricted  region  between  the  head  and  trunk.     The 

BE 


(I  H 

Fig.  53. 
a.  Human  emliryo  at  tlie  29th  day  of  development  ;  H.   At  the  32nd  day  of  development.     (After  His.) 
EE.   Rudiment  of  ear  ;  EY.  Eye  ;  FL.  Fore-limb;  HA.  Hyoid  arch  ;  HL.  Hind-limlp  ;  MA.   Mandibular  arch  : 
MB.   Mid-brain;  MP.   Maxillary  process  ;  OP.   Olfactory  ])it  ;  PPi.   Pericardial  region  ;  UG.   Umbilical 
cord. 

maxillary  processes  fuse  with  the  lateral  nasal  processes,  and  the  lips  and  eyelids  begin  to 
assume  their  characteristic  foi-m.  The  outer  parts  of  all  the  visceral  clefts  except  the 
hyo-mandibular  disappear.     The   external  ear  acquires  its  adult  form.     The  rotation  of 


Fig.  54. — Hdman  F(etus  at  the  sixth  week  Fig.  55. — Human  F(etcs  six  and  a 

OF  Development.     (After  His.)  half  weeks  old.     (After  His.) 

D.   Digits  ;  EE.   Rudiment  of  ear  ;  FL.   Fore-limb  ;  HL.  Hind-limb  ;  MP.  Maxillary  process  ;  N,   Nose  ; 

UC.  Umbilical  cord. 

the  limbs  commences,  and  the  fingers  reach  the  extremity  of  the  hand ;  the  tail  is 
beginning  to  disappear  as  an  external  projection. 

Seventh  week. — The  flexure  of  the  head  upon  the  body  is  reduced.  The  nose 
projects  more  than  in  the  preceding  stage,  and  the  chin  appears.  The  toes  reach  the 
margins  of  the  feet,  and  the  projecting  portion  of  the  tail  is  still  further  reduced  in  length. 

Eighth    week.  —  The    flexure    of    the   head    disappears.     The    forehead    projects. 


68 


GENEEAL  EMBKYOLOGY. 


The  nose  narrows  and  becomes  more  prominent,  but  the  anterior  nasal  orifices  are  still 
directed  forwards.  Tlie  upj)er  lip  is  completed  by  the  fusion  of  the  globular  processes. 
The  tlnnnb  is  widely  separated   from   the   fingers,  and   the   hand   assumes   a  distinctly 

human  appearance.  The  tail  is  reduced  to  a  small 
nodule,  and  the  umbilical  cord  is  attached  to  the 
lower  part  of  the  abdominal  wall.  At  the  end  of 
the  second  month  the  total  length  of  the  foetus, 
excluding  the  legs,  is  28  mm.  (1-|  in.). 

Third  month.  —  The  head  grows  less 
rapidly  and,  though  it  is  still  large,  it  is  relatively 
smaller  in  proportion  to  the  whole  body.  The 
eyelids  close,  and  their  margins  fuse  together. 
The  neck  increases  in  length.  The  various  parts 
of  the  limbsassume  theirdefinite  proportions,  and 
nails  appear  on  the  fingers  and  toes.  The  procto- 
dseum  is  formed  and  the  external  generative  organs 
are  differentiated,  so  that  the  sex  can  be  distin- 
guished on  external  examination.  The  skin  is  a 
rosy  colour,  thin  and  delicate,  but  more  consistent 
than  in  the  preceding  stages.  By  the  end  of  the 
third  month  the  total  length  of  the  foetus,  ex- 
cluding the  legs,  is  7  cm.  (2  ^  in.),  including  the 
legs,  9-10  cm.  (3|-4  in.),  and  it  weighs  from 
100-125  grammes  (3^-4|  oz.). 

Fourth  month. —  In  the  fourth  month 
the  skin  becomes  firmer,  and  fine  hairs  are  de- 
veloped. The  disproportion  between  the  fore 
and  hind  limbs  disappears.  If  the  foetus  is  born 
at  this  period  it  may  live  for  a  few  hours.  Its 
total  length  from  vertex  to  heels  is  16-20  cm.  (6|-8 
in.),  from  vertex  to  coccyx  12-13  cm.  (4-i-5i  in.), 
and  it  weighs  from  230-260  grammes  {8-^-91  oz.). 
Fifth  month. — The  skin  becomes  firmer, 
the  hairs  are  more  developed,  and  sebaceous 
matter  appears  on  the  siirface  of  the  body.  The 
legs  are  longer  than  the  arms,  and  the  umbilicus 
is  farther  from  the  pubis.  At  the  end  of  the 
month  the  total  length  of  the  foetus,  from  vertex 
to  heels,  is  25-27  cm.  (10-101  in.),  from  vertex  to  coccyx  20  cm.  (8  in.),  and  its  average 
weight  is  about  half  a  kilogramme  (Ijo  ^bs.). 

Sixth  month. — The  skin  is  wrinkled  and  of  a  dirty  reddish  colour.  The  hairs 
are  stronger  and  darker.  The  deposit  of  sebaceous  matter  is  greater,  especially  in  the 
axillte  and  groins.  The  eyelashes  and  eyebrows  appear.  At  the  end  of  the  month  the 
total  length  of  the  fcjetus,  from  vertex  to  heels,  is  from  30-32  cm.  (12-12j  in.),  and  its 
average  weight  is  about  one  kilogramme  (2i  lbs.). 

Seventh  month.  —  The  skin  is  still  a  dirty  red  colour,  but  it  is  lighter  than 
in  the  previous  month.  The  body  is  more  plump  on  account  of  a  greater  deposit  of  sub- 
cutaneous fat.  The  eyelids  reopen,  and  the  foetus  is  capable  of  living  if  born  at  this 
period.  Its  total  length  at  the  end  of  the  month,  measured  from  vertex  to  heels,  is  35-36 
cm.  (14-1 4  J  in.),  and  its  weight  is  about  one  and  a  half  kilogrammes  (3)j  lbs.). 

Eighth  month. — The  skin  is  completely  covered  with  sebaceous  deposit  which 
is  thickest  on  the  head  and  in  the  axillsD  and  groins,  and  its  colour  changes  to  a  bright 
flesh  tint.  The  umbilicus  is  farther  from  the  pubis,  but  it  is  not  yet  at  the  centre  of  the 
body.  The  total  length  of  the  foetus,  from  vertex  to  heels,  is  40  cm.  (16  in.),  and  its  weight 
varies  from  2  to  2^  kilogrammes  (4|-5^  lbs.). 

Ninth  month.  —  'i'he  hair  begins  to  disappear  from  the  body,  but  it  remains 
long  and  abundant  on  the  head.  The  skin  becomes  paler,  the  plumpness  increases,  and 
the  umbilicus  reaches  the  centre  of  the  body.  At  the  end  of  the  ninth  month,  when  the 
foetus  is  born,  it  measures  about  50  cm.  from  vertex  to  heels  (20  in.),  and  it  weighs  from 
3-3^  kilogrammes  (6yV*'^ro  lbs.). 

The  age  of  a  foetus  may  he  estimated  approximately  by  Hasse's  rule,  viz.  Up  to  the  fifth 
month  the  length  in  centimeters,  the  lower  limbs  being  included,  equals  the  square  of  the  age 
in  months,  and  after  the  fifth  month  the  length  in  centimeters  equals  the  age  multiplied  by  five. 


Fig.  56. — Human  Fcetus  eight  and  a  half 
WEEKS  OLD.     (After  His. ) 

GE.  Genital  eminence  ;  UC.   Umliilical  cord. 


OSTEOLOGY. 

THE  SKELETON. 

By  Arthue  Thomson. 

The  term  skeleton  (from  the  Greek,  o-KeAero?,  dried)  is  applied  to  the  parts  which 
remain  after  the  softer  tissues  of  the  body  have  been  disintegrated  or  removed, 
and  includes  not  only  the  bones,  but  also  the  cartilages  and  ligaments  which  bind 
them  together.  In  the  restricted  sense  of  the  word  the  skeleton  denotes  the 
osseous  framework  of  the  body.  It  is  in  this  sense  that  it  is  generally  employed  in 
human  anatomy. 

The  skeleton  serves  to  support  the  softer  structures  which  are  grouped  around 
it,  and  also  affords  protection  to  many  of  the  delicate  organs  which  are  lodged 
within  its  cavities.  By  the  articulation  of  its  several  parts,  its  segments  are  con- 
verted into  levers  which  constitute  the  passive  portion  of  the  locomotory  system. 
Eecent  research  has  also  proved  that  certain  cells  found  in  bone -marrow  are 
intimately  associated  with  the  development  and  production  of  some  of  the 
corpuscles  of  the  blood. 

Bone  may  be  regarded  as  white  fibrous  tissue  which,  having  become  calcified, 
has  undergone  subsequent  changes,  so  as  to  be  converted  into  true  osseous  tissue. 
Most  probably  all  bone  is  of  membranous  origin,  but  it  may  pass  through  a  stage 
in  which  cartilage  plays  an  important  part  in  its  development.  In  many  instances 
the  cartilage  persists,  and  is  not  converted  into  bone,  as  in  the  case  of  the  articular 
cartilage  which  clothes  the  joint  surfaces,  the  nasal  septum,  the  cartilages  of  the 
nose,  and  the  cartilages  of  the  ribs.  A  persistence  of  the  membranous  condition 
is  met  with  in  man  in  the  case  of  the  tentorium  cerebelli,  which  in  some  groups 
of  animals  (Carnivora)  is  converted  into  a  bony  partition. 

Skeletal  structures  may  be  derived  from  each  of  the  three  layers  of  the 
trilaminar  blastoderm.  The  exo-skeleton  includes  structures  of  ectodermal,  and 
some  of  mesodermal  origin  in  the  shape  of  hair,  nails,  feathers,  teeth,  scales,  armour- 
plates,  etc.,  whilst  the  endo-skeleton,  with  which  we  are  more  particularly  concerned, 
is  largely  derived  from  the  mesoblastic  tissue,  but  also  includes  the  notochord,  an 
entodermal  structure  which  forms  the  primitive  endo-skeleton,  around  which  the 
axial  skeleton  is  subsequently  developed  in  the  Vertebrata.  The  endo-skeleton  is 
divisible  into  an  axial  portion,  appertaining  to  the  trunk  and  head,  and  an  appen- 
dicular part  associated  with  the  limbs.  It  also  includes  the  splanchnic  skeleton, 
which  comprises  certain  bones  developed  in  the  substance  of  some  of  the  viscera, 
such  as  the  os  cordis  and  os  penis  of  certain  mammals.  In  man,  perhaps,  the 
cartilaginous  framework  of  the  trachea  and  bronchi  may  be  referred  to  this 
system. 

The  number  of  the  bones  of  the  skeleton  of  man  varies  according  to  age. 
Owing  to  a  process  of  fusion  taking  place  during  growth,  the  number  in  the  adult 
is  less  than  the  number  in  the  child.  The  following  table  does  not  include  the 
sesamoid  bones  which  are  frequently  developed  in  tendons,  the  most  constant 
ossicles  of  this  description  being  those  in  relation  to  the  metacarpo-phalangeal 
joint  of  the  thumb,  and  the  metatarso-phalangeal  joint  of  the  great  toe. 

69  5 


70 


OSTEOLOGY. 


life 


The  table  represents  the  number  of  bones  distinct  and  separable  during  adult 


Axial  skeleton 

Appendicular  skeleton 
The  ossicles  of  the  ear 


Single  Bones. 

Pairs. 

Total 

'The  vertebral  column 

26 

26 

The  skull  . 

6 

8 

22 

The  sternum 

1 

1 

The  ribs    . 

12 

24 

The  hyoid  bone 

1 

1 

/The  upper  limbs    . 

32 

64 

I^The  lower  limbs     . 

31 

62 

... 

3 

6 

34 


86 


206 


Bones  are  often  classified  according  to  their  shape.  Thus  long  bones,  that 
is  to  say,  bones  of  elongated  cylindrical  form,  are  more  or  less  characteristic  of 
the  limbs.  Broad  or  flat  bones  are  plate-like,  and  serve  as  protective  coverings  to 
the  structures  they  overlie ;  the  bones  of  the  cranial  vault  display  this  particular 
form.  Other  bones,  such  as  the  carpus  and  tarsus,  are  termed  short  bones  ;  whilst 
the  bones  of  the  cranial  base,  the  face,  and  the  vertebrae,  are  frequently  referred  to 
as  irregular  bones. 

Various  descriptive  terms  are  applied  to  the  prominences  commonly  met  with 
on  a  bone,  such  as  tuberosity,  eminence,  iJrotuberance,  'process,  tuhercle,  spine, 
ridge,  crest,  and  line.  These  may  be  articular  in  their  nature,  or  may  serve  as 
points  or  lines  of  muscular  and  ligamentous  attachment.  The  surface  of  the  bone 
may  be  excavated  into  pits,  depressions,  fossae,  cavities,  furrows,  grooves,  and 
notches.  These  may  be  articular  or  non-articular,  the  latter  serving  for  the  recep- 
tion of  organs,  tendons,  ligaments,  vessels,  and  nerves.  In  some  instances  the 
substance  of  the  bone  is  hollowed  out  to  form  an  air  space,  sinus,  or  antrum. 
Bones  are  traversed  hj  foramina  and  canals ;  these  may  be  for  the  entrance  and  exit 
of  nutrient  vessels,  or  for  the  transmission  of  vessels  and  nerves  from  one  region  to 
another.  A  cleft,  hiatus,  or  fissure  serves  the  same  purpose.  Channels  of  this  kind 
are  usually  placed  in  the  line  of  a  suture,  or  correspond  to  the  line  of  fusion  of  the 
primitive  portions  of  the  bone  which  they  pierce. 

Composition  of  Bone.' — Bone  is  composed  of  a  combination  of  organic  and 
inorganic  substances  in  about  the  proportion  of  one  to  two. 

Organic  matter  (Fat,  etc.,  Collagen)      .  .  .  31  "04 

Mineral  matter — 

Calcic  phosphate  ....  58"23' 


Calcic  carbonate 
Calcic  fluoride 
Magnesic  phosphate 
Sodic  chloride 


7-32 

1-41 

1-32 

•69 


68-97 


100-00 


The  animal  matter  may  be  removed  by  boiling  or  charring.  According  to  the 
completeness  with  which  the  fibrous  elements  have  been  withdrawn,  so  the  brittle- 
ness  of  the  bone  increases.  When  subjected  to  high  temperatures  the  earthy 
matter  alone  remains.  By  soaking  a  bone  in  acid  the  salts  may  be  dissolved  out, 
leaving  only  the  organic  part.  The  shape  of  the  bone  is  still  retained,  though  it 
has  now  become  soft,  and  can  be  bent  about  in  any  direction.  The  touglmess  and 
elasticity  of  bone  depends  therefore  on  its  organic  constituents,  whilst  its  hardness 
is  due  to  its  mineral  matter. 

Bone  may  be  examined  either  in  the  fresh  or  dry  condition.  In  the  former 
state  it  retains  all  its  organic  parts,  which  include  the  fibrous  tissue  in  and  around 
it,  the  blood-vessels  and  their  contents,  together  with  the  cellular  elements  found 
within  the  substance  of  the  bone  itself,  and  the  marrow  which  occupies  the  lacunar 
spaces  and  marrow  cavity.  In  the  dried  or  macerated  bone  most  of  these  have 
disappeared,  though  a  considerable  portion  of  the  organic  matter  still  remains, 
even  in  bones  of  great  antiquity  and  in  a  more  or  less  fossil  condition.  Con- 
sidering its  nature  and  the  amount  of  material  employed,  bone  possesses  a  remark- 


STKUCTUEE  OF  BONE.  71 

able  strength,  equal  to  nearly  twice  that  of  oak,  whilst  it  is  capable  of  resisting  a 
greater  crushing  strain  ;  it  is  stated  that  a  cubic  inch  of  bone  will  support  a  weight 
of  over  two  tons.  Its  elasticity  is  remarkable,  and  is  of  the  greatest  service  in 
enabling  it  to  withstand  the  shocks  to  which  it  is  so  frequently  subjected.  In 
regions  where  wood  is  scarce  the  natives  use  the  ribs  of  large  mammals  as  a  sub- 
stitute in  the  construction  of  their  bows.  Its  hardness  and  density  vary  in  different 
parts  of  the  skeleton,  and  its  permanency  and  durability  exceed  that  of  any  other 
tissue  of  the  body,  except  the  enamel  and  dentine  of  the  teeth.  The  osseous  remains 
of  a  race  over  eighty  centuries  old  are  now  being  excavated  in  Egypt. 

Structure  of  Bone  (Macroscopic). — To  obtain  an  idea  of  the  structure  of  a 
bone  it  is  necessary  to  examine  it  both  in  the  fresh  or  recent  condition  and  in  the 
macerated  state.  In  the  former  the  bone  is  covered  by  a  membrane  which  is  with 
difficulty  torn  off,  owing  to  the  abundance  of  tine  fibrils  which  enter  the  substance 
of  the  bone  from  its  deep  surface.  This  membrane,  called  the  periosteum,  overlies 
the  bone,  except  where  the  bone  is  coated  with  cartilage.  This  cartilage  may  form 
a  bond  of  union  between  contiguous  bones  or,  in  the  case  of  bones  united  to  each 
other  by  movable  joints,  may  be  moulded  into  smooth  articular  surfaces  called  the 
articular  cartilages.  The  attachment  of  the  various  ligaments  and  muscles  can  also 
be  studied,  and  it  will  be  noticed  that  where  tendon  or  ligament  is  attached,  the 
bone  is  often  roughened  to  form  a  ridge  or  eminence ;  where  fleshy  muscular  fibres 
are  attached,  the  bone  is,  as  a  rule,  smooth.  In  the  macerated  condition,  when 
the  cartilage  and  fibrous  elements  have  been  destroyed,  it  is  possible,  however, 
to  determine  with  considerable  accuracy  the  parts  of  the  bone  covered  with 
articular  cartilage,  since  the  bone  here  is  smooth  and  conforms  generally  to  the 
curves  of  the  articular  areas  of  the  joint ;  these  areas  are  referred  to  as  the 
articular  surfaces  of  the  bone.  The  bone  now  stripped  of  its  periosteal  covering 
displays  a  dense  surface  finely  pitted  for  the  entrance  of  the  processes  derived  from 
the  periosteum,  which  thus  establish  a  connexion  between  the  bony  substance  and 
that  vascular  layer ;  here  and  there,  more  particularly  in  the  neighbourhood  of  the 
articular  extremities,  these  pits  increase  in  size  and  number  and  allow  of  the  trans- 
mission of  small  blood-vessels.  If  careful  examination  be  made,  one  or  two  foramina 
of  larger  size  will  usually  be  noticed.  These  allow  the  passage  of  arteries  of  con- 
siderable size  into  the  interior  of  the  bone,  and  are  called  the  vascular  foramina  or 
canals  of  the  bone.  There  are  also  corresponding  channels  for  the  escape  of  veins 
from  the  interior. 

In  order  more  fully  to  ascertain  the  structure  of  bone  it  will  be  necessary  to 
study  it  in  section.  Taking  first  a  long  bone,  such  as  one  meets  with  in  the 
extremities,  one  notices  on  longitudinal  section,  that  the  bone  is  not  of  the  same 
density  throughout,  for,  whilst  the  external  layers  are  solid  and  compact,  the 
interior  is  made  up  of  loose  spongy  bone  called  cancellous  tissue.  Further,  it  will 
be  observed  that  in  certain  situations  this  cancellous  tissue  is  absent,  so  that  there 
is  a  hollow  in  the  interior  of  the  bone  called  the  medullary  cavity.  In  the  recent 
condition  this  cavity  is  filled  with  the  marrow  and  is  hence  often  called  the  marrow 
cavity.  This  marrow,  which  fills  not  only  the  marrow  cavity  but  also  the  interstices 
between  the  cancellous  fibres,  consists  largely  of  fat  cells  together  with  some  marrow 
cells  proper  supported  by  a  kind  of  retiform  tissue.  The  appearance  and  con- 
stituents of  this  marrow  differ  in  different  situations.  In  the  medullary  cavity  of 
long  bones  the  marrow,  as  above  described,  is  known  as  yellow  marrow.  In  other 
situations,  viz.  in  the  diploe  of  the  cranial  bones  (to  be  hereafter  described),  in  the 
cancellated  tissue  of  such  bones  as  the  vertebrae,  the  sternum,  and  the  ribs,  the 
marrow  is  more  fluid,  less  fatty,  and  is  characterised  by  the  presence  of  marrow- 
cells  proper,  which  resemble  in  some  respects  colourless  blood  corpuscles.  In 
addition  to  these,  however,  there  are  small  reddish  -  coloured  cells,  akin  to  the 
nucleated  red  corpuscles  of  the  blood  of  the  embryo.  These  cells  (erythroblasts) 
are  concerned  in  the  formation  of  the  coloured  corpuscles  of  the  blood.  Marrow 
which  displays  these  characteristic  appearances  is  distinguished  from  the  yellow 
variety,  already  described,  by  being  called  the  red  marrow.  The  marrow  met  with 
in  the  cancellous  tissue  of  the  cranial  bones  of  aged  individuals  often  undergoes 
degenerative  changes  and  is  sometimes  referred  to  as  gelatinous  marrow. 


72  OSTEOLOGY. 

A  better  idea  of  the  disposition  of  the  bony  framework  of  a  long  bone  can  be 
obtained  by  the  examination  of  a  section  of  a  macerated  specimen.  Here  the 
marrow  has  been  destroyed  and  the  osseous  architecture  of  the  bone  is  consequently 
better  displayed. 

AVithin  the  shaft  is  seen  the  marrow  cavity  extending  towards,  but  not  reaching, 
either  extremity  of  the  bone.  This  cavity  is  surrounded  on  all  sides  by  a  loose 
spicular  network  of  bone,  which  gradually  increases  in  compactness  until  it  reaches 
the  circumference  of  the  shaft,  where  it  forms  a  dense  surrounding  wall.  In  the 
shaft  of  a  long  bone  the  thickness  of  this  outer  layer  is  not  the  same  throughout, 
but  tends  to  diminish  as  we  approach  the  extremities,  nor  is  it  of  uniform  thickness 
on  all  sides  of  the  bone.  All  the  long  bones  display  curves  in  varying  degree,  and 
it  is  a  uniform  rule  that  the  thicker  dense  bone  is  found  along  the  concave  surface 
of  the  curve,  thus  assisting  in  materially  strengthening  the  bone.  Towards  the 
extremities  of  the  long  bone  the  structure  and  arrangement  of  the  bone  undergoes 
a  change.  There  is  no  marrow  cavity,  the  cancellated  tissue  is  not  so  open  and 
irregular,  and  the  external  wall  is  much  thinner  than  in  the  shaft,  indeed  in  many 
instances  it  is  little  thicker  than  stout  paper.  A  closer  examination  of  the  arrange- 
ment of  this  cancellous  tissue  throughout  the  bone  suggests  a- regularity  in  its 
arrangement  which  might  escape  notice,  and  if  in  place  of  one  bone  only  being 
examined  sections  of  other  bones  be  also  inspected,  it  will  be  observed  that  the 
spicules  of  this  tissue  are  so  arranged  as  best  to  withstand  the  strains  and  stresses 
to  which  the  bone  is  habitually  subjected. 

From  what  has  been  said  it  will  be  obvious  that  the  arrangements  above 
described  are  those  best  adapted  to  secure  the  maximum  of  strength  with  the 
minimum  of  material,  and  a  consequent  reduction  in  the  weight  of  the  skeleton. 
The  same  description  applies,  with  some  modification,  to  bones  of  flattened  form. 
Taking  as  an  example  the  expanded  plate-like  bones  of  the  cranial  vault,  their 
structure  as  displayed  on  section  exhibits  the  following  appearance :  The  outer 
and  inner  surfaces  are  formed  by  two  compact  and  dense  layers,  having  sandwiched 
between  them  a  layer  of  cancellous  tissue  called  the  diploe,  containing  red  marrow. 
Note  that  there  is  no  medullary  cavity,  though  in  certain  situations  and  at  certain 
periods  of  life  the  substance  of  the  diploe  may  become  absorbed  and  converted  by 
the  evagination  of  the  mucous  membrane  of  the  respiratory  tract  into  air-spaces 
or  air-sinuses. 

Microscopic. — True  bone  differs  from  calcified  cartilage  or  membrane  in  that  it 
not  merely  consists  of  the  deposition  of  earthy  salts  within  its  matrix,  but  displays 
a  definite  arrangement  of  its  organic  and  inorganic  parts.  Dense  bone  merely 
differs  from  loose  or  cancellous  bone  in  the  compactness  of  its  tissue,  the  character- 
istic feature  of  which  is  the  arrangement  of  the  osseous  lamellae  to  form  what  are 
called  Haversian  systems.  These  consist  of  a  central  or  Haversian  canal  which 
contains  the  vessels  of  the  bone.  Around  this  the  osseous  lamellae  are  arranged 
concentrically,  separated  here  and  there  by  interspaces  called  lacunae,  in  which  the 
bone  corpuscles  are  lodged.  Passing  from  these  lacunae  are  many  fine  channels 
called  canaliculi.  These  are  disposed  radially  to  the  Haversian  canal,  and  pass 
through  the  osseous  lamellae.  They  are  occupied  by  the  slender  processes  of  the 
bone  corpuscles.  Each  Haversian  system  consists  of  from  three  to  ten  concentric 
rings  of  osseous  lamellae. 

In  addition  to  the  lamellae  of  the  Haversian  systems  there  are  others  which  are 
termed  the  interstitial  lamellae ;  these  occupy  the  intervals  between  adjoining 
Haversian  systems,  and  consist  of  Haversian  systems  which  have  undergone  a  process 
of  partial  absorption.  Towards  the  surface  of  the  bone,  and  subjacent  to  the  peri- 
osteal membrane  which  surrounds  the  shaft,  there  are  lamellae  arranged  circum- 
ferentially ;  these  are  sometimes  referred  to  as  the  outer  fundamental  lamellae. 
The  periosteal  membrane  which  surrounds  the  bone,  and  which  plays  so  important 
a  part  in  its  development,  sends  in  processes  through  the  various  Haversian  systems, 
which  carry  with  them  vessels  and  cells,  thus  forming  an  organic  meshwork 
around  which  the  earthy  salts  are  deposited. 

Ossification  of  Bone.  —  For  an  account  of  the  earlier  development  of  the 
skeleton  the  reader  is  referred  to  the  section  on  Embryology,     Concerning  the 


OSSIFICATION  AND  GEOWTH  OF  BONES.  73 

subsequent  changes  which  take  place,  these  are  dependent  on  the  conversion  of  the 
scleratogenous  tissue  into  membrane  and  cartilage.  A  characteristic  of  this  tissue 
is  that  it  contains  elements  which  become  formed  into  bone-producing  cells,  called 
osteoblasts.  These  are  met  with  in  the  connective  tissue  from  which  the  membrane 
bones  are  formed,  whilst  they  also  appear  in  the  deeper  layers  of  the  investing 
tissue  of  the  cartilage  (perichondrium),  and  so  lead  to  its  conversion  into  the  bone- 
producing  layer  or  periosteum.  All  true  bone,  therefore,  may  probably  be  regarded 
as  of  membranous  origin,  though  its  appearance  is  preceded  in  some  instances  by 
the  deposition  of  cartilage ;  in  this  case  calcification  of  the  cartilage  is  an  essential 
stage  in  the  process  of  bone  formation,  but  the  ultimate  conversion  into  true  bone, 
with  characteristic  Haversian  systems,  leads  to  the  absorption  and  disappearance  of 
this  primitive  calcified  cartilage.  In  considering  the  development  of  bone  an 
inspection  of  the  skeleton  of  a  foetus  will  enable  the  student  to  realise  that  much 
of  what  is  bone  in  the  adult  is  preformed  in  cartilage,  whilst  a  part  of  the  fully- 
developed  skeleton  is  represented  only  by  memltrane:  hence,  in  regard  to  this 
ossification,  bones  have  been  described  as  of  cartilaginous  and  membranous  origin. 
If  the  development  of  a  long  bone  be  traced  through  successive  stages  from  the 
cartilaginous  condition  in  which  it  is  preformed,  it  will  be  noticed  that  ossification 
first  begins  in  the  shaft.  This  ossific  centre  is  referred  to  as  the  diaphysis,  and, 
since  it  is  the  first  to  appear,  is  also  spoken  of  as  the  primary  centre  of  ossification. 
As  yet,  the  extremities  of  the  shaft  are  cartilaginous  knobs,  but  at  a  later  stage 
one  or  more  ossific  centres  appear  in  these  cartilaginous  extremities.  These  centres, 
which  are  independent  of  the  diaphysis  and  appear  much  later,  at  variable  periods, 
are  termed  epiphyses  or  secondary  centres.  If  there  be  more  than  one  such  centre 
at  the  extremity  of  a  bone,  these  associated  centres  unite,  and  at  a  later  stage  the 
osseous  mass  so  formed  joins  with  the  shaft  or  diaphysis,  and  in  this  way  the 
formation  of  the  bone  is  completed.  Complete  fusion  by  osseous  union  of  the 
epiphyses  with  the  diaphyses  occurs  at  variable  periods  in  the  life  of  the  individual. 
Prior  to  this  taking  place,  the  two  are  bonded  together  by  a  cartilaginous  layer 
which  marks  the  position  of  the  epiphyseal  line.  If  the  bone  be  macerated  at  this 
stage  of  growth,  the  epiphysis  falls  away  from  the  diaphysis.  In  the  case  of  the 
articular  ends  of  ])one  it  will  be  noticed  that  the  surfaces  exposed  by  the  separation 
of  the  epiphysis  from  the  diaphysis  are  not  plane  and  smooth,  but  often  irregular, 
notched,  and  deeply  pitted,  so  that  when  the  two  are  brought  together  they 
interlock,  and,  as  it  were,  dovetail  into  each  other.  In  this  way  the  extremities  of 
the  bone  as  yet  ununited  by  osseous  growth  are  during  youth  and  adolescence  able 
to  withstand  the  shocks  and  jars  to  which  during  life  they  are  habitually  subjected. 
A  long  bone  has  been  taken  as  the  simplest  example,  but  it  by  no  means  follows 
that  these  secondary  centres  or  epiphyses  are  confined  to  the  articular  extremities 
of  long  bones.  They  are  met  with  not  only  in  relation  to  the  articular  surfaces  of 
bones  of  varied  form,  but  also  occur  where  bones  may  be  subjected  to  unusual 
pressure  or  to  the  strain  of  particular  muscles.  For  this  reason  epiphyses  of  this 
nature  have  been  called  pressure  and  traction  epiphyses  (Parsons).  There  occur, 
however,  secondary  independent  centres  of  ossification,  which  cannot  be  so 
accounted  for.  Possibly  these  are  of  phylogenetic  interest  only,  and  may  accord- 
ingly be  classed  as  Atavistic. 

Ossification  in  Membrane. — Membrane  bones  are  such  as  have  developed 
from  fibrous  tissue  without  having  passed  through  a  cartilaginous  stage.  Of  this 
nature  are  the  bones  of  the  cranial  vault  and  the  majority  of  the  bones  of  the 
face,  viz.  the  maxillte,  malars,  nasals,  lacrimals,  and  palate  bones,  as  well  as  the  vomer. 
The  internal  pterygoid  plate  (medial  layer  of  the  pterygoid  process)  is  also  of  mem- 
branous origin.  In  the  course  of  the  development  of  a  bone  from  membrane,  as,  for 
example,  the  parietal  bone,  the  fibrous  tissue  corresponding  to  the  position  of  the 
primary  centre  becomes  osteogenetic,  because  here  appear  the  bone-forming  cells 
(osteoblasts),  which  rapidly  surround  themselves  with  a  bony  deposit  more  or  less 
spicular  in  arrangement.  As  growth  goes  on  these  osteoblasts  become  embedded  in 
the  ossifying  matrix,  and  remain  as  the  corpuscles  of  the  future  bone,  the  spaces 
in  which  they  are  lodged  corresponding  to  the  lacunae  and  canaliculi  of  the  fully 
developed  osseous  tissue.     From  the  primary  centre  ossification  spreads  eccentrically 


74  OSTEOLOGY. 

towards  the  margins  of  the  bone,  where  ultimately  the  sutures  are  formed. 
Here  the  growth  rendered  necessary  by  the  expansion  of  the  cranium  takes  place 
through  the  agency  of  an  intervening  layer  of  vascular  connective  tissue  rich  in 
osteoblasts ;  but  in  course  of  time  the  activity  of  this  is  reduced  until  only  a  thin 
layer  of  intermediate  tissue  persists  along  the  line  of  the  suture ;  this  may  eventu- 
ally become  absorbed,  leading  to  uhe  obliteration  of  the  suture  by  the  osseous  union 
of  the  contiguous  bones.  Whilst  the  expansion  of  the  bone  in  all  directions  is 
thus  provided  for,  its  increase  in  thickness  is  determined  by  the  activity  of  the 
underlying  and  overlying  strata.  These  form  the  periosteum,  and  furnish  the 
lamella  which  constitute  the  inner  and  outer  compact  osseous  layers. 

Ossification  in  Cartilage. — Cartilage  bones  are  those  which  are  preformed  in 
cartilage,  and  include  most  of  the  bones  of  the  skeleton.  Their  growth  is  often 
described  as  endochondral  and  ectochondral,  the  former  term  implying  the 
deposition  of  membrane  bone  in  the  centre  of  the  cartilage,  while  the  latter 
signifies  a  deposit  of  membrane  bone  on  the  surface  of  the  cartilage,  the  osteo- 
genetic  layer  on  the  surface  of  the  cartilage  being  named  the  perichondrium  till 
once  bone  has  been  formed,  when  it  is  called  the  periosteum. 

In  a  cartilage  bone  changes  of  a  similar  nature  occur.  The  cartilage,  which  may 
be  regarded  histologically  as  white  fibrous  tissue  +  chondro-sulphuric  acid  and  a 
certain  amount  of  lime  salts,  undergoes  the  following  changes : — First,  the  cartilage 
cells  being  arranged  in  rows,  become  enlarged ;  secondly,  the  matrix  between  the 
cartilage  cells  becomes  calcified  by  the  deposition  of  an  additional  amount  of  lime 
salts ;  thirdly,  the  rows  of  cells  become  confluent ;  and,  fourthly,  into  the  spaces  so 
formed  extend  the  blood-vessels  derived  from  the  vascular  layer  of  the  periosteum. 
Accompanying  these  vessels  are  osteoblasts  and  osteoclasts,  the  former  building  up 
true  bone  at  the  expense  of  the  calcified  cartilage,  the  latter  causing  an  absorption  of 
the  newly-formed  bone,  and  leading  to  its  conversion  into  a  marrow  cavity,  so  that 
in  due  course  all  the  cartilage  or  its  products  disappear.  At  the  same  time  that  this 
is  taking  place  within  the  cartilage,  the  perichondrium  is  undergoing  conversion  into 
the  periosteum,  an  investing  membrane,  the  deeper  stratum  of  which,  highly  vascular, 
furnishes  a  layer  of  osteoblast  cells  which  serve  to  develop  the  circumferential 
lamellae  of  the  bone.  It  is  by  the  accrescence  of  these  layers  externally,  and  their 
absorption  internally  through  the  action  of  the  osteoclast  cells,  that  growth  takes 
place  transversely.  A  transverse  section  of  the  shaft  of  a  long  bone  shows  this 
very  clearly.  Centrally  there  is  the  marrow  cavity,  formed  primarily  by  the 
absorption  of  the  calcified  cartilage;  around  this  the  cancellous  tissue  produced 
by  the  partial  erosion  of  the  primary  periosteal  bone  is  disposed,  whilst  externally 
there  is  the  dense  envelope  made  up  of  the  more  recent  periosteal  growth. 

Growth  of  Bone. — The  above  description,  whilst  explaining  the  growth  of  bone 
circumferentially,  fails  to  account  for  its  growth  in  length ;  hence  the  necessity  in 
long  bones  for  some  arrangement  whereby  ossification  may  take  place  at  one  or  both 
extremities  of  the  shaft.  This  zone  of  growth  is  situated  where  the  ossified  shaft 
becomes  continuous  with  the  cartilaginous  epiphysis.  In  addition,  within  these 
epiphysial  cartilages  calcification  of  the  cartilage  takes  place  centrally,  just  as  in  the 
diaphysis.  The  two  parts  of  the  bone,  viz.  the  diaphysis  and  epiphysis,  are  thus 
separated  by  a  layer  of  cartilage,  sometimes  called  the  cartilage  of  conjuga- 
tion, as  yet  uncalcified,  but  extremely  active  in  growth  owing  to  the  invasion 
of  vessels  and  cells  from  a  vascular  zone  which  surrounds  the  epiphysis.  The 
nucleus  of  the  epiphysis  becomes  converted  into  true  bone,  which  grows 
eccentrically.  This  arrangement  provides  for  the  growth  of  the  shaft  towards 
the  epiphysis,  and  the  growth  of  the  epiphysis  towards  the  shaft ;  so  that  as 
long  as  the  active  intervening  layer  of  cartilage  persists,  extension  of  growth  in 
a  longitudinal  direction  is  possible.  As  might  be  expected,  experience  proves  that 
growth  takes  place  more  actively,  and  is  continued  for  a  longer  time,  at  the  end 
of  the  bone  where  the  epiphysis  is  the  last  to  unite.  In  consequence,  surgeons 
sometimes  term  this  the  "  growing  end  of  the  bone."  Subsequently,  however,  at 
variable  periods  the  intervening  layer  of  cartilage  becomes  calcified,  and  true  bony 
growth  occurs  within  it,  thus  leading  to  complete  osseous  union  between  the  shaft 
and  epiphysis.     When  this  has  taken  place  all  further  growth  in  a  longitudinal 


THE  VERTEBRAL  COLUMN.  75 

direction  ceases.  In  cases  where  the  epiphysis  enters  into  the  formation  of  a  joint, 
the  cartilage  over  the  articular  area  persists  and  undergoes  neither  calcification  nor 
ossification. 

Vascular,  Lymphatic,  and  Nervous  Supply. — From  what  has  been  said  it 
will  be  gathered  that  the  vascular  supply  of  the  bone  is  derived  from  the  vessels 
of  the  periosteum.  These  consist  of  fine  arteries  which  enter  the  surface  of  the 
shaft  and  epiphysis;  but  in  addition  there  is  a  larger  trunk  which  enters  the 
diaphysis  and  reaches  the  medullary  cavity.  This  is  called  the  nutrient  artery  of 
the  bone.  The  direction  taken  by  this  vessel  varies  in  ditlerent  bones.  In  the 
upper  limb  the  artery  runs  downwards  in  the  case  of  the  humerus  and  upwards 
in  the  radius  and  ulna ;  in  the  lower  limb  the  nutrient  vessel  of  the  femur  is 
directed  towards  the  upper  extremity  of  the  shaft,  whilst  in  the  tibia  and  fibula 
it  follows  a  downward  course.  The  direction  of  the  nutrient  artery  in  the  bone  is 
a  mechanical  result  of  the  unequal  growth  of  the  two  extremities  of  the  bone. 
During  the  greater  part  of  intra-uterine  life  the  principal  nutrient  arteries  of  the 
loug  bones  are  directed  towards  the  distal  extremity  of  the  limb.  In  the  process 
of  development  the  point  of  entrance  of  the  artery  is  turned  away  from  the 
epiphysis  which  furnishes  the  greatest  amount  of  bone,  and  thus,  together  with 
the  nutrient  canal,  acquires  an  obliquity  directed  towards  the  extremity  of  the 
bone  which  develops  last  (Pioliet,  J.  de  VAnat.  et  de  la  Phys.,  1905,  p.  57). 

It  may  assist  the  memory  to  point  out  that  when  all  the  joints  are  flexed,  as 
in  the  position  occupied  by  the  fcetus  in  utero,  the  direction  taken  by  the  vessels 
is  the  same,  and  corresponds  to  a  line  passing  from  the  head  towards  the  tail-end 
of  the  embryo.  Consequently,  in  the  upper  limb  the  vessels  run  towards  the 
elbow,  whilst  in  the  lower  Umb  they  pass  from  the  knee. 

The  veins  which  permeate  the  cancellous  texture  of  the  bone  are  large  and  thin- 
walled.  They  do  not  accompany  the  arteries,  and,  as  a  rule,  in  long  bones  they 
escape  through  large  openings  near  the  articular  surfaces.  In  flat  bones  they  occupy 
channels  within  the  diploe,  and  drain  into  an  adjacent  sinus,  or  form  communica- 
tions with  the  superficial  veins  of  the  scalp. 

The  lymphatics  are  mainly  periosteal,  but  enter  the  bone  along  with  the  vessels 
and  become  perivascular. 

The  nerves  which  accompany  the  arteries  are  probably  destined  for  the  supply  of 
the  coats  of  these  vessels.     Whether  they  end  in  the  bony  tissue  or  not  is  unknown. 

The  attention  of  anatomists  has  long  been  directed  to  the  elucidation  of  the  laws 
which  regulate  bone-growth.  Our  present  knowledge  of  the  subject  may  be  briefly 
summarised  in  the  following  generalisations  : — 

1.  In  bones  with  a  shaft  and  two  epiphyses,  the  epiphysis  towards  which  the 
nutrient  artery  is  directed  is  the  first  to  unite  with  the  shaft. 

2.  In  bones  with  a  shaft  and  two  epiphyses,  as  a  rule  the  epiphysis  which  com- 
mences to  ossify  latest  unites  soonest  with  the  shaft.  (The  fibula  is  a  notable 
exception  to  this  rule.) 

3.  In  bones  with  a  shaft  and  one  epiphysis  the  nutrient  artery  is  directed 
towards  the  end  of  the  bone  which  has  no  epiphysis.  (This  arrangement  holds 
good  in  the  case  of  the  clavicle,  the  metacarpus,  metatarsus,  and  phalanges.) 

4.  When  an  epiphysis  is  ossified  from  more  than  one  centre,  coalescence  takes 
place  between  the  separate  ossific  nuclei  before  the  epiphysis  unites  with  the  shaft. 

Highly  suggestive,  too,  are  the  following  propositions — That  ossification  first 
commences  in  the  epiphysis  which  ultimately  acquires  the  largest  relative  propor- 
tion to  the  rest  of  the  bone,  and  that  the  ossification  of  the  epiphysis  is  also 
correlated  with  its  functional  importance.  In  cases  of  long  bones  with  only  one 
epiphysis,  the  epiphysis  is  placed  at  the  end  of  the  bone  where  there  is  most 
movement. 

THE   VERTEBRAL   COLUIVIN. 

The  vertebral  column  (columna  vertebralis)  of  man  consists  of  thirty-three 
superposed  segments  or  vertebrae.  In  the  adult,  certain  of  these  vertebrae  have 
become  fused  together  in   the  process  of  growth  to  form  bones,  the  segmental 


76  OSTEOLOGY. 

arrangement  of  which  is  somewhat  obscured,  though  even  in  their  fully- 
developed  condition  sufficient  evidence  remains  to  demonstrate  their  com- 
pound nature.  The  vertebrse  so  blended  are  termed  the  fixed  or  false  vertebrae, 
whilst  those  between  which  osseous  union  has  not  taken  place  are  described  as  the 
movable  or  true  vertebrae.  This  fusion  of  the  vertebral  segments  is  met  with  at 
either  extremity  of  the  vertebral  column,  more  particularly  below,  where  the  column 
is  modified  to  adapt  it  for  union  with  the  girdle  of  the  lower  limb,  and  also  in 
the  region  of  man's  degenerated  caudal  appendage.  But  a  partial  union  of  the 
vertebral  segments  also  takes  place  above,  between  the  two  highest  vertebrae,  in 
association  with  the  mechanism  necessary  to  provide  for  the  movements  of  the 
head  on  the  column. 

For  descriptive  purposes  the  vertebral  column  is  subdivided  according  to  the 
regions  through  which  it  passes.  Thus  the  vertebrse  are  described  as  cervical 
(vertebrae  cervicales),  dorsal  or  thoracic  (vertebrse  thoracales),  lumbar  (vertebrse 
lumbales),  sacral  (vertebrae  sacrales),  and  coccygeal  (vertebrae  caudales),  according 
as  they  lie  in  the  regions  of  the  neck,  back,  loins,  pelvis,  and  tail.  The  number  of 
vertebrae  met  with  in  these  regions  is  fairly  constant,  though,  as  will  be  hereafter 
pointed  out,  ^'ariations  may  occur  in  the  number  of  the  members  of  the  different 
series.  The  vertebrae  in  man  are  thus  apportioned — 7  cervical,  12  thoracic,  5  lumbar, 
5  sacral,  and  4  or  5  coccygeal ;  the  three  former  groups  comprise  the  true  or  mov- 
able vertebrae,  the  two  latter  the  false  or  fixed  vertebrae.  The  vertebral  formula 
may  be  thus  expressed  : — 

Movable  or  True  Vertebrae.  Fixed  or  False  Vertebrae. 

Cervical.     Thoracic.     Lumbar.  Sacral.      Coccygeal. 

7  12  5  5  4         =33. 

The  vertebrae,  though  displaying  great  diversity  of  characters  in  the  regions  above 
enumerated,  yet  preserve  certain  features  in  common.  All  possess  a  solid  part, 
centnim  or  body  (corpus  vertebrae) ;  all  have  articular  processes  by  which  they 
articulate  with  their  fellows ;  most  have  muscular  processes  developed  in  connexion 
with  them;  whilst  the  majority  display  a  vertebral  or  spinal  foramen  (foramen 
vertebrale)  formed  by  the  union  of  a  bony  arch  (arcus  vertebrae)  with  the  body. 
These  common  characters  may  best  be  studied  by  selecting  for  description  an 
intermediate  member  of  the  series.  For  this  purpose  one  of  the  middle  or  lower 
thoracic  vertebrae  may  be  chosen. 

A  typical  vertebra  may  be  described  as  consisting  of  a  body  or  centrum 
(corpus  vertebrae)  composed  of  a  mass  of  spongy  bone,  more  or  less  cylindrical  in 
form.  The  size  and  shape  of  the  body  is  Hable  to  considerable  variation  according 
to  the  vertebra  examined.  The  upper  and  lower  surfaces  of  the  body  are  very 
slightly  concave  from  before  backwards  and  from  side  to  side,  due  to  the  thickening 
of  the  bone  around  its  margins.  In  the  recent  condition  these  surfaces  afford 
attachment  for  the  intervertebral  discs  which  are  placed  like  pads  between  the 
bodies  of  the  movable  members  of  the  series.  The  circumference  of  the  body, 
formed  as  it  is  of  more  compact  bone  than  the  interior,  is  usually  slightly  concave 
from  above  downwards,  though  it  becomes  flat  behind,  where  the  body  forms  the 
anterior  boundary  of  the  spinal  or  vertebral  foramen,  at  which  point  it  is  usually 
shghtly  concave  from  side  to  side.  The  vertical  surfaces  of  the  body  are  pierced 
liere  and  there  by  foramina  for  the  passage  of  nutrient  vessels,  more  particularly 
on  the  posterior  surface,  where  a  depression  of  considerable  size  receives  the 
openings  of  the  canals  through  which  some  of  the  veins  which  drain  the  body  of 
the  bone  escape.  Connected  with  the  body  posteriorly  there  is  a  bony  vertebral 
arch  (arcus  vertebrae),  which,  by  its  union  with  the  body,  encloses  a  foramen  of  variable 
size,  the  vertebral  foramen  (foramen  vertebrale).  When  the  vertebrse  are  placed 
on  the  top  of  each  other  these  foramina  form  with  the  uniting  ligaments  a  con- 
tinuous canal — spinal  or  neural  canal — in  which  the  spinal  cord  with  its  coverings 
is  lodged.  The  vertebral  arch,  which  is  formed  by  the  union  of  the  pedicles  ^  and 
laminae,  besides  enclosing  the  spinal  foramen,  also  supports  the  spinous  and  trans- 

1  I  retaiu  this  term  in  place  of  the  cumbrous  radix  arcus  vertebrse  or  "root  of  the  vertebral  arch  "  of  the 
B.N.  A.,  classification." — A.T. 


THE  VEETEBKAL  COLUMN. 


77 


Superior 
articular  process    Pedicle 


Facet  for 

tubercle  of  rib 

(Fovea  co^talis 

transversalis) 

Transverse, 
process 


Demi-facet  for  head  of  rib 
(Fovea  costalis  superior) 
Body 


verse  processes,  which  may  be  regarded  as  a  series  of  levers  to  which  muscles  are 
attached,  whilst  others  are  articular  and  assist  in  uniting  the  different  vertebrse 
together  by  means  of  a  series  of  movable  joints.  The  pedicles  are  the  bars  of 
bone  which  pass  from  the  back  of  the  body  of  the  vertebra?  on  either  side  to 
the  points  where  the  articular 
processes  are  united  to  the  arch. 
These  roots  are  compressed  laterally, 
and  have  rounded  superior  and  in- 
ferior borders.  Since  the  vertical 
breadth  of  the  pedicles  is  not  as 
great  as  the  thickness  of  the  body  to 
which  they  are  attached,  it  follows 
that  when  the  vertebrae  are  placed 
one  above  the  other  a  series  of  in- 
tervals is  left  between  the  pedicles 
of  the  different  vertebrae.  These 
spaces,  enclosed  in  front  by  the 
bodies  of  the  vertebras  and  their 
intervertebral  discs,  and  behind  by 
the  coaptation  of  the  articular  pro- 
cesses, form  a  series  of  holes  com- 
municating with  the  neural  or  spinal 
canal ;  these  are  called  the  inter- 
vertebral foramina  (foramina  inter- 
vertebralia),  and  allow  the  trans- 
mission of  spinal  nerves  and  vessels. 


Demi-facet  for 
head  of  rib 
(Fovea  costalis 
inferior) 


Spinous  process 


FticGt  for 

As  each   intervertebral   foramen  is  tubercle  of 

rib 
cea  cos- 


talis tran: 
versalis) 

Superior  articular 
process 


Fig.  57. — Fifth  Thoracic  Vebtebra,  (A)  as  viewed 
from  the  right  side,  (B)  as  viewed  from  above. 


bounded    above    and    below    by    a  (pove 

pedicle,    the    grooved     surfaces    in 

correspondence  with  the  upper  and 

lower  borders   of   the    pedicles    are 

called  the    upper   and    lower  inter-  oemi-facet  fJr'he'l 

vertebral  grooves  or  notches  (incisura  of  nb  (Fovea  cost  Uw 

.  .  ...  inferioi ) 

vertebralis  superior  et  mferior). 
Posteriorly,  the  two  pedicles  are 
united  by  two  somewhat  flattened 
plates  of  bone — ^the  laminae,  which 
converge  towards  the  middle  line, 
and  become  fused  with  the  root  of 
the  projecting  spinous  process  (pro- 
cessus spinosus).  The  breadth  of 
the    laminge  and   their   sloping 

arrangement  are  such,  that  when  the  vertebrae  are  articulated  together  they  leave 
little  space  between  them,  thus  enclosing  fairly  completely  the  neural  canal,  of 
which  they  form  the  posterior  wall.  The  edges  and  inner  surfaces  of  the  laminae 
are  rough  for  the  attachment  of  the  ligaments  which  bind  them  together. 

The  muscular  processes  are  three  in  number,  viz.  two  transverse  processes — one 
on  either  side  —  and  one  central  or  median,  the  spinous  process.  The  former 
(processus  transversus)  project  laterally  on  either  side  from  the  arch  at  the  point 
where  the  pedicle  joins  the  lamina.  The  latter  (processus  spinosus)  extends  back- 
wards in  the  middle  line  from  the  point  of  fusion  of  the  lamina;.  The  spinous 
processes  display  much  variety  of  length  and  form. 

The  articular  processes  (zygapophyses),  four  in  number,  are  arranged  in  pairs — 
one  superior,  the  other  inferior ;  the  former  are  placed  on  the  upper  surface  of  the 
arch  where  the  pedicles  and  laminte  join,  the  latter  below  the  arch  in  correspondence 
with  the  superior.  Whilst  differing  much  in  the  direction  of  their  articular 
surfaces,  the  upper  have  generally  a  backward  tendency,  whilst  the  lower  incline 
forwards. 


78 


OSTEOLOaY. 


THE   TRUE   OR    MOVABLE   VERTEBR/E. 

The  Cervical  Vertebrae. 

The  cervical  vertebrae  (vertebrae  cervicales),  seven  in  number,  can  be  readily 
distinguished  from  all  the  other  vertebras  by  the  fact  that  their  transverse  pro- 
cesses are  pierced  by  a  foramen.  The  two  highest,  and  the  lowest,  require  special 
description ;  the  remaining  four  conform  to  a  common  type. 

Their  bodies,  the  smallest  of  all  the  true  vertebrse,  are  oblong  in  shape,  the 
transverse  diameter  being  much  longer  than  the  antero-posterior  width.  The  upper 
surface,  which  slopes  from  behind  forwards  and  downwards,  is  concave  from  side  to 
side,  owing  to  the  marked  projection  of  its  lateral  margins.  Its  anterior  lip  is 
rounded  oS",  whilst  its  posterior  edge  is  sharply  defined. 

The  inferior  surface,  which  is  more  or  less  saddle-shaped,  is  directed  downwards 
and  backwards.  It  is  convex  from  side  to  side,  and  concave  from  before  backwards, 
with  a  slight  rounding  off  of  the  projecting  anterior  lip.  The  vertical  diameter  of 
the  body  is  small  in  proportion  to  its  width.  The  anterior  surface  is  flat  in  the 
middle  line,  but  furrowed  laterally.  The  posterior  surface,  which  is  rough  and 
pierced  by  many  small  foramina,  is  flat  from  side  to  side  and  above  downwards ;  it 


Bifid  spine 


Superior  articular  process        Superior  notcli 

Vertebrarterial  foramen 


Inferior  notch 
Inferior  articular  process 


Vertebrarterial  foramen 
Anterior  tubercle  A 


Spinous  process 


Fig.  58.— Fourth  Cervical  Vertebra,  (A)  from  above,  and  (B)  from  the  right  side. 

forms  in  its  entire  extent  the  anterior  wall  of  the  spinal  foramen.  The  lateral 
aspects  of  the  body,  particularly  in  their  upper  parts,  are  fused  with  the  costal 
parts  of  the  transverse  processes,  and  form  the  inner  wall  of  the  vertebrarterial 
or  transverse  foramen  (foramen  transversarium).  The  pedicles  which  spring  from 
the  posterior  half  of  the  lateral  aspects  of  the  body,  about  equidistant  from  their 
upper  and  lower  margins,  are  directed  horizontally  backwards  and  outwards.  The 
superior  and  inferior  notches  are  nearly  equal  in  depth.  The  laminse  are  long,  and 
about  as  wide  as  the  body  of  the  bone  is  thick.  The  spinal  foramen  is  larger  than  in 
the  thoracic  and  lumbar  regions ;  its  shape  is  triangular,  or  more  nearly  semilunar. 
The  transverse  processes,  so  called,  are  pierced  by  the  vertebrarterial  or  transverse 
foramen  fforamen  transversarium).  They  consist  of  two  parts — the  part  behind  the 
foramen,  which  springs  from  the  neural  arch  and  is  the  true  transverse  process,  and 
the  part  in  front,  which  is  homologous  with  the  ribs  in  the  thoracic  portion  of  the 
column.  These  two  processes,  united  externally  by  a  bridge  of  bone,  which  thus 
converts  the  interval  between  them  into  a  foramen,  terminate  in  two  tubercles, 
known  respectively  as  the  anterior  and  posterior  tubercles  (tuberculum  anterius  et 
posterius).  The  general  direction  of  tliese  processes  is  laterally,  slightly  forwards, 
and  a  little  downwards,  the  anterior  tubercles  lying  medial  to  the  posterior.  The 
two  tubercles  are  se])arated  above  by  a  groove  directed  laterally,  downwards,  and 
forwards  ;  along  this  tlie  s])inal  nerve  trunk  passes.  The  vertebrarterial  foramen 
(foramen  transversarium),  often  subdivided  by  a  spicule  of  bone,  is  traversed  by  the 
vertebral  artery  and  vein  in  the  upper  six  vertebrte.  The  spinous  processes,  which 
are  directed  downwards,  are  short,  compressed  vertically,  and  bifid.  The  articular 
processes  are  supported  on  cylindrical  masses  of  bone  fused  with  the  arch  where 


THE  CERVICAL  VERTEBRA.. 


79 


the  pedicles  and  lamintB  join.  These  cylinders  are  sliced  away  obliquely  above  and 
below,  so  that  the  superior  articular  facets,  more  or  less  circular  in  form,  are 
directed  upwards  and  backwards,  whilst  the  corresponding  inferior  surfaces  are 
turned  downwards  and  forwards. 

First  Cervical  Vertebra  or  Atlas. — This  bone  may  be  readily  recognised  by 
the  absence  of  the  body  and  spinous  process.  It  consists  of  two  lateral  masses  (massae 
laterales),  which  support  the  articular  and  transverse  processes.  The  lateral  masses 
are  themselves  united  by  two  curved  bars  of  bone,  the  anterior  and  posterior  arches, 
of  which  the  former  is  the  stouter  and  shorter.  Each  lateral  mass  is  irregularly  six- 
sided,  and  so  placed  that  it  lies  closer  to  its  fellow  of  the  opposite  side  in  front  than 
behind.  Its  upper  surface  is  excavated  to  form  an  elongated  oval  facet  (fovea 
articularis  superior),  concave  from  before  backwards,  and  inclined  obliquely  inwards; 
not  infrequently  this  articular  surface  displays  indications  of  division  into  two 
parts.     These  facets  are  for  the  reception  of  the  condyles  of  the  occipital  bone. 

The  inferior  articular  facets  (fovese  articulares  inferiores)  are  placed  on  the  under 
surfaces  of  the  lateral  masses.  Of  circular  form,  they  display  a  slight  side- 
to-side  concavity,  though  g 
flat  in  the  antero-posterior 
direction.  Their  disposi- 
tion is  such  that  their  sur- 
faces incline  downwards 
and  slightly  inwards.  They 
rest  on  the  superior  ar- 
ticular processes  of  the 
second  cervical  vertebra. 
Springing  from  the  anterior 
and  inner  aspects  of  the 
lateral  masses,  and  uniting 
them  in  .front,  is  a  curved 
bar  of  bone,  the  anterior 
arch  (arcus  anterior) ;  com- 
pressed on  either  side,  this 
is  thickened  centrally  so 
as  to  form  on  its  anterior 
aspect  the  rounded  anterior 
tubercle  (tuberculum  an- 
^erius).  In  correspondence 
with  this  on  the  posterior  surface  of  this  arch  is  a  circular  facet  (fovea  dentis)  for 
articulation  with  the  odontoid  process  (dens)  of  the  second  cervical  vertebra  (axis). 

The  inner  surface  of  the  lateral  mass  is  rough  and  irregular,  displaying  a  little 
tubercle  for  the  attachment  of  the  transverse  ligament  which  passes  across  the  space 
included  between  the  two  lateral  masses  and  the  anterior  arch,  thus  holding  the 
odontoid  process  of  the  axis  in  position.  Behind  each  tubercle  there  is  usually  a 
deep  pit,  opening  into  the  bottom  of  which  are  the  canals  for  the  nutrient  vessels. 

Laterally  to  the  lateral  mass,  and  principally  from  its  upper  half,  the  transverse 
process  arises  by  two  roots  which  include  between  them  the  vertebrarterial  foramen. 
The  transverse  process  is  long,  obliquely  compressed,  and  down-turned  ;  the  anterior 
and  posterior  tubercles  have  fused  to  form  one  mass. 

The  posterior  arcb  arises  in  part  from  the  posterior  surface  of  the  lateral  mass, 
and  in  part  from  the  posterior  root  of  the  transverse  process.  Compressed  from 
above  downwards  anteriorly,  where  it  bounds  a  groove  which  curves  around  the 
posterior  aspect  of  the  superior  articular  process,  which  groove  is  also  continuous 
externally  with  the  vertebrarterial  foramen,  the  posterior  arch  becomes  thicker 
mesially,  at  which  point  it  displays  posteriorly  a  rough  irregular  projection — the 
posterior  tubercle  (tuberculum  posterius),  the  feeble  representative  of  the  spinous 
process.  A  prominent  little  tubercle,  arising  from  the  posterior  extremity  of  the 
superior  articular  process,  overhangs  the  groove  above  mentioned,  and  not  in- 
frequently becomes  developed  so  as  to  form  a  bridge  of  bone  across  it,  converting 
the  groove  into  a  canal  through  which  the  vertebral  artery  and  the  first  cervical  or 


Fig.  59.- 

Posterior  arch. 
Transverse  process. 
Tubercle  for  transverse 

ligament. 
Anterior  arch. 
Anterior  tubercle. 


-The  Atlas  from  Above. 

6.  Surface  for  articulation  with  odontoid 

process. 

7.  Superior  articular  process. 

8.  Foramen  for  vertebral  artery. 

9.  Groove  for  vertebral  artery. 
10.  Posterior  tubercle. 


80 


OSTEOLOGY. 


suboccipital  ^  nerve  pass — a  condition  normally  met  with  in  many  animals.  It  is 
noteworthy  that  the  grooves  traversed  by  the  two  highest  spinal  nerves  lie  behind 
the  articular  processes,  in  place  of  in  front,  as  in  other  parts  of  the  column. 

The  ring  formed  by  the  lateral  masses  and  the  anterior  and  posterior  arches  is 
of  irregular  outline.  The  anterior  part,  cut  off  from  the  rest  by  the  transverse 
ligament,  serves  for  the  lodgment  of  the  odontoid  process  of  the  axis ;  the  larger 
part  behind  corresponds  to  the  upper  part  of  the  neural  or  spinal  canal. 

Second  Cervical  Vertebra,  Axis,  or  Epistropheus. — This  is  characterised  by 
the  presence  of  the  tooth-like  dens  (odontoid  process)  which  projects  upwards  from 
the  superior  surface  of  the  body.  Slightly  constricted  where  it  joins  the  body,  the 
odontoid  process  tapers  to  a  blunt  point  superiorly,  on  the  sides  of  which  there  are 
surfaces  for  the  attachment  of  the  odontoid  or  check  (alar)  ligaments.  When  the  atlas 
and  axis  are  articulated  this  process  lies  behind  the  anterior  arch  of  the  atlas,  and 
displays  on  its  anterior  surface  an  oval  or  circular  facet  which  rests  on  that  on  the 
posterior  surface  of  the  anterior  arch  of  the  atlas.  On  the  posterior  aspect  of  the 
neck  of  the  odontoid  process  there  is  a  shallow  groove  in  which  lies  the  transverse 
ligament  which  holds  it  in  position. 

The  anterior  surface  of  the  body  has  a  raised  triangular  surface,  which  ends 


Odontoid  process  (dens)    Groove  for  transverse  ligament 

Superior  articular 
surface 


Odontoid  process  (dens) 


Articular 

surface  for 

anterior  arch 

of  atlas 


Foiamen  foi 

vertebral 

artery 

Inferior 
pre 

articular  ^ 
)cess 

m 

spine 
A 

Foramen 
for  verte' 


Inferior  articular 
process 


bral  artery    Transverse  process 

B 

Fig.  60.— Axis  or  Epistkopheus,  (A)  from  behind  and  ahove,  (B)  from  the  left  side. 

superiorly  in  a  ridge  passing  upwards  to  the  neck  of  the  odontoid  process.  The 
pedicles  are  concealed  above  by  the  superior  articular  processes  ;  inferiorly,  they  are 
deeply  grooved.  The  laminae — prismatic  on  section — are  thick  and  strong,  ending 
in  a  stout,  broad,  and  bifid  spinous  process,  the  under  surface  of  which  is  deeply 
grooved,  whilst  its  sides  meet  superiorly  in  a  ridge.  Placed  over  the  pedicles 
and  the  anterior  root  of  the  transverse  processes  are  the  superior  articular  surfaces. 
These  are  more  or  less  circular  in  shape,  shghtly  convex  from  before  backwards, 
flat  from  side  to  side,  and  are  directed  upwards  and  a  little  outwards.  They 
are  channelled  inferiorly  by  the  vertebrarterial  foramina  which  turn  outwards 
beneath  them.  The  grooves  by  which  the  second  cervical  nerves  (great  occipital) 
leave  the  neural  canal  cross  the  laminee  immediately  behind  the  superior  articular 
processes.  The  inferior  articular  processes  agree  in  form  and  position  with  those  of 
the  remaining  members  of  the  series,  and  are  placed  behind  the  inferior  inter- 
vertebral notches.  The  transverse  process  is  markedly  down-turned,  with  a  single 
pointed  extremity. 

The  sixth  cervical  vertebra  often  displays  an  enlargement  of  the  anterior 
tubercle  on  the  transverse  ])rocess,  called  the  carotid  tubercle  (tuberculum  caroticum) 
from  the  circumstance  that  the  carotid  artery  maybe  conveniently  compressed  against 
it.     It  is  necessary  to  add,  however,  that  tbe  tubercle  is  not  always  well  developed. 

The  seventh  cervical  vertebra  (vertebra  prominens)  receives  the  latter  name 
from  the  outstanding  nature  of  its  spinous  process,  which  ends  in  a  single  broad  tubercle. 

'  Under  the  B.N.  A.  nomenclature  the  name  is  given  to  the  whole  of  the  first  cervical  nerve. 


THORACIC  VERTEBR-^.  81 

This  forms  a  well-marked  surface  projection  at  the  back  of  the  root  of  the  neck. 
The  transverse  processes  are  broad,  being  flattened  from  above  downwards ;  they 
project  considerably  beyond  those  of  the  sixth.  The  maximum  width  between 
their  extremities  agrees  with  that  between  the  transverse  processes  of  the  atlas, 
these  two  constituting  the  widest  members  of  the  cervical  series.  The  anterior 
tubercle  is  very  small  and  is  placed  near  the  body.  The  vertebrarterial  foramen  is 
small  and  does  not  as  a  rule  transmit  the  vertebral  artery.  Usually  a  small  vein 
passes  through  it.  Not  infrequently  the  costal  element  is  separate  from  the  true 
transverse  process,  thus  constituting  a  cervical  rib. 

Thoracic  Vertebrae. 

The  thoracic  or  dorsal  vertebrae  (vertebrae  thoracales),  twelve  in  number, 
are  distinguished  by  having  facets  on  the  sides  of  their  bodies  for  the  heads  of  the 
ribs,  and  in  most  instances  also  articular  surfaces  on  their  transverse  processes  for 
the  tubercles  of  the  ribs  (Fig.  57,  p.  77). 

The  body  is  described  as  characteristically  heart-shaped,  though  in  the  upper 
and  lower  members  of  the  series  it  undergoes  transition  to  the  typical  forms  of  the 
cervical  and  lumbar  vertebrae,  respectively.  Its  antero- posterior  and  transverse 
widths  are  nearly  equal ;  the  latter  is  greatest  in  line  with  the  facets  for  the  heads 
of  the  rib.  The  bodies  are  slightly  thicker  behind  than  in  front,  thus  adapting 
themselves  to  the  anterior  concavity  which  the  column  displays  in  this  region. 
The  bodies  of  the  second  to  the  ninth  thoracic  vertebrae  inclusive,  each  possess  four 
costal  demi-facets  (fovea  costalis  superior  et  inferior)  a  superior  pair  placed  on  the 
upper  margin  of  the  body,  close  to  the  junction  of  the  pedicle  with  the  centrum, 
and  an  inferior  pair  situated  on  the  lower  edge,  close  to  and  in  front  of  the  inferior 
intervertebral  grooves. 

When  contiguous  vertebrae  are  articulated,  the  upper  pair  of  demi-facets  of  the  lower 
vertebra  coincide  with  the  lower  demi-facets  of  the  higher  vertebra,  and,  together  with  the 
intervening  intervertebral  disc,  form  an  articular  cup  for  the  reception  of  the  head  of 
a  rib.  Of  these  facets  on  the  body  the  upper  pair  are  the  primary  articular  surfaces 
for  the  head  of  the  rib ;  the  lower  are  only  acquired  secondai'ily.  Moreover,  these  facets, 
though  apparently  placed  on  the  body,  are  in  reality  developed  on  the  sides  of  the  pedicles 
behind  the  line  of  union  of  the  pedicles  with  the  centrum  (neuro-central  synchondrosis),  as 
will  be  explained  hereafter.  • 

The  pedicles  are  short  and  thick,  and  directed  backwards  and  slightly  upwards. 
The  superior  vertebral  notch  is  faintly  marked  ;  the  inferior  is  deep.  The  laminae  are 
broad,  flat,  and  sloping,  having  sharp  upper  and  lower  margins.  When  the 
vertebrae  are  superposed  the  latter  overlap  the  former  in  an  imbricated  manner. 
The  spinal  foramen  is  smaller  than  in  the  cervical  and  lumbar  regions,  and  nearly 
circular  in  shape. 

The  spinous  processes  vary  in  length  and  direction,  being  shorter  and  more 
horizontal  in  the  upper  and  lower  members  of  the  series,  longest  and  most  oblique 
in  direction  towards  the  middle  of  this  part  of  the  column.  Nearly  all  have  a  down- 
ward inclination,  and  are  so  arranged  that  they  overlap  one  another.  Triangular  in 
section  where  they  spring  from  the  neural  arch,  they  become  laterally  compressed 
towards  their  extremities,  which  are  capped  by  more  or  less  distinct  tubercles.  The 
transverse  processes  are  directed  backwards  and  outwards,  and  a  little  upwards. 
They  gradually  decrease  in  size  and  length  from  above  downwards.  Each  has  a 
somewhat  expanded  extremity,  the  anterior  surface  of  which,  in  the  case  of  the  upper 
ten  vertebrae,  is  hollowed  out  in  the  form  of  a  circular  facet  for  articulation  with 
the  tubercle  of  the  rib  which  rests  in  the  upper  demi-facet  of  the  vertebra  to  which 
the  transverse  process  belongs.  The  superior  articular  processes  are  vertical,  and 
have  their  surfaces  directed  backwards,  slightly  upwards,  and  a  little  outwards; 
the  inferior,  correspondingly  forwards,  downwards,  and  inwards. 

Certain  of  the  thoracic  vertebrae  display  characters  by  which  they  can  readily 
be  recognised.  These  are  the  first,  tenth,  eleventh,  and  twelfth,  and  sometimes 
the  ninth. 

The  first  thoracic  vertebra  resembles  the  seventh  cervical  in  the  shape  of  its 


82 


OSTEOLOGIY. 


body,  and  the  length  and  direction  of  its  spine.  There  is  an  entire  facet  on  either 
side  of  the  body  for  the  head  of  the  first  rib,  and  one  demi- facet  on  each  side  at  the 

lower  border  of  its  body,  to 
complete  the  socket  for  the 
head  of  the  second  rib.  Its 
transverse  processes  are  long, 
and  the  superior  interverte- 
bral notch  is  better  marked 
than  in  other  members  of 
the  thoracic  series.  The 
superior  articular  surfaces 
are  directed  backwards  and 
upwards,  not  outwards  as 
in  the  lower  members  of 
the  series. 

The  ninth  thoracic 
vertebra  occasionally  has 
only  the  upper  pair  of  demi- 
facets  on  its  body ;  at  other 
times  it  conforms  to  the 
usual  type. 

The  tenth  thoracic  ver- 
tebra may  have  only  one 
complete  costal  facet  on  each 
side  for  the  X.  rib,  though 
sometimes  the  articular  socket 
may  be  completed  by  the 
ninth  dorsal  vertebra.  The 
facet  on  the  transverse  pro- 
cess is  generally  small,  and 
sometimes  absent. 

The  eleventh  thoracic 
vertebra  has  a  complete 
circular  facet  on  the  outer 
side  of  each  pedicle  for  ar- 
ticulation with  the  XI.  rib. 
Its  transverse  processes  are 
short  and  stunted,  and  have 
no  facets. 

The  twelfth  thoracic 
vertebra  has  a  single  facet 
on  the  pedicle  on  each  side 
for  the  XII.  rib.  Its  trans- 
verse processes,  short  and 
stunted,  have  no  facets,  and 
are  broken  up  into  smaller 
tubercles,  called  respectively 
the  external,  superior,  and 
inferior  tubercles.  These 
are    homologous    with    the 


Fig.  61. — First,  Ninth,  Tenth,  Eleventh,  and  Twelfth 
Thoracic  Vertebra  fhom  the  Left  Side. 


1.  Inferior   articular   process    with 

out-turned  facet. 

2.  Single  facet  for  head  of  XII.  rib  ; 

no  facet  on  transverse  process. 

3.  Single  facet  for  head  of  XI.  rib  ; 

no  facet  on  transverse  process. 

4.  Single  or  demi-facet  for  head  of 

X.  rib. 
.5.   Occasional  demi-facet   for  head 
of  X.  rib. 

6.  Demi  -  facet    for    head    of    IX. 

rib. 

7.  Demi-facet  for  head  of  II.  ril). 


10. 


Single  facet  for  head  of  I.  rib. 
Facet  on  transverse  process  for 
tuberosity  of  I.  rib. 
Facet  on  transverse  process  for 
tuberosity  of  IX.  rib. 

Facet  ou  transverse  process  for  transvcrsc,  mammillary,  and 
tuberosity  of  X  rib,  in  this  acccssory    proccsses   of    the 

particular       instance        well  ,         ,  ,    ^  t     t 

marked.  lumbar    vertebrse.       indica- 

iiperior'^  Tuberclus  f  M.-uiiniillary.    tioUS       of        tllCSC 
uferior  I     '■'°'\'^-     M«:'=«««o'-y. 

J^r:"r:n:rar.  the  tenth  and  eleventh 
thoracic  vertebrse.  The 
twelfth  thoracic  vertebra  may  usually  be  distinguished  from  the  eleventh  by 
the    arrangement    of  its   inferior   articular   processes,   which   resemble    those   of 


11. 


processes 
may  also   be    met  with    in 


E.  External 


LUMBAR  VP]RTEBE^. 


83 


Inferior  articular  process 

Maminillary  process 

Accessoiv  process 


y      fiaiisverse 
process 


Superior  articular 
process 


the  lumbar  series  in  being  out-turned ;  but  the  eleventh  occasionally  displays 
the  same  arrangement,  in  which  case  it  is  not  always  easy  to  distinguish 
between  them. 

Lumbar  Vertebrae. 

The  lumbar  vertebrae  (vertebrae  lumbales),  five  in  number,  are  the  largest  of 
the  movable  vertebrse.     They  have  no  costal  articular  facets,  nor  are  their  trans- 
verse processes  pierced   by  a  foramen.      In  this  way   they  can    be  readily  dis- 
tinguished from  the  mem- 
bers of  the  cervical  and  '  '"'"^ 
thoracic  series. 

The  body  is  kidney- 
shaped  in  outline,  and 
of  large  size,  exhibiting  a 
gradual  transition  from 
the  thoracic  form  in  the 
higher  segments.  The 
transverse  diameter  is 
usually  about  a  half 
greater  than  the  antero- 
posterior width.  The 
anterior  vertical  thickness 
is  slightly  greater  than 
the  posterior,  being  thus 
adapted  to  the  anterior 
convex  curve  of  the 
column  in  this  region. 
The  pedicles,  directed 
horizontally  backwards, 
are  short  and  stout ;  the 
superior  notches  are 
shallow,  but  deeper  than 
in  the  thoracic  region ;  the 
inferior  grooves  are  deep. 
The  laminae  are  broad  and 
nearly  vertical,  sloping  but 
little.  They  support  on 
their  lower  margins  the 
inferior  articular  processes. 
The  spinal  foramen  is  large 
and  triangular. 

The  spinous  processes, 
spatula  shaped,  with  a 
thickened  posterior  mar- 
gin, project  backwards  and 
slightly  downwards.  The 
transverse  processes,  more 
slender  than  in  the  thor- 
acic region,  pass  horizon- 
tally outwards,  with  a 
slight  backward  inclination  and  usually  with  an  upward  tilt.  Arising  from  the 
junction  of  the  pedicles  with  the  laminae  in  the  higher  members  of  the  series,  they 
tend  to  advance  so  as  to  become  fused  with  the  outer  side  of  the  pedicle  and  back  of 
the  body  in  the  two  lower  lumbar  vertebrae.  In  these  latter  vertebrae  the  superior 
intervertebral  grooves  are  carried  obliquely  across  the  upper  surfaces  of  the  bases  of 
the  transverse  processes.  The  transverse  processes  lie  in  line  with  the  lateral 
tubercles  of  the  lower  thoracic  vertebrae,  with  which  they  are  serially  homologous, 
and  are  to  be  regarded  as  representing  the  costal  element.  Placed  on  their  base 
posteriorly,  and  just  external  to  and  below  the  superior  articular  processes,  are  the 


Body 
Superior  articular  process 


Mammillary  process 


Tians verse  process 


Fig.  62.- 


Iiiferior  articular  process 

-Third  Lumbar  Vertebra,   (A)  from  aliove,  and  (B)  from 
the  left  side. 


84  OSTEOLOGY. 

small  accessory  tubercles  (processus  accessorii)  which  are  in  series  with  the  inferior 
tubercles  of  the  lower  thoracic  vertebrae.  The  superior  articular  processes  are  stout, 
oval,  curved  plates  of  bone,  fused  in  front  with  the  pedicles  and  laminae,  and  having 
their  concave  articular  surfaces  vertical  and  in-turned.  Externally,  and  on  their 
posterior  edge,  the  bone  rises  in  the  form  of  an  elongated  oval  tubercle,  the  mam- 
millary  process  (processus  mammillaris) ;  these  are  in  correspondence  with  the 
superior  tubercles  of  the  lower  thoracic  transverse  processes. 

The  inferior  articular  processes  lie  on  either  side  of  the  root  of  the  spinous 
process,  supported  on  the  inferior  margin  of  the  laminse.  Their  articular  surfaces, 
oval  in  outline,  convex  from  side  to  side,  and  plane  from  above  downwards,  are 
out-turned.  The  inferior  articular  processes  are  much  closer  together  than  the 
superior ;  so  that  when  the  vertebrae  are  articulated  the  superior  articular  processes 
of  the  lower  vertebra  embrace  the  inferior  articular  processes  of  the  higher 
vertebra. 

The  fifth  lumbar  vertebra  is  characterised  by  the  size  of  its  body,  which  is 
the  largest  of  all  the  vertebrae.  Further,  the  under  surface  of  the  body  is  cut 
away  at  the  expense  of  its  posterior  part :  hence  the  thickness  of  the  centrum  in 
front  much  exceeds  that  of  the  vertical  diameter  behind.  By  its  articulation 
with  the  first  sacral  segment  the  lower  border  of  the  body  of  this  bone  assists 
in  the  formation  of  the  sacro-vertebral  angle.  The  transverse  process  is  pyra- 
midal in  form,  and  stouter  than  those  of  the  other  lumbar  vertebrae.  It  arises 
by  a  broad  base  from  the  side  of  the  back  of  the  body,  as  well  as  from  the 
pedicle,  and  is  directed  outwards  and  a  little  backwards  and  upwards.  Its  upper 
surface  is  slightly  grooved  by  the  superior  intervertebral  notch.  A  deep  notch 
separates  it  posteriorly  from  the  superior  articular  processes,  which  are  less 
in-turned  than  in  the  other  members  of  the  series,  their  articular  surfaces  being 
directed  more  backwards  than  inwards,  and  displaying  less  concavity.  The  inferior 
articular  processes  are  further  apart  than  is  the  case  with  the  other  members  of 
the  series,  they  lie  in  line  with  the  superior.  The  spinous  process  is  shorter  and 
narrower  than  the  other  lumbar  spines,  particularly  so  in  the  female.  The  neural 
canal  is  somewhat  compressed  at  its  external  angles. 


THE    FALSE    OR    FIXED    VERTEBRAE. 
The   Sacrum. 

The  sacrum  (os  sacrum),  of  roughly  triangular  shape,  is  formed  normally  by  the 
fusion  of  five  vertebrae.  The  anterior  surface  of  the  bone  is  slightly  hollow  from 
side  to  side  and  concave  from  above  downwards,  the  curve  being  usually  most 
pronounced  opposite  the  third  sacral  segment.  The  central  part  corresponds  to 
the  l^odies  of  the  sacral  vertebrae,  the  lines  of  fusion  of  which  are  indicated  by  a 
series  of  four  parallel  ridges  which  cross  the  median  part  of  the  bone  at  gradually 
diminishing  intervals  from  above  downwards;  externally,  these  ridges  disappear 
on  either  side  on  the  inner  walls  of  the  four  anterior  sacral  foramina  (foramina 
sacralia  anteriora).  The  size  of  these  holes  decreases  from  above  downwards.  The 
upper  and  under  border  of  each  foramen  is  formed  by  a  stout  bar  of  bone,  of  which 
there  are  five  on  each  side,  corresponding  in  number  with  the  vertebrae  present. 
These  unite  externally  so  as  to  form  the  lateral  mass  (pars  lateralis),  thus  en- 
closing the  foramina  to  the  outer  side,  though  here  the  edge  is  not  abrupt,  but 
sloped  so  as  to  pass  gradually  into  the  canal.  The  large  anterior  divisions  of  the 
sacral  nerves  pass  through  these  foramina  and  occupy  the  shallow  grooves.  The 
bone  is  broadest  across  the  first  sacral  vertebra,  tends  to  narrow  opposite  the 
second,  and  again  usually  increases  in  width  opposite  the  third.  When  this 
condition  is  well  marked,  the  edge  has  a  notched  appearance  (sacral  notch)  which 
assists  in  the  interlocking  of  the  sacro-iliac  joint ;  this  feature  is  common  in  the 
Simiidae  and  some  of  the  lower  races  of  mankind  (Paterson).  The  surface  of  bone 
between  and   external   to   the  first,  second,   third,  and  fourth    foramina  affords 


THE  SAOKUM. 


85 


attachment  to  the  fibres  of  origin  of  the  piriformis,  which  may  in  some  instances 
extend  on  to  the  bodies  of  the  second  and  third  segments  (Adolphi),  whilst  on  the 
edge  lateral  to  and  Ijelow  the  fourth  foramen  the  coccygeus  is  inserted. 

The  posterior  surface  is  rough  and  irregular.  Convex  from  aljove  downwards  it 
displays  medially  a  crest  (crista  sacralis  media)  whereon  are  seen  four  elongated 
tubercles — the  spines  of  the  upper  four  sacral  vertebrte.  External  to  these  the 
bone  forms  a  groove — the  sacral  groove — the  floor  of  which  is  made  up  of  the  con- 
Huent  lamiiue  of  the  corresponding  vertebrae.  In  line  with  the  intervals  between 
the  spines,  and  wider  apart  above  than  below,  another  series  of  tubercles  is  to  be 
seen.  These  are  due  to  the  fusion  of  the  articular  processes  of  the  sacral  vertebrie, 
which  thus  form  faint  interrupted  ridges  on  either  side  of  the  bone  (cristas  sacrales 
articulares).     Normally,  the  spine  of  the  lowest  sacral  segment  is  absent,  and  the 


Superior  articular  processes      Transverse  process  of  first  sacral  vertebra 


Anterior  sacra 
foramen 


Inferior  lateral  anirlp. 


Groove  for  fifth  sacral  nerve 


Coccygeal  articular  surface 
Fig.  63. — The  Sacrum  (anterior  view). 

laminse  do  not  coalesce  medially,  thus  leaving  a  gap  in  which  the  spinal  canal  is 
exposed  (hiatus  sacralis) ;  whilst  inferiorly  the  tubercles  corresponding  to  the  inferior 
articular  processes  of  the  last  sacral  vertebra  form  little  down-projecting  processes — 
the  sacral  cornua  (cornua  sacralia) — by  means  of  which  the  sacrum  is  in  part  united 
to  the  coccyx.  Just  wide  of  the  articular  tubercles  are  the  posterior  sacral  foramina 
(foramina  sacralia  posteriora),  for  the  transmission  of  the  posterior  divisions  of  the 
sacral  nerves.  These  are  in  correspondence  with  the  anterior  foramina,  so  that  a 
probe  can  be  passed  directly  through  both  openings ;  but  be  it  noted  that  the 
posterior  are  much  smaller,  and  their  margins  much  sharper,  than  is  the  case  with 
the  anterior.  The  surface  of  the  lateral  mass  lateral  to  the  posterior  sacral 
foramina  is  rough  and  irregular,  owing  to  the  presence  of  four  more  or  less  elevated 
tubercles,  which  constitute  the  lateral  ridges  on  either  side  of  the  bone  (cristse 
sacrales  laterales),  and  which  are  serially  homologous  with  the  true  transverse 
processes  of  the  lumbar  vertebrae.  The  posterior  surface  of  the  bone  furnishes  an 
extensive  surface  for  the  origin  of  the  erector  spinse  (sacro- spinalis),  whilst   the 

6 


86 


OSTEOLOGY. 


edge  of  the  bone  lateral  to  the  third  and  fourth  foramen  gives  attachment  to  the 
glutaius  maximns. 

The  base  of  the  bone  displays  features  more  in  accordance  with  a  typical 
vertebra.  Centrally,  and  in  front,  is  placed  the  body,  the  upper  surface  of  which 
articulates  with  the  last  lumbar  vertebra  through  the  medium  of  an  intervertebral 
disc.  The  anterior  margin  is  thin  and  projecting,  overhanging  the  general  con- 
cavity of  the  front  of  the  bone,  and  forming  what  is  called  the  promontory  (promon- 
torium).  Behind  the  body,  the  spinal  canal,  of  triangular  form  with  slightly 
appressed  sides,  is  seen,  whilst  posteriorly  is  the  short  spinous  process  forming  the 
highest  tubercle  of  the  median  crest.  Spreading  out  from  the  sides,  and  partly  from 
the  back  of  the  body  on  either  side,  is  a  fan-shaped  mass  of  bone,  the  upper  surface 
of  which  is  slightly  concave  from  side  to  side,  and  convex  from  above  and  behind 


Superior  aperture  of 
hacral  canal 


Superior  articular  process 


Transverse  process 


\ 
Posterior  sacral  foramen-^'''^  V 


Inferior  lateral  angle 


Sacial  cornu 


nferior  aperture  of  sacral  canal 
Groove  for  fifth  sacral  nerve 


Coccygeal  articular  surface 
Fig.  64. — The  Saceum  (posterior  view). 

downwards  and  forwards.  This,  the  ala  (ala  sacralis),  corresponds  to  the  thick  upper 
border  of  the  lateral  mass,  and  is  formed,  as  will  be  explained  hereafter,  by  elements 
which  correspond  to  the  pedicles  and  transverse  processes  of  the  sacral  vertebrae, 
together  with  superadded  structures— the  sacral  ribs.  The  lateral  margin  of  the 
lateral  mass,  as  seen  i'rom  aljove,  is  sharp  and  laterally  convex,  terminating  behind 
in  a  x^rominent  tubercle — the  highest  of  the  series  of  elevations  seen  on  the  posterior 
surface  of  the  bone,  which  have  been  already  described  as  serially  homologous  with 
the  true  transverse  processes  of  the  lumbar  vertebrae.  Fused  with  the  back  of  each 
lateral  mass,  and  separated  from  it  laterally  by  a  narrow  but  deep  notch,  is  the 
superior  articular  process.  This  supports  a  vertical  articular  surface,  which  is  of 
circular  or  oval  form,  and  concave  from  side  to  side,  having  a  general  direction 
backwards  and  a  little  medially. 

The  borders  of  the  bone  are  thick  above,  where  they  articulate  with  the  ilia,  thin 
and  tapering  below,  where  they  furnish  attachments  for  the  powerful  sacro-sciatic 
(sacro-tuberous)  ligaments.     The  iliac  articular  surfaces  are  described  as  auricular  in 


COCCYX. 


87 


shape  (fades  auricularis),  and  overlie  tlie  lateral  masses  formed  by  the  first  three 
sacral  vertebne,  though  this  arrangement  is  liable  to  considerable  variation.  Behind 
the  auricular  surface  the  bone  is  rough  and  pitted  by  three  distinct  depressions  for 
the  attachment  of  the  strong  sacro- iliac  ligaments.  Inferiorly,  the  edge  formed 
by  the  lateral  masses  of  the  fourth  and  fifth  sacral  vertebrae  becomes  gradually 
thinner,  and  at  the  inferior  lateral  angle  changes  its  direction  and  sweeps  inwards 
towards  the  body  of  the  fifth  sacral  segment. 

The  apex,  or  lower  end  of  the  sacrum,  is  formed  by  the  small  oval  body  of  the 
fifth  sacral  vertebra,  which  articulates  with  the  coccyx. 

The  sacral  canal  follows  the  curve  of  the  bone ;  more  or  less  triangular  in 
shape  above,  it  becomes  appressed  and  flattened  below.  Inferiorly,  its  posterior 
wall  is  deficient  owing  to  the  imperfect  ossification  of  the  lamina3  of  the  fifth,  and, 
it  may  be,  of  the  fourth  sacral  segments.  Passing  obUquely  downwards  and 
laterally  from  this  canal  into  the  lateral  masses  on  either  side  are  the  four  pairs  of 
intervertebral  foramina,  each  of  which  is  connected  laterally  with  a  V-shaped 
canal  which  terminates  in  front  and  behind  in  the  anterior  and  posterior  sacral 
foramina.     The  hinder  limb  of  the  V  is  shorter  and  narrower  than  the  anterior. 

The  female  sacrum  is  proportionately  broader  than  the  male,  its  curves  are 
liable  to  great  individual  variation,  usually  it  is  flattened  above,  and  somewhat 
abruptly  curved  below  as  contrasted  with  the  male  sacrum  in  which  the  curve  is 
more  uniformly  distributed  throughout  the  bone.  In  the  female  the  absolute 
depth  of  the  curve  is  less  than  in  the  male. 

The  variation  in  the  proportions  of  the  breadth  to  the  length  of  the  sacrum  is 


expressed  by  the  formula 


breadth  x  100 


=  Sacral  Index.     Sacra  with  an  index  above 


length 

100  are  platyhieric  and  are  generally  characteristic  of  the  higher  races,  those  with 
an  index  below  100  are  dolichohieric  and  are  more  commonly  met  with  in  the  lower 
races  of  man.     The  average  European  index  is  112"-4  for  males  and  116"8  for  females 


Coccyx. 

The  coccyx  consists  of  four — sometimes  five,  less  frequently  three — rudimentary 
vertebrae,  which  tend  to  become  fused.  The  first  piece  is  larger  than  the  others ; 
it  has  an  oval  hollow 
facet  on  its  upper  sur- 
face, which  articulates 
with  the  body  of  the  last 
sacral  segment.  Pos- 
teriorly, two  processes, 
comua  coccygea,  which 
he  in  series  with  the 
articular  processes  of  the 
sacrum,  extend  upwards 
and  unite  with  the  sacral 
comua,  thus  bridging 
over  the  notch  for  the 
exit  of  the  fifth  sacral 
nerve,  and  converting 
it  into  a  foramen,  the 
last  of  the  intervertebral 
series.  From  the  outer 
sides  of  the  body  project  rudimentary  transverse  processes  which  may,  or  may 
not,  unite  with  the  sacrum  close  to  the  lower  lateral  angles;  in  the  latter 
case  the  fifth  anterior  sacral  foramina  are  enclosed.  Inferiorly,  the  body  of 
the  bone  articulates  with  the  succeeding  vertebra.  The  second  coccygeal  vertebra 
displays  slight  traces  of  a  transverse  process  and  the  rudiments  of  pedicles.  The 
succeeding  segments  are  mere  rounded  or  oval-shaped  nodules  of  bone. 

Fusion  between  the  lower  elements  occurs  normally  in  middle  life,  whilst  imion  between 
the  first  and  second  segments  occurs  somewhat  later.     It  is  not  unusual,  however,  to  find 


1.  Transverse  process 

2.  Transverse  process 


Fig.  65. — The  Coccyx. 
A.  Posterior  Surface.     B.  Anterior  Surface. 

5.  Sacrum 

6.  Cornu. 


3.  Sacrum. 

4.  Cornu. 


7.  Transverse  process. 

8.  Transverse  process. 


88  OSTEOLOGY. 

that  the  first  coccygeal  vertebra  i*emains  separate  from  the  others.  Though  very  variable, 
as  a  rule,  fusion  occurs  more  commonly  in  the  male,  and  at  an  earlier  age,  than  in  the 
female.  Szawlowski  has  recorded  a  case  in  which  a  curved  process  arose  from  the  ventral 
surface  of  the  first  coccygeal  segment.  He  regards  this  as  possibly  the  homologue  of  a 
ventral  arch  {Anat.  Anz.  Jena,  vol.  xx.  p.  320). 

From  the  posterior  surface  of  the  coccyx  the  glutseus  maximns  arises,  whilst 
to  it  is  attached  the  filum  terminale  of  the  spinal  cord.  To  its  lateral  borders 
are  attached  the  coccygei  and  levatores  ani  muscles,  and  from  its  tip  spring  the 
fibres  of  the  sphincter  ani. 

THE   VERTEBRAL  COLUIYIN    AS   A  WHOLE. 

When  all  the  vertebrse  are  articulated  together,  the  resulting  column  displays 
certain  characteristic  features.  The  division  of  the  column  into  a  true  or  movable 
part,  comprising  the  members  of  the  cervical,  thoracic,  and  lumbar  series,  and  a 
false  or  fixed  portion,  including  the  sacrum  and  coccyx,  can  now  be  readily 
recognised.  The  vertebrae  are  so  disposed  that  the  centra  or  bodies  form  an 
interrupted  column  of  solid  parts  in  front,  which  constitutes  the  axis  of  support 
for  the  head  and  trunk ;  whilst  the  neural  arches  behind  provide  a  canal  for  the 
lodgment  and  protection  of  the  spinal  cord  and  its  membranes.  In  the  movable 
part  of  the  column  both  the  anterior  supporting  axis  and  the  neural  canal  are 
liable  to  changes  in  their  disposition  owing  to  the  movements  of  the  head  and 
trunk.  Like  the  bodies  and  neural  arches,  the  spinous  and  transverse  processes 
are  also  superposed,  and  fall  in  line,  forming  three  series  of  interrupted  ridges — 
one  (the  spinous)  placed  centrally  and  behind,  the  others  (the  transverse)  placed 
laterally.  In  this  way  two  vertebral  grooves  are  formed  which  lie  between  the 
central  and  lateral  ridges.  The  floor  of  each  groove  is  formed  by  the  laminae  and 
articular  processes,  and  in  these  grooves  are  lodged  the  muscles  which  serve  to 
support  and  control  the  movements  of  the  column. 

Further,  the  column  so  constituted  is  seen  to  display  certain  curves  in  an 
antero- posterior  direction.  These  curves  are,  of  course,  subject  to  very  great 
variation  according  to  the  position  of  the  trunk  and  head,  and  can  only  be  satis- 
factorily studied  in  a  fresh  specimen ;  but  if  care  be  exercised  in  the  articulation 
of  the  vertebrae,  the  following  characteristic  features  may  be  observed,  assuming,  of 
course,  that  the  column  is  erect  and  the  head  so  placed  that  the  axis  of  vision  is 
directed  towards  the  horizon.  There  is  a  forward  curve  in  the  cervical  region, 
which  gradually  merges  with  the  backward  thoracic  curve  ;  this  becomes  con- 
tinuous below  with  an  anterior  convexity  in  the  lumbar  region,  which  ends  more 
or  less  abruptly  at  the  union  of  the  fifth  lumbar  with  the  first  sacral  vertebra, 
where  the  sacrum  slopes  suddenly  backwards,  causing  the  column  to  form  a 
marked  projection — the  sacro-vertebral  angle.  Below  this,  the  anterior  concavity  of 
the  front  of  the  sacrum  is  directed  downwards  as  well  as  forwards.  Of  these  four 
curves,  two — the  thoracic  and  sacral — are  primary,  they  alone  exist  during  fcetal 
life ;  whilst  the  cervical  and  lumbar  forward  curves  only  make  their  appearance 
after  birth — the  former  being  associated  with  the  extension  and  elevation  of  the 
head,  whilst  the  latter  is  developed  in  connexion  with  the  use  of  the  hind  limb  in 
the  hyper-extended  position,  which  in  man  is  correlated  with  the  assumption  of 
the  erect  posture ;  this  curve,  therefore,  only  appears  after  the  child  has  begun  to 
walk.  For  these  reasons  the  cervical  and  lumbar  curves  are  described  as  secondary 
and  compensatory. 

Not  infrequently  there  is  a  slight  lateral  curvature  in  the  thoracic  region,  the 
convexity  of  the  curve  being  usually  directed  towards  the  right  side.  This  may 
be  associated  with  a  greater  use  of  the  muscles  of  the  right  upper  limb,  or  may 
depend  on  the  pressure  exercised  by  the  upper  part  of  the  thoracic  aorta  on  the 
vertebne  of  the  thoracic  region,  thus  causing  a  slight  lateral  displacement,  together 
with  a  flattening  of  the  side  of  the  fifth  thoracic  vertebra  (impressio  aortica)  as  was 
first  pointed  out  by  Wood  (Journ.  Anat.  and  Physiol,  vol.  iii.).  Above  and  below 
this  curve  there  are  slight  compensatory  curves  in  the  opposite  direction. 


VERTEBEAL  COLUMN  AS  A  WHOLE. 


89 


•^  < 


The  line  which  unites  the  tips  of  the  spines  is  not  a  repetition  of  the  curves 
formed  by  the  bodies.  This  is  due  to  the  fact  that  the  length  and  direction  of  the 
spines  vary  much  in  different  regions ;  thus  in  the 
neck,  with  the  exception  of  the  second,  sixth,  and 
seventh,  the  spines  are  all  short  (absent  in  the  case 
of  the  atlas).  In  the  thoracic  region  the  spines, 
though  long,  are  obliquely  placed — a  circumstance 
which  much  reduces  their  prominence ;  that  of  the 
seventh  thoracic  vertebra  is  usually  the  longest  and 
most  slanting.  Below  this  point  the  length  of  the 
spines  gradually  decreases,  and  their  position  more 
nearly  approaches  the  horizontal.  In  the  loins  the 
spines  have  all  a  slight  downward  direction. 

The  spines  of  the  upper  three  or  four  sacral 
vertebrae  form  an  osseous  ridge  with  interrupted 
tubercles.  Tlie  ridge  formed  by  the  vertebral  spines 
is  an  important  determinant  of  the  surface  form,  as 
it  corresponds  to  the  median  furrow  of  the  back, 
and  here  the  indi\'idual  spines  may  be  felt  and 
counted  from  the  seventh  cervical  down  to  the  sacral 
region.  This  is  best  done  when  the  back  is  well 
bent  forwards. 

Taken  as  a  whole,  the  spines  of  the  movable  vertebrae  in 
man  have  a  downward  inclination — a  character  which  he 
shares  with  the  anthropoid  apes  and  a  few  other  animals. 
This  character  serves  to  distinguish  his  column  from  tho.se  of 
lower  mammals  in  which  the  spines  of  the  lumbar  vertebrae 
are  directed  headwards  towards  the  "  centre  of  motion,"  which 
is  usually  situated  near  the  hinder  extremity  of  the  thorax, 
where  a  vertebra  is  placed  the  direction  of  whose  spine  is 
vertical  to  the  horizontally  disposed  column ;  this  vertebra 
is  often  referred  to  as  the  anticlinal  vertebra. 

As  viewed  from  the  front,  the  vertebral  bodies 
increase  in  width  from  the  second  cervical  to  the 
first  thoracic ;  thence  a  reduction  in  breadth  takes 
place  to  the  level  of  the  fourth  thoracic,  below  which 
there  is  a  gradual  increase  in  their  transverse  dia- 
meters until  the  sacrum  is  reached.  Here  a  rapid 
reduction  in  width  takes  place,  terminating  inferiorly 
in  the  nodules  of  the  coccyx. 

The  transverse  processes  of  the  atlas  are  wide  and 
outstanding.  The  succeeding  four  cervical  vertebrae 
have  transverse  processes  of  nearly  equal  width ;  the 
seventh,  however,  displays  a  marked  increase  in  its 
transverse  diameter,  and  is  about  equal  in  width  to 
the  first  thoracic  vertebra.  Below  this  a  gradual  and 
regular  diminution  in  width  characterises  the  trans- 
verse processes  of  the  thoracic  vertebrae,  until  ia  the 
case  of  the  eleventh  and  twelfth  they  are  merely 
represented  by  the  small  lateral  tubercles.  In  the 
lumbar  region  the  transverse  processes  again  appear 
outstanding,  and  of  nearly  equal  length. 

The  transverse   diameter  of  the  lateral  mass  of   gi  J 

the  first  sacral  vertebra  forms  the  widest  part  of  the  5  |,  I 

column.     Below  this,  a  decrease  in  width  occurs  until       Fig.  66. 

the  level  of  the  third  sacral  segment  is  reached,  at 

which  point  the  transverse  diameter  is  somewhat  abruptly  diminished,  a  reduction 

in  width  which  is  further  suddenly  accentuated  opposite  the  fifth  sacral  segment. 

As  viewed  from  the  side,  the  bodies  display  a  gradual  increase  in  their  antero- 
posterior width  until  the  second  lumbar  vertebra  is  reached,  below  which,  this 

6a 


■%  < 


C?''-^ 


^Aili 


Vertebral  Coli'mx 
FROM  THE  Left  Side. 


90 


OSTEOLOGY. 


diameter  is  slightly  reduced.  In  the  sacral  region  the  reduction  in  this  diameter 
is  great  in  the  first  and  second  sacral  segments,  more  gradual  and  less  marked  in 
the  last  three  segments.  The  facets  for  the  heads  of  the 
ribs  in  the  upper  thoracic  region  lie  on  the  sides  of  the 
bodies  ;  those  for  the  tenth,  eleventh,  and  twelfth  are  placed 
^sABtiP^'  farther  back  on  the  pedicles. 

<ijj^!^i%         -a  The  intervertebral  foramina  increase  in  size  from  above 

downwards  in  the  movable  part  of  the  column,  being  largest 
in  the  lumbar  region.  In  the  sacral  region  they  decrease 
in  size  from  above  downwards.  In  the  cervical  region  the 
two  highest  cervical  nerves  pass  out  behind  the  articular 
g=~x^  processes  of  the  atlas  and  axis,  and  lie,  therefore,  behind 

the  corresponding  transverse  processes  of  these  vertebrae. 
The  succeeding  cervical  nerves  pass  out  through  the 
intervertebral  foramina  which  are  placed  between  the 
transverse  processes  and  in  front  of  the  articular  processes. 
In  the  thoracic  and  lumbar  vertebrae  the  intervertebral 
foramina  lie  in  front  of  both  the  articular  and  transverse 
processes.  The  arrangement  of  these  foramina  in  the  sacrum 
has  been  already  sufficiently  explained. 

The  neural  canal  for  the  lodgment  of  the  spinal  cord 
and  its  meninges  is  largest  in  the  cervical  and  lumbar 
regions,  in  both  of  which  it  assumes  a  triangular  form ; 
whilst  it  is  narrow  and  circular  in  the  thoracic  region. 
These  facts  are  correlated  with  the  movements  of  the 
column  which  are  most  free  in  those  regions  where  the 
u       canal  is  largest,  i.e.  the  neck  and  loins. 

I  The  average   length   of   the  vertebral  column   is   from  70 

H  to  73  centimetres,  or  from  27|  to  28|  inches.  Of  this  the 
cervical  part  measures  from  13  to  14  cm. ;  the  thoracic,  27  to 
29  cm.;  lumbar,  17  to  18  cm.;  and  the  sacro- coccygeal,  12 
to  15  cm.  The  individual  differences  in  the  length  of  the 
column  are  less  than  one  might  expect,  the  variation  in  height 
of  different  individuals  being  often  largely  dependent  on  the 
length  of  the  lower  limbs.  In  the  female  the  average  length 
of  the  column  is  about  60  centimetres,  or  23|  inches,  and  the 
■n        curve  in  the  lumbar  region  is  usually  more  pronounced. 

-2 

^       DEVELOPIVIENT  OF  THE  VERTEBRAL 

COLUMN. 

The  Cartilaginous  Column. 

As  has  been  already  stated  (p.  26),  the  neural  tube 
and  the  notochord  are  enveloped  by  a  continuous  sheath  of 
mesodermal  tissue  which  forms  the  membranous  vertebral 
9  column.  It  is  by  the  chondrification  of  this  that  the  car- 
ju  'I  tilaginous  column  is  developed.  This  process  commences 
ij  ft  ./  ^  about  the  end  of  the  first  or  the  beginning  of  the  second 
month  of  foetal  life.  In  correspondence  with  each  vertebral 
segment,  two  symmetrical  nodules  of  cartilage  appear  on 
either  side  of  the  notochord ;  these  rapidly  surround  and 
constrict  it.  By  their  fusion  they  constitute  the  body  of 
a  cartilaginous  vertebra,  and  are  so  disposed  that  they 
^'^^''n^I^rnoTBF^iir''  alternate  in  position  with  the  muscle  plates  which  are 
lying  on  either  side.  In  this  way  a  vertebral  body  corre- 
sponds in  position  to  the  posterior  half  of  the  anterior  myotome,  and  the  anterior 
half  of  the  posterior  myotome,  the  intermyotomic  intervals,  which  contain  the 
connective   tissue   plates   separating   the   muscle   segments,  lie   in   line  laterally 


hS, 


THE  CARTILAGINOUS  COLUMN. 


91 


with  the  mid -points  of  the  sides  of  the  cartilaginous  vertebrae.  It  is  by  chondri- 
fication  of  these  intersegmental  layers  that  in  certain  regions  the  ribs  are 
ultimately  developed.  Meanwhile,  the  scleratogenous  tissue  between  the  chondri- 
fying  vertebral  bodies  undergoes  little  change  and  persists  as  the  intervertebral 
disc.  Here  the  embedded  notochord  undergoes  but  slight  compression  and  enlarges, 
so  that  if  a  length  of  the  column  be  examined  in  longitudinal  section  the  noto- 
chord displays  a  moniliform  appearance,  the  constricted  parts  corresponding  to 
the  bodies,  the  enlarged  portions  to  the  discs.  The  former  disappear  at  a  later 
stage  when  ossification  begins,  but  the  latter  persist  in  the  adult  as  the  pulpy 
core  in  the  centre  of  the  intervertebral  disc. 

The  portions  of  the  scleratogenous  tissue  which  lie  lateral  to  the  notochord 
have  next  to  be  considered ;  these  extend  dorsalwards  around  the  neural  canal, 
and  ventralwards  beneath  the  notochord.  The  former  is  sometimes  called  the 
vertebral  bow,  the  latter  the  hypochordal  bow.  The  vertebral  bow  begins  to 
chondrify  on  either  side,  and  forms  the  lateral  portions  of  the  cartilaginous  neural 
arch,  the  extremities  of  which  usually  unite  dorsally  about  the  fourth  month  of 
foetal  life ;  if  from  defective  development  this  union  should  fail  to  occur,  a 
deformity  known  as  spina  bifida  is  the  result. 

From  the  cartilaginous  neural  arch  so  formed  arise  the  chondrified  rudiments 
of  the  spinous,  transverse,  and  articular  processes. 


Neui 


Vertebral  bow 


Notocliord 

Sliei 
Hypochordal  bo 


I// \v 

0 


-Myotome 


0     w 


-Septum 

-Bod J-  of  vertebra 
-Hypochordal 


-  N  otochord 


H 


A  B 

Fig.  68. — The  Development  of  the  Membranous  Basis  of  a  Vertebra  (after  Keith). 

A,  in  transverse  section.      B,  in  horizontal  section,  showing  the  relation  of  the  vertebra  to  the 

primitive  segments. 

The  chondrification  of  the  neural  arch  is  variously  described  as  being  in- 
dependent of  the  body  or  an  extension  from  it ;  in  any  case,  union  between  it  and 
the  body  is  rapidly  effected. 

The  scleratogenous  tissue  between  the  cartilaginous  neural  arches  which  does 
not  undergo  chondrification  persists  as  the  ligaments  uniting  the  neural  laminae. 

As  regards  the  so-called  hypochordal  bow,  for  the  most  part  it  disappears. 
By  some  it  is  regarded  as  being  represented  by  a  fibrous  strand  in  the  inter- 
vertebral disc  in  front  of  the  vertebra  to  which  it  belongs.  It  is,  however, 
noteworthy  that  in  the  case  of  the  atlas  vertebra  there  is  an  exception  to  this 
arrangement;  for  here  the  hypochordal  bow  chondrifies  and  subsequently  by 
ossification  forms  the  anterior  arch  of  that  bone — an  arch  which  lies  ventral  to, 
and  embraces  the  odontoid  process  of  the  axis  (q.v.  p.  92). 

It  is  only  in  the  thoracic  region  that  the  ribs,  developed  as  stated  above  by  the 
chondrification  of  the  intersegmental  septa,  attain  their  full  dimensions.  In  the 
cervical,  lumbar,  and  sacral  regions  they  exist  only  in  a  rudimentary  or  modified 
form,  as  has  been  described  elsewhere.  In  the  construction  of  the  chest  wall 
the  ribs  are  supported  ventrally  by  the  sternum,  as  to  the  development  of  which 
there  is  some  difference  of  opinion.  Euge  has  described  this  bone  as  formed  by 
the  fusion  of  two  cartilaginous  bands  produced  by  the  coalescence  of  the  expanded 
ends  of  the  first  five  or  seven  cartilaginous  ribs.  Paterson,  on  the  other  hand, 
regards  the  sternum  as  arising  independently  of  the  ribs  by  the  union  of  a  right 
and  left  sternal  bar  in  the  median  ventral  line.  There  are  also  reasons  for 
supposing  that  the  presternum  is  intimately  associated  with  the  development  of 
the  ventral  part  of  the  shoulder  girdle. 


92  OSTEOLOGY. 

Ossification  of  the  Vertebrae. — The  vertebree  are  developed  by  ossification  of 
the  cartihxge  which  surrounds  the  notochord  and  which  passes  backwards  over  the  sides  of 
the  neural  canal.  The  centres  for  the  bodies  first  appear  in  the  lower  thoracic  vertebrae 
about  the  tenth  week.  An  oval  nucleus  develops  in  each  body.  At  first  it  is  placed 
dorsal  to  the  notochoi'd,  but  subsequently  surrounds  and  causes  the  disappearance  of 
that  structure.  Occasionally,  however,  the  primitive  centre  appears  to  be  formed  by 
the  coalescence  of  two  primary  nuclei.  Support  is  given  to  this  view  by  the  occasional 
occurrence  of  vertebrae  in  which  the  body  is  developed  in  two  lateral  halves,  or  in  cases 
whei'e  only  one-half  of  the  body  persists  (Turner) ;  normally,  however,  it  is  impossible  to 
make  out  this  division.  From  these  single  nuclei  the  bodies  are  developed,  the  process 
extending  up  and  down  the  column  until,  by  the  fifth  month,  all  the  centra  possess  ossific 
nodules,  except  the  coccygeal  segments.  About  the  seventh  week  a  single  centre  appears  in 
the  neural  arch  on  either  side.  These  commence  first  to  ossify  in  the  upper  cervical  region 
and  extend  rapidly  downwards  throughout  the  column.  They  first  appear  near  the  bases 
of  the  superior  articular  processes,  and  extend  backwards  into  the  laminae,  laterally  into 
the  transverse  processes,  and  forwards  into  the  pedicles.  These  latter 
project  anteriorly  and  form  a  considerable  portion  of  the  postero- 
lateral aspects  of  the  body,  from  which,  however,  they  are  separated 
by  a  cartilaginous  strip — the  neuro-central  synchondrosis — which  does 
not  entirely  disappear  until  about  the  fifth  or  sixth  year.  It  is  im- 
portant to  note  that  in  the  thoracic  region  the  costal  facets  lie  behind 
the  neuro-central  synchondrosis,  and  are  therefore  borne  on  the  lateral 
aspects  of  the  pedicles.  Fusion  of  the  laminae  in  the  mesial  plane 
behind  begins,  after  birth,  in  the  lumbar  region  and  extends  upwards, 
'  OF  VERTEBE.E  ^°  ^^^^  ^J  ^^^  fifteenth    month  or    thereabouts    the  arches  in    the 

cervical  region  are  completed  behind.  In  the  sacral  region  ossifica- 
tion is  slower,  the  spinal  canal  not  being  enclosed  till  the  seventh  to  the  tenth  year. 
The  spinal  processes  are  cartilaginous  at  birth,  but  these  become  ossified  by  the  extension 
into  them  of  the  bony  laminae. 

At  puberty  certain  secondary  centres  or  epiphyses  make  their  appearance ;  these  are 
five  in  number.  One  caps  the  summit  of  the  spinous  process,  except  in  the  cervical 
region.  A  single  epiphysis  on  either  side  appears  at  the  extremity  of  the  transverse 
process,  and  in  the  thoracic  region  assists  in  forming  the  articular  surface  for  the  tubercle 
of  the  rib.  Two  epiphysial  plates  are  formed — one  for  the  upper,  and  the  second  for  the 
lower  surface  of  the  body,  including  also  that  part  which  lies  behind  the  neuro-central 
synchondrosis  and  formed  by  the  pedicle  ;  from  these  the  thickened  circumference  of  both 
upper  and  lower  aspects  of  the  body  are  derived.  Fusion  of  these  centres  with  the  rest 
of  the  bone  is  not  complete  till  the  twenty-fifth  year. 

In  the  cervical  region  independent  centres  are  described  as  occui'ring  in  the  anterior 
roots  of  the  transverse  processes  of  the  sixth  and  seventh  vertebrae.  These  correspond  to 
the  costal  element,  and  may  occasionally  persist  in  the  form  of  cervical  ribs.  Elsewhere 
they  are  formed  by  lateral  extensions  from  the  pedicle. 

In  the  lumbar  region  the  transverse  process  of  the  first  lumbar  vertebra  is  occasionally 
associated  with  an  independent  costal  centre,  which  may  blend  with  it,  or  persist  as  a 
lumbar  rib.  The  mammillary  processes  are  derived  from  separate  epiphyses.  The  neural 
arch  of  the  fifth  lumbar  vertebra  is  occasionally  developed  from  two  centres  on  either  side, 
as  is  demonstrated  by  the  fact  that  the  arch  is  sometimes  divided  bj''  a  synchondrodial 
joint  running  obliquely  across  between  the  superior  and  inferior  articular  processes  on 
either  side.  (See  ante,  p.  91  ;  also  Fortschritte  auf  dem  Gehiete  der  Rmitgenstrahlen. 
Erganzungsheft  i. ;  "die  Entwickelung  des  menschlichen  Knochengerlistes  wahrend  des 
fotalen  Lebens,"  von  Lambertz.) 

Atlas. — The  lateral  masses,  transverse  processes,  and  posterior  arch  are  developed 
from  two  centimes — one  on  either  side — which  correspond  with  the  centres  from  which  the 
neural  arches  of  the  other  members  of  the  series  are  developed.  These  make  their 
appearance  about  the  seventh  week,  and  do  not  unite  posteriorly  till  after  the  third 
year.  Their  point  of  union  is  sometimes  preceded  by  the  formation  of  a  distinct  spinal 
nucleus  (Quain).  The  transverse  processes  are  completed  by  epiphyses  about  the  eigh- 
teenth year  (Fawcett).  The  anterior  arch  is  developed  from  centres  variously  described 
as  single  or  double,  which  appear  in  one  of  the  hypochordal  arches  of  cartilage  described 
by  Froriep  {Arch.  f.  Anat.  u.  Physiol.,  Anat.  Abth.  1886)  which  here  persists.  In  this 
cartilage  ossification  commences  during  the  first  year  of  life.  Union  with  the  lateral 
masses  is  delayed  till  six  or  eight  years  after  birth.  The  lateral  extremities  of  the 
anterior  arch  assist  in  forming  the  fore  part  of  the  superior  articular  processes. 


OSSIFICATION  OF  THE  VEETEBEJE. 


93 


Axis. — The  axis  ossifies  from  five  primitive  centres.  Of  these,  two — one  on  either  side 
— appear  about  the  seventh  week,  and  form  the  articular  and  transverse  processes,  together 
with  the  hxmiupe  and  spine.  One,  or  it  may  be  two,  nuclei  appear  in  the  lower  part  of  the 
body  about  the  fifth  month.  The  upper  part  of  the  body,  including  a  small  part  of  the 
superior  articular  process,  and  the  base  of  the  odontoid  process,  are  developed  from  two 
laterally-placed  nuclei  which  appear  shortly  after,  and  fuse  together  at  the  seventh  or 
eighth  month,  so  that  at  birth  the  bone  consists  of  four  pieces.  Fusion  between  these 
parts  takes  place  in  the  following  order : — The  odontoid  unites  with  the  body  and  lateral 
parts  about  the  third  or  fourth  year ;  union  between  the  two  lateral  portions  posteriorly 
and  the  body  and  lateral  parts  in  front,  is  complete  at  from  four  to  six  years. 

The  summit  of  the  odontoid  pi'ocess  is  developed  from  a  separate  centre,  occasionally 


Fig.  69  h. — Ossification  of  Vertebra. 


Cervical  vertebra. 
Centre  for  body. 
Superior  epiphysial  plate. 
Anterior  bar  of  transverse  process  developed  by 

lateral  extension  from  pedicle. 
Neuro-central  synchondrosis. 
Inferior  epiphysial  plate. 

Lumbar  vertebi-a. 
Body. 

Superior  epiphysial  plate. 
Epiphysis  for  mammillary  process. 
Epiphysis  for  transverse  process. 
Epiphysis  for  spine. 
Neuro-central  synchondrosis. 
Inferior  epiphysial  plate. 

Dorsal  vertebra. 
Centre  for  body. 
Superior  epiphysial  plate,  appears  about  puberty ; 

unites  at  25th  year. 

Neuro-central  synchondrosis  does  not  ossify  till 

5th  or  6th  year. 

Appears  at  puberty  ;  unites  at  25th  year. 
Appears  at  puberty  ;  unites  at  25th  year. 
Appears  about  6th  week. 

A3:is. 
Centre   for  transverse   process  and  neural  arch  ; 
appears  about  8th  week. 
20.  Synchondroses  close  about  3rd  year. 


21.  Centre  for  summit  of  odontoid  process  ;  appears 

3rd  to  5th  year,  fuses  8th  to  12th  year. 

22.  Appears  about   5th  or   6th   mouth  ;   unites  with 

opposite  side  7th  to  8th  month. 

23.  Synchondrosis  closes  from  4th  to  6th  year. 

24.  Inferior  epiphysial  plate  ;  appears  about  puberty, 
unites  about  25th  year. 

25.  Single  or  double  centre  for  body  ;  appears  about 

5th  month. 

A  tlas. 

26.  Posterior  arch  and  lateral  masses  developed  from 
a  single  centre  on  either  side,  which  appears 
about  7th  week.  In  this  figure  the  posterior 
arch  is  represented  complete  by  the  union 
posteriorly  of  its  posterior  elements. 

27.  Anterior  arch   and  portion  of  superior  articular 

surface  developed  from  single  or  double  centre, 
appearing  during  1st  year. 

Dorsal  vertebra. 

28.  Epiphysis  for  transverse  process  ;  appears  about 

pubeity,  unites  about  25th  year. 

29.  Epiphysis  appears  about  puberty ;  unites  about 

25th  or  27th  year. 

30.  Centre  for  neural  arch  on  either  side  ;  appears 
about  6th  or  7th  week,  the  laminae  unite  from 
birth  to  15th  month.  Tlie  arch  is  here  shown 
complete  posteriorly. 

31.  Centre  for  body  ;  appears  about  6th  week,  unites 

with  neural  arch  from  5th  to  6th  year. 


double,  which  appears  from  the  third  to  the  fifth  year,  and  fuses  with  the  rest  of  the  bone 
from  the  eighth  to  the  twelfth  year.  About  puberty  an  annular  epiphysis  is  developed  on 
the  under  surface  of  the  body,  with  which  it  is  completely  united  during  the  twentieth  to 
the  twenty-fifth  year.  Some  authorities  state  that  a  few  granules  between  the  base  of  the 
odontoid  and  the  upper  surface  of  the  body  represent  the  superior  epiphysial  plate  ;  but 
as  fusion  between  the  odontoid  and  the  body  occurs  before  the  time  for  the  appearance  of 
these  secondary  epiphysial  plates,  this  can  hardly  be  regarded  as  correct.  The  line  of 
fusion  of  the  odontoid  with  the  body  is  defined  by  a  small  disc  of  cartilage  which  persists 
within  the  substance  of  the  bone  till  an  advanced  period  of  life. 

A  pair  of  epiphyses  placed  over  the  tubercles  of  the  spine,  if  not  always  present,  are 
at  least  frequent. 


94 


OSTEOLOGY. 


FlQ. 


Ossification  of  the  Sacrum. 


a.a.  Centres  for  bodies  ;  h.h.  Epiphysial 
plates  on  bodies  ;  ex.  Centres  for  costal 
elements  ;  d.d.  Centres  for  neural  arches  ; 
e.e.  Lateral  epiphyses. 


Sacrum. — Each  of  the  sacral  segments  is  ossified  from  three  centres  :  one  for  the 
body,  and  two  for  the  neural  arch — that  for  the  body,  which  makes  its  appearance  in  the 
first  three  sacral  vertebrse  about  the  end  of  the  third  month,  about  the  fifth  to  the 
eighth  month  for  the  last  two  segments.  From  the  two  centres  for  the  neural  arches, 
which  make  their  appearance  about  the  fifth  or  sixth  month  in  the  higher  segments, 
the  laminpe,  articular  processes,  and  the  posterior  half  of  the  alee  on  either  side  are 
developed.  The  spinal  canal  is  not  enclosed  till  the  seventh  to  the  tenth  year,  the 
laminae  usually  failing  to  meet  in  the  lowest  segment,  and  occasion ally^,  to  a  greater  or 
less  extent,  in  some  of  the  higher  segments.  The  anterior  part  of  the  lateral  masses  is 
developed  from  separate  centres  which  represent  the  costal  elements  (Gegenbauer).  These 
appear  about  the  sixth  to  the  eighth  month,  and  may  develop  in  relation  to  the  upper 
four  sacral  segments ;  more  usually  they  are  met  with  in  connexion  with  the  first  three, 
and  exceptionally  they  may  be  found  only  in  the  upper  two.     It  is  by  fusion  of  these 

with  the  posterior  arches 
that  the  lateral  masses  which 
support  the  innominate  bones 
are  formed.  The  costal  ele- 
ments fuse  about  the  second 
to  the  fifth  year  with  the  neural 
arches,  prior  to  their  union 
with  the  centra  ;  and  the  seg- 
ments of  the  lateral  masses 
unite  with  each  other  sooner 
than  the  union  of  the  bodies 
is  effected.  The  latter  only 
takes  place  after  puberty  by  the  fusion  of  the  epiphysial  plates,  a  pair  of  which  make  their 
appearance  between  the  centra  of  each  segment.  The  lower  segments  begin  to  unite 
together  about  the  eighteenth  year,  but  fusion  between  the  first  and  second  sacral  verte- 
brae is  not  completed  till  the  twenty-fifth  year  or  after.  In  addition  to  the  foregoing,  two 
thin  osseous  laminse  are  developed  in  the  cartilage  covering  the  lateral  surface  of  the  alar 
mass.  The  upper  of  these  overspreads  the  auricular  surface,  whilst  the  lower  forms  the 
sharp  edge  below.  These,  as  Fawcett  (Anat.  Anz.  vol.  xxx.  p.  414}  has  pointed  out,  are 
formed  by  the  fusion  of  the  paired  costal  epiphyses  of  the  I.  and  II.  sacral  segments. 
The  edge  of  the  bone  below  as  far  as  the  inferior  lateral  angle  is  formed  by  the  fusion  of 
the  costal  epiphyses  of  segments  III.  and  IV.  with  the  epiphyses  of  the  transverse  processes 
of  IV.  and  V.  The  same  author  describes  the  occurrence  of  separate  epiphyses  on  the 
transverse  processes  of  the  I.  and  III.  segments.  The  extremities  of  the  upper  spinous 
processes  are  occasionally  developed  from  independent  epiphyses.  On  making  a  medial 
section  of  an  adult  bone  the  persistence  of  the  intervertebral  discs  between  the  centra 
is  indicated  by  a  series  of  oval  cavities. 

Coccygeal  Vertebrae. — These  are  cartilaginous  at  birth.  Each  has  a  separate 
centre ;  the  first  appears  from  the  first  to  the  fourth  year,  the  second  from  the  sixth  to 
the  tenth  year,  the  third  and  fourth  segments  at  or  about  puberty.  Secondary  centres, 
for  the  coccygeal  cornua  and  epiphysial  plates  for  the  bodies  are  also  described.  Fusion 
of  the  various  segments  begins  below  and  proceeds  upwards,  but  is  liable  to  great  indi- 
vidual variation.     In  advanced  life  the  coccyx  is  often  ossified  to  the  sacrum. 

THE   STERNUM. 

The  sternum  or  breast  bone  occupies  the  middle  of  the  upper  part  of  the 
thoracic  v^all  anteriorly.  It  is  connected  laterally  with  the  cartilages  of  the  first 
seven  ribs,  and  supports,  superiorly,  the  clavicles.  It  consists  of  three  parts,  named 
respectively  the  manubrium  or  handle  (presternum) ;  the  gladiolus  or  body  (corpus 
stemi)  (mesostemum) ;  and  the  processus  xiphoideus  (ensiform  or  xiphoid  cartilage) 
(metastemum).  Of  these  the  body  is  formed  by  the  fusion  in  early  life  of  four 
segments  or  sternebrae. 

The  manubrium  or  superior  part,  usually  separate  throughout  life  from  the 
rest  of  the  bone,  though  occasionally  fused  with  it,  is  of  a  flattened  triangular 
form.  The  anterior  surface,  slightly  saddle -shaped,  affords  attachment  to  the 
fibres  of  the  pectoralis  major  and  sterno-mastoid  muscles.  It  is  bounded  above  by 
a  thick  border,  the  lateral  parts  of  which  are  hollowed  out  obliquely  to  form  the 
facets  (incisurse  claviculares)  for  the  sternal  ends  of  the  clavicles ;  around  the 
facets,  which  have  an  upward,  lateral,  and  slightly  backward  direction,  the  bone 


THE  STERNUM. 


95 


Interclavicular  notch 
Clavicular  facet 


is  faintly  lipped.  In  the  interval  between  these  two  facets  there  is  a  slight  notch 
(incisura  jugularis)  which  forms  the  floor  of  the  characteristic  hollow  seen  at 
the  root  of  the  neck  anteriorly — the  suprasternal  notch.  The  lateral  borders 
are  excavated  immediately  below  the  clavicular  facets  for  the  reception  of  the 
cartilages  of  the  first  ribs.  Below  this,  the  margin  of  the  bone  slopes  medially, 
and  is  sharp,  except  inferiorly,  where  it 
presents  a  facet  which  supports  a  part  of 
the  second  costal  cartilage.  Around  this 
the  bone  is  usually  lipped  anteriorly.  The 
upper  angles  correspond  to  the  ridge 
separating  the  clavicular  facets  from  the 
first  costal  facets  :  whilst  the  lower  angle, 
which  may  be  regarded  as  cut  across  trans- 
versely, forms  the  surface  which  is  united 
by  cartilage  to  the  body  of  the  sternum. 
The  anterior  edge  of  this  surface  is  usually 
prominent.  The  posterior  aspect  of  the 
manubrium  is  smoother  than  the  anterior, 
is  pierced  by  numerous  foramina,  and 
is  slightly  concave  from  side  to  side  and 
above  downwards.  Here  are  attached 
some  of  the  fibres  of  the  sterno-hyoid  and 
sterno-thyroid  muscles. 

The  body  (corpus  sterni)  or  middle 
part  of  the  bone,  usually  twice  the  length 
and  from  half  to  two-thirds  the  width  of 
the  manubrium,  displays  evidence  of  its 
composite  nature.  If  the  anterior  surface  ^ 
which  is  slightly  convex  from  above 
downwards,  and  faintly  concave  from 
side  to  side,  be  carefully  examined,  three 
ill-marked  ridges  may  be  seen  crossing 
it  transversely ;  these  correspond  to  the 
lines  of  fusion  between  the  four  primitive 
segments.  To  this  surface  of  the  bone 
the  great  pectoral  muscles  are  extensively 
attached  on  either  side  of  the  middle  line. 
The  lateral  borders  are  thick  and  in- 
terrupted at  points  corresponding  to  the 
transverse  Hnes  already  mentioned  by 
U-shaped  hollows,  the  edges  of  which  are 
more  or  less  projecting.  These  are  for 
the  reception  of  the  cartilages  of  the  third, 
fourth,  and  fifth  ribs.  The  upper  border 
is  united  to  the  manubrium  above,  and 
forms  with  it  an  angle  of  variable 
degree — the  sternal  angle  (angulus  sterni). 
A  small  facet  is  formed  at  the  ex- 
pense of  the  lateral  extremity  of  this 
border,  and  in  conjunction  with  the  facet  on  the  lower  edge  of  the  manubrium 
forms  a  recess  on  either  side,  in  line  with  the  articulation  between  the  manubrium 
and  body,  into  which  the  cartilage  of  the  second  rib  fits.  The  lower  border  of  the 
body  is  curved,  and  is  united  in  the  middle  line  with  the  xiphoid  process,  whilst  on 
either  side  it  is  pitted  to  receive  the  cartilages  of  the  sixth  and  seventh  ribs,  the 
latter  being  in  part  supported  by  the  xiphoid  cartilage.  The  middle  line  of  the  body 
of  the  sternum  anteriorly  corresponds  to  the  floor  of  the  median  surface  furrow,  which 
runs  down  the  front  of  the  chest  in  the  interval  between  the  two  great  pectoral 
muscles.     The  posterior  surface  is  slightly  concave  from  above  downwards,  and 

^  I  cannot  agree  to  calling  this  the  sternal  ^^aiw  (planum  steruale). — A.  T. 


IV.  Rib  cartilage 


Rib  cartilage 


VI.  Rib  cartilage 


VII.  Rib  cartilage 


Enaiform  process 


Fig.  71.— The  Sternum  (anterior  view). 


96 


OSTEOLOGY. 


displays  faint  indications  of  three  transverse  lines  in  correspondence  with  those 
placed  anteriorly.  It  is  in  relation  with  the  pleura  and  pericardium,  and  affords 
attachment  at  its  lower  extremity  to  the  transversus  thoracis  muscle. 

The  xiphoid  process  displays  many  varieties  of  form  and  structure.  It 
is  a  pointed  process  of  cartilage,  supported  by  a  core  of  bone  connected  above 
with  the  lower  end  of  the  body  of  the  sternum,  and  having  its  lower  extremity, 
to  which  the  linea  alba  is  attached,  free.  It  lies  somewhat  posterior  to  the  plane 
of  the  anterior  surface  of  the  manubrium,  and  forms  a  floor  to  the  V-shaped 
interval  between  the  cartilages  of  the  seventh  ribs.  In  this  way  a  depression  is 
formed,  the  surface  hollow  in  correspondence  with  which  is  called  the  pit  of  the 
stomach  or  infrasternal  depression.  To  the  sides  of  this  process  are  attached  the 
aponeuroses  of  the  abdominal  muscles,  whilst  posteriorly  the  fibres  of  the  diaphragm 
and  transversus  thoracis  muscles  derive  attachment  from  it.  It  remains  partly 
cartilaginous  until  middle  life,  at  which  time  it  generally  undergoes  ossification, 
particularly  at  its  upper  part,  becoming  fused  with  the  body.  Of  varied  form, 
it  may  be  met  with  of  spatula -shape,  bifid,  circular,  pierced  in  the  centre,  or 
twisted  and  deflected  to  one  or  other  side,  or  turned  forward. 

The  sternum  as  a  whole  is  broadest  above  where  the  first  rib  cartilages  are 
attached.  It  becomes  narrow  opposite  the  second  rib  cartilages,  but  again  expands 
until  the  level  of  the  fifth  rib  cartilage  is  reached,  below  which  it  is  rapidly 
reduced  in  width  and  ends  below  in  the  pointed  xiphoid  cartilage.  Its  position  in 
the  body  is  oblique  from  above  downwards  and  forwards;  its  axis,  if  prolonged 

upwards,  would  touch  the 
column  opposite  the  third  or 
fourth  cervical  vertebra. 
Though  liable  to  changes  in 
position  by  the  rising  and  fall- 
ing of  the  chest  wall,  its  upper 
extremity  corresponds  to  the 
level  of  the  lower  border  of  the 
second  thoracic  vertebra,  whilst 
the  lower  end  of  the  xiphoid 
cartilage  usually  falls  in  line 
with  the  disc  between  the  tenth 
and  eleventh  thoracic  vertebrae. 

In  women  the  sternum  as  a  whole 
is  usually  narrower  and  shorter  than 
in  men,  and  its  position  less  oblique. 
On  the  other  hand,  Paterson  has 
shown  that  the  male  presternum  is 
proi^ortionately  wider  and  shorter 
than  the  female,  whilst  the  male 
mesosternum  is  proijortionately 
longer  and  narrowerthan  the  female. 

Ossification.  —  The  carti- 
laginous sternum,  developed  from 
2.  Appear  about  7th  ^he  fusion  mesially  of  two  car- 
tilaginous bands  •  uniting  the 
anterior  extremities  of  the  car- 
tilages of  the  first  eight  ribs, 
according  to  the  researches  of  Ruge  and  more  recently  of  Eggeling,  begins  to  ossify 
about  the  sixth  month  of  foetal  life.  About  this  time  a  single  centre  appears  in  the 
manubrium ;  at  birth  this  is  well  developed.  Two  centres  placed  vertically  have  also 
been  recorded.  Secondary  epiphyses  have  been  described  in  connexion  with  the  clavicular 
facets ;  these  do  not  unite  with  the  rest  of  the  manubrium  till  adult  life  is  reached. 
The  body  formed  by  the  fusion  of  four  segments  is  ossified  from  independent  centres, 
either  single  or  double,  for  each  segment.  These  appear — the  highest  as  early  as  the 
sixth  month  of  intrauterine  life — in  some  cases  even  before  the  manubrium  has  begun 
to  ossify  (Lambertz),  the  lowest  towards  the  end  of  full  term.  The  common  arrange- 
ment met  with  at  birth  is  a  single  centre  for  the  first,  and  double  centres  for  each 
of  the  succeeding   segments.       Union   between    these    segments    occurs   rather   irregu- 


At  birth. 


Fig.  72. 


At  3  years. 
-Ossification  of  the  Sternum. 


In  this  figure  the  second  as  well  as  the  third  segment  of  the  body 
possesses  two  centres. 

1.  Appears   about  5th   or  sixth    month, 
month  ;  unite  from  20  to  2.5.     3.  Appear  about  8th  or  ninth  month 
III.   segment  unites  witli    II.  about   puberty  ;    IV.    segment  unites 
with  III.  in  early  childhood.     4.  Appears  about  3rd  year  or  later. 


THE  KIBS.  97 

larly,  and  is  liable  to  much  vaz-iation.  The  fourth  unites  with  the  third  segment  in 
early  childhood,  the  third  with  the  second  about  puberty,  whilst  the  fusion  of  the  second 
with  the  first  segment  may  not  be  complete  till  the  twentieth  or  twenty-fifth  year. 

The  xiphoid  process  usually  ossifies  from  a  single  centre,  which  may  appear  as  early  as 
the  third  year,  though  often  very  much  later.  The  xiphoid  process  usually  unites  with  the 
body  about  forty  or  fifty,  and  in  exceptional  cases  osseous  union  between  the  body  and 
manubrium  may  occur  in  advanced  life. 

According  to  Paterson  the  manubrium  or  presternum  is  developed  in  association  with 
the  shoulder  girdle  and  becomes  only  secondarily  associated  with  the  ventrally  growing  ribs. 

THE    RIBS. 

The  ribs  (costae)  of  which  there  are  twelve  pairs,  form  a  series  of  curved  osseous 
bands  which  support  the  thoracic  wall ;  posteriorly  they  articulate  with  the 
thoracic  or  dorsal  vertebric,  anteriorly  each  rib  is  provided  with  a  costal  cartilage. 
The  first  seven  ribs  articulate  with  the  sternum  by  means  of  their  cartilages,  and 
are  termed  the  true  (costae  verae)  or  vertebro-sternal  ribs.  The  lower  five  ribs  are 
not  so  supported,  and  are  described  as  the  false  ribs  (costae  spuriae).  Of  these  the 
eighth,  ninth,  and  tenth  are  united  by  their  cartilages  to  the  cartilage  of  the 
seventh  rib,  and  are  called  the  vertebro-chondral  ribs,  whilst  the  last  two  ribs  are 
free  at  their  anterior  extremities,  and  are  named  the  floating  or  vertebral  ribs. 

A  typical  rib  consists  of  a  head  (capitulum  costae),  a  neck  (collum  costae),  a 
tubercle  (tuberculum  costae),  and  a  shaft  (corpus  costae),  on  which,  near  its  posterior 
end,  is  the  angle  (angulus  costae). 

The  head,  placed  on  the  posterior  or  vertebral  end  of  the  bone,  is  somewhat 
expanded.  ^Medially  its  articular  surface  is  wedge-shaped  and  divided  into  two 
parts,  an  upper  and  lower,  by  a  ridge  or  crest  (crista  capituli),  to  which  the  inter- 
articular  ligament  is  attached.  Of  these  two  facets  the  lower  is  usually  the  larger, 
and  articulates  with  the  upper  facet  on  the  body  of  the  vertebra  in  numerical 
correspondence  with  it,  whilst  the  upper  facet  is  for  the  corresponding  area  on  the 
lower  part  of  the  body  of  the  vertebra  above.  The  head  is  supported  by  a  more 
or  less  constricted  bar  of  bone,  the  neck,  which  lies  in  front  of  the  transverse 
process  of  the  lower  of  the  two  vertebras  with  which  the  rib  articulates  and  thus 
assists  in  the  formation  of  the  costo-transverse  foramen.  The  neck  is  continuous 
with  the  shaft  laterally,  at  which  point  there  is  a  well-marked  tubercle  on  its 
posterior  surface.  The  anterior  surface  of  the  neck  is  smooth  ;  its  posterior  aspect 
is  rough,  and  pierced  by  numerous  small  holes  for  vessels.  Here  is  attached  the 
middle  costo-transverse  ligament.  Not  uncommonly  the  upper  border  of  the  neck 
is  lipped  and  ridged  (crista  colli  costae),  especially  in  the  case  of  the  sixth,  seventh, 
and  eighth  ribs,  and  affords  attachment  to  the  anterior  costo-transverse  ligament. 
The  lower  border  is  continuous  with  the  costal  groove  laterally. 

The  tubercle  consists  of  an  articular  and  a  non-articular  part ;  the  former  is 
internal  to  and  below  the  latter.  Its  articular  surface,  of  rounded  or  oval  shape, 
is  directed  downwards,  backwards,  and  a  little  medially,  and  rests  upon  a  facet  on  the 
transverse  process  of  the  vertebra  in  numerical  correspondence  with  the  rib.  The 
non-articular  part,  most  prominent  in  the  vipper  ribs,  has  the  fibres  of  the  posterior 
costo-transverse  ligament  attached  to  it.  It  is  usually  separated  from  the  upper 
border  of  the  neck  and  shaft  by  a  groove,  in  which  lies  the  lateral  branch  of  the 
posterior  division  of  a  thoracic  nerve. 

The  shaft  (corpus  costae)  is  thin,  flattened,  and  band-like.  Its  length  varies 
much  ;  the  seventh  and  eighth,  which  are  visually  the  longest,  are  from  two  and 
a  half  to  three  times  the  length  of  the  first  and  twelfth  ribs  respectively.  The 
shafts  are  curved  so  as  to  adapt  them  to  the  form  of  the  thoracic  wall.  More  acute 
in  the  upper  members  of  the  series,  where  the  shafts  are  shorter,  the  curve  opens 
out  in  the  middle  and  lower  parts  of  the  thorax,  where  the  diameters  of  that  cavity 
are  greater.  The  curve,  however,  is  not  uniform.  Including  the  whole  length  of 
the  bone,  it  will  be  seen  to  be  most  accentuated  towards  the  hinder  part,  where, 
in  correspondence  with  the  point  at  which  the  bend  is  most  pronounced,  there 
is  a  rough  ridge  placed  obliquely  across  the  outer  surface   of  the  shaft   for   the 


98 


OSTEOLOGY. 


Head       Neck 


Tubercle 


Costal  groove 
ulcus  costalis) 


attachment  of  the  slips  of  the  ilio-costalis  muscle ;  this  is  the  angle  (angulus  costse). 
The  distance  between  the  angle  and  the  tubercle  is  greatest  on  the  eighth  rib ; 
above  that,  the  width  between  these  two  points  gradually  decreases  until,  in  the 
case  of  the  first  rib,  the  two  coincide.  Below  the  level  of  the  eighth  rib  the 
distance  slightly  di- 
minishes in  conform- 
ity with  the  general 
narrowing  of  the 
thorax  below  that 
level.  Towards  the 
anterior  extremity  of 
the  rib  where  the 
digitations  of  the  ser- 

ratus  magnus  and  external  oblique  muscles  are  attached 
to  its  outer  surface  the  curve  of  the  shaft  is  somewhat  more 
pronounced,  and  is  referred  to  as  the  anterior  angle. 

Combined  with  this  curve,  there  is  in  many  of  the  ribs 
a  twist.  This  may  best  be  understood  if  the  student  will 
take  a  strip  of  stiff  paper  and  bend  it  in  the  form  of 
the  curve  of  the  rib.  If,  after  he  has  done  this,  he  pulls 
down  the  fore  end  and  turns  up  the  hind  end  of  the  strip, 
he  will  have  imparted  to  the  strip  of  paper  a  twist  similar 
to  that  met  with  in  the  rib.  This  appearance  is  best 
seen  in  the  middle  members  of  the  series,  notably  in  the 
seventh  and  eighth  ribs,  above  and  below  which  it  gradually 
becomes  less  marked.  It  is  the  occurrence  of  this  twist 
which  prevents  the  extremities  of  the  ribs,  together  with 
the  shaft,  from  resting  on  the  same  plane  surface.  To  this 
rule  there  are  certain  notable  exceptions,  viz.  the  first  and 
second,  the  twelfth,  and  not  infrequently  the  eleventh. 

The  shaft  has  two  surfaces,  medial  and  lateral,  and 
two  borders,  a  superior  and  an  inferior.  The  lateral 
surface,  which  is  smooth,  conforms  to  the  general  vertical 
convexity  of  the  thorax,  being  directed  upwards  in  the 
first  rib,  upwards  and  laterally  in  the  higher  ribs,  laterally 
in  the  middle  series,  and  laterally  and  slightly  downwards 
in  the  tenth,  eleventh,  and  twelfth.  The  medial  surfaces 
are  arranged  conversely  and  are  covered  by  the  parietal 
pleura.  Towards  the  sternal  end  of  the  middle  ribs,  where 
the  downward  twist  is  most  marked,  there  is  often  an 
oblique  line  across  the  lateral  surface.  This  is  sometimes 
referred  to  as  the  anterior  angle.  The  upper  border  of  the 
shaft  is  thick  and  rounded  behind,  thinner  and  sharper  in 
front ;  to  it  are  attached  the  fibres  of  the  internal  and 
external  intercostal  muscles.  The  lower  border  is  grooved 
behind  at  the  expense  of  the  inner  surface,  and  is  over- 
hung laterally  by  a  sharp  margin.  Anteriorly  this  costal 
groove  (sulcus  costalis)  fades  away,  and  its  lips  coalesce 
to  form  a  rounded  edge.  The  intercostal  vessels  and  nerve 
are  lodged  in  this  groove,  whilst  its  lips  afford  attachment 
to  the  external  and  internal  intercostal  muscles  respectively.  On  the  floor  of 
the  groove  may  also  be  seen  the  openings  of  the  canals  for  the  transmission  of 
the  nutrient  vessels,  which  are  directed  towards  the  vertebral  end  of  the  rib. 

The  anterior  or  sternal  extremity  of  the  shaft,  often  slightly  enlarged,  displays 
an  elongated  oval  pit  into  which  the  costal  cartilage  is  sunk. 

Peculiar  Ribs. — The  first,  second,  tenth,  eleventh,  and  twelfth  ribs  all  display 
characters  by  which  they  can  be  readily  recognised. 

The  first  rib  can  be  easily  distinguished  from  the  others  by  its  size,  curvature, 
and  flattened  form.     The  head,  which  is  of  small  size,  has  a  single  oval  or  circular 


.For  costal  cartilage 
Fig.  73. — Fifth  Right  Rib 

AS    SEEN   FROM    BELOW. 


THE  lilBS. 


99 


Articular  part  of  tubercle  Alio 

for  transverse  process  of 
vertebra 

Fig.  74. — Fifth  Right  Rib  as  seen  from  Behind. 


facet,  which  is  directed  medially  and  slightly  backwards  for  articulation  with  the 
side  of  the  body  of  the  first  thoracic  vertebra.  The  neck  is  flattened  from  above 
downwards,  and  is  slightly  down-turned  towards  the  end  which  supports  the 
head.  Its  anterior  border  is  rounded  and  smooth ;  its  posterior  edge  rough  for  the 
attachment    of      ligaments. 

1  ,    , ,  •     ,       1  ;  1  1  Facets  on  head 

At  the  point  where  the  neck 
joins  the  shaft  posteriorly, 
a  prominent  tubercle  curves 
upwards  and  backwards. 
The  inner  and  under  surface 
of  this  process  has  a  small 
circular  facet  which  rests  on 
a  corresponding  articular 
surface  on  the  transverse 
process  of  the  first  thoracic 
vertebra.  The  angle  coin- 
cides with  the  tubercle,  and 
thus  assists  in  emphasising 

its  prominence.  The  surfaces  of  the  body  of  the  rib  are  directed  upwards  and 
downwards,  its  borders  medially  and  laterally.  If  the  finger  be  run  along  the 
thin  medial  border,  a  distinct  spine  or  tubercle  can  be  readily  felt  about  an 
inch  or  an  inch  and  a  quarter  from  its  anterior  extremity.  This  is  the  scalene 
tubercle  of  Lisfranc  (tuberculum  scaleni)  which  also  forms  an  elevation  on  the  upper 

surface  of  the  shaft  and  affords  an 
attachment  for  the  scalenus  anticus 
muscle.  There  is  a  shallow,  oblique 
groove  crossing  the  upper  surface  of 
the  shaft  in  front  of  this  for  the  lodg- 
ment of  the  subclavian  vein ;  whilst 
behind  the  tubercle  there  is  another 
groove,  usually  better  marked,  and 
passing  obliquely  forwards  for  the  sub- 
clavian artery  (sulcus  subclavise).  The 
space  on  the  upper  surface  of  the  rib 
between  this  latter  groove  and  the 
tubercle  posteriorly  is  somewhat  rough, 
and  affords  attachment  to  the  fibres  of 
the  scalenus  medius  muscle.  In  many 
specimens  these  features  are  but  faintly 
marked.  The  anterior  extremity  of 
the  rib  is  thickened  and  often  ex- 
panded for  the  reception  of  its  costal 
cartilage,  which  is  not  infrequently 
ossified.  Here  on  the  upper  surface 
are  attached  the  rhomboid  ligament 
and  the  subclavius  muscle.  The  under 
surface  of  the  rib  is  smooth  and  is 
covered  by  pleura.  The  outer  convex 
border,  thin  in  front,  is  usually  thick 
and  rough  behind  the  subclavian 
groove,  where  it  has  attached  to  it  the 
fibres  of  the  first  digitation  of  the 
serratus  magnus  (s.  anterior).  Along 
this  edge,  also,  are  attached  the  external  and  internal  intercostal  muscles  of  the 
first  intercostal  space.  The  medial  concave  border  is  thin,  and  has  connected 
with  it  the  aponeurotic  expansion  known  as  Sibson's  fascia. 

The  second  rib  may  be  distinguished  by  the  size  of  its  curve ;  the  absence  of 
any  twist  on  its  shaft,  so  that  it  cau  be  laid  flat  on  the  table ;  the  oblique  direction 
of  the  surfaces  of  its  shaft,  the  lateral  being  directed  upwards  and  laterally,  whilst 


Fig.  75. 


-First  and  Second  Right  Ribs  as  seen 
FROM  Above. 


100 


OSTEOLOGY. 


the  medial  is  turned  downwards  and  inwards ;  and  the  presence  of  a  weU-marked, 
rough,  oval  area  about  the  middle  of  its  lateral  surface  and  lower  border  for  part  of 
the  first,  and  the  whole  of  the  second  digitation  of  the  serratus  magnus  (s.  anterior) 
muscle.    The  head  has  two  facets,  and  the  angle  is  close  to  the  tubercle  posteriorly. 

The  tenth  rib  has  usually  only  a  single  articular  facet  on  the  head,  and  may  or 
may  not  have  a  facet  on  the  tubercle. 

The  eleventh  and  twelfth  ribs  are  recognised  by  their  length.  Their  heads, 
usually  large  in  proportion  to  their  shafts,  support  a  single  facet  for  articulation 
with  the  eleventh  and  twelfth  thoracic  vertebrae  respectively.  The  tubercles  are  ill- 
developed  and  have  no  articular  facets.  The  angle  is  faintly  marked  on  the 
eleventh,  scarcely  perceptible  on  the  twelfth.  Their  anterior  extremities  are  narrow 
and  pointed  and  tipped  with  cartilage.  The  subcostal  groove  is  absent  in  the 
twelfth,  and  but  slightly  seen  in  the  eleventh.  The  twelfth  is  considerably  shorter 
than  the  eleventh  rib. 

Ossification. — Ossification  begins  in  the  cartilaginous  ribs  about  the  sixth  week,  and 
rapidly  extends  along  the  shaft,  so  that  by  the  end  of  the  third  month  it  has  reached  the 
permanent  costal  cartilage.  The  sixth  and  seventh  ribs  are  the  earliest  to  ossify ;  the 
first  rib  being  the  last  (Lambertz).  At  puberty,  or  before,  secondaiy  centres  appear. 
Of  these  there  are  three — an  epiphysis  for  the  articular  surface  of  the  tubercle,  one  for  the 
non-articular  part  of  the  same  process,  and  one  for  the  head.  By  the  twenty-fifth  year 
fusion  between  these  and  the  shaft  is  complete. 


THE   COSTAL 


Fig.  76. — The  Thokax  as  seen  from  the  Fuont. 


CARTILAGES. 

The  costal  cartil- 
ages, of  which  there 
are  twelve  pairs,  are  bars 
of  hyaline  cartilage 
united  to  the  anterior 
extremities  of  the  ribs, 
into  which  they  are  re- 
cessed and  held  in 
position  by  the  perio- 
steum. Through  these 
cartilages  the  first  seven 
ribs  are  connected 
directly  with  the 
sternum  by  means  of 
synovial  joints  corres- 
ponding to  the  notches 
along  the  margins  of 
the  breast  bone.  To  this 
there  is  an  exception  in 
the  case  of  the  first  rib, 
the  cartilage  of  which  is 
directly  blended  with 
the  manubrium  sterni. 
The  eighth,  ninth,  and 
tenth  are  connected  in- 
directly with  the 
sternum  by  their  union 
with  each  other,  and 
their  articulation, 
through  the  medium  of 
the  eighth,  with  the 
seventh  rib  cartilage, 
whilst  the  eleventh  and 


twelfth  cartilages  tip  the  ribs  to  which  they  belong,  and  lie  free  in  the  muscles  of 
the  flank.     The  costal  cartilages  increase  in  length  from  the  first  to  the  seventh, 


THE  THOEAX  AS  A  WHOLE. 


101 


below  which  they  become  shorter.  The  first  inclines  obliquely  downwards  and 
medially  to  unite  with  the  upper  angles  of  the  manubrium.  The  second  lies  more 
or  less  horizontally.  The  third  to  the  seventh  gradually  become  more  and  more 
curved,  inclining  downward  from  the  extremities  of  their  respective  ribs,  and  then 
turning  upwards  to  reach  the  sternum.  The  tenth  cartilage  articulates  by  means  of 
a  synovial  joint  with  the  ninth,  the  ninth  with  the  eighth,  and  the  eighth  with  the 
seventh.  There  are  also  surfaces  for  the  articulation  of  the  seventh  with  the 
sixth,  and  sometimes  for  the  sixth  with  the  fifth. 


THE   THORAX   AS   A   WHOLE. 

The  bony  and  cartilaginous  thorax  is  barrel-shaped,  being  narrower  above  than 
below,  and  compressed  from  before  backwards.  Its  posterior  wall  is  longer  than  its 
anterior,  and  its  transverse 
width,  which  reaches  its  maxi- 
mum opposite  the  eighth  or 
ninth  rib,  is  much  in  excess 
of  its  sagittal  diameter.  This 
is  largely  owing  to  the  forward 
projection  of  the  tlioracic  part 
of  the  vertebral  column  into 
the  thoracic  cavity. 

The  anterior  wall  is  formed 
by  the  ribs  and  rib  cartilages, 
together  with  the  sternum. 
The  posterior  wall  comprises 
the  thoracic  part  of  the  verte- 
bral column  and  the  ribs  as 
far  as  their  angles.  Owincr  to 
the  backward  curve  of  the 
ribs,  and  the  projection  for- 
wards of  the  vertebral  bodies, 
the  antero-posterior  diameter 
of  the  thoracic  cavity  is  con- 
siderably greater  on  either 
side  of  the  middle  line  than 
in  the  mesial  plane,  thus  allow- 
ing for  the  lodgment  of  the 
rounded  posterior  borders  of 
the  lungs.  Eor  the  same 
reason  the  furrow  on  either 
side  of  the  spinous  processes 
of  the  thoracic  vertebrae  is 
converted  into  a  broad  groove 
(vertebral  groove),  the  floor  of 
which  is  in  part  formed  by  the 
ribs  as  far  as  their  angles. 
The  grooves  so  formed  are 
each   occupied  by  the  fleshy 


Fig. 


-The  Thorax  as  seen  from  the  Right  Side. 


mass   of    the    erector    spin?e 
(sacro-spinalis)  muscle. 

The  lateral  walls  are  formed  by  the  costal  arches.  The  ribs  which  run  obliquely 
from  above  downwards  and  forwards  do  not  lie  parallel  to  each  other,  but  spread 
somewhat,  so  that  the  intervals  between  them  (intercostal  spaces),  are  wider  in 
front  than  behind. 

The  superior  aperture  or  inlet  formed  by  the  body  of  the  first  thoracic  vertebra 
behind,  the  arches  of  the  first  rib  on  either  side,  and  the  upper  border  of  the 
manubrium  sterni  in  front,  is  contracted  and  of  reniform  shape,  measuring  on  an 

7 


102  OSTEOLOGY. 

average  from  10  to  12  cm.  trausversely  and  5  cm.  in  an  antero-posterior  direction. 
The  plane  of  the  inlet  is  oblique  from  behind  downwards  and  forwards,  so  that  in 
expiration  the  upper  border  of  the  sternum  lies  on  a  level  with  the  disc  between 
the  second  and  third  thoracic  vertebrae. 

The  lower  aperture,  of  large  size,  is  bounded  in  the  middle  line  behind  by  the 
twelfth  thoracic  vertebra ;  passing  thence  the  twelfth  ribs  slope  outwards,  down- 
wards, and  forwards.  From  these  a  line  carried  horizontally  forwards  from  their 
tips  touches  the  end  of  the  eleventh  rib,  and  then  curving  slightly  upward  reaches 
the  cartilage  of  the  tenth  rib.     Here  it  follows  the  confluent  margins  of  the  car- 

O  .... 

tilages  of  the  tenth,  ninth,  eighth,  and  seventh  ribs,  finally  reaching  the  xiphoid 
process,  where  it  forms  with  the  costal  margin  of  the  opposite  side  the  infrasternal 
angle,  the  summit  of  which  coincides  with  the  xiphi-sternal  articulation ;  in 
expiration  this  joint  usually  lies  on  a  level  with  the  intervertebral  disc  between 
the  ninth  and  tenth  thoracic  vertebrae,  and  corresponds  with  the  surface  depression 
familiarly  known  as  the  pit  of  the  stomach.  The  inferior  aperture  of  the  thorax  is 
occupied  by  the  vault  of  the  diaphragm. 

In  the  foetal  condition  the  form  of  the  thorax  differs  from  that  of  the  adult.  It  is 
laterally  compressed— in  this  respect  resembling  the  simian  type.  Its  antero-posterior 
diameter  is  relatively  greater  than  in  the  adult.  At  birth  changes  in  form  take  place 
dependent  on  the  expansion  of  the  lungs;  during  subsequent  growth,  the  further  ex- 
pansion of  the  thoracic  cavity  in  a  transverse  direction  is  correlated  with  the  assumption 
of  the  erect  posture,  and  the  use  of  the  fore-limbs  as  prehensile  organs. 

Sexual  Differences. — The  thorax  of  the  female  is  usually  described  as  being  pro- 
portionately shorter  and  rounder  than  the  male.  It  also  tends  to  narrowness  in  the 
lower  segment.  It  is  hardly  necessary  to  point  out  that  the  natural  form  is  often 
modified  by  the  use  of  tight  or  ill-fitting  corsets. 

m     -T-L  •     T    J  Transverse  diameter  x  100   ,   ,  .  .  u    i       t    e  j.\      ■        l- 

The  Thoracic  Index  = ; -. taken  at  the  level  of  the  junction 

Antero-posterior  diameter 

of  the  xiphi-sternum  with  the  body  expresses  the  proportions  of  these  diameters.     That 

of  the  female  is  on  an  average  lower  than  the  male,  indicating  a  more  rounded  form. 


THE    SKULL. 

In  view  of  the  vast  amomit  of  accurate  knowledge  the  medical  student  is  now  called  upon  to 
acquire,  it  i.s,  in  the  opinion  of  the  writer  of  this  article,  desirable  that  less  stress  should  Le  laid 
upon  tlie  details  of  the  disarticulated  bones  of  the  skull  and  more  emphasis  j)laced  on  the  study 
of  tlie  skull  as  a  whole. 

It  has  hitherto  been  the  custom  to  disarticulate  the  bones  of  the  skull,  imposing  on  the 
student  the  task  of  again  recon.structing  it,  uiuch  after  the  manner  of  a  Chinese  puzzle.  In  this 
way  a  minute  acquaintance  with  the  forms  and  articulations  of  the  individual  bones  became 
necessarj',  and  the  student's  memory  was  burdened  with  a  mass  of  detail  of  little  or  no  practical 
or  .scientific  value,  for  in  regard  to  the  latter  aspect  of  the  suly'ect  the  points  of  jjliylogenetic  and 
ontogenetic  interest  are  best  illustrated  by  a  consideration  of  the  details  of  the  evolution  of  the 
skull  and  the  development  and  ossification  of  its  parts.  Witli  possibly  the  exception  of  the 
temporal  bones  and  the  mandible,  tlie  author  liolds  that  most  of  the  useful  information  relating 
to  the  skull  can  best  be  studied  in  tlie  complete  cranium,  or  in  sections  of  it  made  in  different 
planes.  By  this  method  tlie  student  acquires  a  more  intimate  knowledge  of  its  structure  and 
topograpliy,  and  is  consequently  better  e<pii])ped  to  deal  with  the  rcigions  he  may  have  to  explore 
in  the  hving. 

With  this  object  in  view,  the  writer  of  this  article  has  given  more  space  to  the  description  of 
the  skull  as  a  wliole  and  in  section  than  is  usually  the  case.  Such  a  plan  has  doubtless  given 
rise  to  some  repetition  ;  at  the  same  time  it  renders  more  complete,  and,  it  is  hoped,  also  more 
useful  from  a  jiractical  .standpoint,  the  account  sup])lied. 

It  must,  however,  be  Vjorni-  in  mind  tliut  a  text-b(jok  of  Anatomy  serves  the  double  purpose 
of  a  "  ^lanual  "  of  instruction  and  a  work  of  reference.  In  view  of  this,  the  author  has  furnished 
a  detailed  account  of  the  disarticulated  cranial  bones,  such  as  has  been  hitherto  supplied  in  works 
of  a  like  kind. 

The  student,  however,  must  not  assume  on  this  account  that  this  section  of  the  article  should 
V»e  neglected.  He  will  find  most  of  the  more  imjjortant  details  described  in  the  article  on  the 
skull  as  a  whole  ;  but  he  would  do  well  to  suj)plement  his  knowledge  by  a  reference  to  the  more 
detailed  account  for  information  regarding  the  develoijment,  ossification,  and  variations  of  the 
individual  bones. 


THE  FEONTAL  BONE.  103 

In  this  edition  several  additional  figures  of  sections  of  the  skull  liave  been  introduced,  with 
tlie  object  of  displaying  the  architectural  arrangement  of  the  bones  and  the  relations  of  their 
various  parts  and  cavities. 


THE    BONES   OF  THE   SKULL   (Ossa  Cranii).^ 

The  term  skull  (cranium)  is  commonly  employed  to  signify  the  entire  skeleton 
of  the  head.  •  This  comprises  the  bony  envelope  which  surrounds  the  brain 
(cranium  cerebrale),  and  the  osseous  structures  which  support  the  face  (ossa  faciei). 

The  cranium  cerebrale  is  composed  of  the  occipital  (os  occipitale),  the  sphenoid 
(os  sphenoidale),  the  ethmoid  (os  ethmoidale),  and  the  frontal  (os  frontale),  the  two 
parietals  (ossa  parietalia),  and  the  two  temporals  (ossa  temporalia),  the  inferior 
turbinated  (conchee  nasales  inferiores),  the  lacrimals  (ossa  lacrimalia),  the  nasal 
(ossa  nasalia),  and  the  vomer — fifteen  bones  in  all. 

The  bones  of  the  face  (cranium  viscerale,  ossa  faciei)  include  the  following : — 
One  single,  viz.  the  mandible  (mandibula),  and  six  bones,  arranged  in  pairs,  viz.  the 
maxillary  (maxillffi),  zygomatic  or  malar  (zygomatica),  palate  (ossa  palatina) — seven 
bones  in  all. 

The  hyoid  bone  is  usually  described  along  with  the  skull.  If,  in  addition,  the 
bones  of  the  middle  ear,  three  on  each  side  (malleus,  incus,  and  stapes),  be  in- 
cluded, the  skeleton  of  the  head  consists  of  twenty-nine  bones. 

THE   SEPARATE   BONES   OF   THE    SKULL. 
The   Frontal    Bone. 

The  frontal  bone  (os  frontale),  situated  in  the  fore  part  of  the  cranium,  is  a 
single  bone  formed  by  the  fusion  in  early  life  of  two  symmetrical  halves.  It  con- 
sists of  a  frontal  part,  which  corresponds  to  the  region  of  the  forehead ;  an  orbital 
part,  which  enters  in  the  structure  of  the  roof  of  the  orbits  ;  and  a  nasal  part,  which 
assists  in  forming  the  roof  of  the  nasal  fossse. 

The  frontal  part  (pars  frontalis)  is  the  shell-like  portion  of  the  bone  w^hich 
rises  upw^ards  above  the  orbital  arches.  Its  external  surface  is  rounded  from  side 
to  side  and  from  above  downwards.  This  convexity  is  most  pronounced  about 
1^  inches  above  the  orbital  margins  on  either  side  of  the  middle  line,  constituting 
what  are  known  as  the  frontal  eminences  -  (tubera  frontalia).  These  mark  the 
original  sites  of  the  centres  from  which  the  bone  ossifies.  The  lower  margin  of 
this  part  is  formed  on  either  side  of  the  middle  line  by  the  curved  orbital 
margins  (margines  supraorbitales),  the  outer  and  inner  extremities  of  which 
constitute  the  lateral  and  medial  angular  processes  respectively.  The  latter, 
which  descend  to  a  lower  level  than  the  former,  articulate  with  the  lacrimal 
bones,  and  are  separated  from  each  other  by  a  rough  articulate  surface — the  nasal 
notch  for  the  nasal  and  maxillary  bones.  The  curve  of  the  orbital  margin  varies 
in  different  individuals  and  races ;  towards  its  medial  third  it  is  crossed  by  a  groove, 
not  unfrequently  converted  into  a  foramen — the  supraorbital  notch  or  foramen 
(incisura  sive  foramen  supraorbitalis).  Through  this  there  pass  the  supraorbital  nerve 
and  artery.  Not  unfrequently  a  series  of  grooves  radiating  upwards  and  outwards 
indicate  the  course  of  the  nerve  (Dixon).  Above  the  supraorbital  margin  the 
character  of  the  bone  displays  marked  differences  in  the  two  sexes :  in  the  male, 
above  the  interval  between  the  two  medial  angular  processes,  there  is  usually 
a  well-marked  prominence,  called  the  glabella ;  from  this  the  fulness  extends 
outwards  above  the  orbital  margin,  varying  in  degree  and  extent,  and  forming 
the  elevations  known  as  the  supraorbital  or  superciliary  ridges  (arcus  superciliares). 

1  In  catalogues  of  craniological  collections  the  terms  used  are  as  follows  : — 

Skull       =  entire  skeleton  of  head,  including  the  mandible. 

Cranium  =  the  skull,  minus  the  mandible. 

Calvavia  =that  part  of  the  skull  which  remains  after  the  bones  of  the  face  have  been  removed 
or  destroyed. 
-  This  English  word  I  retain  instead  of  tuber,  which  appears  to  me  meaningless. — A.  T. 


104 


OSTEOLOGY. 


The  prominence  of  these  naturally  reacts  on  the  character  of  the  supraorbital 
margins,  wliich  are  thicker  and  more  rounded  in  the  male  than  in  the  female. 
Passing  upwards  over  the  glabella,  the  remains  of  the  suture  which  originally 
separated  the  two  halves  of  the  frontal  bone  can  usually  be  seen ;  above  this  point 
all  trace  of  the  suture  is  generally  obliterated. 

Extending  from  the  lateral  angular  process  (zygomatic  process)  is  a  well-marked 
ridge,  which  curves  upwards  and  slightly  medially,  then  turning  backwards  it 
arches  across  the  lateral  aspect  of  the  bone.  This  is  the  temporal  ridge  or  crest 
(linea  temporalis),  which  serves  to  separate  the  anterior  surface  of  the  frontal  portion 
of  the  bone  from  its  temporal  aspect.  The  latter  (fades  temporalis)  forms  the  floor 
of  the  upper  and  anterior  part  of  the  temporal  fossa,  and  serves  for  the  attachment 
of  the  temporal  muscle. 

The  orbital  part  of  the  bone  (pars  orbitalis)  consists  of  two  transversely-curved 
plates,  each  having  the  form  of  a  sextant ;  their  medial  edges,  which  are  irregular 


Frontal  eminences 


Temporal  surfac* 


Lateral  angular  process  p^j 
(zygomatic  process)  4^ 


Supraorbital  notch 
For  articulation  with  nasal 


Temporal  line 
Supeiciliary  arch 


lb  il  I  u  \  leniains  of  frontal  suture 
process 


Frontal  spine 
Fig.  78. — The  Frontal  Bone  (Anterior  View). 

and  formed  of  cellular  bone,  lie  parallel  to  each  other,  and  are  separated  in  their 
posterior  half  by  the  ethmoidal  notch  (incisura  ethmoidalis),  in  which  the  ethmoid 
bone  is  lodged.  The  edges  of  the  notch  on  either  side  are  grooved  in  front 
and  behind  by  the  anterior  and  posterior  ethmoidal  foramina,  which  are  completed 
when  the  ethmoid  is  in  situ.  The  anterior  transmits  the  internal  branch  of  the 
nasal  nerve  ^  and  the  anterior  ethmoidal  vessels ;  the  posterior,  the  posterior  eth- 
moidal vessels.  In  front  of  the  ethmoidal  notch  is  the  nasal  notch,  from  the 
centre  of  which  th(3  nasal  process  projects  downwards  and  forwards  to  terminate 
in  the  frontal  spine  (spina  frontalis),  which  lies  l)etween,  and  articulates  with  the 
nasal  bones  and  perpendicular  plate  of  the  ethmoid.  On  either  side  of  the 
root  of  this  process  the  bone  is  grooved  obliquely  from  above  downwards  and 
forwards,  and  enters  into  the  ibrmation  of  the  narrow  roof  (pars  nasalis)  of  the 
nasal  fossae.  Anteriorly  the  nasal  notch  is  limited  by  a  rough  U-shaped  serrated 
surface,  the  median  part  of  which  articulates  with  the  nasal  bones,  whilst  on  either 
side  the  frontal  (nasal)  processes  of  the  maxilla  are  united  with  it.  Behind  this, 
amid  the  broken  cells,  the  passages  leading  into  the  frontal  sinuses  are  readily 
distinguished,  and  here  the  medial  edges  of  the  orbital  plates  articulate  with  the 
lacrimal  bones.     The  orbital  plate  is  thin  and  brittle.     In  front  it  is  bounded  by 

'   Nasal  nerve  =  uaso-ciliary  nerve  (B.N. A.). 


THE  FRONTAL  BONE. 


105 


the  superior  orbital  margin,  just  within  wliich,  midway  between  the  medial  angular 
process  and  the  supraorbital  notch,  there  is  a  small  shallow  depression  (fovea  troch- 
learis),  often  displaying  a  spicule  of  bone  arising  from  its  edge  (spina  trochlearis), 
which' affords  attachment  to  the  pulley  of  the  superior  oblique  muscle  of  the  eyeball. 
Laterally  the  orbital  plate  is  overhung  by  the  orbital  margin  and  the  lateral 
angular  process,  and  in  the  hollow  so  produced  (fossa  glandulaj  lacrimalis)  the 
lacrimal  gland  is  lodged.  The  extremity  of  the  external  angular  process  (pro- 
cessus zygomaticus)  articulates  with  the  frontal  (fronto- sphenoidal)  process  of  the 
malar  Ijone.  Behind  this  the  irregular  edge  of  the  orbital  plate  is  united  with 
the  great  wing  of  the  sphenoid  by  a  triangular  area,  which  also  extends  on  to 
the  inferior  aspect  of  the  temporal  surface  of  the  frontal  bone.  The  apex  of 
the  orbital  plate,  for  the  space  of  about  half  an  inch,  articulates  with  the  lesser 
wing  of  the  sphenoid. 

The  cerebral  surface  of  the  bone  forms  a  fossa  in  which  lie  the  fore  and  under 
parts  of  the  frontal  lobes  of  the  cerebrum,  the  convolutions  of  which  impress  their 
form  on  the  inner  table  of  the  bone.  Here,  too,  on  either  side  of  the  middle  line, 
may  be  seen  depressions  for  the  lodgment  of  Pacchionian  bodies.  Descending  from 
the  centre  of  the  upper  margin  of  the  bone  is  a  vertical  groove,  the  frontal  sulcus ; 


For  articulation  with 
lesser  wing  of  sphenoid 


Pacchionian    Superior  longitudinal  (sagittal) 
depression  sinus  and  falx  cerebri 


Meningeal  groove 

/ 


Orbital  plat' 


Temporal  surface 


Lateral  angular  process 


ternal  orbital  canals 


Ethmoidal  notch 

Frontal  sinus 

Nasal  surface 


Supraorbital  notch 
Trochlear  fossa 


Nasal  notch 
Frontal  spine 

Fig.  79. — The  Frontal  Bone  as  seen  from  Below. 

narrowing  below,  this  ends  in  a  ridge — the  frontal  crest — which  nearly  reaches 
the  fore  part  of  the  ethmoidal  notch,  where  it  terminates  in  a  small  orifice,  the 
foramen  caecum,  placed  usually  in  the  suture  between  the  fore  part  of  the  ethmoid 
and  the  frontal.  This  foramen  may,  or  may  not,  transmit  a  small  vein  from  the 
nose  to  the  commencement  of  the  superior  longitudinal  (sagittal)  sinus.  This  sinus, 
which  is  interposed  between  the  layers  of  the  falx  cerebri,  is  at  first  attached  to  the 
frontal  crest,  but  subsequently  occupies  the  frontal  sulcus.  Deeply  concave  from 
side  to  side  and  from  above  downwards,  the  lateral  aspects  of  the  fossa  are  seen  to 
be  traversed  by  small  grooves  for  the  anterior  branches  of  the  middle  meningeal 
arteries.  Below,  the  orbital  plates  bulge  into  the  floor  of  the  fossa,  so  that  the 
ethmoidal  notch  appears  recessed  between  them.  On  either  side  of  the  notch  faint 
grooves  for  the  meningeal  branches  of  the  ethmoidal  vessels  may  be  seen.  The 
circumference  of  the  fossa  is  formed  by  the  serrated  edges  of  the  bone  which 
articulate  with  the  parietals  above,  and  on  either  side  below  with  the  great  and 
lesser  wings  of  the  sphenoid. 

Connexions. — The  frontal  articulates  with  twelve  bones,  viz.  posteriorly  with  the  parietals 
and  sphenoid ;  laterally  with  the  zygomatic  bones ;  inferiorly  and  medially  with  the  nasals, 
maxillc-e,  lacrimals,  and  ethmoid. 


106 


OSTEOLOGY. 


Ossification 

about  the  sixth 


Ossification  begins   in    membrane   from    two  centres,    wliich  appear 
or  seventh    week,    one    on    either    side    immediately  above  the  orbital 


margm.  From  these  the  two  halves  of  the  frontal 
part  of  the  bone  are  developed,  and  by  extension 
medially  and  backwards  from  their  lower  part  the 
orbital  plates  are  also  formed.  Serres,  Rambaud 
and  Renault,  and  v.  Ihering  describe  the  occurrence 
of  three  pairs  of  secondary  centres  somewhat  later  : 
one  pair  for  the  frontal  spine  on  either  side  of  the 
foramen  csecum  ;  a  centre  on  either  side  in  cor- 
respondence with  the  position  of  each  trochlear 
fossa ;  and  a  centre  for  each  lateral  angular  process. 
Fusion  between  these  secondary  and  the  primary 
centres  is  usually  complete  about  the  sixth  or  seventh 
month  of  foetal  life.  At  birth  the  two  symmetrical 
halves  of  the  bone  are  separated  by  the  metopic 
suture,  obliteration  of  which,  commencing  as  a  rule 
on  a  level  with  the  frontal  tubera,  gradually  takes 
place,  so  that  about  the  fifth  or  sixth  year  it  is 
more  or  less  completely  closed,  traces  only  of  the 
suture  being  left  above  and  below.  In  about  eight 
per  cent  of  Europeans,  however,  the  suture  persists 
in  the  adult  (see  ante).  At  birth  the  supraorbital 
notches  lie  near  the  middle  of  the  supraorbital  arches. 
Traces  of  the  frontal  sinuses  may  be  met  with  about  the  second  year,  but  it  is  only 
about  the  age  of  seven  that  they  can  be  definitely  recognised.  From  that  time  they 
increase  in  size  till  the  age  of  puberty,  subsequent  to  which  time  they  attain  their 
maximum  development. 

The  Parietal  Bones. 

The  parietal  bones  (ossa  parietalia),  two  in  number,  are  placed  on  either  side 
of  the  vault  of  the  cranium,  articulating  with  the  frontal  anteriorly,  the  occipital 

Parietal  eminence 


Fig.  80. — Ossification  of  the  Frontal 
Bone. 

z,  Metopic  suture  still  open,  b,  Position  of 
primary  centre.  c,  Centre  for  lateral 
angular  process,  d,  Centre  for  region  of 
trochlea,     e,  Centres  for  nasal  spine. 


Parietal 
foramen 


Superior  temporal  line 


Inferior  temporal  line 


For  articulatioi 
with  tlie  occipital 


For  ai'ticulalioii  witli  tho 
great  wing  of  the  sphenoid 


For  articulation  with 
the  squamous  part  of 
le  temporal 


Mastoid  angle  ^^ For  articulation  witli  llie  mastoid  jiart  of  the  temporal 

Fig.  81. — The  Right  Parietal  Bone  (Parietal  Surface). 

'posteriorly ,  and  the  temporals  and  sphenoid  inferiorly.      Each  bone  possesses  a 
parietal  and  cerebral  surface,  four  borders,  and  four  angles. 


THE  PAEIETAL  BONES. 


107 


The  parietal  surface,  convex  from  above  downwards  and  from  before  backwards, 
displays  towards  its  centre  a  more  or  less  pronounced  elevation,  the  parietal  eminence  ^ 
(tuber  parietale).  This  marks  the  position  of  the  primitive  ossific  centre,  and  not 
infrequently  corresponds  to  the  point  of  maximum  width  of  the  head.  At  a 
variable  distance  from  the  lower  border  of  the  bone,  and  more  or  less  parallel  to  it,  two 
curved  lines  can  usually  be  distinguished  ;  these  together  constitute  the  temporal  crest. 
The  superior  temporal  line  (linea  temporalis  superior)  serves  for  the  attachment  of 
the  temporal  fascia ;  the  inferior  temporal  line  (linea  temporalis  inferior)  defines  the 
attachment  of  the  temporal  muscle,  the  extent  and  development  of  which  necessarily 
determine  the  position  of  the  crest.  The  surface  below  the  crest  enters  into  the 
formation  of  the  floor  of  the  temporal  fossa,  and  is  called  the  planum  temporale ;  it 
also  affords  origin  to  the  temporal  muscle,  and  is  often  faintly  marked  by  grooves 
which  indicate  the  course  of  the  middle  temporal  artery. 


Depressions  for  raccliionian  bodies 


'aiietal  foramen 


^<  ^N      Groove  for 
''J  r  SB      superior  longi- 
tudinal 
'\ij^  (sagittal)  sinus 


Anterior  inferior  angle 
(sphenoid) 


Mastoid  angle 
Groove  for  lateral  (transverse)  sinus 


Fig.  82.— The  Eight  Parietal  Bone  (Cerebral  Surface). 


Above  the  superior  temporal  line  the  bone  is  covered  only  by  the  tissues  of  the 
scalp.  Near  its  upper  border,  and  about  an  inch  from  its  posterior  superior  angle, 
is  the  small  parietal  foramen  (foramen  parietale),  through  which  pass  a  small 
arteriole  and  an  emissary  vein. 

The  cerebral  surface  is  concave  from  side  to  side  and  from  above  downwards.  It 
is  moulded  over  the  surface  of  portions  of  the  frontal,  parietal,  occipital,  and  temporal 
lobes  of  the  cerebrum,  and  displays  impressions  corresponding  to  the  arrangement 
of  the  convolutions  of  these  portions  of  the  brain.  It  also  presents  a  series  of 
well-marked  grooves  for  the  lodgment  of  the  branches  of  the  middle  meningeal 
artery ;  these  radiate  from  the  anterior  inferior  angle  of  the  bone,  the  best  marked 
running  upwards  at  some  little  distance  behind  and  parallel  to  its  anterior  border. 
Within  the  upper  margin  is  a  series  of  depressions  for  Pacchionian  bodies, 
and  here  also  the  bone  is  channelled  so  as  to  form  a  groove  (sulcus  sagittalis), 
which  is  completed  by  articulation  with  its  fellow  of  the  opposite  side.     Within 


^  Here  agaiu  I  retain  the  original  English. — A.  T. 


7a 


108  OSTEOLOGY. 

this  groove  lies  the  superior  longitudinal  (sagittal)  venous  sinus,  and  to  its  edges  the 
falx  cerebri  is  attached.  Close  to  the  posterior  inferior  angle  there  is  also  a  curved 
groove,  the  lateral  sulcus,  in  which  the  highest  portion  or  bend  of  the  lateral 
(transverse)  venous  sinus  is  lodged. 

The  anterior,  superior,  and  posterior  borders  are  deeply  serrated.  The  anterior 
border  articulates  with  the  frontal  bone,  forming  with  it  the  coronal  suture.  In 
the  upper  part  of  this  suture  the  frontal  bone  overlaps  the  parietal,  while  the 
parietal  overlies  the  frontal  below.  The  posterior  border  is  united  with  the 
occipital  bone,  and  forms  the  lambdoid  suture.  The  superior  border  articulates 
with  its  fellow  of  the  opposite  side  by  means  of  the  sagittal  suture  ;  in  the  interval 
between  the  two  parietal  foramina  this  suture  is-  usually  simple  in  its  outline. 
The  anterior  superior  angle  (angulus  frontalis)  is  almost  rectangular,  and  corre- 
sponds to  the  site  of  the  anterior  fontanelle.  The  posterior  superior  angle  (angulus 
occipitalis),  usually  more  or  less  rounded,  corresponds  in  position  to  the  posterior 
fontanelle.  The  inferior  border  (margo  squamosus)  is  curved,  and  shorter  than  the 
others ;  it  lies  between  the  anterior  and  posterior  inferior  angles.  Sharp  and  bevelled 
at  the  expense  of  its  outer  table,  it  displays  a  fluted  arrangement,  and  articulates 
with  the  squamous  part  of  the  temporal  bone.  The  anterior  inferior  angle  (angulus 
sphenoidalis),  pointed  and  prominent,  articulates  with  the  great  wing  of  the 
sphenoid.  It  is  wedged  into  the  angle  formed  by  the  union  of  that  bone  with  the 
frontal,  and  is  bevelled  at  the  expense  of  its  inner  table  anteriorly,  whilst  inferiorly 
it  is  thinned  at  the  expense  of  its  outer  table.  The  posterior  inferior  angle  (angulus 
mastoideus)  is  a  truncated  angle  lying  between  the  inferior  and  posterior  borders. 
It  is  deeply  serrated,  and  articulates  with  the  mastoid  process  of  the  temporal  bone. 
Not  infrequently  there  is  a  channel  in  this  suture  which  transmits  an  emissary  vein. 

Connexions.  —  The  parietal  bone  articulates  with,  its  fellow,  with  the  frontal,  occipital, 
mastoid  and  squamoas  parts  of  the  temporal,  and  with  the  sphenoid.  Occasionally  the  inferior 
angle  may  not  reach  the  great  wing  of  the  sphenoid,,  being  separated  from  it  by  the  articula- 
tion of  the  squamous  part  of  the  temporal  with  the  frontal  (Appendix  B). 

Ossification. — Ossification  takes  place  in  membrane  by  the  deposition  of  earthy 
matter,  the  centre  for  which,  most  probably  formed  by  the  coalescence  of  two  nuclei — 
in  some  cases  possibly  more — appears  over  the  parietal  eminence  about  the  sixth  or  seventh 
week  of  foetal  life  ;  from  this  it  spreads  in  a  radial  manner  towards  the  edges  of  the  bone, 
where,  however,  the  membranous  condition  still  for  some  time  persists,  constituting  the 
fontanelles.  These  correspond  in  position  to  the  angles  of  the  bone.  Ossification  is  also 
somewhat  delayed  in  the  region  of  the  parietal  foramina,  constituting  what  is  known  as  the 
sagittal  fontanelle,  a  membranous  interval  which  is  not  infrequently  apparent  even  at  birth. 

The  Occipital  Bone. 

The  occipital  bone  (os  occipitale),  placed  at  the  back  and  lower  part  of  the 
cranium,  consists  of  four  parts,  arranged  around  a  large  oval  hole,  called  the 
occipital  foramen  or  foramen  magnum.  At  birth  these  parts  are  all  separate. 
The  expanded  curved  plate  behind  the  foramen  is  the  squamous  or  tabular  part. 
The  thick  rod-like  portion  in  front  of  the  foramen  is  the  basilar  process.  On  either 
side  the  foramen  is  bounded  ])y  the  lateral  or  condylic  or  exoccipital  portions. 

The  squamous  or  tabular  part  (squama  occipitalis)  in  shape  somewhat 
resembles  a  Gothic  arch,  and  is  curved  from  side  to  side  and  from  above  downwards. 
It  forms  inferiorly  a  small  portion  of  the  middle  of  the  posterior  boundary  of  the 
foramen  magnum,  and  unites,  on  either  side  of  that,  with  the  lateral  parts  of  the  bone. 
About  tlie  centre  of  the  parietal  surface  of  the  squama  there  is  a  prominence — the 
external  occipital  protuberance  (protuberantia  occipitalis  externa),  which  varies  con- 
siderably in  its  distinctness  and  projection,  and  serves  for  the  attachment  of  the 
ligamentum  nuchse.  From  the  protuberance  on  either  side  two  lines  curve  out 
towards  the  lateral  angles  of  the  bone.  These  are  known  respectively  as  the  highest 
and  superior  curved  lines  (linea  nuchae  suprema  and  linea  nuchas  superior).  To  the 
upper  of  these  the  epicranial  aponeurosis  is  attached,  whilst  the  lower  serves  for 
the  origin  of  the  trapezius  and  occipitalis  muscles  and  the  insertion  of  the  sterno- 
mastoid  and  splenius  capitis  muscles.     The  two  lines  together  serve  to  divide  the 


THE  OCCIPITAL  BONE.  109 

parietal  surface  ot"  the  squamous  part  into  an  upper  or  occipital  portion  (planum 
occipitale),  covered  by  the  hairy  scalp,  and  a  lower  or  nuchal  part  (planum  nuchale), 
serving  for  the  attachment  of  the  fleshy  muscles  of  the  back  of  the  neck.  As  a  rule 
the  occipital  part  bulges  backwards  beyond  the  external  occipital  protuberance ; 
exceptionally,  however,  the  latter  process  is  the  most  outstanding  part  of  the  bone. 
The  nuchal  plane,  irregular  and  rough,  is  divided  into  two  lateral  halves  by  a 
median  ridge  —  the  external  occipital  crest  (linea  nuchae  mediana),  which  stretches 
from  the  external  occipital  protuberance  above  to  the  posterior  border  of  the  foramen 
magnum  below.  Crossing  the  nuchal  plane  transversely,  about  its  middle,  is  the 
inferior  curved  line  (linea  nuchae  inferior),  which  passes  laterally  and  forwards  on 
either  side  towards  the  lateral  margins  of  the  bone.  The  areas  thus  marked  out 
serve  for  the  attachment  of  the  complexus  (semispinalis  capitis),  obliquus  capitis 
superior,  and  rectus  capitis  posterior  major  and  minor  muscles. 

The  cerebral  surface  of  the  squamous  part,  concave  from  side  to  side  and  from  above 
downwards,  is  subdivided  into  four  fossas  by  a  crucial  arrangement  of  ridges  and 
grooves.  In  the  upper  pair  of  fossse  are  lodged  the  occipital  lobes  of  the  cerebrum, 
whilst  the  lobes  of  the  cerebellum  occupy  the  lower  pair.  Near  the  centre  of  this 
aspect  of  the  bone  is  the  internal  occipital  protuberance  (protuberantia  occipitalis 
interna),  an  irregular  elevation,  the  sides  of  which  are  variously  channelled  according 
to  the  disposition  of  the  grooves.  Leading  from  this  to  the  hinder  margin  of  the 
foramen  magnum  is  a  sharp  and  well-defined  ridge,  the  internal  occipital  crest  (crista 
occipitalis  interna),  which  serves  for  the  attachment  of  the  falx  cerebelli,  a  process  of 
dura  mater  which  separates  the  two  cerebellar  henuspheres.  Passing  upwards  from 
the  internal  occipital  protuberance  there  is  usually  a  well-marked  ridge,  to  one  or 
other  side  of  which,  more  frequently  the  right  (with  the  bone  in  the  normal  position 
and  viewed  from  behind),  there  is  a  well-defined  groove,  the  sulcus  sagittalis,  the 
outer  lip  of  which  is  generally  less  prominent.  Placed  in  this  groove  is  the  superior 
longitudinal  (sagittal)  venous  sinus,  and  attached  to  the  lips  is  the  falx  cerebri.  At 
right  angles  to  the  foregoing,  and  at  the  level  of  the  internal  occipital  protuberance, 
with  which  they  become  confluent,  are  two  transverse  grooves,  the  sulci  transversi. 
These  grooves,  which  have  more  or  less  prominent  edges,  lie  between  the  upper  and 
lower  pairs  of  fossse,  and  serve  for  the  attachment  of  the  tentorium  cerebelli  as  well  as 
the  lodgment  of  the  lateral  (transverse)  sinuses.  Commonly  the  right  lateral  groove 
is  confluent  with  the  groove  to  the  right  side  of  the  median  ridge,  but  exceptions  to 
this  rule  are  not  infrequent.  The  angle  formed  by  the  union  of  the  venous  sinuses 
lodged  in  these  grooves  constitutes  the  torcular  Herophili,  which  may  accordingly  be 
placed  to  one  or  other  side  of  the  internal  occipital  protuberance,  more  frequently 
the  right ;  in  some  cases,  however,  it  may  occupy  a  central  position. 

The  superior  angle,  more  or  less  sharp  and  pointed,  is  wedged  in  between  the 
two  parietal  bones,  its  position  corresponding  to  the  site  of  the  posterior  fontanelle. 
The  lateral  angles  articulate  on  either  side  with  the  posterior  extremity  of  the 
mastoid  portion  of  the  temporal  bone.  The  superior  borders,  much  serrated,  articu- 
late with  the  parietal  bones  forming  the  lambdoid  suture ;  and  the  lateral  borders, 
extending  from  the  lateral  angles  to  the  jugular  process  inferiorly,  are  connected 
with  the  medial  sides  of  the  mastoid  portions  of  the  temporals. 

The  lateral  (condylic  or  exoccipital)  parts  of  the  occipital  bone  (partes 
laterales)  are  placed  on  either  side  of  the  foramen  magnum ;  on  their  under 
surface  they  bear  the  condyles  (condyli  occipitales)  by  means  of  which  the  skuU 
articulates  with  the  atlas.  Of  elongated  oval  form,  the  condyles  are  so  disposed 
that  their  anterior  extremities,  in  line  with  the  anterior  margin  of  the  foramen 
magnum,  lie  closer  together  than  their  posterior  ends,  which  extend  as  far  back 
as  the  middle  of  the  lateral  borders  of  the  foramen.  Convex  from  before 
backwards,  they  are  skewed  so  that  their  surfaces,  which  are  nearly  plane  from 
side  to  side,  are  directed  slightly  outwards.  Each  is  supported  on  a  boss  of  hone, 
pierced  by  the  anterior  condylic  foramen  (canalis  hypoglossi),  which  opens  obliquely 
from  within  laterally  and  forwards  on  the  floor  of  a  fossa  called  the  anterior 
condylic  fossa,  situated  just  lateral  to  the  fore  part  of  the  condyle.  The  foramen 
transmits  the  hypoglossal  or  12th  cranial  nerve,  together  with  a  meningeal  branch 
of  the  ascending  pharyngeal  artery  and  its  companion  veins.     Behind  the  condyle 


110 


OSTEOLOGY. 


is  placed  the  posterior  condylic  fossa,  in  the  floor  of  which  the  posterior  condylic 
foramen  ^  (canalis  condyloideus)  frequently  opens.  Through  this  a  vein  passes  which 
joins  the  lateral  (transverse)  sinus.  The  fosSc©  lodge  the  posterior  margins  of  the 
superior  articular  processes  of  the  atlas  in  extension  of  the  head.  The  edge  of  the 
foramen  magnum  immediately  behind  the  condyle  is  often  grooved  for  the  passage 
of  the  vertebral  artery  around  it.  Jutting  out  from  the  posterior  half  of  the 
condyle  is  a  stout  bar  of  bone,  serially  homologous  with  the  vertebral  transverse 
process — this  is  the  jugular  process  (processus  jugularis) ;  deeply  notched  in  front 
(jugular  notch)  its  anterior  border  is  free  and  rounded,  and  forms  the  posterior 
boundary  of  the  jugular  foramen.  Curving  outwards  from  this  margin,  in  line 
with  the  anterior  condylic  foramen,  there  is  often  a  small  pointed  projection, 
the  processus  intra-jugulare,  which  serves  to  divide  the  jugular  foramen  into  two 


Supreme  nuchal  line 


External  occipital  protuberance 


Superior  nuclial  line 


Posterior  con- 
dylic foramen 
(canalis  condy- 
loideus) 


Jugular  process 


Jugular  notch 


Condyle. 
Pharyngeal  tubercle 


Fig,  8.3. — The  Occipital  Bone  as  seen  from  Below. 

compartments.  Laterally  the  jugular  process  articulates  by  means  of  a  synchon- 
drosis with  the  jugular  surface  of  the  petrous  part  of  the  temporal  bone.  Its 
posterior  border  is  confluent  with  the  lower  and  lateral  portion  of  the  occipital 
squama,  and  its  under  surface  is  rough  and  tubercular  for  the  attachment  of  the 
rectus  capitis  lateralis  muscle.  The  suiierior  aspect  of  the  lateral  part  displays  on 
either  side  of  the  foramen  magnum  an  elevated  surface  of  oval  form,  the  tuberculum 
jugulare ;  this  corresponds  to  the  part  of  the  bone  which  bridges  over  the  canal 
for  the  hypoglossal  nerve.  Its  upper  surface  in  many  instances  displays  an  oblique 
groove  running  across  it;  in  this  are  lodged  the  glosso-pharyngeal,  vagus,  and 
accessory  nerves.  The  jugular  process  is  deeply  grooved  superiorly  for  the  lower 
part  of  the  lateral  (transverse)  blood  sinus,  which  here  turns  round  the  anterior 
free  edge  of  the  process  into  the  jugular  foramen.  Joining  this,  close  to  its  inner 
edge,  is  the  opening  of  the  posterior  condylic  foramen  when  that  canal  exists. 

The  basilar  part  of  the  occipital  bone  (pars  basilaris)  extends  forwards  and 
upwards  from  the  foramen  magnum.  Its  anterior  extremity  is  usually  sawn  across, 
as,  after  adult  life,  it  is  necessary  to  sever  it  in  this  way  from  the  sphenoid,  the 

'  This  I  retail),  the  canal  can  iu  no  way  resemble  a  condyle. — A.  T. 


THE  OCCIPITAL  BONE. 


Ill 


cartilage  uniting  the  two  bones  having  by  that  time  become  completely  ossified. 
Broad  and  thin  behind,  it  narrows  laterally  and  thickens  vertically  in  front,  where 
on  section  it  displays  a  quadrilateral  form.  Projecting  from  its  under  surface  some 
little  distance  in  front  of  the  foramen  magnum  is  the  pharyngeal  tubercle  (tuber- 
culum  pharyngeum)  to  which  the  fibrous  raphe  of  the  pharynx  is  attached ;  on 
either  side  of  this  the  longus  capitis  and  rectus  capitis  anterior  muscles  are  inserted. 
The  upper  surface  forms  a  broad  and  shallow  groove  which  slopes  upwards  and 
forwards  from  the  thin  anterior  margin  of  the  foramen  magnum ;  in  this  rests  the 
medulla  oblongata.  On  either  side  its  lateral  edges  are  faintly  grooved  for  the 
inferior  petrosal  venous  sinuses,  below  which  the  lateral  aspect  of  the  bone  is  rough 
for  the  cartilage  which  unites  it  to  the  sides  and  apex  of  the  petrous  part  of  the 
temporal  bone. 


For  superior  longitudinal  (sagittal)  sinus  and  falx  cerebri 
Cerebral  fossa 


Torcular  Herophili 


Superior  angl"^ 


Internal  occipital 
protuberance 


For  lateral  (trans- 
verse) sinus  and 
tentorium  cerebelli 


Lateral  angle 


Cerebellar  fossa 


Internal  occipital 
crest 


•Jugular  process 


Posterior  condylic 
foramen  (canalis 
condyloideus) 


Jugular  notcl 
Groove  for  inferior  petrosal  sinus 


Tuberculum  pharyngeum 


-Basilar  groove 
Basilar  process 

Fig.    84. — Occipital  Bone  (Cereljral  Surface). 

The  foramen  magnum,  of  oval  shape,  so  disposed  that  its  long  axis  lies  in  the 
sagittal  plane,  is  of  variable  size  and  form.  The  plane  of  its  outlet  differs  somewhat 
in  individual  skulls;  in  most  instances  it  is  directed  downwards  and  slightly 
forwards.  In  front  the  condyles  encroach  upon  it,  and  narrow  to  some  extent  its 
transverse  diameter.  To  its  margins  are  attached  the  ligaments  which  unite  it 
with  the  atlas  and  axis.  Through  it  pass  the  lower  part  of  the  medulla  oblongata 
where  it  becomes  continuous  with  the  spinal  cord,  the  two  vertebral  arteries,  the 
accessory  nerves,  and  the  blood-vessels  of  the  meninges  of  the  upper  part  of 
the  cord. 

Connexions. — The  occipital  bone  articulates  with  the  two  parietals  in  front  and  above,  with 
the  sphenoid  in  front  and  below,  ^vith  the  two  temporals  on  either  side,  and  with  the  atlas 
"by  means  of  its  condyles. 

Ossification. — The  major  part  of  the  bone  ossifies  in  cartilage,  the  upper  part  of  the 
.squamous  part  (interparietal)  alone  developing  in  membrane.     The  basilar  part  begins  to 


112 


OSTEOLOGY. 


ossify  about  the  sixth  week  of  fo3tal  life  by  the  appearance  of  two  centres,  one  in  front  of 
the  other ;  the  anterior,  according  to  Albrecht,  constitutes  the  basiotic,  the  posterior  the 
basi-occipital.  These  two  centres — which  there  is  some  reason  to  believe  may  themselves 
be  formed  by  the  fusion  of  pairs  placed  laterally — rapidly  unite,  so  that  the  occurrence  of 
one  centre  alone  is  frequently  described.  Fi'om  this  the  fore  part  of  the  margin  of  the 
foramen  magnum  is  formed,  together  with  a  portion  of  the  anterior  end  of  the  occipital 
condyle  on  either  side.  It  helps  also  to  close  up  the  front  of  the  hypoglossal  canal. 
Union  with  the  condylic  parts  is  complete  about  the  fourth  or  fifth  year.  Ankylosis 
between  the  basi-occipital  and  the  sphenoid  takes  place  about  the  twenty-fifth  year. 

The  lateral,  condylic,  or  exoccipital  parts  begin  to  ossify  from  a  single  centre  about 
the  end  of  the  second  month  of  foetal  life.  The  notch  for  the  hypoglossal  canal  appears 
about  the  third  month.  From  this  centre  is  formed  the  posterior  three-fourths  of  the 
occipital  condyle.  The  exoccipital  is  usually  completely  fused  with  the  squamous  part 
by  the  third  year  or  earlier. 

As  already  noted,  the  squamous  part  consists  of  two  parts — the  one  above  the  occipital 

crest,  the  other  below  it ;  the  former  develops  in 
membrane,  the  latter  in  cartilage.  In  a  three-months 
foetus  this  difference  is  very  characteristic.  The 
cartilaginous  part  (supra-occipital)  begins  to  ossify 
from  two  centres  about  the  sixth  or  seventh  week, 
which  rapidly  join  to  form  an  elongated  strip  placed 
transversely  in  the  region  of  the  occipital  pro- 
tuberance. The  centres  for  the  upper  part  (inter- 
parietal) appear  later.  According  to  Maggi  (Arch. 
Ital.  Biol,  tome  26,  fas.  2,  p.  301),  they  are  four 
in  number,  of  which  two  placed  on  either  side  of 
the  middle  line  appear  about  the  second  month. 
The  other  pair,  placed  laterally,  are  seen  about  the 
third  month ;  fusion  between  these  takes  place 
early,  but  their  disposition  and  arrangement  explain 
the  anomalies  to  which  this  part  of  the  bone  is 
subject.  The  medial  pair  may  persist  as  separate 
ossicles,  or  fuse  to  form  the  pre-interparietals,  whilst 
the  lateral  pair  may  remain  independent  of  the 
supra-occipital  as  a  single  or  double  interparietal 
bone,  the  former,  owing  to  the  frequency  of  its 
occurrence  in  Peruvian  skulls,  being  sometimes 
called  the  os  Incee.  Union  between  the  supra- 
occipital  and  the  interparietal  elements  occurs  about 
the  third  or  fourth  month ;  but  evidence  of  their 
separation  is  frequently  met  with  even  in  the  adult 
tilage) ;  e,  "Fissure  between' supra-occipital  by  the  persistence  of  a  transverse  suture  running 
and  interparietal  ;  /,  Interparietal  (from  inwards  from  each  lateral  angle  of  the  squamous  part, 
fj,  Fissure  between  inter-  ^^^  ^^  above  mentioned,  there  may  be  an  os  Incse. 
The  supra- occipital  forms  a  small  part  of  the 
middle  of  the  hinder  border  of  the  foramen  magnum,  though  here  a  small  independent 
centre,  known  as  the  ossicle  of  Kerkring,  is  occasionally  met  with.  Other  independent 
centres  are  sometimes  seen  between  the  supra-occipital  and  the  exoccipitals. 

At  birth  the  occipital  consists  of  four  parts — the  interparietal  and  supra-occipital 
combined,  the  basi-occipital,  and  the  exoccipitals — one  on  either  side. 


Fig.  85. — Ossification  of  the  Occipital 

Bone. 

I,  Basilar  centre  ;   h,  Exoccipital  ;   c,  Ossicle 

of  Kerkring  ;  d,  Supra-occipital  (from  car- 


rnembrane) 
parietals. 


The  Temporal  Bones. 

The  temporal  bone  (os  temporale)  lies  about  the  centre  of  the  lower  half  of  either 
side  of  the  skull,  and  enters  largely  into  the  formation  of  the  cranial  base.  It  is 
placed  betvi^een  the  occipital  behind,  the  parietal  above,  the  sphenoid  in  front,  and 
the  occipital  and  sphenoid  medially  and  below.  At  birth  it  consists  of  three  parts 
— an  upper  and  lateral  part,  the  squamous  or  scLuamo- zygomatic  portion ;  a  medial 
and  posterior  portion,  the  petro-mastoid,  which  contains  the  parts  specially  associated 
with  the  sense  of  hearing,  together  with  the  organ  associated  with  equilibration ; 
and  an  under  or  tympanic  part,  from  which  the  floor  and  anterior  wall  of  the 
external  auditory  meatus  is  formed. 

The  squamous  part  (pars  squamosa)  consists  of  a  thin  shell-like  plate  of  bone 


THE  TEMPOEAL  BONES.  113 

placed  vertically,  having  a  medial  (cerebral)  and  a  lateral  (temporal)  surface  and  a 
semicircular  upper  border.  Inferiorly,  behind,  and  medially  it  is  fused  in  early 
life  with  the  petro-mastoid  portion  by  means  of  the  squamoso-mastoid  and  the 
petro-squamosal  sutures,  traces  of  which  are  often  met  with  in  the  adult  bone ; 
whilst  below  and  in  front  it  is  separated  from  the  tympanic  and  petrous  parts  by 
the  Glaserian  fissure.  Its  temporal  surface,  smooth  and  slightly  convex,  enters  into 
the  formation  of  the  floor  of  the  temporal  fossa,  and  affords  attachment  to  the 
temporal  muscle.  Near  its  hinder  part  it  is  crossed  by  one  or  more  ascending 
grooves  for  the  branches  of  the  middle  temporal  artery.  In  front  and  below  there 
springs  from  it  the  zygomatic  process  (processus  zygomaticus).  This  arises  by  a 
broad  attachment,  the  surfaces  of  which  are  inferior  and  superior ;  curving  laterally 
and  forwards,  it  the  nbecomes  twisted  and  narrow,  so  that  its  sides  are  turned  inwards 
and  outwards  and  its  edges  directed  upwards  and  downwards.  Anteriorly  it  ends 
in  an  oblique  serrated  extremity  which  articulates  with  the  temporal  (zygomatic) 
process  of  the  malar  bone.  Posteriorly  the  edges  of  the  zygomatic  process  separate  and 
are  termed  its  roots.  The  upper  edge,  which  becomes  the  posterior  root,  sweeps  back 
over  the  external  auditory  meatus,  and  is  continuous  with  the  supra-mastoid  crest, 
which  curves  backwards  and  slightly  upwards,  and  serves  to  define  the  limit  of  the 
temporal  fossa  posteriorly.  Internally  this  ridge  corresponds  to  the  level  of  the  floor 
of  the  middle  cerebral  fossa.  The  inferior  edge  turns  medially  and  constitutes 
the  anterior  root ;  the  under  surface  of  this  forms  a  transversely-disposed  rounded 
ridge,  the  articular  eminence  (tuberculum  articulare),  behind  which  there  is  a  deep 
hollow,  the  glenoid  fossa  (fossa  mandibularis),  limited  posteriorly  by  the  tympanic 
plate,  and  crossed  at  its  deepest  part  by  an  oblique  fissure,  the  Glaserian  fissure 
(fissura  petro-tympanica).  This  cleft,  which  is  closed  externally,  transmits  about 
its  middle  the  tympanic  branches  of  the  internal  maxillary  artery,  and  lodges  the 
slender  process  of  the  malleus.  At  its  medial  end  the  lips  of  this  fissure  are 
frequently  separated  by  a  thin  scale  of  bone,  a  downgrowth  from  the  tegmen 
tympani  of  the  petrous  part,  which  here  separates  the  tympanic  from  the  squamous 
elements,  forming  in  its  descent  the  major  part  of  the  lateral  wall  of  the  osseous 
Eustachian  canal,  which  lies  just  medial  to  it.  Between  this  scale  of  bone  and 
the  posterior  edge  of  the  fissure  there  is  a  small  canal  (canal  of  Huguier),  which 
transmits  the  chorda  tympani  nerve.  The  part  of  the  glenoid  fossa  in  front  of  the 
Glaserian  fissure  as  well  as  the  articular  eminence  articulate  with  the  condyle 
of  the  mandible,  through  the  medium  of  the  interposed  interarticular  cartilage. 
Posteriorly  the  part  of  the  fossa  behind  the  fissure  is  non-articular  and  lodges 
a  portion  of  the  parotid  gland.  At  the  angle  formed  by  the  divergence  of  the  two 
roots  of  the  zygoma,  in  correspondence  with  the  lateral  part  of  the  articular 
eminence,  there  is  a  rounded  tubercle  ;  to  this  are  attached  the  fibres  of  the  temporo- 
mandibular (external  lateral  ligament)  of  the  temporo-mandibular  joint.  In  front 
of  the  medial  end  of  the  articular  eminence  there  is  a  small  triangular  surface, 
limited  in  front  by  the  edge  of  the  anterior  root,  and  medially  by  a  thick  serrated 
margin  which  articulates  with  the  temporal  aspect  of  the  great  wing  of  the  sphenoid  ; 
this  area  forms  part  of  the  roof  of  the  zygomatic  fossa.  Just  anterior  to  the 
external  auditory  meatus  and  projecting  downwards  from  the  under  surface  of  the 
posterior  root  there  is  a  conical  process,  called  the  post-glenoid  tubercle,  which  forms 
a  prominent  anterior  lip  to  the  lateral  extremity  of  the  Glaserian  fissure ;  it  is  the 
representative  in  man  of  a  process  which  is  developed  in  some  mammals  and  prevents 
the  backward  displacement  of  the  lower  jaw.  By  some  anatomists  it  is  referred  to 
as  the  middle  root  of  the  zygoma. 

The  zygomatic  process  by  its  lower  margin  and  medial  surface  gives  origin  to  the 
masseter  muscle,  whilst  attached  to  its  upper  edge  are  the  layers  of  the  temporal 
fascia.  Behind  the  external  auditory  meatus,  and  below  the  supramastoid  crest,  the 
squamous  element  extends  downwards  as  a  pointed  process,  which  assists  in  forming 
the  roof  and  posterior  wall  of  the  external  auditory  meatus,  where  it  unites 
inferiorly  with  the  tympanic  plate  and  forms  the  outer  wall  of  a  hoUow  within 
called  the  mastoid  antrum.  In  the  adult  this  process  is  occasionally  sharply 
defined  posteriorly  by  an  oblique  irregular  fissure,  the  remains  of  the  masto- 
squamosal  suture.     Immediatelv  above  and  behind  the  external  auditory  meatus 


114 


OSTEOLOGY. 


there   is    often    a   little   projecting   spur  of  bone,  the  supra-meatal   spine  (spina 
suprameatus). 

The  angular  recess  between  this  process  and  the  supramastoid  crest  is  of  interest 
surgically,  and  is  li:no\vn  as  Macewen's  triangle.  The  same  aiithoritj  has  pointed  out  that 
the  masto-squamosal  suture  frequently  remains  open  till  puberty  and  occasionally  after, 
and  may  be  of  importance  as  a  channel  along  which  infective  processes  may  extend. 

The  cerebral  surface  of  the  squamous  part,  less  extensive  than  the  parietal  aspect 
owing  to  the  bevelling  of  the  parietal  border,  is  marked  by  the  impression  of  the 
convolutions  of  the  temporal  lobe  of  the  cerebrum,  and  is  limited  below  by  the 
petro-squamosal  suture,  the  remains  of  which  can  frequently  be  seen.  It  is  crossed 
in  front  by  an  ascending  groove  for  the  middle  meningeal  artery,  branches  from 
which  course  backwards  over  the  bone  in  grooves  more  or  less  parallel  to  its  parietal 
border. 


Groove  for  middle 
temporal  artery 


Supramastoid 

crest 


Temporal  surface 


Parietal  notch 7    V  i 


Supra-meatal  spinn^ 


Remains  of 

ma8to-squamo.sal 

suture 


Mastoid  process 


Eniinentia  articularis 
Glenoid  fossa 


External  auditory  meatus     Tyuipaiiu-  External 

mastoid   auditory 

lissure     process 

Styloid  process 


Fig.  86. — The  Right  Temporal  Bone  seen  from  the  Parietal  Side. 


The  squamo-zygomatic  part  is  coloured  blue  ;  the  petro-mastoid,  red. 

process  are  left  uncoloured. 


The  tympanic  part  and  styloid 


The  parietal  border  of  the  squamous  part  is  curved,  sharp,  and  scale-like,  being 
bevelled  at  the  expense  of  its  inner  table,  except  in  front,  where  the  margin  is  thick 
and  stout.  Here  it  articulates  with  the  great  wing  of  the  sphenoid,  its  union  with 
that  bone  extending  to  near  the  fore  part  of  the  summit  of  the  curve,  behind  which 
it  is  united  to  the  parietal,  overlapping  the  squamous  border  of  that  bone  ;  posteriorly 
the  free  margin  of  the  squamous  part  ends  at  an  angle  formed  between  it  and  the 
mastoid  process  called  the  incisura  parietalis. 

The  tympanic  part  (pars  tympanica)  of  the  temporal  bone  forms  the  anterior, 
lower,  and  part  of  the  posterior  wall  of  the  external  auditory  meatus.  Bounded 
in  front  and  above  by  the  Glaserian  fissure,  it  forms  the  hinder  wall  of  the  non- 
articular  part  of  the  glenoid  fossa.  Fused  medially  with  the  petrous  part,  its 
lower  edge,  sharp  and  well  defined  medially,  splits  to  enclose  the  root  of  the 
projecting  styloid  process,  and  is  hence  called  the  vaginal  process  (vagina  processus 
styioidei).  Laterally  it  unites  with  the  fore  part  of  the  mastoid  process,  and 
higher  up  with  the  descending  process  of  the  squamous  part,  from  both  of  which  it 
is  separated  by  the  auricular  fissure  (fissura  tympano-mastoidea),  through  which  the 
auricular  branch  of  the  vagus  escapes.     Its  free  border,  which  forms  the  anterior, 


THE  TEMPOEAL  BONES. 


115 


lower,  and  part  of  the  posterior  border  of  the  external  auditory  meatus,  is  usually 
somewhat  thickened  and  rough,  and  serves  for  the  attachment  of  the  cartilaginous 
part  of  the  canal. 

The  external  auditory  meatus  (meatus  acusticus  externus)  is  directed  obliquely 
inwards  and  a  little  forwards,  and  describes  a  slight  curve,  the  convexity  of  which 
is  directed  upwards  ;  of  oval  form,  its  long  axis,  close  to  its  orifice,  is  nearly  vertical, 
but,  as  it  passes  inwards,  inclines  somewhat  forwards  so  as  to  give  a  twist  to  the 
canal.  The  depth  of  the  canal  to  the  attachment  of  the  membrana  tympani 
averages  from  14  to  16  mm.  The  upper  margin  of  the  outer  orifice  overhangs 
considerably  the  lower  edge,  but  owing  to  the  obliquity  of  the  inner  aperture,  to 
which  the  membrana  tympani  is  attached,  the  upper  wall  of  the  osseous  canal 
only  exceeds  the  length  of  the  lower  wall  by  one  or  two  millimetres. 

The  petro-mastoid  part  (pars  petrosa  et  mastoidea)  of  the  temporal  bone,  of 
pyramidal  form,  is  fused   to  the  medial  aspect  of  the  tympanic  and  squamosal 


Groove  for  iniddlp 
meningeal  artery 


Eminence  of  sujjerior 
semicircular  canal 


Parietal  notch 


Petro-squamous  sutme 


Groove  for  superior 
petrosal  sinus 


Groove  for  lateral  sinus 
Aqueduct  of  the  vestibule 

Internal  auditory  meatus 
Aqueduct  of  the  cochlea 


Inner  surface  of  mastoid  jirocess 
Groove  for  inferior  petrosal  sinus 

Fig.  87. — The  Right  Temporal  Bone  (Cerebral  aspect). 

The  squamo-zygomatic  part  is  coloured  blue  ;  the  petro-mastoid  part,  i-ed. 
The  styloid  process  is  left  uncoloured. 

portions,  extending  behind  them,  however,  to  form  the  well-marked  and  prominent 
mastoid  process,  which  lies  posterior  to  the  external  auditory  meatus.  This  proces§ 
(pars  mastoidea)  forms  a  nipple-like  projection,  the  size  of  which  differs  considerably 
in  different  individuals.  tJsually  larger  in  the  male  than  in  the  female,  its  rough 
lateral  surface  and  lower  border  serve  for  the  insertions  of  the  sterno-mastoid,  splenius 
capitis,  and  trachelo-mastoid  (longissimus  capitis)  muscles.  Within  and  below  its 
pointed  extremity  there  is  a  deep  groove  (incisura  mastoidea),  usually  well  marked, 
which  gives  origin  to  the  posterior  belly  of  the  digastric  muscle ;  whilst  lying  to  the 
medial  side  of  this,  and  separated  from  it  by  a  more  or  less  well-defined  rough  ridge, 
there  can  oftentimes  be  seen  a  narrow,  shallow  furrow,  which  indicates  the  course 
of  the  occipital  artery.  The  medial  surface  of  the  mastoid  portion  forms,  in  part,  the 
lateral  wall  of  the  posterior  cranial  fossa,  in  which  the  cerebellar  lobes  are  lodged. 
Coursing  across  this  aspect  of  the  bone  there  is  a  broad  curved  groove,  the  con- 
vexity of  which  is  directed  forwards  and  lies  in  the  angle  formed  by  the  base  of  the 
petrous  part  and  its  fusion  with  the  mastoid  portion.  The  depth  to  which  the  bone 
is  here  channelled  varies  considerably,  and  is  important  from  a  surgical  standpoint, 


116  OSTEOLOGY. 

as  herein  lies  the  sigmoid  portion  of  the  lateral  (transverse)  venous  sinus.  Anteriorly 
the  mastoid  is  fused  with  the  descending  process  of  the  squamosal  above,  and  below, 
where  it  is  united  with  the  tympanic,  it  enters  into  the  formation  of  the  posterior 
wall  of  the  external  auditory  meatus  and  the  cavity  of  the  tympanum.  Above,  its 
free  margin  is  rough  and  serrated,  and  articulates  with  the  posterior  inferior  (mastoid) 
angle  of  the  parietal ;  behind  and  below  it  articulates  by  a  jagged  suture  with  the 
occipital.  Traversing  this  suture,  or  near  it,  is  the  mastoid  foramen  (foramen 
mastoideum),  which  transmits  a  vein  from  the  transverse  sinus  to  the  cutaneous 
occipital  vein,  together  with  a  small  branch  of  the  occipital  artery. 

The  petrous  part  (pyramis)  of  the  petro-niastoid  is  of  the  form  of  an  elongated 
three-sided  pyramid.  By  its  base  it  is  united  obliquely  to  the  inner  sides  of-  the 
squamosal  and  tympanic  parts.  Its  apex  is  directed  medially,  forwards,  and  a  little 
upwards.  Its  tln-ee  surfaces  are  arranged  as  follows  : — The  anterior  looks  upwards, 
slightly  forwards,  and  a  little  laterally,  and  forms  part  of  the  floor  of  the  middle 
cranial  fossa.  The  posterior  is  directed  backwards  and  medially,  and  forms  part  of 
the  anterior  wall  of  the  posterior  cranial  fossa.  The  inferior  is  seen  on  the  under 
surface  of  the  base  of  the  skull,  and  is  directed  downwards.  The  borders  or  angles 
are  named  respectively  anterior,  superior,  and  posterior. 

The  anterior  border  or  angle  is  short,  and  forms  an  acute  angle  with  the  fore  part 
of  the  squamous  part;  within  this  angle  is  wedged  the  spinous  part  of  the  great  wing 
of  the  sphenoid.  Here,  too,  the  osseous  Eustachian  canal  (canalis  musculotubarius) 
may  be  seen  leading  backwards  and  laterally  from  the  summit  of  the  angle  to  reach 
the  fore  part  of  the  cavity  of  the  tympanum  in  the  interior  of  the  bone.  On  looking 
into  it,  the  canal  is  seen  to  be  divided  into  two  unequal  parts  by  an  osseous 
partition,  the  cochleariform  process  (septum  tubae).  The  upper  compartment,  the 
smaller  of  the  two  (semicanalis  m.  tensoris  tympani),  lodges  the  tensor  tympani 
muscle,  whilst  the  lower  (semicanalis  tubae  auditivse)  forms  the  osseous  part  of  a 
channel  (the  Eustachian  tube),  which  serves  to  conduct  air  from  the  pharynx  to 
the  tympanum. 

The  posterior  border  or  angle  is  in  part  articular  and  in  part  non-articular.  Pos- 
teriorly and  laterally  it  corresponds  to  the  upper  margin  of  an  area  on  the  inferior 
surface  with  which  the  extremity  of  the  jugular  process  of  the  exoccipital  articulates. 
In  front  of  that  it  is  irregularly  notched,  and  forms  the  free  anterior  edge  of  the 
jugular  foramen,  medial  to  which  it  has  a  sharp  curved  border,  often  grooved, 
reaching  to  the  apex.  This  groove,  which  is  completed  by  articulation  with  the 
lateral  side  of  the  basi-occipital,  lodges  the  inferior  petrosal  venous  sinus. 

The  superior  border  or  angle  is  a  twisted  edge  which  is  continuous  with  the  upper 
margin  of  the  sulcus  for  the  lateral  (transverse)  sinus  posteriorly,  and  anteriorly 
and  medially  reaches  the  apex  of  the  bone.  Eunning  along  it  there  is  usually 
a  well-marked  groove  for  the  superior  petrosal  venous  sinus,  and  near  its  medial 
extremity  it  is  slightly  notched  for  the  passage  of  the  trigeminal  nerve.  Along 
the  entire  length  of  this  border  the  tentorium  cerebelli  is  attached. 

On  the  inferior  surface  of  the  petrous  part,  which  is  bounded  in  front  by  the 
anterior  border  medially,  the  tympanic  plate  laterally,  and  behind  by  the  posterior 
border,  the  following  structures  are  to  be  noted : — Springing  from,  and  ensheathed 
by  the  vaginal  process  is  the  slender  and  pointed  styloid  process  (processus 
styloideus),  the  length  of  which  varies  much.  Projecting  downwards  and  slightly 
forwards  and  medially,  it  affords  attachments  for  the  stylo-glossus,  stylo-hyoid, 
and  stylo-pharyngeus  muscles  as  well  as  the  stylo-hyoid  and  stylo-mandibular 
ligaments.  Just  behind  it,  and  between  it  and  the  mastoid  process,  is  the 
stylo-mastoid  foramen  (foramen  stylomastoideum),  which  lies  at  the  anterior  end 
of  the  mastoid  groove,  and  transmits  the  facial  nerve  and  the  stylo-mastoid  artery. 
Just  medial  to  the  styloid  process  there  is  a  deep,  smootli,  excavated  liollow, 
the  jugular  fossa  (fossa  jugularis),  which  is  converted  into  a  foramen  (jugular)  by 
articulation  with  the  occipital  bone.  Behind  and  lateral  to  the  fossa  there  is  a 
small  quadrilateral  surface  of  variable  size,  which  is  united  to  the  extremity  of  the 
jugular  process  of  the  exoccipital  by  a  synchondrosis.  Inside  the  fossa,  on  its  lateral 
aspect,  or  placed  on  its  lateral  border,  is  the  opening  of  a  small  canal  (canaliculus 
mastoideus),  which  passes  outwards  to  open  into  the  canalis  facialis,  and  transmits 


THE  TEMPOEAL  BONES. 


117 


Temporal  surface 


Zygoma 


Infra-temporal  or  zy{<omatic  surface 

Canal  for  chorda  tympani 
Eustachian  canal 
Carotid  canal 


•  iroove  for 
inferior 
petrosal  sinus 


the  auricular  branch  of  the  vagus,  which  ultimately  escapes  through  the  auricular 
fissure  {vide  antea).  In  front  of  the  jugular  fossa  and  separated  from  it  by  a 
sharp  crest,  and  just  medial  to  the  tympanic  plate,  is  the  circular  opening  of 
the  inferior  orifice  of  the  carotid  canal  (canalis  caroticus).  Directed  at  first 
upwards,  this  canal  bends  at  a  right  angle  and  turns  forwards  and  inwards, 
lying  parallel  to  the  anterior  border ;  reaching  the  fore  part  of  the  apex  of  the 
bone,  it  opens  in  front  by  an  oblique  ragged  orifice.  Through  the  canal  the 
internal  carotid  artery,  accompanied  by  a  plexus  of  sympathetic  nerves,  passes 
into  the  cranium.  On  the  ridge  of  bone  separating  the  jugular  fossa  from  the 
carotid  canal  is  the  opening  of  a  small  canal  (canaliculus  tympanicus),  through 
which  the  tympanic  branch  of  the  glosso-pharyugeal  (nerve  of  Jacobson)  passes 
to  reach  the  tympanum.  Within  the  orifice  of  the  carotid  canal  other  small 
openings  (canaliculi  carotici 
tympanici)  may  be  noticed 
which  atford  passage  to  the 
tympanic  branches  of  the 
internal  carotid  artery  and 
carotid  sympathetic  plexus. 
Occupying  the  interval  pos- 
teriorly and  medially  be- 
tween the  jugular  fossa  and 
the  carotid  canal  is  a 
V-shaped  depression  (fossula 
fenestrse  cocMeae),  on  the 
floor  of  which  and  close  to 
the  posterior  border  is  the 
orifice  of  the  aqueduct  of 
the  cochlea  (apertura  externa 
aquseductus  cochleae).  In 
the  fossa  is  lodged  the  pet- 
rous ganglion  of  the  glosso- 
pharyngeal nerve,  and  the 
aqueduct  transmits  a  tubu- 
lar prolongation  of  the  dura 
mater,  which  forms  a  channel 
of  communication  between 
the  perilymph  of  the  cochlea 
and  the  subarachnoid  space. 
A  small  vein  also  passes 
through  it.  In  front  of 
and  medial  to  the  orifice  of 
the  carotid  canal  the  under 
surface  of  the  apex  of  the 
bone  corresponds  to  a  rough 
quadrilateral  surface  which  forms  the  floor  of  the  carotid  canal,  and  also  serves  for 
the  attachment  of  the  cartilaginous  part  of  the  Eustachian  tube  as  well  as  the 
origin  of  the  levator  veli  palatini  muscle  ;  elsewhere  it  has  attached  to  it  the 
dense  fibrous  tissue  which  fills  up  the  cleft  (petro-basilar  fissure)  between  it  and 
the  basilar  process  of  the  occipital  bone. 

The  anterior  surface  bears  the  impress  of  the  convolutions  of  the  under 
surface  of  the  temporal  lobe  of  the  cerebrum,  which  rests  upon  it;  in  addition, 
there  is  a  distinct  but  shallow  depression  (impressio  trigemini)  near  the  apex, 
corresponding  to  the  roof  of  the  carotid  canal ;  in  this  is  lodged  the  Gasserian 
ganglion  on  the  sensory  root  of  the  5th  cranial  nerve.  Lateral  to  the  middle 
of  the  upper  surface,  and  close  to  its  posterior  border,  is  the  elevation 
(eminentia  arcuata),  more  or  less  pronounced,  which  marks  the  position  of  the 
superior  semicircular  canal,  here  developed  within  the  substance  of  the  bone.  A  little 
in  front  of  this,  and  in  line  with  the  angle  formed  by  the  anterior  border  and  the 
squamous  part,  is  the  slit-like  opening  of  the  hiatus  Fallopii  (hiatus  canalis  facialis), 


Tubercle, 

Eminentia 
articularis 

Glenoid  fossa- 

Glaserian  fissure 
Tympanic  plate 

Ext.  auditory  meatus 
Styloid  proces'5 

Vaginal  process 

Auricular  fissuie 

Stylo-mastoid 

foramen 

Mastoid  process 
Digastric  groove 

Groove  foi 
occipital  arteij 


Aqueduct  of  cochlea 
Canal  for  Jacobson's 

nerve 
•Jugular  fossa 

Canal  for  Arnold's 
nerve 


Jugular  surface 


Fig.  88. — The  Eight  Temporal  Bone  seen  from  Below. 

The  squanio-zygomatic  part  is  coloured  blue  ;  the  petro-mastoid,  red. 
The  tympanic  portion  aud  styloid  process  are  left  uncoloured. 


118 


OSTEOLOGY. 


within  the  projecting  lip  of  which  two  small  orifices  can  usually  be  seen.  These  are 
the  openings  of  the  aquaeductus  Fallopii  (canalis  facialis) ;  if  a  bristle  be  passed  through 
the  inner  of  the  two  openings  it  will  be  observed  to  pass  into  the  bottom  of  the 
internal  auditory  meatus,  if  into  the  outer,  it  will  pass  through  the  aqueduct  of 
Fallopius,  and,  provided  the  channel  be  clear,  will  appear  on  the  under  surface  of 
the  bone  at  the  stylo-mastoid  foramen.  Leading  forwards  and  medially  from  the 
hiatus  towards  the  anterior  border  is  a  groove ;  in  this  lies  the  great  superficial 
petrosal  nerve  which  passes  out  of  the  hiatus.  A  small  branch  of  the  middle 
meningeal  artery  also  enters  the  bone  here.  A  little  lateral  to  the  hiatus  is 
another  small  opening  (apertura  superior  canalis  tympanici),  often  difficult  to  see ; 
from  this  a  groove  runs  forwards  which  channels  the  upper  surface  of  the  roof  of 
the  canal  for  the  tensor  tympani  muscle.  Through  this  foramen  and  along  this 
groove  passes  the  lesser  superficial  petrosal  nerve.     Behind  this,  and  in  front  of 


Mastoid  antrum,  the  medial  wall    V. 
of  which  i.s  related  to  the  externil      \ 
SPimcircular  cnm 


iTiteinal  part  of  posterior  ■\\all  of  external 
auditoiy  meatus  leftiiu  sita 


Pomts  to  the  recessus  epitvmpanicus 
Fenestra  rotunda 


Mastoid  air  cells 


Aqueduct  of  Fallopius  laid  open, 
displaying  the  facial  nerve  within 

Fig.  S9. 
Preparation  to  display  the  position  and  relations  of  the  mastoid  antrum.     The  greater  part  of  the  posterior 
wall  of  the  external  auditory  meatus  has  been  removed,  leaving  only  a  bridge  of  bone  at  its  inner  ex 
trenaity  ;    under  this  a  bristle  is  displayed,  jiassing  from  the  mastoid  antrum  through  the  iter  to  the 
cavity  of  the  tympanum, 

the  arcuate  eminence,  the  bone  is  usually  thin  (as  may  be  seen  by  holding  it  up  to 
the  light  falling  through  the  external  auditory  meatus),  roofing  in  the  cavity 
within  the  bone  called  the  tympanum  and  forming  the  tegmen  tympani.  Laterally 
the  line  of  fusion  of  the  petrous  with  the  squamous  part  is  often  indicated  by  a  faint 
and  irregular  petro-squamous  fissure. 

The  most  conspicuous  oVjject  on  the  posterior  surface  of  the  petrous  part  of  the 
bone  is  the  internal  auditory  meatus  (meatus  acusticus  internus)  about  8  mm.  deep  in 
the  adult.  This  has  an  oblique  oval  aperture,  and  leads  outwards  and  slightly  down- 
wards into  the  substance  of  the  bone,  giving  passage  to  the  auditory  and  facial  nerves, 
together  with  the  nervus  intermedins  (pars  intermedia)  and  the  auditory  branch  of 
the  basilar  artery.  The  canal  appears  to  end  blindly  ;  but  if  it  be  large,  or  still  better, 
if  part  of  it  be  cut  away,  its  fundus  will  be  seen  to  be  crossed  by  a  horizontal  ridge,  the 
falciform  crest,  which  divides  it  into  two  fossae,  the  floors  of  which  (laminae  cribrosae) 
are  pierced  by  numerous  small  foramina  for  the  branches  of  the  auditory  nerve  and 
the  vessels  passing  to  the  membranous  labyrinth,  whilst  in  the  fore  and  upper  part 
of  the  higher  fossa  the  orifice  of  the  Fallopian  aqueduct  (canalis  facialis),  through 
which  the  facial  nerve  passes,  is  seen  leading  in  the  direction  of  the  hiatus  Fallopii 


THE  TEMPOKAL  BONES. 


119 


(jride  supra).  Lateral  to  the  internal  auditory  meatus  and  above  it,  close  to  the 
superior  border,  an  irregular  depression,  often  faintly  marked,  with  one  or  two  small 
foramina  opening  into  it,  is  to  be  noticed.   This  is  the  floccular  fossa  (fossa  subarcuata), 

best  seen  in  young  bones  (see  Fig.  92  c), 

where  it  forms  a  distinct  recess,  which 

is  liounded  above  by  the  bulging  caused 

by  the  superior  semicircular  canal,  within 

the  concavity  of  which  it  is  placed ;  it 

lodges   a   process  of    the   dura  mater. 

Below   and   lateral    to   this,  separated 

from  it  by  a  smooth,  elevated  curved 

ridge,  is   the  opening  of   the  aqueduct 

of  the  vestibule  (apertura  externa  aquae- 

ductus  vestibuli),  often    concealed  in   a 

narrow  curved    fissure   overhung  by  a 

sharp  scale  of  bone.     In  this  is  lodged 

the   saccus   endolymphaticus, 

the  remains  of  the  stalk  of  the 

otocyst,  together  with  a  small 

vein.       The    ridge    above    it 

corresponds  to  the  upper  half 

of  the  posterior  semicircular 

canal. 


meatvis 

Osseous  Eustachian 

cana 


Internal 
auditory 
meatus 


Vestibule 
Aqu;('ductus  Fallopii 
Fenestra  ovalis  cut  across 


Fenestra  rotunda  cut  across 


Superior  opening  of  the  canal  for  the 
tympanic  branch  of  glosso-pharyngeal 

Fig.  90  a. — Vertical  Transverse  Section  through  the  Left 
Temporal  Bone  (Anterior  Half  of  Section). 


Connexions.  —  The  temporal 
bone  articulates  with  the  zygomatic, 
sphenoid,  parietal,  and  occipital 
bones,  and  by  a  movable  joint  with 

the  maxilla.     Occasionally  the  temporal  articulates  with  the  frontal,  as  happens  normally  in 

the  anthropoid  apes ;   although  the  region  of  the  pterion  is  characterised  by  an  X-like  form 

in  the  lower  races   of  man    there  is  no  evidence  that   the   occurrence 

of  a  fronto -squamosal  suture  is  more  frequent  in  the  lower  than  the 

higher  races,  its  occurrence  being  due  to  the  manner  of  fusion  of  the 

so-called  epipteric  ossicles  with  the  surrounding  bones. 

Ossification. — The  temporal  bone  of  man  represents  the  fused 
periotic,  squamosal,  and   tympanic   elements ;    the   two   latter  are 
membrane  or   investing  bones,  whilst  the  former  is  developed  in 
cartilage   around    the   auditory    capsule.       The    cartilages 
I.  and    II.  visceral    arches   are 
also  intimately  associated  with 
its  development,  as  will  be  else- 
where explained  (Appendix  E). 
The    human    temporal    bone  is 
characterised  by  the  large  pro- 
portionate size  of  the  squamosal, 
the  comparatively  small  size  of 
the  tympanic,  the  absence  of  an 
auditory  bulla,  and  the  excep- 
tional development  of  the  mas- 
toid process. 

Ossification  commences  in 
the  ear  capsule  in  the  fifth 
month,  and  proceeds  so  rapidly 
that  by  the  end  of  the  sixth 
month  the  individual  centres 
are  more  or  less  fused.  Of 
these,  one,  the  Pro-otic  (Huxley), 

which  appears  in  the  vicinity  of  the  eminentia  arcuata  is  the  most  definite  in  position 
and  form  ;  from  this  a  lamina  of  bone  of  spiral  form  is  developed,  which  covers  in  the 
medial  limb  of  the  superior  semicircular  canal,  and  forms  the  roof  of  the  internal  auditory 
meatus,  together  with  the  commencement  of  the  Fallopian  aqueduct.  Reaching  forwards, 
it  extends  to  the  apex  of  the  petrous  part ;  whilst  laterally  it  forms  part  of  the  medial 
wall  of  the  tympanum,  surrounds  the  fenestra  ovalis,  and  encloses  within  its  substance 

8a 


External  semicircular  canal 


Superior  semicircular 
canal 


Vestibule  into 
openin 
semicircular  cana 

Internal 
auditory  meatus 


Fenestra  ovali 
cut  acros: 
Fenestra  rotunda 
cut  across 


Opening  leading 
into  mastoid 
antrum, 
Aqufeductus 
Fallopii 
Canalis  stapedii 

Tympanum 

External 
auditory  meatus 


Fig.  90  i!*.— Vertical  Transverse  Section  through  the  Left 
Temporal  Bone  (Posterior  Half  of  Section). 


120 


OSTEOLOGY. 


portions  of    the  cochlea,  vestibule,  and 
the  Opisthotic,  apjDears  in  the  vicinity 


.■^•; 


Osseous  Eustachian  canal 


Styloid  process 
broken  otf 


Glenoid  fossa 

Groove  for 

membrana 

tympaiii 

External 

auditory 

meatus 

Mastoid  air-cells 


Carotid  canal 


Tympanum 


Cochlea 

Internal  auditory 
meatus 
Vestibule,  fenestra 
ovalis  cut  across 
Superior  semicircular 
canals 

AquEeductus  Fallopii 


External  semicircular  canal 


Fig 


90  f. — Horizontal  Section  through  the  Left  Temporal  Bone 
(Lower  Half  of  Section). 


superior  semicircular  canal.  Another  centre, 
of  the  promontory  on  the  medial  wall  of  the 
tympanum,  surrounds  the 
fenestra  rotunda,  forms  the 
floor  of  the  vestibule,  and 
extends  medially  to  complete 
the  floor  of  the  internal 
auditory  meatus.  Surround- 
ing the  cochlea  inferiorly 
and  laterally,  it  completes 
the  floor  of  the  tympanum, 
and  ultimately  blends  with 
the  fore  and  under  part  of  the 
tympanic  ring.  The  carotid 
canal  at  first  grooves  it,  and 
is  then  subsequently  sur- 
rounded by  it.  According  to 
Lambertz  the  lamina  spiralis 
of  the  cochlea  ossifies  in 
membrane.  The  roof  of  the 
tympanum  is  formed  from  a 
separate  centre,  the  Pterotic, 
which  extends  backwards  to- 
wards the  superior  semicir- 
cu.lar  canal,  and  encloses  the 
tympanic  part  of  the  aqueduct 
of  Fallopius ;  laterally  this 
centre  unites  by  suture  with 
the  squamosal,  and  sends  down 
a  thin  process,  which  appears 
between  the  lips  of  the  Gla- 
serian  fissure,  and  forms  the 
lateral  wall  of  the  Eustachian  tube.  Nuclei,  either  single  or  multiple,  Epiotic,  appear  in  the 
base  of  the  petrous  part,  and  envelop  the  posterior  and  external  semicircular  canals.  It  is 
by  extension  from  this  part  that  the  mastoid  process  is  ultimately  developed.  The  styloid 
process,  an  independent  development  from  the  upper  end  of  the  cartilage  of  the  second 
visceral  arch,  is  ossified  from  two  centres.  The  upper  or  basal  appears  before  birth,  and 
rapidly  unites  with  the  petro-mastoid,  the  tympanic  plate  encircling  it  in  front.  This 
represents  the  tympanohyal  of  comparative  anatomy.  At  birth,  or  subsequent  to  it, 
another  centre  appears  in  the  cartilage  below  the  above  :  this  is  the  stylohyal.  Ankylosis 
usually  occurs  in  adult  life  between  the  tympanohyal  and  stylohyal,  the  union  of  the 
two  constituting  the  so-called  styloid  process  of  human  anatomy. 

The  centre  from  which  the  sc[uamo-zygomatic  develops  appears  in  membrane  about 
the  end  of  the  second  month.  Situated  near  the  root  of  the  zygoma,  it  extends  forwards 
and  laterally  into  that  process,  medially  to  form  the  floor  of  the  glenoid  fossa,  and 
upwards  into  the  squamosal.  From  this  latter  there  is  a  downward  and  backward  exten- 
sion, which  forms  the  post-auditory  process  ;  this  ultimately  blends  with  the  posterior  limb 
of  the  tympanic  ring,  being  separated  from  it  in  the  adult  by  the  auricular  fissure.  It  forms 
the  lateral  wall  of  the  mastoid  antrum,  and  constitutes  the  fore  and  upper  part  of  the 
mastoid  process  in  the  adult.  About  the  third  month  a  centre  appears  in  the  outer 
membranous  wall  of  the  tympanum :  from  this  the  tympanic  ring  is  developed.  Incom- 
plete above,  it  displays  two  free  extremities.  Of  these,  the  anterior  is  somewhat  enlarged, 
and  unites  in  front  with  the  glenoid  portion  of  the  squamo-zygomatic,  being  separated 
from  it  by  the  Glaserian  fissure  and  the  downgrowth  from  the  tegmen  tympani  ;  the 
posterior  joins  the  post- auditory  process  of  the  squamo-zygomatic  above  mentioned. 
Below,  it  blends  medially  with  the  portion  of  the  petro-mastoid  which  forms  the  floor  of 
the  tympanum,  and  ensheathes  the  tympanohyal  behind.  From  the  medial  surface  of 
the  ring  below  there  is  an  extension  medially  and  forwards  which  forms  the  floor  of  the 
osseous  Eustachian  canal,  as  well  as  the  lateral  wall  and  half  the  floor  of  the  carotid  canal. 
From  the  lateral  side  of  the  lower  part  of  this  ring  two  tubercles  arise ;  tliese  grow 
laterally,  and  so  form  the  floor  of  the  external  auditory  meatus.  The  interval  between 
them  remains  unossified  till  about  the  age  of  five  or  six,  after  which  closure  takes  place. 
This  deficiency  may,  however,  persist  even  in  adult  life  (see  Appendix  B,  Temporal). 


THE  SPHENOID  BONE. 


121 


At  birth  the  temporal  bone  can  usually  be  separated  into  its  component  parts.  The 
lateral  surface  of  the  petrous  part  not  only  forms  the  medi{il  wall  of  the  tympanum,  but  is 
hollowed  out  behind  and  above  to  form  the  inner  side  of  the  mastoid  antrum,  the 
outer  wall  of  which  is  completed  by  the  post-auditory  process  of  the  squamo-zygomatic. 
As  yet  the  mastoid  process  is  undeveloped.  It  only  assumes  its  nipple-like  form  about  the 
second  year.     Towards  puberty  its  cancellous  tissue  becomes  permeated  with  air  spaces. 


A  B  c: 

The  squamo-zygomatic  part  is  coloured  blue  ;  tlie  petro-mastoid  red.     The  tympanic  ring  is  left  uucoloured. 


Fig.  91. — A.  The  Parietal  Sorface  of  the  Right  Temporal  Bone  at 
Birth.     B.  The  same  with  the  Squamo-zygomatic  Portion  Removed. 

(The  lettering  is  the  same  in  both  A  and  B.)  a,  Tympanic  ring,  b,  Medial  wall 
of  tympanum,  c,  Fenestra  rotunda,  rf,  Foramen  ovale,  e,  Mastoid  antrum. 
/,  Mastoid  process.  g.  Masto- squamosal  suture,  with  foramen  for 
transmission  of  vessels.  A,  Squamo-zygomatic,  removed  in  figure  B  to 
show  how  its  descending  process  forms  the  lateral  wall  of  the  mastoid 
antrum. 


C.  Cerebral  Surface  of  the  Right 
Temporal  Bone  at  Birth. 

«,  Sqiiamo  -  zygomatic.  b,  Petro- 
squamosal  suture  and  foramen  (just 
above  the    end    of   the  lead    line). 

c,  Subarcuate  fossa  (floccular  fossa). 

d,  Aqureductus  vestibuli.  e,  Aquje- 
ductus  cochleae.  /,  Internal  audi- 
tory meatus.  a,  Upper  end  of 
carotid  canal. 


which  are  in  communication  with  and  extensions  from  the  mastoid  antrum.  Occasionally 
this  pneumatic  condition  is  met  with  in  early  childhood.  The  external  auditory  meatus 
is  unossified  in  front  and  below,  the  outgrowth  ffom  the  tympanic  ring  occurring 
subsequent  to  birth.  The  glenoid  fossa  is  shallow  and  everted ;  the  jugular  fossa  is 
ill-marked ;  w^hilst  the  subarcuate  fossa  is  represented  by  a  deep  pit,  the  so-called 
floccular  fossa  of  comparative  anatomy.  The  hiatus  Fallopii  is  an  open  groove,  displaying 
at  either  end  the  openings  of  the  medial  and  lateral  portions  of  the  Fallopian  aqueduct. 


The  Sphenoid  Bone. 

The  sphenoid  bone  (os  sphenoidale)  lies  in  front  of  the  basi-occipital  medially, 
and  the  temporals  on  either  side.  It  enters  into  the  formation  of  the  cranial, 
orbital,  and  nasal  cavities,  as  well  as  the  temporal,  infra- temporal  (pterygoid), 
pterygo-palatine,  (spheno-maxillary)  foss?e.  It  consists  of  a  body  with  three  pairs 
of  expanded  processes,  the  great  wings,  the  lesser  wings,  and  the  pterygoid  processes. 

The  body  (corpus),  more  or  less  cubical  in  form,  is  hollow,  and  contains  within 
it  the  two  large  sphenoidal  air  sinuses.  These  are  separated  by  a  partition,  which 
is  usually  deflected  to  one  or  other  side  of  the  middle  line.  Each  sinus  extends 
laterally  for  a  short  distance  into  the  root  of  the  great  wing,  and  downwards  and 
laterally  towards  the  base  of  the  pterygoid  process  of  the  same  side.  They 
communicate  by  apertures  with  the  upper  and  back  part  of  the  nasal  fossae.  In  the 
adult  the  posterior  aspect  of  the  body  displays  a  sawn  surface  due  to  its  separation 
from  the  basi-occipital  with  which  in  the  adult  it  is  firmly  ankylosed.  The  superior 
surface,  from  the  fore  angles  of  which  the  lesser  wings  arise,  displays  an  appearance 
comparable  to  that  of  an  oriental  saddle,  over  its  middle  there  is  a  deep  depression, 
the  sella  turcica  or  pituitary  fossa  (fossa  hypophyseos),  in  which  is  lodged  the 
pituitary  body.  Behind,  this  is  overhung  by  a  sloping  ridge,  the  dorsum  sellse,  the 
posterior  surface  of  which  is  inclined  upwards,  and  is  in  continuation  with  the 
basilar  groove  of  the  occipital  bone,  supporting  the  Pons  Varolii  and  the  basilar 

8b 


122 


OSTEOLOGY. 


artery.  Anteriorly  and  laterally  the  angles  of  this  ridge  project  over^  the 
pituitary  fossa  in  the  form  of  prominent  tubercles,  called  the  posterior  clinoid 
processes  (processus  clinoidei  posteriores).  To  these  are  attached  the  tentorium 
cerebelli  and  interclinoid  ligaments.     In  front  of  the  pituitary  fossa  there  is  a 


Poiaiiien  ^-v^jji 
rotundum 
Gioo\e  tor 
Eustachian  tube 

Petiohal  pioce^b 
Vidian  canal 


External  pterygoid  plate 
Internal  pterygoid  plate 


Pterygoid  notcli 


Hamular  process 
Fig.  92. — The  Sphenoid  seen  from  Behind. 


transverse  elevation,  the  olivary  eminence  (tuberculum  sellse),  towards  the  lateral 
extremities  of  which,  and  somewhat  behind,  there  are  oftentimes  little  spurs  of 
bone,  the  middle  clinoid  processes  (processus  clinoidei  medii).  In  front  of  the 
olivary  eminence  is  the  optic    groove   (sulcus    chiasmatis),  which    passes  laterally 


Iiifratenipora 
or  zygoiriatic  ''     l<ji:iiiii  n 
surface      rotundum 
Vidian  canal 


Orbital  surface 

Infra-teinjioral  crest 

Spine 
Spheno-maxillary  surface 

External  pterygnid  plate 


Pterygoid  notch 

Fig.  9.3. — T}iE  Sphenoid  seen  kuom  the  Fuont, 


^       Ilaiiiular  jjrocess  of 
internal  pterygoid  jilate 


on  either  side  to  become  continuous,  between  the  roots  of  the  lesser  wings,  with 
the  optic  foramina. 

Thi.s  groove  is  liable  to  considerable  variations,  and  apparently  does  not  always  serve  for  the 
lodgment  of  the  optic  chiasnia.  (Lawrence,  "  Proc.  Soc.  Aiiat.,"  Journ.  Anat.  and  Physiol. 
voL  xxviii.  p.  18.) 

In  front  of  the  optic  groove,  from  which  it  is  often  separated  by  a  thin  sharp  edge, 
the  superior  surface  continues  forwards  on  the  same  plane  as  the  upper  surfaces  of 


THE  SPHENOID  BONE.  123 

the  lesser  wings,  and  terminates  anteriorly  in  a  ragged  edge,  which  articulates  with 
the  cribriform  plate  of  the  ethmoid,  and  has  often  projecting  from  it,  medially,  a 
pointed  process,  the  ethmoidal  spine.  The  lateral  aspects  of  the  body  are  fused 
with  the  great  wings,  and  in  part  also  with  the  roots  of  the  pterygoid  processes. 
Curving  along  the  side  of  the  body,  superior  to  its  attachment  to  the  great  wing, 
is  an  ^-shaped  groove,  the  carotid  groove  (sulcus  caroticus),  which  marks  the 
position  and  course  of  the  internal  carotid  artery.  Posterioi'ly,  the  hinder  margin 
of  this  groove,  formed  by  the  salient  lateral  edge  of  the  posterior  surface  of  the 
body,  articulates  with  the  apex  of  the  petrous  portion  of  the  temporal  bone,  and 
is  hence  called  the  petrosal  process ;  just  above  this,  on  the  lateral  border  of  the 
dorsum  sellae,  tliere  is  often  a  groove  for  the  sixth  nerve. 

The  anterior  surface  of  the  body  displays  a  vertical  medial  sphenoidal  crest 
(crista  sphenoidalis),  continuous  above  with  the  ethmoidal  spine,  and  below  wdth 
the  pointed  projection  called  the  rostrum.  This  crest  articulates  in  front  with  the 
perpendicular  plate  of  the  ethmoid.  On  either  side  of  the  middle  line  are  seen  the 
irregular  openings  leading  into  the  sphenoidal  air  sinuses,  the  thin  anterior  walls 
of  which  are  in  part  formed  by  the  absorption  of  the  sphenoidal  turbinated  bones 
with  wliich  in  early  life  they  are  in  contact.  With  the  exception  of  a  broad  groove 
leading  downwards  from  the  apertures  above  mentioned,  which  enters  into  the 
formation  of  the  roof  of  the  nasal  fossa  of  the  corresponding  side,  the  lateral 
aspects  of  this  surface  of  the  bone  are  elsewhere  in  articulation  with  the  lateral 
masses  of  the  ethmoid  and  the  orbital  processes  of  the  palate  bones.  The  rostrum 
is  continued  medially  for  some  distance  along  the  inferior  surface  of  the  body, 
where  it  forms  a  prominent  keel  which  fits  into  the  recess  formed  by  the  alee  of 
the  vomer.  The  edges  of  the  latter  serve  to  separate  the  rostrum  from  the  incurved 
vaginal  processes  at  the  roots  of  the  internal  pterygoid  plates.  Posteriorly  the 
under  surface  of  the  body  of  the  sphenoid  is  rougher,  and  covered  by  the  mucous 
membrane  of  the  roof  of  the  pharynx ;  here,  occasionally,  a  median  depression  may 
be  seen  which  marks  the  position  of  the  inferior  extremity  of  a  foetal  channel, 
called  the  canalis  cranio -pharyngeus. 

The  lesser  or  orbital  wings  (alae  parvae)  are  two  flattened  triangular  plates  of 
bone  which  project  forwards  and  laterally  from  the  fore  and  upper  part  of  the 
body  of  the  bone,  with  which  they  are  united  by  two  roots  which  enclose  between 
them  the  optic  foramina  (foramina  optica)  for  the  transmission  of  the  optic  nerves 
and  ophthalmic  arteries.  Of  these  roots,  the  posterior  springs  from  the  body  just 
wide  of  the  olivary  eminence,  separating  the  carotid  groove  behind  from  the  optic 
foramen  in  front ;  laterally  this  root  is  confluent  with  the  recurved  posterior  angle 
of  the  lesser  wing,  forming  the  projection  known  as  the  anterior  clinoid  process 
(processus  clinoideus  anterior),  which  overhangs  the  fore  part  of  the  body  of  the 
bone  and  affords  an  attachment  to  the  tentorium  cerebelli  and  interclinoid  liga- 
ments. The  anterior  root,  broad  and  compressed,  unites  the  upper  surface  of  the 
lesser  wing  with  the  fore  and  upper  part  of  the  body.  Laterally  the  outer 
angle  terminates  in  a  pointed  process  which  reaches  the  region  of  the  pterion  and 
there  articulates  with  the  frontal,  and  may  come  in  contact  with  the  great  wing. 
The  superior  aspect  is  smooth,  and  forms  in  part  the  floor  of  the  anterior  cranial 
fossa.  The  inferior  surface  constitutes  part  of  the  posterior  portion  of  the  upper 
wall  of  the  orbit,  and  also  serves  to  roof  in  the  sphenoidal  fissure  (fissura  orbitalis 
superior),  which  separates  the  lesser  from  the  greater  wings  below.  The  anterior 
edge  is  ragged  and  irregular,  and  articulates  with  the  orbital  plates  of  the 
frontal.  The  posterior  margin,  sharp  and  sickle-shaped,  separates  the  anterior 
from  the  middle  cranial  fossa,  and  corresponds  to  the  position  of  the  Sylvian  fissure 
on  the  surface  of  the  cerebrum. 

The  greater  or  temporal  wings  (alee  magnse),  as  seen  from  above,  are  of  a 
somewhat  crescentic  shape  and  form  a  considerable  portion  of  the  floor  of  the 
middle  cranial  fossa.  If  the  medial  convex  edge  of  the  crescent  be  divided  into 
fifths,  the  posterior  fifth  extends  backwards  and  laterally  beyond  the  body  of 
the  bone,  presenting  a  free  posterior  edge,  which  forms  the  anterior  boundary  of 
the  foramen  lacerum.  This  border  ends  behind  in  the  horn  of  the  crescent, 
from  which  a  pointed  process  projects  downwards,  called  the  alar  or  sphenoidal  spine 


124  OSTEOLOGY. 

(spina  angularis),  this  is  wedged  into  the  angle  between  the  petrous  and  squamous 
parts  of  the  temporal  bone.  The  medial  surface  of  the  posterior  border  and  spine  is 
furrowed  for  the  cartilaginous  Eustachian  tube  (sulcus  tubse),  whilst  on  the  medial 
side  of  the  spine  the  course  of  the  chorda  tympani  nerve  is  indicated  by  a  groove 
(Lucas).  The  second  fifth  of  the  convex  border  of  the  crescent  is  fused  to  the  side 
of  the  body  and  united  below  with  the  root  of  the  pterygoid  process.  The  angle 
formed  by  the  union  of  the  great  wing  with  the  side  of  the  body  posteriorly  corre- 
sponds to  the  hinder  end  of  the  carotid  groove,  the  lateral  lip  of  which  is  formed  by 
a  projecting  lamina  called  the  lingula.  The  remaining  three-fifths  of  the  convex 
border  is  divisible  into  two  nearly  equal  parts ;  the  medial  is  a  free,  curved,  sharp 
margin,  which  forms  the  inferior  margin  of  the  sphenoidal  fissure  (fissura  orbitalis 
superior),  the  cleft  which  separates  the  great  wing  from  the  lesser  wing,  and  which 
establishes  a  wide  channel  of  communication  between  the  middle  cranial  fossa  and 
the  cavity  of  the  orbit,  transmitting  the  third,  fourth,  ophthalmic  division  of  the 
tifth,  and  the  sixth  cranial  nerves,  together  with  the  ophthalmic  veins.  Wide  of 
the  sphenoidal  fissure  this  edge  becomes  broad  and  serrated,  articulating  with  the 
frontal  bone  medially,  and  at  the  part  corresponding  to  the  anterior  horn  of  the 
crescent,  by  a  surface  of  variable  width,  it  unites  with  the  anterior  inferior  angle 
of  the  parietal  bone.  The  lateral  border  corresponds  to  the  concave  side  of  the 
crescent,  and  is  serrated  for  articulation  with  the  squamous  part  of  the  temporal, 
being  tliin  and  bevelled  at  the  expense  of  its  parietal  surface  above  and  laterally, 
and  broad  and  thick  behind  as  it  passes  towards  the  alar  spine.  The  superior  or 
cerebral  surface  is  concave  from  behind  forwards,  and  in  its  fore  part  from  side  to 
side  also ;  it  forms  a  considerable  part  of  the  floor  of  the  middle  cranial  fossa,  and 
bears  the  impress  of  the  convolutions  of  the  extremity  of  the  temporal  lobe  of  the 
cerebrum  which  rests  upon  it ;  towards  its  outer  side  it  is  grooved  obliquely  by  an 
anterior  branch  of  the  middle  meningeal  artery.  The  following  foramina  pierce 
the  great  wing :  close  to  and  in  front  of  the  alar  spine  is  the  foramen  spinosum 
for  the  transmission  of  the  middle  meningeal  artery  and  its  companion  vein, 
together  with  a  recurrent  branch  from  the  third  division  of  the  5th  nerve.  In 
front  of  and  medial  to  this,  and  close  to  the  posterior  free  border,  is  the 
foramen  ovale,  of  large  size  and  elongated  form.  This  gives  passage  to  the 
motor  root  and  inferior  sensory  division  of  the  5th  nerve,  and  admits  the  small 
meningeal  branch  of  the  middle  meningeal  artery ;)  a  small  emissary  vein  from  the 
cavernous  sinus  usually  passes  through  this  foramen,  and  occasionally  also  the 
small  superficial  petrosal  nerve.  Near  the  fore  part  of  the  root  of  the  great  wing, 
and  just  below  the  sphenoidal  fissure,  is  the  foramen  rotundum,  of  smaller  size  and 
circular  form.  Through  this  the  second  division  of  the  5th  nerve  escapes  from  the 
cranium.  Occasionally  there  is  a  small  canal — the  foramen  of  Vesalius — which 
pierces  the  root  of  the  great  wing  to  the  medial  side  of  the  foramen  ovale.  This 
opens  below  into  the  scaphoid  fossa  at  the  base  of  the  internal  pterygoid  plate,  and 
transmits  a  small  vein.  Occasionally  there  is  a  small  foramen  (canaliculus 
innominatus)  to  the  medial  side  of  the  foramen  spinosum  for  the  transmission  of 
the  small  superficial  petrosal  nerve. 

The  lateral  or  parietal  squamo-zygomatic  surface  of  the  great  wing  enters  into  the 
formation  of  the  walls  of  the  orbital,  te)ui)oral,  and  infra-temporal  fossai  by  three  well- 
defined  areas  ;  of  these  the  upper  two,  the  orbital  and  tlie  temporal,  are  separated 
Ijy  an  oblique  jagged  ridge,  the  malar  crest  (margo  zygomaticus),  for  articulation 
with  the  orbital  (fronto-sphenoidal)  process  of  the  zygomatic  bone.  Occasionally 
the  lower  part  of  tliis  ridge  articulates  with  the  zygomatic  process  of  the 
maxilla.  The  orbital  (facies  orbitalis)  surface  lies  to  the  medial  side  of  this  crest 
and  is  directed  forwards  and  a  little  medially ;  of  quadrilateral  shape,  it  forms 
the  back  and  lateral  wall  of  the  orbit ;  plane  and  smooth,  it  is  bounded  behind 
by  the  sharp  inferior  free  margin  of  the  sphenoidal  fissure,  towards  the  medial 
extremity  of  which  a  pointed  spine  (spina  recti  externi)  for  the  attachment 
of  the  inferior  common  ligament  of  origin  of  the  ocular  muscles,  can  usually 
be  seen.  It  is  limited  superiorly  hj  the  edge  of  a  rough  triangular  area  'which 
articulates  with  the  frontal  bone ;  anteriorly  by  the  malar  crest ;  whilst  inferiorly 
a  free,  well-defined  oblique  margin  constitutes  the  posterior  and  lateral  boundary 


THE  SPHENOID  BONE.  125 

of  the  spheno  -  maxillary  fissure  (fissura  orbitalis  inferior),  which  separates  this 
part  of  the  bone  from  the  orbital  plate  of  the  maxilla.  Below  this  border  there 
is  a  grooved  surface  which  leads  inwards  toward  the  orifice  of  the  foramen 
rotundum.  In  the  articulated  skull  this  forms  part  of  the  posterior  wall  of  the 
spheno-maxillary  (pterygo-palatine)  fossa. 

To  the  lateral  side  of  the  malar  crest,  which  bounds  it  in  front,  is  the  temporal 
area  (fades  temporalis),  concavo-convex  from  before  backwards.  It  slopes  medially 
below,  where  it  is  separated  from  the  zygomatic  or  infra-temporal  area  by  a  well- 
marked  muscular  ridge,  the  infra-temporal  crest  (crista  infratemporalis).  Behind, 
the  temporal  surface  is  bounded  by  the  margin  of  the  great  wing  which  articulates 
with  the  squamous  part  of  the  temporal  (margo  squamosus),  and  above  by  the  edge 
which  unites  it  with  the  anterior  inferior  angle  of  the  parietal  and  the  frontal  bone. 
The  temporal  surface  enters  into  the  formation  of  the  floor  of  the  fossa  of  the  same 
name,  and  affords  an  extensive  attachment  to  the  fibres  of  origin  of  the  temporal 
muscle.  The  zygomatic  surface  (facies  infratemporalis),  the  third  of  the  areas 
above  referred  to,  is  situated  below  the  infra-temporal  crest,  and  corresponds  to 
the  under  surface  of  the  posterior  half  of  the  great  wing ;  it  extends  as  far  back 
as  the  alar  spine  and  posterior  border.  Opening  on  it  are  seen  the  orifices  of  the 
foramen  spinosum  and  ovale.  It  is  slightly  concave  from  side  to  side,  and  is 
confluent  medially  with  the  lateral  surface  of  the  external  pterygoid  plate.  In 
front  it  is  bounded  by  a  ridge  which  curves  upwards  and  laterally  from  the  fore 
part  of  the  external  pterygoid  plate  to  join  the  infratemporal  crest.  In  the 
articulated  skull  this  ridge  forms  the  posterior  boundary  of  the  ptery go-maxillary 
fissure.  The  zygomatic  surface  overhangs  the  zygomatic  fossa,  and  affords  an  origin 
for  the  upper  head  of  the  external  pterygoid  muscle. 

The  pterygoid  processes  (processus  pterygoidei)  spring  from  the  inferior 
surface  of  the  lateral  aspect  of  the  body  as  well  as  the  under  side  of  the  root  of 
the  great  wings,  and  pass  vertically  downwards.  Each  consists  of  two  laminae,  the 
external  and  internal  pterygoid  plates,  fused  together  anteriorly,  and  enclosing 
between  them  posteriorly  the  pterygoid  fossa  (fossa  pterygoidea).  The  external 
pterygoid  plate  (lamina  lateralis  processus  pterygoidei),  thin  and  expanded,  is 
directed  obliquely  backwards  and  outwards,  its  lower  part  being  often  somewhat 
everted.  Its  hinder  edge  is  sharp,  and  often  has  projecting  from  it  one  or  two 
spines,  to  one  of  which  (processus  pterygo-spinosus)  the  pterygo-spinous  ligament 
which  stretches  towards  the  alar  spine  is  attached.  Laterally  it  furnishes  an 
origin  for  the  lower  head  of  the  external  pterygoid  muscle,  and  on  its  medial  side, 
where  it  forms  the  lateral  wall  of  the  pterygoid  fossa,  it  supplies  an  attachment  for 
the  internal  pterygoid  muscle. 

The  internal  pterygoid  plate  (lamina  medialis  processus  pterygoidei)  is  narrower 
and  somewhat  stouter.  By  its  medial  aspect  it  forms  the  posterior  part  of  the 
lateral  wall  of  the  nasal  fossae ;  laterally  it  is  directed  towards  the  pterygoid 
fossa.  Its  posterior  edge  ends  below  in  the  hook -like  hamular  process  (hamulus 
pterygoidei),  which,  reaching  a  lower  level  than  the  lateral  plate,  curves  back- 
wards and  laterally,  furnishing  a  groove  in  which  the  tendon  of  the  tensor  veli 
palatini  muscle  glides ;  superiorly,  the  sharp  posterior  margin  of  the  medial  plate 
bifurcates,  so  as  to  enclose  the  shallow  scaphoid  fossa  from  which  the  tensor  veli 
palatini  muscle  arises,  and  wherein  may  occasionally  be  seen  the  inferior  aperture 
of  the  foramen  Vesalii.  To  the  medial  edge  of  this  fossa,  as  well  as  to  the  posterior 
border  of  the  medial  pterygoid  plate,  the  pharyngeal  aponeurosis  is  attached. 
Here,  too,  the  cartilage  of  the  Eustachian  tube  is  supported  on  a  slight  projection, 
and  the  palato  -  pharyngeus  (pharyngo-palatinus)  muscle  receives  an  origin, 
whilst  the  superior  constrictor  of  the  pharynx  arises  from  the  lower  third  of 
the  same  border  and  from  the  hamular  process.  Superiorly  and  medially  the 
medial  plate  forms  an  incurved  lamina  of  bone,  the  vaginal  process  (processus 
vaginalis),  which  is  applied  to  the  under  surface  of  the  lateral  aspect  of  the 
body  reaching  medially,  towards  the  root  of  the  rostrum,  from  which,  however, 
it  is  separated  by  a  groove,  in  which,  in  the  articulated  skull,  the  ala  of  the 
vomer  is  lodged.  The  angle  formed  by  the  vaginal  process  and  the  medial 
edge   of    the   scaphoid   fossa   forms   a   projection   called    the   pterygoid    tubercle, 


126 


OSTEOLOGY. 


immediately  above  which  is  the  posterior  aperture  of  the  Vidian  canal  (canalis 
pterygoideus),  through  which  the  Vidian  nerve  and  artery  are  transmitted.  Oil  its 
under  surface  the  vaginal  process  displays  a  groove  (sulcus  pterygo-palatinus) 
which  in  the  articulated  skull  is  converted  into  the  pterygo-palatine  (pharyngeal) 
canal  by  its  union  with  the  palate  bone.  In  front,  at  its  root,  the  pterygoid 
process  displays  a  broad  smooth  surface  (fades  spheno-maxillaris),  which  is  confluent 
above  with  the  root  of  the  great  wing  around  the  foramen  rotundum,  and  forms 
the  posterior  wall  of  the  spheno- maxillary  (pterygo-palatine)  fossa.  Here,  to  the 
medial  side  of  the  foramen  rotundum,  is  seen  the  anterior  opening  of  the  Vidian 
canal.  Below,  the  pterygoid  plates  are  separated  by  an  angular  cleft,  the  pterygoid 
notch  (fissura  pterygoidea) ;  in  this  is  lodged  the  tuberosity  of  the  palate  bone,  the 
margins  of  which  articulate  with  the  serrated  edges  of  the  recess. 

Connexions. — The  sphenoid  articulates  with  the  occipital,  temporals,  parietals,  frontal, 
ethmoid,  sj^henoidal  turbinals,  vomer,  palate  and  zygomatic  bones,  and  occasionally  v/ith  the 
maxillfe. 

Ossification. — The  sphenoid  of  man  is  formed  by  the  fusion  of  two  parts,  the  pre- 
sphenoid  and  the  post-sphenoid,  each  associated  with  certain  processes.  In  most  mammals 
the  orbito-sphenoids  or  lesser  wings  fuse  with  the  pre-sphenoid,  whilst  the  alisphenoids  or 
greater  wings,  together  with  the  internal  pterygoid  plate,  ankylose  with  the  post-sphenoid. 
The  ossification  of  these  several  parts  takes  place  in  cartilage,  with  the  exception  of  the 
internal  pterygoid  plate,  which  is  developed  from  an  independent  centre  in  the  connective 
tissue  of  the  lateral  wall  of  the  oral  cavity  (Hertwig). 

At  the  end  of  the  second  month  a  centre  appears  in  the  root  of  the  great  wing  between 
the  foramen  ovale  and  foramen  rotundum;  from  this  the  ossification  spreads  outwards  and 
backwai'ds  and  also  downwards  into  the  external  pterygoid  plate.  Meanwhile  two  centres 
appear  about  the  same  time  in  the  basi-sphenoid  in  relation  to  the  floor  of  the  sella  turcica  and 
on  either  side  of  the  cranio-pharyngeal  canal,  around  which  they  ossify,  ultimately  leading 
to  the  obliteration  of  this  channel.  Somewhat  later  a  sphenotic  centre  appears  on  either 
side,  from  which  the  lateral  aspect  of  the  body  and  the  lingula  are  developed.  Fusion 
between  these  four  centres  is  usually  complete  by  the  sixth  month. 

In  the  pre-sphenoid  a  pair  of  lateral  nuclei  make  their  appearance  about  the  middle  of 
the  third  month,  just  lateral  to  the  optic  foramina ;  from  each  of  these  the  orbito- 
sphenoids  (lesser  wings)  and  their  roots  are 
developed.  About  the  same  time  another 
pair  of  centres,  placed  medial  to  the  optic 
foramina,  constitute  the  body  of  the  pre- 
sphenoid.  At  first  the  superior  surface  of  the 
body  of  the  pre-sphenoid  is  exposed  in  the 
interval  between  the  orbito-sphenoids,  but  by 
the  ultimate  coalescence  of  the  inner  borders 
of  the  orbito-sphenoids  to  form  the  jugum 
sphenoidale  the  body  of  the  pre-sphenoid  is 
almost  completely  covered  over  superiorly. 
By  the  coalescence  of  these  in  front,  and 
their  ultimate  union  with  the  basi  -  sphenoid 
behind,  a  cartilaginous  interval  is  enclosed,  of  triangular  shape,  which,  however,  becomes 
gradually  reduced  in  size  by  the  ingrowth  of  its  margins  so  as  to  form  two  medially- 
placed  foramina,  as  may  be  frequently  observed  in  young  bones — one  opening  on  the 
surface  of  the  olivary  eminence,  the  other  being  placed  anteriorly.  (Lawrence,  "  Proc. 
Soc.  Anat.,"  Journ.  Annt.  and  Physiol,  vol.  xxviii.  p.  19.) 

As  has  been  seen,  the  internal  pterygoid  plates  are  developed  in  membrane  and  are  the  first 
parts  of  the  sphenoid  to  ossify.  (Fawcett,  Anat.  Anz.,  vol.  xxvi.  1905,  p.  280.)  Each  is  derived 
from  a  single  nucleus  which  appears  about  the  ninth  or  tenth  week,  and  fuses  with  the  under 
surface  of  the  great  wing,  there  forming  a  groove  which  is  converted  into  the  Vidian  canal 
when  the  alisphenoid  and  internal  pterygoid  plates  fuse  later  with  the  body  of  the  post- 
sphenoid.  The  hamular  process,  however,  chondrifies  before  it  ossifies  during  the  third 
month.     Fawcett  also  regards  the  external  pterygoid  plate  as  of  membranous  origin. 

At  hirth  the  sphenoid  consists  of  three  parts  :  one  comprising  the  orbito-sphenoids 
together  with  the  body  of  tlie  pre-sphenoid  and  the  basi-sphenoid,  the  others  consisting  of 
the  alisphenoids,  one  on  either  side.  Fusion  of  the  latter  with  the  former  occui's  near  the 
end  of  the  first  year.     The  dorsum  sellyc  at  birth  consists  of  a  cartilaginous  plate  which 


Ossification  of  the  Sphenoid. 


a,  Pre-sphenoid ;  6,  Orhito-splieuoii.ls  ;  c,  Alisphenoids ; 
d,  Internal  pterygoid  plates  ;  e,  Basi-sphenoid. 


THE  ETHMOID  BONE. 


127 


separates  the  body  of  the  post-sphenoid  from  the  basi-occipital.  This  slowly  ossifies,  but 
the  cartilage  does  not  entirely  disappear  till  the  age  of  twenty-five,  by  which  time  bony  anky- 
losis of  the  basi-cranial  axis  is  complete.  For  a  considerable  time  the  under  surface  of  the 
body  of  the  pi'e-sphenoid  displays  a  buUate  appearance,  with  the  sides  of  which  the 
sphenoidal  turbinated  bones  articulate.  It  is  only  after  the  seventh  or  eighth  year  is 
reached  that  the  cancellous  tissue  within  this  part  of  the  bone  becomes  absorbed  to  form 
the  sphenoidal  sinuses. 

The  sphenoidal  turbinals  (conchae  sphenoidales),  or  bones  of  Bertin,  best  studied 
in  childhood,  are  formed  by  the  fusion  of  four  distinct  ossicles  (Cleland),  the  centres  for 
which  appear  in  the  later  months  of  utero-gestation.  Each  bone  consists  of  a  hollow,  three- 
sided  pyramid,  the  apex  of  which  is  in  contact  with  the  fore  part  of  the  vaginal  process  of 
the  internal  pterygoid,  whilst  the  base  fits  on  to  the  posterior  surface  of  the  lateral  mass 
of  the  ethmoid.  The  inferior  surface  of  each  forms  the  roof  of  the  corresponding  nasal 
fossa,  and  completes  the  formation  of  the  sphenopalatine  foramen,  whilst  the  lateral 
aspect  is  united  with  the  palate  bone  and  forms  the  medial  wall  of  the  (pterygo-palatine) 
fossa,  and  occasionally  constitutes  a  part  of  the  orbital  wall  posterior  to  the  os  planum  of 
the  ethmoid.  The  superior  surface  of  the  sphenoidal  turbinal  is  applied  to  the  fore  and 
under  surface  of  the  body  of  the  pre-sphenoid  on  either  side  of  the  rostrum.  It  is  by  the 
absorption  of  this  wall  that  the  sphenoidal  sinuses  are  ultimately  opened  up.  The  base 
of  the  pyramid  forms  the  aperture  through  which  each  of  these  sinuses  opens  into  the 
nasal  fossae  in  the  adult.  Up  to  the  age  of  five  these  ossicles  remain  independent,  but 
subsequently,  owing  to  their  firm  ankylosis  with  the  surrounding  bones,  they  are  merel}' 
represented  in  the  adult  disarticulated  skull  by  the  ii'regular  fragments  adherent  to  the 
separated  borders  of  the  ethmoid,  palate,  and  sphenoid  bones. 


The   Ethmoid   Bone. 


The  ethmoid  bone  (os  ethmoidale)  lies  in  front  of  the  sphenoid,  and  occupies 
the  interval  between  the  orbital  plates  of  the  frontal,  thus  entering  into  the  forma- 
tion of  the  anterior  cranial  fossa  as  well  as  the  medial  walls  of  the  orbits  and  the 
roof  medial  and  lateral  walls  of  the  nasal  fossse.  The  bone,  which  is  extremely 
light,  consists  of  two  cellular  parts — the  lateral  masses  (labyrinthus  ethmoidalis), 
which  are  united  superiorly  to  a  medial  vertical  plate  (lamina  perpendicularis)  by  a 
thin  horizontal  lamina  which,  from  its  perforated  condition,  is  called  the  cribriform 
plate.  The  general  arrangement  of  the  parts  of  the  bone  resembles  the  capital 
letter  T,the  medial  plate  corresponds 
to  the  vertical  limb,  the  cribriform 
plate  to  the  horizontal  limb  of  the  T, 
whilst  the  lateral  masses  may  be 
regarded  as  comparable  to  the  en- 
larged down -turned  extremities  of 
the  horizontal  limb  of  the  letter. 


Alar  process 


Crista  galli 


The  study  of  this  bone  will  be  much 
facilitated  by  cutting  through  the  cribri- 
form plate  on  one  side  of  the  vertical  plate, 
thus  removing  the  lateral  mass  of  one  side 
and  exposing  more  fully  the  central  per- 
pendicular lamina. 


Superior 
turbinated 
bone 


Superi'i'. 
meatu; 


Os  planum 


Middle  meatu; 


process 


Perpendicular  plate 


Middle 

turbinated' 
bone 

The  vertical  plate  (lamina  per- 
pendicularis), of  irregular  pen- 
tagonal shape,  forms  the  upper  part 
of  the  nasal  septum.  Its  superior 
border  projects  above  the  level  of 
the  cribriform  plate  so  as  to  form  a 
crest,  which  is  much  elevated  anteriorly,  where  it  terminates  in  a  thick,  vertical, 
triangular  process,  called  the  crista  galli,  the  interior  of  which  is  filled  with  fine 
cancellous  bone,  but  is  occasionally  pneumatic.  The  upper  edge  of  this  process  is 
sharp  and  pointed,  and  affords  attachment  to  the  falx  cerebri.  In  front  of  this 
process  there  is  a  groove  which  separates  the  alar  processes  (processus  alares)  which 


Fig.  95. — The  Ethmoid  seen  from  Behind. 


128 


OSTEOLOGY. 


Anterior  and  posterior 
ethmoidal  groo\  as 


Alai  process 


Os  planum 
(orbital  surface) 


Middle  meatuS' 


Infundibulum 


Vertical  plate 


Middle  turbinated  bone 
Fig.  96 


Uncinate  process 
The  Ethmoid  seen  froji  the  Eight  Side. 


project  from  the  crista  galli  ou  either  side.  By  articulation  with  the  frontal  bone 
this  groove  is  converted  into  a  canal,  the  foramen  caecum ;  this,  however,  is  not 
always  bhnd,  but  frequently  transmits  a  vein  to  the  roof  of  the  nose.  The 
posterior  margin  of  the  vertical  plate  is  thin,  and  articulates  with  the  crest  of  the 
sphenoid.  The  posterior  inferior  border  in  the  adult  is  ankylosed  with  the 
vomer ;   and  the  anterior  inferior  edge,  which  is  usually  thicker  than  the  others, 

unites  with  the  carti- 
laginous nasal  septum. 
The  anterior  superior 
border  articulates  with 
the  frontal  spine  of  the 
frontal  bone  and  with 
the  median  crest  formed 
by  the  union  of  the  two 
nasal  bones.  The  verti- 
cal plate,  which  is  usually 
deflected  to  one  or  other 
side,  has  generally  smooth 
surfaces,  except  above, 
where  they  are  chan- 
nelled by  short  and 
shallow  grooves  leading 
to  the  foramina  which 
pierce  the  cribriform  plate ;  these  are  for  the  lodgment  of  the  olfactory  nerves. 

The  lateral  mass  or  labyrinth  (labyrinthus)  is  composed  of  exceedingly  thin 
bone,  enclosing  a  large  number  of  air-cells ;  these  are  arranged  in  three  groups — an 
anterior,  a  middle,  and  a  posterior,  the  walls  of  which  have  been  broken  in  front, 
above,  behind,  and  below,  in  the  process  of  disarticulation.  Laterally  they  are 
closed  in  by  a  thin,  oblong  lamina,  the  orbital  plate  or  os  planum  (lamina  papyracea), 
which  forms  a  part  of  the  medial  wall  of  the  orbit,  and  articulates  above  with 
the  orbital  plate  of  the  frontal,  which  here  roofs  in  the  ethmoidal  cells.  (The 
line  of  this  suture  is  pierced  by  two  canals,  the  anterior  and  posterior  ethmoidal 
foramina,  both  of  which  transmit  small  ethmoidal  vessels,  whilst  the  anterior  also 
gives  passage  to  the  nasal  nerve.)  In  front  the  os  planum  articulates  with  the 
lacrimal  bone;  whilst  below,  by  its  union  with  the  orbital  surface  .of  the 
maxillary  bone,  the  air-sinuses  in  both  situations  are  completed.  Posteriorly 
the  OS  planum  articulates  with  the  sphenoid,  and  at  its  posterior  inferior 
angle  for  a  variable  distance  with  the 
orbital  process  of  the  palate  bone,  both 
of  which  serve  to  close  in  the  air-cells. 
The  medial  aspect  of  the  lateral  mass  dis- 
plays the  convoluted  turbinated  processes, 
usually  two  in  number,  though  occasion- 
ally there  may  be  three — rarely  more.  In 
cases  where  there  are  two  ethmo-turbinals  ^ 
they  are  separated  posteriorly  by  a  deep 
groove.  A  channel  is  thus  formed  in  the 
back  part  of  the  lateral  and  upper  aspect 
of  the  nasal  fossae,  called  the  superior  meatus, 
which  is  roofed  in  Ijy  the  superior  turbin- 
ated process  (concha  superior),  whilst  its 
floor  is  formed  by  the  upper  surface  of  the 
middle  turbinated  process  (concha  media).  The  posterior  ethmoidal  cells  open  into  this 
meatus.  In  front  of  the  superior  meatus,  which  only  grooves  the  posterior  half  of 
this  aspect  of  the  bone,  the  surface  is  rounded  from  above  downwards  and  before 
backwards,  and  forms  the  medial  wall  of  the  anterior  and  middle  ethmoidal  cells. 
Eunning  obliquely  from  above  downwards  and  backwards  over  the  medial  surface 
of  the  superior  concha,  are  a  number  of  fine  grooves  continuous  above  with  the 

^  So-called  to  distinguish  them  from  the  maxillo-turbinals  and  naso-tiirbinals  of  comparative  anatomy. 


Superior 
turbinated  bone 


Anterior  ethmoidal 
groove 


Uncinate  process 

Fig.   97. — Section  showing  the  Nasal  Aspect 
OF  the  Left  Lateral  Mass  op  the  Ethmoid. 


THE  ETHMOID  BONE. 


129 


Os  plaiinni 


E Alar  process 


Perpendicu- 
lar plate 


Uncinate  process 


Lacrimal  process 


Inferior 
turbinated  bone 

Maxillary  process  Ethniuidal  process 

Fig.  98.— Showing  the  Aeticdlation  of  the  Inferior 
Turbinated  Bone  with  the  Ethmoid. 


foramina  in  the   cribriform  plate ;   these  are  fewer  and  more  scattered  in  front, 
do  not  pass  on  to  the  middle  concha,  and  are  for  the  olfactory  nerves. 

The  middle  turbinated  process  (concha  media)  is  nearly  twice  the  length  of  the 
superior.  Its  anterior  extremity  is  united  for  a  short  distance  to  the  superior 
turbinated  crest  on  the  medial 
side  of  the  frontal  process  of  the 
maxilla.  By  its  thickened,  free 
convoluted  border  it  overhangs 
a  deep  groove  which  runs  along 
the  under  surface  of  the  lateral 
mass.  This  is  the  middle  meatus 
of  the  nose.  It  receives  the  open- 
intjs  of  the  middle  ethmoidal  cells, 
which  project  into  the  meatus, 
forming  a  rounded  elevation  called 
the  ethmoidal  bulla.  In  front  and 
below  this  is  a  groove,  hiatus  semi- 
lunaris, which  Ijy  articulation 
above  with  adjacent  bones  is  con-  '^'^''^'"^*f^ 
verted  into  a  canal,  the  infundi- 
bulum,  which  runs  upwards  and 
forwards  and  forms  a  channel  of 
communication  with  the  frontal 
sinus  and  the  anterior  ethmoidal 
cells.  Cur\'ing  downwards,  back- 
w^ards,  and  a  little  laterally  from 
the  roof  of  the  fore-part  of  this  meatus  in  front  of  the  infundibulum  is  the  uncinate 
process  (processus  uncinatus).  This  bridges  across  the  irregular  opening  on  the 
medial  wall  of  the  maxillary  sinus,  and  articulates  inferiorly  with  the  ethmoidal 

process  of  the  inferior  turbinated  bone.  The 
hinder  extremity  of  the  middle  turbinated 
bone  articulates  with  the  ethmoidal  crest 
on  the  vertical  plate  of  the  palate  bone. 

The  cribriform  plate  (lamina  cribrosa)  is 
the  horizontal  lamina  which  connects  the 
lateral  masses  with  the  vertical  plate.  It 
occupies  the  interval  between  the  orbital 
plates  of  the  frontal  bone,  roofing  in  the 
nasal  fosspe  inferiorly,  and  superiorly  forming 
on  either  side  of  the  crista  galli  two  shallow 
olfactory  grooves  in  which,  in  the  recent  con- 
dition, the  olfactory  lobes  of  the  cerebrum 
are  lodged.  Numerous  foramina  for  the  trans- 
mission of  the  olfactory  nerves  pierce  this 
part  of  the  bone ;  those  to  the  medial  and 
lateral  sides  of  the  groove  are  the  largest 
and  most  regular  in  their  arrangement. 
Along  the  lateral  edges  of  the  cribriform  plate 
two  notches  can  usually  be  distinguished ; 
when  articulated  with  the  frontal  bone  these  form  the  medial  openings  of  the 
ethmoidal  foramina.  Leading  forward  from  the  anterior  of  these  there  is  often  a 
groove  which  crosses  to  the  side  of  the  crista  galli,  where  it  ends  in  a  slit  which 
allows  of  the  transmission  of  the  nasal  nerve  to  the  nose.  Posteriorly  the  cribri- 
form plate  articulates  with  the  ethmoidal  spine  of  the  sphenoid. 

Connexions. —  The  ethmoid  articulates  with  the  sphenoid  and  sj^henoidal  tiirbinals,  the 
frontal,  the  two  nasals,  tw^o  maxillae,  two  lacrimals,  two  inferior  turbinals,  two  palates, 
and  the  vomer. 

Ossification  takes  place  in  the  cartilage  of  the  nasal  capsule.  Each  hiteral  mass  has 
one  centre,  which  appears  about  the  fourth  or  fifth  month  in  the  neighbourhood  of  the 


Vertical  plate 


Alar  process 


Crista  galli 


Slit  for  nasal  nerve 


Os  planum 


Cribriform  plate 


Lateral  mass 


Fig.  99. — The  Ethmoid  seen  from  Above. 


130 


OSTEOLOGY. 


OS  plauimi.  According  to  Fawcett  ossification  first  commences  in  a  process  which  passes 
outside  the  nasal  duct  to  reach  tlie  frontal  process  of  the  maxilla.  From  this  the 
laminae  around  the  ethmoidal  air  cells  are  formed  which  are  complete  at  birth,  the  air- 
sinuses  in  this  instance  not  being  formed  by  the  absorption  of  cancellous  bone.  From 
these  centres  the  turbinals  are  also  developed,  and  these,  too,  are  ossified  at  the  ninth 
mouth. 

At  birth  the  ossified  lateral  masses  are  united  to  the  central  cartilaginous  plate  by  a 
fibrous  layer.  Two  centres  make  their  appearance  in  the  medial  cartilage  on  either  side 
of  the  root  of  the  crista  galli  about  the  end  of  the  first  year ;  from  these,  the  crista  galli 
and  the  vertical  plate  are  ossified  as  well  as  the  medial  part  of  the  cribriform  plate,  the 
lateral  portions  of  which  are  derived  from  an  inward  extension  of  the  lateral  mass. 

Ossification  is  usually  complete  about  the  fifth  or  sixth  year.  Abou,t  the  twenty-fifth 
year  bony  union  has  taken  place  between  the  cribriform  plate  and  the  sphenoid,  but 
ankylosis  between  the  vertical  plate  and  the  vomer  is  not  usual  till  the  fortieth  or  forty- 
fifth  year. 

The  Inferior  Turbinated  Bones. 

The  inferior  turbinated  or  spongy  bone  (concha  nasalis  inferior)  is  a  shell-like 
lamina  of  bone  lying  along  the  lower  part  of  the  lateral  wall  of  the  nasal  fossa.  Of 
elongated  form,  the  bone  displays  two  curved  borders  enclosing  a  medial  and 
lateral  surface. 

The  superior  or  attached  border  is  thin  and  sharp  in  front  and  behind,  where 


Lacrimal  process 


Ethmoidal  process 


Lacrimal  proces.s 


Ethmoidal  process 


Maxillaiy  jjiocess 
A  B 

Fig.  100. — The  Right  Inferior  Turbinated  Bone.     A,  Medial  Surface  ;  B,  Lateral  Surface. 

it  articulates  with  the  inferior  turbinal  crests  on  the  medial  surface  of  the  body 
of  the  maxilla  and  the  vertical  plate  of  the  palate  bone  respectively.  Be- 
tween these  two  borders  the  central  part  of  the  upper  edge  rises  in  the  form  of 
a  sharp  crest,  the  fore-part  of  which  forms  the  upstanding  lacrimal  process  (pro- 
cessus lacrimalis)  which  articulates  above  with  the  descending  process  of  the 
lacrimal  bone,  as  well  as  with  the  edges  of  the  nasal  groove  of  the  superior 
maxilla,  thus  completing  the  osseous  canal  of  the  nasal  duct.  The  posterior  end 
of  this  crest  is  elevated  in  the  form  of  an  irregular  projection  called  the  ethmoidal 
process  (processus  ethmoidalis).  This  unites  with  the  uncinate  process  of  the 
ethmoid  bone  (see  Fig.  97).  Spreading  downwards  from  the  middle  of  the 
superior  border,  on  its  lateral  side,  is  a  thin,  irregular  plate  of  bone,  the  maxillary 
process  (processus  maxillaris),  which  partially  conceals  the  lateral  concave  surface 
of  the  bone,  and,  by  its  union  with  the  medial  wall  of  the  maxillary  sinus,  assists  in 
the  completion  of  the  partition  which  separates  that  cavity  from  the  inferior  nasal 
meatus.  The  inferior  or  free  border,  gently  curved  from  before  backwards  and 
slightly  out-turned,  is  rounded  and  full,  and  formed  of  bone  which  is  deeply  pitted 
and  of  a  somewhat  cellular  character.  The  anterior  and  posterior  extremities  of 
the  bone,  formed  by  the  convergence  of  the  upper  and  lower  borders,  are  thin  and 
sharp ;  as  a  rule  the  hinder  end  ,  is  the  more  pointed  of  the  two.  The  medial 
surface  projects  into  the  nasal  fossa ;  convex  from  above  downwards,  and  slightly 
curved  from  before  backwards,  it  forms  the  floor  of  the  middle  meatus.  It  is 
rough  and  pitted,  and  displays  some  scattered  and  longitudinally  directed  vascular 
grooves.  The  lateral  surface  overhangs  the  inferior  meatus  of  the  nose.  Concave  from 
above  downwards,  and  to  some  extent  from  before  backwards,  it  is  directed  towards 
the  lateral  wall  of  the  nasal  fossa.     It  is  smooth  in  front,  where  it  corresponds  to 


THE  LACEIMAL  BONES.  131 

the  opening  of  the  canal  for  the  nasal  duct ;  behind  and  towards  its  lower  border 
it  is  irregular  and  pitted.  In  the  disarticulated  bone  this  surface  is  in  part  con- 
cealed by  the  downward  projecting  maxillary  process. 

Connexions. — The  inferior  turbinal  articulates  with  the  maxilla,  lacrimal,  ethmoid, 
and  palate  bones. 

Ossification.  —  The  inferior  turbinate  bone,  (the  maxillo- turbinal  of  comparative 
anatomy),  is  derived  from  the  cartilage  forming  the  lateral  wall  of  the  nasal  capsule,  the 
upper  portion  of  which  forms  the  ethmo-turbinals.  It  ossifies,  however,  from  a  separate 
centre,  which  appears  about  the  fifth  month  of  foetal  life,  and  later  contracts  a  union 
by  a  horizontal  lamella  on  its  lateral  side  with  the  maxillary  bone. 

The  Lacrimal  Bones. 

The  lacrimal  bone  (os  lacrimale),  a  thin  scale  of  bone  about  the  size  of 
a  finger-nail,  forms  part  of  the  medial  orbital  wall  behind  the  frontal  process  of 
the  maxilla.  Irregularly  quadrangular,  it  has  two  surfaces — a  medial  and  lateral 
— and  four  borders. 

Its  lateral  or  orbital  surface  has  a  vertical  ridge,  the  lacrimal  crest  (crista 
lacrimalis  posterior),  running  downwards  upon  it.  In  front  of  this  is  the  lacrimal 
groove  (sulcus  lacrimalis)  for  the  lodgment  of  the  lacrimal  sac.  The  medial  wall 
of  this  groove  descends  below  the  level  of  the  bulk  of  the  bone,  and  forms  the 
descending  process,  which  helps  to  complete  the  osseous  canal  for  the  nasal  duct, 
and  articulates  inferiorly  with  the  inferior  turbinal.  The  lower  end  of  the 
lacrimal  crest  terminates  in  a  hook- like  projection,  the  hamular  process  (hamulus 
lacrimalis),  which  curves  round  the  posterior  and  lateral 
edge  of    the   lacrimal    notch    of   the    maxilla,   and    thus  orbitai  surface 

defines  the  upper  aperture  of  the  canal  for  the  nasal  duct. 
To  the  free  edge  of  the  crest  behind  the  lacrimal  groove 
are  attached  the  reflected  portion  of  the  tendo  oculi,  and 
the  tensor  tarsi  muscle.  The  part  of  the  bone  behind  the 
lacrimal  crest  is  smooth  and  continuous  with  the  surface 
of  the  OS  planum  of  the  ethmoid.  The  medial  surface 
is  irregular  and  cellular  above  ;  it  closes  in  some  of  the 
anterior  ethmoidal  cells  and  helps  to  complete  the  infundi- 
bulum.  Where  it  is  smoother  it  forms  a  part  of  the  piQ.  loi.— Right  Lacrimal 
lateral  wall  of  the  middle  meatus  of  the  nose  immediately  bone  (Orbital  Surface), 
behind  the  frontal  process  of  the  maxilla,  and  above  the 

inferior  turbinated  bone.  The  superior  border  articulates  with  the  orbital  plate 
of  the  frontal ;  the  anterior  edge  with  the  posterior  border  of  the  frontal  process 
of  the  maxilla,  with  which  it  completes  the  lacrimal  groove  for  the  lodgment 
of  the  lacrimal  sac.  The  inferior  margin  articulates  with  the  orbital  surface  of 
the  maxilla,  and  in  front  by  its  descending  process  with  the  inferior  turbinal. 
Posteriorly  the  bone  articulates  with  the  anterior  border  of  the  os  planum  of 
the  ethmoid. 

Connexions. — The  lacrimal  bone  articulates  with  four  bones — the  frontal,  ethmoid,  inferior 
turbinal,  and  the  maxilla. 

Ossification. — The  lacrimal  is  developed  from  a  single  centre,  which  makes  its 
appearance  about  the  end  of  the  second  or  the  beginning  of  the  third  month  of  intra- 
uterine life  in  the  membrane  around  the  cartilaginous  nasal  capsule. 

The  Vomer. 

The  vomer  or  ploughshare  bone,  a  bone  of  irregular  quadrilateral  shape,  is 
placed  medially  in  the  hinder  part  of  the  nasal  septum.  It'  has  four  borders  and 
two  surfaces.  The  superior  border,  which  can  readily  be  distinguished  by  the  presence 
on  either  side  of  an  everted  lip  or  ala,  slopes  from  behind  upwards  and  forwards, 
and  articulates  with  the  under  surface  of  the  body  of  the  sphenoid,  the  pointed 
rostrum  of  which  is  received  into  the  groove  formed  by  the  projecting  alee. 
Laterally   these   alse   are   wedged    in   between   the   sphenoidal    processes   of  the 


132 


OSTEOLOGY. 


eth  Groove  for 

^o/^    iiaso-palatine 
nerve 


Groove 
for  septal 
cartilage 

/ 


Palate 


Maxilla 


Fig.  102. 


-The  Vomer  as  seen  from  the 
Right  Sidk. 


palate  bone  in  front,  and  the  vaginal  processes  at  the  root  of  the  internal 
pterygoid  plates  behind.  The  posterior  border,  which  slopes  from  behind  down- 
wards and  forwards,  is  free,  and  forms  a  sharp,  slightly  curved  edge ;  this  con- 
stitutes the  posterior  margin  of  the  nasal  septum,  and  serves  to  separate  the 
openings  of  the  posterior  nares.     The  inferior  border,  more  or  less  horizontal  in 

direction,  articulates  with  the  nasal 
crest  formed  by  the  maxillary  and  palate 
bones.  The  anterior  edge  is  the  longest ; 
it  slopes  obliquely  from  above  down- 
wards and  forwards.  In  its  upper  half 
it  is  ankylosed  to  the  perpendicular 
plate  of  the  ethmoid ;  in  its  lower  half 
this  margin  is  grooved  for  the  reception 
of  the  septal  cartilage  of  the  nose.  The 
anterior  extremity  of  the  bone  forms  a 
truncated  angle,  which  articulates  with 
the  hinder  border  of  the  incisor  crest  of 
the  maxillae,  and  sends  downwards  a  pointed  process  which  passes  between 
the  incisor  foramina.  The  right  and  left  surfaces  of  the  bone  are  smooth  and 
covered  by  mucous  membrane.  It  is  not  uncommon  to  find  them  deflected  to 
one  or  other  side.  A  few  vascular  grooves  may  be  noticed  scattered  over  these 
surfaces,  and  one,  usually  more  distinct  than  the  others,  running  obliquely  down- 
wards and  forwards,  indicates  the  course  of  the  naso-palatine  nerve. 

Connexions. — The  vomer  articulates  with  the  sphenoid,  the  ethmoid,  the  palates,  and  the 
maxillae.     In  front  it  supports  the  septal  cartilage. 

Ossification. — The  vomer,  primitively  double,  begins  to  ossify  about  the  end  of  the 
second  month  of  foetal  life.     A  nucleus  appears  on  either  side  in  the  membrane  overlying 
the   back    and    lower   part    of    the    vomerine    cartilage ; 
these  form  the   primitive    lamellse  developed   on    either 
side    of,    and    not  from,  the  cartilage.     About  the  third 
month  these  laminae  become  fused  behind  and  below,  thus 
forming  a  deep  groove  in  which  the  cartilage  is  lodged. 
As  growth  goes  on  the  groove  becomes  reduced  by  the 
further  fusion  of  the  lateral  plates  and  the  absorption  of   Vomer  at  Birth  displaying  its  forma- 
the    cartilage,    until    the   age   of    puberty,    by    which   time        tion  by  two  Osseous  Laminm  united 
the  lateral  laminge  have  united  to  form  a  medial  plate, 
the  primitively  divided  condition  of  which  is  now   only 
represented  by  the  eversion  of  the  alee  and  the  grooving 
along  the  anterior  border.       According  to  Fawcett,  the 

ossification  of  the  Jacobsonian  cartilage  produces  a  hitherto  undescribed  element  in 
the  formation  of  the  osseous  nasal  septum. 


Fig.  10.3. 


inferiorly.  The  figure  to  the  right 
exhibits  the  appearance  of  the  bone, 
in  vertical  section,  at  the  point 
marked  -x-  in  the  left  figure. 


The  Nasal  Bones. 

The  nasal  bones  (ossa  nasalis),  two  in  number,  lie  in  the  interval  between 
the  frontal  processes  of  the  maxillae,  there  forming  the  root  or  bridge  of  the 
nose.  Each  bone  is  of  elongated  quadrangular  form,  having  two  surfaces  —  a 
medial  and  lateral — and  four  borders.  The  lateral  surface,  somewhat  constricted 
about  its  middle,  is  convex  from  side  to  side,  and  slightly  concavo-convex  from 
above  downwards.     Near  its  centre  there  is  usually  the  opening  of  a  nutrient  canal. 

The  medial  surface  is  not  so  extensive  as  the  lateral,  as  the  superior  and 
anterior  articular  borders  encroach  somewhat  upon  it  above.  Concave  from  side  to 
side,  and  also  from  above  downwards,  it  is  covered,  in  the  recent  condition,  by  the 
mucous  membrane  of  the  nose.  Eunning  downwards  along  this  surface  is  a 
narrow  groove  (sulcus  ethmoidalis)  which  transmits  the  anterior  terminal  branch  of 
the  nasal  nerve.  The  anterior  or  medial  border,  narrow  below,  is  thick  above,  and; 
in  conjunction  with  its  fellow  at  the  opposite  side,  with  which  it  articulates, 
forms  a  median  crest  posteriorly,  which  is  united  to'  the  spine  of  the  frontal, 
the  vertical  plate  of  the  ethmoid,  and  the  septal  cartilage  of  the  nose,  in  that  order 


BONES  OF  THE  FACE. 


133 


from    above    downwards.      The   posterior   or   lateral    border,   usually    the    longest, 

is  serrated  and  bevelled  to  fit  on  to  the  anterior  edge  of  the  frontal  process  of  the 

maxilla.      The  superior   border  forms   a  wide   toothed  surface,  which  articulates 

with  the  medial  part  of  the  nasal  notch  of  the  frontal  bone  anteriorly;  whilst, 

behind,  it   rests   in  contact  with   the 

root  of  the  nasal  process  of  the  same 

bone.     The  inferior  border  is  thin  and 

sharp,   and    is    connected    below   with 

the  lateral  cartilage  of  the  nose,  and  is 

usually  deeply  notched  near  its  medial 

extremity. 

Connexions. — Tlie  nasal  bone  articulates 
with  its  fellow  of  the  opposite  side,  with  the 
frontal  above,  behind  with  the  vertical  plate 
of  the  ethmoid  and  with  the  frontal  process 
of  the  maxilla.  It  is  also  united  to  the  septal 
and  upper  lateral  cartilages  of  the  nose. 


Fig.  104. 


-The  Right  Nasal  Bone. 
B,  Medial  side. 


A,  Lateral  side 


Ossification. — The  nasal  bones  are 
each  developed  from  a  single  centre,  which 
makes  its  appearance  about  the  end  of  the  second  month  in  the  membrane  covering  the 
forepart  of  the  cartilaginous  nasal  capsule.  Subsequent  to  birth  the  underlying  carti- 
laginous stratum  disappears,  persisting,  however,  below  in  the  form  of  the  lateral  nasal 
cartilage,  and  behind  as  the  septal  cartilage  of  the  nose. 

Wormian  Bones. 

Along  the  line  of  the  cranial  sutures  and  in  the  region  of  the  fontanelles,  isolated 
bones  of  irregular  form  and  variable  size  are  occasionally  met  with.  These  are  the  so- 
called  Wormian  bones,  named  after  the  Danish  anatomist  Wormius.  They  are  also  called 
sutural  bones  (ossa  suturarum).  Their  presence  depends  on  the  fact  that  they  are  either 
developed  from  distinct  ossific  nuclei,  or  it  may  be  from  a  division  of  the  primary  ossific 
deposit.  Their  occurrence  may  also  be  associated  with  certain  pathological  conditions 
which  modify  the  development  of  the  bone.  They  usually  include  the  whole  thickness 
of  the  cranial  wall,  or  it  may  be  only  involve  the  outer  or  inner  tables  of  the  cranial 
bones.  They  are  most  frequent  in  the  region  of  the  lambda  and  the  lambdoid  suture. 
They  occur  commonly  about  the  pterion,  and  in  this  situation  are  called  epipteric  bones 
(Flower).  By  their  fusion  with  one  or  other  of  the  adjacent  bones  they  here  lead  to  the 
occurrence  of  a  fronto-squamosal  suture.  Their  presence  has  also  been  noted  along  the 
line  of  the  sagittal  suture,  and  sometimes  in  metopic  skulls  in  the  inter-frontal  suture. 
They  are  occasionally  met  with  at  the  asterion  and  more  rarely  at  the  obelion.  They 
appear  less  frequently  in  the  face,  but  their  presence  has  been  noted  around  the  lacrimal 
bone,  and  also  at  the  extremity  of  the  spheno-maxillary  fissure,  where  they  may  form  an 
independent  nodule  wedged  in  between  the  great  wing  of  the  sphenoid,  the  zygomatic,  and 
the  maxillary  bones. 


BONES   OF   THE   FACE. 

The   bones  of  the  face  (ossa  faciei),  seven  in  number,  comprise  two  maxillae, 
two  palates,  two  malars,  with  the  mandible  or  lower  jaw. 


The  Maxillary  Bones. 

The  maxillae  (maxillae),  of  which  there  are  two,  unite  to  form  the  upper  jaw. 
Each  consists  of  a  body,  with  which  are  connected  four  projections,  named  respec- 
tively the  zygomatic,  frontal,  alveolar,  and  palatine  processes. 

The  body  (corpus)  is  of  pyramidal  form,  and  contains  within  it  a  hollow  called 
the  antrum  or  maxillary  air-sinus.  It  has  four  surfaces — an  anterior  or  facial, 
a  postero-lateral,  infra-temporal  or  zygomatic,  a  supero-lateral  or  orbital,  and 
a  medial  or  nasal — and  four  processes— the  malar,  frontal,  alveolar,  and  palatine. 

Surfaces. —  The  anterior  or  facial  surface  (facies  anterior)  is  confluent  below 
with  the  alveolar  process.     Above,  it  is  separated  from  the  orbital  aspect  by  the 

9 


184 


OSTEOLOGY. 


Frontal  process 


Infraorbital 
eroove 


Incisor  fossa 


Tuberosit} 


105  ff. — The  Right  Maxilla 


infraorbital  margin  (margo  infraorbitalis),  whilst  medially  it  is  limited  by  the  free 
margin  of  the  nasal  notcli,  which  ends  below  in  the  pointed  anterior  nasal  spine 
(spina  nasalis  anterior).     Posteriorly  it  is  separated  from  the  zygomatic  surface  by 

the  inferior  border  of 
the  zygomatic  process. 
The  facial  aspect  of  the 
bone  is  ridged  by  the 
sockets  of  the  teeth 
(juga  alveolaria).  The 
ridge  corresponding  to 
the  root  of  the  canine 
tooth  is  usually  the 
most  pronounced;  med- 
ial to  this,  and  over- 
lying the  roots  of  the 
incisor  teeth,  is  the 
shallow  incisive  or  myr- 
tiform  fossa,  whilst 
placed  laterally,  on  a 
higher  level,  is  the 
deeper  canine  fossa,  the 
floor  of  which  is  formed 
in  part  by  the  project- 
ing zygomatic  process. 
Above  this,  and  near 
the  infraorbital  margin, 
is  the  infraorbital  fora- 
men, the  external  opening  of  the  infraorbital  canal,  which  transmits  the  infraorbital 
nerve  and  artery.  The  postero-lateral  or  zygomatic  surface  is  separated  above  from 
the  orbital  aspect  by  a  rounded  free  edge,  which  forms  the  anterior  margin  of  the 
spheno -maxillary  (inferior 
orbital)  fissure  in  the  ar- 
ticulated skull.  In- 
feriorly  and  in  front  it  is 
separated  from  the  facial 
surface  by  the  zygomatic 
process  and  its  free  lower 
border.  Medially  it  is 
limited  by  a  sharp,  ir- 
regular margin  with 
which  the  palate  bone 
articulates.  This  surface 
is  more  or  less  convex, 
and  is  directed  towards 
the  zygomatic  and 
spheno-maxillary  fossae. 
It  is  pierced  in  a  down- 
ward direction  by  the 
apertures  of  the  posterior 
dental  canals  (foramina 
alveolaria),  tw^o  or  more 
ill  number,  which  trans- 
mit the  corresponding 
nerves  and  vessels  to  the 
molar  teeth.  Its  lower 
part,    slightly     more 

prominent  where  it  overhangs  the  root  of  the  wisdom  molar,  is  often  called  the 
tuberosity  (tuber  maxillare).  The  supero-lateral  or  orbital  surface  (planum  orbitale), 
smooth  and  plane,  is  triangular  in  shape  and  forms  part  of  the  floor  of  the  orbit. 


Frontal  process 


Ridge  for  middle 
turbinated  bone 


Middle  meatus' 


Anterior  nasal 
spine 


Palatine 
process 


Alveolar 
process 


Fig.  105 /y. — The  Right  Maxilla  (Medial  Aspect). 


THE  SUPEKIOE  MAXILLAKY  BONES.  135 

Its  anterior  edge  corresponds  to  the  infraorbital  margin ;  its  posterior  border  coin- 
cides with  the  anterior  boundary  of  the  inferior  orbital  or  spheno-maxillary  fissure. 
Its  thin  medial  edge,  which  may  be  regarded  as  the  base  of  the  triangle,  is  notched 
in  front  to  form  the  lacrimal  groove  (sulcus  lacrimalis),  behind  which  it  articulates 
with  the  lacrimal  bone  for  a  short  distance,  then  for  a  greater  length  with  the 
OS  planum  of  the  ethmoid,  and  terminates  posteriorly  in  a  surface  for  articulation 
with  the  orbital  process  of  the  palate  bone.  Its  lateral  angle  corresponds  to  the 
base  of  the  zygomatic  process.  Traversing  its  substance  is  the  infraorbital  canal,  the 
anterior  opening  of  which  has  been  already  noticed  on  the  facial  aspect  of  the  body. 
Behind,  however,  owing  to  deficiency  of  its  roof,  the  canal  forms  a  groove  which  lips 
the  edge  of  the  bone  which  constitutes  the  anterior  boundary  of  the  inferior  orbital  or 
spheno-maxillary  fissure.  If  this  canal  be  laid  open,  the  orifices  of  the  middle  and 
anterior  dental  canals  will  be  seen,  which  transmit  the  corresponding  vessels  and 
nerves  to  the  bicuspid  and  incisor  teeth.  The  medial  or  nasal  surface  (facies  nasalis) 
of  the  body  is  directed  medially  towards  the  nasal  fossae.  Below  it  is  confluent  with 
the  upper  surface  of  the  palatal  process ;  in  front  it  is  limited  by  the  sharp  edge 
of  the  nasal  notch ;  above  and  in  front  it  is  continuous  with  the  medial  surface  of  the 
frontal  process ;  behind  this  it  is  deeply  channelled  by  the  lacrimal  groove,  which 
is  converted  into  a  canal  by  articulation  with  the  lacrimal  and  inferior  turbinated 
bones.  The  channel  so  formed  conveys  the  nasal  duct  from  the  orbital  cavity 
above  to  the  inferior  nasal  meatus  below.  Behind  this  groove  the  upper  edge  of 
this  area  corresponds  to  the  medial  margin  of  the  orbital  surface,  and  articulates 
from  before  backwards  with  the  lacrimal,  os  planum  of  the  ethmoid,  and  the 
orbital  process  of  the  palate  bone.  The  posterior  border,  rough  for  articulation 
with  the  palate  bone,  is  traversed  obliquely  from  above  downwards  and  slightly 
inwards  by  a  groove,  which,  by  articulation  with  the  palate  bone,  is  converted  into 
the  posterior  palatine  or  palato-maxillary  canal  which  transmits  the  descending  pala- 
tine artery  and  great  palatine  nerve.  Towards  its  upper  and  hinder  part  the  nasal 
surface  of  the  body  displays  the  irregular,  more  or  less  triangular,  opening  of  the 
antrum  (sinus  maxillaris).  This  aperture  which,  in  the  articulated  skull  opens 
into  the  middle  meatus  of  the  nose,  is  much  reduced  in  size  by  articulation  with 
the  lacrimal,  ethmoid,  palate,  and  inferior  turbinal  bones.  In  front  of  the 
lacrimal  groove  the  inner  surface  is  ridged  horizontally  by  the  inferior  turbinated 
crest  (crista  conchalis),  to  which  the  inferior  turbinated  bone  is  attached.  Below 
this  the  bone  forms  the  lateral  wall  of  the  inferior  nasal  meatus,  receiving  the 
termination  of  the  lacrimal  groove.  Above,  and  for  some  little  distance  also  on 
the  medial  side  of  the  frontal  process,  it  constitutes  the  smooth  lateral  wall  of 
the  atrium  of  the  middle  meatus. 

Processes. — The  zygomatic  or  malar  process  (processus  zygomaticus),  which 
is  placed  on  the  lateral  surface  of  the  body,  is  confluent  anteriorly  with  the  facial 
surface  of  the  body ;  posteriorly,  where  it  is  concave  from  side  to  side,  with  the 
zygomatic  surface ;  whilst  superiorly,  where  it  is  rough  and  articular,  it  forms  the 
apex  of  the  triangular  orbital  plate,  and  supports  the  malar  bone.  Inferiorly,  its 
anterior  and  posterior  surfaces  meet  to  form  an  arched  border,  which  fuses  with  the 
alveolar  process  opposite  the  root  of  the  first  molar  tooth,  and  serves  to  separate 
the  facial  from  the  zygomatic  aspects  of  the  body. 

The  frontal  (nasal)  process  (processus  frontalis)  rises  from  the  upper  and 
fore-part  of  the  body.  It  has  two  surfaces — one  lateral,  the  other  medial.  The 
lateral  is  divided  into  two  by  a  vertical  ridge  (crista  lacrimalis  anterior),  which 
is  the  upward  extension  of  the  infraorbital  margin.  The  narrow  strip  of  bone 
behind  this  ridge  is  hollowed  out,  and  leads  into  the  lacrimal  groove  below. 
Posteriorly  the  edge  of  the  frontal  process  here  articulates  with  the  lacrimal,  and 
so  forms  the  fossa  for  the  lodgment  of  the  lacrimal  sac  (fossa  sacci  lacrimalis). 
In  front  of  the  vertical  crest,  to  which  the  tendo  oculi  is  attached,  the  lateral 
surface  is  confluent  below  with  the  facial  aspect  of  the  body,  and  forms  the  side  of 
the  root  of  the  nose.  Here  may  often  be  seen  a  vascular  groove  entering  the 
bone.  Its  anterior  edge  is  rough,  or  grooved,  for  articulation  with  the  nasal  bone. 
Superiorly  the  summit  of  the  process  is  serrated  for  articulation  with  the  nasal 
notch  of  the  frontal  bone.    The  medial  surface  of  the  frontal  process  is  directed  towards 

9a 


136  OSTEOLOGY. 

the  nasal  fossae.  It  is  crossed  obliquely  from  below  upwards  and  backwards  by  a 
ridge  —  the  agger  nasi  or  superior  turbinated  crest  (crista  ethmoidalis)  which  is 
considered  to  be  a  vestige  of  the  naso-turbinal  which  is  met  with  in  some  mammals. 
Below  this  the  bone  is  smooth  and  forms  the  upper  part  of  the  atrium  of  the 
middle  meatus,  whilst  the  ridge  itself  articulates  posteriorly  with  the  forepart  of 
the  middle  turbinated  bone,  formed  by  the  inferior  turbinated  process  of  the 
ethmoid  bone. 

The  alveolar  process  (processus  alveolaris)  projects  from  the  under  surface  of 
the  body  of  the  bone  below  the  level  of  the  palatal  process.  Of  curved  form,  it 
completes,  with  its  fellow  of  the  opposite  side,  the  alveolar  arch,  in  which  are 
embedded  in  sockets  or  alveoli  the  roots  of  the  teeth  of  the  upper  jaw ;  ordinarily 
in  the  adult,  when  dentition  is  complete,  each  alveolar  process  supports  eight  teeth. 
Piercing  the  medial  surface  of  the  alveolar  border  behind  the  incisor  teeth  two 
small  vascular  foramina  are  usually  visible.  When  any  or  all  the  teeth  are  shed 
the  alveoli  become  absorbed,  and  the  process  may  under  these  circumstances  be 
reduced  to  the  level  of  the  plane  of  the  palatal  process.  Posteriorly  the  alveolar 
process  ends  below  the  tuberosity  of  the  body ;  anteriorly  it  shares  in  the  formation 
of  the  intermaxillary  suture. 

The  palatal  process  (processus  palatinus),  of  the  form  of  a  quadrant,  lies  in  the 
horizontal  plane ;  it  has  two  surfaces — upper  and  under — and  three  borders,  a  straight 
medial,  a  more  or  less  straight  posterior,  and  a  curved  lateral,  by  which  latter 
it  is  attached  to  the  medial  side  of  the  body  and  alveolar  process  as  far  back  as  the 
interval  between  the  second  and  third  molar  teeth.  Its  under  surface,  together 
with  that  of  its  fellow,  forms  the  anterior  three-fourths  of  the  vaulted  hard  palate ; 
it  is  rough  and  pitted  for  the  glands  of  the  mucous  membrane  of  the  roof  of  the 
mouth,  and  is  grooved  on  either  side  near  the  alveolar  margin  by  a  channel  which 
passes  forward  from  the  posterior  palatine  canal  and  transmits  the  great  palatine 
nerve  and  descending  palatine  artery.  Its  superior  surface,  smooth  and  concave 
from  side  to  side,  forms  the  floor  of  the  corresponding  nasal  fossa.  Its  medial 
border,  broad  and  serrated,  rises  in  a  ridge  superiorly,  so  as  to  form  with  its  fellow 
of  the  opposite  side  the  nasal  crest  (crista  nasalis),  which  is  grooved  superiorly 
to  receive  the  lower  border  of  the  vomer.  In  front  of  its  articulation  with  the 
vomer  this  ridge  rises  somewhat  higher,  being  named  the  incisor  crest,  anterior  to 
which  it  projects  beyond  the  free  border  of  the  nasal  notch,  and  together  with  its 
fellow  forms  the  pointed  projection  called  the  anterior  nasal  spine  (spina  nasalis 
anterior).  These  parts  support  the  septal  cartilage  of  the  nose.  Immediately  to 
the  lateral  side  of  the  incisor  crest  the  superior  surface  of  the  palatal  process  is 
pierced  by  a  foramen  which  leads  downwards,  forward,  and  a  little  medially,  to  open 
into  a  broad  groove  on  the  medial  border  of  the  bone  immediately  behind  the 
central  incisor  tooth.  When  the  two  maxillse  are  articulated,  the  two  grooves 
form  the  oval  anterior  palatine  canal  or  fossa,  into  which  the  two  aforementioned 
foramina  open  like  the  limbs  of  a  Y ;  these  are  called  the  incisor  foramina,  or  the 
foramina  of  Stensen,  and  represent  the  channels  by  which  in  lower  forms  the 
organs  of  Jacobson  open  into  the  mouth.  In  man  they  afford  a  means  of 
establishing  an  anastomosis  between  the  vessels  of  the  mouth  and  nose.  In  front 
and  Ijehind  these,  and  lying  within  the  fossa  and  in  the  line  of  the  suture,  are  the 
smaller  foramina  of  Scarpa,  which  transmit  the  naso-palatine  nerves,  the  right  nerve 
usually  passing  through  the  posterior  foramen,  the  left  through  the  anterior.  The 
posterior  border  of  the  palatal  process,  which  is  sharp  and  thin,  falls  in  line  with 
the  interval  between  the  second  and  third  molar,  and  articulates  with  the  horizontal 
plate  of  the  palate  bone. 

The  maxillary  sinus  (sinus  maxillaris)  lies  within  the  body  of  the 
bone,  and  is  of  corresponding  pyramidal  form,  its  base  being  directed  towards 
the  nasal  fossa,  with  the  middle  meatus  of  which  it  communicates,  its  summit 
extending  laterally  into  the  root  of  the  zygomatic  process.  It  is  closed  in 
laterally  and  above  by  the  thin  walls  which  form  the  facial,  zygomatic,  and 
orbital  surfaces  of  the  body.  Inferiorly  it  overlies  the  alveolar  process  in  which 
the  molar  teeth  are  implanted,  more  particularly  the  first  and  second,  the  sockets 
of  which  are  separated  from  it  by  a  thin  layer  of  bone. 


THE  SUPERIOE  MAXILLARY  BONES. 


L37 


The  augles  and  corners  of  this  cavity  are  frequently  groined  by  narrow  ridges 
of  bone,  one  superiorly  corresponds  to  the  relief  formed  by  the  infraorbital  canal. 
A  vascular  and  nervous  groove  is  often  exposed,  curving  along  the  floor  of  the 
antrum  just  above  the  alveoli  of  the  teeth.  The  interior  of  the  cavity  is  lined  by 
an  extension  from  the  mucous  membrane  of  the  nose. 

Connexions. — The  maxilla  articulates  with  the  nasal,  frontal,  lacrimal,  and  ethmoid 
bones  above,  laterally  with  the  zygomatic,  and  occasionally  with  the  sphenoid,  posteriorly 
and  medially  with  the  palate,  whilst  on  its  medial  side  it  unites  with  its  fellow  of  the  opposite 
side,  and  also  sujjj^oi'ts  the  inferior  turbinated  bone  and  the  vomer. 

Ossification. — The  maxillae  are  developed  in  the  connective  tissue  around  the  oral 
aperture  of  the  embryo.  The  centres  from  which  the  bone  ossifies  are  not  preceded 
by  a  cartilaginous  stage.  Their  number  is  uncertain,  as  early  fusion  occurs  between 
them.  They  first  make  their  appearance  in  the  second  month  of  intrauterine  life, 
shortly  after  the  clavicle  has  begun  to  ossify.  By  the  sixth  month  they  are  so  united 
that  their  independent  character  is  obscured.  Five  centres  are  described  — a  lateral  or 
malar,  which  forms  the  bone  to  the  lateral  side  of  the  infraorbital  canal ;  a  medial  or 
orbito-nasal,  from  which  is  developed  the  medial  part  of  the  floor  of  the  orbit,  the  frontal 
process,  and  the  wall  of  the  antrum ;  a  palatine,  for  the  posterior  three-fourths  of  the 
palatal  process ;  a  nasal,  situated  between  the  frontal  process  and  the  canine  tooth  ;  and 
within  this  and  nearer  the  middle  line  and  below,  an  incisive  centre,  from  which  the  pre- 
maxilljB  are  developed,  thus  forming  the  anterior 
fourth  of  the  palatal  process  in  the  adult.  In  the 
early  stages  of  the  development  of  the  bone  the  alveolar 
groove,  in  which  the  teeth  are  developed,  lies  close  below 
the  infraorbital  groove,  and  it  is  not  till  later  that  they 
become  separated  by  the  growth  of  the  antrum,  which 
first  makes  its  appearance  as  a  shallow  fossa  to  the 
medial  side  of  the  orbito-nasal  element  about  the  fourth 
month.  In  the  adult  bone  the  course  of  the  infra- 
orbital canal  and  foramen  indicates  the  line  of  fusion  of 
the  orbito-nasal  and  malar  elements,  whilst  the  position 
of  the  anterior  palatine  canal  serves  to  determine  the 
line  of  union  of  the  incisive  with  the  palatal  elements. 
In  addition  to  the  foregoing  centres,  Rambaud  and 
Renault  describe  another,  infra  -  vomerine,  which, 
together  with  its  fellow,  is  wedged  in  between  the  in- 
cisive and  the  palatal  elemei:its  beneath  the  vomer,  thus 
explaining  the  Y-shaped  arrangement  of  the  foramina 
of  Stensen,  which  open  into  the  anterior  palatine  canal. 

The  premaxillse,  which  in  most  vertebrates  are 
independent  bones  lying  in  front  of  the  maxillae,  con- 
stitute in  man  and  apes  the  portions  of  the  upper  jaw 
which  lie  in  front  of  the  anterior  palatine  foramen, 
and  support  the  superior  incisor  teeth.  They  are  de- 
veloped from  the  incisive  centres  above  described  ;  the 
line  of  fusion  of  these  elements  with  the  maxillae  proper 
can  be  readily  seen  in  young  skulls,  and  occasionally 
also  in  the  adult.  It  corresponds  to  a  suture  which 
passes  on  the  palate  obliquely  outwards  and  forwards, 
from  the  anterior  palatine  foramen  to  the  interval  be- 
tween the  lateral  incisor  and  the  canine  tooth.  In  cases 
of  alveolar  cleft  palate  the  adjacent  bones  fail  to  unite 
along  the  line  of  the  suture.  In  some  instances,  however, 
the  cleft  passes  outwards  between  the  central  and  lateral  incisor  teeth,  and  this  condition 
suggests  the  explanation  that  the  premaxillary  element  is  derived  from  two  centres — a 
lateral  and  a  medial.  The  researches  of  Albrecht  and  Warinski  have  confirmed  this  view. 
The  latter  anatomist  further  observes  that  the  lateral  cleavage  may  lead  to  a  division  of  the 
dental  germ  of  the  lateral  incisor  tooth,  and  so  explain  the  occurrence  of  the  supernumer- 
ary incisor  which  is  occasionally  met  with.  In  this  way  the  different  varieties  of  cleft 
palate  are  readily  explained  ;  medial  cleft  palate  being  due  to  failure  of  union  between  the 
two  premaxillary  bones.  Lateral  cleft  palate  may  be  of  two  types :  the  cleft  in  one  case 
passing  forward  between  the  central  and  lateral  incisor,  and  being  due  to  the  non-union 


Fig.  106. 


-Ossification  of  the 
Maxilla. 


A,  Lateral  side  ;  B,  Medial  side  ;  C, 
Under  side.  «,  Nasal  process  ;  b, 
Orbital  plate  ;  c,  Anterior  nasal  spine  ; 
d.  Infraorbital  gioove  ;  e.  Infraorbital 
foramen  ;  /,  Anterior  palatine  groove  ; 
ff.  Palatal  process  ;  h,  Premaxillary 
suture  ;  i,  Alveolar  process. 


138 


OSTEOLOGY. 


of  the  two  elements  from  which  the  premaxilla  is  primarily  developed  ;  the  other,  in 
which  the  cleft  passes  between  the  lateral  incisor  and  the  canine,  or  between  the  lateral 
incisor  and  a  supernumerary  incisor,  owing  to  the  imperfect  fusion  of  the  premaxilla 
laterally  with  the  maxilla. 


The  Palate  Bones. 

The  palate  bone  (os  palatinum),  of  irregular  shape,  assists  in  the  formation  of 
the  lateral  wall  of  the  back  part  of  the  nasal  fossae,  the  posterior  portion  of  the  hard 
palate,  the  orbit,  the  pterygo-palatine  (or  spheno-maxillary),  the  infratemporal  (or 
zygomatic),  and  the  pterygoid  fossae.  It  consists  of  horizontal  and  vertical  parts, 
united  to  each  other  like  the  limbs  of  the  letter  L.  At  their  point  of  union  there 
is  an  irregular  outstanding  process,  called  the  pyramidal  process,  whilst  capping  the 
summit  of  the  vertical  plate  and  separated  by  a  deep  cleft  are  two  irregular  pieces 
of  bone,  called  the  sphenoidal  and  orbital  processes. 

The  horizontal  part  (pars  horizontalis)  has  two  surfaces  and  four  borders. 
As  its  name  implies,  it  is  horizontal  in  position,  and  forms  the  posterior  third  of 


Sphenoid 


Spheno- 
maxillary fossa 


Orbital  process 
Ethmoid 


Orbital  surface 


For  maxilla 


Orbital  process 


Orbital  surface 


Ethmoid 


Sphenoid 


Ethmoidal  crest 
Spheno-palatine  notch 


Antral  surface 


J I    Maxillary 
.Nwv^  f   l\      ',  I  reprocess 


Pterygoid  fossa 

For  external 

pterj-goid 

plate 

Pyramidal 

jirocess  /         •         . 

Surface  for  attach.     Surface     Posterior  palatine  canal 
of  pterygoideus    for  maxilla 
externus 

A 


Sphenoidal 
process 


Middle  meatus 


Nasal  crest 

Horizontal 
plate 


Inferior  meatus 


Pterygoid  fossa  j 

|\X  PjTamidal 

».'i^  process 


Posterior         Internal 
nasal  spine         pterygoid  plate 

B 


Fig.  107.— Right  Palate  Bone. 
A,  As  seen  from  the  Outer  Side  ;  B,  As  viewed  from  the  Imier  Side. 

the  hard  palate.  Its  upper  surface,  which  is  smooth,  is  slightly  concave  from  side 
to  side,  aid  forms  the  floor  of  the  hinder  part  of  the  nasal  foss^.  Its  inferior 
surface,  rougher,  is  directed  towards  the  mouth,  and  near  its  posterior  edge  often 
displays  a  transverse  ridge  for  the  attachment  of  a  part  of  the  aponeurosis  of  the 
tensor  veli  palatini  muscle.  The  anterior  border  articulates  by  means  ot  an  irregu  ai 
suture  with  the  hinder  edge  of  the  palatal  process  of  the  maxilla^  The  posterior 
margin  is  free  and  concave  from  side  to  side;  by  its  sharp  edge  it  furnishes 
attachment  to  the  aponeurosis  of  the  soft  palate.  The  medial  border  is  upturned 
and  when  it  articulates  with  its  fellow  of  the  opposite  side  it  forms  superiorly  a 
central  crest  continuous  in  front  with  the  nasal  crest  of  the  maxiUa ;  it  sup- 
ports the  hinder  part  of  the  lower  border  of  the  vomer,  and  projecting  beyond 
the  line  of  the  posterior  border  forms  the  posterior  nasal  spme  (spina  nasa  is 
posterior).  The  lateral  border  fuses  with  the  vertical  part,  forming  with  it  a  right 
angle.  The  hinder  extremity  of  this  edge  is  grooved  by  the  lower  end  of  the 
posterior  V3il3i,tme  c&ndil(  foramen  pakctimtmmajus).  -,      .    i        .u 

The  vertical  part  (pars  perpendicularis)  is  very  much  broader  below  than 
above.  Composed  of  thin  bone,  it  is  Uable  to  be  broken  in  the  process  of  disarticu- 
lation, particularly  at  its  upper  part,  so  that  it  is  somewhat  uncommon  to  meet 
with  a\.erfect  specimen,  'it  may  be  described  as  possessing  two  surfaces  and 
four  borders.  Its  medial  surface,  which  is  directed  towards  the  cavity  of  the  nose 
is  crossed  horizontally  about  its  middle  by  the  turbinated  crest  (crista  turbmalis) 


THE  PALATE  BONES. 


139 


Orbital  process 


Sphenoid 


Sphenoidal  process 

Pterygo-palatine 
groove 


Middle  meatus 


Orbital 

surface 


with  which  the  hinder  end  of  the  superior  border  of  the  inferior  turbinated  bone 
articulates ;  above  and  below  this,  it  enters  into  the  formation  of  the  lateral  wall  of 
the  middle  and  inferior  meatuses  of  the  nose  respectively.  Near  the  upper  extremity 
of  the  vertical  plate,  and  below  the  processes  which  sprin<^  from  it,  there  is  another 
ridge  more  or  less  parallel  to  that  already  described.  This  is  the  ethmoidal  crest 
crista  ethmoidalis),  and  with  this  the  hinder  extremity  of  the  middle  turbinated  bone 
is  united.  The  lateral  surface,  which  forms  the  medial  wall  of  the  pterygo-palatine  or 
spheno-maxillary  fossa,  is  channelled  by  a  vertical  groove  (sulcus  pterygo-palatinus), 
converted  into  a. canal  by  articulation  with  the  maxillary  bone.  This  canal,  called 
the  posterior  palatine  canal,  transmits  the  large  palatine  nerve  and  descending 
palatine  vessels.  Anteriorly  the  lateral  surface  projects  forwards  to  a  variable 
extent,  and  helps  to  close  in  the  antrum  of  the  maxilla  by  its  maxillary  process. 
The  anterior  border  is  a  thin  edge  of  irregular  outline  which  articulates  above 
with  the  ethmoid,  with  the  posterior  edge  of  the  maxillary  process  of  the  in- 
ferior turbinated  bone  about  its  middle,  and  below  with  the  maxilla.  The 
posterior  border,  thin  above,  where  it  articulates  with  the  fore-part  of  the  internal 
pterygoid  plate,  expands  below  into  a  pyramidal  process  called  the  tuberosity  or 
pyramidal  process.  The  inferior  border  of 
the  vertical  plate  is  confluent  with  the 
outer  edge  of  the  horizontal  plate ;  pos- 
teriorly, and  immediately  in  front  of  the 
tuberosity,  it  is  notched  by  the  lower 
extremity  of  the  posterior  palatine  canal. 
The  superior  border  supports  the  orbital 
and  sphenoidal  processes ;  the  former  — 
the  anterior — is  separated  from  the  latter 
by  a  notch  (incisura  spheno-palatina),  which 
is  converted  into  the  spheno -palatine  fora- 
men by  the  articulation  of  the  palate  bone 
with  the  under  surface  of  the  sphenoid. 
Through  this  communication  between  the 
pterygo-palatine  (spheno-maxillary)  and 
nasal  fossae  pass  the  spheno-palatine  artery 
and  the  nasal  branches  of  the  spheno- 
palatine ganglion. 

The  tuberosity  (processus  pyramid- 
alis)  is  directed  backwards  and  laterally 

from  the  angle  formed  by  the  vertical  and  horizontal  parts,  and  presents  on  its 
posterior  surface  a  central  smooth  vertical  groove,  bounded  on  either  side  by  rough 
articular  furrows  which  unite  above  in  a  V-shaped  manner  with  the  upper  thin 
posterior  edge.  These  latter  articulate  with  the  fore-parts  of  the  lower  portions  of  the 
internal  and  external  pterygoid  plates,  while  the  central  groove  fits  into  the  wedge- 
like interval  between  the  two  pterygoid  plates,  thus  entering  into  the  formation  of 
the  pterygoid  fossa.  The  lateral  surface  of  the  pyramidal  process  is  rough  above, 
where  it  is  confluent  with  the  lateral  surface  of  the  vertical  plate  which  articulates 
with  the  tuberosity  of  the  maxilla ;  below,  there  is  a  small,  smooth,  triangular 
area  which  appears  between  the  tuberosity  of  the  maxilla  and  the  lateral  surface 
of  the  external  pterygoid  plate,  and  so  enters  into  the  floor  of  the  zygomatic  fossa. 
Passing  through  the  pyramidal  process  in  a  vertical  direction  are  the  posterior  and 
lateral  accessory  palatine  canals  (foramina  palatina  minora)  for  the  transmission 
of  the  smaller  palatine  nerves  and  vessels. 

The  orbital  process  (processus  orbitalis),  shaped  like  a  hollow  cube,  surmounts 
the  fore-part  of  the  vertical  plate.  The  open  mouth  of  the  cube  is  usually  directed 
backwards  and  medially  towards  the  fore-part  of  the  body  of  the  sphenoid,  with  the 
cavity  of  which  it  commonly  communicates ;  the  fore-part  of  the  cube  articulates 
with  the  medial  end  of  the  angle  formed  by  the  orbital  plate  and  zygomatic 
surface  of  the  maxilla.  Of  the  remaining  four  surfaces,  one  directed  forwards  and 
medially  articulates  with  the  ethmoid.  The  others  are  non-articular :  the  superior 
enters  into  the  formation  of  the  floor  of  the  orbit ;  the  lateral  is  directed  towards 


Inferior  meatus 
Nasal  crest 


Posterior 
nasal 
spine 
Horizontal  plate 


For  internal  pterygoid  plate 

Fig.  108. — The  Right  Palate  Bone. 
As  seen  from  Behind. 


140  OSTEOLOGY. 

the  pterygo-palatine  fossa ;  whilst  the  inferior,  which  is  confluent  with  the  medial 
surface  of  the  vertical  part,  is  of  variable  extent,  and  overhangs  the  superior 
meatus  of  the  nose. 

The  sphenoidal  process  (processus  sphenoidalis),  much  smaller  than  the 
orbital,  curves  upwards,  medially,  and  backwards  from  the  hinder  part  of  the  summit 
of  the  vertical  plate.  Its  superior  surface,  which  is  grooved,  articulates  with  the  fore- 
part of  the  under  surface  of  the  bodj  of  the  sphenoid  and  the  root  of  the  internal 
pterygoid  plate,  thereby  converting  the  groove  into  the  pterygo-palatine  or  pharyngeal 
canal,  which  transmits  an  artery  of  the  same  name  together  with  a  pharyngeal  branch 
from  the  spheno-palatine  ganglion.  Its  lateral  side  enters  into  the  formation  of  part 
of  the  medial  wall  of  the  spheno-maxillary  fossa.  Its  medial  curved  aspect  is 
directed  towards  the  nasal  fossa,  whilst  its  medial  edge  is  in  contact  with  the  ala 
of  the  vomer. 

Connexions. — The  palate  bone  articulates  with  its  fellow  of  the  opposite  side,  with  the 
ethmoid,  vomer,  sphenoid,  maxilla,  and  inferior  turbinated  bones. 

Ossification. — The  palate  bones  are  developed  from  the  ossification  of  the  membrane 
covering  the  sides  of  the  oral  cavity.  According  to  Rambaud  and  Renault,  two  primitive 
centres  appear  about  the  sixth  week  of  foetal  life.  From  one  of  these  the  pyramidal  process 
and  the  part  of  the  vertical  part  behind  the  posterior  palatine  groove  are  developed;  from  the 
other  the  remainder  of  the  bone  is  formed,  with  the  exception  of  the  orbital  and  sphenoidal 
processes,  which  are  derived  from  secondary  centres  Avhich  make  their  appearance  some- 
what later.  Other  authorities  describe  the  bone  as  ossifying  from  a  single  centre  which 
appears  about  the  end  of  the  second  month  in  the  angle  between  the  vertical  and  hori- 
zontal parts,  the  sphenoidal  and  orbital  processes  being  outgrowths  from  the  vertical 
portion. 

At  birth  the  bone  is  much  longer  in  its  antero-posterior  diameter  than  in  its  vertical 
height,  the  converse  of  its  typical  adult  form. 

The    Zygomatic    Bones. 

The  zygomatic  or  malar  bone  (os  zygomaticum)  underlies  the  most 
prominent  part  of  the  cheek,  and  is  hence  often  called  the  cheek-bone.  Placed 
to  the  lateral  side  of  the  orbital  cavity,  it  forms  the  sharp  lateral  border  of 
that  hollow,  and  serves  to  separate  that  space  from  the  temporal  and  infra- 
temporal fossse  which  lie  behind ;  below,  it  rests  upon  and  is  united  to  the 
maxilla ;  behind,  it  enters  into  the  formation  of  the  zygomatic  arch  which  bridges 
across  the  temporal  fossa. 

As  viewed  from  the  lateral  side,  the  bone  is  convex  from  side  to  side,  and  has 
four  angles,  of  which  three  are  prominent.  These  are  the  frontal  (processus 
fronto-sphenoidalis),  the  marginal  or  pointed  extremity  of  the  maxillary  border,  and 
the  posterior  or  temporal  (processus  temporalis). 

The  most  elevated  part  of  the  convex  lateral  surface  (facias  anterior)  forms  the 
malar  tuberosity.  The  processus  temporalis,  sometimes  called  the  zygomatic  process, 
ends  posteriorly  in  an  oblique  edge,  which  articulates  with  the  extremity  of  the 
zygomatic  process  of  the  temporal  bone.  The  frontal,  the  most  prominent  of  its 
processes,  is  united  suyjeriorly  to  the  zygomatic  process  of  the  frontal  bone.  The 
edge  between  the  frontal  and  temporal  processes  is  thin  and  sharp ;  it  affords 
attachment  to  the  temporal  fascia,  and  near  its  upper  end  there  is  usually  a 
pronounced  angle  (processus  marginalis),  formed  by  a  sudden  change  in  the  direc- 
tion of  the  border  of  the  bone.  It  is  just  below  this  point  that  the  temporal 
branch  of  the  orbital  nerve  becomes  cutaneous.  The  lower  margin  of  the  temporal 
process  is  somewhat  thicker  and  rounded;  it  extends  downwards  and  forwards 
towards  the  inferior  angle,  where  tlie  bone  articulates  with  the  maxilla,  and 
is  there  confluent  with  the  ridge  which  separates  the  facial  from  the  zygomatic 
aspect  of  the  upper  jaw.  This  edge  of  the  bone  is  sometimes  called  the  masseteric 
border,  since  it  affords  attachment  to  the  flbres  of  origin  of  the  masseter  muscle. 
Sweeping  downwards  in  front  of  the  frontal  process  is  a  curved  edge  which 
terminates  inferiorly  in  a  pointed  process.  This  border  forms  the  lateral  and,  in 
part,  the  inferior  margin  of  the  orbital  cavity.     Between  the  anterior  extremity  of 


THE  ZYGOMATIC  BONES. 


141 


the  masseteric  edge  and  the  pointed  anterior  angle  there  is  an  irregular  suture  by 
which  the  bone  is  joined  to  the  maxilla.  The  opening  of  the  malar  canal  (foramen 
(zygomatico-faciale)  is  seen  on  the  lateral  surface  of  the  bone ;  its  size  and  position 
are  very  variable. 

The  medial  aspect  of  the  bone  is  distinguished  by  a  curved  elevated  crest,  called 
the  orbital  process,  which  extends  medially  and  backwards,  and  is  confluent 
laterally  with  the  orbital  margin.  This  process  has  two  surfaces — one  anterior, 
which  forms  a  part  of  the  lateral  and  lower  wall  of  the  orbit,  and  one  posterior, 


Frontal  procnss 


Frontal  process 


Temporal  border 


Temporal  canal 
Orbital  surface 


.Maxillary 
border. 


border 


Malar  canal 


For  articulation 
with  maxilla 


Orbital  process 

Temporal 

3f^^l"0cess 


lempoio- 
/j.,'onialic 
surface 


A  B 

Pig.  109.— The  Right  Zygomatic  Bone.     A,  Lateral  Side  ;  B,  Medial  Side. 

which  is  directed  towards  the  temporal  fossa  above  and  the  zygomatic  fossa  below. 
The  free  edge  of  the  orbital  process  is  thin  and  serrated  ;  a  little  below  its  middle  it 
is  usually  interrupted  by  a  non-articular  notch,  which  corresponds  to  the  anterior 
extremity  of  the  pterygo- palatine  or  spheno-maxillary  fissure.  The  part  above  this 
articulates  with  the  great  wing  of  the  sphenoid,  the  portion  below  with  the  orbital 
plate  of  the  maxilla.  Behind  the  orbital  process  the  medial  surface  of  the  bone  is 
concave  from  side  to  side,  and  extends  backwards  along  the  medial  aspect  of  the 
temporal  process  and  upwards  over  the  posterior  half  of  the  medial  side  of  the 
frontal  process,  thus  entering  into  the  formation  of  the  infra- temporal  and  temporal 
fossae  respectively.  The  orbital  surface  of  the  orbital  process  usually  displays  the 
openings  of  two  canals  (foramina  zygomatico  -  orbitalia) — one  which  traverses  the 
bone  below  the  orbital  margin  and  appears  on  the  front  of  the  bone  as  already 
described,  the  other  which  passes  obliquely  upwards  and  outwards  through  the 
orbital  process  and  appears  in  the  temporal  fossa,  to  the  medial  side  of  the  frontal 
process  (foramen  zygomatico-temporale).  The  former 
transmits  the  malar  branch,  the  latter  the  temporal 
branch  of  the  orbital  nerve. 

Below  the  orbital  process  there  is  a  rough  tri- 
angular area,  bounded  laterally  by  the  maxillary 
border.  This  articulates  with  the  zygomatic  process 
of  the  maxilla,  and  occasionally  forms  the  lateral 
wall  of  the  antrum. 

Connexions. — The  zygomatic  bone  articulates  -witli  the 
frontal,  sphenoid,  maxilla,  and  temporal  bones. 

Ossification. — The  zygomatic  ossifies  in  membrane.  Its  basis  appears  about  the  tenth 
week  as  a  thin  ossifying  lamina  which  corresponds  to  the  ox-bital  margin,  attached  to 
which  there  is  a  backward  expansion  con-esponding  to  the  body  of  the  bone ;  from  this 
posteriorly  there  extends  the  element  of  the  temporal  process.  On  the  medial  side,  and 
above  the  angle  formed  by  the  orbital  and  temporal  margins,  there  appears  a  secondary 
thickening,  which  develops  into  a  cap-shaped  layer  which  fits  into  the  recess  and 
ultimately  forms  the  surface  of  the  bone  directed  to  the  temporal  fossa.  Below 
the  orbital  margin  on  the  medial  side,  and  extending  backwards  towards  the  temporal 
process,  is  another  secondary  thickening,  which  forms  a  club-shaped  nodule,  the  thick 
end  of  which  is  directed  forwards,  whilst  posteriorly  it  forms,  in  part,  the  lower  margin 


Club-shaped  process 
Fig.  110. — Medial  Surface  of  the 
Zygomatic  Bone  at  Birth. 


142 


OSTEOLOGY. 


of  the  body  and  temporal  process.  The  overlap  of  these  several  parts  leads  to  the 
formation  of  grooves  which  may  persist  in  the  adult  as  sutures.  (Karl  Toldt,  junr., 
Sitzsbr.  des  Alad.  des  Wiss.,  Wien,  July  1902.) 


The  IVIandible. 

The  mandible  or  lower  jaw  bone,  of  horse-shoe  shape,  with  the  extremities 
upturned,  is  the  only  movable  bone  of  the  face.  Stout  and  strong,  it  supports 
the  teeth  of  the  lower  dental  arch,  and  articulates  with  the  base  of  the  cranium,, 
by  the  joints,  on  either  side,  between  its  condyles  and  the  glenoid  fossae  of  the 
temporal  bones.  The  anterior  or  horizontal  part,  which  contains  the  teeth,  is 
called  the  body  (corpus) ;  the  posterior  or  vertical  portions  constitute  the  rami 
(rami  mandibulae). 

The  body  (corpus  mandibulae)  displays  in  the  middle  line  in  front  a  faint 
vertical  ridge,  the  symphysis,  which  indicates  the  line  of  fusion  of  the  two 
symmetrical  halves  from  which  the  bone  is  ^ 

primarily  developed.  Inferiorly  this  ridge 
divides  so  as  to  enclose,  in  well-marked 
specimens,  a  triangular  area — the  mental 
protuberance  (protuberantia  mentalis),  the  centre 
of  which  is  somewhat  depressed,  thus  em- 
phasising the  inferior  angles,  which  are  known 
as  the  mental  tubercles  (tubera  mentalia).  The 
lateral  surface,  is  crossed  by  a  faint,  elevated 
ridge,  the  oblique  line  (linea  obliqua),  which 
runs  upwards  and  backwards  from  the  mental 
tubercle  to  the  fore-part  of  the  anterior  border 
of  the  ramus,  with 
which  it  is  conflu- 
ent. From  this 
ridge  arise  the  m. 
quadratus  labii  in- 
ferioris  and  the  tri- 
angvdar  muscles. 
A  little  above  this, 
midway  between 
the  upper  and 
lower  borders  of 
the  jaw,  and  in 
line  with  the  root  ^ 
of  the  second  bi- 
cuspid tooth,  the 
bone  is  pierced  by 
the  mental  fora- 
men (foramen  men- 
tale)  ;  this  is  the  anterior  opening  of  the  inferior  dental  canal,  which  traverses  the 
body  of  the  bone.  Through  this  aperture  the  mental  vessels  and  nerves  reach  the 
surface.  The  upper  border  supports  the  sixteen  teeth  of  the  lower  jaw.  It  is  thick 
behind  and  thinner  in  front,  in  correspondence  with  the  size  of  the  roots  of  the 
teeth.  Anteriorly  the  sockets  of  the  incisor  and  canine  teeth  produce  a  series  of 
vertical  elevations  (juga  alveolaria),  of  which  that  corresponding  to  the  canine  tooth 
is  the  most  prominent.  When  this  is  outstanding  it  gives  rise  to  a  hollowing  of  the 
surface  between  it  and  the  symphysis,  often  referred  to  as  the  incisor  fossa;  frequently, 
however,  this  is  only  faintly  marked.  Below  the  oblique  line  the  bone  is  full  and 
rounded,  and  ends  below  in  the  inferior  border  or  base.  This  slopes  laterally  at 
the  sides,  and  forwards  in  front,  where  it  yi  thick  and  hollowed  out  on  either  side 
of  the  symphysis  to  form  the  digastric  fossae  (fossae  digastricse),  to  which  the 
anterior  bellies  of  the  digastric  muscles  are  attached ;  narrowing  somewhat  behind 


Fig.  Ilia.— The  Mandible  as  seen  from  the  Left  Side. 


1.  Mental  tubercle. 

2.  Mental  promiuence. 

3.  Symijhysis. 


4.  Coronoid  pirocess. 

5.  Condyles. 

6.  Neck. 


7.  Angle. 

8.  Obliqne  line.  ' 

9.  Mental  foramen. 


THE  MANDIBLE. 


143 


this,  the  inferior  border  again  expands  opposite  the  molar  teeth,  and  finally 
becoming  reduced  in  width,  terminates  posteriorly  at  the  angle  formed  between  it 
and  the  posterior  border  of  the  ramus.  The  medial  surface  of  the  body  is  crossed 
by  the  mylo-hyoid  line  (linea  mylo-hyoidea).  This  slants  from  above  downwards 
and  forwards  towards  the  lower  part  of  the  symphysis.  It  serves  for  the  origin 
of  the  mylo-hyoid  muscle,  and  also  furnishes  an  attachment  to  the  superior 
constrictor  of  the  pharynx  just  behind  the  last  molar  tooth.  Below  the  hinder 
part  of  this  ridge  the  surface  is  hollowed  to  form  a  fossa  for  the  lodgment  of  the 
submaxillary  gland.  Above  the  fore-part  of  the  mylo-hyoid  line  the  bone  is 
smooth  and  usually  convex.  Here  the  sublingual  gland  lies  in  relation  to  it. 
In  the  angle  formed  by  the  convergence  of  the  two  mylo-hyoid  Lines,  and  in 
correspondence  with  the  back  of  the  lower  part  of  the  symphysis,  there  is  a  raised 
tubercle  surmounted  by  two  laterally  placed  spines,  the  mental  spines  (spinse 
mentales).  Occasionally  these  are  again  subdivided 
into  an  upper  and  lower  pair,  or  it  may  be  that  the 
lower  pair  may  fuse  to  form  a  rough  median  ridge. 
To  the  upper  pair  of  spines  the  genio-glossi  muscles 
are  attached,  whilst  the  lower  pair  serve  for  the 
origin  of  the  genio-hyoid  muscles.  Immediately 
above  the  tubercle  there  is  a  median  foramen  for 
the  transmission  of  a  nutrient  vessel,  and  close 
to  the  alveolar  border  opposite  the  intervals  be- 
tween the  central  and  lateral  incisors,  there  are 
two  little  vascular  canals. 

The  ramus  (ramus  mandibulae)  passes  up- 
wards from  the 
back  part  of  the 
bone,  forming  by 
the  junction  of  its 
posterior  border 
with  the  base  of 
the  body  the  angle 
(angulus  mandi- 
bulse),  which  is 
usually  rounded 
and  more  or  less 
everted.  The  outer 
surface  of  the 
ramus  affords  at- 
tachment to  the 
masseter  muscle, 
and  when  that 
muscle  is  power- 
fully developed 

the  bone  is  usually  marked  by  a  series  of  oblique  curved  ridges,  best  seen 
towards  the  angle.  About  the  middle  of  the  deep  or  medial  surface  is  the 
large  opening  (foramen  mandibulare)  of  the  inferior  dental  canal,  which  runs  down- 
wards and  forwards  to  reach  the  body,  and  transmits  the  inferior  dental  vessels 
and  nerves.  This  aperture  is  overhung  in  front  by  a  pointed  scale  of  bone,  the 
lingula,  to  the  edges  of  which  the  spheno-mandibular  Ligament  of  the  temporo- 
maxillary  articulation  is  attached.  Behind  the  lingula  and  leading  downwards 
and  forwards  for  an  inch  or  so  from  the  opening  of  the  inferior  dental  canal 
is  the  mylo-hyoid  groove  (sulcus  mylo-hyoideus),  along  which  the  mylo-hyoid  artery 
and  nerve  pass.  Behind  and  below  this  groove  the  medial  surface  of  the  angle  is 
rough  for  the  attachment  of  the  internal  pterygoid  muscle.  Superiorly  the  ramus 
supports  the  coronoid  process  in  front,  and  the  condyle  behind,  the  two  being 
separated  by  the  wide  sigmoid  notch  (incisura  mandibulse),  over  which  there  pass 
in  the  recent  condition  the  vessels  and  nerve  to  the  masseter  muscle.  The 
coronoid  process,  of  variable  length  and  beak-shaped,  is  limited  behind  by  a  thin 


Fig.  1116. — The  Medial  Side  of  the  PiIght  Half  of  the  JMandible. 


1. 

2. 

Mental  spines. 
Surface    in    relation   to 

5. 
6. 

Coronoid  process. 
Condyles. 

10. 

Fossa  for  submaxillary 
gland. 

3. 
4. 

the  sublingual  gland. 
Alveolar  border. 
Lingula. 

7. 
8. 
9. 

Mandibular  foramen. 
M^lo-hyoid  groove. 

Angle. 

11. 
12. 

Mylo-hyoid  line. 
Digastric  fossa. 

144 


OSTEOLOGY. 


curved  margin,  which  forms  the  anterior  boundary  of  the  mandibular  notch.  In 
front  its  anterior  edge  is  convex  from  above  downwards  and  forwards,  and  becomes 
confluent  below  with  the  anterior  border  of  the  ramus  and  the  oblique  line. 
To  the  medial  side  of  this  edge  there  is  a  grooved  elongated  triangular  surface, 
the  medial  margin  of  which,  commencing  above  near  the  summit  of  the  coronoid 
process,  leads  downwards  along  the  medial  side  of  the  root  of  the  last  molar  tooth 
towards  the  mylo-hyoid  line.  Behind  this  ridge  the  thickness  of  the  ramus 
is  much  reduced.  The  temporal  muscle  is  inserted  into  the  margins  and  medial 
surface  of  the  coronoid  process.  The  posterior  border  of  the  ramus  is  continued 
upwards  to  support  the  condyle  (capitulum  mandibulse),  below  which  it  is  some- 
what constricted  to  form  the  neck  (collum  mandibulse),  which  is  compressed  from 
before  backwards,  and  bounds  the  mandibular  notch  posteriorly.  To  the  medial  side 
of  the  neck,  immediately  below  the  condyle,  there  is  a  little  depression  (fovea  ptery- 
goidea)  for  the  insertion  of  the  external  pterygoid  muscle.      The  convex  surface  of 

the  condyle  is  trans- 
6  i^h  versely     elongated, 

and  so  disposed  that 
its  long  axis  is  in- 
clined nearly  hori- 
zontally from  within 
laterally  and  a  little 
forwards.  The  con- 
vexity of  the  con- 
dyle is  more  marked 
in  its  antero-pos- 
terior  than  in  its 
transverse  diameter, 
and  tends  slightly 
to  overhang  the 
sigmoid  notch.  The 
medial  and  lateral 
ends  of  the  condyle 
terminate  in  tuber- 
cles which  serve  for 
the  attachment  of 
the  capsular  liga- 
ments of  the  joint. 

Ossification.  — 

The  development  of 
the  mandible  is  intimately  associated  with  Meckel's  cartilage,  the  cartilao-inous  bar 
of  the  first  visceral  or  mandibular  arch.  Meckel's  cartilages,  of  which  ''there  are 
two,  are  connected  proximally  with  the  periotic  capsule  and  cranial  base.  Their 
distal  ends  ai-e  united  in  the  region  of  the  symphysis.  It  is  in  the  connective  tissue 
overlying  the  lateral  surface  of  this  cartilaginous  arch  that  the  bulk  of  the  lower  jaw 
is  developed.  The  cartilage  itself  is  not  converted  into  bone,  but  undergoes  resorption, 
except  its  anterior  extremity,  which  is  stated  to  undergo  ossification  to  form  the 
part  of  the  jaw  lying  between  the  mental  foramen  and  the  symjjhysis.  In  a  third  or 
fourth  month  foetus  the  cartilage  can  be  traced  from  the  under  surface  of  the  fore-part 
of  the  tympanic  ring  downwards  and  forwards  to  reach  the  jaw,  to  which  it  is  attached 
at  the  opening  of  the  mandibular  canal ;  from  this  it  may  be  traced  forwards  as  a 
narrow  strip  applied  to  the  medial  surface  of  the  mandible,  which  it  sensibly  grooves. 
The  proximal  end  of  this  furrow  remains  permanently  as  the  mylo-hyoid  groove.  The 
part  of  the  cartilage  between  the  tympanic  ring  and  the  jaw  becomes  converted  into 
fibrous  tissue,  and  persists  in  the  adult  as  the  so-called  internal  lateral  (spheno-mandibular) 
ligament  of  the  temporo-maxillary  articulation,  its  proximal  end  through  the  Glaserian 
fissure  being  continuous  with  the  slender  process  of  the  malleus,  with  the  development  of 
which  bone  it  is  intimately  associated.  J.  Chaine  {Comptes  Rendus,  Biologic,  1903)  takes 
exception  to  this  view  and  regards  the  spheno-mandibular  ligament  as  the  remnant  of  a 
muscular  slip.  The  part  wliich  is  applied  to  the  medial  surface  of  the  lower  jaw  dis- 
appears.    In  the  tissue  overlying  the  cartilage  ossification  begins  by  several  centres  as 


Fig. 


B  C 

112. — The  Mandible  at  Birth.     A,  As  seen  from  above 
Lateral  side  :  C,  Medial  side. 


Mental  foramen 


h,  Mandibular  (inferior  dental)  canal 
d,  Sockets  for  the  dental  sacs. 


Lingula 


THE  HYOID  BONE.  145 

early  as  the  sixth  or  seventh  week  of  foetal  life,  in  this  respect  resembling  the  clavicle,  by 
which  it  is  alone  preceded.  The  dentary  or  basal  centre  forms  the  lateral  wall  and  lower 
border.  With  this  is  nnited  the  splenial  portion,  which  appears  somewhat  later,  forming 
the  medial  table  from  near  the  symphysis  backwards  towards  the  opening  of  the  mandibular 
canal  where  it  terminates  in  the  lingula.  By  the  union  of  these  two  parts  a  groove 
is  formed,  which  ultimately  becomes  covered  in,  and  in  which  the  inferior  dental  nerve 
and  vessels  are  lodged.  As  has  been  already  stated,  the  part  of  the  body  between  the 
symphysis  and  the  mental  foramen  is  regarded  as  directly  developed  by  the  ossification  of 
the  forepart  of  the  Meckelian  cartilage.  As  will  have  been  gathered  from  the  above 
description,  the  upper  part  of  the  ramus  and  its  processes  have  no  connexion  with  Meckel's 
cartilage.  The  condyle  and  the  coronoid  process  are  each  developed  from  a  separate 
centre,  preceded  by  a  cartilaginous  matrix.  These  several  centres  are  all  united  about  the 
fourth  month. 

At  birth  the  mandible  consists  of  two  lateral  halves  united  at  the  symphysis  by  fibrous 
tissue ;  towards  the  end  of  the  first,  or  during  the  second  year,  osseous  union  between  the 
two  halves  is  complete.  In  infancy  the  jaw  is  shallow  and  the  rami  proportionately  small; 
further,  owing  to  the  obliquity  of  the  ramus  the  angle  is  large,  averaging  about  150*. 
The  mental  foi'amen  lies  near  the  lower  border  of  the  bone.  Coincident  with  the  eruption 
of  the  teeth  and  the  use  of  the  jaw  in  mastication,  the  rami  rapidly  increase  in  size,  and 
the  angle  becomes  more  acute.  After  the  completion  of  the  permanent  dentition  it 
approaches  more  nearly  a  right  angle  varying  from  110°  to  120°.  The  body  of  the  bone 
is  stout  and  deep,  and  the  mental  foramen  usually  lies  midway  between  the  iipper  and 
lower  borders.  As  age  advances,  owing  to  the  loss  of  the  teeth  and  the  consequent 
shrinkage  and  absorption  of  the  alveolar  border  of  the  bone,  the  body  becomes  narrow  and 
attenuated,  and  the  mental  foramen  now  lies  close  to  the  upper  border.  At  the  same  time 
the  angle  opens  out  again  (130°  to  140°),  in  this  respect  resembling  the  infantile  condition. 
In  old  age  the  coronoid  process  and  the  condyle  form  a  more  open  angle  with  each  other 
than  in  the  adult. 

The  Hyoid  Bone. 

The  hyoid  bone  (os  hyoideum),  though  placed  in  the  neck,  is  development- 
ally  connected  with  the  skull.  It  lies  between  the  mandible  above,  and  the 
larynx  below,  and  is  connected  with  the  root  of  the  tongue.  Of  U-shaped  form, 
as  its  name  implies  (Greek  v  and  efSos,  like),  it  consists  in  the  adult  of  a 
central  part,  or  body,  with  which  on  either  side  are  united  two  long  processes 
extending  backwards — the  great  cornua.  At  the  point  where  these  are  ossified 
with  the  body,  the  lesser  cornua,  which  project  up- 
wards and  backwards,  are  placed. 

The  body  (basis)  is  arched  from  side  to  side 

and  compressed  from  before  backwards,  so  that  its 

surfaces    slope    downwards   and    forwards.       Its 

anterior  surface  displays  a  slight  median  ridge,  on 

either  side  of  which  the  bone  is  marked  by  the 

attachment    of    the    mylo  -  hyoid    muscles.      Its 

posterior  surface,  deeply  hollowed,  is  concave  from 

side  to  side  and  from  above  downwards.     Herein 

lie  a  quantity  of  fat  and  a  bursa  which  separates    _      -no     m      u         t> 

^-  .       1  „'^         ,        ,  ,        -1  1  mi         Fig.  113.— The  Hyoid  Bone  as  seen 

this  aspect  irom  the  thyreo-hyoid  membrane.     Ihe  from  the  Front. 

upper  border,  usually  described  with  the  anterior 

surface,  is  broad ;   it  is  separated  from  the  anterior  aspect  by  a  transverse  ridge, 

behind  which  are  the  impressions  for  the  attachment  of  the  genio-hyoid  muscles. 

Its  hinder  edge  is  thin  and  sharp ;   to  this,  above,  are  attached  the  genio-giossi, 

whilst  behind  and  below  the  thyreo-hyoid  membrane  is  connected  with  it.     The 

inferior  border  is  well  defined  and  narrow ;    it  serves  for  the  attachment  of  the 

omo-hyoid,  sterno-hyoid,  thyreo-hyoid,  and  stylo-hyoid  muscles. 

The  great  cornua  are  connected  on  either  side  with  the  lateral  parts  of  the 

body.     At  first,  union  is  effected  by  synchondroses,  which,  however,  ultimately 

ossify.     These  cornua  curve  backwards  as  well  as  upwards,  and  terminate  in  more  or 

less  rounded  and  expanded  extremities.     Compressed  laterally,  they  serve  for  the 

attachments  laterally  of  the  thyreo-hyoid  and  hyo-glossi  muscles,  and  the  middle 


146  OSTEOLOGY. 

constrictor  of  the  pharynx  from  below  upwards,  whilst  medially  they  are  con- 
nected with  the  lateral  expansions  of  the  thyreo-hyoid  membrane,  the  free  edges  of 
which  are  somewhat  thickened,  and  connect  the  extremities  of  the  great  cornua 
with  the  ends  of  the  superior  cornua  of  the  thyreoid  cartilage  below. 

The  lesser  cornua,  frequently  cartilaginous  in  part,  are  about  the  size  of  grains 
of  wheat.  They  rest  upon  the  upper  surface  of  the  bone  at  the  junctions  of  the 
great  cornua  with  the  body.  In  youth  they  are  separated  from,  but  in  advanced 
life  become  ossified  with,  the  rest  of  the  bone,  from  which  they  are  directed  upwards, 
backwards,  and  a  little  outwards.  Their  summits  are  connected  with  the  stylo- 
hyoid ligaments ;  they  also  serve  for  the  attachment  of  muscles. 

Connexions. — The  hyoid  is  slung  from  the  styloid  processes  of  the  temporal  bones  by  the 
stylo-hyoid  ligaments.  Inferioiiy  it  is  connected  with  the  thyreoid  cartilage  of  the  larynx  by 
the  thyreo-hyoid  ligaments  and  membrane.  Posteriorly  it  is  intimately  associated  with  the 
epiglottis. 

Ossification. — In  considering  the  development  of  the  hyoid  bone  it  is  necessary  to  refer 
to  the  arrangement  and  disposition  of  the  cartilaginous  bars  of  the  second  and  third  visceral 
arches.  That  of  the  second  visceral  arch,  the  hyoid  bar — or  Reichert's  cartilage,  as  it  is 
sometimes  called — is  united  above  to  the  petrous  part  of  the  temporal,  whilst  ventrally  it  is 
joined  to  its  fellow  of  the  opposite  side  by  an  independent  medial  cartilage.  Chondrifica- 
tion  of  the  third  visceral  arch  only  occurs  towards  its  ventral  extremity,  forming  what  is 
known  as  the  thyreo-hyoid  bar.  This  also  unites  with  the  medial  cartilage  above  mentioned. 
In  these  cartilaginous  processes  ossific  centres  appear  in  certain  definite  situations. 
Towards  the  end  of  foetal  life  a  single  centre  (by  some  authorities  regarded  as  primarily 
double)  appears  in  the  medial  cartilage,  and  forms  the  body  of  the  bone  (basihyal). 
About  the  same  time  ossification  begins  in  the  lower  ends  of  the  thyreo-hyoid  bars,  and 
from  these  the  great  cornua  are  developed  (thyreo-hyals).  During  the  first  year  the  lower 
ends  of  the  hyoid  bars  begin  to  ossify  and  form  the  lesser  cornua  (cerato-hyals).  The 
cephalic  ends  of  the  same  cartilages  meanwhile  ossify  to  form  the  styloid  process 
(stylohyal ;  see  p.  120)  on  either  side  and  one  of  the  auditory  ossicles  called  the 
stapes,  whilst  the  intervening  portions  of  cartilage  undergo  resorption  and  become 
converted  into  the  fibrous  tissue  of  the  stylo-hyoid  ligaments,  which  in  the  adult 
connect  the  lesser  cornua  with  the  styloid  processes  of  the  temporal  bone.  The  great 
cornua  fuse  with  the  body  in  middle  life ;  the  lesser  cornua  only  at  a  more  advanced 
period.  Variations  in  the  course  of  development  lead  to  interesting  anomalies  of  the 
hyoid  apparatus.  The  lesser  cornua  may  be  unduly  long  or  the  stylo-hyoid  ligament  may 
be  bony  ;  in  this  case  the  cartilage  has  not  undergone  resorption,  but  has  passed  on  to  the 
further  stage  of  ossification,  thus  forming  an  epihyal  element  comparable  to  that  in  the 
dog.  The  ossified  stylo-hyoid  ligament,  as  felt  through  the  pharyngeal  wall,  may  be 
mistaken  for  a  foreign  body.     (Farmer,  G.  W.  S.,  Brit.  Med.  Journ.  1900,  vol.  i.  p.  1405.) 


THE    SKULL    AS    A    WHOLE. 

The  skull  as  a  whole  may  be  studied  as  seen  from  the  front  (norma  frontalis), 
from  the  side  (norma  lateralis),  from  the  back  (norma  occipitalis),  from  above 
(norma  verticalis),  and  from  below  (norma  basalis). 

Norma  Frontalis. 

In  front,  the  smooth  convexity  of  the  frontal  bone  limits  this  region  above, 
whilst  inferiorly,  when  the  lower  jaw  is  disarticulated,  the  teeth  of  the  upper  jaw 
form  its  lower  boundary.  The  large  openings  of  the  orbits  are  seen  on  either  side ; 
whilst  placed  medially  and  at  a  somewhat  lower  level  is  the  anterior  nasal  aperture 
(apertura  pyriformis)  leading  into  the  nasal  fossae. 

The  frontal  region,  convex  from  above  downwards  and  from  side  to  side,  is 
limited  laterally  by  two  ridges,  which  are  the  anterior  extremities  of  the  temporal 
lines.  Superiorly  the  fulness  of  the  bone  blends  with  the  convexity  of  the  vertex. 
Inferiorly  the  frontal  bone  forms  on  either  side  the  arched  superior  border  of  the 
orbit  (margo  supraorbitalis).  The  space  between  these  borders  corresponds  to  the 
root  of  the  nose,  and  here  are  seen  the  sutures  which  unite  the  frontal  with  the 
nasal  bones  in  the  middle  line,  and  with  the  frontal  process  of  the  maxilla  on 


NOEMA  FRONTALIS  OF  THE  SKULL.  147 

either  side,  called  the  naso-frontal  and  fronto-maxillary  sutures  respectively.  The 
orbital  arch  is  thin  and  sharp  laterally,  but  becomes  thick  and  more  rounded 
towards  its  medial  side,  wliere  it  forms  the  medial  angular  process  and  unites 
with  the  frontal  process  of  the  maxilla  and  the  lacrimal  bone  on  the  medial 
wall  of  the  orbit.  This  arched  border  is  interrupted  towards  the  medial  side  by 
a  notch  (incisura  supraorbitalis),  sometimes  converted  into  a  foramen,  for  the 
transmission  of  the  supraorbital  nerve  and  artery.  In  the  middle  line,  just  above 
the  naso-frontal  suture,  there  is  often  the  remains  of  a  median  suture  (sutura 
frontalis),  which  marks  the  fusion  of  the  two  halves  from  which  the  bone  is 
primarily  ossified.  Here  also  a  prominence,  of  variable  extent — the  glabella — is  met 
with ;  from  this  there  passes  out  on  either  side  above  and  over  the  orbital  margin 
a  projection  called  the  superciliary  ridge  (arcus  superciliaris). 

The  orbital  fossae,  of  more  or  less  conical  form,  display  a  tendency  to  assume 
the  shape  of  four-sided  pyramids  by  the  flattening  of  the  superior,  inferior,  and 
lateral  walls.  The  base,  which  is  directed  forwards  and  a  little  laterally, 
corresponds  to  the  orbital  aperture.  The  shape  of  this  is  liable  to  individual  and 
racial  variations,  being  nearly  circular  in  the  Mongoloid  type,  whilst  it  displays  a 
more  or  less  quadrangular  form  in  Australoid  skulls.  The  upper  margin,  as  has 
been  already  stated,  is  formed  by  the  frontal  bone  between  the  medial  and  lateral 
angular  processes.  The  lateral,  and  about  half  the  lower,  margins  are  formed  by  the 
sharp  curved  edge  between  the  facial  and  orbital  surfaces  of  the  malar  bone.  The 
medial  border  and  the  remainder  of  the  lower  margin  are  determined  by  the 
lateral  surface  of  the  frontal  process  of  the  maxilla,  and  the  sharp  edge  separating 
the  facial  from  the  orbital  surface  of  the  same  bone.  Three  sutures  interrupt  the 
continuity  of  the  orbital  margin — zygomatico-frontal  laterally,  the  fronto-maxillary 
medially,  both  lying  about  the  same  level,  and  the  zygomatico-maxillary  inferiorly. 
The  apex  of  the  space  is  directed  backwards  and  medially,  so  that  the  medial 
walls  of  the  two  orbits  lie  nearly  parallel  to  each  other,  whilst  the  lateral  walls 
are  so  disposed  as  to  form  almost  a  right  angle  with  each  other.  The  depth  of  the 
orbit  measures,  on  an  average,  about  two  inches  (5  cm.).  At  the  apex  there  are 
two  openings ;  the  larger,  known  as  the  sphenoidal  fissure  (fissura  orbitalis  superior), 
passes  from  the  apex  of  the  space  laterally  and  a  little  upwards  for  the  distance 
of  three-quarters  of  an  inch  or  so,  between  the  roof  and  lateral  wall  of  the  orbit.  The 
medial  third  of  this  fissure  is  broad  and  of  circular  form.  Laterally  it  is  consider- 
ably reduced  in  width.  Through  this  the  third,  fourth,  ophthalmic  division  of  the 
fifth,  and  the  sixth  nerves  enter  the  orbit,  whilst  the  ophthalmic  veins  pass 
backwards  through  it.  Above  and  medial  to  the  medial  end  of  the  sphenoidal 
fissure  there  is  a  smaller  circular  opening,  the  optic  foramen  (foramen  opticum),  for 
the  transmission  of  the  optic  nerve  and  ophthalmic  artery. 

The  roof  of  the  orbit,  which  is  very  thin  and  brittle  towards  its  centre,  is  formed 
in  front  by  the  orbital  plate  of  the  frontal  bone  (pars  orbitalis)  and  behind  by  a 
small  triangular  piece  of  the  lesser  wing  of  the  sphenoid,  which  surrounds  the 
optic  foramen  and  forms  the  upper  border  of  the  sphenoidal  fissure.  Laterally 
this  surface  is  separated  from  the  lateral  wall  by  the  sphenoidal  fissure  posteriorly, 
anteriorly  by  an  irregular  suture  between  the  orbital  part  of  the  frontal  and 
the  upper  margin  of  the  orbital  surface  of  the  great  wing  of  the  sphenoid, 
lateral  to  which  the  zygomatic  process  of  the  frontal  articulates  with  the  zygo- 
matic bone.  Medially  the  roof  is  marked  off  from  the  medial  wall  by  a  suture, 
more  or  less  horizontal  in  direction,  between  the  orbital  plate  of  the  frontal  and 
the  following  bones  in  order  from  before  backwards,  viz.  the  frontal  process  of 
the  maxilla,  the  lacrimal  bone,  and  the  os  planum  of  the  ethmoid.  In  the 
suture  between  the  last-mentioned  bone  and  the  frontal  there  are  two  foramina, 
the  anterior  and  posterior  ethmoidal  canals  (foramen  ethmoidale  anterius  et 
posterius) ;  both  transmit  ethmoidal  vessels — the  anterior  affording  passage  to 
the  nasal  nerve  as  well.  The  roof  is  concave  from  side  to  side,  and  to  some 
extent  also  from  before  backwards.  About  midway  between  the  fronto- 
maxillary  suture  and  the  supraorbital  notch  or  foramen,  but  within  the 
margin  of  the  orbit,  there  is  a  small  depression,  occasionally  replaced  by  a  spine 
(fovea  vel,   spina   trochlearis),  for    the    attachment    of    the    cartilaginous    pulley 


148  OSTEOLOGY. 

of  tlie  superior  oblique  muscle  of  the  eyeball.     Under  cover  of  the  zygomatic 


The 


Fio.  114. — Norma  Fuoxtalis  uf  the  Skull. 
nasal   Vjones,  os   planum   of  the   ethmoid,  vomer,  inferior  turbinals,  zygomatic,  and  parietal  bones  are 
coloured  red.       The  sphenoid,   lacrimal,   perpendicular  plate  and  middle  turbinals  of  ethmoid,  and  the 
maxilla,  are  coloured  l)lue.     The  maxilla;  are  coloured  yellow.     The  frontal  and  temporal  bones  aud  the 
orbital  process  of  the  palate  bone  (in  the  orbit  on  the  left  side  of  the  figure)  are  left  uncoloured. 


9. 
10. 
11. 
12. 
13. 


Mental  protuberance. 
Body  of  lower  jaw. 
Ramus  of  lower  jaw. 
Anterior  nasal  spine. 
Canine  fossa. 
Infraorbital  canal. 
Zygomatic  canal. 
Orbital  surface  of  maxilla. 
Temporal  fossa. 
Os  planum  of  ethmoid. 
Sphenoidal  fissure. 
Lacrimal  bone  and  groove. 
Optic  foramen. 


14.  Orbital  canals. 

15.  Temporal  ridge. 

16.  Supraorbital  notch. 

17.  Glabella. 

18.  P'lontal  eminence. 

19.  Superciliary  ridge. 

20.  Parietal  bone. 

21.  Pronto-nasal  suture. 

22.  Pterion. 

23.  Great  wing  of  sphenoid. 

24.  Orbital  surface  of  great  wing 

of  sphenoid. 

25.  Squamous partofthetemporal. 


26.  Left  nasal  bone. 

27.  Zygomatic  bone. 

28.  S])heno-maxillary  fissure. 

29.  Zygomatic  arch. 

30.  Anterior  nasal  aperture,  displaying 

nasal    septum    and    inferior    and 
middle  turbinated  bones. 

31.  Mastoid  process. 

32.  Incisor  fossa. 

33.  Angle  of  jaw. 

34.  Mental  foramen. 

35.  Symphysis  menti. 


process  the  roof  is  more  deeply  excavated,  forming  a  shallow  fossa  for  the  lodg- 


NOEMA  FEONTALIS  OF  THE  SKULL.  149 

ment  of  the  lacrimal  gland  (fossa  glandulae  lacrimalis).  In  front,  the  roof 
separates  the  orbit  from  the  frontal  sinus,  and  along  its  medial  border  it  is  in 
relation  with  the  ethmoidal  air-cells.  The  relation  to  these  air  spaces  is  variable, 
depending  on  the  development  and  size  of  the  sinuses.  The  rest  of  the  roof,  which 
is  very  thin,  forms  by  its  upper  surface  the  floor  of  the  anterior  cranial  fossa,  in 
which  are  lodged  the  frontal  lobes  of  the  cerebrum. 

The  floor  of  the  orbit  is  formed  by  the  orbital  plate  of  the  maxilla,  together 
with  part  of  the  orbital  surface  of  the  zygomatic  bone,  and  a  small  triangular 
piece  of  bone,  the  orbital  process  of  the  palate,  which  is  wedged  in  posteriorly. 
Laterally,  for  three-quarters  of  its  length  posteriorly,  it  is  separated  from  the  lateral 
wall,  which  is  here  formed  by  the  great  wing  of  the  sphenoid,  by  a  cleft  called  the 
spbeno  -  maxillary  fissure  (fissura  orbitalis  inferior).  Through  this  there  pass  the 
superior  maxillary  division  of  the  fifth  nerve  on  its  way  to  the  infraorbital  canal, 
the  orbital  or  temporo-malar  branch  of  the  same  nerve,  the  infraorbital  vessels, 
a  branch  connecting  the  inferior  ophthalmic  vein  with  the  pterygoid  plexus,  and 
some  twigs  from  Meckel's  (spheno-palatine)  ganglion.  By  means  of  this  fissure 
the  orbit  communicates  with  the  spheno- maxillary  (or  pterygo- palatine)  fossa 
behind,  and  the  infra-temporal  (or  zygomatic)  fossa  to  the  lateral  side,  though  in 
the  recent  condition  the  fissure  is  bridged  over  by  the  involuntary  orbitalis  muscle 
of  Mliller.  Medially  the  floor  is  limited  from  behind  forwards  by  the  suture 
between  the  following  bones,  viz.  the  orbital  process  of  the  palate  below  with 
the  body  of  the  sphenoid  above  and  behind,  and  the  os  planum  of  the  ethmoid 
above  and  in  front — anterior  to  which  the  orbital  plate  of  the  maxilla  below 
articulates  with  the  os  planum  of  the  ethmoid  and  the  lacrimal  above  and  in 
front.  At  the  anterior  extremity  of  this  line  of  sutures  the  medial  edge  of  the 
orbital  plate  of  the  maxilla  is  notched  and  free  between  the  point  where  it 
articulates  :with  the  lacrimal  posteriorly  and  the  part  from  which  its  frontal 
process  rises.  Here  it  forms  the  lateral  edge  of  a  canal,  down  which  the  mem- 
branous nasal  duct  passes  to  the  nose.  The  floor  of  the  orbit  is  thin  behind  and 
at  the  sides,  but  thicker  in  front  where  it  blends  with  the  orbital  margin. 
Passing  in  a  sagittal  direction  through  its  substance  is  the  infraorbital  canal,  the 
roof  of  which  is  usually  deficient  behind,  where  it  becomes  continuous  with  a 
broad,  shallow  groove,  which  leads  forwards  from  the  anterior  margin  of  the 
spheno-maxillary  fissure.  This  canal  (canalis  infraorbitalis)  opens  on  the  facial 
surface  of  the  maxilla  immediately  below  the  orbital  margin  (foramen  infraorbitale) 
and  transmits  the  superior  maxillary  division  of  the  fifth  nerve,  together  with  the 
infraorbital  vessels.  The  floor  forms  a  thin  partition  which  separates  the  orbit  from 
the  antrum  or  sinus  of  the  maxilla,  which  lies  beneath  it.  Medially  it  completes 
the  lower  ethmoidal  air-cells,  and  separates  the  orbit  from  the  middle  meatus  of  the 
nasal  fossae. 

The  lateral  wall  of  the  orbit,  which  is  the  strongest,  is  formed  by  the  orbital 
surface  of  the  great  wing  of  the  sphenoid  and  the  upper  part  of  the  orbital  surface 
of  the  zygomatic  bone.  Above  it,  behind,  is  the  sphenoidal  fissure  (superior 
orbital  fissure),  whilst  below,  and  extending  much  farther  forward,  is  the  spheno- 
maxillary fissure  (inferior  orbital  fissure).  The  anterior  margin  of  the  lateral  wall 
is  stout  and  formed  by  the  zygomatic  bone,  behind  which,  formed  in  part  by  the 
orbital  process  of  the  zygomatic  bone  and  the  zygomatic  edge  of  the  great  wing  of 
the  sphenoid,  it  forms  a  fairly  thick  partition  between  the  orbit  in  front  and  the 
temporal  fossa  behind.  Crossing  this  surface  from  above  downwards,  close  to  the 
anterior  extremity  of  the  spheno-maxillary  fissure,  is  the  suture  between  the 
zygomatic  bone  and  the  great  wing  of  the  sphenoid  (sutura  spheno-zygomatica). 
This  wall  is  pierced  in  front  by  one  or  two  small  canals  (foramen  zygomatico- 
orbitale),  which  traverse  the  zygomatic  bone  and  allow  the  transmission  of  the 
temporal  and  zygomatic  branches  of  the  orbital  portion  of  the  superior  maxillary 
division  of  the  fifth  nerve. 

The  medial  wall  of  the  orbit  is  formed  from  before  backwards  by  a  small  part 
of  the  frontal  process  of  the  maxilla,  by'  the  lacrimal,  and  by  the  os  planum  or 
orbital  plate  of  the  ethmoid  (lamina  papyracea  ossis  ethmoidalis),  posterior  to  which 
is  a  small  part  of  the  lateral  aspect  of  the  body  of  the  sphenoid  in  front  ot  the 

10 


150  OSTEOLOGY. 

optic  foramen.  Above,  the  orbital  plate  of  the  frontal  bone  forms  a  continuous 
suture  from  before  backwards  with  the  bones  just  enumerated ;  whilst  below,  the 
lacrimal  and  the  os  planum  of  the  ethmoid  articulate  with  the  orbital  plate 
of  the  maxilla;  posteriorly  the  hinder  extremity  of  the  os  planum  and  the 
fore-part  of  the  body  of  the  sphenoid  articulate  with  the  orbital  process  of  the 
palate.  The  orbital  surface  of  the  lacrimal  bone  is  divided  into  two  by  a  vertical 
ridge — the  lacrimal  crest  (crista  lacrimalis  posterior) — which  forms  in  front  the 
posterior  half  of  a  hollow,  the  lacrimal  groove  (sulcus  lacrimalis),  the  anterior 
part  of  which  is  completed  by  the  channelled  posterior  border  of  the  frontal 
process  of  the  maxilla.  In  the  lacrimal  groove  or  fossa  (fossa  sacci  lacrimalis) 
is  lodged  the  lacrimal  sac,  whilst  passing  from  it  and  occupying  the  canal,  of 
which  the  upper  opening  is  at  present  seen,  is  the  membranous  nasal  duct.  The 
extremely  thin  wall  of  the  lower  part  of  the  lacrimal  fossa  separates  the  orbit 
from  the  fore-part  of  the  middle  meatus  of  the  nasal  fossa.  To  the  medial  side  of 
the  upper  and  fore-part  of  the  lacrimal  bone,  and  separated  from  the  orbit  merely 
by  the  thickness  of  that  bone,  is  the  passage  leading  from  the  nose  to  the  frontal 
sinus  (infundibulum  ethmoidale),  whilst  the  part  of  the  bone  behind  the  lacrimal 
crest  forms  the  thin  partition  between  the  orbit  and  the  anterior  ethmoidal  cells. 
Behind,  where  the  body  of  the  sphenoid  forms  part  of  the  medial  wall  of  the  orbit, 
the  sphenoidal  air  sinus  is  in  relation  to  the  apej:  of  that  space,  though  here  the 
partition  wall  between  the  two  cavities  is  much  thicker. 

The  skeleton  of  the  face  on  its  anterior  surface  is  formed  by  the  two  maxillse, 
the  frontal  processes  of  which  have  been  already  seen  to  pass  up  to  articulate 
with  the  mecUal  angular  processes  of  the  frontal  bone,  thus  forming  the  lower 
halves  of  the  inner  margins  of  the  orbit.  Joined  to  the  upper  jaws  laterally 
are  the  zygomatic  or  malar  bones,  which  are  supported  by  their  union  with 
the  temporal  bones  posteriorly  through  the  medium  of  the  zygomatic  arches. 
The  suture  which  separates  the  zygomatic  from  the  maxilla  (sutura  zygomatico- 
maxillaris)  commences  above  about  the  centre  of  the  lower  orbital  margin  and 
passes  obliquely  downward  and  laterally,  its  lower  end  lying  in  vertical  line 
with  the  lateral  orbital  margin.  The  two  maxillse  are  separated  by  the  nasal 
fossae,  which  here  open  anteriorly.  Above,  the  two  nasal  bones  are  wedged  in 
between  the  frontal  processes  of  the  maxillee ;  whilst  below  the  nasal  aperture,  the 
maxillfe  themselves  are  united  in  the  middle  line  by  the  intermaxillary  suture 
(sutura  intermaxillaris). 

The  nasal  aperture  (apertura  pyriformis),  which  lies  below  and  in  part 
between  the  orbits,  is  of  variable  shape  and  size — usually  pyriform,  it  tends  to  be 
long  and  narrow  in  Europeans,  as  contrasted  with  the  shorter  and  wider  form  met 
with  in  the  negroid  races.  Its  edges  are  formed  below  and  on  either  side  by 
the  free  curved  margin  of  the  body  and  the  frontal  process  of  the  maxilla ;  and 
above,  and  partly  at  the  sides,  by  the  free  border  of  the  nasal  bones.  In  the 
middle  line,  inferiorly,  corresponding  to  the  upper  end  of  the  intermaxillary 
suture  there  is  an  outstanding  process — the  anterior  nasal  spine  (spina  nasalis 
anterior)  formed  by  the  coalescence  of  spicules  from  Ijoth  maxilhc ;  arising  from 
this,  and  passing  backwards  and  upwards,  is  a  thin  bony  partition — the  osseous 
septum  of  the  nose.  Often  deflected  to  one  or  other  side,  it  divides  the  cavity  of 
the  nose  (cavum  nasi)  into  a  right  and  left  half.  Projecting  into  these  chambers 
from  their  lateral  walls  can  be  seen  the  medial  surfaces  and  free  borders  of  the  middle 
(concha  media)  and  inferior  (concha  inferior)  turbinated  bones,  the  spaces  below 
and  between  which  form  the  inferior  and  middle  meatuses  of  the  nose  respectively. 

Below  the  orl)it,  and  to  the  lateral  side  of  tlio  nasal  aperture,  the  anterior  or 
facial  surface  of  the  body  of  the  maxilla  (corpus  maxillae)  is  seen ;  this  is  con- 
tinuous inferiorly -with  the  lateral  surface  of  the  alveolar  process  (processus  alveo- 
laris),  in  which  are  embedded  the  roots  of  the  upper  teeth. 

A  horizontal  line  drawn  round  the  jaw  on  the  level  of  a  ])oint  midway  between 
the  lower  border  of  the  nasal  aperture  and  the  alveolar  edge  corresponds  to  the 
plane  of  the  hard  palate.  Below  that  the  alveolar  process  separates  the  cavity  of  the 
mouth  from  the  front  of  the  face;  whilst  above,  the  large  air  space,  the  maxillary 
sinus  (sinus  maxillaris),  or  antrum  of  Highmore,  lies  within  the  body  of  the  maxilla. 


NOEMA  LATEKALIS  OF  THE  SKULL.  151 

The  zygomatic  or  malar  bone  forms  the  lower  half  of  the  lateral  and  lateral 
half  of  the  lower  border  of  the  orbit.  Its  lateral  aspect  corresponds  to  the  point 
of  greatest  width  of  the  face,  the  modelling  of  which  depends  on  the  flatness  or 
projection  of  this  bone. 

When  the  lower  jaw  (mandibula)  is  in  position,  and  the  teeth  in  both  jaws  are 
complete,  the  lower  dental  arch  will  be  seen  to  be  smaller  in  all  its  diameters  than 
the  upper,  so  that  when  the  jaws  are  closed  the  upper  teeth  slightly  overlap  the 
lower  both  in  front  and  at  the  sides.  Exceptionally  a  departure  from  this  arrange- 
ment is  met  with. 

Norma  Lateralis. 

Viewing  the  lateral  aspect  of  the  skull,  in  the  first  instance,  without  the  lower 
jaw,  it  is  seen  to  be  formed  in  part  by  the  bones  of  the  cranium,  and  in  part  by  the 
bones  of  the  face.  A  line  drawn  from  the  fronto-nasal  suture  to  the  tip  of  the  mastoid 
process  serves  to  define  roughly  the  boundary  between  these  portions  of  the  skull. 
Of  ovoid  shape,  the  cranium  is  formed  above  by  the  frontal,  parietal,  and  occipital 
bones  from  before  backwards ;  whilst  below,  included  within  these  are  the  sphenoid 
and  temporal  bones.  The  sutures  between  these  several  bones  are  arranged  as 
follows :  Commencing  at  the  zygomatic  process  of  the  frontal,  the  suture  between 
that  bone  and  the  zygomatic  bone  is  first  seen ;  tracing  this  backwards  and  a  little 
upwards,  the  lower  edge  of  the  frontal  next  articulates  with  the  upper  margin  of  the 
great  wing  of  the  sphenoid  for  a  distance  varying  from  three-quarters  of  an  inch  to 
one  inch.  Here  the  posterior  border  of  the  frontal  turns  upwards  and  slightly  back- 
wards, forming  with  the  parietal  the  coronal  suture  (sutura  coronalis).  The  lower 
border  of  the  parietal  bone,  which  is  placed  immediately  behind  the  frontal,  articulates 
anteriorly  with  the  hinder  part  of  the  upper  edge  of  the  great  wing  of  the  sphenoid. 
The  extent  of  this  suture  (sutura  spheno-parietalis)  is  liable  to  very  great  indi- 
vidual variation — at  times  being  broad,  in  other  instances  being  pointed  and 
narrow,  whilst  occasionally  the  parietal  does  not  articulate  with  the  sphenoid  at  all. 
Behind  the  spheno-parietal  suture  the  parietal  articulates  with  the  squamous  part 
of  the  temporal  (sutura  squamosa),  the  posterior  extremity  of  which  is  about  one 
inch  behind  the  external  auditory  meatus.  Here  the  suture  alters  its  character  and 
direction,  and  in  place  oF  being  scaly,  becomes  toothed  and  irregular,  uniting  for  the 
space  of  an  inch  or  so  the  mastoid  or  posterior  inferior  angle  of  the  parietal  with  the 
mastoid  process  of  the  temporal  bone.  This  suture  (sutura  parieto-mastoidea)  is  more 
or  less  horizontal  in  direction,  and  lies  in  line  and  on  a  level  with  the  upper  border 
of  the  zygomatic  arch.  At  a  point  about  two  inches  behind  the  external  auditory 
meatus  the  posterior  border  of  the  parietal  bone  turns  obliquely  upwards  and 
backwards,  and  forms  with  the  tabular  part  of  the  occipital  bone  the  strongly- 
denticulated  lambdoid  suture  (sutura  lambdoidea).  Inferiorly  this  suture  is  con- 
tinued obliquely  downwards  between  the  occipital  bone  and  the  hinder  border  of 
the  mastoid  portion  of  the  temporal,  where  it  forms  the  occipito- mastoid  suture 
(sutura  occipito -mastoidea),  much  simpler  and  less  serrated  than  the  two  previ- 
ously mentioned.  These  three  sutures  just  described  meet  in  tri-radiate  fashion 
at  a  point  called  the  asterion. 

Anteriorly  the  curve  of  the  squamous  suture  is  continued  downward  between 
the  anterior  edge  of  the  squamous  part  of  the  temporal  and  the  posterior  border  of 
the  great  wing  of  the  sphenoid ;  inferiorly  it  lies  in  plane  with  the  middle  of  the 
zygomatic  arch. 

The  sutures  around  the  summit  of  the  great  wing  of  the  sphenoid  are  arranged 
like  the  letter  H  placed  obliquely,  the  cross-piece  of  the  H  corresponding  to  the 
spheno-parietal  suture.  When  this  is  short,  and  becomes  a  mere  point  of  contact, 
the  arrangement  then  resembles  the  letter  X.     This  region  is  named  the  pterion. 

Curving  over  the  lateral  region  of  the  calvaria  in  a  longitudinal  direction  is 
the  temporal  crest  (linea  temporalis).  This  is  often  double.  The  lower  line  marks 
the  limit  of  the  attachment  of  the  temporal  muscle,  whilst  the  upper  ridge  defines 
the  attachment  of  the  temporal  fascia.  Commencing  in  front  at  the  lateral 
angular  process  of  the  frontal,  the  crest  sweeps  upwards  and  backwards  across 
the  lower  part  of  that  bone,  and  then  crossing  the  coronal  suture — at  a  point 


152 


OSTEOLOGY. 


called  the  stephanion — it  passes  on  to  tlie  parietal,  over  which  it  curves  in  the  direc- 
tion of  its  posterior  inferior  (mastoid)  angle.  Here  it  is  continued  on  to  the  temporal 
bone,  where  it  sweeps  forward  to  form  the  supramastoid  crest,  which  serves  to  separate 
the  squamous  from  the  mastoid  portion  of  the  temporal  bone  laterally.  Carried 
forward,  this  ridge  is  seen  to  become  continuous  with   the  upper  border  of  the 


Fig.  115. — Norma  Lateralis  of  the  Skull. 


The  occipital,  sphenoid,  ethmoid,  and  maxillary  bones  are  coloured  blue.     The  parietal,  zygomatic,  ami 
nasal  bones  are  coloured  red.     The  temporal,  frontal,  and  maxillary  bones  are  left  uucoloured. 


11, 


Mental  foramen. 

Body  of  the  lower  jaw. 

Maxilla. 

Ramus  of  lower  jaw. 

Zygomatic  arch. 

Styloid  process. 

External  auditory  meatus. 

Mastoid  process. 

Asterion. 

Superior  curved  line  of  occipital 

l)one. 
External  occipital  protuberance. 


12.  Lambdoid  suture. 

13.  Occipital  bone. 

14.  Lambda. 

15.  Obelion  placed  between  the  two 

parietal  foramina. 

16.  Parietal  bone. 

17.  Lower  temporal  line. 

18.  Upper  temporal  line. 

19.  Squamous    part    of    temporal 

Vjone. 

20.  Bregma. 

21.  Coronal  suture. 


22.  Stephanion. 

23.  Frontal  bone. 

24.  Pterion. 

25.  Temporal  fossa. 

26.  Great  wing  of  sphenoid. 

27.  Zj'gomatic  bone. 

28.  Zygomatic  canal. 

29.  Lacrimal  bone. 

30.  Nasal  bone. 

31.  Infraorbital  canal. 

32.  Anterior  nasal  aperture. 


zygomatic  arch  over  the  external  auditory  meatus.  In  front,  the  temporal  ridge 
separates  the  temporal  fossa  from  the  region  of  the  forehead ;  above  and  behind,  it 
bounds  the  temporal  fossa  which  lies  within  its  concavity,  and  serves  to  separate  that 
hollow  from  the  surface  of  the  calvaria  which  is  overlain  by  the  scalp.  Above  the 
level  of  the  temporal  lines  the  surfaces  of  the  frontal  and  parietal  bones  are  smooth, 
the  latter  exhibiting  an  elevation  of  varying  prominence  and  position,  but  usually 
situated  about  the  centre  of  the  bone,  called  the  parietal  eminence  (tuber  parietale). 


NOEMA  LATERALIS  OF  THE  SKULL.  153 

A  slight  hollowing  of  the  surface  of  the  parietal  behind  and  parallel  to  the  coronal 
suture  is  not  uncommon,  and  is  referred  to  as  the  post -coronal  depression.  As 
seen  in  profile,  the  part  of  the  calvaria  behind  and  below  the  lambdoid  suture  is 
formed  by  the  tabular  part  of  the  occipital  bone.  In  line  with  the  zygomatic  arch 
this  outline  is  interrupted  by  the  external  occipital  protuberance  or  inion  (protuber- 
antia  occipitalis  externa).  The  projection  of  this  point  is  variable ;  but  its 
position  can  usually  be  easily  determined  in  the  Living.  Passing  forwards  from 
it,  and  blending  anteriorly  with  the  posterior  border  of  the  mastoid  process  of  the 
temporal  bone,  is  a  rough  crest,  the  superior  curved  line  (linea  nuchse  superior),  a 
little  above  which  there  is  often  a  much  fainter  line,  the  highest  curved  line  (linea 
nuchas  suprema) ;  this  aftbrds  attachment  to  the  epicranial  aponeurosis.  These  two 
lines  serve  to  separate  the  part  of  the  cranium  above,  which  is  covered  by  scalp, 
from  that  below,  which  serves  for  the  attachment  of  the  fleshy  muscles  of  the  back 
of  the  neck,  the  latter  surface  (planum  nuchale)  being  rough  and  irregular  as 
contrasted  with  the  smooth  superior  part  (planum  occipitale).  The  fulness  of 
these  two  parts  of  the  occipital  bone  varies  much.  There  is  frequently  a  pronounced 
bulging  of  the  planum  occipitale,  and  the  position  of  the  lambda  can  often  be 
easily  determined  in  the  living ;  similarly  the  planum  nuchale  may  be  either  com- 
paratively flat  or  else  full  and  rounded.  These  differences  are  of  course  associated 
with  corresponding  differences  in  the  development  of  the  cerebral  and  cerebellar 
lobes  which  are  lodged  in  relation  to  the  cerebral  aspect  of  these  parts  of  the  bone. 
The  further  description  of  the  planum  nuchale  is  best  deferred  till  the  base  of 
the  skull  (norma  basalis)  is  studied. 

Temporal  Fossa. — -Within  the  limits  of  the  temporal  lines  the  side  of  the  cranium 
slopes  forwards,  inwards,  and  downwards,  thus  leaving  a  considerable  interval  between 
its  lower  part  and  the  zygomatic  arch.  This  space  or  hollow  is  called  the  temporal 
fossa  (fossa  temporalis) ;  bounded  above  and  behind  by  the  temporal  lines,  its  inferior 
limit  is  defined  by  the  level  of  the  zygomatic  arch.  Deepest  opposite  the  angle  formed 
by  the  frontal  and  temporal  processes  of  the  zygomatic  or  malar  bone,  the  fossa 
becomes  shallow  towards  its  circumference.  Its  floor  or  medial  wall,  which  is 
sUghtly  concavo-convex  from  before  backwards  about  mid-level,  is  formed  above 
by  the  temporal  surface  (facies  temporalis)  of  the  frontal,  behind  by  the  anterior 
inferior  angle  (sphenoidal  angle)  of  the  parietal,  as  well  as  the  lower  portion  of 
that  bone,  below  the  temporal  line ;  below  and  in  front  by  the  temporal  surface  of 
the  great  wing  of  the  sphenoid,  and  behind  and  below  by  the  squamous  portion 
of  the  temporal  bone.  Inferiorly  the  floor  is  limited  in  front  by  the  free 
inferior  border  of  the  great  wing  of  the  sphenoid,  which  forms  the  upper  boundary 
of  the  spheno- maxillary  (pterygo  -  palatine)  fossa;  behind  that,  by  a  rough  ridge, 
the  infra-temporal  crest  or  pterygoid  ridge  (crista  infratemporalis),  which  crosses  the 
lateral  surface  of  the  great  wing  of  the  sphenoid,  to  become  continuous  posteriorly 
with  a  ridge  on  the  lower  surface  of  the  squamous  part  of  the  temporal,  from 
which  the  anterior  root  of  the  zygomatic  process  springs.  Anteriorly  the 
temporal  fossa  is  separated  from  the  orbit  by  the  zygomatic  process  of  the  frontal 
above,  and  by  the  orbital  process  of  the  zygomatic  and  its  junction  with  the  lateral 
border  of  the  great  wing  of  the  sphenoid  between  the  orbital  and  temporal  surfaces 
of  that  process.  Laterally  and  in  front,  the  fossa  is  overhung  by  the  backward  pro- 
jection of  the  frontal  process  of  the  zygomatic  bone,  and  it  is  under  cover  of  this,  and 
within  the  angle  formed  by  the  frontal  and  orbital  processes  of  the  zygomatic  bone, 
that  we  see  the  opening  of  the  temporal  canal,  which  pierces  the  orbital  plate  of  the 
zygomatic  bone  and  transmits  the  temporal  branch  of  the  orbital  nerve — a  filament 
of  the  superior  maxillary  division  of  the  5th  nerve.  The  fore-part  of  the  spheno- 
maxillary fissure  (fissura  orbitalis  inferior)  opens  into  the  lower  part  of  the  temporal 
fossa,  and  thus  establishes  a  communication  between  it  and  the  orbit.  If  the  floor 
of  the  fossa  be  carefully  examined,  some  more  or  less  distinct  vascular  grooves 
may  be  seen.  One  passing  upwards  over  the  posterior  part  of  the  squamous 
temporal,  immediately  in  front  of  and  above  the  external  auditory  meatus,  is  for 
the  middle  temporal  artery ;  two  others,  usually  less  distinct,  pass  up,  one  over  the 
temporal  surface  of  the  great  wing  of  the  sphenoid,  the  other  over  the  fore-part  of 
the  squamous  part  of  the  temporal ;  these  are  for  the  anterior  and  posterior  deep 

10  & 


154  OSTEOLOGY. 

temporal  branches  of  the  internal  maxillary  artery.  Inferiorly  the  temporal  fossa 
communicates  with  the  infra-temporal  (or  zygomatic)  fossa,  beneath  the  zygomatic 
arch,  the  two  being  separated  by  an  imaginary  horizontal  plane  passing  inwards 
at  the  level  of  that  bony  bridge.  The  fossa  contains  the  temporal  muscle  with  its 
vessels  and  nerves,  together  with  the  temporal  branch  of  the  orbital  nerve  and  some 
fat ;  all  of  which  are  enclosed  by  the  fascia  which  stretches  over  the  space  from  the 
upper  temporal  line  above  to  the  superior  border  of  the  zygomatic  arch  below. 
The  extent  and  depth  of  the  fossa  depends  on  the  size  of  the  temporal  muscle,  the 
development  of  which  is  correlated  with  the  size  and  weight  of  the  lower  jaw. 

Springing  from  the  front  and  lower  part  of  the  squamous  part  of  the  temporal 
is  the  zygomatic  process  of  that  bone ;  it  has  two  roots,  an  anterior  and  a  posterior, 
between  and  below  which  are  placed  the  glenoid  fossa  (fossa  mandibularis)  in  front, 
and  the  opening  of  the  external  auditory  meatus  behind.  Of  compressed  triangular 
form,  the  process  at  first  has  its  surfaces  directed  upwards  and  downwards,  but  curving 
laterally  and  forwards,  it  twists  on  itself,  so  that  its  narrowed  surfaces  are  now  turned 
laterally  and  medially,  and  its  edges  upwards  and  downwards ;  passing  forwards,  it 
expands  somewhat,  and  ends  in  an  oblique  serrated  surface,  which  unites  with  the 
temporal  process  of  the  zygomatic  bone  completing  the  zygomatic  arch.  It  is  the 
upper  edge  of  this  bridge  of  bone  which  forms  the  posterior  root.  The  lower  border, 
turning  medially,  forms  the  anterior  root,  and  serves  to  separate  the  temporal  from 
the  zygomatic  surface  of  the  squamous  part  of  the  temporal,  blending  in  front  with 
the  infratemporal  crest  on  the  lateral  surface  of  the  great  wing  of  the  sphenoid.  The 
under  surface  of  this  root  is  convex  from  before  backwards,  and  is  thrown  into  relief 
by  the  glenoid  hollow,  which  passes  up  behind  it.  In  this  way  a  downward  projection, 
which  is  called  the  eminentia  articularis,  is  formed. 

The  alar  spine  of  the  sphenoid  (spina  angularis)  lies  immediately  to  the 
medial  side  of  the  articular  part  of  the  glenoid  fossa.  Its  size  and  projection  vary. 
It  is  well  to  remember  its  relation  to  the  condyle  of  the  lower  jaw  when  that  bone 
is  in  position ;  lying,  as  it  does,  to  the  medial  side  and  a  little  in  front  of  that  pro- 
cess, it  affords  attachment  to  the  so-called  long  internal  lateral  ligament  (spheno- 
mandibular)  of  the  tempore -maxillary  articulation.  As  will  be  seen  hereafter, 
the  anterior  extremity  of  the  osseous  Eustachian  canal  lies  just  to  its  medial 
side  (p.  124).  A  noteworthy  feature  about  the  articular  part  of  the  glenoid  fossa 
is  the  thinness  of  the  bony  plate  which  serves  to  separate  it  from  the  middle 
cranial  fossa  above.  The  vaginal  process  is  a  crest  of  bone  which  runs  obhquely 
forwards  from  the  front  and  medial  side  of  the  mastoid  process,  just  below  the 
external  auditory  meatus,  to  the  alar  spine  of  the  sphenoid.  Passing  downwards 
and  slightly  forwards  from  the  centre  of  this,  and  ensheathed  by  it  in  front  and 
at  the  sides,  is  the  pointed  styloid  process,  the  length  of  which  is  extremely  variable. 

In  the  recess  between  the  posterior  root  of  the  zygoma  and  the  upper  curved 
edge  of  the  meatus  there  is  usually  a  depression,  though  in  some  instances  this 
may  be  replaced  by  a  slight  bulging  of  the  bone.  If  from  the  posterior  root  of 
the  zygoma  a  vertical  line  be  let  fall,  tangential  to  the  posterior  edge  of  the  meatus, 
a  small  triangular  area  is  mapped  off  which  has  been  named  by  Macewen  the  supra- 
meatal  triangle.  Surgically  this  is  of  importance,  as  it  is  the  spot  selected  in  which 
to  trephine  the  bone  to  reach  the  mastoid  antrum  (see  p.  118). 

In  the  suture  between  the  posterior  border  of  the  mastoid  part  of  the  temporal 
and  the  squamous  part  of  the  occipital,  there  is  usually  a  foramen  (mastoid)  for 
the  transmission  of  an  emissary  vein  from  the  lateral  (transverse)  sinus  within 
the  cranium  to  the  cutaneous  occipital  vein  of  the  scalp ;  this  opening,  which 
may  be  double,  varies  greatly  in  size,  and  is  usually  placed  on  a  level  with  the 
external  auditory  meatus. 

Infratemporal  or  Zygomatic  Fossa. — The  side  of  the  cranium  in  front  of  the 
anterior  root  of  the  zygomatic  yjrocess  of  tlie  temporal  bone  is  deeply  hollowed,  form- 
ing the  infratemporal  or  zygomatic  fossa  (fossa  infratemporalis) ;  this  in  topographical 
anatomy  corresponds  to  the  pterygo-maxillary  region.  The  student  must  bear  in 
mind  that,  in  examining  this  space,  the  ramus  and  coronoid  process  of  the  lower 
jaw  form  its  outer  wall ;  but  this  bone  for  the  present  being  withdrawn,  enables  us 
to  get  a  better  view  of  the  boundaries  of  the  space.     In  front  its  anterior  wall 


NORMA  LATERALIS  OF  THE  SKULL.  155 

is  formed  by  the  convex  posterior  or  zygomatic  surface  (facies  infratemporalis) 
of  the  maxilla,  which  rises  behind  the  socket  for  the  last  molar  tooth  to  form 
the  tuberosity  (tuber  maxillare).  Anteriorly,  the  zygomatic  surface  of  the  upper  jaw 
is  separated  from  its  facial  aspect  by  the  rounded  inferior  margin  of  the  malar 
or  zygomatic  process  which  supports  the  malar  bone.  This  latter  curves  laterally 
and  backwards,  forming  part  of  the  upper  and  anterior  wall  of  the  fossa.  On  the  medial 
surface  of  this  wall  will  be  seen  the  suture  uniting  the  zygomatic  and  maxillary 
bones  (sutura  zygomatieo-maxillaris),  which  runs  obliquely  upwards  and  inwards 
to  reach  the  lateral  extremity  of  the  spheno-maxillary  fissure  (inferior  orbital  fissure), 
the  lower  border  of  which  forms  the  superior  boundary  of  the  zygomatic  surface  of 
the  upper  jaw.  On  this  aspect  of  the  bone  are  to  be  seen  the  openings  of  the 
posterior  dental  canals  (foramina  alveolaria)  two  or  more  in  number,  which  transmit 
the  nerves  and  vessels  to  the  upper  molar  teeth.  The  medial  wall  of  the  zygomatic 
fossa  is  formed  by  the  lateral  surface  of  the  external  pterygoid  plate  (lamina  lateralis 
processus  pterygoidei),  the  width  and  shape  of  which  varies  greatly  ;  its  posterior 
border  is  thin  and  sharp,  and  often  furnished  with  spiny  points,  to  one  of  which  the 
pterygo-spinous  ligament,  which  stretches  from  this  border  to  the  alar  spine  of  the 
sphenoid,  is  attached.  It  occasionally  happens  that  this  ligament  becomes 
ossified.  Anteriorly  the  external  pterygoid  plate  is  separated  from  the  maxilla 
above  by  an  interval  called  the  pterygo-maxillary  fissure.  Below  this  the  bones  are 
apparently  fused,  but  a  careful  inspection  of  the  skull,  together  with  an  examina- 
tion of  the  disarticulated  bones,  will  enable  the  student  to  realise  that,  wedged  in 
between  the  two  bones  at  this  point,  is  a  part  of  one  of  the  smaller  bones  of  the 
face,  the  pyramidal  process  of  the  palate  bone  (processus  pyramidalis  ossis  palatini). 

The  lower  border  of  the  external  pterygoid  plate  is  usually  curved  and  slightly 
everted.  Superiorly,  where  the  external  pterygoid  plate  is  generally  narrower,  it 
sweeps  upwards  to  become  continuous  with  the  broad  under  surface  of  the  great 
wing  of  the  sphenoid ;  this,  which  overhangs  in  part  the  zygomatic  fossa  superiorly, 
is  limited  above  by  the  infratemporal  crest  which  separates  its  zygomatic  from  its 
temporal  surface.  The  zygomatic  surface  of  the  great  wing  of  the  sphenoid  is 
limited  in  front  and  below  by  the  edge  which  forms  the  upper  boundary  of  the 
spheno-maxillary  fissure,  whilst  behind  it  reaches  as  far  back  as  the  medial 
extremity  of  the  G-laserian  fissure,  where  it  terminates  in  the  alar  spine.  It  is 
from  this  point  that  the  suture  (sutura  spheno  -  squamosa)  curves  forward  and 
upwards  to  reach  the  region  of  the  pterion.  The  infratemporal  or  zygomatic 
surface  of  the  great  wing  of  the  sphenoid,  and  the  lateral  surface  of  the  external 
pterygoid  plate,  alike  afford  extensive  attachments  for  the  external  pterygoid 
muscle,  whilst  the  former  is  pierced  by  minute  canals  for  the  transmission  of 
emissary  veins.  Occasionally  a  larger  vascular  foramen  is  present  (foramen  Vesalii), 
through  which  a  vein  runs  from  the  cavernous  sinus  within  the  cranium  to  the 
pterygoid  venous  plexus  situated  in  the  pterygo-maxillary  region.  Immediately 
behind  the  root  of  the  external  pterygoid  plate  there  is  a  large  oval  hole,  the  foramen 
ovale,  and  behind  that,  and  in  line  with  the  alar  spine,  is  the  smaller  foramen 
spinosum.  These  two  foramina  cannot  usually  be  seen  in  a  side  view  of  the  skull, 
and  are  better  studied  when  the  base  is  examined ;  they  are  mentioned,  however, 
because  they  transmit  structures  which  here  pass  to  and  from  the  cranium,  viz, 
the  mandibular  division  of  the  fifth  nerve,  together  with  its  motor  root,  and  the 
small  meningeal  artery  through  the  foramen  ovale,  and  the  middle  meningeal  artery 
and  its  companion  veins  through  the  foramen  spinosum.  A  part  of  the  squamous 
part  of  the  temporal  also  forms  a  small  portion  of  the  roof  of  this  fossa ;  it  consists 
of  a  triangular  area  immediately  in  front  of  the  eminentia  articularis,  and  between 
it  and  the  anterior  root  of  the  zygomatic  process  of  the  temporal,  which  is  here 
curving  medially  and  forwards,  to  become  continuous  with  the  infratemporal  crest. 
Medially  this  surface  is  continuous  with  the  zygomatic  surface  of  the  great  wing 
of  the  sphenoid,  separated  from  it,  however,  by  the  hinder  part  of  the  spheno- 
squamosal  suture. 

When  the  lower  jaw  is  in  position,  the  zygomatic  or  infratemporal  fossa  is  concealed 
by  the  ramus  of  the  mandible,  the  medial  surface  of  which,  in  its  upper  half,  forms  the 
lateral  wall  of  that  space.     Viewed  from  the  outer  side,  the  ramus  of  the  mandible 


156  OSTEOLOGY. 

displays  considerable  differences  in  different  skulls.  These  are  mainly  due  to  varia- 
tions in  its  width  and  in  the  nature  of  the  angle  which  it  forms  at  its  fusion  with 
the  body  of  the  bone.  A  considerable  interval  separates  the  posterior  border  of  the 
ramus  from  the  front  of  the  mastoid  process.  Within  this  space  may  be  seen  the 
free  inferior  edge  of  the  tympanic  plate  (vaginal  process),  from  which,  just  below 
the  external  auditory  meatus,  the  styloid  process  of  the  temporal  bone  is  observed 
passing  downwards  and  slightly  forwards.  The  width  and  height  of  the  coronoid 
process  vary  much,  oftentimes  reaching  the  level  of  the  top  of  the  condyle.  Its 
extremity,  when  the  lower  jaw  is  closed,  lies  just  within  the  fore-part  of  the  zygo- 
matic arch  ;  at  other  times  it  rises  to  a  much  higher  level,  so  that  its  point  may  be 
seen  above  the  level  of  the  upper  border  of  the  zygomatic  arch.  The  posterior 
edge  of  the  coronoid  process  forms  the  anterior  border  of  the  sigmoid  or  mandibular 
notch,  and  limits  in  front  the  interval  left  between  the  lower  border  of  the  posterior 
lialf  of  the  zygomatic  arch  and  the  upper  hollowed  edge  of  the  ramus.  On  looking 
into  this  interval,  the  floor  of  the  zygomatic  fossa  may  be  seen,  formed  anteriorly  by 
the  external  pterygoid  plate ;  whilst  posteriorly  it  is  possible  to  pass  a  probe  right 
across  the  base  of  the  skull  from  one  sigmoid  notch  to  the  other,  the  shaft  of  the 
probe  lying  immediately  behind  the  pterygoid  processes  of  the  sphenoid,  and  cross- 
ing the  foramina  ovalia,  through  which  the  mandibular  divisions  of  the  fifth 
nerves  pass. 

The  ramus  and  coronoid  process  are  so  placed  as  to  occupy  a  position  inter- 
mediate between  the  zygomatic  arch  laterally  and  the  external  pterygoid  plate 
medially;  their  medial  surface,  therefore,  forms  the  lateral  wall  of  the  zygomatic  fossa. 
On  a  level  with  the  surface  of  the  crowns  of  the  teeth  of  the  lower  jaw,  and 
situated  about  the  middle  of  this  aspect  of  the  ramus,  is  the  inferior  dental  foramen 
(foramen  mandibulare),  the  superior  opening  of  the  inferior  dental  canal  (canalis 
mandibulae),  which  traverses  the  body  of  the  bone.  Through  this  foramen  there 
pass  the  inferior  dental  branch  of  the  mandibular  division  of  the  fifth  nerve, 
together  with  the  inferior  dental  artery  and  its  companion  veins.  As  will  now 
be  seen,  when  the  lower  jaw  is  in  position,  the  zygomatic  fossa  is  closed  in  later- 
ally by  the  ramus  of  the  mandible.  In  front  there  is  an  interval  between  the 
anterior  border  of  the  ramus  and  the  zygomatic  surface  of  the  maxilla,  through 
which  pass  the  buccal  branch  of  the  fifth  nerve  and  the  communicating  vein 
between  the  pterygoid  plexus  and  the  facial  vein.  Above,  in  the  interval  between 
the  sigmoid  edge  and  the  lower  border  of  the  zygomatic  arch,  there  pass  from  the 
fossa  the  vessels  and  nerves  which  supply  the  masseter  muscle.  Between  the 
posterior  border  of  the  ramus  and  the  styloid  process  there  enter  and  leave  the 
large  vessels  which  are  found  within  the  space.  Superiorly,  under  cover  of  the 
zygomatic  arch,  the  zygomatic  fossa  communicates  with  the  temporal  fossa,  whilst 
inferiorly  it  is  continuous  with  the  inframaxillary  region.  Medially,  on  the 
floor  of  the  fossa  there  is  an  f-shaped  fissure,  the  horizontal  limb  of  which 
corresponds  to  the  spheno-maxillary  fissure  (inferior  orbital  fissure),  forming  a  channel 
of  communication  between  the  fossa  and  the  orbit,  through  which  passes  the 
orbital  branch  of  the  maxillary  division  of  the  fifth  nerve ;  whilst  the  vertical  cleft 
is  the  pterygo -maxillary  fissure,  which  leads  into  a  small  fossa  placed  between  the 
front  of  the  root  of  the  pterygoid  process  of  the  sphenoid  and  the  back  of  the 
maxilla,  called  the  spheno-maxillary  or  pterygo -palatine  fossa. 

The  following  foramina  open  into  the  zygomatic  fossa — the  foramen  ovale, 
foramen  spinosum,  posterior  dental  foramina,  inferior  dental  foramen,  minute 
foramina  for  the  transmission  of  emissary  veins ;  of  these  one  of  large  size  is 
occasionally  present,  the  foramen  of  Vesalius. 

Spheno-Maxillary  or  Pterygo-palatine  Fossa. — This  space,  which  corresponds 
to  the  angular  interval  between  the  pterygo -maxillary  and  spheno-maxillary 
fissures,  and  which  lies  between  the  maxilla  in  front  and  the  root  of  the  pterygoid 
process  behind,  is  bounded  medially  by  the  vertical  part  of  the  palate  bone,  which 
separates  it  from  the  nasal  cavity,  with  which,  however,  it  communicates  by 
means  of  the  spheno-palatine  foramen,  which  lies  between  the  orbital  and 
sphenoidal  processes  of  the  palate  bone  and  the  under  surface  of  the  body  of 
the  sphenoid.      Opening   into   this   fossa,   above   and    behind,   are   the   foramen 


NOEMA  OCCIPITALIS  OF  THE  SKULL. 


157 


rotundum,  the  Vidian  canal  and  the  pterygo-palatine  (pharyngeal)  canal  from 
without  inwards,  whilst  below  is  the  superior  orifice  of  the  posterior  palatine 
canal,  together  with  openings  of  the  accessory  posterior  palatine  canals.  Its 
roof  is  formed  by  the  under  surface  of  the  body  of  the  sphenoid  and  the  orbital 


13 


24     23        22 


Fig.  116. — Coronal  Section  through  the  Spheno-maxillart  (Pterygo-palatine)  Fossa  of  the 

Right  Side. 

The  sphenoid  is  coloured  red.     The  maxilla,  vomer,  middle,  and  inferior  tiirbinals  are  coloured 
blue.     The  palate  bone  is  left  uncoloured. 

L   Anterior  Wall.     B.  Posterior  Wall.     C.   Diagrammatic  representation  of  a  horizontal  section  across  the 

fossa. 


1.  Spheno-palatine  foramen. 

2.  Apex  of  orbital  cavity. 

3.  Spheiio-maxillary  fissure. 

4.  Spheno-maxillary  fi.ssure. 

5.  Pterygo-iiiaxillary  fissure. 

6.  Dental  foramina. 

7.  Part  of  pterygoid  fossa. 

S,  9,  10.  Posterior  palatine  and   ac- 


cessory palatine  (lesser  pala- 
tine) canals. 

11.  Foramen  rotundum. 

12.  Sphenoidal  fissure. 

13.  Optic  foramen. 

14.  Sphenoidal  sinus. 

15.  Pterygo-palatine  canal. 

16.  Vidian  canal. 

17.  Spheno-palatine  foramen. 


IS.  Spheno  -  maxillary  (pterygo  -  pala- 
tine) fossa. 

19.  Infra-orbital  groove. 

20.  Spheno-maxillary  fissure. 

21.  Pterygo-maxillary  fissure. 

22.  Foramen  rotundum. 

23.  Vidian  canal. 

24.  Pterygo-palatine    (pharyngeal) 

canal. 


plate  of  the  palate  bone.  Anteriorly  it  lies  in  relation  to  the  apex  of  the  orbit, 
with  which  it  communicates  by  means  of  the  spheno-maxillary  (inferior  orbital) 
fissure ;  whilst  laterally,  as  already  stated,  it  communicates  with  the  zygomatic 
fossa  through  the  pterygo-maxillary  fissure. 

Norma  Occipitalis. 

The  view  of  the  cranium  as  seen  from  behind  includes  the  posterior  halves  of 
the  two  parietal  bones  above,  the  squamous  part  of  the  occipital  bone  below,  and  the 
mastoid  portions  of  the  temporal  bones  on  either  side  inferiorly.  The  shape  of  this 
aspect  of  the  skull  varies  much,  but  ordinarily  the  greatest  width  corresponds  to  the 
level  of  the  parietal  eminences.  The  sutures  on  this  view  of  the  calvaria  display  a 
tri-radiate  arrangement,  one  limb  of  which  is  vertical,  and  corresponds  to  the  posterior 
part  of  the  interparietal  or  sagittal  suture  (sutura  sagittalis).  The  other  two  limbs 
pass  outwards  and  downwards  in  the  direction  of  the  mastoid  processes,  uniting 
the  two  parietal  bones  in  front  with  the  occipital  bone  behind ;  these  constitute  the 
A-shaped  lambdoid  suture  (sutura  lambdoidea).  The  point  of  confluence  of  the 
sagittal  and  lambdoid  sutures  is  called  the  lambda.  This  can  generally  be  felt  in 
the  living,  owing  to  the  tendency  of  the  tabular  part  of  the  occipital  to  project  slightly 
immediately  below  this  spot.  About  one  inch  and  a  quarter  above  the  lambda  the 
two  small  parietal  foramina  (foramina  parietalia)  are  seen,  through  which  pass  the  small 
emissary  veins  of  Santorini,  which  connect  the  intracranial  venous  system  with 


158  OSTEOLOGY. 

the  superficial  veins  of  the  scalp.  These  small  holes  lie  about  y\  of  an  inch  apart 
on  either  side  of  the  sagittal  suture,  which  here,  for  the  space  of  about  an  inch, 
displays  a  simplicity  of  outline  in  striking  contrast  with  its  serrated  arrangement 
elsewhere.  The  term  obelion  is  applied  to  a  point  on  the  sagittal  suture  in  line  with 
the  two  parietal  foramina.  The  lambdoid  suture  is  characterised  by  great  irregularity 
of  outline,  and  not  unfrequently  chains  of  separated  ossicles  are  met  with  in  it,  the 
so-called  Wormian  bones  (ossa  suturarum).  The  tabular  part  of  the  occipital  bone  is 
divided  into  two  parts  by  the  superior  curved  line  (linea  nuchse  superior),  the  central 
part  of  which  forms  the  external  occipital  protuberance  or  inion  (protuberantia 
occipitalis  exterior).  The  part  above,  called  the  occipital  surface  (planum  occipitale), 
comes  within  our  present  consideration  ;  the  part  below,  the  nuchal  surface  (planum 
nuchale),  though  seen  in  perspective,  had  best  be  considered  when  the  base  is 
examined.  A  little  above  the  level  of  the  superior  curved  line  the  occipital  surface 
is  crossed  on  either  side  by  a  faint  lunated  line,  the  highest  curved  line  (linea 
nuchae  suprema)  to  which  are  attached  the  occipitales  muscles  and  the  epicranial 
aponeurosis.  The  projection  of  the  occipital  surface  varies  much  in  individual 
skulls  ;  most  frequently  it  overhangs  the  external  occipital  protuberance,  forming  a 
distinct  boss  ;  exceptionally,  however,  the  latter  may  be  the  most  projecting  part  of 
the  bone.  The  extremity  of  the  superior  curved  line  on  either  side  corresponds  to 
the  position  of  the  asterion  (p.  151).  Lateral  to  these  points  the  outline  of  the 
skull  is  determined  by  the  downward  projection  of  the  mastoid  processes,  the  medial 
surfaces  of  which  are  deeply  grooved  for  the  attachment  of  the  posterior  belKes  of 
the  digastric  muscles,  thus  causing  these  processes  to  appear  more  pointed  when 
viewed  from  this  aspect. 

Norma  Verticalis. 

This  is  the  view  of  the  calvaria  as  seen  from  above.  It  is  liable  to  great 
diversities  of  form.  Thus  its  shape  may  vary  from  an  elongated  oval  to  an  outline 
more  nearly  circular.  These  differences  have  been  classified,  and  form  important 
distinctions  from  a  craniometrical  standpoint  (Appendix),  the  rounder  varieties  being 
termed  the  brachycephalic,  whilst  the  elongated  belong  to  the  dolichoceplialie  group. 
Another  noteworthy  point  in  this  view  is  the  fact  that  in  some  instances  the 
zygomatic  arches  are  seen,  whilst  in  others  they  are  concealed  by  the  overhang 
and  bulge  of  the  sides  of  the  fore-part  of  the  cranium.  The  former  condition  is 
described  as  phoenozygous,  the  latter  as  cryptozygous,  and  each  is  more  or  less  closely 
associated  with  the  long  or  round  varieties  of  head-form  respectively. 

The  sutures  displayed  have  a  T-shaped  arrangement.  Placed  medially  between 
the  two  parietal  bones  is  the  sagittal  suture.  This  is  fiinely  denticulated,  except  in 
the  region  of  the  obelion,  though,  of  course,  this  will  not  be  apparent  if  obliteration 
of  the  suture  has  taken  place  through  fusion  of  the  two  parietal  bones.  Posteriorly 
the  sagittal  suture  unites  with  the  lambdoid  suture  at  the  lambda,  which  marks 
in  the  adult  the  position  of  the  posterior  fontanelle  of  the  foetus.  Anteriorly  it 
terminates  by  joining  the  transverse  suture  which  separates  the  frontal  bone 
anteriorly  from  the  parietals  behind  ;  this  latter  is  called  the  coronal  suture,  and  the 
point  of  junction  between  the  sagittal  and  coronal  sutures  is  known  as  the  bregma, 
this  corresponds  in  position  to  the  anterior  fontanelle  of  the  foetus.  The  summit 
of  the  vault  of- the  calvaria  corresponds  to  a  variable  point  in  the  line  of  the  sagittal 
suture,  and  is  named  the  vertex.  The  coronal  suture  is  less  denticulated  centrally  than 
laterally.  Occasionally  there  is  a  persistence  of  the  suture  (metopic)  which  unites 
the  two  halves  of  the  frontal  bone ;  under  these  conditions  the  line  of  the  sagittal 
suture  is  carried  forward  to  the  fronto-nasal  suture,  and  a  skull  displaying  this 
peculiarity  is  described  as  metopic.  Behind  the  coronal  suture  may  occasionally 
be  seen  the  post-coronal  depression  (p.  153),  and  in  some  instances  the  vault  of  the 
calvaria  forms  a  broad,  slightly  elevated  crest  along  the  line  of  the  sagittal  suture. 
On  either  side  the  temyjoral  ridges  can  be  seen  curving  over  the  lateral  and  superior 
aspects  of  the  jjarietal  bones.  As  the  lower  of  these  crosses  the  coronal  suture  in 
front  it  marks  a  spot  known  as  the  stephanion,  useful  as  affording  a  fixed  point 
from  which  to  estimate  the  bi-stephanic  diameter.      The  interval  between    the 


NOEMA  BASALIS  OF  THE  SKULL.  159 

temporal  ridges  on  either  side  will  vary  according  to  the  form  of  the  skull  and  the 
development  of  the  temporal  muscle.  In  this  view  of  the  calvaria  a  small  part  of 
the  lambdoid  suture  on  either  side  of  the  lambda  is  visible  posteriorly. 

Norma    Basalis. 

The  base  of  the  cranium — i.e.  the  skull  without  the  mandible — includes  a  descrip- 
tion of  the  under  surfaces  of  the  skeleton  of  the  face  (cranium  viscerale)  and  the 
cranium  (cranium  cerebrale).  The  former  includes  the  hard  palate  formed  by  the 
maxillie  and  palate  bones,  the  superior  dental  arch,  and  the  bodies  of  the  maxillae 
as  seen  from  below  ;  whilst  laterally,  and  united  with  the  bodies  of  the  maxillse, 
the  zygomatic  bones  are  displayed,  curving  backwards  to  form  the  anterior  halves  of 
the  zygomatic  arches.  In  the  middle  line,  passing  from  the  upper  surface  of  the 
hard  palate,  is  the  osseous  septum  of  the  nose,  here  formed  by  the  vomer,  which 
is  united  above  to  the  under  surface  of  the  body  of  the  sphenoid. 

The  under  surface  of  the  cranium  is  pierced  by  the  foramen  magnum  for  the 
transmission  of  the  spinal  cord  and  its  membranes.  In  front  of  this  a  stout  bar  of 
bone  extends  forwards  in  the  middle  line,  formed  by  the  union  of  the  body  of  the 
sphenoid  in  front  with  the  basilar  process  of  the  occipital  bone  behind.  In  adult 
skulls  all  trace  of  the  fusion  of  these  two  bones  has  disappeared  ;  when  union  is  in- 
complete, it  indicates  that  the  skull  is  that  of  a  person  below  the  age  of  twenty-five. 
The  sphenoid  comprises  that  part  of  the  calvaria  which  forms  the  roof  and  sides  of 
the  apertures  which  lie  on  either  side  of  the  nasal  septum  above  the  hard  palate 
— the  choanae  or  posterior  nares.  Laterally  the  under  surfaces  of  the  great 
wings  of  the  sphenoid  extend  as  far  forward  as  the  posterior  border  of  the  spheno- 
maxillary fissure ;  whilst  posteriorly  they  reach  as  far  as  the  alar  spine,  lateral  to 
which  the  spheno-squamosal  suture,  separating  the  great  wing  of  the  sphenoid  from 
the  squamous  portion  of  the  temporal,  curves  forwards  and  upwards,  medial  to  the 
eminentia  articularis,  to  reach  the  floor  of  the  temporal  fossa,  along  which  its  course 
has  been  already  traced  (p.  153).  On  a  level  with  the  front  of  the  foramen 
magnum  the  jugular  process  of  the  occipital  bone  forms  an  irregular  curved  border, 
which  sweeps  outwards  to  terminate  at  a  point  just  medial  to  the  root  of  the 
styloid  process.  Here,  in  line  with  the  spheno-squamosal  suture,  from  which,  how- 
ever, it  is  separated  by  a  considerable  interval,  its  extremity  turns  backwards,  and 
may  be  traced  at  first  medial  to,  and  then  turning  upwards,  behind  the  mastoid 
process  of  the  temporal  bone,  separated  from  this  latter  by  the  occipito-mastoid 
suture.  The  bone  behind  the  foramen  magnum,  which  is  included  between  the 
two  occipito-mastoid  sutures,  comprises  the  nuchal  surface  of  the  squamous  portion 
of  the  occipital  bone,  an  area  which  is  limited  behind  by  the  superior  curved  line 
which  separates  it  from  the  occipital  surface  of  the  same  bone.  The  remaining 
portions  of  the  base  of  the  calvaria,  as  at  present  exposed,  are  formed  by  the 
squamous  and  tympanic  portions  of  the  temporal  bone  together  with  the  petro-mastoid 
part  of  the  same  bone,  the  latter  of  which  is  wedged  in  between  the  great  wing 
of 'the  sphenoid  in  front  and  the  occipital  bone  behind.  Stretching  forwards 
from  the  squamous  part  of  the  temporal  in  front  is  seen  the  zygomatic  process 
which,  by  its  union  with  the  zygomatic  bone,  completes  the  formation  of  the  zygo- 
matic arch. 

Hard  Palate. — Studying  next  the  various  parts  in  detail,  the  hard  palate 
(palatum  durum)  may  be  first  examined.  Of  horse-shoe  shape  as  a  rule,  it  presents 
many  varieties  of  outline  and  size.  Formed  by  the  palatal  processes  (processus 
palatini)  of  the  maxillse  in  front  and  the  horizontal  plates  (partes  horizon- 
tales)  of  the  palate  bones  behind,  its  circumference  in  front  and  at  the  sides  corre- 
sponds to  the  superior  alveolar  arch,  in  which  are  embedded  the  sixteen  teeth  of  the 
upper  jaw;  posteriorly  the  edge  of  the  hard  palate  is  thin,  ending  medially  in  a  pointed 
process,  the  posterior  nasal  spine  (spina  nasalis  posterior),  on  either  side  of  which  the 
posterior  free  border  is  sharp  and  lunated.  The  vault  of  the  palate,  which  is 
concave  from  side  to  side,  and  from  before  backwards,  varies  in  depth  according  to 
the  projection  and  development  of  the  alveolar  processes.  When  the  teeth  are  shed 
and    the  alveoli  are  absorbed,  the   palate   becomes   shallow  and   flat.     Eunning 


160 


OSTEOLOGY. 


Fig.  117. — Norma  Basalts. 
The  occipital,  vomer,  and  maxillary  bones,  are  coloured  red.     The  temporal  and  palate  bones,  blue. 
The  zygomatic  bones,  purple.     The  sphenoid  and  parietal  bones,  and  the  teeth,  are  left  uncoloured. 


E.xternal  occipital  crest.  14. 
Superior  curved  line  of 

the  occipital  bone.  15. 

Foramen  magnum.  16. 

Occipital  condyle.  17. 

Mastoid  groove.  18. 

Mastoid  process.  19. 

External  auditory  meatus.  20. 

Styloid  process.  21. 

Glenoid  fossa.  22. 

Foramen  spinosum.  23. 
Alar  spine  of  the  sphenoid. 

Foramen  ovale.  24. 

External  pterygoid  plate.  25. 


Hamular  process  of  internal  26. 

pterygoid  plate.  27. 

Nasal  septum.  28. 

Posterior  nasal  spine.  29. 

Horizontal  plate  of  palate  Ijone.  30. 

Palatal  process  of  maxilla.  31. 

Anterior  palatine  canal.  82. 

Intermaxillary  suture.  33. 

Posterior  palatine  canal.  34. 

Zygomatic  process  of  maxilla.  35. 
Spheno-maxillary  or  inferior  orbital    36. 

fissure.  37. 

Zygomatic  or  infratemporal  fossa.  38. 

Zygomatic  arch.  39. 


Posterior  opening  of  left  nasal  fossa. 

Pterygoid  fossa. 

Scaphoid  fossa. 

Foramen  lacerum. 

Opening  of  osseous  Eustachian  canal. 

Carotid  canal. 

Jugular  fossa. 

Stylo-mastoid  foramen. 

Jugular  process  of  occipital  bone. 

Grroo\'e  for  occipital  artery. 

Mastoid  foramen. 

Posterior  condylic  foramen. 

Inferior  curved  line  of  occipital  bone. 

External  occipital  protuberance. 


NOEMA  BASALIS  OF  THE  SKULL.  161 

throughout  its  entire  length  in  the  middle  line  is  the  middle  palatine  suture 
(sutura  palatina  mediana),  which  separates  the  palatal  processes  of  the  maxillge 
in  front  and  the  horizontal  plates  of  the  palate  bones  behind.  A  little  behind 
the  central  incisor  teeth,  and  in  the  line  of  this  suture,  is  a  little  pit,  the 
anterior  palatine  canal  (foramen  incisiviun).  At  the  bottom  of  this  may  be  seen 
the  openings  of  some  small  canals,  varying  in  number  from  one  to  four ;  these 
are  usually  described  as  arranged  in  two  pairs,  the  one  pair  placed  side  by  side, 
the  other  lying  medially  in  front  and  behind.  The  former  are  called  the  incisor 
foramina,  or  foramina  of  Stensen,  and  transmit  the  terminal  twigs  of  the  superior 
or  descending  palatine  arteries  which  ascend  to  reach  the  nasal  fossae.  The  latter, 
called  the  foramina  of  Scarpa,  open,  the  anterior  into  the  left,  the  posterior  into  the 
right  nasal  fossa,  and  afford  passage  for  the  fine  filaments  of  the  left  and  right  naso- 
palatine nerves  respectively.  About  half  an  inch  (12  mm.)  in  front  of  the  posterior 
nasal  spine  the  middle  palatine  suture  is  crossed  at  right  angles  by  the  transverse 
palatine  suture  (sutura  palatina  transversa).  This,  which  indicates  the  line  of 
union  of  the  palatal  processes  of  the  maxillte  with  the  horizontal  plates  of  the 
palate  bones,  passes  transversely  outwards  on  either  side  until  it  reaches  the  medial 
aspect  of  the  base  of  the  alveolar  process,  along  which  it  turns  backward,  to 
disappear  within  the  posterior  palatine  canal  (foramen  palatinum  majus),  the  aperture 
of  which  lies  just  medial  to  the  root  of  the  wisdom  molar.  Through  this 
there  pass  the  superior  or  descending  palatine  artery  and  the  large  descending 
palatine  nerve.  Leading  from  this  foramen  is  a  groove  which  curves  forward  im- 
mediately to  the  medial  side  of  the  alveolar  arch  ;  not  unfrequently  the  medial  edge 
of  this  groove  forms  a  thin  and  sharp  ridge  on  the  surface  of  the  palate.  In  this 
groove  are  lodged  the  aforementioned  vessels  and  nerves.  The  surface  of  the  palate 
in  front  of  the  transverse  suture  is  rough,  pitted  for  the  palatine  glands,  and  pierced  by 
numerous  small  vascular  foramina  ;  the  part  of  the  palate  behind  the  suture,  formed 
by  the  under  surface  of  the  horizontal  plate  of  the  palate  bone,  is  much  smoother. 
From  this  there  rises,  just  posterior  to  the  orifice  of  the  posterior  palatine  canal,  a 
thin  sharp  crest  which  curves  medially  immediately  in  front  of  the  posterior  free 
edge ;  to  this  are  attached  some  of  the  tendinous  fibres  of  the  tensor  veli  palatini 
muscle. 

Pterygoid  Processes. — Buttressed  against  the  hinder  extremities  of  the  alveolar 
arch  are  the  pterygoid  processes  of  the  sphenoid.  If  carefully  examined,  these 
will  be  seen  not  to  lie  in  actual  contact  with  the  maxillae,  but  to  be  separated 
from  them  by  the  triangular  wedge-shaped  pyramidal  processes  of  the  palate 
bones.  It  is  these  latter  which  are  pierced  by  the  posterior  and  lateral  accessory 
palatine  canals  (foramina  palatina  minora)  which  lie  just  behind  the  posterior  pala- 
tine canal,  and  through  which  pass  the  lesser  palatine  nerves.  As  here  displayed, 
the  pterygoid  processes  (processus  pterygoidei)  of  the  sphenoid  lie  on  either  side  of 
the  opening  of  the  posterior  nares ;  each  consists  of  two  plates,  an  internal  (lamina, 
medialis)  and  an  external  (lamina  lateralis) ;  the  latter  is  the  broader,  and  is 
directed  backwards  and  slightly  laterally.  Its  lateral  surface  has  been  already 
studied  in  connexion  with  the  zygomatic  fossa  (p.  154).  Medially  it  is  separated 
from  the  inner  pterygoid  plate  by  the  pterygoid  fossa  (fossa  pterygoidea),  wherein 
is  lodged  a  considerable  part  of  the  internal  pterygoid  muscle.  The  floor  of  the 
fossa  is  formed  in  greater  part  by  the  coalescence  of  the  two  pterygoid  plates ;  but 
at  the  level  of  the  hard  palate  the  pyramidal  process  of  the  palate  bone  appears 
wedged  in  between  the  two  plates,  and  so  enters  into  the  formation  of  the  floor  of 
the  pterygoid  fossa.  The  internal  pterygoid  plate  separates  the  nasal  from  the 
pterygoid  fossa ;  to  the  hinder  edge  of  the  internal  pterygoid  plate  are  attached  the 
pharyngeal  aponeurosis,  the  superior  constrictor  of  the  pharynx,  and  the  pharyngo- 
palatinus  muscle.  Above,  the  posterior  border  of  this  plate  is  channelled  to  form 
the  small  scaphoid  fossa  (fossa  scaphoidea),  which  curves  laterally  over  the  summit 
of  the  pterygoid  fossa,  and  furnishes  a  surface  for  the  origin  of  the  tensor  veli  palatini 
muscle.  The  sharp  medial  margin  of  this  fossa,  continuous  below  with  the  posterior 
border  of  the  internal  pterygoid  plate,  extends  upwards,  and  on  either  side  of  the 
body  of  the  sphenoid  forms  a  blunt  pointed  process,  the  pterygoid  tubercle,  which 
extends  backwards  towards  the  apex  of  the  petrous  part  of  the  temporal  bone. 


162  OSTEOLOGY. 

Just  lateral  to  this,  and  concealed  hj  it,  is  the  hinder  extremity  of  the  Vidian 
canal  (eanalis  pterygoideus),  through  which  pass  the  Vidian  vessels  and  nerve/  The 
medial  surface  of  the  internal  pterygoid  plate  is  directed  towards  the  nasal  fossae. 
Superiorly  this  surface  curves  medially  to  meet  the  under  surface  of  the  body  of  the 
sphenoid,  forming  on  either  side  a  lipped  edge,  the  vaginal  process  (processus  vaginalis), 
between  which  the  alse  of  the  vomer,  which  here  forms  the  nasal  septum,  are 
wedged.  Between  the  two  a  small  interval,  however,  is  occasionally  left,  which  forms 
on  either  side  the  basi-pharyngeal  canal.  A  little  lateral  to  the  line  of  union  of 
the  vaginal  process  with  the  vomer  is  the  opening  of  the  pterygo-palatine  canal 
(eanalis  pharyngeus).  This  lies  between  the  under  surface  of  the  vaginal  process 
and  the  sphenoidal  process  of  the  palate  bone,  which  here  articulates  with  the 
inferior  surface  of  the  body  of  the  sphenoid.  The  pharyngeal  branch  of  the 
spheno-palatine  ganglion  and  the  pterygo-palatine  artery  pass  through  this  canal. 
Inferiorly  the  pterygoid  processes  project  below  the  level  of  the  hard  palate.  The 
inner  plate  ends  in  a  slender  recurved  process,  called  the  hamular  process  (hamulus 
pterygoideus),  which  turns  backwards  and  laterally  (this  is  frequently  broken  off  in 
skulls  which  have  been  roughly  handled).  It  reaches  as  low  as  the  level  of  the 
alveolar  margin,  and  lies  just  within  and  behind  the  posterior  extremity  of  the 
alveolar  process.  It  can  readily  be  felt  in  the  living  by  placing  the  finger  against 
the  soft  palate  behind  and  just  within  the  gum  around  the  root  of  the  wisdom 
tooth.  On  the  front  of  and  below  this  process  the  tendon  of  the  tensor  veli  palatini 
muscle  glides  in  a  groove. 

The  posterior  nares  (choanae)  lie  within  and  between  the  pterygoid  processes. 
Of  a  shape  much  resembling  two  Gothic  windows,  their  bases  or  inferior  boundaries 
are  formed  by  the  horizontal  plates  of  the  palate  bone.  Laterally  they  are 
bounded  by  the  medial  surfaces  of  -the  internal  pterygoid  plates,  whilst  above,  the 
lateral  side  of  the  arch  is  formed  by  the  vaginal  processes  of  the  same  plate ;  medi- 
ally they  are  separated  by  the  thin  vertical  posterior  border  of  the  vomer,  whilst 
above  the  everted  alee  of  the  same  bone  form  the  medial  sides  of  the  arch.  The 
plane  of  these  apertures  is  not  vertical  but  oblique,  corresponding  usually  to  a  line 
drawn  from  the  bregma  above  through  the  last  molar  tooth  of  the  upper  jaw  below. 
Their  size  varies  considerably,  but  the  height  is  usually  equal  to  twice  the  width. 

The  region  of  the  cranium  which  lies  lateral  to  the  maxilla  and  external 
pterygoid  plate  corresponds  to  the  zygomatic  or  infratemporal  fossa,  which  has  been 
already  described  as  seen  from  the  side  (norma  lateralis,  p.  154).  Viewed  from 
below,  the  zygomatic  fossa  is  bounded  in  front  by  the  posterior  surface  of  the  body 
of  the  maxilla  and  the  medial  surface  of  the  zygomatic  bone.  The  roof,  which  is 
traversed  by  the  spheno-squamosal  suture,  is  formed  in  front  by  the  under  surface 
of  the  great  wing  of  the  sphenoid,  and  behind  by  a  small  triangular  surface  of  the 
under  side  of  the  squamous  part  of  the  temporal  bone  immediately  in  front  of  the 
eminentia  articularis. 

Circumscril^ed  laterally  and  behind  by  the  anterior  root  of  the  zygoma,  which 
curves  forward  to  become  continuous  in  front  with  the  infra-temporal  crest  crossing 
the  lateral  surface  of  the  great  wing  of  the  sphenoid,  the  roof  of  the  fossa  is 
separated  from  its  anterior  wall  by  the  spheno -maxillary  (inferior  orbital)  fissure, 
which  is  so  inclined  that  with  its  fellow  of  the  opposite  side  it  forms  an  angle  of 
90°.  Superiorly  the  zygomatic  fossa  communicates  freely  with  the  temporal  fossa 
beneath  the  zygomatic  arch,  though  the  student  must  bear  in  mind  the  fact  that 
when  the  mandible  is  in  position  the  lateral  limits  of  the  space  are  very  much 
reduced  (p.  156). 

The  under  surface  of  the  great  wing  of  the  sphenoid  is  here  V-shaped.  The 
angle  corresponds  to  the  spine,  the  lateral  limb  to  the  spheno-squamosal  suture, 
whilst  the  medial  limb  corresponds  to  a  narrow  cleft,  the  fissura  spheno-petrosa, 
which  separates  it  from  the  petrous  portion  of  the  temporal  bone  to  which  it  is 
united  in  the  recent  condition  by  a  synchondrosis.  Along  the  line  of  this  latter 
fissure  the  edges  of  the  adjacent  bones  (sphenoid  and  petrous  part  of  the  temporal)  are 
bevelled  so  as  to  form  a  groove,  which  extends  from  the  root  of  the  internal  pterygoid 
plate  medially,  to  the  medial  side  of  the  base  of  the  alar  spine  laterally,  where 

'  Artery  and  nerve  of  the  eanalis  pterygoideus  (B.N. A.). 


NORMA  BASALTS  OF  THE  SKULL.  163 

the  groove  ends  by  entering  an  osseous  canal.  In  the  groove  (sulcus  tubae  auditivae) 
is  lodfred  the  cartilaginous  part  of  the  Eustachian  tube,  whilst  the  osseous  canal 
includes  the  bony  part  of  the  same  tube,  together  with  the  tensor  tympani  muscle, 
which  is  lodged  in  a  separate  compartment  immediately  above  it.  The  anterior 
extremity  of  the  cartilaginous  part  of  the  Eustachian  tube  is  supported  by  the 
posterior  edge  of  the  internal  pterygoid  plate,  which  is  often  notchetl  for  its  recep- 
tion. Between  the  root  of  the  external  pterygoid  plate  and  the  alar  spine  there 
are  two  foramina  which  lie  immediately  in  front  of  the  sulcus  tubte  auditivse. 
Of  these  the  larger  and  anterior  is  the  foramen  ovale,  through  which  pass  the 
motor  root  and  mandibular  division  of  the  fifth  nerve,  together  with  the  small 
meningeal  artery.  The  smaller,  which  from  its  position  immediately  in  front 
of  the  alar  spine  is  called  the  foramen  spinosum,  transmits  the  middle  meningeal 
artery  and  sympathetic  plexus  surrounding  that  vessel.  The  lesser  superficial 
petrosal  nerve  here  passes  through  the  base  of  the  skull  to  join  the  otic  ganglion 
either  through  a  small  foramen  (canalis  innominatus)  placed  between  the  foramen 
ovale  and  the  foramen  spinosum,  or  through  the  foramen  ovale  or  through  the 
spheno-petrosal  fissure.  The  position  of  the  suture  between  the  basi-occipital  and 
basi-spheuoid  corresponds  to  a  Hne  connecting  the  tips  of  the  pterygoid  tubercles  at 
the  root  of  the  internal  pterygoid  plates. 

Occasionally  in  the  centre  of  this  line  there  is  a  small  pit  with  a  foramen  leading  from  it.    This 
probably  represents  the  lower  end  of  the  cranio-pharyngeal  canal. 

The  under  surface  of  the  basi-occipital  (pars  basilaris)  stretches  between  the 
body  of  the  sphenoid  in  front  and  the  anterior  margin  of  the  foramen  magnum 
behind ;  projecting  from  its  centre  is  a  slight  elevation,  the  pharyngeal  tubercle 
(tuberculiun  pharyngeum),  to  which  the  pharyngeal  aponeurosis,  together  with  the 
central  part  of  the  anterior  atlanto-occipital  ligament,  is  attached.  It  should  be 
noted,  that  when  the  atlas  is  in  position  the  pharyngeal  tubercle  lies  in  line  with 
the  tubercle  on  the  anterior  arch  of  that  bone.  Curving  laterally  and  backwards 
from  the  pharyngeal  tubercle,  on  either  side,  is  an  irregular  ridge  (crista  muscularis), 
in  front  and  behind  which  are  attached  the  longus  capitis^  and  rectus  capitis  anterior 
muscles.  On  either  side  of  the  basi-occipital,  in  front,  there  is  an  irregular  opening 
of  variable  size ;  this  is  placed  between  the  root  of  the  pterygoid  process  anteriorly, 
the  apex  of  the  petrous  portion  of  the  temporal  bone  laterally,  and  the  lateral 
edge  of  the  basi-occipital  and  basi-sphenoid  medially.  It  is  called  the  foramen 
lacerum.  Opening  into  it  in  front,  just  lateral  to  the  pterygoid  tubercle,  is  the 
Vidian  canal,  whilst  in  correspondence  with  the  apex  of  the  petrous  part  of  the 
temporal  the  large  orifice  of  the  carotid  canal  may  be  seen  entering  it  behind  and 
from  the  lateral  side.  In  the  recent  condition  the  lower  part  of  the  foramen  lacerum 
is  occupied  by  fibro-cartilage,  over  the  upper  surface  of  which  the  internal  carotid 
artery  and  great  superficial  petrosal  nerve  pass  to  reach  their  respective  foramina, 
whilst  a  small  meningeal  branch  of  the  ascending  pharyngeal  occasionally  enters 
the  cranium  through  it.  Leading  laterally  from  the  foramen  lacerum  in  the 
direction  of  the  alar  spine  of  the  sphenoid  is  the  spheno-petrosal  fissure,  wdiich  lies 
at  the  bottom  of  the  sulcus  tubae  auditivae,  and  disappears  from  view  within  the 
bony  Eustachian  canal.  Passing  backwards  from  the  foramen  lacerum  there  is  a 
fissure  between  the  lateral  side  of  the  basi-occipital  and  the  posterior  and  medial 
border  of  the  petrous  part  of  the  temporal  bone.  This,  which  is  called  the  petro- 
occipital  fissure  (fissura  petro-occipitalis),  opens  posteriorly  into  the  jugular  foramen. 
In  the  recent  condition  the  fissure  is  filled  up  with  cartilage.  The  under  surface 
of  the  petrous  bone  included  between  these  two  fissures  is  rough  and  irregular,  and 
affords  attachments  near  its  apex  to  two  small  muscles,  the  levator  veli  palatini  and 
the  tensor  tympani.  Immediately  behind  the  alar  spine  the  petrous  part  of  the 
temporal  is  pierced  by  a  circular  hole,  the  inferior  opening  of  the  carotid  canal  (canalis 
caroticus).  This  passes  upwards,  and  then  turns  medially  and  forwards  towards  the 
apex  of  the  bone,  where  it  may  again  be  seen  opening  into  the  lateral  and  upper  side 
of  the  foramen  lacerum.  Laterally  the  wall  of  the  vertical  part  of  this  canal,  which 
is  usually  very  thin,  separates  it  from  the  cavity  of  the  tympanum,  as  may  be  seen 

^  Longus  capitis  =  rectus  capitis  anticus  major. 

Rectus  capitis  anterior  =  rectus  capitis  anticus  niiuor  (old  nomenclature). 


164  OSTEOLOGY. 

by  holding  the  skull  up  to  the  light  and  looking  into  the  external  auditory  meatus. 
The  carotid  canal  transmits  the  internal  carotid  artery,  together  with  the  sym- 
pathetic plexus  around  it.  It  is  noteworthy  that  the  two  carotid  canals  lie  in  line 
with  the  anterior  edges  of  the  two  external  auditory  meatuses. 

The  jugular  foramen  is  an  opening  of  irregular  shape  and  size  placed  be- 
tween the  petrous  part  of  the  temporal  in  front  and  the  jugular  process  of 
the  occipital  bone  iDchind.  The  former  is  excavated  into  a  hollow  called  the 
jugular  fossa,  which  forms  a  roof  to  the  upper  and  lateral  part  of  the  space,  whilst 
the  latter,  by  a  curved  edge,  either  rounded  or  sharp,  constitutes  its  posterior 
border.  There  is  often  considerable  difference  in  the  size  of  the  jugular  foramina ; 
that  on  the  right  side  (with  the  skull  in  its  normal  position)  is  usually  the  larger. 
The  foramen  is  occasionally  subdivided  into  two  by  spicules  of  bone  which  bridge 
across  it.  Lodged  within  the  fossa  is  the  sinus  of  the  internal  jugular  vein,  in  front 
of  which  the  inferior  petrosal  sinus  passes  down  to  join  the  internal  jugular  vein 
below  the  foramen.  Effecting  an  exit  between  the  two  veins,  in  order  from 
before  backwards,  are  the  glosso-pharyngeal,  pneumogastric,  and  accessory  nerves. 
Small  meningeal  branches  from  the  ascending  pharyngeal  and  occipital  arteries 
also  enter  the  foramen.  The  two  jugular  foramina  lie  in  line  with  a  line  drawn 
through  the  centres  of  the  two  external  auditory  meatuses.  Following  the  direction 
of  a  line  connecting  the  alar  spine  of  the  sphenoid  and  the  mastoid  process  of  the 
temporal,  and  placed  immediately  lateral  to  the  apertures  of  the  carotid  canal 
and  jugular  foramen,  is  the  vaginal  process  of  the  tympanic  plate  of  the  temporal 
bone,  the  edge  of  which  is  sharp  and  thin,  and  serves  to  separate  the  under  surface 
of  the  petrous  part  of  the  temporal  from  the  non-articular  part  of  the  glenoid  fossa. 
Springing  from  this  crest  immediately  lateral  to  the  jugular  fossa,  and  in  line 
with  the  middle  of  the  external  auditory  meatus,  is  the  styloid  process  (processus 
styloideus)  of  the  temporal  bone.  Its  relation  to  the  jugular  foramen  is  of  great 
importance,  as  the  internal  jugular  vein  lies  close  to  its  medial  side. 

Immediately  behind  the  root  of  the  styloid  process,  medial  to  and  in  line  with 
the  front  of  the  mastoid  process,  is  the  stylo -mastoid  foramen  (foramen  stylo- 
mastoideum),  the  lower  aperture  of  the  aquseductus  Fallopii  through  which  the  facial 
nerve  passes  out  and  the  stylo-mastoid  branch  of  the  posterior  auricular  artery 
passes  in.  The  medial  surface  of  the  mastoid  process  is  deeply  grooved  at  its  base 
for  the  origin  of  the  posterior  belly  of  the  digastric  muscle.  Medial  to  this,  and 
running  along,  just  wide  of  the  occipito-mastoid  suture,  is  a  shallow  groove  in  which 
the  occipital  artery  is  lodged.  Just  medial  to  the  stylo-mastoid  foramen  is  the 
synchondrosis  between  the  extremity  of  the  jugular  process  (processus  jugularis) 
of  the  occipital  bone  and  the  petrous  part  of  the  temporal.  The  former  is  a  bar  of 
bone  which  limits  the  jugular  fossa  posteriorly  and  abuts  on  the  occipital  condyles 
medially ;  its  under  surface  is  convex  from  before  backwards  and  affords  attach- 
ment to  the  rectus  capitis  lateralis  muscle.  The  occipital  condyles  are  placed 
between  the  jugular  processes  and  the  foramen  magnum.  Limited  in  front  by 
a  rounded  thickening  which  becomes  confluent  with  the  anterior  border  of  the 
foramen  magnum,  they  form  by  their  medial  sides  the  lateral  boundaries  of  that 
aperture  on  its  anterior  half.  Laterally  they  are  continuous  with  the  jugular 
processes,  in  front  of  which  they  overhang  a  fossa  which  is  pierced  behind  by  the 
anterior  condylic  foramen  (canalis  hypoglossi),  through  which  passes  the  hypoglossal 
nerve,  together  with  a  small  vein  and  occasionally  a  small  meningeal  branch 
derived  from  the  ascending  pharyngeal  artery. 

The  posterior  condylic  fossae  are  situated  just  behind  the  posterior  extremities  of 
the  condyles.  Not  unfrequently  their  floor  is  pierced  by  the  posterior  condylic 
foramen  (canalis  condyloideus),  through  which  the  posterior  condylic  vein  emerges. 
The  base  of  the  skull  behind  the  jugular  processes  and  condyles  of  the  occipital 
bone  is  formed  by  the  nuchal  surface  (planum  nuchale)  of  the  s(|uamous  part  of  that 
bone.  Posteriorly  this  surface  is  bounded  by  the  superior  curved  line,  in  the  centre 
of  which  is  placed  the  projecting  external  occipital  protuberance.  Laterally  the 
tabular  plate  is  separated  from  the  mastoid  portion  of  the  temporal  bone  by  the 
occipito-mastoid  suture,  which  curves  backwards  and  laterally,  from  the  extremity 
of  the  jugular  process  in  front,  around  the  base  of  the  mastoid  process  behind.     In 


NOEMA  BASALTS  OF  THE  SKULL.  165 

front  and  in  the  middle  line  this  plate  of  bone  is  pierced  by  the  foramen  magnum, 
the  anterior  half  of  which  has  been  already  seen  to  lie  between  the  occipital 
condyles.  Usually  of  oval  form,  though  in  some  cases  it  tends  to  approach  the 
circular,  the  plane  of  this  opening  is  inclined  downwards  and  slightly  forwards. 
The  extreme  anterior  edge  of  the  foramen  is  sometimes  called  the  basion,  whilst  the 
extreme  posterior  margin  is  termed  the  opistMon.  The  lower  border  of  the  medulla 
oblongata,  where  it  becomes  continuous  with  the  spinal  cord,  is  lodged  within  the 
foramen,  together  with  the  meninges  which  cover  it,  whilst  the  vertebral  arteries 
and  the  spinal  portions  of  the  spinal  accessory  nerves  pass  upwards  through  it. 
The  anterior  and  posterior  spinal  arteries,  some  small  veins,  and  the  roots  of  the 
first  cervical  nerves,  also  traverse  it  from  above  downwards. 

The  student  will,  no  doubt,  experience  considerable  difficulty  in  bearing  in  mind  the  relative 
positions  of  the  various  foramina  and  processes  which  he  has  studied  on  the  under  surface  of  the 
base  of  the  skull. 

If  a  line  be  drawn  on  either  side  from  the  anterior  palatine  canal  in  front,  through  the  stylo- 
mastoid foramina  jjosteriorly,  it  will  be  found  to  cut  or  pass  near  to  the  following  ol)jects  : — On 
the  hard  jjalate  it  will  lie  close  to  the  posterior  and  accessory  palatine  canals.  It  will  then  pass 
between  the  hanuilar  process  and  the  external  pterygoid  plate  overlying  the  foramen  ovale,  the 
foramen  sjjinosum,  the  opening  of  the  osseous  Eustachian  canal  and  the  spine  of  the  sjjlienoid  ; 
behind  this  it  will  cut  through  the  root  of  the  styloid  process  and  define  laterally  the  limits  of 
the  jugular  fossa.  After  passing  through  the  stylo-mastoid  foramen,  if  the  line  be  prolonged 
backwards  it  will  usually  be  found  to  pass  over  the  mastoid  foramen  in  the  occipito-mastoid 
suture.  Another  line  of  much  value  is  one  drawn  across  the  base  of  the  skull  from  the  centre 
of  one  external  auditory  meatus  to  the  other.  This  will  be  found  to  pass  through  the  root  of 
the  styloid  process,  the  jugular  foramen,  the  anterior  condylic  foramen  ;  it  then  crosses  the  front 
of  the  occipital  condyles,  and  corresponds  with  the  anterior  edge  of  the  foramen  magnum. 

A  line  which  may  be  found  useful  is  one  drawn  from  the  stylo-mastoid  foramen  of  one  side  to 
the  posterior  palatine  canal  of  the  opposite  side.  This  will  be  seen  to  overlie,  from  behind 
forwards,  the  lateral  part  of  the  jugular  foramen  and  the  inferior  opening  of  the  carotid  canal. 
The  line  indicates  the  direction  of  the  carotid  canal,  and  cuts  the  foramen  lacerum  anteriorly  ; 
in  front  of  this  it  usually  corresponds  to  the  position  of  the  posterior  aperture  of  the  pterygo- 
palatine (pharyngeal)  canal. 

Mandible  and  Atlas. — The  examination  of  the  base  of  the  skull  is  incomplete 
unless  the  student  examines  it  with  the  lower  jaw  and  atlas  in  position.  The 
relation  of  the  ramus  of  the  lower  jaw  to  the  zygomatic  fossa  has  been  already 
sufficiently  studied  (p.  156) ;  one  or  two  points,  however,  may  be  emphasised. 
The  alar  spine  of  the  sphenoid  lies  just  medial  to  the  condyle  of  the  jaw  when 
that  structure  is  in  position  in  the  articular  part  of  the  glenoid  fossa,  and  it  is 
noteworthy  that  immediately  to  the  medial  side  of  the  alar  spine  is  the  commence- 
ment of  the  osseous  Eustachian  tube.  The  root  of  the  styloid  process  occupies  the 
centre  of  the  interval  between  the  mandibular  ramus  and  the  front  of  the 
mastoid  process. 

Anteriorly  the  arcade  formed  by  the  body  of  the  lower  jaw  adds  greatly  to  the 
depth  of  the  hard  palate.  In  this  space  are  lodged  the  tongue  and  the  structures 
which  form  the  floor  of  the  mouth.  The  medial  surface  of  each  side  of  the  body  of 
the  mandible  is  traversed  by  the  mylo-hyoid  line,  which  commences  posteriorly 
just  behind  the  root  of  the  last  molar  tooth  and  runs  downwards  and  forwards 
towards  the  symphysis  in  front. 

When  the  atlas  is  in  articulation  with  the  occipital  bone  it  is  well  to  recognise 
the  relation  of  its  transverse  processes  to  the  surrounding  structures.  The 
extremities  of  these  processes  lie  in  line  with  the  ends  of  the  jugular  processes  of 
the  occipital  bone,  and  thus  come  to  be  placed  just  medial  to  and  immediately  below 
and  slightly  in  front  of  the  tips  of  the  mastoid  processes.  They  can  thus  be  easily  felt 
in  the  living.  Anteriorly  they  are  separated  by  a  short  interval  from  the  styloid 
processes,  and  the  stylo-mastoid  foramina  lie  immediately  in  front  and  sKghtly  to 
the  lateral  side  of  their  extremities.  The  student  will  note  that  there  is  no  hole  in 
the  jugular  process  of  the  occipital  bone  corresponding  to  the  arterial  foramen  in 
the  transverse  process  of  the  atlas  through  which  the  vertebral  artery  passes.  The 
course  of  this  vessel  over  the  upper  surface  of  the  posterior  arch  behind  the 
superior  articular  processes  of  the  atlas  will  be  seen  to  coincide  with  the  posterior 
condylic  fossae  and  the  margins  of  the  foramen  magnum  immediately  medial 
thereto,  where  a  sUght  grooving  of  the  edge  often  indicates  the  course  of  the  artery. 

11 


166  OSTEOLOGY. 

In  front  the  anterior  tubercle  of  the  atlas  falls  in  line  with  the  pharyngeal  tubercle 
on  the  under  surface  of  the  basi-occipital,  and  the  student  must  not  overlook  the 
fact  that  the  anterior  surface  of  the  cervical  column  does  not  coincide  with  the 
anterior  margin  of  the  foramen  magnum,  but  lies  nearly  half  an  inch  in  front  of 
that,  in  a  coronal  plane  passing  immediately  in  front  of  the  external  auditory 
meatus.  Behind,  the  upper  surface  of  the  posterior  arch  of  the  atlas  overlaps  the 
hinder  margin  of  the  foramen  magnum,  and  it  is  by  the  apposition  of  these  two 
surfaces  that  extension  is  checked  at  the  occipito-atlantal  articulation. 


THE   SKULL   IN    SECTION. 

By  the  removal  of  the  skull-cap  the  cerebral  aspect  of  the  cranial  cavity  is  exposed. 
The  deep  surface  of  the  cranial  vault  is  grooved  medially  for  the  superior  longitudinal 
(sagittal)  sinus,  on  either  side  of  which  are  seen  numerous  depressions  for  the  lodg- 
ment of  Pacchionian  bodies.  On  holding  the  bone  up  to  the  light,  the  floor  of  these 
little  hollows  is  oftentimes  seen  to  be  very  thin.  A  short  distance  in  front  of  the 
lambda,  and  on  either  side  of  the  sagittal  suture,  are  the  cerebral  openings  of  the 
parietal  foramina.  The  inner  tables  of  the  frontal  and  parietal  bones  are  grooved 
for  the  meningeal  arteries.  The  principal  branch  of  the  middle  meningeal  runs  more 
or  less  parallel  to  and  at  a  variable  distance  behind  the  line  of  the  coronal  suture. 
Along  the  bottom  of  these  grooves  small  foramina  may  be  seen  for  the  passage  of 
nutrient  arteries  to  the  bone,  and  the  floor  of  the  longitudinal  sinus  is  likewise 
pierced  by  small  apertures  for  the  transmission  of  veins. 

The  Upper  Surface  of  the  Base  of  the  Skull. 

Cranial  Fossae. — The  upper  surface  of  the  base  of  the  skull  is  divided  into 
three  fossae,  of  which  the  cerebrum  occupies  the  anterior  and  middle,  whilst  in  the 
posterior  is  lodged  the  cerebellum. 

The  anterior  fossa  is  defined  posteriorly  by  the  sharp,  thin  edge  of  the  lesser 
wings  of  the  sphenoid,  which  curve  laterally  and  slightly  upwards  as  well  as  back- 
wards to  reach  the  region  of  the  pterion  laterally.  The  floor  is  formed  from  before 
backwards,  in  the  middle  line,  by  the  upper  surface  of  the  ethmoid  and  the  fore- 
part of  the  body  of  the  sphenoid ;  laterally  it  is  constituted  by  the  orbital  plates 
of  the  frontal  and  the  lesser  wings  of  the  sphenoid.  On  these  the  under  surface 
of  the  frontal  lobes  of  the  cerebrum  rests.  In  front  the  fossa  is  divided  medially 
by  the  frontal  crest,  to  whiG]|i  the  falx  cerebri  is  attached.  This  is  confluent  below 
with  the  fore  part  of  the  crista  galli,  from  which,  however,  it  is  separated  by  the 
foramen  csecum,  which  usually  transmits  a  smaU  vein  from  the  nose.  On  either 
side  of  the  crista  galli  there  are  grooves  which  vary  considerably  in  depth  and 
width :  therein  are  lodged  the  olfactory  lobes.  The  floor  and  sides  of  the  groove 
are  pierced  by  numerous  foramina ;  of  these  the  largest  number  transmit  the 
olfactory  nerves  to  the  nasal  fossse.  In  front  an  elongated  slit,  placed  on  either 
side  of  the  crista,  affords  a  passage  to  the  nose  for  the  internal  ramus  of  the  nasal 
nerve  and  a  small  branch  of  the  anterior  ethmoidal  artery  which  accompanies  it. 
To  the  lateral  side  of  the  olfactory  groove  and  the  cribriform  plate,  the  anterior 
fossse  communicate  on  either  side  by  means  of  the  two  ethmoidal  foramina  with 
the  cavities  of  the  orbits.  The  anterior  foramen  transmits  the  internal  ramus  of 
the  nasal  nerve  and  the  anterior  ethmoidal  artery ;  the  posterior  affords  passage  to 
the  posterior  ethmoidal  artery  and  the  small  spheno-ethmoidal  nerve  of  Luschka. 
Lateral  to  the  olfactory  groove,  the  floor  of  the  fossa,  which  here  corresponds 
to  the  roof  of  the  orbit,  is  very  thin,  as  may  be  seen  by  holding  the  skull  up  to 
the  light ;  it  is  convex  from  side  to  side,  and  bears  the  impress  of  the  convolutions 
of  the  under  surface  of  the  frontal  lobes  of  the  cerebrum  which  rest  upon  it. 
In  front  and  at  the  side  there  are  a  number  of  vascular  grooves  for  the  branches 
of  the  anterior  and  middle  meningeal  arteries  respectively. 

The  middle    fossa,  which  in  form  may  be  compared  to  the  wings  of  a  bird 


41  1 


Fig.  118. — Base  of  the  Skull  seen  from  Above. 

Tlie  frontal  and  occipital  bones  are  coloured  red  ;  the  ethmoid  and  temporal  bones,  blue  ;  the 
parietal,  orange  ;  and  the  sphenoid  is  left  uncoloured. 


9. 
10. 
11. 
12. 
13. 
14. 
15. 
16. 
17. 
18. 
19. 
20. 
21. 
22. 
23, 


Frontal  bone. 

Slit  for  nasal  nerve. 

Anterior  ethmoidal  foramen. 

Posterior  ethmoidal  foramen. 

Optic  foramen. 

Foramen   for   internal    carotid  artery  formed  by 

anterior  and  middle  cliuoid  process. 
Lesser  wing  of  sphenoid. 
Anterior  clinoid  process,  in  this  case  united  on  its 

inner  side  to  the  middle  clinoid  processes. 
Posterior  clinoid  process. 
Foramen  ovale. 

Groove  for  middle  meningeal  artery. 
Foramen  spinosum. 
Hiatus  Fallopii. 

Line  of  petro- squamosal  suture.  - 
Internal  auditory  meatus. 
Groove  for  superior  petrosal  sinus. 
Groove  for  sigmoid  part  of  lateral  sin\is. 
Jugular  foramen. 

Anterior  condylic  foramen  (canalis  hypoglossi). 
Groove  for  lateral  sinus. 
Internal  occipital  protuberance. 
Ridge  for  attachment  of  falx  cerebri. 
Fossa  for  the  lodgment  of  the  occipital  lobes  of 

the  brain. 


24.  Pudge  for  the  attachment  of  the  falx  cerebelli. 

25.  Fossa   for    the   lodgment    of   the  left    cerebellar 

hemisphere. 

26.  Foramen  magnum. 

27.  Groove   for  the   sigmoid  sinus  turning  into   the 

jugular  foramen.  . 

28.  Groove   for  the    inferior   petrosal    sinus  running 

along  the  line  of  suture  between  the  petrous 
part  of  the  temporal  and  the  basi-occipital. 

29.  Depression  for  the  Gasserian  ganglion. 

30.  Middle  cranial  fossa  for  lodgment  of  the  temporal 

lobe's  of  the  brain. 

31.  Foramen  lacerum. 

32.  Carotid  groove. 

33.  Dorsum  sellae  of  sphenoid. 

34.  Leads  into  foramen  rotundum, 

35.  Pituitary  fossa. 

36.  Olivary  eminence  of  the  sphenoid. 

37.  Anterior  cranial  fossa  for  lodgment  of  frontal  lobes 

of  the  brain. 

38.  Cribriform  plate  of  ethmoid. 

39.  Crista  galli  of  ethmoid. 

40.  Foramen  caecum. 

41.  Crest  for  attachment  of  falx  cerebri. 


11a 


168  OSTEOLOGY. 

united  by  the  body,  is  bounded  in  front  by  the  curved  thin  posterior  edge  of  the 
lesser  wings  of  the  sphenoid  ;  posteriorly,  by  the  line  of  attachment  of  the  tentorium 
cerebelli,  extending  from  the  posterior  clinoid  process  along  the  superior  border  of 
the  petrous  portion  of  the  temporal  bone.  The  median  part  of  the  fossa,  which  is 
narrow,  corresponds  to  the  sella  turcica  and  the  olivary  eminence  of  the  sphenoid. 
It  is  limited  anteriorly  by  a  hne  connecting  the  anterior  margins  of  the  two  optic 
foramina,  and  is  overhung  behind  by  the  dorsum  sellse.  In  this  area  are  lodged 
the  structures  which  lie  within  the  interpeduncular  space  on  the  base  of  the  brain. 
The  floor  of  the  lateral  parts  of  the  fossa  on  each  side  is  formed  by  the  great  wing 
of  the  sphenoid  in  front,  the  squamous  part  of  the  temporal  bone  to  the  lateral  side, 
and  the  superior  surface  of  the  petrous  part  of  the  temporal  behind.  In  the  hoUows 
so  formed  the  temporal  lobes  of  the  cerebrum  are  lodged.  On  either  side  of  the 
olivary  eminence  are  seen  the  optic  foramina ;  these  pass  into  the  orbital  cavities 
and  transmit  the  optic  nerves  and  ophthalmic  arteries.  Immediately  behind  these 
openings  the  anterior  and  middle  clinoid  processes  are  sometimes  united,  so  as  to 
enclose  a  foramen.  Through  this  the  internal  carotid  artery  passes  upwards. 
Leading  backwards  from  this,  along  the  side  of  the  body  of  the  sphenoid,  is  the 
carotid  groove,  which  turns  downwards  near  the  apex  of  the  petrous  part  of  the 
temporal,  to  become  continuous  with  the  carotid  canal,  which  here  opens  on  the 
posterior  waU  of  an  irregular  aperture,  placed  between  the  side  of  the  body  of  the 
sphenoid  and  the  summit  of  the  petrous  part  of  the  temporal,  called  the  foramen 
lacerum.  Through  the  medial  angle  of  this  opening  the  carotid  artery  accompanied 
by  its  plexus  of  veins  and  sympathetic  nerves  passes  upwards.  Eunning  through 
the  fibrous  tissue,  which  in  life  blocks  up  this  opening,  the  great  superficial  petrosal 
nerve  coming  from  the  hiatus  Fallopii  passes  downwards  and  forwards  to  reach 
the  posterior  orifice  of  the  Vidian  canal  (canalis  pterygoideus),  which  is  placed  on  the 
anterior  and  inferior  border  of  the  foramen  lacerum. '  A  small  meningeal  branch 
of  the  ascending  pharyngeal  artery  also  passes  upwards  through  this  foramen.  In 
front  and  to  the  lateral  side  of  the  foramen  lacerum,  and  separated  from  it  by  a 
narrow  bar  of  bone,  is  the  foramen  ovale ;  through  this  pass  both  roots  of  the 
mandibular  nerve,  the  small  meningeal  artery,  and  some  emissary  veins.  Some- 
what lateral  and  posterior  to  this  is  the  foramen  spinosum  for  the  transmission  of 
the  middle  meningeal  vessels,  together  with  a  recurrent  branch  from  the  mandibular 
nerve  (nervus  spinosus).  >  Leading  from  the  lateral  extremity  of  the  foramen 
lacerum  there  is  a  groove  which  passes  laterally,  backwards,  and  slightly  upwards 
on  the  superior  surface  of  the  petrous  part  of  the  temporal  to  end  in  the  hiatus 
Fallopii  (a  cleft  opening  into  the  aquseductus  Fallopii),  which  gives  passage  to  the 
great  superficial  petrosal  branch_derived  from  the  geniculate  ganglion  on  the  seventh 
nerve,  together  with  the  small  petrosal  branch  of  the  middle  meningeal  artery. .  Just 
lateral  to  the  hiatus  Fallopii  there  is  another  small  foramen  for  the  transmission  of 
the  lesser  superficial  petrosal  nerve.  Overhung  by  the  posterior  border  of  the  lesser 
wing  of  the  sphenoid  is  the  sphenoidal  fissure  (fissura  orbitalis  superior),  the  cleft 
which  separates  the  lesser  from  the  great  wings  of  the  sphenoid,  and  which  opens 
anteriorly  into  the  hollow  of  the  orbit ;  through  this  pass  the  third,  fourth,  oph- 
thalmic division  of  the  fifth,  and  sixth  nerves,  together  with  the  ophthalmic  veins 
as  well  as  the  sympathetic  filament  to  the  ciliary  ganglion  and  the  small  orbital 
branch  of  tlie  middle  meningeal  artery.  Just  below  its  medial  extremity  is  the 
foramen  rotundum  for  the  passage  of  the  maxillary  nerve  to  the  spheno-maxillary 
fossa.  Behind  this,  and  between  it  and  the  foramen  ovale,  the  foramen  Vesalii  may 
occasionally  be  seen,  through  which  a  vein  passes  to  reach  the  pterygoid  plexus. 

The  lateral  parts  of  the  middle  fossa  are  moulded  in  conformity  with  the 
convolutions  of  the  temporal  lobes,  but  towards  its  medial  part  the  splitting  of 
the  dura  mater  in  the  region  of  the  cavernous  sinus  serves  to  separate  the  cranial 
base  from  the  under  surface  of  the  cerebrum.  As  may  be  seen  by  transmitted  light, 
the  floor  of  the  lateral  parts  of  the  fossa  is  thin  as  it  overlies  the  temporal, 
zygomatic,  and  glenoid  fossae.  The  grooves  for  the  lodgment  of  the  branches  of  the 
middle  meningeal  artery  leading  from  the  foramen  spinosum  are  readily  seen ;  one, 
coursing  backwards  a  little  below  the  line  of  the  squamoso-parietal  suture,  is 
specially  well  marked.     Amongst  other  features  may  be  noticed  the  depression  for 


THE  UPPER  SURFACE  OF  THE  BASE  OF  THE  SKULL.    169 

the  lodgment  of  the  Gasserian  ganglion  overlying  the  summit  of  the  petrous 
temporal;  behind  and  to  the  lateral  side  of  the  hiatus  Fallopii,  the  arcuate 
eminence,  indicating  the  position  of  the  superior  semicircular  canal ;  and  immediately 
anterior  and  slightly  to  the  lateral  side  of  this  the  tegmen  tympani,  which  roofs  in 
the  cavity  of  the  tympanum,  the  thinness  of  which  can  readily  be  demonstrated 
if  hght  be  allowed  to  fall  through  the  external  auditory  meatus. 

The  posterior  fossa  is  larger  and  deeper  than  the  others.  In  front  it  is  limited 
by  a  line  on  either  side  leading  backwards  and  laterally  from  each  posterior  clinoid 
process  along  the  superior  border  of  the  petrous  part  of  the  temporal  bone,  where 
laterally  and  posteriorly  it  becomes  confluent  with  the  superior  lip  of  the  transverse 
groove  for  the  lateral  (transverse)  sinus,  ending  posteriorly  in  the  middle  line  at 
the  internal  occipital  protuberance.  Along  the  line  thus  indicated  the  process  of 
dura  mater  called  the  tentorium  xerebelli,  which  roofs  in  the  posterior  fossa,  is 
attached.  The  floor  of  the  fossa,  in  which  the  cerebellar  lobes,  the  pons,  and 
medulla  are  lodged,  is  formed  by  the  petrous  and  mastoid  portions  of  the  temporal 
bone,  with  part  of  the  body  of  the  sphenoid  and  the  basilar  portion  of  the  occipital 
bone  wedged  in  between  them.  Above  the  mastoid  part  of  the  temporal  a  small  part 
of  the  mastoid  angle  of  the  parietal  enters  into  the  constitution  of  the  outer  wall  of 
the  fossa.  Behind  and  within  these  the  lateral  parts  and  lower  portions  of  the 
squamous  part  of  the  occipital  complete  the  floor.  In  the  middle  line  the  floor  of  the 
fossa  is  pierced  by  the  foramen  magnum,  in  which  lies  the  lower  part  of  the  medulla, 
together  with  its  membranes,  and  through  which  pass  upwards  the  vertebral 
arteries  and  the  accessory  nerves.  Iy  On  either  side  of  the  foramen  magnum,  and 
a  little  in  front  of  a  transverse  line  passing  through  its  centre,  is  the  opening 
of  the  anterior  condylic  foramen  (canalis  hypoglossi)  for  the  passage  of  the  hypo- 
glossal nerve,  a  small  meningeal  branch  from  the  ascending  pharyngeal  artery 
and  an  emissary  vein.  Overhanging  the  opening  of  the  anterior  condylic  foramen 
there  is  a  thickened  rounded  bridge  of  bone,  to  the  lateral  side  of  which  is  placed 
the  irregular  opening  of  the  jugular  foramen.  The  size  of  this  is  apt  to  vary  on 
the  two  sides,  and  the  lumen  is  frequently  subdivided  by  a  spicule  of  bone  which 
runs  across  it ;  the  posterior  and  lateral  rounded  part  of  the  foramen  is  occupied 
by  the  lateral  (transverse)  sinus,  which  here  joins  the  internal  jugular  vein.  A 
meningeal  branch  from  the  ascending  pharyngeal  or  occipital  artery  also  enters  the 
skull  through  this  compartment.  The  fore  and  medial  part  of  the  foramen  is  con- 
fluent with  the  groove  for  the  inferior  petrosal  sinus,  which  turns  downwards  in  front 
of  the  spicule  above  referred  to.  The  interval  between  the  portions  of  the  foramen 
occupied  by  the  two  veins  allows  the  transmission  of  the  glosso-pharyngeal,  vagus, 
and  accessory  nerves  in  this  order  from  before  backwards.  About  a  quarter  of 
an  inch  above  and  to  the  lateral  side  of  the  fore  part  of  the  foramen  jugulare  the 
posterior  surface  of  the  petrous  portion  of  the  temporal  bone  is  pierced  by  the 
internal  auditory  meatus,  through  which  the  facial  and  auditory  nerves,  together 
with  the  pars  intermedia  of  Wrisberg  (n.  intermedins),  and  the  auditory  branch  of 
the  basilar  artery,  leave  the  cranial  cavity.  Behind  the  jugular  foramen  and  close 
to  the  margin  of  the  foramen  magnum  the  opening  of  the  posterior  condylic 
foramen  (canalis  condyloideus),  when  present,  may  be  seen.  This  gives  passage 
to  a  vein  which  joins  the  vertebral  vein  inferiorly.  The  medial  aperture  of  the 
mastoid  foramen  is  noticed  opening  into  the  groove  for  the  lateral  sinus,  a  little  below 
the  level  of  the  superior  border  of  the  petrous  part  of  the  temporal.  Through  it 
passes  an  emissary  vein  which  joins  the  occipital  vein  laterally ;  the  mastoid  branch 
of  the  occipital  artery  also  enters  the  cranial  cavity  through  this  foramen. 

The  posterior  fossa  is  divided  into  two  halves  posteriorly  by  the  internal  occipital 
crest,  to  which  the  falx  cerebelli  is  attached,  the  floors  of  the  hollows  on  either  side 
of  which  are  often  exceedingly  thin  and  are  for  the  lodgment  of  the  lateral  lobes  of 
the  cerebellum.  The  grooves  for  the  following  blood  sinuses  are  usually  distinct — 
the  superior  petrosal  running  along  the  superior  border  of  the  petrous  part  of  the 
temporal,  the  inferior  petrosal  lying  along  the  line  of  suture  between  the  petrous 
part  of  the  temporal  and  the  basilar  process  of  the  occipital  bone ;  the  occipital 
sinus  grooving  the  internal  occipital  crest ;  and  the  lateral  sinus  curving  forwards 
and  laterally  from  the  internal  occipital  protuberance,  across  the  cerebral  surface 


170  OSTEOLOGY. 

of  the  squamous  part  of  the  occipital,  to  reach  the  posterior  inferior  angle  of  the 
parietal  bone,  in  front  of  which  it  turns  downwards  and  medially  to  reach  the 
jugular  foramen,  describing  a  sigmoid  curve,  and  grooving  deeply  the  medial  surface 
of  the  mastoid  and  posterior  aspect  of  the  petrous  portions  of  the  temporal  bone. 
Before  it  terminates  at  the  jugular  foramen  it  again  reaches  the  occipital  bone  and 
channels  the  upper  surface  of  the  jugular  process  of  that  bone.  Slight  grooves  for 
meningeal  arteries  are  also  seen — some  pass  upwards,  whilst  others  turn  downwards 
and  are  occupied  by  branches  from  the  posterior  offsets  of  the  middle  meningeal 
arteries. 

Medial   Sagittal   Section   of  the  Skull. 

Such  a  section  should  be  made  a  little  to  one  or  other  side  of  the  medial  jjlane,  so  as  to  pass 
through  the  nasal  fossae  lateral  to  the  septum  ;  one-half  will  then  display  the  nasal  septum  in 
position,  whilst  in  the  other  the  outer  wall  of  the  nasal  fossa  of  that  side  will  be  exposed. 

The  form  of  the  cranial  cavity  is,  of  course,  subject  to  many  variations  dependent 
on  individual  and  racial  peculiarities.  The  following  details  are,  however,  worthy 
of  note.  The  hinder  border  of  the  foramen  magnum  (opisthion),  and  consequently 
the  floor  of  the  posterior  cranial  fossa,  occupies  the  same  horizontal  plane  as  the 
hard  palate.  The  anterior  border  of  the  foramen  magnum  (basion)  lies  a  little 
higher,  so  that  the  plane  of  the  foramen  is,  in  the  higher  races  at  least,  oblique,  and 
is  directed  downwards  and  slightly  forwards.  From  the  basion  a  line  passing 
upwards  and  forwards  to  reach  the  suture  between  the  sphenoid  and  ethmoid 
passes  through  the  basi-cranial  axis  formed  by  the  basi-occipital,  the  basi-sphenoid, 
and  the  j)resphenoid.  The  basi-cranial  axis  is  wedge-shaped  on  section  posteriorly, 
whilst  anteriorly  it  is  of  considerable  width,  and  has  within  it  the  large  sphenoidal 
air  sinus.  Its  upper  surface  leads  upwards  and  forwards  with  a  varying  degree  of 
obliquity  from  the  basion  to  the  overhanging  edge  of  the  dorsum  sellse,  in  front  of 
which  the  pituitary  fossa,  the  floor  of  which  is  quite  thin,  is  well  seen  in  the 
section. 

From  the  olivary  eminence  the  floor  of  the  anterior  fossa  follows  a  more  or  less 
horizontal  direction,  corresponding  pretty  closely  to  the  level  of  the  axis  of  the  orbital 
cavity.  The  roof  of  the  orbit  is  seen  to  bulge  upwards  to  a  considerable  extent  into  the 
floor  of  the  anterior  fossa ;  whilst  the  floor  of  the  middle  fossa  sinks  to  a  level  corresponding 
to  that  of  the  under  surface  of  the  basi-cranial  axis,  where  it  forms  the  roof  of  the  posterior 
nares.  The  maximum  length  of  the  skull  is  measured  from  the  glabella  (a  point  between 
the  superciliary  ridges)  to  the  occipital  point  posteriorly.  It  is  noteworthy  that  the 
maximum  occipital  point  does  not  necessarily  correspond  to  the  external  occipital  pro- 
tuberance (inion).  The  greatest  vertical  height  usually  corresponds  to  the  distance  from 
the  basion  to  the  bregma  (point  of  union  of  the  sagittal  with  the  coronal  suture),  though 
to  this  rule  there  are  many  exceptions.  On  looking  into  the  posterior  fossa  the  anterior 
condylic  and  jugular  foramina  and  the  internal  auditory  meatus  are  seen  in  line,  sloping 
from  below  upwards.  The  internal  auditory  meatus  lies  in  a  vertical  plane,  passing 
through  the  basion.  The  grooves  for  the  middle  meningeal  artery  and  its  branches  are 
very  obvious.  The  anterior  groove  curves  forwards  and  laterally,  and  reaching  the  cerebral 
surface  of  the  pterion,  passes  towards  the  vertex  at  a  variable  distance  behind  and  more 
or  less  parallel  to  the  coronal  suture.  From  this  grooves  pass  forwards  across  the  suture 
to  reach  the  frontal  bone.  Another  groove  curves  upwards  and  backwards  a  little  below 
the  line  of  the  parieto-squamosal  suture.  From  this  an  upwardly-directed  branch 
radiates  on  the  central  surface  of  the  parietal  bone,  in  the  region  of  the  parietal  eminence, 
whilst  a  lower  branch  passes  backwards  some  little  distance  above  the  lambdoid  suture, 
and  gives  offsets  which  curve  downwards  and  medially  over  the  cerebral  surface  of  the 
squamous  portion  of  the  occipital  bone. 

Nasal  Fossae. — In  the  section  through  the  nasal  fossa  the  structures  which  form 
its  lateral  wall  can  now  be  studied.  These  are — tbe  nasal  bone  ;  the  frontal  process 
of  the  maxilla ;  the  lacrimal  bone ;  the  lateral  mass  of  the  ethmoid,  comprising 
the  superior  and  middle  turbinated  bones ;  the  vertical  part  of  the  palate  bone ; 
the  inferior  turbinated  bone  ;  and  the  medial  surface  of  the  internal  pterygoid  plate. 
The  roof  as  seen  in  the  section  is  formed  by  the  nasal  and  frontal  bones,  the  cribri- 
form plate  of  the  ethmoid,  the  body  of  the  sphenoid  and  the  sphenoidal  turbinals. 


THE  NASAL  FOSS^. 


171 


the  sphenoidal  process  of  the  palate  and  the  ala  of  the  vomer.  The  floor,  which  is 
nearly  horizontal  from  before  backwards,  is  formed  by  the  palatal  processes  of  the 
maxiUa  and  palate   bones.      On  sagittal  section   the  nasal  fossa  appears  some- 


42  41   40  39  38  37  36   35  34  33  32  31  80  29  28   27  26  25   24    23        22       21 

Fig.   119. — Medial  Aspect  of  the  Left  Half  of  the  Skull  sagittallt  divided. 

The  frontal,  ma.xillary,  and  sphenoid  bones  are  coloured  red  ;  the  nasal  and  palate  bones,  blue  ;  and  the 
occipital,  yellow.  The  ethmoid  and  inferior  turbinal,  together  with  the  left  ala  of  the  vomer,  are  left 
uncoloured. 

Posterior  nasal  sjjine. 

Hamular  process  of  internal  pterygoid  plate. 

External  pterygoid  plate. 

Superior  meatus  of  nose. 

Spheno-palatine  foramen. 

Pterygo  -  spinous     ligament     almost     completely 

ossified  to  enclose  a  foramen. 
Styloid  process  of  temporal  bone. 
Alar  spine  of  sphenoid. 
Mastoid  process. 
Basion  (mid-point  of  anterior  border  of  foramen 

magnum). 
Internal  auditory  meatus. 

Anterior  condylic  foramen  (foramen  hypoglossi). 
Leading  into  jugular  foramen. 
Opisthion    (mid-point    of    posterior    border    of 

foramen  magnum). - 
Groove  for  sigmoid  sinus. ' 
Opening  of  mastoid  foramen. 
For    lateral  sinus  and  attachment  of   tentorium 

cerebelli. 
Fossa  for  lodgment  of  cerebellar  hemisphere. 
Internal  occipital  protuberance, 
atal  process  of  palate  bone. 

what  triangular  in  shape  with  the  angles  cut  off;  the  base  corresponds  to  the 
floor ;  the  anterior  and  posterior  nares  to  the  truncated  anterior  and  posterior 
angles  respectively  ;  the  superior  angle  is  cut  off  by  the  cribriform  plate  ;  whilst  the 
sides  correspond  to  the  frontal  and  nasal  bones  anteriorly,  and  the  sphenoidal 


1. 

Suture  between  parietal  and  temporal  bones. 

24. 

2. 

Remains  of  the  subarcuate  fossa. 

25. 

3. 

Grooves  for  branches    of  the  middle   meningeal 

26. 

artery. 

27. 

4. 

Dorsum  sellse. 

28. 

5. 

Pitiiitary  fossa. 

29. 

6. 

Anterior  clinoid  fossa-. 

7. 

Optic  foramen. 

30. 

8. 

Sphenoidal  sinus. 

31. 

9. 

Nasal  surface  of  superior  turbinated  bone. 

32. 

10. 
11. 

Cribriform  plate  of  ethmoid. 

Nasal  surface  of  middle  turbinated  bone. 

33. 

12. 

Frontal  sinus. 

34. 

13. 

Spine  of  frontal. 

35. 

14. 

Nasal  bone. 

36. 

15. 

Frontal  process  of  maxilla. 

37. 

16. 

Middle  meatus  of  nose. 

17. 

Directed  towards  opening  of  antrum. 

38. 

18. 

Nasal  surface  of  inferior  turbinated  bone. 

39, 

19. 

Inferior  meatus  of  nose. 

40. 

20. 

Anterior  nasal  spine. 

21. 

Anterior  palatine  canal. 

41. 

22. 

Palatal  process  of  maxilla. 

42. 

23. 

Palatal  process  of  palate  bone. 

172  OSTEOLOGY. 

turbinals,  sphenoidal  process  of  the  palate,  and  the  ala  of  the  vomer  posteriorly. 
The  cavity  is  therefore  deep  towards  its  middle,  but  gradually  becomes  shallower  in 
front  and  behind  where  the  openings  of  the  nares  are  situated.  The  opening  of 
the  anterior  naris,  which  is  of  half-heart  shape,  is  larger  than  that  of  the  posterior 
naris,  and  is  directed  forwards  and  downwards ;  the  opening  of  the  posterior  is 
of  rhomboidal  form,  and  slopes  backwards  and  downwards.  The  inferior  meatus  is 
the  channel  which  is  overhung  by  the  inferior  turbinated  bone,  and  its  floor  is 
formed  by  the  side-to-side  concavity  of  the  upper  surface  of  the  hard  palate. 
Opening  into  it  above,  under  cover  of  the  fore  part  of  the  inferior  turbinated  bone, 
is  the  canal  for  the  nasal  duct ;  whilst  its  floor  is  pierced  in  front  near  the  middle 
line  by  the  anterior  palatine  canal.  The  middle  meatus  is  the  hollow  between  the 
middle  and  inferior  turbinated  bones ;  it  slopes  from  above  downwards  and  back- 
wards, and  is  overhung  by  the  free  curved  edge  of  the  middle  turbinal,  beneath 
which  there  is  a  passage  called  the  infundibulum,  leading  upwards  and  forwards  to 
open  superiorly  into  the  frontal  sinus,  as  well  as  into  some  of  the  anterior  ethmoidal 
cells.  Under  cover  of  the  centre  of  the  middle  turbinated  bone  and  continuous 
with  the  infundibulum  in  front  there  is  a  curved  groove,  the  hiatus  semilunaris, 
into  which  open  one  or  more  orifices  from  the  maxillary  sinus.  Above  this  groove 
there  is  a  rounded  eminence,  the  bulla  ethmoidalis,  overlying  the  middle 
ethmoidal  cells  which  usually  open  on  its  surface.  The  superior  meatus,  about 
half  the  length  of  the  middle  meatus,  is  placed  between  the  superior  and  middle 
turbinated  bones  in  the  back  and  upper  part  of  the  fossa ;  it  receives  the  openings 
of  the  posterior  ethmoidal  cells.  Near  its  posterior  extremity  the  spheno- 
palatine foramen  pierces  its  outer  wall,  and  brings  it  in  relation  with  the 
spheno- maxillary  fossa.  The  sphenoidal  sinus  opens  on  the  roof  of  the  nose, 
above  the  level  of  the  superior  turbinated  bone,  into  a  depression  called  the  spheno- 
ethmoidal recess. 

Nasal  Septum. — If  the  opposite  half  of  the  section  in  which  the  osseous  nasal 
septum  is  retained  be  now  studied,  it  will  be  seen  to  be  formed  by  the  crests  of 
the  maxillary  and  palate  bones  below,  on  which  rests  the  vomer,  the  posterior 
border  of  which  being  free,  forms  the  posterior  edge  of  the  nasal  septum,  which 
slopes  obliquely  upwards  and  backwards  towards  the  under  surface  of  the  body  of 
the  sphenoid.  Here  the  vomer  articulates  with  the  rostrum  of  the  s^jhenoid.  In 
front  of  this  the  vomer  articulates  with  the  perpendicular  part  of  the  ethmoid, 
between  which  anteriorly  there  is  an  angular  recess  into  which  the  cartilaginous 
septum  fits.  Superiorly  and  anteriorly  the  osseous  septum  is  completed  by  the 
articulation  of  the  perpendicular  part  of  the  ethmoid  with  the  nasal  process  of 
the  frontal,  together  with  the  nasal  crest  formed  by  the  union  of  the  nasal  bones ; 
whilst  posteriorly  and  superiorly  the  perpendicular  plate  of  the  ethmoid  articulates 
with  the  medial  ethmoidal  crest  of  the  sphenoid.  In  most  instances  the  osseous 
septum  is  not  perfectly  vertical,  but  is  deflected  towards  one  or  other  side. 

Air-sinuses  in  connexion  with  the  Nasal  Fossae. — Connected  with  the  nasal 
fosste  are  a  number  of  air-sinuses.  These  are  found  within  the  body  of  the 
sphenoid,  the  lateral  mass  of  the  ethmoid,  the  orbital  process  of  the  palate  bone,  the 
body  of  the  maxilla,  and  the  superciliary  arch  of  the  frontal  bone. 

The  sphenoidal  sinus,  of  variable  size,  occupies  the  interior  of  the  body  of  the 
sphenoid.  In  some  cases  it  extends  towards  the  roots  of  the  pterygoid  processes. 
In  front  it  is  formed  in  part  by  the  absorption  of  the  sphenoidal  spongy  bones, 
and  is  divided  up  into  two  cavities  by  a  sagittally-placed  partition,  which,  however, 
is  frequently  displaced  to  one  or  other  side.  It  opens  anteriorly  into  the  roof 
of  the  nose  in  the  region  of  the  spheno-ethmoidal  recess. 

The  ethmoidal  sinuses  are  placed  between  the  lateral  aspects  of  the  upper  part 
of  the  nasal  fossse,  and  the  cavities  of  the  orbit,  from  which  they  are  separated 
by  thin  and  papery  walls.  These  air-spaces  are  completed  by  the  articulation  of 
the  ethmoid  with  the  maxilla,  lacrimal,  frontal,  sphenoid,  and  palate  bones,  and 
are  divided  into  three  groups — an  anterior,  middle,  and  posterior.  The  latter 
communicates  with  the  superior  meatus ;  the  anterior  and  middle  open  either 
independently  or  in  conjunction  with  the  infundibulum  into  tlie  middle  meatus. 

The  sinus  in  the  orbital  process  of  the  palate  bone  either  communicates  with 


CORONAL  SECTIONS  OF  THE  CEANIUM. 


173 


Frontal    sinus 


Ciista  galH  of  ethmoid 


Cribriform  plate  of  ethmoid 
Sphenoidal   sinus 


Pituitary  fossa 
Dorsum  sellse 
of  sphenoid 


the  sphenoidal  sinus,  or  else  assists  in  closing  in  some  of  the  posterior  ethmoidal 
cells.  Its  communication  with  the  nasal  fossa  is  through  one  or  other  of  these 
spaces. 

The  maxillary  sinus  or  antrum  of  Higlunore  lies  to  the  lateral  side  of  the  nasal 
fossa3,  occupying  the  body  of  the  maxilla.  Its  walls,  which  are  relatively  thin,  are 
directed  upwards  to  the  orbit,  forwards  to  the  face,  backwards  to  the  infra-temporal 
(or  zygomatic)  and  ptery go-maxillary  (or  spheno-maxillary)  fossa3,and  medially  to  the 
nose.  In  the  latter  situa- 
tion the  vertical  plate  of  the 
palate  bone,  the  uncinate 
process  of  the  ethmoid,  the 
maxillary  process  of  the  in- 
ferior turbinated  bone,  and 
a  small  part  of  the  lacrimal 
bone  assist  in  the  formation 
of  the  thin  osseous  partition 
which  separates  it  from  the 
nasal  fossa.  The  floor  corre- 
sponds to  the  alveolar  border 
of  the  jaw,  and  differs  from 
the  other  walls  in  being  stout 
and  thick ;  it  is,  however, 
deeply  pitted  inferiorly  by 
the  alveoli  for  the  teeth. 
The  antrum  opens  by  a 
narrow  orifice  in  the  floor  of 
the  hiatus  semilunaris  into 
the  middle  meatus.  Oc- 
casionally there  are  two 
openings. 

The  frontal  sinuses  lie, 
one  on  either  side,  between 
the  inner  and  outer  tables  of  ^"'"""'  p'^'='^""^  "^^■""''^" 
the  frontal  bone  over  the  root 
of  the  nose,  and  extend 
laterally  under  the  super- 
ciliary arches.  The  parti- 
tion which  separates  them  is  usually  central,  though  it  may  be  deflected  to  one 
or  other  side.  They  communicate  with  the  nose  through  a  passage  called  the 
infundibulum,  which  opens  inferiorly  into  the  fore  part  of  the  middle  meatus, 
below  the  ethmoidal  bulla  and  continuous  with  the  hiatus  semilunaris. 

The  fact  should  not  be  overlooked  that  the  air-spaces  within  the  temporal 
bone,  viz.  the  tympanic  cavity  and  the  mastoid  air  cells,  are  brought  into  com- 
munication with  the  naso-pharynx  through  the  Eustachian  tubes.  Further  details 
regarding  the  air-sinuses  and  the  mode  of  their  growth  will  be  found  under  the 
description  of  the  individual  bones. 


Alar  spine 
Vomer 
External  pterygoid  plate 

Hamular  process 


Fig.  120. — The  Nasal  Septum  as  seen  fkom  the  Left  Side. 
The  froutal,  maxillary,  aud  sphenoid  bones  are  coloured  red  ;  the  nasal, 
vomer,  and  basi-occipital  blue  ;    the  vertical  plate  of  the  ethmoid 
and  the  palatal  process  of  the  palate  bone  are  left  uncoloured. 


Coronal  Sections. 

The  relations  of  many  parts  of  the  cranium  are  best  displayed  in  a  series  of  coronal 
sections. 

By  sawing  off  a  thin  slice  from  the  front  of  the  lower  part  of  the  frontal  bone 
above,  and  carrying  the  section  downwards  through  the  medial  wall  of  the  orbit  and 
the  frontal  process  of  the  maxilla,  into  the  anterior  nares  below,  a  number  of  important 
relations  are  revealed  (see  Fig.  121).  In  the  frontal  region  the  extent  and  arrange- 
ment of  the  frontal  sinuses  are  displayed.  The  partition  between  the  two  sinuses, 
be  it  noted,  is  usually  complete  and  central  in  position,  though  it  may  occasionally  be 
perforated  or  oblique.  The  sinuses  are  hardly  ever  symmetrical,  the  right  being 
usually  the  smaller  of  the  two.     (Logan  Turner,  Edin.  Med.  Jour.  1898.) 

The  infundibulum  on  either  side,  leading  from  the  frontal  sinus  above  to  the  middle 


174 


OSTEOLOGY. 


meatus  below,  is  seen  with  the  middle  turbinated  bone  medial  to  it,  and  the  anterior 
ethmoidal  cells  to  its  lateral  side  above.  If  the  section  passes  through  the  canal  for  the 
nasal  duct  the  continuity  of  that  channel  leading  from  the  orbit  above  to  the  inferior 
meatus  of  the  nose  below  is  clearly  shown.  Its  medial  wall  above,  by  which  it  is  separated 
fi'om  the  cavity  of  the  nose,  is  formed  by  the  thin  lacrimal  bone ;  below,  it  passes  under 
cover  of  the  inferior  turbinated  bone  to  open  into  the  fore  part  of  the  inferior  meatus.     It 


Fig.  121.- 


-Part  of  the  Frontal,  Nasal,  and  Maxillary  Bones  removed  in  order  to 

DISPLAY   THE    RELATION    OF   THE   VARIOUS    CaVITIES   EXPOSED. 


The  frontal  and  maxillary  bones,  where  cut,  are  coloured  blue  ;  the  ethmoid  and  the  inferior  turbinal  red  ; 

the  ethmoid  and  vomer  yellow. 


1.  Frontal  sinus. 

2.  Septum  of  frontal  sinus  deflected  towards  the  right. 

3.  Infundibulum  leading  from  sinus  to  middle  meatus. 

4.  Anterior  ethmoidal  air-sinuses. 

5.  Middle  turl)inated  bone. 

6.  Red  line  in  upjier  part  of  osseous  canal  for  nasal 

duct,  laid  open  throughout  its  entire  length  on 
the  right  side. 


7.  Cavity  of  antrum  laid  open. 

8.  Middle  meatus  of  nose. 

9.  Inferior  meatus  of  nose. 

10.  Inferior  turbinated  bone. 

11.  Nasal  septum. 

12.  Canal   for  nasal    duct    laid  open  throughout  its 

entire  length. 

13.  Anterior  nasal  spine. 


is  separated  from  the  antrum  laterally  by  a  thin  lamina  of  bone.  The  cavity  of  the 
antrum  is  seen  to  extend  upwards  and  forwards  so  as  to  pass  over  the  lateral  side  as  well 
as  slightly  in  front  of  the  canal  for  the  nasal  duct. 

The  lower  margins  of  the  middle  turbinated  bones  lie  pi'etty  nearly  on  a  level  with 
the  most  dependent  parts  of  the  orbital  margins,  whilst  the  lower  borders  of  the  inferior 
turbinals  are  placed  a  little  above  the  lower  margin  of  the  anterior  nares  on  a  level 
with  the  lowest  point  of  the  zygomatico-maxillary  suture. 

Such  a  section  will  reveal  any  deflection  of  the  nasal  septum  should  it  exist,  and  will 
also  show  that  but  a  narrow  cleft  separates  the  upper  part  of  the  septum,  on  either  side, 
from  the  medial  surface  of  the  superior  turbinals. 

The  next  section  (Fig.  122)  passes  through  the  fore  part  of  the  temporal  fossa  just 


COEONAL  SECTIONS  OF  THE  CKANIUM. 


175 


behind   the   zygomatic   process  of  the   frontal   bone  above ;    inferiorly  it  passes  through 

the  alveolar  process  of  the  upper  jaw  in  the  interval  between  the  first  and  second  molar 

teeth.    The  cranial,  orbital,  nasal, 

and  maxillary  cavities  are  all  ex-  '  -'  ^ 

posed,  together  with  the  roof  of 

the  mouth. 

The  anterior  cranial  fossa  is 
deepest  in  its  centre,  where  its 
floor  is  formed  by  the  cribriform 
plate  of  the  ethmoid  ;  this  corre- 
sponds to  the  level  of  the  zygo- 
matico-frontal  suture  laterally. 
On  either  side  the  floor  of  the 
fossa  bulges  upwai'ds,  owing  to 
the  arching  of  the  roof  of  the 
orbit.  Of  the  orbital  walls,  the 
latei'alisthethickestand  stoutest; 
the  superior,  medial,  and  inferior 
walls,  which  separate  the  orbit 
from  the  cranial  cavity,  the  eth- 
moidal cells,  and  the  antrum,  re- 
spectively, are  all  thin.  Thecavity 
of  the  maxillary  sinus  lying  to 
the  lateral  side  of  the  nasal  fossae 
is  well  seen.  Its  roof,  which 
separates  it  from  the  orbital  cav- 
ity, is  thin  and  traversed  by  the 
infraorbital  canal.  Its  medial 
wall,  with  which  the  inferior  tur- 
binal  articulates,  is  very  slender, 
and  forms  the  lateral  walls  of 
both  the  middle  and  inferior 
meatuses  of  the  nose.  Its  lateral 
wall  is  stouter  where  it  arches 
up  to  bracket  the  zygomatic  or 
malar  process.  Its  floor,  which 
rests  upon  the  upper  surface  of 
the  alveolar  border  of  the  upper 
jaw,  sinks  below  the  level  of  the 
hard  palate.  The  fangs  of  the 
teeth  sometimes  project  into  the 
floor  of  the  cavity. 

The  nasal  fossae  are  narrow 
above,  where  they  lie  between 
the  orbital  cavities,  from  which 
they  are  separated  by  the  cells 
within  the  lateral  mass  of  the 
ethmoid.  The  roof  which  cor- 
responds to  the  cribriform  plate 
is  narrow,  and  lies  between  the 
septum  medially  and  the  lateral 
masses  on  either  side. 

At  the  level  of  the  orbital 
floor  the  nasal  fosste  expand  later- 
ally, the  middle  meatus  running 
longitudinally  in  the  angle  formed 
by  the  lateral  mass  of  the  ethmoid 
with    the   body   of    the   maxilla, 


Fig.  122. — Cobonal  Section  passing  inferiorly  through 
THE  Interval  between  the  First  and  Second  Molar  Teeth. 

The  frontal  and  maxillary  bones,  where  cut,  are  coloured  blue  ; 
the  ethmoid  and  inferior  turbinals  I'ed  ;  the  vomer  yellow. 

Groove    for    superior    longi-    11.    Orbital  plate  of  maxilla. 


superior 
tudinal  (sagittal)  sinus. 
Crest  for  attachment  of  falx 
cerebri. 

3.  Crista  galli  of  ethmoid. 

4.  Cribriform  plate  of  ethmoid. 

5.  Perpendicular   plate  of   eth- 

moid, assisting  in  the  forma- 
tion of  the  nasal  septum. 

6.  Lateral  mass  of  ethmoid  con- 

sisting of  the  ethmoidal  cells. 

7.  Os  planum  of  ethmoid. 

8.  Middle  meatus  of  nose. 

9.  Middle  turbinated  bone. 

0.   Opening  from  middle  meatus 
into  antrum. 


2. 


12.    Zygomatico-frontal  suture. 
1.3.   Infraorbital  groove. 

14.  Antrum  or  maxillary  sinus. 

15.  Canal  for  the  anterior  dental 

nerve  and  vessels  exposed. 

16.  Inferior  turbinated  bone. 

17.  Inferior  meatus  of  nose. 

18.  Alveolar  process  of  maxilla. 

19.  Groove  for  anterior  palatine 

nerve  and  vessels. 

20.  Palatal  process  of  maxilla. 

21.  Maxillary  crest  forming  part 

of  nasal  septum. 

22.  Vomer  forming  part  of  nasal 

septam. 


overhung  by  the  middle  turbin- 
ated bone.  This  channel  is  seen  to  have  the  ethmoidal  cells  superior  to  it,  the  orbital 
cavity  above  and  to  the  lateral  side,  the  antrum  laterally,  whilst  its  floor  is  formed  by 
the  upper  surface  of  the  inferior  turbinated  bone. 

The   inferior  meatus,    much  more   roomy,   runs  along   under  cover   of  the    inferior 


176 


OSTEOLOGY. 


turbinated  bone.     Laterally  it  is  related  to  the  antrum,  whilst  its  floor  is  formed  by  the 

concave  superior  surface  of  the  hard  palate. 

The  hard  palate  is  arched  below,  whilst  its  superior  surface  is  concave  upwards  on 

either  side  of  the  median  crest  which 
supports  the  nasal  septum.  The  sides 
of  the  arch  below  correspond  to  the 
medial  surfaces  of  the  alveolar  processes 
and  fall  in  line  with  the  lateral  walls  of 
the  nasal  fossae  superiorly.  The  summit 
of  the  arch  lies  a  quarter  of  an  inch 
above  the  level  of  the  floor  of  the  antrum. 
The  next  section  (Fig.  123)  passes 
through  the  spheno-maxillary  (or  ptery go- 
maxillary)  and  temporal  fossae  inferiorly, 
and  cuts  the  cranial  vault  about  half 
an  inch  in  front  of  the  bregma.  The 
floor  of  the  anterior  cranial  fossa  is  seen 
to  be  formed  by  the  upper  surface  of  the 
body  and  lesser  wings  of  the  sphenoid, 
and  is  almost  horizontal.  In  the  middle 
line  the  sphenoidal  sinuses  are  exposed, 
separated  by  a  thin  bony  partition,  on 
either  side  of  which  the  openings  by 
which  they  communicate  with  the  nasal 
fossae  are  seen.  The  section  passes  in 
front  of  the  optic  foramen,  the  groove 
of  which  may  be  seen  on  the  under 
surface  of  the  lesser  sphenoidal  wing 
close  to  the  body,  and  lays  open  the 
sphenoidal  fissure  which  here  leads  for- 
ward into  the  orbit,  and  which,  inferiorly 
and  laterally,  is  continuous  with  the 
cleft  between  the  maxilla  and  the  lower 
edge  of  the  great  wing  of  the  sphenoid 
— the  spheno  -  maxillary  (or  pterygo  - 
maxillary)  fissure.  This  also  leads  into 
the  orbit. 

The  nasal  fossae,  now  much  dimin- 
ished in  height,  are  roofed  in  above  by 
the  under-surface  of  the  body  of  the 
sphenoid  and  the  aloe  of  the  vomer, 
whilst  the  lateral  walls  are  seen  to  be 
formed  by  the  thin  perpendicular  plates 
of  the  palate  bones,  lateral  to  which 
the  rounded  posterior  surface  of  the 
maxilla    is    directed    backwards,     here 


Fig.  123. — Coronal  Section  passing  through  the 
Spheno-Maxillary  (or  Pterygo- Maxillaby)  Fossa. 


1.  Depression  for  Pacchion- 

ian Vjody. 

2.  Groove  for  superior  longi- 

tndinal  (sagittal)  sinus. 

3.  Crista  galli  of  etliiuoid. 

4.  Opening    of    sphenoidal 

sinus  into  superior 
meatus  of  nose  through 
spheno  -  ethmoidal  re- 
cess. 

5.  Sphenoidal  (superior  or- 

bital) fissure. 

6.  Part     of    middle    fossa 

formed  )>y  cerebral 
surface  of  great  wing 
of  sphenoiil 


9.   Zygomatic  process. 

10.  Zygomatic  or  malar  pro- 
cess of  maxilla. 

11.  Surface  of  maxilla  which 

forms  the  anterior  wall   forming  the  anterior  wall  of  the  spheno- 
of  the  pterygo-maxii-   maxillary  (or  ptery go-maxiUary)  fossa 
— the  space  which  lies  between  the  fore 
part   of   the   pterygoid   process    behind 
and  the  upper  jaw  anteriorly.     As  will 


lary  fossa. 
Spheno-palatine  foramen. 
Opening      of      posterior 

palatine  canal. 


14.  Vertical  part  of  palate   be  seen,  the  medial  wall  of  this  space  is 


bone 

15.  Pterygoid  fossa. 

16.  Superior  meatus  of  nose. 

17.  Middle  meatus  of  nose. 

18.  Inferior  meatus  of  nose. 
Zygomatic  crest  of  great    19.  Inferior  turbinate  bone. 

wing  of  sphenoid.  20.  Middle  turl>inal  bone. 

Spheno-maxillary     (in-    21.  Maxillary  crest  and  vomer 
ferior  orbital)  fissure.  fornung  nasal  septum. 


formed  by  the  vertical  plate  of  the  palate, 
which  is,  however,  deficient  above  im- 
mediately below  the  under  surface  of 
the  body  of  the  sphenoid.  In  the  in- 
terval between  the  orbital  process,  which 
lies  in  front  of  the  section,  and  the 
sphenoidal  process,  which  lies  l^ehind, 
this  forms  the  spheno-palatine  fora- 
men. Laterally  the  section  has  passed  through  the  pterygo-maxillary  fissure,  which 
is  continuous  above  with  the  spheno-maxillary  fossa.  Inferiorly  the  section  passes  through 
the  line  of  fusion  of  the  pterygoid  processes  with  the  pyramidal  process  of  the  palate 


CORONAL  SECTIONS  OF  THE  CRANIUM. 


177 


bone  and  the  union  of  the  latter  with  the  maxilla.  Just  above  this  the  opening  of  the 
posterior  palatine  canal,  which  leads  from  the  pterygo-maxillary  (spheno-maxillary)  fossa  to 
the  under  surface  of  the  hard  palate,  is  visible;  whilst  interiorly  a  small  portion  of  the  lower 
part  of  the  pterygoid  fossa  is  cut 
through.  VV  ithin  tlie  posterior  nares 
the  middle  and  inferior  turbinate 
bones  are  seen ;  the  lower  border  of 
the  former  corresponds  to  the  level 
of  the  upper  border  of  the  zygomatic 
arch,  whilst  the  attached  edge  of  the 
latter  to  the  vertical  plate  of  the 
palate  lies  in  the  same  horizontal 
plane  as  the  lower  margins  of  that 
arch.  Note  also  that  the  internal 
pterygoid  plates  lie  considerably 
within  the  lines  of  the  medial  sur- 
faces of  the  alveolar  border,  and 
reach  some  little  distance  below  the 
level  of  the  hard  palate. 

The  next  section  (Fig.  124) 
passes  through  the  glenoid  fossa 
just  behind  the  articular  eminence ; 
superiorly,  it  cuts  the  vault  half 
an  inch  behind  the  bregma.  The 
middle  cranial  fossa  is  shown  in 
section,  the  floor  of  which  descends 
as  low  as  the  level  of  the  under- 
surface  of  the  body  of  the  sphenoid, 
corresponding  laterally  to  a  hori- 
zontal plane  passing  through  the 
upper  edge  of  the  posterior  root  of 
the  zygomatic  process  of  the  temporal 
bone.  The  body  of  the  sphenoid 
rises  a  finger's  breadth  above  this 
in  the  middle  line,  the  cavity  within 
it  is  exposed,  whilst  on  either  side 
and  below  is  seen  the  groove  for 
the  internal  carotid  artery,  leading 
upwards  from  the  medial  part  of 
the  foramen  lacerum,  which  is 
here  divided.  To  the  lateral  side 
of  the  groove  is  seen  the  prominent 
edge  of  the  lingula,  immediately 
below  which  is  the  posterior  aper- 
ture of  the  Vidian  canal,  the  inferior 
edge  of  which  is  in  part  concealed 
by  the  pterygoid  tubercle.  Im- 
mediately lateral  to  the  foramen 
lacerum  the  foramen  ovale  is  seen 
separated  from  the  surface  of  the 
section  by  a  narrow  bridge  of  bone. 
Here  it  is  seen  to  overlie  the  root  of 
the  external  pterygoid  plate.  The  8, 
section  passes  just  in  front  of  the 
foramen  spinosum,  and  here  is  visible 
the  stout  suture  between  the  great  lo 
wing  of  the  sphenoid  and  the  11 
squamous  part  of  the  temporal  bone.  ^^ 
The  glenoid  fossa  of  the  temporal  jg 
bone  is  cut  on  either  side,  and  in  its   14 


21    2b  25      24 

Fig.  124. — Coronal  Section  of  the  Skull  passing  through 
THE  Glenoid  Fossa  just  behind  the  Articular  Eminence. 

Great  win 


Crista  galli  of  ethmoid. 

Posterior  cliuoid  processes. 

Optic  foraineu. 

Anterior  clinoid  process. 

Orbital  plate  of  frontal. 

Lesser  wing  of  sphenoid. 

Suture  between  squamous 
part  of  the  temporal,  and 
parietal  bones. 

Sphenoidal  (superior  or- 
bital) fissure. 

Cerebral  surface,  great  wing 
of  sphenoid. 

Foramen  rotundum. 

Squamous  part  of  temporal. 

Posterior  root  of  zygomatic 
process. 

Eminentia  articularis. 

Glenoid  fossa. 


15. 

16. 

17. 
18. 


19. 

20. 
21. 
22. 
23. 

24. 
25. 
26. 
27. 


of  siDhenoid  iu 

front  of  spine. 
Foramen  ovale. 
Lingula. 
Anterior  margin  of  foramen 

lacerum  and   opening   of 

Vidian  canal. 
Postero  -  lateral    margin   of 

lateral  pterygoid  plate. 
Groove  for  carotid  artery. 
Pterygoid  fossa. 
Scaphoid  fossa. 
Haniular  process  of  medial 

pterygoid  plate. 
Inferior  turbinate  bone. 
Inferior  meatus  of  the  nose. 
Nasal  septum. 
Opening  of  sphenoidal  sinus. 
Dorsum  ephippii. 


deepest  part  is  separated  from  the 

middle  cranial  fossa  by  but  a  thin  lamina  of  bone.     The  thinness  of  the  squamous  part  of 

the  temporal  and  the  manner  in  which  it  is  sutured  to  the  parietal  is  also  well  displayed. 


178 


OSTEOLOGY. 


The  next  figure  (Fig.  125)  displays  the  anterior  surface  of  the  section  immediately 
behind  that  above  described.  In  the  centre,  is  seen  the  body  of  the  sphenoid,  and  the 
hinder  wall  of  the  sinus  is  now  exposed ;  on  either  side  the  apex  of  the  petrous  part  of  the 
temporal  abuts  upon  the  sides  of  the  body  of  the  sphenoid,  and  the  large  orifice  of  the  carotid 

canal  is  seen  opening  on  to  the 
hinder  wall  of  the  foramen 
lacerum,  which  is  here  divided. 
In  the  recess  between  the  lateral 
wall  of  the  carotid  canal  and  the 
spine  of  the  sphenoid  is  the 
groove  leading  into  the  osseous 
Eustachian  canal,  in  front  of 
which  the  base  is  pierced  by 
the  foramen  spinosum.  Lateral 
to  the  alar  spine,  the  glenoid 
fossa  is  divided  and  its  thin 
roof  displayed.  Crossing  it 
transversely  is  seen  theGlaserian 
fissure  which  divides  the  fossa, 
into  an  articular  and  non- 
articular  part.  The  floor  of  the 
middle  cranial  fossa  is  here 
seen  to  be  formed  by  the  upward 
slope  of  the  superior  surface  of 
the  petrous  part  of  the  temporal, 
which  is  pierced  by  the  hiatus- 
Fallopii,  and  the  foramen  for 
the  lesser  superficial  peti'osal 
nerve.  On  the  upper  surface  of 
the  summit  of  the  petrous  part 
of  the  temporal  the  depression 
for  the  lodgment  of  the  Gasserian 
ganglion  is  well  seen  on  either 
side. 

The  last  section,  the  an- 
terior surface  of  which  Fig. 
126  is  a  representation,  passes 
vertically  through  the  base 
immediately  in  fi'ont  of  the  root 
of  the  styloid  process.  In  the 
middle  line  the  basi-occipital  is 
divided  a  little  in  front  of  the 
anterior  extremities  of  the  oc- 
cipital condyles,  its  upper  surface- 
is  concave  from  side  to  side  and 
forms  a  wide  groove  for  the 
medulla  and  pons.  On  either 
side  there  is  a  narrow  interval 
between  the  lateral  edge  of  the 
basi-occipital  and  the  posterior- 
border  of  the  petrous  part  of 
the  temporal  which  in  life  is. 
occupied  by  dense  fibrous  tissue;, 
running  along  the  upper  surface 
of  this  suture  is  the  inferior 
petrosal  sinus.  Laterally  the 
section  passes  through  the 
temporal  bone,  dividing  the  cavity  of  the  tympanum  and  laying  open  the  external  auditory 
meatus.  To  the  inner  side  of  the  tympanic  wall  the  cocMea  is  exposed,  whilst  above  and' 
lateral  to  it  the  aqueductus  Fallopii  is  twice  divided,  tlie  section  passing  posterior  to  the 
angle  formed  by  its  genu.  Below  the  cochlea,  and  separated  from  it  and  the  medial  part 
of  the  floor  of  the  tympanum,  the  carotid  canal  is  in  part  exposed.  Above  the  tympanum 
is  the  "attic"  leading  into  the  mastoid  antrum,  the  whole  being  roofed  in  by  the  thin. 


Fig. 


11  /  /  i\3 

12  13  14       -^j  161718  19  20  21  22  23 

125. — Anterior  Surface  of  the  Section  of  the  Skull 
immediately  behind  the  preceding  section. 

14. 
15. 


9. 
10. 
11. 

12. 
13. 


Impressio  trigemini  on  apex  of 
petrous  Vjone. 

Squamo-parietal  suture. 

Groove  for  posterior  branch  of 
middle  meningeal  artery. 

Eminence  of  superior  semi- 
circular canal. 

Hiatus  Fallopii. 

Posterior  root  of  zygomatic 
process. 

Leads  into  external  auditory 
meatus. 

Glenoid  cavity. 

Tympanic  plate. 

Mastoid  process. 

Leading  into  stylo -mastoid 
foramen. 

Roof  .of  carotid  canal. 

Alar  spine  of  the  sphenoid. 


Styloid  process. 

Canal  for  Arnold's  nerve  -with 

opening  of  carotid  canal  just 

in  front  and  above  it. 
Position  of  osseous  opening  of 

Eustachian  tube. 
Jugular  foramen. 
Medial   wall   of  open    carotid 

canal. 
Anterior      condylic     foramen 

(canalis  hypoglossi). 
Condyle  of  occipital  bone. 
Petro-occipital  suture. 
Posterior    wall   of   sphenoidal 

sinus. 
Position  of  pharyngeal  tubercle. 
Anterior    margin    of   foramen 

magnum. 
25.    Occipital  condyle. 


HOEIZONTAL  SECTIONS  OF  THE  CEANIUM. 


179 


tegmen  tympani,  which  sepaiates  it  from  the  middle  cranial  fossa, 
medial  end  of  the  external 
auditory  meatus,  together  with 
the  groove  for  the  attachment 
of  the  tympanic  membrane  is 
well  seen,  and  the  thickness  of 
the  upper  wall  of  that  passage 
is  also  noteworthy.  The  floor 
of  the  meatus,  formed  by  the 
tympanic  plate,  which  separ- 
ates it  from  the  glenoid  fossa, 
is  much  thinner,  but  in  the 
region  of  the  root  of  the  styloid 
process  there  is  a  massing  to- 
gether of  dense  bone. 


HORIZONTAL    SECTION. 

Figure  127  represents  a 
horizontal  section  passing- 
through  the  face  a  little  below 
the  level  of  the  inferior  orbital 
margin,  cutting  through  the 
root  of  each  pterygoid  process 
posteriorly.  The  nasal  fossae 
and  the  maxillary  sinuses  are 
thus  exposed.  The  nasal  fossa 
is  divided  slightly  below  the 
inferior  edge  of  the  middle 
turbinated  bone,  along  the  line 
of  the  middle  meatus.  The 
thin  partition,  which  hei'e 
separates  the  nose  from  the 
antrum,  is  cut  through,  and  the 
aperture  into  the  antrum  laid 
open.  In  front  of  this,  the 
canal  for  the  nasal  duct  is  cut 
across,  and  its  relations  to  the 
antrum  in  front  and  to  the 
lateral  side,  and  to  the  nose 
medially,  are  well  displayed. 
The  form  of  the  maxillary 
sinus,  as  exposed,  is  triangular, 
the  summit  of  the  triangle 
being  directed  laterally  to- 
wards the  root    of    the    zygomatic  process, 


The  obliquity  of  the 


Fig. 


'J     10    11    12        13       14 

126. — Vertical  Section  through  the  Skull  immediately 
in  front  of  the  root  of  the  styloid  process. 

Inferior     opening    of    carotid 

canal. 
Jugular  foramen. 
Anterior      coudylic      foramen 

(canalis  hypoglossi). 
Occipital  condyle. 
Foramen  magnum. 
Basi-occipital. 
Tabular  part  of  occipital  bone. 


1. 

Cochlea. 

10. 

2. 

Entrance  to  the  antrum  (attic). 

3. 

Sulcus  tympanicus. 

11. 

4. 

Tympanic  bone. 

12. 

5. 

Auricular  fissure. 

6. 

Part  of  glenoid  cavity. 

13. 

7. 

Tympanic  cavity  (floor). 

14. 

8. 

Styloid  process. 

15. 

9. 

Jugular  fossa. 

16. 

Its  anterior  wall,  which  is  here  stout,  is 
pierced  obliquely  by  the  infra-orbital  canal  which  at  this  point  reaches  the  facial  surface 
of  the  maxilla  at  the  infra-orbital  foramen.  Its  posterior  wall,  thin  and  convex  backwards, 
is  directed  towards  the  zygomatic  fossa  laterally,  and  to  the  spheno-maxillary  (or  pterygo- 
maxillary)  fossa  medially,  where  it  lies  in  front  of  the  pterygoid  processes-  The  latter  fossa 
has  been  cut  across  and  is  seen  to  correspond  to  the  interval  between  the  back  and 
upper  surface  of  the  maxilla,  and  the  anterior  aspect  of  the  root  of  the  pterygoid  process. 
Laterally,  it  is  seen  to  commnnicate  with  the  zygomatic  fossa  by  means  of  the  pterygo- 
maxillary  fissure  which  is  here  cut  across ;  medially,  it  opens  into  the  nose  by  the 
spheno-palatine  foramen,  which  is  also  divided.  On  one  side  the  anterior  orifice  of  the 
Vidian  canal  is  seen  opening  on  to  the  posterior  wall  of  the  fossa.  On  the  other  side, 
the  canal  has  been  laid  open,  by  removing  its  lower  wall,  so  as  to  expose  its  whole  length 
as  it  leads  backward  to  the  anterior  edge  of  the  foramen  lacerum.  In  the  middle 
line,  the  nasal  septum,  here  formed  by  the  vomer  and  perpendicular  of  the  ethmoid, 
is  shown  in  section.  A  line  passing  through  the  pterygo-maxillary  fissures  cuts  the 
zygomatic  arch  where  the  zygomatic  process  of  the  temporal  articulates  with  the  zygo- 
matic bone. 


180 


OSTEOLOGY. 


9. 
10. 


n. 

12. 
13. 
14. 
15. 
16. 
17. 


31     30    29    28 


Fig.  127. — Horizontal  Section  of  the  Skull  a  little  below  the  level  of  the 
Inferior  Orbital  Margin. 


Nasal  duct. 

Middle  turbinal  bone. 

Nasal  septum. 

Middle  meatus  of  nose. 

Nasal  duct. 

Infra-orbital  canal. 

Opening  into  antrum  from  the  middle  meatus 
of  the  nose. 

Roof  of  antrum. 

Spheno-maxillary  (inferior  orbital)  fissure. 

Passing  through  pterygo-maxillary  fissure 
into  spheno-maxillary  fossa  and  ending 
opposite  opening  of  foramen  rotundum. 

Infra- temporal  crest  of  great  wing  of  sphenoid. 

Zygomatic  arch. 

Squamous  part  of  temporal. 

Under  surface  of  great  wing  of  sphenoid. 

Cut  pterygoid  process. 

Eminentia  articularis. 

Foramen  ovale. 


18.  Glenoid  fossa. 

19.  Foramen  siiinosum. 

20.  Spine  of  sphenoid. 

21.  Petro-squamosal  (glenoid)  fissure. 

22.  Openiug  of  bony  canal  of  Eustachian  tube. 

23.  Carotid  canal. 

24.  Upper  opening  of  carotid  canal  (foramen 

lacerum). 

25.  Anterior  opening  of  Vidian  canal. 

26.  Roof  of  spheno-maxillary  fossa  just  above 

spheno-palatine  foramen. 

27.  Superior  turbinal  bone. 

28.  Sujjerior  meatus  of  the  nose. 

29.  Placed     in     position    of    siilieno  -  palatine 

foramen. 

Placed  in  the  spheno  -  maxillary  fossa 
near  the  upper  f>art  of  the  pterygo- 
maxillary  fissure. 

Vidian  canal  laid  open. 


30 


31 


SEXUAL   DIFFERENCES   IN   THE   SKULL. 

Whilst  it  is  a  matter  of  difficulty,  in  all  cases,  to  determine  with  certainty  the  sex  of 
a  skull,  the  following  points  of  difference  are  usually  fairly  characteristic.  The  female  skull 
is,  as  a  rule,  smaller  than  the  male.  In  point  of  cranial  capacity  it  averages  about  a  tenth 
less  than  the  male  of  corresponding  race.  Undue  stress  must  not  be  laid  on  these  facts, 
since  the  female  in  bulk  and  stature  measures  on  an  avei'age  less  than  the  male.  It  is 
lighter,  smoother  as  regards  the  development  of  its  muscular  ridges,  and  possesses  less 
prominent  mastoid  processes.  In  the  frontal  region,  the  superciliary  ridges  are  less  pro- 
nounced, and  this  imparts  a  thinness  and  sharpness  to  the  upper  orbital  margin,  which  is 
fairly  characteristic,  and  can  best  be  appreciated  by  running  the  finger  along  that  edge  of 
bone.  For  the  same  reason,  the  forehead  appears  more  vertical  and  the  projections  of  the 
frontal  eminences  more  outstanding,  though  it  is  stated  that  the  frontal  and  occipital 


THE  CLAVICLE.  181 

regions  are  less  capacious  proportionately  than  in  the  male.  The  vertex  in  the  female  is 
said  to  be  more  flattened,  and  the  height  of  the  skull  consequently  somewhat  reduced.  In 
the  male  the  edge  of  the  tympanic  plate  is  generally  sharp,  and  divides  to  form  the  sheath 
of  the  styloid  process,  whilst  in  the  female  the  corresponding  box'der  is  described  as  being 
rounder  and  more  tubercular. 

Whilst  it  is  true  that  no  one  of  these  diflterences  is  sufficiently  characteristic  to  enable 
us  to  pronounce  with  certainty  on  the  matter  of  sex,  it  is  the  case  that,  taken  together, 
they  usually  justify  us  in  arriving  at  a  conclusion  which,  as  a  rule,  may  be  regarded  as 
fairly  accurate.  In  some  instances,  however,  it  is  impossible  to  express  any  definite 
opinion. 

DIFFERENCES   DUE   TO   AGE. 

At  birth  the  face  is  proportionately  small  as  compared  with  the  cranivim,  constituting 
about  one-eighth  of  the  bulk  of  the  latter.  In  the  adult  the  face  equals  at  least  half  the 
cranium.  About  the  age  of  puberty  the  development  and  expansion  of  some  of  the  air- 
sinuses,  more  particularly  the  frontal  sinus,  lead  to  characteristic  differences  in  form  in 
both  the  head  and  face. 

The  eruption  of  the  teeth  in  early  life  and  adolescence  enables  us  to  determine  the 
age  with  fair  accuracy.  After  the  completion  of  the  permanent  dentition,  the  wear  of  the 
teeth  may  assist  us  in  hazarding  an  approximate  estimate.  The  condition  of  the  sutures, 
too,  may  guide  us,  synostosis  of  the  coronal  and  sagittal  sutures  not  as  a  rule  taking  place 
till  late  in  life.  Complete  obliteration  of  the  synchondrosis  between  the  occipital  bone 
and  sphenoid  may  be  regarded  as  an  indication  of  maturity.  In  old  age  the  skull 
usually  becomes  lighter  and  the  cranial  bones  thinner.  The  alveolar  borders  of  the 
maxillse  and  mandibles  become  absorbed  owing  to  the  loss  of  the  teeth.  This  gives 
rise  to  a  flattening  of  the  vault  of  the  hard  palate  and  an  alteration  in  the  form  of  the 
lower  jaw%  whereby  the  mandibular  angle  becomes  more  obtuse. 

THE    BONES   OF  THE    UPPER    EXTREIYIITY. 
The  Clavicle. 

The  clavicle  (clavicula),  or  collar  bone,  one  of  the  elements  in  the  formation 
of  the  shoulder  girdle,  consists  of  a  curved  shaft,  the  extremities  of  which  are 
enlarged.  The  medial  end,  since  it  articulates  with  the  sternum,  is  called  the 
sternal  end ;  the  lateral  extremity,  from  its  union  with  the  acromion  process  of  the 
scapula,  is  known  as  the  acromial  end. 

The  sternal  end  (extremitas  sternalis)  is  enlarged,  and  rests  upon  the  meniscus 


Conoid  tuberlle 
(Tuberositas  cokacoidea)- 

FiG.  128  a. — The  Right  Clavicle  seen  from  Above. 

of  fibro-cartilage  which  is  interposed  between  it  and  the  clavicular  facet  on  the 
upper  and  lateral  angle  of  the  manubrium  sterni.  It  is  also  supported  by  a  small 
part  of  the  medial  end  of  the  cartilage  of  the  first  rib.  Its  articular  surface,  usually 
broader  from  above  downwards  than  from  side  to  side,  displays  an  antero-posterior 
convexity,  whilst  tending  to  be  shghtly  concave  in  a  vertical  direction.  The  edge 
around  the  articular  area  which  serves  for  the  attachment  of  the  capsule  of  the 
ster no-clavicular  articulation  is  sharp  and  well  defined,  except  below  where  it  is 
rounded. 

The  shaft  exhibits  a  double  curve,  being  bent  forwards  in  the  medial  two- 
thirds  of  its  extent,  whilst  in  its  lateral  third  it  displays  a  backward  curve.     Of 

12 


182 


OSTEOLOGY. 


rounded  or  prismatic  form  towards  its  sternal  end,  it  becomes  compressed 
and  flattened  at  its  acromial  extremity.  It  may  be  described  as  possessing  two 
surfaces,  an  upper  and  an  under,  separated  by  anterior  and  posterior  borders,  which 

are  well  defined  towards  the 
lateral  extremity  of  the  bone, 
but  become  wider  and  less 
well  marked  medially  where 
they  conform  more  to  the 
cylindrical  shape  of  the  bone. 
The  superior  surface,  which  is 
smooth  and  subcutaneous 
throughout  its  whole  length, 
is  directed  upwards  and  for- 
wards. The  anterior  border, 
which  separates  the  upper  from  the  under  surface  in  front,  is  rough  and  tubercular 
towards  its  medial  end  for  the  attachment  of  the  clavicular  fibres  of  the  pectoralis 
major,  whilst  laterally,  where  it  becomes  continuous  with  the  anterior  margin  of 
the  acromial  end,  it  is  better  defined,  and  bears  the  imprint  of  the  origin  of  the 
fibres  of  the  deltoid  muscle  ;  here,  not  uncommonly,  a  projecting  spur  of  bone, 
called  the  deltoid  tubercle,  may  be  seen.     The  posterior  border  is  broad  medially. 


Fig.  128  b.- 


-The  Upper  Surface  op  the  Right  Clavicle 
WITH  Muscle  Attachments. 


Conoid  tubercle 
-(Implssio  coracoidea) 


Rhomboid  impression 
(Impessio  costalis) 


Fig.  129  «. — The  Right  Clavicle  seen  feom  Below. 

where  it  is  lipped  superiorly  to  furnish  an  attachment  for  the  clavicular  fibres  of  the 
sterno-mastoid  muscle  ;  behind  and  below  this  the  sterno-hyoid  and  sterno-thyreoid 
muscles  are  attached  to  the  bone.  Laterally,  the  posterior  border  becomes  more 
rounded,  and  is  confluent  with  the  posterior  edge  of  the  acromial  end  at  a  point 
where  there  is  a  marked  outgrowth  of  bone  from  its  under  surface,  the  conoid 
tubercle  (tuberositas  coracoidea).  Into  the  lateral  third  of  this  border  are  inserted 
the  upper   and    anterior 

fibres    of    the    trapezius  trapezoid 

muscle.  The  inferior 
surface,  inclined  down- 
wards and  backwards,  is 
marked  close  to  the 
sternal  end  by  an  ir- 
regular elongated  im  - 
pression  (tuberositas  cos- 
talis), often  deeply  pitted, 
for  the  attachment  of  the 
rhomboid  ligament,  which  unites  it  to  the  cartilage  of  the  first  rib.  Lateral  to 
this  the  shaft  is  channelled  by  a  groove  which  terminates  close  to  the  conoid 
tubercle ;  into  this  groove  the  subclavius  muscle  is  inserted. 

The  acromial  end  of  the  bone  is  flattened  and  compressed  from  above  down- 
wards, and  expanded  from  before  backwards ;  its  anterior  edge  is  sharp  and  well 
defined,  and  gives  attachment  to  the  deltoid  muscle,  which  also  spreads  over  part 
of  its  upper  surface.  Its  posterior  margin  is  rougher  and  more  tubercular,  and 
provides  a  surface  for  the  insertion  of  the  trapezius.  The  area  between  these  two 
muscular  attachments  is  smooth  and  subcutaneous.  The  lateral  edge  of  this 
forward-turned  part  of  the  bone  is  provided  with  an  oval  facet  (facies  articularis 
acromialis)  for  articulation  with  the  acromion  process  of  the  scapula ;  the  margins 


Fig.  129  b.- 


Rhomboid  ligament 


-The  Under  Surface  of  the  Right  Clavicle  with  the 
Attachments  of  the  Muscles  mapped  out. 


THE  SCAPULA.  183 

around  this  articular  area  serve  for  the  attachment  of  the  capsule  of  the  joint. 
The  inferior  surface  of  the  acromial  end  of  the  bone  is  traversed  obliquely  from 
behind  forwards  and  laterally  by  a  rough  ridge  or  line  called  the  trapezoid  or 
oblique  ridge.  The  posterior  extremity  of  this  ridge,  as  it  abuts  on  the  posterior 
border  of  the  bone,  forms  a  prominent  process,  the  conoid  tubercle  (tuberositas 
coracoidea) ;  to  each  of  these,  respectively,  are  attached  the  trapezoid  and  conoid 
portions  of  the  coraco-clavicular  ligament. 

The  morphology  of  the  clavicle  is  of  special  interest.  Its  presence  is  associated  with 
the  freer  use  and  greater  range  of  movement  of  the  fore-limb,  such  as  are  necessary  for 
its  employment  for  more  specialised  actions  than  those  of  mere  progression.  In  conse- 
quence of  these  requirements,  the  limb,  and  with  it  the  scapula,  become  further  removed 
from  the  trunk,  and  so  the  support  which  the  blade  bone  received  through  tlie  union  of 
its  coracoid  element  with  the  sternum,  as  in  birds  and  reptiles,  and  to  some  extent  in  the 
lowest  mammals,  is  withdrawn.  Some  substitute,  however,  is  necessary  to  meet  the 
altered  conditions,  and  in  consequence  a  new  element  is  introduced  in  the  form  of  a 
clavicle.  The  origin  of  this  bone  appears  to  be  intimately  associated  with  the  precoracoid 
element  met  with  in  amphibia  or  reptiles  but  whereas  the  precoracoid  is  always  laid 
down  in  cartilage,  which,  however,  not  infrequently  disappears,  the  clavicle  develops  in 
the  membrane  overlying  the  precoracoid  cartilage.  In  the  course  of  its  development  it 
may  become  intimately  associated  with  the  remains  of  that  cartilage.  Thus,  it  is  probable 
that  the  interarticular  fibro-cartilages  at  the  sterno-clavicular  and  acromio-clavicular 
joints,  as  well  as  the  sternal  articular  end  of  the  clavicle,  represent  persistent  portions  of 
the  primitive  cartilage,  whilst  it  is  possible  that  the  supra-sternal  ossicles  occasionally 
present  may  be  also  derived  from  it.  In  this  way,  in  its  most  specialised  form,  a  secondary 
support  is  established  between  the  sternum  and  scapula,  which  serves  as  a  movable  fulcrum, 
and  greatly  enhances  the  range  of  movement  of  the  shoulder  girdle. 

Nutrient  Foramina. — The  foramina  for  the  larger  nutrient  vessels,  offsets  of  the  supra- 
scapular artery,!  of  which  there  may  be  one  or  two  directed  outwards,  are  usually  found  about 
the  middle  of  the  posterior  border,  or  it  may  be  opening  into  the  floor  of  the  groove  for  the 
subclavius  muscle. 

Ossification. — The  clavicle  in  man  is  remarkable  in  commencing  to  ossify  before  any 
other  bone  in  the  body ;   this 

nnniTTs  cia  oejrlt-  qc  tV.A   fiftl".  nv      Sternal  epiphysis  Ossifies  about  Primary  centre  appears  about 

occurs  as  eariy  as   tne    nirn  or      ^oth  year  ;  fuses  about  25th  year  5th  or  6th  week  of  fatal  life 

sixth  week  of  foetal  life.  The 
primitive  centre  from  which 
the  shaft  and  lateral  extremity 
ai-e  developed  appears  in  mem- 
brane prior  to  the  formation 
of  any  caililaginous  matrix  ; 
and     it     is   not    till     a     later  Fig.  130. — Ossification  of  the  Clavicle. 

stage  that  cartilage  plays  a 
part  in  the  development  of  the  bone  by  assisting  in  the  growth  of  its  extremities. 

A  secondary  centre  or  epiphysis  appears  at  the  sternal  end  about  the  age  of  twenty 
or  later,  and  fusion  rapidly  occurring  between  it  and  the  shaft,  ossification  is  completed 
at  the  age  of  twenty-five  or  thereabouts. 

The  Scapula. 

The  scapula,  shoulder  blade  or  blade  bone,  is  of  triangular  shape  and 
flattened  form.  It  has  two  surfaces,  costal  or  ventral,  and  dorsal.  From  the  latter 
there  springs  a  triangular  process  called  the  spine,  which  ends  laterally  in  the 
acromion ;  whilst  from  its  superior  border  there  arises  a  beak-like  projection  called 
the  coracoid  process.  The  bone  overlies  the  postero- lateral  aspect  of  the  thoracic 
framework,  reacting  from  the  second  to  the  seventh  rib. 

The  body  of  the  bone,  which  is  thin  and  translucent,  except  along  its  margins 
and  where  the  spine  springs  from  it,  has  three  borders  and  three  angles.  Of  these 
borders  the  vertebral  (margo  vertebralis)  is  the  longest ;  it  stretches  from  the 
medial  angle  above  to  the  inferior  angle  below.  Of  curved  or  somewhat  irregular 
outline,  it  affords  a  narrow  surface  for  the  insertion  of  the  levator  scapulae,  rhom- 
boideus  minor,  and  rhomboideus  major  muscles. 

The  superior  border  (margo  superior),  which  is  thin  and  sharp,  is  the  shortest  of 

^  Suprascapular  artery  =  transverse  artery  of  the  scapula  (B.N.A. ). 


184 


OSTEOLOGY. 


the  three.  It  runs  from  the  medial  angle  towards  the  root  of  the  coracoid  process, 
before  reachini;  which,  however,  it  is  interrupted  by  the  scapular  notch  (supra- 
scapular), which  Hes  very  close  to  the  medial  side  of  the  base  of  that  process. 
This  notch,  which  is  converted  into  a  foramen  by  a  ligament,  or  occasionally  by  a 
spicule  of  bone,  transmits  the  suprascapular  nerve,  whilst  the  suprascapular 
artery  ^  runs  above  it.  Attached  to  the  superior  border,  close  to  the  notch,  is  the 
posterior  belly  of  the  omo-hyoid.  The  lateral  or  axillary  border  (margo  axillaris), 
so  called  from  its  relation  to  the  hollow  of  the  armpit  (axilla),  is  much  stouter 


Clavicular  facet 


Medial  angle 


SUPBASPINOOS  FOSSA 


Spine 


Vertebral  bordep. 


INFRASPINOUS  FOSSA 


Arterial  foramen 


Head  and  glenoid  fossa 


Neck 
Great  scapular  notch 


Groove  for  dorsal  artery  of  scapula 


Axillary  border 


Inferior  angle 
Fig.  1-31  a. — The  Right  Scapula  seen  from  Behind. 

than  either  of  the  others ;  it  extends  from  the  lateral  angle  above  to  the  inferior 
angle  below.  The  upper  inch  or  so  of  this  border,  which  lies  immediately  below 
the  glenoid  articular  surface,  is  rough  and  tubercular  (tuberositas  infraglenoidalis), 
and  affords  attachment  to  the  long  head  of  the  triceps.  Below  this  it  is  usually 
crossed  by  a  groove  which  marks  the  position  of  the  dorsal  artery  of  the  scapula.^ 

The  medial  (superior)  angle  (angulus  medialis)  is  sharp  and  more  or  less  rect- 
angular ;  tlie  inferior  angle  (angulus  inferior)  is  blunter  and  more  acute ;  whilst  the 
lateral  angle  (angulus  lateralis)  corresponds  to  that  part  of  the  bone  which  is  some- 
times called  the  head,  and  which  supports  the  glenoid  surface  and  the  coracoid  process. 

The  glenoid  surface  is  a  pyriform  articular  area,  slightly  concave  from  above  down- 
wards and  from  side  to  side  ;  its  border  is  but  slightly  raised  above  the  general  surface 
and  affords  attachment  in  the  recent  condition  to  the  glenoid  ligament,  which  helps 
to  deepen  the  socket  in  which  the  head  of  the  humerus  rests.     Below,  the  margin 

'  Suprascapular  artery  =  transverse  artery  of  the  scapula  (B.N.  A.). 
*  Dorsalis  .scapulae  artery  =  circumflex  artery  of  the  scapula  (B.N. A.). 


THE  SCAPULA. 


185 


LONO  HEAD 
OF  TRICEPS 


Groove  for  dor- 
sahs  scapul.e 

ARTERY 


of  the  trlenoid  fossa  is  confluent  with  the  infraglenoid  impression  (tuberositas  infra- 
glenoidaiis),  whilst  above  it  blends  with  a  tubercle  (tuberositas  supraglenoidalis), 
to  which  the  long  head  of  the  biceps  muscle  is  attached.  Springing  from  the 
upper  part  of  the  head,  in  line  with  the  superior  border,  is  the  coracoid  process 
(processus  coracoideus).  The  base  of  this  is  limited  laterally  by  the  glenoid 
edge,  whilst  medially  it  is  separated  from  the  superior  border  by  the  scapular 
notch.  Eising  upwards  for  a  short  space,  it  bends  on  itself  at  nearly  a  right 
angle,  and  ends  in  a  process  which  is  directed  laterally  and  slightly  forwards, 
overhanging  the  glenoid  fossa  above  and  in  front.  Compressed  from  above  down- 
wards, it  has  attached  to 
its  upper  surface  near  its 
angle  the  conoid  ligament, 
lateral  to  wdnch  there  is 
a  rough  area  for  the  trape- 
zoid ligament.  Attached 
to  its  dorsal  border  is  the 
coraco- acromial  ligament, 
whilst  at  its  extremity  and 
towards  the  front  of  its 
ventral  border,  is  the  com- 
bined origin  of  the  biceps 
and  coraco-brachialis,  to- 
gether with  the  insertion 
of  the  pectoralis  minor. 
The  neck  (coUum  scapulse) 
is  that  somewhat  con- 
stricted part  of  the  bone 
which  supports  the  head  ; 
it  corresponds  in  front  and 
behind  to  a  line  drawn  from 
the  scapular  notch  to  the 
infraglenoid  tubercle. 

The  body  of  the  bone 
has  two  surfaces,  a  dorsal 
or  posterior  (facies  dorsalis) 
and  a  ventral  or  costal 
(facies  costalis).  The  former 
is  divided  into  two  fossse  by 
an  outstanding  process  of 
triangular  form,  called  the 
spine  (spina  scapulae). 
The  attached  border  of  this 
crosses  the  back  of  the  body 

.obliquely  in  a  direction  laterally  and  slightly  upwards,  extending  from  the  vertebral 
border  near  the  lower  limit  of  its  upper  fourth  towards  the  centre  of  the  posterior 
glenoid  edge,  from  which,  however,  it  is  separated  by  the  great  scapular  notch,  which 
here  corresponds  to  the  dorsal  aspect  of  the  neck.  Within  this  notch  the  supra- 
scapular vessels^  and  nerve  pass  to  the  infraspinous  fossa.  The  surfaces  of  the  spine, 
which  are  directed  upwards  and  downwards,  are  concave,  the  upper  entering  into  the 
formation  of  the  supraspinous  fossa,  which  hes  above  it,  the  lower  forming  the  upper 
wall  of  the  infraspinous  fossa,  which  lies  below  it.  The  two  fossa?  are  in  communica- 
tion with  each  other  round  the  free  lateral  concave  border  of  the  spine,  where 
that  curves  over  the  great  scapular  notch.  The  dorsal  free  border  of  the  spine 
is  subcutaneous  throughout  its  entire  length.  Its  upper  and  lower  edges  are 
strongly  lipped,  and  serve — the  superior,  for  the  attachment  of  the  trapezius ;  the 
inferior,  for  the  origin  of  the  deltoid.  The  intervening  surface  varies  in  width- 
broad  and  triangular  where  it  becomes  confluent  with  the  vertebral  border,  it 
displays  a  smooth  surface,  over  which  the  tendinous  fibres  of  the  trapezius  play ; 

'  Dorsalis  scapulfe  artery  =  circumliex  artery  of  the  scapula  (B.N. A.). 


Scapular  slip  of  latissimus 

DORSI 


Fig.  131  ?>.— The  Dorsum  of  the  Right  Scapula  with  the  Attach- 
ments OF  the  Muscles  mapped  out. 


186 


OSTEOLOGY. 


Clavicular  facet 
'    coracoid  process 


narrowing  rapidly,  it 
forms  a  surface  of  vary- 
ing width  which  blends 
laterally  with  a  flattened 
process,  the  two  forming 
a  compressed  plate  of 
bone  which  arches  across 
the  scapular  notch  above 
and  behind,  and  then 
curves,  upwards  forwards, 
and  laterally  to  overhang 
the  glenoid  fossa.  The 
medial  border  of  this  pro- 
cess is  continuous  with 
the  upper  margin  of  the 
spine,  and  is  gently 
curved.  The  lateral  bor- 
der,more  curved  than  the 
medial,  with  which  it  is 
united  in  front,  is  con- 
fluent with  the  inferior 
edge  of  the  spine,  with 
which  it  forms  an  abrupt 
bend,  termed  the  acromial 
angle.  The  bone  included 


between  these  two  borders  is  called  the  acromion 


CORACO-BRACHIALIS  AND 
SHORT  HEAD  OF 

BICEPS      PeCTORALIS  MINOR 


Ml  DIAL   ANGLE 
/ 


Arterial  foramen 


Subscapular  fossa 


Axillary  border 


Gmo-hyoid 


LOXO  HEAD 
OF  TRICEPS 


Fig. 


132  6. — Ventual  aspkct  ok  the  Right  Scapula,  with  the 
Attachments  ok  Mdscles  mapped  out. 


Inferior  angle 


Fig.  132  «. — The  Right  Scapula 
seen  from  the  Front. 

process.  Of  compressed  form, 
it  much  resembles  the  acromial 
end  of  the  clavicle,  with  which 
it  articulates  by  means  of  a 
facet  (fades  articularis  acromii) 
which  is  placed  on  its  medial 
border  near  its  anterior  ex- 
tremity. The  superior  surface 
of  the  acromion,  which  is  broad 
and  expanded,  is  subcutaneous, 
and  is  directed  upwards  and 
dorsally,  and  in  the  normal 
position  of  the  bone  laterally 
as  well.  Its  medial  edge,  where 
not  in  contact  with  the  clavicle, 
has  attached  to  it  the  fibres  of 
the  trapezius,  whilst  its  lateral 
margin  affords  origin  to  the 
central  part  of  the  deltoid.  At 
its  anterior  extremity  it  is 
connected  with    the  coracoid 


THE  SCAPULA.  187 

process  by  means  of  the  coraco-acromial  ligament.  Its  under  surface  is  smooth  and 
overhangs  the  shoulder-joint. 

The  supraspinous  fossa,  of  much  less  extent  than  the  infraspinous,  is  placed 
above  the  spine,  the  upper  surface  of  which  assists  in  forming  its  curved  floor ;  in 
it  is  lodged  the  supraspinatus  muscle.  The  scapular  notch  opens  into  it  above, 
whilst  below  and  laterally  it  communicates  with  the  infraspinous  fossa  by  the 
great  scapular  notch,  through  which  the  suprascapular  artery  ^  and  nerve  pass  to 
reach  the  infraspinous  fossa. 

The  infraspinous  fossa,  overhung  by  the  spine  above,  is  of  triangular  form.  The 
axillary  border  of  the  bone  limits  it  in  front,  whilst  the  vertebral  margin  bounds  it 
behind  ;  the  greater  part  of  this  surface  aftbrds  origin  to  the  infraspinatus  muscle, 
excepting  a  well-defined  area  which  skirts  the  axillary  border  and  inferior  angle  of 
the  bone,  and  which  affords  an  attachment  to  the  fibres  of  origin,  of  the  teres  minor. 
This  muscle  extends  along  the  dorsal  surface  of  the  axillary  border  in  its  upper 
two- thirds,  reaching  nearly  as  high  as  the  glenoid  edge  ;  whilst  a  crescentic  surface, 
which  occupies  the  lower  third  of  the  axillary  border  and  curves  backward  round 
the  dorsal  aspect  of  the  inferior  angle,  furnishes  an  origin  for  the  teres  major 
muscle.  Here  also,  near  the  inferior  angle,  are  occasionally  attached  some  of  the 
fibres  of  the  latissimus  dorsi  mv;scle. 

The  ventral  aspect  (facies  costalis)  of  the  body  is  hollow  from  above  downwards 
and  from  side  to  side,  the  greatest  depth  being  in  correspondence  with  the  spring  of  the 
spine  from  the  dorsal  surface.  Its  medial  boundary,  which  is  formed  by  the  anterior 
lipped  edge  of  the  vertebral  border,  aftbrds  attachment  to  the  fibres  of  insertion  of 
the  serratus  magnus  (s.  anterior)  along  the  greater  part  of  its  extent.  The  area  of 
insertion  of  this  muscle  is,  however,  considerably  increased  over  the  ventral  aspects 
of  the  medial  and  inferior  angles  respectively.  Eunning  down  from  the  head 
and  neck  above  to  the  inferior  angle  below,  there  is  a  stout  rounded  ridge  of  bone, 
which  imparts  a  fulness  to  the  ventral  aspect  of  the  axillary  border  and  increases  the 
depth  of  the  ventral  hollow ;  to  this,  as  well  as  to  the  floor  of  the  fossa,  the  sub- 
scapularis  muscle  is  attached.  The  tendinous  intersections  of  this  muscle  leave 
their  imprint  on  this  surface  of  the  bone  in  a  series  of  three  or  four  rough  lines 
which  converge  towards  the  neck. 

The  scapula  of  man  is  characterised  by  the  greater  proportionate  length  of  its  base 
or  vertebral  border  as  compared  with  lower  foi-ms.  This  proportion  is  expressed 
by  what  is  termed  the  scapular  index  (Appendix  D).  The  greater  size  of  the 
acromion  process  is  also  a  distinctive  feature.  The  double  ossification  of  the  coracoid 
occurs  only  in  mammals.  It  is  probable  that  the  centre  for  the  upper  and  fore  part  of 
-the  coracoid  process  represents  the  epicoracoid  or  precoracoid  of  lower  forms,  whilst  the 
subcoracoid  centre  (metacoracoid)  which  assists  in  the  formation  of  the  glenoid  fossa  is  the 
reduced  and  vestigial  remains  of  the  stout  coracoid  element  met  with  in  Ornithorhynchus, 
which  articulates  with  the  sternum. 

Nutrient  Foramina. — Foramina  for  the  jjassage  of  nutrient  vessels  are  seen  in  different  parts 
of  tlie  bone  ;  the  most  constant  in  position  is  one  which  opens  into  the  infrasjjinous  fossa,  about  an 
inch  or  so  from  the  scajjular  notch.  Others  are  met  with  on  the  upper  and  under  surfaces  of  the 
spine,  on  the  ventral  aspect  near  its  deepest  part,  and  also  around  the  glenoid  margin. 

Connexions. — The  scapula  is  not  directly  connected  with  the  trunk,  but  articulates  with  the 
latei-al  end  of  the  clavicle,  in  union  with  which  it  forms  the  shoulder  girdle  supporting  the 
humerus  on  its  glenoid  surface.  Placed  on  the  uj^joer  and  back  part  of  the  thorax,  it  covers  the 
ribs  from  the  second  to  the  seventh  inclusive.  Possessed  of  a  wide  range  of  movement,  it  alters 
its  i^osition  according  to  the  attitude  of  the  limb,  rising  or  falling,  being  dra\\Ti  inwards  or 
outwards,  or  being  rotated  uj)on  itself  according  as  the  arm  is  moved  in  various  directions.  These 
changes  in  ijosition  can  easily  be  determined  by  recognising  the  altered  relations  of  the  subcutaneous 
and  l)ony  prominences,  more  especially  the  former,  which  include  the  spine,  the  acromion  process, 
and  the  lower  half  of  the  vertebral  border. 

Ossification. — Ossification  begins  in  the  body  of  the  cartilaginous  scapula  about  the 
end  of  the  second  month  of  foetal  life.  At  birth  the  head,  neck,  body,  spine,  and  base  of 
the  coracoid  process  are  well  defined  ;  the  vertebral  border,  inferior  angle,  glenoid  fossa, 
acromion  and  coracoid  processes,  are  still  cartilaginous.  The  centre  for  the  upper  and 
fore  part  of  the  coracoid  appears  in  the  first  year,  and  fusion  along  an  oblique  line  leading 

^  Suprascapular  artery  =  transverse  artery  of  the  scapula  (B.N. A.). 


188 


OSTEOLOGY. 


from  the  upper  eds;c  of  the  glenoid  fossa   to  the  conoid  tubercle  is  complete  about  the 
fifteenth  year.     Aseparate  centre  (subcoracoid),  which  ultimately  includes  the  upper  part 

of  the  glenoid  fossa  and 

Appears  about 

1(5-17  yrs.  ;  I'uses 

about  20  yrs. 

Subcoracoid  centre 


Primary  centre 
appears  about 
2nd  m.  foetal  life. 


Acromial  centres 
appear  15-16  yrs.  ; 
fuse  about  25  yrs. 

Secondary  centre  for 
coracoid  appears 
about  end  1st  yr.  ; 
fuses  about  IS  yrs. 


appears  10  yrs. ;  fuses 

lb-17  yrs. 

Appears  about 
17  yrs. ;  fuses 
about  20  yrs. 


.  Appears  about 

16  or  17  yrs.  ; 

fuses  18-20  JTS. 


/Appears  16-17 
■  yrs  ,  fuses  20- 
25  yis 


Appears  16-17  yrs.  ; 
"  fuses  20-25  yrs. 

Scapula  at  end  of  First  Year.  Scapiila  about  the  Age  of  Puberty. 

Fig.  133. — Ossification  of  the  Scapula. 


lateral  part  of  the  cora- 
coid process,  makes  its 
appearance  about  the 
tenth  year,  and  fuses 
with  the  surrounding 
bone  about  sixteen  or 
seventeen.  Up  till  the 
age  of  puberty  the  ac- 
romion remains  carti- 
laginous ;  centres,  two 
or  more  in  number,  then 
make  their  appearance, 
which  coalesce  and  ulti- 
mately unite  with  the 
spine  about  the  twenty- 
fifth  year.  Failure  of 
union  may,  however, 
persist  throughout  life 
(see  Appendix  B — Varia- 
tions). 

Ossification  com- 
mences in  the  cartilage 
in     the     inferior    angle 


about  puberty,  and  in- 
dependently and  a  little 
later,  along  the  vertebral 

margin,  fusion  with  the  body  occurring  at  from  twenty  to  twenty-five  years. 

Small  scale-like  epiphyses  make  their  appearance  on  the  upper  surface  and  at  the 

extremity  of  the  coracoid,  and  are  completed  about  the  twentieth  year.     A  thin  epiphysial 

plate  develops  over  the  lower  part  of  the  glenoid  fossa  about  sixteen  or  seventeen,  fusion 

being  complete  about  eighteen  or  tw^enty  years  of  age. 


The  Humerus. 

The  humerus,  or  bone  of  the  upper  arm,  articulates  with  the  scapula  above  and 
with  the  bones  of  the  forearm,  the  radius  and  ulna,  below.  Its  upper  end  com- 
prises the  head  and  greater  and  lesser  tuberosities  ;  ^  its  shaft,  which  is  longer  than  any 
of  the  other  bones  of  the  upper  extremity,  is  cylindrical  above  and  flattened  below. 
At  the  inferior  extremity,  which  is  expanded  to  form  the  epicondyles  on  either  side, 
it  supports  the  trochlear  and  capitular  articular  surfaces  for  the  ulna  and  radius 
respectively. 

The  superior  extremity  is  the  thickest  and  stoutest  part  of  the  bone.  The 
head  (caput  humeri),  which  forms  about  one-third  of  a  spheroid  and  is  covered  by 
articular  cartilage,  is  directed  upwards,  medially,  and  slightly  dorsally,  and  rests  in 
the  glenoid  fossa  of  the  scapula  ;  the  convexity  of  its  surface  is  most  pronounced  in 
its  posterior  half.  Seijarating  the  head  from  the  tuberosities  laterally  is  a  shallow 
groove,  which  fades  away  on  the  surface  of  the  bone  which  supports  the  articular 
part  inferiorly.  This  is  named  the  anatomical  neck  (collum  anatomicum)  and 
serves  for  the  attachment  of  the  capsule  of  the  shoulder  joint.  The  articular  edge  of 
the  groove  opposite  the  lesser  tuberosity  is  usually  notched  for  the  attachment  of  the 
superior  gleno-humeral  ligament.  The  greater  tuberosity  (tuberculum  majus)  abuts 
on  the  lateral  side  of  the  head  and  becomes  continuous  with  the  shaft  below.  Its 
upper  surface  forms  a  quadrant,  which  is  subdivided  into  three  more  or  less  smooth 
areas  of  unequal  size.  Of  these  the  highest  and  anterior  is  for  the  insertion  of  the 
supraspinatus  muscle,  the  middle  for  the  infraspinatus,  wliilst  the  lowest  and 
posterior  serves  for  the  insertion  of  the  teres  minor  muscle.  The  lateral  surface  of 
this  tuberosity,  which  bulges  beyond  the  line  of  the  shaft,  is  rough  and  pierced  by 

'   I  retain  the  Euglish  word  "  tuljerosity  "  for  tuberculum.  ~  A.  T. 


THE  HUMEEUS. 


189 


Greater 
tubkrositv 


Bicipital  groove 


Lesser 

Tl'BEROSITY 


numerous  vascular  foramina.     Anteriorly  the  greater  tuberosity  is  separated  from 
the    lesser   tuberosity   (tuberculum    minus)    by    a   well-defined    furrow,    called    the 

bicipital    groove    (sulcus    inter- 
^  tubercularis).      The    transverse 

humeral  ligament  stretches 
across  the  groove  between  the 
two  tuberosities, thus  convertincr 
the  groove  into  a  canal  in  which 
the  tendon  of  the  long  head  of 
the  biceps  and  the  ascending 
articular  branch  of  the  anterior 
circumflex  artery  are  lodged. 
The  lesser  tuberosity  lies  in  front 
of  the  lateral  half  of  the  head  ; 

SlTPRA-*  SUBSCAPULARIS 


Deltoid  emisesce 


—  Arterial  foramen 


Medial  epicondylic 

RIDGE 


CORONOID  fossa 


Medial 
epicoxdyle 


Lateral 
epicondyle 

Capitulum 


Fig.  1.34  a. — Anterior  View  of  the  Right  Humerus. 


-  Latissimus  dorsi 


■  Pectoralis  major 
Teres  major 


Deltoid 


Coraco-brachialis 


Brachio-radialis 


.  Extensor  carpi 
radialis  longus 


Pronator  teres 
and  flexors 

Fig.  134  6. — The  Anterior  aspect  op 
THE  Humerus  with  Muscular  At- 
tachments  MAPPED  OUT. 


it  forms  a  pronounced  elevation,  which  fades  into  the  shaft  below.     The  surface  of^^ 
this  tuberosity  is  faceted  above  and  in  front  for  the  insertion  of  the  subscapular 


190 


OSTEOLOGY. 


Head- 


Anatomicat. 


Greater 
tuberosity 


/ 


s^ 


Surgical  neck 


Arterial_ 

FORAMEN 


muscle,  whilst  laterally  it  forms  the  prominent  medial  lip  of  the  bicipital  groove. 

Below  the  head  and  tuberosities  the  shaft  of  the  bone  rapidly  contracts,  and  is 

here  named  the  surgical  neck 
(coUum  chirurgicum)  owing  to  its 
liability  to  fracture  at  this  spot. 

The  shaft,  or  body  (corpus 
humeri),  is  cylindrical  in  its  upper 
half.  On  it  the  bicipital  groove  may 
be  traced  downwards  and  slightly 
inwards,  along  its  anterior  surface. 
The  edges  of  the  groove,  which  are 
termed  its  lips,  are  confluent  above 
with  the  greater  and  lesser  tuber- 
osities respectively.  Here  they  are 
prominent,  and  form  the  crests  of 
the  greater  and  lesser  tuberosities 
(cristse  tuberculi  majoris  et  minoris). 
Inferiorly  the  lips  of  the  bicipital 
groove  gradually  fade  away,  the 
medial  more  rapidly  than  the  lateral, 
which  latter  may  usually  be  traced 
down  to  a  rough  elevation  placed 
on  the  lateral  side  of  the  shaft 
about  its  middle,  called  the  deltoid 
tuberosity.  Into  the  lateral  lip  of 
the  bicipital  groove  are  inserted  the 
fibres  of  the  pectoralis  major  muscle ; 
hence  it  is  sometimes  described  as 
the  pectoral  ridge.  To  the  floor  of 
the  groove  the  latissimus  dorsi  is 
attached;  whilst  the  teres  major 
muscle  is  inserted  into  the  medial 
lip. 

The  deltoid  eminence  (tuberositas 
deltoidea),  to  which  the  powerful  del- 
toid muscle  is  attached,  is  a  rough, 
slightly  elevated  V-shaped  surface, 
placed  on  the  lateral  side  of  the 
shaft  about  its  middle.  The  anterior 
limb  of  the  V  is  parallel  to  the  axis 
of  the  shaft,  and  is  continuous 
with  the  lateral  lip  of  the  bicipital 
groove  above,  whilst  the  posterior 
limb  of  the  V  winds  obliquely  round 
the  lateral  side  of  the  bone  towards 
the  posterior  surface,  where  it  be- 
comes continuous  with  a  slightly 
elevated  and  occasionally  rough 
ridge  which  leads  up  the  back  of  the 
bone  towards  the  greater  tuberosity 
superiorly ;  from  this  latter  ridge 
the  lateral  head  of  the  triceps 
muscle  arises. 

The  medial  anterior  surface 
of  the  shaft  about  its  middle 
inclines  to  form  a  rounded  border, 

on  which  there  is    often    a  rough   linear  impression  marking   the   insertion    of 

the   coraco-brachialis    muscle.      Below   this   the   shaft  becomes   compressed   and 
xpanded  laterally,  ending  inferiorly  on  either  side  in  the  epicondyles.     Its  surfaces 


.Deltoid  eminence 


musculo-spiral 
"groove 


Olecranon 
rossA 


-Lateral 

Ivl'ICONDYLE 


Medial 
epicondyle" 


Groove  for  - 
ulnar  nerve 


Fig.  135  rt.- 


Thochlea 
-Posterior  View  ok  the  Right  Humerus. 


THE  HUMERUS. 


191 


Teres  minor 
Infraspinatus 


Triceps  (lateral 

head) 


Brachiai.is- 


I 


musculo-spiral 
groove' 


are  now  anterior  and  posterior,  being  separated  from  each  other  by  two  clearly 
defined  borders,  the  epicondylic  ridges.  Of  these,  the  medial,  margo  medialis,  is  the 
more  curved  and  less  prominent,  and  is  continuous  above  with  the  surface  to 
which  the  coraco-brachialis  is  attached,  whilst  inferiorly  it  ends  by  blending 
with  the  medial  epicondyle.  The  lateral  epicondylic  ridge,  margo  lateralis,  is 
straighter  and  more  projecting ;  its  edge  is  usually  distinctly  lipped.  Confluent 
with  the  lateral  epicondyle  inferiorly,  it  may 
be  traced  upwards  to  near  the  deltoid  eminence, 
where  it  turns  backwards  more  or  less  parallel 
to  the  posterior  oblique  border  of  that  im- 
pression, to  be  lost  on  the  posterior  surface 
of  the  shaft.  The  interval  between  this  bor- 
der and  the  deltoid  eminence  is  thus  con- 
verted into  a  shallow  oblique  furrow,  which 
winds  round  the  lateral  surface  of  the  bone 
just  below  its  middle ;  this  constitutes  the 
musculo-spiral  groove  (sulcus  n.  radialis)  along 
which  the  musculo-spiral  nerve,^  together  with 
the  superior  profunda  artery,-  passes  from  the 
back  to  reach  the  front  of  the  arm.  To  the 
epicondylic  ridges  are  attached  the  inter- 
muscular septa,  whilst  the  lateral  in  its 
upper  two-thirds  furnishes  a  surface  for  the 
origin  of  the  brachio- radialis,  and  in  its 
lower  third  for  the  extensor  carpi  radialis 
longus  muscles. 

The  anterior  surface  of  the  lower  half  of 
the  shaft  is  of  elongated  triangular  form,  the 
base  corresponding  to  the  inferior  extremity 
of  the  bone.  Running  down  the  centre  of 
this  is  a  broad,  rounded,  elevated  ridge, 
most  pronounced  above,  where  it  joins  the 
deltoid  eminence,  and  sloping  on  either  side  medial  head  of 
towards  the  epicondylic  ridges ;  it  is  into  the 
lateral  of  these  slopes  that  the  musculo-spiral 
groove  flows.  Inferiorly  the  elevated  surface 
spreads  out,  and  becomes  confluent  with  the 
epicondyles.  The  medial  epicondyle  (epi- 
condylus  medialis)  is  the  more  prominent  of 
the  two,  and  furnishes  a  surface  for  the  origin 
of  the  pronator  teres,  and  the  superficial 
flexor  muscles  of  the  forearm.  The  lateral 
epicondyle  (epicondylus  lateralis),  stunted  and 
but  little  projecting,  serves  for  the  attachment 
of  the  common  tendon  of  origin  of  the  extensor  Fig.  135  b 
muscles.  The  brachialis  muscle  has  an  ex- 
tensive origin  from  the  anterior  surface  of 
the  lower  half  of  the  shaft,  including  between  its  upper  slips  the  insertion  of  the 
deltoid. 

The  posterior  surface  of  the  low^er  half  of  the  shaft  is  smooth  and  rounded  from 
side  to  side ;  somewhat  flattened  below,  where  the  whole  shaft  tends  to  incline 
forwards,  it  becomes  continuous  on  either  side  with  the  posterior  surfaces  of  the 
epicondyles,  the  medial  of  which  is  grooved  for  the  passage  of  the  ulnar  nerve, 
whilst  the  lateral  supplies  an  origin  for  the  anconasus  muscle.  The  medial  head  of 
the  triceps  muscle  has  an  extensive  attachment  from  the  posterior  surface  of  the 
lower  two-thirds  of  the  shaft,  medial  to  and  below  the  musculo-spiral  groove. 


/>, 


Origin  of 
extensors 
of  forearm 


Anconeus 

Posterior  aspect  of  the  Right 
Humerus  with  Attachments  of  Muscles 
mapped  out. 


1  The  musculo-spiral  uerve  =  the  radial  nerve  (B.N. A.), 
the  groove  for  the  radial  nerve. 

-  The  superior  profuuda  artery  =  prof unda  brachii  (B.N. A. 


Heuce  the  musculo-spiral  groove  is  known  as 


19: 


OSTEOLOGY. 


Lesser  tuberosity 


Head 


iMEDIAL      J 

EPI f 

CONDYLE      '* 


Greater 
tuberosity 

Lateral 
epicondyle 


Fig.  136.— The  Head  of  the  Right  Humerus  seen  from 
Above  (witli  the  outline  of  the  lower  extremity  in  relation 
thereto  shown  in  dotted  line). 


Capitulum 


Olecranon  fossa    Groove  for  ulnar  nerve 
Fig.  137. — The  Lower  Extremity  of  the 
Right  Humerus  seen  from  Below. 


The  lower  extremity  of  the  humerus  is  furnished  with  two  articular  surfaces 

(the  condyles  proper),  the  lateral 
of  which,  called  the  capitulum, 
for  articulation  with  the  upper 
surface  of  the  head  of  the  radius, 
is  a  rounded  eminence,  placed  on 
the  anterior  surface  and  lower 
border,  but  not  extending  up- 
wards on  the  posterior  surface  of 
the  inferior  end  of  the  bone. 
Above  it,  in  front,  there  is  a 
shallow  depression  (fossa  radialis), 
into  which  the  margin  of  the  head 
of  the  radius  sinks  when  the 
elbowis  strongly  flexed.  A  shallow 
groove  separates  the  capitulum 
medially  from  the  trochlea,  which  is  a  grooved  articular  surface,  with  prominent 
edges  winding  spirally  round  the  lower 
extremity  of  the  shaft.  The  spiral  curves 
from  behind  forwards  and  medially,  and  its 
axis  is  slightly  oblique  to  the  long  axis  of 
the  shaft.  The  medial  hp  is  the  more 
salient  of  the  two,  and  forms  a  sharp  and 
well-defined  margin  to  the  articular  area ; 
its  cartilage -covered  surface  is  slightly 
convex.  The  lateral  lip,  much  less  prominent, 
is  rounded  off  into  the  articular  groove 
which  separates  it  from  the  capitulum, 
posterior  to  which,  however,  it  is  carried 

up  as  a  more  or  less  definite  crest.    It  is  by  means  of  the  trochlea  that  the  humerus 

articulates  with  the  semilunar  notch  of  the  ulna. 
On  the  anterior  surface  of  the  bone,  immediately 
above  the  trochlea,  is  a  depression — the  coronoid 
fossa  (fossa  coronoidea) — into  which  the  coronoid 
process  of  the  ulna  slips  in  flexion  of  the  joint,  whilst 
in  a  corresponding  position  on  the  back  of  the 
lower  end  of  the  shaft  there  is  a  hollow,  called 
the  olecranon  fossa  (fossa  olecrani),  just  above  the 
trochlea  posteriorly.  Into  this  the  olecranon  pro- 
cess sinks  when  the  elbow  is  extended.  The  two 
fossae  are  separated  by  a  thin  translucent  layer  of 
bone  which  may  be  deficient,  thus  leading  to  the 
formation  of  a  foramen  between  the  two  hollows  in 
the  macerated  bone.  The  anterior  part  of  the  capsule 
of  the  elbow -joint  is  attached  to  the  superior  margins 
of  the  radial  and  coronoid  fossee  in  front,  whilst  the 
posterior  ligament  is  connected  with  the  upper 
border  and  lateral  edges  of  the  olecranon  fossa 
behind.  The  strong  ulnar  and  radial  collateral 
ligaments  are  attached  superiorly  to  the  medial 
and  lateral  epicondyles  respectively.  The  pro- 
portionate length  of  the  humerus  to  the  body 
height  is  as  1  is  to  4-93-5 -25. 

Nutrient  foramina  are  usually  to  be  seen,  one  at  or 
near  the  surface  for  the  insertion  of  the  coraco-brachialis,  the 
from    the   other  usually  close  to  the  hinder  border  of  the  deltoid  emin- 
ence ;  both  have  a  downward  direction.    Numerous  vascular 
foramina  are  scattered  along   the   line  of  the  anatomical 
neck,  the  larger  ones  being  situated  near  the  upper  end  of  the  bicipital  groove.     The  vascularity 
of  the  bone  is  here  intimately  associated  with  the  activity  of  its  growth  in  this  situation. 


Lateral  epicondylic 
ridge 


Lateral 
epicondyle 


Ext.  lateral 
lioament 
(Radial 
Trochlea  collateral) 

Fig.    138. — The    Lower    End   op   the 
Right    Humerus    seen 
Lateral  Side. 


THE  HUMERUS. 


193 


Connexions. — Tlie  liumerus  articulates  witli  the  scai:>ula  above,  and  radius  and  ulna  below. 
Embedded  as  tlie  humerus  is  in  the  substance  of  the  upjjer  arm,  its  shaft  and  head  are  surrounded 
on  all  sides.  It  is  only  at  its  lower  part  that  it  comes  into  direct  relation  with  the  surface,  the 
medial  epicondyle  forming  a  characteristic  projection  on  the  medial  side  of  the  elbow  ;  whilst  the 
lateral  epicondyle,  less  prominent,  and  the  lateral  epicondylic  ridge  can  best  be  recognised 
when  the  elbow  is  bent. 

Sexual  differences. — Dwight  (American  Journ.  of  Anat.  vol.  iv.  1904)  has  shown  that  the 
head  of  tlic,  humerus  in  the  female  is  proportionately  smaller  than  that  of  the  male. 

Ossification. — At  birth  the  shaft  of  the  humerus  is  usually  the  only  part  of  the 
bone  ossified,  if  we  except  the  occasional  presence  (22  per  cent)  of  an  ossific  centre  in  the 
head.  (H.  R.  Spencer,  Journ.  Anat.  and  Physiol,  vol.  xxv.  p.  552.)  The  centre  for  the 
shaft  makes  its  appearance  early  in  the  second  month  of  intra-uterine  life.  Within  the 
first  six  months  after  birth  a  centre  usually  appears  for  the  head ;  this  is  succeeded  by 


At  birtli.     About  5  years.  About  12  years. 

Fig.  139. — Ossification  of  the  Humerus. 


About  16  years. 


1.  Appears  early  in  2iid  month  fcetal  life. 

2.  For  greater  tuberosity,  appears  2  to  3  years. 

3.  For  head,  appears  within  first  6  months. 

4.  For  medial  epicondyle,  appears  about  5  years. 

5.  For  capitulum,  appears  2  to  3  years. 

6.  Apyjears  about  12  years. 

7.  Centres  for  head  and  greater  tuberosity,  coalesce  about 

5  years. 


S.  Centre   for  lesser  tuberosity  fuses  with  other  centres 

about  7  years. 
9.  Appears  about  11  or  12  years. 

10.  Interior  epiphysis  fuses  with  shaft  about  16  to  17  years. 

11.  Superior  epiphysis  fuses  with  shaft  about  25  years. 

12.  Fuses  with  shaft  about  17  to  18  years. 


one  for  the  greater  tuberosity  during  the  second  or  third  year.  These  soon  coalesce  ;  and 
a  third  centre  for  the  lesser  tuberosity  begins  to  appear  about  the  end  of  the  third  year, 
or  may  be  delayed  till  the  fourth  or  iifth  year.  These  three  centres  are  all  blended  by 
the  seventh  year,  and  form  an  epiphysis,  which  ultimately  unites  with  the  shaft  about 
the  age  of  twenty-five.  It  may  be  noticed  that  the  superior  end  of  the  diaphysis  is 
conical  and  pointed  in  the  centre,  over  which  the  epiphysis  fits  as  a  cap,  an  arrangement 
which  thus  tends  to  prevent  its  displacement  before  union  has  occurred.  The  first  centre 
to  appear  in  the  lower  extremity  is  that  for  the  capitulum  about  the  second  or  third 
year.  This  extends  medially,  and  forms  the  lateral  half  of  the  trochlear  surface,  the 
centre  for  the  medial  half  not  making  its  appearance  till  the  eleventh  or  twelfth  year. 
Separate  centres  are  developed  in  connexion  with  the  epicondyles ;  that  for  the  lateral 
appears  about  the  twelfth  year,  and,  rapidly  coalescing  with  the  centres  for  the  capitulum 
and  trochlea,  forms  an  epiphysis,  which  unites  with  the  shaft  about  the  sixteenth  or 
seventeenth  year.  The  centre  for  the  medial  epicondyle  appears  about  the  fifth  year ; 
it  forms  a  separate  epiphysis,  which  unites  with  the  shaft  about  eighteen  or  nineteen. 
These  two  epiphyses  at  the  lower  end  of  the  bone  are  separated  by  a  down-growth  of  the 


194 


OSTEOLOGY. 


shaft,  which  lies  between  the  medial  epicondyle  and  the  trochlea,  and  forms  part  of  the 
base  and  medial  side  of  the  latter  process. 

The  epicondylic  process  when  present  is  developed  from  the  diaphysis,  and  has  been 

observed  to  be  already  well  ossified  by  the  third  year. 

("Proc.  Anat.  Soc."  Journ.  Anat.  and  Physiol.  1898.) 


Olecrajson  process 


Tuberosity 


Greater  sigmoid  cavity 
(Incisura  semilttnaris) 


The   Ulna. 


Small  sigmoid 
CAVITY  (In- 
cisura RADIALIS) 


~  Bicipital  hollow 


Posterior  border 


-Interosseous  bordep. 


Of  the  two  bones  of  the  forearm,  the  ulna, 
which  is  placed  medially,  is  the  longer.  It  con- 
coRONoiD  process  sists  of  a  large  superior  extremity  supporting 
the  olecranon  and  coronoid  processes ;  a  shaft 
tapering  from  above  downwards ;  and  a  small 
rounded  inferior  end  called  the  head. 

Superior  Extremity. — The  olecranon  process 

(olecranon)  lies  in  line  with  the  shaft.     Its  dorsal 

surface,    more    or    less    triangular    in    form,   is 

smooth  and  subcutaneous  and  covered  by  a  bursa. 

ii  V^B  ^^^  superior  aspect,  which  forms  with  the  posterior 

I'    'f^B  surface  a  nearly  rectangular  projection— the  tip 

of  the  elbow  —  furnishes  a  surface  for  the  in- 
sertion of  the  tendon  of  the  triceps  muscle,  to- 
gether with  a  smooth  area  which  is  overlain  by 
the  same  tendon,  but  separated  from  it  by  a 
bursal  sac.  To  the  anterior  crescentic  border  of 
this  process  are  attached  the  fibres  of  the  posterior 
part  of  the  capsule  and  portion  of  the  ulnar  col- 
lateral ligament  of  the  elbow-joint.  The  ventral 
surface  is  articular,  and  enters  into  the  formation 
of  the  greater  sigmoid  cavity  (semilunar  notch). 

The  coronoid  process  (processus  coronoideus)  is 
a  bracket-hke  process,  which  juts  forwards  from 
the  fore  and  upper  part  of  the  shaft,  and  is  fused 
with  the  olecranon  process  superiorly.  By  its 
upper  surface  it  enters  into  the  formation  of  the 
semilunar  notch  (greater  sigmoid  cavity),  whilst  its 
anterior  aspect,  which  is  separated  from  its  upper 
side  by  a  sharp  irregular  margin,  slopes  downwards 
and  backwards  to  become  confluent  with  the  anterior 
surface  of  the  shaft.  Of  triangular  shape,  this 
area,  which  is  rough  and  tubercular,  terminates 
inferiorly  in  an  oval  elevated  tubercle  (tuberositas 
ulnse),  into  which  the  tendon  of  the  brachialis 
muscle  is  inserted.  Of  the  lateral  margins  of 
the  coronoid  process,  the  medial  is  usually  the 
better  defined.  Above,  where  it  joins  the  superior 
border,  there  is  generally  a  salient  tubercle,  to 
which  one  of  the  heads  of  origin  of  the  flexor  digi- 
torum  sublimis  muscle  is  attached,  whilst  below 
this  point  the  medial  border  furnishes  origins  for 
the  pronator  teres,  and  occasionally  for  the  flexor 
poUicis  longus  muscles,  from  above  downwards. 
The  smooth  medial  surface  of  the  coronoid  process 
merges  with  the  olecranon  behind,  and  with  the 
medial  surface  of  the  shaft  below. 

The  greater  sigmoid  cavity  (incisura  semilunaris), 
for  articulation  with  the  trochlea  of  the  humerus, 
is  a  semicircular  notch,  the  upper  part  of  which  is  formed  by  the  anterior  surface 
of  the  olecranon,  whilst  below  it  is  completed  by  the  upper  surface  of  the  coronoid 


\^  ^Head 

'\ 

Articular  sobface 

i  OR  RADIUS 
" — ^       -ji-.uOVF.  FOB   EXT.    CARPI 
ULNABI8 

Styloid  pbocess 

Fig.  140.— The  Right  Ulna  as  viewed 
FROM  THE  Lateral  Side. 


THE  ULNA. 


195 


Olecranon  process 


Greater  sigmoid  cavity 
(Incisura  semilunaris)^ 

CoRONOiD  process- 


Head 


Lesser 

SIGMOID  cavity 
(  IXCI.SURA  RADI- 
M.I.S) 

Tuberosity 

BK  IPITAL    HOLLOW 


Interosseous 

BORDER 


process.  Constricted  towards  its  deepest  part  by  the  notching  of  its  lateral  borders, 
the  articular  surface  is  occasionally  crossed  by  a  narrow  impression  which  serves 
to  define  the  olecranon  process 
above  from  the  coronoid  below. 
The  articular  area  is  divided  into 
a  medial  portion,  slightly  con- 
cave transversely,  and  a  lateral 
part,  transversely  convex  to  a 
slight  degree,  by  a  longitudinal 
smooth  ridge  which  extends  from 
the  most  prominent  part  of  the 
border  of  the  olecranon  above  to 
the  most  outstanding  point  of 
the  coronoid  process  below.  The 
margins  of  the  semilunar  notch 
are  sharp  and  well  delined,  and 
serve,  with  the  exception  of  the 
area  occupied  by  the  radial  notch 
(lesser  sigmoid  cavity),  for  the 
attachment  of  the  capsule  of  the 
elbow-joint. 

The  lesser  sigmoid  cavity  or 
radial  notch,  placed  on  the  radial 
side  of  the  coronoid  process,  is  an 
oblong  articular  surface  for  the 
reception  of  the  head  of  the 
radius.  It  encroaches  on  the 
lower  and  lateral  part  of  the 
semilunar  notch,  so  as  to  narrow 
it  considerably.  Separated  from 
it  by  a  rectangular  curved  edge, 
it  displays  a  surface  which  is 
plane  from  above  downwards, 
and  concave  from  before  back- 
wards. Its  anterior  extremity 
is  narrower  and  more  pointed 
than  its  posterior,  and  becomes 
confluent  with  the  anterior  edse 
of  the  coronoid  process,  at  which 
point  the  orbicular  (annular) 
ligament,  which  retains  the  head 
of  the  radius  in  position,  is  at- 
tached in  front.  Its  posterior 
border,  wider  and  more  out- 
standing, lies  in  hne,  and  is 
continuous  with  the  interosseous 
margin  of  the  shaft.  Behind 
this  border,  the  orbicular  hga- 
ment  is  attached  posteriorly. 

The  shaft  of  the  ulna  (corpus 
ulnae),  which  is  nearly  straight, 
or  but  slightly  curved,  is  stout 
and  thick  above,  gradually  taper- 
ing towards  its  lower  extremity. 
It  may  be  divided  into  two  sur- 
faces, an  anterior  or  flexor  and  a 
posterior  or  extensor,  by  tw^o  well-defined  borders,  a  lateral  or  interosseous  (crista 
interossea),  and  a  posterior  (margo  dorsalis),  which  latter  is  subcutaneous  throughout 
its  whole  length. 


Interosseous 

BORDER" 


Fig.  141 «. — The  PaoHx  Radius  and  Ulxa  seen 
FROM  THE  Front. 


196 


OSTEOLOGY. 


Flexor  digitorcm  sublimis 
Pronator  teres 
Brachialis 

PlEXORPOLLICIS  LONG0S 


Flexor 

digitordm 

sublimis 


The  lateral,  or  interosseous  border  (crista  interossea),  is  crisp  and  sharp  in  the 
upper  three-fourths  of  the  shaft,  but  becomes  faint  and  ill-defined  in  the  lower 
fourth.  To  this,  with  the  exception  onlj  of  the  part  which  forms  the  posterior 
boundary  of  the  hollow,  in  which  the  tuberosity  of  the  radius  is  disposed  when 
the  two  bones  are  articulated,  is  attached  the  interosseous  membrane  which 
connects  the  two  bones  of  the  forearm.  The  posterior  border  (margo  dorsalis),  of 
sinuous  outline,  curving  laterally  above,  and  slightly  medially  below,  is  continuous 
superiorly  with  the  triangular  subcutaneous  area  on  the  back  of  the  olecranon, 
being  formed  by  the  confluence  of  the  borders  which  bound  that  surface ;  well 

marked  above,  it  becomes  faint  and  more  rounded 
below,  but  may  be  traced  downwards  to  the  pos- 
terior surface  of  the  base  of  the  styloid  process. 
To  this  border  is  attached  an  aponeurosis  common 
to  the  flexor  carpi  ulnaris,  extensor  carpi  ulnaris, 
and  flexor  digitorum  profundus  muscles.  A  note- 
worthy feature  in  connexion  with  this  part  of  the 
shaft  is  the  fact  that  it  is  subcutaneous,  and 
can  easily  be  felt  beneath  the  skin  throughout  its 
whole  length. 

The  anterior  or  flexor  surface  corresponds  to  the 
front  and  medial  side  of  the  shaft.  It  is  frequently 
described  as  consisting  of  two  surfaces,  an  anterior 
and  a  medial,  which  are  separated  by  a  rounded 
anterior  border  (margo  volaris),  which  extends 
from  the  tuberosity  above  towards  the  styloid 
process  below.  The  prominence  of  this  ridge 
varies  in  different  bones,  being  well  marked  in 
bones  of  a  pronounced  type,  but  corresponding 
merely  to  the  rounding  of  the  surfaces  in  poorly- 
developed  specimens.  The  flexor  aspect  of  the 
bone  affords  an  extensive  origin  to  the  flexor 
digitorum  profundus  muscle,  which  clothes  its 
anterior  and  medial  sides  in  its  upper  three-fourths, 
reaching  as  far  back  as  the  posterior  border,  and 
extending  upwards  as  high  as  the  medial  side 
of  the  coronoid  process.  Immediately  below  the 
radial  notch  there  is  a  hollow  triangular  area, 
limited  behind  by  the  upper  part  of  the  inter- 
osseous crest,  and  defined  in  front  by  an  oblique 
Hne  which  extends  downwards  and  backwards 
from  the  lateral  margin  of  the  coronoid  process. 
In  this  hollow  the  tuberosity  of  the  radius  rests 
when  the  forearm  is  in  the  prone  position,  and 
to  its  floor  are  attached  the  fibres  of  origin  of 
the  supinator  muscle.  The  lower  fourth  of  the 
shaft  is  crossed  by  the  fibres  of  the  pronator  quad- 
ratus  muscle,  which  derives  its  origin  from  a 
more  or  less  well-defined  crest,  which  winds 
spirally  downwards  and  backwards  towards  the 
front  of  the  root  of  the  styloid  process,  and  is 
continuous  above  with  the  so-called  anterior  border. 

The  posterior  or  extensor  surface  of  the  shaft  lies  posteriorly  between  the  posterior 
border  and  the  interosseous  crest.  At  its  upper  part  it  is  placed  behind  the  semi- 
lunar and  radial  notches,  extending  on  to  the  lateral  side  of  the  olecranon.  Here 
an  area  corresponding  to  the  upper  third  of  the  length  of  the  bone  is  marked  off 
inferiorly  by  an  oblique  ridge  which  leaves  the  interosseous  crest  about  an  inch  or 
more  Ijelow  the  hinder  edge  of  the  lesser  sigmoid  cavity.  Into  this  somewhat 
triangular  surface  the  fibres  of  the  anconseus  are  inserted.  Below  this  the 
posterior  surface  is  subdivided  by  a  faint  longitudinal  ridge,  the  bone  between 


Fig.  lilb. — Anterior  aspect  ok  Bones 
OF  THE  Right  Forearm  with  Mus- 
cular Attachments  mapped  out. 


THE  ULNA. 


197 


which  and  the  interosseous  crest  furnishes  oi'igins  for  the  abductor  polUcis  longus, 
extensor  pollicis  longus,  and  extensor  iudicis  proprius  muscles,  in  order  from  above 
downwards.  The  surface  of  bone  between  the  posterior  border  and  the  afore-men- 
tioned longitudinal  line  is  smooth  and  overlain  by  the  extensor  carpi  ulnaris  muscle, 
which  does  not  arise  from  it. 

The  inferior  extremity  of  the  ulna  presents  a  rounded  head  (capitulum  ulnae), 
from  which,  on  its  medial  and  posterior  aspect,  there  projects  downwards  a  cylindrical 
pointed  process  called  the  styloid  process  (processus  styloideus).  To  the  extremity 
of  this  latter  is  attached  the  ulnar  collateral  ligament  of  the  carpus,  whilst  in  front 
it  has  connected  with  it  the  antero-medial  portion  of  the  capsule  of  the  wrist-joint. 
The  antero-lateral  half  of  the  circumference  of  the  head  is  furnished  with  a  smooth 
narrow  convex  articular  surface,  which  fits  into  the  ulnar  notch  (sigmoid  cavity) 
of  the  radius.  Its  inferior  surface,  flat  and  semilunar  in  shape,  and  separated  from 
the  root  of  the  styloid  process  by  a  well-marked  groove,  rests  on  the  upper  surface 
of  the  articular  disc  (triangular  tibro-cartilage)  of  the  wrist,  the  apex  of  which  is 
attached  to  the  groove  just  mentioned.  The  margins  of  the  head  in  front  and 
behind  the  radial  articular  surface  have  attached  to  them  the  anterior  and 
posterior  inferior  radio-ulnar  ligaments.  The  hinder  and  medial  surface  of  the 
styloid  process  is  channelled  by  a  groove  which  separates  it  from  the  posterior 
surface  of  the  head,  and  extends  some  little  way  up  the  posterior  aspect  of  the 
lower  end  of  the  shaft.  In  this  is  lodged  the  tendon  of  the  extensor  carpi  ulnaris 
muscle.  The  proportionate  length  of  the  ulna  to  the  body  height  is  as  1  is  to 
6-26-6-66. 

Nutrient  Foramina. — A  foramen,  having  an  upward  direction  for  the  nutrient  artery  of  the 
shaft,  opens  on  the  anterior  surface  of  the  bone  from  two  to  three  inches  below  the  tuberosity. 
Vascular  canals  of  large  size  are  seen  above  and  behind  the  radial  notch,  just  j^osterior  to  the 
notched  lateral  border  of  the  semilunar  notch.  At  the  lower  end  of  the  bone  similar  openings  are 
seen  in  the  groove  between  the  styloid  process  and  the  inferior  articular  surface  of  the  head. 

Connexions. — The  ulna  articulates  above  with  the  trochlea  of  the  humerus.  On  the  lateral 
side  it  is  in  contact  with  the  radius  above  and  below,  the  superior  radio-ulnar  articulation  being 
formed  by  the  head  of  the  radius  and  the  radial  notch  of  the  ulna,  the  inferior  radio-ulnar  joint 
comprising  the  head  of  the  ulna,  which  fits  into  the  ulnar  notch  of  the  radius.  Between  these 
two  joints  the  shafts  of  the  bones  are  united  by  the  interosseous  membrane.  The  inferior  surface 
of  the  head  of  the  ulna  does  not  articulate  with  the  carpus,  but  rests  on  the  upper  surface  of 
the  interposed  articular  disc  (triangular  fibro-cartilage).  The  ulna  is  superficial  throughout 
its  entire  extent.     Superiorly  the   olecranon 

process  can  be  readily  recognised,  particularly  Fuses  with  shaft  about  16  years 

when  the  elbow  is  bent,  as  in  this  position  the  \ 

olecranon  is  withdrawn    from    the   olecranon    .,  Ai)pears  about  lO  years 

fossa  of  the  humerus  in  which  it  rests  when  the 
joint  is  extended.  Below  this  the  subcutaneous 
triangular  area  on  the  back  of  the  olecranon 
can  be  easily  determined,  and  from  it  the 
jjosterior  border  of  the  bone  can  readily  be 
traced  along  the  line  of  the  "  ulnar  furrow  " 
to  the  styloid  process  below.  With  the  hand 
supine  this  latter  process  can  be  felt  to  the 
medial  side  and  slightly  behind  the  wrist. 
When  the  hand  is  pronated,  the  lower  end  •? 
of  the  radius  rolls  round  the  lower  extremity  ^ 
of  the  ulna,  and  the  antero-lateral  surface  of  | 
the  head  of  the  latter  bone  now  forms  a  well- 
marked  j^rojection  on  the  back  of  the  wrist 
in  line  Avith  the  cleft  between  the  little  and 
ring  fingers. 

Ossification. — The  ulna  is  ossified 
from  one  primary  and  two  or  more  secondary 
centres.  The  centre  for  the  shaft  appears 
early  in  the  second  month  of  foetal  life.  At 
birth  the  shaft  and  a  considerable  part  of 
the  upper  extremity,  including  the  coronoid 
process,  are  ossified,  as  well  as  part  of  the 
lower  extremity.  The  olecranon  process  and 
the  inferior  surface  of  the  head  and  the  styloid  process  are  cartilaginous.  About  ten 
years  of  age  a  secondary  centre  appears  in  the  cartilage  at  the  upper  end  of  the  bone,  and 

13 


Appears  about  0  years 


Fuses  with  shaft  20-23  years 
At  Birth.     About  12  years.       About  16  years. 
Fig.  142. — The  Ossification  of  the  Ulxa. 


198 


OSTEOLOGY. 


Subcutaneous 

SURFACE 


Posterior 
border" 


ISTEROSSEOUS . 
B03EIDEB 


Post,  oblique 

LINE 


forms  an  epiphysis  which  unites  with  the  shaft  about  sixteen.     In  this  connexion  Fawcett 
(Proc.  Anat.  Soc.  Great  Britain  and  Ireland,  1904,  p.  xxvii.)  has  described  the  occurrence 

of    two  ossific  centres  in  the 
olecranon.     One,  the  more  an- 
terior, the  beak  centre,  enters 
into     the    formation    of    the 
uppermost  end  of  the  articu- 
lar surface   of  the  semilunar 
notch,  the  other  centre,    not 
in   any   way  forming  it.       A 
scale-like  centre  appears  in  the 
cartilage    of  the   head    about 
the  sixth  year,  from  which  the 
under  surface  of  that  part  of 
the  bone  is  developed,  and  by 
the   extension   of   which   the 
styloid  process  is  also  ossified  ; 
this  epiphysis  does  not  unite 
with  the  shaft  till  the  twenti- 
eth or  twenty-third  year.     In- 
dependent    centres     for     the 
styloid    process    and   for    the 
extreme  edge  of  the  olecranon 
have  also  been  described.  The 
student  may  here  be  warned 
that   the   epiphysial   line   be- 
tween the  shaft  and  superior 
or    olecranon    epiphysis    does 
not    correspond    to   the    con- 
stricted part  of  the  semilunar 
notch,   but   lies    considerably 
above  it. 


The   Radius. 

The  radius,  or  lateral 
bone  of  the  forearm,  is 
shorter  than  the  ulna,  with 
which  it  is  united  on  the 
medial  side.  Superiorly  it 
articulates  with  the  hum- 
erus, and  below  supports  the 
carpus.  It  consists  of  a 
head,  a  neck,  a  tuberosity, 
a  shaft,  and  an  expanded 
lower  extremity.  The  shaft 
is  narrow  above,  but  in- 
creases in  all  its  diameters 
below. 

Upper  Extremity.  — 
The  head  (capitulum)  is 
disc-shaped  and  provided 
with  a  shallow  concave  sur- 
face (fovea  capituli  radii) 
superiorly  for  articulation 
with  the  capitulum  of  the 
humerus.  The  circumfer- 
ence of  the  head  (circum- 
ferentiaarticularis)  is  smooth 
On  the  medial  side  it  is 


Head 


Styloid  proci 


Groove  for  ext.'     Ext.  dig.  commnn. 
CARPI  ui.NARis    and  ext.indicis  propriuM 


Ext.  poll, 
long. 


Ext.  poll,  brevis 

Ext.  carpi  rad. 
longiis 

Ext.  carpi  rad. 
brevi.s 


Styloid  pkockss 


Fig.  143  a. — The  Rk;ht  Radius  and  Ulna  seen  from  Behind. 

and  is  embraced  by  the  orbicular  (annular)  ligament 

usually  much  broader,  and  displays  an  articular  surface,  plane  from  above  down- 


THE  EADIUS. 


199 


Supinator 


wards,  which  rolls  within  the  radial  notch  of  the  ulna  in  the  movements  of 
pronation  and  supination.  The  character  of  the  lateral  half  of  the  circumference 
differs  from  the  medial,  in  being  narrower,  and  rounded  from  above  downwards. 

The  neck  (collum  radii)  is  the  constricted  part  of  the  shaft  which  supports  the 
head,  the  overhang  of  the  latter  being  greatest  towards  the  lateral  and  posterior  side. 
Below  the  neck,  on  the  medial  side,  there  is  an  outstanding  oval  prominence,  the 
bicipital  tuberosity    (tuberositas    radii).     The  posterior  part   of  this  is    rough    for 

the  insertion  of  the  biceps  tendon,  whilst  the  anterior 
half  is  smooth  and  covered  hj  a  bursa  which  inter- 
venes between  it  and  the  tendon. 

The  shaft  (corpus  radii),  which  has  an  outward 
curve  and  is  narrow  above  and  broad  below,  is  wedge- 
shaped  on  section.  The  edge  of  the  wedge  forms  the 
sharp  medial  interosseous  margin  of  the  bone  (crista 
interossea),  whilst  its  base  corresponds  to  the  thick 
and  rounded  lateral  border  over  which  the  anterior 
or  flexor  surface  becomes  confluent  with  the  posterior 
or  extensor  surface. 

The  medial  or  interosseous  crest,  faint  above  where 
it  lies  in  line  with  the  posterior  border  of  the  tuber- 
osity, becomes  sharp  and  prominent  in  the  middle 
third  of  the  bone.  Below  this  it  splits  into  two 
faint  lines,  which  lead  to  either  side  of  the  ulnar 
notch  on  the  lower  end  of  the  bone,  thus  includ- 
ing between  them  a  narrow  triangular  area  into  which 
the  deeper  fibres  of  the  pronator  quadratus  muscle 
are  inserted.  To  this  border,  as  well  as  to  the  pos- 
terior of  the  two  divergent  lines,  the  interosseous 
membrane  is  attached. 

The  lateral  border   (oftentimes  described  as  the 
lateral    surface)    is   thick   and   rounded    above,   but 
becomes  thinner  and  more  prominent  below,  w^here 
it  merges  with  the  base  of  the  styloid  process.     About 
its  middle  the  anterior  and  posterior  oblique  lines 
become  confluent  with  it,  and  here,  placed  between 
them,  is  a  rough  elongated  impression  which  marks 
the  insertion  of  the  pronator  teres  muscle.     Above 
this,  and  on  the  lateral  surface  of  the 
neck,  the  supinator  muscle  is  inserted, 
whilst  inferiorly  this  border  is  over- 
lain by  the  tendons  of  the  brachio- 
radialis  and  the  extensor  carpi  radialis 
longus  and  brevis  muscles. 

The  anterior  or  flexor  surface 
(fades  volaris)  is  crossed  obliquely 
by  a  line  which  runs  from  the  tuber- 
osity above,  downwards,  and  later- 
ally towards  the  middle  of  the  lateral 
border  of  the  shaft.  This,  often  called 
the  anterior  oblique  line,  serves  for  the  attachment  of  the  radial  head  of  origin  of  the 
flexor  digitorum  sublimis  muscle.  Above  it,  the  front  of  the  bone  has  the  fibres  of 
the  supinator  muscle  inserted  into  it,  whilst  below  and  medial  to  it,  extending  as 
far  down  as  the  inferior  limit  of  the  middle  third  of  the  bone,  is  an  extensive 
surface  for  the  origin  of  the  flexor  pollicis  longus  muscle.  In  the  lower  fourth 
of  the  bone,  where  the  shaft  is  broad  and  flat  in  front,  there  is  a  surface  for  the 
insertion  of  the  pronator  quadratus  muscle,  which  also  extends  back  to  the  inter- 
osseous ridge. 

The  extensor  or  posterior  surface  (facies  dorsalis)  is  also  crossed  by  an 
oblique  line,  less  distinct  than  the  anterior.     This  serves  to  define  the  superior 


Extensor 

CARPI 

ULNARIS 


Extensor 

CARPI 
ULNARIb 


Radial  extensors 

Abductor  pollicis 
longus  and  extensor 

POLLICIS  brevis 


Extensor  digitorum  communis 

and  extensor  INDICIS  PROPRIUS 

Extensor  pollicis  longus 
Fig.  143  a. — Posterior  aspect  of  Bones  of  Right  Fore 
ARM  WITH  Attachments  of  Muscles  mapped  out. 


200  OSTEOLOGY. 

limit  of  the  origiu  of  the  abductor  pollicis  longus  muscle.  Above  this,  the  back 
of  the  neck  and  upper  part  of  the  shaft  is  overlain  by  the  fibres  of  the  supinator 
muscle  which  become  attached  to  this  surface  of  the  bone  in  its  lateral  half. 
Below  the  posterior  oblique  line  the  posterior  surface  in  the  upper  part  of  its 
medial  half  gives  origin  to  the  abductor  pollicis  longus  and  the  extensor  pollicis 
brevis  muscles  in  that  order  from  above  downwards. 

The  lower  extremity,  which  tends  to  be  turned  slightly  forward  when  viewed 
from  below,  has  a  somewhat  triangular  form.  Its  inferior  carpal  articular  surface, 
concave  from  before  backwards,  and  slightly  so  from  side  to  side,  is  divided  into  tw^o 
facets  by  a  slight  antero-posterior  ridge,  best  marked  at  its  extremities  where  the 
anterior  and  posterior  margins  are  notched;  the  lateral  of  these  areas,  of  tri- 
angular shape,  is  for  articulation  with  the  navicular,  whilst  the  medial,  quadrilateral 
in  form,  is  for  the  os  lunatum.  The  anterior  border,  prominent  and  turned  forward, 
is  rough  at  its  edge,  where  it  serves  for  the  attachment  of  the  anterior  part  of  the 
capsule  of  the  wrist  joint.  The  posterior  border  is  rough,  rounded,  and  tubercular, 
and  is  grooved  by  many  tendons  ;  of  these  grooves  the  best  marked  is  one  which  passes 
obhquely  across  its  posterior  surface.  This  is  for  the  tendon  of  the  extensor  pollicis 
longus  muscle.  The  lateral  hp  of  this  groove  is  often  very  prominent,  and  forms 
an  outstanding  tubercle.  To  the  ulnar  side  of  this  oblique  groove  there  is  a  broad 
shallow  furrow  in  which  the  tendons  of  the  extensor  digitorum  communis  and 
extensor  indicis  proprius  muscles  are  lodged,  whilst  to  its  radial  side,  and  between  it 
and  the  styloid  process,  there  is  another  broad  groove,  subdivided  by  a  faint  ridge 
into  two,  for  the  passage  of  the  tendons  of  the  extensor  carpi  radialis  brevis  and  the 
extensor  carpi  radialis  longus  in  that  order  from  within  outwards.  The  styloid  process 
(processus  styloideus)  lies  to  the  lateral  side  of  the  inferior  extremity ;  broad  at  its 
base,  it  becomes  narrow  and  pointed  below  where  by  its  medial  cartilage-covered  sur- 
face it  forms  the  summit  of  the  inferior  triangular  articular  area.  The  lateral  surface 
of  this  process  is  crossed  obliquely  from  above  downwards  and  forwards  by  a  shallow 
groove,  the  anterior  lip  of  which  is  sharp  and  well  marked,  and  serves  to  separate  it 
from  the  anterior  surface  of  the  bone,  whilst  the  posterior  lip  is  often  emphasised 
by  a  small  tubercle  above.  The  tendon  of  the  brachio-radialis  muscle  is  inserted 
into  the  upper  part  of  either  lip,  and  also  spreads  out  on  to  the  floor  of  the  groove, 
whilst  the  tendons  of  the  abductor  pollicis  longus  and  the  extensor  pollicis  brevis 
muscles  lie  within  the  groove.  To  the  tip  of  the  styloid  process  is  attached  the 
radial  collateral  ligament  of  the  wrist.  On  the  medial  side  of  the  lower  extremity 
is  placed  the  ulnar  notch  (incisura  ulnaris)  for  the  reception  of  the  head  of  the 
ulna.  Concave  from  before  backwards,  and  plane  from  above  downwards,  it  forms 
by  its  inferior  margin  a  rectangular  edge  which  separates  it  from  the  inferior 
carpal  surface.  To  this  edge  the  base  of  the  articular  disc  (triangular  fibro- 
cartilage)  is  attached,  a  structure  which  serves  to  separate  the  inferior  articular 
surface  of  the  head  of  the  ulna  from  the  carpus.  The  anterior  and  posterior  edges 
of  the  iilnar  notch,  more  or  less  prominent,  serve  for  the  attachment  of  ligaments. 

The  proportionate  length  of  the  radius  to  the  body  height  is  as  1  is  to 
6-70-7-11. 

Nutrient  Foramina. — The  openings  of  several  small  nutrient  canals  may  be  seen  in  the 
region  of  tlie  neck.  That  for  the  shaft,  which  has  an  upward  direction,  is  usually  placed  on  the 
anterior  surface  of  the  bone,  medial  to  the  anterior  oblique  line,  and  from  an  inch  and  a  half  to 
two  inches  below  the  tuberosity.  The  posterior  surface  of  the  lower  extremity  of  the  bone  is 
pierced  by  many  small  vascular  foramina. 

Connexions.  —  The  radius  articulates  with  the  capitulum  of  the  humerus  in  the  flexed 
position  of  the  elbow,  with  the  ulna  to  its  medial  side  by  the  superior  and  inferior  radio-ulnar 
joints,  and  with  the  navicular  and  lunate  bones  of  the  carj^us  below.  Above,  the  head  of  the 
bone  can  be  felt  in  the  intermuscular  depression  on  the  lateral  side  of  the  back  of  the  elbow  ;  here 
the  bone  is  only  covered  by  the  skin,  superficial  fascia,  and  the  thin  common  tendinous  origin  of 
the  extensor  muscles,  as  well  as  the  ligaments  which  support  it.  Its  position  can  best  be  ascer- 
tained by  pronating  and  supinating  the  bones  of  the  forearm,  when  the  head  will  be  felt  rotating 
beneath  the  finger.  The  lower  end  of  the  bone  is  overlain  in  front  and  behind  by  the  flexor  and 
extensor  tendons,  but  its  general  form  can  be  readily  made  out.  The  styloid  process  lying  to  the 
lateral  side  of  the  wrist  in  line  with  the  extended  thumb  can  easily  be  recognised  ;  note  that  it 
reaches  a  lower  level  than  the  corresponding  process  of  the  ulna.  The  lateral  border  of  the  lower 
third  of  the  shaft  can  be  distinctly  felt,  as  here  the  bone  is  only  overlain  by  tendons. 

Ossification. — The  centre  for  the  shaft  makes  its  appearance  early  in  the  second 


THE  EADIUS. 


201 


Fuses  witli  shaft  lS-20  years 


Appears  about  / 

2-3  years  / 

Unites  with  sliaft  20-25  years 
At  Birth.         About  12  years.         About  16  years. 

Fig.  144. — The  Ossification  of  the  Radius. 


epiphysis  capping   the    summit  of  the 
tuberosity  has  been  described  ;  this  ap- 
pears about  the  fourteenth  or  fifteenth 
year,    and    rapidly    fuses 
with  that  process. 

I.  Metacarpal 


month  of  intrauterine  Ufe.  At  birth  the 
shaft  is  well  formed ;  its  upper  and  lower 
extremities  are  capped  with  cartilage,  and 
the  tuberosity  is  beginning  to  appear.  A 
secondary  centre  appears  in  the  cartilage 
of  the  lower  extremity  about  the  second  or 
third  year ;  this  does  not  unite  with  the 
shaft  until  the  twentieth  or  twenty-fifth 
year,  somewhat  earlier  in  the  female.  From 
this  the  carpal  and  ulnar  articular  surfaces 
are  formed.  The  centre  for  the  head 
appears  from  the  fifth  to  the  seventh  year, 
and  fuses  with  the  neck  about  the  age  of 
eighteen  or  twenty.  It  forms  the  capitular 
articular  sui-face  and  combines  with  the  neck 
to  form  the  area  for  articulation  with  the 
radial    notch  of    the    ulna.       A   scale-like 


Os  HAMATUM 

Os   TRIQDETRUM 


PisIFORM 


THE   BONES   OF 
THE   HAND. 


Sesamoid  bones 


The  bones  of  the  baud, 
twenty -seven  in  number,  may 
be  conveniently  divided  into 
three  groups : — 

(1)  The  bones  of  the  \7rist  or 
carpus — eight  in  number. 

(2)  The  bones  of  the  palm  or 
metacarpus — five  in  number. 

(3)  The  bones  of  the  fingers 
and  thumb  or  phalanges — -fotir- 
teen  in  number. 

The  Carpus. 

The  carpal  bones  (ossa  carpi) 
are  arranged  in  two  rows :  the 
first,  or  proximal  row,  comprises 
from  without  inwards,  the  navicu- 
lar or  scaphoid,  os  lunatum  or 
semi-lunar,  os  triquetrum  or  cunei- 
form, and  os  pisiforme  or  pisiform  ; 
the  second  or  distal  row  includes 
the  great  multangular  or  trapezium, 
lesser  multangular  or  trapezoid, 
OS  capitatum  or  os  magnum,  and 
OS  hamatum  or  unciform.     Irregu- 


, —  v.  Metacarpal 


Fig.  145  «. 


-The  Bones  of  the  Right  Wrist  and  Hand 

SEEN    from    the    FRONT. 


202 


OSTEOLOGY. 


Os  CAPITATUM 

Small  multangular 
Naviculak 
Abductor  pollicis  bbevis    \^L,i-} 
Large  multangular    ('^'^l  ^' 
Opponens  pollicis 

Abductor  pollicis  loncjus 


Flexor  carpi  radialis 


Os  lunatum 

Os  hamatum 
Os  triquetrum 

I.EXOR  CARPI   ULNARIS 

Pisiform 

Abductor  dioiti  quinti 
i  1  \or  digiti  quinti 

I  IJ  \  1-1 

1   I?\OE  CARPI  ULNARIS 

)PP(JNENS  DIGITI 


Adductor  pollicis  obliquus 
Adductor  pollicis  transversus 


Fig.   145^. — Palmar  Aspect  ob-  Bones  of  the  Right  Carpus 
AND  Metacarpus  with  Muscular  Attachments  mapped  out. 


larly  six-sided,  each  of   these  bones  possesses    non- articular  palmar   and   dorsal 
surfaces.     In  addition,  the  marginal  bones  are  non-articular  along  their  ulnar  and 
radial  aspects  according  as  they  form  the  medial  or  lateral  members  of  the  series. 
Navicular  or  Scaphoid  Bone. — This  is  the  largest  as  well  as  the  most  lateral 

bone  of  the  first  row. 
Its  palmar  surface, 
rough  for  the  attach- 
ment of  ligaments,  is 
irregularly  triangu- 
lar. The  inferior 
angle  on  the  radial 
side  forms  a  projec- 
tion called  the  tu^ber- 
osity;  this  can  be 
felt  at  the  base  of 
the  root  of  the  thumb. 
Its  superior  surface 
is  convex  from  side  to  side  and 
before  backwards  for  articula- 
tion with  the  radius.  This  area 
extends  considerably  over  the 
posterior  surface  of  the  bone. 
Its  inferior  surface  is  convex 
from  before  backwards,  and  ex- 
tends on  to  the  dorsal  aspect  of 
the  bone,  slightly  convex  from 
side  to  side ;  it  is  divisible  into  two  areas,  the  radial  for  articulation  with  the  large 
multangular,  the  ulnar  for  the  small  multangular.  The  radial  surface  is  narrow 
and  rounded  and  forms  a  non-articular  border,  which  extends  from  the  radial 
articular  surface  above  to  the  tuberosity  below.  The  ulnar  surface  is  hollowed  out 
in  front  for  articulation  with  the  head  of  the  capitate  bone.  Above  this  it  displays 
a  small  semilunar- 
shaped  facet  for  the  os 
lunatum.  The  dorsal 
non  -  articular  surface 
lies  between  the  radial 
articular  surface  above 
and  the  surface  for  the 
large  and  small  mult- 
angular  bones  below. 
It  is  obliquely  grooved 
for  the  attachment  of 
the  posterior  ligaments 
of  the  wrist.  The  navicu- 
lar articulates  with  five 
bones — the  radius,  tlie 
08  lunatum,  the  capi- 
tate, the  small  mult- 
angular, and  the  large 
multangular. 

Os  Lunatum  or 
Semilunar  Bone. — So 
called    from  its  deeply 

excavated  form,  the  os  lunatum  lies  between  the  navicular  on  the  radial  side  and 
the  OS  triquetrum  on  the  ulnar.  Its  palmar  surface,  of  rhombic  form  and  consider- 
able size,  is  rough  for  the  attachment  of  ligaments ;  its  supjerior  surface,  convex  from 
side  to  side  and  from  before  backwards,  articulates  with  the  radius  and  in  part  with 
the  under  surface  of  the  articular  disc  (triangular  fibro- cartilage)  of  the  wrist.  Its 
inferior  aspect,  deeply  hollowed  from  before  backwards,  is  divided  into  two  articular 


Os  triquetrum 
Pisiform 


Os  lunatum 

Os    CAPITATUM 

Navicular 


Os  hamatum 


Extensor  carpi 

ULNARIS 


xtensor  carpi  radialis  brevis 
Small  multangular 
Large  multangular 
Extensor  carpi  radialis  longus 
Abductor  pollicis  longus 


Fig 


145  c. — Dorsal  Aspfx'T  of  Bones  ok  the  Right  Carpus  and 
Metacarpus  with  Muscular  Attachments  mapi'ed  out. 


THE  CARPUS. 


203 


Os  CAPITATl'M 


Os  LU 


Os  TRIQLETRl  M 

Pisiform -T 


TANOULAR 

E  MULTANGULAR 


I.  Meta- 

.i:PAL 


areas,  of  which  the  radial  is  the  larger ;  this  is  for  the  head  of  the  capitate  bone ; 
the  ulnar,  narrow  from  side  to  side,  articulates  with  the  os  hamatum.  Its  radial  sur- 
face, crescentic  in  shape,  serves  for  articulation  with  the  navicular,  and  also  for  the 
attachment  of  the  interosseous  ligaments  which  connect  it  with  that  bone.  Its 
idnar  surface,  of  quadrilateral  form,  is  cartilage-covered  for  articulation  with  the 
08  triquetrum,  and  the  edge  which  separates  this  from  the  superior  surface  has 
attached  to  it  the  interosseous  ligament  which  unites  these  two  bones.  The 
rough  dorsal  non-articular  surface  is  much  smaller  than  the  palmar;  by  this 
means  the  front  and  back  of 
the  bone  can  readily  be  de- 
termined. The  semilunar  ar- 
ticulates with  five  bones — the 
navicular,  the  radius,  the  os 
lunatum,  the  os  hamatum,  and 
the  capitate  bone. 

The  Os  Triquetrum  or 
Cuneiform.  —  This  bone  may 
be  recognised  by  the  small  oval 
or  circular  facet  on  its  anterior 
surface  for  the  pisiform.  This 
is  placed  towards  the  lower  part 
of  the  pcdmar  surface,  which 
is  elsewhere  rough  for  liga- 
ments. The  bone  is  placed 
obliquely,  so  that  its  surfaces 
cannot  be  accurately  described 
as  inferior,  superior,  etc. ;  but  for 
convenience  of  description,  the 
method  already  adopted  is  ad- 
hered to.  The  superior  surface 
has  a  convex  rhombic  surface 
for  articulation  with  the  under 
surface  of  the  triangular  fibro- 
cartilage  in  adduction  of  the 
hand,  though  ordinarily  it  does 
not  appear  to  be  in  contact  with 

that  structure.      To  the  ulnar 

side  of  this  it  is  rough  for  liga- 
ments.    The  inferior  surface  is 

elongated  and  concavo-convex 

from    without    inwards ;    here 

the  bone  articulates  with  the  os 

hamatum.     The  radial  surface, 

broader  in   front  than  behind, 

articulates  with  the  os  lunatum. 

The  ulnar  surface,  rounded  and 

rough,  is  confluent   above  and 

behind  with  the  superior  and 

dorsal  aspects  of  the  bone.    The 

dorsal  surface,  rounded  and  smooth  laterally,  is   ridged  and  grooved  medially  for 

the  attachment  of  ligaments.     The  cuneiform  articulates  with  three  bones,  viz. 

the  pisiform,  the  os  hamatum,  and  the  os  lunatum. 

Pisiform  bone  (os  pisiforme). — About  vthe  size  and  shape  of  a  large  pea,  the 

pisiform  bone  rests  on  the  anterior  surface  of  the  fore  end  of  the  os  triquetrum,  with 

which  it  articulates  by  an  oval  or  circular  facet  on  its  dorsal  aspect.      The  rounded 

mass  of  the  rest  of  the  bone  is  non-articular,  and  inclines  downwards  and  radially 

so  as  to  overhang  the  articular  facet  in  front  and  laterally.      The  mass  of  the 

bone  is  usually  separated  from  the  articular  surface  by  a  small  but  distinct  groove. 

Into  the  summit  of  the  bone  the  tendon  of  the  flexor  carpi  ulnaris  muscle  is 


Second 

PHALANX 


Third 

PHALANX 


Fig.  llhd.- 


-The  Bones  of  the  Right  Weist  and  Hand 
seen  from  behind. 


204 


OSTEOLOGY. 


Capitate 


inserted,  and  here  also  the  anterior  annular  ligament  is  attached.     The  ulnar  artery 
and  nerve  are  in  immediate  relation  with  the  radial  side  of  the  bone. 

Great  Multangular  or  Tra- 
pezium.— The  trapezium  is  the 
most  lateral  bone  of  the  second  row 
of  the  carpus.  It  may  be  readily 
recognised  by  the  oval  saddle- 
shaped  facet  on  its  inferior  surface 
for  articulation  with  the  metacarpal 
bone  of  the  thumb.  From  its 
palmar  as;pect  there  rises  a  pro- 
minent ridge,  within  which  is  a 
groove  along  which  the  tendon  of 
the  flexor  carpi  radialis  muscle 
passes.  The  ridge  furnishes  an 
attachment  for  the  anterior  an- 
dius  nular  ligament,  as  well  as  for  some 
of  the  short  muscles  of  the  thumb. 
The  superior  surface  has  a  half  oval 
■J     '  p\  facet  for  the  navicular,  lateral  to 

^      ,         ^      ^        ..  ^  -__  ^^ ^!l^  which   it  is   rough,  and  becomes 

Fig.  146. — The  Right  Navicular  BonI".'^  ■  , .  ■,,    ?t.  ,  •      i 

^^         ^,  ,     ^         continuous  with  the  non-articular 

JNOTE. — The    bone  is  represented  in  the   centre  of   the  figure  , .    7  ,  t  •   i,  p 

^  -    radial    aspect,   which   serves    tor 

On 


Radius 


Os  lunatuiu 


oca 

-The  Right  Navicular  BonI".' 


Os  hainatuin 


Capitate 


in  the  position  which  it  occupies  in  the  right  hand  viewed  ■I'f^wi.u.v     aspect,    whlch     SCrveS 

from  the  front.     The  views  on  either  side,  and  above  and  the  attachment  of  ligaments. 

below,  represent  respectively  the  corresponding  surfaces  of  j^g    ulnar    surface     there    are     twO 

,      the  bone  turned  towards  the  reader.  ^^^^^^  .    the   upper   is   a   half  OVal, 

concave  from  above  downwards,  and  very  slightly  convex  from  before  backwards, 
and  is  for  articulation  with  the  small  multangular.  The  lower,  small  and  circular, 
and  not  always  present,  is  for  articulation  with  the  radial  side  of  the  base  of  the 
second  metacarpal  bone.  The 
dorsal  surface,  of  irregular 
outline,  is  rough  for  the  attach- 
ment of  hgaments.  The  great 
multangular  articulates  with 
four  bones,  the  navicular,  small 
multangular,  and  the  first  and 
second  metacarpal  bones. 

Small  Multangular  or 
Trapezoid  Bone.  —  With  the 
exception  of  the  pisiform,  this 
is  the  smallest  of  the  carpal 
bones.  Its  rough  palmar  sur- 
face is  small  and  pentagonal 
in  outline.  By  a  small  oblong 
surface  on  its  superior  aspect  it 
articulates  with  the  navicular. 
Inferiorly,  by  a  somewhat 
saddle-shaped  surface,  it  articu- 
lates with  the  base  of  the  second 
metacarpal.  Separated  from 
this  by  a  rough  V-shaped  im-  note.— Tiie 
pression  prolonged  from  its  position 
palmar  aspect,  is    the  surface 


Radiui 


Radius 
Navicular 


FiQ.  147. — The  Right  Os  Lunatum. 
hone  is  rei)re.sented  in  the  centre  of  the  fig 


are  in  the 
whicli   it  occupies  in  the  right  hand  viewed  from  the 
front.    The  views  on  either  side,  and  above  and  below,  represent 
^ ,  T    1      •  T     n  ,  ■      1  respectively  the  corresponding  surfaces  of  the  bone  tui'ned  to- 

On  the  rad%al  side  lor  artlCUla-  ^ards  the  reader.      o 

tionwiththelargemultangular;  "^C  Th  |      ^  U  h  <l  V 

this  appears  as  if  oljliquely  grooved  from  before  backwards  and  downwards.  The 
ulnar  facet  for  articulation  with  the  capitate  is  narrow  from  above  downwards,  and 
deeply  curved  from  before  backwards.  The  dorsal  surface  of  the  bone,  which  is  rough 
and  non-articular,  is  much  larger  than  the  palmar  aspect.     The  mass  of  the  bone, 


THE  CAEPUS. 


205 


The  small  multano-ular 


Os  liamatuni 


Fig.  149.- 


Os  triquetrum 

-The  Right  Pisiform 
Bone. 


Triangular 
tibro-cartilage 

of  wrist  

Fig.  148.— The  Eight  Os  Tkiquetrum. 

Note. — The  bone  is  represented  in  the  centre  of  the  figure 
in  the  position  which  it  occupies  in  the  right  hand 
viewed  from  the  front.  The  views  on  either  side, 
and  above  and  below,  represent  respectively  the 
corresponding  surfaces  of  the  bone  turned  towaids 
the  reader. 


dorsally,  is  directed  downwards  and  towards  the  ulnar  side 
articulates  with  four  bones — the  large 
multangular,    navicular,    and    capitate 
bones,  and  the  second  metacarpal. 

Capitate  Bone  or  Os  Magnum. — 
This  is  the  largest  of  the  carpal  bones. 
Its  palmar  surface  is  rough  and  rounded. 
The  superior  portion  of  the  bone  forms 
the  head,  and  is  furnished  with  convex 
articular  facets  which  tit  into  the  hollows 
on  the  inferior  surfaces  of  the  navicular 
and  OS  lunatum ;  that  for  the  latter  is 
medial  to  and  separated  by  a  slight 
ridge  from  the  navicular  articular  area. 
The  inferior  surface,  narrow  towards  its 
palmar  border  and  broad  dorsally,  is 
sulidivided  usually  into  three  facets  by 
two  ridges— that  towards  the  radial  side 
is  for  the  base  of  the  second  metacarpal ; 

the  middle 
facet  is  for 
the  third 
metacarpal ; 
whilst  the 
medial  facet 
of  the  three, 
not    always 

Note.— The  figure  to  the  left  repre-  present,  very  small  and  placed  near  the  dorsal  side  of 
w^'«,^\^.h^;Igh'  t  th^l^ne,  is  ^  the  fourth  metacarpal.  Th,  radial  side  oi 
dorsal  view.  tlie   body  has  an  articular  surface  for  the  small  mul- 

tangular, not  infrequently  separated  from  the  navicular 
surface  on  the  head  by  a  rough  line,  to 
which  the  interosseous  ligament  con- 
necting it  with  the  navicular  is  at- 
tached. The  ulnar  side  of  the  body 
has  an  elongated  articular  surface,  usu- 
ally deeply  notched  in  front,  or  it  may 
be  divided  anteriorly  into  a  small  cir- 
cular area  near  the  dorsal  edge ;  and 
a  larger  posterior  part.  This  latter 
articulates  either  singly  or  doubly  with 
the  OS  hamatum,  the  interosseous  liga- 
ment which  unites  the  two  bones 
being  attached  either  to  the  notch  or 
to  the  surface  separating  the  two  articu- 
lar facets.  The  dorsal  surface  is  rough 
for  ligaments;  it  is  somewhat  constricted 
below  the  head,  the  articular  surface  of 
which  sweeps  round  its  upper  border. 

The  capitate  bone  articulates  with 
seven  bones — the  os  hamatum,  the  os 
lunatum,  the  navicular,  the  small  mult- 
angular, and  the  second,  third,  and 
fourth  metacarpal  bones ;  occasionally 
the  fourth  metacarpal  does  not  ar- 
ticulate with  the  capitate. 

The   Os   Hamatum    or   Unciform 
Bone. — The  os  hamatum  can  be  readily 
distinguished  by  the  hook-like  process  (hamulus)  which  projects  from  the  lower  and 


Small 
multangular 


Navicular 


:c<\ 

Fig.  150. — The  Right  Large  MultangVlar'"Bone. 

Note. — The  bone  is  rej^resented  in  the  centre  of  the  figure 
in  the  position  which  it  occupies  in  the  right  hand 
viewed  from  the  front.  The  views  on  either  side,  and 
above  and  below,  represent  respectively  the  corre- 
sponding surfaces  of  the  bone  turned  towards  the 
reader. 


.NGCX^ 


206 


OSTEOLOGY. 


ulnar    aspect  of   its  anterior  surface. 


Capitate  bone 


iiiultangular 


-The  Right  Small  Multangular  Bone. 


To  this  is  attached  the  anterior  annular 
ligament  as  well  as  some  of  the 
fibres  of  origin  of  the  short  muscles 
of  the  little  finger.  The  ulnar 
side  of  the  unciform  process  is 
[I.  iietacarpai  sometimcs  groovcd  by  the  deep 
branch  of  the  ulnar  nerve 
(Anderson,  W.,  "  Proc.  Anat.  Soc." 
Journ.  Anat.  and  Physiol,  vol. 
xxviii.  p.  11).  The  palmar  sur- 
face, rough  for  ligaments,  is 
somewhat  triangular  in  shape. 
Swperiorly  and  towards  the  ulnar 
side  there  is  an  elongated  articular 
surface  for  the  os  triquetrum, 
convex  above  and  concave  below. 
The  radial  aspect  of  the  bone  is 
provided  with  a  plane  elongated 
facet,  occasionally  divided  into 
two  (see  above)  for  articulation 
with  the  capitate  bone.  Where 
the  superior   and   radial  surfaces 


III.  Metacarpal 


IV.  Metacarpal 


II.   Metacarpal 


III.  Metacarpal 


Fig.  151. 

Note.— The  bone  is  represented  in  the  centre  of  the  figure  in  meet,  the  angle  is  blunt,  and   has 

the  position  which  it    occupies  in   the  right  hand  viewed  a    narrOW  facet    which    articuktes 

from  the  front.     The  views  on  either  side,  and  above  and  ^„-+.i,  4-i„„„i 4-  t  j>      ■      i 

below,  represent  respectively  the  corresponding  surfaces  of  ^ith  the  OS    luuatum.       Inferiorhj 

the  bone  turned  towards  the  reader.  there     are      tWO     articular     faCCtS 

separated  by  a  ridge ;  these  are 
slightly  concave  from  before  backwards,  and  are  for  articulation,  the  radial  with 
the  fourth,  and  the  ulnar 
with  the  fifth  metacarpal 
bone.  The  dorsal  surface, 
more  or  less  triangular  in 
shape,  is  rough  for  liga- 
ments. 

The  unciform  articulates 
with  five  bones  —  viz.  the 
capitate,  os  lunatum,  os 
triquetrum,  and  the  fourth 
and  fifth  metacarpals. 

The  Carpus  as  a 
Whole. 

When  the  carpal  bones 
are  articulated  together 
they  form  a  bony  mass,  the 
dorsal  surface  of  which  is 
convex  from  side  to  side. 
Anteriorly  they  present  a 
grooved  appearance,  con  - 
cave  from  side  to  side. 
This  arrangement  is  furtlier 
empliasised  by  the  forward 
projection,  on  the  ulnar  side,  f'i«-  152.— The  Right  Capitate  Bone. 

of  the  pisiform   and  hook  of     Note. — The  bone  is  represented    in  the  centre   of   the   figure   in    the 
thp      r.q      hflmatiim       ^^r\^\U^  position    which    it   occupies  in   tlie    riglit  hand    viewed    from   tlie 

tne      OS      namaium,      wnUSt  front.     The  views  on  either  side,  and  above  and  below,  represent 

radially     the     tuberosity     of  respectively  the  corresponding  surfaces  of  the  bone  turned  towards 

the  navicular  and  the  ridge  *^'*^  reader. 

of  the  large  multangular  help  to  deepen  the  furrow  by  their  elevation.     To  these 


Os  luimatum 


THE  METACAEPUS. 


207 


four  points  the  anterior  annular  ligament  of  the  wrist  is  attached,  which  stretches 

across  from  side  to  side, 
and  thus  converts  the 
furrow  into  a  canal  through 
which    the  flexor  tendons 

V.  Metacarpal^..^--^'  '^:  ^JI^M  ^^—-~     tV.  Metacarpal     paSS  tO  rcach  the  fiugCrS. 


%:■ 


Fig. 


Os  lunatuii; 


Fig.  153.— The  Eight  Os  Hama 


TIM.    >^ '»'-'■ 


XoTE. — The  bone  is  represented  in  the  centre  of  the  figure  in  the  position 
which  it  occupies  in  the  right  hand  viewed  from  the  front.     The 

views  on  either  side,  and   above  and  below,   represent  respectively    ijii-th   [^  which  the  tarsus  is  shown 
the  corresponding  surfaces  of  the  bone  turned  towards  the  reader.         in 'part  already  ossified. 


154. — Radiograph  of  the 
Hand  at  Birth. 

It  will  be  noticed  that  whilst  the 
primary  centres  for  the  metacarpus 
and  phalanges  are  well  ossified,  the 
carpus  is  still  entirely  cartilaginous. 

Compare  this  with  the  tarsus  at 


Ossification. — At  birth  the  carpus  is  entirely  cartilaginous.  An  exceptional  case  is 
figured  by  Lambertz,  in  which  the  centres  for  the  os  magnum  and  cuniform  were  already 
present.  The  same  authority  states  that  it  is  not  uncommon  to  meet  with  these  centres 
in  the  second  month  after  birth.  According  to  Debierre  (Journ.  cle  VAnat.  et  de  la 
Physiol,  vol.  xxii.  1886,  p.  285),  ossification  takes  place  approximately  as  follows  : — 


Capitate  Bone  or  Os  magnum     . 
Os  hamatum  or  Unciform 
Os  Triquetrum  or  Cuneiform 
Os  lunatum  or  Semilunar  . 
Large  multangular  or  Trapezium 
Navicular  or  Scaphoid 
Small  multangular  or  Trapezoid 
Pisiform    ..... 


11  to  12  months. 

12  to  14  months. 
3  years. 

5  to  6  years. 

6  years. 
6  years. 

6  to  7  years. 
10  to  12  vears. 


The  same  observer  failed  to  note  the  appearance  of  a  separate  centre  for  the  apophysis 
•of  the  OS  hamatum,  and  records  the  occurrence  of  two  centres  for  the  pisiform. 


The  lYIctacarpus. 

The  metacarpal  bones  form  the  skeleton  of  the  palm,  articulating  proximally 
with  the  carpus,  whilst  by  their  distal  extremities  or  heads  they  support  the  bones 
of  the  fingers.  Five  in  number,  one  for  each  digit,  they  lie  side  by  side  and 
slightly  divergent  from  each  other,  being  separated  by  intervals,  termed  interosseous 
spaces.  Distinguished  numerically  from  the  radial  to  the  ulnar  side,  they  all 
display  certain  common  characters ;  each  possesses  a  body  or  shaft,  a  base  or  carpal 
extremity,  and  a  head  or  phalangeal  end. 

The  shafts,  which  are  slightly  curved  towards  the  palmar  aspect,  are  narrowest 
towards  their  middle.  Their  dorsal  surface  is  marked  by  two  divergent  lines 
which  pass  forward  from  the  back  of  the  base  to  tubercles  on  either  side  of  the 


208 


OSTEOLOGY. 


Head 


Shaft 


Base 


Fig.  155.— First  Right 
Metacarpal  Bone. 


head.     The  surface,  included  between  the  two  lines  is  smooth  and  of  elongated 

triangular  form.  On  either  side  of  these  lines  two  broad  shallow  grooves  wind 
spirally  forward  on  to  the  palmar  surface,  where  they  are 
separated  in  front  by  a  sharp  ridge  which  is  continuous  with 
a  somewhat  triangular  surface  which  corresponds  to  the 
palmar  aspect  of  the  base.  The  grooved  surfaces  on  either 
side  of  the  shaft  furnish  origins  for  the  interossei  muscles. 
Close  to  the  palmar  crest  is  the  opening  of  the  nutrient 
canal,  which  is  directed  towards  the  carpal  extremity,  except 
in  the  case  of  the  first  metacarpal  bone. 

The  head  (capitulum)  is  provided  with  a  surface  for 
articulation  with  the  proximal  phalanx.  This  area  curves 
farther  over  its  palmar  than  its  dorsal  aspect.  Convex  from 
before  backwards  and  from  side  to  side,  it  is  wider  anteriorly 
than  posteriorly ;  notched  on  its  palmar  aspect,  its  edges  form 
two  prominent  tubercles,  which  are  sometimes  grooved  for 
the  small  sesamoid  bones  which  may  occasionally  be  found 
on  the  anterior  surface  of  the  joint.  On  either  side  of  the  head 
of  the  bone  there  is  a  deep  pit,  behind  which  is  a  prominent 
tubercle ;  to  these  are  attached  the  lateral  Ugaments  of  the 
metacarpo-phalangeal  joints. 

The  bases 
(basis),  all  more 
or  less  wedge- 
shaped  in  form, 
articulate       with 

the  carpus ;  they  differ  in  size  and  shape 

according  to  their  articulation. 

Of  the  five  metacarpal  bones,  the 

first,   viz.,   that  of   the  thumb,  is   the 

shortest  and  stoutest,  the  second  is  the 

longest,    whilst    the    third, 

fourth,  and    fifth    display  a 

gradual  reduction  in  length. 
The    four  medial  bones 

articulate    by    their    bases 

with    each   other,    and    are 

united   at   their  distal   ex- 
tremities     by      ligaments. 

They  are  so  arranged  as  to 

conform   to    the   hollow  of 

the    palm,    being    concave 

from  side  to  side  anteriorly, 

and  convex  posteriorly.    The 

first  metacarpal  differs  from 

the  others  in  being  free  at 

its  distal  extremity,  whilst 

its  jjroximal  end   possesses 

only  a  carpal  articular  facet. 
The    first    metacarpal 

bone   is   the   shortest    and 

stoutest  of  the  series.     Its 

shaft    is    compressed    from 

before  backwards.    Its  head, 

of  large  size,  is  but  slightly 

convex    from    side   to  side, 

and   is   grooved   in  front  for  the   sesamoid  bones.      The  base   is   provided  with 

a  saddle-shaped  surface  for  articulation  with  the  large  multangular,  and  has   na 

lateral  facets.     Laterally  there  is  a  slight  tubercle  to  which  the  abductor  poUicis- 


Capitate  bon 


Small 
niultangiilar 

Large  multangulav 


Small  multangular 
Fig.  156  a. — Second  Right  Metacarpal  Bone. 
Note. — The  bone  is    represented    in  the  centre  of  the  figure  iu    the 
position  which  it  occupies  in  tlie  right  hand  viewed  from  the  front. 
The  views  on  eitlier  side,   and   below,   represent  respectively  the 
corresponding  surfaces  of  the  bone  turned  towards  tlie  reader. 


THE  METACAEPUS. 


209 


longus  (extensor  ossis  metacarpi  pollicis)  muscle 
is  attached.  The  caual  for  the  nutrient  artery  is 
directed  towards  the  head  of  the  bone. 

The  second  metacarpal  bone  is  recognised 
by  its  length  and  its  broad  and  deeply -notched 
base  for  articulation  with  the  small  multangular. 
It  has  a  small  half-oval  facet  for  the  large  mult- 
angular on    the  radial  side    of  its   base,    whilst 
on     its    ulnar    aspect     it 
presents  a  narrow  vertical 
strip  for  the   capitate,  in 
front  of  which  there   are 
two  half-oval  surfaces  for 
the  third  metacarpal.     To 
the   dorsal   aspect   of   the 
base  is  attached  the  tendon 
of      the     extensor     carpi 
radialis  longus  muscle, 
whilst    the     flexor    carpi 
radialis  is  inserted  in  front. 

The  third  metacarpal 
bone  can  usually  be  re- 
cognised by  the  pointed 
styloid  process  which 
springs  from  the  back  of 
its  base,  and  is  directed 
towards    the    radial   side. 


styloid  process 


Capitate  bone 


Metacarpal 


Proximal 

Fig.  156  6. — Third  Right  ilEXACARPAL  Bone. 
XoTE. — The  bone  is  represented  in  the  centre  of  the  figure  in  the  position 
which  it  occupies  in   the   right  hand   viewed  from  the  front.     Tlie 
views  on   either  side,    and  below,   represent  respectively  the  corre- 
sponding surfaces  of  the  bone  turned  towards  the  reader. 


Capitate  bone 


Os  liamatmn 
V.  Metacarpa 


III.  -Metacarpal 


Capitate  bone 


Os  hamatum 


IV.  Metacarpal 


Proxiiiial 

Fig.  156  c. — Focrth  Right  Metacarpal  Boxe.  Fig.  156  tf. — Fifth  Right  Metacarpal  Bone. 

Note. — The  bone  in  each  figure  is  represented  in  the  centre  of  the  figure  in  the  position  which  it  occtipies  in  the 
right  hand  viewed  from  the  front.  The  views  on  either  side,  and  below,  represent  respectively  the  corre- 
sponding surfaces  of  the  bone  turned  towards  the  reader. 

Superiorly  there  is  a  facet  on  the  base  for  the  capitate.  To  the  radial  side 
there  are  two  half-oval  facets  for  the  second  metacarpal.  To  the  ulnar  side 
there    are    usually  two    small   oval  or    nearly    circular   facets    for    the    fourth 


210  OSTEOLOGY. 

metacarpal.  The  extensor  carpi  radialis  brevis  muscle  is  inserted  into  the  back 
of  the  base. 

The  fourth  metacarpal  bone  maj  be  recognised  by  a  method  of  exclusion.  It 
is  unlike  either  the  first,  second,  or  third,  and  differs  from  the  fifth,  which  it 
resembles  in  size,  by  having  articular  surfaces  on  both  sides  of  its  base.  Superiorly 
there  is  a  quadrilateral  surface  on  its  base  for  articulation  with  the  os  hamatum. 
On  its  radial  side  there  are  usually  two  small  oval  facets  for  the  third  metacarpal. 
Of  these  facets  the  dorsal  one  not  infrequently  has  a  narrow  surface  for  articula- 
tion with  the  capitate.  On  the  ulnar  side  there  is  a  narrow  articular  strip  for  the 
base  of  the  fifth  metacarpal. 

The  fifth  metacarpal  bone  can  be  recognised  by  its  size  and  the  fact  that  it 
has  only  one  lateral  articular  facet  on  its  base,  namely,  that  on  its  radial  side  for 
the  fourth  metacarpal.  The  carpal  articular  surface  is  saddle-shaped,  and  there  is 
a  tubercle  on  the  ulnar  side  of  the  base  for  the  insertion  of  the  extensor  carpi 
ulnaris  muscle. 

As  has  been  ah-eady  pointed  out,  tlie  ojjenings  of  the  arterial  canals  are  usually  seen  on  the 
pahnar  surfaces  of  the  metacarjsals,  those  of  the  four  inner  bones  being  directed  upwards  towards 
the  base  or  carpal  end,  differing  in  this  respect  from  that  of  the  first  metacarpal,  which  is  directed 
downwards  towards  the  head  or  phalangeal  extremity.  The  opening  of  the  latter  canal  usually 
lies  to  the  ulnar  side  of  the  palmar  aspect  of  the  shaft. 

Ossification. — The  metacarpal  bones  are  developed  from  primary  and  secondary 
centres  ;  but  there  is  a  remarkable  difference  between  the  mode  of  growth  of  the  first  and 
the  remaining  four  metacarpals,  for  whilst  the  shaft  and  head  of  the  first  metacarpal 
are  developed  from  the  primary  ossific  centre,  and  its  base  from  a  secondary  epiphysis,  in 
the  case  of  the  second,  third,  fourth,  and  fifth  metacarpals,  the  shafts  and  bases  are  de- 
veloped from  the  primary  centres,  the  heads  in  these  instances  being  derived  from  the 
secondary  epiphyses.  In  this  respect,  therefore,  as  will  be  seen  hereafter,  the  metacarpal 
bone  of  the  thumb  resembles  the  phalanges  in  the  manner  of  its  growth,  a  circumstance 
which  has  given  rise  to  considerable  discussion  as  to  whether  the  thumb  is  to  be  regarded  as 
possessing  three  phalanges  and  no  metacarpal,  or  one  metacarpal  and  two  phalanges.  Broom 
{Anat.  Anz.  vol.  28),  by  a  reference  to  reptilian  forms  offers  an  explanation  in  regard  to  the 
difference  in  the  mode  of  ossification  of  the  first  metacarpal  on  the  ground  that  the  most 
movable  joint  is  that  between  the  first  metacarpal  and  the  carpus,  whereas  on  the  other 
digits  the  most  movable  joints  are  those  between  the  metacarpals  and  phalanges.  In 
consequence  those  ends  of  the  bones  which  enter  into  the  formation  of  the  joints  where 
movement  is  most  free  are  the  ends  where  the  epiphyses  will  appear.  This  is  in  accord- 
ance with  the  law  suggested  in  connexion  with  the  fibula.  The  primary  centres  for  the  shafts 
and  bases  of  the  second,  third,  fourth,  and  fifth  metacarpals  appear  in  that  order  during  the 
ninth  or  tenth  week  of  intrauterine  life,  some  little  time  after  the  terminal  phalanges 
have  begun  to  ossify,  that  for  the  shaft  and  head  of  the  metacarpal  bone  of  the  thumb  a 
little  later.  At  birth  the  shafts  of  the  bones  are  well  formed.  The  secondary  centres  from 
which  the  heads  of  the  second,  third,  fourth,  and  fifth  metacarpals  and  the  base  of  the 
first  are  developed,  appear  about  the  third  year,  and  usually  completely  fuse  with  the 
shafts  about  the  age  of  twenty.  There  may  be  an  independent  centre  for  the  styloid 
process  of  the  third  metacarpal,  and  there  is  usually  a  scale-like  epiphysis  on  the  head  of 
the  first  metacarpal  which  makes  its  appearance  about  eight  or  ten,  and  rapidly  unites 
with  the  head.  The  occurrence  of  a  basal  epiphysis  in  the  second  metacarpal  bone  has 
been  noticed. 

The   Phalanges. 

The  phalanges  or  finger  bones  (phalanges  digitorum  manus)  are  fourteen  in 
number — three  for  each  finger,  and  two  for  the  thumb. 

Named  numerically  in  order  from  the  proximal  toward  the  distal  ends  of  the 
fingers,  the  first  phalanx  (phalanx  prima),  the  longest  and  stoutest  of  the  three,  has  a 
semi-cylindrical  shaft  which  is  curved  slightly  forwards.  The  palmar  surface  is  flat, 
and  bounded  on  either  side  by  two  sharp  borders  to  which  the  sheath  of  the  flexor 
tendons  is  attached.  The  dorsal  surlace,  convex  from  side  to  side,  is  overlain  by 
the  extensor  tendons.  The  proximal  end,  considerably  enlarged,  has  a  simple  oval 
concave  surface,  which  rests  on  the  head  of  its  corresponding  metacarpal  bone.  On 
either  side  of  this  the  bone  displays  a  tubercular  form,  and  affords  attachment  to 


THE  PHALANGES. 


211 


III. 

Phalanx, 

ungual  or 

terminal 


II.  Phalaiis 


the  lateral  ligaments  of  the  metacarpo-phalangeal  jomt,  and  also  to  the  interossei 
muscles.  The  distal  end  is  much  smaller  than  the 
proximal ;  the  convex  articular  surface  is  divided  into 
two  condyles  by  a  central  groove  running  from  before 
backward.  The  second  phalanx  (phalanx  secunda)  resembles 
the  first  in  general  form,  but  is  of  smaller  size.  It 
differs,  however,  in  the  form  of  its  proximal  articular 
surface,  which  is  not  a  simple  oval  concavity,  but  is  an 
oval  area  divided  into  two  small,  nearly  circular  con- 
cavities by  a  central  ridge  passing  from  before  backwards ; 
these  articulate  with  the  condylic  surfaces  of  the  proximal 
phalanx.  Into  the  margins  of  its  palmar  surface  near 
the  proximal  end  are  inserted  the  split  portions  of  the 
tendon  of  the  flexor  digitorum  sublimis,  whilst  on  the 
dorsal  aspect  of  the  proximal  end  the  central  slip  of  the 
extensor  digitorum  communis  muscle  is  attached.  The 
third,  terminal  or  ungual  phalanx  (phalanx  tertia),  is  the 
smallest  of  the  three ;  it  is  easily  recognised  by  the 
spatula  -  shaped  surface  on  its  distal  extremity  which 
supports  the  nail  The  articular  surface  on  its  proximal 
end  resembles  that  on  the  proximal  end  of  the  second 
phalanx,  but  is  smaller.  On  the  palmar  aspect  of  this 
end  of  the  bone  there  is  a  rough  surface  for  the  insertion 
of  the  tendon  of  the  flexor  digitorum  profundus  muscle. 
The  dorsal  surface  of  the  same  extremity  has  attached  to 
it  the  terminal  portions  of  the  tendon  of  the  extensor 
digitorum  communis  muscle.  The  phalanges  of  the 
thumb  resemble  in  the  arrangement  of  their  parts  the 
first  and  third  phalanges  of  the  fingers. 


Head 


-haft 


The  arterial  canals,  usually  two  in  number,  placed  on  either  i 

side  of  the  palmar  asjsect  and  nearer  the  distal  than  the  proximal  ^  ^  ^  '^°*'  P^ 

end  of  the  bone,  are  directed  towards  the  finger-tiias.  ^^^-  ^^'-     '^^^  Phalasges  of 

THE  Fingers  (pahuar  aspect). 

Ossification. — The  phalanges  are  ossified   from   primary 
and  secondary  centres.      From  the  former,  which  appear  as  early  as  the  ninth  week  of 


%t 


»  1% 

i  f  df 

4 

H 

5 

15S. — Radiographs  of  Fcetal  Hands. 

1.   About  ten  weeks.      Here  the  ossifie  nuclei  of  the  terminal  phalanges  and  the  four  inner  metacarpal  bones 

are  seen. 
•2.   A  little  later.     The  centre  for  the  metacarpal  for  the  thumb  is  now  present,  as  also  the  centres  for  the  first 

row  of  phalanges.     The  centres  of  the  second  row  of  phalanges  have  appeared  in  the  case  of  the  middle 

and  ring  fingers. 
3.    During  tlie   third   month.     All   the   primary   centres  for   the   metacarpal   bones   and   phalanges  are   now 

developed. 
i.   About  the  fourth  to  fifth  month. 
.5.    About  the  sixth  to  seventh  month. 

foetal  life,  the  shaft  and  distal  extremities  are  developed ;  whilst  the  latter,  which  begin 
to  appear  about  the  third  year,  form  the  proximal  epiphyses  which  unite  with  the  shafts 


212  OSTEOLOGY. 

from  eighteen  to  twenty.  Dixey  {Proc.  Roy.  Soc,  xxx.  and  xxxi.)  has  pointed  out  that 
the  primary  centre  in  the  ungual  phah\nges  commences  to  ossify  in  the  distal  part  of 
the  bone  rather  than  towards  the  centre  of  the  shaft.  This  observation  has  been 
confirmed  by  Lambertz,  who  further  demonstrates  the  fact  that  ossification  commences 
earlier  in  the  distal  phalanges  than  in  any  of  the  other  bones  of  the  hand.  Of  the 
other  phalanges,  those  of  the  first  row,  beginning  with  that  of  the  third  finger,  next 
ossify,  subsequent  to  the  appearance  of  ossific  centres  in  the  shafts  of  the  metacarpal 
bones,  whilst  the  second  or  intermediate  row  of  the  phalanges  is  the  last  to  ossify  about 
the  end  of  the  third  month.  Sewell  has  recorded  a  case  in  which  the  proximal  phalanx 
had  a  distal  as  well  as  a  proximal  epiphysis. 

Sesamoid   Bones. 

Two  little  oval  nodules  (ossa  sesamoidea),  which  play  in  grooves  on  the  palmar 
aspect  of  the  articular  surface  of  the  head  of  the  first  metacarpal  bone,  are  constantly 
met  with  in  the  tendons  and  ligaments  of  that  metacarpo-phalangeal  articulation. 
Similar  nodules,  though  of  smaller  size,  are  sometimes  formed  in  the  corresponding 
joints  of  the  other  fingers,  more  particularly  the  index  and  little  finger ;  as  Thilenius 
has  pointed  out  (Morph.  Arheiten,  vol.  v.),  these  are  but  the  persistence  of  cartilaginous 
elements  which  have  a  phylogenetic  interest. 


THE    LOWER    LIMB. 

THE  PELVIC  GIRDLE  AND  THE  LOWER  EXTREMITY. 

The  pelvic  girdle  is  formed  by  the  articulation  of  the  two  innominate  bones 
with  the  sacrum  behind,  and  their  union  with  each  other  in  front,  at  the  joint  called 
the  symphysis  pubis. 

The   Innominate  or  Hip   Bone. 

The  innominate  or  hip  bone  (os  coxae)  is  the  largest  of  the  "  flat "  bones  of  thp 
skeleton.  It  consists  of  three  parts — the  ilium,  the  ischium,  and  the  pubis — 
primarily  distinct,  but  fused  together  in  the  process  of  growth  to  form  one  large 
irregular  bone.  The  coalescence  of  these  elements  takes  place  in  and  around  the 
acetabulum,  a  large  circular  articular  hollow  which  is  placed  on  the  lateral  side  of  the 
bone.  The  expanded  wing-like  part  above  this  is  the  ilium ;  the  stout  V-shaped 
portion  below  and  behind  it  constitutes  the  ischium ;  while  the  <;-shaped  part  to 
the  medial  side,  and  in  front  and  below,  forms  the  pubis.  The  two  latter  portions  of 
the  bone  enclose  between  them  a  large  aperture  of  irregular  outline,  called  the 
obturator  foramen  (foramen  obturatum),  which  is  placed  in  front  and  below,  and  to 
the  inner  side  of  the  acetabulum. 

The  ilium,  almost  a  quadrant  in  form,  consists  of  an  expanded  plate  of  bone, 
having  a  curved  superior  border,  the  iliac  crest  (crista  iliaca).  Viewed  from  the 
side,  this  forms  a  curve  corresponding  to  the  circumference  of  the  circle  of  which 
the  bone  is  the  quadrant ;  viewed  from  above,  however,  it  will  be  seen  to  display 
a  double  bend — convex  anteriorly  and  laterally,  and  concave  posteriorly  and 
laterally.  The  iliac  crest  is  stout  and  thick,  and  for  descriptive  purposes  is 
divided  into  a  lateral  lip  (labium  externum),  a  medial  lip  (labium  internum),  and 
an  intermediate  surface  (linea  intermedia)  which  is  broad  behind,  narrowest  about 
its  middle,  and  wider  again  in  front.  About  21  inches  from  the  anterior  extremity 
of  the  crest  the  lateral  lip  is  usually  markedly  prominent  and  forms  a  projecting 
tubercle,  which  can  readily  be  felt  in  the  living.  Attached  to  these  surfaces  and 
lips  anteriorly  are  the  muscles  of  the  flank,  whilst  from  them  posteriorly  the 
latissimus  dorsi,  quadratus  lumborum,  and  sacro-spinalis  muscles  derive  their 
origins.  The  crest  ends  in  front  in  a  pointed  process,  the  anterior  superior  iliac  spine 
(spina  iliaca  anterior  superior).  To  this  the  lateral  extremity  of  Poupart's  inguinal 
ligament  is  attached,  as  well  as  the  sartorius  muscle,  which  also  arises  from  the 
edge  of  bone  immediately  below  it,  whilst  from  the  same  process  and  from  the 


THE  INNOMINATE  BONE. 


213 


anterior  end  of  the  lateral  lip  of  the  iliac  crest  the  tensor   fasciae  lat»  muscle 
takes  origin. 

The  anterior  border  of  the  ilium  stretches  from  the  anterior  superior  iliac  spine 
to  the  margin  of  tlie  acetabulum  below.  Above,  it  is  thin  ;  but  below,  it  forms 
a  thick  blunt  process,  the  anterior  inferior  iliac  spine  (spina  iliaca  anterior  in- 
ferior).    From  this  the  rectus  femoris  muscle  arises,  whilst  the  stout  fibres  of  the 


Cre^jt  nv  THR   ILIUM 


Middle  gluteal  line 


Posterior 

GLUTEAL  line 


Posterior 
superior 

SPINE 


Posterior  inferior  spi.ne 


Cotyloid  notch 
Groove  for  tendon  of  obturator 


Anterior 
superior  spine 


Inferior  gluteal 

line 


Anterior  inferior 
sriNE 


Acetabulum 
pectineal  eminence 


Lesser  sciatic  notch 


Ischial  tuberosity 


Superior  ramus 
of  pubis 
I'UBic  spine 

Crest  of  pubis 
Body  of  pubis 


us  of  pubis 


Fig.  159  rt. 


Inferior  ramus  of  ischium 
-The  Right  Innominate  Bone  seen  from  the  Lateral  Side. 


ilio-femoral  ligament  of  the  hip-joint  are  attached  to  it  immediately  above  the 
acetabular  margin.  Posteriorly,  the  crest  terminates  in  the  posterior  superior  iliac 
spine  (spina  iliaca  posterior  superior).  Below  this,  the  posterior  border  of  the  bone 
is  sharp  and  irregularly  notched  terminating  in  a  prominent  angle,  the  posterior 
inferior  iliac  spine  (spina  iliaca  posterior  inferior),  in  front  of  which  the  edge  of  the 
bone  becomes  thick  and  rounded,  and  forms  a  wide  notch  which  sweeps  forwards 
and  downwards  to  join  the  mass  of  bone  behind  the  acetabulum,  where  it  becomes 
fused  with  the  ischium ;  this  is  called  the  greater  sciatic  notch  (incisura  ischiadica 
major). 

14 


214 


OSTEOLOGY. 


External  obliqde 


QCADRATUS    LUMBORUM 


Sartorids 

rNSOR  FASCI.'E 

eflected  head 
of  rectus  femoris 
Straight  head  of 
rfctds  femoris 


The  ilium  has  t^vo  surfaces,  medial  and  lateral.  The  lateral  surface  is  divided 
into  two  parts,  viz.  a  lower  acetabular,  aud  an  upper  gluteal  part.  The  lower 
forms  a  little  less  than  the  upper  two-fifths  of  the  acetabular  hollow,  and  is 
separated  from  the  larger  gluteal  surface  above  by  the  upper  prominent  margin  of 
the  articular  cavity.  The  gluteal  surface,  broad  and  expanded,  is  concavo-convex 
from  behind  forward.  It  is  traversed  by  three  rough  curved  lines,  well  seen  in 
strongly  developed  bones,  but  often  faint  and  indistinct  in  feebly  marked  speci- 
mens. Of  these  the  inferior  curved  line  (linea  glutsea  inferior)  curves  backwards 
from  a  point  immediately  above  the  anterior  inferior  spine  towards  the  great  sciatic 
notch  posteriorly ;  the  bone  between  this  and  the  acetabular  margin  is  marked  by 
a  rough  shallow  groove,  from  which  the  reflected  head  of  the  rectus  fern  oris  muscle 

arises.  The  anterior  or 
(middle)  curved  line 
(linea  glutsea  anterior) 
commences  at  the  crest 
of  the  ilium,  about 
one  inch  and  a  half 
behind  the  anterior 
superior  iliac  spine,  and 
sweeps  backwards  and 
downwards  towards  the 
upper  and  posterior 
part  of  the  great  sciatic 
notch.  The  surface  be- 
tween this  line  and  the 
preceding  furnishes  an 
extensive  origin  for 
the  glutseus  minimus 
muscle.  The  posterior 
or  (superior)  curved  line 
(linea  glutsea  posterior) 
leaves  the  iliac  crest 
about  two  and  a  half 
inches  in  front  of  the 
posterior  superior  iliac 
spine,  and  bends  down- 
wards and  slightly  for- 
wards in  a  direction 
anterior  to  the  posterior 
inferior  spine.  The 
area  between  this  and 
the  middle  curved  line 
is  for  the  origin  of  the  glutfeus  medius  muscle,  whilst  the  rough  surface  immediately 
above  and  behind  it  is  for  some  of  the  fibres  of  origin  of  the  gluteus  maximus 
muscle. 

The  medial  surface  of  the  ilium  is  divided  into  two  areas  which  present  very 
characteristic  differences.  The  posterior  or  sacral  part,  which  is  rough,  displays  in 
front  a  somewhat  smooth,  auricular  surface  (facies  auricularis)  which  is  cartilage- 
coated  in  the  recent  condition,  and  articulates  with  the  sacrum. 

Thi.s  area  is  said  to  be  proportionately  smaller  in  the  female,  wliilst  curving  rmuid  in  front 
of  its  anterior  margin  there  is  often  a  groove,  for  the  attachment  of  the  filn-es  of  the  anterior 
sacro-iliac  ligaments,  called  the  ^jre-auricular  sulcus.  According  to  Dcrry  this  groove  is  better 
marked  in  the  female,  and  may  be  regarded  as  characteristic  of  that  sex. 

Above  and  behind  this  there  is  an  elevated  irregular  area,  the  tuberosity 
(tuberositas  iliaca),  which  is  here  and  there  deeply  pitted  for  the  attachment  of  the 
strong  posterior  sacro-iliac  ligaments.  Above  this  the  bone  becomes  confluent  with 
the  medial  lip  of  the  iliac  crest,  and  here  it  affords  an  origin  to  the  sacro-spinalis 
and  multifidus  muscles,  and  some  of  the  fibres  of  the  quadratus  lumljorum. 
The  anterior  part  of  the  medial  aspect  of  the  bone  is  smooth  and  extensive ;   it 


Semimembranosus 


BICEP.S   AND 
SEMITENDINOSUb 


Quadratus  femoris 


Pyramidalis 
Rectus  abdominis 
Adductor  longus 


Gracilis 


Adductor  brevis 

Adductor  magnus 
Fio.  159 /a —Lateral  Aspect  of  the  Right  Innominate  Bone  with  the 
Attachments  of  the  Muscles  mapped  out. 


THE  INNOMINATE  BONE. 


215 


is  subdivided  by  an  oblique  ridge,  called  the  ilio- pectineal  line  (linea  arcuata), 
which  passes  forwards  and  downwards  from  the  most  prominent  point  of  the 
auricular  surface  towards  the  medial  side  of  the  iUo- pectineal  eminence  which 
is  placed  just  above  and  in  front  of  the  acetabulum,  and  marks  the  fusion  of  the 


Crest  of  the  ilum 


IFJUM 


Anterior 
superior 

SPINE 


Anterior  inferior 

SPINE 


Ilio-pectineal 
eminence 


Ilio-pectineal  line 


Superior  ramus 

OF   PUBIS" 

Obturator  groove 

Spine 
of  pubis 

Crest  f 

OF    pubis 


Symphysis  pubi 


Tuberosity 

FOR 

posterior 

sacro-iliac 

ligament 

Posterior 
superior 

SPINE 


Articular 

SURFACE 


Post.  inf.  spine 


Lesser  sciatic  notch 


ISCHIUM 

Ischial  tuberosity 


Inferior  ramus  of  pubis  Ramus  of  ischium 

Fig.  160. — The  Eight  Innominate  Bone  (Medial  Aspect). 

ilium  with  the  pubis.  Above  this  the  bone  forms  the  shallow  iliac  fossa  (fossa 
iliaca),  from  the  iloor  of  which  the  iliacus  muscle  arises,  whilst  leading  from  the 
fossa,  below  and  in  front,  there  is  a  shallow  furrow,  passing  over  the  superior 
acetabular  margin,  between  the  anterior  inferior  iliac  spine  on  the  lateral  side  and 
the  ilio-pectineal  eminence  medially,  for  the  lodgment  of  the  tendinous  and  fleshy 
part  of  the  ilio-psoas  muscle.  If  held  up  to  the  hght  the.  floor  of  the  deepest  part 
of  the  iKac  fossa  will  be  seen  to  be  formed  of  but  a  thin  layer  of  bone.     A  nutrient 


216  OSTEOLOGY. 

foramen  of  large  size  is  seen  piercing  the  bone  towards  the  hinder  part  of  the 
fossa.  Below  and  behind  the  ilio- pectineal  line  the  medial  surface  of  the  ilium 
forms  a  small  portion  of  the  wall  of  the  true  pelvis ;  the  bone  here  is  smooth,  and 
rounded  oti" posteriorly  into  the  greater  sciatic  notch,  where  it  becomes  confluent  with 
the  medial  aspect  of  the  ischium.  This  part  of  the  bone  is  proportionately  longer 
in  the  female  than  in  the  male,  and  forms  with  the  ischium  a  more  open  angle. 
Just  anterior  to  the  great  sciatic  notch  there  are  usually  the  openings  of  one  or 
two  large  vascular  foramina.  From  this  surface  arise  some  of  the  posterior  fibres 
of  the  obturator  internus  muscle. 

The  ischium  constitutes  the  lower  and  hinder  part  of  the  innominate  bone. 
Superiorly  its  body  (corpus)  forms  somewhat  more  than  the  inferior  two-fifths  of 
the  acetabulum  together  with  the  bone  supporting  it  behind  and  within.  Below 
this,  the  superior  ramus  passes  downwards  and  backwards  as  a  stout  three-sided 
piece  of  bone,  from  the  inferior  extremity  of  which  a  compressed  bar  of  bone,  called 
the  inferior  ramus,  extends  forwards  at  an  acute  angle.  This  latter  unites  in  front 
and  above  with  the  descending  ramus  of  the  pubis,  and  encloses  the  aperture  called 
the  obturator  foramen. 

Superiorly,  and  on  the  lateral  aspect  of  the  ischium,  the  acetabular  surface  is 
separated  from  the  bone  below  by  a  sharp  and  prominent  margin,  which  is, 
however,  deficient  in  front,  where  it  corresponds  to  the  cotyloid  notch,  (incisura 
acetabuli)  leading  into  the  articular  hollow ;  the  floor  of  this  notch  is  entirely 
formed  by  the  ischium.  Below  the  prominent  acetabular  margin  there  is  a  well- 
marked  groove  in  which  the  tendon  of  the  obturator  externus  lies.  Beneath  this 
the  antero-lateral  surface  of  the  superior  and  inferior  rami  furnish  surfaces  for  the 
attachments  of  the  obturator  externus,  quadratus  femoris,  and  adductor  magnus 
muscles.  The  postero-lateral  surface  of  the  ischium  forms  the  convex  surface  on 
the  back  of  the  acetabulum.  The  medial  border  of  this  is  sharp  and  well  defined, 
and  is  confluent  above  with  the  border  of  the  ilium,  which  sweeps  round  the  great 
sciatic  notch.  From  this  border,  on  a  level  with  the  lower  edge  of  the  acetabulum, 
there  springs  a  pointed  process,  the  spine  (spina  ischiadica),  to  which  is  attached 
the  lesser  sacro-sciatic  ligament  (sacro-spinous  ligament)  and  the  superior  gemellus 
muscle.  Inferior  to  this,  the  postero-lateral  surface  narrows  rapidly,  its  medial 
border  just  below  the  spine  being  hollowed  out  to  form  the  lesser  sciatic  notch  (incisura 
ischiadica  minor).  The  lower  part  of  this  surface  and  the  angle  formed  by  the  two 
rami  are  capped  by  an  irregularly  rough  pyriform  mass  called  the  tuberosity  ^  (tuber 
ischiadicum).  This  is  divided  by  an  oblique  ridge  into  two  areas,  the  upper  and 
lateral  for  the  tendon  of  origin  of  the  semimembranosus  muscle,  the  lower  and  medial 
for  the  conjoined  heads  of  the  biceps  and  semitendinosus  muscles.  Its  prominent 
medial  lip  serves  for  the  attachment  of  the  great  sacro-sciatic  ligament  (sacrotuber- 
ous  ligament),  whilst  its  lateral  edge  furnishes  an  origin  for  the  quadratus  femoris 
muscle;  in  front  and  below,  the  adductor  magnus  muscle  is  attached  to  it. 

The  medial  surface  of  the  body  and  superior  ramus  of  the  ischium  form  in  part 
the  wall  of  the  true  pelvis.  Smooth  and  slightly  concave  from  before  backwards, 
and  nearly  plane  from  above  downwards,  it  is  widest  opposite  the  level  of  the  ischial 
spine.  Below  this,  its  posterior  edge  is  rounded  and  forms  a  groove  leading  to  the 
lesser  sciatic  notch,  along  and  over  which  the  tendon  of  the  obturator  internus 
passes.  To  part  of  this  surface  the  fibres  of  the  obturator  internus  are  attached, 
whilst  the  medial  aspect  of  the  spine  supplies  points  of  origin  for  the  coccygeus  and 
levator  ani  muscles,  as  well  as  furnishing  an  attachment  to  the  "  white  line  "  of  the 
pelvic  fascia.  The  medial  surface  of  the  inferior  ramus  of  the  ischium  is  smooth, 
and  so  rounded  that  its  inferior  edge  tends  to  be  everted.  To  this,  as  well  as  to  its 
margin,  is  attached  the  crus  penis,  together  with  the  ischio-cavernosus,  obturator 
internus,  transversus  perinei,  and  compressor  urethrse  (sphincter  muscle  of  the 
membranous  urethra)  muscles.  In  the  female,  structures  in  correspondence  with 
these  are  also  found. 

The  fore-part  of  the  innominate  bone  is  formed  by  the  pubis ;  it  is  by  means  of 
the  union  of  this  bone  with  its  fellow  of  the  opposite  side  that  the  pelvic  girdle  is 
completed  in  front. 

^  I  retain  the  word  "tuberosity"  here  instead  of  tlie  meaningless  "tuber." — A.  T. 


THE  INNOMINATE  BONE. 


217 


The  pubis  (os  pubis)  consists  of  two  rami — a  superior  (ascending  or  horizontal) 
(ramus  superior  ossis  pubis)  and  an  inferior  (or  descending)  (ramus  inferior  ossis  pubis). 
The  broad  part  of  the  bone  formed  by  the  fusion  of  these  two  rami  is  the  body. 

The  body  of  the  pubis  has  two  surfaces.  Of  these  the  posterior  or  postero-siiperior 
is  smooth,  and  forms  the  fore-part  of  the  wall  of  the  true  pelvis ;  hereto  are 
attached  the  levator  ani  muscle  and  puboprostatic  ligaments,  and  on  it  rests 
tlie  bladder.  The  anterior  or  antero-ivferior  surface  is  rougher,  and  furnishes 
origins  for  the  gracilis,  adductor  longus,  adductor  brevis,  and  some  of  the  fibres  of 
the  obturator  externus  muscles.  The  medial  border  is  provided  with  an  elongated 
oval  cartilage -covered  surface  by  means  of  which  it  is  united  to  its  fellow  of 
the  opposite  side,  the  joint  being  called  the  symphysis  pubis  (facies  symphyseos). 
The  upper  border,  thick  and  rounded,  projects  somewhat,  so  as  to  overhang  the 
anterior  surface.  It  is  called  the  crest  (pecten).  Internally  this  forms  with  the  medial 
border  or  symphysis  the  angle,  whilst  laterally  it  terminates  in  a  pointed  process, 
the  spine  (tuberculum  pubicum).  From  the  crest  arise  the  rectus  abdominis 
and  pyramidalis  muscles,  and  to  the  spine  is  attached  the  medial  end  of  Poupart's 


Rectus  femoris  (straight  head  of  origin) 

Rectus  femokis  (rfflncted  head  of  origin) 
Attachment  ok 

lO-FEMORAL  BAND  ADDUCTOR  LONOUS  (origin) 

Pyramidalis  abdominis  (origin) 
Rectus  abdominis  (origin) 


Gracilis  (origin) 
Adductor  erevis  (origin) 


Semimembran 

osus  (origin) 

Quadratus 

FEMORis  (origin) 

Biceps  and 

semitendinosus- 

(origin) 


Fig.  161. — Mdscle-Attachments  to  the  Lateral  Surface  of  the  Pubis  and  Ischium. 


inguinal  ligament.  Passing  upwards  and  laterally  from  the  lateral  side  of  the  body 
towards  the  acetabulum,  of  which  it  forms  about  the  anterior  fifth,  is  the 
superior  ramus  (ramus  superior).  This  has  three  surfaces  :  an  antero-superior,  an 
antero- inferior,  and  an  internal  or  posterior.  The  antero-superior  surface  is 
triangular  in  form.  Its  apex  corresponds  to  the  pubic  spine ;  its  anterior  inferior 
border  to  the  obturator  crest  (crista  obturatoria),  leading  from  the  spine  to  the 
upper  border  of  the  cotyloid  notch  ;  whilst  its  sharp  postero-superior  border  trends 
upwards  and  laterally  from  the  spine,  and  is  continuous  with  the  iliac  portion  of 
the  ilio-pectineal  line  just  medial  to  the  iHo-pectineal  eminence,  forming  as  it 
passes  along  the  superior  ramus  the  pubic  portion  of  that  same  line  (pecten  ossis 
pubis).  On  this  line,  just  within  the  ilio-pectineal  eminence,  there  is  often  a  short, 
sharp  crest  which  marks  the  insertion  of  the  psoas  parvus.  The  base  of  the 
triangle  corresponds  to  the  ilio-pectineal  eminence  above  and  the  upper  margin  of 
the  cotyloid  notch  below.  Slightly  hollow  from  side  to  side,  and  convex  from 
before  backwards,  this  surface  provides  an  origin  for,  and  is  in  part  overlain  by,  the 
pectineus  muscle.  The  posterior  or  ptosterior  surface  of  the  superior  ramus  is  smooth, 
concave  from  side  to  side,  and  slightly  rounded  from  above  downwards ;  by  its 
sharp  inferior  curved  border  it  completes  the  obturator  foramen,  as  seen  from  behind. 


218  OSTEOLOGY. 

The  antero-inferior  surface  forms  the  roof  of  the  broad  obturator  groove  (sulcus 
obturatorius)  wliich  passes  obliquely  downwards  aud  forwards  between  the  lower 
margin  of  the  antero-superior  surface  in  front  and  the  inferior  sharp  border  of  the 
medial  surface  behind.  The  inferior  or  descending  ramus  of  the  pubis  (ramus 
inferior)  passes  downwards  and  outwards  from  the  lower  part  of  the  body. 
Flattened  and  compressed,  it  unites  with  the  inferior  ramus  of  the  ischium,  and 
thus  encloses  the  obturator  foramen,  whilst  in  correspondence  with  its  fellow  of 
the  opposite  side  it  completes  the  formation  of  the  pubic  arch.  Anteriorly  it 
furnishes  origins  for  the  gracilis,  adductor  brevis,  and  adductor  magnus  mu.scles, 
as  well  as  some  of  the  fibres  of  the  obturator  externus  muscle.  Its  inedial  surface 
is  smooth,  whilst  its  lower  border,  rounded  or  more  or  less  everted,  has  attached  to 
it  the  fore-part  of  the  crus  penis  and  the  subpubic  ligament 

The  acetabulum  or  cotyloid  cavity  is  the  nearly  circular  hollow  in  which  the 
head  of  the  thigh  bone  fits.  As  has  been  already  stated,  it  is  formed  by  the  fusion 
of  the  ilium  and  ischium  and  pubis  in  the  following  proportions :  the  ilium  a  little 
less  than  two-fifths,  the  ischium  somewhat  more  than  two- fifths,  the  pubis  con- 
stituting the  remaining  one-fifth.  It  is  so  placed  as  to  be  directed  downwards, 
laterally,  and  forwards,  and  is  surrounded  by  a  prominent  margin,  to  which  the 
capsule  and  cotyloid  ligament  of  the  hip  -  joint  are  attached.  Opposite  the 
obturator  foramen  this  margin  is  interrupted  by  the  cotyloid  notch  (incisura 
acetabuli) ;  immediately  lateral  to  the  ilio- pectineal  eminence  the  margin  is 
slightly  hollowed,  whilst  occasionally  there  is  a  feeble  notching  of  the  border 
above  and  behind.  These  irregularities  in  the  outline  of  the  margin  correspond  to 
the  lines  of  fusion  of  the  ilium  and  pubis,  and  the  ilium  and  ischium  respectively. 
The  floor  of  the  acetabulum  is  furnished  with  a  horseshoe-shaped  articular  surface, 
which  lines  the  circumference  of  the  hollow,  except  in  front,  where  it  is  interrupted 
by  the  cotyloid  notch.  It  is  broad  above ;  narrower  in  front  and  below.  Within 
this  articular  surface  there  is  a  more  or  less  circular  rough  area  (fossa  acetabuli) 
continuous  in  front  and  below  with  the  floor  of  the  cotyloid  notch.  This,  some- 
what depressed  below  the  surface  of  the  articular  area,  lodges  a  quantity  of  fat, 
and  provides  accommodation  for  the  intra-articular  ligament  of  the  joint.  As  may 
be  seen  by  holding  the  bone  up  to  the  light,  the  floor  of  this  part  of  the  acetabulum 
is  not  usually  of  great  thickness.  The  major  part  of  the  non-articular  area  is 
formed  by  the  ischium,  which  also  forms  the  floor  of  the  cotyloid  notch. 

The  obturator  foramen  (foramen  obturatum)  lies  in  front  of,  below,  and 
medial  to  the  acetabulum.  The  margins  of  this  opening,  which  are  formed 
in  front  and  above  by  the  pubis,  and  behind  and  below  by  the  ischium,  are 
sharp  and  thin,  except  above,  where  the  under  surface  of  the  superior  ramus  of  the 
pubis  is  channelled  by  the  obturator  groove.  Below,  and  on  either  side  of  this 
groove,  two  tubercles  can  usually  be  seen.  The  one,  situated  on  the  edge  of  the 
ischium,  just  in  front  of  the  cotyloid  notch,  is  named  the  posterior  obturator 
tubercle  (tuberculum  obturatorium  posterius) ;  the  other,  placed  on  the  lower 
border  of  the  posterior  surface  of  the  superior  ramus  of  the  pubis,  is  called  the 
anterior  obturator  tubercle  (tuberculum  obturatorium  anterius).  Between  these 
two  tubercles  there  passes  a  ligamentous  band,  which  converts  the  groove  into  a 
canal  along  which  the  obturator  vessels  and  nerve  pass.  Elsewhere  in  the 
fresh  condition  the  obturator  membrane  stretches  across  the  opening  from  margin 
to  margin.  The  form  of  the  foramen  varies  much,  being  oval  in  some  specimens, 
in  others  more  nearly  triangular ;  its  relative  width  in  the  female  is  greater 
than  in  the  male. 

Nutrient  foramina  ior  tin-  ilium  are  .seen  on  the  floor  of  the  iliac  fossa,  just  in  front  of  the 
sacrfj-auriciilar  surface  ;  on  the  in;lvic  aspect  of  the  bone,  close  to  th«  greater  sciatic  notch  ;  and  on 
the  glvUeal  surface  laterally,  near  the  centre  ui'  the  luiddle  curved  line.  For  the  ischium,  on  its 
pelvic  surface,  and  also  laterally  on  the  groove  l^elow  the  acetabulum.  For  the  pubis,  on  the 
surface  of  the  body,  and  deeply  also  from  the  acetabular  fossa. 

Connexions. — The  innominate  bone  articulates  with  the  sacrum  l)ehind,  with  the  femur  to 
the  lateral  side  and  below,  and  with  its  fellow  of  the  opposite  side  medially  and  in  front.  Each 
of  its  three  ])arts  comes  into  direct  relation  with  the  surface.  Above,  the  iliac  crest  assists  in 
forming  the  iliac  furrow,  which  serves  to  separate  the  region  of  the  flank  from  that  of  the 
buttock.     In  front,  the  anterior  .superior  iliac  spine  forms  a  definite  landmark  :  whilst  behind, 


THE  PELVIS. 


219 


Appears  about 
later  end  of  2iid 
in.  of  foetal  life 


Ajipears  about  15 
years  ;  fuses  •22-25 


the  posterior  superior  iliac  spines  will  Ije  ibuiid  to  correspond  witli  dimples  situated  on 
either  side  of  the  middle  line  of  tlic  root  of  the  l)ack.  The  symphysis,  the  crest,  and  spine  of  the 
pubis  can  all  be  distinguished  in  front,  though  overlain  Ijy  a  considerable  quantity  of  fat, 
whilst  the  position  of  the  tuberosities  of  the  ischia,  Avhen"  uncovered  l)y  the  gi-eat  gluta-al 
muscles  in  the  flexed  position  of  the  thigh,  can  readily  be  ascertained.  In  the  perineal  region 
the  outline  of  the  pubic  and  ischial  rami  can  easily  be  determined  by  digital  e.xamination. 

Ossification  commences  in  the  ilium  about  the  ninth  week  of  intrauterine  life  ; 
about  the  fourth  month  a  centre  appears  below  the  acetabulum  for  the  ischium,  the  pubis 
being  developed  from  a  centre  which  appears  in  front  of  the  acetabulum  about  the  fifth 
or  sixth  month.  At  birth  the  form  of  the  ilium  is  well  defined  ;  the  body  and  part  of 
the  tuberosity  of  the  ischium  are  ossified,  as  well  as  the  superior  ramus  and  part  of 
the  body  of  the  pubis.  All  three  parts  enter  into  the  formation  of  the  sides  of  the 
acetabulum,  and  by  the 
third  year  have  converged 
to  form  the  bottom  of  that 
hollow,  being  separated 
from  each  other  by  a  tri- 
radiate  piece  of  cartilage, 
in  which,  about  the 
twelfth  year,  independent 
ossific  centres  make  their 
appearance,  which  may 
or  may  not  become  fused 
with  the  adjacent  bones. 
In  the  latter  case  they 
unite  to  form  an  inde- 
pendent ossicle,  the  os 
acetabuli,  which  subse- 
quently fuses  with  and 
forms  the  acetabular  part 
of  the  pubis.  By  the  age  Appea'rs  about 
of  sixteen  the  ossification  t^,  '"•  °^  *'**"^ 
of  the  acetabulum  is  usu- 
ally completed,  whilst 
the  rami  of  the  ischium 
and  pubis  commonly  unite 
about    the    tenth    year. 

Secondary  centres,  six  in  number,  make  their  appearance  about  the  age  of  puberty, 
and  are  found  in  the  following  situations :  one  for  the  anterior  inferior  iliac  spine,  one 
for  the  iliac  crest  and  the  anterior  and  posterior  superior  iliac  spines,  a  scale -like 
epiphysis  over  the  tuberosity  of  the  ischium,  a  separate  epiphysis  for  the  spine  of  the 
ischium,  (?)  a  point  for  the  spine  and  another  for  the  angle  of  the  pubis.  Fusion  between 
these  and  the  primary  centres  is  usually  complete  between  the  twenty -second  and 
twenty -fifth  years.  Le  Damany  states  that  the  proportionate  depth  of  the  acetabular 
cavity  at  the  sixth  month  of  foetal  life  is  greater  than  at  birth.  In  the  third  year  a  rapid 
increase  in  its  depth  again  takes  place  correlated  with  the  assumption  of  the  erect  position. 

Parsons  (Joiirn.  Anat.  and  Physiol.,  vol.  xxxvii.  p.  315)  regards  the  ischial  epiphysis  as 
the  homologue  of  the  hypo-ischium  in  reptiles,  and  suggests  that  the  epiphysis  over  the 
angle  of  the  pubis  may  represent  the  epipubic  bone  of  marsupials. 


Appears  about  15 
years ;  fuses  22- 
25  years 

At  Birth.  About  12  or  13  years. 

Fig.  162. — Ossification  of  the  Innominate  Bone. 


Appears 
abdut IS 
years 
Appears 
about  IS 
years 


ite  about  10  years 


The  Pelvis. 

The  pelvis  is  formed  by  the  union  of  the  innominate  bones  with  each  other  in 
front,  and  with  the  sacrum  behind.  In  man  the  dwarfed  caudal  vertebrae 
(coccygeal)  are  curved  forwards  and  so  encroach  upon  the  limits  of  the  pelvic 
cavity  inferiorly.  The  pelvis  is  divided  into  two  parts  by  the  ilio-pectineal  lines, 
which  curve  forwards  from  the  upper  part  of  the  lateral  masses  of  the  sacrum 
behind,  to  the  roots  of  the  spines  of  the  pubis  in  front.  The  part  above  is  called 
the  false  pelvis  (pelvis  major),  and  serves  by  the  expanded  iliac  fossa3  to  support  the 
abdominal  contents;  the  part  below,  the  true  pelvis  (pelvis  minor)  contains  the 
pelvic  viscera,  and  in  the  female  forms  the  bony  canal  through  which,  at  full  term, 
the  foetus  is  expelled. 


220 


OSTEOLOGY. 


The  true  pelvis  is  bounded  in  front  by  the  symphysis  pubis  in  the  middle  Une, 
and  by  the  body  and  rami  of  the  pubis  on  either  side,  laterally  by  the  smooth  medial 
surfaces  of  the  ischia  and  ischial  rami,  together  with  a  small  part  of  the  ilium 
below  the  iliac  portion  of  the  ilio-pectineal  line.  Springing  from  the  posterior 
margin  of  the  ischium  are  the  inturned  ischial  spines.     Behind,  the  broad  curved 


Fig.  163  a. — The  Male  Pelvis  seen  from  the  Front. 

anterior  surface  of  the  sacrum,  and  below  it,  the  small  and  irregular  coccyx,  form 
its  posterior  wall.  Between  the  sides  of  the  sacrum  behind,  and  the  ischium  and 
ilium  in  front  and  above,  there  is  a  wide  interval,  called  the  greater  sciatic  notch, 
which  is,  however,  bridged  across  in  the  recent  condition  by  the  great  and  small 
sacro-sciatic  ligaments  (sacro-tuberous  and  sacro-spinous  ligaments),  which  thus 
convert  it  into  two  foramina,  the  larger  above  the  spine  of  the  ischium— the  greater 


Fig.  16:j//. — The   Femalb  Pelvis  seen  fuu.m  the  Front. 


sacro-sciatic  foramen,  the  lower  and  smaller  below  the  spine,  called  the  lesser 
sacro-sciatic  foramen. 

The  inlet  Tapertura  pelvis  superior)  of  the  pelvis  is  bounded  in  front  by  the 
symphysis  pubis,  witli  the  body  of  the  pubis  on  either  side ;  laterally  by  the  ilio- 
pectineal  lines ;  and  behind  by  the  sacral  prominence.     The  circumference  of  this 


THE  PELVIS.  221 

aperture  is  often  called  the  brim  of  the  pelvis ;  in  the  male  it  is  heart-shaped,  in 
the  female  more  oval.  The  antero-iwsterior  or  conjugate  diavieter  is  measured  from 
the  sacro-vertebral  angle  to  the  symphysis  pubis ;  the  oblique  diameter  from  the 
sacro-iliac  joint  of  one  side  to  the  ilio-pectineal  eminence  of  the  other ;  whilst  the 
transverse  diameter  is  taken  across  the  point  of  greatest  width. 

The  outlet  (apertura  pelvis  inferior)  is  bounded  anteriorly  by  the  pubic  arch 
(arcus  pubis),  formed  in  front  and  above  by  the  bodies  of  the  pubis,  with  the 
symphysis  between  them,  and  the  inferior  pubic  rami  below  and  on  either  side. 
These  latter  are  continuous  with  the  ischial  rami  which  pass  backwards  and 
outwards  to  the  ischial  tuberosities,  which  are  placed  on  either  side  of  this  aperture. 
In  the  middle  line  and  behind,  the  tip  of  the  coccyx  projects  forward,  and  in  the 
recent  condition  the  interval  between  this  and  the  ischial  tuberosities  is  bridged 
across  by  the  great  sacro-sciatic  ligament  (sacro-tuberous  ligament),  the  inferior 
edge  of  which  necessarily  assists  in  determining  the  shape  of  the  outlet. 

As  the  anterior  wall  of  the  cavity,  formed  by  the  symphysis  puljis,  measures 
from  Ih  to  2  inches,  whilst  the  posterior  wall,  made  up  of  the  sacrum  and  coccyx,  is 
from  5  to  6  inches  in  length,  it  follows  that  the  planes  of  the  inlet  and  outlet  are 
not  parallel,  but  placed  at  an  angle  to  each  other.  The  term  axis  of  the  pelvis  is 
given  to  lines  drawn  at  right  angles  to  the  centre  of  these  planes.  Thus,  with  the 
pelvis  in  its  true  position,  when  the  figure  is  erect,  the  axis  of  the  inlet  corresponds 
to  a  line  drawn  downwards  and  backwards  from  the  umbilicus  towards  the  tip  of 
the  coccyx  below,  whilst  the  axis  of  the  outlet  is  directed  downwards  and  slightly 
backwards,  or  downwards  and  a  little  forwards,  varying  according  to  the  length  of 
the  coccyx.  Between  these  two  planes  the  axis  of  the  cavity,  as  it  passes  through 
planes  of  varying  degrees  of  obliquity,  describes  a  curve  repeating  pretty  closely  the 
curve  of  the  sacrum  and  coccyx. 

Position  of  the  Pelvis.^ — The  position  of  the  pelvis  in  the  living  when  the  figure  is 
erect  may  be  approximately  represented  by  placing  it  so  that  the  anterior  superior  iliac 
spines  and  the  symphysis  pubis  lie  in  the  same  vertical  plane.  Under  these  conditions 
the  plane  of  the  inlet  is  oblique,  and  forms  with  a  horizontal  line  an  angle  of  from  50°  to 
60°.  The  position  of  the  pelvis  depends  upon  the  length  of  the  ilio-femoral  ligaments  of 
the  hip-joint,  being  more  oblique  when  these  are  short,  as  usually  happens  in  women  in 
whom  the  anterior  superior  iliac  spines  tend  to  lie  in  a  plane  sliglitly  in  advance  of  that 
occupied  by  the  symphysis  pubis.  In  cases  where  the  ilio-femoral  ligament  is  long,  a 
greater  amount  of  extension  of  the  hip-joint  is  permitted,  and  this  leads  to  a  lessening  of 
the  obliquity  of  the  pelvis.  This  condition,  wliicli  is  more  typical  of  men,  results  in  the 
anterior  superior  iliac  spines  lying  in  a  plane  slightly  posterior  to  the  plane  of  the  sym- 
physis, whilst  the  angle  formed  by  the  plane  of  the  inlet  and  the  horizontal  is  thereby 
reduced.  Bearing  in  mind  the  oblique  position  of  the  pelvis,  it  will  now  be  seen  that  the 
front  of  the  sacrum  is  directed  downwards  more  than  forwards,  and  that  the  sacral  pro- 
montory is  raised  as  much  as  from  3^  to  4  inches  above  the  upper  border  of  the  symphysis 
pubis,  lying  higher  than  the  level  of  a  line  connecting  the  two  anterior  superior  iliac  spines. 
From  the  manner  in  which  the  sacrum  articulates  with  the  ilia,  it  will  be  noticed  that  the 
weight  of  the  trunk  is  transmitted  downwards  through  the  thickest  and  strongest  part  of 
the  bone  (see  Architecture,  Appendix  A)  to  the  upper  part  of  the  acetabula,  where  these 
rest  on  the  heads  of  the  femora. 

Sexual  Differences- — The  female  pelvis  is  lighter  in  its  construction  than  that  of 
the  male ;  its  surfaces  are  smoother,  and  the  indications  of  muscular  attachments  less 
marked.  Its  height  is  less  and  the  splay  of  its  walls  not  so  pronounced  as  in  the  male, 
so  that  the  female  pelvis  has  been  well  described  as  a  short  segment  of  a  long  cone  as 
contrasted  with  the  male  pelvis,  which  is  a  long  segment  of  a  short  cone.  The  cavity  of 
the  true  pelvis  in  the  female  is  more  roomy,  and  the  ischial  spines  not  so  much  inturned. 
The  pubic  arch  is  wide  and  rounded,  and  will  usually  admit  a  right-angled-set  square 
being  placed  within,  so  that  the  summit  touches  the  under  surface  of  the  symphysis  pubis, 
whilst  the  sides  lie  in  contact  with  the  ischial  rami.  In  the  male  the  arch  is  narrow  and 
angular,  forming  an  angle  of  from  65°  to  70°.  The  greater  sciatic  notch  in  the  female  is 
wide  and  shallow.  The  distance  from  the  posterior  edge  of  the  body  of  the  ischium  to  the 
posterior  inferior  iliac  spine  is  longer,  measuring  on  an  average  50  mm.  (2  inches)  in  the 
female,  as  contrasted  with  40  mm.  (1|  inches)  in  the  male.  The  angle  formed  by  the 
ischial  and  iliac  borders  is  more  contracted  and  acute  in  the  male  as  compared  with  the 


222 


OSTEOLOGY. 


female  in  whom  it  is  wider  and  moi-e  open.     In  the  female  the  acetabukim  is  proportion- 
ately smaller  than  in  the  male. 

The  inlet  in  the  female  is  large  and  oval  or  reniform,  as  compared  with  the  cribbed  and 
heart-shaped  aperture  in  the  male.  The  sacro-vertebral  angle  is  more  pronounced  in  the 
female,  and  the  obliquity  of  the  inlet  greater.  The  sacrum  is  shorter  and  wider.  The 
posterior  superior  iliac  spines  lie  wider  apart ;  the  pubic  crests  are  longer ;  and  the  pubic 
spines  are  separated  by  a  greater  interval  than  in  man.  The  outlet  is  larger ;  the  tubero- 
sities of  the  ischia  are  farther  apart ;  and  the  coccyx  does  not  project  forward  so  much. 
The  curve  of  the  sacrum  is  liable  to  very  great  individual  variation.  As  a  rule  the  curve 
is  more  uniform  in  the  male,  whilst  in  the  female  it  tends  to  be  flatter  above  and  more 
accentuated  below.  There  is  a  greater  proportionate  width  between  the  acetabular 
hollows  in  the  female  than  in  the  male.  Of  much  importance  from  the  standpoint  of  the 
obstetrician  are  the  various  diameters  of  the  true  pelvis.  In  regard  to  this  it  is  worthy 
of  note  that  the  plane  of  "  greatest  pelvic  expansion  "  extends  from  the  union  between  the 
second  and  third  sacral  vertebrae  behind,  to  the  middle  of  the  symphysis  pubis  in  front, 
its  lateral  boundaries  on  either  side  corresponding  with  the  mid-point  of  the  medial  surface 
of  the  acetabulum ;  whilst  the  plane  of  "least  pelvic  diameter"  lies  somewhat  lower,  and 
is  defined  by  lines  passing  through  the  sacro-coccygeal  articulation,  the  ischial  spines, 
and  the  lower  third  of  the  symphysis  pubis  (Norris).  Subjoined  is  a  table  showing  the 
principal  average  measurements  in  the  two  sexes  : — 

False  Pelvis  (pelvis  major) 


Males. 

Females. 

Maximum  distance  between  the  iliac  crests 
Distance   between   the    anterior   superior   iliac 

spines 
Distance  t  between   the   last   lumbar   spine  and 

the  front  of  the  symphysis  pubis 

]  1|  in.,  or  282  mm. 
9^  in.,  or  240  mm. 

7  in.,  or  176  mm. 

lOj  in.,  or  273  mm. 
9f  in.,  or  250  mm. 

7^  in.,  or  180  mm. 

True  Pelvis  (pelvis  minor) 


Males.                                                     Females.                                     \ 

1 

Inlet. 

Outlet.      :       Inlet. 

i 

Cavity. 

Outlet. 

Greatest.           Least. 

Antero-posterior  (conju- 
gate) diameter 
Oblique  diameter  . 

Transverse  diameter 

4    in.,  or 
101  mm. 

4|    in.,  or 
120  mm. 

.5    in.,    or 
127  mm. 

j 
3|    in.,  or    4f  in.,   or 

95  mm.         110  mm. 
3^  in.,   or    5     in.,    or 

"88  mm.    '     125  mm. 
3|  in.,  or  l  5j   in.,  or 

88  mm.    1     135  mm. 

5    in.,     or 
127  mm. 

4^  in.,  or 
125  mm. 

4§   in.,  or 
110  mm. 

4f   in.,  or 
110  mm. 

4|  in.,  or 
115  mm. 

4|  in.,  or 
115  mm. 

4§  in.,  or 
110  mm. 

Growth  of  the  Pelvis.— From  the  close  association  of  the  pelvic  girdle  with  the  lower  limb 
we  find  tliat  its  growtli  takes  place  concurrently  with  the  development  of  that  member.  At 
birth  the  lower  limbs  measure  but  a  fourth  of  the  entire  l)ody  lengtli ;  consequently  at  that  time 
the  pelvis,  as  compared  witli  the  liead  and  trunk,  is  relatively  small.  At  this  period  of  life  the 
bladder  in  both  .sexes  is  in  greater  part  an  abdominal  organ,  whilst  in  the  female  the  uterus  has 
not  yet  sunk  into  the  true  pelvic  cavity,  and  the  ovaries  and  Fallopian  tubes  rest  hi  the  iliac 
fossa;.  Tlie  sacro-vertebral  angle,  though  readily  recognised,  is  as  yet  but  faintly  marked. 
Coincident  with  the  remarkable  gi'owth  of  the  lower  limlxs  and  the  assumption  of  the  erect 
position  when  the  child  begins  to  walk,  striking  changes  take  place  in  the  foi-m  and  size  of  the 
pelvis.  These  consist  in  a  greater  expansion  of  the  iliac  bones  necessarily  associated  with  the 
growth  of  the  muscles  which  control  the  movements  of  the  hip,  together  with  a  marked  increase 
in  the  sacro-vertebral  angle  due  to  the  development  of  a  forward  lumbar  curve  ;  at  the  same  time, 
the  weight  of  the  trunk  being  thrown  on  the  sacrum  causes  the  elements  of  that  bone  to  sink  to 
a  lower  level  between  the  innominate  bones.  The  cavity  of  the  true  pelvis  increases  in  size 
proportionally,  and  the  viscera  aforementioned  now  begin  to  sink  down  and  have  assumed  a 
position  within  the  pelvis  by  the  fifth  or  sixth  year.  The  extension  of  the  thighs  in  the 
upright  position  necessarily  brings  about  a  more  pronounced  pelvic  ol)liquity,  whilst  the  stoutness 
and  thickness  of  the  ilium  over  the  upper  part  of  the  acetabulum  is  much  increased  to  withstand 
the  pressure  to  which  it  is  obviously  subjected.     Coincident  with  this  is  the  gradual  development 


THE  FEMUE. 


223 


Head 


of  the  iliac  portion  of  the   ilio-pectineal   line,  which  serves  in  the  adult  to  separate  sharply 
the  false  from  the  true  pelvis.     This  part  of  the  bone  is  reniarkaljly  sti'ong,  as  has  been  shown 

(see  Arcliitecture),  and  serves  to  transmit  the 
body  weight  from  the  sacrum  to  the  thigh  bone. 
The  sexual  differences  of  the  2>elvis,  so  far  as 
they  refer  to  the  general  configviration  of  this 
part  of  the  skeleton,  are  as  pronounced  at  the 
third  or  fourtli  month  of  fojtal  life  as  they  are 
in  the  adult  (Fehling,  Ztschr.  f.  Geburtsh.  u. 
Gynaek.  Bd.  ix.  and  x.  ;  A.  Thomson,  Journ. 
Anaf.  and  Physiol,  vol.  xxxiii.  p.  359).  The 
rougher  appearance  of  the  male  type  is  cor- 
related with  the  more  powerful  muscular 
development. 

The  Femur 

The  femur  or  thigh  bone  is  remark- 
able for   its  length,  being  the  longest 


Obturator  internus        %^ 
Piriformis 


Greatri 
trochantei 


Vastus  medialis 
Ilio-psoas 


Fig.  164 /j. — Front  Aspect  of  Ui'per  Portion  of 
THE  Right  Femur  with  Attachjients  of 
Muscles  mapped  out. 

bone  in  the  body.    Superiorly  the  femora 
are  separated  by  the  width  of  the  pelvis. 
Inferiorly  they  articulate  with  the  tibiaj 
and  patellae.      In  the  military  position 
of  attention,  with  the  knees   close  to- 
gether, the   shafts  of   the  thigh  bones 
occupy  an   oblique   position.      For  de- 
scriptive purposes  the  bone  is  divided 
into  an  upper  extremity,  comprising  the 
head,  neck,  and  two  tro- 
chanters  ;  a  shaft ;  and  a 
lower  extremity,  forming 
the   expansions    known 
as  the  condyles. 

The  head  (caput 
femoris)  is  the  hemi- 
spherical articular  sur- 
face which  fits  into  the 
acetabular  hollow.  Its 
Pig.  164  a.— The  Right  Femur  seen  from  the  Front.  pole  IS  directed  upwards, 

medially,   and    slightly 
forwards.     A   little  below    the    summit,   and  usually  somewhat   behind  it,   is    a 


Lateral  epicondyle 


Adductor 
tubercle 


Medial 
epicondyle 


Lateral  condyle 


Patellar 

SURFACE 


Medial  condyle 


224 


OSTEOLOG-Y. 


Head 
Fossa  for  lio.  teres 


KOCIIANTERIC  FOSSA 


Greater 
trochanter 
Tubercle  of 
quadratns 
Intertrochan- 
teric RIDGE 


Gluteal  ridge 


Arterial  foramen 


hollow  oval  pit  (fovea  capitis  femoris)  for  the  attachment  of  the  ligamentum  teres. 
Piercing  the  floor  of  this  depression  are  seen  several  foramina  through  which  vessels 

pass  to  supply  the  head 
of  the  bone  ;  the  superior 
epiphysis    thus    having  a 
double  blood  supply,  viz. 
from  the  neck  below,  and 
through   the   medium   of 
the      ligamentum      teres 
above.       The    circumfer- 
ence  of   the  head   forms 
a  lip  with  a  wavy  outline, 
more  prominent  above  and 
behind  than  in  front.    The 
head   is    supported    by   a 
stout   compressed    bar    of 
bone,   the    neck  (collum 
femorig),which  forms  with 
the  upper  end  of  the  shaft 
an   angle    of    about    125 
degrees,   and  is   directed 
upwards,  medially,  and  a 
little  forwards.     Its  ver- 
tical   width    exceeds    its 
antero-posterior  thickness. 
Constricted      about      its 
middle,  it  expands  medi- 
ally to  support  the  head, 
whilst  laterally,  where  it 
joins  the  shaft,  its  vertical 
diameter     is     much     in- 
creased.    Anteriorly  it  is 
clearly  defined  from    the 
shaft  by   a  rough    ridge 
which   commences   above 
on   a   prominence,   some- 
times called  the  tubercle 
of  the  femur,  and  passes 
obliquely  downwards  and 
medially.  This  constitutes 
tlie    upper    part    of    the 
spiral  line  (linea  inter-tro- 
chanterica),  and  serves  for 
the    attachment    of    the 
ilio- femoral   ligament   of 
the  hip-joint.    Posteriorly 
where    the    neck    unites 
with  the  shaft,  there  is  a 
full  rounded  ridge  passing 
from  the  trochanter  major 
above  to   the    trochanter 
minor  below ;   this  is  the 
posterior  intertrochanteric 
line  or  ridge  (crista  inter- 
trochanterica).       A    little 
above  the  middle  of  this 
ridge   there   is    usually  a   fulness  which    serves    to   indicate    the    upper  limit  of 
attachment   of  the   quadratus   femoris    muscle,   and    is    called    the   tubercle    for 
the  quadratus.      Laterally  the    neck   is  embedded   in   the  medial  surface  of  the 


Medial 
epicondylic  line 


Lateral  epicondyijc  line 


Popliteal  surface 


Adductor 
tubercle 


Medial 

epicondyle 

Medial 

CONDVr  I 

Surface  for 
attachment 
of  ijosterior 
crucial  ligamunt  I  ■•  im  >  mm,',  i  i,        i    i 

Fig.  165  «. — The  Right  FeiMur  seen  from  Behind. 


■Lateral  epicondyle 
-Surface  for  attachment  of 
ant.  crucial  ligament 

Lateral  condyle 


THE  FEMUE. 


225 


trochanter  major,  by  which,  at  its  upper  and  back 
part,  it  is  to  some  extent  overhung.  Here  is 
situated  the  trochanteric  or  digital  fossa,  into  which 
the  tendon  of  the  obturator  externus  is  inserted. 
Passing  nearly  horizontally  across  the  back  of  the 
neck  there  is  a  faint  groove  leading  into  this  de- 
pression ;  in  this  the  tendon  of  the  obturator 
externus  muscle  lies.  Interiorly  the  neck  becomes 
confluent  with  the  trochanter  minor  behind,  and 
is  continuous  with  the  medial  surface  of  the  shaft 
in  front.  The  neck  is  pierced  by  many  vascular 
canals,  most  numerous  at  the  upper  and  back 
part.  Some  are  directed  upwards  towards  the 
head,  whilst  others  pass  in  the  direction  of  the 
trochanter  major. 

The  trochanter  major  is  a  large  quadrangular 
process  which  caps  the  upper  and  lateral  part  of 
the  shaft,  and  overhangs  the  root  of  the  neck 
above  and  behind.  Its  lateral  surface,  of  rounded 
irregular  form,  slopes  upwards  and  medially,  and 
is  separated  from  the  lateral  surface  of  the  shaft 
below  by  a  more  or  less  horizontal  ridge.  Crossing 
it  obliquely  from  the  posterior  superior  to  the 
anterior  inferior  angle  is  a  rough  line  which  serves 
for  the  insertion  of  the  gluteeus  medius  muscle ; 

Head 


BTURATOR   KXTERNUS 


Outurator  inteenus 


Greater 
trochanter 


Gluteal  ridqe 


--Arterial  foramen 


LiNEA    ASPERA 


Fig.  165  c.- 


-Posterior  View  of  the  Upper  End  of 
THE  Right  Femur. 


Fig.  165  6. — Posterior  Aspect  of  the 
Upper  Portion  of  the  Right  Femur 
WITH  the  Attachments  of  Muscles 

MAPPED    OUT. 

above  and  below  this  the  surface 
of  the  bone  is  smoother  and  is 
overlain  by  bursse.  The  anterior 
surface,  somewhat  oblong  in 
shape,  and  inclined  obliquely 
from  below  upwards  and  medi- 
ally, is  elevated  from  the  general 
aspect  of  the  shaft  below,  from 
which  it  is  separated  in  front  by 
an  oblique  line  leading  upwards 
and  medially  to  the  tubercle  at 
the  upper  end  of  the  superior 
part  of  the  spiral  line.  This 
surface  serves  for  the  insertion  of 
the  glutseus  minimus.  The 
superior  border  is  curved  and 
elevated  ;  into  it  are  inserted  the 
tendons  of  the  obturator  internus 
and  gemelli  muscles  within  and 
in  front,  and  the  piriformis 
muscle  above  and  behind.  The 
posterior  border  is  thick  and 
rounded,  and  forms  the  upper 
part  of  the  posterior  intertro- 
chanteric ridge.  The  angle 
formed  by  the  superior  and 
posterior  borders  is  sharp  and 
pointed,  and  forms  the  tip  of 
the  trochanter  overhanging  the 
trochanteric  fossa,  which  lies 
immediately  below  and  within 
its  medial  surface. 

The  trochanter  minor  is  an 


226  OSTEOLOGY. 

elevated  pyramidal  process  situated  at  the  back  of  the  medial  and  upper  part  of  the 
shaft  where  that  becomes  continuous  with  the  lower  and  posterior  part  of  the  neck. 
Continent  above  with  the  posterior  intertrochanteric  ridge,  it  gradually  fades  away 
into  the  back  of  the  shaft  below.  The  combined  tendon  of  the  ilio- psoas  is 
inserted  into  this  process  and  the  bone  immediately  below  it. 

The  shaft  (corpus  femoris),  which  is  characterised  by  its  great  length,  is  cylin- 
drical in  form.  As  viewed  from  the  front,  it  is  straight  or  but  slightly  curved ;  as 
seen  in  profile,  it  is  bent  forwards,  the  curve  being  most  pronounced  in  its  upper 
part.  The  shaft  is  tliinnest  at  some  little  distance  above  its  middle ;  below  this  it 
gradually  increases  in  width  to  support  the  condyles  interiorly ;  its  antero-posterior 
diameter,  however,  is  not  much  increased  below.  Its  surfaces  are  generally  smooth 
and  rounded,  except  behind,  where,  running  longitudinally  down  the  centre  of  its 
curved  posterior  aspect,  there  is  a  rough-lipped  ridge,  the  linea  aspera  (linea  aspera). 
Most  salient  towards  the  middle  of  the  shaft,  the  linea  aspera  consists  of  a  medial 
lip  (labium  mediale)  and  a  lateral  lip  (labium  laterals),  with  a  narrow  intervening 
rough  surface.  Above,  about  2  to  2^  inches  from  the  trochanter  minor,  the  linea 
aspera  is  formed  by  the  convergence  of  three  lines.  Of  these  the  outer  is  a  rough, 
somewhat  elevated,  ridge,  which  commences  above,  on  the  back  of  the  shaft,  lateral 
to  and  on  a  level  with  the  trochanter  minor,  and  becomes  continuous  below  with 
the  outer  lip  of  the  linea  aspera.  This  serves  for  the  bony  insertion  of  the  gluteus 
maximus,  and  is  occasionally  developed  into  an  outstanding  process  called  the 
trochanter  tertius.  Medially  the  medial  lip  of  the  linea  aspera  is  confluent  above 
with  a  line  which  winds  round  the  shaft  upwards  and  forwards  in  front  of  the 
trochanter  minor  to  become  continuous  with  the  rough  ridge  which  serves  to  define 
the  neck  from  the  shaft  anteriorly  (see  p.  224).  The  whole  constitutes  what  is  known 
as  the  spiral  line,  and  extends  from  the  fore  and  upper  part  of  the  trochanter  major 
above  to  the  linea  aspera  below.  Intermediate  in  position  between  the  spiral  line 
in  front  and  medially,  and  the  gluteal  ridge  laterally,  there  is  a  third  line, 
the  pectineal  line  (linea  pectinea),  which  passes  down  from  the  trochanter  minor 
and  fades  away  inferiorly  into  the  surface  between  the  two  lips  of  the  linea  aspera. 
Into  this  the  pectineus  muscle  is  inserted.  About  the  junction  of  the  middle  with 
the  lower  third  of  the  shaft  the  two  lips  of  the  linea  aspera  separate  from  one 
another,  each  passing  in  the  direction  of  the  condyle  of  the  corresponding  side. 
The  lines  so  formed  are  called  the  medial  and  lateral  epicondylic  lines  respectively, 
and  enclose  between  them  a  smooth  triangular  area  corresponding  to  the  back  of  the 
lower  third  of  the  shaft ;  this,  called  the  popliteal  surface  ^  (planum  popliteum),  forms 
the  floor  of  the  upper  part  of  the  popliteal  space.  The  continuity  of  the  upper  part 
of  tlie  medial  epicondylic  line  is  but  faintly  marked,  being  interrupted  by  a  wide 
and  faint  groove  along  which  the  popliteal  artery  passes  to  enter  the  space  of  that 
name.  Below,  where  the  line  ends  on  the  upper  and  medial  surface  of  the  medial 
condyle,  there  is  a  little  spur  of  bone  called  the  adductor  tubercle,  to  which  the 
tendon  of  the  adductor  magnus  is  attached,  and  behind  which  the  medial  head  of 
the  gastrocnemius  muscle  takes  origin. 

The  linea  aspera  affords  extensive  linear  attachments  to  many  of  the  muscles  of  the  thigh. 
The  vastus  medialis  arises  from  the  spiral  line  above  and  the  medial  lip  of  the  linea  aspera  below. 
This  muscle  overlies  but  does  not  take  origin  from  the  medial  surface  of  the  sliaft.  The 
adductor  longus  is  inserted  into  the  medial  lija  about  the  middle  third  of  the  length  of  the  shaft. 
The  adductor  magnus  is  inserted  into  the  intermediate  part  of  the  line,  extending  as  high  as  the 
level  of  the  trochanter  minor,  where  it  lies  medial  to  tlie  insertion  of  the  glutaeus  maximus. 
Below,  its  insertion  passes  on  the  medial  epicondylic  ridge,  reaching  as  low  as  the  adductor 
tubercle.  The  adductor  brevis  muscle  is  inserted  into  tlie  linea  aspera  above,  between  the  pec- 
tineus and  adductor  longus  muscles  medially  and  the  adductor  magnus  laterally.  Below  the 
insertion  of  tlie  glutfeus  maximus  the  short  head  of  the  biceps  arises  from  tlie  lateral  lij)  as  well  as 
from  the  lateral  epicondylic  line ;  in  front  these  also  serve  for  the  origin  of  the  vastus  lateralis 
muscle.  There  is  frequently  a  small  tubercle  which  marks  the  lower  attachment  of  the  lateral 
intermuscular  septum  on  the  lateral  condylic  line,  alwnit  two  inches  above  the  condyle. 
Immediately  above  this  there  is  often  a  groove  for  a  large  muscular  artery  which  pierces  the 
sei^tum  at  this  point  (Frazer). 

The  canals  for  the  nutrient  arteries  of  the  shaft,  which  have  an  upward  direction,  are  usually 
two  in  number,  and  are  placed  on  or  near  the  linea  aspera— the  upper  one  about  the  level  of  the 

'  This  ;ii)pe;us  jireferable  to  "popliteal  plain." — A.  T. 


THE  FEMUE. 


227 


Medial 
head  of  gas 
trocnemius 


Lateral 
head  of  oas- 

rROCNEMirS 


Posterior  crchial    anterior  crucial 

LIflAMENX      ligament 


junction  of  the  middle  and  upper  third  of  the  bone,  the  lower  some  three  or  four  inches  below — 
usually  on  the  medial  side  of  the  shaft,  immediately  in  front  of  the  medial  lip  of  the  linea  aspera. 

The  front  and  lateral  aspects  of  the  shaft  are  covered  by,  and  furnish  surfaces 
for,  the  origins  of  the  vasti  muscles. 

The  lower  extremity  of  the  femur  comprises  the  two  condyles.    These  are  two 
recurved  processes  of  bone,  each  provided  with  an  articular  surface,  and  separated 

behind  by  a  deep  intercondylic  notch.  United 
in  front,  where  their  combined  articular  surfaces 
form  an  area  on  which  the  patella  rests,  the  two 
condyles  differ  from  each  other  in  the  following 
respects :  If  the  shaft  of  the  bone  be  held  vertically, 
the  medial  condyle  is  seen  to  reach  a  lower  le^el 
than  the  lateral ;  but,  as  the  femur  lies  obliquely 
in  the  thigh,  the  condyles  are  so  placed  that  their 
inferior  surfaces  lie  in  the  same  horizontal  plane. 
Viewed  from  below,  the  medial  condyle  is  seen  to 
be  the  narrower  and  shorter  of  the  two.  The 
lateral  condyle  is  broader,  and  advances  farther 
forward  and  higher  up  on  the  anterior  surface 
of  the  shaft.  The  intercondylic  notch  (fossa  inter- 
FiG.  166.— Posterior  Aspect  of  Lower  condyloidea)  reaches  forwards  as  far  as  a  trans- 
PoKTioN  OF  THE  RiGHT  Fejiur  WITH  yersc  liuc  drawu  through  the  centre  of  the  lateral 
ATTACHMENTS   OF   MuscLEs   MAPPED  condyle.     Its  sides  are  formed  by  the  medial  and 

lateral  surfaces  of  the  lateral  and  medial  condyles 
respectively,  the  latter  being  more  deeply  excavated,  and  displaying  an  oval  surface 
near  its  lower  and  anterior  part  for  the  attachment  of  the  posterior  crucial  hga- 
ment  of  the  knee-joint.  Placed  high  up,  on  the  posterior  part  of  the  medial 
surface  of  the  lateral  condyle,  there  is  a  corresponding  surface  for  the  attachment 
of  the  anterior  crucial  ligament.  The  floor  of  the  notch,  which  is  pierced  by 
numerous  vascular  canals,  slopes  upwards  and  backwards 
towards  the  popliteal  surface  on  the  back  of  the  shaft,  from 
which  it  is  separated  by  a  slight  ridge  (linea  intercondyloidea) 
to  which  the  posterior  part  of  the  capsule  of  the  knee-joint 
is  attached. 

The  cutaneous  aspect  of  each  condyle  (^i.e.  the  lateral 
surface  of  the  lateral  condyle  and  the  medial  surface  of 
the  medial  condyle)  presents  an  elevated  rough  surface, 
called  the  epicondyle,  or  tuberosity,  the  medial  (epicondylus 
medialis)  projecting  more  prominently  from  the  line  of  the 
shaft ;  capped  above  by  the  adductor  tubercle,  it  affords 
attachment  near  its  most  prominent 
point  to  the  fibres  of  the  tibial  collateral 
(internal  lateral)  ligament  of  the  knee- 
joint.  The  lateral  epicondyle  (epicondylus 
lateralis),  less  pronounced  and  lying 
more  in  line  with  the  lateral  surface  of 
the  shaft,  is  channelled  behind  by  a 
curved  groove,  the  lower  rounded  lip  of 
which  serves  to  separate  it  from  the  in- 
ferior articular  surface.  This  groove  ends 
in  front  in  a  pit  which  is  placed  just 
below  the  most  salient  point  of  the  tuberosity ;  hereto  is  attached  the  tendon  of 
the  popliteus  muscle,  which  overlies  the  lower  lip  of  the  groove  in  the  extended 
position  of  the  joint,  but  slips  into  and  occupies  the  groove  wdien  the  joint  is 
flexed.  Behind  the  most  prominent  part  of  the  lateral  epicondyle,  and  just  above 
the  pit  for  the  attachment  of  the  popliteus,  the  fibular  collateral  (external  lateral) 
ligament  of  the  knee-joint  is  attached,  whilst  superior  to  that  there  is  a  circum- 
scribed area  for  the  origin  of  the  tendinous  part  of  the  lateral  head  of  the  gastro- 
cne*tius  muscle. 


Surface  for  the 
attachment  of 
ext.  lateral  (fib- 
ular collateral) 
Groove  for 
tendon  of 
popliteus 


Fig.  167. — Lower  End  of  the  PvIGHt  Femur 
(Lateral  Side). 


228 


OSTEOLOGY. 


Trochlea  or  patellar  surface 


Impression  of 
lateral  semi- 
lunar cartilage 
(meniscus) 

Lateral 
epicondyle 


POPLITEAI 
GROOVf. 


Lateral 
tibial  surface 


Impression  of 
medial  semi- 
lunar cartilage 
(meniscus) 

Semilunar  facet 
for  medial  edge 
of  patella  in 
extreme  flexion 


Medial 

TIBIAL  surface 


The  articular  surface  on  the  lower  extremity  is  divisible  into  three  parts — 
that  which  corresponds  to  the  inferior  surface  of  the  shaft  and  which  is  formed  by  the 
coalescence  of  the  two  condyles  in  front,  and  those  which  overlie  the  under  and 
hinder  aspects  of  each  of  those  processes.  The  former  is  separated  from  the  latter 
by  two  shallow  oblique  grooves  which  traverse  the  articular  surface  from  before 
backwards,  on  either  side,  in  the  direction  of  the  anterior  part  of  the  intercondylic 
notch.  These  furrows  are  the  impressions  in  which  fit  the  fore-parts  of  the  medial 
and  lateral  semilunar  cartilages  of  the  knee-joint  respectively,  when  the  knee-joint 
is  extended.  The  anterior  articular  area  or  trocMea  (facies  patellaris)  is  adapted 
for  articulation  with  the  patella.  Convex  from  above  downwards,  it  displays  a 
broad  and  shallow  central  groove,  bounded  on  either  side  by  two  slightly  convex 
surfaces.  Of  the  two  sides,  the  lateral  is  the  wider  and  more  prominent,  and  rises 
on  the  front  of  the  bone  to  a  higher  level  than  the  medial,  thus  tending  ta 
prevent  lateral  dislocation  of  the  patella.  The  condylar  or  tibial  surfaces  are 
convex  from  side  to  side,  and  convex  from  before  backwards.  Sweeping  round 
the  under  surface  and  posterior  extremities  of  the  condyles,  they  describe  a  spiral 
curve  more  open  in  front  than  behind.     The  medial  condylar  articular  surface  is 

narrower  than  the  lateral^ 
and  when  viewed  from 
below  is  also  seen  to  de- 
scribe a  curve  around  a 
vertical  axis.  Along  the 
lateral  edge  of  this,  and 
in  front,  where  it  bounds 
the  intercondylic  fossa,  is 
a  semilunar  articular  area, 
best  seen  when  the  bone 
is  coated  with  cartilage. 
This  articulates  with  the 
medial  edge  of  the  patella 
in  extreme  flexion  of  the 
joint.  The  articular  sur- 
face of  the  lateral  con- 
dyle is  inclined  obliquely  from  before  backwards  and  slightly  laterally.  The 
surfaces  of  the  condyles  above  the  articular  area  posteriorly  are  continuous 
superiorly  with  the  popliteal  surface  of  the  shaft ;  from  these  areas  the  heads  of 
the  gastrocnemius  muscles  arise.  The  bone  from  which  the  medial  head  of  the 
muscle  springs  is  often  elevated  in  the  form  of  a  tubercle  placed  on  the  lower  part 
of  the  popliteal  surface  of  the  shaft,  just  above  the  medial  condyle. 

The  proportionate  length  of  the  femur  to  the  body  height  is  as  1  is  to  3-53-3*92. 

Arterial  Foramina. — Numerous  vascular  canals  are  seen  in  the  region  of  the  neck,  at  the 
bottom  of  the  trochanteric  fossa,  in  the  fossa  for  the  ligamentum  teres,  on  tlie  posterior  inter- 
troclianteric  ridge,  and  on  tlie  lateral  surface  of  the  great  trochanter.  Tlie  nutrient  arteries  for 
the  shaft  pierce  the  hone  in  an  upward  direction  on  or  near  the  linea  aspera.  Both  back  and 
front  of  tlie  lower  end  of  the  shaft  display  the  openings  of  numerous  vascular  canals,  and  the 
floor  of  the  intercondylic  notch  is  also  similarly  pierced. 

Connexions. — The  iemur  articulates  with  the  os  innominatum  above  and  the  tibia  and  patella 
below.  The  lateral  surface  of  the  greater  trochanter  determines  the  point  of  greatest  hip  wddth 
in  the  male,  being  covered  only  by  the  skin  and  superficial  fascia  and  the  aponeurotic  insertion  of 
the  glutteus  maximus.  In  the  erect  position  the  tip  of  the  trochanter  corresponds  to  the  level  of 
the  centre  of  the  hip-joint.  When  the  thigh  is  flexed  the  trochanter  major  sinks  under  cover 
of  the  antei'ior  fibres  of  the  glutieus  maximus.  In  women  the  hip  width  is  usually  greatest  at 
some  little  distance  below  the  trochanter,  due  to  the  accumulation  of  fat  in  this  region.  The 
shaft  of  tlie  Ijone  is  surrounded  on  all  sides  by  muscles.  Its  forward  curve,  however,  is  account- 
able to  some  extent  for  the  fulness  of  the  front  of  the  thigh.  The  exposed  surfaces  of  the  condyles 
determine  to  a  large  extent  the  form  of  the  knee.  In  flexion  the  articular  edges  can  easily  be 
recognised  on  either  side  of  and  below  the  patella. 

Sexual  Differences. — According  to  Dwight,  the  head  of  the  femur  in  tlie  female  is  propor- 
tionately HiiiHllcr  than  that  of  the  male. 

Ossification. — The  shaft  begins  to  ossify  early  in  the  second  month  of  foetal  life,  and  at 
birth  displays  enlargements  at  both  ends,  which  are  capped  with  cartilage.  If  at  birth  the 
inferior  cartilaginous  end  be  sliced  away,  a  small  ossific  nucleus  for  the  inferior  epiphysis  will 


Fig.  li 


Medial  condyle 

Surface  of  attachment  of  posterior 
crucial  ligament 

-Lower  End  of  the  Right  Femur  seen  from  Below. 


L\TLR\L  CO.N'DYLE 

Intercondylic  notch 


THE  PATELLA. 


229 


cartilaginous  at  birth, 
prises  the   head,   neck, 


Appears  about 

early  part  of 

first  year 


Fuses  with  sliaft 
about  IS-l'.i  years 


Appears  about 
■J-3  year 


usually  be  seen.  This,  as  a  rule,  makes  its  appearance  towards  the  latter  end  of  the  ninth 
month  of  fcetal  life,  and  is  of  service  from  a  medico-legal  standpoint  in  determining  the  age 
of  the  foetus.  According,  to  Hartman,  it  is  absent  in  about  12  per  cent  of  children  at 
term,  and  may  appear  as  early  as  the  eighth  month  of  foetal  life  in  about  7  per  cent.  The 
superior  extremity,  entirely 
com- 
and 
trochanter  major.  A  centre 
appears  for  the  head  during 
the  early  part  of  the  fii'st 
year.  It  is  worthy  of  note 
that  this  epiphysis  has  a 
double  blood  -  supply  —  one 
through  the  neck,  the  other 
through  the  ligamentum 
teres.  That  for  the  tro- 
chanter major  begins  to 
ossify  about  the  second  or 
third  year,  whilst  the  neck 
is  developed  as  an  upward 
extension  of  the  shaft,  which 
is,  however,  not  confined  to 
the  neck  alone,  but  forms 
the  lower  circumference  of 
the  articular  head,  as  may 
be  seen  in  bones  up  to  the 
age  of  twelve  or  sixteen ; 
after  that,  the  separate  epi- 
physis of  the  head  begins  to 
overlap  it  so  as  to  cover  it 
entirely  when  fusion  is  com- 
plete at  the  age  of  eighteen 
or  twenty. 

The  epiphysis  of  the  greater  trochanter  unites  with  the  shaft  and  neck  about  eighteen  or 
nineteen,  whilst  the  epiphysis  for  the  ti'ochanter  minor,  which  usually  makes  its  appearance 
about  the  twelfth  or  thirteenth  year,  is  usually  completely  fused  with  the  shaft  about 
the  age  of  eighteen.  The  epiphysis  for  the  lower  end,  although  the  first  to  ossify,  is  not 
completely  united  to  the  shaft  until  from  about  the  twentieth  to  the  twenty-second  year. 
It  is  worthy  of  note  that  the  line  of  fusion  of  the  shaft  and  inferior  epiphysis  passes 
through  the  adductor  tubercle,  a  point  which  can  easily  be  determined  in  the  living. 
The  lower  end  is  the  so-called  "  growing  end  of  the  bone." 


Usually  appears  in 
tlie  9th  mouth  of 
foetal  life 


Usually  appears 
before  birth 


At  birth. 


Fuses  with  shaft  about  20-22  years 
About  12  years.  About  16  years. 

Fig.  169. — Ossification  of  the  Femur. 


The  Patella. 


The  patella,  the  largest  of  the  sesamoid  bones,  overlies  the  front  of  .the  knee- 
joint  in  the  tendon  of  the  quadriceps  extensor.  Of  compressed  form  and  somewhat 
triangular  shape,  its  lower  angle  projects  downwards  and  forms  a  peak,  called  the 
apex  (apex  patellae),  whilst  its  upper  edge,  or  base  (basis  patellae),  broad,  thick,  and 
sloping  forwards  and  a  little  downwards,  is  divided  into  two  areas  by  a  transverse 
line  or  groove  ;  the  anterior  area  so  defined  serves  for  the  attachment  of  the 
common  tendon  of  the  quadriceps  extensor  muscle,  whilst  the  posterior,  of  com- 
pressed triangular  shape,  is  covered  by  synovial  membrane.  The  medial  and  lateral 
borders,  of  curved  outline,  receive  the  insertions  of  the  vastus  medialis  and  laterahs 
muscles  respectively,  the  attachment  of  the  vastus  medialis  being  more  extensive 
than  that  of  the  vastus  lateralis.  The  anterior  surface  of  the  bone,  slightly  convex 
in  both  diameters,  has  a  fibrous  appearance,  due  to  its  longitudinal  striation,  and  is 
pierced  here  and  there  by  the  openings  of  vascular  canals.  The  posterior  or  femoral 
articular  surface  is  divided  into  two  unequal  parts  (of  which  the  lateral  is  the 
wider)  by  a  vertical  elevation  which  glides  in  the  furrow^  of  the  trochlear  surface  of 
the  femur,  and  in  extreme  flexion  passes  to  occupy  the  intercondylic  notch.  The 
lateral  of  the  two  femoral  surfaces  is  slightly  concave  in  both  its  diameters ;  the 

""      ^  15 


230 


OSTEOLOGY. 


medial,  though  slightly  concave  from  above  downwards,  is  usually  plane,  or  somewhat 
convex  transversely.  Occasionally,  in  the  macerated  bone,  indications  of  a  third 
vertical  area  are  to  be  noted  along  the  medial  edge  of  the  posterior  aspect.     This 

defines    the    part    of 
latehal^articular  FACET  ^^^   artlcukr  surface 

which  rests  on  the 
lateral  border  of  the 
medial  condyle  in 
extreme  flexion.  In 
the  recent  condition, 
when  the  femoral  sur- 
face is  coated  with 
cartilage,  a  more  com- 
plex arrangement  of 
facets  may  be  in  some 
cases  displayed  (as  in- 
dicated in  rig.  170). 

Below  the  femoral 

articular  area  the  deep 

surface  of  the  apex  is 

rough  and  irregular ;  the  greater  part  of  this  is  covered  by  synovial  membrane, 

the  ligamentum  patellse  being  attached  to  its  summit  and  margins,  reaching  some 

little  distance  round  the  borders  on  to  the  anterior  aspect  of  this  part  of  the  bone. 

Ossification. — The  patella  is  laid  down  in  cartilage  about  the  third  month  of  foetal 
hfe.  At  birth  it  is  cartilaginous,  and  the  tendon  of  the  quadriceps  is  continuous  with  the 
ligamentum  patellae  over  its  anterior  surface,  and  can  easily  be  dissected  off.  About  the 
third  year  an  ossific  centre  appears  in  it  and  spreads  more  particularly  over  its  deeper 
surface.  Two  centres,  vertically  disposed,  have  also  been  described.  Ossification  is 
usually  completed  by  the  age  of  puberty. 


Fig.  170, 
A.  Anterior  Surface. 


Surface  for  the  ligamentum  patellae 
-The  Right  Patella. 

B.  Posterior  Surface. 


Tuberosity 


Surf,  for  attachment 
of  ant.  extremity  of 
Literal  semilunar 
ilage  (meniscus) 


The  Tibia. 

The  tibia  is  the  medial  bone  of  the  leg.  It  is  much  stouter  and  stronger  than  its 
neighbour  the  fibula,  with  which  it  is  united  above  and  below.  By  its  superior 
expanded  extremity  it 

supports     the     condyles     ^^^'face  for  attachment  of  anterior  extremity 
rf  J  ,  of  medial  semilunar  cartilage  (meniscus) 

of      the      femur,      while       Anterior  crucial  ligament 

inferiorly  it  shares  in 
the  formation  of  the 
anlde-joint,articula.ting 
with  the  upper  surface 
and  medial  side  of  the 
talus  or  astragalus. 

The  superior  ex- 
tremity comprises  the 
medial  and  lateral  con- 
dyles (tuberosities),  the 

«!-niTiP  and  tVip  tiiliPrnQi+v    '^'"'fiiceforattach.  of  post,  extrem.of 
Spme,  anu  tne  tUOerOSlty    medial  semilunar  cartilage  (meniscus) 

(tubercle).  Each  con- 
dyle is  provided  on  its 
upper   aspect  with   an 

articular  surface  (facies  articularis  superior),  which  supports  the  corresponding 
femoral  condyle,  as  well  as  the  interposed  semilunar  cartilage.  Of  these  two 
condylic  surfaces  the  medial  is  the  larger ;  of  oval  shape,  its  long  axis  is  placed 
antero-posteriorly.  Slightly  concave  from  before  backwards  and  from  side  to  side,  its 
circumference  rises  in  the  form  of  a  sharp  and  well-defined  edge.  The  lateral 
condylic  surface  is  smaller  and  rounder.  Slightly  concave  from  side  to  side,  and 
gently  convex  from  before  backwards,  its  circumference  is  well  defined  in  front,  but 
is  rounded  off  behind,   thus    markedly  increasing  the  convexity  of  its  posterior 


Synovial  curved 

SURFACE 


POPLIII   M 
NOTCH 

Post,  crucial  ligament 


face  for  attach,  of 
post,  extremity  of 
latpial  semilunar 
tartilage  (meniscus) 


Fig.  171. — The  Upper  Surface  of  the  Superior  Extremity  of  the 
Right  Tibia. 


THE  TIBIA. 


231 


part.  Between  the  two  condylic 
surfaces  the  bone  is  raised  in  the 
centre  to  form  the  spine  (eminentia 
intercondyloidea),  which  consists  of 
two  lateral  tubercles  separated  by 
an  obliqu(^  groove,  in  the  anterior 
part  of  which  lies  the  anterior  crucial 
ligament.  The  medial  tubercle 
(tuberculum  intercondyloideum 
mediale),  the  higher,  is  prolonged 
backwards  and  laterally  by  an 
oblique  ridge  to  which  part  of  the 
posterior  corner  of  the  lateral 
semilunar  cartilage  is  attached.  The 
lateral  tubercle  (tuberculum  intercon- 
dyloideum laterale)  is  more  pointed 
and  not  so  elevated.  In  front  and 
behind  the  spine  the  articular  areas 
are  separated  by  two  irregular  V- 
shaped  surfaces,  the  intercondylic 
fossae.  The  anterior  fossa  (fossa  in- 
tercondyloidea anterior),  the  larger 
and  wider,  furnishes  areas  for  the 
attachment  of  the  semilunar  carti- 
lages on  either  side,  and  for  the 
anterior  crucial  ligament  immedi- 
ately in  front  of  the  spine.  The 
floor  of  this  space  is  pierced  by  many 
nutrient  foramina.  The  posterior 
intercondylic  fossa  (fossa  intercon- 
dyloidea posterior)  is  concave  from 
side  to  side,  and  slopes  down- 
wards and  backwards.  The  lateral 
semilunar  cartilage  is  attached  near 
its  apex  to  a  surface  which  rises 
on  to  the  back  of  the  spine ;  the 
medial  semilunar  cartilage  is  fixed 
to  a  groove  which  runs  along  its 
medial  edge,  and  the  posterior 
crucial  Hgament  derives  an  attach- 
ment from  the  smooth  posterior 
rounded  surface. 

The  lateral  condyle^  is  the 
smaller  of  the  two.  It  overhangs 
the  shaft  to  a  greater  extent  than 
the  medial,  though  this  is  obscured 
in  the  living  by  its  articulation 
with  the  fibula.  The  facet  for  the 
fibula,  often  small  and  indistinct, 
IS  placed  postero- laterally  on  the 
under  surface  of  its  most  projecting 
part.  Antero-laterally  the  imprint 
caused  by  the  attachment  of  the 
ilio-tibial  band  is  often  quite  dis- 
tinct. Curving  downwards  and 
forwards    from     the    fibular    facet 


Ilio-tibial  band        SriNK 


Posterior  or  ex- 
tensor SURFACE 


Anterior  or 

flexor  surface 


Subcutaneous 

SURFACE 


Lateral 
malleolo 


Subcutaneous 

MEDIAI 
SURFACE 


Medial 

malleolus 


Fig.  172 «. — The  Right  Tibia  and  Fibula  as  seen 
FROM  THE  Front. 
The  anterior  or  flexor  surface  of  the  fibula  is  coloured  blue.    The 
posterior  or  exteusor  surface  of  the  fibula  is  coloured  red. 
The  lateral  or  peroneal  surface  of  the  fibula  is  left  uncoloured. 


^  I  name  "the  tuberosities"  of  the  tibia  thus,  according  to  international  nomenclature,  although  I  person- 
ally cannot  regard  the  flat  top  of  the  tibia  as  such. — A.  T. 


232 


OSTEOLOGY. 


Biceps 
External  lateral 
ligament  of  knef 

(FiBULAP 

collateral) 


RTOEIUS 

Gracilis 


there  is  often  a  definite  ridge  for  the  attachment  of  the  expansion  of  the  biceps 
tendon ;  below  this  the  areas  for  the  origins  of  the  peronffius  longus  and  extensor 
digitorum  longus  are  often  crisply  defined.  The  circumference  of  the  medial 
condyle  is  grooved  postero-medially  for  the  insertion  of  the  tendon  of  the  semi- 
membranosus. 

In  front  of  the  condyles,  and  about  an  inch  below  the  level  of  the  condylic  sur- 
faces, tliere  is  an  oval  elevation  called  the  tuberosity  or  tubercle  of  the  tibia.  The 
upper  half  of  this  is  smooth  and  covered  by  a  bursa,  while  the  lower  part  is  rough 
and  serves  for  the  attachment  of  the  ligamentum  patellae. 

Considered  in  its  entirety,  the  upper  extremity  of  the  tibia  is  broader  trans- 
versely than  antero-posteriorly,  and  is  inclined  backwards  so  as  to  overhang  the 
shaft  posteriorly. 

The  shaft  (corpus  tibiae)  is  irregularly  three-sided,  possessing  a  medial,  a 
lateral,  and  a  posterior  surface,  separated  by  an  anterior  crest,  medial,  and  lateral  or 
interosseous  borders.  It  is  narrowest  about  the  junction  of  its  middle  and  lower 
thirds,  and  expands  above  and  below  to  support  the  extremities.  Eunning  down 
the  front  of  the  bone  there  is  a  gently-curved,  prominent  margin,  the  anterior 
crest,  confluent  above  with  the  tuberosity,  but  fading  away  inferiorly  on  the  anterior 

surface  of  the  lower  third  of 
the  bone,  where  it  may  be 
traced  in  the  direction  of  the 
anterior  border  of  the  medial 
malleolus.  This  is  the  crest 
or  shin  (crista  anterior),  which 
is  subcutaneous  throughout 
its  entire  length.  To  the 
medial  side  of  this  is  a  smooth, 
slightly  convex  surface,  which 
semitendinosus  reaches  as  high  as  the  medial 
tuberosity  above,  and  in  - 
feriorly  becomes  continuous 
with  the  medial  surface  of  the 
medial  malleolus.  This  is  the 
medial  or  subcutaneous  surface 

(facies  medialis)  of  the  shaft, 
Fig.  Ii2b. — Front  aspect  of  the  Upper  Portions  of  the  Bones       V,'   V,  '  A        1      "K      V 

OF  the  Right  Leg  with  Attachments  op  Muscles  mapped  out.      wnicn  IS  COVerCQ  oniy  Dy  SKin 

and  superficial  fascia,  except 
in  its  upper  fourth,  where  the  tendons  of  the  sartorius,  gracilis,  and  semitendinosus 
muscles  overlie  it,  as  they  pass  towards  their  insertions.  This  surface  is  limited 
posteriorly  by  the  medial  border  (margo  medialis)  which  passes  from  the  medial  and 
under  surface  of  the  medial  condyle  above  to  the  hinder  border  of  the  medial 
malleolus  below.  This  border  is  rounded  and  indefinite  above  and  below,  being 
usually  best  marked  about  its  middle  third.  To  the  lateral  side  of  the  tibial  crest  is  the 
lateral  surface  of  the  bone  (facies  lateralis);  it  is  limited  behind  by  a  straight  vertical 
ridge,  the  crista  interossea  or  lateral  border,  to  which  the  interosseous  membrane, 
which  occupies  the  interval  between  the  tibia  and  the  fibula,  is  attached.  This  ridge 
commences  above,  near  the  middle  of  the  lateral  and  under  surface  of  the  lateral 
condyle,  and  terminates  below  about  two  inches  above  the  lower  extremity  by 
dividing  into  two  lines,  which  separate  and  enclose  between  them  the  surface 
for  articulation  with  the  lower  end  of  the  fibula,  and  the  area  of  attachment  of  the 
inferior  interosseous  ligament,  which  here  unites  the  two  bones.  In  its  upper 
two-thirds  the  lateral  surface  provides  an  extensive  origin  for  the  tibialis  anterior. 
Inferiorly,  where  the  tibial  crest  is  no  longer  well  defined,  the  lateral  surface 
turns  forward  on  to  the  front  of  the  shaft,  and  is  limited  inferiorly  by  the  anterior 
margin  of  the  inferior  articular  surface.  Over  this  the  tendon  of  the  tibialis 
anterior,  and  the  combined  fleshy  and  tendinous  parts  of  the  extensor  hallucis 
proprius  and  extensor  digitorum  communis  muscles  pass  obliquely  downwards. 
The  posterior  surface  (facies  posterior)  of  the  shaft  lies  between  the  interosseous 
ridge  laterally  and  the  medial  border  on  the  medial  side.     Its  contours  are  liable 


THE  TIBIA.  233 

to  considerable  variation  according  to  the  degree  of  lateral  compression  of  the  bone. 
It  is  usually  full  and  rounded  aljove,  and  Mat  below.  Superiorly  it  is  crossed  by 
the  popliteal  or  oblique  line  (linea  poplitea)  which  runs  downwards  and  medially, 
from  the  fibular  facet  above,  to  the  medial  border  on  a  level  with  the  junction  of 
the  middle  with  the  upper  third  of  the  shaft.  To  this  line  the  deep  transverse 
fascia  is  attached,  whilst  below  it,  as  well  as  from  the  medial  border  of  the  bone 
interiorly,  the  soleus  muscle  takes  origin.  Into  the  bulk  of  the  triangular 
area  aljove  it  the  popliteus  muscle  is  inserted.  Arising  from  the  middle  of  the 
popliteal  line  there  is  a  vertical  ridge,  which  passes  downwards  and  divides  the 
posterior  aspect  of  the  shaft  into  two  surfaces — a  lateral  for  the  tibial  origin  of 
the  tibialis  posterior  muscle,  and  a  medial  for  the  flexor  digitorum  longus  muscle. 
The  inferior  third  of  this  surface  of  the  shaft  is  free  from  muscular  attachments, 
but  is  overlain  by  the  tendons  of  the  above  muscles,  together  with  that  of  the  flexor 
hallucis  longus.  A  large  nutrient  canal,  having  a  downward  direction,  opens  on  the 
posterior  surface  of  the  shaft  a  little  below  the  popliteal  line  and  just  lateral  to 
the  vertical  ridge  which  springs  from  it. 

The  inferior  extremity  of  the  tibia  displays  an  expanded  quadrangular  form. 
It  is  furnished  with  a  saddle-shaped  articular  surface  on  its  under  surface  (facies 
articularis  inferior),  which  is  concave  from  before  backwards  and  slightly  convex 
from  side  to  side.  This  rests  upon  the  superior  articular  surface  of  the  body  of  the 
talus  or  astragalus,  and  is  bounded  in  front  and  behind  by  well-defined  borders. 
The  anterior  border  is  the  rounder  and  thicker,  and  is  oftentimes  channelled  by  a 
groove  for  the  attachment  of  the  anterior  ligament  of  the  joint ;  further,  it  is  occa- 
sionally provided  with  a  pressure  facet  caused  by  the  locking  of  the  bone  against 
the  neck  of  the  talus  in  extreme  flexion.  Laterally  the  edge  of  the  articular  area 
corresponds  to  the  base  of  the  triangle  formed  by  the  splitting  of  the  interosseous 
ridge  into  two  parts.  Where  these  two  lines  join  it,  both  in  front  and  behind,  tlie 
bone  is  elevated  into  the  form  of  tubercles,  in  the  hollow  between  which  (incisura 
fibularis)  the  lower  end  of  the  fibula  is  lodged,  being  held  in  position  by  powerful 
ligaments.  The  cartilage-covered  surface  occasionally  extends  for  some  little 
distance  above  the  base  of  the  triangle.  Medially  there  is  a  down  -  projecting 
process,  called  the  medial  malleolus,  the  medial  aspect  of  which  is  subcutaneous 
and  forms  the  projection  of  the  inner  ankle.  Its  lateral  surface  is  furnished 
with  a  piriform  facet  (facies  articularis  malleolaris),  confluent  above  with  the 
cartilage -covered  area  on  the  inferior  extremity  of  the  shaft;  this  articulates 
with  a  corresponding  area  on  the  medial  surface  of  the  body  of  the  talus.  Inferiorly 
the  malleolus  is  pointed  in  front,  but  notched  behind  for  the  attachment  of  the 
tibial  collateral  (internal  lateral  ligament)  of  the  ankle.  Eunning  obliquely 
along  the  posterior  surface  of  the  malleolus  there  is  a  broad  groove  (sulcus 
malleolaris)  in  which  the  tendons  of  the  tibialis  posterior  and  flexor  digitorum 
longus  muscles  are  lodged ;  whilst  a  little  to  the  fibular  side  of  this,  and 
running  downwards  over  the  posterior  surface  of  the  lower  extremity  of  the  bone, 
there  is  another  groove,  often  faintly  marked,  for  the  lodgment  of  the  tendon  of 
the  flexor  hallucis  longus  muscle.  The  proportionate  length  of  the  tibia  to  the 
body  height  is  as  1  is  to  •4-32-4-80. 

Arterial  Foramina. — Nutrient  canals  are  seen  piercing  the  upper  extremity  of  the  bone 
around  its  circumference  and  above  the  tuberosity.  The  floors  of  the  intercondylic  fossae  are  also 
similarly  pierced,  and  there  is  usually  a  canal  of  large  size  opening  on  the  summit  of  the  inter- 
condyloid  eminence.  Two  or  three  foramina  of  fair  size  are  seen  running  upwards  into  the  sub- 
stance of  the  bone  a  little  below  and  to  the  medial  side  of  the  tuberosity,  while  the  principal 
vessel  for  the  shaft  jmsses  downwards  into  the  bone  on  its  jjosterior  surface,  about  the  level  of 
the  junction  of  the  upper  and  middle  thirds.  The  medial  surface  of  the  medial  malleolus,  as 
well  as  the  anterior  and  joosterior  borders  of  the  inferior  extremity,  are  likewise  pitted  by  the 
orifices  of  small  vascular  channels. 

Connexions. — Superiorly  the  tibia  supports  the  condyles  of  the  femur,  and  is  connected  in 
front  with  the  patella  by  means  of  the  patellar  ligament.  Articulating  laterally  with  the 
fibula  above  and  below,  it  is  united  to  that  bone  throughout  nearly  its  entire  length  by  the  inter- 
osseous membrane.  The  crest  and  medial  surface  can  be  readily  examined,  as  they  are  sub- 
cutaneous, except  above  where  the  medial  surface  is  overlain  by  the  thin  tendinous  aponeurosis 
of  the  muscles  passing  over  the  inner  side  of  the  knee.  The  form  of  the  lower  part  of  the  knee  in 
front  is  determined  by  the  condyles  on  either  side  crossed  centrally  by  the  ligamentum  patellae. 


234 


OSTEOLOGY. 


Interiorly  the  medial  malleolus  forms  the  j^rojection  of  the  imier  ankle,  which  is  wider,  not  so 
low,  less  pointed,  and  placed  in  advance  of  the  projection  of  the  outer  ankle.  The  front  and 
back  of  the  lower  end  of  the  bone  are  crossed  by  tendons,  which  mask  to  a  certain  extent  its 
form. 

Ossification. — The  shaft  begins  to  ossify  early  in  the  second  month  of  intrauterine 

life.    At  birth  it  is  well  formed,  and 


Fuses  -with  shaft  about  20-24  years 


May  apjiear 
Appears  indeijendeutly 

before  birth      about  11  years 
\ 


Appears  about  Ik  years 

Fuses  about  ISth  year 
At  birth.  About  12  years.  About  16  years. 

Fig.  173. — Ossification  of  the  Tibia. 

upper  end  is  the  so-called   "growing  end  of  the 


capped  above  and  below  by  pieces 
of  cartilage,  in  the  upper  of  which 
the  centre  for  the  superior  epiphysis 
has  already  usually  made  its  ap- 
pearance. From  this  the  condyles 
and  tuberosity  are  developed,  though 
sometimes  an  independent  centre  for 
the  latter  appears  about  the  eleventh 
or  twelfth  years,  rapidly  joining 
with  the  already  well  -  developed 
mass  of  the  rest  of  the  epiphysis. 
Complete  fusion  between  the  super- 
ior epiphysis  and  the  shaft  does  not 
take  place  until  the  twentieth  or 
the  twenty-fourth  year.  The  centre 
for  the  lower  articular  surface  and 
the  medial  malleolus  makes  its 
appearance  about  the  end  of  the 
second  year,  and  union  with  the 
shaft  is  usually  complete  by  the  age 
of  eighteen.  Lambertz  notes  the 
occasional  presence  of  an  accessory 
nucleus  in  the  malleolus.  The 
bone." 


The   Fibula. 

The  fibula  is  a  slender  bone  with  two  enlarged  ends.  It  lies  to  the  lateral 
side  of  the  tibia,  with  which  it  is  firmly  united  by  ligaments,  and  nearly  equals  that 
bone  in  length. 

The  first  difficulty  which  the  student  has  to  overcome  is  to  determine  which  is  the  upper  and 
which  the  lower  extremity  of  the  bone.  This  can  easily  he  done  by  recognising  the  fact  that 
there  is  a  deep  pit  on  the  medial  aspect  of  the  lower  extremity  immediately  behind  the  triangular 
articular  surface.  Holding  the  bone  vertically  with  the  lower  extremity  downwards  and  so 
turned  that  the  triangular  articular  area  lies  in  front  of  the  notch  already  spoken  of,  the 
subcutaneous  non-articular  aspect  of  the  inferior  extremity  will  point  to  the  side  to  which  the 
bone  belongs. 

The  superior  extremity  or  head  of  the  fibula  (capitulum  fibulae),  of  irregular 
rounded  form,  is  bevelled  on  its  medial  surface  so  as  to  adapt  it  to  the  form  of  the 
under  surface  of  the  lateral  condyle  of  the  tibia.  At  the  border,  where  this 
surface  becomes  confluent  with  the  lateral  aspect  of  the  head,  there  is  a  pointed 
upstanding  eminence  called  the  styloid  process  (apex  capituli  fibulae) ;  to  this 
the  short  fibular  collateral  (external  lateral)  ligament  is  attached,  as  well  as  a 
piece  of  the  tendon  of  the  biceps,  which  is  inserted  into  its  fore-part.  Immediately 
to  the  medial  side  of  this,  and  occupying  the  summit  of  the  medial  sloping  surface, 
there  is  an  articular  area  (fades  articularis  capituli),  of  variable  size  and  more  or 
less  triangular  shape.  This  serves  for  articulation  with  the  lateral  condyle"  of  the 
tibia.  The  long  fibular  collateral  (external  lateral)  ligament,  together  with  the 
remainder  of  the  tendon  of  the  biceps  muscle  which  surrounds  it,  is  attached  to  the 
lateral  and  upper  side  of  the  head  in  front  of  the  styloid  process.  In  front  and 
behind  the  head  there  are  usually  prominent  tubercles.  The  anterior  of  these  is 
associated  with  the  origin  of  the  peronteus  longus  muscle ;  the  posterior,  whilst 
furnishing  an  origin  for  the  upper  fibres  of  the  soleus,  serves  to  deepen  the  groove, 
behind  the  superior  tibio-fibular  articulation,  in  which  the  tendon  and  fleshy  part 
of  the  popliteus  muscle  play.     The  constricted  portion  of  the  shaft  below  the  head 


THE  FIBULA. 


235 


is  often  referred   to  as  the  neck ;    around  the 


Medial  coni>vli 


LaTKKAL  CONDYLIC 


Oblique  line. 


Posterior  or  Ex- 
tensor SURFACE 


Posterior  surface 


Groove  for 
tendons  of 

PERONiKUS 

LONOUS  AND 
BREVIS 


Lateral 
malleolus 


Groove  for- 
flexor  halluois 

LONOUS 

Fig.  174  a. — The  Right  Tibia  and  Fibula  seen  from 

Behind. 

Posterior  or  extensor  surface  of  the  fibula  is  coloured  red  ; 

tlie  lateral  or  peroneal  surface  is  left  uncoloured. 


lateral  side  of  this   the  peroneal 
nerve  winds. 

Tlie  shaft  of  the  fibula  (cor- 
pus fibulae)  presents  many  varieties 
of  shape  and  form,  being  ridged 
and  channelled  in  such  a  way  as 
greatly  to  increase  the  difficulties 
of  the  student  in  recognising  the 
various  surfaces  described.  The 
most  important  point  is  first  to 
determine  the  position  of  the 
interosseous  ridge.  Holding  the 
bone  in  the  position  which  it 
normally  occupies  in  the  leg,  it 
will  be  noticed  that  the  lateral 
surface  of   the    lower   extremity 

Semimembranosus 


SOLEUS 


:#; 


Tibialis  posterior 
Flexor  hallucis  lonous 

Perox.-eus  LOSGC'S 

and   BREVIS 

Fig.  174  5. — Posterior  aspect  of  the 
Bones  of  the  Leg  with  Attach- 
ments OF  Muscles  mapped  out. 


is  limited  in  front  and  behind  by  two  lines,  which,    converging    above,   enclose 


236 


OSTEOLOaY. 


Styloid  process 


Facet  for  tibia  . 


Interosseous  crest— - 


Interosseous_ 

CREST 


RocoH  surface 

FOR  INTKR- 
OSSKOUS" 

ligament 

Facet  for  talus 

or  astragalu.s- 

■<       M  fj  g 

•<  O  0. 

Lateral 
malleolus 

Fio.  175.— Right  Fibula  as 

SEEN   FROM   THE    MEDIAL   SiDE. 

The  anterior  surface  is  coloured 
blue  ;  the  posterior  surface  is 
coloured  red. 


between  them  a  triangular  subcutaneous  area  which  lies 
immediately  above  the  outer  ankle.  From  the  summit 
of  the  triangle  so  formed  a  well-defined  ridge  may  be 
traced  up  the  front  of  the  shaft  to  reach  the  anterior 
aspect  of  the  head.  This  is  the  anterior  crest,  and  must 
not  be  mistaken  for  the  interosseous  crest,  which  is  now 
easy  to  find,  for  the  next  ridge  which  lies  just 
medial  to  the  anterior  crest,  or  towards  the  tibial  side 
on  the  anterior  aspect  of  the  bone,  is  the  line  to  which 
the  interosseous  membrane  is  attached.  As  a  rule  these 
two  lines  are  separated  by  a  considerable  interval  in  the 
lower  half  of  the  bone,  but  tend  to  run  much  closer 
together  above ;  indeed  it  is  not  uncommon  to  find  that 
they  coalesce  to  form  a  single  crest.  Let  it  therefore  be 
clear  that  the  interosseous  line  is  that  which  lies  just 
medial  to  the  ridge  which  springs  inferiorly  from  the 
malleolar  subcutaneous  triangular  surface,  notwith- 
standing the  differences  in  width  of  the  surface  which 
separates  the  lines,  or  their  occasional  coalescence  above. 

The  position  of  the  interosseous  ridge  enables  us  at 
once  to  separate  the  anterior  or  flexor  aspect  of  the  bone 
from  its  posterior  or  extensor  surface,  using  these  terms 
in  relation  to  the  movements  of  the  anhle} 

In  addition,  there  is  the  lateral  or  peroneal  surface, 
which  corresponds  to  the  lateral  side  of  the  shaft.  Start- 
ing then  at  the  interosseous  crest,  and  passing  forwards 
round  the  lateral  side  of  the  shaft,  the  anterior  or 
flexor  surface  is  the  first  met  with ;  this  is  bounded 
laterally  by  the  anterior  crest,  and,  as  has  been  said, 
may  be  either  of  considerable  width  or  almost  linear.^ 
From  this  arises  the  extensor  digitorum  communis, 
together  with  the  peronseus  tertius  and  the  extensor 
hallucis  proprius  muscles,  which,  though  extensors  of  the 
toes,  are  also  important  flexors  of  the  ankle. 

The  anterior  crest  serves  for  the  attachment  of  the 
intermuscular  septum,  which  separates  the  foregoing 
group  of  muscles  from  that  which  lies  along  the  lateral 
side  of  the  shaft,  viz.  the  perongeus  longus  and  brevis 
muscles.  The  surface  from  which  these  arise  is  limited 
behind  by  the  posterior  border,  which  is  usually  sharp 
and  well  defined  below,  where  it  is  continuous  with  the 
bone  immediately  above  the  pit  on  the  medial  surface 
of  the  lower  extremity,  whilst  it  tends  to  be  less  distinct 
and  more  rounded  above  where  it  runs  into  the  base  of 
the  styloid  process.  In  its  upper  third  or  fourth  this 
border  is  often  rough  and  tubercular  where  it  serves  for 
the  origin  of  the  soleus.  The  lateral  or  peroneal 
surface  4s  somewhat  twisted,  being  directed  rather 
forwards  above,  but  tending  to  turn  backwards  below 
where  it  becomes  continuous  with  the  groove  which 
courses  along  the  back  of  the  lateral  malleolus  and 
which  lodges  the  tendons  of  the  peronseus  longus  and 


^  The  use  of  these  terms  is  not,  strictly  speaking,  correct,  and  they  are 
here  used  in  a  physiological  and  not  in  a  morphological  sense.  The 
anterior  surface  of  the  leg  is  the  true  extensor  surface,  and  is  comparable 
with  the  posterior  surface  of  the  forearm,  the  change  in  position  having 
been  brought  about  developmentally  by  difference  in  the  rotation  of  the 
limbs.  Flexion  of  the  ankle,  so  called,  is  in  reality  an  extensor  movement, 
and  corresponds  to  extension  at  the  wrist.  (See  Humphry,  Journ.  Anat.  and  Physiol.,  vol.  xxviii.  p.  15.) 
^  This  is  not  recognised  as  a  surface  but  as  a  crest  only  (crista  anterior)  by  the  B.N.A. 


THE  FIBULA.  237 

brevis  muscles.  The  remainder  of  the  shaft,  included  between  the  posterior 
border  behind  and  the  interosseous  ridge  in  front  and  medially,  is  the  posterior 
or  extensor  surface,  for  here  arise  the  several  muscles  wJwse  action  in  j^ja?-^ 
is  to  extend  the  anide.  This  surface  is  cut  up  by  a  curved  ridge  often  the 
most  prominent  and  outstanding  on  the  bone,  and  hence  frequently  mistaken  by 
the  student  for  the  interosseous  ridge ;  it  serves  to  define  the  area  for  the  origin 
of  the  tibialis  posterior,  and  arises  below  from  the  posterior  border  of  the  inter- 
osseous ridge  at  the  junction  of  the  middle  and  inferior  thirds  of  the  shaft,  curves 
a  little  backwards,  and  passing  upwards  and  obliquely  forwards  again  joins  the 
interosseous  ridge  once  more  in  the  region  of  the  neck.  This  is  oftentimes  called 
the  medial  border  (crista  medialis) ;  and  the  surface  so  mapped  oft",  the  medial 
surface.  The  ridge  itself  serves  for  the  attachment  of  the  aponeurosis  which 
covers  the  tibialis  posterior  muscle.  The  remainder  of  the  posterior  aspect  of  the 
shaft,  which,  above,  is  directed  backwards,  is  so  twisted  that  inferiorly  it  is 
directed  medially.  Prom  this,  in  its  upper  part,  the  soleus  muscle  arises ;  whilst 
lower  down,  the  flexor  hallucis  longus  muscle  derives  an  extensive  origin.  Both 
of  these  muscles,  together  loith  the  tibialis  posterior,  act  as  extensors  of  the  anide. 
On  this  aspect  of  the  bone,  at  or  near  the  middle  of  the  shaft,  and  just  behind 
the  prominent  tibial  ridge,  is  the  opening  of  the  nutrient  canal,  which  has  a 
downward  direction. 

The  inferior  extremity  of  the  fibula,  or  lateral  raalleolus,  is  of  pyramidal 
form.  Its  medial  surface  is  furnished  with  a  triangular  articular  area  (facies 
articularis  malleoli),  plane  from  before  backwards,  and  slightly  convex  from  above 
downwards,  which  articulates  with  a  corresponding  surface  on  the  lateral  side  of  the 
body  of  the  talus  or  astragalus.  Behind  this  there  is  a  deep  pit,  to  which  the 
posterior  fasciculus  of  the  external  lateral  (posterior  talo-fibular  lig.)  ligament  is 
attached.  Above  the  articular  facet  there  is  a  rough  triangular  area  on  the  posterior 
surface  of  the  shaft,  from  tlie  summit  of  which  the  interosseous  ridge  arises  ;  to  this 
are  attached  the  strong  fibres  of  the  inferior  interosseous  ligament  which  binds 
together  the  opposed  surfaces  of  the  tibia  and  fibula.  The  lateral  surface  of  the 
inferior  extremity  forms  the  elevation  of  the  lateral  malleolus  which  determines  the 
shape  of  the  projection  of  the  outer  ankle.  Bounded  from  side  to  side  and  from 
above  downwards,  it  terminates  below  in  a  pointed  process,  which  reaches  a  lower 
level  than  the  corresponding  process  of  the  tibia,  from  which  it  also  difters  in  being 
narrower  and  more  pointed  and  being  placed  in  a  plane  nearer  the  heel.  Superiorly, 
this  surface,  which  is  subcutaneous,  is  continuous  with  the  triangular  subcutaneous 
area  so  clearly  defined  by  the  convergence  above  of  the  lines  which  unite  to  form 
the  anterior  border.  The  anterior  border  and  tip  of  the  lateral  malleolus  furnish 
attachments  to  the  anterior  and  middle  bands  of  the  external  lateral  ligament  of 
the  ankle  (anterior  talo-fibular  and  calcaneo-fibular  ligs.).  The  posterior  surface 
of  the  lateral  malleolus,  broad  above,  where  it  is  confluent  with  the  lateral  or 
peroneal  surface,  is  reduced  in  width  below  by  the  presence  of  the  pit  which 
lies  to  its  inner  side.  This  aspect  of  the  bone  is  grooved  (sulcus  malleolaris) 
by  the  tendons  of  the  peronseus  longus  and  brevis  muscles,  which  curve  round 
the  posterior  and  lower-pointed  aspect  of  the  malleolus.  The  proportionate 
length  of  the  fibula  to  the  body  height  is  as  1  is  to  4-37-4-82.    ^ 

Arterial  Foramina. — Numerous  minute  vascular  canals  are  seen  piercing  tlie  lateral  surface  of 
the  head,  and  one  or  two  of  larger  size  are  seen  on  the  medial  surface  immediately  in  front  of  the 
superior  articular  facet.  The  canal  for  the  nutrient  artery  of  the  sliaft,  which  has  a  downward 
direction,  is  situated  on  the  back  of  the  bone  about  its  middle.  The  lateral  surface  of  the  lateral 
malleolus  displays  the  openings  of  many  small  canals,  and  one  or  two  larger  openings  are  to  be 
noted  at  the  bottom  of  the  pit  behind  the  inferior  articular  surface. 

Connexions. — The  head  and  lateral  malleolus,  and  jaart  of  the  shaft  immediately  above  the 
latter,  are  subcutaneous.  The  remainder  of  the  shaft  is  covered  on  all  sides  by  the  muscles  which 
surround  it.  Superiorly  the  bone  plays  no  jiart  in  the  formation  of  the  knee-joint,  but  inferiorly 
it  assists  materially  in  strengthening  the  ankle-joint  by  its  union  with  the  tibia  and  its  articulation 
with  the  talus.  In  position  the  bone  is  not  jjarallel  to  the  axis  of  the  tibia,  but  oblique  to  it, 
its  upper  extremity  lying  posterior  and  lateral  to  a  vertical  line  passing  through  the  lateral 
malleolus. 

Ossification. — -The  shaft  begins  to  ossify  about  the  middle  of  the  second  month  of 
foetal  life.     At  the  end  of  the  third  month  there  is  but  little  difference  in  size  between  it 


238 


OSTEOLOGY. 


and  the  tibia,  and  at  birth  the  fibula  is  much  larger  in  propoi'tion  to  the  size  of   the 
tibia  than  in  the  adult.     Its  extremities  are  cartilaginous,  the  lower  extremity  not  being 

as  long  as  the  medial  malleolar  cartilage  of  the 
^^3.Tyea,^°"*       ^^^'^h^ut  20--2Vy'ea?s  tibia.    It  is  in  this,  however,  that  an  ossific  centre 
'^""     "  '  first  appears  about  the  end  of  the  second  year, 

which  increases  rapidly  in  size,  and  unites  with 
the  shaft  about  nineteen  years.  The  centre  for  the 
superior  epiphysis  begins  to  ossify  about  the  third  or 
fourth  year,  and  union  with  the  shaft  is  not  complete 
until  a  period  somewhat  later  than  that  for  the  inferior 
epiphysis.  The  mode  of  ossification  of  the  lower  ex- 
tremity is  an  exception  to  the  general  rule  that  epi- 
physes which  are  the  first  to  ossify  are  the  last  to  unite 
with  the  shaft.  This  may  possibly  be  accovmted  for 
by  the  fact  that  the  lower  end  is  functionally  more 
important  than  the  rudimentary  upper  end,  since  in  man 
alone,  of  all  vertebrates,  does  the  lateral  malleolus 
reach  beyond  the  level  of  the  medial  malleolus.  Its 
early  union  with  the  shaft  is  doubtless  required  to 
ensure  the  stability  of  the  ankle  joint  necessitated  by 
the  assumption  of  the  erect  position. 

Appears  about 
2ud  year 


In  its  earlier  stages  of  development  it  has  been  stated, 
on  the  authority  of  Leboucq,  Gegenbaur,  and  others,  that 
the  fibula  as  well  as  the  tibia  is  in  contact  with  the  femur. 
This  is,'  however,  denied  by  Grimbaiim  ("Proc.  Anat.  See," 
Journ.  Anat.  and  Physiol,  vol.  xxvi.  p.  22),  who  states  that 
after  the  sixth  week  the  fibula  is  not  in  contact  with  the 
femur,  and  that  prior  to  that  date  it  is  impossible  to 
differentiate  the  tissue  which  is  to  form  femur  from  that  wliich  forms  fibula. 


At 
birth. 

Fig.  176.- 


Fuses  with  shaft 
about  19  years 

About  About 

12  years.  16  years. 

-Ossification  of  Fibula. 


BONES  OF  THE  FOOT. 

The  bones  of  the  foot,  twenty -six  in  number,  are  arranged  in  three  groups  :  the  tarsal,  seven 
in  number  ;  the  metatarsal,  five  in  number  ;  the  phalanges,  fourteen  in  number. 

Comparing  the  foot  with  the  hand,  the  student  will  be  struck  with  the  great  proportionate 
size  of  the  tarsus  as  compared  with  the  carpus,  and  the  reduction  in  size  of  the  bones  of  the  toes 
as  compared  with  the  fingers.  The  size  of  the  metatarsal  segment  more  nearly  equals  that  of 
the  metacarpus. 

The  Tarsus. 

The  tarsus  (ossa  tarsi)  consists  of  seven  bones — the  talus  or  astragalus,  cal- 
caneus, navicular  or  scaphoid,  three  cuneiforms,  and  the  cuboid.  Of  irregular  form 
and  varying  size,  they  may  be  described  as  roughly  cubical,  presenting  for  examina- 
tion dorsal  and  plantar  surfaces,  as  well  as  anterior  or  distal,  posterior  or  proximal, 
medial,  and  lateral  aspects. 

The  Astragalus. 

The  talus  or  astragalus  is  the  bone  through  which  the  body  weight  is  trans- 
mitted from  the  leg  above  to  the  foot  below.  Superiorly  the  tibia  rests  upon  it, 
whilst  on  either  side  it  articulates  with  the  medial  and  lateral  malleolar  processes 
of  the  tibia  and  fibula  respectively  ;  interiorly  it  overlies  the  calcaneus,  and  anteriorly 
it  articulates  with  the  navicular.  For  descriptive  purposes  the  bone  is  divisible  into 
two  parts — the  body  (corpus  tali)  blended  in  front  with  the  neck  (collum  tali), 
which  supports  the  head  (caput  tali). 

The  upper  surface  of  the  body  is  provided  with  a  saddle-shaped  articular 
surface  (trochlea  tali),  broader  in  front  than  behind,  for  articulation  with  the. under 
surface  of  the  tibia.  The  medial  edge  of  the  trochlea  is  straight ;  whilst  the  lateral 
border,  which  is  sharp  in  front  and  more  rounded  behind,  is  curved  medially  pos- 
teriorly where  it  is  bevelled  to  form  a  narrow,  elongated,  triangular  facet,  which 
is  in  contact  with  the  transverse  or  inferior  tibio-fibular  ligament  during  flexion  of 


THE  ASTEAGALUS. 


239 


the  ankle  (Fawcett,  Ed.  Med.  Journ.,  1895).  Over  the  lateral  border  the  cartilage- 
covered  surface  is  continvious  laterally  with  an  extensive  area  of  the  form  of  a 
quadrant.  This  is  concave  from  above  downwards,  and  articulates  with  the  medial 
surface  of  the  lateral  malleolus.     The  inferior  angle  of  this  area  is  prominent  and 


Surface  of  talus 

for  articulation 

with  flbula 


Surface  of  talus  for 
articulation  with  tibia 


V.  Metatarsal 


I.  Metatarsal 


Sesamoid  bone 


First 

PHALANX 


Third  or  terminal  phalanx 
Fig.   177. — Bones  of  the  Right  Foot  as  seen  from  Above. 

somewhat  everted,  and  sometimes  referred  to  as  the  lateral  process  (processus 
lateralis  tali).  The  medial  aspect  of  the  body  has  a  comma-shaped  facet,  conflu- 
ent with  the  superior  articular  surface,  over  the  medial  edge  of  the  trochlea ;  this 
articulates  with  the  lateral  surface  of  the  medial  malleolus.  Inferior  to  this  facet 
the  bone  is  rough  and  pitted  by  numerous  small  openings,  and  just  below  the  tail 


240 


OSTEOLOGY. 


of  the  comma  there  is  a  circular  impression  for  the  attachment  of  the  deep  fibres 
of  the  internal  lateral  (deltoid)  ligament  (talo-tibial  fibres).  On  the  inferior  surface 
of  the  body  there  is  a  deep  concave  facet,  called  the  posterior  calcanean  facet  (facies 
calcanea  articularis  posterior),  which  is  of  more  or  less  oval  or  oblong  form  and 


Calcaneus 


SUSTEXTACULL'M  TALI 


Surface  of  tains  m 

blue  rests  on  the  plant  i 

calcaneo-navicu    i 

ligamei     ]~ 


First 
cuneiform 


I.  Metatarsal 


Sesamoid  bote 


First  phalanx  "   / 


Cuboid 

Second  cuneiform 
Third 
cuneiform 


V.  Metatarsal 


Third  or  terminal  phalanx 
Fig.  178  «. — Bones  of  the  Right  Foot  seen  from  Below. 

is  placed  obliquely  from  behind  forwards  and  laterally;  this  rests  upon  a  corre- 
sponding surface  on  the  upper  aspect  of  the  calcaneus.  In  front  of  this,  and 
crossing  the  bone  from  within  outwards  and  forwards,  is  a  deep  furrow  (sulcus  tali), 
the  floor  of  which  is  pierced  by  numerous  large  canals.  It  serves  for  the  attach- 
ment of  the  strong  interosseous  ligament  which  unites  the  talus  with  the  calcaneus, 


THE  ASTEAGALUS. 


241 


and  separates  the  facet  already  described  from  a  smaller  oval  articular  area  having 
a  slightly  convex  surface,  which  lies  immediately  in  front  of  it.  This  is  called 
the  middle  calcanean  facet  (fades  articularis  calcanea  media),  and  articulates  with 
the  upper  surface  of  the  sustentaculum  tali  of  the  calcaneus.  Posteriorly  the 
body  is  provided  with  two  tubercles,  separated  by  a  groove ;  the  lateral  of  these 
(processus  posterior  tali)  is  usually  the  larger,  and  is  occasionally  a  separate  ossicle 
(os  trigonum).  To  it  is  attached  the  posterior  fasciculus  of  the  external  lateral 
ligament  (posterior  talo-fibular  lig.)  of  the  ankle-joint.     The  groove,  which  winds 


Abductor  digiti  quiuti 
(origin) 


Quadratus  plants 
(accessorius)  (origin)       |L!"ll 

Long  and  sliort  plantar  / 
ligaments  |^ 


Tibialis  posterior  (part  of 
insertion")' 


Perona>us  brevis 
(insertion) 

Flexor  digiti  quinti 
brevis  (origin) 


Adductor  liallucis 
obliqiuis  (origin)' 


Flexor  digitorum  brevis  (origin) 
Abductor  hallucis  (origin) 


Attachments  of 
plantar  calcaneo- 
navicular ligament 


Flexor  hallucis  brevis 

(origin) 


Tibialis  posterior  (part 
of  insertion) 


Peronteus  longus 
(insertion) 


Tibialis  anterior 
insertion) 


Fig.  178  i. — Muscle-Attachmexts  to  Left  Tarsus  axd  Metatarsus  (Plantar  Aspect). 

obhquely  from  above  downwards  and  medially  over  the  posterior  surface  of  the 
bone,  lodges  the  tendon  of  the  flexor  hallucis  longus  muscle. 

The  head  (caput  tali),  of  oval  form,  is  directed  forwards  and  medially.  Its 
anterior  surface  is  convex  from  side  to  side  and  from  above  downwards,  and  articu- 
lates with  the  navicular  bone  (facies  articularis  navicularis).  Inferiorly  this  surface 
is  confluent  with  the  middle  calcanean  facet,  but  in  well-marked  specimens,  or  when 
the  bones  are  articulated,  it  will  be  seen  that  a  small  area  in  front  of,  and  lateral 
to,  the  middle  calcanean  facet  rests  upon  an  articular  surface  on  the  upper  part  of 
the  fore  portion  of  the  calcaneus,  and  is  called  the  anterior  calcanean  facet  (facies 
articularis  calcanea  anterior).  To  the  medial  and  under  surface  of  the  head  there  is  a 
cartilage-covered  surface  which  does  not  articulate  with  any  bone,  but  rests  on  the 
upper  surface  of  the  plantar   calcaneo-navicular   ligament,  and   is  supported   on 


242 


OSTEOLOGY. 


the  medial  side  by  the  tendon  of  the  tibialis  posterior  muscle  (Fawcett,  Ed.  Med. 
Journ.,  1895,  p.  987). 


Fig.  179  «. — The  Right  Talus. 


A.   Upper  Surface. 


B.   Under  Surface. 


1.  Groove  fob  flex,  hallucis.  long. 

2.  Median  tubercle. 

3.  Trochlear  surface  for  tibia. 

4.  Body. 

5.  For    articulation    with    medial 

malleolus. 

6.  Head. 

7.  For  articulation  with  navicular. 

8.  Xeck. 


9.  For  articulation  with  lateral 
malleolus. 

10.  Surface     against     which    the 

posterior  talo-fibular  liga- 
ment rests. 

11.  Lateral  tubercle. 

12.  Lateral  tubercle. 

13.  Posterior,  middle,  and  anterior 

facets  for  calcaneus. 


14.  For     ARTICULATION     WITH      NAVI- 

CULAR. 

15.  Surface    resting    on    plantar 

calcaneo- navicular       liga- 
MENT. 

16.  Interosseous  groove. 

17.  Medial  tubercle. 

IS.  Groove    for    flexor    hallucis 

LONOUS. 


The  neck  (coUum  tali),  best  seen  above,  passes  from  the    front  of  the  body 
and  inclines  towards  the  medial  side.     It  is  confluent  with  the  medial  surface  in 


C.  Seen  from  the  Lateral  Side 


Seen  from  the  Medial  Side. 


Lateral  tubercle. 

Groove    for    flexor    hallucis 

i.ongus. 
Medial  tubercle. 
Surface    aoain.st    which     the 

posterior  talo-fibular  i.kia- 

ment  rests. 
Trochlea  for  tibia. 
For      articulation      with 

lateral  malleolus. 
Neck.  8.  Head. 

For     articulation      with 

navicular. 


10.  Interosseous  groove. 

11.  Anterior       middle,       and 

posterior    facets    for    cal- 
caneus. 

12.  Body. 

13.  Surface    resting    on    plantar 

CALCANEO  -  navicular  LIGA- 

MENT. 

14.  For     ARTICULATION    WITH      NAVI- 

CULAR. 

15.  Head. 

16.  Neck. 

17.  Trochlea  for  tibia. 


For  articulation  with  medial 
malleolus. 

Body. 

Impression  for  deltoid  liga- 
ment. 

Lateral  tubercle. 

Groove  for  flexor  hallucis 
long  us. 

IjATERAL  TUBERCLE. 

Interosseous  groove. 
Posterior  and   middle    facets 

FOR  calcaneus. 


front  of   the  medial    malleolar  facet,  and    laterally  forms   a  wide   groove,  which 
becomes  continuous  inferiorly  with  the  outer  end  of  the  interosseous  groove. 


THE  CALCANEUS. 


243 


The  Calcaneus. 

The  calcaneus  is  the  largest  of  the  tarsal  bones.  It  supports  the  talus  above 
and  articulates  with  the  cuboid  in  front.  Inferiorly  and  behind,  its  posterior  ex- 
tremity, or  tuberosity  (tuber  calcanei),  forms  the  heel  on  which  so  large  a  proportion 
of  the  body  weight  rests.  The  long  axis  of  the  bone  inclines  forwards  and  a  little 
laterally. 

The  upper  surface  of  the  calcaneus  is  divisible  into  two  parts — a  posterior  non- 
articular  part  and  an  anterior  articular  portion.  The  length  of  the  former  varies 
according  to  the  projection  of  the  heel ;  rounded  from  side  to  side,  it  is  slightly  con- 
cave from  before  backwards.  In  front  of  this  there  is  a  convex  articular  area  of 
variable  shape  (fades  articularis  posterior),  sometimes  nearly  circular,  at  other  times 
oval  and  occasionally  almost  triangular.  This  is  directed  upwards  and  forwards, 
and  articulates  with  the  posterior  calcanean  facet  on  the  under  surface  of  the 
talus.     Anterior  to  this  facet  the  bone  is  deeply  excavated,  forming  a  fossa  from 


Surface  for 
attachment 
/■of  short 
plantar 
ligament 


SUSTENTA- 

CDLtJM 

TALI 

Groove  fok 

FLEXOR 

HALLUCIS 

LONQUS 

Surface  for 
attachment 
of  long 
plantar  liga- 
ment 

Medial 

PROCESS 


TUBEROSITY 

A  Fig.  IS 

A.    Seen  from  Above. 


-The  Right  Calcaneus. 


B 
B.  Seen  from  Below. 


which  a  groove  (sulcus  calcanei)  leads  backwards  and  medially  around  the  antero- 
medial  border  of  the  articular  surface.  When  the  calcaneus  is  placed  in  contact 
with  the  talus,  this  groove  coincides  with  the  sulcus  on  the  under  surface  of 
the  latter  bone,  and  so  forms  a  canal  or  tunnel  (sinus  tarsi)  in  which  the  strong 
interosseous  ligament  which  vmites  the  two  bones  is  lodged.  To  the  front  and 
medial  side  of  this  groove  there  is  an  elongated  articular  facet  directed  obliquely 
from  behind  forwards  and  laterally,  and  concave  in  the  direction  of  its  long  axis. 
This  is  frequently  divided  into  two  smaller  oval  areas  by  an  intermediate  non- 
articular  surface.  Of  these  facets  the  hinder  (fades  articularis  media)  articulates 
with  the  middle  calcanean  facet  on  the  under  surface  of  the  talus,  whilst  the 
anterior  (facies  articularis  anterior)  supports  the  under  surface  of  the  head  of  the 
talus  (facies  articularis  calcanei  anterior).  The  lateral  side  of  the  upper  surface 
of  the  anterior  extremity  of  the  bone  is  rough,  and  to  this  is  attached  the  origin 
of  the  short  extensor  muscle  of  the  toes. 

The  inferior  surface  of  the  bone  is  slightly  concave  from  before  backwards,  and 
convex  from  side  to  side.  The  under  aspect  of  the  tuberosity  is  provided  with  two 
tubercles,  a  medial  (processus  medialis  tuberis  calcanei)  and  a  lateral  (processus 
lateralis  tuberis  calcanei),  of  which  the  former  is  the  larger.  From  this  the  short 
flexor  of  the  toes  and  the  abductor  hallucis  muscle  arise,  whilst  from  both  tubercles 


244 


OSTEOLOGY. 


Facets  foe  talus  or  astkagalus 


Sulcus 
calcanei 


PERU^EAL  SPINE 


Lateral  process 


c 


C.  Seen  from  the  Lateral  Side. 


Facets  for  talus  or  astraoalur 


spring  the  fibres  of  origin  of  the  abductor  digiti  quinti  muscle.  On  the  fore-part  of 
the  under  surface  there  is  an  elevated  elongated  tubercle,  which  terminates  some- 
what abruptly  just  behind  the  anterior  border  of  this  aspect  of  the  bone,  giving 
rise  at  times  to  a  notch.  From  the  former  spring  the  fibres  of  the  long  plantar 
ligament,  \Yhilst  the  latter  serves  for  the  attachment  of  the  deeper  fibres  of  the 
short  plantar  ligament.  The  two  heads  of  origin  of  the  quadratus  plantse  muscle 
arise  from  the  bone  on  either  side  of  the  long  plantar  ligament.  The  medial 
surface  of  the  calcaneus  is  crossed  obliquely,  from  above  downwards  and  forwards, 
by  a  broad  groove  of  considerable  depth ;  along  this  pass  many  of  the  structures 
which  enter  the  sole  of  the  foot  from  the  back  of  the  leg.     The  groove  is  overhung 

in  front  and  above  by  a  pro- 
jecting bracket -like  process, 
called  the  sustentaculum  tali. 
The  under  surface  of  the  sus- 
tentaculum is  channelled  by  a 
groove,  in  which  is  lodged  the 
tendon  of  the  flexor  hallucis 
longus  muscle;  whilst  its  medial 
border,  to  which  is  attached  a 
part  of  the  internal  lateral 
(deltoid)  ligament  (tibio-cal- 
canean  fibres)  of  the  ankle,  is 
overlain  by  the  tendon  of  the 
flexor  digitorum  longus.  To 
the  anterior  border  of  the 
sustentaculum  is  attached  the 
plantar  calcaneo-navicular  liga- 
ment, and  placed  on  its  upper 
surface  is  the  articular  facet 
already  alluded  to  (fades  articu- 
laris  media).  Posteriorly  the 
medial  surface  of  the  bone  is 
limited  inferiorly  by  the  pro- 
jection of  the  medial  tubercle, 
and  above  by  the  medial  lipped 
edge  of  the  tuberosity. 

The  lateral  surface,  broad 
behind  and  narrower  in  front, 
is  of  flattened  form.  Springing 
from  it,  just  below  the  outer 
end  of  the  sinus  tarsi,  is  the 
peroneal  spine  (processus  troch- 
learis),  often  indistinctly 
marked.  To  this  the  fibres  of 
the  lateral  annular  ligament 
are  attached  ;  whilst  in  grooves, 
above  and  below  it,  pass  the 
tendons  of  the  perontcus  brevis  and  longus  muscles  respectively.  To  the  upper 
and  back  part  of  this  surface  are  attached  the  tiljres  of  the  middle  fasciculus  of  the 
external  lateral  ligament  of  the  ankle. 

The  anterior  extremity,  sometimes  called  the  greater  process,  is  furnished  with  a 
saddle-shaped  surface  on  its  anterior  aspect  for  articulation  with  the  cuboid.  This 
facet  is  concave  from  above  downwards,  and  slightly  convex  from  side  to  side ;  its 
edges  are  sharply  defined,  except  medially,  and  serve  for  the  attachment  of 
ligaments. 

The  posterior  extremity,  called  the  tuberosity  (tulier  calcanei),  forms  the 
projection  of  the  heel.  Of  oval  form  and  rounded  surface,  it  rests  upon  the  two 
tubercles  inferiorly  and  is  divisible  into  three  areas.  Of  these  the  highest  is  smooth 
and  crescentic,  and  is  covered  by  a  bursa ;   the  intermediate  is  also  fairly  smooth, 


SrSTENTACbLUM 

tali 


Groo\  e  for 
flex.  hallucis 

LONGUS 


Lateral  process 
D 
D.  Seen  from  the  Medial  Side. 
Fig.   ISOh. — The  RuiHT  Calcaneus. 


AIedi  \l  PROcrss 


THE  CUNEIFOEM  BONES. 


245 


and  is  defined  inferiorly  by  an  irregular  line,  sometimes  a  definite  ridge,  the  edges 
of  which  are  striated.  Into  this  surface  the  tendo  calcaneus  is  inserted.  The  lowest 
surface  is  rough  and  striated,  and  is  confluent  below  with  the  medial  and  lateral 
tubercles ;  this  is  overlain  by  the  dense  layer  of  tissue  which  forms  the  pad  of 
the  heel. 


Second  cuneiform 


Third 
cuneiform 


The  Navicular  Bone. 

The  navicular  or  scaphoid  bone,  of  compressed  piriform  shape,  is  placed  on 
the  medial  side  of  the  foot,  between  the  head  of  the  talus  posteriorly  and  the 
three  cuneiform  bones  anteriorly.  The  bone  derives  its  name  from  the  oval  or 
boat-shaped  hollow  on  its  proximal  surface,  which  rests  upon  the  head  of  the 
talus.  Its  distal  aspect  is  furnished  with  a  semilunar  articular  area,  which  is  sub- 
divided by  two  faint  ridges  into  three  wedge-shaped  facets  for  articulation,  from 
within  outwards,  with  the  first,  second,  and  third  cuneiform  bones.  The  dorsal 
surface  of  the  bone, 
convex  from  side  to 
side,  is  rough  for  the 
attachment  of  the  liga- 
ments on  the  dorsal 
aspect  of  the  foot.  On 
its  plantar  aspect  the 
bone  is  irregularly  con- 
cave ;  projecting  down- 
wards and  backwards 
from  its  lateral  side 
there  is  often  a  pro- 
minent spur  of  bone, 
the  inferior  navicular 
tubercle  or  plantar 
point  (processus  plantaris),  to  which  is  attached  the  plantar  calcaneo  -  navicular 
ligament.  The  lateral  surface  is  narrow  from  before  backwards,  and  rounded 
from  above  downwards.  In  70  per  cent  of  cases  (Manners  Smith)  it  is  provided 
with  a  facet  which  rests  upon  a  corresponding  area  on  the  cuboid.  Behind  this 
in  rare  instances  there  is  a  facet  for  the  calcaneus.  The  tibial  surface  of  the 
bone  projects  beyond  the  general  line  of  the  medial  border  of  the  foot,  so  as  to 
form  a  thick  rounded  tuberosity  (tuberositas  oss.  navicularis),  the  position  of  which 
can  be  easily  determined  in  the  living.  To  the  medial  and  under  surface  of  this 
process  an  extensive  portion  of  the  tendon  of  the  tibialis  posterior  muscle  is 
inserted. 


Tuberosity 


For  head  of  talus  q 

A  B 

Fig.  181. — The  Right  Navicular  Bone. 

A.  Seen  from  Behind.     B.  Seen  from  the  Front. 


The  Cuneiform  Bones. 

The  cuneiform  bones,  three  in  number,  are  placed  between  the  navicular 
posteriorly  and  the  bases  of  the  first,  second,  and  third  metatarsal  bones  anteriorly, 
for  which  reason  they  are  now  named  the  first,  second,  and  third  cuneiforms, 
or,  from  their  position,  internal,  middle,  and  external.  More  or  less  wedge- 
shaped,  as  their  name  implies,  the  first  or  internal  is  the  largest,  whilst  the  second 
or  middle  is  the  smallest  of  the  group.  Combined,  they  form  a  compact  mass, 
the  proximal  surface  of  which,  fairly  regular  in  outline,  rests  on  the  anterior 
surface  of  the  navicular ;  whilst  in  front  they  form  a  base  of  support  for  the 
three  inner  metatarsals,  the  outline  of  which  is  irregular,  owinir  to  the  base  of  the 
second  metatarsal  bone  being  recessed  between  the  first  and  thiid  cuneiforms 
as  it  articulates  with  the  distal  extremity  of  the  shorter  second  cuneiform. 

The  first  or  internal  cuneiform  bone,  the  largest  of  the  three,  Lies  on  the 
medial  border  of  the  foot  between  the  base  of  the  metatarsal  bone  of  the  great 
toe  in  front,  and  the  fore  and  medial  part  of  the  navicular  behind.  In  form 
the  bone  is  less  characteristically  wedge-shaped  than  those  of  its  fellows  of  the 
same  name,  and  differs  from  them  in  this  respect,  that  whilst  the  second  and  third 

16 


2^:6 


OSTEOLOGY. 


II.  Metatarsal 


I.    MeI  \.T  iRSAL 


III.   Mfc-r\T4.RS\L 


cuneiforms  are  so  disposed  that  the  bases  of  their  wedges  are  directed  upwards 
towards  the  dorsum  of  the  foot,  the  first  cuneiform  is  so  placed  that  its  base  is 
directed  towards  the  plantar  aspect ;  further,  the  vertical  diameter  of  the  bone  is  not 
the  same  throughout,  but  is  much  increased  at  its  anterior  or  distal  end.     The 

dorsal  and  medial  surfaces  are  confluent,  and 
form  a  convexity  from  above  downwards,  which 
is  most  pronounced  inferiorly,  where  it  is  turned 
to  become  continuous  with  the  plantar  or  inferior 
aspect,  which  is  rough  and  irregular  round  the 
plantar  side  of  the  foot.  On  the  fore-part  of 
the  medial  aspect  of  the  bone  there  is  usually  a 
distinct  oval  impression,  which  indicates  the 
surface  of  insertion  of  a  portion  of  the  tendon 
of  the  tibialis  anterior  muscle.  Elsewhere  this 
surface  is  rough  for  ligamentous  attachments. 
The  lateral  surface  of  the  bone,  quadrilateral  in 
shape,  is  directed  towards  the  second  cunei- 
form; but  as  it  exceeds  it  in  length,  it  also 
comes  in  contact  with  the  medial  side  of  the 
base  of  the  second  metatarsal  bone.  Eunning  along  the  posterior  and  upper 
edges  of  this  area  is  an  r-shaped  articular  surface,  the  fore  and  upper  part  of 
which  is  for  the  base  of  the  second  metatarsal  bone,  the  remainder  articulating 
with  the  medial 
side  of  the  second 
cuneiform.  The 
non-articular  part 
of  this  aspect  of 
the  bone  is  rough 
for  the  attachment 
of  the  strong  inter- 
osseous ligaments 
which  biud  it   to    impression 

, -l  n  •  FOR  TENDON 

the  second  cunei 


Fig.  182. — Anterior  View  of  the  three 
Cuneiform  Bones  of  the  Right  Foot. 


II.  Metatarsal 


Second  cuneiform 


OF  TIBIALIS' 
ANTERIOR 


Fig.  183.— The  Right  First 
Cuneiform  (Medial  Side). 


Fig.  184. — The  Eight  First 

Cuneiform  (Lateral  Side). 


II.  First 

Metatarsal  cuneiform 


form  and  second 
metatarsal  bones 
respectively.  The 
proximal  end  of  the 

bone  is  provided  with  a  piriform  facet  which  fits  on  the  medial  articular  area  of 
the  navicular.  Here  the  wedge-shaped  form  of  the  bone  is  best  displayed. 
Distally  the  vertical  diameter  of  the  bone  is  much  increased,  and  the  facet  for  the 

base  of  the  metatarsal  bone  ol  the  great 
Third  CUNEIFORM  ^^^  -^  consequently  much  larger  than 
that  for  the  navicular.  This  metatarsal 
facet  is  usually  of  semilunar  form,  but  not 
y_  \  m¥'^7mssm;']  infrequently  is  more  reniform  in  shape, 
and  may  iu  some  cases  display  complete 
separation  into  two  oval  portions. 

The  second  or  middle  cuneiform  is 

of  a   typical  wedge   shape,  the   base   of 

II.  Metatarsal  ^^^    wcdgc   being   directed   towards    the 

Fig.  185  6.— The  Right  dorsum  of   the    foot ;    shorter   than   the 

Second   Cuneiform  f^^Y^Qy,^^  ^^  Hq^  between  them,  articulating 

(Lateral  Side).  ^.^^  ^^^  ^^^^  ^^  ^j^^  second  metatarsal 

in  front,  and  the  middle  facet  on  the  anterior  surface  of  the  navicular  behind. 
Its  dorsal  surface  which  corresponds  to  the  base  of  the  wedge,  conforms  to  the 
roundness  of  the  instep,  and  is  slightly  convex  from  side  to  side,  affording  attach- 
ments f.jr  the  dorsal  ligaments.  Its  plantar  aspect  is  narrow  and  rough,  forming  the 
edge  of  the  wedge;  with  this  the  plantar  ligaments  are  connected.  The  medial  surface, 
quadrilateral  in  outline,  is  furnished  with  an    T-shaped   articular  area  along  its 


Fig.  18.5  «.— The  Right 
Sec(jnu  Cuneiform 
(Medial  Side). 


THE  CUBOID  BONE. 


247 


Second  cuneiform 


Cdboid        IV.  Metatarsal 


posterior  and  superior  borders  in  correspondence  with  the  similar  area  on  the  lateral 
side  of  the  first  cuneiform.  The  rest  of  this  aspect  is  rough  for  ligaments. 
The  lateral  side  displays  a  facet  arranged  along  its  posterior  border,  and  usually 
somewhat  constricted  in  the  middle;  tliis  is  fur  the  third  cuneiform.  In  front 
of  this  the  bone  is  rough  for  the  interosseous  ligaments,  which  bind  the  two  bones 
together.  The  proximal  end  is  provided  with  a  triangular  facet  slightly  concave 
from  above  downwards ;  this  rests  on  the  central  articular  surface  on  the  anterior 
aspect  of  the  navicular.  In  front  the  bone  articulates  by  means  of  a  wedge- 
shaped  facet  with  the  base 
of  the  metatarsal  bone  of  the 
second  toe. 

The  third  or  external 
cuneiform,  intermediate  in 
size  between  the  first  and 
second,  is  also  of  a  fairly 
typical  wedge  shape ; 
though  its  antero-posterior 
axis  is  not  straight  but  bent, 
so  that  the  distal  end  of  the 
bone  turns  slightly  medially. 
Its  dorsal  surface,  which  corresponds  to  the  base  of  the  wedge,  is  slightly  convex 
from  side  to  side,  and  provides  attachments  for  the  dorsal  ligaments.  Its  inferior 
or  plantar  aspect  forms  a  rough  blunt  edge,  and  serves  for  the  attachment  of 
the  plantar  ligaments.  Its  medial  side,  of  quadrilateral  form,  displays  two  narrow 
articular  strips,  placed  along  its  distal  and  proximal  borders  respectively,  each 
somewhat  constricted  in  the  middle.  The  distal  articulates  with  the  lateral 
side  of  the  base  of  the  second  metatarsal  bone,  the  proximal  with  the  lateral 
side  of  the  second  cuneiform.  The  rough  non-articular  surface,  which  separates 
the  two  elongated  facets,  serves  for  the  attachment  of  ligaments.  The  lateral 
aspect  of  the  bone  is  characterised  by  a  large  circular  or  oval  facet,  placed  near 
its  proximal  border,  for  articulation  with  the  cuboid ;  in  front  of  this  the  distal 
border  is  lipped  above  by  a  small  semi-oval  facet  for  articulation  with  the  medial 
side  of  the  base  of  the  fourth  metatarsal.  The  rest  of  the  bone  around  and 
between  these  facets  is  rough  for  ligaments.  Proximally  the  bone  is  furnished  with 
a  blunt,  wedge-shaped  facet  for  articulation  with  the  corresponding  area  on  the 
front  of  the  navicular.  Below  this  the  surface  is  narrow  and  rough  for  the  attach- 
ment of  ligaments.  The  distal  end  of  the  bone  articulates  with  the  base  of  the 
third  metatarsal  by  a  surface  of  triangular  shape. 


Fig.  186  a. — Right  Third 
Cuneiform  (Medial  Side). 


Fig.  186  6.— Right  Third 
Cuneiform  (Lateral  Side). 


The  Cuboid   Bone. 

The  cuboid  lies  on  the  lateral  side  of  the  foot,  about  its  middle,  articulating 
with  the  calcaneus  behind  and  the  fourth  and  fifth  metatarsal  bones  in  front. 
Its  dorsal  surface,  plane  in  an  antero-posterior  direction,  is  slightly  rounded  from 
side  to  side,  and  provides  attachment  for  ligaments.  Its  plantar  aspect  is  tra- 
versed obliquely  from  without  medially  and  forwards  by  a  thick  and  prominent 
ridge,  the  lateral  extremity  of  which,  at  the  point  where  it  is  confluent  with  the 
outer  surface,  forms  a  prominent  tubercle  (tuberositas  oss.  cuboidei),  the  anterior 
and  lateral  surface  of  which  is  smooth  and  facetted  to  allow  of  the  play  of 
a  sesamoid  bone  which  is  frequently  developed  in  the  tendon  of  the  peronaeus 
longus  muscle.  In  front  of  this  ridge  there  is  a  groove  (sulcus  peronsei)  in 
which  the  tendon  of  the  peronseus  longus  muscle  is  lodged  as  it  passes  across  the 
under  surface  of  the  bone.  Behind  the  ridge  the  bone  is  rough,  and  serves  for 
the  attachment  of  the  short  plantar  ligament,  the  superficial  fibres  of  which  pass 
forwards  and  are  attached  to  the  summit  of  the  ridge.  The  lateral  aspect  of  the 
bone  is  short  and  rounded,  and  is  formed  by  the  confluence  of  the  superior  and  in- 
ferior surfaces  ;  it  is  more  or  less  notched  by  the  peroneal  groove  which  turns  round 
its  lower  edge.     The  medial  surface  of  the  bone  is  the  most  extensive ;  it  is  easily 


248 


OSTEOLOGY. 


recognisable  on  account  ot  the  presence  of  a  rounded  or  oval  facet  situated  near 
its  middle  and  close  to  its  upper  border.  This  is  for  articulation  with  the  lateral 
side  of  the  third  cuneiform  ;  in  front  and  behind  this  the  surface  is  rough  for 
ligaments.     Not  infrequently  behind  the  facet  for  the  third  cuneiform  there  is  a 

small  articular 


Tuberosity 


Groove  for  peron/eus 

LONG OS 

A 


Fig.  187. — Thk  Right  Cuboid  Bone. 
Lateral  Side.  B.  Medial  Side 


Navicular 
Third  Cuneiform  (occasional) 


surface  for  the 
navicular,  as  is  the 
case  normally  in 
the  gorilla,  whilst 
behind  and  below, 
the  projecting  in- 
ferior angle  is 
sometimes  pro- 
vided with  a  facet 
on  which  the  head 
of  the  talus  rests 
(Sutton,  "  Proc. 
Anat.  Soc,"  Jour. 
The  distal  surface  is  oval  or  conical  in  outline  ; 


..'  Groove  for  Tuberosity 

per0n.eu8  longus 


Anat.  and  Physiol.,  vol.  xxvi.  p.  18) 
sloping  obliquely  from  within  laterally  and  backwards,  it  is  divided  about  its 
middle  by  a  slight  vertical  ridge  into  two  parts,  the  medial  of  which  articulates 
with  the  base  of  the  fourth  metatarsal  bone,  the  lateral  with  that  of  the  fifth.  The 
proximal  surface,  also  articular,  has  a  semilunar  outline,  the  convex  margin  of  which 
corresponds  to  the  dorsal  roundness  of  the  bone.  The  inferior  lateral  angle  corre- 
sponds to  the  tubercle  on  the  lateral  border  of  the  bone,  whilst  the  inferior  medial 
angle  forms  a  pointed  projection  which  is  sometimes  called  the  calcanean  process. 
This  surface  articulates  with  the  calcaneus  by  means  of  a  saddle-shaped  facet, 
which  is  convex  from  side  to  side,  and  concave  from  above  downwards. 

The  tarsus  as  a  whole  may  be  conveniently   described   as   arranged   in    two 


^^^^. 


Fig.  188. — Radiographs  of  the  Fcetal  Foot. 

1.  Aljout  fifth  luoutli.     No  ossification  in  the  tarsus  visible. 

2.  About  sixth  month.     Appearance  of  a  nucleus  for  the  calcaneus. 

3.  About  seventh  month.     Nucleus  for  calcaneus  well  developed. 

4  and  5.  About  eighth  month.     Centres  for  talus  and  calcaneus  now  seen. 

6.   About  birth.      Centres  for  the  talus  and  calcaneus  are  well  developed,  there  is  also  a  considerable  centre 
for  the  cuboid,  and  the  appearance  of  a  centre  for  the  third  cuneiform  is  now  displayed. 

columns ;  the  medial,  corresponding  to  the  medial  border  of  the  foot,  comprising 
the  talus,  navicular,  and  tliree  cuneiforms,  and  forming  a  base  for  the  support  of 
the  three  medial  metatarsal  bones  and  their  phalanges.  The  lateral  column, 
formed  by  the  calcaneus  and  cuboid,  supports  the  fourth  and  fifth  metatarsal  bones 
together  with  their  phalanges.     The  superior  surface  of  the  anterior  portion  of  the 


THE  METATARSUS. 


249 


tarsus  determines  the  side-to-side  roundness  of  the  instep,  whilst  its  under  surface 
forms  arches  in  both  a  transverse  and  longitudinal  direction,  in  which  the  softer 
tissues  of  the  sole  are  lodged,  and  so  protected  from  injury. 

Ossification. — Unlike  the  carpus,  the  tarsus  is  at  birth  partially  ossified.  At  this 
period  there  is  a  well-marked  osseous  nucleus  within  the  body  and  neck  of  the  talus, 
and  the  calcaneus  is  extensively  ossified.  In  the  latter  the  deposition  of  earthy  matter 
appears  as  early  as  the  sixth  mouth  of  foetal  life,  whilst  in  the  talus  the  ossific  centre 
makes  its  appearance  in  the  later  weeks  of  gestation.     Shortly  before  or  after  birth  the 


Fig. 


189  «. — Radiograph  of  the  Hand 
AT  Birth. 


Fig. 


189  6. — Radiograph  of  the  Foot 
AT  Birth. 


It  will  be  noticed  that  whilst  the  primary 
centres  for  the  metacarpus  and  phalanges 
are  well  ossified,  the  carpixs  is  still 
entirely  cartilaginous. 


The  centres  of  ossification  for  the  calcaneus 
and  talus  are  well  developed,  the  nucleus  for 
the  cuboid  is  quite  distinct,  and  in  this  instance 
the  third  cuneiform  is  already  commencing 
to  ossify. 


cuboid  begins  to  ossify,  succeeded  early  in  the  first  year  by  the  third  cuneiform,  followed 
in  order  by  the  second  cuneiform,  first  cuneiform,  and  navicular.  The  ossific  centre 
of  the  latter  appears  at  the  third  year  or  somewhat  later.  An  epiphysis,  which  forms  a 
cap  over  the  extremity  of  the  tuberosit}^  of  the  calcaneus,  appears  from  the  seventh  to  the 
ninth  year,  and  fusion  is  completed  between  the  ages  of  sixteen  and  twenty. 

To  emphasize  the  different  conditions  which  obtain  in  the  wrist  and  ankle,  at,  and  for 
some  time  after  birth,  drawings  of  I'adiographs  of  both  are  given. 


The   Metatarsus. 

The  metatarsal  bones,  five  in  number,  in  their  general  configuration  resemble 
the  metacarpus.  They  are,  however,  slightly  longer,  their  bases  are  proportionately 
larger,  their  shafts  more  slender  and  laterally  compressed,  and  their  heads  propor- 
tionately smaller.  They  are  named  numerically  the  first,  second,  third,  fourth,  and 
fifth  metatarsal  bones,  in  order  from  the  tibial  to  the  fibular  side.  The  first  can 
be  readily  recognised  on  account  of  its  stoutness ;  it  is  also  the  shortest  of  the 
series.  The  second  is  the  longest  of  the  five,  and  the  fifth  can  easily  be  dis- 
tinguished by  the  projecting  tubercle  at  its  base. 


250 


OSTEOLOGY. 


Grooves  for  sesamoid  bones 


Shaft 


The  first  metatarsal  or  metatarsal  bone  of  the  great  toe,  the  shortest  of  the 
series,  is  reuiarkable  for  its  stoutness.     Its  proximal  end  or  base,  where  the  bone 

is  provided  with  a  reniform  facet  for  articula- 
tion with  the  first  cuneiform,  is  wider  from  the 
dorsal  to  the  plantar  aspect  than  from  side  to 
side.  The  concavity  of  the  kidney -shaped  arti- 
cular area  is  directed  to  the  fibular  side.  As  a 
rule  the  lateral  aspects  of  the  base  are  non-arti- 
cular, though  occasionally  on  its  outer  side  there 
is  a  "pressure"  facet  for  the  base  of  the  second 
metatarsal  bone.  The  inferior  basal  angle  pro- 
jects backwards  and  laterally,  and  forms  a  pro- 
minent tubercle  which  is  pitted  for  the  insertion 
of  the  tendon  of  the  peronteus  longus  muscle, 
whilst  its  tibial  margin  is  lipped  by  a  surface 
for  the  attachment  of  part  of  the  tendon  of  the 
tibialis  anterior.  The  shaft,  short,  thick,  and  pris- 
matic on  section,  tapers  rapidly  towards  the  head, 
the  fore  and  under  surfaces  of  which  are  articular. 
The  former  is  convex  from  side  to  side,  and  from 
above  downwards,  and  supports  the  proximal 
phalanx.  It  is  confluent  below  with  the  inferior 
articular  surface,  which  is  divided  by  a  median 
ridge  into  two  shallow  grooves,  of  which  the  tibial 
is  the  wider.  In  these  grooves  are  lodged  the 
two  sesamoid  bones  which  underlie  the  metatarso- 
phalangeal joint.  On  either  side  of  the  head,  the  bone  is  pitted  for  the  strong 
lateral  ligaments  of  the  joint. 

The  second  metatarsal,  the  longest  of  the  series,  has  a  base  of  wedge-shaped 


Base 


TuBEROSiTV      Tibialis  anterior 

Fig.  190.  —  The  First  Metatarsal 
Bone  of  the  Right  Foot  (Plantar 
Aspect). 


Shaft 


I.  Metatarsal' 
(pressure  facet) 


II.  Metatarsal^ 


11.  METATARSAL 


First 
cuneiform 


Til.  Metatarsal 


III.  METATARSAL 


IV.  Metatarsal 


IV.  METATARSAL 


Third  cuneiform 

33R 


in.  Metatarsal 


A.  Medial  sides 


V.  Metatarsal 

B.  Lateral  sides 


Fig.   191. — View  of  the  Bases  and  Shafts  of  the  Second,  Third,  and  Fourth  Metatarsal  Bones 

OP  the  Right  Foot. 


form,  the  proximal  aspect  of  which  articulates  with  the  second  cuneiform.      On 
its  tibial  aspect,  near  its  superior  edge,  there  is  a  small  circular  facet  for  the  first 


THE  PHALANGES. 


251 


Its  proximal  aspect 


cuneiform;  below  and  in  front  of  this  there  is  sometimes  a  tubercle  with  a 
"  pressure "  facet  on  it,  where  the  bone  comes  in  contact  with  the  base  of  the 
first  metatarsal.  On  the  fibular  side  of  the  base  there  is  one,  more  usually  two 
small  facets,  each  divided  into  two  parts,  a  proximal  for  articulation  with  the 
third  cuneiform,  and  a  distal  for  the  base  of  the  third  metatarsal."  The  shafts 
of  this  and  the  three  succeeding  bones  are  slender  and  laterally  compressed. 
The  heads  are  small  and  narrow,  and  display  a  pronounced  side-to-side  and 
vertical  convexity. 

The  third  metatarsal  bone  also  possesses  a  base  of  wedge-shaped  form, 
the  proximal  surface  of  which  articulates  with  the  third  cuneiform.  On  its 
tibial  side  it  is  provided  with  one,  more  usually  two,  small  facets,  for  articu- 
lation with  the  base  of  the  second  metatarsal.  Laterally  the  base  has  a  larger 
facet  for  articulation  with  the  base  of  the  fourth  metatarsal,  more  or  less  conical 
in  outline,  and  having  its  lower  edge  sharply  defined  by  a  narrow  groove  which 
underlies  it. 

The  fourth  metatarsal  has  a  base  more  cubical  in  shape, 
articulates  with  the  cuboid,  whilst  medially  an  elongated 
oval  facet,  divided  by  a  slight  vertical  ridge,  provides  sur- 
faces for  articulation  with  the  third  metatarsal  in  front  and 
the  lateral  side  of  the  first  cuneiform  behind.  On  the  lateral 
side  there  is  a  demi-oval  facet,  bearing  a  slightly  saddle- 
shaped  surface,  for  articulation  with  the  tibial  side  of  the 
base  of  the  fifth  metatarsal. 

The  fifth  metatarsal  can  be  readily  recognised  by 
the  peculiar  shape  of  its  base,  from  the  lateral  side  of 
which  there  projects  backwards  and  laterally  a  pro- 
minent tubercle  (tuberositas  oss.  metacarpi  quinti).  To  the 
hinder  extremity  of  this  is  attached  the  tendon  of  the 
peroneeus  brevis  muscle.  To  its  dorsal  surface  the  tendon  of 
the  peronseus  tertius  is  inserted,  whilst  its  plantar  surface 
provides  an  origin  for  the  flexor  digiti  quinti  brevis  muscle. 
The  tibial  surface  of  the  base  is  provided  with  a  demi-oval, 
slightly  concave  facet,  for  the  lateral  side  of  the  base  of  the 
fourth  metatarsal,  whilst  proximally  it  articulates  with  the 
cuboid  by  means  of  a  semicircular  facet. 

Vascular  Foramina. — The  canals  for  the  nutrient  vessels  open, 
as  a  rule,  on  the  plantar  aspects  of  the  middle  of  the  shafts.  Those  of 
the  outer  metatarsals  are  directed  towards  the  bases  of  the  bones,  whilst 
that  for  the  metatarsal  of  the  great  toe  passes  towards  its  head. 

Ossification. — In  correspondence  with  the  mode  of  ossification  which  obtains  in 
the  metacarpus,  the  primary  centres  for  the  metatarsus  appear  as  early  as  the  third 
month  of  foetal  life.  In  the  case  of  the  second,  third,  fourth,  and  fifth,  these  centres 
furnish  the  bases  and  shafts  of  the  bones,  the  heads  being  developed  from  secondary 
centres  which  appear  from  two  to  four  years  after  birth,  fusion  with  the  shaft  being 
usually  completed  about  the  eighteenth  year.  In  striking  contrast  to  this  is  the  mode 
of  ossification  of  the  first  metatarsal.  From  its  primary  centre  the  head  and  shaft  is 
developed ;  the  secondary  centre  appears  at  its  base  about  the  second  or  third  year, 
and  fuses  with  the  shaft  about  eighteen.  In  this  respect,  therefore,  the  metatarsal  bone 
of  the  great  toe  resembles  in  its  mode  of  development  the  phalanges.  Mayet,  however 
{Bull.  Soc.  Anat.  Paris,  1895),  describes  the  occurrence  of  two  ossific  centres  in  the 
proximal  epiphysis.  These  fuse  early,  and  he  considers  that  the  one  represents  the 
metatarsal  element,  whilst  the  other  may  be  regarded  as  phalangeal  in  its  origin. 


ClBoIi 


Peronaus  brevis 


Fig.  192. — Fifth  Right 
Metatarsal  Bone 
(Dorsal  Aspect). 


The  Phalanges. 

The  phalanges  of  the  toes  (phalanges  digitorum  pedis)  differ  from  those  of  the 
fingers  in  the  striking  reduction  of  their  size,  and  in  the  case  of  the  bones  of  the 
first  row,  in  the  lateral  compression  of  their  shafts.  Each  toe  is  provided 
normally  with  three  phalanges,  except  the  great  toe,  which  has  only  two.      In 


252 


OSTEOLOGY 


III.  Ungual' 
OR  terminal' 

PHALANX 


11.  Phalanx 


their  general  configuration  and  in  the  arrangement  of  their  articular  facets  they 
resemble  the  digital  phalanges,  though  owing  to  the  reduction  in  their  size,  the 
shafts,  particularly  those  of  the  second  row,  are  often  so  compressed  longitudin- 
ally as  to  reduce  the  bone  to  a  mere  nodule.  The 
proximal  end  of  each  of  the  bones  of  the  first  row  is  pro- 
portionately large,  and  is  provided  with  a  simple  hollow  in 
which  the  head  of  the  metatarsal  bone  rests ;  the  distal 
ends  are  furnished  with  condyloid  surfaces.  The  proximal 
extremities  of  the  second  row  are  each  provided  with  two 
small  concavities,  separated  by  a  slight  ridge  for  articulation 
with  the  condyles  of  the  first  row.  The  joint  between  the 
second  and  third  row  displays  the  same  arrangement — the 
third,  terminal  or  ungual  phalanx,  being  easily  distinguished 
by  the  spatula-shaped  surface  at  its  extremity  on  which 
the  bed  of  the  nail  is  supported. 

The  phalanges  of  the  great  toe,  two  in  number,  differ 
from  the  others  in  their  size  and  length.  Into  the  base  of 
the  first  phalanx  are  inserted  the  short  muscles  of  the  great 
toe,  whilst  the  second  phalanx  receives  on  its  plantar  aspect 
the  insertion  of  the  flexor  hallucis  longus  muscle,  the  tendon 
of  the  extensor  hallucis  longus  being  inserted  into  the 
dorsal  aspect. 

Ossification. — Each  phalanx  is  developed  from  two  centres 
— one  primary  for  the  shaft  and  distal  extremity,  the  other  for 
the  epiphysis  on  the  proximal  end.  The  primary  centres  for  the 
ungual  phalanges  are  the  first  to  appear,  commencing  to  ossify 
from  the  eleventh  to  the  twelfth  week  of  fcetal  life.  The  centre  for  the  ungual  phalanx 
of  the  great  toe  makes  its  appearance  before  that  of  its  corresponding  metatarsal  bone. 
The  primary  centres  for  the  phalanges  of  the  first  row  appear  from  the  fourteenth 
to  the  sixteenth  week.     The  primary  centres  for  the  middle  phalanges  of  the  second  and 


I.  Phalanx 


Metatarsal 


Fig.  193.— The  Phalanges 
OF  THE  Toes  (Dorsal 
Aspect). 


I 


-m: 


Fig.  194. 

A.  Aliout  the  end  of  the  third  month.  The  primary  centres  of  all  the  metacarpus  are 
shown  as  well  as  the  centres  for  the  phalanges  of  the  great  toe  and  the  terminal 
phalanx  of  the  third  toe. 

B.^  A  little  later.  Tlie  centres  for  the  terminal  phalanges  of  the  four  inner  toes  are 
seen,  as  well  as  the  centres  for  the  first  phalanges  of  the  great  and  second  toe. 

C.  About    the    fourth    mouth.      The    centres  for    all    the   terminal  phalanges  as   well    as 

those  of  the  first  row  are  well  ossified. 

D.  About  the  fifth  month.      In  this  the  centre  for  the  second  phalanx  of  the  second  toe  has 

already  made  its  appearance. 

1  ITiis  specimen  displays  the  occurrence  of  anomalou.s  centres  within  llie  tarsus  the  .significance  of 
which  is  not  apparent.  The  appearance  is  not  due  to  any  delect  in  tlie  plate,  but  recurred  in  repeated 
radiographs. 


third  toes  begin  to  ossify  about  the  sixth  month,  those  for  the  fourth  and  fifth  toes  not 
till  later — the  shaft  of  the  middle  phalanx  of  the  fourth  toe  being  frequently  cartilaginous 
at  birth,  the  normal  condition  in  the  case  of  the  fifth  toe  (Lambertz).  The  proximal 
epiphyses  do  not  begin  to  ossify  until  about  the  fourth  year,  and  are  usually  fused  with 
the  diaphyses  about  the  age  of  sixteen  or  eighteen.  Union  between  the  shafts  and 
epiphyses  of  the  first  row  precedes  that  of  the  second  and  third  rows. 


SESAMOID  BONES.  253 


Sesamoid  Bones. 

As  in  the  hand,  small  independent  nodules  of  bone,  called  sesamoid  bones,  are  met 
with  in  the  ligaments  and  tendons  of  the  foot.  The  most  constant  of  these  are  found  in 
connexion  with  the  metatarso-phalangeal  articulation  of  the  great  toe,  where  they  lie  in 
grooves  on  the  under  surface  of  the  head  of  the  metatarsal  bone  in  connexion  with  the 
tendons  of  the  short  muscles  of  the  great  toe.  Small  osseous  nodules  occupying  a 
corresponding  position  are  occasionally  met  with  in  the  other  toes,  and  instances  have 
been  recorded  of  like  ossicles  occurring  on  the  plantar  aspect  of  the  interphalangeal  joint 
of  the  great  toe. 

An  osseous  nodule  is  not  infrequently  met  with  in  the  tendon  of  the  peronpeus  longus 
as  it  turns  round  the  lateral  box'der  of  the  foot  to  lie  in  the  groove  on  the  under  surface  of 
the  cuboid. 


17 


APPENDIX   TO   THE   SECTION   ON   OSTEOLOGY. 


A.  Architecture  of  the  Bones  of  the  Skeleton. 

B.  Variations  in  the  Skeleton. 

C.  Serial  Homologies  of  the  Vertebrae. 

D.  Measurements  and  Indices  employed  in  Physical  Anthropology. 

E.  Development  of  the  Chondro-Cranium  and  Morphology  of  the  Skull. 

F.  Morphology  of  the  Limbs. 


of  Fhvti^cians  &  SurFGona, 

APPENDIX   A. 


ARCHITECTURE  OF  THE  BONES  OF  THE  SKELETON. 

The  Vertebrae. — The  vertebra?  are  formed  of  spongy  bone  confined  witliin  a  thin  and  dense 
envelope.  In  the  bodies  the  arrangement  of  the  cancellous  tissue,  wliich  is  traversed  by  venous 
channels,  is  such  as  to  display  a  vertical  striation  with  lamellaj  arranged  horizontally.  The 
lateral,  superior,  and  inferior  walls  are  very  tliin  —  that  directed  to  the  neural  canal  being 
usually  thicker  and  denser  than  the  others.  In  the  pedicles  and  roots  of  the  transvei"se  pro- 
cesses the  cancellous  tissue  is  much  more  open.  The  outer  envelope  is  much  thicker  where  it 
bounds  the  neural  ring,  and  where  it  forms  the  bottom  of  the  superior  and  inferior  intervertebral 
notches.  In  the  laminae  the  spongy  tissue  is  confined  between  two  compact  layers,  of  which 
that  directed  to  the  spinal  canal  is  the  thicker.  In  the  spinous  processes  the  upper  edge 
is  always  the  more  compact. 

The  Sternum  consists  of  large-celled  spongy  bone,  which  is  highly  vascular,  and  is  contained 
between  two  layers  of  thin  compact  tissue. 

The  Ribs. — Each  rib  consists  of  a  curved  and  compressed  bar  of  bone,  the  interior  of  which 
consists  of  highly  vascular  cancellous  tissue  with  an  external  envelope  of  compact  bone.  The 
inner  table  is  much  the  stronger,  attaining  its  maximum  thickness  opi^osite  the  angle — in  front 
and  behind  which  it  becomes  gradually  reduced.  The  outer  table,  much  thinner,  is  stoutest 
opposite  the  angle ;  on  the  posterior  surface  of  the  tubercle  and  neck  it  forms  but  a  thin  layer. 
The  compact  layers  forming  the  upper  and  lower  borders  are  not  so  thick  as  those  forming 
the  inner  and  outer  surfaces.  The  cancellous  tissue,  loose  and  open  in  the  shaft,  is  most  compact 
in  the  region  of  the  head  and  towards  the  anterior  extremity. 

The  Frontal  Bone. — The  frontal  bone  is  composed,  like  the  other  bones  of  the  cranial  vault, 
of  two  layers  of  compact  tissue,  enclosing  between  them  a  layer  of  spongy  cancellous  texture — the 
diploe.  In  certain  definite  situationSj  owing  to  the  absorption  of  this  intermediate  layer,  the 
bone  is  hollow,  forming  the  frontal  air  sinuses.  The  position  and  extent  of  these  is  to  some 
extent  indicated  by  the  degree  of  projection  of  the  suj)erciliary  ridges,  though  this  must  not  be 
taken  as  an  absolutely  reliable  guide,  for  cases  are  recorded  where  the  ridges  were  low  and  the 
sinuses  large,  and  vice  versa.  Of  much  surgical  importance,  these  air-spaces  only  attain  their  full 
development  after  the  age  of  puberty,  being  of  larger  size  in  the  male  than  in  the  female,  a 
circumstance  which  accounts  for  the  more  vertical  appearance  of  the  forehead  in  woman  as  con- 
trasted ^v^th  man.  Usually  two  in  number,  they  are  placed  one  on  either  side  of  the  middle 
line,  and  Jfeommunicate  by  means  of  the  infundibulum  with  the  nasal  fossa  of  the  same  side. 
It  is  exceptional  to  find  the  sinuses  of  opposite  sides  in  communication  with  each  other,  as  they 
are  generally  separated  by  a  complete  partition  which,  however,  is  occasionally  much  deflected 
to  one  or  other  side.  Logan  Turner  ("  On  the  Illumination  of  the  Air  Sinuses  of  the  Skull,  with 
some  Observations  vij^on  the  Surgical  Anatomy  of  the  Frontal  Sinus,"  Edin.  Med.  Jour..,  May  1898) 
gives  the  average  dimensions  of  these  sinuses  as  follows  : — Height,  31  mm.,  i.e.  from  the  fronto- 
nasal aperture  upwards  ;  breadth,  30  mm.,  i.e.  from  the  sejjtum  hoi-izontally  outwards  ;  depth,  17 
mm.,  from  the  anterior  wall  at  the  level  of  fronto-nasal  suture  backwards  along  tlie  orbital  roof. 
Exceptionally  large  sinuses  are  sometimes  met  with  extending  backwards  over  the  orbit  so  as  to 
form  a  double  roof  to  that  space.  There  is  a  specimen  in  the  Oxford  collection  in  which  the 
sinus  is  so  large,  and  extends  so  far  back,  that  the  optic  nerve  is  transmitted  through  it  in  a  bony 
tube.  Another  point  of  some  practical  importance  is  that  the  sinuses  are  hardly  ever  sym- 
metrical. It  is  rare  to  meet  with  cases  of  their  complete  absence,  although  sometimes  the  sinus 
on  one  or  other  side  may  be  wanting. 

The  lateral  angular  process,  from  the  arrangement  of  its  surfaces  and  tlie  density  of  its 
structure,  is  particularly  well  adapted  to  resist  the  pressui-e  to  which  it  is  subjected  when  the 
jaws  are  firmly  closed. 

The  Parietal  Bone. — Thin  towards  its  lower  part,  where  it  enters  into  the  formation  of  the 
temporal  fossa,  it  is  thickest  along  the  superior  border  and  in  the  neighbourhood  of  the  posterior 
superior  angle. 

The  Occipital  Bone. — The  squamous  part  displays  thickenings  in  the  position  of  the  various 
ridge  and  crests,  the  stoutest  part  corresponding  to  the  internal  and  external  occipital  protuberances, 
though  it  should  be  noted  that  the  two  protuberances  do  not  necessarily  coincide,  the  internal 
being,  as  a  rule,  placed  at  a  higher  level  than  the  external     If  the  bone  be  held  up  to  the  light 


ii  OSTEOLOGY. 

it  will  be  at  once  apparent  that  it  is  mucli  thinner  wliere  it  forms  the  floor  of  the  inferior  fossse 
than  in  the  upper  part.  The  basilar  portion  consists  of  a  spongy  core  surrounded  by  a  more 
compact  outer  envelope,  thickest  on  its  lower  surface.  In  the  condj'les  the  spongy  tissue  is 
arranged  radially  to  their  convex  articular  surfaces,  the  hypoglossal  canal  being  surrounded  by 
]»articularly  dense  and  compact  bone,  which  assists  in  strengthening  this  naturally  weak  jaart 
of  the  Ijone. 

The  Temporal  Bone. — The  temporal  bone  is  remarkable  for  the  hardness  and  density  of  its 
petrous  part,  wherein  is  lodged  the  osseous  labyrinth  Avhich  contains  the  delicate  organs  associated 
with  the  senses  of  hearing  and  equilibration.  The  middle  ear  or  tympanum  is  a  cavity  which 
contains  the  small  auditory  ossicles,  and  is  separated  from  the  external  auditory  meatus  by  the 
membrana  tympani.  In  front  it  communicates  with  the  pharynx  by  the  Eustachian  tube  ;  behind, 
it  opens  into  the  mastoid  antrum  and  mastoid  air-cells  by  the  aditus  ad  antrum.  Superiorhj,  it  is 
separated  from  the  middle  cranial  fossa  by  a  thin  plate  of  bone  called  the  tegmen  tympani. 
Inferiorlij,  its  floor  is  formed  in  part  by  the  roof  of  the  jugular  fossa  and  the  carotid  canal. 
Medially,  it  is  related  to  the  structures  which  form  the  inner  ear,  notably  the  cochlea  and 
vestibule,  in  front  of  which  it  is  separated  by  a  thin  plate  of  bone  from  the  carotid  canal. 
Owing  to  the  disposition  of  the  internal  and  external  auditory  canals  the  weakest  part  of  the 
bone  corresponds  to  a  line  connecting  these  two  channels,  the  only  parts  intervening  being  the 
cochlea  and  tympanum.  It  is  usually  in  this  position  that  fracture  of  the  bone  occurs. 
Curving  over  the  cavity  of  the  tympanum  is  the  aquseductus  Fallopii,  the  thin  walls  of 
which  are  occasionally  deficient.  These  details,  together  with  an  account  of  the  tympanic 
ossicles,  will  be  further  dealt  with  in  the  section  devoted  to  the  Organs  of  Sense. 

The  Sphenoid  Bone. — In  the  adult  the  body  of  the  bone  is  hollow  and  encloses  the  sphenoidal 
air-cells,  usually  two  in  number,  separated  by  a  septum.  The  arrangement  and  extent  of  these  air- 
cells  vary  ;  sometimes  they  are  multilocular,  at  other  times  simple,  while  occasionally  they  extend 
backwards  into  the  basi-occipital  and  outwards  and  downwards  into  the  roots  of  the  great  wings 
and  pterygoid  processes.  Cases  are  on  record  in  which  in  the  adult  the  body  of  the  bone  was  not 
pneumatic. 

The  Lacrimal  Bone. — The  bone  consists  of  a  thin  papery  translucent  lamina,  somewhat 
strengthened  by  the  addition  of  the  vertical  crest. 

The  Vomer. — The  bone  is  composed  of  two  compact  layers  fused  below,  but  separated  above 
by  the  groove  for  the  lodgment  of  the  rostrum  of  the  sphenoid  behind,  and  the  septal  cartilage  in 
front.  The  lamellae  are  also  separated  from  each  other  by  a  canal  which  runs  horizontally  from 
behind  forwards  in  the  substance  of  the  bone,  and  which  transmits  the  nutrient  vessel  of 
the  bone. 

The  Nasal  Bone. — Formed  of  dense  and  compact  bone ;  the  strength  of  the  nasal  bones  is 
increased  by  their  mode  of  union  and  the  formation  of  a  median  crest  posteriorly. 

The  Maxillary  Bone. — The  disposition  of  the  maxillary  sinus  within  the  body  of  the  bone 
has  been  already  referred  to.  In  union  with  its  fellow,  the  vaulted  arrangement  of  the  hard  palate 
is  well  displayed,  and  the  arched  outline  of  the  superior  ah^eolar  processes  is  obvious.  It  is  in 
these  latter  processes  around  the  sockets  for  the  reception  of  the  teeth  that  the  cancellous  tissue 
of  the  bone  is  seen  ;  elsewhere  its  walls  are  formed  by  thin  and  dense  bone. 

The  Zygomatic  Bone.  —  In  structure  the  bone  is  compact,  with  little  cancellous  tissue. 
Together  with  the  zygomatic  process  of  the  temporal  bone  it  forms  the  buttress  which  supports 
the  maxilla  and  the  lateral  wall  of  the  orbit.  Additional  strength  is  imj)arted  to  the  bone  by 
the  angular  mode  of  union  of  its  orbital  and  facial  parts. 

The  Mandible. — The  mandible  is  remarkable  for  the  density  and  thickness  of  its  medial  and 
lateral  walls.  Where  these  coalesce  below  at  the  base  of  the  body,  the  bone  is  particularly  stout. 
Superiorly,  where  they  form  the  walls  of  the  alveoli,  they  gradually  thin,  being  thicker, 
however,  on  the  medial  than  the  lateral  side,  except  in  the  region  of  the  last  molar  tooth, 
where  the  medial  wall  is  the  thinner.  The  cancellous  substance  is  open-meshed  below,  finer 
and  more  condensed  where  it  surrounds  the  alveoli.  The  mandibular  canal  is  large  and 
has  no  very  definite  wall ;  it  is  prolonged  beyond  the  mental  foramen  to  reach  the  incisor 
teeth.  From  it  numerous  channels  pass  upwards  to  the  sockets  of  the  teeth,  and  it  com- 
municates freely  with  the  surrounding  cancellous  tissue.  Above  the  canal  the  substance  of  the 
bone  is  broken  up  by  the  alveoli  for  the  reception  of  the  roots  of  the  teeth.  In  the  substance 
of  the  condyle  the  cancellous  tissue  is  more  compact,  with  a  general  striation  vertical  to  the 
articular  surface. 

The  mental  prominence  is  an  essentially  human  characteristic;  by  some  it  is  associated  with  the 
development  of  speech  in  man,  others  regard  it  as  due  to  the  reduction  in  the  size  of  the  teeth. 

The  Clavicle. — The  shaft  consists  of  an  outer  layer  of  compact  bone,  thickest  towards  the 
centre,  but  gradually  thinning  towards  the  extremities,  the  investing  envelope  of  which  consists 
merely  of  a  thin  sliell.  Within  the  shaft  the  cancellous  tissue  displays  a  longitudinal  striation, 
which  internally  assumes  a  more  cellular  appearance.  At  the  acromial  end  the  general  arrange- 
ment of  tlie  fil;res  resembles  the  appearance  of  the  sides  of  a  Gothic  arch.  The  curves  of  the 
bone  imj)art  an  elasticity  to  it,  which  is  of  much  service  in  reducing  the  effects  of  the  shocks  to 
which  it  is  so  frequently  subjected. 

The  Scapula. — For  so  light  and  thin  a  bone,  the  scapula  possesses  a  remarkable  rigidity.  This 
is  owing  to  tlie  arrangement  of  its  jmrts.     Stout  and  thick  where  it  supjjorts  the  glenoid  surface 


ARCHITECTURE  OF  THE  BONES  OF  THE  SKELETON.  iii 

and  coracoid  process,  the  rest  of  the  bone  is  thin,  except  along  the  axillary  border  ;  but  strength  is 
imparted  to  the  body  by  the  manner  in  which  the  s^jine  is  fused  at  right  angles  to  its  dorsal  surface. 

The  Humerus. — The  shaft  consists  of  a  layer  of  compact  bone  surrounding  a  long  medullary 
canal.  The  outer  shell,  thickest  in  the  lower  third  of  the  bone,  gradually  thins  until  it  reaches 
the  superior  epiphysial  line,  where  it  forms  a  layer  no  thicker  than  stout  paper.  Inferiorly 
the  external  shell  is  thicker  and  stouter  than  above,  until  it  reaches  the  epicondyles,  below 
which  the  articular  surfaces  are  formed  of  a  layer  of  compact  spongy  bone.  The  upj^er  end  of 
the  medullary  canal  is  surrounded  by  loose  sjjongy  tissue,  the  fibres  of  which  arch  inwards 
from  the  inner  surface  of  the  compact  outer  layer,  whilst  inferiorly  the  cancellous  tissue 
which  springs  from  the  outer  shell  sweeps  downwards  in  a  radiating  fashion  on  either  side 
of  the  olecranon  fossa  towards  the  epicondyles.  Above  the  olecranon  fossa  there  is  a 
number  of  laminee  of  dense  bone  which  arch  across  from  one  side  to  the  other,  the  con- 
vexity of  the  arches  being  directed  downwards.  The  superior  epijihysis,  formed  of  spongy 
bone,  is  united  to  the  shaft  by  a  wavy  line,  concave  laterally  and  convex  medially,  leading 
from  the  base  of  the  greater  tuberosity  on  the  outer  side  to  the  inferior  articular  edge  on  the  medial 
side.  The  mass  above  this  includes  the  head  and  two  tuberosities.  The  spongy  tissue  of  the 
head  is  fine,  and  is  arranged  generally  in  lines  radial  to  its  surface  ;  that  of  the  greater  tuberosity 
is  more  open,  and  often  displays  large  spaces  towards  its  interior,  which  in  old  bones  communi- 
cate freely  with  the  medullary  cavity  of  the  shaft.  The  general  direction  of  the  fibres  is 
parallel  to  the  outer  surface  of  the  tuberosity.  The  lower  articular  end  is  formed  of  fine  spongy 
tissue,  more  compact  towards  the  surface,  and  arranged  in  lines  more  or  less  at  right  angles  to  its 
articular  planes.  In  the  adult  the  principal  nutrient  canal,  viz.  that  which  opens  on  the 
surface  near  the  insertion  of  the  coraco-brachialis,  traverses  the  outer  compact  wall  of  the  shaft 
obliquely  downwards  for  a  distance  of  two  and  a  quarter  inches  before  it  opens  into  the 
medullary  cavity. 

The  Ulna. — The  weakest  parts  of  the  bone  are  the  constricted  portion  of  the  semilunar 
notch,  and  the  shaft  in  its  lower  third,  the  bone  being  most  liable  to  fracture  at  these 
points.  On  section  the  medullary  cavity  is  seen  to  extend  upwards  as  high  as  the  base  of  the 
coronoid  process ;  inferiorly  it  reaches  as  low  as  the  upper  end  of  the  lower  fifth  of  the  bone.  The 
walls  of  the  shaft,  which  are  formed  of  dense  bone,  are  much  thicker  posteriorly  than  anteriorly. 
Above  they  are  continuous  with  the  front  of  the  coronoid  process  and  the  back  of  the  olecranon, 
where  they  are  composed  of  layers  of  looser  texture,  which,  however,  gradually  become  thinner  as 
the  points  of  these  processes  are  reached.  Inferiorly  they  gradually  tajaer  until  the  head  and 
styloid  process  are  reached,  round  which  they  form  a  thin  shell,  considerably  thickened,  however, 
in  the  region  of  the  groove  for  the  extensor  carpi  ulnaris  muscle.  The  bulk  of  the  upper 
extremity  is  formed  of  loose  cellular  bone,  arranged  in  a  series  of  arcades,  stretching  from  the 
anterior  to  the  posterior  wall  over  the  upper  end  of  the  medullary  canal.  Above  the  constricted 
part  of  the  semilunar  notch  the  bone  displays  a  dift'erent  structure  ;  here  it  is  formed  of 
spongy  bone,  of  closer  texture,  arranged  generally  in  lines  radial  to  the  articular  surface.  At  the 
point  of  constriction  of  the  semilunar  notch  the  layer  immediately  subjacent  is  much  denser 
and  more  compact. 

The  lower  fifth  of  the  bone  is  formed  of  loose  spongy  bone,  the  fibres  of  which  have  a  general 
longitudinal  arrangement ;  towards  its  extremity  the  meshes  become  smaller. 

The  Radius. — The  neck  is  the  narrowest  part  of  the  bone  ;  here  fracture  may  occur,  though 
not  commonly.  The  point  at  which  the  bone  is  usually  broken  is  about  one  inch  above  the 
lower  extremity.  This  is  accounted  for  by  the  fact  that  the  radius  supports  the  hand  at  the 
radio-carpal  articulation,  and  the  shocks  to  which  the  latter  is  subjected,  as  in  endeavouring  to 
save  oneself  from  falling,  are  naturally  transmitted  to  the  radius.  On  section,  the  medullary 
canal  is  seen  to  extend  as  high  as  the  neck  ;  below,  it  reaches  to  the  level  of  the  inferior  fifth  of 
the  bone.  Its  walls  are  thick  as  compared  with  the  diameters  of  the  bone,  particularly  along  the 
interosseous  border,  thus  imparting  rigidity  to  the  curve  of  the  shaft ;  these  walls  thin  out 
above  and  below.  Superiorly,  the  surface  of  the  tuberosity  is  formed  of  a  thin  shell  of 
bone,  which,  however,  thickens  again  where  it  passes  on  to  the  neck.  The  upper  extremity 
is  formed  of  spongy  bone  arranged  in  the  form  of  arcades,  reaching  below  the  level  of  the 
tuberosity  medially,  but  not  extending  below  the  level  of  the  neck  laterally.  Beneath  the 
capitular  articular  surface  there  is  a  dense  layer,  thickest  in  the  centre,  and  thinning  towards 
the  circumference  ;  this  is  overlain  by  a  very  thin  layer  of  less  compact  bone. 

The  inferior  fifth  of  the  shaft  and  lower  extremity  are  formed  of  loose  spongy  bone 
arranged  more  or  less  longitudinally.  Immediately  subjacent  to  the  carpal  articular  surface 
the  tissue  is  more  compact,  and  displays  a  striation  parallel  to  the  articular  plane.  The  nutrient 
canal  of  the  shaft  pierces  the  anterior  wall  of  the  upper  part  of  the  medullary  cavity  obliquely 
from  below  upwards  for  the  space  of  half  an  inch. 

The  Carpus. — The  bones  are  formed  of  fairly  compact  spongy  tissue,  surrounded  by  a  thin 
shell  of  denser  bone.  They  are  very  vascular,  and  their  non-articular  surfaces  are  pierced  by 
many  foramina. 

The  Metacarpus. — Similar  in  arrangement  to  that  of  long  bones  generally,  though  it  may 
be  noted  that  the  compact  walls  of  the  shaft  are  thicker  in  proportion  to  the  length  of  the  bone 
than  in  the  other  long  bones  of  the  upper  extremity. 

The  Phalanges. — Each  j^halanx  has  a  medullary  cavity,  the  walls  of  the  shaft  being  formed  of 
dense  comjaact  bone,  especially  thick  along  the  dorsal  aspect.  The  extremities  are  made  up  of 
spongy  bone  within  a  thin  dense  shell. 


IV 


OSTEOLOGY. 


DlOirAI.    KOSSA 


•^ 


Posterior  siirface 

OF   NECK 


Base  of  trochanter  minor 
cut  through 

Space  containing  loose  cancellous 
tissue  (scraped  away)  between  the 
calcar  and   the  base  of  the   tro- 
chanter minor 


Great 
trochanter 

Interior  of  tro- 
chanter major 
ooutaining  loose 
cancellous  tissue 
scraped  away 


Compact  tissue 
with  dense  core 
forming  the 
calcar  lemorale 


The  Innominate  or  Hip  Bone. — As  a  flat  bone  the  os  iimominatum  consists  of  spongy 
tissue  between  two  comjjact  external  layers.  These  latter  vary  much  in  thickness,  being 
exceptionally  stout  along 
the  ilio-pectineal  line  and 
the  floor  of  the  iliac  fossa 
immediately  above  it. 
The  gluteal  aspect  of  the 
ilium  is  also  formed  by 
a  layer  of  considerable 
thickness.  The  si:)ongy 
tissue  is  loose  and  cellular 
in  the  tliick  part  of  the 
ilium  and  in  the  body 
of  the  ischium  ;  absent 
where  the  floor  of  the 
iliac  fossa  is  formed  by 
the  coalescence  of  the 
thin  dense  confining 
layers  ;  fine  grained  and 
more  compact  in  the 
tuberosity  of  the  ischium, 
the  iliac  crest,  and  the 
floor  of  the  acetabulum, 
in  which  latter  situation 
it    is   striated   by    fibres 

which  are  directed  radially  to  the  surface  of  that 
hollow,  these  again  being  crossed  at  right  angles  by 
others  which  are  arranged  circumferentially.  This 
spongy  tissue  forms  a  more  compact  layer  over  the 
surface  of  the  upjier  and  back  portion  of  the  acetabular 
articular  area.  The  bottom  of  the  floor  of  the  acetab- 
ulum varies  in  thickness ;  in  most  cases  it  is  thin, 
and  in  exceptional  instances  the  bone  is  here  deficient. 
The  same  condition  has  been  met  with  in  the  iliac 

Fig.  195. — Dissection  showing  the  Calcar 
Femorale. 

A  slice  of  bone  has  been  removed  from  the  pos- 
terior aspect  of  the  upper  part  of  the  shaft 
of  the  femur,  passing  through  the  trochanter 
major  superiorly  and  the  trochanter  minor 
inferiorly  and  to  the  medial  side.  The  loose 
cancellous  tissue  has  been  scraped  away, 
leaving  the  more  compact  tissue  with  the 
dense  core  forming  the  calcar  femorale.  By 
a  similar  dissection  from  the  front  the  an- 
terior surface  of  the  calcar  may  be  exposed. 

amerior  fossa,  where  absorption  of  the  thin  bony  plate 
has  taken  jjlace. 

The  Femur. —  Tlie  shaft  has  a  medullary 
cavity  which  reaches  as  high  as  the  root  of 
the  lesser  trochanter.  Inferiorly  it  extends  to 
within  3^  inches  of  the  lower  articular  surface. 
In  the  upper  half  the  outer  compact  wall  is 
very  thick,  but  below  the  middle  of  the  shaft 
it  gradually  thins  until  it  reaches  tlie  condyles 
inferiorly,  over  which  it  passes  as  a  thin, 
hardly  definable  external  layer.  Above,  it  is 
especially  thick  along  the  line  of  the  linea 
aspera,  and  here  the  large  nutrient  caual  may 
be  seen  passing  obliquely  upwards  in  the  sub- 
stance of  the  dense  bone  for  the  space  of  two 
inches.  In  the  up])er  end  of  the  shaft  the 
osseous  lamellae  springing  from  the  sides  of 
the  medullary  cavity  arch  inwards  towards  the 
centre,  intersecting  each  other  in  a  manner 
comparable  to  the  tracery  of  a  Gothic  window. 
The  lower  wall  of  the  neck  is  thick  below,  near 
the  trochanter  minor,  but  thins  rapidly  before 
it  reaches  the  head.  From  this  aspect  of  the  neck  there  spring  a  series  of  oblique  lamellae 
which  pass  upwards  and  inwards,  spreading  in  fan-shaped  manner  into  the  under  surface  of  the 
head.     These  are  intersected  above  by  lamellai  which  arch  inwards  from  the  lateral  side  of  the 


Posterior  suri-aci- ^ 

OF  ^ECh        \ 


Calcar  femoimlp 


Trochanter 
minor 


Fig. 


196.  —Section  through  Head  and  Neck  of 
Femur  to  show  Calcar  Femorale. 


ARCHITECTUEE  OF  THE  BONES  OF  THE  SKELETON.      v 

sliaft  below  tlie  greater  trochanter,  as  well  as  from  the  iiiuler  surface  of  the  thin  but  compact 
outer  shell  of  the  upper  surface  of  the  neck,  the  whole  forming  a  bracket-like  arrangement  which 
assists  materially  in  adding  to  the  strength  of  the  neck.  Further  support  is  affoi'ded  by  the 
addition  of  a  vertical  layer  of  more  comjiact  bone  within  the  cancellous  tissue  of  the  neck.  In- 
feriorly,  as  may  be  seen  in  Fig.  196,  this  is  continuous  with  the  dense  jjosterior  wall  of  the  shaft 
below  ;  whilst  superiorly  it  sweeps  up  beneath  the  lesser  trochanter,  from  which  it  is  separated 
by  a  quantity  of  loose  cancellous  tissiie,  to  fuse  superiorly  with  the  posterior  dense  wall  of  the 
neck  above  and  medial  to  the  posterior  intertrochanteric  line.  It  may  be  regarded  as  a  con- 
tinuation upwards  of  the  posterior  wall  of  the  shaft  beneath  the  trochanteric  epiphysis.  When 
studied  in  section  (see  Fig.  197),  the  central  dense  core  of  this  partition  exhibits  a  spur-like 
appearance  :  hence  the  name  calcar  femorale  a})2)lied  to  it.  It  is  of  surgical  importance  in  cases 
of  fracture  of  the  neck  of  the  femur  (E.  Thompson,  Journ.  Anat.  and  Physiol.,  vol.  xlii.  p.  60). 
From  it,  stout  lamella;  having  a  vertical  direction  arise.  The  sjaongy  tissue  of  the  head  and 
greater  trochanter  is  finely  reticulated,  that  of  the  lower  part  of  the  neck  and  upper  part  of  the 
shaft  being  more  open  in  its  texture.  Passing  vertically  dowoiAvards  through  this  tissue  there  is 
a  vascular  canal,  the  orifice  of  which  oj)ens  externally  on  the  floor  of  the  trochanteric  fossa. 

The  spongy  tissue  of  the  lower  part  of  the  shaft  is  more  delicate  and  uniform  in  its 
arrangement,  displaying  a  more  or  less  parallel  striation  in  a  longitudinal  direction.  Subjacent 
to  the  articular  surface  the  tissue  is  rendered  more  compact  by  the  addition  of  lamellae  disposed 
in  curves  in  harmony  with  the  external  aspect  of  the  bone. 

The  Patella. — The  bone  consists  of  a  thick  dense  layer  anteriorly,  which  thins  towards  the 
edges  on  either  side  and  below ;  above,  it  corresponds  to  the  area  of  insertion  of  the  quadriceps. 
The  femoral  articular  surface  is  composed  of  a  layer  of  compact  bone,  thickest  in  correspondence 
with  the  vertical  elevation.  Sandwiched  between  these  two  layers  is  a  varying  thickness  of 
spongy  tissue  of  fairly  close  grain,  the  striation  of  which  on  cross  section  runs  in  parallel  lines 
from  back  to  front ;  on  vertical  section  the  tissue  appears  to  be  arranged  in  lines  passing  radially 
from  the  deep  surface  of  the  femoral  area  to  the  more  extensive  anterior  dense  plate. 

The  Tibia.  —  The  shaft  of  the  bone  is  remarkable  for  the  thickness  and  density  of  the 
osseous  tissue  which  underlies  the  crest.  The  posterior  wall  is  stout,  but  the  medial  and 
lateral  walls  are  thinner.  The  several  walls  are  thickest  oj^posite  the  middle  of  the  shaft,  and 
thin  out  above  and  below  where  the  shaft  unites  with  the  epiphyses.  The  medullary  canal, 
narrow  and  circular  in  the  middle  of  the  bone,  increases  in  all  its  diameters  above  and  below, 
and  reaches  to  within  2^  to  3  inches  of  either  extremity.  Superiorly  the  arrangement  of 
the  lameUcB  of  the  spongy  tissue  resembles  a  series  of  arches  springing  from  the  dense  outer  walls. 
These  form  a  platform  on  which  the  superior  epiphysis  rests,  the  sjiongy  tissue  of  which  displays 
a  more  or  less  vertical  striation.  This  is  much  more  compact  under  the  condylic  surfaces,  the 
superficial  aspect  of  which  is  formed  by  a  thin  layer  of  dense  bone.  The  spine  and  tuberosity  are 
also  formed  of  compact  tissue,  whilst  the  circumference  of  the  tuberosities  is  covered  by  a 
thinner  and  less  dense  wall  In  the  lower  end  of  the  shaft  the  spongy  tissue,  of  a  loose  and 
cellular  character,  is  arranged  in  vertical  fibres,  blending  inferiorly  with  the  closer  tissue  of  the 
inferior  epiphysis,  the  articular  surface  of  which  is  covered  by  a  thin  but  dense  layer. 

In  the  adult  bone  the  nutrient  canal  for  the  shaft  is  embedded  in  the  dense  posterior  wall  for 
the  space  of  two  inches. 

The  Fibula. — A  medullary  canal  runs  throughout  the  length  of  the  shaft,  reaching  as  high 
as  the  neck  above,  and  extending  as  low  as  a  point  about  2^  inches  above  the  inferior  extremity 
of  the  lateral  malleolus.  The  lateral  wall  of  the  shaft  is  usually  considerably  thicker  than  the 
medial.  The  head  is  formed  of  loose  cellular  bone,  enclosed  within  a  very  thin  dense  envelope.  The 
spongy  tissue  of  the  lower  extremity  is  more  compact,  and  acquires  considerable  density  on  the 
surfaces  underlying  the  articular  area  and  the  pit  behind  it.  The  canal  for  the  nutrient  artery  of 
the  shaft  ojiens  into  the  medullary  cavity  about  an  inch  below  its  external  aperture. 

The  Bones  of  the  Foot. — A  longitudinal  section  through  the  articulated  bones  of  the  foot 
reveals  the  fact  that  the  cancellous  structure  of  each  individual  bone  is  determined  by  the  stress 
to  which  it  is  habitually  subjected.  In  this  connexion  it  is  necessary  to  refer  to  the  arched 
arrangement  of  the  bones  of  the  foot,  a  subject  which  is  also  treated  in  the  section  which  deals 
with  the  Joints.  The  summit  of  the  arch  is  formed  by  the  talus,  on  which  rests  the  tibia. 
Subjected  as  the  talus  is  to  a  crushing  strain,  it  is  obvious  that  this  load  must  be  distributed 
throughout  the  arch,  of  which  the  calcaneus  is  the  j^osterior  pillar,  whilst  the  heads  of  the  meta- 
tarsal bones  constitute  the  anterior  pillar.  It  is  found,  consequently,  that  the  lamellse  of  the 
cancellous  tissue  of  the  talus  are  arranged  in  two  directions,  which  intercross  and  terminate 
below  the  superior  articular  surface.  Of  these  fibres,  some  sweej)  backwards  and  downwards 
towards  the  posterior  calcanean  facet,  bej'-ond  which  they  are  carried  in  the  substance  of  the  cal- 
caneus in  a  curved  and  wavy  manner  in  the  direction  of  the  heel,  where  they  terminate ;  whilst 
others,  curving  downwards  and  forwards  from  the  trochlea  of  the  talus,  pass  through  the 
neck  to  reach  the  articular  surface  of  the  head,  through  which  in  like  manner  they  may  be 
regarded  as  passing  onwards  through  the  several  bones  wliich  constitute  the  anterior  jjart  of  the 
arch,  thus  accounting  for  the  longitudinal  striation  as  displayed  in  the  structure  of  the  navi- 
cular, cuneiform,  and  metatarsal  bones.  In  the  calcaneus,  in  addition  to  the  foregoing  arrange- 
ment, another  set  of  curving  fibres  sweep  from  back  to  front  of  the  bone  beneath  the  more  com- 
pact tissue  which  forms  its  under  shell.  These  are  obviously  of  advantage  to  prevent  the  spread 
of  the  bone  when  subjected  to  the  crushing  strain.     In  the  sustentaculum  tali  a  bracket-like 


vi  OSTEOLOGY. 

arrangement  of  fibres  is  evident,  and  tlie  under  surface  of  tlie  neck  of  the   talus  is  further 
strengthened  by  lamellae  arranged  vertically. 

In  the  separate  bones  the  investing  envelope  is  thin,  though  xinder  the  articular  surfaces 
there  is  a  greater  density,  due  to  the  accession  of  lamellae  lying  parallel  to  the  articular  planes. 
The  stoutest  bony  tissue  in  the  talus  is  met  with  in  the  region  of  tlie  under  surface  of  the 
neck,  whilst  in  the  calcaneus  the  greatest  density  occurs  along  the  floor  of  the  sinus  tarsi. 

The  Metatarsus. — In  structure  and  the  arrangement  of  their  lamellae  the  metatarsal  bones 
agree  witli  the  metacarjjus. 

The  Phalanges. — In  their  general  structure  they  resemble  the  bones  of  the  fingers, 


APPENDIX   B. 

VARIATIONS   IN    THE    SKELETON. 

Cervical  Vertebrae. — Szawlowski  records  the  presence  of  an  independent  rib  element  in  the 
transverse  process  of  the  fourth  cervical  vertebra.     (Anat.  Anz.  Jena,  vol.  xx.  p.  306.) 

Atlas. — The  vertebrarterial  foramen  is  often  deficient  in  front.  Imperfect  ossification 
occasionally  leads  to  the  anterior  and  more  frequently  the  posterior  arches  being  incomplete.  The 
superior  articular  surfaces  are  occasionally  partially  or  com j)letely  divided  into  anterior  and  posterior 
portions.  In  some  instances  the  extremity  of  the  transverse  process  has  two  tubercles.  The  trans- 
verse process  may,  in  rare  cases,  articulate  with  a  projecting  process  (paroccipital)  from  the  under 
surface  of  the  jugular  process  of  the  occipital  bone  (see  p.  ix).  An  upward  extension  from  the 
median  part  of  the  anterior  arch,  due  jDrobably  to  an  ossification  of  the  anterior  occipito-atlantal 
ligament,  may  articulate  with  the  anterior  surface  of  the  summit  of  the  odontoid  process  of 
the  axis.  Allen  has  noticed  the  articulation  of  the  suj^erior  border  of  the  posterior  arch  with 
the  posterior  border  of  the  foramen  magnum.  Cases  of  partial  or  complete  fusion  of  the  atlas 
with  the  occipital  bone  are  not  uncommon  (see  p.  ix). 

Axis. — In  some  instances  the  summit  of  the  odontoid  process  articulates  with  a  prominent 
tubercle  on  the  anterior  border  of  the  foramen  magnum  (third  occii^ital  condyle,  see  p.  viii). 
Bennett  {Trans.  Path.  Soc.  Dublin,  vol.  vii.)  records  a  case  in  which  the  odontoid  process  was 
double,  due  to  the  persistence  of  the  primitive  condition  in  which  it  is  develojDed  from  two 
centres.  Occasionally  the  odontoid  process  fails  to  be  united  with  the  hodj  of  the  axis,  forming 
an  OS  odontoideum  comparable  to  that  met  with  in  the  crocodilia  (Giacomini,  Eomiti,  and 
Turner).  The  vertebrarterial  foramen  is  not  infrequently  incomplete,  owing  to  the  imperfect 
ossification  of  the  posterior  root  of  the  transverse  process.  Elliot  Smith  has  recorded  a  case  in 
which  there  was  fusion  between  the  atlas  and  axis  without  any  evidence  of  disease. 

Seventh  Cervical  Vertebra. — The  vertebrarterial  foramen  may  be  absent  on  one  or  other 
side. 

Thoracic  Vertebrae. — Barclay  Smith  (Joum.  Anat.  and  Physiol.  Lond.  1902,  ]).  372)  records 
five  cases  in  which  the  superior  articular  processes  of  the  twelfth  thoracic  A^ertebra  disj)layed 
thoracic  and  lumliar  characteristics  on  the  opposite  sides. 

Lumbar  Vertebrae. — The  mammillary  and  accessory  processes  are  sometimes  unduly  de- 
veloped. The  neural  arch  of  the  fifth  lumbar  vertebra  is  occasionally  interrupted  on  either  side 
by  a  synchondrosis  which  runs  between  the  upper  and  lower  articular  processes.  In  macerated 
specimens  the  two  parts  of  the  bone  are  thus  sejDarate  and  independent.  The  anterior  includes 
the  centrum,  together  witli  the  pedicles,  transverse  and  superior  articular  processes  ;  the  posterior 
comprises  the  inferior  articular  processes,  the  laminte,  and  the  spine  (Turner,  Challenger  Reports, 
vol.  xvi.).  Szawlowski  and  Dwight  record  instances  of  the  occurrence  of  a  foramen  in  the 
transverse  process  of  the  Vth  lumliar  vertebra  {Anat.  Anz.  Jena,  vol.  xx.),  and  Ramsay  Smith 
describes  a  case  in  which  the  right  transverse  process  of  the  IVth  lumbar  vertebra  of  an 
Australian  sprang  from  the  side  of  the  body  in  front  of  the  j)edicle,  being  unconnected  either 
with  the  pedicle  or  articular  process. 

Sacrum. — The  number  of  sacral  segments  may  be  increased  to  six  or  reduced  to  four  (see 
p.  vii).  Transition  forms  are  occasionally  met  with  in  which  the  first  sacral  segment  disjalays 
on  one  side  purely  sacral  characters,  i.e.  it  articulates  with  the  innominate  bone,  whilst  on  the 
opposite  side  it  may  present  all  the  features  of  a  lumbar  vertebra.  Through  deficiency  in  the 
develoj)ment  of  the  laminte,  the  neural  canal  may  be  exposed  throughout  its  entire  length,  or 
to  a  greater  extent  than  is  normally  the  case  (Paterson,  Roy.  Dublin  Soc.  Scientific  Trans. 
voL  V.  Series  II.).  Szawlowski  and  Barclay  Smith  record  the  occurrence  of  a  foramen  in  the 
lateral  mass  of  the  1st  sacral  vertebra  {Jonrn.  of  Anat.  and  Physiol.,  Lond.  voL  xxxvi.  p.  372). 

Vertebral  Column  as  a  Whole. — Increase  in  the  number  of  vertebral  segments  is  usually 
due  to  ditfc.reiices  in  the  numl;er  of  the  coccygeal  vertebra;;  these  may  vary  from  four — 
which  may  Ije  regarded  as  the  normal  number — to  six.  The  number  of  jH'esacral  or  movable 
vertebrte  is  normally  24  (7  C,  12  D,  and  5  L) ;  in  wliich  case  the  25th  vertebra  forms  the 
fii-st  sacral  segment  (vertebra  fulcralis  of  Welcker).  The  number  of  presacral  vertebrae  may 
be  increased  by  the  intercalcation  of  a  segment  either  in  the  thoracic  or  lumbar  region  without 


VAEIATIONS  IN  THE  SKELETON.  vii 

any  alteration  in  the  number  of  the  sacral  or  coccygeal  elements  :  thus  we  may  have  7  C,  13  D, 
and  5  L,  or  7  C,  12  D,  and  6  L,  or  it  may  be  reduced  by  the  disappearance  of  a  vertebral  segment 
— thu.-r,  7  C,  12  D,  and  4  L.  Such  an  arrangement  presupposes  developmental  errors  either 
of  excess  or  default  in  the  segmentation  of  the  column.  On  the  other  hand,  the  total  number  of 
vertebral  segments  remaining  the  same  (24  or  25),  we  may  have  variations  in  the  number  of  those 
assigned  to  different  regions  due  to  the  addition  of  a  vertebral  segment  to  one,  and  its  consequent 
subtraction  from  another  region.  Thus,  in  the  24  ^'resacral  vertebrae,  in  cases  of  the  occurrence  of 
cervical  ribs  the  formula  is  rearranged  thus — 6  C,  13  D,  and  5  L,  or,  in  the  case  of  a  thirteenth 
rib  being  jj resent,  the  formula  would  be  7  C,  13  D,  4  L,  as  hajj^^ens  normally  in  the  gorilla  and 
chimpanzee.  Similarly,  the  number  of  the  presacral  vertebi'je  (24)  may  be  increased  by  the 
withdrawal  of  a  segment  from  the  sacral  region — 7  C,  12  D,  6  L,  and  4  S — or  diminished  by  an 
increase  in  the  number  of  the  sacral  vertebrge,  as  in  the  formula  7  C,  12  D,  4  L,  and  6  S.  In- 
crease in  the  number  of  sacral  segments  may  be  due  to  fusion  with  a  lumbar  vertebra,  or  by  the 
addition  of  a  coccygeal  element :  the  latter  is  more  frequently  the  case.  This  variability  in  the 
constitution  of  the  sacrum  is  necessarily  correlated  with  a  shifting  backwards  and  forwards  of 
the  pelvic  girdle  along  the  vertebral  column.  Rosenburg  considers  that  the  26th,  27th,  and  28th 
vertebrte  are  the  jirimitive  sacral  segments,  and  that  the  sacral  characters  of  the  25th  vertebrae 
(the  first  sacral  segment  in  the  normal  adult  column)  are  only  secondarily  acquired.  He  thus 
supposes  that  during  development  there  is  a  forward  shifting  of  the  sacrum  and  pelvic  girdle, 
with  a  consequent  reduction  in  the  length  of  the  presacral  portion  of  the  column.  This  view  is 
opposed  by  Paterson  (Eoy.  Dublin  Soc.  Scientific  Trans,  vol.  v.  Ser.  II.),  who  found  that  ossification 
took  place  in  the  alas  of  the  25th  vertebra  (first  adult  sacral  segment)  before  it  made  its  appear- 
ance in  the  alae  of  the  26th  vertebra.  He  thus  assumes  that  the  alee  of  the  25th  vertebra  may 
be  regarded  as  the  main  and  j^rimary  attachment  with  the  ilium.  His  conclusions,  based  on  a 
large  number  of  observations,  are  at  variance  with  Rosenburg's  views,  for,  according  to  his  opinion, 
liberation  of  the  first  sacral  segment  is  more  common  than  assimilation  with  the  fifth  lumbar 
vertebra,  and  assimilation  of  the  first  coccygeal  vertebra  with  the  sacrum  is  more  common  than 
liberation  of  the  fifth  sacral,  thus  leading  to  the  inference  that  the  sacrum  tends  to  shift  back- 
wards more  often  than  forwards.  Dwight  (Anat.  Anz.  Jena,  vol.  xxviii.  p.  33),  after  a  study  of 
this  question,  whilst  admitting  that  some  of  these  variations  may  be  reversive,  denies  that  there 
is  any  evidence  that  they  are  jjrogressive,  and  further  states  that  after  the  occurrence  of  the 
original  error  in  development,  there  is  a  tendency  for  the  vertebral  column  to  assume  as  nearly 
as  possible  its  normal  disposition  and  j^roportions. 

Sternum. — The  sternum  is  liable  to  considerable  individual  variations  affecting  its  length 
and  direction.  The  majority  of  bones  are  asymmetrical,  displaying  irregularities  in  the  levels  of 
the  clavicular  facets.  The  higher  costal  facets  may  be  closer  together  on  one,  usually  the  right 
side,  than  the  other,  whilst  the  pre-mesosternal  joint  is  often  oblique,  sloping  somewhat  to  the 
right.  According  to  Birmingham,  these  are  the  result  of  the  strain  thrown  on  the  shoulder  by 
pressure  either  directly  applied  or  through  the  pull  of  a  weight  carried  in  the  hand. 

Sometimes  the  sternum  articulates  with  eight  rib  cartilages.  This  may  happen  on  one  or 
both  sides,  but  when  unilateral,  much  more  frequently  on  the  right  side — a  condition  by  some 
associated  with  right-handedness.  It  is,  however,  more  probably  a  persistence  of  the  primitive 
condition  of  the  cartilaginous  sternum,  in  which  each  half  is  connected  with  the  anterior 
extremities  of  the  first  eight  costal  arches.  In  some  rare  cases  only  six  pairs  of  ribs  articulate 
by  means  of  their  costal  cartilages  with  the  sternum.  Recently  Lickley  has  brought  forward 
evidence  to  show  that  the  seventh  rib  is  undergoing  regressive  changes  (Anat.  Anz.  vol.  xxiv. 
p.  326). 

Occasionally  the  presternum  supports  the  first  three  ribs ;  in  other  words,  the  manubrium 
has  absorbed  the  highest  segment  of  the  body.  Keith  has  pointed  out  that  this  is  the  condition 
most  commonly  met  with  in  the  gibbon,  and  regards  its  occurrence  in  man  as  a  reversion  to  the 
simian  type.  As  far  as  is  at  present  known,  its  occurrence  seems  more  common  in  the  lower 
races.  Through  errors  of  development  the  sternum  may  be  fissured  throughout,  due  to  failure 
of  fusion  of  the  cartilaginous  hemisterna.  The  two  ossified  halves  are  usually  widely  separated 
above,  but  imited  together  below  by  an  arthrodial  joint.  The  heart  and  pericardium  are  thus 
uncovered  by  the  bone.  Occasionally  this  condition  is  associated  with  ectopia  cordis,  under 
which  circumstances  life  is  rendered  impossible.  Through  defects  in  ossification  the  mesosternum 
may  be  pierced  by  a  hole,  usually  in  its  lower  part,  or  through  failure  of  fusion  of  the  lateral 
centres  one  or  more  of  the  segments  of  the  body  may  be  divided  longitudinally. 

Sometimes  small  ossicles  are  found  in  the  ligaments  of  the  sterno-clavicular  articulation. 
These  are  the  so-called  episternal  bones,  the  morphological  significance  of  which,  however,  has 
not  yet  been  satisfactorily  determined.  They  are  by  some  regarded  as  the  homologues  of  the 
interclavicle  or  episternal  bone  of  monotremata,  whilst  by  others  they  are  considered  to  represent 
persistent  and  detached  portions  of  the  pre-coracoids. 

Ribs. — The  number  of  ribs  may  be  increased  or  diminished.  Increase  may  occur  by  the 
addition  of  a  cervical  rib  due  to  the  independent  development  of  the  costal  element  in  the 
transverse  process  of  the  seventh  cervical  vertebra.  This  may  happen  on  one  or  both  sides.  The 
range  of  development  of  these  cervical  ribs  varies ;  they  may  unite  in  front  with  the  sternum, 
or  they  may  be  fused  anteriorly  with  the  cartilage  of  the  first  rib,  or  the  cervical  rib  may  be 
free.  It  may  in  some  instances  be  represented  mainly  by  a  ligamentous  band,  or  its  vertebral 
and  sternal  ends  may  be  alone  developed,  the  intermediate  part  being  fibrous.  At  times  the 
vertebral  end  only  may  be  formed,  and  may  be  fused  with  the  first  rib,  thus  leading  to  the 
formation  of  a  bicipital  rib  such  as  occurs  in  many  cetaceans.     Increase  in  the  number  of  ribs 

17* 


viii  OSTEOLOGY. 

may  also  be  due  to  the  ossification  of  the  costal  element  which  is  normally  present  in  the  embryo 
in  connexion  with  the  first  lumbar  vertebra.  (Rosenberg,  Morph.  Jahrb.  i.)  Reduction  in  the 
number  of  ribs  is  less  common.  The  twelfth  rib  rarely  aborts ;  in  some  cases  the  first  rib  is 
rudimentary.  Cases  of  congenital  absence  of  some  of  the  ribs  have  been  recorded  by  Hiitchinson, 
Murray,  and  Ludeke.  Fusion  of  adjacent  ribs  may  occur.  (Lane,  Giiy's  Hosp.  Reports,  1883.) 
In  this  way,  too,  the  occurrence  of  a  bici25ital  rib  is  explained.  This  anomaly  occurs  most 
usually  in  connexion  with  the  first  rib,  which  either  fuses  with  a  cervical  rib  above  or  with  the 
second  rib  below. 

Variations  in  form  may  be  in  great  jiart  due  to  the  occupation  of  the  individual  and  the  con- 
stricting influence  of  corsets.  Independently  of  these  influences,  the  fore  part  of  the  shaft  is 
sometimes  cleft  so  as  to  appear  double  ;  at  other  times  the  cleft  may  be  incomplete  so  as  to  form 
a  perforation.  Occasionally  adjacent  ribs  are  united  towards  their  posterior  part  by  processes 
liaving  an  intermediate  ossicle  between  (Meckel),  thus  recalling  the  condition  normally  met  with 
in  birds ;  more  usually,  however,  the  bony  projections  are  not  in  contact. 

The  number  of  true  or  vertebro-sternal  ribs  may  be  reduced  to  six,  or  increased  to  eight  {vide 
ante,  ji.  vii). 

Costal  Cartilages. — Occasionally  a  costal  cartilage  is  unduly  broad,  and  may  be  pierced  by  a 
foramen.  The  number  of  costal  cartilages  connected  with  the  sternum  may  be  reduced  to  six  or 
increased  to  eight  (see  p.  vii).  In  advanced  life  there  is  a  tendency  towards  ossification  in  the 
layers  underlying  the  perichondrium,  more  particularly  in  the  case  of  the  first  rib  cartilage,  in 
which  it  may  be  regarded  as  a  more  or  less  normal  occurrence. 

Frontal  Bone,  etc. — The  variation  most  frequently  met  with  is  a  persistence  of  the  suture 
which  unites  the  two  halves  of  the  bone  in  the  infantile  condition :  skulls  disj)laying  this  peculiarity 
are  termed  metopic.  The  researches  of  various  observers — Broca,  Ranke,  Gruber,  Manouvrier, 
Anoutchine,  and  Papillault  {Rev.  mens,  de  Vecole  d'Anthropol.  de  Paris,  annee  6,  n.  3) — point  to  the 
more  frequent  occurrence  of  this  metopic  suture  in  the  higher  than  in  the  lower  races  of  man  ;  and 
Calmette  asserts  its  greater  frec|uence  in  the  brachycei)halic  than  the  dolichocephalic  type. 
Separate  ossicles  (Wormian  bones)  may  occur  in  the  region  of  the  anterior  fontanelle.  The  fusion 
of  these  with  one  or  other  half  of  the  frontal  explains  how  the  metopic  suture  is  not  always  in 
line  with  the  sagittal  suture  (Stieda,  Anat.  Anz.  1897,  p.  227) ;  they  occasionally  persist,  however, 
and  form  by  their  coalescence  a  bregmatic  bone  (G.  Zoja,  Bull.  Scientifico,  xvii.  p.  76,  Pavia), 
Turner  {Challenger  Reports,  part  xxix.)  records  an  instance  of  direct  articulation  of  the  frontal 
with  the  orbital  plate  of  the  maxilla  in  a  Bush  skull,  and  other  examples  of  the  same  anomaly, 
which  obtains  normally  in  the  skulls  of  the  chimpanzee  and  gorilla,  haA^e  been  observed  {Jour. 
Anat.  and  Physiol.  voL  xxiv.  p.  349). 

There  is  sometimes  a  small  arterial  groove  just  medial  to  the  supraorbital  notch  or  foramen, 
and  occasionally  the  latter  is  double,  the  lateral  aperture  piercing  the  orbital  margin  wide  of 
its  middle  jDoint. 

Schwalbe  (1901)  records  the  presence  of  small  independent  ossicles  (supranasal  bones)  in  the 
anterior  part  of  the  metopic  suture.  The  same  anatomist  has  also  directed  attention  {Zeit.  f. 
Morph.  und  Anthr.  vol.  iii.  p.  93)  to  the  existence  of  the  metopic  fontanelle,  first  described  by 
Gerdy,  and  the  occurrence  of  metopic  ossicles  (ossa  interfrontalia)  and  canals. 

Parietal. — A  number  of  cases  have  been  recorded  in  which  the  parietal  is  divided  into  an 
upper  and  lower  part  by  an  antero-posterior  suture  parallel  to  the  sagittal  suture.  Coraini 
(Atti.  d.  XL  Gongr.  Med.  Internaz.  Roma,  1894,  vol.  v.)  records  a  case  in  which  the  parietal  was  in- 
completely divided  into  an  anterior  and  posterior  part  by  a  vertical  suture.  A  tripartite 
condition  of  the  bone  has  also  been  observed  (Frasetto).  The  parietal  foramina  vary  greatly 
in  size,  and  to  some  extent  in  position.  They  are  sometimes  absent  on  one  or  other  side, 
or  both.  They  correspond  in  position  to  the  sagittal  fontanelle.  Sometimes  the  ossification 
of  this  fontanelle  is  incomplete  and  a  small  transverse  fissure  remains.  The  jmrietal  foramen 
represents  the  patent  lateral  extremity  of  this  fissiire  after  its  edges  have  coalesced.. 
Occasionally  in  the  region  of  the  anterior  fontanelle  an  ossicle  of  variable  size  may  be  met  with. 
This  is  the  so-called  pre-interparietal  bone.  According  to  its  fusion  with  adjacent  bones  it 
may  disturb  the  direction  of  the  sagittal  suture. 

Occipital. — The  torus  occipitalis  transversus  is  the  term  applied  to  an  occasional  eleva- 
tion of  the  bone  which  includes  the  external  occipital  j^rotuberance  and  extends  laterally  along 
the  superior  curved  line.  Occasionally  an  emissary  vein  pierces  the  bone  opposite  the  occipital 
protuberance.  In  about  15  per  cent  of  cases  the  anterior  condylic  canal  is  double.  Much  rarer 
three  or  even  four  foi-amina  may  be  met  with.  The  most  striking  of  the  many  variations  to 
which  this  bone  is  subject  is  the  separation  of  the  upper  part  of  the  squamous  part  of  tlie 
occipital  to  form  an  independent  bone — the  interparietal  bone,  called  also,  from  the  frequency 
of  its  occurrence  in  Peruvian  skulls,  the  os  Incse.  By  a  reference  to  the  account  of  the  ossi- 
fication of  the  bone  (p.  112),  the  occurrence  of  this  anomaly  is  explained  developmentally.  In 
T)lace  of  forming  a  single  bone  the  interparietal  is  occasionally  met  with  in  two  symmetrical 
halves,  and  instances  have  been  recorded  of  its  occurrence  in  three  or  even  four  pieces.  In 
the  latter  cases  the  two  anterior  parts  form  the  pre-interparietals.  Not  uncommonly  the 
internal  occipital  crest  is  split  and  furrowed  clo,se  to  the  foramen  magnum  for  tlie  lodgment  of 
the  vermiform  lobe  of  the  cerebellum,  and  is  hence  called  the  vermiform  fossa.  Instances 
are  recorded  of  the  presence  of  a  separate  epiphysis  between  the  basi-occipital  and  the  sphenoid, 
the  03  basioticum  (Albrecht)  or  the  os  pre-basi-occipital.  An  oval  pit,  the  fovea  bursse  or 
pharyngeal  fossa,  is  sometimes  seen  in  front  of  the  tuberculum  pharyngeum.     This  marks  the 


VARIATIONS  IN  THE  SKELETON.  ix 

site  of  the  bursa  i)liaryngea.  Occasionally  the  basilar  process  is  pierced  l:)y  a  small  venous 
canal.  The  articular  surface  of  the  condyles  is  sometimes  divided  into  an  anterior  and  posterior 
part.  The  so-called  third  occipital  condyle  is  an  outstanding  process  rising  from  the  anterior 
border  of  the  foramen  magnum,  the  extremity  of  which  articulates  with  the  odontoid  process 
of  the  axis.  Guerri  has  recorded  a  case,  in  which  in  a  foetal  skull,  there  were  two  projecting 
tubercles  in  the  position  of  the  third  occipital  condyle,  independent  of  the  basi-occipital  portions 
of  the  condyles  {Anat.  Anz.  vol.  xix.  p.  42).  This  appears  to  confirm  the  view  of  Macalister 
that  there  are  two  different  structures  included  under  this  name — one  a  medial  ossification  in 
the  .sheath  of  the  notochord,  and  the  second,  a  lateral,  usually  paired  process,  caused  by  the 
deficiency  of  the  medial  part  of  the  hypochordal  element  of  the  hindmost  occij)ital  vertebra, 
with  thickenings  of  the  lateral  parts  of  the  arch.  Springing  from  the  under  surface  of  the 
extremity  of  the  jugular  process,  a  rough  or  smooth  elevated  surface,  or  else  a  projecting  process, 
the  extremity  of  which  may  articulate  with  the  transverse  process  of  the  atlas,  is  sometimes 
met  with.  This  is  the  paroccipital  or  paramastoid  process.  The  size  and  shape  of  the  foramen 
magnum  varies  much  in  different  individuals  and  races,  as  also  the  disposition  of  its  plane, 
Elliot  Smith  has  called  attention  to  the  asymmetry  of  the  cerebral  fossa3,  which  is  correlated 
with  asj^mmetry  of  the  caudal  poles  of  the  cerebral  hemispheres.  Numerous  instances  of  fusion 
of  the  atlas  with  the  occipital  bone  have  been  recorded.  Many  are,  no  doubt,  pathological  in 
their  origin ;  others  are  associated  with  errors  in  development.  Interesting  anomalies  are  those 
in  which  there  is  evidence  of  the  intercalation  of  a  new  vertebral  element  between  the  atlas  and 
occipital,  constituting  what  is  termed  a  pro-atlas. 

Temporal  Bone. — The  occurrence  of  a  deficiency  in  the  floor  of  the  external  auditory  meatus 
is  not  uncommon  in  the  adult.  It  is  met  with  commonly  in  the  child  till  about  the  age  of  five, 
and  is  due  to  incomplete  ossification  of  the  tympanic  plate.  The  line  of  the  petro-squamosal 
suture  is  occasionally  grooved  for  the  lodgment  of  a  sinus  (petro-squamosal) ;  sometimes  the 
posterior  end  of  this  is  continuous  with  a  canal  which  pierces  the  superior  border  of  the  bone 
and  opens  into  the  lateral  sinus.  Anteriorly  the  groove  may  pass  into  a  canal  which  pierces 
the  root  of  the  zygoma  and  appears  externally  above  the  lateral  extremity  of  the  Glaserian 
fissure.  These  are  the  remains  of  channels  through  which  the  blood  passed  in  the  foetal  condition 
(see  ante).  Kazzander  has  recorded  a  case  in  which  the  squamous  jiart  of  the  temporal  was 
pneumatic,  the  sinus  reaching  as  higli  as  the  parietal  and  the  squamoso  -  sphenoidal  suture. 
Symington  has  described  a  case  in  which  the  squamous  part  was  distinct  and  separate  from 
the  rest  of  the  temporal  bone  in  an  adult ;  whilst  Hyrtl  has  observed  the  division  of  the 
squamous  part  of  the  temporal  into  two  by  a  transverse  suture.  The  zygomatic  process  has  been 
observed  separated  from  the  rest  of  the  bone  by  a  suture  close  to  its  root  (Adacni).  P.  P.  Laidlaw 
{Journ.  Anat.  and  Physiol,  vol.  xxxvii.  p.  364)  describes  a  temporal  bone  in  which  there  was 
absence  of  the  internal  auditory  meatus  and  of  the  stylo-mastoid  foramen.  The  jugular  fossa 
also  was  absent,  and  there  was  partial  absence  of  the  groove  for  the  lateral  sinus  associated  with 
the  presence  of  a  large  mastoid  foramen.  An  instance  of  a  rudimentary  condition  of  the  carotid 
canal  is  also  referred  to  in  the  same  volume  by  G.  H.  K.  Macalister. 

G.  Caribbe  {Anat.  Anz.  vol.  xx.  p.  81)  notes  the  occurrence  in  idiots  and  imbeciles  of  a  more 
pronounced  form  of  j^ost-glenoid  tubercle,  and  associates  it  with  regressive  changes  in  the  develop- 
ment of  the  temporal  bone. 

Sphenoid. — Through  imperfect  ossification  the  foramen  sjDinosum  and  foramen  ovale  are 
sometimes  incomplete  posteriorly.  Le  Double  {Bull,  et  to^t?).  de  la  Soc.  d'Anth.  de  Paris,  5"^  ser. 
vol.  iii.  p.  550)  records  a  case  in  which  the  foramen  rotundum  and  the  sphenoidal  fissure  were 
united  so  as  to  form  a  single  cleft. 

Through  deficiency  of  its  lateral  wall,  the  optic  foramen,  in  rare  instances,  communicates 
with  the  sphenoidal  fissure.  Duplication  of  the  ojotic  foramen  is  also  recorded  as  a  rare 
occurrence,  the  artery  passing  through  one  canal,  the  nerve  through  the  other.  Persistence  of 
the  cranio -pharyngeal  canal  is  also  occasionally  met  with.  Owing  to  the  ossification  of  fibrous 
bands  which  frequently  connect  the  several  bony  points,  anomalous  foramina  are  frequently 
met  with.  Of  such  are  the  carotico-clinoid  formed  by  the  union  of  the  anterior  and  middle 
clinoid  processes,  the  pterygo-spinous  foramen  enclosed  by  the  ossification  of  the  ligament  con- 
necting the  alar  spine  with  the  external  jDterygoid  j^late,  and  the  porus  crotaphitico-buccina- 
torius  similarly  developed  by  the  ossification  of  ligament  immediately  below  and  lateral  to  the 
inferior  ajDerture  of  the  foramen  ovale. 

Ethmoid. — The  size  of  the  os  planum  is  liable  to  considerable  variations.  In  the  lower 
races  it  tends  to  be  narrower  from  above  downwards  than  in  the  higher,  in  this  respect  resem- 
bling the  condition  met  with  in  the  anthrojjoids.  The  os  planum  may  fail  to  articulate  with 
the  lacrimal  owing  to  the  union  of  the  frontal  with  the  orbital  process  of  the  maxilla 
in  front  of  it.  (Orbito-maxillary-frontal  suture.  A.  Thomson,  Journ.  Anat.  and  Physiol. 
vol.  xxiv.  p.  349.)  Division  of  the  os  planum  by  a  vertical  suture  into  an  anterior  and  posterior 
part  has  been  frequently  recorded.  The  number  of  the  turbinals  may  be  increased  from  two  to 
four,  or  may  be  reduced  to  one.  (Eeport  of  Committee  of  Collect.  Invest.,  Journ.  Anat.  and 
Physiol,  vol.  xxviii.  p.  74.) 

Maxillae. — Not  unfrec^uently  there  is  a  suture  rumiing  vertically  through  the  bar  of  bone 
which  separates  the  infraorbital  foramen  from  the  infraorbital  margin.  Through  imperfections 
in  ossification,  the  infraorbital  canal  may  form  an  open  groove  along  the  floor  of  the  orbit. 

Duckworth  records  four  instances  of  a  spinous  process  projecting  inwards  into  the  apertura 

17*  a 


X  OSTEOLOGY. 

jivriformis  from  the  lower  jiart  of  the  nasal  notch.     A  case  has  been  described  (Fischel)  hi  which 
there  was  complete  absence  of  the  premaxillfe,  together  with  the  incisor  teeth. 

A  not  uncommon  anomaly  is  the  occurrence  of  a  rounded  elongated  ridge  extending  along 
the  interj^alatal  or  intermaxillary  sutures  on  the  under  surface  of  the  hard  j^alate.  This  is  called 
the  torvs  2^alatinus,  and  is  of  interest  because  its  presence  has  given  rise  to  the  assumj^tion  that  it 
was  due  to  a  pathological  growth.     (See  Stieda,  Virchoiv's  Festschrift,  vol.  i.  p.  147.) 

Zygomatic  Bone. — Cases  of  division  of  the  zygomatic  bone  by  a  horizontal  .suture  have  been 
recorded,  as  well  as  instances  of  its  separation  into  two  parts  by  a  vertical  suture.  OMdng  to  the 
supposed  more  frequent  occurrence  of  this  divided  condition  in  Asiatics  the  zygomatic  has  l)een 
named  the  os  Japonicum.  Barclay  Smith  ("  Proc.  Anat.  Soc,"  Joiir.  Anat.  and  Physiol,  A^jril  1898, 
p.  40)  describes  a  case  in  which  the  zygomatic  bone  was  divided  into  two  parts,  an  upper  and 
lower,  bj'  a  backward  extension  of  the  maxilla,  which  articiilated  with  the  zygomatic  process  of 
the  temporal,  thus  forming  a  temporo-maxillary  arch.  Varieties  of  a  like  kind  have  also  been 
described  by  Gruber  and  others.  Cases  have  been  noted  where,  owing  to  deficiency  in  the  develop- 
ment of  the  zygomatic,  the  continuity  of  the  zygomatic  arch  lias  been  incomjjlete. 

Nasal  Bones. — The  size  and  configuration  of  the  nasal  bones  vary  greatly  in  different  races, 
being,  as  a  ride,  large  and  prominent  in  the  white  races,  and  flat  and  reduced  in  size,  as  well  as 
depressed,  in  the  Mongolian  and  Negro  stock.  ComjDlete  absence  of  the  nasal  bones  has  been 
recorded,  and  their  division  into  two  or  more  parts  has  also  been  noted.  Obliteration  of  the 
internasal  suture  is  unusual ;  it  is  stated  to  occur  more  frequently  in  negroes,  and  is  the 
recognised  condition  in  adult  apes. 

Duckworth  has  recorded  a  case  {Journ.  Anat.  and  Physiol,  vol.  xxxvi.  jj.  257)  of  undue  extension 
doMTiwards  of  the  nasal  bone,  which  may  be  perhaps  accounted  for  on  the  supposition  that  the 
lower  i^art  is  a  jjersistent  portion  of  the  i)remaxilla. 

Lacrimal. — The  lacrimal  is  occasionally  absent.  In  some  cases  it  is  divided  into  two 
parts  ;  in  others  replaced  by  a  number  of  smaller  ossicles.  In  rare  instances  the  hamular  process 
may  extend  forwards  to  reach  the  orbital  margin,  and  so  bear  a  share  in  the  formation  of  the  face, 
as  in  lemurs  (Gegenbauer).  In  other  instances  the  hamulus  is  much  reduced  in  size.  Occasion- 
ally the  lacrimal  is  separated  from  the  os  planum  of  the  ethmoid  by  a  down-growth  from  the 
frontal,  which  articulates  with  the  orbital  jjrocess  of  the  maxilla,  as  is  the  normal  disposition 
in  the  gorilla  and  chimpanzee.  (Turner,  Challenger  Piejjorts,  "  Zoology,"  vol.  x.  Part  IV.  Plate  I. ; 
and  A.  Thomson,  Journ.  Anat.  and  Physiol.,  London,  vol.  xxiv.  p.  349.) 

Inferior  Turbinal. — A  case  in  which  the  inferior  turbinals  were  aljsent  has  been  recorded 
by  Hyrtl. 

Vomer. — Owing  to  imperfect  ossification  there  may  be  a  deficiency  in  the  bone,  filled  up 
during  life  by  cartilage.  The  separation  of  the  two  lamellae  along  the  anterior  border  varies 
considerably,  and  instances  are  recorded  where  they  were  separated  by  a  considerable  cavity 
within  the  substance  of  the  bone.  Instances  of  an  extension  forwards  of  the  sphenoidal  air 
sinus  into  and  sej^arating  the  laminae  of  the  bone  have  also  been  described.  The  spheno-vomerine 
canal  is  a  minute  opening  behind  the  rostrum  of  the  sphenoid,  and  between  it  and  the  alae  of  the 
vomer,  by  which  the  nutrient  artery  enters  the  bone. 

Palate  Bones. — The  occurrence  of  a  torus  palatinus  may  be  noted  (see  Variations  of  Maxilla). 

Mandible. — Consideral:>le  differences  are  met  with  in  the  height  of  the  coronoid  process  : 
usually  its  summit  reaches  the  same  level  as  the  condyle,  or  slightly  above  it ;  occasionally,  how- 
ever, it  rises  to  a  much  higher  level ;  in  other  cases  it  is  much  reduced.  These  dift'erences 
naturally  react  on  the  form  of  the  sigmoid  notch.  The  projection  of  the  mental  protuberance 
is  also  liable  to  vary.  Occasionally  the  mental  foramen  in  double,  and  sometimes  the  mylo-hyoid 
groove  is  for  a  short  distance  converted  into  a  canal.  There  is  often  a  marked  eversion  of  the 
angle  of  the  mandible,  which  Dieulafe  homologises  with  the  angular  apophysis  met  with  in 
lemurs  and  carnivora. 

Clavicle. — The  clavicles  of  women  are  more  slender,  less  curved,  and  shorter  than  those  of 
men.  In  the  latter  the  bone  is  so  inclined  that  its  acromial  end  lies  .slightly  higher  or  on  the  same 
level  with  tlie  sternal  end.  In  women  tiie  bone  usually  slopes  a  little  downward  and  laterally. 
The  more  pronounced  curves  of  some  bones  are  probably  associated  with  a  more  powerful 
development  of  the  pectoral  and  deltoid  muscles,  a  circumstance  which  also  affords  an  exjjlana- 
tion  of  the  differences  usually  seen  between  the  right  and  left  bones,  the  habitual  use  of  the  right 
upper  limlj  reacting  on  the  form  of  the  bone  of  tliat  side.  The  influence  of  muscular  action, 
however,  does  not  wliolly  account  for  the  production  of  the  curves  of  the  bone,  since  the  bone 
has  Ixjen  shown  to  display  its  characteristic  features  in  cases  where  there  has  been  defective 
development  or  absence  of  the  iipper  limb  (Reynault).  Partial  or  comjjlete  absence  of  the 
clavicle  has  Ijeen  recorded.  W.  S.  Taylor  exhiljited  an  interesting  case  of  tliis  kind  at  the 
Clinical  Society  of  London,  October  25,  1901.  Sometimes  there  is  a  small  canal  through  the 
anterior  border  of  the  bone  near  its  middle  for  the  transmission  of  one  of  the  supraclavicular 
nerves. 

Scapula. — The  most  common  variation  met  with  is  a  .separated  acromion  i)roce.ss.  In 
these  cases  tliere  has  been  failure  in  the  ossific  union  between  the  spine  and  acromion,  the 
junction  between  the  two  being  effected  by  a  layer  of  cartilage  or  by  an  articulation  jjossessing  a 
joint  cavity.  The  condition  is  u.sually  symmetrical  on  both  sides,  though  instances  are  recorded 
where  this  arrangement  is  unilateral     Very  much  rarer  is  the  condition  in  which  the  coracoid 


VAEIATIONS  IN  THE  SKELETON.  xi 

process  is  sejjarable  from  the  rest  of  the  bone.  The  size  and  form  of  the  scapular  notch  differs. 
In  certain  cases  the  superior  border  of  the  bone  describes  a  unciform  curve  reaching  the  base 
of  the  coracoid  without  any  indication  of  a  notch.  In  some  scapulaj,  more  particularly  in 
those  of  very  old  people,  the  floor  of  the  subscapiilar  fossa  is  deficient  owing  to  the  absorption  of 
the  thin  bone,  the  periosteal  layers  alone  filling  up  the  gap. 

At  birth  the  vertical  length  of  the  bone  is  less  in  proportion  to  its  width  than  in  the  adult. 

Humerus. — As  has  been  stated  in  the  description  of  the  bone,  the  olecranon  and  coro- 
noid  fossaj  may  communicate  with  each  other  in  the  macerated  bone.  The  resulting  supra- 
trochlear foramen  is  most  commonly  met  with  in  the  lower  races  of  man,  as  well  as  in  the 
anthropoid  &i)es,  and  in  some  other  mammals.  The  occurrence  of  a  liook-like  spine,  called  tlie 
epicondylic  process,  which  projects  in  front  of  the  medial  epicondylic  ridge,  is  not  uncommon. 
Its  extremity  is  connected  with  the  medial  epicondyle  by  means  of  a  fibrous  band,  underneath 
which  the  median  nerve,  accompanied  by  the  brachial  artery,  or  one  of  its  large  branches,  may 
pass,  or  in  some  instances,  the  nerve  alone,  or  the  artery  unaccompanied  by  the  nerve.  This 
arrangement  is  the  homologue  in  a  rudimentary  form  of  a  canal  present  in  many  animals, 
notably  in  the  carnivora  and  marsujiials.  In  addition  to  the  broad  musculo-spiral  groove  already 
described,  and  which  is  no  doubt  produced  by  the  twisting  or  torsion  of  the  shaft,  there  is 
occasionally  a  distinct  narrow  groove  posterior  to  it,  which  marks  precisely  the  course  of  the 
musculo-siiiral  nerve  as  it  turns  round  the  lateral  side  of  the  shaft  of  the  bone. 

Ulna. — Cases  of  partial  or  complete  absence  of  the  ulna  through  congenital  defect  have 
been  recorded.  Rosenm  tiller  has  described  a  case  in  which  the  olecranon  was  separated  from  the 
ujDper  end  of  the  bone,  resembling  thus  in  some  respects  the  patella.  In  powerfully  developed 
bones  there  is  a  tendency  to  the  formation  of  a  sharp  projecting  crest  corres^jonding  to  the  inser- 
tion of  the  triceps. 

Radius. — Cases  of  congenital  absence  of  the  radius  are  recorded ;  in  these  the  thumb  is 
not  infrequently  wanting  as  well. 

Carpus. — Increase  in  the  number  of  the  carpal  elements  is  occasionally  met  with,  and 
these  have  been  ascribed  to  division  of  the  navicular,  os  lunatum,  os  triquetrum,  caj^itate,  lesser 
multangular,  and  os  hamatum.  Of  these  the  most  interesting  is  the  os  centrale,  first  described 
by  Rosenberg,  and  subsequently  investigated  by  Henke,  Leboucq,  and  others.  This  is  met  with 
almost  invariably  as  an  independent  cartilaginous  element  during  the  earlier  months  of  foetal 
life,  and  occasionally  becomes  developed  into  a  distinct  ossicle  placed  on  the  back  of  the  carpus 
between  the  navicular  and  capitate  bones  and  the  small  multangular.  Its  significance  depends 
on  the  fact  that  it  is  an  important  component  of  the  carpus  in  most  mammals,  and  is  met 
with  normally  in  the  orang  and  most  monkeys.  Ordinarily  in  man,  as  was  pointed  out  by 
Leboucq,  it  becomes  fused  with  the  naviciilar,  where  its  presence  is  often  indicated  by  a  small 
tubercle,  a  condition  which  obtains  in  the  chimpanzee,  the  gorilla,  and  the  gibbons.  Dwight 
has  described  a  case  in  which  there  was  an  OS  subcapitulum  in  both  hands.  The  ossicle  lay 
between  the  base  of  the  middle  metacarpal  bone  and  the  capitate  bone  with  the  small  multangular 
to  its  radial  side  {Anat.  Anz.  vol.  xxiv.).  Further  addition  to  the  number  of  the  carpal  elements 
may  be  due  to  the  separation  of  the  styloid  process  of  the  third  metacarpal  bone  and  its  persistence 
as  a  separate  ossicle. 

Reduction  in  the  number  of  the  carpus  has  been  met  with,  but  this  is  probably  due  to 
pathological  causes.  Morestin  {Bull.  Soc.  Anat.  de  Paris,  tome  71,  p.  651),  who  has  investigated 
the  subject,  finds  that  ankylosis  occurs  most  frequently  between  the  bases  of  the  second  and 
third  metacarpal  bones  and  the  carpus,  seldom  or  never  between  the  carpus  and  the  first  meta- 
carpal, or  between  the  pisiform  and  os  triquetrum.  Instances  of  complete  fusion  of  the  os 
lunatum  and  os  triquetrum  bones,  without  any  apparent  pathological  change,  have  been  recorded 
in  Europeans,  Negroes,  and  an  Australian. 

Metacarpal  Bones-  —  As  previously  stated  above,  the  styloid  apophysis  of  the  third 
metacarpal  bone  ajapears  as  a  separate  ossicle  in  about  1"8  per  cent  of  cases  examined  ("Fourth 
Annual  Report  of  the  Committee  of  Collect.  Invest.  Anat.  Soc.  Gt.  Brit,  and  Ireland,"  Journ. 
Anat.  and  Physiol.,  vol.  xxviii.  p.  64).  In  place  of  being  united  to  the  third  metacarj^al, 
the  styloid  apophysis  may  be  fused  with  either  the  capitate  bone  or  the  small  multangular,  under 
which  conditions  the  base  of  the  third  metacarpal  bone  is  without  this  characteristic  process. 

Phalanges. — Several  instances  have  been  recorded  of  cases  in  which  there  were  three  phalanges 
in  the  thumb.  Bifurcation  of  the  terminal  phalanges  has  occasionally  been  met  with,  and  examples 
of  supjjression  of  a  phalangeal  segment  or  its  absorption  by  another  phalanx  have  also  been  de- 
scribed (Hasselwander,  Zeits.  F.  Morph.  u.  Anthr.,  vol.  vi.  1903). 

Innominate  Bone, — Some  of  the  anomalies  met  with  in  the  innominate  bone  are  due  to  ossifica- 
tion of  the  ligaments  connected  with  it ;  in  other  cases  they  depend  on  errors  of  development. 
Failure  of  union  between  the  pubic  and  ischial  rami  has  also  been  recorded.  Cases  have  occurred 
where  the  obturator  groove  has  been  bridged  across  by  bone,  and  one  case  is  noted  of  absence  of 
the  cotyloid  notch  on  the  acetabular  margin.  In  rare  cases  the  os  acetabuli  (see  Ossification) 
remains  as  a  separate  bone. 

Femur. — Absence  of  the  pit  on  the  head  of  the  femur  for  the  attachment  of  the  liga- 
mentum  teres  has  been  recorded.  This  corresponds  with  the  condition  met  with  in  the  orang. 
Not  infrequently  there  is  an  extension  of  the  articular  surface  of  the  head  on  to  the  fore  and 
upper  aspect  of  the  neck  :  this  is  a  "  pressure  facet "  caused  by  the  contact  of  the  iliac  portion 


xii  OSTEOLOGY. 

of  the  acetabular  margin  witli  the  neck  of  the  bone,  when  the  limb  is  maintained  for  long  periods 
in  the  flexed  jjosition,  as  in  tailors,  and  also  in  those  races  who  habitually  squat  (Lane,  Journ. 
Anat.  and  Physiol.,  vol.  xxii.  p.  606). 

The  occurrence  of  a  trochanter  tertius  has  been  already  referred  to.  Its  presence  is  not 
confined  to  individuals  of  powerful  j^hysique,  but  may  occur  in  those  of  slender  build,  so  far 
suggesting  that  it  is  not  to  be  regarded  merely  as  an  indication  of  excessive  muscular  develop- 
ment. The  observations  of  Dixon  {Joihrn.  Anat.  and  Physiol.,  vol.  xxx.  p.  502),  who  noted  the 
occurrence  of  a  sejsarate  epiphysis  in  three  cases  in  connexion  with  it,  seem  to  point  to  its 
possessing  some  morjjhological  significance.  Occasionally  the  gluteal  ridge  may  be  replaced  by  a 
hollow,  the  fossa  hypotrochanterica,  or  in  some  cases  the  two  may  co-exist. 

The  angle  of  the  neck  is  more  open  in  the  child  than  in  the  adult,  and  tends  to  be  less 
when  the  femoral  length  is  short  and  the  pehdc  width  great — conditions  which  particularly 
appertain  to  the  female.  There  is  no  evidence  to  show  that  after  growth  is  completed  any 
alteration  takes  place  in  the  angle  Avith  advancing  years  (Humphry). 

The  curvature  of  the  shaft  may  undergo  considerable  variations,  and  the  appearance  of  the 
posterior  surface  of  the  bone  may  be  modified  by  an  absence  of  the  linea  aspera,  a  condition 
resembling  that  seen  in  apes ;  or  by  an  unusual  elevation  of  the  bone  which  supj)orts  the  ridge 
{femur  a  inlastre),  produced,  as  Manouvrier  has  suggested,  by  the  excessive  development  of  the 
muscles  here  attached. 

Under  the  term  " platymerie,"  Manouvrier  describes  an  an tero -posterior  compression  of  the 
upper  jjart  of  the  shaft,  frequently  met  with  in  the  femora  of  prehistoric  races. 

Patella. — Cases  of  congenital  absence  of  the  patella  have  been  recorded. 

F.  C.  Kempson  {Journ.  Anat.  and  Physiol.,  vol.  xxxvi.)  has  recently  drawn  attention  to  the 
condition  described  as  emargination  of  the  patella.  In  specimens  displaying  this  appearance  the 
margin  of  the  bones  is  concave  from  a  j)oint  about  half  an  inch  to  the  oliter  side  of  the  middle 
line,  to  a  jjoint  half-way  down  the  outer  margin  of  the  bone,  here  there  is  usually  a  pointed 
sj^ine  directed  uja wards  and  outwards.  The  condition  ajspears  to  be  associated  with  the  insertion 
of  the  tendon  of  the  vastus  lateralis.  G.  Joachimstal  {Archiv  u.  Atlas  der  nomalen  und  patholo- 
gischen  Anatomie  in  typischen  R'dntgenhildern,  Bd.  8)  figures  a  case  in  which  on  both  sides  the 
patella  was  double  in  an  adult,  the  lower  and  much  the  smaller  portion  was  embedded  in  the 
ligamentum  patellae. 

Tibia. — The  tibia  is  often  unduly  laterally  compressed,  leading  to  an  increase  in  its 
antero-jjosterior  diameter  as  compared  with  its  transverse  width.  This  condition  is  more 
commonly  met  with  in  the  bones  of  j)rehistoric  and  savage  races  than  in  modern  Europeans. 
Attention  was  first  directed  to  this  particular  form  by  Busk,  who  named  the  condition 
platyknemia.  The  general  appearance  of  such  tibiae  resembles  that  seen  in  the  apes,  and 
depends  on  an  excejational  development  of  the  tibialis  posterior  muscle,  though,  as  Manouvrier 
has  pointed  out,  in  apes  this  is  associated  with  the  direct  action  of  the  muscle  on  the  foot,  as  in 
climbing,  whereas  in  man,  as  a  consequence  of  the  bipedal  mode  of  progression,  the  muscle  is 
employed  in  an  inverse  sense,  viz.  by  steadying  the  tibia  on  the  foot,  and  thus  providing  a  fixed 
base  on  which  the  femur  can  move.  This  explanation,  however,  is  disputed  by  Derry  {Journ. 
Anat.  and,  Phys.,  vol.  xli.  p.  123).  Such  jalatyknemic  tibiae  are  occasionally  met  Avith  in  the 
more  highly  ciAdlised  races,  and  are,  according  to  Manouvrier,  associated  with  habits  of  great 
activity  among  the  inhabitants  of  rough  and  mountainous  districts. 

Another  interesting  condition  is  one  in  which  the  upper  extremity  is  more  strongly  recurved 
than  is  usuaL  This  retroversion  of  the  head  of  the  tibia  was  at  one  time  supposed  to  rejDresent 
an  intermediate  condition  in  Avhich  the  knee  could  not  be  fully  extended  so  as  to  bring  the  axis 
of  the  leg  in  line  with  the  thigh ;  but  such  oj^inion  has  now  been  upset  by  the  researches  of 
ManouAa'ier,  Avho  claims  that  it  is  the  outcome  of  a  habit  not  iincommon  amongst  peasants  and 
countrymen,  viz.  that  of  Avalking  habitually  with  the  knees  slightly  bent. 

Habitual  posture  also  leaves  its  impress  on  the  form  of  the  tibia,  and  in  races  in  which  the 
use  of  the  chair  is  unknown,  the  extreme  degree  of  flexion  of  the  knee  and  ankle  necessitated  by 
the  adoption  of  the  squatting  position  as  an  attitude  of  habitual  rest  is  associated  Avith  an  increase 
in  the  convexity  of  the  lateral  condylic  surface,  and  the  aj^pearance,  not  infrequently,  of  a 
pressure  facet  on  the  anterior  border  of  the  lower  extremity,  Avhicli  rests  in  that  position  on  the 
neck  of  the  talus.  Cases  of  congenital  absence  of  the  tibia  ha\'e  been  frequently  described, 
amongst  the  most  recent  being  those  recorded  Ijy  Clutton,  Joachimsthal,  Bland-Sutton,  and 
Waitz. 

Fibula. — The  filjula  may  be  ridged  and  grooved  in  a  remarkable  manner,  as  is  the  case  in 
many  bones  of  prehistoric  races.  This  is  probably  associated  with  a  greater  or  perhaps  more 
active  develoi>ment  of  tlie  muscles  attached  to  it. 

The  superior  articular  facet  varies  much  in  size.  Bennett  {Dublin  Journ.  Med.  Sc,  Aug. 
1891)  records  a  case  in  Avhich  it  was  doul^le,  and  also  notes  the  occurrence  of  specimens  in  which 
it  Avas  absent  and  in  which  the  head  of  the  bone  did  not  reach  as  high  as  the  lateral  condyle  of 
the  tibia. 

Many  instances  of  partial  or  complete  absence  of  the  bone  have  been  published.  (Leffebre 
Contribution  h  I'dtude  de  I'absence  cong6nitale  du  f&ron^,  Lille,  1895.) 

Talus  or  Astragalus. — The  anterior  is  sometimes  separated  from  the  middle  calcanean 
facet  by  a  non-articular  furrow.  The  posterior  lateral  tubercle,  often  largely  developed,  is 
occasionally  (2-6  per  cent)  a  separate  ossicle  forming  what  is  known  as  the  os  trigonum 
(Bardeleben) ;  or  it  may  be  united  to  the  body  of  the  astragalus  by  a  distinct  synchondrosis.     A 


SEKTAL  HOMOLOGIES  OF  THE  VERTEBE^.  xiii 

smooth  articular  surface  may  occasionally  be  found  on  the  medial  side  of  the  upper  surface  of  the 
neck.  This  is  a  pressure  facet  dependent  on  the  frequent  use  of  the  ankle-joint  in  a  condition  of 
extreme  flexion,  and  is  caused  by  the  opi:)Osition  of  the  bone  against  the  anterior  edge  of  the  lower 
end  of  the  tibia. 

The  form  of  the  bone  at  birth  difi'ers  from  that  of  the  adult  in  that  the  inward  splay  of  the 
neck  on  the  body  is  more  pronounced,  forming  on  an  average  an  angle  of  35°  as  compared  with 
a  mean  of  12"  in  the  adult ;  moreover,  the  articular  surfece  for  the  medial  malleolus  extends 
forwards  along  the  medial  side  of  the  neck,  and  to  some  extent  overruns  its  upper  surface.  This 
is  doubtless  a  consequence  of  the  inverted  position  of  the  foot  maintained  by  the  foetus  during 
intrauterine  life.     In  these  respects  the  foetal  astragalus  conforms  to  the  anthro^^oid  type. 

For  a  detailed  study  of  the  varieties  of  this  bone,  see  R.  B.  S.  Sewell  {Journ.  Anat.  and  Physiol., 
vol.  xxxviii.) 

Calcaneus. — The  peroneal  tubercle  is  occasionally  unduly  prominent,  constituting  the  sub- 
malleolar  apophysis  of  Hyrtl,  and  cases  are  recorded  of  the  calcaneus  articulating  with  the 
navicular  (Morestin,  H.,  Bull,  de  la  Soc.  Anat.  de  Paris,  1894,  ser.  v.  t.  8,  n.  24,  p.  798  ;  and 
Petrini,  Atti  del  XL  Congr.  Med.  Internaz.  Roma,  1894,  vol.  ii.,  "Anat."  p.  71).  Pfitzner  {Moriiho- 
logische  Arheiten,  vol.  vi.  p.  245)  also  records  the  separation  of  the  sustentaculum  tali  to  form  an 
OS  sustentacixli.      (See  also  P.  P.  Laidlaw,  Journ.  Anat.  and  Physiol.,  vol.  xxxviii.  p.  133.) 

Navicular  or  Scaphoid. — According  to  Manners  Smith  this  bone  displays  more  variety  ol 
form  than  any  other  of  the  tarsal  bones.  He  accounts  for  this  both  on  morjihological  and 
mechanical  grounds.  He  regards  the  tubercle  as  probably  of  threefold  origin,  an  apojjhj^sial,  an 
epii^hysial,  and  a  sesamoid  element,  the  latter  being  the  so-called  sesamoid  bone  in  the  tendon 
of  the  tibialis  posticus.    Cases  are  recorded  where  the  tubercle  has  formed  an  independent  ossicle. 

Cuneiform  Bones. — Numerous  cases  of  division  of  the  first  cuneiform  bone  into  dorsal 
and  plantar  parts  liave  been  recorded  ;  the  frequent  division  of  its  metatarsal  articular  facet  is  no 
doubt  correlated  with  this  anomalous  condition.  T.  Dwiglit  has  described  {Anat.  Anz.,  vol.  xx. 
IX  465)  in  two  instances  the  occurrence  of  an  Os  Intercuueiforme.  The  ossicle  so  named  lies  on 
the  dorsum  of  the  foot  at  the  proxiuial  end  of  the  line  of  articulation  between  the  first  and 
second  cuneiform  bones. 

Cuboid. — Blandin  has  recorded  a  case  of  division  of  the  cuboid.  Occasionally  there  is  a 
facet  on  the  lateral  surface  of  the  bone  for  articulation  with  the  tuberosity  of  the  Vth  metatarsal 
(Manners  Smith). 

Tarsus  as  a  Whole. — Increase  in  the  number  of  the  tarsal  elements  may  be  due  to  the 

occurrence  of  division  of  either  the  first  cuneiform  or  the  cuboid  bone,  or  to  the  occasional 
presence  of  an  os  trigonum.  Cases  of  separation  of  the  tuberosity  of  the  navicular  bone  have 
been  recorded,  and  instances  of  su23ernumerary  ossicles  between  the  first  cuneiform  and 
second  metatarsal  bone  have  been  noted.  Stieda  mentions  the  occurrence  of  a  small  ossicle 
in  connexion  with  the  articular  surface  on  the  fore  and  upper  jjart  of  the  os  calcis,  and  Pfitzner 
notes  the  occurrence  of  an  os  sustentacula  For  further  information  on  the  variations  of  the 
skeleton  of  the  foot,  see  Pfitzner  {Morphologische  Arheiten,  vol.  vi.  p.  245). 

The  jjossibility  of  an  injury  having  been  the  cause  of  the  occurrence  of  some  of  these  so-called 
supernumerary  ossicles  must  not  be  overlooked.  The  use  of  the  Rontgen  rays  has  proved  that 
accidents  of  this  kind  are  much  more  frec[uent  than  was  at  first  supposed. 

The  reduction  in  the  number  of  the  tarsus  is  clue  to  the  osseous  union  of  adjacent  bones.  In 
many  instances  this  is  undoubtedly  pathological,  but  cases  have  been  noticed  (Lebouccj)  of  fusion 
of  the  cartilaginous  elements  of  the  calcaneus  and  talus,  and  the  calcaneus  and  navicular 
in  foetuses  of  the  third  month. 

Metatarsal  Bones. — Several  instances  of  sej^aration  of  the  tuberosity  of  the  fifth  metatarsal 
(os  Vesaleanum)  have  been  recorded,  whilst  numerous  examples  of  an  os  intermetatarsum  between 
the  bases  of  the  first  and  second  metatarsal  bones  have  been  I'ecorded  by  Gruber  and  others. 
Tae  tubercle  on  the  base  of  the  first  metatarsal  for  the  attachment  of  the  peronnsus  longus  tendon 
is  occasionally  met  with  as  a  separate  ossicle.  An  epijihysis  over  the  spot  where  the  tuberosity 
of  the  Y.  metatarsal  rests  on  the  ground  has  been  described  (Kirchner,  Archiv.  Klin.  Chir.,  B  80). 

Phalanges. — It  is  not  uncommon  to  meet  with  fusion  of  the  second  and  third  phalanges, 
particularly  in  the  fifth,  less  frequently  in  the  fourth,  and  occasionally  in  the  second  and  third 
toes.  The  union  of  the  phalangeal  elements  has  been  observed  in  the  foetus  as  well  as  the 
adult  (Pfitzner).  The  proportionate  length  of  the  jjhalanges  varies  much ;  in  some  cases  the 
ungual  jahalanges  are  of  fair  size,  the  bones  of  the  second  row  being  mere  nodules,  whilst  in  other 
instances  the  reduction  in  size  of  the  terminal  phalanges  is  most  marked. 


APPENDIX   a 

SERIAL  ]  HOMOLOGIES  OF  THE  VERTEBRA. 

It  is  a  self-evident  fact  that  the  vertebral  column  consists  of  a  number  of  segments  or  verte- 
brte  all  possessing  some  characters  in  common.  These  vertebrse  or  segments  undergo  modifications 
according  to  the  region  they  occupy  and  the  functions  they  are  called  upon  to  serve,  so  that 

17  *& 


XIV 


OSTEOLOGY. 


CERVICAL 


True  traxsver 

I'ROCESS  — 

Vertebrarterial 

FORAMEN 

Costal  process 

Xeuro-central  suture 


Transverse 

PROCESS 


True  trans- 
verse PROCESS 


Costal  process 


Rib 


LUMBAR 


Accessory 
process 


their  correspondence  and  identity  is  thereby  obscured.  There  is  no  difl&culty  in  recognising  the 
homology  of  the  bodies  and  neural  arches  throughout  the  column.  According  to  some 
anatomists  the  neural  arch  is  the  more  primitive  element  in  the  formation  of  a  vertebra,  whilst 
others  hold  that  the  centra  are  the  foundation  of  the  column.  Be  that  as  it  may,  we  find  that  in 
the  higher  vertebrates,  at  least,  the  bodies  are  the  parts  which  most  persist.     They  are,  however, 

subject  to  modifications  dependent 
on  their  fusion  with  one  another. 
This  occurs  in  the  cervical  part  of 
the  column  where  the  centrum  of 
the  first  cervical  or  atlas  vertebra 
has  for  functional  reasons  become 
fused  with  the  body  of  the  second 
or  axis  vertebra  to  form  the  odon- 
toid process  of  that  segment.  For 
similar  reasons,  and  in  association 
with  the  union  of  the  girdle  of 
the  hind-limb  with  the  column, 
the  bodies  of  the  vertebrae  which 
correspond  to  the  sacral  segment 
become  fused  together  to  form  a 
solid  mass.  In  the  terminal  por- 
tion of  the  caudal  region  the  centra 
■R[B-/^       "V — \       V^  /-^   J-X^~\   Transverse    alone  represent  the  vertebral  seg- 

process  ments. 

As  regards  the  neural  arch,  this 
in  man  Toecomes  deficient  in  the 
lower  sacral  region,  and  absent 
altogether  in  the  lower  coccygeal 
segments.  The  spinous  processes 
are  absent  in  the  case  of  the  first 
cervical,  lower  sacral,  and  all  the 
coccygeal  vertebrae,  and  display 
characteristic  differences  in  the 
cervical,  thoracic,  and  lumbar 
regions,  which  have  been  already 
described.  The  articular  processes 
(zygajjophyses)  are  secondary  de- 
velopments, and  display  great 
diversity  of  form,  determined  by 
their  functional  requirements.  It 
is  noteworthy  that,  in  the  case  of 
the  upper  two  cervical  vertebrae, 
they  are  so  disposed  as 
to  lie  in  front  of  the 
foramina  of  exit  of  the 
upper  two  spinal  nerves, 
and  by  this  arrangement 
the  weight  of  the  head 
is  transmitted  to  the 
solid  column  formed  by 
the  vertebral  bodies,  and 
not  on  to  the  series  of 
neiiral  arches.  It  is  in 
regard  to  the  homology 
of  the  transverse  pro- 
cesses, so  called,  that 
most  difficulty  arises.  In 
the  thoracic  region  they 
can  best  be  studied  in 
their  simplest  form ; 
here  the  ribs — which 
Gegenbauer  regards  as  a 
dift'erentiation  from  the 
inferior  or  luemal  arches, 
in  opposition  to  the  view 
advanced  by  others  that 
they  are  a  secondary  development  from  the  fibrous  intermuscular  septa— articulate  with  the 
transverse  processes  and  bodies  of  the  thoracic  vertebrae  through  the  agency  of  the  tuljercular 
(diapophyse.s)  and  capitular  (parapophyses)  processes  respectively,  the  latter  being  placed,  strictly 
speaking,  on  the  neural  arch  behind  the  line  of  the  neuro-central  synchondrosis. 

An  interval  is  thus  left  between  the  neck  of  the  ril)  and  the  front  of  the  transverse  process ; 
this  forms  an  arterial  passage  which  corresponds  to  the  vertebrarterial  canal  in  the  transverse 


Costo-traxsverse  fora- 

i  MEN  (vertebrarterial)  ] 

Neuro-central  suture 


Accessory 
tubercle 

Costal  elejiext 
(lumbarial) 

OCCASIOXAL  VERTE 

brarterial  foramen 
Neuro-central  suture 


Transverse 
process' 


Costal  element  (rib) 
SACRAL 


Costal  element 

Occasional  foramen 
(vertebrarterial)      I 
N'euro-central  suture 


Transverse 
processes 


Fig.  19/ 


Costal  elements 


A  B 

Diagram  to  illustrate  the  Homologous  Parts  of  the  VERTEBKiE. 

the  neural  arch  and  its  processes,  red  ;  the  costal 
A,  from  above.      B,  from  the  side. 


The  centra  are  coloured  purple 
elements,  lilue. 


MEASUEEMENTS  AND  INDICES.  xv 

processes  of  the  cervical  vertebrie,  the  anterior  Itar  of  which  is  homologous  with  the  head  and 
tubercle  of  the  tlioracic  rib,  whilst  the  posterior  part  lies  in  series  with  the  thoracic  transverse 
process.  These  homologies  are  further  enqjhasised  by  the  fact  that  in  the  case  of  the  seventh 
cervical  vertebra  the  anterior  limb  of  the  so-called  transverse  process  is  developed  from  an 
independent  ossific  centre,  which  occasionally  persists  in  an  indejjendent  form  as  a  cervical  rib. 

In  the  lumbar  region  the  lateral  or  transverse  process  is  serially  homologous  with  the 
thoracic  ribs,  though  here,  owing  to  the  coalescence  of  the  contiguous  parts,  there  is  no  arterial 
channel  between  the  rib  element  and  the  true  transverse  process,  which  is  represented  by  the 
accessory  processes  (anajjophyses),  placed  posteriorly  at  the  root  of  the  so-called  transverse 
process  of  human  anatomy.  Support  is  given  to  this  view  by  the  presence  of  a  distinct  costal 
element  in  connexion  with  the  transverse  process  of  the  first  lumbar  vertebra,  which  accounts 
for  the  occasional  formation  of  a  supernumerary  rib  in  this  region.  The  cases  of  foramina  in  the 
transverse  processes  of  the  lumbar  vertebrae  (see  p.  vi)  are  also  noteworthy  as  supporting  this  view. 

In  the  sacrum  the  lateral  mass  of  the  bone  is  made  up  of  combined  transverse  and  costal 
elements,  with  only  very  exceptionally  an  intervening  arterial  channel  (see  p.  vi).  In  the 
case  of  the  upper  three  sacral  segments  the  costal  elements  are  largely  developed,  assist  in 
sujjporting  the  ilia,  and  are  called  the  true  sacral  vertebrae ;  whilst  the  lower  sacral  segments, 
which  are  not  in  contact  with  the  ilia,  are  referred  to  as  the  pseudo-sacral  vertebrte. 

The  anterior  arch  of  the  atlas  vertebra  is,  according  to  Froriep,  developed  from  a  hypochordal 
strip  of  cartilage  (hypochordal  spange). 


APPENDIX   D. 

MEASUREMENTS  AND  INDICES  EMPLOYED  IN  PHYSICAL  ANTHROPOLOGY. 

(1)  Craniometry. 

The  various  grouj)s  of  mankind  display  in  their  physical  attributes  certain  features  which  are 
more  or  less  characteristic  of  the  stock  to  which  they  belong.  Craniology  deals  with  these 
differences  so  far  as  they  affect  the  skulL  The  method  whereby  these  differences  are  recorded 
involves  the  accurate  measurement  of  the  skull  in  most  of  its  details.  Such  procedure  is  included 
under  the  term  craniometry.  Here  only  the  outlines  of  the  subject  are  briefly  referred  to  ; 
for  such  as  desire  fuller  information  on  the  subject,  the  works  of  Broca,  Topinard,  Flower,  and 
Turner  may  be  consulted. 

The  races  of  man  display  great  variations  in  regard  to  the  size  of  the  skull.  Apart  altogether 
from  individual  differences  and  the  proportion  of  head-size  to  body -height,  it  may  be  generally 
assumed  that  the  size  of  the  skull  in  the  more  highly  civilised  races  is  much  in  excess  of  that 
displayed  in  lower  types.  The  size  of  the  head  is  intimately  correlated  with  the  develop- 
ment of  the  brain.  By  measuring  the  capacity  of  that  part  of  the  skull  occupied  by  the 
encephalon,  we  are  enabled  to  form  some  estimate  of  the  size  of  the  brain.  The  cranial  capacity 
is  determined  by  filling  the  cranial  cavity  with  some  suitable  material  and  then  taking  the 
cubage  of  its  contents.  Various  methods  are  employed,  each  of  which  has  its  advantage.  The  use 
of  fluids,  which  of  course  would  be  the  most  accurate,  is  rendered  impracticable,  without  special 
precautions,  owing  to  the  fact  that  the  macerated  skull  is  pierced  by  so  many  foramina.  As  a 
matter  of  practice,  it  is  found  that  leaden  shot,  glass  beads,  or  seeds  of  various  sorts  are  the  most 
serviceable.  The  results  obtained  display  a  considerable  range  of  variation.  For  purposes  of 
classification  and  comi^arison,  skulls  are  grouped  according  to  their  cranial  capacity  into  the 
following  varieties : — 

Microcephalic  skulls  are  those  with  a  capacity  below  1350  cc,  and  include  such  well-known 
races  as  Andamanese,  Veddahs,  Australians,  Bushmen,  Tasmanians,  etc. 

Mesocephalic  skulls  range  from  1350  cc.  to  1450  cc,  and  embrace  examples  of  the  following 
vai'ieties  :  American  Indians,  Chinese,  some  African  Negroes. 

Megacephalic  skulls  are  those  with  a  capacity  over  1450  cc,  and  are  most  commonly  met 
with  in  the  more  highly  civilised  races :  Mixed  Europeans,  Japanese,  etc. 

Apart  from  its  size,  the  form  of  the  cranium  has  been  regarded  as  an  important  factor  in  the 
classification  of  skulls ;  though  whether  these  differences  in  shape  have  not  been  unduly  em- 
phasised in  the  past  is  open  to  question. 

The  relation  of  the  breadth  to  the  length  of  the  skull  is  expressed  by  means  of  the  cephalic 
index  which  records  the  proportion  of  the  maximum  breadth  to  the  maximum  length  of  the 
skull,  assuming  the  latter  equal  100,  or — 

Max.  breadth  x  100     ~    ,    , .    .    , 

,^       ^,      y,      =Cepnahc  index. 

Max.  length 

The  results  are  classified  into  three  groups  : — 

1.  Dolichocephalic,  with  an  index  below  75  :  Australians,  Kaffirs,  Zulus,  Eskimo,  Fijians. 

2.  Mesaticephalic,  ranging  from  75  to  80  :  Europeans  (mixed),  Chinese,  Polynesians  (mixed). 

3.  Brachycephalic,  with  an  index  over  80  :  Malays,  Burmese,  American  Indians,  Anda- 


XVI 


OSTEOLOGY. 


In  order  to  provide  for  uniformity  in  tlie  results  of  different  observers,  some  system  is  neces- 
sary by  which  the  A'arious  25oints  from  which  the  measurements  are  taken  must  correspond. 
Whilst  there  is  much  difference  in  the  yalne  of  the  measurements  insisted  on  by  individual 
anatomists,  all  agree  in  endeavouring  to  select  such  jwints  on  the  skull  as  may  be  readily  deter- 
mined, and  which  have  a  fairly  fixed  anatomical  position.  The  more  important  of  these  "  fixed 
points  "  are  included  in  the  subjoined  table  : — 


Bregma 


Stephanion 


Obelion 


Pterion 


Lambda 


Maximum  occipital  \         \ 

POINT    \  \, 


ASTERIOK 


Supra-auricular 

POINT 


Nasion 

Dacryon 
Khinion 

Jugal  point 

Akanthion 

Pbosthion 
(alveolar  point) 


POQONION 


Nasion. — The  middle  of  the  naso-frontal  suture. 

Grlabella. — A  point  midway  between  the  two  superciliary  ridges. 

Ophryon. — The  central  point  of  the  narrowest  transverse  diameter  of  the  forehead,  measured 

from  one  temporal  line  to  the  other. 
Inion. — The  external  occipital  protuberance. 
Maximum  Occipital  Point. — The  point  on  the  squamous  jjart  of  the  occipital  in  the  sagittal 

plane  most  distant  from  the  glabella. 
OpistMon. — The  middle  of  the  posterior  margin  of  the  foramen  magnum. 
Basion. — The  middle  of  the  anterior  margin  of  the  foramen  magnum. 
Bregma. — The  point  of  junction  of  the  coronal  and  sagittal  sutures. 
Ehinion. — The  most  i^rominent  point  at  which  the  nasal  bones  touch  one  another. 
Alveolar  Point  or  Prosthion. — The  centre  of  the  anterior  margin  of  the  upper  alveolar 

margin. 
Subnasal  Point. — The  middle  of  the  inferior  border  of  the  anterior  nasal  aperture  at  the 

centre  of  the  nasal  spine. 
Akanthion. — The  most  i)rominent  jsoint  on  the  nasal  spine. 
Vertex. — The  summit  of  the  cranial  vault. 

Obelion. — A  j^oint  over  the  sagittal  suture,  on  a  line  with  the  parietal  foramina. 
Lambda.. — The  meeting-point  of  the  sagittal  and  lambdoid  sutures. 
Pterion. — The  region  of  the  antero-lateral  fontanelle  where  the  angles  of  the  frontal,  parietal, 

squamous  part  of  tlie  temporal,  and  alisphenoid  lie  in  relation  to  one  another.     As  a 

rule,  the  sutures  are  arranged  like  the  letter  H ,  the  parietal  and  alisijhenoid  separating 

the  frontal  from  the  squamous  temi^oral.     In  other  cases  the  form  of  the  suture  is  like 

an  X  ;   wliilst  in  a  third  variety  the  frontal  and   squamous   part  of  the  temporal 

articulate  with  eacli  other,  thus  sej^arating  the  alisphenoid  from  the  parietal. 
Asterion  is  the  region  of  the  jjostero-lateral  fontanelle  where  the  lambdoid,  jjarieto-mastoid, 

and  occipito-mastoid  sutures  meet. 
Stephanion.— Tlie  point  where  the  coronal  suture  crosses  the  temporal  crest. 
Dacryon. — The  point  where  the  vertical  lacrimo-maxillary  suture  meets  tlie  fronto-nasal 

suture  at  the  inner  angle  of  the  orbit. 
Jugal  Point. — Corresponds  to  tlie  angle  between  the  vertical  border  and  the  margin  of  the 

temporal  process  of  the  zygomatic  bone. 
Supra-auricular  Point.— A  point   immediately  above  the  middle  of  the  orifice  of  the 

external  auditory  meatus  close  to  the  edge  of  the  posterior  root  of  the  zygoma. 
Gon-ion. — The  outer  side  of  the  angle  of  the  maxilla. 
Pogonion. — The  most  pi'ominent  point  of  the  chin  as  represented  on  the  mandible. 


MEASUREMENTS  AND  INDICES.  xvii 

The  measurements  of  the  length  of  the  skull  may  be  taken  between  a  variety  of  points — the 
nasion,  glabella,  or  ophryon  in  front,  and  the  inion  or  maximum  occipital  point  behind.  Or  the 
maximum  length  alone  may  be  taken  without  reference  to  any  fixed  points.  In  all  cases  it  is 
better  to  state  larecisely  where  the  measurement  is  taken.  The  maximum  breadth  of  the  head  is 
very  variable  as  regards  its  position ;  it  is  advisal^le  to  note  whether  it  occurs  above  or  below  the 
parieto-squamosal  suture.  The  inter-relation  of  these  measurements  as  expressed  by  the  cephalic 
index  has  been  already  referred  to.  The  width  of  the  head  may  also  be  measured  from  one  asterion 
to  tlie  other,  biasterionic  width,  or  by  taking  the  bistephanic  diameter. 

The  height  of  the  cranium  is  usually  ascertained  by  measuring  the  distance  from  the  basion 

to  tlie  bregma.     The  relation  of  the  height  to  the  length  may  be  expressed  by  the  height  or 

vertical  index,  thus — 

Height  X 100     ^    ..     ... 

— ~ -, — = Vertical  index. 

Length 

Skulls  are  classified  in  accordance  with  the  relations  of  length  and  height  as  follows  : — 

Tapeinocephalic  index  below  72.  Chamaecephalic  index  up  to  70. 

Metriocephalic  index  between  72  and  77.  Orthocephalic  index  from  701  to  75. 

Akrocephalic  index  above  77  (Turner).  Hypsicephalic  index  75'1  and  upwards 

(Kollmann,  Ranke,  and  Virchow). 

The  horizontal  circumference  of  the  cranium,  which  ranges  from  450  mm.  to  550  mm.,  is 
measured  around  a  plane  cutting  the  glabella  or  ophryon  anteriorly,  and  the  maximum  occipital 
point  posteriorly.  The  longitudinal  arc  is  measured  from  the  nasion  in  front  to  the  opisthion 
behind ;  if  to  this  be  added  the  basi-nasal  length  and  the  distance  between  the  basion  and  the 
opisthion,  we  have  a  record  of  the  vertico-medial  circumference  of  the  cranium.  This  may  further 
be  divided  by  measuring  the  lengths  of  the  frontal,  j)arietal,  and  occipital  portions  of  the 
superior  longitudinal  arc.  In  this  way  the  relative  proportions  of  these  bones  may  be 
expressed. 

The  measureuients  of  the  skeleton  of  the  face  are  more  complex,  but,  on  the  whole,  of  greater 
value  than  the  measurements  of  the  cranium.  It  is  in  the  face  that  the  characteristic  features  of 
race  are  best  observed,  and  it  is  here  that  osseous  structure  most  accurately  records  the  form  and 
proportions  of  the  living. 

The  form  of  the  face  varies,  like  that  of  the  cranium,  in  the  relative  proportions  of  its  length 
and  breadth.  Generally  sj^eaking,  a  dolichocephalic  cranium  is  associated  with  a  long  face,  whilst 
the  brachycephalic  type  of  head  is  correlated  with  a  rounder  and  shorter  face.  This  rule,  how- 
ever, is  not  universal,  and  there  are  many  exceptions  to  it. 

The  determination  of  the  facial  index  varies  according  to  whether  the  measurements  are  made 
with  or  without  the  mandible  in  position.  In  the  former  case  the  length  is  measured  from  the 
ojihryon  or  nasion  above  to  the  mental  tubercle  below,  and  compared  with  the  maximum 
bizygomatic  width.  This  is  referred  to  as  the  total  facial  index,  and  is  obtained  by  the 
formula — 

Ophryo-m^ntal  l^igthxlOO^^^^^j  ^^^.^^  .^^^^ 
Uizygomatic  width 

More  usually,  however,  owing  to  the  loss  of  the  lower  jaw,  the  proportions  of  the  face  are 
expressed  by  the  superior  facial  index.  This  is  determined  by  comparing  the  ophryo-alveolar  or 
naso-alveolar  length  with  the  bizygomatic  width,  thus — 

Ophryo-alveolar  length  x  100     „         .      „.,.■, 

— £ — ^. -■ ?itt =  Superior  facial  index. 

Jjizygomatic  width 

The  terms  dolichofacial  or  leptoprosope  and  brachyfacial  or  chamceprosope  have  been 
employed  to  express  the  differences  thus  recorded. 

Uniformity  in  these  measurements,  however,  is  far  from  complete  since  many  anthropologists 
compare  the  width  with  the  length  =  100. 

The  proportion  of  the  face-width  to  the  width  of  the  calvaria  is  roughly  expressed  by  the  use  of 
the  terms  cryptozygous  and  phsenozygous  as  applied  to  the  skull.  In  the  former  case  the 
zygomatic  arches  are  concealed,  when  the  skull  is  viewed  from  above,  by  the  overhanging  and 
projection  of  the  sides  of  the  cranial  box  ;  in  the  latter  instance,  owing  to  the  narrowTiess  of  the 
calvaria,  the  zygomatic  arches  are  clearly  visible. 

The  projection  of  the  face,  so  characteristic  of  certain  races  (Negroes  for  example),  may  be 

estimated  on  the  living  by  measuring  the  angle  formed  by  two  straight  lines,  the  one  passing  from 

the  middle  of  the  external  auditory  meatus  to  the  lower  margin  of  the  septum  of  the  nose  ;  the 

other  drawn  from  the  most  prominent  part  of  the  forehead  above  to  touch  the  incisor  teeth 

below.     The  angle  formed  by   the  intersection  of  these  two  lines  is  called  the  facial  angle 

(Camper),  and  ranges  from  62°  to  85°.     The  smaller  angle  is  characteristic  of  a  muzzle-like 

projection  of  the  lower  part  of  the  face.     The  larger  angle  is  the  concomitant  of  a  more  vertical 

profile.     The  degree  of  projection  of  the  upper  jaw  in  the  macerated  cranium  is  most  commonly 

expressed  by  employing  the  gnathic  or  alveolar  index  of  Flower.     This  records  the  relative 

proportions   of  the   basi-alveolar   and    basi-nasal  lengths,  the  latter   being  regarded   as  =  100, 

thus — 

Basi-alveolar  length  x  100     _      . ,  .    .    , 

¥s    -■ T-T-^ — 1 =  Gnathic  index. 

Easi-nasal  length 


xviii  OSTEOLOGY. 

The  results  are  conveniently  grouped  into  three  classes  : — 

Orthognathous,  index  below  98  :  including  mixed  Europeans,  ancient  Egyptians,  etc. 
Mesognathous,  index  from  98  to  103  :  Chinese,  Japanese,  Eskimo,  Polynesians  (mixed). 
Prognathous,  index  above  103 :  Tasmanians,  Australians,  Melanesians,  various  African 

Negroes. 

Unfortunately,  however,  little  reliance  can  be  placed  on  the  results  obtained  by  this  method, 
since  it  takes  no  account  of  the  proportion  of  the  third  or  facial  side  of  the  gnathic  triangle. 
For  a  further  discussion  of  this  matter  see  Thomson  and  Maclver,  Races  of  the  Thebaid  (Oxford  : 
Clarendon  Press,  1905). 

Tlie  form  of  the  nasal  aperture  in  the  macerated  skull  is  of  much  value  from  an  ethnic 
standjioint,  as  it  is  so  intimately  associated  with  the  shape  of  the  nose  in  the  living.  The 
greatest  width  of  the  nasal  aperture  is  compared  with  the  nasal  height  (measured  from  thenasion 
to  the  lower  border  of  the  nasal  aperture)  and  the  nasal  index  is  thus  determined  : — 

Nasal  width  x  100     „      ,  .    , 
— ^r:,^ — ,-1    ^^r-. —  =  Nasal  index. 

Nasal  heiglit 

Skulls  are — 

Leptorhine,  with  a  nasal  index  below  48  :  as  in  mixed  Europeans,  ancient  Egyptians, 

American  Indians,  etc. 
Mesorhine,  with  an  index  ranging  from  48  to  53  :  as  in  Chinese,  Japanese,  Malays,  etc. 
Platyrhine,  with  an  index  above  53  :  as  in  Australians,  Negroes,  Kafl&rs,  Zulus,  etc. 

The  form  of  the  orbit  varies  considerably  in  different  races,  but  is  of  much  less  value  from  the 
standpoint  of  classification.  The  orbital  index  expresses  the  proportion  of  the  orbital  height  to 
the  orbital  width,  and  is  obtained  by  the  following  formula  : — 

Orbital  height  x  100 


Orbital  width 


=  Orbital  index. 


The  orbital  height  is  the  distance  between  the  ujaper  and  lower  margins  of  the  orbit  at  the 
middle ;  whilst  the  orbital  width  is  measured  from  a  point  where  the  ridge  which  forms  the 
posterior  boundary  of  the  lacrimal  groove  meets  the  fron to  -  lacrimal  suture  (Flower),  or  from 
the  dacryon  (Broca)  to  the  most  distant  point  from  these  on  the  anterior  edge  of  the  outer 
border  of  the  orbit. 

The  form  of  the  orbital  aperture  is  referred  to  as — 

Megaseme,  if  the  index  be  over  89  ; 
Mesoseme,  if  the  index  be  between  89  and  84  ; 
Microseme,  if  the  index  be  below  84. 

The  variations  met  with  in  the  form  of  the  palate  and  dentary  arcade  may  be  expressed  by 
the  palato-maxillary  index  of  Flower.  The  length  is  measured  from  the  alveolar  point  to  a 
line  drawn  across  the  hinder  borders  of  the  maxillary  bones,  whilst  the  width  is  taken  between 
the  outer  borders  of  the  alveolar  arch  immediately  above  the  middle  of  the  second  molar 
tooth.     To  obtain  the  index,  the  following  formula  is  employed  : — 

Palato-maxillary  width  x  100     ^  ,   .  .,,        .    , 

— V,  1  . 11       1       .1       =  Palato-maxillary  index. 

Palato-maxillary  length 

For  purposes  of  classification  Turner  has  introduced  the  following  terms  : — 

Dolichuranic,  index  below  110. 
Mesuranic,  index  between  110  and  115. 
Brachyuranic,  index  above  115. 

As  is  elsewhere  stated  (p.  108),  the  size  of  the  teeth  has  an  important  influence  on  the 
architecture  of  the  skull.  Considered  from  a  racial  standpoint,  the  relative  size  of  the  teeth  to 
the  length  of  the  cranio-facial  axis  has  been  found  by  Flower  to  be  a  character  of  much  value. 
The  dental  length  is  taken  by  measuring  the  distance  between  the  anterior  surface  of  the  first  jjre- 
molar  and  the  posterior  surface  of  tlie  tliird  molar  of  the  upper  jaw. 

To  obtain  the  dental  index  the  followiug  formula  is  used  : — 


Dental  length  x  100 
Basi-nasal  length 


=  Dental  index. 


Following  the  convenient  method  of  division  adopted  with  other  indices,  the  dental  indices 
may  be  divided  into  three  series,  called  respectively — 

Microdont,  index  below  42  :  including  the  so-called  Caucasian  or  white  races. 
Mesodont,  index  between  42  and  44  :  including  the  Mongolian  or  yellow  races. 
Megadont,  index  above  44  :  comprising  the  black  races,  including  the  Australians. 

Many  complicated  instruments  have  been  devised  to  take  the  various  measuraments  required, 
but  for  all  practical  purposes  the  calipers  designed  by  Flower  or  the  compas  glissihe  of  Broca  are 
sufficient. 

As  an  aid  to  calculating  the  indices,  the  tables  published  in  the  Osteological  Catalogue  of  the 
Royal  College  of  Surgeons  of  England,  Part  I.,  Man.;  Index- Tahellen  zuin  Anthropometrischen 
Gebrauche,  C.  M.  Furst,  Jena,  1902 ;  or  the  index  calculator  invented  by  Dr.  Waterston  will  be 
found  of  much  service  in  saving  time. 


MEASUEEMENTS  AND  INDICES.  xix 

(2)  Indices  and  Measurements  of  other  Parts  of  the  Skeleton 

111  addition  to  the  indices  employed  to  express  the  proportions  of  the  cranial  measurements, 
there  are  otliers  similarly  made  use  of  to  convey  an  idea  of  the  proportions  of  different  parts  of 
the  skeleton.     Of  these  the  following  may  be  mentioned  as  those  in  most  common  use  : — 

Scapula. — At  birth  the  form  of  the  human  scapula  more  closely  resembles  the  mammalian 
tyjje  in  tliat  its  breadth,  measured  from  the  glenoid  margin  to  the  vertebral  border,  is  greater  in 
comparison  with  its  length  than  in  the  adult.     This  proportion  is  expressed  as  follows  : — 

Breadth  from  glenoid  margin  to  vertebral  border  x  100     „         i      •    •. 

T ?c-^ j°  w    •  r    • ^ =  Scapular  index. 

Length  irom  medial  to  interior  angle 

The  index  ranges  from  87  in  African  pygmies,  which  therefore  have  proportionately  broader 
scapidaj,  to  61  in  Eskimos.     The  average  European  index  is  about  65. 

Innominate  Bone. — The  relation  of  the  breadth  of  this  bone  to  its  height  is  computed  as 

follows : — 

Iliac  breadth  x  100     _  ■     j.    ■    , 

T    ,. — ^^^ — i — r-^i—  =  Innominate  index. 
Ischio-iliac  height 

Man  as  compared  with  the  apes  is  distinguished  by  possessing  proportionately  broader  and 
shorter  innominate  bones.     The  index  in  man  ranges  from  74  to  90. 

Pelvis. — The  form  of  the  human  pelvis  is  characterised  by  an  increased  proi^ortionate  width 
and  a  reduced  proportionate  height  or  length.  The  relation  of  these  diameters  is  expressed  by 
the  formula  : — 

Ischio-iliac  height  X  100  -r.  i    •    i.      j^j.-,.  -,.  ■  ^.J.  ■    :, 

^ 7— TT — j^i   .   ^ Tu ? — V ftt — T- T  =  Pelvic  breadth-height  index. 

Greatest  breadth  between  the  outer  lips  ot  the  iliac  crests 

The  average  index  for  white  races  is  73. 

Pelvic  Cavity. — The  measurements  usually  taken  are  those  of  the  brim.  In  man  there  is  a 
proportionate  increase  in  the  transverse  diameter  as  compared  with  lower  forms  : — 

Antero-posterior  diameter  (conjugate)  from  mid-point  of  sacral  promontory 

to  the  posterior  margin  of  pubic  svmphvsis  x  100  .r.  i   •         ,    •      ■    , 

^ — ——^ ■  ^  1  ,   f ^P — ^^-^. rr- =  Pelvic  or  brim  index. 

Greatest  transverse  width  between  ino-peetmeai  lines 

Turner  has  classified  tlie  indices  into  three  groups  : — 

Dolichopellic,  index  above  95  :  Australians,  Bushmen,  Kaflfirs. 
Mesatipellic,  index  between  90-95  :  Xegroes,  Tasmanians,  New  Caledonians. 
Platypellic,  index  below  90  :  Europeans  and  Mongolians  generally. 

Vertebral  Column. — A  characteristic  feature  of  man's  vertebral  column  is  the  pronounced 
lumbar  curve  associated  with  the  erect  posture  in  the  living.  Apart  from  the  consideration  of 
the  interposition  of  the  intervertebral  discs  between  the  segments,  the  bodies  of  the  lumbar 
vertebrae  influence  and  react  on  the  curve  by  exhibiting  differences  in  their  anterior  and  pos- 
terior vertical  diameters.  Advantage  has  been  taken  of  this  to  endeavour  to  reconstruct  the 
lumbar  curve  from  the  dried  and  macerated  bones,  but  it  must  be  borne  in  mind  that  habitual 
posture  or  increased  range  of  movements  may  yield  results  which  are  possibly  misleading. 
Thus  there  is  reason  for  believing  that  the  squatting  position,  when  habitually  adopted,  may  give 
rise  to  a  compression  of  the  anterior  parts  of  the  bodies  of  the  vertebrse  which  it  might  be 
assumed  was  associated  with  an  absence  of  or  flattening  of  the  lumbar  curve,  which  in  fact  did 
not  exist  during  life. 

The  quality  of  the  ciu've  is  estimated  from  the  macerated  bones  by  an  index  which  is  com- 
puted as  follows  : — 

Sum  of  posterior  vertical  diameters  of  the  bodies  of  five  lumbar 

A'ertebrse  x  100  _  p  ,  ,      ,       .    , 

Sum  of  anterior  vertical  diameters  of  the  bodies  of  five  lumbar 
vertebrae 

The  results  are  classified  as  follows  : — 

Kurtorachic,   index   below   98,   displaying    a    forward   convexity :    includes   Europeans 

generally,  Chinese. 
Orthorachic,  index  between  98  and  102,  column  practically  straight :  includes  examples 

of  Eskimo  and  Maori. 
Koilorachic,  index  above  102,  displaying  a  backward  concavity  :    includes  Australians, 

Xegroes,  Bushmen,  and  Andamanese. 

Sacrum. — Man's  sacrum  is  characterised  by  its  great  breadth  in  proportion  to  its  length. 
These  relations  are  expressed  as  follows  : — 

Greatest  breadth  of  base  of  sacrum  x  100 


Length  from  middle  of  promontory  to  middle  of  anterior  inferior  border  of 
V.  sacral  vertebrae 


=  Sacral  index. 


XX  OSTEOLOGY. 

The  diverse  forms  are  groiij^ed  as  follows  : — 

Dolichohieric,  index  below  100,  sacra  longer  than  broad  :  includes  Australians,  Tasmanians, 

Buslimen,  Hottentots,  Kaffirs,  and  Andamanese. 
Platyhieric,  index   above  100,  sacra  broader  tban   long :  includes   Europeans,  Negroes, 

Hindoos,  Nortli  and  Soutli  American  Indians. 

Limb  Bones. — The  proportionate  length  of  the  limb  bones  to  each  other  and  to  the  body- 
height  is  of  i:)ractical  interest.  It  is  a  matter  of  common  knowledge  that  the  forearms  of  Negroes 
are  ijroportionately  longer  than  those  of  Europeans.  Great  differences,  too,  are  met  with  in  the 
absolute  and  proportionate  length  of  the  lower  limbs,  nor  must  the  relation  of  these  to  body- 
height  be  overlooked.  Aii  enumeration  of  the  more  important  of  these  indices,  and  the  manner 
of  their  comjJutation,  will  suffice.  The  proportion  of  the  length  of  the  radius  to  the  length  of 
the  humerus  is  expressed  as  follows  : — 

Length  of  radius  x  100     „  j-    i.  i  •    j 

-r  ^   ^-, — n-T =Kaaio-huineral  index. 

Length  oi  humerus 

Sub-divided  into  three  groups  : — 

Brachykerkic,  index  less  than  75  :  includes  Europeans,  Lapjjs,  Eskimo. 
Mesatikerkic,  index  between  75-80  :  Chinese,  Australians,  Polynesians,  Negroes. 
Dolichokerkic,  index  above  80  :  Andamanese,  Negritoes  and  Fuegians,  Bonindae  in  general 

The  proportion  of  the  length  of  the  tibia  to  the  femur  is  computed  by  the  formula — 

Length  of  tibia  from  surface  of  condyle  to  articular  surface  for  astragalus  x  100     m-u  •    if  i  •   j 

§ -^^^^. f — -= — jr-c =  Tibio-femoral  index. 

Oblique  length  oi  lemur 

Sub-divided  into  two  groups  : — 

Brachyknemic,  index  82  and  under  :  includes  Europeans  and  Mongolians  generally. 
Dolichoknemic,  index  83  and  over  :  includes  Australians,  Negroes,  Negritoes,  American- 
Indians. 

The  proportion  of  the  length  of  the  upper  limb  to  that  of  the  lower  limb  is  obtained  thus  :^ 

Lengths  of  humerus  +  radius  x  100     ^  i.  i.     i  -   j 
^ = ;n T^T-- =  Intermembral  index. 

Lengths  oi  lemur  +  tibia 

A  comparison  between  the  relative  lengths  of  the  upper  segments  of  the  limbs  is  obtained  by 
the  following  formula  : — 

Length  of  humerus  x  100     ^t  j?  i  •    j 

— Of = — jn. =  Humero-iemoral  index. 

Length  ot  lemur 

Platymeria  (see  -p.  xii.) — The  amount  of  compression  of  the  femur  is  estimated  as  follows  : — 

Sagittal  diameter  of  shaft  immediately  below  lesser  trochanter  x  100     _  p.  tvmpric  index 

Transverse  diameter  of  shaft  immediately  below  trochanter  minor 

Platyknemia  (see   p.    xii.) — The  degree  of  compression  of  the  tibia  is  estimated   by  the 

formula— 

Tiansverse  diameter  of  shaft  at  level  of  nutrient  foramen  X  100     t,,  ,    ,         ■    •   j„„ 

. T-- ?— ^i — ? 1 :, — T' ■■ T- =  Platyknemic  index. 

Antero-posterior  diameter  oi  shait  at  level  oi  nutrient  toramen 

The  index  ranges  from  60  in  a  Maori  tibia  to  80  to  108  in  modern  French  tibiaj. 

For  further  and  more  detailed  information  relating  to  the  various  measurements  and  indices 
employed  by  the  jjhysical  anthropologist,  the  reader  is  referred  to  Topinard's  Elements  d'Anthro- 
polofjie ;  Sir  W.  Turner's  Challenger  Memoirs,  Part  47,  vol.  xvi. ;  and  Duckworth's  Morphology 
and  Anthropology. 


APPENDIX   E. 

DEVELOPMENT    OF    THE    CHONDRO-CRANIUM    AND    MORPHOLOGY    OF 

THE    SKULL. 

As  has  been  already  stated  (p.  24),  the  chorda  dorsalis  extends  forwards  to  a  point  immediately 
beneath  the  anterior  end  of  the  mid-l)rain.  In  front  of  this  the  head  takes  a  bend  so  that  the 
large  fore-ljrain  overlaps  tlie  anterior  extremity  of  tlie  notochord.  At  this  stage  of  deveh)pment 
the  cerebral  vesicles  are  enclosed  in  a  memljranous  covering  derived  from  the  mesenchyme  surround- 
ing the  notocliord  ;  this  differentiated  mesodermal  layer  is  called  tlie  primordial  membranous 
CJ-aniuni.  From  it  the  meninges  which  invest  the  lirain  are  derived.  In  lower  vertebrates  this 
memljranous  capsule  becomes  converted  into  a  thick-walled  cartilaginous  envelope,  the  j)rimordial 
cartilaginous  cranium.  In  mammals,  liowever,  only  tlie  basal  part  of  this  capsule  becomes 
chondrified,  the  roof  and  part  of  the  sides  remaining  membranous.  In  considering  the  cliond- 
rification  of  the  skull  in  mammals,  it  must  be  noted  that  jmrt  only  of  the  base  is  traversed  by  the 


MOKPHOLOGY  OF  THE  SKULL. 


XXI 


notochord,  viz.  that  portion  wliicli  extends  from  the  foramen  magnum  to  the  doi-sum  selLx'  of  the 
sphenoid.  It  is,  therefore,  conveniently  divided  into  two  parts— one  posterior,  surrounding  the 
notochord,  and  hence  called  cliordal,  and  one  in  front,  into  which  the  notochord  does  not  extend, 
and  hence  termed  prechordal.  These  correspond  respectively  to  the  vertebral  and  evertebral 
regions  of  Gegenbauer.  In  the  generalised  type,  a  j^air  of  elongated  cartilages  called  the  para- 
chordal cartilages  appear  on  either  side  of  the  chorda  in  the  chordal  region,  similarly  in  the 
precliordal  region  two  curved  strips  of  cartilage  named  the  prechordal  cartilages,  or  the 
trabeculse  cranii  of  Rathke,  develop  on  either  side  of  the  crauio-pharyngoal  canal.  In  the 
human  embryo,  however,  this  symmetrical  arrangement  has  not  hitherto  been  observed.  Taking 
the  i^lace  of  the  parachordal  cartilages  is  a  mass  of  cartilage  called  the  basi-cranial  or  occipital 
plate,  which  partly  encloses  tlie  chorda,  and  extends  as  far  forwards  as  the  dorsum  selhe  ;  from 
this  by  subsequent  ossification  are  formed  the  basilar  process  of  the  occipital  bone  and  the  dorsum 
sellaj  of  the  sphenoid.  By  backward  extension  from  the  occipital  plate,  on  either  side  and  around 
the  foramen  magnum,  the  cartilaginous  exoccipitals  and  supraoccipitals  are  also  formed.  These, 
Froriep  and  others  regard  as  the  fused  neural  arches  of  four  rudimentary  verteljra?. 

In  the  prechoi-dal  region  in  man  the  trabeculfe  cranii  are  replaced  by  a  median  sheet  of 

Crista  Galli 


Pars  ethmoidal  i 


\     ,  Lamina  cribrosa 


Orbito-sphenoid 


Sphenoidal  fissure 7~^5*  ^- '  >»^ 

Alisphenoid nj  5~  jg^  >,  > 

Carotid  canal —  ~ 


Meatus  auditoriu 
internus 

Subarcuate  fossa 
Jugular  foramen 

Canalis  hypoglossi 

Foramen  magnum 


\  \       Orbital  portion  of  orbito-sphenoid 


Optic  foramen 


( ilivary  process 

\   I 

r~T      ^ella  turcica 

y  \-  yA —  Uorsum  sells 

-   ^'  '      . 

I  'ars  petrosa 


niperior  semicircular  canal 
/       Pars  mastoidea 


Supra-occipital 


Occipital  fontanelle 


Fig.  199. — View  of  the  Chondro-Craxidm  of  a  Human  Fcetus  5  cm.  in  length  from  Vertex  to 
Coccyx  (about  the  middle  of  the  third  month) ;  the  cartilage  is  coloured  blue.  The  line  to  the  right 
of  the  di-awing  shows  the  actual  size. 


cartilage,  the  ethmoidal  plate,  which  is  cleft  posteriorly  for  the  cranio  -  pharyngeal  canal. 
Posteriorly  this  unites  with  the  basi-cranial  plate,  thus  enclosing  the  cranio-pharyngeal  canal, 
the  lumen  of  which  is  subsequently  filled  up  to  form  the  floor  of  the  pituitary  fossa  in  which 
rests  the  pituitary  body. 

Owing  to  the  presence  of  the  nasal  capsules,  the  forepart  of  the  ethmoidal  plate  becomes 
differentiated  into  an  ethmo -vomerine  region,  from  the  medial  portion  of  which  the  nasal  septum 
and  its  associated  cartilages  is  derived,  whilst  from  the  lateral  parts  are  developed  the  lateral 
masses  of  the  ethmoid,  the  ethiuo-turbinals,  the  maxillo-turbinals,  and  the  alar  cartilages  of  the 
nose.  Posteriorly  the  medial  portion  of  the  ethmoidal  plate  forms  the  presphenoid,  whilst  as 
lateral  expansions  appear  the  orbito-sphenoids  and  alisphenoids,  both  of  which  assist  in  com- 
pleting the  orbital  cavity  for  the  lodgment  of  the  eyeball.  The  membranous  ear  capsules  which 
lie  lateral  to  the  parachordal  cartilages  become  chondrified  and  form  the  cartilaginous  ear 
capsules.  These  soon  miite  with  the  lateral  aspects  of  the  basilar  plate,  but  are  separated  in  front 
from  the  cartilaginous  alisphenoid  of  the  ethmoidal  plate  by  a  membranous  interval,  which  is 
subsequently  occupied  by  the  squamosal,  a  bone  of  dermic  origin.  This  disappearance  of  the 
cartilage  under  the  squamosal  was  regarded  by  Parker  as  the  diagnostic  mark  of  the  mammalian 
chondro-cranium. 


xxii  OSTEOLOGY. 

The  various  foramina  met  with  in  the  cranial  base  are  formed  either  as  clefts  in  the  line  of 
union  of  the  several  caitilaginous  elements,  or  through  inclusion  by  means  of  bridging  processes 
derived  from  these  same  elements. 

From  tlie  veiitral  surface  of  this  cartilaginous  platform — formed,  as  described,  by  the  union 
of  the  trabeculje,  parachordal  cartilages,  and  cartilaginous  ear  capsules — is  suspended  the 
cartilaginous  framework  of  the  visceral  arches,  which  play  so  important  a  part  in  the  develop- 
ment of  the  face,  an  account  of  which  is  elsewhere  given   (p.  35). 

A  consideration  of  the  facts  of  comparative  anatomy  and  embryology  appears  to  justify  the 
assumption  that  the  mammalian  skull  is  of  twofold  origin — that,  in  fact,  it  is  composed  of  two 
envelopes,  an  outer  and  an  inner,  primarily  distinct,  but  which  in  the  process  of  evolution  have 
become  intimately  fused  together.  The  inner,  called  the  primordial  skull,  is  that  which  has 
just  been  described,  and  consists  of  the  chondro-cranium  and  the  branchial  skeleton.  The  outer, 
which  is  of  dermic  origin,  includes  the  bones  of  the  cranial  vault  and  face  which  are  developed 
in  membrane.  This  secondary  skull,  which  first  appears  in  higher  fishes  as  ossified  dermal  plates 
overlying  the  primary  skull,  acquires  a  great  importance  in  the  mammalia,  as  owing  to  the 
expansion  of  the  brain  and  the  progressive  reduction  of  the  chondro-cranium,  these  dermal  bones 
become  engrafted  on  and  incorporated  Avith  the  ^^rimordial  skull,  and  act  as  covering  bones  to 
the  cavities  of  the  cranium  and  face  ;  for  it  may  be  well  to  point  out  that  these  dermal  or 
membrane  bones  are  not  necessarily  external  in  position,  as  over  the  cranial  vault,  but  also 
develop  in  the  tissues  underlying  the  mucous  membrane  of  the  cavities  of  the  face. 

Advantage  is  taken  of  this  difference  in  the  mode  of  develojjment  of  the  bones  of  the  skull  to 
classify  them  according  to  their  origin  into  cartilage  or  primordial  bones,  and  membrane  or 
secondary  bones.  These  differences  in  the  growth  of  the  bone  must  not  be  too  much  insisted 
on  in  determining  the  homologies  of  the  bones  of  the  skull,  as  it  is  now  generally  recognised  that 
all  bone  is  of  membranous  origin,  and  that  whilst  in  some  cases  cartilage  may  become  calcified, 
it  never  undergoes  conversion  into  true  bone,  but  is  replaced  by  ossific  deposit  derived  from  a 
membranous  source.  In  the  subsequent  growth  of  the  skull,  j)arts  of  the  cartilaginous  cranium 
persist  as  the  septal  and  alar  cartilages  of  the  nose,  whilst  for  a  considerable  period  the  basi- 
sphenoid  and  basi-occiioital  are  still  united  by  cartilage.  The  cartilage  also  which  blocks  the 
foramen  lacerum  may  be  regarded  as  a  remnant  of  the  chondro-cranium. 

Fontanelles. — Till  two  years  after  birth  there  are  membranous  intervals  between  the  edges 
and  angles  of  the  Ijones  of  the  cranial  vault.  These  are  termed  the  fontanelles.  Normally  they 
are  six  in  number,  and  correspond  in  the  adiilt  to  the  position  of  the  bregma  and  lambda  in  the 
middle  line  and  the  pterion  and  asterion  on  either  side.  The  anterior  or  bregmatic  fontanelle 
is  diamond-shaped,  and  corresponds  to  the  converging  angles  of  the  parietals  and  two  halves  of 
the  frontal  l3one.  The  posterior  fontanelle  is  triangular  in  form,  and  lies  between  the  two 
parietals  and  the  summit  of  the  squamous  part  of  the  occipital.  The  antero-lateral  fontanelle 
lies  between  the  contiguous  margins  of  the  frontal,  parietal,  squamous  part  of  the  temporal, 
and  great  wing  of  the  sj^henoid,  whilst  the  postero-lateral  fontanelle  is  situated  between  the 
adjacent  borders  of  the  jaarietal,  occipital,  and  mastoid  j)ortion  of  the  temporal.  The  term  occipital 
fontanelle  is  applied  to  a  membranous  interval  which  occurs  in  the  foetal  condition  posterior  to 
the  foramen  magnum,  and  between  the  lateral  halves  of  the  cartilaginous  supra-occipital.  Its 
persistence  accounts  for  the  occasional  occurrence  of  an  occipital  meningocele.^ 

Whilst  in  many  instances  the  primordial  and  secondary  bones  remain  distinct  in  the  fully- 
developed  condition,  they  sometimes  fuse  to  form  complex  bones,  such  as  the  temporal  and 
.sphenoid  (see  pp.  119  and  126). 

Various  theories  have  been  advanced  to  account  for  the  mode  of  formation  of  the  skull.  The 
earliest  of  these  was  called  the  vertebrate  theory,  which  assumed  that  the  cranium  was  built  up 
of  a  series  of  modified  vertebrae,  the  centra  of  which  corresjDonded  to  the  basi-cranial  axis,  whilst 
the  neural  arches  were  represented  by  the  covering  bones  of  the  cranium.  In  view  of  the  more 
recent  researches  regarding  the  composite  origin  of  the  skull  above  referred  to,  this  theory  was 
necessarily  abandoned.  It  gave  way  to  the  suggestion  of  Gegenbauer  that  the  primordial 
cranium  has  arisen  by  the  fusion  of  several  segments  equivalent  to  vertebrae,  the  number  of 
which  he  determined  by  noting  the  metameric  arrangement  of  the  cranial  nerves,  of  which  he 
concluded  there  were  nine  pairs,  arranged  much  like  s^jinal  nerves,  both  as  to  their  origin  and 
distribution.  The  olfactory  and  ojjtic  nerves,  though  frequently  referred  to  as  cranial  nerves, 
are  excluded,  since  from  tlie  nature  of  their  development  they  are  to  be  regarded  as  meta- 
morphosed parts  of  the  brain  itself.  Gegenbauer  therefore  assumed  that  that  portion  of  the 
cranial  base  which  is  traversed  by  the  nine  pairs  of  segmentally  arranged  cranial  nerves  must 
be  formed  Ijy  the  fusion  of  nine  vertebral  segments  ;  and  as  the  region  where  the  nerves  escape 
corre.sponds  to  the  part  of  the  chondro-cranium  traversed  bj^  the  notochord,  he  calls  it  the 
vertebral  portion  of  the  cranial  base,  in  contradistinction  to  the  trabecular  or  non-vertebral  part 
which  lies  in  front.  This  latter  he  regards  as  a  new  formation  adapted  to  receive  the  greatly- 
developed  brain  and  afl'ord  protection  to  the  organs  of  sight  and  smell. 

As  has  been  pointed  out  by  Hertwig,  there  is  an  essential  difference  between  the  development 
of  the  axial  cartilaginous  skeleton  of  the  trunk  and  head.  The  former  becomes  segmented  into 
distinct  vertebrae  alternating  with  intervertebral  ligaments  ;  whilst  the  latter,  in  order  to  attain 
the  rigidity  necessary  in  this  part  of  the  skeleton,  is  never  so  divided.  It  follows  from  this  that 
the  original  segmentation  of  the  head  is  only  expressed  in  three  ways,  viz.  in  the  appearance  of 
several  ijrimitive  segments  (myotomes),   in  the  arrangement  of  the  cranial  nerves,  and  in  the 

*  For  further  information  regarding  anomalous  conditions  of  the  fontanelles  and  tlie  occurrence  of  Wormian 
or  sutural  ossicles,  see  F.  Frassetto,  Ann,  des  Sci.  Nat.  Zool.  8"  ser.  xviii.  1903. 


MOKPHOLOGY  OF  THE  LIMBS.  xxiii 

fundament  of  the  visceral  skeleton  (visceral  arclies).  According  to  Froriep  the  mammalian 
occipital  corresponds  to  the  fusion  of  four  vertebrte,  and  there  is  some  reason  for  supposing  that 
in  some  classes  of  vertebrates  the  occipital  region  of  the  primordial  cranium  is  increased  by 
fusion  with  the  higher  cervical  segments. 

The  form  of  skull  characteristic  of  man  is  dependent  on  the  large  proportionate  development 
of  the  cranial  jaart,  which  contains  the  brain,  and  the  reduction  in  size  of  the  visceral  part 
(face),  which  protects  the  organs  of  special  sense.  This  leads  to  a  decrease  in  the  mass  and 
projection  of  the  jaws,  as  well  as  a  reduction  in  the  size  of  the  teeth.  Associated  with  the 
smaller  mandible  there  is  a  feebler  musculature,  with  a  reduced  area  of  attachment  to  the  sides 
of  the  skull.  In  this  wav  the  disappearance  of  the  muscular  crests  and  fosste,  so  characteristic 
of  lower  forms,  is  accounted  for.  At  the  same  time  the  fact  that  the  skull  is  poised  on  the 
summit  of  a  vertical  column,  leads  to  important  modifications  in  its  structure.  The  disposition 
of  parts  is  such  that  the  occipito-vertebral  articulation  is  so  placed  that  the  fore  and  hind  parts 
of  the  head  nearly  balance  each  other,  thus  obviating  the  necessity  for  a  powerful  muscular  and 
ligamentous  mechanism  to  hold  the  head  erect. 

Another  noticeable  feature  in  connexion  with  man's  skeleton  is  the  prolonged  period  during 
which  growth  may  occur  before  maturity  is  reached ;  this  is  associated  with  a  more  complete 
consolidation  of  the  skull,  since  bones,  which  in  lower  forms  remain  throughout  life  distinct,  are 
in  man  fused  with  each  other,  as  exemplified  in  the  case  of  the  presphenoid  and  postsphenoid, 
the  occipital  and  the  interparietal,  to  mention  one  or  two  instances  among  many.  It  is 
noteworthy,  however,  that  during  ontogeny  the  morphological  significance  of  these  bones  is 
clearly  demonstrated  by  their  independent  ossification. 

The  points  of  exit  of  the  various  cranial  nerves  remain  remarkably  constant,  and  in  their 
primitive  condition  serve  to  suggest  the  segmental  arrangement  of  the  cartilaginous  chondro- 
cranium  already  referred  to.  Owing  to  the  very  great  modifications  which  the  mammalian  skull 
has  undergone  in  the  process  of  its  evolution,  it  may  be  pointed  out  that  the  passage  of  the 
nerves  through  the  dura  mater — a  derivative,  the  readers  may  be  remiiided,  of  the  primordial 
membranous  cranium  (see  ante) — alone  represents  the  primitive  disposition  of  the  nerves.  Their 
subsequent  escape  through  the  bony  base  is  a  later  and  secondary  development.  In  some  cases 
the  two,  membranous  or  primary  and  the  osseous  or  secondary  foramina,  correspond.  In  other 
instances  the  exit  of  the  nerves  through  the  dura  mater  does  not  coincide  with  the  passage 
through  the  bone. 

Of  interest  in  this  connexion  it  may  be  pointed  out  that  the  foramina  and  canals  which 
traverse  the  skull  are  either  situated  in  the  line  of  suture  between  adjacent  bones  or  in  the  line 
of  fusion  of  the  constituent  parts  of  which  the  bone  pierced  is  made  up.  For  example,  the 
sphenoidal  fissure  is  situated  between  the  orbito  and  aKsphenoids ;  the  anterior  condylic  between 
the  basi  and  exoccipitals ;  the  jugular  between  the  petrous,  basi,  and  exoccipital ;  the  optic 
between  the  orbito-sphenoid  and  the  presphenoid  ;  the  Vidian  between  the  alisphenoid,  internal 
pterygoid  plate,  and  the  lingula. 


APPENDIX   F. 

MORPHOLOGY  OF   THE  LIMBS. 

Development  and  Morphology  of  the  Appendicular  Skeleton. 

The  paired  limbs  first  appear  in  the  human  embryo  about  the  third  week  as  small  buds  on 
either  side  of  the  cephalic  and  caudal  ends  of  the  trunk.  That  these  outgrowths  are  derived  from 
a  lar»e  number  of  trunk  segments  is  assumed  on  the  ground  that  they  are  supjslied  by  a  corre- 
sponding number  of  segmental  nerves,  and  the  circumstance  that  they  are  more  particularly 
associated  with  the  ventral  offsets  of  these  nerves  would  point  to  the  conclusion  that  they  belong 
rather  to  the  ventral  than  the  dorsal  surface  of  the  body. 

At  first  the  surfaces  of  these  limb  buds  are  so  disposed  as  to  be  directed  ventrally  and  dorsally, 
the  ventral  aspect  corresponding  to  the  future  flexor  surface  of  the  limb,  the  dorsal  to  the  ex- 
tensor side.  At  the  same  time,  the  borders  are  directed  headwards  (pre-axial),  and  tailwards 
(post-axial).  As  the  limbs  grow,  they  soon  display  evidence  of  division  into  segments  correspond- 
ing to  the  hand  and  foot,  forearm  and  leg,  upper  arm  and  thigh.  Coincident  with  this  (about  the 
second  month)  the  cartilaginous  framework  of  the  limb  is  being  differentiated.  The  disposition 
of  these  cartilages  furnishes  a  clue  to  their  homologies.  In  the  fore  limb  the  radius  and  thumb 
lie  along  the  pre-axial  borders,  and  correspond  to  the  tibia  and  great  toe,  which  are  similarly  dis- 
posed in  the  hind  limb  ;  whilst  the  ulna  and  fifth  finger  are  homologous  with  the  fibula  and  fifth 
toe,  which  are  in  like  manner  arranged  in  relation  to  the  posterior  (post-axial)  border  of  their 
respective  limbs.  Up  to  this  time  the  limbs  are  directed  obliquely  ventralwards.  During  the 
third  month  a  change  in  the  position  of  the  limbs  takes  place,  associated  with  the  assumption 
of  the  foetal  position.  Owing  to  the  elongation  of  the  limbs,  they  become  necessarily  bent 
at  the  elbow  and  knee,  the  upper  arm  inclining  downward  along  the  thoracic  wall,  whilst 
the  thigh  is  directed  upwards  in  contact  with  the  abdominal  parietes.     At  the  same  time  a 

17** 


XXIV 


OSTEOLOGY. 


Fig.  200. — Diagram  to  illcstrate  the  Homologies  op 
THE  Bones  of  the  Limbs. 

The  two  limb  buds  of  an  embryo  prior  to  Hexion  and  rotation. 
The  anterior  or  pre-axial  border  is  coloured  red;  the 
posterior  or  post-axial  border,  blue.  B.  After  the 
assumption  of  the  fcetal  position.  Flexion  and  rotation 
have  now  taken  place.  The  red  and  blue  lines  indicate 
the  altered  position  of  the  pre-axial  and  post-axial 
borders.  C.  The  fully  developed  limbs  with  the  flexor 
aspects  directed  towards  the  reader.  The  coloured 
lines  indicate  the  effect  of  the  torsion  of  the  upper 
segment  of  the  limb  through  quarters  of  a  circle. 


rotation  of  each  of  these  segments  of  the  limb 
takes  place  in  an  inverse  direction,  so  that  the 
pre-axial  border  of  the  humerus  is  turned 
laterally,  whilst  the  pre-axial  border  of  the 
femur  is  turned  medially.  Assuming  that 
these  borders  are  homologous,  it  results  from 
this,  that  the  lateral  condyle  of  the  humerus 
correspouds  to  the  medial  condyle  of  the 
femur.  This  torsion  of  the  limb  is  in  part 
effected  at  the  shoulder  and  hip  joints, 
and  to  some  extent  also  in  the  shafts  of  the 
bones.  Some  anatomists  hold  that  this 
I'otation  is  not  confined  to  the  limb,  but 
involves  the  dorsal  part  of  the  limb  girdles. 
Others  maintain  that  there  is  no  evidence 
that  such  takes  place.  In  the  upper  limb, 
owing  to  a  certain  amount  of  j^ronation,  the 
pre-axial  (radial)  side  of  the  forearm  is  now 
directed  forwards  and  somewhat  laterally, 
wliilst  in  the  hind  limb  the  pre-axial  (tibial) 
side  of  the  leg  is  turned  backwards  and 
laterally,  the  pi'e-axial  borders  of  the  hand 
with  thumb,  and  foot  with  great  toe  being 
in  corres^jondence.  In  consequence  of  these 
changes  in  the  position  of  the  limbs,  amount- 
ing in  all  in  the  upper  segments  to  a  rotation 
through  an  angle  of  90^,  the  extensor  surface 
of  tlie  fore  limb  is  directed  backwards, 
whilst  that  of  the  hind  limb  is  directed 
forwards.  In  order  to  homologise  the  ar- 
rangement of  the  bones  in  the  extended 
limb,  it  is  necessary  to  place  them  so  that 
their  flexor  or  extensor  surfaces  are  similarly 
disposed.  It  will  then  be  observed  (see  dia- 
gram) that  the  medial  or  tibial  side  of  the 
leg  and  foot  (primitively  pre-axial)  corre- 
sponds to  the  lateral  or  radial  side  of  the 
forearm  and  hand  (primitively  pre-axial), 
whilst  the  fibula  and  lateral  border  *of  the 
foot  homologise  with  the  ulnar  or  medial 
border  of  the  forearm  and  hand  (primitively 
post -axial),  the  result,  as  previously  ex- 
plained, of  the  torsion  or  twisting  in  opposite 
directions  through  an  angle  of  90'  of  the 
upper  segment  of  the  limb.  In  accordance 
with  this  view,  it  will  be  evident  that  in  the 
fore  limb  there  is  nothing  homologous  witli 
the  patelhi,  whilst  in  the  hind  limb  there 
is  no  part  to  represent  the  olecranon. 

In  the  axial  mesoderm  of  each  member, 
differentiation  into  cartilaginous  segments 
begins  about  the  second  month ;  each  of 
these  cartilages  becomes  invested  by  a  peri- 
chondria! layer  which  stretches  from  segment 
to  segment,  and  ultimately  forms  the  liga- 
ments surrounding  the  joints,  which  are 
subsequently  developed  between  the  seg- 
ments. Chondrification  first  begins  in  the 
basal  part  of  the  limb,  and  extends  towards 
the  digits. 

The  homodynamy  of  the  carpal  and 
tarsal  elements  may  be  tabularly  expressed, 
and  compared  with  the  more  generalised 
types  from  wliich  they  are  evolved. 


Type. 

Radiale  (Tibiale) 

Intermedium 

Ulnare  (Fibulare) 

Centrale 

Carpale  (Tarsale),  i. 


Hand. 


Foot. 


=  Navicular  (Ijody)  =  Talus. 

=  Os  lunatum  =  Absent,  or  Os  trigonum  (?) 

=  0s  triquetrum  =  Calcaneus. 

=  Absent,  or  fused  with  Navicular  =  Navicular,  less  its  tuberosity. 

=  Large  multangular  =  First  Cuneiform. 


MOEPHOLOGY  OF  THE  LIMBS.  xxv 

Type.  Hand.  Foot. 

Carpale  (Tarsale),  ii.  =  Small  multangular  =  Second  Cuneiform. 

Carpale  (Tarsale),  iii.  =  Capitate  =  Third  Cuneiform. 

Carpale  (Tarsale)   iv.  I  =Osliamatum  =  Cuboid,    plus    the    peroneal 
Carpale  (iarsale),  v.  J  sesamoid. 

The  pisiform  is  omitted  from  the  above  table,  since  it  is  now  generally  regarded  as  being  a 
vestige  of  an  additional  digit  placed  post-axial  to  the  little  j&nger  (digitus  post-minimus).  Its 
homologue  in  the  foot  is  by  some  considered  as  fused  with  the  calcaneus.  The  tuberosity  of  the 
navicular,  formed,  as  has  been  stated,  of  three  elements,  of  Avhich  the  sesamoid  bone  in  the 
tendon  of  the  tibialis  posterior  may  be  one,  is  to  be  regarded  as  the  homologue  of  the  radial 
sesamoid  in  the  hand,  which  probably  fuses  with  the  navicular  to  form  its  tuberosity.  The 
l^eroneal  sesamoid  probably  corresponds  to  the  navicular  process  (sometimes  an  independent 
ossicle)  of  the  os  hamatum.  Similarly,  on  the  pre-axial  border  of  the  hand  and  foot,  vestiges  of  a 
suppressed  digit  (prepollex  and  prehallux)  may  occasionally  be  met  with.  The  frequent  occur- 
rence of  an  increase  in  the  number  of  digits  seems  to  indicate  that  jjliylogenetically  the  number 
of  digits  was  greater  than  at  present,  and  included  a  prepollex  or  prehallux,  and  a  digitus  post- 
minimus.  The  correspondence  of  the  metacarjjus  with  the  metatarsus  and  tlie  phalanges  of  the 
fingers  with  those  of  the  toes  is  so  obvious  that  it  is  sufficient  merely  to  mention  it. 

The  differences  in  size,  form,  and  disposition  of  the  skeletal  elements  of  the  hand  and  foot  is 
easily  accounted  for  by  a  reference  to  the  functions  they  subserve. 

In  the  hand  strength  is  sacrificed  to  mobility,  thus  leading  to  a  reduction  in  the  size  of  the 
carpal  elements,  and  a  marked  increase  in  the  length  of  the  digital  jjhalanges.  The  freedom  of 
movement  of  the  thumb,  and  its  opposability  to  the  other  digits,  greatly  enhances  the  value  of 
the  hand  as  a  grasping  organ.  In  the  foot,  where  stability  is  the  main  requirement,  the  tarsus 
is  of  much  greater  jjroportionate  size,  whilst  the  phalanges  are  correspondingly  reduced.  Since 
the  foot  no  longer  serves  as  a  grasping  organ,  the  great  toe  is  not  free  and  opposable  like  the 
thumb. 

Limb  Girdles. — The  free  limbs  are  linked  to  the  axial  skeleton  by  a  chain  of  bones  which 
constitute  their  girdles.  The  fundamental  form  of  these  limb  girdles  consists  each  of  a  pair  of 
curved  cartilages  placed  at  right  angles  to  the  axis  of  the  trunk  on  either  side,  and  embedded 
within  its  musculature.  Each  cartilage  has  an  articular  surface  laterally,  about  the  middle,  for 
the  reception  of  the  cartilage  of  the  first  segment  of  the  free  limb.  In  this  way  each  pectoral 
and  pelvic  cartilage  is  divided  into  an  ujjper  or  dorsal  half  and  a  lower  or  ventral  half.  The 
dorsal  halves  constitute  the  scajjula  and  ilium  of  the  pectoral  and  pelvic  girdles  resi^ectively. 
With  regard  to  the  ventral  halves  there  is  more  difficulty  in  establishing  their  homologies.  The 
original  condition  is  best  displayed  in  the  pelvic  girdle  ;  here  the  ventral  segment  divides  into 
two  branches — one  anterior,  which  represents  the  jjubis,  the  other  posterior,  which  ultimately 
forms  the  ischium.  Ventrally,  the  extremities  of  these  cartilages  unite  to  enclose  the  obturator 
foramen.  In  the  pectoral  girdle  the  disijosition  of  the  ventral  cartilages  is  not  so  clear,  consisting 
primitively  of  an  anterior  branch  or  precoracoid,  and  a  posterior  jDortion  or  coracoid ;  these,  in 
higher  forms,  have  undergone  great  modifications  in  adaptation  to  the  requirements  of  the  fore 
limbs.  The  posterior  or  coracoid  element,  the  homologue  of  the  ischial  cartilage  in  the  pelvic 
girdle,  is  but  feebly  represented  in  man  by  the  coracoid  process  and  the  coraco-clavicular  ligament. 
With  regard  to  the  homologue  of  the  pubic  element  in  the  pectoral  girdle,  there  is  much  difl'erence 
of  opinion ;  in  reptiles  and  ami^hibia  it  corresponds  most  closely  to  the  jjrecoracoid,  but  it  is 
doubtful  what  represents  it  in  mammals.  According  to  Goette  and  Hoffman,  the  clavicle  is  a 
primordial  bone,  and  not,  as  suggested  by  Gegenbaur,  of  secondary  or  dermic  origin.  If  this  be 
so,  it  corresponds  to  the  ventral  anterior  segment  of  the  pectoral  girdle,  and  is  therefore  homo- 
logous with  the  ventral  anterior  (pubic)  segment  of  the  pelvic  girdle.  On  the  other  hand,  if 
Gegenbaur's  view  be  accepted,  the  clavicle  has  no  representative  in  the  pelvic  girdle.  It  must, 
however,  be  borne  in  mind  that  during  its  ossification  it  is  intimately  associated  with  cartilage, 
and  that  that  cartilage  may  represent  the  precoracoid  bar ;  nor  must  too  great  stress  be  laid  upon 
the  fact  that  the  clavicle  begins  to  ossify  before  it  is  preformed  in  cartilage,  since  that  may  be 
merely  a  modification  in  its  histogenetic  development. 

According  to  another  view  (Sabatier),  the  subcoracoid  centre  (see  Ossification  of  Scapula)  is 
derived  from  the  jjosterior  ventral  segment,  and  corresponds  to  the  ischium,  whilst  the  coracoid 
process  is  the  remains  of  the  anterior  ventral  segment  (precoracoid),  and  is  homodynamous  with 
the  pubis. 

In  no  part  of  the  skeleton  does  function  react  so  much  on  structure  as  in  the  arrangement  of 
the  constituent  parts  of  the  pectoral  or  pelvic  girdles.  In  man,  owing  to  the  assumption  of  the 
erect  position  and  the  bipedal  mode  of  progression,  the  jaelvic  girdle  acquires  those  characteristics 
which  are  essentially  human,  viz.  its  great  relative  breadth  and  the  exp»ansion  of  its  iliac 
portions,  which  serve  as  a  support  to  the  abdominal  viscera,  and  also  furnish  an  extensive  origin 
for  the  powerful  muscles  which  control  the  movements  of  the  hip-joint.  The  stability  of  the 
pelvic  girdle  is  insured  by  the  nature  of  its  union  with  the  axial  skeleton,  as  well  as  by  the 
osseous  fusion  of  its  several  parts,  and  their  union  in  front  at  the  symphysis  pubis. 

Various  attempts  have  been  made  to  homologise  the  several  parts  of  the  ilium  and  scapula. 
All  are  open  to  objection ;  that  by  Flower  is  perhaps  the  most  generally  accepted.  Assuming 
that  the  primitive  type  is  represented  by  a  prismatic  rod,  of  which  the  dorsal  end  represents 
•either  the  epiphysial  border  of  the  vertebral  edge  of  the  scapula  or  the  iliac  crest,  whilst  the 
ventral  end  corresponds  to  the  glenoid  or  cotyloid  articular  areas  respectively,  the  surfaces  of 
the  three-sided  rod  are  disposed  so  that  one  is  vertebral  or  internal,  another  pre-axial,  and  the 


XXVI 


OSTEOLOGY. 


third  post-axial.  These  surfaces  are  separated  by  borders,  of  which  one  is  lateral,  separating 
the  pre-axial  and  post-axial  surfaces,  whilst  the  antero- medial  and  postero- medial  margins 
separate  the  pre-axial  and  post-axial  surfaces  respectively  from  the  vertebral  or  medial  aspect. 
It  is  a  necessity  of  Flower's  theory  that  this  part  of  the  girdle  undergoes  a  rotation  along  with 
the  rest  of  the  limb.  Thus  in  the  fore  limb  the  surfaces  of  the  jjrimitive  type  are  turned  so  that 
the  vertebral  surface  looks  forward,  whilst  in  the  case  of  the  hind  limb  the  vertebral  surface  is 
turned  backward.  A  study  of  the  accompanying  diagram  will  enable  the  reader  to  realise  how 
the  ventral  surface  of  the  scapula  is  thus  rendered  homologous  with  the  gluteal  surface  of  the 
ilium,  for  by  reference  to  the  type,  both  these  surfaces  will  be  seen  to  correspond  to  the  j^ost- 
axial  areas  of  the  primitive  condition.  In  accordance  with  this  view  the  surfaces  and  borders  of 
the  scapula  are  homologised  by  Flower,  as  shewn  in  the  subjoined  table  : — 


Scapula. 

Supra-spinous  fossa 


Infra-spinous  fossa 
Subscapular  fossa 


Surfaces 
Ideal. 
1.  Vertebral 


2.  Pre-axial 

3.  Post-axial 


Pelvis. 

Inner  surface  of  ilium  behind  linea  ar- 
cuata  interna,  including  the  articular 
surface  for  the  sacrum  and  the  portion 
of  the  bone  above  and  below  this 

Internal  iliac  fossa 

Gluteal  surface  of  ilium 


Borders 


Axillary  border,  posterior  on 
most  animals  (attachment  of 
biceps  muscle) 

Spine  continued  into  acromion 

Superior  border,  anterior  in 
most  animals,  with  scapulo- 
coracoid  notch 


1.  Lateral 


2.  Antero -medial 

3.  Postero-medial 


Anterior   border  (attachment   of  rectus 
muscle) 

Linea   arcuata   interna   continued    into 

pubis 
Posterior  border  with  great  sciatic  notch 


'Vertebral  or  internal  surfaces 


Fig.  201.- 


-DlAGRAM    TO    ILLUSTRATE    THE    HOMOLOGOUS    PaRTS    OF    THE    SCAPULA    AND    ILIUM, 
ACCORDING   TO    FlOWER. 


A,  ideal  type  ;  three-sided  rod.  B,  scapula  rotated  forward  through  quarter  of  a  circle  (90°),  so  that  the 
primitive  internal  or  vertebral  surface  is  now  directed  anteriorly.  C,  ilium  rotated  backwards  through 
quarter  of  a  circle  so  that  the  primitive  internal  surface  is  now  turned  posteriorly.  In  the  diagram  the 
primitive  internal  or  vertebral  surface  of  each  figure  is  coloured  black,  the  pre-axial  surfaces  red,  and  the 
post-axial  surfaces  blue. 

Flower's  views  of  this  matter  were  strenuously  opjDOsed  by  Humphry,  who  maintained  that 
there  is  strong  presumptive  evidence  against  any  rotation  of  the  superior  parts  of  the  girdles, 
since  it  is  difficult  to  suppose  that  the  scapula  and  ilium  can  undergo  a  rotation  which  is  not 
participated  in  by  the  coracoid  and  ischium.  According  to  this  anatomist  the  homologous  parts 
of  the  two  bones  are  as  stated  below  : — 


Scapula. 

Pre-spinal  ridge  forming  the  floor  of  the  pre- 

spinal  fossa 
Spine  and  acromion 

Post-spinal  part  of  scapula  forming  the  floor  of 

the  post-spinal  fossa 
Posterior  angle 
Posterior  border 
Medial  or  ventral  surface 


Ilium. 
Linea  ilio-pectinea 

Fore  part  of  the  blade  and  crest  of  the  ilium, 

with  its  anterior  spine  or  angle 
Hinder  part  of  blade  and  crest  of  ilium 

Posterior  spine  or  angle 
Posterior  or  sciatic  border  of  ilium 
Inner  or  true  pelvic  surface  of  ilium,  including 
the  surface  for  the  articulation  of  the  sacrum 


MOKPHOLOGY  OF  THE  LIMBS. 


XXVll 


Fig.  202. — Diagram  to  illustrate  the  Homologous  Parts  of  the  Scapula  and  Ilium, 

according  to  humphry. 

A,  primitive  rod-like  ilium  of  kangaroo,  prismatic  on  section.     B,  scapula.     C,  ilium.     The  corresponding 

surfaces  are  similarly  coloured. 

The  difficulty  arising  in  this  scheme  of  attempting  to  homologise  the  attachments  of  the 
triceps  and  rectus  femoris,  Humphry  explains  by  pointing  out  that  the  former  muscle  also  arises 
from  the  lateral  surface  of  the  scapula,  whilst  the  rectus  overruns  the  lateral  surface  of  the  ilium 
above  the  acetabulum,  so  that  there  is  a  correspondence  in  the  origins  of  both  these  muscles  from 
the  lateral  surface  of  their  respective  bones  ;  but  in  consequence  of  the  rotation  of  the  extensor 
surfaces  of  the  limbs  in  opposite  directions  the  triceps  has  been  turned  backwards  on  to  the 
posterior  border  of  the  scapula,  whilst  the  rectus  has  been  turned  forwards  on  to  the  anterior 
border  of  the  ilium.  Sufficient  has  been  said  to  enable  the  reader  to  recognise  that  all  attempts 
to  determine  in  detail  the  homologies  of  these  parts  is  beset  with  difficulty.  It  is  wiser,  therefore, 
in  our  present  state  of  knowledge  to  be  content  with  establishing  a  general  correspondence,  and 
so  avoid  the  error  of  endeavouring  to  establish  a  closer  homological  relationship  than  actually  . 
exists. 

In  man,  since  the  erection  of  the  figure  no  longer  necessitates  the  use  of  the  fore  limb  as  a 
means  of  support,  the  shoulder  girdle  has  become  modified  along  lines  which  enhance  its  mobility 
and  determine  its  utility  in  association  with  a  prehensile  limb.  Some  of  its  parts  remain 
independent  (clavicle  and  scapula),  and  are  united  by  diarthrodial  joints,  whilst  others  have 
become  much  reduced  in  size  or  suppressed  (coracoid-precoracoid,  see  ante).  The  dorsal  part 
of  the  girdle  (scapula)  is  not  directly  united  with  the  axial  skeleton  as  is  the  ilium,  but  is  only 
indirectly  joined  to  it  through  the  medium  of  the  clavicle,  which  is  linked  in  front  with  the 
presternum.  The  same  underlying  principles  determine  the  diff"erences  in  mobility  and  strength 
between  the  shoulder,  elbow,  and  wrist,  and  the  hip,  knee,  and  ankle  joints  of  the  fore  and  hind 
Umbs  respectively,  whilst  the  utility  of  the  hand  is  further  enhanced  by  the  movements  of 
pronation  and  supination  which  occur  between  the  bones  of  the  forearm.  In  the  leg  such 
movements  are  absent,  as  they  would  interfere  with  the  stability  of  the  limb. 


THE   ARTICULATIONS   OR  JOINTS. 

ARTHROLOGY. 

By  David  Hepburn,  M.D.,  F.R.S.E., 

Professor  of  Anatomy,  University  College,  Cardiff. 


THE   ARTICULATIONS   OR  JOINTS. 

ARTHROLOGY. 

By  David  Hepbuen. 

Arthrology  is  that  branch  of  human  anatomy  which  treats  of  the  articulations 
or  joints. 

An  articulation  or  joint  constitutes  a  mode  of  union  or  connexion  subsisting 
between  any  two  separate  segments  or  parts  of  the  skeleton,  whether  osseous  or 
cartilaginous,  and  having  for  its  primary  object  either  the  preservation  of  a  more 
or  less  rigid  continuity  of  the  parts  joined  together,  or  else  to  permit  of  a  variable 
degree  of  mobility,  subject  to  the  restraints  of  the  uniting  media. 

Classification  of  Joints. — In  attempting  to  frame  a  classification  of  the 
numerous  joints  in  the  body,  several  considerations  must  be  taken  into  account, 
viz.  the  manner  and  sequence  of  their  appearance  in  the  embryo ;  the  nature  of  the 
uniting  media  in  the  adult,  and  also  the  degree  and  kind  of  movement  permitted 
in  those  joints  where  movement  is  possible. 

In  this  way  we  obtain  two  main  subdivisions  of  joints  : — 

(1)  Those  in  which  the  uniting  medium  is  coextensive  with  the  opposed  sur- 
faces of  the  bones  entering  into  the  articulation,  and  in  which  a  direct 
union  of  these  surfaces  is  thereby  effected. 

(2)  Those  in  which  the  uniting  medium  has  undergone  more  or  less  of  interrup- 
tion in  its  structural  continuity,  and  in  which  a  cavity  of  greater  or  less 
extent  is  thus  formed  in  the  interior  of  the  joint. 

To  the  first  group  belong  all  the  immovable  joints,  many  of  which  are  likewise 
of  temporary  duration ;  to  the  second  group  belong  all  joints  which  possess  as  their 
outstanding  features  mobility  and  permanence. 


Iiitei'veiiiiig 
iiiPinbiaiie 


SYNARTHROSES. 

The  general  characteristics  of  this  group  are  partly  positive  and  partly  nega 
tive.  Thus  there  is  uninterrupted  union  between  the 
opposed  surfaces  of  the  bones  joined  together  at  the  plane 
of  the  articulation,  i.e.  there  is  no  trace  of  a  joint  cavity, 
and  further,  there  is  an  entire  absence  of  movement. 
Developmen tally,  these  joints  result  from  the  approxi- 
mation of  ossific  processes  which  have  commenced  from 
separate  centres  of  ossification,  and  therefore  the  nature 
of  the  uniting  medium  varies  according  as  the  bones 
thus  joined  together  have  originally  ossified  in  membrane 
or  in  cartilage.  In  the  former  case  union  is  effected  by 
an  interposed  fibrous  membrane  continuous  with  and 
corresponding  to  the  periosteum.  To  such  articulations 
the  term  suture  (Fig.  203)  is  applied.  In  the  latter  case 
the  uniting  medium  is  a  plate  of  hyaline  cartilage.  Such 
articulations  are  called  synchondroses  (Fig.  204).  In  all  the  synchondroses,  and  in 
many  of  the  sutures,  the  uniting  medium  tends  to  disappear  in  the  progress  of 


Fici.   203. — Vkktical  Skction 

THROUGH    A    SUTURE. 


256 


THE  ARTICULATIONS  OR  JOINTS. 


ossification,  and  thus  the  plane  of  articulation  becomes  obliterated,  so  that  direct 
structural  continuity  between   the  osseous  segments  takes  place.     The  primary 

features  common  to  all  synarthroses  are — (a)  continuous 
and  direct  union  of  the  opposing  surfaces ;  (&)  no  joint 
cavity  ;  (c)  no  movement. 

Suture. — This  form  of  synarthrosis  is  only  found  in 
connexion  with  the  bones  of  the  skull.  In  a  large 
number  of  cases  the  bones  which  articulate  by  suture 
present  irregular  interlocking  margins,  between  which 
there  is  the  interposed  fibrous  membrane  to  which  refer- 
ence has  already  been  made.  When  these  interlocking 
margins  present  well-defined  projections  they  are  said  to 
form  true  sutures — sutura  vera  ;  on  the  other  hand,  when 
Fig.  204.  — Section  thkough  the  opposed  surfaces  present  ill-defined  projections,  or 
THE  OccipiTo-spHENoiD  Syn-  gyeu  flat  arcas,  they  are  described  as  false  sutures — 
cHONDRosib.  sutura  notha.     In  each  of  these  subdivisions  the  particular 

characters  of  the  articulating  margins  are  utilised  in  framing  additional  descriptive 
terms.  Thus  true  sutures  may  possess  interlocking  margins  whose  projections  are 
tooth-like  (sutura  dentata),  e.g.  in  the  interparietal  suture  ;  saw-like  (sutura  serrata), 
(Fig.  205)  e.g.  in  the  interfrontal  suture ;  ridge-like,  or  comparable 
to  the  parallel  ridges  on  the  welt  of  a  boot  (sutura  limbosa). 
Similarly  false  sutures  may  articulate  by  margins  which  are  scale- 
like (sutura  squamosa),  e.g.  in  the  squamoso-parietal  suture ;  or  by 
rough  opposed  surfaces  (sutura  harmonia),  e.g.  in  the  suture  between 
the  palate  plates  of  the  superior  maxillary  bones.  There  is  one 
variety  of  synarthrosis  which,  in  the  adult,  can  scarcely  be  called  a 
suture,  although  the  differences  are  of  minor  importance,  viz. 
schindylesis,  which  is  an  articulation  between  the  edge  of  a  plate- 
like bone,  such  as  the  rostrum  of  the  sphenoid,  and  the  cleft  in 
another,  such  as  the  vomer. 

Synchondrosis. — Illustrations  of  this  group  can  only  be  found  ^^^-  IH^^^^^^^^^ 
in  the  young  growing  individual,  because  as  age  advances  and 
growth  ceases,  the  process  of  ossification  affects  the  hyaline  cartilage  which  con- 
stitutes the  uniting  medium,  and  the  plane  of  articulation  disappears.  Under  this 
heading  we  may  include  the  planes  of  junction  between  all  epiphyses  and  the 
shafts  or  diaphyses  to  which  they  severally  belong.  The  occipito- sphenoid  (Fig. 
204)  and  the  petro-jugular  articulations  in  the  base  of  the  skull  provide  other 
well-marked  examples. 


MOVABLE  JOINTS. 

The  leading  features  of  this  group  are  capability  of  movement  and  permanence. 
In  very  few  instances  do  such  joints  ever  become  obliterated  under  normal  con- 
ditions. Determining  their  permanence,  and  regulating  the  amount  of  possible 
movement,  there  is  always  more  or  less  of  interruption  in  the  continuity  of  the 
structures  which  bind  the  osseous  elements  together.  That  is,  there  is  always  some 
evidence  of  a  joint  cavity,  although  as  a  matter  of  course  such  interruption  can 
never  be  so  extensive  as  to  entirely  disassociate  the  articulating  elements.  There- 
fore in  all  movable  joints  a  new  class  of  structures  is  found,  viz.  the  ligaments,  by 
means  of  which  continuity  is  maintained  even  when  all  the  other  uniting  media 
have  given  i)lace  to  a  joint  cavity.  The  further  subdivision  of  this  group  is  founded 
upon  the  amount  of  movement  permissible,  and  the  extent  to  which  the  joint  cavity 
takes  the  yjlace  of  the  original  continuous  uniting  medium.  Thus  we  obtain  the 
partly  movable  or  ampMarthroses,  and  the  freely  movable  or  diarthroses. 

An  amphiarthrosis  (Fig.  208)  presents  the  following  characteristics :  {a) 
partial  movement ;  (h)  union  by  ligaments  and  by  an  interposed  plate  or  disc  of 
fibro-cartilage,  in  the  interior  of  which  there  is,  (c)  an  incomplete  or  partial  joint 
cavity  which  may  be  lined  by  a  rudimentary  synovial  membrane  whose  function  it 
is  to  secrete  a  lubricating  fluid,  the  synovia  or  joint-oil;   {d)  a  plate  of  hyaline 


STKUCTUKE  OF  JOINTS. 


257 


,  Articular 
cartilage 


.Joint 
capsule 

Synovial 
membrane 


cartilage  coating  each  of  the  opposing  surfaces  of  the  bones  concerned.     All  the 

joints  belonging  to  this  group  occur  in  the  mesial  plane  of  the  body.     It  includes 

the  symphysis  pubis,  the  joints  between  the  bodies  of  the  vertebrae,  and  the  joint 

between  the  manubrium  sterni  and  the  gladiolus. 

A  diarthrosis  (Fig.  206)  is  the  most  elaborate  as  well  as  the  most  complete  form 

of  articulation.     It  is  characterised  by  («)  capability  of  movement  which  is  more  or 

less  free  in  its  range ;  (6)  a  reduction  of  the 

uniting  structures  to  a  series  of  retaining  liga- 
ments ;    (c)   a   joint    cavity    which    is    only 

limited  by  the   surrounding   ligaments ;   {d) 

the  constant  presence  of  synovial  membrane  ; 

(e)  hyaline  encrusting  cartilage  which  clothes 

the  opposed  surfaces  of  the  articulating  bones. 

The  majority  of  the  joints  in  the  adult  belongs 

to  this  group.     This  series  of  joints  has  been 

subdivided  into  a  number  of  minor  sections, 

in   order    to   emphasise    the    occurrence    of 

certain    well-marked   structural   features,   or 

because  of  the  particular  nature  of  the  move- 
ment by  which  they  are  characterised. 
Although  in  all  diarthroses  there  is  a  certain 
amount  of  gliding  movement  between  the 
opposed  surfaces  of  the  bones  which  enter  into  their  formation,  yet,  when  this  gliding 
movement  becomes  their  prominent  feature,  as  in  most  of  the  joints  of  the  carpus  and 

tarsus,  they  are  termed  arthrodia.  But  bones  may  be  articulated  together  so  as  to 
permit  of  movement  in  one,  two,  or  more  fixed  axes  of  movement,  or  in  modifications 
of  these  axes.  Thus  in  uniaxial  joints  the  axis  of  movement  may  lie  in  the  longi- 
tudinal axis  of  the  joint,  in  which  case  the  rotatory  form  of  joint  results,  as  in 
the  superior  and  inferior  radio-ulnar  articulations  ;  or  it  may  correspond  with  the 
transverse  axis  of  the  articulation,  as  in  the  elbow-joint  and  knee-joint,  when  the 
ginglymus  or  hinge  variety  results.  If  movement  takes  place  about  two  principal 
axes  situated  at  right  angles  to  each  other,  as  in  the  radio-carpal  joint,  the  terms 
biaxial  or  condyloid  are  applied.  Movements  occurring  about  three  principal  axes 
placed  at  right  angles  to  each  other,  or  in  modifications  of  these  positions,  con- 
stitute multiaxial  joints,  in  which  the  associated  structural  peculiarities  provide  the 
alternative  terms  of  enarthrodial  or  ball-and-socket  joints. 


Articular 
cartila.i^e 


Fig.  206 


DiARTHRODIAL 


STRUCTURES  WHICH  ENTER  INTO  THE  FORMATION  OF  JOINTS. 

The  structures  which  enter  into  the  formation  of  joints  vary  with  the  nature 
of  the  articulation.  In  every  instance  there  are  two  or  more  skeletal  elements, 
whether  bones  or  cartilages,  and  in  addition  there  are  the  uniting  media,  which  are 
either  simple  or  elaborate  according  to  the  provision  made  for  rendering  the  joint 
more  or  less  rigid  or  capable  of  movement.  We  have  already  seen  that  the  uniting 
medium  in  synarthrodial  joints  is  a  remnant  of  the  common  matrix,  whether  fibro- 
vascular  membrane  or  hyaline  cartilage,  in  which  ossification  has  extended  from 
separate  centres.  Among  the  ampbiarthroses  there  is  still  extensive  union  between 
the  opposing  surfaces  of  the  articulating  bones,  but  the  character  of  the  uniting 
medium  has  advanced  from  the  primitive  embryonic  tissue  to  fibrous  and  fibro- 
cartilaginous material,  as  well  as  hyaline  cartilage.  These,  with  very  few  exceptions, 
are  permanent,  non-ossifying  substances,  such  as  may  be  seen  between  the  opposing, 
osseous  surfaces  of  two  vertebral  bodies.  The  joint  cavity,  more  or  less  rudimentary, 
is  confined  to  the  centre  of  the  fibro-cartilaginous  plate,  and  may  result  from  the 
softening  or  imperfect  cleavage  of  the  central  tissue.  It  may  also  present  rudiments 
of  a  synovial  membrane. 

In  the  diarthrodial  group  the  extensive  cavity  has  produced  great  interruption 
in  the  continuity  of  the  uniting  structures  which  originally  existed  between  the 
bones  forming  such  a  joint.  Ligaments  have  therefore  additional  importance  in 
this  group,  for  not  only  do  they  constitute  the  uniting  media  which  bind  the 
articulating  bones  together,  but  to  a  large  extent  they  form  the  peripheral 
18 


258 


THE  AKTICULATIONS  OE  JOINTS. 


boundary  of  the  joint  cavity,  although  not  etj[ually  developed  in  all  positions. 
Thus  every  diarthrodial  joint  possesses  a  fibrous  or  ligamentous  envelope  or 
capsule  which  is  attached  to  the  adjacent  ends  of  the  articulating  bones.  For 
special  purposes,  particular  parts  of  the  capsule  may  undergo  enlargement  and 
thickening,  and  so  constitute  strong  ligamentous  bands,  although  still  forming  con- 
tinuous constituents  of  the  capsule. 

Within  the  capsule  a  series  of  intracapsular  structures  are  present.  Thus  the 
capsule  itself  is  always  lined  by  a  synovial  membrane,^  which  is  continued  from  the 
inner  surface  of  the  capsule  to  the  surface  of  the  intracapsular  portion  of  each 
articulating  bone.  The  part  of  the  bone  included  within  the  capsule  consists  of  a 
"  non-articular  "  portion  covered  by  synovial  membrane,  and  an  "  articular  "  portion 
covered  by  encrusting  hyaline  cartilage.  The  latter  provides  the  surface  which 
comes  into  apposition  with  the  corresponding  area  of  another  bone.  In  its  general 
disposition  the  synovial  membrane  may  be  likened  to  a  cylindrical  tube  open  at 
each  end.  This  membrane  is  richly  supplied  by  a  close  network  of  vessels  and 
nerves. 

Certain  diarthroses  present  additional  intracapsular  structures  which  may  be 
distinguished  as  interarticular  ligaments  and  interarticular  fibro-cartilages. 

Interarticular  ligaments  extend  between  and  are  attached  to  non-articular  areas 
of  the  intracapsular  portions  of  the  articulating  bones.  They  usually  occupy  the 
long  axis  of  the  joint,  and  occasionally  they  widen  sufficiently  to  form  partitions 
v^hich  divide  the  joint-cavity  into  two  compartments,  e.g.  the  costo-central,  and 
certain  of  the  chondro-sternal  joints. 

Interarticular  fibro-cartilages  or  menisci  (Fig.  207)  are  more  or  less  complete 
partitions  situated  between  and  separating  opposing  articular  surfaces,  and  when 
complete  they  divide  the  joint  cavity  into  two  distinct  compartments.     By  its 

periphery,  a  meniscus  is  rather  to  be  associated 
with  the  joint  capsule  than  with  the  articu- 
lating bones,  although  its  attachments  may 
extend  to  non-articular  areas  on  the  latter. 

Both  interarticular  ligaments  and  menisci 
have  their  free  surfaces  covered  by  syno\dal 
membrane. 

Adipose  tissue  forming  pads  of  varying  size 
is  usually  found  in  certain  localities  within 
the  joint,  between  the  synovial  membrane  and 
the  surfaces  which  it  covers.  These  pads  are 
soft  and  pliable,  and  act  as  packing  material, 
filling  up  gaps  or  intervals  in  the  joint. 
During  movement  they  ada^^t  themselves  to 
the  changing  conditions  of  the  articulation. 
In  addition  to  merely  binding  together  two 
jNo  THE  Joint  -  Cavity  into  two  Com-  or  more  articulating  bones,  ligaments  perform 
PAKTMENT.s.  ^^^^  importaut  functions  in  connexion  with 

the  different  movements  taking  place  at  a  joint.  They  do  not  appreciably  lengthen 
under  strains,  and  thus  ligaments  may  act  as  inhibitory  structures,  and  by  becom- 
ing tense  may  restrain  or  check  movement  in  certain  directions. 

Synovial  iiieuiljranes,  in  the  form  of  closed  sacs  termed  synovial  bursse,  are  frequently  found 
in  other  situations  Ijesides  the  interior  of  joints.  Such  bursie  are  developed  for  the  purpose  of 
reducing  the  friction,  (a)  Ijetween  the  integument  and  certain  prominent  suljcutaneous  bony  i^ro- 
jections,  as,  for  instance,  the  point  of  tlie  elljow,  or  the  front  surface  of  the  patella  (subcutaneous 
synovial  burste) ;  Qj)  between  a  tendon  and  some  surface,  bony  or  cartilaginou.s,  over  which  it 
plays  (subtendinous  synovial  burste) ;  (c)  between  a  tendon  or  a  group  of  tendons  and  the  walls 
of  osteo-fascial  tunnels,  in  which  tliey  play  (thecal  synovial  bursa;).  Subtendinous  synovial 
bursse  are  often  placed  in  the  neighbourhood  of  joints,  and  in  such  cases  it  not  infrequently 


Synovial 
membrane 


Fig.  207. — Diagram  ok  a  Diarthrodial  Joint 
WITH  AN  Interarticular  Meniscus  mvin- 


'  The  terra  "  .synovial  membrane  "  has  been  so  long  in  use  that  one  hesitates  to  discard  it,  even  although  the 
structure  so  described  is  not  in  many  cases  capable  of  being  removed  from  the  objects  of  which  it  forms  a  part. 
A  more  precise  description  in  these  cases  would  be  "synovial  surface."  There  is  still  considerable  doubt 
whether  the  "synovial  fluid  "  is  a  true  secretion  or  merely  a  diluted  friction  product. 


THE  DIFFERENT  KINDS  OF  MOVEMENT  AT  JOINTS.  259 

happens  that  there  is  a  direct  continuity  between  the  bursa  and  the  synovial  niembi'ane  which 
lines  the  cavity  of  the  joint  through  an  aperture  in  the  joint  capsule. 

THE  DIFFERENT  KINDS  OF  MOVEMENT  AT  JOINTS. 

Reference  has  already  been  made  to  the  existence  of  fixed  axes  of  movement  as 
a  basis  for  the  classification  of  certain  forms  of  diarthrodial  joints.  Hence  it  is 
evident  that  the  movements  which  are  possible  at  any  particular  joint  depend  to  a 
large  extent  upon  the  shape  of  its  articular  surfaces  as  well  as  upon  the  nature  of 
its  various  ligaments.  Therefore  the  technical  terms  descriptive  of  movements 
either  indicate  the  directions  in  which  they  occur,  or  else  the  character  of  the  com- 
pleted movement. 

In  the  great  majority  of  articulations  between  short  bones,  the  amount  of  move- 
ment is  so  restricted,  and  the  displacement  of  the  opposing  articular  surfaces  so 
slight,  that  the  term  gliding  sufficiently  expresses  its  character. 

A  gliding  movement  of  an  extensive  kind,  for  example  that  of  the  patella  upon  the  femur,  in 
which  the  movement  largely  resembles  that  of  the  tyre  of  a  wheel  revolving  in  contact  with  the 
ground  so  that  different  parts  are  successively  adaj^ted  to  each  other,  is  called  co-aptation. 

Articulations  between  long  bones,  on  the  other  hand,  are  usually  associated 
with  a  much  freer  range  of  movement,  with  a  corresponding  variety  in  its  character. 
Rotation  is  a  movement  about  an  axis  which  is  longitudinal.  Sometimes  it  is  the 
only  form  of  movement  which  a  joint  possesses  ;  at  other  times  it  is  merely  one  of  a 
series  of  movements  capable  of  execution  at  the  same  joint.  Flexion  or  bending  is 
a  movement  in  which  the  formation  of  an  angle  between  two  parts  of  the  body  is 
an  essential  feature.  As  it  is  possible  to  perform  this  movement  in  relation  to  two 
axes,  viz.  a  transverse  and  an  antero-posterior  axis,  it  is  necessary  to  introduce 
qualifying  terms.  Thus,  when  two  anterior  or  ventral  surfaces  are  approximated, 
as  at  the  hip-,  elbow-,  or  wrist-joints,  the  movement  is  called  ventral,  anterior,  or 
palmar  flexion ;  but  if  posterior  or  dorsal  surfaces  be  approximated  by  the  process  of 
bending,  then  the  flexion  becomes  posterior  or  dorsi-flexion,  as  at  the  knee-  or  wrist- 
joints.  Further,  at  the  wrist-joint,  the  formation  of  an  angle  between  the  ulnar 
border  of  the  hand  and  the  corresponding  aspect  of  the  forearm,  produces  ulnar 
flexion,  and  similarly  the  bending  of  the  hand  towards  the  radial  border  of  the 
forearm  is  radial  flexion. 

Extension  or  straightening  consists  in  obliterating  the  angle  which  resulted  from 
flexion.  In  the  case  of  certain  joints,  therefore,  such  as  the  elbow,  wrist,  and  knee, 
the  segments  of  the  limb  occupy  a  straight  line  as  regards  each  other  when 
extended. 

At  the  ankle-joint  the  natural  attitude  of  the  foot  to  the  leg  is  flexion  at  a  right  angle.  The 
diminution  of  this  angle  by  approximating  the  dorsum  of  the  foot  towards  the  front  of  the  leg 
constitutes  flexion  ;  while  any  effort  at  placing  the  foot  and  leg  in  a  straight  line,  i.e.  obliteration  of 
the  angle,  as  in  pointing  the  toes  towards  the  ground  and  raising  the  heel,  constitutes  extension. 

Abduction  is  a  term  which  either  expresses  movement  of  an  entire  limb,  in  a 
direction  away  from  the  mesial  plane  of  the  body,  or  of  a  digit,  away  from  the 
plane  of  the  middle  finger  in  the  hand,  or  the  plane  of  the  second  toe  in  the  case 
of  the  foot. 

Adduction  is  the  reverse  of  abduction,  and  signifies  movement  towards  the 
mesial  plane  of  the  body,  or  towards  the  planes  indicated  for  the  digits  of  the  hand 
and  foot. 

Circumduction  is  a  movement  peculiarly  characteristic  of  multiaxial  or  ball- 
and-socket  joints.  It  consists  in  combining  such  angular  movements  as  flexion, 
extension,  abduction,  and  adduction,  so  as  to  continue  the  one  into  the  other, 
whereby  the  joint  forms  the  apex  of  a  cone  of  movement,  and  the  free  end  of  the 
limb  travels  through  a  circle  which  describes  the  base  of  this  cone. 

THE  DEVELOPMENT  OF  JOINTS. 

Just  as  the  question  of  structure  determines  to  a  large  extent  the  presence  or  absence 
of    movement   in  joints,    so   in    tracing   their    development   it   will    be    found    that    the 
18  a 


260  THE  AETICULATIONS  OE  JOINTS. 

manner  of  their  appearance  forecasts  their  ultimate  destination  as  immovable  or  mov- 
able articulations. 

All  joints  arise  in  mesodermic  tissue  which  has  undergone  more  or  less  differentiation. 
When  this  differentiation  has  produced  a  continuous  membranous  layer,  in  which 
ossific  centres  representing  separate  skeletal  segments  make  their  appearance,  we  get  the 
primitive  form  of  suture.  The  plane  of  the  articulation  merely  indicates  the  limit  of 
the  ossific  process  extending  from  different  directions.  If,  again,  the  differentiation  of 
the  mesoblast  has  resulted  in  the  formation  of  a  continuous  cartilaginous  layer,  in  which 
ossification  commences  at  separate  centres,  the  plane  of  the  articulation  is  marked 
out  by  the  unossified  cartilage — in  other  words,  the  articulation  is  a  synchondrosis.  Ulti- 
mately this  disappears  through  the  extension  of  the  process  of  ossification. 

To  some  extent  sutures  also  disappear,  although  their  complete  obliteration  is  not 
usual  even  in  aged  people.  Developmentally,  therefore,  synarthroses  or  immovable' 
joints  do  not  present  any  special  structural  element,  and,  speaking  generally,  they  have 
only  a  temporary  existence. 

The  development  of  all  movable  joints  is  in  marked  contrast  to  that  of  synar- 
throses. Not  only  are  they  permanent  arrangements  so  far  as  concerns  normal  conditions, 
but  they  never  arise  merely  as  planes  which  indicate  the  temporary  phase  of  an  ossific 
process.  From  the  outset  they  present  distinct  skeletal  units,  from  which  the  special 
structures  of  the  joint  are  derived. 

The  primitive  movable  joint  is  first  recognised  as  a  mass  of  undifferentiated  meso- 
dermic cells  situated  between  two  masses,  which  have  differentiated  into  primitive  cartilage. 

The  cell-mass  which  constitutes  the  joint- unit  presents  the  appearance  of  a  thick 
cellular  disc,  the  proximal  and  distal  surfaces  of  which  are  in  accurate  apposition  with  the 
primitive  cartilages,  while  its  circumference  is  defined  from  the  surrounding  mesoderm  by 
a  somewhat  closer  aggregation  of  the  cells  of  which  the  disc  is  composed.  From  this 
cellular  disc  or  joint-unit  all  the  structures  characteristic  of  amphiarthrodial  and  diar- 
throdial  joints  are  ultimately  developed. 

Thus  by  the  transformation  of  the  circumferential  cells  into  fibrous  tissue  the  invest- 
ing ligaments  are  produced.  Within  the  substance  of  the  disc  itself  a  transverse  cleft, 
more  or  less  well-defined  and  complete,  makes  its  appearance.  In  this  manner  the  disc  is 
divided  into  proximal  and  distal  segments,  sepai-ated  from  each  other  by  an  interval 
which  is  the  primitive  joint  cavity.  This  cleft,  however,  never  extends  so  far  as  to  inter- 
rupt the  continuity  of  the  circumferential  part  of  the  disc  which  develops  into  the  fibrous 
tissue  of  the  investing  ligaments.  From  the  proximal  and  distal  segments  of  the 
articular  disc  the  various  structures,  distinctive  of  movable  joints,  are  developed. 

Thus,  in  amphiarthrodial  joints  the  cellular  articular  disc  or  primitive  joint-unit  gives 
origin  to  the  following  structures  : — From  its  circumference,  investing  ligaments ;  from 
its  interior,  the  fibro-cartilaginous  plate  or  disc  in  which  an  imperfect  joint  cavity  with 
corresponding  imperfect  synovial  may  be  found. 

In  the  case  of  a  diarthrodial  joint  the  changes  take  place  on  a  more  extended  scale. 
The  joint  cavity  becomes  a  prominent  feature,  in  relation  to  which  the  surrounding 
fibrous  structures  form  an  investing  capsule,  lined  by  a  synovial  membrane. 

When  a  single  cleft  arises,  but  does  not  extend  completely  across  the  longitudinal  axis 
of  the  articular  disc,  the  undivided  portion  develops  into  fibrous  interarticular  ligaments. 
On  the  other  hand,  when  two  transverse  clefts  are  formed,  that  portion  of  the  cellular 
disc  which  remains  between  them  becomes  transformed  into  a  fibro-cartilaginous  inter- 
articular disc  or  meniscus,  which  in  its  turn  may  either  be  complete  or  incomplete,  and 
thus  we  may  obtain  two  distinct  synovial  joint  cavities  belonging  to  one  articulation. ^ 

In  considering  the  development  of  the  synovial  membrane,  and  the  surfaces  on  which 
it  is  found  in  the  interior  of  a  joint,  it  is  necessary  to  keep  clearly  in  mind  that  a  synovial 
membrane  is  a  special  structure,  whose  function  it  is  to  produce  a  lubricating  fluid  or 
synovia,  and  that,  therefore,  its  position  is  determined  by  the  essential  necessity  of 
proximity  to  a  direct  blood-supply.  In  other  words,  this  condition  is  provided  by  all 
parts  of  the  interior  of  a  joint  cavity  except  the  articular  encrusting  cartilage.  Conse- 
quently synovial  membrane  is  only  absent  from  the  free  surface  of  articular  cartilage, 
although  it  forms  a  thicker  layer  upon  the  inner  surface  of  the  joint  capsule  than  upon 
the  free  surfaces  of  interarticular  ligaments  and  menisci. 

'  From  a  serie.i  of  observations  upon  the  development  of  diarthrodial  joints,  the  writer  considers  that 
there  is  evidence  to  show  that  the  "cellular  articular  disc "  is  directly  responsible  for  tlie  production  of 
the  epiphyses  which  adjoin  the  completed  joint  cavity,  and  that,  among  such  ainjihiarthroses  as  exist 
between  the  bodies  of  vertebra',  not  only  the  intervertebral  disc,  but  the  proximal  and  distal  epiphyses 
which  ultimately  unite  with  the  vertebral  bodies  have  a  common  origin  in  the  joint-unit. 


LIGAMENTS  OF  THE  VERTEBRAL  COLUMN.  261 

It  is  not  necessary  to  suppose  that  the  synovial  membrane  has  disappeared  from  these 
articular  cartilages  as  the  result  of  friction,  because,  notwithstanding  constant  friction, 
such  parts  as  the  interior  of  capsular  ligaments  or  the  semilunar  cartilages  of  the  knee- 
joint  have  not  been  denuded  of  their  synovial  covering. 

MORPHOLOGY  OF  LIGAMENTS. 

From  what  has  been  said  in  connexion  with  the  development  of  joints,  it  will  be  evident 
that  ligaments  are  essentially  products  derived  from  the  cellular  articular  disc. 

Nevertheless,  in  relation  to  the  fully-formed  joint,  many  structures  are  described  as  ligaments 
which  do  not  take  origin  in  the  manner  just  indicated.  Some  of  these  ligamentous  structures 
remain  fairly  distinct  from  the  capsular  ligaments  wdth  which  they  are  immediately  associated  ; 
others  become  thoroughly  incorporated  with  the  capsular  ligaments  and  cannot  be  separated 
therefrom,  while  yet  others  may  be  found  situated  within  the  capsule  of  a  joint,  and  thus  play 
the  pai't  of  interarticular  ligaments. 

Instances  of  each  of  these  forms  of  adventitious  ligaments  may  be  readily  given.  For 
example,  we  may  instance  the  expansion  of  the  tendon  of  the  semimembranosus  muscle  to  the 
posterior  ligament  of  the  knee-joint,  and  the  ofl'shoots  from  the  tendon  of  the  tibialis  posticus 
muscle  to  the  plantar  aspects  of  various  tarsal  bones,  as  illustrations  of  structures  which  play 
an  important  part  as  ligaments,  but  are  not  indelibly  incorporated  with  the  joint  capsule. 

Of  structures  which  have  become  indelibly  incorporated  with  the  primitive  capsule,  we  may 
instance  the  broad  tendinous  expansions  of  the  quadriceps  extensor  muscle  around  the  knee-joint. 

The  internal  lateral  ligament  of  the  same  joint  is  regarded  as  a  detached  portion  of  the 
tendon  belonging  to  that  part  of  the  adductor  magnus  muscle  which  takes  origin  from  the 
ischium,  while  the  external  lateral  ligament  of  the  knee  is  considered  by  some  to  be  the  primi- 
tive femoral  origin  of  the  peroneus  longus  muscle.  Another  illustration  of  the  same  condition 
is  found  in  the  coraco-humeral  ligament,  which  is  regarded  by  some  as  representing  a  detached 
portion  of  the  pectoralis  minor  muscle. 

Two  illustrations  may  be  given  of  structures  plajang  the  part  of  ligaments  within  the 
capsule  of  a  joint,  although  in  the  first  instance  they  are  not  developed  as  ligaments.  It  is 
questionable  if  the  ligamentum  teres  of  the  hip-joint  is  an  interarticular  ligament  in  the  true 
sense  of  the  term  ;  it  has  been  regarded  as  the  isolated  and  displaced  tendon  of  the  ambiens  muscle 
found  in  biixls.  In  the  shoulder-joint,  many  observers  look  upon  the  superior  gleno-humeral 
ligament  as  representative  of  the  ligamentum  teres. 

Such  structures  a^  the  stylohyoid  ligament  and  the  internal  lateral  ligament  of  the  temporo- 
mandibular joint,  although  described  as  ligaments,  are  in  reality  skeletal  parts  which  have  not 
attained  their  complete  ossific  development. 

Again,  certain  portions  of  the  deep  or  muscular  fascia  of  the  body  which  become  specialised 
into  restraining  and  supporting  bands  {e.g.  the  ilio-tibial  band  of  the  fascia  lata  ;  the  stylo-mandi- 
bular  ligament ;  the  anterior  and  posterior  annular  ligaments  of  the  wrist-joint ;  the  anterior, 
inner,  and  outer  annular  ligaments  of  the  ankle-joint),  although  called  ligaments,  have  no 
direct  developmental  association  with  articular  ligaments. 

Lastly,  the  ligament  of  Poupart  and  the  ligament  of  Gimbernat,  being  special  develoi^ments 
in  connexion  with  an  expanded  tendon  or  aponeurosis,  are  still  further  removed  from  associa- 
tion with  an  articulation. 


LIGAMENTS  OF  THE  VERTEBRAL  COLUMN  AND  SKULL. 

All  vertebrae,  with  the  exception  of  those  which  deviate  from  the  common 
vertebral  type,  present  two  sets  of  articulations  whose  various  parts  are  arranged 
upon  a  uniform  pattern.  Thus  every  pair  of  typical  vertebrie  presents  an  articula- 
tion between  the  centra,  termed  intercentral,  and  a  pair  of  articulations  between 
the  neural  arches,  called  interneural.  With  the  latter  there  are  associated  various 
important  accessory  ligaments  which  bind  together  laminie,  spinous  processes,  and 
transverse  processes. 

Intercentral  Articulations. — These  are  amphiarthrodial  joints.  Singly,  they 
present  only  a  slight  degree  of  mobility,  but  when  this  amount  of  movement  is 
added  to  that  of  the  whole  series,  the  range  of  movement  of  the  spine  becomes 
considerable.  The  articular  surfaces  are  the  flattened  surfaces  of  adjacent  vertebral 
bodies.     They  are  bound  together  by  the  following  structures : — 

Intervertebral  Discs  (tibro-cartilagines  intervertebrales,  Fig.  208). — Each  disc 
accommodates  itself  to  the  space  it  occupies  between  the  two  vertebral  bodies,  to 
both  of  which  it  is  firmly  adherent.  The  discs,  from  different  parts  of  the  spinal 
column,  vary  in  vertical  thickness,  being  thinnest  from  the  third  to  the  seventh  dorsal 
vertebra,  and  thickest  in  the  lumbar  region.  In  the  cervical  and  lumbar  regions 
each  disc  is  thicker  in  front  than  behind,  thereby  assisting  in  the  production  of  the 
18  6  '  . 


262 


THE  AETICULATIONS  OK  JOINTS. 


anterior  convexity  which  characterises  the  spinal  column  in  these  two  regions.  In 
the  dorsal  region  the  discs  are  thinnest  on  their  anterior  aspects  in  correspondence 
with  the  anterior  concavity  of  this  section  of  the  spine. 

Each  disc  consists  of  a  circumferential  portion  (annulus  fibrosus),  formed  for 


Vertebral  body 


Intervertebral  disc     (/ 


Ligaiiientum  flavum 
or  subflavum 


Nucleus  pulposus 


Spinous  process 


Fig.  208. — Mesial  Section  through  a  Portion  of  the  Lumbar  Part  of  the  Spine. 

the  most  part  of  oblique  parallel  fibres  running  from  one  vertebra  to  the  other. 
Horizontal  fibres  are  also  found.  The  axial  or  central  part  of  the  disc  is  elastic, 
soft,  and  pulpy  (nucleus  pulposus).^ 

The  upper  and  lower  surfaces  of  the  disc  are  closely  adherent  to  the  adjoining 

interior  conimon  ligament 

Anterior  or 
superior  costo- 
transverse 
ligament 


:  slips  of  the  ) 


Three 
stellate  ligament 


Anterior  or 
superior  costo- 
transverse 
ligament 


Fig.  209. — Antekiok  Common  Ligament  of  the  Vektebkal  Column,  and  the  Costo-vertebral 

.Joints  as  seen  fr(jm  the  Front. 

epiphyseal  plates  of  the  vertel^ral  bodies,  and  as  ossification  advances,  the  distinc- 
tion between  epiphyseal  plates  and  vertebral  ])ody  disappears. 

As  a  rule  the  transverse  diameter  of  the  disc  corresponds  to  that  of  the  verte- 
bral bodies  which  it  joins  together ;  but  in  the  cervical  region,  where  the  lower 

1  This  pulpy  substance  does  not  present  a  joint  cavity,  but  in  certain  cases  it  is  more  or  less  divided 
by  fissures  which  occupy  a  transverse  horizontal  direction. 


LIGAMENTS  OF  THE  VERTEBEAL  COLUMN. 


263 


margin  of  the  superimposed  vertebra  is  overlapped  on  each  side  by  the  one  which 
bears  it,  the  disc  does  not  extend  to  the  extreme  lateral  margin,  and  in  this  position 
a  small  diarthrosis  may  be  seen  at  each  lateral  margin  of  the  disc. 

The  anterior  common  ligament  (lig.  longitudinale  anterius,  Fig.  209)  consists 
of  a  wide  stratum  of  longitudinal  fibres  which  extends  from  the  front  of  the  axis 
vertebra  to  the  front  of  the  upper  segment  of  the  sacrum,  and  becomes  gradually 
wider  from  above  downwards.  It  lies  in  front  of  the  intervertebral  discs,  to  which 
it  is  firmly  attached  as  it  passes  from  one  vertebra  to  the  other.  Its  fibres  vary  in 
length.  fSome  are  attached  to  contiguous  margins  of  two  adjoining  vertebrae ; 
others  pass  in  front  of  one  vertebra  to  be  attached  to  the  next  below,  and  yet 
others  lind  their  lower  attachment  three  or  four  vertebree  below  the  one  from  which 
they  started.  None  of  the  fibres  are  attached  to  the  transverse  depression  on  the 
front  of  a  vertebral  body. 

The  posterior  common  ligament  (lig.  longitudinale  posterius,  Fig.  210)  is  found 
within  the  spinal  canal  upon  the  posterior  aspect  of  the  vertebral  bodies.  It  con- 
sists of  longitudinal  fibres,  and  it  extends  from 
the  back  of  the  sacrum  to  the  axis  vertebra,  superior 
to  which  it  is  continued  to  the  skull  as  the  posterior 
occipito-axial  ligament.  Opposite  each  interverte- 
bral disc  it  is  attached  to  the  entire  width  of  the 
adjacent  margins  of  the  two  vertebral  bodies,  its 
fibres  being  continued  over  the  posterior  surface  of 
the  disc.  In  the  lumbar  and  dorsal  regions  the 
width  of  the  ligament  is  considerably  reduced 
opposite  the  back  of  each  vertebral  body,  and  thus 
it  forms  a  series  of  dentate  projections  along  both 
of  its  margins ;  but  in  the  cervical  region  the 
width  of  the  ligament  is  more  uniform. 

One  or  two  large  thin -walled  veins  escape  from 
the  l3ody  of  each  vertebra  under  cover  of  this  liga- 
ment. 

Interneural  Articulations. — The  neural  arch 
of  each  typical  verteljra  carries  two  pairs  of 
articular  processes,  by  means  of  which  it  articu- 
lates with  adjacent  neural  arches.  The  articu- 
lations between  tliese  processes  are  true  diarthroses 
of  the  arthrodial  variety. 

The  distinctive  characters  of  these  articular  sur- 
faces, as  regards  their  shape  and  direction  in  the  different  groups  of  vertebrae,  have 
been  referred  to  in  the  section  on  osteology. 

All  these  articulations  are  provided  with  complete  but  very  thin -walled  cap- 
sules (capsulae  articulares),  which  are  thinnest  and  loosest  in  the  cervical  region, 
where  also  the  movements  are  freest.  Each  capsule  is  lined  by  a  synovial 
membrane. 

Associated  with  these  interneural  joints  are  certain  ligaments  which  are 
accessory  to  the  articulations,  although  they  are  quite  distinct  from  the  capsule. 

The  laminae  of  adjoining  vertebrae  are  bound  together  by  the  ligamenta  subflava 
(ligamenta  flava  vel  subflava.  Fig.  211),  which  consist  of  yellow  elastic  fibres.  The 
ligamenta  subflava  close  the  spinal  canal  in  the  intervals  between  the  laminae. 
Each  ligament  is  attached  superiorly  to  the  anterior  aspect  of  one  lamina  at  a 
short  distance  above  its  lower  border,  and  inferiorly  it  is  attached  to  the  posterior 
aspect  of  the  subjacent  lamina. 

In  the  dorsal  region,  where  the  imbrication  of  adjoining  laminae  is  a  prominent 
feature,  these  ligaments  are  not  so  distinctly  visible  from  behind  as  they  are  in  the 
regions  where  imbrication  of  the  laminae  is  not  so  marked. 

Laterally  they  extend  as  far  as  the  articular  capsules,  while  mesially  the  margins 
of  the  ligaments  of  opposite  sides  meet  under  cover  of  the  root  of  the  spinous  process. 

Contiguous  pairs  of  spinous  processes  are  also  attached  to  each  other  by  inter- 
spinous  ligaments  (ligamenta  interspinalia.  Fig.  208).     These  are  strongest  in  the 


Interverte- 
bral fibro- 
cartilaginous 
disc 


Fig.  210  — Posterior  Common  Ligament 
OF  THE  Vertebral  Column. 


264 


THE  AETICULATIONS  OK  JOINTS. 


Pedicle  of 

^'el■tebra 

i.Uvided 


lumbar,  and  weakest  in  the  dorsal  region.     Each  consists  of  layers  of  obliquely 
interlacing  fibres  which  spring  from  near  the  tips  of  the  two  adjacent  spines  and 

radiate  to  their  opposing 
margins.  In  the  antero- 
posterior direction  they 
extend  from  the  base  to 
the  tip  of  the  spinous 
process. 

The  supraspinous  liga- 
ments (ligg.  supra- 
spinalia,  Fig.208)consist 
of  longitudinal  bands  of 
fibres  of  varying  lengths. 
They  extend  from  spine 
t  o  spine,  being  attached  to 
their  tips,and  are  situated 
superficial  to,  although 
in  continuity  with,  the 
interspinous  ligaments. 

In  the  cervical  region 
this  series  of  ligaments 
is  extensively  developed, 
where  they  project  back- 
wards from  the  spinous 
processes  between  the 
muscles  of  the  two  sides 

„      „        ^  ^  of  the  neck  in  the  form 

Fig.  211. — Ligamenta  Subflava  as  seen   from  the  Front  after    Re-     n  i     .  •  .  ■■• 

MOVAL     OF    the    BODIES    OF    THE    VeRTEBR^    BY     SAWING    THROUGH    THE  *^        ^^      ClaStlC      partition 

Pedicles.  called    the    ligamentum 

nuclise. 

The  antero-posterior  extent  of  the  ligamentum  nuchse  increases  as  it  approaches 
the  occiput,  where  it  is  attached  to  the  occipital  crest  from  the  external  occipital 
protuberance  to  the  posterior  border  of  the  foramen  magnum.  Its  posterior  margin 
is  free,  and  extends  from  the  external  occipital  protuberance  to  the  spine  of  the 
vertebra  prominens. 

Between  the  transverse  processes  there  are  intertransverse  ligaments  (ligg.  inter- 
transversaria),  which  consist  of  vertical  fibres  extending  from  the  postero-inferior 
aspect  of  one  transverse  process  to  the  superior  margin  of  that  next  below.  These 
ligaments  are  generally  absent  from  the  cervical  and  upper  dorsal  regions. 

Sacro-coccygeal  Joint. — The  last  piece  of  the  sacrum  is  joined  to  the  first 
piece  of  the  coccyx  by  an  intervertebral  disc,  and  the  junction  is  rendered 
more  secure  by  the  presence  of  certain  strong  ligaments.  An  anterior  ligament 
(lig.  sacro-coccygeum  anterius),  continuous  with  the  anterior  common  ligament,  is 
placed  in  front.  A  posterior  ligament  (lig.  sacro-coccygeum  posterius),  which 
stretches  downwards  from  the  sharp  border  of  the  lower  opening  of  the  sacral 
canal,  strengthens  the  joint  behind.  A  lateral  ligament  (lig.  sacro-coccygeum 
laterale)  supports  the  joint  on  each  side,  whilst  strong  bands  pass  between  the 
cornua  of  the  two  bones  and  constitute  the  interarticular  ligaments. 

Inter-coccygeal  Joints. — So  long  as  they  remain  separate,  the  different  pieces 
of  the  coccyx  are  joined  by  intervertebral  discs  and  by  anterior  and  posterior  liga- 
ments. 

Movements  of  the  Vertebral  Column. — Although  the  amount  of  movement  permissible 
between  any  two  verteljraj  is  exti-emely  limited,  yet  the  total  range  of  movement  capable  of 
being  attained  by  the  entire  vertebral  column  is  very  considerable. 

Flexion  may  occur  both  forwards  and  backwards  at  the  intercentral  articulations,  but  more 
freely  in  the  lumbar  and  cervical  regions  than  in  the  dorsal  region,  where  the  limited  amount  of 
intervertebral  disc  and  the  imbrication  of  the  laminai  and  spines  restrict  the  movement.  Back- 
ward flexion  is  most  pronoiuiced  in  the  cervical  region,  and  forward  flexion  in  the  lumbar  region. 
Between  the  articular  surfaces  of  the  interneural  articulations  a  variety  of  movements  are  per- 
mitted, dependent  upon  the  directions  of  these  surfaces.     Thus  lateral  flexion  is  permitted  in 


AETICULATIOX  OF  ATLAS  WITH  AXIS. 


265 


the  lumbar,  but  not  in  the  cervical  or  dorsal  regions.  Again,  in  the  lumbar  region  rotation 
•does  not  occur,  owing  to  the  shape  of  the  articular  processes,  while  it  is  possible  in  the  dorsal 
region.  In  the  cervical  region  the  shape  and  position  of  the  articular  surfaces  prevent  the 
■occurrence  both  of  lateral  flexion  and  of  rotation  as  isolated  movements,  but  a  combination  of 
these  two  movements  may  take  place,  whereby  rotatory  movement  in  an  oblicpie  median  axis 
results.  Finally,  in  the  lumbar  region,  l>y  coml)ining  the  four  forms  of  flexion,  viz.  forward, 
backward,  and  lateral,  a  certain  amount  of  circumduction  is  possible. 

Articulation  of  Atlas  with  Axis. 

Between  these  two  vertebrae  three  diarthroses  occur.  Two  of  them  are 
situated  laterally  in  relation  to  the  articular  processes,  and  are  called  artlirodial 
diarthroses,  because  of  the  flattened  nature  of  the  articulating  surfaces.  The  third 
articulation  is  mesial  in,  position.  It  is  found  between  the  smooth  anterior  surface 
of  the  odontoid  process  of  the  axis  and  the  articular  facet  on  the  posterior  aspect  of 
the  anterior  arch  of  the  atlas.     This  joint  is  a  rotatory  diarthrosis. 

Ligaments. — Each  of  the  joints  is  furnished  with  a  capsular  ligament  whereby 


Membrana  tectoria 


Basi-occipital  bone 


Anterior  occipito-atloid  ligament 
Liganientum  apicis  denti 


Transverse 


Inferior  crus  of 

Rudimentary  intervertebral  disc 


Superior  crus  of  crucial  ligament 
Synovial  cavity 

Posterior  occipito-atloid 
ligament 


-Occipital  bon"e 


Posterior  common  ligament 
Posterior  arch  of  atlas 


?pine  of  axis 


Fic.  212. — Mesial  Section  through  the  Occipito-atloid  and  Atlo-axoid  Joints. 


the  joint  cavity  is  circumscribed.  In  the  case  of  the  lateral  articulations,  each 
capsular  ligament  presents  a  distinct  band,  named  the  accessory  ligament,  which  is 
situated  within  the  neural  canal  (Fig.  213),  and  passes  downwards  and  inwards 
from  the  lateral  mass  of  the  atlas  to  the  superior  aspect  of  the  body  of  the  axis. 

The  following  additional  ligaments  constitute  the  leading  bonds  of  union : — 

The  anterior  atlo-axoid  ligament  (Fig.  212)  is  a  membranous  structure  which  is 
thin  laterally,  but  strong  mesially  where  it  is  thickened  by  a  prolongation  of  the 
anterior  common  ligament.  It  extends  from  the  anterior  arch  of  the  atlas  to  the 
front  of  the  body  of  the  axis. 

The  posterior  atlo-axoid  ligament  (Fig.  212)  occupies  the  position  which  is 
elsewhere  taken  by  the  ligamenta  subflava.  It  extends  from  the  posterior  arch 
of  the  atlas  to  the  upper  border  of  the  neural  arch  of  the  axis. 

The  transverse  ligament  of  the  atlas  (lig.  transversum  atlantis,  Figs.  212  and 
213)  is  a  strong  band,  placed  transversely,  which  arches  backwards  behind  the 
neck  of  the  odontoid  process  of  the  axis.  By  its  extremities  it  is  attached  to  the 
tubercle  on  the  inner  aspect  of  each  lateral  mass  of  the  atlas.  A  thin  plate  of 
fibro-cartilage  is  developed  in  its  central  part. 

Synovial  membrane  lines  each  of  the  three  capsular  ligaments,  and  in  addition  a 
synovial  sac  is  developed  between  the  odontoid  process  and  the  transverse  Ligament. 
This  is  more  extensive  than  the  synovial  cavity  between  the  odontoid  process  and 
the  atlas. 


266 


THE  ARTICULATIONS  OE  JOmTS. 


Articulation  of  Spine  with  Cranium. 

There  are  two  articulations  between  the  atlas  and  the  occiput.  Each  is  a 
diarthrosis  in  which  movement  takes  place  in  relation  to  two  axes,  viz.  the 
transverse  and  the  antero-posterior.  The  condyle  of  the  occiput  being  biconvex, 
fits  into  the  biconcave  superior  articular  surface  of  the  atlas,  while  the  long  axes  of 
the  two  joints  are  directed  horizontally  forwards  and  inwards. 

Ligaments. — Each  articulation  is  provided  with  a  capsular  ligament  which  is 
thin  but  complete.  It  is  attached  to  the  rough  non-articular  surfaces  surrounding 
the  articular  areas  on  the  atlas  and  occiput. 

The  following  supplementary  ligaments  are  the  chief  structures  which  bind  the 
atlas  to  the  occiput : — 

The  anterior  occipito-atloid  ligament  (membrana  atlanto-occipitalis  anterior, 
Fig.  212)  is  a  strong  although  thin  membrane,  attached  inferiorly  to  the  anterior 
arch  of  the  atlas,  and  superiorly  to  the  anterior  half  of  the  circumference  of  the 
foramen  magnum.  Laterally  it  is  in  continuity  with  the  capsular  ligaments,  while 
in  the  mesial  plane,  where  it  extends  from  the  anterior  tubercle  of  the  atlas  to  the 
basi-occiput,  it  presents  a  specially  well-defined  thickened  band  which  might  be 
regarded  as  a  separate  accessory  ligament  or  as  the  beginning  of  the  anterior 
common  ligament  of  the  vertebrae. 

The  posterior  occipito-atloid  ligament  (membrana  atlanto-occipitalis  posterior, 
Fig.  212)  is  another  distinct  but  still  thin  membrane  which  is  attached  superiorly 
to  the  posterior  half  of  the  circumference  of  the  foramen  magnum,  and  inferiorly  to 
the  upper  border  of  the  posterior  arch  of  the  atlas.  Laterally  it  also  is  continuous 
with  the  capsular  ligaments.  On  each  side  of  the  mesial  plane  its  inferior  border 
is  arched  in  relation  to  the  vertebral  groove,  and  is  therefore  to  some  extent  free, 
in  order  to  permit  the  passage  of  the  posterior  primary  division  of  the  first  cervical 
nerve  and  the  vertebral  artery.  IMot  infrequently  this  arched  border  becomes 
ossified,  thus  converting  the  groove  in  the  bone  into  a  foramen. 

Synovial  membrane  lines  each  of  the  capsular  ligaments.  There  is  no  direct 
articulation  between  the  axis  and  the  occiput,  but  union  between  them  is  effected 
by  means  of  the  following  accessory  ligaments : — 

The  posterior  occipito-axoid  ligament  (membrana  tectoria,  Fig.  213)  is  situated 
within  the  neural  canal,  and  is  usually  regarded  as  the  upward  continuation  of  the 
posterior  common  ligament  of  the  vertebral  bodies.     It  extends  from  the  posterior 


Membrana  tectoria 

Cius  superius 


Occipi 


Lateral  ma.s.s  of  atla.s 
Atlanto-ax 


Ligaineiitum  apicis  dentis 
(middle  odontoid) 


Ligainentum  alare 
or  check  ligament 

Crus  superius 

Ligameiitum  cnicia- 
tum  atlantis 


Accessorj'  atlanto- 
axial ligament 


Crus  inferius 


Membrana  tectoria 


Fig.  213. — Dissection  from  behind  of  the  Ligaments  connecting  the  Occipital  Bone,  the  Atlas, 

AND  the  Axis  with  each  other. 

surface  of  the  body  of  the  axis  to  the  basilar  groove  on  the  upper  surface  of  the 
basi-occipital  bone,  spreading  laterally  on  the  circumference  of  the  foramen 
magnum.  Some  of  its  deepest  fibres  are  attached  to  the  atlas  immediately  above 
the  atlo-axoid  articulation. 


TEMPOEO-MANDIBULAE  JOINT. 


267 


Subjaceut  to  the  preceding  ligament  there  is  the  ligamentum  cruciatum  atlantis 
(Fig.  213),  a  structure  which  is  very  closely  associated  with  the  lig.  transversum 
atlantis.  It  consists  of  a  cms  transversum,  formed  by  the  superficial  fibres  of 
the  transverse  ligament  of  the  atlas  ;  a  cms  inferius,  consisting  of  mesial  longi- 
tudinal fibres  which  are  attached  below  to  the  posterior  surface  of  the  body  of  the 
axis,  and  above  to  the  crus  transversum  and  a  cms  superius,  also  mesial  and 
longitudinal,  whose  fibres  extend  from  the  crus  transversum  upwards  to  the 
posterior  surface  of  the  basi-occiput,  immediately  subjacent  to  the  posterior 
occipito-axoid  ligament. 

The  check  ligaments  or  lateral  odontoid  ligaments  (ligamenta  alaria.  Fig.  213)  are 
two  very  powerful,  short,  and  somewhat  rounded  bands.  They  are  attached  mesially 
to  the  sides  of  the  summit  of  the  odontoid  process,  and  laterally  to  the  tubercle 
on  the  inner  aspect  of  the  condylar  portions  of  the  occipital  bone,  viz.  the  ex- 
occipital  bones. 

The  middle  odontoid  ligament  (ligamentum  apicis  dentis,  Fig.  213)  consists  of 
fibres  running  vertically  upwards  from  the  apex  of  the  odontoid  process  to  the 
mesial  pan  of  the  anterior  margin  of  the  foramen  magnum.  This  ligament 
to  some  extent  represents  an  intervertebral  disc,  in  the  centre  of  which  remains  of 
the  notochord  may  be  regarded  as  present. 

Even  in  advanced  life  a  small  lenticular  mass  of  cartilage,  completely  sur- 
rounded by  bone,  persists  in  the  plane  of  fusion  between  the  odontoid  process  and 
the  body  of  the  axis. 

Movements  at  these  Joints. — At  the  joints  between  occiirat  and  atlas  the  movements  are 
very  simple,  and  consist  essentially  of  movements  whereby  the  head  is  elevated  and  depressed 
upon  the  vertebral  column  (nodding  movements).  In  addition  a  certain  amount  of  oblique 
movement  is  jjossible,  during  which  great  stability  is  attained  by  resting  the  front  and  hinder 
parts  of  oi^ijosite  condyles  upon  corresponding  parts  of  the  atlas. 

The  head  and  the  atlas  rotate  together  upon  the  axis,  the  pivot  of  rotation  being  the  odontoid 
process,  and  the  amount  of  rotation  is  limited  by  the  check  ligaments.  No  rotation  can  occur 
between  the  occijjut  and  atlas,  and 

.stability  between  atlas _  and  axis  is  EMp.nal  Hteiai  ligament 

best  attained  after  a  slight  amount  (antenoi  and  postenoi  paits) 

of  rotation,  similar  to  the  oblique 
movement  between  occiput  and 
atlas. 

TEMPORO-MANDIBULAR 
JOINT. 

This  joint  is  an  arthrodial 
diarthrosis.  It  occurs  between 
the  articular  part  of  the  glenoid 
fossa  of  the  temporal  bone  and 
the  condylar  head  of  the 
mandible.  These  two  articular 
surfaces  are  markedly  dissimilar 
both  in  size  and  shape.  In  its 
general  outline  the  articular 
surface  of  the  head  of  the 
mandible  is  cylindrical,  having 
its  long  axis  directed  from 
within  outwards  and  forwards. 
On  the  other  hand,  the  articular 
part  of  the  glenoid  fossa  in 
front  of  the  Grlaserian  fissure 
is  concavo-convex  from  behind 
forwards.  Its  articular  surface  includes  the  emiuentia  articularis,  the  eminence  at 
the  base  of  the  anterior  root  of  the  zygoma.  The  articular  surfaces  of  the  bones 
are  clothed  by  hyaline  encrusting  cartilage,  whilst  the  joint  cavity  is  divided  into 
an  upper  and  lower  part  by  a  meniscus  of  fibro-cartilage. 

Ligaments. — The  joint  is  invested  by  a  capsular  ligament  which  is  quite  com- 


Stjloul  ijruci 


Stylo-mandibular  ligament 


Fig.  214. — Temporo-Mandibular  Joint. 


268 


THE  ARTICULATIONS  OE  JOINTS. 


Z  ^  Eminentia  articularis 


Fig.  215. 


MANDIBLE 


-Section  through  the  Temporo- 
mandibular Joint. 


plete,  but  is  very  thin  on  the  inner  side.  The  outer  wall  of  the  capsule — the 
external  lateral  ligament  (lig.  temporo-mandibulare.  Fig.  214) — is  divisible  into 
anterior  and  posterior  portions  which  are  attached  superiorly  to  the  root  tubercle 
^  and   lower   border    of    the   zygoma,   and 

inferiorly  to  the  outer  side  and  posterior 
border  of  the  neck  of  the  mandible.  The 
direction  of  its  fibres  is  downwards  and 
backwards. 

Within  the  capsule  there  is  an  inter- 
articular  disc  or  meniscus  of  fibro-cartilage, 
the  discus  articularis  (Fig.  205),  which  is 
moulded  upon  the  condyle  of  the  mandible 
below,  and  on  the  articular  surface  of  the 
temporal  bone  above.  It  thus  compensates 
for  the  incongruity  between  the  articular 
surfaces  of  the  two  bones.  The  disc  is 
attached  circumferentially  to  the  capsule. 
It  is  widest  in  the  transverse  direction, 
thicker  behind  than  in  front,  and  thinnest 
towards  the  centre,  where  it  may  be  per- 
forated. Its  anterior  margin  is  intimately  associated  with  the  insertion  of  the 
external  pterygoid  muscle. 

A  synovial  membrane  hnes  each  of  the  compartments  into  which  the  joint 
ca^dty  is  divided  by  the  meniscus.  As  a  rule  these  membranes  are  separate  from 
each  other,  but  they  become  continuous  when  the  disc  is  perforated.  The  upper 
synovial  membrane  is  larger  and  more  loosely  disposed  than  the  lower. 

Situated  on  the  mesial  aspect  of  the  joint,  but  at  a  short  distance  from  it,  and 
quite  distinct  from  the  capsule,  there  is  an  accessory  band  called  the  internal 
lateral  ligament  (lig.  spheno-mandi- 
bulare.  Fig.  216).  Superiorly  it  is 
attached  to  the  spinous  process  of  the 
great  wing  of  the  sphenoid  bone,  and   spheno-mandibuiar 

•     o      ■      1       ,       ii        1  n  ,T  or  internal  laterak 

interiorly  to  the  lower  as  well  as  the  lisament 

hinder    border   or    lingula    of     the 

inferior  dental  foramen.    It  is  not  an 

articular  ligament  in  the  true  sense, 

for  instead  of  being  connected  with  the 

joint,  it  is   developed  in  the    tissue 

surrounding  part  of  Meckel's  cartilage. 

Portions  of  the  following  structures  are 
found  in  the  interval  between  the  spheno- 
mandibuiar  ligament  and  the  ascending 
ramus  of  the  mandible — viz.  the  external 
pterygoid  muscle  ;  internal  maxillaiy 
vessels  ;  inferior  dental  vessels  and  nerve  ; 
middle  meningeal  vessels  ;  auriculo  -  tem - 
poral  nerve  ;  a  deep  portion  of  the  parotid 
gland. 

Movements  of  the  Mandible. — The  nature  of  the 
perform  is  determined  partly  by  the  character  of  the  articular  surfaces  of  the  temporo-mandibular 
joint,  and  partly  by  the  fact  that,  while  the  two  joints  always  act  simultaneously,  they  may 
also,  to  some  extent,  jaerform  the  same  movement  alternately. 

When  movement  takes  place  through  the  long  or  transverse  horizontal  axis  of  each  joint, 
the  mandible  may  be  elevated,  as  in  clenching  the  teeth,  or  it  may  be  depressed,  as  in  gaping. 
In  the  latter  movement  the  condyle  leaves  the  glenoid  fossa,  and,  along  with  the  meniscus,  it 
moves  forwards  until  they  rest  ui^on  tlie  articular  eminence.  Meantime  the  chin  describes  the 
arc  of  a  circle,  of  which  the  centre  or  point  of  least  movement  corresponds  to  the  position  of  the 
inferior  dental  foramen,  and  thus  the  structures  which  enter  at  that  foramen  are  protected 
against  stretching.  Coincidently  with  the  forward  movement  of  the  condyle,  it  glides  in  a 
revolving  manner  upon  the  inferior  aspect  of  the  meniscus. 

At  any  stage  in  the  movement  of  depressing  the  chin  the  mandible  may  be  protruded,  so 
that  the  inferior  incisor  teeth  are  projected  in  front  of  the  upper  set,  a  movement  which  results 
from  the  condyles  of  the  jaw  being  drawn  forwards  upon  the  articulai'  eminences.     A  similar 


mandibular 
ligament 


Fig.   216. 


-Internal  Lateral  Ligament  ok  the 
Temporo-Maxillary  Joint. 

movements  which  the  lower  jaw  can 


THE  JOINTS  OF  THE  THOEAX.  269 

relation  of  the  condyle  to  the  articular  eminence  occurs  during  the  exaggerated  depression  of 
the  mandible  which  results  from  yawning,  in  which  jjosition  tlie  articulation  is  liable  to  be 
dislocated.  When  the  two  joints  perform  tlie  same  movement  alternately,  a  certain  amount  of 
lateral  motion  results,  from  the  fact  that  the  long  axis  of  each  joint  i)resents  a  sliglit  oljliquity 
to  the  transverse  axis  of  tlie  skull,  and  consequently  a  grinding  or  oblique  movement  in  the 
horizontal  plane  is  produced.  Excessive  depression,  wdtli  the  risk  of  dislocation,  is  resisted  by 
the  fibres  of  the  external  lateral  ligament  which  Ijecomes  tense. 

In  all  movements  of  the  mandible  the  meniscus  conforms  closely  to  the  position  of  the  con- 
dyle, and  they  move  forwards  and  backwards  together,  Itut  at  the  same  time  the  meniscus  does 
not  restrict  tlie  movements  of  the  condyle.  Thus  while  the  meniscus,  along  with  the  condyle,  is 
gliding  upon  the  temporal  aspect  of  the  joint,  the  condyle  itself  revolves  upon  tlie  inferior 
surface  of  the  meniscus. 

Cranial  Ligaments  not  directly  associated  with  Articulations. 

The  stylo -mandibular  ligament  (lig.  stylo-mandibulare,  Figs.  214  and  216)  is  a 
specialised  portion  of  the  deep  cervical  fascia  which  extends  from  the  anterior  aspect 
of  the  tip  of  the  styloid  process  of  the  temporal  bone  to  the  posterior  border  of  the 
angle  of  the  mandible,  between  the  insertions  of  the  masseter  and  internal  pterygoid 
muscles. 

The  pterygo-spinous  ligament  (lig.  pterygo-spinosum)  is  a  membrane  extending 
from  the  upper  part  of  the  posterior  free  margin  of  the  external  pterygoid  plate, 
backwards  and  slightly  outwards,  to  the  spinous  process  of  the  sphenoid.  An 
interval  is  left  between  its  upper  border  and  the  floor  of  the  skull  for  the  outward 
passage  of  those  branches  of  the  inferior  maxillary  nerve  which  supply  the 
external  pterygoid,  temporal,  and  masseter  muscles.  This  ligament  has  a  tendency 
to  ossify  either  wholly  or  partially. 

The  stylo-hyoid  ligament  (lig.  stylo-hyoideum)  may  be  regarded  as  the  down- 
ward continuation  of  the  styloid  process  of  the  temporal  bone.  Inferiorly  it  is 
attached  to  the  lesser  cornu  of  the  hyoid  bone.  It  is  not  infrequently  ossified,  in 
which  case  it  constitutes  the  epihyal  bone  found  in  many  animals. 


THE   JOINTS   OF   THE   THORAX. 

Costo-vertebral  articulations  (articulationes  costo-vertebrales).  The  typical 
rib  articulates  with  the  vertebral  column  both  by  its  head  and  by  its  tubercle. 
Thus,  two  sets  of  articulations,  with  their  associated  ligaments,  exist  between  the 
ribs  and  the  vertebree,  but  each  set  is  constructed  upon  a  common  plan,  with  the 
exception  of  certain  joints  situated  at  the  upper  and  lower  ends  of  the  series,  where 
the  ribs  themselves  deviate  from  the  typical  form. 

Costo-Central  Joints. 

The  articulations  of  the  heads  of  the  ribs  with  the  centra  or  bodies  of 
the  vertebne  (articulationes  capitulorum,  Fig.  209)  are  all  diarthroses,  which,  from 
their  somewhat  hinge-like  action,  may  be  classed  as  ginglymoid. 

The  head  of  every  typical  rib  is  wedge-shaped,  and  presents  two  articular 
facets,  an  upper  and  a  lower,  separated  from  each  other  by  an  antero-posterior 
ridge  which  abuts  against  an  intervertebral  disc,  while  the  articular  facets  articu- 
late with  similar  surfaces  on  the  contiguous  margins  of  the  two  vertebrae  adjoining 
the  disc.  These  surfaces  form  a  wedge-shaped  depression  or  cup,  the  bottom  of 
which  is  more  elastic  than  the  sides,  and  thus  an  arrangement  is  provided  which 
tends  to  reduce  the  shock  of  blows  upon  the  walls  of  the  chest. 

Each  of  these  articulations  is  provided  with  a  capsular  ligament  which 
surrounds  and  encloses  the  joint,  and  is  attached  to  contiguous  non-articular 
margins  on  the  head  of  the  rib  and  the  two  vertebral  bodies.  On  its  anterior  or 
ventral  aspect  the  capsule  presents  three  radiating  fasciculi  which  collectively  form 
the  stellate  or  anterior  costo-vertebral  ligament  (lig.  capituli  costas  radiatum,  Fig. 
209).  These  fasciculi  radiate  from  a  centre  on  the  front  of  the  head  of  the  rib,  so 
that  the  middle  fasciculus    becomes    attached  to  the    intervertebral  disc    while 


270  THE  AETICULATIONS  OK  JOINTS. 

the  upper  and  lower  fasciculi  proceed  to  the  adjacent  margins  of  the  two  vertebrae 
between  which  the  disc  is  situated,  and  with  which  the  rib  articulates.  To  a  slight 
extent  these  radiating  fasciculi  pass  under  cover  of  the  lateral  margin  of  the  anterior 
common  ligament  of  the  vertebral  bodies.  In  those  joints  in  which  the  head  of 
the  rib  does  not  articvilate  with  an  intervertebral  disc  the  central  fasciculus  of 
the  stellate  ligament  is  wanting,  but  the  other  two  retain  the  same  general 
arrangement. 

The  interarticular  ligament  (lig.  capituli  costse  interarticulare)  consists  of  short 
transverse  fibres  within  the  capsule.  These  are  attached,  on  the  one  hand,  to 
the  ridge  which  intervenes  between  the  two  facets  on  the  head  of  the  rib,  and 
on  the  other  to  the  lateral  aspect  of  the  intervertebral  disc.  This  ligament 
is  not  a  meniscus,  but  merely  an  interarticular  ligament,  of  width  sufficient 
to  divide  the  joint  cavity  into  an  upper  and  a  lower  compartment.  It  is  absent 
from  those  joints  which  do  not  articulate  with  an  intervertebral  disc,  i.e.  from 
those  ribs  which  only  articulate  with  the  body  of  one  vertebra. 

The  interarticular  ligament  is  supijosed  to  represent  tlie  outer  end  of  a  ligament  which, 
under  the  name  of  the  lig.  conjugale  costarum,  connects  the  heads  of  the  ribs  of  certain  mammals 
across  the  posterior  asj^ect  of  the  intervertebral  disc,  and,  in  the  human  subject,  until  the 
seventh  month  of  foetal  life,  connects  the  posterior  aspect*  of  the  necks  of  a  pair  of  ribs  with  each 
other  across  the  mesial  plane. 

Synovial  membrane  lines  each  joint  cavity,  and  therefore,  in  all  cases  where  the 
joint  is  divided  into  two  compartments,  each  one  has  its  own  synovial  lining. 

Costo-Transverse  Joints. 

The  tubercle  of  each  typical  rib  articulates  with  the  transverse  process  of  the 
lower  of  the  two  dorsal  vertebrae  with  which  the  head  of  the  rib  is  associated 
(articulatio  costo-transversaria).  Near  the  tip  of  the  transverse  process  there  is 
an  articular  facet,  on  its  anterior  aspect,  for  articulation  with  the  corresponding 
facet  on  the  mesial  articular  part  of  the  rib  tubercle.  The  joint  so  formed  is  an 
arthrodial  diarthrosis. 

The  joint  cavity  is  surrounded  by  a  comparatively  feeble  capsular  ligament, 
which  is  attached  immediately  beyond  the  margins  of  the  articular  facets,  and  in 
which  no  special  bands  can  be  distinguished. 

A  simple  synovial  membrane  lines  the  capsular  ligament  in  all  cases  where  the 
latter  is  present. 

The  following  accessory  ligaments,  in  connexion  with  this  joint,  strengthen  and 
support  the  articulation : — 

The  anterior  or  superior  costo-transverse  ligament  (ligamentum  costo-transver- 
sarium  anterius,  Fig.  209)  consists  of  strong  bands  of  fibres  which  are  attached  to 
the  upper  border  of  the  neck  of  the  rib,  extending  from  the  head  outwards  to  the 
non-articular  part  of  the  tubercle.  All  these  fibres  may  be  traced  upwards.  Those 
situated  nearest  to  the  head  of  the  rib  proceed  obliquely  upwards  and  outwards,  to 
be  attached  to  the  transverse  process  immediately  above,  but  with  extensions  to  the 
adjoining  rib  and  its  costo-transverse  capsular  ligament.  Others  proceed  almost 
vertically  upwards  to  the  adjoining  transverse  process,  while  those  which  ascend 
from  the  upper  surface  of  the  tubercle  pass  obliquely  upwards  and  inwards  to  reach 
the  postero-inferior  aspect  of  the  adjoining  transverse  process. 

The  posterior  costo-transverse  ligament  (ligamentum  costo-transversarium  pos- 
terius)  is  a  band  of  transverse  fibres  applied  to  the  postero-external  aspect  of  the 
capsule.  By  one  end  these  fibres  are  attached  to  the  tip  of  the  transverse  process 
behind  its  articular  facet,  and  by  the  other  to  the  external  rough  surface  of  the 
tubercle  of  the  rib. 

The  middle  costo-transverse  ligament  (lig.  colli  costaj)  consists  of  short  fibres 
which  stretch  from  the  posterior  aspect  of  the  neck  of  the  rib,  backwards  and  in- 
wards, to  the  front  of  the  transverse  process,  but,  in  addition,  a  proportion  of  the 
fibres  passes  to  the  posterior  aspect  of  the  inferior  articular  process  of  the  upper  of 
the  two  vertebrte  with  which  the  head  of  the  rib  articulates. 


COSTO-STERNAL  JOINTS.  271 

The  following  exceptions  to  the  general  plan  of  rib-articulation  indicated  above 
must  be  noted  : — 

1.  There  is  no  articulation   between    the  eleventh  and   twelfth  ribs  and  the 

transverse  processes  of  the  corresponding  vertebrae. 

2.  The  superior  costo-transverse  ligament  is  wanting  from  the  first  rib,  and  is 

either  rudimentary  or  wanting  in  the  case  of  the  twelfth  rib. 

3.  The  middle  costo-transverse  ligament  is  rudimentary  in  the  eleventh  and 

twelfth  ribs. 
The  ligamentum  lumbo-costale  extends  from  the  upper  surface  of  the  base  of  the 
transverse  process  of  the  first  lumbar  vertebra  to  the  under  surface  of  the  neck  of 
the  twelfth  rib,  as  well  as  to  the  under  surface  of  the  transverse  process  of  the 
twelfth  dorsal  vertebra. 

Akticulations  betW'Een  the  Ribs  and  their  Cartilages. 

Each  rib  possesses  an  unossitied  portion,  termed  its  costal  cartilage.  As  age 
advances,  this  cartilage  may  undergo  a  certain  amount  of  superficial  ossification, 
but  it  never  becomes  entirely  transformed.  The  line  of  demarcation  between 
bone  and  cartilage  is  clear  and  abrupt,  and  usually  the  bone  forms  an  oval  cup,  in 
which  the  end  of  the  cartilage  is  retained  by  means  of  the  continuity  which  exists 
between  the  periosteum  and  the  perichondrium.  There  is  no  articulation  in  the 
proper  sense  between  the  rib  and  its  cartilage,  although  a  synovial  cavity  has 
occasionally  been  found  between  the  first  rib  and  its  cartilage. 

Interchondral  Joints. 

These  articulations  are  arthrodial  diarthroses,  and  they  are  found  between  ad- 
joining margins  of  certain  of  the  costal  cartilages,  viz.  from  the  fifth  to  the  eighth 
or  ninth.  The  cartilages  which  thus  articulate  develop  flattened,  somewhat  conical, 
prolongations  of  their  substance,  and  thereby  the  intercostal  spaces  are  interrupted 
where  these  flat  articular  facets  abut  against  each  other.  Each  joint  is  closed 
by  a  surrounding  capsular  ligament,  the  superficial  and  deep  aspects  of  which  are 
specially  strengthened  by  external  and  internal  interchondral  ligaments.  These 
bands  extend  obliquely  between  adjacent  cartilages. 

A  synovial  membrane  lines  each  joint  capsule. 

Costo-sternal  Joints. 

The  upper  seven  pairs  of  costal  cartilages,  as  a  rule,  extend  to  the  lateral 
margins  of  the  sternum  (articulationes  sternocostales).  Of  these,  the  first  pair  is 
implanted  directly  upon  the  manubrium  sterni.  The  ossific  process  ends  abruptly 
in  connexion  with  the  rib,  and  also  ceases  as  suddenly  in  connexion  with  the 
sternum,  and  hence  the  cartilage  does  not  normally  present  an  articulation  at 
either  end. 

From  the  second  to  the  seventh  pairs  of  ribs  inclusive,  the  costo-sternal  joints 
are  constructed  upon  the  type  of  arthrodial  diarthroses,  although,  in  the  case  of 
the  sixth  and  seventh  cartilages,  the  joint  cavity  is  always  small,  and  is  frequently 
obliterated. 

The  sternal  end  of  each  of  these  costal  cartilages  presents  a  slight  antero-pos- 
terior  ridge  which  fits  into  a  shallow  V-shaped  depression  upon  the  lateral  margin 
of  the  sternum.  With  the  exception  of  the  sixth  cartilage,  the  others  articulate 
opposite  the  lines  of  union  between  the  primary  segments  of  the  sternum,  whereas 
the  sixth  articulates  upon  the  side  of  the  lowest  segment  of  the  meso-sternum. 

Each  joint  is  enclosed  by  a  capsular  ligament,  composed  of  fibrous  tissue,  attached 
to  the  adjacent  borders  of  the  articulating  elements.  Specially  strong  fibres  dis- 
tinguish the  superficial  and  deep  aspects  of  the  capsule. 

The  anterior  costo-sternal  ligament  (lig.  costo-sternalium  radiatum,  Eig.  217)  is 
composed  of  strong  fibres  which  radiate  from  the  anterior  surface  of  the  costal 
cartilage,  near  its  sternal  end,  to  the  front  of  the  sternum.  The  ligaments  of 
opposite  sides  interlace  with  each  other,  and  so  cover  the  front  of  the  sternum  with 
a  felted  membrane — the  membrana  sterni. 


272 


THE  AETICULATIONS  OE  JOINTS. 


The  posterior  costo-sternal  ligament — also  a  part  of  the  capsule — has  attach- 
ments similar  to  the  foregoing,  but  the  arrangement  of  its  fibres  is  not  so  powerful. 

The  ligamentum  costo-xiphoidea  passes  from  the  i'rout  of  the  upper  part  of  the 
xiphoid  cartilage,  obliquely  upwards  and  outwards  to  the  front  of  the  seventh,  and 
sometimes  to  the  Iront  of  the  sixth  costal  cartilage. 

Within  the  capsules  of  these  joints  interarticular  ligaments  (ligg.  sterno-costalia 
interarticularia,  Fig.  217)  may  be  found.    Their  disposition  is  somewhat  uncertain,  for 


.    Costo-clavicular  or 

jfM  rhomboid  ligament 


Anterior  sterno-clavicular 
ligament 


Joint  capsule 
Joint  cavity 


Interarticular  ligament 

Joint  cav 


Anterior  chondro-sternal  or 
radiate  ligament 


Fig.  217. — ST^R^o-CL\MCULVR  A^D  (  osto-sternal  Joints. 

whereas,  in  the  case  of  the  second  pair  of  cartilages,  they  invariably  divide  the  joint 
cavity  into  two  distinct  compartments — an  upper  and  a  lower — such  an  arrange- 
ment is  very  uncertain  in  the  other  joints,  and  they  occasionally,  especially  in  the 
cases  of  the  sixth  and  seventh  cartilages,  entirely  obliterate  the  joint  cavity.  These 
ligaments  extend  horizontally  between  the  ends  of  the  costal  cartilages  and  the 
side  of  the  sternum. 

Synovial  membrane  is  found  wherever  a  joint  cavity  is  developed,  and  therefore 
there  may  be  one  or  two  synovial  membranes,  according  to  the  presence  or  absence 
of  a  proper  interarticular  ligament.  When  the  joint  cavity  is  obliterated  by  the 
fibrous  structure  which  represents  the  interarticular  ligament,  a  synovial  membrane 
is  also  absent. 

Sternal  Articulations. 

Primarily  the  sternum  consists  of  an  elongated  plate  of  hyaline  cartilage,  which 
becomes  subdivided  into  segments  by  the  process  of  ossification. 

The  four  segments  of  which  the  gladiolus  is  originally  composed  unite  with 
each  other  after  the  manner  of  typical  synchondroses. 

Similarly  the  ensiform  cartilage  and  the  gladiolus  ultimately  become  united. 
It  is  not  usual  to  find  the  manul)rio-gladiolar  joint  obliterated  by  the  ossification  of 
the  two  bony  segments.  Even  in  advanced  life  it  remains  open,  and  the  joint  par- 
takes of  the  nature  of  an  amphiarthrosis  (Fig.  217),  although  a  joint  cavity  is  not 
found  under  any  circumstances  in  the  plate  of  fibro-cartilage  which  intervenes 
between  the  manubrium  and  the  gladiolus. 

The  membrana  stemi,  to  which  reference  has  already  been  made,  assists  in 
strengthening  the  union  between  the  different  segments  of  the  sternum. 

Movements  of  the  Ribs  and  Sternum. — Tliese  movements  may  be  considered  either 
independently  of,  or  as  associated  witli,  respiration. 

In  the  former  condition  the  ribs  move  in  connexion  with  flexion  and  extension  of  the 
vertebral  column,  being  more  or  less  depressed  and  approximated  in  the  former,  and  elevated  or 


STERNO-CLAVICULAR  JOINT.  273 

pulled  apart  in  the  latter  case.  Considered  iu  connexion  with  respiration,  it  is  necessary  to 
observe  that,  to  all  intents  and  purposes,  the  vertebral  column  and  the  sternum  are  rigid  structures. 
Next  we  must  remember  that  the  heads  of  all  the  ribs  occupy  fixed  positions,  and  similarly 
the  anterior  ends  of  seven  jjairs  of  cartilages  are  fixed  to  the  lateral  margins  of  the  sternum. 
The  ribs  thus  form  arches,  presenting  a  large  amount  of  obliquity  from  behind  forwards.  There- 
fore, during  ins])iration,  when  the  rib  is  elevated,  the  arch  becomes  more  horizontal,  and  the 
transverse  diameter  of  the  chest  is  increased.  At  the  same  time,  the  anterior  ends  of  the  sternal 
ribs  tend  to  thrust  the  sternum  forwards  and  upwards ;  but  the  nature  of  the  attachment  of  the 
first  pair  of  ribs  to  the  sternxim,  as  well  as  the  attachment  of  the  diaphragm  to  the  ensiform 
cartilage,  prevents  this  moveiuent  from  becoming  excessive,  and  hence  the  sternum  becomes  a  line 
of  resistance  to  the  forward  thrust  of  the  ribs.  As  a  consequence,  the  ribs  rotate  upon  themselves 
about  an  oblique  axis  which  passes  downwards,  outwards,  and  backwards  through  the  capitular 
joint  and  the  neck  of  the  rib  anterior  to  the  costo-transverse  joint. 

In  this  way  increase,  both  of  the  antero-posterior  and  transverse  diameters  of  the  thorax,  is 
jjrovided  for,  although  the  amount  of  increase  is  not  equally  pronounced  in  all  planes.  Thus  at 
the  level  of  the  first  rib  very  little  ever'sion  is  possible,  because  the  axis  of  rotation  is  nearly 
transverse,  and  therefore  any  increase  in  the  transverse  or  antero-posterior  thoracic  diameters  at 
this  level  may  be  disregarded,  although  a  certain  amount  of  elevation  of  the  manuljrium  sterni 
and  anterior  end  of  the  first  rib  is  evident. 

Below  the  level  of  the  sixth  rib  elevation  and  rotation  of  the  rib  during  inspiration  are 
usually  said  to  be  complicated  by  a  certain  amount  of  backward  movement,  due  to  the  character 
of  the  costo-transverse  joint,  until,  in  the  case  of  the  last  two  ribs,  which  are  destitute  of  costo- 
transverse joints,  a  movement  backwards  is  almost  entirely  substituted  for  elevation.  It  is 
probable,  however,  that  the  movements  of  the  asternal  ribs  exactly  correspond  to  those  of  the 
sternal  series,  and  that  by  the  contraction  of  the  costal  digitations  of  the  diajihx-agm  the 
anterior  ends  of  the  asternal  ribs  are  provided  with  fixed  positions  comparable  to  those  supplied 
by  the  sternum  to  the  ribs  of  the  sternal  series. 

We  may  therefore  say  that  during  insjoiration  the  ribs  move  upwards  and  outwards  between, 
their  fixed  ends,  while  as  a  whole  the  rib  rotates,  and  its  anterior  end  is  thrust  slightly  forwards. 

During  exj^iration  these  movements  are  simply  reversed. 

THE  ARTICULATIONS  OF  THE  SUPERIOR  EXTREMITY. 

The  bony  arch  formed  by  the  clavicle  and  scapula  articulates  directly  with  the 
axial  skeleton  only  at  one  point,  viz.  the  sterno-clavicular  joint. 

ARTICULATIONS  OF  THE  CLAVICLE. 

The  Sterno-clavicular  Joint. 

The  sterno-clavicular  joint  (articulatio  sterno-cla\"icularis)  is  an  example  of  an 
arthrodial  diarthrosis.  The  articular  surfaces  concerned  in  its  formation  present 
the  following  appearances  : — 

1.  The  sternal  end  of  the  clavicle  is  somewhat  triangular  iu  outline,  having  its 
most  prominent  angle  directed  downwards  and  backwards.  The  anterior  and 
posterior  sides  of  the  triangle  are  slightly  roughened  for  the  attachment  of 
Ugaments,  while  the  base  or  inferior  side  is  smooth  and  rounded,  owing  to  the 
prolongation  of  the  articular  surface  to  the  inferior  aspect  of  the  l^one.  In  the 
antero-posterior  direction  the  articular  surface  tends  to  be  concave,  while  vertically 
it  is  slightly  convex. 

2.  An  articular  facet,  situated  on  the  superior  lateral  angle  of  the  manubrium 
sterni,  but  in  a  plane  slightly  behind  the  supra-sternal  notch,  articulates  with  the 
clavicle.  This  facet  is  considerably  smaller  than  the  clavicular  facet  with  which  it 
articulates. 

3.  The  superior  surface  of  the  first  costal  cartilage  close  to  the  sternum  also 
participates  to  a  small  extent  in  the  articulation. 

It  should  be  noted  that  the  articular  surfaces  of  the  clavicle  and  sternum  are 
covered  mainly  by  fibro-cartilage. 

A  capsular  ligament  is  well  marked  on  all  sides  except  inferiorly,  where  it  is 
very  thin. 

The  anterior  sterno-clavicular  ligament  (Fig.  217)  forms  part  of  the  capsule,  and 
consists  of  short  fibres  which  extend  obliquely  downwards  and  inwards  from  the 
anterior  aspect  of  the  sternal  end  of  the  clavicle  to  the  adjoining  anterior  surface 
of  the  sternum  and  the  anterior  border  of  the  first  costal  cartilage. 

The  posterior  sterno-clavicular  ligament  also  forms  part  of  tlie  capsule,  and 
19 


274  THE  ARTICULATIONS  OE  JOINTS. 

consists  of  similarly  disposed,  but  not  so  strong,  oblique  fibres  situated   on    the 
posterior  aspect  of  the  articulation. 

A  flbro-cartilaginous  meniscus  (discus  articularis,  Fig.  217)  divides  the  joint 
cavity  into  two  compartments.  It  is  nearly  circular  in  shape,  and  adapts  itself  to 
the  articular  surfaces  between  which  it  lies.  It  is  thickest  at  the  circumference  and 
thinnest  at  the  centre,  where  it  occasionally  presents  a  perforation,  thereby 
permitting  the  two  synovial  cavities  to  intercommunicate.  By  its  cu'cumference  it 
is  in  contact  with,  and  adherent  to,  the  surrounding  capsule,  but  its  upper  margin  is 
attached  to  the  apex  of  the  articular  surface  of  the  clavicle,  while  by  its  lower 
margin  it  is  fixed  to  the  sternal  end  of  the  first  costal  cartilage. 

Two  accessory  ligaments  are  associated  with  this  joint,  viz.  the  interclavicular 
and  the  rhomboid. 

The  interclavicular  ligament  (Fig.  217)  is  a  structure  of  considerable  strength, 
forming  a  broad  band  of  fibrous  tissue  which  is  attached  to  the  superior  rounded  angle 
or  apex  of  the  sternal  end  of  the  clavicle  as  well  as  to  the  adjacent  margins  of  the 
articular  surface.  Its  fibres  pass  across  the  interclavicular  notch  to  become  attached 
to  corresponding  parts  of  the  opposite  clavicle,  but  in  their  course  they  dip  down  into 
the  suprasternal  notch,  in  which  many  of  them  are  fixed  to  the  sternum.  In  this 
way  their  presence  neither  bridges  nor  obliterates  the  notch  between  the  two 
clavicles,  and  the  hgament  really  becomes  a  superior  sterno-clavicular  Hgament  for 
each  joint. 

The  rhomboid  ligament  (lig.  costo-claviculare.  Fig.  217)  consists  of  short,  strong 
fibres  which  are  attached  inferiorly  to  the  upper  surface  of  the  first  costal  cartilage. 
They  pass  obhquely  upwards  and  outwards  to  a  rough  impression  situated  on  the 
lower  aspect  of  the  sternal  end  of  the  clavicle,  and  are  distinct  from  the  capsular 
Ligament.     Occasionally  a  bursa  is  found  in  the  interior  of  this  ligament. 

As  a  rule  there  are  two  synovial  membranes  lining  the  two  joint  cavities  (Fig. 
217),  separated  from  each  other  by  the  interarticular  meniscus.  Sometimes,  however, 
the  two  membranes  establish  continuity  through  a  perforation  in  the  meniscus. 

The  Acromio-clavicular  or  Scapulo-clavicular  Joint. 

The  acromio  -  clavicular  joint  (articulatio  acromio  -  clavicularis)  is  another 
instance  of  an  arthrodial  diarthrosis.  It  is  situated  between  the  acromial  end  of 
the  clavicle  and  the  inner  aspect  of  the  acromion  process  of  the  scapula.  Each 
articular  surface  is  an  oval,  flattened  facet,  covered  by  fibro-cartilage. 

The  ligaments  which  surround  this  small  joint  form  a  complete  capsule 
(capsula  articularis),  of  which  the  upper  and  lower  parts  are  specially  strong,  and 
are  therefore  named  the  superior  and  inferior  acromio-clavicular  ligaments  (Fig.  219). 
These  consist  of  short  fibres  passing  between  the  adjacent  rough  margins  of  the 
two  bones  in  the  positions  indicated  by  their  names. 

A  meniscus  (discus  articularis),  which  is  nearly  always  incomplete,  and  may 
occasionally  be  wanting,  is  usually  found  within  the  joint  cavity,  where  it  lies 
obliquely,  with  its  upper  margin  farther  from  the  mesial  plane  than  its  lower 
margin,  and  having  its  borders  attached  to  the  surrounding  capsule.  Frequently 
the  meniscus  is  wedge-shaped,  with  its  base  directed  upwards  and  its  apex  free. 

A  synovial  membrane  is  found  forming  either  a  single  or  a  double  sac,  according  to 
the  condition  of  the  meniscus.  Complete  division  of  the  joint  cavity,  however,  is  rare. 
Ligamentum  Coraco-claviculare.^ — Accessory  to  this  articulation  there  is  the 
strong  coraco-clavicular  ligament  which  binds  the  acromial  end  of  the  clavicle  to 
the  coracoid  process  of  tlie  scapula.  It  is  readily  divisible  into  two  parts,  viz.  the 
conoid  and  trapezoid  ligaments. 

The  conoid  ligament  (Fig.  219)  is  situated  internal  to  and  sUghtly  behind  the 
trapezoid.  It  is  narrow  and  pointed  at  its  inferior  end,  by  which  it  is  attached 
to  the  upper  aspect  of  the  coracoid  process,  in  close  proximity  to  the  suprascapular 
notch.  Its  upper  end  widens  out  in  the  manner  expressed  by  its  name,  and  is 
attached  to  the  conoid  tubercle  of  the  clavicle. 

The  trapezoid  ligament  (Fig.  219)  is  attached  inferiorly  to  the  u^jper  surface  of  the 
posterior  half  of  the  coracoid  process,  external  and  anterior  to  the  attachment  of 


ACEOMIO-CLAVICULAE  JOINT.  275 

the  conoid  ligament.  Superiorly  it  is  attached  to  the  trapezoid  ridge  on  the  under 
surface  of  the  acromial  end  of  the  clavicle.  Its  outer  and  inner  borders  are  free. 
Its  anterior  surface  is  principally  directed  upwards,  and  its  posterior  surface,  to  a 
similar  extent,  looks  downwards. 

A  synovial  bursa  usually  occupies  the  re-entrant  angle  between  these  two 
ligaments. 

Movements  at  the  Clavicular  Joints. — The  movements  of  the  inner  end  of  the  clavicle  at 
the  sternoclavicular  joint  are  limited  m  their  range,  owing  to  the  tension  of  the  ligaments. 
When  the  shoulder  is  raised  or  depressed  the  outer  end  of  the  clavicle  moves  uj^wards  and 
downwards,  whilst  its  sternal  end  glides  upon  the  surface  of  the  interarticular  meniscus  within 
the  joint ;  when,  on  the  other  hand,  the  shoulder  is  carried  forwards  or  backwards,  the  inner 
end  of  the  clavicle  along  with  the  interarticular  meniscus  moves  upon  the  sternal  facet.  In 
addition  to  these  movements  of  elevation,  depression,  forward  movement  and  backward  move- 
ment of  the  clavicle,  there  is  also  allowed  at  the  sterno-clavicular  joint  a  certain  amoimt  of 
circumduction  of  the  clavicle. 

The  part  which  is  played  by  certain  of  the  ligaments  in  restraining  movement  requires 
careful  con.sideration.  The  rhomboid  ligament  checks  excessive  elevation  of  the  shoulder,  and 
restrains  within  certain  limits  Ijoth  backward  and  forward  movement  of  the  clavicle.  When  the 
clavicle  is  depressed,  as  in  cases  where  a  heavy  weight,  such  as  a  bucket  of  water,  is  carried  in  the 
hand,  it  receives  support  by  resting  upon  the  first  rib,  and  the  tendency  for  the  inner  end  of  the 
bone  to  start  uja  out  of  its  sternal  socket  is  obviated  by  the  tension  of  the  interarticular 
meniscus,  the  interclavicular  ligament,  and  the  anterior  and  posterior  sterno  -  clavicular 
ligaments. 

The  interarticular  meniscus  not  only  acts  as  a  cushion  which  lessens  the  shock  of  blows 
received  upon  the  shoulder,  but  it  also  acts  as  a  most  important  bond  of  union,  and  prevents  the 
inner  end  of  the  clavicle  from  being  driven  upwards  upon  the  top  of  the  sternum  when  force  is 
applied  to  its  outer  end. 

The  movements  at  the  aero mio -clavicular  joint  are  of  such  a  kind  as  to  allow  the  inferior 
angle,  and  to  some  extent  the  base  of  the  scapula,  to  remain  more  or  less  closely  applied  to  the 
chest-wall  during  the  various  movements  of  the  shoulder.  The  strong  connexion  between  the 
coracoid  process  and  the  acromial  end  of  the  clavicle,  by  means  of  the  conoid  and  trapezoid 
ligaments,  renders  it  necessary  that  the  scapula  should  follow  the  clavicle  in  its  various 
excursions.  The  presence  of  the  acromio-claAncular  joint,  however,  enables  the  scaj^ula  to  change 
its  position  somewhat  with  reference  to  the  clavicle  as  the  shoulder  is  moved.  Thus,  when  the 
shoulder  is  raised  and  depressed,  a  marked  difference  takes  place  in  the  angle  between  the  two 
bones ;  again,  when  the  shoulder  is  thrown  forwards  or  backwards,  these  movements  can  be 
performed  without  altering  in  a  material  degree  the  direction  of  the  glenoid  cavity  of  the  scapula, 
or  in  other  words,  the  socket  of  the  shoulder-joint. 

The  conoid  and  trapezoid  ligaments  set  a  limit  irpon  the  movements  of  the  scapida  at  the 
acromio-clavicular  joint.  They  both,  but  more  particularly  the  trapezoid  ligament,  prevent  the 
acromion  process  of  the  scapula  from  being  carried  inward  below  the  outer  end  of  the  clavicle 
when  blows  fall  upon  the  outer  aspect  of  the  shoulder. 

Ligaments  of  the  Scapula. 

These  ligaments  are  not  directly  connected  with  any  articulation.  The  coraco- 
acromial  ligament  (lig.  coraco-acromiale,  Fig.  219)  completes  the  arch  between  the 
coracoid  and  acromion  processes  of  the  scapula,  and  thus  provides  a  secondary 
socket  for  the  greater  protection  and  security  of  the  shoulder-joint.  It  is  a  flat 
triangular  structure  stretched  tightly  between  its  lines  of  attachment.  By  its  base 
it  is  fixed  to  a  varying  amount  of  the  postero-external  border  of  the  coracoid 
process,  and  by  its  narrower  apical  end  to  the  tip  of  the  acromion  process,  im- 
mediately external  to  the  acromio-clavicular  joint.  Its  surfaces  look  upwards  and 
downwards,  and  its  free  borders  outwards  and  inwards.  It  is  thinnest  in  the 
centre,  where  it  is  sometimes  perforated  by  a  prolongation  of  the  tendon  of  the 
pectoralis  minor  muscle. 

The  suprascapular  ligament  (lig.  trausversum  scapulae  superius)  is  a  distinct  but 
short  flat  band  which  bridges  the  notch  of  the  same  name.  It  may  be  continuous 
with  the  conoid  ligament,  and  it  is  frequently  ossified.  As  a  rule  the  foramen 
completed  by  this  ligament  transmits  the  suprascapular  nerve,  while  the  corre- 
sponding vessels  travel  above  the  ligament  to  reach  the  supraspinous  fossa. 

A  small  duplicate  of  this  ligament  may  often  be  found  bridging  the  foramen  on 
its  ventral  aspect,  subjacent  to  which  small  branches  of  the  suprascapular  artery 
return  from  the  supraspinous  to  the  subscapular  fossa. 

The  spino- glenoid  ligament  (lig.  trans versum  scapulae  inferius)  consists  of 
another  set  of  bridging  fibres  which  are  situated  on  the  posterior  aspect  of  the 


276 


THE  ARTICULATIONS  OE  JOINTS. 


neck  of  the  scapula.  By  one  end  they  are  attached  to  the  external  border  of  the 
scapular  spine,  and  by  the  other  to  the  adjacent  part  of  the  posterior  aspect  of 
the  head  of  the  scapula.  The  suprascapular  nerve  and  vessels  pass  subjacent  to 
this  ligament. 

THE  SHOULDER-JOINT. 

The  shoulder-joint  (articulatio  humeri)  is  one  of  the  largest  as  well  as  the  most 
important  of  the  joints  of  the  upper  hmb.  It  is  an  example  of  the  enarthrodial, 
i.e.  ball-and-socket  variety  of  a  diarthrosis,  and,  at  the  cost  of  a  certain  amount  of 
security,  it  has  obtained  an  extended  range  of  movement. 

The  bones  which  enter  into  its  formation  are  the  glenoid  fossa  of  the  scapula 
and  the  head  of  the  humerus. 

The  glenoid  fossa  is  a  shallow  pyriform  articular  surface,  having  its  narrow  end 
directed  upwards  and  slightly  forwards.  The  upper  half  of  the  anterior  margin  of 
the  fossa  is  characterised  by  a  shallow  notch  which  accommodates  the  narrow  part 
of  the  subscapularis  muscle  as  it  runs  outwards  to  its  insertion.  At  the  apex  of  the 
fossa  there  is  a  flat  area  for  the  attachment  of  the  long  tendon  of  the  biceps  flexor 
cubiti  muscle.  The  head  of  the  humerus  is  hemispherical  and  articular,  while, 
external  to  its  articular  margin,  there  is  a  slight  constriction  (the  anatomical  or 
true  neck  of  the  humerus),  which  is  most  strongly  marked  in  relation  to  the 
greater  and  lesser  tuberosities  of  the  humerus. 

Under  ordinary  conditions  the  two  articular  surfaces  are  maintained  in 
apposition  by  muscular  action,  aided  by  atmospheric  pressure,  and  thus,  when  the 
muscles  are  removed,  the  bones  fall  asunder  to  the  full  extent  of  the  restraining 
ligaments.  Only  a  small  part  of  the  humeral  head  is  in  contact  with  the  glenoid 
fossa  at  any  particular  moment,  because  the  former  is  much  larger  than  the  latter, 
but,  by  reason  of  the  shallow  character  of  this  fossa,  all  parts  of  the  two  articular 
surfaces  may  successively  be  brought  into  contact  with  each  other. 

In  the  position  of  rest,  as  the  Hmb  hangs  parallel  to  the  vertical  axis  of  the 
trunk,  the  inferior  aspect  of  the  neck  of  the  humerus  is  brought  into  close  relation 
with  the  lower  part  of  the  glenoid  fossa. 

The  glenoid  ligament  (labrum  glenoidale.  Fig.  219)  deepens  the  glenoid  fossa, 
and  thus  extends  the  articular  surface.     It  is  situated  within  the  joint  capsule,  and 

to  some  slight   ex- 

Coraco-acromial  ligament  Acromion  proces.s 

/  /= 
Coracoid  pioce-^b 


\ 


Curaco  humeral 
li_,  anient 


Communication 

between  subscapular, 
bur.sa  and  joint  cavity 


Capsule  of  joint 


Fig.  218. — Cap.sulk  of  thk  Shouldek-Joint  and  Cokaco-acromiai,  Lr(;AMHNT 


tent  increases  the 
security  of  the  arti- 
culation. It  con- 
sists of  a  strong 
hubscapuiaris  ring  of  dcnsc  fibrous 
tissue  attached  to 
the  free  margin  of 
the  glenoid  fossa. 
Many  of  its  fibres- 
are  short,  and  pass 
obliquely  from  the 
inner  to  the  outer 
aspect  of  the  ridge, 
so  that  its  attached 
base  is  broader  than 
its  free  edge,  and 
there  fore  in  cross  sec- 
tion it  appears  some- 
what triangular. 
The  long  tendon  of 
the  biceps,  which 
considerable  extent  in- 


arises  from  the  apex  of  the  glenoid  fossa,  becomes  to  a 
corporateil  with  this  linainent. 

The  capsular  ligament  (capsula  articularis.  Fig.  218)  presents  the  general  shape 
which  is  characteristic  of  the  corresponding  ligament  in  other  ball-and-socket  joints, 


THE  SHOULDEE-JOINT. 


277 


viz.  a  hollow  cylinder.  By  its  upper  end  the  capsule  is  attached  to  the  circum- 
ference of  the  glenoid  fossa,  external  to  the  glenoid  ligament,  and  also,  to  a  consider- 
able extent,  to  the  glenoid  ligament  itself. 

By  its  lower  end  it  is  attached  to  the  neck  of  the  humerus,  and  therefore 
beyond  the  articular  area  of  the  head.  The  capsule  is  strongest  on  its  superior 
aspect,  while  inferiorly,  where  the  neck  of  the  bone  is  least  defined,  it  extends 
downwards  for  a  short  distance  upon  the  humeral  shaft.  Its  fibres  for  the  most 
part  run  longitudinally,  but  a  certain  number  of  them  pursue  a  circular  direction. 

A  prolongation  of  the  capsule,  the  transverse  humeral  ligament  presenting  both 
longitudinal  and  transverse  fibres,  bridges  that  part  of  the  bicipital  groove  which  is 
situated  between  the  tuberosities  of  the  humerus.  At  this  point  an  interruption 
in  the  capsule,  beneath  the  transverse  humeral  ligament,  permits  the  long  tendon 
of  the  biceps  to  escape  from  its  interior.  In  addition  to  the  opening  just  referred 
to,  there  is  another  very  constant  deficiency  in  the  upper  and  anterior  part  of 
the  capsule,  where  the  narrowing  tendon  of  the  subscapularis  muscle  is  brought 
into  contact  with  a  bursa  formed  by  a  protrusion  of  the  syno^dal  membrane.  This 
defect  in  the  capsule  has  its  long  axis  in  the  direction  of  the  longitudinal  fibres. 
Occasionally  there  is  a  similar  but  smaller  opening  under  cover  of  the  tendon  of 
the  infraspinatus  muscle.  Through  the  two  latter  openings  the  joint  cavity 
communicates  with  bursae  situated  between  the  capsule  and  the  muscles  re- 
ferred to. 

The  tendons  of  the  subscapularis,  supraspinatus,  and  infraspinatus  muscles 
fuse  with,  and  so  strengthen,  the  capsule  as  they  approach  their  respective 
insertions. 

On  the  superior  aspect  of  the  articulation  the  capsule  is  augmented  by  an 
accessory  structure,  the  ligamentum  coraco-humerale  (Fig.  218).  By  its  inner  end, 
which  is  situated  immediately  above  the  glenoid  fossa,  but  subjacent  to  the  coraco- 
acromial  ligament,  it  is  attached  to  the  external  border  of  the  root  of  the  coracoid 
process,  while  its  outer  end  is  attached  to  the  humeral  neck  close  to  the  great  tuberosity. 
This  ligament  forms  a  flattened  band,  having  its  hinder  and  lower  border  fused  with 
the  capsule,  but 
its  anterior  and 
upper  margin 
presents  a  free 
edge,  slightly 
raised  above  the 
level  of  the  cap- 
sule. This  struc- 
ture is  believed 
to  represent  that 
portion  of  the 
pectoralis  minor 
to  which  refer- 
ence has  already 
been  made  in  con- 
nexion with  the 
coraco  -  acromial 
ligament  (p.  275). 

The  coraco- 
glenoid  ligament  is 
another  accessory 
structure  which  is 
not  always  present. 
It  springs  from  the 
coracoid  process 
along  with  the 
former  ligament,  and  extends  to  the  upper  and  hinder  margin  of  the  head  of  the  scapula. 

Gleno-humeral  Ligaments  (Fig.  219). — If  the  capsule  be  opened  from  behind,  and  the  head  of  the 
humerus  be  removed,  it  will  be  seen  that  the  longitudinal  fibres  of  the  anterior  part  of  the  capsule 
are  specially  developed  in  the  form  of  thick  flattened  bands  which  extend  from  the  anterior  border 
of  the  glenoid  fossa  to  the  anterior  aspect  of  the  neck  of  the  humerus.     These  gleno-humeral 


Coraco-      "\       Conoid 
clavicular  -Trapezoid 
ligament  J 
Coraco-acroinial  ligament 


Coracoid  process 


;;leno-humeral 
liaament 


Superior 


Bursal  perforation  in  capsule 


Inferior  gleno-liumeral 
li.arament 


Glenoid  cavit\ 


Glenoid 
licament 


Fig.  219.- 


-Capsdlar  Ligament  of  Shoulder-Joixt  cut  across  and 
Humerus  removed. 


278 


THE  AETICULATIONS  OE  JOINTS. 


ligaments  are  three  in  numbei',  and  occu^)}'  tlie  following  positions  :  the  superior  is  placed  above  the 
aperture  in  the  front  of  the  capsule  ;  the  middle  and  inferior  on  the  antero-inferior  aspect  of  the 
capsule,  and  heloiv  the  apertiire  mentioned. 

The  superior  gleno-humeral  ligament,  which  some  believe  to  reiDi-esent  the  ligamentum  teres 
of  the  hip-joint,  springs,  along  with  the  middle  gleno-humeral  band,  from  the  upper  j^art  of  the 
anterior  glenoid  margin.  The  inferior  band  is  the  strongest  of  the  three,  and  springs  from  the 
lower  part  of  the  anterior  glenoid  margin. 

Intra-capsular  Structures. — 1.  The  glenoid  ligament,  already  described.  2. 
The  long  tendon  of  the  biceps  passes  outwards  from  its  attachment  to  the  apex  of 
the  glenoid  fossa  and  the  adjoining  part  of  the  glenoid  ligament,  above  the  head  and 
neck  of  the  humerus,  to  escape  from  the  interior  of  the  capsule  by  the  opening 
between  the  tuberosities  of  the  humerus,  subjacent  to  the  transverse  humeral 
ligament. 

Synovial  membrane  (Fig.  220)  lines  the  capsule  of  the  joint,  and  extends  from 
the  margin  of  the  glenoid  fossa  to  the  humeral  attachments  of  the  capsule,  where  it 

is  reflected  towards  the 
margin  of  the  articular 
cartilage.  It  is  there- 
fore important  to  note 
that  the  inferior  aspect 
of  the  humeral  neck  has 
the  most  extensive 
clothing  of  synovial 
membrane.  Further, 
the  synovial  membrane 
envelops  the  intra-cap- 
sular part  of  the  tendon 
of  the  biceps,  and  al- 
though this  tubular 
sheath  is  prolonged  upon 
the  tendon  into  the 
upper  part  of  the  bi- 
cipital groove,  yet  the 
closed  character  of  the 
synovial  cavity  is  main- 
tained. Thus,  while  the 
tendon  is  within  the 
capsule,  it  is  not  within 
continuous  with  those  bursas 
the 


Head  of 
scapula 


CaMt^  ofjomt 


Fig.  220. — Vertical  Section  through  the  Shouldee-Joint. 


the   synovial   cavity.     The    synovial  membrane   is 

which  communicate  with  the  joint  cavity  through  openings  in 

capsule. 


ligamentous 


Bursse  (a)  Communicating  vjith  the  Joint  Cavity. — Practically  there  is  only  one  bursa  which 
is  constant  in  its  position,  viz.  the  subscapular,  between  the  capsule  and  the  tendon  of  the  sub- 
scapularis  muscle.  It  varies  considerably  in  its  dimensions,  but  its  lining  membrane  is  always 
continuous  with  that  which  lines  the  capsule  (Figs.  21*7  and  218),  and  therefore  it  may  be 
regarded  merely  as  a  prolongation  of  the  articular  sjTiovial  membrane.  Occasionally  a  similar 
but  smaller  bursa  occurs  between  the  capsule  and  the  tendon  of  the  infraspinatus  uiuscle. 

(h)  Not  com/rmmicating  with  the  Joint  Cavity. — The  sub-deltoid  or  sub-acromial  bursa  is 
situated  between  tlie  muscles  on  the  superior  aspect  of  the  shoulder-joint  on  the  one  hand  and 
the  deltoid  muscle  on  the  other.  It  is  an  extensive  bursa,  and  is  j^rolonged  subjacent  to  the 
acromion  process  and  the  coraco-acromial  ligament.  It  does  not  communicate  with  the  shoulder- 
joint,  but  it  gi'eatly  facilitates  the  movements  of  the  upper  end  of  the  humerus  against  the  under 
surface  of  the  coraco-acromial  arch. 

Movements  at  the  Shoulder-Joint. — A  ball-and-socket  joint  permits  of  a  great  variety  of 
movements,  practically  in  all  directions  ;  but  if  these  movements  be  analysed,  it  will  be  seen  that 
they  resolve  themselves  into  movements  about  three  primary  axes  at  right  angles  to  each  other, 
or  about  axes  which  are  the  possible  combinations  of  tlie  primary  ones. 

Thiu3,  about  a  transverse  axis,  the  limb  may  move  forwards  (flexion)  or  backwards  (extension). 
About  an  antero-posterior  axis  it  may  move  outwards,  i.e.  away  from  the  mesial  plane  of  the 
trunk  fabduction),  or  inwards,  i.e.  towards,  and  to  some  extent  up  to,  the  mesial  plane 
(adduction;. 

About  a  vertical  axis,  the  humerus  may  rotate  upon  its  axis  in  an  inward  or  out-ward  direction 
to  the  extent  of  a  quarter  of  a  circle. 


THE  ELBOW-JOINT. 


279 


Since  these  axes  all  pass  through  the  shoulder-joiut,  and  since  each  may  present  varying 
degrees  of  obliquity,  it  follows  that  very  elaborate  comljiuations  are  possible  until  the  movement 
of  circumduction  is  evolved.  In  this  movement  the  head  of  the  humerus  act-s  as  the  apex  of  a 
cone  of  movement  with  the  distal  end  of  the  humerus,  describing  the  base  of  the  cone. 

The  range  of  the  shoulder-joint  movements  is  still  further  increased  from  the  mobility  of 
the  scapula  as  a  whole,  and  from  its  association  with  the  movements  of  the  cla\dcle  already 
described. 


THE  ELBOW-JOINT. 


lisameiit 


This  articulation  (articulatio  cubiti)  provides  an  instance  of  a  diarthrosis  capable 
of  performing  the  movements  of  flexion  and  extension  about  a  single  axis  placed 
transversely,  i.e.  a  typical  ginglymus  diarthrosis  or  hinge-joint. 

The  bones  which  enter  into  its  formation  are  the  humerus,  ulna,  and  radius. 
The  trochlea  of  the  humerus  articulates  with  the  greater  sigmoid  cavity  of  the 
ulna  (articulatio  humero-ulnaris) ;  the  capitellum  of  the  humerus  articulates  with 
the  shallow  depression  or  cup  on  the  superior  aspect  of  the  head  of  the  radius  (articu- 
latio humero-radialis).  The  articular  cartilage  clothing  the  trochlea  of  the  humerus 
terminates  in  a  sinuous  or  concave  margin  both  anteriorly  and  posteriorly,  so  that 
it  does  not  line  either  the 
coronoid  or  the  olecranon 
fossa.  Internally,  it  merely 
rounds  off  the  inner  margin 
of  the  trochlea,  but  exter- 
nally it  is  continuous  with 
the  encrusting  cartilage 
covering  the  capitellum,  to 
the  margin  of  which  the 
cartilage  extends  in  all 
directions,  and  thus  it  pre- 
sents a  convex  edge  in 
relation  to  the  supra-capi- 
tellar  or  radial  fossa.  The 
cartilage  which  lines  the 
greater  sigmoid  ca"sdty  of 
the  ulna  presents  a  trans- 
verse interruption,  consider- 
ably wider  on  its  inner  as 
compared  with  its  outer 
aspect.  Thereby  the  coro- 
noid and  olecranon  seg- 
ments of  the  fossa  are 
separated  from  each  other. 
The  cartilage  which  clothes 
the  coronoid  segment  is 
continuous  with  that  which 
clothes  the  lesser  sigmoid 
cavity.  The  shallow  cup- 
shaped  depression  on  the 
head  of  the  radius  is  covered 
by  cartilage  which  rounds 
off  the  margin,  and  is  pro- 
longed without  interruption 
upon  the  vertical  aspect  of  the  head,  descending  to  its  lowest  level  on  that  part 
opposed  to  the  lesser  sigmoid  ca-sdty. 

Ligaments. — Taken  as  a  whole,  the  ligaments  form  a  complete  capsule  (capsula 
articularis),  which  is  not  defective  at  any  point,  although  it  is  not  of  equal  thick- 
ness throughout,  and  certain  bands  of  fibres  stand  out  distinctly  because  of  their 
greater  strength. 

The  anterior  ligament  (Fig.  221)  consists  of  a  layer  whose  fibres  run  in  several 


Internal  lateral 
igament 


don  of  insertion  of 
biceps  muscle 


Oblique  (ulno-radial) 
licraiaent 


Fig.  221. — Axxekior  View  of  Elbow-Joixt. 


280 


THE  AETICULATIONS  OE  JOINTS. 


directions — obliquely,  transversely,  and  vertically — and  of  these  the  vertical  fibres 
are  of  most  importance.  It  is  attached  above  to  the  upper  margins  of  the  coronoid 
and  supracapitellar  fossse  ;  below,  to  the  margins  of  the  coronoid  process  and  to  the 
orbicular  ligament  of  the  superior  radio-ulnar  joint,  but  some  loosely  arranged 
fibres  reach  as  far  as  the  neck  of  the  radius.  The  lateral  portions  of  this  ligament, 
which  are  situated  in  front  of  the  capitellum  and  the  inner  margin  of  the  trochlea 
respectively,  are  much  thinner  and  weaker  than  the  central  part.  Fibres  of  origin 
of  the  brachialis  anticus  muscle  are  attached  to  the  front  of  this  ligament. 

The  posterior  ligament  is  an  extremely  thin,  almost  redundant  layer. 
Superiorly  it  is  attached,  in  relation  to  the  margin  of  the  olecranon  fossa,  at  a 
varying  distance  from  the  trochlear  articular  surface,  and  inferior ly  to  the  summit 
and  sides  of  the  lip  of  the  olecranon  process.  Externally  some  of  its  fibres 
pass  from  the  posterior  aspect  of  the  capitellum  to  the  posterior  border  of  the  lesser 
sigmoid  cavity  of  the  ulna.  This  ligament  derives  material  support  from,  and 
participates  in  the  movements  of,  the  triceps  extensor  cubiti  muscle,  since  they  are 
closely  adherent  to  each  other  in  the  region  of  the  olecranon  process. 

The  internal  lateral  ligament  (lig.  collaterale  ulnare.  Figs.  221  and  222)  is  a  fan- 


Interosseous  membrane  Radius  Coronoid  proce=& 


L Internal  condyle 


^Anterior  part  of  internal 
lateral  ligament 

Posterior  part  of 
T        Mis      internal  lateral  ligament 

Olecranon  process 


Ulna  Transverse  part  of  internal  lateral  ligament 

Fig.  222. — Elbow- Joint  (inner  aspect). 

shaped  structure  of  unequal  thickness,  but  its  margins,  which  are  its  strongest  bands, 
are  continuous  with  the  adjoining  parts  of  the  anterior  and  posterior  ligaments. 
By  its  upper  end  it  is  attached  to  the  anterior,  inferior,  and  posterior  aspects  of  tlie 
internal  condyle  of  the  humerus.  By  its  broad  lower  end  it  is  attached  to  the 
inner  margin  of  the  greater  sigmoid  cavity,  so  that  the  anterior  hand  is  associated 
principally  with  the  inner  margin  of  the  coronoid  process,  and  the  posterior  hand 
with  the  inner  margin  of  the  olecranon  process,  while  the  intermediate  weaker 
portion  sends  its  fibres  downwards  to  join  a  transverse  hand,  sometimes  very  strong, 
which  bridges  the  notch  between  the  adjoining  inner  margins  of  the  coronoid  and 
olecranon  processes. 

The  external  lateral  ligament  (lig.  collaterale  radiale,  Fig.  221)  is  a  strong 
flattened  band  attached  superiorly  to  the  lower  and  posterior  aspects  of  the  external 
condyle  of  the  humerus.  It  completes  the  continuity  of  the  capsule  on  the  outer 
side,  and  blends  inferiorly  with  the  orbicular  ligament,  on  the  surface  of  which  its 
fibres  may  be  traced  both  to  the  anterior  and  posterior  ends  of  the  lesser  sigmoid 


THE  KADIO-ULNAE  JOINTS. 


281 


Olecranon  pad  of  fat 


Coronoid  process 


Trochlea 


Olecranon  process 


Fig.  223. 


Vertical  Section  through  the  Trochlear  Part  of 
Elbow-Joint. 


notch.     Both  of  the  lateral  ligaments  are  intimately  associated  with  the  muscles 
which  take  origin  from  the  inner  and  outer  condyles  of  the  humerus. 

Synovial  Pads  of  Fat  (Fig.  22.3).— Internal  to  the  capsule,  there  are  several  pads 
of  fat  situated  be- 
tween it  and  the  sy- 
novial membrane. 
Small  pads  are  so 
placed  as  to  lie  im- 
mediately in  front 
of  the  coronoid  antl 
supra-capitellar 
foss?e,  but  a  larger 
one  projects  to- 
wards the  olecra- 
non fossa. 

Synovial  mem- 
brane (Fig.  223) 
lines  the  entire 
capsule  and  clothes 
the  pads  of  fat 
above  referred  to, 
as  well  as  those 
portions  of  bone 
enclosed  within  the 
capsule  which  are 
not  covered  by 
articular  cartilage. 
By  its  disposition 
the  elbow  and  the 
superior  radio- 
ulnar joints  possess  a  common  joint  cavity.  It  should  be  specially  noted  that  the 
upper  part  of  the  neck  of  the  radius  is  surrounded  by  this  synovial  membrane. 

Movements  at  the  Elbow-Joint. — The  movements  of  the  radius  and  ubia  upon  the  humerus 
have  already  been  referred  to  as  those  characterising  a  uniaxial  joint  constructed  on  the  plan  of 
a  hinge.  In  this  case  the  axis  of  the  joint  is  obliquely  transverse,  so  that  in  the  extended 
position  the  humerus  and  ulna  form  an  obtuse  angle  open  towards  the  radius,  whereas  in  the 
flexed  position  the  hand  is  carried  inwards  in  the  direction  of  the  mouth.  Extreme  flexion  is 
checked  by  the  soft  parts  in  front  of  the  arm  and  of  the  fore-arm  coming  into  contact,  and 
extreme  extension  by  the  restraining  effect  of  the  ligaments  and  muscles.  In  each  case  the 
movement  is  checked  before  either  coronoid  or  olecranon  processes  come  into  contact  with  the 
humerus.  The  anterior  and  posterior  bands  of  the  internal  lateral  ligament  are  important  factors 
in  these  results.  Lateral  movement  of  the  ulna  is  not  a  characteristic  movement,  although  it 
may  occur  to  a  slight  extent,  owing  to  a  want  of  complete  adajitation  between  the  trochlear 
surface  of  the  humerus  and  the  sigmoid  caAdty  of  the  ulna.  This  incongruence  is  noteworthy 
since  the  inner  lip  of  the  trochlea  is  prominent  in  front,  and  the  outer  lip  is  prominent  behind. 
Consequently,  this  latter  part  is  associated  with  a  surface  on  the  outer  side  of  the  olecranon 
which  is  only  utilised  in  complete  extension. 

The  capitellum  and  the  opposing  surface  ui^on  the  head  of  the  radius  are  always  in  varying 
degrees  of  contact.  The  head  of  the  radius  jsarticipates  in  the  movements  of  flexion  and  exten- 
sion, and  is  most  closely  and  completely  in  contact  with  the  humerus  during  the  position  of  semi- 
flexion and  semi-pronation.  In  complete  extension  a  very  considerable  part  of  the  capitellum  is 
uncovered  by  the  radius. 

THE  RADIO-ULNAR  JOINTS. 

These  articulations,  which  are  two  in  number,  are  situated  at  the  proximal  and 
distal  ends  of  the  radius  and  ulna.  They  provide  an  adaptation  whereby  the  radius 
rotates  around  a  longitudinal  axis  in  the  movements  of  pronation  and  supination, 
and  hence  this  form  of  uniaxial  diarthrosis  is  termed  lateral  ginglymus. 

Superior  Radio-ulnar  Joint  (articuktio  radio-ulnaris  proximalis). — In  this 
joint  the  articular  surfaces  which  enter  into  its  formation  are  the  lesser  sigmoid 
cavity  of  the  ulna  and  the  lateral  aspect  of  the  head  of  the  radius.  In  each  case 
the  articular  cartilage  is  continuous  with  an  articular  surface  entering  into  the 
formation  of  the  elbow-joint,  consequently  the  joint  cavity  is  continuous  with  that 


282 


THE  ARTICULATIONS  OE  JOINTS. 


Olecranon  process 


Lessei  sia;mOKl 
caMty 


Transvei'se 
portion  of 
internal  lateral 
lisament 

llll     Greater  sigmoid 
peavity 


Orbicular  ligament  Coronoid  process 

Fig.  224. — Orbicular  Ligament  of  the  Radius. 


of  the  elbow-joint,  and  therefore,  in  a  sense,  it  lies  within  the  cover  of  the  capsule 
of  the  elbow-joint ;  but  its  special  feature  is  the — 

Orbicular  ligament  (hg.  annulare  radii,  Figs.  221  and  224),  which  has  formerly  been 

mentioned  as  the  inferior  line  of 
attachment  of  the  external  lateral 
ligament  and  the  ligaments  on 
the  front  and  back  of  the  elbow- 
joint. 

It  is  a  strong,well-defined  struc- 
ture, attached  by  its  extremities 
to  the  anterior  and  posterior 
margins  of  the  lesser  sigmoid 
cavity,  and  thus  it  forms  nearly 
four-fifths  of  an  osseo-tendinous 
circle  or  ring.  This  circle  is  some- 
what wider  at  the  upper  than  at 
the  lower  margin  of  the  orbicular 
ligament,  which,  by  encircling  the 
upper  part  of  the  neck  of  the 
radius,  tends  to  prevent  displace- 
ment of  the  head  of  that  bone  in  a  downward  direction.  The  lower  margin  of 
this  ligament  is  not  directly  attached  to  the  radius. 

The  synovial  membrane  is  continuous  with  that  which  lines  the  elbow-joint.  It 
closes  the  joint  cavity  at  the  inferior  unattached  margin  of  the  orbicular  ligament, 
where  it  is  somewhat  loosely  arranged  in  its  reflexion  from  the  ligament  to  the 
neck  of  the  radius. 

Inferior  Radio-ulnar  Joint  (articulatio  radio-ulnaris  distalis). — This  joint  is 
situated  between  the  sigmoid  cavity  on  the  inner  side  of  the  lower  end  of  the 
radius  and  the  lateral  aspect  of  the  head  of  the  ulna.  In  addition,  it  includes  the 
inferior  surface  of  the  head  of  the  ulna,  which  articulates  with  the  superior 
surface  of  a  triang'ular  plate  of  fibro-cartilage,  by  means  of  which  the  joint  is 
excluded  from  the  radio-carpal  articulation 

The  triangular  interarticular  fibro-cartilage  (discus  articularis,  Figs.  225  and  227), 
besides  presenting  articular  surfaces  to  two  separate  joints,  is  an  important  ligament 
concerned  in  binding  together  the  lower  ends  of  the  radius  and  ulna.  It  is  attached 
by  its  apex  to  the  de- 
pression at  the  outer 
side  of  the  root  of  the 
styloid  process  of  the 
ulna,  and  by  its  base  to 
the  sharp  line  of  de- 
marcation between  the 
sigmoid  cavity  and  the 
carpal  articular  surface 
of  the  radius. 

The  ligamentous  cap- 
sule is  very  imperfect,  and  consists  of  scattered  fibres,  termed  the  anterior  and 
posterior   radio-ulnar   ligaments  (Fig.   226).      These  ligaments   pass    transversely 
between  adjoining  non-articular  surfaces  on  the  radius  and  ulna,  and  are  of  sufficient 
length  to  ]jermit  of  tiie  movements  of  the  radius  in  pronation  and  supination. 

The  synovial  membrane  completes  the  closure  of  the  joint  cavity.  It  forms  a 
loose  bulging  projection  (recessus  sacciformis),  passing  upwards  between  the  lower 
ends  of  the  shafts  of  the  radius  and  ulna,  and  it  also  clothes  the  upper  surface  of 
the  trkingular  fibro-cartilage  (Fig.  227).  The  cavity  of  this  joint  is  quite  distinct 
from  that  of  the  radio-carpal  articulation,  except  when  the  triangular  fibro-cartilage 
presents  a  perforation. 

Between  the  foregoing  articulations  there  are  two  accessory  ligaments,  viz.  the 
interosseous  membrane  and  the  oblique  ligament,  which  connect  together  the  shafts 
of  the  radius  and  ulna. 


Sui'face  for 
scaphoid  bone 
Groove  for  tendni    ^ 
of  extensor  longus-^     ^ 
polliois 


Head  of  ulna 

Styloid  process  of  ulna 

Ij  — ■  I         Apex  of  triangular  tibro-cartilage 

Triangular  fibro-cartilage 
Surface  for  semilunar  bone 


Fig.  225. — Carpal  Articular  Surface  of  the  Radius,  and 
Triangular  Fibro-cartilage  of  the  Wrist. 


THE  EADIO-CARPAL  JOINT.  283 

The  interosseous  membrane  (Fig.  222)  of  the  fore-arm  (membrana  interossea  inter- 
brachii)  is  a  strong  filn'ous  membrane  which  stretches  across  the  interval  between 
the  radius  and  uhia,  and  is  firmly  attached  to  the  interosseous  border  of  each.  Below 
it  extends  downwards  to  the  lower  limit  of  the  space  between  the  bones,  whilst 
above  it  does  not  reach  higher  than  a  point  about  one  inch  below  the  tuberosity 
of  the  radius.  A  gap,  called  the  hiatus  interosseus,  is  thus  left  above  its  upper 
margin,  and  through  this  the  posterior  interosseous  vessels  pass  backwards  between 
the  bones  to  reach  the  dorsal  aspect  of  the  fore-arm.  This  gap  is  bounded  above 
by  the  oblique  ligament.  The  fibres  which  compose  the  interosseous  membrane 
run  for  the  most  part  downwards  and  inwards  from  the  radius  to  the  ulna,  although 
on  its  dorsal  aspect  several  bands  may  be  observed  stretching  in  an  opposite  direc- 
tion. The  interosseous  membrane  augments  the  surface  available  for  the  origin  of 
the  muscles  of  the  fore-arm ;  it  braces  the  radius  and  ulna  together  ;  and  when 
shocks  are  communicated  from  the  hand  to  the  radius,  owing  to  the  direction  of  its 
fibres,  the  interosseous  membrane  transmits  these,  to  some  slight  extent,  to  the  ulna. 

The  oblique  ligament  (Fig.  222)  is  a  slender  tendinous  band  of  very  varying 
strength  which  springs  from  the  outer  part  of  the  coronoid  process  of  the  ulna,  and 
stretches  oljliquely  downwards  and  outwards  to  the  radius  where  it  is  attached 
immediately  below  the  bicipital  tuberosity. 

Movements  of  the  Eadius  on  the  Ulna. — The  axis  about  wlucli  the  radius  moves  is  a 
longitudinal  one,  having  one  end  j^assing  through  the  centre  of  the  head  of  the  radius  and 
the  other  through  the  styloid  process  of  the  iilna  and  the  line  of  the  ring-finger.  In  this  axis 
the  head  of  the  radius  is  so  secured  that  it  can  only  rotate  upon  the  lesser  sigmoid  cavity 
of  the  ulna  within  the  orbicular  ligament,  and  consequently  the  radial  head  remains  upon  the 
same  plane  as  the  ulna  ;  but  the  lower  end  of  the  radius  being  merely  restrained  by  the 
triangular  fibro-cartilage,  is  able  to  describe  nearly  a  half-circle,  of  which  the  apex  of  this 
ligament  is  the  centre.  In  this  movement  the  radius  carries  the  hand  from  a  position  in  which 
the  palm  is  directed  forwards,  and  in  which  the  radius  and  ulna  lie  parallel  to  each  other 
(supination),  to  one  in  which  tliepalm  is  directed  backwards,  and  the  radius  lies  diagonally  across 
the  front  of  the  ulna  (pronation). 

The  ulna  is  unable  to  rotate  upon  a  long  axis,  but  while  the  radius  is  travelling  through  the 
arc  of  a  circle  from  without  inwards  in  front  of  the  ulna,  it  will  usually  be  seen  that  the  ulna 
ajJi^ears  to  move  through  the  arc  of  a  smaller  circle  in  the  reverse  direction,  viz.  from  within 
outwards.  If  the  humerus  be  j)revented  from  moAdng  at  the  shoulder-joint,  a  very  large  propor- 
tion, if  not  the  entire  amount,  of  this  apparent  movement  of  the  ulna  will  disappear-.  At  the 
same  time  some  observers  maintain  that  it  really  occurs  at  the  elbow -joint,  associated  with  lateral 
movement  during  slight  degrees  of  flexion  and  extension  at  that  joint. 

THE  RADIO-CARPAL  JOINT. 

This  joint  (articulatio  radiocarpea)  is  a  bi-axial  diarthrosis,  frequently  called  a 
condyloid  joint. 

The  articular  elements  which  enter  into  its  formation  are:  on  its  proximal  side,  the 
inferior  surface  of  the  lower  end  of  the  radius,  together  with  the  inferior  surface  of 
the  triangular  fibro-cartilage  ;  on  its  distal  side,  the  superior  articular  surfaces  of  the 
scaphoid,  semilunar,  and  cuneiform  bones.  The  articular  surface  of  the  radius  is 
concave  both  in  its  antero-posterior  and  transverse  diameters,  in  order  to  adapt 
itself  to  the  opposing  surfaces  of  the  scaphoid  and  semilunar,  which  are  convex  in 
the  two  axes  named.  In  the  ordinary  straight  position  of  the  hand  the  triangular 
fibro-cartilage  is  in  contact  with  the  semilunar  bone,  and  the  upper  articular  surface 
of  the  cuneiform  bone  is  in  contact  with  the  capsule  of  the  joint.  When,  however, 
the  hand  is  bent  towards  the  ulna,  the  cuneiform  bone  is  carried  outwards  as  well 
as  the  semilunar  and  scaphoid,  and  the  triangular  fibro-cartilage  comes  into  contact 
with  the  cuneiform.  The  articular  surface  of  the  radius  is  subdivided  by  an  antero- 
posterior, slightly  elevated  ridge,  into  an  outer  triangular  facet  which  usually  arti- 
culates with  the  scaphoid,  and  an  inner  quadrilateral  facet  for  articulation  with  a 
portion  of  the  semilunar  bone. 

In  the  intervals  between  the  scaphoid,  semilunar,  and  cuneiform  bones,  the  con- 
tinuity of  the  articular  surfaces  is  usually  maintained  by  the  presence  of  interosseous 
ligaments  which  are  situated  upon  the  same  level  as  the  articular  cartilage. 

Ligaments. — A  capsular  ligament  completely  surrounds  the  joint.  It  is  some- 
what loosely  arranged,  and  permits  of  subdivision  into  the  following  portions : — 

The  external  lateral  ligament  (Fig.  226)  is  a  well-defined  band  which  is  attached 


284 


THE  AETICULATIOXS  OE  JOINTS. 


Anterior  radio- 
ulnar liframent 


Internal  lateral 
ligament 


Pisiform  bone 


bj  one  end  to  the  tip  of  the  styloid  process  of  the  radius,  and  by  the  other  to  a 

rough  area  at  the  base  of  the  tubercle  of  the  scaphoid  bone,  i.e.  external  to  its 

radial  articular  surface. 

The  internal  lateral  ligament  (Fig.  226)  is  also  a  distinct  rounded  structure, 

having  one  end  attached  to  the  tip  of  the  styloid  process  of  the  ulna,  and  the  other  to 

the  rough  non  -  articular 
border  of  the  cuneiform 
bone,  some  of  its  fibres 
being  prolonged  to  the 
pisiform  bone. 

The  anterior  ligament 
(Fig.  226)  is  attached 
superiorly  to  the  anterior 
margin  of  the  lower  end 
of  the  radius,  as  well  as 
rubercie  of  .scaphoid  sHghtly  to  the  base  of 
the  styloid  process  of  tlie 

Ridge  oil  T  ri  , 

trapezium  uina.  feomc  transversc 
fibres  may  be  seen,  but 

riapezium  the  greater  number  pass 
obliquely  downwards  and 
inwards  to  the  palmar 
non-articular  surfaces  of 
the  scaphoid,  semilunar, 
and  cuneiform  bones, 
while  some  of  them  may 
even  be  continued  as  far 
as  the  OS  magnum. 
Those  fibres  from  the 
ulna  run  obliquely  out- 
wards. On  its  deeper 
aspect  this  ligament  is 
the  triangular  fibro-cartilage  of   the 


Os  magnum,  with 
ligaments  radiat- 
ing from  it 

Unciform  proves: 


Fig.  226. — Ligaments  on  Anterior  Aspect  of  Radio-carpal, 
Carpal,  and  Carpo-metacarpal  Joints. 


closely  adherent  to  the  anterior  border  of 
inferior  radio-ulnar  articulation. 

The  posterior  ligament  extends  from  the  posterior  margin  of  the  lower  end 
of  the  radius,  obliquely  downwards  and  inwards,  to  the  dorsal  non  -  articular 
areas  on  the  proximal  row  of  the  carpal  bones.  The  slip  to  the  latter  assists  in 
forming  the  fibrous  sheath  through  which  the  tendon  of  the  extensor  carpi  ulnaris 
muscle  travels  to  its  insertion.  The  principal  bundle  of  fibres  is  connected  with 
the  cuneiform  bone. 

The  synovial  membrane  (Fig.  227)  is  simple,  and  is  confined  to  the  articulation, 
except  in  those  cases  in  which  the  triangular  fibro-cartilage  is  perforated,  or  in  which 
one  of  the  interosseous  ligaments  between  the  carpal  bones  of  the  first  row  is  absent. 

Movements  at  the  Radio-carpal  Joint. — The  radio-carpal  joint  affords  an  excellent  example 
of  a  biaxial  articulation,  in  which  a  long  transverse  axis  of  movement  is  situated  more  or  less  at 
right  angles  to  a  short  axis  placed  in  the  antero-posteiior  direction.  The  nature  of  the  move- 
ments which  are  possible  about  these  two  axes  is  essentially  the  same  in  both  cases,  viz.  flexion 
and  extension._  The  movements  about  the  longer  transverse  axis  are  anterior  or  palmar  flexion, 
extension,  and  its  continuation  into  dorsi-flexion.  About  the  shorter  antero -posterior  axis  we  get 
movements  which  re.sult  from  combined  action  by  certain  flexor  and  extensor  muscles,  whereby 
the  radial  or  ulnar  borders  of  the  hand  may  be  approximated  towards  the  corresponding  borders 
of  the  fore-arm.  Lateral  movement  may  also  be  possible  to  a  slight  extent.  The  range  of  move- 
ment in  connexion  with  either  of  the  principal  axes  is  largely  a  matter  of  individual  peculiarity, 
for,  with  the  excej)tion  of  the  lateral  ligaments,  there  is  no  serious  obstacle  to  the  cultivation  of 
greater  mobility  at  the  radio-carpal  joint. 


CARPAL  JOINTS. 

The  articulations  subsisting  between  the  individual  carpal  bones  (articulationes 
mtercarpeffi)  are  all  diarthroses,  and  although  the  total  amount  of  movement 
throughout  the  series  is  considerable,  yet  the  extent  of  movement  which  is  possible 


ARTICULATIONS  OF  THE  CAEPUS.  285 

between  the  two  rows  or  between  any  two  carpal  bones  is  extremely  limited. 
Yov  this  reason,  as  well  as  because  of  the  nature  of  the  movement,  these  articula- 
tions are  called  gliding  joints  (arthrodia). 

It  is  advisable  to  consider,  j^rs^,  the  articulations  between  individual  bones  of 
the  proximal  row ;  second,  the  articulations  between  the  separate  bones  of  the 
distal  row  ;  third,  the  articulation  of  the  proximal  and  distal  rows  with  each  other ; 
fourth,  the  pisiform  articulation. 

The  proximal  row  of  carpal  articulations  (Fig.  226)  comprises  the  joints 
between  the  scaphoid,  semilunar,  and  cuneiform  bones.  On  their  adjacent  lateral 
aspects  these  bones  are  partly  articular  and  partly  non-articular. 

Three  sets  of  simple  but  strong,  although  short  ligamentous  bands  bind  these 
three  carpal  bones  together,  and  form  an  investment  for  three  sides  of  their  inter- 
carpal joints.  These  are — (1)  the  anterior  or  palmar  ligaments,  two  in  number,  which 
consist  of  transverse  fibres  passing  between  the  adjacent  rough  palmar  surfaces  of 
the  bones ;  (2)  the  posterior  or  dorsal  ligaments,  also  two  in  number,  and  composed 
of  similar  short  transverse  fibres  passing  between  the  adjacent  dorsal  surfaces ; 
(3)  the  interosseous  ligaments  (Fig.  227),  again  two  in  number,  and  transverse  in 
direction,  situated  on  a  level  with  the  superior  articular  surfaces,  and  extending  from 
the  palmar  to  the  dorsal  aspect  of  the  bones,  while  attached  to  non-articular  areas  of 
the  opposing  surfaces.  The  radio-carpal  joint  is  entirely  shut  off  from  the  inter- 
carpal joints,  and  also  from  the  joint  between  the  two  rows  of  carpal  bones,  except  in 
rare  cases,  when  an  interosseous  ligament  is  wanting;. 

The  distal  row  of  carpal  articulations  (Fig.  226)  includes  the  joints  between 
the  trapezium,  trapezoid,  os  magnum,  and  unciform  bones.  Articular  facets  occur 
on  the  opposing  lateral  faces  of  the  individual  bones. 

Associated  with  this  row  there  are  again  simple  bands  of  considerable  strength, 
and  presenting  an  arrangement  similar  to  that  seen  in  the  proximal  row.  As  in 
the  former  case,  they  invest  the  intercarpal  articulations,  except  on  the  superior 
aspect,  where  they  communicate  with  the  transverse  carpal  joint,  and  on  the  inferior 
aspect,  where  they  communicate  with  the  carpo-metacarpal  joint  cavity. 

The  anterior  or  palmar  ligaments  are  three  in  number.  They  extend  in  a  trans- 
verse direction  between  contiguous  portions  of  the  rough  palmar  surfaces  of  the 
bones.  The  posterior  or  dorsal  ligaments,  also  three  in  number,  are  similarly  dis- 
posed on  the  dorsal  aspect.  The  interosseous  ligaments  (Fig.  227)  are  two  or  three 
in  number.  That  which  joins  os  magnum  to  unciform  is  the  strongest ;  that 
between  the  trapezoid  and  os  magnum  is  situated  towards  the  dorsal  parts  of  their 
opposing  surfaces  ;  the  third,  situated  between  contiguous  non-articular  surfaces 
of  the  trapezium  and  trapezoid,  is  always  the  feeblest,  and  is  frequently  absent. 

The  transverse  carpal  articulation  (Fig.  227)  is  situated  between  the  proxunal 
and  distal  rows  of  the  carpus.  The  bones  of  the  proximal  row  present  the  following 
characters  on  iheir  inferior  or  distal  aspect.  The  outer  part  of  the  articular  surface 
is  deeply  concave,  both  in  the  antero-posterior  and  in  the  transverse  directions,  but 
the  inner  part  of  the  same  surface  is  concavo-convex,  more  especially  in  the  trans- 
verse direction. 

Superiorly,  the  articular  surfaces  of  the  distal  row  of  carpal  bones  present  an 
irregular  outline.  That  part  pertaining  to  the  trapezium  and  trapezoid  is  concave 
in  the  antero-posterior  and  transverse  directions,  and  lies  at  a  considerably  lower 
level  than  the  portion  belonging  to  the  os  magnum  and  unciform,  which  is,  more- 
over, markedly  convex  in  the  antero-posterior  and  transverse  directions,  with  the 
exception  of  the  innermost  part  of  the  unciform,  where  it  is  concavo-convex  in 
both  of  these  directions. 

This  articulation  is  invested  by  a  complete  short  capsule  (Fig.  226)  which  binds 
the  two  rows  of  the  carpus  together,  and  sends  prolongations  to  the  investing 
capsules  of  the  proximal  and  distal  articulations.  The  ligament  as  a  whole  is  very 
strong,  and  individual  bands  are  not  readily  defined,  although  certain  special  bands 
may  be  described.  The  palmar  ligaments  radiate  from  the  os  magnum  to  the  scaphoid, 
cuneiform,  and  pisiform.  The  interval  between  the  os  magnum  and  semilunar  is 
occupied  by  oblique  fibres,  some  of  which  pass  from  scaphoid  to  cuneiform,  while 
these  are  joined  by  others,  prolonged  obliquely  downwards  and  inwards,  from  the 


286 


THE  AETICULATIONS  OK  JOINTS. 


radial  end  of  the  anterior  radio-carpal  ligament.     By  these  different  bands    the 
palmar  aspect  of  the  joint  is  completely  closed. 

The  dorsal  ligaments  are  more  feeble  than  the  palmar.  They  form  a  thin,  loosely- 
arranged  stratum,  in  which  the  only  noteworthy  bands  are  one  which  joins  the 
scaphoid  to  os  magnum,  and  another  which  joins  cuneiform  to  unciform. 

The  external  lateral  ligament  (lig.  collaterale  carpi  radiale.  Fig.  227)  extends 
between  contiguous  rough  areas  on  the  radial  aspects  of  the  scaphoid  and 
trapezium.  By  its  margins  it  is  continuous  both  with  the  palmar  and  dorsal 
ligaments. 

The  internal  lateral  ligament  (lig.  collaterale  carpi  uluare.  Fig.  227)  is  arranged 
Uke  the  former  in  regard  to  its  margins,  and  by  its  ends  it  is  attached  to  the  con- 
tiguous rough  ulnar  surfaces  of  the  cuneiform  and  unciform  bones. 

Both  of  these  lateral  hgaments  are  directly  continuous  with  the  corresponding 
lateral  ligaments  of  the  radio-carpal  joint. 

An  interosseous  ligament  (Fig.  227)  is  occasionally  found  within  the  capsule, 
extending  across  the  joint  cavity  between  the  os  magnum  and  the  scaphoid. 

The  pisi-cuneiform  articulation  is  an  arthroidal  diarthrosis.  The  mutual 
articular  surfaces  of  the  two  bones  are  flattened  and  circular,  and  only  permit  of  a 
small  amount  of  gliding  movement. 

The  joint  is  provided  with  a  thin  but  complete  capsule  of  fibrous  tissue,  which 
is  specially  strengthened  inferiorly  by  two  strong  bands,  viz.  pisi-unciform  (lig.  piso- 
hamatum)  and  pisi-metacarpal  (lig.  pisometacarpeum.  Fig.  226).  Both  of  these 
bands  extend  from  the  lower  and  inner  aspect  of  the  pisiform  to  adjoining  parts  of 
the  hook  of  the  unciform  and  base  of  the  fifth  metacarpal  bone  respectively.  To  a 
great  extent  these  ligamentous  bands  may  be  regarded  as  extensions  of  the  in- 
sertion of  the  tendon  of  the  flexor  carpi  ulnaris  muscle  which  is  attached  to  the 
upper  part  of  the  pisiform  bone.  Looked  at  as  ligaments,  however,  they  are 
specially  strong  to  prevent  the  displacement  of  the  pisiform  bone  during  contrac- 
tion of  the  muscle  inserted  into  it. 

The  synovial  membranes  (Fig.  227)  of  the  carpal  joints  are  two  in  number.     Of 

these,  one   is   restricted   to 

I-  ' 

fr-    ,\ 


/  ,     Recessus 

/  /     sacciformis 

/  I  -—  of  inferior 

radio-ulnar 
Joint 

Triangular 
'fibro- 
cartilage 


Traijfzoi'l 


Trapezium —I 


the  pisi-cuneiform  articula- 
tion, and  is  correspondingly 
simple,  although  occasionally 
the  joint  cavity  may  com- 
municate with  that  of  the 
radio-carpal  joint. 

The  other  synovial  mem- 
brane is  associated  with  the 
transverse  carpal  joint  which 
extends  transversely  be- 
tween the  two  rows  of  carpal 
bones,  with  prolongations 
into  the  vertical  intervals 
between  the  adjoining  bones 
of  each  row,  i.e.  the  inter- 
carpal articulations.  It  is, 
therefore,  an  elaborate  cavity, 
which  may  be  still  further 
extended,  by  the  absence  of 
interosseous  ligaments,  so  as 
to  reach  the  radio-carpal  and 
carpo- metacarpal  series  of 
joints.  The  first  condition 
is  rare,  but  the  second  is  not  uncommon,  and  results  from  the  absence  of  the  inter- 
osseous ligament  Ijetween  trapezium  and  trapezoid,  or  of  that  between  trapezoid 
and  OS  majmum. 


Fig.  227. — Coro.nal  Section  through  the  radio-carpal,  carpal,  carpo- 
metacarpal, an<I  intermetacarpal  joints,  to  show  joint  cavities  and 
interosseous  ligaments  (diagrammatic). 


CAEPO-METACAEPAL  JOINTS.  287 

INTERMETACARPAL   JOINTS. 

The  four  inner  metacarpal  bones  articulate  with  each  other  at  their  proximal 
ends  or  bases,  between  the  opposing  surfaces  of  which  joint  cavities  are  found — 
arthrodial  diarthroses.  These  cavities  are  continuous  with  the  carpo-metacarpal 
joint  (not  yet  described),  and  hence  the  ligamentous  arrangements  only  enclose 
three  aspects  of  each  joint. 

Three  strong  transverse  ligaments  (Figs.  226  and  227)  bind  adjacent  palmar, 
dorsal,  and  interosseous  areas  of  the  bases  of  the  metacarpal  bones,  and  hence  they 
are  called  ligamenta  basium  (oss.  metacarp.)  volaria,  dorsalia  et  interossea.  A 
synovial  membrane  is  associated  with  each  of  these  joints,  but  it  may  be  regarded 
as  a  prolongation  from  the  carpo-metacarpal  articulation. 

CARPO-METACARPAL   JOINTS. 

The  articulation  of  the  metacarpal  bone  of  the  thumb  with  the  trapezium 
differs  in  so  many  respects  from  the  articulation  between  the  other  metacarpal 
bones  and  the  carpus,  that  it  must  be  considered  separately. 

(A)  The  articulatio  carpo-metacarpea  poUicis  (Figs.  226  and  227)  is  the  joint 
between  the  infero-external  surface  of  the  trapezium  and  the  superior  surface  of 
the  base  of  the  first  metacarpal  bone.  Both  of  these  surfaces  are  saddle-shaped,  and 
they  articulate  by  mutual  co-aptation. 

The  joint-cavity  is  surrounded  by  a  fibrous  capsule,  in  which  we  may  recognise 
palmar,  dorsal,  external,  and  internal  lateral  bands,  the  last  being  the  strongest  and 
m.ost  important. 

Synovial  membrane  lines  the  capsule,  and  the  joint-cavity  is  isolated  and  quite 
separate  from  the  other  carpal  and  carpo-metacarpal  articulations. 

At  this  joint  movements  occur  about  at  least  three  axes.  Thus,  around  a  more  or  less  trans- 
verse axis,  flexion  and  extension  take  jAace  ;  in  an  antero-posterior  axis  abduction  and  adduction 
(movements  which  have  reference  to  the  middle  line  of  the  hand)  are  found  ;  while  a  certain 
amount  of  rotation  is  2>ossible  in  the  longitudinal  axis  of  the  digit.  The  very  characteristic 
movement  of  opposition,  in  which  the  tijs  of  the  thumb  may  be  applied  to  the  tips  of  all  the 
fingers,  results  from  a  combination  of  flexion,  adduction,  and  rotation,  and  Ijy  combining  all  the 
movements  possible  at  the  various  axes  a  considerable  degree  of  circumduction  may  be  produced, 
in  spite  of  the  fact  that  this  is  not  a  ball-and-socket  joint.- 

(B)  The  articulationes  carpo-metacarpese  digitorum  are  the  joints  between 
the  bases  of  the  four  inner  metacarpal  bones  and  the  four  bones  of  the  distal  row 
of  the  carpus.  They  are  all  arthrodial  diarthroses,  and  the  opposed  articular 
surfaces  present  alternate  elevations  and  depressions  which  form  a  series  of 
interlocking  joints.  The  joint  cavities  between  the  carpal  bones  of  the  distal 
row,  and  also  the  more  extensive  intermetacarpal  joint  cavities,  open  into  this 
articulation. 

This  series  of  joints  is  invested  by  a  common  capsule  which  is  weakest  on  its 
radial  side,  but  is  otherwise  well  defined.  Its  fibres  arrange  themselves  in  small 
slips,  which  pass  obliquely  in  different  directions,  and  vary  in  number  for  each 
metacarpal  bone.  Thus  the  oblique  palmar  ligaments  (ligamenta  carpo-metacarpea 
volaria.  Fig.  225)  usually  consist  of  one  slip  for  each  metacarpal  bone,  but  there 
may  be  two  slips,  and  the  third  metacarpal  bone  frequently  has  three,  of  which  one 
lies  obliquely  in  front  of  the  tendon  of  the  flexor  carpi  radialis  muscle. 

The  oblique  dorsal  ligaments  (ligamenta  carpo-metacarpea  dorsalia)  are  similar 
short  bands,  of  greater  strength  and  clearer  definition,  by  which  the  index  meta- 
carpal is  bound  to  the  trapezium  and  trapezoid ;  the  middle  metacarpal  to  the  os 
magnum,  and  frequently  to  the  trapezoid ;  the  ring  metacarpal  to  the  os  magnum 
and  unciform,  and  the  metacarpal  of  the  minimus  to  the  unciform. 

Interosseous  ligaments,  one  or  sometimes  two  in  number,  occur  within  the  capsule. 
They  are  usually  situated  in  relation  to  one  or  both  of  the  contiguous  margins  of 
the  bases  of  the  third  and  fourth  metacarpal  bones,  from  which  they  extend 
upwards  to  adjacent  margins  of  the  os  magnum  and  unciform.  Occasionally  they 
are  sufficiently  developed  to  divide  the  joint  cavity  into  radial  and  ulnar  sections. 


288 


THE  AETICULATIONS  OR  JOINTS. 


Accessory  pal- 
mar ligament  \ 


The  synovial  membrane  (Fig.  227)  is  usually  single  and  lines  the  capsule,  but, 
as  already  explained,  it  has  prolongations  into  the  intermetacarpal  and  inter- 
carpal series  of  joints.  In  connexion  with  the  latter,  the  frequent  absence  of 
the  interosseous  ligament  between  the  trapezium  and  trapezoid  permits  the  free 
communication  of  this  joint-cavity  with  that  of  the  transverse  carpal  joint. 

METACARPO-PHALANGEAL  JOINTS. 

In  the  case  of  the  pollex  this  joint  is  constructed  on  the  plan  of  a  gingiymus 
diarthrosis ;  the  four  corresponding  joints  of  the  fingers  are  also  diarthroses  of  a 
shghtly  modified  ball-and-socket  variety.     With  the  exception  of  the  metacarpal 

bone  of  the  pollox,  each  metacarpal  bone  has  a  somewhat 
spherical  head  articulating  with  a  shallow  oval  cup  upon 
the  base  of  the  first  phalanx.  It  is  important  to  note  that 
the  articular  surface  upon  the  head  of  each  of  these  meta- 
carpal bones  is  wider  on  the  palmar  aspect  and  narrower 
on  the  dorsal  aspect.  The  articulation  in  the  thumb 
presents  features  similar  to  those  of  an  inter-phalangeal 
joint. 

Each  joint  possesses  an  articular  capsule  (Eig.  228) 

which   presents  very  different  degrees   of  strength   in 

different  aspects  of  the  articulation.     Thus,  on  the  dorsal 

aspect,  it  cannot  be  demonstrated  as  an  independent 

^  structure,  but  the  necessity  lor  dorsal  hgaments  is  to  a 

I  large  extent  obviated  by  the  presence  of   the    strong 

.1  flattened  expansions  of  the  extensor  tendons. 

i          The  internal  and  external  lateral  ligaments  (hgamenta 

I  collateralia,  Eig.  228)  are  strong  cord-like  bands  which 

"  pass  from  the  tubercles  and  adjacent  depressions  on  the 

sides  of  the  heads  of  the  metacarpal  bones  to  the  contiguous 

non-articular  areas  on  the  bases  of  the  proximal  phalanges. 

They  are  intimately  connected  on  their  anterior  aspects 

with  the  palmar  ligaments. 

^         The  palmar  ligaments  consist  of  thick  plates  of  fibro- 

I  cartilage  loosely  connected  to  the  metacarpal  bones,  but 

1'^  firmly  adherent  to   the  phalanges.      They   are   placed 

£  between  the  lateral  ligaments,  to  both  of  which  they  are 

I  in  each  case  connected.     Each  plate  is  grooved  on  the 

palmar  surface  for  the  long  flexor  tendons,  whilst  on  its 

reverse  or  joint  surface  it  supports  and  glides  upon  the 

head  of  the  metacarpal  bone  during  flexion  and  extension 

of  the  joint.     In  the  case  of  the  thumb  this  plate  of 

Fig.  228.— Metacarpo-phalan-  fibro-cartilage  usually  develops  to  sesamoid  bones,  and 

GEAL  AjiD  iNTERPHALANGEAL  jj^  thc  casc  of  thc  luclex  fiugcr  ouB  such  sesamoid  nodule 

'^"^'^"^■'^'  is  frequently  found  at  the  radial  side  of  the  plate. 

An  important  accessory  ligament  is  found  in  connexion  with  the  four  inner 

metacarpo-phalangeal  articulations,  viz.  : — 

The  Transverse  Metacarpal  Ligament. — This  structure  binds  together  the  distal 
extremities  of  the  four  inner  metacarpal  Ijones.  The  name  is  applied  to  three  sets 
of  transverse  fibres  of  great  strength  which  are  situated  in  front  of  the  three  inner 
interosseous  spaces.  These  fibres  are  continuous  with  the  palmar  metacarpo- 
phalangeal ligaments  at  their  lateral  margins. 

A  synovial  membrane  lines  the  investing  capsule  of  each  joint. 

INTERPHALANGEAL   JOINTS. 

Of  these  joints  there  are  two  for  each  finger  and  one  for  the  thumb.  They  all 
correspond,  in  being  gingiymus  diarthroses  in  which  the  trochlear  character  of  their 
articular  surfaces  is  associated  with  one  axis  of  movement  directed  transversely. 

In  their  general  arrangement  they  correspond  wdth  each  other,  and  to  a  large 
extent  with  the  metacarpo-phalangeal  series  already  described.     Each  is  provided 


•  ■ '  ,Cap.sule 


Lateral  ligament 


LUMBO-SACEAL  JOINTS.  289 

with  a  definite  capsule  (Fig.  228),  of  which  the  palmar  and  cord-like  lateral  portions 
are  well  marked,  while  on  the  dorsal  aspect  the  extensor  tendons  act  as  the  chief 
support.  The  palmar  ligaments  are  fibrous  plates  of  considerable  thickness,  and 
are  attached  to  the  two  lateral  ligaments  and  to  the  intervening  rough  surface  on 
the  distal  phalanges,  while  their  proximal  margins  are  not  attached  to  bone.  Each 
ligament  has  its  lateral  margins  prolonged  proximally  to  the  adjacent  sharply- 
defined  lateral  ridges  on  the  phalangeal  shafts. 

The  lateral  ligaments  (Fig.  228)  are  strong,  rounded,  short  bands,  continuous  with 
the  preceding,  and  attached  to  adjacent  non-articular  lateral  aspects  of  the  phalanges. 

Each  joint  possesses  a  synovial  membrane  which  lines  its  capsule,  but  its 
arrangement  presents  no  special  peculiarity. 

Movements  of  the  Cakpal,  Intermetacarpal,  Metacarpo-phalangeal 
AND  Interphalangeal  Joints. 

The  ainouut  of  movement  wliicli  is  possible  at  individual  joints  of  the  intercarpal,  inter- 
metacari^al,  and  carj^o-metacarpal  series  is  extremely  limited,  both  on  account  of  the  interlocking 
nature  of  the  articular  surfaces  and  the  restraining  character  of  the  ligamentous  bands.  Taken 
as  a  whole,  however,  the  movements  of  the  carpus  and  metacarpus  enable  the  hand  to  perform 
many  varied  and  important  functions.  This  is  largely  due  to  the  greater  mobility  of  those  joints 
on  the  radial  and  ulnar  borders  of  the  hand,  as  well  as  to  the  general  elasticity  of  the  arches 
formed  by  the  carpus  and  metacai'i^us.  These  conditions  jjarticularly  favour  the  movements  of 
ojj position  and  prehension.  In  the  opposite  direction,  i.e.  when  pressure  is  applied  from  the 
palmar  aspect,  the  metacarpal  and  carpal  arches  tend  to  become  flattened,  but  great  elasticity  is 
imparted  by  the  tension  of  the  various  ligaments. 

The  four  inner  metacarjjo-phalangeal  joints  are  ball-and-socket  joints,  and  movements  of 
palmar-flexion  and  extension  are  freely  performed  about  a  transverse  axis.  In  exceptional  cases 
a  certain  amount  of  dorsi-flexion  is  possible.  About  an  antero-jwsterior  axis  movements  occur 
which  are  usually  referred  to  the  middle  line  of  the  hand,  and  hence  called  abduction  and 
adduction,  but  in  consequence  of  the  difference  in  the  width  of  the  articular  surface  on  the  dorsal 
and  palmar  aspects  of  the  heads  of  the  four  inner  metacarpal  bones  it  is  only  j^ossible  to  obtain 
abduction  when  the  joints  are  extended,  while  in  the  flexed  position  the  joints  become  locked  and 
abduction  is  impossible. 

The  movements  of  the  index  finger  are  less  hampered  than  in  the  case  of  the  others,  but 
each  of  them  can  perform  a  modified  kind  of  circumduction. 

The  metacarjjo-phalangeal  joint  of  the  thumb  and  all  the  interphalangeal  joints  are  uniaxial 
or  hinge-joints  acting  about  a  transverse  axis,  which  permits  of  palmar-flexion  and  extension 
being  freely  performed,  but  dorsi-flexion  is,  as  a  rule,  entirely  prevented  by  the  j^almar  and  lateral 
ligaments. 

ARTICULATIONS   AND   LIGAMENTS   OF   THE   PELVIS. 

Although  we  may  consider  the  pelvis  as  a  separate  part  of  the  skeleton,  yet  it 
is  essential  to  remember  that  the  bones  which  enter  into  its  composition  belong  to 
the  spinal  column  (sacrum,  coccyx)  and  the  lower  limb  (innominate  bone).  Accord- 
ingly, the  articulations,  with  their  corresponding  ligaments,  may  be  arranged  as 
follows  : — 

(a)  Those  by  which  the  segments  of  the  coccyx  are  joined  together  (already 

described,  v.  p.  264) ; 
(h)  That  by  which  the  sacrum    articulates  with    the  coccyx    (already  de- 
scribed, V.  p.  264) ; 

(c)  Those  by  which  the  sacrum  articulates  with  the  last  lumbar  vertebra 

(Lumbo-sacral  joints) ; 

(d)  Those   by  which    the   innominate   bones   are   attached    to   the   spinal 

column  (Sacro-iliac  joints) ; 
{e)  That  by  which  the  innominate  bones  are  attached  to  each  other  (Sym- 
physis pubis). 

LUMBO-SACRAL  JOINTS. 

The    articulation   of   sacrum  with    the    fifth    lumbar    vertebra  is  constructed 

precisely  on  the  principle  of  the  articulations  between  two  typical  vertebrae,  and 

the  usual  ligaments  associated  with  such  joints  are  repeated.     There  is,  however,  an 

additional  accessory  ligament,  termed  the  lateral  lumbo-sacral  ligament  (Fig.  229). 

20 


290 


THE  AETICULATIONS  OK  JOINTS. 


This  extends  from  the  front  of  the  inferior  border  of  the  transverse  process  of  the 
last  lumbar  vertebra,  downwards  and  slightly  outwards,  to  the  front  of  the  lateral 
aspect  of  the  ala  of  the  sacrum,  close  to  the  sacro-iliac  joint.  Further,  a  variable 
membranous  band  extends  between  the  lateral  aspect  of  the  lower  part  of  the  body 
of  the  last  lumbar  vertebra  and  tlie  front  of  the  ala  of  the  sacrum.  This  band  lies 
in  front  of  the  auterior  primary  division  of  the  fifth  lumbar  nerve. 

SACRO-ILIAC  JOINT. 

Each  innominate  bone  articulates  with  the  sacral  section  of  the  spinal  column 
on  each  side  through  the  intervention  of  a  diarthrosis,  termed  the  sacro-iliac  joint 
(articulatio  sacro-iliaca). 

This  joint  is  formed  between  the  contiguous  auricular  surfaces  of  the  sacrum 
and  ihum.  Each  of  these  surfaces  is  more  or  less  completely  clothed  by  hyaline 
articular  cartilage.  The  joint  cavity,  which  is  little  more  than  a  capillary  interval, 
may  be  crossed  by  fibrous  bands. 

The  joint  cavity  is  surrounded  l)y  ligaments  of  varying  thickness  and  strength. 


Posterior  sacro-iliac 
ligament 


Sacrum 


[Great  sacro-sciatic 
foramen 


Small  sacro-sciatic  foramen 


Great  sacro- 
sciatic  ligament 


Inter-pubic  fibro-cartilage 


Fio.  229. — Coronal  Section  of  Pelvis. 


which  constitute  its  capsule.  Thus  the  anterior  part  of  the  investing  capsule  is 
thin,  and  consists  of  short  but  strong  fibres  which  pass  between  adjoining  surfaces 
on  the  ala  of  the  sacrum  and  the  iliac  fossa  of  the  innominate  bone ;  they  form  the 
anterior  sacro-iliac  ligament  (lig.  sacro-iliacum  aiiterius,  Fig.  229).  On  the  posterior 
aspect  there  are  two  ligtiments.  The  short  posterior  sacro-iliac  ligament  (lig.  sacro- 
iliacum  posterius  breve,  Fig.  230)  consists  of  numerous  strong  fasciculi,  which  pass 
from  the  rough  area  on  the  inner  aspect  of  the  ilium,  above  and  behind  its 
auricular  surface,  downwards  and  inwards  to  the  transverse  tubercles  and  the 
depressions  behind  the  first  and  second  segments  of  the  sacrum.  This  ligament 
is  of  great  strength,  and  with  its  fellow  it  is  respoMsit)le  for  suspending  the 
sacrum  and  the  weiti;lit  of  the  su])C!rim])Osed  trunk  from  the  innominate  bones. 

The    long  or  oblique  posterior  sacro-iliac  ligament    (lig.    sacro-iliacum  posterius 
longum,  Fig  230)  is  a   superficial  thickened  portion    of  the   preceding  ligament. 


SYMPHYSIS  PUBIS. 


291 


It  consists  of  a  definite  band  of  fibres  passing  from  tht*-  postero-superior  iliac  spine 
to  the  transverse  tubercles  of  the  third  and  fourth  segments  of  the  sacrum. 

The  synovial  cavity  of  this  joint  is  very  imperfect  and  rudimentary. 

Several  accessory  ligaments  are  associated  witli  the  articulati(in  of  the  in- 
nominate bone  to  the  sacral  section  of  the  spinal  column. 

The  ilio-lumbar  ligament  (lig.  ilio-lumbale,  Fig.  229),  which  is   merely    the 


■lumbar  liifaiiient 


Posterior  sacro-iliac 
ligament 


Long  or  oblique 
posterior  sacro-iliac 
ligament 


Reflected  head  of i ectus 


_  Great  sacro-sciatic 

tVjianieu 


Small  sacro-sciatic 

liL;ament 


Small  sacro-sciatic 
foramen 


Great  sacro-sciatic 
ligament 


^-Obturator  membrane 


Fig.  230. — Posterior  View  of  the  Pelvic  Ligajients  and  of  the  Hip-Joint. 


thickened  anterior  lamina  of  the  fascia  lumborum,  extends  from  the  tip  of  the 
transverse  process  of  the  last  lumbar  vertebra,  almost  horizontally  outwards,  to  the 
inner  lip  of  the  iliac  crest  at  a  point  a  short  distance  behind  its  highest  level. 
A  proportion  of  these  fibres  is  attached  to  the  inner  rough  surface  of  the  ilium 
between  the  iliac  crest  and  the  auricular  impression.  To  these  the  name  of  the 
lig.  ilio-lumbale  inferius  is  applied. 

The  great  or  posterior  sacro-sciatic  ligament  (lig.  sacro-tuberosum,  Fig.  230) 
is  somewhat  triangular  in  outline.  It  occupies  the  interval  between  the  sacrum 
and  the  innominate  bone,  and  is  attached  mesially  to  the  posterior  inferior  spine 
of  the  ilium ;  to  the  posterior  aspect  of  the  transverse  tubercles  and  lateral 
margins  of  the  third,  fourth,  and  fifth  segments  of  the  sacrum,  as  well  as  to  the 
side  of  the  first  segment  of  the  coccyx.  It  passes  downwards  and  outwards, 
becoming  narrower  as  it  approaches  the  ischium,  near  to  which,  however,  it  again 
expands,  to  be  attached  to  the  inner  side  of  the  ischial  tuberosity,  immediately 
below  the  groove  for  the  tendon  of  the  obturator  internus  muscle,  i.e.  the  lesser 
sciatic  notch.     A  continuation  of  the  inner  border  of  the  ligament — the  processus 


292  THE  ARTICULATIONS  OR  JOINTS. 

falciformis  (Fig.  230) — runs  upwards  and  forwards  on  the  inner  aspect  of  the 
ramus  of  the  ischium. 

The  great  sacro-sciatic  ligament  is  believed  by  many  to  represent  the  original 
or  proximal  end  of  the  long  or  ischial  head  of  the  biceps  flexor  cruris  muscle. 

The  si^iall  or  anterior  sacro-sciatic  ligament  (lig.  sacro-spinosum,  Figs.  229  and 
230)  is  situated  in  front,' and  in  a  measure  under  cover  of  the  great  sacro-sciatic 
ligament.  Triangular  in  form,  it  is  attached  by  its  base  to  the  last  two  segments  of 
the  sacrum  and  the  first  segment  of  the  coccyx,  and  by  its  pointed  apex  to  the  tip 
and  upper  aspect  of  the  ischial  spine.  This  ligament  is  intimately  associated 
with  the  coccygeus  muscle,  and  by  some  it  is  regarded  as  being  derived  from  it  by 
fibrous  transformation  of  the  muscle  fasciculi. 

By  the  great  and  small  sacro-sciatic  ligaments  the  two  sciatic  notches  of  the 
innominate  bone  are  converted  into  foramina.  Thus  the  small  sacro-sciatic  liga- 
ment completes  the  boundaries  of  the  great  sciatic  foramen  (foramen  ischiadicum 
majus) ;  while  the  great  sacro-sciatic  ligament,  assisted  by  the  small  sacro-sciatic 
ligament,  closes  the  small  sciatic  foramen  (foramen  ischiadicum  minus). 

SYMPHYSIS  PUBIS. 

The  anterior  wall  of  the  osseous  pelvis  is  completed  by  the  articulation  of  the 
bodies  of  the  two  pubic  bones  constituting  the  symphysis  pubis.  This  joint  con- 
forms in  its  construction  to  the  general  plan  of  an  amphiarthrosis.  Thus  it  is 
mesial  in  position ;  each,  pubic  bone  is  covered  by  a  layer  of  hyaline  cartilage, 
which  closely  adapts  itself  to  the  rough  tuberculated  surface  of  the  pubic  bone  ; 
while  between  these  two  hyaline  plates  there  is  an  interposed  fibro-cartilage 
(lamina  fibro-cartilaginea  interpubica),  in  the  interior  of  which  there  is  usually 
a  vertical  antero-posterior  cleft.  This  cavity,  which  is  placed  nearer  the  posterior 
than  the  anterior  aspect  of  the  joint,  does  not  appear  until  between  the  seventh 
and  tenth  years,  and  as  it  is  not  lined  by  a  synovial  membrane,  it  is  supposed  to 
result  from  the  breaking  down  of  the  interpubic  lamina. 

The  anterior  pubic  ligament  (lig.  pubioum  anterius.  Fig.  229)  is  a  structure  of 
considerable  thickness  and  strength.  Its  superficial  fibres,  which  are  derived  very 
largely  from  the  tendons  and  aponeuroses  of  adjoining  muscles,  are  oblique,  and 
form  an  interlaced  decussation.  The  deeper  fibres  are  short,  and  extend  trans- 
versely from  one  pubic  bone  to  the  other. 

The  posterior  pubic  ligament  (lig.  pubicum  posterius.  Fig.  230)  is  very  weak, 
and  consists  of  scattered  fibres  which  extend  transversely  between  contiguous 
j)ubic  surfaces  posterior  to  the  articulation. 

The  superior  pubic  ligament  (lig.  pubicum  superius,  Fig.  229)  is  likewise  weak, 
and  consists  of  transverse  fibres  passing  between  the  two  pubic  crests. 

The  inferior  or  subpubic  ligament  (lig.  pubicum  inferius  vel  lig.  arcuatum  pubis. 
Fig.  230)  occupies  the  arch  of  the  pubis,  and  is  of  considerable  jstrength.  It  gives 
roundness  to  the  pubic  arch  and  forms  part  of  the  pelvic  outlet.  It  liks  con- 
siderable vertical  thickness  immediately  below  the  interpubic  disc  to  which  it  is 
attached.  Laterally  it  is  attached  to  adjacent  sides  of  the  descending  rami  of  the 
pubis.  Its  lower  border  is  free,  and  separated  from  the  triangular  hgament  of 
the  perineum  by  a  transverse  oval  interval  through  which  the  dorsal  vein  of  the 
penis  passes  backwards  to  the  interior  of  the  pelvis. 

The  Triangular  Ligament  of  the  Perineum. 

The  triangular  ligament  of  the  perineum  is  a  membranous  structure  which 
occupies  the  X"ihic  arch  jjelow  and  distinct  from  the  subpubic  ligament.  It  assists 
in  completing  the  pelvic  walls  anteriorly  in  the  same  manner  that  the  obturator 
membrane  does  laterally.  Indeed,  these  two  structures  occupy  the  same  mor- 
phological plane.  The  triangular  ligament  presents  two  surfaces — one  superficial 
or  perineal ;  the  other  deep,  or  pelvic,  and  both  of  these  surfaces  are  associated 
with  muscles.  Its  lateral  borders  are  attached  to  the  sides  of  the  pubio  arch, 
while  its  base  is  somewhat  ill-defined,  by  reason  of  its  fusion  with  the  fascia  of 
Colles  in  the  urethral  region  of  the  perineum. 


HIP-JOINT.  293 

The  apex  of  the  triangular  ligament  is  truncated,  free,  and  well  defined,  constitut- 
ing the  transverse  perineal  ligament,  above  which  there  is  the  interval  for  the  dorsal 
vein  of  the  penis.  It  is  pierced  hy  a  number  of  vessels  and  nerves,  but  the 
principal  opening  is  situated  mesially  one  inch  below  the  pubic  arch,  and  transmits 
the  urethra.  0 

The  Obturatoe  Membrane. 

The  obturator  membrane  (membrana  obturatoria.  Fig.  232)  occupies  the 
obturator  or  thyroid  foramen.  It  is  attached  to  the  pelvic  aspect  of  the 
circumference  of  this  foramen.  It  consists  of  fibres  irregularly  arranged  and  of 
varying  strength,  so  that  sometimes  it  almost  appears  fenestrated.  At  the  highest 
part  of  the  foramen  it  is  incomplete  and  forms  a  U-shaped  border,  between  which 
and  the  bony  circumference  of  the  foramen,  the  obturator  canal  (canalis  obtura- 
torius)  is  formed.  In  this  position  the  membrane  is  continuous  with  the  parietal 
pelvic  fascia  which  clothes  the  inner  side  of  the  obturator  internus  muscle,  above 
the  upper  free  margin  of  the  muscle.  From  the  outer  or  crural  aspect  of  the 
membrane  some  of  its  fibres  are  prolonged  to  the  antero-inferior  aspect  of  the 
capsule  of  the  hip-joint. 

Mechanism  and  Movements  of  the  Pelvis. — The  liuman  pelvis  i^resents  a  meclianism  the 
principal  reqmrement  of  ^yhich  is  stability  and  not  movement,  for,  through  the  pelvis,  the  weight 
of  the  trunk,  superimposed  upon  the  sacrum,  is  transmitted  to  the  lower  limbs.  Moreover,  its 
stability  is  largely  concerned  in  the  maintenance  of  the  erect  attitude.  The  movements  of  its 
various  parts  are  therefore  merely  such  as  are  consistent  with  stability,  without  producing  absolute 
rigidity. 

The  two  innominate  bones,  being  bound  together  by  powerful  ligaments  at  the  pubic  articula- 
tion, constitute  an  inverted  arch,  of  which  the  convexity  is  directed  downwards  and  forwards, 
while  its  piers  are  turned  upwards  and  backwards,  and  considerably  expanded  in  relation  to  the 
hinder  parts  of  the  ihac  bones.  Between  the  piers  of  this  inverted  arch  the  sacrum  is  situated. 
This  bone  is  in  no  sense  a  key-stone  to  an  arch,  because,  as  may  readily  be  seen  in  antero-posterior 
transverse  section,  the  sacrum  is  wider  in  front  than  behind,  and  the  superposed  weight  naturally 
tends  to  make  the  sacrum  fall  towards  the  pelvic  cavity,  and  so  fit  less  closely  between  the 
innominate  bones.  The  sacrum  is  in  reality  an  oblique  platform,  in  contact  with  each  innominate 
bone  through  its  articular  auricular  surfaces,  and  in  this  position  it  is  suspended  by  the  posterior 
sacro-iliac  ligaments,  and  kept  securely  in  place  by  the  "  grip  "  due  to  the  irregularity  of  the 
opposed  surfaces  of  the  two  sacro-iliac  articivlations.  Since  the  weight  of  the  trunk  is  trans- 
mitted to  the  anterior  and  upper  end  of  this  sacral  platform,  there  is  a  natural  tendency  for  the 
sacrum  to  revolve  ujjon  the  transverse  axis  which  j^asses  through  its  sacro-iliac  joints.  If  this 
wei'e  permitted,  the  promontory  of  the  sacrum  would  rotate  do^vnwards  and  forwards  towards 
the  pelvic  cavity,  as  really  does  occiu'  in  certain  deformities.  This  revolution  or  tilting  down- 
wards of  the  forepart  of  the  sacrum  is  prevented  by  the  action  of  the  great  and  small  sacro- 
sciatic  ligaments,  extending  from  the  ischial  tuberosity  to  the  hinder  and  lower  end  of  the 
suspended  platform  of  the  sacrum.  Not  only  so,  but  these  ligaments,  acting  on  a  rigid  sacrum, 
tend  to  hold  up  the  weight  upon  the  sacral  promontory. 

The  various  ligaments  passing  between  the  last  lumbar  vertebra  and  the  sacrum  and  ilium 
retain  the  weight  of  the  trunk  in  position  upon  the  anterior  end  of  the  sacrum,  and  resist  its 
tendency  to  slip  forwards  and  downwards  towards  the  pelvic  cavity.  The  entire  weight  of  the 
trunk  and.  pelvis  is  transmitted  to  the  heads  of  the  thigh  bones  in  the  most  advantageous 
position,  both  for  effectiveness  and  the  strengthening  of  the  inverted  innominate  arch,  for  it  will 
be  evident  that  the  heads  of  the  femora  thrust  inwards  upon  the  convex  side  of  the  az'ch,  very 
much  at  the  place  where  the  arches  are  weakest,  viz.  at  the  sj) ringing  of  the  arch  from  its  piers. 
The  forces  which  tend  to  cause  movement  of  the  pelvic  bones  during  parturition  act  from  within 
the  pelvis,  and  have  for  their  object  the  increase  of  the  various  i^elvic  diameters,  in  order  that 
the  foetal  head  may  more  readily  be  transmitted.  For  this  purpose  the  wedge-like  dorsal  surface 
of  the  sacrum  is  driven  backwards,  and  a  certain  amount  of  extra  space  may  thereby  be  obtained. 
An  important  factor,  however,  in  the  increase  of  the  pelvic  capacity  at  this  peiiod  is  found  in 
the  relaxation  of  its  various  ligaments. 

THE   ARTICULATIONS   OF   THE   LOAVER  EXTREMITY. 

THE   HIP-JOINT. 

The  human  body  provides  no  more  perfect  example  of  an  enarthrodial  diarthrosis 
than  the  hip-joint  (articulatio  coxse).  Combined  with  all  that  variety  of  movement 
which  characterises  a  multi-axial  joint,  it  nevertheless  presents  great  stability,  which 
has  been  obtained  by  simple  arrangements,  for  restricting  the  range  of  its  natural 


294 


THE  AETICULATIONS  OE  JOINTS. 


Ischial  spine 


movements.  This  stability  is  of  paramount  importance  for  the  maintenance  of  the 
erect  attitude,  and  the  mechanical  adaptations  whereby  this  result  is  obtained  are 
such  that  the  erect  attitude  may  be  preserved  without  any  great  degree  of  sustained 
muscular  effort. 

Articular  Surfaces. — The  head  of  the  femur  is  globular  in  shape,  and  consider- 
ably exceeds  a  hemisphere.     It  is  clothed  by  hyaline  articular  cartilage  on  those 

parts  which  come  into  direct 
contact  with  the  acetabulum. 
There  is  frequently  more  or 
less  of  extension  of  the 
articular  cartilage  from  the 
head  to  the  adjoining  anterior 
part  of  the  neck,  an  extension 
which  is  accounted  for  by  the 
close  and  constant  apposition 
of  this  portion  of  the  neck 
with  the  hinder  aspect  of 
the  ilio  -  femoral  ligament. 
The  limit  of  the  articular 
cartilage  covering  the  head 
is  indicated  by  a  sinuous 
border.  Further,  there  is  an 
absence  of  articular  cartilage 
from  the  pit  or  depression 
on  the  head  of  the  femur. 

The  acetabulum  is  a  deep 
cup-shaped  cavity  which  pre- 
sents an  interruption  or  notch 
on  its  antero-inferior  margin. 
The  interior  of  the  cup  is 
lined  by  a  ribbon -like  band 
of  articular  cartilage  which 
extends  to  the  brim  of  the 
cavity,  but  does  not  cover  the 
floor  of  the  cup.  This  ar- 
ticular ribbon  -  shaped  band 
is  widest  on  its  supero-posterior  aspect,  and  narrowest  at  the  anterior  margin  of 
the  notch. 

The  transverse  ligament  (lig.  transversum  acetabuli,  Fig.  231)  bridges  the  ace- 
tabular notch,  and  consists  of  strong  transverse  fibres  which  are  attached  to  both 
of  its  margins,  but  more  extensively  to  the  postero-inferior.  This  ligament  does 
not  entirely  fill  the  notch,  but  leaves  an  open  interval  between  its  lower  border  and 
the  bottom  of  the  notch  through  which  vessels  and  nerves  enter  the  cup.  The 
acetabular  aspect  of  this  ligament  constitutes  an  articular  surface. 

The  acetabulum  is  deepened  by  the  cotyloid  ligament  (labrum  glenoidale,  Figs. 
231  and  232),  which  consists  of  a  strong  ring  of  fibro-cartilaginous  tissue  attached 
to  the  entire  rim  of  the  cup.  The  attached  surface  of  the  ring  is  broader  than  its 
free  edge,  and,  moreover,  the  latter  is  somewhat  contracted,  so  that  the  ligament 
grasps  the  head  of  the  femur  which  it  encircles.  Its  fibres  are  partly  oblique  and 
partly  circular  in  their  direction.  By  the  former  it  is  firmly  implanted  on  the  rim 
of  the  acetabulum  and  the  transverse  ligament  of  the  notch ;  by  the  latter  the 
depth  of  the  cup  is  increased  through  the  elevation  of  its  edge,  and  its  mouth 
slightly  narrowed.     By  one  surface  this  ligament  is  also  articular. 

A  capsule  (capsula  articularis.  Figs.  230  and  232)  completely  invests  the  joint 
cavity.  This  is  a  fibrous  membrane  of  great  strength,  although  it  is  not  of  equal 
thickness  throughout,  being  considerably  thicker  on  the  supero-anterior  aspect  than 
at  any  other  part.  Unlike  the  corresponding  structure  of  the  shoulder-joint,  it  does 
not  permit  of  the  withdrawal  of  the  head  of  the  femur  from  contact  with  the  aceta- 
Vjular  articular  surfaces,  except  to  a  very  limited  extent.     Its  fibres  are  arranged 


Transverse  acetabular  ligament 

Retinacula 


Fig.  231. — Dissection  of  the  Hip-Joint. 

Bottom  of  the  acetabulum  removed,  and  capsule  of  the  joiut  thrown 
outwards  towards  the  trochanters. 


HIP-JOINT.  295 

both  in  the  circular  and  in  the  longitudinal  direction,  the  former,  known  as  the 
zona  orbicularis,  beiug  best  marked  posteriorly,  while  the  longitudinal  fibres  stand 
out  more  distinctly  in  front,  where  they  constitute  special  ligaments.  Looked  at 
as  a  whole,  the  capsule  has  the  following  attachments :  superiorly  it  surrounds 
the  acetabulum,  on  the  upper  and  hinder  aspects  of  which  it  is  attached  directly 
to  the  innominate  bone,  while  on  the  front  and  lower  aspects  it  is  attached  to  the 
non- articular  surfaces  of  the  cotyloid  and  transverse  ligaments ;  inferiorly  it 
encircles  the  neck  of  the  fenmr,  where  it  is  attached  in  front  to  the  anterior  inter- 
trochanteric line ;  above,  to  the  inner  aspect  of  the  root  of  the  great  trochanter ; 
below,  to  the  lower  part  of  the  neck  of  the  femur,  in  close  proxindty  to  the  small 
trochanter ;  behind,  to  the  line  of  junction  of  the  outer  and  middle  thirds  of  the 
neck  of  the  femur.  It  is  a  matter  of  some  importance  to  note  that  only  part 
of  the  posterior  surface  of  the  neck  of  the  femur  is  enclosed  within  the  capsule. 
The  femoral  attachments  of  the  capsule  vary  considerably  in  their  strength,  ^being 
particularly  firm  above  and  in  front,  but  much  weaker  below  and  behind,  where 
the  orbicular  fibres  are  well  seen.  Many  fibres  of  the  capsule  are  reflected  from 
its  deep  aspect  upwards  upon  the  neck  of  the  femur,  where  they  form  ridges,  and 
to  these  the  term  rectinacula  (Fig.  231)  is  applied. 

The  longitudinal  fibres  of  the  capsule  are  arranged  so  as  to  form  certain  definite 
bands,  viz : — 

(1)  The  ilio-femoral  ligament  (Kg.  ilio-femorale,  Fig.  232)  consists  of  a  triangular 
set  of  fibres  attached  above,  by  their  apex,  to  the  lower  part  of  the  anterior  inferior 
iliac  spine  and  the  immediately  adjoining  part  of  the  rim  of  the  acetabulum,  and 
below,  by  their  base,  to  the  anterior  intertrochanteric  line  of  the  femur.  This 
ligament  is  the  thickest  part  of  the  capsule,  but  its  sides  are  more  pronounced  than 
its  centre,  especially  towards  its  base.  Consequently  the  ilio-femoral  band  presents 
some  resemblance  to  an  inverted  Y  (A),  and  therefore  it  is  very  generally  known 
as  the  Y-shaped  ligament  of  Bigelow. 

The  outer  or  upper  limb  of  tlie  ilio-femoral  ligament  maj"  be  somewhat  extended  by  the 
inclusion  of  additional  longitudinal  fibres,  and  described  as  the  ilio-trochanteric  ligament  (lig. 
ilio-trochantericum}.  This  band  arises  from  the  anterior  part  of  the  dorsum  of  the  acetabulum, 
and  extends  to  the  femoral  neck,  close  to  the  anterior  end  of  the  inner  surface  of  the  great 
trochanter. 

(2)  The  pubo-femoral  or  pubo-capsular  ligament  (lig.  pubo-femorale  v.  pubo- 
capsulare.  Fig.  232)  is  composed  of  some  bands  of  fibres  of  no  great  strength, 
which  extend  from  the  outer  end  of  the  horizontal  ramus  of  the  pubis,  the  ilio- 
pectineal  eminence,  the  obturator  crest  and  the  obturator  membrane,-  to  lose  them- 
selves for  the  most  part  in  the  capsule,  although  a  certain  proportion  of  them  may 
be  traced  to  the  inferior  aspect  of  the  femoral  neck,  where  they  adjoin  the  lower 
attachment  of  the  Y-shaped  ligament. 

(3)  The  iscMo-capsular  ligament  (lig.  ischio-capsulare.  Fig.  230)  consists  of  a  broad 
band  of  short,  fairly  strong  longitudinal  fibres,  which,  by  their  upper  ends,  are 
attached  to  the  ischium  between  the  small  sciatic  notch  and  the  obturator  foramen, 
while  their  lower  ends  become  merged  in  the  zona  orbicularis  of  the  general  capsule. 

Within  the  capsule,  and  quite  distinct  from  it,  there  are  the  ligamentum  teres 
and  the  Haversian  gland. 

The  inter  articular  ligament  (lig.  teres  femoris.  Fig.  231)  is  a  strong,  somewhat 
flattened  band  of  fibrous  tissue,  attached  by  one  end  to  the  upper  half  of  the  pit 
or  depression  on  the  head  of  the  femur.  By  its  inner  end  it  is  attached  to  the 
lower  edge  of  the  articular  surface  of  the  transverse  ligament,  with  extensions  to 
the  opposite  borders  of  the  acetabular  notch,  but  chiefly  to  the  hinder  or  ischial 
border.  This  ligament  varies  very  greatly  in  its  strength  and  development  in 
different  subjects,  and  in  certain  rare  cases  it  is  absent. 

The  so-called  Haversian  gland  occupies  the  bottom  or  non-articular  area  of  the 
acetabulum.  It  consists  of  a  mass  of  fat  covered  by  synovial  membrane.  This 
pad  of  fat  is  continuous  with  the  extra-capsular  fat  through  the  passage  subjacent 
to  the  transverse  ligament  of  the  notch. 

A  synovial  membrane  lines  the  capsule  from  which  it  is  reflected  to  the  neck  of 
the   femur  along   a   line  which  corresponds  to  the  femoral  attachments  of  the 


296 


THE  AETICULATIONS  OE  JOINTS. 


Anterior  infei  loi 
iliac  spine 


Cotyloid  ligament 


Head  of  femur 


capsule.     Thus  the  synovial  membrane  clothes  more  of  the  femoral  neck  anteriorly 
than  in  any  other  position.     Posteriorly,  where  the  capsule  is  feebly  attached  to 

the  neck  of  the  femur, 
the  synovial  mem- 
brane may  be  seen 
from  the  outside  of 
the  capsule.  The 
synovial  membrane 
extends  close  up  to 
the  articular  margin 
of  the  head  of  the 
femur,  and  on  the 
upper  and  lower  as- 
pects of  the  neck  it 
in  gathered  into  loose 
folds  upon  the  re- 
tinacula.  These  folds 
or  plications  are  best 
marked  along  the 
line  of  synovial  re- 
flection, and  do  not 
reach  as  far  as  the 
femoral  head.  At  its 
acetabular  end  the 
synovial  membrane 
is  prolonged  from  the 
inside  of  the  capsule 
to  the  outer  non- 
articular  surface  of 
the  cotyloid  and 
transverse  liga- 
ments, upon  which  it  is  continued  as  a. lining  for  their  acetabular  or  ^'ticular 
surfaces,  and  further,  it  provides  a  covering  for  the  fat  at  the  bo^m  of  the 
acetabular  fossa,  as  well  as  a  complete  tubular  investment  for  the  ligamentum  teres. 
Occasionally  the  synovial  bursa,  which  is  subjacent  to  the  tendon  of  the  ilio- 
psoas muscle,  communicates  with  the  interior  of  the  hip-joint  through  an  opening 
in  the  anterior  wall  of  the  capsule  (Fig.  232),  situated  between  the  pubo-femoral 
ligament  and  the  inner  or  lower  limb  of  the  iUo-femoral  ligament. 

Movements  at  the  Hip-Joint. — Tlie  movements  whicli  occur  at  the  liip-joint  are  those  of 
a  multiaxial  joint.  These  are  flexion,  extension,  abduction,  adduction,  rotation,  and  circumduction. 
The  range  of  each  of  these  movements  is  less  extensive  than  in  the  case  of  the  shoulder -joint,  be- 
cause, at  the  hip,  the  freedom  of  movement  is  subordinated  to  that  stability  which  is  essential  alike 
for  the  maintenance  of  the  erect  attitude  and  for  locomotion.  When  standing  at  rest  in  the  erect 
attitude  the  hip-joint  occujiies  the  position  of  extension,  and  as  the  weight  of  the  trunk  is  trans- 
mitted in  a  perpendicular  which  falls  behind  the  centres  of  the  hii^-joints,  both  the  erect  attitude 
and  the  extended  position  are  maintained  to  a  large  extent  mechanically,  without  sustained  mus- 
cular action,  by  means  of  the  tension  of  the  ilio-femoral  ligament.  Moreover,  the  tension  of  this 
ligament  is  sustained  by  the  pressure  of  the  front  of  the  head  and  neck  of  the  femur  against  its 
synovial  surface.  In  this  association  of  parts  it  is  important  to  note  that  the  articular  cartilage 
of  tlie  f(;moral  head  may  l)e,  and  in  certain  races  is,  prolouged  to  the  front  of  the  femoral  neck  ; 
and  further,  that  the  constant  friction  does  not  destroy  tlie  synovial  lining  of  the  capsule. 
Again,.the  same  mechanism  which  preserves  the  erect  attitude  ])revents  an  excessive  degree  of 
extension  or  dorsiflexion.  In  movement  forwards,  i.e.  ventral  flexion,  the  front  of  the  thigh 
is  approximated  to  the  anterior  abdominal  wall.  The  amount  of  this  movement  depends  upon 
the  position  of  the  knee-joint,  because  when  the  latter  is  flexed  the  thigh  may  be  brought  into 
contact  with  the  abdominal  wall,  whereas  when  the  knee-joint  is  straightened  {i.e.  extended) 
the  tension  of  the  hamstring  muscles  greatly  restricts  the  amount  of  flexion  at  the  hip-joint. 
Abduction  and  adduction  are  likewise  much  more  restricted  than  at  the  shoulder-joint.  Abduc- 
tion is  lirouglit  to  a  close  by  the  tension  of  the  pubo-femoral  band  and  the  lower  part  of  the 
capsule,  and,  in  addition,  the  upper  aspect  of  the  neck  of  the  femur  locks  against  the  margin 
of  the  acetabulum.  Excessive  adduction  is  prevented  by  the  tension  of  the  upper  band  of  the 
ilio-femoral  ligament  and  the  upper  part  of  the  capsule.  Rotation  or  movement  in  a  longi- 
tudinal axis  may  be  either  inwards,  i.e.  towards  the  front,  or  outwards,  i.e.  toward  the  hack. 


Fig.  282. — Dissection  of  the  Hip- Joint  fkom  the  front. 


THE  KNEE-JOINT.  297 

In  the  former  the  movement  is  brought  to  a  close  by  the  tension  of  the  ischio-capsular  ligament 
and  Ijack  part  of  the  capsule,  aided  by  the  muscles  on  the  back  of  the  joint ;  in  the  latter — 
rotation  outwards — the  chief  restraining  factor  is  the  outer  or  upper  limb  of  the  ilio-femoral 
ligament.     The  total  amount  of  rotation  is  probably  less  than  60°. 

Circumduction  is  only  slightly  less  free  than  at  the  shoulder,  but  it  is  complicated  by  the 
preservation  of  the  balance  upon  one  foot. 

The  value  and  influence  of  the  ligamentum  teres  are  not  easily  estimated,  because  it  may  be 
absent  without  causing  any  known  interference  with  the  usefulness  of  the  joint.  In  the  erect  attitude 
this  ligament  lies  lax  between  the  lower  part  of  the  femoral  head  and  the  acetabular  fat.  In  the 
act  of  walking  it  is  rendered  tense  at  the  moment  when  the  pelvis  is  balanced  on  the  summit  of  the 
supporting  femur.  Analysis  of  this  position  shows  the  femur  to  be  adducted,  with  probably,  in 
addition,  a  small  amount  of  flexion  {i.e.  bending  forwards)  and  internal  rotation.  Again,  this 
ligament  is  said  to  be  tense  when  the  thigh  is  rotated  outwards.  The  equivalent  of  this 
movement  is  doubtless  found  in  the  rotation  of  the  jaelvis,  which  occurs  in  the  act  of  walking 
at  the  moment  of  transition  from  the  toe  of  the  supporting  foot  to  the  heel  of  the  advancing 
foot.  The  interest  connected  with  this  ligament  is  ^jerhaps  morphological  rather  than  physio- 
logical It  is  believed  by  some  to  represent  the  tendon  of  a  muscle  which  in  birds  occuijies  a 
position  external  to  the  joint  capsule. 

THE  KNEE-JOINT. 

The  knee-joint  (articulatio  genu)  is  the  largest  articulation  in  the  body,  and 
its  structure  is  of  a  very  elaborate  nature.  The  part  it  plays  in  maintaining  the 
erect  attitude  materially  influences  its  construction,  and  special  arrangements  are 
provided  for  the  mechanical  retention  of  the  joint  in  the  extended  position,  in  view 
of  the  fact  that  the  line  of  gravity  falls  in  front  of  the  centre  of  the  articulation. 
Its  principal  axis  of  movement  is  in  the  transverse  direction,  consequently  it  Ijelongs 
to  the  ginglymus  or  hinge  variety  of  the  diarthroses.  At  the  same  time  a  sHght 
amount  of  rotation  of  the  tibia  in  its  long  axis  is  permitted  during  extreme  flexion  ; 
but  while  this  fact  is  of  considerable  importance  in  the  study  of  certain  accidents 
to  which  the  joint  is  liable,  as  well  as  in  the  study  of  its  comparative  morphology,  it 
is  not  sufficiently  pronounced  to  interfere  with  its  classification  as  a  hinge-joint. 

Articular  surfaces  pertaining  to  the  femur,  tibia,  and  patella,  enter  into  the 
formation  of  the  knee-joint.  The  articular  surface  of  the  femur  extends  over  a 
large  part  of  both  condyles,  and  may  be  divided  into  patellar  and  tibial  portions 
by  fain tly^- marked,  almost  transverse  grooves,  which  pass  across  the  articular 
surface  immediately  in  front  of  the  intercondylar  notch.  As  a  rule  marginal 
indentations  of  the  articular  surface  render  the  positions  of  these  transverse 
grooves  more  distinct. 

The  patellar  portion  (Fig.  233)  is  situated  anteriorly,  and  is  common  to  both 
condyles,  although  developed  to  a  larger  extent  in  association  with  the  outer  condyle, 
on  which  it  ascends  to  a  higher  level  than  on  the  inner  condyle.  This  surface  is 
trochlear,  and  forms  a  vertical  groove  bordered  by  prominent  lateral  borders. 

The  tibial  portion  of  the  articular  surface  of  the  femur  is  divided  into  two 
articular  areas,  in  relation  to  the  inferior  aspects  of  the  two  condyles,  by  the  wide 
non- articular  intercondyloid  notch.  These  two  surfaces  are  for  the  most  part 
parallel,  but  in  front  the  internal  tibial  surface  turns  obliquely  outwards  as  it 
passes  into  continuity  with  the  patellar  trochlea,  while  posteriorly,  under  certain 
circumstances,  e.g.  the  squatting  posture,  the  articular  surface  of  the  inner  condyle 
may  extend  to  the  adjoiniug  portion  of  the  popliteal  area  of  the  bone. 

When  the  joint  is  in  the  position  of  extreme  flexion,  the  patella  is  brought  into 
direct  contact  with  that  part  of  the  articular  surface  on  the  inner  condyle  which 
bounds  the  intercondyloid  notch  upon  its  inner  and  anterior  aspects.  This  relation- 
ship is  indicated  by  the  presence  of  a  distinct  semilunar  facet  on  the  cartilage  in 
that  situation  (Eig.  233).  The  articular  surface  of  the  femur  may  therefore  be 
regarded  as  presenting  femoro-patellar  and  femoro -tibial  areas. 

The  patella  presents  on  its  posterior  aspect  a  transversely  -  elongated  oval 
articular  facet  and  an  inferior  rough,  triangular,  non-articular  area.  The  articular 
facet  is  divided  into  two  principal  lateral  portions  by  a  prominent  rounded  vertical 
ridge.  Of  these  the  outer  is  the  wider.  A  less  pronounced  and  nearly  vertical 
ridge  marks  off  an  additional  facet  called  the  internal  perpendicular  facet,  close  to 
the  inner  margin  of  the  articular  surface.     Two  faint  transverse  ridses  cut  off 


298 


THE  AETICULATIONS  OR  JOINTS. 


narrow  upper  and  lower  facets  from  the  general  articular  surface  without  encroach- 
ing on  the  narrow  innermost  vertical  facet  (Goodsir)  (Fig.  233). 

The  head  of  the  tibia  presents  on  its  superior  aspect  two  condylar  articular 
surfaces,  separated  from  each  other  by  a  non-articular  antero-posterior  area,  which 
is  wider  in  front  and  behind  than  in  the  middle,  where  it  is  elevated  to  form  a 
bifid  tibial  spine. 

The  external  condylar  facet  is  slightly  concavo-convex  from  before  backwards, 
and  slightly  concave  transversely.  This  surface  is  almost  circular,  and  extends 
to  the  free  external  border  of  the  tibial  head,  where  it  is  somewhat  flattened. 
Posteriorly  the  articular  surface  is  prolonged  downwards  on  the  tuberosity  in 
relation  to  the  position  occupied  by  the  tendon  of  the  popliteus  muscle.      The 


P  itellar  surface  of  femur 


Impression  of  external  semi- 
lunar cartilage 


External  tibial  surface  of 

femur  — 


External  lateral  ligament 


Cut  tendon  of  biceps  flexor 
cruris  muscle 

Anterior  superior  tibio-fibular 
ligament 

External  lateral  ligament 


opening  in  interosseous 

membrane  for  anterior  tibial 

vessels 


Semilunar  facet  for  patella 


Internal  tibial  surface  of 
femur 


Posterior  crucial  ligament 


Anterior  crucial  ligament 

Transverse  ligament 
Internal  semilunar  ttbi'o- 
cartilage 


Internal  lateral  ligament 


Ligamentum  patellee 


Inner  perpendicular  facet  on 
patella 


Fig.  233. — Dissection  of  the  Knee- Joint  fkom  the  front  :  Patella  thrown  down. 

internal  condylar  facet  is  oval  in  outline,  and  distinctly  concave  both  in  its  antero- 
posterior and  transverse  diameters. 

Ligaments. — Like  all  diarthroses,  this  joint  is  invested  by  an  envelope  or 
capsule  (capsula  articularis),  which  does  not,  however,  entirely  surround  the  joint 
cavity,  for  it  is  aljsent  as  a  fibrous  membrane  above  the  joint  cavity,  subjacent  to 
the  tendon  of  the  quadriceps  extensor  muscle.  Its  specially  named  bands  are  not 
of  themselves  sufficient  to  form  a  complete  investment,  and  a  capsular  membrane, 
which  largely  consists  of  augmentations  from  the  fascia  lata  and  the  t^endons  of 
surrounding  muscles,  supplies  the  defective  areas.  Thus,  anteriorly,  on  each  side 
of  the  patella  and  the  ligamentum  patellar,  expansions  of  the  vasti  tendons  and 
fascia  lata,  constituting  lateral  patellar  ligaments,  are  evident.  On  the  outer  side  of 
the  joint  the  external  lateral  ligament  is  hidden  within  a  covering  derived  from 
the  ilio-tibial  band  of  the  fascia  lata.  On  the  inner  side  expansions  from  the 
tendons  of  the  sartorius  and  semi-membranosus  muscles  augment  the  capsule,  which 
here  becomes  continuous  with  the  internal  lateral  ligament.  Posteriorly  the  capsule 
also  receives  augmentation  from  the  tendon  of  the  semi-membranosus  muscle,  but 
it  is  very  thin  subjacent  to  the  origins  of  the  gastrocnemius  muscle,  where  it  covers 
the  hinder  parts  of  the  condyles.  Not  unfrequently  the  capsule  presents  an 
opening  of  communication  between  the  interior  of  the  joint  cavity  and  a  bursa 
which  lies  under  cover  of  the  inner  head  of  the  gastrocnemius  muscle. 


THE  KNEE-JOINT. 


299 


The  anterior  ligament  (lig.  ijatellis,  Fig.  233),  also  called  the  ligamentum 
patellge,  is  a  powerful  flattened  band,  attached  superiorly  to  the  apex  and  adjoining 
margins  of  the  patella,  and  interiorly  to  the  rough  anterior  tuberosity  at  the  upper 
end  of  the  shaft  of  the  tibia.  This  Hgament  also  serves  as  a  tendon  of  insertion  for 
the  quadriceps  extensor  muscle,  and  a  certain  number  of  the  filjres  of  the  tendon 
may  be  observed  to  descend  as  a  thin  fibrous  covering  for  the  anterior  surface  of 
the"^  patella.  The  deep  surface  of  the  tendon  is  separated  from  the  front  of  the  head 
of  the  tibia  by  a  synovial  bursa,  and  above  this  it  rests  upon  the  infrapatellar  pad 
of  fat,  which  is  placed  between  the  tendon  and  the  synovial  membrane  of  the  joint. 

The  posterior  ligament  (Fig.  234)  is  a  compound  structure  of  unequal  strength, 


Tendon  of  adductor  luaguus  muscle  (cut) 


Inner  head  of  gastrocuemms 

Posterior  ligament  or  ligament 
of  ■Winslo^\ 

Bursa  beneath  tendon  of 
semi-membrau 


Popliteal  surface  of  femur 


Plantaris  muscle  (cut) 


Tendon  of  semi-membiranosus 
muscle  (cut) 


Posterior  ligament 

(oblique  slip) 

Internal  lateral  ligament- 


Outer  head  of  gastro- 
cnemius muscle  (cut) 


Long  external  lateral 
ligament 


Short  external  lateral 

ligament 

Popliteus  muscle  (cut) 


Biceps  flexor 
"cruris  muscle  (cut) 


Head  of  iibula 


Popliteal  surface  of  tibia 


Popliteal  fa-,cia — ^■ 
Popliteus  muscle  (cut) 


Fig.  234. — The  Kxee-Joixt.     Posterior  View. 

and  those  portions  by  which  it  establishes  continuity  with  the  lateral  parts  of  the 
capsule  are  remarkably  thin.     It  is  attached  superiorly  to  the  popKteal  surface  of 
the  femur,  close  to  the  intercondyloid  notch,  with  lateral  extensions  to  the  non 
articular  areas  immediately  above  the  posterior  articular  margins  of  the  two  con- 
dyles, where  it  is  closely  associated  with  the  origins  of  the  gastrocnemius  muscle. 

Inferiorly  it  is  attached  to  the  rough  non-articular  posterior  border  of  the  head 
of  the  tibia,  where,  to  its  fibular  side,  it  presents  an  opening  of  exit  for  the  tendon 
of  the  popliteus  muscle  (Fig.  234). 

The  tendon  of  insertion  of  the  semi  -  membranosus  muscle  contributes  an 
important  expansion  which  augments  the  posterior  ligament  on  its  superficial 
aspect.  This  expansion — ligamentum  posticnm  Winslowii — passes  obliquely  upwards 
and  outwards  to  lose  itself  in  the  general  ligament,  but  it  is  most  distinct  in  the 
region  between  the  femoral  condyles,  where  it  may  present  upper  and  lower  arcuate 


300  THE  AKTICULATIONS  OE  JOINTS. 

borders.  A  number  of  vessels  and  nerves  perforate  this  ligament,  and  hence  it 
presents  a  number  of  apertures. 

The  internal  lateral  ligament  (hg.  coUaterale  tibiale,  Figs.  233  and  235)  is  a  well- 
defined,  strong,  flat  band  which  is  applied  to  the  inner  side  of  the  knee-joint,  and  is 
rather  wider  in  the  middle  than  at  either  end.  It  is  frequently  regarded  as  consisting 
of  two  portions — an  anterior  or  long  portion,  and  a  posterior  or  short  one.  The  two 
parts  arise  close  together  from  the  non-articular  inner  surface  of  the  inner  condyle, 
immediately  below  the  adductor  tubercle.  The  short  or  posterior  portion  descends 
shghtly  backwards,  to  be  attached  to  the  postero-internal  aspect  of  the  inner  part  of 
the  tibia  above  the  groove  for  the  semi-membranosus  tendon.  The  long  or  anterior 
portion  inclines  somewhat  forwards,  and  descending  superficially  to  the  tendon  of 
the  semi-membranosus,  it  is  continued  downwards,  to  be  attached  to  the  upper  part  of 
the  inner  surface  of  the  shaft  of  the  tibia  below  the  level  of  the  anterior  tuberosity. 

On  its  superficial  aspect  the  internal  lateral  ligament  is  augmented  by  prolonga- 
tions from  the  tendons  of  the  semi-membranosus  and  sartorius  muscles,  but  is 
separated  by  a  bursa  from  the  tendons  of  adductor-gracilis,  semi-tendinosus,  and 
sartorius.  Its  deep  surface  is  adherent  to  the  convex  edge  of  the  internal  semilunar 
cartilacje,  but  lower  down  the  inferior  internal  articular  vessels  intervene  between 
the  Kgament  and  the  shaft  of  the  tibia. 

The  external  lateral  ligament  (lig.  collaterale  fibulare,Figs.  233  and  235),  sometimes 
called  the  ligamentum  laterale  externum  longum,  is  a  distinct  rounded  band  which 
is  under  cover  of  the  ordinary  capsule,  and  yet  well  separated  from  the  joint  cavity  by 
intervening  objects.  It  is  attached  superiorly  to  a  tubercle  on  the  outer  surface  of 
the  external  condyle,  immediately  above  the  groove  occupied  by  the  tendon  of  the 
pophteus  muscle,  superficial  to  which  the  ligament  descends.  By  its  lower  end  it  is 
attached  to  the  outer  side  of  the  head  of  the  fibula,  in  front  of  the  styloid  process. 
In  its  course  vertically  downwards  it  splits  the  tendon  of  insertion  of  the  biceps 
flexor  cruris  (Fig.  233),  the  portions  of  which  are  fixed  to  the  head  of  the  fibula  on 
either  side  of  the  hgament,  and  a  bursa  may  intervene  between  the  tendon  and  the 
ligament.  The  inferior  external  articular  vessels  pass  forwards  subjacent  to  this 
ligament  and  above  the  head  of  the  fibula.  Unlike  the  internal  ligament,  it  is  not 
attached  to  the  corresponding  semilunar  cartilage. 

The  ligamentum  laterale  externum  breve  seu  posticum  (Fig.  234)  is  an  inconstant  structure 
which  is  attached  by  its  upper  end  immediately  behind  the  j^receding,  and  subjacent  to  the 
outer  head  of  the  gastrocnemius  muscle.  It  likewise  descends  superficial  to  the  jjopliteal  tendon, 
and  is  affixed  inferiorly  into  the  styloid  process  of  the  fibula. 

The  intra-articular  structures  of  the  knee-joint  are  more  important  and  more 
numerous  than  in  any  other  joint  of  the  body. 

The  crucial  ligaments  (ligamenta  cruciata  genu)  are  two  strong,rounded,  tendinous 
bands,  which  extend  from  the  non-articular  area  on  the  upper  surface  of  the  head 
of  the  tibia  to  the  non-articular  sides  of  the  intercondyloid  notch  of  the  femur. 
These  interarticular  ligaments  are  distinguished  from  each  other  as  the  anterior  or 
external  and  the  posterior  or  internal.  They  cross  each  other  like  the  limbs  of 
an  X,  yet  they  remain  distinct  throughout,  and  each  has  its  own  partial  synovial 
covering.  They  lie  within  the  capsule  of  the  joint,  and  extend  between  non- 
articular  surfaces  in  relation  to  the  longitudinal  axis  of  the  limb. 

The  ligamentum  cruciatum  anterius  (Figs.  233,  235,  and  236)  is  attached  inferiorly 
to  the  inner  part  of  the  rough,  depressed  area  in  front  of  and  close  to  the  spine  of 
the  tibia.  It  passes  obliquely  upwards,  outwards,  and  backwards  to  the  inner 
non-articular  surface  of  the  external  condyle,  where  it  finds  attachment  far  back  in 
the  posterior  part  of  the  intercondyloid  notch.  This  ligament  is  tense  in  the  position 
of  extension,  and  therefore  it  assists  in  maintaining  the  erect  attitude. 

The  ligamentum  cruciatum  posterius  (Figs.  233,  235,  and  236)  is  somewhat  shorter 
than  the  preceding.  It  is  attached  inferiorly  to  the  hinder  part  of  the  depressed 
surface  behind  the  spine  of  the  tibia  and  close  to  the  popliteal  notch.  Its  fibres 
pass  obliquely  upwards,  forwards,  and  inwards,  to  be  inserted  into  the  outer  non- 
articular  surface  of  the  inner  condyle,  far  forwards  towards  the  anterior  margin  of 
the  intercondyloid  notch.     It  is  rendered  tense  in  the  position  of  flexion. 


THE  KNEE-JOINT. 


301 


The  semilunar  interarticular  fibro-cartilages  are  two  in  number — an  inner  and  an 
outer — placed  horizontally  Ijetween  the  articular  surfaces  of  the  femur  and  til)ia. 
In  general  outHne  they  correspond  to  the  circumferential  portions  of  the  tibial 
facets  upon  which  they  rest.  Each  has  a  thick,  convex,  fixed  border  in  relation  to 
the  periphery  of  the  joint,  and  a  thin,  concave,  free  border  directed  towards  the 
interior  of  the  joint.  Neither  of  them  is  sufficiently  large  to  cover  the  whole  of  the 
tibial  articular  surface  upon  which  it  rests.  The  upper  and  lower  surfaces  of  each 
semilune  are  smooth  and  free,  and  each  cartilage  terminates  in  an  anterior  and  a 
posterior  fibrous  horn  or  cornii. 

The  internal  semilunar  fibre  -  cartilage  (meniscus  medialis.  Figs.  235  and  236) 


Tendon  of  insertion  of 

adductor  niagnus' 

muscle  (cut) 


Popliteal  surface  of  fenuir 


Anterior  crucial  ligament 


Tendon  of  popliteus  muscle 
(cut) 


Accessorj-attachment 

of  external  semilunar 

cartilage 


Internal  semilunar 
cartilasre 


L\tt  uial  semilunar 
I  ulilase 


Posterior  crucial 
ligament 


Groove  on  tibia  for  tendon 
I  if  popliteus  muscle 
Superior  portion  of  cap- 
sule of  superior  tibio- 
fibular articulation 
External  lateral  ligament 
Mf  knee-joint 


Posterior  superior  tibio- 
fibular ligament 


Tendon  of  semi-membranosus 
muscle  (cut) 
Internal  lateral  ligament 


Head  of  fibula 


Popliteal  surface  of  tibia  --'^iH 

1 


Fig.  23.5. — The  Knee-.Joint  opened  from  Behixd  by  the  Eemoval  of  the  Posterior  Ligament. 


forms  very- nearly  a  semicircle.  It  is  attached  by  its  anterior  horn  to  the  non- 
articular  surface  on  the  head  of  the  tibia,  in  front  of  the  tibial  attachment  of  the 
anterior  crucial  ligament,  and  by  its  posterior  horn  to  the  non-articular  surface 
immediately  in  front  of  the  tibial  attachment  of  the  posterior  crucial  ligament. 
The  deep  or  hinder  part  of  the  internal  lateral  ligament  is  attached  to  its  periphery. 
The  external  semilunar  fibre -cartilage  (meniscus  lateralis,  Figs.  235  and  236)  is 
attached  by  its  anterior  horn  to  the  non-articular  surface  of  the  tibia  in  front  of 
the  tibial  spine,  where  it  is  placed  to  the  outer  side,  and  partly  under  cover  of  the 
tibial  end  of  the  anterior  crucial  ligament.  By  its  posterior  horn  it  is  attached  to  the 
interval  between  the  two  tubercles  which  surmount  the  tibial  spine,  i.e.  in  front  of 
the  attachment  of  the  posterior  horn  of  the  internal  semilunar  cartilage.  This  fibro- 
cartilage,  with  its  two  horns,  therefore  forms  almost  a  complete  circle.  Posteriorly 
it  is  attached  by  its  periphery  to  the  posterior  ligament,  but  on  the  outer  side  it 


302 


THE  AETICULATIONS  OE  JOINTS. 


Transverse  ligament 
Anterior  cornu  of  internal 
semilunar  cartila 


Anterior  cornu  of  external 
semilunar  cartilage 


Posterior  cornu 
of  internal  semi- 
■  -lunar  cartilage 


Posterior  crucial  ligament 


Posterior  cornu  of  exter- 
nal semilunar  cartilage 
FabCiculu-5  from  external  semilunar 
cartilage  to  posterior  crucial  ligament 


b'lG.  236. — Upper  End  of  Tibia  with  Semilunar  Cartilages  and  Attached 
Portions  op  Crucial  Ligaments. 


is  separated  from  the  external  lateral  ligament  by  the  tendon  of   the  popliteus 
muscle,  and  on  this  aspect  its  periphery  is  free. 

The  two  horns  of  the  external  semilune  are  eiuLraced  by  the  two  horns  of  the 
internal  one,  and,  while  the  anterior  crucial  ligament  has  its  tibial  attachment  almost 
between  the  anterior  horns  of  the  two  semilunes,  the  tibial  attachment  of  the 
posterior  crucial  ligament  is  situated  behind  the  posterior  horns  of  the  two 
semilunes. 

Both  semilunes  possess  certain  accessory  attachments.  Thus  the  external  semi- 
lune sends  a  large  bundle  of  fibres  from  its  convex  posterior  border  to  augment  the 

posterioraspect 
of  the  posterior 
crucial  liga- 
ment, by  which 
these  fibres  are 
conducted  to 
the  femur. 
Again,  the  con- 
vex or  periph- 
eral margins  of 
each  semilune 
possess  certain 
attachments  to 
the  deep  surface 
of  the  capsule 
on  its  inner  and 
posterior  as- 
pects, as  has 
already  been 
explained,  but, 
in     addition, 

they  are  attached  to  the  non-articular  circumference  of  the  tibial  head  by  short 
fibrous  bands  known  as  the  ligamenta  coronaria.  Lastly,  a  rounded  band  which 
varies  in  strength,  the  transverse  ligament  (lig.  transversum  genu,  Figs.  233  and 
236),  stretches  between  the  anterior  convex  margins  of  the  two  semilunes,  crossing 
the  front  part  of  the  non-articular  area  on  the  tibial  head  in  its  course. 

The  synovial  membrane  of  the  knee-joint  is  not  only  the  largest,  but  the  most 
/elaborately  arranged  of  its  kind  in  the  body.  It  not  only  lines  the  capsule,  but  it 
forms  a  more  or  less  extensive  covering  for  the  intracapsular  ligaments  and  the 
free  surface  of  the  infra-patellar  pad  of  fat.  This  pad  acts  as  a  wedge  which  fits 
into  the  interval  between  the  patella,  tibia,  and  femoral  condyles,  and  the  synovial 
membrane  upon  its  surface  forms  a  band  or  fold  which  extends  from  below  the 
level  of  the  patellar  articular  surface  to  the  anterior  part  of  the  intercondyloid 
notch.  This  is  in  no  sense  a  ligament,  although  it  is  named  the  ligamentum 
mucosum,  or  plica  synovialis  patellaris.  At  its  femoral  end  it  is  narrow  and  attenu- 
ated, but  at  its  patellar  end  it  expands  laterally  to  form  wing-like  fringes  or  mem- 
branes— the  alar  ligaments  (plicae  alares) — which  are  often  distinguished  from  each 
other  as  the  inner  (yjlica  aliformis  medialis)  and  the  ;.  ^'^•r  (plica  aliformis  lateralis). 
These  folds  are  more  or  less  loaded  with  fat.  ^ 

Apart  from  these  special  foldings,  the  synovial  membrane  lines  the  deep  surface 
of  the  common  extensor  tendon,  and  extends  upwards  for  a  variable  distance  above 
the  patella.  This  extension  of  the  joint  cavity  almost  always  communicates  with 
a  large  bursa  situated  still  higher  on  the  front  of  the  femur.  Tracing  the  synovial 
membrane  downwards,  it  will  he  found  to  cover  both  surfaces  of  the  semilunar  fibro- 
cartilages.  The  peripheral  or  convex  margins  of  tliese  cartilages  are  only  covered 
by  ;this  membrane  where  they  are  unattached  to  the  capsule.  A  prolongation 
invests  the  intracapsular  portion  of  the  tendon  of.  the  popliteus  muscle,  and 
separates  this  tendon  from  the  back  part  of  the  tibial  head,  besides  intervening 
between  the  external  semilune  and  the  head  of  the  tibia. 

From  the  back  jjart  of  the  joint  cavity  the  synovial  membrane  extends  forwards, 


THE  KNEE-JOINT.  303 

and  provides  a  partial  covering  for  the  crucial  ligaments  between  which  a  bursa  may 
be  found. 

This  somewhat  complicated  arrangement  of  the  synovial  membrane  may  be 
readily  comprehended  if  it  be  borne  in  mind  that  it  really  represents  the  fusion  of 
three  separate  synovial  cavities,  which  in  some  animals  are  permanently  distinct. 
These  are  indicated  in  the  two  femoro-tibial  and  the  single  femoro-patellar  parts  of 
the  articulation. 

The  joint  cavity  may  communicate  with  bursse  situated  in  relation  to  the  inner 
head  of  the  gastrocnemius  muscle  and  the  tendon  of  the  semi-membranosus  muscle, 
besides  the  large  supra-patellar  bursa  already  described.  Lastly,  there  may  be 
intercommunication  between  this  joint  cavity  and  that  of  the  superior  tibio-fibular 
articulation. 

Movements  at  the  Knee- Joint. — In  studying  the  movements  which  may  occur  at  the 
human  knee-joint,  it  is  necessary  to  bear  in  mind  that  the  lower  limb  of  man  is  primarily  required 
for  jjurposes  of  support  and  locomotion.  The  j^rincipal  requirement  of  the  former  function  is 
stability  accompanied  by  rigidity,  whereas  in  the  latter  function  the  special  desideratum  is  regu- 
lated and  controlled  mobility.  Thus,  in  the  same  joint,  two  entirely  opposite  conditions  have 
to  be  provided.  The  stable  conditions  of  support  are  chiefly  concerned  in  the  maintenance 
of  the  erect  attitude,  and  the  mechanism  associated  therewith  does  not  call  for  the  exertion  of  a 
large  degree  of  sustained  muscular  effort. 

In  standing  erect  the  attitude  of  the  limb  is  that  of  extension,  which  mainly  concerns  the 
femoro-tibial  parts  of  the  joint.  In  this  position  the  force  of  gravity  acts  along  a  vertical  line 
which  falls  in  front  of  the  transverse  axis  of  the  joint,  and  therefore  any  tendency  to  flexion,  i.e. 
bending  backwards,  is  mechanically  counteracted  by  the  ajaplication  of  a  force  which  tends  to 
produce  bending  forwards  (so-called  over-extension).  This,  however,  is  absolutely  prohibited  in 
normal  states  of  the  joint,  by  the  tension  of  the  posterior  and  lateral  ligaments  aided  by  the 
anterior  crucial  ligament.  The  value  of  this  fact  may  be  seen  by  observing  the  eftect  produced  by 
giving  the  joint  a  sudden  push  from  behind,  which  causes  an  immediate  reversal  of  the  positions  of 
the  transverse  and  vertical  axes,  whereby  the  body  weight  at  once  produces  flexion  of  the  joint. 

The  semilunar  cartilages  and  the  infra-patellar  pad  of  fat  also  assist  in  maintaining  extension, 
by  reason  of  their  close  adaptation  to,  and  packing  round  the  condyles  as  these  rest  upon  the  tibia. 
The  anterior  margin  of  the  intercondyloid  fossa  is  also  brought  into  contact  with  the  front  of 
the  anterior  crucial  ligament. 

In  the  position  of  extension  the  patella  is  retained  at  a  high  level  in  relation  to  the  trochlear  sur- 
face of  the  femur,  so  that  the  lower  articular  facets  of  the  patella  are  in  contact  with  the  trochlea. 

During  locomotion  the  movements  of  the  knee-joint  are  somewhat  intricate,  for  both  the 
femoro-tibial  and  the  femoro-patellar  sections  of  the  joint  are  brought  into  action.  The  principal 
movement  which  results  is  flexion,  with  which  there  is  associated,  both  at  its  beginning  and 
ending,  a  certain  amount  of  screw  movement  or  rotation.  Flexion  and  rotation  occur  at  the 
femoro-tibial  sections  of  the  joint,  whereas  the  movement  at  the  femoro-patellar  portion  produces 
a  regulating  and  controlling  influence  upon  flexion. 

Taking  these  factors  separately,  we  observe  that  each  condyle  adapts  itself  to  a  shallow  cup 
formed  by  the  head  of  the  tibia  and  the  corresponding  semilunar  cartilage,  and  as  the  two 
condyles  move  simultaneously  and  parallel  to  each  other,  there  is  more  than  the  characteristic 
hinge-joint  action,  for  each  condyle  glides  and  rolls  in  its  cup  "  like  a  wheel  restrained  by  a 
drag  "  (Goodsir)  when  the  movement  of  bending  occurs.  Thus  the  difl'erent  parts  of  the  condyles 
are  successively  brought  into  relation  with  the  transverse  axis  of  the  joint  while  it  passes  from 
extension  to  flexion  and  vice  versa.  From  the  fact  that  the  internal  condyle  is  longer  than  the 
external,  it  is  believed  that  extension  is  completed  by  a  movement  of  rotation  whereby  the  joint 
becomes  locked,  and  the  anterior  crucial,  the  posterior  and  the  lateral  ligaments,  become  tense.  A 
similar  rotation  initiates  the  movement  of  flexion,  and  unlocks  the  joint  by  relaxing  the  liga- 
ments just  mentioned. 

Since  the  tibia  and  foot  are  fi'-ed  in  the  act  of  walking,  it  is  the  femur  which  rotates  upon 
the  tibia  in  passing  from  ex'  i  to  flexion  and  vice  versa  ;  and  as  relaxation  of  the  ilio-femoral 

ligament  is  essential  for  this  rotation,  some  observers  are  of  opinion  that  the  body  weight  falls 
behind  the  transverse  axis  of  the  knee-joint,  as  in  the  case  of  the  hip-joint,  and  consequently  that 
extension  of  the  knee-joint  is  maintained  by  the  ilio-femoral  ligament,  as  it  is  not  possible  to 
bend  the  knee  without  first  having  bent  the  hip-joint. 

During  flexion  and  extension  the  semilunar  cartilages  glide  along  with  the  condyles,  so  as  to 
maintain  their  close  adaptation  and  preserve  their  value  as  packing  agents.  When  the  movement 
of  flexion  is  completed,  the  condyles  are  retained  upon  the  tibia,  and  prevented  from  slipping  off 
by  the  tension  of  the  posterior  crucial  ligament.  In  this  position  a  small  degree  of  rotation  of 
the  tibia,  both  inwards  and  outwards,  is  also  permissible. 

The  regulating  and  controlling  influence  of  the  femoro-jjatellar  portion  of  the  articulation  is 
brought  into  play  during  the  movements  of  flexion  and  extension.  In  the  latter  position  the 
inferior  pair  of  patellar  facets  is  in  apposition  with  the  up^ier  part  of  the  femoral  trochlea.  As 
flexion  advances,  the  middle  j^air  of  facets  adapt  themselves  to  a  deeper  area  of  the  trochlea,  into 
which  the  patellar  keel  fits.  When  flexion  is  still  further  advanced,  tlie  upper  pair  of  patellar 
facets  will  be  found  fitting  into  that  part  of  the  trochlea  adjoining  the  intercondyloid  notch  ; 


304  THE  AKTICULATIONS  OK  JOINTS. 

and  tiually,  Avlieu  flexion  is  complete,  tlie  patella  lies  opposite  tlie  intercondyloid  notch,  wMle 
the  forward  thrust  of  the  longer  internal  condyle  brings  its  semilunar  facet  (Goodsir)  into 
apposition  -with  the  somewhat  vertical  facet  at  the  inner  border  of  the  patella.  The  wedge-like 
influence  of  the  patella  is  most  marked,  for  it  is  only  in  the  position  of  extension  that  it  can  be 
moved  from  side  to  side.  The  movements  of  the  j^atella  may  be  described  as  gliding  and 
co-aptation,  as  it  slips  or  rocks  from  one  pair  of  facets  to  another  in  its  progress  along  the  trough 
of  the  femoral  trochlea. 

THE   TIBIO-FIBULAR   JOINTS. 

The  upper  and  lower  ends  of  the  fibula  articulate  with  the  tibia.  Primarily, 
the  fibula  is  required  to  form  a  strong  lateral  support  for  the  ankle-joint,  and 
therefore  its  articulations  are  so  arranged  as  to  provide  a  certain  amount  of 
elasticity  without  any  sacrifice  of  the  rigidity  necessary  for  security.  Hence  the 
amount  of  movement  is  very  small,  but  what  there  is  enables  these  joints  to  be 
classified  as  arthrodial  diarthroses. 

The  superior  tibio-fibular  joint  (articulatio  tibio-fibularis)  is  formed,  on  the 
one  hand,  by  a  flat  oval  or  circular  facet  which  is  situated  upon  the  postero-external 
aspect  of  the  outer  tuberosity  of  the  head  of  the  tibia,  and  is  directed  downwards 
and  backwards ;  on  the  other,  by  a  similar  facet  on  the  upper  surface  of  the  head 
of  the  fibula  in  front  of  the  styloid  process. 

A  fibrous  capsule  (capsula  articularis.  Fig.  234)  invests  the  joint,  and  it  may 
be  regarded  as  holding  the  articular  surfaces  in  apposition,  although  certain 
special  bands  receive  separate  designations.  Occasionally  there  is  an  opening  in  the 
capsule  by  which  communication  is  established  between  the  joint  cavity  and  the 
knee-joint  through  the  intermediation  of  the  synovial  prolongation,  subjacent  to  the 
tendon  of  the  popliteus  muscle. 

The  anterior  superior  tibio-fibular  ligament  (lig.  capituli  fibulae  anterius,  Fig.  233) 
is  a  strong  flat  band  whose  fibres  extend  from  the  anterior  aspect  of  the  fibular 
head,  upwards  and  inwards,  to  the  adjoining  part  of  the  tuberosity  of  the  tibia. 

The  posterior  superior  tibio-fibular  ligament  (lig.  capituli  fibulse  anterius, 
Fig.  234)  is  a  similar,  but  weaker  band,  passing  upwards  and  inwards  from  the 
posterior  aspect  of  the  fibular  head  to  the  posterior  aspect  of  the  outer  tuberosity 
of  the  tibia,  w^here  they  are  attached  immediately  below  the  opening  in  the 
capsule  of  the  knee-joint,  from  which  the  tendon  of  the  popliteus  muscle  escapes. 

Equally  strong  but  much  shorter  bands  are  found  on  the  superior  and  inferior 
aspects  of  the  joint.  The  former  is  intimately  associated  with  the  tendon  of  the 
biceps  flexor  cruris  muscle  which  strengthens  the  upper  aspect  of  the  joint,  and 
here  also  is  found  the  occasional  opening  by  which  it  communicates  with  the  knee- 
joint.  . 

The  synovial  membrane  is  in  certain  cases  continuous  with  that  of  the  knee- 
joint  in  the  manner  already  described. 

The  interosseous  membrane  (membrana  interossea  cruris,  Figs.  234  and  237) 
plays  the  part  of  an  accessory  ligament  both  for  the  upper  and  the  lower  tibio-fibular 
joint.  It  is  attached  to  the  interosseous  borders  on  the  shafts  of  the  tibia  and 
fibula,  and  binds  them  together.  The  general  direction  of  its  fibres  is  from  the 
tibia  downwards  and  outwards  to  the  fibula,  but  many  fibres  pass  in  the  opposite 
direction.  The  membrane  may  extend  upwards  until  it  comes  into  contact  with 
the  ligaments  of  the  superior  tibio-fibular  joint,  but  there  is  always  a  vertical  oval 
aperture  in  its  upper  part  for  the  forward  passage  of  the  anterior  tibial  vessels. 
This  aperture  (Fig.  234),  which  is  about  one  inch  long,  adjoins  the  shaft  of  the 
fibula  at  a  point  rather  less  than  one  inch  below  its  head.  Towards  the  lower  end 
of  the  leg  the  distance  between  the  tibia  and  the  fibula  rapidly  diminishes,  and 
consequently  the  width  of  the  interosseous  membrane  is  correspondingly  reduced, 
80  that  it  is  tense  throughout  its  entire  length.  In  the  lower  part  of  the  membrane 
there  is  a  small  opening  for  the  passage  of  the  anterior  perforating  vessels.  There 
is  no  sharply-marked  demarcation  between  the  interosseous  membrane  and  the 
interosseous  ligament  which  connects  the  lower  ends  of  the  tibia  and  fibula — the 
one,  indeed,  may  be  said  to  run  into  the  other. 

The  inferior  tibio-fibular  joint  (syndesmosis  tibio-fibulare)  is  not  on  all 
occasions  provided  with  articular  cartilage,  so  that  it  may  either  be  a  separate  articu- 


THE  TIBIO-FIBULAK  JOINTS. 


305 


lation,  or  it  may  merely  present  a  series  of  ligaments  which  are  accessory  to  the  ankle- 
joint,  because  it  is  clear  that,  under  any  circumstances,  the  object  aimed  at  in  this 
articulation  is  to  obtain  additional  security  for  the  ankle-joint.  The  articular  surface 
on  the  tibia,  when  present,  constitutes  a  narrow  articular  strip  on  the  outer  side  of 
the  lower  end  of  the  bone,  and  the  joint-cavity  is  practically  an  upward  extension 
of  the  ankle-joint.  The  corresponding  fibular  facet  is  continuous  with  the  ex- 
tensive articular  area,  by  means  of  which  the  fibula  articulates  with  the  astragalus. 
By  far  the  greater  part  of  the  opposing  surfaces  of  tibia  and  fibula  are,  however, 
non-articular  and  rough. 

The  supporting  ligaments  are  of  great  strength. 

I--  Tibio-fibular  interosseous  membrane 

^^     Lower  end  of  shaft  of  fibula 

Lower  end  of  shaft  of  tibia 


Groove  ou  internal  malleolus 

for  tendon  of  tibialis  posticus 

tendon 

Trochlear  surface  of 
astragalus 


Internal  lateral  ligament 


Kbrous  sheath  for  tendon  of  flexor 
longus  hallucis 

Sustentaculum  tal 
Flexor  longus  hallucis  tendon  (tut)— 

Posterior  calcaneo-astragaloid  ligament 


Posterior  inferior  tibio- 
fibular ligament 

Transverse  inferior  tibio- 
fibular ligament 

Facet  ou  astragalus  for 
transverse  inferior  tibio- 
fibular ligament 

Posterior  talo-fibular  ligament 
(posterior  fasciculus  of  external 
lateral  ligament) 


Calcaneo-fibular  ligament 
—  (middle  fasciculus  of  external 
"ateral  ligament) 


Tuberosity  of  os  calcis 


Fig.  2-37. — Axkle- Joint  Dissected  from  Behind  with  Part  of  the  Capsllar  Ligament  Removed. 

The  anterior  inferior  tibio-fibular  ligament  (lig.  malleoli  lateralis  anterius,  Fig. 
240)  consists  of  strong  fibres  which  pass  ol»liqueiy  downwards  and  outwards  from 
the  front  of  the  lower  end  of  the  tibia  to  the  front  of  the  external  malleolus. 

The  posterior  inferior  tibio-fibular  ligament  (lig.  malleoli  laterahs  posterius.  Figs. 
237  and  238)  is  equally  strong,  and  passes  in  a  similar  direction  between  corre- 
sponding posterior  surfaces. 

A  transverse  inferior  tibio-fibular  ligament  (Figs.  237  and  238)  stretches,  in  the 
direction  indicated  by  its  name,  between  the  posterior  inferior  border  of  the  tibia 
and  the  upper  end  of  the  pit  on  the  inner  and  posterior  aspect  of  the  external 
malleolus. 

An  interosseous  ligament,  powerful  and  somewhat  extensive,  connects  the  con- 
tiguous rough  non-articular  surfaces.  Superiorly,  as  already  mentioned,  it  is  con- 
tinuous with  the  interosseous  membrane.  Anteriorly  and  posteriorly  it  comes 
into  contact  with  the  more  superficial  ligaments.  Inferiorly  it  descends  until  it 
comes  into  intimate  association  with  the  joint-cavity. 
21 


306 


THE  AETICULATIONS  OR  JOINTS. 


A  synovial  membrane  is  found  lining  the  small  joint-cavity,  but  it  is  always  a 
direct  prolungatiuu  Irom  that  which  lines  the  ankle-joint. 

JOINTS    OF   THE   FOOT. 


THE   ANKLE-JOINT. 

The  ankle-joint  (articulatio  talo-cruralis)  is  a  giugl^uuus  variety  of  a  diarthrosis. 
The  bones  which  enter  into  its  formation  are  the  lower  ends  of  the  til)ia  and  fibula, 
with  the  articular  areas  on  the  upper,  lateral,  and  mesial  surfaces  of  the  astragalus. 
The  tibia  and  tibula,  aided  by  the  transverse  inferior  tibio-fibular  ligament,  form  a 
three-sided  socket  within  which  the  astragalus  is  accommodated.  The  roof  or 
higliest  part  of  the  socket,  which  is  wider  in  front  than  behind,  is  formed  chiefly  by 
the  quadrilateral  articular  surface  which  characterises  the  lower  end  of  the  tibia, 
but  towards  its  postero-external  margin  the  transverse  inferior  tibio-fibular  liga- 
ment assists  in  its  formation.  Here  also  the  tibial  articular  surface  is  continuous 
with  the  narrow  articular  facet  already  described  as  forming  part  of  the  inferior 
tibio-fibular  joint.  The  inner  wall  of  the  socket  is  formed  by  the  articular  facet  on 
the  outer  side  of  the  internal  malleolus,  and  there  is  no  interruption  of  the  articular 
cartilage  between  the  roof  and  inner  wall.  The  outer  wall  of  the  socket  is  quite 
separate  from  the  foregoing  parts,  and  consists  of  a  large  triangular  facet  upon  the 
inner  side  of  the  external  malleolus.  This  facet  is  situated  immediately  in  front  of 
the  deep  pit  which  characterises  the  posterior  part  of  this  surface  of  the  fibula. 

A  small  lunated  facet  is  frequently  found  upon  the  anterior  surface  of  tlie  lower  end  of  the 
tibia,  particularly  among  those  races  characterised  by  the  adoption  of  the  "  sc|uatting '"  posture. 
When  this  facet  exists  it  is  continuous  Avith  the  anterior  margin  of  the  roof  of  the  socket,  and  it 
articulates  with  a  similar  facet  upon  the  upper  surface  of  the  neck  of  the  astragalus  in  the 
extreme  flexion  of  the  ankle-joint  wliicli  "sqi^atting"  entails. 

The  articular  surface  upon  the  body  of  the  astragalus  adapts  itself  to  the  tibio- 
fibular socket,  and  presents  articular  facets  corresponding  to  the  roof  and  sides  of 
the  socket.  Thus  the  superior  surface  of  the  astragalus  possesses  a  quadrilateral 
articular  area,  wider  in  front  than  behind,  distinctly  convex  in  the  antero-posterior 
direction,  and  slightly  concave  transversely.  In  addition,  towards  its  postero- 
external margin,  there  is  also  a  narrow  antero-posterior  facet  corresponding  to  the 
transverse  inferior  tibio-fibular  ligament.  The  articular  cartilage  of  this  upper 
surface  is  continued  without  interruption  to  the  tibial  and  fibular  sides  of  the  bone, 
although  the  margins  of  the  superior  area  are  sharply  defined  from  the  lateral 
facets,  the  outer  of  which  is  triangular  in  outline,  while  the  inner  is  pyriform,  but 
in  each  case  the  surface  is  vertical. 

Ligaments. — The  ligaments  form  a  complete  investment  for  the  joint,  i.e.  a 
capsule  in  which  the  individual  parts  vary  considerably  in  strength,  and  are 
de.scribed  under  separate  names. 

Tlie  anterior  ligament  is  an  extr>'inely  thin  membrane,  containing  very  few 
longitudinal    fibres.       It   extends   from    the   lower    border    of    the    tibia   to   the 

upper  border  of  the  head  of 

the    astragalus,    passing    in 

front  of  a  pad  of  fat  which 

gament  of  fills  uTj  the  hollow  abovc  the 

ankle-joint  i        f.  ,1      .    i 

neck  01  that  bone. 

The  posterior  ligament 
is  attached  to  contit^u- 
ous  non- articular  borders 
of  the  tibia  and  astragalus. 
Many  of  its  fibres  radiate 
inwards  from  the  external 
malleolus.  Tliis  aspect  of  the 
joint  is  strengthened  by  the 
strong,  well-defined,  trans- 
verse ligament  already  described  in  connexion  witli  the  inferior  tibio-fibular  joint. 


Anterior  talc 
fibular  ligament 


Articular  facet  on 
external  malleolus 


Anterior  inferior  tibio-fibular  lit;aineiit 

Internal 

lateral  or 

eltoid 


Caleaneo- fibular 
ligament 

Posterior  inferior 
tibio-fibular 
ligament 
Posterior  talo-flbular 
ligament 

Fig.  2.38. — Articulau  Scrkaces  of  Tibia  and  Fibula  which 
are  opposed  to  the  astragalus. 


Internal 
malleolus 


Transverse  inferior 
tibio-libular  ligament 


Synovial  pad  of  fat 


THE  ANKLE-JOINT. 


307 


The  external  lateral  Ugament  (Figs.  237,  238,  and  2-iOj  is  very  powerful,  and  is 
divisible  into  three  fasciculi,  which  are  distinguished  from  each  other  by  names 
descriptive  of  their  chief  points  of  attachment. 

The  anterinr  fasciculus  (lig.  talo-fibulare  anterius)  is  the  shortest.  It  extends 
from  the  anterior  border  of  the  external  malleolus  to  the  astragalus  immediately  in 
front  of  its  external  articular  surface. 

The  middle  fascictdus  (lig.  calcaneo-fibulare)  is  a  strong  and  rounded  cord.  It 
is  attached  by  one  end  to  the  front  of  the  tip  of  the  external  malleolus,  and  by 
the  other  to  the  outer  side  of  the  os  calcis,  immediately  above  the  groove  for  the 
peroneal  tendons. 

The  posterior  fasciculus  (lig.  talo-fibulare  posterius)  is  the  strongest.  It  runs 
transverselv  between  the  lower  part  of  the  fibular  or  digital  fossa  on  the  inner 
aspect  of  the  malleolus  and  the  posterior  surface  of  the  astragalus,  where  it  is  attached 


Inner  tarso- 
metatarsal joint 
(opened) 


Internal  malleolus 


Internal  lateral  or  deltoid 
ligament  of  the  ankle 


Trochlear  surface  of  astragalus 

Groove  for  tendon  of  tibialis 
l)0-,ticu»  mn-iple  on  inferior 
ealcaneo-soaplioid  ligament 

Groove  and  tunnel  for  the 
tendon  of  flexor  longus 
hallucis  muscle 
^'Os  calcis 


Long  plantar  ligauient  , 

Tendon  of  tibialis  posticus  muscle  (cut) 

Sustentaculum  tali 

Fig.  239. — Axkle  and  Tarsal-.Joints  from  the  Tibial  Aspect. 

to  the  external  tubercle  and  the  adjoining  rough  surface.  Sometimes  this  tubercle 
is  detached  from  the  astragalus,  and  represents  a  separate  bone — the  os  trigonum. 

The  internal  lateral  ligament  (lig.  deltoideum,  Figs.  238  and  239)  has  the  general 
shape  of  a  delta, and  is  even  stronger  than  the  external  ligament.  It  is  attached  above 
to  a  marked  impression  on  the  lower  part  of  the  internal  malleolus,  and  below,  in  a 
continuous  layer,  to  the  scaphoid,  astragalus,  and  os  calcis.  In  it  we  may  recog- 
nise the  following  special  bands — (a)  the  lig.  talo-tibicde  anterius,  which  extends 
from  the  front  of  the  inner  malleolus  to  the  neck  of  the  astragalus;  (b)  the  lig. 
talo-tibiale  jyosterius,  stretching  between  the  back  of  the  inner  malleolus  and  the 
postero-internal  rough  surface  of  the  astragalus  ;  (c)  the  lig.  tibio-nariculare,  which 
extends  from  the  tip  of  the  inner  malleolus  to  the  inner  side  of  the  scaphoid ;  (d) 
the  lig.  calcaneo-tihiale,  which  extends  between  the  tip  of  the  inner  malleolus  and 
the  inner  side  of  the  sustentaculum  tali;  (e)  lig.  talo-tibiale  profundum,  which 
consists  of  deeper  fibres  extending  from  the  tip  of  the  internal  malleolus  to  the 
inner  side  of  the  astragalus. 

Synovial  membrane  lines  the  capsular  ligament,  and,  as  already  described,  the 
joint-ca%'ity  communicates  directly  with  the  inferior  tibio-fibular  joint.  Both  at 
the  front  and  back  of  the  ankle-joint,  as  well  as  superiorly  in  the  angle  formed  by 
the  three  bones,  the  synovial  membrane  covers  pads  of  fat. 


308 


THE  AETICULATIONS  OR  JOINTS. 


Movements  at  tlie  Ankle-Joint. — In  the  erect  attitude  the  foot  is  i^laced  at  right  angles  to 
the  leg ;  in  other  words,  the  normal  position  of  the  ankle-joint  is  flexion.  Those  movements 
which  tend  to  diminish  the  angle  so  formed  hj  the  dorsum  of  the  foot  and  the  front  of  the 
leg  are  called  dorsiflexion,  while  those  which  tend  to  increase  the  angle,  i.e.  to  straighten  the 
foot  upon  the  leg,  are  called  extension.  As  a  matter  of  fact  neither  dorsiflexion  nor  extension 
is  ever  completely  carried  out,  and  the  range  of  movement  of  which  the  foot  is  capable  is  limited 
to  about  90".  These  movejnents  occur  about  an  obliquely  transverse  axis,  as  is  indicated  by  the 
natural  outward  pointing  of  the  toes.  The  weight  of  the  body  falls  slightly  anterior  to  the  ankle- 
joint,  so  that  a  certain  amount  of  muscular  action  is  necessitated  in  order  to  maintain  the  foot  at 
right  angles  to  the  leg ;  but  additional  stability  is  obtained  from  the  obliquity  above  mentioned. 

When  the  foot  is  raised  from  the  ground,  muscular  action  tends  naturally  to  produce  a  certain 
amount  of  extension.  "When  the  foot  is  extended,  as  in  standing  on  the  toes,  the  hinder  narrow 
part  of  the  astragalus  moves  forwards  into  the  wider  part  of  the  interval  between  the  tibia  and 
fibula,  whereas  in  dorsiflexion,  as  in  raising  the  fore  part  of  the  foot  from  the  ground,  the  widest 
part  of  the  astragalus  is  forced  back  between  the  tibia  and  fibula  ;  but  notwithstanding  the  dif- 
ference between  these  two  movements,  the  fibula  remains  in  close  contact  with  the  astragalus  by 
reason  of  the  action  of  the  transverse  inferior  tibio-fibular  ligament  and  the  posterior  talo-fibular 
ligament,  so  that  lateral  movement  is  prevented. 

It  is  doubtful  whether  lateral  movement  at  the  ankle-joint  can  be  obtained  by  any  natural 
movement  of  the  foot,  although  it  is  generally  belieA^ed  that  in  the  position  of  partial  extension 
a  small  amount  of  lateral  movement  may  be  produced  by  the  application  of  external  force. 
"  This  ajiparent  play  "  of  the  ankle-joint  during  extension  "  is  really  due  to  oscillation  of  the 
small  bones  of  the  foot  on  each  other,  largely  of  the  scaphoid  on  the  astragalus,  but  also  of  the 
cuboid  on  the  calcaneum.  Excessive  mobility  of  these  latter  is  restrained  by  an  important 
function  of  the  posterior  tubercle  of  the  cuboid  which  locks  into  a  notch  in  the  os  calcis" 
(Blake). 

INTERTAESAL  JOINTS. 

These  joints  (articulationes  intertarsese)  are  all  diarthroses  in  which  the  gliding 
movement  is  characteristic,  as  in  the  carpus.    With  the  view  of  obtaining  a  proper  con- 


Fibula 


Posterior  inferior  L/,*\> 
tibio-fibular  ligament' 


Articular  surface  of  astragalus 
Posterior  fasciculus  of  external 
lateral  ligament  of  ankle 


Middle  fasciculus  of  external 
lateral  ligament  of  ankleN 
Posterior  talo-t-alcaneal 
ligaiiienf 
Os  calcis 


Tibia 


'j    \iiterior  inferior  tibio-fibular  ligament 


Articular  surface  of  astragalus 

Anterior  fasciculus  of  external  lateral  ligament 
y^  of  ankle 
/  1 '01  sal  astragalo  na\icular  ligament 

Z        \stragdlo  na\icular  joint 

Ext   calcaneo  navicular  ligament 
Dorsal  scapho-cuneiform 
(  .  V^^i^r^l   '■'i-  scapho-cuboid  ligaments 
I  '       v*  j^^    ~>^  Middle  cuneiform 


External  (■•uueiform 


Cnboiii 


rsal  calcaneo-cuboid  ligament 
Calcaneo-cnboid  joint 
Tendon  of  peroneus longus 
Intel  osseous  tiilo-calcaneal  ligament 
Talo-calcaiieal  joint 
External  talo-calcaneal  ligament 

Fig.  240.— Ligaments  on  the  Outer  Aspect  of  the  Ankle-Joint  and  on  the  Dorsum  of  the  Tarsus. 

caption  of  the  many  beautiful  mechanical  principles  involved  in  the  construction  of  the 
foot,  it  is  necessary  to  study  these  articulations  with  considerable  attention  to  detail. 

Articulatio  Talo-calcanea. — The  astragalus  and  os  calcis  articulate  with  each 
other  in  the  articulatio  talo-calcanea  or  calcaneo-astragaloid  joint. 

This  joint  is  situated  between  the  inferior  facet  on  the  body  of  the  astragalus 


INTEKTAESAL  JOINTS. 


309 


^^eaphoi^l  bone 


Inferior  calcaneo- 
scaphoid  ligament 
Internal  calcane;- 
scaphoid  ligameu: 

Tendon  of  tibialis 

posticus  muscle 

(cut) 


Sustentaculum  tali ;  articular 
surface  for  astraealu 


Articular  surface  on 
scaphoid  for  head  of 
astragalus 

Inner  surface  of  external 
calcaneo-scaplioid  ligament 
External  calcaneo-scaphoid 

t 


Interosseous  cal- 
caneo-astragaloid 
ligament 

Articular  surface 
on  OS  calcis  for 
liody  of  astragalus 


Os  calcis 


and  a  corresponding  facet  on  the  upper  aspect  of  the  hinder  part  of  the  os  calcis. 
On  each  bone  the  articulation  is  limited  in  front  by  a  wide,  deep  groove  which 
runs  obliquely  across  each  bone  from  within  outwards  and  forwards. 

The  supporting  and  investing  ligaments  form  a  capsule,  consisting  for  the  most 
part  of  short  fibres,  but  the  joint  derives  additional  strength  from  the  external  and 
internal  lateral  ligaments  of  the  ankle-joint.  The  capsule  is  subdivided  into  the 
following  astragalo-calcaneal  or  talo-calcaneal  bands : — 

The  anterior  talo-calcaneal  ligament  coDsists  of  a  band  of  short  fibres 
placed  immediately  in  relation  to  the  anterior  end  of  the  deep  groove  which 
bounds  the  articular  facets. 
They  are  attached  to  the 
antero  -  external  aspect  of 
the  neck  of  the  astragalus, 
from  which  they  extend 
downwards  to  the  adjacent 
superior  surface  of  the  os 
calcis. 

The  external  talo-cal- 
caneal ligament  (Fig.  240) 
is  in  continuity  with  the 
hinder  border  of  the  pre- 
ceding ligament,  and  it  is 
placed  parallel  to,  but  on 
a  deeper  plane  than,  the 
middle  fasciculus  of  the 
external  lateral  ligament 
of  the  ankle-joint.  It  con- 
sists of  short  fibres  passmg 
between  the  adjacent  rough 
outer  margins  of  the  two 
bones. 

The  posterior  talo-cal- 
caneal ligament  (Fig.  240) 
closes  the  joint-cavity  on  its 
posterior  aspect.  It  consists  of  fibres  which  radiate  from  the  posterior  aspect  of 
the  external  tubercle  of  the  astragalus  to  the  upper  surface  of  the  os  calcis, 
immediately  behind  the  articular  facet. 

The  internal  talo-calcaneal  ligament  Ues  obliquely  on  the  inner  side  of  the  joint, 
and  consists  of  fibres  which  extend  from  the  inner  posterior  tubercle  of  the 
astragalus  to  the  hinder  roughened  border  of  the  sustentaculum  tali.  Sonie  of  its 
fibres  become  continuous  with  the  internal  calcaneo-scaphoid  Hgament. 

The  interosseous  talo-calcaneal  ligament  (Fig.  240)  closes  the  antero-internal 
aspect  of  the  joint.  It  is  the  strongest  of  the  series  of  ligaments  entering  into  the 
capsule.  Compared  with  it  the  other  bands  are,  comparatively  speaking,  insigni- 
ficant. Its  attachments  are  to  the  bottom  of  each  groove,  so  that  it  occupies  the 
tarsal  canal  formed  by  these  opposing  grooves. 

A  synovial  membrane  lines  the  capsule,  and  it  is  distinct  from  other  tarsal 
synovial  membranes. 

Articulatio  Talo-calcaneo-navicularis. — This  is  one  of  the  most  important  of 
the  joints  of  the  foot,  not  only  because  the  astragalus  is  here  situated  in  relation 
to  the  summit  of  the  antero-posterior  arch  of  the  foot,  but  because  the  head  of 
the  astragalus  is  received  into  a  composite  socket  made  up  of  sustentaculum  tali, 
scaphoid,  and  the  inferior  or  internal  calcaneo-scaphoid  ligament. 

The  articular  surface  on  the  head  of  the  astragalus  presents  anteriorly  a 
convex  rounded  facet  for  articulation  with  the  scaphoid,  inferioiiy  a  convex  facet 
which  rests  upon  the  sustentaculum  tali,  and  intermediate  between  these  two  there 
is  a  triangular  facet  which  articulates  with  the  inferior  calcaneo-scaphoid  ligament. 
All  these  facets  are  in  continuity  with  each  other,  and  are  in  front  of  the  tarsal 
groove  on  the  under  surface  of  the  astragalus.     Occasionally  a  fourth  narrow  facet  is 


Fig.  2-11. — The  Composite  Articular  Socket  for  the  Head  of 
the  astraualus. 


310 


THE  AETICULATIONS  OR  JOINTS. 


found  along  the  outer  and  hinder  part  of  the  articular  surface  of  the  head  of  the 
astragalus,  whereby  it  articulates  with  superior  or  external  calcaneo-scaphoid  ligament. 

The  scaphoid  or  navicular  bone  presents  a  shallow,  cup-shaped,  articular  cavity 
towards  the  head  of  the  astragalus. 

The  articular  surface  of  the  sustentaculum  tali  is  concave,  and  is  usually  marked 
off  into  two  facets. 

Two  ligaments  play  an  important  part  in  binding  together  the  os  calcis  and 
the  scaphoid,  although  these  bones  do  not  directly  articulate ;  and  further,  these 
ligaments  provide  additional  articular  surfaces  for  the  head  of  the  astragalus. 
These  are  the  two  following  : — 

(a)  The  inferior  or  internal  calcaneo-scaphoid  ligament  (Figs.  239  and  242)  is  an 


Tpiidon  of  insertion  of 
peioneus  longus  muscle 


Base  of  metatarsal  bone  of 
hiUnx 


Plantar  inter-metatarsal  .- 
ligaments 


Plantar  cuboid  i  idge 
Plantar  cubo-cuneiform  ligament 

Short  plantar  ligament  -^jlifflWMf ! 

I 

Tendon  of  peroneus  longus  muscle  —'-^^ 
Long  plantar  ligament 


Tendon  of  insertion  of 
tibialis  anticus  muscle 


—  Internal  cuneiform  bone 

Plantar  scapho-cuneiform 
ligament 


iidon  of  tibialis  posticus 
iscle 
<  1 3ove  for  tendon  of  tibialis 
i    posticus  muscle 

Inferior  calcaneo-scaphoid 
ligament 


Inteinal  lateral  or  deltoid 
i„ainent  of  ankle 


Internal  malleolus 


Gino\e  for  tendon  of  flexor  longus 
hrllucis  muscle 


( )s  c  ikis 

Fig.  242. — Plantar  Aspect  ok  Taksal  and  Tahso-metatarsal  Joints. 

extremely  powerful  fibro-cartilaginous  tie-band.  It  extends  between  the  anterior 
margin  of  the  sustentaculum  tali  and  the  inferior  surface  of  the  scaphoid  bone.  Certain 
of  its  upper  filjres  radiate  upwards  on  the  inner  surface  of  the  scaphoid,  and  become 
continuous  with  the  tibio-navicular  portion  of  the  deltoid  ligament  of  the  ankle- 
joint.  The  plantar  aspect  of  this  ligament  is  in  contact  with  the  tendon  of  the 
tibialis  posticus  muscle,  through  which  the  head  of  the  talus  receives  great  support. 
Superiorly  it  contributes  an  articular  surface  which  forms  a  triangular  portion  of 
the  iloor  of  the  composite  socket  in  which  the  head  of  the  talus  is  received. 

(6)  The  superior  or  external  calcaneo-scaphoid  ligament  (Fig.  241)  lies  deeply 
in  the  front  part  of  the  sinus  tarsi,  i.e.  the  interval  l)etween  the  astragalus  and  os 
calcis.  Its  fibres  are  short,  and  extend  from  the  dorsal  surface  of  the  front  part  of 
the  os  calcis,  immediately  to  the  outer  side  of  the  sustentacular  facet,  forwards  to 
the  outer  side  of  the  scaphoid  bone.     Frequently  the  ligament  presents  a  surface 


INTEETARSAL  JOINTS.  311 

which  articulates  with  the  head  of  the  astragalus,  and  in  these  cases  it  forms  a  part 
of  the  composite  socket. 

The  cavity  of  the  talo-calcaneo-navicular  joint  is  closed  posteriorly  by  the 
interosseous  talo-calcaneal  ligament  already  described.  On  its  inner  and  outer 
inferior  aspects  it  is  closed  by  the  calcaneo-scaphoid  ligaments. 

The  superior  and  lateral  aspects  are  covered  by  an  astragalo-scaphoid  membrane 
or  ligament.  This  ligament  is  thin,  and  extends  from  the  upper  non-articular  area 
on  the  head  of  the  astragalus  to  the  dorsal  surface  of  the  scaphoid  bone.  It  may 
be  subdivided  into  dorsal  (superior),  lateral  (external),  and  medial  (internal), 
astragalo-scaphoid  ligaments  (Fig.  239),  which,  with  the  calcaneo-scaphoid  and 
interosseous  talo-calcaneal  Ligaments,  complete  the  capsular  investment  of  the  joint. 

A  distinct  synovial  membrane  lines  all  parts  of  the  capsule  of  the  joint. 

Articulatio  Calcaneo-cuboidea. — This  is  situated  between  the  anterior  concavo- 
convex  surface  of  the  os  calcis  and  the  posterior  similar  surface  of  the  cuboid. 

The  ligaments  which  invest  this  joint  constitute  a  calcaneo-cuboid  capsule,  whose 
parts  are  arranged  in  relation  to  the  four  non-articular  sides  of  the  cuboid  bone, 
and  are  especially  strong  upon  the  plantar  aspect,  in  relation  to  their  great  import- 
ance in  resisting  strains. 

The  internal  calcaneo-cuboid  ligament  occupies  part  of  the  interval  between 
the  astragalus  and  os  calcis — sinus  tarsi.  It  is  sometimes  called  the  interosseous 
calcaneo-cuboid  ligament,  and,  in  conjunction  with  the  superior  or  external 
calcaneo-scaphoid  ligament,  it  forms  a  V-shaped  structure,  of  which  the  single  end 
is  attached  to  the  os  calcis,  and  the  double  ends  separate  to  reach  contiguous 
areas  on  the  scaphoid  and  cuboid  respectively. 

The  dorsal  calcaneo-cuboid  ligament  (Fig.  240)  is  a  broad  portion  of  the  capsule 
extending  between  the  dorsal  surfaces  of  the  two  bones. 

The  external  calcaneo-cuboid  ligament  is  another  but  narrower  part  of  the 
capsule  which  extends  from  the  outer  aspect  of  the  os  calcis  to  the  outer  side  of 
the  cuboid,  immediately  behind  the  facet  on  the  tuberosity. 

The  inferior  calcaneo-cuboid  ligaments  are  two  in  number — a  superficial  and  a 
deep.  The  superficial  series  of  fibres,  the  long  plantar  ligament  (Fig.  242),  is 
attached  to  the  under  surface  of  the  os  calcis  in  front  of  its  tuberosities.  It  forms 
a  long  powerful  structure  which  runs  forwards  to  be  fixed  to  the  under  surface  of  the 
cuboid  ridge,  but  many-  of  its  fibres  pass  superficial  to  the  tendon  of  the  peroneus 
longus,  and  extend  to  the  bases  of  the  third,  fourth,  and  fifth  metatarsal  bones. 

The  deep  series  of  fibres,  the  short  plantar  ligament  (Fig.  242), is  distinctly  separated 
from  the  former  by  a  layer  of  areolar  tissue.  It  forms  a  broad  but  short  band  of  great 
strength,  which  is  attached  to  the  under  surface  of  the  front  end  of  the  os  calcis, 
and  extends  to  the  under  surface  of  the  cuboid  just  behind  the  ridge.  Both  of 
these  ligaments  are  of  great  importance  in  maintaining  the  longitudinal  arch  of  the 
foot,  and  in  this  respect  are  only  second  to  the  inferior  calcaneo-scaphoid  ligaments. 

A  synovial  membrane  lines  the  capsule. 

Transverse  Tarsal  Articulation. — This  is  a  term  sometimes  applied  to  the 
astragalo-scaphoid  and  calcaneo-cuboid  joints.  These  articulations  do  not  com- 
municate with  each  other;  and  although  there  is  an  occasional  direct  articula- 
tion between  the  scaphoid  and  cuboid,  it  does  not  constitute  an  extension  of  the 
transverse  tarsal  joint,  but  is  a  prolongation  from  the  series  of  scapho-cuneiform 
and  cuneo-cuboid  articulations. 

iS'evertheless  there  is  always  a  set  of  ligaments  which  bind  the  scaphoid  and 
cuboid  bones  together,  and  these  may  be  regarded  as  accessory  to  the  various 
transverse  tarsal  joints. 

The  dorsal  scapho-cuboid  ligament  (Fig.  240)  consists  of  short  oblique  fibres  which 
attach  the  contiguous  dorsal  surfaces  of  the  cuboid  and  scaphoid  bones. 

The  plantar  scapho-cuboid  ligament  is  transverse  in  direction,  and  extends 
between  adjacent  plantar  areas  of  the  cuboid  and  scaphoid  bones. 

The  interosseous  scapho-cuboid  ligament  intervenes  between  contiguous  surfaces 
of  the  same  bones.  When  there  is  an  extension  of  the  scapho-cuneiform  joint  back- 
wards between  the  scaphoid  and  cuboid,  it  is  situated  in  front  of  the  last-men- 
tioned ligament,  and  is  called  the  articulatio  scapho-cuboidea.     Around  this  joint 


312  THE  AETICULATIONS  OR  JOINTS. 

the  preceding  Jigaments  are  grouped.  Since,  liowever,  the  joint  is  inconstant  while 
the  ligaments  are  always  present,  it  is  preferable  to  consider  them  as  above  indicated. 

Scapho-cuneiform  Articulation  (articulatio  cimeo-navicularis). — This  joint  is 
situated  between  the  scaphoid  and  the  three  cuneiform  bones.  The  anterior  surface 
of  the  scaphoid  presents  facets  for  each  of  the  cuneiform  bones,  but  its  articular  surface 
is  not  interrupted.  These  facets  form  a  somewhat  convex  anterior  surface  which  fits 
into  the  shallow  articular  concavity  presented  by  the  proximal  ends  of  the  three 
cuneiform  bones.  This  joint  may  be  extended  by  the  occasioual  scapho-cuboid 
articulation  already  referred  to. 

The  capsule  is  composed  of  short,  strong  bands  which  are  distinctly  visible 
on  all  sides  except  towards  the  cuboid  bone,  where  the  joint  may  communicate 
with  the  cuneo-cuboid  and  scapho-cuboid  joints.  Anteriorly  the  joint  communi- 
cates with  the  intercuneiform  articulations.  The  dorsal  parts  of  the  capsule  are 
short  longitudinal  bands  termed  dorsal  scapho-cuneiform  ligaments  (Figs.  239  and 
240).  These  extend  without  interruption  to  the  inner  aspect  of  the  joint. 
Inferiorly  there  are  similar  bands,  known  as  plantar  scapho-cuneiform  ligaments, 
also  longitudinal  in  direction,  but  intimately  associated  with  offsets  from  the 
tendon  of  the  tibialis  posticus  muscle. 

The  synovial  membrane  which  lines  the  capsule  sends  prolongations  forwards  on 
each  side  of  the  middle  cuneiform  bone,  and  in  addition  it  often  communicates 
with  the  cuneo-cuboid  joint  cavity,  and  it  always  communicates  with  the  scapho- 
cuboid  cavity  when  that  joint  exists. 

Intercuneiform  Articulations. — These  are  two  in  number,  and  exist  between 
adjacent  contiguous  surfaces  of  the  three  cuneiform  bones.  These  surfaces  are  partly 
articular  and  partly  non-articular.  The  small  size  of  the  middle  cuneiform  bone 
allows  the  internal  cuneiform  as  well  as  the  external  cuneiform  to  project  forwards 
beyond  it  on  both  sides,  and  therefore  the  articular  surfaces  turned  towards  the  middle 
cuneiform  are  not  entirely  occupied  by  that  bone.  They  form  a  recess  towards 
the  metatarsus,  into  which  the  base  of  the  second  metatarsal  bone  is  thrust. 

Dorsal  intercuneiform  ligaments  constitute  fairly  strong  transverse  bands 
which  extend  between  adjacent  dorsal  surfaces  and  invest  the  joint  cavities  in  this 
direction. 

The  plantar  or  interosseous  intercuneiform  ligaments  are  two  strong  bands 
which  pass  from  the  rough  non-articular  areas  on  opposite  sides  of  the  middle 
cuneiform  to  the  opposing  surfaces  of  the  inner  and  outer  cuneiform  bones.  These 
ligaments  shut  in  the  joint  cavities  inferiorly,  and  also  anteriorly  in  the  case  of  the 
outer  of  the  two  joints. 

The  synovial  membrane  is  an  extension  of  that  which  lines  the  scapho-cuneiform 
joint ;  but  while  it  is  restricted  to  the  outer  of  the  two  joints,  in  the  case  of  the 
inner  one  it  is  prolonged  still  farther  forward  to  the  tarso-metatarsal  series  of  joints. 

Cubo-cuneiform  Articulation. — This  occurs  between  the  rounded  or  oval  facets 
on  the  opposing  surfaces  of  tlie  cuboid  and  external  cuneiform. 

The  dorsal  cubo-cuneiform  ligament  is  a  flat,  somewhat  transverse  band  which 
closes  the  joint  on  its  superior  aspect,  and  extends  between  the  dorsal  surfaces  of 
the  two  bones. 

The  plantar  cubo-cuneiform  ligament  is  difficult  to  determine.  It  is  situated 
subjacent  to  the  long  plantar  ligament,  and  extends  between  adjacent  rough  surfaces 
of  the  two  bones. 

The  interosseous  cubo-cuneiform  ligament  is  the  strongest.  It  closes  the  joint 
cavity  anteriorly,  and  is  attached  to  the  contiguous  non-articular  surfaces  of  the 
two  bones. 

The  synovial  membrane  is  frequently  distinct,  but  at  other  times  the  joint  cavity 
communicates  with  those  of  the  scapho-cuneiform  and  scapho-cuboid  articulations. 

Synovial  Membranes  of  the  Intertarsal  Joints. — Four  and  sometimes  five 
distinct  and  separate  synovial  membranes  may  thus  be  enumerated  in  connexion 
with  the  tarsal  articulations,  viz. :  (1)  talo-calcaneal ;  (2)  talo-calcaneo-navicularis ; 
(3)  calcaneo-cuboid ;  (4)  scapho-cuneiform  and  its  extensions ;  (5)  occasionally 
cubo-cuneiform. 


TAESO-METATAKSAL  JOINTS.  313 


TARSO-METATARSAL  JOINTS. 


The  tarso-metatarsal  joints  are  found  between  certain  articular  facets  on  the 
cuboid  and  three  cuneiform  bones  on  the  one  hand,  and  others  on  the  bases  of  the 
five  metatarsal  bones.  These  articulations  are  associated  with  three  distinct 
synovial  cavities — namely,  an  inner,  middle,  and  outer. 

(1)  The  inner  tarso-metatarsal  articulation  occurs  between  the  distal  convex 
reniform  surface  of  the  internal  cuneiform  bone  and  the  concavo-reniform  surface 
on  the  proximal  aspect  of  the  base  of  the  first  metatarsal  bone. 

Ligaments  which  form  a  capsule  surround  the  articulation.  In  the  capsule  the 
dorsal  and  plantar  tarso-metatarsal  bands  are  its  strongest  parts,  but  it  is  not 
deficient  either  on  the  inner  or  on  the  outer  aspects. 

A  separate  synovial  membrane  lines  the  capsule. 

(2)  The  middle  tarso-metatarsal  articulation  is  an  elaborate  joint.  It 
involves  the  three  cuneiform  bones  and  the  bases  of  the  second,  third,  and  part  of 
the  fourth  metatarsal  bones. 

The  articulation  presents  the  outline  of  an  indented  parapet  both  on  its  tarsal 
and  its  metatarsal  aspects.  Thus,  on  its  tarsal  side,  the  inner  and  the  outer  cunei- 
form bones  project  in  front  of  the  middle  cuneiform,  so  that  the  latter  only  presents 
a  distal  surface  to  the  articulation ;  while  the  internal  cuneiform  presents  a  portion 
of  its  external  surface,  and  the  external  cuneiform  presents  both  its  distal  and 
portions  of  its  outer  and  inner  surfaces,  since  it  projects  in  front  of  the  cuboid 
bone.  On  its  metatarsal  side  the  base  of  the  second  metatarsal  bone  fits  into  the 
indentation  between  the  outer  and  inner  cuneiforms,  to  which  it  presents  external 
and  internal  articular  facets,  but  its  proximal  facet  rests  upon  the  distal  facet  of  the 
middle  cuneiform.  The  base  of  the  third  metatarsal  bone  rests  its  proximal  facet 
upon  the  outer  cuneiform.  The  fourth  metatarsal  base  presents  part  of  its  internal 
facet  to  the  external  side  of  the  outer  cuneiform.  In  this  way  the  indentations 
alternate  on  the  two  sides  of  the  articulation,  and  an  extremely  powerful  interlock- 
ing of  parts  is  provided,  which  places  any  marked  independent  movement  of  these 
metatarsal  bones  entirely  out  of  the  question. 

The  dorsal  tarso-metatarsal  ligaments  are  broad,  flat  bands  which  represent  the 
most  distinct  part  of  an  investing  capsule.  They  pass  from  behind  forwards,  and 
while  the  second  metatarsal  bone  receives  three,  i.e.  one  from  each  cuneiform,  the 
third  metatarsal  only  receives  one — from  the  external  cuneiform. 

The  plantar  tarso-metatarsal  ligaments  correspond  with  the  foregoing  in  their 
general  arrangement,  but  they  are  weaker.  Tliat  for  the  second  metatarsal  is  the 
strongest.  Oblique  bands  extend  from  the  inner  cuneiform  bone  to  the  second 
and  third  metatarsals. 

The  interosseous  cuneo -metatarsal  ligaments  are  three  in  number.  The  inner 
connects  the  outer  side  of  the  internal  cuneiform  with  the  inner  side  of  the  base  of 
the  second  metatarsal  bone.  The  middle  connects  the  inner  side  of  the  external 
cuneiform  with  the  outer  side  of  the  base  of  the  second  metatarsal.  The  outer 
connects  the  adjacent  outer  sides  of  the  external  cuneiform  and  third  metatarsal. 

The  synovial  membrane,  which  lines  this  articulation,  sends  a  prolongation  back- 
wards between  the  inner  and  middle  cuneiform  bones,  where  it  opens  into  the 
scapho-cuneiform  joint.  It  is  likewise  prolonged  forwards  upon  both  sides  of  each 
of  the  bases  of  the  second  and  third  metatarsal  bones. 

(3)  The  external  tarso-metatarsal  articulation  is  found  between  the  proximal 
surfaces  of  the  bases  of  the  fourth  and  fifth  metatarsal  bones  and  the  distal  surface 
of  the  cuboid. 

The  investing  capsule  may  be  resolved  into  the  following  ligaments : — 
The  dorsal  tarso-metatarsal  ligaments  resemble  those  already  described.     The 
base  of  the  fourth  metatarsal  receives  one  from  the  external  cuneiform  and  one 
from  the  cuboid.     The  base  of  the  fifth  metatarsal  receives  one  from  the  cuboid. 

The   plantar   tarso-metatarsal   ligaments  are  the   weakest  bands  of  the  series, 
and   consist  of  scattered   fibres  passing   from  the  cuboid   to   the   bases   of   the 
two   metatarsals.     Some    fibres,   which    are   almost   transverse,  extend   from   the 
22 


314  THE  ARTICULATIONS  OR  JOINTS. 

external  cuneiform  to  the  fifth  metatarsal,  and  additional  fibres  reach  the  meta- 
tarsals in  question  from  the  long  plantar  ligament  (calcaneo-cuboid). 

Occasionally  the  tarsal  end  of  the  external  interosseous  (cuneo-metatarsal)  liga- 
ment is  attached  to  the  inner  margin  of  the  cuboid. 

The  synovial  membrane  is  restricted  to  this  articulation,  and  merely  sends  a 
prolongation  forwards  between  the  opposing  articulate  aspects  of  the  fourth  and 
fifth  metatarsal  bases. 

INTERMETATARSAL  JOINTS. 

The  intermetatarsal  articulations  are  found  between  adjacent  lateral  aspects  of 
the  bases  of  the  four  outer  metatarsal  bones.  The  articular  facets  are  small,  oval, 
or  rounded  surfaces  which  occupy  only  a  limited  portion  of  the  flattened  contiguous 
surfaces  of  the  bones.  Each  joint  is  provided  with  a  capsule,  which,  however,  is  not 
a  complete  investment,  because  the  three  joint  cavities  are  in  free  communication 
on  their  proximal  aspects  with  the  tarso-metatarsal  joint  cavities— one  with  the 
outer  and  two  with  the  middle.  The  definite  fibres  of  each  capsule  are  situated 
chiefly  in  the  transverse  direction. 

The  dorsal  ligaments  are  short  bands  which  extend  from  one  base  to  the  other. 

The  plantar  and  interosseous  ligaments  are  similarly  arranged,  but  the  latter  are 
the  strongest  and  most  important  members  of  this  series. 

The  synovial  membranes  are  extensions  from  those  which  line  the  outer  and 
middle  tarso-metatarsal  joint  cavities. 

Frequently  a  bursa  is  found  between  the  bases  of  tbe  first  and  second  metatarsal  bones.  It 
produces  an  appearance  of  indistinct  facetting  upon  these  bones,  and  it  may  communicate  with 
the  inner  tarso-metatarsal  (cuneo-metatarsal)  joint. 

The  transverse  metatarsal  ligament  lies  upon,  and  is  attached  to,  the  non- 
articular  plantar  aspects  of  the  heads  of  all  the  metatarsal  bones.  It  differs 
from  the  corresponding  ligament  in  the  palm  in  the  fact  that  it  binds  all  the 
metatarsal  bones  together,  whereas  in  the  palm  the  thumb  is  left  free.  It  is 
closely  associated  with  the  plantar  fibrous  plates  of  the  metatarso-phalangeal  joints, 
to  the  plantar  surfaces  of  which  it  contributes  prolongations  termed  ligamenta 
accessoria  plantaria. 

METATARSO-PHALANGEAL  JOINTS. 

Each  of  these  joints  is  a  modified  ball-and-socket  in  which  a  shallow  cup  upon  the 
bases  of  the  first  phalanges  receives  the  somewhat  globular  head  of  a  metatarsal  bone. 

Each  joint  retains  a  modified  capsule  which  invests  the  joint.  Its  only  distinct 
bands  are  the  ligamenta  coUateralia.  These  are  strong  cord-like  bands  which  are 
situated  on  the  inner  and  outer  sides  of  each  joint,  where  they  extend  between 
adjacent  rough  surfaces. 

On  the  dorsal  aspect  ligaments  distinct  from  the  dorsal  expansion  of  the  ex- 
tensor tendons  can  hardly  be  said  to  exist.  The  plantar  aspect  of  the  capsule 
consists  of  a  thick  fibrous  plate,  which  in  the  case  of  the  great  toe  presents 
developed  within  it^vo  large  sesamoid  bones.  In  the  other  toes  this  plate  remains 
fibrous  throughout,  and  is  grooved  on  its  plantar  aspect  for  the  accommodation  of 
the  long  flexor  tendons.  It  will  thus  be  seen  that  the  metatarso-phalangeal  joints  are 
constructed  upon  a  plan  very  similar  to  that  of  the  corresponding  joints  in  the  hand. 

A  synovial  membrane  lines  the  capsule  of  each  articulation. 

INTERPHALANGEAL  JOINTS. 

Each  toe  possesses  two  interphalangeal  joints  except  the  great  toe,  which  has 
only  one.  Not  unfrequently  in  the  little  toe  the  distal  joint  is  obliterated  through 
ankylosis.  All  the  joints  of  this  series  are  uniaxial  or  hinge  joints.  The  nature 
of  the  articular  surfaces  closely  resembles  the  corresponding  joints  in  the  fingers. 

Each  joint  possesses  a  capsule  which  is  either  very  thin  or  limited  to  synovial 
membrane  on  the  dorsal  aspect.     The  plantar  surface  of  the  capsule  is  strength- 


INTEKPHALANGEAL  JOINTS.  315 

ened  by  a  fibroiis  plate.  The  lateral  ligaments  (ligamenta  collateralia)  are  well- 
defined  bands  similar  to  those  already  described  in  connexion  with  the  metatarso- 
phalangeal joints. 

A  ssmovial  membrane  lines  each  capsule  in  the  series. 

Mechanism  of  the  Foot. — The  bones  of  the  foot  are  arranged  in  the  form  of  a  longitudinal 
and  a  tran-svei.se  arch.  The  longitudinal  arch  is  built  on  a  very  remarkable  plan.  Posteriorly 
the  mass  of  the  os  calcis  constitutes  a  rigid  and  stable  j^ier  of  support,  while  anteriorly,  by  increasing 
the  number  of  component  parts,  the  anterior  pier  acquires  great  flexibility  and  elasticity  witliout 
sacrificing  strength  or  stability.  The  summit  of  the  arch  is  formed  by  the  astragalus,  which 
receives  the  weight  of  the  body  from  the  tibia,  and  the  resilience  of  the  arch  is  assured  by  the 
calcaneo-scaphoid  and  calcaneo-cuboid  ligaments,  together  with  the  plantar  fascia,  which  act  as 
powerftil  braces  or  tie  bands,  preventing  undue  separation  of  the  piers  of  the  arch,  and  consequent 
flattening  of  the  foot.  The  weight  of  the  body  is  distributed  over  all  the  five  digits,  owing  to 
the  arrangement  of  the  bones  of  the  foot  in  two  parallel  columns,  an  inner  and  an  outer.  The 
former,  consisting  of  the  astragalus,  scaphoid,  and  the  three  cuneiforms,  with  the  three  inner 
metatarsal  bones,  distributes  weight  through  the  talo-scaphoid  joint,  while  the  latter  {i.e.  the 
outer  column),  comj^rising  the  calcaneum,  cuboid,  and  the  two  outer  metatarsal  bones,  acts  in  a 
similar  manner  through  the  talo-calcanean  joint.  The  main  line  of  immobility  of  this  arch 
passes  from  the  heel  forwards  through  the  middle  toe,  but  its  anterior  section,  which  is  slender, 
is  supported  on  either  side  by  two  metatarsal  bones,  with  their  proximal  tarsal  associations,  in 
all  of  which  greater  freedom  of  movement  is  found.  The  transverse  arch  is  most  marked  at  the 
level  of  tarso-metatarsal  articulations.  The  intersection  of  these  two  arches  at  right  angles  to 
each  other  introduces  an  architectural  feature  of  great  importance  in  connexion  with  the 
support  of  heavy  weights.  These  longitudinal  and  transverse  arches  of  the  foot  are  in  effect 
"  vaults  "  intereecting  each  other  at  right  angles,  and  in  relation  to  the  area  which  is  common  to 
both  "  vaults "  the  body  weight  is  superposed  exactly  as  the  dome  of  a  cathedral  is  carried 
upon  two  intereecting  vaults. 

Movements  at  the  Joints  of  Tarsus,  Metatarsus,  and  Phalanges. — Considered  in  detail, 
the  amount  of  movement  which  takes  jjlace  between  any  two  of  these  bones  is  extremely  smali, 
and,  so  far  as  the  tarsus  and  metatarsus  are  concerned,  it  is  mostly  of  the  nature  of  a  gliding 
motion. 

At  the  metatarso-phalangeal  and  interphalangeal  joints  movement  is  much  more  free,  and 
is  of  the  nature  of  flexion  (bending  of  the  toes  towards  the  sole  of  the  foot,  i.e.  plantar  flexion) 
and  extension.  The  latter  movement  when  continued  so  as  to  raise  the  toes  from  the  ground, 
and  bend  or  approximate  them  towards  the  front  of  the  leg,  is  termed  dorsiflexion.  Coincident 
with  dorsiflexion  there  is  always  associated  a  certain  amount  of  spreading  of  the  toes,  which  is 
called  abduction,  and  similarly  with  prolonged  flexion  there  follows  a  diminution  or  narrowing 
of  the  transverse  diameter  of  the  front  part  of  the  foot  by  drawing  the  toes  together — a  move- 
ment termed  adduction.  In  the  foot  the  movements  of  abduction  and  adduction  take  place  in 
regard  to  a  plane  which  bisects  the  foot  antero-posteriorly  through  the  second  toe,  for  this  toe 
carries  the  fii'st  and  second  dorsal  interosseous  muscles. 

Notwithstanding  the  small  amount  of  possible  movement  in  connexion  with  individual 
tarsal  and  metatarsal  joints,  yet  the  sum  total  of  these  movements  is  considerable  as  regards  the 
entire  foot.  In  this  way  the  movements  of  inversion  and  eversion  of  the  foot  result.  By 
inversion  we  mean  the  raising  of  the  inner  border  of  the  foot  so  that  the  sole  looks  inwards, 
while  the  toes  are  depre.ssed  towards  the  ground,  and  the  outer  border  of  the  foot  remains  down- 
wards. This  takes  place  chiefly  at  the  talo-calcanean  joint,  but  the  transverse  tarsal  joints  also 
participate. 

Eversion  is  chiefly  the  opposite  of  inversion,  and  the  return  of  the  foot  to  the  normal  position 
of  the  erect  attitude ;  but  under  certain  conditions  it  may  be  carried  further,  so  that  the  outer 
border  of  the  foot  is  raised  from  the  ground,  while  the  inner  border  is  depressed.  In  both  of  these 
movements  there  is  rotation  between  the  astragalus  and  os  calcis  about  an  oblique  axis  which 
passes  from  the  inner  side  of  the  neck  of  the  astragalus  to  the  outer  and  lower  part  of  the  os 
calcis. 

Of  course  all  the  movements  of  the  foot  are  subordinated  to  its  primary  functions  as  an  organ 
of  support  and  progression.  For  these  purposes  its  longitudinal  and  transverse  arches  are  of 
extreme  importance.  The  longitudinal  arch  resting  on  the  os  calcis  behind  and  the  heads  of 
the  metatarsal  bones  in  front  receives  the  weight  of  the  body,  as  already  explained,  on  the  summit 
of  the  astragalus  in  the  line  of  the  third  toe.  Hence  it  is  that  the  inner  malleolus  appears  to  be 
unduly  prominent  on  the  inner  side  of  the  ankle.  The  transverse  arch  buttresses  the  longitudinal 
one,  and  therefore,  whether  the  body  weight  fall  to  the  outer  or  the  inner  side  of  the  longitudinal 
arch,  it  is  supported  by  a  mechanism  at  once  stable,  flexible,  and  elastic,  or  resilient,  and  capable 
of  reducing  to  a  minimum  all  jars  that  may  be  received  by  the  fore-part  of  the  foot.  As  the  heel 
is  raised  in  the  act  of  walking,  the  weight  is  gradually  transferred  from  the  outer  to  the  inner 
side  of  the  foot,  until  the  foot  finally  leaves  the  ground  with  a  propulsive  movement,  which 
results  from  flexion  of  the  phalanges  of  the  great  toe.  In  this  connexion  it  is  worthy  of  note 
that  the  longitudinal  line  of  greatest  strength  is  on  the  inner  side  of  the  longitudinal  arch,  i.e. 
in  relation  to  the  great  toe. 

22  a 


THE    MUSCULAR    SYSTEM. 

MYOLOGY. 

By  A.  M.  Paterson/ M.D., 
Professor  of  Anatomy,  University  College,  Liverpool. 


THE   MUSCULAR  SYSTEM. 

MYOLOGY. 

By  A.  M.  Pateeson. 

The  movements  of  the  various  parts  and  organs  of  the  body  are  brought  about  by 
the  agency  of  muscle-cells,  which  are  characterised  by  a  special  histological  structure 
and  by  the  special  function  of  contracting  in  length  under  the  influence  of  a  proper 
stimulus. 

There  are  three  classes  of  muscle-cells  :  (1)  the  striated,  and  usually  voluntary 
muscle-cells,  out  of  which  the  skeletal  muscular  system  is  constructed  ;  (2)  the  non- 
striated,  involuntary  muscle-cells,  occurring  in  the  walls  of  vessels  and  hollow 
viscera,  etc. ;  and  (3)  the  cardiac  muscle-cells,  striated  but  involuntary,  of  which  the 
substance  of  the  heart  is  composed. 

The  following  section  deals  solely  with  the  skeletal  muscles,  the  structure, 
arrangement,  and  mechanical  action  of  which  are  based  upon  a  common  plan. 

The  cells  of  which  the  skeletal  muscles  are  composed  are  long,  narrow,  and 
characterised  by  a  peculiar  striation,  which  is  different  from  the  striation  of 
the  muscle-cells  of  the  heart ;  they  also  differ  both  in  structure  and  function 
from  the  non-striated  muscle-cells  which  occur  in  viscera  and  vessels. 

A  typical  skeletal  muscle  consists  of  a  fleshy  mass  enveloped  in  a  membranous 
aponeurosis  or  fascia,  and  provided  at  its  extremities  or  borders  with  membranous 
or  tendinous  attachments  to  bone,  cartilage,  or  fascia. 

Each  muscle  is  made  up  of  a  number  of  fasciculi  or  bundles,  arranged  together 
in  different  muscles  in  different  ways,  so  as  to  give  rise  to  the  particular  form  of 
the  muscle  in  question.  These  fasciculi  are  clothed  and  connected  together  by  a 
delicate  connective  tissue,  the  perimysiuin  externum,  continuous  externally  with  the 
aponeurosis  enclosing  the  muscle. 

Each  muscular  bundle  or  fasciculus  is  composed  of  a  number  of  narrow,  elon- 
gated muscle-cells  or  fibres,  held  together  by  a  still  more  delicate  connective  tissue, 
the  perimysium  internum.  This  tissue  is  connected  on  the  one  hand  with  the  sarco- 
lemma  or  cell-wall  of  the  muscle-cell,  and  on  the  other  hand  with  the  coarser 
tissue  of  the  perimysium  externum  enclosing  the  muscular  bundles. 

By  means  of  these  connective  tissue  envelopes  the  muscle-cells,  the  essential 
agents  of  motor  activity,  are  brought  into  firm  and  intimate  relation  with  the 
osseous  or  other  attachments  of  the  muscle.  Through  the  agency  of  sarcolemma, 
perimysium  internum,  perimysium  externum,  aponeurosis,  and  tendon,  the  muscle- 
cell  when  it  contracts  can  produce  a  precise  and  definite  effect  upon  the  weight  to 
be  moved. 

Each  muscle  is  supplied  by  one  or  more  nerves,  which,  in  their  course 
through  the  muscle,  separate  into  smaller  and  smaller  branches,  ultimately,  by 
their  terminal  filaments  (axons),  forming  special  end-organs  in  relation  to  each 
muscle-cell. 

While  a  muscle  may  thus  be  looked  upon  as  an  organ  endowed  with  particular 
properties,  and  executing  a  definite  movement  in  response  to  a  stimulus  by  the 
simultaneous  contraction  of  its  constituent  cells,  the  various  muscles  may  further 
be  considered  in  groups,  associated  together  by  mode  of  development,  nerve-supply, 
and  co-ordination  of  action.     For  example,  we  speak  of  the  hamstring  muscles  of 

317  22  h 


318  THE  MUSCULAE  SYSTEM. 

the  thigh,  the  muscles  of  the  back,  and  the  prsevertebral  muscles, — groups  in  which 
separate  muscles  are  associated  together  by  development,  nerve-supply,  and  action. 
In  their  development  the  separate  muscles  arise  from  the  subdivision  of  a  larger 
stratum,  as  in  the  limbs,  or  from  the  fusion  of  segmental  elements  (myotomes),  as  in 
the  case  of  the  axial  muscles.  The  peripheral  nerves  supplying  skeletal  muscles  are 
distributed,  through  the  plexuses  or  directly,  so  as  to  associate  particular  muscles 
morphologically  and  physiologically,  and  to  secure  a  co-ordinated  movement  by  the 
simultaneous  contraction  of  several  muscles. 


FASCIiE. 

Beneath  the  skin  there  are  two  (or  in  some  regions  three)  layers  of  tissue  which 
require  consideration  in  relation  to  the  muscular  system :  the  superficial  fascia 
(panniculus  adiposus),  the  deep  fascia  (fascia  lata),  and,  in  animals,  the  panniculus 
carnosus  (rudimentary  in  man,  and  represented  chiefly  by  the  platysma  in  the 
neck). 

Superficial  Fascia. — The  superficial  fascia  is  a  continuous  sheet  of  areolar 
tissue  which  underlies  the  skin  of  the  whole  body.  It  is  closely  adherent  to  the 
cutis  vera,  and  is  sometimes  termed  panniculus  adiposus,  from  the  fact  that,  except 
beneath  the  skin  of  the  eyelids,  penis,  and  scrotum,  it  is  usually  more  or  less 
impregnated  with  fat.  The  cutaneous  vessels  and  nerves  ramify  in  this  fascia ;  and 
its  deep  surface,  membranous  in  character,  is  in  loose  connexion  with  the  subjacent 
deep  fascia.     It  is  in  this  layer  that  dropsical  effusions  chiefly  occur. 

Deep  Fascia. — Underneath  the  skin  and  superficial  fascia  is  a  fibrous 
membrane,  bluish  white  in  colour,  devoid  of  fat,  and  in  closest  relation  to  skeleton, 
hgaments,  and  muscles.  This  is  the  deep  fascia.  It  covers,  invests,  and  in  some 
cases  forms  the  means  of  attachment  of  the  various  muscles.  It  has  a  special 
tendency  to  become  attached  to  all  subcutaneous  bony  prominences,  and  to  be 
continuous  with  the  connecting  ligaments.  It  forms  septal  laminae,  which 
separate  groups  of  muscles  and  individual  muscles ;  enclose  glands  and  viscera ; 
and  form  sheaths  for  vessels  and  nerves.  Around  joints  it  gives  rise  to  bands 
which  strengthen  the  capsule  or  limit  the  mobility  of  the  joint,  or,  as  in  the  case 
of  annular  ligaments,  bind  down  the  tendons  passing  over  the  joint.  It  not  only 
ensheathes  vessels  and  nerves,  but  is  perforated  by  those  which  pass  between  super- 
ficial and  deeper  parts. 

The  term  aponeurosis  is  used  in  relation  to  muscles.  It  is  synonymous  with  deep 
fascia,  either  as  an  investing  fascia,  or  as  a  membranous  layer  which  (e.g.  vertebral 
aponeurosis)  performs  at  one  and  the  same  time  the  purpose  of  a  deep  fascia  and 
the  expanded  membranous  attachment  of  a  muscle. 

The  panniculus  carnosus  is  a  thin  muscular  layer  enveloping  the  trunk  of 
animals  with  a  hairy  or  furry  coat.  It  is  strongly  developed  in  the  hedgehog.  In 
man  it  is  represented  mainly  by  the  (rudimentary)  platysma.  It  is  placed  between 
the  superficial  and  the  deep  fascia. 

Bursae. — Where  a  tendon  passes  over  a  bony  surface,  or  where  the  superficial 
fascia  and  skin  cover  a  bony  prominence,  there  is  generally  formed  a  synovial 
sac,  or  bursa,  containing  fluid,  for  the  purpose  of  lubricating  the  surface  over 
which  the  tendon  or  fascia  glides.  Allied  to  these  are  the  synovial  sheaths 
which  envelop  tendons  beneath  the  annular  ligaments  in  relation  to  the  several 
joints. 

Description  of  Muscles. — In  studying  the  muscular  system  it  is  necessary  to 
note  the  following  characters  in  reference  to  each  individual  muscle  :  (1)  The  shape 
of  the  muscle — flat,  cylindrical,  triangular,  rhomboidal,  etc. — ^and  the  character  of 
its  extremities — membranous,  tendinous,  or  fleshy.  (2)  The  attachments  of  the 
muscle.  The  origin  is  the  more  fixed  or  central  attachment :  the  insertion  is  the 
more  movable  or  peripheral  attachment.  (3)  The  relations  of  the  surfaces  and 
borders  of  the  muscle  to  bones,  joints,  muscles,  and  other  important  structures. 
(4)  Its  vascular  and  nervous  supply ;  and  (5)  its  action.  It  must  be  borne  in  mind 
that  hardly  any  single  muscle  acts  alone.     Each  muscle,  as  a  rule,  forms  one 


FASCIA  AND  SUPEKFICIAL  MUSCLES  OF  THE  BACK.         319 

of  a  group  acting  more  or  less  in  harmony  with,  and  antagonised  by,  other  and 
opposite  groups. 

DESCRIPTION   OF   THE   MUSCLES. 

The  skeletal  muscles  may  be  divided  into  two  series  :  axial  and  appendicular. 
The  axial  muscles  comprise  the  muscles  of  the  trunk,  head,  and  face,  including 
the  panniculus  carnosus  (platysma).  These  muscles  are  more  or  less  segmental 
in  arrangement,  grouped  around  the  axial  skeleton.  The  appendicular  muscles, 
the  muscles  of  the  limbs,  are  grouped  around  the  appendicular  skeleton.  They 
are  not  segmental  in  arrangement,  they  are  morphologically  separate  from  the 
axial  muscles,  and  they  are  arranged  in  definite  strata  in  relation  to  the  bones  of 
the  limbs. 


APPENDICULAR    MUSCLES. 

THE    UPPER    LIIVIB. 

FASOIiE   AND   SUPERFICIAL   MUSCLES   OF   THE   BACK. 

Fasciae. 

The  superficial  fascia  of  the  back  presents  no  peculiarity.  It  is  usually 
of  considerable  thickness,  and  contains  a  quantity  of  fat. 

The  deep  fascia  closely  invests  the  muscles.  It  is  attached  in  the  middle  line 
of  the  back  to  the  ligamentum  nuchee,  supraspinous  ligaments,  and  vertebral  spines  ; 
laterally  it  is  attached  to  the  spine  of  the  scapula  and  the  clavicle,  and  is  continued 
over  the  deltoid  region  to  the  arm.  In  the  neck  it  is  attached  above  to  the 
superior  curved  line  of  the  occipital  bone,  and  is  continuous  laterally  with  the  deep 
cervical  fascia.  Below  the  level  of  the  arm  it  is  continuous,  round  the  border  of  the 
latissimus  dorsi  muscle,  with  the  fascia  of  the  axilla  and  of  the  abdominal  wall. 
In  the  back  and  loin  it  constitutes  the  vertebral  aponeurosis  (fascia  lumbodorsalis) 
or  aponeurosis  of  the  latissimus  dorsi.  This  layer  conceals  the  sacro-spinalis 
(erector  spin^e)  muscle,  forming  the  posterior  layer  of  the  lumbar  fascia,  and  is 
attached  medially  to  the  vertebral  spines,  and  laterally  to  the  angles  of  the  ribs, 
to  the  lumbar  fascia,  and  to  the  iliac  crest. 

The  Superficial  lYIuscIes  of  the  Back. 

The  muscles  of  the  back  are  arranged  in  four  series  according  to  their  attach- 
ments: (1)  vertebro-scapularand  vertebro-humeral;  (2)  vertebro-costal;  (3)vertebro- 
cranial ;  and  (4)  vertebral.  The  first  of  this  series  consists  of  the  posterior  muscles 
connecting  the  upper  limb  to  the  trunk,  and  comprises  the  first  two  layers  of  the 
muscles  of  the  back — (1)  trapezius  and  latissimus  dorsi,  and  (2)  levator  scapulae 
and  rhomboidei  (major  and  minor).  The  deeper  (axial)  muscles  of  the  back  are 
dealt  with  later  (p.  384). 

The  trapezius  is  a  large  triangular  muscle  occupying  the  upper  part  of 
the  back.  It  arises  from  the  superior  curved  line  of  the  occipital  bone  in  its  medial 
third,  from  the  external  occipital  protuberance  (Fig.  312,  p.  400),  from  the 
ligamentum  nuchse,  from  the  spines  of  the  seventh  cervical  and  all  the  thoracic 
vertebrae,  and  the  intervening  supraspinous  ligaments.  The  origin  is  by  direct 
fleshy  attachment,  except  in  relation  to  the  occipital  bone,  the  lower  part  of  the 
neck,  and  the  lower  thoracic  vertebrae,  in  which  places  the  origins  are  tendinous. 
From  their  origin  the  muscular  fibres  converge  towards  the  bones  of  the  shoulder, 
to  be  inserted  continuously  from  before  backwards  as  follows :  (1)  The  occipital 
and  upper  cervical  fibres — into  the  posterior  surface  of  the  clavicle  in  its  lateral 
third  (Figs.  243,  p.  320,  and  248,  p.  325);  (2)  the  lower  cervical  and  upper 
thoracic  fibres — into  the  medial  border  of  the  acromion  process,  and  the  upper 

22  c 


320  THE  MUSCULAE  SYSTEM. 

border  of  the  spine  of  the  scapula ;  and  (3)  the  lower  thoracic  fibres,  by  a 
triangular  flat  tendon,  beneath  which  a  bursa  is  placed — into  a  rough  tuberosity 
at  the  base  of  the  spine  of  the  scapula  (Fig.  245,  p.  322).  The  fibres  inserted 
into  the  clavicle,  acromion,  and  the  upper  border  of  the  spine  of  the  scapula,  spread 
over  the  adjacent  subcutaneous  surfaces  of  these  bones  for  a  variable  distance. 
The  occipital  portion  of  the  muscle  may  be  in  the  form  of  a  separate  slip,  or  may 
be  entirely  absent. 

The  trapezius  is  superficial  in  its  whole  extent.  Its  upper  lateral  border  forms 
the  posterior  limit  of  the  posterior  triangle  of  the  neck.  The  lower  lateral  border, 
passing  over  the  upper  edge  of  the  latissimus  dorsi  and  the  vertebral  border  of  the 
scapula,  forms  a  boundary  of  the  so-called  triangle  of  auscultation,  completed  below 
by  the  latissimus  dorsi,  and  laterally  by  the  vertebral  border  of  the  scapula.  This 
space  is  partly  filled  up  by  the  rhomboideus  major.  The  muscle  overlaps  the 
latissimus  dorsi,  and  covers  the  levator  scapulae,  rhomboidei,  and  the  deeper  axial 
muscles  of  the  back,  along  with  the  superficial  cervical  and  posterior  scapular^ 
arteries,  the  spinal  accessory  nerve,  and  muscular  branches  from  the  cervical  plexus. 

The  latissimus  dorsi  is  a  large  triangular  muscle  occupying  the  lower  part  of 
the  back.     It  has  a  triple  origin.     The  greater  part  of  the  muscle  arises — (1)  from 

Pectoralis  major  (origin) 


Trapezius  (insertion)- 
Fig.  243. — Muscle-Attachments  to  the  Right  Clavicle  (Upper  Surface). 

the  vertebral  aponeurosis  (posterior  layer  of  the  lumbar  fascia  or  aponeurosis  of  the 
latissimus  dorsi).  This  is  a  thick  membrane  which  conceals  the  erector  spinas  m 
the  lower  part  of  the  back.  Through  it  the  latissimus  dorsi  gains  attachment  to 
the  spines  of  the  lower  six  thoracic  vertebrae,  the  spines  of  the  lumbar  vertebrae, 
and  the  tendon  of  the  sacro-spinalis,  with  which  the  aponeurosis  blends  below. 
It  also  arises  laterally  from  the  posterior  part  of  the  iliac  crest.  From  this 
origin  the  muscle  is  directed  upwards  and  laterally,  its  fibres  converging  to 
the  lower  angle  of  the  scapula.  In  relation  to  its  lateral  and  upper  borders 
additional  fibres  arise.  (2)  Along  the  lateral  border  muscular  slips  arise  from  the 
lower  three  or  four  ribs,  inter-digitating  with  the  origins  of  the  obliquus  externus 
abdominis.  (3)  As  the  upper  border  of  the  muscle  passes  horizontally  over  the 
lower  angle  of  the  scapula,  an  additional  fleshy  slip  usually  takes  origin  from  this 
part  of  the  bone  to  join  the  muscle  on  its  deep  surface  (Eig.  245,  p.  322). 

Beyond  the  lower  angle  of  the  scapula  the  latissimus  dorsi,  greatly  narrowed, 
curves  spirally  round  the  teres  major  muscle,  and  forms  the  prominence  of  the 
posterior  axillary  fold.  It  ends  in  a  ribbon-like  tendon,  closely  adherent  at  first  to 
the  teres  major,  which  is  inserted  into  the  floor  of  the  bicipital  groove  of  the 
humerus  (sulcus  intertubercularis),  extending  for  about  three  inches  below  the 
lower  and  lateral  part  of  the  lesser  tuberosity  (Fig.  253,  p.  330).  It  is  placed 
behind  the  axillary  vessels  and  nerves,  and  in  front  of  the  insertion  of  the  teres 
major,  from  which  it  is  separated  by  a  bursa. 

In  the  back  the  latissimus  dorsi  is  superficial,  except  in  its  upper  part, 
which  is  concealed  by  the  trapezius.  It  covers  the  lumbar  fascia,  serratus  posterior 
inferior,  the  ribs,  and  lower  angle  of  the  scapula,  and  at  its  borders  two  triangular 
spaces  are  formed ;  at  the  upper  border  is  the  so-called  triangle  of  auscultation ;  at 
the  outer  border  is  the  triangle  of  Petit  (trigonum  lumljale  Petiti),  a  small  space 
bounded  by  the  iliac  crest,  the  latissimus  dorsi,  and  the  obliquus  externus 
abdominis.     This  is  sometimes  the  site  of  a  lumbar  hernia. 

The  levator  scapulae  is  a  strap-like  muscle,  arising  by  tendinous  slips  from 

'   Posterior  scapular  artery  =  descending  ramus  of  the  tra versus  colli  artery  (B.N.  A.). 


THE  SUPEEFICIAL  MUSCLES  OE  THE  BACK. 


321 


the  posterior  tubercles  of  the  transverse  processes  of  the  first  three  or  four  cervical 
vertebrte,  between  the  attachments   of  the    scalenus   medius   in    front    and    the 


Posterior  Triangle, 


STEBNO-CLEI  DO-MASTOir 


SeMISPINALIS  CAPl'llS 
(COMPLEXUS) 


Scapular  aponeurosi 
Deltoid 


Teres.-' 

MAJOli. 


Lumbar  Triangle  of  Petit- 


Serratus  posterior  inferior 

Latissimi'S  dor&;i  (reflected) 


Latissimus  dorsi 

Obliqtjus  internus  abdominis 

Obliquus  extebnus  abdominis 


GlUT/EUS  maximus, 


Fig.  244. — Superficial  Muscles  of  the  Back,  and  Vebtebro-scapular  Muscles. 

splenius  cervicis  behind.  It  is  directed  downwards  along  the  side  of  the  neck,  to  be 
inserted  into  the  vertebral  border  of  the  scapula  in  its  upper  fourth,  from  the 
superior  angle  to  the  spine  (Fig.  245,  p.  322).     It  is  concealed  in  its  upper  third 


322 


THE  MUSCULAE  SYSTEM. 


Deltoid  (origin) 


Triceps  Braehii 
(origin  of  long  head) 


Teres  minor  (origin)  with 
gap  for  dorsal  scapular 
artery 


by  the  sterno-mastoid  muscle.     In  its  middle  third  it  occupies  the  floor  of  the 

posterior  triangle.    In  its  lower  third  it  is  again  hidden  from  view  by  the  trapezius. 

It  conceals  the  splenius  cervicis  and  ilio-costalis  cervicis  (cervicalis  asceudens). 
The  rhomboideus  minor  may  be  regarded  as  a  separated  slip  of  the  rhom- 

boideus  major,  with  which  it  is  often  continuous.     It  arises  from  the  ligamentum 

nuchce  and  the  spines  of 
the  seventh  cervical  and 
first  thoracic  vertebrae. 
Passing  obliquely  down- 
wards and  laterally  it  is 
inserted  into  the  vertebral 
border  of  the  scapula  be- 
low the  levator  scapulae 
muscle,  and  opposite  to 
the  base  of  the  spine 
(Fig.  245,  p.  322). 

The  rhomboideus 
major  arises  from  the 
spinous  processes  of  the 
thoracic  vertebrae  from 
the  second  to  the  fifth 
inclusive,  and  from  the 
corresponding  supraspin- 
ous ligaments.  Passing 
downwards  and  laterally 
it  is  inserted  below  the 
rhomboideus  minor  into 
the  vertebral  border  of 
the  scapula,  between  the 
spine  and  the  lower  angle 
(Fig.  245,  p.  322).  The 
muscle  is  only  inserted 
directly  into  the  scapula 
by  means  of  its  lower 
fibres.  Its  upper  part  is 
attached  to  a  membranous 

band,  which,  connected  for  the  most  part  by  loose  areolar  tissue  to  the  vertebral 

border  of  the  scapula,  is  fixed  to  the  bone  at  its  extremities,  above  near  the  base 

of  the  spine,  and  below  at  the  inferior  angle. 

The  rhomboid  muscles  are  concealed  for  the  most  part  by  the  trapezius.     The 

lower  part  of  the  rhomboideus  major  is  superficial  in  the  triangle  of  auscultation. 

The  muscles  cover  the  serratus  posterior  superior  and  vertebral  aponeurosis. 


Teres  major  (origin) 


Latissimus  dorsi  (origin) 


Fig.  245.- 


-Muscle-Attachments  to  the  Right  Scapula 
(Posterior  Surface). 


THE    FASCIvE   AND    MUSCLES    OF   THE 
PECTORAL    REGION. 

FASCIA. 


The  superficial  fascia  of  the  chest  usually  contains  a  quantity  of  fat,  in  which 
the  mamma  is  embedded.  The  origin  of  the  platysma  muscle  lies  beneath  its  upper 
part. 

The  deep  fascia  is  attached  above  to  the  clavicle,  and  in  the  middle  line  to  the 
sternum.  Below  it  is  continuous  with  the  fascia  of  the  abdominal  wall.  It  gives 
origin  to  the  platysma  and  invests  the  pectoralis  major.  At  the  lateral  border 
of  the  great  pectoral  muscle  it  is  thickened,  and  forms  the  floor  of  the  axillary 
space  (axillary  fascia),  continued  posteriorly  on  to  the  posterior  fold  of  the  axilla 
and  laterally  into  connexion  with  the  deep  fascia  of  the  arm. 


FASCI.^:  AND  MUSCLES  OF  THE  PECTOEAL  EEGION. 


123 


Costo-Coracoid  Membrane, — Beneath  the  pectorahs  major  a  deeper  stratum  of 
fascia  invests  the  pectoralis  minor  muscle.  At  the  upper  border  of  this  muscle  it 
forms  the  costo-coracoid  membrane,  which  passes  upwards  to  the  lower  border  of  the 
subclavius  muscle,  where  it  splits  into  two  layers,  attached  in  front  of  and  behind 
that  muscle  to  the  borders  of  the  under  surface  of  the  clavicle.  The  membrane 
traced  medially  along  the  subclavius  muscle  is  attached  to  the  first  costal  cartilage  ; 
passing  laterally  along  the  upper  border  of  the  pectoralis  minor  it  reaches  the 
coracoid  process.  The  part  of  the  membrane  extending  directly  between  the  first 
costal  cartilage  and  the  coracoid  process  is  thickened  and  forms  the  costo-coracoid 
ligament.  The  costo-coracoid  membrane  is  otherwise  thin  and  of  comparatively 
small  importance.  It  is  pierced  by  the  cephalic  vein,  thoracic  axis  artery  and 
vein,  and  branches  of  the  external  anterior  thoracic  nerve.  By  its  deep  surface  it  is 
connected  to  the  sheath  of  the  axillary  vessels. 

At  the  lower  border  of  the  pectoralis  minor  there  is  a  further  extension  of  the 
deep  fascia  beneath  the  pectoralis  major.  It  passes  downwards  to  join  the  fascia 
forming  the  floor  of  the  axilla,  and  is  continued  laterally  into  the  fascia  covering 
the  biceps  and  coraco-brachialis  muscles. 


MUSCLES  OF  THE  PECTORAL  REGION. 


The  anterior  muscles  connecting  the  upper  limb  to  the  axial  skeleton  comprise 
the  pectoralis  major,  pectoralis  minor,  subclavius,  ser-  stemo-cieido-mastoid  (origin 

ratus  anterior  (s.  magnus),  and  sterno-cleido-mastoid. 
The  last  is  described  in  a  later  section  (p.  420). 

The  pectoralis  major  is  a  large  fan-shaped  muscle 
arising  in  three  parts :  (!)  a  pars  clavicularis  arising 
from  the  front  of  the  clavicle  in  its  medial  half  or  two- 
thirds  (Figs.  243,  p.  320,  and  248,  p.  325) ;  (2)  a  pars 
sterno-costalis,  the  largest  part  of  the  muscle,  arising 
from  the  anterior  surface  of  the  pre-sternum  and  meso- 
sternum  by  tendinous  fibres  decussating  with  those  of  the 
opposite  muscle  (Fig.  247,  p.  324),  and  more  deeply  from 
the  cartilages  of  the  first  six  ribs;  (3)  a  pars  abdominalis, 
a  small  and  separate  slip,  arising  from  the  aponeurosis  of 
the  obliquus  externus  muscle.  The  abdominal  slip,  at  first 
separate,  soon  merges  with  the  sterno-costal  portion,  but 
a  distinct  interval  usually  remains  between  the  two  first- 
named  parts  of  the  muscle.  The  fibres  converge  towards 
the  upper  part  of  the  arm,  and  are  inseparably  blended  at 
a  point  half  an  inch  from  their  insertion  into  the  humerus. 
The  muscle  is  inserted  into  (1)  the  lateral  border  of  the 
bicipital  groove  (sulcus  intertubercularis)  of  the  humerus, 
extending  upwards  to  the  greater  tuberosity,  and  blending 
laterally  with  the  insertion  of  the  deltoid,  medially  with 
the  insertion  of  the  latissimus  dorsi  (Fig.  247,  p.  324) ; 
(2)  from  the  upper  border  of  the  insertion  a  membranous 
band  extends  upwards  to  the  capsule  of  the  shoulder-joint, 
enveloping  at  the  same  time  the  tendon  of  the  biceps; 
and  (3)  from  the  lower  border  a  band  of  fascia  passes 
downwards  to  join  the  fascia  of  the  arm. 

The  arrangement   of   the   fibres  of  the  muscle  at  its 
insertion  is  peculiar.     The  muscle  is  twisted  on  itself,  so 
that  the  lower  (sterno-costal)  fibres  are  directed  upwards  Fig.  246.  —  Muscle- Attach- 
and  outwards  behind  the  upper  (clavicular)  part  of  the        '^'ents  to  the  Front  of 
muscle ;  in  consequence  the  clavicular  part  is  attached  to        ™^  Sternum. 
the  humerus  lower  down  than  the  sterno-costal  portion,  and  is  inserted  also  into 
the  fascia  of  the  arm.     The  twisting  of  the  fibres  is  specially  found  in  the  lower 


Rectus 

abdomini.s 

(insertion) 


324 


THE  MUSCULAE  SYSTEM. 


sterno-costal  fibres  of  the  muscle  and  the  abdominal  fibres.  These  curve  upwards 
behind  the  upper  sterno-costal  fibres,  and  have  the  highest  attachment  to  the  shaft 
of  the  humerus,  helping  to  form  the  fascial  expansion  which  extends  upwards  over 
the  biceps  tendon  to  tlie  capsule  of  the  shoulder-joint.  In  this  way  a  bilaminar 
tendon  is  produced  united  along  its  lower  border ;  consisting  of  a  superficial 
lamina  formed  by  the  upper  sterno-costal  fibres,  blending  for  the  most  part  with  the 


/  H 


\.  _.I)iGASTKic  (anterior  belly) 


Platysma/ 


Pectoralis  major  (pars  sternalis) 
Pectoralis  major  (pars  clavicularis)         ''■. 


Stekko-cleido-mastoid 
Stepno-thyeeoid 
subclavius 
,--''         ..■•         Pectoralis  major  (sternal  origin) 


Pectoralis 
MAJOR  (pars 
aMominalis) 


Obliql-vs 

EXTERSf.S 
ABDOMINIS 


Sheath  of  rectu 
abdomini 


Rectus  abdominis 


Fig.  247. — The  Muscles  of  the  Front  of  the  Chest. 


tendon  of  the  clavicular  portion  ;  and  a  deep  lamina,  composed  of  the  twisted  lower 
sterno-costal  and  abdominal  fibres.  The  disposition  of  the  muscular  fibres  at  their 
insertions  is  the  reason  for  the  application  of  the  terms  "  2:)ortio  attollens"  to  the 
clavicular  portion,  and  " portio  deprimens"  to  the  sterno-costal  and  abdominal  por- 
tions of  the  muscle. 

Placed  superficially,  the  pectoralis  major  forms  the  front  wall  and  anterior 
fold  of  the  axilla.  Its  upper  border  is  separated  from  the  edge  of  the  deltoid 
muscle  by  an  interval  in  which  lie  the  cephalic  vein  and  humeral  artery.     Its  deep 


MUSCLES  OF  THE  PECTOKAL  EEGION. 


325 


surface  is  in  relation  with  the  ribs  and  intercostal  muscles,  the  costo-coracoid 
membrane  and  the  structures  piercing  it,  the  pectoralis  minor,  the  axillary  vessels, 
and  the  nerves  of  the  brachial  plexus. 

Stemalis  muscle. — The  sternalis  is  an  occasional  mnscle  placed,  when  present,  parallel  to 
the  sternum  upon  the  stemo-costal  origin  of  the  ijectoralis  major.  It  has  attachments  which 
are  very  variable  both  above  and  below,  to  the  costal  cartilages,  sternum,  rectus  sheath,  stemo- 
mastoid,  and  pectoralis  major.  Its  nerve-supply  is  from  one  or  both  of  the  anterior  thoracic 
nerves.  In  certain  rare  cases  it  has  been  said  to  be  innervated  by  intercostal  nerves.  It  is 
present  in  4'4  cases  out  of  100,  and  it  is  slightly  more  frequent  in  the  male  than  in  the  female. 
It  has  been  regarded  by  different  observers  as  (1)  a  vestige  of  the  panniculus  carnosus,  (2)  a 
homologue  of  the  sterno-mastoid,  or  (3)  a  displaced  slij)  of  the  pectoralis  major. 

Chondro-epitrochlearis,  dorso-epitrochlearis,  axillary  arches,  costo-coracoideus. — One 
or  other  of  the  above-named  slips  is  occasionally  present,  crossing  the  floor  of  the  axilla  in  the 
interval  between  the  latissimus  dorsi  and  the  pectoralis  major.  They  take  origin  from  the  costal 
cartilages,  ribs,  or  borders  of  the  pectoralis  major  {chondro-epitrochlearis,  axillary  arches,  costo- 
coracoideus),  or  from  the  border  of  the  latissimus  dorsi  {dorso-epitrochlearis,  axillary  arches,  costo- 
coracoideus).  Their  insertion  is  variable.  The  chondro-epitrochlearis  and  clorso-epitrochlearis  are 
inserted  into  the  fascia  of  the  arm,  the  medial  intermuscular  septum,  or  the  mesial  condyle 
of  the  humerus.  The  axillary  arches  are  inserted  into  the  border  of  the  pectoralis  major,  the 
fascia  of  the  arm,  or  the  coraco-brachialis  or  biceps  muscle.  The  costo-coracoideus,  arising 
from  the  ribs  or  the  ajjoneurosis  of  the  obliquus  externus,  or  detaching  itself  from  the  border 
of  the  pectoralis  major  or  latissimus  dorsi,  is  attached  to  the  coracoid  process,  alone  or  along 
with  one  of  the  muscles  attached  to  that  bone.  These  variable  slips  of  muscle  are  supplied 
by  the  internal  anterior  thoracic  nerve,  the  lesser  internal  cutaneous  nerve,  or  the  intercosto- 
humeral. 

The  pectoralis  minor  is  a  narrow,  flat,  triangular  muscle.  It  arises  under 
cover  of  the  pectoralis  major  from  (1)  the  surfaces  and  upper  borders  of  the 
third,  fourth,  and  fifth  ribs  near  their  anterior  ends,  and  (2)  from  the  fascia 
covering  the  third  and  fourth  intercostal  spaces  between  these  ribs.  It  may  have 
an  additional  origin  from  the  second  rib  (Eig.  247,  p.  324) ;  and  that  from  the  fifth 
rib  is  often  absent.  Directed  obliquely  laterally  and  upwards,  it  is  inserted  by 
a  short,  flat  tendon  into  the  lateral  half  of  the  anterior  border  and  upper 
surface  of  the  coracoid  process  (Fig.  258,  p.  326),  and  usually  also  into  the 
conjoint  origin  of  the  biceps  brachii  and  coraco-brachialis.  It  enters  into  the 
formation  of  the  front  wall  of  the  axilla,  and  gives  attachment  along  its  upper 
border  to  the  costo-coracoid  membrane.  It  crosses  the  axillary  vessels  and  the 
cords  of  the  brachial  plexus,  and  is  pierced  by  branches  of  the  anterior  thoracic 
nerves. 

Either  in  j^art  or  wholly  the  pectoralis  minor  may  pass  over  the  coracoid  process  of  the 
scapula,  sejDarated  from  it  by  a  bursa,  to  be  inserted  into  the  coraco-acromial  ligament,  or  the 
acromion  jJrocess  ;  or  piercing  the  coraco-acromial  ligament,  it  may  be  attached  to  the  capsule  of 
the  shoulder-joint  (coraco-humeral  ligament). 

Pectoralis  minimus. — This  is  a  slender  slip,  rarely  present,  which  extends  between  the  first 
costal  cartilage  and  the  coracoid  process.  *r 

The  subclavius  muscle  arises  from  the  upper  surface  of  the  first  costal  cartilage 
in  front  of  the    costo  -  clavicular  ligament,  and  from  the  upper  surface  of  the 


Coraco-clavic- 

ular  ligament 

(trapezoid) 


Pectoralis  major  (origin) 


Costo-clavic- 
ular  ligament 
(rhomboid) 


Subclavius  (insertion) 
Conoid  ligament 
Fig.  248. — Mttscle-Attachmexts  to  the  Right  Clavicle  (Under  Surface). 

distal  end  of  the  first  rib  (Fig.  247,  p.  324).  It  is  inserted  into  a  groove  in  the 
middle  third  of  the  under  surface  of  the  clavicle  (Fig.  248,  p.  325).  The  muscle 
is  invested  by  the  fascia  which  forms  the  costo-coracoid  membrane,  and  is  concealed 
by  the  clavicle  and  the  clavicular  origin  of  the  pectoralis  major. 


326 


THE  MUSCULAE  SYSTEM. 


Triceps  biacl 


Fig.  249. — The  Left  Serratds  Magnus  (see- 

EATCS    anterior)    MUSCLE. 

partly  superficial  below  the  axil- 
lary space,  on  the  side  wall  of  the 
chest,  where  its  slips  of  origin  are 
seen  inter-digitating  with  those 
of  the  obhquus  externus  abdom- 
inis. Higher  up  it  forms  the  medial 
wall  of  the  axilla,  and  is  in  con- 
tact with  the  pectoral  muscles  in 
front  and  the  subscapularis  be- 
hind. Its  upper  border  appears 
in  the  floor  of  the  posterior  tri- 
angle, and  over  it  the  axillary 
artery  and  the  cords  of  the  brachial 
plexus  pass  in  their  course  through 
the  axilla.  The  lower  border  is 
oblique,  and  is  in  contact  with 
the  latissimus  dorsi  muscle.  The 
muscle  may  extend  higher  than  usual,  so  as  to 
be  continuous  in  the  neck  with  the  levator 
scapulae. 

Nerve-Supply. 

The  nen'e-supply  of  the  muscles  connecthig  the 
upper  limb  to  tlie  trunk  is  in  the  main  derived  from 
the  cervical  and  brachial  plexuses.  The  trapezius  is 
innervated  from  two  sources,  by  the  spinal  accessory- 
nerve  1  and  by  the  cervical  plexus  (C.  3.  and  4.). 
Tlie  latissimus  dorsi  is  innervated  by  the  long  sub- 
scapular nerve  -  from  the  brachial  plexus  (C.  6.  7.  8.).  The 
levator  scapulas  receives  two  neives  from  the  cervical 
plexus  (C.  3.  and  4.),  and  a  branch  from  the  posterior 

1  Spinal  accessory  nSrve  =  accessory  nerve  (B.N. A.). 

2  Long  subscapular  nerve  =  thoraco-dorsal  nerve  (B.N. A.). 


The  sterno-clavicularis  is  a  small  separate 
slip,  rarely  present,  extending  beneath  the  pector- 
alis  major  from  the  up^^er  part  of  the  sternum  to 
the  clavicle. 

The  serratus  anterior  (serratus  mag- 
nus)  is  a  large  curved  quadrilateral  muscle 
occupying  the  side  of  the  chest  and  medial 
wall  of  the  axilla.  It  arises  by  fleshy  slips 
from  the  lateral  aspect  of  the  upper  eight 
and  occasionally  (as  in  the  figure)  from  nine 
ribs.  The  first  slip  is  a  double  one,  arising 
from  the  first  two  ribs  and  the  fascia  cover- 
ing the  intervening  space  (Fig.  249,  p.  326). 
The  insertion  of  the  muscle  is  threefold. 
(1)  The  first  portion  of  the  muscle  (from 
the  first  and  second  ribs)  is  directed  back- 
wards to  be  inserted  into  the  ventral  aspect 
of  the  upper  angle  of  the  scapula.  (2)  The 
next  three  slips  of  the  muscle  (from  the 
second,  third,  and  fourth  ribs)  are  inserted 
into  the  vertebral  border  of  the  scapula. 
(3)  The  last  four  slips  (from  the  fifth,  sixth, 
seventh,  and  eighth  ribs)  are  directed  ob- 
liquely upwards  and  backwards,  to  be  in- 
serted on  the  ventral  aspect  of  the  lower 
angle  of  the  scapula  (Fig.  250,  p.  326). 

The   lateral   surface   of  the   muscle   is 


Deltoid  (origin) 

Biceps  and  coraeo-brachialis  (origin) 
Pectoralis  minor  (insertion) 

Omohyoid  (origin) 


Fig.  250. — Muscle-Attachments  to  the 
PacHT  Scapula  (Anterior  Aspect). 


FASCIA  AND  MUSCLES  OF  THE  SHOULDER 


327 


scapular  nerve  ^  from  the  brachial  plexus  (C.  5.),  which  supplies  also  the  rliomljoid  muscles.  Each 
of  the  pectoral  muscles  is  imiervated  by  both  tlie  external  and  internal  anterior  thoracic  nerves 
from  the  brachial  plexus  (C.  5.  6.  7.  and  C.  8.  T.  1.)  (p.  626).  The  subclavius  receives  its  nerve 
from  the  brachial  plexus  (C.  5.  6.).  The  serratus  anterior  is  supplied  by  the  posterior  thoracic 
nerve '-^  from  tlie  brachial  plexus  (C.  5.  6.  7.). 

Actions. 

The  muscles  of  this  group  (together  with  the  sterno-cleido-mastoid  and  omohyoid  muscles)  act 
for  the  most  part  in  the  movements  of  the  shoulder  girdle  at  the  sterno-clavicular  and  acromio- 
clavicular joints.  At  the  former  joint  they  produce  the  various  movements  of  the  clavicle  on  the 
sternum,  and  cause  the  shoulder  to  move  in  an  arc  the  centre  of  which  is  the  sterno-clavicular  joint. 
At  the  acromio-clavicular  articulation  they  produce  a  rotation  of  the  scapula  on  the  clavicle,  and  a 
consequent  alteration  in  the  direction  of  the  glenoid  fossa.  At  the  same  time  the  several  muscles 
are  agents  in  other  equally  important  movements,  when  the  shoulder  girdle  is  fixed  ;  movements 
of  the  head  and  neck  ;  movements  of  the  trunk  and  ribs  ;  and,  in  addition  in  the  case  of  the 
pectoralis  major  and  latissimus  dorsi,  important  movements  of  the  arm  at  the  shoulder-joint. 

1.  Movements  of  the  Shoulder  Girdle. — The  action  of  this  group  of  muscles  on  the  shoulder 
girdle  (mainly  corresponding  to  movements  at  the  sterno-clavicular  joint)  may  be  expressed  in 
the  following  table  : — 


a.  Movement  in  a  Vertical  Plane.         ,       i-  Movement  in  a  Horizontal  Plane. 

Elevation. 

Depression. 

Forwards. 

Backwards. 

Trapezius     (upper 

fibres) 
Levator  scapulee 
Rhomboidei 
Sterno-mastoid 
Omohyoid 

Trapezius      (lower 

fibres) 
Subclavius 
Pectoralis  minor 
Latissimus  dorsi 
Pectoralis       major 

(lower  fibres) 

Serratus  anterior 
Pectoralis  major 
Pectoralis  minor 

Traj^ezius 
Rhomboidei 
Latissimus  dorsi 

c.  Rotation — a  combination  of  these 
muscles. 

2.  Movements  of  the  scapula  on  the  clavicle  produce  an  alteration  of  the  direction  of  the 
glenoid  fossa  of  the  scapula,  and  are  accompanied  by  movements,  inwards  or  outwards,  forwards 
or  backwards,  of  the  inferior  angle  of  the  scapula.  By  the  combined  action  of  the  muscles 
acting  upon  the  shoulder  girdle  a  rotatory  movement  of  the  scapula  at  the  acromio-clavicular 
joint  is  effected,  by  which  the  relation  of  the  glenoid  fossa  to  the  head  of  the  humerus  is  preserved 
in  movements  of  the  arm. 

3.  In  forced  inspiration,  the  sterno-mastoid,  trapezius,  levator  scapulae,  rhomboidei,  sub- 
clavius, omohyoid,  serratus  anterior,  pectoral  muscles,  and  latissimus  dorsi,  acting  together,  raise 
and  fix  the  shoulder  girdle ;  while  those  of  them  which  have  costal  attachments— subclavius, 
pectoral  muscles,  serratus  anterior,  and  latissimus  dorsi — simultaneously  elevate  the  ribs  and 
expand  the  thorax. 

4.  Lateral  flexion  and  rotation  of  the  spine  in  the  neck  is  effected  partly  by  the  action  of 
the  trapezius,  levator  scapulae,  and  rhomboid  muscles  (with  the  shoulder  fixed).  The  latissimus 
dorsi  and  pectoralis  major  act  in  climbing  in  a  similar  way,  raising  up  the  trunk  towards  the 
shoulder. 

5.  Action  on  the  Upper  Limb. — By  reason  of  their  insertion  into  the  humerus  the  pectoralis 
major  and  latissimus  dorsi  muscles  assist  the  movements  of  the  upper  limb.  Acting  together,  the 
two  muscles  depress  the  shoulder,  and  draw  the  arm  to  the  side  of  the  body,  at  the  same  time 
rotating  the  humerus  inwards.  The  two  parts  of  the  pectoralis  major  have  slightly  different 
actions  on  the  humerus.  The  clavicular  part  of  the  muscle  (portio  attollens)  draws  the  arm  in- 
wards and  upwards  ;  the  sterno-costal  part  of  the  muscle  (jjortio  deprimens)  draws  it  inwards  and 
downwards.  The  latissimus  dorsi  acting  alone,  besides  rotating  the  limb,  draws  it  inwards  and 
backwards,  as  in  the  act  of  swimming. 


FASCIAE  AND    MUSCLES   OF  THE   SHOULDER. 

The  deep  fascia  covering  the  scapular  muscles  presents  no  feature  of  special 
importance.  Attached  to  the  clavicle,  acromion,  and  scapular  spine,  it  is  thin  over 
the  deltoid  muscle.  Below  the  deltoid  it  is  thicker ;  it  encases  and  gives  origin  to 
the  infraspinatus  muscle,  and  is  continuous  with  the  fasciae  of  the  axilla  and  the 
back. 

lYIuscIes. 

The  muscles  proper  to  the  shoulder  comprise  the  deltoid,  supraspinatus,  infra- 
spinatu.s,  teres  minor,  teres  major,  and  subscapularis. 

^  Posterior  .scapular  nerve  =  dorsal  nerve  of  the  scapula  (B.N. A.). 
-  Posterior  thoracic  nerve  =  long  thoracic  or  external  respiratory  nerve  of  Bell  (B.N.A.). 


328  THE  MUSCULAR  SYSTEM. 

The  deltoid  (m.  deltoideus),  a  coarsely  fasciculated,  multipennate  muscle,  has  an 
extensive  origin  from  (1)  the  front  of  the  clavicle  in  its  lateral  third  (Figs.  243,  p.  320, 
and  248,  p.  325);  (2)  the  lateral  border  of  the  acromion  process;  (3)  the  lower  edge 

of  the  free  border  of 

Lkvator  scapul.-e 

*^,^_gg^  the    spme    of    the 

H^^^^T^k"-^'""''"'"'"''^'^  '"^°''  scapula  (Figs.  245, 

'fliSSift  ^  p.  322,  and  254,  p. 

^SBf     -^^*-  330) ;  and  (4)  from 

.W^ .^^^^^^>»^        rhombo.b-  the    deep    fascia 

Eus  MAJOR  covering  the  infra- 
spinatus muscle. 

Spine  of  .scapula ^'iSHBBfe. '•k.  Its  Origin  embraces 

^^^^^  the  insertion  of  the 

/'  ^^HHP,     a  trapezius.       The 

spi.xATis  —-J' ''''^/^^^^^B^KSB/tUSSB^Sm^^SM  y  tibres  of  the  muscle 

^  — ^>^^^^^^^^i^^^^^**5S«SI^H»''-f'|^  converge    to    the 

-|g  lateral  aspect  of 

^^^_^^^^_.  e,,,       1°  the    shaft    of    the 

' /mU^K^^  humerus,  to  be  in- 

teres     ;;>^^^^^^»bh^^~;  ./^mJI^^P^^teres  major  serted  into  a  well- 

"^'^^^^^^^^T^^^M^B^^  marked      V-shaped 

J4_^J||^^^^'^"'^"^'"'^'^^P^'=e  impression      above 

^    ,  .,  ,     ,  the    spiral     groove 

Quadrilateral  space  ,„.         j^^„  o^      \ 

(Fig.  253,  p.   330). 
Triceps  BRACHii  The      insertion     is 

(Lateral  head)  partly  United  with  the  tendon  of  the 

H  '  -  '^g'  ^1   M1MB|2"    'A  pectoralis  major. 

hJS^^  ,  I    BiailL¥-TBr-'  T-cEPs  (medial  ^hc  most  anterior  part  of  the 

.  deltoid  muscle  is  formed  of  parallel 

'.t\  H^BitW  rWHI-MuscuIo-spiral  nerve     £!.>.„„„ j.  i  ^ 

Deltoid      ' '    '.  WHi'li  WW  iibres,    uot    Uncommonly   separate 

Triceps  brachii        from  the  rcst  of  the  musclc  at  their 

(longhead)  ^^^-g-^^     f^,^^     ^^^    claviclc.        ThcSC 

fibres  may  be  continuous  with  the 
trapezius  over  the  clavicle.  The 
most  posterior  part  arises  by  a 
fascial  origin  from  the  spine  of  the 
scapula  and  the  fascia  over  the 
infraspinatus  muscle.  These  por- 
tions are  attached  respectively  to 
the  front  and  back  of  the  main 
Extensor  CARPI         tcndou  of  insertion.      The   inter- 

RADIALIS  LONGUS  T      j_  r>l  i,. 

mediate   fibres  are  multi-pennate. 
Triceps  brachii         attached  abovc  and  below  to  three 
(tendon  of  insertion)    or  four  Septal  tcudous,  which  ex- 
tend for  a  variable  distance  down- 
iRAmTLTBREvrs         wards  and  upwards  from  the  origin 

and  insertion  of  the  muscle. 
Olecranon  process  xhc  deltoid  is  Superficial  in  its 

whole  extent,  and  forms  the  pro- 
minence of  the  shoulder.  Its  an- 
terior border  is  separated  from  the 
pectoralis  major  by  a  narrow  in- 

r  1(1.  251.- — LKFT    SCAILLAI;    .\lu.-,i  I.Lb    AND    TlUCEPS.  4.^  1       •„  1    •     I,     L.\.  ■!_     T 

terval,  m  which  the  cephalic  vein 
and  humeral  artery  are  placed.  The  deep  surface  of  the  muscle,  separated  from  the 
capsule  of  the  shoiilder-joint  by  a  large  bursa,  is  related  to  (1)  the  coracoid  process, 
associated  with  which  are  the  coraco-acromial  ligament,  and  the  attachments  of 
the  pectoralis  minor,  the  coraco-brachialis,  and  the  short  head  of  the  biceps  brachii ; 
(2)  the  capsule  of  the  shoulder-joint  covering  the  head  of  the  humerus,  associated 
with  which  are  the  long  head  of  the  biceps,  and  the  attachments  of  the  subscapularis. 


MUSCLES  OF  THE  SHOULDEE 


329 


SeRRATI'S  ASTERllpR 
(S.   MAfiNUS) 

.StIBSCAPULARIS 

Slpkaspinatus 

I'KriORALIS 
MINOR 

Coracoid 
locess 

Triangular 
■ipace 


See- 
rat  u  a 

AN- 
TERIOR (S.  MA(iNUS)       '. 

IjATISSIMUS  DORSr 

Teres  major 

CORACO-BRACHIALIb 

Biceps  (short  head) ' 

Teres  major 


supraspinatus,  infraspinatus,  and  teres  minor ;  and  (3)  the  upper  part  of  tlie  lateral 
surface  of  the  shaft  of  the  humerus,  associated  with  which  are  the  posterior  circumflex 
vessels  and  circumflex  nerve.^ 

The  supraspinatus 
arises  by  fleshy  fibres  froLu 
the  supraspinous  fossa  (ex- 
cept near  the  neck  of  the 
bone)  and  from  the  deep 
fascia  over  it  (Eig.  245, 
p.  322).  It  is  directed 
outwards  under  the  acro- 
mion process  and  coraco- 
acromial  ligament  to  be 
inserted  by  a  broad  thick 
tendon  into  the  uppermost 
facet  on  the  greater  tuber- 
osity of  the  humerus,  and 
into  the  capsule  of  the 
shoulder-joint  (Fig.  253, 
p.  330). 

The  infraspinatus 
arises  from  the  infraspin- 
ous  fossa  of  the  scapula  (excepting  near 
the  neck  of  the  bone  and  the  flat  surface 
along  the  axillary  border)  and  from  the 
thick  fascia  over  it  (Fig.  245,  p.  322). 
The  fibres  of  the  muscle  converge  to  the 
neck  of  the  scapula ;  and  are  inserted  by 
tendon  into  themiddle  facet  on  the  greater 
tuberosity  of  the  humerus,  and  into  the 
capsule  of  the  shoulder-joint  (Fig.  253, 
p.  330).  A  bursa  separates  the  muscle 
from  the  neck  of  the  scapula,  and  in  a 
minority  of  cases  communicates  with  the 
synovial  cavity  of  the  shoulder- joint. 

The  supraspinatus  and  the  upper  part 
of  the  infraspinatus  muscles  are  concealed 
by  the  trapezius,  acromion  process,  and 
deltoid.  They  cover  theneckof  thescapula, 
the  suprascapular  artery  and  nerve,-  and 
the  capsule  of  the  shoulder -joint. 

The  teres  minor  is  a  small  muscle, 
arising  by  fleshy  fibres  from  the  upper 
two- thirds  of  the  flat  surface  on  the 
dorsal  aspect  of  the  axillary  border  of  the 
scapula,  and  from  fascial  septa  separating 
it  from  the  infraspinatus  and  teres  major 
muscles  (Fig.  245,  p.  322).  Lying  along- 
side the  lateral  border  of  the  infraspinatus, 
it  is  inserted  under  cover  of  the  deltoid 
by  a  thick  flat  tendon  into  the  lowest  of 
the  three  facets  on  the  greater  tuberosity 
of  the  humerus  and  into  the  capsule  of 
the  shoulder-joint,  and  by  fleshy  fibres  into  the  posterior  aspect  of  the  surgical 
neck  and  shaft  of  the  humerus  below  the  tuberosity  for  about  an  inch  (Fig.  253, 
p.  330).  It  is  separated  from  the  teres  major  by  the  long  or  scapular  head  of  the 
triceps  brachii,  and  by  the  posterior  circumflex  vessels  and  the  cii-cumflex  nerve. ^ 

^  Circumflex  nerve  =  axillarj'  nerve  (B.N. A.). 
^  Suprascapular  artery  =  transverse  artery  of  the  scapula  (B.N.  A.). 


Brachio-radialis 

Flexor  carpi 
radialis 

Pronator  teres 


Fig.  252. — Muscles  of  Posterior  Wall  of 
Left  Axilla  and  Front  of  Arm. 


330 


THE  MUSCULAE  SYSTEM. 


Its  origin  is  pierced  by  the  dorsal  scapular  artery.^  The  muscle  is  invested  by 
the  deep  fascia  enclosing  the  infraspinatus,  and  is  sometimes  inseparable  from 
that  muscle. 

The  teres  major  is  much  larger  than  the  preceding  muscle.  It  arises  by  fleshy 
fibres  from  the  lower  third  of  the  flat  surface  on  the  dorsum  of  the  scapula  along  its 
axillary  border  (except  for  a  small  area  at  the  lower  angle),  and  from  fascial  septa, 
which  separate  it  on  the  one  side  from  the  subscapularis,  and  on  the  other  from  the 
infraspinatus  and  teres  minor  (Fig.  245,  p.  322).      The  muscle  is  directed  along 

the  axillary  border  of  the  scapula  to  the  front  of 
the  shaft  of  the  humerus,  where  it  is  inserted  by  a 
broad  flat  tendon  into  the  medial  border  of  the 
bicipital  groove  (sulcus  inter  tubercularis)  medial 
to  the  latissimus  dorsi  muscle  (Fig.  253,  p.  330). 
Just  before  its  insertion  it  is  closely  adherent  to 
the  tendon  of  the  latissimus  dorsi. 

The  teres  major  lies  below  the  subscapularis 
muscle  on  the  posterior  wall  of  the  axilla.  The 
latissimus  dorsi  muscle,  sweeping  round  from  the 
back,  covers  its  axillary  surface  on  its  way  to  its 
insertion.     The  muscle  forms  the  lower  boundary 


Supraspinatus 
-(insertion) 


Subscapularis 
["(insertion) 


Pectoralis  major 
■(insertion) 

Latissimus  dorsi 
"(insertion) 


Teres  major 
'(insertion) 


Deltoid'. 

(insertion) 
Coraco-brachialis 

4 

(insertion) 

^/7 

u  ^' 

Brachialis . 

(origin) 

•^Iv 

o\\ 

_Bracliio-radialis 

"^  V 

■(origin) 

41 

s 

U: 


Extensor  carpi 
radialis  longus 
-(origin) 

Common  tendon 
for  origin  of 
pronator 
"teres  and  flexor 
muscles  of 
forearm 


Common  tendon  for  origin  of 
extensoE  muscles  of  forearm 

Fio.  253. — Muscle- Attachments  to 
THE  Front  of  the  Right  Humerus. 


Teres  minor 
(origin)  with  gap 
for  dorsal  scap- 
ular artery 


Teres  major  (origin) 


Latissimus  dorsi  (origin) 


Fig.  254. — Muscle- Attachments  to  the  Right  Scapula 
(Posterior  Surface). 


of  a  triangular  space  on  the  posterior  wall  of  the  axilla,  of  which  the  other  boundaries 
are,  above,  the  borders  of  the  subscapularis  and  teres  minor  muscles,  and  laterally 
the  surgical  neck  of  the  humerus.  This  space  is  subdivided  by  the  long  head  of 
the  triceps  brachii,  which  passes  behind  the  teres  major  muscle,  into  (a)  a  quadri- 
lateral space   above,  for  the  passage  of  the  circumflex  nerve-  and  posterior  cir- 

^  Dorsalis  scapulae  =  circumflex  artery  of  the  scapula  (B.N. A.). 
'^  Circumflex  nerve  =  axillary  nerve  (B.N.A.). 


MUSCLES  OF  THE  SHOULDER 


331 


ciimflex  artery ;  ^  and  (b)  a  smaller  triangular  space  below,  for  the  dorsal  scapular 
artery.- 

The  subscapularis  is  a  large  triangular  muscle  occupying  the  venter  of  the 
scapula.  It  arises  by  tleshy  fibres  from  the  whole  of  the  subscapular  fossa  and  the 
groove  along  tlie  axillary  border,  excepting  the  surfaces  at  the  angles  of  the  bone 
(Fig.  250,  p.  326).  Springing  from  several  ridges  in  the  fossa  are  septa  projecting 
into  the  substance  of  the  muscle,  which  increase  the  extent  of  its  attachment.  Con- 
verging to  the  head  of  the  humerus,  the  muscular  fibres  are  inserted  by  a  broad,  thick 
tendon  into  the  lesser  tuberosity  of  the  humerus  and  into  the  capsule  of  the  shoulder- 
joint,  and  by  fleshy  fibres  into  the  surgical  neck  and  the  shaft  of  the  humerus 
below  the  tuberosity  for  about  an  inch,  under  cover  of  the  coraco-brachialis  and 
short  head  of  the  biceps  (Fig.  253,  p.  330).  This  muscle  forms  the  greater  part  of 
the  posterior  wall  of  the  axilla.  Its  medial  or  anterior  surface  is  in  contact  with  the 
serratus  anterior  (s.  magnus)  and  the  axillary  vessels  and  nerves.  It  is  separated 
from  the  neck  of  the  scapula  by  a  bursa,  which  is  in  direct  communication  with 
the  synovial  cavity  of  the  shoulder-joint. 

The  subscapularis  minor  is  an  occasional  muscle  situated  below  the  capsule  of  the  shoulder- 
joint.  It  arises  from  the  axillary  border  of  the  scapula  below  the  subscapularis,  and  is  inserted 
into  the  capsule  of  the  joint  or  the  upper  part  of  the  shaft  of  tlie  humerus. 

Nerve-Supply. 

The  muscles  of  this  group  are  all  supplied  by  the  fifth  and  sixth  cervical  nerves,  through 
nerves  arising  from  posterior  trunks  of  the  brachial  plexus.  The  deltoid  and  teres  minor  receive 
their  nerve-supply  from  the  circumflex  nerve  ^  (C.  5.  6.)  ;  the  supraspinatus  and  infraspinatus 
from  the  suprascapular  (C.  5.  6.)  ;  the  teres  major  from  the  lower  subscapular  nerve  (C.  5.  6.) ; 
and  the  subscapularis  from  the  upper  and  lower  subscapular  nerves  (C.  5.  6.). 

Actions. 

The  principal  action  of  this  group  of  muscles  is  on  the  shoulder-joint.  They  have  also 
secondary  actions  in  relation  to  movements  of  the  trunk  and  limbs. 

1.  Movements  at  the  Shoulder -Joint. 


a.  Abduction. 

Deltoid 
Supraspinatus 


Adduction. 


Teres  major 
Teres  minor 
Pectoralis  major 
Latissimus  dorsi 
Coraco-brachialis 
Biceps  (short  head) 
Triceps  brachii  (long 

head) 
Weight  of  limb 


b.  Flexion  (Forwards). 

Deltoid  (anterior  fibres) 
Subscapularis 
Pectoralis  major 
Coraco-brachialis 
Biceps  brachii 


Extension  (Backwards). 

Deltoid  (posterior  fibres) 
Teres  major 
Infraspinatus 
Latissimus  dorsi 
Triceps  brachii 


c.  Rotation  Outwards. 

Deltoid  (posterior  fibres) 

Infraspinatus 

Teres  minor 

Rotation  Inwards. 

Deltoid  (anterior  fibres) 
Teres  major 
Pectoralis  major 
Latissimus  dorsi 

d.  Circumduction— combination  of  previous  muscles. 

The  various  movements  at  the  slioulder-joint  are  greatly  aided  by  the  muscles  acting  on  the 
shoulder  girdle.  In  raising  the  arm  above  the  head,  for  instance,  the  humerus  is  brought  to  the 
horizontal  position  by  the  deltoid  and  supraspinatus,  and  the  movement  is  continued  by  the 
elevators  of  the  shoulder  girdle.  Again,  in  forward  and  backward  movements  at  the  shoulder- 
joint,  great  assistance  is  derived  from  muscles  acting  directly  on  the  shoulder  girdle— pectoralis 
minor  and  serratus  anterior  ;  trapezius  and  rhomboidei. 

2.  In  relation  to  the  trunk  and  limbs,  the  shoulder  muscles,  by  fixing  the  humerus,  have 
auxiliary  power  on  the  one  hand  in  movements  of  the  trunk,  such  as  forced  inspiration ;  on  the 
other  hand,  acting  along  with  muscles  fixing  the  elbow-joint,  they  stiften  the  limb  so  as  to 
permit  of  the  more  refined  movements  of  the  wrist  and  fingers. 


^  Posterior  circumflex  artery  =  posterior  circumflex  artery  of  the  humerus  (B.N.A. 
-  Dorsal  scapular  artery  =  circumflex  artery  of  the  scapula  (B.N.  A.). 
3  Circumflex  nerve  =  axillary  (B.N.A. ). 


23 


332  THE  MUSCULAE  SYSTEM. 

FASCIAE   AND    IVIUSCLES   OF  THE   ARM. 

FASCIiE. 

The  superficial  fascia  presents  no  features  of  importance.  There  is  a  bursa 
beneath  it  over  the  olecranon  process,  and  occasionally  another  over  the  medial 
condyle  of  the  humerus. 

The  deep  fascia  forms  a  strong  tubular  investment  for  the  muscles  on  the  front 
and  back  of  the  humerus.  It  is  continuous  above  with  the  deep  fascia  of  the 
shoulder  and  axilla,  and  is  further  strengthened  by  fibres  derived  from  the  insertions 
of  the  pectoralis  major,  latissimus  dorsi,  and  deltoid  muscles.  At  the  elbow  it 
becomes  continuous  with  the  deep  fascia  of  the  forearm,  and  gains  attachment  to 
the  condyles  of  the  humerus  and  the  olecranon  process  of  the  ulna ;  it  is  strengthened 
also  by  important  bands  associated  with  the  insertions  of  the  biceps  in  front  and  the 
triceps  behind,  to  which  reference  will  be  made  in  the  account  of  these  muscles. 

About  the  middle  of  the  upper  arm  on  the  mesial  side,  the  deep  fascia  is 
perforated  for  the  passage  of  the  basilic  vein  and  the  internal  cutaneous  nerve.^ 

The  intermuscular  septa  are  processes  of  the  deep  fascia  attached  to  the 
epicondylic  ridges  of  the  humerus.  The  medial  and  stronger  septum  is  placed 
between  the  brachiahs  muscle  in  front  and  the  medial  head  of  the  triceps  behind, 
and  gives  origin  to  both.  It  extends  upwards  to  the  insertion  of  the  coraco- 
brachialis  (which  is  often  continued  into  it),  and  the  ulnar  nerve  and  inferior 
profunda  -  vessels  pass  down  over  its  inner  edge.  The  lateral  septum  is  thinner. 
It  separates  the  brachialis  muscle  and  brachio-radialis  in  front  from  the  medial 
and  lateral  heads  of  the  triceps  behind,  and  gives  origin  to  these  muscles.  It 
extends  upwards  to  the  insertion  of  the  deltoid,  and  is  pierced  by  the  musculo- 
spiral  nerve  ^  and  superior  profunda  vessels.^ 

MUSCLES   OF   THE   ARM. 

The  muscles  of  the  arm  comprise  the  biceps,  coraco-brachialis,  and  brachialis 
on  the  front,  and  the  triceps  brachii  on  the  back  of  the  humerus.  Except  at  its 
extremities,  the  biceps  brachii  is  superficial,  and  forms  a  rounded  fleshy  mass  on  the 
front'of  the  arm.  The  coraco-brachialis  is  visible  on  its  medial  side  in  the  upper  half 
of  the  arm,  particularly  when  the  arm  is  raised.  The  brachialis  is  concealed  by  the 
biceps.  The  triceps  brachii  forms  the  thick  mass  of  muscle  covering  the  posterior 
surface  of  the  humerus. 

The  coraco-brachialis  is  a  rudimentary  muscle.  It  arises  under  cover  of  the 
deltoid  from  the  tip  of  the  coracoid  processes  by  fleshy  fibres  in  common  with  the 
short  head  of  the  biceps,  and  also  frequently  from  the  tendon  of  insertion  of  the 
pectoralis  minor  muscle.  The  fleshy  belly  is  pierced  by  the  musculo-cutaneous 
nerve,  and  ends  in  a  flat  tendon  inserted  into  a  faint  linear  impression  about  an  inch 
in  length  on  the  middle  of  the  medial  border  of  the  shaft  of  the  humerus  (Fig.  253, 
p.  330).     It  is  often  continued  into  the  medial  intermuscular  septum. 

The  coraco-bracliialis  is  the  remains  of  a  threefold  muscle,  of  which  only  two  elements  are 
usually  present  in  man,  but  of  which  in  anomalous  cases  all  the  parts  may  be  more  or  less  fully 
developed.  The  passage  of  the  musculo-cutaneous  nerve  through  the  muscle  is  an  indication  of 
its  natural  sejjaration  into  two  parts,  which  represent  the  persistent  middle  and  inferior  elements. 
The  commonest  variety  is  one  in  which  the  more  superficial  (inferior)  part  of  the  muscle  extends 
farther  down  the  arm  than  usual,  so  as  to  be  inserted  into  the  medial  intermuscular  septum,  or  even 
into  the  medial  condyle  of  the  humerus.  A  third  slip  (coraco-brachialis  superior  or  brevis, 
rotator  humeri)  may  more  rarely  be  present,  forming  a  short  muscle  arising  from  the  root  of  the 
coracoid  process,  and  inserted  into  the  medial  side  of  the  liumerus  just  below  the  capsule  of  the 
shoulder-joint. 

The  biceps  brachii  arises  by  two  tendinous  heads.  (1)  The  short  head 
(caput  breve)  is  attached  in  common  with  the  coraco-brachialis  to  the  tip  of  the 
coracoid  process  of  the  scapula  (Fig.  250,  ix  326).  Concealed  by  the  deltoid  and 
tendinous  at  first,  this  head  forms  a  separate  fleshy  belly,  which  is  united  to  the 
long  head  by  an  investment  of  the  deep  fascia.     (2)  The  long  head  (caput  longum) 

1  Internal  cutaneous  =  medial  uerve  of  the  forearm  (B.N.  A). 

2  Inferior  profunda  artery  =  superior  ulnar  collateral  (B.N. A.). 

•*  Musculo-spiral  =  radial  nerve.  ■*  Superior  profunda  artery  =  profunda  brachii  (B.N.  A.). 


MUSCLES  OF  THE  AEM. 


333 


arises  by  a  round  tendon  from  the  supra-glenoid  impression  at  the  root  of  the 
coracoid  process  and  from  the  glenoid  ligament  on  either  side.     Its  tendon  passes 


Insertion 

of  pectok-  . 
alis  major 
coraco-brachialis 

Short  head  of  ' 

BICEPS  ' 
LOSO  HEAD  OF  , 
BICEPS 


Musculo-cutaneons 

nerve" 

Musculo-spiral 
nerve" 


Brachio-radialis^ 


Extensor  carpi 

RADIALIS  LONOrS" 


Radial  artery  (cut) 


Abductor  pollicis 

ONGUS  (EXIENSOR  OSSIS 

metacarpi  pollicis) 
Radial  artery  (cut) 

Anterior  annular 
ligament 


Insertion  of 
.-    PEG! oralis 

MINOR 


Axillary  artery 


\  Musculo- 

f  rjYstg:^^«^~^~~  cutaneous  ner\e 

-TjA^^»iv  ■  \'  ■  Median  nerve 

'  (lateral  head) 

Median  nerve 

(medial  head) 

Ulnar  nerve 


^ 


^ 


■  Triceps  (medial  head) 


Lacertus  fibrosus  or 
"bicipital  fascia 


-Pronator  teres 
"Deep  fascia  of  forearm 

-Flexor  carpi  radialis 

-Palmaris  longus 
-Flexor  carpi  ulnaris 

;,FlEX0R  Dir.ITORUM  SUBLIMIS 

-Flexor  pollicis  longus 

-Pronator  quadratus 
-Ulnar  artery 


Fig.  255. — Superficial  Muscles  on  the  Front  of  the  Right 
Arm  and  Forearm. 


Trapezius 


Latissimus 

do  RSI 


Deep  fascia  of  forearm 


Extensor  carpi  ulnaris 

Abductor  pollicis  longus 
(extensor  ossis  metacarpi 
pollicis) 

Extensor  pollicis  brevis 
Extensor  digiti 

QUINTI  PROPRIUS 

Tendons  of  Radial  Extensoi 
OF  carpus 

Posterior  annular  ligament 

Extensor  pollicis  longus 

Extensor  indicis  proprius 


Fig.  256. — The  Muscles  on  the  Back  of  the 
Left  Arm,  Forearm,  and  Hand. 


through  the  cavity  of  the  shoulder-joint,  and  emerging  from  the  capsule  beneath 
the  transverse  ligament  (invested  by  a  prolongation  of  the  synovial  membrane),  it 
occupies  the  bicipital  groove  of  the  humerus  (sulcus  inter tubercularis),  covered  by  a 


)0-± 


THE  MUSCULAE  SYSTEM. 


fascial  prolongation  of  the  tendon  of  the  pectoralis  major.  In  the  upper  arm  it 
forms  a  fleshy  belly  united  to  that  derived  from  the  short  head  by  an  envelope 
of  deep  fascia  (inter tubular  mucous  sheath). 

The  insertion  of  the  muscle  is  likewise  twofold.  (1)  The  two  bellies  become 
connected  with  a  strong  te7idon,  attached  deeply  in  the  hollow  of  the  elbow 
to  the  rough  posterior  portion  of  the  tuberosity  of  the  radius  (Figs.  264,  p.  3^2, 

and    271,   p.  ^mf^-H  V' 


Siipvaspinatiis 
"(insertion) 


_Subscapularis 
(insertion) 


Pectoralis  major 
(insertion) 

Latissimus  dorsi 
(insertion) 

Teres  major 
"(insertion) 


Infraspinatus 
(insertion) 


Triceps :  lateral  head 
(origin) 


_Coraco-brachialis 
"(insertion) 


Deltoid  (insertion) 


Brachio-radialis 
"(origin) 


Extensor  carpi 
-radialis  longus 
rigin) 

Common  tendon 
for  origin  of 
,  ])ronator  teres 
and  flexor 
muscles  of 
forwujn 


Common  tendon  fer  origin  of 
extensor  muscles  oT  forearm 

Fig.  2.57  a. — Muscle- Attachments  to 
THE  Front  of  the  Right  Humerus. 


A  bursa  separates 
the  tendon  from  the 
anterior  portion  of 
the  tuberosity.  (2) 
From  the  medial 
and  anterior  part  of 
the  tendon,  and 
partly  in  continuity 
with  the  fleshy  fibres 
of  the  muscle,  a 
strong  membranous 
hand  (the  lacertus 
fibrosus  or  bicipital 
fascia)  extends 
downwards  and 
medially  over  the 
hollow  of  the  elbow 
to  join  the  deep 
fascia  covering 
the  origins  of  the 
flexor  and  pronator 
muscles  of  the  fore- 
arm. Its  upper  part 
is  thickened  and  can 
be  felt  subcutane  - 
ouslyas  a  crescentic 
border. 

In  the  arm  the 
biceps  conceals  the 
brachialis  muscle 
and  the  musculo- 
cutaneous nerve. 
Its  medial  border 
is  the  guide  to 
the  position  of  the 
Common  tendon    brachial  artery  and 

for  origm  of  "^ 

extensormuscies  median  uervc. 

of  forearm 
Anconteus 
(origin) 


Triceps  :  medial 
head  (origin) 


Fig.  257  6. — Muscle- Attachments  to 
THE  Back  of  the  Right  Humerus. 


The  biceps  is  an 
extremely  variable 
muscle.  Its  chief  aii- 
omalies  are  due  to  an 
increase  or  diminution 
in     the     number     of 

origins.  A  third  head  of  origin  is  common  (10  per  cent),  and  usually  arises  from  the  humerus, 
between  the  insertions  of  the  deltoid  and  coraco-brachialis.  Two  or  even  three  additional  heads 
may  be  present  at  the  same  time.  The  long  head  of  the  muscle  may  be  absent,  or  may  take 
origin  from  the  bicipital  groove.  The  muscle  may  have  an  additional  insertion  into  the  medial 
condyle  of  the  humerus,  or  into  the  fascia  of  the  forearm. 

The  brachialis  is  a  large  muscle  arising  from  the  lower  two-thirds  of  the  front 
of  the  shaft  of  the  humerus  and  from  the  intermuscular  septum  on  each  side 
(Figs.  257  a  and  257  h,  p.  334).  Clasping  the  insertion  of  the  deltoid  above,  it  ends 
iDelow  in  a  strong  tendon  inserted  deep  in  the  hollow  of  the  elbow  into  the  anterior 
ligament  of  the  elbow-joint,  the  inferior  surface  of  the  coronoid  process,  and  slightly 


MUSCLES  OF  THE  AEM. 


335 


into  the  anterior  surface  of  the  shaft  of  the  uhiu  immediately  below  (Fig.  264, 
p.  342).  The  lateral  part  of  the  muscle  arising  from  the  lateral  epicondylic  ridge 
and  lateral  intermuscular  septum  forms  a  slip  mure  or  less  separate,  which  may 
be  partially  fused  with  the  brachio-radialis  muscle. 

The  triceps  brachii  is  the  ouly  muscle  on  the  back  of  the  arm.  It  arises  by 
three  heads :  a  lateral  and  a  medial  head,  from  the  humerus,  and  a  long  or  middle 
head  from  the  scapula.  (1)  The  long,  middle  or  scapular  head  (caput  longum)  begins 
as  a  strong  tendon  attached  to  a  rough  triangular  surface  on  the  axillary  border 
of  the  scapula  just  below  the  glenoid  fossa  (infraglenoidal  tuberosity)  (Figs. 
245,  p.  322,  and  250,  p.  326).  This  gives  rise  to  a  fleshy  belly  which,  after  passing 
between  the  teres  major  and  teres  minor  muscles,  occupies  the  middle  of  the  back 
of  the  arm.  (2)  The  lateral  head  is  attached  by  fibres,  partly  tendinous  and  partly 
fleshy,  to  the  curved  lateral  border  of  the  humerus  from  the  insertion  of  the  teres 
minor  above  to  the  musculo-spiral  groove  below,  and  receives  additional  fibres  from 
the  back  of  the  lateral  intermuscular  septum  (Fig.  257  h,  p.  334).  Its  fibres  are 
directed  downwards  and  medially  over  the  musculo-spiral  groove,  concealing  the 
musculo-spiral  nerve,  the  superior  profunda  artery,^and  the  medial  head  of  the  muscle, 
to  the  tendon  of  insertion.  (3)  The  medial  head  arises  by  fleshy  fibres  from  an 
elongated  triangular  area  on  the  back  of  the  humerus,  extending  upwards  to 
the  level  of  the  insertion  of  the  teres  major,  and  downwards  nearly  to  the  margin 
of  the  olecranon  fossa  (Fig.  257  h,  p.  334).  It  also  arises  on  each  side  from  the 
intermuscular  septum, — from  the  whole  length  of  the  medial  septum,  and  from  the 
part  of  the  lateral  septum  which  is  below  the  passage  of  the  musculo-spiral  nerve.^ 
The  three  heads  of  origin  are  inserted  by  a  common  tendon,  broad  and  membranous, 
into  an  impression  occupying  the  posterior  part  of  the  upper  end  of  the  olecranon 
process  of  the  ulna  (Fig.  271,  p.  349),  and  into  the  deep  fascia  of  the  forearm 
on  either  side  of  it.  The  long  and  lateral  heads  join  the  borders  of  the  tendon  of 
insertion,  and  the  medial  head  is  attached  to  its  deep  surface.  A  small  thick-walled 
bursa  separates  the  tendon  of  the  triceps  from  the  posterior  ligament  of  the  elbow- 
joint  and  the  upper  end  of  the  olecranon  process. 

The  sub-anconseus  is  a  small  muscle  occasionally  present,  which  consists  of  scattered  fibres 
arising  from  the  lower  end  of  the  humerus  beneath  the  triceps,  and  inserted  into  the  posterior 
ligament  of  the  elbow-joint. 

Nerve-Supply. 

The  muscles  of  the  arm  are  supjilied  by  two  of  the  nerves  of  the  brachial  plexus.  The 
musculo-cutaneous  nerve  (C.  5,  6)  supplies  the  biceps  and  lu-achialis  muscles,  and  conveys  to  the 
coraco-brachialis  its  nejve,  derived  from  the  seventh  cervical  nerve.  The  brachialis  muscle  usually 
receives  an  additional  small  nerve  from  the  musculo-spiral  (C.  5,  6).^  The  trice jss  is  supplied  by 
the  musculo-spiral  nerve,  the  fibres  for  the  several  heads  being  derived  usually  from  the  seventh 
and  eighth  cervical  nerves. 

Actions. 

(1)  The  chief  action  of  these  muscles  (exceiDting  the  coraco-brachialis)  is  on  the  elbow-joint, 
producing  along  with  other  muscles  flexion  and  extension.  The  flexor  muscles  are  much  more 
powerful  than  the  extensors. 

Table  of  Muscles  acting  on  the  Elbow-Joint. 


Flexors. 

Extensors. 

Bicejis  brachii 

Brachialis 

Brachio-radialis 

Pronator  teres 

Flexors  of  wrist  and  fingers 

Extensors  of  wrist  (in  pronation) 

Triceps  brachii 

Ancouaius 

Extensors  of  wrist  and  fingers  (in  supination) 

(2)  The  coraco-brachialis  muscle  acts  only  on  the  shoulder-joint,  assisting  the  biceps  as  an 
adductor  and  flexor  of  the  humerus. 

(3)  Subordinate  and  accessory  movements  are  performed  by  all  the  muscles  of  this  group 
except  the  In-achialis.  The  biceps  supinates  the  forearm,  flexes  the  elbow,  and  with  the  aid  of 
the  coraco-brachialis  adducts  and  flexes  the  humerus  at  the  shoulder-joint.  The  triceps  through 
its  scapular  head  adducts  and  extends  the  humeriis,  besides  extending  the  elbow-joint. 

^  According  to  the  B.N.  A.  nomenclature,  the  musculo-.spiral  nerve  is  named  the  radial,  the  present  radial 
nerve  being  known  a.s  the  superficial  ramus,  the  posterior  interosseous  as  the  deep  ramus,  thus  the  musculo- 
spiral  groove  is  known  as  the  "radial  groove." 


336 


THE  MUSCULAR  SYSTEM. 


FASCIi^E  AND  MUSCLES  OF  THE  FOREARIYI 
AND  HAND. 


Flexor  digitorum 
profundus 


Digital  sheath 

LUMfcKICAL  ^ICSCLES 


Fasciae. 

The  superficial  fascia  in  the  forearm  presents  no  exceptional  features.  On 
the  dorsum  of  the  hand  it  is  loose  and  thin ;  in  the  palm  it  is  generally^  well 
furnished  with  fat,  forming  pads  for  the  protection  of  the  vessels  and  nerves.     It  is 

closely  adherent  to  the 
palmar  fascia  and  to 
the  skin,  especially 
along  the  lines  of 
flexure. 

The  palmaris 
brevis  is  a  quadri- 
lateral subcutaneous 
muscle  occupying  the 
medialsideof  the  hand 
under  the  superficial 
fascia.  It  arises  from 
the  medial  border  of 
the  thick  central  por- 
tion of  the  palmar 
fascia  and  from  the 
front  of  the  anterior 
annular  ligament  of  the  wrist, 
and  is  inserted  into  the  skin  of 
the  medial  border  of  the  hand  for 
a  variable  distance.  It  covers 
the  ulnar  artery  and  nerve, 
branches  of  which  supply  it. 
Its  action  is  to  wrinkle  the 
skin  of  the  medial  border  of  the 
hand,  and  by  raising  up  the 
skin  and  superficial  fascia,  to 
deepen  the  hollow  of  the  hand. 
The  deep  fascia  of  the 
forearm  and  hand  is  continuous 
above  with  the  deep  fascia  of  the 
arm.  In  the  upper  part  of  the  fore- 
arm it  is  strengthened  by  additional 
fibres  around  the  elbow;  in  front 
by  fibres  from  the  lacertus  fibrosus 
of  the  biceps,  behind  by  the  fascial 
insertions  of  the  triceps,  and  laterally 
by  fibres  derived  from  the  humeral 
condyles  in  relation  to  the  common  tendons  of  origin  of  the  flexor  and  extensor 
muscles  of  the  forearm  which  take  in  part  their  origin  from  it.  It  is  attached  to 
the  posterior  border  of  the  ulna,  and  affords  increased  attachment  to  the  flexor  and 
extensor  carpi  ulnaris  and  the  flexor  digitorum  profundus  muscles.  Above  the 
wrist  the  fascia  is  pierced  anteriorly  by  the  tendon  of  the  palmaris  longus,  and 
by  the  ulnar  artery  and  nerve.  At  the  wrist  it  gains  attachment  to  the  bones  of 
the  forearm  and  carpus,  is  greatly  strengthened  by  addition  of  transverse  fibres, 
and  constitutes  the  annular  ligaments  (ligamenta  carpi). 

The  anterior  annular  ligament  (transverse  carpal  ligament)  is  a  band  about  an 
inch  and  a  half  in  depth,  continuous  above  and  below  with  the  deep  fascia  of  the  fore- 
arm and  the  yjalm  of  the  hand.  It  is  attached  laterally  to  the  navicular  and  large 
multangular;  medially  to  the  pisiform  and  os  hamatum;  and  it  forms  a  membranous 


Palmar 
fascia 


Thenar 
eminence 

Hypothenar 
eminence 


Palmaris  brevis  - 

Anterior  annul 
ligament 
Abductor 
pollicis  longus 

Flexor  carpi  radialis 
Palmaris  longus 


Flexor  pollicis  longus  — 
Flexor  digitorum  ., 
sublimis 

Flexor  carpi  ulnarh-. 


Fig.  258. — The  Left  Palmar  Fascia. 


FASCIA  AND  MUSCLES  OF  THE  ^OTIEAEM  AND  HAND.       33V 


Flexor  caepi  ulnaris 

Flexor  dioitorum  sublimis 
-Flexor  carpi  radialis 

Palmakis  longus 

Pisiform  bone 

Abductor  pollicis  longus 

Anterior  annular  ligament 


-Abductor  digiti  quinti 
Abductor  pollicjs  brevis 


Flexor  dioiti 

quinti  brevis 

_^Flexor  pollicis 

BREVIS 

_.  Adductor 
pollicis 
Flexor  pollicis 

LONGUS 


arch  binding  down  in  the  hollow  of  the  carpus  the  flexor  tendons  of  the  fingers,  and 

the  median  nerve.     It  is  divided  into  hvo  compartments,  the  larger  accommodating 

the  tendons  of  the  flexors  of  the  digits  and  the  median  nerve,  the  smaller  (placed 

laterally)    containing    the    tendon   of   the  flexor  carpi  radialis.     There   are  three 

synovial  membranes  in   these  compartments :    one   for   the  flexor   carpi  radialis 

tendon,  and  two  others,  which  often  communicate  together,  enveloping  the  tendon 

of  the  flexor  pollicis  longus  and   the  flexor  tendons  of  the  fingers  respectively. 

The  surface   of   the    ligament  is 

crossed  by  the   palmar  branches       iW^tv 

of  the  median  and  ulnar  nerves ; 

by  the   tendon   of   the    palmaris 

longus  muscle,  which  is  attached 

to  its  surface ;  and  by  the  ulnar 

artery  and  nerve,  which  are  again 

bridged  over  and  protected  by  a 

band    of    fibrous    tissue    passing 

from  the  pisiform  bone 

and  the  superficial  fascia 

to   the   surface   of    the 

ligament.     To  the  lower 

border  of  the  ligament 

are  attached  the  palmar 

fascia  in  the  centre,  and 

the   superficial  muscles 

of  the  thumb  and  the 

muscles    of    the    little 
finger  on  each  side. 

The  posterior  an- 
nular ligament  (dorsal 
carpal  liga- 
ment) is  placed 
at  a  higher  level 
than  the  previ- 
ous ligament.  It 
consists  of  an 
oblique  band  of 
fibres  about  an 
inch  broad,  con- 
tinuous above 
and  below  with 
the  deep  fascia 
of  the  forearm 
and  hand.  It  is 
attached  later- 
ally to  the  lateral  Fig.  259.— Superficial  Muscles  and  Tendons  in  the  Palm  of  the  Left  Hand. 
side  of  the  lower 

end  of  the  radius,  and  medially  to  the  lower  end  of  the  ulna  (styloid  process),  the 
carpus,  and  the  medial  lateral  ligament  of  the  wrist.^  It  is  crossed  by  veins,  by 
the  radial  nerve,  and  by  the  dorsal  branch  of  the  ulnar  nerve.  Six  comimrtments 
are  formed  beneath  it  by  the  attachment  of  septal  bands  to  the  lower  ends  of  the 
radius  and  ulna.  Each  compartment  is  provided  with  a  synovial  membrane,  and 
they  serve  to  transmit  the  extensor  tendons  of  the  wrist  and  fingers  in  the  followmg 
order  from  without  inwards : — 

(1)  Abductor  pollicis  longus  (extensor  ossis  metacarpi  pollicis)  and  extensor 
pollicis  brevis,  (2)  Extensores  carpi  radiales,  longus  and  brevis,  (3)  Extensor  pollicis 
longus,  (4)  Extensor  digitorum  communis  and  extensor  indicis  proprius,  (5) 
Extensor  digiti    quinti  proprius,  (6)  Extensor  carpi  ulnaris. 

The  thin  deep  fascia  of  the  dorsum  of  the  hand  is  lost  over  the  expansions  ot 

1  Ulnar  collateral  ligament  (B.N. A.). 


LUMBRICAL  MUSCLES 

Tendons  of  flexor  digitorum 
^v^sublimis 

Flexor  digitorum  sublimis 
-    lexor  digitorum  profundus 


338  THE  MUSCULAE  SYSTEM. 

the  extensor  tendons  on  the  fingers.  Between  the  metacarpal  bones  a  strong  layer 
of  fascia  covers  and  gives  attachment  to  the  interossei  muscles. 

The  palmar  fascia  (palmar  aponeurosis)  is  of  considerable  importance.  In  the 
centre  of  the  palm  it  forms  a  thick  triangular  membrane,  the  apex  of  which  joins 
the  lower  edge  of  the  anterior  annular  ligament,  and  more  superficially  receives 
the  insertion  of  the  tendon  of  the  palmaris  longus  muscle.  The  fascia  separates 
below  into  four  slips,  one  for  each  finger,  connected  together  by  transverse  fibres,  and 
forming  beneath  the  webs  of  the  fingers  the  superficial  transverse  metacarpal  ligament 
(fasciculi  transversi).  Beyond  this  each  slip  separates  into  two  parts,  to  be  con- 
nected to  the  sides  of  the  metacarpo-phalangeal  joints  and  the  first  phalanx  of  the 
inner  four  digits.  In  the  cleft  between  the  two  halves  of  each  slip  the  digital 
sheath  is  attached  and  extends  downwards  on  to  the  finger.  The  lateral  borders  of 
this  triangular  central  portion  of  the  palmar  fascia  are  continuous  with  thin  layers 
of  deep  fascia,  which  cover  and  envelop  the  muscles  of  the  thenar  and  hypothenar 
eminences.     The  inner  border  gives  origin  to  the  -palmaris  hrevis  muscle  (p.  336). 

The  digital  sheaths  (vaginae  mucosae)  are  tubular  envelopes  extending  along 
the  anterior  aspect  of  the  digits  and  enclosing  the  flexor  tendons.  Each  consists  of 
a  fibrous  sheath  attached  to  the  lateral  borders  of  the  phalanges  and  inter-phalan- 
geal  joints,  and  continuous  above  with  the  palmar  fascia.  Opposite  each  inter- 
phalangeal  articulation  the  digital  sheath  is  loose  and  thin ;  opposite  the  first  two 
phalanges  (the  first  only  in  the  case  of  the  thumb)  it  becomes  extremely  thick, 
and  gives  rise  to  the  ligamenta  vaginalia,  which  serve  to  keep  the  tendons  closely 
applied  to  the  bones  during  flexion  of  the  fingers.  Within  each  digital  sheath  are 
the  flexor  tendons,  enveloped  in  a  synovial  membrane  which  envelops  the  tendon, 
and  lines  the  interior  of  the  sheath.  The  synovial  membranes  of  the  digital 
sheaths  extend  a  short  distance  upwards  in  the  palm,  and  in  some  cases  com- 
municate with  the  large  synovial  membranes  lining  the  flexor  tendons  beneath 
the  annular  ligament.  There  may  be  a  separate  distinct  synovial  membrane  for 
each  digit ;  but  most  commonly  only  the  sheaths  for  the  three  middle  digits  have 
separate  synovial  membranes ;  those  for  the  flexor  poUicis  longus  and  the 
flexor  tendons  of  the  little  finger  usually  communicate  with  the  synovial  mem- 
branes placed  beneath  the  anterior  annular  (transverse  carpal)  ligament.^ 

THE  MUSCLES  ON  THE  FRONT  AND  MEDIAL  ASPECT  OF  THE  FOREARM. 

The  muscles  on  the  front  and  medial  aspect  of  the  forearm  comprise  the  pronators 
and  the  flexors  of  the  wrist  and  fingers.  In  the  forearm  they  are  arranged  in  three 
strata :  (1)  a  superficial  layer  consisting  of  four  muscles  which  radiate  from  the 
medial  epicondyle  of  the  humerus,  from  which  they  take  origin  by  a  common  tendon, 
and  named,  from  without  inwards,  pronator  teres,  flexor  carpi  radialis,  palmaris 
longus,  and  flexor  carpi  ulnaris.  These  muscles  conceal  the  muscle  which  by  itself 
constitutes  (2)  the  intermediate  stratum,  the  flexor  digitorum  sublimis,  which  again 
conceals  for  the  most  part  (3)  the  deep  layer  of  muscles,  including  the  flexor 
digitorum  profundus  covering  the  ulna,  the  flexor  pollicis  longus  on  the  radius,  and 
the  pronator  quadratus,  which  is  more  deeply  placed  than  the  previous  muscles,  and 
stretches  across  the  forearm  between  the  lower  ends  of  the  radius  and  ulna. 

I.     Superficial  IVluscIes. 

The  pronator  teres  is  the  shortest  muscle  of  this  group.  It  has  a  double 
origin:  (1)  a  superficial  head,  the  main  origin,  partly  fleshy,  partly  tendinous,  from 
the  lowest  part  of  the  medial  epicondylic  ridge  of  the  humerus  and  from  the 
medial  intermuscular  septum,  from  the  medial  epicondyle  of  the  humerus,  from 
the  fascia  over  it,  and  from  an  intermuscular  septum  between  it  and  the  flexor 
carpi  radialis  (Fig.  257  a,  p.  334) ;  (2)  a  deep  head,  a  slender  tendinous  slip  from 
the  medial  side  of  the  coronoid  process  of  the  ulna,  whicli  joins  the  superficial 
origin  of  the  muscle  on  its  deep  surface  (Tig.  264,  p.  342).  I'he  median  nerve 
separates  the  two  heads  from  one  another.  The  muscle  is  directed  downwards 
and  laterally  to  be  inserted  by  tendon  into  an  oval  impression  on  the  middle 
of  the  lateral  surface  of  the  shaft  of  the  radius  (Figs.  264,  p.  342,  and  265,  p. 

'   Anterior  annular  ligament  =  transverse  carpal  (B.N. A.). 


MUSCLES  ON  FEONT  AND  MEDIAL  ASPECT  OF  FOEEAEM.     339 


Fig.  260. 


-Section  across  the  Forearm  in  the  Middle 
Third. 


343).  The  fibres  of  the  muscle  are  twisted  on  themselves,  so  that  the  highest 
humeral  fibres  form  the  lowest  fibres  of  the  tendon  of  insertion,  and  the  lowest 
humeral  fibres  and  those  arising  from  the  coronoid  process  are  highest  at  the 
insertion.  The  muscle  forms  the  medial  boundary  of  the  hollow  of  the  elbow.  It 
is  superficially  placed,  except  near  its  insertion,  where  it  is  covered  by  the  brachio- 
radiaiis  mviscle  and  by  the  radial  vessels  and  nerve. 

The  flexor  carpi  radialis  muscle  takes  its  origin  from  the  common  tendon  from 
the  medial  epicondyle  of  the  humerus,  from  the  fascia  over  it,  and  from  the  inter- 
muscular septa  on  either  side. 
Its  fleshy  belly  gives  place  to 
a  strong  round  tendon  in  the 
lower  half  of  the  forearm,  which, 
at  the  wrist,  enters  the  hand 
in  a  special  compartment  be- 
neath the  anterior  annular 
ligament,  and  after  occupying 
the  groove  on  the  large  mult- 
angular bone,  is  inserted  into 
the  upper  ends  of  the  second 
and  third  metacarpal  bones  on 
theiranteriorsurfaces  (Fig.267, 
p.  345).  Thechieftendonisthat 
to  the  second  metacarpal  bone. 

The  flexor  carpi  radialis 
is  superficial  except  near  its 
insertion.  Its  tendon  in  the 
lower  half  of  the  forearm  is 
an  important  guide  to  the 
radial  vessels,  which  are  placed 
to  its  radial  side.  After 
passing  beneath  the  anterior 
annular  ligament  the  tendon 
is  concealed  by  the  origins  of 
the  short  muscles  of  the  thumb, 
and  is  crossed  from  within 
outwards  by  the  tendon  of  the 

flexor  pollicis  longus.     Besides  the  synovial  bursa  enveloping  the  tendon  beneath 
the  ligament,  another  is  found  beneath  the  tendons  at  their  insertion. 

The  palmaris  longus  arises  also  from  the  common  flexor  tendon,  from  the 
medial  epicondyle  of  the  humerus,  from  the  fascia  over  it,  and  from  intermuscular 
septa  on  either  side.  It  forms  a  short  fusiform  muscle,  which  ends  in  the  middle 
of  the  forearm  in  a  long  flat  tendon.  This  pierces  the  deep  fascia  above  the  wrist, 
and  passing  over  the  anterior  annular  ligament,  is  inserted  (1)  into  the  surface  of 
the  anterior  annular  ligament,  and  (2)  into  the  apex  of  the  thick  central  portion  of 
the  palmar  fascia.  A  tendinous  slip  is  frequently  sent  to  the  short  muscles  of  the 
thumb  and  the  fascia  covering  them.  The  palmaris  longus  is  the  smallest  muscle 
of  the  forearm.  In  the  lower  third  of  the  forearm  its  tendon  is  placed  directly  over 
the  median  nerve,  alono;  the  radial  border  of  the  tendons  of  the  flexor  digitorum 
sublimis. 

The  iDalmaris  longus  is  the  most  variable  muscle  in  the  body,  and  is  often  absent  (10  per  cent). 

The  flexor  carpi  ulnaris  muscle  has  a  double  origin,  from  the  humerus  and  from 
the  ulna.  (1)  It  arises  from  the  common  tendon  attached  to  the  medial  condyle  of  the 
humerus,  from  the  fascia  over  it,  and  from  an  intermuscular  septum  laterally.  (2) 
By  means  of  the  deep  fascia  of  the  forearm  it  obtains  an  attachment  to  the  medial 
border  of  the  olecranon  process  and  the  posterior  border  of  the  ulna  in  its  upper 
three-fifths.  The  fleshy  fibres  join  a  tendon  which  lies  on  the  anterior  border  of  the 
muscle  and  is  inserted  into  the  pisiform  bone,  and  in  the  form  of  two  ligamentous 

^  Radial  nerve  =  superficial  ramus  of  radial  nerve  (B.N. A.). 


A,  Pronator  teres  (insertion) ;  B,  Flexor  carpi  radialis  ;  C,  Flexor 
DIGITORUM  sublimis  ;  D,  Palmaris  longus  ;  E,  Flexor  carpi  ulnaris  ; 
F,  Flexor  digitorum  profundus;  G,  Extensor  carpi  ulnaris; 
H,  Extensor  pollicis  longus  ;  I,  Extensor  digitorum  communis  and 
extensor  dioiti  qdinti  proprius  ;  J,  Abductor  pollicis  longus  ;  K, 
Extensor  carpi  radialis  brevis  ;  I;,  Extensor  carpi  radialis  longus  ; 
M,  Brachio-radialis.  a,  Radius  ;  b,  Interosseous  membrane  ;  c,  Ulna. 
1,  Radial  nerve ;  2,  Radial  artery ;  3,  Anterior  superficial  ran^us  of 
interosseous  artery  ;  4,  Anterior  interosseous  nerve  (underneath  flexor 
pollicis  longus) ;  5,  Median  nerv'e ;  6,  Ulnar  artery  ;  T,  Ulnar  nerve ;  8, 
Posterior  interosseous  artery  ;  9,  Posterior  interosseous  nerve. 


340 


THE  MUSCULAR  SYSTEM. 


bands  (pisi-unciform  and  pisi-metacarpal)  into  the  hook  of  the  unciform  bone,  and 
the  upper  end  of  the  fifth  metacarpal  bone  (Fig.  267,  p.  345). 

The  muscle  is  superficially  placed  along  the  medial  border  of  the  forearm.     It 


Biceps  brachii 
Medial  ixter- 

ML"SCrLAR  SEPTUM 


Brachialis 


Medial  condyle 


Lacertus 

FIBROSrs 

(bicipital  fasci  ■ 

SuPIXATOR  MUSI  I. 

(Supinator  brevis)  -j 


Pronator  teres 


Flexor  carpi 
radialis 

Palmaris 

LOKGUS 

Flexor  carpi 

ULNARI.S 

Extensor 

CARPI.; 

radialis 

LONCrS 


Brachio- 
radialis 


Flexor  digi- 

TORUM  SUBLIMIS 


Flexor  polligis. 

LONODS 


Brachio-radialis 

(tendon) -•■- 


Flexor  carpi  radialis 
(tendon) 


Palmaris  longds 
(t<;ndon) 


Flexor  carpi  ulnaris 
(tendon) 


Pisiform  bone 
Abdtjctor  pollicis 

LONG  us 

(extensor  ossis 
metacarpi  pollicis) 
Palmar  fascia 'j 


Biceps  brachi 


Brachialis 

Medial  intermuscular 
septum 
Bicipital  fascia 
(lacertus  fibrosus) 


Biceps  tendon 
Pronator 
teres  (humeral 
origin) 
Pronator 

TEKESv^ 

(ulnar  origm)  '; 


Flexor 

carpi  ._' 
radialis 


Supinator  muscle 


Brachio-radialis  •- 

Pronator  teres 
(insertion) 

Flexor  digitor'  m 
sublimis  (radial .. 
ongin) 

Flexor  carpi  ulnaris 


Flexor  digitortjm 

sublimis  -- 


Brachio-radialis  tendon  .. 


Flexor  pollicis  longus 


Pronator  quadratus  \A' 


Flexor  digitorum 
profundus 


Pisiform  bone 


Flexor  carpi  radialis 

Abductor  pollicis  longus 

(extensor  ossi- 

metacarpi  POLLICli) 


Fig.  261. — The  Superficial  Muscles  ok 
THE  Left  Forearm. 


Fig.  262. — Deeper  Muscles  of  the  Left 
Forearm. 


conceals  the  flexor  digitorum  profundus  muscle,  the  ulnar  nerve  (which  enters 
the  forearm  between  the  two  heads  of  origin  of  the  muscle),  and  the  ulnar 
artery.  The  tendon  serves  as  a  guide  to  the  artery  in  the  lower  half  of 
the  forearm. 


MUSCLES  ON  FEONT  AND  MEDIAL  ASPECT  OF  FOEEARM.     341 


Ligament 


2.    Intermediate  Layer. 

The  flexor  digitorum  sublimis  occupies  a  deeper  plane  than  the  four  previous 
muscles.  It  has  a  threefold  origin,  from  the  humerus,  radius,  and  ulna.  (1)  The 
chief  or  humeral  head  of  origin  is  from  the  medial  condyle  of  the  humerus  by  the 
common  tendon,  from  the  internal  lateral  (ulnar  collateral)  ligament  of  the  elbow, 
and  from  adjacent  intermuscular  septa.  (2)  The  ulnar  head  of  origin  is  by  a  slender 
fasciculus  from  the  medial  border  of  the  coronoid  process  of  the  ulna,  above  and 
medial  to  the  origin  of  the  pronator  teres  (Fig.  264,  p.  342).  (3)  The  radial  head 
of  origin  is  from  the  oblique  line  and 
middle  third  of  the  anterior  border  of 
the  radius  by  a  thin  fibro-muscular 
attachment  (Fig.  264,  p.  342). 

The   muscle   di^ddes   in    the  lower 
third  of  the  forearm  into   four   parts,  L'gainentum 
each  provided  with  a  separate  tendon         __ 
which  goes  beneath  the  transverse  carpal 
ligament,  passes  through  the  palm  of 
the  hand,  and  enters  the  corresponding 
digital  sheath  of  the    finger.     At  the 
wrist  the  four  tendons  are  arranged  in 
pairs,  those  for  the   middle   and   ring 
fingers  in  front,  and  those  for  the  fore 
and  little  fingers  behind,  and  are  sur- 
rounded by  a    synovial  sheath,  along 
with  the   tendons   of  the  flexor  digi- 
torum profundus,  beneath  the  anterior 
annular  ligament.     In  the  palm  of  the 
hand  the  tendons  separate,  and  conceal 
the  deep  flexor  tendons  and  lumbrical 
muscles.      Within   the   digital   sheath 
each    tendon   is   split    into   two   parts 
by  the  tendon  of  the  flexor  digitorum 
profundus ;     after     surrounding     that 
tendon    the    two    parts   are   partially 
re-united  on  its  deep  surface,  and  are  inserted,  after  partial  decussation,  in  two 
portions  into  the  sides  of  the  second  phalanx. 

The  vincula  tendinum  form  additional  insertions  of  the  muscle.  They 
consist  of  delicate  bands  of  connective  tissue  enveloped  in  syno%'ial  membrane, 
and  are  known  as  the  ligamenta  longa  and  brevia.  The  ligamentum  breve  is  a 
triangular  band  of  fibres  containing  yellow  elastic  tissue  (ligamentum  sub- 
flavum),  occupying  the  interval  between  the  tendon  and  the  digit  for  a  short  distance 
close  to  the  insertion.  It  is  attached  to  the  front  of  the  inter -phalangeal 
articulation  and  the  head  of  the  first  phalanx.  The  ligamentum  longum  is  a 
long  narrow  band  extending  from  the  back  of  the  tendon  to  the  upper  part  of 
the  anterior  surface  of  the  first  phalanx. 


Ligamentum  breve 
Flexor  digitorum  sfblimis 

Expansion  of  extensor  tendon 

Flexor  digitorum 
profundus 

First  luiibrical  muscle 

First  dorsal  ixter- 
\\\    osseous  muscle 

In     Extensor  indicis 
I  h     PROPRius  tendon 

Extensor  digitorum 
communis  tendon 


Fig.  263. 


-The  Tendoxs  attached  to  the 
Index  Finger. 


3.   Deep   Layer. 

The  flexor  digitorum  profundus  is  a  large  muscle  arising  from  the  ulna,  the 
interosseous  membrane,  and  the  deep  fascia  of  the  forearm,  under  cover  of  the 
flexor  digitorum  sublimis  and  the  flexor  carpi  ulnaris.  Its  ulnar  origin  is  from 
the  anterior  and  medial  surfaces  of  the  bone  in  its  upper  two-thirds,' extending  up 
so  as  to  include  the  medial  side  of  the  olecranon  process,  and  to  embrace  the 
insertion  of  the  brachialis  muscle  into  the  coronoid  process.  It  arises  laterally 
from  the  medial  half  of  the  interosseous  membrane  in  its  middle  third  (Figs.  264, 
p.  342,  and  265,  p.  343),  and  medially  from  the  deep  fascia  of  the  forearm  behind 
the  origin  of  the  flexor  carpi  ulnaris. 


342 


THE  MUSCULAK  SYSTEM. 


Brachialis  muscle  (insertion) 
Supinalor  muscle 
(ulnar  origin) 


(occasional  origin) 


Biceps  bracliii 
(insertion) 


Flexor  digi- 

tonini  sublimis 

(radial  origin) 


Pronator  teres 
(insertion) 

Flexor  pollicis 
longus  (origin) 


Flexor  digitorum 
profundus  (origin) 


The  muscle  forms  a  broad  thick  tendon  which  passes  beneath  the  anterior 
annular  ligament,  covered  by  the  tendons  of  the  flexor  digitorum  sublimis,  and 
enveloped  in  the  same  synovial  sac,  and  divides  in  the  palm  into  four  tendons  for 
insertion  into  the  terminal  phalanges  of  the  fingers.  The  tendon  associated  with 
the  forefinger  is  usually  separate  from  the  rest  of  the  tendons  in  its  whole  length. 
Each  tendon  enters  the  digital  sheath  of  the  finger  beneath  the  tendon  of  the  flexor 
digitorum    sublimis,  which  it  pierces   opposite    the  first  phalanx,  and  is  finally 

inserted  into  the  base  of  the  terminal 
phalanx.      Like     the    tendons    of 
•\  ■',-    ra  the    flexor   sublimis,  those  of  the 

deep     flexor     are     provided    with 
vincula,    viz.    ligamenta   brevia  at- 
-Hmfs°(£™inf  ■  tached  to  the  capsule  of  the  second 
(^iin"r^ori"?nr  inter  -  phalangeal  articulation,  and 

Flexor  poUicis  longus  ligamenta  longa,  which  are  in  this 
case  connected  to  the  tendons  of 
the  subjacent  flexor  digitorum  sub- 
limis. 

Lurabricales. — Eour  small  cy- 
lindrical muscles  are  associated 
with  the  tendons  of  the  flexor  digi- 
torum profundus  in  the  palm  of 
the  hand.  The  two  lateral  muscles 
arise  each  by  a  single  head  from 
the  radial  sides  of  the  tendons 
of  the  flexor  digitorum  profundus 
destined  respectively  for  the  fore 
and  middle  fingers.  The  two 
medial  muscles  arise,  each  by  two 
heads,  from  the  adjacent  sides  of 
the  second  and  third,  and  third  and 
fourth  tendons.  From  these  origins 
the  muscles  are  directed  downwards 
to  the  radial  side  of  each  of  the 
metacarpo-phalangeal  joints,  to  be 
inserted  into  the  capsules  of  these 
articulations,  the  radial  border  of 
the  first  phalanx,  and  chiefly  into 
the  radial  side  of  the  extensor  tendon 
on  the  dorsum  of  the  phalanx. 
The  lumbricales  vary  considerably 
in  number,  and  may  be  increased 
to  six  or  diminished  to  two. 

The  flexor  pollicis  longus 
arises  beneath  the  flexor  digitorum 
sublimis  by  fleshy  fibres  from  the 
volar  or  anterior  surface  of  the  shaft 
of  the  radius  in  its  middle  two- 
fourths,  and  from  a  corresponding 
portion  of  the  interosseous  mem- 
brane. It  has  an  additional  origin  occasionally  from  the  medial  border  of  the  coronoid 
process  of  the  ulna  (Fig.  264,  p.  342).  Its  radial  origin  is  limited  above  by  the 
oblique  line  and  the  origin  of  the  flexor  digitorum  sublimis,  and  below  by  the  insertion 
of  the  pronator  quadratus  muscle.  The  muscle  ends  above  the  wrist  in  a  tendon, 
which  passes  over  the  pronator  quadratus  into  the  hand  beneath  the  transverse 
carpal  ligament,  enveloped  in  a  special  synovial  sheath.  In  the  palm  the  tendon 
is  directed  downwards  along  the  ulnar  side  of  the  thenar  eminence,  between  the 
flexor  brevis  and  adductor  muscles  of  the  thumb,  to  be  inserted  into  the  base  of 
the  terminal  phalanx  of  the  thumb  on  its  anterior  surface. 


Pronator  quadratus 
(origin) 


Pronator  quad- 
ratus (insertion) 


Brachio-radia 

(insertion)    IXJ 


Fig.  264. — Muscle-Attachments  to  the  Right  Radius 
AND  Ulna  (Anterior  Aspects). 


SHOKT  MUSCLES  OF  THE  HAND. 


343 


The  pronator  quadratus  is  a  quadrilateral  fleshy  muscle,  occupying  the  lower 
fourth  of  the  forearm.  It  is  placed  beneath  the  deep  flexor  tendons,  and  arises 
from  the  lower  fourth  of  the  anterior  border  and  surface  of  the  ulna  (Fig.  2G4, 
p.  342),  and  is  directed  trans- 
versely outwards  to  be  inserted 
into  the  lower  fourth  of  the 
anterior  surface  of  the  radius,  and 
into  the  narrow  triangular  area 
on  its  ulnar  side  in  Iront  of  the 
attachment  of  the  interosseous 
membrane  (Fig.  264,  p.  342). 

The  pronator  quadratus  is  sub- 
ject to  considerable  variations.  It 
may  even  be  absent ;  or  it  may 
have  an  origin  from  radius  or  ulna, 
or  from  both  bones,  and  an  inser- 
tion into  the  carpus. 


Biceps  brachii 


IjACiSBTDS  FIBROSUS  OR      j^ 

Bicipital  fascia  • 

Brachialis  muscle 


Pronator 

TERES 

Superficial 
FLEXOR  (origin)' 


SHORT  MUSCLES  OF  THE 
HAND. 

The  short  muscles  belonging  to 
the  hand,  in  addition  to  the  pal- 
maris  brevis  and  the  lumbrical 
muscles,  already  described,  include 
the  six  muscles  of  the  thumb 
constituting  the  thenar  eminence, 
the  three  muscles  of  the  little 
finger  constituting  the  hypothenar 
eminence,  and  the  interossei 
muscles,  which  are  deeply  placed 
between  the  metacarpal  bones. 

Muscles  of  the 
Thumb. 


Biceps  tendon 


BiClPITAI 
TL'BEROSI  1  -1 


Supinator  muscle. 


Brachio-kadialis. 


Pronator  teres- 


The  short  muscles  of  the 
thumb  are  the  abductor,  opponens, 
and  flexor  brevis  (with  its  deep 
portion,  interosseus  privius  volaris), 
and  the  adductor  muscle,  subdivided 
into  two  parts,  adductor  obUquus, 
and  adductor  pollicis  transversus. 

The  abductor  pollicis  brevis 
(abductor  pollicis)  arises  by 
fleshy  fibres  from  the  tubercle  of 
the  navicular,  the  ridge  of  the  large 
multangular,  the  anterior  surface  of 
the  transverse  carpal  ligament,  and 
from  tendinous  slips  derived  from 
the  insertions  of  the  palmaris 
longus  and  abductor  pollicis  longus  muscles  (Fig.  266,  p.  344).  Strap-like  in  form, 
it  is  inserted  by  a  short  tendon  into  the  radial  side  of  the  first  phalanx  of  the  thumb 
at  its  upper  end,  and  into  the  capsule  of  the  metacarpo-phalangeal  joint. 

The  opponens  pollicis,  partially  concealed  by  the  preceding  muscle,  arises  by 
fleshy  and  tendinous  fibres  from  the  anterior  surface  of  the  anterior  annular  liga- 


Flexor  digitorum 
profundus 


Flexor  carpi 

ULNARIS"' 

Flexor  digitorum 

profundus  (foi' 

index  finger) 

Flexor  pollicis  lonou 


Brachio-radialis 


Plexor  digitorum 

sublimis 


Pronator  quadratus 


Flexor  digitorum 

sublimis 

Pisiform  bone 

Flexor  carpi  radialis 


Abductor  pollk  i 
long I  - 


Fig.  265. — The  Drepest  Muscles  in  the  Front 
OP  THE  Left  Foeeahm. 


su 


THE  MUSCULAE  SYSTEM. 


ment  and  from  the  ridge  on  the  large  multangular  bone.  Extending  downwards 
and  laterally  it  is  inserted  into  the  whole  length  of  the  lateral  border  and  the  radial 
half  of  the  palmar  surface  of  the  first  metacarpal  bone  (Fig.  267,  p.  345). 

The  flexor  pollicis  brevis  consists  of  two  parts,     a.  The  superficial  'part  of  the 
muscle,  partly  concealed  by  the  abductor  pollicis,  arises  by  fleshy  and  tendinous 


Abductor  pollicis  longus 
Extensor  pollicis  brevis 

Abductor  pollicis  brevis 
Opponens  pollicis 

Flexok  pollicis  brevis 

(superficial  part)    ^.^^ 
iAdductor  pollicis  OBLIQirS  .,     _.f^~ 
Adductor  pollicis  trans-  .  ~-,, 

versus 

Abductor 
pollicis- 
(brevis) 


Pronator  quadratus 


Flexor  carpi  ulnaris 


Pisiform  bone 
Hook  of  oh  hamatum 
Abductor  dioiti  quinti  (cut) 
'^-   Plexor  digiti  quinti  brevis  (cut) 


Third  palmar  interosseous  muscle 
Fourth  dorsal  interosseous  muscle 
Second  palmar  interosseous  muscle 
Third  dorsal  interosseous  muscle 


Flexor  digiti  "j 
quinti  brevis   I  Attach- 


and  Abductor  j  ments 
digiti  quinti    J 

is  Tendons  of  third  and 
fourth  lumbkicals 


Flexor  dioitoru.m  sublimis  tendon 


Tendon  sheath 

Flexor  digitorum  profundus 

tendon 


Flexor  digitorum  profundus 
attachment 


Fir;.  266.— The  Palmar  Muscles  (Right  Side). 

fibres  from  the  lower  border  of  the  anterior  annular  ligament,  and  sometimes  from 
the  ridge  of  the  large  multangular,  and  is  inserted  into  the  radial  side  of  the  base  of  the 
first  phalanx  of  the  thumb,  a  sesamoid  bone  being  present  in  the  tendon  of  insertion. 
h.  The  deep  part  of  the  muscle  (interosseus  primus  volaris)  arises  from  the 
ulnar  side  of  the  base  of  the  first  metacarpal  bone,  and  is  inserted  into  the  ulnar 
side  of  the  base  of  the  first  phalanx  of  the  thumb  along  with  the  adductor 
pollicis  obliquus.     This  little  muscle  is  deeply  situated  in  the  first  interosseous 


SHOET  MUSCLES  OF  THE  HAND. 


345 


space,  in  the  interval  between  the  adductor  pollicis  obliquus  and  the  first  dorsal 
interosseous  muscle.  It  may  be  regarded  as  homologous  with  the  palmar  interossei 
muscles,  with  which  it  is  in  series, 

The  adductor  pollicis  is  separated  into  two  parts  by  the  radial  artery. 

(1)  The  adductor  pollicis  obliquus  lies  deeply  in  the  palm,  covered  by  the  tendons 
of  the  long  tiexors  of  the  thumb  and  fingers.  It  arises  by  fleshy  fibres  from  the 
anterior  surfaces  of  the  large  and  small  multangular  and  capitate  bones,  from  the 
sheath  of  the  tendon  of  the  flexor  carpi  radialis,  from  the  bases  of  the  second,  third, 
and  fourth  metacarpal  bones,  and  from  the  palmar  ligaments  connecting  these  bones 
together  (Fig.  267,  p.  345).  It  is  inserted  by  a  tendon,  in  which  a  sesamoid  bone 
is  developed,  into  the  ulnar  side  of  the  base  of  the  first  phalanx  of  the  thumb. 
At  its  lateral  border  a  slender  slip  separates  from  the  rest  of  the  muscle,  and  passing 
obliquely  beneath  the  tendon  of  the  flexor  pollicis  longus,  is  inserted  into  the  radial 


Capitate  bone  or  os  magnum 
Navicular  bone 


Abductor  pollicis  brevis  (origin) 

Opponens  pollicis  (origin) 

Large  multangular  or  trapezium! 
Abductor  pollicis  longus 
(insertion) 


Opponens  pollicis  (insertion) 

Flexor  carpi  radialis 
(insertion) 


Os  Ir.natum  or  semilunar  bone 
Os  hamatum  or  unciform 

riuetrum  or  cuneiform  bone        , 
iiform  bone 

Abductor  digit!  quinti  (origin) 


Flexor  carpi  ulnaris  (insertion) 

Flexor  brevis  digiti  quinti 
(origin) 

Flexor  carpi  ulnaris  (insertion) 


Adductor  pollicis 
obliquus  (origin) 


First  dorsal  interosseous  muscle 
(one  origin) 


First  palmar  interosseous  muscle 
(origin) 


Second  dorsal  interosseou-, 
muscle  (one  origin) 


Opponens  digiti  quinti 
(origin  and  insertion) 


Third  palmar  mter- 
'^  osseous  muscle 
(origin) 


Fourth  dorsal  interosseous 
muscle  (one  origin) 

Se(  ond  palmar  interosseous 

muscle  (origin) 


Adductor  pollicis 
tians\ersu3  (ougm) 


Third  doi^al  interosseous 
muscle  (one  origin) 


Fig.   267. — Muscle-Attachments  to  the  Palmar  Aspect  of  the  Carpus  and  Metacarpus. 

side  of  the  base  of  the  first  phalanx  along  with  the  superficial  part  of  the  flexor 
pollicis  brevis. 

(2)  The  adductor  pollicis  transversus,  lying  deeply  in  the  palm  beneath  the 
flexor  tendons,  arises  by  fleshy  fibres  from  the  medial  ridge  on  the  palmar  aspect  of 
the  shaft  of  the  third  metacarpal  bone,  in  its  distal  two-thirds  (Fig.  267,  p.  345),  and 
from  the  fascia  covering  the  interosseous  muscles  in  the  second  and  third  spaces. 
Triangular  in  form,  it  is  directed  laterally,  over  the  interossei  muscles  of  the  first 
two  spaces,  to  be  inserted  by  tendon  into  the  ulnar  side  of  the  base  of  the  first 
phalanx  of  the  thumb  along  with  the  adductor  obliquus. 


lYIuscIes  of  the  Little  Finger. 

The  short  muscles  of  the  little  finger  are  the  adductor,  opponens.  and  flexor 
brevis  digiti  quinti. 

The  abductor  digiti  quinti  is  most  superficial.     It  arises  from  the  pisiform 


346 


THE  MUSCULAE  SYSTEM. 


bone  and  from  the  tendon  of  the  flexor  carpi  ulnaris  and  its  ligamentous  con- 
tinuations (Fig.  267,  p.  345),  and  is  inserted  bj  tendon  into  the  ulnar-  side  of  the 
base  of  the  first  phalanx  of  the  little  finger. 

The  opponens  digiti  quinti  arises  beneath  the  preceding  muscle  by  tendinous 
fibres  from  the  anterior  annular  ligament  and  from  the  hook  of  the  os  hamatum, 
and  is  inserted  into  the  ulnar  margin  and  ulnar  half  of  the  palmar  surface  of  the 
fifth  metacarpal  bone  in  its  distal  three-fourths  (Fig.  267,  p.  345). 

The  flexor  digiti  quinti  brevis  may  be  absent  or  incorporated  with  either  the 
opponens  or  abductor  minimi  digiti.    It  arises  by  tendinous  fibres  from  the  anterior 

annular  ligament  and  from  the  hook 
of  the  OS  hamatum  (Fig.  267,  p. 
345),  and  is  inserted  along  with  the 
abductor  into  the  ulnar  side  of  the 
first  phalanx  of  the  little  finger. 

The  Interosseous 
IVIuscIes. 

The  interosseous  muscles  of  the 
hand  occupy  the  spaces  between  the 
metacarpal  bones.  They  are  ar- 
ranged in  two  sets,  palmar  and 
dorsal. 

The  palmar  interossei  (m.  in- 
terossei  volares)  are  three  in  num- 
ber, occupying  the  three  inner  inter- 
osseous spaces.  Each  arises  by  a 
single  head ;  the  first  from  the  ulnar 
side  of  the  shaft  of  the  second 
metacarpal  bone ;  the  second,  and 
third,  from  the  radial  sides  of  the 
shafts  of  the  fourth  and  fifth  meta- 
carpal bones  respectively  (Fig.  268,  p.  346).     Each   ends  in  a    tendon  which  is 

Extensor  carpi  radialis 
brevis  (insertion) 

„  ^  .,,/  ^^     Extensor  carpi  radialis 

Extensor  carpi  ulnaris  (insertion)  J^j.    ^j^y  lon^us  (insertion) 

First  dorsal  inter- 
osseous muscle 
(origin) 


Fourth  dorsal  interosseous 
muscle  (origin) 


Fig.  268. — The  Palmar  Interosseous  Muscles 
(Right  Side). 

P^,  first  ;  P^,  second  ;  and  P'^,  third  palmar  interosseous 
muscles. 


Third  dorsal  inter- 
osseous muscle 
(origin) 


Second  dorsal  interosseous 
muscle  (origin) 


Fig.  269. — Muscle-Attachments  to  the  Dorsal  Aspect  ov  the  Right  Metacarpus. 

directed  downwards  behind  the  deep  transverse  metacarpal  ligament,  to  be  inserted 
into  the  dorsal  expansion  of  the  extensor  tendon,  the  capsule  of  the  metacarpo- 


MUSCLES  ON  THE  BACK  OF  THE  FOEEAEM. 


347 


phalangeal  articulation,  and  the  side  of  the  first  phalanx  of  the  finger ;  the  first 
is  inserted  into  the  ulnar  side  of  the  second  finger ;  the  second  and  third  into  the 
radial  sides  of  the  fourth  and  fifth  fingers.  The  deep  part  of  the  flexor  poUicis 
brevis  (iuterosseus  primus  volaris)  is  to  be  regarded  as  the  homologous  muscle 
of  the  first  interosseous  space. 

The  dorsal  interossei  are  four  in  number.     Each  arises  by  two  heads  from  the 
sides  of  the  metacarpal  bones  bounding  each  interosseous  space  (Figs.  269,  p.  346, 


Abductor  pollicis  brevis  :  origin  (cut) 
Insertion  of  flexor  carpi  radialis 

Insertion  of  opponens  pollicis 
Interosseds  primus  volaris 


Abductor  pollicis  brevis  : 

insertion  (cut)  -j,,- 
Adductor  pollicis  obliquus_  '-'-^ 
(insertion) 
Adductor  pollicis  transversus  - 
(insertion) 
First  dorsal  interosseous  muscle 
Second  dorsal  interosseous  muscle 
Third  dorsal  interosseous  muscle 
Fourth  dorsal  interosseous  muscle 


Insertion  of  flexor 
carpi  ulnaris 


Origins  of 
palmar  inter- 
osseous muscles 
Insertion  of 
opponens  digiti 

QUINT! 

Insertion  of 
abductor  digiti 

QUINTI 


Fig.  270. — Dorsal  Interosseous  Muscles  of  the  Hand  (seen  from  the  Palmar  Aspect). 

and  270,  p.  347).  Each  forms  a  fleshy  mass,  ending  in  a  membranous  tendon, 
which,  passing  downwards  behind  the  deep  transverse  metacarpal  ligament,  is 
inserted  exactly  like  the  palmar  muscles  into  the  dorsal  aspect  of  each  of  the  four 
fingers.  The  insertion  of  the  first  dorsal  interosseous  muscle  is  into  the  radial 
side  of  the  index  finger ;  the  second  muscle  is  attached  to  the  radial  side  of  the 
middle  finger ;  the  third  muscle  to  the  ulnar  side  of  the  same  finger ;  and  the  fourth 
muscle  to  the  ulnar  side  of  the  ring  finger. 

The  interosseous  muscles  of  the  hand  in  some  cases  have  a  disposition  similar  to 
that  of  the  corresponding  muscles  of  the  foot  (p.  383). 


THE  MUSCLES  ON  THE  BACK  OF  THE  FOREARM. 

The  group  of  muscles  occupying  the  radial  side  of  the  elbow  and  the  back  of  the 
forearm  and  hand  include  the  supinator  muscles  of  the  forearm  and  the  extensors 
of  the  wrist  and  digits.     They  are  divisible  into  a  superficial  and  a  deep  layer. 

The  superficial  layer  comprises  seven  muscles,  which  are  in  order,  from  without 
inwards,  the  brachio-radialis,  the  two  radial  extensors  of  the  carpus,  the  extensor 
digitoruin  communis  and  extensor  digiti  quinti  proprius,  the  extensor  carpi  ulnaris, 
and  the  anconeus. 

The  deep  muscles  are  five  in  number :  one,  the  supinator,  extends  between 
the  upper  parts  of  the  ulna  and  radius ;  the  others  are  the  special  extensors 
of  the  thumb  and  forefinger,  viz.  the  abductor  pollicis  longus,  extensor  pollicis  longus 
and  extensor  pollicis  brevis,  and  extensor  indicis  proprius.  They  cover  the  back  of 
the  bones  of  the  forearm  and  the  interosseous  membrane,  and  are  almost  wholly 
concealed  by  the  superficial  muscles.  Only  the  abductor  pollicis  longus  and 
the  extensor  pollicis  brevis  become  superficial  in  the  lower  part  of  the  forearm, 
emerging  between  the  radial  extensors  of  the  carpus  and  the  extensor  communis 
digitorum. 

24 


348  THE  MUSCULAE  SYSTEM. 

Superficial  IVIuscIes. 

The  brachio-radialis  (supinator  radii  longus)  arises  by  fleshy  fibres  from  the 
anterior  aspect  of  the  upper  two-thirds  of  the  lateral  supra-condylic  ridge  of 
the  humerus,  and  from  the  front  of  the  lateral  intermuscular  septum  (Fig.  257  a, 
p.  334).  Occupying  the  lateral  side  of  the  hollow  of  the  elbow,  the  muscle  descends 
along  the  radial  border  of  the  forearm,  and  ends  about  the  middle  in  a  narrow  flat 
tendon  which  is  inserted  under  cover  of  the  tendons  of  the  abductor  pollicis  longus 
and  extensor  pollicis  brevis,  by  a  transverse  linear  attachment,  into  the  upper 
limit  of  the  groove  for  the  above-named  muscles  on  the  lateral  side  of  the  lower 
extremity  of  the  radius.  Some  of  its  fibres  gain  an  attachment  to  the  ridge 
in  front  of  the  groove,  and  others  spread  over  the  surface  of  the  groove  for  a 
variable  distance  (Figs.  264,  p.  342,  and  265,  p.  343). 

The  extensor  carpi  radialis  longus  arises  by  fleshy  fibres  from  the  anterior 
aspect  of  the  lower  third  of  the  lateral  supra-condylic  ridge  of  the  humerus, 
from  the  front  of  the  lateral  intermuscular  septum,  and  from  the  common 
tendon  of  origin  of  succeeding  muscles,  which  is  attached  to  an  impression  on 
the  antero- lateral  surface  of  the  lateral  condyle  (Figs.  257  a,  and  257  &,  p.  334). 
It  ends  in  a  tendon  in  the  lower  half  of  the  forearm,  which  passes  beneath 
the  dorsal  carpal  ligament,  to  be  inserted  into  the  back  of  the  base  of  the  second 
metacarpal  bone  on  its  radial  side  (Fig.  269,  p.  346). 

The  extensor  carpi  radialis  brevis  arises  from  the  common  tendon,  from 
the  external  lateral  (radial  collateral)  ligament  of  the  elbow,  from  the  fascia 
over  it,  and  from  intermuscular  septa  on  either  side.  It  passes  down  the  back 
of  the  forearm  and  under  the  posterior  carpal  ligament  in  close  relation  to  the 
previous  muscle,  to  be  inserted  by  a  tendon  into  the  bases  of  the  second  and  third 
metacarpal  bones  (Fig.  269,  p.  346).  A  bursa  is  placed  beneath  the  two  radial 
extensor  tendons  close  to  their  insertion. 

The  extensor  digitorum  communis  arises  from  the  common  tendon,  from  the 
lateral  condyle,  from  the  fascia  over  it,  and  from  intermuscular  septa  on  either  side. 
Extending  down  the  back  of  the  forearm  it  ends  above  the  wrist  in  four  tendons,  of 
which  the  outermost  often  has  a  separate  fleshy  belly.  After  passing  beneath  the 
posterior  annular  ligament  in  a  compartment  along  with  the  extensor  indicis  proprius, 
the  tendons  separate  on  the  back  of  the  hand,  where  the  three  innermost  tendons  are 
joined  together  by  two  obliquely-placed  bands.  One  passes  downwards  and  later- 
ally, and  connects  together  the  third  and  second  tendons ;  the  other  is  a  broader 
and  shorter  band,  which  passes  also  downwards  and  laterally,  and  joins  the 
fourth  to  the  third  tendon.  In  some  cases  a  third  band  is  present,  which  passes 
downwards  and  medially  from  the  first  to  the  second  tendon ;  and  frequently  the 
tendon  for  the  little  finger  is  joined  to  the  tendon  for  the  ring  finger,  and  separates 
from  it  only  a  short  distance  above  the  lower  end  of  the  metacarpal  bone. 

The  tendons  are  inserted  in  the  following  manner :  on  the  finger  each  tendon 
spreads  out  so  as  to  form  a  membranous  expansion  over  the  knuckle  and  on  the 
back  of  the  first  phalanx.  The  border  of  the  tendon  is  indefinite  over  the  meta- 
carpo-phalangeal  articulation,  of  which  it  forms  the  posterior  ligament.  On  the 
back  of  the  first  phalanx  the  tendon  receives  laterally  the  insertions  of  the  inter- 
osseous and  lumbrical  muscles.  At  the  lower  end  of  the  first  phalanx  it  splits 
into  iU- defined  medial  and  lateral  slips,  proceeding  over  the  back  of  the  first 
inter-phalangeal  articulation,  of  which  they  form  the  posterior  ligament.  The 
medial  slip  is  inserted  into  the  back  of  the  base  of  the  second  phalanx,  while  the 
two  lateral  yjieces  become  united  to  form  a  membranous  tendon  on  the  back  of 
the  second  X->halanx,  which,  after  passing  over  the  second  inter-phalangeal  articula- 
tion, is  inserted  into  the  base  of  the  terminal  phalanx. 

The  extensor  digiti  quinti  proprius  has  an  origin  similar  to  and  closely 
connected  with  that  of  the  preceding  muscle,  from  the  common  tendon,  the 
fascia  over  it,  and  from  intermuscular  septa.  Passing  down  the  back  of  the 
forearm  as  a  narrow  fleshy  slip,  between  the  extensor  digitorum  communis  and 
the  extensor  carpi  ulnaris,  it  ends  in  a  tendon  which  occupies  a  groove  between 
the  radius  and  ulna  in  a  special  compartment  of  the  posterior  annular  ligament 


MUSCLES  ON  THE  BACK  OF  THE  FOREAKM. 


349 


Tricei)s  bracliii  (insertion) 


Biceps  bracliii  (insertion 

Supinator  muscle 
(insertion 


of  the  wrist.  Ou  the  back  of  the  hand  the  tendou,  usually  split  into  two  parts, 
lies  to  the  ulnar  side  of  the  tendons  of  the  extensor  digitorum  communis,  and 
is  finally  inserted  into  the  expansion  of  the  extensor  tendon  on  the  dorsum  of 
the  first  plialanx  of  the  little  finger. 

The  extensor  carpi  ulnaris  has  a  double  origin :  (1)  from  the  common  tendon 
from  the  lateral  condyle  of  the  humerus,  from  the  fascia  over  it,  and  from  the 
intermuscular  septa;  and  (2)  through  the  medium  of  the  deep  fascia,  from  the 
dorsal  margin  of  the  ulna  in  its  middle  two-fourths.  Lying  in  the  forearm  upon 
the  dorsal  surface  of  the  ulna,  it  ends  in  a  tendon  which  occupies  a  groove  on  the 
back  of  the  ulna  in  a  special  compartment  of  the  dorsal  ligament  of  the  wrist,  and  is 
inserted  into  the  ulnar  side  of  the  base  of  the  fifth  metacarpal  bone  (Fig.  269,  p.  346). 

The  anconaeus  is  a  small  triangular  muscle  arising  by  a  separate  tendon  from 
the  lower  part  of  the  dorsal  surface 
of  the  lateral  condyle  of  the 
humerus  (Fig.  267  h,  p.  334),  and 
from  the  posterior  ligament  of  the 
elbow-joint.  Spreading  out  over 
the  dorsal  surface  of  the  elbow- 
joint  and  upper  part  of  the  ulna,  it 
is  inserted  by  fleshy  fibres  into  a 
triangular  surface  on  the  lateral 
aspect  of  the  olecranon  process  and 
dorsal  surface  of  the  ulna,  as  low 
down  as  the  oblique  line  (Fig.  271, 
p.  349).  It  is  also  inserted  into 
the  fascia  which  covers  it. 

The  epitrocMeo-anconseus  is  an  oc- 
casional small  muscle  arising  from  the 
dorsal  surface  of  the  medial  condyle  of 
the  humerus,  and  inserted  into  the  medial 
side  of  the  olecranon  process.  It  covers 
the  ulnar  nerve  in  its  passage  to  the 
forearm. 

Deep  IVIuscIes. 

The  supinator  muscle  (supi- 
nator    radii     brevis)     is    the 

highest  of  the  deeper  muscles. 
It  is  almost  wholly  concealed 
by  the  superficial  muscles,  and 
has  a  complex  origin, — (1)  from 
the  lateral  condyle  of  the  hu- 
merus ;  (2)  from  the  external 
lateral  and  orbicular  (radial 
collateral  and  annular)  ligaments 
of  the  elbow-joint ;  (3)  from  the 
triangular  surface  on  the  shaft 
of  the  ulna  just  below  the  radial 
notch ;  and  (4)  from  the  fascia 
over  it.  From  this  origin  the 
muscle  spreads  laterally  and 
downwards,  enveloping  the  upper 
part  of  the  radius,  and  is  inserted 
into  the  palmar  and  lateral  sur- 
faces of  the  bone,  as  far  forwards  as 
the  tuberosity  of  the  radius,  as  far 
upwards  as  the  neck,  and  as  far 
downwards  as  the  oblique  line  and 
the  insertion  of  the  pronator  teres.     (Figs.  271,  p.  349,  and  273,  p.  350.) 

The  muscle  is  divisible  into  superficial  and  deep  imrts  with  humeral  and  ulnar 


Abductor  longus  pollicis 
(origin) 


rronator  teres 
(insertion) 


Extensor  pollicis  brevis 
(oiigin) 


Fig.  271.- 


J3rachio-radialis 

(insertion) 

Groove  for  tendons  of 

ladial  extensors  of 

carpus 

(jroove  for  extensor 

pollicis  longus 


Groove  for  extensor  digitornm  com- 
munis and  extensor  mdicis  proprius 

-Muscle-Attachments  to  the  Right  Radius 
AND  Ulna  (Posterior  Aspects). 


350 


THE  MUSCULAR  SYSTEM. 


origins,  between  which  the 

dorsal  part  of  the  forearm. 

The  abductor  poUicis 


posterior  interosseous  nerve  ^  passes  in  its  course  to  the 
longns  (extensor  ossis  metacarpi  pollicis)  arises  by 


Triceps 

BRACK  1 1 
TEKDON" 

Brachio- 
radialis 


Lateral  _ 
epicondyle 
Deep  fascia  of 
the  forearm 

Ancon.«us 

Extensor  carpi 
radialis 

LONG  us 


Dorsal  border        ^jj  | 
of  ulna 

Extensor  carpi 

radialis 

BREVIS 

Extensor  digitorum 

communis 

Extensor  digiti 

quinti  proprius 

Extensor  carpi 

ULNARIS 


Flexor  carpi  ulnaris 


Abductor  pollicis 

LONGUS 

Extensor  indicis 

proprius 

Extensor  pollicis 

brevis 

Extensor  pollicis 

LONGUS 


Posterior  ligament 
of  the  wrist 

Extensor  carpi 
radialis  longus 
extenhor  carpi  \  .... 

RADIALIS  brevis/ 

Extensor  carpi | 

ULNARIS  / 


Triceps 

BRACHII 

TENDON 

Brachio- 

radialis 

Origin  of 

superficial 

extensor 

MUSCLES 


Proximal  radio- 
ulnar JOINT 

Anconeus 

Extensor  carpi 

radialis  longus 

Dorsal 

border  of  ulna 

Extensor  carpi 

RADIALIS  brevis 

Supinator 
muscle 


Abductor  pollicis 

LONGUS  (extensor  OSSIS 

metacarpi  pollicis' 
Dorsal  border 

OF  ULNA 


Fig.  272. — Suj-erficial  Muscles  on  the 
Back  of  the  Left  Fokearm. 


Extensor  pollicis 

LONGUS 


Extensor  indicis  proprius  ----t— S- 


Bxtensor  pollicis  brevis.. 


Posterior  ligament 
of  the  wrist' 


Extensor  carpi  ) 

RADIALIS  LONGl'S  f 

Extensor  carhi  \ 
radialis  brevis  / 
Extensor  carpi  | 

ULNARIS  f 

Extensor  digiti  ^ 
quinti  proprius  / 
Extensor... 
pollicis  longus 

Extensor  INDICIS 

PROPRIUS  T, 


Fig.  273. — Deep  Muscles  on  the  Back 
OF  THE  Left  Forearm. 


fleshy  fibres  below  the  supinator  muscle  from  the  uppermost  of  the  narrow 
impressions  on  the  lateral  half  of  the  dorsal  surface  of  the  ulna ;  from  the  middle 
third  of  the  dorsal  surface  of  the  radius ;  and  from  the  intervening  portion  of  the 
interosseous  membrane  (Fig.  271,  p.  349).     Becoming  superficial  in  the  lower  part 

'  Posterior  interosseous  uerve  =  deep  ramus  of  the  radial  nerve  (B.N. A.). 


MUSCLES  ON  THE  BACK  OF  THE  FOEEAEM.  351 

of  the  forearm  along  with  the  extensor  poUicis  brevis,  between  the  extensors  of  the 
wrist  and  the  common  extensor  of  the  fingers,  its  tendon  passes  with  the  latter 
muscle  beneath  the  posterior  ligament  of  the  wrist,  to  be  inserted  into  the  radial  side 
of  the  base  of  the  first  metacarpal  bone  (Fig.  269,  p.  346).  From  the  tendon  close  to 
its  insertion  a  tendinous  slip  passes  to  the  abductor  poUicis  brevis  and  the  fascia 
over  the  thenar  eminence,  and  another  is  frequently  attached  to  the  large  mult- 
angular boue. 

The  extensor  poUicis  brevis  (extensor  primi  internodii  poUicis),  an  essentially 
human  muscle,  is  a  specialised  portion  of  the  previous  muscle.  It  arises  from  a 
rhomboid  impression  on  the  dorsal  surface  of  the  radius,  and  from  the  interosseous 
membrane,  below  the  abductor  pollicis  longus  (extensor  ossis  metacarpi  polHcis) 
(Fig.  271,  p.  349).  It  is  closely  adherent  to  that  muscle,  and  accompanies  it  beneath 
the  posterior  ligament  of  the  wrist  and  over  the  radial  artery  to  the  thumb.  Its 
tendon  is  then  continued  along  the  dorsal  surface  of  the  first  metacarpal  bone,  to 
be  inserted  into  the  dorsal  surface  of  the  base  of  the  first  phalanx  of  the  thumb. 
Before  reaching  its  insertion  the  tendon  helps  to  form  the  capsule  of  the  metacarpo- 
phalangeal joint. 

The  extensor  pollicis  longus  (extensor  secundi  internodii  pollicis)  arises  from 
the  lateral  part  of  the  dorsal  surface  of  the  ulna  in  its  middle  third,  and  from  the 
interosseous  membrane,  below  the  abductor  pollicis  longus  (Fig.  271,  p.  349).  Its 
tendon  grooves  the  dorsal  surface  of  the  radius,  and  occupies  a  special  compartment 
beneath  the  posterior  ligament  of  the  wrist.  Extending  obliquely  across  the  dorsal 
surface  of  the  hand,  the  tendon  crosses  the  radial  artery,  and  helps  to  form  the 
capsule  of  the  first  metacarpo-phalangeal  articulation,  and  is  inserted  into  the  dorsal 
surface  of  the  base  of  the  second  phalanx  of  the  thumb. 

At  the  wrist  the  tendons  of  the  muscles  of  the  thumb,  the  abductor  pollicis  longus 
(extensor  ossis  metacarpi  pollicis)  and  extensor  pollicis  Ijrevis  laterally,  and  the 
extensor  pollicis  longus  medially,  bound  a  hollow  (the  "  anatomical  snuff-box ") 
best  seen  in  extension  and  abduction  of  the  thumb,  which  corresponds  to  the  position 
of  the  radial  artery  as  it  winds  round  the  wrist  to  reach  the  palm  of  the  hand. 

The  extensor  indicis  proprius  (extensor  indicis)  arises  below  the  extensor 
pollicis  longus  from  the  lowest  impression  on  the  dorsal  surface  of  the  ulna,  extending 
down  from  the  middle  of  the  shaft  to  within  two  inches  of  its  lower  end,  and  sometimes 
also  from  the  interosseous  membrane  (Fig.  271,  p.  349).  Its  tendon  passes  through 
a  compartment  of  the  posterior  ligament  of  the  wrist  along  with  the  tendons  of  the 
extensor  digitorum  communis.  On  the  back  of  the  hand  the  tendon  lies  on  the 
ulnar  side  of  the  tendon  of  the  common  extensor  destined  for  the  forefinger, 
and  is  inserted  into  the  forefinger,  joining  the  membranous  expansion  of  the 
tendon  of  the  extensor  digitorum  communis  on  the  dorsum  of  the  first  phalanx. 

Nerve-Supply. 

Four  nerves  are  engaged  in  supplying  the  muscles  of  the  forearm  and  hand, — the  median  and 
ulnar  on  the  front,  tlie  musculo-spiral ^  and  posterior  interosseous-  nerves  on  the  back  of  the 
limb.  Of  the  muscles  on  front  of  the  forearm,  the  median  nerve  supplies  the  pronator  teres, 
flexor  carpi  radialis,  palmaris  longus,  flexor  digitorum  sublimis  directly,  the  fibres  being 
ultimately  traceable  to  the  sixth  cervical  nerve.  By  means  of  its  anterior  interosseous  branch  ^ 
(C.  7.  8.  T.  1.)  it  also  supplies  the  flexor  pollicis  longus,  pronator  quadratus,  and  the  lateral  half  of 
the  flexor  digitorum  profundus.  The  ulnar  nerve  (C.  8.  T.  1)  supplies  the  flexor  carpi  ulnaris 
and  the  medial  half  of  the  flexor  digitorum  profundus. 

The  muscles  in  the  palm  of  the  hand  are  innervated  by  the  median  nerve  (C.  6.  7.),  and  by  the 
ulnar  nerve  (C.  8.  T.  1).  The  median  nerve  suppUes  the  abductor,  opponens,  and  flexor  pollicis 
brevis  (superficial  head),  and  the  first  two  lumbricals.  The  ulnar  nerve  supjjlies  the  jmlmaris 
brevis,  and  by  its  deep  branch,  the  three  muscles  of  the  little  finger,  the  two  ulnar  lumbrical 
muscles,  all  the  interossei,  the  two  adductors  of  the  thumb,  and  the  interosseus  primus  volaris. 

The  muscles  on  the  dorsal  surface  of  the  forearm  are  supplied  by  the  musculo-spiral  nerve 
and  by  its  terminal  muscular  branch,  the  posterior  interosseous  nerve.  The  musculo-spiral 
nerve'  supplies  directly  the  brachio- radialis  (C.  5.  6.),  and  the  abductor  pollicis  longus 
(C.  6.  7.).  The  anconseus  is  supplied  by  a  branch  from  the  musculo-spiral  nerve '  to  the 
medial  head  of  the  triceps  (C.  7.  8.).  The  posterior  interosseous  nerve  -  supplies  the  other 
muscles  on  the  back  of  the  forearm, — extensor  carpi  radialis  brevis  (C.  6.  7.),  extensor  digitorum 

1  Musculo-spiral  nerve  =  ratlial  nerve  (B.N. A.). 

-  Posterior  interosseous  nerve  =  deep  ramus  of  radial  nerve  (B.N. A.). 

^  Anterior  interosseous  nerve  =  volar  interosseous  nerve  of  forearm  (B.N. A.). 


352 


THE  MUSCULAE  SYSTEM. 


communis,  extensor  digiti  quinti  proprius,  extensor  carpi  ulnaris  (C.  6.  7.  8.),  supinator,  abductor 
pollicis  longus  (C.  6.),  the  two  extensors  of  the  thumb,  and  the  extensor  indicis  proprius  (C.  6.  7.  8.). 

Actions  of  the  Muscles  of  the  Forearm  and  Hand. 

These  muscles  are  concerned  in  the  movements  of  the  elbow,  wrist,  and  fingers. 
In  the  majority  of  cases  the  muscles  act  uj)on  more  than  one  joint. 

1.  Action  on  the  Elbow- Joint. — It  has  been  shown  already  that  flexion  and  extension 
of  the  elbow  are  assisted  by  certain  of  these  muscles.  The  flexor  muscles  are  the  pronator 
teres,  and  the  flexor  muscles  of  the  wrist  and  fingers.  In  the  position  of  pronation,  the  move- 
ment of  flexion  is  aided  by  the  brachio-radialis  and  extensor  muscles  of  the  wrist  and  fingers. 
The  extensors  are  the  supinator  muscle  and  anconseus,  and  the  extensor  muscles  of  the  wrist  and 
fingers. 

2.  Pronation  and  supination  of  the  hand  are  performed  by  special  muscles,  aided  by  muscles 
which  act  also  upon  other  joints.  The  brachio-radialis  assists  in  flexion  and  pronation  on  the  one 
hand,  and  in  extension  and  supination  on  the  other  hand.  In  the  supine  position  it  assists 
pronation,  and  in  the  prone  position  it  assists  supination,  in  each  case  bringing  the  hand  into 
the  position  intermediate  between  pronation  and  supination. 


Pronation. 

Supination. 

Pronator  teres 
Pronator  quadratus 
Brachio-radialis 
Flexor  carpi  radialis 
Weight  of  the  limb 

Supinator 

Biceps  brachii 

B  rachio  -radialis 

Extensors  of  thumb  and  fingers 

Weight  of  the  limb 

3.  Action  on  the  Wrist-Joint. — The  movements  at  the  wrist-joint  are  flexion  and  extension, 
abduction  and  adduction.  Flexion  and  adduction  are  much  more  extensive  movements  than 
extension  and  abduction,  on  account  of  the  form  of  the  wrist-joint.  The  following  muscles  pro- 
duce these  movements  : — 


Flexion. 

Extension. 

Adduction. 

Abduction. 

Flexor  carpi  radialis 
Palmaris  longus 
Flexor  carpi  ulnaris 
Long   flexors   of 
thumb  and  fingers 

Extensors  of  the  wrist 
Extensors    of    thumb 
and  fingers 

Flexor  carpi  ulnaris 
Extensor  carpi  ulnaris 

Flexor  carpi  radialis 
Extensors  of  wrist 
Extensors  of  thumb 

4.  Movements  of  the  Fingers. — Two  separate  series  of  movements  occur  in  relation  to  the 
articulations  of  the  fingers  :  flexion  and  extension  (at  the  metacarpo -phalangeal  and  inter- 
phalangeal  joints),  and  abduction  and  adduction  (only  at  the  metacarpo-phalangeal  joints).  The 
movements  and  the  muscles  concerned  are  given  in  the  following  tables  : — 


Flexion. 

Extension. 

Flexor  digitorum  sublimis 
Flexor  digitorum  profundus 
Lumbricales   '^  {acting  on   the  metacarpo- 
Interossei        /  phalangeal  articulations) 
Flexor  digiti  quinti  brevis 

Extensor  digitorum  communis 
Extensor  indicis  proprius 
Extensor  digiti  quinti  proj)rius 
Lumbricales  \  {acting   on   the   inter -pha- 
Interossei        /  langeal  articulations) 

Abduction. 

Adduction. 

Lumbricales          ^ 

Flexor  brevis  and  1  (from  the  inner  side 
Opponens,    digiti  '     of  the  hand) 
quinti                  J 

C  (from     the     middle 
1  Dorsal  interossei  ^      line  of  the  middle 
I     finger) 

/-(to  the  middle  line 
Palmar  interossei]      of    tlie     middle 
i      finger) 

Flexion  is  more  powerful  and  complete  than  extension  of  the  fingers.  The  flexor  digitorum 
profundus  alone  acts  on  the  terminal  phalanges  ;  the  flexor  sublimis  and  flexor  profundus  together 
flex  the  proximal  inter-jjhalangeal  joint ;  and  flexion  of  the  metacarpo-phalangeal  articulation  is 
effected  by  the.se  muscles,  assisted  by  the  intero.ssei,  lumbricales,  and  flexor  digiti  quinti  brevis. 
Extension  of  the  phalanges  is  eft'ected  Ijy  the  united  action  of  the  extensors  of  the  digits,  the 
interossei  and  lumbricales  ;  extension  of  the  fingers  at  the  metacar])o-phalaiigeal  joints  is  produced 
solely  by  the  long  extensor  muscles,  tieparate  extension  of  the  index  finger  only  \^  possible;  the 
three  inner  fingers  can  only  be  flexed  and  extended  together,  on  account  of  the  connecting  bands 
joining  the  extensor  tendons  together  on  the  back  of  the  hand. 


FASCIA  AND  MUSCLES  OF  THE  THIGH  AND  BUTTOCK.      353 

5.  Movements  of  the  Thumb. — The  movements  of  wliich  tlie  thumb  is  capable  are  flexion 
and  extension  (occurring  at  the  carpo-metacarpal,  metacarpo-phalangeal,  and  inter-phalangeal 
joints) ;  abduction  and  adduction,  together  with  circumduction  (occurring  at  the  carpo-metacarpal 
joint). 

The  muscles  and  their  respective  actions  are  given  in  the  following  table  : — 


The  characteristic  features  of  the  movements  of  the  upper  limb  are  their  range  and 
refinement.  The  hand,  in  addition  to  its  intrinsic  powers,  can  be  moved  through  a 
wide  range  and  in  several  planes  by  the  muscles  acting  on  the  wrist  and  radio-ulnar 
joints ;  this  range  is  increased  by  the  fore  and  aft  movements  at  the  elbow-joint,  and  the 
extensive  movements  of  which  the  shoulder  and  clavicular  joints  are  capable.  The 
result  is  that  the  hand  can  be  brought  into  a  position  to  cover  and  guard  any  portion 
of  the  body.  The  precision  and  refinement  of  movement  is  made  possible  by  the  co- 
ordinate movements  of  the  various  muscles  acting  upon  the  several  joints,  so  that 
actions  can  be  performed  (as  raising  the  food  to  the  mouth)  in  which  all  the  articulations  of 
the  limb  are  brought  into  play ;  while  others  (such  as  writing)  are  possible  by  movements 
at  the  joints  of  the  wrist  and  fingers  along  with  fixation  of  the  elbow-joint. 


THE   LOWER  LIMB. 

FASCI>E   AND    IVIUSCLES   OF  THE   THIGH 
AND    BUTTOCK. 

FASCIA. 

The  superficial  fascia  of  the  thigh  and  buttock  is  continuous  above  with  the 
fascia  of  the  abdomen  and  back,  medially  with  that  of  the  perineum,  and  below 
with  that  of  the  leg.     It  presents  noticeable  features  in  the  buttock  and  groin. 

In  the  buttock  the  superficial  fascia  is  of  considerable  thickness,  and  is  usually 
loaded  with  fat,  whereby  it  assists  in  forming  the  contour  of  the  buttock  and  the 
fold  of  the  nates. 

In  the  groin  it  is  divisible  into  two  layers :  a  superficial  fatty  layer,  continuous 
with  a  similar  layer  on  the  front  of  the  abdominal  wall  above,  and  over  the 
perineum  medially,  and  a  deeper  membranous  layer,  which  is  attached  above  to  the 
medial  half  of  Poupart's  ligament  (Lig.  inguinale  Pouparti),  and  to  the  deep  fascia 
of  the  thigh  just  below  the  lateral  half  of  that  ligament.  Medially  it  is  attached 
to  the  pubic  arch,  and  below  the  level  of  Scarpa's  triangle  (trigonum  femorale)  it 
blends  inseparably  with  the  superficial  fatty  layer.  The  separation  of  these  two 
layers  of  the  superficial  fascia  is  occasioned  by  the  presence  between  them  of  the 
femoral  and  inguinal  lymphatic  glands,  the  large  saphenous  vein  and  its  tributaries, 
and  some  small  arteries.  The  attachment  of  the  deeper  layer  of  the  fascia 
to  the  pubic  arch  and  Poupart's  ligament  cuts  off  the  superficial  tissues  of  the 
thigh  from  the  perineum  and  the  abdominal  wall,  and  prevents  the  passage  down  the 
thigh  of  fluid  collected  in  the  perineum  or  beneath  the  fascia  of  the  abdominal  wall. 

The  deep  fascia  or  fascia  lata  forms  a  tubular  investment  for  the  muscles  and 
vessels  of  the  thigh  and  buttock.     It  is  firmly  attached  above  to  the  iliac  crest,  the 


354 


THE  MUSCULAE  SYSTEM. 


great  sacro-sciatic  (sacro-tuberous)  ligament,  the  ischium,  the  pubic  arch,  the  pubic 
symphysis  and  crest,  and  Poupart's  ligament.  In  the  lower  part  of  the  thigh  it 
forms  the  intermuscular  septa ;  and  in  relation  to  the  knee,  it  is  continuous  with 
the  deep  fascia  of  the  leg,  gains  attachment  to  the  patella,  the  condyles  of  the 
tibia  and  the  head  of  the  fibula,  and  forms  the  lateral  ligaments  of  the  patella. 

On  the  front  of  the  thigh  the  deep  fascia  is  thick  and  strong.  It  is  pierced  by 
numerous  openings  for  vessels  and  nerves,  the  most  important  of  which  is  the  saphen- 
ous opening  (fossa  ovalis)  for  the  passage  of  the  saphenous  vein.  A  femoral  hernia 
passes  through  this  opening  to  reach  the  groin  and  anterior  abdominal  wall.    It  is  an 


Linea  alba  "^ ~ — ""~' 


Lig.  fundiforme  penis 


Intercrural  fibres 
Dorsal  vein  of  penis 


Obliquus  Externus 

abdominis 


Anterior  superior 
iliac  spine 


External  oblique 
aponeurosis 

Superficial  circum- 
flex iliac  artery 

Intercrural  fibres 

(  Attachment  of  mem- 
■  -  branous  layer  of 

(  superficial  fascia 
Poupart's  inguinal 
ligament 

Superficial  inferior 
epigastric  artery 


Superior  external 
pudendal  artery 

Femoral  lymphatic 
gland 


Large  saphenous 
vein  (internal) 


Fig.  274. — Superficial  Anatomy  of  the  Left  Groin. 

oval  opening  of  variable  size  situated  just  below  the  medial  half  of  Poupart's  ligament, 
and  immediately  in  front  of  the  femoral  vessels.  It  is  covered  by  the  superficial 
fascia,  and  by  a  special  layer  of  fascia,  the  cribriform  fascia,  a  thin  perforated  lamina, 
attached  to  the  margins  of  the  opening.  The  lateral  edge  of  the  opening  (margo 
falciforuiis)  is  formed  by  the  margin  of  the  iliac  portion  of  the  fascia  lata,  which  is 
attached  above  to  the  iliac  crest  and  Poupart's  ligament ;  the  medial  edge  is  formed 
by  the  puhic  portion  of  the  fascia  lata  (fascia  pectinea),  which  is  continued  upwards 
behind  the  femoral  sheath,  over  the  adductor  longus  and  pectineus  muscles  to  the 
ilio-pectineal  line  and  the  capsule  of  the  hip-joint.  These  two  layers  of  the  fascia 
lata  are  continuous  at  tlie  lower  concave  margin  of  the  saphenous  opening,  forming 
its  inferior  comu.  As  they  pass  upwards  towards  the  pelvis  they  occupy  different 
planes,  the  iliac  portion  being  in  front  of  the  sheath  of  the  femoral  vessels,  while  the 
pectineal  fascia  is  Vjehind  it.  The  superior  comu  of  the  saphenous  opening, 
placed  in  front  of  the  sheath,  is  derived  solely  from  the  iHac  portion  of  the  fascia  lata. 


FASCIA  AND  MUSCLES  OF  THE  THIGH  AND  BUTTOCK.      355 


It  forms  a  strong  triangular  band  of  fascia  known  as  the  falciform  ligament,  attached 
above  to  the  medial  half  of  Poupart's  ligament.  It  has  an  important  share  in 
directing  the  course  of  a  femoral  hernia  upwards  on  to  the  abdominal  wall. 

On  the  medial  side  of  the  thigh  the  fascia  lata  is  thin  where  it  covers  the 
adductor  muscles.  At  the  knee  it  is  associated  with  the  tendons  of  the  vasti 
muscles,  and  forms  the  lateral  ligaments  of  the  patella,  attached  to  the  borders  of 
the  patella  and  to  the  condyles  of  the  tibia.  On  the  lateral  side  of  the  thigh  it 
forms  the  ilio-tibial  band  ( tractus  ilio-tibialis) — a  broad  thick  layer  of  fascia  which 
is  attached  above  to  the  iliac  crest,  and  receives  the  insertions  of  the  tensor  fasciae 
lat*,  and  part  of  the  glutajus  maximus  muscles ;  it  is  attached  below  to  the  capsule 


Obliquus  externts 
abdominis 
(reflected) 


Spermatic  cord.. 


Intercolumnar  fascia- 


Obliquus  externus 
abdominis 


Obmquus  INTERNDS 
abdominis 

.\nterior  superior 
iliac  spine 

Transversus 
abdominis 

Obliquus  internus 
ABDOMINIS  (reflected) 


Aponeurosis  of  obliquus 
externus  (reflected) 
Abdominal  inguinal  ring 
Spermatic  cord  and 
infundibuliform  fascia 
Fascia  transversalis 
Conjoint  tendon 
■(Inguinal  aponeurotic 
falx) 

Saphenous  opening 


Large  saphenous  vein 


Fig. 


-The  Dissection  of  the  Left  Inguinal  Canal. 


of  the  knee-joint  and  the  lateral  condyle  of  the  tibia.  A  strong  band  of  fascia 
continued  upwards  from  the  iho-tibial  band  beneath  the  tensor  fascise  latae  muscle 
joins  the  tendon  of  origin  of  the  rectus  femoris  and  the  capsule  of  the  hip-joint. 

On  either  side  of  the  thigh  above  the  knee  an  intermuscular  septum  is  formed. 
The  lateral  intermuscular  septum  extends  medially  from  the  ilio-tibial  band  to  the 
lateral  epicondylic  line  and  linea  aspera  of  the  femur,  and  gives  attachment  to 
the  vastus  lateralis  (externus)  and  vastus  iutermedius  (crureus)  in  front,  and  the  short 
head  of  the  biceps  behind.  The  medial  intermuscular  septum  in  the  lower  third  of  the 
thigh  is  associated  with,  and  to  a  large  extent  represented  by,  the  tendon  of  insertion 
of  the  adductor  magnus  muscle.  It  is  also  related  to  the  fascia  which  envelops  the 
adductor  muscles,  and  forms  the  sheaths  for  the  sartorius  and  gracihs  muscles.  In 
the  middle  third  of  the  thigh  the  fascia  under  the  sartorius  is  greatly  thickened  by 
transverse  fibres  and  binds  together  the  vastus  medialis  (internus)  and  adductor 


356  THE  MUSCULAK  SYSTEM. 

longus  and  adductor  magnus  muscles.  This  layer  of  fascia  roofs  over  the  femoral 
vessels  in  their  course  through  Hunter's  canal  (canalis  adductorius  Hunteri). 

The  fascia  lata  of  the  buttock  is  thick  in  front  where  it  covers  and  gives  origin 
to  the  glutieus  medius,  thinner  behind  over  the  glutaius  maximus,  at  the  upper 
border  of  which  it  splits  to  enclose  the  muscle.  It  is  thickened  over  the  greater 
trochanter,  where  it  forms  the  insertion  of  the  greater  part  of  the  latter  muscle. 

On  the  back  of  the  thigh  and  over  the  popliteal  space  the  fascia  is  strengthened 
by  transverse  fibres  derived  from  the  hamstring  muscles.  The  popliteal  fascia 
forming  the  roof  of  the  popliteal  space  is  specially  thick,  and  is  usually  pierced 
by  the  small  saphenous  vein. 

Femoral  Sheath. — This  is  a  conical  membranous  investment,  derived  from 
the  fascial  lining  of  the  abdominal  cavity,  the  fascia  transversalis  in  front  and  the 
fascia  iliaca  behind,  prolonged  along  the  femoral  vessels  in  their  passage  behind 
Poupart's  ligament  into  Scarpa's  triangle.  The  sheath  is  about  an  inch  and  a  half 
in  length,  and  is  divided  into  three  compartments  —  a  lateral  space  for  the 
artery,  an  intermediate  space  for  the  vein,  and  a  medial  channel  containing 
lymphatics  and  fat,  and  named  the  femoral  canal.  The  wall  of  this  channel 
is  known  as  the  femoral  sheath.  This  canal  is  the  passage  through  which 
a  femoral  hernia  enters  the  thigh.  Its  upper  limit  is  the  femoral  ring,  bounded 
in  front  by  Poupart's  inguinal  ligament,  behind  by  the  origin  of  the  pectineus 
muscle  from  the  pubis,  medially  by  Gimbernat's  ligament  (lig.  lacunare), 
and  laterally  by  the  femoral  vein.  In  front  of  it  the  fascia  transversalis 
forming  the  sheath  is  thickened  to  form  the  deep  femoral  arch.  The  part 
of  Poupart's  ligament  in  front  of  the  ring  is  called  the  superficial  femoral  arch. 
The  deep  epigastric  artery  ^  separates  the  ring  from  the  internal  abdominal  ring. 
The  canal  ordinarily  contains  fat  which  is  continuous  above  with  the  extra- 
peritoneal tissue.  The  ring  is  filled  by  a  plug  of  fat  or  a  lymphatic  gland,  con- 
stituting the  femoral  septum  (septum  femorale  Cloqueti). 

The  femoral  canal  ends  behind  the  saphenous  opening,  covered  by  the  cribriform 
fascia,  while  the  falciform  ligament  crosses  over  it  and  conceals  its  upper  portion. 
The  course  of  a  femoral  hernia  is  determined  by  this  band.  The  hernia  descends 
through  the  femoral  ring,  pushing  the  femoral  septum  before  it ;  after  passing  through 
the  femoral  canal,  it  is  directed  forwards  through  the  saphenous  opening.  The 
anterior  part  of  the  hernia  being  pressed  upon  and  retarded  by  the  femoral  arches 
and  by  the  falciform  ligament,  the  posterior  part  pushes  onwards,  hooks  round 
the  falciform  ligament,  and  is  directed  upwards  over  Poupart's  ligament.  The 
coverings  of  a  femoral  hernia,  in  addition  to  peritoneum  and  extra-peritoneal  tissue 
(femoral  septum),  are  femoral  sheath,  cribriform  fascia,  superficial  fascia,  and  skin. 

MUSCLES  OF  THE  THIGH  AND  BUTTOCK. 

The  muscles  of  the  thigh  and  buttock  are  divisible  into  four  main  groups  by 
their  situation, action,  and  nerve-supply.  On  the  front  of  the  thigh  are  the  quadriceps 
femoris,  the  sartorius,  ilio-psoas,  and  pectineus  muscles ;  on  the  inner  or  medial  side 
of  the  thigh  are  the  adductor  muscles;  in  the  region  of  the  buttock,  the  glutsei 
and  rotators  of  the  hip-joint ;  and  on  the  back  of  the  thigh,  the  hamstring  muscles. 

THE  MUSCLES  ON  THE  FRONT  OF  THE  THIGH. 

The  chief  muscle  on  the  front  of  the  thigh  is  the  quadriceps  femoris,  which 
occupies  the  space  between  the  tensor  fasciae  latse  and  ilio  -  tibial  band 
laterally,  and  the  sartorius  medially.  The  sartorius  crosses  the  thigh  obliquely ; 
it  separates  the  quadriceps  femoris  from  the  adductor  muscles ;  it  forms  in  the 
upper  third  of  the  thigh  the  lateral  boundary  of  Scarpa's  triangle,  and  in  the  middle 
third  of  the  thigh,  the  roof  of  Hunter's  canal.  The  ilio-psoas,  passing  into  the 
thigh  beneath  Poupart's  ligament,  assists  along  with  the  pectineus  and  adductor 
muscles  in  forming  the  floor  of  Scarpa's  triangle  (trigonum  femorale). 

The  sartorius.  a  long  strap-like  muscle,  arises  from  the  superior  anterior  spine 
of  the  ilium  and  half  of  the  notch  below  it  (Fig.  276,  p.  357).  It  passes  down  the 
thigh  to  the  medial  side  of  the  knee,  where  it  is  inserted  by  aponeurotic  fibres 

^  Deep  ejiigastric  =  inferior  epigastric  artery  (B.N.  A.). 


THE  MUSCLES  ON  THE  FEONT  OE  THE  THIGH. 


357 


into  the  medial  surface  of  the 
shaft  of  the  tibia  just  below  the 
medial  condyle,  and  by  its  borders 
into  fascial  expansions  which  join 
the  capsule  of  the  knee-joint,  the 
internal  lateral  (tibial  collateral) 
ligament,  and  the  fascia  lata  of 
the  leg  (Fig.  279,  p.  359). 

The  sartorius  is  superficial  in 
its  whole  extent.  Its  upper  third 
forms  the  lateral  boundary  of 
Scarpa's  triangle  ;  its  middle  third 
forms  the  roof  of  Hunter's  canal 
(canalis  adductorius)  ;  and  its 
lower  third,  in  contact  with  the 
medial  side  of  the  knee,is  separated 
from  the  tendon  of  the  gracilis 
muscle  by  the  large  saphenous  nerve 
and  a  branch  of  the  anastomotica 
magna  artery.^  A  bursa  lies  be- 
neath the  tendon  at  its  insertion. 

The  quadriceps  femoris  is 
composed  of  four  muscles — the 
rectus  femoris,  vastus  lateralis 
(externus),  intermedins  (crureus), 
and  vastus  medialis  (internus). 

The  rectusfemoris  is  superficial 
except    at    its    origin,    which    is 
covered  by  the  glutsei,  sartorius, 
and  tensor   fascipe  latse  muscles. 
The  vasti  lie  on  either  side  of  the 
rectus  muscle,  the  vastus  lateralis 
being  partially  concealed   by  the 
tensor  fasciae  lat?e  and  ilio-tibial  band, 
the  vastus  medialis   by  the  sartorius 
muscle.     The  vastus  intermedins  en- 
velops the  femur,  and  is  concealed  by 
the  other  muscles. 

The  rectus  femoris  has  a  double 
tendinous  origin.    (1)  The  straight  head 
arises  from  the  anterior  inferior  spine 
of  the  ilium   (Fig.  282,"  p.  362);   (2) 
the  reflected  head  springs  from  a  rough 
groove  on  the  dorsum  ilii  just  above  the 
highest   part  of   the  acetabulum    (Fig 
p.  362).      A  bursa   lies   beneath  this 
of  origin.      The  two  heads,  bound  together 
and  connected  to  the  capsule  of  the  hip- joint 
by  a  band  of  fascia  derived  from  the  under 
surface    of    the    tensor    fasciae     latse    (ilio- 
tibial   band),  give    rise    to  a    single    tendon 
which  extends  for  some  distance  on  the  front 
of  the  muscle,  and  from  which  the  muscular 
fibres  arise.     The  lauscular  fibres  springing 
from  this  tendon,  and  also    from  a  median 
septal  tendon,  present  a  bipennate  arrange- 
ment, and  end  below  in  a  broad  tendon  which 
passes  upwards  for  some  distance  along  the  posterior  surface  of  the  muscle, 

^  Anastomotica  magna  artery  =  arteria  genu  suprema  (B.N. A,). 


282, 
head 


ri:N90R  KASCI.*: 


Pectineijs 


Adductor 

LONGUSi 


Sartorius 


Uio-tibial  band 

Gracilis 
Adductor 

MAGNUS 


Vastus 
lateralis 
(externus) 
Rectus  femoris 


Vastus 

medialis 

(internus) 


Tendon  of 
rectus  femoris 


Ligamentum 

PATELLA 


Fig.  276. — The  Muscles  of  the  Front 
OF  THE  Right  Thigh. 


This 


358 


THE  MUSCULAK  SYSTEM. 


Piriformis  (insertion) 


tendon  gradually  narrows  towards  the  knee,  and  spreading  out  again,  is  inserted 

into  the  upper  border  of  the  patella.  It 
receives  laterally  parts  of  the  insertions  of 
the  vasti  muscles  (lateral  and  medial),  and 
on  its  deep  surface  is  joined  by  the  insertion 
of  the  vastus  iutermedius  (crureus).  A 
bursa,  which  communicates  with  the  synovial 
membrane  of  the  knee-joint,  lies  beneath  its 
tendon  in  front  of  the  lower  end  of  the  shaft 
of  the  femur. 

The  vastus  lateralis  has  an  origin,  partly 
fleshy,  partly  membranous,  from  (1)  the  cap- 
sule of  the  hip-joint,  (2)  the  tubercle  of  the 
femur,  (3)  a  concave  surface  on  the  front  of 
the  shaft  of  the  bone  medial  to  the  greater  tro- 
chanter, (4)  the  lower  border  of  the  greater  tro- 
chanter, (5)  the  lateral  margin  of  the  gluteal 
ridge  of  the  femur  and  the  tendon  of  the 
glutseus  maximus,  (6)  the  upper  half  of  the 
linea  aspera,  and  (7)  the  fascia  lata  and  lateral 
intermuscular  septum  (Fig.  277,  p.  358). 

It  forms  a  thick,  broad  muscle  directed 
downwards  and  forwards,  and  is  inserted 
by  a  broad  membranous  tendon  into  (1)  the 
lateral  border  of  the  tendon  of  the  rectus 
femoris,  (2)  the  upper  and  lateral  border  of 
the  patella,  and  (3)  the  capsule  of  the  knee- 
joint,  and  the  external  lateral  (fibular  col- 
lateral)  ligament  of  the  patella.     A  bursa 

intervenes  between  it  and  the  membranous  insertion  of  the  glutseus  maximus. 

The  vastus  medialis  is  larger  than  the  vastus  lateralis  and  has  a  more  extensive 

origin,  from  (1)  the  lower  two-thirds  or  more  of  the  spiral  (anterior  intertrochanteric) 


Vastus  lateralis 
(externus)  (origin) 


Fig.   277.- 

TERIOR 


-Muscle-Attachments   to  the   An- 
sueface    of   the    upper   part   of 


THE  Left  Femur. 


Vastus  mediai.is 


Saphenous  nerve  (Internal)^^ 
Femoral  vessels. 
Sartorius 

Adductor  lonous 


Adductor  magnus 
Gracilis 


Rectus  femoris 


Vastus  lateralis 

Vastus 

intermedius 

(Crureus) 

Femur 


Biceps  Femoris  (short  hear!) 


Semimembranosus 


BicEi'S  Femoris  (long  head) 


Semitendinosus 


Sciatic  nerve  (Great) 
Fio.  278. — Transverse  Section  of  the  Thigh  (Hunter's  Canal). 

line,  the  linea  aspera,  and  the  upper  two-thirds  of  the  line  leading  from  the  linea 
aspera  to  the  medial  condyle  of  the  femur  ;  (2)  the  membranous  expansion  of  the 
fascia  lata  which  lies  beneath  the  sartorius  and  forms   the  roof  of  the   adductor 


THE  MUSCLES  ON  THE  EEONT  OF  THE  THIGH. 


359 


Semi-membranosus 
(insertion) 
amentum  patellse 
(in&ertiou) 


Popliteus 

Attachment  of  internal 
lateral  ligament  of  the  knee 
(tibial  collateral) 
Gracilis  (insertion) 


Semi-tendinosus  (insertion) 


canal  of  Hunter :   and  (3)  the  medial  intermuscular  septum  and  the  tendon  of  the 
adductor  magnus  (Figs.  277,  p.  358,  and  281,  p.  361). 

From  its  origin  the  muscle  is  directed  downwards  and  laterally  towards  the 
knee  ;  it  is  inserted  by  a  strong  aponeurotic  tendon  into  (1)  the  medial  border  of  the 
rectus  tendon ;  (2)  into  the  upper  and  medial  border  of  the  patella ;  and  (3)  the 
capsule  of  the  knee-joint  and  the  internal  lateral  ligament  of  the  patella.  The 
muscle  conceals  the  medial  side  of  the  shaft  of  the  femur  and  the  vastus  inter- 
medialis,  with  which  it  is  closely  incorporated  in  its  lower  two-thirds. 

The  vastus  intermedius  muscle  (crureus)  arises  by  fleshy  fibres  from  (1)  the 
upper  two-thirds  of  the  shaft  of  the  femur  on  the  anterior  and  lateral  surfaces,  (2)  the 
lower  half  of  the  lateral  lip  of  the  linea  aspera  and  the  upper  part  of  the  line  lead- 
ing therefrom  to  the  lateral  condyle,  and  (3)  a  corresponding  portion  of  the  lateral 
intermuscular  septum  (Fig.  277,  p.  358). 

For  the  most  part  deeply  placed, 
the  muscle  is  directed  downwards  to 
an  insertion  into  the  deep  surface  of  the 
tendons  of  the  rectus  and  vasti  muscles 
by  means  of  jfibres  which  join  a  mem- 
branous expansion  on  its  surface.  It 
is  closely  adherent  to  the  vastus 
lateralis  muscle  in  the  middle  third  of 
the  thigh ;  it  is  inseparable  from  the 
vastus  medialis  below  the  upper  third. 
In  the  lower  third  of  the  thigh  it  con- 
ceals the  articularis  genu  muscle  (sub- 
crureus),  a  bursa,  and  the  upward  pro- 
longation of  the  synovial  membrane  of 
the  knee-joint. 

The  articularis  genu  (subcrur- 
eus)  consists  of  a  number  of  separate 
bundles  of  muscular  fibres  arising  be- 
neath the  vastus  intermedius  from  the 
lower  fourth  of  the  front  of  the  femur, 
and  inserted  into  the  synovial  mem- 
brane of  the  knee-joint. 

The  four  elements  composing  the 
quadriceps  femoris  muscle  have  been 
traced  in  their  convergence  to  the 
patella.  Their  ultimate  insertion  is  into 
the  tuberosity  of  the  tibia  (Fig.  279,  p. 
359),  by  means  of  the  ligamentum  patellae, 
and  the  vasti  muscles  are  in  addition 
connected  with  the  lateral  ligaments  of  the  patella.  The  patella,  indeed,  is  in  one  sense 
a  sesamoid  bone  formed  in  the  tendon  of  the  muscle,  the  ligamentum  patellse  being 
the  real  tendon  of  insertion,  and  the  lateral  ligaments  fascial  expansions  from  its 
borders.     The  insertion  of  the  muscle  forms  the  front  of  the  capsule  of  the  knee-joint. 

The  ilio-psoas  muscle  is  a  compound  muscle,  consisting  of  two  elements, — 
psoas  (major  and  minor),  connecting  the  femur  and  pelvic  girdle  to  the  axial 
skeleton ;  and  another  element,  the  iliacus,  extending  between  the  innominate 
bone  and  the  femur.  The  muscles  chiefly  occupy  the  posterior  wall  of  the  abdomen 
and  false  (large)  pelvis,  their  insertions  only  appearing  in  the  thigh  below  Poupart's 
ligament,  in  the  lateral  part  of  Scarpa's  triangle  (trigonum  femorale). 

The  psoas  magnus  (m.  psoas  major)  is  a  large  piriform  muscle,  which  has  an 
extensive  origin  by  fleshy  fibres  from  the  vertebral  column  in  the  lumbar  region. 
It  arises  from  (1)  the  intervertebral  discs  above  each  lumbar  vertebra,  and  the 
adjacent  margins  of  the  vertebree — from  the  lower  border  of  the  12th  thoracic 
to  the  upper  border  of  the  5th  lumbar  vertebra;  (2)  it  arises  also  from  four 
aponeurotic  arches  which  pass  over  the  sides  of  the  bodies  of  the  first  four 
lumbar  vertebrae  ;  and  (3)  it  has  an  additional  origin  posteriorly  from  the  transverse 


Fig.  279. — Muscle-Attachments  to  the  medial  side 
OF  the  upper  part  op  the  left  Tibia. 


360 


THE  MUSCULAR  SYSTEM. 


processes  of  all  the  lumbar  vertebrae.  The  fibres  form  a  fusiform  muscle  directed 
downwards  over  the  pelvic  brim  and  beneath  Poupart's  ligament,  ending  in  a 
tendon  which  is  inserted  into  the  apex  of  the  lesser  trochanter  of  the  femur  (Fig. 
281,  p.  361).  A  bursa,  which  may  be  continuous  with  the  synovial  cavity  of 
the  hip-joint,  separates  the  tendon  from  the  pubis  and  the  capsule  of  the  hip-joint. 
The  psoas  parvus  (m.  psoas  minor)  is  often  absent  (40  per  cent).     It  arises 


Opening  of  the  vena  cava    CEsoplia_' 


Central  tendon  (middle  part) 


Central  tendon  (right  ijart) 

DiAPHKAGM,  COSTAL  FIBRES 

Internal  arcuate  ligament 
External  arcuate  ligament 

End  of  last  rib- 
Last  thoracic  ner\e- 
Ant.  layer  of  lumbar  fascia. 
Lumbar  fascia  . 
Ilio-h}-pogastric_ 
Lumbar  vessels  and  sympa- 
thetic communicating  nerves" 
Ilio-lnguinal- 

QUADKATCS  LUJIBORDJI  - 


External  cutaneous  nerve - 

PSOA.S  MAJOR  j 

Iliaccs* 
Lumbo-sacral  cord- 


Genito-crural  nerve 

(genito-femoral) 

Anterior  crural  nerve  (femoral) 

Obturator  nerve 

Great  sciatic  nerve 


Diaphragm,  right 

lateral  cr0s 

Middle  arcuate  ligament 
^    Aortic  opening 

Central  tendon 
(left  part) 
Diaphragm,  left 
lateral  crus 


Last  thoracic  nerve 
End  of  last  rib 
Lumbar  nerve  I. 

Ilio-hypogastric 
Lumbar  nerve  IL 

-Ilio-inguinal 
Quadratus 
lumborum 
Lumbar  nerve  IIL 


_^_^  Genito-crural  nerve 
li  V\      (genito-femoral) 

' — ' —  Lumbar  nerve  IV. 


Lumbo-sacral  cord 


^\    External  cutaneous  nerve 
'^ '^  Anterior  crural  (femoral) 
iierxe 
-1 — ,-  . ..— Obturator  nerve 


Gieat  sciatic  nerve 


Obturator  nerve 
Addoctor  longus  (origin) 
Adductor  brevis  (origin 

Gracilis  (origin) 

I  i    Adductor  magncs  (origin) 

I  I     Pectineus  (cut) 

I     Superticial  branch  of  obturator  nerve 
I     Deep  branch  of  obturator  nerve 
Obturator  extf.bnus 

Fig.  280.— View  of  the  PosTEnioK  Abdominal  Wall,  to  show  the  Muscles  and  the  Nerves  of 

THE  Lumbo-Sacbal  Plexus. 

from  the  intervertebral  disc  between  the  last  thoracic  and  first  lumbar  vertebrae,  and 
from  the  contiguous  margins  of  these  vertebrae.  The  muscle  is  closely  apposed 
to  the  anterior  surface  of  the  psoas  major.  It  forms  a  slender  fleshy  belly,  and  is 
inserted  by  a  narrow  tendon  into  the  middle  of  the  ilio-pectinoal  Line  and  the  ilio- 
pectineal  eminence,  its  margins  blending  with  the  fascia  covering  the  psoas  major. 

Jjiaphragm  Note. — Arcuate  ligaments,  internal  and  external  =  medial  and  lateral  lumbocostal  arches. 
Lateral  and  medial  crura  =  lateral  and  intermedial  crura. 
Middle  arcuate  ligament  =  medial  crus.  (B.N. A.) 


THE  MUSCLES  ON  THE  INNER  SIDE  OF  THE  THIGH. 


361 


Piriformis 
(insertion) 


Glutii-us  medius 
(insertion) 


Obturator  intemus  and 
gemelli  (insertion) 

Obturator  externus 

(insertion) 

Qiiadratus  femoris 
(insertion) 


llio-psoas  (insertion) 


The  iliacus  muscle  arises  in  the  false  (large)  pelvis  by  fleshy  fibres,  mainly  from 
a  horseshoe-shaped  origin  around  the  margin  of  the  iliac  fossa ;  it  has  additional 
origins  also  from  the  ala  of  the  sacrum,  the  anterior  sacro-iliac,  lumbo-sacral, 
and  ilio- lumbar  ligaments,  and 
outside  the  pelvis,  from  the  upper 
part  of  the  capsule  of  the  hip- 
joint  (ilio-femoral  band).  It  is  a 
fan-shaped  muscle,  its  fibres  pass- 
ing downwards  over  the  hip-joint 
towards  the  lesser  trochanter  of 
the  femur.  Lying  lateral  to  the 
psoas  muscle,  it  passes  through 
Scarpa's  triangle,  and  is  inserted 
by  fleshy  fibres  (1)  into  the  lateral 
side  of  the  tendon  of  the  psoas 
major;  (2)  into  the  concave 
anterior  and  upper  surfaces  of  the 
lesser  trochanter  ;  and  (3)  into  the 
shaft  of  the  femur  below  the  lesser 
trochanter  for  about  an  inch  (Fig. 
281,  p.  361) ;  and  (4)  by  its  most 
lateral  fibres  into  the  capsule  of 
the  hip-joint.  These  fibres  are 
often  separate,  forming  the  iliacus 
minor,  or  ilio-capsularis. 

The  pectineus  muscle  arises 
by  fleshy  fibres  from  (1)  the 
sharp  anterior  portion  of  the  ilio- 
pectineal  line  of  the  pubis,  and 
the  triangular  surface  of  the  pubic 
bone  in  front  of  this  (Fig.  282, 
p.  362),  (2)  the  femoral  surface 
of  Gimbernat's  ligament,  and  (3) 
the  pubic  portion  of  the  fascia  lata 
which  covers  it.  Forming  a 
broad  muscular  band,  occupying 
the  floor  of  Scarpa's  triangle,  medial  to  the  ilio-psoas,  it  is  inserted  by  a  thin  flat 
tendon  about  two  inches  in  length  into  the  upper  half  of  the  pectineal  line, 
leading  from  the  back  of  the  lesser  trochanter  of  the  femur  towards  the  linea 
aspera ;  its  lower  attachment  being  placed  in  front  of  the  insertion  of  the 
adductor  brevis  muscle  (Fig.  282,  p.  362).  The  muscle  may  be  occasionally 
divided  into  medial  and  lateral  parts,  the  former  innervated  by  the  obturator,  the 
latter  by  the  anterior  crural  nerve.^ 


Glutseus  maxinius 
(insertion) 

Adductor  magnus 
(insertion) 

Adductor  brevis 
(insertion) 


Pectineus  (insertion) 


Vastus  medialis  (origin) 


Fig.  281. — Muscle-Attachments  to  the  Posterior  Aspect 
OF  the  Upper  Part  of  the  Left  Femur. 


THE   MUSCLES   ON   THE   MEDIAL   SIDE    OF   THE    THIGH. 

The  muscles  on  the  medial  side  of  the  thigh  include  the  adductors  of  the  femur, 
— the  adductor  longus,  adductor  brevis,  and  adductor  magnus;  the  gracilis,  and  the 
obturator  externus. 

The  gracilis  is  superficially  placed  along  the  medial  side  of  the  thigh.  The 
adductor  muscles,  occupying  the  space  between  the  hip  bone  and  the  femur,  are 
placed  on  different  planes,  the  adductor  longus  being  in  the  same  plane  as  the 
pectineus  and  lying  superficially  in  Scarpa's  triangle ;  the  adductor  brevis,  on  a 
deeper  level,  is  in  contact  with  the  obturator  externus,  and  along  with  it  is  largely 
concealed  by  the  pectineus  and  adductor  longus ;  the  adductor  magnus,  the  largest 
and  deepest  of  these  muscles,  is  in  contact  with  the  other  adductors  and  the 
sartorius  anteriorly,  while  its  posterior  surface  is  in  relation  to  the  hamstring 
muscles  on  the  back  of  the  thigh. 


^  Anterior  crural  nerve  =  femora!  uerve  (B.N. A). 


562 


THE  MUSCULAE  SYSTEM. 


The  gracilis  muscle  is  a  long  flat  band  placed  on  the  medial  side  of  the  thigh 
and  knee.  It  arises  by  a  tendon  from  the  lower  half  of  the  edge  of  the  symphysis 
pubis,  and  for  a  similar  distance  along  the  border  of  the  pubic  arch  (Fig.  282, 
p.  362).  Its  flattened  belly  passes  down  on  the  medial  side  of  the  thigh  to  the  knee, 
to  end  in  a  tendon,  placed  between  the  sartorius  and  semitendinosus,  which  expands 
to  be  inserted  into  the  medial  side  of  the  shaft  of  the  tibia  just  below  the  medial 
condyle,  behind  the  sartorius,  and  above  and  in  front  of  the  semitendinosus 
(Fig.  279,  p.  359).  It  is  separated  from  the  sartorius  tendon  by  a  bursa,  and 
beneatli  its  tendon  is  another  bursa  common  to  it  and  the  semitendinosus. 

The  adductor  longus  is  a  triangular  muscle  occupying  Scarpa's  triangle  and 
the  floor  of  Hunter's  canal.      It  arises  from  the  anterior  surface  of  the  body  of 


-  Rectus  femoris  (straight  head  of  origin) 

.Rectus  femoris  (reflected  head  of  origin) 
.  Attachment  of  ilio-femoral  band 


Pyramidalis  abdominis  (origin) 
\Rectus  abdominis  (origin) 


Gracilis  (origin) 


Adductor  brevis 
(origin) 


Senii-membranosus 
(origin) 

Quadratus  femoris 
(origin) 


Biceps  and  semi-tendin-       \    \\ \ 
osus  (origin) 


Fig.  282. — Mu.scle- Attachments  to  the  outer  surface  of  the  Right  Pubis  and  Ischium. 

the  pubic  bone  in  the  angle  between  the  crest  and  symphysis  (Eig.  382,  p.  362). 
Extending  downwards  and  laterally,  it  is  inserted  into  the  middle  two-fourths 
of  the  medial  lip  of  the  linea  aspera  in  front  of  the  adductor  magnus. 

The  adductor  brevis  is  a  large  muscle  which  arises  from  an  elongated  oval 
surface  on  the  front  of  the  body  and  upper  part  of  the  inferior  ramus  of  the  pubic 
bone,  surrounded  by  the  other  muscles  of  this  group  (Fig.  282,  p.  362).  Directed 
downwards  and  laterally,  the  muscle  expands,  to  be  inserted  by  a  short  aponeurotic 
tendon,  behind  the  insertion  of  the  pectineus,  into  the  lower  two-thirds  of  the  line 
leading  from  the  lesser  trochanter  of  the  femur  to  the  linea  aspera,  and  to  the  upper 
fourth  of  the  linea  aspera  itself  (Fig.  281,  p.  361). 

The  adductor  magnus,  the  largest  of  the  adductor  group,  is  a  roughly  tri- 
angular muscle  arising  mainly  by  fleshy  fibres  by  a  curved  origin  from  the  lower 
part  of  the  lateral  border  and  a  large  portion  of  the  adjoining  inferior  surface  of  the 
ischial  tuberosity,  from  the  edge  of  the  inferior  ramus  of  the  ischium,  and  from  the 


THE  MUSCLES  ON  THE  INNER  SIDE  OF  THE  THIGH. 


363 


anterior  surface  of  the  inferior  ramus  of  the  pubic  bone,  its  most  anterior  fibres 
arising  between  the  obturator  externus  and  adductor  brevis  (Figs.  282,  p.  362). 
Its  upper  fibres  are  directed  horizontally  and  laterally  from  the  pubic  bone 
towards  the  upper  part  of  the  femur  ;  the  lowest  fibres  are  directed  downwards  from 
the  ischial  tuberosity  to  the  medial  condyle  of  the  femur ;  while  the  intermediate 
fibres  radiate  obliquely  laterally  and  downwards.  The  muscle  is  inserted  by 
tendinous  fibres  (1)  into  the  space  below  the  insertion  of  the  quadratus  femoris, 
above  the  linea  aspera ;  (2)  into  the  whole  length  of  the  linea  aspera ;  (3)  into  the 
medial  epicondylic  line  of  the  femur;  (4)  into  the  adductor  tubercle  on  the 
medial  condyle  of  the  femur;  and  (5)  into  the  medial  intermuscular  septum 
(Fio-.  281,  p.  361).  The  part  of  the  muscle  attached  to  the  space  above  the  linea 
aspera  is  often  separated  from  the  rest  as  the  adductor  minimus.     The  attachment 


Obturator  nerve 


Pubis 
Psoas  major 

Branch  to  hip-jo 
Deep  brai 
Superficial  braiiLli 
Descending  muscular  branches 

Pectinel 
Ascending  branch  to  obturatoi 
extern  U-? 

Medial  (internal)  circumflex  artery 

Adductor  lonous 
Adductor  brevis 


'IRIFORMIS 


GlUT,«1'S  MAXIMUS 


Pelvic  fascia 

ObTURATOE  1NTERNC3 


Cutaneous  branch 


Obturator  externus 
schium 


Ascending  branch  of  medial  (in- 
ternal) circumflex  artery  of  femur 
Quadratus  femoris 

Medial  circumflex  artery 

Descending  muscular  branches 
Adductor  maonus 


Blanch  to  knee-joint 


Branch  to  femoral  artery  Gracilis 

Fig.  283.— Scheme  of  the  Course  and  Distribution  of  the  Plight  Obturator  Ner\t;. 

of  the  muscle  to  the  supracondylic  ridge  is  interrupted  for  the  passage  of  the 
femoral  vessels  to  the  popliteal  space.  The  attachment  to  the  medial  condyle 
is  by  means  of  a  strong  tendon  which  receives  the  fibres  arising  from  the  ischium 
(the  part  of  the  muscle  associated  with  the  hamstring  group).  This  tendon  is  closely 
connected  with  the  internal  lateral  (tibial  collateral)  Hgament  of  the  knee-joint. 

The  obturator  externus  is  placed  deeply  under  cover  of  the  previous  muscles. 
It  is  a  fan-shaped  muscle  lying  horizontally  in  the  angle  between  the  hip  bone  and 
the  neck  of  the  femur.  It  arises  from  the  surfaces  of  the  pubic  bone  and  ischium, 
which  form  the  inferior  half  of  the  margin  of  the  obturator  foramen,  and  from  the 
corresponding  portion  of  the  superficial  surface  of  the  obturator  membrane  (Figs. 
282,  p.  362,  and  283,  p.  363).  Its  fibres  converge  towards  the  great  trochanter,  and 
end  in  a  stout  tendon  which,  after  passing  below  and  behind  the  hip-joint,  is  inserted 
into  the  trochanteric  fossa  of  the  greater  trochanter  of  the  femur  (Figs.  281 
p.  361,  and  289,  p.  367). 

Scarpa's  triangle  (trigonum  femorale)  is  a  large  triangular  space  on  the  front 
of  the  thigh  in  its  upper  third,  which  contains  the  femoral  vessels  in  the  upper  part 


364 


THE  MUSCULAK  SYSTEM. 


of  their  course  and  the  anterior  crural  nerve.^     It  is  bounded  above  by  Poupart's 
ligament,  laterally  by  the  sartorius,  and  medially  by  the  medial  border  of  the  adductor 

longus  muscle.  Its  floor  is 
formed  laterally  by  the  ilio- 
psoas, and  medially  by  the 
pectineus,  adductor  longus,  and 
a  small  part  of  the  adductor 
brevis. 

Hunter's  canal  (canalis 
adductorius)  occupies  the 
middle  third  of  the  medial  side 
of  the  thigh,  and  contains  the 
femoral  vessels  in  the  lower 
part  of  their  course.  It  is 
bounded  superficially  by  the 
sartorius,  under  which  is  a 
dense  fascia  derived  from  the 
fascia  lata,  binding  together 
the  vastus  medialis,  which 
forms  the  lateral  wall  of  the 
canal,  and  the  adductors, longus 
and  magnus,  which  form  the 
I  medial  wall  or  floor  of  the  canal. 

■*  Besides    the    femoral    vessels 

and   their   sheath,    the    canal 
contains  the  large  saphenous  nerve. 


Great  sacro- 
sciatic  liga- 
ment 
Gluteus 
MAxmus 

Obturator 
intern ds 
Biceps  and 
semitendin- 

OSUS 

Semimem- 
branosus 
quadratus 

FEMORIS 


IA.DDUCTOR 
jVIAGNUS 


THE  MUSCLES  OF  THE 
BUTTOCK. 

Gracilis 

This  group  includes  the  three  gluteei 
muscles,   the    tensor   fascise   latae,   piri- 
formis, obturator  internus  and  gemelli. 
Biceps        ^nd  quadratus  femoris. 
(short  head)         'j'^-^g  glutsBus  maximus  and  tensor  fasciae 
latse    muscles    are    in    the    same     plane, 
invested  by  envelopes  of  the   fascia  lata. 
The  glutceus  medius,  partially  covered  by 
•Oong'head)   the  glutseus  maximus,  conceals  the  glutaeus 
minimus ;   while  the  piriformis,  obturator 
internus,  gemelli,  and  quadratus  femoris, 
intervene  between   the  glutseus  maximus 
and  the  back  of  the  hip-joint. 

The  glutseus  maximus  is  a  large 
quadrilateral  muscle,  with  a  crescentic 
origin,  from  (1)  a  portion  of  the  area 
on  the  dorsum  ilii  above  the  superior 
curved  line  (Fig.  285,  p.  365;;  (2)  the 
tendon  of  the  sacrospinal  muscle ;  (3)  the 
posterior  surface  of  the  sacrum  and  coccyx 
(Fig.  311,  p.  390);  and  (4)  the  posterior 
surface  of  the  great  sacro- sciatic  liga- 
ment. The  fibres  which  form  its  upper 
and  lateral  border  take  origin  directly  from 
the  fascia  lata  which  envelops  the  muscle.  The  muscle  forms  a  large  fleshy  mass, 
whose  fibres  are  directed  obHquely  laterally  over  the  buttock,  invested  by  the  fascia 
lata,  and  are  inserted  by  short  tendinous  fibres,  partly  into  the  fascia  lata  over  the 
great  trochanter  of  the  femur  (joining  the  ilio-tibial  band),  and  partly  into  the 

^   Anterior  crural  nerve  =  femoral  nerve  (B.N. A.). 


Semimem- 
branosus 


Fig.  284.- 


-Deki'  Muscles  on  the  Back  op 

THE    RtcHT    THICH. 


THE  MUSCLES  OF  THE  BUTTOCK. 


365 


gluteal  ridge  (Fig.  281,  p.  361).  The  fascia  lata  receives  the  insertion  of  the 
whole  of  the  superficial  fibres  of  the  muscle  and  the  upper  half  of  the  deep  fibres. 
The  lower  half  of  the  deep  portion  of  the  muscle  is  inserted  for  the  most  part  into 
the  gluteal  ridge ;  but  the  lowest  fibres  of  all  are  inserted  into  fascia  lata,  and 
are  thereby  connected  with  the  lateral  intermuscular  septum  and  the  origin  of 
the  short  head  of  the  biceps. 

The  gliita3us  maximus  is  the  coarsest  and  heaviest  muscle  in  the  body.  By  its 
weight  it  helps  to  form  the  fold  of  the  nates.  It  is  superficial  in  its  whole  extent. 
The  gluteus  medius  is  visible  at  its  upper  border,  covered  by  the  fascia  lata ;  at  its 
lower  border  the  hamstring  muscles  and  great  sciatic  nerve  appear  on  their  way  down 
the  thigh.  Three  bursse  are  beneath  it :  one  (not  always  present)  over  the  tuberosity 
of  the  ischium  (tuber  ischiadicum),  a  second  over  the  lateral  side  of  the  greater  tro- 
chanter, and  a  third  over  the  vastus  lateralis.  The  filjres  of  the  glutseus  maximus 
arising  from  the  coccyx  may  form  a  separate  muscle  (agitator  caudse). 

The  tensor  fasciae  latae  arises  from  the  iliac  crest  and    the  dorsum  ilii  just 

Obliquus  exteruus  abdominis 
(iiisfrtiun) 


Glutii'US  maximus 
(origin) 


Tensor  fascise  latse 
(origin) 


Savtorius  (origin) 


Rectus  femoris  (reflected  head 
of  ou^in) 


Gemellus  superior  (origin) 

Gemellus  inferior  (origin). 

Semimembranosus  (origin). 

Biceps  and  semitendinosus  (origin) 


Adductor  magnus  (origin) 


Quadratus  femoris  (origin) 
Obturator  externus  (origin) 
Adductor  magnus  (origin) 


Fig.  285. — Muscle- Attachmexts  to  the  Right  Dorsum  Ilii  and  Tubek  Ischiadicum. 


lateral  to  the  anterior  superior  spine,  and  from  the  fascia  covering  its  lateral 
surface  (Fig.  285,  p.  365).  Invested  like  the  glutseus  maximus  by  the  fascia 
lata,  it  is  inserted  below  the  level  of  the  great  trochanter  of  the  femur  into  the 
fascia,  which  forms  the  ilio-tibial  band  (p.  355).  The  muscle  is  placed  along 
the  anterior  borders  of  the  glutseus  medius  and  glutseus  minimus. 

The  g-lutseus  medius  arises  from  (1)  the  dorsum  ilii,  between  the  iliac  crest  and 
superior  (posterior)  curved  line  above  and  the  middle  curved  line  below  (Fig. 
285,  p.  365),  and  (2)  the  strong  fascia  lata  covering  its  surface  anteriorly.  It  is 
a  fan-shaped  muscle,  its  fibres  converging  to  the  greater  trochanter,  to  be  inserted 
by  a  strong,  short  tendon  into  the  postero-superior  angle  of  the  greater  trochanter, 
and  into  a  well-marked  diagonal  line  on  its  lateral  surface  (Figs.  277,  p.  358,  281, 
p.  361).     A  bursa  is  placed  beneath  the  tendon  at  its  insertion. 

The  glutseus  minimus  arises,  under  cover  of  the  glutseus  medius,  by  fleshy  fibres 
from  the  dorsum  ilii  between  the  middle  (anterior)  and  inferior  curved  lines  (Fig.  285, 
p.  365).     This  muscle  is  fan-shaped  and  its  fibres  converge  to  the  antero-superior 


366 


THE  MUSCULAE  SYSTEM. 


Piriformis  (insertion) 

Glutrens  medius       I 
(insertion) 


angle  of  the  greater  trochanter, 
to  be  inserted  into  the  anterior 
surface  of  the  trochanter,  and 
sometimes  also  into  the  front  part 
of  the  upper  border  (Figs.  277, 
p.  358,  and  289,  p.  367).  It  is 
also  inserted  into  the  capsule  of 
the  hip-joint.  A  bursa  is  placed 
beneath  the  tendon  in  front  of 
the  greater  trochanter. 

The  piriformis  is  one  of  the 
few  muscles  connecting  the  lower 
limb  to  the   axial   skeleton.      It 
arises  (1)  within  the  pelvis  from 
the  pedicles  of  the  second,  third, 
and   fourth  sacral  vertebrae,  and 
from    the   adjacent    part  of   the 
bone  lateral  to  the  anterior  sacral 
foramina.     Passing   out  through 
the  greater  sacro-sciatic  foramen, 
it  receives  an  origin  from  (2)  the 
upper  margin  of  the  greater  sciatic 
notch  of  the  ilium,  and  (3)  the 
pelvic  surface  of  the  great  sacro-sciatic  (sacro- 
tuberous)  ligament.     In  the  buttock  it  forms 
a   rounded   tendon,  which  is  inserted   into  a 
facet  on  the  upper  border  and  medial  aspect 
of  the  greater  trochanter  of  the  femur  (Figs. 
286,  p.  366,  288,  p.  367,  and  289,  p.  367). 

The  piriformis,  at  its  origin,  lines  the  pos- 


Obturator  internus  and 
gemelli  (insertion) 

Obturator  externus 

(insertion) 

Quadratus  femoris 
(insertion) 


^     Ilio-psoas  (insertion) 


Glutseus  maximus 
(insert!' 

Adductor  magnus 
(insertion) 


Adductor  brevis 
(insertion) 


_  Pectineus  (insertion) 


Vastus  medialis  (internus) 


Fig.  286. — Muscle -Attachments  to  the 
Posterior  Aspect  of  the  Upper  Part 
OF  THE  Left  Femur. 


The  lumbar 

triangle 
OF  Petit 


Fascia  lata 


Adductor  maonus 


Semimembranosus 


Semitendinosus 


Ciroat  sciatic 
nerve 

Biceps  (long 
"  ead) 


Fig.  287. — The  Right  Glutaius  Maximus  Muscle. 


terior  wall  of  the  pelvis.  In 
the  buttock  it  is  covered 
by  the  glutseus  maximus,^ 
and  lies  behind  the  cap- 
sule of  the  hip -joint,  be- 
tween the  glutseus  medius 
and  superior  gemellus. 

The  obturator  inter- 
nus arises  on  the  pelvic 
aspect  of  the  hip  bone, 
from  (1)  the  whole  of  the 
margin  of  the  obturator 
foramen  (except  the  ob- 
turator notch);  (2)  the 
surface  of  the  obturator 
membrane;  (3)  the  whole 
of  the  pelvic  surface  of  the 
hip  bone  behind  and  above 
the  obturator  foramen ; 
and  (4)  the  parietal  pelvic 
fascia  covering  it  medi- 
ally. It  is  a  fan -shaped 
muscle,  and  its  fibres  con- 
verging to  the  lesser  sacro- 
sciatic  foramen,  give  rise 
to  several   tendons  united 


THE  MUSCLES  OF  THE  BUTTOCK. 


367 


Internal  pudic  nerve 

Nerve  to  obturator 

intern  us 


Gracu 


ADDrCTOR  MAG 


Hamstring  mus' 
(bic 


Superior  gluteal  nerve 

Gldt^eus  medics  (cut) 
Inferior  gluteal  nerve 
Piriformis 

Obturator  internos 
AND  gemelli 
Obturator  externus 

quadratus  femoris 

Great  sciatic  )ier\'e 
(and  subdivisions) 

Small  sciatic  nerve 
(posterior  cutaneous 
of  thigli) 

GUT.EUS  MAXIMUS 

(insertion) 
Adductor  magnus 


together,  which  hook  round  the  margin  of  the  foramen  (a  bursa  intervening),  and 
after  passing  over  the  back  of  the  hip-joint,  are  inserted  into  a  facet  on  the  medial 
surface  of  the  greater"  trochanter  of  the  femur  above  the  trochanteric  fossa 
(Figs.  288,  p.  367,  and 
289,  p.  367).  In  the 
pelvis  the  muscle  oc- 
cupies the  lateral  wall, 
covered  by  the  parietal 
(obturator)  layer  of 
pelvic  fascia,  which 
separates  it  from  the 
pelvic  cavity  above 
and  the  ischio-rectal 
fossa  below.  In  the 
buttock  the  tendon 
is  embraced  by  the 
gemelli  muscles  which 
are  attached  to  its 
upper  and  lower 
margins. 

The  gemelli 
muscles  form  acces- 
sory portions  of  the 
obturator  internus. 

The  superior 
gemellus  arises  from 
the  gluteal  surface  of 
the  ischial  (sciatic) 
spine(Fig.  285,p.36o). 
It  is  inserted  into  the 
upper  margin  and  sup- 
erficial surface  of  the 
tendon  of  the  obtur- 
ator internus  muscle. 

The  gemellus  inferior  arises  from  the  upper  part  of  the  gluteal  surface  of  the 
ischial  tuberosity  (Fig.  285,  p.  365).     It  is  inserted  into  the  lower  margin  and 

__  superficial     aspect    of 

Obturator  internus  and  gemelli  (insertion)  ^^^^^^^^^^^^  ^j_^g    tcudon   of   the   ob- 

turator  internus. 

The  quadratus 
femoris  arises  from 
the  lateral  margin  of 
the  ischial  tuberosity 
(tuber  ischiadicum) 
(Figs.  284,  p.  364,  and 
285,  p.  365),  and  is  in- 
serted into  the  quad- 
rate tubercle  and 
quadrate  line  of  the 
femur  (Fig.  286,  p. 
366).  The  muscle  is 
concealed  by  the 
glutseus  maximus  and  the  hamstring  muscles.  Its  deep  surface  is  in  contact  with 
the  obturator  externus  muscle  and  the  lesser  trochanter  of  the  femur,  a  bursa 
intervening.     The  muscle  is  not  infrequently  fused  with  the  adductor  magnus. 


Fig.  288. — The  Muscles  and  Nerves  of  the  Eight  Buttock. 


The 


jlutseus  maximxis  is  reflected 
show  the 


and  the  glutaeus  medius  is  cut  in  part  to 
arlutaiiis  minimus. 


Glutfeus  minimu 
(insert 
Piriformis 
(insertion) 


Fig 


Obtuiator  e\tei  nus 
(insertion) 

289. — Muscle  -  Attachments  to  the  Upper  Aspect  of  the  Greater 
Trochanter  of  the  Left  Femuk. 


868 


THE  MUSCULAK  SYSTEM. 


THE  MUSCLES  ON  THE  BACK  OF  THE  THIGH. 
The  Hamstring  Muscles. 

The  muscles  comprised  in  this  series  include  the  biceps,  semitendinosus,  and 
semimembranosus.  A  part  of  the  adductor  magnus,  already  described,  also  belongs 
morphologically  to  this  group.  They  occupy  the  buttock  and  back  of  the  thigh,  and 
diverge  at  the  knee  to  bound  the  popliteal  space.  The  origins  of  the  muscles  are 
concealed  by  the  gluteus  maximus.  In  the  back  of  the  thigh,  enveloped  by  the 
fascia  lata,  they  are  placed  behind  the  adductor  magnus,  the  semitendinosus  and 
semimembranosus  medially,  the  biceps  laterally.  The  two  former  muscles  help 
to  form  the  medial  boundary  of  the  popliteal  space,  of  which  the  biceps  is  a  lateral 
boundary. 

The  biceps  femoris  has  a  double  origin.     (1)  Its  long  head  arises  by  means  of  a 

^  Obliquus  extenius  abdominis 
(insertion) 


Tensor  fascite 
lat.e 


Gluticus  maximus 
(origin) 


Rectus  femoris  (reflected 
head  of  origin) 


Gemellus  superior  (origin) 

Gemellus  inferior  (origin) 

Semimembranosus  (origin) 

Biceps  and  semitendinosus  (origin) 


Quadratus  femoris  (origin) 

Obturator  externus  (origin) 

Adductor  magnus  (origin) 


Adductor  magnus  (origin)' 
Fig.  290. — Muscle- Attachments  to  the  Right  Dorsum  Ilii  and  Tuber  Ischiadicum. 

tendon,  in  common  with  the  semitendinosus,  from  the  lower  and  medial  facet  upon 
the  tuberosity  of  the  ischium  (Figs.  284,  p.  364,  and  290,  p.  368)  and  from  the  great 
sacro-sciatic  (sacro-tuberous)  ligament.  This  head,  united  for  a  distance  of  two  or 
three  inches  with  the  semitendinosus,  forms  a  separate  fleshy  mass,  which  extends 
to  the  lower  third  of  the  thigh,  to  end  in  a  tendon  joined  by  the  short  head  of  the 
muscle.  (2)  The  short  head  arises  separately  from  (1)  the  whole  length  of  the 
lateral  lip  of  the  linea  aspera  and  the  upper  two-thirds  of  the  lateral  epicondylic 
line  of  the  femur,  and  (2)  the  lateral  intermuscular  septum.  The  upper  limit  of 
its  origin  is  sometimes  blended  with  the  insertion  of  the  lowest  fibres  of  the 
glutseus  maximus.  The  fibres  of  the  short  head,  directed  downwards,  join  the 
tendon  of  the  long  head,  and  the  muscle  is  inserted  (1)  into  the  head  of  the  fibula 
by  a  strong  tendon,  which  is  split  into  two  parts  by  the  long  external  lateral 
(fibular  collateral)  ligament  of  the  knee-joint;  (2)  by  a  slip  attached  to  the  lateral 
condyle  of  the  tibia ;  and  (3)  along  its  posterior  border  by  a  fascial  expansion 
which  connects  the  tendon  with  the  popliteal  fascia.  There  is  a  bursa  between 
the  tendon  and  the  external  lateral  (fibular  collateral)  ligament  of  the  knee-joint. 


THE  MUSCLES  ON  THE  BACK  OF  THE  THIGH. 


369 


Obtqrator 

internus 
andciemelli 

Obitjeator 
externus 


The  short  head  may  be  absent :  there  may  be  an  additional  origin  from  the 
ischium  or  femur ;  and  the  long  head  may  send  a  slip  to  the  gastrocnemius  or  teudo 

calcaneus  (tensor  fasciae  suralis). 

The  semitendinosus  arises,  in 
common  with  the  long  head  of  the 
biceps,  from  the  lower  and  medial 
facet  upon  the  ischial  tuberosity 
(Fig.  290,  p.  368).  Separating 
from  the  common  tendon  two  or 
three  inches  from  its  origin,  the 
muscle  forms  a  long,  narrow  band 
which  becomes  tendinous  in  the 
middle  third  of  the  thigh.  Pass- 
ing over  the  medial  side  of  the 
knee  it  spreads  out  and  becomes 
membranous,  and  is  inserted  (1) 
into  the  medial  side  of  the  shaft 
of  the  tibia  just  below  the  medial 
condyle,  below  the  gracilis  and 
behind  the  sartorius  (Fig.  292, 
p.  369),  and  (2)  into  the  fascia  lata 
of  the  leg.      A  bursa  separates  it 


Adductor  magnus 


Semitendinosus 


Semimembranosus. 


Sartorius  tendon 


Biceps  tendon 
(along  with 
peroneal  nerve) 
Plantaris 


SemiinembraD- 
osus  (insertion) 

Ligamentnm 

patellae  (insertion) 


Popliteiis 
Attachment  of  in- 
ternal lateral  ligament 
of  the  knee  (tibial 
collateral) 
Gracilis  (insertion) 


Gastro- 
cnemius 


Semitendinosus 
(insertion) 


Fig.  291. 


-The  Muscles  un  the  Back  of  the 
Right  Thigh. 


FiQ.  •A'd2. — Muscle- Attachments  to  the  Medial 
Side  of  the  Upper  Part  op  the  Right  Tibia. 


from  the  sartorius  in  front,  and  another,  common  to  it  and  the  gracihs,  lies  beneath 
its  insertion.  The  belly  of  the  muscle  is  marked .  by  an  oblique  septal  tendinous 
intersection  about  its  middle. 

The  semimembranosus  arises  by  a  tendon  from  the  upper  and  lateral  facet  on 
the  ischial  tuberosity  (Figs.  290,  p.  368,  and  291,  p.  369).  In  the  upper  third 
of  the  thigh  the  tendon  gives  place  to  a  rounded  fleshy  belly,  which  lies  beneath 


370 


THE  MUSGULAE  SYSTEM. 


the  ischial  origin  of  the  biceps  and  semitendinosus  muscles.  Becoming  tendinous 
at  the  back  of  the  knee,  it  is  inserted  into  the  horizontal  groove  on  the  back  of  the 
medial  condyle  of  the  tibia  above  the  insertion  of  the  popliteus  (Figs.  299,  p.  377, 
and  300,  p.  377).  A  bursa  lies  beneath  the  tendon  at  its  insertion.  It  has  three 
additional  memhranous  insertions:  (1)  a  fascial  band  extends  downwards  and  medially 
to  join  the  posterior  border  of  the  internal  lateral  (tibial  collateral)  ligament  of 
the  knee-joint ;  (2)  another  fascial  band  extends  downwards  and  laterally,  forms 
the  fascia  covering  the  pophteus  muscle  {popliteus  fascia),  and  is  attached  to  the 
obUque  line  of  the  tibia;  and  (3)  a  third  strong  band  extends  upwards  and 
laterally  to  the  back  of  the  lateral  condyle  of  the  femur,  forming  the  posterior 
(oblique  popliteal)  ligament  of  the  knee-joint. 

Nerve-Supply  of  the  Muscles  of  the  Thigh  and  Buttock. 

The  nerves  which  supply  these  muscles  have  collectively  a  wide  origin  from  the  spinal  cord, 
from  the  second  lumbar  to  the  third  sacral  nerve,  through  the  trunks  of  the  lumbar  and  sacral 
plexuses.  The  anterior  crural  nerve  ^  (L.  2.  3.  4.)  supplies  the  pectineus  (L.  2.  3.),  sartorius 
(L.  2.  3.),  iliacus  and  psoas  (L.  2.  3.  4.),  and  quadriceps  muscles  (L.  3.  4.).  The  obturator  nerve 
(L.  2.  3.  4.)  supiDlies  the  obturator  externus  (L.  3.  4.),  adductor  longus  (L.  2.  3.),  gracilis  (L.  2.  3.  4.), 
adductor  brevis,  and  adductor  magnus  (L.  3.  4.), — the  last-named  muscle  being  also  supplied  by  the 
nerve  to  the  hamstring  muscles.  The  gluteeus  maximus  is  supplied  by  the  inferior  gluteal 
nerve  (L.  5.  S.  1.  2.) ;  while  the  superior  gluteal  nerve  (L.  4.  5.  S.  1.)  supplies  the  glutajus 
medius,  glutseus  minimus,  and  tensor  fasciae  latae.  The  piriformis  is  supplied  directly  by 
branches  from  the  first  and  second  sacral  nerves.  Special  branches  from  the  sacral  plexus 
supply  (1)  the  obturator  internus  and  superior  gemellus  (S.  1.  2.  3.),  and  (2)  the  quadratus  femoris 
and  inferior  gemellus  (L.  4.  5.  S.  1.).  A  special  nerve  to  the  hamstring  muscles  from  the 
sacral  plexus  (L.  4.  5.  S.  1.  2.  3.)  supplies  the  semitendinosus  (L.  5.  S.  1.  2.),  semimembranosus 
(L.  4.  5.  S.  1.),  adductor  magnus  (L.  4.  5.  S.  1),  and  the  long  head  of  the  biceps  (S.  1.  2.  3.).  The 
short  head  of  the  biceps  is  supplied  by  the  peroneal  nerve  ^  (L.  5.  S.  1.  2.)  by  means  of  a  branch, 
which  may  arise  in  common  with  the  inferior  gluteal  nerve. 

Actions  of  the  Muscles  of  the  Thigh  and  Buttock. 

Most  of  the  above  muscles  act  on  the  pelvis  and  on  the  hip-  and  knee-joints.  The  psoas 
muscle  in  addition  assists  in  tlie  movements  of  the  vertebral  column  (p.  392). 

1.  Movements  at  the  Hip- Joint. — The  movements  of  the  thigh  at  the  hip-joint  are  flexion 
and  extension,  adduction  and  abduction,  internal  and  external  rotation.  The  following  table 
gives  the  muscles  producing  these  movements  : — 


a.  Flexion        and        Extension. 

Sartorius 

Glutaeus  maximus 

Iliacus 

„         medius 

Psoas 

„         minimus 

Rectus  femoris 

Biceps  femoris 

Pectineus 

Semitendinosus 

Adductor  longus 

Semimembranosus 

Gracilis 

Adductor  magnus 

Obturator  externus 

b.  Adduction      and      Abduction. 

Pectineus 

Tensor  fascise  latse 

Adductor  longus 

Glutseus  medius 

„         brevis 

„         minimus 

„         magnus 

Obturator  externus 

Gracilis 

Piriformis                  "i 

Quadratus  femoris 

Obturator  internus 

Glutseus  maximus 

Gemelli 

during 

(lower  fibres) 

Sartorius 
Gluteus  maximus 

flexion 

(upper  fij^rcs) 

^  Anterior  crural  nerve ^femcjig,]  nerve  (B.N. A.). 
^  Peroneal  nerve  =  common  peroneal  (B.N. A.). 


THE  FASCIA  AND  MUSCLES  OF  THE  LEG  AND  FOOT. 


371 


c.  Internal  Rotation      and      External  Rotation. 

Tensor  fasciae  latse 

Obturator  externiis 

Glutseus  medius  (anterior  fibres) 

Glutteus  maximus  (lower  fibres) 

„        minimus       „           „ 

Quadratus  femoris 

Glutseus  medius      "1  (jjosterior 

„        minimus  j  fibres) 

Pintbrmis                  |  ^^^^. 
Obturator  mternus    -      ,      °. 
Gemelli                      J  extension 

Sartorius 

Ilio-psoas 

Pectineus 

Adductor  longus 

„         brevis 

„         magnus 

Biceps  femoris 

2.  Movements  of  the  Pelvis  on  the  Thigh. — It  is  to  be  noted  that  the  several  movements 
tabulated  above  refer  to  the  movements  of  the  femur  at  the  hip-joint.  The  contraction  of  the 
same  groups  of  muscles  produces  similar  movements  of  the  pelvis  on  the  femur,  exemplified  in 
the  various  changes  in  the  attitude  of  the  i^elvis  in  relation  to  the  thigh  and  the  vertebral 
column,  which  occur  in  locomotion. 

3.  Movements  at  the  Knee- Joint. — The  movements  at  the  knee-joint  are  mainly  flexion 
and  extension.  Flexion  is  much  more  powerful  than  extension.  There  is  also  a  limited  amount 
of  rotation  of  the  tibia.  The  movements  are  produced  by  certain  of  the  muscles  described  above, 
associated  with  certain  of  the  muscles  of  the  leg. 


a.  Flexion      ar 

id      Extension. 

b.  Rotation  inwards  and  Rotation  outwards. 

Sartorius 

Quadriceps  femoris 

Sartorius 

Biceps  femoris 

Gracilis 

Gracilis 

Semitendinosus 

Semitendinosus 

Semimembranosus 

Semimembranosus 

Biceps  femoris 

Popliteus 

Gastrocnemius 

Plantaris 

Popliteus 

THE    FASCIvC 


AND    lYIUSCLES 
AND    FOOT. 

FASCIiE. 


OF   THE    LEG 


The  superficial  fascia  of  the  leg  presents  no  special  features  except  in  the 
sole,  where  it  is  greatly  thickened  by  pads  of  fat,  particularly  under  the  tuberosity 
of  the  calcaneum,  and  under  the  balls  of  the  toes. 

The  deep  fascia  has  numerous  important  attachments  about  the  knee. 
Posteriorly  it  forms  the  popliteal  fascia,  and  is  joined  by  expansions  from  the  tendons 
of  the  sartorius,  gracilis,  semitendinosus,  and  biceps  femoris  muscles.  In  front  of 
the  knee  it  is  attached  fco  the  patella,  the  ligamentum  patellae,  and  the  tubercle  of 
the  tibia ;  laterally  it  is  connected  to  the  condyles  of  the  tibia  and  the  head  of 
the  fibula,  and  forms  the  lateral  patellar  ligaments,  broad  fascial  bands  which  pass 
obliquely  from  the  sides  of  the  patella  to  the  condyles  of  the  tibia,  and  are  joined 
by  fibres  of  the  vasti  muscles.  Passing  down  the  leg,  the  fascia  blends  over  the 
medial  surface  of  the  tibia  with  the  periosteum  of  the  bone.  It  extends  round 
the  lateral  side  of  the  leg  from  the  anterior  to  the  medial  border  of  the  tibia, 
binding  together  and  giving  origin  to  the  muscles,  and  gaining  an  attachment  to 
the  lower  part  of  the  shaft  of  the  fibula.  Two  septa  pass  from  its  deep  surface ; 
one  septum  (anterior  peroneal  septum),  attached  to  the  anterior  crest  of  the  fibula, 
encloses  the  musculo -cutaneous  nerve,^  and  separates  the  extensor  from  the 
peronsei  muscles.  The  other  septum  (posterior  peroneal  septum)  is  attached  to 
the  lateral  crest  of  the  fibula,  and  separates  the  peronaei  from  the  flexor  muscles. 
From  the  last-named  septum  another  extends  across  the  back  of  the  leg,  forms  a 
partition  between  the  superficial  and  deep  flexor  muscles,  and  encloses  the  posterior 

^  Musculo-cutaneous  nerve  —  superficial  peroneal  nerve  (B.N.A.). 


372 


THE  MUSCULAR  SYSTEM. 


Extensor  halldcis  lonct 
Anterior  tibial  nerve  an 

dorsalis  pedis  aitei)~7~;^7pi 
Extensor  DiGiTORUM  LONOUb ^ <,2c^i 


PeRON.EUS  TERTIUi 


Fibula. 


Interosseous  talo 
calcaneal  ligament 


Calcaneus 


Peron.«us  brevis 


Lateral  annular  ligament 


Peron^eus  longus 


Abductor  dioiti  quinti 


Plantar  aponeurosi 


Anterior  annular  ligament 
Tibialis  anterior 


Tibia 


tiliial  vessels  and  nerves.^  It  gives  rise  to  subordinate  septa  attached  to  the  vertical 
line  of  the  tibia  and  the  medial  crest  or  oblique  line  of  the  fibula,  which  separate 
the  tibiaUs  posterior  from  the  flexors  of  the  toes  on  either  side. 

At  the  ankle  the  deep  fascia  is  strengthened  by  additional  transverse  fibres, 
and  gives  rise  to  the  three  annular  ligaments. 

The  internal  annular  ligament  (Lig.  laciniatum)  stretches  between  the 
medial  malleolus  and  the  tuberosity  of  the  calcaneus.  While  it  is  continuous  at 
its  upper  border  with  the  general  investment  of  the  deep  fascia,  it  is  chiefly 
formed  by  the  septal  layer  covering  the  deep  muscles  on  the  back  of  the  leg. 
It  sometimes  gives  insertion  to  the  plantaris  muscle.  It  is  continuous  below  with 
the  plantar  fascia,  and  gives  origin  to  the  abductor  hallucis  muscle.  It  is  pierced 
by  the  calcanean  vessels  and  nerve.  Along  with  the  posterior  tibial  vessels  and 
nerve,  the  tendons  of  the  tibialis  posterior,  flexor  digitorum  longus,  and  flexor 
hallucis  longus,  pass  beneath  it,  each  enclosed  in  a  separate  synovial  sheath. 

The  lateral  annular  ligament,  much  smaller,  is  a  thickened  band  of  the 
deep  fascia  stretching  between  the  lateral  malleolus  and  the  calcaneus.     It  binds 

down  the  tendons 
of  the  peronsei, 
which  occupy  a 
space  beneath  the 
ligament,  lined  by 
a  single  synovial 
membrane. 

The  anterior 
annular  ligament 
is  in  two  parts.  An 
upper  band,  (lig. 
transversum  cruris) 
broad  and  unde- 
fined at  its  upper 
and  lower  borders, 
stretches  across  the 
front  of  the  ankle 
between  the  two 
malleoli.  This  band 
binds  down  to  the 
lower  end  of  the 
tibia  the  tendons 
of  the  tibialis  an- 
terior and  extensor 
One  synovial  sheath  is  found  beneath  it,  surrounding  the 


Talus  or  Astragalus 


—Tibialis  posterior 


Medial  annular 
igament 

Flexor  digitorum 
longus 

— ^Medial  plantar  artery 

Tjjrf-T-Medial  plantar  nerve 

^'■^^^/'^Flexor  hallucis  longus 

Abductor  hallucis 


Lateral  plantar  nerve 
Lateral  plantar  artery 
Plexor  digitorum  brevis 


Fig.  293.- 


Quadratus  plant.e  (accessorius) 


-Coronal  Section  through  the  Left  Ankle-Joint,  Talus, 
AND  Calcaneus. 


muscles  of  the  toes. 

tendon  of  the  tibialis  anterior. 

On  the  dorsum  of  the  foot,  where  the  general  covering  of  deep  fascia  is  much 
thinner,  a  special  well-defined  band  stretches  over  the  extensor  tendons.  This  lower 
band  of  tlie  anterior  annular  ligament  (lig.  cruciatum  cruris)  has  an  attachment 
laterally  to  the  lateral  border  of  the  greater  process  of  the  calcaneus.  It  divides 
into  two  bands  as  it  passes  medially  over  the  dorsum  of  the  foot  —  an  wpper 
part,  wl)ich  joins  the  upper  ligament  and  is  attached  to  the  medial  malleolus,  and 
a  loioer  part,  which  passes  across  the  dorsum  of  the  foot,  and  joins  the  fascia  of 
the  sole  at  its  medial  border.  Beneath  this  ligament  are  three  special  compartments 
with  separate  synovial  sacs,  one  for  the  tibialis  anterior  tendon,  a  second  for  that 
of  the  extensor  hallucis  longus,  and  a  third  for  the  extensor  digitorum  longus 
and  peroneeus  tertius  tendons.  There  are  occasionally  other  additional  bands  of 
the  deep  fascia  passing  like  the  straps  of  a  sandal  across  the  dorsum  of  the  foot. 

The  plantar  fascia  or  aponeurosis  is  of  great  importance.  In  the  centre  of  the 
sole  it  forms  a  thick  triangular  band,  attached  posteriorly  to  the  tuberosity  of  the 
calcaneus.  It  spreads  out  anteriorly  and  separates  mio  Jive  slips,  which  are  directed 
forwards  to  the  bases  of  tlie  toes.    These  slips  as  they  separate  are  joined  together  by 

^  Posterior  tibial  nerve  =  tibial  nerve  (B.N. A.). 


THE  MUSCLES  OF  THE  LEG  AND  FOOT. 


373 


ill-defined  bands  of  transverse  fibres,  which  constitute  the  superficial  transverse  meta- 
tarsal ligament  (fasciculi  transversi  aponeurosis  plantae).  The  slip  for  each  toe  joins 
the  tissue  of  the  web  of  the  toe  and  is  continuous  with  the  digital  sheath.  It  splits 
to  form  a  band  of  fibres  directed  forwards  on  each  side  of  the  toe  to  be  attached  to 
the  sides  of  the  metatarso-phalangeal  articulation  and  the  base  of  the  first  phalanx. 

This  central  portion  of  the  plantar  aponeurosis  assists  in  preserving  the  arch  of 
the  foot,  by  drawing  the  toes  and  the 
calcaneus  together. 

On  each  side  it  is  continuous  with 
a  much  thinner  layer  which  covers  the 
lateral  and  medial  muscles  of  the  sole, 
and  joins  the  fascia  of  the  dorsum  of 
the  foot  at  each  border.  It  also  gives 
rise  to  intermuscular  septa,  which  pass 
upwards  on  each  side  of  the  flexor 
digitorum  brevis,  enclosing  that  muscle 
in  a  separate  sheath,  and  giving  in- 
vestments on  either  side  to  the  ab- 
ductor muscles  of  the  great  and  little 
toes.  At  the  lateral  border  of  the  foot 
the  calcaneo  -  metatarsal  ligament,  a 
thickened  band  of  the  fascia,  connects 
the  tuberosity  of  the  calcaneus  with 
the  base  of  the  fifth  metatarsal  bone. 

The  digital  sheaths,  though  smaller, 
are  the  same  in  arrangement  as  those 
of  the  fingers  (p.  341).  Vaginal  liga- 
ments are  present  in  relation  to  the 
first  and  second  phalanges. 

THE   MUSCLES   OF   THE   LEG 
AND   FOOT. 

The  muscles  of  the  leg  and  foot  are 
divisible  into  three  series :  (1)  the 
extensor  muscles  on  the  front  of  the 
leg  and  dorsum  of  the  foot ;  (2)  the 
peronsei  on  the  lateral  aspect  of  the  leg; 
and  (3)  the  flexor  muscles  on  the  back 
of  the  leg  and  in  the  sole  of  the  foot. 

The  IVIuscIcsonthc  Front 
of  the  Leg  and  Dorsum 
of  the  Foot. 

The  muscles  on  the  front  of  the 
leg  and  dorsum  of  the  foot  include 
two  groups :  (1)  on  the  front  of  the 
leg,  the  tibialis  anterior,  long  extensors 
of  the  toes  and  peronaeus  tertius  ;  and 
(2)  on  the  dorsum  of  the  foot,  the 
extensor  digitorum  brevis. 

On  the  front  of  the  leg  the  tibialis  anterior  and  the  extensor  digitorum  longus 
and  peronasus  tertius  are  superficially  placed,  and  conceal  the  extensor  hallucis 
longus  muscle.  On  the  dorsum  of  the  foot  the  extensor  digitorum  brevis  muscle 
lies  beneath  the  tendons  of  the  long  extensor  of  the  toes. 

The  tibialis  anterior  arises  from  the  lateral  condyle  and  the  upper  two-thirds 
of  the  lateral  surface  of  the  shaft  of  the  tibia,  from  the  interosseous  membrane,  from 


Plantar 
aponeurosis 


Fig.  294. — The  Left  Plantar  Fascia. 


374 


THE  MUSCULAE  SYSTEM. 


the  fascia  over  it,  and  from  an  intermuscular  septum  laterally.  The  muscle 
ends  in  a  strong  tendon  which  passes  over  the  dorsum  of  the  foot,  to  be  inserted 
into  a  facet  on  the  medial  surface  of  the  first  cuneiform  and  the  medial  side  of  the 
base  of  the  first  metatarsal  bone  (Fig.  295,  p.  374).  Its  tendon  occupies  special 
compartments  beneath  both  upper  and  lower  parts  of  the  anterior  annular  liga- 
ment, enclosed  in  a  separate,  single,  synovial  sac. 

Tlie  tibio-fascialis  anterior  is  a  sei^arated  i^ortion  of  the  muscle  occasionally  present,  inserted 
into  the  fascia  on  the  dorsum  of  the  foot. 

The  extensor  digitorum  longus  arises  by  fleshy  fibres  from  the  lateral  side  of 
the  lateral  condyle  of  the  tibia,  from  the  upper  two-thirds  or  more  of  the  anterior 


Abductor  digiti  quinti 
(oiigin) 


Quadratus  plantfe 
(Accessorius)  origu] 

Long  and  short  plantar/ 
ligaments  I 


Tibialis  posterior  (part  of 
insertion) 


Peronseus  brevis 
(insertion) 

Flexor  digiti  quinti 
brevis  (origin) 


Adductor  hallucis 
obliquus  (origin) 


Flexoi  digitorum  brevis  (origin) 
Abductoi  hallucis  (origin) 


Attachments  of 
plantar  calcaneo- 
navicular ligament 


Flexorhallucis  brevis 
(origin) 


Tibialis  posterior 
(part  of  insertion) 

Peronseus  longus 
(insertion) 


Tibialis  anterior 
(insertion) 


Fig.  295. — Muscle- Attachments  to  Left  Tarsus  and  Metatarsus  (Plantar  Aspect). 


surface  (crest)  of  the  shaft  of  the  fibula,  from  the  fascia  over  it,  and  from  inter- 
muscular septa  on  either  side.  It  gives  rise  to  a  tendon  which  passes  beneath  the 
anterior  annular  ligament,  and  in  front  of  the  ankle  subdivides  into  four  tendons, 
inserted  into  the  four  outer  toes,  exactly  in  the  same  way  as  the  corresponding 
tendons  in  the  hand  (see  p.  341).  They  form  membranous  expansions  on  the 
dorsum  of  the  first  phalanx,  joined  by  the  tendons  of  the  extensor  digitorum  brevis, 
lumbricales,  and  interossei,  which  separate  into  one  central  and  two  lateral  slips, 
attached  respectively  to  the  middle  and  terminal  phalanges.  The  tendon  occupies 
a  separate  compartment  along  with  the  peronseus  tertius  beneath  the  lower  part 
of  the  anterior  annular  ligament,  invested  by  a  special  synovial  membrane. 


THE  MUSCLES  ON  THE  OUTER  SIDE  OF  THE  LEG. 


375 


the  anterior  surface  of  the  fibula 


SOLEUS. 

Extensor 
digitorum 

LONGUS 

Peron^eus 

LONGUS 


The  peronaeus  tertius  is  a  separated  portion  of  the  extensor  digitorum  longus. 
It  is  an  essentially  liuman  muscle.  It  arises  (inseparably  from  the  extensor  digitorum 
longus)  from  the  anterior  surface  (crest)  of  the  fibula,  and  from  the  inter-muscular 
septum  lateral  to  it.  The  tendon  of  the  muscle  is  inserted  into  the  dorsal  aspect 
of  the  base  of  the  fifth  metatarsal  bone. 

The  extensor  hallucis  longus  arises  from 
in  its  middle  three-fifths,  medial  to  the  origin 
of  the  extensor  digitorum  longus,  and  for  a 
corresponding  extent  from  the  interosseous 
membrane.  Its  tendon  passes  over  the  dorsum 
of  the  foot,  to  be  inserted  into  the  base  of  the 
terminal  phalanx  of  the  great  toe. 

The  extensor  primi  internodii  longus  and  ex- 
tensor ossis  metatarsi  hallucis  are  occasional 
separate  slips  of  this  muscle  inserted  into  the  proximal 
phalanx  and  the  metatarsal  bone. 

The  extensor    digitorum   brevis   arises 

on  the  dorsum  of  the  foot  from  a  special 
impression  on  the  upper  surface  of  the  cal- 
caneus, and  from  the  deep  surface  of  the 
ligamentum  cruciatum. 

It  usually  gives  rise  to  four  fleshy  bellies, 
from  which  narrow  tendons  are  directed  for- 
wards and  inwards,  to  be  inserted  into  the 
four  inner  toes.  The  three  lateral  tendons  join 
those  of  the  loner  extensor  muscle  to  form 
the  membranous  expansions  on  the  dorsum 
of  the  toes.  The  innermost  tendon  (extensor 
hallucis  brevis)  is  inserted  separately  into  the 
base  of  the  first  phalanx  of  the  great  toe. 

Peron.eus  brevis 

The  IVIuscIes  on  the  Lateral 
Side  of  the  Leg. 

These  muscles  comprise  the  perontei,^ 
longus  and  brevis.  They  are  placed  on  the 
lateral  side  of  the  leg  between  the  extensor 
digitorum  longus  in  front,  and  the  soleus  and 
flexor  hallucis  longus  behind,  enclosed  in  a 
special  compartment  of  the  deep  fascia. 

The  peronaeus  longus  arises  from  the  head 
and  the  upper  two-thirds  of  the  lateral  surface 
of  the  shaft  of  the  fibula,  from  inter-muscular 
septa  on  either  side,  and  from  the  fascia  over  it. 
It  forms  a  stout  tendon,  which,  lying  superficial 
to  the  peronieus  brevis,  hooks  round  the  lateral 
malleolus  beneath  the  lateral  annular  ligament, 
crosses  the  lateral  side  of  the  calcaneus,  and 
passing  through  a  groove  on  the  cuboid  bone,  is 
directed  across  the  sole  of  the  foot  to  be  inserted 
into  the  lateral  sides  of  the  first  cuneiform  and 
the  base  of  the  first  metatarsal  bones  (Fig.  295, 
p.  374).    As  it  enters  the  sole  of  the  foot  afilro- 

cartilage  is  formed  in  the  tendon,  which  plays  over  a  smooth  tubercle  on  the  cuboid 
bone,  a  bursa  intervening.  In  its  passage  across  the  foot  the  tendon  is  enclosed  in  a 
sheath  derived  from  the  plantar  calcaneo-cuboid  ligaments  and  the  tibialis  posterior 
tendon. 

The  peronaeus  brevis  arises  by  fleshy  fibres  from  the  lower  two-thirds  of  the 


Lower  portion  of  an- 
terior annular  liga- 
ment (lig.  cruciatum) 

Tendon  or  peron.eus 

TERTIUS 

Innermost  slip  of 
extensor  digitorum 

BREVIS  (extensor 

hallucis  bkevis) 


Fig.  296. — Muscles  of  the  Front  of  the 
Right  Leg  and  Dorsum  of  the  Right  Foot. 


376 


THE  MUSCULAE  SYSTEM. 


lateral  surface  of  the  shaft  of  the  fibula,  and  from  an  intermuscular  septum  along  its 

anterior  border.     Its  tendon  grooves 

the  back  of  the  lateral  malleolus  and 

%  ^  ^    m  ^^®  lateral  side  of  the  calcaneus,  in- 

r   K       .«  ilk  vested  by  a  synovial  sheath  common 

to  it  and  the  peronseus  longus,  and  is 
inserted  into  the  tubercle  and  dorsal 
surface  of  the  base  of  the  fifth  meta- 
tarsal bone. 

jGus  The  perontBUS  longus  and  brevis  may  be 

fused  together,  or  additional  sli^DS  may  be 
l^resent,  as  peronseus  accessorius,  peronseus 
digiti  quinti,  peronseo-calcaneus  externus, 
and  peronseo-cuboideus. 


Semimembranosus 
TEXDox  (cut) ' 


Tibial  nerve  and 
popliteal  vessels' 


Plantaris  tendon 
(cut) 


Fig.  297. — The  Insertions  of  the  Tibialis 
Posterior  and  Peron^ieus  Longus  in  the  Sole 
of  the  Left  Foot. 


The   Muscles  on  the 
Back  of  the   Leg. 

The  muscles  on  the  back  of  the 
leg  are  divisible  into  two  groups, 
superficial  and  deep. 

The  superficial  group  comprises 
the  gastrocnemius  and  soleus  (con- 
stituting together  thetriceps  surse)and 
the  plantaris.  The  gastrocnemius  forms 
the  prominence  of  the  calf  of  the  leg, 
and  is  superficial  except  at  its  origin, 
where  the  two  bellies  forming  the 
boundaries  of  the  popliteal  space  are 
overlapped  by  the  tendons  of  the 
hamstring  muscles.  The  soleus  muscle 
is  partially  concealed  by  the  gastro- 
cnemius and  plantaris,  and  becomes 
superficial  in  the  lower  part  of  the  leg 
on  each  side  of  the  common  tendon 
(tendo  Achillis  or  calcaneus) 


Tendo  Achillis 

(Tendo" 

calcaneus) 


Medial  annular 
ligamoiit- 


PERONiEUS  LONGUS 


I>iileral  annular 
meiit 


Fig.  298. — The  Plight  Soleus  Muscle. 


The  gastrocnemius  arises  by  hvo  heads,  medial  and  lateral,  by  means  of  strong 


THE  MUSCLES  ON  THE  BACK  OF  THE  LEG. 


377 


Tl 


Mkdial  head  of 
-uastrocnemius 

•Plantaris 
_Lateralheadof  1 
"oastrocnemius 
-Semimem- 

BKAN0i3US 


i — POPLITEUS 


HiiLEUs  (fibular 
"origin) 


_SoLEUs  (tibial 
origin) 


yr 


I  Tibialis 
"posterior 


rrR0N.«U8 

LONGUS 


Poplitpus^ 
(inseitioii) 


Soleus 
(origin)" 


'  Tibialis 

^  H_  posterior 
(origin) 


tendons  which  are  prolonged  over  the  surface  of  the  muscle.     The  lateral  head  arises 
from  an  impression  on  the  upper  and  posterior  part  of  the  lateral  surface  of  the  lateral 

condyle  of  the  femur,  and  from  the  lower  end 
of  the  lateral  epicondylic  line ;  while  the 
medial  head  arises  from  a  prominent  rough  mark 
on  the  popliteal  surface  of  the  femur  ahove  the 
medial  condyle  behind  the  adductor  tubercle. 
Each  head  has  an  ad- 
ditional origin  from  the 
rback  of  the  capsule  of 
the  knee-joint.  A  bursa 
lies  beneath  each  ten- 
don of  origin.  Each 
fleshy  belly  of  the 
muscle  is  inserted  separ- 
ately into  a  broad  mem- 
branous tendon,  pro- 
longed upwards  on  its 
deep  surface  for  some 
distance.  The  medial 
head  is  the  larger. 

The  tendo  Achillis 
(tendo  calcaneus)  is 
formed  by  the  union 
of  the  two  membranous 
insertions  of  the  bellies 

of   the    gastrocnemius. 

Prolonged  upwards  be- 
neath     the      separate 

bellies,      the      tendon 

forms  a  broad  mem- 
branous band  connect- 
ing together  the  lower 

parts  of  the  two  bellies. 

Narrowing     gradually, 

and  becoming  thicker 

in      the      lower      half 

of  the  leg,  the  tendon 

is  finally  inserted  into 

the  posterior  aspect  of 

the  calcaneus.    A  bursa 

lies  beneath  the  tendon 

at  its  insertion.     The 

tendo    calcaneus    also 

affords  insertion  to  the 

soleus  and  (sometimes) 

the  plantaris  muscles. 
Theplantaris  arises 

by    fleshy    fibres    from 

the  lateral  epicondylic 

line     of      the     femur 

for    about    an    inch 

at  its  lower  end,  from 

the  adjacent  part  of  the 

popliteal  surface  of  the 
femur,  and  from  the  posterior  (oblique)  ligament  of  the  knee-joint.  It  forms  a  narrow 
fleshy  slip  which  ends  in  a  tendon  extending  down  the  back  of  the  leg,  to  be 
inserted  into  the  medial  side  of  the  tuberosity  of  the  calcaneus,  or  the  tendo 
calcaneus,  or  the  medial  annular  ligament.     The  tendon  of  the  muscle  is  capable 


Pli  \ordigitorum 
'  1  oNi.  rs 


I  I  fxor  hallucis 

LON'l.US 


/J 


_.Peron.eus  beevis 


Medial  annular 
"'ligameut 

..Tendo  calcaneus 

Lateral  annular 


m 


Fig.  299. — The  Deep  Muscles  on  the 
Back  of  the  Right  Leg. 


Fig.  300. — Muscle  -  Attach- 
ments TO  the  Posterior 
Surface  of  the  Right  Tibia  . 


378 


THE  MUSCULAR  SYSTEM. 


of  considerable  lateral  extension.  The  plantaris  lies  between  the  lateral  head  of 
the  gastrocnemius  and  the  soleiis.  In  the  lower  half  of  the  leg  its  tendon  lies 
along  the  medial  border  of  the  tendo  calcaneus.  The  muscle  is  not  always  present. 
The  soleus  has  a  triple  origin  from  (1)  the  posterior  surface  of  the  head  and 
the  shaft  of  the  fibula  in  its  upper  third ;  (2)  a  fibrous  arch  (arcus  tendineus 

m.  solei)  stretching  over  the 
popliteal  vessels  and  tibial  nerve 
between  the  tibia  and  fibula ;  and 
(3)  the  oblique  line  and  middle 
third  of  the  medial  border  of  the 
tibia  (Fig.  300,  p.  377).  From 
this  origin  the  upper  muscular 
fibres  are  directed  downwards  to 
join  a  tendon  placed  on  the  super- 
ficial aspect  of  the  muscle,  which 
is  inserted  into  the  tendo-  calcaneus  ; 
the  lower  fibres  are  inserted  directly 
into  the  tendo  calcaneus  to  within 
one  or  two  inches  of  the  calcaneus. 
The  deep  muscles  of  the  back  of 
the  leg  comprise  the  popliteus,  flexor 
digitorum  longus,  flexor  hallucis 
-LuMBEicALs  longus,  and  tibialis  posterior. 

The  popliteus  muscle  is  deeply 
placed  behind  the  knee-joint  in  the 
floor  of  the  pophteal  space,  and  is 
covered  by  the  popliteal  vessels  and 
tibial  nerve.  The  flexor  digitorum 
longus  lies  behind  the  tibia,  the 
flexor  hallucis  longus  behind  the 
fibula,  and  the  tibialis  posterior 
lying  between  them  is  related  to  the 
interosseous  membrane  and  both 
bones  of  the  leg.  All  these  muscles 
are  concealed  by  the  superficial 
group,  and  are  bound  down  to  the 
bones  of  the  leg  by  layers  of  the 
deep  fascia. 

The  popliteus  arises  by  a  stout 
tendon  from  a  rough  impression  in 
front  of  a  groove  on  the  lateral 
aspect  of  the  lateral  condyle  of  the 
femur.  The  tendon  passes  between 
the  lateral  semilunar  cartilage 
and  the  capsule  of  the  knee-joint, 
and  pierces  the  posterior  (oblique) 
ligament,  from  which  it  takes  an 
additional  fleshy  origin.  A  bursa 
is  placed  beneath  the  tendon, 
which  usually  communicates  with 
the  synovial  cavity  of  the  knee- 
joint.  The  muscle  is  inserted  by 
fleshy  fibres  (1)  into  a  triangular  surface  on  the  back  of  the  tibia  above  the  oblique 
line  (Fig.  300,  p.  377),  and  (2)  into  the  fascia  over  it  (the  popliteus  fascia,  derived 
from  the  tendon  of  the  semi-merabranosus  muscle). 

The  popliteus  minor  is  a  small  occasional  muscle  attached  to  the  popliteal  space  of  the  femur 
and  the  posterior  ligament  of  the  knee-joint. 

The  flexor  digitorum  longus  occupies  both  the  back  of  the  leg  and  the  sole  of 


Plexoe  hallucis 

-BREVIS 

Flexor 
digitorum 

LO>rGUS 

Flexor  digiti 
quinti  brevis 
quadratus 

PLANTS 
(ACCESSORIUS) 

Abductor 
hallucis 

Abductor  digiti 

QUINTI 

PERON/EUS 
-•LONGUS 

Flexor 
"digitorum 

LONGUS 

_ Flexor  hallucis 

LONGUS 

_  Long  plantar 
""ligament 


Fig.  -301. — The  Muscles  of  tiik  FiIcht  Foot  (sccoikI  layer). 


THE  MUSCLES  IN  THE  SOLE  OF  THE  FOOT.  379 

the  foot.  Its  origin  is  by  fleshy  fibres  from  the  posterior  surface  of  the  shaft  of  the 
tibia  in  its  middle  three-fifths,  below  the  oblique  line,  medial  to  the  vertical  line 
and  the  origin  of  the  tibialis  posterior,  from  the  fascia  over  it,  and  from  an  inter- 
muscular septum  on  each  side  (Fig.  300,  p.  377)-  Its  tendon,  after  crossing 
obliquely  over  the  tendon  of  the  tibialis  posterior,  passes  beneath  the  medial 
annular  ligament,  invested  in  a  special  synovial  sheath,  and  enters  the  sole  of  the 
foot.  There  it  crosses  superficially  the  tendon  of  the  flexor  hallucis  longus,  and  finally 
divides  into  four  subordinate  tendons,  which  are  inserted  into  the  four  outer  toes 
in  precisely  the  same  manner  as  the  flexor  digitorum  profundus  is  inserted  in  the 
hand  (p.  341).  Each  tendon  enters  the  digital  sheath  of  the  toe,  perforates  the 
tendon  of  the  flexor  digitorum  brevis,  and  is  inserted  into  the  base  of  the  terminal 
phalanx.     Ligamenta  accessoria  (longa  and  brevia)  are  present  as  in  the  hand. 

The  tendon  of  the  flexor  hallucis  longus  sends  a  fibrous  band  to  the  tendon  of 
the  fiexor  digitorum  longus  as  it  crosses  it  in  the  sole  of  the  foot,  which  usually 
passes  to  the  tendons  destined  for  the  second  and  third  toes.  Associated  with  this 
muscle  in  the  sole  of  the  foot  are  the  lumbricales  and  quadratus  plantai  muscles. 

The  lumbricales  are  four  small  muscles  arising  in  association  with  the  tendons 
of  the  flexor  digitorum  longus  in  the  sole.  The  first  muscle  arises  by  a  single  origin 
from  the  tibial  side  of  the  tendon  of  the  flexor  digitorum  longus  for  the  second  toe  ; 
the  other  three  arise  by  two  heads  from  the  adjacent  sides  of  all  four  tendons. 
Each  muscle  is  inserted  into  the  dorsal  expansion  of  the  extensor  tendon,  the 
metatarso-phalaugeal  capsule,  and  the  base  of  the  first  phalanx,  precisely  as  in  the 
case  of  the  lumbrical  muscles  of  the  hand.  Each  muscle  passes  forwards  on  the 
tibial  side  of  the  corresponding  toe,  superficial  to  the  transverse  metatarsal  ligament. 

The  quadratus  plantae  (accessorius)  arises  by  two  heads :  (1)  the  lateral 
tendinous  head  springs  from  the  lateral  border  of  the  inferior  surface  of  the 
calcaneus  and  from  the  lateral  border  of  the  long  plantar  ligament ;  (2)  the 
medial  head,  which  is  fleshy,  arises  from  the  concave  medial  surface  of  the  calcaneus 
in  its  whole  extent,  and  from  the  medial  border  of  the  long  plantar  ligament 
(Fig.  295,  p.  37-1).  The  long  plantar  ligament  separates  the  two  origins.  The 
two  heads  unite  to  form  a  flattened  band,  which  is  inserted  into  the  upper  aspect 
of  the  tendons  of  the  flexor  digitorum  longus,  and  usually  into  those  destined 
for  the  second,  third,  and  fourth  toes. 

In  the  sole  of  the  foot  the  tendons  of  the  flexor  digitorum  longus,  along  with  the 
lumbricales  and  quadratus  plantse,  and  the  flexor  hallucis  longus  muscles,  constitute 
the  second  layer  of  muscles,  lying  between  the  abductors  of  the  great  and  little  toes 
and  the  flexor  digitorum  brevis  superficially,  and  the  flexor  brevis  and  adductors  of 
the  great  toe  more  deeply. 

The  flexor  hallucis  longus  arises  on  the  back  of  the  leg,  between  the  tibialis 
posterior  and  the  peronoei  muscles,  from  the  lower  two-thirds  of  the  posterior  surface 
of  the  shaft  of  the  fibula,  from  the  fascia  over  it,  and  from  intermuscular  septa 
on  either  side.  Its  tendon  passes  beneath  the  medial  annular  ligament  en- 
closed in  a  .special  synovial  sheath,  and  after  grooving  the  back  of  the  lower  end 
of  the  tibia,  the  talus,  and  the  under  surface  of  the  sustentaculum  tali  of  the 
calcaneus,  it  is  directed  forwards  in  the  sole  of  the  foot,  to  be  inserted  into  the  base 
of  the  terminal  phalanx  of  the  great  toe.  In  the  foot  it  crosses  over  the  deep 
aspect  of  the  tendon  of  the  flexor  digitorum  longus,  and  gives  to  it  a  strong  fibrous 
slip,  which  is  prolonged  into  the  tendons  for  the  second  and  third  toes. 

The  tibialis  posterior  muscle  has  a  fourfold  fleshy  origin  in  the  leg.  It 
arises  (1)  from  the  upper  four-fifths  of  the  shaft  of  the  fibula  between  the  oblique 
line  and  the  interosseous  border  (the  medial  surface)  ;  (2)  from  the  lower  part  of 
the  lateral  condyle,  and  from  the  upper  two-thirds  of  the  shaft  of  the  tibia  below 
the  oblique  line  and  between  the  vertical  line  and  the  interosseous  border 
(Fig.  300,  p.  277) ;  (3)  from  the  interosseous  membrane ;  and  (4)  from  the  fascia 
over  it  and  the  septa  on  either  side.  The  muscle  gives  rise  to  a  strong 
tendon  which  passes  beneath  the  medial  annular  ligament,  invested  by  a  special 
synovial  sheath,  and  grooves  the  back  of  the  medial  malleolus,  on  its  way  to  the 
medial  border  of  the  foot.  After  crossing  over  the  inferior  calcaneo- navicular 
ligament   between  the   sustentaculum  tah  and  the  navicular  bone,  the   tendon 

26 


380 


THE  MUSCULAE  SYSTEM. 


spreads  out  and  is  inserted  by  three  bands  into  (1)  the  tubercle  of  the  navicular 
bone  and  the  plantar  surfaces  of  the  first  and  second  cuneiform  bones,  (2)  the 
plantar  aspects  of  the  second,  third,  fourth,  and  sometimes  the  fifth  metatarsal 
bones,  the  second  and  third  cuneiform  bones,  and  the  groove  on  the  cuboid, 
and  (3)  into  the  medial  border  of  the  sustentaculum  tali  of  the  calcaneus  (Fig. 
302,  p.  380). 

The  peronseo-calcaneus  muscle,  when  present,  arises  from  the  fibula,  and  is  inserted  into  the 
calcaneus. 

The  Muscles  in  the  Sole  of  the  Foot. 

The  muscles  in  the  sole  of  the  foot  are  divisible  into  four  layers  placed  beneath 
the  plantar  fascia. 

The  first  layer  includes  the  abductor  hallucis,  flexor  digitorum  brevis,  and 


Abductor  digiti  quiiiti 
(origin) 


Quadratus'plant.*' 
(accessorius)  (origin) 

Long  and  short  plantar/ 
ligaments'! 


Tibialis  posterior  (part  of 
insertion 


Peronteus  brevis 
(insertion) 

Flexor  brevis  digiti 
quinti  (origin) 


Adductor  hallucis 
obliquus  (origin) 


Flexor  digitorum  brevis  (origin) 
Abductor  hallucis  (origin) 


Attachments  of 
plantar  calcaneo- 
navicular ligament 


Flexor  hallucis  brevis 
(origin) 


_\Tibialis  posterior  (part 
of  insertion) 

Peronsus  longus 
(insertion) 


Tibialis  anterior 
(insertion) 


Fig.  302.— Muscle-Attachments  to  Left  Tarsus  and  Metatak.sus  (Plantar  Aspect). 


abductor  digiti  quinti.  The  second  layer  consists  of  the  lumbricales  and  quadratus 
plantte  (accessorius),  together  with  the  tendons  of  the  flexor  hallucis  longus  and  flexor 
digitorum  longus.  The  third  layer  comprises  the  flexor  hallucis  brevis,  adductor 
hallucis  obliquus  and  transversus,  and  flexor  brevis  digiti  quinti.  The  fourth 
layer  consists  of  the  interossei  (plantar  and  dorsal),  placed  between  the  metatarsal 
bones :  and  the  tendons  of  insertion  of  the  tibialis  posterior  and  peronseus  longus. 


THE  MUSCLES  IN  THE  SOLE  OF  THE  FOOT. 


381 


FIRST    LAYER. 

The  abductor  hallucis  has  a  double  origin:  (1)  by  a  short  tendon  from  the  medial 
side  of  the  medial  process  of  the  tuberosity  of  the  calcaneus  (Fig.  302,  p.  380), 
and  (2)  by  fleshy  fibres  from 
the  medial  annular  ligament,  the 
plantar  aponeurosis  which  covers 
it,  and  the  intermuscular  septum 
between  it  and  the  flexor  digi- 
torum  brevis.  Lying  superficially 
along  the  medial  border  of  the 
sole,  its  tendon  is  inserted,  along 
with  part  of  the  flexor  hallucis 
brevis,  into  the  medial  side  of 
the  posterior  end  of  the  first 
phalanx  of  the  great  toe. 

The  flexor  digitorum  brevis 
has  likewise  a  double  origin :  (1) 
from  the  fore-part  of  the  medial 
process  of  the  tuberosity  of  the 
calcaneus  (Fig.  302,  p.  380),  and 
(2)  from  the  thick  central  part 
of  the  plantar  aponeurosis  which 
covers  it,  and  from  the  inter- 
muscular septa  on  either  side. 
Passing  forwards,  it  gives  rise  to 
four  slender  tendons,  which  are 
inserted  into  the  second  phalanges 
of  the  four  outer  toes,  after  hav- 
ing been  perforated  by  the  long 
flexor  tendons,  just  as  in  the  case 
of  the  tendons  of  the  flexor 
digitorum  sublimis  of  the  hand 
(p.  341). 

The  abductor  digiti  quinti 
has  also  a  double  origin :  (1)  by 
fleshy  and  tendinous  fibres  from 
the  fore-part  of  both  processes  of 
the  tuberosity  of  the  calcaneus, 
partly  concealed  by  the  flexor 
digitorum  brevis  (Fig.  302,  p.  380), 
and  (2)  by  fleshy  fibres  from  the 
lateral  portion  of  the  plantar 
aponeurosis  and  the  calcaneo- 
metatarsal  ligament,  and  from  the 
intermuscular  septum  between  it 
and  the  flexor  digitorum  brevis. 
Its  tendon  lies  along  the  fifth 
metatarsal  bone,  and  is  inserted 
into  the  lateral  side  of  the  pos- 
terior end  of  the  first  phalanx  of 
the  little  toe.  The  outermost  fibres  usually  obtain  an  additional  insertion  into 
the  lateral  side  of  the  plantar  surface  of  the  fifth  metatarsal  bone. 


Plantar 
aponeurosis 


Abductor  digiti 

QUINTI 

QUADRATUS 
PLANT.-E 

(aocessorius) 

Flexor 
digitorum  brevis 

Abductor 

hallucis 


Flexor  digiti 
quinti  brevis 


Flexor  hallucis 

BREVIS 

Fourth 
lumbrioal 

Third 

lumbrical 

Second... 

LUMBRICAr, 

First-- 
lumbrical 

Flexor 
hallucis  longus 


Fig.  303. — Superficial  Muscles  of  the  Right  Foot. 


SECOND    LAYER. 


The  tendons  of  the  long  flexors  of  the  toes,  the  lumbricales  and  quadratus 
plantae  (accessorius)  muscles,  constituting  the  second  layer  of  muscles,  have  already 
been  described  (p.  379).     Lying  beneath  the  abductor  hallucis  and  the  flexor  digi- 


382 


THE  MUSCULAE  SYSTEM. 


torum  brevis,  thej  occupy  the  hollow  of  the  tarsus  and  the  space  between  the  first 
and  fifth  metatarsal  bones ;  their  deep  surfaces  are  in  contact  with  the  adductors 
of  the  o;reat  toe  and  the  interossei  muscles. 


Long  plantar 

ligament  - 
Flexor  hal- 
lucis  lonous  - 
Flexor  digi- 
torum  loxous  "' 
quadratus    — 

PLANTS  / 

(accessorius)  \  - 
(origins) 

Peron^us  ,. 

LONGUS 


THIRD    LAYER. 

The  flexor  hallucis  brevis  arises  by  tendinous  fibres  from  (1)  the  medial  part 
of  the  plantar  surface  of  the  cuboid   bone  (Pig.  302,  p.  380),  and  (2)  the  tendon 

of  the  tibialis  posterior.  Directed  for- 
wards over  the  first  metatarsal  bone,  the 
muscle  separates  into  two  parts,  between 
which  is  the  tendon  of  the  flexor  hallucis 
longus.  Each  portion  gives  rise  to  a 
tendon  which  is  inserted  into  the  corre- 
sponding side  of  the  base  of  the  first 
phalanx  of  the  great  toe ;  in  each  tendon, 
under  the  metatarso-phalangeal  articula- 
tion, a  sesamoid  bone  is  developed.  The 
medial  tendon  is  united  with  the  insertion 
of  the  abductor,  the  lateral  tendon  with 
the  insertions  of  the  adductor  muscle  of 
the  great  toe. 

The  adductor  hallucis^  consists  of  two 
parts.  The  oblicLue  head  (caput 
obliquum)  of  the  muscle  arises  (1) 
from  the  sheath  of  the  peronaeus 
longus,  and  (2)  from  the  plantar 
surfaces  of  the  posterior  extremities 
of  the  second,  third,  and  fourth 
metatarsal  bones  (Fig.  302,  p.  380). 
Occupying  the  hollow  of  the  foot, 
on  a  deeper  plane  than  the  long 
flexor  tendons  and  lumbricales, 
and  on  the  lateral  side  of  the  flexor 
hallucis  brevis,  it  is  directed  ob- 
liquely medially  and  forwards,  to  be 
inserted  on  the  lateral  side  of  the 
base  of  the  first  phalanx  of  the  great 
toe  between  and  along  with  the 
flexor  brevis  and  the  transverse 
head  of  the  adductor  hallucis. 

The  transverse  head  (caput 
transversum)  arises  from  (1)  the 
capsules  of  the  lateral  four  meta- 
tarso-phalangeal articulations  and 
(2)  the  transverse  metatarsal  Liga- 
ment. Directed  transversely  in- 
wards, under  cover  of  the  flexor 
tendons  and  lumbricales,  the  muscle 
is  inserted,  along  with  the  oblicpe 
head,  into  the  lateral  side  of  the 
base  of  the  first  phalanx  of  the 
great  toe. 

The  flexor  digiti  quinti  brevis 

arises  from  (1)  the  sheath  of  the 

peronseus  longus  and  (2)  the  base  of  the  fifth  metatarsal  bone  (Fig.  302,  p.  380). 

Partially  concealed  by  the  abductor  digiti  quinti,  the  muscle  passes  along  the  fifth 

1  The  ailchictor  hallucis  obliquus  ami  adductor  hallucis  transversus  are  now  described  as  two  heads  of  the 
same  muscle  (B.N. A.). 


Flexor  digiti 
quinti  brevis 


Flexor  hal- 
lucis BREVIS 

Interosseous 

MUSCLES 

Adductor 

hallucis 

(oblique  head) 

Adductor 

hallucis 

(transverse  head) 


Fig,  304. — Deep  Muscles  of  the  Sole  of  the  Foot. 


THE  MUSCLES  IN  THE  SOLE  OF  THE  FOOT. 


383 


Fig.  305. — Interosseous  Muscles  of  the  Right  Foot. 


metatarsal  bone,  to  be  inserted,  in  common  with  that  muscle,  into  the  lateral  side 
of  the  base  of  the  first  phalanx  of  the  little  toe. 

FOURTH  LAYER. 

The  interossei  muscles  of  the  foot  resemble  those  of  the  hand  except  in  one 
respect.  In  the  hand  the  line  of  action  of  the  muscles  is  the  middle  line  of  the 
middle  finger.  In  the  foot  the  second  toe  is  the  digit  round  which  the  muscles  are 
grouped,  and  their  attachments  and  their  actions  differ  accordingly. 

There  are  four  dorsal  and  three  plantar  muscles,  which  occupy  together  the  four 
interosseous    spaces, 
and  project  into  the 
hollow  of  the  foot. 

The   four    dorsal 
muscles^  one  in  each 
interosseous   space, 
arise    by    two    heads 
each  from  the  shafts       ^, 
of  the   metatarsal  dorsal. 
bones.       Each    gives    'os 
rise  to  a  tendon,  which, 
after    passing    dorsal 
to    the    transverse 
metatarsal    ligament, 
is  inserted  on  the  dor- 
sum of  the  foot,  into 
the  side  of  the  first 
phalanx,    the    meta- 
tarso-phalangeal  cap- 
sule, and  the   dorsal 
expansion  of  the  ex- 
tensor tendon.  The  Jirst  and  second  muscles  are  inserted  respectively  into  the  tibial  and 
fibular  sides  of  the  proximal  end  of  the  first  phalanx  of  the  second  toe.     The  third 
and  fourth  muscles  are  inserted  into  the  fibular  sides  of  the  third  and  fourth  toes. 

The  three  plantar  muscles  occupy  the  three  outer  interosseous  spaces.  Each 
arises  by  a  single  head  from  the  tibial  side  of  the  third,  fourth,  and  fifth  metatarsal 
bones  respectively.  Each  ends  in  a  tendon  which  passes  dorsal  to  the  transverse 
metatarsal  ligament,  and  is  inserted,  in  the  same  manner  as  the  dorsal  muscles,  into 
the  tibial  sides  of  the  third,  fourth,  and  fifth  toes. 

Nerve-Supply  of  the  Muscles  of  the  Leg  and  Foot. 

The  nerves  supplying  the  muscles  of  the  leg  and  foot  are  branches  of  the  peroneal  or  tibial 
nerves  from  the  sacral  plexus.  The  anterior  tibial  nerve  ^  from  the  peroneal  supplies  the 
muscles  on  the  front  of  the  leg  and  dorsum  of  the  foot  (L.  4.  5.  S.  1.),  tibialis  anterior,  extensor 
digitorum  longus,  peronajus  tertius,  extensor  hallucis  longus,  and  extensor  digitorum  brevis. 
The  musculo-cutaneous  nerve,-  also  a  branch  of  the  peroneal  nerve,  supplies  the  peronseus  longus 
and  peronjeus  brevis  (L.  4.  5.  S.  1.).  The  tibial  nerve  innervates  directly  the  plantaris,  popliteus 
(L.  4.  5.  S.  1.),  each  head  of  the  gastrocnemius,  and  the  soleus  (S.  1.  2.).  The  soleus  receives  on 
its  deep  surface  an  additional  nerve  from  the  tibial  (L.  5.  S.  1.  2.).  This  nerve  supplies 
also  the  flexor  digitorum  longus  and  tibialis  posterior  (S.  1.  2.),  and  the  flexor  hallucis  longus 
(L.  5.  S.  1.  2.).  The  plantar  nerves,  terminal  branches  of  the  posterior  tibial,  innervate  the  small 
muscles  of  the  sole  of  the  foot.  The  internal  plantar  nerve  ^  (L.  5.  S.  1.)  supplies  the  abductor 
hallucis,  flexor  digitorum  brevis,  flexor  hallucis  brevis,  and  first  lumbrical  muscle  ;  the  external 
plantar  nerve*  (S.  1.  2.)  supjjlies  the  other  three  lumbrical  muscles,  the  quadratus  plantse, 
adductor  of  the  great  toe,  interossei,  flexor  brevis  and  abductor  digiti  quinti. 

Actions  of  the  Muscles  of  the  Leg  and  Foot. 

The  muscles  of  the  leg  and  foot  act  chiefly  in  the  movements  of  the  ankle-joint  (assisted  by 
movements  of  the  inter-tarsal  joints) ;  of  the  metatarso-phalangeal  joints  (assisted, by  movements 
of  the  tarso-metatarsal  and  inter-metatarsal  joints) ;  and  of  the  inter-phalangeal  joints. 

I.  Tibio-Fibular  Articulations. — The  upper  tibio-fibular  articulation  is  only  capable  of 

1  Anterior  tibial  nerve  =  deep  peroneal  nerve  (B.N. A.). 

-  Musculo-cutaneous  nerve  =  superficial  peroneal  nerve  (B.N. A.). 

•*  Internal  plantar  nerve  =  medial  plantar  nerve  (B.N.  A.). 

■*  External  plantar  nerve  =  lateral  plantar  nerve  (B.N.A.). 

26  a 


384 


THE  MUSCULAK  SYSTEM. 


slight  gliding  movement,  occasioned  by  the  action  of  the  biceps  and  popliteus  and  the  muscles 
arising  from  the  fibula. 

II.  Movements  at  the  Ankle-Joint. — The  movements  at  the  ankle-joint  are  movements  of 
flexion  and  extension  of  the  foot  on  the  leg,  along  with  inversion  and  eversion  (only  during 
extension).  These  movements  are  produced  at  the  ankle,  aided  by  movements  in  the  inter-tarsal 
joints,  and  are  occasioned  by  the  following  muscles  : — 


a.  Flexion. 

Extension. 

h.  Inversion. 

Eversion. 

Tibialis  anterior 

Gastrocnemius 

Tibialis  anterior 

Peroneeus  tertius 

Extensor  digitorum  longus 

Plantaris 

Peronseus  longus 

Extensor  hallucis  longus 

SoleuR 

Tibialis  posterior 

Peronseus  brevis 

Peronseus  tertius 

Tibialis  posterior 
Peronseus  longus 
Peronseus  brevis 
Flexor  digitorum  longus 
Flexor  hallucis  longus 

III.  Movements  of  the  Toes. — A.  At  the  Metatarso-Phalangeal  Joints  (assisted  by  move- 
ments at  the  tarso-metatarsal  and  inter-metatarsal  joints). — These  movements  are  flexion  and 
extension,  abduction  and  adduction  (in  a  line  corresponding  to  the  axis  of  the  second  toe). 


a.  Flexion. 

Extension. 

Flexor  digitorum  longus 
Quadratus  plantse  (accessorius) 
Lumbricales 
Flexor  hallucis  longus 
Flexor  hallucis  brevis 
Flexor  digitorum  brevis 
Flexor  digiti  quinti  brevis 
Interossei 

Extensor  digitorum  longus 
Extensor  digitorum  brevis 
Extensor  hallucis  longus 
Extensor  hallucis  brevis 

h.  Abduction. 


Adduction. 


{From  and  to  the  middle  line  of  the  second  toe.) 


Abductor  hallucis 
Dorsal  interossei 
Abductor  digiti  quinti 


Adductor  hallucis 
Plantar  interossei 


B.  At  the  inter-phalangeal  joints  the  movements  are  Kmited  to  flexion  and  extension. 


Flexion. 

Extension. 

Flexor  digitorum  brevis  {acting  on  the  first 

joint) 
Flexor    digitorum   longus    {acting    on   both 

joints) 
Flexor  hallucis  longus  {acting  on  the  hallux) 

Extensor  digitorum  longus   a 

Extensor  digitorum  brevis 

Interossei 

Lumbricales 

Extensor  hallucis  longus 

{acting  on  both 
joints) 

Movements  of  the  Lower  Limb  generally. 

The  characteristic  features  of  the  lower  limb  are  stability  and  strength,  and  its  muscles  and 
joints  are  both  subservient  to  the  functions  of  transmission  of  weight  and  of  locomotion.  In  the 
standing  position  the  centre  of  gravity  of  the  trunk  falls  between  the  heads  of  the  femora, 
and  is  located  about  the  middle  of  the  body  of  the  last  lumbar  vertebra.  It  is  transmitted 
from  the  sacrum  through  the  posterior  sacro-iliac  ligaments  to  the  hip  bone,  and  through  the 
bones  of  the  lower  limb  to  the  arch  of  the  foot,  where  the  astragalus  distributes  it  backwards 
through  the  calcaneus  to  the  heel,  and  forwards  through  the  tarsus  and  metatarsus  to  the  balls 
of  the  toes. 

Locomotion. — The  three  chief  means  of  progression  are  walking,  running,  and  leajjing.  In 
walking,  the  body  and  its  centre  of  gravity  are  inclined  forwards,  the  trunk  oscillates  from  side  to 
.side  as  it  is  supported  alternately  by  each  foot,  the  arms  swing  alternately  with  the  corresponding 
leg,  and  one  foot  is  always  on  the  ground.  The  act  of  progression  is  performed  by  the  leg,  aided  in 
two  ways  by  gravity.  The  movements  of  the  leg  occur  in  the  following  way.  At  the  beginning 
of  a  step,  one  leg,  so  to  speak,  "  shoves  ofl^"  ;  the  heel  is  raised  and  the  limb  is  extended  By  the 
action  of  the  muscles  flexing  the  hip  and  knee-joints,  and  extending  the  ankle-joint  and  toes,  this 
limb  is  raised  from  the  ground  sufficiently  to  clear  it,  and  passes  forwards  by  the  action  of 
gravity,  aided  by  the  force  given  to  the  movement  by  the  extensor  muscles.     After  passing  the 


AXIAL  MUSCLES. 


385 


line  of  the  centre  of  gravity  the  flexion  of  the  joints  ceases,  the  muscles  relax,  and  the  limb 
gradually  returns  to  the  ground.  The  other  limb  then  passes  through  the  same  cycle,  the  weight 
of  the  body  now  resting  on  the  limb  which  is  in  contact  with  the  ground.  As  the  foot  reaches 
the  groimd  it,  as  it  were,  rolls  over  it ;  the  heel  touches  it  first,  then  the  sole,  and  lastly,  as  the 
foot  leaves  the  ground  again,  only  the  toes.  In  running,  the  previous  events  are  all  exaggerated. 
The  time  of  the  event  is  diminished,  while  the  force  and  distance  are  increased.  Both  feet  are  oflf 
the  ground  at  one  time  ;  the  action  of  flexors  and  extensors  alternately  is  much  more  powerful,  so 
that  on  the  one  hand  the  knees  are  drawn  upwards  to  a  greater  extent  in  the  forward  movement, 
and  not  the  whole  foot,  but  only  the  toes  reach  the  ground  in  the  extension  of  the  limb.  The 
attempt  is  made  to  bring  the  foot  to  the  ground  in  front  of  the  line  of  the  centre  of  gravitj'-.  At 
the  same  time  the  trunk  is  sloped  forwards  much  more  than  in  walking.  In  leaping,  the  actions 
of  the  limbs  are  still  more  exaggerated.  The  movements  of  flexion  of  the  limb  are  still  more 
marked,  and  the  foot  reaches  the  ground  still  farther  in  front  of  the  line  of  the  centre  of  gravity. 


Obliquus  extersus 
abdominis  \ 
Obliquus  isternus    \ 
abdominis 
Transversus 
abdominis 
Fascia  transversali 
Peritoneum 

Colon 


AXIAL   MUSCLES. 
THE    FASCIit   AND    MUSCLES    OF   THE    BACK. 

THE  FASCIA  OF  THE  BACK. 

The  general  fascial  investments  of  the  back  have  been  described  along  with  the 
superficial  muscles  associated  with  the  shoulder -girdle  (p.  319).  The  latissimus 
dorsi  muscle  has  been  described  as  arising  in  large  part  from  the  vertebral  apo- 
neurosis. This  is  a  strong  fibrous  lamina  which  conceals  the  sacro-spinalis  muscle. 
In  the  loin  it  extends  from  the  spines  of  the  lumbar  vertebrfe  outwards  to  the 
interval    between 

,,         1      j_       -1  1  Rectus  ABDOMINIS 

the  last  nb  and 
the  iliac  crest, 
where  it  is  con- 
cerned in  forming 
the  lumbar  fascia 
(fascia  lumbodor- 
salis).  Below  the 
loin  the  vertebral 
aponeurosis  is  at- 
tached to  the  iliac 
crest,  and  more 
medially  blends 
with  the  subjacent 
tendinous  origin  of 
the  sacro-spinalis  ^'^''^^^"t^.^e^ 
(erector  spinas). 
The  fascia  can  be 
followed  upwards 
over  the  sacro- 
spinalis  in  the 
region  of  the 
thorax,  where  it  is 
attached  laterally 
to  the  ribs  and  is 
continuous  with 
the  intercostal 
aponeuroses.  In 
the  lower  part  of 

the  thorax  it  is  replaced  by  the  muscular  slips  of  the  serratus  posterior  inferior ; 
in  the  upper  part  of  the  thorax  it  passes  beneath  the  serratus  posterior  superior 
and  blends  with  the  deep  cervical  fascia. 

The  lumbar  fascia  (fascia  lumbodorsalis)  is  a  narrow  ligamentous  band  which 
connects  the  last  rib  to  the  iliac  crest  between  the  muscles  of  the  back  on  the  one 
hand  and  those  of  the  abdominal  wall  on  the  other.  It  is  formed  by  the  union  of 
three  fascial  strata,  called  respectively  the  vertebral  aponeurosis  or  posterior  layer,  just 
described ;  the  middle,  and  the  anterior  layers.     The  middle  layer  is  a  fascia  which 


Kidney 


Lumbar  fascia 


Latissimus  dorsi 
quadratus  lumborum 


Psoas  fascia 


Second  lumbar 
vertebra 


Psoas  major 


Anterior  layer  of 
lumbar  fascia 


MULTIFIDUS 


L  Semispinalis 

dorsi 


Middle  layer  of  lumbar  fascia 

Ilio-costalis 

Vertebral  aponeurosis 


LONGISSIMUS  DORSI 


Fig.  306.- 


-Traxsverse  Section  through  the  Abdomen,  opposite  the 
Second  Lumbar  Vertebra. 


386 


THE  MUSCULAE  SYSTEM. 


stretches  laterally  from  the  ends  of  the  transverse  processes  of  the  lumbar  vertebrse, 
between  the  sacro-spinalis  behind  and  the  quadratns  lumborum  muscle  in  front.  The 
anterior  layer  is  attached  to  the  lumbar  vertebrse  near  the  bases  of  their  transverse 
processes.  It  covers  the  front  of  the  quadratus  lumborum  muscle,  and  separates 
it  from  the  psoas.     The  psoas  fascia  is  continuous  at  the  lateral  border  of  the  psoas 

muscle  with  the  anterior  layer  of  the 
lumbar  fascia.  At  the  lateral  borders 
of  the  quadratus  lumborum  and  sacro- 
spinalis  muscles  the  three  layers  blend 
together  to  form  the  lumbar  fascia, 
which  in  turn  gives  partial  origin  to 
the  obliquus  internus  and  transversus 
abdominis  muscles. 


LONOISSIMUS 
CAPITIS  (tRACHELO- 

mastoid) 


CAPITIS 
(COMPLEXUS) 


IlIO-COSTALI: 

DORSI 

(accessoeius) 


LONGISSIMUS 
DORSI 


Ilio-costaus 
lumborum 


THE  MUSCLES  OF  THE  BACK. 

The  muscles  of  the  back  are  ar- 
ranged in  four  series  according  to  their 
attachments  :  (1)  vertebro  -  scapular 
and  vertebro -humeral,  (2)  vertebro- 
costal, (3)  vertebro -cranial,  and  (4) 
vertebral.  They  are  in  irregular 
strata,  the  most  superficial  muscles 
having  the  most  widely  spread  attach- 
ments. 

The  first  series  of  muscles  of  the 
back,  connecting  the  axial  skeleton  to 
the  upper  limb,  have  already  been 
described.  They  are  arranged  in  two 
layers :  (1)  trapezius  and  latissimus 
dorsi  superficially ;  (2)  levator  scapulae, 
and  rhomboidei,  beneath  the  trapezius 
(p.  319). 

The  remaining  muscles  are  almost 
entirely  axial,  and  may  be  divided  into 
four  groups  :  (1)  serrati  posteriores, 
superior  and  inferior,  splenius  capitis 
and  splenius  cervicis  ;  (2)  sacro-spinalis 
(erector  spinse)  and  semi-spinalis  capitis 
(complexus) ;  (3)  transverse  -  spinales 
(semispinalis  and  multifidus) ;  and  (4) 
the  small  deep  muscles  (rotatores,  inter- 
spinales,  inter-transversarii,  and  sub- 
occipital muscles).  They  extend  from 
the  sacrum  to  the  head,  forming  a 
cylindrical  column  in  the  loin,  filling 
up  the  vertebral  groove  in  the  thorax, 
and  giving  rise  to  the  muscular  mass 
at  the  back  of  the  neck. 

First  Group. 

The  serratus  posterior  superior 

has  a  membranous  origin  from  the  liga- 
mentum  nuchse  and  the  spines  of  the  last  cervical  and  upper  three  or  four  thoracic 
vertebrte.  It  is  directed  obliquely  downwards  and  laterally,  to  be  inserted  by 
separate  slips  into  the  second,  third,  fourth,  and  fifth  ribs.  The  muscle  is  concealed 
by  the  vertebro-scapular  muscles,  and  crosses  obliquely  over  the  splenius,  sacro- 
spinalis  (erector  spinas),  and  semispinalis  capitis  (complexus).  It  lies  superficial 
to  the  vertebral  aponeurosis. 


Fig.  307  — Schematic  Repuesentation  of  the  Parts 
OF  THE  Left  Sacuo-Spinams  (Ehector  Spin^e)  Muscle. 


THE  MUSCLES  OF  THE  BACK. 


387 


The  serratus  posterior  inferior  has  a  membranous  origin  through  the  medium 
of  the  vertebral  aponeurosis  from  the  last  t^Yo  thoracic  and  first  two  lumbar  spinous 
processes.  It  forms  four  muscular  bands  which  pass  almost  horizontally  to  an 
insertion  into  the  last  four  ribs.  The  muscular  slips  overlap  one  another  from 
below  upwards.  The  muscle  is  on  the  same  plane  as  the  vertebral  aponeurosis,  and 
is  concealed  by  the  latissimus  dorsi. 

The  splenius  muscle  is  a  broad,  flattened  band  which  occupies  the  back  of  the 
neck  and  the  upper  part  of  the  thoracic  region.  It  arises  from  the  ligamentum  nucha? 
(from  the  level  of  the  fourth  cervical  vertebra  downwards)  and  from  the  spinous 
processes  of  the  last  cervical  and  higher  (four  to  six)  thoracic  vertebrse.  Its  fibres 
extend  upwards  and  laterally  into  the  neck,  separating  in  their  course  into  an 
upper  and  a  lower  part.  The  upper  part  forms  the  splenius  capitis,  which  is 
inserted  into  the  mastoid  process  and  the  lateral  part  of  the  superior  curved  line  of 
the  occipital  bone  (Fig.  310,  p.  390).  The  lower  part  forms  the  splenius  cervicis, 
which  is  inserted  into  the  posterior  tubercles  of  the  transverse  processes  of  the 
upper  three  or  four  cervical  vertebrae,  behind  the  origin  of  the  levator  scapulee. 
The  muscle  is  partially  concealed  by  the  trapezius  and  sterno-mastoid,  and  appears 
between  them  in  the  floor  of  the  posterior  triangle  of  the  neck  (splenius  capitis). 
It  is  covered  by  the  rhomboid  muscles,  levator  scapulae,  and  serratus  posterior 
'superior. 


Second  Group. 

The  sacro-spinalis  (erector  spinae)  possesses  vertebral,  vertebro-cranial,  and 
vertebro-costal  attachments.  It  consists  of  an  elongated  mass  composed  of  separated 
slips  extending  from  the  sacrum  to  the  skull.  Simple  at  its  oricrin,  it  becomes 
more  and  more  complex  as  it  is  traced  upwards  towards  the  head.     It  arises  (1)  by 


Posterior 

tubercles  of 

transverse 

processes 


Scalenus  medius 
Levator  scAPULiE 
Splenius  cervicis 


Scalenus  posterior 
Ilio-costalis  cervicis 

LONGISSIMUS  cervicis 


r       LONOISSIMUS  CAPITIS 

Articular.!     Semispinalis  capitis 

processes'!  Semispinalis  cervicis, 

L  Multifidus 


^C\LENUS 

(,    anterior 

Anterior 
_  ,  tubercles  of 

^.ONG us  capitis    ^trausversB 

processes 

ONGUS  COLLI 


Fig.  308. — Scheme  of  Muscular- Attachments  to  the  Transverse  Processes  of  the 

Cervical  Vertebra. 

fleshy  fibres  from  the  iliac  crest ;  (2)  from  the  posterior  sacro-iliac  ligament ;  and 
(3)  by  tendinous  fibres  continuous  with  the  former  from  the  ihac  crest,  the  back  of 
the  sacrum,  and  the  spines  of  the  upper  sacral  and  all  the  lumbar  vertebrae.  Its 
fibres  extend  upwards  through  the  loin,  enclosed  between  the  posterior  and  middle 
layers  of  the  lumbar  fascia,  and  separate  into  two  columns — a  lateral  portion 
derived  from  the  lateral  fleshy  origin,  the  ilio-costalis,  and  a  medial  portion  com- 
prising the  remaining  larger  part  of  the  muscle,  the  longissimus. 

The  ilio-costalis  lumborum  (ilio-costalis)  is  inserted  by  six  slender  shps  into 
the  lower  six  ribs. 


388 


THE  MUSCULAR  SYSTEM. 


Rectus  capitis  posterior  mikor 
Rectus  capitis  posterior  m  \jor 

Obuquus  capitis  -^llprRlOK 

OBLIQUUS  capitis  INFERIOR-.^ 

Splenius  CA.piris 

SpLENIUS  (  FR%  Klt)-- 

Sterno-cleido-m  \stoid 

SbMISPIN  \I  lb  clrvicis 

LONGISSIMUS  cervicis  (tran'sversalis 
colli) 


Semispinalis  dorsi 


Levatores  costarum 


QL'ADRATUS  lumborum 


Mi'LTIFIDU 


LiGAMENTUM  NUCH.E 

SeM  I SPI NALIS ;  CAPITIS^(COMPLEXUS) 


LONGISSIMUS  CAPITIS  (TRACHELO- 

JI  \stoid) 


Splenius  capitis'et  cervicis 


LeVAIOR  SCAPULA 


Ilio-costalis  cervicis  (cervicalis 
asc  endens) 

LON&ISSIMUS  CERVICIS  (TRANSVERSALIS 

colli) 


Ilio-costalis  dorsalis 
(accessorius) 


Spinalis  dorsi 


LONGISSIMUS  dorsi 


Ilio-costalis  lumborum 


■■•-  Sacrospinalis  (erector 

SPIN/E) 


Fig,  309. — The  Deep  Muscles  of  the  Back. 


THE  MUSCLES  OE  THE  BACK.  389 

Medial  to  the  insertion  of  each  of  these  slips  is  the  origin  of  the  ilio-costalis 
dorsi  (accessorius),  which,  arising  from  the  lower  six  ribs  medial  to  the 
iUo-costalis  lumborum,  is  inserted  in  Line  with  it  by  similar  slips  into  the  upper 
six  ribs. 

The  ilio-costalis  cervicis  (cervicalis  ascendens)  arises  in  the  same  way  by 
six  slips  from  the  upper  six  ribs,  medial  to  the  insertions  of  the  previous  muscle. 
It  forms  a  narrow  band,  which,  extending  into  the  neck,  is  inserted  into  the  posterior 
tubercles  of  the  transverse  processes  of  the  fourth,  fifth,  and  sixth  cervical  vertebrae, 
behind  the  scalenus  posterior.  The  ilio-costales- lumborum,  dorsi,  and  cervicis 
form  together  a  continuous  muscular  column,  and  constitute  the  most  lateral  group 
of  the  component  elements  of  the  sacro-spinalis  or  erector  spinse. 

The  longissimus  is  the  largest  element  in  the  sacro-spinalis  mviscle.  The 
longissimus  dorsi  forms  the  middle  column  of  the  muscle.  It  is  continued  up 
into  the  neck  as  the  longissimus  cervicis  (transversalis  cervicis)  and  longissimus 
capitis  (trachelo-mastoid).  Mostly  tendinous  on  the  surface  at  its  origin,  it  becomes 
fleshy  in  the  upper  part  of  the  loin.  It  is  thickest  in  the  loin,  and  becomes  thinner 
as  it  passes  upwards  in  the  back  between  the  column  formed  by  the  iho-costalis  and 
its  upward  continuations  laterally,  and  the  spinalis  dorsi  medially.  It  is  inserted 
by  two  series  of  slips,  medial  and  lateral,  laterally  into  nearly  all  the  ribs,  and 
medially  into  the  transverse  processes  of  the  thoracic  and  the  accessory  processes  of 
the  upper  lumbar  vertebrse.  It  is  prolonged  upwards  into  the  neck  by  its  associa- 
tion with  the  common  origin  of  the  longissimus  cervicis  (transversalis  cervicis)  and 
the  longissimus  capitis  (trachelo-mastoid). 

The  longissimus  cervicis  (transversalis  cervicis)  has  an  origin  from  the 
transverse  processes  of  the  upper  six  thoracic  vertebree,  medial  to  the  insertions  of 
the  longissimus  dorsi.  Extending  upwards  into  the  neck,  it  is  inserted  into  the 
posterior  tubercles  of  the  transverse  processes  of  the  second,  third,  fourth,  fifth, 
and  sixth  cervical  vertebrae.  It  is  concealed  in  the  neck  by  the  ilio-costalis 
cer\'icis  (cervicaHs  ascendens)  and  splenius  cervicis  muscles.  ^ 

The  longissimus  capitis  (trachelo-mastoid)  arises,  partly  by  an  origin  common 
to  it  and  the  previous  muscle,  from  the  transverse  processes  of  the  upper  six  thoracic 
vertebriB,  and  partly  by  an  additional  origin  from  the  articular  processes  of  the 
lower  four  cervical  vertebrae.  Separating  from  the  longissimus  cervicis  (trans- 
versalis cervicis),  the  muscle  ascends  through  the  neck  as  a  narrow  band  which  is 
inserted  into  the  mastoid  process  beneath  the  splenius  capitis  muscle.  In  the  neck 
the  muscle  is  placed  between  the  splenius  capitis  and  semispinalis  capitis  (complexus). 

The  spinalis  dorsi  forms  the  medial  column  of  the  sacro-spinalis.  It 
occupies  the  thoracic  region,  and  arises  by  tendinous  fibres  from  the  lower 
two  thoracic  and  upper  two  lumbar  spinous  processes,  and  also  directly  from 
the  tendon  of  the  longissimus  dorsi.  It  is  a  narrow  muscle  which,  lying  close  to 
the  thoracic  spinous  processes  medial  to  the  longissimus  dorsi,  is  inserted  into 
the  upper  (four  to  eight)  thoracic  spines.     It  is  not  prolonged  into  the  neck. 

The  semispinalis  capitis  (complexus)  closely  resembles  in  position  and 
attachments  the  longissimus  capitis  (trachelo-mastoid).  It  takes  origin  from  the 
transverse  processes  of  the  upper  six  thoracic  and  the  articular  processes  of  the  lower 
four  cervical  vertebrae,  medial  to  the  longissimus  cervicis  and  longissimus  capitis. 
It  has  an  additional  origin  also  from  the  spinous  process  of  the  last  cervical  vertebra. 
It  forms  a  broad  muscular  sheet  which  extends  upwards  in  the  neck,  to  be  inserted 
into  the  medial  impression  between  the  superior  and  inferior  curved  lines  of  the 
occipital  bone  (Fig.  312,  p.  391).  The  medial  portion  of  the  muscle  is  separate, 
and  forms  the  biventer  cervicis,  consisting  of  two  fleshy  bellies  with  an  intervening 
tendon,  placed  vertically  in  contact  with  the  ligamentum  nuchae.  The  muscle 
is  covered  mainly  by  the  splenius  and  longissimus  capitis  muscles.  It  conceals  the 
semispinalis  cer\dcis  and  the  muscles  of  the  suboccipital  triangle. 

Third  Group. 

This  group  comprises  the  semispinals  (dorsi  and  cervicis)  and  multifidus.  They 
occupy  the  vertebral  furrow  under  cover  of  the  sacro-spinalis  and  semispinalis 


390 


THE  MUSCULAE  SYSTEM. 


Insertion  of  sterno 

MASTOID 

Splenius  capitis. 

IjONOISSIMUS  capiti 

(trachelo-mastoid) 

Semispinalis  capitis 

(complexus). 

(thrown  outwards) 

Least  occipital  nerve. 


Splenius  capitis 


longissimus  capitis 
(trachelo-mastoid)' 


Trapezius 

Semispinalis  capitis  (complex us 
Great  occipital  nerve 
Obliquus  superior 
Rectus  capitis  posterior  major 
Rectus  capitis  posterior  minor 
Vertebral  artery 
Suboccipital  nerve 
Posterior  arch  of  atlas 

Obliquus  capitis  inferior 

Posterior  primary  division  of  second 
cervical  nerve 


Posterior  primary  division  of  third 
cervical  nerve 

Deep  cervical  artery 

Posterior  primary  division  of  fourth 

cervical  nerve 


Semispinalis  cervicis 


Fig.   310. — The  Suboccipital  Triangle  op  the  Left  Side. 


capitis  (complexus)  muscles-.    They  are  only  incompletely  separate  from  one  another. 


Attachment  of 
posterior  sacro- 
iliac ligaments 


Glutseus  maxiinus  (origin) 
Fig.  311. — Muscle-Attachments  to  the  Sacrum  (Posterior  Aspect). 


THE  MUSCLES  OF  THE  BACK. 


391 


The  semispinales,  dorsi  and  cervicis,  form  a  superficial  stratum,  the  multifidus  being 
more  deeply  placed.  The  more  superficial  muscles  have  the  longer  fibres ;  the 
fibres  of  the  multifidus  pass  over  fewer  vertebra.  Both  muscles  extend  obliquely 
upwards  from  transverse  to  spinous  processes. 

The  semispinalis  muscle  extends  from  the  loin  to  the  axis  vertel)ra.  Its 
fibres  are  artificially  separated  into  an  inferior  part,  the  semispinalis  dorsi,  and 
a  superior  part,  the  semispinalis  cervicis. 

The  semispinalis  dorsi  arises  from  the  transverse  processes  of  the  lower  six 
thoracic  vertebrte.  It  is  inserted  into  the  spinous  processes  of  the  last  two  cervical 
and  first  four  thoracic  vertebne. 

The  semispinalis  cervicis  arises  from  the  transverse  processes  of  the  upper 
six  thoracic,  and  the  articular  processes  of  the  lower  four  cervical  vertebrtTe.  It  is 
inserted  into  the  spines  of  the  cervical  vertebrte  from  the  second  to  the  fifth. 

The  multifidus  differs  from  the  previous  muscle  in  extending  from  the 
sacrum  to  the  axis,  and  in  the  shortness  of  its  fasciculi,  which  pass  over  fewer 
vertebrae  to  reach  their  insertion.  It  arises  from  the  sacrum,  from  the  posterior 
sacro-iliac  ligament  (Fig.  311,  p.  390),  from  the  mammiUary  processes  of  the 
lumbar  vertebrae,  from  the  transverse  processes  of  the  thoracic  vertebrae,  and  from 
the  articular  processes  of  the  lower  four  cervical  vertebra.  It  is  inserted  into  the 
spines  of  the  vertebree  up  to  and  including  the  axis.  Lying  in  contact  with  the 
vertebral  lamina,  the  muscle  is  covered  in  the  neck  and  back  ])y  the  semispinalis, 
and  in  the  loin  by  the  sacro-spinalis  muscle. 

Fourth   Group. 

This  group  includes  several  sets  of  small  muscles,  which  are  vertebro-cranial  or 
inter-vertebral  in  their  attachments. 

The  muscles  bounding  the  suboccipital  triangle  are  four  in  number — obliqui 
capitis,  inferior  and  superior,  and  recti  capitis  posteriores,  major  and  minor 

Semispinalis  capitis  (complexus)  (insertion) 


Rectus  capitis  posterior  minor 
(insertion) 


Rectus  capitis  posterior  major 
(insertion) 


Trapezius  (origin) 


Stenio-cleido-mastoid 
'insertion) 


Splenius  capitis 
(insertion) 


Obliquus  capitis  superior 
(insertion) 


Rectus  capitis  lateralis  (insertion) 

Rectus  capitis  anterior  (insertion 
(rectus  capitis  anterior  minor) 

Longus  capitis  (rectus  cai)itis  anterior 
major)  (insertion) 


ouperior  constrictor  of  pharynx  (insertion) 


Fig.  312.— Muscle- Attachments  to  the  Occipital  Bose  (Parietal  Surface). 


These  muscles  are  concealed  by  the  semispinalis  capitis  (complexus)  and 
splenius  capitis;  they  enclose  a  triangular  space  (the  suboccipital  triangle)  in 
which  the  vertebral  artery,  the  posterior  primary  division  of  the  suboccipital  nerve, 
and  the  posterior  arch  of  the  atlas  are  contained. 

The  obliquus  capitis  inferior  arises  from  the  spine  of  the  axis,  and  is  inserted 
into  the  transverse  process  of  the  atlas. 


392 


THE  MUSCULAE  SYSTEM. 


The  obliquus  capitis  superior  arises  from  the  transverse  process  of  the  atlas, 
and  is  inserted  into  the  occipital  bone  beneath  and  lateral  to  the  semispinalis  capitis 
and  above  the  inferior  curved  line  (Fig-  312,  p.  391). 

The  rectus  capitis  posterior  major  arises  from  the  spine  of  the  axis,  and  is 
inserted  into  the  occipital  bone  beneath  the  obliquus  capitis  superior  and  semi- 
spinalis capitis  and  below  the  inferior  curved  line  (Fig.  312,  p.  391). 

The  rectus  capitis  posterior  minor  arises  beneath  the  previous  muscle  from  the 
spine  of  the  atlas,  and  is  inserted  into  the  occipital  bone  below  the  inferior  curved 
line  medial  to  and  beneath  the  rectus  capitis  posterior  major  (Fig.  312,  p.  391). 

The  rotatores  are  eleven  pairs  of  small  muscles  occupying  the  vertebral  groove 
in  the  thoracic  region,  beneath  the  transverso-spinales,  of  which  they  form  the 
deepest  fibres.  Each  consists  of  a  small  slip  arising  from  the  transverse  process  and 
inserted  into  the  lamina  of  the  vertebra  directly  above. 

The  inter-spinales  are  bands  of  muscular  fibres  connecting  together  the  spinous 
processes  of  the  vertebrae. 

The  inter-transversarii  are  slender  slips  extending  between  the  transverse 
processes.  They  are  double  in  the  neck,  the  anterior  divisions  of  the  spinal  nerves 
passing  between  them.  In  the  loin  the  inter-transverse  muscles  are  usually 
double,  but  they  are  often  absent,  or  are  replaced  by  membrane. 

The  rectus  capitis  lateralis,  extending  from  the  transverse  process  of  the  atlas 
to  the  jugular  process  of  the  occipital  bone  (Fig.  312,  p.  391),  is  homologous  with 
the  posterior  of  the  two  inter-transverse  muscles. 


Nerve-Supply. 

With  the  exception  of  the  vei'tebro- scapular  and  vertebro- humeral  muscles  (trapezius, 
latissimus  dorsi,  levator  scapulae,  rhomboidei,  p.  327),  the  muscles  of  the  back  are  all  sup- 
plied hj  the  posterior  primary  divisions  of  the  spinal  nerves.  In  the  upper  part  of  the  trunk 
the  muscles  are  supplied  mainly  by  the  lateral  branches ;  in  the  lower  part  chiefly  by  the 
medial  branches  of  the  nerves.  In  tlie  cervical  and  sacral  regions  a  A^ariable  plexiform  arrange- 
ment of  the  nerves  occurs  (posterior  cervical  sjoA  posterior  sacral  plexuses). 


Actions. 

The  action  of  these  muscles  is  extremely  complex.  Not  only  do  they  act  on  the  spinal 
column,  ribs,  head,  and  jjelvis,  in  conjunction  with  other  muscles,  but  some  of  them  act  also  in 
relation  to  the  movements  of  the  limbs  as  well.  In  this  section  will  be  given  an  analysis  of  their 
movements  in  relation  to  the  sjjinal  column,  head,  and  pelvis.  The  movements  of  the  limbs  and 
of  the  ribs  (respiration)  are  dealt  with  in  other  sections.  The  chief  muscles  are  engaged  in  pre- 
serving the  erect  position,  and  in  the  movements  of  the  trunk  they  are  assisted  in  large  measure 
by  muscles  whose  chief  actions  are  referred  to  elsewhere. 

1.  Movements  of  the  Spinal  Column. — The  movements  of  the  vertebral  column  are  flexion, 
extension,  and  lateral  movement  or  rotation.  These  movements  occur  in  all  regions — neck, 
thorax,  and  loin  ;  flexion  and  extension  and  lateral  movement  are  most  limited  in  the  region  of 
the  thorax  ;  while  rotation  is  most  limited  in  the  region  of  the  loin. 


a.  Flexion      and      Extension. 

Longus  colli 

Serrati  jDOsteriores 

Longus  cajjitis  (rectus  capitis  anterior  major) 

Splenius  capitis 

Scaleni  anteriores  (together) 

SiDlenius  cervicis 

Psoas  major  and  minor 

Sacro-si^inalis  (erector  spinas) 

Levator  ani 

Semispinalis  dorsi 

Coccygeus 

Semispinalis  cervicis 

Semis2)inalis  cajjitis  (complexus) 

Sphincter  ani  extemus 

Multifidus 

Rectus  abdominis 

Interspinales 

Pyramidalis 

Obliquus  externus  abdominis 

Intercostal  muscles 

Obliquus  intemus         „ 

Diaphragm 

Transversus                   „ 

Transversus  thoracis  (triangularis  stemi) 

THE  MUSCLES  OF  THE  BACK. 


393 


b.  Lateral  Movement  (Rotation).                                                      1 

Levator  scapulae 

Loiigus  capitis  (rectus  capitis  anterior 

major) 

Serrati  posteriores 

Scaleni,  anterior,  ruedius,  posterior 

Splenius  cervicis 

Psoas  (major  and  minor) 

Sacro-spinalis  (erector  spin?e) 

Quadratus  lumborum 

Semispinalis  capitis  (complexus) 

Obliquus  externus  abdominis 

Semispinalis  (dorsi  and  cervicis) 

Obliquus  internus           „ 

Multitidus 

Transversus                     „ 

Eota  tores 

Eectus                              „ 

Inter-transversarii 

Pyramidalis                     „ 

Longus  colli 

2.  Movements  of  the  Head. — The  movements  of  the  head  are  flexion  and  extension,  at  the 
occipito-atlantoid  articulation ;  lateral  movement  and  rotation  at  the  atlanto-axial  joint. 


a.  Flexion      and      Extension. 


Digastric 

Stylo -hyoid 

S  ty  lo -pharyngeus 

Mylo-hyoid 

Hyo-glossus 

Sterno-hyoid 

Sterno-thyreoid 

Omo-hyoid 

Recti  capitis  anteriores  (major  and  minor) 

{the  muscles  of  both  sides  acting  together) 


Sterno-mastoid 

Splenius  capitis 

Longissimus  ca23itis  (trachelo-mastoid) 

Semispinalis  capitis  (complexus) 

Obliquus  capitis  inferior 

Recti  capitis  posteriores  (major  and  minor) 


b.  Lateral  Movement. 

c.  Rotation. 

Sterno-mastoid 

Splenius  capitis 

Longissimus  capitis  (trachelo-mastoid) 

Semispinalis  capitis  (complexus) 

Obliquus  cajsitis  superior 

Rectus  capitis  lateralis 

Sterno-mastoid 
Splenius  capitis 

Longissimus  capitis  (trachelo-mastoid) 
Semispinalis  capitis  (complexus) 
Obliquus  capitis  inferior 
,,              „      superior 
Recti  capitis  posteriores  (major  and  minor) 

Movements  of  the  Pelvis. — The  movements  of  the  pelvis  (as  in  locomotion)  are  partly 
caused  by  certain  of  the  muscles  of  the  back.  Those  muscles,  which  are  attached  to  the  spinal 
column  or  the  ribs  on  the  one  hand,  and  to  the  innominate  bone  on  the  other,  produce  the 
movements  (flexion,  extension,  and  lateral  movement)  of  the  whole  pelvis.  In  addition,  the 
muscles  jjassing  between  the  innominate  bone  and  femur,  in  certain  positions  of  the  lower  limb, 
assist  in  these  movements. 


a.  Extension 

and       Flexion. 

Latissimus  dorsi 

Psoas  major  and  minor 

Sacro-spinalis  (erector  spinse) 

Rectus  abdominis 

Multifidus  (acting  on  both  sides) 

Pyramidalis  abdominis 

Obliquus  externus  abdominis 

Obliquus  internus         „ 

Transversus  abdominis  (acting  on  both 

sides) 
Piriformis 
Glutaii 

Obturator  (externus  and  internus) 
Sartorius 

Tensor  fasciae  latae 
Iliacus 

Rectus  femoris 
Adductors  (in  the  erect  position) 

b.  Lateral 

Movement. 

Flexors  and  extensors  of  one  side 

only         1 

Quadratus  lumborum 

394 


THE  MUSCULAE  SYSTEM. 


THE    FASCIi^ 


AND    IVIUSCLES 
AND    NECK. 

FASCIiE. 


OF    THE    HEAD 


The  superficial  fascia  of  the  head  and  ueck  possesses  certain  features  of  special 
interest.  Over  the  scalp  it  is  closely  adherent  to  the  skin  and  subjacent  epicranial 
aponeurosis,  and  contains  the  superficial  vessels  and  nerves.     Beneath  the  skin  of 

the  eyelids  it  is  loose  and 
thin  and  contains  no 
fat.  Over  the  face  and 
at  the  side  of  the  ueck 
it  is  separated  from  the 
deep  fascia  by  the  facial 
muscles  and  the  platy  sma. 
Between  the  buccinator 
and  the  masseter  it  is 
continuous  with  a  pad 
of  fat  {suctorial  pad) 
occupying  the  interval 
between  these  muscles. 

The  deep  fascia  of 
the  head  and  neck  pre- 
sents many  remarkable 
characters.  Over  'the  scalp 
it  is  represented  by  the  epi- 
cranial aponeurosis  (galea 
aponeurotica),  the  tendon 
of  the  epicraneus  or  occi- 
pito  -  frontalis  muscle. 
This  is  a  tough  mem- 
brane, tightly  stretched 
over  the  calvarium,  from 
which  it  is  separated  by 
loose  areolar  tissue.  It 
is  attached  posteriorly, 
partly  through  the 
agency  of  the  occipitalis 
muscle,  to  the  superior 
curved  line  of  the  oc- 
cipital bone  ;  anteriorly 
it  joins  the  frontalis 
muscle  and  the  orbicu- 
laris oculi,  and  has 
no  bony  attachment ; 
laterally  it  is  attached 
to  the  temporal  ridge 
and  the  mastoid  process. 
Below  the  temporal  ridge 
it  is  continuous  with  the 
temporal  fascia,  a  stout 
layer  of  fascia  attached  to  the  temporal  ridge  and  zygomatic  arch,  which  covers  and 
gives  origin  to  the  temporal  muscle.  This  fascia  separates  into  two  layers  above 
the  zygoma,  to  enclose  a  quantity  of  fat  along  with  Ijranches  of  the  temporal 
and  orbital  arteries.  On  the  face  the  fascia  is  practically  non-existent  anteriorly 
in  relation  to  the  facial  muscles.  Posteriorly  it  forms  the  thin  masseteric  fascia, 
and  is  much  thicker  in  relation  to  the  parotid  gland,  for  which  it  forms  a  capsule. 

In  the  neck  the  deep  fascia  invests  the  muscles,  and  forms  aponeurotic  coverings 
for  the  pharynx,  trachea,  oesophagus,  glands,  and  large  vessels.      It  encloses  the 


Fig.  313. 


45     44  ~-'43 

-Transverse  Section  in  the  Cervical  Region  (between  the 
iourth  and  fifth  cervical  vertebrae). 


1.  Crico-thyreoid  mtiscle. 

2.  Inkekior  constrictor  muscle. 

3.  Pharynx. 

4.  Cricoid  cartilage. 

5.  Vocal  cord. 

6.  THYRE0-ARYT.«N01I1  MUSCLE. 

7.  Thyreoid  cartilage. 

8.  Glottis. 

9.  Layers  of  deep  cervical  fascia. 

10.  Sterno-hyoid  muscle. 

11.  Omohyoid  muscle. 

12.  .Sterno-thyreoid  muscle. 

13.  Cervical  fascia. 

14.  Thyreoid  body.  . 

15.  CoiiiTiioii  carotid  artery. 

16.  Descendens  hypoglossi  nerve. 

17.  Sterno-mastoid  muscle. 

18.  Internal  .jngnlar  .vein. 

19.  Pnenniogastric  nerve. 

20.  Synipatlietic  nerve. 

21.  Carotid  sheath. 

22.  Phrenic  nerve. 

23.  I.ONGUS  COLLI  MUSCLH. 

24.  LONOUS       CAPITIS       (RECTUS 

ANTERIOR  major). 

25.  Scalenus  antk.rior. 

26.  Vertebral  vein. 


27. 

Scalenus  medius. 

28. 

Posterior  triangle. 

29. 

Scalenus  posterior. 

30. 

Levator  scapul.e. 

.Tl. 

Spinal  accessory  nerve. 

3-J. 

Spt.enius  ceevicis. 

33. 

LONKISSIMUS      CERVICIS 
ALIS  CERVICIS). 

(transvers- 

34. 

lonoissimus      capitis 
mastoid). 

(trachelo- 

35. 

Spinal  nerve. 

3(3. 

Vertebral  artery. 

37. 

Profunda  cervieis  vein. 

38. 

Profunda  cervieis  artorj 

39. 

MULTIFIDUS. 

40. 

SEMISPINALIS  CERVICIS. 

41. 

Semispinalis  capitis  (c 

omplexus). 

42. 

Splenius  capitis. 

43. 

Trapezius. 

44. 

Ligamentuni  nuclue. 

4i. 

Spine  of  fourth  cervical 

vertebra. 

46. 

Lamina  of  fifth  cervical 

\'ertebra. 

47. 

Uura  mater. 

CAPITIS      48. 

Spinal  cord. 

49. 

Transverse  i)rocess. 

50. 

Disc  between  fourth  an( 

fifth  cervical 

• 

vertebra-. 

THE  MUSCLES  OF  THE  HEAD.  395 

sterno- mastoid  muscle,  and  can  be  traced  backwards  over  the  posterior  triangle 
to  the  trapezius  and  deeper  muscles,  which  it  surrounds ;  it  can  be  traced  forwards 
over  the  anterior  triangle  to  the  middle  line  of  the  neck,  where  it  forms  a 
continuous  membrane.  Above  the  sternum  the  fascia,  after  enclosing  the  sterno- 
mastoid  muscles,  is  attached  in  the  form  of  two  layers  to  the  front  and  back  of  the 
episternal  notch.  The  layer  enclosing  the  infrahyoid  muscles  passes  across  the 
middle  line  of  the  neck  in  front  of  the  trachea,  and  is  attached  above  to  the  hyoid 
bone,  below  to  the  sternum,  clavicle,  and  first  rib.  A  third  layer  of  fascia  passes 
inwards  in  front  of  the  trachea,  enclosing  the  thyreoid  body.  Beneath  the  sterno- 
mastoid  the  fascia  helps  to  form  the  carotid  sheath,  which  is  completed  by  septal 
processes  stretching  inwards  across  the  neck  in  relation  to  the  infrahyoid  muscles, 
trachea,  oesophagus,  and  pharynx,  and  the  prsevertebral  muscles.  The  trachea, 
oesophagus,  and  pharynx  are  likewise  encapsuled  in  cervical  fascia,  a  septal  layer 
passing  across  the  middle  line  of  the  neck  between  the  trachea  and  oesophagus. 
Lastly,  a  strong  prsevertebral  fascia  passes  across  the  neck  in  front  of  the  prevertebral 
muscles,  and  behind  the  oesophagus  and  pharynx. 

The  cervical  fascia  is  attached  above  to  the  bones  of  the  skull :  superficially  to 
the  superior  curved  line  of  the  occipital  bone,  the  mastoid  process,  the  zygoma 
(over  the  parotid  gland),  and  the  lower  border  of  the  mandible  ;  more  deeply  to  the 
styloid  and  vaginal  processes  of  the  temporal  bone,  the  great  wing  of  the  sphenoid 
and  the  basilar  process.  This  deeper  attachment  {prcevertehral  fascia)  is  behind  the 
parotid  gland  and  pharynx,  and  is  associated  with  the  formation  of  three  ligaments  : 
stylo-mandibular  ligament,  internal  lateral  ligament  of  the  lower  jaw  (spheno- 
mandibular),  and  pterygo-spinous  ligament.  The  fascia  is  attached  below,  through 
its  muscular  connexions,  to  the  sternum,  first  rib,  clavicle,  and  scapula.  By  means 
of  its  connexion  with  the  trachea  and  the  common  carotid  artery  it  is  carried  down 
behind  the  first  rib  into  the  superior  mediastinum,  and  so  becomes  continuous  with 
the  pericardium.  By  means  of  its  connexion  vv^ith  the  subclavian  vessels  and 
brachial  nerves  it  is  carried  down  to  the  axilla,  as  the  subclavian  sheath,  which 
becomes  connected  with  the  costo-coracoid  membrane. 


THE   MUSCLES   OF   THE   HEAD. 

The  muscles  of  the  head  are  divisible  into  three  separate  groups :  the  super- 
ficial muscles,  muscles  of  the  orbit,  and  muscles  of  mastication. 

Superficial    IVIuscIes. 

The  superficial  muscles  comprise  a  large  group,  including  the  muscles  of  the 
scalp  and  face,  and  the  platysma  in  the  neck. 

The  platysma  is  a  thin  quadrilateral  sheet  extending  from  chest  to  face 
over  the  side  of  the  neck,  between  the  superficial  and  deep  fasciae.  It  arises 
from  the  deep  fascia  of  the  pectoral  region  and  the  clavicle.  It  is  directed 
upwards  and  forwards,  and  is  partly  inserted  (by  its  intermediate  fibres)  into  the  lower 
border  of  the  mandible,  becoming  connected  with  the  quadratus  labii  inferioris 
(depressor  labii  inferioris)  and  triangularis  (depressor  anguli  oris)  muscles  (Eig. 
314,  p.  396).  The  more  anterior  fibres  pass  across  the  middle  line  of  the  neck 
and  decussate  for  a  variable  distance  below  the  chin  with  those  of  the  opposite  side. 
The  posterior  fibres  sweep  over  the  angle  of  the  jaw  and  become  continuous  with 
the  risorius  muscle.  The  platysma  is  the  rudiment  of  the  cervical  portion  of  the 
panniculus  carnosus  of  lower  animals,  in  which  it  has  a  much  more  intimate 
connexion  with  the  muscles  of  the  face  than  is  usually  the  case  in  man. 

The   IVIuscIes  of  the  Scalp. 

The  muscles  of  the  scalp  comprise  the  occipito-frontalis  (epicranius)  muscle  and 
the  muscles  of  the  external  ear. 

The  epicranius  (occipito-frontalis)  is  a  muscle  with  two  bellies  and  an 
intervening  tendon  (the  galea  aponeurotica)  which  stretches  uninterruptedly  across 
the  middle  line  of  the  cranium.     The  posterior  belly  (occipitalis)  arises  as  a  broad 

27 


396 


THE  MUSCULAE  SYSTEM. 


flat  band  from  the  lateral  two-thirds  of  the  superior  curved  Hne  of  the  occipital 
bone.  The  anterior  belly  (frontalis)  has  no  bony  attachments ;  arising  from  the 
epicranial  aponeurosis  about  the  level  of  the  coronal  suture,  it  passes  downwards 
to  the  supra-orbital  arch,  where  it  blends  with  the  orbicularis  oculi  and  corru gator 
supercilii  muscles.  It  extends  across  the  full  width  of  the  forehead,  and  blends 
in  the  middle  line  with  the  muscle  of  the  opposite  side. 

The  epicranial  aponeurosis  or  galea  aponeurotica,  extending  between  the  two 
fleshy  bellies,  is  a  continuous  membrane  which  glides  over  the  calvarium,  and  has 
attachments  laterally  to  the  temporal  ridge,  and  behind,  between  the  posterior 
belhes,  to  the  superior  curved  lines  of  the  occipital  bone.     It  has  no  osseous  attach- 


Epicranial 

aponeurosis 

(Galea 

aponeurotica) 


Superior 

ACRICULAIl 

MUSCLE  _ 

Anterior 
auricular 

MUSCLE 


Occipitalis 


-Orbicularis  oculi 


M.  PROCERUS 
(PVRAMIDALIS  NASI) 


f —  Caput  angulare 
-  Compressor  naris 


"Caput  angulare 


]. 


Caput  infraorbitale  j 
^^  Caput  zygomaticum  J 

Caninus  (levator  anguli  oris) 
Zyoomaticds  (major) 
Orbicularis  oris 
Buccinator 

RiSORIUS 


-  M.  triangularis 
(depressor  anguli  oris) 

-  m.  qoadratus  labii  inferioris 

(depressor  LABII  INFERIORIS) 


Masseter 

I'l.A'l  VSMA 

Fig.  314. — The  Muscles  of  the  Face  and  Scalp  (Muscles  of  Expression). 

ment  anteriorly.  The  epicraneus  is  usually  rudimentary.  By  the  contrac- 
tion of  the  fibres  of  the  frontalis  muscle  the  skin  of  the  forehead  is  thrown 
into  horizontal  parallel  folds. 

The  extrinsic  muscles  of  the  ear  are  three  in  number :  posterior,  superior,  and 
anterior  (retrahens,  attollens,  and  attrahens  aurem).  They  are  rudimentary  and 
usually  function  less. 

The  m.  auricularis  posterior  (retrahens  aurem)  is  a  narrow  fleshy  slip  which 
arises  from  tbe  surface  of  the  mastoid  process  and  is  inserted  into  the  deep  surface 
of  the  pinna.  It  bridges  across  the  groove  between  the  mastoid  process  and  the 
pinna,  and  conceals  the  posterior  auricular  vessels  and  nerve. 

The  m.  auricularis  superior  (attollens  aurem)  is  a  small  fan-shaped  muscle 
which  arises  from  the  temporal  fascia,  and  descends  to  be  inserted  into  the  top  of 
the  root  of  the  pinna. 

The  m.  auricularis  anterior  (attrahens  aurem)  is  a  similar  small  muscle,  placed 


J 


THE  MUSCLES  OF  THE  FACE.  397 

in  front  of  the  attollens,  and  stretching  obUquely  between  the  temporal  fascia  and 
the  top  of  the  root  of  the  pinna. 

The   IVIuscIes  of  the   Face. 

The  facial  muscles  are  divided  into  tliree  groups,  associated  with  the  several 
apertures  of  the  eye,  nose,  and  mouth. 

1.  The  muscles  of  the  eyelids  include  four  muscles :  the  levator  palpebrte 
superioris  (described  with  the  orbital  muscles  (p.  399)),  orbicularis  oculi  (palpe- 
brarum), tensor  tarsi  (tarsal  part  of  the  orbicularis  oculi),  and  corrugator  supercilii. 

The  orbicularis  oculi  is  a  transversely  oval  sphincter  muscle  surrounding  and 
occupying  the  eyelids.  It  is  divisible  into  a  'peripheral  'portion  (j)ars  orhitalis)  com- 
posed of  coarse  fibres,  spreading  on  to  the  forehead,  temple,  and  cheek,  and  a 
central  portion  (pars  palpebralis),  composed  of  finer  fibres,  situated  beneath  the 
skin  of  the  eyelids.  At  the  medial  canthus  of  the  eye  the  muscle  (by  its  palpebral 
fibres)  gains  an  attachment  to  the  tarsal  ligament  and  the  borders  of  the  naso- 
lacrimal groove.  Its  fibres  enclose  the  lacrimal  sac  and  the  canaliculi.  The 
posterior  fibres,  extending  between  the  posterior  edge  of  the  naso-lacrimal  groove 
and  the  tarsal  ligaments  behind  the  lacrimal  sac,  constitute  the  pars  lacrimalis 
or  tensor  tarsi  muscle.  The  fibres  of  the  muscle  which  extend  along  the  margins  of 
the  lids  constitute  a  separate  ciliary  bundle. 

Laterally  the  orbicularis  oculi  has  no  bony  attachment ;  so  that  when  it 
contracts  and  closes  the  eyelids,  both  lids  at  the  same  time  tend  to  be  drawn 
inwards  towards  the  medial  canthus  of  the  eye. 

The  corrugator  supercilii  arises  from  the  nasal  eminence,  and  passing  horizon- 
tally outwards,  blends  with  the  upper  fibres  of  the  orbicularis  oculi  on  its  under 
surface.  The  contraction  of  this  muscle  throws  the  skin  of  the  forehead  into  vertical 
folds,  while  at  the  same  time  drawing  the  medial  half  of  the  eyebrow  upwards,  it 
produces  concentric  curved  folds  on  each  side  of  the  middle  line  of  the  forehead. 

2.  The  muscles  of  the  nose  comprise  five  small  muscles  proper  to  the  nose,  and 
one  common  to  the  nose  and  upper  lip  :  the  m.  procerus  (or  pyramidalis  nasi), 
compressor  naris,  dilatores  naris  (anterior  and  posterior),  depressor  alee  nasi,  and 
angular  head  of  the  quadratus  labii  superioris  (levator  labii  superioris  alseque  nasi). 
They  are  all  small  and  feeble  muscles. 

The  m.  procerus  (pyramidalis  nasi)  arises  from  the  epicranius  muscle  and 
the  skin  over  the  glabella ;  it  is  inserted  into  a  membrane  stretching  over  the  nose, 
which  also  gives  attachment  to  the  compressor  naris. 

The  m.  nasalis  (compressor  naris)  arises  by  a  narrow  origin  from  the  maxilla, 
under  cover  of  the  quadratus  (levator  labii  superioris  alseque  nasi).  It  passes 
forwards  over  the  bridge  of  the  nose,  and  ends  in  a  membranous  insertion  common 
to  it  and  the  previous  muscle. 

The  dilatores  naris  are  feeble  muscular  slips  placed  on  the  lateral  surface  of 
the  margin  of  the  nostril,  one  anteriorly,  the  other  posteriorly. 

The  depressor  alse  nasi  is  a  small  muscle  arising  from  the  upper  part  of  the 
incisor  fossa  of  the  maxilla ;  it  divides  into  two  parts  as  it  passes  upwards  and 
medially,  and  is  inserted  into  the  ala  and  the  septum  of  the  nose  (depressor  septi). 

The  levator  labii  superioris  alaeque  nasi  now  forms  a  portion  (caput  angxdare) 
of  the  quadrate  muscle  of  the  upper  lip,  and  is  a  narrow  band  arising  from  the  root 
of  the  frontal  process  of  the  maxilla.  It  descends  alongside  the  nose,  and  is 
inserted,  partly  into  the  ala  of  the  nose  and  partly  into  the  orbicularis  oris  muscle. 

3.  The  muscles  of  the  mouth  comprise  a  number  of  muscles,  of  which  all 
but  one,  the  orbicularis  oris,  are  bilaterally  placed.  The  muscles  are :  quadratus 
labii  superioris,  which  includes  the  angular  head  or  levator  labii  superioris  alaeque 
nasi,  the  infra-orbital  head  or  levator  labii  superioris,  and  the  zygomatic  head  or 
zygomaticus  minor,  the  canine  muscle  or  levator  anguli  oris,  zygomaticus  (m.  zygo- 
maticus  major),  risorius,  orbicularis  oris,  triangularis  or  depressor  anguh  oris, 
m.  quadratus  labii  inferioris  or  depressor  labii  inferioris,  m.  mentalis  (levator 
menti),  and  buccinator. 


398  THE  MUSCULAR  SYSTEM. 

The  orbicularis  oris  is  the  sphincter  muscle  surrouuding  the  lips.  It  is  con- 
tinuous with  the  other  muscles  converging  to  the  mouth.  It  lies  between  the  skin 
and  mucous  membrane  of  the  mouth,  and  is  limited  above  by  the  nose,  below  by 
the  junction  of  the  lower  lip  and  chin.  Its  medial  fibres  are  attached  above  to  the 
septum  of  the  nose  {naso-lahial  band)  and  to  the  incisor  fossa  (superior  incisive 
bundle) ;  below  they  are  attached  to  the  lower  jaw  on  each  side  of  the  symphysis 
(inferior  incisive  bundle).  These  bundles  radiate  laterally  to  join  the  rest  of  the 
muscle,  which  is  joined  at  its  margin  by  the  elevators  and  depressors  of  the  lower 
lip  and  angle  of  the  mouth,  and  by  the  buccinator  muscle.  The  lower  fibres  of  the 
muscle  are  continued  laterally  into  the  buccinator  and  canine  (levator  anguli 
oris)  muscles ;  its  ^tp^jer  fibres  are  continued  into  the  buccinator  and  triangular 
(depressor  anguli  oris)  muscles. 

The  quadratus  labii  superioris  comprises  three  muscles. 

(1)  The  caput  angulare  (levator  labii  superioris  alaeque  nasi)  has  already 
been  described. 

(2)  The  caput  infra- orbitale  (levator  labii  superioris)  arises  from  the  maxilla 
just  above  the  infra-orbital  foramen.  It  passes  almost  vertically  downwards  to 
join  the  orbicularis  oris  and  the  skin  of  the  upper  lip  between  the  attachments 
of  the  previous  muscle  (caput  angulare)  and  the  caninus  (levator  anguli  oris). 
It  conceals  the  infra-orbital  vessels  and  nerve. 

(3)  The  caput  zygomaticum  (zygomaticus  minor)  arises  from  the  zygomatic 
bone,  and  is  often  continuous  with  the  most  peripheral  fibres  of  the  orbicularis 
oculi.  It  is  directed  obliquely  downwards  and  forwards  over  the  caninus  (levator 
anguli  oris),  to  be  inserted,  along  with  the  previous  muscle  (c.  infra -orbitale), 
into  the  margin  of  the  orbicularis  oris. 

The  caninus  (levator  anguli  oris)  arises  from  the  canine  fossa  of  the  maxilla 
below  the  infra -orbital  foramen  and  under  cover  of  the  foregoing  muscle.  It 
is  directed  laterally  and  downwards,  to  be  inserted  into  the  orbicularis  oris  and 
the  skin  at  the  angle  of  the  mouth. 

The  zygomaticus  (zygomaticus  major)  is  a  narrow  muscular  band  which 
arises  from  the  zygomatic  portion  of  the  zygomatic  arch.  It  passes  to  the  angle  of 
the  mouth,  to  be  inserted  partly  into  the  skin,  partly  into  the  orbicularis  oris. 

The  risorius  is  a  thin  flat  muscle  which  forms  in  part  a  continuation  of  the 
platysma  on  the  face,  in  part  a  separate  muscle,  with  an  origin  from  the  masseteric 
fascia.  It  passes  transversely  forwards,  to  be  inserted  at  the  angle  of  the  mouth 
into  the  orbicularis  oris  and  skin. 

The  triangularis  (depressor  anguli  oris)  arises  from  the  oblique  line  of 
the  lower  jaw  and  is  continuous  with  the  platysma  (Fig.  314,  p.  396).  It  is 
triangular  in  form,  its  fibres  converging  to  the  angle  of  the  mouth,  where  they 
are  inserted  into  the  orbicularis  oris  and  the  skin.  Some  of  the  fibres  reach 
the  upper  lip  through  the  orbicularis  muscle. 

The  quadratus  labii  inferioris  (depressor  labii  inferioris)  arises  from  the 
lateral  surface  of  the  lower  jaw  beneath  and  medial  to  the  previous  muscle  (Fig. 
314,  p.  396).  It  is  quadrilateral  in  form,  and  is  directed  upwards,  to  be  inserted  . 
into  the  orbicularis  oris  and  the  skin  of  the  lower  lip.  Its  lateral  fibres  are 
overlapped  by  the  triangularis  oris.  Its  medial  fibres  join  with  those  of  the 
opposite  muscle. 

The  mentalis  ^levator  menti)  is  a  small  muscle  which  arises  from  the  incisor 
fossa  of  the  mandible  and  is  inserted  into  the  skin  of  the  chin. 

Tiie  buccinator  muscle  forms  the  lateral  wall  of  the  mouth,  and  is  in  series 
posteriorly  with  the  constrictor  muscles  of  the  pharynx.  It  arises  (1)  from  the 
alveolar  arches  of  the  upper  and  lower  jaws  (Fig.  322,  p.  404),  and  between  these 
attachments,  (2)  from  the  pterygo- mandibular  ligament.  Its  fibres  are  directed 
forwards  to  the  angle  of  the  mouth,  where  they  blend  with  the  corresponding 
(upper  and  lower)  portions  of  the  orbicularis  oris  muscle.  The  middle  fibres  of  the 
muscle  decussate  at  the  angle  of  the  mouth,  so  as  to  pass,  the  lower  set  to  the 
upper  lip,  the  upper  set  to  the  lower  lip.  The  buccinator  is  covered  on  its  deep 
surface  by  the  mucous  membrane  of  the  mouth.     Superficially  it  is  concealed  by 


FASCIA  AND  MtTSCLES  OF  THE  ORBIT. 


399 


the  muscles  above  mentioned,  which  converge  to  the  angle  of  the  mouth ;  it  is 
separated  from  the  masseter  by  the  suctorial  pad  of  fat ;  it  is  pierced  by  the  duct 
of  the  parotid  gland,  and  by  branches  of  the  long  buccal  nerve. 

Nerve-Supply. 

The  facial  and  scalp  muscles  are  all  innervated  by  tlie  facial  nerve.  The  posterior  auricular 
branch  supj)lies  the  posterior  auricular  muscle  and  occipitalis  ;  tlie  branches  forming  the  pes 
anserinus  supply  the  frontalis,  superior  and  anterior  auricular  muscles,  the  several  muscles 
associated  with  the  apertures  of  the  eye,  nose,  and  mouth  (including  the  buccinator),  and  the 
platysma. 

Actions. 

The  almost  infinite  variety  of  facial  expression  is  produced  partly  by  the  action  of  these 
muscles,  partly  by  their  inactivity,  or  by  the  action  of  antagonising  muscles  (antithesis).  On  the 
one  hand  joy,  for  example,  is  betrayed  by  the  action  of  one  set  of  muscles,  while  grief  is  accom- 
panied by  the  contraction  of  another  (opposing)  set.  Determination  or  eagerness  is  accompanied 
by  a  fixed  expression  due  to  a  combination  of  muscles  acting  together ;  despair,  on  the  other 
hand,  is  expressed  by  a  relaxation  of  muscular  action.  For  a  philosophical  account  of  the  action 
of  the  facial  muscles,  the  student  should  consult  Darwin's  Expression  of  the  Emotions  in  Man  and 
Animals,  and  Ducheune's  MScanisme  de  la  Physiologic  humaine. 

The  platysma  retracts  and  depresses  the  angle  of  the  mouth,  and  depresses  the  lower  jaw. 
The  epicranius,  by  its  anterior  bellj^,  raises  the  eyebrows ;  both  bellies  acting  together 
tighten  the  skin  of  the  scalp ;  acting  along  with  the  orbicularis  oculi,  it  shifts  the  scalp  back- 
wards and  forwards.  The  corrugator  supercilii  draws  inwards  the  eyebrow  and  vertically 
wrinkles  the  skin  of  the  forehead.  The  m.  procerus  (pyramidalis  nasi)  draws  downwards  the 
skin  between  the  eyebrows,  as  in  frowTiing.  The  upper  eyelid  is  raised  by  the  levator  palpebrae 
superioris.  The  closure  of  the  lids  is  effected  by  the  orbicularis  oculi,  whose  fibres  also 
assist  in  the  lowering  of  the  ej'ebrows,  in  tlie  protection  of  the  eyeball,  and,  by  j^ressure  on 
the  lacrimal  gland,  in  the  secretion  of  tears.  The  tarsal  part,  acting  along  with  the  orbicularis 
oculi,  compresses  the  lacrimal  sac  and  aids  in  the  passage  of  its  contents  into  the  nasal 
duct.  The  muscles  of  the  ear  and  nose  have  quite  rudimentary  actions.  Of  the  muscles  of  the 
mouth,  the  orbicularis  oris  has  a  complex  action,  dejiending  on  the  degree  of  contraction  of  its 
component  parts.  It  causes  compression  and  closure  of  the  lips  in  various  ways,  tightening  the 
lips  OA'er  the  teeth,  contracting  them  as  in  osculation,  or  causing  pouting  or  protrusion  of  one  or 
the  other.  The  accessory  muscles  of  the  lips  draw  them  upwards  (zygomaticus,  m.  quadratus 
labii  superioris),  laterally  (zygomaticus,  risorius,  platysma,  triangularis,  buccinator),  and  down- 
wards (triangularis,  quadra tus  labii  infiTioris,  platysma).  The  mental  muscle  elevates  the  skin 
of  the  chin  and  protrudes  the  lower  lip.  The  buccinator  retracts  the  angles  of  the  mouth, 
flattens  the  cheeks,  and  brings  them  in  contact  with  the  teeth. 


Levator  palpekr.e  superioris 
Hkctus  superior 

Obliquus  Superior 

Rectus  medialis 


The   Fasciae  and   IVIuscIes  of  the  Orbit. 

The  eyeball,  with  its  muscles,  vessels,  and  nerves,  is  lodged  in  a  mass  of  soft 
and  yielding  fat  which  entirely  fills  up  the  cavity  of  the  orbit.  Surrounding  the 
posterior  part  of  the  eyeball  is  the  fascia  bulbi  (capsule  of  Tenon),  which  constitutes  a 
large  lymph  space  or  synovial  bursa  in  relation  to  the  posterior  part  of  the  eyeball. 
Anteriorly  the  capsule  is  in 
contact  with  the  conjunctiva, 
and  intervenes  between  the 
latter  and  the  eyeball ;  pos- 
teriorly it  is  pierced  by  and 
prolonged  along  the  optic 
nerve.  It  is  a  smooth  mem- 
brane connected  to  the  globe 
of  the  eye  by  loose  areolar 
tissue.  It  is  pierced  by  the 
tendons  of  the  ocular  muscles, 
along  which  it  sends  prolonga- 
tions   continuous    with     the 

muscular  sheaths.  ^      ,,-     ^  ^^  ^  t      ^ 

rp,  p +1,  K-+   Fig.  315. — Transverse  \  ERTiCAL  Section  THROUGH  THE  Left  Orbft 

Ine  muscles  or  the  orbit     behind  the  Eyeball  to  show  the  Arrangement  of  Muscles. 
are    seven    in   number :    one, 

the  levator  palpebr^  superioris,  belongs  to  the  upper  eyelid ;    the  other  six  are 
muscles  of  the  eyeball. 

The  levator  palpebrae  superioris  lies  immediately  beneath  the  orbital  peri- 
osteum and  covers  the  superior  rectus  muscle.     It  has  a  narrow  origin  above  that 


Rectus  lateralis 
Obliquus  inferior 


Rectus  inkerior 


400 


THE  MUSCULAE  SYSTEM. 


Levator  PALPEBRiE 

SUPERIORIS 


Fig.  3 1 6. — The  Muscles  op  the  Eight  Orbit  (from  above). 


muscle  from  the  margin  of  the  optic  foramen.     It  expands  as  it  passes  forwards, 

to  end,  in  relation  to  the  upper  lid,  in  a  membranous  expansion  which  is  inserted 

in  a  fourfold  manner :   (1)  into  the  orbicularis  oculi  and  skin  of  the  upper  lid, 

Orbicularis  oculi  (2)  mainly  into  the  Upper  border  of  the 

superior  tarsal  plate,  (3)  into  the  con- 
junctiva, and  (4)  by  its  edges  into  the 
upper  border  of  the  margin  of  the 
orbital  opening. 

The  recti  muscles  are  four  in  number 
— superior,  inferior,  medial,  and  lateral. 
They  all  arise  from  a  membranous 
ring  surrounding  the  optic  foramen, 
which  is  separable  into  two  parts — a 
swperior  common  tendon,  giving  origin 
to  the  superior  and  medial  recti  and 
the  upper  head  of  the  lateral  rectus; 
and  an  inferior  common  tendon,  giving 
origin  to  the  medial  and  inferior  recti 
and  th6  lower  head  of  the  lateral 
rectus.  The  two  origins  of  the  lateral 
rectus  muscle  are  separated  by  the 
passage  into  the  orbit  of  the  oculo- 
motor, nasal,  and  abducent  nerves. 
Forming  flattened  bands  which  lie  in 
the  fat  of  the  orbit  around  the  optic 
nerve  and  eyeball,  the  four  muscles  end 
in  tendons  which  pierce  the  fascia  bulbi 
(capsule  of  Tenon),  and  are  inserted 
into  the  sclera  about  eight  millimetres  (three  to  four  lines)  behind  the  margin 
of  the  cornea.  The  superior  and  inferior  recti  are  inserted  in  the  vertical  plane 
slightly  medial  to  the  axis  of  the  eyeball ;  the  lateral  and  medial  recti  in  the  trans- 
verse plane  of  the  eyeball ;  and  all  are  attached  in  front  of  the  equator  of  the 
eyeball. 

The  obliquus  superior 
arises  from  the  margin  of 
the  optic  foramen  between  the 
rectus  superior  and  rectus 
medialis.  It  passes  for- 
wards as  a  narrow 
muscular  band  medial 
to  the  rectus  superior, 
and  at  the  anterior 
margin  of  the  orbit 
forms  a  narrow  tendon 
which  passes  through 
a  special  fibrous  pulley 
(trochlea)  attached  to 
the  roof  of  the  orbit. 
Its  direction  is  then 
altered,  and  passing 
laterally  between  the 
tendon  of  the  superior  rectus  and  the  eyeball,  it  is  inserted  into  the  sclera  between 
the  superior  and  lateral  recti,  midway  between  the  margin  of  the  cornea  and  the 
entrance  of  the  optic  nerve. 

The  obliquus  inferior  arises  from  the  medial  side  of  the  floor  of  the  orbit  just 
behind  its  anterior  margin,  and  lateral  to  the  naso- lacrimal  groove.  It  forms 
a  slender  rounded  slip,  which  curls  round  the  inferior  rectus  tendon,  and  passes 
between  the  lateral  rectus  and  the  eyeball,  to  be  inserted  into  the  sclera  between 
the  superior  and  lateral  recti,  and  farther  back  than  the  superior  oblique  muscle. 


Obliquus  superior 


Levator  PALPEBRiE  superioris  (cut) 

Rlctus  superior 

Rectus  lateralis 

Oculo-motor 
nerve 


Nasal  nerve 
Abducent  nerve 


Rectus  inferior 


Obliquus  inferior 
Fio.  317. — The  Muscles  of  the  Left  Orbit  (from  without). 


MUSCLES  OF  MASTICATION. 


401 


Miiller's  muscle  is  a  rudimentary  bundle  of  non-striated  muscular  fibres  bridging  across  the 
spheno-maxillary  fissure  and  infra-orbital  groove.  It  is  supplied  by  fibres  from  the  sympathetic, 
and  may  have  a  slight  influence  in  the  protrusion  of  the  eyeball. 


Lacrimal  nerve 


Nerves  to  rectus  superior  and 

levator  palpebra?  superioris 

from  oculo-motor  nervt 

Trochlear  nerv 


Rectus  laterali 

Abducent  nervi 

Oculo-motor  nerve  (inferior, 
division) 

Ciliary  ganglion' 

Nerve  to  rectus  inferior,  from 

oculo-motor  nerve' 

Nerve  to  obllquus  inferior, 

from  oculo-motor  nerve 


Lacrimal  gland 


Frniit.ll  VPvve 


Supra-orbital  nerve 


Supra-trochlear  nerve 

Levator  palpebr* 

sliperioris 

ItECTUS  SUPERIOR 

Obliquus  superior 

Nasal  nerve 

Infra-troclilear  nerve 

Rectus  medialis 

Nerve  to  rectus  medialis  from 

oculo-motor 

Oplitlialmic  ai-tery 

Optic  nerve 

Long  ciliary  nerves 

Rectus  inferior 


Obliquus  inferior 
FiQ.  318. — Schematic  Representation  of  the  Nerves  which  traverse  the  Cavity  of  the  Right  Orbit. 


Nerve-Supply. 

The  muscles  of  the  orbital  cavity  are  supplied  by  the  third,  fourth,  and  sixth  cranial  nerves. 
The  fourth  nerve  (trochlearis)  supplies  the  obliquus  superior ;  the  sixth  (abducens)  supplies  the 
rectus  lateralis;  the  third  nerve  (motor  oculi)  supplies  the  others — levator  palpebrse  superioris, 
recti,  superior,  inferior,  and  medialis,  and  obliquus  inferior. 

Actions. 

The  levator  palpebrae  superioris  elevates  the  upper  eyelid  and  antagonises  the  orbicularis 
oculi  muscle.  The  six  muscles  inserted  into  the  eyeball  serve  to  move  the  longitudinal  axis 
of  the  eyeball  upwards,  downwards,  inwards,  and  outwards,  besides  causing  a  rotation  of  the 
eyeball  on  its  o-mi  axis.  The  following  table  expresses  the  action  of  individual  muscles.  It  must 
be  remembered  that,  while  similar  movements  occur  simultaneously  in  the  two  eyeballs,  the 
horizontal  movements  may,  by  adduction  of  the  muscles  of  both  sides,  cause  convergence  of  the 
axes  of  the  two  eyeballs  for  the  purposes  of  near  vision. 


a.  Adduction 

xnd 

Abduction. 

Rectus  medialis 
Rectus  superior 
Rectus  inferior 

Rectus  lateralis 

Obliquus  superior  \(correc<m^ 

Obliquus  inferior  J  adductors) 

h.  Elevation       a 

nd 

Depression. 

Rectus  superior 
Obliquus  inferior 

Rectus  inferior 
Obliquus  superior 

c.  Rotation  outwards. 

Rotation  inwards. 

Obliquus  inferior 

Obliquus  superior 

Rectus  superior  1^.^^^^^^^.^^) 

Rectus  inferior  j  ^                      ^ 

IVIuscIes  of  Mastication. 

The  muscles  of  mastication  comprise  the  masseter,  temporal,  external  and 
internal  pterygoids,  and  buccinator  (described  above). 

The  masseter  is  the  most  superficial.  Covered  by  the  parotid  gland  on  the 
side  of  the  face,  it  has  an  origin  which  is  partly  tendinous  and  partly  fleshy. 
It   arises  in  two   parts:   (1)  superficially  from  the  lower   border  of   the  zygoma 


402 


THE  MUSCULAE  SYSTEM. 


Temporal  (part 
of  iiisprtion) 


in  its  anterior  two -thirds,  and  (2)  more  deeply  from  the  deep  surface  of  the 
zygoma  in  its  whole  length.  The  superficial  fibres  are  directed  downwards  and 
backwards  towards  the  angle  of  the  jaw ;  the  deeper  fibres  are  directed  vertically 

External  ptery-  /-^    downwards.      The 

Did  (inseition)-;^^^^- — ^    ^  luusclc  is  Inserted  by 

tleshy  and  tendinous 
fibres  into  the  outer 
surface  of  the  ramus 
and  angle  of  the  lower 
jaw  and  the  coronoid 
process  (Fig.  319  «,  p. 
402).  The  deepest 
fibres  bkmd  with  the 
fibres  OT  the  sub- 
jacent temporal 
muscle. 

The  temporal 
muscle  is  a  fan- 
shaped  muscle  aris- 
ing from  the  whole 
area  of  the  temporal 
fossa,  as  well  as  from 
the  temporal  fascia 
Its  converging  fibres  pass  beneath  the  zygomatic  arch.     The 


M.  triangularis 

(depressor  anguli 

oris)  (oiigiii). 

M.  quadratus 

(depressor  labn 

inferioris)  (ongiii) 

M.  mentalis 

(origin) 

Platysma' 
(insertion) 


External  Ptery- 
goid (insertion) 


Fig.  319  a. — Muscle-Attachments  to  the  Lateral  Aspect  of  the  Lower  Jaw. 

which  covers  it-  _     _ 

muscle  is  inserted  into  the  deep  surface  and  apex  of  the  coronoici  process,  and  into  the 

anterior  border  of  the  ramus  of  the  lower  jaw  (Figs.  319  a,  p.  402,  and  319  h,  p.  402). 

The  external  pterygoid  muscle  is  deeply  placed  under  cover  of  the  temporal 
muscle  in  the  zygomatic 
fossa.  It  arises  by  two 
heads,  upper  and  lower. 
The  ui'^per  head  is  at- 
tached to  the  under  sur- 
face of  the  great  wing  of 
the  sphenoid ;  the  lower 
head  takes  origin  from 
the  lateral  surface  of  the 
lateral  pterygoid  plate 
of  the  pterygoid  process. 
The  muscle  is  ciirected 
laterally  and  backwards, 
to  be  inserted  into  (1) 
the  depression  in  front 
of  the  neck  of  the  lower 
jaw  (Figs.  319  a,  p.  402,  ^''"'Sn^ 
and  319  &,  p.  402),  and 
(2)  the  inter  -  articular 
fibro-cartilage  and  cap- 
sule of  the  tempore - 
mandiliular  articulation. 

The  internal  pterygoid  muscle,  placed  beneath  the  external  pterygoid  muscle 
and  the  ramus  of  the  lower  jaw,  has  likewise  a  douljle  origin— (1)  from  the  deep 
surface  of  the  lateral  pterygoid  plate  and  the  pyramidal  process  of  the  palate 
bone,  and  (2)  by  a  stout  tendon  from  the  tuberosity  of  the  maxilla.  Its  two  heads 
of  origin  embrace  the  lower  fibres  of  the  external  pterygoid  muscle.  It  is  quadri- 
lateral in  form,  and  is  directed  downwards,  laterally,  and  backwards  over  the 
Eustachian  tube  and  the  tensor  and  levator  muscles  of  the  palate,  to  be  inserted 
into  a  triangular  impression  on  the  medial  surface  of  the  lower  jaw,  between  the 
mylo-hyoid  groove  and  the  angle  of  the  bone  (Fig.  319  I,  p.  402). 


Genio- 
glossns 
(origin) 


FlO.  319 />. 


-Muscle-Attachmknts  on  the  Medial  Side  of  the 
Lower  Jaw. 


MUSCLES  OF  MASTICATION. 


403 


Galpa  aponeurotica  -, 


Temporal  fascia 


Temporal  fascia  (deep 
layer) 


EpICRANIUS  Ml'SCLK 

Temporal  muscle 

Aiiriculo-tem])oral  nerve 

Superficial  temporal 
artery 

"  Masseter  (deep  fibres) 


Parotid  gland 

(drawn  backwards- 

and  downwards 


Orbicularis  oculi 

Caput  zyoomaticus 
M.  OF  quadratus 

LABII  SUPERIORIS 

Masseter  (superficial 

fibres) 

Stenson's  duct 


-^  Buccinator 

Triangularis 
(depressor  anguli  oris) 


Facial  artery 


Fig.  320.— Muscles  of  Mastication  (superficial  view). 


Temporal  muscle 


Buccinator 


Fig.  321. 


-The  Right  Temporal  Muscle  (the  zygonia  and  the  masseter  muscle  have  been  removed). 


404 


THE  MUSCULAE  SYSTEM. 


Nerve-Supply. 
Tlie  inferior  maxillary  division  of  the  fifth,  nerve  ^  supplies  all  the  muscles  of  mastication 
except  the  bueeiuator,  which  is  supplied  by  the  facial  nerve.     The  internal  pterygoid  muscle  is 
supplied  by  the  nerve  before  its  division  into  anterior  and  posterior  parts  ;  the  other  muscles  are 
innervated  by  the  anterior  trunk. 


Temporal  muscle  (reflected) 


/  I 

External  pterygoid 

Internal  pterygoid 


Pterygo-mandibiilar  ligament 

Bdccinator 
Fig.  322. — The  Pteeygoid  Muscles  of  the  Right  Side. 


Actions. 

The  above  muscles,  assisted  by  others  in  the  neck,  produce  the  various  movements  of  the 
lower  jaw,  as  follows  : — 


a.  Openin'g        and        Closure  of  the  Jaw. 


Weight  of  the  jaw 

Digastric 

Mylo-hyoid 

Genio-hyoid 

Genio-glossus 

Infra-hyoid  muscles 


Masseter 
Temporal 
Internal  pterygoid 


b.  Protrusion 


and 


Retraction. 


External  pterygoid 
Internal  pterygoid 
Temporal  {anterior  fibres) 


Temporal  {posterior  fibres) 


c.  Lateral  Movement  of  the  Jaw. 


^  fntS/  P*^'^^°'^}(«/''^«  ^de) 


THE   MUSCLES   OF   THE   NECK. 

In  addition  to  those  included  among  the  muscles  of  the  back  (p.  386),  the 
following  series  of  muscles  occur  in  the  neck  :  (1)  sterno-cleido-mastoid';  (2)  the 

^  The  3rd  or  inferior  maxillary  division  of  the  5th  =  the  mandibular  nerve  of  the  B.N. A.  classification. 


THE  MUSCLES  OF  THE  HYOID  BONE. 


405 


muscles  of  the  hyoid  bone  (supra-hyoid  and  infra-hyoid) ;  (3)  the  muscles  of  the 
tongue  (extrinsic  and  intrinsic) ;  (4)  the  muscles  of  the  pharynx  and  soft  palate  ; 
and  (5)  the  praevertebral  muscles. 

The  sterno-cleido-mastoid  muscle  is  the  prominent  muscle  projecting  on  the 
side  of  the  neck,  and  separating  the  anterior  from  the  posterior  triangle.  It  arises 
by  two  heads — (1)  a  narrow  tendinous  sternal  head,  from  the  anterior  surface  of 
the  manubrium  sterni  (Fig.  246,  p.  323),  and  (2)  a  broader  clavicular  origin,  partly 
tendinous,  partly  fleshy,  from  the  upper  surface  of  the  clavicle  in  its  medial  third 


Semispinalis  capitis  (complexus)  (insertion) 

Rectus  capitis  posterior  minor 
(insertion) 


Rectus  capitis  posterior  major 
(insertion) 


Trapezius  (origin) 


Sterno-cleido-mastoid 
(insertion) 


Splenius  capitis 
(insertion) 


Obliquus  capitis  superior' 
(insertion) 


Rectus  capitis  lateralis  (insertion) 


Rectus  capitis  anterior  (insertion^ 
(rectus  capitis  anterior  minor) 

Longus  capitis  (rectus  capitis  anterioi    V 

minor)  (insertion) 


Superior  constrictor  of  pharynx  (insertion) 


Fig.  323. — Muscle-Attachments  to  the  Occipital  Bone  (Parietal  Surface). 

(Fig.  325,  p.  407).  The  muscle  is  inserted  into  the  lateral  surface  of  the  mastoid 
process  and  into  the  superior  curved  line  of  the  occipital  bone  (Fig.  312,  p.  391). 
It  conceals  the  cervical  plexus  and  the  (spinaJ)  accessory  nerve.  The  last-named 
nerve  pierces  the  muscle. 

The  sterno-cleido-mastoid  muscle  is  properly  divisible  into  three  parts  :  (1)  sterno-mastoid, 
placed  superficially,  and  passing  obliquely  from  tbe  sternum  to  the  mastoid  process  ;  (2)  cleido- 
mastoid,  placed  more  deeply,  and  directed  vertically  upwards  from  the  clavicle  to  the  mastoid 
process  ;  and  (3)  cleido-occipitalis,  passing  obliquely  upwards  and  backwards  behind  the  cleido- 
mastoid  to  the  superior  curved  line  of  the  occipital  bone. 

Nerve-Supply. 

The  sterno-mastoid  muscle  is  innervated  by  the  (spinal)  accessory  nerve,  joined  by  a  branch 
from  the  cervical  plexus  (C.  2.). 

The  action  of  the  muscle  is  referred  to  below. 


The  Muscles  of  the  Hyoid  Bone. 

The  muscles  attached  to  the  hyoid  bone  are  in  three  series:  (1)  infra-hyoid 
muscles,  connecting  the  hyoid  bone  to  the  scapula,  thorax,  and  thyreoid  cartilage ; 

(2)  supra-hyoid  muscles,  connecting  it  to  the  lower  jaw,  cranium,  and  tongue ;  and 

(3)  the  middle  constrictor  muscle  of  the  pharynx  (p.  411). 

The  infra-hyoid  muscles  comprise  the  omo-hyoid,  sterno-hyoid,  sterno-thyreoid, 
and  thyreo-hyoid  muscles. 

The  omo-hyoid  is  a  muscle  with  two  beUies,  anterior  and  posterior.     The 


406 


THE  MUSCULAE  SYSTEM. 


posterior  belly  arises  from  the  superior  border  of  the  scapula  and  the  suprascapular 
ligament  (Fig.  250,  p.  326).  It  forms  a  narrow  muscular  band,  which  is  directed 
obliquely  forwards  and  upwards,  to  end  in  an  intermediate  tendon  beneath  the 
sterno-mastoid  muscle.  From  this  tendon  the  anterior  belly  proceeds  upwards  to 
be  inserted  into  the  lateral  part  of  the  lower  border  of  the  body  of  the  hyoid  bone. 

The  posterior  belly  of  the  muscle  separates  the  posterior  triangle  into  occipital 
and  subclavian  parts;  the  anterior  belly  crosses  the  common  carotid  artery  at  the 
level  of  the  cricoid  cartilage,  and  in  the  anterior  triangle  forms  the  boundary 
between  the  muscular  and  carotid  triangles.  A  process  of  the  deep  cervical  fascia 
binds  down  the  tendon  and  the  posterior  belly  to  the  scapula  and^^he  first  rib. 

The  sterno-hyoid  muscle  arises  from  the  posterior  surface  of  the  manubrium, 
from  the  back  of  the  first  costal  cartilage,  and  from  the  clavicle  (Fig.  243,  p.  320). 


STYLO-GLOSSUb; 

Stylo-hyoid 

ligament 

Stylo 

pharyngeus 

Stylo-hyoid— 


Digastric  (posterior- 
belly) 


Middle  coNSTRiCTOEm. 


— ^~f«Y-  -V-  Hyo-glossus 
■■*'~I-Genio-hyoid 


-Var ^aj^~  Sterno-thyreoid 

.Sterno-hyoid 


Fig.  324. — The  Mcscles  of  the  Tongue  and  Hyoid  Bone  (right  side). 


It  passes  vertically  upwards  in  the  neck,  medial  to  the  omo-hyoid  and  in  front  of 
the  sterno-thyreoid  muscle,  to  be  inserted  into  the  medial  part  of  the  body  of  the 
hyoid  bone.     Except  near  its  origin  the  muscle  is  superficially  placed. 

The  sterno-thyreoid  muscle  arises  beneath  the  sterno-hyoid  from  the  back  of 
the  manubrium  and  first  costal  cartilage.  Broader  than  the  preceding  muscle,  it 
passes  upwards  and  slightly  in  a  lateral  direction  in  the  neck  in  front  of  the  trachea 
and  thyreoid  body,  and  beneath  the  omo-hyoid  and  sterno-hyoid  muscles,  to  be  inserted 
into  the  oblique  line  of  the  thyreoid  cartilage.  The  muscle  is  marked  by  an  obhque 
tendinous  intersection  in  the  middle  of  its  length. 

The  thyreo-hyoid  muscle  continues  the  line  ot"  the  preceding  muscle  to  the 
hyoid  bone.  Short  and  quadrilateral,  it  arises  from  the  oblique  line  of  the  thyreoid 
cartilage,  and  passing  over  the  thyreo-hyoid  membrane  beneath  the  omo-hyoid  and 
sterno-hyoid,  it  is  inserted  into  the  body  and  great  cornu  of  the  hyoid  bone. 

The  levator  glandulse  thyreoideae  is  an  occasional  slip  stretcliing  between  the  hyoid  bone 
and  the  isthmus  or  pyramid  of  tlie  tliyreoid  body. 

The  supra-hyoid  muscles  comprise  the  digastric,  stylo-hyoid,  mylo-hyoid  and 


THE  MUSCLES  OF  THE  HYOID  BONE. 


407 


genio-hyoid  muscles,  and  also  two   muscles,  the   genio-glossus   and  hyo-glossus, 
which  will  be  described  along  with  the  extrinsic  muscles  of  the  tongue. 

The  digastric  muscle,  as  its  name  implies,  possesses  two  bellies — anterior  and 
posterior.  The  posterior  belly  arises  under  cover  of  the  sterno-mastoid  muscle  from 
the  digastric  groove  beneath  the  mastoid  process.  It  is  directed  forwards  and  down- 
wards, in  company  with  the  stylo-hyoid  muscle,  to  end  in  an  intermediate  tendon, 
which  is  connected  by  a  pulley-like  band  of  cervical  fascia  to  the  body  of  the  hyoid 
bone.  The  anterior  belly  of  the  muscle  is  directed  forwards  and  upwards  over  the 
mylo-hyoid  muscle  to  the  chin,  and  is  inserted  into  an  oval  impression  on  the  lower 


Sterso-cleido- 

MASTOID 


Semispinalis  capitis 
(com  plexus) 


Splenius  capitis 


Scalenus  ajjterior — 
Omo-hvoid 
Trapezius 


Mylo-hyoid 
Digastric 
Hyoglossus 
Stylo-hyoid 

JIlDDLE  constrictor 

Thyreo-hyoid 

Inferior 
constrictor 

0.M0-HY0ID 

Inferior 
constrictor 

Sterno-hyoid 
Sterno-thyreoid 


Fig.  325. — The  Muscles  of  the  Side  of  the  Neck  (anterior  and  posterior  triangles). 


border  of  the  mandible  close  to  the  symphysis  (Fig.  319  h,  p.  402).  The  muscle  forms 
the  lower  boundary  of  the  submaxillary  division  of  the  anterior  triangle. 

The  stylo-hyoid  muscle  arises  from  the  lower  border  of  the  styloid  process  of 
the  temporal  bone.  Crossing  the  anterior  triangle  obliquely  along  with  the 
posterior  belly  of  the  digastric  muscle,  it  is  inserted  into  the  body  of  the  hyoid 
bone  by  two  slips  which  enclose  the  tendon  of  the  digastric  muscle. 

The  mylo-hyoid  muscle  forms  with  its  fellow  a  diaphragm  in  the  floor  of  the 
mouth.  It  arises  from  the  lower  three-fourths  of  the  mylo-hyoid  ridge  of  the  lower 
jaw  (Fig.  319  &,  p.  402).  It  is  directed  downwards  and  medially,  to  be  inserted  into  (1) 
the  upper  border  of  the  body  of  the  hyoid  bone,  and  more  anteriorly  (along  with  the 
opposite  muscle)  into  (2)  a  median  raphe  extending  from  the  hyoid  bone  nearly  to 


408 


THE  MUSCULAE  SYSTEM. 


External  Ptery- 
goid (insertion) 


the  chin.      The  muscle  has  in  contact  with  its  superficial  or  lateral  surface  the 

digastric  muscle  and   the   submaxillary  gland.      Its    deep  or   medial   surface   is 

partially  covered  by  the 
mucous  membrane  of 
the  floor  of  the  mouth, 
and  is  separated  from 
the  muscles  of  the  tongue 
by  the  deep  part  of  the 
submaxillary  gland,  the 
sublingual  gland,  Whar- 
ton's duct  and  the  lingual 
and  hypoglossal  nerves. 
The  genio  -  hyoid 
muscle,  lying  beneath 
the  digastric  and  mylo- 
hyoid muscles,  arises 
from  the  lower  of  the 
two  mental  spines  on 
the  back  of  the  sym- 
physis of  the  lower  jaw 
(Fig.  326,  p.  408).  It 
is  directed  downwards 
and  backwards,  along 
the  lower  border  of  the 

genio-glossus,  to  be  inserted  into  the  front  of  the  body  of  the  hyoid  bone.     The 

muscles  of  opposite  sides  are  often  fused  together. 


Fig.  326. — Muscle-Attachments  on  the  Medial  Side  of  the 
Lower  Jaw. 


-,         ,.     ,.  Superior 

M.  transyersus    M.  yerticalis    longitudinal  muscle 
Imguse  linguae 


M.  vertiealis 
linguae 


The  Muscles  of  the  Tongue. 

The  muscular  substance  of  the  tongue  consists  of  two  symmetrical  series  of 
muscles  placed  on  either  side  of  a  membranous  raphe  in  the  middle  line.  The 
series  comprise  (1)  extrinsic  muscles  arising  from  the  soft  palate,  styloid  process, 
hyoid  bone  and  lower  jaw,  and  (2)  intrinsic  muscles  proper  to  the  tongue  itself. 
Each  set  consists  of  four 
series  of  muscles. 

The  extrinsic  muscles 
are  four  in  number :  (1) 
genio  -  glossus,  (2)  hyo  - 
glossus,  (3)  stylo  -  glossus, 
and  (4)  glosso-palatinus 
(palato- glossus). 

The  genio-glossus 
muscle  (genio-hyo-glossus) 
(Fig.  324,  p.  406)  is  an  ex- 
trinsic muscle  of  the  tongue 
as  well  as  a  supra-hyoid 
muscle.  It  is  a  fan-shaped 
muscle  arising  by  its  apex 
from  the  upper  of  the  two 
mental  spines,  behind  the 
symphysis  of  the  lower  jaw 
(Fig.  326,  p.  408).  From 
this  origin  the  muscular 
fibres  diverge;  the  lowest 
fibres  are  directed  down- 
wards and  backwards,  to  be  inserted  into  the  body  of  the  hyoid  bone ;  the  highest 
fibres  curve  forwards,  to  be  attached  to  the  tip  of  the  tongue ;  the  intermediate 
fibres  are  attached  to  the  substance  of  the  tongue  in  its  whole  length  between  the 
base  and  tip.     The  muscles  of  opposite  sides  are  separated  by  the  median  raphe  of 


.Septum 


M.  transversus 
B  lingUiB 
Inferior  longitudinal 
muscle 


Fig.  327. — A,  Transverse,  and  B,   Longitudinal  Vertical 
Sections  through  the  Tongue  (Krause). 


THE  MUSCLES  OF  THE  TONGUE.  409 

the  tongue.  On  the  lateral  aspect  of  each  are  the  hyo-glossus  and  mylo-hyoid 
muscles. 

The  hyo-glossus  muscle  is  also  an  extrinsic  muscle  of  the  tongue  as  well  as  a 
supra-hyoid  muscle.  It  arises  from  the  body  and  great  cornu  of  the  hyoid  bone, 
and  is  directed  upwards  and  forwards,  to  be  inserted  into  the  side  of  the  tongue, 
its  fibres  interlacing  with  the  fibres  of  the  stylo-glossus.  The  muscle  is  quadrilateral^ 
and  lies  between  the  genio-glossus  and  mylo-hyoid  muscles,  separated  from  the  latter 
by  the  mucous  membrane  of  the  floor  of  the  mouth,  the  sublingual  and  part  of  the 
submaxillary  glands,  the  lingual  and  hypoglossal  nerves,  and  Wharton's  duct. 

The  chondro-glossus  is  a  small  separated  slip  of  the  hyo-glossus,  not  always  present. 

The  stylo-glossus  muscle  arises  from  the  upper  border  of  the  styloid  process 
near  its  tip,  and  from  the  stylo-mandibular  ligament.  It  sweeps  forwards  and 
medially,  and  is  inserted  into  the  side  and  under  surface  of  the  tongue,  its  fibres 
spreading  out  to  decussate  with  those  of  the  palato-glossus  and  hyo-glossus  muscles 
beneath  the  parotid  gland  and  the  mucous  membrane  of  the  tongue. 

The  glosso-palatinus  (palato-glossus)  is  a  thin  sheet  of  muscular  fibres 
arising  from  the  under  surface  of  the  soft  palate,  where  it  is  continuous  with  fibres 
of  the  opposite  muscle.  It  passes  downwards  in  the  anterior  pillar  of  the  fauces, 
and  spreads  out,  to  be  inserted  into  the  sides  of  the  tongue,  blending  with  the 
stylo-glossus  and  the  deep  transverse  fibres  of  the  tongue.  The  muscle  is  placed 
directly  beneath  the  mucous  membrane  of  the  soft  palate  and  tongue. 

Intrinsic  Muscles  of  the  Tongue. — Besides  receiving  the  fibres  of  insertion 
of  the  extrinsic  muscles,  the  substance  of  the  tongue  is  composed  of  four  intrinsic 
muscles  on  either  side,  two  in  the  sagittal  plane,  the  superior  and  inferior  longi- 
tudinal muscles ;  two  in  the  coronal  plane,  the  transverse  and  vertical  muscles. 

The  superior  longitudinal  muscle  extends  from  base  to  tip  of  the  tongue.  It  is 
placed  on  its  dorsum  immediately  under  the  mucous  membrane,  into  which  many 
of  its  fibres  are  inserted. 

The  inferior  longitudinal  muscle  is  a  cylindrical  band  of  muscular  fibres  occupying 
the  under  part  of  the  organ  on  each  side,  in  the  interval  between  the  genio-glossus 
and  the  hyo-glossus  muscles.  Posteriorly  some  of  its  fibres  extend  to  the  hyoid  bone. 

The  transversus  linguae  (transverse  fibres)  arise  from  the  median  raphe,  and 
radiate  outwards  to  the  dorsum  and  sides  of  the  tongue,  intermingling  with  the 
extrinsic  muscles  and  the  fibres  of  the  vertical  muscle.  They  occupy  the  substance 
of  the  tongue  between  the  superior  and  inferior  longitudinal  muscles. 

The  so-called  verticalis  linguae  (vertical  fibres)  arise  from  the  dorsal  surface  of 
the  tongue,  and  sweep  downwards  and  laterally  to  its  sides,  intermingled  with  the 
fibres  of  the  previous  muscle  and  the  insertions  of  the  extrinsic  muscles.  These  two 
muscles  form  a  very  considerable  part  of  the  to.tal  muscular  substance  of  the  organ. 

Nerve-Supply. 

Most  of  the  muscles  of  the  hyoid  bone  and  tongue  are  supplied  by  the  hypoglossal  nerve, 
or  through  the  hypoglossal,  by  cervical  nerves  with  which  it  is  connected.  The  hypoglossal 
nerve  receives  a  communicating  branch  from  the  loop  between  the  first  and  second  cervical 
nerves,  which  thereby  directly  innervate  the  genio-hyoid  and  thyreo-hyoid  muscles,  and  con- 
stitute the  descendens  hypoglossi.  This  nerve  is  joined  by  the  descendens  cervicis  formed 
from  the  second  and  third  cervical  nerves,  to  form  the  ansa  hypoglossi,  from  which  branches  go 
to  the  omo-hyoid,  sterno-hyoid,  and  sterno-thyreoid  muscles.  The  genio-glossus,  hyo-glossus, 
stylo-glossus,  and  the  intrinsic  muscles  of  the  tongue  are  supplied  by  the  hypoglossal  nerve. 
The  glosso-palatinus  receives  its  nerve-supjily  from  the  spinal  accessory  nerve  ^  through  the 
pharyngeal  plexus.  The  mylo-hyoid  and  anterior  belly  of  the  digastric  are  supplied  by  the 
mylo-hyoid  branch  of  the  inferior  dental  nerve.-  The  posterior  belly  of  the  digastric  and  the 
stylo-hyoid  muscles  are  innervated  by  the  facial  nerve. 

Actions. 

These  muscles  have  a  complexity  of  action,  owing  to  their  numerous  attachments  to  more  or  less 
movable  points.  The  movements  for  which  they  are  responsible  in  whole  or  part  are  (1)  movements 
of  the  hyoid  bone  in  mastication  and  deglutition,  (2)  movements  of  the  thyreoid  cartilage,  (3)  move- 
ments of  the  tongue,  (4)  movements  of  the  head,  (5)  movements  of  the  shoulder,  and  (6)  respiration. 

(1)  Movements  of  the  Hyoid  Bone. — The  hyoid  bone  is  elevated  or  depressed,  and  moved  for- 
wards or  backwards  along  with  the  lower  jaw  and  tongue,  in  speech,  mastication,  and  swallowing. 

^  Spinal  accessory  =  accessory  nerve  (B.N.  A.).  -  Inferior  dental  nerve  =  inferior  alveolar  (B.N. A.). 


410 


THE  MUSCULAE  SYSTEM. 


a.  Elevation     and     Depression. 

b.  Protraction 

and     Retraction. 

Digastric 

Thyreo-hyoid 

Genio-hyoid 

Stylo-iiyoid 

Stylo-hyoid 

Sterno-hyoid 

]  Genio-glossus 

Middle  constrictor 

Mylo-hyoid 

Omo-hyoid 

Genio-liyoid 

Sterno-thyreoid 

■ 

Genio-glossus 

1 

Hyo-glossus 

Muscles    closing    tlie 

1 

mouth 

(2)  Movements  of  the  Thyreoid  Cartilage. 

during  speech  and  deglutition. 


-The  thyreoid  cartilage  is  raised  and  lowered 


Elevation. 

Depression. 

Sterno-thyreoid 
Crico- thyreoid 
Depressors  of  hyoid  bone 

Thyreo-hyoid 

Stylo-pharyngeus 

Pharyngo-palatinus  (palato-pharyngeus) 

Elevators  of  hyoid  bone 

Muscles  closing  mouth 

(3)  Movements  of  the  Tongue.— The  chief  movements  of  the  tongue  in  speech  and  de- 
glutition are  elevation  and  depression,  protrusion  and  retraction,  and  lateral  movements. 


Elevation      and      Depression. 


Stylo-glossus  (base) 

Glosso-palatinus 

Muscles  elevating  hyoid  bone 

Muscles  closing  mouth 


Genio-glossus 

Hyo-glossus 

Chondro-glossus 

Muscles  depressing  the  hyoid  bone 


h.  Protrusion 

and      Retraction. 

Genio-glossus  {•posterior  fibres) 

1         Genio-glossus  {anterior  fibres) 
1         Stylo-glossus 

c.  Lateral  Movements. - 

—The  muscles  of  one  side  only. 

] 

i 

(4)  Movements  of  the  Head. — The  sterno-mastoid  muscles,  acting  together,  flex  the  head  on 
the  spinal  column,  assisted  by  the  supra-hyoid  and  infra-hyoid  muscles.  The  sterno-mastoid 
muscle  of  one  side,  acting  alone,  bends  the  head  to  the  same  side,  and  simultaneously  rotates  it 
to  the  opposite  side,  as  seen  in  torticollis  (wryneck). 

(5)  Movements  of  the  Shoulder  Girdle. — The  omo-hyoid  and  sterno-mastoid  muscles  have 
already  been  included  among  the  elevators  of  the  shoulder  girdle. 

(6)  Respiration. — The  muscles  in  the  front  of  the  neck  are  auxiliary  muscles  in  extraordinary 
or  ditficidt  inspiration.  The  masseter  and  temjDoral  muscles  fix  the  lower  jaw  ;  the  hyoid  bone 
is  raised  and  fixed  by  the  supra-liyoid  muscles ;  and  the  sternum  is  raised  by  the  sterno-mastoid 
and  infra-hyoid  muscles. 

The  Muscles  of  the  Pharynx. 

The  muscular  envelope  of  the  pharynx  is  composed  of  two  strata.  The  external 
or  circular  layer  consists  of  the  three  fan-shaped  constrictor  muscles ;  the  internal 
or  longitudinal  layer  consists  of  the  fibres  of  the  stylo-pharycgeus  and  pharyngo- 
palatinus  (palato-pharyngeus)  muscles. 

The  superior  constrictor  muscle  arises  successively  from  the  lower  half  of 
the  posterior  Ijorder  of  the  medial  plate  of  the  pterygoid  process  (pterygo- 
pharyngeus),  from  the  pterygo-mandibular  ligament  (bucco-pharyngeus),  from 
the  mylo-hyoid  ridge  of  the  lower  jaw  (mylo-pharyngeus)  (Fig.  o26,  p.  408),  and 
from  the  mucous  membrane  of  the  floor  of  the  mouth  (glosso-pharyngeus). 
The  muscular  fibres  radiate  backwards,  and  are  inserted  for  the  most  part  into 
a  raphe  extending  down  the  posterior  wall  of  the  pharynx  in  the  middle 
line.  The  highest  fibres  are  attached  to  the  pharyngeal  spine  of  the  occipital 
bone  (Fig.  323,  p.  405),  and  the  lowest  fibres  are  overlapped"  by  the  middle 
constrictor.      A    crescentic    interval   occurs  above    the    muscle,    below    the   base 


THE  MUSCLES  OF  THE  PHAEYNX. 


411 


Fibrous  aponeurosis  of  the  pharynx 


Levator  \  eli 
palatini 

MUSCLE  (cut) 

Tensor  \r^j 

palatini 

superiop 

constrictor 

Buccinator 

Pterygo-mandi- 
bular  ligament 

St\lo 

pharyngeus 

Middle 
constrictor 


of  the  skull,  in  which  the  Eustachian  tube  and  the  levator  and  tensor  palati 
muscles  (levator  and  tensor  veli  palatini)  appear.  Its  lower  border  is  separated 
from  the  middle  constrictor  by  the  stylo-pharyngeus  muscle. 

The  middle  constrictor  muscle  arises  from  the  stylo -hyoid  ligament  and 
from  both  cornua  of  the  hyoid  bone  (chondro-pharyngeus,  cerato-pharyngeus). 
From  its  origin  the  muscular  fibres  radiate  backwards,  to  be  inserted  into  the 
medial  raphe  on  the  posterior  aspect  of  the  pharynx.  The  upper  fibres  overlap 
the  lower  part  of  the  superior  constrictor ;  the  lower  fibres  are  concealed  from  view 
by  the  inferior  constrictor  muscle.  In  the  interval  between  the  middle  and 
inferior  constrictors  are  found  the  superior  laryngeal  artery  and  nerve. 

The  inferior  constrictor  muscle  arises  from  the  oblique  line  of  the  thyreoid 
cartilage  (thyreo-pharyngeus),  and  from  the  side  of  the  cricoid  cartilage  (crico- 
pharyngeus).  Its  fibres  radiate  back- 
wards, to  be  inserted  into  the  median 
raphe  on  the  back  of  the  pharynx,  the 
upper  fibres  overlapping  the  lower  part  Eustachian  tube- 
of  the  middle  constrictor,  the  lower 
fibres  blending  with  the  muscular 
fibres  of  the  oesophagus.  Below  the 
lower  border  of  the  muscle  the  inferior 
laryngeal  artery  and  recurrent  nerve 
enter  into  relation  with  the  larynx. 

The  deeper  longitudinal  stratum 
of  muscles  in  the  pharyngeal  w^all 
is  composed  of  the  insertions  of  the 
stylo  -  pharyngeus  and  pharyngo  - 
palatinus  muscles. 

The  stylo-pharyngeus  arises  from 
the  root  of  the  styloid  process  on  its 
medial  side,  and  passes  downwards  be- 
tween the  externaland  internal  carotid 
arteries.  It  enters  the  wall  of  the 
pharynx  in  the  interval  between  the 
superior  and  middle  constrictor 
muscles.  Spreading  out  beneath  the 
middle  constrictor  muscle, it  is  inserted 
into  the  superior  and  posterior  borders 
of  the  thyreoid  cartilage  and  into  the 
wall  of  the  pharynx  itself,  becoming 
continuous  posteriorly  with  thepalato- 
pharyngeus.  In  the  neck  the  glosso- 
pharyngeal nerve  winds  round  it  on 
its  way  to  the  tongue. 

The  pharyngo-palatinus  (palato- 
pharyngeus)  occupies  the  soft  palate  and  the  pharyngeal  wall.  In  the  sub- 
stance of  the  soft  palate  it  consists  of  ttvo  layers,  a  postero-superior  layer,  thin, 
and  continuous  across  the  middle  line  with  the  corresponding  layer  on  the 
opposite  side,  and  an  antero-inferior  layer,  which  is  thicker,  and  is  attached  to  the 
posterior  border  of  the  hard  palate.  The  elevator  of  the  palate  and  uvular  muscles 
are  enclosed  between  the  two  layers,  which  unite  at  the  posterior  edge  of  the  palate, 
receiving  at  the  same  time  additional  fibres  arising  from  the  Eustachian  tube 
(salpingo-pharyngeus).  The  muscle  descends  to  the  pharynx  in  the  posterior 
pillar  of  the  fauces.  Its  fibres  spread  out  in  the  form  of  a  thin  sheet  in  the  wall 
of  the  pharynx,  in  continuity  anteriorly  with  the  stylo-pharyngeus,  and  are  inserted 
into  the  posterior  border  of  the  thyreoid  cartilage,  and  behind  that  into  the 
aponeurosis  of  the  pharynx,  reaching  down  as  far  as  the  lower  border  of  the  inferior 
constrictor.  The  muscle  is  placed  beneath  the  middle  and  inferior  constrictors  in 
the  pharyngeal'wall,  and  the  fibres  of  the  muscles  of  opposite  sides  decussate  in  the 
middle  line  in  the  lower  part  of  the  pharyngeal  wall. 

28 


Inferior  constrictor  ■ — 


Fig.  328. 


-Posterior  View  of  the  Pharynx  and 
Constrictor  Mdscles. 


412 


THE  MUSCULAE  SYSTEM. 


The   muscular  fold   is   composed   of   five 


The  IVIuscIes  of  the  Soft  Palate. 

The  soft  palate  and  uvula  form  a  muscular  fold,  covered  on  each  surface  by 
mucous  membrane,  projecting  backwards  into  the  pharynx,  and  forming  the  posterior 
part  of  the  floor  of  the  nose  and  the  roof  of  the  mouth. 

pairs  of  muscles — the  pharyngo- 
palatinus  (palato-pharyngeus),  m. 
uvulae  (azygos  uvulae),  levator  veli 
palatini,  tensor  veli  palatini  and 
glosso-palatinus  (palato-giossus). 
The  pharyngo-palatinus 
muscle  has  been  already  described 
(p.  411). 

The  m.  uvulae  (azygos  uvulae) 
consists   of    two    narrow   bundles 
enclosed,    along    with    the    inser- 
tion   of    the    elevator    muscle   of 
the      palate,     be- 
tween  the   layers 
of       the     "  pha- 
ryngo  -  palatinus. 
The     slips     arise 
from  the  posterior 
nasal  spine  and  the 
aponeurosis  of  the 
soft    palate,    and 
unite  as  they  pro- 
ceed backwards  to 
end  in  the  uvula. 
The     levator 
veli  palatini  has 
a    double    origin : 

(1)  from  the 
under  surface  of 
the  apex  of 
the  petrous  por- 
tion of  the  tem- 
poral   bone,    and 

(2)  from  the  lower 
part  of  the  car- 
tilaginous Eus  - 
tachian  tube.  It 
passes  obliquely 
downwards  and 
medially,      across 

the  upper  border  of  the  superior  constrictor  muscle,  and  enters  the  soft  palate  be- 
tween the  two  layers  of  the  pharyugo-palatinus  muscle.  It  is  inserted  into  the  aponeu- 
rosis of  the  soft  palate,  and  some  of  its  fibres  become  continuous  with  those  of  the 
opposite  muscle.  It  is  separated  from  the  tensor  veli  palatini  muscle  by  the 
Eustachian  tube  and  the  deeper  layer  of  the  pharyngo-palatinus  muscle. 

The  tensor  veli  palatini  arises  (1)  from  the  scaphoid  fossa  and  the  alar  spine 
of  the  sphenoid  bone,  and  (2)  from  the  lateral  side  of  the  cartilaginous  Eustachian 
tube.  It  descends  between  the  internal  pterygoid  muscle  and  the  internal  ptery- 
goid plate,  and  ends  in  a  tendon  which  hooks  round  the  pterygoid  hamulus,  and 
is  inserted  beneath  the  levator  veli  palatini  into  the  posterior  border  of  the 
hard  palate,  and  into  the  aponeurosis  of  the  soft  palate. 

The  glosso-palatinus  ri)alato-glossus),  occupying  the  under  surface  of  the  soft 
palate  and  the  anterior  pillar  of  the  fauces,  has  already  been  described  with  the 
muscles  of  the  tongue  (jj.  409). 


Buccinator 


Mylo-hvoid 

Hyo-olossl's 

Digastric 

Stvlo-hyoid 

Omo-hyoid 
Steeno-hyoid 

Thyreo-hyoid 


Crico-thyreoid. 


Tensor  veli  palatini 

MIISCLE 

Eustacliian  tube 
■Levator  veli  palatini 
Pterygo-iiiandibular 
ligament 
■Superior  constrictor 

.Stylo-pharyngeus 

Stylo-glossds 

.Glosso-pliaryiigeal 

nerve 

Stylo-hyoid  ligament 

Hypoglossal  nerve 

Middle  constrictor 

Digastric 
Superior  laryngeal 
nerve 

■Inferior  constrictor 


External  laryngeal 
'nerve 


CEsophagus 
Interior  laryngeal 
nerve 


Fig.  .329.— Lateral  View  of  the  Wall  ok  the  Pharynx. 


LATERAL  AND  PE^VERTEBEAL  MUSCLES  OF  THE  NECK.     413 

Nerve-Supply. 

Most  of  the  muscles  of  the  pharynx  and  soft  palate  are  innervated  by  the  (spinal)  accessory 
nerve,  through  the  pharyngeal  plexus.  These  muscles  include  the  constrictors  of  the  pharynx, 
glosso-palatinus  and  pharyngo-^ialatinus,  levator  veli  palatini  and  uvular  muscle.  The  tensor 
veli  palatini  is  supplied  by  the  trigeminal  nerve  through  the  otic  ganglion  ;  the  stylo- 
pharyngeus  by  the  glosso-pharyngeal  nerve.  In  addition  to  branches  from  the  pharyngeal 
plexus,  thf  inferior  constrictor  ruceives  tibres  from  the  external  ramus  of  the  superior 
laryngeal  nerve  and  from  the  recurrent  or  inferior  laryngeal  nerve. 

Actions. 

The  muscles  of  the  pharpix  and  soft  palate  are  chiefly  brought  into  action  in  the  act  of 
swallowing.  This  act  is  divided  into  a  voluntary  stage,  in  which  the  bolus  lies  m  front  of  the 
pillars  of  the  fauces,  and  an  involuntary  stage,  during  which  the  food  passes  from  the  mouth 
through  the  pharj-nx.  The  movements  occurring  during  the  passage  of  food  through  the  mouth 
are  as  follows  :  the  cheeks  are  compressed  by  the  action  of  the  buccinator  muscles  ;  the  tongue, 
hyoid  bone,  and  thyreoid  cartilage  are  successively  raised  upwards  by  the  action  of  the  muscles 
which  close  the  mouth  and  elevate  the  hyoid  bone.  By  these  means  the  food  is  pushed  back- 
wards between  the  pillars  of  the  fauces. 

At  the  same  time,  by  the  contraction  of  the  glosso-palatinus  and  pharyngo-palatinus,  the  pillars 
of  the  fauces  are  narrowed,  while  the  muscles  of  the  soft  palate,  contracting,  tighten  the  soft  palate, 
and  by  bringing  it  in  contact  with  the  posterior  wall  of  the  pharynx,  shut  off  the  upper  (nasal) 
portion  of  the  cavity.  The  elevation  of  the  tongue,  hyoid  bone,  and  larynx  simultaneously  causes 
the  elevation  of  the  epiglottis  and  the  aperture  of  the  glottis,  which  is  closed  by  the  approxima- 
tion of  the  arytsenoid  cartilages  and  the  combined  action  of  laryngeal  muscles  (aryta^noideus, 
thj-reo-arytsenoideus,  and  thyreo-epiglotticus).  The  food  thus  slips  over  the  posterior  surface  of 
the  epiglottis  and  the  closed  aperture  of  the  glottis,  and  between  the  pillars  of  the  fauces  on 
either  side,  into  the  pharynx.  It  is  now  clasped  by  the  constrictor  muscles,  which,  by  their 
contractions,  force  it  do\vn  into  the  oesophagus.  The  contraction  of  the  constrictor  muscles  results 
in  a  flattening  of  the  pharjnix  and  elevation  of  its  anterior  attachments. 

During  the  act  of  swallowing,  it  is  generally  thought  that  the  Eustachian  tube  is  opened  by 
the  contraction  of  the  tensor  veli  palatini  muscle  which  arises  from  it.  It  has  been  held,  on 
the  other  hand,  that  the  Eustachian  tube  is  closed  during  swallowing  by  the  compression  of  its 
waU  by  the  contraction  of  the  levator  veli  palatini. 


Serratus  posterior 
superior  (insertion) 


Deep  Lateral  and  Praevertebral  IVIuscIes  of  the  Neck. 

Three  series  of  muscles  are  comprised  in  this  group  :  (1)  vertebro-costal  (scaleni, 
anterior,  medius,  and  pos- 
terior), (2)  vertebro- cranial 
(longus  capitis  and  rectus 
capitis  anterior,  and  lateralis), 
and  (3)  vertebral  (longus 
colli).  They  clothe  the  front 
of  the  cervical  portion  of 
the  vertebral  column  for  the 
most  part,  and  are  in  relation 
anteriorly  with  the  pharynx 
and  cesophagus,  and  the  large 
vessels  and  nerves  of  the  neck. 

The  scalenus  anterior 
arises  from  the  anterior 
tubercles  of  the  transverse 
processes  of  the  third,  fourth, 
fifth,  and  sixth  cervical  ver- 
tebrae, and  descends  behind 
the  carotid  sheath  and  sub- 
clavian vein,  to  be  inserted 
into  the  scalene  tubercle 
and  ridge  on  the  first  rib 
(Fig.  33^0,  p.  413).  It  is 
separated  posteriorly  from 
the  scalenus  medius  by  the 
cords  of  the  brachial  plexus, 
the  subclavian  artery,  and 
the  pleura. 


Serratus  anterior 

(s.  niagnus) 

(origin) 


Pectoralis  minor  (occasional  origin) 


Fig.  330.— Muscle -Attachments  to  the  Upper  Surface  of  the 

FlKST     ElB,    AND    THE    LATERAL    SURFACE    OF    THE    SECOND    RiB 

(Right  Side).  a,  First  rib  ;  B,  Second  rib. 


414 


THE  MUSCULAE  SYSTEM. 


Rectus  capitis 
anterior 


lateralis 
Rectus  capitis 


LOXCUS  CAPITIS 


The  scalenus  medius  arises  from  the  posterior  tubercles  of  the  transverse  processes 

of  the  cervical  vertebrae,  from 
the  second  to  the  sixth  in- 
clusive.    It  descends  in  the 
',  posterior  triangle  behind  the 
^  subclavian    artery   and    the 
Rectus  capitis  cords  of  the  brachial  plexus, 
to  be  inserted  into  the  rough 
impression  on  the   first   rib 
behind  the  subclavian  groove 
(Fig.     330,   p.    413).       The 
muscle    is    pierced    by    the 
posterior  scapular  and  pos- 
terior thoracic  nerves.^  . 

The  scalenus  posterior 
arises  behind  the  scalenus 
medius  from  the  posterior 
tubercles  of  the  fourth,  fifth, 
and  sixth  cervical  transverse 
processes,  and  is  inserted  into 
an  impression  on  the  lateral 
side  of  the  second  rib. 

The  longus  capitis 
(rectus  capitis  anterior 
major)  arises  from  the  an- 
terior tubercles  of  the  trans- 
verse processes  of  the  third, 
fourth,  fifth,  and  sixth  cervi- 
cal vertebrae.  It  forms  a  flat 
triangular  muscle,  which  is 
directed  upwards  alongside 
the  longus  colli  muscle  and 
behind  the  carotid  sheath,  to  be  inserted  into  an  impression  on  the  under  surface  of 


Longus  colli 


Fig.  331. — The  Pr.evertebRx\l  Muscles  of  the  Neck. 


Posterior 

tuberoles  of 

transverse 

processes 


Scalenus  medius 

Levator  scapul.13 

Splenius  colli 


Scalenus  posterior 
Ilio-costalis  cervicis 
lonoissimus  cervicis 


Scalenus 
anterior 

lonous  capitis 

"(rectus  CAPITIS 
ANTERIOR 
.MA.IOU) 

Longus  colli 


Anterior 
tubercles  of 
"transverse 
roccsses 


r     LONOISSIMUS  CAPITIS 

Articular  I    Semispinalis  capitis 

processes"!  Semispinalis  cervicis 

V.  Multifidus 


Fig,  332. — Scheme  of  Muscular  Attachments  to  Ckhvical  Vertebra.. 

the  basilar  process  of  the  occipital  bone,  anterior  and  lateral  to  the  pharyngeal  spine 
(Fig.  333,  p.  415). 

^  Posterior  scapular  nerve  =  dorsal  nerve  of  scapula  (B.N.  A.). 
Posterior  thoracic  nerve  =  long  thoracic  nerve  (B.N. A.). 


THE  MUSCLES  OF  THE  THOKAX. 


415 


The  rectus  capitis  anterior  (rectus  capitis  anterior  minor)  arises  under  cover 
of  the  previous  muscle  from  the  anterior  arch  of  the  atlas,  and  is  inserted  into  the 
basilar  process  between  the  previous  muscle  and  the  occipital  condyle  (Fig.  333,p.415). 

The  longus  colli  is  a  flattened  muscular  band  extending  from  the  third  thoracic 
vertebra  to  the  atlas.  It  i|^  divisible  into  three  portions — a  vertical,  a  lower 
oblique,  and  an  upper  oblique  portion. 

The  vertical  portion  of  the  muscle  arises  from  the  bodies  of  the  first  three 
thoracic  and  the  last  three  cervical  vertebra} ;  and  passing  vertically  upwards,  it  is 
inserted  into  the  bodies  of  the  second,  third,  and  fourth  cervical  vertebrae. 

The  lower  oblique  portion  arises  from  the  bodies  of  the  first  three  thoracic  vertebrse, 
and  is  inserted  into  the  anterior  tubercles  of  the  fifth  and  sixth  cervical  vertebrre. 

The  upper  oblique  portion  arises  from  the  anterior  tu})ercles  of  the  transverse 

Semisiiinalis  capitis  (iiiserLioii) 
Rectus  capitis  posterior  minor         \,^-^  ^>^   Trapezius  (origin) 

(insertion) 
\ 
Rectus  capitis  posterior  major 
(insertion) 

Sterno-cleido-niastoid 
(insertion) 

Splenius  capitis 
(insertion) 


Obliquus  capitis  supenoi 
(inseition) 


Rectus  capitis  lateralis  (insertion) 

Rectus  capitis  anterior  (insertion) 


Superior  constrictor  of  jjharynx  (insertion) 


Lonjjus  capitis  (in->eition) 


Fig.  333. — Muscle-Attachjie^'ts  to  the  Occipital  Bone  (Inferior  Surface). 

processes  of  the  third,  fourth,  and  fifth  cervical  vertebrte,  and  is  directed  upwards, 
to  be  inserted  into  the  anterior  tubercle  of  the  atlas. 

The  rectus  capitis  lateralis,  in  series  with  the  posterior  inter -transverse 
muscles  in  the  neck,  arises  from  the  transverse  process  of  the  atlas,  and  is  inserted 
into  the  under  surface  of  tlie  jugular  process  of  the  occipital  bone.  It  is  placed 
alongside  the  rectus  capitis  anterior,  separated  from  it  by  the  anterior  primary 
division  of  the  first  cervical  nerve. 

Nerve-Supply. 

The  prteverteLral  muscles  are  all  suj^phed  by  anterior  ijrimary  divisions  of  the  cervical  spinal 
nerves  :  the  rectus  capitis  anterior,  and  rectus  capitis  lateralis,  by  the  looj)  between  the  first 
two  nerves  ;  the  longus  capitis  (rectus  capitis  anterior  major)  by  the  first  four  ;  the  longus  colli 
by  the  second,  third,  and  fourth  ;  the  scaleni  by  the  loM'er  four  or  five  cervical  nerves. 

Actions. 

The  movements  produced  by  these  muscles  are  considered  along  with  those  of  other  muscles 
acting  on  the  head,  siDinal  column,  and  thorax  (pp.  392,  395). 

THE   MUSCLES   OF   THE    THORAX. 
Muscles  of  Respiration. 

The  muscles  which  complete  the  boundaries  of  the  thorax  are  the  diaphragm 
and  intercostal  muscles  (external  and  internal),  along  with  three  series  of  smaller 
muscles— the  transversus  thoracis  (triangularis  sterni),  the  levatores  costarum, 
and  the  subcostal  muscles. 


416 


THE  MUSCULAR  SYSTEM. 


The  intercostal  muscles  are  arranged  in  eleven  pairs,  which  occupy  the  inter- 
costal spaces. 

Each  external  muscle  arises  from  the  sharp  lower  l)order  of  a  rib,  and 
is  directed  downward  and  forward,  to  be  inserted  into  the  lateral  edge  of  the 
upper  border  of  the  rib  below.  It  extends  from  the  tubercle  of  the  rib  behind 
nearly  to  the  costal  cartilage  in  front.  The  anterior  intercostal  aponeurosis  is 
continuous  with  it  anteriorly,  and  extends  forwards  to  the  side  of  the  sternum. 

Each  internal  muscle  arises  from  the  costal  cartilage  and  the  medial  edge  of  the 
subcostal  groove,  and  is  directed  downwards  and  backwards,  to  be  inserted  into  the 
medial  edge  of  the  upper  border  of  the  rib  and  costal  cartilage  below.     It  extends 


External  intekcostal 

MUSCLE 


Obliqdds  externus. 
ABDOMINIS  (reflected) 


Anterior  intercostal 
membrane 


Internal  inter- 
costal MUSCLE 


Rectus  abdominis- 
(insertion) 


Sheath  of  the  rectus 
abdominis 


Fig.  334. — The  Muscles  of  the  Right  Thokacic  Wall. 

from  the  side  of  the  sternum  in  front  to  the  angle  of  the  rib  behind,  where  it 
becomes  continuous  with  the  'posterior  intercostal  aponeurosis  extending  to  the 
tubercle  of  the  rib. 

The  superficial  surface  of  the  external  muscle  is  covered  by  the  muscles  of 
the  chest,  axilla,  abdomen,  and  back.  The  deep  surface  of  the  internal  muscle  is  in 
contact  with  the  pleura. 

The  levatores  costarum  are  in  series  with  the  external  intercostal  muscles.  They 
are  twelve  small  sH})S  arising  from  the  transverse  processes  of  the  seventh  cervical 
and  upper  eleven  thoracic  vertebne.  They  spread  out  in  a  fan-like  manner  as  they 
descend,  to  be  inserted  into  the  lateral  surface  of  each  of  the  ribs  posterior  to  the  angles. 

The  subcostal  muscles  are  slips  of  muscles  found  on  the  medial  surface 
of  the  lower  ribs  near  their  angles.  They  are  in  series  with  the  internal  inter- 
costal muscles,  but  pass  over  the  deep  surface  of  several  ribs. 

The  transversus  thoracis  (triangularis  sterni)  occupies  the  posterior  aspect 


THE  MUSCLES  OF  THE  THOEAX. 


417 


of  the  anterior  thoracic  wall,  and  is  separated  from  the  costal  cartilages  by  the 
internal  mammary  vessels.  It  arises  from  the  back  of  the  ensiform  cartilage 
and  mesosternum  as  high  as  the  level  of  the  third  costal  cartilage.  From  this 
origin  its  fibres  radiate  laterally,  the  lower  horizontally,  the  upper  fibres  obliquely 
upwards,  to  be  inserted  into  the  costal  cartilages  of  all  the  sternal  ribs  except  the 
first  and  seventh.  The  muscle  is  continuous  below  with  the  transversus  abdominis. 
The  diaphragm  is  the  great  membranous  and  muscular  partition  separating 
the  cavities  of  the  thorax  and  abdomen.  It  forms  a  thin  lamella  arching  over 
the  abdominal  cavity,  and  clothed  on  this  surface  for  the  most  part  by  peritoneum. 
It  is  related  on  its  lower  concave  surface  to  the  liver,  stomach,  and  spleen,  the 
kidneys  and  suprarenal  capsules,  and  the  duodenum  and  pancreas.  Its  upper 
convex  surface  projects  into  the  thoracic  cavity,  rising  higher  on  the  right  than  on 


(Esophagus  and  its 
opening 


Foramen  qnaJratuni 
(for  inferior  vena  cava)^^ 


Middle  arcuate  liga-' 
ment  (in  front  of 
aortic  openin 


-_-    -    Ual  arcuate 
'  ''    hgament 
^ —    Lateral  arcuate 
ligament 

QUADRATUS  LUMBORUM 
MUSCLE 


Right  cru3  of  diaphragm 

Fig.  335. — The  Diaphragm  (fioni  below). 


Psoas  muscle 
diaphragm 


the  left  side,  and  is  related  to  the  pericardium  and  pleurae,  and  along  its  margin  to 
the  chest  wall.    The  oesophagus  and  thoracic  aorta  are  in  contact  with  it  posteriorly. 

It  possesses  a  peripheral  origin  from  the  sternum,  ribs,  and  vertebral  column, 
and  an  insertion  into  a  central  tendon.  It  arises  (1)  anteriorly  (pars  stemalis)  from 
the  posterior  surface  of  the  ensiform  cartilage  by  two  slender  fleshy  slips,  directed 
backwards  ;  (2)  laterally  (pars  costalis),  from  the  deep  surface  of  the  lower  six  costal 
cartilages  on  each  side  by  fleshy  bands  which  interdlgitate  with  those  of  the  trans- 
versus abdominis ;  (3)  'posteriorly  (pars  liimbalis),  from  the  lumbar  vertebrse,  by 
the  crura,  and  the  arcuate  ligaments  (medial  and  lateral  lumbo-costal  arches). 
The  crura  are  two  elongated  fibro-muscular  bundles  which  arise  on  each  side  of  the 
aorta  from  the  front  of  the  bodies  of  the  lumbar  vertebrae,  on  the  right  side  from 
the  first  three,  on  the  left  side  from  the  first  two  lumbar  vertebrse.  They  are 
directed  upwards  and  decussate  across  the  middle  line  in  front  of  the  aorta,  the 
fibres  of  the  right  cms  passing  in  front  of  those  of  the  left  crus.  The  fibres  then 
encircle  the  oesophagus,  forming  an  elliptical  opening  for  its  passage,  and  finally 
join  the  central  tendon,  after  a  second  decussation  in  front  of  the  gullet. 

The  arcuate  ligaments  (arcus  lumbo-costales  Halleri)  are  five  in  number. 

The  middle  arcuate  ligament  is  a  fibrous  arch  connecting  together  the  crura  of 
the  diaphragm  in  front  of  the  aorta,  and  giving  origin  to  fibres  (crus  mediale)  which 
join  the  crura  as  they  decussate  to  encircle  the  gvillet. 


418 


THE  MUSCULAR  SYSTEM. 


The  medial  arcuate  ligament  (arcus  lumbo-costalis  medialis)  is  a  thickening 
formed  by  the  attachment  of  the  psoas  fascia  to  the  body  of  the  first  lumbar 
vertebra  medially  and  its  transverse  process  laterally.  Stretching  across  the  upper 
end  of  the  psoas  muscle,  the  ligament  gives  origin  to  muscular  fibres  directed 
upwards  on  each  side  of  the  crura. 

The  lateral   arcuate  ligament  (arcus  lumbo-costalis  lateralis)  is  the  thickened 


Opening  for  inferior  vena  cava     (Ksophageal  opening  Central  tendon  (middle  part) 


Central  tendon  (right  pait) 

Diaphragm,  costal  fibhts 

Medial  arcuate  ligament 

Lateral  arcuate  ligament 

End  of  last  rib 

Last  thoracic  ner\  e 

Tendon  of  transversus  abdominis 

Transversus  abdominis 

Ilio-hypogastric  nerve  — ^ — 

Lumbar  vessels  and  sympa-       ' 
thetic  communicating  nerves 
Uio-inguinal  uer\e 


QUADRATCS  LUilBORUM 


External  cutaneous  nen  e 

Psoas  major 

Iliacds 

Lumbo-sacral  coid 

Genito-crural  (genito 

2  femoral)  nerve 

Anterior  crural  (femoral)  nerv  r 

Obturator  nerv  c 

Great  sciatic  nerv  < 


Diaphragm,  right  crus 

Aliddle  arcuate  ligament 
Aoitic  opening 

Central  tendon 
(left  part) 
Diaphragm,  left 

CRUS 


Last  thoracic  nerve 
End  of  last  rib 
Lumbar  nerve  L 

^ r-j'f'ii' — Uio-hypogastric  nerve 

-Lumbar  nerve  II. 


Iho  inguinal  nerve 
Quadratus 
lumborom 
Lumbar  nerve  III. 

Genito-crural  (genito- 
fpnioral)  nerve 

Lumbar  nerve  IV. 


Lumbo-sacral  cord 


lj\tHinal  cutaneous  nerve 
inteiioi  crural  (femoral) 
nerve 
Obturator  nerve 

Great  sciatic  nerve 


Fig.  336. 


I  Adductor  brevis  (origin) 
Gracilis  (origin) 
Adductor  magnus  (origin) 
I    Pectineus  (cut) 

Superficial  branch  of  obturator  nerve 
I      Deep  branch  of  obturator  nerve 
Obturator  e-xternum 

-View  of  the  Postekioe  Abdominal  Wall,  to  show  the  Muscles  and  the  Nerves  of 
THE  Lumbo-Sackal  Plexus. 


upper  border  of  the  fascia  over  the  quadratus  lumborum  muscle  (anterior  layer 
of  the  lumbar  fascia),  and  is  attached  medially  to  the  transverse  process  of 
the  first  lumbar  vertebra,  and  laterally  to  the  last  rib.  It  gives  origin  to  a 
broad  band  of  muscular  fibres,  separated  by  an  interval  from  the  fibres  arising 
from  the  medial  arcuate  ligament  which  sweep  upwards  to  the  central  tendon. 

From  this  extensive  origin  the  muscular  fibres  of  the  diaphragm  converge  to 
an  insertion  into  a  large  trilobed  central  tendon  (centrum  tendineum").  Of  its  lobes 
the  right  one  is  the  largest,  the  middle  or  anterior  is  intermediate  in  size,  and  the 


FASCIA  AND  MUSCLES  OF  ABDOMINAL  WALL.  419 

left  is  the  smallest.  It  does  not  occupy  the  centre  of  the  muscle,  being  placed 
nearer  the  front  than  the  back.  The  fibres  of  the  crura  are  consequently  the 
longest ;  those  from  the  sternum  are  the  shortest. 

The  diaphragm  is  pierced  by  numerous  structures.  The  superior  epigastric 
artery  enters  the  sheath  of  the  rectus  abdominis  lietween  its  sternal  and  costal 
origins ;  the  musculo-phrenic  artery  passes  between  its  attachments  to  the  seventh 
and  eighth  ribs.  The  sympathetic  cord  and  the  splanchnic  nerves  pierce,  or  pass 
behind  the  diaphragm ;  the  last  thoracic  nerve  passes  beneath  the  lateral 
arcuate  ligament ;  and  the  aorta,  the  azygos  vein,  and  thoracic  duct  pass  between 
the  crura,  underneath  the  middle  arcuate  ligament  {aortic  opening  or  hiatus  aorticus). 
The  special  foramina  are  two  in  number.  T\\q  foramen  quadratum  {foramen  vence 
cavcc)  in  the  right  lobe  of  the  central  tendon  transmits  the  iuferior  vena  cava,  and 
small  branches  of  the  right  phrenic  nerve.  The  oesophageal  opening  {hiatus 
cesophageus)  is  in  the  muscular  substance  of  the  diaphragm,  behind  the  central 
tendon,  and  is  surrounded  by  a  sphincter -like  arrangement  of  the  crural  fibres. 
Besides  the  oesophagus,  this  opening  transmits  the  two  pneumogastric  nerves. 

The  diajihragiu  is  found  as  a  complete  septum  between  the  thorax  and  abdomen  only  in 
mammals.  It  is  occasionally  deficient  in  the  human  subject,  producing  hernia  of  the  diaphragm, 
either  into  the  pericardial  cavity  through  the  central  tendon,  or  into  the  thoracic  cavity  through 
the  lateral  portions  of  the  muscle.  A  rare  condition  is  congenital  deficiency  of  a  part  of  the 
lateral  half  of  the  muscle,  generally  placed  posteriorly,  and  on  the  left  side.  This  produces,  by 
continuity  of  the  pleural  and  peritoneal  cavities  behind  the  diaphragm,  a  congenital  diaphragmatic 
hernia. 

Nerve-Supply. 

The  intercostal  muscles,  levatores  costarum,  subcostal  muscles,  and  transversus  thoracis,  are 
all  supplied  by  the  anterior  primary  divisions  ^  of  the  thoracic  (intercostal)  nerves.  The  diaphragm 
receives  its  chief,  if  not  its  entire,  motor  supply  from  the  phrenic  nerves  (C.  3.  4.  5.).  It  is  in- 
nervated also  by  the  diaphragmatic  plexus  of  the  sympathetic,  and  is  sometimes  said  to  receive 
fibres  from  the  lower  intercostal  nerves. 

Actions. 

The  act  of  respiration  consists  of  two  opposite  movements — inspiration  and  expiration. 

1.  The  movement  of  expiration  is  performed  by  (1)  the  elasticity  of  the  lungs,  (2)  the  weight 
of  the  chest  walls,  (3)  the  elevation  of  the  diaphragm,  (4)  the  action  of  muscles — transversus 
thoracis  and  muscles  of  the  abdominal  wall.  It  is  sometimes  stated  that  the  interosseous  fibres  of 
the  internal  intercostal  muscles  are  depressors  of  the  ribs. 

2.  The  movement  of  inspiration  results  in  the  enlargement  of  the  thoracic  cavity  in  aU 
its  diameters.  Its  antero-posterior  and  transverse  diameters  are  increased  by  the  elevation  and 
forward  movement  of  the  sternum,  and  by  the  elevation  and  eversion  of  the  ribs,  while  its 
vertical  diameter  is  increased  by  the  descent  of  the  diaphragm. 

The  muscles  of  inspiration  are  divided  into  two  series — ordinary  and  accessory. 


a.  Ordinary  Muscles. 

h.  Extraordinary  and  Accessory  Muscles. 

Diaphragm 

Intercostals 

Scaleui 

Serrati  posteriores 

Levatores  costarum 

Subcostales 

Quadra tus  lumborum 

Pectorales 

Serratus  anterior  (magnus) 

Sterno-mastoid 

Latissimus  dorsi 

Infra-hyoid  muscles 

Extensors  of  the  spine 

Of  the  ordinary  muscles  the  diaphragm  is  the  most  important.  Its  action  is  twofold — 
centrifugal,  elevating  the  ribs  and  increasing  the  transverse  and  antero-posterior  diameters  of 
the  thorax,  and  centripetal,  drawing  downwards  the  central  tendon  and  increasing  the  vertical 
diameter  of  the  thorax.  Of  the  two  movements  the  former  is  the  more  important.  There  has 
been  considerable  diversity  of  opinion  regarding  the  action  of  the  intercostal  muscles.  It  is 
generally  agreed  that  the  external  muscles  eleA-ate  the  ribs ;  it  is  probable  that  the  whole  of  each 
internal  muscle  acts  in  the  same  way,  although  it  has  been  stated  by  difterent  observer  that  the 
whole  internal  muscle  is  a  depressor ;  or  that  the  interosseous  part  is  a  dej)ressor,  the  inter- 
chondral  portion  of  the  muscle  an  elevator  of  the  ribs. 

FASCIAE  AND  lYIUSCLES  OF  THE  ABDOIVIINAL  WALL. 

The  space  between  the  base  of  the  bony  thorax  and  the  pelvis  is  filled  up  by 
a  series  of  muscular  sheets,  covered  externally  and  internally  by  fascite. 

^  Anterior  primary  divisions  =  anterior  rami  (B.X.A.). 


420 


THE  MUSCULAE  SYSTEM. 


FASCIiE. 

The  fasciae  of  the  abdominal  wall  q.xq— externally ,  the  superficial  and  deep  fasciae  ; 
internalhj,  the  fascia  transversalis,  which  is  continuous  with  the  diaphragmatic, 
lumbar,  psoas,  iliac,  and  pelvic  fasciae,  and  is  Hned  within  by  the  extraperitoneal 
tissue. 

The  superficial  fascia  of  the  abdomen  is  liable  to  contain  a  large  quantity 
of  fat.  In  the  groin  it  is  separated  into  hvo  layers :  a  superficial  fatty  layer  con- 
tinuous over  Poupart's  inguinal  ligament  with  the  fascia  of  the  front  of  the  thigh 
(p.  353),  and  a  deeper  membranous  layer  attached  to  the  medial  half  of  Poupart's 


Linea  alba" 


Lig.  fundiforme  penis" 


Subcutaneous   \.-\ 
inguinal  riii^""]»*~' 
Superior  pill  it  -A 
Inferior  pill  u  — 

Spermatic  coi  1-*— 


Intercrural  fibn  ^ 

Dorsal  vein  of  penis 

Dorsal  arti'i  \  - 
Dorsal  iiei\     —  - 


Obliquus  Bxteenus 

abdominis 


Anterior  superior 
iliac  spine 


External  oblique 
Liponeurosis 

•Superficial  circum- 
flex iliac  artery 

— Intercrural  fibres 

( Attachment  of  mem- 
—  l  branous  layer  of 

(  superficial  fascia 
■""Ir'oupart's  inguinal 
ligament 

...Superficial  inferior 
epigastric  artery 


Superior  external 
pudendal  artery 

.Femoral  lymphatic 
gland 


Large  saphenous 
vein  (internal) 


Fig.  -337  ff. — Supkhi-icial  Anatomy  of  the  Gkoin. 

ligament,  and  more  laterally  to  the  fascia  lata  of  the  thigh  below  Poupart's  ligament. 
The  two  layers  are  separated  by  the  lymphatic  glands  and  the  superficial  vessels  of 
the  groin.  Higher  up  in  the  abdominal  wall  the  two  layers  blend  together. 
Passing  downwards  over  the  spermatic  cord,  they  unite  to  ibrm  the  fascfa  and 
dartos  muscle  of  the  scrotum.  The  attachment  of  the  fascia  to  the  groin  prevents 
the  passage  into  the  thigh  of  fluid  extravasated  in  the  abdominal  wall. 

The  deep  fascia  of  the  abdominal  wall  resembles  similar  fasciae  in  other  situa- 
tions. It  forms  an  investment  for  the  obliquus  externus  muscle,  and  becomes  thin 
and  almost  imperceptible  in  relation  to  the  aponeurosis  of  tliat  muscle. 

The  fascial  lining  of  the  abdominal  cavity  (fascia  transversalis)  consists  of  a 
continuous  layer  of  membrane  which  receives  different  names  in  dilTercnt  parts  of 
its  extent.  It  covers  the  deep  surface  of  the  transversus  muscle,  and  is  continuous 
medially  (through  the  lumbar  fascia)  with  the  fasciae  of  the  quadratus  lumborum 


THE  MUSCLES  OF' THE  ABDOMINAL  WALL. 


421 


and  the  psoas  muscles.  It  is  continuous  above  with  the  diaphragmatic  fascia, 
and  below  the  ihae  crest  and  Poupart's  ligament  with  the  fascia  iliaca.  Along 
with  the  last-named  fascia  it  forms  the  femoral  sheath,  enclosing  the  femoral  vessels 
and  the  femoral  canal  in  their  passage  to  the  thigh  behind  the  medial  part 
of  Poupart's  ligament  (p.  356).  It  is  pierced  by  the  spermatic  cord  or  round 
ligament  of  the  uterus  at  the  abdominal  or  deep  inguinal  ring  (annulus  inguinalis 
abdominalis),  and  its  prolongation  into  the  inguinal  canal  around  the  cord  forms 
the  infundibuliform  fascia.  It  is  lined  internally  by  the  peritoneum,  from  which  it 
is  separated  by  a  layer  of  extraperitoneal  tissue. 

The  extraperitoneal  tissue  is  usually  loaded  with  fat ;  it  envelops  the  kidneys, 
ureters,  suprarenal  capsules,  abdominal  aorta  and  inferior  vena  cava  and  their 
branches,  and  forms  sheaths  for  the  vessels  and  ducts  (ureter,  vas  deferens, 
etc.).  It  is  continued  upwards  into  the  posterior  mediastinum  of  the  thorax 
through  the  aortic  opening  in  the  diaphragm,  and  below  is  in  continuity  with  the 
extraperitoneal  tissue  in  the  pelvis.  It  not  only  completely  invests  the  kidneys 
and  suprarenal  capsules,  but  it  also  becomes  interpolated  between  the  layers  of 
peritoneum  upholding  and  enveloping  the  intestines.  This  tissue  is  absent  in 
relation  to  the  diaphragm,  on  the  under  surface  of  which  there  is  no  fat. 

THE  MUSCLES  OF  THE  ABDOMINAL  WALL. 

Themusclesof  the  abdominal  wall  are  in  threeseries — lateral,  anterior,  and  posterior. 


Obliquus  externds 
abdominis' 
(reflected) 


Spermatic  cord- 
Intercolumuar  fascia' 


Obliquus  externus 
abdominis 


Obliquus  internus 
abdominis 

Anterior  superior 
'iliac  spine 

Transversus 
abdominis 

.Obliquus  internus 
ABDOMINIS  (reflected) 


Aponeurosis  of  obliquus 
'externus  (reflected) 
•Abdominal  inguinal  ring 
Spermatic  cord  and 
"infundibuliform  fascia 
.  Fascia  transversalis 
Conjoint  tendon 
•(Inguinal  aponeurotic 
falx) 

■  Saphenous  opening 


Large  saphenous  vein 


Fig.  337ft. — The  Dissection  (<v  the  I\m  ixai.  Canal. 


The  lateral  muscles  of  the  abdominal  wall  comprise  the  obliquus  externus, 
obliquus  internus,  and  transversus  abdominis. 


422 


THE  MUSCULAR  SYSTEM. 


Rectus  abdominis 


The  obliquus  externus  abdominis  is  a  broad  thin  sheet  of  muscle,  with  an  origin 
from  the  lateral  surfaces  of  the  lower  eight  ribs,  by  slips  which  interdigitate 
with  the  serratus  anterior  (s.  magnus)  and  latissimus  dorsi  muscles.  The  mus- 
cular fibres  radiate  downwards  and  forwards,  the  lowest  fibres  passing  vertically 
downwards.  The  lower  and  posterior  part  of  the  muscle  is  inserted  directly 
by  fleshy  fibres  into  the  lateral  lip  of  the  iliac  crest  in  its  anterior  half  or  two- 
thirds  (Fig.  339,  p.  423).  The  rest  of  the  muscle  is  inserted  into  an  extensive 
triangular  aponeurosis  covering  the  anterior  abdominal  wall.  This  aponeurosis 
is  broader  below  than  above ;  it  is  united  with  part  of  the  aponeurosis  of  the 
obliquus  internus  in  the  upper  three-fourths  of  its  extent,  to  form  the  anterior 
layer  of  the  sheath  of  the  rectus  muscle.  It  thus  gains  an  attachment,  above  to  the 
ensiform  cartilage,  below  to  the  symphysis  pubis,  and  by  its  intermediate  fibres  to 
the  linea  alba,  a  broad  interlacing  band  of  fibres  about  half  an  inch  in  width  which 

occupies  the  mid- 
dle line  of  the 
anterior  abdomi- 
nal wall  in  its 
whole  extent,  is 
pierced  by  the  um- 
bilicus  (annulus 
umbilicus),  and 
forms  the  greater 
part  of  the  ulti- 
mate insertion  of 
all  the  lateral  ab- 
dominal muscles. 

The  upper  part 
of  the  aponeurosis 
covers  the  inser- 
tion of  the  rectus 
abdominis  muscle 

I     ^Anterior  layer  of  oil  the    chcSt  Wall, 

and  gives  origin 
to  fibres  of  the 
pectoralis  major. 
Below,  in  the  groin, 
it  gives  rise  to  Pou- 
part's  ligament, 
Gimbernat's  liga- 
ment (ligamen- 
tum  lacunare),  the 
superficial  ab- 
dominal ring  with  its  two  pillars,  the  intercolumnar  fascia  and  fibres  (intercrural 
fibres),  and  the  triangular  fascia  (ligamentum  inguinale  reflexum  of  Colles). 

Poupart's  ligament  (lig.  inguinale  Pouparti)  is  a  fascial  band  which  extends  from 
the  anterior  superior  iliac  spine  to  the  spine  of  the  pubis,  arching  over  the  iliacus, 
psoas,  and  pectineus  muscles.  It  represents  the  lower  limit  of  the  aponeurosis  of  the. 
■obliquus  externus  abdominis,  and  it  gives  attacliment  l)elow  to  the  iliac  portion  of 
the  fascia  lata  of  the  thigh.  Its  lateral  part  affords  partial  origin  to  the  obliquus 
internus  and  transversus  muscles,  and  receives  the  attachment  of  the  fascia  trans- 
versalis  and  fascia  iliaca ;  the  medial  part  forms  the  gutter-like  floor  of  the  inguinal 
canal.  At  its  medial  end  a  triangular  band  of  fibres  is  reflected  horizontally  back- 
wards to  the  ilio-pectineal  line,  forinin;,^  Gimbernat's  ligament  (lig.  lacunare  Gimber- 
nati),  the  lateral  edge  of  which  forms  tlie  medial  Itoundary  of  the  femoral  ring 
(annulus  femoralis).  The  femoral  vessels  enclosed  in  the  femoral  sheath  enter 
the  thigh  beneatli  Poupart's  ligament,  in  front  of  the  psoas  muscle,  and  the 
term  superjicicd  femoral  arch  is  given  to  the  part  of  the  ligament  which  covers 
the  vessels. 

The  superficial  inguinal  ring  (annulus  inguinalis  subcutaneus),  the  place  of  exit  of 


Extra  peritonpil 
tishue 

Kid  lie} 


Lumbar  l<iscia 


LATIbSIMUS  DORSl 


QUADRATUS  LUMBORUM 


Second  lumbar 
\'ertebra 


umbar  fascia 


JIULTIFIDUS 


Semispinalis 

DORSI 


Middle  layer  of  lumbar  fascia 

Ilio-costalis 

Vertebral  aponeurosis 


LONGISSIMUS  DORSI 


Fig.  338. 


-Transverse  Section  through  the  Abdomen,  opposite  the 
Second  Lumbar  Vertebra. 


THE  MUSCLES  OF  THE  ABDOMINAL  WALL. 


423 


an  inguinal  hernia,  is  a  split  in  the  aponeurosis  of  the  obliquus  externus,  just  above 
the  spine  of  the  pubis.  It  transmits  the  spermatic  cord,  or  (in  the  female)  the 
round  ligament  of  the  uterus,  covered  by  the  cremaster  muscle  or  cremasteric 
fascia.  The  opening  is  of  considerable  extent,  and  its  edges  are  drawn  together 
by  a  thin  fascia,  strengthened  superficially  by  a  number  of  arched  and  horizontal 


rORALIS   MAJOR 


SKRRATUS    AXTERIOR 

(maonus) 


Anterior  superior 
\    iliac  .spine 
J/f 
■f 

ifv     .  '% 

f,  __ _ _ Poupart's  ligament 

SuperBcial  inguinal 

ring  (ann.  inguinalis 

subcutaneus) 

Suspensory  ligament 
"of  penis 

Spermatic  cord 


Fig.  339. — The  Left  Obliqits  ExxEiiNUS  Abdominis. 

fibres,  called  the  intercolumnar  fibres  (fibrse  intercrurales),  which  arise  from  Poupart's 
ligament  and  sweep  medially  across  the  cleft  in  the  aponeurosis. 

The  margins  of  the  ring  constitute  its  pillars.  The  external  or  inferior  pillar 
(cms  inferius)  is  narrow,  and  is  formed  from  that  part  of  the  aponeurosis  which  joins 
the  pubic  spine,  and  is  continuous  with  the  medial  end  of  Poupart's  ligament.  The 
internal  or  superior  pillar  (crus  superius)  is  the  part  of  the  aponeurosis  medial  to  the 
ring  which  is  attached  to  the  crest  and  symphysis  of  the  pubis.    It  is  flat  and  broad. 

The  intercolumnar  fibres  and  the  pillars  of  the  superficial  inguinal  ring  are 
continuous  with  a  thin  tubular  sheath,  the  intercolumnar  or  external  spermatic  fascia, 


424 


THE  MUSCULAE  SYSTEM. 


which  IS  attached  to  the  margins  of  the  "  ring,"  and  forms  an  envelope  for  the 
spermatic  cord  or  round  hgament  in  their  further  passage  beyond  the  abdominal  wall. 
The  triangular  fascia  (lig.  inguinale  reflexum  CoUesi),  lastly,  is  a  triangular  band 
ol  fibres  placed  behind  the  internal  (superior)  pillar  of  the  superficial  inguinal  ring. 
it  consists  of  fibres  from  the  opj^osite  external  oblique  aponeurosis,  which,  having 
traversed  the  linea  alba,  gain  an  insertion  into  the  crest  and  spine  of  the  pubis. 


Aponeurosis  ov 

obliqtjus  externus 

(reflected) 


Aponeurosis  of 

OBLIQUUS  INTERN  us 


Aponeurosis  of         jt  \t« 

obliquus  externus.. 
(reflected) 

Cremaster  muscle-- 

Suspensory  ligament ___^ae- 

of  penis"' 

Spermatic  cord-- 


FiG.  340. — The  Right  Obijquus  Internus  Abdominis. 

The  obliquus  externus  muscle  is  superficial  in  almost  its  whole  extent.  It  is 
overlapxjed  posteriorly  by  the  latissimus  dorsi  muscle,  but  may  be  separated  from 
it  just  above  the  iliac  crest  by  an  angular  interval  rtrigonum  lumbale  or  triano-le  of 
Petit).  ~  ^ 

The  obliquus  internus  abdominis,  a  broad  thin  sheet  lying  between  the 
obliquus  externus  and  the  transversus,  arises  from  (1)  the  lumbar  fascia,  (2)  the 
anterior  half  of  the  iliac  crest,  and  (3)  the  lateral  half  of  Poupart's  ligament. 
Directed  for  the  most  part  upwards  and  forwards,  its  highest  fibres  are  inserted 


THE  MUSCLES  OF  THE  ABDOMINAL  WALL. 


425 


directly  into  the  last  three  ribs.  The  rest  of  the  fibres  form  an  extensive  aponeu- 
rosis, broader  above  than  below,  which  spUts  along  the  linea  semilunaris,  to  form,  along 
with  the  aponeuroses  of  the  obliquus  externus  and  transversus  muscles,  the  sheath 
of  the  rectus  abdominis,  and  is  thereafter  inserted  into  the  seventh,  eighth,  and  ninth 
costal  cartilages,  and  into  the  linea  alba  from  the  ensiform  cartilage  to  the  symphysis 
pubis.  The  fibres  arising  from  Poupart's  ligament  join  with  those  of  the  trans- 
versus muscle  having  a  similar  origin  to  form  the  conjoint  tendon  (falx  aponeurotica 
inguinalis),  which  passes  altogether  in  front  of  the  rectus  muscle,  to  be  attached  to 
the  pubic  crest  and  spine,  and  to  the  ilio-pectineal  line. 

The   obliquus   internus  is  limiterl  al>"ve  by  the  costal  arch.     Its  lower  fibres, 


Aponeurosis  of 

obliquus  externus 

(reflected) 


Linea  alba 


Superficial 
inguinal  ring 
Jriangolar  fascia 
External  or  in- 
ferior pillar  of  ring 

Pubic  fascia  and 
suspensor\-  liga- 
ment of  penis 


Obliqucs  exterkus 
abdominis 


Anterior  superior 
iliac  spine 


^-^    Obliqx'us  internus 
abdominis 


Aponeurosis  of 
■  -obliquus  externus 
(reflected) 


Spermatic  cord 

Inquinal  canal 

Conjoint  tendon 

Triangular  fascia 

External  pillar  of 

superficial  inguinal 
ring  (Poupart's 
ligament) 


Spermatic  cord  (cut) 


Fig.  341a. — The  Left  Inguinal  Canal.     Stkuctcres  seen  on  keflection  of  the  Obliquus  Externus. 


arching  over  the  spermatic  cord,  assist  in  forming,  laterally,  the  anterior  wall  of 
the  inguinal  canal ;  medially,  by  means  of  the  conjoint  tendon,  it  helps  to  form 
the  posterior  wall  of  the  canal. 

Its  lowest  fibres  are  continued  into  the  cremaster  muscle,  which  is  prolonged 
along  the  spermatic  cord  through  the  inguinal  canal. 

The  cremaster  muscle  forms  an  investment  for  the  testicle  and  spermatic  cord 
beneath  the  intercoUimnar  fascia.  In  the  female  it  is  more  largely  represented  by  fascia 
than  muscular  fibres,  and  constitutes  the  cremasteric  fascia.  It  may  be  said  to  have  an 
origin  from  the  lower  edge  of  the  obliquus  iuternus  and  the  adjacent  part  of  Poupart's 
ligament.  Its  fibres  form  loops  over  the  spermatic  cord  and  testicle,  the  highest  fibres 
getting  an  insertion  into  the  pubic  spine. 

The  transversus  abdominis  muscle  arises  (1)  from  the  deep  surface  of  the 
costal  cartilages  of   the  lower  six  ribs,  interdigitating  with   the    origins  of  the 


426 


THE  MUSCULAE  SYSTEM. 


diaphragm  ;  (2)  from  the  himbar  fascia ;  (3)  from  the  anterior  half  of  the  medial  lip 
of  the  iliac  crest ;  and  (4)  from  the  lateral  third  of  Poupart's  ligament.  The 
muscular  fibres  are  directed  for  the  most  part  horizontally  forwards,  and  end  in 
an  aponeurosis  which  has  a  twofold  insertion.  (1)  After  forming  (along  with  the 
aponeurosis  of  the  obliquus  internus)  the  posterior  layer  of  the  sheath  of  the  rectus, 
the  aponeurosis  is  attached  to  the  ensiform  cartilage  and  Knea  alba.  (2)  The 
lower  fibres  of  the  muscle  arising  from  Poupart's  ligament  are  joined  by  the  lower 


Obliquus  exteknu 
abdomini 
(reflectt'il ) 


Spermatic  cord-- 
Intercolumnar  fascia" 


Obliquus  externus 
abdominis 


,Obi,iquus  internus 
abdominis 

Anterior  superior 
'iliac  sijine 

^Transversus 
'abdominis 

,Obliquus  internus 
abdominis  (reflected) 


Aponeurosis  of  obliquus 
■externus  (reflected) 
■•Abdominal  inguinal  ring 

Spermatic  cord  and 
"infundibuliform  fascia 
.  Fascia  transversalis 

Conjoint  tendon 
■•(Inguinal  aponeurotic 

falx) 


—Saphenous  opening 


-Large  saphenous  vein 


Fig.  341  b. — The  Dissection  of  the  Inguinal  Canal. 


part  of  the  obliquus  internus  to  form  the  larger  part  of  the  conjoint  tendon  (falx 
aponeurotica  inguinalis),  which  passes  in  front  of  the  lower  part  of  the  rectus  muscle, 
to  be  inserted  into  the  crest  and  spine  of  the  pubis  and  the  ilio-pectineal  line. 

The  transversus  muscle  is  separated  by  the  lower  intercostal  nerves  from  the 
obliquus  internus  muscle,  and  is  lined  on  its  deep  surface  by  the  fascia  transversalis. 
Its  lower  border  fprms  a  concave  edge,  separated  from  Poupart's  ligament  by  a 
lunular  interval  in  which  the  fascia  transversalis  appears,  and  through  which^  the 
spermatic  cord  emerges  at  the  abdominal  inguinal  ring,  under  cover  of  the  obliquus 
internus  muscle  and  the  aponeurosis  of  the  oblicpius  externus. 

The  anterior  muscles  of  the  abdominal  wall  include  the  pyramidalis  and  rectus 
abdominis,  enveloped  by  the  sheath  of  the  rectus  on  either  side  of  the  linea  alba. 

The  pyramidalis  abdominis  is  a  small  triangular  muscle  arising  from  the  pubic 
crest  in  front  of  the  rectus  muscle  (Fig.  342,  p.  427).  It  is  directed  obHquely 
upwards,  to  be  inserted  for  a  variable  distance  into  the  linea  alba.  The  muscle 
is  often  absent.  j 

The  rectus  abdominis  muscle  is  broad  and  strap-like,  and  arises,  by  a  medial 


THE  MUSCLES  OF  THE  ABDOMINAL  WALL. 


427 


and  a  lateral  head,  from  the  symphysis  and  crest  of  the  pubis  (Fig.  282,  p.  362). 
Expanding  as  it  passes  upwards,  the  muscle  is  inserted  from  within  outwards  into 
the  front  of  the  ensiform  cartilage  (Fig.  342,  p.  427),  and  into  the  front  of  the 
seventh,  sixth,  and  fifth  costal  cartilages.  On  its  anterior  surface,  but  not 
extending  through  the  entire  substance  of  the  muscle,  are  three  or  more  transverse 


Aponeurosis  of 

.obliquus  exteruus 

abdominis  (reflected) 


Rectts  abdominis 


Anterior  lamella  of 

sheath  of  rectus  rr— - 


Linea  alba 
Obliqcxs  ex- 

TERXrS  ABCOMIXIS 


'rOBUQrcs  ix- 

TERSrS  ABDOMIXIS 


Aponeurosis  of 
obliquus  extemus 


Pouparfs  ligament  ... 


Aponeurosis  of 

■  obliquus  extemus 

(reflected) 

CrEJLASTER  Ml'SCLE 


Spermatic  cord    Z 


OBLigrUS  EXTERN l"8 
ABDOMIXIS 


Rectus  abdominis 
(cut) 


Posterior  lamella  of 
rectal  sheatli 


Anterior  lamella  oi 
sheatli  of  rectus 


Aponeurosis  of 
obliquus  externus 


Obliquus  internts 
abdominis 


Transvebsus 
abdominis 


Fold  of  Douglas 

Fascia  transversalis 

Rectus  abdominis 
(cut) 

Poupart's  ligament 
Obliquus  externus 

(aponeurosis 
reflected) 
Pvramidalis 
abdominis 


Suspensory  ligament 
—  uf  penis 


Fig.  .342. — Deep  Dissectiox  of  the  Abdumi.nal  Wall.     The  Rectus  Muscle  and  its  Sheath. 

tendinous  intersections  (inscriptiones  tendinese),  adherent  to  the  sheath  of  the 
muscle  ;  the  lowest  opposite  the  umbilicus,  and  the  highest  about  the  level  of  the 
ensiform  cartilage.  The  medial  border  of  the  muscle  lies  alongside  the  linea  alba  ; 
its  lateral  border  is  convex,  and  corresponds  to  the  linea  semilunaris.  The  muscle 
is  pierced  by  the  terminal  branches  of  the  lower  thoracic  nerves. 

The  sheath  of  the  rectus  muscle  (vagina  m.  recti  abdominis)  is  derived  from 
the  aponeuroses  of  the  lateral  muscles  of  the  abdominal  wall,  which,  after  enclosing 
the  muscle,  give  rise  in  the  middle  line  to  the  linea  alba.    At  the  linea  semilunaris, 

29 


428 


THE  MUSCULAE  SYSTEM. 


the  lateral  border  of  the  rectus  muscle,  the  aponeurosis  of  the  obliquus  internus 
splits  into  anterior  and  posterior  layers.  The  anterior  layer,  joined  by  the 
aponeurosis  of  the  obliquus  externus,  passes  in  front  of  the  rectus,  and  constitutes 
the  anterior  lamina  of  the  sheath.  The  posterior  layer,  joined  by  the  aponeurosis  of 
the  transversus  muscle,  passes  behind  the  rectus,  and  constitutes  the  posterior 
lamina  of  its  sheath.  This  arrangement  obtains  in  the  upper  three-fourths  of  the 
abdominal  wall.  Below  the  level  of  the  iliac  crest  the  sheath  of  the  muscle  is 
deficient  posteriorly,  and  a  crescentic  border,  the  semilunar  fold  of  Douglas  (linea 
semicircularis),  marks  the  lower  limit  of  the  posterior  lamina.  In  consequence,  the 
rectus  in  the  lower  fourth  of  the  abdominal  wall  rests  directly  upon  the  fascia  trans- 

versalis.  Close  examination,  however, 
usually  reveals  a  thin  layer  behind  the 
muscle  in  continuity  with  the  fold  of 
Douglas,  and  merging  below  with  the 
fascia  transversalis.  In  this  region  the 
rectus  is  covered  anteriorly  by  the  con- 
joint tendon  (falx  aponeurotica  in- 
guinalis)  of  the  obliquus  internus  and 
transversalis,  and  by  the  aponeurosis 
of  the  obliquus  externus,  which  gradu- 
ally separates  from  the  subjacent 
aponeurosis.  The  upper  part  of  the 
rectus,  lying  on  the  chest  wall,  is  only 
covered  anteriorly  by  a  single  layer  of 
aponeurosis  derived  from  the  obliquus 
externus,  which  in  this  situation  is  giving 
origin  to  the  pectoralis  major  muscle. 

Inguinal  Canal. — The  spermatic 
cord  in  the  male,  and  the  round  liga- 
ment in  the  female,  in  their  passage 
through  the  lower  part  of  the  ab- 
dominal wall,  pass  through  the  inguinal 
canal,  which  is  bounded  by  these  ab- 
dominal muscles.  The  canal  begins  at 
the  abdominal  inguinal  ring  (anrmlus 
inguinalis  ahdominalis),  placed  half  an 
inch  above  Poupart's  inguinal  ligament, 
and    midway    between    the     anterior 


Fig.  343.- 


pubis.  It  ends  at  the  superficial  in- 
guinal ring  (annulus  inguinalis  suhcu- 
taneus),  placed   above   the   spine  and 


sheath  ;  /,  Fascia  transversalis  ;  g,  Peritoneum 
Linea  alba.     1,  Deep  (inferior)  epigastric  artery. 


-The  Sheath  of  the  Rectus  Abdominis 
Muscle. 

(I.)  In  the  thoracic  wall;  (II.)  In  the  upper  three-  """  "TT^iii""!  ^-nTnp  ai^l  thrsvmTihvql^ 
quarters  of  the  abdominal  wall  ;  (III.)  In  the  lower  SUpCllOr  ^liiac  SpiUC  and  tnc  SympnySlS 
fourth  of  the  abdominal  wall. 

A,  Rectus  muscle  ;   B,  Obliquus  externus  ;   C,  Dia- 
phragm ;   D,  Obliquus  internus  ;   E,  Transver- 
salis abdominis,    a,  Anterior  layer  of  rectus  sheath  ; 
b,  Fifth  costal  cartilage  ;    c,  Sixth  costal  cartilage  ;  crest  ot  the  publS.     ihe  anterior  wall  ot 
d,   Xiphoid   cartilage  ;    e,  Posterior  ^ayer  of  rectus   ^^^q  canal  is  formed  by  the  aponeurosis 

of  the  obliquus  externus,  and  in  its 
lateral  part  by  the  muscular  fibres  of" 
the  obliquus  internus  ;  the  posterior  ivall  of  the  canal  is  formed  by  the  fascia 
transversalis,  and  in  its  medial  part  by  the  conjoint  tendon  (falx  aponeurotica 
inguinalis) ;  while  the  floor  of  the  canal  is  formed  by  Poupart's  ligament,  and  in  its 
medial  part  by  Gimbernat's  ligament.  The  spermatic  cord,  piercing  the  transversalis 
fascia,  enters  the  inguinal  canal  at  the  abdominal  inguinal  ring,  and  is  there  invested 
by  its  first  envelope,  the  infundibuliform  or  internal  spermatic  fascia,  a  sheath  of  fascia 
derived  from  the  margin  of  the  ring  and  continuous  witli  the  lascia  transversalis. 
It  then  passes  obliquely  medially,  downwards,  and  forwards,  and  escapes  below  the 
lower  border  of  the  obliquus  internus  muscle,  from  which  it  carries  off  a  second 
investraent,  partly  fascial,  partly  muscular, — the  cremaster  muscle  or  cremasteric 
fascia.  Continuing  its  course  in  front  of  the  conjoint  tendon,  it  emerges  through 
the  superficial  inguinal  ring,  from  the  edges  of  which  the  intercolumnar  fascia  is 
derived,  the  third  or  external  investment  for  the  cord. 


THE  MUSCLES  OF  THE  ABDOMINAL  WALL. 


429 


Hesselbach's  triangle,  bounded  below  by  the  line  of  Poupart's  ligament,  medially 
by  the  rectus  abdominis  muscle,  and  laterally  by  the  deep  epigastric  artery  ^ 
coursing  upwards  and  medially  beneath  the  fascia  transversalis  on  the  medial 
side  of  the  abdominal  inguinal  ring,  is  the  site  of  one  form  of  inguinal  hernia. 
The  spermatic  cord  passes  over  the  base  of  the  triangle,  covered  over  by  the 
aponeurosis  of  the  obliquus  externus.     Behind  the  cord,  and  forming  the  floor  of 


Vena  caval  opening    Oesophageal  opening     Central  tendon  (middle  part) 


y    Central  ten 
^  (left  part) 


Central  tendon  (rii;ht  part) 

Diaphragm,  costal  fibres 

Medial  arcuate  ligament 

Lateral  arcuate  ligament 

End  of  last  rib 
Last  thoracic  nerve 
Tendon  of  transversus 
abdominis 
Transversus  abdominis 
Ilio-hypogastric  nerve 
Luni))ar  vessels  and  sympa- 
thetic communicating  nerves 
Ilio-inguinal  nerve 

QUADRATUS  LUMBOKUM 


External  cutaneous  nerve 

Psoas  major 

Iliacus 

Lumbo-sacral  cord 


Genito-crural  (genito-femoral) 

nerve 

Anterior  crural  (femoral)  nerve 

Obturator  nerve 

Great  sciatic  nerve 


Diaphragm,  right  crus 

Middle  arcuate  ligament 
y  Aortic  opening 
tendon 


Diaphragm,  lekt 

D-T^CRUS 


Last  thoracic  nerve 
End  of  last  rib 
Lumbar  nerve  I. 
Ilio-hypogastric  nerve 
Lumbar  nerve  II. 

Ilio-inguinal  nerve 

QUADRATUS 
LUMBORUM 

Lumbar  nerve  III. 
Genito-cniral  (genito- 


jFvT"  femoral)  nerve 


Lumbar  nerve  IV. 


Lumbo-sacral  cord 


External  cutaneous  nerve 
Anterior  crural  (femoral) 
nerve 

Obturator  nerve 
Great  sciatic  nerve 


(Jbturator  nerve 
ADDrcTOR  LONGUs  (origin) 
\     Adductor  brevis  (origin) 
Gracilis  (origin) 
I  Adductor  magnus  (origin) 

Pectineus  (cut) 
Superficial  branch  of  obturator  nerve 
I    Deep  branch  of  obturator  nerve 
Obturator  externus 

Fig.  344. — View  op  the  Posterior  Abdominal  Wall,  to  show  the  Muscles  and  the  Xerves  of 

THE  Lumbo-Sacral  Plexus. 

the  triangle,  is  the  fascia  transversalis  partially  covered  in  the  medial  portion 
of  the  triangle  by  the  conjoint  tendon  of  the  obliquus  internus  and  transversus 
muscles. 

Inguinal  Hernia. — Eor  an  account  of  the  anatomical  relations  of  the  inguinal 
canal  to  the  various  forms  of  inguinal  hernia,  see  the  section  on  "  Applied  Anatomy  " 
(p.  1265). 

The   posterior   muscles   of  the  abdominal   wall   and   false  (large)  pelvis 

^  Deep  epigastric  =  inferior  epigastric  artery  (B.N. A.). 


430  THE  MUSCULAR  SYSTEM. 

include  the  psoas  (major  and  minor)  and  iliacus,  described  already  (p.  361),  and 
the  quadrat  us  lumborum. 

The  quadratus  lumborum  lies  on  the  posterior  wall  of  the  abdomen,  lateral 
to  the  psoas,  and  extends  between  the  iliac  crest  and  the  last  rib.  ,  It  arises  from 
the  posterior  part  of  the  iliac  crest,  from  the  ilio-lumbar  ligament,  and  from  the 
transverse  processes  of  the  lower  lumbar  vertebrae.  It  is  inserted  above  into  the 
medial  part  of  the  lower  border  of  the  last  rib  and  the  transverse  processes  of 
the  upper  lumbar  vertebrse.  Its  lateral  border  is  directed  obliquely  upwards  and 
medially.  It  is  enclosed  between  the  anterior  and  middle  layers  of  the  lumbar 
aponeurosis  (p.  385),  between  the  psoas  muscle,  in  front,  and  the  sacro-spinalis 
behind. 

Nerve-Supply. 

The  nerve -svipi^ly  of  the  majority  of  the  foregoing  muscles  is  derived  from  the  anteriar 
primary  divisions  ^  of  the  lower  six  thoracic  nerves.  The  pj-ramidalis  muscle  is  imiervated  by  the 
last  thoracic  nerve.  The  cremaster  muscle  receives  its  supply  from  the  genito-crural  nerve,^ 
(L  1.  2.),  whilst  the  quadratus  lumborum  is  innervated  by  ihe  first  three  or  four  lumbar  nerves. 
The  psoas  and  iliacus  muscles  are  supplied,  directly  or  through  the  anterior  crural  nerve,^  from 
the  second,  third,  and  fourth  lumbar  nerves. 

Actions. 

Many  of  the  actions  of  the  above  muscles  have  already  been  given  in  previous  sections.  (1) 
Their  chief  action  is  to  retract  the  abdominal  walls,  and,  by  compressing  the  contents  of  the 
abdomen,  they  are  powerful  agents  in  vomiting,  defsecation,  micturition,  parturition,  and 
laboured  expiration.  (2)  They  are  also  flexors  of  the  spine  and  pelvis — the  muscles  of  both  sides 
acting  together  ;  the  spine  and  pelvis  are  laterally  flexed,  when  one  set  of  muscles  acts  alone.  (3) 
The  quadratus  lumborum  is  a  muscle  of  inspiration,  an  extensor  of  the  spine,  and  a  lateral  flexor 
of  the  spine  and  pelvis. 

FASCIAE  AND    MUSCLES   OF  THE    PERINEUIVI 

AND    PELVIS. 

FASCIiE  OF  THE  PERINEUM. 

The  superficial  fascia  of  the  perineum  possesses  certain  special  features.  It 
is  continuous  with  the  superficial  fascia  of  the  abdominal  waU,  thigh,  and  buttock, 
and  is  prolonged  on  to  the  penis  and  scrotum.  In  relation  to  the  penis,  it  is 
devoid  of  fat  and  consists  only  of  areolar  tissue.  In  relation  to  the  scrotum,  it  is 
intermino-led  with  involuntary  muscular  fibres,  and  constitutes  the  dartos  muscle, 
which  assists  in  suspending  the  testicles  and  corrugating  the  skin  of  the  scrotum. 
This  fascia  also  forms  the  septum  of  the  scrotum,  which,  extending  upwards,  in- 
completely separates  the  two  testicles  and  their  coverings.  In  the  female  the 
superficial  fascia,  in  which  there  is  a  considerable  quantity  of  fat,  takes  a  large 
share  in  the  formation  of  the  mons  veneris  and  labia  majora. 

The  fascia  over  the  ^josterior  part  of  the  'perineum  fiUs  up  the  ischio-rectal  fossse, 
in  the  form  of  two  pads  of  adipose  tissue,  on  either  side  of  the  rectum  and  anus. 
Over  the  tuberosities  of  the  ischium  the  fat  is  intermingled  with  bands  of  fibrous 
tissue  closely  adherent  to  the  subjacent  deep  fascia. 

The  fascia  in  the  anterior  part  of  the  perineum  closely  resembles  the  same 
fascia  in  the  groin.  It  is  divisible  into  a  superficial  fatty  and  a  deeper  membranous 
layer ;  the  former  continuous  with  the  same  layer  in  the  thigh,  and  with  the  fat 
of  the  ischio-rectal  fossa  posteriorly.  The  deeper  membranous  layer  is  attached 
laterally  to  the  pubic  arch,  posteriorly  to  the  base  of  the  triangular  ligament  (dia- 
phragma  urogenital),  and  in  the  middle  hne  to  the  root  of  the  penis  (bulb  and 
corpus  spongiosum)  by  a  median  raphe  continuous  farther  forwards  with  the  septum 
of  the  scrotum  mentioned  above.  Anteriorly  the  fascia  is  continued  over  the  sper- 
matic cords  to  the  anterior  abdominal  wall.  The  importance  of  this  fascia  lies  in 
relation  to  the  extravasation  of  urine  from  a  rupture  of  the  urethra.  By  the  fascial 
attachments  the  fluid  is  prevented  from  passing  backwards  into  the  ischio-rectal 
fossa,  or  laterally  into  the  thigh.  It  is  directed  forwards  into  relation  with  the 
scrotum  and  penis,  and  along  the  spermatic  cord  to  the  anterior  abdominal  wall. 

1  Anterior  primary  divisions  =  anterior  rami  (B.N. A.). 
'^  Genito-crural  nerve  =gemto-femoral  nerve         ,, 

2  Anterior  crural  nerve  =  femoral  nerve  , , 


THE  MUSCLES  OF  THE  PEEINEUM. 


431 


The  septum  of  the  scrotum  being  incomplete,  fluid  extravasated  on  one  side  can 
pass  across  the  middle  line  to  the  opposite  half  of  the  perineum  and  scrotum. 

The  deep  fascia  of  the  perineum  only  exists  in  the  form  of  the  delicate 
aponeuroses  of  the  muscles. 

THE  MUSCLES  OF  THE  PERINEUM. 

The  perineal  muscles  are  naturally  separated  into  a  superficial  and  a  deep  set 
by  the  triangular  ligament  (diaphragma  urogenitale).  Superficial  to  it  are  the 
sphincter  ani  externus,  transversus  perinei  superficialis,  bulbo-cavernosus,  and 
ischio-cavernosus ;  beneath  the  triangular  ligament  is  the  sphincter  muscle  of  the 
membranous  urethra  (compressor  urethrpe). 

Sphincter  ani  Externus. — This  muscle  is  fusiform  in  outline,  flattened,  and 
obliquely  placed  around  the  anus  and  anal  canal.  It  can  be  separated  into 
three  layers, — subcutaneous,  superficial,  and  deep.  (1)  The  most  superficial  lamina 
consists  of  subcutaneous  fibres  decussating  behind  and  in  front  of  the  anus,  but 


Perineal  branch  of  small 
sciatic 


Anterior 

superticial 

perineal 


Posterior 

superticial 

perineal 

nerve 

GlutealV 
branches  ol'_^ 
small  sciatic 
nerve 


BULBO-CA  \  ERNOSUS 

ISCHIO-CAVERNOSCS 


Transversus 

PERINEI 


Ischial  tuberosity 


Levator  ani 


Parietal  pelvic 
fascia 


Inferior  hemorrhoidal  nei  \ 


Levator  ani 
Sphincter  ani  externus 
Anterior  sacro-coccygeal  nerve 
Fig.  345. — The  Muscles  and  Nerves  of  the  Male  Perineum. 


Perforating  cutaneous  iier\ 
Perineal  branch  of  fourth  sacral  utrvu 


without  bony  attachments.  (2)  The  sphincter  ani  superficialis  constitutes  the  main 
portion  of  the  muscle.  It  is  attached  posteriorly  to  the  coccyx,  and  in  front  of 
the  anus  reaches  the  central  point  of  the  perineum.  (3)  The  deep  fibres  of  the  muscle 
form  for  the  most  part  a  complete  sphincter  for  the  anal  canal.  They  are  continuous 
with  the  fibres  of  the  levator  ani ;  they  encircle  the  anal  canal,  and  blend  anteriorly 
with  the  central  point  of  the  perineum  and  the  transversus  perinei  muscle. 

The  corrugator  cutis  ani  consists  of  bundles  of  unstriped  muscular  fibres  which 
radiate  from  the  margin  of  the  anal  opening  superficial  to  the  external  sphincter. 

The  transversus  perinei  superficialis  is  not  always  present.  It  consists  of  a 
more  or  less  feeble  bundle  of  fibres,  arising  from  the  inferior  or  ascending  ramus  of 
the  ischium  and  the  fascia  over  it,  and  from  the  base  of  the  triangular  ligament 
(diaphragma  urogenitale).  It  passes  obliquely  over  the  base  of  the  triangular 
ligament  to  be  inserted  into  the  central  point  of  the  perineum. 

The  bulbo-cavernosus  (ejaculator  urinse),  tw  the  male,  surrounds  the  bulb,  corpus 
spongiosum,  and  root  of  the  penis.  It  is  sometimes  separated  into  two  parts — 
posterior  (compressor  bulbi),  and  anterior  (compressor  radicis  penis).     It  arises  from 


432 


THE  MUSCULAR  SYSTEM. 


the  central  point  of  the  perineum,  and  from  a  median  raphe  on  the  under  surface  of 
the  bulb  and  corpus  spongiosum.  The  muscular  fibres  are  directed  laterally  and 
forwards  and  have  a  triple  insertion :  from  behind  forwards,  (1)  into  the  under  sur- 
face of  the  triangular  ligament ;  (2)  into  the  dorsal  aspect  of  the  corpus  spongiosum; 
and  (3),  after  encircling  the  corpora  cavernosa,  into  the  fascia  covering  the  dorsum 
of  the  penis. 

The  ischio-bulbosus,  not  always  present,  arises  from  the  ischium,  and  passes 
obliquely  inwards  and  forwards  over  the  bulbo-cavernosus,  to  be  inserted  into  the  raphe 
superficial  to  that  muscle.  It  belongs  to  the  same  stratum  as  the  transversus  perinei 
superficialis  and  erector  penis  (ischio-cavernosus). 

The  compressor  hemispherium  bulbi  is  frequently  absent.  It  consists  of  a  thin 
cap-like  layer  of  muscular  fibres  surrounding  the  extremity  of  the  bulb  under  cover  of  the 
bulbo-cavernosus. 

The  bulbo-cavernosus  (sphincter  vaginse),  in  the  female,  is  separated  into  lateral 

halves  by  the  vaginal 
and  urethral  openings. 
It  forms  two  thin 
lateral  layers  covering 
the  vaginal  bulbs,  and 
arises  behind  the  va- 
ginal orifice  from  the 
central  point  of  the 
perineum.  Anteriorly 
it  is  inserted  into  the 
root  of  the  clitoris, 
some  of  its  fibres  em- 
bracing the  corpora 
cavernosa  so  as  to 
reach  the  dorsum  of 
the  clitoris. 

The  ischio-cavern- 
osus (erector  penis),  in 
the  male,  covers  the 
crus  penis.  It  arises 
from  the  ischial  tuber- 
osity and  the  greater 
sacro-sciatic  ligament, 
and  passing  forwards, 
is  inserted  by  a  fascial 
attachment  into  the 
under  surface  of  the 
crus  penis,  and  into 
the  lateral  and  dorsal 
aspects  of  the  corpus 
cavernosum. 


Bulbo- 
cavernosus 


Transversus 

PERINEI 
SUPER- 
FICIALIS 


Levator  ani 


\  Gluteus 

MAXIMUS 


SpH1>-CTER  ANI  EXTERNUS 


Fio. 


■346. — The  Muscles  of  the  Female  Perineum  (after  Peter 
Thompson). 


The  erector  clitoridis  (ischio-cavernosus),  in  the  female,  has  a  similar  disposi- 
tion, but  is  of  much  smaller  size  than  in  the  male. 

The  pubo-cavemosus  is  an  occasional  slip  arising  from  the  pubic  ramus,  and  inserted  into 
the  dorsum  of  the  penis.     It  corresponds  to  the  levator  penis  of  lower  animals. 

The  sphincter  urethrse  membranacese  (compressor  urethrae)  constitutes 
the  deej)er  muscular  stratum  of  the  perineum.  It  is  placed  on  the  pelvic  aspect 
of  the  triangular  ligament.  It  arises  from  the  lower  part  of  the  pubic  ramus,  and 
is  directed  medially,  its  fibres  radiating  so  as  to  enclose  the  membranous  urethra. 
It  is  inserted  into  a  medial  raphe,  partly  in  front  of  the  urethra,  but  for  the  most 
part  behind  it.  The  fibres  most  intimately  related  to  the  urethra  form  a  muscular 
sheath  for  the  canal,  and  have  no  bony  attachments. 

The  most  posterior  and  most  anterior  fibres  of  the  compressor  urethrse  exist  sometimes 
as  separate  muscles,  as  the  transversus  perinei  profundus,  and  the  ischio-pubicus. 


FASCIA  OF  THE  PELVIS. 


433 


The  transversus  perinei  profundus  consists  of  a  bundle  of  fibres  on  either  side, 
arising  from  tlie  inferior  ramus  of  the  ischium  just  below  the  compressor  urethrse.  It 
is  inserted  into  a  medial  raphe  continuous  with  that  of  the  compressor  urethrse.  The 
muscle,  in  fact,  constitutes  a  separate  bvuidle  below  and  behind  the  compressor  urethne. 

The  ischio-pubicus  is  a  term  applied  to  a  feeble  bundle  of  fibres  which,  when 
present,  lies  above  and  in  front  of  the  compressor  urethrte.  It  arises  from  the  pubic 
ramus,  and  is  inserted  into  a  median  raphe  on  the  dorsum  of  the  membranous  urethra. 
This  muscle  is  homologous  with  the  compressor  venae  dorsalis  penis  of  lower  animals. 

The  compressor  urethrae  in  the  female  is  smaller  than  in  the  male.  Its 
insertion  is  modified  by  the  relations  of  the  urethra  to  the  vagina.  The  anterior 
fibres   are   continuous  with   those  of  the  opposite   side  above  the  urethra  ;    the 


Corpus  cavernosuni 

(cut) 

Nerve  to  corpus 

cavernosum 

Nerve  to  dorsum  of  penis 

Sphincter  urethr.e 

membranace.-b 

(compressor  urethr.«) 

Nerve  to  bulb 

Triangular  ligament 

(posterior  layer) 

Internal  pudic  nerve 


Bulb  of  penis 

Triangular  ligament 
—. — ^  (anterior  layer) 

•  "  '^ Cms  penis 

-5 — ^ — Lev  ATOP.  ANi 


Fig.  347. — The  Triangular  Ligament  (diaphragma  urogenitale)  of  the  Perineum,  and  the 
Termination  of  the  Pudic  Nerve.' 

intermediate  fibres  pass  between  the  urethra  and  vagina,  and  the  posterior  fibres 
are  attached,  along  with  the  transversus  perinei  profundus  (transversus  vaginae),  into 
the  side  of  the  vagina. 

Nerve-Supply. 
The  pudic  nerve  i  (S.  2.  3.  4.)  supplies  all  the  muscles  in  this  group ;  the  external  sphincter 
through  the  inferior  hemorrhoidal,  and  the  others  through  the  perineal  branch  of  the  nerve. 
The  external  .sphincter  is  also  supplied  by  the  perineal  branch  of  the  fourth  sacral  nerve. 

Actions. 

The  external  sphincter  closes  the  anal  canal.  The  transversus  perinei  superficialis  draws 
back  and  fixes  the  central  point  of  the  perineum,  assisted  by  the  external  sphincter.  The  bulbo- 
cavernosus  of  the  male  constricts  the  bulb  and  corpus  spongiosum,  and  so  expresses  the  last  drops 
of  urine  or  semen.  In  the  female  it  acts  as  a  feeble  sphincter  of  the  vagina.  The  ischio- 
cavernosus  and  bulbo-cavernosus  help  in  erection  of  the  penis  or  clitoris.  The  sphincter 
of  the  membranous  urethra  constricts  the  membranous  urethra,  and  in  the  female  helps  to 
flatten  and  fix  the  wall  of  the  vagina.  It  also  assists  in  causing  erection  of  the  penis  or  clitoris 
by  compression  of  the  veins  in  relation  to  it. 

THE   FASCIiE   OF   THE   PELVIS. 

The  extra-peritoneal  tissue  in  the  pelvic  cavity  is  of  great  importance.  The 
internal  iliac  vessels  and  their  branches,  the  visceral  nerves  and  plexuses,  the 
ureters,  and  vasa  deferentia,  take  their  course  in  this  tissue  beneath  the  peri- 
toneum. It  forms  in  relation  to  the  rectum  a  thick  sheath,  for  the  most  part 
devoid  of  fat,  which  encloses  the  lower  part  of  the  rectum  completely,  down  to  its 
termination  in  the  anal  canal.  It  forms  a  kind  of  packing  for  the  parts  of  the 
bladder  uncovered  by  peritoneum,  and  is  present  under  the  organ  in  relation  to  the 

^  Pudic  nerve  =  pudendal  nerve  (B.N. A.). 


434  THE  MUSCULAE  SYSTEM. 

symphysis  pubis  and  pubo-prostatic  ligaments.  In  the  female  it  forms  in  addition 
the  basis  or  matrix  of  the  broad  ligament,  and  also  occurs  as  a  layer  devoid  of  fat, 
which  loosely  connects  the  front  of  the  cervix  uteri  with  the  base  of  the  bladder. 

PELVIC    FASCIA. 

The  cavity  of  the  true  (small)  pelvis  in  the  erect  position  resembles  a  basin  tilted 
forward,  with  its  margin  formed  by  the  inlet  or  brim  of  the  pelvis,  and  with  a 
cylindrical  wall,  and  a  concave  floor,  formed  by  bones,  ligaments,  and  muscles. 
The  deficiencies  in  the  bony  walls  of  the  cavity  are  filled  up  laterally  by  the 
obturator  membrane  and  the  sacro-sciatic  ligaments.  Below  and  in  front,  behind 
the  symphysis  pubis,  the  triangular  ligament  (fascia  diaphragmatis  urogenitalis 
inferior)  fills  up  the  pubic  arch,  and  separates  the  fore  part  of  the  pelvic  cavity 
from  the  fore  part  of  the  perineum.  Within  this  osseo-ligamentous  chamber  a 
series  of  muscles  clothe  its  interior;  the  piriformis  and  coccygeus  behind,  the 
obturator  internus  on  each  side,  and  the  compressor  urethrte  below  and  in  front, 
on  the  pelvic  surface  of  the  triangular  ligament. 

The  pelvic  fascia,  continuous  above  with  the  fascial  lining  of  the  abdominal 
cavity,  forms  a  continuous  cylindrical  investment  for  these  muscles.  On  the  pelvic 
surface  of  the  pubis,  where  muscles  are  absent,  it  is  merged  with  the  periosteum. 
It  gains  an  attachment  to  the  spine  of  the  ischium  as  that  projects  between  the 
piriformis  and  obturator  internus  muscles.  Perforations  occur  in  relation  to  it 
for  the  transmission  of  the  obturator  nerve  and  the  parietal  branches  of  the 
internal  iliac  artery.  Eeaching  the  outlet  of  the  pelvis,  it  is  attached  to  the 
posterior  border  or  base  of  the  triangular  ligament,  to  the  ischial  ramus  and 
tuberosity,  and  to  the  lower  edge  of  the  great  sacro-sciatic  ligament.  Different 
names  are  applied  to  the  fascia  in  relation  to  the  several  muscles  which  it  covers. 
Posteriorly  it  constitutes  the  piriformis  fascia :  laterally  it  is  the  obturator  fascia, 
while  that  part  of  the  sheet  of  fascia  which  covers  the  pelvic  surface  of  the  com- 
pressor urethrEe  is  known  as  the  deep  layer  of  the  triangular  ligament  (f.  diaphragmatis 
urogenitalis  superior) 

The  disposition  of  the  pelvic  fascia  is  complicated  by  its  relations  to  (1)  the 
structures  which  constitute  the  pelvic  floor,  and  (2)  the  genito-urinary  passages 
and  rectum. 

The  pelvic  floor,  tense  in  its  fore  part  and  flexible  behind,  may  be  said  to  be 
formed  behind  the  symphysis  pubis  by,  successively,  (1)  the  triangular  ligaments 
and  the  sphincter  muscle  of  the  membranous  urethra  between  them  enclosing 
the  urethra,  and  the  vagina  in  the  female ;  (2)  the  perineal  body ;  (3)  the 
levator  ani  and  external  sphincter  of  the  anus  on  each  side  of  the  anal  canal ; 
(4)  the  ano-coccygeal  body,  between  the  anal  canal  and  the  coccyx,  containing 
the  main  insertions  of  the  levatores  ani  and  external  sphincter. 

The  levator  ani  muscle  completes  the  concave  floor  of  the  pelvic  cavity, 
sweeping  downwards  and  backwards  from  its  lateral  wall,  so  as  to  form  a 
muscular  diaphragm,  with  an  intra-pelvic  and  a  perineal  surface.  Its  upper 
concave  pelvic  surface  occupies  the  lateral  part  of  the  pelvic  floor.  Its  lower 
convex  surface  forms  the  oblique  medial  wall  of  the  ischio-rectal  fossa,  the  lateral 
wall  of  which  is  formed  by  the  obturator  fascia  covering  the  pelvic  surface 
of  the  obturator  internus.  In  this  wall  is  a  fascial  sheath  (Alcock's  canal), 
containing  the  internal  pudic  ^  vessels  and  nerve.  The  levator  ani  is  covered  on 
both  surfaces  by  pelvic  fascia.  The  anal  fascia  clothing  its  perineal  surface  is 
thin  and  unimportant.  The  fascia  covering  its  intra-pelvic  surface  is  thick  and 
strong.  At  the  origin  of  the  muscle  it  is  continuous  with  the  general  fascial 
lining  of  the  pelvic  cavity,  and  gives  rise  to  a  conspicuous  thickening,  the  linea 
alba  or  white  line  (arcus  tendinous),  which  stretches  like  a  bow-string  from  the  back 
of  the  symxjhysis  pubis  to  the  ischial  spine.  This  band  is  related  not  so  much  to 
the  origin  of  the  levator  ani  muscle,  which  often  extends  higher  up  beneath  the 
pelvic  fascia,  as  to  the  attachments  of  the  fascial  investments  of  the  genito-urinary 
passages,  to  be  described  below.     There  are  sometimes  additional  thickenings  of 

^  Pudic  vessels  =  pudendal  (B.N. A.). 


FASCIA  OF  THE  PELVIS. 


435 


the  fascia,  branching  upwards  from  the  white  line  towards  the  pelvic  brim.  At  the 
insertion  of  the  levator  ani,  the  fascia  clothing  its  pelvic  surface  is  attached  to  the 
perineal  body,  the  margin  of  the  anal  canal,  and  the  ano-coccygeal  body,  over  which 
it  passes  to  be  continuous,  above  the  raphe  of  insertion  of  the  levatores  ani,  with 
the  layer  of  the  opposite  side.  At  the  antero-inferior  border  of  the  muscle  the 
fascise  enclosing  it  become  continuous  with  the  deep  layer  of  the  triangular  ligament 
(superior  fascia  of  the  urogenital  diaphragm) :  at  its  postero-superior  border  they  join 
the  fascia  enclosing  the  coccygeus  muscle. 

Within  the  pelvic  basin,  the  walls  and  floor  of  which  are  thus  continuously 


Ve.sicula  scminalis 


Rfctal  diaiiui-1 


Recto- vesical  layer  of  pelvic  fascia 
Vas  deferens 


Obturator  foramen 

Suspensory  ligament 
of  prostate 


Lateral  true  ligament  of  bladder 


Wliite  line 


Prostate 
Pubo-prostatic  ligament 

Cavum  Retzii 


Urethra 
Fig.  3 i8.— Relations  of  the  Pelvic  Fascia  to  the  FvEctum  and  Prostate. 

invested  by  the  pelvic  fascia,  are  contained  the  rectum  and  bladder,  and  in  the  female 
the  uterus,  suspended  and  maintained  in  position  by  the  peritoneum,  extra-peritoneal 
tissue,  and  the  pelvic  vessels  and  nerves.  They  are  essentially  free  to  distend  or 
collapse,  and  are  not  bound  down  by  the  pelvic  fascia.  The  rectum  in  both  sexes 
extends  down  to  the  floor  of  the  pelvis,  where  the  anal  canal  takes  its  origin, 
invested  by  the  peritoneum  and  extra-peritoneal  tissue,  and  occupying  a  special 
rectal  channel ;  this  is  lined  by  pelvic  fascia,  which  gains  an  attachment  to  the 
floor  of  the  pelvis  at  the  margin  of  the  anal  canal. 

The  arrangement  of  the  fascia  in  relation  to  the  genito-urinary  passages  is 


•436 


THE  MUSCULAE  SYSTEM. 


essentially  different.  Just  as  from  the  perineal  aspect  the  pelvic  outlet  is  divisible 
into  two  different  parts, — a  posterior  or  dorsal  part,  comprising  the  ischio-rectal 
fosste  for  the  passage  of  the  anal  canal,  and  characterised  by  looseness  and  dis- 
tensibility ;  and  an  anterior  or  ventral  part, — the  urethral  triangle  for  the  genito- 
urinary passages,  and  characterised  by  firm  fixation  to  the  pubic  bones ;  so  also 
from  the  abdominal  aspect  it  is  found  that,  while  in  the  posterior  part  of  the  pelvis 
a  rectal  channel  exists,  in  which  the  rectum  is  free  to  collapse  and  distend,  in  the 
ventral  part  of  the  basin  the  genito-urinary  passages  are  firmly  fixed  by  means  of 
the  pelvic  fascia,  which  gives  rise  to  a  special  suspensory  ligament  for  the  prostate 
gland  and  the  prostatic  urethra  in  the  male,  and  for  the  urethra  and  vagina  in  the 
female.  A  crescentic  fold  of  pelvic  fascia  arises  in  the  neighbourhood  of  the  ischial 
spine  from  the  general  fascia  covering  the  pelvic  wall.     It  has  a  posterior  free 


Posterior  (recto-vesical)  layer 
Superior  layer  :  lateral  true  ligament  of  the  bladder 


Suspensory  ligament  of  the  prostate  gland 
:  Rectal  channel 


White  line 

Lateral  true 
ligament 

Pubo-prostatic 

ligament 

Cavum  Retzii 


Pubo-prostatic  [ 
ligament! 


Sheath  of  the 

prostate  gland' 

Deeji  layer  of, 

triangular  ligament 

Superficial  layer  of. 

triangular  ligament 


Compressor  urethr.«  muscle       ]  Anal  canal 

Sheath  of  the  prostate  gland 

Fig.  349. — Relations  op  Pelvic  Fascia  to  the  Rectum  and  Prostate 
(Medial  Section  of  the  Pelvis). 

edge,  through  which  the  vas  deferens,  vesical  vessels,  and  nerves  pass.  Sweeping 
across  the  middle  line,  this  border  is  continuous  with  the  fold  of  the  opposite 
side,  the  two  together  constituting  the  anterior  limit  of  the  rectal  channel.  The 
fascial  fold  is  composed  of  two  layers,  posterior  and  superior,  between  which  is  a 
large  plexus  of  veins.  They  have  separate  attachments  laterally  to  the  general 
pelvic  fascia.  The  posterior  (recto-vesical)  layer  passes  across  the  pelvis  between 
the  prostate  gland  and  the  rectum.  Its  lower  edge  is  attached  to  the  perineal 
body  between  the  base  of  the  triangular  ligament  and  the  beginning  of  the  anal 
canal.  It  forms  a  sheath  for  the  vesiculse  seminales  and  vasa  deferentia.  This  is 
rather  in  the  form  of  a  septum  than  a  complete  sheath ;  it  effectually  separates 
the  vesicuhe  seminales  and  the  bladder  from  the  rectum,  forming  the  front  wall  of 
the  rectal  channel,  but  it  allows  the  vesiculse  seminales  to  rest  directly  against  the 
bladder.  The  superior  layer  extends  forwards  to  the  symphysis  pubis.  It  has  a 
lateral  origin  from  the  white  Line  (arcus  tendineus)  in  its  whole  length,  and  sweeping 
over  the  prostate  gland,  it  is  inserted  along  its  line  of  junction  with  the  bladder, 
and  constitutes  the  so-called  lateral  true  lig-ament  of  the  bladder  (lig.  pubo-prostaticum 


FASCIA  OF  THE  PELVIS. 


437 


laterale).  It  contains  numerous  bundles  of  muscular  fibres  in  its  anterior  part, 
and  forms  a  sheath  for  the  passage  of  the  inferior  vesical  vein  along  the  lateral 
surface  of  the  prostate  gland.  In  front  the  fascia  stretches  from  the  back  of  the 
symphysis  pubis,  the  sub-pubic  ligament,  and  the  deep  layer  of  the  triangular 
ligament  (superior  fascia  of  the  urogenital  diaphragm)  to  the  neck  of  the  bladder 


Psoas  mltscle 


Suspensory  ligament  of 
tlie  vatcina  ami  iiretlira 


Obturator  foramen 

White  line 

Recto-vaginal  layer. 

'\^ 

Lateral  true  ligament        '\, 

of  bladder..         "'-^^ 

\         . 

Urethro- vaginal  layer           "•,_         ^\-ii'- 

jO^ 

Anterior  true  liga-         '■■._          "\       ^g 
ment  of  the  bladder,^                   ^jftSlH 

Cavum  Retzii                     \^!^l^l 

R,-'^ '"'.  '^ 

Clitori; 


Bulb  of  the  vagina 


Pubo-urethral  fascia  (anterior  true 

ligament  of  bladder)              ;         ;       ,'      ;  j 

Urethral  layer  of  pelvic  fascia       ;       .'       .'  ; 

Urethra      !       .'  j 

Vagina     •  ! 

Bulb  of  the  vagina  ; 

BtTLBO-CAVERXOSUS 


Ischial 
spine 
Rectal  channel 

•  ■;  •       External  sphiscter  ani 

'•  \  Levator  axi 

\  Intermai,  sphincter  ani 

Anal  canal 
Junction  of  rectum  and  anal  canal 
Internal  sphincter  ani 
External  sphincter  ani 

Fig.  350. — Relations  of  the  Pelvic  Fascia  to  the  Rectum,  Urethra,  and  Vagina  (Medial  Sectiou). 

and  the  prostate  gland,  forming  the  anterior  true  ligament  of  the  bladder,  or  pubo- 
prostatic ligament  (lig.  pubo-prostaticum  mediale).  It  is  continuous  across  the  middle 
line  with  the  ligament  of  the  opposite  side.  In  the  middle  line,  where  the  two 
ligaments  unite,  a  hollow  occurs  behind  the  symphysis  pubis,  known  as  the  cavum 
Retzii.  This  ligament  is  composed  of  several  layers  separated  by  large  veins  (the 
prostatic  plexus),  which  connect  the  inferior  vesical  vein  with  the  dorsal  vein  of  the 
penis  and  the  internal  iliac  vein. 

The  sheath  of  the  prostate  gland  (fascia  prostatae)  is  formed  by  (1)  the  deep  layer 
of  the  triangular  ligament  on  which  it  lies,  (2)  by  the  general  pelvic  fascia  covering 


438  THE  MUSCULAE  SYSTEM. 

the  intra-pelvic  surfaces  of  the  levatores  ani  on  each  side,  and  (3)  it  is  completed 
by  the  two  special  layers  of  pelvic  fascia  just  described  above  and  behind.  By 
these  means  the  prostate  gland  and  prostatic  urethra  are  given  a  lirm  attachment 
to  the  fore  part  of  the  pelvic  walls  and  floor. 

In  the  female  an  essentially  similar  arrangement  of  the  pelvic  fascia  occurs  in 
relation  to  the  vagina  and  urethra.  A  crescentic  fold  of  the  fascia  springs  from 
the  pelvic  wall  in  the  neighbourhood  of  the  ischial  spine,  and  sweeping  medially 
to  the  lateral  fornix  of  the  vagina  and  in  front  of  the  rectum,  separates  into  two 
layers,  posterior  and  superior.  Between  the  layers  are  numerous  vessels,  which, 
along  with  the  visceral  nerves,  pierce  its  free  edge.  The  posterior  (recto-vaginal) 
layer  passes  medially  behind  the  vagina,  and  gaining  the  middle  line  between  the 
vagina  and  rectum,  gives  rise  to  the  anterior  wall  of  the  rectal  channel,  and  is 
attached  below  to  the  perineal  body  in  the  floor  of  the  pelvis.  The  superior  layer, 
taking  origin  from  the  white  line,  is  attached  medially  to  the  neck  of  the  bladder, 
and  constitutes  the  lateral  true  ligament  of  the  bladder.  It  is  continuous  in  front 
with  the  anterior  true  ligament  of  the  bladder,  which,  as  in  the  male,  is  divisible  into 
several  layers  separated  by  veins.  An  intermediate  (urethro-vaginal)  layer  of  the 
fascia  passes  between  and  separates  the  urethra  and  vagina. 

The  urethra  and  vagina  are  by  means  of  these  layers  of  fascia  firmly  bound  to 
the  pelvic  walls  and  floor,  while  the  uterus  and  bladder  are  free  to  distend  in  the 
pelvic  cavity. 

MUSCLES   OF   THE   PELVIS. 

The  pelvic  diaphragm  consists  of  several  more  or  less  rudimentary  muscular 
slips,  constituting  the  levator  ani  and  coccygeus  muscles,  which  serve  to  uphold 
the  pelvic  floor,  and  are  related  to  the  rectum  and  the  prostate  gland  or  vagina. 

The  levator  ani  arises  from  (1)  the  lower  part  of  the  back  of  the  body  of 
the  pubis,  (2)  the  general  pelvic  fascia  above  or  along  the  ivhite  line  (arcus 
tendineus),  and  (3)  the  pelvic  surface  of  the  spine  of  the  ischium.  Its  fibres  are 
directed  downwards  and  backwards,  to  be  inserted  into  (1)  the  central  point  of 
the  perineum  (perineal  body),  (2)  the  external  sphincter  around  the  origin  of  the 
anal  canal,  (3)  the  ano-coccygeal  raphe  behind  the  anus,  and  (4)  into  the  sides  of 
the  lower  sacral  and  the  coccygeal  vertebrse. 

The  levator  ani  muscle  fills  up  and  completes  the  pelvic  floor  on  each  side  of 
the  middle  line.  Enclosed  in  a  sheath  derived  from  the  general  pelvic  fascia  along 
the  white  line,  the  muscle  presents  an  upper  concave  surface  in  relation  to  the 
pelvic  cavity,  prostate  gland,  and  rectum,  and  an  inferior  convex  surface  which 
appears  in  the  perineum  and  forms  the  inner  wall  of  the  ischio-rectal  fossa. 

The  levator  ani  is  divisible  into  four  parts — pubo-rectalis,  pubo-coccygeus,  ilio- 
coccygeus,  and  ilio-sacralis.  The  pubo-rectalis  (levator  prostata))  is  the  part  inserted  into 
the  central  point  of  the  perineum.  The  pubo-coccygeus  is  the  part  inserted  into  the  anus 
and  the  ano-coccygeal  raphe,  and  the  ilio-coccygeus  and  ilio-sacralis  are  represented  by 
the  fibres  attached  to  the  sacrum  and  coccyx.  The  first  two  are  best  developed  ;  the  last 
two  series  of  fibres  are  the  most  rudimentary.  These  several  parts  of  the  muscle  represent 
the  remains  of  the  flexor  caudse  of  tailed  animals. 

The  coccygeus  is  a  rudimentary  muscle  overlapping  the  posterior  border  of  the 
levator  ani.  It  arises  from  the  ischial  spine  and  the  lesser  sacro-sciatic  ligament, 
and  is  inserted  into  the  sides  of  the  lower  two  sacral  and  upper  two  coccygeal 
vertebrae.  The  muscle  is  in  contact  by  its  anterior  border  with  the  levator 
ani.  It  is  enclosed  in  pelvic  fascia,  assists  in  forming  the  pelvic  floor,  and  is  in 
contact  laterally  with  the  sacro-sciatic  ligaments. 

Nerve-Supply. 

The  levator  ani  is  suppHed  from  two  sources  :  by  the  perineal  (nuisf'ular)  branch  of  the  internal 
pudic  nerve,!  ^^d^  on  its  pelvic  surface,  by  special  bi'anches  froiii  tla-  third  and  fourth  sacral 
nerves.    The  coccygeus  is  supphed  on  its  pelvic  surface  by  the  third  and  fourth  sacral  nerves. 

1  Internal  pudic  nerve  =  iiudendal  nerve  (B.N. A.). 


MOEPHOLOGY  OF  THE  SKELETAL  MUSCLES. 


439 


Actions. 

(1)  The  levator  ani  and  coccygeus  serve  to  uphold  and  slightly  raise  the  pelvic  floor.  (2) 
They  are  likewise  capable  of  producing  slight  flexion  of  the  coccyx.  (3)  The  anterior  fibres 
of  the  levator  ani,  in  the  female,  sweeping  round  the  vagina,  compress  its  walls  laterally,  and 
along  with  the  sphincter  vaginae,  help  to  voluntarily  diminish  the  lumen  of  the  tube.  (4)  The 
same  jsart  of  the  muscle  in  the  male  elevates  tlie  prostate  gland  (levator  prostatte).  (5)  The  chief 
action  of  the  levator  ani  is  in  defcecation.    Along  with  the  external  sphincter  it  acts  as  a  sjjhincter 


Sacro-sciatic 
ligament  (cut) 


Sphincter  ani 
externus 


Fig.  351. 


-The  Fascial  and  Muscular  Wall  of  the  Pelvis  after  Removal  of  Part  of  the 
Left  Innominate  Bone. 


of  the  rectum,  closing  the  anal  canal.  During  defsecation  the  muscle  draws  uj^wards  the  anus 
over  the  faecal  mass,  and  so  assists  in  its  expulsion.  (6)  In  parturition,  in  the  same  way,  the 
muscle,  contracting  below  the  descending  foetal  head,  retards  delivery.  Contracting  on  the  foetal 
head,  it  draws  upwards  the  pelvic  floor  over  the  foetus,  and  so  assists  delivery. 

THE   DEVELOPMENT   AND   MORPHOLOGY   OF   THE   SKELETAL 

MUSCLES. 


It  has  already  been  shown,  in  the  chapter  on  general  embryology,  that  the  meso- 
blast  on  either  side  of  the  embryonic  medullary  tube  separates  into  three  main  parts — 
the  myotome,  nephrotome,  and  sclerotome  or  lateral  plates  (somatopleure  and  splanchno- 
pleure). 


440 


THE  MUSCULAK  SYSTEM. 


The  myotomes  ai-e  probably  directly  or  indirectly  the  source  of  the  striated  muscles 
of  the  whole  body.  Each  consists  at  first  of  a  quadrilateral  bilaminar  mass,  resting 
against  the  medullary  tube  and  notochord  on  either  side.  The  cleft  between  its  two  layers 
represents  the  remains  of  the  coelomic  cavity.  In  the  early  stages  of  embryonic  life  the 
growth  of  the  myotome  is  rapid.  On  its  inner  side  masses  of  cells  arise,  which  grow  in- 
wards and  surround  the  medullary  tube  and  notochord  to  form  the  foimdation  of  the 
vertebral  column.  On  its  outer  side  cells  appear  to  be  given  off  which  participate  in  the 
formation  of  the  cutis  vera.  At  the  same  time  the  dorsal  and  ventral  borders  of  the 
myotome  continue  to  extend,  and  present  extremities  (growing  points)  with  an  epithelial 
structure  for  a  considerable  period.      On  the  dorsal  side  it  overlies  the  medullary  tube,  and 


Fig.  352. — Scheme  to  Illustrate  the  Disposition  of  the  Myotomes  in  the  Embryo  in  Relation  to 

THE  Head,  Trunk,  and  Limbs. 

A,  B,  C,  First  three  ceithalic  myotomes ;  N,  1,  2,  3,  4,  Last  persisting  cephalic  myotomes  ;  C,  T.,  L.,  S.,  Co., 
The  myotomes  of  the  cervical,  thoracic,  lumbar,  sacral,  aud  caudal  regions;  I.,  IL,  IIL,  IV.,  V.,  VI., 
VTL,  VIII.,  IX.,  X.,  XL,  XII.,  refer  to  the  cranial  nerves  aud  the  structures  with  which  thej'  may  b© 
embryologically  associated. 


gives  rise  to  the  muscles  of  the  back  ;  while  by  its  ventral  extension,  which  traverses  the 
somatopleuric  mesoblast  in  the  body  wall,  it  produces  the  lateral  and  ventral  muscles  of 
the  trunk.  By  an  inward  extension  it  probably  gives  rise  also  to  the  hypaxial  muscles  of 
the  neck  and  loin.  The  cells  of  the  inner  layer  of  the  myotome  are  responsible  for  the 
formation  of  the  muscle  fibres.  The  cells  elongate  in  a  direction  parallel  to  the 
long  axis  of  the  embryo,  and  give  rise,  by  fusion  with  the  cells  of  neighbouring  myotomes, 
to  the  columns  and  sheets  of  muscles  of  the  back  and  trunk.  For  the  most  part  {e.g.  back 
and  abdomen)  the  originally  segmental  character  of  the  nuiscular  elements  is  lost  by  the 
more  or  less  complete  fusion  of  adjacent  myotomes.  The  intercostal  muscles,  however, 
are  the  direct  derivatives  of  individual  myotomes. 

Muscles  of  the  Limbs. — In  fishes  and  (doubtfully)  reptiles  there  is  evidence  that 
the  myotomes  are  concerned  in  the  formation  of  the  limb-muscles  by  their  extension  into 
the  limb-bud  in  a  manner  similar  to  that  described  for  the  trunk.     In  birds  and  mammals, 


MOEPHOLOGY  OF  a:HE  SKELETAL  MUSCLES.  441 

however,  in  which  the  limb -bud  arises  as  an  undifferentiated,  unsegmented  mass  of 
mesoblastic  tissue,  partly  from  the  mesoblast  surrounding  the  notochord,  and  partly  from 
the  somatopleuric  mesoblast,  the  myotomes  stop  short  at  the  root  of  each  limb,  and 
do  not  penetrate  into  its  substance.  Instead,  the  muscular  elements  of  the  limb  take 
origin  independently  as  double  dorsal  and  ventral  strata  of  fusiform  cells  on  the  dorsal  and 
ventral  surfaces  of  the  limb-bud.  These  strata  are  xmsegmented  ;  they  are  grouped  around 
the  skeletal  elements  of  the  limb,  and  they  gradually  become  differentiated  into  the  muscle 
masses  and  individual  muscles  of  the  limb. 

Muscles  of  the  Head. — Notwithstanding  the  obscurity  and  complexity  of  this 
subject,  it  appears  certain  that  at  least  tivo  series  of  elementary  structures  are  concerned 
in  the  formation  of  the  muscles  of  the  head  and  face — the  cephalic  myotomes  and  the 
muscular  structure  of  the  branchial  arches. 

The  number  of  myotomes  originally  existing  in  the  region  of  the  head  is  not  known, 
although  it  is  stated  with  some  authority  that  nine  is  the  complete  number.  The  first  three 
are  described  as  persisting  in  the  form  of  the  ocular  muscles,  the  last  three  in  relation  to 
the  muscles  of  the  tongue,  while  the  three  intervening  myotomes  disappear. 

The  following  table  shows  the  possible  fate  of  the  cephalic  myotomes  : — 

First,  Superior,  medial  and  inferior  recti,  obliquus  inferior,  levator  ijaljiebrse  superioris. 

Second,  Obliquus  superior. 

TJiird,  Eectus  lateralis. 

Fourth,  Fifth  and  Sixth,  Absent. 

Seventh,  ^ 


Eighth,  \  Muscles  of  the  tongue 

Ninth, 

Tenth  (first  cervical) 


Ninth,  j  Muscles  connecting  the  ci-anium  and  shoulder  girdle. 


The  mesoblastic  tissue  of  the  branchial  arches  is  probably  concerned  in  the  production  of 
the  following  muscles  of  the  face  and  neck  : — 

First  (mandibular)  arch  .         .  Muscles  of  mastication. 

iPlatysma  and  facial  muscles. 
Muscles  of  the  soft  palate. 
Stapedius,  stylo-hyoid,  and  digastric. 

Third  (thyro-hyoid)  arch  .         .         (iJ^^erforSrSor. 

jj,      ,,        7  rvii  /i        1  •  ;\        7  f  Middle  and  inferior  constrictors. 

Fourth  and  Ftfth  (branchial)  arches         ^Muscles  of  the  larynx. 


THE    NERVOUS    SYSTEM. 

THE  BEATN  AND  SPINAL  CORD,  WITH  THEIR  MENINGES. 

By  D.  J.  Cunningham,  M.D.,  F.E.S., 

Po^ofessor  of  Anatomy,  University  of  Edinhurgh. 


THE    NERVOUS    SYSTEM. 

THE  BRAIN  AND  SPINAL  CORD,  WITH  THEIR  MENINGES. 

By  D.  J.  Cunningham. 

The  nervous  system  connects  the  various  parts  of  the  body  with  each  other  and 
co-ordinates  them  into  one  harmonious  whole.  Its  relatively  great  bulk  and  its 
extreme  complexity  constitute  two  of  the  most  distinctive  structural  features 
of  man.  It  consists  of  two  parts,  viz.  the  cerebrospinal  nervous  system  and  the 
sympathetic  nervous  system. 

The  sympathetic  nervous  system  is  composed  of  a  chain  of  serially  disposed 
ganglia,  bound  to  each  other  by  intervening  nervous  cords,  and  placed  one  on  either 
side  of  the  vertebral  column.  In  addition  to  these  gangliated  cords,  the  sympathetic 
system  includes  certain  dense  plexuses  of  nerves  and  numerous  scattered  ganglia. 
The  whole  is  most  intimately  connected  with  the  cerebrospinal  nervous  system,  and 
both  have  apparently  a  common  developmental  origin.  The  separation  of  the 
nervous  system  into  the  two  leading  subdivisions  of  sympathetic  and  cerebro- 
spinal is  therefore  of  a  somewhat  arbitrary  kind. 

The  cerebrospinal  nervous  system  consists  of  the  brain,  which  very  nearly 
completely  fills  the  cranial  cavity,  and  the  spinal  cord  or  spinal  marrow,  which  only 
partially  fills  the  vertebral  canal.  These  are  continuous  with  each  other,  and  together 
constitute  the  cerebrospinal  axis.  Attached  to  the  brain  and  spinal  cord  are  the 
numerous  nerves  which  bring  the  various  parts  of  the  body  into  connexion  with  the 
central  nervous  axis.  There  are  thirty-one  pairs  of  symmetrically  disposed  spinal 
nerves  attached  to  the  sides  of  the  spinal  cord.  Each  of  these  nerves  is  connected 
to  the  side  of  the  cord  by  a  ventral  or  anterior  and  a  dorsal  or  posterior  root,  and 
the  dorsal  root  is  distinguished  by  presenting  a  distinct  oval  swelling,  termed  a 
spinal  ganglion,  on  that  part  of  its  course  immediately  internal  to  the  place  where 
the  two  roots  unite  to  form  the  spinal  nerve-trunk  (Fig.  365,  p.  453). 

The  cranial  nerves  are  twelve  in  number  on  each  side,  but  one  only  (viz.  the 
fifth  or  trigeminal)  presents  a  double-rooted  attachment  similar  to  a  spinal  nerve 
Several,  however,  possess  ganglia  in  every  respect  comparable  with  the  ganglia  on 
the  dorsal  roots  of  the  spinal  nerves.  These  are  the  fifth  or  trigeminal,  the  seventh 
or  facial,  the  eighth  or  auditory,  the  ninth  or  glosso-pharyngeal,  and  the  tenth  or 
vagus  cranial  nerves. 

CEREBROSPINAL  NEEVOUS  SYSTEM. 

The  brain  and  spinal  cord  are  composed  of  two  substances  which  present  a 
different  appearance  to  the  eye,  and  which  are  distinguished  by  the  terms  wliite 
matter  and  gray  martter.  The  difference  in  colour  between  these  two  substances 
depends  not  only  upon  the  different  elements  which  enter  into  their  formation,  but 
also  upon  the  fact  that  the  gray  matter  is  the  more  vascular  of  the  two.  The 
white  matter  is  chiefly  composed  of  nerve-fibres,  whilst  the  essential  constituents 
of  the  gray  matter  are  nerve-cells  which  give  origin  to  nerve-fibres.  An  all  per- 
vading matrix  termed  the  neuroglia  forms  the  bed  in  which  the  nerve-fibres  and 

443 


444 


THE  NEKVOUS  SYSTEM. 


nerve-cells  lie,  and  is  present  both  in  the  gray  and  the  white  matter.  The  elements, 
therefore,  which  constitute  nervous  tissue  are  nerve-cells,  nerve-fibres,  and  neuroglia. 
Nerve-fibres. — Nerve-fibres  arranged  in  bundles  of  greater  or  less  bulk  form 
the  nerves  which  pervade  every  part  of  the  body.  They  also  constitute  the  greater 
part  of  the  brain  and  spinal  cord.  Nerve-fibres  are  the  conducting  elements  of  the 
nervous  system ;  they  serve  to  bring  the  nerve-cells  into  relation  both  with  each 
other  and  with  the  various  tissues  of  the  body. 

There  are  different  varieties  of  nerve-fibres,  but  in  all  the  leading  and  essential 
constituent  is  a  delicate  thread-like  band,  termed  the  axis-cylinder.  The  difference 
between  individual  fibres  depends  upon  the  fact  that  in  some  cases  the  axis-cylinder 
becomes  invested  by  one  or  two  coats,  whilst  in  other  cases  it  remains  naked.  When 
the  axis-cylinder  is  coated  on  the  outside  by  a  more  or  less  thick  sheath  of  a  fatty 
substance  termed  myelin,  it  is  said  to  be  a  myelinated  or  medullated  fibre.  When  the 
coating  of  myelin  is  absent,  the  fibre  is  termed  a  non-myelinated  or 
a  non- medullated  fibre.  A  second  sheath — thin,  delicate,  and 
membranous,  and  placed  externally — may  also  be  present  in  both 
cases.  It  is  termed  the  primitive  sheath  or  the  neurolemma.  From 
a  structural  point  of  view,  therefore,  four  different  forms  of  nerve- 
fibre  may  be  recognised  : — 


Axis 
/cylinder 


Myelin 


^_^^Primitive 
J^  sheath 


TVT  J   m  i.  J  f  !•  Naked  axis-cvhnders. 

JNon-meaullated  <  n     \    ■       i-   j  -^.i       •    -u.-        i,     ^\. 

(  2.  Axis-cyhuders  with  primitive  sheaths. 

j  3.  Primitive  sheath  absent. 


Medullated 


\  4.  Primitive  sheath  present. 


Every  nerve-fibre  near  its  origin  and  as  it  approaches  its  termination 
is  unprovided  with  sheaths  of  any  kind,  and  is  simply  represented 
by  a  non -medullated  naked  axis  -  cylinder.  The  fibres  of  the 
olfactory  nerves  afford  us  an  example  of  non-meduUated  fibres 
furnished  with  a  primitive  sheath. 

Medullated  fibres  are  present  in  greater  quantity  in  the  cerebro- 
spinal system  than  non-medullated  fibres.  Thus  all  the  nerves 
attached  to  the  brain  and  cord,  with  the  exception  of  the  olfactory 
and  optic,  are  formed  of  medullated  fibres  provided  with  a  primitive 
sheath ;  whilst  the  entire  mass  of  the  white  substance  of  the  brain 
and  cord,  and  also  the  optic  nerves,  are  formed  of  medullated  fibres 
devoid  of  a  primitive  sheath. 

It  is  important  to  note  that  the  distinction  between  the  medul- 
lated and  non-medullated  fibres  is  not  one  which  exists  throughout 
all  stages  of  development.  As  will  be  presently  pointed  out,  every 
fibre  is  a  direct  outgrowth  from  a  cell,  and  in  the  first  instance  it  is 
not  provided  with  a  medullary  sheath.  Indeed,  it  is  not  until 
about  the  fifth  month  of  foetal  life  that  those  fibres  which  are  to 
form  the  white  substance  of  the  cerebrospinal  axis  begin  to  acquire 
their  coating  of  myelin.  Further,  this  coating  appears  in  the  fibres 
of  different  strands  or  tracts  at  different  periods,  and  a  knowledge 
FROM  A  FaoG  (after  ^^  ^^^^  ^^^^  ^yg.^  enabled  the  anatomist  to  follow  out  the  connexions' 
of  the  tracts  of  fibres  which  compose  the  white  matter  of  the 
brain  and  cord. 

But  it  may  be  asked :  How  does  a  nerve-fibre  arise  and  how  does  it  end  ? 
Every  fibre  is  directly  continuous  by  one  extremity  with  a  nerve-cell,  whilst  its 
opposite  extremity  breaks  up  into  a  number  of  ramifications,  all  of  which  end 
freely  in  relation  to  another  nerve-cell,  or  in  relation  to  certain  tissues  of  the  body, 
as,  for  example,  to  muscle-fibres  or  to  the  epithelial  cells  of  the  epidermis.  The 
length  of  nerve-fibres,  therefore,  varies  very  greatly.  Some  fibres  are  short  and 
merely  bring  two  neighbouring  nerve-cells  into  relation  with  each  other :  others 
travel  long  distances.  Thus  a  fibre  arising  from  one  of  the  motor  cells  of  the  lower 
end  of  the  spinal  cord  may,  after  leaving  the  cord,  extend  to  the  most  outlying 
muscle  in  the  sole  of  the  foot  before  it  reaches  its  destination.  But  even  when  a 
fibre  does  not  leave  the  central  axis  a  great  length  may  be  attained,  and  cells 


Fig.  .353. 
Nerve-fibhe 


CEKEBKOSPINAL  NEKVOUS  SYSTEM. 


445 


situated  in  the  motor  area  of  the  cortex  of  the  cerebrum  give  origin  to  fibres  which 
pass  down  to  the  lower  end  of  the  cord. 

Physiologists  classify  the  fil^res  whicli  form  the  nerves  into  two  sets,  afferent 
and  efferent.  Afferent  nerve-fibres  conduct  the  impulse  of  impressions  from  the 
peripheral  organs  into  the  central  nervous  system  ;  and  as  a  change  of  consciousness, 
or,  in  other  words,  a  sensation  is  a  frequent  result,  these  fibres  are  often  called 
sensory.  Efferent  nerve-fibres  carry  impulses  out  from  the  brain  and  cord  to  peri- 
pheral organs.  The  majority  of  these  fibres  go  to  muscles  and  are  termed  motor ; 
others,  however,  go  to  glands  and  are  called  secretory ;  whilst  some  are  inhibitory 
and  serve  to  carry  impulses  which  restrain  or  check  movement  or  secretion.  As 
previously  stated, 
the  spinal  nerves  are 
each  attached  to  the 
cord  by  a  ventral  or 
anterior  root,  and  a 
dorsal  or  posterior 
root;  the  fibres  com- 
posing the  former 
are  efferent ;  whilst 
the  fibres  of  the 
posterior  root  are 
almost  entirely 
afferent. 

Nerve  -  cells.  — 
The  nerve-cells  con- 
stitute the  active 
and  all-essential 
elements  of  nerve- 
tissue.  At  the  very 
start  it  is  necessary 
to  draw  a  broad 
distinction  between 
the  ganglionic  cells, 
wliich  are  found  in 
the  spinal  ganglia, 
and  the  cells  which 
are  so  plentifully 
scattered  through 
the  gray  matter  of 
the  brain  and  cord. 
They  differ  not  only 
in  their  mode  of 
origin  and  in  their 
subsequent  develop- 
ment, but  also  in  the  connexions  of  the  nerve-fibres  to  which  they  give  origin. 

Nerve-cells  of  the  Brain  and  Cord. — The  cells  in  the  gray  matter  of  the 
cerebrospinal  axis  are  variable  both  in  size  and  form.  Some  are  relatively  large, 
as,  for  example,  certain  of  the  pyramidal  cells  of  the  cerebral  cortex  and  the  motor 
cells  in  the  gray  matter  of  the  cord,  w^hich  almost  come  within  the  range  of  unaided 
vision ;  others  are  exceedingly  minute,  and  require  a  high  power  of  the  microscope 
to  bring  them  into  view.  The  cell  consists  of  a  protoplasmic  nucleated  body,  from 
which  certain  processes  proceed.  One  process  is  termed  the  axis-cylinder  process  or 
axon ;  and  as  a  rule  it  is  easily  distinguished  from  the  others,  which  are  collectively 
called  the  protoplasmic  processes  of  Deiters,  or  the  dendrites. 

The  axon  presents  a  uniform  diameter  and  a  smooth  and  even  outline.  It  gives 
off  in  its  course  fine  collateral  branches,  but  does  not  suffer  thereby  any  marked 
diminution  in  its  girth.  The  most  important  point  to  note  in  counexion  with  the 
axon,  however,  is  the  fact  that  it  becomes  continuous  with  the  axis-cylinder  of  a 
nerve- fibre.     The  significance  of  this  is  obvious,  and  will  become  more  striking 


Fic.  354. 


-Three  Nerve-Cells  from  the  Antekiur  Horn  ok  Gray 
Matter  of  the  Human  Spixal  Cord. 


446 


thp:  nervous  system. 


when  the  development  of  the  nerve-cells 
is  studied.  The  axon  then  is  simply  a 
nerve-fibre,  and  in  certain  circumstances  it 
assumes,  as  already  stated,  one  or  two 
investing  sheaths.  The  axon  may  run  its 
entire  course  within  the  substance  of  the 
brain  or  cord  either  for  a  short  or  a  long 
distance,  or  it  may  emerge  from  the  brain 
or  cord  in  one  of  the  cranial  or  spinal 
nerves  as  the  essential  part  of  an  efferent 
nerve -fibre,  and  run  a  variable  distance 
before  it  finally  reaches  the  peripheral 
structure  in  relation  to  which  it  ends.  The 
axon  and  the  collaterals  which  spring  from 
it  terminate  either  in  small  button-like 
swellings  or  knobs,  or  more  frequently  in 
terminal  arborisations,  the  extremities  of 
which  are  free  and  are  furnished  with  ex- 
ceedingly small  terminal  varicosities.  In 
those  cases  where  the  axon  or  its  collaterals 
end  within  the  brain  or  cord,  some  of  the 
terminal  arborisations  interlace  with  the 
dendrites  of  nerve-cells,  whilst  others  are 
twined  around  the  bodies  of  other  cells. 
In  the  latter  case  the  interlacement  may 
be  so  close  and  complete  that  it  almost 
presents  the  appearance  of    an   enclosing 


Fig.  355. — Two  Multipolar  Nebve- 
Cells,  from  a  specimen  prepared 
by  the  Golgi  method. 


basket  -  work.  In  cases 
where  the  axon  emerges 
from  the  cerebrospinal  axis 
its  terminal  arborisation 
ends  in  relation  to  a  muscle- 
fibre  or  some  other  tissue 
in  the  manner  already  re- 
ferred to.  In  all  cases, 
however,  it  would  appear 
that  the  terminal  branches 
of  the  axon,  no  matter  how 
complicated  the  connexion 
may  seem,  are  free,  and 
that  the  connexion  is 
simply  one  of  contact  or 
contiguity,  and  not  one  of 
continuity. 

Held  maintains  that, 
although  at  first  the  terniinal 
arborisations  of  an  axon  are 
quite  free,  in  the  process  of 
growth  and  development  they 
exhibit  a  tendency  to  become 
fused  with  the  dendrites  and 
even  the  bodies  of  other 
nerve-cells. 


Fin.   356. — Nrrve-Cki.l   from    Cekebei  lUiM    (Cell   ov   Porkin.ie) 

SHOWING    THE    BRANCHING    OK     THE     DkNDRITIC     PROCESSES    (from 

a  lantern  slide  by  Professor  Symington). 


CEKEBROSPINAL  NERVOUS  SYSTEM. 


447 


The  dendrites,  or  protoplasmic  processes  of  the  nerve-cell,  are  thicker  than  the 
axon,  and  present  a  rough  -  edged  irregular  contour.  They  divide  into  numerous 
branches,  and  these  gradually,  as  they  pass  from  the  cell-body,  become  more  and 
more  attenuated  until  they  finally  end  in  free  extremities.  The  branching  of  the 
dendritic  processes  sometimes  attains  a  marvellous  degree  of  complexity  (Fig.  356), 
but  except  in  exceptional  circumstances,  there  is  no  anastomosis  between  the 
dendrites  of  neighbouring  cells,  or  between  the  dendrites  of  the  same  cell.  It 
would  appear,  therefore,  tliat  nothing  in  the  shape  of  a  network  is  formed  by  tliese 
processes. 

In  the  chapter  upon  Embryology  it  has  been  shown  that  in  the  early  condition 
of  the  cerebrospinal  axis  the  brain  and  cord  consist  simply  of  a  tube  (p.  21).  The 
wall  of  this  tube  is  formed  of  a  single  layer  of  tall  colunniar  neuro-epithelial  cells, 


MID-DORSAL  LAMINA 


MVELO- 

SPONIGIUM 


NEURO- 
BLAST 


RETIC- 
ULUM 


MID-VENTRAL  LAMINA 


Fig.  357. — Transverse  Section  through  the  early  Neural 
Tube,  diagraiiimatically  represented  (Alfred  H.  Young). 

The  left  side  of  the  section  exhibits  an  earlier  stage  of 
development  than  the  right  side. 


Fig.  358. — The  Developmental 
Stages  exhibited  by  a  pyra- 
midal Cell  of  the  Brain  (after 
Ramon  y  Cajal). 

a,  Neuroblast  with  rudimentary 
axon,  but  no  dendrites  ;  b  and  c, 
The  dendrites  beginning  to  sprout 
out ;  d  and  e.  Further  develop- 
ment of  the  dendrites  and  ap- 
pearance of  collateral  branches 
on  tlie  axon. 


and  in  its  deepest  or  most  internal  part  large  round  cells  make  tlieir  appearance 
in  the  intervals  between  the  epithelial  columns.  These  new  cells  are  termed  the 
germinal  cells,  and  from  them  the  nerve-cells  are  derived.  They  are  present  in 
considerable  numbers,  and  towards  the  fourth  week  of  embryonic  life  they  form  an 
almost  continuous  layer.  Although  these  cells  ultimately  become  nerve-cells  they 
are  absolutely  without  processes  in  their  early  state,  and  therefore  at  this  period, 
although  there  is  a  nervous  system,  there  are,  as  His  remarks,  no  nerves.  In 
course  of  time,  and  as  the  wall  of  the  neural  tube  thickens,  the  germinal  cells 
begin  to  migrate  in  an  outward  direction.  They  leave  the  deep  part  of  the  wall 
of  the  neural  tube  and  proceed  to  take  up  the  positions  they  occupy  in  the  gray 
matter  of  the  cord  and  brain  of  the  adult.  These  migrating  cells  assume  a  pyriform 
shape,  and  are  termed  neuroblasts.  The  drawn-out  portion  or  stalk  of  the  pear- 
shaped  neuroblast  represents  the  early  axon,  and  this  continues  to  grow  and  increase 
in  length  until  it  ultimately  attains  the  terminal  relations  characteristic  of  the 
adult.  The  study  of  embryology  presents  few  more  remarkable  phenomena  than  the 
manner  in  which  this  axon  grows  out,  and,  in  the  efferent  nerve-fibres,  emerges 


448  THE  NEKVOUS  SYSTEM. 

from  the  central  axis,  and  yet  pursues  its  allotted  path  with  the  most  unerring 
exactitude  and  precision  until  it  ultimately  reaches  the  nerve-cell  or  the  peripheral 
tissue  element  with  which  it  becomes  associated.  The  growing  point  of  both  it 
and  its  collaterals  is  slightly  bulbous,  and  it  is  out  of  this  that  the  terminal 
arborisation  is  formed. 

This  conception  in  regard  to  the  outgrowth  of  the  axon  in  the  case  of  the  peripheral 
nerve-fibres  has  not  been  allowed  to  pass  unchallenged,  and  it  must  be  admitted  that 
certain  facts  recently  observed  militate  against  it. 

Whatever  opinion  may  be  held  in  regard  to  the  developmental  origin  of  the  axis- 
cylinder  and  medullary  sheath  of  a  peripheral  nerve-fibre,  there  is  every  reason  for  the 
belief  that  the  neurolemma  is  mesodermic  in  its  origin,  and  is  therefore  formed  from  cells 
outside  the  ectodermic  neural  tube.  There  are  some  who  think  that  the  axis-cylinder  is 
secreted  in  situ  by  a  chain  of  these  cells,  whilst  others  consider  that  the  mesoblastic  cells 
of  a  nerve-fibre  merely  constitute  a  cellular  tube  through  which  the  growing  axon  worms 
its  way  to  its  destination,  and  perhaps  also  supply  the  pabulum  necessary  for  its  growth. 

The  dendritic  processes  of  the  nerve-cell  appear  at  a  later  period  than  the  axon. 
The  surface  of  the  neuroblast  becomes  rough  and  then  somewhat  spiny.  By  the 
growth  and  subdivision  of  these  spiny  projections  the  dendrites  are  formed.  As 
His  remarks,  the  nerve-cell  is  therefore  the  genetic  centre  from  which  all  the  parts 
of  a  nervous  element  proceed. 

It  must  now  be  clear  that  each  nerve-cell  is  a  unit  which  is  separate  and  distinct 
from  the  nerve-cells  which  lie  around  it.  Further,  it  is  obvious  that  it  is  wrong  to 
consider  the  nerve-cell  as  something  apart  from  the  nerve-fibre.  The  nerve-cell 
with  its  dendrites  and  axon,  however  wide-spreading  these  processes  may  be, 
constitutes  an  independent  system  to  which  the  term  neuron  is  applied,  and 
the  only  relation  which  it  has  with  other  neurons  or  with  peripheral  tissues  is  one 
of  contact. 

Ganglionic  Nerve-Cells. — The  ganglionic  neurons  found  in  the  ganglia  of  the 
cranial  nerves  and  in  the  ganglia  on  the  dorsal  roots  of  the  spinal  nerves  have  a 
different  origin,  and  present  many  points  of  contrast  with  neurons  in  the  gray  matter 
of  the  brain  and  cord.  As  already  indicated  in  the  chapter  on  Embryology  (p.  21) 
the  ganglia  in  question  are  derived  from  the  neural  crest.  The  cells  forming  these 
ganglionic  masses  are  somewhat  oval  in  form,  and  from  either  extremity  or  pole  a 
process  grows  out,  and  the  neurons  in  this  manner  become  bipolar.  These  processes 
are  distinguished  as  central  and  peripheral,  according  to  the  direction  which  they 
take.  The  central  processes  grow  inwards,  and  penetrate  the  wall  of  the  neural 
tube.  In  the  region  of  the  spinal  cord  they  form  almost  the  whole  of  the  fibres 
which  enter  into  the  composition  of  the  dorsal  roots  of  the  spinal  nerves.  In  the 
substance  of  the  cerebrospinal  axis  they  give  off  numerous  collaterals,  and  after  a 
course  of  varying  extent  they  end,  after  the  manner  of  an  axon,  in  terminal 
arborisations,  which  enter  into  relationships  of  contact  with  certain  nerve-cells  in 
the  cerebrospinal  axis.  The  peripheral  processes  grow  outwards  along  the  path  of 
the  particular  nerve  with  which  they  are  associated,  and  they  finally  establish 
peripheral  contact  relations.  Thus,  to  take  one  example  :  the  majority  of  the  fibres 
which  go  to  the  skin  break  up  into  fine  terminal  filaments,  which  end  freely 
between  the  epithelial  cells  of  the  epidermis.  The  two  processes  of  a  ganglion  cell, 
therefore,  form  the  afferent  fibres  of  the  cerebrospinal  nerves,  and  constitute  the 
path  along  which  the  influence  of  peripheral  impressions  is  conducted  towards  the 
brain  and  cord.  The  body  of  the  cell  is  as  it  were  interposed  in  the  path  of  such 
impulses. 

But  the  original  bipolar  character  of  these  cells,  with  very  few  exceptions 
(ganglia  in  connexion  with  the  auditory  nerve  and  the  bipolar  nerve-cells  in  the 
olfactory  mucous  membrane),  gradually  undergoes  a  change  which  ultimately  leads 
to  their  transformation  into  unipolar  cells.  This  is  brought  about  by  the  tendency 
which  the  cell-body  has  to  grow  to  one  side,  viz.  the  side  towards  the  surface  of  the 
ganglion  (v.  Lenhossek).  This  unilateral  growth  leads  to  a  gradual  approxima- 
tion of  the  attached  ends  of  the  processes,  and  finally  to  a  condition  in  which  they 
appear  to  arise  from  the  extremity  of  a  short  common  stalk  in  a  T-shaped  manner 


CEEEBROSPIXAL  NERVOUS  SYSTEM. 


449 


.c« 


pAL 


^!i 


SPINAL 

'ganglion 


(Fig.  360).       It  is  interesting  to  note  that    in  certain  fish  the  original   bipolar 
condition  of  these  cells  is  retained  throughout 
life  without  change. 

Both  the  central  and  peripheral  processes 
of  these  ganghonic  cells  become  the  axis- 
cylinders  of  nerve-fibres,  which,  acquiring  a 
medullary  sheath,  belong  therefore  to  the 
medullated  variety.  From  this  it  might  very 
naturally  be  thought  that  the  ganglionic 
neuron,  with  its  two  axons  and  no  typical 
dendrites,  is  a  nervous  unit  very  different 
from  a  neuron  in  the  gray  matter  of  the 
cerebrospinal  axis.  It  is  believed  by  some, 
however  (van  Gehuchten  and  Cajal),  that  the 
peripheral  process,  in  spite  of  its  enclosure 
within  a  medullary  sheath,  and  though  pre- 
senting all  the  characters  of  a  true  axon,  is  in 
reality  a  dendrite.  If  this  be  the  case,  the 
morphological  difference  between  a  dendrite 
and  an  axon  disappears,  and  van  Gehuchten's 
functional  distinction  alone  remains  character- 
istic, viz.  that  the  axon  is  ceUulifugal  and 
conducts  impulses  away  from  the  cell,  whilst 
the  dendrites  are  celhdipetal  and  conduct  im- 
pulses towards  the  cell. 

In  the  foregoing  brief  account  of  the  elements  which 

build  up  the  nervous  system,  the  neuron  doctrine,  as  it 

has  been  enunciated  by  Waldeyer,  has  been  followed. 

The   observations   of  Ramon  y  Cajal  and   His  form 

the  foundation  upon  which  this  doctrine  mainly  rests, 

although  it  should  not  be  forgotten  that  many  other 

anatomists,   amongst   whom    may   be    mentioned    v. 

KoUiker,  van  Gehuchten,  and  v.  Lenhossek,  have  by 

their  investigations  greatly  strengthened  the  concep- 
tion.    Two  primary  considerations  may  be  considered 

to  constitute  its  leading  support :  (1)  the  absolute 
independence  of  the  early  nerve-cell  or  neuroblast 
and  its  processes,  as  was  first  clearly  shown  by  His  ; 
(2)  the  fact  that  when  nerve  tissue  is  treated  by  the 
Golgi  method  or  by  the  vital  methylene  blue  method 
no  continuity  of  any  kind  can  lie  observed  between 
neighbouring  cells,  although  the  processes  of  the  cells 
can  apparently  be  traced  to  their  ultimate  divisions. 
Fiu-ther,  it  should  be  noted  that  the  neuron  doctrine 
receives  strong  support  from  pathological  observa- 
tions, and  that  before  it  assumed  concrete  form  ideas 
of  a  somewhat  similar  kind  were  present  in  the 
minds  of  pathologists. 

Still  the  neuron  theory  is  not  accepted  by  several 
leading  Histologists.  Apathy,  Xissl,  and  Bethe  at 
the  present  moment  form  a  powei-ful  combination 
against  it.  It  is  therefore  necessary  to  indicate  the 
views  entertained  by  these  observers. 

More  than  thirty  years  ago  Max  Schultze  called 
attention  to  the  fact  that  the  axis  -  cylinder  of  a 
nerve-fibre  is  composed  of  exceedingly  fine  fibrils^ 
which,  when  traced  to  the  cell  from  which  the 
fibre  takes  origin,  are  there  seen  to  enter  the  cell- 
body  and  spread  out  within  it.  By  more  delicate 
methods  of  research,  Apathy  and  Bethe  have  been 
able  to  place  this  early  observation  of  Schultze 
beyond  the  realm  of  doulit.  Apathy,  who  worked 
chiefly  at  the  invertebrate  nervous  system,  not  only 
traced  the  neuro-fibrilla3  through  the  cell-body  but 

'  It  may  be  mentioned  that  Eemak,  the  discoverer  of  the  axis-cylinder  in  1838,  stated  that  it  was  finely 
striated  in  the  longitudinal  direction. 


Fig.  359. — Diagram  of  the  Connexion  estab- 
lished BY  A  Ganglionic  and  a  Motor 
Necron  (Ramou  y  Cajal). 

A.  Fibre  coining  down  from  a  pjTamiclal  cell  in  the 

motor  area  of  the  cerebral  cortex. 

B.  Motor  cell  in  gray  matter  of  spinal  cord. 

C.  Muscle-fibres. 

D.  Collateral  branch  from  the  pyramidal  fibre. 

E.  Cell  in   the   medulla  oblongata  sending  its  axon 

upwards  to  the  cerebral  cortex. 

F.  Cells  in  the  spinal  ganglion. 

G.  Peripheral  process  of  ganglionic  cell  ending  in  skin. 
I.    Collateral   branches   of    central   process   of   gan- 
glionic cell. 

S.X.  Spinal  nerve. 


Fig.  360. — Three  Stages  in  the  Development 
of  a  Cell  from  a  Spinal  Ganglion. 


450 


THE  NERVOUS  SYSTEM. 


into  all  its  processes,  aud  lie  believes  that  he  has  been  able  to  follow  them  beyond  these  into  a 
delicate  fibrillar  interlacement  which  constitutes  a  bond  of  union  between  all  the  nerve-cells  of  the 
nervous  sj'stem.  Bethe's  observations  have  been  carried  out  in  vertebrates.  Two  illustrations  from 
his  book  are  reproduced  in  Fig.  361.  The  cell  represented  in  A  is  from  the  gray  matter  of  the 
anterior  horn  of  the  human  spinal  cord,  and  the  relation  presented  by  the  neuro-fibrils  within  the 
cell  and  to  its  various  processes  are  very  clearly  depicted.  The  axon  appears  to  receive  a  con- 
tribution of  neuro-fibrilhe  from  all  the  dendritic  processes  ;  this,  according  to  Bethe,  is  character- 
istic of  the  great  majority  of  nerve-cells.  In  the  cells  indicated  by  the  letter  B,  Avhich  are  from 
the  cerebral  cortex  of  man,  it  will  be  noticed  that  tlie  axons  as  they  leave  the  cell  become  ex- 
ceedingly fine  and  delicate,  and  the  neuro-fibrillte  which  compose  them  are  so  closely  packed 
together  that  all  trace  of  their  individual  existence  disappears.  When  the  medullary  sheath 
is  assumed  by  the  fibi-e  the  neuro-fibrillae  of  the  axis-cylinder  again  become  apparent. 


!f  .',1  ■'■,  .\  V  \ 


■7^ 


Axon 


MM 


•^^<^ 


.;// 


Axons 


Fig.  361. — Neuve  Cells  as  DEriCTEU  by  Bethe. 

A,  A  cell  from  the  anterior  horn  of  gray  matter  of  the  spinal  cord  of  man. 

B,  Two  cells  from  the  human  cerebral  cortex. 

In  vertebrates  Bethe  has  not  been  able  to  trace  the  neuro-fibrils  into  an  all-pervading 
filjrillar  network  such  as  Apdthy  has  described  as  binding  the  various  nerve  elements  together  in 
the  invertel)rates,  but  lie  has  followed  them  into  the  finest  of  the  dendritic  branchings,  and  he 
a,ssumes  that  the  connecting  network  exists  in  the  higher  as  well  as  in  the  lower  members  of  the 
animal  kingdom. 

This  conception  of  the  structure  of  the  axon  renders  the  giving  off  by  the  nerve-fibre  ol 
collateral  brandies  and  also  its  terminal  splitting  or  arborisation,  matters  which  can  be  the  more 
easily  understood. 

On  the  strength  of  the  observations  detailed  above,  Apathy,  Bethe,  and  Nissl,  all  of  whom  are 
authorities  who  deserve  the  highest  degree  of  attention,  have  assailed  the  neuron  theory. 
Apdthy  has  advanced  the  liypothesis  that  the  all-pervading  filnillar  interlacement,  which  streams 
continuously  throughout  the  whole  nervous  system  and  is  found  not  only  in  the  cell  and  its 
proces.ses  but  also  in  the  form  of  a  connecting  network  outside  the  cells,  is  the  essential  part 
of  the  nervous  system  and  not  the  so-called  indejjcndent  neurons  of  the  neuron  theory.  It  is 
aiso  contended  that  axons  or  axis-cylinders  may  ari.se  in  two  ways  :  (1)  directly  from  the  nervc- 
celLs  ;  (2)  indirectly  from  the  neuro-fibrillar  network  between  the  nerve-cells. 

In  a  striking  address  recentl^y  delivered  by  Profes.sor  Waldeyer  to  the  Eoyal  Society  of  Edin- 


CEREBROSPINAL  NERVOUS  SYSTEM. 


451 


burgh  the  essential  iDoints  of  the  neuron  doctrine  were  vigorously  maintained  and  several  new 
preparations  by  Raniun  y  Cajal  and  Beilschowsky  were  demonstrated.  In  the  latter  the  neuro- 
fibrillaj  were  seen  to  enter  the  cell-body,  spread  out  and  break  up  into  a  plexus  within  it,  but 
none  could  be  detected  pursuing  an  uninterrupted  course  right  through  tlie  cell  and  then  passing 
out  from  it. 

As  Edinger  remarks,  investigation  in  the  immediate  future  will  be  largely  concerned  in  the 
attempt  to  further  elucidate  the  following  questions  :  (1)  Are  the  connexions  between  neurons 
merely  those  of  contact?  (2)  Do  the  fibres  which  proceed  from  one  cell  fuse  witli  the  constituent 
parts  of  another  neuron  ?  (3)  Do  the  neuro- fibril Ite  form  an  inter-connecting  network  between 
the  nerve-cells,  and  do  axons  or  axis-cylinders  arise  from  such  a  network  ?  It  is  questionable 
even  if  the  last  two  of  these  queries  are  answered  more  or  less  in  the  affirmative  whether  it  will 
be  necessary  to  abandon  the  essential  points  in  the  neuron  theory. 

Since  the  foregoing  has  been  printed  an  instructive  monograph  on  the  subject  has  been 
published  by  Professor  Gustaf  Retzius  ("Punktsubstanz  '  Nervoses  Grau'  und  Neuronenlehre," 
Biologische  Unfersuchungen,  Neue  Folge,  xii.). 

Neuroglia. — The  neuroglia  is  the  supporting  tissue  of  the  cerebrospinal  axis. 
It  may  be  considered  to  include  two  different  forms  of  tissue,  viz.  the  lining 
ependymal  cells  and  the  neuroglia  proper.  We  place  these  under  the  one  heading, 
seeing  that  in  all  probability  they  both  have  a  common  developmental  origin. 

The  ependymal  cells  are  the  columnar  epithelial  cells  which  line  the  central 
canal  of  the  spinal  cord  and  the  ventricles  of  the  brain.  In  the  embryonic  condi- 
tion a  process  from  the  deep  extremity  of  each  cell  traverses  the  entire  thickness 
of  the  neural  wall  and  reaches  the  surface.  It  is  not  known  whether  this  process 
exists  in  the  adult. 

The  neuroglia  proper  is  present  in  both  the  white  and  the  gray  matter  of  the 
cerebrospinal  axis.  It  constitutes  an  all- 
pervading  basis  substance,  in  which  the 
various  nerve  elements  are  embedded  in 
such  a  way  that  they  are  all  bound  together 
into  a  consistent  mass  and  are  yet  all  sever- 
ally isolated  from  each  other.  Neuroglia 
consists  of  cells  and  fine  filaments.  The 
fibrils  are  present  in  enormous  numbers, 
and  by  their  interlacements  they  constitute 
what  appears  to  be  a  fine  feltwork.  At  the 
points  where  the  fibrils  intercross  may  be 
seen  the  flattened  glial  cells.  Whilst  the 
neuroglia  is  for  the  most  part  intimately 
intermixed  with  the  nerve  elements,  there 
are  in  both  brain  and  cord  certain  localities 
where  it  is  spread  out  in  more  or  less  pure 
layers.  Thus  upon  the  surface  of  the  brain 
and  of  the  spinal  cord  there  is  such  a  layer ; 
likewise  beneath  the  epithelial  lining  of  the 
central  canal  and  of  the  cavities  of  the  brain 
there  is  a  thin  stratum  of  neuroglia. 

The  ependymal  cells  are   derived  from 
the   original   neuro- epithelial    cells   of   the 
early  neural    tube,  and   in    all    probability 
the  neuroglia  proper  has  a  similar  origin.     They  both,  therefore,  are  products  of  the 
ectoderm. 

Summary. — 1.  The  cerebrospinal  nervous  system  is  composed  of  two  parts,  viz. 
(a)  a  medullary  part,  consisting  of  the  brain  and  spinal  cord,  with  the  efferent  nerve- 
fibres  which  pass  out  from  them:  (&)  the  ganglionic  part,  with  the  afferent  nerve-fibres. 

2.  Each  of  these  parts  has  a  different  origin  and  is  composed  of  neurons  which 
possess  characteristic  features. 

3.  The  ganglionic  neurons  are  derived  from  the  primitive  cells  of  the  neural 
crest,  and  have  each  one  process  which  divides  into  two.  Of  these  the  central 
division  enters  the  cerebrospinal  axis  and  probably  represents  the  axon,  whilst  the 
peripheral  division,  which  becomes  connected  with  a  peripheral  part,  may  pro- 
visionally be  regarded  as  a  dendrite.     The  central  fibres  from  the  ganglionic  cells 


Fig.  362.  —  Section    THiiouciH     the     Central 
Canal  ok  the  Spinal  Cord  of  a  Human 
Embryo,  showino  Ependymal  and  Neur- 
oglial Cells  (after  v.  Leuhossek). 
A,  Ependymal  cell.  B,  Neuroglial  cell. 


452 


THE  NEEVOUS  SYSTEM. 


in  the  region  of  the  cord  form  the  dorsal  or  posterior  roots  of  the  spinal  nerves. 
These  roots  have  thus  an  origin  outside  the  cord,  and  grow  into  its  substance  in 
the  process  of  development  in  the  same  manner  that  the  roots  of  a  plant  strike 
into  the  soil. 

4.  The  cerebrospinal  neurons  are  derived  from  the  germinal  cells  in  the  wall 
of  the  early  neural  tube.  Certain  of  these  furnish  efferent  nerve-fibres,  which 
issue  from  the  cord  in  separate  bundles  termed  the  anterior  or  ventral  roots  of  the 
spinal  nerves.  In  the  case  of  the  cranial  nerves,  however,  with  the  exception  of 
the  trigeminal  and  facial  nerves,  the  efferent  fibres  are  not  thus  separated  from  the 
afferent  fibres  at  their  attachment  to  the  brain. 

5.  The  brain  and  cord  when  studied  by  the  naked  eye  are  seen  to  be  composed 
of  white  matter  and  gray  matter.  The  white  matter  forms  very  nearly  two-thirds 
of  the  entire  cerebrospinal  axis.  It  is  composed  of  medullated  nerve -fibres 
embedded  in  neuroglial  tissue.  The  gray  matter  is  composed  of  nerve-cells  with 
their  dendrites  and  axons.  Some  of  the  axons  are  in  the  form  of  naked  axis 
cylinders,  whilst  others  have  a  coating  of  medulla.  Intimately  intermixed  with 
these  parts  is  the  neuroglia,  which  isolates  them  more  or  less  completely  from 
each  other. 

SPINAL  COED. 


The  spinal  cord  is  that  part  of  the  cerebrospinal  axis  which  occupies  the  upper 
two-thirds  of  the  spinal  canal  of  the  vertebral  column.  It  is  an  elongated  cylin- 
drical structure,  slightly  flattened  in  front  and  behind,  which  extends  from  the 
margin  of  the  foramen  magnum  to  the  level  of  the  lower  border  of  the  body  of  the 

first  lumbar  vertebra  or  to  the  upper  border  of 
the  body  of  the  second  lumbar  vertebra.  Its 
average  length  in  the  male  is  45  cm.  and  in  the 
female  43  cm. 


^Mesencephalon 

Cerebellum 
Fourtli  ventricle 


Cervical  swellin: 
of  the  cord 


Luuiliar  swelling 
of  the  coi'd 


A  considerable  amount  of  variation  within  certain 
limits  (viz.  the  mid-point  of  the  body  of  the  last  dorsal 
vertebra  and  the  upper  border  of  the  body  of  the 
third  lumbar  vertebra)  is  observed  in  different  in- 
dividuals as  to  the  precise  level  at  which  the  spinal 
cord  ends  inferiorly,  and  in  the  female  there  would 
appear  to  be  a  tendency  for  the  cord  to  reach  a 
slightly  lower  point  in  the  canal  than  in  the  male. 
Further,  the  relation  presented  by  the  spinal  cord  to 
the  vertebral  column  differs  in  a  marked  degree  in  the 
foetus  and  infant  at  different  periods  of  development. 
Up  to  the  third  month  of  intrauterine  life  the  cord 
occupies  the  entire  length  of  the  spinal  canal  ;  it  ex- 
tends downwards  to  the  lowest  limit  of  the  canal.  But 
from  this  time  on,  as  growth  proceeds,  the  vertebral 
column  lengthens  at  a  more  rapid  rate  than  the  cord. 
The  spinal  cord,  therefore,  has  the  appearance  of 
shrinking  in  an  upward  direction  within  its  canal,  and 
at  birth  its  lower  end  is  usually  found  to  be  opposite 
the  body  of  the  third  lumbar  vertebra. 

The  attitude  assumed  by  the  individual  affects  to 
a  small  degree  the  position  of  the  lower  end  of  the 
cord.  Thus,  when  the  trunk  is  bent  well  forwards, 
it  is  noticed  that  the  terminal  part  of  the  cord  rises 
slightly  within  its  bony  canal. 

At  the  margin  of  the  foramen  magnum  the 
spinal  cord  becomes  continuous  with  the  medulla  oblongata  of  the  brain,  whilst 
below,  it  tapers  rapidly  to  a  point  and  forms  a  conical  extremity  termed  the  conus 
medullaris.  From  the  end  of  the  conus  medullaris  a  slender  glistening  thread  is 
prolonged  downwards  within  the  spinal  canal,  and  finally  anchors  the  spinal  cord 
to  the  back  of  the  coccyx.      This  prolongation  receives  the  name  of  the  filum 


Fk;.  363. — Human  F(etds  in  the  'rHiRD 
Month  of  Development,  with  the 
Brain    and    Spinal    Cord    exposed 

FROM    behind. 


SPINAL  COED. 


453 


fJoiuis  iiieilullaris 


terminale.  The  diameter  of  the  cord  is  very  much  shorter  than  that  of  the  spinal 
canal  within  which  it  lies.  A  wide  interval 
is  left  between  its  surface  and  the  walls  of 
its  canal,  and  this  excess  of  space  is  clearly  a 
provision  for  allowing  free  movement  of  the 
vertebral  column  without  producing  any  jar- 
ring contact  between  the  delicate  spinal  cord 
and  the  surrounding  bones. 

Three  protective  membranes  are  wrapped 
around  the  cord.  From  within  outwards  these 
are  termed  (1)  the  pia  mater,  (2)  the  arachnoid 
mater,  and  (3)  the  dura  mater.  The  pia  mater 
is  a  fibrous  membrane  which  forms  the  im- 
mediate investment.  It  is  closely  applied  to 
the  cord,  and  from  its  deep  surface  numerous 
fine  septa  penetrate  into  the  substance  of  the 
cord.  The  arachnoid  mater  is  an  exceedingly 
delicate  transparent  membrane  which  is  loosely 
wrapped  around  the  cord  so  as  to  leave  a 
considerable  interval,  termed  the  subarachnoid 
space,  between  itself  and  the  pia  mater,  in  which 
there  is  always  a  varying  amount  of  cerebro- 
spinal fluid.  Outside  the  arachnoid  mater,  the 
dura  mater  forms  a  wide,  dense,  fibrous,  tubular 
sheath,  which  extends  downwards  within  the 
spinal  canal  for  a  considerable  distance  beyond 
the  conical  extremity  of  the  cord.  The  spinal 
cord  is  suspended  within  its  sheath  or  tJieca  of 
dura  mater  by  two  lateral  wing-like  ligaments.   Fig.  364.— The  Conos  Medullaris  and  the 


termed  the  ligamenta  denticulata. 
outwards  from  the  sides  of  the 
attached  by  a  series  of  pointed 


FiLUM  Terminale  exposed  within 
Spinal  Canal. 


Postero-lateral 
iiroove  ^ 


These  extend 

cord  and  are 

or  tooth-like  processes  to  the  inner  surface  of 
the  theca  of  dura  mater.  Between  the  wall 
of  the  spinal  canal  and  the  dura  mater 
there  is  a  narrow  interval,  which  is  filled  up 
by  soft  areolo- fatty  tissue  and  numerous 
thin- walled  veins  arranged  in  a  plexiform 
manner. 

Thirty-one  pairs  of  spinal  nerves  arise 


Anterior  nerve-root 
Posterior  nerve-root 


First  lumbar 
\ertebra 


Spinal  ganglion 

Anterior  primary 
division  of  nervn 
Posterior  primary 
division  of  nerve 


Fig.  365. — The  Roots  of  Origin  of  the 
Seventh  Dorsal  Nerve  (semi -diagram- 
matic). 


Fig.  366.— Section  through  the  Conus  Medullaris  and 
the  Cauda  Equina  as  they  lie  in  the  Spinal  Canal. 


from  the  sides  of  the  spinal  cord.     These  are  classified  into  eight  cervical,  twelve 
33  a 


454  THE  NEKVOUS  SYSTEM. 

dorsal,  live  lumbar,  five  sacral,  and  one  coccygeal ;  and  according  to  the  attach- 
ments of  these  groups  of  nerves  the  spinal  cord  is  arbitrarily  subdivided  into 
cervical,  dorsal,  lumbar,  and  sacral  regions.  In  employing  these  terms,  therefore, 
for  different  districts  of  the  cord,  it  must  be  understood  that  the  regions  are  deter- 
mined by  the  nerve  attachments,  and  not  by  any  direct  relationship  between  these 
parts  of  the  cord  and  the  sections  of  the  vertebral  column  which  bear  the  same 
names. 

Each  spinal  nerve  is  attached  to  the  cord  by  a  ventral  and  a  dorsal  root,  and  as 
these  are  traced  to  their  central  attachments  they  are  seen  to  break  up  into  a 
number  of  separate  nerve  fascicles  or  bundles,  which  spread  out,  in  some  cases  very 
mdely  from  each  other,  as  they  approach  the  side  of  the  cord  (Fig.  365).  Each 
pair  of  nerves  is  therefore  attached  to  a  portion  of  spinal  cord  of  some  length,  and 
such  a  portion,  with  its  pair  of  nerves,  receives  the  name  of  a  "  segment  of  the 
spinal  cord."  It  must  be  clearly  understood,  however,  that,  in  so  far  as  the  surface 
of  the  cord  is  concerned,  there  is  absolutely  no  means  of  marking  off  one  segment 
from  another,  except  by  the  nerve  attachments. 

In  the  cervical  and  lumbar  regions  of  the  cord  the  nerve-roots  are  somewhat  crowded 
together,  so  that  little  or  no  interval  is  left  between  the  adjoining  root  fascicles  of  neighbouring 
nerves.  In  the  dorsal  region,  however,  distinct  intervals  may  be  observed,  and  the  root  fascicles 
ai'e  more  loosely  arranged.  From  this,  it  will  be  evident  that  the  cord  segments  in  different  parts 
of  the  cord  are  not  of  equal  length.  In  the  cervical  region  the  segments  measure  about  12  mm. 
in  length,  in  the  dorsal  region  from  20  to  24  mm.,  and  in  the  lumbar  region  about  10  mm.  The 
number  of  fascicles  which  attach  the  different  nerve -roots  to  the  cord  is  very  different  in 
different  nerves,  and  is  not  necessarily  the  same  in  the  same  nerve-root  in  different  individuals. 

Owing  to  the  great  difference  which  exists  between  the  length  of  the  spinal 
cord  and  the  length  of  the  vertebral  column,  the  farther  we  pass  down  the  greater 
the  distance  becomes  between  the  attachment  of  the  various  nerve-roots  to  the 
cord  and  the  invertebral  foramina  through  which  the  corresponding  nerves  leave 
the  spinal  canal.  The  lower  nerve-roots,  therefore,  have  to  traverse  the  spinal  canal 
for  a  considerable  distance  before  they  reach  their  apertures  of  emergence.  It  thus 
happens  that  the  nerve-roots  which  spring  from  the  lumbar  and  sacral  regions  of 
the  cord  attain  a  very  great  length  and  descend  vertically  in  the  lower  part  of 
the  spinal  canal  in  a  bunch  or  leash,  in  the  midst  of  which  lie  the  conus  medullaris 
and  the  filum  terminale.  This  great  bundle  of  nerve-roots  receives  the  appropriate 
name  of  the  cauda  equina. 

Enlargements  of  the  Cord. — Throughout  the  greater  part  of  the  dorsal  region, 
the  spinal  cord  presents  a  uniform  girth  and  a  very  nearly  circular  outline  when 
seen  in  transverse  section.  In  the  cervical  and  lumbar  regions,  however,  it  shows 
marked  swellings.  The  cervical  enlargement  (intumescentia  cervicalis)  is  the  more 
evident  of  the  two.  It  begins  very  gradually  at  the  upper  end  of  the  cord,  attains 
its  greatest  breadth  (12  to  14  mm.)  opposite  the  fifth  or  sixth  cervical  vertebra, 
and  finally  subsides  opposite  the  second  dorsal  vertebra.  To  this  portion  of  the 
cord  are  attached  the  great  nerves  which  supply  the  upper  limbs.  The  lumbar 
enlargement  (intumescentia  lumbalis)  begins  at  the  level  of  the  tenth  dorsal 
vertebra,  and  acquires  its  maximum  transverse  diameter  (11  to  13  mm.)  opposite 
the  last  dorsal  verteljra.  Below,  it  rapidly  tapers  away  into  the  conus  medullaris. 
To  the  lumbar  enlargement  are  attached  the  great  nerves  of  the  lower  limbs. 

These  enlargemeuts  of  the  cord  are  associated  with  the  outgrowth  of  the  limbs.  In 
the  earlier  developmental  stages  of  the  spinal  cord  they  are  not  present,  and  they  only 
take  form  as  the  limbs  become  developed.  In  the  lower  mammalia  their  size  corresponds 
with  the  degree  of  development  of  the  limbs.  Thus,  in  the  long-armed  orang  and  gibbon, 
the  cervical  swelling  stands  out  with  a  remarkable  degree  of  pi'ominence.  It  is,  however, 
interesting  to  note  that  although  in  the  cetacea  there  are  no  visible  hind-limbs,  there  is 
nevertheless  a  well-marked  lumbar  enlargement  of  the  cord. 

Fissures  and  Furrows  of  the  Cord. — When  cross-sections  of  the  spinal  cord 

are  made,  it  is  seen  to  be  a  bilateral  structure  which  is  partially  subdivided  into  a 
right  and  left  half  by  two  median  clefts — one  upon  the  anterior  and  the  other  upon 
the  posterior  aspect.  These  clefts  are  termed  the  antero-median  and  the  postero- 
median fissures,  and  they  extend  along  the  entire  length  of  the  cord.     At  the  same 


SPmAL  COED. 


455 


Postevo-mediaii_ 
tissui'e' 


Cervical  swelling- 
Posterior  i)ar.i-_ 
median  fissure 

Postero-lateraL 
fissure 


-CVv 


-DVii 


time  it  must  be  noted  that  these  two  median  clefts  present  many  points  of  differ- 
ence. The  antero-median  fissure  (fissura  mediana  anterior)  is  for  the  greater  part  of 
its  length  much  shallower  than  the  postero-median  fissure. 
In  the  cervical  and  dorsal  regions  it  only  penetrates  for  a 
distance  corresponding  to  somewhat  less  than  a  third  of  the 
antero-posterior  diameter  of  the  cord.  Further,  the  antero- 
median cleft  is  much  the  wider  and  more  apparent  of  the 
two,  and  the  pia  mater  dips  down  into  it  and  forms  a  fold 
or  reduplication  within  it.  The  postero-median  fissure 
(fissura  mediana  posterior)  in  the  cervical  and  dorsal  regions 
penetrates  into  the  cord  until  it  reaches  a  point  somewhat 
beyond  its  centre.  It  is  extremely  narrow,  and  contains 
a  single  septum  which  is  derived  from  ependymal  and 
neuroglial  elements,  and  is  intimately  connected  with  the 
adjacent  sides  of  the  two  halves  of  the  cord,  between  which 
it  intervenes.  The  pia  mater,  which  invests  the  surface  of 
the  cord,  passes  continuously  over  the  postero-median  fissure 
and  sends  no  prolongation  of  any  kind  into  it.  In  the 
lumbar  region  of  the  cord  the  postero-median  fissure  becomes 
shallower,  whilst  the  antero-median  fissure  deepens,  and 
ultimately  in  the  lower  part  of  the  cord  the  two  fissures 
present  a  very  nearly  equal  depth. 

The  two  halves  of  the  cord,  which  are  marked  off  from 
each  other  by  the  median  fissures,  may  show  trifling  differ- 
ences in  the  arrangement  of  the  parts  w^hich  compose  them ; 
but  to  all  intents  and  purposes  they  are  symmetrical.  They 
are  joined  together  by  a  more  or  less  broad  band  or  com- 
missure, which  intervenes  between  the  two  median  fissures. 

An  inspection  of  the  surface  of  each  lateral  half  of  the 
cord  brings  into  view  a  longitudinal  groove  or  furrow,  at 
some  little  distance  from  the  postero-median  cleft,  which 
extends  along  the  whole  length  of  the  cord.  Along  the 
bottom  of  this  groove  the  fascicles  of  the  posterior  nerve- 
roots  enter  the  cord  in  accurate  linear  order.  It  is  called 
the  postero-lateral  sulcus  (sulcus  lateralis  posterior).  There 
is  no  corresponding  furrow  on  the  forepart  of  each  lateral 
half  of  the  cord  in  connexion  with  the  emergence  of  the 
fascicles  of  the  anterior  nerve-roots.  These  fascicles  emerge 
irregularly  over  a  broad  strip  of  the  surface  of  the  cord, 
which  corresponds  in  its  width  to  the  thickness  of  the 
subjacent  extremity  of  the  anterior  horn  of  gray  matter. 

The  postero-lateral  groove  subdivides  each  lateral  half  of 
the  cord  into  a  small  posterior  column  (funiculus  posterior) 
and  a  much  larger  antero- lateral  column,  and  it  is  customary 
to  arbitrarily  map  off  the  latter  into  a  lateral  column 
(funiculus  lateralis)  and  an  anterior  column  (funiculus 
anterior)  by  a  line  corresponding  to  the  emergence  of  the 
outermost  fascicles  of  the  anterior  nerve-roots. 

In  the  cervical  region  a  distinct  longitudinal  groove 
may  be  observed  on  the  surface  of  the  posterior  column.  It 
is  placed  rather  nearer  to  the  postero-median  than  to  the 
postero-lateral  furrow  and  as  it  is  traced  down  into  the 
dorsal  region  it  gradually  becomes  indistinct  and  finally 
disappears.  This  is  called  the  posterior  paramedian  groove, 
and  it  marks  on  the  surface  the  position  of  a  septum  of 
pia  mater  which  dips  into  the  cord  and  subdivides  the 
posterior  column  into  an  outer  part,  termed  the  funiculus 
cuneatus  or  the  column  of  Burdach,  and  an  inner  portion,  which  receives  the  name 
of  the  funiculus  gracilis  or  the  column  of  Goll. 
33  h 


-DVx 


Lumbar  .swell! ns- 


U 

Fig.  367. — Diagram  of  the 
Spinal  Cord  as  seen 
from  behind. 

CVi  shows  tlie  level  of  the  1st 
cervical  vertebra  ;  CVv  of  the 
5th  cervical  vertebra ;  DVii 
of  the  2nd  dorsal  vertebra  ; 
DVx  of  the  lOtli  dorsal  verte- 
bra :  DVxii  of  the  12th  dorsal 
vertebra ;  LVii  of  the  2nd 
lumbar  vertebra. 


456 


THE  NEKVOUS  SYSTEM. 


Column  of  Goll 


Posterior  coin 


Column  of  Burdach 


Internal  Structure  of  the  Spinal  Cord. 

The  spinal  cord  is  composed  of  a  central  core  of  gray  matter  thickly  coated  on 
the  outside  by  white  matter.  At  only  one  spot  does  the  gray  matter  come  close  to 
the  surface,  viz.  at  the  bottom  of  the  postero-lateral  groove. 

Gray  Matter  of  the  Cord. — The  gray  matter  in  the  interior  of  the  cord  has 
the  form  of  a  fluted  column,  but  it  is  customary  to  describe  it  as  it  appears  in 
transverse  sections  through  the  cord.  It  then  presents  the  appearance  of  the 
capital  letter  H.  In  each  lateral  half  of  the  cord  there  is  a  semilunar  or  crescentic 
mass,  shaped  somewhat  like  a  comma,  the  concavity  of  which  is  directed  outwards 
and  the  convexity  inwards.  The  two  crescents  of  opposite  sides  are  connected 
across  the  middle  line  by  a  transverse  band,  which  receives  the  name  of  the  gray 
commissure  (commissura  grisea).  The  postero- median  fissure  cuts  through  the 
cord  until  it  reaches  the  gray  commissure.     The  bottom  of  the  antero-median 

fissure, however,  is  separated 
from  it  by  an  intervening 
strip  of  white  matter,  which 
is  termed  the  anterior  white 
commissure  (commissura  an- 
terior alba).  la  the  gray 
commissure  may  be  seen 
the  central  canal  of  the 
cord  (canalis  centralis), 
which  tunnels  the  entire 
length  of  the  cord  and  is 
just  visible  to  the  naked 
eye  as  a  minute  speck.  The 
portion  of  the  gray  com- 
missure which  lies  behind 
the  central  canal  is  called 
the  'posterior  gray  commis- 
sure (commissura  grisea 
posterior) ;  whilst  the  portion  in  front  receives  the  name  of  the  anterior  gray 
commissure  (commissura  grisea  anterior). 

Each  crescentic  mass  of  gray  matter  presents  certain  well-defined  parts.  The 
projecting  portions  which  extend  behind  and  in  front  of  the  connecting  transverse 
gray  commissure  are  termed  respectively  the  posterior  and  the  anterior  cornua  of 
gray  matter  (column^e  grisese).  These  stand  out  in  marked  contrast  to  each  other. 
The  anterior  cornu  (columna  grisea  anterior)  is  short,  thick,  and  very  blunt  at  its 
extremity.  Further,  its  extremity  falls  consideraljly  short  of  the  surface  of  the 
cord  and  is  separated  from  it  by  a  tolerably  thick  coating  of  white  matter. 
Through  this  the  fascicles  of  the  anterior  nerve-roots,  as  they  emerge  from  the 
gray  matter  of  the  anterior  horn,  pass  on  their  way  to  the  surface.  The  thickened 
end  of  the  anterior  cornu  is  called  the  caput  cornu,  whilst  the  part  close  to  the 
gray  commissure  is  termed  the  cervix  or  basis  cornu.  Throughout  the  greater  part 
of  the  cord  the  posterior  cornu  (columna  grisea  posterior)  is  elongated  and  narrow, 
and  is  drawn  out  to  a  fine  point,  which  almost  reaches  the  bottom  of  the  postero- 
lateral sulcus.  This  pointed  extremity  receives  the  name  of  the  apex  cornu ;  the 
slightly  swollen  part  which  succeeds  it  is  the  caput  cornu;  whilst  the  slightly 
constricted  part  adjoining  the  gray  commissure  goes  under  the  name  of  the  cervix 
or  basis  cornu. 

The  apex  or  tip  of  the  posterior  cornu  differs  considerably  in  appearance  from 
the  general  mass  of  the  gray  matter.  It  is  composed  of  a  material  which  presents 
a  lighter  hue  and  has  a  somewhat  translucent  look.  It  is  called  the  substantia 
gelatinosa  Eolandi,  and,  when  seen  in  transverse  section,  it  exhibits  a  V-shaped  out- 
lin«  and  fits  on  the  caput  cornu  like  a  cap. 

A  pointed  and  prominent  triangular  projection  juts  out  from  the  external 
aspect  of  gray  matter  nearly  opposite  the  gray  commissure.  This  is  the  lateral 
horn  (columna  grisea  lateralis),  and  it  is  best  iiiarked  in  the  upper  dorsal  region  (Fig. 


Formatio  reticulaiis 

Lateral  colun 

Central  can  u 

Spinal  accessory  root 

Origin  of  spinal 
accessory  ner\  e 


Anterior  column 
Fig.  368. — Transverse  Section  through  the  Upper   Part  of  the 
Cervical  Region  of  the  Cord  of  an  Orang.     (From  a  specimen 
prepared  by  the  Weigert-Pal  method,  by  which  the  white  matter 
is  rendered  dark  whilst  the  gray  matter  is  bleached. ) 


INTEENAL  STKUCTUKE  OF  THE  SPINAL  CORD.  457 

369,  B).  Traced  upwards  it  becomes  absorbed  in  the  greatly  expanded  anterior  horn 
of  the  cervical  swelling,  but  it  reappears  again  in  the  upper  part  of  the  cord  and 
is  particularly  noticeable  in  the  second  and  third  cervical  segments ;  followed  in  a 
downward  direction  it  blends  with  the  anterior  horn  in  the  lumbar  swelling  and 
contributes  to  the  thickening  ot  that  coruu. 

The  gray  matter  is  for  the  most  part  mapped  oft" from  the  surrounding  white  matter 
with  a  considerable  degree  of  sharpness ;  but  in  the  cervical  region,  on  the  outer 
aspect  of  the  crescentic  mass  and  in  the  angle  between  the  anterior  and  posterior 
horns,  fine  bands  of  gray  matter  penetrate  the  white  matter,  and,  joining  with  each 
other,  form  a  network  the  meshes  of  which  enclose  small  islands  of  white  matter. 
This  constitutes  what  is  called  the  formatio  or  processus  reticularis.  Although 
best  marked  in  the  cervical  region,  traces  of  the  same  reticular  formation  may  be 
detected  in  lower  segments  of  the  cord. 

Characters  presented  by  the  Gray  Matter  in  Different  Regions  of  the  Cord. 
— The  gray  matter  is  not  present  in  equal  quantity  nor  does  it  exhibit  the  same 
form  in  all  regions  of  the  cord.  Indeed,  each  cord  segment  presents  its  own 
special  characters  in  both  of  these  respects.  It  is  not  necessary,  however,  in  the 
present  instance  to  enter  into  this  matter  with  any  degree  of  minute  detail.  It 
will  be  sufiicient  if  we  point  out  the  broad  distinctions  which  are  evident  in  the 
different  regions. 

It  may  be  regarded  as  a  general  law  that,  wherever  there  is  an  increase  m  the 
size  of  the  nerves  attached  to  a  particular  part  of  the  cord,  a  corresponding 
increase  in  the  amount  of  gray  matter  will  be  observed.  It  follows  from  this 
that  the  regions  where  the  gray  matter  bulks  most  largely  are  the  lumbar  and 
the  cervical  swellings.  The  great  nerve-roots  which  go  to  form  the  nerves  of  the 
large  limb-plexuses  enter  and  pass  out  from  those  portions  of  the  cord.  In  the 
dorsal  region  there  is  a  reduction  in  the  quantity  of  gray  matter  in  correspondence 
with  the  smaller  size  of  the  dorsal  nerves. 

In  the  dorsal  region  (Fig.  369,  B)  both  horns  of  gray  matter  are  narrow,  although 
the  distinction  between  the  anterior  horn  and  the  still  more  attenuated  posterior 
horn  is  sufficiently  manifest.  In  this  region  the  lateral  horn  of  gray  matter  is 
likewise  characteristic,  and  the  substantia  gelatinosa  Eolandi  in  transverse  section 
is  pointed  and  spear-shaped. 

In  the  upper  three  segments  of  the  cervical  region  the  anterior  horns  of  gray 
are  not  large  and  resemble  the  corresponding  horns  in  the  dorsal  region.  A  lateral 
horn  is  also  present.  But  in  these  segments  (and  more  especially  in  the  first  and 
second)  there  is  a  marked  attenuation  of  the  neck  of  the  posterior  horn,  and  the 
posterior  gray  commissure  is  very  broad. 

In  the  cervical  sivelling  of  the  cord  the  contrast  between  the  two  cornua  is 
most  striking ;  the  anterior  horn  is  of  great  size  and  presents  a  very  broad  surface 
towards  the  anterior  aspect  of  the  cord,  whilst  the  posterior  horn  remains  narrow. 
This  great  increase  in  the  bulk  of  the  anterior  horn  is  due  to  a  marked  addition 
of  gray  matter  on  the  outer  side  of  the  horn,  and  seeing  that  this  additional  matter 
is  traversed  by  a  greater  number  of  fibres,  it  stands  out,  in  well-prepared  specimens, 
more  or  less  distinctly  from  the  part  of  the  horn  which  lies  to  the  inner  side,  and 
which  may  be  considered  to  represent  the  entire  anterior  horn  in  the  dorsal  and 
upper  cervical  segments.  Within  this  lateral  addition  to  the  anterior  horn  are 
placed  those  collections  of  cells  which  constitute  the  nuclei  of  origin  of  the  motor 
nerves  of  the  muscles  of  the  upper  limb.  The  characteristic  thickening  of  the 
anterior  horn  of  gray  matter  is  e^'ident,  therefore,  in  those  segments  of  the  cord 
to  which  the  nerves  which  enter  the  brachial  plexus  are  attached,  viz.  the  lower 
five  cervical  segments  and  the  first  dorsal  segment. 

In  the  lumbar  sicelling  the  anterior  horns  again  broaden  out,  and  for  the  same 
reason  as  in  the  case  of  the  corresponding  horns  in  the  cervical  swelling.  The 
nuclear  masses  which  contain  the  cells  from  which  the  motor  fibres  which  supply 
the  muscles  of  the  lower  limbs  take  origin  are  added  to  the  outer  aspect  of  the 
horns  and  give  them  a  very  characteristic  appearance.  In  this  region  of  the  cord, 
however,  the  posterior  horns  are  also  broad  and  capped  by  substantia  gelatinosa 
Rolandi,  which   in    transverse   section  presents  a  semilunar   outline.      There   is 


458 


THE  NEEVOUS  SYSTEM. 


consequently  no  difficulty  in  distinguishing  from  an  inspection  of  the  gray  matter 
alone  between  transverse  sections  of  the  cord  taken  from  the  cervical  and  lumbar 
swellings  of  the  cord. 


A.  — Cervical  region — at  the  level  of  the  fifth  cervical  nerve 
(From  a  specimen  prepared  by  Dr.  A.  Bruce.) 

1.  Postero-inedian  fissure. 

2.  Paramedian  septum. 

3.  Postero-lateral  groove. 

4.  Posterior  nerve-root. 

5.  Substantia  gelatinosa  Rolandi. 

6.  Root-Kljres  entering  gray  matter.   11.  Anterior  nerve-root. 

7.  Formatio  reticularis.  12.  Antero-median  fissure. 


S.  Central  canal. 
0.  Nuclei     from    which    motor- 
fibres  for  muscles  of  upper 
limb  arise. 
10.  Anterior  commissure. 


B. — Through  the  mid-dorsal  region. 


1.  Postero-median  fissure. 

2.  Postero-lateral  groove. 

3.  Posterior  cornu. 

4.  Posterior  vesicular  column  of  cells. 

5.  Lateral  cornu. 

6.  Central  canal.   ' 

7.  Anterior  cornu. 

8.  Antero-median  fissure. 


1  S 

1    / 


C. — Tlirough  the  luniT»ar  region  at  the  level  of  the 
fourth  huiibar  nerve. 


.\uclei  of  origin  from 

which    the    motor- 

(ibres  for  mnscles  of 

the  lower  limb  arise. 

Anterior  nerve-root. 

9.  Antero-)iiedian  fissure. 


-Tlirough  the  sacral  region  at  tlie  level  of  the 
third  sacral  nerve.  (From  a  sijecimen  pre- 
pared by  Dr.  A.  Bruce. ) 

1.  Postero-niedi.in  fissure. 

2.  Posti'rior  nerve-root. 

3.  Substantia  gelatinosa  Rolandi. 

4.  Postorioi'  giay  conunissure. 

5.  Anterior  ciminiissiu-e. 
C.  Antero-median  fissure. 


1.  Po.sterior  nerve-root. 

2.  Postero-median  fissure. 

3.  Substantia  gelatino.sa  Rolandi. 

4.  Root- fibres      entering      gray 
)natter.  ; 

f>.  Central  canal. 

6.  Anterior  commissure. 

Fi(i.  369. — Section  through  each  ok  the  Four  IlECiiONS  of  the  Cord.  (From  specimens  prepared  by 
the  Weigert-Pal  method,  therefore  the  white  matter  is  rendered  dark  in  colour  whilst  the  gray 
matter  is  bleached. ) 

In  the  lower  part  of  tlie  conus  meduHaris  the  gray  matter  in  each  lateral  half 
of  the  cord  assumes  the  form  of  an  oval  mass  joined  to  its  iellow  of  the  opposite 
side  by  a  thick  gray  commissure.     Here  almost  the  entire  bulk  of  the  cord  consists 


INTEENAL  STEUCTURE  OF  THE  SPINAL  COED.  459 

of  gray  matter,  seeing  that  the  white  matter  is  reduced  to  such  an  extent  that  it 
forms  only  a  thin  coating  on  the  outside. 

White  Matter  of  the  Spinal  Cord. — In  transverse  sections  of  the  cord  the 
three  cohmms  into  which  the  white  matter  is  subdivided  become  very  apparent. 
The  posterior  column  is  wedge-shaped,  and  lies  between  the  postero-median  fissure 
and  the  posterior  horn  of  gray  matter.  The  lateral  column  occupies  the  concavity 
of  the  gray  crescent.  Behind,  it  is  bounded  by  the  posterior  horn  of  gray  matter 
and  the  postero-lateral  sulcus,  whilst  in  front  it  extends  as  far  as  the  outermost 
fasciculi  of  the  anterior  nerve-roots  as  they  pass  out  from  the  anterior  gray  horn. 
The  anterior  column  includes  the  white  matter  between  the  antero-median  fissure 
and  the  anterior  horn  of  gray  matter,  and  also  the  white  matter  which  separates  the 
broad  extremity  of  the  anterior  gray  cornu  from  the  surface  of  the  cord.  This 
latter  portion  of  the  anterior  columu  is  traversed  by  the  emerging  fascicles  of  the 
anterior  nerve-roots. 

In  cross-sections  of  the  cord  the  partition  of  pia  mater,  which  dips  in  at  the 
posterior  paramedian  groove  and  divides  the  posterior  column  into  the  column  of 
Goll  and  the  column  of  Burdach,  is  very  strongly  marked  in  the  cervical  regions, 
but  as  it  is  traced  downwards  into  the  dorsal  region  it  becomes  shorter  and  fainter, 
and  finally  disappears  altogether  at  the  level  of  the  eighth  dorsal  nerve.  Below 
this  point  there  is  no  visible  demarcation  of  the  posterior  column  into  two  parts. 

The  white  matter  is  not  present  in  equal  quantity  throughout  the  entire  length 
of  the  cord.  It  increases  steadily  from  below  upwards,  and  this  increase  is  most 
noticeable  in  the  lateral  and  posterior  columns.  In  the  lower  part  of  the  conus 
medullaris  the  amount  of  gray  matter  is  actually  greater  than  that  of  the  white 
matter  :  but  verv  soon  this  state  of  affairs  is  chanoed,  and  in  the  lumbar  region  the 
proportion  of  gray  to  white  matter  is  approximately  as  1:2-1;  in  the  dorsal  region 
as  1 :  5  ;  and  in  the  cervical  region  as  1 :  5'1.  When  it  is  remembered  how  the  gray 
matter  expands  in  the  lumbar  and  cervical  regions,  and  how  greatly  it  becomes  reduced- 
in  the  dorsal  region,  the  significance  of  these  figures  will  become  more  apparent. 

Central  Canal  (canahs  centrahs). — As  previously  stated,  the  central  canal  is 
found  in  the  gray  commissure.  It  is  a  very  minute  tunnel,  barely  visible  to  the 
naked  eye  when  seen  in  transverse  section,  and  it  traverses  the  entire  length  of  the 
cord.  Above,  it  passes  into  the  medulla  oblongata,  and  finally  opens  into  the  fourth 
ventricle  of  the  brain ;  below,  it  is  continued  for  a  variable  distance  into  the  filum 
terminale,  and  in  this  it  ends  bHndly.  Only  in  the  lumbar  region  does  the  central 
canal  occupy  the  centre  of  the  cord.  Above  this  level,  in  the  dorsal  and  cervical 
regions,  it  lies  very  much  nearer  the  anterior  than  the  posterior  aspect  of  the  cord ; 
whilst  below  the  lumbar  region,  as  it  is  traced  down  into  the  conus  medullaris,  it 
inclines  backwards  and  approaches  the  posterior  aspect  of  the  cord.  The  calibre  of 
the  canal  likewise  varies  somewhat  in  different  parts  of  the  cord.  It  is  narrowest 
in  the  dorsal  region ;  and  in  the  lower  part  of  the  conus  medullaris  it  expands  into 
a  distinct  fusiform  dilatation  (very  nearly  1  mm.  in  transverse  diameter),  which  is 
termed  the  ventriculus  terminalis  (Krause). 

The  central  canal  is  lined  by  a  layer  of  ciliated  columnar  cells,  the  deep  taper- 
ing ends  of  which  are  prolonged  into  slender  processes,  which  penetrate  into  the 
substance  of  the  cord.  These  cells  constitute  the  lining  ependymal  cells  of  the 
canal.  The  cilia  of  the  epithelial  cells  are  very  early  lost,  and  it  is  not  uncommon 
to  find  the  canal  blocked  up  by  epithelial  debris. 

The  central  canal  is  of  interest  because  it  represents  in  tlie  adult  the  relatively 
wide -lumen  of  the  early  ectodermal  neural  tube  from  which  the  spinal  cord  is 
developed. 

Filum  Terminale. — The  delicate  thread  to  which  this  name  is  applied  is  con- 
tinuous with  the  lower  tapered  end  of  the  conus  medullaris.  It  is  easily  distin- 
guished by  its  silvery  and  glistening  appearance  from  the  numerous  long  nerve-roots 
(cauda  equina)  amidst  which  it  lies.  It  is  about  six  inches  long,  and  down  to  the 
level  of  the  second  sacral  vertebra  it  is  inclosed  with  the  surrounding  nerve-roots 
within  the  theca  of  dura  mater.  Piercing  the  tapered  and  closed  end  of  the  theca 
at  this  point,  and  receiving  an  investment  from  it,  the  filum  terminale  proceeds 
downwards  in  the  sacral  canal,  and  finally  receives  attachment  to  the  periosteum  on 


460 


THE  NEEVOUS  SYSTEM. 


the  dorsal  aspect  of  the  coccyx  (Fig.  364,  p.  453).  It  is  customary  to  speak  of  the 
filum  as  consisting  of  two  parts,  viz.  the  filum  terminale  internum  and  the  filum 
terminale  externum,  or  the  part  inside  and  the  part  outside  the  theca  of  dura  mater. 
The  filum  terminale  externum  is  simply  a  fibrous  thread,  strengthened  by  the 
prolongation  it  receives  as  it  pierces  the  dura  mater.  The  filum  terminale  intemiun 
is  largely  composed  of  pia  mater ;  but  in  its  upper  half  it  incloses  the  terminal  part 
of  the  central  canal,  and  around  this  a  variable  amount  of  the  gray  substance  of  the 
cord  is  prolonged  downwards  into  the  filum.  When  transverse  sections  are  made 
through  the  upper  part  of  the  filum  terminale  internum  some  bundles  of  medul- 
lated  nerve-fibres  are  observed  chnging  to  its  sides,  and  with  these  are  associated 
some  nerve-cells  identical  with  those  in  the  spinal  ganglia.  These  represent  rudi- 
mentary or  aborted  caudal  nerves  (Eauber). 

Summary  of  the  Chief  Chaeacters  presented  by  the  Coed  in  its 

Different  Eegions. 


Cervical  Region. 

Dorsal  Region. 

Lumbar  Region. 

Sacral  Region. 

In     transverse     section, 

In     transverse    section, 

In     transverse    section. 

In     transverse     section, 

outline  of  cord  trans- 

outline of  cord  more 

outline  of  cord  more 

outline    of    cord, 

versely    oval  ;   in    the 

nearly    circular  ;    but 

nearly  circular  than  in 

nearly    circular,     but 

middle  of  the  cervical 

still  the  transverse  di- 

dorsal region. 

still    somewhat   com- 

svifelling the  transverse 

ameter  is  greater  than 

pressed    from    before 

diameter  being  nearly 

the    antero  -  posterior 

backwards. 

one -third  longer  than 

diameter. 

the    antero  -  posterior 

diameter. 

Postero  -  median  cleft 

Postero  -  median   cleft 

Postero  -  median  cleft 

Postero  -  median     and 

very   deep,   extending 

very   deep,    extending 

not  nearly  so  deep  as 

antero-median  clefts 

beyond  the  centre  of 

beyond  centre  of  cord  : 

in  regions  above  :  an- 

of equal  depth. 

cord ;  antero-median 

anteromedian  cleft 

tero-median  cleft,  on 

cleft  shallow. 

shallow. 

the  other  hand,  much 

deeper. 

Gray  matter  greatly  in- 

Gray   matter    greatly 

Gray  matter  greatly  in- 

Both    horns     of    gray 

creased  in  quantity  in 

i-educed   in   quantity. 

creased  in  the  lumbar 

matter  very  thick  and 

the  cervical  swelling  : 

Both    horns    slender. 

swelling.     Both  horns 

massive.    Lateral  horn 

anterior     horn     thick 

Lateral      horn      well 

very  thick  and  massive. 

apparent.     No    form- 

and massive;  posterior 

marked.       Formatio 

Lateral  horn  absorbed 

atio  reticularis. 

horn  slender  in  com- 

reticularis scarcely  ap- 

in anterior  horn.  For- 

parison.   Lateral  horn 

parent. 

matio   reticularis    ab- 

only evident  above  the 

sent. 

level  of  the  fourth  cer- 

vical nerve.    Formatio 

reticnlaris  strongly 

marked. 

White  matter  in  great 

White    matter   less 

White  matter  small  in 

White      matter     very 

quantity,  and  especi- 

in   quantity   than    in 

quantity  in  relation  to 

small  in   quantity  in 

ally    massed    in    the 

cervical     region,     but 

higher     regions,     and 

comparison   with   the 

lateral    and    posterior 

bulking     largely     in 

very  small  in  amount 

gray  matter. 

columns. 

comparison   with   the 

in     relation      to     in- 

quantity   of     gray 

creased     quantity    of 

matter. 

gray  matter. 

Posterior  paramedian 

Posterior  paramedian 

No   posterior   para- 

No  posterior   para- 

groove   and    septum 

groove    absent ;    but 

median     groove     or 

median  groove  and  no 

well  marked. 

the  corresponding  sep- 
tum can  be  traced  as 
low  down  as  the  eighth 
dorsal  nerve. 

septum. 

corresponding  septum. 

Central  canal  consider- 

Central canal  consider- 

Central canal    in    the 

Central    canal   in    the 

ably  nearer  the  anterior 

ably  nearer  the  anterior 

centre  of  the  cord. 

centre  of  the  cord. 

surface  than  the  pos- 

surface than  the  pos- 

terior  surface   of   the 

terior  surface  of  the 

cord. 

cord. 

COMPONENT  PARTS  OF  GRAY  MATTER  OF  SPINAL  CORD.     461 

Component  Parts  of  the  Geay  Matter  of  the  Spinal  Cord. 

Neuroglia  enters  largely  into  the  constitution  of  the  gray  matter  of  the  cord. 
It  forms  a  bed  within  which  the  nervous  elements  are  distributed.  These  nervous 
elements  consist  of  (1)  nerve-cells  and  (2)  nerve-fibres — both  medullated  and  non- 
medullated.  The  nerve-cells  lie  in  small  spaces  within  the  neuroglia,  whilst  the 
nerve-fibres  traverse  tine  passages  the  waUs  of  which  are  formed  of  the  same  sub- 
stance. The  neurogha  is  thus  an  all-pervading  basis  substance,  which  isolates  more 
or  less  completely  the  nervous  elements  from  each  other,  and  at  the  same  time 
binds  them  together  into  a  consistent  solid  mass.  In  two  situations  the  gray 
matter  presents  special  characteristics  which  have  earned  for  it  the  name  of 
substantia  gelatinosa,  viz.  the  gray  matter  which  constitutes  the  immediate  sur- 
rounding of  the  central  canal,  and  which  is  called  the  substantia  gelatinosa 
centralis;  and  that  which  forms  the  apical  part  of  the  posterior  horn  of  gray 
matter,  and  which  receives  the  name  of  substantia  gelatinosa  Rolandi.  In  botli 
situations  the  substantia  gelatinosa  stains  more  deeply  with  carmine  and  presents 
a  more  translucent  appearance ;  in  other  respects  the  substantia  centrahs  and  the 
substantia  Rolandi  are  very  different. 

The  substantia  gelatinosa  centralis  forms  a  thick  ring  around  the  central  canal, 
which  is  traversed  by  the  fine  processes  which  proceed  from  the  deep  ends  of  the 
ependymal  cells  whicli  line  the  canal.  It  is  almost  entirely  composed  of  neuroglia. 
In  transverse  sections  of  the  cord  the  substantia  Rolandi,  in  the  cervical  and 
dorsal  regions,  presents  the  appearance  of  a  V-shaped  mass,  embracing  the  extremity 
of  the  caput  of  the  posterior  horn  of  gray  matter ;  in  the  lumbar  region  this  cap 
assumes  a  semilunar  outline. 

In  the  substantia  gelatinosa  Rolandi  the  neuroglia  is  present  in  small  quantity, 
and  small  nerve-cells  are  developed  within  it  in  considerable  numbers. 

Nerve-Cells. — The  nerve-cells  are  scattered  plentifully  throughout  the  gray 
matti'r,  but  perhaps  not  in  such  great  numbers  as  might  be  expected  when  we  note 
the  enormous  number  of  nerve-fibres  with  which  they  stand  in  relation.  They  are 
all,  without  exception,  multipolar,  and  send  off  from  their  various  aspects  several 
branching  protoplasmic  processes  or  dendrites,  and  one  axon,  which  becomes  the 
axis-cylinder  of  a  nerve- fibre.  In  size  they  vary  considerably,  and  it  is  generally 
admitted  that  the  bulk  of  a  nerve-cell  has  a  more  or  less  definite  relation  to  the 
length  of  the  axis-cylinder  which  proceeds  from  it. 

When  the  nerve-cells  are  studied  in  a  series  of  transverse  sections  of  the  cord, 
it  will  be  noticed  that  a  large  proportion  of  them  are  grouped  in  clusters  in  certain 
districts  of  the  gray  matter ;  and  as  these  groups  are  seen  in  very  much  the  same 
position  in  successive  sections,  it  is  clear  that  these  cells  are  arranged  in  longitudinal 
columns  of  greater  or  less  length.  Thus  we  recognise  (1)  a  ventral  group  or  column 
of  cells  in  the  anterior  horn  of  gray  matter;  (2)  an  intermedio-lateral  group  or 
column  in  the  lateral  horn  of  gray  matter,  where  this  exists ;  and  (3)  a  posterior 
vesicular  column  of  cells  (Clarke's  column),  forming  a  most  conspicuous  group  in 
the  mesial  part  of  the  cervix  of  the  posterior  horn  in  the  dorsal  region  of  the 
cord. 

Other  cells  besides  those  forming  these  columns  are  scattered  somewhat  irregu- 
larly  throughout  the  gray  matter  of  the  posterior  horn  and  the  part  of  the  gray 
crescent  which  Hes  l)etween  the  two  horns  ;  and  although  these  also  in  some  measure 
may  be  classified  into  groups,  the  arrangement  thus  effected  is  not  of  so  definite  a 
character  as  to  justify  us  in  dwelling  upon  it  in  the  present  instance. 

Ventral  Cell- Column  and  the  Origin  of  the  Fibres  of  the  Anterior  Nerve- 
Roots. — The  ventral  cell-group  occupies  the  anterior  horn  of  gray  matter,  and  in 
it  are  found  the  largest  and  most  conspicuous  cells  in  the  spinal  cord.  It  extends 
from  one  end  of  the  cord  to  the  other.  These  ventral  nerve-cells  have  numerous 
wide-spreading  dendritic  processes,  and  it  is  to  be  noticed  that  certain  of  these 
dendrites  do  not  confine  their  ramifications  to  the  gray  matter.  Thus,  some  of  the 
cells  along  the  mesial  border  of  the  anterior  horn  of  gray  matter  send  dendrites 
across  the  mesial  plane  in  the  anterior  commissure  to  end  in  the  anterior  gray 
horn  of  the  opposite  side ;  whilst  others,  lying  along  the  lateral  or  outer  margin  of 


462 


THE  NERVOUS  SYSTEM. 


the  anterior  horn  of  gray  matter,  send  dendrites  in  amongst  the  nerve-fibres  of  the 
adjoining  white  matter. 

The  axons  or  axis-cylinder  processes  of  a  large  proportion  of  the  ventral  cells 
converge  together ;  and,  becoming  meduUated,  form  bundles  which  pass  out  from 
the  gray  matter,  and  through  the  white  matter  which  separates  the  thick  end  of 
the  anterior  horn  from  the  surface  of  the  cord,  to  finally  emerge  as  the  fascicles  of 
the  anterior  nerve-roots.     These  cells,  then,  are  the  sources  from  which  the  nerve- 

Postero-lateral  furrow 

Posterior  horn  of 
gray  matter 


Postero-median  fissure 


Gray  commissure 


Postero-lateral  group  of 
luotor  cells 


Autero-mertian 
furrow 

Fig.  370. — Section  through  the 


Autero-mesial  group 
of  motor  cells 


Autero-lateral 
group  of  motor  cells 


Fifth   Cervical  Segment  ok  the  Cord. 
on  Plates  in  Dr.  Bruce's  Atlas.) 


(To  a  large  extent  founded 


fibres  of  the  anterior  nerve-roots  proceed,  and  in  consequence  they  are  frequently 
spoken  of  as  the  "  motor  cells  "  of  the  cord.  Whilst  this  is  the  arrangement  of  the 
axons  of  the  great  majority  of  the  motor  cells,  it  should  be  noted  that  a  few  cross 
the  mesial  plane  in  the  anterior  white  commissure  and  emerge  in  the  fascicles  of 
origin  of  the  opposite  anterior  nerve-root. 

The  ventral  cells  are  not  scattered  uniformly  throughout  the  anterior  horn  of  gray 
matter.  They  are  aggregated  more  closely  together  in  certain  parts  of  the  anterior  horn, 
and  thus  form  sub-groups  or  columns  more  or  less  perfectly  marked  off  from  each  other. 

Thus  one  sub-group  or  column  of  ventral  cells  occupies  the  inner  or  mesial  part  of  the 
anterior  horn  of  gray  matter  throughout  almost  its  whole  length.  In  only  two  segments 
of  the  cord  is  it  absent,  viz.  the  fifth  lumbar  and  the  first  sacral ;  at  this  level  in  the  cord 
alone  is  its  continuity  broken  (Bruce).  It  is  termed  the  ventro-mesial  column  or  group  of 
ventral  cells.  Behind  this  cell-column  there  is  another  which  is  classed  with  it  to  which 
'>the  name  of  dorso-7)iesial  cohtmn  or  group  is  given,  but  this  column  of  cells  is  not  con- 
tinuous throughout  the  entire  length  of  the  cord.  It  is  present  in  the  dorsal  region  of 
the  cord  where  the  motor  nuclei  for  the  muscles  of  the  limbs  are  absent,  and  it  is  also  seen 
in  two  or  three  of  the  segments  of  the  cervical  region  and  in  the  first  lumbar  segment 
(Bruce)  ;  elsewhere  it  is  not  represented. 

In  the  cervical  and  lumbar  swellings  of  the  cord,  where  the  marked  lateral  outgrowth 
is  added  to  the  outer  side  of  the  anterior  horn  of  gray  matter,  certain  groups  of  lai'ge 
multipolar  cells  are  visible.  These  are  the  nuclei  of  origin  of  the  motor-fibres  which 
supply  the  muscles  of  the  limbs,  and  consequently  they  are  not  represented  in  the  upper 
three  cervical  segments  of  the  cord  ;  nor  in  any  of  the  dorsal  segments,  with  the  exception 
of  the  first  dorsal  segment ;  nor  in  the  two  lowest  sacral  segments. 

These  lateral  cells  are  arranged  in  several  columns,  which  extend  for  varying  distances 
in  the  superadded  lateral  parts  of  the  anterior  horn  of  gray  matter.  The  two  main 
columns  are  a  ventro-lateral  and  a  dor  so-later  at  column ;  in  certain  segments  there  is 
likewise  a,  pjost-dorso-lateral  column,  and  in  a  number  of  segments  in  the  lumbar  and  sacral 
regions  a  central  column  of  cells  (Bruce). 


COMPONENT  PAETS  OF  GEAY  MATTER  OF  SPINAL  CORD.     463 


I'ostt'io-inediai 
lissurt 


Posterior  vesicular 
column  (Clarke's 
column  of  cells) 

Gray  commissure 


Aiitero-inedian 
farrow 


Antero-mesial  grouj 
of  motor  cells 


Postero-mesial  group 
of  motor  cells 


Fig.  371. — Section  thhotjgh  the  Eighth  Dorsal  Segment  of  the 
Spinal  Cord.  (To  a  large  ".xteiit  founded  on  Plates  in  Dr. 
Bruce's  Atlas.) 


There  cannot  be  a  doubt  that  the  grouping  of  the  motor  cells  in  the  anterior  horn  of 
gray  matter  of  the  cord  stands  in  relation  to  the  muscle  groups  to  which  their  axis-cylinder 
processes  are  distributed ;  but 
from  what  has  been  said  it  will  ''    irT7TT^'~r>-^  ,>„.*„    ,.     ,  ^ 

II    ;   /  I      /    '    7^-^  I'ostero-latei-al  furrow- 

be  apparent  that  sharply  defined 

cell -clusters  associated  with  par- 
ticular  muscles    do    not    exist. 

Still,   much  can  be  learned  re- 
garding the  localisation  of  the 

motor   nuclei    in    the    anterior 

horn  of  gray  matter  of  the  cord 

from  the  study  of  the  changes 

which  occur  in  the  cell-columns 

afteratrophiesof  isolated  muscles 

or  groups  of  muscles,  and  after 

complete  or  partial  amputations 

of  limbs.     It  has  been  pointed 

out  that    the    long  muscles    of 

the  trunk  (as,  for  example,  the 

different    parts    of    the    erector 

spinae    muscle)    receive    nerve - 

fibres    from   all    the   segments 

of    the   cord.     Now,    we    have 

noted    that    there    is  only    one 

cell-column,  the   ventro-mesial 

column,  which  pursues  an  almost 

uninterrupted  course  throughout  the  entire  length  of  the  cord.       It  may  be   assumed, 

therefore,  that  the  nerve-fibres  which  go  to  these  long  trunk-muscles  take  origin  in  these 

mesial  cells. 

Edinger  states  that  in  the  anterior  horn  of  gray  matter  the  nuclei  of  origin  of  the 

nerves  which  supply  the 
proximal  muscles  are  medially 
placed  ;  that  those  for  the 
distal  muscles  are  in  general 
situated  laterally.  If  this 
be  the  case,  the  cells  con- 
nected with  the  shoulder 
muscles  would  lie  nearer  the 
middle  of  the  anterior  horn 
of  gray  matter  than  those 
which  are  connected  with 
the  hand-muscles.  In  cases 
where  the  forearm  and  hand, 
or  the  leg  and  the  foot,  are 
amputated,  it  would  appear 
that  it  is  the  postero-latei'al 
column  of  cells  that  shows 
changes  in  consequence  of  its 
separation  from  the  muscles 
to  which  its  fibres  are  dis- 
tributed. ^ 


lateral  furrow 


Posterior  lioni  of 
matter 


Antero-median 
furrow 


Postero- lateral  group 
of  cells 


Central  group 
of  Cf Us 


Antero-lateral 
grouj)  of  cells 


Intermedio  -  lateral  Cell- 
column. —  The  intermedio- 
LuMBAR  Segment  of  the  lateral  cells  form  a  long 
^  °  slender  column  which  ex- 
tends throughout  theentire 
dorsal  region  of  the  cord  in  the  lateral  horn  of  gray  matter.  It  is  also  prolonged 
downwards  into  the  first  and  second  lumbar  segments,  where  it  disappears.     In 


Antero-niesial 
group  of  cells 

Fi<i.  372.— Section  through   the   Third 

Spinal  Cord  to  show  the  grouping  of  the  Motor  Cells 
a  large  extent  founded  on  Plates  in  Dr.  Bruce's  Atlas.) 


'  Those  who  seek  further  information  regarding  the  grouping  of  the  \entral  cells  of  the  cord,  may  with 
advantage  <tudy  Dr.  Alexander  Brace's  ^Itlas  of  the  Spinal  Cord. 


464 


THE  NEKVOUS  SYSTEM. 


Postero-lateral  furrow 


Posterior  horn  of  gray 
matter 


Postero-median 
fissure 


Gray  commis- 
•  sure 


Antero-median 
furrow 


Central  group  of  cells 


Postero-lateral  group 
of  cells 


Antero-lateral  group  of  cells 


Fig.  373. — Section  '  through  the  First  Sacral  Segment  of  the 
Spinal  Cord  to  show  the  grouping  op  the  Motor  Nerve- cells. 
(To  a  large  extent  founded  on  Plates  in  Dr.  Brace's  Atlas.) 


transverse  sections  through  the  cord  this  cell-group  presents  a  very  characteristic 
appearance,  because  the  cells  which  compose  it  are  small  and  are  closely  packed 

together.  Although  these 
cells,  as  a  continuous 
column,  are  restricted  to 
the  region  indicated,  it 
should  be  noted  that  the 
same  group  of  cells  re- 
appears above  in  certain  of 
the  cervical  segments  and 
also  in  the  third  and  fourth 
sacral  segments.  The  func- 
tion and  connexions  of 
these  cells  are  unknown. 
It  has  been  suggested  that 
they  give  origin  to  vaso- 
motor, pilo  -  motor,  and 
sweat  -  gland  nerves,  and 
have  a  very  close  connexion 
with  the  sympathetic  ner- 
vous system. 

In  a  recent  researcli  by 
Bruce  tlie  following  important 
points  in  regard  to  the  inter- 
medio-lateral  cell-column  have 
been  determined. 

It  is  not  quite  continuous. 
In  the  eighth  cervical,  first 
dorsal,  and  also  in  a  part  of  the 
second  dorsal  segment,  as  wel^ 
as  in  the  first  and  second  lumbar  segments,  the  cells  are  in  separate  clusters.  Throughout  the 
rest  of  the  dorsal  region  it  forms  a  moniliform  chain  of  cells,  situated  partly  in  the  lateral  horn 
and  partly  in  the  gray  matter  behind  it.  Some  outlying  cells  are  situated  in  the  white  matter 
in  the  neighbourhood  of  the  lateral  horn. 

The  limits  of  the  tract  are  from  lower  two-thirds  of  eighth  cervical  to  the  lower  end  of  the 
second  lumbar  or  perhaps  the  upper  end  of  the  third  lumbar  segment.  It  is  found  also  in  the 
first,  second,  and  third  cervical,  and  in  the  third  and  fourth  sacral  segments.  It  reaches  its 
maximum  size  in  the  third  and  fourth  dorsal  segments. 

Posterior  Vesicular  Column — Clarke's  Column. — This  occupies  the  posterior 
horn  of  gray  matter  and  is  the  most  conspicuous  of  all  the  cell-groups  in  the 
cord.  It  does  not,  however,  extend  along  the  whole  length  of  the  cord ;  indeed 
it  is  almost  entirely  confined  to  the  dorsal  region,  and  in  consequence  it  is  some- 
times referred  to  as  the  "  dorsal  nucleus."  Above,  it  begins  opposite  the  seventh  or 
eighth  cervical  nerve,  whilst  below,  it  may  be  traced  to  the  level  of  the  second 
lumbar  nerve,  where  it  disappears.  In  transverse  section  of  the  cord  it  presents  an 
oval  outline,  and  is  seen  in  the  inner  part  of  the  cervix  of  the  posterior  horn  of 
gray  matter  immediately  behind  the  gray  commissure  (Fig.  369  B,  p.  458).  On  the 
outer  side  it  is  circumscribed  by  numerous  curved  fibres  from  the  entering  posterior" 
nerve-root,  and  in  the  lower  dorsal  region  of  the  cord  (opposite  the  eleventh  and 
twelfth  dorsal  nerves)  it  becomes  so  marked  that  it  forms  a  bulging  on  the  inner 
aspect  of  the  posterior  gray  horn. 

The  cells  of  Clarke's  column  are  large,  and  possess  several  dendritic  processes. 
The  axons  enter  the  lateral  column  of  white  matter  and  there  form  a  strand  of 
fibres,  which  will  later  on  be  described  under  the  name  of  the  direct  cerebellar  tract. 

In  addition  to  the  topographical  subdivision  of  the  nerve-cells  of  the  cord  indicated  above,  it 
is  now  usual  to  classify  them  according  to  the  nature  of  the  axons  whicli  proceed  from  them. 
Thus  we  have  (1)  the  cells  of  Golgi  or  cells  with  short  axons,  and  (2)  cells  with  long  axons. 

The  cells  of  Golgi  possess  axons  which  do  not  emerge  from  the  gray  matter,  but  bring  neigh- 
bouring cells  into  touch  with  each  other.  Tlie  cells  with  long  axons  are  of  two  kinds,  viz. 
radicular  cells  and  strand-cells. 

The  radicular  cells  are  those  fj'om  which  the  axon  cinei'ges  from  the  cord  in  the  shape  of  an 
efferent  nerve-fibre.     Thus  the  "motor  cells"  which  suDolv  the  axis-cvlinder  processes  of  the 


»ONENT  PARTS  OF  WHITE  MATTER  OF  SPINAL  CORD.     465 

ve-roots  belong  to  this  class.  Tlie  strand-cells  are  those  which  contribute  their  axons 
.nation  of  those  fibres  wliich  form  certain  of  the  strands  or  tracts  which  are  found  in 
'  matter  of  the  cord. 

ve-fibres  in  the  Gray  Matter  of  the  Cord. — Nerve-fibres  both  of    the 

ed  and  non-meduUated  variety  pervade  every  part  of  the  gray  matter. 

3  of  three  kinds,  viz.  (1)  collaterals,  (2)  terminations  of  nerve-fibres,  (3) 

'en  off  by  the  cells.     Many  of  the  nerve-fibres  which  compose  the  columns 

•natter  of  the  cord  give  off  numerous  fine  collateral  branches,  which  pass 

^ray  matter  from  all  sides  and  finally  end  in  relation  with  the  nerve- 

3  majority  of  the  nerve-fibres  themselves,  which  thus  give  off  collaterals, 

er  the  gray  matter,  and  end  similarly.     As  already  noted,  the  axons  of 

>f  Golgi  remain  within  the  gray  matter,  but  the  others  emerge  either  for 

se  of  entering  a  peripheral  nerve  or  for  the  purpose  of  entering  a  strand 

I  the  white  matter  of  the  cord. 

•rve-fibres  thus  derived  are  interwoven  together  in  the  gray  ma,tter  of  the 
lense  inextricable  interlacement. 


Component  Parts  of  the  White  Matter  of  the  Coktx 

hite  matter  of  the  cord  is  composed  of  medullated  nerve-fibres  embedded 
,dia.  The  fibres,  for  the  most  part,  pursue  a  longitudinal  course ;  and 
^    deep    surface    of    the    pia    mater   which 

the   cord    fibrous   septa   or   partitions  are 

along  vertical  planes  between  the  fibres,  so 
n  an  irregular  and  very  imperfect  fibrous 
c,  of  support.  The  neuroglia  is  disposed  in 
:'  varying  thickness  around  the  cord,  sub- 
the  pia  mater,  and  is  carried  into  the  cord 
ve  a  coating  to  both  sides  of  the  various  pial 
'he  neuroglia  also  is  disposed  around  the 
:rve- fibres,  so  that  each  of  these  may  be  said 
a  canal  or  tunnel  of  this  substance.  The 
•es  are  all  medullated,  but  they  are  not 
vith  primitive  sheaths.     It  is  the  medullary 

of  the  nerve -fibres  which  gives  to  the 
tter  its  opaque,  milky -white  appearance, 
hin  transverse  section  of  the  cord  is  stained 
e  and  examined  under  the  microscope  the 
tter  presents  the  appearance  of  a  series  of 
plied  circles,  each  with  a  dot  in  the  centre. 
s  the  transversely  divided  axis -cylinder  of 
ibre,  and  the  dark  ring  which  forms  the 
3nce  of  the  circle  represents  the  wall  of  the 
canal  which  is  occupied  by  the  fibre. 
Lillary  substance  is  very  faintly  seen.  It 
I  filmy  or  cloudy  appearance  between  the 
ler  and  the  neuroglial  ring. 
gement  of  the  Nerve-fibres  of  the  White 
n  Strands  or   Tracts. — When   the   white 

a  healthy  adult  cord  is  examined  the  fibres  which  compose  it  are 
iry  considerably  in  point  of  size ;  and  although  there  are  special  places 
^e  fibres — or  it  may  be  small  fibres — are  present  in  greater  numbers 
where,   yet    as    a    rule    both    great    and    small    fibres    are    mixed   up 

Absolutely  no  evidence  can  be  obtained  in  such  a  cord,  by  any  means 
sposal,  of  the  fact  that  the  longitudinally  arranged  fibres  are  grouped 
u  more  or  less  definite  tracts  or  strands,  the  fibres  of  which  run  a  definite 
1  present  definite  connexions.  Yet  we  know  this  to  be  the  case,  and  the 
of  these  separate  tracts  has  been  proved  both  by  physiological  and  by 
;ical  investigation. 


Fig.    374. — Transverse     Section 

THKOaCiH  THE  WHITE   MATTER   OF 

THE    Cord,    as   .seen   tlirough   the 
microscope. 


466  THE  NERVOUS  SYSTEM. 

The  physiological  evidence  depends  on  the  fact  that  when  a  nerve-fibre  is  severed  the  part 
which  is  detached  from  the  nerve-cell  from  which  it  is  an  offshoot  degenerates,  whilst  the  part 
which  remains  connected  with  the  nerve-cell  undergoes  little  or  no  change.  This  is  called  the 
law  of  "  Wallerian  "  degeneration.  Thus,  if  in  a  living  animal  one-half  of  the  cord  be  cut  across, 
and  after  a  few  weeks  the  animal  be  killed  and  the  cord  examined,  it  will  be  seen  that  there 
are  degenerated  tracts  of  fibres  in  the  white  matter,  both  above  and  below  the  plane  of  division  ; 
but,  still  fui'ther,  it  will  also  be  manifest  that  the  tracts  which  are  degenerated  above  the  plane 
of  division  are  not  the  same  as  those  which  are  degenerated  in  the  part  of  the  cord  which  lies 
below  this  level  The  interpretation  of  this  is  obvious.  The  nerve -tracts  which  have  degenerated 
above  the  plane  of  section  are  the  offshoots  of  nerve-cells  which  lie  in  lower  segments  of  the  cord 
or  in  spinal  ganglia  below  the  plane  of  section.  Severed  from  these  nerve-cells,  they  undergo 
what  is  called  ascending  degeneration.  The  nerve-tracts,  on  the  other  hand,  which  have 
degenerated  in  the  portion  of  the  cord  below  the  plane  of  division  are  the  axons  of  cells  which 
lie  at  a  higher  level  than  the  j^lane  of  section,  either  in  higher  segments  of  the  cord  or  in  the 
brain  itself.  Cut  off  from  the  nerve-cells  from  which  they  proceed,  they  present  an  example  of 
descending  degeneration. 

The  embryological  evidence  we  owe  to  Flechsig,  and  it  is  no  less  satisfactory.  It  depends 
upon  the  fact  that  nerve-fibres  in  the  earliest  stages  of  their  develoi^ment  consist  of  naked  axis- 
cylindei-s,  and  are  not  provided  with  medullary  sheaths.  Further,  the  nerve-fibres  of  different 
strands  assume  the  medullary  sheaths  at  difterent  periods.  By  examining  the  foetal  cord  at 
different  stages  of  its  development,  it  is  a  comparatively  easy  matter  to  locate  the  different  tracts 
of  fibres  by  evidence  of  this  kind.  Speaking  broadly,  the  tracts  which  myelinate  first  are  those 
which  bring  the  cord  into  relation  with  the  jjeripheral  parts  (skin,  muscles,  etc.) ;  then  those 
fibres  which  Ijind  the  various  segments  of  the  cord  together ;  next,  those  which  connect  the  cord 
with  the  cerebellum  ;  and,  lastly,  the  tracts  which  connect  the  cord  with  the  cerebrum.  The 
nervous  apparatus  for  the  performance  of  automatic  movements  is  fully  provided,  therefore,  before 
this  is  put  under  the  control  and  direction  of  the  higher  centres.  It  by  no  means  follows  that  in 
all  the  higher  animals  corresj^onding  strands  myelinate  at  relatively  corresponding  periods.  Take 
the  case  of  a  young  animal  which  from  the  time  of  its  birth  is  able  to  move  about  and  perform 
voluntary  movements  of  various  kinds  in  a  more  or  less  perfect  manner,  and  comj^are  it  with  the 
helpless  new-born  human  infant  which  is  only  capable  of  exhibiting  automatic  movements.  In 
the  former  the  pyramidal  tracts,  or  motor  tracts,  which  descend  from  the  cerebrum  into  the  cord, 
and  which  are  the  paths  along  which  the  mandates  of  the  will  travel,  myelinate  at  an  early  period  ; 
whilst  in  the  human  infant  the  corresponding  fibres  do  not  obtain  their  medullary  sheaths  until 
after  birth.  The  study  of  the  dates,  therefore,  at  which  the  various  strands  of  nerve-fibres 
myelinate  not  only  gives  the  anatomist  a  means  of  locating  their  position  in  the  white  matter  of 
the  cord,  but  it  also  affords  the  physiologist  most  important  information  regarding  their  functions, 
and  also  the  periods  at  which  these  functions  are  called  into  play. 

It  is  a  matter  of  interest  to  note  that  influences  which  either  accelerate  or  retard  the  periods 
at  which  nerve  fibres  are  brought  into  functional  activity  have  also  an  ett'ect  in  determining  the 
dates  at  ■\\'hich  these  fibres  assume  their  sheaths  of  mj^eliir.  Thus,  when  a  child  is  prematurely 
born  the  whole  process  of  myelinisation  is,  as  it  were,  hurried  up  ;  and  further,  when  in  new 
born  animals  light  Ls  freely  admitted  to  one  eye  whilst  it  is  carefully  excluded  from  the  other, 
the  filjres  of  the  optic  nerve  of  the  former  myelinate  more  rapidly  than  those  of  the  opposite  nerve. 

Posterior  Column  of  the  Cord  and  the  Posterior  Roots  of  the  Spinal 
Nerves. — In  the  cervical  and  upper  dorsal  regions  of  the  cord  the  posterior  column 
is  divided  by  the  posterior  paramedian  septum  into  the  tract  of  Burdach,  which 
lies  externally  and  next  the  posterior  horn  of  gray  matter,  and  the  tract  of  Goll, 
which  lies  internally  and  next  the  postero-median  septum.  The  tract  of  Burdacl  i 
is  compo.sed  of  nerve-fibres,  which  are  for  the  most  jjart  larger  than  those  entering 
into  the  formation  of  Goll's  tract,  and  both  tracts  have  a  most  intimate  relation 
to  the  posterior  nerve-roots ;  indeed,  they  are  both  almost  entirely  composed  o  f 
fibres  which  enter  the  cord  by  these  roots  and  then  pursue  a  longitudinal  course.    • 

The  nerve-fibres  which  form  the  posterior  nerve-roots,  on  entering  the  cord  along  the 
postero-lateral  groove,  divide  within  the  tract  of  Burdach  into  ascending  and  descending 
branches.  These  l>ranches  diverge  abruptly  from  each  other ;  and  the  former  take  an 
upward  course,  whilst  the  latter  proceed  dowuwards.  The  descending  fibres  are  as  a  rule 
short,  and  soon  end  in  the  gray  matter  of  the  cord.  These  descending  fibres  occupy  an 
area  in  the  posterior  column  near  to  the  place  of  entrance  of  the  nerve-root.  This  area, 
when  the  spinal  cord  is  divided,  undergoes  descending  degeneration  and  then  presents  ; 
comma-shaped  outline.  The  fibres  in  question  are  included  xmder  the  name  of  the  commfc 
tract  of  Schultze. 

The  ascending  fibres  vary  greatly  in  length,  and  at  varying  distances  from  the  poin 
where  the  parent  fibres  enter  the  cord  they  end  in  the  gray  matter.  A  small  contributior 
of  ascending  fibres,  however,  from  each  posterior  nerve-root,  extends  upwards  to  the  uppe 
end  of  the  cord,  to  end  in  the  medulla  oblongata. 

As  each  posterior  nerve-root  enters,  its  fibres  range  themselves  in  the  outer  part 


COMPONENT  PARTS  OF  WHITE  MATTER  OF  SPINAL  CORD.     467 


the  tract  of  Burdach   close  up  against  the  posterior  horn  of  gray  matter.     Tlie  nerve- 

Tlie  oval  field  of  Flochsig  CoiMiua  tract  of  Scliultzo 


Fig.  375. — Diacjram  to  show  the  Arrangement  of  the  Fibres  of  the  Posterior  Nerve -Roots  in 
THE  Posterior  Columns  of  the  Cord.  Tlie  oval  field  of  Flechsig  is  present  in  the  lumbar  region 
and  is  composed  of  fibres  which  degenerate  in  a  downward  direction,  and  which  are  not  derived  from 
the  posterior  nerve-roots.      In  all  probaliility  they  are  connnissural  fibres  (from  Edinger,  modified). 

fibres  of  the  nerve-root  next  above  take  the  same  position,  and  consequently  those  which 

entered  from  the  nerve  immediately  below  are  displaced 

inwards,  and  come  to  lie  in  the  tract  of  Burdach  nearer 

to   the  mesial    plane.      This    process    goes    on    as    each 

nerve-root  enters,  and    the   result    is  that   the  fibres  of 

the  lower  nerves  ai'e  gradually  pushed  nearer  and  nearer 

to  the  postero-median  septum    in  a  successive  series  of 

lamellar    tracts.      Of    course    the  greater    proportion  of 

the    fibres,   which    are    thus  carried    upwards    from  the 

posterior  nerve-roots,  sooner  or  later  leave  the  posterior 

column  and  enter  the  gray  matter,  to  end  there  in  relation 

to  some  of  its  cells  ;  but,  as  we  have  said,  every  posterior 

nerve-root  sends  a  few  fibres  up  the  whole  length  of  that 

portion  of  the  cord  which  lies  above,  and  thus  the  posterior 

column  gradually  increases  in  bulk  as  it  is  traced  upwards, 

and   in   the   upper  reaches   of    the  cord  a  tract  of  Goll 

becomes  evident.     This  tract  of  Goll  is  composed  of  the 

long  ascending  fibres  of  the  posterior  nerve-roots,  which 

have  entered  the  lower  segments  of  the  cord.     To  put 

the    matter   differently,   the    fibres    of    the    sacral    roots 

'•e  displaced  inwards  by  the  entering  lumbar  fibres, 
while  the  fibres  of  the  lumbar  roots  are  in  their  turn 
pushed  inwards  by  the  entering  dorsal  fibres,  and,  lastly, 
the  fibres  of  the  cervical  roots  displace  the  dorsal  fibres. 
The  difference  between  the  tract  of  Goll  and  the  tract  of 
Burdach  simply  consists  in  this,  that  the  former  is  com- 
posed of  the  fibres  of  posterior  nerve-roots  which  have 
entered  the  cord  at  a  lower  level  than  those  which  enter 
into  the  formation  of  the  column  of  Burdach.  The 
fibres  of  Goll's  tract,  taking  them  as  a  whole,  must  there- 
fore necessarily  run  a  very  much  longer  course. 

Our  knowledge  of  the  constitution  of  the  posterior 
columns  of  the  cord  is  largely  derived  from  studying 
the  course  of  degeneration  in  monkeys,  in  which  the  cord 
has  been  cut  across — either  partially  or  completely.  It 
would  appear,  from  the  examination  of  the  human  cord  Fig.  376.— Diagram  to  show  the 
which  has  been  injured  or  compressed,  that  the  lamination       Banner  in  which  the  Fibres  op 

„   ,      „,  •       ,.  1  •        ,.        ,     •  ^         THE  Posterior  Ner\t;- Roots  enter 

or  the  fibres  entering  trom  the  sei'iesoi  posterior  nerve-roots       ^^^   ascend    in    the    Posterior 

is  not  nearly  so  complete  as  in  the  case  of  the  monkey.  Column  of  the  Cord  (from  Edinger). 


468  THE  NERVOUS  SYSTEM. 

Numerous  collateral  fibrils  stream  into  the  gray  matter  of  the  posterior  horu  both 
from  the  ascending  and  descending  branches  of  the  entering  fibres  of  the  posterior  nerve- 
roots.  These  ai-e  classified  into  long  and  short  collaterals.  The  long  collaterals  extend 
forward  into  the  anterior  horn  of  gray  matter  and  end  in  relation  to  the  ventral  nerve- 
cells.  The  short  collaterals  end  in  relation  to  the  nerve-cells  in  the  substantia  Rolandi, 
and  other  nerve-cells  of  the  posterior  horn  of  gray  matter. 

The  majority  of  the  fibres  of  the  posterior  nerve-root  enter  the  cord  on  the  inner  side 
of  the  apex  of  the  posterior  horn  of  gi'ay  matter.  The  manner  in  which  these  are  related 
to  the  columns  of  Burdach  and  Goll  has  been  noticed  ;  but  a  certain  number  of  those  fibres 
which  lie  most  externally  take  a  curved  course  forwards  on  the  inner  side  of  the  posterior 
horn  of  gray  matter  and  then  pass  into  it.  In  the  dorsal  region  these  curved  fibres  end  in 
connexion  with  the  cells  of  Clarke's  column  (Fig.  369,  p.  458). 

Tract  of  Lissauer. — This  is  a  small  tract  of  nerve-fibres  of  minute  calibre  which 
assume  their  medullary  sheaths  at  a  comparatively  late  period.  It  is  placed  at  the 
surface  of  the  cord  close  to  the  postero-lateral  furrow.  It  is  formed  by  some  of  the 
outer  fibres  of  the  posterior  nerve-roots,  which  do  not  enter  the  tract  of  Burdach,  and 
which  pass  upwards  in  the  cord  close  to  the  substantia  gelatinosa  Rolandi,  in  which  they 
ultimately  end. 

It  must  now  be  evident  that  the  fibres  which  enter  the  cord  througli  each  posterior  nerve-root 
have  three  main  modes  of  distribution  :  (1)  the  majority  take  part  in  the  forniation  of  the  columns 
of  Burdach  and  Goll  ;  (2)  a  few  lie  close  to  the  posterior  horn  of  gray  matter  and  describe  a  series 
of  graceful  curves  as  they  pass  forwards  prior  to  turning  outwards  into  the  gray  matter,  to  end,  in 
the  dorsal  region,  in  Clarke's  A^esicular  column  ;  (3)  a  third  series  form  Lissauer's  tract  and  end  in 
connexion  with  the  cells  of  the  substantia  gelatinosa  Rolandi  and  other  cells  in  the  posterior  and 
anterior  horns  of  gray  matter. 

The  fil^res  derived  from  the  posterior  nerve-roots  which  ascend  in  the  posterior  columns  of  the 
cord  to  the  medulla  oblongata  of  the  brain  constitute  a  direct  sensory  tract ;  other  fibres  are 
described  which  give  rise  to  a  crossed  sensory  tract  termed  the  spino-thalamic  tract.  These 
latter  fibres  arise  as  the  axons  of  certain  of  the  cells  in  the  posterior  horn  in  connexion  Avith 
which  fibres  from  the  posterior  nerve-roots  have  ended,  and  crossing  to  the  opposite  side  of 
the  cord  through  the  anterior  commissure  they  ascend  in  the  anterolateral  column  to  the  brain, 
where  they  ultimately  reach  the  optic  thalamus.  As  the  spino-thalamic  tract  ascends  in  the 
cord  its  fibres  are  not  gathered  into  a  compact  strand,  but  are  more  or  less  loosely  scattered 
in  the  lateral  column. 

Association  Fibres  in  the  Posterior  Column. — But  the  whole  of  the  fibres  of  the 
posterior  column  are  not  derived  from  the  posterior  nerve-roots.  A  few  fibres  exist  in 
this  column  which  have  a  different  origin.  They  are  derived  from  certain  of  the  cells  of 
the  gray  matter  of  the  coi'd,  and  entering  the  posterior  column  divide  into  ascending  and 
descending  branches  which  pass  upwards  and  downwards  in  the  column  for  a  varying 
distance  before  they  finally  turn  in  to  end  in  the  gray  matter  at  a  higher  and  a  lower  level. 
These  fibres,  therefore,  constitute  links  of  connexion  between  different  cord  segments,  and 
thus  they  are  termed  association  or  longitudinal  commissural  fibres.  Our  information 
regarding  these  fibres  at  present  is  somewhat  defective ;  but  it  is  believed  that  the  deepest 
part  of  the  column,  i.e.  the  part  next  the  posterior  gray  commissure  and  termed  the 
ventral  field,  and  also  the  descending  septo-marginal  tract  of  Bruce,  placed  in  apposition 
with  the  postero-median  septum  and  in  the  adjoining  jjart  of  the  surface,  belong  mainly  to 
this  category. 

Lateral  Column  of  the  Cord. — -In  the  lateral  column  of  the  cord  the  well- 
e.stablished.  tracts  are  : — 

1.  The  direct  cerebellar  tract. 

2.  The  tract  of  Gowers. 

3.  The  crossed  pyramidal  tract. 

The  remainder  of  the  column  goes  under  the  name  of  the  lateral  basis-bundle. 

The  direct  cerebellar  tract  (fasciculus  cerebello-spinalis)  is  a  band-like  strand 
which  lies  in  relation  to  the  surface  of  the  cord  immediately  in  front  of  the  postero- 
lateral groove.  It  is  an  ascending  tract,  and  is  composed  for  the  most  part  of 
coarse,  large  nerve-fibres,  which  are  derived  from  the  nerve-cells  of  the  posterior 
vesicular  column  (Clarke's  column)  in  the  posterior  horn  of  gray  matter.  It  is, 
therefore,  not  found  tliroughout  the  whole  length  of  the  cord.  It  first  appears  in 
the  lower  part  of  the  dorsal  region  ;  and  as  it  ascends  it  gradually  increases  in  size 
as  it  is  joined  by  the  axons  of  the  cells  of  Clarke's  column,  which  lie  at  higher 
levels.  It  finally  enters  the  medulla  oblongata,  and  through  this  proceeds  to  the 
cerebellum,  in  which  it  ends. 


COMPONENT  PAETS  OF  WHITE  MATTEK  OF  SPINAL  COED.     469 


Entering 


Lissaupr's  tract 


It  must  not  be  forgotten  that  each  posterior  nerve-root  in  the  doi-sal  region  of  the  cord  gives 
a  contribution  of  fibres  to  the  posterior  vesicular  column  of  cells  from  which  the  fibres  of  the  direct 
cerebellar  tract  arise  (see  p.  468).  In  this  way  a  connexion  is  established  between  the  posterior 
roots  of  the  dorsal  nerves  and  the  cortex  of  the  cerebellum.  It  is  believed  that  the  direct  cerebellar 
tract  is  an  important  tactor  in  bringing  about  a  proper  co-ordination  of  muscular  movements. 

Gowers's  tract  (fasciculus  antero-lateralis  superficialis)  lies  in  front  of  the  direct 
cerebellar  tract,  and,  like  it,  next  the  surface  of  the  lateral  column.  It  is  also  an 
a.scending  tract,  and  it  likewise  (in  part  at  least)  ultimately  reaches  the  cerebellum, 
although  after  leaving  the  cord  it  takes  a  different  route  to  gain  its  destination. 
In  transverse  sections  of  the  cord  it  presents  a  comma-shaped  appearance,  the 
thick  part  abutting 
against  the  direct  cere- 
bellar tract,  and  the 
narrower  portion  taper- 
ing forwards  into  the 
recjion  of  the  emercjincj 
anterior  nerve-roots. 
The  tract  of  Gowers 
begins  at  a  lower  level 
in  the  cord  than  the 
direct  cerebellar  tract 
and  it  increases  in  vol- 
ume as  it  is  traced  up- 
wards. The  fibres  of 
this  tract  have  probably 
their  origin  in  the  cells 
of  the  posterior  horn  of 
gray  matter,  but  on  this 
point  there  is  at  present 
no  precise  information. 

The  crossed  pyramidal 
tract  (fasciculus  cerebro- 
spinalis  laterahs)  is  a 
large  well-defined  de- 
scending tract,  which  lies  immediately  in  front  of  the  posterior  horn  of  gray 
matter  and  subjacent  to  the  direct  cerebellar  tract,  which  shuts  it  out  from 
the  surface  of  the  cord.  Below  the  point  where  the  direct  cerebellar  tract  begins 
the  crossed  pyramidal  tract  becomes  superficial,  and  in  this  position  it  can  be 
traced  as  low  as  the  fourth  sacral  nerve,  at  which  level  it  ceases  to  exist  as  a 
distinct  strand.  The  crossed  pyramidal  tract  is  composed  of  an  admixture  of  both 
large  and  small  fibres.  These  arise  in  the  brain  from  the  large  pyramidal  cells 
of  the  motor  or  Eolandic  area  of  the  cerebral  cortex,  and  pass  downwards  through 
various  subdivisions  of  the  brain  to  gain  the  spinal  cord.  As  they  enter  the  cord 
they  cross  the  mesial  plane  from  one  side  to  the  other,  and  it  thus  happens  that 
the  crossed  pyramidal  tract  in  the  right  lateral  column  of  the  cord  has  its  origin 
in  the  cortex  of  the  left  cerebral  hemisphere,  and  vice  versa.  As  the  tract  descends 
in  the  cord  it  gradually  diminishes  in  size ;  and  this  is  due  to  the  fact  that,  as  it 
traverses  each  spinal  segment,  numerous  fibrts  leave  it  to  enter  the  anterior  horn 
of  gray  matter,  and  end  in  connexion  with  the  ventral  motor  cells  from  which  the 
fibres  of  the  anterior  nerve-roots  arise.  The  entire  strand  is  ultimately  exhausted 
in  this  way.  Numerous  collateral  fibrils  spring  from  the  pyramidal  fibres,  and, 
entering  the  gray  matter,  end  in  a  similar  manner,  and  in  this  way  a  single  pyra- 
midal fibre  may  be  connected  with  several  spinal  segments  before  it  finally  ends. 
The  crossed  pyramidal  tract  must  be  regarded  as  a  great  motor  strand  which 
brings  the  spinal  motor  apparatus  under  the  control  of  the  will. 

Schafer  believes  that  many  of  the  pyramidal  fibres  end  in  counexion  with  the  cells 
of  Clarke's  column. 

In  the  rat,  mouse,  guiuea-pig,  squirrel,  sheep,  kangaroo,  etc.,  the  pyramidal  tract  lies 
in  the  posterior  column  of  the  cord. 


Fn 


Emerging  anterior  root 


;.  377. — Diagrammatic  Representation  of  a  Transverse  Section 

THROUGH   THE    SpINAL   CORD. 

Tlie  nerve  tracts  in  the  white  matter  and  the  clusters  of  nerve-cells 
in  the  sn-av  matter  are  shown. 


470  THE  NEEVOUS  SYSTEM. 

The  lateral  basis-bundle  (fasciculus  lateralis  proprius)  represents  the  remainder 
of  the  lateral  column.  Our  information  regarding  it  is  still  imperfect ;  but  it 
would  appear  th  it  its  fibres  are  largely  derived  from  the  cells  situated  in  all  parts 
of  the  gray  matter,  and  also  from  the  nerve-cells  of  the  opposite  side  of  the  cord. 
After  a  course  of  very  varying  length  in  the  basis-bundle,  these  fibres  turn  inwards 
and  re-enter  the  gray  matter.  Such  fibres  may  thus  be  regarded  as  inter- segmental 
association  fibres  binding  two  or  more  segments  of  the  cord  together.  It  may  be 
mentioned  that  the  association  fibres  which  link  together  segments  of  the  cord 
which  are  near  to  each  other  lie  close  to  the  gray  matter,  whilst  those  which 
connect  the  more  distant  segments  are  situated  further  out  in  the  lateral 
basis-bundle. 

Anterior  Column  of  the  Cord. — One  well-defined  tract  is  situated  in  the 
anterior  column.  This  is  termed  the  direct  pyramidal  tract.  The  remainder  of 
the  column  receives  the  name  of  the  anterior  basis-bundle. 

The  direct  pyramidal  tract  (fasciculus  cerebro-spinalis  anterior)  is  usually  a 
nerve-strand  of  small  size  which  lies  next  the  antero-median  fissure.  As  a  rule, 
it  cannot  be  traced  lower  than  the  middle  of  the  dorsal  region  of  the  cord.  It  is 
a  descending  tract  and  must  be  associated  with  the  crossed  pyramidal  tract  of  the 
opposite  side,  seeing  that  both  of  these  strands  arise  from  the  motor  area  of  the 
cortex  of  the  same  cerebral  hemisphere.  Erom  this,  it  must  be  clear  that  the 
direct  pyramidal  tract  does  not  cross  the  mesial  plane  as  it  enters  the  cord,  but 
descends  on  the  side  of  the  cord  corresponding  to  the  cerebral  hemisphere  in 
which  it  arises.  All  the  same  its  fibres  do  not  end  in  the  same  side  of  the 
cord,  but  at  every  step  along  the  path  of  the  strand  they  make  use  of  the  anterior 
commissure  and  cross  to  the  opposite  side  of  the  cord,  to  terminate  in  relation 
to  the  opposite  ventral  motor  cells  in  the  same  manner  as  the  crossed  pyramidal 
fibres. 

From  this  crossing  ot  the  pyramidal  tracts,  it  results  that  the  destruction  of  the  fibres  which 
compose  them  as  they  descend  in  one  side  of  the  brain  must  result  in  paralysis  of  the  muscles 
supplied  by  the  efferent  nerves  of  the  opposite  side  of  the  cord. 

In  cases  of  old  brain  lesion  it  is  sometimes  possible  to  detect  some  degenerated  fibres  in  the 
crossed  pyramidal  tract  of  the  sound  side  of  the  spinal  cord,  and  from  this  it  is  supposed  that  this 
tract  contains  a  few  uncrossed  fibres.  If  this  be  the  case,  each  side  of  the  cord  stands  in 
connexion  with  the  motor  area  of  both  cerebral  hemispheres. 

It  is  well  to  note  that  the  fibres  of  both  pyramidal  tracts  are  not  medullated  until  the  time  of 
birth.     They  are  the  latest  of  all  the  cord-tracts  to  myelinate. 

The  anterior  basis-bundle  (fasciculus  anterior  proprius),  like  the  lateral  basis- 
bundle,  is  composed  largely  of  fibres  which  arise  from  the  cells  of  the  gray  matter 
of  the  cord,  and  act  the  part  of  intersegmental  association  fibres. 

Summary  of  the  Constitution  of  the  White  Matter  of  the  Cord. — The 
white  columns  of  the  cord  are  formed  of  two  kinds  of  nerve-fibres  : — 

1.  Those  which  enter  the  cord  from  without. 

2.  Those  which  take  their  origin  from  the  cells  within  the  gray  matter  of  the 
cord  itself. 

Under  the  first  categoiy  we  include  (a)  the  greater  part  of  the  fibres  of  the 
posterior  column  (columns  of  Burdach  and  Goll),  which  arise  from  the  cells  of  the 
spinal  ganglia,  and  which  enter  the  cord  as  the  posterior  nerve-roots ;  and  (h)  the 
crossed  and  direct  pyramidal  tracts  which  come  from  the  motor  cells  of  the  cerebral 
cortex. 

The  fibres  which  arise  within  the  gray  matter  of  the  cord  may  be  classified 
thus:  (a)  Fibres  which  pass  out  from  the  cord  as  efferent  nerves  (anterior  ntrve- 
roots) ;  (b)  fibres  which  form  long  tracts  and  pass  up  the  cord  to  enter  the  brain 
(direct  cerebellar  tract  and  the  tract  of  Gowers);  (c)  fibres  which  form  short  tracts, 
linking  together  different  segments  of  the  cord  (intersegmental  association  fibres  in 
each  of  the  three  columns  of  the  cord). 

Anterior  White  Commissure. — The  anterior  commissure  is  composed  of 
medullated  nerve- Hbres  passing  from  one  side  of  the  cord  to  the  other  and  entering 
the  anterior  horn  of  gray  matter,  and  also  the  anterior  column  of  white  matter.  It 
is  to  be  regarded  more  as  a  decussation  than  as  a  commissure,  and  its  width,  which 


DEVELOPMENT  OF  THE  SPINAL  CORD. 


471 


varies  somewhat  in  diflerent  regions,  fluctuates  in  correspondence  with  tlie  diameter 
of  the  cord. 

Amongst  tlie  fibres  wliicli  cross  in  the  anterior  commissure  may  be  mentioned  :  (1)  The  fibres 
of  the  direct  i^yramidal  tract ;  (2)  collaterals  from  both  the  ventral  and  lateral  columns  ;  (3)  axons 
of  many  of  the  cells  of  the  gray  matter  ;  (4)  the  dendritic  processes  of  some  of  the  mesial  ventral 
cells. 

Posterior  Gray  Commissure. — Although  this  is  composed  of  gray  matter  with 
a  large  admixture  of  neuroglia,  numerous  transverse  nerve-fibres  pass  through  it,  so 
as  to  bind  the  cells  of  one  side  of  the  cord  to  those  of  the  other. 


MID-DORSAL  LAMINA 


MVELO- 

SPONGIUM 


Development  of  the  Spinal  Cord. 

In  the  chapter  upon  General  Embryology  it  has  been  pointed  out  (p.  21)  that  the 
brain  and  cord  first  take  shape  in  the  form  of  a  tube  of  ectoderm,  which  receives  the  name 
of  the  neural  tube.  Three  expansions,  placed  one  behind  the  other  at  the  cephalic  end  of 
the  tube,  represent  the  early  brain  ;  whilst  behind  these  primitive  cerebi'al  vesicles  comes 
the  elongated  narrower  part  of  the  tube,  which  at  this  stage  rejiresents  the  spinal  cord. 
By  a  developmental  process,  which  we  now  have  to  study,  the  walls  of  this  portion  of  the 
neural  canal  give  rise  to  the  various  elements  which  build  up  the  substance  of  the  cord, 
whilst  a  portion,  if  not  the  whole,  of  the  primitive  cavity  is  preserved  as  the  central  canal 
of  the  cord.  The  account  which  is  here  given  of  the  development  of  the  cord  is  taken 
almost  entirely  from  the  writings  of  Professor  His. 

When  first  formed,  the  neural  tube  is  compressed  from  side  to  side  and  presents  an  oval 
outline  in  transverse  section  (Fig.  16,  p.  21).  The  two  lateral  walls  are  very  thick,  whilst 
the  narrow  dorsal  and  ventral  portions  of  the  wall  are  thin,  and  are  termed  the  mid-dorsal 
and  mid-ventral  laminae  (Fig.  378).  The  cavity  of  the  tube  in  transverse  section  appears  as 
a  narrow  slit.  At  this  stage  the  wall  of  the  neural  tube  is  formed  of  a  series  of  elongated 
neuro-epithelial  columnar  cells,  closely  applied  to  each  other  and  extending  throughout  the 
whole  thickness  of  the  wall.  The 
inner  ends  of  these  long  columnar 
cells  unite  to  form  a  delicate  mem- 
brane termed  the  internal  limiting 
membrane,  which  lines  the  lumen  of 
the  tube,  whilst  their  outer  ends 
present  a  similar  relation  to  an  ex- 
ternal limiting  membrane,  which 
invests  the  outer  surface  of  the  tube. 
The  name  of  spongioblasts  is  given 
to  these  cells,  and  they  soon  develop 
in  such  a  manner  as  to  form  the 
sustentacular  framework  of  the 
growing  cord.  Between  their  inner 
parts,  immediately  subjacent  to  the 
internal  limiting  membrane,  a  series 
of  clefts  or  open  spaces  are  formed, 
in  which  appear  large  numbers  of 
round  cells  called  germinal  cells. 
The  precise  origin  of  these  germinal 
cells  is  not  at  present  satisfactoril}' 
established ;  but  they  rapidly  in- 
crease in  number,  and  in  the  human 
embryo  of  four  weeks  they  are  seen 
to  form  an  almost  continuous  layer 
Vieneath  the  internal  limiting  mem- 
brane. It  is  well  to  note,  however, 
that  in  the  thin  mid-dorsal  and  mid- 
ventral  laminpe  no  germinal  cells  are 
formed.  Here  the  wall  remains 
purely  spongioblastic.  The  peri- 
pheral portions  of  the  spongioblasts  likewise  undergo  a  marked  transformation.  They 
give  off  branches  or  processes,  and  by  the  interlacement  of  these  a  sponge-like  network 
with  irregular  meshes  is  formed  in  the  outer  portion  of  the  wall  of  the  neural  tube.     The 


mid-ventral  lamina 
Fig.  378. — Schema  of  a  Transverse  Section  through  the 
Early  Neural  Tube  (Young). 

The  left  side  of  the  section  shows  an  earlier  stage  than 
the  right  side. 


472 


THE  NERVOUS  SYSTEM. 


entire  sustentacular  framework  into  which  the    spongioblasts  are  developed    is   termed 
the  myelosponge. 

The  numerous  germinal  cells  which  are  placed  in  the  clefts  between  the  inner 
columnar  portion  of  the  myelosponge  are  the  progenitors  of  the  nerve-cells.  Many  of 
them  show  karyokinetic  stages,  and  by  their  division  they  give  rise  to  the  neuroblasts  or 
young  nerve-cells.  A  neuroblast  presents  a  very  characteristic  pear-shaped  appearance. 
From  the  body  of  the  cell  a  tapering  process  grows  out,  and  this  represents  the  early  axis- 
cylinder  process  or  axon  of  the  cell.  But  the  crowds  of  neuroblasts  which  are  thus  formed 
do  not  remain  in  their  early  primitive  position  beneath  the  internal  limiting  membrane. 
They  migrate  outwards,  and  in  the  course  of  time  they  come  to  lie  in  the  part  of  the 
myelosponge  immediately  adjoining  the  reticular  mesh  work,  which  is  formed  by  the  outer 
parts  of  the  spongioblasts.  Here  their  further  outward  migration  is  arrested.  The 
reticular  meshwork  would  almost  appear  to  act  as  a  sieve  or  a  filter,  which  prevents  their 
progress  towards  the  periphery  of  the  wall  of  the  tube.  It  offers  no  impediment  to  the 
actively  growing  axons  of  the  neuroblasts,  however,  which  freely  enter  it  and  thread  their 
way  through  it.  At  this  stage  the  thick  lateral  wall  of  the  neural  tube  presents  three 
layers,  viz.  : — 

1.  An  inner  layer,  formed  by  the  columnar  part  of  the  myelosponge  forsaken  by  the 
neuroblasts.  This  is  termed  the  ependymal  layer,  and  it  ultimately  resolves  itself  into 
the  layer  of  columnar  ciliated  epithelial  cells  which  lines  the  central  canal  of  the  cord. 

2.  An  intermediate  layer,  in  which  the  neuroblasts  are  present,  and  which  is  afterwards 
converted  into  the  gray  matter  of  the  cord.     This  is  called  the  mantle  layer. 

3.  An  outer  layer,  formed  of  the  sponge-like  meshwork  of  the  outer  parts  of  the 
original  spongioblasts.  Into  this  the  axons  of  many  of  the  neuroblasts  are  seen  threading 
their  way.  This  layer  is  ultimately  transformed  into  the  white  matter  of  the  cord,  and 
at  this  stage  it  may  be  termed  the  peripheral  reticular  layer. 

Alar  and  Basal  Laminae  of  the  Lateral  Wall  of  the  Neural  Tube.— From 

what  has  been  said,  it  must  be  evident  that  the  changes  detailed  above  are  confined  to 
the  thick  lateral  walls  of  the  neural  tube.  In  these  alone  do  neuroblastic  cells  arise, 
whilst  the  thin  mid-dorsal  and  mid-ventral  laminae  remain  spongioblastic  throughout. 
But  whilst  these  changes  are  going  on,  the  thick  lateral  wall  begins  to  bulge  outwards  in 
-an  angular  fashion,  so  as  to  widen  the  central  cavity  of  the  tube  and  become  itself,  along 
the  line  where  the  cavity  is  widest,  demarcated  into  two  portions — a  narrow  dorsal  strip 
termed  the  alar  lamina,  and  a  broader  ventral  strip  called  the  basal  lamina.     The  cavity 


AC. 
AH. 

AL. 

AMF. 

AR. 


Fig.  379.- 

Aiiterior  column.  BC. 

Anterior   horn   of  gi'ay  BL. 

matter.  E. 

Alar  lamina.  GC. 

Antero-median  fissure.  LC. 

Anterior  nerve-root.  MDL. 


AMF  AC  AMF  AC 

-Thrke  Stages  in  the  Development  of  the  Spinal  Cord  (His). 


Column  of  Burdach. 
Basal  lamina. 
Ependyma. 
Column  of  Goll. 
Lateral  column. 
Mid-dorsal  lamina. 


MVL.   Mid-ventral  lamina. 
PC.       Early  posterior  column. 
PH.       Posterior  horn   of  gray 

matter. 
PMF.    Postero-median  fissure. 
PR.       Posterior  nerve-root. 


of  the  tube  now  appears  on  transverse  section  more  or  less  lozenge-shaped,  and  it  is  at  the 
lateral  angles  of  the  lozenge  that  this  subdivision  of  the  lateral  wall  becomes  evident. 

This  subdivision  is  a  fundamental  one,  being  present  in  the  brain-part  as  well  as  the 


DEVELOPMENT  OF  THE  SPINAL  COED.  473 

cord-part  of  the  neural  tube.  By  it  the  thick  Uiteral  wall  is  resolved  into  two  longitudinal 
strips  (the  alar  and  basal  laminte),  which  extend  along  the  whole  length  of  the  tube,  and 
which  present  definite  and  precise  relations  with  the  entering  and  emerging  roots  of  the 
various  cranial  and  spinal  nerves.  Confining  our  attention  to  the  spinal  cord,  the  posterior 
nerve-root  is  seen  to  enter  the  alar  lamina,  whilst  the  anterior  nerve-root  takes  origin 
within  and  emerges  from  the  basal  lamina. 

Further  Development  of  the  Gray  and  White  Matter  of  the  Cord.— In  the 
ventral  part  of  the  basal  lamina  the  mantle  layer  thickens  into  a  mass,  which  is  readily 
recognised  as  the  rudiment  of  the  anterior  horn  of  gray  matter,  and  in  this  neuroblastic 
cells  congregate  in  much  larger  numbers  than  elsewhere.  Fui-ther,  these  neuroblastic 
cells  begin  to  arrange  themselves  into  groups,  and  the  axis-cylinder  processes  of  a  large 
proportion  of  them  converge  and  form  bundles  of  fibres,  which  penetrate  into  the  peri- 
pheral layer,  and  finally  pierce  the  external  limiting  membrane,  to  emerge  as  the  fascicles 
of  the  anterior  nerve-roots.  Behind  the  anterior  horn  the  mantle  layer  still  remains  very 
thin,  and  the  neuroblasts  are  few  in  number.  There  is,  therefore,  at  this  stage  no  appear- 
ance of  the  posterior  horn  of  gray  matter.  Many  of  the  axons  of  the  neuroblasts  which 
occupy  this  region  are  seen  curving  forwards,  and,  after  traversing  the  anterior  horn,  they 
find  their  way  across  the  middle  line  in  the  mid-ventral  lamina.  In  this  manner  is  laid 
down,  at  a  very  early  stage,  the  rudiment  of  the  anterior  white  commissure  of  the  cord. 

The  white  matter  of  the  anterior  and  lateral  columns  is  gradually  established  by  axons 
from  various  neuroblasts  in  different  parts  of  the  mantle  layer,  entering  the  peripheral 
reticular  layer  and  taking  a  longitudinal  course  within  it.  The  anterior  horn  is  well 
coated  with  white  matter,  however,  before  the  lateral  column  takes  definite  shape. 

The  posterior  columns  of  white  matter  are  formed  in  a  totally  different  manner,  viz. 
by  the  introduction  into  the  cord  of  nerve-fibres  from  without.  The  fibres  of  the  posterior 
nerve-roots  coming  from  the  spinal  ganglia  strike  the  outer  surface  of  the  alar  lamina  of 
the  lateral  wall  of  the  neural  tube,  and,  piercing  the  external  limiting  membrane,  take  a 
longitudinal  course  in  the  peripheral  reticular  layer.  On  cross  section  these  fibres  first 
appear  as  an  oval  bundle,  which  lies  in  the  outer  part  of  the  alar  lamina  (Fig.  379  pc). 
This  bundle  is  the  rudiment  of  Burdach's  column,  and  at  first  it  has  a  somewhat  loose 
connexion  with  the  cord ;  but  as  the  posterior  horn  of  gray  matter  gradually  takes 
shape,  the  bundle  in  question  increases  in  volume,  and,  changing  its  position,  comes  to  lie 
on  the  inner  aspect  of  the  posterior  horn.  The  column  of  Goll  gradually  assimies  form 
between  the  tract  of  Burdach  and  the  postero-median  septum.  Later  on  the  lateral  and 
anterior  columns  are  increased  in  bulk  by  the  descent  into  them  of  the  pyramidal  tracts 
from  the  brain. 

The  gray  matter,  in  the  first  instance,  is  chiefly  massed  in  the  basal  lamina ;  but  as 
the  posterior  columns  of  white  matter  begin  to  take  shape  it  extends  backward,  and  in 
the  course  of  time  the  posterior  horns  are  developed. 

The  manner  in  which  the  dendritic  processes  of  the  neuroblasts  are  developed  has 
been  sufficiently  described  (p.  -147).  The  ensheathment,  also,  of  the  axons  by  medulla 
has  been  referred  to,  and  the  fact  that  the  different  tracts  of  fibres  receive  their  medullary 
sheaths  at  different  periods  mentioned.  It  is  now  only  necessary  to  state  that  the  oi'der 
of  myeliuisation  of  the  several  tracts  is  as  follows  : — (1)  Fibres  of  the  anterior  nerve-roots  ; 
(2)  tract  of  Burdach ;  (3)  fibres  in  the  basis-bundles ;  (4)  tract  of  Goll ;  (5)  direct  cere- 
bellar tract :  (6)  tract  of  Gowers  ;  (7)  pyramidal  tracts  (Kahler). 

Development  of  the  Median  Fissures  and  of  the  Central  Canal. — As  the 
anterior  horns  of  gray  matter  covered  by  the  anterior  columns  of  white  matter  increase  in 
size,  the  anterior  surface  of  the  cord  on  either  side  of  the  mesial  plane  bulges  forwards, 
and  the  antero-median  fissure  is  produced  as  the  natural  result. 

The  manner  in  which  the  postero-median  fissure  comes  into  existence  is  not  fully 
understood,  but  the  majority  of  embryologists  believe  that  it  is  produced  by  the  approxi- 
mation and  fusion  of  the  walls  of  the  posterior  part  of  the  primitive  cavity  of  the  neural 
tube.     The  postero-median  septum  would  thus  appear  to  be  formed  of  spongioblastic  tissue. 

If  the  above  view  of  the  formation  of  the  postero-median  fissure  be  correct,  it  must 
be  evident  that  the  central  canal  of  the  cord  does  not  represent  the  whole  of  the  pi'imitive 
cavity  of  the  early  neural  tube,  but  only  the  anterior  portion  of  it. 

Among  those  observers  who  do  not  hold  that  the  central  canal  and  posterior  fissure  have  this 
mode  of  origin  the  most  prominent  is  Professor  A.  W.  Eobinson,  of  Birmingham  ;  and  he  has 
brought  forward  evidence  which  seems  to  indicate  that  it  is  doubtful  if  the  fusion  of  the  walls 
of  the  posterior  part  of  the  canal,  referred  to  above,  takes  place.  Certainly  the  arrangement  of 
the  ependymal  elements  of  the  postero-median  septum,  as  seen  in  the  preparations  of  Cajal 
and  V.  Lenhossek,  are  extremely  difficult  to  understand  on  the  fusion  theory.     They  run  in  the 


474 


THE  NEEVOUS  SYSTEM. 


aiitero-posterior  direction,  whereas,  if  fusion  has  taken  place,  most  of  them  would  present  a 
transverse  arrangement,  and  thus  lie  at  right  angles  to  the  postero-median  septu.m. 


THE  BRAIN  OR  ENCEPHALON. 

The  brain  is  the  enlarged  and  greatly  modified  upper  part  of  the  cerebrospinal 
nervous  axis.  It  is  surrounded  by  the  same  membranes  that  envelop  the  spinal 
cord  (viz.  the  dura  mater,  the  arachnoid  mater,  and  the  pia  mater),  and  it  almost 
completely  fills  up  the  cavity  of  the  cranium.  So  closely,  indeed,  is  the  skull 
capsule  moulded  upon  the  brain  that  the  impress  of  the  latter  is  almost  everywhere 
evident  upon  the  deep  surface  of  the  cranial  wall.  The  relations,  therefore,  of 
cranium  to  brain  are  totally  different  from  those  presented  by  the  vertebral  canal 


Ojitic  tract 


Olfactory  bulb 


Corpora  mammillaria 


TjOcus  perforatus  posticus 


Cms  cerebri 


Olfactory  tract 


Optic  nerve 


Sixth  nerve 


Hypoglossal  nerv 


Locus  perforatus 
anticus 

Optic  tract 


Tuber  cinereum 
Third  nerve 

-Fourth  nerve 
Fifth  nerye 

Facial  nerve 
Auditory  nerve 
Pars  intermedia 
Glosso-pharyngeal  nerve 

Vagus  nerve 


accessory  nerve 

Spinal  cord  (cut)  Hypoglossal  nerve 

Fits.  380.— The  Base  of  the  Brain  wrrn  the  Ckanial  Nerves  attached.   ' 

to  the  spinal  cord.  As  we  have  noted,  the  cord  occupies  only  a  part  of  its  bony 
case ;  and  there  is  not  only  a  wide  and  roomy  space  between  the  arachnoid  mater 
and  pia  mater,  but  also  an  interval  of  some  width  l)etween  the  dura  mater  and  the 
walls  of  the  vertebral  canal. 

General  Appearance  of  the  Brain. — When  viewed  from  above  the  brain 
presents  an  ovoid  figure,  the  broad  end  of  which  is  directed  backwards.  Its 
greatest  transverse  diameter  is  usually  found  in  the  neighbourhood  of  that  part 
which  lies  between  the  two  parietal  eminence-i  of  the  cranium.  The  only  parts 
which  are  visible  when  the  brain  is  inspected  I'rom  this  point  of  view  are  the  two 
convoluted  cerebral  hemispheres.  These  present  an  extensive  convex  surface,  which 
is  closely  applied  to  the  deep  aspect  of  the  cranial  vault,  and  Mre  separated  from 
each  other  by  a  deep  median  cleft,  termed  the  great  longitudinal  fissure,  which 
extends  from  the  front  to  the  back  of  the  brain. 


THE  BEAIN  OK  ENCEPHALON.  475 

The  iuferior  aspect  of  the  braiu  is  usually  termed  the  "  base. '  It  presents  an 
uneven  and  irregular  surface,  which  is  more  or  less  accurately  adapted  to  the 
inequalities  on  the  tioor  of  the  cranium.  Upon  this  aspect  of  the  brain  some  of 
its  main  subdivisions  may  be  recognised.  Thus  behind  is  seen  the  short  cylindrical 
portion,  called  the  bulb  or  medulla  oblongata,  through  which,  at  the  foramen  maguuni, 
the  brain  becomes  continuous  witli  the  spinal  cord.  The  bulb  lies  on  the  ventral 
aspect  of  the  cerebellum,  and  occupies  the  vallecula  or  hollow  which  intervenes 
between  the  two  cerebellar  hemispheres.  The  cerebellum  is  a  mass  of  considerable 
size  which  is  placed  below  the  hinder  portions  of  the  two  cerebral  hemispheres.  It 
is  easily  recognised  on  account  of  the  closely-set,  curved,  and  parallel  fissures  which 
traverse  its  surface  and  give  it  a  foliated  appearance.  Above  the  medulla,  and  in 
close  connexion  with  it,  is  a  prominent  white  elevation  called  the  pons  Varolii.  Im- 
mediately in  front  of  the  pons  there  is  a  deep  hollow  or  recess.  This  is  bounded 
behind  by  the  pons  Varolii,  on  either  side  by  the  projecting  temporal  lobe  of  the 
cerebral  hemisphere,  and  in  front  by  the  orbital  portions  of  the  frontal  lobes  of  the 
cerebral  hemispheres.  Passing  out  from  either  side  of  the  fore-part  of  this  recess  is 
the  deep  Sylvian  fissure  which  intervenes  between  the  pointed  and  projecting 
extremity  of  the  temporal  lobe  and  the  frontal  lobe  of  the  cerebrum,  whilst  in  the 
middle  line  in  front  the  great  longitudinal  fissure,  which  separates  the  frontal 
portions  of  the  cerebral  hemispheres,  opeus  into  it. 

Within  the  limits  of  this  deep  hollow,  in  the  base  of  the  brain,  two  large  rope- 
like strands,  the  crura  cerebri,  may  be  seen  issuing  from  the  upper  aspect  of  the 
pons  Varolii.  Placed  close  together  as  they  emerge  from  the  pons,  these  crura 
diverge  as  they  proceed  upwards  and  forwards,  and  finally  each  disappears  by 
plunging  into  the  corresponding  side  of  the  cerebrum.  Turning  round  the  outer 
side  of  each  crus,  where  it  enters  the  cerebrum,  a  flattened  band  termed  the  optic 
tract  may  be  observed.  These  bands  converge  in  the  fore-part  of  the  holhtw,  and 
are  finally  joined  together  by  a  short  commissural  portion,  termed  the  optic  chiasma. 
The  optic  nerve  is  continued  forwards  and  outwards,  on  either  side,  from  the  chiasma 
and  tract. 

The  crura  cerebri,  the  optic  tracts,  and  the  optic  chiasma  enclose  a  deep 
rhomboidal  or  lozenge-shaped  interval  on  the  base  of  the  brain,  which  is  termed 
the  interpeduncular  space.  Within  the  limits  of  this  area  the  following  parts  may 
be  seen  as  we  pass  from  behind  forwards :  (1)  the  locus  perforatus  posticus  ;  (2)  the 
corpora  mammillaria :  (3)  the  tuber  cinereum  and  the  stalk  of  the  pituitary  body. 

At  its  posterior  angle,  immediately  in  front  of  the  pons  Varolii,  the  inter- 
peduncular space  is  very  deep  and  is  floored  by  a  layer  of  gray  matter,  which  is 
perforated  by  numerous  small  apertures.  This  is  the  locus  perforatus  posticus. 
Through  the  apertures  which  are  dotted  over  its  surface  the  small  postero-mesial 
basal  branches  of  the  posterior  cerebral  artery  enter  the  brain. 

The  corpora  mammillaria  are  two  small  white  pea-like  eminences  placed  side  by 
side  in  front  of  the  locus  perforatus  posticus. 

The  tuber  cinereum  is  a  slightly  raised  field  of  gray  matter,  which  occupies  the 
interval  between  the  anterior  portions  of  the  optic  tracts  in  front  of  the  corpora 
mammillaria.  Springing  from  the  fore-part  of  the  tuber  cinereum,  immediately 
behind  the  optic  chiasma,  is  the  infundibulum,  or  the  stalk  which  connects  the 
pituitary  body  with  the  base  of  the  brain. 

Outside  the  limits  of  the  fore-part  of  the  interpeduncular  space  there  is  on 
either  side  a  small  depressed  triangular  field  of  gray  matter,  which  leads  outwards 
into  the  Sylvian  fissure.  It  is  perforated  by  the  antero-mesial  and  the  antero- 
lateral groups  of  basal  arteries,  and  receives  the  name  of  the  locus  perforatus 
anticus. 

General  Connexions  of  the  Several  Parts  of  the  Brain.  — The  medulla 
oblongata,  the  pons  Varolii,  and  the  cerebellum  occupy  the  posterior  cranial  fossa, 
and  they  are  separated  from  the  cerebral  hemispheres  which  lie  above  them  by  a 
partition  of  dura  mater,  termed  the  tentorium  cerebelK.  Further,  they  surround 
a  cavity,  a  portion  of  the  primitive  cavity  of  the  early  neural  tube,  which  is  termed 
the  fourth  ventricle  of  the  brain,  and  they  all  stand  in  intimate  connexion  with 
each  other.     The  medulla  is  for  the  most  part  carried  upwards  into  the  pons 


476 


THE  NEKVOUS  SYSTEM. 


Varolii ;  but  at  the  same  time  two  large  strands  from  its  dorsal  aspect,  termed  the 
restiform  bodies,   are  prolonged  into  the  cerebellum,  and  constitute  its  inferior 

peduncles,  or  the  chief  bonds  of  union 
between  the  medulla  and  the  cere- 
bellum. The  pons  Varolii  has  large 
numbers  of  transverse  fibres  enter- 
ing into  its  composition,  and  the 
great  majority  of  these  are  gathered 
together  on  either  side  in  the  form 
of  a  large  rope-like  strand.  This 
plunges  into  the  corresponding  hemi- 
sphere of  the  cerebellum,  and  con- 
stitutes its  middle  peduncle. 

The  cerebrum,  which  forms  the 
great  mass  of  the  brain,  occupies  the 
anterior  and  middle  cranial  fossae, 
and  extends  backwards  into  the  oc- 
cipital region  above  the  tentorium 
and  the  cerebellum.  The  greater  part 
of  the  cerebrum  is  formed  by  the 
cerebral  hemispheres,  which  are 
separated  from  each  other  in  the 
mesial  plane  by  the  great  longi- 
tudinal hssure.  At  the  bottom  of  this  fissure  is  the  corpus  callosum,  a  broad 
commissural  band  which  connects  the  two  hemispheres  with  each  other.  Each 
hemisphere  is  hollow,  the  cavity  in  its  interior  being  termed  the  lateral  ventricle 
of  the  brain.  Between  and  below  the  cerebral  hemispheres,  and  almost  com- 
pletely concealed  by  them,  is  the  inter-brain  or  diencephalon.  The  principal  parts 
forming  this  portion  of  the  brain  are  two  large  masses  of  gray  matter,  termed 
the  optic  thalami.  Between  these  is  the  third  ventricle  of  the  brain — a  deep  narrow 
cavity  occupying  the  mesial  plane.  The  third  ventricle  communicates  with  the 
lateral  ventricles  by  two  small  apertures,  called  the  foramina  of  Monro. 

The  cerebrum  is  connected  with  the  parts  in  the  posterior  cranial  fossa  (pons 
Varolii,  cerebellum,  and  bulb)  by  a  narrow  stalk  called  the  mid-brain,  or 
mesencephalon.  The  mid-brain  is  built  up  of  the  crura  cerebri,  passing  from  the 
pons  Varolii  to  the  cerebrum  ;  the  corpora  quadrigemina,  forming  its  dorsal  part ;  and 
the  superior  cerebellar  peduncles,  proceeding  from  the  cerebellum  to  the  cerebrum. 
It  is  tunnelled  by  a  narrow  passage,  the  aqueduct  of  Sylvius,  which  extends  between 
the  fourth  and  third  ventricles. 


Fig.  381.- 


Inferior  cerebellar  peduncle 


-Schema,  showing  the  connexions  of  the  several 
parts  of  the  brain. 


Genekal  Outline  of  the  Development  of  the  Brain. 

The  brain  is  developed  from  the  expanded  anterior  portion  of  the  primitive 
neural  tube.  In  the  section  deahng  with  the  general  principles  of  Embryology  it 
has  been  pointed  out  that  this  part  of  the  neural  tube  is  marked  off  by  two  con- 
strictions into  three  primitive  cerebral  vesicles,  which  are  termed  respectively  the 
hind-brain  or  rhombencephalon,  the  mid -brain  or  mesencephalon,  and  the  fore- 
brain  or  prosencephalon. 

Hind-brain  or  Rhombencephalon. — The  hind-brain  is  the  largest  of  the  three 
primary  expansions  of  the  neural  tube :  indeed,  it  may  be  said  that  in  the  earlier 
stages  of  brain  development  it  is  larger  than  both  of  the  other  primary  subdivisions 
taken  together.  The  portion  immediately  adjoining  the  mid-brain  is  constricted, 
and  is  termed  the  isthmus  rhombencephali.  This  is  a  very  small  part,  forming  the 
extreme  upper  end  of  the  vesicle,  and  i'rom  its  walls  are  developed  the  superior 
cerebellar  peduncles  and  a  thin  lamina,  which  is  stretched  across  the  middle  line 
between  them,  called  the  valve  of  Vieussens  or  the  superior  medullary  velum. 
Immediately  behind  the  isthmus  the  hind-brain  expands  suddenly,  and  then  slowly 
and  gradually  tapers  as  it  passes  downwards  towards  the  spinal  cord  part  of  the 
neural  tube.     Its  junction  with  the  latter  is  very  early  indicated  by  a  sharp  bend 


GENEEAL  OUTLINE  OF  DEVELOPMENT  OF  THE  BEAIN.      477 


iu  the  tube,  which  is  termed  the  cervical  flexure.  The  large  portion  of  hind-brain 
which  extends  from  the  isthmus  to  the  cervical  flexure  is  usually  considered  as 
being  composed  of  two  parts,  viz.  an  upper  portion,  termed  the  metencephalon,  and 
an  inferior  portion,  called  the  myelencephalon. 

From  the  metencephalon  are  derived  the  cerebellum  and  pons  Varolii.  The 
cerebellum  arises  by  a  thickening  of  the  dorsal  wall  of  this  portion  of  the  vesicle, 
whilst  the  pons  is  formed  by  a  thickening  of  the  lateral  and  ventral  walls.     The 


""•^AUC    TL, 


^^'2J:ifi. 


OPTIC  VESICLE 


Fig.  382. — Two  Stages  in  the  Development  of  the  Human  Brain  (after  His). 
A.  Brain  of  an  embryo  of  the  third  week.     B.   Brain  of  an  embryo  of  five  weeks. 

myelencephalon  gives  origin  to  the  bulb  or  medulla  oblongata.  This  is  chiefly 
formed  by  a  thickening  of  the  lateral  walls  of  this  part  of  the  vesicle.  These  fall 
away  from  each  other  in  an  outward  direction,  and  thus  the  ventral  angle  between 
them  becomes  greatly  opened  up.  The  growth  which  leads  to  the  formation  of  the 
bulb  appears,  therefore,  to  take  place  chiefly  on  the  ventral  aspect  of  the  vesicle. 
The  dorsal  wall  remains  thin  and  epithelial,  and  undergoes  little  or  no  development 
into  nervous  elements. 

The  cavity  of  the  original  hind-brain  is  retained  iu  the  adult  brain  as  the  fourth 
ventricle ;  and  from  what  has  been  said  regarding  the  development  of  the  different 
portions  of  the  wall  of  the 
primitive  hind-brain,  it  will 
be  seen  that  in  its  lower  or 
medullary  part  its  dorsal 
wall  or  roof,  to  a  large 
extent,  remains  epithelial. 

The  parts  of  the  adult 
brain  which  are  derived 
from  the  rhombencephalon 
or  hind -brain  are  those 
which  lie  below  the  ten- 
torium cerebelli  in  the 
posterior  cranial  fossa  of 
the  skull. 

Mesencephalon  or 
Mid -brain. — The  mid -brain  takes  a  much  more  prominent  part  in  the  forma- 
tion of  the  early  primitive  brain  than  it  does  in  the  construction  of  the  adult 
brain.  It  forms  a  very  small  part  of  the  adult  brain,  and  constitutes  a  stalk  of 
connexion  between  the  parts  which  are  developed  from  the  walls  of  the  rhomben- 
cephalon and  those  which  are  developed  from  the  walls  of  the  prosencephalon 
or  fore -brain.  The  entire  wall  of  the  mid-brain  is  transformed  into  nervous 
tissue.  Thus,  by  the  special  development  of  the  dorsal  section  of  the  wall,  the 
corpora  quadrigemina  are  formed.  The  lateral  and  ventral  sections  of  the  wall 
undergo  a  still  inore  marked  degree  of  growth-thickening,  and  the  result  is  the 


OPTIC  VESICLE 


OPTIC  VES 
OPTIC  STALK 


A  B 

Fig.  383. — Two  Cross  Sections  through  the  Fore-Brain. 

Through  the  fore-brain  of  the  early  human  embryo.  B.  Through 
the  fore-brain  and  optic  vesicles  of  a  Lepidosteus  embryo  of  eight 
days  (after  Balfour  and  Parker,  modified). 


478 


THE  NEEVOUS  SYSTEM. 


F  ORp   __ 


formation  of  the  two  crura  cerebri.  The  cavity  of  the  inid-braiii  is  retained  as  the 
narrow  passage  termed  the  aqueduct  of  Sylvius,  which  connects  the  third  ventricle 
of  the  brain  with  the  fourth  ventricle. 

Prosencephalon  or  Fore-brain. —In  its  early  condition  one  of  the  leading 
peculiarities  of  the  fore-brain  is  its  great  width.  It  extends  outwards  on  either 
side  for  a  considerable  distance  beyond  the  lateral  walls  of  the  mid- brain.  These 
lateral  expansions  of  the  fore-brain  are  the  optic  vesicles,  and  at  this  stage  they  are  in 
no  way  constricted  off  from  the  central  part  of  the  cavity  (Fig.  383).  Soon,  however, 
the  central  portion  of  the  fore-brain  begins  to  expand  upwards  and  forwards,  whilst 
the  terminal  portions  of  the  optic  vesicles  likewise  undergo  enlargement ;  and  the 
result  is,  that  the  originally  single  chamber  shows  subdivision  into  three  parts, 
viz.  a  central  portion  or  fore-brain  proper,  and  two  expanded  optic  vesicles,  which 

are  joined  to  the  lower 
parts  of  the  lateral  aspects 
of  the  fore-brain  proper  by 
two  short  constricted 
tubular  passages  termed 
the  optic  stalks. 

The  optic  vesicle  and 
the  optic  stalk  become  ulti- 
mately transformed  into  the 
retina  of  the  eye-ball  and 
the  optic  nerve.  The 
changes  which  lead  to  this 
result  are  detailed  in  the 
section  dealing  with  the 
anatomy  of  the  organ  of 
vision. 

The  fore-brain  under- 
goes a  series  of  remarkable 
developmental  changes,  the 
most  striking  of  which  is 
the  formation  of  the  cere- 
bral hemispheres.  The 
terminal  or  fore-portion  of 
the  fore-brain,  in  the  first 
instance,  expands  in  a  for- 
ward and  downward  direc- 
tion, and  from  the  upper 
and  lateral  aspects  of  the 
new  portion  of  the  vesicle 
thus  formed  the  cerebral 
hemispheres  bulge  outwards 
in  the  form  of  two  hollow 
pouches.  The  hinder 
original  part  of  the  fore- 
brain  is  termed  the  thal- 
mamencephalon  or  dien  - 
cephalon,  whilst  the  an- 
terior part  with  the  cerebral  hemispheres,  which  protrude  out  i'rom  it,  receives  the 
name  of  telencephalon. 

The  side  walls  of  the  diencephalon  become  thickened  into  the  two  large  masses 
of  gray  matter  termed  tbe  optic  thalami ;  the  floor  or  ventral  wall  develops  into 
those  structures  which  occupy  the  interpeduncubir  space  in  the  base  of  the  brain 
(viz.  the  posterior  perforated  spot,  the  corpora  mammillaria,  and  the  tuber  cinereum) ; 
whilst  the  roof  or  dorsal  wall  remains  thin  and  epithelial,  and  undergoes  no 
nervous  development. 

The  hollow  cerebral  hemispheres  soon  outstrip  all  the  other  parts  of  the  brain 
in  their  development.     They  expand  not  only  in  an  upward  and  forward  direction, 


Fk;.   384. — The  Brain  ok 


Brain  as  seen  in  profile 
Manimillary    eminence 


A.  Human  Embryo  in  thk  Fifth  Wkkk 
(from  His). 

B,  Mesial  section  tlirougli  the  same  brain. 
Tc.    Tuljer  cinereum  ;    Hp,   Hypojiliysis 

(pituitary  diverticulum  from  buccal  cavity)  ;  Opt,  Optic  stalk  ; 
TH,  Optic  tlialamus  ;  Tg,  Tegmental  part  of  mesencephalon  ;  Ps, 
Pars  subthalamica  ;  Cs,  Corpus  striatum  ;  FM,  Foramen  of  Monro  ; 
L,  Lamina  terminalis  ;  RO,  Recessus  opticus  ;  Ri,  Recessus  infun- 
dibuli. 


GENEEAL  OUTLINE  OF  DEVELOPMENT  OF  THE  BEAIN.      479 


but  chiefly  in  a  backward  direction ;  and  by  their  excessive  growth  backwards 
they  gradually  come  to  overlie  the  diencephalon,  the  mesencephalon,  and  at 
last  the  parts  derived  from  the  rhombencephalon.  It  thus  comes  about  that, 
when  the  adult  brain  is  viewed  from  above  nothing  but  the  cerebral  hemispheres 
are  visible — all  the  other  parts  of  the  brain  lie  under  cover  of  them. 

At  first  the  cavity  of  each  cerebral  hemisphere  is  connected  with  the  cavity 
of  the  front  portion  of  the  fore-brain  by  an  exceedingly  short  but  relatively  wide 
passage.  This  is  the  early  condition  of  the  foramen  of  Monro.  The  fore-part  of 
the  fore -brain  is  now  seen  to  be  bounded  in  front  between  the  two  hollow  cerebral 
hemisphere-pouches  by  a  narrow  thin  strip,  which  represents  the  extreme  anterior 
wall  of  the  neural  tube,  and  consequently  it  receives  the  name  of  lamina  terminalis. 
The  cavity  of  the  fore-brain  not  only  in  its  hinder  diencephalic  part,  but  also  in 
its  anterior  telencephalic  part  (i.e.  the  part  from  which  the  cerebral  hemispheres 
bud  out),  persists  as  the  third  ventricle  of  the  brain,  whilst  the  cavities  of  the 
primitive  cerebral  hemispheres  are 
represented  in  the  adult  by  the 
lateral  ventricles  of  the  brain.  The 
foramina  of  Monro,  relatively  much 
reduced  in  size,  are  preserved  as 
narrow  throats  of  communication 
between  the  lateral  ventricles  and 
the  third  ventricle.  The  olfactory 
lobes  are  formed  as  hollow  out- 
growths from  the  cerebral  hemi- 
spheres. 

Flexures  of  the  Brain-tube. — 
At  a  very  early  period,  and  while  the 
changes  detailed  above  are  being 
carried  on,  the  cerebral  portion  of  the 
neural  tube  becomes  sharply  bent 
upon  itself  at  certain  points.  The 
first  flexure  which  occurs  is  the 
primary  cephalic  flexure.  It  occurs 
in  the  region  of  the  mesencephalon, 
and  involves  the  entire  head.  The 
fore-brain  becomes  bent  in  a  ventral 
direction  round  the  fore-end  of  the 
notochord  and  the  fore-gut,  until  the 
long  axis  of  the  fore-brain  forms  an 
acute  angle  with  the  long  axis  of 
the  hind-brain  and  the  ventral  wall 
of  the  one  comes  to  lie  nearly  parallel  with  the  corresponding  wall  of  the  other. 
Through  this  curvature  the  mid-brain  is  considerably  modified  in  form,  and  for  a 
time  it  comes  to  occupy  the  most  prominent  and  foremost  part  of  the  embryonic  head. 

The  primary  cephalic  flexure  is  soon  followed  by  the  cervical  flexure.  This 
occurs  at  the  junction  of  the  hind-brain  with  the  spinal  cord.  Here  the  entire 
head  is  bent  in  a  ventral  direction,  and  at  the  end  of  the  fifth  week  the  flexure  is 
so  pronounced  that  the  cerebral  and  spinal  cord  portions  of  the  neural  tube  meet 
each  other  at  a  right  angle  (Fig.  385).  In  the  later  stages  of  development  the 
cervical  flexure  becomes  obliterated  by  the  elevation  of  the  head  and  the  straighten- 
ing of  the  neck  of  the  embryo. 

The  third  bend  takes  place  in  the  region  of  the  future  pons  Varolii  (meten- 
cephalon),  and  is  consequently  termed  the  pontine  flexure.  It  differs  from  the 
other  flexures  in  being  confined  to  the  brain  tube  and  in  not  in  any  way  involving 
the  entire  head.  Further,  the  bend  is  much  more  marked  in  the  thick  ventral 
wall  than  in  the  thin  dorsal  wall  of  the  tube.  The  neural  tube  is  doubled  forwards 
on  itself  and  the  pons  Varolii  becomes  developed  in  connexion  with  the  summit  of 
the  curvature.  In  the  further  growth  of  the  brain  the  pontine  flexure  becomes 
almost  completely  obliterated. 


Fig.  385.- 


-Profile  View  of  the  Brain  of 
Embryo  of  Ten  Weeks  (His). 


Human 


The  various  cranial  nerves  are  indicated  by  numerals. 

A,  Cerebral  diverticulum  of  pituitarj^  body.     B,  Buccal 
diverticulum  of  pituitary  body. 


480 


THE  NEEVOUS  SYSTEM. 


By  reason  of  these  curvatures  the  early  brain  assumes  a  sinuous,  zigzag  or 
S-shaped  outline  when  viewed  from  the  side,  and  the  relationship  of  its  various 
parts  becomes  materially  altered.  The  essential  factor  at  work  in  the  production 
of  the  brain  flexures  is  clearly  the  very  unequal  growth  which  takes  place  in 
different  parts  of  the  cerebral  wall. 

Basal  and  Alar  Laminae  of  His. — It  has  been  pointed  out  that,  in  the 
development  of  the  spinal  cord,  each  of  the  thick  lateral  walls  of  the  neural  tube 
is  marked  off  into  a  dorsal  or  alar  and  a  ventral  or  basal  lamina.  This  subdivision 
is  also  noticeable  in  the  cerebral  part  of  the  neural  tube,  and  the  furrow  on  the 
inner  aspect  of  the  lateral  wall,  which  indicates  this  subdivision,  can  be  traced 
even  in  the  adult  brain  throughout  a  considerable  part  of  its  length. 

In  the  spinal  cord  the  motor  cells  are  gathered  in  the  basal  lamina  in  more  or 

less  continuous 
columns.  In  the 
brain  the  corre- 
sponding cells 
from  which  the 
efferent  fibres  of 
the  cranial  nerves 
are  given  off  are 
also  placed  within 
the  basal  lamina, 
but  they  are  ar- 
ranged differently. 
They  are  collected 
together  in  dis- 
connec  ted  clusters 
termed  the  motor 
nuclei,  and  they 
do  not  extend 
higher  up  than 
the  mid-brain. 
No  motor  nuclei 


In  both 


Fig.  386. — Diagrams  to  illustrate  the  Alar  and  Basal  Lamina 
cases  the  emljryonic  brain  is  represented  in  mesial  section  (Hi: 

A,   The  different  subdivisions  of  the  brain  are  marked  off  from  each  other  by  dotted   ocCUr  in  the   forC- 
lines,  and  the  dotted  line  running  in  the  long  axis  of  the  neural  tube  indicates  the    l-,™„;,-,         Tnrlppfi 


separation  of  the  alar  from  the  basal  lamima  of  the  lateral  wall 

B.   Mesial  section  through  the  brain  of  a  human  embryo  at  the  end  of  the  first 
month.     Dotted  lines  mark  off  the   different  regions    and  also    the    alar  and  liasal 
laminaa  from  each  other. 
H,  Buccal  part  of  pituitary  body  ;   RL,   Olfactory  lobe  ;    C.Str,    Corpus   striatum 


the  importance  of 
the  basal  lamina' 
diminishes  as  we 
pass    from    the 


A,  Entrance  to  optic  stalk;  0,  Optic  recess;  I',  Infundibular  recess;  T,  Tuber   Inwpr  to  the  higher 
cinereum  ;  M.  Mammillary  enuuence.  ,        ,,  ,.,      ,  *  . 

parts  of  the  brain. 

In  the  rhombic  or  hind-brain  the  greater  part  of  the  medulla  oblongata  and  of 
the  pons  Varolii  is  formed  from  the  basal  laminje,  whilst  the  cerebellum,  with  its 
superior  and  inferior  cerebellar  peduncles,  is  derived  from  the  alar  laminse.  In 
the  mid-brain  the  crura  cerebri  are  the  derivatives  of  the  basal  laminae,  whilst  the 
corpora  quadrigemina  are  developed  from  the  alar  famime.  In  the  fore-brain  the 
subthalamic  region  and  the  optic  vesicles  are  products  of  the  growth  of  the  basal 
laminae,  whilst  the  optic  thalami  and  cerebral  hemispheres  spring  from  the  alar 
laminae. 

The  fact  that  the  cerebellum  and  the  cerebral  hemispheres  owe  their  origin 
to  the  alar  laminae  is  sufficient  to  show  the  predominant  part  wliich  these  laminae 
play  in  brain  development,  and  the  higher  we  ascend  in  the  animal  scale  the  more 
pronounced  does  this  predominance  become. 

The  following  table  gives  a  summary  of  the  various  developmental  processes 
which  have  been  described  in  the  foregoing  pages : — 


MEDULLA  OBLONGATA  OE  BULB. 


481 


Encejjlialon 

or 

Brain 


Rhombencephalon 

or 

Hind-brain 

(posterior  cerebral 

vesicle) 


Myelencephalon 


Mesencephalon 

or  Mid-brain 

(middle  cerebral 

vesicle) 


Prosencephalon 

or  Fore-brain 

(anterior  cerebral 

vesicle) 


Metencephalon 

Isthmus  rhonibencephali 

(narrow  constricted  part 

immediately  adjoining 

the  mesencephalon) 

Mesencephalon 

or 

Mid-brain 


Thalamencephalon 

or 

Diencephalon 


L 


Telencephalon 


( Bulb  or  medulla  oblongata 
-|  Lower  part  of  the  fourth  ven- 
'      tricle 
/'Cerel^elluiii 
J  Pons  Varolii 

I  Ui)per  part  of  the   fourth  veii- 
^     tricle 

I.Superior  cerebellar  peduncles 
j  Valve  of  Vieiissens 

j  Corpora  quadrigemina 

-,  Crura  cerebri 

I  Aqueduct  of  Sylvius 

Optic  thalami 

Suljthalamic  tegmental  regions 

Pituitary  and  pineal  bodies 

Structures  in  interj^eduncular 
space 

Optic  nerve  and  retina 

Hinder  part  of  the  third  ven- 
tricle 

Cereljral  hemispheres 

Olfactory  lobes 

Lateral  ventricles 

Foramina  of  Monro 

Anterior  portion  of  the  third 
ventricle 


THE  PAETS  OF  THE  ENCEPHALON  DEEIVED  EEOM  THE 

HIND-BEAIN. 


MEDULLA  OBLONGATA  OR  BULB. 

The  medulla  oblongata  or  bulb  is  the  continuation  upwards  of  the  spinal  cord. 
It  is  not  more  than  one  inch  in  length,  and  it  may  be  regarded  as  beginning  at  the 
decussation    of     the 

pyramidal    tracts,  ^..=. .,.: "  ^v_/^ — -optic nerve 

which  takes  place 
about  the  level  of 
the  foramen  magnum. 
From  this  it  proceeds 
upwards  in  a  very 
nearly  vertical  direc- 
tion, and  ends  at  the 
lower  border  of  the 
pons  Varolii.  At  first 
its  girth  is  similar  to 
that  of  the  cord,  but 
it  rapidly  expands  as 
it  approaches  the 
pons,  and  conse- 
quently it  presents  a 
more  or  less  conical 
form.  Its  ventral 
surface  lies  behind 
the  grooved  surface 
of  the  basilar  portion 
of  the  occipital  bone, 
whilst  its  dorsal  sur- 
face is  sunk  into  the  vallecula  of  the  cerebellum.  The  medulla  oblongata  is  a 
bilateral  structure,  and  this  is  indicated  on  the  surface  by  a  continuation  upwards 
of  the  antero-median  and  postero-median  fissures  of  the  cord  on  the  ventral  and 
dorsal  aspects  of  the  medulla. 
35 


optic  chiasina  — 

Optic  tract. 

Corpus  geiiiculatuni 
externum 

Corpus  geniculatuiii 

internum 

Locus  perforatus 

posticus 


Middle  peduncle 
of  the  cerebellum 


Restifonn  body 

Olive 

Pyramid 

Anterior  superficial 

arcuate  fibres 

Decussation  of 
pyramid 


fnfundibulum 

Tuber  cinereinn 

Corpora  mammillaria 

Oculo-motor  nerve  (III.) 

Trochlear  nerve  (IV.) 
winding  round  the  cms 
cerebri 

Trigeminal  nerve  (V.) 

Abducent  nerve  (VI.) 
Facial  nerve  (VII.) 
Auditory  nerve  (VIII.) 

^_  Vago-glossopharyngeal 
nerve  (IX.  and  X.) 

Hypoglossal 
nerve  (XII.) 

Spinal  accessory 

nerve  (XI.) 

First  cervical  nerve 


Fio.  387. 


-Front  View  of  the  Medulla,  Pons,  and  Mesencephalon  of 
FULL-TIME  Human  Fcetus. 


482 


THE  NEEVOUS  SYSTEM. 


The  antero-median  groove  (fissura  mediana  anterior),  as  it  passes  from  the  cord 
on  to  the  medulla,  is  interrupted  at  the  level  of  the  foramen  magnum  by  several 
strands  of  fibres,  which  cross  the  mesial  plane  from  one  side  to  the  other.  This 
intercrossing  is  termed  the  decussation  of  the  pyramids.  Above  this  level  the 
furrow  is  carried  upwards  to  the  lower  border  of  the  pons,  but  is  often  rendered 
very  shallow  by  numerous  superficial  arcuate  fibres  which  emerge  upon  the  surface 
between  its  lips  and  then  curve  outwards  to  reach  the  hinder  part  of  the  medulla. 
At  the  lower  margin  of  the  pons  Varolii  it  expands  slightly  and  ends  in  a  blind  pit, 
which  receives  the  name  of  the  foramen  caecum  of  Vicq  d'Azyr.  The  postero-median 
fissure  (fissura  mediana  posterior)  is  only  carried  up  on  the  lower  half  of  the 
medulla.  As  it  ascends  it  rapidly  becomes  shallower,  and,  halfway  up,  the  central 
canal  of  the  cord  opens  on  the  dorsal  surface  of  the  medulla.  At  this  point  the 
lips  of  the  postero-median  fissure  are  thrust  apart  from  each  other  and  constitute 
the  boundaries  of  a  triangular  field,  which  is  thus  opened  up  on  the  dorsal  aspect 
of  the  medulla.  This  triangular  field  is  the  lower  part  of  the  fossa  rhomboidalis, 
or  the  floor  of  the  fourth  ventricle  of  the  brain.  The  lower  half  of  the  medulla, 
containing  as  it  does  the  continuation  of  the  central  canal  of  the  cord,  is  frequently 
termed  the  closed  part  of  the  medulla ;  the  upper  half,  above  the  opening  of  the 
canal,  which  by  its  dorsal  surface  forms  the  lower  part  of  the  floor  of  the  fourth 
ventricle,  is  then  called  the  open  part  of  the  medulla. 

Deferring  for  the  present  the  examination  of  the  medullary  part  of  the  floor 
of  the  fourth  ventricle,  the  appearance  presented  by  the  surface  of  each  side  of 
the  medulla,  from  the  antero-median  fissure  in  front  to  the  postero-median  fissure 
and  the  lateral  limit  of  the  floor  of  the  fourth  ventricle  behind,  may  now  engage 
our  attention.  In  the  spinal  cord  the  corresponding  surface  area  is  divided  into 
three  districts  or  columns  by  the  emerging  motor  roots  and  the  entering  sensory 
roots  of  the  spinal  nerves.  Of  these  the  latter  enter  along  the  bottom  of  the 
postero-lateral  groove,  whilst  the  motor  fascicles  are  spread  over  a  relatively  broad 

surface  area  and  have 
no  groove  in  connexion 
with  their  emergence 
from  the  cord.  In  the 
case  of  the  medulla 
corresponding  rows  of 
nerve  -  fascicles  enter 
and  emerge  from  the 
surface  of  each  side. 
The  efferent  fascicles 
are  the  root -bundles  of 
the  hypoglossal  nerve, 
and  they  carry  up  the 
line  of  the  anterior 
nerve-roots  of  the  cord. 
In  one  respect,  however, 
they  differ:  they  emerge  • 
in  linear  order  and  along 
the  bottom  of  a  dis- 
tinct furrow,  termed  the 
antero  -  lateral  furrow, 
which  proceeds  upwards 
on  the  surface  of  the 
medulla.  The  fascicles 
which  carry  up  the  line 
of  the  posterior  nerve- 
roots  on  the  surface  of 
the  medulla  are  the  root-bundles  of  the  spinal  accessory,  the  vagus,  and  the  glosso- 
pharyngeal nerves.  These  are  attached  along  the  bottom  of  a  furrow  which  is  the 
direct  continuation  upwards  of  the  postero-lateral  furrow  of  the  cord,  and  therefore 
receives  the  name  of  the  postero-lateral  furrow  of  the  medulla.      The  root-bundles 


Valve  of  Vieussenb. 


Superior  peduncle  of 
the  cerebellum 

Middle  peduncle  of 
the  cerebellum 


Striw  acustictu 
Area  acusticte 
Trigonum  vagi 


Cuneate  tubercle 
Funiculus  gracilis 


Tsonia  thalami 


Pineal  body 

Superior  quadri- 
geminal  body- 
Inferior  quadri- 
geminal  body 


Crus  cerebri 

Pontine  part  of  floor 
of  ventricle  IV. 

Eminentia  teres 

Fovea  superior 

Restiform  body 
Trigonum  hypoglossi 


Rolandic  tubercle 


Funiculus  cuneatus 


Fig.  388. — Back  View  of  the  Medulla,   Pons,  and  Mesencephalon  of 
a  full-time  human  fcetus. 


MEDULLA  OBLONGATA  OE  BULB. 


483 


of  these  nerves  differ,  however,  in  so  far  that  they  are  not  all  composed  of  afferent 
fibres  springing  from  ganglionic  cells  placed  without  and  entering  the  medulla. 
Certain  of  them  are  purely  efferent  (spinal  accessory  roots),  whilst  others  likewise 
contain  a  considerable  number  of  efferent  fibres,  and  are  therefore  to  be  regarded 
as  mixed  roots. 

By  the  postero-lateral  and  the  antero-lateral  grooves,  and  also  by  the  two  rows 
of  nerve  fascicles  attached  along  the  bottom  of  these  furrows,  the  surface  of  the 
medulla  on  each  side  is  divided  into  three  districts,  viz.  an  anterior,  a  lateral,  and  a 
posterior,  similar  to  the  surface  areas  of  the  three  columns  on  the  side  of  the  cord. 
Indeed,  at  first  sight,  they  appear  to  be  a  direct  continuation  upwards  of  these  three 
portions  of  the  cord ;  this  is  not  the  case,  however,  because  the  fibres  of  the  three 
columns  of  the  cord  undergo  a  rearrangement  as  they  proceed  upwards  into  the 
medulla. 

Anterior  Area  of  the  Medulla — Pyramid  (pyramis). — The  district  between 
the  antero-median  fissure  and  the  antero-lateral  furrow,  along  the  bottom  of 
which  the  root-fascicles  of  the  hypoglossal  nerve  issue  from  the  medulla,  receives 
the  name  of  the  pyramid.  An  inspection  of  the  surface  is  sufficient  to  show 
that  the  pyramid  is  composed  of  a  compact  strand  of  longitudinally  directed 
nerve-fibres.  Tapering  below,  it  expands  and  assumes  a  prominent  appearance 
as  it  is  traced  upwards,  and,  finally  reaching  the  lower  border  of  the  pons  Varolii, 
it  becomes  shghtly  constricted  and  disappears  from  view  by  plunging  into  that 
portion  of  the  brain.  The  two  pyramids,  separated  from  each  other  by  the  antero- 
median furrow,  are  the  great  motor  strands  of  the  medulla. 

Although  the  pyramid  at  first  sight  appears  to  be  continuous  with  the  anterior 
column  of  the  cord,  only  a  very  small  pro- 
portion of  the  fibres  contained  in  the  latter 
are  derived  from  the  pyramid.  This  at  once 
becomes  manifest  when  the  lips  of  the 
antero-median  fissure  are  thrust  apart  at  the 
place  of  junction  between  the  cord  and  the 
medulla.  The  pyramid  is  then  seen  to  divide 
at  this  level  into  two  parts,  viz.  a  small 
portion  composed  of  a  variable  number  of 
the  outermost  fibres  of  the  pyramid,  termed 
the  direct  pyramidal  tract,  and  a  much  larger 
portion  situated  next  the  antero-median 
fissure,  called  the  crossed  pyramidal  tract. 
The  direct  pyramidal  tract  is  continued  down 
into  the  anterior  column  of  the  cord,  and 
in  this  it  takes  up  a  mesial  position  next 
the  antero-median  fissure.  The  crossed  pyra- 
midal tract  is  broken  up  into  three  or  more 
coarse  bundles,  which  sink  backwards  and  at 
the  same  time  cross  the  mesial  plane,  to  take 
up  a  position  in  the  posterior  part  of  the 
opposite  lateral  column  of  the  cord.  The 
term  decussation  of  the  pyramids  (decussatio 
pyramidum)  is  applied  to  the  intercrossing 
of  the  corresponding  bundles  of  the  crossed 
pyramidal  tracts  of  opposite  sides. 

The  direct  pyramidal  tract  is,  therefore, 
the  only  part  of  the  pyramid  which  has  a 
place  in  the  anterior  column  of  the  cord. 
The  much  larger  part  of  this  column,  termed 
the  anterior  basis-bundle,  as  it  is  traced  up  into  the  medulla  is  seen  to  be 
thrust  aside  by  the  decussating  bundles  of  the  crossed  pyramidal  tract.  It  thus 
comes  to  occupy  a  deep  position  in  the  substance  of  the  medulla  behind  and  to  the 
outer  side  of  the  pyramid. 

Lateral  Area  of  the  Medulla. — This  is  the  district  on  the  surface  of  the  medulla 
35  a 


CROSSED  PYR.TR. 


Fig.  389. — Diagram  of  the   Decussation  of 
THE  Pyramids  (modified  from  van  Gehuchten). 

NH,  Nucleus  hypoglossi ;  NV,  Vago- glosso- 
pharyngeal nucleus  ;  FS,  Fasciculus  soli- 
tarius  ;  NA,  Nucleus  ambiguus. 


484 


THE  NEEVOUS  SYSTEM. 


which  is  iucluded  between  the  two  rows  of  nerve-roots,  viz.  the  hypoglossal  roots  in 
front,  and  the  root-bundles  of  the  spinal  accessory,  the  vagus,  and  the  glosso- 
pharyngeal nerves  behind.  It  presents  a  very  different  appearance  in  its  upper  and 
lower  parts.  In  its  lower  portion  it  simply  appears  to  be  a  continuation  upwards 
of  the  lateral  area  of  the  cord  ;  in  its  upper  part  a  striking  oval  prominence  bulges 
out  on  the  surface  of  the  medulla,  and  receives  the  name  of  the  olivary  eminence. 

The  lower  part  of  this  district,  however,  is  very  far  from  being  an  exact  counter- 
part of  the  lateral  column  of  the  cord.  The  large  crossed  pyramidal  tract  is  no 
longer  present,  seeing  that  it  forms  in  the  medulla  the  greater  part  of  the  pyramid 
of  the  opposite  side.  Another  strand  of  fibres,  viz.  the  direct  cerebellar  tract, 
prolonged  upw^ards  in  the  lateral  column  of  the  cord,  gradually  leaves  this 
portion  of  the  medulla.  This  tract  lies  on  the  surface,  and  is  frequently  visible 
to  the  naked  eye  as  a  white  band,  which  inclines  obliquely  backwards  into 
the  posterior  district  of  the  medulla  to  join  its  upper  part,  or  in  other  words  the 
restiform  body.  The  remainder  of  the  fibres  of  the  lateral  column  of  the  cord, 
comprising  the  lateral  basis-bundle  and  the  tract  of  Gowers,  are  continued  upwards 
in  the  lateral  area  of  the  medulla,  and  at  the  lower  border  of  the  olive  the  majority 
of  these  fibres  disappear  from  the  surface  by  dipping  into  the  substance  of  the 
medulla  under  cover  of  that  projection.  A  small  proportion  of  the  fibres,  how- 
ever, are  retained  on  the  surface  and  travel  upwards  towards  the  pons  in  the  interval, 
which  exists  between  the  hinder  border  of  the  olive  and  the  roots  of  the  vagus  and 
glosso-pharyngeal  nerves. 

The  olivary  eminence  (oliva)  is  a  smooth  oval  projection  which  bulges  out  from 
the  upper  part  of  the  lateral  area  of  the  medulla.  Its  long  axis  is  vertical  and  is 
about  half  an  inch  long.  It  marks  the  position  of  the  subjacent  inferior  olivary 
nucleus,  a  flexuous  lamina  of  gray  matter  (nucleus  olivaris  inferior),  which  is  only 
separated  from  the  surface  by  a  very  thin  layer  of  superficial  white  matter. 

Posterior  Area  of  the  Medulla. — In  its  lower  half,  this  district  is  bounded 
behind  by  the  postero-median  fissure,  and  in  ifcs  upper  half  by  the  lateral  margin 
of  the  medullary  part  of  the  floor  of  the  fourth  ventricle  of  the  brain.  In  front 
it  is  separated  from  the  lateral  area  by  the  row  of  root-fascicles  belonging  to 

the  spinal  accessory,  vagus,  and  glosso- 
pharyngeal nerves.  As  in  the  lateral 
area,  we  recognise  a  lower  portion  and  an 
upper  portion,  which  appear  continuous 
but  in  reahty  are  almost  quite  distinct 
from  each  other. 

The  lower  part  of  the  posterior  area 
corresponds  more  or  less  closely  with  the 
posterior  column  of  the  cord.  In  the 
cervical  part  of  the  cord  the  posterior 
column  is  divided  by  the  paramedian 
septum  of  pia  mater  into  an  inner  column 
of  Goll  and  an  outer  column  of  Burdach. 
These  are  prolonged  upwards  into  the 
medulla,  and  in  the  lower  part  of  the 
posterior  area  they  stand  out  distinctly, 
and  are  separated  from  each  other  by  a 
continuation  upwards  from  the  cord  of  the 
paramedian  groove.  In  the  medulla  the 
inner  of  these  strands  is  called  the  funiculus 
gracilis,  whilst  the  outer  one  is  designated 
the  funiculus  cuneatus.  Each  of  these 
strands,  when  it  reaches  the  level  of 
the  lower  part  of  the  floor  of  the  fourth 
ventricle,  ends  in  a  slightly  expanded 
bulbous  prominence.  The  swoUen  extremity  of  the  funiculus  gracilis  is  called  the 
clava.  This  is  thrust  aside  from  its  neighbour  of  the  opposite  side  by  the  opening 
up  of  the  medulla  to  form  the  floor  of  the  fourth  ventricle,  and  the  central  canal  of 


Optic  tract 

Crus  cerebri 
Corpus  geniculatuin 
externum 

Pulvinar 

Corpus  geniculatmu 

internum 

Superior  bracliiuni 

Inferior  brachiuni 

Inferior  quadrigeminal  body 

Lateral  fillet 

Superior  cerebellar  peduncle 
nia  pontis 

Middle  i)eduncle  of 
•erebellum 


/  Kpstiforni  body 

l^igula  bounding  lateral 
recess  of  ventricle  IV. 
I  )b\ai  y  eminence 

Aicuate  fibres  (anterior  superficial) 
Clava, 

Cuneate  tubercle 
Roland  ic  tuljercle 
Lateral  district  of  medulla 

Anterior  column  of  cord 


Fio.  390.  —  Lateral  View  of  the 
Pons,  and  Me.sencephalon  of  a 
Human  Fcetds. 


Medulla, 
full-time 


MEDULLA  OBLONGATA  OK  BULB.  485 

the  cord  opens  on  the  surface  in  the  angle  between  the  two  clavfe.  Tlie  bulbous 
end  of  the  fasciculus  cuneatns  receives  the  name  of  the  cuneate  tubercle  (tuberculuna 
cinereum),  but  it  is  only  in  the  foetal  or  very  young  brain  that  it  is  well  marked. 

The  elongated  promineQces  formed  on  the  surface  of  the  medulla  by  these  two 
strands  and  their  enlarged  extremities  are,  in  a  great  measure,  due  to  the  presence 
of  two  elongated  nuclei  or  collections  of  gray  matter  which  make  their  appearance 
subjacent  to  the  strands,  and  which  gradually  increase  in  bulk  as  they  are  traced 
upwards.  These  are  termed  respectively  the  gracile  (nucleus  funiculi  gracilis)  and 
cuneate  (nucleus  funiculi  cuneati)  nuclei,  and  it  can  be  easily  shown  that  as  the 
gray  matter  increases  in  quantity  the  fibres  of  the  two  corresponding  strands 
diminish  in  number  by  coming  to  an  end  in  connexion  with  the  cells  of  the 
subjacent  nuclei.  Indeed,  it  is  doubtful  if  any  of  the  fibres  of  the  gracile  and 
cuneate  strands  extend  upwards  beyond  these  nuclei. 

But  a  third  longitudinal  elevation  is  also  apparent  on  the  surface  of  the  lower 
part  of  the  posterior  area  of  the  medulla.  This  is  placed  on  the  outer  side  of  the 
funiculus  cuneatus — between  it  and  the  posterior  row  of  nerve-roots — and  it  has 
no  counterpart  in  the  posterior  column  of  the  cord.  It  is  called  the  funiculus  of 
Rolando,  because  it  is  produced  by  the  substantia  gelatinosa  Eolandi,  which  caps  the 
posterior  horn,  coming  close  to  the  surface  and  forming  a  bulging  in  this  situation. 
The  funiculus  of  Eolando  is  wedge-shaped  in  outline.  Extremely  narrow  below,  it 
widens  as  it  is  traced  upwards,  and  finally  ends  in  an  expanded  extremity  called 
the  tubercle  of  Rolando  (tuberculum  Eolandi).  A  thin  layer  of  white  matter,  com- 
posed of  longitudinally  arranged  fibres,  is  spread  over  this  district,  and  separates  the 
substantia  Eolandi  from  the  surface.  These  fibres  constitute  the  spinal  root  of  the 
fifth  or  trigeminal  nerve,  which  here  assumes  a  superficial  position  as  it  descends 
in  the  medulla. 

The  restiform  body  (corpus  restiforme)  forms  the  uj^per  part  of  the  posterior 
area  of  the  medulla.  It  lies  between  the  floor  of  the  fourth  ventricle  and  the 
roots  of  the  vagus  and  glosso-pharyngeal  nerves.  It  is  a  large  and  prominent 
rope -like  strand,  which  inclines  upwards  and  outwards,  and  then  finally  takes 
a  turn  backwards  and  enters  the  cerebellum.  It  forms  the  great  link  of  connexion 
between  the  cerebellum  on  the  one  hand  and  the  medulla  and  spinal  cord 
on  the  other,  and  consequently  it  also  receives  the  name  of  the  inferior  cerebellar 
peduncle.  At  the  same  time  it  must  be  understood  that  it  is  not  formed  by  fibres 
which  are  prolonged  into  it  from  the  funiculus  cuneatus  and  funiculus  gracilis 
of  the  medulla.  It  is  true  that  a  surface  inspection  of  the  medulla  might  very 
naturally  lead  the  observer  to  this  supposition,  because  there  is  no  sharp  line  of 
demarcation  marking  it  off  from  the  tubercles  of  these  strands.  Such  a  conclusion, 
however,  would  be  altogether  erroneous,  because  it  would  appear  that  none  of  the 
fibres  of  the  posterior  columns  of  the  cord  are  carried  beyond  the  gracile  and  cuneate 
nuclei  of  the  medulla.  A  study  of  the  surface  of  the  medulla  yields  some  important 
information  regarding  the  constitution  of  the  restiform  body.  Thus  the  direct 
cerebellar  tract  from  the  lateral  column  of  the  cord  can  be  traced  into  it,  and  large 
numbers  of  fibres  which  take  a  curved  course  on  the  surface  of  the  medulla  may 
likewise  be  followed  into  it.  These  are  the  superficial  arcuate  fibres.  Numerous 
other  fibres  enter  the  restiform  body  on  its  deep  aspect,  but  these  will  be  studied 
at  a  later  stage. 

Superficial  Arcuate  Fibres  (fibrae  arcuate  externa). — These  fibres  enter 
into  the  constitution  of  the  restiform  body,  and  they  may  be  regarded  as  con- 
sisting of  two  sets,  viz.  the  anterior  superficial  arcuate  fibres  and  the  posterior 
superficial  arcuate  fibres,  both  of  which  present  this  feature  in  common  that  they 
run  on  the  surface  of  the  medulla. 

The  anterior  superficial  arcuate  fibres  are  more  particularly  seen  in  the  neighbour- 
hood of  the  olivary  eminence,  round  the  lower  border  of  which,  and  also  over  the 
surface  of  which,  they  may  be  observed  coursing  in  the  form  of  a  number  of  coarse 
curved  bundles.  They  vary  greatly  in  number  and  in  distinctness,  and  they  are 
sometimes  so  numerous  as  to  cover  over  almost  entirely  the  eminence.  An  attentive 
examination  will  show  that  they  come  to  the  surface  in  the  antero-median  fissure 
between  the  pyramids,  and  also  not  unfrequently  in  the  groove  between  the 
35  h 


486  THE  NEEVOUS  SYSTEM. 

pyramid  and  olive,  or  through  the  substance  of  the  pyramid  itself.  The  antero- 
median fissure  in  its  upper  part  is  often  almost  completely  blocked  up  by  these 
emerging  fibres.  The  anterior  superficial  arcuate  fibres  reaching  the  surface  of  the 
medulla  in  this  manner  turn  backwards,  and  the  great  majority  enter  the  restiform 
body  and  form  a  considerable  part  of  its  outer  portion. 

The  posterior  superficial  arcuate  fibres  arise  in  the  cuneate  and  gracile  nuclei,  and 
enter  the  restiform  body  of  the  same  side. 

THE  PONS  VAROLII. 

The  pons  Varolii  is  a  marked  white  prominence  on  the  basal  aspect  of  the  brain 
which  is  interposed  between  the  medulla  and  the  crura  cerebri,  and  which  lies  in 
front  of  the  cerebellum.  It  is  convex  from  side  to  side,  as  well  as  from  above 
downwards,  and  transverse  streaks  on  its  surface  show  that,  superficially  at  least,  it 
is  composed  of  bundles  of  nerve-fibres  which  course  transversely  over  it.  On  either 
side  these  transverse  fibres  are  collected  together  in  the  form  of  a  large  compact 
strand,  which  sinks  in  a  backward  and  outward  direction  into  the  white  matter  of 
the  corresponding  hemisphere  of  the  cerebellum.  This  strand  is  termed  the  middle 
peduncle  of  the  cerebellum,  and  the  term  "pons,"  applied  to  the  entire  structure, 
expresses  in  an  admirable  way  the  arch-like  manner  in  which  this  portion  of  the 
brain  bridges  across  between  the  two  cerebellar  hemispheres. 

The  ventral  surface  of  tbe  pons  is  in  relation  to  the  basilar  process  of  the 
occipital  bone  and  the  dorsum  sellse  of  the  sphenoid  bone.  It  presents  a  mesial 
groove  (sulcus  basilaris),  which  gradually  widens  as  it  is  traced  upwards,  and  in 
which  the  basilar  artery  lies.  This  mesial  depression  is  produced  by  the  prominence 
which  is  caused  on  either  side  by  the  passage  of  the  pyramidal  tract  of  fibres 
downwards  through  the  pons.  The  trigeminal  or  fifth  cranial  nerve,  with  its  large 
entering  sensory  root  and  its  small  emerging  motor  root,  is  attached  to  the  side  of 
the  ventral  aspect  of  the  pons,  nearer  its  upper  than  its  lower  border.  It  is  usual 
to  restrict  the  term  "  pons  "  to  that  portion  of  the  structure  which  lies  between  the 
two  trigeminal  nerves,  and  to  apply  the  designation  of  middle  cerebellar  peduncle 
to  the  part  which  extends  beyond  the  nerve  into  the  hemisphere  of  the  cerebellum. 
The  sixth  or  abducent  nerve,  tbe  seventh  or  facial  nerve,  and  the  eighth  or  auditory- 
nerve  are  attached  to  the  brain  at  the  lower  border  of  the  pons.  The  sixth  emerges 
at  the  outer  border  of  the  pyramid,  the  seventh  immediately  in  front  of  the  resti- 
form body,  whilst  the  auditory  nerve  reaches  the  brain  close  to  the  facial  nerve,  on 
the  ventral  aspect  of  the  restiform  body. 

The  whole  of  the  medulla  enters  the  lov-er  aspect  of  the  pons,  and,  with  the 
exception  of  the  restiform  bodies,  its  constituent  parts  are,  to  a  large  extent,  carried 
up  within  it.     The  crura  cerebri  emerge  from  its  upper  as2Ject. 

The  dorsal  surface  of  the  pons  looks  backwards  towards  the  cerebellum,  and 
presents  a  triangular  area  covered  with  gray  matter,  which  forms  the  upper  part  of 
the  anterior  wall  or  floor  of  the  fourth  ventricle.  This  area  is  directly  continuous 
below  with  the  medullary  part  of  the  floor  of  the  fourth  ventricle,  and  is  bounded 
on  either  side  by  a  band  of  white  matter  termed  the  superior  peduncle  of  the 
cerebellum. 

Superior  Cerebellar  Peduncles  (brachia  conjunctiva). — These  are  hidden  from 
view  by  the  upper  part  of  the  cerebellum,  under  cover  of  which  they  he.  They 
emerge  from  the  lateral  hemispheres  of  the  cerebellum,  and,  as  they  proceed 
upwards  on  the  dorsal  aspect  of  the  pons,  they  converge  towards  each  other  until, 
at  the  level  of  the  inferior  corpora  quadrigemina,  the  inner  margins  of  the  two 
peduncles  almost  become  contiguous  (Fig.  388,  p.  482).  At  first  they  form  the 
lateral  boundaries  of  the  upper  part  of  the  fourth  ventricle ;  but,  as  they  ascend 
and  approach  closer  to  each  other,  they  gradually  come  to  overhang  that  cavity 
and  thus  enter  into  the  formation  of  its  roof.  They  disappear  from  the  surface 
by  dipping  under  cover  of  the  quadrigeminal  bodies  and  entering  the  substance  of 
the  mesencephalon. 

Valve  of  Vieussens  or  the  Superior  Medullary  Velum  (velum  medullare 
anterius). — Filling   up   the   triangular   interval   between    the  two  superior  cere- 


THE  PONS  VAROLII. 


487 


bellar  peduncles,  and  stretching  across  from  the  inner  and  free  margin  of  the  one 
to  the  corresponding  margin  of  the  other,  is  a  thin  layer  of  white  matter  which 
completes  the  roof  or  dorsal  wall  of  the  upper  part  of  the  fourth  ventricle,  and 
receives  the  name  of  the  superior  medullary  velum.  When  traced  downwards,  it 
is  seen  to  be  carried  with  the  superior  peduncles  into  the  white  matter  of  the  cere- 
bellum. Spread  out  on  its  dorsal  surface  is  a  small,  thin,  tongue-shaped  prolongation 
of  gray  matter  from  tlie  cortex  of  the  cerebellum,  which  is  termed  tho  lingula, 
whilst  issuing  from  its  substance  close  to  the  inferior  quadrigeminal  bodies  are  the 
two  fourth  or  trochlear  cranial  nerves. 

Fourth  Ventricle  of  the  Brain  (ventriculus  quartus). — The  fourth  ventricle  is 
somewhat  rhomboidal  in  form.  Below,  it  tapers  to  a  point  and  becomes  continuous 
with  the  central  canal  of  the  cord ;  above,  it  narrows  in  a  similar  manner  and  is 
continued  into  the  aqueduct  of  Sylvius,  which  tunnels  the  mesencephalon.  The 
posterior  wall  is  termed  the  roof  and  is  concealed  by  the  cerebellum.  The  anterior 
wall  is  called  the  floor  and  is  formed  by  the  dorsal  surfaces  of  the  medulla  and 
pons.  On  either  side  a  long,  curved  and  narrow  prolongation  of  the  ventricular 
cavity  is  carried  outwards  from  its  widest  part  and  curves  round  the  upper  part 
of  the  corresponding  restiform  body.  This  is  termed  the  lateral  recess.  The  roof 
of  the  cavity  is  very  thin  and  intimately  connected  with  the  cerebellum.  It 
is  better,  therefore,  to  defer  its  description  until  that  part  of  the  brain  has  been 
studied. 

Floor  of  the  Fourth  Ventricle  (fossa  rhomboidea).— In  its  lower  part  the 
floor  of  the  fourth  ventricle  is  formed  by  the  dorsal  surface  of  the  open  part  of  the 


Frenulum-  -, 


Valve  of  Vieussens 
with  lingula 


Eminentia  tei-es 


Area  acustica 

crossed  by  strife - 

acusticfe 


Fovea  inferior  -  - 


Trigonuni 
liypoglossi 


Inferior  quadrigeminal  body 
Fourth  nerve 


_  Superior  cerebellar 
peduncle 


•  Fovea  superior 

Middle  cerebellar 
-peduncle 
.Superior  cere- 
bellar peduncle- 

L  Inferior  cere- 
bellar peduncle 

Stri;e  acusticse 

'-  -  -Area  acusticte 

Trigonum  vagi 
Funiculus  separans 
Area  postrema 


Obex 
Clava 


Funiculus  cuneatus 


Fifl.  .391.— Floor  of  the  Fourth  Ventricle.  Ou  the  right  side  the  riglit  half  of  the  cerebellum  has  been 
removed  by  cutting  through  its  three  peduncles  and  dividing  it  in  the  mesial  plane.  On  the  left  side 
the  left  half  of  the  cerebellum  is  drawn  over  to  the  left  so  as  to  expose  fully  tlie  floor  of  the  ventricle. 

medulla,  whilst  in  its  upper  part  it  is  formed  by  the  dorsal  surface  of  the  pons 
Varolii  (Fig.  388,  p.  482).  The  area  thus  constituted  is  lozenge-shaped,  its  widest 
part  being  opposite  the  upper  ends  of  the  restiform  bodies  or  inferior  peduncles 
of  the  cerebellum.  A  thick  layer  of  gray  matter,  continuous  with  that  which 
surrounds  the  central  canal  of  the  cord,  is  spread  out  like  a  carpet  over  the 
ventricular  floor,  and  covering  this  is  the  usual  ependymal  layer,  which  lines  all 
the  ventricles  of  the  brain.     The  area  is  circumscribed  by  definite  lateral  boundaries. 


488  THE  NEEVOUS  SYSTEM. 

Thus,  heloic  it  is  bounded  on  either  side  by  the  clava,  the  cuneate  tubercle,  and 
the  restiform  body ;  whilst  alove  the  lateral  limits  are  formed  by  the  superior 
cerebellar  peduncles. 

The  floor  of  the  fourth  ventricle  is  divided  into  two  lateral  and  symmetrical 
portions  by  a  median  groove.  Its  lower  narrow  pointed  portion  between  the  two 
clavfe  receives  the  name  of  the  calamus  scriptorius,  from  its  fancied  resemblance  to 
the  point  of  a  pen.  Crossing  each  half  of  the  floor,  at  its  widest  part,  are  several 
more  or  less  conspicuous  bundles  of  fibres  termed  the  striae  acusticae.  They  appear 
to  emerge  from  the  mesial  groove  and  they  are  carried  outwards  over  the  floor  of 
the  ventricle  in  the  region  between  its  upper  pontine  and  lower  medullary  portions. 
The  strise  acusticse  exhibit  a  large  amount  of  variation  in  different  individuals  both 
in  their  degree  of  prominence  and  also  in  the  direction  which  they  pursue.  As  a 
general  rule  they  proceed  towards  the  upper  part  of  the  restiform  body,  where  they 
are  connected  with  the  cochlear  nuclei.  Except  for  this  break  on  the  surface,  the 
medullary  and  pontine  portions  of  the  floor  of  the  fourth  ventricle  are  quite 
continuous  with  each  other. 

On  the  lower  medullary  district  of  the  ventricular  floor  a  small  triangular 
depression,  placed  immediately  below  the  strise  acusticae,  catches  the  eye.  This  is 
termed  the  fovea  inferior.  It  is  shaped  somewhat  like  an  arrow-head.  The  apex 
or  point  looks  towards  the  strise,  whilst  the  lateral  angles  of  the  base  are  prolonged 
downwards  in  the  form  of  diverging  grooves  (Eig.  391,  p.  487).  Of  these,  the  inner 
groove  runs  towards  the  opening  of  the  central  canal  at  the  calamus  scriptorius, 
whilst  the  outer  groove  runs  towards  the  lateral  boundary  of  the  floor.  In  this 
manner  the  portion  of  the  floor  which  lies  below  the  strise  acusticae  is  mapped  out 
into  three  triangular  areas.  The  mesial  subdivision  is  slightly  elevated  and  is 
termed  the  trigonum  hypoglossi,  because  subjacent  to  the  inner  part  of  this  area  is 
the  nucleus  of  origin  of  the  hypoglossal  or  twelfth  cranial  nerve.  The  intermediate 
area  between  the  two  diverging  grooves  which  proceed  from  the  base  of  the  fovea 
inferior  is  the  trigonum  vagi  (ala  cinerea),  so  called  because  the  nucleus  of  the 
vagus  or  tenth  and  the  giosso-pharyngeal  or  ninth  cranial  nerves  lies  subjacent  to 
it.  The  external  area  is  the  trigonum  acustici.  The  base  of  this  area  is  directed 
upwards  and  runs  continuously  into  an  eminence — the  acustic  area  (area  acustica) 
— over  which  the  strise  acusticse  pass.  Subjacent  to  this  district  of  the  floor  of  the 
ventricle  lies  the  large  terminal  chief  nucleus  of  the  vestibular  division  of  the 
auditory  or  eighth  cranial  nerve. 

A  close  inspection  of  tlie  medullary  part  of  the  floor  of  tlie  fourth,  ventricle  in  the  region  of 
the  calamus  scriptorius  will  show  that  the  base  of  the  trigonum  vagi  is  sejiarated  from  the  inner 
margin  of  the  clava  by  a  narrow  lanceolate  strip  of  the  ventricular  floor,  to  which  Retzius  has 
given  the  name  of  area  postrema.  Beneath  this  area  is  some  vascular  tissue  (Streeter),  and  mark- 
ing it  off  on  its  upper  and  inner  aspect  from  the  base  of  the  trigonum  vagi  there  is  a  translucent 
cord-like  ridge  caUed  the  funiculus  separans. 

Wlien  the  floor  of  the  A^entricle  is  examined  under  water  with  a  magnifying  glass,  the 
trigonum  hypoglossi  is  seen  to  consist  of  a  narrow  inner  strij)  which  corresponds  to  the  hypo- 
glos.sal  nucleus,  and  a  wider  lateral  part  which  has  been  shown  to  be  the  surface  representation 
of  another  nucleus  termed  the  nucleus  intercalatus  (Streeter). 

On  the  part  of  the  floor  of  the  ventricle  which  lies  above  the  strias  acusticse,  and 
which  corresponds  to  the  dorsal  surface  of  the  pons,  there  is  also  a  slight  depression  ' 
termed  the  fovea  superior.  Between  it  and  the  median  groove  is  a  marked  pro- 
minence called  the  eminentia  teres.  Interiorly  this  elevation  passes  downwards 
and  becomes  continuous  with  the  trigonum  hypoglossi,  whilst  above  it  is  carried 
upwards  towards  the  opening  of  the  aqueduct  of  Sylvius.  In  both  directions  it 
becomes  gradually  less  prominent,  but  still  it  forms  a  distinct  elongated  elevation, 
which  stretches  along  the  whole  length  of  the  median  groove.  As  already  stated, 
the  area  acustica  extends  upwards  into  the  pontine  part  of  the  ventricular  floor  and 
forms  an  elevated  region  in  the  outermost  part  of  its  widest  portion,  below  and  to 
the  outer  side  of  the  fovea  superior.  Proceeding  upwards  from  the  fovea  superior 
to  the  opening  of  the  Sylvian  aqueduct  there  is  a  shallow  depression  termed  the 
locus  caeruleus,  seeing  that  it  usually  presents  a  faint  slate-gray  colour.  When  the 
ependyma  is  scraped  away  from  the  surface  of  this  part  of  the  floor,  the  colour  is 
seen  to  be  due  to  the  substantia  ferruginea, — a  name  applied  to  a  linear  group  of 


INTERNAL  STRUCTtlRE  OF  THE  MEDULLA. 


489 


strongly  pigmented  cells,  which  lies  in  the  lateral  part  of  the  gray  matter  covering 
this  portion  of  the  ventricular  floor.  When  transverse  sections  are  made  through 
the  upper  part  of  the  pons,  the  substantia  ferruginea  appears  on  tlie  cut  surface 
as  a  small  black  spot  or  dot. 

INTERNAL  STRUCTURE  OF  THE  MEDULLA. 

The  internal  structure  of  the  medulla  differs  in  a  marked  degree  from  that  of 
the  spinal  cord  ;  indeed,  in  its  upper  part  it  presents  very  little  in  common  with  the 
latter.  The  various  strands  of  the  cord  either  come  to  an  end  within  the  medulla 
or  undero-o  changes  in  their  relative  position,  whilst  the  gray  matter  is  much  modi- 
fied and  new  masses  are  added.  Like  the  cord,  however,  the  medulla  consists  of 
two  nearly  symmetrical  right  and  left  halves.  When  transverse  sections  are  made 
throuo-h  it  at  different  levels  each  lateral  half  is  seen  to  be  partly  marked  off  from 
the  other  in  the  lower  closed  part  of  the  medulla  by  the  anterior  and  posterior 
median  fissures,  whilst  in  the  upper  open  part  of  the  medulla  the  subdivision  is 
rendered  evident   in  transverse  sections   by  the  presence  of  a  distinct  median 


Funiculus  gracilis 


Oraoile  uucIrus 


Funiculus  cuneatus 


(  uiuatf  iiucltus 


Spinal  root  of  trigeminal 
ner  re 


Central  gray  matli  i^ 

Central  canal 

Anterior  basis-bundle 


-^     ;     *  ^ 


Substantia  gelatinosa 
Rolandi 


ios->icl  pyramidal  tract 


Detached  head  of  anterior  horn  of 
gray  matter 


Decussation  of  pyramids 


Pyramid 


Fig.  392. — Section  through  the  Lower  End  of  the  Meddlla  Oblongata  of  a  Chimpanzee 
TO  show  the  Decussation  of  the  Pyramids. 


line,  called  the  raphe,  which  occupies  the  mesial  plane.  The  raphe  is  formed  by  the 
close  intersection  of  fibres  running  in  different  directions  and  crossing  from  one  side 
to  the  other. 

Each  half  of  the  medulla  is  composed  of :  (a)  strands  of  white  matter ;  (6)  gray 
matter ;  and  (c)  the  formatio  reticularis. 

The  white  matter,  as  in  the  cord,  is  to  a  large  extent  disposed  on  the  surface,  and 
the  gray  matter  in  the  interior ;  but  in  the  upper  open  part  of  the  medulla  the  gray 
matter  comes  to  the  surface  on  the  dorsal  aspect,  and  is  spread  out  over  that  area 
which  forms  the  medullary  part  of  the  floor  of  the  fourth  ventricle.  In  the  cord 
the  white  matter,  in  the  shape  of  massive  longitudinal  strands  of  fibres,  forms  a 
thick  coating  round  the  central  gray  matter.  In  the  medulla  the  only  massive 
longitudinal  strands  which  are  seen  on  the  surface  are  the  gracile  and  cuneate 
strands  (until  they  become  absorbed  by  the  subjacent  nuclei),  the  inferior  cerebellar 
peduncles  or  restiform  bodies  and  the  pyramidal  tracts.  Elsewhere  the  coating  of 
white  matter  is  thin,  and  in  certain  places  is  composed  chiefly  of  the  superficial 
arcuate  fibres.  New  longitudinal  strands,  however,  take  shape  within  the  medulla, 
and  two  of  the  most  important  are  placed  on  either  side  of  the  median  raphe. 

The  gray  matter  of  the  cord,  as  it  is  continued  upwards  into  the  medulla, 


490  THE  NERVOUS  SYSTEM. 

becomes  greatly  modified.  A  considerable  part  of  it  is  broken  up  in  the  formatio 
reticularis,  whilst  the  only  portions  which  remain  as  compact  masses  in  direct 
continuity  with  the  gray  matter  of  the  cord  are :  (1)  the  thick  layer  which 
surrounds  the  central  canal,  and  which,  in  the  open  part  of  the  medulla,  becomes 
spread  out  on  the  floor  of  the  fourth  ventricle ;  and  (2)  the  substantia  gelatinosa 
Eolandi.  New  masses  of  gray  matter,  which  are  not  represented  in  the  cord,  and 
which  in  some  cases  appear  in  isolated  clumps,  are  also  added.  The  chief  of  these 
are  the  gracile  and  cuueate  nuclei,  the  inferior  olivary  nuclei,  and  the  arcuate  or 
pyramidal  nuclei. 

The  formatio  reticularis  is  only  feebly  represented  in  the  cord,  but  in  the 
medulla  it  forms  a  very  considerable  part  of  its  bulk.  It  is  composed  of  gray 
matter  coarsely  broken  up  by  fibres,  which  traverse  it  in  different  directions. 

In  the  following  detailed  account  of  the  internal  structure  of  the  medulla,  it 
must  be  understood  that  the  appearances  described  are  such  as  are  seen  when 
successive  transverse  sections  through  the  bulb  are  examined. 

Decussation  of  the  Pyramids  and  the  Changes  produced  thereby. — As  we 
pass  under  the  microscope  a  series  of  successive  transverse  sections  through  the 
upper  end  of  the  cord  and  the  lower  end  of  the  medulla,  the  most  striking  change 
which  meets  the  eye  is  the  decussation  of  the  pyramids.  The  crossed  pyramidal 
tract  in  the  lateral  column  of  the  cord  is  seen  to  become  looser  in  its  formation ; 
then  coarse  strands  leave  it,  pass  right  through  the  anterior  horn  of  gray  matter, 
and,  crossing  the  mesial  plane,  take  up  their  position  in  the  other  side  of  the 
medulla,  close  to  the  antero-median  fissure.  Strands  from  the  right  crossed 
pyramidal  tract  alternate  with  corresponding  strands  from  the  left  side,  and  the 
interval  between  the  bottom  of  the  antero-median  furrow  and  the  gray  matter 
surrounding  the  central  canal  becomes  filled  up  with  a  great  mass  of  intercrossing 
bundles  of  fibres.  When  the  decussation  is  completed  the  pyramid  is  seen  to  be 
composed  of  a  solid  and  compact  bundle  of  fibres,  well  marked  off  from  the 
surrounding  structures,  which  lies  at  the  side  of  the  antero-median  fissure  of  the 
medulla. 

As  a  rule  the  inner  three-fourths  of  the  pyramid  is  composed  of  fibres  which,  lower 
down  in  the  opposite  lateral  column  of  the  cord,  form  the  crossed  pyramidal  tract,  whilst 
the  outer  fourth  of  the  pyramid  proceeds  downwards  in  the  anterior  column  of  the  cord  of 
the  same  side  as  the  direct  pyramidal  tract.  A  considerable  amount  of  variation,  however, 
occurs  in  the  proportion  of  fibres  which  is  allotted  to  the  formation  of  these  two  tracts  of 
the  cord.  Sometimes  the  crossed  pyramidal  tract  is  much  larger  than  usual,  and  then 
the  direct  pyramidal  tract  suffers  a  corresponding  diminution  in  size.  Cases  indeed  occur 
in  which  the  entire  pyramid  enters  into  the  decussation,  and  in  these  there  is  no  direct 
pyramidal  tract  in  the  cord.  Further,  it  is  not  uncommon  to  meet  with  variations  of  an 
opposite  kind  which  lead  to  an  increase  of  the  direct  pyramidal  tract  at  the  expense  of  the 
crossed  tract.  In  the  majority  of  cases  the  decussation  appears  to  be  symmetrical — the 
division  of  the  pyramid  at  the  lower  end  of  the  medulla  being  into  parts  of  corresponding- 
size  on  the  two  sides ;  in  certain  instances,  however,  the  decussation  is  asymmetrical,  and 
the  corresponding  yjyramidal  tracts  on  opposite  sides  of  the  cord  are  then  unequal  in  size. 
Seeing  that  the  direct  pyramidal  tracts  undergo  a  gradual  decussation  in  the  anterior 
commissure,  as  they  descend  in  the  cord,  the  final  result  is  the  same,  no  matter  what . 
variations  occur  in  the  decussation  at  the  lower  part  of  the  medulla. 

The  variations  indicated  above  receive  an  additional  interest  when  viewed  in  the  light 
of  comparative  anatomy.  It  would  appear  that  only  in  man  and  the  anthropoid  apes  is 
the  decussation  of  the  pyramids  in  the  lower  part  of  the  medulla  incomplete.  According 
to  Sherrington,  a  direct  pyramidal  tract  in  the  cord  of  the  anthropoid  apes  stands  in  con- 
nexion with  the  arm-centre  in  the  cerebral  cortex.  If  this  be  the  case  in  man  it  must  like- 
wise have  other  connexions  as  well,  seeing  that  it  is  carried  down  the  cord  for  a  considerable 
distance  beyond  the  level  of  the  cord-segments  which  give  motor  fibres  to  the  arm.  In 
the  lower  apes  a  direct  pyramidal  tract  does  not  seem  to  exist :  the  whole  pyramid  crosses 
over  to  the  opposite  side  of  the  cord  in  the  shape  of  the  crossed  pyramidal  tract. 

As  we  have  noted,  the  decussating  pyramidal  bundles  pass  through  the  anterior 
horn  of  gray  matter  of  the  cord,  and  cut  it  into  two  portions  (Figs.  392  and  395). 
The  basal  part  remains  in  position  on  the  anterior  and  lateral  aspect  of  the  central 
canal,  and  forms  part  of  the  thick  layer  of  gray  matter  which  surrounds  it.     The 


INTERNAL  STRUCTURE  OF  THE  MEDULLA. 


491 


Decussatiou  of 
pyramids 


Fig.  393. 


racilis 

Funiculus 

cnneatus 

Spinal  root 
of  tiftli  nerve 

Substantia 
^elatinosa 
Rolandi 

Direct 
cerebellar 

tract 

Detached  head 
of  anterior 
eornu 

_  Vnterior  basis- 
bundle 


Antero-median  furrow 


-Transverse  Section  through  Lower  End  of  the  Medulla 
OF  A  full-time  Fcetus, 

Treated  by  the  Weigert-Pal  method.     The  gray  matter  is  bleached  white,  and 
the  raedullated  tracts  of  tibres  are  black. 


detached  head  of  the  anterior  horn  is  set  free ;  and  from  the  large  multipolar  cells 
which  lie  in  its  midst  some  of  the  tibres  of  the  anterior  root  of  the  first  cervical 
nerve,  and  also  some  of  the  root  fibres  of  the  spinal  accessory  nerve,  take  origin. 

On  proceeding  up  into  the  medulla  another  effect  of  the  decussation  of  the 
pyramids  is  seen  in  the  submergence  from  the  surface  of  the  strand  of  fibres  which, 
in  the  anterior  column  of  the  cord,  lies  to  the  outer  side  of  the  direct  pyramidal 
tract,  and  which  receives  the  name  of  the  anterior  basis-bundle.  While  the  decus- 
sation is  going  on  the  anterior  basis-bundle  is  thrust  aside,  and,  sinking  from  the 
surface,  it  takes  up  its 
position  as  a  flattened 
band -like  strand  on 
the  outer  side  of  the 
gradually  increasing- 
pyramid'  (Fig.  393). 
When  the  decussatiou 
is  completed,  this 
strand  is  seen  to  lie 
close  to  the  median 
plane  on  the  dorsal 
aspect  of  the  pyramid, 
where  it  is  separated 
from  its  fellow  of  the 
opposite  side  by  the 
median  raphe  alone 
(Fig.  394).  In  the 
upper  part  of  the 
medulla  it  approaches 
still    nearer    to    the 

dorsal  surface  and  appears  to  form  the  greater  part  of  a  strand,  which  is 
termed  the  posterior  longitudinal  bundle  (Figs.  397  and  398).  The  detached  head 
of  the  anterior  horn  of  gray  matter  of  the  cord,  as  it  is  traced  upwards,  is  observed 
to  cling  closely  to  its  original  relationship  with  the  anterior  basis-bundle.  It  is 
applied  to  the  outer  side  of  this  strand,  and,  gradually  becoming  smaller,  finally 
disappears  at  the  level  of  the  lower  part  of  the  inferior  olivary  nucleus. 

Cuneate  and  Gracile  Strands,  with  their  Nuclei. — As  the  funiculus  gracilis 
and  the  funiculus  cuneatus  of  the  posterior  column  of  the  cord  are  traced  up 
into  the  medulla  they  seem  to  increase  in  bulk,  and  in  transverse  sections  they 
assume  the  form  of  massive  wedge-shaped,  strands,  quite  distinct  from  each  other. 
When  the  decussation  of  the  pyramids  is  fully  established  they  change  their  shape. 
They  increase  in  width  and  lose  considerably  in  depth,  and  consequently  the 
transverse  diameter  of  the  area  which  they  occupy  becomes  greater.  As  a  result 
of  this,  and  also  owing  to  the  removal  of  the  crossed  pyramidal  tract  from  the 
lateral  region  of  the  cord  immediately  in  front,  the  posterior  horn  of  gray  matter 
is  gradually  rotated  forwards  and  comes  to  lie  transversely  and  in  the  same  straight 
line  with  its  fellow  of  the  opposite  side  (Figs.  393  and  395).  The  substantia 
gelatinosa  Rolandi,  at  the  same  time,  becomes  increased  in  quantity  and  presents 
a  horseshoe- shaped  outline  in  transverse  section.  It  clasps  within  its  concavity  the 
somewhat  reduced  head  of  the  posterior  horn,  and  forms  with  it  a  conspicuous 
circular  mass  of  gray  matter  which  lies  close  to  the  surface,  and  produces  upon  it 
the  bulging  termed  the  funiculus  and  tubercle  of  Rolando.  The  basal  portion  of 
the  posterior  horn  of  gray  matter  remains  upon  the  dorsal  and  lateral  aspect  of  the 
central  canal,  and  forms  a  portion  of  the  central  gray  mass  of  the  closed  part  of 
the  medulla ;  but  very  soon  the  neck  of  the  horn,  which  at  this  level  is  greatly 
reduced  owing  to  the  absence  of  entering  posterior  nerve-roots,  is  invaded  by 
bundles  of  fibres  which  traverse  it  in  different  directions  and  convert  it  into  a 
formatio  reticularis.  By  this  means  the  rounded  head  of  the  posterior  horn  becomes 
cut  off  from  the  central  gray  matter,  and  from  this  point  upwards  it  remains  as 
an  isolated  gray  column  intimately  associated  with  the  spinal  root  of  the  trigeminal 
nerve. 


492 


THE  NEEVOUS  SYSTEM. 


The  gracile  and  cuneate  nuclei  take  shape  before  the  decussation  of  the  pyramids 
is  fully  completed  (Fig.  395).  The  gracile  nucleus  appears  in  the  form  of  a  small 
irregular  mass  of  gray  matter  in  the  interior  of  the  funiculus  gracihs,  which 


Central  canal 


Internal  arcnate 
fibres 


Anterior  basis- 
bnndle 

Decussation  of 
fillet 


Inferior 
olivary  nucleus 


Funiculus  gracilis 

Gracile  nucleus 

Funiculus  cnneatus 
'"ff^^^^SSfc-,/  .  Cuneate  nucleus 

Accessory  cuneate 
nucleus 

Spinal  root  of  fifth 
nerve 

Substantia 
■jf^*(^\-  gelatinosa 
•^j      Rolandi 

Formatio 
reticularis 


Anterior  basis- 
bundle 

Mesial  olivary 
nucleus 


Pyramid 


Arcuate  nucleus  covered 
superficially  by  anterior 
superficial  arcuate  fibres 


Fig.  394.— Section  through  the  Closed  Part  of  Human  Medulla  immediately  above  the 
Decussation  of  the  Pyramids  (Weigert-Pal  Specimen). 

gradually  infiltrates  the  entire  strand.  At  first  it  is  not  directly  connected  with 
the  gray  matter  which  surrounds  the  central  canal ;  but  as  it  is  traced  upwards 
it  increases  in  bulk,  absorbs  more  of  the  strand  in  which  it  lies,  and  such  a  con- 
nexion becomes  established  (Figs.  393  and  394). 

The  cuneate  nucleus,  from  the  first,  is  a  direct  offshoot  from  that  part  of  the  base 
Gracile  nucleus  of  thc   postcrior   hom    of    gray 

Cuneate  nucifus  ^^ matter  which  is  preserved  as  a 

portion  of  the  central  gray  mass. 
Cuneate  nucleus  In  transvcrsc  scctiou  it  is  seen  to 

Spinal  root  of  fifth  ^^^^^^     ^hc     fuuiculuS  .  CUncatUS 

RoS'i*''' ^^^''*'"°'''  "P°^  ^^^  ^®®P  aspect,  and  it 
Direct  cerebellar  tract  gradually  grows  backwards  into 
its  substance.  It  presents  a  very 
different  appearance  from  the. 
gracile  nucleus,  because  through- 
out its  whole  length  the  gray 
nucleus  and  the  fibres  of  the 
strand  are  separated  from  each 
other  by  a  sharp  line  of  demarca- 
tion. A  second  and  much  smaller 
mass  of  gray  matter  appears  in 
the  funiculus  cuneatus,  super- 
ficial to  the  main  nucleus,  soon  after  the  region  of  the  decussation  of  the  pyramids 
is  left.     This  is  termed  the  accessory  or  the  external  cuneate  nucleus  (Fig.  394). 

Gradually  the  fibres  of  the  gracile  and  cuneate  strands  become  absorbed  in  these 
nuclei.  As  the  gray  masses  gain  in  size  a  corresponding  diminution  in  the  number 
of  fibres  composing  the  corresponding  tracts  is  observed,  until,  at  the  level  of  the 
clava  and  cuneate  tubercles,  it  is  seen  that  these  eminences  are  composed  almost 


Crossed  pyramidal 
tract 


Detached  anterior 
horn  of  gray  matter 

Decussation  of 
jiyraniids 


Anterior  basis-bundle 
Fig.  395. — Section  through  the  lower  part  of  the 
Medulla  of  the  Orang. 


INTERNAL  STRUCTURE  OF  THE  MEDULLA. 


493 


entirely  of  the  gray  nuclei,  covered  by  a  thin  skin  of  the  few  remaining  fibres  of 
the  two  strands  involved.  It  would  appear  that  no  fibres  belonging  to  the  funiculus 
gracilis  and  funiculus  cuneatus  get  beyond  these  nuclei.     They  all  end  in  fine 

'  '      In  the  case  of  the  funiculus 


terminal  ramifications  around  the  cells  of  the  nuclei 
cuneatus  the  bundles 

1  uiiiculu'5  ^lacili^ 


of    fibres, 
pass    from 


as  they 
the  sur- 
face into  the  sub- 
jacent gray  nucleus, 
are  very  distinctly 
seen  in  transverse 
sections  through  the 
medulla. 

When  the  med- 
ulla oblongata  opens 
up  into  the  fourth 
ventricle  the  gracile 
and  cuneate  nuclei 
are  pushed  outwards 
by  the  expanding 
ventricular  floor,  and 
the  gracile  nucleus 
soon  conies  to  an 
end :  but  the  cuneate 


Funiculu'5 
( unpatii'5 


(.ia(  ilr  iiucli  us 


Cuneate 
nucleus 


Lowei  eiiil 
of  olnaij 
ennnence 


Mesial 

accessory 

oli\iiy  nucleus 
Fascicles  of 
hypoglossal 
nerve 


Fxu.  396. — Transverse  Section  through  the  Closed  Part  of  a  Fcetal 
Medulla,   immediately  above  the  Decussation  of  the  Pyramids. 

Treated  by  Weigert-Pal  method. 


nucleus  extends  upwards  for  a  short  distance  farther,  and  only  terminates  when 
the  restiform  body  begins  to  take  definite  shape  on  its  outer  aspect. 

Decussation  of  the  Fillet  (decussatio  lemniscorum). — Immediately  above  the 
level  of  the  decussation  of  the  pyramids  another  decussation  of  fibres  in  the  median 
plane,  and  upon  the  dorsal  aspect  of  the  pyramids,  takes  place  in  the  substance  of 

the  medulla.     This 


Gricile  nucleus 


is  termed  the  decus- 
sation of  the  fillet, 
or  the  sensory  de- 
cussation, in  contra- 
distinction to  the 
term  "  motor  decus- 
sation," which  is 
sometimes  applied 
to  the  decussation 
of  the  pyramids. 
The  fibres  which 
take  part  in  this 
decussation  are 
called  deep  arcuate 
fibres  (fibraj  arcuatse 
interme),  and  they 
are  derived  from 
the  cells  of  the 
gracile  and  cuneate 
nuclei.  From  the 
deep  aspects  of  these 
nuclei  these  fibres 
stream  forwards  and 
inwards  towards  the 
median  raphe,  form- 
ing a  series  of  con- 

•centric  curves  in  the  substance  of  the  medulla.  They  cross  the  mesial  plane 
and  decussate  with  the  corresponding  fibres  of  the  opposite  side,  upon  the  dorsal 
•aspect  of  the  pyramids.     Having  thus  gained  the  opposite  side  of  the  medulla  they 


Cuneate  stiaud 


Cuneate  nucleus 

Fasciculus  sdlitarius 

Spinal  root  ot, 

trigeminal  nerve 

Substantia 

gelatinosa  Rolandi 

Deep  arcuate  fibres 
Hyposlossal  nerve 


Anterior  superficial (i_ 

arcuate  fibres 


Inferior  olivarj 
nucleus 


Mesial  accessoi  \ 
olivary  nucleus 

Pyiannd 


anterior 
arcuate  fibres 


Fl(i 


397. — Transverse  Section  through  the  Human  Medulla  in  the 
Lower  Olivary  Region. 


494  THE  NEEVOUS  SYSTEM. 

immediately  turn  upwards  and  form  a  conspicuous  strand  of  longitudinal  fibres, 
which  ascends  close  to  the  mesial  plane  and  is  separated  from  its  fellow  of  the 
opposite  side  bj  the  median  ra]3he  alone.  This  strand  is  termed  the  fillet  or 
lemniscus. 

As  we  proceed  up  the  medulla  the  deep  arcuate  fibres  which  first  come  into  sight 
appear  as  coarse  bundles  which  curve  forwards  in  a  narrow  group  around  the  central  gray 
matter  (Figs.  394  and  396).  Soon  other  fiuer  bundles  appear,  which  describe  wider  curves 
on  the  outer  side  of  the  coarser  group  until  a  very  large  part  of  each  lateral  half  of  the 
medulla  is  seen  to  be  traversed  by  these  arcuate  fasciculi  (Fig.  397).  As  they  approach 
the  mesial  plane  they  come  in  contact  with  the  remains  of  the  anterior  basis-bundle, 
which  at  this  level,  as  already  mentioned,  lies  upon  the  dorsal  aspect  of  the  pyramid, 
flattened  up  against  the  raphe.  The  deep  arcuate  fibres  pierce  the  anterior  basis-bundle 
obliquely,  and  in  the  interval  between  it  and  the  corresponding  strand  of  the  opposite  side 
they  decussate  in  the  middle  line  with  the  deep  arcuate  fibres  of  the  opposite  side.  They 
then  change  their  direction  and  turn  upwards,  and  the  fillet,  as  already  stated,  takes 
form  and  gradually  increases  in  volume  as  it  ascends.  This  great  and  important  tract  is 
thus  laid  down  between  the  pyramid  and  the  anterior  basis-bundle ;  and  the  consequence 
of  this  is  that  the  latter  tract  is  pushed  still  fai'ther  backwards,  and,  when  the  fillet  is 
fully  established,  it  comes  to  lie  immediately  beneath  the  gray  matter  of  the  floor  of  the 
fomth  ventricle  (Fig.  398). 

It  is  important  that  we  should  realise  at  this  stage  the  full  significance  of  the  decussation 
of  the  fillet  and  have  a  clear  conception  of  the  connexions  of  the  fibres  which  take  joart  in  it. 
The  columns  of  Burdach  and  GoU,  Avhich  end  in  the  cuneate  and  gracile  nuclei,  are  derived  from 
the  posterior  roots  of  the  spinal  nerves.  The  fillet  fibres  therefore  carry  on  the  continuity  of  the 
posterior  columns  of  the  cord,  the  gracile  and  cuneate  nuclei,  which  are  thrown  across  their  path 
in  the  lower  part  of  the  medulla,  merely  constituting  an  internodal  interruption.  At  this  point 
the  fillet  strand  is  transferred  to  the  opposite  side  of  the  medulla.  But  it  will  be  remembered 
that  a  large  proportion  of  the  fibres  of  the  entering  posterior  nerve-roots  of  the  spinal  nerves  end 
in  connexion  with  the  cells  of  the  posterior  horn  of  gray  matter  of  the  cord.  It  must  not  be 
supposed  that  the  path  represented  by  these  latter  fibres  comes  to  a  termination  thereby ;  from 
these  posterior  horn  cells  other  fibres  arise  which  cross  to  the  opposite  side  of  the  cord  in  the 
anterior  white  commissure  and  proceed  up  the  cord  to  the  lateral  part  of  the  medulla.  These 
fibres  con>stitute  the  spino-thalamic  tract  already  referred  to.  The  practical  bearing  of  this  is 
that  owing  to  the  crossing  of  the  fillet  and  lower  down  of  the  spino-thalamic  tract  unilateral 
lesions  of  the  medulla  are  apt  to  produce  complete  hemi-ansesthesia  ;  whilst  unilateral  lesions  of 
the  cord  produce  only  partial  hemi-anfesthesia. 

When  the  fillet  is  fully  formed  three  longitudinal  strands  are  observed  travers- 
ing the  medulla,  close  to  the  mesial  plane.  From  before  backwards  these  are :  (1) 
the  pyramid,  (2)  the  fillet,  and  (3)  the  posterior  longitudinal  bundle. 

The  pyramid  forms  a  massive  tract  in  front  of  and  quite  distinct  from  the 
fillet.  The  fillet  and  the  posterior  longitudinal  bundle  are,  in  the  first  instance, 
not  marked  off  from  each  other.  They  appear  as  a  broad  flattened  band  applied 
to  the  raphe.  One  edge  of  this  band  is  directed  backwards  and  reaches  the  gray 
matter  on  the  floor  of  the  fourth  ventricle,  while  the  other  edge  looks  forwards, 
and  is  in  contact  with  the  pyramid.  In  the  upper  part  of  the  medulla  the  fillet 
and  the  posterior  longitudinal  fasciculus  begin  to  draw  asunder  from  each  other. 
The  intermediate  longitudinal  fibres  become  reduced  in  number  and  the  two 
strands  grow  denser — the  one  on  the  dorsal  aspect  of  pyramid,  and  the  other  ". 
immediately  beneath  the  gray  matter  of  the  floor  of  the  fourth  ventricle  (Fig.  398). 

The  posterior  longitudinal  bundle  (fasciculus  longitudinalis  medialis)  is  thus 
largely  formed  out  of  fibres,  which  in  the  cord  constitute  the  anterior  basis-bundle. 
These  fibres  are  thrust  back  by  the  two  decussations :  the  first  decussation  pushing 
them  behind  the  pyramids,  and  the  second  decussation  displacing  them  still  farther 
backwards  to  a  position  behind  the  fillet. 

Olivary  Nuclei. — The  most  conspicuous  of  the  isolated  clumps  of  gray  matter 
in  the  medulla  are  the  inferior  olivary  nucleus  and  the  two  accessory  olivary 
nuclei.  The  inferior  olivary  nucleus  (nucleus  olivaris  inferior)  lies  subjacent  to  the 
olivary  eminence,  and  constitutes  a  very  striking  object  in  transverse  sections 
through  this  region.  It  presents  the  appearance  of  a  thick  wavy  or  imdulating  line 
of  gray  matter,  folded  on  itself,  so  as  to  enclose  a  space  filled  with  white  matter. 
It  is  in  reality  a  crumjjled  lamina  arranged  in  a  purse-like  manner,  with  an  open 


INTERNAL  STRUCTURE  OF  THE  MEDULLA. 


495 


mouth  or  slit,  which  is  called  the  hilum  (hilum  nuclei  olivaris).  directed  towards  the 
mesial  plane.     The  hilum  does  not  reach  either  extremity,  so  that  in  transverse 


Vago- 
,     ,     glossopharyngeal 
R.st. form  body  j.^^t.  Nucleus  of  the 

fasciculus  solitdiiu-i 
Iji„'ula 


Vagus  nucleus 

Tisficulus  solitarius 

I)(  sCLuding  root  of  vestihulai- 
nerve  (VIll.) 

i^ago-glossopharyngeal  roots 


Posterior  longitudinal 

fasficulus 

Sulistantia  gelatinosa 

7f  Rulandi 
Ifjll^f  Spinal  root  of  fifth  nerve 


Nucleus  ainbiguus 
— j=_Csi'ebello-olivary  fibres 
^Dorsal  accessory  olivary  nucleus 

\ntt  rior  superficial  arcuate  fibres 

1  ill(t 

M  si  il  accessory  olivary  nucleus 

Inferior  olivary  nucleus 


Pyramid 


Arcuate  nucleus 

Anterior  superficial  arcuate  fibres 

Fig.  398. — Transverse  Section  through  the  Middle  of  the  Olivary  Region  of  the  Human  Medulla 

OR  Bulb. 

The  floor  of  the  fourth  ventricle  is  seen,  and  it  will  be  noticed  that  the  restiforni  body  ou  each  side  has 

now  taken  definite  shape. 

sections  through  each  end  of  the  nucleus  the  gray  lamina  is  seen  in  the  form  of  a 
completely  closed  capsule.  Into  and  out  of  the  open  mouth  of  the  olivary  capsule 
streams  a  dense  crowd  of  fibres.     These  constitute  what  is  called    the   olivary 

peduncle. 

The  accessory  olivary 
nuclei  are  two  band-like 
laminae  of  gray  matter,  which 
are  respectively  placed  on  the 
dorsal  and  mesial  aspects  of 
the  main  nucleus.  In  trans- 
verse section  each  of  these 
nuclei  presents  a  rod  -  like 
appearance  (Eig.  398). 

The  mesial  accessory  oli- 
vary nucleus  (nucleus  olivaris 
accessorius  mesialis)  extends 
lower  down  in  the  medulla  than 
the  main  nucleus,  and  it  is  much 

Fig.  399.— The  Inferior  Olivary  Nucleus,  as  reconstructed  and   larger  in  its  lower  than  its  upper 

part.  It  begins  immediately 
above  the  decussation  of  the 
pyramids,  where  it  is  seen  lying 

on  the  outer  side  of  the  pyramidal  tract  and  the  anterior  basis-bundle  (Figs.  394  and  396). 

Higher  up  it  lies  across  the  movith  of  the  main  nucleus  and  on  the  outer  side  of  the  fillet. 

The  dorsal   accessory  olivary  nucleus   (nucleus  olivaris  accessorius   dorsalis)  is  placed 

close  to  the  dorsal  aspect  of  the  main  nucleus.     The  two  accessory  nuclei  fuse  together 

before  they  finally  disappear. 

The  gray  matter  forming  the  three  inferior  olivary  nuclei  consists  of  a  close  feltwork 

of   neuroglia   in   which   are   interspersed   numerous   small   round   cells,  each  of  which  is 

provided  with  one  axon  and  numerous  dendrites.     It  is  traversed  by  fibres,  some  of  which 


-The  Inferior  Olivary  Nucleus,  as  reconstructed  and 
figured  by  Miss  Florence  R.  Sabin. 

View  of  the  dorso-lateral  and  lateral  surfaces. 


496 


THE  NEEVOUS  SYSTEM. 


.GRACILENUCL. 

CUNEATENUCL. 


Fig.  400. — Diagram, 

Which  shows  in  part  the  fibres  which  enter  into 
the  constitution  of  the  restiform  body. 


pass  straight  through  the  gray  lamina,  whilst  others  end  in  connexion  with  the  cells.  It 
is  onh-  in  man  and  the  higher  apes  that  the  infei'ior  olivary  nuclei  are  found  strongly 
developed.  In  other  mammals  they  are  much  smaller.  The  size  of  the  olive  appears  to 
be  correlated  with  that  of  the  lateral  hemisphere  of  the  cerebellum  and  not  in  any  way  to 
be  dependent  on  the  development  of  the  cerebral  hemisphere.  Thus  in  cetacea  with  a 
very  extensive  cerebral  cortex  the  inferior  olivary  nuclei  are  small  (Edinger). 

As  the  fibres  of  the  fillet  decussate  and  assume  a  longitudinal  direction  they 
RESTIFORM  come  to   lie    betv^een    the   olivary  nuclei   of 

opposite  sides,  and  hence  the  term  inter- 
olivary  stratum  (stratum  interolivare  lem- 
nisci)  is  frequently  applied  to  them. 

Restiform  Body  (corpus  restiforme). — 
The  gracile  and  cuneate  nuclei  gradually  give 
place  to  the  restiform  body  in  the  upper  part 
of  the  posterior  district  of  the  medulla.  Fibres 
from  various  quarters  converge  to  form  this 
great  strand.  It  first  takes  shape  as  a  thin 
superficial  layer  of  longitudinal  fibres,  which 
are  gathered  together  on  the  outside  of  the 
cuneate  nucleus ;  but  after  that  nucleus  has 
come  to  an  end,  and  as  the  upper  part  of  the 
medulla  is  reached,  the  restiform  body  is 
seen  to  have  grown  into  a  massive  strand, 
which  presents  a  kidney-shaped  or  oval  out- 
line on  transverse  section  (Fig.  398),  and 
which  ultimately  enters  the  white  central 
core  of  the  cerebellum  as  its  inferior  peduncle.  The  fibres  which  build  up  the 
restiform  body  are  the  following :  (1)  the  direct  cerebellar  tract ;  (2)  the  posterior 
superficial  arcuate  fibres ;  (3)  the  anterior  superficial  arcuate  fibres ;  and  (4) 
cerebello- olivary  fibres. 

The  direct  cerebellar  tract  extends  upwards  from  the  lateral  column  of  the  cord. 
In  the  lateral  district  of  the 
medulla  it  occupies  a  similar 
position  ;  but  before  the  olivary 
eminence  is  reached  it  inclines 
backwards,  crosses  the  postero- 
lateral furrow  and  passes  ob- 
liquely upwards  into  the  resti- 
form body.  As  its  fibres  diverge, 
backwards  they  pass  over  the 
tubercule  of  Eolando  and  cover 
up  the  spinal  root  of  the  tri- 
geminal nerve  and  the  substantia 
Rolandi,  thus  shutting  them  ovit 
from  the  surface.  The  fibres 
of  the  direct  cerebellar  tract 
in  the  first  instance  enter  into 
the  outer  or  superficial  part  of 
the  restiform  body. 

Bruce  has  shown  that  the  fibres  of  the  direct  cerebellar  tract  ultimately  lie  in  the  centre  of  the 
restiform  body,  forming  as  it  were  its  central  core,  and  that  in  the  cerebellum  they  can  be  traced 
to  the  superior  vermis. 

The  posterior  superficial  arcuate  fibres  take  origin  from  the  gracile  and  cuneate 
nuclei,  and  enter  the  superficial  part  of  the  restiform  body  of  the  same  side. 

The  anterior  superficial  arcuate  fibres  proceed  from  the  lower  portions  of  the 
gracile  and  cuneate  nuclei  of  the  opposite  side.  After  decussating  in  the  middle 
line,  it  can  easily  be  determined  that  all  the  deep  arcuate  fibres  which  arise  from 
these  nuclei  do  not  enter  the  fillet.  A  large  proportion  of  them  gain  the  surface  by 
sweeping  round  the  inner  aspect  of  the  pyramid  in  the  antero-mesial  fissure.     Many 


Funiculus  gracilis 

Gracile  nucleus 


Funiculus  cuneatus 


Substantia  gelatinosa 
Rolandi 

Spinal  root  of 
trigeminal  nervp 

Direct  cerebellar 
tract 

Crossed  pyramidal 
tract 


Central  canal 
Decussation  of  pyramids 
Detached  anterior  hoin  of  gray  matter 

Fig.  401. — Section   through   the   Junction   between 
THE  Cord  and  Medulla  of  the  Orang. 

The  direct  cerebellar  tract  is  well  seen,  especially  on  the  right  side. 


INTEKNAL  STEUCTTJEE  OF  THE  MEDULLA. 


497 


of  them  likewise  gain  the  surface  by  piercing  the  pyramid  or  by  passing  out 
between  it  and  the  olive.  These  fibres  constitute  the  anterior  superficial  arcuate 
group,  and  on  the  surface  of  the  medulla  they  sweep  backwards  around  it,  forming 
a  thin  layer  over  the  olivary  eminence  and  ultimately  reaching  the  restiform  body. 
The  anterior  superficial  arcuate  fibres,  as  well  as  the  direct  cerebellar  tract-fibres, 
cover  over  the  trigeminal  spinal  root,  which  thus  comes  to  take  up  a  deeper  posi- 
tion in  the  substance  of  the  medulla  (Figs.  397  and  398). 

Amongst  the  fibres  which  reach  the  surface  of  the  medulla  in  this  way  Krilliker  includes 
fibres  from  the  striae  acustic£e.  If  this  be  the  case,  these  fibres  connect  the  cochlear  nucleus 
with  the  cerebellum,  the  path  l^eing  stripe  acusticae,  superficial  arcuate  fibres,  and  restiform 
body  {vide  p.  522). 

The  fibres  of  the  direct  cerebellar  tract,  which  come  from  the  cells  of  the  posterior  vesicular 
column  of  the  cord,  and  the  superficial  posterior  arcuate  fibres,  wliicli  are  derived  from  the  cells 
of  the  gracile  and  cuneate  nuclei,  do  not  cross  the  mesial  plane,  but  enter  the  restiform  body  of 
the  same  side.  The  anterior  superficial  arcuate  fibres  arise  from  the  cells  of  the  cuneate  and 
gracile  nuclei,  and  cross  the  mesial  plane  so  as  to  gain  the  restiform  body  of  the  opjjosite  side. 

The  cerebello-olivary  fibres  are  only  seen  in  the  upper  part  of  the  medulla.     They 
form  the  deep  part  of  the  restiform  body  and  constitute  its  chief  bulk.     Streaming 

DESCENDING 
ROOTVlll.    \ 


SPINAL       \        JS?^?;"" 
ROOT  v. 


XII. 

\       \>\  /^[hypoglossal] 

'  ARCUATE       ^--i^_— ^ 
NUCLEUS 

Fig.  402. — Diagram  of  the  Cerebello-Olivary  Fibres. 
(This  diagram  has  been  constructed  from  the  specimen  figiu-ed  on  p.  495.) 
N.X.,  Vago-glossopharyngeal  nucleus.  N.XII.,  Hypoglossal  nucleus. 

out  from  the  hilum  of  the  inferior  olivary  nucleus,  they  cross  the  mesial  plane,  and 
in  the  opposite  side  of  the  medulla  they  either  pass  through  the  inferior  olivary 
nucleus  of  that  side  or  sweep  around  it.  Ultimately,  on  the  dorsal  aspect  of  the 
ohvary  nucleus,  they  are  gathered  together  in  the  form  of  a  conspicuous  group  of 
arcuate  fibres,  which  curve  backwards  to  take  up  a  position  in  the  deep  part  of  the 
restiform  body.  In  passing  back,  they  traverse  the  spinal  root  of  the  trigeminal 
nerve  and  break  it  up  into  several  separate  bundles.  The  cerebello-olivary  fibres 
thus  connect  the  inferior  olivary  nucleus  of  one  side  with  the  opposite  side  of  the 
cerebellum. 

Although  we  have  traced  the  cerebello-olivary  tract  in  an  upward  direction  from  the  olive  to 
the  cerebellum,  and  have  thus  inferred  that  it  is  composed  of  fibres  which  proceed  from  the  cells 
of  the  inferior  olivary  nucleus  of  the  oj^posite  side,  it  is  right  to  state  that  this  view  is  not  uni- 
versally accepted.  There  are  some  who  regard  these  fibres  as  constituting  an  efferent  tract  from 
the  cerebellum,  or,  in  other  words,  as  arising  in  the  cerebellar  cortex  (probably  as  the  axons  of 
the  cells  of  Purkinje),  and  descending  in  the  inferior  cerebellar  peduncle  to  establish  connexions 
with  the  cells  of  the  inferior  olivary  nucleus  of  the  opposite  side.     If  this  view  be  correct,  the 

36 


498  THE  NERVOUS  SYSTEM. 

destination  of  tlie  axons  of  the  cells  of  tlie  inferior  olivary  nucleus  becomes  a  difficulty,  but 
Kolliker  considers  that  they  enter  the  lateral  column  of  the  cord. 

Arcuate  Nucleus  (nucleus  arcuatus). — Immediately  above  the  decussation  of 
the  pyramids,  a  small  fattened  mass  of  gray  matter,  covered  by  superficial  arcuate 
fibres,  makes  its  appearance  on  the  ventral  or  superficial  aspect  of  the  pyramid 
(Fig.  393).  At  a  higher  level,  when  the  open  part  of  the  medulla  is  reached,  this 
gray  mass  shifts  its  position  and  comes  to  lie  upon  the  mesial  aspect  of  the 
pyramid,  and  thus  constitutes  the  immediate  boundary  of  the  antero- median 
fissure  (Fig.  398).  From  its  intimate  connexion  with  the  anterior  superficial 
arcuate  fibres,  as  they  sweep  out  from  the  antero-median  fissure,  it  receives  the 
name  of  the  arcuate  nucleus. 

The  nerve-cells  which  lie  in  its  midst  are  smaller  than  those  of  the  inferior  olivary  nucleus, 
and  are  fusiform  in  shape.  It  would  appear  that  large  numbers  of  the  anterior  superficial  arcuate 
fibres  end  in  this  nucleus,  whilst  others  take  origin  within  it.  Many  of  the  anterior  arcuate 
fibres,  hoM^evei',  sweej:!  continuously  over  its  surface  and  bind  it  down  to  the  pyramid.  At  the 
upper  end  of  the  medulla  the  arcuate  nucleus  increases  in  size,  and  ultimately  it  becomes  con- 
tinuous with  the  gray  matter  of  the  ventral  part  of  the  pons. 

Formatio  Reticularis. — Behind  the  olive  and  the  pyramid  is  the  formatio 
reticularis.  In  the  medulla  it  occupies  a  position  which,  to  a  large  extent,  corre- 
sponds with  that  of  the  lateral  column  in  the  spinal  cord.  In  transverse  section  it 
appears  as  an  extensive  area,  which  is  divided  into  a  lateral  and  a  mesial  field  by 
the  root  fascicles  of  the  hypoglossal  nerve  as  they  traverse  the  substance  of  the 
medulla  to  reach  the  surface.  In  the  lateral  portion  which  lies  behind  the  olive 
there  is  a  considerable  quantity  of  gray  matter,  continuous  with  that  in  the  cord, 
present  in  the  reticular  formation ;  it  is,  therefore,  called  the  formatio  reticularis 
grisea.  In  the  mesial  part  which  lies  behind  the  pyramid  the  gray  matter  is 
extremely  scanty,  and  the  reticular  matter  here  is  termed  the  formatio  reticularis 
alba. 

In  the  formatio  grisea  many  of  the  cells  which  are  scattered  thickly  amongst  the  intersecting 
bundles  of  fibres  are  to  be  regarded  as  association  cells.  They  possess  short  axons,  which  serve  to  bind 
different  levels  of  the  medulla  to  each  other,  and  therefore  constitute  association  filsres.  Probably 
the  combined  and  harmonious  activity  exhibited  by  the  nuclei  of  the  vagus,  facial  and  phrenic 
nerves  in  the  process  of  respiration,  is  attained  through  the  nuclear  connexions  established  by 
these  fibres  (Edinger).  Certain  compact  masses  of  gray  matter  are  also  seen  in  the  formatio 
grisea.  Of  these  may  be  mentioned  (a)  the  dorsal  accessory  olivary  nucleus,  which  has  been 
already  described,  and  (6)  the  nucleus  lateralis.  The  nucleus  lateralis  is  seen  in  the  region 
between  the  olive  and  the  substantia  gelatinosa  Rolandi.  In  the  upper  part  of  the  medulla  it 
gradually  becomes  diffuse  and  disappears. 

Except  in  the  immediate  vicinity  of  the  raphe,  the  formatio  alba  may  be  said  to  be  devoid  of 
cells.  The  mesial  accessory  olive,  however,  forms  an  isolated  compact  mass  of  gray  matter  within 
its  limits. 

The  nerve  fibres  which  traverse  the  formatio  reticularis  run  both  in  a  transverse 
and  a  longitudinal  direction.  The  transverse  fibres  are  the  deep  arcuate  fibres. 
The  longitudinal  fibres  are  derived  from  different  sources  in  the  two  fields.  In  the 
formatio  grisea  they  represent  to  a  large  extent  the  fibres  of  the  lateral  column  of 
the  cord,  after  the  removal  of  the  direct  cerebellar  and  the  crossed  pyramidal  tracts. 
They  consist,  therefore,  of  the  fibres  of  the  tract  of  Gowers  and  of  fibres  correspond- 
ing to  the  lateral  basis-bundle  of  the  cord.  In  the  formatio  alba  the  longitudinal 
fibres  are  the  tract  of  the  fillet  and  the  posterior  longitudinal  bundle,  both  of  which 
have  already  been  suriiciently  described. 

Central  Canal  and  the  Gray  Matter  which  surrounds  it. — The  central  canal, 
as  it  proceeds  u[)vvards  through  the  closed  part  of  the  medulla,  is  gradually  forced 
to  assume  a  more  dorsal  position,  owing  to  the  accumulation  of  fibres  on  its  ventral 
aspect.  First  the  decussation  of  the  pyramids,  and  then  the  decussation  of  the 
fillet,  both  of  which  take  place  in  front  of  the  canal,  tend  to  push  it  backwards ; 
and  the  formation  of  the  longitudinal  strands  in  which  these  intercrossings  result 
(viz.  the  pyramid  and  the  fillet),  together  with  the  continuation  upwards  of  the 
anterior  basis -bundle,  lead  to  a  great  increase  in  the  amount  of  tissue  which 
sejjarates  it  from  the  anterior  surface  of  the  medulla.  In  the  closed  part  of  the 
medulla  it  is  surrounded  by  a  thick  layer  of  gray  matter,  which  is  continuous  with 


INTEENAL  STEUCTUEE  OF  THE  MEDULLA.  499 

the  basal  portions  of  the  anterior  and  posterior  horns  of  gray  matter  in  the  cord. 
This  central  gray  matter  is  sharply  defined  on  each  side  by  the  deep  arcuate  fibres 
which  curve  forwards  and  inwards  around  it.  Finally,  the  central  canal  opens  on 
the  dorsal  aspect  of  the  medulla  into  the  cavity  of  the  fourth  ventricle.  The 
central  mass  of  gray  matter  which  surrounds  the  canal  in  the  closed  part  of  the 
medulla  is  now  spread  out  in  a  thick  layer  on  the  floor  of  the  fourth  ventricle,  and 
in  such  a  manner  that  the  portion  which  corresponds  to  the  basal  part  of  the 
anterior  horn  of  the  cord  is  situated  close  to  the  mesial  plane,  whilst  the  part  which 
represents  the  Ijase  of  the  posterior  horn  occupies  a  more  lateral  position.  This  is 
important,  because  the  nucleus  of  origin  of  the  motor  hypoglossal  nerve  is  placed 
in  the  mesial  part  of  the  floor,  whilst  the  nuclei  of  termination  of  the  afferent  fibres 
of  the  vagus,  glosso-pharyngeal,  and  auditory  nerves  lie  in  the  lateral  part  of  the 
floor.     The  gray  matter  of  the  ventricular  floor  is  covered  by  epeudyma. 

Three  Areas  of  Flechsig.  —  In  transverse  sections,  througli  the  upper  oimi  jiart  of  the 
medulla,  the  root  fibres  of  the  hypoglossal  and  vagus  nerves  are  seen  traversing  the  sulistance  of 
the  medulla.  The  nucleus  of  origin  of  the  hypoglossal  is  placed  in  the  gray  matter  of  the  floor 
of  the  fourth  ventricle  close  to  the  mesial  plane ;  the  nucleus  of  the  vagus  is  situated  in  the 
gray  matter  of  the  ventricular  floor  immediately  to  the  outer  side  of  the  hyi^oglossal  nucleus. 
From  these  nuclei  the  root-bundles  of  the  two  nerves  diverge  from  each  other  as  they  are  traced 
to  the  surface  and  subdivide  the  substance  of  the  medulla,  as  seen  in  transverse  section,  into  the 
three  areas  of  Flechsig,  viz.  an  anterior,  a  lateral,  and  a  posterior. 

The  anterior  area,  which  is  bounded  internally  by  the  median  raphe  and  externally  liy  the 
hypoglossal  roots,  presents  within  its  limits :  (a)  the  formatio  alba ;  (b)  the  j^yramid ;  (c)  the 
fillet ;  (d)  the  posterior  longitudinal  fasciculus ;  (e)  the  mesial  accessory  olivary  nucleus ;  (/)  the 
arcuate  nucleus. 

Tlie  lateral  area  lies  between  the  root  fibres  of  the  hypoglossal  and  those  of  the  vagus.  It 
contains  :  (a)  the  inferior  olivary  nucleus ;  (b)  the  doreal  accessory  olivary  nucleus ;  (c)  the  niicleus 
lateralis ;  {d)  the  nucleus  ambiguus,  or  the  motor  nucleus  of  the  vagus  and  glosso-pliaryngeal 
nerves  ;  (c)  the  formatio  reticularis  grisea. 

The  posterior  area  is  situated  behind  the  vagus  roots,  and  within  its  limits  are  seen  :  (1)  the 
restiform  body  ;  (2)  the  upjjer  part  of  the  cuneate  nucleus  ;  (3)  to  the  inner  side  of  this  a  crowd 
of  transversely-cut  bundles  of  fibres,  loosely  arranged  and  forming  the  descending  root  of  the 
vestibular  part  of  the  auditory  nerve ;  (4)  close  to  these,  but  placed  more  deejily,  a  round,  com- 
pact, and  very  conspicuous  bundle  of  transversely- cut  fibres,  viz.  the  fasciculus  solitarius,  or 
descending  root  of  the  vagus  and  glosso-pharyngeal  nerves  ;  (5)  the  substantia  gelatinosa  liolandi, 
much  reduced,  with  the  large  spinal  root  of  the  trigeminal  nerve  close  to  its  outer  side. 

INTERNAL  STRUCTURE  OF  THE  PONS  VAROLII. 

When  transverse  sections  are  made  through  the  pons,  it  is  seen  to  be  composed 
of  a  ventral  part  and  a  dorsal  or  tegmental  part.  The  ventral  part  is  much  the 
larger  of  the  two,  and,  broadly  speaking,  it  corresponds  to  the  pyramidal  portions 
of  the  medulla  and  the  pedal  portions  of  the  two  crura  cerebri,  which  lie  above  it  and 
appear  to  issue  from  it.  The  dorsal  tegmental  part  may  be  regarded  as  the  con- 
tinuation upwards  of  the  formatio  reticularis  grisea  and  the  formatio  reticularis 
alba.  As  these  parts  are  traced  upwards  into  the  pons  they  become  much  modified, 
and  new  constituents  are  added. 

Ventral  Part  of  the  Pons  (pars  basilaris  poutis). — This  constitutes  the  chief 
bulk  of  the  pons.  It  is  composed  of:  (1)  transverse  fibres  arranged  in  coarse 
bundles;  (2)  longitudinal  fibres,  gathered  together  in  massive  bundles;  and  (3)  a 
large  amount  of  gray  matter,  termed  the  nucleus  pontis,  which  fills  up  the  inter- 
stices between  the  intersecting  bundles  of  fibres. 

The  longitudinal  fibres,  to  a  large  extent,  consist  of  the  same  fibres  which,  lower 
down,  are  gathered  together  in  the  two  solid  pyramidal  tracts  of  the  medulla. 
When  the  pyramids  are  traced  upwards  they  are  seen  to  enter  the  pons  in  the 
form  of  two  compact  bundles.  Soon,  however,  they  become  broken  up  into 
smaller  bundles  by  the  transverse  fibres  of  the  pons,  and  are  spread  out  over  a 
wider  area.  At  the  upper  border  of  the  pons  they  again  come  together  and  form 
two  solid  strands,  each  of  which  is  carried  into  the  central  papt  of  the  correspond- 
ing pedal  portion  of  the  crus  cerebri. 

The  transverse  fibres  at  the  lower  border  of  the  pons  are  placed  on  the  super- 
ficial or  ventral  aspect  of  the  pyramidal  bundles.  As  we  proceed  upwards  they 
increase  in  number,  and  many  are  seen  breaking  through  the  pyramids  and  even 


500 


THE  NEEVOUS  SYSTEM. 


passing  across  upon  the  dorsal  aspect  of  the  latter.  Laterally  these  transverse 
fibres  are  collected  together  into  one  compact  mass,  which  enters  the  white  central 
core  of  the  cerebellum  and  constitutes  the  middle  cerebellar  peduncle.  At  the 
mesial  plane  the  transverse  fibres  of  the  two  sides  of  the  ventral  portion  of  the 
pons  intercross  and  form  a  coarse  decussation. 

The  gray  matter  (the  nucleus  pontis)  forms  a  considerable  part  of  the  bulk  of 
the  ventral  portion  of  the  pons.  It  is  packed  into  the  intervals  between  the  inter- 
secting transverse  and  longitudinal  bundles. 

There  is  a  close  analogy  between  the  pyramidal  portions  of  the  medulla  and  the  ventral 
part  of  the  pons.  In  the  medulla  fine  arcuate  fibres  on  their  way  to  the  surface  pass  through 
the  pyramids.  Other  superficial  arcuate  fibres  sweep  over  the  surface  of  the  pyramids.  These 
present  a  strong  resemblance  to  the  transverse  fibres  of  tbe  pons.  They  likewise  reach 
the  cerebellum,  although  by  a  different  route,  viz.  the  inferior  cerebellar  peduncle.  The 
nucleus  pontis  is  also  represented  in  the  pyramidal  part  of  the  medulla  by  the  arcuate 


Spinal  root  of 
fifth  nerve 

Substantia  gela- 
tinosa  Rolandi 

Facial  nerve 
Facial  nucleus 
Sui^erior  olive 

Central  teg- 
mental tract' 

Fillet 


Middle  jiedunclc  of 
cerebellum 


\  rran!5ver.se  fibres  of 
pons 


Pyramidal  bundles 
Transverse  fibres  of  jjons 

Fig.  403. — Section  through  the  Lowek  Part  of  the  Human  Pons  Varolii  immediately  above 

THE  Medulla. 


nuclei,  which  are  covered  over  by  the  superficial  arcuate  fibres,  and  even  tend  to  penetrate, 
to  a  slight  extent,  into  the  pyramidal  tracts.  These  arcuate  nuclei,  as  already  pointed  out, 
are  continuous  with  the  nucleus  pontis. 

Connexions  of  the  Longitudinal  and  Transverse  Fibres. — Our  knowledge  of 
the  connexions  of  the  longitudinal  and  transverse  fibres  of  the  ventral  part  of  the  pons  is 
very  far  from  being  complete.  When  a  transverse  section  through  the  uj)per  part  of  the 
pons  is  compared  with  one  close  to  its  lower  border,  it  becomes  at  once  apparent  that  the 
numerous  scattered  bundles  of  longitudinal  fibres  which  enter  the  ventral  part  of  the  pons 
from  above,  if  brought  together  into  one  tract,  would  form  a  strand  very  much  larger  than 
the  two  pyramids  which  leave  its  lower  aspect  and  enter  the  medulla.  It  is  clear,  there- 
fore, that  many  of  the  longitudinal  fibres  which  pass  into  the  pons  from  above  do  not  pass 


INTERNAL  STRUCTUEE  OF  THE  PONS  VAROLII. 


501 


out  from  it  below  into  the  medulla.  What  becomes  of  these  fibres  that  are  thus  absorbed  in 
the  pons  1  It  is  known  that  the  pj-ramidal  bundles  sutler  a  small  loss  by  the  fibres  which 
they  send  to  the  nuclei  of  origin  of  the  efferent  nerves  which  arise  within  the  pons  (viz.  the 
motor  root  of  the  fifth,  the  sixth,  and  seventh  nerve  nuclei) ;  but  this  loss  is,  comparatively 
speaking,  trifling.  It  is  clear,  therefore,  that  other  longitudinal  bundles  enter  the  pons 
from  above  than  those  which  form  the  pyramidal  tracts.  These  bundles  occupy  a  lateral 
and  dorsal  position  in  the  ventral  part  of  the  pons,  and  may  be  termed  the  cortico-pontine 
fibres,  seeing  that  they  come  from  tlie  cerebral  cortex  and  end  in  fine  ramifications  around 
the  cells  of  the  nucleus  pontis. 

The  transverse  fibres  are  of  two  kinds,  viz.  :  (1)  those  which  ai'ise  in  the  cortex  of  the 
cerebellum ;  and  (2)  those  which 
take  origin  in  the  nucleus  pontis. 
The  former  are  the  axons  of  certain 
of  the  cells  of  the  cortex  of  the  cere- 
bellum (cells  of  Purkinje).  They 
come  chiefly  from  the  lateral  hemi- 
sphere, but  also  to  some  extent  from 
the  median  lobe  of  the  cerebellum, 
and  enter  the  pons  by  the  middle 
peduncle.  They  end  in  fine  rami- 
fications around  the  cells  of  the 
nucleus  pontis,  some  on  the  same 
side  as  the  peduncle  through  which 
they  reach  the  pons,  but  the  majority 
in  the  gray  matter  of  the  opposite 
side. 

The  transverse  fibres  which  arise 
in  the  pons  take  origin  as  axons  of 
the  cells  of  the  nucleus  pontis. 
Crossing  the  mesial  plane,  they  enter 
the  middle  peduncle  of  the  opposite 
side,  and  thus  reach  the  cerebellar 
cortex,  where  they  end  in  ramifica- 
tions round  certain  of  the  cortical 
cells.  The  middle  peduncle  thus 
contains  both  efferent  and  afferent 
cerebellar  fibres,  and  no  fibres  pass 
continiiously  through  the  pons  from 
one  middle  peduncle  into  the  other. 
In  opposition  to  this  view,  Klimoft' 
and  others  hold  that  the  middle 
peduncle  is  composed  solely  of  centri- 
petal or  afferent  fibres,  which  pass 
from  the  nucleus  pontis  to  the  cere- 
bellum. Some  of  these  fibres  are 
crossed  and  others  direct. 

Certain  of  the  transverse  fibres  Fio.   404.  —  Diagram   to  show  connexions  of  the  Direct 

of    the    pons    turn    backwards    and  Cerebellar  and  the  Olivo-Cerebellar   Tracts.      The 

enter   the    dorsal  or    tegmental    part  couuexions  of  the  fibres  of  the  middle  pedunde  of  the  cere- 

,     .,  1     .     ,1  •  belluiu  are  likewise  dia£;raiiimaticiulv  shown  (trom  LdiDger, 

of   the  pons,   but    the  precise    con-  modified)  -  ^  = 

nexions  of  these  are  doubtful. 

Corpus  Trapezoides. — This  name  is  applied  to  a  group  of  transverse  fibres 
which  traverse  the  lower  part  of  the  pons  (Fig.  405).  They  are  quite  distinct  from 
those  which  have  been  just  described  as  entering  the  middle  peduncle  of  the 
cerebellum,  and  they  lie  in  the  boundary  between  the  dorsal  and  ventral  parts  of 
the  pons,  but  encroaching  considerably  into  the  ground  of  the  former.  They  arise 
from  the  cells  of  the  terminal  nucleus  of  the  cochlear  division  of  the  auditory  nerve, 
and  constitute  a  tract  which  establishes  certain  central  connexions  for  that  nerve. 
They  will  be  more  fully  described  when  w^e  treat  of  the  cerebral  connexions  of  the 
auditory  nerve. 

Dorsal  or  Tegmental  Part  of  the  Pons  (pars  dorsalis  pontis). — On  the  dorsal 
surface  of  the  tegmental  part  of  the  pons  there  is  spread  a  thick  layer  of  gray 


Iiifevior  olivary 
nucleus 


Posterior  nerve 
root 


Posterior  vesicular 
column  of  cells 


502  THE  NERVOUS  SYSTEM. 

matter,  covered  by  ependyma,  which  forms  the  floor  of  the  upper  or  pontine 
part  of  the  fourth  ventricle.  Beneath  this  the  mesial  raphe  of  the  medulla  is 
continued  up  into  tlie  pons,  so  as  to  divide  its  tegmental  part  into  two  symmetrical 
halves. 

In  the  lower  'part  of  the  pons,  immediately  beyond  the  medulla,  the  restiform 
body  is  placed  on  the  outer  side  of  the  tegmental  part  (Fig.  403).  In  transverse 
sections  through  the  pons  it  appears  as  a  large,  massive  oval  strand  of  fibres  which 
gradually  inchnes  backwards  into  the  cerebellum,  and  thus  leaves  the  pons. 
Between  the  restiform  body  and  the  median  raphe  the  tegmental  part  of  the  pons 
is  composed  of  forma tio  reticularis,  continuous  with  the  same  material  in  the 
medulla.  Thus  arcuate  or  transverse  fibres,  curving  in  towards  the  raphe,  and  also 
longitudinal  fibres,  are  seen  breaking  through  a  mass  of  gray  matter  which  occupies 
the  interstices  of  the  intersecting  fibres.  To  the  naked  eye  the  formatio  reticularis 
presents  a  uniform  gray  appearance,  but  its  constituent  parts  are  revealed  by  low 
powers  of  the  microscope  in  properly-stained  and  prepared  specimens.  Embedded 
in  this  formatio  reticularis  are  various  clumps  of  compact  gray  matter  and  certain 
definite  strands  of  fibres.  These  we  shall  describe  as  we  pass  from  the  restiform 
body  inwards  towards  the  median  raphe. 

(1)  Spinal  root  of  the  trigeminal  nerve  and  the  substantia  gelatinosa  Rolandi.- — 
Close  to  the  inner  side  of  the  restiform  body,  but  separated  from  it  by  the  vesti- 
bular root  of  the  auditory  nerve  as  it  proceeds  backwards  through  the  pons,  is  seen 
a  large  crescentic  group  of  coarse  transversely-divided  bundles  of  fibres.  This  is  the 
spinal  root  of  the  fifth  nerve,  and  applied  to  its  inner  concave  side  is  a  small  mass 
of  gray  matter,  which  is  the  direct  continuation  upwards  of  the  substantia  gelatinosa 
Eolandi. 

(2)  The  nucleus  of  the  facial  or  seventh  nerve  comes  next.  It  is  sunk  deeply 
in  the  tegmental  part  of  the  pons  and  lies  close  to  the  transverse  fibres  of  the 
corpus  trapezoides.  It  is  a  conspicuous,  obliquely  placed,  ovoid  clump  of  gray 
matter.  From  its  outer  and  dorsal  aspect  the  root-fibres  of  the  facial  nerve 
stream  backwards  and  inwards  towards  the  gray  matter  on  the  floor  of  the  fourth 
ventricle.  Passing  forwards  between  this  nucleus  and  the  substantia  Eolandi  a 
solid  nerve-bundle  may  be  observed.  This  is  the  facial  nerve,  traversing  the  pons 
towards  its  place  of  emergence  from  the  brain. 

(3)  Immediately  internal  to  the  facial  nucleus,  but  placed  more  deeply  in  the 
tegmental  part  of  the  pons,  is  the  superior  olivary  nucleus  (nucleus  olivaris  superior). 
It  lies  in  a  bay  formed  for  it  by  the  transverse  fibres  of  the  corpus  trapezoides. 
These  fibres  curve  round  its  ventral  aspect,  and  many  of  them  may  be  observed  pene- 
trating into  its  svibstance.  In  man  it  is  a  very  small  mass  of  gray  matter,  and 
presents  little  resemblance  to  the  inferior  olivary  nucleus,  except  in  the  size  and 
shape  of  its  constituent  cells.  In  sections  through  the  part  of  the  pons  where  it 
attains  its  greatest  size,  it  appears  in  the  form  of  two,  or  it  may  be  three,  small 
isolated  masses  of  gray  matter.  It  is  intimately  connected  with  the  trapezial 
fibres,  many  of  which  end  in  it,  whilst  others  take  origin  within  it. 

Upon  the  inner  and  dorsal  aspect  of  tlie  superior  olive  there  is  a  dense  grouj)  of  longitudinal 
fibres.  These  constitute  the  central  tegmental  tract;  but  as  precise  information  in  regard  to 
its  connexions  is  still  to  a  large  extent  wanting,  it  is  not  necessary  to  do  more  than  indicate  its 
position. 

(4)  The  posterior  longitudinal  bundle  and  the  fillet  come  next.  As  they  proceed 
upwards  through  the  tegmental  part  of  the  pons,  these  longitudinal  tracts  occupy 
the  same  relative  position  as  in  the  medulla.  They  are  placed  close  to  the  median 
raphe ;  but  they  have  drawn  further  apart  from  each  other,  and  their  fibres  are 
more  distinctly  concentrated  into  separate  strands,  with  an  interval  of  some  little 
width  between  them.  The  posterior  longitudinal  bundle  lies  immediately  under 
cover  of  the  gray  matter  of  the  floor  of  the  iburth  ventricle.  The  fillet  is  placed 
close'  to  the  trapezial  fibres,  many  of  which  traverse  it  as  they  pass  towards  the 
mesial  plane. 

(5)  The  nucleus  of  the  sixth  nerve  also  forms  a  conspicuous  object  in  sections 
through  the  lower  part  of  the  pons.  It  is  a  round  mass  of  gray  matter,  which  is 
situated  close  to  the  outer  side  of  the  posterior  longitudinal  bundle,  and  immediately 


INTERNAL  STRUCTURE  OF  THE  PONS  VAROLII. 


503 


under  cover  of  the  gray  matter  of  the  floor  of  the  fourth  ventricle.  From  its  inner 
side  numerous  root-bundles  of  the  sixth  nerve  pass  out  and  proceed  forwards 
beween  the  fillet  and  the  superior  olivary  nucleus.  They  occupy  in  the  pons, 
therefore,  a  position  similar  to  that  occupied  by  the  hypoglossal  root-fibres  in  the 
medulla. 

Up  to  the  present  only  the  lower  part  of  the  tegmental  portion  of  the  jjons 
has  been  described,  i.e.  the  portion  immediately  adjoining  the  medulla.  As  we 
proceed  upwards  and  gain  a  point  above  the  level  of  the  trajtezial  fihrcs,  many  of 
the  structures  which  have  attracted  attention  lower  down  gradually  disappear 
from  the  formatio  reticularis.  The  posterior  longitudinal  bundle,  the  fillet,  and 
the  spinal  root  of  the  fifth  nerve,  however,  are  still  carried  upwards.     Further,  the 


Superior  cprebollar  piidniicle- 


Mesenoephalic  root  of  tlif  fifth  ncr\( 


Motor  nucleus  of  the  lifth  nene 


Motor  root  of  the  fifth  nerve 


Superior  medullary  velum 
or  valve  of  Vieussens 


Corpus 
trai)ezoi(les 


Sensory  nucleus  of  the  fifth  nerve 

Superior  olive  -.^^ 

Sensory  root  of  ' 

fifth  nerve  ^~ 


Middle  peduncle 
of  cerebellum 


Transverse 
fibres  of  i)ons 


Pyramidal 
binidle.s 


Fig.  405. 


-Transverse  Section  throuoh  the  Pons  Varolii  at  the  Level  of  the  Nuclei  ok 
THE  Trigeminal  Nerve  (Oraiig). 


floor  of  the  fourth  ventricle  becomes  narrower,  and  other  objects  appear  in  the 
tegemental  substance. 

The  superior  cerebellar  peduncle  (brachium  conjunctivum)  is  a  very  con- 
spicuous object,  in  sections,  through  the  middle  and  upper  parts  of  the  pons.  In 
transverse  section  it  presents  a  semilunar  outhne,  and  as  it  emerges  from  the 
cerebellum  it  lies  immediately  on  the  outer  side  of  the  fourth  ventricle,  towards 
which  its  concave  aspect  is  turned  (Fig.  405).  Its  dorsal  border  is  joined  with  the 
corresponding  peduncle  of  tlie  opposite  by  the  thin  lamina  of  white  matter, 
termed  the  superior  medullary  velum,  whilst  its  ventral  border  is  sunk  to  a  small 
extent  in  the  dorsal  part  of  the  pons.  As  it  is  traced  upwards  it  sinks  deeper  and 
deeper  into  the  pons  until  it  becomes  completely  submerged,  with  the  exception 
of  the  posterior  border  to  which  the  superior  velum  is  attached.  It  now  lies  on 
the  outer  side  of  the  tegmental  or  reticular  substance  of  the  pons,  and  this  position 
it  maintains  until  the  mesencephalon  is  reached  (Fig.  406). 

About  half-wccij  uf  the  pons  the  nuclei  of  the  trigeminal  or  fifth  cranial  nerve 
mark  a  very  important  stage  in  its  tegmental  portion.     Tliese  nuclei  are  two  in 


604 


THE  NEEVOUS  SYSTEM. 


number  on  each  side,  viz.  a  large  oval  terminal  nvicleus  for  certain  of  the  sensory 
fibres  of  the  nerve  and  a  nucleus  of  origin  equally  conspicuous  for  certain  of  the 
motor  fibres  (Fig.  405).  The  sensory  nucleus  lies  close  to  the  outer  surface  of  the 
pons,  deeply  sunk  in  its  tegmental  part,  and  in  the  interval  between  the  submerged 
anterior  border  of  the  superior  cerebellar  peduncle  and  the  ventral  part  of  the  pons. 
The  motor  nucleus  is  placed  on  the  inner  side  of  the  sensory  nucleus,  but  somewhat 
nearer  the  dorsal  surface  of  the  pons.  At  this  level  the  spinal  root  of  the  fifth 
nerve  disappears  by  joining  the  fibres  of  the  sensory  portion.  The  sensory  and 
motor  roots  of  the  fifth  nerve  traverse  the  ventral  part  of  the  pons  on  their  way 
to  and  from  the  region  of  the  nuclei. 

Above  the  level  of  the  nuclei  of  the  trigeminal  nerve  a  new  tract  of  fibres 
comes  into  view.  This  is  the  mesencephalic  root  of  the  fifth  nerve,  as  it  descends 
to  join  the  emerging  fibres  of  the  motor  part  of  the  fifth  nerve.  It  is  a  small 
bundle  of  nerve  fibres,  semilunar  in  cross  section,  which  hes  close  to  the  inner  side 


Upper  end  of  Ventricle  IV 
Mesencephalic  root  of  the  fifth  neive 

Posterior  longitudinal  bundle 


Forinatio  reticularis 
Nucleus  of  lateral  fillet  - 


Vah  e  of  Vieussens 

Gray  matter  on  floor  of  Ventricle  IV. 
Superior  cerebellar  peduncle 


Lateral  fillet 


Commencing  decussa- 
tion of  superior 
cerebellar  peduncles 

Mesial  fillet 


Transverse  fibres 
of  pons 


Pyramidal  bundle 


Fig.  406.— Section  theodgh  the  Upper  Part  of  the  Pons  Varolii  of  the  Orang,  above  the 

Level  of  the  Trigeminal  Nuclei. 


of  the  superior  cerebellar  peduncle  and  on  the  outer  and  deep  aspect  of  the  gray 
matter  on  the  floor  of  the  fourth  ventricle  (Figs.  406  and  407). 

On  a  slightly  deeper  plane  than  the  mesencephalic  root  of  the  fifth  nerve, 
between  it  and  the  posterior  longitudinal  bundle,  and  in  close  relation  to  the  gray 
matter  of  the  floor  of  the  ventricle,  is  the  collection  of  pigmented  cells  which  con- 
stitutes the  substantia  ferruginea. 

The  posterior  longitudinal  bundle,  as  it  is  traced  upwards  through  the  tegmental 
part  of  the  pons,  maintains  the  same  position  throughout,  and  as  it  ascends  it 
becomes  more  clearly  mapped  out  as  a  definite  and  distinct  tract.  It  lies  close 
to  the  mesial  raphe,  and  immediately  subjacent  to  the  gray  matter  of  the  floor  of 
the  fourth  ventricle. 

The  fillet  as  it  ascends  through  the  tegmental  part  of  the  pons  undergoes 
striking  changes  in  shape.  In  the  lower  portion  of  the  pons  its  fibres,  which  in 
the  medulla  are  spread  out  along  the  side  of  the  median  raphe,  are  collected 
together  in  the  form  of  a  loose  bundle,  which  occupies  a  wide  field,  somewhat 
triangular  in  shape,  on  either  side  of  the  median  raphe  and  immediately  behind 
the  ventral  portion  of  the  pons.  As  it  proceeds  up,  the  fibres  spread  out  laterally 
until  a  compact  ribbon-like  layer  is  formed  in  the  interval  between  the  tegmental 
and  ventral  portions  of  the  pons.  This  constitutes  what  is  termed  the  mesial 
fillet  (Figs.  406  and  407). 

Above  the  level  of  the  trigeminal  nuclei  another  flattened  layer  of  fibres  comes 


THE  CEEEBELLUM. 


505 


into  view  to  the  outer  side  of  the  mesial  fillet.  To  this  the  name  of  lateral  fillet  is 
given.  These  fibres  spread  outwards  and  backwards,  and  finally  take  vip  a  position 
on  the  outer  surface  of  the  superior  cerebellar  peduncle.  In  the  angle  between 
the  mesial  and  lateral  fillets  a  little  knot  of  compact  gray  matter,  termed  the  lateral 


Upper  end  of  ventricle  IV, 
Tioohleai  nene 
Mesencephalic  root  ot  lifth  nerve^  ^^ 

Gowerb  tract 
Posterior  longi 
tudinal  bundle 

Superior  cere- 
bellar peduncle 


Infeiior  quadri- 
f^pnnnal  body 
Decussation 
ot  ti'ochlear 
iH  I  ves 
Upper  end  of 
ventiicle  IV. 

Supeiior  cere- 
bi  llai  ])eduncle 
I' jsterior  Icingi- 
tudinil  bundle 
T  iteial  fillet 


Fig.  407.— Two  Sections  through  the  Tegmentum  of  the  Pons  at  its  Upper  Part,  clo.se  to 

THE    MeSENCEPHALOX. 

A  is  at  a  slightly  lower  level  than  B. 

fillet  nucleus,  comes  into  view  (Fig.  406).  This  appears  to  be  in  more  or  less 
direct  continuity  with  the  superior  olivary  nucleus.  Many  of  the  fibres  of  the 
lateral  fillet  take  origin  in  this  nucleus.  Bruce  has  called  attention  to  the  continuity 
between  the  superior  olive  and  the  lateral  fillet  nucleus  in  man,  and  the  writer 
can  confirm  his  statement  in  so  far  as  the  orang  brain  is  concerned. 


THE    CEREBELLUM. 

The  cerebellum  lies  behind  the  pons  Varolii  and  the  medulla  oblongata,  and 
below  the  hinder  portions  of  the  cerebral  hemispheres.     From  the   latter  it  is 


Central  lobule 


Mesencephalon 


Autenor  crescentio  lobule 


Posterior  cres- 
centio lobule 


Postero- 
superior  lobule 


Folium  cacuniinis 


Postero-inferior  lobule 


Tuber  valvulie  Posteiiur  nuLch 

Fig.  408. — Upper  Surface  of  the  Cerebellum. 


separated  by  an  intervening  partition  of  dura  mater,  termed  the  tentorium  cerebelli. 
It  is  distinguished  by  the  numerous  parallel  and  more  or  less  curved  sulci,  which 
traverse  its  surface  and  give  it  a  foliated  or  laminated  appearance.  It  is  composed 
of  a  cortex  of  gray  matter  (substantia  corticalis)  spread  over  its  surface,  with  white 
matter  in  the  interior,  forming  a  central  core  (corpus  medullare). 


50G  THE  NERVOUS  SYSTEM. 

The  cerebellum  is  subdivided  somewhat  arbitrarily  into  a  median  portion 
termed  the  vermis,  and  two  much  larger  lateral  portions,  called  the  lateral  hemi- 
spheres (hemispha^ria  cerebelli).  The  demarcation  jjetween  these  main  subdivisions 
of  the  organ  is  not  very  evident  from  every  point  of  view.  In  front,  and  also 
behind,  there  is  a  marked  deficiency  or  notch.  The  posterior  notch  (incisura  cere- 
belli posterior)  is  smaller  and  narrower  than  the  anterior  notch.  It  is  bounded 
laterally  by  the  lateral  hemispheres,  whilst  its  bottom  is  formed  by  the  median  lobe 
or  vermis.  It  is  occupied  by  a  fold  of  dura  mater,  called  the  falx  cerebelli.  The 
anterior  notch  (incisura  cerebelli  anterior)  is  wide,  and,  when  viewed  from  above,  it 
is  seen  to  be  occupied  by  the  inferior  quadrigeminal  bodies  and  by  the  superior 
peduncles  of  the  cerebellum.  As  in  the  case  of  the  hinder  notch,  its  sides  are 
formed  by  the  lateral  hemispheres  and  the  bottom  by  the  vermis. 

On  the  superior  surface  of  the  cerebellum  there  is  little  distinction  to  be  noted 
between  the  median  lobe  and  the  upper  surface  of  each  lateral  hemisphere.  On 
this  aspect  the  median  lobe  receives  the  name  of  superior  vermis,  and  it  forms  a 
high  median  elevation,  from  which  the  surface  slopes  gradually  downwards  on  each 
side  to  the  margin  of  the  hemisphere.  The  superior  vermis  is  highest  in  front, 
immediately  behind  the  anterior  notch,  and  from  this  it  shows  a  somewhat  sharp 
descent  towards  the  posterior  notch.  This  elevation  of  the  superior  worm  is 
frequently  called  the  monticulus  cerebelli.  The  folia  on  the  surface  of  the  superior 
vermis  are  thicker  and  fewer  in  number  than  those  on  the  upper  surface  of  the 
lateral  hemisphere.  It  is  this  which  gives  it  the  worm-like  appearance  from  which 
it  derives  its  name. 

On  the  inferior  surface  of  the  cerebellum  the  distinction  between  the  three  main 
constituent  parts  of  the  organ  is  much  better  marked  (Fig.  409).  On  this  aspect 
the  lateral  hemispheres  are  full,  prominent,  and  convex,  and  occupy  the  cerebellar 
fossa3  in  the  floor  of  the  cranium.  They  are  separated  by  a  deep  mesial  hollow, 
which  is  continued  forwards  from  the  posterior  notch.  This  hollow  is  termed  the 
vallecula  cerebelli,  and  in  its  fore-part  is  lodged  the  medulla  oblongata.  When  the 
medulla  is  raised  and  the  lateral  hemispheres  are  pulled  apart,  so  as  to  expose  the 
bottom  of  the  vallecula,  it  will  be  seen  that  this  is  formed  by  the  vermis  inferior, 
or  inferior  aspect  of  the  median  lobe,  and,  further,  that  the  latter  is  separated  on 
each  side  from  the  corresponding  lateral  hemisphere  by  a  distinct  furrow,  termed 
the  sulcus  valleculas. 

Sulci  Cerebelli. — Certain  of  the  fissures  which  traverse  the  surface  of  the 
cerebellum  are  deeper  and  longer  than  the  others,  and  they  map  out  districts  which 
are  termed  lobes.  One  of  the  most  conspicuous  of  these  clefts  is  the  great  horizontal 
fissure. 

The  great  horizontal  fissure  (sulcus  liorizontalis  cerebelli)  of  the  cerebellum 
begins  in  front  and  passes  continuously  round  the  circumference  of  the  organ, 
cutting  deeply  into  its  outer  and  posterior  margins.  In  front,  its  lips  diverge  to 
enclose  the  three  cerebellar  peduncles  as  they  pass  into  the  interior  of  the 
cerebellum.  The  great  horizontal  fissure  divides  the  organ  into  an  upper  and  a 
lower  part,  which  may  be  studied  separately. 

The  prominence  which  is  accorded  to  the  great  horizontal  fissure  in  descriptive  anatomj'  is 
not  justified  by  its  develo^jmental  histor}^  and  morphological  status.  It  is  very  late  in  making 
its  appearance  in  the  fcetal  cerebellum,  and  not  infrecpiently  the  part  of  the  fissure  on  the  one 
side  fails  to  establish  a  continjiity  across  the  vermis  with  the  part  of  the  fissure  on  the  other 
side  of  the  organ. 

Lobes  on  the  Upper  Surface  of  the  Cerebellum. — When  examined  from 
before  backwards,  the  superior  vermis  presents  the  following  sulidivisions :  (1)  the 
lingula;  (2)  the  central  lobule  (lo})ulus  centralis);  (3)  tlie  culmen  monticuli;  (4)  the 
clivus  monticuli ;  (5)  the  folium  cacuminis  (folium  vermis).  With  the  exception  of 
tlie  lingula,  each  of  these  is  continuous  on  either  side,  witli  a  corresponding  district 
on  tiie  upper  surface  of  the  hemisphere,  thereby  forming  a  cerebellar  lobe.  Thus 
the  central  lobule  is  prolonged  outwards  on  either  side  in  the  form  of  a  small, 
flattened,  wing-like  expansion  called  the  ala ;  the  culmen  constitutes  the  median 
connecting  piece  between  the  two  anterior  crescentic  lobules  of  the  liemjs])heres ; 
the  cHvus  stands  in  the  same  relation  to  the  two  posterior  crescentic  lobules ;  and 


THE  CEREBELLUM.  507 

the  folium  cacuminis  is  the  connecting  band  between  the  postero- superior  lobules  of 
the  hemispheres. 

It  should  be  noted  that  this  subdivision  of  tlie  uiijjer  surface  of  the  cerebellum  is  to  some 
extent  conventional,  and  in  certain  2:)articulars  receives  little  suppoi't  from  morphological  data. 

The  lingula  can  only  be  seen  when  the  part  ol"  the  cerebellum  which  forms  the 
bottom  of  the  anterior  notch  is  pushed  backwards.  It  consists  of  four  or  five  small 
fiat  folia  continuous  with  the  gray  matter  of  the  vermis  superior,  which  are  pro- 
longed forwards  on  the  upper  surface  of  the  superior  medullary  velum  in  the  interval 
between  the  two  superior  cere1)ellar  peduncles. 

Lobus  Centralis  with  its  Alae. — The  loljulus  centralis  lies  at  the  bottom  of 
the  anterior  cerebellar  notch,  and  is  only  seen  to  a  very  small  extent  on  the  upper 
surface  of  the  organ.  It  is  a  little  median  mass  which  laterally  is  prolonged  out- 
wards for  a  short  distance  round  the  anterior  notch  in  the  form  of  two  expansions, 
termed  the  alse. 

Lobus  Culminis. — The  culnien  monticuli  constitutes  the  highest  part  or  summit 
of  the  monticulus  of  the  vermis  superior.  It  is  bounded  behind  by  a  deep  and 
strongly  marked  fissure  called  the  fissura  prima  (Elliot  Smith),  and  is  prolonged 
outwards  on  either  side  into  the  lateral  hemisphere  as  the  anterior  crescentic  lobule. 
This  is  the  most  anterior  subdivision  on  the  upper  surface  of  the  hemisphere.  The 
two  anterior  crescentic  lobules,  with  the  culmen  monticuli,  form  the  lobus  culminis 
cerebelli. 

Lobus  Clivi. — The  clivus  monticuli  lies  behind  the  culmen,  from  which  it  is 
separated  by  the  fissura  prima,  and  it  forms  the  sloping  part  or  descent  of  the 
monticulus  of  the  vermis  superior.  On  each  side  it  is  continuous  with  the  posterior 
crescentic  lobule  of  the  lateral  hemisphere,  and  the  three  parts  are  included  under 
the  one  name  of  lobus  clivi. 

The  two  crescentic  lobules  on  the  upper  surface  of  the  liemisjihere  are  sometimes  classed 
together  and  described  as  the  lobulus  quadrangularis.  They  are  separated  from  each  other  by  a 
lateral  extension  on  the  upper  surface  of  the  hemisphere  of  the  fissura  prima,  whilst  the 
posterior  crescentic  lobule  is  bounded  behind  by  a  curved  sulcus  termed  by  Elliot  Smith  the 
fissura  postlunata.  The  union  of  the  two  postlunate  furrows  across  the  vermis  separates  the 
clivus  from  the  folium  cacuminis,  but  in  many  cases  this  junction  fails  to  take  place. 

Lobus  Cacuminis. — The  folium  cacuminis  forms  the  most  posterior  part  of  the 
vermis  superior,  and  when  the  right  and  left  portions  of  the  great  horizontal  fissure 
are  continuous  across  the  vermis  it  bounds  that  fissure  superiorly  at  the  posterior 
notch.  It  is  a  single  folium,  subject  to  considerable  variation  in  the  degree  of  its 
development,  and  its  surface  may  be  smooth  or  beset  with  rudimentary  secondary 
folia.  It  is  the  median  connecting  link  between  the  two  postero-superior  lobules 
of  the  hemispheres,  the  three  parts  forming  the  lobus  cacuminis.  As  the  folium 
cacuminis  is  traced  outwards  into  the  postero-superior  lobule,  it  is  found  to 
expand  greatly,  and  as  a  result  of  this  the  postero-superior  lobule  on  each  side 
forms  an  extensive  foliated  district  bounding  the  great  horizontal  fissure  above. 

Lobes  on  the  Under  Surface  of  the  Cerebellum. — The  connexion  between 
the  several  parts  of  the  inferior  vermis  and  the  corresponding  districts  on  the 
under  surface  of  the  two  hemispheres  is  not  so  distinct  as  in  the  case  of  the  vermis 
superior  and  the  lobules  on  the  upper  surface  of  the  hemispheres.  A  groove,  the 
sulcus  valleculas,  intervenes  between  the  vermis  inferior  and  the  hemisphere  on 
each  side. 

From  behind  forwards  the  following  subdivisions  of  the  vermis  inferior  may  be 
recognised :  (1)  the  tuber  valvulse  (tuber  vermis) ;  (2)  the  pyramid  (pyramis) ;  (3) 
the  uvula ;  (4)  the  nodule  (nodulus). 

On  the  under  surface  of  the  hemis]3here  there  are  four  main  lobules  nuipped  out 
by  intervening  fissures.  From  behind  forwards  these  are:  (1)  the  postero-inferior 
lobule,  a  large  subdivision  which  bounds  the  o-reat  horizontal  fissure  on  its  under 
aspect ;  (2)  the  biventral  lobule  (lobulus  biventer)  which  lies  in  front  of  the  postero- 
inferior  lobule,  and  is  partially  divided  into  two  parts  by  a  curved  fissure  which 
traverses  its  surface ;  (3)  the  tonsil  or  amygdala  (tonsilla),  a  small  rounded  lobule 
which  bounds  the  fore-part  of  the  vallecula,  and  is  lodged  in  a  deep  concavity  on 


508 


THE  NERVOUS  SYSTEM. 


the  inner  aspect  of  the  biventral  lobule ;  (4)  the  flocculus,  a  minute  lobule  situated 
on  the  middle  peduncle  of  the  cerebellum  in  front  of,  and  partially  overlapped  by, 
the  anterior  border  of  the  l^iventral  lobule. 

These  lobules,  with  the  corresponding  portions  of  the  vermis  inferior,  constitute 
the  lobes  on  the  under  surface  of  the  cerebellum.  Still,  it  should  be  noted  that, 
just  as  in  the  case  of  the  upper  surface  of  the  organ,  this  subdivision  is  to  some 
extent  artificial,  and  is  not  in  every  particular  provided  with  a  sound  morphological 
basis. 

Lobus  Tuberis. — The  tuber  valvule,  which  forms  tlie  most  posterior  part  of 
the  vermis  inferior,  is  composed  of  several  transversely  arranged  folia  which,  on 
either  side,  run  directly  into  the  postero-inferior  lobule.  The  three  parts  of  the 
lobus  tuberis  are  thus  linked  together. 

The  postero-inferior  lobule,  which  is  wider  towards  the  vallecula  than  it  is 
further  out,  is  traversed  by  two  or  it  may  be  three  curved  fissures.  The  most 
anterior  of  these  cuts  off  a  narrow,  curved  strip  of  cerebellar  surface,  which  presents 
a  more  or  less  uniform  width  throughout  its  whole  length.  This  is  the  so-called 
lobulus  gracilis. 

Lobus  Pyramidis. — The  pyramid  is  connected  with  the  biventral  lobule  on 
each  side  by  an  elevated  ridge  which  crosses  the  sulcus  valleculse.  The  term  lobus 
pyramidis  is  applied  to  the  three  lobules,  which  are  thus  associated  with  each 
other. 

The  pyramid  is  separated  from  the  tuber  valvulse  by  a  deep  furrow  which  has  been  termed 
by  Elliot  Smith  the  suprapyramidal  fissure.  It  is  in  a  measure  continuous  with  the  curved 
fissure,  whicli  on  the  under  surface  of  the  hemisphere  intervenes  between  the  biventral  lobule 
and  the  lobulus  gracilis  or  fore  part  of'  the  postero-inferior  lobule.  The  name  applied  to  the 
latter  fissure  by  Elliot  Smith  is  fissura  parapyramidalis. 

Lobus  Uvulae. — The  uvula  is  a  triangular  elevation  of  the  vermis  inferior.  It 
lies  between  the  two  tonsils,  and  is  connected  with  each  of  these  by  a  low-lying 


Cpntral  lobule    Superior  inedullary  velum 


Superior  peduncle  of  c£j' ^  11  im 
Middle  peduncle  of  cerebellum 

Ventricle  IV 


Nodule 


Flocculus 

Tonsil 


Postero-inferior  lobule^ 


1  jstero  inferior  lobule 


Lobulus  gracilis/ 
Bi\    I 


Pyj-anud  Tubei  \al\ulte 

Fig.  409. — Lower  Surface  of  the  Cerebellum. 
The  tonsil  on  the  right  side  has  been  removed  so  as  to  display  more  fully  the  inferior  medullary  velum  and 

the  furrowed  band. 

band-like  ridge  of  gray  matter  scored  by  a  few  shallow  furrows,  and  in  consequence 
termed  the  furrowed  band.     The  two  tonsils  and  the  uvula  form  the  lobus  uvulae. 

Ji«tw(;eii  tlie  pyi'amid  and  the  uvula  there  is  a  deep  cleft  which  may  be  termed  the  infra- 
pyramidal  fissure  (tlie  fissura  secunda  of  Elliot  Smith).  This  is  more  or  less  directly  connected 
with  the  retrotonsillar  fissure  which  curves  round  the  tonsil.  Tlic  large  size  of  the  tonsil  is 
characteristic  of  the  Ijraiii  of  man  and  the  anthropoid  apes. 

Lobus  Noduli. — The  lobus  noduli  comprises  the  nodule  and  the  flocculus  of 
each  side,  with  a  delicate  connecting  lamina  of  white  matter  termed  the  inferior 
medullary  velum. 


THE  CEREBELLUM. 


509 


Tlie  cleft  l)et\veen  the  nodule  and  the  uvula  is  termed  the  postnodular  fissure  (Elliot  Smith) ; 
that  between  the  flocculus  and  the  l)i ventral  lolnile  is  called  tlie  floccular  fissure. 

The  flocculus  will  usually  be  ol>served  to  be  partially  divided  into  two  pieces.  The  smaller 
hinder  portion,  which,  as  a  rule,  is  completely  overlapped  by  the  overhanging  edge  of  tlie 
biventral  lolnile,  is  the  paraflocculus.  This  assumes  very  large  proportions  in  certain  of  the 
lower  mammals. 

Arrangement  of  the  Gray  and  White  Matter  of  the  Cerebellum.— The  white 
matter  of  the  cereLellum  forms  a  solid  compact  mass  in  the  interior,  and  over  this 
is  spread  a  con- 
tinuous and  uui-  <^"''"«""  '"on«cuii 
form  layer  of  gray 
matter.  In  each 
lateral  hemi- 
sphere the  white 
central  core  is 
more  bulky  than 
in  the  median 
lobe  or  worm,  in 
which  the  central 
white  matter  is 
reduced  to  a  re- 
latively thin 
bridge  thrown 
across  between 
the  two  lateral 
hemispheres.  The 
white  matter  in 
the  interior  of  the 

median  lobe  or  worm  is  termed   the  corpus  trapezoides.     When  sagittal  sections 
are  made  through  the  cerebellum,  the  gray  matter  on  the  surface  stands  out  clearly 

Further,  from  all  parts  of  the  surface  of 


Inferior  olivary  nucleus 


Fici.  410. 


-Sagittal  Section  through  the  Left  Lateral  Hemisphere 
OF  the  Cerebellum, 

Showing  tlie  "  arbor  vits"  and  the  corpus  dentatum. 


from  the  white  matter  in  the  interior. 


TH'uia  semicircularis- 

Pulvinar" 
Inferior  quadrigeminal  body 

Middle  cerebellar  peduncle 

Inferior  cerebellar  peduncle 


Ay^ Third  ventricle 

-1 Titnia  tlialanii 


--Trigonuni  liabenuke 

.  -  Pineal  body 

—Superior  quadrigeminal  body 

--Inferior  braeliiuni 
Fourth  nerve 


Valve  of  Vieus.sens 
Superior  cerebellar  peduncle 


-.Corpus  dentatum 


Fig.  411.— From  a  dissection  by  Dr.  Edward  B.  Janiieson  in  the  Anatoniical  Department  of  the  University  of 
Edinburgh.  The  corpus  dentatum  is  displayed  from  above  ard  the  superior  cerebellar  peduncle 
has  been  traced  from  it  to  the  mesencephalon. 

the  central  core  stout  stems  of  white  matter  are  seen  projecting  into  the  lobes  of 
the  cerebellum.     From  the  sides  of  these  white  stems  secondary  branches  proceed 


510  THE  NEKVOUS  SYSTEM. 

at  various  angles,  and  from  these  again  tertiary  branches  are  given  off.  Over  the 
various  lamellas  of  white  matter  thus  formed  the  gray  cortex  is  spread,  and  the 
fissures  on  the  surface  show  a  corresponding  arrangement,  dividing  up  the  organ 
into  lobes,  lobules,  and  folia.  When  the  cerebellum  is  divided  at  right  angles  to 
the  general  direction  of  its  fissures  and  folia,  a  highly  arborescent  appearance  is 
thus  presented  by  the  cut  surface.  To  this  the  term  arbor  vitse  cerebelli  is  applied. 
Corpus  Dentatum  and  other  Gray  Nuclei  in  the  White  Matter  of  the 
Cerebellum. — Eml  ledded  in  the  midst  of  the  mass  of  white  matter  which  forms  the 
central  core  of  each  lateral  hemisphere  there  is  an  isolated  nucleus  of  gray  matter, 
which  presents  a  strong  resemblance  to  the  inferior  olivary  nucleus  of  the  medulla. 
It  is  called  the  corpus  dentatum  (nucleus  dentatus),  and  it  consists  of  a  corrugated 
or  plicated  lamina  of  gray  matter,  which  is  folded  on  itself  so  as  to  enclose,  in  a 
flask-like  manner,  a  portion  of  the  central  white  matter  (Figs.  410  and  411). 
This  gray  capsule  is  not  completely  closed.  It  presents  an  open  mouth,  termed 
the  hilum,  whicli  is  directed  inwards  and  upwards,  and  out  of  this  stream  the 
great  majority  of  the  fibres  of  the  superior  cerebellar  peduncle. 

Three  small  additional  masses  of  gray  matter  are  also  present  on  either  side  of  the  mesial 
plane  in  the  central  white  matter  of  the  cerebellum.  These  are  termed  the  nucleus  emboli- 
formis,  the  nucleus  globosus,  and  the  nucleus  fastigii.  The  nucleus  emboliformis  or  embolus  is  a 
small  lamina  of  gray  matter  which  lies  immediately  internal  to  the  hilum  of  the  corpus  dentatum, 
being  thus  related  to  it  somewhat  in  the  same  manner  that  the  mesial  accessory  olivary  nucleus 
is  related  to  the  main  inferior  olivary  nucleus.  The  nucleus  globosus  lies  internal  to  the  embolus 
and  on  a  somewhat  deeper  horizontal  plane.  The  nucleus  fastigii  or  roof  nucleus  is  placed  in 
the  white  substance  of  the  worm  (corpus  trapezoides)  close  to  the  mesial  plane  and  its  fellow  of 
the  opposite  side.     It  is,  therefore,  situated  on  the  mesial  aspect  of  the  nucleus  globosus. 

Although  isolated  from  the  gray  matter  of  the  surface,  these  small  nuclei  and  the  corpus 
dentatum  are  connected  at  certain  points  with  each  other.  The  corpus  dentatum  and  the 
embolus  present  a  structure  very  similar  to  that  of  the  inferior  olivary  nucleus.  In  the  •  nucleus 
gloljosus  and  the  nucleus  fastigii  the  cells  are  somewhat  larger  in  size. 

Cerebellar  Peduncles. — These  are  three  in  number  on  each  side,  viz.  the  middle, 
the  inferior,  and  the  superior  (Fig.  391,  p.  487).  The  fibres  of  which  they  are 
composed  all  enter  or  emerge  from  the  white  medullary  centre  of  the  cerebellum. 

The  middle  peduncle  is  much  the  largest  of  the  three,  and  has  already  been 
described  on  pp.  486  and  501.  It  is  formed  by  the  transverse  fibres  of  the  pons, 
and  it  enters  the  cerebellar  hemisphere  on  the  outer  aspect  of  the  other  two 
peduncles.  The  lips  of  the  anterior  part  of  the  great  horizontal  fissure  are 
separated  widely  from  each  other  to  give  it  admission  (Fig.  409).  Within  the 
cereljellar  hemisphere  its  fibres  are  distributed  in  two  great  bundles.  Of  these, 
one,  composed  of  the  upper  transverse  fibres  of  the  pons,  radiates  out  in  the  lower 
part  of  the  hemisphere ;  whilst  the  other,  consisting  of  the  lower  transverse  fibres 
of  the  pons,  spreads  out  in  the  upper  part  of  the  hemisphere. 

The  inferior  peduncle  is  simply  the  restiform  body  of  the  medulla.  After 
leaving  the  medulla  it  ascends  for  a  short  distance  on  the  dorsal  surface  of  the 
pons  and  then  turns  sharply  backwards,  to  enter  the  cerebellum  between  the  other 
two  peduncles. 

The  superior  peduncle,  as  it  issues  from  the  cerebellum,  lies  close  to  the  inner 
side  of  the  middle  peduncle  (Fig.  409).  Its  further  course  upwards  on  the  dorsum. 
of  the  pons  to  the  inferior  quadrigeminal  body  lias  been  previously  described  (pp. 
486  and  503). 

Connexions  established  by  the  Peduncular  Fibres.— The  fibres  of  the  middle 
peduncle  are  both  afferent  and  efferent.  The  connexions  which  they  establish  in  the 
pons  are  described  on  p.  501.  The  efferent  fibres  arise  from  cells  in  the  gray  cortex  of  the 
lateral  hemisphere  (also  probably  to  some  small  extent  in  the  cortex  of  the  vermis),  and 
end  in  connexion  with  the  cells  of  the  nucleus  pontis,  and  likewise  in  the  tegmental  part 
of  the  pons.  The  afferent  fibres,  arising  in  the  pons,  end  in  the  gray  cortex  of  the  lateral 
hemisphere  of  the  cerebellum,  and  perhaps  also  in  the  cortex  of  the  worm. 

The  inferior  peduncle  is  also  composed  of  afferent  and  efferent  fibres  (see  p.  496)  ;  only 
the  more  important  connexions  which  these  establish  in  the  cerebellum  can  be  touched  on 
here.  The  principal  afferent  strand  is  the  direct  cerebellar  tract.  The  fibres  of  this 
strand  end  in  the  cortex  of  the  superior  worm  on  both  sides  of  the  mesial  plane,  but 
chiefly  on  the  opposite  side.     The  cerehello-olivary  fibres  are  also  probably  afferent.     It 


THE  CEREBELLAIl  PEDUNCLES.  511 

appears  that  thoy  end  iu  connexion  with  cells  in  the  cortex  of  both  the  worm  and  hemi- 
sphere, and  also  cells  in  the  nucleus  deutatus.  The  numerous  arcudte  fibres,  which  enter 
the  inferior  peduncle  establish  connexions  with  cells  in  the  cortex  of  the  lateral  hemisphere 
and  of  the  worm. 

The  superior  peduncle  is  an  eflferent  tract.  The  majority  of  its  fibres  come  from 
the  cells  of  the  nucleus  dentatus,  whilst  a  small  proportion  appear  to  come  from  the  cere- 
bellar cortex.  According  to  Risien  Russell,  the  fibres  which  form  the  dorsal  edge  of  the 
band  come  from  the  opposite  side  of  the  cerebellum  and  cross  the  mesial  plane  to  join  the 
peduncle. 

Our  knowledge  of  the  connexions  of  the  peduncles  of  the  cerebellum  has  been  greatly 
extended  by  Ferrier  and  Aldren  Turner ;  and  the  account  which  is  given  above,  and  also  at 
p.  501,  is  lai'gely  derived  from  their  memoir  on  this  subject. 

Commissural  and  Association  Fibres. — In  addition  to  those  fibres  of  the  white 
medullary  centre  which  belong  to  the  system  of  peduncles,  there  are  others  which  have 
exclusively  cerebellar  connexions.  Thus  the  vai'ious  folia  are  bound  together  by  numerous 
association  fibres,  which  pass  from  one  folium  into  anotlier  around  the  bottom  of  the  inter- 
vening fissure.  Tracts  of  transversely-directed  commissural  fibres  cross  the  mesial  plane 
in  the  white  centre  of  the  vermis,  connecting  corresponding  parts  of  opposite  sides.  These, 
in  some  measure,  are  analogous  to  the  corpug  callosum  of  the  cerebrum.  The  roof  nuclei 
are  also  closely  bound  by  connecting  fibres  with  the  cortex. 

Medullary  Vela. — The  medullary  vela  are  closely  associated  with  the  cerebellar 
peduncles.  They  consist  of  two  thin  laminte  of  white  matter,  which  are  projected 
out  from  the  white  central  core  of  the  cerebellum. 

The  superior  medullary  velum  is  described  on  p.  486.  Laterally,  it  is  continuous 
with  the  dorsal  edges  of  the  superior  cerebellar  peduncles ;  whilst,  interiorly,  it 
is  prolonged  downwards  and  backwards  under  the  lingula  and  the  central  lobule  of 
the  superior  worm,  to  become  continuous  with  the  central  white  matter  or  corpus 
trapezoides  of  the  worm. 

The  inferior  medullary  velum  is  more  complicated  in  its  connexions.  It  presents 
much  the  same  relations  to  the  nodule  of  the  inferior  vermiform  process  that  the 
superior  velum  presents  to  the  lingula  of  the  superior  vermiform  process.  It  is  a 
wide  thin  lamina  of  white  matter — so  thin  that  it  is  translucent — which  is  pro- 
longed out  from  the  white  centre  of  the  cerebellum  above  the  nodule.  From  the 
nodule  it  stretches  outwards  to  the  flocculus  on  each  side,  thereby  bringing  these 
three  small  portions  of  the  cerebellum  into  association  with  each  other  (Fig.  409). 
Where  it  issues  from  the  white  matter  of  the  cerebellum  it  is  in  contact  with  the 
superior  medullary  velum,  but,  as  the  two  laminte  are  traced  forwards,  they 
diverge  from  each  other.  The  superior  velum  is  carried  upwards  between  the 
two  superior  cerebellar  peduncles,  whilst  the  inferior  medullary  velum  is  curved 
forwards  and  then  downwards  round  the  nodule,  and  ends  at  a  variable  point  in 
a  free,  slightly  thickened,  crescentic  edge.  The  cavity  of  the  fourth  ventricle 
is  carried  backwards  into  the  cerebellum  between  the  two  vela,  which  thus  form 
a  peaked  and  tent-like  root  for  it. 

Relation  of  the  Tract  of  Gowers  to  the  Superior  Medullary  Velum. — The 

ascending  tract  of  Gowers  has  been  noticed  in  connexion  with  the  latei'al  column  of  the 
cord  (p.  469).  The  fibres  which  compose  it  are  carried  upwards  through  the  foi-matio 
reticvdaris  grisea  of  the  medulla  and  the  corresponding  part  of  the  tegmental  portion  of 
the  pons.  In  this  part  of  its  course  the  fibres  are  scattered  and  do  not  form  a  compact 
strand.  Reaching  the  upper  end  of  the  pons  the  tract  turns  backwards,  enters  the 
superior  medullary  velum,  and  proceeds  downwards  in  it  into  the  cerebellum. 

Roof  of  the  Fourth  Ventricle. — In  its  upper  part  the  roof  of  the  fourth 
ventricle  is  formed  by  the  superior  medullary  velum  as  it  stretches  across  between 
the  two  superior  cerebellar  peduncles,  and  also,  to  some  extent,  by  the  approximation 
of  these  peduncles  themselves  as  they  approach  the  mesencephalon. 

In  its  lower  part  the  roof  of  the  ventricle  is  exceedingly  thin  and  is  not  all 
formed  of  nervous  matter.  The  inferior  medullary  velum  enters  into  its  formation, 
and,  where  this  fails,  the  epithelial  lining  of  the  cavity,  supported  by  pia  mater,  is 
carried  downwards  towards  the  lower  boundaries  of  the  floor  of  the  ventricle.  At 
the  lowest  part  of  the  calamus  scriptorius,  and  also  along  each  lateral  boundary  of 


512 


THE  NEEVOUS  SYSTEM. 


the  floor,  a  thin  lamina  of  white  matter  is  carried  for  a  short  distance  over  the 
epithelial  roof.  The  small  semilunar  lamina  which  stretches  across  between  the 
lower  parts  of  the  two  clavfe  at  the  calamus  scriptorius  and  overhangs  the  opening 


Fornix 
Foramen  of  Jlonro      ^ 

Septum  lucidum ,  X, 


Genu  of  corpus 
callosum  / 


Declive 


Anterior  commissure 

Corpus  mammillare' 
Lamina  cinerea  ' 


Optic  nerve 


Tuber 
valvnlse 


Pyramid 


Pituitary  b 

Tuber  cinereum 

Tliird  nerve 


■    Uvula 
Central  lobule 


Fig.  412.- 


Pons 
Valve  of  Vieussens 

Ventricle  IV.  \    ,     Module 

Medulla  choroid  plexus  in  ventricle  IV. 

-Mesial  Section  through  the  Corpus  Callosum,  the  Mesencephalon,  the  Pons,  Medulla, 

AND  Cerebellum. 
ShoT\-ing  the  third  and  fourth  ventricles  joined  liy  the  aqueduct  of  Sylvius. 


of  the  central  canal  is  termed  the  obex  (Fig.  391,  p.  487).  The  lamina  in  connexion 
with  the  lateral  boundary  of  the  ventricular  floor  is  more  extensive,  and  is  called 
the  ligula  (Figs.  388  and  390).  It  begins  on  the  clava  and  passes  upwards  over  the 
cuneate  tubercle  to  the  restiform  body.  On  the  outer  surface  of  the  restiform  body 
it  turns  outwards  so  as  to  bound  the  lateral  recess  of  the  ventricle  below,  and  in  some 
cases  it  may  be  seen  to  become  continuous  around  the  extremity  of  the  lateral 
recess  with  the  inferior  medullary  velum. 

A  short  distance  above  the  calamus  scriptorius  there  is,  in  the  mesial  plane,  an 
opening  in  the  epithelial  and  pial  roof  of  the  ventricle,  by  which  the  cavity  of  the 
ventricle  communicates  with  the  subarachnoid  space.  This  opening  is  termed  the 
foramen  of  Majendie.  There  is  also  an  aperture  of  a  similar  nature  in  the  epithelial 
and  pial  roof  at  the  extremity  of  each  lateral  recess. 

Two  choroid  plexuses,  or  highly  vascular  infoldings  of  the  pia  mater,  invaginate 
the  lower  part  of  the  roof  of  the  fourth  ventricle.  These  are  placed  one  on  either 
side  of  the  mesial  plane,  and,  although  they  appear  to  lie  within  the  cavity,  they 
are  in  reality  excluded  from  it  by  the  epithelial  lining  of  the  ventricle,  which  covers 
over  and  is  adapted  to  every  sinuosity  on  their  surface. 

Two  lateral  offshoots  from  these  longitudinal  choroid  plexuses  proceed  outwards, 
and  protrude  in  a  similar  manner  into  the  lateral  recesses. 


Minute  Structure  of  a  Cerebellar  Folium. 

A  cerebellar  folium  is  composed  of  a  central  core  of  white  matter,  covered  by  a  layer 
of  gray  matter.  The  gray  cortex  is  arranged  in  two  very  evident  layers,  viz.  a  superficial 
molecular  layer  and  a  subjacent  rust-coloured  granular  layer.  Between  these  strata  a 
single  layer  of  large  cells,  termed  the  cells  of  Purkinje,  are  disposed  in  the  form  of  a 
very  nearly  continuous  sheet.  The  cells  of  Purkinje  constitute  the  most  characteristic, 
and  probably  the  most  essential,  constituents  of  the  cerebellar  cortex. 

The  cells  of  Purkinje  are  most  numerous  on  the  summit  of  the  folium.  At  the 
bottom  of  the  sulci  which  intervene  between  the  folia  they  become  fewer  in  number,  and, 
therefore,  looser  in  their  arrangement.     Each  consists  of  a  large  flask-shaped  or  pyriform 


MINUTE  STEUCTUEE  OF  A  CEEEBELLAE  FOLIUM. 


5U 


cell  body,  the  narrow  end  of  which  projects  into  the  molecular  layer,  whilst  the  thicker, 
deeper  end  rests  on  the  granular  layer.  From  the  latter  arises  a  single  axon,  which  passes 
into  the  granular  layer  and  presents  the  peculiarity  of  almost  immediately  assuming  its 
medullary  sheath.  From  this  axon  a  few  collateral  branches  soon  arise,  which,  taking  a 
recurrent  coui^se,  enter  the  niolecular  layer,  to  end  in  connexion  with  certain  of  the 
adjoining  cells  of  Purkinje.     They  would  seem  to  have  the  function  of  binding  together 

adjacent     cells,     and     thus  

enabling  them  to  carry  on 
their  operations  in  harmony 
with  each  other. 

The  dendritic  processes 
spring  from  the  narrow  end 
of  the  cell  either  in  the  form 
of  one  or  perhaps  two  stout 
stalks.  These  ascend  into 
the  molecular  layer,  branch- 
ing and  rebranching  until 
an  aborescent  arrangement 
of  extraordinary  richness  and 
extent  results.  The  den- 
dritic branches  extend 
throughout  the  entire 
thickness  of  the  molecular 
layer,  and  the  branching 
takes  place  in  one  plane  only, 
viz.  in  a  plane  which  is  trans- 
verse to  the  long  axis  of  the 
folium.  Consequently,  it  is 
only  when  transvei*se  sections 
are  made  through  a  folium 
that  the  full  dendritic  effect 
is  obtained  ;  in  sections 
made  parallel  to  the  long 
axis  of  the  folium  the  cells 
are  seen  in  profile,  and  are 
observed  to  occupy  qmte  a 
narrow  area  (Fig.  414).  The 
bi'anching  of  the  dendrites 
of  a  cell  of  Purkinje  may, 
therefore,  be  compared  to 
that  which  takes  place  in 
the  case  of  a  fniit-tree 
which  is    trained  against  a 


Fig.  41.3.- 


Cerebellar  Folium 


Transverse  Section  through 
(after  Kolliker). 

Treated  by  the  Golgi  method. 

P.       Axon  of  cell  of  Piukinje. 

F.       Moss  fibres. 

K  and  K^.    Fibres  from  white  core  of  folium  ending  in  molecular  layer  in 

connexion  with  the  dendrites  of  the  cells  of  Purkinje. 
M.      Small  cell  of  the  molecular  layer. 
GR.    Granule  cell. 

GR^.  Axons  of  granule  cells  in  molecular  layer  cut  transversely. 
Ml.     Basket-cells. 

Basket-work  around  the  cells  of  Purkinje. 

Neuroglial  cell. 

Axon  of  an  association  cell. 


ZK. 

GL. 


wall. 

In  the  molecular  layer  x. 
the  cells  are  not  particularly 

numei-ous,  and  of  these  the  most  characteristic  are  the  basket -cells  which  lie  in  the 
deeper  part  of  the  layer.  In  addition  to  numerous  dendrites  the  basket-cell  gives  off  an 
axon  which  runs  transversely,  as  regards  the  long  axis  of  the  folium,  between  the  planes 
of  adjacent  dendritic  arborisations  of  the  cells  of  Purkinje.  At  first  very  fine  these  axons 
gradually  become  coarse  and  thick,  and  at  intervals  they  give  oft"  collaterals  which  run 
towards  the  bodies  of  the  cells  of  Purkinje.  Reaching  these,  they  break  up  into  an 
enormous  number  of  fine  terminal  branches,  which  enclose  the  cells  of  Purkinje,  as  well 
as  the  short  non-medullated  portions  of  their  axons,  in  a  close  basket-work  of  fine 
filaments. 

The  granular  layer  is,  for  the  most  part,  composed  of  large  numbers  of  small 
granule-like  bodies  closely  packed  together.  Each  of  these  possesses  a  somewhat  large 
nucleus,  with  a  very  small  amount  of  surrounding  protoplasm.  From  the  cell  body  three 
or  four,  or  perhaps  five,  dendrites  and  one  axon  proceed.  The  dendrites  are  short  and 
radiate  out  from  different  aspects  of  the  cell  body.  They  end  in  tufts  of  claw-like  twigs, 
which  either  embrace  or  are  otherwise  in  contact  with  neighbouring  granule  cells.  The 
whole  multitude  of  granule  cells,  therefore,  are  brought  into  intimate  connexion  with 
each  other.  The  axon  passes  into  the  molecular  layer,  in  which  it  ends  at  a  varying 
37 


514 


THE  NEEVOUS  SYSTEM. 


distance  from  the  surface  by  dividing  into  two  branches.  These  diverge  so  sharply  from 
each  other  that  they  almost  form  a  right  angle  with  the  parent  stem,  and  they  run 
parallel  to  the  long  axis  of  the  folium,  threading  their  way  between  the  branches  of  the 
various  dendritic  planes  of  the  cells  of  Purkinje  and  entering  into  contact  association  with 
them.  When  the  great  number  of  granule  cells  is  borne  in  mind,  and  the  fact  that  each 
sends  an  axon  into  the  molecular  layer,  the  important  part  which  these  fibres,  with  their 
longitudinal  branches,  take  in  building  up  the  molecular  layer  will  be  understood.  They 
are  found  pervading  its  entire  thickness — from  the  surface  down  to  the  bodies  of  the  cells 
of  Purkinje. 

Near  the  cells  of  Purkinje  a  few  scattered  cells  are  seen  in  the  granular  layer  of  a 

different  kind.  These  are  much  larger  than  the 
ordinary  granule  cells,  and  are  probably  of  the 
nature  of  association  cells.  They  are  stellate  in 
form,  and  have  numerous  long  branching  dendrites 
and  an  axon  which  divides  up  in  the  granular 
layer  to  a  singular  extent. 

The  white  centre  of  the  folium  becomes 
thinner  as  it  approaches  the  summit.  This  is  due 
to  the  fibres  which  compose  it  gradually  entering 
the  gray  matter  on  the  surface.  These  fibres 
are  of  three  kinds,  viz.  :  (1)  axons  of  the  cells 
of  Purkinje;  (2)  fibres  which  apparently  end 
in  the  granular  layer ;  and  (3)  fibres  which 
end  in  the  molecular  layer. 

The  axons  of  the  cells  of  Purkinje  are 
medullated  fibres  which,  entering  the  white 
centre  of  the  folimn,  form  a  not  inconsiderable 
part  of  it. 

The  fibres  which  end  in  the  granular  layer 
are  called  moss-fibres.  This  name  is  applied  to 
them  because,  in  the  granular  layer,  they 
present  at  certain  points  moss-like  thickenings, 
from  which  short  rough  twigs  proceed. 

The  fibres  which  proceed  into  the  molecular 
layer  give  off"  few  or  perhaps  no  branches  as  they 
traverse  the  granular  layer.  In  the  deeper  part 
of  the  molecular  layer  they  break  up  into 
varicose  branches,  which  twine  around  the 
primary  and  secondary  stems  of  the  Purkinje  dendrites. 

Entering  into  the  constitution  of  the  molecular  layer  are  the  following  elements  :  (1) 
dendrites  of  the  cells  of  Purkinje;  (2)  basket-cells  and  somewhat  smaller  cells  nearer  the 
surface ;  (3)  axons  of  the  granule  cells,  with  their  longitudinally  arx'anged  branches ;  (4) 
the  terminations  of  certain  fibres  from  the  white  core  of  the  folium,  which  end  in  contact 
with  the  Purkinje  dendrites. 

In  the  granular  layer  are  found:  (1)  granule  cells;  (2)  larger  stellate  association 
cells;  (3)  axons  of  the  cells  of  Purkinje;  (4)  moss-fibres  ;  (5)  fibres  traversing  this  layer, 
to  end  in  the  molecular  layer. 


Fig.  414. — Section  through  the  Molecular 
AND  Granular  Layers  in  the  Long  Axis 
OF  a  Cerebellar  Folium  (after  Kolliker). 

Treated  by  the  Golgi  method. 

P.      Cell  of  Purkuije. 

GR.  Granule  cells. 

N.     Axon  of  a  granule  cell. 

N^.    Axons  of  granule  cells  iu  molecular  layer. 


THE  DEEP  CONNEXIONS  OF  THE  CRANIAL  NERVES  ATTACHED  TO  THE 

MEDULLA  AND  PONS. 

There  are  twelve  pairs  of  cranial  nerves,  of  which  the  lower  eight  are  attached 
to  the  medulla  and  pons  Varolii.  From  above  downwards  these  are  named  the 
fifth  or  trigeminal,  the  sixth  or  abducent,  the  seventh  or  facial,  the  eighth  or 
auditory,  the  ninth  or  glossopharyngeal,  the  tenth  or  vagus,  the  eleventh  or  spinal 
accessory,  and  the  twelfth  or  hypoglossal.  The  liypoglossal,  the  spinal  accessory, 
the  greater  part  of  the  facial,  the  abducent,  and  the  motor  root  of  tlie  trigeminal 
are  efferent  nerves;  the  aiiditory,  the  pars  intermedia  of  the  facial,  and  the  sensory 
root  of  the  trigeminal  are  purely  afferent  nerves ;  whilst  the  vagus  and  the  glosso- 
pharyngeal are  composed  of  both  efferent  and  afferent  fibres.  In  all  cases  afferent 
fibres  arise  from  ganglionic  cells  placed  outside  the  brain  and  penetrate  the  brain- 
stem, to  end  iu  connexion  with  the  cells  of  certain  nuclei  of  termination.     Efferent 


THE  DEEP  CONNEXIONS  OF  THE  CKANIAL  NERVES.         515 

fibres,  on  the  other  hand,  take  origin  within  the  brain  as  the  axons  of  cells  which 
are  grouped  together  in  certain  places  in  the  form  of  nuclei  of  origin. 

Nuclei  of  Origin,  or  Motor  Nuclei. — In  the  spinal  cord  the  nuclei  of  origin  are 
represented  by  elongated  columns  of  cells  which  run  more  or  less  continuously  in 
the  anterior  horn  of  gray  matter  of  successive  cord-segments,  and  from  these  the  series 
of  efferent  anterior  nerve-roots  take  origin.  In  the  medulla  and  pons  the  nuclei  of 
origin,  or,  in  other  words,  the  motor  nuclei  of  the  individual  nerves  become,  for  the 
most  part,  discontinuous,  and  are  represented  by  certain  isolated  clumps  of  compact 
gray  matter,  in  which  are  placed  the  clusters  of  cells  from  which  the  fibres  of  the 
efferent  nerves  arise.  The  nucleus  ambiguus,  however,  which  consists  of  a  column  of 
cells  from  which  root  fibres  of  the  medullary  part  of  the  spinal  accessory,  of  the  vagus, 
and  possibly  also  of  the  glossopharyngeal  are  derived,  is  an  exception  to  this  rule. 
At  the  decussation  of  the  pyramids,  the  anterior  horn  of  gray  matter  of  the  cord  is 
broken  up  by  the  intercrossing  bundles  into  a  detached  head  and  a  basal  part  which 
remains  in  relation  with  the  ventro-lateral  aspect  of  the  central  canal.  Certain 
of  the  efferent  or  motor  nuclei  of  the  medulla  and  pons  lie  in  the  line  of  the  basal 
portion  of  the  ventral  horn  of  gray  matter  of  the  spinal  cord,  and  thus  close  to 
the  mesial  plane.  These  are  termed  mesial  nuclei  of  origin,  and  are  met  with  at 
different  levels  in  the  brain-stem.  This  group  comprises  the  hypoglossal  nucleus, 
the  dorsal  motor  nucleus  of  the  vago-glossopharyngeal  nerve,  the  abducent  nucleus 
(and,  in  the  mesencephalon,  the  trochlear  nuclevis  and  the  oculo-motor  nucleus). 
Other  motor  nuclei  of  origin  are  present  in  the  form  of  isolated  clumps  or  columns 
of  gray  matter,  which  lie  at  different  levels  in  the  medulla  and  pons  in  the  line  of 
the  detached  head  of  the  anterior  horn  of  gray  matter.  They  are  the  nucleus 
ambiguus  of  the  spinal  accessory,  the  vagus  and  glossopharyngeal,  the  facial 
nucleus,  and  the  nucleus  of  the  motor  root  of  the  trigeminal  nerve.  From  their 
position  in  the  tegmental  substance  of  the  medulla  and  pons  they  constitute  a  group 
to  which  the  name  of  lateral  motor  nuclei  is  applied. 

The  different  nuclei  of  origin  of  the  efferent  fibres  which  belong  to  the  various 
cranial  nerves,  both  mesial  and  lateral,  are  connected  with  the  motor  area  of  the 
cerebral  cortex  by  fibres  from  the  pyramidal  tract,  which  enter  the  nuclei  and  end 
in  connexion  with  their  cells. 

Nuclei  of  Termination. — In  the  brain  the  nuclei  of  termination  are  likewise 
discontinuous,  and  are  represented  by  more  or  less  isolated  clusters  or  columns  of 
cells.  Unlike  the  motor  nuclei,  however,  these  nuclei  show  no  regular  or  definite 
position  within  the  medulla  and  pons.  Some  are  found  in  the  gray  matter  which 
surrounds  the  central  canal,  and  in  its  continuation  upwards  as  the  gray  matter  in 
the  floor  of  the  fourth  ventricle  ;  others  are  placed  in  the  tegmental  substance  ;  whilst 
two  actually  lie  on  the  surface  of  the  brain- stem,  viz.  the  lateral  and  ventral  nuclei 
of  the  cochlear  or  outer  division  of  the  auditory  nerve. 

The  axons  of  the  cells  of  the  nuclei  of  termination  enter  the  reticular  formation 
of  the  tegmental  substance  as  arcuate  fibres,  and,  crossing  the  mesial  plane,  are 
carried  upwards  in  the  tegmental  substance  of  the  opposite  side  to  establish  direct 
connexions  with  the  optic  thalamus  and  indirect  connexions  with  the  cerebral 
cortex. 

Hypoglossal  Nerve  (nervus  hypoglossus). — ^The  nucleus  of  origin  of  the  hypo- 
glossal nerve,  the  motor  nerve  of  the  tongue,  lies  in  the  substance  of  the  medulla 
oblongata.  It  is  composed  of  several  groups  of  large  multipolar  cells,  which  closely 
resemble  the  cells  in  the  ventral  horn  of  gray  matter  in  the  spinal  cord,  and  is 
pervaded  by  an  intricate  network  of  fine  fibrils.  In  form  it  is  elongated  and 
rod-like,  and  in  length  it  is  somewhere  about  18  mm.  It  extends  from  a  point 
immediately  above  the  decussation  of  the  pyramids  up  to  the  level  of  the  stride 
acusticse.  The  lower  portion  of  the  nucleus  is  thus  placed  in  the  closed  part  of  the 
medulla  (Fig.  397,  p.  493),  whilst  its  upper  part  is  situated  in  the  open  part  of  the 
medulla  (Fig  402,  p.  497).  The  former  lies  in  that  part  of  the  central  gray  matter 
which  is  continuous  with  the  basal  part  of  the  ventral  horn  of  gray  matter  of  the 
cord.  It  is  thus  placed  on  the  ventral  and  lateral  aspect  of  the  central  canal, 
close  to  the  mesial  plane  and  the  corresponding  nucleus  of  the  opposite  side.  The 
upper  part  of  the  nucleus  occupies  a  position  in  the  gray  matter  on  the  floor  of 


516 


THE  NERVOUS  SYSTEM. 


the  fourth  ventricle,  subjacent  to  the  inner  part  of  the  surface  area,  which  has  been 
described  under  the  name  of  the  trigonum  hypoglossi.  Within  the  nucleus  the 
axons  of  the  cells  arrange  themselves  in  converging  bundles  of  fine  fibres,  which 
come  together  and  leave  the  ventral  aspect  of  the  nucleus  as  the  fasciculi  of  the 
nerve.  The  nerve  bundles  thus  formed  traverse  the  entire  antero-posterior  thickness 
of  the  medulla  between  the  formatio  reticularis  grisea  and  the  formatio  reticularis 
alba,  and  emerge  on  the  surface  in  linear  order  at  the  bottom  of  the  furrow  between 
the  olivary  eminence  and  the  pyramid.  In  the  substance  of  the  medulla  the  root- 
bundles  of  the  hypoglossal  pass  between  the  main  inferior  olivary  nucleus  and  the 
mesial  accessory  olivary  nucleus,  and  many  of  them  on  their  way  to  the  surface 
pierce  the  ventral  lamina  of  the  main  olivary  nucleus. 

No  decussation  between  the  nerves  of  opposite  sides  takes  place  in  the  medulla,  but 
commissural  fibres  pass  between  the  two  nuclei  (Kolliker).  Further,  numerous  fibres  from 
the  opposite  pyramidal  tract  enter  the  nucleus  and  end  in  connexion  with  its  cells.  The 
nucleus  is  thus  brought  into  connexion  with  the  motor  area  of  the  opposite  side  of  the 
cerebral  cortex. 

Spinal  Accessory  Nerve  (nervus  accessorius). — The  spinal  accessory  is  likewise 
a  motor  nerve,  and  it  is  generally  described  as  consisting  of  a  spinal  and  a  medullary 
or  accessory  part. 


Column  of  GoU 


Column  of  Burdach 


POST.ROO 


ANTROG, 


Fig.  415. — Diagram  of  the  Spinal 
Origin  of  the  Spinal  Accessory 
Nerve  (after  Bruce). 


Entering 
— posterior  nerve 
root 


Substantia 
gelatinosa 
Rolandi 


Emerging 
■ — fascicle  of  spinal 

accessory  nerve 

Fibres  of  origin 
— of  spinal 

accessory 

Emerging 
— anterior  nerve 

root 


Fig.  416. — Section  through  the  Upper  Part  of  the 

Cervical  Region  of  the  Cord  (Orang), 

Showing  the  origin  of  the  spinal  part  of  the  spinal  accessory 

nerve. 


The  spinal  part  of  the  nerve  emerges  by  a  series  of  roots  which  issue  from  the 
surface  of  the  lateral  column  of  the  upper  part  of  the  cord  as  low  down  as  the  fifth 
cervical  nerve.  These  take  origin  in  a  column  of  cells  situated  in  the  anterior  horn 
of  gray  matter  of  the  cord  close  to  its  lateral  margin,  and  immediately  behind  the 
nerve-cells  which  give  rise  to  the  fibres  of  the  anterior  roots  of  the  upper  five 
cervical  nerves.  The  cells  of  the  accessory  nucleus  are  large,  multipolar,  and  in 
every  respect  similar  to  the  motor  cells  of  the  spinal  nerves.  The  axons  from  these 
cells  leave  the  dorsal  aspect  of  the  nucleus  in  converging  groups  to  form  the  root- 
bundles  of  the  nerve.  These,  in  the  first  place,  proceed  straight  backwards  in  the 
anterior  horn  of  gray  matter.  Reaching  the  bay  between  the  two  horns  of  gray 
matter,  they  turn  sharply  outwards  into  the  white  matter  and  traverse  the  lateral 
column  to  gain  their  points  of  exit  from  the  cord.  At  the  decussation  of  the 
pyramids,  root-bundles,  which  join  the  spinal  accessory  nerve,  are  seen  to  proceed 
from  the  detached  head  of  the  anterior  horn  of  gray  matter. 

The  medullary  part  of  the  spinal  accessory  nerve  has  its  nucleus  of  origin  in  the 
medulla ;  and  its  root-bundles,  as  they  proceed  outwards  from  this,  can  be  distin- 


THE  DEEP  CONNEXIONS  OF  THE  CEANIAL  NEEVES.  517 

guished  by  the  tact  that  they  pursue  a  course  on  the  ventral  side  of  the  spinal  root 
of  the  trigeminal  nerve,  whereas  the  vagus  roots,  with  which  they  are  apt  to  be 
confused,  pass  through  or  lie  on  the  dorsal  aspect  of  the  trigeminal  root  (Kolliker). 
The  nucleus  of  origin  of  the  medullary  part  of  the  accessory  nerve  is  formed  by  the 
same  column  of  cells  which  constitutes  the  nucleus  ambiguus,  and  which,  at  a  higher 
level,  gives  motor  fibres  to  the  vagus  and  glossopharyngeal  nerves. 

The  part  of  the  spinal  accessory  nerve  which  takes  origin  in  the  spinal  cord  supplies  the 
stemo -mastoid  and  tiapeziiis  muscles.  The  medullary  or  accessor}-  portion  joins  the  vagiis,  and 
through  the  external  and  recurrent  lar^Tigeal  nerves  it  supplies  the  muscles  of  the  larj-nx.  The 
portion  of  the  nucleus  ambiguus  from  which  it  arises  has  tlius  been  termed  the  laryngeal  nucleus 
(Edinger). 

Collaterals  and  fibres  of  the  opposite  pyramidal  tract  end  in  connexion  with  the  cells  of 
origin  of  the  accessory  nerve,  and  thus  bring  its  nucleus  into  connexion  with  the  motor  area  of 
the  cerebral  cortex.  Fibres  also  from  the  posterior  roots  of  the  spinal  nerves  (afferent  or  sensory 
fibres)  end  in  the  nucleus. 

Va^s  and  Glossopharyngeal  Nerves  (nervus  vagus,  nervus  glossopharyu- 
geus). — These  nerves  present  similar  connexions  with  the  brain,  and  they  may 
therefore  be  studied  together.  The  greater  part  of  both  nerves  is  composed  of 
afferent  fibres,  which  arise  outside  the  brain-stem  from  ganglionic  cells  placed  in 
relation  to  the  nerve-trunks.  Both  nerves  likewise  possess  motor  or  efferent  fibres, 
which  spring  from  two  special  nuclei  of  origin  situated  within  the  medulla  and 
termed  respectively  the  dorsal  motor  nucleus  and  the  nucleus  ambiguus.  The  afferent 
ganglionic  fibres  of  the  vagus  and  glossopharyngeal  enter  the  brain  by  a  series  of 
roots  which  penetrate  the  medulla  along  the  outer  or  ventral  side  of  the  restiform 
body.  Within  the  medulla  they  separate  into  two  sets,  viz.  a  series  of  bundles 
(chiefly  composed  of  vagus  fibres),  which  end  in  the  dorsal  nucleus  of  termination 
of  the  vagus  and  glossopharyngeal  nerves,  and  another  series  of  bundles  (chiefly 
composed  of  glossopharyngeal  fibres),  which  join  a  conspicuous  longitudinal  tract 
of  fibres  called  the  fasciculus  solitarius. 

The  dorsal  nucleus  (Figs.  398,  p.  495,  and  402,  p.  497)  of  the  vagus  and  glosso- 
pharyngeal nerves  is  mixed,  and  contains  both  motor  cells  which  give  origin  to 
efferent  fibres  and  cells  around  which  afterent  fibres  of  the  vagus,  and  possibly  also 
of  the  glossopharyngeal  nerve,  break  up  into  terminal  arborisations.  It  very  nearly 
equals  in  length  the  nucleus  of  the  hypoglossal  nerve,  with  which  it  is  closely 
related.  Above,  it  reaches  as  high  as  the  strife  acusticse,  whilst  below  its  lower  end 
falls  sUghtly  short  of  that  of  the  hypoglossal  nucleus.  In  specimens  stained  by 
the  "Weigert-Pal  method  the  two  nuclei  offer  a  marked  contrast.  The  hypoglossal 
nucleus  presents  a  dark  hue,  owing  to  the  enormous  numbers  of  fine  fibres  which 
twine  in  and  out  amidst  its  cells ;  the  vago-glossopharyngeal  dorsal  nucleus  is  pale 
from  the  scarcity  of  such  fibres  within  it.  In  the  closed  part  of  the  medulla  the 
dorsal  vago-glossopharyngeal  nucleus  lies  in  the  central  gray  matter  immediately 
behind  the  hypoglossal  nucleus,  and  upon  the  lateral  aspect  of  the  central  canal ; 
in  the  open  part  of  the  medulla  it  lies  in  the  gray  matter  of  the  floor  of  the  fourth 
ventricle,  immediately  to  the  outer  side  of  the  hypoglossal  nucleus  and  subjacent 
to  the  surface  area  termed  the  trigonum  vagi. 

The  ceUs  in  the  portion  of  the  dorsal  nucleus  which  acts  as  a  nucleus  of 
termination  are  spindle-shaped  in  form  and  similar  to  those  found  in  the  posterior 
horn  of  gray  matter  in  the  cord.  In  connexion  with  these  cells,  the  greater 
number  of  the  afferent  fibres  of  the  vagus  nerve,  and  a  small  proportion  of  the 
afterent  fibres  of  the  glossopharyngeal  nerve  end  in  fine  terminal  arborisations. 
A  small  part  of  the  upper  portion  of  the  nucleus  may  be  said  to  belong  to  the 
glosso-pharyngeal  nerve  aud  the  remainder  of  the  nucleus  to  the  vagus  nerve. 

The  cells  which  constitute  the  dorsal  motor  or  efferent  nucleus  as  seen  in  trans- 
verse section  appear  in  a  more  or  less  compact  cluster,  which  lies  immediately  to 
the  outer  side  of  the  hypoglossal  nucleus.  These  cells,  although  very  conspicuous, 
are  not  so  large  as  those  in  the  hypoglossal  nucleus,  nor  as  those  in  the  anterior 
horn  of  gray  matter  of  the  cord ;  nor  do  they  stain  so  deeply. 

The  fasciculus  soUtarius  (Figs.  397,  p.  493 ;  398,  p.  495  ;  and  402,  p.  497)  is  a 
round  bundle  of  longitudinal  fibres  which  forms  a  very  conspicuous  object  in  trans- 
verse sections  through  the  meduUa.  It  begins  at  the  upper  limit  of  the  medulla, 
37  « 


518 


THE  NEEVOUS  SYSTEM. 


and  can  be  traced  downwards  through  its  whole  length.  Its  precise  point  of 
termination  is  not  known,  but  it  is  believed  that  it  is  carried  for  some  distance 
downwards  into  the  upper  part  of  the  cord,  viz.  to  the  level  of  the  fourth  cervical 
nerve,  according  to  Kolhker.  The  relations  of  the  fasciculus  solitarius  are  not 
the  same  in  all  parts  of  its  course.  It  lies  immediately  to  the  outer  side  of  the 
dorsal  vago-glossopharyngeal  nucleus;  but  whereas  in  the  upper  part  of  the  medulla 
it  is  situated  somewhat  on  the  ventral  side  of  that  nucleus,  in  the  lower  closed  part 
of  the  medulla  it  is  placed  on  its  dorsal  aspect.     Throughout  its  entire  length  it  is 

intimately  associ- 
ated with  a  column 
of  gelatinous  gray 
substance  which 
constitutes  the 
nucleus  of  ter- 
mination in  which 
its  fibres  end. 
When  traced  from 
above  downwards, 
the  solitary  tract 
is  observed  to  be- 
come gradually 
smaller  from  the 
loss  of  fibres  which 
it  thus  sustains. 
The  great  bulk  of 
the  solitary  tract 
is  formed  of  fibres 
derived  from  the 
gl  0  s  s  op  hary  n  geal 
nerve ;  only  a  few 
of  the  afferent 
fibres  of  the  vagus 
enter  it.  As  the 
fibres  of  the  two 
nerves  join  the 
tract  they  im- 
mediately turn 
downwards,  and  at 
different  levels 
come  to  an  end  in 
the  associated 
gelatinous  gray 
nucleus. 

As  the  root- 
bundles  of  the vagus 
and  the  glosso- 
phai'yngeal    nerves 

traverse  the  substance  of  the  medulla  in  a  backward  and  inward  direction  to  reach  the 
fasciculus  solitarius  and  the  dorsal  nucleus  of  termination,  they  pass  through  the  spinal 
root  of  the  trigeminal  nerve  and  the  substantia  gelatinosa  liolandi  associated  with  it. 
The  term  ascending  root  is  sometimes  applied  to  the  fasciculus  sohtarius ;  but  as  this 
conveys  an  altogether  false  conception  of  its  character  it  should  be  discarded.  The 
axons  of  the  nucleus  of  termination  and  of  the  nucleus  of  the  fascicidus  solitarius 
form  central  connexions  with  other  parts  of  the  brain,  but  these  have  not  as  yet  been 
completely  elucidated. 

The  dorsal  efferent  nucleus  gives  off  fibres  which  join  the  afferent  fibres  of  the 
vago-glossopharyngeal  rootlets  as  they  traverse  the  medulla,  and  mixing  with 
them  they  X->ass  along  the  same  path  to  emerge  from  the  medulla. 

The  nucleus  ambiguus  (Figs.  398,  p.  495,  and  402,  p.  497)  also  gives  origin  to 


Fig.  417. — Diagram,  showing  the  brain  connexions   of  the   vagus,  glosso- 
pharyngeal, auditory,  facial,  abducent,  and  trigeminal  nerves. 


THE  DEEP  CONNEXIONS  OF  THE  CKANIAL  NERVES.         519 

motor  or  efferent  fibres  which  join  the  vagus  and  glossopharyngeal  nerves.  The 
cells  which  compose  it  are  large,  multipolar,  and  similar  in  every  respect  to  the 
large  cells  in  the  ventral  horn  of  gray  matter  of  the  spinal  cord.  These  cells  are 
arranged  in  a  slender  column  which  is  best  developed  in  the  upper  open  part  of  the 
medulla.  Here  the  nucleus  can  easily  be  detected  in  transverse  sections  as  a  small 
area  of  compact  gray  matter  which  lies  in  the  formatio  reticularis  grisea,  midway 
between  the  dorsal  accessory  olive  and  the  substantia  gelatinosa  Eolaudi.  It  there- 
fore lies  more  deeply  in  the  substance  of  the  medulla  than  the  mixed  dorsal  vago- 
glossopharyngeal nucleus.  Kolliker  states  that  it  can  be  traced  downwards  as  low 
as  the  level  of  the  decussation  of  the  fillet,  and  upwards  as  high  as  the  place  of 
entrance  of  the  cochlear  root  of  the  auditory  nerve.  From  its  dorsal  aspect  the 
axons  of  the  cells  proceed,  and  in  the  first  instance  they  pass  backwards  towards 
the  floor  of  the  lourth  ventricle ;  then,  bending  suddenly  outwards  and  forwards, 
they  join  the  afferent  roots  of  the  vagus  and  possibly  also  of  the  glossopharyngeal 
nerves,  and  emerge  from  the  brain  in  company  with  these. 

Upon  anatomical  grounds  it  might  be  questioned  whether  the  ghjssopharyngeal  nerve  contains 
any  efferent  fibres.  It  gives  off,  it  is  true,  one  motor  branch,  viz.  to  the  stylo-pharjTigeus 
muscle,  but  there  are  paths  by  means  of  which  these  fibres  might  enter  the  nerve  other  than  by 
coming  directly  from  the  motor  nuclei,  which  have  been  described  in  connexion  with  the  vago- 
glossopharyngeal nerve-roots. 

There  is,  further,  some  ground  for  the  belief  that  all  the  fibres  of  the  glossoi^liaryngeal  pass 
into  the  fasciculus  solitarius.  In  a  very  instructive  case  descril^ed  by  Alexander  Bruce  in  which 
the  glossopharyngeal  was  destroyed  in  the  jugular  foramen  by  the  pressure  of  a  tumour,  no 
degenerated  fibres  could  be  traced  beyond  the  fasciculus  solitarius. 

Auditory  Nerve  (nervus  acusticus). — -This  is  a  large  nerve  which  joins  the  brain 
at  the  lower  border  of  the  pons  Varolii  and  on  the  ventral  aspect  of  the  restiform 
body.  It  is  an  afferent  nerve,  and  its  fibres  spring  from  bipolar  ganglionic  cells 
either  within  or  in  the  immediate  neighbourhood  of  the  labyrinth  or  internal  ear 
(see  section  dealing  with  the  organs  of  sense).  Eeaching  the  brain  the  auditory 
nerve  divides  into  two  parts,  viz.  the  nervus  cochlearis  and  the  nervus  vestibularis, 
which  present  totally  ditlerent  connexions  and  apparently  exercise  absolutely 
distinct  functions.  In  their  further  course  these  two  divisions  de\'iate  from  each 
other  so  as  to  embrace  the  restiform  body — the  vestibular  part  entering  the  pons 
on  the  inner  or  mesial  aspect  of  the  restiform  body,  whilst  the  cochlear  part 
sweeps  round  its  outer  surface.  Special  nuclei  of  termination  require  to  be 
studied  in  connexion  with  each  part  of  the  nerve. 

The  cochlear  nerve  is  composed  of  finer  fibres  than  the  vestibular  nerve, 
and  these  acquire  their  medullary  sheaths  at  a  later  period.  It  is  the  true  nerve 
of  hearing,  and  its  fibres  end  in  a  ganglion  which  lies  in  intimate  relation  to  the 
restiform  body,  and  which  may  be  described  as  consisting  of  two  parts.  Of  these 
one,  called  the  tuberculum  acusticum  or  the  lateral  cochlear  nucleus,  is  a  pyriform 
mass  which  is  placed  on  the  outer  aspect  of  the  restiform  body — between  it  and 
the  flocculus  of  the  cerebellum.  The  second  part,  termed  the  ventral  cochlear 
nucleus,  does  not  extend  so  low  down  as  the  tuberculum  acusticum.  It  is  a  wedge- 
shaped  nuclear  mass  which  is  placed  on  the  ventral  aspect  of  the  restiform  body  in 
the  interval  between  the  cochlear  and  vestibular  divisions  of  the  auditory  nerve, 
after  they  have  separated  from  each  other.  The  fibres  of  the  cochlear  nerve  enter 
these  two  ganglia  and  end  around  the  cells  in  terminal  arborisations,  which  are 
finer,  closer,  and  more  intricate  than  those  met  with  in  any  other  nerve  nucleus  in 
the  brain. 

The  vestibular  nerve  enters  the  brain  at  a  slightly  higher  level  than  the  cochlear 
nerve  and  on  the  mesial  aspect  of  the  ventral  cochlear  nucleus.  It  forces  its  way 
backwards  through  the  pons  between  the  restiform  body,  which  lies  on  its  outer 
side,  and  the  spinal  root  of  the  fifth  nerve,  which  is  placed  on  its  inner  side.  Its 
fibres  come  to  an  end  in  three  nuclei  of  termination,  which  are  situated  in  the 
dorsal  part  of  the  pons  and  medulla,  viz.  (1)  the  principal  nucleus  or  dorsal  nucleus; 
(2)  the  nucleus  of  the  descending  root ;  and  (3)  the  nucleus  of  Deiters. 

The  principal  nucleus  (Figs.  403,  p.  500,  and  418,  p.  o'lO)  is  a  large  diffuse 
nuclear  mass,  which  lies  in  the  floor  of  the  fourth  ventricle  subjacent  to  the  surface 
37  h 


520 


THE  NERVOUS  SYSTEM. 


CORPORA  QUADRIGEMINA 


district  known  as  the  area  acustica  (Fig.  391,  p.  487).  It  is  situated,  therefore,  in 
both  the  pons  and  the  medulla  to  the  outer  side  of  the  fovea  superior  and  the  fovea 
inferior.     In  transverse  section  it  is  prismatic  in  outline,  and  crossing  the  surface 

of  its  upper  or  pontine  part 
immediately  under  the 
ependyma  of  the  ventricle 
are  the  strife  acusticse. 

When  the  nervus  vesti- 
bularis, as  it  traverses  the 
brain,  reaches  the  inner 
aspect  of  the  dorsal  portion 
of  the  restiform  body,  a 
very  large  proportion  of 
its  fibres  turn  vertically 
downwards  in  separate 
bundles  and  form  the  de- 
scending root  of  the  vesti- 
bular nerve  (Figs.  398,  p. 
495;  402,  p.  497;  403, 
p.  500;  418,  p.  520). 
This  proceeds  through  the 
lower  part  of  the  pons  into 
the  medulla,  in  which  it 
may  be  traced  as  far  as 
the  level  of  the  decussa- 
tion of  the  fillet.  As- 
sociated with  the  descend- 
ing root  there  is  a  column 
of  gray  matter,  with  nerve- 
cells  strewn  sparsely 
throughout  it.  This  is 
the  nucleus  of  the  de- 
scending root,  and  the 
fibres  end  in  fine  arborisa- 
tions around  these  nerve- 
cells. 

The  fibres  of  the  vestibular  nerve  likewise  end  in  the  nucleus  of  Deiters.  This 
aucleus  is  composed  of  a  number  of  large  and  conspicuous  multipolar  nerve-cells, 
which  are  scattered  amidst  the  bundles  of  the  upper  part  of  the  descending  root 
of  the  vestibular  nerve.  As  it  is  traced  upwards  into  the  pons  the  nucleus 
gradually  inclines  backwards,  and  finally  it  occupies  a  place  in  the  lateral  wall  of 
the  fourth  ventricle.  It  attains  its  greatest  development  at  the  level  of  the 
emerging  part  of  the  facial  nerve,  and  this  upper  part  is  sometimes  termed  the 
nucleus  of  Becliterew. 


Fig. 


418. — Central  CoNNfiXiONs   of   the   Cochlear  and  Vestibular 
Divisions  op  the  Auditory  Nerve. 

(Diagram  founded  on  drawings  by  Edinger  and  Ferrier  and  Turner.) 


Central  Connexions  of  the  Cochlear  Nerve.— The  cochlear  nerve  is  brought 
into  connexion  with  the  inferior  quadrigeniinal  body,  and  the  corpus  geniculatum 
internum  of  the  opposite  side  by  the  fibres  of  the  corpus  trapezoides  and  the  lateral 
fillet.  But  this  connexion  is  not  direct ;  the  chain  is  composed  of  several  separate  links 
or  neurons  superimposed  one  over  the  other. 

The  fibres  of  the  cochlear  nerve  end  in  the  ventral  cochlear  nucleus  and  in  the  tuber- 
culum  acusticum.  From  the  cells  of  these  nuclei  two  tracts  arise,  viz.  a  ventral  tract, 
composed  of  the  fibres  of  the  corpus  trapezoides,  and  a  dorsal  tract,  which  is  represented 
by  the  stria;  aciisticte. 

The  corpus  trapezoides  (Figs.  418  and  419)  is  formed  of  the  axons  of  the  cells  of  the 
ventral  cochlear  nucleus,  as  well  as  certain  of  the  axons  of  the  cells  of  tuberculum 
acusticum.  In  the  midst  of  the  corpus  trapezoides  are  lodged  large  cells  which  are  known 
as  the  nucleus  trapezoideus,  and  these  give  off  axons  which  join  the  strand  with  which 
they  are  associated.  Further,  the  superior  olive  forms  an  important  internode  in  the 
path  of  the  corpus  trapezoides.     Many  of  the  fibres  of  the  corpus  trapezoides  end  in  this 


THE  DEEP  CONNEXIONS  OF  THE  CEANIAL  NERVES.  521 

internode,  whilst  othei's  are  added  to  the  tract  from  the  cells  of  that  nuclear  mass.  So 
constituted,  the  trapezial  fibres  cross  the  mesial  plane  and  decussate  with  the  correspond- 
ing fibres  of  the  opposite  side.  Reaching  the  opposite  superior  olivary  nucleus  a  further 
interchange  of  fibres  takes  place,  and  almost  inmiediately  after  this  the  strand  turns 
upwards  and  becomes  the  lateral  fillet  (Figs.  405,  p.  .503 ;  406,  p.  504).  But  still 
another  nucleus  is  interposed  in  its  path,  viz.  the  nucleus  of  the  lateral  fillet.  Here 
some  fibres  are  dropped,  whilst  from  the  nuclear  cells  others  are  acquired,  and  the  lateral 
fillet  then  proceeds  onwards  without  further  interruption  until  it  reaches  the  inferior 
quadrigeminal  body  and  the  corpus  geniculatum  internum,  in  which  its  fibres  end.  It  is 
probable,  however,  that  some  likewise  extend  into  the  superior  quadrigeminal  body. 

But  the  latei-al  fillet  also  includes  the  fibres  of  the  striae  acusticse  of  the  opposite 
side.  These  fibres  arise  from  the  cells  of  the  tuberculum  acusticum,  and  arrange  them- 
selves in  the  conspicuous  bundles  which  sweep  round  the  dorsal  aspect  of  the  resti- 
form  body  and  proceed  inwards  across  the  floor  of  the  fourth  ventricle,  immediately 
beneath  the  ependyma  (Fig.  391,  p.  487).  Reaching  the  middle  line  they  dip  forwards 
into  the  substance  of  the  medulla,  and,  crossing  the  mesial  plane,  thev  join  the  lateral 
fillet. 

It  is  well  to  remember  that  the  connexion  between  the  terminal  cochlear  nuclei  and 
the  inferior  quadrigeminal  body  is  not  altogether  with  that  of  the  opposite  side,  as  the 
foregoing  description  and  the  diagram  (Fig.  418)  might  lead  one  to  infer.  A  few  fibres 
pass  directly  to  the  inferior  quadrigeminal  body  of  the  same  side,  but  none  to  the  corre- 
sponding corpus  geniculatum  internum  :  the  connexion  with  the  latter  is  entirely  crossed 
(Ferrier  and  Turner). 

From  the  corpus  geniculatum  internum  there  proceeds  a  tract  to  the  gray  cortex  of 
the  superior  convolution  of  the  temporal  lobe.  The  whole  nervous  apparatus  is  thus 
linked  on  to  the  cerebral  cortex,  and  the  succession  of  neurons  which  build  up  the  entire 
chain  are  therefore  :  ( 1 )  the  bipolar  cells  of  the  ganglion  spirale ;  (2)  the  neurons  of  the 
terminal  cochlear  nviclei ;  (3)  the  neurons  of  the  superior  olive  and  the  nucleus  of  the 
lateral  fillet ;  (4)  the  neurons  of  the  corpus  geniculatum  internum. 

It  must  be  bpme  in  mind  that  all  the  axons  of  the  cells  of  the  superior  olive  do  not 
join  the  trapezoid  strand.  Many  leave  its  dorsal  aspect  and  pass  backwards  in  a  group 
called  the  pedicle  of  the  superior  olive,  to  end  in  the  nucleus  of  the  sixth  nerve,  and, 
through  the  posterior  longitudinal  bundle,  in  the  nuclei  of  the  fourth  and  third  nerves. 
In  this  way  the  organ  of  hearing  is  brought  into  connexion  with  the  nuclei,  which  preside 
over  the  movements  of  the  eyeballs  (Figs.  403,  p.  500,  and  420,  p.  523). 

Central  Connexions  of  the  Vestibular  Nerve. — Although  the  central  con- 
nexions of  the  vestibular  nerve  have  been  closely  studied  by  many  observers,  they  are 
still  very  far  from  being  fully  understood.  The  principal  nucleus  and  the  nucleus  of 
Deiters  both  stand  in  intimate  relation  with  the  superior  vermis  of  the  cerebellum ;  and 
in  consideration  of  the  fact  that  the  vestibular  nerve  is  the  nerve  of  equilibration,  this 
is  an  important  and  significant  circumstance.  The  strand  which  establishes  this  con- 
nexion has  been  termed  by  Edinger  "the  direct  sensory  cerebellar  tract,"  and  in  all 
probability  it  is  an  efferent  tract  from  the  cerebellum.  Its  fibres  arise  to  a  large  extent 
in  the  cerebellar  roof  nuclei  of  the  opposite  side,  and,  crossing  the  mesial  plane,  they 
sweep  forwards  around  the  outer  side  of  the  superior  cerebellar  peduncle  as  it  emerges 
from  the  cerebellum  to  end  in  the  nucleus  of  Deiters,  the  chief  vestibular  nucleus,  and 
very  possibly  also  in  the  terminal  sensory  nuclei  of  certain  other  cranial  nerves,  such  as 
the  trigeminal,  vagus,  and  glossopharyngeal. 

Until  the  precise  nature  of  the  nucleus  of  Deiters  is  discovei'ed,  the  exact  character 
of  the  central  connexions  of  the  vestibular  nerve  will  remain  more  or  less  obscure.  It 
cannot  be  regarded  as  a  nucleus  specially  given  over  to  the  vestibular  nerve.  Composed 
of  large  cells  scattered  amidst  the  bundles  of  the  upper  part  of  the  descending  root  of  the 
vestibular  nerve,  it  only  becomes  a  compact  nucleus  above  the  level  of  that  nerve,  viz. 
at  the  point  where  the  restiform  body  turns  backwai-ds  into  the  cerebellum,  or,  in 
other  woi-ds,  at  the  level  of  the  emerging  facial  nerve  and  the  lower  end  of  the  abducent 
nucleus.  Here,  in  the  outer  part  of  the  floor  of  the  fourth  ventricle,  its  cells  are  gathered 
together  in  a  crowded  mass.  Deiters  himself  considered  that  this  nucleus  should  be 
regarded  as  an  internode  between  the  cerebellum  and  the  spinal  cord,  and  Ferrier  and 
Turner  have  brought  forward  strong  evidence  in  support  of  this  view.  Klimoff  attaches 
a  very  high  importance  to  the  direct  "  sensory  "  tract  of  Edinger.  From  his  description 
it  would  appear  that  he  regai-ds  it  as  the  only  cerebellar  efferent  tract  which  takes  a 
downward  direction.  He  believes,  further,  that  the  axons  of  the  cells  of  Deiters  form  the 
anterior  marginal   tract   of    Lowenthal    (tractus    vestibulo-spinalis  of    Monakow),    which 


oz 


2v> 


THE  NEEVOUS  SYSTEM. 


descends  in  the  antero-lateral  column  of  the  cord  as  far  as  the  lumbar  region.  It  is 
supposed  that  the  fibres  of  this  tract  end  in  the  cord  in  arborescent  terminations  around 
the  motor  cells  in  the  ventral  horn  of  gray  matter. 

From  what  has  been  said  it  must  be  apparent  that  the  nucleus  of  Deiters  plays  a  most 
important  part  in  connexion  with  the  maintenance  of  the  equilibrium  of  the  body  and 
the  co-ordination  of  its  muscular  movements.  Thus  it  constitutes  an  internode  in  the 
path  of  those  fibres  which  connect  the  cortex  and  roof  nuclei  of  the  cerebellum  with  the 
motor  apparatus  of  the  spinal  cord ;  it  receives  fibres  through  the  vestibular  nerve  from 
the  labyrinth  of  the  ear ;  and  it  sends  fibres  into  the  posterior  longitudinal  bundle, 
through  which  it  in  all  probability  exercises  some  iniiuence  over  the  nuclei  of  the  ocular 
nerves. 

Opinion  is  also  divided  as  to  the  composition  and  nature  of  the  so-called  descending 
root  of  the  vestibular  nerve.  After  division  of  the  eighth  nerve,  Ferrier  and  Turner  were 
unable  to  detect  any  degeneration  in  this  root,  and  they  therefore  are  inclined  to  call  in 
question  its  direct  continuity  with  the  nerve.  They  consider  that  in  all  probability  it 
forms  an  internuncial  connexion  between  the  nucleus  of  Deiters  and  the  cuneate  nucleus, 
in  which  Bruce  has  seen  its  lower  end  to  terminate. 


Fig.  419. — Section  thkough  the  Pons  Varolii  of  the  Orang, 

Showing  the  nucleus  and  intrapontine  course  of  the  facial  nerve.     The  left  side  of  the  drawing  is  taken 
from  a  section  at  a  slightlv  lower  level  than  the  section  from  which  the  right  side  is  taken. 


1.  Ascending  part  of  facial  nerve. 

2.  Posterior  longitudinal  bundle. 

3.  Descending  root  of  eighth  nerve. 

4.  Radicular  fibres  of  facial  nerve. 

5.  Restiforin  body. 
C.  Facial  nucleus. 

7.  .Spinal  root  of  fifth  nerve. 

8.  Ve.stibular  nerve. 

9.  Superior  olive. 

10.  Fillet. 

11.  Pyramidal  tract. 

12.  Transver.se  fibres  of  pons. 


B 

1.  Ascending  part  of  facial  nerve. 

2.  Emergent  portion  of  facial  nerve. 

3.  Restiform  body. 

4.  Nucleus  of  sixth  nerve. 

5.  Sixth  Nerve. 

6.  Emergent  part  of  facial  nerve. 

7.  Peduncle  of  superior  olive. 

8.  Superior  olive. 

9.  Corpus  trapezoides. 

10.  Facial  nerve. 

11.  Sixth  nerve. 

12.  Pyramidal  tract. 

13.  Transverse  fibres  of  pons. 


Facial  Nerve  (nervus  i'acialis)  (Figs.  419  and  420). — The  facial  nerve  is  com- 
posed of  two  distinct  parts,  viz.  a  large  efferent  or  motor  portion,  the  facial  nerve 
proper,  and  a  small  efferent  sensory  portion  termed  the  pars  intermedia  of  Wrisberg. 
The  facial  nerve  emerges  from  the  brain  at  the  lower  border  of  the  pons,  immediately 
in  front  and  to  the  inner  side  of  the  auditory  nerve,  whilst  the  pars  intermedia 
sinks  into  the  upper  part  of  the  medulla  between  the  facial  and  auditory  nerves. 
The  three  nerves,  therefore,  lie  in  intimate  relation  with  each  other,  where  they 
are  attached  to  the  surface  of  the  brain,  and  they  pass  in  company  into  the  internal 
auditory  meatus. 


THE  DEEP  CONNEXIONS  OF  THE  CRANIAL  NERVES. 


523 


The  nucleus  of  origin  of  the  facial  nerve  is  an  oval  mass  of  gray  matter,  about 
five  mm.  in  length,  and  containing  numerous  groups  of  large  multipolar  cells.  It 
is  sunk  deeply  in  the  dorsal  or  tegmental  part  of  the  lower  portion  of  the  pons 
Varolii,  and  is  placed  close  to  the  inner  side  of  the  spinal  root  of  the  fifth  nerve. 
When  transverse  sections  are  made  through  the  brain-stem,  the  facial  nucleus  is 
encountered  the  moment  the  boundary  line  between  the  medulla  and  pons  is 
passed,  and  the  region  immediately  above  the  inferior  olivary  nucleus  is  reached. 
At  first  it  lies  so  deeply  in  the  tegmentum  of  the  pons  that  it  actually  rests  upon 
the  dorsal  aspect  of  the  corpus  trapezoides ;  but  a  little  farther  up  the  superior 
olive  comes  into  view,  and  insinuates  itself  between  the  facial  nucleus  and  the 
trapezial  fibres.  The  upper  part  of  the  nucleus  is  in  this  way  tilted  somewhat 
backwards,  and  thus  comes  to  lie  on  the  dorsal  and  outer  aspect  of  the  superior 
olive. 

The  facial  nucleus  is  situated  close  to  the  place  where  the  nerve  emerges  from 
the  brain,  but  the  nerve  does  not  at  once  pass  to  this  point  of  exit.  It  pursues 
a  long  and  devious  path  within  the  pons  before  it  finally  reaches  the  surface. 
This  intrapontine  part  of  the  nerve  may  be  divided  into  three  parts,  viz. :  (1)  a 
radicular  part,  (2)  an  ascending  portion,  and  (3)  an  emergent  part. 

The  radicular  part  of  the  facial  nerve  (Fig.  420)  is  composed  of  a  large  number 
of  fine  loosely-arranged  bundles  of  fibres,  which  issue  from  the  outer  and  dorsal 
aspect  of  the  nucleus  and  proceed  backwards  and  slightly  inwards  through  the 
pons.  Reaching  the  floor  of  the  fourth  ventricle  they  curve  inwards,  and  the 
bundles  which  lie  highest  up  sweep  over  the  outer  and  dorsal  aspect  of  the  lower 
part  of  the  nucleus  of  the  sixth  nerve.  Close  to  the  mesial  plane  they  turn 
sharply  upwards  and  are  collected  into  a  single  solid  nerve-bundle,  which  consti- 
tutes the  ascending  part  of  the  facial  nerve  (Figs.  419  and  420).  This  proceeds 
vertically  upwards  immediately 
beneath  the  ependyma  of  the 
ventricular  floor,  on  the  dorsal 
aspect  of  the  posterior  longitudinal 
bundle,  and  along  the  inner  side 
of  the  sixth  or  abducent  nucleus 
for  a  distance  of  about  five  milli- 
metres. Suddenly  the  nerve  bends 
outwards  at  a  right  angle,  and 
curves  a  second  time  over  the 
dorsal  aspect  of  the  sixth  or 
abducent  nucleus.  The  nerve  now 
passes  straight  to  the  place  of  exit 
from  the  brain,  and  this  part  of 
the  intrapontine  trunk  may  be 
termed  the  emergent  portion  (Figs. 
419  and  420).  The  facial  nerve 
thus  forms  a  curved  loop  over  the 
dorsal  aspect  of  the  abducent 
nucleus.  The  emergent  part  of 
the  nerve  takes  an  oblique  course 
through  the  pons  to  reach  the 
surface.  It  inclines  outwards  and 
downwards  as  it  proceeds  towards 
the  ventral  aspect  of  the  pons, 
and  on  its  way  it  passes  between 
its  own  nucleus  and  the  spinal  root 
of  the  fifth  nerve. 


Fig.  420.- 


-DlAGRAM  OF  THE  INTRAPONTINE  CoURSE  PURS0ED 

BY  THE  Facial  Nerve. 


Entering  tlie  facial  nucleus,  and  ending  in  fine  terminal  arborisations  around  its  cells,  are 
many  fibres  from  the  opposite  pyramidal  tract ;  fibres  from  the  sj^inal  root  of  the  fifth  nerve ; 
fibres  from  the  corpus  trapezoides,  etc.  The  nucleus  is  thus  brought  into  connexion  with  the 
motor  area  of  the  cerebral  cortex,  with  the  trigeminal  nerve  or  sensory  nerve  of  the  face,  and 
with  the  auditory  nerve,  etc. 


524  THE  NEEVOUS  SYSTEM. 

The  fibres  of  the  pars  intermedia  of  Wrisberg  arise  from  the  cells  of  the  geni- 
culate ganglion  of  the  facial  nerve.  These,  like  the  cells  of  a  spinal  ganglion,  are 
unipolar,  the  single  process  in  each  case  dividing  into  a  peripheral  and  a  central 
branch.  The  group  of  peripheral  fibres  represent  the  chorda  tympani  branch  of 
the  facial  nerve,  whilst  the  central  fibres  form  the  pars  intermedia.  The  latter 
penetrate  the  brain,  and,  passing  either  through  or  on  the  dorsal  side  of  the  spinal 
root  of  the  fifth  nerve,  they  finally  reach  the  upper  part  of  the  column  of  gray 
matter  in  connexion  with  the  fasciculus  solitarius,  and  in  this  they  end.  The  pars 
intermedia  presents,  therefore,  the  same  terminal  connexions  within  the  brain  as 
the  glossopharyngeal  nerve. 

Efferent  secretory  fibres  are  also  described  as  being  present  in  the  pars  intermedia.  These 
are  said  to  spring  from  cells  wliich  constitute  a  salivary  nucleus  placed  in  the  pons  on  the  dorsal 
aspect  of  the  facial  nucleus. 

Abducent  or  Sixth  Nerve  (nervus  abducens)  (Eigs.  419  and  420).- — This  is  a 
small  motor  nerve  which  emerges  from  the  brain  at  the  lower  border  of  the  pons 
on  the  outer  side  of  the  pyramid  of  the  medulla.  It  is  the  nerve  of  supply  to 
the  external  rectus  muscle  of  the  eyeball.  Its  nucleus  of  origin  is  a  small 
spherical  mass  of  gray  matter,  containing  large  multipolar  cells,  which  lies  in 
the  dorsal  part  of  the  tegmental  portion  of  the  pons,  close  to  the  mesial  plane  and 
immediately  subjacent  to  the  gray  matter  of  the  floor  of  the  fourth  ventricle.  Its 
position  can  be  easily  indicated  on  the  ventricular  floor,  seeing  that  it  is  placed 
subjacent  to  the  emenentia  teres  and  immediately  above  the  level  of  the  striae 
acusticas.  Its  peculiar  and  intimate  relation  to  the  intrapontine  portion  of  the 
facial  nerve  has  already  been  indicated.  It  lies  on  the  ventral  aspect  of,  and  within 
the  concavity  formed  by,  the  two  limbs  of  the  loop  of  that  nerve. 

The  axons  of  the  multipolar  cells  of  this  nucleus  emerge  from  the  inner  aspect 
of  the  nucleus  in  the  form  of  several  bundles,  which  proceed  through  the  whole 
antero-posterior  thickness  of  the  pons  towards  the  place  of  exit.  As  they  pass 
forwards  they  incline  downwards  and  slightly  outwards.  In  the  tegmental  part 
of  the  pons  they  proceed  forwards  on  the  inner  side  of  the  superior  olive,  whilst  in 
the  ventral  part  of  the  pons  they  keep  for  the  most  part  to  the  outer  side  of 
the  pyramidal  bundles,  although  several  of  the  nerve  fasciculi  pierce  these  on 
their  way  to  the  surface. 

It  would  appear  probable  that  certain  of  the  axons  of  the  cells  of  the  abducent  nucleus  enter 
the  posterior  longitudinal  fasciculus  and  proceed  upwards  in  it  to  join  the  third  or  oculo- 
motor nerve  of  the  oj^posite  side.  Further  mention  of  these  will  be  made  later  on.  Fibres 
and  collaterals  from  the  pyramidal  tract  of  the  opposite  side  enter  the  nucleus,  and,  ending 
around  the  cells,  bring  the  nucleus  into  connexion  with  the  motor  area  of  the  cerebral  cortex. 
The  pedicle  of  the  superior  olive  ends  partly  within  the  nucleus  of  the  abducent  nerve  (p.  621). 

Trigeminal  or  Fifth  Nerve  (nervus  trigeminus). — The  trigeminal  nerve  strikes 
its  roots  deeply  into  the  brain  and  establishes  a  connexion  with  it  which  extends 
from  the  upper  part  of  the  mesencephalon  above  to  the  level  of  the  second  cervical 
nerve  below.  No  other  cranial  nerve  presents  so  extensive  a  connexion  (Fig. 
417,  p.  518).  It  is  composed  of  two  roots — a  large  afferent  or  sensory  root  and 
a  small  efferent  or  motor  root.  Both  roots  appear  close  together  on  the  surface 
of  the  pons,  rather  nearer  its  upper  border  than  its  lower  border,  and  in  the  same 
line  as  the  facial  and  auditory  nerves. 

The  sensory  root  of  the  fifth  nerve  is  composed  of  fibres  which  arise  outside  the 
brain  from  the  cells  of  the  G-asserian  ganglion.  They  end  within  the  brain  in  two 
nuclei  of  termination.  One  of  these  is  situated  in  the  pons  and  is  termed  the 
sensory  nucleus  of  the  trigeminal  nerve,  and  tlie  other  is  a  long  column  of 
gray  matter  which  is  directly  continuous  below  with  the  substantia  gelatinosa 
Eolandi  of  the  spinal  cord. 

The  sensory  nucleus  (Fig.  421)  is  an  oval  mass  of  gray  matter  which  is  placed 
half-way  up  the  pons  in  the  outer  part  of  its  tegmental  portion.  It  lies  close  to 
the  outer  surface  of  the  pons  and  immediately  subjacent  to  the  ventral  submerged 
margin  of  the  superior  cerebellar  peduncle.  It  is  directly  continuous  with  the 
substantia  gelatinosa  Eolandi,  and  may  be  regarded  as  being  merely  the  enlarged 
upper  end  of  that  column  of  gray  matter. 


THE  DEEP  CONNEXIONS  OP  THE  CEANIAL  NEKVES. 


525 


The  fibres  of  the  sensory  root  of  the  fifth  nerve,  on  reaching  the  sensory  nucleus, 
divide  in  a  manner  similar  to  the  fibres  of  the  entering  posterior  roots  of  the  spinal 
nerves  into  a  system  of  ascending  and  descending  branches  (Fig.  417,  p.  518). 
The  ascending  fibres  are  short,  and  almost  immediately  enter  the  sensory  nucleus 
and  end  within  it ;  the  descending  fibres  turn  sharply  downwards  and  form  the  spinal 
root  (tractus  spinalis :  the  ascending  root  of  many  text-books).  This  root  descends 
on  the  outer  side  of  the  column  of  gray  matter  formed  by  the  substantia  gelatinosa 
Eolandi,  which  constitutes  its  terminal  nucleus.  Fibres  constantly  leave  it  to 
enter  the  nucleus,  so  that  tlie  lower  it  gets  the  smaller  does  the  spinal  root  become 
until,  in  the  upper  part  of  the  spinal  cord,  about  the  level  of  the  first  or  second 
spinal  nerve,  it  disappears  altogether. 


Superior  cerebellar  peduncle 

Mesencephalic  root  of  the  fifth  nerve 

Alotor  nucleus  of  the  fifth  nerve 
>[otor  root  of  tlie  fifth  nerve-— 

Sensory  nucleus  of  the  fifth  nerve 

Superior  olive  - 

Sensory  root  of  ^^ 

fifth  nerve^  ^  ~  _ 


Middle  peduncle 
of  cerebellum 


Superior  medullary  velum 
or  valve  of  Vieussens 


Floor  of 
s-entricle  IV'. 

Posterior 

longitudinal 

fasciculus 


Format  io 
reticularis 


Fig.  421. 


-Section  through  the  Pons  Varolii  of  the  Orang,  at  the  Le\t;l  of  the  Nuclei 
OF  the  Trigeminal  Nerve. 


The  large  spinal  root  of  the  fifth  nerve  is  a  conspicuous  object  in  sections  through  the 
pons  and  medulla.  In  the  former  it  traverses  the  tegmental  part,  first,  between  the 
emei-gent  part  of  the  facial  nerve  and  the  vestibular  nerve  ;  and  then  lower  down,  between 
the  restiform  body  and  the  nucleus  of  the  facial  nerve  (Fig.  419,  A,  p.  522).  In  cross 
sections  it  presents  a  well-defined  semilunar  or  curved  pyriform  outline.  In  the  upper 
part  of  the  medulla  it  lies  on  the  ventral  aspect  of  the  restiform  body,  and  therefore 
nearer  to  the  surface  (Fig.  398,  p.  495).  Here  it  is  traversed  and  broken  up  into 
separate  bundles  by  the  cerebello-olivary  fibres  and  the  roots  of  the  glossopharyngeal  and 
vagus  nerves.  Finally,  it  comes  to  the  surface  and  its  fibres  are  spread  over  the  area  on 
the  side  of  the  medulla  known  as  the  tubercle  and  funiculus  of  Rolando  (Fig.  394, 
p.  492). 

The  small  motor  part  of  the  trigeminal  nerve  is  chiefly  distributed  to  the  muscles 
of  mastication,  and  derives  its  fibres  from  two  sources,  viz.  from  the  motor  nucleus 
and  from  the  mesencephalic  root  of  the  trigeminal  nerve. 

The  motor  nucleus  (Fig.  421)  lies  in  the  lateral  part  of  the  tegmental  portion  of 
the  pons,  close  to  the  inner  side  of  the  sensory  terminal  nucleus,  but  somewhat 


526  THE  NEEVOUS  SYSTEM. 

nearer  to  the  floor  of  the  fourth  ventricle.  It  is  not  placed  iu  the  exact  line  of  the 
facial  nucleus,  as  it  is  situated  somewhat  nearer  the  dorsal  aspect  of  the  pons ;  but, 
nevertheless,  it  may  be  considered  as  being  equivalent  in  this  region  to  the  detached 
head  of  the  anterior  horn  of  graj  matter  in  the  lower  part  of  the  medulla.  The 
cells  of  this  nucleus  are  large  and  multipolar,  and  their  axons  run  together  to  form 
the  greater  portion  of  the  motor  root  of  the  fifth  nerve. 

The  mesencephalic  root  takes  origin  in  the  mesencephalon  from  a  column  of 
large  loosely-arranged  cells  which  are  placed  in  the  extreme  lateral  part  of  the 
gray  matter  which  surrounds  the  Sylvian  aqueduct.  As  the  lower  end  of  this  column 
of  cells  reaches  the  pontine  part  of  the  floor  of  the  fourth  ventricle  it  becomes 
continuous  with  the  dark  cells  of  the  locus  coeruleus.  The  mesencephalic  root 
as  it  is  traced  downwards  gradually  gains  strength  by  the  addition  of  new  fibres, 
and  it  assumes  a  crescentic  form  in  transverse  section  (Figs.  430,  p.  535  ;  432,  p. 
537 ;  407,  p.  505  ;  406,  p.  504).  In  the  lower  part  of  the  mesencephalon  it  lies  on 
the  inner  side  of  the  superior  cerebellar  peduncle ;  and  the  fourth  nerve,  on  its  way 
to  the  surface,  runs  downwards  in  its  concavity  and  on  its  mesial  aspect.  In  the 
upper  part  of  the  pons,  it  continues  its  course  downwards  on  the  outer  and  deep 
aspect  of  the  gray  matter  which  forms  the  floor  of  the  fourth  ventricle,  and  here  it 
stands  in  relation  to  the  cells  of  the  locus  coeruleus.  Finally,  reaching  the  level  of 
the  nuclei  of  the  trigeminal  nerve,  the  fibres  of  the  mesencephalic  root  turn 
forwards  and  join  the  motor  part  of  the  trigeminal  nerve  (Fig.  421). 

S.  Eamon  y  Cajal  lias  shown  tliat  an  intimate  relationship  is  established  between  the 
mesencephalic  nucleus  and  the  principal  motor  nucleus  of  the  trigeminal  nerve.  Large  numbers 
of  collaterals  from  the  fibres  of  the  mesencephalic  root  enter  the  latter  nucleus  and  break  up  into 
close  networks  around  its  cells.  It  has  been  suggested  that  through  this  connexion  a  weak 
impulse  proceeding  from  the  higher  nucleus  may  be  transformed  within  the  lower  or  princijDal 
nucleus  into  a  powerful  excitation. 

(1)  It  is  not  known  to  what  parts  the  fibres  of  the  mesencephalic  root  go.  KoUiker  suggests 
that  they  sujjply  the  tensor  veli  palatini  and  the  tensor  tympani ;  perhaps,  also,  they  may  be  dis- 
tributed to  the  mylo-hyoid  and  the  anterior  belly  of  the  digastric.  (2)  Fibres  from  the  ojjposite 
pyramidal  tract  go  to  the  motor  nucleus  and  bring  it  into  connexion  with  the  motor  area  of  the 
cerebral  cortex.  (3)  By  degeneration  methods  the  root  of  the  fifth  nerve  has  been  traced  down  to 
the  level  of  the  second  cervical  nerve  (Ferrier  and  Turner).  (4)  The  axons  of  the  terminal  nuclei 
emerge  as  arcuate  fibres,  and,  proceeding  through  the  raphe,  assume  a  longitudinal  course  in  the 
tegmentum  of  the  opposite  side,  and  thus  establish  connexions  with  parts  higher  up  (tractus 
quinto-thalamicus).  (5)  Some  of  the  axons  of  the  cells  of  the  terminal  nucleus  enter  the  motor 
nucleus,  and  thus  establish  a  simple  reflex  apparatus. 

The  Development  of  the  Parts  derived  from  the  Ehombencephalon. 

A  general  sketch  of  the  development  of  the  me'dulla,  pons,  and  cerebellum  has  already 
been  given  (p.  476).  It  is  only  necessary,  therefore,  in  this  section  to  call  attention  to 
some  of  the  more  important  details  connected  with  the  pi'ocess. 

Medulla. — In  the  embryo  the  cervical  flexure  indicates  in  a  sharp  and  definite  manner 
the  point  of  junction  between  the  cord  and  the  brain  (Fig.  382,  p.  477).  In  the  early 
condition  of  the  rhombencephalon  the  calamus  scriptorius  extends  downwards  to  this  level, 
so  that,  in  the  first  instance,  there  is  no  part  of  the  medulla  which  corresponds  to  the 
closed  portion  present  in  the  adult.  The  lower  closed  part  of  the  medulla  makes  its 
appearance  at  a  later  period,  and  is  termed  by  His  the  intercalated  portion  (Schaltstlick). 

In  our  study  of  the  development  of  that  part  of  the  neural  tube  which  forms  the  spinal 
cord  we  have  recognised  two  thick  lateral  walls  connected  in  front  and  behind  by  narrow 
mid-ventral  and  mid-dorsal  laminse.  The  same  parts  are  seen  in  the  developing  medulla. 
Owing,  however,  to  the  expansion  of  the  cavity  in  this  portion  of  the  tube  the  mid-dorsal 
lamina  is  stretched  out  into  an  extensive  and  thin  epithelial  membrane  which  forms  the 
dorsal  wall  or  roof  of  the  ventricle  in  this  section  of  the  early  brain.  The  thick  lateral 
walls  have  also  fallen  away  from  each  other,  and  are  joined  in  front  by  the  narrow 
mid-ventral  lamina.  On  section,  therefore,  the  medullary  part  of  the  neural  tube  presents 
a  triangular  figure — the  base,  which  is  directed  backwards,  being  formed  by  the  thin 
epithelial  expansion  derived  from  the  mid-dorsal  lamina,  the  apex  by  the  narrow  mid- 
ventral  lamina,  and  the  sides  by  the  thick  lateral  walls  of  the  tube.  Further,  each  lateral 
wall  consists  of  an  alar  or  dorsal  and  a  basal  or  ventral  lamina.  Tliis  subdivision  is  more 
clearly  indicated  than  in  the  cord,  and  on  the  inner  surface  of  the  lateral  wall  a  strongly- 
marked  longitudinal  furrow  marks  the  line  of  junction  of  the  two  laminae.     The  histo- 


DEVELOPMENT  OF  THE  MEDULLA. 


527 


«f;*«/s/- 


logical  development  of  these  several  parts  of  the  wall  of  the  medullary  portion  of  the 
neural  tube  proceeds  in  a  manner  very  similar  to  that  already  detailed  in  the  case  of  the 
cord.  No  neuroblasts  are  formed  in  the  mid-ventral  and  mid-dorsal  laminse ;  the  entire 
neuroblastic  formation  is  confined  to  the  basal  and  alar  lamina;.  Within  the  basal  lamina, 
likewise,  are  collected  the  neuroblasts  which  form  the  nuclei  of  origin  of  the  effei-ent 
nerves  ;  whilst  within  the  alar  lamina  are  developed  the  neuroblasts  which  constitute  the 
nuclei  of  termination  for  the  fibres  of  the 
afferent  nerves. 

As  development  pi'oceeds,  the  two  laminae 
of  the  lateral  wall  fall  outwards  to  a  still 
greater  extent,  so  that  they  come  to  lie  very 
nearly  in  the  same  horizontal  plane.  In  this 
manner  their  originally  mesial  or  ventricular 
surfaces  come  to  form  the  floor  of  the  fourth 
ventricle.  Even  in  the  adult  the  groove, 
which  sepai-ates  the  basal  and  alar  laminae 
so  clearly  from  each  other  in  the  early  con- 
dition, is  more  or  less  distinctly  perceptible  on 
the  ventricular  floor.  It  is  represented  by  the 
fovea  inferior  and  by  the  fovea  superior. 
Between  these  depressions  and  the  mesial 
groove  on  the  floor  of  the  fully -developed 
fourth  ventricle  there  is  an  elongated  eleva- 
tion, which,  in  its  lower  part,  forms  the  tri- 
gonum  hypoglossi,  above  this  the  emenentia 
teres,  whilst  higher  up  it  is  continued  towards 
the  commencement  of  the  Sylvian  aqueduct. 
This  clearly-marked  and  bulging  mesial  strip 
of  the  ventricular  floor  corresponds  to  the 
basal  lamina,  whilst  the  part  of  the  floor  which 
lies  to  the  outer  side  of  it  and  the  two  foveas 
is  derived  from  the  alar  lamina.  The  latter, 
therefore,  includes  the  trigonum  vagi,  the  area 
acustica,  and  the  locus  coeruleus. 

The  further  development  of  the  medulla 
takes  place  on  the  ventral  aspect  of  the  two 
laminae  by  the  deposition  of  new  parts  on 
those  which  are  already  formed.  An  oval 
bundle  of  longitudinal  fibres  makes  its  ap- 
pearance on  the  outer  surface  of  the  alar 
lamina,  at  the  point  where  this  joins  the 
basal  lamina.  This  is  the  early  fasciculus 
solitarius.  It  is  composed  of  afferent  fibres 
from  the  glossopharyngeal  and  vagus  nerves. 
These,  on  I'eaching  the  surface  of  the  medulla, 
turn  downwards  upon  it.  At  first  the  con- 
nexion of  the  fasciculus  solitarius  with 
the  medulla  is  very  loose,  and  it  may  be 
regarded  as  being  the  equivalent  in  this 
part  of  the  neural  tube  of  the  oval  bundle 
of  longitudinal  fibres  which,  in  the  early  cord, 
constitutes  the  first  stage  of  the  column 
of  Burdach.  Throughout  the  further  stages 
of  development  the  fasciculus  solitarius  in- 
dicates in  a  sufliciently  clear  manner  the  point  of  jvinction  between  the  alar  and 
basal  laminae.  Very  soon  it  becomes  covered  over  by  parts  developed  on  its  ventral 
aspect,  and  it  ultimately  comes  to  lie  deeply  in  the  substance  of  the  medulla.  This 
change  in  the  position  of  the  fasciculus  solitarius  with  reference  to  the  surface  is  asso- 
ciated with  a  striking  developmental  process  which  leads  to  certain  remarkable  results, 
and  which  is  termed  the  formation  of  the  rhombic  lip  of  His  (Fig.  422,  B  and  C).  Before 
the  alar  lamina  falls  outwards,  while  it  still  stands  erect  and  its  inner  surface  faces  the 
corresponding  surface  of  the  opposite  lamina,  its  dorsal  edge  is  folded  outwards  and 
becomes  fused  with  the  outer  surface  of  the  remaining  portion  of  the  alar  lamina.     This 


HOMBIC  LIP 


HYPOGLOSSAL 


Fig.  422. — Three  Stages  in  the  De\t;lopment  of 
THE  Medulla  Oblongata  (from  His — slightly 
modified). 


528  THE  NERVOUS  SYSTEM. 

is  the  rhombic  lip,  and,  when  the  fusion  is  complete,  a  multitude  of  neuroblasts  take  form 
within  it  and  migrate  in  a  forward  and  inwards  direction  into  the  ventral  parts  of  the 
alar  and  basal  laminae.  The  mid-ventral  lamina — which  consists  of  spongioblastic  cells 
alone,  and  which  forms  a  narrow  partition  between  the  two  basal  laminae — is  reached  on 
either  side  by  the  axons  of  many  of  these  migrating  cells.  Whilst  acting  as  an  impassable 
barrier  to  the  neuroblasts,  this  spongioblastic  septum  gives  free  passage  from  one  side  to 
the  other  to  their  axons,  and  a  decussation  of  arcuate  fibres  in  the  mesial  plane  results. 
In  this  way  the  raphe  of  the  medulla  is  formed.  The  process  is  very  similar  to  that  which 
takes  place  in  the  course  of  the  formation  of  the  anterior  coinmissure  of  the  cord,  of 
which  the  raphe  may  be  regarded  as  the  equivalent  in  the  medulla. 

The  development  of  the  inferior  olivary  nucleus  and  of  its  two  accessory  parts  is  like- 
wise closely  connected  with  the  migration  of  the  neuroblasts  from  the  region  of  the 
rhombic  lip.  Many  of  these  cells  collect  together  so  as  to  form  a  nuclear  lamella,  which 
afterwai'ds  assumes  its  characteristic  crumpled  form. 

As  the  neuroblasts  of  the  rhombic  lip  stream  inwards  they  pass  both  on  the  dorsal 
and  the  ventral  aspects  of  the  fasciculus  solitarius,  which  thus  comes  to  be  covered  over 
and  separated  from  the  surface.  The  spinal  root  of  the  trigeminal  nerve,  like  the 
fasciculus  solitarius,  is  also,  in  the  first  instance,  throughout  its  entire  course  on  the 
surface  of  the  medulla,  and  its  change  of  position  in  the  greater  part  of  its  course  within 
the  pons  and  medulla  is  due  to  the  subsequent  development  of  those  parts  which  cover  it 
over. 

The  importance  of  the  rhombic  lip  in  the  development  of  the  medulla  will  be  better 
appreciated  if  we  enumerate  the  parts  which  spring  from  it :  (1)  the  inferior  olivary  nuclei; 
(2)  the  cuneate  nucleus ;  (3)  the  substantia  gelatinosa  Rolandi ;  (4)  the  arcuate  nucleus ; 
(5)  the  internal  arcuate  fibres ;  (6)  the  olivary  system  of  fibres ;  (7)  the  restiform  body. 
From  this  it  is  evident  that  the  formation  of  the  rhombic  lip  constitutes  an  extremely 
important  step  in  the  development  of  the  human  brain.  Recent  investigation,  however, 
makes  it  clear  that  in  most  of  the  lower  mammals  the  rhombic  lip  does  not  attain  any- 
thing like  the  degree  of  prominence  which  it  presents  in  the  early  brain  of  man. 

The  pyramidal  tracts  which  come  down  from  the  cerebral  cortex  are  late  in  making 
their  appearance  in  the  medulla.  The  formatio  reticularis  precedes  them  in  development. 
They  appear  in  the  fourth  month  of  fcetal  life,  and  as  they  are  developed  the  antero- 
median furrow  between  them  takes  form  on  the  ventral  aspect  of  the  medulla. 

His  has  pointed  out  that  the  earliest  formed  part  of  the  medulla  is  the  floor  of  the 
fourth  ventricle,  and  that  the  other  parts,  speaking  generally,  are  added  in  succession  as 
we  pass  towards  the  surface.  "  The  oldest  layer  of  the  medulla  is  the  floor  of  the  fourth 
ventricle  with  its  nuclei.  It  is  followed,  in  the  first  instance,  by  the  reticular  formation, 
and  afterwards  by  the  layer  containing  the  olivary  and  other  nuclei.  Last  of  all  come 
the  pyramids  and  the  outer  (superficial)  arcuate  fibres  "  (His). 

Pons  Varolii. — The  information  which  we  possess  at  the  present  moment  regarding 
the  development  of  the  pons  Varolii  is  somewhat  deficient ;  but  there  is  little  doubt  that 
the  course  pursued  is,  in  general,  very  similar  to  that  which  has  been  described  for  the 
medulla.  It  has  been  seen  to  be  composed  of  parts  which  are  in  a  great  measure 
equivalent  to  those  met  with  in  the  medulla,  the  formatio  reticularis  of  the  latter 
passing  into  the  tegmental  substance  in  the  former,  while  the  pyramids  and  arcuate  nuclei 
and  anterior  superficial  arcuate  fibres  of  the  medulla  are  represented  by  the  large  venti'al 
part  of  the  pons.  Further,  as  His  points  out,  similar  relations  between  the  chronological 
and  local  succession  of  layers  may  be  recognised.  Thus  the  primitive  position  of  the 
motor  nucleus  of  the  trigeminal  nerve,  and  also  of  its  spinal  root,  is  a  superficial  one,  and 
it  is  only  by  a  later  process  of  develoj^ment  that  the  nucleus  pontis  and  the  thick  layer 
of  transverse  and  longitudinal  fibres  are  formed. 

From  the  phylogenctic  point  of  view  the  tegmentum  is  the  oldest  part  of  the  pons. 
The  study  of  the  compai^ative  anatomy  of  the  brain  makes  it  evident  that  the  large 
ventral  part  is  comparatively  a  recent  acquisition.  As  the  cerebral  cortex  extends  with 
the  increasing  evolution  of  the  cerebral  hemispheres  (pallium),  the  ventral  part  of  the 
pons  is  seen  to  keep  pace  with  it  in  its  development.  This  should  easily  be  understood 
from  what  has  been  said  in  regard  to  its  structure  and  connexions.  It  is  composed 
of  the  nucleus  pontis,  the  transverse  fibres,  and  the  pyramidal  and  cortico-pontine  fibres, 
all  of  which  stand  in  direct  relation  to  the  cerebral  cortex.  One  of  the  striking  features 
of  the  brain  of  a  microcephalic  idiot,  where  the  cerebral  cortex  is  greatly  rediiced,  is  the 
corresponding  marked  diminution  in  the  size  of  the  ventral  part  of  the  pons. 

Cerebellum. — The  roof  of  the  fourth  ventricle  is  formed  for  the  most  part  by  the 
thin  epitholi^d  layer  already  described  as  being  formed  Vjy  the  expanded  mid-dorsal  lamina. 


DEVELOPMENT  OF  THE  CEREBELLUM. 


529 


This  does  not  stretch,  however,  over  its  entire  extent.  As  we  approach  the  upper  part  of 
the  ventricle,  it  is  seen  to  become  continuous  in  the  region  of  tlio  isthmus  with  a  thicker 
lamella.  This  lamella  is  bounded  above  by  the  intercrossing  of  the  two  trochlear  nerves, 
which  marks  on  the  dorsal  aspect  of  the  neural  tube  the  place  of  junction  between  the 
rhombencephalon  and  the  mesencephalon  ;  hdow,  it  is  limited  by  a  forwardly-directed 
semilunar    fold    of 


'^^tL 


the  thin  epithelial 
ventricular  roof, 
which  takes  place 
into  the  ventricular 
cavity  at  the  level 
of  the  pontine  flex- 
ure of  the  brain. 
The  fold  so  con- 
stituted is  termed 
the  plica  choroidea, 
seeing  that  meso- 
derm is  introduced 
between  its  two 
layers,  and  this  ul- 
timately gives  rise 
to  the  choroid 
plexus  of  the  fourth  ventricle  (Fig.  425,  A) 


MONTICULUS 


wr 


B  C 

Drawings  to  illustrate  thk  Development  of  the  Cerebellum 
(from  Kuithan). 

Transverse  section  through  the  forepart  of  the  cerebelluni  of  a  sheep  eiiiliryo. 
Transverse  section  through  the  hinder  part  of  the  cereliellum  of  a  sheep  embryo. 
Cerebellum  of  a  human  foetus  17  cm.  long. 

1.  Sulcus  primarius.  3.  Sulcus  infrapyramidalis. 

2.  Sulcus  suprapyramidalis.  "  4.   Fissura  post-lunata. 
r.l.  Lateral  recess  ventricle  IV. 


Mesencephalon 


Early  cerebellum 


Cavity  of 
fourth  ventricle 


The  lamella  whicli  forms  tlie  roof  or  dorsal 
wall  of  the  ventricle  in  front  of  the  plica  choroidea  is  developed  into  the  cerebellum, 
and  the  superior  medullary  velum  (valve  of  Vieussens). 

The  cerebellar  part  of  this  lamella  consists  of  two  thick  lateral  plates  which  meet  in  the 
middle  line  and  are  joined  there  by  an  extremely  thin  dorsal  seam  or  lamina  (Fig.  423,  A). 
The  inner  extremities  of  the  two  cerebellar  plates  are  thus  separated  by  a  median  groove, 
which  opens  into  the  cavity  of  the  hind-brain  (fourth  ventricle).  The  statement,  there- 
fore, that  the  median  lobe  or  vermis  of  the  cerebellum  is  the  most  archaic  part  of  the 

organ  and  is  the  part  which 
IS  developed  nrst  is  not 
supported  by  fact ;  indeed, 
the  reverse  of  this  is  the 
case,  because  at  this  early 
stage  the  lateral  portions 
are  alone  represented. 

In    the  course  of    time 
the  inner  ends  of  the  cere- 
bellar plates  become  fused 
in  the  middle  line,  and  the 
median      furrow      between 
them    disappears.      In    the 
process  of  this    fusion    the 
deep  part  of  the  intervening 
furrow     remains     enclosed 
within     the    substance    of 
the    median    part    of     the 
cerebellum  and  persists  for 
Fiti.  424. — The  Brain  op  an  Embryo  ok  eleven  weeks,  viewed  from    a   short    time  as  a  minute 
behind  to  show  the  development  of  the  cerebellunL     At  this  stage  the    cerebellar  ventricle  (Blake), 
cerebellum  is  in  the  form  of  a  simple  band  or  plate  which  arches  over  The  cerebellum  llOWDre- 

the  hinder  aspect  of  the  fore  part  of  the  cavity  of  the  hind  brain  (from  .       .i  K 

jjj^x  r  r  J  sents  the  appearance  or   a 

simple  uniform  arch  which 
bridges  across  the  dorsal  aspect  of  the  upper  part  of  the  early  fourth  ventricle ;  and  very 
soon  the  sulci  begin  to  appear.  Of  late  years  the  development  and  morphological  import 
of  these  sulci  have  received  much  attention.  Stroud,  Kuithan,  Blake,  Flliot  Smith,  and 
Bradley  have  published  valuable  papers  on  this  subject,  and  what  is  written  here  is 
largely  gathered  from  the  writings  of  these  observers.  Further,  the  terminology 
suggested  by  Elliot  Smith  has  been  chiefly,  but  not  entirely,  followed. 

The  first  fissure  to  appear  is  the  floccular  fissure,  which  cuts  off  the  postero-lateral 
corner  of  the  cerebellar  plate.     The  portion  thus  marked  off  is  the  flocculus,  and  its  early 
appearance  and  relatively  large  size  at  this  stage  are  significant  of  its  high  morphological 
38 


Medulla 


530 


THE  NEKVOUS  SYSTEM. 


SUR 
N/IED 
VEL. 


Fig.  425. 

A.    Mesial  section  through  the  cerebellimi  of  an  early  liuman  foetus 

(semi-diagrammatic). 

B.    Mesial  section  through  the  cerebellum  of  a  human  foetus  17  cm.  long 

(from  Kuithan). 

1.  Fissura  prima.  4.   Fissura  postnodularis. 

2.  Fissura  suprapyramidalis.  T.  Transverse  groove  on  the  roof  of 

3.  Fissura  infrapyramidalis.  the  foiirth  ventricle. 


Nodnle 


Uvula 


Post-nodular  Assure 
/ 


importance  as  a  lobule  of  the   cerebellum.     The  floccular  fissure  is   continued  inwards 

close  to  the  posterior  border 
of  the  cei-ebellar  plate,  join- 
ing its  fellow  of  the  opposite 
side  in  the  middle  line. 
Here  it  receives  the  name 
of  post-nodular  fissure.  A 
narrow  strip  of  cerebellar 
surface  is  thus  marked  out. 
The  median  part  of  this 
strip,  by  special  growth,  be- 
comes the  nodulus,  whilst  the 
part  which  extends  between 
this  and  the  flocculus  remains 
narrow  and  band-like,  and 
ultimately  forms  a  portion 
of  the  inferior  medullary 
velum. 

The  next  furrow  which 
appears  is  the  sulcus  prim- 
arius  (Kuithan)  or  fissura 
prima  (Elliot  Smith).  It 
cuts  deeply  into  the  vermis 
in  a  transverse  direction  be- 
tween the  culmen  monticuli 
and  the  clivus  monticuli,  and  is  then  carried  outwards  over  each  hemisphere  so  as  to 
separate  the  two  crescentic  lobules.  The  fissura  prima  is  the  deepest  of  all  the  fissures 
of  the  vermis,  and  it  is 
developed  towards  the  end 
of  the  third  month.  A 
little  later  two  other  fur- 
rows are  observed  in  the 
vermis.  These  are  the 
suprapyramidal  and  the 
infrapyramidal  (the  fissura 
secunda  of  Elliot  Smith). 
By  the  former  the  pyramid 
is  limited  above ;  by  the 
latter  the  pyramid  is  separ- 
ated from  the  uvula. 

After  the  main  fissures 
of  the  vermis  are  estab- 
lished, four  important  sulci 

on  the  surface  of  each  cerebellar  hemisphere  come   into   view,  viz.   the  postlunate 
post-tonsillar,  the  parapyramidal,  and  the  great  horizontal  sulci. 

The  fissura  postlunata  ap- 
pears in  the  fourth  month,  and 
curves  inwards  on  the  upper 
surface  of  the  organ  behind  the 
posterior  crescentic  lobule.  In 
many  cases  it  becomes  con- 
fluent with  its  fellow  of  the 
opposite  side  behind  the  clivus 
monticuli.  The  posttonsillar 
fissure  is  seen  on  the  under 
surface  of  the  cerebellum  about 
thcbeginningof  thefifth month. 
It  circumscribes  the  prominent 
and  conspicuous  tonsil  and 
becomes  confluent  with  the 
fissura  infrapyi-amidalis.  The  parapyramidal  fissure  ap])cars  on  the  under  sui-face  of  the 
cerebellar  hemisphere  behind  the  bivcntral  lobule,  and  usually  joins  the  suprapyramidal 
fissiire  of  the  inferior  vermis. 


Ploccular  fissure. 

Tonsil 

Biventral  lobule. 


Flocculus 
Paraflocculus 

Peduncle  of 
flocculus 
Post- tonsillar 
sulcus 

Parapyramidal 
sulcus 

Postero-inferior 
lobule 


Infrapyramidal  fissure  / 
Suprapyramidal  fissure 


\  Pyramid 
Tuber  valvula 
Great  liorizontal  sulcus 

Fig.   426. — Under   Surface   of  the   Cerebellum   of  a  Human    F(etus 
which  has  reached  the  end  of  the  fifth  month  of  development. 


the 


fJuhnen  monticuli 
Clivus  monticuli  |        Fissura  prima 


Fissura  postlunata 


Postero-superior  lobule 


Fig, 


Suprapyramidal  fissure 
427. — Cerebellum  of  a 


Great  horizontal  Hssurii 
N  Postero-inferior  lobule 

Infrapyramidalis  liss\ire 

Human   Fostus   which   has   reached 


THE  End  of  the 
above  aud  behind. 


Fifth  Month  op  Development.     Viewed  from 


THE  MESENCEPHALON.  531 

The  great  horizontal  fissure,  in  spite  of  its  depth  in  the  adult  brain — a  depth  which 
is  due  to  the  excessive  growth  in  the  later  months  of  development  of  the  two  lobules  that 
bound  it — appears  very  late  in  the  development  of  the  cerebellum.  It  is  first  seen  as  a 
verv  broad  shallow  gi-oove  or  furrow  on  the  outer  margin  of  the  hemisphere.  From  this 
it  runs  forwards  to  the  middle  peduncle  and  backwards  towards  the  vermis,  where  it 
usuallv  joins  the  postlunate  fissure.  At  this  stage  there  is  no  folium  cacuminis,  so  that 
tlie  combined  portion  of  the  postlunate  and  great  horizontal  fissures  intervenes  between 
the  clivus  monticuli  and  the  tuber  valvule.  Even  at  the  time  of  birth  the  folium 
cacuminis  is  not  seen  on  the  sui'face.  It  rises  up  from  the  bottom  of  the  combined  portions 
of  the  great  horizontal  and  postlunate  fissures  so  as  to  form  a  barrier  between  them. 

Verv  early  a  transvei-se  groove  appears  on  the  smooth  anterior  or  ventricular  surface 
of  the  cerebellum  (Fig.  425,  B,  t).  This  is  placed  much  nearer  the  lower  than  the  upper 
border  of  the  organ,  and  it  represents  at  this  stage  the  angular  peak  of  the  tent-like  roof 
of  the  fourth  ventricle  in  the  adult  brain.  As  growth  goes  on,  the  portions  of  the  cere- 
bellum in  front  and  behind  this  groove  approach  each  other,  so  as  to  deepen  the  groove 
and  bring  about  the  backward  prolongation  of  the  ventricular  cavity  towards  the  cerebellum. 

The  leading  distinctive  characters  of  the  hviman  cerebellum  are:  (1)  the  small  size 
of  the  flocculus  :  (2)  the  lai-ge  size  of  the  tonsil  ;  (3)  the  excessive  development  of  the 
lateral  hemisphere,  and  particularly  of  the  postero-superior  and  postero-inferior  lobules 
which  bound  the  great  hoi'izontal  fissure. 

THE  MESENCEPHALON. 

The  mesencephalon  or  mid-brain  is  the  short,  narrow  part  of  the  brain -stem 
which  occupies  the  aperture  of  the  tentorium  cerebelli  (incisura  tentorii),  and 
connects  the  cerebrum  which  lies  above  with  the  parts  which  occupy  the  posterior 
cranial  fossa.  It  is  about  three-quarters  of  an  inch  in  length,  and  it  consists  of  a 
dorsal  part,  composed  of  the  corpora  quadrigemina,  and  a  much  larger  ventral  part, 
which  is  formed  by  the  two  crura  cerebri. 

In  the  undissected  brain  the  corpora  quadrigemina  are  completely  hidden  from 
view  by  the  splenium  of  the  corpus  callosum,  which  projects  backwards  over  them, 
and  also  by  the  superimposed  cerebral  hemispheres.  The  hinder  end  of  each  optic 
thalamus  likewise,  to  some  extent,  overhangs  the  upper  part  of  the  mesencephalon 
on  its  dorsal  and  lateral  aspect  (Fig.  388,  p.  482).  On  this  portion  of  the  optic 
thalamus  are  seen  two  projections,  which  are  specially  related  to  the  mesencephalon. 
These  are  the  cushion-like  pulvinar,  which  forms  the  inner  and  hinder  part  of  the 
thalamus,  and  the  corpus  geniculatum  externum,  an  ill-defined  oval  swelling  on  the 
outer  and  under  aspect  of  the  posterior  end  of  the  thalamus. 

The  crura  cerebri  can  to  some  extent  be  seen  on  the  base  of  the  brain,  where 
they  bound  the  posterior  part  of  the  interpeduncular  space.  Encircling  the  upper 
end  of  each  cms  cerebri,  where  it  plunges  into  the  cerebrum,  is  the  optic  tract 
(Fig.  380,  p.  474). 

The  mesencephalon  is  tunnelled  from  below  upwards  by  a  narrow^  passage, 
caUed  the  aqueduct  of  Sylvius,  which  connects  the  fourth  ventricle  with  the  third 
ventricle  (Fig.  429,  p.  533).  This  channel  lies  much  nearer  the  dorsal  than  the 
ventral  aspect  of  the  mesencephalon. 

Corpora  Quadrigemina. — This  name  is  applied  to  four  rounded  eminences  on 
the  posterior  aspect  of  the  mesencephalon  (Fig.  388,  p.  482).  The  superior  pair  are 
larger  and  broader  than  the  inferior  pair,  but  they  are  not  so  well  defined  nor  are 
they  so  prominent.  A  longitudinal  and  a  transverse  groove  separate  the  quad- 
rigemina! bodies  from  each  other.  The  longitudinal  groove  occupies  the  mesial  plane 
and  extends  upwards  to  the  posterior  commissure  of  the  brain.  The  upper  end  of 
this  groove  widens  out  into  a  shallow  depression,  in  which  the  pineal  body,  a  small 
conical  structure  which  belongs  to  the  diencephalon,  rests.  From  the  lower  end  of 
the  same  groove  a  short  but  well-defined  and  projecting  band,  the  frenulum  veli, 
passes  to  the  valve  of  Vieussens,  w^hich  Hes  immediately  below  tjie  inferior  pair 
of  quadrigeminal  bodies.  The  transverse  groove  curves  round  below  each  of  the 
superior  pair  of  Cjuadrigeminal  bodies  and  separates  them  from  the  inferior  pair. 
It  is  also  continued  in  an  upward  and  forward  direction  on  the  lateral  aspect 
of  the  mesencephalon. 


LATERAL  ROOT. 

OPTIO  TRACT 


532  THE  NERVOUS  SYSTEM. 

The  quadrigcmiual  bodies  are  not  marked  off  laterally  from  the  sides  of  the 
mesencephalon,  but  each  has  in  connexion  with  it,  on  this  aspect,  a  prominent 
strand  of  white  matter,  which  is  prolonged  upwards  and  forwards  under  the 
projecting  pulvinar  and  corpus  geniculatum  externum.  These  strands  are  called 
the  brachia  of  the  corpora  quadrigemina,  and  they  are  separated  from  each  other  by 
a  continuation  on  the  side  of  the  mesencephalon  of  the  transverse  groove,  which 
intervenes  between  the  two  pairs  of  bodies. 

The  corpus  geniculatum  internum  (corpus  geniculatum  mediale)  is  closely 
associated  with  the  brachia.  It  is  a  small,  sharply-defined  oval  eminence,  which 
lies  on  the  side  of  the  upper  part  of  the  mesencephalon  under  shelter  of  the  pulvinar 
of  the  optic  thalamus. 

The  inferior  bracMum  (brachium  quadrigeuiinum  inferius),  proceeding  upwards 
from  the  lower  quadrigeminal  body,  advances  towards  the  corpus  geniculatum 
internum  and  disappears  from  view  under  cover  of  this  prominence.  Upon  the 
opposite  side  of  the  same  geniculate  body  the  mesial  root  of  origin  of  the  optic  tract 
takes  shape  on  the  surface,  and  the  appearance  is  such  that  the  conclusion  might 
very  naturally  be  arrived  at  that  the  inferior  brachium  and  this  root  of  the  optic 

tract  are  continuous  with  each  other  under  the  genicu- 
,corp:gen:ext:  latc   clovatlon.      This   is   not   the  case,  however ;    the 

fibres  of  the   inferior    brachium,    to    a    large   extent, 
proceed  iuto  the  subjacent  tegmentum  under  cover  of 
the  internal  geniculate  body  and  help  to  constitute  an 
MESIAL  ROOT.  ascending  tract  from  the  inferior  quadrigeminal  body, 

-corp:gen:int:  wlilch  procceds  upwards  to  the  optic  thalamus.     Of  the 

fibres  of  the  mesial  root  of  the  optic  tract  some  end  in 
'supR. QUAD  BODY;  t ho  gray  matter  of  the  internal  geniculate  body,  whilst 

,„rrt.QUAD:BODY.  othcrs  SbVi&e  within  it.     They  constitute  what  is  called 

Fig.  428.  -Diagram  of  the  roots    Qudden's  commissure. 

OF  THE  Optic  IServe.  „i  ■■,■•■  /i         i  •  i   •  • 

Ihe   superior  bracnmm    (brachium   qnadrigemmum 

superius)  is  carried  upwards  and  forwards  between  the  overhanging  pulvinar 
and  the  corpus  geniculatum  internum.  A  surface  examination  of  the  mesen- 
cephalon is  sufficient  to  show  that,  while  a  large  part  of  this  strand  enters  the 
corpus  geniculatum  externum,  a  considerable  portion  runs  into  the  lateral  root  of 
the  optic  tract. 

The  optic  tract  is  thus  attached  to  the  brain-stem  by  two  roots,  viz.  a  mesial 
and  a  lateral,  which  are  separated  from  each  other  by  a  distinct  groove.  The 
mesial  root  disappears  under  the  internal  geniculate  body.  The  lateral  root  spreads 
out  and  some  of  its  fibres  enter  the  superior  quadrigeminal  body  through  its 
brachium,  whilst  others  find  their  way  into  the  corpus  geniculatum  externum  and 
the  pulvinar  of  the  optic  thalamus  (Fig.  428). 

Crura  Cerebri  (pedunculi  cerebri). — The  crura  cerebri  constitute  the  chief  bulk 
of  the  mesencephalon  (Fig.  429,  p.  533).  Upon  the  basal  aspect  of  the  brain  they 
appear  as  two  large  rope-like  strands,  which  emerge  close  together  from  the  upper 
aspect  of  the  pons  Varolii  and  diverge  as  they  proceed  upwards  to  enter  the 
cerebrum.  At  the  place  where  each  crus  disappears  into  the  corresponding  side 
of  the  cerebrum,  it  is  encircled  by  the  optic  tract. 

Each  crus  cerebri  is  composed  of  two  parts,  viz.  a  dorsal  tegmental  part  (teg- 
mentum), which  is  prolonged  upwards  into  the  region  below  the  optic  thalamus 
(subthalamic  tegmental  region),  and  a  ventral  pedal  portion  or  crusta  (basis  pedun- 
culi), which,  when  traced  upwards  into  the  cerebrum,  is  seen  to  take  up  a  position 
on  the  outer  side  of  the  optic  thalamus  and  to  be  continuous  with  the  internal 
capsule  of  the  brain.  When  the  base  of  the  brain  is  examined  it  is  the  crusta 
which  is  seen,  and  it  is  observed  to  be  wiiite  in  colour  and  streaked  in  tlie  longi- 
tudinal direction.  In  the  tegmentum  the  longitudinally-arranged  fibres  are,  for 
the  most  part,  corticipetal,  or,  in  other  words,  fibres  which  are  ascending  towards 
the  cortex  of  the  cerebrum  ;  the  crusta,  on  the  other  liand,  is  entirely  composed  of 
longitudinal  strands  of  fibres  which  are  coi'ticifugal ,  or  fibres  which  descend  from 
the  cortex  cerebri. 

On  the  surface  of  the  mesencephalon  the  separation  between  the  tegmental  and 


IN  TEEN  AL  STEUCTUEE  OF  THE  MESENCErHALON. 


533 


pedal  portions  of  the  crus  cerebri  is  clearly  indicated  by  an  inner  and  an  outer  groove. 
The  inner  or  mesial  furrow  is  the  more  distinct  of  the  two.  It  looks  into  the 
interpeduncular  space,  and  from  it  emerge  the  fascicles  of  the  tliird  or  oculo-motor 
nerve.  It  is,  therefore,  termed  the  sulcus  oculo-motorii  (sulcus  nervi  oculo-motorii). 
The  outer  groove,  which  is  placed  on  the  lateral  aspect  of  the  mesencephalon, 
receives  the  name  of  the  sulcus  lateralis  mesencephali.  When  traced  downwards,  it 
is  observed  to  become  continuous  with  the  furrow  which  intervenes  between  the 
middle  and  superior  peduncles  of  the  cerebellum. 

A  close  inspection  of  the  outer  surface  of  the  tegmental  part  of  the  crus  cerebri, 
below  the  level  of  the  quadrigeminal  brachia,  will  reveal  some  faintly-marked 
bundles  of  fibres  curving  obliquely  upwards  and  backwards  to  reach  the  inferior 
quadrigeminal  body  (Fig.  390,  p.  484).  These  are  fibres  of  the  lateral  fillet,  coming 
to  the  surface  at  the  sulcus  lateralis  and  sweeping  over  the  subjacent  superior 
cerebellar  peduncle  to  gain  the  inferior  quadrigeminal  body. 


POSTERIOR 

LONCITUDINAI 

BUNDLE 


AQUEDUCT  OF  SYLVIUS. 


SULCUS  LATERALtS 


INTERNAL  STRUCTURE  OF  THE  MESENCEPHALON. 

When  transverse  sections  are  made  through  the  mesencephalon  the  aqueduct  of 
Sylvius  is  seen  to  be  surrounded  by  a  thick  layer  of  gray  matter,  which  receives  the 
name  of  the  Sylvian  gray  matter  or  the  central  gray  matter  of  the  aqueduct  (stratum 
griseum  centrale).  On  the  dorsal  aspect  of  the  Sylvian  gray  matter  the  corpora 
quadrigemina  form  a  layer  which  separates  it  from  the  surface,  and  to  which  the 
term  lamina  quadrigemina  is  applied. 
On  the  ventral  and  lateral  aspects 
of  the  Sylvian  gray  matter  are  the 
tegmental  portions  of  the  crura 
cerebri;  whilst,  intervening  between 
each  of  the  latter  and  the  corre- 
sponding crusta,  there  is  a  con- 
spicuous mass  of  dark  pigmented 
matter  termed  the  substantia  nigra. 

Sylvian  Aqueduct  and  Sylvian 
Gray  Matter  (aquseductus  cerebri 
— stratum  griseum  centrale).  —  The 
aqueduct  of  Sylvius  is  the  canal 
which  leads  from  the  fourth  ventricle 
below,  upwards  through  the  mesen- 
cephalon, to  the  third  ventricle  above. 
It  is  not  quite  three-quarters  of  an  inch  in  length,  and  it  lies  much  nearer 
the  dorsal  than  the  ventral  surface  of  the  mesencephalon.  When  examined  in 
transverse  section,  it  presents  a  triangular  outline  as  it  passes  into  the  fourth 
ventricle  and  a  T-shaped  outline  close  to  the  third  ventricle.  In  the  intermediate 
part  of  its  course  it  assumes  different  outlines,  and  not  always  the  same  form  at 
the  same  level  in  different  individuals. 

The  aqueduct  of  Sylvius  is  lined  by  ciliated  epithelium,  and  outside  this  is  the 
thick  layer  of  Sylvian  gray  matter,  which  is  directly  continuous  below  with  the  gray 
matter  spread  out  on  the  floor  of  the  fourth  ventricle,  and  above  with  gray  matter 
on  the  floor  and  sides  of  the  third  ventricle.  Scattered  more  or  less  irregularly 
throughout  the  Sylvian  gray  matter  are  numerous  nerve-cells  of  varying  forms  and 
sizes,  whilst  in  addition  to  these  there  are  three  definite  collections  or  chisters  of 
cells,  which  constitute  the  nuclei  of  origin  of  the  trochlear  nerve,  the  oculo-motor 
nerve,  and  the  mesencephalic  root  of  the  trigeminal  nerve.  The  position  and 
relations  of  these  will  be  given  at  a  later  stage. 

Substantia  Nigra. — When  seen  in  transverse  section,  the  substantia  nigra 
presents  a  semilunar  outline.  It  consists  of  a  mass  of  gray  matter,  in  the  midst  of 
which  are  large  numbers  of  deeply  pigmented  nerve-cells.  It  is  only  when  this 
substance  is  examined  in  bulk  that  it  appears  dark ;  in  thin  sections  it  does  not 
differ  much  in  colour  from  ordinary  gray  matter,  although,  under  the  microscope, 
the  brown -coloured  cells  stand  out  very  conspicuously,  even  under  low  powers. 


NERVE  SULCUS    OCULOMOTORIUS 

Fig.  429. — Diagrammatic  View  of  the  Oct  Surface  of 
A  Transverse  Section  through  the  Upper  Part 
OF  THE  Mesencephalon. 


534  THE  NEEVOUS  SYSTEM. 

The  substantia  nigra  is  disposed  in  the  form  of  a  thick  layer,  interposed  between 
the  tegmental  and  pedal  portions  of  the  cms  cerebri.  It  begins  below  at  the 
upper  border  of  the  pons  Varolii  and  extends  upwards  into  the  subthalamic 
region.  The  margins  of  this  layer  of  dark-coloured  substance  come  to  the  surface 
at  the  oculo-motor  and  the  lateral  sulci  of  the  mesencephalon,  and  its  inner  part  is 
traversed  by  the  emerging  fascicles  of  the  oculo-motor  nerve.  It  is  not  equally 
thick  throughout.  Towards  the  lateral  sulcus  it  becomes  thin,  whilst  it  thickens 
considerably  near  the' inner  aspect  of  the  crus  cerebri.  The  surface  of  the  sub- 
stantia nigra,  which  is  turned  towards  the  tegmentum,  is  concave  and  uniform ; 
the  opposite  surface  is  convex  and  rendered  irregular  by  the  presence  of  numerous 
slender  prolongations  of  the  substance  into  the  crusta. 

The  morphological  and  physiological  .significance  of  the  substantia  nigra  is  not 
fully  understood,  and  the  connexions  established  by  its  cells  are  imperfectly 
known. 

Inferior  Quadrigeminal  Bodies  (colliculi  inferiores). — Each  of  the  inferior 
quadrigemiual  bodies  is  largely  composed  of  a  mass  of  gray  matter  which,  in 
transverse  section,  presents  an  oval  outline  (Fig.  432,  p.  537).  This  central 
nucleus  is,  to  a  large  extent,  encapsulated  by  white  matter.  Numerous  cells  of 
different  sizes  are  scattered  throughout  it,  and  the  whole  mass  is  pervaded  by  an 
intricate  interlacement  of  fine  fibres,  which,  to  a  large  extent,  are  derived  from  the 
lateral  fillet  and  the  inferior  brachium. 

In  transverse  sections,  through  this  region,  the  lateral  fillet  is  seen  to  abut 
against  the  outer  margin  of  the  central  nucleus.  Many  of  the  fibres  of  this  tract 
enter  it  at  once  and  become  dispersed  amongst  its  cells ;  others  sweep  over  its 
dorsal  surface,  so  as  to  give  it  a  superficial  covering ;  whilst  a  third  group  is  carried 
in  the  form  of  a  thin  layer  inwards  on  its  ventral  aspect,  so  as  to  mark  it  off  from 
the  subjacent  Sylvian  gray  matter  of  the  aqueduct  (Fig.  432,  p.  537).  In  this 
manner,  therefore,  the  inferior  quadrigeminal  nucleus  becomes  partially  circum- 
scribed by  the  fibres  of  the  lateral  fillet.  Several  of  the  lateral  fillet  fibres,  which 
proceed  over  the  superficial  or  dorsal  aspect  of  the  nucleus,  reach  the  mesial  plane 
and  form  a  loose  decussation  with  the  corresponding  fibres  of  the  opposite  side. 

The  intimate  connexion  wliicli  is  thus  exhibited  between  the  fibres  of  the  lateral  fillet  and 
the  nucleus  of  the  inferior  quadrigeminal  body  is  very  significant.  It  has  already  been  shown 
that  the  lateral  fillet,  to  a  large  extent,  comes  from  the  nuclei  of  termination  of  the  cochlear 
nerve  of  the  opjDosite  side,  although  most  of  its  fibres  have  to  jjass  through  several  nuclear  inter- 
nodes  before  they  reach  the  inferior  quadrigeminal  body.  We  must  associate,  therefore,  the 
inferior  quadrigeminal  body,  and  also  the  corpus  geniculatum  internum,  which  likewise  receives 
lateral  fillet  fibres,  with  the  organ  of  hearing. 

This  view  of  the  inferior  quadrigeminal  bodies  is  supported  both  by  experimental  and  by 
morphological  evidence.  Speaking  broadly,  it  may  be  stated  that  the  inferior  quadrigeminal 
bodies  are  only  present  as  distinct  eminences  in  mammals,  and  then  they  are  invariably  correlated 
with  a  spirally-wound  and  well-developed  cochlea.  That  tliey  have  nothing  to  do  with  sight, 
is  shown  by  the  fact  that,  when  the  eyeballs  are  extirpated  in  a  young  animal,  the  inferior 
quadrigeminal  bodies  remain  unaft'ected,  whilst  the  superior  quadrigeminal  bodies  after  a  time 
atrophy  (Gudden).  When,  on  the  other  hand,  the  cochlear  terminal  nuclei  are  destroyed,  fibres 
which  have  undergone  atrophy  may  be  followed  to  the  inferior  quadrigeminal  bodies  of  both 
sides,  but  particularly  to  that  of  the  opj)Osite  side  (Baginski,  Bumm,  and  Ferrier  and  Turner).  A 
very  considerable  tract  of  ascending  fibres  takes  origin  within  the  inferior  quadrigeminal  body . 
and  passes  upwards,  in  the  inferior  brachium,  into  the  tegmentum  subjacent  to  the  internal  geni- 
culate body.  Within  the  tegmentum  they  proceed  u})  to  the  optic  thalamus  (Ferrier  and 
Turner). 

Superior  Quadrigeminal  Bodies  (colliculi  superiores). — The  superior  quadri- 
geminal body  presents  a  more  complicated  structure  (Fig.  431).  Superficially,  it  is 
coated  with  a  very  thin  layer  of  white  matter,  which  is  termed  the  stratum  zonale. 
Underneath  this  there  is  a  gray  nucleus,  called  the  stratum  cinereum,  which  in 
transverse  section  exhiljits  a  crescentic  outline  and  rests  in  a  cap-like  manner  upon 
the  subjacent  part  of  the  eminence  The  succeeding  two  strata,  which  respectively 
receive  the  names  of  stratum  opticum  and  the  stratum  lemnisci,  present  this  feature 
in  common,  that  they  are  composed  of  gray  matter,  traversed  by  numerous  fibres. 
The  source  from  which  the  fibres  are  derived  differs,  however,  in  each  case. 

Nerve-fibres  reach  the  superior  quadrigeminal  body  through — (1)  the  lateral 
and  mesial  fillets,  and  (2)  through  the  superior  brachium.     Tlie  fillet  fibres  enter 


INTERNAL  STRUCTURE  OF  THE  MESENCEPHALON. 


535 


InUuoi  quiflrij; 


MeseiiceiiUalic  loot  of  Ifftli 
iiei\  e 

ISuclcus  of  fourth  nerve 

Bi  ichiuiii  iiiforiiis 


Postcrioi  longitudinal 
\bundlo 

Mesial  fillet 


the  stratum  lemnisci,  and,  in  all  probability,  end  there.  The  superior  bracMum 
contains  fibres  of  two  different  kinds,  viz.  fibres  from  the  optic  tract  and  fibres  from 
the  cortex  of  the  occipital  lobe  of  the  cerebrum.  By  the  former  it  is  connected 
with  the  retina,  and  by  the  latter  with  the  visual  centre  in  the  occipital  region  of 
the  cerebral  cortex.  The  retinal  fibres,  for  the  most  part,  spread  out  on  the  surface 
of  the  quadrigeminal  body  and  form  the  stratum  zonale.  Most  of  them  dip  down 
into  the  substance  of  the  body  and  end  in  connexion  with  the  cells  of  the  deeper 
layers ;  several,  liowever,  are  carried  across  the  mesial  plane,  to  end  in  the  superior 
quadrigeminal  body  of  the  opposite  side.  The  occipital  fibres,  and  probably  also 
some  of  the  retinal  fibres,  enter  the  stratum  opticum.  The  fibres  from  the  occipital 
cortex  form  part  of  the  optic  radiation,  and  the  course  which  they  pursue  will  be 
dealt  with  later  on. 

Tegmental  Portions  of  the  Crura  Cerebri  (tegmenta). — The  tegmentum  of 
the  crus  cerebri  may  be  regarded  as  the  continuation  upwards  of  the  formatio 
reticularis  of  the  medulla 
and  the  dorsal  or  tegmental 
portion  of  the  pons  into 
the  mesencephalon.  It 
therefore  consists  of  fine 
bundles  of  longitudinal 
fibres  intersected  by  arch- 
ing fibres,  which  take  a 
transverse  and  curved 
course.  The  interstices 
between  these  nerve- 
bundles  is  occupied  by 
gray  matter  containing  ir- 
regularly scattered  nerve - 
cells.  On  its  dorsal  aspect 
the  tegmentiun  is  con- 
tinuous, at  the  side  of  the 
Sylvian  gray  matter,  with 
the  bases  of  the  corpora 
quadrigemina,  whilst  ven- 
trally  it  is  separated  from 
the  crusta  by  the  sub- 
stantia nigra.  The  two 
tegmenta  of  opposite  sides 
are,  to  some  extent,  marked 
off  from  each  other  in  the 
mesial  plane  by  a  pro- 
longation upwards  of  the 
median  raphe  of  the  pons 
and  medulla,  although,  in  the  lower  part  of  the  mesencephalon,  this  is  much 
obscured  by  the  decussation  of  the  superior  peduncles  of  the  cerebellum.  The  two 
longitudinal  strands,  termed  the  posterior  longitudinal  bundle  and  the  fillet,  are 
prolonged  upwards  throughout  the  entire  length  of  the  mesencephalon ;  and  they 
present  the  same  relations  to  the  tegmentum  as  in  the  lower  parts  of  the  brain. 
The  former  is  placed  in  relation  to  its  dorsal  aspect,  whilst  the  fillet  is  carried  up 
in  its  ventral  part. 

The  tegmentum  of  the  crus  cerebri  may  be  considered  as  presenting  two  parts  : 
viz.  (1)  a  lower  part,  which  is  placed  subjacent  to  the  inferior  quadrigeminal  bodies 
and  which  is  largely  occupied  by  the  decussation  of  the  superior  cerebellar  peduncles 
(Fig.  430);  and  (2)  a  superior  part,  subjacent  to  the  superior  quadrigeminal 
bodies,  which  is  traversed  by  the  emerging  bundles  of  the  third  nerve  and  which 
contains  a  large  and  striking  nuclear  mass,  termed  the  nucleus  ruber  or  the  red  teg- 
mental nucleus  (Fig.  431).  In  the  lower  part  of  the  mesencephalon  is  the  nucleus 
of  the  fourth  nerve  ;  in  the  upper  part,  the  nucleus  of  the  third  nerve. 

Superior  Cerebellar  Peduncles  (brachia  conjunctiva). — As  the  superior  cere- 


Substantia 
nii^ra 


Fig. 


Crusta 


430. — Transverse  Section  through  the  Human  Mescencephalon 
AT  the  Level  of  the  Inferior  Quadrigeminal  Body. 


536 


THE  NERVOUS  SYSTEM. 


bellar  peduncles  leave  the  pons  and  sink  into  the  tegmenta  of  the  mesencephalon, 
they  undergo  a  complete  decussation  subjacent  to  the  inferior  quadrigeminal  bodies 
and  the  Sylvian  gray  matter  (Figs.  407,  p.  505 ;  432,  p.  537  ;  and  430,  p.  535). 
In  this  manner  each  peduncle  is  transferred  from  one  side,  across  the  mesial 
plane,  to  the  opposite  side.  The  decussation  is  completed  at  the  level  of 
the  upper  borders  of  the  inferior  quadrigeminal  bodies,  and  then  each  peduncle 
proceeds  upwards  into  the  superior  part  of  the  tegmentum,  where  it  encounters 
the  red  nucleus.  Into  this  a  large  proportion  of  its  fibres  plunge  and  come  to  an 
end  in  connexion  with  the  nuclear  cells.  Many  of  the  peduncular  fibres,  how- 
ever, are  carried  around  the  nucleus  so  as  to  form  for  it  a  capsule  which  is  thicker 
on  the  inner  than  on  the  outer  side  (Fig.  431).  These  are  prolonged  into  the 
subthalamic  region,  and  ultimately  penetrate  the  ventral  aspect  of  the  optic  thala- 

Superior  quadrigeminal 
body 


External  geniculate 
bnily 


Inferior  bracliiuni 


Internal  geniculate 
body 


Mesial  fillet 


Crusta 


^»w&^i  /  'I '  Kt'il  nucleus 


Optic  tract 


^;^j^p4-  Sylvian  gray  matter 


Sj  Ivian  aqueduct 

Tegmentum 
-  -  Nucleus  of  third  nerve 

Posterior  longitudinal 
bundle 


Fibres  of  superior 
cerebellar  peduncle 


Third  nerve 
Substantia  nigra 

Corpus  mammillare 


Fig.   431. 


-Transverse  Section  through  the  Human  Mesencephalon  at  the  Level  ov  the  Superior 
Quadrigeminal  Body. 


mus,  where  they  end  in  connexion  with  the  thalamic  cells.  The  superior  cerebellar 
peduncle  is,  therefore,  a  great  efferent  tract  which  issues  from  the  lateral 
hemisphere  of  the  cerebellum,  crosses  the  mesial  plane  in  the  lower  part  of  the 
mesencephalon,  and  ends  in  the  red  nucleus  and  the  ventral  part  of  the  optic 
thalamus. 

Red  Nucleus  (nucleus  ruber). — This  is  a  rounded  nuclear  mass,  of  a  reddish 
tint  in  the  fresh  brain,  which  lies  in  the  upper  part  of  the  tegmentum,  and  in  the 
path  of  the  superior  cerebellar  peduncle.  In  transverse  section  it  presents  a  circular 
outline.  It  begins  at  the  level  of  the  lower  border  of  the  superior  quadrigeminal 
body  and  it  extends  upwards  into  the  subthalamic  tegmental  region.  At  first  it  is 
small  and  is  placed  at  a  little  distance  from  the  mesial  plane  ;  but  as  it  proceeds 
towards  the  subthalamic  region,  it  increases  in  bulk  and  approaches  more  nearly 
to  the  mesial  raphe,  and  its  neighbour  of  the  opposite  side.  The  curved  emerging 
bundles  of  the  third  nerve  pass  through  it  on  their  way  to  the  surface.  The 
relation  which  the  fibres  of  the  opposite  superior  cerebellar  peduncle  present  to  it 
has  been  described.  These  fibres  traverse  its  lower  part  in  such  numbers  that  in 
Weigert-Pal  specimens  it  presents  a  very  dark  colour ;  but  higher  up,  as  the  fibres 


IXTERXAL  STRUCTUEE  OF  THE  MESENCEPHALON. 


537 


Inferior 

qnadrigeininal 

nucleus 

Mesencephalic 

root  of  fifth 

nerve 


are  gradually  absorbed  by  the  nuclear  mass,  they  become  less    numerous  in  its 
midst,  and  the  nucleus  assumes  a  paler  tint. 

Xumeroiis  fibres  which  descend  from  the  cerebral  cortex  and  others  from  the  corpus  striatum 
enter  the  red  nucleus.  It  likewise  sends  out  fibres  which  proceed  in  two  directions  :  (1)  upwards 
into  the  thalamus ;  (2)  downwards  to  the  spinal  cord.  The  former  may  be  regarded  as  cariying 
on  the  continuity  of  the  superior  cerebellar  path  after  its  internodal  interruption  in  the  red 
nucleus.  The  fibres  to  the  spinal  cord,  called  the  rubrospinal  tract  and  first  described  by 
Monakow,  cross  to  the  opposite  side  and  then  descend  in  the  tegmentum  to  reach  the  lateral 
column  of  the  cord. 

Posterior  Longitudinal  Fasciculus. — This  is  a  very  conspicuous  tract  of  longi- 
tudinal fibres  ^vhich  extends  throughout  the  whole  length  of  the  medulla,  pons,  and 
mesencephalon,  in  the  formatio  reticularis  or  tegmental  part  of  each.  Below,  at  the 
level  of  the  decussation  of  the  pyramids,  it  becomes  continuous  with  the  anterior 
basis-bundle  of  the  spinal  cord  (p.  491),  whilst,  by  its  opposite  or  upper  end,  it 
establishes  intricate  connexions  in 
the  region  immediately  above  the 
mesencephalon.  Throughout  its 
whole  length  it  lies  close  to  the 
mesial  plane  and  its  fellow  of  the 
opposite  side.  In  the  mesen- 
cephalon it  is  applied  to  the 
ventral  aspect  of  the  Sylvian  gray 
matter,  whilst  in  the  pons  and 
medulla  it  is  situated  immediately 
subjacent  to  the  gray  matter  of  the 
floor  of  the  fourth  ventricle.  One 
of  its  most  salient  features  is  the 
intimate  association  which  it  pre- 
sents with  the  three  motor  nuclei 
from  which  the  nerves  for  the 
supply  of  the  muscles  of  the  eye- 
ball take  origin,  ^iz.  the  oculo-motor 
or  third  nucleus,  the  trochlear  or 
fourth  nucleus,  and  the  abducent 
or  sixth  nucleus.  The  first  two  of 
these  are  closely  applied  to  its  inner 
and  dorsal  aspect,  whilst  the  ab- 
ducent nucleus  is  placed  on  its 
outer  side.  Into  each  of  these  nuclei  it  sends  many  collaterals,  and  probably  also 
some  of  its  constituent  fibres,  and  these  end  in  terminal  arborisations  around  the 
nuclear  cells.  It  would  appear,  therefore,  that  one  of  the  most  important  functions 
of  this  strand  is  to  bind  together  these  nuclei,  and  thus  enable  them  to  act  in 
harmony  with  each  other.  Fibres  also  enter  the  posterior  longitudinal  fasciculus 
from  the  auditory  system  and  perhaps,  also,  from  the  facial  and  other  motor 
nuclei.  The  results  obtained  by  degeneration  would  seem  to  indicate  that,  to  a 
larcre  extent,  it  is  formed  of  fibres  which  run  a  short  course  within  it. 

In  spite  of  the  large  amount  of  attention  which  has  been  given  to  the  study  of  the  posterior 
longitudinal  bundle,  it  must  be  admitted  that  there  is  little  unanimity  of  opinion  regarding  its 
connexions  and  functions.  That  it  is  a  brain  tract  of  high  importance,  is  evident  from  the  fact 
that  it  is  present  in  all  vertebrates,  and,  further,  that  its  fibres  assume  their  medullary  sheaths 
at  an  extremelv  early  period.  In  fish,  amphibians,  and  reptiles,  it  is  one  of  the  most  powerful 
bundles  of  the"  medulla.  In  man  its  fibres  medullate  between  the  sixth  and  seventh  months  of 
foetal  life,  and  at  the  same  time  as  the  fibres  of  the  anterior  basis-bundle  of  the  cord,  with  which 
it  stands  in  connexion. 

According  to  Van  Gehuchten  and  Edinger,  it  extends  upwards  beyond  the  level  of  the 
oculo-motor  nucleus,  and  in  the  subthalamic  region  its  fibres  take  origin  from  a  special  nucleus  of 
its  o'i^-n  in  the  gray  matter  of  the  third  ventricle,  immediately  below  the  level  of  the  corpora 
mammillaria.  Fibres  also  enter  the  posterior  longitudinal  bundle  from  a  nucleus  common  to  it 
and  the  posterior  commissure  of  the  brain.  This  nucleus  is  placed  in  the  fore-part  of  the  Sylvian 
grav  matter  of  the  mid-brain.  Held  asserts  that  numerous  fibres,  arising  from  cells  in  the  superior 
quaVlrigeminal  body,  curve  in  an  arcuate  manner  in  the  tegmentum  outside  the  Sjlvian  gray 


Fig. 


432. — Section  thr(jugh  the  inferior  Quadrigeminal 

BODT  AN'D  THE  TeGMENTDM  OF  THE  MESENCEPHALON 
BELOW    THE    LEVEL    OF    THE    NUCLEUS    OF    THE    FOURTH 

Nerve  in  the  Orang.  (The  decussation  of  the  superior 
cerebellar  peduncles  and  the  course  of  the  fourth  nerve 
in  the  Sylvian  gray  matter  are  seen. ) 


538 


THE  NERVOUS  SYSTEM. 


Decussating 
fibres 

Nucleus  of  in- 
I'erioi'  quadii- 
geminal  body 
Meseuceplialic 
root  of  fifth 
nerve 
Fourtli  nerve 

Posterior 

longitudinal 

bundle 

Lateral  fillet 
Superior 
cerebellar 
peduncle 


Mesial  lillet 


matter,  to  take  part  on  the  ventral  aspect  of  this  in  what  is  called  the  "  fountain  decussation." 

Reaching  the  opposite  side  tliese  fibres  turn  downwards  and  join  the  posterior  longitudinal 

fasciculus.      Tlie  same  authority  considers  that  iibres  from  the  ventral  part  of  the  posterior 

commissure  can  also  be  traced  down- 
wards into  the  posterior  longitudinal 
bundle.  Edinger,  on  the  other  hand, 
jilaces  these  fibres  as  a  distinct  tract  on 
the  ventral  and  lateral  aspect  of  the 
posterior  longitudinal  bundle,  although 
in  apposition  with  it. 

Mendel  believes  that  fibres  from  the 
oculo-motor  nucleus  are  carried  down  in 
the  posterior  longitudinal  bundle,  and, 
from  this,  into  the  facial  nerve  for  the 
supply  of  the  orbicularis  palpebrarum 
and  the  corrugator  suj)ercilii,  bringing 
these  muscles  therefore  under  the  control 
of  the  same  nucleus  as  the  levator  palpe- 
brse  superioris  muscle.  This  view  has 
received  corroboration  at  the  hands  of 
Tooth  and  Turner.  It  has  been  further 
suggested  that  fibres  from  the  hypoglossal 
nucleus  may,  by  theposterior  longitudinal 
fasciculus,  reach  the  facial  nerve,  and 
through  it  the  orbicularis  oris.  In  this 
manner   the   same  nucleus  would   hold 

Fig.  433. — Section  through  the  inferior  Quadrigeminal  sway  over  the  tongue  and  the  sphincter 
Body  and  the  Tegmentum  of  the  Mesencephalon,  muscle  of  the  lips.  The  close  relation 
AT  A  SLIGHTLY  LowER  Level  THAN  FiG.  432.  which  exists  between  the  ascending  part 

of  the  intrapontine  portion  of  the  facial 

nerve  and  the  posterior  longitudinal  bundle  would  render  the  passage  of  fibres  from  one  to  the 

other  a  matter  which  could  easily  be  understood.     Another  interchange  of  fibres  through  the 

posterior  longitudinal  Ixtndle  has  been  described  by  Duval  and  Laborde.     According  to  these 

authorities,    filjres   from  the  abducent  nucleus  ascend   in    the 

posterior    longitudinal    bundle   into   the   mesencephalon,    and 

establish  connexions  with  that  part  of  the  ocido-motor  nucleus 

from  which  the  nerve  for  the  internal  rectus  of  the  opposite 

side   derives   its    fibres.     If  this   view  be  correct,  it  affords  a 

ready  and  simple  anatomical  explanation  of  the   harmonious 

action  of  the  external  and  internal  recti  muscles  in  producing 

movements  of  the  two  eyeballs  simultaneously  to  the  right  and 

to  the  left.     From  the  investigations  of  E.  H.  Eraser  it  would 

appear  that  no  fibres  from  the  abducent  nucleus  go  directly  into 

the  oculo-motor  nerve.      The  same   observer   has  sho-wTi  that 

many  filjres  from  Deiters'  nucleus,  through  the  patli  aft'orded 

by  the  posterior  longitudinal  bundle,  enter  the  third  and  the 

fourth  nuclei. 


^^'r^^<C 


Lateral  Fillet  (lemniscus  lateralis). — The  lateral 
fillet  is  a  definite  tract  of  longitudinal  fibres,  which 
extends  upwards  through  the  lateral  part  of  the  teg- 
mental substance  of  the  upper  portion  of  the  pons  and 
the  mesencephalon.  It  is  formed  by  the  fibres  of  the 
corpus  trapezoides  in  the  lower  part  of  the  pons, 
abruptly  turning  upwards  and  taking  a  course  towards 
the  quadrigeminal  region.  Entering  into  its  constitu- 
tion, therefore,  are  fibres  from  several  sources,  viz.  (1) 
from  the  terminal  cochlear  nuclei  of  the  opposite 
side;  (2)  from  the  terminal  cochlear  nuclei  of  the 
same  side ;  (3)  from  the  superior  olivary  nuclei.  As 
the  tract  proceeds  upwards  a  continuation  of  the 
gray  matter  of  the  superior  olivary  nucleus  is  carried 
up  in  connexion  with  it  to  form  the  nucleus  of  the  lateral  fillet,  and  from  this 
fibres  are  also  added  to  the  strand.  In  the  mesencephalon  the  fibres  of  the 
lateral  fillet  end  in  the  nucleus  of  the  inferior  quadrigeminal  body  (p.  534)  and 
in  the  gray  substance  of  the  corpus  geniculatum  internum,  whilst  a  few  are 
carried  into  the  suyjerior  quadrigeminal  body.  The  fibres  which  go  to  the  inferior 
quadrigeminal  body  sweep  outwards  round  the  outer  side  of   the  superior  cere- 


FiG.  434. — Diagram  of  the  Con- 
nexions OF  THE  Posterior 
Longitudinal  Bundle  (after 
Held — modified), 


LATEKAL  AND  MESIAL  FILLETS. 


539 


bellar  peduncle,  and  to  some  extent  appear  on  the  surface  of  the  mesencephalon 
(p.  533). 

But  the  lateral  fillet  cannot  be  considered  as  a  tract  composed  entirely  of  ascending  fibres 
belonging  to  the  auditory  system.  It  also  contains  descending  fibres,  the  coiinexions  and 
functions  of  which  are  not  fully  understood.  These  have  been  traced  ))y  Feriier  and  Turnei' 
through  the  pons  and  medulla  into  the  lateral  column  of  the  cord. 

Mesial  Fillet  (lemniscus  mesialis). — The  mesial  fillet  has  already  been  followed 
through  the  medulla  and  pons,  and  its  position  in  each  of  tliese  portions  of  the 
brain-stem  has  been  defined  (pp.  493  and  504).  In  the  tegmentum  of  the  lower 
part  of  the  mesencephalon  it  is  carried  up  in  the  form  of  a  more  or  less  flattened 
band  on  the  ventral  aspect  of  the  decussating  superior  cerebellar  peduncles.  To 
its  outer  side,  and  forming  an  angle  with  it  (as  seen  in  transverse  section),  is  the 
lateral  fillet  (Figs.  432  and  433),  and  at  this  level  there  is  no  clear  demarcation 
between  these  two  tracts.  In  the 
upper  part  of  the  mesencephalon  the 
appearance  of  the  red  nucleus  in  the 
tegmentum  causes  the  mesial  fillet  to 
take  up  a  more  lateral  and  dorsal 
position,  so  that  it  now  comes  to  lie 
subjacent  to  the  corpus  geniculatum 
internum  (Fig.  431,  p.  536).  At  this 
level  it  exhibits  a  crescentic  outline 
in  '  transverse  section,  and  the  lateral 
fillet  has  to  a  large  extent  disappeared 
from  its  outer  side. 

The  mesial  fillet  takes  origin  in 
the  lower  part  of  the  medulla  ob- 
longata from  the  gracile  and  cuneate 
nuclei  of  the  opposite  side  (p.  493). 
Seeing  that  the  posterior  column  of 
the  cord  ends  in  these  nuclei,  the  fillet 
may  be  considered  to  continue  that 
column  upwards  into  the  brain.  In 
the  mesencephalon  a  considerable  con- 
tribution of  fibres  is  given  by  the  mesial 
fillet  to  the  superior  quadrigeminal 
body,  and  then  the  remainder  of  the 
tract  proceeds  through  the  subthalamic 
tegmental  region  into  the  hinder  part 
of  the  lateral  nucleus  of  the  optic 
thalamus.  Here  its  fibres  end  in  ter- 
minal arborisations  around  the  thala-  p^^  435. —diagram  of  the  Connexions  of  the 
mic  cells.  Mesial    Fillet    and    also    of    certain    of    the 

Thalamo-cortical  Fibres. 

G-anglion  Interpedunculare  and  Fasci- 
culus Retrofiexus.— On  the  ventral  aspect  of  the  tegmentum,  close  to  the  surface  and  to  the 
mesial  plane,  there  is  a  small  group  of  cells  in  the  lower  part  of  the  gray  matter  which  forms 
the  locus  perforatus  posticus.     This  is  termed  the  ganylion  interpedunculare. 

The  fasciculus  retrofiexus  is  a  small  band  of  fibres  which  arises  above  in  the  ganglion 
habenulffi— a  nuclear  mass  ivhich  will  be  studied  in  connexion  with  the  diencephalon— and 
which  runs  downwards  and  forwards  in  the  tegmentum  of  the  upper  part  of  the  mesencephalon 
between  the  inner  aspect  of  the  nucleus  ruber  and  the  mesial  plane,  to  end  in  the  ganglion 
interpedunculare. 

Fountain  Decussation.— If  the  region  in  front  of  the  posterior  longitudinal  bundles  be 
examined  in  the  upper  part  of  the  mesencephalon  a  very  close  decussation  of  fibres  m  the  mesial 
plane  will  be  observed  in  the  interval  between  the  two  red  nuclei.  This  is  the  "  fountain 
decussation."  According  to  Held,  the  fibres  which  take  part  in  the  dorsal  portion  of  tlie 
fountain  decussation  (decussation  of  Meynert)  come  from  the  superior  quadrigeminal  Ijodies,  and 
after  they  have  gained  the  opposite  side,  they  turn  downwards  in  tlie  posterior  longitudinal 
fasciculus.  The  ventl-al  part  of  the  decussation  (decussation  of  Forel)  would  appear  to  be  formed 
by  arcuate  fibres  of  the  tegmentum  which  arise  in  the  gray  matter  of  the  Sylvian  aqueduct. 

Crusta  or  Pes  of  the  Crus  Cerebri  (basis  pedunculi).— The  crusta  presents  a 


540 


THE  NEEVOUS  SYSTEM. 


somewhat  crescentic  outline  when  seen  in  section,  and  it  stands  quite  apart  from 
its  fellow  of  the  opposite  side.  It  is  composed  of  a  compact  mass  of  longitudinally 
directed  fibres,  all  of  which,  as  Dejerine  has  shown,  arise  in  the  cortex  of  the 
cerebrum  and  pursue  an  unbroken  corticifugal  course  into  and  through  the  crusta 
of  the  crus  cerebri.  These  fibres  may  be  classified  into  two  distinct  sets,  viz. 
cortico-pontine  and  pyramidal. 

The  cortico-pontine  fibres  possess  this  leading  peculiarity :  in  their  course  down- 
wards they  are  all  arrested  in  the  ventral  part  of  the  pons  Varolii  and  end  in 
fine  terminal  arborisations  around  the  cells  of  the  nucleus  pontis.  They  come  from 
certain  well-defined  areas  of  cerebral  cortex,  viz.  (1)  the  cortex  of  the  prefrontal 
part  of  the  frontal  lobe,  and  (2)  the  cortex  of  the  middle  portion  of  the  temporal 
lobe.  These  tracts  would  appear  to  hold  a  very  definite  position  within  the  crus. 
Thus  it  has  been  satisfactorily  established  that  the  temporo-pontine  strand  forms  the 
outer  or  lateral  fifth  of  the  crusta,  whilst  the  researches  of  Ferrier  and  Turner 
render  it  more  than  likely  that  the  fronto-pontine  strand  holds  a  similar  position 
in  the  inner  or  mesial  part  of  the  crusta. 

The  pyramidal  fibres  constitute  the  great  motor  tract  from  the  cerebral  cortex. 
They  occupy  a  position  corresponding  to  the  middle  three-fifths  of  the  crusta. 
The  pyramidal  tract  differs  from  the  cortico-pontine  strands  in  being  carried 
downwards  through  the  ventral  part  of  the  pons  and  on  the  ventral  aspect  of  the 
medulla  into  the  cord,  which  it  enters  in  the  form  of  the  crossed  and  direct 
pyramidal  tracts.  On  its  way  through  the  pons  and  medulla  it  sends  fibres  to  the 
various  motor  nuclei  in  those  sections  of  the  brain-stem. 


Deep  Origin  of  the  Cranial  Nerves  which  arise  within  the 

Mesencephalon. 

Two  of  the  motor  cranial  nerves,  viz.  the  oculo-motor  and  the  trochlear  nerves, 
as  well  as  the  mesencephalic  root  of  the  trigeminal  nerve,  obtain  origin  within  the 

mesencephalon.       The     nuclei 

Decussation  of  lateral  fillet  fibres    — __. , 


from  which  they  spring  are 
all  situated  within  the  gray 
matter  of  the  Sylvian  aque- 
duct. 

Mesencephalic  Root  of  the 
Trigeminal  Nerve  (radix  de- 
scendens).  —  The  fibres  of  this 
root  arise  from  a  column  of 
large,  sparsely -arranged  cells, 
which  extends  throughout  the 
entire  length  of  the  mesen- 
cephalon. These  cells  lie  in 
the  outer  part  of  the  Sylvian 
gray  matter,  close  to  the  teg- 
mentum. The  axons  which- 
emerge  from  the  cells  run 
downwards  close  to  the  outer 
surface  of  the  Sylvian  gray 
matter  in  the  form  of  a  small, 
gradually-increasing  tract.  In 
the  lower  part  of  the  mesen- 
FiG.  4.36.~Srction  through  the  iNFERtoR  QuADRioEMiNAL  BoDY  ccphalou  thls  tract  assumcs  a 

AND  THE  TEOMEXTUM    OF   THE    MESENCEI'HALON    AT  THE    LEVEL    crCSCCntic       OUtliuC         aud       ultl- 

NErE^OrTn^  ''"'"  "'  ™'  '''"''"'  ""'  '"'  '^""'"'^•'''''  mately  comes  to  lie'on  the  inner 

aspect  of  the  superior  cerebellar 
peduncle  (Fig.  406,  p.  504).  The  further  course  of  the  mesencephalic  root  of  the 
fifth  nerve  through  the  upper  jjart  of  the  pons,  to  the  point  where  it  joins  the 
emerging  motor  root  of  the  trigeminal  nerve,  has  already  been  traced  (p.  526). 

Trochlear  or  Fourth  Nerve  (nervus  trochlearis). — The  trochlear  nerve  supplies 


Sylvian  aqueiliict 

Sylvian  gray  n  atter 

Nucleus  of  inferior 
qnadrigerainal  body 

Inferior  brachium 

Mesencephalic  root 
of  fifth  nerve 

Nucleus  of  fourth 
nerve 

Po.sterior  lonjii- 
tudinal  bundle 

Lateral  fillet 

Decussation  of  the 

superior  cerebellar 

peduncles 


Mesial  111 


DEEP  OKIGIN  OF  THE  TEOCHLEAR  NERVE. 


541 


the  superior  oblique  muscle  of  the  eyeball.  It  emerges  from  the  brain,  ou  its 
dorsal  aspect,  at  the  upper  part  of  the  superior  medullary  velum,  immediately 
below  the  lower  border  of  the  inferior  quadrigeminal  body  (Fig.  438,  p  543).  The 
nucleus  from  which  it  arises  is  a  small  oval  mass  of  gray  matter,  placed  in  the 
ventral  part  of  the  Sylvian  gray  matter  at  the  level  of  the  upper  part  of  the 
inferior  quadrigeminal  body.  The  close  association  of  this  nucleus  with  the 
posterior  longitudinal  bundle  has  already  been  alluded  to.  It  is  sunk  deeply  in  a 
bay,  which  is  hollowed  out  on  the  dorsal  and  inner  aspect  of  that  tract.  The 
nerve  has  a  course  of  some  length  within  the  mesencephalon.  The  axons  of  the 
cells  leave  the  outer  aspect  of  the  nucleai-  mass,  and  curve  backwards  and  outwards 
in  the  Sylvian  gray  matter  until  they  reach  the  concave  inner  surface  of  the 
mesencephalic  root  of  the  trigeminal  nerve.  Here  they  are  gathered  together  into 
one  or  two  round  bundles,  which,  bending  sharply,  turn  downwards  at  a  right 
angle  and  descend  on  the  inner  side  of  the  trigeminal  root.  When  the  region 
below  the  inferior  quadrigeminal  body  is  reached,  the  nerve  makes  another  sharp 
bend.  This  time  it  turns  inwards,  enters  the  upper  end  of  the  superior  medullary 
velum,  in  which  it  decussates  with  its  fellow  of  the  opposite  side.  Having  thus 
crossed  the  mesial  plane,  the  trochlear  nerve  emerges  at  the  inner  border  of  the 
superior  cerebellar  peduncle.  The  course  pursued  by  the  fourth  nerve  within  the 
Sylvian  gray  matter  may  be  traced  by  examining  in  succession  Fig.  437 ;  Fig.  432, 
p.  537 ;  Fig.  433,  p.  538  ;  and  Fig.  407,  p.  505. 

Oculo-motor  or  Third  Nerve  (nervus  oculo-motorius). — The  oculo-motor  nerve 
supplies  the  levator  palpebrse  superioris,  all  the  ocular  muscles,  with  the  exception 
of  the  superior  oblique  and 
the  external  rectus,  and  also 
two  muscles  within  the  eyeball, 
viz.  the  sphincter  iridis  and 
the  musculus  ciliaris.  The 
nucleus  of  origin  is  placed  in 
the  ventral  part  of  the  Sylvian 
gray  matter  subjacent  to  the 
superior  quadrigeminal  body 
(Fig.  431,  p.  536).  In  length 
it  measures  from  5  to  6  mm. 
Its  lower  end  is  partially  con- 
tinuous with  the  nucleus  of 
the  trochlear  nerve,  whilst  its 
upper  end  extends  upwards  for 
a  short  distance  beyond  the 
mesencephalon  into  the  gray 
matter  on  the  lateral  wall  of 
the  third  ventricle.  Its  relation 
to  the  posterior  longitudinal 
bundle  is  even  more  intimate 
than  that  of  the  trochlear  fig.  437 
nucleus.  It  is  closely  applied 
to  the  dorsal  and  inner  aspect 
of  this  strand ;  many  of  its 
cells  occupy  a  position  in  the  iatervals  between  the  nerve -bundles  of  the 
tract,  and  some  even  are  seen  on  its  ventral  or  tegmental  aspect.  The  axons  of 
the  nuclear  cells  leave  the  nucleus  in  numerous  bundles,  which  describe  a  series 
of  curves  as  they  proceed  forwards  through  the  posterior  longitudinal  bundle,  the 
tegmentum,  red  nucleus,  and  inner  margin  of  the  sulistantia  nigra,  to  finally  emerge 
from  the  brain-stem  along  the  bottom  of  the  sulcus  oculo-motorius  on  the  inner 
aspect  of  the  crus  cerebri. 

The  cells  of  the  oculo-motor  nucleus  are  not  uniformly  distributed  throughout  it.  They  are 
grouped  into  several  more  or  less  distinct  collections  or  clumps,  some  of  which  possess  cells  which 
differ  in  size  and  appearance  from  the  others.  These  cell-clusters  are  very  generally  believed  to 
possess  a  definite  relation  to  the  several  branches  of  the  nerve  and  the  muscles  Avhich  they 
supply.     Perlia  recognises  no  less  than  seven  such  cell-clustei-s  in  each  nucleus,  with  a  small 


Sylvian  gray 
matter 

Sylvian 
aqueduct 
Mesencephalic 
-  root  of  tilth 
nerve 

Fourtli  nerve 
leaving 
nucleus 

Posterior 

longitudinal 

bundle 

Decussation  of 
the  superior 
cerebellar 
jieduncles 


Section  through  the  Inferior  Quadrigeminal  Body 
AND  THE  Tegmentum  of  the  Mesencephalon  at  the 
Level  of  the  Lower  Part  of  the  Nucleus  of  the  Troch- 
lear Nerve  (Orang). 


542  THE  NERVOUS  SYSTEM. 

median  nucleus  placed  accurately  on  the  middle  line,  and  IVoiu  which  fibres  for  both  nerves 
spring.  Whilst  tlie  majority  of  the  filjres  in  the  oculo-motor  nerve  arise  from  the  cell-groups 
which  lie  on  its  own  side  of  the  mesial  plane,  it  has  been  satisfactorily  established  that  a  certain 
proportion  of  its  fibres  are  derived  from  the  nucleus  of  the  opposite  side,  thus  forming  a  crossed 
connexion  and  giving  rise  to  a  median  decussation.  These  crossed  fibres  are  supposed  by  some 
to  supply  the  internal  rectus  muscle  ;  and  we  have  seen  that  there  is  reason  to  believe  that  the 
part  of  the  nucleus  from  which  these  fibres  are  derived  stands  in  connexion  through  the  posterior 
longitudinal  fasciculus  with  the  abducent  or  sixth  nucleus  from  which  proceeds  the  nerve  of 
supply  for  the  external  rectus  muscle.  The  harmonious  action  of  the  internal  and  external  recti 
in  producing  the  conjugate  movements  of  the  eyeballs  is  thus  exjilained. 

The  oculo-motor  nucleus  is  connected — (1)  with  the  occipital  part  of  the  cerebral  cortex  by 
fibres  which  reach  it  through  the  optic  radiation  ;  (2)  with  the  trochlear  and  abducent  nuclei 
(and  probably  with  other  nuclei)  by  fibres  which  come  to  it  through  the  posterior  longitudinal 
bundle  ;  (3)  possibly  with  the  facial  nerve  by  fibres  which  i)ass  out  from  it  into  the  posterior 
longitudinal  Inmdle  (p.  538) ;  (4)  with  the  visual  system  by  fibres  wdiich  enter  it  from  the  cells  of 
the  .superior  quadi-igeminal  l;)ody. 

Development  of  the  Mesencephalon. 

Even  in  the  early  embryo  the  mesencephalon  constitutes  the  smallest  section  of  the 
braiu-tube,  although  the  disproportion  in  size  between  it  and  the  other  primitive  sub- 
divisions of  the  brain  is  not  nearly  so  marked  as  in  the  adult.  Owing  to  the  cephalic 
flexure,  the  mid-brain  for  a  time  occupies  the  highest  part  of  the  summit  of  the  head. 
Later  on  it  becomes  completely  covered  over  by  the  expanding  cerebral  hemispheres. 

The  corpora  quadrigemina  are  derived  from  the  alar  lamina;  of  the  lateral  walls  of  the 
brain-tube,  whilst  the  basal  laminae  thicken  and  ultimately  form  the  tegmenta  and  crustte 
of  the  two  crura  cerebri.  The  original  cavity  of  the  mid-brain  is  retained  as  the  aqueduct 
of  Sylvius. 

For  a  considerable  time  the  cavity  of  the  mesencephalon  remains  relatively  large,  and 
the  lower  part  of  its  dorsal  wall  is  carried  downwards  in  the  form  of  a  diverticulum  or 
recess,  which  overlaps  the  cerebellar  plate.  About  this  time,  also,  the  dorsal  wall  shows  a 
median  fold  or  ridge.  Both  of  these  conditions  are  transitory.  As  the  corpora  quadri- 
gemina take  shape,  the  median  ridge  disappears  and  is  replaced  by  the  median  longitudinal 
groove,  which  separates  the  quadrigeminal  bodies.  Only  its  lower  part  is  retained,  and  this 
is  represented  by  the  frenulum  veli  of  the  adult  brain.  The  diverticulum  of  the  cavity 
gradually  becomes  reduced,  and  finally  disappears  as  the  aqueduct  assumes  form. 

FORE-BRAIN. 

Parts  derived  from  the  Diencephalon. 

Under  this  heading  we  have  to  consider :  (1)  the  thalamus  ;  (2)  the  epithalamus, 
which  comprises  the  pineal  body  and  the  habenular  region  ;  (3)  the  metathalamus, 
or  the  corpora  geaiculata  ;  and  (4)  the  hypothalamus. 

The  hypothalamus  consists  of  two  portions,  viz.  the  pars  mammillaris  hypothalami, 
which  comyjrises  the  corpus  mammillare  and  the  portion  of  the  central  gray  matter 
which  forms  the  floor  of  the  third  ventricle  in  its  immediate  vicinity ;  and  the  pars 
optica  hypothalami,  which  embraces  the  tuber  cinereum,  the  infundibulum,  the 
pituitary  body,  and  the  lamina  cinerea.  Strictly  speaking,  the  optic  part  of  the 
hyxxjthalamus  does  not  belong  to  the  diencephalon,  })ut  it  is  convenient  to  study 
the  parts  which  it  represents  at  this  stage.  It  is  also  convenient  to  examine,  at 
the  same  time,  the  subthalamic  tegmental  region,  although  a  very  considerable  part  of 
this  is  apparently  developed  in  connexion  with  the  mesencephalon. 

The  original  cavity  of  that  part  of  the  brain-tu})e  whicli  Ibrms  the  diencephalon 
is  represented  by  the  greater  part  of  the  third  ventricle  of  tlie  brain. 

Optic  Thalamus  (thalamus). — The  optic  thalamus  is  the  principal  object  in 
this  section  of  the  brain  (Fig.  438).  It  is  a  large  ovoid  mass  of  gray  matter,  which 
lies  obliquely  across  the  path  of  the  cms  cerebri  as  it  ascends  into  the  cerebrum. 
The  smaller  anterior  end  of  the  thalamus  lies  close  to  the  mesial  plane,  and  is  only 
separated  from  the  corresponding  part  of  the  opposite  side  ))y  a  very  narrow 
interval.  The  enlarged  posterior  ends  of  tlie  two  thalami  are  placed  more  widely 
apart,  and  in  the  interval  between  them  the  corpora  quadrigemina  are  situated, 
As  previously  stated,  the  crusta  of  the  crus  cerebri,  composed  of  corticifugal  fibres 


OPTIC  THALAMUS. 


543 


gradually  inclines  outwards  as  it  is  traced  upwards,  and  thus  it  assumes  a  place  on 
the  outer  aspect  of  the  optic  thalamus  and  passes  into  the  internal  capsule  of  the 
brain.  The  tegmental  part  of  the  crus,  on  the  other  hand,  comes  into  relation 
with  the  under  surface  of  the  thalamus,  and  forms  in  this  situation  the  sub- 
thalamic tegmental  region.  To  a  large  extent  the  longitudinal  fibres  of  the 
tegmentum  are  corticipetal.  For  the  most  part  they  enter  the  thalamus,  and 
end  within  it  in  fine  arborisations  around  the  thalannc  cells. 

The  two  optic  thalami,  in  their  anterior  two-thirds,  lie  close  together  on  either 
side  of  a  deep  mesial  cleft,  which  receives  the  name  of  the  third  ventricle  of  the 
brain.  Each  thalamus  presents  an  anterior  and  a  posterior  extremity  and  four 
surfaces.  The 
inferior  and  ex- 
ternal surfaces 
are  in  apposition, 
and,  indeed,  di- 
rectly connected 
witli  adjacent 
parts  of  the  brain, 
and  on  this  ac- 
count it  is  only 
possible  to  study 
them  by  means  of 
sections  through 
the  Ijrain.  The 
superior  and  in- 
ternal  surfaces 

are  tree.  Xon-ventiicvilar 

The  external  ^^''^  °^'  ^'i^i^'""" 
or  lateral  surface 
of  the  thalamus 
is  applied  to  a 
thick  layer  of 
white  matter  in- 
terposed between 
it  and  the  lenti- 
cular nucleus, 
called  the  internal 
capsule,  and  com- 
posed of  fibres 
passing  both  up- 
wards towards 
and  downwards 
from  the  cerebral 

cortex.  A  large  proportion  of  these  fibres  descend  to  form  the  crusta  or  ventral 
part  of  the  crus  cerebri.  From  the  entire  extent  of  the  external  surface  of 
the  thalamus  large  numbers  of  fibres  stream  out  and  enter  the  internal  capsule, 
to  reach  the  cerebral  cortex  ;  over  the  same  area  other  fibres  which  arise  in  the  cortex 
of  the  cerebrum  enter  the  thalamus.  Both  of  these  sets  of  fibres  constitute  what  is 
termed  the  thalamic  radiation,  and  by  this  tlie  thalamus  establishes  a  double  con- 
nexion with  the  entire  extent  of  the  cerebral  cortex.  As  the  fibres  leave  and  enter 
tlie  thalamus  they  intersect  each  other  at  acute  angles,  and  over  the  whole  of  the 
external  surface  of  the  ganglionic  mass  they  form  a  very  distinct  reticulated  zone 
or  stratum,  which  is  termed  the  external  medullary  lamina. 

The  inferior  or  ventral  surface  of  the  thalamus  rests  chiefly  on  the  subthalamic 
tegmental  region  and  the  corpus  mammillare.  In  front,  however,  as  the  tegmental 
substance  gradually  disappears,  the  thalamus  comes  to  lie  over  the  outer  part  of  the 
tuber  cinereum.  From  the  subthalamic  region  many  fibres  enter  the  thalamus  on 
its  under  aspect,  whilst  other  fibres  leave  this  surface  of  the  thalamus  to  take  part 
in  the  thalamic  radiation. 


Groove 

corresponding 

to  fornix 

Quaih'igeininal 

bodies 

Trochlear  nerve. 
Middle  cere- 
bellar peduncle 
Superior  cere- 
bellar jieduncle 
Linirula 


fienu  of  corpus 
I'allosuni 
Corpus  callosuni 
(cut) 

Ventricle  V. 
Septum  luciduni 

Cau<late  nucleus, 

Fornix 

Foramen  of  Monro 

Anterior  conunissurc 
Anterior  tubercle 
of  thalamus 

Gray  commissure 

Third  ventricle 

Taenia  semicircularis 

Tsenia  thalami 

Trigonum  habenulse 

Posterior 

commissure 

Stalk  of  pineal  body 

Pulvinar 
Pineal  body 


Fi(!.  438.— The  Tw( 


Optic  Thalami  (as  seen  from  aliove) 


544  THE  NERVOUS  SYSTEM. 

The  superior  or  dorsal  surface  of  the  thalamus  is  free.  Externally  it  is  bounded 
by  a  groove,  which  traverses  the  floor  of  the  lateral  ventricle  of  the  brain  and 
intervenes  between  the  thalamus  and  the  caudate  nucleus.  In  this  groove  are 
placed  a  slender  band  of  longitudinal  fibres,  termed  the  taenia  semicularis,  and  in 
its  fore-part  the  vein  of  the  corpus  striatum.  Internally,  the  superior  surface  of 
the  thalamus  is  separated  from  the  internal  or  mesial  surface  in  its  anterior  half  by 
a  sharp  edge  or  prominent  ledge  of  the  ependyma  of  the  third  ventricle.  This  is 
termed  the  taenia  thalami,  and  the  ridge  which  it  forms  is  accentuated  by  the  fact 
that,  subjacent  to  it,  there  lies  a  longitudinal  strand  of  fibres  called  the  stria 
medullaris.  When  these  two  structures,  viz.  the  ependymal  ridge  and  the  subjacent 
tract,  are  traced  backwards,  they  are  seen  to  turn  inwards  and  become  continuous 
with  the  stalk  or  peduncle  of  the  pineal  body.  Behind  the  portion  of  the  taenia 
thalami  which  turns  inwards  towards  the  pineal  body  a  small  depressed  triangular 
area,  the  trigonum  habenulse,  situated  in  front  of  the  superior  quadrigeminal  body, 
forms  a  very  definite  inner  boundary  for  the  hinder  part  of  the  superior  surface  of 
the  thalamus. 

The  superior  surface  of  the  thalamus  is  slightly  bulging  or  convex,  and  is  of  a 
whitish  colour,  owing  to  the  presence  of  a  thin  superficial  covering  of  nerve-fibres, 
termed  the  stratum  zonale.  It  is  divided  into  two  areas  by  a  faint  oblique  groove, 
which  begins  in  front  at  the  inner  border,  a  short  distance  behind  the  anterior 
extremity  of  the  thalamus,  and  extends  outwards  and  backwards  to  the  outer  part 
of  the  hinder  end.  This  groove  corresponds  to  the  outer  edge  of  the  fornix.  The 
two  areas  which  are  thus  mapped  out  are  very  differently  related  to  the  ventricles 
of  the  brain,  and  also  to  the  parts  which  lie  above  the  thalamus.  The  outer  area, 
which  includes  the  anterior  extremity  of  the  thalamus,  forms  a  part  of  the  floor  of 
the  lateral  ventricle.  It  is  covered  with  ependyma,  overlapped  by  the  choroid 
plexus  of  this  ventricle,  and  lies  immediately  subjacent  to  the  corpus  callosum. 
Along  the  line  of  the  groove  the  epithelial  lining  of  the  lateral  ventricle  is  reflected 
over  the  choroid  plexus  of  this  cavity.  The  inner  area,  which  includes  the  hinder 
end  of  the  thalamus,  intervenes  between  the  lateral  and  third  ventricles  of  the 
brain,  and  takes  no  part  in  the  formation  of  the  walls  of  either.  It  is  covered  by  a 
fold  of  pia  mater,  termed  the  velum  interpositum,  above  which  is  the  fornix,  and 
these  two  structures  intervene  between  the  thalamus  and  the  corpus  callosum. 

The  anterior  extremity  of  the  thalamus,  called  the  anterior  tubercle  (tuberculum 
anterius  thalami),  forms  a  marked  bulging.  It  projects  into  the  lateral  ventricle, 
behind  and  to  the  outer  side  of  the  free  portion  of  the  anterior  pillar  of  the  fornix. 
The  foramen  of  Monro,  a  narrow  aperture  of  communication  between  the  lateral 
and  third  ventricles  of  the  brain,  is  bounded  in  front  by  the  anterior  pillar  of  the 
fornix  and  behind  by  the  anterior  tubercle  of  the  thalamus. 

The  -posterior  extremity  of  the  thalamus  is  very  prominent  and  forms  a  cushion - 
like  projection,  which  overhangs  the  brachia  of  the  corpora  quadrigemina.  This 
prominence  is  called  the  pulvinar.  Another  oval  bulging  on  the  hinder  part  of  the 
thalamus  receives  the  name  of  the  corpus  geniculatum  externum.  It  is  situated 
below,  and  to  the  outer  side  of,  the  pulvinar,  and  presents  a  very  intimate  connexion 
with  the  optic  tract. 

The  mesial  surfaces  of  the  two  thalami  are  placed  close  together,  and  are" 
covered  not  only  by  the  lining  ependyma  of  the  third  ventricle,  but  also  by  a 
tolerably  thick  layer  of  gray  matter,  continuous  below  with  the  central  gray 
substance  which  surrounds  the  aqueduct  of  Sylvius  in  the  mesencephalon.  A  band 
of  gray  matter,  termed  the  gray  or  soft  commissure  (commissura  mollis),  crosses  the 
third  ventricle  and  jr)ins  the  inner  surfaces  of  the  two  thalami  together. 

Intimate  Structure  and  Connexions  of  the  Optic  Thalamus. — The  upper 
surface  of  the  thalamus  is  covered  by  the  stratum  zonale,  a  thin  coating  of  white 
fibres  derived  to  some  extent  from  the  optic  tract,  and  probably  also  from  the  optic 
radiation.  The  inner  surface  has  a  thick  coating  of  central  gray  matter,  whilst 
intervening  between  the  internal  capsule  and  the  outer  surface  is  the  lamina 
medullaris  externa.     The  lower  surface  merges  into  the  subthalamic  region. 

'J'he  gray  matter  of  the  optic  thalamus  is  marked  off  into  three  very  apparent 
parts — termed  the  anterior,  the  mesial,  and  the  lateral  thalamic  nuclei — by  a  thin 


OPTIC  THALAMUS.  545 

vertical  sheet  of  white  matter,  continuous  with  the  stratum  zonale,  termed  the 
lamina  medullaris  interna.  The  lateral  nucleus  (nucleus  lateralis  thalami)  is  by  far 
the  largest  of  the  three.  It  is  placed  between  the  internal  and  the  external 
medullary  laniina3,  and  it  stretches  backwards  beyond  the  mesial  nucleus,  and  thus 
includes  the  whole  of  the  pulvinar  (Fig.  440).  The  mesial  nucleus  (nucleus  medialis 
thalami)  only  reaches  as  far  back  as  the  habenular  region.  It  is  placed  between 
the  central  gray  matter  of  the  third  ventricle  and  the  internal  medullary  lamina. 
The  lateral  nucleus  is  more  extensively  pervaded  by  tiljres  than  the  mesial  nucleus. 
From  the  lateral  nucleus  by  far  the  greatest  number  of  the  fibres  which  form  the 
radiatio  thalami  pass,  and  these  are  seen  crossing  it  in  various  directions  towards 
the  lamina  medullaris  externa.  The  anterior  nucleus  (nucleus  anterior  thalami)  is 
the  smallest  of  the  three  thalamic  nuclei.  It  forms  the  prominent  anterior  tubercle, 
and  is  prolonged  in  a  wedge-shaped  manner,  for  a  short  distance,  downwards  and 
backwards  between  the  anterior  parts  of  the  mesial  and  lateral  nuclei.  The  internal 
medullary  lamina  splits  into  two  parts  and  partially  encloses  the  anterior  nucleus. 
In  connexion  with  its  large  cells  a  very  conspicuous  bundle  of  fibres,  the  bundle 
of  Vicq  d'Azyr  (fasciculus  thalamo-mammillaris),  which  arises  in  the  corpus 
maramillare,  comes  to  an  end 

A  diffuse  gray  mass  imperfectly  marked  off  from  the  under  surface  of  the  lateral  nucleus 
receives  the  name  of  the  ventral  nucleus.  Its  lower  part  is  composed  of  the  central  nucleus  of 
Luys  and  the  nucleus  arcuatus.  In  section  the  former  apjoears  as  a  circular  mass  of  gray  matter, 
which  comes  into  view  immediately  behind  the  point  where  the  internal  medullary  lamina 
disappears.  It  would  seem  to  be  intimately  connected  with  fibres  which  reach  it  from  the  red 
nucleus  and  from  the  posterior  commissure.  These  fibres  pass  round  it  so  as  to  mark  it  off  from 
the  rest  of  the  thalamus,  and  in  front  of  the  nucleus  many  of  them  enter  the  internal  medullary 
lamina.  The  nucleus  arcuatus  is  a  small  semilunar  mass  of  gray  matter  placed  below  and  to  the 
outer  side  of  the  central  nucleus  of  Luys, 

The  connexions  of  the  thalamus  are  of  an  extremely  intricate  kind.  It  would 
appear  to  be  a  ganglionic  mass  interposed  between  the  tegmental  corticipetal  tracts 
and  the  cerebral  cortex.  In  its  liiuder  part,  and  through  its  stratum  zonale,  it  also 
has  important  connexions  with  the  optic  tract.  The  corticipetal  tegmental  tracts, 
which  enter  it  from  below,  will  be  noticed  in  connexion  with  the  subthalamic 
region.  Suf&ce  it  to  say,  for  the  present,  that  these  fibres  end  in  the  midst  of  the 
thalamus  in  connexion  with  the  thalamic  cells.  In  addition  to  these,  enormous 
numbers  of  fibres,  arising  within  the  thalamus  as  the  axons  of  its  cells,  stream  out 
from  its  outer  and  under  surfaces  to  form  the  thalamic  radiation.  These  thalamo- 
cortical fibres  pass  to  every  part  of  the  cortex  ;  and  although  there  is  no  separation 
of  them  into  distinct  groups  as  they  leave  the  thalamus,  it  is  customary  to  regard 
them  as  constituting  a  frontal  stalk,  a  parietal  stalk,  an  occipital  stalk,  and  a 
ventral  stalk.  But  fibres  from  the  cortex,  cortico -thalamic  fibres,  likewise  stream 
into  the  thalamus  in  large  numbers,  and  end  in  fine  arborisations  around  its  cells. 
A  double  connexion  with  the  cerebral  cortex  is  thus  established  by  the  thalamus. 

The  frontal  stalk  of  the  thalamic  radiation  emerges  from  the  anterior  part  of  the  lateral 
surface  of  the  thalamus  and  passes  through  the  anterior  limb  of  the  internal  capsule,  to  reach  the 
cortex  of  the  frontal  lobe.  Many  of  these  fibres  end  in  the  caudate  and  lenticular  nuclei,  between 
which  they  proceed.  The  parietal  stalk  issues  from  the  lateral  surface  of  the  thalamus,  and, 
passing  through  the  internal  capsule  (and  to  some  extent,  also,  through  the  lenticular  nucleus 
and  the  external  capsule),  gains  the  cortex  of  the  hinder  part  of  the  frontal  lobe  and  of  the 
parietal  lobe.  The  occipital  stalk  emerges  from  the  outer  aspect  of  the  pulvinar  and  constitutes 
the  so-called  optic  radiation.  These  fibres  sweep  outwards  and  backwards  round  the  outer  side 
of  the  posterior  horn  of  the  lateral  ventricle  to  gain  the  cortex  of  the  occipital  lobe.  The 
ventral  stalk  streams  out  from  the  under  aspect  of  the  anterior  jjart  of  the  thalamus,  in  front 
of  the  suljthalamic  tegmental  region  and  the  corpus  mammillare.  Its  fibres  arise  in  Ijoth  the 
mesial  and  lateral  nuclei,  and  sweep  downwards  and  outwards  to  reach  the  region  below  the 
lenticular  nucleus.  One  A-ery  distinct  band  which  lies  dorsal  to  the  other  fibres  (ansa  lenticu- 
laris)  enters  the  lenticular  nucleus,  whilst  the  remainder  (ansa  pedunculai-is)  continue  in  an 
outward  direction  below  the  lenticular  nucleus  and  gain  the  cortex  of  the  temporal  lobe  and  of 
the  insula  or  island  of  Eeil. 

Flechsig  divides  the  thalamo-cortical  fibres  of  ordinary  sensation  into  three  sensory  systems. 
These  he  has  lieen  able  to  distinguish  by  studying  the  order  in  which  they  assume  their  sheaths 
of  myelin  in  the  fcctus  and  infant. 

Ferrier  and  Turner,  by  the  degenerative  method  of  investigation,  corroborate  Flechsig's 
results.     They  confirm  the  observation  of  Flechsig  that,  while  thalamic  fibres  are  distributed  to 

39 


546 


THE  NEEVOUS  SYSTEM. 


the  several  regions  of  the  cerebral  cortex  to  an  almost  equal  extent,  there  is  one  district,  viz.  the 
frontal  pole,  to  -which  the  supply  is  scanty.     Another  very  important  result  has  been  obtained 

by  these  authors.     They  have  established 

oe^ ^  the  fact  that  many  of  the  thalamic  fibres 

cross  the  mesial  plane  in  the  corpus  cal- 
losum,  and  thus  gain  the  cortex  of  the 
opposite  cerebral  hemisphere.  Hamilton's 
crossed  callosal  tract  thus  receives  con- 
formation. 


CALLOSUM 


LIMB 
NT'rCAPSULf 


UADir  BODY 


LOBE 

Fig,  439. — Schema.     Founded  on  the  observations  of 
Flechsig,  and  Ferrier  and  Turner. 


Intimate  Structure  of  the  Corpus 
Geniculatum  Externum.  —  Sections 
through  the  external  geniculate  body 
reveal  the  fact  that  it  is  composed  of 
a  series  of  alternately  placed  gray  and 
white  curved  laminee.  This  gives  it 
a  very  characteristic  appearance.  The 
white  laminae  are  composed  of  fibres 
which  enter  the  body  from  the  optic 
tract  and  the  optic  radiation.  The 
connexions  of  the  geniculate  bodies 
will  be  studied  with  the  optic 
tract. 

Subthalamic  Tegmental  Region. 
— The  tegmental  part  of  the  crus  cere- 
bri is  prolonged  upwards  and  assumes 
a  position  below  the  hinder  part  of  the 
thalamus.  The  red  nucleus  is  a  con- 
spicuous object  in  sections  through  the 
lower  part  of  this  region  (Fig.  440).  It 
presents  the  same  appearance  as  lower 
down  in  the  mesencephalon,  and, 
gradually  diminishing,  it  disappears 
before  the  level  of  the  corpus  mam- 
millare  is  reached.  Carried  up  around  it  are  the  same  longitudinal  tracts  of  fibres 
which  have  been  studied  in  relation  to  it  in  the  tegmental  part  of  the  mesencephalon. 
Certain  of  these  fibres,  placed  in  immediate  relation  to  the  red  nucleus,  form  a 
coating  or  capsule  for  it.  This  coating  is  partly  derived  from  those  fibres  of  the 
superior  cerebellar  peduncle  which  pass  directly  up  into  the  thalamus  and  also 
partly  from  fibres  which  issue  from  the  nucleus  itself.  The  mesial  fillet,  also, 
which  in  the  upper  part  of  the  mesencephalon  is  observed  to  take  up  a  position  on 
the  lateral  and  dorsal  aspect  of  the  red  nucleus,  maintains  a  similar  position  in  the 
subthalamic  region.  When  the  red  nucleus  comes  to  an  end  these  various  fibres 
are  continued  onwards  and  form,  in  the  position  previously  occupied  by  the  nucleus, 
a  very  evident  and  dense  mass  of  fibres.  The  fibres  of  the  mesial  fillet,  of  the 
superior  cerebellar  peduncle,  and  of  the  red  nucleus  are  prolonged  upwards  into  the 
ventral  part  of  the  thalamus,  where  they  end  in  connexion  with  the  thalamic  cells. 
The  substantia  nigra  is  likewise  carried  into  the  subthalamic  region,  where  it. 
maintains  its  original  position  on  the  dorsal  aspect  of  the  crusta  of  the  crus  cerebri. 
As  it  is  traced  upwards,  it  is  seen  to  gradually  diminish  in  amount.  It  shrinks 
from  within  outwards,  and  finally  disappears  when  the  hinder  part  of  the  corpus 
mammillare  is  reached. 

In  coronal  sections  through  the  subthalamic  region,  the  most  conspicuous  object 
which  comes  into  view  is  the  corpus  subthalamicum  or  tlie  nucleus  of  Luys  (Fig.  440). 
It  is  a  small  mass  of  gray  matter,  shaped  like  a  biconvex  lens,  which  makes  its  appear- 
ance on  the  dorsal  aspect  of  the  crusta  of  the  crus  cerebri  immediately  to  the  outer 
side  of  the  substantia  nigra.  At  first  it  lies  in  an  angle,  which  is  formed  by  the 
meeting  of  the  crusta  and  the  internal  capsule  ;  but,  rapidly  enlarging  in  an  inward 
direction,  it  takes  the  place  of  the  diminishing  substantia  nigra  on  the  dorsal 
surface  of  the  crusta  at  the  level  of  the  lower  part  of  the  corpus  mammillare.  The 
corpus  subthalamicum  is  rendered  all  the  more  evident  by  the  fact  that  it  is 


SUBTHALAMIC  TEGMENTAL  EEGION. 


547 


sharply  defined  by  a  thin  capsule  of  white  fibres.  On  its  mesial  aspect  these  fibres 
proceed  inwards  and  form  a  very  evident  decussation  across  the  middle  line  in  the 
floor  of  the  third 
ventricle,  immed- 
iately above  the 
hinder  ends  of  the 
corpora  mammil- 
laria. 

The  corpus 
subthalamicum,  in 
the  fresh  condi- 
tion, presents  a 
brownish  colour, 
partly  from  the 
fact  that  its  cells  pormx 

arepigmented,and  Anterior  nucipus 


Intersection  nf 

the  coroiix 

railiata  an  1 

callosal  systems 

of  fibies 

Caudate  nucleus 

Corpus  callosum 


External  caijsule 


of  tlialaniu 
Stria  niedullai  is 

Internal  capsule 

Internal  nncltus 

of  tlialanuis 

External  nucleus 
of  thalamus 


Red  nucleus 
Nucleus  of  Luys 


Substantia  nigra 


Crusta  of  cius 
cerebn 


Putanien 

Fronto-parietal 

(jperculum 


^^^7^=^- — Globus  pallidas 


Caudate  nucleus 


Fig.  440. 


-Coronal  Section  through  the  Cerebrdm  of  an  Orang 
through  the  subthalamic  tegmental  region. 


partly  also  on 
account  of  the 
numerous  capil- 
lary blood-vessels 
which  pervade  its 
substance. 

Pineal  Body 
(corpus  pineale). 
— This  is  a  small, 
dark,  reddish  body, 
about  the  size  of  a 
cherry-stone  and 
shaped  after  the 
fashion  of  a  fir- 
cone. Placed  be- 
tween the  hinder 
ends    of    the    two 

thalami,  it  occupies  the  depression  on  the  dorsal  aspect  of  the  mesencephalon, 
which  intervenes  between  the  two  superior  quadrigeminal  bodies.  Its  base,  which 
is  directed  upwards,  is  attached  by  a  hollow  stalk  or  peduncle.  This  stalk  is 
separated  into  a  dorsal  and  a  ventral  part  by  the  prolongation  backwards  into  it 
of  a  small  pointed  recess  of  the  cavity  of  the  third  ventricle.  The  dorsal  part  of 
the  stalk  curves  outwards  and  forwards,  and  on  each  optic  thalamus  becomes 
continuous  with  the  ttenia  thalami  and  the  subjacent  stria  medullaris;  the 
ventral  part  is  folded  round  a  narrow  but  conspicuous  cord-like  band  of  white 
matter,  which  crosses  the  mesial  plane  immediately  above  the  base  of  the  pineal  body 
and  receives  the  name  of  the  posterior  commissure  of  the  cerebrum  (Eig.  438,  p.  543). 

The  pineal  body  is  not  composed  of  nervous  elements.  The  only  nerves  in  its  midst  are  the 
sympathetic  filaments  which  enter  it,  with  its  blood-vessels.  It  is  composed  of  spherical  and 
tubular  follicles,  filled  with  epithelial  cells,  and  containing  a  variable  amount  of  gritty,  calcareous 
matter. 

The  pineal  body  is  a  rudimentary  structure,  but  in  certain  vertebrates  it  attains  a  much 
higher  degree  of  development  than  in  man.  In  the  lizard,  blind- worm,  etc.,  it  is  present  in  the 
form  of  the  so-called  pineal  eye.  In  structure  it  resembles,  in  these  animals,  an  invertebrate  eye, 
and  it  possesses  a  long  stalk,  in  which  nerve-fibres  are  developed.  Further,  it  is  carried  through 
an  aperture  in  the  cranial  wall,  and  consequently  lies  close  to  the  surface  on  the  dorsum  of  the 
head  between  the  parietal  bones. 

Trigonum  Habenulae. — The  small,  triangular,  depressed  area  which  receives  this 
name  is  placed  immediately  in  front  of  the  superior  quadrigeminal  body  in  the 
interval  between  the  peduncle  of  the  pineal  body  and  the  hinder  end  of  the  thalamus 
(Fig.  438,  p.  543).  It  marks  the  position  of  an  important  collection  of  nerve-cells, 
which  constitute  the  ganglion  habenulae.  The  axons  of  these  cells  are  collected  on 
the  ventral  aspect  of  the  ganglion  into  a  bundle,  called  the  fasciculus  retroflexus, 
which  takes  a  curved  course  downwards  and  forwards  in  the  tegmentum  of  the 


548  THE  NERVOUS  SYSTEM. 

mesencephalon.  The  fasciculus  retroflexus  lies  close  to  the  inner  side  of  the 
red  nucleus,  and  finally  comes  to  an  end  in  a  group  of  cells  termed  the  ganglion 
interpedunculare,  situated  in  the  lower  part  of  the  locus  perforatus  posticus 
(see  p.  539). 

The  ganglion  habenuhe  is  likewise  intimately  connected  with  the  stria  medul- 
laris  and  the  dorsal  part  of  the  stalk  of  the  pineal  body. 

As  previously  stated,  the  stria  medullaris — a  very  evident  band  of  white 
matter — lies  on  the  optic  thalamus,  subjacent  to  the  ependymal  ridge  termed  the 
tccnia  thalami.  When  traced  backwards,  many  of  the  fibres  of  the  stria  medullaris 
are  observed  to  end  amongst  the  cells  of  the  ganglion  habenulye,  whilst  others  are 
continued  past  the  ganglion  to  enter  the  peduncle  of  the  pineal  body,  and,  through 
it,  to  reach  the  ganglion  habenulae  of  the  opposite  side,  in  connexion  with  the  cells 
of  which  they  terminate.  The  stria  medullaris,  therefore,  ends  partly  in  the 
ganglion  habenulge  of  its  own  side  and  partly  in  the  corresponding  ganglion  of  the 
opposite  side.  The  decussation  of  fibres  across  the  middle  line  forms  the  dorsal 
part  of  the  pineal  stalk  or  peduncle,  and  is  frequently  termed  the  commissura 
habenularum. 

When  the  stria  medullaris  is  traced  in  the  opposite  direction,  it  is  noticed  to 
split  into  a  dorsal  and  ventral  part  near  the  anterior  pillar  of  the  fornix.  The 
dorsal  part  turns  abruptly  upwards,  and,  joining  the  fornix,  is  carried  in  it  to  the 
hippocampus  major  or  cornu  ammonis  from  cells  in  which  its  fibres  take  origin. 
The  ventral  'part  turns  downwards  and  appears  to  spring  from  a  collection  of  cells 
in  the  gray  matter  on  the  base  of  the  brain  close  to  the  optic  chiasma.  The  stria 
medullaris  is  believed  to  form  a  part  of  the  olfactory  apparatus. 

Commissura  Posterior. — The  posterior  commissure  is  a  slender  band  of  white 
matter,  which  crosses  the  middle  line  under  cover  of  the  stalk  of  the  pineal  body 
and  overlies  the  entrance  of  the  aqueduct  of  Sylvius  into  the  third  ventricle.  The 
fibres  which  enter  into  the  formation  of  the  posterior  conmiissure  are  believed  to 
arise  in  a  special  nucleus,  which  is  placed  in  the  central  gray  matter  immediately 
above  the  oculo-motor  nucleus.  They  decussate  with  each  other  across  the  mesial 
plane  and  thus  the  commissure  is  formed.  The  other  connexions  of  this  little 
band  are  not  satisfactorily  established,  but  Held  believes  that  some  of  its  ventral 
fibres  pass  downwards  into  the  posterior  longitudinal  bundle. 

Locus  Perforatus  Posticus  (substantia  perforata  posterior). — This  has  already 
been  described  on  p.  475.  Some  delicate  bands  of  white  matter,  termed  the  taenia 
pontis,  may  frequently  be  seen  emerging  from  the  gray  matter  of  this  region ;  they 
then  curve  round  the  crura  cerebri  in  close  relation  to  the  upper  border  of  the 
pons,  into  which  they  ultimately  sink  (Fig.  390,  p.  484). 

Corpora  Mammillaria. — The  corpora  mammillaria  are  two  round  white  bodies, 
each  about  the  size  of  a  pea,  which  lie  side  by  side  in  the  interpeduncular  space  on 
the  base  of  the  brain,  immediately  in  front  of  the  locus  perforatus  posticus. 

Each  corpus  mammillare  is  coated  on  the  outside  by  white  matter  derived 
from  the  anterior  pillar  of  the  fornix,  and  contains,  in  its  interior,  a  composite  gray 
nucleus  with  numerous  nerve-cells.  Several  important  strands  of  fibres  are  con- 
nected with  the  corpus  mammillare :  (1)  The  anterior  pillar  of  the  fornix  curves 
downwards  in  the  lateral  wall  of  the  third  ventricle  to  reach  the  corpus  mammillare, 
and  its  filjres  end  amidst  the  cells  of  that  body.  (2)  A  bundle  of  fibres,  called 
the  bundle  of  Vicq  dAzyr,  which  at  first  sight  appears  to  be  continuous  with  the 
anterior  pillar  of  the  fornix,  takes  origin  in  its  midst  and  extends  upwards  into 
the  optic  thalamus,  to  end  in  fine  arborisations  around  the  large  cells  in  the  anterior 
thalamic  nucleus.  (3)  Another  bundle  of  fibres,  the  pedunculus  corporis  mammillaris, 
takes  form  within  the  corpus  mammillare  and  extends  downwards  in  the  gray 
matter  of  the  floor  (jf  the  third  ventricle,  to  reach  tlie  tegmentum  of  the  mesen- 
cephalon.    The  ultimate  destination  of  these  fibres  is  doubtful. 

Tuber  Cinereum  and  Infundibulum. — The  tuber  cinereum  is  a  small,  slightly 
prominent  field  of  gray  matter,  wliich  occupies  the  anterior  part  of  the  inter- 
peduncular space  between  the  corpora  mammillaria  l)ehind  and  the  optic  chiasma 
in  front.  From  its  fore-part  the  infundibulum,  or  stalk  of  the  pituitary  body, 
projects  downwards  and  connects  that  body  with  the  base  of  the  brain.     In  its 


PITUITAEY  BODY. 


549 


upper  part  the  infundibulum  is  hollow,  a  small,  tunnel-shaped  diverticulum  of  the 
cavity  of  the  third  ventricle  being  prolonged  downwards  into  it. 
Pituitary  Body  (hypophysis). 


— This  is  a  small  oval  structure, 
flattened  from  above  downwards, 
and  with  its  long  axis  directed 
transversely,  which  occupies  the 
pituitary  fossa  in  the  floor  of  the 
cranium.  It  is  composed  of  two 
lobes — a  large  anterior  lobe  and  a 
smaller  posterior  lobe,  which  are 
closely  applied  the  one  to  the  other. 
The  infuudibulum,  which  extends 
downwards  from  the  tuber  cin- 
ereum,  is  attached  to  the  posterior 
lobe. 


iraincii  of 

Monro 

Antt'i-ioi- 

coiiiiiiissmv 


Pituitary  body 


Fio.  441. — iMESiAL  Section  through  thk  Pituitary  Reoion 
IN  A  Child  of  Twelve  Months  old. 

In  this  section,  as  well  as  in  the  section  figured  in  Fig.  442,  the 
inftindibuliim  has  the  appearance  of  being  attached  to  the 
anterior  lobe.  This  is  due  to  the  way  in  wliich  the  larger 
anterior  lobe  grows  backwards  so  as  to  embrace  the  smaller 
posterior  lobe.  The  latter  is,  as  it  were,  accommodated  in  a 
hollow  in  the  hinder  aspect  of  the  anterior  lobe. 
From  a  photograph  by  Professor  Symington. 


The  infuudibulum  and  posterior 
lobe  of  the  pituitary  body  are  de- 
veloped in  the  form  of  a  hollow  diver- 
ticulum, which  grows  downwards  from 
the  floor  of  that  part  of  the  embryonic 
brain  which  afterwards  forms  the 
third  ventricle.  The  original  cavity 
of  this  diverticvilum  becomes  obliter- 
ated, except  in  the  upper  part  of  the 
infundibulum.  In  structure,  the  pos- 
terior lobe  of  the  pituitary  body  shows 
little  trace  of  its  origin  from  the 
wall  of  the  brain-tube.  It  is  chiefly  composed  of  connective  tissue  and  blood-vessels,  with 
branched  cells  scattered  throughout  it. 

The  anterior  lobe  has  quite  a  different  origin,  and  may  be  regarded  as  the  functional 

part  of  the  pituitary  body.     It  is  de- 


rived from  a  tubular  diverticulum, 
which  grows  upwards  from  the  primi- 
tive buccal  cavity  or  stomodseimi.  Its 
connexion  with  the  latter  (canalis 
cranio-pharyngeus)  is  in  the  course  of 
time  cut  off,  and  the  diverticulum  be- 
comes encased  within  the  cranial  cavity 
in  intimate  association  with  the  cerebral 
portion  of  the  organ.  Structurally,  it 
consists  of  tubules  or  alveoli,  lined  by 
epithelial  cells  and  surrounded  by 
capillary  vessels.  Its  structure  is  in 
some  respects  not  unlike  that  of  the 
parathyroid  bodies.  In  giants,  and  in 
cases  of  acromegaly,  the  pituitary  body 
is  usually  greatly  enlarged. 


Foramen  of  Monro 


Anterior  commissure 


-Corpus  mannnillare 

Subarachnoid  tissue 
in  cistevna  basalis 

Iiifunditiulum 


Pituitary  body 


Cisterna  pontis 


Basi-octipital 


Sphenoidal  sinus 


Lamina    Cinerea. — This    is  a 

thin,  delicate  lamina  which  may  be 

seen  on    the   basal   aspect   of   the 

brain,    stretching    from   the  upper 

aspect  of  the  optic  chiasma  in  an 

upward  direction   to    become  con- 

-Mesial  Section  through  the  Pituitary  Region  nected    with    the    rostrum    of    the 

^^  ™^  ^°"''^-  corpus  callosum. 

Anterior  Commissure  of  the  Cerebrum. — In  the  anterior  part  of  the  cleft, 

between  the  two  optic  thalami  and  immediately  in  front  of  the  anterior  pillars  of 

the  fornix,  a  round  bundle  of  fibres  crosses  the  mesial  plane.     This  is  the  anterior 

commissure.     It  is  much  larger  than  the  posterior  commissure. 


Fig.  442.- 


550 


THE  NEEVOUS  SYSTEM. 


Third  Ventricle  (ventriculus  tertius).  —  This  is  the  narrow  cleft  which 
separates  the  two  optic  thalami.  Its  depth  rapidly  increases  from  behind  for- 
wards, and  it  may  be  said  to  extend  from  the  pineal  body  behind  to  the  lamina 
cinerea  in  front.  Its  floor  is  formed  by  the  structures  already  studied  within 
the  area  of  the  interpeduncular  space  on  the  base  of  the  brain,  viz.  the  tuber 
cinereum,  the  corpora  mammillaria,  the  gray  matter  of  the  locus  perforatus  posticus, 
and  also  to  some  extent  behind  this  by  the  tegmenta  of  the  crura  cerebri.  It  is 
interesting  to  note  that  the  central  gray  matter  which  surrounds  the  Sylvian 
aqueduct  is  directly  continuous  with  the  gray  matter  of  the  locus  perforatus  posti- 
cus and  tuber  cinereum,  and  in  this  way  it  comes  to  the  surface  in  the  base  of  the 
brain.  The  optic  chiasma  crosses  the  floor  in  front  and  marks  the  place  where  the 
latter  becomes  continuous  with  the  anterior  wall  of  the  cavity.  The  front  wall  of 
the  third  ventricle  is  formed  by  the  lamina  cinerea,  which  extends  upwards  from 
the  optic  chiasma.  The  anterior  commissure,  as  it  crosses  from  one  side  to  the  other, 
projects  into  the  ventricle,  but  of  course  it  is  excluded  from  the  cavity  by  the 
ventricular  epithelial  lining.  It  may  be  taken  as  indicating  the  place  where  the 
roof  joins  the  anterior  wall.  The  roof  of  the  third  ventricle  is  formed  by  a  thin 
epithelial  layer,  continuous  with  the  thin  epithelial  lining  of  the  cavity,  which 
stretches  across  the  mesial  plane  from  one  ttenia  thalami  to  the  other.  Applied 
to  the  upper  surface  of  the  epithelial  roof  is  the  fold  of  pia  mater,  termed  the  velum 
interpositum,  and  the  roof  is  invaginated  into  the  cavity  along  its  whole  length  by 
two  delicate  choroid  plexuses,  which  hang  down  from  the  under  surface  of  this 
fold.  When  the  velum  interpositum  is  removed  the  thin  epithelial  roof  is  torn 
away  with  it,  leaving  only  the  lines  of  attachment  in  the  shape  of  the  tsenia 
thalami. . 

The  lateral  wall  of  the  third  ventricle  is  formed  for  the  greater  part  of  its 
extent  by  the  inner  surface  of  the  optic  thalamus,  covered  by  a  thick  layer  of 


Fornix 
Foramen  of  Monro      ^ 

Septum  lucidum .      -      ^^^ 


Genu  of  corpus 
callosum 


Anterior  coninii.ssnre 

Corpus  maminillare 
Lamina  cinerea 


Optic  nerve' 


Tuber 
valvulK 


Pituitary  body 

Tuber  cinereum      \ 
Third  nerve 


I 'y  ram  id 


Pons  I       I 

Valve  of  Vieussens     | 
Ventricle  IV. 
Medulla 


-   Uvula 
Central  lobule 


Fig 


Nodule 
Choroid  plexus  in  ventricle  TV. 

44.3. — Mesial  Mkction  tiihou(ih  thu  Cohi'us  Callosum,  Diencephalon,  etc. 

Shows  the  third  ami  fourtli  ventricles  coniicctccl  by  the  aqueduct  of  Sylvius. 


central  gray  matter  continuous  with  the  Sylvian  gray  matter  of  the  mesencephalon. 
A  little  in  front  of  the  middle  of  the  ventricle  the  cavity  is  crossed  by  the  middle 
or  soft  commissure,  which  connects  the  thalami  with  each  other,  and  in  front  of  this 
the  anterior  pillar  of  the  fornix  is  seen  curving  downwards  and  backwards  in  the 
lateral  wall.  At  first  the  bulging  which  it  forms  is  distinctly  prominent,  but  it 
gradually  su])8ides  as  the  strand,  on  its  way  to  end  in  the  corpus  mammillare, 
becomes  more  and  more  sunk  in  the  gray  matter  on  the  side  of  the  ventricle. 


THIRD  VENTRICLE. 


551 


The  third  ventricle  communicates  with  l)oth  of  tl)e  lateral  ventricles,  and  also 
with  the  fourth  ventricle.  The  aqueduct  of  Sylvius,  the  narrow  channel  which 
tunnels  the  mesencephalon,  brings  it  into  communication  with  the  fourth  ventricle. 
The  opening  of  this  aqueduct  is  placed  at  the  posterior  part  of  the  floor  of  the  third 
ventricle,  immediately  below  the  posterior  commissure.      The  foramina  of  Monro 


^^l^^-t^^-Hj^iTf,, 


OPTIC  RECESS 


INFUNDIBULAR 
RECESS 


Fig.  444. — Profile  View  of  a  Cast  op  the  Ventricles  of  the  Brain  (from  Eetzius). 

R.SP.  Recessus  suprapinealis.  A.S.   Aqueduct  of  Sylvius. 

R.P.    Recessus  jmiealis.  F.M.  Foramen  of  Monro. 

bring  it  into  communication  with  the  lateral  ventricles.  These  apertures  are 
placed  at  the  upper  and  fore  parts  of  the  lateral  walls,  and  lead  outwards  and 
slightly  upwards  between  the  most  prominent  parts  of  the  anterior  pillars  of  the 
fornix  and  the  anterior  tubercles  of  the  optic  thalami.  They  are  just  large  enough 
to  admit  a  crow-quill,  and  through  these  passages  the  epithelial  lining  of  the  three 
ventricles  becomes  continuous.  From  the  foramen  of  Monro  ■  a  distinct  groove  on 
the  lateral  wall  of  the  ventricle  leads  backwards  towards  the  mouth  of  the  Sylvian 
aqueduct.  It  is  termed  the  sulcus  of  Monro,  and  is  of  interest,  inasmuch  as  it  is 
considered  by  His  to  represent  in  the  adult  brain  the  furrow  which  divides  the 
lateral  wall  of  the  embryonic  brain-tube  into  an  alar  and  a  basal  lamina. 

The  outline  of  the  third  ventricle,  when  viewed  from  the  side  in  a  mesial  section 
through  the  brain,  or  as  it  is  exhibited  in  a  plaster  cast  of  the  ventricular  system  of  the 
brain,  is  seen  to  be  very  irregular  (Fig  444).  It  presents  several  diverticula  or  recesses. 
Thus,  in  the  fore-part  of  the  floor  there  is  a  funnel-shaped  pit  or  recess,  leading  down 
through  the  tuber  cinereum  into  the  infundibulum  of  the  pituitary  body.  Another  recess, 
the  recessus  opticus,  leads  forwards  immediately  in  front  of  this,  above  the  optic  chiasma. 
Posteriorly  two  diverticula  are  present.  One,  the  recessus  pinealis,  passes  backwards 
above  the  posterior  commissure  and  the  mouth  of  the  Sylvian  aqueduct  for  a  short 
distance  into  the  stalk  of  the  pineal  body.  The  second  is  placed  above  this  and  is  carried 
backwards  for  a  greater  distance.  It  is  a  diverticuhim  of  the  epithelial  roof,  and,  there- 
fore, is  difficult  to  demonstrate.     It  is  termed  the  recessus  siqwapinealis. 


Cerebral  Connexions  of  the  Optic  Tract. 

One  nerve,  the  optic  nerve  or  the  nerve  of  sight,  is  connected  with  this  section 
of  the  brain.  At  the  optic  chiasma  the  optic  nerves  of  the  two  sides  are  joined 
together  and  a  partial  decussation  of  fibres  takes  place.  The  fibres  which  arise  in 
the  mesial  half  of  each  retina  cross  the  mesial  plane  and  join  the  optic  tract  of  the 


552 


THE  NEEVOUS  SYSTEM. 


opposite  side.  The  optic  tract  proceeds  backwards  round  the  cms  cerebri,  and  in 
the  neighbourhood  of  the  corpora  geniculata  di\ides  into  two  roots,  viz.  a  lateral 
and  a  mesial  (p.  532). 

Mesial  Root  of  the  Optic  Tract — Commissure  of  Gudden. — The  mesial  root 
of  the  optic  tract  disappears  under  cover  of  the  corpus  geniculatum  internum  and  a 
large  proportion  of  its  fibres  arise  or  end  in  this  nuclear  body.  As  to  the  connexions 
of  the  otlier  fibres,  we  possess  at  present  no  precise  information.  The  mesial 
root,  although  it  is  composed  of  fibres  which  run  in  the  optic  tract,  has  absolutely 
nothing  to  do  with  the  optic  nerve.  These  fibres,  when  traced  forwards,  cross  the 
mesial  plane  in  the  posterior  angle  of  the  optic  chiasma  and  are  carried  backwards 
in  the  opposite  optic  tract,  to  form  on  that  side  its  mesial  root.  The  fibres,  there- 
fore, are  commissural,  and  constitute  a  bond  of  union,  called  the  commissure  of 
Grudden,  between  the  internal  geniculate  bodies. 

Lateral  Root  of  the  Optic  Tract. — The  lateral  or  true  visual  root  of  the 
optic  tract  is  composed  of  fibres  which  come — (1)  from  the  lateral  half  of  the  retina 
of  its  own  side ;  and  (2)  from  the  mesial  half  of  the  retina  of  the  opposite  side,  and 
which  have  crossed  the  mesial  plane  in  the  optic  chiasma.  But  in  addition  to  the 
afferent  retinal  fibres  there  are  a  certain  number  of  efferent  fibres  in  the  optic 
tract,  fibres  which  take  their  origin  in  the  brain  and  end  in  the  retina.  These  are 
distinguished  from  the  afferent  retinal  fibres  by  their  exceeding  fineness. 

The  fibres  of  the  lateral  root  of  the  optic  tract  end  in  the  superior  quadrigeminal 
body,  in  the  external  geniculate  body,  and  in  the  pulvinar  of  the  optic  thalamus. 
The  fibres  to  the  superior  (juadrigeminal  body  reach  it  through  the  superior  brachium 

(p.  435),  and  for  the  most  part  spread  out 
on  its  surface  in  the  stratum  zonale  before 
they  sink  into  its  substance,  to  end  in 
terminal  arborisations  around  its  cells.  The 
corpus  geniculatum  externum  receives  the 
largest  contribution  of  fibres  from  the 
lateral  root  of  tlie  optic  tract.  These  partly 
sink  into  its  interior  and  partly  spread  out 
over  its  surface.  The  former  enter  into 
the  construction  of  the  curved  lamellae 
of  white  matter  which  traverse  this  nuclear 
mass,  and  to  a  large  extent  end  in  the 
gray  matter  which  intervenes  between 
these  lamellae.  The  deep  fibres  which  are 
not  exhausted  in  this  way  proceed  onwards 
through  the  external  geniculate  body  and 
enter  the  pulvinar.  Of  the  superficial  fibres 
which  spread  over  the  surface  of  the  external 
geniculate  body  some  dip  into  its  substance 
and  end  there,  but  the  majority  are  carried 
over  it  and  enter  the  stratum  zonale  of 
the  pulvinar.  The  fibres  of  the  lateral 
root  of  the  optic  tract,  which  end  in  the 
pulvinar,  therefore  reach  their  destination 
by  passing  either  over  or  through  the 
external  geniculate  body. 

Cortical    Connexions    of    the   Optic 
Nerve.  -  -The  superior  quadrigeminal  body, 
the  external  geniculate  body,  and  the  pul- 
vinar constitute  tl)e  lower  visual  centres 
or    terndnal   nuclei   of    the    visual    part 
of    the   optic   tract.     The    liigher   visual 
centre    is   placed    in    the   cortex   of    the 
occipital  lobe  of  the  cerebral  hemisphere,  and  the  connexions  between  this  and 
the  lower  centres  are  establislied  by  a  large  strand  of  fil)r(!S  wliich  runs  in  the 
central  white  matter  of  the  hinder  part  of   the  cerebral  hendsphere,  and  which 


FKJ.  445. — DiAGKAM     Ol 

IONS  OK  THE  Optic  Nehve  and  Optic 


CEEEBRAL  HEMISPHEEES.  553 

constitutes  the  optic  radiation.  The  optic  radiation  is  composed  both  of  corticipetal 
and  corticifugal  fibres.  The  former  arise  as  tlie  axons  of  the  cells  in  the  external 
geniculate  body  and  the  pulvinar,  around  which  the  retinal  fibres  end,  and  they 
terminate  in  the  cortex  of  the  occipital  lobe.  The  corticifugal  fibrt's  take  origin 
in  the  cortex  of  the  occipital  lobe  and  end  in  the  pulvinar  and  superior  quadri- 
geminal  body  (Ferrier  and  Turner).  Thus  constituted,  the  optic  radiation  forms 
a  conspicuous  strand  (Figs.  462,  p.  576;  465,  p.  579 ;  473,  p.  592),  which,  reaching 
the  retrolenticular  part  of  the  internal  capsule,  sweeps  backwards  into  the  occipital 
lobe  of  the  cerebral  hemisphere  on  the  outer  side  of  the  posterior  horn  of  the 
lateral  ventricle.     Its  connexions  will  be  studied  more  fully  at  a  later  stage. 

Flechsig  does  not  believe  that  the  pulvinar  is  an  internode  interposed  in  the  path  of  the  optic 
nerve  as  it  proceeds  toAvards  the  visual  area  of  the  cerebral  cortex.  He  states  that  he  has  not 
been  able  to  convince  himself  that  any  fibres  of  the  ojitic  tract  end  in  the  optic  thalamus. 

Other  Connexions  of  the  Lower  Group  of  Visual  Centres. — (1)  The  nuclei  of  the  nerves 
which  supply  the  muscles  which  move  the  eyeball  would  appear  to  stand  in  intimate  connexion 
with  the  lower  grouji  of  visual  centres.  Most  probably  this  connexion  is  established  through 
the  posterior  longitudinal  bundle.  As  previously  stated,  Held  believes  that  axons  of  certain  of 
the  cells  of  the  superior  quadrigeminal  body  enter  this  tract.  (2)  Through  the  mesial  fillet,  the 
superior  quadrigeminal  body  is  connected  with  the  medulla  and  cord. 

THE   PARTS   DERIVED    FROM   THE   TELENCEPHALON. 
Ceeebral  Hemispheres. 

The  cerebral  hemispheres  form  the  largest  part  of  the  fully-developed  brain. 
When  viewed  from  above  they  form  an  ovoid  mass,  the  broadest  end  of  which  is 
directed  backwards,  and  the  longest  transverse  diameter  of  which  will  be  found  in 
the  vicinity  of  the  parts  which  lie  subjacent  to  the  parietal  eminences  of  the 
cranium.  The  massive  rounded  character  of  the  anterior  or  frontal  end  of  each 
cerebral  hemisphere  constitutes  a  leading  human  characteristic ;  but  the  hinder  or 
occipital  end  is  narrow  and  pointed,  and  is  directed  somewhat  downwards.  The 
two  cerebral  hemispheres  are  separated  from  each  other  by  a  deep  mesial  cleft, 
termed  the  great  longitudinal  fissure. 

Great  Longitudinal  Fissure  (fissura  longitudinalis  cerebri). — In  front  and 
behind  the  great  longitudinal  fissure  passes  from  the  dorsal  to  the  ventral  aspect  of 
the  cerebral  hemispheres,  so  as  to  separate  them  completely  from  each  other.  In 
its  middle  part,  however,  the  fissure  is  interrupted  and  floored  by  the  corpus 
callosum,  a  white  commissural  band,  which  passes  between  the  hemispheres  and 
connects  them  together.  The  upper  surface  of  the  corpus  callosum  can  be 
displayed  by  gently  drawing  asunder  the  contiguous  mesial  surfaces  of  the 
cerebral  hemispheres.  The  great  longitudinal  fissure  is  occupied  by  a  mesial 
fold  of  dura  mater,  termed  the  falx  cerebri,  which  partially  subdivides  the  part 
of  the  cranial  cavity  allotted  to  the  cerebrum  into  a  right  and  left  chamber. 

External  Configuration  of  each  Cerebral  Hemisphere. — Each  cerebral  hemi- 
sphere presents  an  external,  an  internal,  and  an  inferior  surface.  The  external 
surface  is  convex  and  is  adapted  accurately  to  the  deep  surface  of  the  cranial 
vault.  The  internal  or  mesial  surface  is  flat  and  perpendicular,  and  bounds  the 
great  longitudinal  fissure.  In  great  part  it  is  in  contact  with  the  falx  cerebri ;  and 
where  that  partition  is  deficient,  it  is  applied  to  the  corresponding  portion  of  the 
internal  surface  of  the  opposite  hemisphere.  The  inferior  surface  is  irregular  and 
is  adapted  to  the  anterior  and  middle  cranial  fossse  of  the  cranial  floor  and,  behind 
these,  to  the  upper  surface  of  the  tentorium  cerebelli.  Traversing  this  surface  in  a 
transverse  direction,  nearer  the  anterior  end  of  the  hemisphere  than  the  posterior 
end,  is  the  stem  of  the  Sylvian  fissure.  This  deep  cleft  divides  the  inferior  surface 
into  an  anterior  or  orbital  area,  which  rests  on  the  orbital  plate  of  the  frontal  bone, 
and  is  consequently  concave  from  side  to  side,  and  a  more  extensive  posterior  or 
tentorial  area,  which  lies  on  the  floor  of  the  lateral  part  of  the  middle  cranial  fossa 
and  upon  the  upper  surface  of  the  tentorium  cerebelli.  This  surface  is  arched 
from  before  backwards,  and  looks  inwards  as  well  as  downwards.  In  its  hinder 
two-thirds  it  lies  above  the  cerebellum,  from  which  it  is  separated  by  the  tentorium 
cerebelli. 


554  THE  NERVOUS  SYSTEM. 

The  borders  which  intervene  between  these  surfaces  are  the  supero-mesial,  the 
superciliary,  the  infero-lateral,  and  the  internal  occipital.  The  supero-mesial 
border,  convex  from  before  backwards,  intervenes  betw^eeu  the  convex  external 
surface  and  the  flat  internal  surface  of  the  hemisphere.  The  sujjerciliary  harder  is 
highly  arched  and  separates  the  orbital  surface  from  the  external  surface.  The 
infero-lateral  harder  marks  off  the  tentorial  surface  from  the  external  surface.  The 
internal  occipital  harder  can  only  be  seen  in  cases  where  the  brain  has  been  hardened 
in  situ  and  faithfully  retains  the  natural  form.  It  extends  from  the  posterior  end 
of  the  hemisphere  towards  the  hinder  extremity  of  the  corpus  callosum,  and  inter- 
venes between  the  mesial  and  tentorial  surfaces.  It  is  the  border  which  lies  along 
the  straight  blood  sinus,  and  it  therefore  occupies  the  angle  which  is  formed  by  the 
attachment  of  the  posterior  part  of  the  falx  cerebri  to  the  upper  surface  of  the 
tentorium  cerebeUi. 

The  most  projecting  part  of  the  anterior  end  of  the  cerebral  hemisphere  is  called 
the  frontal  pole,  whilst  the  most  projecting  part  of  the  hinder  end  is  termed  the 
occipital  pole.  On  the  under  surface  of  the  hemisphere  the  prominent  point  of 
cerebral  substance  which  extends  forwards  below  the  Sylvian  fissure  receives  the 
name  of  the  temporal  pole.  In  a  well-hardened  brain  a  broad  groove  is  usually 
present  on  the  inner  and  lower  aspect  of  the  occipital  pole  of  the  right  hemisphere. 
This  corresponds  to  the  commencement  of  the  right  lateral  venous  sinus.  A  less 
distinct  groove  on  the  occipital  pole  of  the  left  hemisphere  frequently  indicates  the 
commencement  of  the  left  lateral  sinus.  On  the  tentorial  surface,  a  short  distance 
behind  the  temporal  pole,  a  well-marked  depression  is  always  visible.  This  corre- 
sponds to  the  elevation  on  the  anterior  surface  of  the  petrous  portion  of  the 
temporal  bone  over  the  superior  semicircular  canal. 

Cerebral  Gyri  and  Sulci. — The  surface  of  the  cerebral  hemispheres  is  rendered 
highly  irregular  by  the  presence  of  convolutions  or  gyri,  separated  from  each  other 
by  intervening  furrows  of  very  varying  depth,  termed  sulci  or  fissures.  The  surface 
pattern  which  is  presented  by  these  gyri  and  sulci  is,  in  its  general  features,  the 
same  in  all  normal  human  brains ;  but  when  the  comparison  is  pushed  into  detail 
many  differences  become  manifest,  not  only  in  the  brains  of  different  individuals, 
but  also  in  the  two  cerebral  hemispheres  of  the  same  individual. 

There  are  two  varieties  of  furrows,  viz.  complete  and  incomplete.  The  complete 
fissures  are  few  in  number,  and  are  formed  by  inwardly -directed  infoldings 
involving  the  entire  thickness  of  the  cerebral  wall.  They  consequently  show 
in  the  interior  of  the  cerebral  cavity  or  lateral  ventricle  in  the  form  of  internal 
elevations  on  its  waU.  The  complete  fissures  are  the  following :  (1)  the  dentate  or 
hippocampal  fissure ;  (2)  the  anterior  part  of  the  calcarine  fissure ;  and  (3)  a 
portion  of  the  collateral  fissure.  The  incomplete  fissures  are  merely  surface  furrows 
of  varying  depth,  which  do  not  produce  any  effect  on  the  inner  surface  of  the 
ventricular  wall. 

General  Structure  of  the  Cerebral  Hemispheres. — Each  cerebral  hemisphere 
is  composed  of  an  outside  coating  of  gray  matter,  spread  in  a  continuous  and  un- 
interrupted layer  over  its  surface,  and  an  internal  mass  of  white  matter,  which  forms 
a  considerable  X-'art  of  the  immediate  wall  of  the  ventricular  cavity.  The  gray 
coating  is  termed  the  cerebral  cortex,  and  the  internal  white  matter  is  called  the 
medullary  centre.  Each  convolution  shows  a  corresponding  structure.  On  trans- 
verse section  it  is  seen  to  present  an  external  covering  of  gray  cortex,  supported  by 
a  central  core  of  white  matter. 

But,  in  addition  to  the  gray  matter  on  the  outside,  there  are  certain  large 
deposits  of  gray  matter  embedded  in  the  basal  part  of  each  cerebral  hemisphere. 
These  cerebral  nuclei  constitute  the  corpus  striatum,  and,  although  to  some  extent 
isolated  from  the  gray  matter  on  the  surface,  it  can  be  easily  shown  that  at  certain 
points  they  are  directly  continuous  with  it. 

By  means  of  the  convolutions  and  sulci,  the  gray  matter  on  the  surface  of  the 
hemisphere  is  enormously  increased  in  quantity  without  unduly  adding  to  the  bulk 
of  the  organ ;  and,  further,  the  vascular  pia  mater,  which  dips  into  every  fissure,  is 
increased  in  extent  to  a  like  degree.  Opportunity  is,  therefore,  afforded  to  the 
cortical  vessels  of  breaking  up  into  twigs  of  exceeding  fineness  before  they  enter  the 


FISSUKE  OF  SYLVIUS. 


555 


substance  of  the  hemisphere.  The  distributiou  of  blood  to  the  gray  cortex  is,  in 
this  way,  equahsed  and  rendered  uniform. 

Cerebral  Lobes  and  Interlobar  Fissures. — Certain  of  the  fissures  which 
traverse  the  surface  of  the  cerebrum  are  more  or  less  arbitrarily  chosen  for  sub- 
dividing the  surface  into  districts  or  areas,  which  are  termed  lobes.  These  fissures 
are  termed  interlobar,  and  are  the  following:  (1)  the  fissure  of  Sylvius;  (2)  the 
fissure  of  Eolando ;  (3)  the  parieto-occipital ;  (4)  the  calloso-marginal ;  (5)  the 
collateral ;  and  (6)  the  limiting  sulcus  of  Eeil. 

The  lobes  which  are  mapped  out  by  these  fissures  are :  (1)  the  frontal;  (2)  the 
parietal ;  (3)  the  occipital ;  (4)  the  temporal ;  (5)  the  insula,  or  the  island  of  Eeil ; 
(6)  the  limbic.  To  these  may  be  added  a  seventh  lobe,  in  no  way  related  to  the 
interlobar  fissures,  viz.  the  olfactory  lobe.  "With  the  exception  of  the  occipital  and 
olfactory  lobes  and  the  insula,  this  subdivision  of  the  hemisphere  possesses  Uttle 
morphological  value,  and  is  chiefly  adopted  for  topographical  purposes. 

Fissure  of  Sylvius  (fissura  cerebri  laterahs). — This  is  the  most  conspicuous 


o^c 


Fig.  446. — Gtri  and  Sulci,  on  the  outer  surface  of  the  cerebral  hemisphere. 


f\ 

^. 

f.m, 

p.m. 

A. 

B. 

C. 

S. 


p.c.i. 
p.c.s 


Sulcus  frontalis  superior. 
Sulcus  frontalis  inferior. 
Sulcus  frontalis  medius. 
Sulcus  pararaedialis. 
Pars  basilaris. 
Pars  triangiUaris. 
Pars  orbitalis. 
Sylvian  iissure. 

Anterior  horizontal  limb  (Sylvian  fissure). 
Ascending  limb  (Syhian  fissure). 
Posterior  horizontal  limb  (Sylvian  fissure). 
Ascending  terminal  part  of  the  posterior  hori- 
zontal limb  of  the  Sylvian  fissure. 

Inferior  prsecentral  sulcus. 

Superior  prrecentral  sulcus. 


r.  Fissure  of  Rolando.  . 

g.s.  Superior  genu. 

g.i.  Inferior  genu. 

d.  Sulcus  diagonalis. 

t^  Superior  temporal  sulcus  (parallel  sulcus). 

t'^.  Inferior  temporal  sulcus. 

pi.  Inferior  postcentral  sulcus. 

p-.  Superior  postcentral  sulcus. 

p^.  Ramus  horizoutalis. 

p^.  Ramus  occipitalis. 

s.o.t.  Sulcus  occipitalis  transversus. 

occ.  lat.  Sulcus  occipitalis  lateralis  (the  sulcus  lunatus 

of  Elliot  Smith), 

cm.  Calloso-marginal  sulcus, 

c.t.r.  Inferior  transverse  furrow. 


fissure  on  the  surface  of  the  cerebral  hemisphere.  It  is  composed  of  a  short  main 
stem,  from  the  outer  extremity  of  wliich  three  branches  or  limbs  radiate.  The 
stem  of  the  Sylvian  fissure  is  placed  on  the  inferior  surface  of  the  hemisphere.  It 
begins  at  the  locus  perforatus  anticus  in  a  depression  termed  the  vallecula  Sylvli. 
From  this  it  passes  horizontally  outwards,  forming  a  deep  cleft  between  the 
temporal  pole  and  the  orbital  surface  of  the  frontal  lobe.  Appearing  on  the 
outer  surface  of  the  hemisphere  at  a  point  called  the  Sylvian  point,  the  Sylvian 
fissure  immediately  di-sddes  into  three  radiating  branches.     These  are :   (1)  the 


556  THE  NEEVOUS  SYSTEM. 

ramus  horizontalis  posterior ;  (2)  the  ramus  horizontalis  anterior ;  (3)  the  ramus 
anterior  ascendens. 

The  posterior  horizontal  limb  is  the  longest  and  best  marked  of  the  three  limbs. 
It  extends  backwards,  with  a  slight  inclination  upwards  on  the  outer  surface  of  the 
hemisphere  for  a  distance  which  may  vary  from  about  two  to  three  inches.  It 
intervenes  between  the  frontal  and  parietal  lobes  which  lie  above  it  and  the 
temporal  lobe  which  lies  below  it,  and  it  finally  ends  in  the  region  subjacent  to  the 
parietal  eminence  of  the  cranial  wall  by  turning  upwards  into  the  parietal  lobe  in 
the  form  of  an  ascending  terminal  piece. 

The  anterior  horizontal  limb  extends  horizontally  forwards  in  the  frontal  lobe  for 
a  distance  of  about  three-quarters  of  an  inch  immediately  above  and  parallel  to  the 
posterior  part  of  the  superciliary  margin  of  the  hendsphere. 

The  ascending  limb  proceeds  upwards,  with  a  slight  inclination  forwards,  into  the 
lower  part  of  the  outer  surface  of  the  frontal  lobe  for  a  distance  of  about  an  inch. 
In  many  cases  the  two  anterior  limbs  spring  from  a  common  stem  of  greater  or 
less  length,  and  not  infrequently  both  are  replaced  by  a  single  anterior  limb. 

Limiting  Sulcus  of  Reil  (sulcus  circularis  Eeilii). — If  the  lips  of  the  posterior 
horizontal  limb  of  the  Sylvian  fissure  be  widely  pulled  asunder  from  each  other,  the 
insula  or  island  of  Reil  will  be  seen  at  the  bottom.  The  insular  district  of  the 
cortex  is  completely  hidden  from  view  when  the  Sylvian  fissure  is  closed  by  over- 
lapping portions  of  the  cerebral  hemisphere,  and,  when  brought  into  view  in  the 
manner  indicated,  it  is  observed  to  present  a  triangular  outline  and  to  be  surrounded 
by  a  limiting  sulcus,  of  which  three  parts  may  be  recognised,  viz. :  an  upper  'part, 
bounding  it  above  and  separating  it  from  the  parietal  and  frontal  lobes ;  a  lower 
part,  marking  it  off  below  from  the  temporal  lobe;  and  an  anterior  part,  separating 
it  in  front  from  the  frontal  lobe. 

Opercula  Insulae. — The  overlapping  portions  of  the  cerebral  substance  which 
cover  over  the  insula  are  termed  the  insular  opercula,  and  they  form,  by  the  apposi- 
tion of  their  margins,  the  three  limbs  of  the  Sylvian  fissure.  The  opercula  are  four 
in  number  and  are  named:  (1)  temporal;  (2)  fronto-parietal ;  (3)  frontal ;  and  (4) 
orbital.  The  limbs  of  the  Sylvian  fissure  cut  right  through  between  the  different 
opercula  and  extend  from  the  exposed  surface  of  the  hemisphere  to  the  submerged 
surface  of  the  insula,  and,  in  this  manner,  separate  the  opercula  from  each  other. 

The  temporal  operculum  extends  upwards  over  the  insida  from  the  temporal  lobe, 
and  its  upper  margin  forms  the  lower  lip  of  the  posterior  horizontal  Umb  of  the 
Sylvian  fissure. 

The  fronto-parietal  operculum  is  carried  downwards  from  the  parietal  and  frontal 
regions  over  the  insula,  and  its  lower  margin,  meeting  the  temporal  operculum, 
forms  the  upper  lip  of  the  posterior  limb  of  the  Sylvian  fissure. 

The  frontal  operculum  is  the  small  triangular  piece  of  cerebral  substance  which 
intervenes  between  the  ascending  and  anterior  horizontal  limbs  of  the  Sylvian 
fissure.  It  covers  over  a  small  part  of  the  anterior  portion  of  the  insula,  and  is 
sometimes  termed  the  pars  triangularis. 

The  orbital  operculum  is,  for  the  most  part,  on  the  under  surface  of  the  hemi- 
sphere.    It  lies  below  and  to  the  inner  side  of  the  anterior  horizontal  limb  of  the- 
Sylvian  fissure,  and  proceeds  backwards  from  the  orbital  aspect  of  the  frontal  lobe 
over  the  ibre-part  of  the  insula. 

Development  of  the  Sylvian  Fissure  and  of  the  Insular  District  of  the  Cerebral  Hemi- 
sphere.— It  is  only  during  tlie  latter  half  of  the  intrauterine  period  of  develoijment  that  the 
(jjjercula  take  shape  and  grow  over  the  insula,  so  as  to  shut  it  out  from  the  surface.  In  its  early 
condition  the  insula  presents  the  form  of  a  depressed  area  on  the  side  of  tlie  cerebral  hemisphere, 
surrounded  by  a  distinct  boundary  wall  formed  by  the  surrounding  more  elevated  surface  of  the 
hemisphere  (Fig.  447,  A).  After  a  time  this  depressed  area,  which  is  called  the  Sylvian  fossa, 
assumes  a  triangular  outline,  and  then  the  bounding  wall  is  observed  to  l)e  composed  of  three 
distinct  parts,  viz.  :  an  upper  or  fronto-parietal,  a  lower  or  temporal,  and  an  anterior  or  orbital 
part  (Fig.  447,  B).  The  rounded  angle,  iVn-med  l^y  tlie  meeting  of  the  u])per  and  anterior  portions 
of  the  boundary,  now  becomes  llattened,  and  a  short  oblique  ])art  of  the  limiting  wall,  termed  the 
frontal  portion,  assumes  shape  in  this  position.  Each  of  these  four  portions  of  the  bounding 
wall  of  the  Sylvian  fossa  becomes  a  line  of  growth,  from  which  an  operculum  takes  origin,  and 
by  the  approximation  of  these  opercula,  as  they  grow  ovei'  the  sui-face  of  the  Sylvian  fossa,  the 
insula  becomes  closed  in  and  the  limbs  of  the  Sylvian  fissure  are  formed  (Fig.  448). 


INSULAE'OPEKCULA. 


557 


The  temporal  and  fronto-parietal  opercula  make  their  ajipearance  somewhere  about  the  end 
of  the  fifth  nKJiith  of  foetal  development,  long  before  the  other  two  opercula  show  any  indication 
of  growth.  The  temporal  operculum  grows  more  rapidly  than  the  fronto-parietal  ;  so  that,  when 
the  margins  of  these  two  opercula  come  together  to  form  the  posterior  limb  of  the  Sylvian  fissure, 
there  is  a  greater  extent  of  the  Sylvian  fossa  covered  by  the  temporal  operculum  than  by  the  fronto- 
parietal operculum.  This  accounts  for  the  more  oblique  direction  of  the  Sylvian  fissure  in  the  foetal 
brain.  But  at  this  stage  a  growth-antagonism  between  the  two  opercula  takes  place,  and  in  this 
the  fronto-parietal 
operculum  jjroves  the 
victor.  The  contigu- 
ous lijjs  of  the  two 
opercula  become,  in  the 
first  instance,  tightly 
pressed  together,  and 
then,  as  the  upper  ojjer- 
culum  proves  the 
stronger  and  the  niori- 
vigorous  in  its  growtli, 
the  posterior  limli  ot 
the  Sylvian  fi.ssure  be- 
comes gradually  de- 
pres.sed  until  it  assumes 
the  inclination  char- 
acteristic of  the  adult. 
It  would  ajijiear  that 
the  opercular  growth- 
antagonism  which  pro- 
duces this  effect  in  the 
human  brain  does  not 
occur  to  the  same  ex- 
tent, if  indeed  it  occurs 

at  all,  in  the  ape.  This  F.P.  Frouto-parietal  opercuhun 
is  evident  from  the  ob- 
lique direction  of  the  posterior  liml)  of  the  Sylvian  fissure  in  the  simian  brain.  The  greater 
growth -energy  of  the  fronto  -  jiarietal  operculum  in  the  human  brain  is  not  confined  to  the 
fcetal  stage  of  develojjment,  but  is  carried  into  the  earlier  stages  of  infantile  growth,  and  it  is 
probable  that  it  is  due  to  an  extension  of  that  district  of  the  cortex  in  which  the  centres 
for  the  skilled  movements  of  the  upper  limbs  reside,  and  also  to  an  extension  of  Flechsig's 
parieto-occijjital  association  area. 

The  orbital  and  frontal  opercula  are  late   in  aiijiearing  and  very  tardy  in  their  growth. 
Indeed,  it  is  only  during  the  course  of  the  first  year  of  infantile  life  that  they  come  into  apposition 


lJb-_ 


Fig.  447. 


-Three  St.vges  in  the  Development  of  the  Insula  and  the 
Insular  Opercula. 


lu 


Right  cerebral  heiiiisphere  from  a  foetu.s  iu  the  latter  part  of  the  fourth  month 
of  development  ;  B,  Right  cerebral  hemisphere  from  a  foetus  in  the  fifth 
month  of  development  ;  C,  Right  cerebral  hemisphere  from  a  fretus  in  the 
latter  part  of  the  eighth  month  of  development. 

C  the  temi^oral  operculum  has  Ijeen  removed,  and  thus  a  large  part  of  the 
insula  is  exposed.  The  outline  of  the  temporal  operculum  is  indicated  by  a 
dotted  line. 

F,  Frontal  operculum.     0,  Orbital  operculum. 


Fig.   448. — Diagram  to  Illustrate  the  Development  ob'  the  Opercula  which  cover  the  Insula. 

A,  Sylvian  fossa  before  opercula  lie^^in  to  form  ;   B,  Fronto-parietal  and  temporal  oi^ercula  well  advanced  ; 
C,  All  the  four  opercula  developed  but  not  in  apposition. 

F.P.  Fronto-parietal  operculum.      O.R.  Orbital  wall  of  fossa.        s-.   Anterior  horizontal  limb  of  Sylvian  fissure. 

T.      Temporal  operculum.  F.      Frontal  operculum.  .s^.   Ascending  limb. 

F.R.  Frontal  wall  of  fossa.  0.      Orbital  operculum.  s"*.    Posterior  horizontal  limb. 


with  each  other  and  with  the  other  two  ojiercula,  so  as  to  close  in  the  fore-jjart  of  the  Sylvian  fossa 
and  form  the  anterior  limbs  of  the  Sylvian  fissure.  They  do  not  begin  to  take  shape  until  more 
than  half  of  the  Sylvian  fossa  has  already  been  closed  by  the  fronto-jiarietal  and  the  temjioral 
opercula.  The  orbital  ojierculuni  appears  first  and  is  much  more  constant  in  its  growth  than 
the  frontal  operculum,  which  indeed  frequently  fails  altogethei',  and,  even  when  present,  shows 
the  greatest  amount  of  variability  in  the  degree  to  which  it  is  develoi^ed. 

Variations  in  the  degree  of  development  of  the  frontal  operculum  influence  greatly  the  form 
presented  by  the  t^^'0  anterior  limbs  of  the  Sylvian  fissure,  between  which  it  lies.  When  strongly 
developed,  it  sejjarates  the  two  Sylvian  limbs  from  each  other  to  such  an  extent  that  they  assume 
the  api^earance  of  the  letter  U  ;  when  the  frontal  02)erculum  is  less  strongly  marked,  the  anterior 
Sylvian  limbs  may  assume  a  V  form  or  a  Y  form.  In  the  latter  case,  the  orbital  and  the  fronto- 
parietal opercula  meet  below  the  frontal  operculum  to  form  the  stem  of  the  Y.     In  those  cases 


558 


THE  NEEVOUS  SYSTEM. 


Ascendiiif;  / 

parietal 

convolution 


where  tlie  frontal  operculum  is  absent  altogether,  a  single  anterior  limb  of  the  Sylvian  fissure  is 
the  result. 

The  late  appearance,  the  slow  growth,  the  variability  of  these  two  opercula,  and  also  the 
tendency  to  abortive  growth  or  conqjlete  suppression  of  the  frontal  operculum,  all  bespeak  the 
fact  that,  from  a  phylogenetic  point  of  view,  the  frontal  and  orbital  opercula  are,  comparatively 
speaking,  recent  laroductions  in  the  eA^olution  of  the  human  brain.  In  the  anthropoid  ape  they 
are  absent,  and,  consequently,  the  fore-part  of  the  island  of  Reil  is  exposed  on  the  surface  of  the 
simian  brain.  The  same  condition  is  not  at  all  an  uncommon  occurrence  in  the  brain  of  the 
microcephalic  idiot. 

Fissure  of  Rolando  (sulcus  centralis). — The  fissure  of  Eolando  takes  an  oblique 
course  across  the  outer  convex  surface  of  the  cerebral  hemisphere,  and  intervening 
between  the  frontal  and  parietal  lobes  it  forms  the  immediate  posterior  boundary 
of  the  motor  area  of  the  cortex.  Its  upper  end  cuts  the  supero-mesial  border  of 
the  hemisphere  a  short  distance  behind  the  mid-point  between  the  frontal  and 
occipital  poles,  whilst  its  lower  end  terminates  above  the  middle  of  the  posterior 
horizontal  limb  of  the  fissure  of  Sylvius.     Its  superior  extremity,  as  a  rule,  turns 

round  the  supero-mesial  border  of  the 
hemisphere,  and  is  then  continued  back- 
wards for  a  short  distance  on  the  mesial 
surface.  Although,  in  its  general  direc- 
tion, the  fissure  is  oblique,  it  is  very  far 
from  being  straight.  It  takes  a  sinuous 
course  across  the  hemisphere.  This  is 
largely  due  to  the  area  of  cortex  which 
represents  the  motor  centre  for  the  arm, 
and  which  lies  in  front  of  the  sulcus, 
growing  backwards  in  the  course  of  its 
development  so  as  to  produce  a  bay  in 
the  fissure  within  which  this  portion  of 
the  cortex  is  accommodated.  The  bends 
in  the  fissure  which  indicate  the  upper 
and  lower  limits  of  the  arm  centre  (Griin- 
baum  and  Sherrington)  are  termed 
respectively  the  superior  and  inferior 
genua.  The  angle  which  the  general 
direction  of  the  fissure  of  Eolando  makes 
with  the  mesial  plane  is  termed  the 
Rolandic  angle.  In  the  adult  brain  the 
average  Eolandic  angle  is  71°  7',  and  the  limits  of  variation  would  appear  to  be  69° 
and  74'. 

When  the  fissure  of  Eolando  is  widely  opened  up,  so  that  its  bottom  and  its  opposed  sides  may 
be  fully  inspected,  it  will  be  seen  that,  between  the  two  genua,  the  two  bounding  convolutions  are 
dovetailed  into  each  other  by  a  number  of  interlocking  gyri,  Avhich  do  not  appear  on  the  surface 
(Fig.  449).  Further,  two  of  these,  placed  on  opposite  sides  of  the  fissure,  are  frequently  joined 
across  the  bottom  of  the  sulcus  in  the  form  of  a  sunken  bridge  of  connexion,  which  constitutes 
what  is  termed  a  deep  annectant  gyrus.  The  continuity  of  the  fissure  is  thus,  to  some  extent, 
interrupted.  This  condition  is  rendered  interesting  when  considered  in  connexion  with  the 
development  of  the  sulcus.  The  deep  interlocking  gyri  indicate  a  great  eituberance  of  cortical 
growth  in  this  situation  in  the  early  stages  of  the  develojjment  of  the  fissure  ;  and  the  presence  of 
the  deep  annectant  gyrus  is  explained  by  the  fact  that  the  fissure  of  Rolando  generally  develops  in 
two  pieces,  which  run  into  each  other  to  form  the  continuous  sulcus  of  the  adult,  viz.  a  part  cor- 
responding to  the  lower  two-thirds,  and  an  upper  part,  which  rej^resents  the  upper  third  and 
which  appears  at  a  slightly  later  date.  In  certain  very  rare  cases  the  fissure  of  Rolando  is  found  to 
remain  double  throughout  life,  through  a  failure  of  its  two  pieces  to  unite.  In  such  cases  the  deep 
annectant  gyrus,  which  is  i'requently  seen  at  the  bottom  of  the  furrow,  remains  on  the  surface. 
Heschl,  who  examined  2174  cerebral  hemispheres,  only  found  this  anomaly  six  times  ;  Eberstaller 
niet  with  it  twice  in  200  brains. 

Parieto-occipital  Fissure. — A  small  part  of  tliis  fissure  appears  on  the  outer 
face  of  the  cerebral  hemisphere.  For  the  most  part  it  is  situated  on  the  internal 
surface.  It  is  customary,  therefore,  to  describe  an  external  parieto-occipital  and 
an  internal  parieto-occipital  fissure.  It  must  be  clearly  understood,  however,  that 
they  are  directly  continuous  with  each  other  round  the  supero-mesial  border  of  the 


Fig.  449. — Fissure  of  Rolando  fully  opened  up, 
so  as  to  exhibit  the  interlocking  gyri  and  deep 
annectant  gyrus  within  it. 


PAEIETO-OCCIPITAL  AND  COLLATERAL  FISSURES. 


559 


hemisphere.     The   parieto- occipital   fissure   intervenes   between   the  parietal  and 
occipital  lobes. 

The  external  parieto-occipital  fissure  cuts  the  supero-mesial  border  of  the  hemi- 
sphere in  a  transverse  direction  at  a 

distance  of  from  one  and  a  half  to  two  ^ 

inches  in  front  of  the  occipital  pole. 
It  is,  as  a  rule,  not  more  than  about  a 
half  an  inch  long,  and  it  is  brought 
to  an  abrupt  t(3rnunation  by  an  arching 
convolution,  which  winds  round  its 
extremity  and  receives  the  name  of 
arcus  parieto-occipitalis. 

The  internal  parieto-occipital  fissure 
is  carried  downwards  on  the  inner 
surfoce  of  the  hemisphere  in  a  nearly 
vertical  direction  as  a  conspicuous  and 
deep  cleft.  A  short  distance  behind 
the  hinder  end  of  the  corpus  callosvim 
its  lower  extremity  runs  into  the 
calcarine  fissure. 


p.c.s. 
p.c.i. 


Pig.  450. — Left  Cehkbk.m.  Hkmisphkhe,  from  ;i  fcetu.s  in 
the  early  part  of  the  seventh  month  of  development. 

Sulcus  prfficentralis  superior. 

Sulcus  prajcentralis  inferior. 

Lower  part  of  Rolandic  fissui'e. 

Upper  part  of  Rolandic  fissure. 

Inferior  postcentral  sulcus  ^ 

Ramus  horizontalis  i- Intraparietal  fissure. 

Ramus  occipitalis  j 

External  perpendicular  lissure  of  Bischoff. 

Parallel  sulcus. 

Sylvian  fossa. 

Pronto-parietal  wall. 

Prontal  wall. 

Orbital  wall. 


The  parieto-occipital  fissure  is  developed, 
as  a  rule,  after  the  manner  of  a  complete 
fissure.  In  the  foetal  brain  it  forms  a  very 
evident  infolding  of  the  cerebral  wall.  In 
the  adult  brain,  however,  it  does  not  form 
any  eminence  on  the  inner  wall  of  the 
ventricle,  because  it  does  not  extend  down- 
wards as  far  as  the  cavity.  The  wall  of  the 
ventricle  during  the  growth  of  the  hemi- 
sphere has  thickened  to  such  an  extent  that  the  part  corresponding  to  the  fissTire  has  become  solid. 

Collateral  Fissure  (fissura  coUaterahs).— The  collateral  sulcus  is  a  strongly- 
marked  fissure  on  the  tentorial  face  of  the  cerebral  hemisphere.  It  begins  near 
the  occipital  pole  and  extends  forwards  towards  the  temporal  pole.  In  its  posterior 
part  it  is  placed  below,  and  parallel  to,  the  calcarine  fissure,  whilst  in  front  it  is 


p'- 

e.p. 
t\ 

a. 

p.p. 

p. 

0. 


Pig.  451.— The  Gybi  and  Sulci  on  the  Mesial  Aspect  of  the  Cerebral  Hemisphere. 
r.  Pissure  of  Rolando.     r\o.  Rostral  sulcus,     i.t.  Incisura  temporalis. 

separated  from  the  hippocampal  or  dentate  fissure  by  the  hippocampal  gyrus,  which 
is  the  innermost  convolution  on  the  tentorial  surface  of  the  hemisphere. 

In  front  of  the  anterior  extremity  of  the  collateral  fissure  a  shallow  sulcus  turns 
round  the  anterior  end  of  the  temporal  lobe,  so  as  to  intervene  between  the  temporal 


560  THE  NEKVOUS  SYSTEM. 

pole  and  the  uncinate  or  hook-like  extremity  of  the  hippocampal  convolvition. 
This  is  the  incisura  temporalis,  or  ecto-rhinal  fissure.  The  collateral  fissure  and  the 
incisura  temporalis  intervene  between  the  limbic  and  temporal  lobes. 

The  collateral  fissure  is  developed,  as  a  rule,  in  tlu'ee  portions — a  liinder  or  occipital,  an 
intermediate,  and  an  anterior  or  temporal  part.  These  ultimately  run  into  each  other  and  form 
the  continuous  fissure.  The  middle  part  is  usually  a  conqDlete  fissure  and  responsible  for  the 
production  of  the  emincntia  collateralis  posterior  in  the  floor  of  the  trigonum  of  the  lateral 
ventricle  ;  the  temporal  part  is  sometimes  a  complete  fissure,  forming  when  it  is  so  the  eminentia 
collateralis  anterior ;  the  occipital  part  is  always  incomplete. 

Calloso-marg-inal  Fissure. — This  fissure  is  a  strongly-marked  sulcus  on  the 
fore-part  of  the  mesial  surface  of  the  hemisphere.  It  divides  the  front  portion  of 
the  mesial  surface  into  an  upper  marginal  and  a  lower  callosal  convolution,  and 
intervenes  between  the  frontal  and  limbic  lobes.  Beginning  below  the  fore-end  of 
the  corpus  callosum,  close  to  the  locus  perforatus  anticus,  the  calloso-marginal 
fissure  curves  round  in  front  of  the  genu  of  the  corpus  callosum,  and  then  extends 
backwards  to  a  point  a  short  distance  behind  the  middle  of  the  mesial  surface.  It 
then  turns  upwards  and  cuts  the  supero-mesial  border  of  the  hemisphere,  immed- 
iately behind  the  upper  end  of  the  fissure  of  Eolando.  The  relation  presented  by 
the  two  extremities  of  these  fissures  is  such  that  they  can  both  be  readily  recognised 
either  when  examined  on  the  outer  or  mesial  aspect  of  the  cerebrum. 

The  calloso-marginal  sulcus  is  developed  in  two  or  three  separate  pieces,  which,  as  growth 
proceeds,  run  into  each  other  and  form  the  continuous  fissure.  The  numerous  cases  of  irregular 
arrangement  met  with  in  connexion  with  this  fissure  can  generally  be  exjDlained  by  this  inter- 
rupted mode  of  development. 

Frontal  Lobe. — The  frontal  lobe  is  the  largest  of  the  cerebral  lobes.  On  the 
outer  surface  of  the  hemisphere,  it  is  bounded  behind  by  the  fissure  of  Eolando 
and  below  by  the  posterior  horizontal  limb  of  the  fissure  of  Sylvius.  On  the  mesial 
face  it  is  limited  by  the  calloso-marginal  fissure,  whilst  on  the  inferior  surface  of 
the  hemisphere  the  stem  of  the  Sylvian  fissure  forms  its  posterior  boundary.  It 
presents  an  outer  surface,  a  mesial  surface,  and  an  inferior  or  orbital  surface. 

On  the  outer  surface  of  the  frontal  lohe  the  following  sulci  and  gyri  may  be 
recognised : — 


Sulci 


Sulcus  praicentralis  inferior. 

Sulcus  prtecentralis  suj^erior. 

Sulcus  paramedians. 

Sulcus  frontalis  suioei'ior.  C    ■'   J 

Sulcus  frontalis  raedius.  ^       * 

Sulcus  frontalis  iufeiior. 


/  Gja'us  frontalis  ascendens  or  gyrus 
centralis  anterior. 

Gyrus  frontalis  superior    jP^^'^  superior. 
''  ^  (pars  imerior. 

Gyrus  frontalis  medius      (P''^'"'  superior. 
''  l^pars  interior. 


Sulcus  diagonalis.  rpars  basilaris, 

Sulcus  fronto-marginalis.  '  v  Gyrus  frontalis  inferior     | 


pars  triangul- 
j  aris. 

Ipars  orbitalis. 

The  inferior  prsecentral  sulcus  consists  of  a  vertical  and  a  horizontal  part,  and 
when  developed  in  a  typical  manner,  it  presents  a  figure  like  the  letter  T  or  F. 
The  vertical  portion  lies  in  front  of  the  lower  part  of  the  fissure  of  Eolando,  whilst 
the  horizontal  part  extends  obliquely  forwards  and  upwards  into  the  middle  frontal" 
convolution. 

The  superior  praecentral  sulcus  is  a  short  vertical  sulcus  which  lies  at  a  higher 
level  than  the  inferior  praecentral  furrow,  in  front  of  the  upper  part  of  the  fissure 
of  Eolando.  It  is  almost  invarial)ly  connected  with  the  hinder  end  of  the  superior 
frontal  sulcus. 

The  anterior  central  convolution  (ascending  frontal  gyrus)  is  a  long  continuous 
gyrus,  which  is  limited  in  front  by  the  two  pnccentral  furrows  and  behind  by 
the  fissure  of  Eolando.  It  extends  obliquely  across  the  hemisphere  from  the 
supero-mesial  margin  above  to  the  yjosterior  horizontal  limb  of  the  Sylvian  fissure 
below. 

The  superior  frontal  sulcus  extends  forwards  in  a  more  or  less  horizontal  direc- 
tion from  tlie  sulcus  praeceiitralis  superior. 

The  gyrus  frontalis  superior  is  the  narrow  convolution  between  the  supero-mesial 


FKONTAL  LOBE.  561 

border  of  the  hemisphere  and  the  superior  frontal  sulcus.  It  takes  a  horizontal 
course  to  the  frontal  pole. 

The  inferior  frontal  sulcus  occupies  a  lower  level  than  the  superior  frontal  furrow. 
Its  hinder  end  is  placed  in  the  angle  between  the  vertical  and  horizontal  parts  of 
the  inferior  praicentral  sulcus,  and  is  not  infrequently  confluent  with  one  or  other 
of  these.  It  proceeds  forwards  towards  the  superciliary  margin  of  the  hemisphere 
and  ends  a  short  distance  from  this  in  a  terminal  bifurcation. 

The  gyrus  frontalis  medius  is  the  name  given  to  the  broad  convolution  which 
lies  between  the  superior  and  inferior  frontal  sulci. 

The  gyrus  frontalis  inferior  is  that  portion  of  the  outer  surface  of  the  frontal 
lobe  which  is  placed  in  front  of  the  inferior  priecentral  sulcus  and  below  the  inferior 
frontal  sulcus.  The  inferior  frontal  convolution  is  cut  into  three  pieces  by  two 
anterior  limbs  of  the  Sylvian  fissure.  These  are  termed  the  pars  basilaris,  the  pars 
triangularis,  and  the  pars  orbitalis. 

The  pars  basilaris  is  that  part  which  lies  between  the  vertical  limb  of  the  inferior 
praicentral  sulcus  and  the  ascending  limb  of  the  Sylvian  fissure.  It  forms  the  anterior 
part  of  the  fron to-parietal  operculum,  and  it  is  traversed  in  an  oblique  direction  by 
a  shallow  but  constant  furrow,  termed  the  sulcus  diagonalis.  The  pars  triangularis  is 
simply  another  name  for  the  frontal  operculum.  It  is  triangular  in  form,  and  lies 
between  the  anterior  ascending  and  the  anterior  horizontal  limbs  of  the  Sylvian 
fissure.  The  pars  orbitalis  is  placed  below  the  anterior  horizontal  limb  of  the 
Sylvian  fissure. 

The  inferior  frontal  convolution  possesses  a  special  interest  on  account  of  the  locali.sation 
M'ithin  it,  on  the  left  side,  of  the  speech  centre.  From  it,  also,  the  front  part  of  the  fronto-parietal 
and  the  whole  of  the  frontal  oi^erculum  are  develojied.  This  opercular  development  in  connexion 
■with  the  inferior  frontal  gyrus  constitutes  a  leading  point  of  difference  between  the  brain  of  man 
and  that  of  the  ape.  Even  in  the  highest  ape  the  inferior  frontal  convolution  is  not  opercular. 
The  frontal  operculum  is  not  present  and  the  anterior  part  of  the  insula  is  exposed  on  the  surface. 
Probablv  the  excess  of  growth  which  determines  the  formation  of  the  frontal  operculum  in  man 
has  some  connexion  with  the  development  of  the  speech  centre. 

The  sulcus  paramedians  is  the  term  ap^jlied  to  a  series  of  short  irregular  depres- 
sions or  furrows,  arranged  longitudinally,  close  to  the  supero-mesial  border  of  the 
hemisphere.  These  rudimentary  sulci  partially  subdivide  the  superior  frontal  con- 
volution into  an  upper  and  a  lower  part,  and  they  are  of  interest  in  so  far  that  they 
are  not  as  a  rule  developed  in  the  higher  apes,  and  are  deeper  and  better  marked  in 
the  higher  than  the  lower  types  of  human  brain. 

The  sulcus  frontalis  medius  (Eberstaller)  proceeds  horizontally  forwards  in  the 
forepart  of  the  middle  frontal  convolution,  so  as  to  subdivide  it  into  an  upper  and  a 
lower  part.  When  the  furrow  reaches  the  superciliary  margin  of  the  hemisphere 
it  bifurcates,  and  its  terminal  branches  spread  out  widely  and  constitute  a  trans- 
verse furrow,  called  the  fr  onto -marginal  sulcus.  The  sulcus  frontalis  medius  is  only 
found  in  man  and  the  anthropoid  apes.     It  is  not  present  in  any  of  the  lower  apes. 

Owing  to  the  subdivision  of  the  superior  and  middle  frontal  convolutions  in  the 
manner  indicated,  the  typical  arrangement  of  the  convolutions  in  the  anterior  part 
of  the  outer  surface  of  the  frontal  lobe  is  in  five  horizontal  tiers,  and  not  in  three 
tiers,  as  formerly  described. 

As  a  rule,  the  sulci  on  the  outer  surface  of  the  frontal  lobe  during  the  process  of  development 
appear  in  the  following  order :  (1)  sulcus  prsecentralis  inferior ;  (2)  sulcus  frontalis  inferior  ; 
(3)  sulcus  pra?centralis  superior  and  sulcus  frontalis  superior ;  (4)  sulcus  frontalis  medius ; 
(5)  sulcus  paramedians.  This  gives  some  indication  of  the  relative  morphological  importance  of 
these  sulci,  although  it  should  be  borne  in  mind  that  the  period  at  which  sulci  appear  on  the 
fcetal  brain  cannot  in  every  case  be  taken  as  affording  an  infallible  guide  in  our  attempts  to 
assign  to  them  their  relative  morphological  value. 

On  the  mesial  aspect  of  the  frontal  lohe  there  is  an  elongated  more  or  less 
continuous  convolution,  called  the  gyrus  marginalis.  It  lies  between  the  supero- 
mesial  margin  of  the  hemisphere  and  the  calloso-marginal  fissure.  In  the  fore-part 
of  this  gyrus  one  or  two  curved  sulci  are  usually  present.  They  are  termed  the 
sulci  rostrales.  The  posterior  part  of  the  marginal  convolution  is  more  or  less 
completely  cut  off  from  the  portion  which  lies  in  front.  This  part  is  called  the 
40 


562 


THE  NEEVOUS  SYSTEM. 


paracentral  lobule,  and  into  it  the  upper  end  of  the  fissure  of  Eolando  is  prolonged 

as  it  turns  over  the  supero-mesial  border  of  the  hemisphere. 

On  the  orUtal  aspect  of  the  frontal  lobe  there  are  two  sulci,  viz.  the  olfactory 

and  the  orbital. 

The  olfactory  sulcus  is  a  straight  furrow  which  runs  parallel  to  the  mesial  border 

of  the  hemisphere.     It  is  occupied  by  the  olfactory  tract  and  bulb,  and  it  cuts  off  a 

narrow  strip  of  the  orbital  surface  close  to  the  mesial  border,  which  receives  the 

name  of  gryus  rectus. 

The  orbital  sulcus  is  a  composite  furrow  which  assumes  many  different  forms. 

As  a  general  rule  it  presents  a  shape  similar  to  that  of  the  letter  H,  and  is  then 

composed  of  three  parts,  viz.  an  external  limb,  an  internal  limb,  and  a  transverse 

limb.  The  external  limb  (sulcus 
orbitalis  externus)  curves  round 
the  orbital  part  of  the  inferior 
frontal  convolution,  so  as  to 
limit  it  on  this  aspect  of  the 
brain.  The  internal  limb  (sulcus 
orbitalis  intern  us)  is  frequently 
broken  up  into  two  pieces.  It 
marks  oft' a  convolution  between 
itself  and  the  olfactory  sulcus, 
called  the  gyrus  orbitalis  in- 
ternus.  The  transverse  limb 
(sulcus  orbitalis  transversus) 
takes  a  curved  course  between 
the  internal  and  external  limbs. 
The  district  in  front  is  termed 
the  gyrus  orbitalis  anterior,  and 
that  behind  the  gyrus  orbitalis 
posterior.  The  latter,  in  its 
outer  part,  corresponds  with  the 
orbital  operculum. 

Parietal  Lobe.  —  The 
parietal  lobe  forms  a  consider- 
able part  of  the  external  surface 
of  the  cerebral  hemisphere,  and 
it  also  appears  on  the  inner 
surface  in  the  form  of  the  pre- 
cuneus or  the  quadrate  lobule. 
In  front,  it  is  bounded  by  the 


Fig.  452. — Gyri  and  Sulci  on  the  tentorial  and  orbital  aspects    fissure  of  Eolando   whioh  SPr)"r- 
of  the  cerebral  hemispheres.  ,  •,      p  ^     '  n  ■,     i    , 

ates  it  Irom  the  frontal  lobe. 
Below,  it  is  limited  in  its  fore-part  by  the  posterior  horizontal  limb  of  the  fissure  of 
Sylvius.  Behind  the  upturned  end  of  this  fissure  the  surface  of  the  parietal  lobe 
is  continuous  inferiorly  with  that  of  the  temporal  lobe,  and  an  arbitrary  line  drawn 
backwards  on  the  surface  of  the  brain,  in  continuation  of  the  horizontal  part  of  the 
posterior  limb  of  the  Sylvian  fissure,  is  taken  as  its  inferior  limit.  Posteriorly,  it 
is  separated  from  the  occipital  lobe  at  the  supero-mesial  border  of  the  hemisphere 
by  the  external  parieto-occipital  fissure.  Below  this  fissure  the  surface  of  the 
parietal  lolje  is  continuous  with  that  of  the  occipital  lobe ;  and  an  arbitrary  line 
drawn  across  the  outer  surface  of  the  hemisphere,  I'rom  the  extremity  of  the  external 
parieto-occipital  fissure  to  an  indentation  on  the  infero-lateral  border  of  the  hemi- 
sphere, termed  the  prseoccipital  notch,  may  be  regarded  as  furnishing  a  posterior 
limitation. 

The  prseoccipital  notch  is,  as  a  rule,  only  visible  in  brains  that  have  been  hardened  in  situ.  It 
is  placed  on  the  infero-lateral  border  of  the  heniisi^here,  about  an  inch  and  a  lialf  in  front  of  the 
occipital  pole,  and  is  produced  by  a  vertical  f(jld  or  wrinkle  of  the  dura  mater  on  tlie  deep  aspect 
of  the  parieto-mastoid  suture,  and  immediately  above  the  highest  jmrt  of  the  lateral  blood-sinus. 

There  is  great  variability  in  the  degree  to  which  this  fold  of  dura  mater  projects  in  different 


PAEIETAL  LOBE. 


563 


iudividuals.  In  the  cliild  it  is  always  very  salient,  and  often  produces  a  deep  cleft  in  the  brain, 
but  as  tlie  full  size  of  the  cranium  is  gradually  attained  it  becomes  much  less  projecting.  In  the 
young  skull  two  or  three  such  folds  in  this  locality  are  frequently  appai-ent.  Related  to  the  prae- 
occipital  notch  tliere  are  likewise  some  cerebral  veins  wliich  turn  round  tlie  infero-lateral  margin 
of  the  hemisphere  to  join  the  lateral  blood -sinus. 

On  the  mesial  surface  of  the  honisphere  the  parietal  lobe  is  represented  by 
the  prsecuneus  or  quadrate  lobule.  This  district,  which  is  somewhat  quadrilateral  in 
form,  lies  between  the  upturned  end  of  the  calloso-marginal  sulcus  and  the  internal 
parieto-occipital  fissure.  It  is  imperfectly  separated  below  from  the  limbic  lobe  hj 
a  somewhat  variable  furrow  called  the  post-limbic  sulcus. 

The  gyri  and  sulci,  on  the  outer  surface  of  the  parietal  lobe,  are  the  followino- : — 


Sulci 


Sulcus  jjostcentralis 

Sulcus  intrapari- 1  ^   /°f^"^T-     ,    ,. 
etalis  (of  Tur-    Sulcus  postcentralis 
ner)  superior. 

^  Ramus  horizontalis. 

I  Ramus  occipitalis. 
Upturned  ends  of — 

(a)  Sylvian  fissure. 

(b)  Parallel  fissure. 

(c)  Second  tempo- 

ral fissure. 


Gyri 


Gyrus    ascendens 
jjostcentralis. 
Gyrus  parietalis  superior. 


Ijarietalis    or    gyrus 


Gyrus  parietalis  inferior 


'Gyrus  supra- 
marginalis. 

1  Gyrus   angn- 
laris. 
Gyrus     post- 
jjarietalis. 


The  intraparietal  sulcus  (of  Turner)  is  a  composite  furrow,  and  is  built  up 
of  four  originally  distinct  factors.  Two  of  these,  termed  the  sulcus  postcentralis 
inferior  and  the  sulcus  postcentralis  superior,  take  a  more  or  less  oblique  course 
across  the  hemisphere,  and  are  most  frequently  united  into  one  continuous  fissure. 
The  other  two  factors  are  placed  horizontally,  one  behind  the  other,  and  are  termed 
the  ramus  horizontalis  and  the  ramus  occipitalis. 

The  sulcus  postcentralis  inferior  lies  behind  the  lower  part  of  the  fissure  of 
Kolaudo,  whilst  the  sulcus  postcentralis  superior  occupies  a  similar  position  in 
relation  to  the  upper  part  of  that  fissure.  When  confluent  they  form  a  long,  con- 
tinuous fissure,  which  stretches  across  the  hemisphere  behind  the  fissure  of  Eolando 
and  parallel  to  it. 

The  ramus  horizontalis  is  continuous,  as  a  rule,  with  the  upper  end  of  the  sulcus 
postcentralis  inferior,  and  extends  backwards,  with  a  slight  inclination  upwards 
between  the  superior  parietal  gyrus,  which  lies  above  it,  and  the  inferior  parietal 
gyrus,  which  is  placed  below  it.  With  the  two  confluent  postcentral  sulci  it 
presents  a  figure  like  the  letter  H  placed  on  its  side. 

The  ramus  occipitalis  is  a  curved  sulcus  which  bounds  externally  the  arcus 
parieto-occipitalis,  or,  in  other  words,  the  arching  convolution  which  surrounds  the 
external  parieto-occipital  fissure.  The  ramus  occipitalis  lies  behind  the  ramus 
horizontalis,  and  is  generally  linked  on  to  it ;  less  frequently  it  is  separate.  The 
posterior  end  of  the  ramus  occipitalis  enters  the  occipital  lobe,  and,  behind  the  arcus 
parieto-occipitalis,  bifurcates  into  two  widely  spread-out  branches.  These  form  a 
short  transverse  fissure  in  the  occipital  lobe,  termed  the  sulcus  occipitalis  transversus. 

In  the  human  brain  the  intraparietal  sulcus  is  usually  developed  in  four  separate  pieces, 
corresponding  to  the  four  portions  of  the  fissure  which  have  been  described  as  being  present  in 
the  adult  brain.  The  sulcus  postcentralis  inferior  appears  first  (somewhere  about  the  end  of  the 
sixth  month),  then  the  ramus  occipitalis  and  the  ramus  horizontalis  ;  last  of  all  the  sulcus  post- 
centralis superior  comes  into  view.  The  further  development  of  the  sulcus  consists  in  the 
running  together  of  these  early  pieces.  This  takes  place  in  diff'erent  ways,  and  not  infrequently 
union  fails  at  one  or  more  points,  and  thus  a  great  variety  of  combinations  may  be  noted 
in  different  individuals  ;  indeed,  it  may  be  said  that  every  possible  kind  of  combination  may  be 
met  with.  The  most  common  form  which  the  fissure  assumes,  however,  is  that  in  which  all  its 
factors  have  become  confluent  and  one  continuous  furrow  results.  When  such  an  intraparietal 
fvirrow  is  widely  opened  up,  certain  deep  annectant  gyri,  which  cross  the  bottom  of  the  sulcus, 
come  into  view.  These  interrupt  the  sulcus  at  the  points  of  union  between  its  several  pieces  and 
indicate  its  original  multii3le  formation. 

There  is  reason  to  believe  that  three  of  the  elements  of  the  human  intraparietal  sulcus,  viz. 
the  sulcus  postcentralis  inferior,  the  ramus  horizontalis,  and  the  ramus  occipitalis,  are  disruj)ted 
portions  of  the  primitive  single  continuous  fissure  which  is  seen  in  certain  of  the  lower  apes 
(Cebus),  whilst  one,  the  sulcus  jjostcentralis  superior,  is  a  superadded  element. 

There  is  a  strong  analogy  between  the  postcentral  sulcus,  the  fissure  of  Rolando,  and  the 
40  a 


564 


THE  NERVOUS  SYSTEM. 


praecentral  sulcus.  They  form  a  group  of  radial  sulci  on  tlie  outer  surface  of  the  fcBtal  cerebrum 
above  the  Sylvian  region.  The  fissure  of  Rolando  makes  its  appearance  first,  then  the  prsedentral 
sulcus,  and,  lastly,  the  postcentral  sulcus.  Each  assumes  shape  in  tlie  first  instance  in  two  pieces, 
viz.  an  upper  and  lower.  The  two  pieces  of  the  fissiire  of  Rolando  join  early,  and  only  in  very 
rare  instances  remain  separate  ;  the  two  pieces  of  the  postcentral  furrow  usually  join,  but  in  19 
per  cent  of  cerebral  hemispheres  they  remain  separate  ;  the  tw<j  pieces  of  the  prjtcentral  furrow, 
as  a  rule,  remain  separate  and  distinct. 

The  sulcus  transversus  occipitalis,  or  bifurcated  extremity  of  the  ramus  occipitalis,  has  been 


Deep  gyms 


Ascending  parietal  gyrn 


External  pane  to-occipital  fissure 


Transverse 
■y — occipital 
fissure 


Termination  of  Sylvian  fissure 
Fig.  453. — The  Intrapabietal  Sulcus  fully  opened  up,  so  as  to  show  its  several  parts  and  the 
deep  annectant  gyri  intervening  between  them. 

p^.  Sulcus  postcentralis  inferior.  p-'.    Ramus  horizontalis. 

p-.  Sulcus  postcentralis  superior.  p'*.   Ramus  occipitalis. 

until  lately  generally  believed  to  be  the  representative  in  the  humaii  brain  of  the  conspicuous 
"  Afl'enspalte,"  in  the  cerebrum  of  the  ape.  The  accuracy  of  this  view  was  challenged  in  1892 
{Gmmiiujham  Memoir^  No.  vii.  Roy.  Irish  Acad.),  and  recently  Elliot  Smith  has  brought  forward 
evidence  of  a  very  convincing  kind  which  seems  to  show  that  in  the  human  brain  the  "  Afl'en- 
spalte  "  is  represented  by  the  sulcus  occipitalis  lateralis  of  Eberstaller. 

The  intraparietal  sulcus  maps  out  three  districts  or  gyri  on  the  external  surface 
of  the  parietal  lobe,  viz.  the  posterior  central  convolution,  the  superior  parietal 
gyrus,  and  the  inferior  parietal  gyrus. 

The  upturned  ends  of  the  fissure  of  Sylvius,  of  the  first  temporal  or  parallel 
sulcus,  and  of  the  second  temporal  sulcus  ascend  for  a  short  distance,  one  behind 
the  other,  into  the  inferior  parietal  gyrus. 

The  posterior  central  convolution  (ascending  parietal  convolution)  is  a  long  gyrus 
which  extends  obliquely  across  the  hemisphere  from  the  supero-mesial  border  above 
to  the  Sylvian  fissure  below.  It  is  bounded  in  front  by  the  fissure  of  Rolando  and 
behind  by  the  superior  and  inferior  postcentral  sulci. 

The  superior  parietal  gyrus  is  the  area  of  cerebral  cortex  which  lies  between  the 
supero-mesial  border  of  the  hemisphere  above  and  the  ramus  horizontalis  below.  In 
front  it  is  bounded  by  the  superior  postcentral  sulcus,  whilst  behind  it  is  connected 
with  the  occipital  lobe  by  the  arcus  parieto-occipitalis.  It  is  continuous  round  the 
supero-mesial  border  with  the  pr&ecuneus. 

The  inferior  parietal  gyrus  lies  below  the  ramus  horizontalis  and  the  ramus  occi- 
pitahs  and  behind  the  inferior  prsecentral  sulcus.  It  is  more  or  less  directly  con- 
tinuous with  the  occipital  lobe  behind  and  the  temporal  lobe  below.  From  before 
backwards  it  presents  three  arching  convohitions,  viz.  the  supra-marginal,  the 
angular,  and  the  postparietal.  The  supramarginal  convolution  is  bent  round  the 
upturned  end  of  the  posterior  limb  of  the  Sylvian  fissure,  and  stands  in  continuity 
behind  and  below  this,  with  the  first  temporal  gyrus.  The  angular  convolution 
arches  over  the  upturned  end  of  the  parallel  sulcus  and  becomes  continuous  with 
the  second  temporal  convolution.  The  postparietal  convolution  winds  round  the 
upturned  end  of  the  second  temporal  sulcus  and  runs  into  tlie  third  temporal  gyrus. 

Occipital  Lobe. — The  occipital  lobe  forms  the  hinder  pyramidal  part  of  the 


OCCIPITAL  LOBE. 


565 


cerebral  hemisphere ;  and  although  very  imperfectly  mapped  off  from  the  temporal 
and  parietal  lobes,  which  lie  in  front  of  it,  it  is  nevertheless  one  of  the  most  natural 
subdivisions  of  the  cerebral  hemisphere.  It  is  not  developed  in  the  brain  of  the 
quadruped.  Man  and  the  ape  alone  possess  a  well-marked  occipital  lobe,  and  it 
may  be  defined  as  being  that  part  of  tlie  hemisphere  which  encloses  the  posterior 
horn  of  the  lateral  ventricle.  Being  pyramidal  in  form,  it  presents  three  surfaces 
and  an  apex  or  occipital  pole.  On  the  mesial  aspect  of  the  hemisphere  it  is 
separated  from  the  parietal  lobe  {i.e.  the  precuneus)  by  the  internal  parieto-occi- 
pital  fissure.  On  the  tentorial  or  inferior  surface  it  is  not  marked  off  in  any  way 
from  the  temporal  lobe  and  the  limbic  lobe,  which  lie  in  front  of  it.  It  is  necessary, 
therefore,  on  this  aspect  to  employ  an  arbitrary  line  of  demarcation ;  one  which 
extends  from  the  praBoccipital  notch  on  the  infero-lateral  border  of  the  hemisphere 
to  the  isthmus  of  the  Umbic  lobe  {i.e.  the  narrow  part  of  the  liml)ic  lobe  immedi- 
ately below  the  hinder  end  of  the  corpus  callosum)  will  serve  the  purpose.  On  the 
external  surface  the  external  parie to-occipital  fissure,  and  an  arlntrary  line  from 
this  to  the  preoccipital  notch,  may  be  regarded  as  separating  the  occipital  from  the 
parietal  and  temporal  lobes.  The  upturned  end  of  the  second  temporal  sulcus  may 
lie  in  the  course  of  this  line. 

On  the  mesial  asj^ect  of  the  occiiyitcd  lobe  we  find:  (1)  the  calcarine  fissure, 
(2)  the  cuneus,  and  (3)  the  gyrus  lingualis. 

The  calcarine  fissure  begins  on  the  occipital  pole  by  a  bifurcated  extremity, 
which  lies  in  the  groove  which  is  formed  on  this  part  of  the  brain  by  the  lateral 
sinus.  From  this  it  pursues  a  slightly  arched  course  forwards,  and  ends  by  cutting 
into  the  limbic  lobe  immediately  below  the  spleuium  or  thickened  hinder  margin  of 
the  corpus  callosum.  The  calcarine  fissure  is  joined  by  the  internal  parieto-occipital 
fissure  at  a  point  somewhat  nearer  its  anterior  than  its  posterior  extremity. 
Together,  the  two  fissures  present  a  -<-shaped  figure.  Between  the  two  limbs  of 
the  Y  is  placed  the  cuneus. 

If  the  calcarine  and  internal  parieto-occijjital  fissures  are  opened  up  so  as  to  expose  the 
bottom  in  each  case,  three  well-marked  deep  or  suljnierged  annectant  gyri  will  usually  be  dis- 
played.   One  of  these,  the  best  marked,  called  the  gyrus  cunei,  marks  off  the  parieto-occipital  from 


Parieto  occipital  fissure 


Cuneus 

Anterior  cuneo- 

lingual  gyrus 

Posterior  calcarine 

fissure 

Posterior  cuneo- 

lingual  gyru: 


Callosal  gyrus 


Corpus  callosum 


Oi)tic  tlialanuis 
Gyrus  cunei 


Anterior  calcarine 
fissure 


Gyrus  lingualis 

Collateral  fissure 


Fig.  454. — Internal  Parieto-occipital  and  the  Calcarine  fifaSUREs  klllv  uiened  up,  so  aa  to  show  the 
deep  anuectant  gyri  marking  off  the  several  elements  of  the  -<-shaped  system. 

the  calcarine  fissure  and  joins  the  cuneus  witli  the  limbic  lobe.     In  the  chimpanzee  and  in  the 
lower  apes  the  gyrus  cunei  is  on  the  surface,  and  there  is  no  communication  between  the  two 
fissures  ;  in  the  orang,  gibbon,  and  microcephalic  idiot,  it  may  either  be  submerged  or  on  the 
40  6 


566 


THE  NERVOUS  SYSTEM. 


surface.  The  second  deep  annectant  gyrus,  termed  the  anterior  cuneo-lingual,  crosses  the  bottom 
of  the  calcarine  fissure  a  short  distance  behind  the  point  where  it  is  joined  by  the  parieto-occi- 
pital  fissure,  and  divides  it  into  an  anterior  and  a  posterior  part.  The  anterior  calcarine  fissure  is 
slightly  longer  and  much  deej^er  than  the  posterior  part.  It  includes  the  whole  of  the  stem  of 
the  Y-shaped  fissural  arrangement  and  extends  backwards  for  a  short  distance  into  the  cuneus. 
It  is  the  comjjlete  part  of  the  fissure  and  gives  rise  to  an  elevation  on  the  inner  wall  of  the 
posterior  horn  of  the  lateral  ventricle,  to  which  the  name  of  calcar  avis  or  hippocampus  minor  is 
given.  The  posterior  calcarine  fissure  is  shallower  and  is  usually  interrupted  by  the  third  deep 
annectant  gyrus,  viz.  the  posterior  cuneo-lingual;  this  divides  it  into  two  parts,  of  which  the 


Fig.  455. — Development  of  the  Parieto-occipital  and  the  Calcakine  i<'issuKES. 

A,  Mesial  aspect  of  a  left  cerebral  liemis])here  of  a  foetus  approaching  the  end  of  the  fifth  mouth   of  develop- 
ment ;  B,   Mesial  aspect  of  a  right  cerebral  hemisphere  of  a  fcetus  in  the  beginning  of  the  seventh 
month  of  development. 
S.  L.  Septum  lucidum.  e\      Anterior  calcarine  fissure. 

,',      TT         ■  ..'    >Two  imrts  of  posterior  calcarine  fissure. 

U.     Uncus.  c".  J  ^  '■ 

g.d.  Gj'rus  dentatus.  c.a.    Anterior  collateral  fissure. 

p.o.   Parieto-occipital  fissure.  cm.  Mid-collateral  fissure. 

hinder  is  little  more  than  the  bifurcated  extremity  of  the  fissure.  Very  frequently  this  deep 
gA'rus  reaches  the  surface,  and  then  the  hinder  end  of  the  sulcus  is  completely  cut  off.  The 
posterior  calcarine  fissure  is  not  a  complete  fissure. 

When  the  manner  in  which  the  calcarine  fissure  is  developed  is  studied,  the  various  apjDear- 
ances  which  come  into  view  when  the  bottom  of  the  adult  fissure  is  inspected  receive  the  fullest 
explanation.  The  anterior  calcarine  fissure  is  formed  very  early  as  an  infolding  of  the  wall  of 
the  cerebral  hemisphere.  The  posterior  calcarine  fissure  is  a  secondary  formation.  It  appears 
much  later,  and  usually  in  two  pieces,  which  run  together  and  then  join  the  anterior  calcarine 
fissure.     The  points  of  union  are  indicated  in  the  adult  by  the  two  cuneo-lingual  deep  gyri. 

The  cuneus  is  the  wedge-shaped  or  triangular  district,  on  the  mesial  aspect  of 
the  occipital  lobe,  which  lies  between  the  internal  parieto-occipital  and  calcarine 
fissures. 

The  gyrus  lingualis  is  a  well-marked  convolution  between  the  calcarine  fissure 
above  and  the  posterior  part  of  the  collateral  fissure  below,  which  stretches 
forwards  from  the  occipital  pole.  Anteriorly,  it  becomes  very  narrow  and  joins 
the  hippocampal  part  of  the  limbic  lobe.  It  lies  partly  on  the  mesial  surface  and 
partly  on  the  tentorial  surface  of  the  occipital  lobe. 

On  the  tentorial  surface  of  the  occipital  lobe  there  is  only  one  convolution, 
viz.  the  posterior  part  of  the  occipito- temporal  gyrus.  It  proceeds  continuously 
forwards  into  the  temporal  lobe  on  tbe  outer  side  of  the  collateral  fissure,  and  is 
bounded  externally  by  the  occipito-temporal  sulcus,  a  furrow  which  is  rarely  con- 
tinuous, but  is  usually  represented  by  a  series  of  detached  pieces. 

There  are  two  well-marked  sulci  on  the  external  surface  of  the  occipital  lobe, 
viz.  the  sulcus  occipitalis  transversus  and  the  sulcus  occipitalis  lateralis.  The  sulcus 
occipitalis  transversus  extends  transversely  across  the  upper  part  of  the  lobe,  behind 
the  arcus  parieto-occipitalis.  As  already  explained,  it  is  the  terminal  bifurcation  of 
the  ramus  occipitalis  of  the  intraparietal  sulcus.  The  sulcus  occipitalis  lateralis  is 
a  short  horizontal,  often  sharply-curved,  furrow,  which  divides  the  outer  surface  of 
the  lobe  into  an  upper  and  a  lower  area  of  very  nearly  equal  extent.  These  areas 
are  connected  by  superficial  annectant  gyri  with  the  parietal  and  temporal  lobes. 

Elliot  Smith  has  brought  forward  very  convincing  proof  in  favour  of  regarding  the 
sulcus  occipitalis  lateralis  as  the  representative  of  the  "  Affenspalte  "  in  the  brain  of  the 


TEMPORAL  LOBE.  567 

ape.  He  calls  it  the  sulcus  lunatus  occipitalis,  and  shows  that  iu  the  bi'aius  of  Egyptian 
Fellaheen  it  not  infrequently  possesses  an  opercnlum,  and  presents  an  appearance  which 
closely  corresponds  with  the  condition  distinctive  of  the  gorilla.  The  same  may  occasion- 
ally be  seen  in  the  brain  of  the  aboriginal  Australian. 

Tempokal  Lobe. — The  temporal  lobe  lies  behind  the  stem  and  below  the 
posterior  horizontal  limb  of  the  Sylvian  fissure.  It  is  somewhat  pyramidal  in  form, 
and  presents  an  upper,  an  outer,  and  a  tentorial  surface,  with  a  free  projecting  apex 
or  pole.  Above,  it  is  bounded  by  the  posterior  liorizontal  limb  of  the  fissure  of 
Sylvius,  together  with  the  artificial  line  which  is  drawn  backwards  from  this.  On 
the  tentorial  face  it  is  separated  from  the  liippocampal  part  of  the  limbic  lobe  by 
the  collateral  fissure,  whilst  behind  it  is  marked  off  from  the  occipital  lobe  by  the 
artificial  lines  already  described.  The  temporal  pole  projects  forwards  on  the  under 
surface  of  the  brain  beyond  the  stem  of  the  Sylvian  fissure.  It  should  be  noticed 
that  the  recurved  end  of  the  hippocampal  part  of  the  limbic  lobe  (uncus),  which  lies 
to  the  inner  side  of  the  temporal  pole,  does  not  extend  so  far  forwards  as  the  latter, 
and  is  separated  from  the  pole  by  the  incisura  temporalis  or  ecto-rhinal  fissure. 

The  upper  or  opercular  surface  of  the  temporal  lohe  is  turned  towards  the 
island  of  Eeil  and  the  fronto- parietal  operculum.  The  fissure  of  Sylvius  must, 
therefore,  be  widely  opened  up  to  expose  it.  For  the  most  part  the  surface  is 
smooth,  but  towards  the  back  part  there  are  a  few  transverse  furrows,  which 
separate  two  or  three  weakly-expressed  gyri. 

The  anterior  transverse  gyrus  is  miicli  more  strongly  expressed  iu  the  fcetal  than  in  the  adidt 
brain.  It  appears  in  the  early  j^art  of  the  seventh  month,  and  is  only  subsequently  completely 
liidden  within  the  Sylvian  fissure.  The  fact  of  the  auditory  centre  being  localised  in  this  region 
of  the  temporal  lobe  makes  this  fact  of  interest. 

On  the  deep  surface  of  the  temporal  pole  there  are  also  a  few  feeble  furrows. 

On  the  outer  surface  of  the  temporal  lohe  there  are  two  horizontal  sulci,  called 
respectively  the  first  temporal  or  parallel  and  the  second  temporal  sulcus. 

The  parallel  sulcus  is  a  long,  continuous,  and  deep  fissure,  which  begins  near  the 
temporal  pole  and  proceeds  backwards  below  the  posterior  limb  of  the  Sylvian 
fissure.  Its  hinder  end  turns  upwards  into  the  parietal  lobe  and  is  surrounded  by 
the  angular  gyrus.  The  second  temporal  sulcus  is  placed  midway  between  the 
parallel  sulcus  and  the  infero-lateral  border  of  the  hemisphere.  It  is  very  rare  to 
find  it  in  the  form  of  a  continuous  cleft ;  usually  it  is  broken  up  into  several 
isolated  pieces,  one  behind  the  other.  Its  hinder  part,  which  turns  upwards  into 
the  parietal  lobe,  lies  close  to  the  artificial  line  of  demarcation  between  the  occipital 
and  parietal  lobes,  and  is  surrounded  by  the  postparietal  gyrus. 

By  the  two  temporal  sulci  the  outer  surface  of  the  temporal  lobe  is  mapped  out 
into  three  tiers  of  horizontal  convolutions,  which  are  termed  the  first,  second,  and 
third  temporal  gyri. 

On  the  tentorial  surface  of  the  temporal  lohe  there  is  one  fissure,  termed  the 
occipito-temporal  sulcus.  The  occipito-temporal  sulcus  lies  to  the  outer  side  of  the 
collateral  fissure  and  close  to  the  infero-lateral  margin  of  the  hemisphere.  It  runs 
in  an  antero- posterior  direction,  and  is  not  confined  to  the  temporal  lobe,  but 
extends  backwards  towards  the  occipital  pole.  It  is  usually  broken  up  into  two 
or  more  separate  pieces. 

The  occipito-temporal  convolution  is  situated  between  the  collateral  fissure  and 
the  occipito-temporal  sulcus.  It  extends  from  the  occipital  pole  behind  to  the 
temporal  pole  in  front. 

The  narrow  strip  of  surface  on  the  outer  side  of  the  occipito-temporal  sulcus  is 
continuous,  round  the  infero-lateral  margin  of  the  hemisphere,  with  the  third 
temporal  convolution  on  the  outer  surface  of  the  cerebrum,  and  may  be  reckoned 
as  a  part  of  it. 

The  three  temporal  convolutions  and  the  occipito-temporal  convolutions  run 
into  each  other  at  the  temporal  pole. 

Island  of  Eeil  or  Insula. — The  insula  is  a  triangular  and  somewhat  bulging 
field  of  cerebral  cortex,  which  lies  on  a  deeper  plane  than  the  general  surface  of  the 
hemisphere  and  is  hidden  from  view  by  the  four  opercula  which  overlap  it.  It  is 
circumscribed  by  a  limiting  sulcus  (sulcus  circularis),  already  described,  and  its 


568  THE  NERVOUS  SYSTEM. 

dependent  apical  part,  which  is  directed  downwards,  is  in  close  relation  to  the 
anterior  perforated  spot  and  the  Sylvian  vallecula.  Here  the  limiting  sulcus  is 
absent  and  the  gray  matter  on  the  surface  of  the  insula  passes  continuously  into 
the  anterior  perforated  spot.     The  place  of  transition  is  called  the  limen  insulse. 

The  insula  is  divided  into  several  diverging  convolutions  by  a  series  of  radiating 
sulci.  Of  the  latter,  one,  which  presents  the  same  direction  and  lies  in  the  same 
plane  as  the  fissure  of  Rolando,  receives  the  name  of  the  sulcus  centralis  insulse 
(Fig.  447,  0,  p.  557).  It  divides  the  insula  into  an  anterior  frontal  part  and  a 
posterior  parieto-limhic  part. 

Limbic  Lobe. — This  lobe  is  seen  on  the  mesial  surface  of  the  hemisphere  in  the 
form  of  an  elongated  ring -like  convolution,  the  extremities  of  which  approach 
closely  to  each  other  at  the  locus  perforatus  anticus.  These  extremities  are  con- 
nected by  the  roots  of  the  olfactory  tract,  and  in  this  manner  the  limbic  ring  may 
be  considered  to  be  closed.  The  upper  part  of  the  limbic  lobe  is  placed  in  intimate 
relation  to  the  extremities  and  upper  surface  of  the  corpus  callosum,  and  receives 
the  name  of  callosal  convolution  or  gyrus  fornicatus.  The  lower  portion  of  the 
lobe  is  termed  the  hippocampal  convolution  and  forms  the  inner  part  of  the 
tentorial  surface  of  the  hemisphere.  The  continuity  between  the  hippocampal 
gyrus  and  the  callosal  convolution  is  established  below  the  hinder  end  of  the  corpus 
callosum  by  a  narrow  portion  of  the  limbic  lobe,  called  the  isthmus.  From  this 
point  the  hippocampal  convolution  extends  forwards  towards  the  temporal  pole. 
Finally,  on  the  side  of  the  crus  cerebri,  the  hippocampal  gyrus  is  folded  back  on 
itself  and  ends  in  a  recurved  hook-like  extremity  called  the  uncus.  The  uncus  does 
not  reach  so  far  forwards  as  the  temporal  pole. 

The  callosal  convolution  begins  below  the  anterior  end  of  the  corpus  callosum  at 
the  locus  perforatus  anticus,  and,  winding  round  the  genu  of  the  corpus  callosum,  it 
is  continued  backwards  on  its  upper  surface  to  its  hinder  thickened  extremity  or 
splenium.  Curving  round  this,  it  becomes  greatly  narrowed  through  the  calcarine 
fissure  cutting  into  it.  This  narrow  part  is  termed  the  isthmus,  and  constitutes  the 
link  of  connexion  between  the  callosal  gyrus  and  the  hippocampal  gyrus.  The 
callosal  gyrus  is  separated  from  the  marginal  convolution  by  the  callo  so -marginal 
fissure,  and  behind  this  it  is  imperfectly  marked  off  from  the  prsecuneus  by  the 
post-limbic  sulcus.  The  furrow  which  separates  it  from  the  corpus  callosum  is 
termed  the  callosal  sulcus. 

The  hippocampal  convolution  is  bounded  on  the  outer  side  by  the  anterior  part 
of  the  collateral  fissure,  and  in  front  of  this  by  the  incisura  temporalis,  which 
separates  its  hooked  extremity,  or  uncus,  from  the  temporal  pole.  On  the  inner  side 
it  is  limited  by  the  hippocampal  or  dentate  fissure,  whilst  posteriorly  it  is  divided 
into  two  parts  by  the  anterior  extremity  of  the  calcarine  fissure.  Of  these,  the 
upper  is  the  isthmus,  which  connects  it  with  the  callosal  gyrus,  whilst  the  lower 
portion  brings  it  into  continuity  with  the  gyrus  lingualis.  The  surface  of  the 
hippocampal  convolution  is  covered  by  a  white  reticular  stratum  of  fibres,  termed 
the  substantia  reticularis  alba. 

Altliougli  the  hippocampal  convolution  and  uncus  in  descriptive  anatomy  are  classed  together 
there  is  a  marked  morphological  distinction  between  them.  Tlie  uncus  is  the  feeble  representative 
in  man  of  the  important  pyriform  lobe  in  ceiiain  of  the  lower  mammals,  and  consequently  it 
belongs  to  the  rhinencephalon ;  the  hippocampal  convolution,  on  the  other  hand,  is  to  be  regarded 
as  forming  a  part  of  the  neo-'palliuvi  of  Elliot  Smith.  The  unimportant  incisura  temporalis  of 
the  liuman  brain  in  lower  types  of  brain  in  which  the  rhinencei)halon  bulks  largely  is  represented 
Vjy  tlie  conspicuous  ecfo-rhinal  fissure. 

Gyrus  Dentatus  and  the  Fimbria. — If  tlie  dentate  fissure,  which  lies  along 
the  inner  side  of  the  hippocampal  convolution,  be  opened  up,  the  gyrus  dentatus 
and  the  fimbria,  lying  side  by  side,  will  be  brought  into  view  (Fig.  451,  p.  559). 

The  fimbria  is  simply  a  portion  of  the  posterior  pillar  of  the  fornix  prolonged 
into  this  region.  It  is  a  conspicuous  band  of  white  matter,  which  presents  a 
prominent  free  border.  In  front  it  runs  into  the  recurved  extremity  of  the  uncus, 
whilst,  if  traced  lja(;kwards,  it  will  be  seen  to  curve  upwards  Ijchind  the  posterior 
end  of  the  optic  thalamus  and  become  continuous  with  the  posterior  pillar  of  the 
fornix  below  the  hinder  part  of  the  corpus  callosum. 


GYEUS  1)ENTATUS. 


569 


The  gyrus  dentatus  is  the  free  edge  of  gray  matter  which  is  placed  between  the 
fimbria  and  the  deep  part  of  the  upper  surface  of  the  hippocampal  convolution. 
The  groove  between  it  and  the  fimbria  is  termed  the  fimbrio-dentate  sulcus,  whilst 
the  furrow  between  it  and  the  hippocampal  convolution  forms  the  bottom  of  the 
dentate  fissure.  The  dentate  gyrus  is  notched  along  the  marghi,  whilst  its  surface 
is  scored  by  numerous  parallel  and  closely-placed  transverse  grooves.  It  begins 
behind  in  the  region  of  the  splenium  or  thickened  posterior  margin  of  the  corpus 


Caudate  nucleus 


Optic  radiation 

Caudate  nucleus 

Optic  radiation 

Inferior  longitudinal  bundle 


Tapetum 
Descending  horn  of  lateral  ventricle 


Choroid  plexus  in  lateral 
ventricle 


Corpus  callosum 
Fornix 

Thalamus  (pulvinar) 
Occipital  corticifugal  tract  to 
superior  quadrigeminal  body 
Superior  quadrigeminal  body 
Corpus  geniculatuni  externum 

Corpus  geniculatum  internum 

.Sylvian  gray  matter 

Inferior  brachium 

Lateral  fillet 

Superior  cerebellar  peduncle 

Cerebellum 
Pons 


Fimbria' 
Gyrus  dentatus ' 

Dentate  fissure  ' 

Fig.  456. — Coronal  Section  through  the  Left  Side  of  the  Cerebrum,  Mesencephalon,  and  Pons, 
IN  the  Region  of  the  Pulvinar  of  the  Thalamus  and  the  Corpora  Geniculata  (Chimpanzee  ; 
Weigert-Pal  specimen). 

callosum,  and  is  carried  forwards  into  the  cleft  of  the  uncus.  From  this  it  emerges 
in  the  form  of  a  delicate  band,  which  crosses  the  surface  of  the  recurved  part  of  the 
uncus  in  a  transverse  direction,  thereby  constituting  the  frenulum  Giacomini. 

The  dentate  fissure  is  a  complete  fissure,  and  the  elevation  on  the  ventricular 
wall  which  corresponds  to  it  is  called  the  hippocampus  major.  It  begins  behind 
the  splenium  of  the  corpus  callosum,  where  it  is  continuous  with  a  shallow  part  ot 
the  callosal  fissure,  and  it  proceeds  forwards  between  the  gyrus  dentatus  and  the 
hippocampal  convolution.     Its  anterior  end  is  enclosed  within  the  uncus. 

When  coronal  sections  are  made  through  the  callosal  part  of  the  limbic  lobe  and  the  subjacent 
corpus  callosum,  the  cortical  gray  matter  is  seen  to  be  reflected  from  the  bottom  of  the  callosal 
tissure  in  the  form  of  an  exceedingly  fine  layer,  which  forms  a  thin  coating  for  the  upper  surface 
of  the  corpus  callosum.  In  the  midst  of  this  certain  delicate  strands  of  longitudinal  fibres,  the 
striae  longitudinales,  are  embedded,  and,  with  the  gray  matter  associated  with  them,  they  re- 
present an  aborted  or  vestigial  convolution,  termed  the' gyrus  supracallosus.  This  gyrus  is  con- 
tinuous with  the  gyms  dentatus  round  the  hinder  margin  of  the  corpus  callosum. 

Olfactory  Lobe. — The  olfactory  lobe  is  small  and  rudimentary  in  the  human 
brain,  and  the  description  which  is  given  here  does  not  include  all  the  parts  which, 
from  the  morphological  point  of  \aew,  belong  to  this  portion  of  the  cerebral  hemi- 
sphere (see  p.  584).  Under  this  heading  we  shall  study  merely  :  (1)  the  olfactory 
bulb  and  tract,  with  the  two  roots  of  the'latter ;  (2)  the  trigonum  olfactorium. 

The  olfactory  tract  is  a  narrow,  white,  prismatic  band,  which  expands  anteriorly 
into  a  swollen  bulbous  extremity,  termed  the  olfactory  bulb.  Both  the  tract  and 
the  bulb  lie  upon  the  olfactory  sulcus  on  the  orbital  surface  of  the  frontal  lobe^ 


570 


THE  NERVOUS  SYSTEM. 


whilst  the  inferior  surface  of  the  bulb  rests  on  the  cribriform  plate  of  the  ethmoid 
bone,  and  receives  the  numerous  olfactory  nerves  which  reach  it  through  the  foramina 
in  that  part  of  the  cranial  floor. 

Posteriorly,  the  olfactory  tract  divides  into  two  diverging  roots.  The  mesial 
root  curves  abruptly  inwards  and  is  continued  into  the  callosal  and  sub-callosal 
gyri.  The  lateral  root  runs  outwards  and  backwards  over  the  outer  part  of  the 
locus  perforatus  anticus,  and  gradually  disappears  from  view.  In  animals,  in 
which  the  olfactory  apparatus  is  better  developed  than  in  man,  it  may  be  traced 
into  what  corresponds  to  the  uncinate  extremity  of  the  hippocampal  convolution 
in  man  (Fig.  380,  p.  474). 

The  trigonum  olfactorium  or  olfactory  tubercle  is  the  small  triangular  field  of 
gi'ay  matter  which  occupies  the  interval  between  the  roots  of  the  olfactory  tract 
at  the  point  where  they  begin  to  diverge.  Some  fibres  from  the  posterior  end  of 
the  olfactory  tract  enter  the  trigonum,  and,  in  certain  cases,  these  constitute  a 
more  or  less  distinct  middle  root. 

Corpus  Callosum,  Septum  Lucidum,  and  Fornix. 

Corpus  Callosum. — -The  corpus  callosum  is  the  great  transverse  commissure 
which  passes  lietween  the  two  cerebral  hemispheres.     It  is  placed  nearer  the  anterior 


Ciii^uluni      ^^Wss. 


Fiontal  fibres 


Cut  -iiirface 


Fibre.s  of  corona  radiata 


Intersection  of 

callosal  and  corona 

radiata  systems  of 

fibres 


Transverse  fibres 
of  corpus 
callosum 


Cor])ns  callosum 


CiuKuluin 


Inferior  longi- 
tudinal bundle 


Forceps  major 


Tapetum 


Splenium 


Stria  louHitudinalis  niesialis 


Fio.  4.^)7. — Thk  CoiiPU.s  Callosum,  exposed  from  above  and  the  rif,dit  lialf  dissected, 
to  show  the  course  taken  by  its  fibres. 


than  the  posterior  aspect  of  the  brain,  and  it  unites  the  inner  surfaces  of  the  hemi- 
spheres throughout  very  nearly  a  half  of  their  antero-posterior  length.  The  corpus 
callosum  is  highly  arched  from  before  backwards,  and  presents  a  convex  upper 
surface  and  a  concave  lower  surface. 


CORPUS' CALLOSUM.  571 

The  upper  surface  of  the  corpus  callosum  forms  the  bottom  of  the  great  longi- 
tudinal fissure,  and  on  each  side  of  this  it  is  covered  by  the  callosal  gyrus.  Only 
in  its  posterior  part  is  it  touched  by  the  falx  cerebri ;  in  front,  this  process  of  dura 
mater  falls  considerably  short  of  it.  The  upper  surface  of  the  callosum  is  covered 
by  a  thin  layer  of  gray  matter  continuous  at  the  bottom  of  the  callosal  sulcus  with 
the  gray  cortex  on  the  surface  of  the  hemisphere.  In  this  there  are  embedded  on 
either  side  of  the  mesial  plane  two  delicate  longitudinal  bands  of  fibres,  called 
respectively  the  stria  longitudinalis  medialis  and  lateralis.  The  stria  longitudinalis 
medialis  is  the  more  strongly  marked  of  the  two,  and  it  is  separated  from  its  neigh- 
bour of  the  opposite  side  by  a  faint  mesial  furrow.  The  stria  longitudinalis  lateralis 
is  placed  farther  out,  under  cover  of  the  callosal  gyrus.  The  thin  coating  of  gray 
matter,  with  the  two  stride,  represents  an  aborted  convolution,  termed  the  gyrus 
supracallosus.  So  thin  is  the  gray  coating  supplied  by  this  gyrus  that  the  trans- 
verse direction  pursued  by  tlie  callosal  fibres  proper  can  be  easily  perceived 
through  it. 

The  two  extremities  of  the  corpus  callosum  are  much  thickened,  whilst  the 
intermediate  part  or  body  is  considerably  thinner.  The  massive  posterior  end, 
which  is  full  and  rounded,  lies  over  the  mesencephalon  and  extends  backwards  as 
far  as  the  highest  point  of  the  cerebellum.  It  is  called  the  splenium,  and  it  consists 
of  an  upper  and  a  lower  part.  The  latter  is  bent  forwards  under  the  upper  part,  to 
tbe  inferior  surface  of  which  it  is  closely  applied.  The  anterior  end  of  the  corpus 
callosum  is  not  quite  so  massive  and  is  folded  downwards  and  backwards  on  itself. 
It  is  termed  the  genu.  The  recurved  lower  part  of  the  genu  is  separated  from  the 
part  of  the  corpus  callosum,  which  lies  above,  by  an  interval.  It  rapidly  thins  as 
it  passes  backwards  and  receives  the  name  of  the  rostrum.  The  fine  terminal  edge 
of  the  rostrum  becomes  connected  with  the  lamina  cinerea. 

The  gyrus  supracallosus,  with  its  contained  medial  and  lateral  longitudinal  striae,  when  traced 
backwards,  is  seen  to  turn  round  the  sjslenium  and  become  continuous  with  the  gyrus  dentatus. 
In  front  the  mesial  strife,  with  the  associated  gray  matter,  are  carried  round  the  genu  and  then 
backwards  on  the  under  surface  of  the  rostrum.  As  they  turn  round  the  anterior  extremity  of 
the  corpus  callosum,  each  stria  runs  into  the  corresjsonding  gyrus  subcallosus — a  narrow  cortical 
strip  which  lies  on  the  mesial  surface  of  the  hemisphere  immediately  below  the  genu  of  the 
corpus  callosum.  The  gyrus  subcallosus  is  often  called  the  jieduncle  of  the  corpus  callosum,  and 
the  fibres  of  the  stria  which  it  contains,  emerging  from  its  substance,  proceed  backwards  and 
outwards  along  the  ]30sterior  limit  of  the  anterior  perforated  spot  towards  the  anterior  extremity 
of  the  temj)oral  lobe.  Elliot  Smith  has  shown  that  these  parts  have  an  important  morphological 
significance. 

The  under  surface  of  the  corpus  callosum  on  either  side  of  the  mesial  plane  is 
for  the  most  part  free,  and,  lined  by  ependyma,  it  forms  the  roof  of  the  anterior 
horn  and  body  of  the  lateral  ventricle.  In  the  mesial  plane,  however,  it  is  attached 
to  subjacent  parts,  viz.  to  the  septum  lucidum  in  front  and  to  the  body  of  the 
fornix  behind. 

The  transverse  fibres  of  the  corpus  callosum,  as  they  enter  the  white  medullary 
centre  of  the  cerebral  hemisphere,  radiate  from  each  other  so  as  toji'each  every  part 
of  the  cerebral  cortex.  This  radiation  is  termed  the  radiatio  corporis  callosi  and 
the  fibres  which  compose  it  intersect  the  fibres  which  form  the  corona  radiata,  or,  in 
other  words,  the  fibres  which  extend  between  the  internal  capsule  and  the  cerebral 
cortex  (Figs.  440,  p.  547  ;  and  468,  p.  582).  The  more  anterior  of  the  fibres  which 
compose  the  genu  of  the  corpus  callosum  sweep  forwards  in  a  series  of  curves  into 
the  prefrontal  region  of  the  hemisphere.  A  large  part  of  the  splenium,  forming  a 
solid  bundle  termed  the  forceps  major,  bends  suddenly  and  abruptly  backw.ards 
into  the  occipital  lobe  (Fig.  463,  p.  577).  Fibres  from  the  body  and  upper  part 
of  the  splenium,  curving  round  the  lateral  ventricle,  form  a  very  definite  stratum, 
called  the  tapetum.  This  is  a  thin  layer  in  the  medullary  centre  of  the  hemisphere, 
which  constitutes  the  immediate  roof  and  outer  wall  of  the  posterior  horn  a.nd  the 
outer  wall  of  the  hinder  part  of  the  descending  horn  of  the  lateral  ventricle.  In 
coronal  sections  through  the  occipital  and  hinder  temporal  regions  the  tapetum 
stands  out  very  distinctly  (Figs.  456,  p.  569  ;  462,  p.  576 :  and  465,  p.  579). 

Fornix. — The  fornix  is  an  arched  bilateral  structure  composed,  for  the  most 
part,  of  longitudinally-directed  fibres.     In  its   intermediate  part   its  two   lateral 


572  THE  NEEVOUS  SYSTEM. 

halves  are  joined  together  in  the  mesial  plane,  and  form  what  is  called  the  body  of 
the  fornix :  but  in  front  and  behind  they  are  quite  separate,  and  constitute  the 
anterior  and  posterior  pillars  of  the  fornix. 

The  body  of  the  fornix  is  triangular  in  form.  In  front,  where  it  is  continuous 
with  the  anterior  pillars,  it  is  narrow ;  whilst  behind  it  broadens  out,  becomes 
flattened,  and  is  finally  prolonged  into  the  posterior  pillars.  The  upper  surface  of 
the  body  of  the  fornix  is  in  contact  with  the  under  surface  of  the  hinder  part  of 
the  body  of  the  corpus  callosum,  and  posteriorly  is  adherent  to  it.  In  front  of  this 
adhesion,  and  in  the  mesial  plane,  it  is  attached  to  the  septum  lucidum.     Beyond 

these  attachments,  on  each  side,  the  upper  surface 

^"'""X^nro    v^^^^"^^"^^  of  *^he  body  of  the  fornix  forms  a  part  of  the 

Anterior  Jr  yi  floor  of  the   lateral  ventricle  and  is  clothed  by 

commissure  MA/^- jj- yi^'^^'Azyv    ^hc  lining  cpcndyma.     It  presents  a  sharp  lateral 

kJj__^_^..^^  edge  or   margin,  from  under  which    the  choroid 

X^T^^^^^  plexus    proiects  into    the  cavity   of  the  lateral 

^A-~~  ventricle   and   with   which    the  epithelial   layer 

Fig.   458. -Diagrammatic  Profile  View   which   COVerS    that    plexus    is   continuous.        The 

OP  THE  Fornix.  lower  surface  of  the   body   of   the   fornix   rests 

upon   the  velum   interpositum,  which   separates 

it  from  the  roof  of  the  third  ventricle  and  the  upper  surface  of  the  optic  thalami. 

It  is  not  at  all  an  uncommon  occurrence  to  find  the  two  lateral  portions  of  the 

body  of  the  fornix  of  unequal  size  (Fig.  461,  p.  575). 

The  anterior  pillars  of  the  fornix  (columnee  fornicis)  are  two  rounded  strands 
which  emerge  from  the  anterior  part  of  the  body  of  the  fornix,  and  then  diverge 
very  slightly  from  each  other  as  they  curve  downwards  in  front  of  the  foramina  of 
Monro.  Sinking  into  the  gray  matter  on  the  lateral  wall  of  the  third  ventricle, 
each  anterior  pillar  proceeds  downwards  to  the  base  of  the  brain,  and  in  the  inter- 
peduncular space  protrudes,  to  take  part  in  the  formation  of  the  corpus  mammillare. 
When  the  corpus  mammillare  is  dissected  it  appears  to  be  largely  formed  of  a 
twisted  loop  of  the  anterior  pillar  of  the  fornix,  in  which  the  pillar  bends  upon 
itself,  and,  is  then  continued  upwards  and  backwards  into  the  optic  thalamus. 
This  appearance,  however,  is  misleading.  The  fibres  of  the  anterior  pillar  end  in 
the  gray  nucleus  of  the  corpus  mammillare,  and  the  strand  which  passes  from  this 
to  the  thalamus  is  the  bundle  of  Vicq  d'Azyr  (p.  548). 

The  posterior  pillars  of  the  fornix  (crura  fornicis)  are  flattened  bands  which 
diverge  widely  from  each  other.  At  first  they  are  adherent  to  the  under  surface 
of  the  corpus  callosum,  but  soon  they  sweep  downwards  round  the  posterior  ends  of 
the  optic  thalami  and  enter  the  descending  horns  of  the  lateral  ventricles.  Here 
each  pillar  comes  into  relation  with  the  corresponding  hippocampus  major,  and  a 
portion  of  its  fibres  are  spread  out  on  the  surface  of  this  prominence,  thereby 
giving  it  a  white  coating  termed  the  alveus,  whilst  the  remainder  of  the  fibres 
constitute  the  fimbria  or  taenia  fornicis — a  narrow  but  very  distinct  band  of  white 
matter,  which  ^is  attached  by  its  outer  margin  along  the  inner  border  of  the 
hippocampus  major  and  ends  in  front  by  joining  the  uncus  (p.  568). 

A  certain  number  of  transverse  fibres  enter  into  the  formation  of  the  fornix. 
The  diverging  posterior  pillars  enclose  between  them  a  small  triangular  space  oh 
the  under  surface  of  the  hinder  part  of  the  corpus  callosum.  This  area  is  crossed 
by  transverse  fibres,  which  form  a  thin  lamina  called  the  psalterium  or  lyra.  Some- 
times the  psalterium  is  not  completely  fused  to  the  under  surface  of  the  corpus 
callosum,  and  in  these  cases  a  narrow  space  is  left  between  them,  which  receives  the 
name  of  Verga's  ventricle. 

The  fornix  is  intimately  connected  with  the  olfactory  apparatus.  Its  fibres  for  the  most  part, 
arise  from  the  pyramidal  cells  in  the  cornu  ammonis  or  hippocampus  major  and  ascend  in  the 
fimbria  and  posterior  pillar.  In  the  region  of  the  iisalterium  numerous  fibres  cross  the  mesial 
plane,  enter  the  opposite  posterior  pillar,  and  in  it  proceed  to  the  opposite  cornu  ammonis. 
These  fibres  constitute  a  commissure  Ijetween  the  two  cornua  ammonis.  The  remainder  of  the 
fibres  proceed  forwards  in  the  Ijody  of  the  fornix,  and  by  means  of  the  anterior  pillar  the 
majority  of  the  filjres  are  carried  downwards,  behind  the  anterior  commissure,  to  tlie  corpus 
mamijiillare.  Some,  bowever,  curve  backwards  into  tbe  stria  medullaris  (p.  548) ;  whilst  others, 
forming  the  olfactory  bundle  of  the  cornu  ammonis,  jiass  in  front  of  the  anterior  commissure  and 


LATERAL  VENTRICLE.  573 

enter  the  seijtum  lucidvmi,  through  which  they  reach  the  subcallosal  gyrus  and  the  locus  per- 
foratus  anticus.  Finally,  this  bundle  divides  into  two  parts,  of  which  one  joins  the  inner  root  of 
the  olfactory  tract,  whilst  the  other  goes  to  the  uncus. 

The  greater  number  of  tlie  longitudinal  fibres  of  the  fornix  must,  therefore,  be  regarded  as 
establishing  a  connexion  between  the  ciirnu  ammonis  and  the  optic  thalamus.  The  inner  portion 
of  the  composite  nucleus  of  the  corjius  mammillare  is  an  internode  interposed  in  the  path  of  this 
connecting  tract.  The  bundle  of  Vicq  d'Azyr,  formed  by  the  relay  of  fibres  which  takes  origin 
in  this  internode,  forms  the  second  link  in  the  chain. 

The  stria;  longitudinales  in  the  gyrus  suisracallosus  on  the  upper  surface  of  the  corjnis 
callosum  are  to  be  regarded,  from  a  morj^hological  jioint  of  view,  as  forming  an  outlying  part  of 
the  fornix  system. 

There  can  be  little  doubt  that  the  gyrus  supracallosus  represents  a  wasted  portion  of  the 
hippocampus  formation.  In  monotremes  and  marsuijials  the  hippocampus  occupies  a 
corresponding  position,  but,  with  the  greater  development  of  the  corj)us  callosum  in  higher 
mammals,  atrophy  and  stretching  occur  and  the  structure  is  reduced  to  a  vestigial  condition 
(Elliot  Smith).  That  fox-nix  tibres  therefore  should  be  found  in  connexion  with  the  supracallosal 
gyrus  is  not  surprising. 

Septum  Lucidum  (septum  pelliicidum). — The  septum  lucidum  is  a  thiu  vertical 
partition  which  intervenes  between  the  anterior  cornua  and  foreparts  of  the  bodies 
of  the  two  lateral  ventricles.  It  is  triangular  in  shape,  and  posteriorly  it  is 
prolonged  backwards  for  a  variable  distance  between  the  body  of  the  corpus  callosum 
and  the  fornix,  to  both  of  which  it  is  attached  by  its  upper  and  lower  edges.  In 
front  it  occupies  the  gap  behind  the  genu  of  the  corpus  callosum,  whilst  below,  in 
the  narrow  interval  between  the  posterior  edge  of  the  rostrum  of  the  corpus  callosum 
and  the  fornix,  it  is  prolonged  downwards  towards  the  base  of  the  brain  in  the 
gyrus  subcallosus.  The  septum  lucidum  is  composed  of  two  thin  laminae  in  appo- 
sition with  each  other  in  the  mesial  plane  (Fig.  461,  p.  575). 

Fifth  Ventricle  (cavum  septi  pellucidi). — This  name  is  applied  to  the  mesial 
cleft  between  the  two  laminae  of  the  septum  lucidum.  It  varies  greatly  in  size  in 
different  brains  and  contains  a  little  fluid.  It  is  completely  isolated  and  presents 
no  communication  with  the  other  ventricles  of  the  brain.  Indeed,  the  term"  ventricle," 
as  applied  to  it,  is  quite  inappropriate,  seeing  that  at  no  period  in  the  development 
of  the  brain  has  it  any  connexion  with  the  general  ventricular  system. 

Lateral  Ventpjcle. 

The  cavity  in  the  interior  of  the  cerebral  hemisphere  is  called  the  lateral 
ventricle.  It  is  lined  throughout  by  ependyma  continuous  with  the  ependymal 
lining  of  the  third  ventricle.  In  many  places  the  walls  of  the  cavity  are  in  appo- 
sition, whilst  in  other  localities  spaces  of  varying  capacity,  and  containing  cerebro- 
spinal fluid,  are  left  between  the  bounding  walls. 

The  lateral  ventricle  (ventriculus  lateralis)  communicates  with  the  third  ventricle 
of  the  brain  by  means  of  a  small  foramen,  just  large  enough  to  admit  a  crow-quill, 
which  is  termed  the  foramen  of  Monro.  This  aperture  is  placed  in  front  of  the  fore 
end  of  the  optic  thalamus  and  behind  the  anterior  pillar  of  the  fornix. 

The  highly- irregular  shape  of  the  lateral  ventricle  can  be  best  understood  by  the 
study  of  a  cast  of  its  interior  (Figs.  459  ;  and  444,  p.  551).  It  is  usual  to  describe 
it  as  being  composed  of  a  body  and  three  horns,  viz.  an  anterior,  a  posterior,  and  a 
descending  horn.  The  anterior  horn  is  that  part  of  the  cavity  which  lies  in  front  of 
the  foramen  of  Monro.  The  body  is  the  portion  of  the  ventricle  which  extends 
from  the  foramen  of  Monro  to  the  splenium  of  the  coipus  callosum.  At  this  point 
the  posteiior  and  descending  horns  diverge  from  the  hinder  part  of  the  body.  The 
posterior  horn  curves  backwards  and  inwards  into  the  occipital  lobe.  It  is  very 
variable  in  its  length  and  capacity.  The  descending  horn  proceeds  with  a  bold  sw^eep 
round  the  hinder  end  of  the  optic  thalamus,  and  then  tunnels  in  a  forward  and 
inward  direction  through  the  temporal  lobe  towards  the  temporal  pole.  The  early 
fcetal  lateral  ventricle  is  very  capacious  and  presents  an  arched  or  semilunar  form. 
It  is  composed  of  parts  which  correspond  to  the  anterior  horn,  the  body,  and  the 
descending  horn,  and  there  is  little  or  no  demarcation  between  them.  The 
posterior  horn  is  a  later  production.  It  comes  into  existence  with  the  occipital 
lobe  and  is  produced  as  a  diverticulum  or  elongated  pouch,  which  grows  backwards 
from  the  upper  and  hinder  part  {i.e.  the  convexity)  of  the  primitive  cavity. 


574 


THE  NEEVOUS  SYSTEM. 


Anterior  Horn  of  the 
Lateral  Ventricle  (cornu  an- 
terius).  —  The  anterior  horn 
forms  the  foremost  part  of  the 
cavity,  and  extends  in  a  for- 
ward and  outward  direction  in 
the  frontal  lobe.  When  seen 
in  coronal  section  (Fig.  460)  it 
presents  a  triangular  outline, 
the  floor  sloping  upwards  and 
outwards  to  meet  the  roof  at 
an  acute  angle.  It  is  bounded 
in  front  by  the  posterior  sur- 
face of  the  genu  of  the  corpus 
callosum;  the  roo/ is  also  formed 
by  the  corpus  callosum.  The 
inner  wall,  which  is  vertical, 
is  formed  by  the  septum 
lucidum;  whilst  the  sloping 
^007'  presents  a  marked  eleva- 
tion or  bulging,  viz.  the  smooth, 
rounded,  and  prominent  ex- 
tremity of  the  pear-shaped 
caudate  nucleus. 

Body  of  the  Lateral  Ven- 
tricle (pars  centralis). — The 
body  of  the  cavity  is  likewise 
roofed  by  the  corpus  callosum. 
On  the  inner  or  mesial  side  it 
is  bounded  by  the  attachment 
of  the  fornix  to  the  under  sur- 
face of  the  corpus  callosum  and 
by  the  hinder  part  of  the 
septum  lucidum.  On  the  outer  side  it  is  closed,  as  in  the  case  of  the  anterior  horn, 
by  the  meeting  of  the  floor  and  the  roof  of  the  cavity.  On  the  floor  a  number 
of  important  ob- 
jects may  be  re- 
cognised. Erom 
without  inwards 
these  are  met  in 
the  following 
order:  (1)  the  cau- 
date nucleus ;  (2) 
a  groove  which 
extends  obliquely 
from  before  back- 
wards and  out- 
wards between  the 
caudate  nucleus 
and  the  optic 
thalamus,  and  in 
which  are  placed 
the  vein  of  the 
corpus  striatum 
and  a  white  band 
called  the  taenia 
semicircularis;  (3) 
a  portion  of  the 
upper    surface    of 


Fig.   459. — Drawing  taken  from  a  Cast  of  the  Ventricular 
System  of  the  Brain,  as  seen  from  above  (after  Retzius). 

Vent.  III.   Third  ventricle.  Vent.  IV.   Fourth  ventricle. 

R.SP.   Recessus  suprapinealis. 


Great  longitudinal  lissure 


Corpus  callo.suiii  (genu) 


Anterior  liorn  of " 
lateral  ventricle 


Caudate  nucleus 


Caudate  nucleus 
(in  section) 


Fig.   460.- 


Corpus  callosum  (genu) 


(iival  longitudinal  (issure 

-C()ron'al  Section  through  the  Frontal  Lobes  and  the 
Anterior  Horks  of  the  Lateral  Ventricles. 


LATERAL  'VENTRICLE. 


575 


the  optic  thalamus ;  (4)  the  clioroid  plexus ;   (5)  the  thin,  sharp  lateral  edge  of 
the  fornix. 

The  caudate  nucleus  narrows  rapidly  as  it  proceeds  ])ackwards  on  the  outer  part 
of  the  floor  of  the  hody  of  the  lateral  ventricle.  The  vein  of  the  corpus  striatum  is 
covered  over  by  ependyma.  It  joins  the  vein  of  Galen  close  to  the  foramen  of 
Monro.  The  connexions  of  the  taenia  semicircularis  will  be  dealt  with  later.  The 
portion  of  the  upper  surface  of  the  optic  thalamus  which  appears  in  the  floor  of  the 


Ventricle  V 


Corpus  callosum 


Corpus  callosum 
turned  to  the  left  side 


Septum  Incidum 


Foramen  of  Monro 
Caudate  nucleus 
:  Optic  thalamus 

Clioroid  plexus 

Taenia  semicircularis 


Trigouum  ventricul 

Hippocampus  major 


Calcar  avis 


tJulb  of  the  cornu 


Fimbria 

Forceps  major 


•     Hippocampus  major 
Posterior  pillar  of  the  fornix 


Body  of  the  fornix 


Fig.  461.— Dissectiox,  to  show  the  fornix  and  lateral  ventricles  ;  the  body  of  the  corpus  callosum 
has  been  turned  over  to  the  left. 


ventricle  is  in  great  part  hidden  by  the  choroid  plexus,  which  lies  upon  it.  The 
choroid  plexus  is  a  rich  vascular  fringe  which  appears  from  under  cover  of  the  sharp 
lateral  edge  of  the  fornix.  In  front  it  is  continuous,  behind  the  foramen  of  Monro, 
with  the  corresponding  choroid  plexus  of  the  opposite  side,  whilst  behind,  it  is 
carried  into  the  descending  horn  of  the  ventricle.  Although  the  choroicl  plexus 
has  all  the  appearance  of  lying  free  within  the  ventricle,  it  must  be  borne  in  mind 
that  it  is  invested  by  an  epithelial  layer  which  represents  a  portion  of  the  hemi- 
sphere wall  and  excludes   it  from  the  cavity.     This  thin  layer  is  continuous  on  the 


576 


THE  NERVOUS  SYSTEM. 


one  hand  with  the  sharp  edge  of  the  fornix,  and  on  the  other  it  is  attached  to  the 
upper  surface  of  the  optic  thalamus. 

Posterior  Horn  of  the  Lateral  Ventricle  (cornu  posterius). — The  posterior 
horn  is  an  elongated  diverticulum  carried  backwards  into  the  occipital  lobe  from  the 
hinder  end  of  the  body  of  the  ventricle.  It  tapers  to  a  point  and  describes  a  gentle 
curve,  the  convexity  of  which  is  directed  outwards.  The  ?-oo/ and  outer  v)all  of  this 
portion  of  the  ventricular  cavity  are  formed  by  the  tapetum  of  the  corpus  callosum. 
In  coronal  sections  through  the  occipital  lobe  this  is  seen  as  a  thin  but  distinct 
layer  of  white  fibres,  which  lies  immediately  outside  the  ependyma  and  to  the  inner 
side  of  a  much  larger  strand  of  fibres  in  the  medullary  substance  of  the  occipital 
lobe,  viz.  the  optic  radiation. 

On  the  inner  wall  two  elongated  curved  elevations  may  be  observed.  The 
uppermost  of  these  is  termed  the  bulb  of  the  cornu  (bulbus  cornu  posterioris),  and  is 
produced  by  the  fibres  of  the  forceps  major  of  the  corpus  callosum  as  they  curve 
abruptly  backwards  from  the  lower  part  of  the  splenium  of  the  corpus  callosum  into 
the  occipital  lobe.  Below  this  is  the  elevation  known  as  the  calcar  avis.  It  varies 
greatly  in  size  in  different  brains,  and  is  caused  by  an  infolding  of  the  ventricular 
wall  in  correspondence  with  the  anterior  calcarine  fissure  on  the  exterior  of  the 
hemisphere. 

Descending  Horn  of  the  Lateral  Ventricle  (cornu  inferius). — The  descending 
horn  is  the  continuation  of  the  cavity  into  the  temporal  lobe.  At  first  directed  back- 
wards and  outwards  the  descending  horn  suddenly  sinks  downwards  behind  the  optic 
thalamus  into  the  temporal  lobe,  in  the  centre  of  which  it  takes  a  curved  course  for- 
wards and  inwards  to  a  point  about  an  inch  behind  the  extremity  of  the  temporal  pole. 

In  the  angle  between  the  diverging  posterior  and  descending  horns  the  cavity 
of  the  ventricle  presents  an  expansion  of  a  somewhat  triangular  shape.  To  this 
the  name  of  trigonum  ventriculi  is  sometimes  given. 

The  roof  of  the  descending  horn  is  formed  for  the  most  part  by  the  tapetum  of 


SiJlenium  of  corpus  callosum 


Bulb  of  the  posterior  cornu 


Bulb  of  tht^  posterior  cornu 


Fig.   462. 


Inferior  longitudinal  fasciculus. 
-Coronal  Section  thuouoh  the  Posterior  Horns  of  the  Lateral  Ventricles. 


the  corpus  callosum.  At  the  extremity  of  the  horn  the  roof  presents  a  bulging 
into  the  cavity.  This  is  the  amygdaloid  tubercle,  and  it  is  produced  by  a  super- 
jacent collection  of  gray  matter  termed  the  amygdaloid  nucleus.  The  taenia  semi- 
circularis  and  the  attenuated  tail  of  the  caudate  nucleus  are  both  prolonged  into  the 
descending  horn  and  are  carried  forwards,  in  its  roof,  to  the  amygdaloid  nucleus. 

On  the  floor  of  the  descending  horn  the  following  structures  are  seen :  (1) 
hippocampus  major,  or  the  cornu  ammonis  ;  (2)  the  choroid  plexus  ;  (3)  the  fimbria ; 
and  (4)  the  eminentia  collateralis. 

The  hippocampus  major  (hippocampus)  is  for  the  most  part  covered  by  the 


LATEEAL  VENTEICLE. 


577 


choroid  plexus.  It  is  a  prominent  elevation  on  the  lioor  of  the  descending  horn  of 
the  lateral  ventricle  and  is  strongly  curved,  in  conformity  with  the  course  taken 
by  the  horn  in  which  it  lies.  It  therefore  presents  an  internal  concave  margin  and 
an  external  convex  border.  Narrow  behind,  it  enlarges  as  it  is  traced  forwards, 
and  it  ends  below  the  amygdaloid  tubercle  in  a  tliickened  extremity,  which 
presents  some  faint  grooves  or  notches  on  its  surface.  In  consequence  of  this,  the 
anterior  end  of  the  hippocampus  major  receives  the  name  of  the  pes  hippocampi. 
The  hippocampus  major  is  the  internal  elevation  which  corresponds  to  the  dentate 
j&ssure  on  the  exterior  of  the  hemisphere  (Fig.  464). 

If  an  incision  be  made  along  the  outer  convex  edge  of  the  hii^pocampus  major,  and  the  surface 
lamina  be  raised,  the  central  core  will  be  seen  to  present  the  curious  ajspearance  of  two 
corrugated  layers  dove-tailed  into  each  other  (M'Carthy). 

The  fimbria  (fimbria  hippocampi)  is  the  narrow  band  of  white  matter  which  is 
attached  by  its  outer  margin  along  the  inner  concave  border  of  the  hippocampus 
major.  The  white  matter  composing  it  is  continuous  with  the  thin  white  layer 
(the  alveus)  which  is  spread  over  the  surface  of  the  hippocampus  major,  and  it 
presents  two  free  surfaces  and  a  sharp  free  inner  border.  The  fimbria  has  already 
been  examined  in  connexion  with  the  hippocampal  fissure  and  the  gyrus  dentatus 


Caudate  nuelens 


Genu  of  corpus  callosum 

Septum  lucicluiii 
Ventricle  V. 
Caudate  nucleus 

Foramen  of  Monro 

Twnia  semicireularis 

Optic  thalamus 
Fornix 


Mesial  longitudinal  stria  on  the 
splenium  of  the  corpus  callosum 


Fig.  463. — Dissection,  to  show  the  fornix  and  the  posterior  and  descending  cornua 
of  the  lateral  ventricle  of  the  left  side. 


(p.  568),  and  the  relations  which  it  presents  to  the  fornix  and  the  uncus  have  been 
pointed  out. 

When  the  pia  mater  in  the  region  of  the  hippocampal  fissure  is  removed  from 
the  surface  of  the  brain,  the  choroid  plexus  in  the  interior  of  the  descending  horn 
41 


578 


THE  NEEVOUS  SYSTEM. 


of  the  lateral  ^'entricle  is  usually  withdrawn  with  it,  and  a  fissure  appears  between 
the  fimbria  and  the  roof  of  the  ventricular  horn.  This  is  the  choroid  fissure.  It 
appears  at  a  very  early  date  in  the  development  of  the  cerebral  hemisphere,  and 
takes  an  arcuate  course  upwards  and  forwards  round  the  hinder  end  of  the  optic 
thalamus.  In  the  region  of  the  body  of  the  lateral  ventricle  it  extends  as  far 
forwards  as  the  foramen  of  Monro,  and  is  formed  by  the  involution  of  an  epithelial 
part  of  the  wall  of  the  ventricle  over  the  choroid  plexus  (p.  575).  In  the  region  of 
the  descending  horn,  when  the  choroid  plexus  with  the  involuted  epithelial  layer 
which  covers  it  is  withdrawn,  the  choroid  fissure  is  converted  into  an  artificial  gap 
which  leads  directly  into  this  part  of  the  ventricular  cavity. 

The  choroid  plexus  is  a  convoluted  system  of  blood-vessels  in  connexion  with  a 
fold  of  pia  mater,  which  is  prolonged  into  the  descending  horn  of  the  lateral 
ventricle.  It  lies  on  the  surface  of  the  hippocampus  major  and  is  continuous 
behind  the  posterior  part  of  the  optic  thalamus,  with  the  choroid  plexus  in  the  body 
of  the  lateral  ventricle.  But  it  must  not  be  supposed  that  the  choroid  plexus  lies 
free  in  the  ventricular  cavity.  It  is  clothed  in  the  most  intimate  manner  by  an 
epithelial  layer,  which  represents  the  inner  or  mesial  wall  of  the  descending  horn 
involuted  into  the  cavity  over  the  choroid  plexus.  The  ventricle,  therefore,  only 
opens  on  the  surface  through  the  choroid  fissure  when  this  thin  epithelial  layer  is 
torn  away  by  the  withdrawal  of  the  choroid  plexus.  From  the  above,  it  will  be 
understood  that  the  arcuate  choroid  fissure,  throughout  its  whole  length  (viz.  from 

the  foramen  of  Monro  to  the 
extremity  of  the  descending 
horn  of  the  lateral  ventricle), 
is  formed  by  the  involution  of 
a  portion  of  the  wall  of  the 
hemisphere  which  remains  epi- 
thelial. In  the  body  of  the 
ventricle  this  layer  is  attached, 
on  the  one  hand,  to  the  sharp 
lateral  margin  of  the  fornix, 
and  on  the  other  to  the  upper 
surface  of .  the  optic  thalamus  ; 
in  the  descending  horn  it  is 
attached,  in  like  manner,  to  the 
edge  of  the  fimbria  or  posterior 
pillar  of  the  fornix,  whilst  above 
it  joins  the  roof  of  this  portion 
of  the  ventricle  along  the 
line  of  the  taenia  semicircularis. 
The    eminentia    collateralis 

Posterior  lioni  of     i  j_    t^c 

lateral  ventricle  SHOWS  vcry  great  dinerenccs  m 
-Caicaravis  its  dcgrcc  of  development,  and 
it  may  present  two  distinct 
-Buii.oftiiocoriiu  forms,  which  may  be  distin- 
guished from,  each  other  as  the 
eminentia  collateralis  posterior 
and  the  eminentia  collateralis 
anterior. 

The  2^osterior  collateral 
eminence  is  a  smooth  eleva- 
tion in  the  floor  of  the  tri- 
gonum  ventriculi,  in  the  in- 
terval which  is  left  between 
the  calcar  avis  and  the  hippo- 
campus major  as  they  diverge 
from  each  otlier.  In  the  foetal  brain  this  is  always  a  very  strongly -marked 
elevation,  whicli  corresponds  with  the  mid-collateral  fissure,  but  in  the  course  of 
growth  it  is  apt  to  lose  much  of  its  prominence. 


Pes  hippocariipi 


Hippocampus 
major 


Fig.  464. — DL-^^-htiidN  liom  above,  to  .show  the  posterior  and 
descending  coniua  of  the  lateral  veutricle. 

B.G.  Giacomini's  band. 
F.        Fimbria. 


F.D.  Gyrn.s  dentatus. 

H.C.  Hippocampal  convolution. 


BASAL  GAXGLIA  OF  THE  CEEEBEAL  HEMISPHEEE. 


579 


Claustruiii 


Putamen 


The  anterior  collateral  eminence  is  only  occasionally  present.  It  appears  as  an 
eloncjated  elevation  of  varying  length  and  prominence,  on  the  tioor  of  the  descend- 
ing iiorn  of  the  lateral  veiitricle,  on  the  outer  side  of  the  hippocampus  major.  It 
is  formed  by  the  anterior  portion  of  the  fcetal  collateral  sulcus,  when  this  develops 
as  a  complete  fissure. 

Basal  Ganglia  of  the  Cerebral  Hemisphere. 

Under  this  heading  are  included  certain  masses  of  gray  matter  more  or  less 
completely  embedded  in  the  white  medullary  substance  of  the  hemisphere,  and 
which  are'  developed  in  its  wall.  They  compose  the  caudate  and  lenticular  nuclei, 
which  together  form  the  corpus  striatum,  the  claustrum,  and  the  amygdaloid 
nucleus. 

The  caudate 
nucleus  bulges 
into  the  lateral 
ventricle.  It  is  a 
pyriform,  highly- 
arched  mass  of 
gray  matter,  which 
presents  a  thick, 
swollen  head,  or 
anterior  extremity, 
and  a  long,  attenu- 
ated tail.  The  head 
projects  into  the 
anterior  horn  of  the 
lateral  ventricle, 
whilst  its  narrower 
part  is  prolonged 
outwards  and 
backwards  in  the 
floor  of  the  body 
of  the  yentricle, 
where  it  is  separ- 
ated from  the  optic 
thalamus  by  the 
taenia  semicircul- 
aris.  Finally,  its 
tail  curves  down- 
wards 's\"ith  a  bold 
sweep  and  enters 
the  descending 
horn  of  the  lateral 
ventricle.  In  the 
roof  of  this  horn 
it  is  prolonged 
forwards  to  the 
amygdaloid  nu- 
cleus, the  lower 
part  of  which  it 
joins.  The  caudate 
nucleus  thus  pre- 
sents a  free  ventricular  surface,  covered  with  ependyma,  and  a  deep  surface 
embedded  in  the  white  substance  of  the  cerebral  hemisphere,  and  for  the  most  part 
related  to  the  internal  capsule. 

Owing  to  its  arched  form  it  follows  that,  in  horizontal  sections  through  the 
cerebral  hemisphere  below  a  particular  level,  it  is  cut  at  two  points,  and  both  the 
head  and  the  tail  appear  on  the  field  of  the  section  (Fig.  465).     In  coronal  sections 
behind  the  amygdaloid  nucleus,  it  is  also  divided  at  two  places  (Fig.  440,  p.  547). 
41a 


Genu  of  corpus  callosuiu 

Anterior  horn  of  lateral, 
ventricle 

Caudate  nucleus 

Anterior  limb  of  internal 

capsule 

Ventricle  V. 

Genu  of  internal  capsule 
Anterior  pillars  of  fornix 
Globus  pallida 


Bundle  of  Vicq  d' Azyr 

Posterior  limb  of  internal 
capsule 

Tbalamu 

Retrolenticular  part  of    y-'^^ 
internal  capsule 

Hippocampus  major. 

Splenium 

Choroid  plexus 

Band  ?of  Vicq  d'Azjr 
Calcarine  fissure- 


^ Optic 

I       radiation 

—J- Tapetum 

/  Inferior 

longitudinal 

bundle 


Fig.  465.— Horizontal  Section  thruuoh  the  Right  Cerebral  Hemisphere 
AT  the  Level  of  the  Widest  Part  of  the  Lenticular  Nucleus. 


580 


THE  NEEYOUS  SYSTEM. 


The  anterior  extremity  of  the  head  of  the  caudate  nucleus  coincides  very  nearly 
with  that  of  the  anterior  horn  of  the  lateral  ventricle.  In  the  region  of  the  locus 
perforatus  anticus,  the  head  of  the  caudate  nucleus  gains  the  surface  and  its  gray 
matter  becomes  continuous  with  that  of  the  cerebral  cortex. 

The  lenticular  nucleus  lies  on  the  outer  side  of  the  caudate  nucleus  and  optic 
thalamus,  and  is  for  the  most  part  embedded  within  the  white  medullary  substance 
of  the  cerebral  hemisphere.  It  does  not  extend  either  so  far  forwards  or  so  far 
backwards  as  the  caudate  nucleus.  Indeed,  it  presents  a  very  close  correspondence 
in  j)oint  of  extent  with  the  insula  or  island  of  Eeil  on  the  surface.  When  seen  in 
horizontal  section,  it  presents  a  shape  similar  to  that  of  a  biconvex  lens.  Its 
inner  surface  bulges  more  than  the  outer  surface,  and  its  point  of  highest  convexity 
is  placed  opposite  the  taenia  semicircularis  or  the  interval  between  the  caudate 
nucleus  and  the  optic  thalamus.  In  coronal  section  the  appearance  presented  by 
the  lenticular  nucleus  differs  very  much  in  different  planes  of  section.     Eig.  466 

represents  a  sec- 
tion through  its 
anterior  portion. 
Here  it  is  semi- 
lunar or  crescentic 
in  outline  and  is 
directly  continu- 
ous below  with 
the  head  of  the 
caudate  nucleus ; 
above,  also,  it  is 
intimately  con- 
nected with  the 
caudate  nucleus 
by  bands  of  gray 
matter,  which 
pass  between  the 
two  nuclei  and 
break  up  the  white 
matter  of  the  fore- 
part of  the  inter- 
vening internal 
capsule.  It  is 
due  to  the  ribbed 
or  barred  appear- 
ance, which  is  pre- 
sented by  such  a 

section  as  this,  that  the  term  corpus  striatum  is  applied  to  the  two  nuclei.  In 
the  region  of  the  locus  perforatus  anticus  both  nuclei  reach  the  surface  and  become 
continuous  with  the  cortex. 

When  a  section  is  made  in  a  plane  further  back  {e.g.  immediately  posterior  to 
the  anterior  commissure,  as  in  Fig.  467)  the  divided  lenticular  nucleus  assumes  an 
altogether  different  shape,  and  is  seen  to  be  completely  cut  off  from  the  caudate 
nucleus  by  tlie  internal  capsule.  It  is  now  triangular  or  wedge-shaped.  Its  hase 
is  turned  towards  the  island  of  Reil  and  is  in  direct  relation  to  a  thin  lamina  of 
white  matter,  termed  the  external  capsule.  Its  internal  surface  is  oblique  and  is 
applied  to  the  internal  capsule,  whilst  its  inferior  surface  is  horizontal  and  is 
directed  downwards  towards  the  base  of  the  brain.  But,  further,  two  white  laminse, 
the  external  and  internal  medullary  laminae,  are  now  evident,  which  traverse  its 
substance  in  a  vertical  direction  a.nd  divide,  it  into  three  zones.  The  outer,  basal, 
and  larger  zone  is  termed  the  putamen ;  the  two  inner  portions  together  constitute 
the  globus  pallidus. 

The  putamen  forms  much  the  largest  part  of  the  lenticular  nucleus.  It  is 
darker  in  colour  than  the  globus  pallidus,  and  in  this  respect  resembles  the  caudate 
nucleus.     It  is  traversed  by  fine  radiating  bundles  of  fibres,  which  enter  it  from  the 


Great  longi- 
tudinal Assure 


Corpus  callosum. 

Lateral  ventricle. 

Anterior  pillar 

of  fornix 

Choroid  plexus. 

Foi-amen  of 
Monro' 


Septum  lucidum 


Caudate  nucleus 
Internal  capsule 

Putamen 
Claustruni 
Fig.  466. — Coronal  Section  throdoh  the  Cerebral  Hemispheres  so  as  to  exit 
through  the  anterior  part  (putamen)  of  the  lenticular  nucleus  in  front  of  the 
globus  pallidus. 


BASAL  GANGLIA  OF  THE  OEEEBRAL  HEMISPHEEE. 


581 


external  medullary  lamina.  Both  in  point  of  structure  and  in  mode  of  development 
it  is  closely  associated  with  the  caudate  nucleus,  and  it  is  the  only  part  of  the  len- 
ticular nucleus  which  is  connected  by  intervening  bands  of  gray  matter  with  the 
caudate  nucleus.  The  antero-posterior  length,  as  well  as  the  vertical  depth  of  the 
putamen,  is  much  greater  than  in  the  case  of  the  globus  pallidus ;  consequently,  in 


ChoroiJ  plexus 


Lateral  ventricle 


Claustrum, 


Bundle  of  Vicq 
d'Azyr 


Globus  pallidu; 

Anterior  pillar 
of  fornix' 


I  Ireat  longitudinal 
lissure 

Corpus  callosuni 

Fornix 

Caudate  nucleus 
Vein  of  corpus 
striatum 

Velum  interpositum 
Thalamus 
Third  ventricle 
Choroid  plexns 
Internal  capsule 

Foramen  of  Monro 

Anterior  pillar  of 

fornix 

Anterior  commissure 

Optic  ti'act 

Infundibulum 
Optic  chiasma 
Optic  nerve 


Locus  perforatus  auticus 


Olfactory  peduncle 


Fig.  467. — Coronal  Section  through  the  Cerebrum  so  as  to  cut  through  the  three  divisions  of  the 
lenticular  nucleus  ;  posterior  surface  of  the  section  depicted. 


both  coronal  and  horizontal  sections  through  the  cerebrum  it  is  encountered  before 
the  plane  of  the  globus  pallidus  is  reached. 

The  external  capsule  is  loosely  connected  with  the  outer  surface  of  the  putamen,  and  it  can  be 
readily  stripped  off.  This  accounts  for  the  tendency,  exhibited  in  hsemorrhages  in  this  locality, 
for  the  effused  blood  to  sjiread  out  in  the  interval  between  these  structures. 

The  globus  pallidus  is  composed  of  the  two  smaller  and  inner  zones  of  the  lenti- 
cular nucleus.  They  present  a'  faint  yellowish  tint,  and  are  paler  and  more 
abundantly  traversed  by  fibres  than  the  putamen.  The  zone  next  the  putamen  (i.e. 
the  intermediate  zone)  is  much  larger  than  the  innermost  subdivision.  It  extends 
forwards  to  a  point  a  little  in  front  of  the  plane  of  the  anterior  commissure.  When 
the  lenticular  nucleus  is  cut  in  a  coronal  direction,  and  in  its  widest  part,  the 
innermost  zone  shows  an  indication  of  a  separation  into  two  parts,  so  that  here  the 
globus  pallidus  appears  to  consist  of  three  subdivisions.  The  morphology  of  the 
globus  pallidus  is  by  no  means  clear. 

Connexions  of  the  Corpus  Striatum. — (1)  Numerous  fibres  pass  from  the  optic 
thalamus  to  the  corpus  striatum,  and  in  the  reverse  direction  from  the  corpus  striatum 
into  the  thalamus  through  the  anterior  limb  of  the  intei-nal  capsule.  These  may  be 
termed  the  thalamo- striate  and  the  strio  -  thalamic  fibres.  (2)  Edinger  describes  a 
connexion  between  the  caudate  nucleus  and  the  substantia  nigra.  The  connecting  fibres 
pass  through  the  subthalamic  region  and  constitute  a  tract  in  the  mesencephalon,  in  close 
apposition  with  the  substantia  nigra,  called  the  stratum  intermedium.  (3)  The  ansa 
lenticularis  has  previously  been  mentioned.  It  is  composed  of  fibres  which  come  from  the 
inferior  part  of  the  fore  portion  of  the  thalamus  and  curve  outwards  under  the  lenticular 
nucleus.  They  stream  upwards  into  this  and  through  its  medullary  laminae.  Many  of 
them  apparently  proceed  onwards  to  the  cerebral  cortex.  (4)  Fibres  from  the  posterior 
41  & 


582 


THE  NERVOUS  SYSTEM. 


limb  of  the  internal  capsule  (thalamic  fibres  chiefly)  enter  the  lenticular  nucleus  and 
stream  through  it,  and  its  medullary  laminae,  on  their  way  to  the  cerebral  cortex. 

Claustrum.— This  is  a  thin  plate  of  gray  substance  embedded  in  the  white 
matter,  which  mtervenes  between  the  lenticular  nucleus  and  the  gray  cortex  of  the 
insula  or  island  of  Eeil.  Followed  in  an  upward  direction,  it  becomes  gradually 
thinner   and    ultimately   disappears.      As   it   is    traced   downwards,    however,    it 


Intersection  of  corona  radiata 
and  callosal  systems  of  fibres 

Corpus  callosum  — 3 
Caudate  nucleus 
Fornix 
Internal  capsule 


Occipito-frontal  association  bundle 
Putamen 

External  capsule 


Claustruni 

-    ^-   Frontoparietal  operculum 
i_-  Insula 

Temporal  operculum 


Globas  pallidus 

Optic  tract 

Anterior  commissun 


Fig.  468.— Cokonal  Sectton  through  the  Left  Side  of  the  Cerebrum  of  an  Orang 

(Weigert-Pal  specimen). 

The  section  pas.ses  tlirougyi  the  niiddle  of  the  lenticular  nucleus. 

thickens  considerably,  and  at  the  base  of  the  brain  it  conies  to  the  surface  at  the 
anterior  perforated  spot  and  becomes  continuous  with  the  gray  matter  of  the  cortex. 
Its  extent  corresponds  very  closely  with  the  area  occupied  by  the  insula,  and  its 
surface  towards  this  portion  of  the  cerebral  cortex  shows  ridges  and  depressions 
corresponding  to  the  insular  gyri  and  sulci. 

Amygdaloid  Nucleus.— In  the  forepart  of  the  temporal  lobe,  in  front  of,  and 
to  some  extent  above  the  extremity  of  the  descending  horn  of  the  lateral  ventricle, 
there  is  a  round  mass  of  gray  matter,  called  the  amygdaloid  nucleus.  The  tail  of 
the  caudate  nucleus  joins  its  lower  part,  whilst  above  it  is  carried  up  into  the  X3uta- 
men.     In  front  it  is  continuous  with  the  gray  cortex  of  the  cerebrum. 

Taenia  Semicircularis. — This  is  a  band  of  fibres  which,  for  the  most  part,  arise 
in  the  amygdaloid  nucleus.  From  this  it  runs  backwards  in  the  roof  of  the  de- 
scending horn  of  the  lateral  ventricle,  and  then  arches  upwards  and  forwards,  so  as 
to  gain  the  floor  of  the  body  of  the  lateral  ventricle.  In  both  situations  it  lies 
close  to  the  inner  side  of  the  nucleus  caudatus,  and  finally,  at  the  foramen  of 
Monro,  it  bends  downwards  towards  the  anterior  commissure.  Some  of  its  fibres 
pass  in  front  and  others  behind  the  commissure,  and  ultimately  they  end  in  the 
locus  perforatus  anticus  (Kolliker). 

Internal  Capsule. — This  term  is  applied  to  the  broad  l)and  of  white  matter 
which  intervenes  between  the  lenticular  nucleus,  on  the  outside,  and  the  optic 


INTERNAL  CAPSULE.  583 

thalamus,  taenia  semicircularis,  and  caudate  nucleus  on  the  inner  side.  It  presents 
many  different  appearances,  according  to  the  plane  in  which  the  brain  is  cut.  In 
the  region  of  the  mesencephalon,  a  coronal  section  through  the  brain  shows  that  in 
great  part  the  internal  capsule  is  directly  continuous  with  the  crusta  of  the  crus 
cerebri  (Fig.  440,  p.  547).  In  horizontal  section  the  internal  capsule  is  observed  to 
be  bent  upon  itself  opposite  the  taenia  semicircularis,  or  the  interval  between  the 
caudate  nucleus  and  the  thalamus.  This,  bend,  which  points  inwards,  is  called  the 
genu.  About  one-third  of  the  internal  capsule  lies  in  front  of  the  genu,  and  is 
termed  the  anterior  limb ;  the  remaining  two-thirds,  which  lie  behind  the  genu, 
constitute  the  posterior  limb. 

The  anterior  limb  of  the  internal  capsule  intervenes  between  the  lenticular 
nucleus  and  the  caudate  nucleus.  In  its  lower  and  forepart  it  is  much  broken  up 
by  the  connecting  bands  of  gray  matter  which  pass  between  the  forepart  of  the 
putamen  and  the  lenticular  nucleus. 

The  anterior  limb  of  the  iuterual  capsule  is  largely  composed  of  corticipetal  fibres 
belonging  to  the  thalamic  radiation.  It  Hkewise  contains  corticifugal  fibres.  The 
corticipetal  fibres  are  of  two  kinds,  viz.  thalamo-frontal  and  thalamo-striate.  The 
former,  which  arise  in  the  optic  thalamus,  go  through  the  anterior  limb  of  the  internal 
capsule  to  reach  the  cortex  of  the  frontal  lobe.  The  thalamo-striate  fibres  likewise  arise 
in  the  thalamus  and  enter  the  anterior  limb,  to  reach  the  caudate  and  lenticular  nuclei. 

The  corticifugal  fibres  are  represented  by  the  fronto-thalamic,  the  strio-thalamic,  and 
the  frouto-pontine  tracts. 

The  fronto-pontine  tract  arises  in  the  cortex  of  the  prefrontal  region,  traverses  the 
anterior  limb  of  the  internal  capsule,  forms  the  inner  fifth  of  the  crusta  of  the  crus  cerebri, 
and  finally  ends  in  the  nucleus  pontis. 

The  posterior  limb  of  the  internal  capsule  is  placed  between  the  optic  thalamus 
and  the  lenticular  nucleus,  and  it  extends  backwards  for  a  short  distance  beyond 
the  hinder  end  of  the  putamen  on  the  outer  side  of  the  posterior  part  of  the 
thalamus  and  of  the  tail  of  the  caudate  nucleus.  The  posterior  limb,  therefore,  is 
spoken  of  as  consisting  of  a  lenticular  and  a  retrolenticular  part. 

The  lenticular  part  of  the  posterior  limb  is  composed  of  both  corticipetal  and  cortici- 
fugal  fibres.  The  corticipetal  fibres  enter  the  internal  capsule  from  the  outer  aspect  of 
the  optic  thalamus,  and  are  composed  of  fibres  which  arise  within  the  thalamus,  and  proceed 
upwards  to  the  cerebral  cortex. 

The  corticifugal  fibres  consist  of  the  pyramidal  tract  and  the  cortico-thalamic  fibres. 

The  great  motor  or  pyramidal  tract,  descending  from  the  Rolandic  area  of  the  cortex, 
occupies  the  anterior  half  of  the  lenticular  part  of  the  internal  capsule.  The  fibres,  which 
go  to  the  nucleus  of  the  facial  nerve,  lie  close  to  the  genu,  and  behind  these  are  the 
fibres  which  go  to  the  hypoglossal  nucleus ;  still  further  back  are  pyramidal  fibres  which 
enter  the  spinal  cord  and  end  around  the  motor  cells  of  the  anterior  horn  of  gray  matter. 
This  pyramidal  tract  has  been  observed  occupying  the  middle  part  of  the  crusta  of  the 
crus  cerebri,  into  which  it  passes  directly  from  the  internal  capsule. 

The  retrolenticular  part  of  the  posterior  limb  contains  :  (1)  the  fibres  of  the  optic 
radiation  as  they  pass  to  establish  their  connexions  with  the  thalamus,  superior  quadri- 
geminal  body,  and  corpus  geniculatum  externum  ;  (2)  the  fibres  of  the  auditory  radiation, 
or  those  which  connect  the  auditory  cortical  field  in  the  temporal  lobe  with  the  corpus 
geniculatum  internum  (Figs.  418,  p.  520,  and  Fig.  439,  p.  546)  ;  (3)  the  temporo-pontine 
tract,  which  is  composed  of  fibres  which  take  origin  in  the  two  upper  convolutions  of  the 
temporal  lobe  and  pass  through  this  section  of  the  internal  capsule  to  reach  the  outer 
part  of  the  crusta  of  the  crus  cerebri.  Through  this  they  reach  the  ventral  part  of  the 
pons,  in  the  gray  matter  of  which  they  end. 

When  the  fibres  of  the  internal  capsule  are  traced  upwards  they  are  found  to 
spread  out  widely  from  each  other  in  a  radiating  or  fan-shaped  manner,  so  as  to 
reach  the  various  convolutions  of  the  cerebral  hemisphere.  This  arrangement  is 
termed  the  corona  radiata.  The  callosal  system  of  fibres,  as  they  proceed  into  the 
hemisphere,  also  radiate,  and  they  intersect  the  fibres  of  the  corona  radiata  (Fig. 
468,  p.  582). 

External  Capsule. — The  thin  lamina  of  white  matter  between  the  outer  aspect 
of  the  putamen  and  the  claustrum  is  called  the  external  capsule.     This  joins  with 


584  THE  NERVOUS  SYSTEM. 

the  internal  capsule  in  front  of  and  behind  the  putamen,  and  in  this  manner  the 
lenticular  nucleus  is  encapsulated  by  white  matter. 

Morphological  Subdivision  of  the  Cerebral  Hemisphere.— In  many  respects  the  descrip- 
tive anatomy  of  tlie  liiunan  cerebral  lieniispliere  is  not  in  accord  with  the  facts  which  haA^e  been 
acquired  regarding  its  morphological  evolution  ;  and  of  recent  years  this  discrepancy  has  become 
more  marked  through  the  important  researches  of  Elliot  Smith. 

From  the  morphological  point  of  view  the  cerebral  hemisphere  may  be  regarded  as  being 
composed  of  three  parts,  viz.  the  rhinencephalon,  the  corpus  striatum,  and  the  neo-pallium. 

The  rhinencephalon  is  the  most  archaic  part  of  the  hemisphere,  and  in  the  brains  of  the 
lower  vertebrates  (fishes,  amphibians,  reptiles)  it  constitutes  its  chief  bulk.  In  the  human  brain 
it  is  represented  by  the  olfactory  bulb,  olfactory  tract  and  its  roots,  the  anterior  perforated 
space,  the  imcus,  the  gyrus  subcallosus,  the  septum  lucidum,  the  hippocampus,  fornix,  gyrus 
dentatus,  and  the  gvrus  supracallosus. 

The  uncus,  with  the  aborted  lateral  stria  of  the  olfactory  peduncle,  is  all  that  remains  in  the 
human  lirain  of  the  relatively  huge  pyriform  lobe  of  many  of  the  lower  mammals.  The  hippo- 
campal  convolution  which  lies  to  the  outer  side  of  the  dentate  fissure,  although  it  runs  con- 
tinuously into  the  uncus,  is  not  a  part  of  the  rhinencephalon.-  It  belongs  to  the  neo-pallium. 
The  feeble  furrow,  termed  the  incisura  temporalis  which  separates  the  uncus  from  the  temporal 
pole,  is  one  of  the  most  primitive  of  the  cerebral  fissures.  It  represents  the  rhinal  or  ecto-rhinal 
fissure — the  bounding  fissure  of  the  rhinencephalon. 

The  neo-pallium  is  represented  by  the  rest  of  the  hemisphere,  exclusive  of  the  corpus  striatum. 
It  therefore  comprises  almost  the  whole  of  the  convoluted  cortex  on  the  surface  together  with  its 
associated  white  matter.  The  great  development  of  the  neo-pallium  in  man  is  one  of  the  most 
distinctive  characters  of  the  human  brain. 

In  their  phylogenetic  evolution  the  rhinencephalon  and  the  neo-pallium  appear  to  develop 
more  or  less  independently  of  each  other.  In  certain  cases  the  former  atrophies,  whilst  the 
neo-pallium  attains  a  high  degree  of  development  {e.g.  man,  monkey,  whale,  etc.),  in  others  the 
reverse  development  occurs  {e.g.  hedgehog  and  many  other  mannnals),  in  which  the  rhinencephalon 
forms  a  large  part  of  the  hemisphere  and  the  neo-pallium  is  relatively  small 

Intimate  Structure  of  the  Cerebral  Hemisphere. 

The  cerebral  hemisphere  is  composed  of  an  external  coating  of  gray  matter, 
termed  the  cortex,  spread  over  an  internal  mass  of  white  matter,  which  is  called  the 
medullary  centre.  The  cortex  is  of  peculiar  interest,  seeing  that  there  is  good  reason 
for  believing  that  in  it  the  higher  functions  of  the  brain,  or  those  which  may  be 
classed  under  the  general  designation  of  the  intellectual  functions,  take  place.  It 
is  within  the  same  layer  of  gray  matter  that  the  influence  of  those  external  impres- 
sions, which  gain  access  to  the  cerebro-spinal  axis  through  the  senses,  finally  take 
shape  as  consciousness ;  and  in  it  also  are  placed  the  centres  which  carry  on  the 
psycho-motor  functions.  The  white  medullary  centre  is  composed  of  nerve-fibres 
which  constitute  the  paths  along  which  the  influence  of  impressions  is  carried  to 
and  from  the  cortex,  and  from  one  part  of  the  cortex  to  another. 

The  Cerebral  Cortex. 

The  gray  cortex  is  spread  over  the  entire  surface  of  the  cerebral  hemisphere,  but 
it  does  not  form  a  layer  of  equal  thickness  in  all  localities.  At  the  summit  of  a 
convolution  it  is  always  thicker  than  at  the  bottom  of  a  furrow.  The  maximum 
thickness  of  cortex  (about  6  mm.)  is  attained  in  the  upper  parts  of  the  two  central 
convolutions,  whilst  the  minimum  (about  2-5  mm.)  may  be  observed  in  the  region 
of  the  occipital  pole.  The  amount  of  gray  cortex  differs  considerably  in  different 
individuals,  and  appreciably  diminishes  in  old  age.  It  is  also  stated,  but  upon 
imperfect  evidence,  that  it  is  relatively  more  abundant  in  the  male  than  in  the 
female. 

In  structure,  likewise,  marked  differences  may  be  noted  in  the  gray  cortex  of 
different  regions,  and  excellent  work  has  been  recently  done  in  the  direction 
of  connecting  these  structural  peculiarities  with  the  functional  characteristics 
of  particular  areas  and  applying  them  to  the  determination  of  morphological 
problems  connected  with  the  cerebral  surface  (Campbell  and  Bolton).  In  certain 
localities  this  structural  difference  is  quite  apjjarent  to  the  naked  eye  when  sections 
are  made  through  the  cortex.  There  are,  however,  no  sharp  transitions  in  structure. 
One  form  of  cortex  passes,  as  a  rule  gradually  and  almost  insensibly,  into  the  variety 
of  cortex  which  is  distinctive  of  an  adjoining  region,  and  throughout  the  whole 


STRUCTUEE  OF  THE  CEREBEAL  COETEX.         585 

mass  a  general  ground  type  may  be  recognised.  It  is  only  to  those  general 
structural  features  which  more  or  less  characterise  the  entire  cortical  layer  that  we 
shall  be  able  to  refer. 

When  sections  are  made  through  the  fresh  brain,  and  the  cut  surface  is  closely 
inspected,  it  will  usually  be  apparent  that  the  cortex  is  indistinctly  stratified.  On 
the  outside  there  is  a  thin,  whitish  layer,  and  beneath  this  the  gray  matter  presents 
two  strata  of  very  nearly  equal  thickness,  viz.  a  middle,  gray-coloured  stratum  and 
an  inner,  yellowish-red  stratum.  Between  the  two  latter  layers  a  narrow  white 
band  is,  in  many  places,  visible.  This  is  termed  the  outer  band  of  Baillarger.  When 
the  layers  indicated  above  are  present,  four  strata  superimposed  on  each  other  are 
recognised ;  but  in  certain  regions,  as,  for  instance,  in  the  anterior  central  convolu- 
tion, a  second  white  streak  traverses  the  deep  or  inner  gray  layer  and  divides  it  into 
two.  This  is  termed  the  inner  white  band  of  Baillarger,  and,  when  it  is  present,  the 
gray  cortex  becomes  divided  obscurely  into  six  alternating  white  and  gray  layers. 

The  outer  band  of  Baillarger  is  strongly  marked  in  the  region  of  the  calcarine 
fissure  and  gives  a  characteristic  appearance  to  this  portion  of  the  cortex.  In  this 
locality  it  receives  the  name  of  the  band  of  Vicq  d'Azyr  or  the  stria  of  Gennari 
(Fig.  465,  p.  579). 

According  to  Henschen  the  visual  centre  is  strictly  limited  to  the  region  in 
which  the  stria  of  Gennari  is  present.  Elliot  Smith  applies  the  name  of  "  striated 
area  "  to  this  cortical  district,  and  considers  that  it  afibrds  a  means  of  identifying 
hom.ologous  sulci  in  the  brains  of  man  and  the  apes. 

To  obtain  a  full  understanding  of  the  minute  structure  of  the  cerebral  cortex  many 
different  methods  must  be  employed,  and  it  is  only  by  combining  the  several  separate 
pictures  which  are  thus  afforded  that  the  end  in  view  is,  in  some  measure,  reached. 

The  stratification  indicated  above  has  little  bearing  upon  the  more  essential  points  of 
the  intimate  structure  of  the  cortex.  The  three  white  layers  are  brought  about  by 
aggregations  of  fibres  running  in  a  tangential  direction,  or,  in  other  words,  in  a  direction 
parallel  to  the  surface  of  the  convolution. 

Nerve-cells. — According  to  the  arrangement  and  the  characters  presented  by  the 
nerve-cells  which  are  met  with  at  difterent  depths,  it  is  now  usual  to  recognise  four  layers 
in  the  cortex.     These  are  :  (1)  the  stratum  zonale  ;  (2)  the  layer  of  small  pyramidal  cells  ; 

(3)  the  layer  of  large  pyramidal  cells ;  and  (4)  the  layer  of  polymorphic  cells. 

As  the  pyramidal  cells  are  specially  characteristic  of  the  cerebral  cortex,  we  shall,  in 
the  first  instance,  describe  the  two  layei's  which  contain  them.  The  difference  between 
these  two  layers  largely  depends  upon  the  diffei'ence  in  the  size  of  the  constituent  cells. 
Taken  together,  the  second  and  third  layers  constitute  the  chief  part  of  the  cortex  ;  they 
merge  insensibly  into  each  other,  and,  in  the  parietal  and  frontal  lobes,  the  layer  of  large 
pyramidal  cells  is  the  thickest  of  all  the  layers.  In  both  of  these  strata  the  pyramidal 
cells  present  the  same  form,  and  apparently  also  similar  connexions. 

A  pyramidal  cell  has  a  triangular  outline.  Its  apex  is  directed  towards  the  surface 
of  the  convolution  and  is  drawn  out  into  a  long,  tapering,  apical,  dendritic  process ;  its 
base  is  turned  towards  the  medullary  centre  of  the  gyrus,  and  from  this  (usually  from  the 
centre)  a  slender  axon  proceeds.  Numerous  lateral  dendrites  are  given  off  from  both  sides 
of  the  cell-body,  and  particularly  from  the  two  basal  corners.  The  apical  dendrite  varies 
in  length,  according  to  the  depth  at  w^hich  the  cell  is  placed  in  the  cortex.  In  every  case 
it  passes  sti'aight  towards  the  surface  of  the  convolution.  Every  here  and  there  fine 
lateral  branches  come  off  from  it,  and  ultimately  it  enters  the  stratum  zonale,  where, 
close  to  the  surface,  it  ends  by  breaking  up  into  a  large  number  of  fine  terminal  filaments, 
which  spread  out  horizontally  in  every  direction  and  interlace  closely  with  the  corre- 
sponding filaments  of  other  pyramidal  cells  and  wnth  the  other  elements  of  this  layer. 

The  axon  of  the  cell  descends,  gives  off  collaterals,  assumes  a  medullary  sheath,  and 
enters  the  central  white  core  of  the  gyrus  as  a  nerve  fibre. 

The  stratum  zonale  is  chiefly  composed  of  fibres  which  run  in  a  tangential  direction,  or, 
in  other  words,  pai-allel  to  the  surface.  These  form  an  interlacement  of  considerable  density 
and  extreme  complexity.  The  elements  which  for  the  most  part  enter  into  the  formation 
of  this  feltwork  are  :  (1)  the  terminal  filaments  of  the  apical  dendrites  of  the  pyramidal 
cells ;  (2)  the  terminal  filaments  of  certain  corticipetal  fibres,  which  enter  the  cortex  from 
the  white  centre  of  the  gyrus  ;  (3)  the  axons  of  certain  small  cells  peculiar  to  this  stratum  ; 

(4)  the  axons  of  the  cells  of  Martinotti.     Spread  over  the  surface  of  this  tangential  inter- 
lacement of  fibres,  which  constitutes  the  most  important  part  of  the  stratum  zonale,  there 


586 


THE  NERVOUS  SYSTEM. 


~    BAND   OF 

3cchte:rew 


OUTER  BAND 


BAILLARGER 


is  a  thiu  layer  of  neuroglia  which  intervenes  between  it  and  the  pia  mater,  which  covers 
the  convolution.  The  stratum  zonale  is  not  devoid  of  nerve-cells,  although  these  are 
small  and  somewhat  indefinite  in  their  connexions.  The  most  characteristic  form  is  a 
small  fusiform  cell  described  by  Cajal,  which  sends  out  from  either  end  a  long  process 

and  which  lies  in  the  deeper 
part  of  the  layer.  The 
long  filamentous  processes 
of  this  cell  thread  their  way 
betw^een  the  other  fibres  in 
a  tangential  direction  and 
give  off  minute  branches 
which  pass  towards  the 
surface. 

The  deepest  layer  of  the 
cortex  contains  the  poly- 
morphic cells.  These  cells 
are  not  large,  and  they 
present  many  different 
forms.  Numerous  dendrites 
proceed  from  the  cells  of 
this  group,  but  none  of 
these  reach  the  stratum 
zonale,  and  in  this  respect 
the  polymorphic  cells  offer 
a  marked  contrast  to  the 
pyramidal  cells.  The  axons 
of  the  polymorphic  cells, 
however,  like  those  of  the 
pyramidal  cells,  enter  the 
white  centre  of  the  gyms 
in  the  shape  of  nerve-fibres. 
In  addition  to  the  cells 
characteristic  of  the  several 
layers,  there  are  two  which 
may  be  found  amongst  the 
pyramidal  or  amongst  the 
polymorphic  cells.  These 
are  :  (1)  the  cells  of  Golgi  ; 
(2)  the  cells  of  Martinotti. 

A  cell  of  Grolgi  has  this 
peculiarity — that  its  axon, 
close  to  its  origin,  begins 
to  divide,  and  very  soon 
loses  its  individuality  by 
breaking  up  into  a  perfect 
maze  of  branches,  none  of 
which  pass  far  from  the 
neighbourhood  of  the  cell- 
body  and  none  of  which 
enter  the  stratum  zonale. 


NNEB   BAND 

OF 
BAILLARGCR 


ITRACORTICAL 
ASSOCIATION 
FIBRES 


Fig.  469.- 


-DiAGRAM  TO  Illustrate  Minute  Structure  of  the 
Cerebral  Cortex. 


}^ 


euioglia  cells. 

Cell  with  short  axon  (N)  which  breaks 

up  in  a  free  arborisation. 
Spindle-shaped  cell  in  stratum  zonale. 


E.  Small  pj'ramidal  cell. 

F.  Large  pyramidal  cell. 
(t.  Cell  of  Martinotti. 
H.  Polymorphic  cell. 

K.  Corticijietal  fibres. 


The  cell  of  Martinotti  is  small  and  is  chiefly  found  in  the  deeper  part  of  the  cortex. 
Its  leading  peculiarity  is,  that  its  slender  axon  runs  in  a  contrary  direction  to  the  axons  of 
the  pyramidal  cells  and  of  the  polymorphic  cells.  In  other  words,  it  proceeds  towards  the 
surface,  and,  entering  into  the  stratum  zonale,  divides  into  terminal  filaments,  which  spi-ead 
out  in  tlie  tangential  interlacement  characteristic  of  this  layer. 

Nerve-Fibres. — The  arrangement  of  the  nerve-fibres  can  best  be  studied  in  vertical 
sections  through  the  gray  cortex,  which  have  been  specially  treated  with  this  end  in 
view.  In  such  preparations  bundles  of  nerve-fibres  are  seen  to  radiate  into  the  gray 
cortex  from  the  surface  of  the  white  centre  of  the  gyrus.  As  these  proceed  through  the 
polymorphic  layer  into  the  layer  of  large  pyramidal  cells,  they  gradually  become  less 
distinct,  and,  finally,  they  disperse  and  are  lost  to  view  before  they  reach  the  layer  of 
small  pyramidal  cells.  In  the  intervals  between  the  radiating  bundles  the  polymorphic 
and  large  pyramidal  cells  are  arranged  in  columns,  and  in  the  same  intervals  an  open 


THE  OLFACTOEY  TRACT  AND  BULB. 


587 


feltwork  of  intercrossing  fibres  is  evident.  After  the  radiating  fibre-bundles  have  dis- 
appeared the  same  feltwork  of  fibres  is  visible  in  the  gray  matter,  and  consequently  it  is 
convenient  to  distinguish,  with  Edinger,  an  inter-radial  feltwork  and  a  supra-radial  felt- 
work of  fibres  in  the  cortex.  The  fibres  which  enter  into  the  composition  of  the  difterent 
radial  bundles  vary  in  number  from  ten  to  twenty,  and  they  gradually  diminish  in  number 
as  they  proceed  onwards.  This  diminution  is  due  to  their  joining  the  various  cells  that 
they  meet  (both  polymorphic  and  pyramidal)  as  their  axons.  The  fibres  in  a  given  bundle 
also  vary  much  in  size,  and  it  may  be  noticed  that  the  largest  fibres  disappear  in  the 
vicinity  of  the  large  pyramidal  cells,  which  shows  clearly  that  it  is  with  these  that  they 
are  connected.  But,  in  addition  to  cell-axons,  the  radial  bundles  contain  fibres  of  an 
altogether  difterent  type,  viz.  corticipetal  fibres,  which  pass  through  all  the  layers  of  the 
cortex  and  end  in  fine  terminal  filaments  in  the  tangential  interlacement  of  the  stratum 
zonale. 

The  inter-radial  and  supra-radial  feltwork  is  largely  formed  of  the  collaterals  which 
issue  from  the  axons.  By  a  condensation  of  this  feltwork  the  two  bands  of  Baillarger  are 
formed.  The  outer  band,  which  is  the  broader  and  better  marked,  occurs  in  the  deeper 
part  of  the  layer  of  the  large  pyramidal  cells.  The  inner  band,  when  present,  is  formed 
in  the  superficial  part  of  the  layer  of  polymorphic  cells. 

Another  condensation  of  the  fibre-feltwork  in  the  superficial  part  of  the  supra-radial 
region  may  be  noted  in  certain  localities.     This  is  termed  the  band  of  Bechterew. 

It  has  been  noted  that  up  to  a  certain  point  the  tangential  fibres  increase  in  quantity 
as  age  advances,  and  there  is  reason  to  believe  that  upon  the  richness  with  which  the 
gray  cortex  is  supplied  with  fibres — more  especially  of  the  tangential  variety — depends  to 
some  extent  the  intellectual  capacity  of  an  individual. 

Whilst  the  general  mass  of  the  cortex  for  the  most  part  conforms  more  or  less  closely 
to  the  ground-type  described  above,  showing  merely  deviations  characteristic  of  the 
difterent  regions,  there  is  one  part  of  the  cortex,  viz.  the  cornu  ammonis  and  the  fascia 
dentata,  in  which  the  structural  arrangement  of  the  elements  is  very  markedly  difterent. 
To  some  extent  this  is  due  to  the  complicated  manner  in  which,  in  this  region,  the  cortex 
is  folded  upon  itself. 

Olfactory  Tract  and  Bulb, 

The  olfactory  tract  and  bulb  arise  as  a  hollow  outgrowth  from  the  primitive  cerebral 
vesicle.  In  many  animals  with  a  well-developed  olfactory  apparatus,  the  tract  and  bulb 
remain  hollow ;  but  in  man  the  central  cavity  becomes 
obliterated,  although  traces  of  the  original  hollow  persist 
in  the  shape  of  ependymal  remains,  visible  in  the  centre 
of  both  tract  and  bulb.  Outside  these  ependymal 
elements  is  a  coating  of  white  matter,  upon  which  is 
laid  the  gray  matter.  The  gray  matter,  however,  is 
by  no  means  uniformly  distributed  over  the  surface. 
In  the  tract,  except  along  the  dorsal  edge,  it  is  so  thinly 
spread  that  it  is  hardly  appreciable.  In  the  bulb,  on 
the  other  hand,  there  is  very  little  gray  matter  on  the 
doi'sum,  but  a  considerable  quantity  on  the  ventral 
surface  ;  and  it  is  into  this  that  the  delicate  nerves  which 
enter  the  cranium  thi'ough  the  cribriform  plate  of  the 
ethmoid  bone  sink,  k  brief  description  of  the  structure 
of  this  infrabulbar  mass  of  gray  matter,  as  well  as  of 
the  connexions  established  by  its  elements,  now  becomes 
necessary. 

The  fibres  of  the  delicate  olfactory  nerves  are  to 
be  regarded  as  the  axons  of  the  olfactory  cells  of  the 
olfactory  mucous  membrane.  They  enter  the  ventral 
surface  of  the  olfactory  bulb,  and  there  each  breaks  up 
in  an  arborescent  fashion  into  a  tuft  of  terminal  filaments. 
A  thick  dendrite  from  a  mitral  cell  of  the  bulb  passes 
down  towards  this  terminal  tuft,  and,  coming  into  con- 
tact with  it,  breaks  up  and  terminates  in  a  similar 
mannei*.  In  this  way  a  large  number  of  globular  bodies, 
formed    by   the    arborescent    terminations    of    a    mitral 

dendrite  and  of  certain  olfactory  nerve-fibres,  are  formed.  These  are  the  olfactory 
glomeruli  of  the  bulb.     The  mitral  cells  lie  deeper  in  the  olfactory  bulb.     Each  gives 


Fig.  470. — Diagram  of  the  Minute 
Structure  of  the  Olfactory  Bulb. 


588  THE  NEEVOUS  SYSTEM. 

off  several  dendrites  and  one  axon.  Only  one  dendrite  enters  into  the  formation  of  a 
glomerulus,  but  several  nerve-fibres  may  be  connected  with  such  a  body.  It  thus  happens 
that,  through  its  dendrite,  a  mitral  cell  may  stand  in  connexion  with  several  olfactory 
nerve-fibres.  The  axon  of  the  mitral  cell  passes  upwards  to  the  white  matter  of  the 
bulb,  enters  this,  and  is  conducted  through  the  tract  towards  the  cerebral  cortex. 

White  Medullary  Centre  of  the  Cerebral  Hemisphere. 

The  white  matter  of  the  hemisphere  which  hes  subjacent  to  the  gray  cortex  is 
composed  of  medullated  nerve-fibres,  arranged  in  a  very  intricate  manner.  Accord- 
ing to  the  connexions  which  they  establish  these  fibres  may  be  classified  into  three 
distinct  groups,  viz.  (1)  commissural  fibres ;  (2)  association  fibres ;  and  (3)  projec- 
tion fibres. 

Commissural  Fibres. — These  are  fibres  which  link  together  portions  of  the 
gray  cortex  of  opposite  cerebral  hemispheres.  They  are  arranged  in  three  groups 
forming  three  definite  structures,  viz.  the  corpus  callosum,  the  anterior  commissure, 
and  the  psalterium  or  the  hippocampal  commissure. 

The  corpus  callosiun  has  in  a  great  measure  been  already  studied  (p.  570).  As 
it  enters  each  hemisphere,  its  fibres  spread  out  in  an  extensive  radiation  (the  radia- 
tion of  the  corpus  callosum).  It  thus  comes  about  that  every  part  of  the  cerebral 
cortex,  with  the  exception  of  the  bulbus  olfactorii  and  the  under  and  fore  part  of 
the  temporal  lobe,  is  reached  by  the  callosal  fibres.  But  it  should  be  clearly  under- 
stood that  all  the  regions  of  the  cortex  do  not  receive  an  equal  proportion  of  fibres ; 
in  other  words,  some  cortical  areas  would  appear  to  be  more  plentifully  supplied 
than  others.  Another  point  of  some  importance  consists  in  the  fact  that  the  callosal 
fibres  do  not,  as  a  rule,  connect  together  symmetrical  portions  of  the  gray  cortex. 
As  the  fibres  cross  the  mesial  plane  they  become  greatly  scattered,  so  that  most 
dissimilar  parts  of  the  cortex  of  opposite  hemispheres  come  to  be  associated  with 
each  other. 

Each  callosal  fibre  arises  in  one  hemisphere  and  ends  by  fine  terminal  arborisations 
in  the  cortex  of  the  opposite  hemisphere.  It  may  arise  in  any  one  of  three  ways,  viz. 
(1)  as  the  axon  of  one  of  the  cortical  cells,  either  pyramidal  or  polymorphic;  (2)  as  the 
collateral  of  a  fibre  of  association ;  (3)  as  the  collateral  of  a  fibre  of  projection. 

Many  cases  have  been  recorded  in  which,  through  congenital  defect,  the  corpus 
callosum  has  not  been  developed.  In  the  description  of  this  structure  on  p.  570  attention 
has  been  called  to  a  layer  of  callosal  fibres  which  sweep  over  the  posterior  and  descending 
horns  of  the  lateral  ventricle,  so  as  to  form  the  immediate  outer  wall  of  the  cavity.  This 
layer  is  called  the  tapetum,  and  it  has  been  stated  that  when  the  corpus  callosum  is 
absent  the  tapetum  is  found  in  a  well-developed  condition.  Further,  it  has  been  asserted 
that  in  cases  where  the  corpus  callosum  has  been  experimentally  destroyed  the  tapetum 
suffered  no  degeneration  (Muratofl^).  Certain  anatomists  are,  therefore,  inclined  to  argue 
that  the  tapetum  has  little  or  no  connexion  with  the  corpus  callosum.  This  assertion, 
however,  cannot  by  any  means  be  regai'ded  as  being  proved.  There  is  a  large  amount  of 
evidence  on  the  other  side.  Thus,  Mingazzini  has  seen  a  case  of  failure  of  the  corpus 
callosum  which  was  accompanied  by  a  corresponding  defect  in  the  tapetum,  whilst  soften- 
ing of  the  splenium  and  the  forceps  major  has  been  observed  by  Anton  to  be  accompanied 
by  a  secondary  degeneration  of  the  tapetum.  Further,  the  recent  experimental  evidence 
of  Ferrier  and  Turner  would  appear  to  support  the  older  view  that  the  tapetum  is  associated 
in  the  closest  manner  with  the  corpus  callosum. 

The  anterior  commissure  (commissura  anterior)  is  a  structure  supplemental  to 
the  corpus  callosum.  It  connects  together  the  two  olfactory  lobes,  and  also  portions 
of  opposite  temporal  lobes.  It  presents  a  cord-like  appearance  and  is  arranged  in 
the  form  of  a  horse-shoe,  the  concavity  of  wliich  looks  backwards.  The  middle  free 
portion  is  placed  immediately  in  front  of  tlie  anterior  pillars  of  the  fornix  as  they 
curve  downwards,  and  also  in  intimate  relation  to  the  anterior  end  of  the  third 
ventricle.  Posteriorly,  tlie  small  portion  of  tlie  anterior  commissure  which  appears 
in  the  ventricle  between  the  two  pillars  of  the  fornix  is  clothed  with  the  ventricular 
ependyma ;  anteriorly,  the  commissure  is  connected  with  the  lamina  cinerea  as  it 
stretches  from  the  optic  chiasma  upwards  towards  the  rostrum  of  the  corpus 
callosum. 


COMMISSUEAL  FIBEES. 


589 


The  lateral  part  of  the  anterior  comuiissure  penetrates  the  cerebral  hemisphere, 
and,  gaining  the  lower  part  of  the  anterior  end  of  the  internal  capsule,  divides  into 
two  portions,  viz.  a  small  lower  olfactory  part  and  a  much  larger  temporal  part. 

The  olfactory  portion  of  the  anterior  commissure  is  an  exceedingly  small  fasci- 
culus. It  passes  downwards  and  forwards,  and  finally  enters  the  olfactory  tract. 
It  is  composed  (1)  of  true  commissural  fibres,  which  land  one  olfactory  bulb  to  the 
other ;  and  (2)  of  other  fibres,  which  connect  the  olfactory  bulb  of  one  .side  with 
the  temporal  lobe  of  the  other  side. 

The  temporal  portion  is  formed  of  almost  the  whole  of  the  fibres  of  the  com- 
missure. It  is  carried  transversely  outwards,  under  the  lenticular  nucleus,  until  it 
gains  the  interval  between  the  globus  pallidus  and  the  putamen.     At  this  point  it 

Ventricle  V.  Corpus  callosum 

Corpus  callosum 


LatPial  \entncle 


Lateral  ventricle 


Caudate  nucleus 


Internal 
capsule 


g^  V^  Putamen 


Temporal- 
operculum 


Anterior 
commissure 


Fig.  471. — Two  Coronal  Sections  through  the  Cerebral  Hemispheres  of  an  Orang, 
IN  the  Plane  of  the  Anterior  Commissure. 

A,  Section  through  the  left  hemisphere  in  a  phine  a  short  distance  behind  B,  which  is  a  section 
through  the  right  hemisphere. 

changes  its  direction  and  sweeps  backwards.  In  coronal  sections  through  the 
brain,  behind  this  bend,  the  temporal  portion  of  the  anterior  commissure  appears  as 
an  oval  bundle  of  fibres  cut  transversely  and  placed  in  close  contact  with  the  under 
surface  of  the  lenticular  nucleus  (Fig.  468,  p.  582).  Finally,  it  turns  sharply  down- 
wards on  the  outer  aspect  of  the  amygdaloid  nucleus,  and  its  fibres  are  lost  in  the  white 
medullary  centre  of  the  temporal  lol;»e.  The  precise  part  of  the  cerebral  cortex  with 
which  these  fibres  stand  in  connexion  is  not  known.  When  the  lateral  part  of  the 
anterior  commissure  is  displayed  by  dissection,  it  is  seen  to  be  twisted  like  a  rope. 

The  psalterium,  or  the  hippocampal  commissure,  is  composed  of  fibres  which  con- 
nect the  cornu  ammonis  of  one  side  with  the  corresponding  structure  of  the  opposite 
side.     It  is  described  on  p.  572. 

Association  Fibres. — The  association  fibres  bind  together  different  portions  of 
the  cortex  of  the  same  hemisphere.  They  are  grouped  into  long  and  short  associa- 
tion bundles. 

The  greater  number  of  the  short  association  fibres  pass  between  adjacent 
convolutions.  They  curve  round  the  bottom  of  the  sulci  in  U-shaped  loops.  Some 
of  these  occupy  the  deepest  part  of  the  gray  cortex  itself,  and  are  termed  intracortical 
association  fibres  (Fig.  469,  p.  586) ;  others  lie  immediately  subjacent  to  the  gray 
matter — between  it  and  the  general  mass  of  the  white  matter — and  receive  the 
name  of  subcortical  fibres.  Many  groups  of  short  association  fibres,  instead  of  linking 
together  contiguous  convolutions,  pass  between  gyri  more  or  less  remote.     It  is  only 


590 


THE  NEEVOUS  SYSTEM. 


after  birth,  when  intellectvial  ettbrt  and  education  have  stimulated  different  portions 
of  tlie  cortex  to  act  in  harmony  and  in  conjunction  with  each  other,  that  these 
association  fibres  assume  their  sheaths  of  medulla  and  become  functional. 

The  long  association  fibres  are  arranged  in  bundles  which  run  for  considerable 
distances  within  the  white  medullary  centre  of  the  cerebral  hemisphere,  and  unite 
districts  of  gray  cortex  which  may  be  far  removed  from  each  other.  The  better 
known  of  these  fasciculi  are  the  following :  (1)  the  uncinate ;  (2)  the  cingulum ; 
(3)  the  superior  longitudinal ;  (4)  the  inferior  longitudinal ;  (5)  the  occipito-frontal. 

The  fasciculus  uncinatus  is  composed  of  fibres  w-hich  arch  over  the  stem  of  the 
Sylvian  fissure  and  connect  the  frontal  pole,  and  the  orbital  convolutions  of  the 
frontal  lobe,  with  the  front  portion  of  the  temporal  lobe. 

The  cingulum  is  a  very  well-marked  and  distinct  band,  which  is  closely  associated 
with  the  limbic  lobe.  Beginning  in  front,  in  the  region  of  the  anterior  perforated 
spot,  it  arches  round  the  genu  of  the  corpus  callosum  and  is  carried  backwards  on 
the  upper  surface  of  this  structure  at  the  place  where  its  fibres  pass  into  the 


ASSOCIATION 


Fig.  472. — Diagram  of  the  Leading  Association  Bundles  of  the  Cerebral  Hemisphere. 
(Fouuded  on  the  drawings  of  Dejerine.) 

A.    Outer  aspect  of  hemisphere.  B.  Inner  aspect  of  hemisphere. 

callosal  radiation.  The  cingulum,  therefore,  lies  under  cover  of  the  callosal  gyrus 
and  stands  in  intimate  relation  to  the  white  centre  of  this  convolution  (Fig.  457, 
p.  570).  At  the  hinder  end  of  the  corpus  callosum  the  cingulum  turns  round 
the  splenium  and  is  carried  forwards,  in  relation  to  the  hippocampal  gyrus,  to  the 
uncus  and  the  temporal  pole.  The  cingulum  is  composed  of  several  systems  of 
fibres  which  only  run  for  short  distances  within  it. 

The  fasciculus  longitudinalis  superior  is  an  arcuate  bundle  which  is  placed  on  the 
outer  aspect  of  the  foot  or  basal  part  of  the  corona  radiata  and  connects  the  frontal, 
occipital,  and  temporal  regions  of  the  hemisphere.  It  lies  in  the  base  of  the  fronto- 
parietal operculum  and  sweeps  backwards  over  the  insular  region  to  the  posterior 
end  of  the  Sylvian  fissure.  Here  it  bends  downwards  round  the  hinder  end  of  the 
putameu  and  proceeds  forwards  in  the  temporal  lobe,  to  reach  its  anterior  extremity. 
As  it  turns  downwards  to  reach  the  temporal  lobe  numerous  fil^res  radiate  from  it 
into  the  occipital  lol^e. 

The  fasciculus  longitudinalis  inferior  is  a  very  conspicuous  bundle  which  extends  ■ 
along  the  whole  length  of  the  occipital  and  temporal  lobes  (Fig.  457,  p.  570).  In  the 
occipital  lobe  it  is  placed  on  the  outer  aspect  of  the  optic  radiation,  which  takes  a  similar 
direction  and  from  which  it  is  distinguished  by  the  greater  coarseness  of  its  fibres 
(Figs.  462,  p.  576 ;  465,  p.  578 ;  473,  p.  592).  It  is  not  present  in  the  macaque 
monkey  (Ferrier  and  Turner),  but  is  well  developed  in  the  orang  and  the  chimpanzee. 

The  fasciculus  occipito-frontalis  is  a  bundle  of  fibres  which  runs  in  a  sagittal  direction 
in  intimate  relation  to  the  lateral  ventricle  (Fig.  46)^,  p.  582).  It  has  been  pointed  out 
(Forel,  Onufrowicz,  and  others)  that,  in  cases  where  the  corpus  callosum  fails  to  develop, 
the  tapetum  remains  apparently  unaffected,  and  Dejei'ine  has  endeavoured  to  prove  that 
the  fibres  of  this  layer  i-eally  belong  to  the  fasciculus  occipito-frontalis.  According  to 
Dejerine,  the  fasciculus  occipito-frontalis  lies  on  the  inner  aspect  of  the  corona  radiata  in 
intimate  relation  to  the  caudate  nucleus,  and  posteriorly  it  spreads  out  over  the  upper 
and  outer  aspect  of  the  lateral  ventricle,  immediately  outside  the  ependyma,  where 
it  constitutes  the  tapetum  (see  p.  588).     There  is  a  considerable  amount  of  literature 


PEOJECTION  FIBEES.  591 

dealing  with  this  subject,  and  the  most  probable  explanation  of  the  difficulty  would 
appear  to  be  that  the  tapetum  is  composed  of  fibres  derived  from  both  the  corpus 
callosum  and  the  fasciculus  occipito-frontalis  of  Dejerine. 

Projection  Fibres. — The  projection  fibres  are  those  which  connect  the  cerebral 
cortex  with  nuclear  masses  placed  at  a  lower  level.  The  great  bulk  of  these  fibres 
are  found  in  the  corona  radiata.  This  has  already  been  seen  to  be  formed  by  the 
continuation  upwards  of  the  internal  capsule  (p.  583).  In  the  corona  radiata  the 
fibres  which,  lower  down,  are  gathered  together  in  the  compact  mass  which  con- 
stitutes the  internal  capsule,  radiate  in  every  direction,  intersect  the  radiation  of 
the  corpus  callosum,  and  finally  reach  every  region  of  the  cortex.  Although  the 
fibres  of  the  corona  radiata  represent  the  chief  bulk  of  the  projection  fibres,  it  should 
also  be  borne  in  mind  that  a  certain  number  gain  the  cortex  by  a  different  route, 
notably  through  and  under  the  lenticular  nucleus  and  by  the  path  offered  by  the 
external  capsule. 

The  projection  fibres  of  the  cerebral  hemisphere  may  be  classified  into  (1) 
corticipetal,  and  (2)  corticifugal  groups ;  and  under  these  headings  the  following 
great  strands  may  be  arranged  : — 


Corticifugal  Projection  Strands. 
1.  The  pyramidal  or  great  motor  tract. 


Corticipetal  Projection  Strands. 

1.  Thalamo-cortical. 

2.  CorticiiDetal  fibres  of  the  optic  radiation.  2.  Tlie  cortico-tlialamic, 

3.  The  auditory  radiation.  [   3.  The  fronto-pontine  strand. 

4.  The  temporo-pontine  strand. 

5.  The  corticifugal  iibres  of  the  optic  radia- 
tion. 

The  great  motor  or  pyramidal  tract  is  composed  of  fibres  which  arise  from  pyramidal 
cells  in  that  portion  of  the  cortex  which  is  spread  over  the  Eolandic  area,  or,  in 
other  words,  in  the  district  immediately  in  front  of  the  fissure  of  Eolando.  The 
fibres  descend  through  the  corona  radiata  into  the  posterior  limb  of  the  internal 
capsule.  From  this  point  the  further  course  of  the  pyramidal  tract  has  been 
traced,  viz.  through  the  central  part  of  the  crusta  of  the  crus  cerebri,  the  ventral 
part  of  the  pons,  and  the  pyramid  of  the  medulla  oblongata.  At  the  level  of  the 
foramen  magnum  it  decussates  in  the  manner  already  descril^ed,  and  enters  the 
spinal  cord  as  the  crossed  and  direct  pyramidal  tracts.  The  fibres  composing  these 
end  in  connexion  with  the  ventral  or  motor  column  of  cells,  from  which  the  fibres 
of  the  anterior  roots  of  the  spinal  nerves  arise. 

The  fronto-pontine  strand  is  composed  of  fibres  which  arise  as  the  axons  of  the 
cells  in  the  cortex  which  covers  the  portion  of  the  frontal  lobe,  which  lies  in  front  of 
the  prtecentral  furrows.  It  descends  in  the  anterior  limb  of  the  internal  capsule, 
enters  the  mesial  part  of  the  crusta  of  the  crus  cerebri,  through  which  it  gains  the 
ventral  part  of  the  pons.  In  this  its  fibres  end,  l3y  forming  arborisations  around  the 
cells  of  the  nucleus  pontis. 

The  temporo-pontine  tract  consists  of  fibres  which  spring  from  the  cells  of  that 
part  of  the  cortex  which  covers  the  middle  portions  of  the  two  upper  temporal  con- 
volutions. It  probably  represents  a  corticifugal  tract  belonging  to  the  auditory 
system,  seeing  that  it  springs  to  some  extent  from  the  auditory  cortical  area.  The 
temporo-pontine  tract  passes  inwards  under  the  nucleus  lenticularis,  enters  the 
retrolenticular  part  of  the  hinder  limb  of  the  internal  capsule,  and  thus  gains  the 
outer  part  of  the  crusta  of  the  crus  cerebri.  From  this  it  descends  into  the  ventral 
part  of  the  pons,  in  which  it  ends  in  the  nucleus  pontis  (Fig.  439,  p.  546). 

The  optic  radiation  forms  a  very  definite  and  easily  demonstrated  tract  of 
longitudinally-directed  fibres  in  the  white  medullary  centre  of  the  occipital  lobe. 
It  lies  on  the  outer  side  of  the  ventricular  cavity,  from  which  it  is  separated  by  the 
fibres  of  the  tapetum  and  the  ependyma  of  the  ventricle  (Figs.  462,  p.  576  ;  and  465, 
p.  579).  To  the  outer  side  of,  and  applied  closely  to,  the  optic  radiation  is  another 
longitudinal  tract  of  fibres  in  this  part  of  the  medullary  centre  of  the  cerebral  hemi- 
sphere, viz.  the  inferior  longitudinal  association  bundle ;  but  the  fibres  of  the  latter 
fasciculus  are  coarser  and  are  stained  more  deeply  by  the  Pal-Weigert  method,  and 
thus  they  can,  as  a  rule,  be  easily  distinguished  from  the  optic  radiation.     Traced 


592 


THE  NEEVOUS  SYSTEM. 


in  a  backward  direction,  the  fibres  of  the  optic  radiation  disperse  and  pass  to  the 
cortex  of  the  occipital  lobe  on  both  its  mesial  and  outer  aspects.  This  is  a  matter 
of  interest,  seeing  that  the  visual  centre  is  placed  in  this  cortical  district,  and  more 
particularly  on  the  mesial  aspect  in  the  immediate  neighbourhood  of  the  calcarine 
fissure  (Flechsig  and  Henschen).  When  the  optic  radiation  is  followed  in  a  forward 
direction  it  is  seen  to  enter  the  retrolenticular  part  of  the  posterior  limb  of  the 
internal  capsule,  from  whence  its  fibres  pass  to  the  pulvinar  of  the  optic  thalamus, 
to  the  corpus  geniculatum  externum  and  the  superior  quadrigeminal  body. 

As  we  have  noted,  the  optic  radiation  is  composed  partly  of  corticifugal  and 
partly  of  corticipetal  fibres  (p.  552).  The  former  arise  from  cells  in  the  occipital 
cortex  and  end  in  the  pulvinar  and  the  superior  quadrigeminal  body ;  the  cortici- 
petal fibres  arise  in  the  pulvinar  and  in  the  corpus  geniculatum  externum  and 
end  in  the  occipital  cortex  (Ferrier  and  Turner). 

The  system  of  fibres  which  belong  to  the  mesial  fillet  and  the  superior  cerebellar 


Caudate  nucleu  — 


Choroid  plexus  in  lateral 
ventricle 


y-      \  ^Corpus  callosum 
Fornix 


^^_ — Tlialamus  (pulvinar) 

Occipital  corticifugal  tract  to 
superior  quadrigeminal  body 

,  ^^     Superior  quadrigeminal  body 

^^^^ 

£_ Corpus  geniculatum  externum 

Corpus  geniculatum  internum 
Syhnan  gray  matter 
Inferior  bracliium 
Lateral  fillet 

Superior  cerebellar  peduncle 
^ —  Cerebelhun 
S —  Pons 


Optic  radiation 

Caudate  nucleus 

Optic  radiation 

Inferior  longitudinal  bundle 

Tapetum 

Descending  horn  of  lateral  ventricle 

Fimbria 

Gjrus  dentitus 

Dentate  fissure 

Fig.  473.  —  Coroxal  Section  through  the  Left  Side  of  the  Cerebrum,  Mesencephalon,  and  Pons, 
IN  the  Region  of  the  Pulvinar  of  the  Thalamus,  and  the  Corpora  Geniculata  (Chimpanzee  ; 
Weigert-Pal  specimen). 

peduncle  have  been  already  more  or  less  fully  dealt  with  (pp.  535  and  539).  The  fillet 
system  represents  the  continuation  upwards  of  the  posterior  columns  of  the  cord. 
The  first  nuclear  internodes  in  the  system  are  met  with  in  the  medulla  in  the  shape  of 
the  cuneate  and  gracile  nuclei.  It  is  here  that  the  fillet  first  takes  definite  shape,  and, 
as  it  passes  ujjwards  through  the  tegmental  part  of  the  medulla  and  pons,  it  receives 
many  additions  to  its  strength  in  the  form  of  fibres  from  the  nuclei  of  termination 
of  the  afferent  cranial  nerves.  Finally,  passing  through  the  tegmentum  of  the 
mesencephalon,  it  reaches  the  subthalamic  region  and  enters  the  ventral  aspect  of 
the  thalamus.  This  may  be  looked  upon  as  being  the  second  internode  laid  across 
the  path  of  the  fillet,  and  its  fibres  end  in  arborisations  around  the  thalamic  cells. 

The  fibres  of  the  superior  cerebellar  peduncle  encounter  two  nuclear  internodes  as 
they  pass  towards  the  cerebral  cortex,  viz.  the  red  tegmental  nucleus  and  the  optic 
thalamus  (yj.  536). 

The  fibres  of  the  auditory  radiation  arise  as  the  axons  of  cells  situated  in  tlie 
internal  geniculate  body.  They  enter  the  retrolenticular  part  of  the  posterior  limb 
of  the  internal  capsule  and  proceed  under  the  lenticular  nucleus  towards   the 


PROJECTION  FIBRES. 


593 


temporal  lobe.  Here  they  end  in  the  area  of  cortex  which  constitutes  the  auditory 
centre.  This  corresponds  to  the  middle  portion  of  the  superior  temporal  convolu- 
tion, and  also  to  the  rudimentary  transverse  gyri  of  Heschl,  which  are  present  on 
the  insular  surface  of  the  temporal  operculum. 

The  thalamo-cortical  cortico-thalamic  systems  include  the  fibres  which  constitute 
a  double  bond  of  connexion  between  the  thalamus  and  all  parts  of  the  cortex. 
They  are  sufficiently  described  at  p.  545. 

The  remarkable  researches  of  Flechsig  have  added  greatly  to  our  knowledge  of  the  different 
tracts  of  fibres  in  the  cerebral  hemisjDliere.  By  studying  the  periods  at  -which  these  tracts 
myelinate  he  lias  been  able  to  note  the  manner  in  Avhich  the  different  areas  of  the  cortex  are 
bound  together  and  also  linked^on  to  subjacent  centres.  He  has  arrived  at  a  highly  important 
concei^tion  regarding  the  functional  value  of  different  districts  of  the  cortex,  foiuided  upon  their 
anatomical  connexions.  He  recognises  four  sense-areas  in  the  cortex,  viz.  the  somajsthetic  area, 
the  visual  area,  the  auditorj^  area,  and  the  olfactory  area. 

The  somsestlietic  area  is  the  field  of  general  sensibility  and  is  the  most  extensive  of  all.  It 
includes  the  two  central  convolutions,  the  posterior  jjortions  of  the  three  frontal  convolutions,  the 
paracentral  convolution,  and  the  adjoining  part  of  the  callosal  convolution. 

The  visual  area  is  jilaced  on  the  inner  aspect  of  the  occipital  lobe,  and  more  ^particularly  in 
the  immediate  neighbourhood  of  the  calcarine  fissure. 

The  auditory  area  corresponds  to  the  middle  third  of  the  superior  temporal  convolution 
and  to  the  transverse  gyri  of  Heschl. 

The  olfactory  area  includes  the  locus  perforatus  anticus,  the  trigonum  olfactorium,  the 
anterior  part  of  the  callosal  convolution,  and  the  uncus. 

These  sense -areas  are  peculiarly  rich  in  their  supply  of  j)rojection  fibres,  and  each  is  provided 
with  an  extensive  system  of  both  corticifugal  and  corticipetal  fibres.     Thus  the  somaesthetic  area 


AREA 


Fig.  474. 


-Diagrams  to  show  Flechsig's  sensory  and  association  areas  on  the  surface  of  the  cerebral 

hemisphere. 


is  the  field  Avhere  the  motor  pyramidal  tract  takes  origin  and  within  which  the  tracts  of  general 
sensibility  end.  The  visual  area  has  the  corticipetal  and  corticifugal  filjres  of  the  optic  radiation. 
The  auditory  area  has  the  corticipetal  auditory  radiation  and  also  the  corticifugal  temporo- 
pontine tract.  In  man  the  olfactory  area  is  feebly  develojied,  and  Flechsig  has  not  been  able 
to  establish,  with  certainty,  its  corticipetal  and  corticifugal  projection  tracts. 

The  sense-areas  differ  greatly  from  each  other  in  the  extent  of  cerebral  surface  which  they 
cover.  The  size  in  each  case  is  in  strict  conformity  with  the  peripheral  area  with  which  each  is 
in  connexion.  It  can  easily  be  understood,  therefore,  how  the  somassthetic  area,  representing  as 
it  does  on  the  cortex  all  the  jiarts  of  the  body  outside  the  sj^ecial  organs  of  sense,  from  which 
sensory  nerves  proceed,  should  be  so  large.  Further,  it  is  manifest  why  the  visual  sensorial  area, 
which  in  the  cortex  is  the  corresponding  part  to  the  retina,  should  be  of  greater  extent  than  the 
auditory  field,  which  re^iresents  the  cochlea,  and  the  olfactory  area,  which  represents  a  small 
amount  of  olfactory  mucous  membrane  in  the  nasal  chamlier. 

The  four  sensorial  areas,  taken  together,  only  form  about  one-third  of  the  entire  cerebral 
surface.  The  remaining  two-thirds  of  the  cortex  constitute  what  Flechsig  has  termed  the 
association  centres.  The  great  extent  of  these  in  man  must  be  regarded  as  a  special  human 
characteristic.  These  centres  differ  from  the  sensorial  areas  in  being  poorly  provided  with  pro- 
jection fibres.  They  have  little  direct  connexion  with  the  centres  which  lie  at  a  lower  level. 
Indeed,  the  only  direct  bond  of  union  over  a  very  large  extent  of  these  association  areas  with 
lower  centres  consists  of  the  thalamo-cortical  fibres,  which  pass  to  them  from  the  thalamus. 
But,  on  the  other  hand,  they  are  rich  in  association  fibres,  and  are  linked  in  the  most  complete 
and  perfect  manner  by  these  fibres  to  the  sensorial  areas. 

Flechsig  regards  these  association  areas  as  constituting  the  portions  of  cortex  in  which  the 
higher  intellectual  activities  are  carried  on,  and  he  further  believes  that  they  exercise  an 
important  controlling  influence  over  the  sense-areas.  More  particularly  is  this  control  exhibited 
in  the  case  of  the  great  somtesthetic  area,  within  which  the  influence  of  all  bodily  impressions  is 
received  and  transformed  into  consciousness,  and  within  which  the  impulses  which  are  thereby 
42 


594  THE  NEEVOUS  SYSTEM. 

excited  take  definite  form.  These  imjxilses,  according  to  Flechsig,  are,  in  a  measure,  in  all 
properly-balanced  minds,  held  in  sulijection  bj^  the  higher  feelings,  which  assume  shape  in  the 
association  centres. 

In  his  study  of  the  foetal  and  infantile  brain  Flechsig  has  shown  that  the  fibres  of  the  sensory 
paths  become  niedullated  in  the  first  instance  ;  then  the  corticifugal  fibres  which  go  out  from  the 
sense-areas  assume  their  sheaths  of  myelin  ;  and,  further,  that  it  is  not  until  a  month  after  birth, 
and  after  the  projection  fibres  in  connexion  with  the  sense-areas  are  myelinated,  that  the  associa- 
tion areas  liecome  linked  on  by  medullated  association  fibres  with  the  sense-areas. 

Development  of  the  Parts  derived  from  the  Fore-brain. 

It  has  been  previousl}^  noted  that  the  fore-brain  very  early  shows  an  obscure  sub- 
division into  a  front  portion,  termed  the  telencephalon,  and  a  hinder  part,  called  the 
diencephalon,  which  corresponds  more  nearly  to  the  original  cavity  of  the  fore-brain. 
The  cavity  of  third  ventricle  is  derived  from  both,  and  stretches  forwards,  therefore,  to 
the  lamina  terminalis,  which  in  its  lower  part  is  represented  in  the  adult  by  the  lamina 
cinerea. 

The  lateral  wall  of  both  sections  of  the  primitive  fore-brain  shows  a  subdivision  into 
a  dorsal  or  alar  and  a  ventral  or  basal  lamina.  The  groove  which  indicates  this  separa- 
tion is  the  sulcus  of  Monro,  and  is  evident  even  in  the  adult  brain. 

In  recognising  an  alar  and  basal  lamina  in  the  fore-brain  the  teaching  of  Professor  His  is 
followed.  This  subdivision,  however,  is  not  admitted  by  all  observers,  and  some  hold  that  the 
fore-brain  is  to  be  regarded  as  a  great  diverticular  expansion  which  grows  out  from  the  mid- 
dorsal  and  alar  laminje  of  the  mesencephalon. 

Alar  Lamina. — The  alar  part  of  the  lateral  wall  of  the  telencepl talon  is  pushed  out 
to  form  the  diverticulum,  which  ultimately  constitutes  the  cerebral  hemisphere,  and  thus 
from  a  very  early  period  the  primitive  position  of  this  part  of  the  lateral  wall  is  indicated 
by  the  wide  foramen  of  Monro,  or  aperture  of  communication  between  the  cavity  of  the 
cerebral  hemisphere  and  the  third  ventricle. 

The  alar  part  of  the  lateral  wall  of  the  diencephalon  is  utilised  for  the  development  of 
the  thalamus,  the  epithalamus,  and  the  metathalamus.  Of  these  the  optic  thalamus  is 
derived  from  the  anterior  and  by  far  the  greatest  part  of  the  alar  wall.  It  arises  as  a 
large  oval  swelling,  which  gradually  approaches  its  fellow  of  the  opposite  side,  and  thus 
diminishes  the  width  of  the  third  ventricle.  Finally,  the  two  bodies  come  into  contact  in 
the  mesial  plane  and  cohere  over  an  area  corresponding  to  the  gray  commissure.  This 
occurs  aljout  the  end  of  the  second  month. 

From  that  section  of  the  lateral  wall  to  which  the  name  of  metathalamus  is  given  the 
two  geniculate  bodies  arise.  Each  of  these  shows,  in  the  first  place,  as  a  depression  on 
the  inside,  and  a  slight  elevation  on  the  outside,  of  the  wall  of  the  diencephalon.  As  the 
thalamus  grows  backwards,  it  encroaches  greatly  upon  the  territory  occupied  by  the  geni- 
culate bodies.  It  thus  comes  about  that  in  the  adult  brain  the  internal  geniculate  body 
seems  to  hold  a  position  on  the  lateral  aspect  of  the  mesencephalon,  whilst  the  external 
geniculate  body,  viewed  from  the  surface,  appears  to  be  a  part  of  the  thalamus. 

From  the  epithalamic  region  of  the  wall  of  the  diencephalon  are  developed  the  pineal 
gland,  its  peduncle,  and  the  habenular  region.  These  parts  are  relatively  much  more 
evident  in  the  embryonic  than  in  the  adult  brain.  The  pineal  body  is  developed  as  a 
diverticulum  of  the  posterior  part  of  the  roof  of  the  diencephalon.  Viewed  from  the 
dorsal  aspect  of  the  brain-tube,  this  diverticulum  shows  in  the  first  instance  as  a  rounded 
elevation,  from  either  side  of  which  a  broad  ridge  runs  forwards.  This  ridge  becomes 
the  ttenia  thalami,  whilst  in  the  region  of  its  junction  with  the  pineal  elevation  the 
trigonum  habenulte  takes  shape.  The  pineal  diverticulum  ultimately  becomes  solid,  but 
a  small  ]:)ortion  of  the  original  cavity  is  retained  as  the  reccssus  pinealis  of  the  third 
ventricle. 

Basal  Lamina. — The  part  of  the  diencephalon  and  telencephalon  which  represents 
the  basal  lamina  lies  below  the  level  of  the  sulcus  of  Monro,  retains  its  primitive  form,  and 
undergoes  only  slight  change.  Consequently,  when  this  region  in  the  adult  brain  is  com- 
pared with  the  corresponding  I'egion  in  the  embryonic  brain,  the  resemblance  between  the 
two  is  very  striking. 

In  the  fore-brain,  therefore,  it  is  the  alar  lamina  whicli  plays  the  predominant  part  in 
the  formation  of  the  cerel)rum.  The  value,  also,  of  the  basal  part  of  the  wall  of  this 
portion  of  the  neural  tube  is  still  further  reduced  by  the  fact  that  it  no  longer  contains 
the  nuclei  of  origin  of  efferent  nerves.  The  highest  of  these  nuclei  (the  oculo-motor)  is 
placed  in  the  mesencephalon. 


DEVELOPMENT  OF  PAKTS  DEEIVED  FEOM  FOEE-BEAIN.      595 


The  region  of  the  fore-brain  which  lies  below  the  sulcus  of  Monro  is  termed  the  hypo- 
thalamus. The  part  of  this  which  corresponds  to  the  diencephalon  is  called  the  pars 
m  a  m  m  i  1 1  a  r  i  s     hypothalami, 

whilst  the  part  in  front,  which  — — ^  ^  ~~ 

belongs  to  the  telencephalon, 
receives  the  name  of  pars  optica 
hypothalami. 

From  the  pars  mammillaris 
hypothalami  are  derived  the 
corpus  mammillare  and  a 
portion  of  the  tuber  cinereum. 
With  the  pars  optica  hypo- 
thalami are  associated  the 
following  parts,  viz.  the  tuber 
cinereum,  with  the  infundi- 
bulum  and  the  cei-ebral  part 
of  the  pituitary  body,  the  optic 
chiasma,  the  optic  recess,  and 
the  lamina  cinerea. 

The  corpora  mammillaria 
form,  in  the  first  instance,  a 
relatively  large  downward 
bulging  of  the  floor  of  the 
brain-tube.  As  development 
goes  on  this  bulsing  becomes 
relatively  small,  and  about  the 
fourth  month  the  single  pro- 
jection becomes  divided  into 
the  two  tubercles. 

The  infundibulum  and 
posterior  or  cerebral  lobe  of 
the  pituitary  body  are  de- 
veloped as  a  hollow  downward 
diverticulum  of  the  floor  of 
the  telencephalon  (p.  549).  A 
portion  of  the  original  cavity  -^ 
is  retained  in  the  upper  part 
of  the  infundibulum,  and  con- 
stitutes the  infundibular  recess 
in  the  floor  of  the  third  ventricle. 

The  optic  nerve  is  chiefly 
formed  by  the  passage  of  fibres 
backwai'ds     from    the    retina 

in  the  wall  of  the  original  optic  stalk,  whilst  the  chiasma  takes  form  by  the  transit  of 
fibres  across  the  middle  line  in  front  of  the  infundibulum  and  behind  the  optic  recess.  To 
a  large  extent  these  fibres  are  derived  from  the  optic  nerve.  The  optic  recess  of  the  third 
ventricle  marks  the  spot  where  the  hollow  optic  vesicle  originally  bulged  out  from  the 
lower  and  lateral  part  of  the  fore-brain,  and  in  the  adult  it  therefore  represents  a  portion 
of  the  primitive  cavity  of  the  tubular  stalk  of  the  optic  vesicle.  In  the  course  of  develop- 
ment the  optic  nerve  fibres,  which  appear  in  the  stalk  of  the  optic  vesicle  to  form  the 
optic  nerve,  seek  an  attachment  much  further  back,  and  through  the  optic  tract  they  are 
even  carried  as  far  as  the  mesencephalon. 

The  roof  of  the  fore-brain  remains  thin,  and  does  not  proceed  to  the  development 
of  nervous  elements,  except  in  its  posterior  part.  Here  it  forms  the  pineal  body  and  the 
posterior  commissure.  In  front  of  these  structures  the  roof  of  the  fore-brain  is  epithelial, 
and  remains  so  during  life.  It  constitutes  the  epithelial  roof  of  the  third  ventricle,  and 
it  becomes  involuted  along  the  middle  line  into  the  cavity  by  the  choroid  plexuses  of  the 
ventricle.  The  posterior  commissure  appears  as  a  transverse  thickening  at  the  bottom  of 
a  transverse  groove  which  appears  in  the  roof  of  the  early  brain-tube  behind  the  pineal 
diverticulum. 

Cerebral  Hemisphere. — The  cerebral  hemisphere  is  derived  from  the  alar  section 
of  the  lateral  wall  of  the  telencephalon.     From  this  it  grows  out  and  soon  assumes  very 
large  dimensions.     At  first  it   grows  forwards  and  upwards,  and  a  distinct  fissure,  the 
42a 


M, 


Fig.  475. — Two  DRAwrsGS  of  the  Embryonic  Brain  (by  His). 
Reconstruction  of  the  fore-brain  and  mid-braiu  of  His's  embryo  KO  ; 

profile  view.     B,   Same  brain  as  A,  divided  along  the  mesial  plane 

and  viewed  upon  its  inner  aspect. 

Mammillary    eminence  ;    T.c,    Tuber    cinereum  ;    Hp,    Hypophysis 

(pituitary    diverticulum    from    buccal    cavity)  ;    Opt,    Optic    stalk ; 

TH,   Optic  thalanms  ;  Tg,  Tegmental  part  of  mesencephalon  ;  P.s, 

Par  subthalamica  ;  C.s,  Corpus  striatum  ;  F.M,  Foramen  of  Monro  ; 

L,  Lamina  terminalis  ;  R.O,   Recessus  opticus  ;  R.i,  Recessus  iufun- 

dibuli. 


596 


THE  NEEVOUS  SYSTEM. 


early  incisura  longitudinalis  cerebri,  appears  between  the  cerebral  hemispheres  of 
opposite  sides.  The  separation  of  the  two  cerebral  vesicles  by  the  longitudinal  fissure 
begins  at  the  end  of  the  first  month.  This  fissure  becomes  occupied  by  mesoblastic  tissue, 
which  later  on  forms  the  falx  cerebri.  The  cerebral  hemisphere,  in  its  further  growth,  is 
carried  progressively  backwards  over  the  hinder  parts  of  the  developing  brain.  At  the 
end  of  the  third  month  it  has  covered  the  optic  thalamus.  A  month  later  it  reaches  the 
corpora  quadrigeniina,  and  by  the  seventh  month  it  has  not  only  covered  these,  but  also 
the  entire  upper  surface  of  the  cerebellum. 

At  the  end  of  the  first  month  the  olfactory  lobe  grows  out  as  a  hollow  protrusion  from 


RECESS       CHIASMA 


Fig.  476. — Two  Drawings  by  His,  illustrating  the  development  of  the  human  brain. 

A,  Median  section  through  a  foetal  human  brain  in  the  third  month  of  development. 

B,  Schema  showing  the  directions  in  which  the  cerebral  hemisphere  expands  during  its  growth. 

P.  M.H.  Pars  mammillaris  hypothalami.  M,    Mammillary  region.  0.  Occipital  lobe. 

P.O.H.    Pars  optica  hypothalami.  F.   Frontal  lobe.  T.  Temporal  lobe. 

P.    Parietal  lobe. 


the  lower  and  fore  part  of  the  cerebral  vesicle.  This  in  course  of  time  becomes  solid  and 
forms  the  olfactory  tract  and  bulb.  In  the  adult  brain  the  point  which  corresponds  to 
the  original  connexion  between  the  early  hollow  olfactory  diverticulum  and  the  cavity  of 
the  cerebral  vesicle  is  represented  by  the  extremity  of  the  anterior  cornu  of  the  lateral 
ventricle. 

In  the  floor  of  the  hollow  cerebral  hemisphere  a  thickening  takes  origin,  and  this 
ultimately  is  developed  into  the  corpus  striatum.  On  the  outer  surface  of  the  vesicle  this 
thickening  is  seen  to  correspond  to  a  depression  which  constitutes  the  early  Sylvian  fossa, 
the  further  development  of  which  is  described  on  p.  556. 

In  the  earlier  stages  of  its  development  the  cerebral  hemisphere  is  a  thin-walled  vesicle 
with  a  relatively  large  cavity,  which  represents  the  primitive  condition  of  the  lateral 
ventricle.  At  first  the  vesicle  is  bean-shaped  and  the  cavity  is  curved.  At  this  stage  the 
outline  is  very  similar  to  that  presented  by  the  cerebral  hemisphere  of  a  quadruped,  and 
there  is  little  or  no  trace  of  an  occipital  lobe  or  of  a  posterior  horn  of  the  lateral  ventricle. 
As  development  goes  on,  however,  the  occipital  portion  of  the  hemisphere  grows  backwards 
over  the  cerebellum  in  the  shape  of  a  hollow  protrusion,  and  a  distinct  occipital  lobe 
enclosing  the  posterior  horn  of  the  lateral  ventricle  is  the  result.  This  developmental 
stage,  which  is  distinctive  of  man  and  the  apes,  begins  about  the  fourth  month. 

On  the  mesial  aspect  of  the  cerebral  hemisphere,  in  the  early  stages  of  its  development, 
an  invagination  of  the  wall  of  the  vesicle  takes  place  into  the  cavity  immediately  above 
and  behind  the  large  foramen  of  Monro.  This  is  the  choroidal  fissure,  and  the  fold  of  the 
cerebral  wall,  which  is  thus  thrust  into  the  cavity,  remains  thin  and  entirely  epithelial. 
After  a  time  mesoblastic  tissue  from  the  great  longitudinal  fissure  finds  its  way  into  the 
choroidal  fissure  and  occupies  the  interval  between  the  two  thin  layers  which  form  the  fold. 
This  mesoVjlastic  tissue  forms  the  choroid  plexus  of  the  lateral  ventricle,  and  in  the  early 
stages  of  the  hemisphere  it  is  so  voluminous  tliat  it  fills  up  the  relatively  large  cavity  of 
the  lateral  ventricle. 

Development  of  the  Gyri  and  Sulci. — In  the  early  stages  of  its  development,  the 
surface  of  the  cerebral  hemispliere  is  smooth  and  closely  applied  to  the  deep  surface  of 
the  cranial  capsule  within  which  it  is  enclosed. 

After  the  occipital  lobe  is  fully  formed  and  the  fifth  month  is  reached,  the  cranium 
grows  for  a  time  more  rapidly  than  the  brain,  with  the  result  that  a  relatively  wide  space  is 


DEVELOPMENT  OF  PARTS  DERIVED  FROM  FORE-BRAIN.      597 

left  between  the  cerebral  surface  and  the  surrounding  cranial  envelope.  This  is  occupied 
by  sodden  subarachnoid  tissue,  and  when  this  stage  is  reached  (in  the  latter  part  of  the 
fifth  month)  the  sulci  and  gyri  begin  to  make  their  aj^pearance.  The  incomplete  sulci  owe 
their  origin  to  the  upheaval  of  the  cerebral  cortex  on  either  side  of  the  appearing  fissures, 
and  the  gyri  which  bound  them  are  formed  as  the  result  of  an  exuberance  of  surface 
growth  in  localised  areas.  Owing  to  the  wide  interval  between  the  cranial  wall  and  the 
surface  of  the  cerebral  hemisphere,  the  particular  surface  areas  which  grow  and  foreshadow 
the  future  gyri  sutler  no  restriction,  and  they  take  the  form  of  rounded  eminences  which 
rise  from  the  general  surface  level  of  the  cerebral  hemisphere.  As  growth  goes  on,  how- 
ever, the  brain  gradually  assumes  a  bulk  more  nearly  in  accord  with  the  cavity  of  the 
cranium,  and  the  space  for  extension  becomes  more  limited.  Finally,  about  the  beginning 
of  the  eighth  month,  the  gyral  elevations  come  into  close  contact  with  the  cranial  wall, 
and  a  stage  of  growth-antagonism  between  the  brain  and  its  enclosing  capsule  is  entered 
upon.  As  a  result  of  this  the  gyri  are  pressed  together,  the  fissures  assume  more  definite 
shape,  and  the  ordinary  convolutionary  forms  make  their  appearance.  So  intimate,  indeed, 
is  the  contact  between  the  cerebral  hemisphere  and  the  skull  capsule  that  the  gyri,  to 
some  extent,  produce  an  imprint  on  the  deep  aspect  of  the  cranial  bones. 

As  already  explained,  the  complete  fissures  are  produced  by  an  infolding  of  the  wall 
of  the  cerebral  vesicle. 

Cerebral  Commissures. — The  development  of  the  cerebral  commissures  is  sur- 
rounded with  much  difficulty.  It  would  seem  that  the  corpus  callosum,  the  anterior 
commissure,  and  the  fornix  all  take  origin  in  the  lamina  terminalis.  The  triangular 
interval  which  is  left  between  these  commissures  is  occupied  by  the  septum  lucidum — a 
structure  which  has  an  intimate  developmental  and  morphological  connexion  with  the 
gyrus  subcallosus.  The  great  development  of  the  corpus  callosum  in  man  is  to  be 
associated  with  the  enormous  expansion  of  the  human  neo-pallium  of  which  it  is  the 
commissure. 

Weight  of  the  Brain. 

The  average  weight  of  the  adult  male  brain  may  be  said  to  be  about  1360 
grammes.  The  female  brain  weighs  rather  less,  but  this  is  to  be  expected  from  the 
smaller  bulk  of  the  female  body.  Probably  the  relative  weight  of  the  brain  in  the 
two  sexes  is  very  much  the  same.  The  variations  met  with  in  brain-weight  are 
very  great,  but  it  is  doubtful  if  normal  intellectual  functions  could  be  carried  on  in 
a  brain  which  weighs  less  than  960  grammes.  In  microcephalic  idiots  brains  of 
extremely  small  size  are  met  with. 

THE  MENINGES  OF  THE  BRAIN  AND  SPINAL  CORD. 

The  brain  and  spinal  cord  are  enclosed  within  three  membranes,  which  are 
termed  the  meninges  or  meningeal  membranes.  From  without  inwards  these  are  : 
(1)  the  dura  mater,  (2)  the  arachnoid  mater,  and  (3)  the  pia  mater.  The  space 
between  the  dura  mater  and  the  arachnoid  receives  the  name  of  subdural  space, 
while  the  much  more  roomy  interval  between  the  arachnoid  and  the  pia  mater  is 
called  the  subarchnoid  space. 

Dura  Mater. 

The  dura  mater  is  a  dense  and  thick  fibrous  membrane  winch  possesses  a  very 
considerable  degree  of  strength.  Its  arrangement  within  the  cranial  cavity  is  so 
different  from  that  within  the  spinal  canal  that  it  is  customary  to  speak  of  it  as 
consisting  of  two  parts,  viz.  a  cranial  and  a  spinal,  although  in  adopting  this  sub- 
division it  must  be  clearly  understood  that  both  portions  are  continuous  with  each 
other  at  the  foramen  magnum. 

Cranial  Dura  Mater  (dura  mater  cerebri). — The  cranial  dura  mater  is  adherent 
to  the  inner  surface  of  the  cranial  wall,  and  performs  a  double  office.  It  serves  as 
an  internal  periosteum  for  the  bones  which  it  lines  and  constitutes  an  envelope 
for  the  brain.  Its  inner  surface,  which  bounds  the  subdural  space,  is  smooth  and 
glistening,  and  is  covered  by  a  layer  of  endothelial  cells.  The  outer  surface,  when 
separated  from  the  cranial  wall,  is  rough,  this  being  due  to  numerous  fine  fibrous 
processes  and  blood-vessels  which  pass  between  it  and  the  bones.  Its  degree  of 
42  & 


598 


THE  NEKVOUS  SYSTEAI. 


adhesion  to  the  cranial  wall  differs  considerably  in  different  regions.  To  the  vault 
of  the  cranium,  except  along  the.  lines  of  the  sutures,  the  connexion  is  by  no  means 
strong,  and  in  the  intervals  between  the  fibrous  processes  which  pass  into  the  bone 
there  are  small  lymph  spaces  (epidur,al  jpaces)  where  the  outer  surface  of  the 
membrane  is  covered  by  endothelial  cells.  So  long  as  the  sutures  are  open  the 
dura  mater  is  connected  with  the  periosteum  on  the  exterior  of  the  skull,  along  the 
sutural  lines,  by  a  thin  layer  of  fibrous  tissue  which  intervenes  between  the  bony 
margins.  Around  the  foramen  magnum,  and  to  the  floor  of  the  cranium,  the  dura 
mater  is  very  firmly  adherent.  This  is  more  particularly  marked  in  the  case  of  the 
projecting  parts  of  the  cranial  floor,  as,  for  example,  the  petrous  portions  of  the 
temporal  bones,  the  clinoid  processes,  and  so  on.  This  firm  adhesion  in  these 
regions  is  still  further  strengthened  by  the  fact  that  the  nerves,  as  they  leave  the 
cranium  through  the  various  foramina,  are  followed  l^y  sheaths  of  the  fibrous  dura 


Inferior  petrosal  sinu'j 


Superioi  petmsal  smus 
Liteial  sinub 


Fig.  477. — SAf;iTTAL  Sectiox  thbouch  the  Skxtll,  a  little  to  the  Left  of  the  Mesial  Plane, 
to  show  the  arrangenieut  of  the  dura  mater. 

Tlie  cranial  nerves  are  indicated  by  numerals. 

mater.  Outside  the  cranium  these  prolongations  of  tlie  membrane  blend  with  the 
fibrous  sheaths  of  the  nerves,  and  likewise  become  connected  with  the  periosteum  on 
the  exterior  of  the  skull.  In  the  child,  during  the  growth  of  the  cranial  bones,  and 
also  in  old  age,  the  dura  mater  is  more  adherent  to  the  cranial  wall  than  during  the 
intermediate  portion  of  life. 

The  cranial  dura  mater  is  composed  of  two  layers  intimately  connected  with 
each  other,  but  yet  capable  of  })eing  demonstrated  in  most  regions  of  the  cranium. 
Along  certain  lines  these  two  layers  separate  from  eacli  other  so  as  to  form  channels 
lined  by  endothelium.  These  channels  are  the  venous  blood-sinuses  which  receive  the 
blood  from  veins  which  come  from  various  parts  of  the  brain.  They  are  described 
in  the  section  dealing  with  the  Vascular  System. 

Strong  fibrous  partitions  or  septa  are  given  off  along  certain  lines  from  the  deep 
surface  of  the  dura  mater.  These  project  into  the  cranial  cavity,  and  subdivide  it 
partially  into  comi>artments  which  all  freely  communicate  with  each  other,  and 


DURA  MATER.  599 

each  of  which  contains  a  definite  subdivision  of  the  brain.  These  septa  are  :  (1)  the 
falx  cerebri ;  (2)  the  tentorium  cerebelh ;  (3)  the  falx  cerebelU ;  and  (4)  the 
diaphragma  sellte. 

The  falx  cerebri  is  a  sickle-shaped  partition  which  descends  in  the  great  longi- 
tudinal fissure  between  the  two  hemispheres  of  the  cerebrum.  In  front  it  is  narrow, 
and  attached  to  the  crista  galli  of  the  ethmoid  bone.  As  it  is  followed  backwards 
it  increases  in  breadth,  and  behind  it  is  attached  along  the  mesial  plane  to  the 
upper  surface  of  the  tentorium.  The  anterior  narrow  part  of  the  falx  is  frequently 
cribriform,  and  is  sometimes  perforated  by  apertures  to  such  an  extent  that  it  almost 
resembles  lace-work.  Along  each  border  it  splits  into  two  layers,  so  as  to  enclose  a 
blood-sinus.  Along  its  upper  convex  attached  border  runs  the  (jreat  longitudinal 
simcs ;  along  its  concave  free  border  courses  the  much  smaller  inferior  longihidinal 
sinus ;  whilst  along  its  attachment  to  the  tentorium  is  enclosed  the  straight  sinus. 

The  tentorium  cerebelli  is  a  large  crescentic  partition  of  dura  mater,  which  forms 
a  membranous  tent-like  roof  for  the  posterior  cranial  fossa,  and  thus  intervenes 
between  the  posterior  portions  of  the  cerebral  hemispheres  and  the  cerebellum.  It 
is  accurately  applied  to  the  upper  surface  of  the  cerebellum.  Thus  its  highest  point 
is  in  front  and  in  the  mesial  plane,  and  from  this  it  slopes  downwards  towards  its 
attached  border.  It  is  kept  at  a  high  degree  of  tension,  and  this  depends  on  the 
integrity  of  the  falx  cerebri,  which  is  attached  to  its  upper  aspect  in  the  mesial 
plane. 

The  posterior  border  of  the  tentorium  is  convex,  and  is  attached  to  the  hori- 
zontal ridge  which  marks  the  deep  surface  of  the  occipital  bone.  Beyond  this,  on 
each  side,  it  is  fixed  to  the  postero-inferior  angle  of  the  parietal  bone,  and  then 
forwards  along  the  superior  border  of  the  petrous  portion  of  the  temporal  bone. 
From  the  internal  occipital  protuberance  to  the  postero-inferior  angle  of  the 
parietal  bone  this  border  encloses  the  lateral  blood-sinus,  whilst  along  the  upper 
border  of  the  petrous  bone  it  encloses  the  superior  petrosal  simcs.  The  anterior 
border  of  the  tentorium  is  sharp,  free,  and  concave,  and  forms  with  the  dorsum 
sellas  an  oval  opening  shaped  posteriorly  like  a  pointed  arch.  This  opening  receives 
the  name  of  the  incisura  tentorii,  and  within  it  is  placed  the  mesencephalon,  or  the 
stalk  of  connexion  between  the  parts  which  lie  in  the  posterior  cranial  fossa  and 
the  cerebrum.  Beyond  the  apex  of  the  petrous  part  of  the  temporal  bone  the  two 
margins  of  the  tentorium  cross  each  other  like  the  limbs  of  the  letter  X ;  the  free 
margin  is  continued  forwards,  to  be  attached  to  the  anterior  clinoid  process,  whilst 
the  attached  border  proceeds  inwards,  to  be  fixed  to  the  posterior  clinoid  process. 

The  falx  cerebelli  is  a  small,  sickle-shaped  process  of  dura  mater  placed  below 
the  tentorium,  which  projects  forwards  in  the  mesial  plane  from  the  internal  occi- 
pital crest.  It  occupies  the  notch  which  separates  the  two  hemispheres  of  the 
cerebellum  posteriorly.  Inferiorly  it  bifurcates  into  two  small  diverging  ridges 
which  gradually  fade  away  as  they  are  traced  forwards  on  either  side  of  the  foramen 
magnum. 

The  diaphragma  sellae  is  a  small  circular  fold  of  dura  mater  which  forms  a  roof 
for  the  pituitary  fossa.  A  small  opening  is  left  in  its  centre  for  the  transmission 
of  the  infundibulum. 

Spinal  Dura  Mater  (dura  mater  spinalis). — In  the  spinal  canal  the  dura  mater 
forms  a  tube  which  encloses  the  spinal  cord,  and  which  extends  from  the  foramen 
magnum  above  to  the  level  of  the  second  or  third  piece  of  the  sacrum  below.  It 
is  very  loosely  applied  to  the  spinal  cord  and  the  nerve-roots  which  form  the 
Cauda  equina ;  in  other  words,  it  is  very  capacious  in  comparison  with  the  volume 
of  its  contents.  Moreover,  its  calibre  is  not  uniform.  In  the  cervical  and  lumbar 
regions  it  is  considerably  wider  than  in  the  dorsal  region,  whilst  in  the  sacral 
canal  it  rapidly  contracts,  and  finally  ends  by  blending  with  the  filum  terminale 
externum,  the  chief  bulk  of  which  it  forms.  At  the  upper  end  of  the  spinal 
canal  the  spinal  dura  mater  is  firmly  fixed  to  the  third  cervical  vertebra,  to  the 
axis  'vertebra,  and  around  the  margin  of  the  foramen  magnum.  In  the  sacral 
canal  the  filum  terminale  externum,  with  which  it  blends,  extends  downwards  to 
the  back  of  the  coccyx,  to  the  periosteum  of  which  it  is  fixed.  The  lower  end  of 
the  tube  is  thus  securely  anchored  and  held  in  its  place. 
42  c 


600  THE  NEEVOUS  SYSTEM. 

Within  the  cranial  cavity  the  dura  mater  is  closely  adherent  to  the  bones,  and 
forms  for  them  an  internal  periosteum.  As  it  is  followed  into  the  spinal  canal  its 
two  constituent  layers  separate.  The  inner  layer  is  carried  downwards  as  the  long 
cyUndrical  tube  which  encloses  the  spinal  cord.  The  outer  layer,  which  is  much 
thinner,  becomes  continuous  behind  and  on  each  side  of  the  foramen  magnum  with 
the  periosteum  on  the  exterior  of  the  cranium,  whilst  in  front  it  is  prolonged 
downwards  into  the  vertebral  canal  in  connexion  with  the  periosteum  and  ligaments 
on  the  anterior  wall  of  the  canal.  The  spinal  dura  mater,  therefore,  corresponds  to 
the  inner  layer  of  the  cranial  dura  mater,  and  to  it  alone.  It  is  separated  from  the 
walls  of  the  spinal  canal  by  an  interval,  the  epidural  space,  which  is  occupied  by 
soft  fat  and  a  plexus  of  thin-walled  veins.  In  connexion  with  the  spinal  dura 
mater  there  are  no  blood-sinuses  such  as  are  present  in  the  cranial  cavity,  but  it 
should  be  noted  that  the  veins  in  the  epidural  space,  placed  as  they  are  between 
the  periosteum  of  the  spinal  canal  and  tube  of  dura  mater,  occupy  the  same 
morphological  plane  as  the  cranial  blood-sinuses.  Another  feature  which  serves  to 
distinguish  the  spinal  dura  mater  from  the  cranial  dura  mater  consists  in  the  fact 
that  it  gives  off  from  its  deep  surface  no  partitions  or  septa. 

The  cylindrical  tube  of  spinal  dura  mater  does  not  lie  absolutely  free  within 
the  vertebral  canal.  Its  attachments,  however,  are  of  such  a  character  that  they 
in  no  way  interfere  with  the  free  movement  of  the  vertebral  column.  On  either 
side  the  spinal  nerve-roots,  as  they  pierce  the  dura  mater,  carry  with  them  into  the 
intervertebral  foramina  tubular  sheaths  of  the  membrane,  whilst  in  front  loose 
fibrous  prolongations — -more  numerous  above  and  below  than  in  the  dorsal  region — 
connect  the  tube  of  dura  mater  to  the  posterior  common  ligament  of  the  vertebral 
column.  No  connexion  of  any  kind  exists  between  the  dura  mater  and  the  posterior 
wall  of  the  spinal  canal. 

When  the  interior  of  the  tube  of  spinal  dura  mater  is  inspected,  the  series  of 
apertures  of  exit  for  the  roots  of  the  spinal  nerves  is  seen.  These  are  ranged  in 
pairs  opposite  each  intervertebral  foramen. 

Viewed  from  the  inside  of  the  tube  of  dura  mater,  each  of  the  two  roots  of  a 
spinal  nerve  is  seen  to  carry  with  it  a  special  and  distinct  sheath.  When  examined 
on  the  outside,  however,  the  appearance  is  such  that  one  miglit  be  led  to  conclude 
that  both  roots  are  enveloped  in  one  sheath  of  dura  mater.  This  is  due  to  the  fact 
that  the  two  sheaths  are  firmly  held  together  by  intervening  connective  tissue. 
The  two  tubular  sheaths  remain  distinct  as  far  as  the  ganglion  on  the  posterior 
root,  and  then  blend  with  each  other. 

Subdural  Space. — The  dura  mater  and  the  arachnoid  mater  are  closely  applied 
to  each  other,  and  the  capillary  interval  between  them  is  termed  the  subdural 
space.  It  contains  a  minute  quantity  of  fluid,  which  is  just  sufiicient  in  amount  to 
moisten  the  opposed  surfaces  of  the  two  bounding  membranes. 

The  subdural  space  in  no  way  communicates  with  the  subarachnoid  space. 
The  fluid  which  it  contains  is  led  into  the  venous  blood-sinuses  around  the 
Pacchionian  bodies,  and  thus  gains  exit.  The  subdural  space  is  carried  outwards 
for  a  very  short  distance  on  the  various  nerves  which  are  connected  with  the 
brain  and  the  spinal  cord,  and  it  has  a  free  communication  with  the  lymph-paths 
present  in  these  nerves.  In  the  case  of  the  optic  nerve  the  sheath  of  dura  mater 
is  carried  along  its  whole  length,  and  with  it  the  subdural  space  is  likewise  pro- 
longed to  the  back  of  the  eyeball. 

The  Arachnoidea. 

The  arachnoid  mater  is  a  very  thin  membrane,  remarkable  for  its  delicacy  and 
transparency,  which  envelopes  both  the  brain  and  the  cord  between  the  dura  mater 
and  the  pia  mater.  The  cranial  part  of  the  arachnoid  mater  or  the  arachnoidea 
encephali,  except  in  the  case  of  th3  great  longitudinal  and  the  Sylvian  fissures,  does 
not  dip  into  the  sulci  on  the  surface  of  the  brain.  In  this  respect  it  differs  from 
the  pia  mater.  It  bridges  over  the  inequalities  on  the  surface  of  the  brain. 
Consequently,  on  the  basal  aspect  of  the  encephalon  it  is  spread  out  in  the  form  of 
a  very  distinct  sheet  over  the  medulla,  the  pons  Varolii,  and  the  hollow  which  lies 


THE  ARACHNOIDEA. 


601 


in  front  of  the  pons,  and  in  certain  of  these  regions  it  is  separated  from  the  brain- 
surface  by  wide  intervals. 

The  spinal  part  of  the  arachnoid  mater  or  arachnoidea  spinalis,  which  is  directly 
continuous  with  the  cranial  arachnoidea,  forms  a  loose  wide  investment  for  the 
spinal  cord.  This  arachnoidal  sac  is  most  capacious  towards  its  lower  part,  where  it 
envelopes  the  lower  end  of  the  cord  and  the  collection  of  long  nerve-roots  which 
constitute  the  cauda  equina. 

As  the  nerves,  both  from  the  brain  and  the  cord,  pass  outwards  they  receive  an 
investment  from  tlie  arachnoid,  which  runs  for  a  short  distance  upon  them  and 
then  comes  to  an  end. 

Subarachnoid  Space  (cavum  subarachnoidale). — The  interval  between  the 
arachnoidea  and  tlie  pia  mater  receives  the  name  of  the  subarachnoid  space.     It 


racfhiuuiiiii  lioiiv 


Licuiia  lateralis. 


Dura  mater- 
SubJuial  spic 

Araohiioidea 

Subarach 
noid  space 
and  ti-ssue 

Pia  m-itei 


Fig.  478. — Diagram  to  show  the  relations  of  the  membranes  of  the  brain  to  the  cranial  wall  and  the  cerebral 
convolutions,  and  also  of  the  Pacchionian  bodies  to  the  superior  longitudinal  sinus  and  the  lateral  lacuuifi. 

contains  the  cerebro-spinal  fluid,  and  communicates  freely  through  certain  well- 
defined  apertures  with  the  ventricular  cavities  in  the  interior  of  the  brain.  Three 
of  these  (viz.  the  foramen  of  Majendie  and  another  at  the  extremity  of  each  lateral 
recess)  are  in  connexion  with  the  fourth  ventricle ;  two  are  slit-like  openings  into 
the  lateral  ventricles,  and  are  placed  at  the  extremity  of  each  descending  horn. 

Within  the  cranium  the  subarachnoid  space  is  broken  up  by  a  meshwork  of  fine 
filaments  and  trabeculse,  which  connects  the  two  bounding  membranes  (viz.  the 
arachnoidea  and  the  pia  mater)  in  the  most  intimate  manner,  and  forms  a  delicate 
sponge-like  interlacement  between  them.  Where  the  arachnoidea  passes  over  the 
summit  of  a  cerebral  convolution,  and  is  consequently  closely  applied  to  the  sub- 
jacent pia  mater,  the  meshwork  is  so  dense  and  the  trabeculse  so  short  that  it  is 
hardly  possible  to  discriminate  between  the  two  membranes.  To  all  intents  and 
purposes  they  form  in  these  localities  one  lamina.  In  the  intervals  between  the 
rounded  margins  of  adjoining  convolutions,  however,  distinct  angular  spaces  exist, 
where  the  subarachnoid  trabecular  tissue  can  be  studied  to  great  advantage.  These 
intervals  on  the  surface  of  the  cerebrum  constitute  numerous  communicating 
channels  which  serve  for  the  free  passage  of  the  subarachnoid  fluid  from  one  part  of 
the  brain  to  another.  The  larger  branches  of  the  arteries  and  veins  of  the  brain 
traverse  the  subarachnoid  space ;  their  walls  are  directly  connected  with  the  sub- 
arachnoid trabeculse,  and  are  bathed  by  subarachnoid  fluid. 

In  certain  situations  within  the  cranium  the  arachnoidea  is  separated  from  the 


602 


THE  NEEVOUS  SYSTEM. 


pia  mater  by  intervals  of  considerable  width  and  extent.  These  expanded  portions 
of  the  subarachnoid  space  are  termed  cisternae  subarachnoidales.  In  these  the  sub- 
arachnoid tissue  is  much  reduced.  There  is  no  longer  a  close  meshwork;  the 
trabeculte  connecting  the  two  bounding  membranes  take  the  form  of  long  fila- 
mentous intersecting  threads  which  traverse  the  spaces.  All  the  subarachnoid 
cisterns  communicate  in  the  freest  manner  with  each  other  and  also  with  the 
narrow  channels  on  the  surface  of  the  cerebrum. 

Certain  of  these  cisterns  require  special  mention.  The  largest  and  most  con- 
spicuous is  the  cistema  magna.  It  is  formed  by  the  arachnoid  membrane  bridging 
over  the  wide  interval  between  the  back  part  of  the  under  surface  of  the  cerebellum 
and  the  medulla.  It  is  continuous  through  the  foramen  magnum  with  the  posterior 
part  of  the  wide  subarachnoid  space  of  the  cord. 

The  cisterna  pontis  is  the  continuation  upwards  on  the  floor  of  the  cranium  of 
the  anterior  part  of  the  subarachnoid  space  of  the  spinal  cord.  In  the  region  of 
the  medulla  it  is  continuous  behind  with  the  cisterna  magna,  so  that  this  sub- 
division of  the  brain,  like  the  spinal  cord,  is  surrounded  by  a  wide  subarachnoid 
space. 

In  front  of  the  pons  Varolii  the  arachnoidea  bridges  across  between  the  pro- 
jecting temporal  lobes,  and  covers  in  the  deep  hollow  in  this  region  of  the  brain. 
This  space  is  called  the  cisterna  basalts,  and  within  it  are  placed  the  large  arteries 
which  take  part  in  the  formation  of  the  circle  of  Willis.  Leading  out  from  the 
cisterna  basahs  there  are  certain  wide  subarachnoid  channels.  Two  of  these  are 
prolonged  into  the  Sylvian  fissures,  and  in  these  are  accommodated  the  middle 
cerebral  arteries.  Anteriorly  the  basal  cistern  passes  into  a  space  in  front  of  the 
optic  chiasma,  and  from  this  it  is  continued  into  the  great  longitudinal  fissure 
above  the  corpus  callosum.  In  this  subarachnoid  passage  the  anterior  cerebral 
arteries  are  lodged. 

The  spinal  part  of  the  subarachnoid  space  is  a  very  wide  interval  which  i& 
partially  subdivided  into  compartments  by  three  incomplete  septa.  One  of  these 
is  a  mesial  partition  called  the  septum  posticum,  which  connects  the  pia  mater 
covering  the  posterior  aspect  of  the  cord  with  the  arachnoid  mater.  In  the  upper 
part  of  the  cervical  region  the  septum  posticum  is  imperfect,  and  is  merely  repre- 
sented by  some  strands  pass- 
ing between  the  two  mem- 
branes ;  in  the  lower  part  of 
the  cervical  region  and  in 
the  dorsal  region  it  becomes 
tolerably  complete.  The- 
other  two  septa  are  formed 
by  the  ligamenta  denticulata 
which  spread  outwards  from 
either  side  of  the  spinal  cord. 
These  will  be  described  with 
the  pia  mater. 

Pacchionian  Bodies 
(granulationes  arach- 
noidales). — When  the  sur- 
face of  the  dura  mater  is 
inspected  after  the  removal 
of  the  calvaria,  a  number  of 
small  fleshy-looking  excres- 
cences, purplish-red  in  colour, 
are  seen  ranged  in  clusters  on 
either  side  of  the  superior 
longitudinal  sinus,  and  when 
this  sinus  is  opened  they  are- 
also  observed  protruding  in  considerable  numbers  into  its  interior.  These  are  the 
Pacchionian  bodies,  and  they  are  also  found  in  smaller  number  and  distinctly 
smaller  size  in  connexion  with  other  blood-sinuses,  such  as  the  lateral  sinus,  the- 


Arachnoid 


Posterior  nerve-roo' 


Spinal  ganglion 


Anterior  division 
of  nerve > 

Posterior  division_ 
of  nerve" 


Dura  mater 

Arachnoid 

LiKamentum  ileiiticulatum 


Dura  mater 


Anterior  nerve- 
root  (cut) 
Posterior  nerve- 
root 

Anterior  nerve- 
root  (cut) 


Ligamentum 
denticulatuni 


Anterior  nerve-root 


Fig.  479.- 


-Membranes  of  the  Spinal  Cokd,  and  the  mode  ok 
Origin  of  the  Shn.vl  Nerves. 


THE  AKACHNOIDEA.  603 

straight  sinus,  and  the  civernous  sinus.  At  first  sight  they  appear  to  belong  to 
the  dura  mater,  but  in  reality  they  are  projections  from  the  arachnoidea.  In  the 
child  they  are  exceedingly  small  and  rudimentary,  and  it  is  only  as  life  advances 
that  they  become  large  and  conspicuous. 

Each  Pacchionian  liody  is  a  bulbous  protrusion  of  the  arachnoid  membrane. 
It  is  attached  to  the  arachnoidea  by  a  narrow  pedicle,  and  into  its  interior  is  pro- 
longed through  this  a  continuation  of  the  subarachnoid  space  and  its  characteristic 
meshwork.  The  Pacchionian  bodies  do  not  pierce  the  dura  mater.  As  they  push 
their  way  into  a  blood-sinus  they  carry  before  them  a  thin  covering  continuous 
with  the  sinus  wall.  On  either  side  of  the  superior  longitudinal  sinus  there  are  a 
number  of  irregular  spaces  in  the  dura  mater  which  communicate  with  the  sinus 
either  by  a  small  aperture  or  a  narrow  channel.  These  spaces  are  called  the 
parasinoidal  sinuses  or  the  lacunas  laterales,  and  certain  of  the  meningeal  veins  and 
some  of  the  diploic  veins  open  into  them.  Pacchionian  bodies  push  themselves 
into  the  parasinoidal  sinuses  from  below  in  such  a  manner  that  they  receive  a 

Pafcliiijiiiaii  body  Muuth  of  a  vein 


^B     Superior 
CS'fl     longitudinal 
^  ^        siiins 


Fig.  480. — Mesial  Sectiox  through  the  Crakial  Vault  in  the  Frontal  Region.     Displays  a  ijortion 
of  the  superior  longitudinal  sinus  and  tlie  Pacchionian  bodies  protruding  into  it  (enlarged). 

complete  covering  from  the  layer  of  dura  mater  which  forms  the  sinus  floor.  Nor 
does  the  bone  escape.  As  the  Pacchionian  bodies  enlarge  they  cause  absorption 
of  the  cranial  wall,  and  small  pits  are  hollowed  out  on  its  deep  surface  for  their 
reception.  It  must  be  clearly  understood,  however,  that  in  such  cases  the 
Pacchionian  body  is  separated  from  the  bone  by  the  following  : — (1)  A  con- 
tinuation round  the  Pacchionian  body  of  the  subdural  space  ;  (2)  the  thinned 
floor  of  the  parasinoidal  sinus ;  (3)  the  lumen  of  the  sinus ;  and  (4)  the  greatly 
thinned  upper  wall  of  the  sinus. 

The  Pacchionian  bodies  have  a  special  function  to  perform.  Through  them 
fluid  can  pass  from  the  subarachnoid  space  into  the  venous  sinuses  with  which  they 
stand  in  connexion.  Whenever  the  pressure  of  blood  in  the  sinuses  is  lower  than 
that  of  the  fluid  in  the  subarachnoid  space  and  the  ventricles  of  the  brain,  the 
cerebro-spinal  fluid  filtrates  through  the  Pacchionian  bodies  into  the  blood-sinuses. 
This  is  not  the  only  way  that  subarachnoid  fluid  may  obtain  exit.  The  sub- 
arachnoid space  is  carried  outwards  for  a  short  distance  on  the  nerves  in  connexion 
with  their  arachnoidal  sheaths,  and  communicates  with  the  lymph  channels  of  the 
nerves.  This  connexion  is  more  complete  in  the  case  of  the  olfactory,  the  optic, 
and  the  auditory  nerves,  than  in  other  nerves.  A  very  free  communication  between 
the  subarachnoid  space  and  the  lymphatics  of  the  nasal  mucous  membrane  is  said 
to  exist. 

The  Pi  a  Mater. 

The  pia  mater  forms  the  immediate  investment  of  the  brain  and  cord.  It  is  a 
delicate  and  very  vascular  membrane. 

Pia  mater  encephali. — The  pia  mater  which  covers  the  brain  is  finer  and 
more  delicate  than  that  which  clothes  the  spinal  cord.  It  follows  closely  all  the 
inequalities  on  the  surface  of  the  brain,  and  in  the  case  of  the  cerebrum  it  dips 
into  each  sulcus  in  the  form  of  a  fold  which  lines  it  completely.  On  the  cerebellum 
the  relation  is  not  so  intimate ;  it  is  only  into  the  larger  fissures  that  it  penetrates 
in  the  form  of  folds. 


604 


THE  NEEVOUS  SYSTEM. 


The  larger  blood-vessels  of  the  brain  lie  in  the  subarachnoid  space.  The  finer 
twigs  ramify  in  the  pia  mater  before  they  proceed  into  the  substance  of  the  brain. 
As  they  enter  they  carry  with  them  sheaths  derived  from  the  pia  mater.  When 
a  portion  of  the  membrane  is  raised  from  the  surface  of  the  encephalon,  numerous 
fine  processes  are  withdrawn  from  the  cerebral  surface.  These  are  the  blood-vessels 
with  their  sheaths,  and  they  give  the  deep  surface  of  the  pia  mater  a  rough  and 
flocculent  appearance. 

As  the  pia  mater  is  carried  over  the  lower  part  of  the  roof  or  posterior  wall  of 
the  fourth  ventricle  of  the  brain  it  receives  the  name  of  the  tela  choroidea  inferior, 
and  it  is  in  connexion  with  this  portion  of  the  pia  mater  that  the  choroid  plexuses 
of  that  cavity  are  developed.  The  tela  choroidea  superior  or  velum  interpositum 
is  a  fold  of  pia  mater  which  is  invaginated  into  the  brain,  so  that  it  comes  to  lie 
over  the  third  ventricle  and  project  in  the  shape  of  choroid  plexuses  into  the 
lateral  ventricles.     This  invagination  requires  special  notice. 

The  velum  interpositum  (tela  choroidea  superior)  is  a  double  layer  or  fold  of  pia 
mater  which  intervenes  between  the  body  of  the  fornix  which  lies  above  it  and  the 
epithelial  roof  of  the  third  ventricle,  and  the  two  optic  thalami  which  lie  below  it. 
Between  its  two  layers  are  blood-vessels,  and  some  subarachnoidal  trabecular 
tissue.  In  shape  the  velum  interpositum  is  triangular,  and  the  narrow  anterior 
end  or  apex  reaches  forwards  as  far  as  the  foramina  of  Monro.     The  base  lies 

under  the  splenium  of  the  corpus 
callosum,  and  here  the  two  layers 
of  the  velum  separate  and  become 
continuous  with  the  investing  pia 
mater  on  the  surface  of  the  brain 
by  passing  out  through  a  cleft 
called  the  transverse  fissure. 

Along  each  lateral  margin  the 
velum  interpositum  is  bordered 
by  the  choroid  plexus  of  the  body 
of  the  lateral  ventricle,  which 
projects  into  the  ventricular  cavity 
from  under  cover  of  the  free 
lateral  margin  of  the  fornix.  It 
should  be  borne  in  mind  that  the 
epithelial  lining  of  the  ventricle 
gives  a  complete  covering  to  the 
choroid  plexus.  Posteriorly  the 
choroid  plexus  is  continuous  with 
the  similar  structure  in  the  de- 
scending horn  of  the  ventricle, 
whilst  in  front  it  narrows  greatly, 
and  becomes  continuous  across  the 
mesial  plane  with  the  correspond- 
ing plexus  of  the  opposite  side, 
behind  the  epithelial  lajer  which 
lines  the  foramen  of  Monro.  From 
this  median  junction  two  much 
smaller  choroid  plexuses  run  back- 
wards on  the  under  surface  of  the  velum  interpositum,  and  project  downwards  into 
the  third  ventricle.     These  are  the  choroid  plexuses  of  the  third  ventricle. 

The  most  conspicuous  blood-vessels  in  the  velum  interpositum  are  the  two 
veins  of  Galen,  which  run  backwards,  one  on  either  side  of  the  mesial  plane.  In 
front,  each  is  formed  at  the  apex  of  the  fold  by  the  union  of  the  vein  of  the 
corpus  striatum  and  a  large  vein  issuing  from  the  choroid  plexus  ;  behind,  they 
unite  to  form  the  vena  magna  Galeni,  and  this  pours  its  blood  into  the  anterior 
end  of  the  straight  sinus  (Fig.  477,  p.  598). 

The  continuous  cleft  in  the  brain  through  which  the  velum  interpositum  and 
the  choroid  plexuses  of  the  two  descending  horns  of  the  lateral  ventricles   are 


Genu  of  cori5us 
callosum 


Ventricle  V. 
Septum  lucidum 
Caudate  nucleus 

P'ornix 

Anterior  pillar  of  fornix 
Vein  of  corpus  striatum 

optic  thalamus 

Velum  interpositum 
of  Galen 

Choroid  plexiis  oi 
teral  ventricle 


Lyra 


Posterior  pillar  of  fornix 
(under  surface) 


Body  of  fornix  (thrown 
backwards) 


Fig.  481. — Dissection  to  show  the  Velum  Intekpositum, 
AND  the  Parts  in  immediate  Relation  to  it. 


THE  PIA  MATEE. 


605 


Lateral  ventricle 

Ohoioiil  plexus  ( 


Position  of  tx 
seniiciicul 


Ttenia  tlialanii 


Choroid  plexus  Vent 


of  Galen 


Fig.  482. — Diagrammatic  Coronal  Section  throu^ 
thalanii,  and  the  parts  in  immediate  relation  to  tlieni. 
mediate  part  of  the  great  transver-e  fissure  holding 
interpositum  is  seen,  and  also  the  manner  in  wliicli  this  fissure  is 
shut  out  from  the  lateral  ventricles  hy  the  epithelium  which  covers 
the  choroid  plexus  on  each  side. 


tlie 
Tht 
the 


optic 
inter- 
velum 


introduced  into  the  interior  of  the  brain  is  sometimes  called  the  transverse  fissure. 
It  consists  of  an  upper  intermediate  part  and  two  lateral  parts.  The  former 
passes  forwards  between  the 
corpus  callosum  and  the 
fornix  above  and  the  roof  of 
the  third  ventricle  and  the 
optic  thalami  below.  It  is 
limited  on  either  side  by 
the  epithelial  covering  of  the 
choroid  plexuses,  which  shuts 
out  these  structures  from 
the  cavity  of  the  lateral  ven- 
tricles. The  lateral  part  is 
the  choroidal  fissure.  This 
is  continuous  with  the  in- 
termediate part,  and  has 
already  been  described  in 
connexion  with  the  descend- 
ing horn  of  the  lateral 
ventricle  (p.  578). 

Pia  mater  spinalis. — 
The  pia  mater  of  the  cord 
is  thicker  and  denser  than 
that  of  the  brain.  This  is 
largely  due  to  the  addition  of  an  outside  fibrous  layer,  in  which  the  fibres  run 
chiefly  in  the  longitudinal  direction.  The  pia  mater  is  very  firmly  adherent  to 
the  surface  of  the  cord,  and  in  front  it  sends  a  fold  into  the  antero-median  fissure 
of  the  cord.     The  septum  which  occupies  the  postero-median  fissure  is   likewise 

firmly  attached  to  its  deep 
surface.  In  front  of  the 
antero  -  median  furrow  of 
the  cord  the  pia  mater  is 
thickened  in  the  form  of 
a  longitudinal  glistening 
band,  termed  the  linea 
splendens,  which  runs  along 
the  whole  length  of  the 
cord,  and  blends  with  the 
filum  terminale  below.  The 
blood-vessels  of  the  spinal 
cord  lie  between  the  two 
layers  of  the  pia  mater. 

The  nerves  which  leave 
both  the  brain  and  cord 
receive  closely -applied 
sheaths  from  the  pia  mater. 
These  blend  with  the  con- 
nective-tissue sheaths  of  the 
nerves. 

The  ligamentum  denticu- 
latum  is  a  strong  fibrous 
band  which  stretches  out 
like  a  wing  from  the  pia  mater  on  either  side  of  the  spinal  cord,  so  as  to  connect 
the  pia  mater  with  the  dura  mater.  The  pial  or  inner  attachment  of  the  ligament 
extends  in  a  continuous  line  between  the  anterior  and  posterior  nerve-roots,  from 
the  level  of  the  foramen  magnum  above  to  the  level  of  the  first  lumbar  vertebra 
below.  Its  outer  margin  is  serrated  or  denticulated,  and  for  the  most  part  free. 
From  twenty  to  twenty-two  denticulations  may  be  recognised.  They  occur  in  the 
intervals  between  the  spinal  nerves,  and  pushing  the  arachnoid  before  them,  they 


Araehnoi 


Posterior  nerve-root 


Spinal  gang! 

Anterior  division 
of  nerved 
Posterior  division 
of  nerve" 


Dm  a  mater 

Ai.itlnioiii 

Ligamentum  dentieulatum 


Anterior  nerve- 
loot  (cut) 
Posterior  nerve- 
loot 

Anterior  nerve- 
root  (cut) 


Ligamentum 
dentieulatum 


Anterior  nerve-root 


Fig.  483. — Membranes  of  the  Spinal  Cord,  and  the  mode  of 
Origin  of  the  Spinal  Nerves. 


606  THE  NEEVOUS  SYSTEM. 

are  attached  by  their  pointed  ends  to  the  inner  surface  of  the  dura  mater.  The 
ligamenta  denticulata  partially  subdivide  the  wide  subarachnoid  space  in  the  spinal 
canal  into  an  anterior  and  a  posterior  compartment.  The  anterior  nerve-roots 
traverse  the  anterior  compartment,  whilst  the  posterior  nerve-roots  traverse  the 
posterior  compartment.  Further,  the  posterior  compartment  is  imperfectly  sub- 
divided into  a  right  and  a  left  lateral  part  by  the  septum  posticum. 

By  means  of  the  ligamenta  denticulata  the   spinal  cord  is  suspended  in  the 
middle  of  the  tube  of  dura  mater. 


THE   PERIPHERAL   NERVES   AND   THE   SYMPATHETIC 
NERVOUS   SYSTEM. 

By  A.  M.  Patekson. 


THE   SPINAL 
NERVES. 

The  spinal  nerves 

are  arranged  in  pairs, 
of  which  there  are 
usually  thirty  -  one. 
Each  nerve  arises  by 
two  roots  from  the 
spinal  cord,  which 
separately  pierce  the 
membrane,  the  nerve 


Dorsal  nerve-root 
Ligamentum 
tlenticulatum 
Ventral  nerve-root 


Akising  from  the  brain  and  spinal  cord  respectively,  the  cranial  and  spinal 
nerves  are  responsible,  collectively,  for  the  central  localisation  of  peripheral 
stimuli,  or  for  the  transmission  peripherally  of  central  impulses.  The  sense 
organs  and  the  somatic  regions  of  the  body  are  in  direct  communication  by 
the  nerves  with  the 
brain  and  spinal  cord. 
The  splanchnic  area, 
and  the  viscera  which 
it  contains,  are  gov- 
erned by  nerves  con- 
nected with  the  central 
nervous  system.  By 
means  of  the  sym- 
pathetic nervous  sys- 
tem, the  nerves  from 
the  cerebro-spinal  sys- 
tem are  directed  to 
their  several  destina- 
tions in  the  splanchnic 
area :  and  connexions 
are  effected  with  the 
roots  of  the  nerves  on 
the  one  hand,  and 
through  their  peri- 
pheral branches,  with 
the  somatic  region,  on 
the  other  hand. 


Dorsal  nerve-root 
Ventral  nerve-root 

Ventral  nerve-root 
[jiganientum 
Jenticulatum 
Arachnoid 


Dorsal  nerve-root 


Dorsal  ganglion 


Posterior  priraar 

division 
Anterior  primary \_J 

division 


Posterior  primary 
division 


Anterior  primary  division 
Ventral  nerve-root 


Spinal  cord 


Fig. 


484. — Scheme  of  the  Arrangement  of  the  Membranes  of  the 
Spinal  Cord  and  the  Roots  of  the  Spinal  Nerves. 


dura   mater.      Enclosed  in  a   tubular   investment  of  this 
emerges  from  the  spinal  canal  through   the  intervertebral 
foramen,  and  is  distributed  to  the  trunk  and  limbs  in  a  manner  to  be  described  below. 
The  nerves  are  designated  cervical,  thoracic,  lumbar,  sacral,  and  coccygeal,  in  rela- 
tion to  the  vertebrae  between  which  they  emerge  from  the  spinal  canal.     Each  nerve 
appears  below  the  corresponding  vertebra,  except  the  first  of  the  cervicaP  series, 

607 


608 


THE  NEEVOUS  SYSTEM. 


which  passes  out  of  the  spinal  canal  between  the  occipital  bone  and  the  atlas. 
There  are  thus  eight  cervical  nerves  (the  last  appearing  between  the  seventh 
cervical  and  first  thoracic  vertebme)  ;  there  are  twelve  thoracic,  ^i?e  lumbar,  j^'we 
sacral,  and  one  coccygeal  nerve,  all  appearing  below  the  corresponding  vertebrpe. 

The  thirty-first  nerve  is  occasionally  absent ;  and  there 
are  sometimes  one  or  two  additional  pairs  of  minute 
filaments  below  the  thirty-first,  which,  however,  do  not 
emerge  from  the  spinal  canal.  These  are  rudimentary 
caudal  nerves. 

The  size  of  the  spinal  nerves  varies  extremely.  The 
largest  are  those  which  take  part  in  the  formation  of  the 
great  nerve -trunks  for  the  supply  of  the  limbs  (lower 
cervical  and  first  thoracic,  and  lower  lumbar  and  upper 
sacral  nerves) ;  and  of  these  the  nerves  destined  for  the 
lower  limbs  are  the  larger.  Tlie  coccygeal  nerve  is  the 
smallest  of  the  spinal  nerves;  the  thoracic  nerves  (except 
the  first)  are  much  more  slender  than  the  limb  nerves ; 
and  the  cervical  nerves  diminish  in  size  from  below  up- 
wards. 

Origin  of  the  Spinal  Nerves.— Each  spinal 
nerve  is  attached  to  the  spinal  cord  by  two  roots, 
called  respectively  dorsal  (posterior)  and  ventral 
(anterior). 

The  dorsal  root  is  larger  than  the  ventral  root ; 
it  contains  a  larger  number  of  rootlets,  and  the  in- 
dividual rootlets  are  of  larger  size  than  in  the  ventral 
root.  It  has  a  vertical  linear  attachment  to  the 
postero-lateral  sulcus  of  the  spinal  cord.  The  rootlets 
of  contiguous  dorsal  roots  are  in  close  relation,  and,  in 
some  instances,  overlap.  The  dorsal  root  separates  as 
it  passes  away  from  the  cord  into  two  bundles,  both 
of  which  become  connected  with  the  inner  end  of  a 
spinal  ganglion.  From  the  outer  end  of  this  ganglion 
the  dorsal  root  proceeds  to  its  junction  with  the 
ventral  root  in  the  intervertebral  foramen. 

The  spinal  ganglia  are  found  on  the  dorsal  roots 
of  all  the  spinal  nerves.  (In  the  case  of  the  first 
cervical  or  sub-occipital  nerve,  the  spinal  ganglion  may 
be  rudimentary  or  absent ;  and  the  dorsal  root  itself 
may  be  wanting,  or  derived  from  the  spinal  accessory 
nerve.)  They  occupy  the  intervertebral  foramina, 
except  in  the  case  of  the  sacral  and  coccygeal  nerves, 
the  ganglia  of  which  lie  vnthin  the  vertebral  canal : 
and  the  first  and  second  cervical  nerves,  the  ganglia 
of  which  lie  upon  the  neural  arches  of  the  atlas  and 
axis  respectively.  With  the  exception  of  the  coccygeal 
ganglia  they  are  outside  the  cavity  of  the  dura  mater, 
but  are  invested  by  the  membrane.  The  ganglia 
are  of  ovoid  form,  bifurcated  in  some  cases  at  their 
inner  ends.  They  consist  of  unipolar  nerve -cells, 
whose  processes,  after  a  very  short  course,  divide  into 
respectively  in  relation  to  the  spinal  central  (root)  and  peripheral  (trunk)  fibres.  The 
'°!T,";   T\^  nerves  are  shown  as  central  fibres  form  the  portion  of  the  root  entering 

thick  black  lines  on  the  lelt  .side.  .  .       ,  -,       .^  •    ^         i    ni  j.-  j  :„ 

the  spmal  cord  ;  the  peripheral  fibres  are  continued  in 
an  outward  direction  from  the  ganglion  into  the  spinal  nerve. 

Accessory  spinal  ganglia  (ganglia  aberrantia).— Between  the  spinal  ganglion  and  the  spinal 
cord  small  collections  of  cells  are  occasionally  found  on  the  dorsal  roots,  either  as  scattered  cells 
or  distinct  ganglia.  They  are  most  frequently  met  with  on  the  dorsal  roots  of  the  lumbar  and 
sacral  nerve.s. 


Fig.  485. — Diagrammatic  Repke- 
sentation'  of  the  origin  of  the 
Spinal  Nerves,  sho-wing  the  posi- 
tion   of    their    roots    and    ganglia 


DIVISIONS  OF' A  SPINAL  NEEVE. 


609 


eXTEfl/VM. 


The  ventral  root  is  smaller  than  the  dorsal  root.  It  arises  from  the  anterior 
surface  of  the  spinal  cord  {anterior  root  zone)  by  means  of  scattered  bundles  of 
nerve-fibres,  which  occupy  a  greater  horizontal  area  and  are  more  irregular  in  their 
arrangement  than  the  fascicles  of  the  dorsal  root.  It  possesses  no  ganglion  in  its 
course.  The  rootlets  sometimes  overlap,  and  are  not  unfrequently  connected  with 
neighbouring  rootlets  above  and  below. 

The  dorsal  and  ventral  roots,  from  their  attachment  to  the  spinal  cord,  proceed 
outwards  in  the  spinal  canal  towards  the  intervertebral  foramina,  where  they 
unite  to  form  the  spinal  nerve.  The  direction  of  the  roots  of  the  first  two  nerves 
is  upwards  and  outwards ;  the  roots  of  the  remaining  nerves  course  obliquely 
downwards  and  outwards,  the  obliquity  gradually  increasing  until,  in  the  case  of 
the  lower  lumbar,  the  sacral  and  coccygeal  nerve-roots,  their  course  is  vertically 
downwards  in  the  spinal  canal.  The  collection  of  nerve -roots  which  occupies 
the  lower  part  of  the  canal  below  the  first  lumbar  vertebra,  and  comprises  all  the 
nerve-roots  below  those  of  the  first  lumbar  nerve,  is  designated  the  cauda  equina. 
They  arise  from  the  lumbar  enlarge- 
ment and  conus  medullaris,  and  sur- 
round the  filum  terminale  of  the  spinal 
cord. 

Within  the  spinal  canal  the  nerve- 
roots  are  in  relation  with  the  meninges 
of  the  cord,  and  are  separated  from  one 
another  by  the  ligamentum  denti- 
culatum,  and,  in  the  neck,  by  the  spinal 
part  of  the  spinal  accessory  nerve.  Each 
receives  a  covering  of  pia  mater,  con- 
tinuous with  the  neurilemma ;  the 
arachnoid  invests  each  root  as  far  as 
the  point  where  it  meets  with  the  dura 
mater;  and  each  root  pierces  the  dura 
mater  separately.  The  two  roots  are 
thereafter  enclosed  in  a  single  tubular 
sheath  of  dura  mater,  in  which  is  included 
the  spinal  ganglion  of  the  dorsal  root. 
The  spinal  nerve  thus  formed  lies  in 
the  intervertebral  foramen,  except  in 
the  case  of  the  first  two  cervical  and 
the  sacral  aud  coccygeal  nerves. 

Divisions  of  a  Spinal  Nerve. — 
After  emerging  from  the  intervertebral 
foramen  the  nerve  immediately  divides 
into  two  primary  divisions,  named  respectively  the  posterior  and  anterior 
primary  divisions.  Just  before  its  division  each  nerve  gives  off  a  minute 
recurrent  branch,  which  re-enters  the  vertebral  canal  after  effecting  a  junction 
with  a  branch  from  the  sympathetic  cord,  and  is  distributed  to  the  spinal  cord 
and  its  membranes. 

The  posterior  and  anterior  primary  divisions  of  the  spinal  nerve  are  responsible 
for  the  innervation  of  the  skeletal  muscles  and  the  skin  covering  the  trunk 
and  limbs.  They  are  thus,  properly  speaking,  the  somatic  branches  of  the 
spinal  nerve. 

In  relation  to  certain  of  the  nerves,  a  series  of  mucli  smaller  branches  exist  which  are  connected 
with  the  sympathetic  system  (Fig.  486,  SF),  in  a  way  to  be  described  later.  These  constitute  the 
white  rami  communicantes,  and  may  be  termed  the  visceral  divisions  of  the  spinal  nerves.  They 
are  derived  from  the  anterior  primary  divisions  of  the  nerves,  and  receive  their  fibres  mainly 
from  the  ventral  roots,  though,  at  least  in  the  case  of  certain  nerves,  from  the  dorsal  roots  as  well. 
These  nerves  are  directed  inwards  from  the  intervertebral  foramen  over  the  vertebral  column,  and, 
becoming  connected  with  the  sympathetic  cord,  convey  spinal  fibres  to  the  organs  and  tissues  in 
the  splanchnic  area. 

The  posterior  and  anterior  primary  divisions  of  the  nerves  contain  fibres  from 
43 


efUNCH 


Fig.  486. 


iANT£fllOR 


-Scheme  of  the  Distribdtion  of  a 
Typical  Spinal  Nerve. 


610  THE  NEEVOUS  SYSTEM. 

both  dorsal  and  ventral  roots.  Indeed,  each  root  can  be  seen,  on  removal  of  its 
sheath,  to  divide  into  two  portions,  of  which  one  portion  enters  into  the  formation 
of  the  posterior,  the  other  into  the  formation  of  the  anterior  primary  division. 
The  posterior  primary  divisions,  with  the  exception  of  the  first  two,  are  smaller 
than  the  anterior  primary  divisions ;  and  they  are,  generally  speaking,  responsible  for 
the  innervation  of  the  skin  and  muscles  of  the  back.  They  do  not  supply  the  muscles 
of  the  limbs ;  although  in  their  cutaneous  distribution  they  are  prolonged  on  to 
the  back  of  the  head,  the  shoulder,  and  the  buttock.  They  form  two  small  plexuses 
— the  posterior  cervical  and  the  posterior  sacral  plexuses.  The  anterior  primary 
divisions  are,  with  the  exception  of  the  first  two  cervical  nerves,  much  larger  than 
the  posterior  primary  divisions.  They  supply  the  sides  and  fore-parts  of  the  body, 
the  limbs,  and  the  perineum.  For  the  most  part  they  have  a  complicated 
arrangement.  The  thoracic  or  intercostal  nerves  alone  have  a  simple  mode  of  dis- 
tribution ;  the  other  nerves  give  rise  to  the  three  great  plexuses — cervical,  brachial, 
and  lumbo-sacral. 

Distribution  of  the  Spinal  Nerves. — The  distribution,  like  the  origin  of  the 
posterior  and  anterior  primary  divisions  of  the  spinal  nerves,  presents  primarily  and 
essentially  a  segmental  arrangement,  masked  and  in  some  cases  obliterated  by  develop- 
mental changes  which  have  occurred  in  the  parts  supplied.  In  no  region  can  a  single 
nerve  be  traced  to  a  complete  segment.  In  the  trunk  between  the  limbs  the  nearest 
approach  to  a  complete  girdle  is  formed  by  such  a  nerve  as  the  sixth  thoracic  nerve. 
In  its  cutaneous  distribution  it  forms  a  perfect  belt,  the  nerve  by  its  posterior  and 
anterior  primary  divisions  supplying  a  distinctly  segmental  area  from  the  middle  line 
of  the  trunk  behind  to  the  sternum  in  front.  Its  muscular  distribution,  also,  is 
almost  perfectly  segmental.  The  anterior  primary  division  supplies,  unaided,  the 
intei'costal  muscles  of  the  segment  in  which  it  lies.  The  posterior  primary  division 
supplies  muscles  in  the  back,  not,  however,  in  a  strictly  segmental  manner,  on  account 
of  the  fact  that  the  segmental  myotomes  have  fused  together  in  the  back  to  give  rise 
to  complex  longitudinal  muscles,  which  are  together  supplied  by  the  series  of  muscular 
branches  derived  from  the  posterior  primary  divisions  of  contiguous  nerves.  In  other 
regions  greater  changes  cause  more  marked  deviations  from  a  simple  segmental  type  of 
distribution  and  give  rise  to  the  various  plexuses,  by  which  the  trunk,  and  more  particu- 
larly the  limbs,  are  innervated. 


POSTERIOPv  PRIMARY  DIVISIONS  OF  THE  SPINAL  NERVES. 

The  posterior  primary  divisions  of  the  spinal  nerves  are  distributed  generally  to 
the  skin  of  the  back  of  the  trunk,  the  back  of  the  head,  the  shoulder  and  the 
buttock,  and  to  the  longitudinal  muscles  of  the  back,  but  not  to  the  muscles  of  the 
limbs. 

Each  posterior  primary  division  divides  as  a  rule  into  two  parts,  an  internal  and 
an  external  trunk  ("Fig.  486,  p.  609).  In  the  upper  half  of  the  body  the  internal 
trunks  generally  supply  the  cutaneous  branches,  while  the  external  trunks  are 
purely  muscular  nerves.  In  the  lower  part  of  the  body  the  opposite  is  the  case : 
the  external  trunks  provide  the  cutaneous  nerves  and  the  internal  trunks  are 
distributed  entirely  to  muscles.  The  cutaneous  braiiches  have  a  different  course 
in  the  two  cases.  In  the  upper  half  of  the  back  they  course  inwards  and  back- 
wards beneath  and  among  the  muscles  to  within  a  short  distance  of  the  spinous 
processes  of  the  vertebree,  close  to  which  they  become  superficial.  They  then 
extend  outwards  in  the  superficial  fascia.  In  the  lower  half  of  the  back  the 
cutaneous  nerves  are  directed  downwards  and  outwards  among  the  muscles,  and 
become  superficial  at  a  greater  distance  irom  the  middle  line. 


CERVICAL  NERVES. 


611 


CERVICAL  NERVES. 

First  Cervical  Nerve  (n.  sub-occipi- 
talis). — It  has  already  been  pointed  out 
that  the  dorsal  root  of  this  nerve  may 
be  rudimentary,  or  even  absent  altogether. 
Its  posterior  primary  division  is  larger 
than  the  anterior  primary  division ;  it 
does  not  diWde  into  internal  or  external 
branches,  and  it  does  not  directly  supply 
any  cutaneous  branch. 

Passing  backwards  in   the  space  be- 
tween the  occipital  bone  and  the  posterior 
arch  of  the  atlas,  the  nerve  occupies  the 
sub  -  occipital 
triangle,    and    is 
placed      below 
and    behind  the 
vertebral  artery, 
and  under  cover 
of  the  complexus 
muscle.     It  sup- 
plies the  follow- 
ing branches : — 

(a)  Muscular 
branches  to  the 
complexus,  recti 
capitis  postici, 
major  and  minor, 
and  obliqui, 
superior  and  in- 
ferior. 

(c)  A  commu- 
nicating branch 
descends  to  join 
the  second  cervi- 
cal nerve. 

The  communi- 
cating branch  may 
arise  in  common 
with  the  nerve  to 
the  obliquus  in- 
ferior, and  reach 
the  second  cervical 
nerve  by  piercing 
or  passing  over  or 
beneath  the  obli- 
quus inferior.  Or 
it  may  accompany 
the  nerve  to  the 
complexus,  and 
communicate  with 
the  great  occipital 
nerve,  after  pierc- 
ing that  muscle. 

Fig.  487. — The  Distribution  of  Cutaneous  Nerves  ox  the  Back  ok  the  'J'runk. 

Oil  one  side  the  distribution  of  the  several  nerves  is  represented,  the  letters  indicating  their  nomenclature. 

G.O  (C.2),  Great  occipital  ;  C.3,  Least  occipital ;  T.l  et  seq.,  Posterior  pi-imary  divisions  of  thoracic  nerves  ; 
L.l  et  seq.,  Posterior  primary  divisions  of  first  three  lumbar  nerves  ;  S.l  et  seq.,  Posterior  primary 
divisions  of  sacral  nerves  ;  Acr,  Acromial  branches  from  cenucal  plexus  ;  T.2-12,  Lateral  branches  of 
thoracic  neives  ;  C'irc,  Cutaneous  branches  of  circumflex  nerve  ;  L.l,  Iliac  branch  of  ilio-hypogastric 
nerve  ;  E.C,  External  cutaneous  nen-e  ;  S.Sc,  Small  sciatic  nerve. 

On  the  other  side  a  schematic  representation  is  given  of  the  areas  supplied  by  the  above  ners'es,  the  numerals 
indicating  the  spinal  origin  of  the  branches  of  distribution  to  each  area. 


612 


THE  NERVOUS  SYSTEM. 


Second  Cervical  Nerve. — The  posterior  primary  division  of  this  nerve  is 
larger  than  the  corresponding  anterior  primary  division.  It  passes  backwards 
between  the  atlas  and  axis,  and  in  the  interval  between  the  obliquus  inferior 
and  the  semispinalis  colli  muscles,  under  cover  of  the  complex  us  muscle.  In  this 
situation  the  nerve  gives  off  several  small  muscular  and  communicating  branches. 
The  main  trunk,  after  piercing  the  complexus  and  trapezius  muscles,  accompanies 
the  occipital  artery  to  the  scalp  as  the  great  occipital  nerve  (n.  occipitalis  major). 
This  is  the  chief  cutaneous  nerve  for  the  back  part  of  the  scalp.  It  enters  the 
superficial  fascia  at  the  level  of  the  superior  curved  line  of  the  occipital  bone  and 
about  an  inch  from  the  external  occipital  protuberance.  Ramifying  over  the 
surface,  it  supplies  the  skin  of  the  scalp  as  far  as  the  vertex.     It  communicates  on 


Insertion  of  stern  o- 

mastoid 

Splenius  capitis 

Trachelo-mastoid 


Complexus 
Least  occipital  nerve 


Splenius  capitis 


Trachelo-mastoid 


Occipital  attachment  of 
trapezius 

Insertion  of  complexus 
Great  occipital  nerve 
Obliquus  superior 
Rectus  capitis  posticus  major 
Rectus  capitis  posticus  minor 
Vertebral  artery 

Suboccipital  nerve 
Posterior  arch  of  atlas 

Obliquus  inferior 

Posterior  division  of  second  cervical 

NTRVE 


Posterior  division  of  third  cervical 

NERVE 

Deep  cer^^cal  artei-y 

Posterior  division  of  fourth  cervical 

NERVE 


Fig.  488. — Posterior  Cervical  Plexus. 


the  scalp  with    the   following  nerves  :  great   auricular,  small   occipital,  posterior 
auricular,  and  least  occipital. 

The  muscular  branches  of  the  second  cervical  nerve  are  destined  for  the  com- 
plexus, obliquus  inferior,  semispinalis  colli,  and  multifidus  spinse. 

Its  communicating  branches  form  the  posterior  cervical  plexus.  Descending  over 
tVie  posterior  arch  of  the  atlas  is  a  branch  from  the  sub-occipital  nerve  which  forms  a  loop 
or  network  with  a  corresponding  branch  of  the  second  nerve.  From  this  loop  twigs  are 
supplied  to  the  surrounding  muscles.  A  similar  loop  is  formed  by  a  communication 
between  branches  of  the  second  and  third  nerves,  from  which  muscles  are  also  supplied. 
Occasionally  an  additional  loop  is  formed  between  branches  of  the  third  and  fourth  nerves. 

Third  Cervical  Nerve. — This  is  much  smaller  than  the  second  nerve.  Near 
its  origin  it  forms  a  loop  of  communication  with  the  second,  and  it  may  give  off 
a  similar  communicating  branch  to  the  fourth  nerve.  The  main  trunk  divides 
into  internal  cutaneous  and  external  muscular  branches.  The  external  muscular 
branch  enters  contiguous  muscles  ;  the  internal  cutaneous  branch  passes  backwards 
and  inwards,  and  becomes  superficial  as  the  third  or  least  occipital  nerve  (n.  occipi- 
talis minimus),  close  to  the  middle  line  of  the  neck.  It  supplies  fine  branches  to 
the  neck  and  scalp,  and  communicates  with  the  great  occipital  nerve. 


LUMBAE  NERVES.  613 

The  fourth,  fifth,  and  sixth  cervical  nerves  are  still  smaller.  Beneath  the  com- 
plexus  each  divides  into  external  muscular  and  internal  cutaneous  branches.  The 
muscular  branches  supply  neighbouring  muscles ;  the  cutaneous  branches  are  small 
nerves,  which,  passing  backwards,  become  superficial  close  to  the  middle  line.  They 
supply  the  skin  of  the  back  of  the  neck.  The  sixth  is  the  smallest,  and  its  cutaneous 
branch  is  minute,  and  may  be  absent  altogether.  In  certain  cases  the  fourth  nerve 
forms,  with  the  third,  a  loop  of  communication  from  which  muscles  are  supplied. 

Seventh  and  Eighth  Cervical  Nerves. — These  are  the  smallest  of  the  posterior 
primary  divisions  of  the  cervical  nerves.  They  give  off  ordinarily  no  cutaneous 
branches,  and  end  in  the  deep  muscles  of  the  back. 

THORACIC  NERVES. 

The  posterior  primary  division  of  each  thoracic  nerve  divides  into  an  internal 
and  external  branch.  In  the  case  of  the  upper  six  thoracic  nerves  the  internal 
branches  are  chiefly  distributed  as  cutaneous  nerves, — only  giving  off  small  muscular 
branches — while  the  external  branches  are  wholly  muscular  in  their  distribution  ; 
in  the  case  of  the  lower  six  thoracic  nerves  the  opposite  is  the  case.  In  all  cases 
the  muscular  branches  serve  to  innervate  the  longitudinal  muscles  of  the  back. 
The  distribution  of  the  cutaneous  branches  is  different  in  the  upper  and  lower 
part  of  the  back.  The  uppe7'  six  or  seven  thoracic  nerves  innervate  the  skin  of 
the  scapular  region.  The  internal  cutaneous  branches,  after  passing  backwards  from 
their  origin  among  the  dorsal  muscles,  reach  the  surface  near  the  spines  of  the 
vertebrae  and  are  directed  almost  horizontally  outwards  over  the  vertebral  border 
of  the  scapula.  The  first  is  small ;  the  second  is  very  large  and  reaches  to  the 
acromion  process.  The  rest  diminish  in  size,  from  above  downwards,  and  become 
more  and  more  oblique  in  direction.  The  external  cutaneous  branches  of  the  lovjer 
five  or  six  thoracic  nerves  are  directed  from  their  origin  obliquely  downwards  and 
outwards  among  the  parts  of  the  erector  spinte  muscle.  Becoming  cutaneous  by 
piercing  the  latissimus  dorsi  at  some  distance  from  the  middle  line,  they  supply 
the  skin  of  the  back  in  the  lower  part  of  the  chest  and  loin,  the  lowest  nerves 
(eleventh  and  twelfth)  reaching  over  the  iliac  crest  on  to  the  buttock.  The  lower 
nerves  often  subdivide  into  two  branches  before  or  after  their  emergence  from  the 
latissimus  dorsi  muscle. 

LUMBAR  NERVES. 

First  three  Lumbar  Nerves. — The  posterior  primary  divisions  of  the  first 
three  lumbar  nerves  subdivide  into  internal  and  external  branches,  in  the  same 
way  as  the  lower  thoracic  nerves.  The  internal  branches  are  muscular  and 
innervate  the  deep  muscles  of  the  back.  The  external  branches  are  chiefly 
cutaneous.  They  are  directed  obliquely  downwards  and  outwards  among  the 
fibres  of  the  erector  spinse  and  become  superficial  by  piercing  the  vertebral 
aponeurosis,  just  above  the  iliac  crest  and  a  short  distance  in  front  of  the  posterior 
iliac  spine.  They  are  then  directed  downwards  in  the  superficial  fascia  of  the 
buttock,  and  supply  a  lengthy  strip  of  skin,  extending  from  the  middle  hue  above 
the  iliac  crest  to  a  point  below  and  behind  the  great  trochanter  of  the  femur. 

The  fourth  and  fifth  lumbar  nerves  (like  the  last  two  cervical  nerves)  usually 
supply  only  muscular  branches  to  the  longitudinal  muscles  of  the  back.  The  fifth 
nerve  in  many  cases  sends  a  minute  branch  to  form  a  loop  of  connexion  with  the 
posterior  primary  division  of  the  first  sacral  nerve  (posterior  sacral  plexus). 

SACRAL  AND  COCCYGEAL  NERVES. 

The  posterior  primary  divisions  of  the  sacral  nerves  issue  from  the  posterior 
sacral  foramina.  As  in  the  case  of  the  thoracic  and  lumbar  nerves,  the  upper 
sacral  nerves  differ  from  the  lower  in  their  distribution. 

The  first  three  sacral  nerves  supply  internal  muscular  branches  for  the 
multifidus  spinge,  and  external  cutaneous  branches  which  pierce  the  fibres  of  the 
sacro-sciatic  ligament  and  the  gluteus  maximus  muscle,  and  supply  the  skin  over 


614  THE  NEEVOUS  SYSTEM. 

the  back  of  the  sacrum  and  contiguous  part  of  the  buttock,  giving   rise  to  the 
posterior  sacral  plexus. 

The  posterior  sacral  plexus  consists,  like  the  posterior  cervical  plexus,  of  loops 
or  plexiform  cornmunications  over  the  back  of  the  sacrum  between  the  posterior  primary 
divisions  of  the  first  three  sacral  nerves,  to  which  are  frequently  joined  branches  of  the 
last  lumbar  nerve  and  fourth  sacral  nerve.  From  these  loops  branches  proceed  to 
supply  the  multifidus  spinte  muscle  ;  others,  piercing  the  great  sacro-sciatic  ligament,  form 
secondary  loops  beneath  the  gluteus  maximus  muscle.  From  the  secondary  loops,  two  or 
more  cutaneous  branches  arise,  which,  after  traversing  the  muscle,  supply  the  skin  over 
the  sacrum  and  inner  part  of  the  buttock. 

Posterior  Sacro-coccygeal  Nerve. — The  posterior  divisions  of  the  fourth  and 
fifth  sacral  nerves  do  not  divide  into  internal  and  external  branches.  They  unite 
together  to  form  a  cord  which,  descending  behind  the  coccyx,  receives  the  minute 
posterior  primary  division  of  the  coccygeal  nerve.  The  union  of  the  three  nerves 
constitutes  the  posterior  sacro-coccygeal  nerve,  which,  after  perforating  the  sacro- 
sciatic  ligament,  is  distributed  to  the  skin  in  the  neighbourhood  of  the  coccyx.  It 
supplies  no  muscles.  This  nerve  is  the  representative  of  the  superior  caudal  trunk 
of  tailed  animals. 

Morphology  of  the   Posterior  Primary  Divisions. 

There  are  several  points  of  morphological  interest  in  relation  to  the  posterior  primary 
divisions  of  the  spinal  nerves. 

1.  Muscular  Distribution. — In  their  muscular  distribution  they  are  strictly  limited  to  the 
longitudinal  muscles  of  the  back  :  namely,- those  associated  with  the  axial  skeleton  alone. 

2.  Cutaneous  Distribution. — Their  cutaneous  distribution  represents  two  points  of  interest. 

A.  In  the  first  place,  while  the  skin  of  the  back  is  supplied  in  a  regularly  segmental  manner 
by  the  several  nerves,  certain  of  them  fail  to  reach  the  siuface  at  all.  The  absence  of  a  cutaneous  - 
branch  from  the  sub-occijntal  nerve  may  be  due  either  to  the  absence  of  a  perfect  dorsal  root,  or 
to  its  communication  -with  the  second  nerve.  The  other  nerves,  which  do  not  usually  supply  the 
skin,  are  the  seventh  and  eighth  cervical,  and  the  fourth  and  fifth  lumbar  nerves.  These  nerves 
are  placed  in  the  centre  of  regions  in  which  the  upper  and  lower  limbs  are  developed.  They  are 
minute  nerves,  while  the  corresponding  anterior  primary  divisions  are  among  the  largest  of  the 
spinal  nerves.  Thus,  opposite  the  centre  of  each  limb,  posteriorly,  there  is  a  hiatus  in  the 
segmental  distribution  of  the  posterior  primary  di-\dsions  of  the  spinal  nerves  to  the  skin  of  the 
shoulder  and  buttock,  attributable  to  the  formation  of  the  limbs,  and  the  extension  into 
them  of  the  greater  part  of  the  nerves  of  the  region.  This  gap,  in  the  case  of  the  upper  limb, 
commences  at  the  level  of  the  vertebra  jjrominens  ;  in  the  case  of  the  lower  limb  it  commences 
opposite  the  level  of  the  posterior  superior  iliac  spine.  It  can  be  continued  on  to  each  limb  as 
a  hypothetical  area  (the  dorsal  axial  line),  which  indicates  the  area  of  contact  (and  overlaj)ping) 
of  cutaneous  nerves  not  in  strictly  numerical  sequence.  Thus,  in  the  region  of  the  shoulder,  the 
sixth  (or  fifth)  cervical  nerve  innervates  an  are^  of  skin  adjoining  that  supplied  by  the  first 
thoracic  nerve  ;  in  the  region  of  the  buttock  the  third  lumbar  nerve  supplies  an  area  contiguous 
with  that  supplied  by  the  first  sacral  nerve. 

B.  The  cutaneous  branches  of  the  posterior  primary  divisions  of  the  spinal  nerves  differ  from 
the  muscular  branches  in  respect  of  their  penetration  into  regions  beyond  those  supplied  by 
their  motor  roots.  The  cutaneous  branches,  in  regions  where  outgrowths  or  extensions  from  the 
trunk  have  occuixed,  follow  these  extensions ;  and,  in  consequence,  supply  skin  covering  j)arts 
which  do  not  belong  to  segments  represented  by  the  nerves  in  question.  Thus  the  second  and 
third  cervical  nerves  (great  and  least  occipital)  are  dra'wn  ujjwards  so  as  to  suj^ply  the  posterior 
part  of  the  scalp  ;  the  upper  thoracic  nerves  are  drawn  outwards  over  the  scapular  region ;  the 
upper  lumbar  and  sacral  nerves  supply  the  skin  of  the  buttock ;  and  the  sacro-coccygeal  nerve 
forms  a  rudimentary  caudal  nerve. 

3.  Plexuses. — The  plexuses  formed  by  the  posterior  primary  divisions  of  the  upper 
cervical  and  upper  sacral  nerves  are  the  simplest  met  with  in  the  human  body.  The  posterior 
cervical  jjlexus  is  one  from  wliich  miLScular  branches  are  supplied  ;  the  posterior  sacral  plexus  is 
mainly  concerned  in  producing  cutaneous  offsets.  In  the  case  of  the  posterior  cervical  plexus 
the  loops  of  communication  between  the  finst  three  or  four  cervical  nerves  result  in  the  formation 
of  a  series  of  nerves  for  the  supply  of  the  semispinalis,  complexus,  and  other  muscles,  which 
bring  intrj  contact  witli  these  muscles,  simultaneously,  a  considerable  area  of  the  spinal  cord,  and 
provide  a  comljined  and  simultaneous  innervation  for  the  several  parts  of  each  muscle.  In  the  case 
of  the  posterior  sacral  plexus,  the  formation  of  loops  between  the  nerves  results  in  the  innerva- 
tion of  any  given  spot  in  the  cutaneous  area  supplied  from  these  loops  by  more  than  one  spinal 
nerve.  As  has  been  said  already,  the  cutaneous  nerves,  even  without  the  formation  of  plexuses, 
overlap  in  their  cutaneous  distribution.  The  formation  of  a  plexus  causes  a  more  intimate 
union  of  neigh  1>ouring  spinal  nerves,  so  that  stimulation  of  the  surface  affects  a  wider  area  in 
the  spinal  cord  than  if  the  nerves  passed  separately  to  it  from  the  surface.  While  segmentation 
becomes  less  obvious,  increased  co-ordination  is  effected  both  of  movement  and  sensation. 


AXTEEIOR  PEIMARY  DIVISIONS  OF  THE  SPINAL  NERVES.     615 


ANTERIOR   PRIMARY   DIVISIONS   OF   THE   SPINAL   NERVES. 

The  anterior  prim- 
ary divisions  of  the 
spinal  nerves,  are,  with 
the  exception  of  the 
first  two  cervical 
nerves,  much  larger 
than  the  corresponding 
posterior  primary  divi- 
sions. Composed  of 
elements  of  both  dorsal 
and  ventral  roots,  each 
nerve  separates  from 
the  posterior  primary 
division  on  emerging 
from  the  intervertebral 
foramen,  and,  proceed- 
ing outwards,  is  dis- 
tributed to  structures 
on  the  lateral  and 
anterior  aspects  of  the 
body, — including  the 
limbs. 

Each  nerve  is  joined 
near  its  origin  by  a 
gray  ramus  communi- 
cans  from  the  s}Tn- 
pathetic  gangliated 
cord ;  and  in  the  case 
of  certain  thoracic, 
lumbar,  and  sacral 
nerves,  the  anterior 
primary  division  gives 
off  a  delicate  bundle 
of  fibres,  which  forms 
the  wMte  ramus  com- 
municans  of  the  sym- 
pathetic cord.  That 
part  of  the  spinal  nerve 
which  is  distributed  to 
the  body  wall  and  limbs 
maybe  termed  somatic: 
the  small  white  ramus 
communicans,  in- 
nervating the  struc- 
tures in  the  splanchnic 
area,  may  be  termed  the 

visceral    or    splanchnic      ^^^  489.— The  Distribution  of  Cutaneous  Nerves  on  the  Front  of 
part  ot  the  spmal  nerve.  the  Trunk. 

The  anterior  prim-    On  one  side  the  distribution  of  tlie  several  nerves  is  represented,  the  letters 

ary     divisions      of     the  indicating  their  nomenclature. 

spinal  nerves  are  only,  G.A,  Great  auricular  nerve  ;  S.C,  Superficial  cervical  nerve  ;  S.Cl,  Supra- 
clavicular nerves  ;  AcR,  Acromial  ;  Cl,  Clavicular  ;  St,  Sternal  ;  T.2-12, 
Lateral  and  anterior  branches  of  thoracic  nerves  ;  I.H,  Ilio-h  Jiiogastric  nerve  ;  l.l,  Ilio-inguinal  nerve  ;  CiRC, 
Cutaneous  branch  of  circumflex  nerve  ;  L.I.C,  Lesser  internal  cutaneous  nerve  ;  I.H,  Intercosto-humeral ;  LC, 
Internal  cutaneous  :  M.S.  Cutaneous  branch  of  musculo-spiral  nerve  ;  E.C,  External  cutaneous  nerves  ;  G.C, 
Genito-crural  nerve  ;  M.C'  -,  Middle  cutaneous  nerves  ;  I.C^,  Branch  of  internal  cutaneous  nerve  ;  P.  Branches 
of  pudic  nerve  ;  S.Sc,  Branches  of  small  sciatic  nerve. 

On  the  other  side  a  schematic  representation  is  given  of  the  areas  supplied  by  the  above  nerves,  the  numerals 
indicating  the  spinal  origin  of  the  branches  of  distribution  to  each  area. 


616 


THE  NEEVOUS  SYSTEM. 


in  certain  cases,  distributed  in  a  regular  segmental  manner.  Except  in  the  case  of 
the  thoracic  nerves,  the  anterior  primary  divisions  combine  to  form  the  three  great 
plexuses— cervical,  brachial,  and  lumbo-sacral— and  their  arrangement  and  distribu- 
tion is  rendered  exceedingly  complex. 

A  thoracic  nerve,   such  as  the  fifth  or  sixth,  may  be  regarded  as  a  type  to 

illustrate  the  mode 
'^■^"  of    distribution    of 

the  anterior  primary 
divisions    of    the 
spinal  nerves  (Fig. 
486,    p.    609).      It 
occupies    an    inter- 
costal  space ;    near 
its  origin  it  possesses 
gray  and  white  rami 
■  communicantes ;     it 
courses  through  the 
interval  between  the 
intercostal  muscles ; 
it  supplies  branches 
to     these     muscles 
and  gives  off,  when 
it  reaches  the  side 
of  the  chest, a  lateral 
branch,  which,  after 
supplying    small 
muscular   branches, 
pierces  the  external 
intercostal    muscle, 
and    is    distributed 
to  an  area  of  skin 
over  the  lateral  part 
of  the  trunk,    con- 
tiguous   dorsally 
with  a  similar  area, 
innervated   by   the 
cutaneous  branches 
of      the     posterior 
primary  division  of 
the    same    nerve. 
The  lateral  branch 
generally  subdivides 
into  a  smaller  pos- 
terior  and  a  larger 
anterior  trunk,  as  it 
pierces  the  muscles 
clothing  the  wall  of 
the  chest.     The  an- 
terior primary  divi- 
sion  of    the   nerve 
then     pursues     its 
course  obliquely  for- 
wards to  the  side  of 
the  sternum,  where, 
after    piercing    the 
pectoral  muscles,  it 

appears  superficially  as  the  anterior  terminal  cutaneous  branch.  This  supplies  an  area, 
of  skin  continuous  with  that  supplied  by  the  anterior  part  of  the  lateral  branch  of 
the  same  nerve.     Such  a  nerve  thus  supplies,  by  means  of  its  lateral  and  anterior 


STA 


FfG. 


Superficial  Division. 


Ascending  branches  (Asc.) — 
S.O.  Small  occipital. 
G.A.  Great  auricular. 
S.C.    Superficial  cervical. 

Descending  (supra-clavicular)  branches 
(Desc.)— 
Acr.   Acromial. 
CI.      Clavicular. 
St.      Sternal. 

Deep  Division. 

External  branches — 

Communicating  (C.)  to  spinal  acces- 
sory nen'e  (Sp.  Ace). 

Muscular — 

S.M.       Sterno-mastoid. 

Tr.         Trapezius. 

L.A.S.  Levator  anguli  scapuhc. 

Sc.M.    Scalenus  medius. 


490. — The  Cervical  Plexus. 

Internal  branches- 
Communicating  to 


Hy. 
Va. 

sy. 

D.Cerv. 

Muscular- 
Mi. 


Hypoglossal. 
Vagus. 

Sympathetic  ganglion 
Descenden.s  cervicis. 


Sc.A. 

Phr. 

G.Hy. 

Tli.Hy. 

D.Hy. 

Ansa. 

S.Th. 

S.Hy. 

O.Hy. 


Rectus  eapiti.s  anticus  minor, 

and  lateralis. 
Longus    colli,    and    rectus 

capitis  anticus  major. 
Scalenus  anticus. 

Phrenic  nerve. 
Nerve  to  genio-hyoid. 
Nerve  to  thyro-hyoid. 
Descendens  hy])oglo.s.si. 
Ansa  hypoglossi. 
Nerve  to  sterno-thyroid. 
Nerve  to  steruo-hyoid. 
Nerves  to  omo-hyoid. 


THE  CERVICAL  PLEXUS.  617 

branches,  an  area  of  skin  which  (with  the  area  supplied  by  the  cutaneous  branch 
of  its  posterior  primary  division)  forms  a  continuous  and  uninterrupted  belt, 
extending  from  the  middle  line  behind  to  the  middle  line  in  front.  The  lateral 
and  anterior  branches  of  the  nerve  innervate  in  their  course  the  intercostal  and  other 
muscles,  to  be  afterwards  mentioned  in  detail. 

CERVICAL   NERVES. 

The  anterior  primary  divisions  of  the  cervical  nerves,  together  with  parts  of  the 
first  and  second  thoracic  nerves,  are  distributed  to  the  head,  neck,  and  upper 
extremity.  The  first  four  cervical  nerves,  by  means  of  the  cervical  plexus,  innervate 
the  neck ;  the  last  four  cervical  nerves,  together  with  a  large  part  of  the  first 
thoracic  nerve,  through  the  brachial  plexus,  supply  the  upper  limb.  The  second 
thoracic  nerve  may  contribute  a  trunk  to  this  plexus,  and  always  assists  in  the 
innervation  of  the  arm. 

THE   CERVICAL    PLEXUS. 

The  anterior  primary  divisions  of  the  first  four  cervical  nerves  are  concerned 
in  forming  the  cervical  plexus.  Each  nerve  emerges  from  the  spinal  canal  behind 
the  vertebral  artery.  Each  is  joined  on  its  emergence  from  the  intervertebral 
foramen,  at  the  side  of  the  vertebral  column,  by  a  gray  ramus  communicans  from  the 
superior  cervical  ganglion  of  the  sympathetic.  In  the  neck  the  cervical  nerves  are 
concealed  by  the  sterno-mastoid  muscle ;  in  front  lies  the  rectus  capitis  anticus 
major,  and  behind  are  the  scalenus  medius,  and  (behind  the  first  or  sub-occipital 
nerve)  the  rectus  capitis  lateralis.  The  cervical  plexus  is  constituted  by  the  com- 
bination of  these  nerves  in  an  irregular  series  of  loops  under  cover  of  the  sterno- 
mastoid  muscle. 

From  these  loops  the  branches  of  distribution  arise,  as  {a)  cutaneous  branches  to 
the  head,  neck,  and  shoulder ;  (&)  muscular  branches  to  the  muscles  of  the  neck  and 
the  diaphragm ;  and  (c)  communicating  branches  to  the  vagus,  spinal  accessory, 
hypoglossal,  and  sympathetic  nerves. 

For  convenience  of  description,  the  nerves  derived  from  the  plexus  may  be 
classified  as  follows : — 

I.  Superficial  (cutaneous)  Branches — 

A.  Ascending  Branches  (C.  2,  3).  B.  Descending  (supra-clavicular)  Branches  (C.  3,  4). 

Small  occipital,  Acromial, 

Great  auricular,  Clavicular, 

Superficial  cervical.  Sternal. 

II.  Deep  (muscular  a^d  communicating)  Branches — 

A.  External  Branches.  B.  Internal  Branches. 

1.  Muscular  branches  to  1.     Muscular  to 

Sterno-mastoid  (C.  2),  Prevertebral  muscles  (C.  1,  2,  3,  4), 

Trapezius  (C.  3,  4),  Infra-hyoid  muscles  (C.  1,  2,  3) 

Levator  anguli  scapulae  (C.  3,  4),  (ansa  hypoglossi), 

Scaleni  (medius  and  posticus)  (C.  3,  4).  Diaphragm  (C.  3,  4)  (phrenic 

2.  Comijfiunicating  branches  to  nerve). 

Spinal  accessory  nerve  (C.  2,  3,  4).  2.  Communicating  branches  to 

Vagus  nerve  (C.  1,  2), 
Hypoglossal  nerve  (C.  1,  2), 
C.  Hypoglossi  (C.  2,  3), 
Sympathetic  (C.  1,  2,  3,  4). 

The  second,  third,  and  fourth  cervical  nerves  are  the  chief  nerves  engaged  in 
forming  the  plexus.  The  first  cervical  nerve  only  enters  into  the  formation  of  a 
small  part — the  internal  portion  of  the  deep  part  of  the  plexus. 

Superficial  Cutaneous  Branches.— These  nerves,  six  in  number,  are  entirely 
cutaneous.     They  radiate  from  the  plexus,  and  appear  in  the  posterior  triangle  of 


618 


THE  NERVOUS  SYSTEM. 


the  neck  at  the  posterior  border  of  the  sterno-mastoid  muscle.  They  are  divisible 
into  two  series,  the  one  ascending :  small  occipital,  great  auricular,  and  superficial 
cervical ;  the  other  descending  (supra-clavicular) :  sternal,  clavicular,  and  acromial. 
Ascending  Branches. — The  small  occipital  nerve  (n.  occipitalis  minor)  is  variable 
in  size  and  is  sometimes  double.  Its  origin  is  from  the  second  and  third  cervical 
nerves  (more  rarely  from  the  second  only).  It  extends  backwards  beneath  the 
sterno-mastoid,  and  then  upwards  along  its  posterior  border.  Piercing  the  deep 
fascia  near  the  apex  of  the  posterior  triangle,  it  divides  into  auricular,  mastoid,  and 

occipital  branches,  and  supplies  small 
cervical  branches  to  the  upper  part 
of  the  neck.  The  auricular  branch 
supplies  the  skin  of  the  deep  surface 
of  the  pinna ;  the  mastoid  and  occipital 
branches  supply  the  scalp.  The  nerve 
communicates  on  the  scalp  with  the 
great  occipital  and  great  auricular 
nerves,  and  with  the  posterior  auricular 
branch  of  the  facial  nerve. 

The  great  auricular  nerve  (n.  auri- 
cularis  magnus)  is  the  largest  of  the 
cutaneous  branches.  It  arises  from 
the  second  and  third  cervical  nerves 
(or,  more  rarely,  from  the  third  alone). 
Winding  round  the  posterior  border 
of  the  sterno-mastoid  muscle, it  courses 
vertically  upwards  towards  the  ear. 
In  this  course  it  crosses  the  sterno- 
mastoid  muscle  obliquely  and  is 
covered  by  the  platysma  myoides. 
Before  arriving  at  the  ear  it  subdivides 
into  mastoid,  auricular,  and  facial 
branches.  The  mastoid  branches  ascend 
over  the  mastoid  process  and  supply 
the  skin  of  the  scalp  behind  the  ear, 
communicating  with  the  small  oc- 
cipital and  posterior  auricular  nerves. 
The  auricular  branches  ascend  to  the 
ear  and  supply  the  lower  part  of  the 

Ophth,  Ophthalmic  division  of  the  fifth  nerve  ;  S.T,  Supra-  pinna  On  both  aspectS  ;  they  COm- 
trochlear  branch  ;  S.O,  Supra-orbital  branch  ;  I.T, 
Infra-trochlear  branch  ;  L,  Lachrymal  branch  ;  N, 
External  nasal  Vjranch-;  Sup.  Max,  Superior  maxillary 
division  ;^  T,  Temporal  branch  ;  M,  Malar  branch  ; 
I.O,  Infra-orbital  Vjranch  ;  Inf.Max,  Inferior  maxillary 

division;  A.T    Auriculo-temporal  branch  ;  B,  Buccal    ^f   ^j^g  ^.j^eck  OVCr    the    iVwer    part    of 
branch  ;  M,  Mental  branch  ;  C.2,  3,  Branches  of  the      ,  i      i  •  i 

second  and  third  cervical  nerves  ;  G.O,  Great  occipital    the   masseter  muscle  and  the  parotid 
nerve;     S.O,    Small    occipital    nerve;     G.A,    Great    gland.  They      communicate      with 

branches  of  the  facial  nerve  in  the 
parotid  gland. 

The  superficial  cervical  nerve  (n. 
cutaneus  colli)  arises  from  the  second  and  third  cervical  nerves.  It  winds  round 
the  posterior  Ijorder  of  the  sterno-mastoid  muscle,  and  crosses  the  muscle  to  reach 
the  anterior  triangle,  under  cover  of  the  platysma  myoides  muscle  and  the  external 
jugular  vein.  It  divides  near  the  anterior  edge  of  the  sterno-mastoid  muscle  into 
upper  and  lower  branches,  which  are  distributed  through  the  platysma  myoides  to 
the  skin  covering  the  anterior  triangle  of  the  neck.  The  upper  branches  com- 
municate freely  beneath  the  platysma  myoides  with  the  infra-mandibular  branch  of 
the  facial  nerve. 

Descending  (supra-clavicular)  Branches. — By  the  union  of  two  roots  derived 
from  the  third  and  fourth  cervical  nerves  a  considerable  trunk  is  formed,  which 


Fig.  491. — Distribution  of  Cutaneods  Nerves  to 
THE  Head  and  Neck. 


municate  with  the  same  nerves.  The 
facial  branches,  passing  over  the  angle 
of  the  jaw  and  through  the  substance 
of  the  parotid  gland,  supply  the  skin 


auricular  nerve  ;  S.C,  Superficial  cervical  nerve  ;  C.3, 
Least  occipital  nerve ;  4,  5,  6,  Posterior  primary 
divisions  of  4tli,  5th,  and  6th  cervical  nerves. 


THE  CERVICAL  PLEXUS. 


619 


emerges  from  under  cover  of  the  sterno-mastoid  muscle  and  extends  obliquely 
downwards  tlirough  the  lower  part  of  the  posterior  triangle  of  the  neck.  It  sub- 
divides into  radiating  branches — sternal,  clavicular,  and  acromial — which  pierce  the 
deep  fascia  of  the  neck  above  the  clavicle,  and  are  distributed  to  the  skin  of  the 
lower  part  of  the  side  of  the  neck,  the  front  of  the  chest,  and  the  slioulder.  The 
sternal  branches  (rami  supra-sternales)  are  the  smallest.  Passing  over  the  inner 
end  of  the  clavicle,  they  supply  the  skin  of  the  neck  and  chest  as  far  down  as 
the  manubrio-sternal  joint.  The  clavicular  branches  (rr.  supra-claviculares)  pass 
over  the  middle  third  of  the  clavicle,  beneath  the  platysma,  and  can  be  traced 


Great  occipita 
nerve 

Small  occipital 
nerve 

Great  auricular 
nerve 

Nerves  to  levator 
anguli  seapulse' 


Snperticial  cervical 
nerve 

Spinal  accessory 
Nerve  to  trapezius 


Posterior  scapular 
nerve 

Posterior  thoracic 
nerve 


Internal  laryn- 
geal nerve 


Fig.  492. — The  Triangles  of  the  Neck  (Nerves). 

as  low  as  the  nipple.  The  acromial  branches  (rr.  supra-acromiales)  pass  over  or 
through  the  insertion  of  the  trapezius  muscle,  and  over  the  outer  third  of  the 
clavicle,  to  the  shoulder,  where  they  supply  the  skin  as  far  down  as  the  lower  third 
of  the  deltoid  muscle. 

Deep  Branches. — The  deep  branches  of  the  cervical  plexus  are  naturally 
separated  into  an  external  and  an  internal  set  by  their  relation  to  the  sterno-mastoid 
muscle.  Beneath  the  muscle,  the  external  branches  are  directed  outwards  towards 
the  posterior  triangle,  the  internal  branches  inwards  towards  the  anterior  triangle. 

The  external  branches  consist  of  muscular  and  communicating  nerves,  which 
for  the  most  part  occupy  the  posterior  triangle. 

The  muscular  branches  are  the  following :  (1)  To  the  sterno-mastoid,  from  the 
second  cervical  nerve.     This  enters  the  muscle  on  its  deep  surface  and  communicates 


620 


THE  NEKVOUS  SYSTEM. 


with  the  spinal  accessory  nerve.  (2)  To  the  trapezius,  from  the  third  and  fourth 
cervical  nerves.  These  nerves  cross  the  posterior  triangle  and  end  in  the  trapezius, 
after  ha^dng  communicated  with  the  spinal  accessory  nerve,  in  the  posterior  triangle, 
and  beneath  the  muscle.  (3)  To  the  levator  anguli  scapulm,  from  the  third  and 
fourth  cervical  nerves.  Two  independent  branches  enter  the  outer  surface  of  the 
muscle  in  the  posterior  triangle.  (4)  To  the  scaleni  (medius  and  posticus),  from 
the  third  and  fourth  cervical  nerves. 

The  communicating  branches,  already  mentioned,  are  three  in  number.     They 


HyPOGLOSSAI,  NEBVli         VaGUS  NERVE 

Recurrent  branch     |       |      Superior  cervical  ganglion  of  the  syinx)atlietic 


First  cervical  nerve 


Second  cervical  nerve 


Glorro-pharyngeal 
nerve 


Third  cervical  nerve 
Stylopharyngeu: 


Pharyngeal  branxo  of  vagus 

Digastric 

Descendens  hypoglossi 

Middle  constrictor 

Descendens  cervicis 

Internal  laryngeal  neeve 
Ansa  hypoglossi 

Inferior  constrictor 


t)nio-hyoid 


Hyoglossus 
Genio-hyoglossns 

Genio-hyoid 
Mylo-hj-oid  (cut) 
Digastric 

Thyro-hyoid 


Fig. 


493. — The  Muscles  of  the  Htoid  Bone  and  STyLOiD  Process,  and  the  Extrinsic  Muscles  ok 
THE  Tongue,  with  thkir  Nerves. 


join  the  spinal  accessory  nerve  in  three  situations : — («)  A  branch  from  the  second 
cervical  nerve  to  the  sterno-mastoid  joins  the  spinal  accessory  nerve  beneath  that 
muscle,  (b)  Branches  to  the  trapezius  from  the  third  and  fourth  nerves  are  con- 
nected with  the  spinal  accessory  nerve  in  the  posterior  triangle,  (c)  Branches  from 
the  same  nerves  join  the  spinal  accessory  nerve  beneath  the  trapezius  muscle. 

The  internal  branches  of  the  plexus  also  comprise  muscular  and  communi- 
cating branches.  The  first  cervical  nerve  assists  in  the  formation  of  this  series  of 
nerves,  forming  a  slender  loop  with  part  of  the  second  nerve  in  iront  of  the  trans- 
verse process  of  the  atlas. 

Communicating  Branches.  (a)  With  the  sympathetic. — Gray  rami  communi- 
cantes  pass  to  each  of  the  first  lour  cervical  nerves,  near  their  origins,  from  the 


PHEENIC  NEKVE.  621 

superior  cervical  ganglion  or  from  the  cord  below  the  ganglion,  (b)  With  the 
pneumogastric  nerve. — The  ganglion  of  the  trunk  of  the  pneumogastric  nerve  may 
be  connected  by  a  slender  nerve  with  the  loop  between  the  first  two  cervical  nerves. 
This  communication  is  not  constant,  (c)  With  the  hypoglossal. — An  important 
communication  occurs  between  the  hypoglossal  nerve  and  the  loop  between  the  first 
and  second  cervical  nerves  (Fig.  493).  A  trunk  from  the  last-named  nerves  joins  the 
hypoglossal  just  beyond  its  exit  from  the  skull.  One  fine  branch  from  this  trunk 
passes  upwards  along  the  hypoglossal  nerve  towards  the  skull  (meningeal  branch). 
The  main  part  of  the  trunk  accompanies  the  hypoglossal  and  separates  from  it  succes- 
sively in  three  nerves  —the  descendens  hypoglossi,  and  the  nerves  to  the  thyro-hyoid 
and  genio-hyoid  muscles.  The  portion  of  the  nerve  which  remains  accompanies  the 
hypoglossal  to  the  muscles  of  the  tongue.  It  is  probable  that  no  part  of  the  hypo- 
glossal nerve  itself  is  concerned  in  the  formation  of  these  three  branches.  The 
descending  branch  of  the  hypoglossal  (r.  descendens  hypoglossi)  descends  in  front  of 
the  common  carotid  artery,  and  is  joined  in  the  anterior  triangle  of  the  neck  by 
the  descending  cervical  nerve,  to  form  the  ansa  hypoglossi,  from  which  the  infra- 
hyoid muscles  are  innervated.  (The  descending  branch  of  the  hypoglossal,  in  some 
cases,  arises  from  the  pneumogastric  nerve.) 

Muscular  Branches. — The  muscles  supplied  by  the  internal  branches  of  the 
plexus  are  the  prevertebral  muscles,  the  genio-hyoid  and  infra-hyoid  muscles,  and 
the  diaphragm. 

(a)  Prevertebral  Muscles. — 1.  From  the  loop  between  the  first  and  second 
cervical  nerves  a  small  branch  arises,  for  the  supply  of  the  rectus  capitis  lateralis 
and  the  recti  capitis  antici  (major  and  minor).  2.  From  the  second,  third,  and 
fourth  nerves  small  branches  supply  the  inter- trans versales,  longus  colli,  and  rectus 
capitis  anticus  major.  3.  From  the  fourth  nerve  a  branch  arises  for  the  upper  part 
of  the  scalenus  anticus. 

(b)  G-enio-hyoid  and  Infra-hyoid  Muscles. — The  descending  cervical  nerve  (n. 
cervicaKs  descendens)  is  formed  in  front  of  the  internal  jugular  vein  by  the  union 
of  two  slender  trunks  from  the  second  and  third  cervical  nerves.  It  forms  a  loop 
of  communication  in  front  of  the  carotid  sheath  with  the  descending  branch  of  the 
hypoglossal  nerve  (derived  ultimately  from  the  first  two  cervical  nerves).  This 
loop  of  communication  is  called  the  ansa  hypoglossi.  It  is  often  plexiform ;  and 
from  it  branches  are  given  to  the  sterno-hyoid,  sterno- thyroid,  and  omo-hyoid 
muscles.  The  nerve  to  the  sterno-hyoid  muscle  is  often  continued  behind  the 
sternum,  to  join  in  the  thorax  with  the  phrenic  nerve  or  the  cardiac  plexus. 

The  thyro-hyoid  muscle  and  the  genio-hyoid  muscle  are  supplied  by  branches  of 
the  hypoglossal  nerve,  which  are  also  traceable  back  to  the  communication  between 
the  hypoglossal  and  the  first  two  cervical  nerves. 

The  anterior  muscles  in  immediate  relation  to  the  middle  line  of  the  neck, 
between  the  chin  and  the  sternum,  are  thus  continuously  suppHed  by  the  first 
three  cervical  nerves.  The  hypoglossal  is  the  nerve  of  the  muscles  of  the  tongue, 
and  it  is  not  certain  that  it  contributes  any  fibres  to  the  above-named  muscles. 

(c)  Diaphragm. — The  phrenic  nerve  supplies  the  diaphragm. 

Phrenic  Neeve. 

The  phrenic  nerve  (u.  phrenicus)  is  derived  mainly  from  the  fourth  cervical 
nerve,  reinforced  by  roots  from  the  third  (either  directly  or  through  the  nerve  to 
the  sterno-hyoid)  and  fifth  (either  directly  or  through  the  nerve  to  the  subclavius 
muscle).  It  passes  downwards  in  the  neck  upon  the  scalenus  anticus  muscle ;  at 
the  root  of  the  neck  it  enters  the  thorax  between  the  subclavian  artery  and  vein, 
and  traverses  the  mediastinum  to  reach  the  diaphragm,  lying  in  the  middle 
mediastinum  between  the  pericardium  and  pleura,  and  in  front  of  the  root  of  the 
lung.  In  its  course  it  presents  certain  differences  on  the  two  sides.  In  the  neck, 
on  the  left  side,  it  crosses  the  first  part  of  the  subclavian  artery :  on  the  right  side 
it  crosses  the  second  part.  In  the  superior  mediastinum,  on  the  left  side,  it  lies 
between  the  left  subclavian  and  carotid  arteries,  and  crosses  the  pneumogastric 
nerve  and  the  aortic  arch.     On  the  right  side  it  accompanies  the  innominate  vein 


622  THE  NEKVOUS  SYSTEM. 

and  superior  vena  cava,  and  is  entirely  separate  from  the  pueumogastric  nerve. 
The  left  nerve  is  longer  than  the  right,  owing  to  the  position  of  the  heart  and  the 
left  half  of  the  diaphragm.  The  right  nerve  sends  fibres  along  the  inferior  vena 
cava  through  the  foramen  quadratum.  Eeaching  the  diaphragm  the  nerve  separates 
into  numerous  branches  for  the  supply  of  the  muscle ;  ■  some  enter  its  thoracic 
surface  (sub-pleural  branches),  but  most  of  the  fibres  supply  it  after  piercing  the 
muscle  (sub-peritoneal  branches). 

The  branches  of  the  phrenic  nerve  are — 1.  Muscular  (to  the  diaphragm) ;  2. 
pleural ;  3.  pericardiac ;  4  inferior  vena  caval ;  5.  capsular ;  and  6.  hepatic. 

The  branches  to  the  pleura  and  pericardium  arise  as  the  phrenic  nerve 
traverses  the  mediastinum.  The  branches  to  the  inferior  vena  cava,  suprarenal 
capsule,  and  liver  arise  after  communication  of  the  phrenic  nerve  with  the 
diaphragmatic  plexus  of  the  sympathetic  on  the  abdominal  surface  of  the 
diaphragm. 

Communications  of  the  Phrenic  Nerve. — 1.  The  phrenic  nerve  may  communicate 
with  the  nerve  to  the  subclavius  muscle.  2.  It  may  communicate  with  the  ansa 
hypoglossi,  or  a  branch  from  it  (the  nerve  to  the  sterno-hyoid).  3.  It  frequently  com- 
municates with  the  cervical  part  of  the  sympathetic.  4.  It  communicates  with  the 
solar  plexus  by  a  junction  upon  the  abdominal  surface  of  the  diaphragm  with  the 
diaphragmatic  plexus  on  the  inferior  phrenic  artery,  in  which  a  small  diaphragmatic 
ganglion  is  found  on  the  right  side.  From  this  junction  branches  are  given  off  to  the 
inferior  vena  cava,  suprarenal  capsule,  and  hepatic  plexus. 

Morphology  of  the  Cervical  Plexus. 

The  characteristic  feature  of  the  cervical  plexus  is  the  combination  of  parts  of  adjacent  nerves 
into  compound  nerve -trunks  by  the  formation  of  series  of  loops.  The  result  of  the  formation  of 
these  loops  is  that  parts  (particularly  cutaneous  areas)  are  supplied  by  branches  of  more  than  one 
spinal  nerve. 

A.  Cutaneous  Distribution. — By  the  combinations  of  the  nerves  into  loops  the  discrimination 
of  the  elements  in  the  upper  cervical  nerves,  corresponding  to  the  lateral  and  anterior  branches 
of  a  typical  thoracic  nerve,  is  made  a  matter  of  some  difficulty.  The  second,  third,  and 
fourth  nerves,  through  the  cervical  plexus,  supply  an  area  of  skin  extending,  laterally,  from  the 
side  of  the  head  to  the  shoulder ;  anteriorly,  from  the  face  to  the  level  of  the  nipple.  The  higher 
nerves  supply  the  upjDer  region  (second  and  third) ;  the  lower  nerves  supply  the  lower  region 
(third  and  fourth).  It  is  not  possible  to  strictly  compare  the  individual  nerves  with  the  lateral 
and  anterior  branches  of  a  thoracic  nerve.  A  line  drawn  from  the  ear  to  the  middle  of  the 
clavicle  separates,  however,  a  lateral  from  an  anterior  cutaneous  area ;  and  certain  of  the 
cutaneous  nerves  fall  naturally  into  one  of  these  two  categories.  The  nerves  homologous  with 
anterior  branches  of  intercostal  nerves  are  the  superficial  cervical  and  the  sternal  branches  of 
the  supra-clavicular  series ;  those  homologous  with  lateral  branches  are  the  small  occipital  and 
acromial  branches.  The  great  auricular  and  clavicular  branches  are  mixed  nerves,  comprising 
elements  belonging  to  both  sets. 

B.  Muscular  Distribution. — The  nerves  from  the  cervical  plexus,  sujjplying  muscles,  are 
simpler  in  their  arrangement.  They  are  not  generally  in  the  form  of  loops,  and  they  are  easily 
separated  into  latei'al  and  anterior  series.  The  lateral  nerves  comprise  the  branches  to  the 
rectus  capitis  lateralis,  sterno-mastoid,  trajjezius,  levator  anguli  scapulae.  The  nerves  in  the 
anterior  series  are  those  to  the  recti  antici,  the  hj'-oid  muscles,  and  the  diaphragm. 

It  is  noteworthy  that  the  last-named  muscles — genio-hyoid,  thyro-hyoid,  sterno-hyoid,  omo- 
hyoid, sterno-thyroid,  and  diaj^hragm — are  continuously  supj)lied  by  branches  from  the  first  five 
cervical  nerves  :  tlie  higlier  muscles  by  the  higher  nerves  ;  the  lower  muscles  by  the  lower  nerves. 


THE   BRACHIAL   PLEXUS. 

The  brachial  plexus  is  formed  by  the  anterior  primary  divisions  of  the  fifth, 
sixth,  seventh,  and  eighth  cervical  nerves,  along  with  the  greater  part  of  the  first 
thoracic  nerve.  In  some  cases  a  slender  branch  of  the  fourth  cervical  nerve  is  also 
engaged ;  and  the  second  thoracic  nerve,  in  all  cases,  also  contributes  to  the 
innervation  of  the  arm,  through  the  intercosto-humeral  nerve.  It  many  cases  it 
contributes  also  directly  to  the  plexus,  by  an  intra-thoracic  communication  with 
tlie  first  thoracic  nerve. 

Position  of  the  Plexus. — The  nerves  forming  the  brachial  plexus  appear  in 
the    posterior   triangle  of   the  neck   between   the  scalenus  anticus  aud  scalenus 


THE  BKACHIAL  PLEXUS. 


623 


inedius  muscles ;  the  plexus  is  formed  in  close  relation  to  the  subclavian  and 
axillary  arteries  ;  the  nerves  emanating  from  it  accompany  the  artery  to  the  axilla, 
where  they  are  distributed  to  the  shoulder  and  upper  limb. 

Communication  with  the  Sympathetic. — The  lower  four  cervical  nerves  counnunicate 
with  the  cervical  portion  of  the  sympathetic  by  means  of  gray  rami  communicantes. 
Two  branches  arise  from  the  middle  cervical  ganglion,  and  join  the  anterior  primary 
divisions  of  the  fifth  and  sixth  nerves.  Two  arising  from  the  inferior  cervical  ganglion 
join  the  seventh  and  eighth  nerves.  They  reach  the  nerves  either  by  piercing  the 
prevertebral  nmscles  or  by  passing  round  the  border  of  the  scalenus  anticus  muscle. 

Composition  of  the  Brachial  Plexus. — In  an  analysis  of  the  brachial  plexus 
four  stages  may  be  always  seen  : — 
(1)  The  undivided  nerves. 


Fig.  -494. — The  Nerves  of  the  Brachial  Plexus. 

Sy,  Synipatlietic  gaugliated  cord  ;  Phr,  Phrenic  nerve  ;  C.4,  5,  6,  7,  8,  T.l,  2,  3,  Anterior  primary  divisions  of  tlie 

lower  cervical   and  upper  thoracic  nerves  ;  M^,  M"^,  Muscular  branches  to  axial  muscles  ;  P.  T,  Long 

thoracic  nerve  ;  Rh,   Nerve  to  rhomboids  (posterior  scapular)  ;    Subcl,  Nerve  to  subclavius  muscle  ; 

Jut,   Intercostal  nerves  ;  S.Sc,  Supra-scapular  nerve.     The  intercostal  part  of  the  first  thoracic  nerve 

is  omitted. 
Outer  Cord. — E.A.  T,  External  anterior  thoracic  nerve  ;  M.C,  Musculo-cutaneous  nerve  ;  Cb,  Nerve  to  coraco- 

brachialis  ;  M,  Median  nerve. 
Inner  Cord. — I.A.T,  Internal  anterior  thoracic  nerve  ;  U,  Ulnar  nerve  ;  I.C,  Internal  cutaneous  nerve  ;  L.I.C, 

Lesser  internal  cutaneous  nerve. 
Posterior  Cord. — Circ,  Circumflex  nerve  ;  M.S,  Musculo-spiral  nerve;  S. Sub,  Short  subscapular  nen-e  ;  M.Sub, 

Lower. subscapular  nerve  ;  L.Sub,  Long  subscapular,  nerve  ;  l.H,  lutercosto-humeral  nerve  ;  Lat,  Lateral 

brancli  of  third  intercostal  nerve. 

(2)  The  separation  of  the  nerves  into  ventral  (anterior)  and  dorsal  (posterior) 

trunks ;  and  the  formation  of  three  primary  cords. 

(3)  The  formation  of  three  secondary  cords — outer,  inner,  and  posterior. 

(4)  The  origin  of  the  nerves  of  distribution. 

(1)  The  undivided  nerves  have  only  a  very  short  independent  course  a,t  the  side 
of  the  neck,  after  passing  between  the  scalene  muscles. 

(2)  Almost  immediately  after  entering  the  posterior  triangle  there  are  formed 
three  primary  cords  :  the  first  cord  is  formed  by  the  union  of  the  fifth  and  sixth 
nerves  together ;  the  second,  by  the  seventh  nerve  alone ;  and  the  third,  by  the 
union  of  the  eighth  cervical  and  first  thoracic  nerves  together.  While  these  cords 
are  being  formed,  a  division  occurs  in  each  of  the  last  four  cervical  nerves,  into 
ventral  (anterior)  and  dorsal  (posterior)  trunks ;  the  first  thoracic  nerve  usually 
gives  rise  to  no  dorsal  trunk.     The  ventral  and  dorsal  trunks  of  the  fifth,  sixth. 


624  THE  NEEVOUS  SYSTEM. 

and  seventh  nerves  are  nearly  equal  in  size.     The  dorsal  trunk  of  the  eighth 
cervical  nerve  is  much  smaller. 

(3)  The  secondary  cords  of  tlie  plexus  are  formed  by  combinations  of  these 
ventral  and  dorsal  trunks  in  relation  to  the  axillary  artery.  They  are  three  in 
number.  The  outer  cord  (fasciculus  laterahs)  is  formed  by  a  combination  of  the 
ventral  trunks  of  the  fifth,  sixth,  and  seventh  nerves,  and  lies  on  the  outer  side  of 
the  axillary  artery.  The  inner  cord  (fasciculus  medialis)  is  formed  by  a  combination 
of  the  ventral  trunk  of  the  eighth  cervical  with  the  part  of  the  first  thoracic 
nerve  engaged  in  the  formation  of  the  plexus ;  it  lies  on  the  inner  side  of  the 
axillary  artery.  The  posterior  cord  (fasciculus  posterior)  is  made  up  of  all  the 
dorsal  trunks  from  the  fifth,  sixth,  seventh,  and  eighth  cervical  nerves,  and  lies 
behind  the  axillary  artery.  The  first  thoracic  nerve  does  not  usually  contribute  to 
the  posterior  cord,  and  the  branch  when  present  is  a  fine  nerve. 

(4)  The  nerves  of  distribution  for  the  shoulder  and  arm  are  derived  from  these 
secondary  cords,  and  receive  in  this  way  various  contributions  from  the  constituent 
spinal  nerves.  From  the  outer  cord  arise  the  external  anterior  thoracic  and  musculo- 
cutaneous nerves,  and  the  outer  head  of  the  median  nerve.  From  the  inner  cord 
arise  the  inner  head  of  the  median,  the  ulnar,  internal  cutaneous,  lesser  internal 
cutaneous,  and  the  internal  anterior  thoracic  nerves.  From  the  -posterior  cord  arise 
the  circumflex,  the  three  subscapular,  and  the  musculo-spiral  nerves. 

It  is  to  be  remembered  tbat,  although  derived  from  a  secondary  cord  formed  by  a  certain 
set  of  spinal  nerves,  any  given  nerve  does  not  necessarily  contain  fibres  from  all  the  constituent 
nerves ;  exj.  both  the  musculo -cutaneous  and  circumflex  nerves,  from  the  outer  and  jjosterior 
cords  respectively,  are  ultimately  derived  only  from  the  fifth  and  sixth  cervical  nerves. 

The  Branches  of  the  Brachial  Plexus. 

It  is  customary  to  separate  artificially  the  nerves  of  distribution  of  the  brachial 
plexus  into  two  sets :  (1)  supra-clavicular  and  (2)  infra-clavicular.  Clinically  it  is 
important  to  realise  the  position  of  origin  of  certain  nerves.  The  nerves  to  the 
prevertebral  muscles,  the  communication  with  the  phrenic,  the  posterior  scapular, 
and  long  thoracic  nerves,  arise  from  the  roots  of  the  nerves  involved  in  the  plexus. 
The  supra-scapular  and  the  nerve  to  the  subclavius  arise  at  the  level  of  formation  of 
the  secondary  cords ;  and  the  anterior  thoracic  and  subscapular  nerves  arise  from  the 
secondary  cords,  prior  to  their  ultimate  subdivision  into  the  nerves  of  distribution 
for  the  upper  limb. 

Supra-clavicular  Nerves. — The  nerves  derived  from  the  plexus  above  the 
level  of  the  clavicle  are,  like  the  main  trunks,  divisible  into  two  series ;  anterior 
branches  arising  from  the  front,  and  posterior  branches  arising  from  the  back  of  the 
plexus  (Fig.  494,  p.  623). 

Anterior  Branches.  Posterior  Branches. 

1.  Xerves  to  scalenus  anticus  and  1.   Nerves  to  scaleni,  medius  and 

longus  colli.  posticus. 

2.  Communicating  nerve  to  join  2.   Posterior  scapular  nerve. 

the  phrenic  nerve.  3.   Long  thoracic  nerve. 

3.  Nerve  to  the  subclavius  muscle.  4.   Supra-scapular  nerve. 

The  muscular  twigs  to  the  scalenus  anticus  and  longus  colli  arise  from  the  lower 
four  cervical  nerves,  as  they  emerge  from  the  intervertebral  foramina. 

The  communicating  nerve  to  the  phrenic  arises  usually  from  the  fifth  cervical 
nerve  at  the  outer  border  of  the  scalenus  anticus.  It  is  sometimes  absent,  and 
occasionally  an  additional  root  is  present  from  the  sixth  cervical  nerve.  In  some 
instances  the  nerve  is  replaced  by  a  branch  from  the  nerve  to  the  subclavius, 
which  passes  inwards  behind  the  sterno-mastoid  muscle  to  join  the  phrenic  at  the 
inlet  of  the  thorax. 

The  nerve  to  the  subclavius  is  a  slender  nerve,  which  arises  from  the  front  of 
the  cord  formed  by  the  fifth  and  sixth  cervical  nerves.  It  descends  in  the  posterior 
triangle  of  the  neck  over  the  third  part  of  the  subclavian  artery.  It  often  com- 
municates with  the  phrenic  nerve. 


THE  ANTEEIOR  THORACIC  NERVES. 


625 


Outer 


Cord 


The  branches  to  the  scaleni,  medius  and  posticus,  are  small  trunks  which  arise 
from  the  lower  four  cer\acal  nerves  as  they  emerge  from  the  intervertebral  foramina. 

The  posterior  scapular  nerve  (n.  dorsalis  scapula?,  nerve  to  the  rhomboids) 
arises  from  the  back  of  the  fifth  cervical  nerve,  as  it  emerges  from  the  interverteliral 
foramen.  It  appears  in  the  posterior  triangle  of  the  neck,  after  piercing  the 
scalenus  medius  muscle.  It  is  directed  downwards,  under  cover  of  the  levator 
anguli  scapulae  and  rhomboid  muscles,  and  along  the  vertebral  border  of  the 
scapula,  to  be  distributed  to  the  levator  anguli  scapuhe,  rhomboideus  minor,  and 
rhomboideus  major  muscles.     It  occasionally  pierces  the  levator  anguli  scapula?. 

The  long  thoracic  nerve  (n.  thoracalis  longus,  external  respiratory  nerve  of 
Bell)  arises  by  three  roots,  of  which  the  middle  one  is  usually  the  largest,  from  the 
back  of  the  fifth,  sixth,  and  seventh  nerves,  as  they 
emerge  from  the  intervertebral  foramina.  The  nerve 
pierces  the  scalenus  medius  as  two  trunks,  of  which 
the  lower  represents  the  contribution  from  the  seventh 
cervical  nerve,  and,  descending  along  the  side  of  the 
neck  behind  the  cords  of  the  brachial  plexus,  it 
enters  the  axilla  between  the  upper  edge  of  the 
serratus  magnus  and  the  axillary  artery.  It  con- 
tinues its  downward  course  over  the  outer  surface 
of  the  serratus  magnus,  to  which  it  is  distributed. 

Tliere  is  a  more  or  less  definite  relation  between  the  roots 
of  this  nerve  and  the  parts  of  the  serratus  niagnns.  The  first 
part  of  tlie  muscle  is  innervated  by  the  fifth  nerve  alone  ; 
the  second  part  by  the  fifth  and  sixth,  or  the  sixth  alone  ; 
the  third  itart  by  the  sixth  and  seventh,  or  the  .seventli 
nerve  alone. 

The  suprascapular  nerve  (n.  suprascapularis) 
arises  from  the  l)ack  of  the  cord  formed  by  the 
fifth  and  sixth  cervical  nerves  in  the  posterior 
triangle  of  the  neck.  It  occupies  a  position  aboye 
the  main  cords  of  the  brachial  plexus,  and  courses 
downwards  and  outwards  parallel  to  them  towards 
the  superior  l:»order  of  the  scapula.  It  passes  through 
the  suprascapular  foramen  to  reach  the  dorsum  of 
the  scapula.  After  supplying  the  supraspinatus 
muscle  it  winds  round  the  great  scapular  notch  in 
compaiiiy  with  the  suprascapular  artery  and  terminates 
in  the  infraspinatus  muscle.  It  also  suppKes  articular 
branches  to  the  l)ack  of  the  shoulder  joint. 

Infra -clavicular  Nerves. —The  so-called  infra -clavicular  branches  of  the 
brachial  plexus  are  distributed  to  the  chest,  shoulder,  and  arm.  According  to 
tlieir  origin  they  are  divisible  into  two  sets — an  anterior  set,  derived  from  the 
outer  and  inner  cords,  and  a  posterior  set,  derived  from  the  posterior  cord.  In 
their  distribution  the  same  division  is  maintained.  The  anterior  nerves  of 
distributioii,  springing  from  the  outer  and  inner  cords,  supply  generally  the  chest 
and  the  front  of  the  limb ;  the  posterior  nerves,  springing  from  the  posterior  cord, 
supply  the  shoulder  and  the  back  of  the  limb. 

Anterior  Branches. 
Nerves  from  the  Outer  Cord. 

External  anterior  thoracic.  Outer  head  of  median.  Musculo-cutaneous. 

Nerves  from  the  Inner  Cord. 

Internal  anterior  thoracic.  Ulnar.  Inner  laead  of  median. 

Intei'ual  cutaneous.  Lesser  internal  cutaneous. 


Fig.  49.">. — DiAtatAM  of  the  oricin 
AND  Distribution  ok  the  Nerves 
to  the  Pectoral  Muscles. 

E.A.T.  Exterual  anterior  thoracic  nerve  ; 
I.A.T,  Internal  anterior  thoracic 
nerve  ;  C.5,  6,  7,  C.S,  T.l,  Nerves  of 
the  brachial  plexus  ;  Art,  Axillary 
artery  ;  Cl,  Clavicle  ;  ScL,  Sub- 
clavius  muscle  ;  P.  Mi,  Pectoralis 
minor,  joined  to  subclavius  by 
costo-coracoid  membrane  :  P.Ma, 
Pectoralis  major. 


Circumflex. 
44 


Posterior    Branches. 
Nerves  from  the  Posterior  Cord. 

Musculo-spiral.  Three  subscapular  nerves. 


626 


THE  NERVOUS  SYSTEM. 


Anterior  Thoracic  Nerves. 

The  anterior  thoracic  nerves  (nn.  thoracicales  anteriores)  are  two  in  number, 
external  and  internal.     The  external  anterior  thoracic  nerve  arises  from  the  outer 


Trapezia 
Clavicle  (cuf; 

Coraco-claviuular  ligaments. 
Pectoralis  iiiinoi 
Coracoid  process' 
Coraco-acromial  ligament 

Circunirtex  arterysi^^ 

Circumflex  nerve 


^L'PRASCAFULAR  NERVE 


Pectoralis  major 
Coraco-bracliialis  ,,^ 


Biceps 


Posterior  cord  of  brachial 

LExrs 
Short  scbscapular  nerve 

Long  subscapular  nerve 
Lower  subscapular  nerve 

Serratns  inagnus 
Dorsal  scapular  artery 
Subscapularis 

.Teres  major 


Latissimus  ilorsi 


Internal 
cutaneous  branch 
of  musculo-spiral 

NERVE 


Triceps  (long  head) 

Nerve  to  inner  head  of 
TRICEPS  (ulnar  collateral) 


Muscu  i.o-cutaneous 

NERVE 


MUSCOLO-SI'IRAL  NERVE  


Brachio-radialis 

Biceps  (cut) 

Kxteiisor  carpi  radialis 

longior 


Poster 


Supinator  radii  brevis 


Flexor 

profundus 

diRitorum 


Vui.  496. -Thk  Postehioh  Wall  ok  the  Axilla  and  the 
Fkont  ok  the  Arm  (the  biceps  being  divided). 


cord  of  the  brachial  plexus  by  three 
roots — from  the  fifth,  sixth,  and 
seventli  cervical  nerves.  The  in- 
ternal anterior  thoracic  nerve  arises 
from  the  inner  cord  of  the  plexus, 
from  the  eighth  cervical  and  first 
thoracic  nerves.  Each  courses  down- 
wards and  forwards  on  either  side 
of  the  axillary  artery.  A  loop  of 
communication  is  formed  between 
them  over  the  artery.  They  are 
finally  distributed  to  the  pectoralis 
major  and  minor  muscles  (Fig.  495). 

The  nerves  are  distributed  to  the 
pectoral  muscles  in  the  following- 
way  : — Two  sets  of  branches  from  the 
external  anterior  thoracic  nerve  pierce 
the  costo-coracoid  membrane.  The 
upper  branches  supply  the  clavicular 
part  of  the  pectoralis  major  ;  the  lower 
branches  arc  distributed  to  the  upper 
fibres  of  the  sternal  j)ortion  of  the 
nuiscle.  The  upper  branches  come 
from  the  fifth  and  sixth  cervical  nerves; 
the   lower    branches,    from    the    fifth, 


sixth,  and  seventh  nerves.  The  pectoralis  minor  is  pierced  by  two  sets  of  nerves — the 
upper  set  is  derived  from  the  loop  of  communication  between  the  external  and  internal 
anterior  thoracic  nerves  over  the  axilhiry  artery ;  the  lower  set  is  derived  from  the 
internal  anterior  thoracic  nerve  alone.  These  nerves  supply  the  pectoralis  minor  muscle, 
and,  after  piercing  it,  supply  the  stenud  part  (A  the  pectoralis  major.     The  lower  nerve,  in 


MEDIAN  NERVE.  627 

many  cases,  sends  its  branches  to  the  pectoralis  major  round  the  lower  border  of  the 
pectoral  is  minor,  and  it  may  supply  on  its  way  the  axillary  arches,  if  present.  These  two 
branches  are  derived — the  upper  from  the  seventh,  eighth  cervical,  and  first  thoracic 
nerves ;  the  lower  from  the  eighth  cervical  and  first  thoracic  nerves.  The  pectoral 
muscles  are  thus  both  supplied  by  the  two  anterior  thoracic  nerves.  The  clavicular  fibres  of 
the  pectoralis  major  are  innervated  by  the  fifth  and  sixth  nerves ;  the  sternal  fibres,  from 
above  downwards,  by  the  fifth,  sixth,  seventh,  and  eighth  cervical,  and  first  thoracic 
nerves;  and  the  pectoralis  minor  is  supplied  by  the  seventh  and  eighth  cervical,  and 
first  thoracic  nerves. 

MUSCULO-CUTANEOUS    NeRVE. 

The  musculo-cutaneous  nerve  (u.  musculo-cutaneus)  takes  origin  from  the 
outer  cord  of  the  plexus,  from  the  fifth  and  sixth  cervical  nerves  (Fig.  496).  The 
nerve  to  the  coraco-bracliialis  muscle,  arising  from  the  seventh  or  sixth  and  seventh 
nerves,  is  usually  associated  with  it.  Separating  from  the  outer  head  of  the 
median  nerve,  the  musculo-cutaneous  nerve  lies  at  first  between  the  coraco- 
l)rachialis  muscle  and  the  axillary  artery.  It  is  then  directed  downwards  between 
the  two  parts  of  the  coraco- brachial  is,  and  passes  between  the  biceps  and  brachialis 
anticus  muscles,  to  the  bend  of  the  elbow.  In  its  course  it  may  send  a  brancli 
\mder  the  biceps  to  join  the  median  nerve.  It  pierces  the  deep  fascia  over  the 
front  of  the  elbow,  between  the  biceps  and  brachio-radialis,  and  terminates  in 
cutaneous  branches  for  the  supply  of  the  outer  side  of  the  forearm. 

The  branches  of  the  nerve  are  muscular  and  cutaneous.  The  muscular  branches 
are  supplied  to  the  two  heads  of  the  biceps  and  the  brachialis  anticus,  as  the  nerve 
lies  between  the  muscles.  The  nerve  to  the  coraco-brachialis  (usually  incorporated 
with  the  trunk  of  the  musculo-cutaneous  nerve)  has  an  independent  origin  from 
the  seventh  or  sixth  and  seventh  nerves.  It  is  usually  double,  one  branch  entering 
each  portion  of  the  muscle.  The  cutaneous  branches  are  anterior  and  posterior 
(Fig.  497,  p.  628).  The  anterior  branch  descends  along  the  front  of  the  outer  side 
of  the  forearm  to  the  wrist,  and  supplies  an  area  extending  inwards  to  the  middle 
line  of  the  forearm  anteriorly,  and  downwards  so  as  to  include  the  ball  of  the 
thumb.  It  communicates  above  the  wrist  with  th^  radial  nerve,  and  supplies 
branches  to  the  radial  artery.  The  posterior  branch  passes  backwards  and 
downwards  over  the  extensor  muscles  and  supplies  the  skin  on  the  outer  aspect 
of  the  forearm  posteriorly  in  its  upper  three-fourths,  communicating  witli  the 
cutaneous  branches  of  the  musculo-spiral  nerve. 

In  addition  to  the  above  branches,  the  musculo-cutaneous  nerve  supplies  in  many 
cases  the  following  small  twigs  in  the  arm  :  (1)  a  medullary  branch  to  the  humerus  ;  (2) 
a  periosteal  branch  to  the  lower  end  of  the  humerus  on  its  anterior  sui'face ;  and  (3)  a 
branch  to  the  brachial  artery. 

Median  Nerve. 

The  median  nerve  (n.  medianus)  arises  by  two  roots — one  from  the  outer 
cord,  the  other  from  the  inner  cord  of  the  brachial  plexus.  The  outer  head,  from 
the  (fifth),  sixth,  and  seventh  nerves,  descends  along  the  outer  side  of  the  axillary 
artery ;  the  inner  head,  from  the  eighth  cervical  and  first  thoracic  nerves,  crosses 
the  end  of  the  axillary  artery  or  the  beginning  of  the  brachial  artery,  to  join  the  other 
head  in  the  upper  part  of  the  arm.  Descending  along  the  outer  side  of  the  brachial 
*:tery,  the  nerve  crosses  over  it  obliquely  in  the  lower  half  of  the  arm.  In  the 
hollow  of  the  elbow,  it  lies  internal  to  the  brachial  artery,  beneath  the  bicipital 
fascia  and  the  median  basilic  vein.  It  passes  into  the  forearm  between  the  two 
heads  of  the  pronator  radii  teres  muscle,  separated  from  the  ulnar  artery  by  the 
deep  origin  of  that  muscle.  Extending  down  the  middle  of  the  forearm,  between 
the  superficial  and  deep  muscles  to  the  wrist,  it  enters  the  palm  of  the  hand  on  the 
outer  side  of  the  flexor  tendons  of  the  fingers  beneath  the  anterior  annular 
ligament.  In  the  hand  it  spreads  out  at  the  lower  border  of  the  annular  ligament 
beneath  the  palmar  fascia  and  superficial  palmar  arch,  and  separates  into  its  six 
terminal  branches.  In  the  forearm  a  small  artery  accompanies  it, — ^the  comes  nervi 
mediani.  Above  the  wrist  it  is  comparatively  superficial,  lying  on  the  outer  side  of 
the  superficial  flexor  tendons  and  directly  beneath  the  tendon  of  the  palmaris  longus. 


628 


THE  NERVOUS  SYSTEM. 


Communications. — (1)  The  median,  in  some  cases,  receives  a  communicating  branch 
from  the  musculo-cutaneous  nerve  in  the  arm.  (2)  It  communicates  in  some  cases,  in 
the  upper  part  of  the  forearm,  with  the  uhiar  nerve  beneath  the  flexor  muscles.  (3)  It 
communicates  by  means  of  its  cutaneous  branches  with  the  ulnar  nerve  in  the  palm  of 
the  hand. 

Branches.— The  median  uerve  usually  gives  off  no  branches  in  the  upper  arm. 
Branches  in  the  Forearm.— (1)  Articular  Branches.— Minute  articular  filaments 

are   distributed    to   the 
front  of  the  elbow-joint. 

(2)  Muscular  Bran- 
ches.—  Just  below  the 
elbow  a  bundle  of  nerves 
arise  which  is  distributed  . 
to  the  following  muscles: 
pronator  radii  teres, 
flexor  carpi  radialis,  pal- 
maris  longus,  flexor  sub- 
limis  digitorum.  Nerves 
are  also  generally  trace- 
able from  this  bundle  to 
the  upper  fibres  of  the 
flexor  longus  poUicis 
and  flexor  profundus 
digitorum.  The  nerve 
to  the  pronator  radii 
teres  often  arises  inde- 
pendently in  the  hollow 
of  the  elbow. 

(3)  The  anterior  in- 
terosseous nerve  arises 
from  the  back  of  the 
median  nerve  in  the 
forearm,  descends  in 
front  of  the  interosseous 
membrane  along  with 
the  anterior  interosseous 
artery,  passes  behind 
the  pronator  quadratus 
muscle,  and  terminates 
by  supplying  articular 
filaments  to  the  radio- 
carpal articulation.  In 
its  course  the  nerve 
supplies  muscular 
branches  to  the  flexor 
longus  poUicis,  the  outer 
half  of  the  flexor  pro- 
fundus digitorum,  and 
the  pronator  quadratus, 
minute  medullary 
l)ranches  to  the  radius 
and  ulna,  and  twigs  to 
the  periosteum  and  in- 
terosseous membrane. 

(4)  Palmar  Cutaneous  Branch. — In  the  lower  third  of  the  forearm  a  small 
cutaneous  branch  arises,  which  pierces  the  deep  fascia  and  crosses  the  anterior 
annular  ligament  to  reach  the  iialm  of  the  hand.  It  supplies  the  skin  of  the  palm 
and  communicates  with  a  similar  brancli  of  the  ulnar  nerve.  1'his  branch  is  not 
always  present. 


Fig.  497. — The  Distribution  of  Cutaneous  Nehves  on  the  Front  of 
THE  Arm  and  Hand. 

(A)  reiiresents  tlic  distribntion  of  the  several  nerves,  tlie  letters  indicating 

their  nomenclature.  Acu,  Acromial  branch  (cervical  plexus)  ;  CiKC, 
Cutaneous  branch  of  circuniHe.x  nerve  ;  M.Se,  Superior  external 
cutaneous  branch  of  niuscnlo-spiral  nerve  ;  M.C,  Musculo-cutaneous 
nerve;  M,  Median  nerve;  U,  Ulnar  nerve;  I.C,  Internal  cutaneous 
nerve  ;  L.I.C,  Lesser  internal  cutaneous  nerve  (Wrisberg)  ;  T.H,  luter- 
costo-humeral  nerve  ;  T.2,  3,  4,  5,  6,  Anterior  and  lateral  branches  of 
intercostal  nerves. 

(B)  -is  a  schematic  represeutation  of  the  areas  sujiplied  by  the  above  nerves, 

the  lettering  indicating  the  spinal  origin  of  the  branches  of  distriliution 
to  each  area.     V.A.L,  Ventral  axial  line. 


ULNAK  NEKVE.  629 

Branches  in  the  Hand. — In  the  hand  the  median  nerve  gives  oCf  its  terminal 
branches.     These  are  muscular  and  cutaneous. 

The  main  muscular  branch  arises  just  below  the  anterior  annular  ligament  and 
passes  outwards  to  the  l)ase  of  the  thenar  eminence  ;  entering  the  ball  of  the  thumb 
superficially  on  the  inner  side,  it  supplies  branches  to  the  abductor  pollicis, 
opponens  pollicis,  and  the  superficial  head  of  the  flexor  brevis  pollicis. 

The  cutaneous  branches  are  five  in  number.  Three  separate  branches  supply  each 
side  of  the  thumb  and  the  radial  side  of  the  index  finger.  The  two  remaining 
branches  subdivide  at  the  cleft  between  the  second  and  third,  and  the  third  and 
fourth  fingers  respectively,  into  branches  which  supply  the  adjacent  sides  of  the 
second  and  third,  and  the  third  and  fourth  fingers.  From  the  nerves  which  supply 
respectively  the  radial  side  of  the  index  finger,  and  the  contiguous  sides  of  the 
index  and  third  fingers,  fine  muscular  branches  arise  for  the  two  outer  lumbrical 
muscles.  The  cutaneous  branches  of  the  median  nerve  are  placed  in  the  palm 
between  the  superficial  palmar  arch  and  the  flexor  tendons.  They  become  super- 
ficial at  the  roots  of  the  fingers  between  the  slips  of  the  palmar  fascia,  or,  in  the 
case  of  the  nerves  to  the  thumb  and  radial  side  of  the  index  finger,  at  the  outer 
edge  of  the  central  portion  of  the  palmar  fascia.  In  the  fingers  they  are  placed 
superficial  to  the  digital  arteries,  and  are  distributed  to  the  sides  and  front  of  the 
fingers.  Each  nerve  supplies  one  or  more  dorsal  branches,  distributed  to  the  skin 
on  the  dorsal  aspect  of  the  terminal  phalanx  of  the  thumb  and  the  two  distal 
phalanges  of  the  first  two  and  a  half  fingers,  thus  making  up  for  the  deficiency  of 
the  radial  nerve  in  these  situations. 

Ulnar  Nerve. 

The  ulnar  nerve  (u.  ulnaris)  arises  from  the  inner  cord  of  the  brachial  plexus, 
from  the  eighth  cervical  and  first  thoracic  nerves.  It  also  occasionally  has  a  root 
from  the  outer  cord  of  the  plexus  (seventh  cervical  nerve).  In  the  axilla  it  hes 
between  the  axillary  artery  and  vein,  and  behind  the  internal  cutaneous  nerve ;  in 
the  upper  half  of  the  upper  arm  it  lies  on  the  inner  side  of  the  brachial  artery  in 
front  of  the  triceps  muscle.  In  the  lower  half  of  the  arm  it  is  separated  from  the 
brachial  artery ;  and  passing  behind  the  intermuscular  septum,  and  in  front  of  the 
inner  head  of  the  triceps  in  company  with  the  inferior  profunda  artery,  it  reaches  the 
interval  between  the  internal  condyle  of  the  humerus  and  the  olecranon  process.  It 
is  here  protected  by  an  arch  of  deep  fascia  stretching  between  the  internal  condyle 
and  the  olecranon  process.  It  enters  the  forearm  between  the  humeral  and  ulnar 
origins  of  the  flexor  carpi  ulnaris,  and  courses  downwards  between  the  flexor  carpi 
ulnaris  and  flexor  profundus  digitorum.  In  the  lower  half  of  the  forearm  it  becomes 
comparatively  superficial,  lying  on  the  inner  side  of  the  ulnar  artery  beneath  the 
tendon  of  the  flexor  carpi  ulnaris.  Just  above  the  anterior  annular  ligament  of  the 
wrist,  and  external  to  the  pisiform  bone,  it  pierces  the  deep  fascia  in  company  with 
the  artery  and  passes  into  the  hand  over  the  anterior  annular  ligament.  Reaching 
the  palm  it  divides  beneatli  the  palmaris  brevis  muscle  into  its  two  terminal 
branches,  superficial  and  deep. 

"Communications.— (1)  The  ulnar  nerve  communicates  in  some  cases  with  the  median 
nerve  in  the  forearm ;  (2)  with  the  internal  cutaneous  and  sometimes  the  median  nerve 
by  its  palmar  cutaneous  branch  ;  (3)  with  the  cutaneovis  part  of  the  median  nerve  in  the 
palm  by  means  of  its  terminal  cutaneous  branches  ;  (4)  with  the  radial  nerve  on  the 
dorsum  of  the  hand  by  means  of  its  dorsal  branch. 

Branches. — The  ulnar  nerve  gives  off  no  branches  till  it  reaches  the  forearm. 

In  the  forearm  it  gives  off  articular,  muscular,  and  cutaneous  branches. 

The  articular  branch  is  distributed  to  the  elbow  joint  and  arises  as^the  nerve 
passes  behind  the  internal  condyle. 

The  muscular  branches  arise  as  soon  as  the  nerve  enters  the  forearm.  They  are 
distributed  to  the  muscles  between  which  the  ulnar  nerve  lies — the  flexor  carpi 
ulnaris  and  the  inner  half  of  the  flexor  profundus  digitorum. 

The  cutaneous  branches  are  two  in  number,  palmar  and  dorsal. 


630 


THE  NERVOUS  SYSTEM. 


The  palmar  cutaneous  branch  is  variable  in  size  and  position.  It  pierces  the 
deep  fascia  in  the  lower  third  of  the  forearm  and  passes  to  the  hypothenar 
eminence  and  palm  of  the  hand,  to  the  skin  over  which  it  is  distributed.     It  gives 

branches  to  the 
ulnar  artery,  and 
communicates  often 
with  the  internal 
cutaneous  and 
palmar  branch  of 
the  median  nerve. 

The  dorsal  cut- 
aneous branch  is 
much  larger  (Fig. 
498).  It  arises 
from  the  ulnar  nerve 
in  the  middle  third 
of  the  forearm; 
and,  directed  ob- 
liquely downwards 
and  backwards  be- 
neath the  tendon  of 
the  flexor  carpi 
ulnaris,  it  becomes 
cutaneous  on  the 
inner  side  of  the 
forearm  in  its  lower 
fourth.  It  passes 
on  to  the  back  of  the 
hand,  and  after  giv- . 
ing  off  branches  to 
the  skin  of  the  wrist 
and  hand,  which 
communicate  with 
the  radial  nerve,  it 
terminates  in  two 
branches,  to  supply 
the  little  finger  and 
half  the  ring-finger 
in  the  following 
way  :  —  the  inner 
branch  courses 
along  the  inner  side 
of  the  dorsum  of 
the  hand  and  little 
finger :  the  outer  • 
branch  subdivides 
at  the  cleft  between 
the  ring  and  little 
fingers  to  supply 
the  adjacent  sides 
of  these  fingers ; 
The  nerve  may  supply  two  and 


Frci, 


498. — The  Distribution  of  Cutaneous  Nerves  on  the  Back  of  the 
Arm  and  Hand. 


(A)  represents  tlie  distribution  of  tlie  several  nerves,  the  letters  indicating  their 

nomenclature.  AcR,  Acromial  branches  (cervical  plexus)  ;  CiRC,  Cutaneous 
branch  of  circumflex  nerve  ;  Ms.E.C.s,  Ms.E.C.i,  Superior  and  inferior  external 
cutaneous  branches  of  luusculo-spiral  nerve  ;  M.C,  Musculo-cutaneons  nerve  ; 
R,  Radial  nerve  ;  M,  Branches  of  median  nerve  to  fingers  ;  U,  Ulnar  nerve  ; 
I.C,  Internal  cutaneous  nerve  ;  Ms.I.C,  Internal  cutaneous  branch  of  musculo- 
spiral  nerve  ;  L. I.C,  Lesser  internal  cutaneous  nerve  (Wrisberg)  ;  I.H,  Inter- 
costo-hunieral  ;  T.l.  2,  3,  4,  ,'),  6,  Lateral  and  posterior  branches  of  upper 
thoracic  nerves. 

(B)  is  a  schematic  representation  of  the  areas  supplie<l  by  the  above  nerves,  the 

lettering  indicating  the  spinal  oiigiu  of  the  branches  of  distribution  to  each 
area.     D.A.L,  Dorsal  axial  line.  if 


this  branch  communicates  with  the  radial  nerve, 
a  half  fingers  on  the  dorsum  of  the  hand. 

In  the  palm  the  ulnar  nerve  supplies  a  small  muscular  branch  to  the  palmaris 
brevis  muscle,  and  then  subdivides  into  its  terminal  branches,  which  are  named 
superficial  and  deep. 

The  superficial  branch  is  purely  cutaneous ;  it  passes  downwards  beneath  the 
palmar  fascia,  and  sulxlivides  into  an  inner  and  an  outer  branch.  The  inner 
branch  courses  along  the  inner  border  of  the  little  finger,  whiclvit  supplies  on   its 


INTEENAL  CUTANEOUS  NERVE. 


631 


palmar  aspect.  The  outer  branch  becomes  superficial  at  the  cleft  between  the 
fourth  and  fifth  fingers,  between  the  slips  of  the  palmar  fascia,  and  subdivides  into 
two  branches  which  supply  the  adjacent  sides  of  these  fingers  on  their  palmar  aspect. 
It  communicates  with  the  adjacent  digital  branch  of  the  median  nerve. 

Tlie  deep  branch  is  purely  muscular.     It  separates  from  the  superficial  branch, 


Levator  .iiiguli  scapula 


Rhomboidpiw 
iiiaioi 

Scapular  fa.sc  i 


Dorsal  Scaiiulai / 

artery  (branch  of)  / 

Teres  iiiaioi  - 


I.atissiiiius  (loiM 


Supraspinatus  muscle 
Scapular  spine  (cut) 

—  Iiifia>)iiiiatus 


-^^^ '1  eres  minor 

;^__ —  Nervk  to  teres  minor 

'"^'         CiRCrSIFI.EX  NERVE  AND 
ARTERY 

Deltoid  (reflected) 

Cutaneous  branch 
of  circlimflex 

Triceps  (outer  head) 
i  i  icep-,  (long  head) 

Ml  SCI  LO-SPIRAL 

(outer  head) 
Biacliialis  anticus 

Triceps  (inner  head) 

External  intermuscular  septum 

External  citaneous 
branches  of  mtscdlo- 

PIRAL 


Flexor 

carpi 

ulnaris 


Braohio-radialis 


Extensor  carpi  radialis  longior 


Extensor  muscles  of  forearm 
(common  tendon) 


and  passes  deeply  between  the 
flexor  brevis  and  abductor  minimi 
digiti  muscles ;  it  supplies  these 
muscles  and  the  opponens  minimi 
digiti,  and- turninCToutwards  along 
the  line  of  the  deep  palmar  arch 
and  under  cover  of  the  deep  flexor 
tendons,  it  supplies  branches  to  uln 
the  following  muscles  :  interossei,  ^'^'^ 
two  inner  (third  and  fourth)  lum- 
bricales  (on  their  deep  surfaces),  the 
adductores  pollicis,  obliquus  and 
transversus,  and  deep  part  of  the 
flexor  brevis  pollicis. 

Internal  CuTA:ifE0us  Nerve. 

The  internal  cutaneous  nerve  (n.  cutaneus  brachii  medialis)  arises  from 
the  inner  cord  of  the  brachial  plexus,  from  the  eighth  cervical  and  first  thoracic 
nerves  (Figs.  497  and  498).  In  the  axilla  and  upper  half  of  the  arm  it  lies  superficial 
to  the  main  artery.  It  becomes  cutaneous  by  piercing  the  deep  fascia  about  the 
middle  of  the  inner  side  of  the  upper  arm,  and  accompanying  the  basilic  vein 
through  the  lower  half  of  the  arm,  it  divides  at  the  front  of  the  elbow  into  its  two 
terminal  branches. 

Communication. — The  internal  cutaneous  nerve  communicates  with  the  palmar 
branch  of  the  ulnar  nerve  in  the  lower  part  of  the  forearm. 


Fig.  499. — Deltoid  Region  and  Back  of  Ar.m. 


632  THE  NEEVOUS  SYSTEM. 

Branches. — lu  the  arm,  as  soon  as  it  becomes  superficial,  the  internal  cutaneous 
nerve  gives  oft'  a  branch  which  supplies  the  skin  of  the  lower  half  of  the  anterior 
surface  of  the  arm  on  its  inner  side.  At  the  elbow  it  divides  into  two  terminal 
branches — anterior  and  internal,  which,  crossing  over  or  under  the  median  basilic 
vein,  are  distributed  to  the  inner  side  of  the  forearm. 

The  anterior  branch  can  be  followed  to  the  wrist  and  supplies  the  whole  of  the 
front  of  the  forearm  in  the  inner  half;  the  internal  branch  is  not  so  large,  and, 
passing  ol^liquely  backwards  and  downwards  over  the  origins  of  the  pronator  and 
flexor  muscles,  it  is  distributed  to  the  upper  two-thirds  or  three-fourths  of  the 
posterior  aspect  of  the  forearm  on  the  inner  side. 

Lesser  Internal  Cutaneous  Nerve. 

The  lesser  internal  cutaneous  nerve  (n.  cutaneus  brachii  medialis  minor) 
arises  from  the  inner  cord  of  the  brachial  plexus,  and  ultimately  from  the  first 
thoracic  nerve  (Fig.  494,  p.  624).  It  lies  at  first  between  the  axillary  artery  and 
vein ;  and  after  descending  over,  under,  or  even,  in  some  cases,  through  the  axillary 
vein,"  it  perforates  the  deep  fascia  on  the  inner  side  of  the  arm,  and  is  distributed  to 
the  skin  of  the  arm  for  the  upper  half  or  more  on  its  inner  side. 

The  nerve  varies  considerably  in  size.  It  may  be  absent,  its  jslace  being  taken  by  brandies 
of  the  intercosto-liunieral  or  by  branches  from  the  internal  cutaneous  offset  of  the  musculo- 
sjjiral  nerve.  It  generally  bears  a  distinct  relation  in  size  to  the  intercosto-humeral,  due  to  the  fact 
that  the  size  of  the  latter  depends  upon  the  size  of  the  part  of  the  second  thoracic  nerve  con- 
nected witli  the  first  in  the  thorax.  If  an  intra-thoracic  connexion  occurs  between  the  first  and 
second  tlioracic  nerves,  the  intercosto-Iiumeral  may  be  deprived  of  a  certain  number  of  its 
fibres,  wliich  in  that<-.case  reach  the  upper  limb  through  the  lesser  internal  cutaneous  nerve. 
When  traced  up  to  the  plexus  the  lesser  internal  cutaneous  is  found  to  have  an  origin  from  the 
bacK  of  the  cord  formed  by  the  eighth  cervical  and  first  thoracic  nerves,  and  usually  receives 
fibres  from  the  first  thoracic  nerve  only.  In  cases  where  "  axillary  arches  "  ai'e  present  they  may 
be  supplied  by  tliis  nerve. 

Circumflex  Nerve. 

The  circumflex  nerve  (n.  axillaris),  at  its  origin  is  just  below  the  supra- 
scapular and  comes  from  the  same  spinal  nerves — the  fifth  and  sixth  cervical 
nerves  (Fig.  494,  p.  623).  Extending  downwards  and  outwards  behind  the  axillary 
artery,  it  leaves  the  axilla  by  passing  round  the  external  border  of  the  subscapularis 
muscle,  in  company  with  the  posterior  circumflex  artery,  in  a  quadrilateral  space 
bounded  by  the  humerus,  sul  »sca]3ularis,  triceps  (long  head),  and  teres  major. 
Winding  round  the  surgical  neck  of  the  humerus  from  within  outwards,  it 
terminates  under  the  deltoid  by  supplying  that  muscle  (Fig.  499,  p.  631). 

Branches. — Muscular  branches  are  supplied  to  the  teres  minor  -^and  deltoid 
muscles.  Tlie  nerve  to  the  teres  minor  enters  the  outer  side  of  the  muscle.  It 
possesses  a  pseudo-ganglion,  a  thickening  of  fibrous  tissue,  on  its  trunk. 

Articular  branches  enter  the  back  part  of  the  capsule  of  the  shoulder-joint. 

A  cutaneous  branch  (n.  cutaneus  brachii  lateralis)  of  considerable  size  passes 
oldifiuely  downwards  and  forwards  from  beneatli  the  deltoid  muscle,  becoming 
superficial  at  its  posterior  border.  Sometimes  tlie  branches  pierce  the  muscle.  It 
supplies  the  skin  over  the  insertion  of  the  deltoid  and  tlie  upper  half  of  the  arm 
on  the  outer  side  (Fig.  498,  x>-  630). 

Musculo-Spiral  Nerve. 

The  musculo-spiral  nerve  (n.  radialis)  appears  to  be  tlie  continuation  into  the 
upper  limb  of  the  posterior  cord  of  the  brachial  plexus.  It  usually  takes  origin 
from  all  the  nerves  wliich  form  the  posterior  cord — the  fifth,  sixth,  seventh,  and 
eighth  cervical  nerves  (Fig.  494,  p.  623).  In  a  minority  of  cases  the  first  thoracic 
contributes  a  few  fibres,  and  more  frequently  the  fifth  cervical  nerve  is  excluded 
from  it.  It  extends  from  the  axilla  round  the  back  of  the  humerus  to  the  bend  of 
the  elbow,  where  it  ends  by  dividing  into  its  terminal  branches. 

In  the  axil/o  it  lies  behind  the  axillary  artery,  and  in  front  of  the  subscapularis, 
teres  major,  and  latissiums  dorsi  muscles. 


THE  MUSCULO-SPIEAL  NERVE. 


633 


In  the  arm,  iu  the  upper  third,  it  lies  on  the  inner  side  of  the  humerus  behind 
the  brachial  artery,  and  upon  the  long  head  of  the  triceps.  In  the  middle  third  of 
the  arm  it  courses  obliquely  outwards  and  downwards  in  the  spiral  groove  of  the 
humerus,  along  with  the  superior  profunda  artery,  separating  the  long,  external, 
and  internal  heads  of  the  triceps  muscle  (Fig.  499,  p.  631).  In  the  lower  third  of 
the  arm,  piercing  the  upper  part  of  the  intermuscular 
septum  at  the  outer  border  of  the  triceps  muscle,  it 
descends  to  the  bend  of  the  elbow  in  front  of  the  external 
condyle  of  the  humerus,  in  the  interval  between  the 
brachio-radialis  and  brachialis  anticus  muscles.  Under 
cover  of  the  former  muscle,  in  the  hollow  of  the  elbow, 
it  divides  into  its  two  terminal  branches,  the  radial  and 
posterior  interosseous  nerves. 

The  collateral  branches  are  in  three  sets,  arising 
(a)  on  the  inner  side,  (6)  on  the  back,  and  (c)  on  the 
outer  side  of  the  humerus  (Fig.  500). 

Branches  arising  internal  to  the  humerus, — 1. 
Internal  cutaneous  (n.  cutaneus  brachii  posterior). — This 
branch,  arisintj  in  common  with  one  of  the  following,  or 
independently,  pierces  the  fascia  on  the  inner  side  of 
the  arm  near  the  axilla.  It  supplies  the  skin  of  the 
inner  side  of  the  arm  in  the  upper  third,  above  and 
behind  the  area  supplied  by  the  lesser  internal  cutaneous 
nerve  (Fig.  498,  p.  630).  This  nerve  varies  in  size, 
according  to  the  bulk  of  the  lesser  internal  cutaneous 
and  intercosto-humeral  nerves. 

2.  Muscular  branches  (rr.  musculares). — These  are 
in  two  sets.  One  series  supplies  the  long  head  of  the 
triceps  muscle  near  its  origin ;  the  other  series  enters 
the  inner  head  of  the  muscle.  One  of  the  latter, 
separating  itself  from  the  rest,  accompanies  the  ulnar 
nerve  in  the  middle  third  of  the  arm,  and  supplies  the 
lower  part  of  the  muscle.  This  is  sometimes  calkd  the 
collateral  ulnar  nerve. 

Branches  arising  on  the  back  of  the  humerus.- — 
Muscular  branches  arise  from  the  nerve  in  the  musculo- 
spiral  groove  for  the  supply  of  all  three  heads  of  the 
triceps  muscle.  The  branch  which  enters  the  inner 
head  of  the  muscle,  besides  supplying  it,  passes  through 
the  muscle  and  behind  the  external  condyle  of  the 
humerus,  to  terminate  in  the  anconeus. 

Branches  arising  at  the  outer  side  of  the 
humerus.  —  1.  The  cutaneous  branches  (n.  cutaneus 
antiljrachii  dorsalis)  are  two  in  number,  superior  and 
inferior.  Arising  from  the  musculo-spiral  nerve  before 
it  pierces  the  external  intermuscular  septum,  these 
branches  pierce  the  deep  fascia  close  together  on  the 
outer  side  of  the  arm  in  its  lower  half.  Descending 
over  the  back  of  the  external  condyle,  the  superior 
branch  supplies  the  skin  of  the  outer  side  and  back  of 
the  arm  in  its  lower  third,  and  the  back  of  the  forearm  in  its  upper  half.  The 
inferior  branch  supplies  an  area  of  skin  on  the  back  of  the  forearm  in  the  upper 
two-thirds  internal  to  the  area  innervated  by  the  musculo  -  cutaneous  nerve 
(Fig.  498,  p.  630). 

2.  Muscular  branches. — The  musculo-spiral  nerve,  as  it  lies  in  the  interval 
between  the  brachialis  anticus  and  brachio-radialis,  supplies  a  small  branch  to  the 
brachialis  anticus  (which  in  some  cases  is  not  present)  and  nerves  to  the  brachio- 
radialis  and  extensor  carpi  radialis  longior.  It  may  also  provide  the  nerve  to  the 
extensor  carpi  radialis  brevier. 


7^/:  n. 


Fio.  500. — Diagrammatic  Repre- 
sentation OF  THE  Branches 
OF  THE  Musculo-spiral  Nerve. 

M.S,  Musculo-spiral  nerve  ;  L.H, 
Nerve  to  long  head  of  triceps  ; 
I.C,  Internal  cutaneous  branch  ; 
I.H,  Nerve  to  inner  head  of 
triceps;  O.H,  Nerve  to  outer  head 
of  triceps  ;  I.H,  Second  nerve 
to  inner  head  of  triceps  ;  Auc. 
Nerve  to  anconeus  ;  Art,  Ar- 
ticular branch  ;  E.Cs,  Superior, 
external  cutaneous  branch  ;  E.Ci, 
Inferior  external  cutaneous 
branch  ;  B.  A,  Nerve  to  brachialis 
anticus  ;  Br,  Nerve  to  brachio- 
radialis  ;  E.C.R.L,  Nerve  to  ex- 
tensor carpi  radialis  longior  ;  P.I, 
Posterior  interosseous  nerve  ;  R, 
Radial  nerve. 


G34 


THE  NERVOUS  SYSTEM. 


Radial  JSTerve. 
The  radial    nerve  (r.  superficialis)  is  entirely 


External  condyle 


Extensor  muscles 
(origin) 


Supinator  radii 
brevis 


Extensor  carpi 
ulnaris 


Triceps  (long  head) 
Triceps  (outer  head) 
Brachio-radialis 

Brachialis  antieus 
Biceps 
/ — ^Triceps  (inner  head) 


Extensor  carpi  I'adialis 
longior  (origin) 

Extensor  carpi  radialis 
brevior  (origin) 

MUSCULO-SPIRAL  NERVE 


Posterior  interhssrous 

NERVE 


Extensor  ossis  metacarpi 
]iollicis 

Extensor  carpi  radialis 
longior  (tendon) 


cutaneous  in  its  distribution. 
Arising  in  the  hollow  of  the 
elbow  beneath  the  brachio- 
radialis,  it  courses  downwards 
under  cover  of  that  muscle 
through  the  upper  two-thirds 
of  the  arm,  and  accompanies 
the  radial  artery  in  the  middle 
third  of  the  forearm.  It  then 
passes  backwards  beneath  the 
tendon  of  the  brachio-radialis 
and  pierces  the  deep  fascia  in 
the  outer  side  of  the  forearm 
in  the  lower  third.  It  is 
distributed  to  the  skin  of  the 
back  of  the  wrist,  the  outer 
side  and  the  back  of  the  hand, 
and  the  back  of  the  thumb  and 
outer  two  and  a  half  fingers 
(Fig.  498,  p.  630).  Its  branches 
communicate  on  the  ball  of 
the  thumb  with  the  musculo- 
cutaneous nerve,  and  on  the 
back  of  the  hand  with  the 
dorsal  branch  of  the  ulnar 
nerve.  The  digital  branches 
are  small,  and  are  five  in 
number.  Two  pass  to  the 
back  of  the  thumb  and  reach 
the  inter-phalangeal  articula- 
tion. One  supplies  the  radial 
side  of  the  index  finger  as  far 
as  the  second  phalanx.  The 
remaining  two  branches  divide 
at  the  clefts  between  the  second 
and  third,  and  third  and  fourth 
fingers  respectively,  and  in- 
nervate the  adjacent  sides  of 
these  fingers  as  faras  thesecond 
phalanx.  The  rest  of  the  skin 
of  these  digits  to  the  tips  is 
supplied  by  digital  branches 
of  the  median  nerve.  The 
nerve  may  only  supply  one 
and  a  half  fingers,  being  re- 
placed  by  branches  from  the 
ulnar  nerve. 

Posterior  Interosseous 
Nerve. 

The  posterior  inter- 
osseous nerve  (r.  profundus, 
n.  interosseus  antibrachii 
dorsalis)  is  entirely  muscular 
and  articular  in  its  distribution,  and  it  arises  like  the  radial  beneath  the 
brachio-radialis    muscle.       Directed    obliquely    downwards    and     l)ackwards,    it 


Dorsal  branch  of 

ulnar  nerve 

Extensor  minimi 

digiti  (tendon) 

Extensor  communis 

digitorum  (tendon) 


Extensor  cai'pi  radialis 
brevior  (tendon) 

Extensor  brevis  poUicis 


Extensor  carpi  radialis 

longior  (tendon) 

Extensor  ossis  metacarpi 

pollicis 

Extensor  carpi  radialis 

brevior  (tendon) 

Extensor  brevis  pollicis 

Extensor  longus 
pollicis 

First  dorsal  inter- 
osseous muscle 


Fig.  501. — The  Muscles  op  the  Back  ok  thic  Foreau.m 
(the  superficial  muscles  have  been  reflected). 


THOEACIC  NERVES.  G35 

reaches  the  back  of  the  forearm,  alter  passing  round  the  outer  side  of  the 
radius,  by  piercing  the  fibres  of  the  supinator  radii  brevis  muscle  (Fig.  501). 
On  the  back  of  the  forearm  it  is  placed  in  the  upper  part  of  its  course  beneath  the 
superficial  extensor  muscles,  and  upon  the  supinator  radii  brevis  and  extensor  ossis 
metacarpi  pollicis,  along  with  the  posterior  interosseous  artery.  In  the  lower  half 
of  the  forearm  it  passes  beneath  the  extensor  longus  pollicis,  and  lies  upon  the 
interosseous  membrane.  At  the  wrist  it  passes  beneath  the  extensor  tendons  on  to 
the  back  of  the  carpus,  where  it  terminates  in  a  gangliform  enlargement  of  small 
size,  from  which  branches  pass  to  the  inter-carpal  articulations.  The  posterior  inter- 
osseous nerve  supplies  the  following  branches : — 

( 1 )  Terminal  articular  branches  to  the  carpal  joints. 

(2)  Muscular  branches,  in  its  course  through  the  forearm.  Thus  on  the  outer 
side  of  the  radius  it  supplies  the  extensor  carpi  radialis  brevior  and  the  supinator 
brevis  muscle  before  it  enters  the  fibres  of  the  last-named  muscle.  After  emerging 
from  the  supinator  brevis  it  supplies  a  large  bundle  of  nerves  which  enter  the 
extensor  communis  digitorum,  extensor  minimi  digiti,  and  extensor  carpi  ulnaris 
near  their  origins.  Lower  down  the  forearm  the  nerve  gives  off  branches  to  the 
extensor  ossis  metacarpi  pollicis,  extensor  longus  and  extensor  brevis  pollicis,  and 
extensor  indicis. 

Subscapular  Nerves. 

There  are  three  subscapular  nerves  (nn.  subscapu lares)  (Figs.  494  and  496). 

The  first  or  short  subscapular  nerve  is  generally  double,  and  there  may  be 
three  trunks  present.  It  arises  from  the  posterior  cord  of  the  plexus  behind  the 
circumflex  nerve,  and  comes  from  the  fifth  and  sixth  cervical  nerves.  It  passes 
downwards  behind  the  axillary  artery  and  enters  the  subscapularis  muscle. 

The  second  or  lower  subscapular  nerve  also  arises  behind  the  circumflex 
from  the  posteri©r  cord  of  the  plexus,  and  from  the  fifth  and  sixth  cervical  nerves. 
Its  origin  is  below  and  external  to  that  of  the  first  nerve.  It  courses  outwards  and 
downwards  behind  the  axillary  artery,  and  the  circumflex  and  musculo-spiral 
nerves  to  the  teres  major  muscle.  It  supplies  branches  to  the  outer  part  of  the 
subscapularis  muscle  and  ends  in  the  teres  major. 

The  third  or  long  subscapular  nerve  (n.  thoraco-dorsalis)  arises. from  the  back 
of  the  posterior  cord  of  the  plexus,  behind  the  musculo-spij'"'""  ve,  and  from  the 
sixth,  seventh,  and  eighth  cervical  nerves,  or  from  the  f  ./^,,  , ,  .^-Sand  eighth  nerves 
only.  It  is  directed  downwards  and  outwards  between  the  two  previous  nerves, 
behind  the  axillary  artery  and  over  the  posterior  wall  of  the  axilla,  in  company 
with  the  subscapular  artery,  to  the  latissimus  dorsi  muscle,  which  it  supplies  on  its 
anterior  (inner)  surface. 

THORACIC  NERVES. 

The  thoracic  nerves  are  twelve  in  number,  each  nerve  emerging  below  the 
corresponding  vertebra  and  rib.  Eleven  of  the  series  are  intercostal,  the  twelfth 
lying  below  the  last  rib.  The  first,  second,  third,  and  twelfth  nerves  present 
peculiarities  in  their  course  and  distribution.  The  other  thoracic  nerves,  as  already 
stated,  are  simple,  and  may  be  regarded  as  types  both  in  course  and  distribvition. 

The  first  thoracic  nerve  is  the  largest  of  the  series.  It  emerges  from  the 
spinal  canal  below  the  neck  of  the  first  rib,  and  divides  in  the  first  intercostal 
space  into  two  very  unequal,  upper  and  lower,  parts.  The  upper  larger  part  ascends 
obliquely  over  the  neck  of  the  first  rib,  lying  external  to  the  superior  intercostal 
artery,  and  enters  the  neck  behind  the  sul)clavian  artery  and  the  pleura.  It  pro- 
ceeds outwards  upon  the  scalenus  medius  muscle  and  enters  into  the  formation  of 
the  brachial  plexus,  as  already  described. 

The  loiver,  intercostal  part  of  the  nerve  is  much  smaller  in  size.  It  courses 
forwards  in  the  first  intercostal  space  and  supplies  the  intercostal  muscles.  It 
usually  gives  off  no  anterior  branch  to  the  skin  of  the  chest  and  no  lateral 
cutaneous  branch. 


636 


THE  NEKVOUS  SYSTEM. 


lu  some  cases  a  lateral  cutaneous  branch  emerges  from  the  side  of  the  first  intercostal  space. 
This  may  be  derived  from  the  first  nerve,  or  it  may  be  the  intercosto-humeral  nerve,  derived 
from  the  second  thoracic  nerve.  In  many  cases  an  anterior  cutaneous  branch  perforates  the  first 
intercostal  space  and  suj^plies  the  skin  on  the  front  of  the  chest.  This  Ijranch,  similarly,  is  some- 
times traceable  to  the  second  thoracic  nerve. 

Communications. — Besides  its  junction  with  the  eighth  cervical  to  form  the 
brachial  plexus,  the  first  thoracic  nerve  effects  the  following  communications : — (a)  The 
last  cervical  or  first  thoracic  ganglion  of  the  sympathetic  sends  a  gray  ramus  communi- 
cans  to  join  the  nerve  on  its  appearance  in  the  thoi'ax.  (6)  The  second  thoracic  nerve  in 
a  majority  of  cases  communicates  with  the  first.  This  communication  varies  considerably 
in  size  and  distribution.  It  may  reinforce  the  intercostol  branch  of  the  nerve,  it  may 
send  one  branch  to  the  intercostal  portion  and  another  to  the  part  of  the  nerve  joining  the 
brachial  plexus,  or  it  may  consist  of  a  nerve  proceeding  solely  to  join  the  brachial  plexus  by 
a  junction  in  the  first  intei'costal  space  with  the  part  of  the  first  thoracic  nerve,  which- is 
engaged  in  forming  the  plexus,  (c)  It  is  possible  that  the  first  white  ramus  communicans 
in  the  thoracic  region  connects  the  first  thoracic  nerve  with  the  gangliated  cord  of  the 
sympathetic,  but  this  is  not  known  with  certainty. 


The  second  thoracic  nerve  is  of  large  size,  though  much  smaller  than  the 
first.  It  passes  forwards  in  the  second  intercostal  space,  lying  at  first  in  the  sub- 
costal groove  between  the  external  and  internal  intercostal  muscles.  At  the  level 
of  the  mid-axillary  line  it  gives  off  a  large  lateral  branch ;  continuing  its  course 
it  pierces  the  internal  intercostal  muscle  and  lies  upon  the  pleura ;  finally,  at  the 
lateral  border  of  the  sternum,  it  passes  forwards  in  front  of  the  internal  mammary 
artery  and  through  the  internal  intercostal  muscle,  and  the  aponeurosis  of  the 
external  intercostal  muscle,  and  ends  by  supplying  the  skin  of  the  front  of  the 
chest  over  the  second  intercostal  space. 

The  nerve  supplies  the  following  branches : — 


£XTEfi/\/AL 


1.  Muscular  branches  to  the  muscles 
of  the  second  intercostal  space. 

2.  Cutaneous  branches,  (a)  Anterior 
terminal  branches  (rr.  cutaneus  anterior)  to 
the  skin  over  the  second  intercostal  space 
(Fig.  503).  (6)  A  large  lateral  cutaneous 
branch,  the  intercosto-humeral  nerve  (n. 
intercosto-brachialis)  (Fig.  494,  p.  623). 
This  nerve  piei'ces  the  intercostal  muscles 
and  the  serratus  magnus,  and,  crossing  the 
axilla,  extends  to  the  arm.  It  pierces  the 
deep  fascia  just  beyond  the  posterior  fold  of 
the  axilla,  and  can  be  traced  down  the  arm 
as  far  as  the  interval  between  the  internal 
condyle  of  the  humerus  and  the  olecranon 
process.  It  supplies  an  area  of  skin  stretch- 
ing across  tlie  armpit  and  along  the  posterior 
surface  of  the  arm  on  the  inner  side  as  far 
as  the  elbow  (Fig.  497,  p.  628). 

The  intercosto-humeral  nerve  varies  in  size. 
It  may  piei'ce  tlie  first  intercostal  sjmce,  and  it  is 
often  divisible  into  anterior  and  posterior 
l)ranch(;s,  like  the  lateral  branch  of  an  ordinary 
intercostal  nerve. 

Communications.  —  (1)  The  intercosto- 
humeral  nerve  communicates  with  two 
adjacent  nerves.  Either  before  or  after 
piercing  the  fascia  of  the  axilla  it  is  joined  by 
the  lesser  internal  cutaneous  nerve  of  the  brachial  plexus.  It  also  communicates  with  the 
posterior  part  of  the  lateral  branch  of  tlie  third  intercostal  nerve  by  means  of  the  branches 
distributed  to  the  floor  and  boundaries  of  the  axilla.  It  may  supply  the  axillary  arches, 
when  present.     (2)  Besides  the  branches  referred  to,  the  second  thoracic  nerve  in  many 


BRANCH 


Fk;, 


s02.  —  schkmk  ok  the  distribution  ok 
Tyi'ical  Spinal  Nerve. 


THOEACIC  NEEVES. 


637 


cases  transmits  a  nerve  to 
the  brachial  plexus,  which 
becomes  incorporated 
with  the  first  thoi'acic 
nerve  after  passing  over 
the  neck  of  the  second  rib. 
This  branch  is  inconstant. 
As  already  mentioned,  it 
may  join  only  the  inter- 
costal part  of  the  first 
thoracic  nerve,  it  may  join 
the  brachial  plexus  only, 
or  it  may  send  bi'anches 
to  both  pai'ts  of  the  first 
thoracic  nerve.  (3)  Be- 
sides the  communications 
effected  by  bran  dies  of  the 
second  thoracic  nerve  in 
its  course,  it  also  receives 
\\,(jrayramuscommunicans 
from  the  second  thoracic 
ganglion  of  the  sym- 
pathetic cord  in  the 
thorax.  It  probably  also 
sends  to  the  sympathetic 
the  first  white  ramus  coin- 
niunicans,  though  this  is 
not  known  with  certainty. 

The  third  thoracic 
nerve  only  differs  from 
a  typical  thoracic  nerve 
in  one  respect.  Its 
lateral  branch  divides 
in  the  usual  way  into 
anterior  and  posterior 
parts,  of  which  the  latter 
is  carried  to  the  arm  and 
supplies  an  area  of  skin 
on  the  posterior  half  of 
the  inner  side  near  the 
root  of  the  limb.  It 
effects  a  junction  with 
the  intercosto-humeral 
nerve  (Fig.  494,  p.  623). 

The  fourth,  fifth, 
and  sixth  thoracic 
nerves  have  a  course 
and  distribution  which 
is  simple  and  typical. 
Except  for  the  peculi- 
arities above  mentioned, 
the  second  and  third 
thoracic  nerves  have  a 
similar  distribution. 

The  nerves  appear 
on  the  posterior  wall  of 
the  thorax,  in  the  sub- 
costal groove  of  the  cor- 
responding rib.  They 
extend  forwards  be- 
tween   the    intercostal 


Fig.   503. — The  Distribution  of  Cutaneous  Nekves  on  the  Front  op" 
THE  Trunk. 

On  one  side  the  distribution  of  the  several  nerves  is  represented,  the  letters 
indicating  their  nomenclature. 

G.A,  Great  auricular  nerve ;  S.C,  Superficial  cervical  nerve  ;  S.Cl,  Supra- 
clavicular nerves  ;  AcR,  Acromial  ;  Cl,  Clavicular  ;  St,  Sternal  ;  T.2-12, 
Lateral  and  anterior  branches  of  thoracic  nerves  ;  I.H,  Ilio-hypogastric 
nerve  ;  I.I,  Ilio-inguinal  nerve  ;  CiRC,  Cutaneous  branch  of  circumtie.x 
nerve  ;  L.I.C,  Lesser  internal  cutaneous  nerve  ;  I.H,  Intercosto-humeral  ; 
I.C,  Internal  cutaneous  ;  M.S,  Cutaneous  branch  of  musculo-spiral  nerve, 
E.C,  External  cutaneous  nerves  ;  G.C,  Geuito-crural  nerve  ;  M.C'  ^,  Middle 
cutaneous  nerves  ;  I.C\  Branch  of  internal  cutaneous  nerve  ;  P,  Branches 
of  pudic  nerve  ;  S.Sg,  Branches  of  small  sciatic  nerve. 

On  the  other  side  a  schematic  representation  is  given  of  the  areas  sujiplied  by 
the  above  nerves,  the  numerals  indicating  the  spinal  origin  of  the  branches 
of  distribution  to  each  area. 


638  THE  NEEVOUS  SYSTEM. 

muscles  as  far  as  the  middle  of  the  chest  wall,  lying  at  a  lower  level  than  the  inter- 
costal vessels.  At  the  side  of  the  chest  each  nerve  passes  obliquely  through  the  internal 
intercostal  muscle^  and  comes  to  lie  upon  the  pleura,  triangularis  sterni  muscle, 
and  internal  mammary  artery.  Thereafter,  piercing  the  fibres  of  the  internal 
intercostal  muscle  and  the  aponeurosis  of  the  external  intercostal  muscle,  each 
nerve  ends  by  supplying  the  skin  of  the  front  of  the  chest,  over  an  area  correspond- 
ing to  the  inner  or  anterior  part  of  the  intercostal  space  to  which  it  belongs. 

Branches. — Each  intercostal  nerve  supplies,  in  addition  to  the  anterior  terminal 
cutaneous  branches,  muscular  hranches  to  the  intercostal  muscles  and  a  lateral 
trunk  (r.  cutaneus,  lateralis),  which,  piercing  the  intercostal  muscles  and  the 
serratus  magnus,  divides  into  anterior  and  posterior  branches  for  the  innervation 
of  the  skm  over  the  side  of  the  chest.  Each  area  of  skin  thus  innervated  is 
continuous  anteriorly  with  the  area  innervated  by  the  anterior  terminal  branches 
of  the  same  nerves,  and  posteriorly  with  the  areas  supplied  by  their  posterior 
primary  divisions. 

The  upper  six  intercostal  nerves  supply  the  muscles  of  the  first  six  intercostal 
spaces  and  the  triangularis  sterni  (3,  4,  5,  6).  The  second,  third,  fourth,  fifth,  and 
sixth  nerves  supply  the  skin  of  the  front  of  the  chest :  the  second,  opposite  the 
manubrio-sternal  joint;  the  sixth,  opposite  the  base  of  the  xiphoid  cartilage.  Their 
lateral  branches  supply  branches  to  the  intercostal  muscles  and  the  skin  of  the  side 
of  the  chest,  the  second  (intercosto-humeral)  and  the  third  in  part  being  drawn  out 
on  to  the  arm.     The  fourth  supplies  the  nipple  (Fig.  503). 

Communications. — Each  of  these  intercostal  nerves  communicates  with  the  sympathetic 
cord  and  ganglia  by  two  branches — a  ivhite  ramus  communicans  to  the  corresponding  sym- 
pathetic ganglion  or  the  adjacent  part  of  the  sympathetic  cord ;  and  a  gray  ramtis  com- 
municans, which  passes  to  each  nerve  from  the  corresponding  ganglion. 

The  seventh,  eighth,  ninth,  tenth,  and  eleventh  thoracic  nerves  only  differ 
from  the  preceding  nerves  in  regard  to  a  part  of  their  course  and  distribution.  Each 
has  the  same  course  and  communications  as  the  preceding  nerves  in  the  thoracic  wall. 
In  addition,  these  nerves  have  a  further  course  and  distribution  in  the  abdominal 
wall.  Each  nerve  traverses  its  intercostal  space  in  the  way  described.  At  the 
anterior  end  of  the  space,  the  nerve  pierces  the  attachment  of  the  diaphragm  and 
the  transveralis  abdominis  muscles  to  the  costal  cartilages,  and  courses  forwards  in 
the  abdominal  wall  between  the  transversaUs  and  obliquus  internus  muscles.  The 
nerve  then  passes  between  the  rectus  muscle  and  the  posterior  layer  of  its  sheath, 
and  eventually  reaches  the  anterior  abdominal  wall  and  becomes  cutaneous  by 
piercing  the  rectus  itself  and  the  anterior  layer  of  its  sheath. 

Muscular  Branches. — The  lower  intercostal  nerves  supply  the  intercostal 
muscles  of  the  spaces  in  which  they  lie ;  and  in  the  abdominal  wall  they  innervate 
the  transversalis,  obliqui,  and  rectus  abdominis.  The  branches  arise  from  the 
main  trunk  as  well  as  from  its  lateral  and  anterior  branches.  (The  ninth,  tenth, 
and  eleventh  nerves  are  described  as  assisting  in  the  innervation  of  the  diaphragm 
by  communications  with  the  phrenic  nerve.) 

Cutaneous  Branches. — These  are  lateral  and  anterior.  The  lateral  branches 
divide  into  anterior  and  posterior  parts,  and,  becoming  superficial  along  the  line  of 
inter-digitation  of  the  obliquus  externus  muscle  with  the  serratus  magnus  and 
latissimus  dorsi,  they  are  directed  more  obliquely  downwards  than  the  lateral 
branches  of  the  higher  intercostal  nerves,  and  are  distributed  to  the  skin  of  the 
loin  as  low  down  as  the  buttock.  The  lateral  branch  of  the  eleventh  nerve  can  be 
traced  over  the  iliac  crest  (Fig.  503). 

The  anterior  branches  are  small.  That  of  the  seventh  nerve  innervates  the  skin 
at  the  level  of  the  ensiform  cartilage.  The  eighth  and  ninth  appear  between  the 
ensiform  cartilage  and  the  umbilicus ;  the  tenth  nerve  supplies  the  region  of  the 
umbilicus;  and  the  eleventh,  the  area  immediately  below  the  umbilicus. 

The  cutaneous  branches  of  these  nerves,  including  the  posterior  primary  divisions,  thus  supply 
continuous  belts  of  skin,  wliich  can  be  mapped  out  on  the  body  from  the  vertebral  column 
behind  to  the  middle  line  in  front.  These  areas  are  not  placed  liorizontally,  but  tend  to  be 
drawn  downwards  as  the  series  is  followed  from  the  upper  to  tlie  lower  nerves. 

The  twelfth  thoracic  nerve  is  peculiar  in  its  course  and  distribution.     It 


THE  LUMBO-SACRAL  PLEXUS.  639 

emerges  below  the  last  rib  (Fig.  504),  and  passes  outwards  and  downwards  in  the 
posterior  abdominal  wall  under  cover  of  the  psoas  muscle,  and  between  the  external 
arcuate  ligament  and  the  quadratus  lumborum  muscle ;  it  pierces  the  transversalis 
muscle,  and  courses  forwards  in  the  interval  between  it  and  the  obliquus  internus 
as  far  as  the  sheath  of  the  rectus  muscle.  After  piercing  the  posterior  layer  of  the 
sheath,  the  rectus  muscle,  and  the  anterior  layer  of  the  sheath,  it  terminates  by 
supplying  the  skin  of  the  anterior  abdominal  wall  midway  between  the  umbilicus 
and  the  pubis.  The  branches  of  the  nerve  are  muscular,  to  the  transversalis, 
obliqui,  rectus,  and  pyramidalis  muscles  of  the  abdominal  wall,  and  cutaneous 
branches,  two  in  number — an  anterior  terminal  branch,  which  supplies  the  skin  of 
the  anterior  abdominal  wall  midway  between  the  umbilicus  and  the  pubis,  and  a 
large  lateral  cutaneous  (iliac)  hranch,  which,  passing  obliquely  downwards  through 
the  lateral  muscles  of  the  abdominal  wall,  becomes  superficial  above  the  iliac  crest, 
a  couple  of  inches  behind  the  anterior  superior  spine.  It  supplies  the  skin  of  the 
buttock  as  far  down  as  a  point  below  and  in  front  of  the  great  trochanter  of  the 
femur  (Fig.  507,  p.  645). 

Tlie  twelfth  thoracic  nerve,  in  many  cases,  receives  a  communicating  branch  from  the  eknenth, 
near  its  origin,  and  still  more  frequently  sends  a  fine  hrancli  to  join  the  origin  of  the  first 
lumbar  nerve  in  the  psoas  muscle.  It  may  communicate  also  with  the  ilio-hypogastric  nerve,  as 
they  lie  together  in  the  abdominal  wall. 

THE  LUMBO-SACRAL  PLEXUS. 

The  lumbo-sacral  plexus  is  formed  by  the  union  of  the  anterior  primary  divisions 
of  the  remaining  spinal  nerves  —  five  lumbar,  five  sacral,  and  one  coccygeal. 
Frequently,  a  fine  communicating  branch  of  the  twelfth  thoracic  nerve  joins  the 
first  lumbar  nerve  near  its  origin. 

Of  the  nerves  in  question  the  first  sacral  is  generally  the  largest  in  size,  the 
nerves  diminishing  gradually  above  and  rapidly  below  the  first  sacral.  The  plexus, 
for  the  most  part,  forms  the  nerves  destined  for  the  supply  of  the  lower  limb.  In 
addition,  however,  nerves  arise  at  its  upper  limit  w^hich  are  distributed  to  the  trunk 
above  the  level  of  the  limb,  and  at  the  lower  end  of  the  plexus  nerves  arise  for  the 
supply  of  the  perineum. 

Partly  for  convenience  of  description,  and  partly  on  account  of  the  differences 
in  position  and  course  of  some  of  the  nerves  emanating  from  it,  the  plexus  is  sub- 
divided into  three  subordinate  parts  —  lumbar,  sacral  or  sciatic,  and  pudendal 
plexuses.  There  is,  however,  no  strict  line  of  demarcation  between  the  three  parts. 
The  lumbar  plexus  is  formed  by  the  first  four  lumbar  nerves,  and  is  often 
joined  by  a  branch  from  the  twelfth  thoracic  nerve  as  well,  [t  is  limited  below  by 
the  fourth  lumbar  nerve  (n.  furcalis),  which  also  enters  into  the  composition  of  the 
sciatic  or  sacral  plexus.  The  nerves  of  the  lumbar  plexus  are  formed  in  the  loin, 
and  supply  that  region  as  well  as  part  of  the  lower  limb.  They  are  separated  from 
the  nerves  of  the  sacral  portion  of  the  plexus  by  the  articulation  of  the  innominate 
bone  with  the  sacrum. 

The  sacral  or  sciatic  plexus  is  formed  by  the  fourth  and  fifth  lumbar,  and  the 
first  two  or  three  sacral  nerves.  It  is  generally  limited  below  by  the  third  sacral 
nerve  (n.  bigeminus),  which  also  assists  in  forming  the  pudendal  plexus.  The  nerves 
of  the  sacral  plexus  are  placed  on  the  posterior  wall  of  the  pelvis,  and  are  destined 
almost  entirely  for  the  lower  limb. 

The  pudendal  plexus  is  formed  by  the  second,  third,  fourth,  and  fifth  sacral 
nerves,  and  the  minute  coccygeal  nerve.  It  is  placed  on  the  back  wall  of  the  pelvis 
and  supplies  branches  mainly  to  the  perineum. 

Communications  with  the  Sympathetic. — Each  of  these  nerves  has  commuulca- 
tious  with  the  gangliated  cord  of  the  sympathetic  in  the  abdomen  and  pelvis. 

G-ray  Rami  Communicantes. — From  the  lumbar  and  sacral  ganglia  long  slender  yray 
rami  comtnunicantes  are  directed  backwards  and  outwards  over  the  bodies  of  the  vertebrae, 
and  (in  the  lumbar  region)  beneath  the  origins  of  the  psoas  muscle,  to  reach  the  anterior 
primary  divisions  of  the  nerves.  These  branches  are  irregular  in  their  arrangement.  A 
given  nerve  may  receive  branches  from  two  ganglia,  or  one  ganglion  may  send  branches 
to  two  nerves.  The  rami  are  longer  in  the  loin  than  in  the  pelvis,  owing  to  the  projection 
of  the  lumbar  portion  of  the  vertebral  column. 


6-40 


THE  NEEVOUS  SYSTEM. 


White  Rami  Communicantes. — Certain  lumbar  and  sacral  nerves  are  also  connected 
with  the  abdominal  and  pelvic  sympathethic  by  means  of  white  o-ami  communicantes.  From 
the  first  two,  and  possibly  also  the  third  and  fourth  lumbar  nerves,  white  rami  communi- 


FiG.  .501. — Neuves  of  the  Lumbij-Sachai,  1'lkxus. 

Sy,  Syiiipatlietic  cord  ;  T.12,  L.l,  2,  3,  4,  5,  S.l,  2,  3,  4,  5,  Co,  Anterior  primary  divisions  of  the  last  tlioracic, 
the  liiinhar,  .sacral,  and  coccygeal  nerves  ;  Q,  Nerves  to  quadratns  Inniborum  ;  Ps,  Nerves  to  psoas 
niu.scle  ;  G.C,  Genito-crural  nerve  ;  II,  Iliac  branches  of  last  thoracic  and  ilio-hypogastric  nerves  ;  Hy, 
Hypogastric  branch  of  Ilio-hypogastric  nerve  ;  I.I,  Ilio-inguinal  nerve  ;  E.C,  p]xternal  cutaneous  nerve  ; 
A.C,  Anterior  crural  nerve  ;  01)t,  Obturator  nerve  ;  Py,  Nerves  to  pyriformis  muscle  ;  0.1,  Nerve  to 
obturator  internus  ;  Q.F,  Nerve  to  quadratns  fenioris  mu.scle  ;  Art,  Articular  branch  ;  S.G,  Superior 
gluteal  nerve  ;  I.G,  Inferior  gluteal  nerve  ;  P,  Peroneal  nerve  ;  Bi.2,  Nerve  to  short  head  of  biceps 
muscle  ;  T,  Tibial  nerve  ;  Art,  Articular  branch  ;  H.S,  Nerve  to  the  hamstring  muscles  ;  Bi.l,  Nerves 
to  biceps  (long  head),  and  St.l,  to  semitendinosus  ;  St.2,  Semitendinosus  ;  Sm,  Semimembranosus  ; 
A.m,  Adductor  magnus  ;  S.Sc,  Small  sciatic  nerve  ;  Perf,  Perforating  cutaneous  nerve  ;  Pud,  Pudic  nerve  ; 
M.  Muscular  branches  ;  Per,  Perineal  branch  of  fourth  sacral  ;  A. Co,  Anterior  sacro-coccygeal  nerve. 


THE  LUMBAR  PLEXUS. 


641 


cantes  are  directed  forwards,  either  independently  or  incorporated  with  the  correspondino- 
gray  rami,  to  join  the  upper  part  of  the  kuiibar  gangHated  cord.  The  fifth  kuiibar  nerve 
and  the  first  sacral  nerves  are  unprovided  with  white  rami  connnunicantes.  From  the 
third,  and  usually  also  the  second  or  fourth  sacral  nerves,  white  rami  (visceral  branches) 
pass  inwards,  and,  crossing  over  (without  joining)  the  gangliated  cord,  enter  the  pelvic 
plexus  of  the  sympathetic.  The  fifth  sacral  and  coccygeal  nerves  possess  no  white  rami 
communicantes. 

THE  LUMBAR  PLEXUS. 

The  lumbar  plexus  is  formed  by  the  anterior  primary  divisions  of  the  first  three 

Vena  caval  opening     CEsophageal  opening     Central  tendon  (middle  part) 

Diaphragm  (right  cms) 

Middle  arcuate  ligament 
^Aortic  opening 
Central  tendon 
(left  part) 
Eiiaphragin  (left 
„.■ .  ^  I       —  I   ,  cw  -  -       -    /      /       ^   ^-^r^^^^  ^^\  v^^    cms) 

Central  tendon  (right  part)  ^      ^       ^        ^  .  -» \  r-^ 

Diaphragm  (costal  fibies)^ 

Internal  arcuate  ligament 


External  arcuate  ligament 

End  of  last  rib 

Last  thoracic  nervl 

Ant.  layer  of  lumbar  fascia 

Lumbar  fascia 

iLIO-HYPOGASTRIf 

Lumbar  vessels  and  synipa 

thetic  communicating  neives 

Ilio-ingdinal 

Quadratus  lumboiun 

External  cutaneous  nerve- 

Psoas  niagnu^ 

Iliacus. 

Llimbo-sacral  cord 

Genito-crural  nerve 

Anterior  crural  ner\  e. 

Obturator  nerve. 

Great  sciatic  ner^  e 


Trn      Lumbar  ne 
~j  vlj — Ilio-hypoo. 

-T    I     ' I    Tl.ri,   .   „     ,,„ 


Last  thoracic 

NERVE 

End  of  last  rib 

NERVE  L 


POOASTRIC 

Lumbar  nerve  II. 


„,.|  ^ Ilio-incuinal 

_^^|  r Quadratus 

^^RTd      hiinborum 

Lumbar  nerve  III. 


Genito-crural 


Lumbar  nerve  IV. 


Lumbo-sacral  cord 


\ternal  cutaneous 

NER%  E 

Ant   crural  nerve 
Obturator  nerve 
Gre\t  sciatic  nerve 


Adductor  longus  (origin) 
Adductor  brevis  (origin) 
Gracilis  (origin) 
Adductor  niagnus  (origin) 
Pectinens  (cut) 
I      I    Superficial  branch  of  obturator  nerve 
I     Deep  branch  of  obturator  nerve 
Obturator  externus 

Fig.  505.— View  of  the  Posterior  Abdominal  Wall,  to  show  the  Muscles  and  the  Nerves  of 

THE  Lumbo-Sacral  Plexus. 

and  a  part  of  the  fourth  lumbar  nerves,  with  the  addition,  in  some  cases,  of  a  small 
branch  from  the  twelfth  thoracic  nerve.  The  nerves  increase  in  size  from  above 
downwards  (Fig.  505). 

Position  and  Constitution.— The  plexus  is  placed  deeply  in  the  substance  of 
the  psoas  muscle,  in  front  of  the  transverse  processes  of  the  lumbar  vertebra?.     The 
45 


642  THE  NEEVOUS  SYSTEM. 

nerves,  on  emergiug  from  the  intervertebral  foramina,  are  connected  as  above 
described  with  the  sympathetic  system,  and  then  divide  in  the  following  manner  in 
the  substance  of  the  psoas  muscle.  The  first  and  second  nerves  divide  into  upper 
and  lower  branches.  The  upper  branch  of  the  first  nerve  (which  may  be  joined  by 
the  branch  from  the  twelfth  thoracic  nerve)  forms  two  nerves,  ilio-hypogastric  and 
ilio-inguinal.  The  lower  branch  of  the  first  joins  the  upper  branch  of  the  second 
nerve,  to  produce  the  genito-crural  nerve.  The  lower  branch  of  the  second  nerve, 
the  whole  of  the  third,  and  that  part  of  the  fourth  nerve  engaged  in  the  con- 
stitution of  the  plexus  divide  each  into  two  unequal  parts — smaller  anterior  and 
larger  'posterior  ptarts.  The  smaller  anterior  portions  combine  together  to  form 
the  obturator  nerve,  which  is  thus  formed  by  the  second,  third,  and  fourth  lumbar 
nerves.  The  root  from  the  second  nerve  is  not  always  present.  The  larger 
posterior  portions  of  the  same  nerves  combine  together  to  form  the  anterior 
crural  nerve.  Erom  the  back  of  the  posterior  parts  of  the  second  and  third 
nerves,  the  external  cutaneous  nerve  arises.  The  nerves  also  provide,  near  their 
origins,  irregular  muscular  branches,  for  the  psoas  and  quadratus  lumborum 
muscles.  The  following  is  a  list  of  the  nerves  which  spring  from  the  lumbar 
plexus  (Figs.  504  and  505) : — 

(1)  Muscular  branches  to  the  quadratus  (4)  Genito-crural. 

lumborum  and  psoas.  (5)  External  cutaneous. 

(2)  Ilio-hypogastric.  (6)  Obturator. 

(3)  Ilio-inguinal.  (7)  Anterior  crural. 

Muscular  Branches. — The  nerves  to  the  quadratus  lumborum  muscle  arise 
independently  from  the  first  three  or  four  lumbar  nerves  (and  sometimes  also  from 
the  twelfth  thoracic  nerve).  The  nerves  to  the  psoas  muscles  arise  from  the  second 
and  third  lumbar  nerves,  with  additions,  in  some  cases,  from  the  first  or  fourth. 
They  are  often  associated  in  their  origin  with  the  nerve  to  the  iliacus  from  the 
anterior  crural.  The  psoas  minor,  when  present,  is  innervated  by  the  first  or 
second  lumbar  nerve. 

The  ilio-hypogastric  and  ilio-inguinal  nerves  closely  resemble  in  their  course 
and  distribution  the  lower  thoracic  nerves,  with  which  they  are  in  series. 

The  ilio-hypogastric  nerve  (n.  ilio-hypogastricus)  is  the  highest  branch  of 
the  first  lumbar  nerve.     It  receives  fibres  also  from  the  twelfth  thoracic,  when  that 
nerve  communicates  with  the  first  lumbar  nerve.     After  traversing  the  psoas  muscle 
obliquely,  it  appears  at  its  outer  border  on  the  surface  of  the  quadratus  lumborum 
and  behind  the  kidney.     It  courses  through  the  loin,  lying  between  the  transversalis 
and  obliquus  internus  muscles,  above  the  crest  of  the  ilium.     About  an  inch  in  front  of 
the  anterior  superior  sxDine  it  pierces  the  obliquus  internus,  and  continues  its  course 
in  the  groin  beneath  the  aponeurosis  of  the  obliquus  externus.     It  finally  becomes 
cutaneous  in  the  anterior  abdominal  wall,  by  piercing  the  aponeurosis  of  the  obliquus 
externus  about  an  inch  and  a  half  above  the  external  abdominal  ring  (Fig.  507  p.  645). 
Its  branches  are — (1)  muscular  to  the  muscles  of  the  abdominal  wall ;  and  (2) 
cutaneous  tranches,  two  in  numljcr.     The  iliac  branch  corresponds  with  the  lateral 
branch   of  an   intercostal   nerve,  and,  after  piercing  the  obliquus  internus  and. 
obliquus  externus,  becomes  cutaneous  just  above  the  iliac  crest,  below  and  behind 
the  iliac  branch-of  the  last  thoracic  nerve.     It  is  small,  and  may  be  absent.     It  is 
distributed  to  the  skin  over  the  upper  part  of  the  outer  side  of  the  buttock,  in  con- 
tinuity with  the  cutaneous  branch  of  the  posterior  primary  division  of  the  first 
lumbar  nerve.     The  hypogastric  branch  is  the  anterioi-  terminal  branch  of  the  nerve. 
It  supplies  the  skin  of  the  anterior  abdominal  wall  below  the  level  of  the  last 
thoracic  nerve  and  a})Ove  the  pu])is. 

The  ilio-inguinal  nerve  (n.  ilio-iuguinalis)  is  the  second  branch  given  off 
from  the  first  lumbar  nerve.  It  also  may  receive  fibres  from  the  last  thoracic 
nerve.  Not  unfrequcntly  the  ilio-hypogastric  and  ilio-inguinal  nerves  are  repre- 
sented for  a  longer  or  shorter  part  of  their  course  by  a  single  trunk.  When  separate 
the  nerve  takes  a  course  similar  to  that  of  the  ilio-hypogastric  nerve,  but  at  a  lower 
level,  as  far  as  the  anterior  abdominal  wall.  It  then  pierces  the  obliquus  internus 
farther  forward  and  lower  down  than  the  ilio-hypogastric;  and  coursing  forwards 


OBTUKATOE  NERVE.  643 

beneath  the  aponeurosis  of  the  obliquus  externus,  just  above  Poupart's  ligament,  it 
becomes  superficial  after  passing  through  the  external  abdominal  ring  and  external 
spermatic  fascia  (Fig.  507,  p.  645). 

Its  branches  are  muscular  to  the  muscles  of  the  abdominal  wall,  among  which  it 
passes,  and  cutaneous  hra7iches,  which  innervate  the  skin  (1)  of  the  anterior  abdominal 
wall  over  the  symphysis  pubis,  (2)  of  the  thigh  over  the  upper  and  inner  part  of 
Scarpa's  triangle,  and  (3)  of  the  upper  part  of  the  scrotum,  and  root  and  dorsum  of 
the  penis  (of  the  mons  Veneris  and  labium  majus  in  tho  female).  These  last-named 
branches  are  contiguous  to  branches  of  the  pudendal  and  pudic  nerves.  No  lateral 
cutaneous  branch  arises  from  the  ilio-inguinal  nerve.  It  thus  corresponds,  like  the 
hypogastric  part  of  the  ilio-hypogastric  nerve,  to  the  anterior  trunk  of  a  typical 
thoracic  nerve. 

The  genito-crural  nerve  (u.  genito-femoralis)  usually  arises  by  two  independent 
roots  from  the  front  of  the  first  and  second  lumbar  nerves,  which  unite  in  the  substance 
of  the  psoas  to  form  a  slender  trunk.  It  appears  on  the  posterior  abdominal  wall, 
lying  on  the  psoas  magnus,  internal  to  the  psoas  parvus,  and,  piercing  the  psoas 
fascia,  it  extends  downwards  on  the  outer  side  of  the  common  and  external  iliac  vessels 
and  behind  the  ureter  to  Poupart's  ligament  (Fig.  505,  p.  641).  At  a  variable  point 
above  that  ligament  it  divides  into  genital  and  crural  branches.  The  genital  branch 
is  a  minute  nerve.  It  crosses  the  terminations  of  the  external  iliac  vessels,  and, 
along  with  the  vas  deferens  and  spermatic  vessels,  enters  the  inguinal  canal  through 
the  internal  abdominal  ring.  It  terminates  by  supplying  small  branches  to  the 
skin  of  the  scrotum  and  adjacent  part  of  the  thigh.  In  the  female  it  accompanies 
the  round  ligament  to  the  labium  majus.  This  nerve  gives  off  in  its  course  the 
following  small  branches :  (1)  to  the  external  iliac  artery ;  (2)  to  the  cremaster 
muscle ;  (3)  to  communicate  with  the  spermatic  plexus  of  the  sympathetic.  The 
crural  branch  continues  the  course  of  the  parent  nerve  into  the  thigh,  lying  on  the 
■outer  side  of  the  femoral  artery.  It  becomes  cutaneous  by  passing  through  the 
saphenous  opening  or  the  iliac  portion  of  the  fascia  lata,  and  supplies  an  area  of 
skin  over  Scarpa's  triangle,  external  to  that  supplied  by  the  ilio-inguinal  nerve 
(Fig.  507,  p.  645).  It  communicates  in  the  thigh  with  the  middle  cutaneous 
branch  of  the  anterior  crural  nerve.  Before  piercing  the  deep  fascia  it  gives  a 
minute  branch  to  the  femoral  artery. 

The  external  cutaneous  nerve  (n.  cutaneus  femoris  lateralis)  is  only  distri- 
buted to  skin  (Fig.  505).  It  arises  from  the  back  of  the  lumbar  plexus,  and  usually 
from  the  second  and  third  lumbar  nerves.  Emerging  from  the  psoas  muscle  at  its 
outer  border,  the  nerve  crosses  the  iliacus  muscle,  beneath  the  fascia  iliaca,  to  reach 
the  anterior  superior  iliac  spine.  It  enters  the  thigh  beneath  the  outer  extremity 
of  Poupart's  ligament,  and  either  over,  under,  or  through  the  origin  of  the  sartorius 
muscle.  It  extends  down  the  outer  side  of  the  front  of  the  thigh  for  a  few  inches, 
lying  at  first  beneath  the  fascia  lata,  and  afterwards  in  a  tubular  investment  of  the 
fascia.  It  gives  off  small  branches  in  this  part  of  its  course,  and  finally,  piercing  the 
fascia  about  four  inches  below  the  anterior  superior  iliac  spine,it  separates  intoanterior 
and  posterior  terminal  branches.  The  anterior  branch  is  the  larger,  and  is  distributed 
on  the  outer  side  of  the  front  of  the  thigh  almost  to  the  knee.  The  smaller  posterior 
branch  supplies  the  skin  of  the  outer  side  of  the  buttock  below  the  great  trochanter 
and  of  the  upper  two-thirds  of  the  outer  side  of  the  thigh  (Fig.  507,  p.  645). 

Obturator  Nerve. 

The  obturator  nerve  (n.  obturatorius)  supplies  the  muscles  and  skin  on  the 
inner  side  of  the  thigh.  It  arises  in  the  substance  of  the  psoas  muscle  by  three 
roots  placed  in  front  of  those  of  the  anterior  crural  nerve,  and  derived  from  the 
second,  third,  and  fourth  lumbar  nerves  (Fig.  505,  p.  641).  Sometimes  the  root 
from  the  second  nerve  is  absent.  Passing  vertically  downwards,  the  nerve  emerges 
from  the  psoas  at  its  inner  border,  behind  the  common  iliac,  and  on  the  outer  side 
of  the  internal  iliac  vessels.  It  passes  forwards  below  the  pelvic  brim  in  company 
with  the  obturator  artery  to  the  obturator  groove  of  the  thyroid  foramen,  through 
which  it  reaches  the  thigh.  While  in  the  obturator  groove  it  separates  into  its 
two  main  branches,  named  superficial  and  deep  (Fig.  506,  p.  644). 
45  « 


644 


THE  NERVOUS  SYSTEM. 


The  superficial  branch  enters  the  thigh  in  front  of  the  obturator  externus  and 
adductor  brevis  muscles,  and  beneath  the  pectineus  and  adductor  longus.  In  the 
middle  third  of  the  thigh  it  is  found  coursing  along  the  inner  border  of  the  adductor 
lono'us,  anterior  to  the  gracilis;  and  it  finally  divides  into  two  slender  terminal 
filaments,  of  which  one  enters  Hunter's  canal  and  ends  on  the  femoral  artery,  while 
the  other  supplies  the  skin  for  a  variable  distance  on  the  inner  side  of  the  thigh  and 
joins  in  the  obturator  (sub-sartorial)  plexus. 

The  branches  of  the  superficial  part  of  the  nerve  are  : — 

1.  An  articular  branch  to  the  hip-joint  which  arises  from  the  nerve  as  soon  as 
it  enters  the  thigh,  and  supplies  the  joint  through  the  acetabular  notch. 


Obturator  nerve 


Pubisv\ 

Psoas  magnus 

Branch  to  hip-joint. 

Deep  branch 

Superficial  branch 

Descending  muscular  branches 

Pectineus 

Ascending  branch  to  obturator 
externus 

Internal  circumflex  artery 

Adductor  longus 
Adductor  brevis 


Cutaneous  Branch 


Gluteus  maximus 
Pelvic  fascia 
Obturator  internus 
Obturator  externus 

ihium 

Ascending  branch  of  internal 
circumflex  artery 
Quadratus  femoris 
ternal  circumflex  artery 

ing  muscular  branches 
Adductor  magnus 

Branch  to  knee-joint 


Branch  to  femoral  artery  Gracilis 

Fig.  506. — Scheme  of  the  Course  and  Distribution  of  the  Obturator  Nerve. 

2.  Muscular  branches  to  the  adductor  longus,  gracilis,  adductor  brevis  (usually), 
pectineus  (occasionally).  The  last-named  muscle  is  not  usually  supplied  from  the 
obturator  nerve. 

3.  A  cutaneous  branch  of  very  variable  size  forms  one  of  the  terminal  branches 
(Fig.  507).  It  becomes  superficial  between  the  gracilis  and  adductor  longus,  in  the 
middle  third  of  the  thigh,  and  may  supply  the  skin  of  the  lower  two-thirds  of  the 
thigh  in  its  injier  side.  It  is  generally  of  small  size,  and  is  connected  with 
branches  of  the  internal  cutaneous  and  internal  saphenous  nerves  behind  the 
sartorius  muscle  to  form  the  obturator  (sub-sartorial)  plexus.  The  branch  from  the 
internal  saphenous  nerve  to  the  plexus  passes  inwards  behind  the  sartorius  after 
piercing  the  aponeurotic  covering  of  Hunter's  canal.  The  In-anch  from  the  internal 
cutaneous  nerve  is  generally  superficial  at  the  point  of  formation  of  the  plexus. 

4.  The  branch  to  the  femoral  artery  is  the  other  terminal  branch  of  the 
nerve.  It  enters  Hunter's  canal  along  the  inner  edge  of  the  adductor  longus,  and 
ramifies  over  the  lower  part  of  the  artery. 

5.  A  fine  communicating  branch  sometimes  joins  the  anterior  crural  nerve  in 
front  of  the  hip-joint. 

The  deep   part  of  the  obturator  nerve  reaches  the  thigh   by  piercing  the 


ANTERIOR  CRURAL  NERVE. 


645 


It  passes  downwards  between  the  adductor  brevis  and 
After  passing  obliquely 


obturator  ex  tern  us  muscle, 
adductor  magnus  muscles 

through  the  adductor  magnus,  it  appears  in  the  popliteal 
space  on  the  popliteal  vessels,  and  terminates  by  piercing 
the  poiterior  ligament  and  supplying  the  knee-joint. 
Its  branches  are :— (1)  muscular  branches  to  the 
obturator  externus,  adductor  magnus,  and  (when  the 
muscle  is  not  supplied  by  the  superficial  part  of  the 
nerve)  the  adductor  brevis.  The  branch  to  theoljturator 
externus  arises  before  the  nerve  enters  the  muscle,  in 
the  obturator  groove.  The  nerve  to  the  adductor 
magnus  is  given  off  as  the  obturator  nerve  passes 
through  the  substance  of  the  muscle.  (2)  An  articular 
terminal  branch  is  supplied  to  the  back  of  the  knee-joint. 

Anterior  Crural  Nerve. 

The  anterior  crural  nerve  (n.  femoralis)  is  the 
great  nerve  for  the  muscles  and  skin  of  the  front  of 
the  thigh.  It  arises  in  the  substance  of  the  psoas 
muscle,  from  the  back  of  the  second,  third,  and  fourth 
lumbar  nerves,  behind  the  obturator  nerve.  Passing 
obUquely  through  the  psoas  muscle,  it  emerges  from 
its  outer  border  in  the  false  pelvis  (Fig.  505,  p.  641). 
Passing  downwards  in  the  groove  between  the  psoas 
and  iliacus,  it  enters  the  thigh  beneath  Poupart's  liga- 
ment, external  to  the  femoral  sheath  and  femoral 
vessels.  In  Scarpa's  triangle  it  breaks  up  into  a  large 
number  of  branches,  among  which  the  external  cir- 
cumflex artery  passes. 

The  branches  of  the  anterior  crural  nerve,  which 
are  (1)  muscular,  (2)  articular,  and  (3)  cutaneous, 
arise  in  the  following  way : — 

In  the  abdomen  a  muscular  branch  arises  from 
the  outer  side  of  the  nerve  and  enters  the  iliacus 
muscle. 

In  Scarpa's  triangle  the  terminal  muscular, 
articular,  and  cutaneous  l:)ranches  arise  in  the  form 
of  a  large  bundle  of  nerves. 

1.  The  muscular  branches  supply  the  pectineus,  Fig.  507.— Distribution  of  Cuta- 
sartorius,  and  quadriceps  extensor.  The  nerve  to  the  the^LowerYimb^  ^^^  ^'^^^  '^^ 
pectineus  arises  close  to  Poupart's  ligament,  and  ^^^  ^^^^  ^^^  ^^^^  ^^^/^i^^^i^^^^.^^  ^^  ^i^^ 
coursnig  obliquely  downwards  and  mw^ards  behind 
the  femoral  vessels  enters  the  muscle  at  its  outer 
border.  It  is  not  infrequently  double.  It  some- 
times gives  off  a  fine  communicating  branch  to  the 
superficial  part  of  the  obturator  nerve.  The  nerves 
to  the  sariorius  are  in  two  sets  :  an  outer  short  set  of 
nerves  associated  with  the  outer  part  of  the  middle 
cutaneous  nerve,  which  enter  the  upper  part  of  the 
muscle ;  and  an  inner  longer  set  which  are  associated 
with  the  inner  part  of  the  middle  cutaneous  nerve, 
and  supply  the  middle  of  the  muscle.  The  parts  of 
the  quadriceps  extensor  are  supplied  by  several 
branches.  The  vastus  externus  and  rectus  femoris 
are  supplied  on  their  deep  surface  by  separate  nerves 
which  are  accompanied  by  branches  of  the  external 
circumflex  artery.  The  crureus  muscle  is  supplied 
superficially  by  a  nerve  which  passes  through  the 
muscle,  and  innervates  also  the  subcrureus.  It  also  receives  fibres  from  one  of 
45  6 


several    nerves    is    represented,   the 
letters  indicating  their  nomenclature. 

T.ll,  Branches  of  eleventh  thoracic 
nerve;  T.  12,  Branches  of  twelfth 
thoracic  nerve  ;  l.H,  Ilio-hypogastric; 
I.I,  Ilio-ingninal ;  E.C,  External  cuta- 
neous ;  G.  C,  Genito-crural  ;  M.C^,-, 
Middle  cutaneous  ;  I.C\-,  Internal 
cutaneous  ;  Obt,  Obturator  ;  S.Sc, 
Small  sciatic  ;  Pat.  Plex,  Patellar 
plexus ;  Pat.  Patellar  branch  of 
internal  saphenous;  E. P.S,  Sural 
branches  of  peroneal  nerve  ;  I.  S, 
Internal  saphenous  ;  M.  C,  Musculo- 
cutaneous ;  E.S, Externalsaphenous; 
A.T,  Anterior  tibial. 

On  the  other  side  a  schematic  repre- 
sentation is  given  of  the  areas  sup- 
plied by  the  above  nerves,  the  figures 
indicating  the  spinal  origin  of  the 
branches  of  distribution  to  each  area. 


646  THE  NEEVOUS  SYSTEM. 

the  nerves  to  the  vastus  internus.  The  vastus  internus  muscle  is  supplied  hy  two 
nerves  :  an  upper  trunk,  which  supplies  the  higher  part  of  the  muscle,  and  sends  fibres 
to  the  crureus  as  well ;  and  a  lower  trunk,  which  descends  on  the  outer  side  of  the 
femoral  artery  along  with  the  internal  saphenous  nerve,  and  passing  beneath  the 
sartorius,  over  or  under  the  aponeurotic  covering  of  Hunter's  canal,  enters  the  inner 
side  of  the  vastus  internus  muscle.  This  nerve  gives  off  a  small  branch  which  enters 
the  medullary  canal  of  the  femur. 

2.  The  articular  branches  supply  the  hip  and  knee-joints.  The  articular  branch  to 
the  hip-joint  arises  from  the  nerve  to  the  rectus  femoris,  and  is  accompanied  by 
branches  from  the  external  circumflex  artery.  The  articular  branches  to  the  knee- 
joint  are  four  in  nvimber.  Three  of  them  arise  from  the  nerves  to  the  vastus  externus, 
crureus,  and  vastus  internus,  which,  after  the  muscular  nerves  are  given  off,  are 
continued  downwards  to  the  knee-joint  along  the  front  of  the  femur.  A  fourth 
articular  branch  arises  (sometimes)  from  the  internal  saphenous  nerve. 

3.  The  cutaneous  branches  are  the  middle  and  internal  cutaneous,  and  the 
internal  saphenous  nerves  (Fig.  507). 

The  middle  cutaneous  nerve  arises  in  two  parts,  an  external  and  an  internal 
branch,  in  the  upper  part  of  Scarpa's  triangle.  The  two  branches  descend  vertically 
and  become  cutaneous  by  piercing  the  fascia  lata  over  the  upper  third  of  the 
sartorius  muscle.  They  carry  muscular  branches  to  the  sartorius,  and  the  external 
branch  in  many  cases  pierces  the  muscle.  These  two  nerves  supply  the  skin  of 
the  lower  three-fourths  of  the  front  of  the  thigh,  between  the  external  cutaneous 
nerve  on  the  outer  side  and  the  internal  cutaneous  on  the  inner  side.  They 
reach  down  to  the  front  of  the  patella,  and  there  assist  in  the  formation  of  the 
patellar  plexus.  The  external  branch  communicates  in  the  upper  third  of  the 
thigh  with  twigs  from  the  crural  branch  of  the  genito-crural  nerve. 

The  internal  cutaneous  nerve  lies  at  first  in  Scarpa's  triangle  on  the  outer  side 
of  the  femoral  vessels.  At  the  apex  of  the  triangle  it  crosses  over  the  femoral  vessels, 
and  is  directed  downwards  over  or  through  the  sartorius  muscle,  and  beneath  the 
fascia  lata,  to  the  lower  third  of  the  thigh.  It  is  distributed  to  the  skin  of  the 
lower  two-thirds  of  the  thigh  on  the  inner  side  by  means  of  three  branches — upper, 
middle,  and  lower. 

The  upper  branch  may  be  represented  by  two  or  more  twigs.  It  arises  from  the 
main  nerve  near  its  origin,  and  pierces  the  fascia  lata  near  the  apex  of  Scarpa's 
triangle.  It  is  distributed  to  the  skin  of  the  upper  part  of  the  thigh,  along  the 
line  of  the  saphenous  vein.  The  middle  or  anterior  branch  is  a  larger  nerve.  It 
separates  from  the  lower  branch  at  the  apex  of  Scarpa's  triangle,  and  passing  over 
the  sartorius  muscle  becomes  cutaneous  in  the  middle  third  of  the  thigh  on  the 
inner  side.  It  supplies  the  skin  of  the  lower  half  of  the  thigh  on  the  inner  side, 
extending  as  low  as  the  knee,  where  it  joins  in  the  formation  of  the  patellar  plexus. 

The  lovjer  or  internal  brancJi,  represents  the  termination  of  the  nerve.  It  passes 
down  the  inner  side  of  the  thigh  over  the  sartorius  muscle,  and  communicates  in 
the  middle  third  of  the  thigh  with  the  internal  sapheaous  and  obturator  nerves  to 
form  the  obturator  plexus.  Piercing  the  fascia  lata  on  the  inner  side  of  the  thigh 
in  the  lower  third,  it  ramifies  over  the  inner  side  of  the  knee,  and  assists  in  the 
formation  of  the  patellar  plexus. 

The  size  of  the  internal  cutaneous  nerve  varies  with  the  size  of  the  cutaneous 
part  of  the  obturator,  and  of  the  internal  saphenous  nerve. 

The  long  or  internal  saphenous  nerve  (n.  saphenus)  may  be  regarded  as  the 
terminal  branch  of  the  anterior  crural  uerve.  It  is  destined  for  the  skin  of  the  leg 
and  foot.  From  its  origin  in  Scarpa's  triangle  it  descends  alongside  the  femoral 
vessels  to  Hunter's  canal.  Id  the  canal  it  crosses  over  the  femoral  sheath  from 
without  inwards.  At  the  lower  end  of  the  canal,  accompanied  by  the  superficial 
branch  of  the  anastomotic  artery,  it  passes  over  the  tendon  of  the  adductor  magnus, 
and  opposite  the  inner  side  of  the  knee-joint  becomes  cutaneous  by  passing  between 
the  sartorius  and  gracilis  muscles.  Jhe  nerve  then  extends  down  the  leg  along 
with  the  internal  saphenous  vein,  and  coursing  over  the  front  of  the  inner  ankle  it 
terminates  at  the  middle  of  the  inner  border  of  the  foot. 

Branches. — 1.  A  communicating  branch  arises  in  Hunter's  canal,  and  passing 


THE  SACEAL  OE  SCIATIC  PLEXUS.  647 

inwards  beneath  the  sartorius  joins  with  branches  of  the  obturator  nerve  in  forming 
the  obturator  plexus. 

2.  The  patellar  branch  arises  at  the  lower  end  of  Hunter's  canal,  and  piercing  the 
sartorius  muscle  is  directed  downwards  and  forwards  below  the  patella,  and  over 
the  inner  tuberosity  of  the  tibia  to  the  front  of  the  knee  and  upper  part  of  the 
leg.     It  enters  into  the  formation  of  the  patellar  plexus. 

3.  An  articular  branch  sometimes  arises  from  the  nerve  at  the  inner  side  of  the  knee. 

4.  The  terminal  branches  of  the  internal  saphenous  nerve  are  distributed  to  the 
skin  of  the  front  and  inner  side  of  the  leg,  and  the  posterior  half  of  the  dorsum 
and  inner  side  of  the  foot. 

Patellar  plexus. — This  plexus  consists  of  fine  communications  beneath  the 
skin  in  front  of  the  knee,  between  the  branches  of  the  cutaneous  nerves  supplying 
that  region.  The  nerves  which  enter  into  its  formation  are  the  patellar  branch  of 
the  internal  saphenous,  internal  and  middle  cutaneous  nerves,  and  sometimes  the 
external  cutaneous  nerve. 

The  accessory  obturator  nerve  (n.  oljturatorius  accessorius,  n.  accessorius  aiiterioris  cruralis 
Winslow)  is  only  occasionally  jiresent  (29  per  cent,  Eisler).  It  arises  from  the  third,  or  third  and 
fourth  lumbar  nerves,  between  the  roots  of  the  obturator  and  anterior  crural  nerves.  Associating 
itself  with  the  obturator,  from  which,  however,  it  is  quite  separable,  it  appears  in  the  abdomen 
at  the  inner  side  of  the  psoas  muscle,  and  coursing  over  the  pelvic  brim  behind  the  external  iliac 
vessels,  it  leaves  the  obturator  nerve,  and  enters  the  thigh  in  front  of  the  pubis. 

In  the  thigh,  behind  the  femoral  vessels,  it  usually  ends  in  three  branches :  a  nerve  which 
replaces  the  branch  from  the  anterior  crural  to  the  2Jectineus,  a  nerve  to  the  hijj-joint,  and  a 
nerve  which  communicates  with  the  suj^erficial  part  of  the  obturator  nerve.  In  some  cases  it 
only  su^^iilies  the  nerve  to  the  pectineus  ;  more  rarely  it  is  of  considerable  size,  and  reinforces  the 
obturator  nerve  in  the  innervation  of  the  adductor  muscles. 

The  accessory  obturator  nerve  was  first  described  by  Winslow  as  the  n.  accessorius  anferioris 
crurcdis.  Schmidt  later  described  it  in  great  detail,  and  gave  it  the  name  it  now  bears.  It  is 
more  closely  associated  with  the  anterior  crural  than  with  the  obturator.  Its  origin  is  behind 
the  roots  of  the  obturator :  it  is  separated,  like  the  anterior  crural,  from  the  obturator  by  the 
pubic  bone,  and  its  chief  branch,  to  the  pectineus  muscle,  replaces  the  normal  branch  from  the 
anterior  crural  nerve.  On  the  other  hand,  for  a  part  of  its  course  it  accomj)anies  the  obturator, 
and  in  rare  cases  it  may  replace  branches  of  that  nerve. 

THE  SACRAL  OR  SCIATIC  PLEXUS. 

The  sacral  or  sciatic  portion  of  the  lumbo-sacral  plexus  is  destined  almost 
entirely  for  the  lower  limb.  It  is  usually  formed  by  the  anterior  primary  divisions 
of  a  part  of  the  fourth  lumbar  nerve  (n.  furcalis),  the  fifth  lumbar,  the  first,  and 
parts  of  the  second,  and  third  sacral  nerves  (n.  bigeminus). 

Communications  with  the  Sympathetic. — Each  of  the  nerves  named  is  connected 
to  the  lumbar  or  pehnc  sympathetic  by  gray  rami  communicantes,  as  already  described  ; 
and  white  rami  communicantes  pass  usually  from  the  third  and  usually  also  from  the 
second  or  fourth  sacral  nerves  to  join  the  pelvic  plexus  of  the  sympathetic. 

Position  and  Constitution. — The  plexus  is  placed  on  the  back  wall  of  the 
pelvis  between  the  parietal  pelvic  fascia  and  the  pyriformis  muscle.  In  front  of  it 
are  the  pelvic  colon,  the  internal  iliac  vessels,  and  the  ureter. 

The  plexus  is  constituted  by  the  convergence  of  the  nerves  concerned  towards 
the  lower  part  of  the  great  sacro-sciatic  foramen,  and  their  union  to  form  a  broad 
triangular  band,  the  apex  of  which  is  continued  through  the  great  sacro-sciatic 
foramen  below  the  pyriformis  muscle  into  the  buttock,  as  the  great  sciatic  nerve. 
From  the  anterior  and  posterior  surfaces  of  this  triangular  band  numerous  small 
branches  arise,  which  are  distributed  to  the  parts  in  the  neighbourhood  of  the 
origin  of  the  nerve. 

The  great  sciatic  nerve  ends  in  the  thigh  by  dividing  into  two  large  nerves,  the 
tibial  (internal  popliteal),  and  peroneal  (external  popliteal).  In  many  cases  these 
two  nerves  are  distinct  from  their  origin,  and  are  separated  sometimes  by  fibres 
of  the  pyriformis  muscle.  In  all  cases  on  removal  of  the  sheath  investing  the 
great  sciatic  nerve  the  tibial  and  peroneal  nerves  can  be  traced  up  to  the  plexus, 
from  which  they  invariably  take  origin  by  distinct  and  separate  roots. 

The  descending  branch  of  the  fourth  lumbar  nerve  (n.  furcalis)  after  emerging 
from  the  inner  border  of  the  psoas  muscle  internal  tr^  the  obturator  nerve,  divides 


648  THE  NEEVOUS  SYSTEM. 

behind  the  ihac  vessels  into  anterior  and  posterior  (ventral  and  dorsal)  parts,  each 
of  which  joins  a  corresponding  part  of  the  fifth  lumbar  nerve.  The  anterior 
primary  division  of  the  fifth  lumbar  nerve  descends  over  the  ala  of  the  sacrum,  and 
divides  into  anterior  and  posterior  parts,  which  are  joined  by  the  corresponding  parts 
of  the  fourth  lumbar  nerve.  The  two  resulting- trunks  are  sometimes  called  the 
lumbo-sacral  cord.  The  first  and  second  sacral  nerves  pass  almost  horizontally  out- 
wards from  the  anterior  sacral  foramina,  and  divide  in  front  of  the  pyriformis  into 
similar  anterior  and  posterior  parts.  The  third  sacral  nerve  (n.  bigeminus)  divides 
into  upper  and  lower  parts.  The  lower  part  is  concerned  in  forming  the  pudendal 
plexus.  The  upper  part  is  directed  outwards,  and  slightly  upwards,  towards  the 
preceding  nerve,  and  does  not  separate  into  two  parts,  but  remains  undivided. 

These  trunks  combine  to  form  the  sciatic  or  sacral  plexus,  and  its  main  sub- 
divisions, in  the  following  way.  Lying  in  apposition,  and  converging  to  the  lower 
part  of  the  great  sacro-sciatic  foramen,  the  posterior  (dorsal)  trunks  of  the  fourth  and 
fifth  lumbar  nerves  (lumbo-sacral  cord),  and  of  the  first  and  second  sacral  nerves, 
combine  to  form  the  peroneal  nerve  and  the  subordinate  nerves  which  arise  from  the 
posterior  aspect  of  the  plexus.  The  anterior  (ventral)  trunks  of  the  fourth  and  fifth 
lumbar  nerves  (lumbo-sacral  cord),  and  of  the  first  and  second  sacral  nerves,  together 
with  that  part  of  the  third  sacral  nerve  which  is  contributed  to  the  plexus,  unite  to 
form  the  tibial  nerve  and  the  subordinate  nerves  arising  from  the  front  of  the  plexus. 
Of  these  nerves  the  fifth  lumbar  and  first  sacral  are  the  largest ;  the  others 
diminishing  in  size  as  they  are  traced  upwards  and  downwards.  There  is  no 
distinct  demarcation  between  the  sacral  and  pudendal  plexuses.  The  second  and 
third  sacral  nerves  (and  in  some  cases  the  first  sacral  also)  are  concerned  in  the 
formation  of  both  plexuses. 

Branches.  —  The  nerves  of  distribution  derived  from  the  sacral  plexus  are 
divided  according  to  their  origin  into  an  anterior  (ventral)  and  a  posterior  (dorsal) 
series.     Each  set  comprises  one  of  the  two  essential  terminal  parts — peroneal  and 
tibial  nerves — of  the  great  sciatic,  and  numerous  smaller  collateral  branches. 
Anterior  Branches.  Posterior  Branches. 

Tibial  (internal  popliteal)  nerve  Peroneal  (external  popliteal)  nerve 

Muscular  branches —  Muscular  branches — 

Nerves  to  hamstring  muscles  Nerves  to  short  head  of  biceps 

,,  quadratus  femoris  ,,         pyriformis 

,,         gemelli  Superior  gluteal  nerve 

,,  obturator  internus  Inferior  gluteal  nerve 

Articular  branches  (to  hip-joint)  Articular  branches  (to  knee-joint) 

Gee  AT  Sciatic  Nerve. 

The  great  sciatic  nerve  (n.  ischiadicus).- — It  has  already  been  shown  how 
this  nerve  is  formed.  It  comprises  the  two  main  nerves  of  the  sacral  plexus,  bound 
together  by  an  investing  sheath,  which  contains,  in  addition  to  the  peroneal  and 
tibial  nerves,  a  subordinate  branch  of  each,  the  nerve  to  the  hamstring  muscles, 
from  the  tibial,  and  the  nerve  to  the  short  head  of  the  biceps  flexor  cruris,  from 
the  peroneal  nerve.  A  thick  band  about  half  an  inch  in  breadth  is  formed,  con- 
sisting from  within  outwards  of  (1)  nerves  to  the  hamstring  muscles,  (2)  tibial 
(internal  popliteal),  (3)  peroneal  (external  popliteal),  (4)  nerve  to  the  short  head  of  the 
biceps  muscle.  The  great  sciatic  nerve  extends  through  the  buttock  and  the  back 
of  the  thigh.  Forming  a  continuation  of  the  sacral  plexus,  it  enters  the  buttock 
by  passing  through  the  great  sacro-sciatic  foramen,  in  the  interval  between  the 
pyriformis  and  superior  gemellus.  Concealed  by  the  gluteus  maximus  muscle,  it 
passes  downwards  to  the  thigh,  accompanied  by  the  sciatic  artery,  and  the  arteria 
comes  nervi  ischiadici.  It  lies  in  the  hollow  between  the  great  trochanter  of  the 
femur  and  the  tuVjerosity  of  the  ischium,  and  enters  the  thigh  beneath  the  fold  of  the 
nates  at  the  lower  border  of  the  gluteus  maximus.  At  this  spot  it  is  comparatively 
superficial,  lying  in  the  angle  between  the  edge  of  the  gluteus  maximus  above  and 
externally,  and  the  origins  of  the  hamstring  muscles  internally.  In  the  thigh  it 
is  placed  upon  the  adductor  magnus  beneath  the  hamstring  muscles,  and  it 
terminates  at  a  variable  point  by  dividing  into  the  tibial  and  peroneal  nerves.     As 


NEKVES  or  DISTKIBUTION  FEOM  THE  SACKAL  PLEXUS.     649 

already  stated,  these  two  nerves  may  be  separate  from  their  origins,  and  their 
separation  may  occur  at  any  point  between  the  great  sacro-sciatic  foramen  and  the 
upper  part  of  the  popliteal  space. 

The  Nerves  of  Distribution  from  the  Sacral  Plexus. 

These  are  divisible  into  two  series — collateral  and  terminal  branches.  Each 
subdivision  consists  of  a  series  of  aiiterior  (ventral)  and  posterior  (dorsal)  trunks. 

Collateral  Branches. — The  anterior  branches  are  (a)  muscular  branches  (to  the 
quadratus  femoris,  gemelli,  obturator  internus,  and  hamstring  muscles) ;  and  (b) 
articular  branches  (to  the  hip -joint).  These  nerves  all  arise  from  the  anterior 
aspect  of  the  sacral  plexus. 

The  nerve  to  the  quadratus  femoris  (and  inferior  gemellus)  arises  from  the 
front  of  the  fourth  and  fifth  lumbar  and  tirst  sacral  nerves.  It  passes  downwards 
over  the  back  of  the  capsule  of  the  hip-joint  (to  which  it  sends  a  fine  branch)  beneath 
the  sacral  plexus,  gemelli,  and  obturator  internus  muscles.  It  supphes  a  nerve  to 
the  inferior  gemellus,  and  terminates  in  the  deep  surface  of  the  quadratus  femoris. 

The  nerve  to  the  obturator  internus  (and  superior  gemellus)  arises  from  the 
anterior  aspect  of  the  fifth  lumbar  and  first  two  sacral  nerves.  In  the  buttock  it 
lies  below  the  great  sciatic  nerve  on  the  outer  side  of  the  pudic  vessels ;  crossing 
the  ischial  spine,  it  enters  the  ischio-rectal  fossa  through  the  lesser  sciatic  foramen. 
The  nerve  supplies  in  the  buttock  a  branch  to  the  superior  gemellus,  and  terminates 
by  entering  the  pelvic  surface  of  the  obturator  internus. 

The  nerve  to  the  hamstring  muscles  forms  the  innermost  part  of  the  great 
sciatic  trunk  in  the  lower  part  of  the  buttock.  It  arises  from  all  the  roots  of  the 
tibial  nerve  on  their  anterior  aspect,  viz.,  from  the  fourth  and  fifth  lumbar  and 
the  first  three  sacral  nerves.  These  roots  unite  to  form  a  cord  which  is  closely 
associated  with  the  tibial  nerve  and  is  placed  in  front  of  and  afterwards  on  its 
inner  side.  Extending  into  the  thigh,  the  trunk  is  distributed  to  the  hamstring 
muscles  by  means  of  two  sets  of  branches.  Just  below  the  level  of  the  ischial 
tuberosity  an  upper  set  of  nerves  passes  inwards  to  enter  the  upper  part  of  the 
semi-tendinosus  and  the  ischial  head  of  the  biceps.  Lower  down  in  the  thigh  the 
remaining  portion  of  the  nerve  separates  off  from  the  great  sciatic  (tibial)  trunk 
and  supplies  branches  to  the  semi-membranosus,  the  lower  part  of  the  semi-tendi- 
nosus, and  the  adductor  magnus. 

Articular  branches  for  the  hip-joint  arise  from  the  nerve  to  the  quadratus 
femoris,  and  often  directly  from  the  front  of  the  great  sciatic  (tibial)  nerve  near  its 
origin.     They  enter  the  back  of  the  capsule  of  the  joint  in  the  region  of  the  buttock. 

The  posterior  branches  are  :  (a)  muscular  branches,  viz.  a  nerve  to  the  pyriformis, 
the  superior  gluteal  nerve,  the  inferior  gluteal  nerve,  and  a  nerve  to  the  short  head 
of  the  biceps ;  (b)  articular  branches  (to  the  knee-joint). 

These  nerves  all  arise  from  the  posterior  aspect  of  those  roots  of  the  sacral 
plexus,  which  are  associated  with  the  origin  of  the  peroneal  nerve. 

The  nerve  to  the  pyriformis  muscle  may  be  double.  It  arises  from  the  back 
of  the  second,  or  first  and  second  sacral  nerves,  and  at  once  enters  the  anterior 
surface  of  the  muscle. 

The  superior  gluteal  nerve  (n.  gluta?us  superior)  arises  from  the  back  of  the 
fourth  and  fifth  lumbar  and  first  sacral  nerves,  and  is  directed  backwards  and 
outwards  into  the  buttock,  above  the  pyriformis  muscle,  along  with  the  gluteal 
artery.  Under  cover  of  the  gluteus  maximus  and  gluteus  medius,  it  extends 
outwards  over  the  gluteus  minimus,  along  with  the  inferior  part  of  the  deep  gluteal 
artery,  to  the  under  surface  of  the  tensor  vaginse  femoris,  in  which  it  ends.  On 
its  way  it  supplies  branches  to  the  gluteus  medius  and  gluteus  minimus. 

The  inferior  gluteal  nerve  (n.  glutseus  inferior)  arises  from  the  back  of  the  fifth 
lumbar  and  first  two  sacral  nerves.  It  appears  in  the  buttock  at  the  lower  border 
of  the  pyriformis  muscle,  superficial  to  the  great  sciatic  nerve,  and  at  once  breaks 
up  into  a  number  of  branches  for  the  supply  of  the  gluteus  maximus.  In  its  course 
in  the  buttock  it  is  closely  associated  with  the  small  sciatic  nerve.  Its  origin  is 
sometimes  combined  with  that  of  the  following  nerve. 

The  nerve  to  the  short  head  of  the  biceps  springs  from  the  outer  side  of  the 


650  THE  NEEVOUS  SYSTEM. 

great  sciatic  (peroneal)  trunk  in  the  upper  part  of  the  thigh.  When  traced  to  its 
origin,  it  is  found  to  arise  (sometimes  in  combination  with  the  inferior  gluteal  nerve) 
from  the  fifth  lumbar  and  first  two  sacral  nerves.  In  its  course  it  is  closely 
applied  to  the  outer  side  of  the  peroneal  nerve,  from  which  it  separates  in  the 
middle  third  of  the  thigh,  usually  in  combination  with  the  articular  branches  of 
that  nerve  for  the  knee-joint.  In  some  cases  it  has  an  independent  course  in  the 
thigh,  and  it  may  be  associated  in  the  buttock  with  the  inferior  gluteal  nerve. 

An  articular  branch  for  the  outer  side  and  front  of  the  knee-joint  generally 
arises  from  the  great  sciatic  or  peroneal  nerve  in  common  with  the  nerve  to  the 
short  head  of  the  biceps.  When  traced  up  to  the  plexus,  it  is  found  to  arise  from 
the  back  of  the  fourth  and  fifth  lumbar  and  first  sacral  nerves.  It  passes  through 
the  upper  part  of  the  popliteal  space  concealed  by  the  biceps  muscle,  and  separates 
into  upper  and  lower  branches,  which  accompany  the  upper  and  lower  external 
articular  arteries  to  the  outer  side  of  the  knee-joint. 

Terminal  Branches. — The  peroneal  (external  popliteal)  and  tibial  (internal 
popliteal)  nerves  are  the  two  main  trunks  resulting  from  the  combination  of  the 
posterior  and  anterior  cords  respectively  of  the  sacral  plexus.  The  peroneal  nerve 
is  homologous  with  the  musculo-spiral  nerve  in  the  upper  limb  ;  the  tibial  nerve 
represents  a  medio-ulnar  trunk  ;  and,  as  already  stated,  the  two  nerves,  constituting 
the  great  sciatic  nerve,  are  enveloped  in  a  common  sheath  for  a  variable  distance 
before  pursuing  .an  independent  course  in  the  leg. 

Peeoneal  Nerve. 

The  peroneal  or  external  popliteal  nerve  (n.  peron?eus  communis)  arises  from 
the  back  of  the  sacral  plexus  from  the  fourth  and  fifth  lumbar  and  first  two 
sacral  nerves.  Incorporated  with  the  great  sciatic  nerve  in  the  buttock  and 
upper  half  of  the  thigh,  it  passes  downwards  from  the  bifurcation  of  that  nerve 
through  the  popliteal  space,  to  its  termination  at  a  point  about  an  inch  below  the 
head  of  the  fibula.  It  is  concealed  at  first  by  the  biceps  muscle.  Following 
the  tendon  of  that  muscle,  it  passes  obliquely  through  the  upper  and  outer  part 
of  the  popliteal  space  and  over  the  outer  head  of  the  gastrocnemius  muscle  to  the 
back  of  the  head  of  the  fibula.  In  the  lower  part  of  its  course  and  at  its  termination 
it  is  directly  beneath  the  deep  fascia. 

Collateral  Branches. — These  are  divided  into  two  sets  :  (a)  Xerves  arising  from 
the  roots  or  trunk  of  the  nerve  while  it  is  in  combination  with  the  tibial  nerve  in 
the  great  sciatic  trunk.  These  have  been  already  described,  ^^z.  a  muscular  branch 
to  the  short  head  of  the  biceps,  and  an  articular  branch  to  the  knee-joint,  (h)  Nerves 
arising  in  the  popliteal  space.  These  are  cutaneous  branches,  viz.  a  sural  branch  and 
the  peroneal  communicating. 

The  sural  branch  (n.  cutaneus  surse  lateralis)  is  irregular  in  size  and  distribution, 
and  may  be  represented  by  two  or  more  branches  (Fig.  507,  p.  645).  Arising  from 
the  peroneal  nerve  in  the  popliteal  space,  often  in  common  with  the  succeeding 
nerve,  it  pierces  the  deep  fascia  over  the  outer  head  of  the  gastrocnemius,  and  is 
distributed  to  the  skin  on  the  outer  aspect  of  the  back  of  the  leg  in  the  upper 
two-thirds.  The  extent  of  its  distribution  varies  with  that  of  the  small  sciatic 
and  external  saphenous  nerves. 

The  peroneal  communicating  nerve  (r.  anastomoticus  peronseus,  r.  communicans 
fibularis),  arising  in  the  popliteal  space,  passes  over  the  outer  head  of  the  gastro- 
cnemius beneath  the  deep  fascia  to  the  middle  third  of  the  leg,  where  it  assists  in 
forming  the  external  saphenous  nerve  by  its  union  with  the  tibial  communicating 
branch  of  the  tibial  nerve.  In  many  cases  the  two  branches  do  not  unite.  In  such 
cases  the  peroneal  communicating  nerve  may  be  limited  in  its  distribution  to  the 
skin  of  the  outer  side  of  the  leg,  heel,  and  ankle,  or  it  may  be  distributed  to  the 
area  usually  supplied  by  the  external  saphenous  nerve. 

Terminal  Branches.  —  The  terminal  branches  of  the  peroneal  nerve  are 
recurrent  tibial,  anterior  tibial,  and  musculo-cutaneous.  They  arise  just  below 
the  head  of  the  fibula,  and  are  directed  forwards,  diverging  in  their  course, 
beneath  the  peroneus  longus  muscle. 

The  recurrent  tibial  nerve  is  the  smallest  branch.     Passing  forwards  beneath 


MUSCULO-CUTANEOUS  NEEVE. 


651 


the  origin  of  the  peroneus  longus  and  the  extensor  longus  digitoriim  muscles,  it 
divides  below  the  outer  tuberosity  of  the  til)ia  into  branches  which  supply  the  upper 
fibres  of  the  tibialis  anticus  muscle,  the  tibio-fibular  articulation,  and  the  knee-joint. 

Anterior  Tibial  Nerve. 

The  anterior  tibial  nerve  (n.  peronseus  profundus)  passes  downwards  and  in- 
wards, beneath  the  peroneus  longus,  extensor  longus  digitorum,  and  extensor  proprius 
hallucis  muscles,  to  the  front  of  the  leg.  In  its  course  down  the  leg  it  is  deeply 
placed  upon  the  interosseous  membrane  and  the  lower  part  of  the  tibia,  in  company 
with  the  anterior  tibial  artery.  At  the  ankle  it  lies  beneath  the  anterior  annular 
ligament  and  the  tendon  of  the  extensor  proprius  hallucis,  and  crossing  over  the 
ankle-joint,  it  divides  on  the  dorsum  of  the  foot  into  its  terminal  branches. 

1.  Collateral  Branches  (in  the  leg). — These  are  given  off  to  the  muscles  between 
which  the  anterior  tibial  nerve  passes :  tibialis  anticus,  extensor  proprius  hallucis, 
extensor  longus  digitorum,  and  peroneus  tertius.  A  fine  articular  branch  supplies 
the  ankle-joint. 

2.  Terminal  Branches  (on  the  foot). — The  terminal  branches  are  internal  and 
external.  The  internal  branch  passes  along  the  dorsum  of  the  foot  on  the  outer 
side  of  the  dorsalis  pedis  artery  to  the  first  interosseous  space,  where  it  divides  into 
two  dorsal  digital  branches  for  the  supply  of  the  skin  of  the  outer  side  of  the  great 
toe  and  the  inner  side  of  the  second  toe.      Each  of  these 

branches  communicates  with  branches  of  the  musculo- 
cutaneous nerve.  It  gives  off  one  or  two  dorsal  inter- 
osseous branches,  which  supply  the  inner  tarso-metatarsal 
and  metatarso-phalangeal  articulations,  and  also  enter  the 
first  dorsal  interosseous  mviscle. 

The  external  branch  passes  outwards  over  the  tarsus 
beneath  the  extensor  brevis  digitorum,  and  ends  in  a 
ganghform  enlargement  (similar  to  the  gangliform  enlarge- 
ment on  the  posterior  interosseous  nerve  at  the  back  of  the 
wrist).  From  this  enlargement  muscular  branches  arise 
for  the  supply  of  the  extensor  brevis  digitorum,  along  with 
branches  for  the  tarsal,  tarso-metatarsal,  and  metatarso- 
phalangeal articulations.  Its  dorsal  interosseous  hranches 
may  be  as  many  as  four  in  number.  Of  these  the  outer  two, 
extremely  small,  may  only  reach  the  tarso-metatarsal 
articulations.  The  inner  two  are  fine  branches,  which, 
besides  supplying  the  articulations,  may  give  branches  to 
the  second  and  third  dorsal  interosseous  muscles. 

The  branches  from  the  anterior  tibial  nerve  to  the 
interosseous  muscles  are  probably  sensory,  the  motor  supply 
of  these  muscles  being  certainly  derived  from  the  external 
plantar  nerve. 

MUSCULO-CUTANEOUS    NeRVE. 


Dorsum      of     the 


The     mUSCUlO-CUtaneOUS     nerve     (n.     peronseus    super-  Fig.  508.— Distribution  of 
ficialis),  the  last   of  the   branches   of   the   peroneal  nerve,     Cutaneous    Nerves    on 
passes  below  the  head  of  the  fibula  and  beneath  the  upper 
fibres  of  the  peroneus  longus  muscle.     Lying  in  a  sheath  in  t  t.  t  +      i      i 

.  ^  ^  Jo  I.b,  Internal  sapr 

the  intermuscular  septum,  between  the  peronei  externally 
and  the  extensor  longus  digitorum  internally,  it  proceeds 
downwards  in  front  of  the  fibula  to  the  lower  third  of 
the  leg,  where  it  pierces  the  deep  fascia  in  two  branches, 
internal  and  external. 

Its  branches  are :  (1)  collateral  muscular  branches  dis- 
tributed to  the  peroneus  longus  and  peroneus  brevis,  as  the   nerve  lies  in  relation 
to  these  muscles ;  (2)  terminal  cutaneous  branches,  internal  and  external. 

The  internal  terminal  branch  courses  downwards  over  the  anterior  annular  liga- 


lenous  nerve  ; 
M.C,  Musculo  -  cutaneous 
nerve  ;  A.T,  Anterior  tibial 
nerve ;  E.S,  External  sa- 
phenous nerve.  The  ex- 
tremities of  the  toes  are 
supplied  1)}'  the  plantar 
nerves  (I.P,  E.P). 


652  THE  NEEVOUS  SYSTEM. 

ment  of  the  ankle,  and  after  supplying  offsets  to  the  lower  third  of  the  leg  and  dorsum 
of  the  foot,  divides  into  three  branches.  (1)  The  internal  branch  supplies  the  skin 
of  the  dorsum  of  the  foot  and  the  inner  side  of  the  great  toe,  and  communicates 
with  the  internal  saphenous  nerve.  (2)  The  intermediate  branch  passes  to  the 
interval  between  the  great  toe  and  the  second,  and  divides  into  two  branches  which 
communicate  with  the  internal  branch  of  the  anterior  tibial  nerve.  (3)  The 
external  branch  passes  to  the  interval  between  the  second  and  third  toes,  and 
divides  into  two  digital  branches  to  supply  the  adjacent  sides  of  these  toes. 

The  external  terminal  branch  of  the  nerve  descends  over  the  anterior  annular 
ligament,  and  after  supplying  branches  to  the  lower  part  of  the  leg  and  the 
dorsum  of  the  foot,  divides  into  two  parts,  internal  and  external,  which,  passing  to 
the  intervals  between  the  third  and  fourth,  and  fourth  and  fifth  toes  respectively, 
divide  into  dorsal  digital  branches  for  the  adjacent  sides  of  these  toes.  These 
branches  communicate  with  offsets  of  the  external  saphenous  nerve. 

The  arrangement  of  the  cutaneous  branches  of  the  musculo-cutaneous  is  liable  to  considerable 
variation.  The  outer  division  of  the  nerve  may  be  increased  in  size,  and  may  sup]Dly  the  nerve 
to  the  adjacent  sides  of  the  second  and  third  toes ;  or  in  other  cases,  it  may  be  reduced  in  size,  in 
Avhich  case  the  external  saphenous  nerve  takes  its  place  on  the  dorsum  of  the  foot,  often  supplying 
as  many  as  two  and  a  half  toes  on  the  outer  side. 

The  cutaneous  nerves  on  the  dorsum  of  the  toes  from  the  anterior  tibial  and  musculo-cutaneous 
nerves  are  much  smaller  than  the  corresponding  plantar  digital  nerves.  They  are  reinforced  on 
the  dorsum  of  the  terminal  phalanges  by  twigs  from  the  plantar  nerves,  which  supply  the  tips  of 
the  toes  and  the  nails. 

Tibial  Nerve. 

The  tibial  or  internal  popliteal  nerve  (n.  tibialis)  arises  from  the  front  of 
the  sacral  plexus,  usually  from  the  fourth  and  fifth  lumbar  and  first  three  sacral 
nerves  (Fig.  511,  p.  656).  It  is  incorporated  in  the  great  sciatic  trunk  in  the 
buttock  and  upper  part  of  the  thigh.  At  the  bifurcation  of  the  great  sciatic  nerve 
it  passes  onwards  through  the  popliteal  space  and  the  back  of  the  leg.  The  part 
of  the  nerve  from  its  origin  from  the  plexus  or  the  bifurcation  of  the  great  sciatic 
nerve  to  the  lower  border  of  the  popliteus  muscle,  is  sometimes  called  internal 
popliteal ;  the  part  of  the  nerve  in  the  back  of  the  leg  being  then  designated 
posterior  tibial.  The  course  of  the  nerve  through  the  buttock  and  thigh  has  already 
been  described  (p.  648).  In  the  popliteal  space  it  is  concealed  at  first  by  the 
semi-membranosus  and  other  hamstring  muscles.  It  crosses  the  popliteal  vessels 
from  without  inwards,  and  is  thereafter  found  upon  the  popliteus  muscle,  under 
cover  of  the  gastrocnemius  and  plantaris.  In  the  back  of  the  leg,  from  the  lower 
border  of  the  popliteus  muscle  to  the  ankle,  the  tibial  (or  posterior  tibial)  nerve 
lies  on  the  tibialis  posticus  muscle  and  the  tibia,  and,  along  with  the  posterior 
tibial  vessels,  occupies  a  sheath  in  the  intermuscular  septum  separating  the  super- 
ficial and  deep  muscles  of  the  back  of  the  leg.  In  the  upper  part  of  the  leg  the 
nerve  is  internal  to  the  vessels,  but,  crossing  over  them,  it  lies  on  their  outer  side 
in  the  lower  portion  of  its  course.  It  terminates  beneath  the  internal  annular 
ligament  by  dividing  into  the  external  and  internal  plantar  nerves. 

The  collateral  branches  may  be  divided  into  three  series  arising  respectively 
in  the  region  of  the  thigh,  the  popliteal  space,  and  the  back  of  the  leg : — 

(a)  Branches  arising  from  the  Roots  or  Trunk  of  the  Nerve  ivhUe  it  is  incor- 
porated %vith  the  Great  Sciatic  Nerve. — These  have  been  already  described,  viz. 
muscular  branches  to  the  quadratus  feinoris,  gemelli,  obturator  internus,  and  the 
hamstring  muscles,  and  an  articular  branch  to  the  hip-joint  (Fig.  511,  p.  656). 

(i))  Branches  arising  in  the  Foplitejd  Space  ahove  the  Knee- Joint. — These  are 
in  three  sets — articular,  nmscular,  cutaneous. 

1.  The  articular  branches  are  slender  nerves,  variable  in  number.  There  are 
usually  two,  an  azggos  branch  which  pierces  the  posterior  ligament  of  the  knee- 
joint,  and  an  internal  branch,  a  long  fine  nerve  which,  crossing  the  popliteal  vessels, 
descends  on  the  inner  side  of  the  space  to  accompany  the  lower  internal  articular 
artery  to  the  knee-joint.  In  its  course  it  gives  off  a  branch,  often  absent,  which 
accompanies  the  upper  internal  articular  artery. 

2.  The  muscular  branches  are  five  in  num})er.  Nerves  for  the  two  heads  of  the 
gastrocnemius,  and  the  plantaris  enter  these  muscles  at  the  borders  of  the  popliteal 


TIBIAL  NEEVE. 


653 


space.  A  nerve  for  the  soleus  enters  the  superficial  surface  of  the  muscle.  A 
nerve  for  the  popliteus  muscle  passes  over  the  surface  of  that  muscle,  and  after 
winding  round  its  lower  border,  supplies  it  on  its  deep  (anterior)  surface.  As  this 
nerve  passes  beneath  the  popliteus  it  supplies  branches 
to  the  tibialis  posticus  muscle,  an  interosseous  branch 
for  the  interosseous  membrane,  which  can  be  traced  as 
far  as  the  lower  tibio-tibular  articulation,  an  articular 
branch  for  the  upper  tibio-fibular  joint,  and  a  medullary 
branch  for  the  shaft  of  the  tibia. 

3.  The  cutaneous  branch  is  the  tibial  communicating 
nerve  (n.  communicans  tibialis,  n.  cutaneus  surse 
medialis).  This  nerve  passes  from  the  popliteal  space 
in  the  groove  between  the  two  heads  of  the  gastro- 
cnemius muscle,  and  afterwards  lies  upon  the  tendo 
achillis.  It  pierces  the  deep  fascia  in  the  middle  third 
of  the  back  of  the  leg,  and  is  joined  immediately 
afterwards  by  the  peroneal  communicating  nerve 
from  the  peroneal  nerve.  From  their  union  the 
external  or  short  saphenous  nerve  results,  which 
reaches  the  foot,  winding  round  the  back  of  the 
external  malleolus  along  with  the  external  saphenous 
vein.  The  external  saphenous  nerve  supplies  cuta- 
neous branches  to  the  outer  side  and  back  of  the 
lower  third  of  the  leg,  the  ankle  and  heel,  and  the 
outer  side  of  the  foot  and  little  toe,  as  well  as  ar- 
ticular branches  to  the  ankle  and  tarsal  joints. 

The  external  saphenous  nerve  communicates  on  the 
foot  with  the  musculo-cutaneous  nerve,  and  its  size  varies 
with  the  size  of  that  nerve.  It  may  extend  on  to  the 
dorsum  of  the  foot  for  a  considerable  distance,  and  may 
either  reinforce  or  replace  the  branches  of  the  musculo- 
cutaneous nerve  to  the  intervals  between  the  fourth  and 
fifth  and  the  third  and  fourth  toes.  The  mode  of  forma- 
tion of  the  external  saphenous  nerve  is  very  variable.  The 
usual  ai'rangement  is  that  described.  Frequently  the 
peroneal  and  tibial  communicating  nerves  do  not  unite, 
and  in  such  cases  the  more  usual  arrangement  is  for  the 
tibial  communicating  nerve  to  form  alone  the  external 
saphenous  nerve,  the  peroneal  communicating  nerve  ex- 
tending only  to  the  ankle  and  heel.  It  is  less  nsual  for 
the  peroneal  communicating  nerve  to  form  alone  the  ex- 
ternal saphenous  nerve,  the  tibial  communicating  nerve  in 
these  cases  ending  at  the  heel. 

(c)  Branches  arising  in  the  Back  of  the  Leg  helov: 
the  Knee-Joint.— These  branches  are  mainly  muscular  ^^  ^^^  ^^^  ^-^^  ^^^  distributiou  of 

and  cutaneous.  the  several  nerves  is  represented. 

The  muscular  branches  are  four  in  number,  com- 
prising nerves  to  the  soleus  (entering  its  deep  surface) 
and  tibialis  posticus,  often  arising  by  a  common  trunk, 
and  nerves  to  the  flexor  longus  digitorum  and  flexor 
longus  hallucis,  the  latter  generally  accompanying 
the  peroneal  artery  for  some  distance. 

The  cutaneous  branch  is  the  internal  calcanean  nerve 
(rr.  calcanei  mediales),  wdiich  pierces  the  internal 
annular  ligament,  and  is  distributed  to  the  skin  of 
the  heel  and  back  part  of  the  sole  of  the  foot. 


Fig.  509. — Distribution  of  Cuta- 
neous Nerves  on  the  Back  of 
the  Lower  Lijib. 


the  letters  indicating  their  nomen- 
clature. 

L.l,  2,  3,  S.l,  2,  .3,  Posterior  primary 
divisions  of  lumbar  and  sacral 
nerves  ;  I.H,  Ilio-hypogastric;  T.12, 
Lateral  and  posterior  branches  of 
last  thoracic  nerve;  A.Co',  Posterior 
sacro-coccygeal  nerve  ;  A. Co'-,  An- 
terior sacro-coccygeal  nerve  ;  Perf, 
Perforating  cutaneous  nerve  ;  S.Sc, 
Small  sciatic  ;  E.C,  External  cuta- 
neous ;  Obt,  Obturator  ;  LC,  In- 
ternal   cutaneous  ;    E.  P.S,    Sural 


branches  of  peroneal  ;  I. S,  Internal 
saphenous  ;  E.S,  External  saphenous  ;  M.C,  Musculo-cutaneous  ;  Calc,  Calcanean  branch  of  posterior 
tibial  ;  LP,  Internal  plantar  ;  E.P,  E.xternal  plantar  nerve. 
On  the  other  side  a  schematic  representation  is  given  of  the  areas  supplied  by  the  above  nerves,  the  figures 
indicating  the  spinal  origin  of  the  branches  of  distribution  to  each  area. 


654 


THE  NERVOUS  SYSTEM. 


In  addition  a  medullary  nerve  to  the  fibula,  and  a  small  articular  branch  to 
the  ankle-joint,  are  supplied  by  the  posterior  tibial  nerve. 

The  terminal  branches  of  the  tibial  nerve  are  the  internal  and  external 
plantar  nerves. 

Internal  Plantar  Nerve. 

The  internal  plantar  nerve  (n.  plantaris  medialis)  is  homologous  with  the 
median  nerve  in  the  hand  (Fig.  510,  p.  654).  It  is  rather  larger  than  the  external 
plantar.  It  courses  forwards  in  the  sole  of  the  foot  beneath  the  internal  annular 
ligament  and  abductor  hallucis  to  the  interval  between  that  muscle  and  the  flexor 
brevis  digitorum,  in  company  with  the  internal  plantar  artery. 

The  collateral  branches  are  muscular,  cutaneous,  and  articular.  The  muscular 
branches  supply  the  abductor  hallucis  and  the  flexor  brevis  digitorum.  The  plantar 
cutaneous  branches  are  small  twigs  which  pierce  the  plantar  fascia  in  the  interval 
between  these  muscles  to  supply  the  inner  part  of  the  sole  of  the  foot.  The  arti- 
cular branches  are  minute  twigs  which  supply  the  inner  tarsal  and  tarso-metatarsal 
articulations. 

The  terminal  branches  are  four  in  number,  and  may  be  designated  first, 
second,  third,  and  fourth,  from  within  outwards. 

The  first  (most  internal)  branch  separates  from  the  nerve  before  the  others, 
and  pierces  the  plantar  fascia  behind  the  ball  of  the  great 
toe.  It  supplies  a  muscular  branch  to  the  flexor  brevis 
hallucis,  and  cutaneous  branches  to  the  inner  side  of  the 
foot  and  ball  of  the  great  toe.  It  terminates  as  the 
plantar  digital  nerve  for  the  inner  side  of  the  great  toe. 

The  second  branch  arises  along  with  the  third  and 
fourth ;  after  supplying  a  branch  to  the  first  lumbrical 
muscle,  it  becomes  superficial  in  the  interval  between  the 
first  and  second  toes,  and  terminates  by  dividing  into  two 
collateral  digital  nerves  for  the  supply  of  the  adjacent  sides 
of  these  toes. 

The  third  and  fourth  branches  are  entirely  cutaneous  in 
their  distribution.  They  become  superficial  in  the  intervals 
between  the  second  and  third  and  the  third  and  fourth 
toes  respectively,  and  there  divide  into  collateral  digital 
branches  for  the  supply  of  the  adjacent  sides  of  these  toes. 
The  plantar  digital  nerves  supply  the  whole  length  of 
the  toes  on  the  plantar  aspect,  and,  in  relation  to  the 
terminal  phalanges,  furnish  minute  dorsal  offsets  for  the 
supply  of  the  nails  and  tips  of  the  toes  on  their,  dorsal 
surface.  The  internal  plantar  nerve  thus  supplies  the  skin 
of  the  three  and  a  half  inner  toes  in  the  sole  of  the  foot ; 
and  four  muscles  : — the  abductor  hallucis  and  flexor  brevis 
digitorum,  the  flexor  brevis  hallucis,  and  the  first  lumbrical 
muscle. 

External  Plantar  Nerve. 


PB.M.D. 


Fig.  510. — Scheme  of  Distri- 
bution OF  THE  Plantar 
Nerves. 

LPl,  Internal  plantar  nerve,  and 
its  cutaneous  and  muscular 
branches ;  F.B.D,  Flexor 
brevis  digitorum  ;  Abd.H, 
Abductor  hallucis  ;  F.B.  H, 
Flexor  brevis  hallucis  ;  L.I, 
First  lumbricalis  ;  E.Pl,  Ex- 
ternal plantar  nerve,  and  its 
cutaneous  and  muscular 
branches  ;  Ace,  Accessorius  ; 
Abd.m.d,  Abductor  minimi 
digiti ;  F.B.  M.D,  Flexor  brevis 
minimi  digiti  ;  R.P,  Ramus 
profundus. 


The  external  plantar  nerve  (n.  plantaris  lateralis) 
is  homologous  with  the  ulnar  nerve  in  the  hand.  From 
its  origin  beneath  the  internal  annular  ligament  it 
extends  forwards  and  outwards  in  the  sole,  in  company 
with  the  external  plantar  artery,  between  the  flexor  brevis 
digitorum  and  accessorius  muscles,  towards  the  head  of 
the  fifth  metatarsal  bone.  Here  it  terminates  by  dividing 
into  superficial  and  deep  branches. 

-Muscular  branches  are  given  off  from  the  undivided  nerve 
to  the  accessorius  and  abductor  minimi  digiti  muscles.  Cutaneous  branches 
pierce  the  plantar  fascia  at  intervals  along  the  line  of  tlie  intermuscular  septum, 
between  the  flexor  brevis  digitorum  and  abductor  minimi  digiti. 

Terminal  Branches. — The  superficial  branch  (r.  superficialis)  is  mainly  cutaneous. 


Collateral  Branches. 


THE  PUDENDAL  PLEXUS.  655 

Passing  forwards  between  the  tlexor  brevis  digitoriiiu  and  abductor  minimi  digiti, 
it  divides  into  external  and  internal  parts. 

The  external  Irandi,  after  supplying  the  llexor  brevis  minimi  digiti  muscle,  and 
sometimes  one  or  both  interossei  of  the  fourth  space,  becomes  superficial  behind 
the  ball  of  the  little  toe,  and  supplies  cutaneous  twigs  to  the  sole  of  tlie  foot  and  ball 
of  the  toe.     It  terminates  as  the  digital  branch  for  the  outer  side  of  the  little  toe. 

The  internal  branch  passes  forwards  to  the  interval  between  the  fourth  and  fifth 
toes,  where  it  becomes  cutaneous,  and  divides  into  two  collateral  digital  branches  for 
the  supply  of  the  adjacent  sides  of  these  toes.  It  communicates  with  the  fourth 
terminal  branch  of  the  internal  plantar  nerve. 

The  deep  branch  (r.  profundus)  of  the  external  plantar  nerve,  passing  deeply 
along  with  the  external  plantar  artery,  extends  inwards  towards  the  great  toe, 
beneath  the  accessorius  and  adductor  obliquus  hallucis.  It  gives  off'  articular 
tranches  to  the  tarsal  and  tarso-metatarsal  articulations,  and  muscular  branches 
to  the  interossei  of  each  space  (except  in  some  cases  the  muscles  of  the  fourth 
space) :  to  the  adductor  obliquus  and  adductor  transversus  hallucis,  and  the  outer 
three  lumbrical  muscles.  These  nerves  enter  the  deep  surface  of  the  muscles,  that 
to  the  second  lumbrical  reaching  its  muscle  after  passing  forwards  beneath  the 
adductor  transversus  hallucis. 

THE  PUDENDAL  PLEXUS. 

The  pudendal  plexus  constitutes  the  third  and  last  subdivision  of  the  lumbo- 
sacral plexus.  It  is  composed  for  the  most  part  of  the  spinal  nerves  below  those 
which  form  the  sacral  plexus ;  but,  as  already  stated,  there  is  no  distinct  point  of 
separation  between  the  two  plexuses.  On  the  contrary,  there  is  considerable  over- 
lapping, so  that  two  and  sometimes  three  of  the  principal  nerves  derived  from  the 
pudendal  plexus  have  their  origin  in  common  with  nerves  of  the  sacral  plexus. 

The  plexvis  is  formed  by  fi]jres  from  the  anterior  primary  divisions  of  the  first 
three  sacral  nerves,  and  by  the  whole  of  the  anterior  primary  divisions  of  the  fourth 
and  fifth  sacral  and  coccygeal  nerves.  The  size  of  the  nerves  diminishes  rapidly 
from  the  first  sacral  to  the  coccygeal,  which  is  extremely  slender. 

Position  and  Constitution. — The  plexus  is  formed  on  the  back  wall  of  the 
pelvis.  Of  the  nerves  forming  it,  the  upper  ones  emerge  from  the  anterior  sacral 
foramina ;  the  fifth  sacral  nerve  appears  between  the  last  sacral  and  first  coccygeal 
vertebra ;  and  the  coccygeal  nerve  appears  below  the  transverse  process  of  that 
vertebra.     The  nerves  of  distribution  derived  from  the  plexus  are  the  following : — 

1.  Visceral  branches.  4.   Pudic  nerve. 

2.  Small  sciatic  nerve.  5.  Muscular  branches. 

3.  Perforating  cutaneous  nerve.  6.   Sacro-coccygeal  nerve. 

Omitting  the  visceral  branches,  all  the  nerves  are  distributed  to  the  perineum. 
Only  two,  the  small  sciatic  and  perforating  cutaneous  nerves,  send  branches  to  the 
lower  liml). 

Visceral  Branches. — Like  the  other  spinal  nerves,  the  fourth  and  fifth  sacral 
and  coccygeal  nerves  are  provided  with  fine  gray  rami  communicantes  from 
the  sacral  gangliated  cord,  which  joins  them  after  a  short  course  on  the  front  of 
the  sacrum.  The  third  (along  with  the  second  or  fourth)  sacral  nerve  in  addition 
sends  a  considerable  ^ohite  ramus  com.municans  or  visceral  branch  inwards  to  the 
pelvic  plexus  and  viscera. 

Small  Sciatic  Nerve  (n.  cutaneus  femoris  posterior). — This  nerve  is  complex 
both  in  origin  and  distribution  (Fig.  511,  p.  656).  Springing  from  the  junction  of 
the  sacral  and  pudendal  plexuses,  it  is  derived  from  the  first  three  or  second  and 
third  sacral  nerves.  It  is  distributed  to  the  lower  limb  and  perineum,  and  is 
associated  with  other  nerves  belonoinff  to  both  regions.  It  arises  from  the  back  of 
the  roots  of  the  sacral  plexus  in  the  pelvis.  Its  higher  roots  from  the  first  and 
second  sacral  nerves  are  intimately  associated  with  the  origin  of  the  inferior  gluteal 
nerve ;  its  lowest  ri  ot  from  tlie  third  sacral  nerve  is  associated  with  the  origins  of 
the  perforating  cutaneous  or  pudic  nerve.  It  enters  the  buttock  through  the  great 
sciatic  notch  below  the  pyriformis,  along  with  the  sciatic  artery  and  inferior  gluteal 


656 


THE  NERVOUS  SYSTEM. 


nerve.  Proceeding  downwards  behind  the  great  sciatic  nerve,  it  enters  the  thigh 
at  the  lower  border  of  the  ghiteus  maximus  muscle,  where  it  gives  off  considerable 
branches.     Becoming  gradually  smaller  as  it  courses  downwards  over  the  hamstring 


Fig.  511. — Nerves  of  the  Lumbo-Sacual  Plexus. 


Sy,  Sympathetic  cord  ;  T.12,  L.l,  2,  3,  4,  5,  S.l,  2,  3,  4,  5,  Co,  Anterior  primary  divisions  of  the  last  thoracic, 
the  lumbar,  sacral,  and  coccygeal  nerves  ;  Q,  Nerves  to  qnadratus  luniborum  ;  Ps,  Nerves  to  psoas 
muscle  ;  G.C,  Genito-cniral  nerve  ;  II,  Iliac  branches  of  last  thoracic  and  ilio-liypogastric  nerves  ;  Hy, 
Hypograstic  branch  of  ilio-hypogastric  nerve  ;  I.I,  Ilio-inguinal  nerve  ;  E.C,  External  cutaneous  nerve  ; 
A.C,  Anterior  crural  nerve  ;  Obt,  Obturator  nerve  ;  Py.  Nerves  to  pyriforniis  muscle  ;  O.I  Nerve  to 
obturator  internus  ;  Q.F,  Nerve  to  qnadratus  femoris  muscle  ;  Art,  Articular  branch  ;  S.G,  Superior 
gluteal  nerve  ;  I.  G.  Inferior  gluteal  nerve  ;  P,  Peroneal  nerve  ;  Bi.  2,  Nerve  to  short  head  of  biceps  muscle  ; 


M,  Muscular  branches  ;  Per,  Perineal  branch  of  fourth  sacral  ;  A.Co,  Anterior  sacro-coccygeal  nerve. 


PUDENDAL  PLEXUS.  657 

muscles  to  the  popliteal  space,  it  finally  pierces  the  popliteal  fascia  in  one  or  more 
cutaneous  branches,  which  supply  the  skin  over  the  calf  of  the  leg  for  a  variable 
distance  (Fig.  509,  p.  653). 

Branches. — The  small  sciatic  is  a  purely  cutaneous  nerve.  It  supplies  branches 
to  the  perineum,  buttock,  thigh,  and  leg. 

The  perineal  branch  (rr.  perinseales ;  inferior  pudendal  nerve ;  long  scrotal 
nerve)  arises  from  the  small  sciatic  nerve  at  the  lower  border  of  the  gluteus 
maximus  muscle  (Pig.  512,  p.  658).  It  sweeps  inwards  towards  the  perineum, 
lying  on  the  origin  of  the  hamstring  muscles  below  the  ischial  tuberosity,  and 
becomes  subcutaneous  after  passing  over  the  pubic  arch.  Its  terminal  branches 
supply  the  skin  of  the  scrotum  and  root  of  the  penis,  or  in  the  female  the  labium 
majus  and  clitoris,  some  of  them  being  directed  backwards  towards  the  anus  and 
central  point  of  the  perineum.  They  communicate  with  the  inferior  haemorrhoidal 
and  perineal  branches  of  the  pudic  nerve,  and  with  the  iho-inguinal  nerve.  In  its 
course  to  the  perineum  the  nerve  gives  off  collateral  branches  to  the  skin  of  the 
upper  and  inner  part  of  the  thigh. 

The  gluteal  branches  (rr.  clunium  inferiores)  are  large  and  numerous  (Fig. 
509,  p.  653).  They  arise  from  the  small  sciatic  nerve  beneath  the  gluteus 
maximus,  and  become  subcutaneous  by  piercing  the  fascia  lata  at  different  points 
along  its  lower  border.  They  supply  the  skin  of  the  lower  half  of  the  buttock. 
The  outermost  branches,  reaching  to  the  back  of  the  great  trochanter,  overlap  the 
terminal  filaments  of  the  gluteal  branches  of  the  external  cutaneous  nerve,  and  the 
posterior  primary  divisions  of  the  first  three  lumbar  nerves.  The  innermost  branches, 
which  may  pierce  the  great  sacro-sciatic  ligament,  reach  nearly  to  the  coccyx,  and 
are  co-terminous  in  their  distribution  with  the  branches  of  the  perforating  cutaneous 
nerve,  which  they  reinforce  and  not  infrequently  replace. 

The  femoral  branches  are  divisible  into  two  sets — internal  and  external.  They 
pierce  the  fascia  lata  of  the  thigh  at  intervals,  and  supply  the  skin  of  the  back  of 
the  thigh  on  its  inner  and  outer  sides  respectively. 

The  sural  branches  are  two  or  more  slender  nerves  which  pierce  the  fascia 
over  the  popliteal  space,  and  are  distributed  for  a  variable  extent  to  the  skin  of 
the  back  of  the  leg.  They  may  stop  short  over  the  popliteal  space,  or  may  extend 
as  far  as  the  ankle.  Usually  they  innervate  the  skin  as  far  as  the  middle  of  the 
calf.     They  communicate  with  the  external  saphenous  nerve. 

lu  cases  where  the  great  sciatic  nerve  is  naturally  divided  at  its  origin  into  tibial  (internal 
popliteal)  and  peroneal  (external  popliteal)  nerves  {e.cj.  by  the  pyriformis  muscle),  the  small 
sciatic  nerve  is  also  separated  into  tAvo  parts  :  a  dorsal  part,  associated  with  the  peroneal  nerve 
and  arising  in  common  with  the  lower  roots  of  the  inferior  gluteal  nerve  (lusually  from  the  first 
and  second  sacral  nerves),  and  comprising  the  gluteal  and  external  femoral  branches  ;  and  a 
ventral  part,  associated  with  the  tibial  nerve  and  arising  usually  from  the  second  and  third 
sacral  nerves,  along  with  the  perforating  cutaneous  and  pudic  nerves,  and  comprising  the 
perineal  and  internal  femoral  branches. 

Perforating  Cutaneous  Nerve  (n.  perforans  ligamenti  tuberoso  -  sacri 
(Schwalbe),  n.  cutaneus  clunium  inferior  medialis  (Eisler)). — This  nerve  arises 
from  the  back  of  the  second  and  third  sacral  nerves  (Fig.  512,  p.  658).  At  its 
origin  it  is  associated  with  the  lower  roots  of  the  small  sciatic  nerve.  Passing  down- 
wards it  pierces  the  great  sacro-sciatic  ligament,  along  with  the  coccygeal  branch 
of  the  sciatic  artery ;  and  after  winding  round  the  lower  border  of  the  gluteus 
maximus  muscle,  or  in  some  cases  piercing  its  lower  fibres,  it  becomes  subcutaneous 
a  little  distance  from  the  coccyx,  and  supplies  the  skin  over  the  lower  part  of  the 
buttock  and  the  inner  part  of  the  fold  of  the  nates. 

The  perforating  cutaneous  nerve  is  not  always  jjresent.  In  a  minority  of  cases  it  is  associated 
at  its  origin  with  the  pudic  nexwe.  When  absent  as  a  separate  nerve,  its  place  is  taken  by  (1) 
gluteal  branches  of  the  small  sciatic  nerve,  or  (2)  a  branch  from  the  pudic  nerve,  or  (3)  a  small 
nerve  (n.  perforans  coccygeus  major,  Eisler),  arising  separately  from  the  back  of  the  third  and 
fourth  sacral  nerves. 

Muscular  Branches. — Between  the  third  and  fourth  sacral  nerves  (occasion- 
ally reinforced  by  the  second,  Eisler)  a  plexiform  loop  is  formed,  from  which 
muscular  nerves  are  given  off  to  the  levator  ani  (supplying  the  muscle  on  its  pelvic 
surface),  coccygeus,  and  external  sphincter.     The  nerve  to  the  external  sphincter 
46 


658 


THE  NERVOUS  SYSTEM. 


{perineal  branch  of  fourth  sacral)  pierces  the  great  sacro-sciatic  ligament  and  the 
coccygeus  muscle,  to  which  it  gives  offsets,  and  appears  in  the  ischio-rectal  fossa 
between  the  gluteus  maxinius  and  the  external  sphincter.  Besides  supplying  the 
posterior  fibres  of  the  external  sphincter,  it  distributes  cutaneous  offsets  to  the  skin 
of  the  ischio-rectal  fossa  and  the  fold  of  the  nates  behind  the  anus.  This  nerve 
replaces  in  some  instances  the  perforating  cutaneous  nerve. 

Anterior  Sacro-coccygeal  Nerves  (nn.  ano-coccygei). — By  the  union  of  the 
remaining  part  of  the  fourtli  with  the  fifth  sacral  and  coccygeal  nerves,  the 
so-called  coccygeal  plexus  is  formed.  A  fine  descending  branch  of  the  fourth 
sacral  nerve  passes  over  or  through  the  great  sacro-sciatic  ligament,  to  join  the 
fifth  sacral  nerve.  This  fifth  sacral  nerve,  joined  by  the  descending  branch  of 
the  fourth,  descends  alongside  the  coccyx  and  is  again  joined  by  the  coccygeal 
nerve,  so  that  a  plexiform  cord  results,  homologous  with  the  inferior  caudal  trunk 
of  tailed  animals.  Fine  twigs  arise  from  it,  which  pierce  the  sacro-sciatic  ligament 
and  supply  the  skin  in  the  neighbourhood  of  the  coccyx,  internal  to  the  perforating 
cutaneous  nerves  and  behind  the  anus. 


The  Pudic  Nerve. 

The  pudic  nerve  (n.  pudendus)  is  the  principal  nerve  for  the  supply  of  the 
perineum.     It  arises  in  the  pelvis  usually  by  three  roots  from  the  second,  third,  and 


Perineal  branch  of  small 

SCIATIC 


Anterior 

superficial 
perineal 

NERVE 


Posterior 

superficial 

perineal 

NERVE 

Gluteal 
branciie; 

or  SMALI, — 
SCIATJ' 
NERVE 


chial  tuberosity 


Legator  ani 


Parietal  pelvic 
fascia 


Inferior  u.«morrhoii)ai 

NERVE 


Levator  ani 
External  sphincter  ani 


Perforating  cutaneous  nerve 
Perineal  branch  of  fourth  sacral  nerve  Anterior  sacro-coccvgeal  nerve 

Fio.  512. — The  Muscles  and  Nerves  of  the  Male  Perinedm. 

fourth  sacral  nerves  (Fig.  511,  p.  656).  (Frequently  one  of  its  branches,  the  inferior 
htemorrhoidal  nerve,  arises  independently  from  the  third  and  fourth  sacral  nerves). 
The  nerve  passes  to  the  buttock  through  the  great  sacro-sciatic  foramen  below  the 
great  sciatic  nerve,  and  lies  on  the  lesser  sacro-sciatic  ligament,  or  the  spine  of  the 
ischium,  internal  to  the  internal  pudic  artery.  It  enters  the  jjerineum  along  with 
the  pudic  artery  through  the  small  sacro-sciatic  foramen.  In  the  perineum  it  is 
deeply  yjlaced  in  the  outer  wall  of  the  ischio-rectal  fossa,  enclosed  in  a  special 
sheath  derived  from  the  parietal  pelvic  fascia  covering  the  inner  surface  of  the 
obturator  internus  nmscle.  At  the  anterior  limit  of  the  ischio-rectal  fossa,  the 
nerve  approaches  the  surface  and  divides  at  the  base  of  the  triangular  ligament 
into  its  terminal  branches,  the  perineal  nerve  and  the  dorsal  nerve  of  the  penis. 


THE  PUDIC*  NERVE. 


659 


The  branches  of  the  pudic  nerve  are  essentially  the  same  in  the  two  sexes.  As 
a  rule  no  branches  are  given  off  till  the  nerve  enters  the  perineum,  but  sometimes 
the  inferior  hfemorrhoidal  ner^'e  has  an  independent  origin  from  the  plexus,  merely 
accompanying  the  pudic  nerve  in  the  first  part  of  its  course ;  and  in  exceptional 
cases  the  perforating  cutaneous  nerve  of  the  buttock  is  a  branch  of  the  pudic  nerve. 

The  inferior  haemorrhoidal  nerve  (n.  hiemorrhoidalis  inferior)  arises  from  the 
pudic  nerve  under  cover  of  the  gluteus  maximus,  at  the  posterior  part  of  the 
ischio-rectal  fossa.  In  cases  in  which  it  has  an  independent  origin  from  the  plexus, 
it  arises  from  the  third  and  fourth  sacral  nerves.  It  crosses  the  ischio-rectal  fossa 
in  company  with  the  inferior  hemorrhoidal  vessels,  and  separates  into  numerous 
branches — muscular,  cutaneous,  and  communicating. 

The  muscular  branches  end  in  the  external  sphincter  ani  muscle.  The  cutaneous 
branches  supply  the  skin  around  the  anus.  The  communicating  branches  connect 
the  inferior  htemorrhoidal  with  three  other  nerves — the  perineal  l:)ranches  of  the 
small  sciatic,  pudic,  and  fourth  sacral  nerves. 

The  perineal  nerve  (u.  perineus),  one  of  the  two  terminal  branches  of  the 
pudic  nerve,  arises  near  the  base  of  the  triangular  ligament.  It  almost  immediately 
divides  into  two  parts,  superficial  and  deep. 

The  superficial  part  is  purely  cutaneous  and  consists  of  two  nerves,  the  posterior 


Corpus  cavernosuiiT 

(cut) 

Nerve  to  corpus 

cavernosum 

Nerve  to  dorsum 

OF  penis 

Compressor  urethrse 

Nerve  to  bulb 
Triangular  ligament 
(posterior  la\  er) 
Internal  pudic  ner\  e   .- 


Balb  of  penis 

Triangular  ligament 
(anterior  layer) 

Crus  penis 


Fig.  513. — The  Triangular  Ligament  of  the  Perineum. 

or  external  and  the  anterior  or  internal  superficial  perineal  nerves,  which  pass, 
along  with  the  superficial  perineal  vessels,  to  the  anterior  part  of  the  perineum. 
The  posterior  or  external  superficial  perineal  nerve,  at  the  anterior  limit  of  the  ischio- 
rectal fossa,  usually  passes  over  the  base  of  the  triangular  ligament  and  over  the 
transversus  perinei  muscle.  The  anterior  or  internal  superficial  perineal  nerve,  lying- 
more  deeply,  pierces  the  base  of  the  triangular  ligament  and  goes  underneath  or 
through  the  transversus  perinei  muscle.  Becoming  superficial  in  the  anterior 
(urethral)  triangle  of  the  perineum,  they  are  distributed  to  the  skin  of  the  scrotum 
(or  labium  majus),  and  communicate  with  the  pei  ineal  branch  of  the  small  sciatic 
nerve  and  with  the  inferior  hemorrhoidal  nerve. 

The  deep  part  of  the  perineal  nerve  is  mainly  but  not  entirely  muscular. 
Coursing  forwards  through  the  anterior  part  of  the  ischio-rectal  fossa,  it  passes 
between  the  two  layers  of  the  triangular  ligament  towards  the  urethra.  It  supplies 
muscular  branches  to  the  anterior  parts  of  the  levator  ani  and  external  sphincter, 
to  the  transversus  perinei,  erector  penis  (or  clitoridis),  bulbo-cavernosus  (ejaculator 
urinae  or  sphincter  vaginse),  and  compressor  urethre.  It  terminates  as  the  nerve 
to  the  bulb,  which,  piercing  the  triangular  ligament,  enters  the  bulb  of  the  urethra 


660  THE  NEEVOUS  SYSTEM. 

and  supplies  the  erectile  tissue  of  the  bulb  and  corpus  spongiosum,  as  well  as  the 
mucous  membrane  of  the  urethra  as  far  as  the  glans  peni^  (or  clitoridis). 

The  dorsal  nerve  of  the  penis,  the  other  terminal  branch  of  the  pudic  nerve 
accompanies  the  internal  pudic  artery  beneath  the  superficial  layer  of  the  triangular 
ligament.  It  passes  forward  close  to  the  pubic  arch,  lying  beneath  the  crus  and 
erector  penis  (or  clitoridis),  and  triangular  ligament,  and  upon  the  compressor 
urethras  muscle ;  piercing  the  triangular  ligament  near  its  apex,  at  the  outer  side 
of  the  dorsal  artery  of  the  penis  (or  clitoris),  it  passes  on  to  the  dorsum  of  the 
penis  or  clitoris,  to  which  it  is  distributed  in  its  distal  two-thirds,  sending  branches 
round  the  sides  of  the  organ  to  reach  its  under  surface.  In  the  female  the  nerve  is 
much  smaller  than  in  the  male.  The  dorsal  nerve  of  the  penis  supplies  one  branch, 
the  nerve  to  the  corpus  cavernosum,  as  it  lies  beneath  the  triangular  ligament. 
This  is  a  slender  nerve,  which,  piercing  the  triangular  ligament,  supplies  the 
erectile  tissue  of  the  crus  and  corpus  cavernosum. 

Morphology  of  the  Pudendal  Plexus.— The  structures  occupying  the  perineum  are  placed 
in  the  ventral  axis  of  the  body,  and  comprise  from  before  backwards,  the  penis  and  scrotum,  or 
mons  Veneris  and  vulva,  the  central  point  of  the  perineum,  the  anus  and  ischio-rectal  fossa,  and 
the  coccyx.  They  are  placed  on  the  mesial  side  of  the  attachment  of  the  lower  limbs — the  penis 
or  mons  Veneris  in  relation  to  tlie  preaxial  border ;  the  coccyx  in  relation  to  the  postaxial  border 
of  the  limb. 

The  nerves  of  the  perineum,  thus  reaching  the  ventral  axis  of  the  trunk,  are  homologous  with 
the  anterior  (ventral)  terminations  of  other  nerves.     They  are  separated  into  two  series.     Mainly 

supplied  through  the  pudendal  plexus  by  the  last  four  sacral 

^ 7       /    /  and  the  coccygeal  nerves,  the  perineum  is  also  innervated 

y^fz    /  '■■'  /  '^  /  "  1°         to  a  minor  extent  by  the  first  lumbar  nerve  through  the 

/     /^^=''r=^5^ — f     /  ilio-inguinal  nerve,  which  reaches  the  root  of  the  penis  and 

/fc  IJ"^^^  ^        a\         /  the   scrotum.     The   region   is   thus   supplied   by  two  series 

/  y^  a/l  ^^  widely  separated  nerves,  Avhich  have  their  meeting-place 

Aw  ^11  \      V  ^^^  ^^^  dorsum  and  side   of  the   penis  and  scrotum.     This 

[£1  yjcx — \  junction  of  the  ilio-inguinal  and  pudendal  nerves  constitutes 

\^^:;;^^._^^  the   beginning  of    the  ventral   axial   area   or   line,   which 

\j\j^^^"''^!^'"4r^    \     \  extends  peripherally  along  the  inner  side  of  the  lower  limb. 

Ah^^^^    ^  s^~T~^^  Aj)art   from   this    break   in   their   distribution,    a    definite 

^--— ^  numerical  order  may  be  followed  in  the  arrangement  of  the 

Fig.   5U.-SCHEME  of  the  inuervation    perineal  nerves.     The  higher  parts  of  the  perineum  are  in- 

of  the  hinder  portion  of  the  trunk    nervated  by  the  higher  spmal  nerves  ;  the  lower  parts,  by  the 

and  of  the  perineum,  and  the  in-    lower  nerves.     This  is  best  exemplified  m  the_ distribution  ot 

terruption  of  the  segmental  arrange-    the  cutaneous  nerves.     The  base  of  the  penis  and  scrotum 

ment  of  the  nerves'  associated  with    (or  mons  Veneris)  is  supplied  by  the  first  lumbar  nerve  (ilio- 

the  f(5rmation  of  the  liml).  inguinal).     The  dorsal  nerve  of  the  penis  (or  clitoris),  when 

T  10    11    12    The  areas  of  distribution    traced  back  to  the  pudendal  plexus,  is  found  to  come  from 

of  the  lower  thoracic  nerves  ;  L.l,  2,    the  second,  and  to  a  less  extent  from  the  third  sacral  nerves  ; 

3,  The  posterior  primary  divisions  of  the  scrotal  nerves  (perineal  branches  of  the  pudic  and  small 
the  first  three  lumbar  nerves  ;  L.l,  sciatic)  similarly  arise  from  the  third,  and  to  a  less  extent 
The  ilio-inguinal  nerve;  S.l,  2,  .3,    from  the  second  sacral  nerves;    the  skin  of  the  ischio-rectal 

4,  5,  6,  The  posterior  primary  divi-  fogga  and  anus  is  innervated  by  the  inferior  heemorrhoidal 
sions  of  the  sacral  and  coccygeal  (third  and  fourth  sacral  nerves),  and  the  perineal  branch  of 
nerves  (6)  ;  S.3,  2,  S.3,  2,  Branches    ^]-^g  fourth  sacral  nerve.     The  coccygeal  plexus,  lastly,  supplies 

.       of  pudic  nerve  to  penis  and  .scrotum;    ^|^g    g-j^-^    ^.^^^^^^    ^1^^,   coccyx    (fourth    and    fifth   sacral    and' 
S.3,  4,  Inferior  hsemoiTlioidal  nerve  ;    ^        „^^i  nerves).    Judged  from  its  nerve  supply  the  perineum 
4,   Perineal  branch  of  the   fourth    jg  ^olje  regarded  as  occupying,  for  the  most  part,  a  position 
sacral  nerve;  4, 5, 6,  Anterior  sacro-    ,    ,  :    ,        °  i   i  ^i        ^i    V     f  ^^      ^  i-     i    •         i   i.- 

coccygeal  ne^ve  ;  D.i.  L.  Dorsal  axial  ^^ehind  or  more  caudal  than  that  of  the  lower  limb  m  relation 
line;  V.A.L,  Ventral  axial  line.         to   the   trunk.      There   is   here   a   remarkable    gap    m    the 

numerical  sequence  ot  the  nerves  supplying  the  ventral  axis 
of  the  body.  All  tlie  nerves  between  the  first  lumbar  and  the  second  sacral  fail  to  reach  the  mid 
ventral  line  of  the  trunk  and  are  wholly  concerned  in  the  innervation  of  the  lower  Umb. 

At  the  preaxial  border  of  the  limb  (groin)  the  first  lumbar  nerve,  the  highest  nerve  supplying 
the  perineum,  is  concerned  also  in  innervating  the  skin  of  the  hmb.  At  the  postaxial  border  of 
the  limlj  (fold  of  the  nates  and  back  of  the  thigh),  the  nerves  which  are  the  highest  of  those  con- 
stituting the  pudendal  plexus  (the  second  and  tliird  sacral  nerves)  are  also  implicated  in  inner- 
vating that  border  of  the  limb.  Tlie  fourth  sacral  nerve  is  only  concerned  to  a  very  slight 
extent  in  the  innervation  of  the  limb  by  means  of  tlie  perineal  branch,  which  reaches  the 
beginning  of  its  postaxial  border  ;  the  last  two  spinal  nerves  are  wlioUy  unrepresented  in  the 
limb  proper  and  end  entirely  in  the  ti'unk  behind  the  limb. 

Development  ok  the  Spinal  Nerves. 
I.  Origin  of  the  Spinal  Nerve  Roots. — The  process  of  development  of  the  spinal 


DEVELOPMENT  OF  THE  SPINAL  NERVES. 


661 


nerves  commences  by  means  of  the  outgrowth  of  the  dorsal  and  ventral  roots  from  the 
medullary  tube.     The  two  roots  take  origin  in  quite  different  ways. 

The  dorsal  root  is  the  first  to  appear, — before,  during,  or  after  the  union  of  the 
medullary  plates  and  the  formation  of  the  neural  tube.  It  takes  oi'igin  as  a  cellular  bud 
from  the  dorsal  surface  of  the  medullary  tube  in  one  of  three  ways : — (1)  It  may  arise 
from  the  junction  of  the  medullary  plate  and  surface  epiblast  before  the  closure  of  the 
medullary  groove.  (2)  It  may  spring  from  the  neural  crest,  a  ridge  on  the  dorsal  aspect 
of  the  medullary  tube,  after  its  closure  is  complete.  (3)  It  may  be  simply  a  direct  out- 
growth from  the  dorsal  surface  of  the  medullary  tube.  Pyriform  in  shape,  the  bud 
enlarges  and  becomes  separated  from  the  medullary  tube,  and  projects  ventrally  in  the 
space  between  the  myotome  and  the  medullary  tube.  Each  bud  is  separated  by  only  a 
slight  interval  from  its  neighbour. 

The  cells  (neuroblasts)  composing  the  bud  become  rapidly  spindle-shaped,  and  by  the 
middle  of  the  fourth  week  give  rise  to  two  sets  of  processes ;  (1)  a  central  series,  which 


Fig.   515. — Development  of  the  Spinal  Nerves. 


A,   Formation  of  nerve  roots. 

D.R,  Dorsal  root. 
V.R,  Ventral  root. 


N.T,  Neural  tube. 
No,    Notocliord. 

C,  Formation  of  nerves. 

So,  Somatic  division. 
Vi,  Visceral  branch. 
P,    Posterior  primary  division. 


Al.C,  Alimentary  canal. 
Ao,      Aorta. 
V,        Cardinal  vein. 
M.P,    Muscle  plate. 

D,   E,   Formation  of  subordinate 
branches. 

Lat,  Lateral,  and 

Ant,  Anterior,  branches. 


B,   Formation  of  nerve  trunk  (N). 

D.G,     Dorsal  ganglion. 
Sy,       Sympathetic  cord. 
W.D,  Wolffian  duct. 
Co,       Cceloni . 

Formation  of  nerve  trunks  in  relation 
to  the  limb  :  dorsal  and  ventral 
trunks  corresponding  to  lateral  and 
anterior  trunks  in  D  and  E. 


grow  backwards  and  are  secondarily  connected  with  the  dorso-lateral  aspect  of  the 
medullary  tube  as  the  fibres  of  the  dorsal  root ;  and  (2)  a  peripheral  series,  which  con- 
stitute the  dorsal  root  fibres  of  the  spinal  nerve  and  join  the  ventral  root,  to  form  the 
spinal  nerve  proper.     The  intermediate  cellular  mass  remains  as  the  spinal  ganglion. 

The  ventral  root  of  a  spinal  nerve  arises  in  quite  a  different  way,  from  cells  (neuro- 
blasts) in  the  substance  of  the  medullary  tube.  In  the  account  of  the  development  of  the 
spinal  cord  it  has  been  shown  how  the  cellular  constituents  of  the  medullaiy  tube  are  con- 
verted into  two  classes  of  cells  :  (1)  spongioblasts,  which  produce  the  matrix  (neuroglia)  of 
the  spinal  cord ;  and  (2)  germ-cells  or  neuroblasts,  which  produce  the  nei've-cells  of  the 
gray  matter  of   the   cord.     The  neuroblasts  give  rise   to   the  axis-cylinder  processes  or 


662  THE  NERVOUS  SYSTEM. 

axons,  which,  penetrating  the  spongy  tissue  of  the  meduUary  tube  and  the  outer  limiting 
membrane,  find  their  way  into  the  mesoblastic  tissue  on  the  ventro-lateral  surface  of  the 
tube.  Fibrous  from  their  earliest  origin  and  derived  from  nerve-cells  which  remain  within 
the  medullary  tube,  the  axons  of  which  the  ventral  root  is  composed  become  surrounded  by 
mesoblastic  cells  immediately  on  their  emergence,  which  give  rise  to  the  sheaths  of  the  nerve. 
The  ventral  root  is  a  little  later  in  its  date  of  appearance  than  the  dorsal  root.  It  begins 
to  be  evident  at  the  twenty-fourth  day  and  is  completely  formed  by  the  twenty-eighth  day. 
II.  Formation  of  the  Spinal  Nerve. — The  fibres  of  the  dorsal  root  ganglion  and 
the  ventral  root  grow  by  extension  from  the  cells  with  which  they  are  respectively  con- 
nected, and  meet  in  the  space  between  the  myotome  and  the  side  of  the  medullary  tube 
to  form  the  spinal  nerve.  It  has  been  already  shown  that  in  the  adult  there  is  a  funda- 
mental division  of  the  spinal  nerve  into  posterior  and  anterior  primary  divisions.  In  the 
process  of  development  this  separatioii  is  even  more  obvious.  As  the  fibres  of  the  dorsal 
and  ventral  roots  approximate,  they  separate  at  the  same  time  each  into  two  unequal 
portions  :  the  smaller  parts  of  the  two  roots  unite  together  to  form  the  posterior,  and  the 
larger  parts  imite  to  form  the  anterior  primary  division  of  the  spinal  nerve. 

The  posterior  primary  division,  curving  outwards  and  dorsally,  passes  through  the 
myotome  and  is  connected  with  it.  In  the  substance  of  the  myotome  it  separates  into 
branches  as  it  proceeds  towards  the  dorsal  wall  of  the  embryo.  At  a  later  stage,  the 
branches  are  definitely  arranged  into  an  outer  and  an  inner  set. 

The  anterior  primary  division  grows  gradually  in  a  ventral  direction  to  reach  the 
somato-splanchnopleuric  angle,  mider  cover  of  the  growing  myotome.  It  spreads  out  at 
its  distal  end  and  eventually  separates  into  two  portions  :  a  smaller,  splanchnic,  or  visceral; 
and  a  larger,  somatic,  or  parietal  portion.  (1)  The  smaller,  splanchnic,  or  visceral  portion 
grows  inwards,  dorsal  to  the  Wolffian  ridge,  to  be  connected  with  the  sympathetic  cord 
and  the  innervation  of  organs  in  the  splanchnic  area.  This  branch  of  the  spinal  nerve 
becomes  the  white  ramus  communicans  of  the  sympathetic.  It  is  not  pi-esent  in  the  case 
of  all  the  spinal  nerves  (cervical,  lower  lumbar,  and  upper  sacral).  It  will  be  referred  to 
again  in  connexion  with  the  sympathetic  system.  (2)  The  larger,  somatic,  or  parietal 
portion  becomes  the  main  part  of  the  anterior  primary  division  of  the  nerve.  It 
continues  the  original  ventral  course  of  the  nerve,  and,  reaching  the  body  wall,  sub- 
divides into  two  terminal  branches — a  lateral  branch,  which  grows  outwards  and  down- 
wards and  reaches  the  lateral  aspect  of  the  trunk,  after  piercing  the  myotome ;  and  a 
ventral  or  anterior  branch,  which  grows  onwards  in  the  body  wall  to  reach  the  ventral 
axis.     This  arrangement  is  met  with  in  the  trunk  between  the  limbs  and  in  the  neck. 

III.  Formation  of  Limb-plexuses. — The  method  of  growth  of  the  spinal  nerves, 
just  described,  is  modified  in  the  regions  where  the  limbs  are  developed.  In  relation  to 
the  limbs,  which  exist  in  the  form  of  buds  of  cellular  undifferentiated  mesoblast  before 
the  spinal  nerves  have  any  connexion  with  them,  the  development  of  the  nerve  proceeds 
exactly  in  the  way  described  up  to  the  point  of  formation  of  somatic  and  splanchnic 
branches.  The  somatic  branches  then  stream  out  into  the  limb  bud,  passing  into  it 
below  the  ends  of  the  myotomes  and  spreading  out  into  a  bundle  of  fibres  at  the  basal 
attachment  of  the  limb.  Later  on,  the  nerves  separate  each  into  a  pair  of  definite  trunks, 
which  are  named  dorsal  and  ventral,  and  which,  dividing  round  a  central  core  of  meso- 
blast, proceed  to  the  dorsal  and  ventral  surfaces  respectively  of  the  limb  bud.  While  this 
process  is  going  on,  a  secondary  tmiion  takes  place  between  (parts  of)  adjacent  dorsal  and 
ventral  trunks.  Dorsal  trunks  unite  with  dorsal  trunks,  ventral  trunks  unite  with  ventral 
trunks,  to  form  the  nerves  distributed  ultimately  to  the  surfaces  and  periphery  of  the 
limb.  These  dorsal  and  ventral  trunks  are  homologous  with  the  lateral  and  ventral 
branches  of  the  somatic  nerves  in  other  regions. 

Morphology  of  the  Limb-plexuses. 

The  arrangement  of  the  linil)  nerves  is  rendered  complex  and  the  significance  of  the  plexuses 
is  obscured  l)y  the  changes  through  which,  coincidently,  the  nerves  on  the  one  hand  and  the 
parts  su])])li('d  by  them  on  the  other  hand  have  passed  in  the  course  of  development. 

Nature  of  the  Limbs. — As  already  described,  the.  maiumalian  limljs  arise  as  flattened  buds 
fi'om  the  extremities  of  tlie  "Wolffian  ridge.  Each  hud  possesses  a  preaxial  and  a  postaxial  border, 
and  a  dorsal  and  a  ventral  surface,  continuous  with  the  dorsal  and  ventral  aspects  of  the  trunk 
and  homologous  with  its  lateral  and  ventral  surfaces.  Each  bud  consists  at  first  of.  a  mass  of 
undifferentiated,  unsegmented  mesoljlast,  covered  by  e]nthelium.  Around  the  central  core  of 
mesoblast  which  produces  the  skeletal  axis,  the  vessels  and  muscles  of  the  limb  are  formed 
in  situ,  the  muscles  as  double  dorsal  and  ventral  strata,  beneath  the  corresponding  surfaces  of 
the  bud. 

Each  limb  bud  is  connected  to  the  lateral  and  ventral  aspects  of  the  trunk,  and  is  associated 
with  a  number  of  body  segments,  varying  in  the  two  extremities  and   in  different  animals. 


MOEPHOLOGY  OF  THE  LIMB-PLEXUSES. 


66^ 


Althougli  the  mesoblastic  material  of  which  the  limb  bud  is  composed  exhibits  in  itself  no 
segmental  divisions  at  any  period  of  its  development,  a  clear  indication  of  the  segmental  relations 
of  the  limlis  is  obtained  from  the  arrangement  of  the  limb  nerves.  Taking  the  nerves  which 
supply  the  limbs  as  a  guide,  the  segments  engaged  in  the  formation  of  the  upj^er  extremity  are 
the  last  five  cervical  and  first  two  thoracic.  The  lower  extremity  is  related  by  its  nerves  to  all 
the  lumliar  and  the  first  three  sacral  segments.  In  each  limb,  the  segments  at  the  preaxial  and 
postaxial  borders  are  only  partially  concerned  in  limb  formation. 

It  has  been  already  shown  that  the  somatic  l)ranclies  of  the  nerves  enter  the  substance  of  the 
embryonic  limb  and  divide  in  their  course  into  dorsal  and  ventral  trunks,  which  supply  tlie 
dorsal  and  ventral  surfaces  of  the  limb  bud.  The  higher  nerves  supjjly  the  preaxial  border,  the 
lower  nerves  sujjply  the  postaxial  border,  while  the  nerves  most  centrally  situated  extend  furthest 
towards  the  periphery  of  the  limb. 

In  order  to  undei-stand  properly  the  constitution  of  the  limb-jjlexuses,  it  is  necessary  further 
to  make  a  comparison  of  the  surfaces  and  borders  of  the  embryonic  and  adult  limbs. 

Upper  Limb. — (A)  Borders. — The  preaxial  border  of  the  upper  extremity  extends  from  the 
middle  of  the  clavicle,  in  the  line  of  the  cephalic  vein,  do^v^^  the  front  of  the  shoulder,  the  outer 
side  of  the  arm,  forearm  and  hand,  to  the  outer  border  of  the  thumb.  The  postaxial  border 
extends  from  the  middle  of  the  axilla  along  the  inner  side  of  the  arm  (in  the  line  of  the  basilic 
vein),  the  inner  side  of  the  forearm  and  hand,  to  the  inner  border  of  the  little  finger. 

(B)  Surfaces. — The  areas  of  the  limb  between  these  lines,  anteriorly  and  posteriorly,  correspond 
to  the  ventral  and  dorsal  surfaces  of  the  embryonic  limb  liud.  The  ventral  surface  is  rejiresented 
by  the  front  of  the  chest,  arm,  and  forearm,  and  the  palm  of  the  hand.  Tlie  dorsal  surface  is 
represented  by  the  scapular  and  deltoid  regions,  the  back  of  the  arm,  forearm,  and  hand. 

Lower  Limb. — (^4)  Borders. — The  preaxial  border  of  the  lower  limb  extends  from  the  middle 
of  Poupart's  ligament  down  the  inner  side  of  the  thigh  and  leg  in  the  line  of  the  internal 
saphenous  vein,  to  the  inner  side  of  the  great  toe.  The  postaxial  border,  beginning  at  the  coccyx, 
extends  along  the  fold  of  the  nates  and  the  outer  side  and  back  of  the  thigh  and  leg  (in  the  line 
of  the  external  saphenous  vein)  to  the  outer  border  of  the  foot  and  little  toe. 

(B)  Surfaces. — The  areas  between  these  lines  correspond  to  the  primitive  dorsal  and  ventral 
surfaces  of  the  embryonic  limb  bud.  The  imecpial  amount  of  rotation  in  the  parts  of  the  lower 
limb  obscures  the  relation  of  foetal  and  adult  surfaces,  which  are  most  easily  made  out  in  the 
infantile  position  of  the  limbs,  with  the  thighs  and  knees  flexed  and  the  soles  of  the  feet 
inverted.  The  ventral  surface  of  the  embyronic  limb  is  represented  by  the  inner  side  and 
back  of  the  thigh,  the  back  of  the  leg,  and  the  sole  of  the  foot.  The  dorsal  surface  is  rejiresented 
by  the  front  of  the  thigh  and  buttock,  the  front  of  the  leg,  and  the  dorsum  of  the  foot. 

Composition  of  the  Limb-plexuses. — In  all  mammals  the  same  definite  plan  underlies  tho 
constitution  of  the  linib-j)lexuses.  Tlie  nerves  concerned  are  the  anterior  primary  divisions  of 
certain  segmental  spinal  nerves,  which  (with  certain  exceptions  at  the  preaxial  and  postaxial 
borders)  are  destined  wholly  and  solely  for  the  innervation  of  the  limb.  Each  of  the  anterior 
primary  divisions  engaged  divides  into  a  pair  of  secondary  trunks,  named  dorsal  or  posterior, 
ventral  or  anterior.  The  dorsal  and  ventral  trunks  again  sulxlivide  into  tertiary  trunks,  which 
combine  with  the  corresponding  subdivisions  of  neighbouring  dorsal  and  ventral  trunks  to  form 
the  nerves  of  distribution.  The  combinations  of  dorsal  trunks  provide  a  series  of  nerves  for  the 
supply  of  that  part  of  the  limb  which  is  derived  from  the  dorsal  surface  of  the  embryonic  limb 
bud  ;  the  combinations  of  ventral  trunks  give  rise  to  nerves  of  distribution  to  the  regions 
corresponding  to  its  ventral  surface.  The  relation  of  the  nerves  derived  from  the  limb-plexuses 
to  the  areas  of  the  limbs  is  given  in  the  accompanying  tables  : — 

I.  Upper  Limb. 


Origin. 


I  Dorsal  trunks 
\  (Posterior  cord) 


Brachial 
Plexus 


Nerves. 


Distribution. 


^Posterior  scapular 
Postei'ior  thoracic 
Suprascapular 
Subscapular  (3)     . 
Circumflex    .         .         .         . 
(Lesser  internal  cutaneous  (?)  ] 
(Intercosto-humeral  (?) ) 

Musculo-spiral 


Scapular  region  and 
shoulder 


Arm,  inner  side 

Back  of  arm,  fore- 
arm, and  hand 


Ventral  trunks 

{Outer  and     ■ 
inner  cords)    1 


/-Nerve  to  subclavius  \ 
Anterior  thoracic  (2)) 

^lusculo-cutaneous 

Lesser  internal  cutaneous 

Internal  cutaneous 

Median .... 
■^Ulnar    .... 


Front  of  chest 


and 


Front   of   arm 

forearm 
Inner  side  of  arm 
Front   of  arm   and 

forearm 
Front  of  forearm  and 

hand 


Ventral 
surface 


664 


THE  NEEVOUS  SYSTEM. 


11.  Lower  Limb. 


Origin. 


Lumbo- 
sacral 
Plexus 


Nerves. 


Dorsal 
trunks 


Ventral 
trunks 


'Ilio-hypogastric  (iliac  l^ranch 
Superior  gluteal 
Inferior  gluteal  j 

Nerve  to  pyrifonnis 


Small  sciatic 
External  cutaneous       .         .   / 
Genito-crural  (crural  branch) 
Anterior  crural      .         .         .    { 
Peroneal        .... 


Ilio-liypogastric   (hypogastric 
branch) 

Ilio-inguinal 

Genito-crural  (genital  branch) 


Obturator 


Nerve  to  obturator  internus 
and  superior  gemellus 

Nerve   to  quadratus   femoris 
and  inferior  gemellus 

Nerve  to  hamstrings 

Small  sciatic 

f 


VTibial 


Distribution. 


Buttock 


Buttock  and  thigh,  outer  side  '' 

and  front 
Front  of  thigh 
Front  and  inner  side  of  thigh, 

leg,  and  foot 
Front  of  leg  and  foot 


Abdominal  wall  (ventral  sur-. 

face) 
Abdominal    wall,    thigh,  and 

perineum 
Groin 
Thigh  (inner   side)   and   knee 

(back) 


Buttock  and  back  of  thigh 


Back  of  thigh  and  perineum 
Back  of  knee,  leg,  and  sole  of 
foot 


Dorsal 
surface 


Ventral 
surface 


In  the  regions  of  the  limbs  no  anterior  cutaneous  branches,  derived  from  the  limb  nerves, 
supply  the  trunk.  The  whole  of  the  nerve  is  carried  into  the  limb  and  is  absorbed  in  its 
innervation,  and  the  dorsal  and  ventral  trunks  forming  the  limb-plexuses  are  to  be  looked  upon 
as  homologous  with  the  lateral  and  anterior  trunks  of  an  intercostal  nerve.  Two  series  of 
anomalies  in  relation  to  the  formation  and  distribution  of  the  nerves  to  the  limbs  must,  however, 
be  considered,  because  it  has  been  suggested  (Goodsir)  that  the  nerves  of  the  limbs  are  serially 
homologous  with  not  the  whole,  but  with  only  the  lateral  branches  of  the  anterior  primary 
divisions  of  the  intercostal  nerves. 

(1)  Nerves  in  connexion  with  the  primitive  borders  of  the  Limbs.— At  the  preaxial 
border  of  the  upper  limb,  at  its  root,  the  fourth  cervical  nerve,  which  supplies  the  anterior  and 
lateral  surfaces  of  the  neck,  is  also  distributed  through  the  supraclavicular  nerves  to  the  skin  of 
both  ventral  and  dorsal  surfaces  of  the  limb.  The  nerves  and  surfaces  are  here  not  merely 
liomologous,  but  in  actual  continuity. 

At  the  preaxial  border  of  the  lower  limb,  similarly,  the  first  lumbar  nerve,  by  means  of  the 
ilio-hypogastric  and  ilio-inguinal  branches,  supplies  on  the  one  hand  the  buttock,  in  series  with 
the  lateral  branches  of  the  lower  thoracic  nerves,  and,  on  the  other  hand,  the  lower  part  of  the 
abdominal  wall  and  the  adjacent  inner  side  of  the  thigh,  in  series  with  the  anterior  terminal 
branches  of  the  lower  thoracic  nerves. 

At  the  postaxial  border  of  the  upper  limb  the  first  and  second  thoracic  nerves  are  concerned 
in  supplying  trunk  segments  as  well  as  parts  of  the  limb.  The  first  thoracic  nerve,  besides 
supplying  the  limb  through  the  inner  cord  of  the  plexus,  also  innervates  at  least  the  muscles  of 
the  first  intercostal  space  ;  the  second  thoracic  nerve  is  concerned  in  the  innervation  of  the  limb, 
principally  by  means  of  its  lateral  branch  only,  which,  as  the  intercosto-humeral  nerve,  supplies 
the  skin  along  the  postaxial  border  of  the  limb  and  on  its  dorsal  side.  At  the  postaxial  border  of 
the  lower  limb,  in  the  same  way,  the  tliird  and  fourth  sacral  nerves,  partially  implicated  in  the 
innervation  of  the  limb  (through  the  tibial,  small  sciatic,  perforating  cutaneous  nerve,  and 
l)erineal  branch  of  the  fourth  sacral  nerve),  are  also  engaged  in  supplying  the  trunk  (perineum) 
through  the  pudic  nerve.  These  peculiarities  of  arrangement  of  the  nerves  at  the  borders  of  the 
limbs  may  be  explained  on  the  supposition  that  the  segment  corresponding  to  the  nerve  named 
is  only  partially  concerned  in  limb  formation,  ancl  is,  at  tlie  same  time,  implicated  to  a  greater 
or  less  extent  in  the  formation  of  structures  belonging  to  tlje  trunk. 

(2)  The  origin  and  distribution  of  the  nerves  at  the  postaxial  border  of  the  limbs  present 
a  special  difficulty.  In  the  composition  respectively  of  the  bi'achial  and  lumbo-sacral  i3lexuses, 
the  first  thoracic  and  third  sacral  nerves  do  not  as  a  rule  divide  into  ventral  and  dorsal  trunks, 
but  contribute  only  to  the  formation  of  the  ventral  series  of  nerves.  A  solution  of  this  difficulty 
may  be  found  in  the  examination  of  the  areas  of  distribution  of  the  nerves  derived  from  the 
first  thoracic  and  third  sacral  nerves.     In  the  case  of  the  brachial  plexus  (the  inner  cord  of  which 


THE  DISTKIBUTION  OF  THE  SPINAL  NERVES. 


665 


receives  normally  the  whole  contribution  of  the  first  thoracic  nerve)  the  lesser  internal  cutaneous, 
the  inner  branch  of  the  internal  cutaneous,  and  the  dorsal  branch  of  the  ulnar  nerve  supply  the 
dorsal  aspect  of  the  limb  on  its  postaxial  border.  These  nerves  are  in  serial  homology  with  the 
intercosto-humeral  and  lateral  trunks  of  intercostal  nerves.  In  the  case  of  the  lumbo-sacral  plexus 
similarly,  in  which  the  third  sacral  nerve  does  not  divide  into  ventral  and  dorsal  trunks,  the 
small  sciatic  and  tibial  nerves  containing  the  contribution  from  the  third  sacral  nerves  innervate, 
by  means  of  the  gluteal  and  external  femoral  branches  of  the  former  and  the  tibial  communi- 
cating branch  of  the  latter,  the  dorsal  surface  of  the  limb  along  the  postaxial  border,  in  series 
with  the  perforating  cutaneous  nerve  and  the  jaerineal  branch  of  the  fourth  sacral. 

These  apparent  anomalies  appear  to  indicate  that,  instead  of  dividing  into  its  pro2:)er  dorsal 
and  ventral  trunks,  the  entire  contribution  of  the  spinal  nerve  concerned  is  in  these  instances 
carried  undivided  along  the  postaxial  border  of  the  limb  in  association  with  the  ventral  trunks, 
and  that  the  dorsal  subdivisions  are  thrown  off  successively  as  the  plexus  cords  approach  the 
periphery.  Indeed,  in  the  case  of  the  small  sciatic  nerve,  Eisler  has  shown  that,  when  the 
peroneal  and  tibial  nerves  are  separated  at  their  origin,  its  gluteal  and  external  femoral  branches 
arise  from  and  are  connected  with  the  dorsal,  and  the  perineal  and  internal  femoral  branches 
with  the  ventral  trunk. 


The  DISTKIBUTION  of  the  Spinal  Nerves  to  the  Muscles  and  Skin 

OF  the  Limbs. 

By  dissection,  experiment,  and  clinical  observation,  it  is  conclusively  proved  that 
as  a  rule  each  nerve  of  distribution  in  the  limb,  whether  to  muscle  or  skin,  is  made  up  of 
fibres  derived  from  more  than  one  spinal  nerve  ;  and,  further,  that  in  cutaneous  distribution 
a  considerable  overlapping  occui's  in  the  course  of  the  several  peripheral  nerves.  Moreover, 
the  arrangement  of  the  distribution  of  the  nerves  to  skin  and  to  muscles  is  not  identical. 
In  the  case  of  the  skin  of  the  limbs,  by  the  covering  of  the  limb  being  drawn  on  to  it  from 
adjacent  parts  in  the  process  of  growth,  cutaneous  nerves  are  engaged,  which  are  derived 
from  sources  not  represented  in  the  muscular  innervation  of  the  limbs.  Again,  among  the 
muscles,  some  have  undergone  fusion,  others  have  become  rudimentary,  and  others  again 
have  altered  their  position  in  the  limb.  Bearing  these  qualifications  in  mind,  it  is 
possible  to  formulate  a  definite  plan  for  the  innervation  of  the  skin  and  muscles  of  the 
upper  and  lower  limb.  The  accompanying  tables  give  an  analysis  of  the  distribution  of 
the  spinal  nerves  to  the  skin  and  muscles  of  the  upper  and  lower  limb  respectively  : — 


I.  Upper  Limb. 

A.  Cutaneous  Nerves. 
1.  Dorsal  (Posterior)  Surface. 


Regions. 


Upper  part 
(preaxial) 
Scapular- 
Lower  part 

(postaxial) 

j  Upper  part 

DeltoidJ  T  (^'■^^^^■'*? 
Lower  part 

(postaxial) 

C  Outer  side 

(preaxial) 


Upper  arm 


Inner  side 
(postaxial) 


Nerves. 


Posterior  primary  divisions, 
cervical     

Cervical  plexus,  acromial 

Posterior  primary  divisions, 
thoracic 

Intercostal  nerves,  lateral  branches 

Cervical  plexus,  acromial 

Circumflex 

Intercostal  nerves,  lateral 
branches 

Circumflex  ..... 
Musculo-spiral,  upper  external 
branch  ..... 
Musculo-spiral,  internal  branch  . 
Lesser  internal  cutaneous 
Intercosto-humeral 


Spinal  Origins. 

Preaxial  Postaxial 


Nerves. 


C.  4.  5.  6. 
C.  3.  4. 

T.  1.-7. 
T.  2.  3.  4. 

C.  3.  4. 

C.  5.  6. 


C.  5.  6. 


Nerves. 


T.  2.  3. 


C.  (5).  6. 

C.  8. 
T.  1. 
T.  2. 


666 


THE  NEBVOUS  SYSTEM. 
1.  Dorsal  (Posterior)  Surface — continued. 


Spinal  Origins.             ' 

Regions. 

Nerves. 

Preaxial 
Nerves. 

Postaxial 
Nerves. 

/ 

Musculo-spiral,     upper 

external 

branch 

C.  (5).  6. 

'^  Outer  side 

Musculo-spiral,     lower 

external 

(preaxial) 

branch 
Musculo  -  cutaneous, 

posterior 

C.  6.  7.  8. 

Forearm- 

branch 
Radial    . 

C.  5.  6. 

C.  6.  7. 

I 

Internal       cutaneous, 

internal 

. 

Inner  side          | 

branch 

C.  8.  T.  1. 

[     (postaxial)     'i 

1  Ulnar,  dorsal  branch 

C.  8. 

i                          /'Outer  side 

Radial    . 

C.  6.  7. 

Hand '  r  (^'™«^) 
1  Inner  side 

I     (postaxial) 

Ulnar     . 

C.  8. 

i 

I.  Upper  Limb. 

A.  Cutaneous  Nerves. 

2.  Ventral  (Anterior)  Surface. 


Regions. 


Chest 


Upper  arm 


Forearm 


/Upi^er  part 
I      (j)reaxial) 

\  Lower  part 
I      (postaxial) 

r 

I  Outer  part 
(preaxial) 

Inner  part 
(postaxial) 

r  Outer  part 
I      (jneaxial) 
I  Inner  part 
-     (postaxial) 
"Outer  part 
(preaxial) 


Hand 


Inner  part 
(postaxial) 


Nerves. 


Cervical    plexus,    supraclavicular 

branches   .... 
Intercostal        nerves,        anterior 

branches   .... 
Intercostal  nerves,  lateral  branches^ 
Circumflex     .... 
Musculo-spiral,     upper     external 

branch       .... 
Internal  cutaneous 
Lesser  internal  cutaneous 
I  ntercosto-humeral 
Musculo  -  cutaneous,  anterior 

branch      .... 
Internal       cutaneous,       anterior 

branch      .... 
Musculo-cutaneous,  ball  of  thumli 
Median,  palmar  branch 
digital  branches 
thumb,  outer  side     . 

„       inner  side ) 
index,  outer  side  j 
„       inner  side'^ 
middle,  outer  side/ 
„       inner  side) 
ring,  outer  side      ( 
Ulnar,  palmar  branch    . 
„      digital  branches 


Spinal  Origins, 

Preaxial  Postaxial 

Nerves.  Nerves. 


C.  3.  4. 

! 

C.  5.  6. 
C.  5.  6. 

C.  5.  6. 


T.  2.-7. 


C.  8.  T.  1. 
T.  L 
T.  2. 


C.  8.  T.  1. 


C.  5.  6. 

C.  6.  7. 

C.  6.  7.  8.  T.  1. 
C.  6.  (7). 

C.  6.  7. 


C  (6).  7.  8.  (T.  1). 


C.  8.  T.  1. 

T.  1. 
T.  1. 


THE  DISTKIBUTION  OF  THE  SriNAL  NEKVES. 


667 


I.  Upper  Limb. 

B.  Muscular  Nerves. 
1.  Dorsal  (Posterior)  Surface. 


Regions. 


'Upper  part 
(preaxial 
muscles) 


Shoulder- 


Lower  part 
[fostaxial 
muscles) 


Upper  arm 


Forearm 


Muscles. 


Trapezius 

Levator  anguli  scapulae 

Rhomboidei    . 
Serratus  magnus    . 
Supraspinatus  \ 
Infraspinatus  / 

Subscajiularis 

Teres  major  . 
Teres  minor  ) 
Deltoid  I 

Latissimus  dorsi 
Triceps  .... 
Outer  head 
Middle  head 
Inner  head 
Anconeus 
Brachio-radialis 
Extensor        carpi        radialis 

longior 
Extensor        carpi        radialis 

brevior 
Supinator  radii  brevis   . 
Extensor  communis  digitorum 
„         minimi  digiti  . 
„         carpi  ulnaris    . 
Extensor  ossis  metacarpi  pol- 
licis  .... 
Extensor  longus  pollicis 
„         brevis  pollicis 
indicis     . 


Nerves. 

Cervical  plexus     . 

/Cervical  plexus    . 

I  Posterior  scapular 
Posterior  scajjular 
Posterior  thoracic 

Suprascapular 

/Short  subscapular 
l  Lower        „ 
Lower  subscaj^ular 

Circumflex    . 

Long  subscapular 

j  Musculo-spiral 
j-  Musculo-spiral 


Posterior 
osseous 


inter- 


Spinal  Origins. 

Preaxial  Postaxial 
Nerves.      Nerves. 


I.  Upper  Limb. 

B.  Muscular  Nerves. 

2.  Ventral  (Anterior)  Surface. 


Regions. 

Muscles. 

Nerves. 

Spinal  Origins. 

Preaxial    Postaxial 
Nerves.      Nerves. 

Pectoral 
Region 

'Upper  part 
{preaxial 
muscles) 

Lower  part 
(postaxial 
'     muscles) 

Sterno-mastoid 
Omo-liyoid      ) 
Sterno-hyoid   /      '         '         " 
Subclavius    .... 
Pectoralis  major    . 

Clavicular  part 

Sternal  part 
Pectox'alis  minor   . 

Cervical  plexus 
Ansa  hypoglossi     . 
Brachial  plexus 

(Anterior    thoracic 
1     nerves 

C.  2. 

C.  1.  2.  3. 

C.  5.  6. 

C.  5.  6.  7.  8.  T.  1. 

C.  5.  6. 

C.  5.  6.  7.  8.  T.  1. 

C.  7.  8.  T  1. 

668 


THE  NERVOUS  SYSTEM. 
2.  Ventral  (Anterior)  Surface — continued. 


Spinal  Origins. 

Regions. 

Muscles. 

Nerves. 

Preaxial  Postaxial 
Nerves.      Nerves. 

^Outer  part 

Biceps 

1 
Musculo-cutaneous 

}C.  5.  6. 

C.  (5).  6. 

(preaxial) 

Brachialis  anticus 

f  Musculo-cutaneous 
(Musculo-spiral 

Coraco-brachialis  . 

Musculo-cutaneous 

C.  7. 

Upper 

, 

'Internal  anterior 

arm 

thoracic,  or  lesser 

Inner  part 

Axillary  arches     . 

internal  cutane- 
ous,    or     inter- 
,    costo-humeral 

C.  8.  T.  1.  (2). 

(postaonal) 

I 

,  Outer  part 

Pronator  radii  teres 

-Median 

C.  6. 

1 

{'preaxiaV) 

Flexor  carpi  radialis     . 

C.  6. 

Palmaris  longus    . 

Flexor  subliniis  digitorum    . 

Forearm- 

Flexor  profundus  digitorum 

/"Anterior        inter- 
\     osseous :  Ulnar 

C.  7.  8.  T.  1. 
C.  8.  T.  1. 

Flexor  carpi  ulnaris 

Ulnar     . 

C.  8.  T.  1. 

Inner  part 

Flexor  longus  poUicis  . 

\  Anterior        inter- 

|c.  7.  8.  T.  1. 

^     (postaxicd) 

Pronator  quadratus 

)      osseous 

'Outer  part 

Abductor  pollicis  . 

•MpdiaTi 

-C.  6.  7. 

(preaxial) 

Opponens  pollicis 

Flexor  brevis  pollicis    . 

1                             ■ 

Two  outer  lumbricales . 

j 

Two  inner  lumbricales . 

^ 

^ 

Hand 

■< 

Interossei      .... 
Adductores    pollicis    (trans- 

versus  et  obliquus)  . 

.  Ulnar    . 

•C.  8.  (T.  1). 

Abductor  minimi  digiti 

Inner  part 

Opponens  minimi  digiti 

' 

(postaxial) 

F  exor  brevis  minimi  digiti 

J 

II.  Lower  Limb. 

A.  Cutaneous  Nerves. 

1.  Dorsal  Surface. 

{Front  and  outer  side  of  thigh,  buttock,  front  of  leg,  dorsum  of  foot.) 


Regions. 


Nerves. 


Spinal  Origins. 

Preaxial  Postaxial 

Nerves.  Nerves. 


Front  of  thigh  and 
front  part  of  but- 
tock 
(preaxial  nerves) 


TlliLdl 


Buttock 


Outer  side  of  thigh  ,- 
and  buttock,  back  | 
and  lower  part     i 

(pjosf axial  nerves)       I, 

f  Inner  side 


Genito-crural,  crural  branch 
Anterior  crural,  internal  branch 
Anterior  cniral,  uiiddle  branch 
External  cutaneous 
Twelfth  thoracic,  iliac  branch 
Ilio-hypogastric,  iliac  branch 
Posterior       primary 
lumbar     . 

primary 


divisions, 
divisions. 


L.  1.  2. 

L.  2.  3. 

T.  12. 
L.  1. 


L.  1.  2.  3. 


Leg 


Dorsum 
foot 


of 


(preaxial) 
Outer  side 

(postaxial) 
Inner  side 

(preaxial) 
Outer  side 

(postaxial) 


Posterior 

sacral 
Posterior       primary       divisions, 

coccygeal ..... 
Small  sciatic  :  gluteal,  and  femoral 

branches  ..... 
Internal  saphenous 

Patellar  branch 
Mu.sculo-cutaneous 
Peroneal,  sural  branches 
Internal  saphenous 
Anterior  tibial 
Masculo-cutaneous 
External  saphenous 


S 

1. 

-5 

Co 

S 

1. 

2. 

3. 

4. 

L. 

4.  5 

S.  1. 

L. 

(4). 

5.  S.  1. 

3. 

4. 

L. 

4.  5 

(S.  1). 

L. 

4.  5 

S.  1. 

S.  1.  (2). 

THE  DISTEIBUTION  OF  THE  SPINAL  NERVES. 


669 


II.  Lower  Limb. 

A.  Cutaneous  Nerves. 

2.  Ventral  Surface. 

{Inner  side  and  hack  of  thigh,  hack  of  leg,  and  sole  of  foot.) 


Spinal  Origins. 

Regions. 

Nerves. 

Preo.xiul           Postaxial 
Nerves.               Nerves. 

[   Inner  side   of 

1  Ilio-inguinal          .... 
/Obturator 

L.  1. 

Inner      side 

thigh 

L.  2.  3.  (4). 

and  back  of 

(preaxial) 

thigh 

Back  of  thigh 
(nostaxial) 

[Small  sciatic,  femoral  branches     . 

S.  1.  2.  3. 

Back  of  leg 

Peroneal,  sural  branches  .      . 

|l.  (4).  5.  S.  1. 
S.  1.  2.  3. 

Peroneal,  communicans  fibularis  . 
Small  sciatic          .... 

External  saphenous 

S.  1.  (2). 

1' Inner  side 

Internal  sai:)henous 

L.  3.  4. 

(preaxial) 

Posterior  tibial,  calcanean 
Internal  plantar    . 
Great  toe,  inner  side . 
„        „    outer  side. 

S.  1.  2. 
L.  4.  5.  S.  1. 
L.  4.  5. 

}l.  4.  5.  S.  1. 

Second  toe,  inner  side 

Sole  of  foot 

„         „    outer  side 
Third  toe,  inner  side 

-L.  5.  8.  1. 

„         „     outer  side 

Fourth  toe,  inner  side 

External  plantar  . 

-S.  1.  2. 

Fourth  toe,  outer  side 

Outer  side 

Fifth  toe,  inner  side  . 

1      (postaxial) 

„       „    outer  side  . 

External  saphenous 

S  1.  (2). 

II.  Lower  Limb. 

B.  Muscular  Nerves. 

I.   Dorsal  Surface. 

{Front  and  outer  side  of  thigh,  huttock,  front  and  outer  side  of  leg,  dorsum  of  foot.) 


Spinal  Origins. 

Regions. 

j              Muscles. 

Nerves. 

Preaxial      Postaxial 

1 

Nerves.         Nerves.     1 

i 
Pectineus 

I 
JL.  2.  3. 

Sartorius  . 

Front  of  thigh 

{preaxiat) 

Iliacus      .         .         .  ' 

Psoas 

Quadriceps  extensor 

y  Anterior  crural 

JL.  2.  3.  4. 

Vastus  internus    . 

Rectus  femoris      .  } 

[l.  3.  4. 

V 

Crureus          .         .   - 

Vastus  externus    . 

. 

'•  Tensor  fasciae  femoris 

1 

L.  4.  5.  S.  1           1 

Gluteus  minimus      .  ' 

rSujierior  gluteal 

Buttock  and  outer  side  of  thigh- 

„        medius 

1 

{fostaxial) 

1         „        maximus     .  : 

Inferior  gluteal   . 

j         L.  5.  S.  1.  2. 

Biceps,  short  head    . 

Peroneal 

Pyriformis 

Sacral  plexus 

S.  1.  2.  1 

670 


THE  NERVOUS  SYSTEM. 
1.  Dorsal  Surface — continued. 


Regions. 

j              Muscles. 

Nerves. 

Spinal  Origins. 

Preaxial  Nerves. 

Front  of  leg 
Dorsum  of  foot 

! 

f  Inner  side 
{preaxial) 

Outer  side 
(jjost  axial) 

Tibialis  anticus 
Extensor      proprius 
hallucis 
;  Extensor          longus 
digitorum 
Peroneus  tertius 
Peroneus  longus 
Peroneus  brevis 
Extensor  bre^^s  digi- 
torum   . 
1 

-  Anterior  tibial   . 

M  usculo  -  cutaneous 
Anterior  tibial  . 

■L.  4.  5.  S.  1. 

II.  Lower  Limb. 

B.  Muscular  Nerves. 

2.  Ventral  Surface. 

{Inner  side  and  hack  of  thigh,  hack  of  leg,  and  sole  of  foot.) 


•       Spinal  Origins. 

Regions. 

Muscles. 

Nerves.                Preaxial       Postaxial 

Nerves.           Nerves. 

Adductor  longus       .    ' 

\                                        '^ 

Thigh,  inner 

Gracilis    .        .        .     | 

L.  2.  3. 

side 
(preaxial) 

Adductor  brevis 

-  Oljturator  . 

-  L.  2.  3.  4. 

Obturator  externus  . 

L.  3.  4. 

Adductor  magnus     . 

1                                    J 

Thigh      and 
buttock 

Thigh,  outer 
side 
{postaxial)  1 

Adductor  magnus     . 
;  Semi-membranosus  . 
Semi-tendinosus 
Biceps,  long  head     . 
Quadratus      femoris 

1    Nerve   to    ham-  ]  J'"  J  J  ?•  l' 

i  string,  .    ..^"^fU:!: 

r 

1 

and  superior  gem-  i 

-   L.  4.  5.  S.  1. 

Buttock - 

ellus 
Inferior       gemellus 

■  Sacral  plexus      .     ' 

' 

and  obturator  in- 

I       S.  1.  2.  3. 

1 

ternus   . 

Plantaris  . 
'  Popliteus . 
1  Flexor   longus  digi- 

} Tibial         .         .  !|   L.  4.  5.  S.  1. 

1                                   1 

torum   . 

1-  L.  5.  S.  1. 

Back  of  leg  . 

Tibialis  posticus 
Flexor   longus    lial- 

'  Posterior  tibial  .    ^ 

lucis 

-  L  5.  S.  1.  2. 

Soleus 

Soleus 

1 

S.  1.  2. 

i  Gastrocnemius  (each 

-  Tibial 

head)     . 

'                                   ^i                                   1 

'  Abductor  hallucis    .  ' 
Flexor    brevis   digi- 

Inner .side 
{preaxial) 

torum    . 
j  Flexor    brevis    lial- 
;       lucis 
First  lumbricalLs 

-  Internal  jilantar 

.   L.  4.  5.  S.  1. 

, 

-    Second,    third,    and 

,                                                                                       s 

Sole  of  foot 

fourth  lumbricales 
Flexor  accessorius    . 

Outer  side 

{postaxial) 

Adductores  hallucis . 
Intero.ssei 

External  ])lantar 

S.  1.  2. 

Flexorbrevis  minimi 

digiti     . 

Abductor       minimi 

•j      digiti    . 

THE  DISTKIBUTION  OF  THE  SPINAL  NERVES. 


671 


A.  Innervation  of  the  Muscles  of  the  Limbs. — The  following  laws  appear  to  be  applicable 

to  the  upper  and  lower  limbs  alike  : — 

1.  No  limb-muscle  receives  its  nerve-supply  from  posterior  primary  divisions. 

2.  The  dorsal  and  ventral  strata  of  muscles  are  ahoays  supplied  by  the  corresponding  dorsal  and 
ventral  branches  of  the  nerves  concerned.  The  ventral  muscular  stratum  is  more  extensive  than  the 
dorsal;  the  ventral  nerves  are  the  more  numerous,  and  the  additional  nerves  are  postaxially  placed. 
The  spinal  nerves  supplying  muscles  of  the  upper  limb  are  C.  5,  6,  7,  8  (dorsal),  and  C.  5,  6,  7,  8, 
T.  1  (ventral) ;  tlie  nerves  for  the  muscles  of  the  lower  limb  are  L.  2,  3,  4,  5,  S.  1,  2  (dorsal),  and 
L.  2,  3,  4,  5,  S.  1,  2,  3  (ventral). 

3.  The  dorsal  and  ventral  trunks  of  the  nerves  are  distributed  in  the  limb  in  a  continuous, 
segmental  manner ;  so  that,  "  of  two  muscles,  that  nearer  the  head  end  of  the  body  tends  to  be 
supplied  by  the  higher  nerve,  and  that  nearer  the  tail  end  by  the  lower  nerve  "  (Herringham). 

4.  The  nerves  placed  most  centrally  in  the  plexus  extend  furthest  into  the  limb,  and  the  more 
preaxial  nerves  terminate  sooner  in  the  limb  than  the  more  jjostaxial  nerves. 


Upper  Limb 
Dorsal  Surface. 

Muscles  of  shoulder     .     C.  3,  4,  5,  6,  7,  8. 
„         arm    .         .     C.  6,  7,  8. 
„         forearm      .     C.  6,  7. 


Ventral  Surface. 


Muscles  of  thigh  and 
buttock    . 


Muscles  of  leg  and  foot     L.  4,  5,  S.  1. 


Muscles  of  chest 
„         arm 
„         forearm 
„         hand 
Lower  Limb. 

Muscles  of  thigh 
L.  2,  3,  4,  D,  S.  1,  2.  ,  ' 


foot 


C.  .5,  6,  7,  8,  T.  1. 

C.  5,  6,  7. 

C.  6,  7,  8,  T.  1. 

C.  6,  7,  8  (T.  1). 

L.  2,  3,  4,  5,  S.  1,  2,  3. 
L.  4,  5,  S.  1,  2. 
L.  5,  S.  1,  2. 


The  only  exception  to  this  rule  is  on  the  ventral  (anterior)  surface  of  the  upper  arm,  where  a 
suppression  of  the  muscle  elements  leads  to  an  absence  of  the  regular  series  of  segmental  nerves 
(C.  8,.  T.  1)  on  its  postaxial  border.     Tliese  nerves  reappear  in  the  forearm,  and  the  occasional 


(yPPS/7  L/AfB 


C.3 

Shovclder 

DORSAL 

A/TTt 

SURFACE 
Forearm 

1                       \ 

Hand. 

C.5 
6 

7 

8 
T.I 

Chest 

VENTRAL 
Arm. 

SURFACE 
Forearm 

Jfand 

4 

5 

\ 

6 

I 

J 

7 

'■                       \ 

\ 

:                         .                           i                       ] 

8 

^ 

1                       J 

1 

;                     .                       \                   \ 

DORSAL 
ThigTi    &■    BuHock. 


SURFACE 
Ley 


LOlVEFi  L/MB 


VENTRAL     SURFACE 
Thigh  Z  e^ 


L.2 

\                       ■ 

L.2 
3 
4 
5 

S.I 
2 
3 

} 

3 

\ 

s 

4 

\ 

■             J 

5 

\ 

;^  1 

'                       ) 

2 

;                     ] 

) 

Fig.  516. — Scheme  of  the  segmental  distribution  of  the  muscular  nerves  of  the  upper  ami  lower  limbs. 

"  axillary  arclies "  may  be  regarded  as  the  muscular  elements  usually  suppressed,  and,  when 
present,  supplied  by  these  nerves. 

Muscles  with  a  Double  Nerve-supply. — The  existence  of  more  than  one  nerve  to  a  muscle 
indicates  usually  that  the  muscle  is  composite  and  is  the  representative  of  originally  separate 
elements,  belonging  to  more  than  one  segment  or  to  both  surfaces  of  the  limb.  In  the  case  of 
the  pectoralis  major,  subscapularis  and  flexor  profundus  digitorum,  adductor  magnus,  and  soleus, 
parts  of  the  same  (ventral  or  dorsal)  stratum  have  fused,  to  form  muscles  innervated  from  the 
corresponding  ventral  or  dorsal  nerves.  The  other  muscles  having  a  double  nerve-supply — 
brachialis  anticus,  biceps  flexor  cruris,  and  (sometimes)  pectineus — are  examples  of  fusion  at  the 
jjreaxial  or  postaxial  border  of  muscular  elements  derived  from  the  dorsal  and  ventral  surfaces  of 
the  limb,  which  are  correspondingly  innervated  by  branches  from  both  dorsal  and  ventral  series  : 
e.g.  the  brachialis  anticus  is  innervated  by  the  musculo-cutaneous  and  musculo -spiral  nerves  ;  the 
biceps  flexor  cruris,  by  the  peroneal  (short  head)  and  tibial  (long  head)  nerves  ;  and  the  pectineus, 
by  the  anterior  crural  and  (sometimes)  obturator  nerves. 

B.  Innervation  of  the  Skin  of  the  Limbs. — While  the  scheme  of  cutaneous  innervation  of 
the  limbs  is  fundamentally  segmental,  yet  the  arrangement  is  confused  and  complicated  by 
various  causes.  The  growth  of  the  limb  from  the  trunk  has  caused  the  skin  to  be  drawn  out 
over  it  like  a  stretched  sheet  of  india-rubber  (Herringham),  and  at  the  same  time  the  extent  of 
the  dorsal  area  of  the  limb  is  increased  at  the  expense  of  the  ventral  area.  The  central  nerves  of 
the  plexus  remain  buried  deeply  in  the  substance  of  the  limb,  only  coming  to  the  surface  towards 
the  periijhery.     The  proximal  parts  of  both  surfaces  of  the  limb  thus  become  innervated  by 


672 


THE  NEEVOUS  SYSTEM. 


cutaneous  nerves  otlierwise  not  necessarily  concerned  in  the  innervation  of  the  limbs.  Herring- 
ham  has  shown  that — (A)  Of  two  spots  on  the  skin,  that  nearer  the  preaxial  border  tends  to  he 
supplied  by  the  higher  nerve.  (B)  Of  two  spots  in  the  preaxial  area,  the  lower  tends  to  be  supplied  by 
the  loiver  nerve ;  and  of  two  spots  in  the  postaxial  area,  the  loioer  tends  to  be  supplied  by  the  higher 
nerve.  In  other  Avords,  from  the  root  of  the  limb  clown  the  preaxial  border  to  its  distal  extremity, 
and  up  the  postaxial  border  to  the  root  of  the  limb  again,  there  is  a  defiiiite  numerical  sequence 
of  spinal  nerves  supplying  skin  areas  through  nerves  of  the  limb-jjlexuses.  A  similar  numerical 
sequence  in  the  arrangement  of  the  nerves  is  also  found  extending  over  the  dorsal  and  ventral 
surfaces  of  the  limbs  from  preaxial  to  postaxial  border,  excejDt  in  certain  situations. 

On  the  dorsal  and  ventral  surfaces  of  both  upper  and  lower  limbs  tliere  is  a  hiatus,  for  a 
certain  distance,  in  the  numerical  sequence  of  the  spinal  nerves  in  their  cutaneous  distribution, 
explicable  on  the  ground  that  the  central  nerves  of  the  plexus,  which  fail  to  reach  the  surface  in 
these  situations,  are  replaced  by  cutaneous  branches  from  neighbouring  nerves.  This  hiatus  has 
been  named  the  axial  area  or  line. 

In  the  upper  limb,  the  dorsal  axial  area  or  line  extends  from  the  middle  line  of  the  back, 
opposite  the  vertebra  prominens,  to  the  insertion  of  the  deltoid. 

The  ventral  axial  area  or  line  extends  anteriorly  from  the  middle  line  of  the  trunk,  at  the 
manubrio-sternal  joint,  across  the  chest,  down  the  front  of  the  arm  and  forearm  to  the  wrist. 

In  the  lower  limb,  the  dorsal  axial  area  or  line  may  be  traced  from  the  middle  line  of  the 
back  over  the  posterior  superior  iliac  spine,  across  the  buttock  and  thigh,  to  the  head  of  the 
fibula. 

A  ventral  axial  area  or  line  can  also  be  traced  from  the  root  of  the  penis  along  the  inner  side 
of  the  thigh  and  knee,  and  down  the  back  of  the  leg  to  the  heel. 

These  areas  or  lines  represent  the  meeting-place  and  overlapping  of  nerves,  which  are  not  in 
numerical  sequence  ;  and  it  is  only  at  the  peripheral  parts  of  the  limbs,  on  the  dorsal  and  ventral 
surfaces,  that  the  nerves  appear  in  numerical  sequence  from  the  preaxial  to  the  postaxial  border. 
In  tlie  case  of  the  upj^er  limb  the  hiatus  is  caused,  in  both  surfaces  of  the  limb,  by  the  absence  of 
cutaneous  branches  of  the  seventh  cervical  nerve ;  in  the  case  of  the  lower  limb  the  hiatus  is  due 
to  the  absence  of  branches  from  the  fifth  lumbar  nerve  on  both  surfaces  of  the  limb,  and  the 
absence  of  branches  from  the  fourth  lumbar  nerve,  in  addition,  on  the  dorsal  surface. 

Understanding  the  significance  of  these  dorsal  and  ventral  axial  areas  or  lines,  and  at  the 
same  time  bearing  in  mind  the  overlapping  which  occurs  in  the  cutaneous  distribution  of  each 
spinal  nerve,  the  areas  of  skin  supjDlied  through  the  limb-jDlexuses  can  be  maj)ped  out  with  con- 
siderable precision,  as  indicated  in  the  following  tables  : — 

A.  Upper  Limb. 
Cutaneous  Distribution. 


Nerves. 

Spinal  Origin. 

Distribution. 

r 

Supraclavicular  nerves 

C. 

3.  4. 

Chest,   shoulder,    deltoid,    and 
scapular  regions. 

Circumflex  . 

C. 

5.  6. 

Deltoid  region,  outer  side  of  arm. 

Preaxial  border 

Musculo-spiral    (upper 

c. 

(5).  6. 

Outer  side  and  back  of  arm  and 

from  neck  to     • 

external) 

forearm. 

hand 

Musculo-spiral    (lower 

c. 

6.  7.  8. 

Outer  side  and  back  of  elbow 

^k 

external) 

and  forearm. 

Musculo-cutaneous 

c. 

5.  6. 

Outer  side  of  forearm,  in  front 

V 

and  behind. 

r  Dorsum  | 
Hand  . 

I  Palm 

Radial 

Ulnar  .... 

c. 

c. 

6.  7. 

8. 

Outer  side  1    ,.  ■,              e-u     j 
Inner  side  /°^^°^'^^"^°f^^^^- 

Musculo-cutaneous 

c. 

5.  6. 

Ball  of  thumb. 

Median 

Ulnar  .... 

c. 

T. 

6.  7. 
1. 

Outer  side  1    ,.     ,        o^       , 
Inner  side  r^P^l"^^^^*^^- 

r 

r 

Thumb          C.  6.  7. 

First  finger,  C.  6.  7.  8. 

Digits 

Median 

c. 

6.  7.  8.  T.  1. 

Second    „      C.  7.  8.  T.  1. 

Ulnar 

c. 

8.  T.  1. 

Third     „      C.  8.  T.  1. 
Fourth    „    Im  T 
Fifth       „   j-^-l- 

V 

V 

f 

Internal  cutaneous 

c. 

8.  T.  1. 

Inner  side  of  forearm,  in  front 

and  behind. 

Musculo-spiral    (inter- 

c. 

8. 

nal) 

Postaxial  border 

Lesser  internal  cutane- 

T. 

1. 

Inner  side  of  arm. 

from  hand  to 

ous 

chest 

Intercosto-humeral 

T. 

2. 

^ 

Intercosto-huuieral 

T. 

2.                     1 

Third  intercostal 

T. 

3. 

4.                    J 

Axillary  folds. 

^ 

Fourth         „ 

T. 

VAEIATI0N8  IN  THE  rOSITION  OF  THE  LIMB-PLEXUSES.      673 


B.  Lower  Limb. 
Cutaneous  Distribution. 


Nerves. 

Spinal  Origin. 

Distribution. 

Iliac  branch  of  twelfth 
thoracic 

T.  12. 

Outer  side  of  buttock. 

Iliac    branch    of    ilio- 

L.   1. 

Outer  side  of  buttock. 

hyjjogastric 

Ilio-inguinal 

L.  1. 

Groin  and  over  Scarjm's  triangle. 

Preaxial  border 

Genito-crural 

L.   1.  2. 

Front  of  thigh,  upper  third. 
Front  and  outer  side  of  thigh. 

from  trunk  to   ■ 

External  cutaneous 

L.  2.  3. 

foot 

Anterior  crural  (middle 

L.  2.  3. 

Front  and  inner  side  of  thigh, 

^ 

and  internal) 

lower  two-thirds. 

Obturator     . 

L.  2.  3.  (4). 

Inner    side    of    thigh,    middle 
third. 

Anterior  crural  (inter- 

L.  3.  4. 

Knee  and  leg,  inner  side  and 

'       nal  saphenous) 

front. 

Internal  saphenous 

L.  3.  4. 

Inner  side  of  foot. 

Anterior  tibial     . 

L.  4.  5.  S.  (1). 

Interval     between     first     and 

^  Dorsum  - 

second  toes. 

Musculo-cutaneous 

L.  4.  5.  S.  1. 

Dorsum  of  foot  and  toes. 

Foot- 

Uole 

j  External  saphenous 

S.  1.  (2). 

Outer  side  of  foot. 

Internal  jjlantar 

L.  4.  5.  S.  1. 

Inner  part                 \ 

External  jjlantar 

S.  1.  2. 

Outer  part                  Vof  sole. 

j  Posterior    tibial    (cal- 

S.  1.  2. 

Heel  and  back  part  J 

canean) 

Great  toe,    L.  4.  5.  S.  1. 

Digits 

Internal  and  external 
plantar 

L.  4.  5.  S.  1.     J 
S.  1.  2.               1 

Second  toe,  L.  4.  5.  S.  1. 
Third      „    L.  5.  S.  1. 
Fourth    „    L.  5.  S.  1.  2. 

Fifth       „    S.  1.  2. 

External  sajjlienous 

S.  1.(2). 

Outer  side  of  foot  and  leg,  lower 

Postaxial  border 

third. 

from  foot  to     ■ 

Small  sciatic 

S.   1.  2.  3. 

Back  of  leg,  thigh,  and  buttock. 

coccyx 

Perforating  cutaneous . 

S.  2.  3. 

Buttock   (fold   of   nates,   inner 

^ 

1 

half). 

Sacro-coccygeal    .  •     . 

S.  4.  5.  Co.  1. 

Anal  fold. 

Variations  in  the  Position  of  the  Limb-plexuses. 

Two  different  kinds  of  variations  occur  in  relation  to  the  limb-nerves. 

(1)  Individual  variations,  in  both  the  extent  of  origin  and  in  the  area  of  distributicju  of  a 
given  nerve,  are  not  uncommon  ;  these  variations  are  usually  concomitant  with  compensatory 
variations  in  adjacent  nerves,  and  are  due  to  the  fibres  of  a  given  spinal  nerve  taking  an 
abnormal  course  in  the  trunk  of  another  nerve  of  distribution  and  effecting  a  communication 
with  the  i^roper  nerve  peripiherally.  In  this  way  the  variations  in  the  origin  and  distribution 
of  the  intercosto-humeral  nerve  may  be  exj^lained ;  and,  similarly,  the  uhiar  nerve  may  have 
some  of  its  fibres  carried  as  far  as  the  forearm  incorporated  with  the  median  and  transferred  to 
it  by  a  communication  between  the  two  nerves  in  that  region. 

(2)  Variations  in  the  limb-plexus,  in  relation  to  the  vertebral  column,  are  the  chief  cause  of 
variations  in  the  constitution  of  the  limb-nerves.  These  variations  aft'ect  more  or  less  the  whole 
series  of  nerves  in  the  plexus. 

The  brachial  plexus  is  subject  only  to  very  slight  variation  in  position  and  arrangement 
It  may  l)e  reinforced  at  the  upjjer  end  by  a  slender  trunk  from  the  fourth  cervical  nerve,  and, 
more  frequently,  by  an  intra -thoracic  communication  between  the  second  and  first  thoracic 
nerves.  The  presence  of  one  or  other  of  these  nerves  is  an  indication  of  a  slight  tendency 
towards  a  cephalic  or  caudal  shifting  of  the  whole  jslexus  in  relation  to  the  spinal  cord.  It  is, 
however,  never  sufficient  to  cause  the  exclusion  to  any  extent  of  the  nerves  normally  imj)licated. 
The  presence  of  a  cervical  rib  may  coincide  with  little  or  no  change  in  the  relation  of  the  nerves. 
Indeed,  the  inclusion  of  the  second  thoracic  nerve  in  the  plexus  may  be,  as  ah-eady  stated, 
merely  an  individual  variation,  a  change  in  the  jtath  to  the  limb  of  the  intercosto-humeral 
nerve.  Concomitant  variations  occur  among  gi'oujis  of  nerves,  however,  which  indicate  a  certain 
tendency  to  variation  in  the  position  of  the  whole  plexus.  At  one  end,  the  suprascapular  and 
musculo-cutaneous  nerves  may  arise  from  the  fourth  and  fifth,  fifth  alone,  or  fifth  and  sixth 
cervical  nerves.  At  the  other  end  of  the  j^lexus,  the  musculo -spiral  may  or  may  not  receive  a 
root  from  the  first  thoracic  nerve,  and  this  addition  is  rather  more  likely  to  occur  when  the 
second  thoracic  nerve  is  implicated  in  the  plexus. 

The  lumbo-sacral  plexus  shows  a  very  considerable  variability  in  position  and  constitution. 
Eisler  records  concomitant  variations  in  the  plexus  in  18  per  cent  of  the  cases  examined  by  him. 

47 


674 


THE  NERVOUS  SYSTEM. 


The  variations  occur  within  wide  limits.  The  plexus  may  begin  at  the  eleventh  or  twelfth 
thoracic  or  lii'st  lumbar  nerve.  The  last  nerve  in  the  great  sciatic  cord  may  be  the  second,  third, 
or  fourth  sacral  nerve.  The  position  of  the  n.  furcalis  is  a  guide  to  the  arrangement  of  the 
plexus.  It  may  be  formed  by  the  third,  third  and  fourth,  fourth,  fourth  and  fifth,  or  fifth 
lumbar  nerves.     The  resulting  variations  are  illustrated  by  the  following  extreme  cases  : — 

(1)  Prefixed  Variety.  (2)  Postfixed  Variety. 

Nervus  furcalis     .         .         .         L.  3  and  4  (double).  L.  5. 

Obturator     .  .         L.  1,  2,  3.  L.  2,  3,  4,  5. 

Anterior  crural     .         .         .         T.  12,  L.  1,  2,  3,  4.  L.  2,  3,  4,  5. 

Tibial L.  3,  4,  5,  S.  1,  2.  L.  5,  S.  1,  2,  3,  4. 

Peroneal  .         .         .         L.  3,  4,  5,  S.  1.  L.  5,  S.  1,  2,  3. 

Those  variations  in  the  constitution  of  the  lumbo-sacral  plexus  are  most  numerous  which 
are  due  to  the  inclusion  of  nerves  more  caudally  placed.  Thus,  out  of  twenty -two  variations 
in  the  position  of  the  n.  furcalis,  in  nineteen  Eisler  found  it  formed  by  the  fifth  lumbar  nerve ; 
in  two  cases  only,  by  the  third  lumbar  nerve.  There  is  further  evidence  that  variations  in  the 
position  of  the  plexus  are  accompanied  by  variations  in  the  vertebral  column  itself.  Out  of  the 
twenty -two  abnormal  plexuses  examined  by  Eisler,  sixteen  were  coincident  with  abnormal 
arrangement  of  the  associated  vertebrae. 

Significance  of  the  Limb-plexuses. 

From  the  above  considerations,  it  is  obvious  that  something  more  than  convenience  of  transit 
for  the  spinal  nerves  to  skin  and  muscles  is  secured  by  the  formation  of  the  limb-plexuses.  It 
has  been  shown  that  by  their  combinations  in  the  plexuses,  every  spot  or  area  of  skin  in  the 
limbs  is  innervated  by  more  than  one  spinal  nerve ;  and  generally,  also,  each  limb -muscle  is 
supplied  by  more  than  one  spinal  nerve.  Each  cutaneous  area  and  each  limb  -  muscle  is  thus 
brought  into  relationship  with  a  wider  area  of  the  spinal  cord  than  would  occur  if  the 
plexuses  were  non-existent.  A  simultaneous  record  of  sensation  is  thus  transmitted  from  any 
given  point  on  the  surface  of  the  limb  through  more  than  one  dorsal  root ;  and  a  more  ready 
co-ordination  of  muscular  movement  is  brought  about  by  the  transmission  of  motor  impulses 
from  the  ventral  root  of  a  given  spinal  nerve  to  more  than  one  muscle  at  the  same  time.  In  a 
word,  a  plexus  exists  to  supply  the  wliole  limb  and  the  limb  as  a  whole,  as  an  organ  which  has 
its  different  active  parts  connected  with  the  central  nervous  system  by  means  of  the  limb-plexus. 


THE  CEANIAL  NEEVES. 

The  series  of  cranial  nerves  is  arranged  in  twelve  pairs,  which  present  striking 
differences  in  origin,  in  distribution,  and  in  functions. 


! 
Number.               Name. 

Function. 

Superficial  Attachment 
to  Brain. 

I.    Olfactory     . 

SmeU 

Olfactory  bulb. 

II.    Optic    . 

Sight        

Optic  thalamus. 

III.    Oculo-motor 

Motor  to  the  muscles  of  eyeball  and 

orbit 
Motor  to  superior  oblique  muscle  of 

Crus  cerebri. 

IV.     Trochlear    . 

Superior      medullary 

eyeball 

velum. 

V. 

Trigeminal  . 

Sensory  to  face,  tongue,  and  teeth  ; 
motor  to  muscles  of  mastication 

Pons  Varolii. 

1        ^I- 

Abducent 

Motor  to  external  rectus  muscle  of 

Junction  of  pons  and 

eyeljall 

medulla. 

VII.    Facial  . 

Motor  to  muscles  of  scalp  and  face. 

Posterior     border     of 

! 

sensory  to  tongue 

pons  Varolii. 

VIII.    Auditory     . 

Hearing  and  equilibrium 

Posterior     border     of 
pons  Varolii 

IX.     Glossopharyngeal 

Sensory  to  tongue  and  pharynx 

Medulla  oblongata. 

X.     Pneumogastric    . 

Sensory  to  jjliar^Tix,  oesophagus  and 
stomach,  and  respiratory  organs 

Medulla  oblongata. 

XI. 

Spinal  accessory 

(«)  Accessory  to  vagus.— Motor  to 
muscles  of  palate,  pharynx,  oeso- 
phagus, stomach  and   intestines, 
and  respiratory  organs ;  inhibitory 
for  heart 

Medulla  oblongata. 

(6)  Spinal  part ;  motor  to  trapezius 

Spinal  cord. 

and  stei'iio-mastoid  muscles 

XII. 

Hypoglossal 

Motor  to  muscles  of  the  tongue 

Medulla  oblongata. 

THE  riKST  OK  OLFACTOEY  NEEVE. 


675 


The  deep  cerebral  connexions  of  the  cranial  nerves  are  dealt  with  in  the 
section  which  treats  of  the  Brain  (pp.  514  and  540).  Certain  general  points  in 
connexion  with  these  nerves  are  also  touched  upon  in  the  chapter  introductory  to 
the  Nervous  System  (p.  443). 


The  First  or  Olfactory  Nerve. 

The  olfactory  nerve  (n.  olfactorius)  consists  of  several  parts  :  (1)  a  series  of  fine 
nerves,  which  arise  from  (2)  the  olfactory  bulb.     This  again  is  connected  by  (3) 


Olfactorj-  Inilb 


Olfactory  tract 


Olfactory  tubercle 

Optic  nerve 

Optic  cliiasma 

Oonlo-motor  nerve 
Trochlear  nerve 

Trigeminal  nerve 
Abducent  nerve- 
Facial  nerve 
Pars  intermedia. 
Auditory  nerve. 


Olfactory  bulb 


Olfactory  tract 
Broca's  area 
Olfactory  tubercle 
Mesial  root  of  olfactory 
inerve 

Lateral  root 

Optic  chiasma 

Ant.  perforated  spot 

Temporal  lobe  (cut)  • 

<  'ptic  tract 

I  iculo-motor  nerve 

Tiochlear  nerve 
^  T.tnia  semicircularis 
i'liigeminal  nerve 
-Ext.  geniculate  body 
Abducent  nerve 
Int.  geniculate  body 
Pulvinar 
Facial  nerve 
Pars  intermedia 
Auditory  nerve 
Lateral  ventricle 
Mid.  cerebellar  peduncle 

Glosso-pharyngeal  nerve 

;us  nerve 

nal  accessory  nerve 
(accessory) 
Spinal  accessory  nerve 

_  nal) 
Occipital  lobe  (cut) 


Glosso-pharyngeal  mn  \ . 

Vagus  Ufi  \  L 
Spinal  accessory  nerve  (accessory) 

Spinal  accessory  nerve  (spinal)      | 
Hypoglossal  nerve 


Hypoglossal  nerve 
Spinal  cord 
Vermis  of  cerebellum  (cut) 


Fig.  517. — View  of  thk  Under  Surface  of  thk  Brain. 

with  the  lower  portion  of  the  temporal  and  occipital  lobes,  and  the  cerebelhini  on  the  left  side  removed, 

to  show  the  origins  of  the  cranial  nerves. 

the  olfactory  tract  with  the  brain,  to  which  it  is  attached  by  (4)  two  roots  (Fig.  517). 

The  anatomy  of  the  roots,  tract,  and  liulb  of  the  olfactory  nerve  are  described 
elsewhere  (pp.  569  and  587). 

The  olfactory  nerves,  about  twenty  in  number,  arise  from  the  under  surface  of 
the  olfactory  bulb.  The  fibres  are  non-medullated.  Piercing  the  cribriform  plate 
of  the  ethmoid  bone,  enveloped  in  sheaths  of  dura  mater,  they  are  distributed  in 
the  nasal  cavity  as  the  nerves  of  smell.  The  fibres  form  fine  plexuses  over  a  limited 
area  on  the  upper  portion  of  the  nasal  septum,  and  to  even  a  less  extent  over  the 
outer  wall  of  the  nose. 

The  Second  or  Optic  Nerve. 

The  optic  nerve  (n.  opticus)  arises  from  the  brain  by  means  of  the  optic  tract 
(Fig.  551).     This  takes  origin  from  the  external  and  internal  geniculate  bodies. 


676 


THE  NERVOUS  SYSTEM. 


situated  on  the  under  surface  of  the  optic  thalamus  at  its  posterior  end,  and  also 
from  the  brachium  of  the  upper  of  the  two  corpora  quadrigemina  (vide  pp.  532 
and  551).     The  optic  tract  reaches  the  base  of  the  brain  after  sweeping  round 


li[  Olfactory  nerves 

Superior  nasal  nerve 

\  Inferior  nasal  nerve 


Olfactory  bulb 
Branflie-%  of  naso-palatme  nerve  ^^j^     \ 


Fig.  518. — Innervation  of  the  Nasal  Cavity. 

between  the  crus  cerebri  and  the  hippocampal  convolution  of  the  temporal  lobe. 
The  two  optic  tracts  converge  in  front  of  the  inter -peduncular  space,  internal  to 
the  anterior  perforated  spot  and  the  termination  of  the  internal  carotid  artery, 

and  unite  to  form  the  optic  chiasma  or 
commissure.  This  adheres  to  the  under 
surface  of  the  floor  of  the  third  ventricle  in 
front  of  the  tuber  cinereum,  and  gives 
rise  at  each  end  to  the  optic  nerve.  The 
optic  nerve,  directed  outwards  and  for- 
ward, pierces  the  dura  mater,  and  passes 
from  the  cranial  cavity  into  the  orbit 
through  the  optic  foramen  in  company  with 
the  ophthalmic  artery.  In  the  orbit  the 
nerve  is  imbedded  in  the  fat  behind  the 
eyeball,  and  is  surrounded  by  the  ocular 
muscles.  It  is  connected  with  the  globe  of 
the  eye  at  a  point  one-eighth  of  an  inch 
on  the  inner  side  of  the  axis  of  the  eyeball. 
After  piercing  the  fibrous  and  vascular  coats, 
the  nerve  spreads  out  at  the  optic  disc  to 
form  the  innermost  layer  of  the  retina. 
In  the  orbit  the  nerve  is  crossed  by  the 
ophthalmic  artery  and  the  nasal  nerve,  and 
nearer  to  its  termination  it  is  surrounded 
by  the  ciliary  vessels  and  nerves,  and  by 
the  capsule  of  Tenon.  It  is  pierced  ob-- 
liquely  on  its  under  surface  by  the  central 
artery  of  the  retina. 

Decussation  in  the  Optic  Commissure. —In 

tlie  optic  connnissurc  tlic  tibres  of  the  two  optic 
tracts  separate,  tlic  inner  half  of  each  tract  de- 
cussating to  form  the  mesial  half  of  tlie  opposite 
ojjtic  nerve.  The  otlier,  onter  half  of  each  tract, 
continues  its  course  to  form  the  outer  half  of  the 
optic  nerve  on  the  same  side.  At  tlie  back  of 
the  commissure  another  bundle  of  fibres  is  found 

passing   from  tract  to  tract  behind  the  decussating  fi])res,  and  known  as  Gudden's  commissure 

(see  p.  552). 

The  Third  or  Oculo-motor  Nerve. 
t  The  oculo-motor  nerve  (n.  oculo-motorius)  arises  from  the  brain,  in  the  region 
of  the  posterior  perforated  spot,  by  several  radicles  emerging  from  the  oculo-motor 


CORP.  CEN. INT. 


Fig.  519. — Diagram  ok  the  Central  Connexions 
OK  THE  Optic  Nerve  and  Optic  Tract. 


THE  THIED  OE  OCULO-MOTOE  NEEVE. 


677 


sulcus,  on  the  inner  side  of  the  crus  cerebri,  just  in  front  of  the  pons  Varolii  (Fig. 
517).  Passing  forwards  between  the  posterior  cerebral  and  superior  cerebellar 
arteries,  the  nerve  pierces  the  dura  mater  on  the  outer  side  of  the  posterior  clinoid 
process,  in  a  small  triangular  space  between  the  free  and  attached  borders  of  the 
tentorium  cerelielli.  Beneath  the  dura  mater  the  nerve  courses  through  the  outer 
wall  of  the  cavernous  sinus,  and  enters  the  orbit  through  the  sphenoidal  fissure 


Diaphragma  sellne 


Pituitary  fossa 


Internal  carotid  artery    Optic  nerve 
Trochlear  nerve  I       I      Ophthalmic  artery 

Oculo-motor  nerve         |  ,       '        '       Anterior  clinoid  process 


Trochlear  nerve 

Frontal  branch 

Lachrymal  branch 


Sphenoidal  sinus 


Abducent  nerve 

Cavernous  sinus 

Ophthalmic  division  of  trigeminal  nerve 

Superior  niaxillarj-  division  of  trigeminal  nerve  i 

Inferior  maxillary  division  of  trigeminal  nerve 


Oculo-motor  nerve 
(superior  division) 

Xasal  branch  of  ophthalmic 
nerve 
Uculo-motor  nerve 
(inferior  division) 
Abducent  nerve 
.Superior  maxillary  division  of 
trigenunal  nerve 


Foramen  ovale 
''    Inferior  maxillary  division  of  trigeminal  nen-e 
Motor  root 


Fig.  520. — Relations  of  Structures  in  the  Cavernous  Sinus  and  Sphenoidal  Fissure. 


and  between  the  two  heads  of  the  external  rectus  muscle.     As  it  enters  the  orbit 
it  divides  into  upper  and  lower  branches,  separated  by  the  nasal  nerve. 

Branches. — The  superior  branch  of  the  nerve  supplies  two  muscles  of  the  orbit 
— the  superior  rectus  and  the  levator  palpebrse  superioris. 

The  inferior  brancli 
passes  forwards,  and  after 
giving  branches  to  the 
internal  and  inferior  recti, 
ends  in  the  inferior  oblique 
muscle.  The  short  root  of 
the  ciliary  ganglion  arises 
from  the  terminal  branch 
which  goes  to  the  last- 
named  muscle. 


Posterioi 
commissure 


I'ineal  body  ^—g^-'  — 


Corpora 
quadrigemina 


Optic  thalamus 


Brachia  conjunctiva 
Fourtli  nerve 
Fillet 


Superior  peduncle  of 
cerebellum 
/  ^'*\~^~^ — Crus  cerebri 


Frenulum  veli 
Superior  medullary  velum 


Communications. — 1.  In 

the  cavernous  sinus  tlie  third 
nerve  communicates  with  the 
cavernous  plexus  on  the  in- 
ternal carotid  ai'tery.  2.  In 
the  cavernous  sinus  it  also 
receives 'a  slender  communi- 
cation from   the  ophthalmic 

division  of  the  fifth  nerve.     3.    The  short  root  of  the  ciliary  ganglion  passes  upwards 
from  the  branch  of  the  nerve  which  supplies  the  inferior  oblique  muscle. 


Fig. 


521. — Dorsal  Surface  of  the  Mid-Brain,  to  show  the  origin 
of  the  trochlear  (fourth)  uerve. 


The  Fourth  or  Trochlear  Nerve. 

The  trochlear  nerve  (n.  trochlearis  or  patheticus)  emerges  from  the  dorsal 
surface  of  the  mid-biain.  It  springs  at  the  side  of  the  frenulum  from  the 
anterior  end  of  the  superior  medullary  velum,  just  behind  the  corpora  quadri- 
gemina (for  deep  origin,  see  p.  540).  It  is  extremely  slender,  and  of  consider- 
able length.  Passing  round  the  crus  cerebri,  the  nerve  appears  in  the  base  of 
the  brain  behind  the  optic  tract,  in  the  interval  between  the  crus  cerebri  internally 
and  the  temporal  lobe  of  the  cerebrum  externally.  Continued  forwards  to  the  base 
of  the  skull,  it  pierces  the  free  border  of  the  tentorium  cerebelli,  on  the  outer  side 
47  a 


678 


THE  NEEVOUS  SYSTEM. 


of  the  third  nerve,  and  proceeds  forwards  in  the  outer  wall  of  the  cavernous  sinus, 
to  the  sphenoidal  fissure  lying  between  the  third  and  ophthalmic  nerves.  It 
enters  the  orbit  above  the  muscles  of  the  eyeball,  and  terminates  in  the  orbital 
(superior)  surface  of  the  superior  oblique  muscle. 

Communications. — Tn   the  cavernous  sinus  the  nerve  receives  (1)  a  communicating 


Olficton  bulb 


optic  iiei  \  e 


Optic  coiiimis.suie 
Anterior  cerebral         Ty-^ 

Middle  cerebial     ^"^^ ' 
aitpn 
Posterioi  j-j 

comiiiuni- // 

eating  artery      ~^~rTr 
Oculo-motor  — __x//-i 
nerve        I  If 
Posterior  cere-  — LL 
bral  artery       /  / 


Infra-trochlear  nerve 

Supra-trochlear  nerve 

Oculo-motor  nerve 

Splieno-parietal  sinus 
Ophthalmic  vein 

Anterior  clinoid 
process 

Trochlear  nerve 


Oculo-motor 
nerve 

Abducent  nerve 

Circular  sinus 
^  Ophthalmic  nerve 
Superior 
maxillary  nerve 
Inferior 

maxillary  nerve 

Cavernous  sinus 

Basilar  sinus 

Gasserian 

ganglion 

Basilar 

artery 

Inferior 

petrosal 

sinus 

Vertebral 
arterj' 


Glosso-ijliaryn  ^ 
geal  ner\  e 
Pneumogasti  le/ 
nerve 
Spinal  accessory  ner\  e 

Hypoglossal  nene 

Lateral  sinus/ 


Tentorium  cerebelli 
(cut)  . 

Occipital  sinuses 


\'ertebral  artery 

Spinal  cord' 
Openings  of  occipital  .sinuses 


Straight  sinus 
Torcular  Herophili 


Superior  longitudinal  sinus 


Falx  cerebri  (cut) 
Fig.  522. — The  Bask  oi'  the  Skvll,  to  show  the  dura  mater,  sinuses,  arteries,  and  nerves. 


branch  from  the  cavernous  or  carotid  plexus  on  the  internal  carotid  artery,  and  (2)  a 
slender  filament  from  the  ophthalmic  division  of  the  fifth  nerve. 


The  Fifth,  Trigeminal  or  Trifacial  Nerve. 

The  trigeminal  nerve  (u.  trigeminus;  arises  from  the  surface  of  the  pons  Varolii  in 
its  outer  part  by  two  roots,  a  large  sensory  root  (portio  major)  and  a  small  motor  root 
(portio  minor)  (Fig.  517,  p.  675).  The  two  roots  proceed  forwards  in  the  posterior 
fossa  of  the  base  of  the  skull,  and  piercing  the  dura  mater  beneath  the  attachment 
of  the  tentorium  cerebelli  to  the  superior  border  of  the  petrous  portion  of  the 


THE  FIFTH,  TKIGEMINAL  OE  TKIFACIAL  NERVE. 


679 


temporal  bone,  enter  a  cavity  in  the  dura  mater  (cavum  Meckelii)  over  the  apex  of 
the  petrous  bone.  The  large  sensory  root  gradually  conceals  the  small  motor  root 
in  its  course  forwards,  and  expands  beneath  the  dura  mater  into  a  large  flattened 
ganglion, — the  Gasserian  ganglion  (ganglion  semilunare).  This  ganglion  occupies 
an  impression  on  the  apex  of  tlie  petrous  portion  of  the  temporal  bone,  and  from  it 
three  large  trunks  arise  — the  ophthalmic 
or  lirst,  the  superior  maxillary  or  second, 
and  the  inferior  maxillary  or  third 
divisions  of  the  nerve.  The  small 
motor  root  of  the  nerve  passes  forward 
beneath  the  Gasserian  ganglion,  and  is 
wholly  incorporated  with  the  inferior 
maxillary  division  of  the  nerve. 

Ophthalmic  Division  (n.  ophthal- 
micus).— The  ophthalmic  nerve  passes 
forwards  to  the  orbit  through  the  middle 
fossa  of  the  base  of  the  skull,  beneath 
the  dura  mater.  It  lies  in  the  outer 
wall  of  the  cavernous  sinus,  at  a  lower 
level  than  the  fourth  nerve,  and  reaches 
the  orbit  through  the  sphenoidal  fissure 
(Fig.  520). 

In  the  wall  of  the  cavernous  sinus  the 
ophthalmic  nerve  gives  off  (1)  a  small 
recurrent  branch  to  the  dura  mater  (n. 
tentoi'ii),  (2)  communicating  branches  to 
the  cavernous  plexus  of  the  sympathetic 
on  the  internal  carotid  artery,  and  (3) 
small  communicating  twigs  to  the  trunks^ 
of  the  third,  fourth,  and  sixth  nerves. 

In  the  sphenoidal  Jissure  the  nerve 
divides  into  three  main  branches — 
lachrymal,  frontal,  and  nasal  (Fig.  524). 

The  lachrymal  nerve  (n.  lacrymalis) 
enters  the  orbit  through  the  outer  angle 
of  the  sphenoidal  fissure,  above  the 
orbital  muscles.  Passing  forwards  be- 
neath the  periosteum  to  the  anterior 
part  of  the  orbit,  the  nerve  ends  by 
supplying  branches  (a)  to  the  lachrymal 
gland,  (&)  to  the  conjunctiva,  and  (c) 
to  the  skin  of  the  outer  canthus  of 
the  eye. 


Fig 


523. — Distribution  of  Sensory  Nerves  to  the 
Head  and  Neck. 


Ophth,  Ophtlialiiiic  division  of  the  fifth  nerve  ;  St,  Supra- 
trochlear braucli  ;  S.  0,  Supra -orbital  brauch  ;  I.T, 
Infra-trochlear  branch  ;  L,  Lachrymal  branch  ;  N, 
External  nasal  branch  ;  Sup. Max,  Superior  maxillary 
division  ;  T,  Temporal  branch ;  M,  Malar  branch  ; 
I.O,  Infra-orbital  branch  ;  Inf.Max,  Inferior  maxillary 
division  ;  A.T,  Auriculo-temporal  branch  ;  B,  Buccal 
branch  ;  M,  Mental  brauch  ;  C2,  3,  Branches  of  the 
second  and  third  cervical  nerves  ;  G.O,  Great  occipital 
nerve  ;  S.O,  Small  occipital  nerve  ;  G.A,  Great 
auricular  nerve  ;  S.C,  Superficial  cervical  nerve  ;  03, 
Least  occipital  nerve  ;  4,  5,  6,  Posterior  primary 
division  of  4th,  5th,  and  6th  cervical  nerves. 


The  lachrymal  Jierve  communicates  in  the 
orbit  with  the  orbital  branch  of  the  superior 

maxillary   nerve,    and   on   the   face,   by    its  terminal    branches,    with    the    tem^ioral   branches 
of  the  facial  nerve  (Fig.  523). 

The  frontal  nerve  (n.  frontalis),  entering  the  orbital  cavity  through  the 
sphenoidal  fissure,  courses  forwards  above  the  ocular  muscles,  and  divides  at  a 
variable  point  into  two  branches — a  larger  supra-orbital  and  a  smaller  supra- 
trochlear nerve.  The  supra-orbital  nerve  (n.  supra-orbitalis)  passes  directly  forwards, 
and  leaves  the  orbit  through  the  supra-orbital  groove  or  foramen  to  reach  the  fore- 
head. It  gives  off  the  following  secondary  branches :  (1)  the  principal  branches 
(rr.  frontales)  are  distributed  to  the  forehead  and  scalp,  reaching  backwards  as  far 
as  the  vertex ;  (2)  small  branches  supply  the  upper  eyelid ;  and  (3)  twigs  are 
distributed  to  the  frontal  sinus.  On  the  forehead  the  supra-orbital  nerve  com- 
municates with  the  temporal  branches  of  the  facial  nerve.  The  supra-trochlear 
nerve  (n.  supra-trochlearis)  courses  obliquely  forwards  and  inwards  over  the  tendon 
47  & 


680 


THE  NEKVOUS  SYSTEM. 


of  the  superior  oblique  muscle  to  reach  the  inner  side  of  the  supra-orbital  arch. 
Leaving  the  cavity  of  the  orbit,  the  nerve  is  distributed  to  the  skin  of  the  mesial 
part  of  the  forehead,  the  root  of  the  nose,  and  the  inner  canthus  of  the  eye. 

It  communicates  with  the  infra-trochlear  branch  of  the  nasal  nerve,  either  before  or 
after  leaving  the  orbital  cavity. 

The  nasal  nerve  (n.  naso-ciliaris)  enters  the  orbit  through  the  sphenoidal 
fissure,  between  the  heads  of  the  external  rectus  muscle,  and  between  the  two 
divisions  of  the  third  netve  (Fig.  520,  p.  677).  It  crosses  the  orbital  cavity 
obliquely  to  reach  the  anterior  ethmoidal  foramen,  lying  in  its  course  below  the 
superior  rectus  and  superior  oblique  muscles,  and  above  the  optic  nerve  and  internal 
rectus  muscle.  The  nerve  is  transmitted  through  the  anterior  ethmoidal  foramen 
into  the  cranial  cavity,  where  it  lies  on  the  cribriform  plate  of  the  ethmoid  bone. 

It  enters  the  nasal  cavity 
through  the  nasal  fissure,  and 
terminates  by  dividing  into 
internal  andexternalbranches. 
The  internal  division  supplies 
the  mucous  membrane  over  the 
upper  and  anterior  part  of  the 
nasal  septum  (rr.  mediales). 
The  external  branch,  after 
supplying  collateral  offsets  to 
the  outer  wall  of  the  nose  (rr. 
laterales),  finally  appears  on 
the  face  between  the  nasal 
bone  and  lateral  cartilage,  and 
supplies  branches  to  the  skin 
of  the  lower  part  and  tip  of 
the  nose. 

The  branches  of  the  nasal 
nerve  may  be  divided  into 
three  sets,  arising  (a)  in  the 
orbit,  (&)  in  the  nose,^nd^  (c) 
on  the  face. 

In  the  orbit  the  branches 
are  given  off  in  three  situa- 
tions— -external  to,  over,  and 
internal  to  the  optic  nerve. 
(a)  As  the  nasal  nerve  lies 
to  the  optic  nerve, 
it  gives  off  the  long  root  of  the 
ciliary  ganglion  (radix  longa). 
(6)  As  it  crosses  the  optic  nerve  two  long  ciliary  branches  (nn.  ciliaris  longi)  arise, 
and  pass  forwards  alongside  tlie  optic  nerve  to  the  eyeltall.  (c)  On  the  inner  side 
of  the  optic  nerfe  the  infra-trochlear  nerve  (n.  infra-trochlearis)  arises,  a  slender 
branch  which  courses  forward  beneath  the  pulley  of  the  superior  oblique  muscle  to 
the  front  of  the  orbit.  It  ends  on  the  face  by  supplying  the  skin  of  the  root  of  the 
nose  and  the^ eyelids,  and  communicates  either  in  the  orbit  or  on  the.j"ace  with 
the  supra-trochlear  nerve.  On  the  face  it  also  communicates  with  infra-orbital 
branches  of  the  facial  nerve. 

In  the  nose  the  internal  nasal  branch  supplies  tlie  mucous  membrane  of  the 
fore-yjart  of  the  nasal  septum :  the  external  nasal  branch  supplies  the  fore-part  of 
the  outer  wall  of  the  nose. 

On  the  face  the  terminal  filaments  of  the  nerve  are  distributed  to  the  skin  of 
the  lower  half  and  tip  of  the  nose.  The  superficial  terminal  branch  communicates 
with  the  infra-orljital  branches  of  the  facial  nerve  (Fig.  523). 

The  ciliary  or  lenticular  ganglion  (ganglion  ciliare)  is  associated  with  the 
nasal  branch  of  the  ophthalmic  nerve  and  with  the  lower  division  of  the  third 
nerve.  •  It  is  a  small  reddish  ganglion,  placed  between  the  external  rectus  muscle 


Fig.  524. 


-Scheme  of  the  Disteibdtion  of  the  Ophthalmic 
Nerve. 


V.s,  Trigeminal  nerve,  afferent  root ;  Mo,  Efferent  root :  G.G,  Gasserian 
ganglion  ;  M,  Meningeal  branch  ;  I.C,  Branch  to  internal  carotid 
artery  ;  Oph,  Ophthalmic  nerve  ;  S.M,  Superior  maxillary  nerve  ; 
I.  M,  Inferior  maxillary  nerve  ;  III,  Communication  to  oculo- 
motor nerve  ;  IV,  To  trochlear  nerve  ;  VI,  To  abducent  nerve. 
Frontal  nerve  ;  f.s,  Branches  to  frontal  sinus  ;  S.o,  Supra-orbital 
nerve  ;  S.t,  Supra-trochlear  nerve;  L,  Branches  to  upper  eyelid. 
Xasal  nerve  ;  L.G,  Long  root  to  lenticular  ganglion  ;  Sy,  Root 
from  sympathetic  (on  carotid  artery)  ;  III,  Short  root  from  motor 
oculi  nerve  ;  C,  Short  ciliary  branches  ;  L.  C,  Long  ciliary  nerves  ; 
I.T,  Infra-trochlear  nerve ;  E.N,  External,  and  I.N,  Internal 
nasal  nerves.  Lachrymal  nerve  ;  0,  Orbital  branch  of  superior  external 
maxillary  nerve  ;  L.Gl,  Lachrymal  gland  ;  C,  Conjunctival 
branch  ;  L,  Branch  to  eyelids  and  face. 


THE  FIFTH,  TEIGEMINAL  OE  TEIFACIAL  NEEVE. 


681 


and  the  optic  nerve,  and  in  front  of  the  ophthalmic  artery.  Its  roots  are  three  in 
number :  (1)  sensory  or  long  (radix  longa),  derived  from  the  nasal  branch  of  the 
ophthahnic  nerve ;  (2)  motor  or  short  (radix  brevis),  derived  from  the  inferior 
division  of  the  third  nerve ;  and  (3)  sympathetic,  a  slender  filament  from  the 
cavernous  plexus  on  the  internal  carotid  artery,  which  may  exist  as  an  independent 
root  or  may  be  incorporated  with  the  long  root  from  the  nasal  nerve.  The  branches 
from  the  ganglion  are  twelve  to  fifteen  short  ciliary  nerves  (nn.  ciliares  breves), 
which  pass  to  the  eyeball  in  two  groups  above  and  below  the  optic  nerve.  They 
supply  the  coats  of  the  eyeball,  including  the  iris  and  ciliary  muscles.  The  circular 
fibres  of  the  iris  and  the  ciliary  7nuscle  are  innervated  by  the  third  nerve  ;  the 
radial  fibres  of  the  iris  by  the  sympathetic. 

Superior  Maxillary  Division  of  the  Fifth  Nerve  (n.  maxillaris). — This  large 
nerve  courses  forwards  from  its  origin  in  the  Gasseriau  ganglion  through  the  middle 
fossa  of  the  base  of  the  skull,  beneath  the  dura  mater,  and  in  relation  to  the  lower 
part  of  the  cavernous  sinus  (Fig.  520,  p.  677).  Passing  through  the  foramen 
rotundum  in  the  root  of  the  pterygoid  process,  it  traverses  the  spheno-maxillary 
fossa.     It  enters  the  orbit  as  the  infra-orbital  nerve,  through  the  spheno-maxillary 


Lachryma 


Frontal  nerve 


Supra-orbital  iierv( 


Ijacluymal  nerve 

Nerves  to  superior  rectus  and 

levator  palpebrw  snperioris, 

from  oculo-niotor  nerve, 

superior  division 

Trochlear  nerve 


Rectus  externus 


Abducent  nerve 

Oculo-inotor  nerve 
(inferior  division) 

Lenticular  ganglion    - 

Nerve  to  rectus  inferior,  from 
oculo-niotor  nerve 

Nerve  to  obliquus  inferior, 
from  oculo-niotor  nerve 


Sui)ia-trochlear  nerve 
Levator  palpebrie  superioris 
Rectus  superior 
Obliquus  superior 
Nasal  nerve 
Infra-trochlear  nerve 

Rectus  internuM 

Nerve  to  rectus  interims  from 

oculo-inotor 

Ophthalmic  artery 

Optic  nerve 

Long  ciliary  nerves 

Rectus  inferior 


( )bliiiuui  inteii(]i 
Fi(i.  525. — Schematic  Representation  uf  the  Nerves  which  traverse  the  Cavity  of  the  Orbit. 


fissure,  and  occupying  successively  the  infra-orbital  groove  and  canal,  it  finally 
appears  on  the  face  through  the  infra-orbital  foramen  (Fig.  526). 

The  branches  and  communications  of  this  nerve  occur  (a)  in  the  cavity  of  the 
cranium,  (&)  in  the  spheno-maxillary  fossa,  (c)  in  the  infra-orbital  canal,  and  {d) 
on  the  face. 

In  the  cavity  of  the  cranium  the  nerve  gives  off  a  minute  recurrent  branch  (il 
meningeus)  to  the  dura  mater  of  the  middle  fossa  of  the  base  of  the  skull. 

In  the  spheno-maxillary  fossa  the  nerve  gives  off — (1)  two  short  thick  spheno- 
palatine nerves  (nn.  spheno-palatini),  the  short  or  sensory  roots  of  the  spheno- 
palatine (Meckel's)  ganglion.  (2)  A  posterior  dental  nerve,  which  may  be  double 
(nn.  alveolares  superiores),  descends  through  the  ptery go-maxillary  fissure  to  the 
outer  side  of  the  upper  jaw,  and  proceeds  forwards  along  the  alveolar  arch,  in 
company  with  the  posterior  dental  artery.  It  supplies  the  gum  and  the  upper 
molar  teeth  by  branches  which  perforate  the  bone  to  reach  the  alveoli.  The  nerve 
forms  a  fine  plexus  joined  by  the  middle  dental  nerve  before  finally  reaching  the 
teeth.  (3)  A  small  orbital  branch  (n.  zygomaticus)  enters  the  orbital  cavity  through 
the  spheno-maxillary  fissure,  and  proceeding  along  the  outer  wall,  communicates 
with  the  lachrymal  nerve,  and  passes  through  the  orbital  canal  in  the  malar  bone, 
where  it  divides  into  malar  and  temporal  branches.  The  malar  branch  (n.  zygo- 
matico-facialis)  appears  on  the  face,  after  traversing  the  malar  bone,  and  supplies 
the  skin  over  that  bone.  It  communicates  with  the  malar  branches  of  the  facial 
nerve.     The  temporal  branch  (n.  zygomatico-temporalis)  perforates  the  zygomatic 


682 


THE  NEEVOUS  SYSTEM. 


surface  of  the  malar  bone,  and  is  distributed,  after  piercing  the  temporal  fascia,  to 
the  skin  over  the  fore-part  of  the  temple.  It  communicates  with  the  temporal 
branches  of  the  facial  nerve.  It  may  be  very  minute,  and  not  pass  further  than 
the  temporal  fascia,  between  the  two  layers  of  which  it  may  form  a  communication 
with  the  facial  nerve.  (4)  The  infra-orbital  nerve  (n.  infra-orbitalis)  is  the  terminal 
branch  of  the  superior  maxillary  nerve,  which  enters  the  orbit  through  the  spheno- 
maxillary fissure  and  traverses  the  infra-orbital  canal  to  reach  the  face. 

In  the  infra-orbital  canal  the  infra-orbital  nerve  supplies  one  and  sometimes 
two  branches  to  the  teeth — the  middle  and  anterior  dental  nerves  (rr.  alveolares 
superiores  medius  and  anterior).  The  former  may  be  only  a  secondary  branch  of 
the  latter  nerve,  or  they  may  arise  independently  from  the  infra-orbital  nerve. 

However  formed, 
the  nerves  descend 
in  bony  canals  in 
the  wall  of  the  an- 
trum of  Highmore 
(to  the  lining  of 
which  branches  are 
given),  and  reach 
the  alveolar  arch, 
where  they  form 
miniite  plexuses 
and  supply  the 
teeth  (joining  pos- 
teriorly with  the 
branches  of  the 
posterior  dental 
nerve).  The  an- 
terior dental  nerve 
supplies  the  incisor 
and  canine  teeth ; 
the  middle  dental 
nerve  supplies  the 
premolar  teeth. 

After  emerging 

on  the  face  from  the 

infra-orbital   fora- 

the     infra  - 

di- 


P-t  Pal 


Fig.  526.- 


Rec, 


-Scheme  of  the  Course  and  L>isthibution  of  the  Superior 
Maxillary  Nerve. 

Recurrent  branch  in  the  middle  fossa  of  the  skull  ;  M.G,  Meckel's  ganglion  in  msn, 

the  splieno-maxillary  fossa  ;.S.P,  Sjiheuo-palatine  nerves  ;  S.N,  Sui:)erior  nasal  orbital     nerVC 

branch  ;  Orb,   Orbital   nerve  ;  T,    Temporal,   and   M,    Malar   branches  ;  I.O,  yif^po    info  a    num- 

Infra-orbital   nerve,    appearing   on   the   face  ;  P,   Paljjebral  ;  N,   Nasal,    and  ,  „  i  •     4.  • 

L,    Labial   branches;   A.D,    Anterior   dental   branch;    M.D,    Middle    dental  '^er   Ol    radiating 

branch;  N.P,  Naso-palatine  nerve  ;  P.D,  Posterior  dental  branch  ;  l.N,  Inferior  branches   arranged 

nasal  branch  ;  ^ij^P,^. Large  posterior  palatine  nerve  ;  S.P.P,  Small  i>osterior  •;„    three    sets (o^ 

jjalatine  nerve  ;  Ace,  Accessory  posterior  palatine  nerve  ;  Vid,  Vidian  nerve  ;        y      -u     ^      r         A, 

Pt.Pal,  Pterygo-palatine  branch.  palpebral,     lOT     the 

lower  eyelid ;  (&) 
nasal,  for  the  skin  of  the  side  of  the  nose  ;  and  (c)  labial,  for  the  cheek  and  upper  lip. 
These  branches  form  communications  with  the  infra-orbital  branches  of  the  facial 
nerve,  and  give  rise  to  the  infra-orbital  iilexus  (Fig.  523,  p.  679). 

The  spl^jao-palatine  or  Meckel's  ganglion  (g.  spheno-palatiuuiii)  occupies  the 
upper  part  of  the  spheno-maxillary  fossa.  \  It  is  a  small  reddish-gray  ganglion, 
suspended  from  the  superior  maxillary  nerve  by  the  two  spheno-palatine  branches 
which  constitute  its  sensory  roots.  The  motor  and  sympathetic  roots  of  tlie  ganglion 
are  derived  from  the  vidian  nerve.  This  nerve  is  formed  in  tlie  cavity  of  the  skull 
upon  the  cartilage  filling  up  the  foramen  lacerum  medium,  by  the  union  of  the 
great  superficial  petrosal  nerve  from  the  geniculate  ganglion  of  the  facial  nerve 
(emerging  from  the  temporal  bone  through  the  hiatus  Fallopii)  with  the  great  deep 
petrosal  nerve,  a  branch  of  the  carotid  plexus  of  "the  sympathetic  on  the  internal 
carotid  artery.  The  vidian  nerve  passes  through  the  vidian  canal  to  the  spheno- 
maxillary fossa,  where  it  ends  in  Meckel's  ganglion. 


THE  FIFTH,  TEIGEMINAL  OK  TEIFACIAL  NEKVE.  683 

The  branches  from  the  ganglion  are  seven  in  number,  (a)  The  pterygo-palatine 
or  pharyngeal  branch  passes  backwards  through  the  pterygo-palatine  canal  to 
supply  the  mucous  membrane  of  the  roof  of  the  pharynx. 

(b)  The  posterior  palatine  nerves,  three  in  number,  are  directed  downwards  to  the 
palate  through  the  posterior  palatine  canals.  The  large  posterior  palatinenerve  emerges 
on  the  under  surface  of  the  palate  through  the  large  posterior  palatine  canal,  and  at 
once  separates  into  numerous  branches  for  the  supply  of  the  mucous  membrane  of  the 
soft  and  the  hard  palate.  Its  anterior  filaments  communicate  with  branches  of  the 
naso-palatine  nerve.  The  main  nerve  gives  off,  as  it  lies  in  the  posterior  palatine  canal, 
a  small  inferior  nasal  nerve  which  enters  the  nasal  cavity  and  supplies  the  mucous 
membrane  of  the  lower  part  of  the  outer  wall  of  the  nose.  The  small  posterior 
palatine  nerve  descends  through  the  small  posterior  palatine  canal,  and,  piercing 
the  tuberosity  of  the  palate  bone,  is  distril:)uted  to  the  mucous  membrane  of  the 
soft  palate,  uvula,  and  tonsil.  It  possil>ly  conveys  motor  fibres  to  tbe  levator  palati 
and  azygos  uvulse  muscles.  The  accessory  posterior  palatine  nerves  are  one  or 
more  small  twigs  which  pass  through  accessory  posterior  palatine  canals,  and 
supply  branches  to  the  mucous  membrane  of  the  tonsil,  soft  palate,  and  uvula. 

(c)  The  branches  directed  inwards  from  Meckel's  ganglion  enter  the  nasal 
cavity  through  the  spheno- palatine  foramen.  They  are  two  in  number — the 
superior  nasal  and  the  naso-palatine.  The  superior  nasal  nerve  is  a  small  nerve 
destined  for  the  mucous  membrane  of  the  upper  and  back  part  of  the  outer  wall  of 
the  nose.  The  naso-palatine  nerve,  after  passing  through  the  spheno-palatme 
foramen,  crosses  the  roof  of  the  nose,  and  extends  obliquely  downwards  and 
forwards  along  the  nasal  septum,  grooving  the  vomer  in  its  course,  to  reach  the 
incisor  foramen  near  the  front  of  the  hard  palate.  The  nerves  pass  through  the 
subordinate  mesial  foramina  (of  Scarpa),  the  left  nerve  in  front  of  the  right.  In 
the  incisor  foramen  the  two  nerves  communicate  together.  They  then  turn  back- 
wards and  supply  the  mucous  membrane  of  the  hard  palate.  They  communicate 
posteriorly  with  terminal  filaments  of  the  large  posterior  palatine  nerves.  In  its 
course  through  the  nasal  cavity  the  naso-palatine  nerve  furnishes  collateral  branches 
to  the  mucous  membrane  of  the  roof  and  septum  of  the  nose  (Fig.  518,  p.  676). 

(d)  The  orbital  branches,  one  or  more  minute  branches,  pass  upwards  to  the 
periosteum  of  the  orbit  from  Meckel's  ganglion. 

Inferior  Maxillary  Nerve  (n.  mandibularis). — The  inferior  maxillary  nerve 
is  formed  by  the  union  of  two  roots :  a  large  sensory  root,  from  the  Gasserian 
ganglion,  and  the  small  motor  root  of  the  trigeminal  nerve,  which  is  wholly 
incorporated  with  this  trunk.  The  two  roots  pass  together  beneath  the  dura  mater 
of  the  middle  fossa  of  the  1  jase  of  the  skull  to  the  iWamejL-Ovale,  through  which 
they  emerge  into  the  pterygoid  region.  Outside  the  skull  they  combine  to  form  a 
single  trunk,  which  soon  separates  into  anterior  and  posterior  divisions. 

At  its  emergence  from  the  skull  the  nerve  is  deeply  placed  beneath  the  middle 
of  the  zygomatic  arch,  and  is  concealed  by  the  ramus  of  the  lower  jaw,  and  by  the 
temporal,  masseter,  and  external  pterygoid  muscles. 

The  branches  of  the  inferior  maxillary  nerve  may  be  divided  into  two  series — 
(1)  those  derived  from  the  undivided  nerve,  and  (2)  those  derived  from  the  terminal 
divisions  of  the  nerve. 

The  branches  of  the  undivided  nerve  are  two  in  number,  (a)  A  small 
recurrent  branch  (n.  spinosus)  arises  just  outside  the  skull,  and  accompanying  the 
middle  meningeal  artery  through  the  foramen  spinosum,  supplies  the  dura  mater. 
(h)  In  the  pterygoid  region  a  small  branch  arises  for  the  supply  of  the  internal 
pterygoid  muscle.     This  nerve  forms  a  connexion  with  the  otic  ganglion. 

The  terminal  divisions  of  the  nerve  are  a  small  anterior  and  a  large  posterior 
trunk. 

The  small  anterior  trunk  passes  downwards  and  forwards  beneath  the  external 
pterygoid  muscle,  and  separates  into  the  following  branches  : — (1)  A  branch  for  the 
external  pterygoid  muscle  (n.  pterygoideus  externus),  which  supplies  it  on  its  deep 
surface ;  (2)  a  branch  to  the  masseter  muscle  (n.  massetericus),  which  passes  over 
the  upper  border  of  the  external  pterygoid  and  through  the  sigmoid  notch  of  the 
lower  jaw ;  (3)  and  (4)  two  branches  to  the  temporal  muscle  (nn.  temporales  pro- 


684 


THE  NERVOUS  SYSTEM. 


fundi,  anterior  et  posterior),  which  also  ascend  above  the  external  pterygoid 
muscle;  and  (5)  the  buccal  nerve  (n.  buccinatorius),  which  passes  obliquely 
forwards  between  the  two  heads  of  the  external  pterygoid  to  reach  the  buccinator 
muscle.  This  nerve  is  sensory,  and  its  fibres  are  in  part  distributed  to  the  skin  of 
the  cheek  (communicating  with  buccal  branches  of  the  facial  nerve) ;  they  are  also 
in  part  distributed  to  the  mucous  membrane  of  the  inside  of  the  mouth,  to  reach 
which  they  pierce  the  fibres  of  the  buccinator  muscle.     The  buccal  nerve  usually 

supphes  a  third  branch  to 
the  temporal  muscle,  after 
emerging  between  the  two 
heads  of  the  external 
pterygoid  muscle  (Fig.  523, 
p.  679). 

The  large  posterior 
trunk  extends  downwards 
a  short  way  beneath  the 
external  pterygoid  muscle. 
After  giving  off  by  two 
roots  the  auriculo-temporal 
nerve,  it  ends  by  dividing 
into  two,  the  lingual  and 
the  inferior  dental  nerves. 
The  auriculo-temporal 
nerve  (n.  auriculo-tempor- 
alis)  is  formed  by  the  union 
of  two  roots  which  embrace 
the  middle  meningeal 
artery.  The  nerve  passes 
backwards  beneath  the 
external  pterygoid  muscle 
and  between  the  internal 
lateral  ligament  and  the 
neck  of  the  lower  jaw. 
Entering  the  substance  of 
,  ,,   ^^  ,.    the    parotid    gland,   it    is 

V.I. M,  Inferior  maxillary  nerve  ;  b,  Afferent,  and  Mo,  Efferent  roots  ;  M,  ■..        /■    -,  '^  -,  ■, 

Meningeal  branch  ;  O.G,  Otic  ganglion  ;  I.Pt,  Nerve  to  internal  ptery-  ClireCtea     upwarOS      tO     tJie 

gold  ;  S.S.P,  Small  superficial  petrosal  nerve  ;  T.T,  Nerves  to  tensor  temple  OVCr  the  ZygOma  in 

tympani,  and  T.P,  Tensor  palati ;  Ty.Plex,  Tympanic  plexus  ;  I.C,  company  with  the  temporal 
Internal  carotid  artery;  S. D.P,   Small   deep  petrosal  nerve;  G.G,  ,    ■'■  j,      •       n       ii       j" 

Geniculate  ganglion  ;  F,  Facial  nerve  ;  Ty,  Tympanic  branch  ;  G.Ph,  artery.       it    IS     Unaliy    QIS- 
Glosso-pharyngeal   nerve  ;    M.M,   Middle   meningeal    artery  ;    A.T, 
Auricuk 
Nerve  to  ^ 

to  pinna  ;    T,   Temporal  branch  ;    A,  Anterior  division  of  inferior 

maxillary  nerve  ;  E.Pt,  Nerves  to  external  pterygoid  ;  M,  Masseter  ;  the  VertCX  of  the  skull. 
T.T.T,   Temporal,    and   Bucc,    Buccinator   muscles;    Po,    Posterior  The     auriculo-temnoral 

division  of  inferior  maxillary  nerve  ;  L,  Lingual  nerve  ;  C.T,  Chorda  .  rp   ii        f-  ji 

tympani  nerve;  Sub.G,  Sub-maxillary  ganglion;  Hy,  Hypoglossal  ^Crve    glVeS  Ott    tHC   lOllOW- 

nerve  ;  I.D,   Inferior  dental  nerve  ;  My.liy,  Mylohyoid  nerve;  My,  ing  branches: — (1)  A  Small 

Nerve    to    myloliyoid  ;    Di,   Nerve    to    digastric   (anterior    belly)  ;  branch      tO      the      tcmporO- 
Ment.,  Mental  Branch  ;   Sty.Gl,  Stylo-glossus  ;  H.Gl,  Hyoglossus  ;  .,,  .•      i    -  •  /.in 

G.H.G,  Genio-hyogiossus  muscles.  maxillary  articulation.    (2) 

Branches  to  the  parotid 
gland.  (3)  A  twig  for  the  supply  of  the  skin  of  the  external  auditory  meatus 
(and  membrana  tympani).  (4)  Branches  to  the  upper  half  of  the  pinna  on  its 
outer  aspect.     (5)  Terminal  branches  to  the  skin  of  the  temple  and  scalp. 

It  has  the  following  communications  with  other  nerves : — (1)  Important  communica- 
tions are  effected  by  the  roots  of  the  nerve,  which  are  separately  joined  by  small  branches 
from  the  otic  ganglion.  (2)  The  parotid  branches  of  the  nerve  are  connected  with  branches 
of  the  facial  nerve  in  the  substance  of  the  gland.  (3)  The  temporal  branch  of  the  nerve 
is  in  communication  superficially  with  the  temporal  branches  of  the  facial  nerve. 

The  lingual  nerve  (n.  lingualis)  is  the  snialler  of  the  two  termiual  branchea 


Fig.  527. — Scheme  of  the  Distribution  of  the  Inferior 
Maxillary  Nerve. 


tributed    as    a    cutaneous 

lo-temporal  nerve  ;  F,  Communication  with  facial  nerve  ;  Par,    ngj-ve    of    the    tcmplc    and 
to  parotid  {(land  ;   Me,  Branch  to  meatus  of  ear  ;   Pi,  Branch  ,  ,  i  i  ^   j 

-  -         scalp,  and  reaches  almost  to 


THE  FIFTH,  TKTGEMINAL  OE  TEIFACIAL  NERVE.  685 

of  the  posterior  division  of  the  inferior  maxillary  nerve.  It  proceeds  downwards  in 
front  of  the  inferior  dental  nerve,  beneath  the  external  pterygoid  muscle,  to  its  lower 
border.  After  passing  between  the  internal  pterygoid  muscle,  and  the  ramus  of  the 
lower  jaw,  it  crosses  beneath  the  mucous  membrane  of  the  floor  of  the  mouth  in  the 
interval  between  the  mylohyoid  and  hyoglossus  muscles  and  beneath  the  duct  of 
the  submaxillary  gland.  It  sweeps  forwards  and  inwards  to  the  side  of  the 
tongue,  to  the  mucous  membrane  over  the  anterior  two-thirds  of  which  it  is 
distributed. 

Two  nerves  communicate  with  the  lingual  nerve  in  its  course  to  the  tongue  : — 

(1)  The  chorda  tympani  branch  of  the  facial  nerve  joins  it  beneath  the  external 
pterygoid  mviscle,  and  is  incorporated  with  it  in  its  distribution  to  the  tongue. 

(2)  The  hypoglossal  nerve  forms  larger  or  smaller  loops  of  communication  with 
the  lingual  nerve  as  they  course  forwards  together  over  the  hyoglossus  muscle. 

Besides  supplying  the  aforesaid  branches  to  the  mucous  membrane  over  the 
sides  and  dorsum  of  the  tongue  in  its  anterior  two-thirds,  the  lingual  nerve  supplies 
the  mucous  membrane  of  the  outer  wall  and  floor  of  the  mouth.  It  also  assists, 
along  with  the  chorda  tympani  nerve,  in  forming  the  roots  of  the  submaxillary 
ganglion. 

The  submaxillary  ganglion  (ganglion  submaxillare)  is  a  minute  reddish 
ganglion  placed  on  the  hyoglossus  muscle,  between  the  lingual  nerve  and  the 
duct  of  the  submaxillary  gland.  It  is  suspended  from  the  former  by  two  trunks, 
consisting  for  the  most  part  of  fibres  of  the  lingual  and  chorda  tympani  nerves 
which  at  this  point  become  separated  from  the  lingual  nerve  and  incorporated  with 
the  ganglion.  The  roots  of  the  ganglion  are — (1)  an  afterent  root,  derived  from 
the  lingual  nerve ;  (2)  an  efferent  root,  derived  from  the  chorda  tympani :  and  (3)  a 
sympathetic  root,  from  the  sympathetic  plexus  upon  the  facial  artery. 

The  branches  from  the  ganglion  are  distributed  to  the  submaxillary  gland  and 
Wharton's  duct,  and  by  fibres  which  become  reunited  with  the  trunk  of  the  lingual 
nerve,  to  the  sublingual  gland. 

The  inferior  dental  nerve  (n.  alveolaris  inferior)  is  larger  than  the  lingual 
nerve.  It  passes  from  beneath  the  lower  border  of  the  external  pterygoid  muscle 
to  reach  the  interval  between  the  ramus  and  internal  lateral  ligament  of  the  lower 
jaw.  Entering  the  inferior  dental  canal  through  the  inferior  dental  foramen,  it 
traverses  the  substance  of  the  ramus  and  body  of  the  lower  jaw,  distributing 
branches  in  its  course  to  the  teeth.  A  fine  plexus  is  formed  by  the  dental  branches 
before  they  finally  supply  the  teeth. 

Branches  and  Communications. — (1)  The  mylohyoid  nerve  is  a  small  branch 
arising  just  before  the  inferior  dental  nerve  passes  through  the  inferior  dental 
foramen.  Grooving  the  ramus  of  the  jaw^  in  its  course,  it  descends  into  the 
submaxillary  triangle  on  the  superficial  aspect  of  the  mylohyoid  muscle.  Concealed 
in  this  situation  by  the  submaxillary  gland  and  the  facial  artery,  it  is  distributed 
to  the  mylohyoid  and  anterior  belly  of  the  digastric  muscles.  (2)  The  mental 
branch  of  the  inferior  dental  nerve  is  a  trunk  of  considerable  size  arising  from  the 
main  nerve  in  the  inferior  dental  canal.  It  emerges  from  the  lower  jaw  through 
the  mental  foramen,  and  is  distributed  by  many  branches  to  the  chin  and  lower 
lip.  It  communicates  beneath  the  facial  muscles  with  the  supra-mandibular 
branches  of  the  facial  nerve  (Fig.  523,  p.  679).  (3)  The  incisor  branch  is  the  terminal 
part  of  the  inferior  dental  nerve  remaining  after  the  origin  of  the  mental  branch. 
It  supplies  the  incisor  and  canine  teeth. 

The  otic  ganglion  (g.  oticum)  is  situated  beneath  the  inferior  maxillary  nerve 
just  below  the  foramen  ovale.  Like  the  other  ganglia  described  above,  it  possesses 
three  roots : — (1)  A  motor  root,  derived  from  the  nerve  to  the  internal  pterygoid 
muscle ;  (2)  a  sensory  root,  formed  by  the  smcdl  superficial  i^etrosal  nerve  from  the 
tympanic  plexus  (through  which  communications  are  effected  with  the  tympanic 
branch  of  the  glosso-pharyngeal  nerve,  and  a  branch  from  the  geniculate  ganglion 
of  the  facial  nerve) ;  (3)  a  sympathetic  root,  from  the  plexus  on  the  middle 
meningeal  artery  (Fig.  527). 

Five  branches  arise  from  the  ganglion — three  communicating  and  tw^o  motor 
branches.    The  three  communicating  nerves  are  fine  branches  which  join  respectively 


686  THE  NERVOUS  SYSTEM. 

the  vidian  nerve,  the  roots  of  the  auriculo-temporal,  and  the  chorda  tympani 
nerve.  The  two  motor  nerves  supply  the  tensor  tympani  and  tensor  palati 
muscles. 

Summary. — The  trigeminal,  tlie  largest  and  most  complex  of  the  cranial  nerves,  is  (1)  the 
chief  sensory  nerve  for  the  face,  the  anterior  half  of  the  scalp,  the  orbit  and  eyeball,  the  nose  and 
nasal  cavity,  the  lips,  teeth,  mouth,  and  two-thirds  of  the  tongue  ;  (2)  the  motor  fibres  of  the 
nerve  supi:)ly  the  muscles  of  mastication,  the  mylohyoid  and  anterior  belly  of  the  digastric, 
possibly  the  levator  palati  and  azygos  uvulae  (through  Meckel's  ganglion),  and  the  tensor  tympani 
and  tensor  palati  muscles  (through  the  otic  ganglion) ;  (3)  through  the  ganglia  placed  on  the 
three  divisions  of  the  nerve,  not  only  are  important  organs,  areas,  and  muscles  innervated,  but 
communications  are  also  effected  with  the  symi:)athetic  system,  with  the  third  nerA^e  (lenticular 
ganglion),  facial  nerve  (splieno -palatine  and  otic  ganglia),  and  glosso-pharjaigeal  nerve  (otic 
ganglion). 

In  its  distribution  to  the  skin  of  the  face  the  l^ranches  of  the  fifth  nerve  present  two  striking 
peculiarities  : — (1)  While  the  brandies  to  the  skin  reach  the  surface  at  many  points  and  in 
diverse  ways,  the  three  main  divisions  are  severally,  by  their  branches,  responsible  for  the  supply 
of  three  clearly  demarcated  cutaneous  areas  (Fig.  523,  p.  679).  (2)  By  numerous  communications 
with  the  facial  nerve,  sensory  fibres  are  given  to  the  muscles  of  expression  supplied  by  the 
facial  nerve. 

The  Sixth  oe  Abducent  Nerve. 

The  aljducent  nerve  (n.  abducens)  issues  from  the  brain  at  the  lower  border  of 
the  pons  Varolii,  just  above  the  pyramid  of  the  medulla  oblongata  (for  deep  origin, 
see  p.  524).  It  is  directed  forwards,  and  pierces  the  dura  mater  in  the  posterior 
fossa  of  the  base  of  the  skull  alongside  the  dorsum  sellse  (Fig.  522,  p.  678).  It 
then  occupies  the  inner  wall  of  the  cavernous  sinus  and  is  placed  on  the  outer 
side  of  the  internal  carotid  artery.  It  passes  through  the  sphenoidal  fissure  below 
the  third  and  nasal  nerves  and  between  the  two  heads  of  the  external  rectus 
muscle  (Fig.  520,  p.  677).  In  the  cavity  of  the  orbit  it.  supplies  the  external  rectus 
muscle  on  its  inner  (ocular)  surface. 

Communications. — In  the  wall  of  the  cavernous  sinus  the  sixth  nerve  receives  two 
commuuicating  filaments  : — (1)  From  the  carotid  plexus  of  the  sympathetic,  and  (2)  from 
the  ophthalmic  division  of  the  trigeminal  nerve. 

The  Seventh  or  Facial  Nerve. 

The  facial  nerve  (n.  facialis)  emerges  from  the  brain  at  the  posterior  border  of 
the  pons  Varolii,  below  the  trigeminal  nerve  and  internal  to  the  auditory  nerve  (for 
deep  origin,  see  p.  522).  Between  it  and  the  latter  nerve  is  the  minute  pars  intermedia 
of  Wrisberg  (Fig.  517,  p.  675).  The  nerve  passes  outwards  through  the  internal 
auditory  meatus,  courses  through  the  aqueduct  of  Fallopius  in  the  petrous  portion 
of  the  temporal  bone,  emerges  in  the  base  of  the  skull  by  the  stylo-mastoid  foramen, 
and  passes  forwards  through  tlie  parotid  gland  to  supply  the  muscles  of  the  face. 
In  the  internal  auditory  meatus  the  nerve  is  placed  upon  the  auditory  nerve,  the 
pars  intermedia  intervening.  In  the  aqueduct  of  Fallopius  the  nerve  first  passes 
backwards  on  the  inner  side  of  the  tympanum,  and  then  downwards  behind  the 
tympanum,  in  the  inner  wall  of  the  tympanic  antrum.  In  the  parotid  gland 
the  nerve  crosses  superficially  the  external  carotid  artery  and  the  temporo -maxillary 
vein.  On  the  face  its  branches  radiate  from  the  anterior  border  of  the  parotid  gland 
and  enter  the  deep  surface  of  the  facial  muscles. 

Branches  and  Communications. — fi.)  In  the  internal  auditory  meatus  the  pars 
intermedia  (n.  intermedins),  lying  between  the  facial  and  auditory,  sends  com- 
municating branches  to  both  nerves.  The  branch  to  the  auditory  nerve  probably 
separates  from  it  again  to  join  the  geniculate  ganglion  of  the  facial  nerve. 

(ii.)  In  the  aciufduct  of  Fallopius  the  geniculate  ganglion  (g.  geniculi)  is  formed 
at  the  point  where  the  facial  nerve  bends  backwards  (geniculiim  n.  facialis).  It  is 
an  oval  swelling  on  the  nerve,  and  is  joined  by  a  branch  from  the  upper  (vestibular) 
trunk  of  the  auditory  nerve,  l)y  which  it  probably  receives  libres  of  i\\e  pars  inter- 
media. From  the  ganglion  three  small  nerves  arise : — (1)  The  large  sul)erficial 
petrosal  nerve  passes  forwards  through  the  hiatus  Fallopii  to  the  middle  fossa  of  the 
base   of  the  skull.     On  the  upper  surface  of  the  foramen  lacerum  medium  it  is 


THE  SEVENTH  OK  FACIAL  NEEVE. 


687 


joined  by  the  great  deep  petrosal  nerve  from  the  sympathetic  plexus  ou  the  internal 
carotid  artery  to  form  the  vidian  nerve,  which,  after  traversing  the  vidian  canal, 
ends  in  Meckel's  ganglion.  (2)  A  minute  nerve  pierces  the  temporal  bone  and  joins' 
the  tympanic  branch  of  the  glosso-pharyngeal  in  the  substance  of  the  bone.  By 
their  union  the  small  superficial  petrosal  nerve  is  formed,  which  pierces  the  temporal 
bone  and  ends  in  the  otic  ganglion.  (3)  The  external  superficial  petrosal  nerve  is  a 
minute  inconstant  branch  which  joius  the 
sympathetic  plexus  on  the  middle  meningeal 
artery. 

In  the  course  of  the  facial  nerve  in  the 
lower  part  of  the  aqueduct  of  Fallopius, 
behind  the  tympanum,  three  branches  arise — 
(1)  The  small  nerve  to  the  stapedius  muscle, 
which  passes  forwards  to  the  tympanum.  (2) 
The  chorda  t3nnpani  nerve  (probably  associated 
with  the  pars  intermedia),  which  enters  the 
tympanic  cavity  through  the  iter  chorda' 
posterius,  passes  over  the  membrana  tympani 
and  the  handle  of  the  malleus,  and  leaves 
the  ca\'ity  through  the  iter  chordce  anterius 
to  reach  the  pterygoid  region.  Beneath  the 
external  pterygoid  muscle  it  becomes  incor- 
porated with  the  lingual  branch  of  the  in- 
ferior maxillary  nerve,  and  in  its  further 
course  is  inseparable  from  that  nerve.  It 
supplies  a  root  to  the  sub-maxillary  ganglion, 
and  is  finally  distributed  (probably  as  a 
nerve  of  taste)  to  the  side  and  dorsum  of 
the  tongue  in  its  anterior  two-thirds.  The 
chorda  tympani  nerve  receives  beneath  the 
external  pterygoid  muscle  a  fine  communica- 
tion from  the  otic  ganglion.  (3)  Before  it 
leaves  the  aqueduct  of  Fallopius  a  fine  com- 
municating branch  arises  from  the  facial  nerve 
to  join  the  auricular  branch  of  the  pneumo- 
gastric  nerve. 

(iii.)  In  the  neck  the  facial  nerve  gives  off 
three  muscular  branches :  (1)  and  (2)  small 
branches  supply  the  stylo- hyoid  and  the 
posterior  belly  of  the  digastric,  the  latter 
nerve  sometimes  communicating  with  the 
glosso-pharyngeal.  (3)  The  posterior  auricular 
nerve  bends  backwards  and  upwards  over 
the  anterior  border  of  the  mastoid  process 
along  with  the  posterior  auricular  artery. 
It  di^^[des  into  two  branches — an  auricular 
branch  for  the  retrahens  aurem  and  the  intrinsic  muscles  of  the  pinna,  and  an 
occipital  branch  for  the  posterior  belly  of  the  occipito-frontalis  muscle.  The 
posterior  auricular  nerve  communicates  with  the  great  auricular,  small  occipital, 
and  auricular  branch  of  the  pneumogastric  nerves  in  its  course. 

(iv.)  In  the  parotid  gland  the  facial  nerve  spreads  out  in  an  irregular  series  of 
branches  (pes  anserinus),  indefinitely  divided  into  a  temporo-facial  and  a  cervico- 
facial division.  Communications  occur  in  the  substance  of  the  gland  between  the 
main  trunks  and  the  great  auricular  and  auriculo- temporal  nerves. 

The  temporo-facial  division  gives  off  three  series  of  subordinate  branches 
which  radiate  forwards  and  upwards  from  the  parotid  gland. 

1.  The  temporal  branches  are  of  large  size,  and,  sweeping  out  of  the  parotid  gland 
over  the  zygomatic  arch,  are  distributed  to  the  orbicularis  palpebrarum,  frontalis, 
corrugator  supercilii,  attraheus,  and  attoUens  aurem.     The  temporal  branches  com- 


I.M. 

Fig.  528. —  The  Facial  Nerve  with  its 
Branches  and  Communications  in  the 
Aqueduct  of  Fallopius. 

VII,  Facial  nerve  ;  P.I,  Pars  iiiteimedia  ;  VIII, 
Auditory  nerve  ;  Aq.Fal,  Aqueduct  of  Fallo- 
pius ;  G.G,  Geniculate  ganglion  ;  E.S.P,  Ex- 
ternal superficial  petrosal  nerve  ;  M.M,  Middle 
meningeal  artery  ;  G.S.P,  Great  superficial 
petrosal  nerve  :  G.  P.  D,  G  reat  deep  petrosal 
nerve  ;  I.C,  Internal  carotid  artery  ;  Vid, 
Vidian  nerve;  M.G,  Meckel's  ganglion  ;  Ty.  PI, 
Tympanic  plexus  ;  S.D.P,  Small  deep  petrosal 
nerve  ;  G.Ph,  Glosso-pharyngeal  nerve;  Ty, 
Tympanic  branch  ;  S.S.P,  Small  superficial 
petrosal  nerve  ;  O.G,  Otic  ganglion  ;  Stap, 
Nerve  to  stapedius  ;  C.T,  Chorda  tympani 
nerve ;  L,  Lingualnerve  ;  A.Va,  Communication 
with  auricular  branch  of  vagus  ;  P.A,  Posterior 
auricular  nerve  ;  Sty.hy,  Nerve  tostylo-byoid  ; 
Di,  Nerve  to  digastric  (posterior  belly)  ;  T.F, 
Temporo-facial  division  ;  C.  F,  Cerviso-facial 
division  ;  T.  Temporal  ;  M,  Malar ;  I.O,  Infra- 
orbital ;  B.  Buccal  ;  S.M,  Supra-mandibular, 
and  I.M,  Infra- mandibular  branches. 


688 


THE  NEEVOUS  SYSTEM. 


mimicate  in  their  course  with  the    auriculo-temporal,  temporal  (of  the  superior 
maxillary),  lachrymal,  and  supra-orbital  branches  of  the  trigeminal  nerve. 

2.  The  malar  branches  are  small,  and  sometimes  are  inseparable  from  the  temporal 
or  infra-orbital  nerves.  Extending  forwards  across  the  malar  bone,  they  supply 
the  orbicularis  palpebrarum  and  zygomatic  muscles,  and  communicate  with  the  malar 

branch  of*  the  superior  maxillary  nerve. 
3.  The  infra-orbital  branches  are  of 
considerable  size.  Passing  forwards  over 
the  masseter  muscle  in  company  with 
Stenson's  duct,  they  supply  the  orbi- 
cularis palpebrarum,  the  zygomatici, 
buccinator,  and  the  muscles  of  the  nose 
and  upper  lip.  The  infra-orbital  plexus 
is  formed  by  the  union  of  these  nerves 
with  the  infra-orbital  branch  of  the 
superior  maxillary  nerve  below  the 
lower  eyelid.  Smaller  communica- 
tions occur  with  the  infra-trochlear  and 
nasal  nerves  on  the  side  of  the  nose. 

The  cervico-facial  division  of  the 
facial  nerve  also  supplies  three  series 
of  secondary  branches. 

1.  The  buccal  branch  (or  branches) 
extends  forwards  to  the  angle  of  the 
mouth  to  supply  the  muscles  con- 
verging to  the  mouth,  including  the 
buccinator.  It  communicates  with  the 
buccal  branch  of  the  inferior  maxillary 
nerve  in  front  of  the  anterior  border 
of  the  masseter  muscle. 

2.  The  supra  -  mandibular  branch 
passes  along  thelower  jaw  to  the  interval 

Facial  nerve. —P. A,  Posterior  auricular  uerve  ;  S.H,  between  the  lower  lip  and  chin,  and 
Nerve  to  stylo-hyoid  ;  Di,  Nerve  to  digastric  (posterior  supplies  the  deprCSSOr  anguli  Oris,  de- 
helly)  ;    T.F,   Temporo-facial  division;  T,    Temporal-         '- '-         f    .      .  o         _         ' 


Fig.  529.  —  Distribution  of  Facial  Nerve  outside 
THE  Skull,  and  Communications  with  Trigeminal 
Nerve  on  the  Face. 


M,  Malar;  I.O,  Infra-orlntal  branches;  C. F,  Cervico- 
facial division  ;  B,  Buccal  ;  Sm,  Supra-mandibular  ; 
Im,  Infra-mandiljular  Ijrauches. 
Trigeminal  nerve. — Ophth,  Oplithalmic  division  ;  S.O, 
Supra-orbital  ;  I.T,  Infra  -  trochlear  ;  N,  External 
nasal;  L,  Lachrymal  branches.  Sup. Max,  Superior 
maxillary  division  ;  T,  Temporal  ;  M,  Malar  ;  I.O, 
Infra-orbital  branclies.  Inf.  Max,  Inferior  maxillary 
division  ;  A.T,  Auriculo-temporal  ;  B,  Buccal  ;  M, 
Mental  branches  ;  S.G,  Superficial  cervical  nerve. 


pressor  labii  inferioris,  and  orbicularis 
oris.  It  communicates  with  the  mental 
branch  of  the  inferior  dental  nerve. 

3.  The  infra  -  mandibular  branch 
emerges  from  the  parotid  gland  near 
its  lower  end,  and  sweeps  forwards 
below  the  angle  of  the  jaw  to  the  front 


of  the  neck.     It  supplies  the  platysma 
myoides,  and  forms  loops  of  communica- 
tion with  the  superficial  cervical  nerve  from  the  cervical  plexus. 


The  Eighth  or  Auditory  Nerve. 

The  auditory  nerve  (n.  acusticus)  arises  from  the  brain  by  two  roots,  mesial  and 
lateral.  The  mesial  root  (radix  vestibularis)  emerges  between  the  olive  and  the 
restiform  body.  The  lateral  root  (radix  cochlearis),  continuous  through  the  cochlear 
nucleus  with  the  striae  acusticije  of  the  fourth  ventricle,  winds  round  the  outer  side 
of  the  restiform  body  (for  deep  connexions,  see  p.  519).  The  two  roots  become 
incorporated  to  form  the  trunk  of  the  nerve,  which  is  attached  to  the  brain  on  the 
outer  side  of  the  facial  nerve  and  pars  intermedia  at  the  posterior  border  of  the 
pons  Varolii  (Fig.  517,  p.  675). 

The  nerve  extends  outwards  through  the  internal  auditory  meatus,  lying  beneath 
the  facial  nerve  and  pars  intermedia  (Fig.  522,  p.  678).  In  the  meatus  its  two 
component  parts  separate  from  one  another,  forming  a  superior  or  vestibular  trunk 
continuous  with  tlie  mesial  root,  and  an  inferior  or  cochlear  trunk  continuous  with 


THE  NINTH  OE  GLOSSO-PHARYNGEAL  NERVE. 


689 


the  lateral  root.     These  trunks  again  subdivide,  and  piercing  the  lamina  cribrosa, 
supply  the  several  parts  of  the  labyrinth. 

The  superior  or  vestibular  trunk  (n.  vestibuli)  in  the  internal  auditory  meatus 
usually  receives  fibres  from  the  yars  intermedia, aM&  gives  off  a  (jommunicating  branch 


yramia  ;  Ol,  Olive  ;  R.B,  Kestifonn  body;  A.St,  Striit- acustic;i 
Dorsal  micleus  ;  G,  Lateral  cochlear  nucleus  :  Ve,  Ventral  nu- 
cleus ;  P.I,  Pars  intermedia;  G.O,  Geniculate  ganglion ;  Co,  Cochlea  ; 
Sacc,  Saccule  ;   Po,  Posterior  semicircular  canal ;  Ext,  External 
semicircular  canal ;  Sup,  Superior  semicircular  canal;  Utr,  Utricle. 

to  the  geniculate  ganglion  of  the  facial  nerve.  It  then  separates  into  three  terminal 
branches  which  pierce  the  lamina  cribrosa,  and  supply  (1)  the  macula  acustica  of 
the  utricle  and  the  ampulla?  of  (2)  the  superior  and  (3)  external  semicircular  canals. 

The  inferior  or  cochlear  trunk  (n.  cochleae)  gives  off  branches  (1)  to  the 
macula  acustica  of  the  saccule,  (2)  to  the  ampulla  of  the  posterior  semicircular  canal, 
and  (3)  is  continued  through  the  lamina  cribrosa  to  the  labyrinth  as  the  cocMear 
nerve,  which  is  distributed  through  the  modiolus  and  osseous  spiral  lamina  to  the 
organ  of  Corti  in  the  cochlea. 

Both  the  vestibular  and  cochlear  nerves  contain  among  their  fibres  collections  of  nerve 
cells,  forming  in  each  nerve  a  distinct  ganglion — the  vestibular  ganglion  (g.  vestibulare)  on 
the  vestibular  trunk,  and  the  spiral  ganglion  of  the  cochlea  (g.  spirale)  on  the  cochlear  trunk. 

The  Ninth  or  Glosso-pharyngeal  Nerve. 

The  glosso-pharyngeal  nerve  (n.  glosso-pharyngeus)  (Fig.  517,  p.  675)  arises  from 
the  brain  by  five  or  six  fine  radicles  which  emerge  from  the  medulla  oblongata  between 
the  olive  and  the  restiform  body,  close  to  the  facial  nerve  above,  and  in  series  with 
the  roots  of  the  pneumogastric  nerve  below  (for  deep  connexions,  seep.  517).  The 
rootlets  combine  to  form  a  nerve  which  extends  outwards  to  the  jugular  foramen, 
through  which  it  passes,  along  with  the  pneumogastric  and  spinal  accessory  nerves, 
but  enveloped  in  a  separate  sheath  of  dura  mater  (Fig.  522,  p.  678).  Reaching  the 
neck,  the  nerve  arches  downwards  and  forwards  to  the  interval  between  the  hyoid 
bone  and  the  lower  jaw.  It  lies  at  first  between  the  internal  carotid  artery  and 
the  internal  jugular  vein,  and  then  between  the  internal  and  external  carotid 
arteries,  in  its  course  to  the  side  of  the  pharynx.  It  sweeps  round  the  stylo- 
pharyngeus  muscle  and  the  stylo-hyoid  ligament,  and  disappears  beneath  the 
hyoglossus  muscle,  to  reach  its  termination  in  the  tongue. 

The  branches  of  tlie  nerve  may  be  classified  in  three  series  according  to  their 
origin — (i.)  in  the  jugular  foramen ;  (ii.)  in  the  neck  ;  (iii.)  in  relation  to  the  tongue. 

In  the  jugular  foramen  there  are  two  enlargements  upon  the  trunk  of  the  nerve 
— the  jugular  and  petrous  ganglia.  The  jugular  ganglion  (g.  superius)  is  small,  does 
not  implicate  the  whole  width  of  the  nerve,  and  may  be  fused  with  the  petrous 
ganglion,  or  even  absent  altogether.     No  branches  arise  from  it. 

The  petrous  ganglion  (g.  petrosum)  is  distinct  and  constant.  It  is  placed 
upon  the  nerve  at  the  lower  part  of  its  course  through  the  jugular  foramen. 

Branches  and  Communications  of  the  Petrous  Ganglion. — The  tympanic  branch  (n. 
tjmipanicus,  Jacobson's  nerve)  is  the  most  important  ofiset  from  this  ganglion.  It 
passes  through  a  small  canal  in  the  bridge  of  bone  between  the  jugular  foramen 
and  the  carotid  canal  .to  reach  the  cavity  of  the  tympanum,  where  it  breaks  up  into 
branches,  to  form,  along  with  branches  from  the  carotid  plexus  of  the  sympathetic  on 
the  internal  carotid  artery  (small  deep  petrosal  nerve),  the  tympanic  plexus  for  the  supply 
of  the  mucous  lining  of  the  tympanum,  mastoid  cells,  and  Eustachian  tube  (Fig.  528, 
48 


690 


THE  NEEVOUS  SYSTEM. 


p.  687).  The  fibres  of  the  tympanic  branch  of  the  glosso-^Jharyngeal  nerve  become 
reunited  to  form,  by  their  union  with  a  small  nerve  from  the  geniculate  ganglion  of  the 
facial  nerve,  the  small  superficial  petrosal  nerve  in  the  substance  of  the  temporal  bone. 
This  passes  forwards  through  the  temporal  bone,  and  eventually  joins  the  otic  ganghon. 

Besides  forming  the  tympanic  branch,  the  petrous  gangHon  of  the  glosso-pharyngeal 
nerve  communicates  with  three  other  nerves — (1)  with  the  superior  cervical  ganglion  of 

the      sympathetic  ;      (2)     with      the 

auricular     branch    of    the    pneumo- 

gastric ;  and  (3)  sometimes  with  the 

Aur.\^     Mni/// WWII////       /^Trpiex!Sr'"iW  ganghon  of  the  root  of  the  pneumo- 

gastric. 

In  thenech  the  glosso-pharyngeal 
nerve  gives  off  two  branches.  (1) 
As  it  crosses  over  the  stylo-pharyn- 
geus  muscle  it  supplies  the  nerve 
to  that  muscle,  which  sends  fibres 
through  it  to  reach  the  mucous 
membrane  of  the  pharynx.  (2) 
The  pharyngeal  branches  of  the  nerve 
supply  the  mucous  membrane  of 
the  pharynx  directly  after  piercing 
the  superior  constrictor  muscle,  and 
indirectly  after  joining,  along  with 
the  pharyngeal  offsets  from  the 
pneumogastric-  and  the  superior 
cervical  ganglion  of  the  sym- 
pathetic, in  the  formation  of  the 
pharyngeal  plexus. 

The  terminal  branches  of  the 
nerve  supply  the  mucous  mem- 
brane of  the  tongue  and  adjacent 
parts.  A  tonsillitic  branch  forms  a 
plexus  (circulus  tonsillaris)  to 
supply  the  mucous  membrane 
covering  the  tonsil,  the  adjacent 
part  of  the  soft  palate,  and  the 
pillars  of  the  fauces.  Lingual 
branches  supply  the  mucous  mem- 
brane of  the  dorsal  third  and 
lateral  half  of  the  tongue,  extend- 
ing backwards  to  the  glosso-epi- 
glottidean  folds  and  the  front  of 
the  epiglottis. 


Fig.  5-31. — Scheme  of  the  Distribution  of  the  Glosso- 

PHARTNGEAL    NeRVE. 

G.Pli,  Glosso-pharyngeal  nerve  ;  J,  Jugular,  and  P,  Petrous 
ganglia ;  Ty,  Tympanic  branch  (Jacobson's  nerve)  ; 
Ty.Plex.,  Tympanic  plexus  ;  Fa,  Root  from  geniculate 
ganglion  of  facial  nerve  ;  S.S.P,  Small  superficial  petrosal 
nerve  to  the  otic  ganglion  ;  S.D.P,  Small  deep  petrosal 
nerve  ;  I.C,  Internal  carotid  artery ;  Va,  Pneumogastric 
nerve  ;  Aur.,  Auricular  branch  (Arnold's  nerve)  ;  Sy., 
Superior  cervical  sj'mpathetic  ganglion  ;  F,  Communi- 
cating branch  to  facial  nerve  ;  Pli,  Pharyngeal  branch  of 
vagus  ;  E.C,  External  carotid  artery ;  Ph.Pl,  Pharyngeal 
plexus;  S.Ph,  Stylo-pharyngeus  muscle;  S. H.L,  Stylo- 
hyoid ligament;  H.G,  Hyo-glossus  ;  S.G,  Stylo-glossus  ; 
Ton,  Tonsil  ;  S.  Pal.,  Soft  palate  ;  G.  H.G,  Genio-hyoglossus  ; 
G.H,  Genio-hyoid  ;  Hy,  Hyoid  bone. 


The  Tenth  or  Pneumogastric  Nerve. 

The  pneumogastric  or  vagus  nerve  (n.  vagus)  arises  from  the  brain  by  numerous 
radicles  attached  to  the  front  of  the  restiform  })ody  of  the  medulla  oblongata,  in  series/ 
with  the  glosso-pharyngeal  nerve  above  and  the  spinal  accessory  nerve  below  it  (for 
deej)  connexions,  see  p.  517).    Uniting  to  form  a  single  trunk,  the  roots  of  the  nerve 
pass  outwards  to  the  jugular  foramen,  through  which  they  emerge  into  the  neck. 

In  the  jugular  foramen  the  nerve  occupies  the  same  sheath  of  dura  mater  as  the 
spinal  accessory  nerve,  and  is  placed  behind  the  glosso-pharyngeal  nerve.  Two 
ganglia  are  present  on  the  trunk  in  this  situation.  The  higher  and  smaller  is  the 
ganglion  of  the  root  fg.  jugulare) ;  the  lower  and  larger  is  the  ganglion  of  the  trunk 
of  the  nerve  (g.  nodosum). 

In  the  neck  the  pneumogastric  nerve  pursues  a  vertical  course  in  front  of  the 
spinal  column.  It  occupies  the  carotid  sheath,  lying  between  and  behind  the 
internal  and  common  carotid  arteries  and  the  internal  jugular  vein.     It  enters  the 


THE  TENTH  OE  PNEUMOGASTKIC  NEEVE. 


691 


thorax  behind  the  large  veins  :  on 
the  right  side,  after  crossing  over 
the  subclavian  artery ;  on  the  left 
side,  in  the  interval  Ijetween  the 
left  common  carotid  and  subclavian 
arteries. 

In  the  thorax  the  nerves 
occupy  the  superior  and  posterior 
mediastinal  spaces,  and  their  re- 
lations are  different  on  the  two 
sides,  (a)  In  the  superior  media- 
stinum the  right  nerve  continues 
its  course  alongside  the  innominate 
artery  and  the  trachea,  and  behind 
the  right  innominate  vein  and 
superior  vena  cava,  to  the  back  of 
the  root  of  the  lung.  The  left 
nerve  courses  downwards  between 
the  left  common  carotid  and  sub- 
cla^dan  arteries,  and  behind  the 
left  innominate  vein  and  the 
phrenic  nerve.  It  passes  over  the 
aortic  arch,  and  then  proceeds  to 
the  back  of  the  root  of  the  left 
lung.  (6)  In  the  posterior  media- 
stinum the  pneumogastric  nerves 
are  concerned  in  the  formation  of 
two  great  plexuses — the  pulmon- 
ary and  the  cesophageal.  Behind 
the  root  of  each  lung  the  nerve 
breaks  up  to  form  the  large 
posterior  pulmonary  plexus,  from 
the  lower  end  of  wliich  two  nerves 
emerge  on  each  side.  These  nerves 
on  the  right  side  pass  obliquely 
over  the  vena  azygos  major;  on 
the  left  side  they  cross  the  thoracic 
aorta.  Both  series  reach  the  oeso- 
phagus, and  divide  into  small 
anastomosing  branches  which  form 
the  (Esophageal  plexus.  At  the 
oesophageal  opening  of  the  dia- 
phragm the  two  nerves  become 
separated  from  the  plexus,  and 
entering  the  abdomen — the  left 
nerve  in  front  of  the  oesophagus, 
the  right  nerve  behind  it — they  ter- 
minate by  supplying  the  stomach 
and  other  abdominal  organs. 

The  communications  and 
branches  of  the  pneumogastric 
nerve  may  be  described  as  (i.)  gan- 
glionic, (ii.)  cervical,  (iii.)  thoracic, 
and  (iv.)  abdominal  (Fig.  532). 


Fig. 


532. — The  Distribution  of  the  Pneumogastric  Nerve. 
Var.R,  Ya.L,  Riglit  ami  left  vagi  ;  r,  Ganglion  of  the  root  and 
connexions  with  S}-,  Sympathetic,  superior  cervical  gang- 
lion ;  G.Ph,  Glosso -pharyngeal  ;  Ace,  Spinal  accessory 
nerve  ;  m,  Meningeal  branch  ;  Aur,  Auricular  branch  ;  t, 
Ganglion  of  the  trunk  and  connexions  with  Hy,  Hypo- 
glossal nerve  ;  CI,  C'2,  Loop  between  the  first  two  cervical 
nerves  ;  Sy,  Sympathetic  ;  Ace,  Spinalaccessory  nerve  ;  Ph,  Pliaryngeal  branch  ;  Ph.  PI,  Pharyngeal 
plexus  ;  S.L,  Superior  laryngeal  nerve  ;  I.L,  Internal  laryngeal  branch  ;  E.L,  External  laryngeal  branch  ; 
I.e.  Internal,  and  E.C,  External  carotid  arteries  ;  Cal,  Superior  cervical  cardiac  branch  ;  C'a2,  Inferior 
cervical  cardiac  branch  ;  R.L,  Recurrent  laryngeal  nerve  ;  C'a3,  Cardiac  branches  from  recurrent  laryngeal 
nerves  ;  Ca4,  Thoracic  cardiac  branch  (right  vagus)  ;  A.P.Pl,  Anterior,  and  P.P.Pl,  Posterior  pulmonary 
plexuses  ;  Oes.Pl,  (Esophageal  plexus  ;  Gast.R,  and  Gast.L,  Gastric  branches  of  vagus  (right  and  left)  : 
Coe.Pl,  Cceliac  plexus  ;  Hep. PI,  Hepatic  plexus  ;  Spl.Pl,  Splenic  j^lexus  ;  Een.PI,  Renal  plexus. 

48  a 


692  THE  NEEVOUS  SYSTEM. 

The  ganglion  of  the  root  (g.  jugulare)  is  small  and  spherical.  It  occupies 
the  jugular  foramen,  and  gives  off  two  branches — meningeal  and  auricular. 

The  meningeal  branch  passes  backwards  to  supply  the  dura  mater  of  the  posterior 
fossa  of  the  base  of  the  skull. 

The  auricular  branch  (Arnold's  nerve)  ascends  to  the  ear  in  a  fissure  between  the 
jugular  and  stylo-mastoid  foramina.  It  receives  near  its  origin  a  twig  from  the 
tympanic  branch  of  the  giosso-pharyngeal  nerve,  and  usually  communicates  with 
the  facial  nerve  by  a  branch  arising  from  the  latter  in  the  aqueduct  of  Eallopius. 
The  nerve  is  distributed  to  the  back  of  the  pinna  and  the  external  auditory  meatus, 
and  communicates  superficially  with  the  posterior  auricular  nerve. 

Communications. — Besides  supplying  the  meningeal  and  auricular  branches,  the 
ganglion  of  the  root  of  the  pneumogastric  nerve  receives  communications  from  (1)  the 
superior  cervical  ganglion  of  the  sympathetic ;  (2)  the  spinal  accessory  nerve ;  and  (3)  the 
petrous  ganglion  of  the  giosso-pharyngeal  nerve  (sometimes). 

The  ganglion  of  the  trunk  of  the*  nerve  (g.  nodosum),  placed  immediately 
below  the  preceding,  is  large  and  fusiform.  Like  the  previous  ganglion,  it  supplies 
two  branches — the  pharyngeal  and  superior  laryngeal  nerves. 

The  pharyngeal  branch  receives  its  fibres  (through  the  ganglion)  from  the  spinal 
accessory  nerve.  It  passes  obhquely  downwards  and  inwards  to  the  pharynx 
between  the  internal  and  external  carotid  arteries,  and  combines  with  the  pharyn- 
geal nerves  from  the  giosso-pharyngeal  and  superior  cervical  ganglion  of  the 
sympathetic  to  form  the  pharyngeal  plexus.  From  this  plexus  the  muscles  of  the 
pharynx  and  soft  palate  (except  the  stylo-pharyngeus  and  tensor  palati)  are 
supplied.  The  lingual  branch  is  a  small  nerve  which  separates  itself  from  the 
plexus  and  joins  the  hypoglossal  nerve  in  the  anterior  triangle  of  the  neck. 

The  superior  laryngeal  nerve  (n.  laryngeus  superior)  passes  obliquely  down- 
wards and  inwards,  behind  the  external  and  internal  carotid  arteries,  towards  the 
thyroid  cartilage.  It  divides  in  its  course  into  two  unequal  parts — a  larger  internal 
and  a  smaller  external  laryngeal  nerve. 

The  internal  laryngeal  nerve  (ramus  internus)  passes  inwards  into  the  larynx 
between  the  middle  and  inferior  constrictor  muscles  of  the  pharynx  and  through  the 
thyro-hyoid  membrane.  It  supplies  the  mucous  membrane  of  the  larynx,  reaching 
upwards  to  the  epiglottis  and  base  of  the  tongue,  and  forms  communications  beneath 
the  ala  of  the  thyroid  cartilage  with  the  branches  of  the  inferior  laryngeal  nerve. 

The  external  laryngeal  nerve  (ramus  externus)  passes  downwards  upon  the 
inferior  constrictor  muscle  of  the  pharynx.  It  supplies  branches  to  that  muscle, 
and  ends  in  the  crico-thyroid  muscle. 

Communications. — Besides  supplying  these  pharyngeal  and  laryngeal  nerves,  the 
ganglion  of  the  trunk  of  the  pneumogastric  has  the  following  communications  with  other 
nerves:  (1)  with  the  superior  cervical  ganglion  of  the  sympathetic ;  (2)  with  the  hypo- 
glossal ;  (3)  with  the  loop  between  the  first  and  second  cervical  nerves ;  and  (4)  with  the 
accessory  part  of  the  spinal  accessory  nerve.  This  part  of  the  nerve  applies  itself  to  the 
ganglion,  and  thereby  supplies  to  the  vagus  nerve  the  inhibitory  fibres  for  the  heart,  as 
well  as  the  motor  fibres  for  the  pharynx,  oesophagus,  stomach  and  intestines,  larynx  and 
respiratory  organs. 

Branches  of  the  Pneumogastric  in  the  Neck. — In  the  neck  the  pneumo-^ 
gastric   nerve  supplies  cardiac  Ijranches  and   (on  the  right   side)  the  inferior  or 
recurrent  laryngeal  nerve  (Fig.  532). 

The  cardiac  branches  are  superior  and  inferior.  On  tlie  right  side  both  cardiac 
branches  pass  downwards  into  the  thorax  liehind  the  subclavian  artery,  and  proceed 
alongside  the  trachea  to  join  the  deep  cardiac  plexus.  On  the  left  side  the  two 
nerves  separate  on  reaching  the  thorax.  The  superior  nerve  passes  deeply  along- 
side the  trachea  to  join  the  deep  cardiac  plexus.  The  inferior  nerve  accompanies 
the  pneumogastric  nerve  over  the  aortic  arch,  along  with  the  superior  cervical 
cardiac  branch  of  the  sympathetic,  to  end  in  the  superficial  cardiac  plexus. 

The  right  inferior  laryngeal  nerve  arises  at  the  root  of  the  neck,  as  the 
pneumogastric  nerve  crosses  over  the  first  part  of  the  subclavian  artery.  It  hooks 
round  the  artery,  and  passes  obliquely  upwards  and  inwards  behind  the  subclavian, 


THE  THOEACIC  PLEXUSES.  693 

the  common  carotid,  and  the  inferior  thyroid  artery  and  the  thyroid  body.  It  finally 
disappears  beneath  the  lower  border  of  the  inferior  constrictor  muscle,  and  ends 
in  supplying  the  muscles  of  the  larynx.  In  its  course  it  gives  off  the  following 
branches : — 

(1)  Cardiac  branches  arise  as  the  nerve  winds  round  the  subclavian  artery,  and 
course  downwards  alongside  the  trachea  to  end  in  the  deep  cardiac  plexus. 

(2)  Communicating  branches  to  the  inferior  cervical  ganglion  of  the  sympathetic 
arise  from  the  nerve  behind  the  subclavian  artery. 

(3)  Muscular  branches  supply  the  trachea,  cesophagus,  and  the  inferior  constrictor 
of  the  pharynx. 

(4)  Terminal  branches  supply  the  muscles  of  the  larynx  (except  the  crico-thyroid) 
and  communicate  beneath  the  ala  of  the  thyroid  cartilage  with  branches  of  the 
internal  laryngeal  nerve. 

Branches  of  the  Vagus  in  the  Thorax. — In  the  thorax  the  pneumogastric 
nerve  forms  the  great  pulmonary  and  oesophageal  plexuses.  The  right  nerve,  in 
addition,  furnishes  cardiac  branches ;  and  the  left  nerve  gives  off  the  inferior  or 
recurrent  laryngeal  nerve. 

The  left  inferior  laryngeal  nerve  differs  from  the  nerve  of  the  right  side  only 
in  its  point  of  origin  and  in  the  early  part  of  its  course.  It  springs  from  the 
pneumogastric  nerve  as  it  crosses  the  aortic  arch,  and,  after  hooking  round  the 
arch  external  to  the  ligamentum  arteriosuni,  it  passes  upwards  in  the  superior 
mediastinum  in  the  interval  between  the  trachea  and  cesophagus  to  the  neck.  In 
the  neck  its  course  and  relations  are  similar  to  those  of  the  nerve  of  the  right  side. 
The  branches  of  the  nerve  are  the  same  as  those  of  the  right  nerve.  The  cardiac 
branches  are  larger,  and,  arising  below  the  aortic  arch,  proceed  to  the  deep  cardiac 
plexus. 

Cardiac  branches  from  the  right  pneumogastric  nerve  arise  in  the  superior 
mediastinum,  and  pass  downwards  alongside  the  trachea  to  join  the  deep  cardiac 
plexus.  On  the  right  side  thoracic  cardiac  branches  are  thus  supplied  from  both 
the  trunk  of  the  nerve  and  its  recurrent  branch  ;  on  the  left  side  the  cardiac  branches 
in  the  thorax  arise  solely  from  the  recurrent  branch. 

Abdominal  Branches. — After  the  formation  of  the  oesophageal  plexus  the 
two  pneumogastric  nerves  resume  their  course,  and  passing  along  with  the  gullet 
through  the  diaphragm,  terminate  by  supplying  the  stomach.  The  right  nerve 
enters  the  abdominal  cavity  behind  the  gullet,  and  is  distriljuted  to  the  posterior 
surface  of  the  stomach.  It  sends  communicating  offsets  to  the  ccgliac,  splenic,  and 
renaLplasttses.  The  left  nerve  applies  itself  to  the  anterior  surface  and  lesser  cur- 
vature of  the  stomach,  to  which  it  is  distributed.  It  sends  communicating  offsets 
along  the  lesser  curvature  of  the  stomach  to  the  right  pneumogastric,  and  between 
the  layers  of  the  small  omentum  to  the  hepatic  plexus. 

The  Thoracic  Plexuses. 

Cardiac  Plexuses. — The  cardiac  branches  of  the  pneumogastric  nerve  (both 
cervical  and  thoracic)  combine  with  the  cervical  cardiac  branches  of  the  sympathetic 
to  form  the  superficial  and  deep  cardiac  plexuses. 

The  superficial  cardiac  plexus  is  placed  in  the  hollow  uf  the  aortic  arch, 
superficial  to  the  pericardium.  It  contains  a  small  ganglion  (ganglion  of  Wrisberg), 
and  is  joined  by  two  small  nerves — (1)  the  cardiac  branch  from  the  superior 
cervical  ganglion  of  the  sympathetic,  and  (2)  the  inferior  cervical  cardiac  branch 
of  the  pneumogastric — both  of  the  left  side — which  reach  it  after  passing  over  the 
arch  of  the  aorta. 

Branches  and  Communications. — From  the  plexus  branches  of  communication 
pass  (1)  to  the  left  half  of  the  deep  cardiac  plexus,  between  the  aortic  arch  and  the 
bifurcation  of  the  pulmonary  artery ;  (2)  to  the  left  anterior  pulmonary  plexus 
along  the  left  branch  of  the  pulmonary  artery;  (3)  the  branches  of  distribution  to 
the  heart  extend  along  the  pulmonary  artery  to  join  the  anterior  or  right  coronary 
plexus,  which  supplies  the  substance  of  the  heart  in  the  course  of  the  right 
coronary  artery. 
48  6 


69-4 


THE  NEEVOUS  SYSTEM. 


The  deep  cardiac  plexus  is  much  the  larger.  It  is  placed  behind  the  arch  of 
the  aorta,  on  the  sides  of  the  trachea,  just  above  its  bifurcation.  It  consists  of 
two  lateral  parts,  joined  together  bj  numerous  connnunications  around  the  termina- 
tion of  the  trachea.  The  two  portions  of  the  plexus 
are  different  in  their  constitution  and  distribution. 
The  right  half  of  the  plexus  is  joined  by  both  the 
cervical  and  thoracic  branches  of  the  right  pneumo- 
gastric  and  by  the  branches  of  the  right  inferior 
laryngeal  nerve,  as  well  as  by  branches  from  the 
superior,  middle,  and  inferior  cervical  ganglia  of  the 
sympathetic.  The  left  half  of  the  plexus  is  joined  by 
the  superior  cervical  cardiac  branch  of  the  left  pneumo- 
gastric,  by  branches  from  the  left  inferior  laryngeal 
nerve,  and  by  branches  from  the  middle  and  inferior 
cervical  ganglia  of  the  left  sympathetic ;  it  also 
receives  a  contribution  from  the  superficial  cardiac 
plexus. 

The  deep  cardiac  plexus  is  distributed  to  the 
heart  and  lungs.  The  right  half  of  the  plexus  for 
the  most  part  constitutes  the  anterior  or  right  coronary 
plexus,  reaching  the  heart  alongside  the  ascending 
aorta,  and  is  distributed  to  the  heart  substance  in 
the  course  of  the  right  coronary  artery.  It  is  rein- 
forced by  fibres  from  the  superficial  cardiac  plexus, 
which  reach  the  heart  along  the  pulmonary  artery. 
Fibres  from  the  right  half  of  the  deep  cardiac  plexus 
pass  also  to  join  the  posterior  or  left  coronary  plexus, 
and  others  extend  outwards  to  join  the  anterior 
pulmonary  plexus  of  the  right  side. 

The  left  half  of  the  deep  cardiac  plexus,  reinforced 
by  fibres  from  the  superficial  cardiac  plexus,  is  dis- 
tributed to  the  heart  in  the  form  of  the  left  or 
posterior  coronary  plexus,  which  is  joined  by  a  few 
filjres  behind  the  pulmonary  artery  from  the  right 
half  of  the  plexus,  and  supplies  the  heart  substance 
in  the  course  of  the  left  coronary  arbery.  The  left 
half  of  the  plexus  contributes  also  to  the  left  anterior 
pulmonary  plexus  by  fibres  which  extend  outwards  to 
the  root  of  the  lung  along  the  left  branch  of  the 
pulmonary  artery. 

Pulmonary  Plexuses. — As  already  stated,  the 
pneumogastric  nerve  on  each  side,  on  reaching  the 
back  of  the  root  of  the  lung,  breaks  up  into  numerous 
plexiform  branches  for  the  formation  of  the  posterior 
pulmonary  plexus.  From  eacli  nerve  a  few  fibres  pass 
to  the  front  of  the  root  of  the  lung,  above  its  uppet- 
theticbranches;Va,  Pneumogastric  i^Q^.^^yr,  to  form  the  much  smaller  anterior  pulmonary 

nerve  ;    R.L,    Recurrent    laryngeal  '  i  j 

nerve  ;  s,  Superior,  ami  i,  Inferior    piCXUS. 

The  anterior  pulmonary  plexus  on  each  side  is 
joined  by  a  few  fibres  from  the  corresponding  part  of 
the  deep  cardiac  plexus,  and  on  the  left  side  from 
the  superficial  cardiac  plexus  as  well.  It  surrounds 
and  supplies  the  constituents  of  the  root  of  the  lung 
anteriorly. 

The  posterior  pulmonary  plexus,  placed  behind 
the  root  of  the  lung,  is  formed  by  the  greati^r  part  of  the  pneumogastric  nqrve, 
reinforced  by  fine  branches  from  the  second,  third,  and  fourth  thoracic  ganglia 
of  the  sympathetic.  Numerous  branches  proceed  from  it  in  a  plexiform  manner 
along  the  bronchi  and  vessels  into  the  substance  of  the  lung. 


Fig.  533.— The  Coxstitutio.^j  of 
THE  Cardiac  Plexuses. 

Sy,  Cervical  sympathetic  cord  ;  C.l, 
Superior,  C.2,  Middle,  and  C.3,  In- 
ferior cervical  ganglia  ;  Car.  1,  Su- 
perior, Car.  2,  Middle,  and  Car.  3, 
Inferior    cervical    cardiac    synipa- 


Kervical  cardiac  Ijranches  of  vagus  ; 
D.C.P,  Deep  cardiac  plexus;  S.C.P, 
Superficial  cardiac  plexus;  A.P.P, 
Anterior  pulmonary  plexus  ;  P.P.P, 
Posterior  jiulmonary  jdexus  ; 
R.Car.P,  Right,  and  L.Car.P,  Left 
coronary  plexuses;  Art. Pul,  Pul- 
monary artery. 


THE  ELEVENTH  OE  SPlNAL  ACCESSORY  NERVE. 


695 


(Esophageal  Plexus  (plexus 
guke).  —  The  oesophagus  in  the 
thorax  is  supplied  by  the  pneu mo- 
gastric  nerve  both  in  the  superior 
and  posterior  mediastinum.  In 
ihe superior  mediastintwi  it  receives 
branches  from  the  pneumogastric 
nerve  on  the  right  side,  and  from 
its  recurrent  laryngeal  branch  on 
the  left  side. 

In  the  posterior  mediastinum 
it  is  surrounded  by  the  oesophageal 
plexus,  formed  from  the  trunks  of 
the  pneumogastric  nerves  emerg- 
ing from  the  posterior  pulmonary 
plexus,  which  form  a  large  plexus 
surrounding  the  gullet.  This  part 
of  thecesophagus  also  receives  fibres 
from  the  great  splanchnic  nerve 
and  ganglion.  From  the  oesophageal 
plexus  branches  supply  the  mus- 
cular wall  and  mucous  membrane 
of  the  oesophagus. 

Pericardiac  branches  are  also 
supplied  from  the  plexus  to  the 
posterior  surface  of  the  peri- 
cardium. 

The  Eleventh  or  Spinal 
Accessory  Nerve. 

The  spinal  accessory  nerve  (u. 
accessorius)  consists  of  two  es- 
sentially separate  parts,  different 
both  in  origin  and  in  distribution. 
One  portion  is  accessory  to  the 
vagus  nerve,  and  arises,  in  series 
with  tlie  fibres  of  that  nerve,  from 
the  side  of  the  medulla  oblongata. 
The  other,  spinal  portion,  arises 
from  the  lateral  aspect  of  the 
spinal  cord,  between  the  ventral 
and  dorsal  roots  of  the  spinal 
nerves,  its  origin  extending  from 
the  level  of  the  accessory  portion 
as  low  as  the  origin  of  the  sixth 
cervical  nerve  (for  the  deep  origin, 
see  p.  516).     Successively  joining 

together,  the  rootlets  form  a  trunk    j,^^  534.__the  Distribution  of  the  Pxeumogastric  Nerve. 
which   ascends    m    the    subdural  ^.  d  t^  t    d-  t,<.      i  i  <■  *.  n     r      f  *\,       *■     i 

.  .va.  K,  Va.  L,   Right  and  left  vagi  ;  r,  Oanglion  oi  the  root  and 

space    01    the    spinal    cord,    behind  connexions  with  Sy,  Sympathetic,   superior  cervical  gang- 

the    ligamentum   denticulatum,  to  lio"  ;    G.Ph,    Olosso-pharyngeal ;    Acc,    Spinal    accessory 

the  foramen  magnum.       There  the  IT'V'    "i,  Meningeal  Wh  ;  Aur,  Auricular  branch  ;  t, 

o  Ganglion  of  the  trunk   and   connexions  with    Hy,   Hypo- 

glossal nerve  ;  CI,  C2,  Loop  between  the  first  two  cervical 
nerves  ;  Sy,  Sympathetic  ;  Acc,  Spinal  accessory  nerve  ;  Ph.  Pharyngeal  branch  ;  Ph. PI,  Pharyngeal  plexus  ; 
S.L,  Superior  laryngeal  nerve;  LL,  Internal  laryngeal  branch;  E.L,  External  laryngeal  branch;  I.C, 
Internal,  and  E.C,  External  carotid  arteries  ;  Cal,  Superior  cervical  cardiac  branch  ;  C'a2,  Inferior  cervical 
cardiac  branch  ;  R.L,  Recurrent  laryngeal  nerve  ;  Ca3,  Cardiac  branches  from  recurrent  laryngeal  nerves  ; 
Ca4,  Thoracic  cardiac  branch  (right  vagus)  ;  A.P.Pl,  Anterior,  and  P.P. PI,  Posterior  pulmonary  plexuses  ; 
Oes.Pl,  Oesophageal  plexus  ;  Gast.R,  and  Gast.L,  Gastric  branches  of  vagus  (right  and  left)  ;  Coe.Pl, 
Cceliac  plexus  ;  Hep. PI,  Hepatic  plexus  ;  Spl.Pl,  Splenic  plexus  ;  Ren.  PI,  Renal  plexus. 

48  c 


696 


THE  NEEVOUS  SYSTEM. 


accessory  aud  spinal  portions  unite  into  a  single  trunk,  which  leaves  the  cranial 
cavity  through  the  jugular  foramen  in  the  same  compartment  of  dura  mater 
as  the  pneumogastric  nerve  (Fig.  522,  p.  678). 

In  the  jugular  foramen  the  accessory  portion 
of  the  nerve  (after  furnishing  a  small  branch  to 
the  ganglion  of  the  root  of  the  pneumogastric 
nerve)  applies  itself  to  the  ganglion  of  the  trunk, 
and  in  part  joins  the  ganglion,  in  part  the  trunk 
of  the  nerve  beyond  the  ganglion.  By  means  of 
these  connexions  the  pneumogastric  receives 
viscero-motor  and  cardio-inhibitory  fibres. 

The  spinal  portion  of  the  nerve  extends  into 
the  neck,  where  at  first  it  lies  along  with  other 
nerves,  in  the  interval  between  the  internal 
carotid  artery  and  the  internal  jugular  vein. 
Passing  obliquely  downwards  and  outwards  over 
the  vein,  it  descends  beneath  the  sterno-mastoid 
muscle,  which  it  supplies  as  it  pierces  it  on  its 
deep  surface.  After  crossing  the  posterior 
triangle  the  nerve  ends  by  supplying  the 
trapezius  muscle  on  its  under  surface.  The 
spinal  portion  of  the  nerve  communicates  in  three 
situations  with  nerves  from  the  cervical  plexus — 
(1)  in  or  beneath  the  sterno-mastoid,  with  the 
branch  for  the  muscle  derived  from  the  second 
cervical  nerve  ;  (2)  in  the  posterior  triangle,  with 
branches  from  the  third  and  fourth  cervical 
nerves ;  (3)  beneath  the  trapezius,  with  the 
branches  for  the  muscle  derived  from  the  third 
and  fourth  cervical  nerves. 


Fig.  535. — Schbjie  of  the  Origin,  Con- 
nexions, AND  Distribution  of  the 
Spinal  Accessory  Nerve. 

Sp  Ace,  Spinal  accessory  uerve  ;  C.1-4,  First 
four  cervical  nerves  (dorsal  roots)  ; 
Va,  Pneumogastric  nerve  ;  R,  Ganglion 
of  the  root  ;  T,  Ganglion  of  the  trunk  ; 
G.Ph,  Glosso-pharyngeal  nerve  ;  S.M, 
Nerves  to  sterno-cleido-mastoid  ;  Tr, 
Nerves  to  trapezius ;  F.M,  Foramen 
magnum  ;  J.  F,  Jugular  foramen. 


The  Twelfth  or  Hypoglossal  Nerve. 


The  hypoglossal  nerve  (n.  hypoglossus)  arises 
by  numerous  radicles  from  the  front  of  the  med- 
ulla oblongata  between  the  pyramid  and  the  olive 
(Fig.  517,  p.  675)  (for  deep  origin,  see  p.  51.5). 
The  root  fibres  arrange  themselves  in  two  bundles 
which  separately  pierce  the  dura  mater,  and  unite  in  the  anterior  condyloid  foramen, 
or  after  emerging  from  the  skull.  In  the  neck  the  nerve  arches  downwards 
and  forwards  towards  the  hyoid  bone,  and  then  turns  inwards  among  the  supra- 
hyoid muscles  to  the  tongue.  At  first  it  is  placed  deeply,  along  with  other  cranial 
nerves,  on  the  outer  side  of  the  internal  carotid  artery ;  it  then  curves  forwards^ 
and  downwards  over  the  two  carotid  arteries  lying  beneath  the  digastric  and  stylo- 
hyoid muscles.  As  it  crosses  the  external  carotid  artery  it  hooks  round  the  occipital 
artery.  Above  the  great  cornu  of  the  hyoid  bone  the  nerve  conceals  the  lingual" 
artery ;  and  it  then  disappears  between  the  mylo-hyoid  and  hyo-glossus  muscles  to 
reach  the  tongue,  in  the  muscular  substance  of  which  it  terminates. 


Communications. — In  its  course  the  hypoglossal  nerve  has  the  following  communica- 
tions with  other  nerves : — Near  the  base  of  the  skull  it  is  connected  by  small  branches 
with  (1)  the  superior  cervical  ganglion  of  the  sympathetic ;  (2)  the  ganglion  of  the  trunk 
of  the  pneumogastric  ;  (3)  by  a  larger  branch,  with  the  loop  between  the  first  two  cervical 
nerves ;  (4)  as  it  crosses  the  external  carotid  artery  it  receives  a  communication  from  the 
pharyngeal  plexus  {lingual  branch  of  the  vagus) ;  and  (5)  beneath  the  mylo-hyoid  muscle, 
at  the  anterior  border  of  the  hyo-glossus,  it  forms  loops  of  conununication  with  the  lingual 
branch  of  the  inferior  maxillary  nerve. 

The  branches  of  the  nerve  are: — (1)  Recurrent;  (2)  Descending;  (3)  Thyro- 
hyoid ;  and  (4)  Lingual. 


THE  TWELFTH  OK  HYPOGLOSSAL  NEEVE. 


G97 


The  recurrent  branch  passes  from  the  nerve  near  its  orign  to  supply  the  dura 
mater  of  the  posterior  fossa  of  the  base  of  the  skull.  It  probably  derives  its  fibres 
from  the  communication  with  the  first  and  second  cervical  nerves. 

The  descending  hypoglossal  nerve  (n.  descendens)  is  the  chief  branch  given  off  in 
the  neck.  It  arises  from  the  hypoglossal  nerve  as  it  crosses  the  internal  carotid 
artery,  and  descends  in  the  anterior  triangle  in  front  of  the  carotid  sheath.  It  is 
joined  about  the  middle  of  the  neck  by  the  descending  cervical  nerve  (from  the 
second  and   third   cervical  nerves).     By  their   union   the  hypoglossal  loop   (ansa 


Hypoglossal  nerve 
Recurrent  branch 


First  cervical  nerve 


Second  cervical  nerve 


Glosso-pharyngeal 

nerve 


Third  cervical  nerve 

Stylo-pharyngeusi 


Pharyngeal  branch  or  vagus — ' 
Digastric 
Descendens  hypoqlossi 

Middle  [ onstrictor 
Descendens  cervicis 


Internal  laryngeal  nerve 
Ansa  hypoolossi 


Inferior  constrictor 


Vagus  nerve 

Superior  cervical  ganglion  of  the  sympathetic 


Ouio-liyoid 


^^^^^^^^        Hyoglos.. 

/ m  ^*^^^>^'==::^i  'k  F'X      Genio-liyogloss\is 

""^v-rfT  'V    Genio-hyoid 

Mylo-hyoid  (cut) 
Digsstrip 


Thyro-hyoid 


Fig.  536. 


-The  Muscles  of  the  Htoid  Bone  and  Styloid  Process,  and  the  Extrinsic  Muscles  of 
THE  Tongue  with  their  Nerves. 


hypoglossi)  is  formed,  from  which  branches  are  distributed  to  the  majority  of  the 
infra-hyoid  muscles — both  bellies  of  the  omo-hyoid,  the  sterno-hyoid,  and  the 
sterno-thyroid.  The  descending  hypoglossal  nerve  derives  its  fibres  from  the  com- 
munication to  the  hypoglossal  nerve  from  the  loop  between  the  first  and  second 
cervical  nerves ;  so  that  the  ansa  hypoglossi  is  made  up  of  fibres  of  the  first  three 
cervical  nerves. 

The  nerve  to  the  thyro-hyoid  muscle  is  a  small  branch  which  arises  from  the 
hypoglossal  nerve  before  it  passes  beneath  the  mylo-hyoid  muscle.  It  descends 
behind  the  great  cornu  of  the  hyoid  bone  to  reach  the  muscle.  When  traced 
backwards  this  nerve  is  found  associated  with  the  loop  between  the  first  and  second 
cervical  nerves. 


698  THE  NEEVOUS  SYSTEM. 

The  lingual  branches  of  the  hypoglossal  nerve  are  distributed  to  the  hyo-glossus, 
genio-hyoid,  and  genio-hyo-glossus,  and  to  all  the  intrinsic  muscles  of  the  tongue. 
The  nerve  to  the  genio-hyoid  is  said  to  be  derived  from  the  loop  between  the 
first  and  second  cervical  nerves.  It  is  not  known  if  these  two  nerves  are  implicated 
in  the  innervation  of  the  proper  muscles  of  the  tongue,  but  it  appears  certain  that 
the  muscles  named — the  genio-hyoid,  thyro-hyoid,  sterno-hyoid,  omo-hyoid,  and 
sterno-thyroid — are  not  supplied  by  the  hypoglossal,  but  only  by  cervical  nerves, 
the  genio-hyoid  by  the  first  two,  the  other  muscles  by  the  first  three  cervical  nerves. 

THE  DEVELOPMENT  OF  THE  CEANIAL  NEEVES. 

Omitting  the  first  and  second  nerves,  there  is  an  obvious  likeness  in  the 
development  of  the  several  cranial  nerves  to  the  formation  of  the  dorsal,  afferent  or 
sensory,  and  the  ventral,  efferent  or  motor,  roots  of  the  spinal  nerves.  The  afferent 
roots  of  the  cranial  nerves  arise  from  collections  of  cells  which  bud  off  from  the 
alar  lamina  of  the  brain,  homologous  with  the  dorso-lateral  part  of  the  spinal  cord. 
These  cells  give  rise  to  central  and  peripheral  processes,  hke  the  similar  processes 
from  the  dorsal  ganglia  of  the  spinal  nerves,  producing  on  the  one  hand  the  root 
fibres  connected  with  the  brain,  and  on  the  other  hand  the  fibres  of  the  nerve 
proceeding  to  the  periphery.  The  efferent  roots,  like  the  ventral  roots  of  the  spinal 
nerves,  arise  as  the  peripheral  processes  of  neuroblasts  located  in  the  basal  lamina 
of  the  primitive  brain,  which  is  homologous  with  the  ventro-lateral  portion  of  the 
spinal  cord.  The  different  efferent  nerves  may  be  separated  into  two  series, 
according  as  they  arise  from  the  mesial  or  lateral  parts  of  the  basal  lamina.  The 
third,  fourth,  sixth,  and  twelfth  nerves  arise  from  the  mesial  part  of  the  lamina ;  the 
efferent  fibres  of  the  fifth,  seventh,  ninth,  tenth,  and  eleventh  nerves  arise  from  the 
lateral  part  of  the  lamina. 

The  olfactory  nerves  are  associated  in  their  development  with  the  formation  of  the 
nasal  pit  and  the  olfactory  bulb. 

The  nasal  pits  appear  in  each  side  of  the  front  of  the  head  at  a  little  later  period  than 
the  formation  of  the  lens  and  the  auditory  vesicle.  They  become  converted  into  the  nasal 
cavities  by  the  formation  of  the  pre-oral  visceral  clefts  and  arches, — fronto-nasal  and 
ethmo-vomerine  in  the  middle  line,  and  lateral  ethmoid  and  maxillary  processes  at  the 
sides  (p.  .38). 

The  Rhinencephalon  or  olfactory  bulb  is  a  hollow  outgrowth  from  each  telencephalon 
or  cerebral  hemisphere,  which  appears  in  the  first  month.  It  grows  forwards  into  relation 
with  the  deep  surface  of  the  nasal  pit.  In  many  animals  (as  in  the  horse)  the  olfactory 
bulb  remains  hollow  ;  but  in  the  human  subject  it  loses  its  lumen  and  becomes  a  solid 
bulb  (olfactory  bulb)  connected  to  the  brain  by  a  narrow  stalk,  the  olfactory  tract. 

The  epithelium  of  the  nasal  pit  is  responsible  for  the  formation  of  the  olfactory  nerves. 
There  are  two  views  as  to  the  mode  of  their  development  from  the  epithelial  cells.  Both 
views  admit  the  proliferation  of  the  epithelium  of  the  nasal  pit  so  as  to  produce  neuroblasts. 
According  to  the  one  view  these  neuroblasts  detach  themselves  from  the  epithelial  surface, 
and  constitute  an  olfactory  ganglion  which  becomes  applied  to  and  incorporated  with  the 
olfactory  bulb.  The  cells  of  the  ganglion  become  bi-polar,  and  the  peripheral  axons 
constitute  the  olfactory  nerves,  while  the  central  axons  (in  the  second  month)  proceed  back- 
wards to  the  brain  along  the  olfactory  tract.  According  to  the  other  view  (based  on  Disse's 
investigations),  the  proliferating  cells  of  the  nasal  epithelium  I'emain  in  the  wall  of  the 
nasal  pit,  and  become  the  olfactory  cells  of  the  nasal  cavity,  with  peripheral  processes 
projecting  to  the  surface  of  the  epithelium.  Their  central  axons  become  the  olfactory 
nerve  fibres  which  end  in  the  olfactoiy  bulb,  forming  dendrites  associated  with  the  dendritic 
processes  of  the  nerve-cells  of  the  bulb.  The  central  axons  of  these  latter  cells  develop 
into  the  fibres  of  the  olfactory  tract. 

The  optic  nerve  is  developed  wholly  from  the  brain.  Its  formation  begins  with  the 
outgrowth  of  the  optic  vesicle,  a  paired  hollow  outgrowth  from  the  ventral  surface  of  the 
thalamencephalon.  The  epiblastic  invagination  of  the  lens,  growing  inwards  from  the 
surface  of  the  head,  causes  the  collapse  of  the  vesicle  and  its  convez'sion  into  the  optic 
cup,  the  narrow  tube  connecting  the  vesicle  to  the  brain  becoming  the  optic  stalk.  This 
stalk  becomes  solid,  and  forms  the  basis  of  the  optic  tract,  optic  commissure,  and  optic 
nerv-e.  The  optic  cup,  bilaminar  in  form,  and  by  its  edge  clasping  the  lens,  is  embedded 
in  mesoblastic  tissue,  which  gives  rise  to  the  envelopes  of  the  eyeball,   etc.     The  outer 


THE  DEVELOPMENT  OF  THE  CEANIAL  NERVES.      699 

layer  of  the  optic  cup  produces  the  layer  of  hexagonal  pigment  cells  of  the  retina.  The 
cells  of  the  mntr  layer  produce  the  tissue  of  the  retina  proper.  They  form  neuroblasts 
with  peripheral  and  central  processes.  The  peripheral  processes  are  converted  into  retinal 
nerve  tissues ;  the  central  processes  extend  backwards  along  the  optic  stalk,  and  give  rise 
to  the  fibrous  structure  of  the  optic  nerve,  optic  commissure,  and  optic  tract.  Spongio- 
blasts in  the  inner  lamina  of  the  optic  cup  produce  the  sustentacular  tissue  of  the  retina 
(Midler's  fibres).  The  mesoblastic  tissue  surrounding  the  optic  cup  and  lens  gives  rise  to 
the  rest  of  the  structure  of  the  eyeball,  the  formation  of  which  is  described  in  the  section 
whicli  deals  with  the  organs  of  sense. 

The  oculo-motor  nerve  arises,  like  the  ventral  root  of  a  spinal  nerve,  from  a  group 
of  neuroblasts  in  the  mesial  part  of  the  basal  lamina  of  the  mid-brain.  The  peripheral 
fibres  extend  forwards,  to  end  around  the  optic  cup  in  the  mesoblastic  tissue,  from  which 
the  eye  muscles  are  derived.  Numerous  cells  are  carried  along  with  the  cell  processes  in 
their  course,  and  these  have  been  described  as  being  concerned  in  the  formation  of  the 
ciliary  ganglion. 

The  trochlear  nerve  also  arises  from  a  group  of  neuroblasts  occupying  the  mesial 
part  of  the  basal  lamina  of  the  mid-brain,  close  to  its  junction  with  the  hind-brain.  The 
peripheral  processes  do  not  emerge  directly  from  the  brain,  but  extend  dorsally  from  their 
origin  along  the  side  of  the  brain  to  its  dorsal  aspect,  where  they  appear,  after  decussating 
with  the  fibres  of  the  opposite  nerve,  just  behind  the  quadrigeminal  lamina. 

The  trigeminal  nerve  is  developed  by  means  of  a  large  dorsal  and  a  small  ventral 
root.  Their  origin  to  a  large  extent  resembles  the  mode  of  formation  of  the  roots  of  a 
spinal  nerve. 

The  large  dorsal  (afferent)  root  is  formed  by  means  of  a  cellular  bud  from  the  alar 
lamina  of  the  hind-brain.  This  bud  separates  from  the  brain,  and  forms  the  Gasserian 
ganglion.  Its  cells  becoming  bipolar,  like  the  cells  of  a  spinal  ganglion,  are  secondarily 
connected  with  the  brain  by  means  of  their  central  processes ;  while  the  peripheral  pro- 
cesses, separating  into  three  groups,  proceed  along  the  fronto-nasal  and  maxillary  processes, 
and  along  the  mandibular  arch,  to  form  the  three  main  divisions  of  the  nerve.  Numerous 
cells  accompany  each  main  division  in  its  course  from  the  ganglion,  and  form  eventually 
the  subordinate  ganglia — the  ciliary  on  the  ophthalmic  nerve,  the  qjlteno-palatine  on  the 
superior  maxillary  nerve,  and  the  otic  ganglion  on  the  inferior  maxillary  nerve. 

The  small  ventral  (efferent)  root  of  the  trigeminal  nerve,  like  the  motor  ventral  root 
of  a  spinal  nerve,  is  later  in  its  appearance  than  the  sensory  root.  It  arises  as  the  peri- 
pheral fibres  of  a  group  of  neuroblasts  occupying  the  lateral  part  of  the  basal  lamina  of 
the  hind-brain,  which  proceed  directly  to  the  surface  to  join  the  inferior  maxillary  division 
of  the  nerve. 

The  abducent  nerve  resembles  in  its  mode  of  development  the  oculo-motor  and 
trochlear  nerves  with  which  in  its  origin  it  is  in  series.  It  is  formed  by  the  peripheral 
processes  of  a  group  of  neuroblasts  in  the  mesial  part  of  the  basal  lamina  in  the  upper 
part  of  the  hind-brain.  These  processes  pierce  the  part  of  the  brain  in  which,  at  a  later 
stage,  the  fibres  of  the  pyramid  are  developed.  They  then  proceed  to  the  mesoblastic 
tissue  round  the  optic  cup,  which  is  destined  to  form  the  eye  muscles. 

The  facial  nerve  has  developmentally  a  double  origin.  (1)  In  connexion  with 
the  formation  of  the  auditory  nerve  a  group  of  cells  becomes  separated  from  the  alar 
lamina  of  the  hind-brain  opposite  the  auditory  vesicle.  This  group  becomes  separated 
into  three  parts,  of  which  the  middle  portion  is  the  rudiment  of  the  geniculate  ganglion 
(or  afferent  root).  (2)  The  efferent  root  of  the  nerve  arises  from  a  group  of  neuroblasts 
in  the  lateral  part  of  the  basal  lamina  of  the  hind-brain,  in  series  with  efferent  fibres  of 
the  vago-glosso- pharyngeal  nerves;  after  a  tortuous  course  within  the  bi'ain  its  fibres 
emerge  beneath  the  above-mentioned  cellular  mass,  opposite  the  auditory  vesicle.  They 
are  joined  by  the  ganglionic  root,  and  in  their  course  round  the  auditory  vesicle  become 
embedded  in  the  auditory  capsule  (aqueduct  of  Fallopius).  The  chorda  tympani  nerve 
appears  early  as  a  branch  of  the  facial  nerve.  It  is  probable  that  the  pars  intermedia, 
the  geniculate  ganglion,  and  the  chorda  tympani  nerve  together  represent  the  dorsal 
afferent  element  in  the  constitution  of  this  nerve. 

The  auditory  nerve  arises  as  a  cellular  bud  from  the  alar  lamina  of  the  hind-brain, 
dorsal  to  the  efferent  portion  of  the  facial  nerve  and  opposite  to  the  auditory  vesicle,  and 
in  close  association  with  the  latter. 

Becoming  separated  from  the  brain,  the  cellular  mass  separates  into  three  portions,  of 
which  the  middle  part  is  associated  with  the  facial  nerve  and  pars  intermedia  (as  the 
geniculate  ganglion),  while  the  mesial  and  lateral  parts  are  converted  into  the  mesial 
(vestibular)  and  lateral  (cochlear)  ganglia  and  roots  of  the  auditory  nerve.     The  cells 


700 


THE  NEEVOUS  SYSTEM. 


becoming  bipolar,  their  central  processes  are  secondarily  connected  Avith  the  brain  on 
the  dorsal  (lateral)  aspect  of  the  facial  nerve ;  the  peripheral  processes  proceed  to  the 
auditory  vesicle,  to  which  they  are  distributed  as  the  vestibular  and  cochlear  nerves. 
Numerous  cells  are  carried  along  with  the  nerve  trunks  into  relation  with  the  auditory 
capsule,  and  constitute  the  vestibular  and  cochlear  ganglia. 

The  glosso-pharyngeal  and  pneumogastric  nerves  are  developed  from  the  side 
of  the  hind-brain,  both  in  the  same  way,  and  each  by  two  roots.  A  collection  of  cells 
separates  itself  from  the  alar  lamina  of  the  hind-brain  behind  the  auditory  vesicle  to  form 
the  ganglionic  afferent  root.  The  ganglion  of  the  pneumogastric  is  much  larger  than  that 
of  the  glosso-pharyngeal.  Each  ganglion  becomes  divided  into  two  parts,  a  proximal  and  a 
distal  portion,  connected  together  by  a  commissural  band  of  fibres.  The  proximal  ganglion 
(jugular  ganglion  of  the  glosso-pharyngeal ;  ganglion  of  the  root  of  the  pneumogastric) 
is  secondarily  connected  by  centripetal  fibres  to  the  hind-brain.  From  the  distal  ganglion 
(petrous  ganglion  of  the  glosso-pharyngeal ;  ganglion  of  the  trunk  of  the  pneumogastric) 
peripheral  fibres  grow  outwards  to  form  the  nerve  trunk. 

Each  nerve  is  also  provided  with  a  small  efferent  root,  consisting  of  nerve  fibres, 
arising  from  a  collection  of  neuroblasts  in  the  lateral  part  of  the  basal  lamina  of  the  hind- 


LATERAL  AREA 

MESIAL  AREA 


VENTRAL  ROOT 
DORSAL  ROOT 

A        ■■■"■■    '""'  ■ixx.xr.  g 

Fig.  537. — Cojiparisox  of  Origins  ob"  Xerve  Roots  from  Spixal  Cord  and  Hixd-Bkain  (after  His). 

A.  Spinal  cord ;  B.    Hind-brain. 

brain,  and  emerging  beneath  the  ganglionic  root  at  the  junction  of  the  alar  and  basal 
laminae  (in  series  Avith  the  fibres  of  the  efferent  root  of  the  facial  nerve  above  and  of  the 
spinal  accessory  nerve  below). 

The  spinal  accessory  nerve  arises  in  two  parts — one  medullary,  the  other  spinal. 
The  medullary  (accessory)  portion  develops  as  the  processes  of  a  series  of  neuroblasts  in 
the  lateral  portion  of  the  basal  lamina  of  the  hind-brain,  which  emerge  in  series  with  the 
efferent  roots  of  the  glosso-pharyngeal  and  pneumogastric  nerves.  The  spinal  portion 
arises  as  the  processes  of  a  group  of  neuroblasts  in  the  ventral  part  of  the  medullary  tube 
(anterior  cornu),  which,  turning  outwards,  emerge  as  a  series  of  roots  on  the  lateral  aspect, 
of  the  spinal  cord. 

The  hypoglossal  nerve  is  developed,  not  in  series  with  the  nerves  above  mentioned, 
but  like  the  third,  fourth,  and  sixth  nerves,  from  the  mesial  part  of  the  basal  lamina 
of  the  hind-brain,  in  the  space  between  the  glosso-pharyngeal  and  other  nerves  above, 
and  the  first  cervical  nerve  below.  It  is  formed  as  a  series  of  peripheral  processes  from  a 
collection  of  neuroblasts  occupying  the  hind -brain.  Froriep's  ganglion  is  a  transitory 
collection  of  nerve  cells  developed  from  the  alar  lamina  of  the  hind-brain  on  the  dorsal 
aspect  of  the  nerve,  and  represents  in  a  rudimentary  condition  its  dorsal  ganglionic  root. 
It  gives  off  no  branches  and  soon  disappears. 


THE  MORPHOLCGY  OF  THE  CRANIAL  NERVES. 

The  head  and  face,  possibly  the  oldest,  and  from  every  point  of  view  the  most  fundamental 
and  important  poiiion  of  the  bodily  fabric,  present  in  some  respects  a  more  conservative  type  of 
structure,  and  in  other  aspects  have  been  subject  to  more  profound  alterations  than  otlier  parts 


THE  MOEPHOLOGY  0^   THE  CEAXIAL  XERVES.      701 

of  the  body.  Segmentation  is  characteiistic  of  tlie  trunk,  pervading  bones,  mvuscles,  vessels,  and 
nerves.  An  absence  of  true  segmentation  is  characteristic  of  the  head  region — omitting  for  the 
moment  the  cranial  nerves.  The  head  is  characterised  by  the  possession  of  an  uiisegmented 
tubular  nervous  system,  enclosed  in  a  bony  caj>sule  not  obviously  segmental,  with  which  the 
capsules  of  the  sense-organs  become  imited.  Tlie  pre-oral  aud  post-oral  visceral  arches  and  clefts 
are  not  truly  segmental  like  the  costal  arches  of  the  trunk.  The  branchial  clefts  are  said  to  be 
inter-segmeutal ;  and  their  muscles  (associated  with  the  myoblast  surroundiug  the  developing 
heart)  are  described  as  visceral,  and  not  myotomic,  so  that  the  branchial  vessels  and  nerves 
similarly)  are  not  to  be  regarded  as  comparable  to  the  segmental  vessels  and  nerves  of  the  trunk. 
The  truly  Segmental  structiu-es  present  are  certain  pei-sisteut  myotomes  or  muscle  plates,  whicli 
give  rise  to  muscles  innervated  by  the  third,  fourth,  sixth,  and  twelfth  cranial  nerves. 

Another  difficulty  m  the  morphology  of  the  head  arises  in  the  absence  of  body  cavity,  and 
the  consequent  difficidty  of  differentiating  the  somatic  and  splanchnic  mesoblast,  and  the  somatic 
and  splanchnic  distribution  of  a  given  nerve. 

Under  these  circumstances  there  is  little  help  to  be  derii«d'  fi'om  head  structures  other  than 
the  nerves  themselves  in  seeking  a  solution  of  the  question  of  the  morphological  relations  of  the 
cranial  nerves.  The  spinal  nerves  are,  generally  speaking,  all  alike.  The  cranial  nerves,  on  the 
other  hand,  ai-e  all  ditlerent.     Scarcely  any  two  nerves  are  alike  ;  and  no  single  cranial  nerve 

Possesses  in  itself  all  the  characteristic  features  of  a  spinal  nerve.  As  seen  in  relation  to  their 
evelopment,  the  cranial  nervous  system  possesses  a  series  of  doi-sal  ganglia,  comparable  in 
position  and  development  to  the  spinal  ganglia  fiom  which  afferent  nerves  arise  ;  and  the 
efferent  roots  are  developed  in  the  same  way,  and  occupy  somewhat  the  same  position  as  the 
ventral  roots  of  the  spinal  nerves.  But  there  is  no  single  complete  segmental  nerve  in  the  head. 
The  very  essence  of  the  architecture  of  the  head  is  a  want  of  segmentation ;  and  this  character 
is  shared  by  the  cranial  nerves.  In  addition  it  must  be  borne  in  mind  that,  in  relation  to  the 
mammalian  head,  there  are  organs  which  have  no  homologues  in  the  trunk,  and  on  whose 
existence  the  arrangement  of  the  cranial  nerves  depends — e.g.  sense-organs  and  gill-arches. 

Among  the  cranial  nerves  there  are  several  which  possess  a  resemblance  to  one  or  other  of 
the  elements  of  a  typical  spinal  nerve.  In  the  neck  the  origin  of  the  fibres  of  the  spinal 
accessory  nerve  is  fiom  the  side  of  the  spinal  cord,  and  it  is  in  series  with  the  motor  roots  of 
the  vago-glosso-pharyngeal,  facial,  and  fifth  nerves.  His  (as  shown  in  the  account  of  the 
development  of  the  nerves)  has  described  the  neuroblastic  origin  of  the  motor  roots  of  these 
nei-ves  from  the  lateral  part  of  the  basal  lamina  of  the  primitive  brain.  They  thus  form  a  series 
apart — lateral  motor  roots — separable  from  the  series  of  motor  roots  originating  from  the  mesial 
part  of  the  basal  lamina,  comprising  those  of  the  third,  fourth,  sixth,  and  twelfth  nerves ;  the 
latter  nerve  roots  being  comparable  to  and  in  series  with  the  ventral  roots  of  the  spinal  nerves. 
The  lateral  motor  roots  are  not  represented  in  the  spinal  series  excejjt  in  the  neck.  It  is 
questionable  if  there  is  any  fimdamental  distinction  between  the  lateral  and  ventral  motor  roots 
of  the  cranial  nerves.  The  spinal  accessory  fibres,  for  example,  when  traced  into  the  spinal  cord, 
have  an  origin  from  the  anterior  comu  of"  the  cord,  and  only  differ  from  the  motor  or  ventral 
root  fibres  of  a  spinal  nerve  in  their  different  course  to  the  sluface.  The  ganglia  in  association 
with  the  cranial  nerves  are  comparable  to  the  spinal  ganglia.  The  fifth  nerve,  with  the  Gasserian 
gangUon,  the  ganglion  of  the  facial,  the  ganglia  of  the  auditory,  of  the  glosso-pharyngeal  and  the 
vagus,  and  the  transitory  (Froriep's)  ganglion  of  the  hypoglossal  nerves,  arise  from"  the  brain  in  a 
comparable  position,  and  in  the  same  way  as  the  spinal  ganglia.  But  another  series  of  structures 
— the  sense  organs  of  the  lateral  line,  and  the  so-caUed  "  epibranchial "  organs  which  are  highly 
developed  in  lower  vertebrates  (e.g.  elasmobranchs),  and  which  appear  transitorily  onlv,  or  are 
absent  altogether  in  mammalian  development,  may  possibly  have  a  share  in  the  formation  of 
certain  of  these  ganglia  or  parts  of  them  (e.g.  ciliary  ganglion,  genicidate  ganglion,  ganglia  of  the 
auditory  nerve,  petrosal  ganglion  of  the  glosso-pharvngeal,  and  the  ganglion  of  the  trunk  of  the 
vagus). 

Certain  of  the  cranial  nerves  are  apparently  distinctly  segmental,  supplying  muscles  derived 
from  the  pei-sisting  myotomes  of  the  head.  The  first  three  myotomes  are  said  to  give  rise  to  the 
muscles  of  the  eyeball  The  first  produces  the  superior  rectus,  inferior  rectus,  internal  rectus, 
and  inferior  oblique  muscles,  and  its  segmental  nerve  is  the  oculo-motor.  The  second  myotome 
is  said  to  produce  the  superior  oblique  muscle,  and  its  segmental  nerve  is  the  trochlear.  The 
third  myotome  is  said  to  produce  the  external  rectus  muscle,  and  its  segmental  nerve  is  the 
abducent.  It  has  been  asserted  that  the  tongue  muscles  are  derived  from  the  last  three  or  four 
cephalic  and  fijst  cervical  myotomes,  and  that  the  hypoglossal  nerve  is  the  segmental  nerve  for 
these  myotomes,  comprising  the  motor  elements  of  several  (four  or  five)  segmental  nerves.  The 
intervening  myotomes  between  the  fii-st  three  and  this  occipital  series  disappearing,  the  corre- 
sponding elements  of  segmental  nerves  are  supposed  to  be  absent  also  (Fig.  538). 

Certain  of  the  cranial  nerves  are  essentially  related  to  the  structures  derived  from  and  asso- 
ciated with  the  pre-oral  and  post-oral  visceral  clefts  and  arches  Fig.  539).  The  trigeminal  nerve 
is  essentially  the  nerve  of  the  mandibular  arch.  By  its  efferent  root  it  supplies  the  muscles  of 
that  arch.  By  its  afferent  root  and  branches  it  is  related  to  (1)  the  fronto-nasal  process  (oph- 
thalmic division  and  ciliary  ganglion) ;  (2)  the  maxillary  arch  (superior  maxillary  nerve) ;  and 
(3)  the  mandibidar  arch  (inferior  maxillary  nerve).  The  mandibidar  is  at  first  the  main  nerve  ; 
and  the  maxillary  division  is  sometimes  regarded  as  a  suboi-dinate  branch  (pr^-brancliial,  prte- 
trematic)  for  the  supply  of  the  anterior  margin  of  the  cleft  (mouth),  with  which  the  nerve  is  m 
relation.  The  ophthalmic  nerve  is  sometimes  regaixled  as  a  morjjhologically  separate  nerve. 
The  nerves  to  these  arches  have  been  compared   to  the  anterior  primary  divisions  of  spinal 


702 


THE  NEEVOUS  SYSTEM. 


nerves,  the  branches  which  they  supjjly  to  tlie  forehead  and  temi^le  (frontal,  orbital,  _  and 
aiiricnlo-temporal)  representing  the  posterior  primary  divisions.  The  ganglia  on  each  division 
of  the  nerve  are  formed  as  extensions  from  the  Gasserian  ganglion. 

The  facial  nerve  is  essentially  the  nerve  of  the  second  (hyoid)  arch^  and  the  cleft  in  front  of 
that  arch  (spiracular  cleft,  Eustachian  tube).  Its  motor  root  supplies  the  muscles  of  that  arch 
(stapedius,  stylo-hyoid,  and  digastric),  and  the  epicranial  and  facial  muscles  and  platysma 
myoides,  which  are  developments  from  the  hyoid  arch  (Eabl).  The  chorda  tympani  nerve  is 
regarded  as  the  subordinate  (prai-branchial,  prte-trematic)  branch  to  supply  the  anterior  margin 
of  the  first  post-oral  cleft.  It  is  possible  that  the  geniculate  ganglion,  with  the  pars  intermedia 
and  the  chorda  tympani,  may,  in  part  at  least,  represent  the  ganglionic  and  afferent  element  of 

the  nerve.  Or  the 
geniculate  ganglion,  and 
the  nerves  in  relation 
to  it,  may  be  associated 
with  an  "  epibranchial " 
sense-organ. 

The  auditory  nerve, 
on  the  other  hand,  may 
be  either  the  sensory 
element  of  the  branchial 
nerve,  associated  with  the 
hyoid  arch,  and  first  post- 
oral  cleft,  or  it  may  repre- 
sent the  nerve  or  nerves 
belonging  to  ancestral 
sense  -  organs  of  the 
lateral  line. 

The  glosso  -  pharyn- 
geal is  the  branchial 
nerve  of  the  third  post- 
oral  (thyro -hyoid)  arch 
and  the  cleft  in  front. 
Its  efferent  fibres  supply 
the  muscle  of  this  arch, 
— the  stylo-pharyngeus. 
The  superior  constrictor 
of  the  pharynx  is  also 
assigned  to  this  arch  ; 
the  middle  and  inferior 
muscles  to  the  fourth  (first 
branchial)  arch.  The 
afferent  portion  of  the 
nerve  is  possibly  com- 
posed of  two  separate 
parts  ;  the  petrous  gan- 
glion being  associated 
with  an  epibranchial  or 
lateral  line  sense-organ, 
and  the  rest  of  the  n^rve 
forming  the  afferent 
fibres  for  the  gill -cleft 
and  arch.  The  lingual 
branches  are  regarded  as 
the  main  stem  (post  - 
trematic),  the  pharyngeal 


Fig.  538. — Scheme  to  illustrate  the  Disposition  of  the  Myotomes  in 
THE  Embryo  in  Eelation  to  the  Head,  Trunk,  and  Limbs. 
A,  B,  C,  First  three  cephalic  myotomes ;  N,  1,  2,  3,  4,  Last  persisting  cephalic 
myotomes  ;  C,  T,  L,  S,  Co,  The  myotomes  of  the  cervical,  thoracic, 
lumbar,  sacral,  and  caudal  regions  ;  I.,  IL,  IIL,  IV.,  V.,  VI.,  Vll.,  VIIL, 
IX.,  X.,  XL,  XII.,  refer  to  the  cranial  nerves,  and  the  structures  with 
which  they  may  be  emliryologically  associated. 

branches  as  subordinate  branches  ;  the  tympanic  branch  being  th&prse -branchial  or  prse-trematic 
branch  for  the  anterior  margin  of  the  third  gill-cleft. 

The  pneumogastric  nerve  is  generally  regarded  as  representing  the  fusion  of  all  the  branchial 
nerves  behind  the  glosso-pharyngeal.     Its  efferent  fibres  are  in  series  with  those  of  the  glosso- 

Fharyngeal  above  and  the  spinal  accessory  nerve  below,  and  belong  to  the  lateral  series  of  His. 
ts  afferent  fibres,  like  those  of  the  glosso-pharyngeal,  represent  two  elements.  The  lower 
ganglion  has  possible  connexions  with  epibranchial  sense-organs— the  rest  of  the  nerve  rejDre- 
senting  the  fused  branchial  branches  of  fishes.  The  superior  laryngeal  nerve  is  looked  upon 
as  the  branchial  nerve  of  the  fourth,  and  the  inferior  laryngeal  nerve  as  the  branchial  nerve 
of  the  fifth  arch.  While  tlie  relation  of  the  nerve  to  the  hinder  giU-arches  and  clefts  makes 
it  possible  to  understand  the  innervation  by  the  vagus  of  the  heart  and  lungs,  no  satisfactory 
explanation  is  forthcoming  of  tlie  pas.sage  of  the  nerve  into  the  abdomen,  and  its  distribution  to 
the  stomach  and  other  organs  below  the  diapliragm. 

The  spinal  accessory  nerve  consists  of  two  jjarts.  The  accessory  portion  of  the  nerve 
consists  of  efferent  fibres  for  the  branchial  region,  in  series  with  the  lateral  motor  roots  of  the 
glosso-pharyngeal  and  vagus  nerves.  The  spinal  portion  of  the  nerve  is  also  composed  of  efferent 
fibres,  and  represents  the  only  lateral  motor  elements  arising  from  the  spinal  cord. 


THE  SYMPATHETIC  NEEVOUS  SYSTEM. 


703 


Olfactory  Nerve. — There  is  absolute  uncertainty  regarding  the  mori^hology  of  tliis  nerve. 
It  consists  of  three  elements  :  (1)  the  olfactory  bulb,  derived  from  the  cerebral  hemisphere, 
solid  in  man,  but  a  hollow  cerebral  divertieidum  in  certain  animals,  and  forming  the 
rhinencejihalon ;  (2)  tlie  olfactory  ganglion,  witli  its  central  and  peripheral  processes,  derived 
from  the  ectoderm  ;  (3)  the  nasal  pit.  Attention  has  lieen  specially  fixed  on  the  olfactory 
ganglion,  whicli  has  been  compared  to  (1)  a  dorsal  spinal  ganglion,  derived  from  the  anterior  end 
of  the  niedullary  groove  ;  and  to  (2)  a  lateral  line  sense-organ. 

The  optic  nerve  also  presents  an  insoluble  proldem  in  regard  to  its  morphological  jjosition 
in  the  series  of  cranial  nerves.  The  optic  stalk  and  ojjtic  cup  have  been  regarded  as  a  highly- 
modified  dorsal  ganglion ;  but  there  is  insuperable  ditficvilty  in  accepting  this  view.  The 
peripheral  jirocesses  do  not  become  connected  witli  either  ectodermal  or  mesoblastic  structures, 
but  become  the  tissue  of  the  retina  ;  while  tlie  central  processes,  growing  backwards,  envelop 
the  optic  stalk,  and  obtain  connexions  Avith  the  brain.  The  retina  must  be  regarded  as  a  highly- 
modified  layer,  morphologically  in  series  with  the  wall  of  the  fore-brain  ;  and  the  ectodermal 
structiire  of  superficial  origin  comparable  to  the  olfactory  ganglion  or  the  auditory  vesicle  is  the 
lens  (which  may  po-ssibly  be  homologous  with  a  lateral  line  sense-organ).  The  optic  nerve,  optic 
commissure,  and  optic  tract  are  then  to 
be  looked  upon  as  cerebral  commissures, 
and  not  as  nerves  in  the  ordinary  sense. 

The  simplest  and  most  primitive  con- 
dition of  the  head,  in  relation  to  the 
morphology  of  the  cranial  nerves,  is  found 
before  the  formation  of  the  gill-clefts,  when 
the  salient  features  are  a  tubular  and  simple 
brain,  and  a  series  of  superficial  invagina- 
tions which  pass  from  the  surface  inwards 
to  become  connected  with  outgrowths  cor- 
resijonding  to  them  from  the  primitive 
brain.  On  either  side  of  the  head  three 
hollow  invaginations  occur : — (1)  The  nasal 
pit  bearing  the  olfactory  epithelium  becomes 
connected  by  the  olfactory  ganglion  with  the 
rhinenceplialon,  an  outgrowthfrom  the  fore- 
brain,  and  so  forms  the  basis  of  an  olfactory 
organ  and  nerve  ;  (2)  a  similar  invagination 
produces  the  lens,  connected  with  a  jJro- 
trusion  of  the  optic  vesicle  from  the  fore- 
brain,  by  which  the  basis  of  the  eye  and 
the  optic  nerve  is  formed  ;  (3)  behind  the 
buccal  cavity  a  third  invagination  forms 
the  auditory  vesicle,  which  is  connected 
with  the  soKd  extension  from  the  hind- 
brain  of  the  acoustic  ganglia,  to  form  the 
essentials  of  the  organ  of  hearing  and 
auditory  nerve. 

The  trigeminal  nerve  is  essentially  the 
nerve  of  the  buccal  cavity  and  the  sub- 
ordinate cavities,  nasal  and  oral,  derived 
from  it.     The  branchial  arches  and  clefts 


Fig. 


)39. — Scheme  to  illustrate  the  Embrtological 
Arraxgejiext  of  the  Cranial  Nerves. 

are  secondary  structures,  and  their  nerves   I.  to  XII.  Cranial  Nerves  ;  Fr,  Froriep's  ganglion  ;  CI.,  Roots 

are  (1)  the  trigeminal  for  the  first  (mandi-  and  trunk  of  the  first  cervical  nerve. 

bular)  arch  and  the  cleft  in  front  of  it ; 

(2)  the  facial  for  the  second  (hyoid)  arch  and  cleft ;  (3)  the  glosso-pharyngeal  for  the  third 

(thyro-hyoid)  arch  and  cleft ;  and  (4)  the  pneumogastric  for  the  succeeding  arches  and  clefts. 

The  bulbar  part  of  the  spinal  accessory  nerve  is  inseparable  from  the  motor  portion  of  the  vago- 

glosso-pharjTigeal  nerves  ;  the  spinal  part  is  beyond  the  series  of  the  cranial  nerves. 

Lastly,  there  are  certain  truly  segmental  nerve  elements,  motor  fibres  which,  remaining 
associated  with  certain  persistent  cephalic  myotomes,  give  rise  to  the  oculo-motor,  trochlear, 
abducent,  and  hypoglossal  nerves. 


THE   SYMPATHETIC   NERVOUS   SYSTEI\L 


The  sympathetic  nervous  system  consists  of  a  pair  of  elongated  gangliated 
cords  (nervi  sympathici),  extending  from  the  base  of  the  skull  to  the  coccyx ;  con- 
nected, on  the  one  hand,  by  a  series  of  branches  to  the  spinal  nervous  system,  and 
on  the  other  hand  giving  off  an  irregular  series  of  branches  to  the  viscera.  At  its 
cephalic  end  each  sympathetic  cord  is  continued  in  a  plexiform  manner  into  the 
cranial  cavity  along  with  the  internal  carotid  artery,  and  forms  complex  relation- 


704 


THE  NEEVOUS  SYSTEM. 


ships  with  certain  cranial  nerves.  At  their  caudal  ends  the  two  sympathetic 
cords  become  joined  together  by  fine  filaments,  and  are  connected  by  the  coccygeal 
ganglion  (g.  impar). 

The  sympathetic  system  (1)  serves  to  rearrange  and  distribute  fibres  derived 
from  the  cerebro-spinal  system  to  the  viscera  and  vessels  of  the  splanchnic  area ; 

(2)  it  transmits  to  the  cerebro-spinal  system  afferent  fibres  from  the  viscera ;  and 

(3)  it  transmits  fibres  to  the  vessels,  involuntary  muscles,  and  glands,  in  the  course 
of  the  somatic  divisions  of  the  spinal  nerves. 

General  Structure  of  the  Sympathetic  System. — The  sympathetic  system  is 

composed  of  two  elements — ganglia  and  nerve  fibres. 

The  ganglia  (g.  trunci  sympathici)  are  variable  in  number,  form,   size,  and 

position.  They  are  not  definitely  segmental  in 
position,  but  they  are  always  connected  together 
by  a  system  of  narrow  commissural  cords  of  nerve 
fibres.  A  ganglion  consists  of  a  larger  or  smaller 
number  of  multipolar  nerve  cells,  enclosed  in  a 
capsule  of  connective  tissue.  Each  cell  is  pro- 
vided with  one  axon  and  a  number  of  dendrites. 
The  axon  may  enter  into  the  composition  of 
(a)  the  commissural  cord ;  (h)  a  central  branch 
(gray  ramus  communicans) ;  or  (c)  a  peripheral 
branch  from  the  sympathetic  cord.  These  axons 
are  commonly  medullated  at  their  origin,  but 
become  non-meduUated  in  their  course  from  the 
parent  cell.  Besides  these  ganglia,  two  other 
series  of  ganglia  are  present  in  connexion  with 
the  peripheral  branches  of  the  sympathetic : 
intermediate  or  collateral  ganglia,  on  the  branches 
or  in  the  sympathetic  plexuses ;  and  terminal 
ganglia,  in  close  relation  to  the  endings  of  the 
nerves  in  the  viscera. 

The  nerve  fibres  in  the  sympathetic  system 
are  of  two  classes,  medullated  and  non-medul- 
lated.     The   distinction   is   not  absolute.     The 

Fig.  540.-SCHEJIE  of  the  Coxstitction  of  medullated    fibres    may   lose    their    medullary 
THE  W  HiTE  Ramus  Communicans  OF  THE      ,       ,,      i     /.  ^  ■      \_^     •     ,  •      ^-  ^ 

Sympathetic.  sheaths  beiore  reaching  their  terminations ;  and 

The  roots  and  trunks  of  a  spinal  nerve  are  the  non-mcduUated  fibres  may  at  their  origin 
sho^\•n,  with  the  white  ramus  passing  be-  possess   a  medullary   slieath.      The  medullated 

tween  the  spinal  nerve  and  a  sympathetic  g|jj.gg  ^^^^^^  ^^^^  SCrieS  of  wllite  rami  COVimUni- 
ganglion  (Sy).       The   splanchnic   efferent  ,      /,-i         ■  i  i  i  f  j-i  •       i  n 

fibres  (in  red)  are  shown,  partly  ending  c«7i^es  (the  visccral  branches  of  the  spmal  nerves). 
in  the  ganglion,  and  partly  passing  ije-  They  take  Origin  from  the  anterior  primary 
yond  the  ganglion  into  a  peripheral  branch,  cjiyisions  of  Certain  Spinal  ncrvcs  in  two  streams  : 

The  splanchnic  aff'erent  fibres  (in  blue)  are    .,  .       ,        ,         x-  i.\       n     ^  "  j  xi 

shown,  partly  entering  the  ganglion,  and  thoracico-lumbar  from  the  first  or  sccoud  thoracic 
passing  upwards  or  downwards  in  the  to  the  sccoud  or  third  lumbar  ncrvc,  and  pelvic, 
gangiiated  cord ;  partly  passing  over  the  ^^  gacial,  from  the  sccond  and  third,  or  third  and 
con  m  o  perip  era    ranc  les.  fourth  sacral  nerves.     The  roots  of  these  nerves 

arise  from  both  dorsal  and  ventral  roots  of  the  spinal  nerves,  hut  in  largest  numbers 
from  the  ventral  root.  The  fibres  from  the  ventrcd  root  are  of  very  small  size.  They 
are  the  axons  of  nerve  cells  within  the  spinal  cord,  which  enter  the  sympathetic  cord 
through  the  white  ramus,  and  end  by  forming  arborisations  around  the  cells  of  a  sym- 
pathetic ganglion.  There  are  three  known  courses  for  such  a  fibre  to  take  in  relation 
to  the  sympathetic  system— (a)  It  may  end  in  the  ganghon  with  which  it  is  im- 
mediately related  ;  {h)  it  may  course  upwards  or  downwards  in  the  commissural  cord 
to  reach  a  neighbouring  ganglion  ;  (c)  it  may  pass  beyond  the  gangiiated  cord  to  end 
in  relation  to  cells  of  the  peripheral  (collateral)  ganglia  along  with  fibresof  distribu- 
tion from  the  sympathetic  ganglia.  These  fibres  are  splanchnic  efferent  fibres ;  motor 
for  the  unstriped  muscular  tissue  of  the  vessels  and  viscera,  and  secretory  for  the 
glands  in  the  splanchnic  area.  The  fibres  from  the  dorsal  root  of  the  spinal  nerve 
entering  into  the  composition  of  the  white  ramus  communicans  are  the  axons  of  spinal 


SPLANCHNIC 
AFFERENT 


THE  SYMPATHETIC  NERVOUS  SYSTEM. 


705 


ganglion  cells.  They  constitute  the  splanchnic  afferent  fibres,  and  probably  traverse 
the  sympathetic  gangliated  cord,  passing  upwards,  downwards,  and  outwards,  without 
being  connected  with  its  cells.  They  are  the  sensory  fibres  for  the  viscera,  which 
they^  reach  along  with  the  peripheral  branches  arising  from  the  sympathetic 
cord  itself.  It  is  not  certain  that  fibres  from  the  dorsal  ganglia  are  only  found  in 
connexion  with  nerves  provided  with  distinct  white  rami.  Similar  medullated 
fibres  are  found  also  in  the  gray  rami  communicantes. 

The  non-medullated  fibres  in  the  sympathetic  system  are  derived  from  the  axons 
of  the  sympathetic  ganglion  cells.     They  have  different  destinations,     {a)  Some 
fibres  appear  to  contribute  to  the  formation  of  the  commissural  cord  connecting 
the  uanglia  together, 
and  to  end  in  arborisa- 
tions round  the  cells 
of     a     neighbouring 
ganglion.      (&)  Non- 
medullated    fibres 
form  a  large  part  of 
the   system  of  j^je?'i- 
pheral  (splanchnic 
eff'erent)    tranches, 
streaming    into    the 
splanchnic  area  in  an 
irregular   manner, 
both  from  the  gangha 
and    the    connecting 
commissures,  (c)  The 
gray  rami  communi- 
cantes  form  a  series 
of     non  -  medullated 
fibres  (with   a  small 
number  of  medullated 
fibres    intermingled) 
proceeding    centrally 
from  the  ganglia  to  the 
spinal  nerves.     These 
gray  rami  are  found 
in     connexion    with 
each  and  all  of  the 
spinal  nerves.    Their 
origin  from  the  gan- 
gliated   cord    is    ir- 
regular :     they    may 
come  from  the  gan- 
glia or  the  commis- 
sure; they  may  divide 
after  their  origin,  so 
that  two  spinal  nerves 
are  supplied  from  one 
ganglion  ;      or     two 
ganglia   may  supply 
branches  to  a  single 
spinal    nerve.      The 
gray  ramus  is  distri- 
buted along  the  somatic  divisions  of  the  spinal  nerves,  supplying  branches    to 
unstriped  muscular  fibres  (vaso-motor,  pilo-motor)  and  glands  (secretory )._    They 
also  provide  small  recurrent  branches,  ending  in  the  membranes  enveloping  the 
spinal  nerve-roots.      Mingled  with  the  non-medullated   fibres  of  the  gray  rami 
are  found  a  small  number  of  medullated  fibres,  regarded  as  medullated  sympathetic 
fibres,  and  axons  from  the  dorsal  spinal  ganglia  incorporated  with  this  ramus. 
49 


Fig.  541.— Scheme  of  the  Constitution  and  Connexions  of  the 
Gangliated  Cord  of  the  Sympathetic. 
The  gangliated  cord  is  indicated  on  the  right,  with  the  arrangement  of  the  tibres 
arising   from    the    ganglion    cells.      On  the  left  the  roots  and  trunks  of 
spinal  nerves  are  shown,  with  the  arrangement  of  the  white  ramus  com- 
municans  above  and  of  the  gray  ramus  below. 


706  THE  NEEVOUS  SYSTEM. 

The  commissural  cords  of  the  sympathetic  system  are  composed  of  white  and 
gray  fibres.  The  white  fibres  are :  (1)  splanchnic  efferent  fibres,  passing  to  a 
ganglion  above  or  below  the  point  of  entrance  into  the  sympathetic  system ;  (2) 
splanchnic  afferent  fil^res,  guided  along  the  commissure  and  over  or  through  the 
ganglia.  The  (jray  fibres  are  the  axons  of  sympathetic  ganglion  cells :  (1)  true 
commissural  fibres  passing  into  connexion  with  the  cells  of  a  neighbouring 
ganglion ;  (2)  fibres  passing  along  the  commissure  for  a  certain  distance  upwards 
or  downwards  before  entering  the  splanchnic  area  as  peripheral  branches. 

The  peripheral  (splanchnic)  branches  from  the  sympathetic  cord  consist. of — 

(1)  white  fibres — splanchnic  afferent  fibres  unconnected  with  cells,  and  splanchnic 
efferent  fibres  which,  after  passing  over  the  gangliated  cord,  are  on  their  way  to 
join  peripheral  (collateral)  or  terminal  ganglia  in  relation  to  the  viscera ;  and  of 

(2)  gray  fibres,  splanchnic  efferent  branches,  the  axons  of  sympathetic  ganglion 
cells  distributed  to  the  vessels  and  viscera  in  the  splanchnic  area.  , 

THE  CEKVICAL  PAET  OF  THE  SYMPATHETIC  COED. 

The  cervical  part  of  the  sympathetic  cord  may  be  regarded  as  an  upward 
prolongation  of  the  primitive  sympathetic  system  along  the  great  vessels  of  the 
neck.  It  is  characterised  by  the  absence  of  white  rami  communicantes  connecting 
it  with  the  cervical  spinal  nerves.  Its  spinal  fibres  ascend  in  the  commissural 
cord  from  the  upper  thoracic  nerves  to  be  connected  with  the  cells  of  the 
cervical  ganglia.  The  branches  from  the  ganglia  in  the  neck  are  distributed  to 
structures  in  the  head,  neck,  and  thorax :  (1)  motor  fibres  to  involuntary  muscles 
(e.g.  dilator  of  the  pupil) ;  (2;  vaso-motor  fibres  along  the  arteries  of  the  head  and 
neck  and  upper  limbs ;  (.3)  pilo-motor  fibres  along  the  cervical  spinal  nerves  to  the 
skin  of  the  head  and  neck :  (4)  cardio-motor  fibres ;  (5)  and  secretory  fibres  (for 
the  submaxillary  gland). 

The  gangliated  cord  in  the  neck  is  placed  upon  the  prevertebral  muscles  and 
behind  the  carotid  vessels.  It  extends  from  the  root  of  the  neck,  where  it  is  con- 
tinuous behind  the  subclavian  artery  with  the  thoracic  portion  of  the  cord,  to  the 
base  of  the  skull,  where  it  ends  in  the  formation  of  plexiform  branches  upon  the 
internal  carotid  artery.  It  consists  of  a  narrow  commissural  cord  composed  of 
medullated  and  non-medullated  fibres,  on  which  are  two  or  three  ganglia — a 
superior  ganghon  at  the  upper  end,  an  inferior  ganglion  at  the  point  of  junction 
with  the  thoracic  portion  of  the  cord,  and  an  intermediate  middle  ganglion  varying 
in  position  and  often  absent. 

The  superior  cervical  ganglion  (g.  cervicale  superius)  situated  at  the  base  of  the 
skull,  lies  between  the  internal  jugular  vein  and  the  internal  carotid  artery.  It  is 
the  largest  of  the  sympathetic  ganglia,  measuring  an  inch  or  more  in  length.  The 
commissural  cord  connects  it  with  the  middle  ganglion  (g.  cervicale  medium),  which  is 
of  small  size,  is  frequently  aljsent,  and  may  be  divided  into  two  parts.  It  is  usually 
placed  o^'er  the  inferior  thyroid  artery  as  it  passes  behind  the  carotid  sheath. 

The  inferior  ganglion  (g.  cervicale  inferius)  is  joined  by  the  commissural  cord  to 
the  middle  (or  superior)  ganglion  above,  and  is  only  imperfectly  separated  from  the 
first  thoracic  ganglion  iDelow.  It  is  of  considerable  size,  irregular  in  shape,  and  is 
placed  behind  the  first  part  of  the  subclavian  artery  in  the  interval  between  the 
last  cervical  transverse  process  and  the  neck  of  the  first  rib. 

The  branches  from  the  cervical  sympathetic  ganglia  and  cord  are  divisible  into 
two  sets — {A)  Central  communicating  branches  for  other  nerves ;  {B)  peripheral 
branches  of  distribution,  which  alone,  or  along  witli  (jther  nerves,  form  plexuses, 
accompanying  and  supplying  vessels  and  viscera  of  tlie  head,  neck,  and  thorax. 
Although  this  distinction  is  made,  it  is  to  be  borne  in  mind  that  the  branches  of 
communication  are  as  much  nerves  of  distribution  as  the  others. 

Superior  Cervical  Ganglion. 

Central  Communicating  Branches. — 1.  Gray  rami  communicantes  pass  from 
the  ganglion  to  tlie  anterior  primary  divisions  of  the  first  four  cervical  nerves. 

2.  Communications  with  Cranial  Nerves. — Just  outside  the  skull,  in  the  deep 


SUPEKIOK  CEEVICAL  GANGLION. 


707 


part  of  the  neck,  communicating  branches  pass  to  the  following  cranial  nerves :  (a) 
to  the  petrous  ganglion  of  the  giosso-pharyngeal  and  the  ganglion  of  the  root  of 
the  pneumogastric  (n.  jugularis) ;  (b)  to  the  ganglion  of  the  trunk  of  the  pneumo- 
gastric ;  (c)  to  the  hypoglossal  nerve. 

Peripheral  Branches  of  Distribution. — 1.  Pharynx. — A  pharyngeal  branch 
courses  downwards  and  inwards  behind  the  carotid  sheath  to  reach  the  wall  of  the 
pharynx,  where  it  joins  (along  with  the 
pharyngeal  branches  of  the  giosso-pharyngeal 
and  pneumogastric  nerves)  in  the  formation 
of  the  pharyngeal  plexus,  an.d  assists  in  supply- 
ing the  muscles  and  mucous  membrane  of  the 
pharynx 

2.  Heart. — The  superior  cervical  cardiac 
branch  is  a  slender  nerve  which,  on  the  right 
side,  descends  behind  the  large  vessels  into 
the  thorax  to  join  the  deep  cardiac  plexus. 
On  the  left  side  the  course  of  the  nerve  is 
similar  in  the  neck,  but  in  the  superior 
mediastinum  it  passes  between  the  left 
carotid  and  subclavian  arteries,  and  over  the 
aortic  arch,  to  join  with  the  inferior  cervical 
cardiac  branch  of  the  pneumogastric  in  the 
formation  of  the  superficial  cardiac  plexus. 
In  their  course  both  nerves  form  connexions 
with  the  other  cervical  cardiac  nerves  of  the 
sympathetic,  and  with  cardiac  and  other 
branches  of  the  pneumogastric  (external  and 
inferior  laryngeal). 

3.  Vessels.  —  (ft)  The  external  carotid 
branch  passes  forwards  to  the  external  carotid 
artery,  and  forms  the  external  carotid  plexus, 
which  supplies  offsets  to  that  artery  and  its 
branches,  as  well  as  to  the  inter-carotid  body. 
From  the  subordinate  plexuses  on  the  facial 
and  middle  meningeal  arteries  sympathetic 
fibres  are  supplied  to  the  submaxillary  and 
otic  ganglia  respectively. 

(h)  The  internal  carotid  branches  form  an 
upward  prolongation  of  the  ganglion,  which 
applies  itself  in  the  form  of  bundles  of  nerve- 
fibres  to  the  internal  carotid  artery  as  it 
enters  the  carotid  canal  in  the  temporal  bone. 
The  branches  separate  into  outer  and  inner 
paYts,  wdiich  form  plexuses  investing  the 
artery  in  the  cranium.  The  outer  division 
forms  the  lower  or  carotid  plexus  (pi.  caroticus 
internus) ;  the  inner  division  gives  rise  to 
the  upper  or  cavernous  plexus  (pi.  cavernosus). 
Both  plexuses  supply  offsets  to  the  artery  and 
its  branches,  and  form  communications  with 
certain  cranial  nerves. 

The  carotid  plexus  communicates  by  fine  branches  with  (a)  the  abducent  nerve, 
and  (&)  the  Gasserian  ganglion,  and  gives  off  (c)  the  great  deep  petrosal  and  (d) 
the  small  deep  petrosal  nerves.  The  great  deep  petrosal  nerve  joins  the  great- 
superficial  petrosal  nerve  from  the  geniculate  ganglion  of  the  facial,  over  the 
foramen  lacerum  medium.  By  their  union  the  Vidian  nerve  is  formed,  which, 
after  traversing  the  Vidian  canal,  ends  in  Meckel's  ganglion.  The  small  deep 
petrosal  nerve  passes  to  the  tympanic  plexus.  This  plexus,  formed  by  the  small 
deep  petrosal  nerve,  the  tympanic  branch  of  the  giosso-pharyngeal,  and  a  twig 


Fig.  542. — The  Distribution  of  the  Sympa- 
thetic Gangliated  Cord  in  the  Neck. 

Sy.l,  Superior  cervical  ganglion,  and  connexions - 
and  branches  ;  I.C,  Internal  carotid  artery 
G.Ph,  Giosso-pharyngeal  ;  Va,  Vagus  ;  Hy, 
Hypoglossal  ;  C.l,  2,  .3,  4,  First  four  cervical 
nerves  ;  Plex,  Pharyngeal  plexus  ;  G.  Ph, 
Giosso-pharyngeal  nerve  ;  E.C,  To  external 
carotid  artery  ;  Sy.2,  Middle  cervical  gang- 
lion, connexions,  and  branches  ;  Co,  6,  Fifth 
and  sixth  cervical  nerves  ;  I.Thy,  luferioi 
thyroid  artery ;  A. V,  Ansa  Vieussenii ;  Sy.3, 
Inferior  cervical  ganglion,  connexions,  and 
branches;  C. 7,  8,  Seventh  and  eighth  cer- 
vical nerves  ;  Vert,  Vertet)ral  plexus  ;  Car, 
Cardiac  branches. 


708 


THE  NEEVOUS  SYSTEM. 


from  the  geniculate  ganglion  of  the  facial  nerve,  is  placed  on  the  inner  wall  of  the 
tympanum.  It  supplies  the  mucous  lining  of  the  tympanum  and  Eustachian 
tube ;  and  the  small  superficial  petrosal  nerve  passes  from  it  to  the  otic  ganglion. 

The  cavernous  plexus  communicates  with  (a)  the 
oculo- motor,  and  (h)  the  trochlear  nerves,  and  (c) 
the  ophthalmic  division  of  the  trigeminal  nerve ;  it 
also  (d)  supplies  twigs  to  the  pituitary  body,  and  (e) 
forms  the  sympathetic  root  of  the  ciliary  ganglion. 
This  may  pass  to  the  ganglion  independently,  or  it 
may  be  incorporated  ia  the  long  root  of  the  ganglion 
from  the  nasal  branch  of  tlie  ophthalmic  nerve. 

Middle  Cervical  Ganglion. 

Central  Communicating  Branches. — 1.  G-ray 
rami  communicantes  arise  from  the  ganglion  or  from 
the  cord  for  the  anterior  primary  divisions  of  the 
fifth  and  sixth  cervical  nerves.  2.  The  subclavian 
loop  (ansa  Vieussenii)  is  a  loop  of  communication  from 
this  ganglion,  which,  after  passing  over  and  supplying 
offsets  to  the  subclavian  artery  and  its  branches,  joins 
the  inferior  cervical  cjancrlion. 

Peripheral  Branches  of  Distribution. — 1.  Heart. 
— A  slender  middle  cervical  cardiac  branch  descends, 
either  separately  or  in  company  with  other  cardiac 
nerves,  behind  the  large  vessels  into  the  thorax, 
where  it  ends  in  the  deep  part  of  the  cardiac  plexus 
on  each  side. 

2.  Thyroid  Body.  —  Branches  extend  inwards 
along  the  inferior  thyroid  artery  to  supply  the  thyroid 
body. 

When  the  middle  ganglion  is  absent  the  branches 
described  arise  from  the  commissural  cord. 


Inferior  Cervical  Ganglion. 

Central  Communicating  Branches. — 1.  Gray 
rami  communicantes  arise  from  this  ganglion  for  the 
anterior  primary  divisions  of  the  seventh  and  eighth 
cervical  nerves.  2.  The  subclavian  loop  already 
mentioned  connects  the  middle  and  inferior  ganglia 
over  the  front  of  the  subclavian  artery.  3.  A  com- 
munication frequently  occurs  with  the  inferior 
laryngeal  nerve. 

Peripheral  Branches  of  Distribution. — 1.  Heart. 
— An  inferior  cervical  cardiac  branch  is  given  off  on 
each  side  to  euter  the  deep  cardiac  plexus. 

2.  Vessels. — («)  The  vertebral  plexus  is  a  dense 
Superficial  cardiac  plexus;  A.P.P,  plexus  of  fibres  surrounding  the  vertebral  artery  and 
P.*rr^"'T«Sr;"V.»;r;  -»oompa„yi.,g  Its  branches  in  the  neck  and  the 
R.Car.P,  Right,  and  L.Car.p,  Left  cranial  cavity.  (o)  The  subclavian  plexus  is  derived 
coronary  piexu.se.s ;  Art.Pui,  Pui-  from  the  subclavian  loop,  and  supplies  small  offsets  to 
monary  artery.  ^-^^   Subclavian   artery.      It   gives  branches   to  the 

internal  mammary  artery,  and  communicates  with  the  phrenic  nerve. 

THE  THORACIC  PAKT  OF  THE  SYMPATHETIC  CORD. 

The  thoracic  part  of  the  sympathetic  cord  consists  of  a  variable  number  of 
ganglia  of  an  irregularly  angular  or  fusiform  shape,  joined  together  by  commissural 


Fig.  543. — The  Constitution  of 
THE  Cardiac  Plexuses. 

Sy,  Cervical  .sympathetic  cord  ;  C.l, 
Superior,  C.2,  xMiddle,  and  C.3,  In- 
ferior cervical  ganglia ;  Car.  ], 
Superior,  Car. 2,  Middle,  and  Car.3, 
Inferior  cervical  cardiac  sympa- 
thetic branches ;  Va,  Pneumogastric 
nerve ;  R.L,  Recurrent  laryngeal 
nerve  ;  .s,  Superior,  and  i,  Inferior 
cer%'ical  cardiac  branches  of  vagus  ; 
D.C.P,  Deep  cardiac  plexus  ;  S.C.P, 


THE  THOEACIC  PART  OF  THE  SYMPATHETIC  CORD. 


709 


cords  of  considerable  thickness.  The  number 
of  ganglia  is  usually  ten  or  eleven  ;  but  the  first 
and  sometimes  others  may  be  so  fused  with  the 
neighbouring  ganglia  as  to  still  further  reduce 
the  number.  This  part  of  the  sympathetic  cord 
is  characterised  by  its  union  with  the  thoracic 
spinal  nerves.  Each  thoracic  nerve,  with  the 
possible  exception  of  the  first,  sends  a  visceral 
branch  (white  ramus  communicans)  to  join  the 
gangliated  cord  in  the  thorax.  These  white 
rami  separate  into  two  main  streams  in  relation 
to  the  sympathetic  cord.  Those  of  the  upper 
Jive  nerves  are  for  the  most  part  directed 
upwards  to  be  distributed  through  the  cervical 
part  of  the  sympathetic  ganghated  cord  in 
the  manner  already  described.  The  white  rami 
of  the  lovjer  thoracic  nerves  are  for  the  most 
part  directed  downwards  in  the  lower  part  of 
the  sympathetic  cord  and  its  branches,  to  be 
distributed  in  the  abdomen ;  at  the  same  time 
some  of  their  fibres  are  directly  associated  with 
the  supply  of  certain  thoracic  viscera, — lungs, 
aorta,  cesophagus. 

These  white  rami  are  composed  of  (1) 
splanchnic  afferent  fibres  passing  from  its  peri- 
pheral branches  through  the  sympathetic  cord 
into  the  dorsal  ganglia  of  the  spinal  nerves — 
medullated  nerve-fibres  unconnected  with  sym- 
pathetic ganglion  cells ;  and  (2)  somatic  and 
splanchnic  efferent  fibres,  small  medullated 
nerves  which,  after  a  longer  or  shorter  course 
in  the  gangliated  cord  or  its  peripheral 
branches,  become  connected  with  the  sym- 
pathetic ganglion  cells,  or  with  the  cells  of 
peripheral  (collateral  or  terminal)  ganglia,  from 
which  again  (non-medullated)  axous  proceed  to 
supply  branches  to  viscera  and  vessels.  The 
ultimate  destination  of  the  upper  stream  of 
white  rami  from  the  thoracic  nerves  has  been 
mentioned  in  the  description  of  the  cervical 
sympathetic;  the  peripheral  branches  supply- 
ing thoracic  organs  contain  vaso-motor  fibres 
for  the  lungs  and  aorta.  The  peripheral  branches 
from  the  lower  part  of  the  sympathetic  cord 
in  the  thorax,  receiving  white  rami  from  the 
lower  thoracic  nerves,  are  mainly  destined  for 
distribution  to  structures  below  the  diaphragm. 
They  comprise  (a)  viscero-inhibitory  fibres  for 
the  btomach  and  intestines ;  (h)  motor  fibres  for 
part  of  the  rectum  ;  (c)  pilo-motor  fibres  for  the 
lower  part  of  the  body ;  (d)  vaso-motor  fibres 
for  the  abdominal  aorta  and  its  branches,  and   T.i-12;  L.i-5  ;  s.i-5  ;  Co,  Anterior  primary 

divisions  of  spinal  nerves,  connected  to  tlie 
gangliated  cord  of  the  sympathetic  by 
rami  commuuicantes,  white  (double  lines)  and  gray  (single  lines)  ;  Oes,  Oesophagus  and  o?sophageal 
plexus  ;  Ao,  Aorta  and  aorta  plexus  ;  Va,  Vagus  nerve  joining  oesophageal  plexus  ;  S.l,  Great  splanchnic 
nerve  ;  X,  Great  splanchnic  ganglion  ;  S.2,  Small  splanchnic  nerve  ;  S.3,  Least  splanchnic  nerve  ;  Co, 
Coronary  artery  and  plexus  ;  Spl,  Splenic  artery  and  plexus  ;  H.  Hepatic  artery  and  plexus  ;  SL,  Semi- 
lunar ganglion  ;  Di,  Diaphragm  ;  S.R,  Sujirarenal  capsule  ;  Re,  Renal  artery  and  plexus  ;  S.M,  Superior 
mesenteric  artery  and  plexus  ;  Sr,  Spermatic  artery  and  plexus  ;  I.M,  Inferior  mesenteric  artery  and 
plexus  ;  Ht,  Hypogastric  nerves  and  plexus  ;  Rec,  Rectal  plexus  ;  Ut,  Uterine  plexus  ;  Ves,  Vesical 
plexus  ;  V.V.V,  Visceral  branches  from  sacral  nerves. 

49  a 


REC.      UT       VES. 

Fig.  544.  —  The  Arhangement  of  the 
Sympathetic  System  i:<  the  Thokax, 
Abdomen,  and  Pelvis. 


710  THE  NEEYOUS  SYSTEM. 

for  the  lower  lirabs ;  (e)  secretory,  and  (/)  sensory  fibres  for  the  abdominal  viscera. 
The  thoracic  part  of  the  sympathetic  cord  is  placed  upon  the  heads  of  the  ribs, 
and  is  covered  over  by  the  pleura. 

The  branches  from  the  gangiiated  cord  are,  as  in  the  neck,  divisible  into  two 
sets- — (A)  Central  branches,  communicating  with  other  nerves,  and  (B)  peripheral 
branches,  distributed  in  a  plexitbrm  manner  to  the  thoracic  and  abdominal  viscera. 

Central  Communicating  Branches. — The  white  rami  communicantes  from 
the  thoracic  nerves  have  already  been  described.  Passing  forwards  from  the 
beginning  of  the  anterior  primary  divisions  of  the  nerves,  they  become  connected 
with  the  ganglia  or  the  commissural  cord  of  the  sympathetic. 

The  gray  rami  communicantes  are  branches  arising  irregularly  from  each  thoracic 
ganglion,  which,  passing  backwards  along  with  the  white  rami,  join  the  anterior 
primary  divisions  of  the  thoracic  nerves. 

Peripheral  Branches  of  Distribution. — These  branches  arise  irregularly 
from  the  ganglia  and  the  commissural  cord.  They  are  composed  of  non-meduUated 
fibres  (splanchnic  efferent)  derived  from  the  ganglion  cells,  and  medu  Hated  fibres 
(splanchnic  efferent  and  afferent)  derived  directly  from  the  white  rami,  without 
the  intervention  of  the  cells  of  the  ganglia. 

1.  Pulmonary  Branches. — From  the  gangiiated  cord  opposite  the  second,  third, 
and  fourth  ganglia  fine  filaments  arise  which  join  the  posterior  pulmonary  plexus. 

2.  Aortic  Branches. — The  upper  part  of  the  thoracic  aorta  receives  fine  branches 
from  the  upper  five  thoracic  ganglia. 

3.  Splanchnic  Nerves. — Three  nerves  arise  from  the  lower  part  of  the 
gangiiated  cord,  partly  from  the  ganglia  themselves,  and  partly  from  the  com- 
missural cord  between  the  ganglia.  Passing  downwards  over  the  bodies  of  the 
thoracic  vertebrae  they  pierce  the  diaphragm,  to  end  in  the  abdomen. 

(a)  The  great  splanchnic  nerve  (n.  splanchnicus  major)  arises  from  the 
gangiiated  cord  between  the  fifth  and  ninth  ganglia.  By  the  union  of  several 
irregular  strands  a  nerve  of  considerable  size  is  formed,  which  descends  in  the 
posterior  mediastinum,  and  piercing  the  crus  of  the  diaphragm,  joins  at  once  the 
upper  end  of  the  semilunar  ganglion  of  the  solar  plexus.  In  its  course  in  the 
thorax  the  great  splanchnic  ganglion  (g.  splanchnicum)  is  formed  upon  the  nerve. 
It  is  more  prominent  in  the  foetus  than  in  the  adult.  From  both  nerve  and  ganglion 
branches  arise  in  the  thorax  for  the  supply  of  the  oesophagus  and  descending 
thoracic  aorta  (Fig.  544). 

(b)  The  small  splanchnic  nerve  (n.  splanchnicus  minor)  arises  from  the  gangiiated 
cord  opposite  to  the  ninth  and  tenth  ganglia.  It  passes  over  the  bodies  of  the 
lower  thoracic  vertebrae,  pierces  the  diaphragm  near  or  along  with  the  great 
splanchnic  nerve,  and  ends  in  the  solar  plexus  {aortico-renal  ganglion). 

(c)  The  least  splanchnic  nerve  (n.  splanchnicus  imus)  arises  from  the  last 
thoracic  ganglion  of  the  sympathetic,  or  it  may  be  a  branch  of  the  smaller 
splanchnic  nerve.     It  pierces  the  diaphragm,  and  ends  in  the  renal  plexus. 


THE  LUMBAE  PAET  OF  THE  SYMPATHETIC  COED. 

The  lumbar  part  of  the  sympathetic  cord  is  placed  upon  the  bodies  of  the 
lumbar  vertebra,  internal  to  the  origins  of  the  psoas  muscle,  and  in  front 
of  the  lumbar  vessels.  It  is  connected  with  the  thoracic  portion  of  the  cord  by  an 
attenuated  commissural  cord,  which  either  pierces  or  passes  behind  the  diaphrao'm. 
It  is  continuous  below  with  the  sacral  portion  of  the  cord  by  a  commissure,  which 
passes  behind  the  common  iliac  artery.  It  is  joined  by  medullated  fibres  (white 
rami  communicantes)  from  the  first  two  lumbar  spinal  nerves,  and  it  contains  as 
well  medullated  fibres  continued  down  from  the  lower  part  of  the  thoracic 
gaugliated  cord,  and  derived  from  the  visceral  branches  (white  rami  com- 
municantes) of  the  lower  thoracic  nerves.  This  part  of  the  gaugliated  cord  is 
characterised  by  great  irregularity  in  the  numljer  of  the  ganglia.  They  are  usually 
four  in  number,  but  there   are  frequently  more  (up  to  eight) ;  and  in   extreme 


THE  SACBAL  PAET  OF  THE  GANGLIATED  COED. 


711 


cases  fusion  may  occur  to  such  an  extent  that  the  separation  of  individual  ganglia 
becomes  impossible. 

White  rami  communicantes. — The  first  two  (or  three)  lumbar  spinal  nerves 
possess  visceral  branches  which  form 
white  rami  communicantes  joining 
the  upper  lumbar  ganglia  or  the 
gangliated  cord.  These  nerves 
form  the  lower  limit  of  the  thoracic- 
lumbar  visceral  branches  of  the 
spin;il  nerves.  They  comprise  vaso- 
motor fibres  (for  the  genital  organs), 
and  motor  fibres  for  the  bladder  and 
uterus. 

Central  Communicating 
Branches.  —  Gray  rami  communi- 
cantes pass  from  the  gangliated  cord 
to  the  anterior  primary  divisions 
of  the  lumbar  nerves  in  an  ir- 
regular manner.  One  ramus  may 
divide  so  as  to  supply  branches  to 
two  adjacent  spinal  nerves ;  or  a 
spinal  nerve  may  be  joined  by  two 
to  five  separate  gray  rami  from  the 
gangliated  cord. 

The  rami  course  beneath  the 
origin  of  the  psoas  magnus  muscle 
and  over  the  bodies  of  the  vertebrae. 
Gray  rami  sometimes  pierce  the 
fibres  of  the  psoas  muscle. 

Peripheral  Branches  of  Dis- 
tribution.— From  the  lumbar  gan- 
gliated cord  numbers  of  small 
branches  arise  irregularly,  and 
pass  inwards  to  supply  the  ab- 
dominal aorta,  reinforcing  the 
aortic     plexus     (from     the     solar 


plexus). 


Fig.  545. — The  Lumbar  Portion  of  the  Sympathetic 
Gangliated  Cord  and  Lumbar  Plexus.  (From  a  dissection.) 

T.ll,  T.12,  L.l,  L.2,  L.3,  L.4,  L.5,  Anterior  primary  divisions 
of  spinal  nerves,  with  -white  and  gray  i-ami  communicantes. 
THE    SACRAL    PART    OF    THE  ^>''  '^y™P'''*'^^*^''''^Sangliated  cord  ;  Va,  Vagus  nerve  ;  G.S,  Great 

splanchnic  nerve,  joining  semilunar  ganglion  ;  S.R.C,  Supra- 
renal capsule  and  plexus  ;  R.  PI,  Renal  plexus  ;  Ao.Pl, 
Aortic  plexus  ;  S.  M,  Superior  mesenteric  plexus  ;  I.M, 
Inferior  mesenteric  plexus;  Hy.Pl,  Hypogastric  plexus; 
Q,  Nerves  to  quadratus  lumborura  ;  I.H,  Ilio-hypogastric 
nerve  ;  I.I,  Ilio-inguinal  nerve  ;  G.C,  Genito-crural  nerve  ; 
E.C,  External  cutaneous  nerve  ;  A.C,  Anterior  crural  nerve  ; 
Ace.  Obt,  Accessory  obturator  nerve  ;  Obt,  Obturator  nerve 
4,  5,  Lumbo-sacral  cord. 


GANGLIATED  CORD. 


The  sacral  part  of  the  gan- 
gliated cord,  like  the  cervical  and 
lower  lumbar  portions  of  this 
system,  receives  no  white  rami 
communicantes  from  the  spinal 
nerves.  The  visceral  branches  (pelvic  splanchnic)  of  the  third,  and  usually,  also, 
the  second  or  fourth  sacral  nerves,  enter  the  pelvic  plexus  without  being  directly 
connected  with  the  gangliated  cord.  These  nerves,  however,  are  to  be  regarded  as 
homologous  with  the  white  rami  communicantes  of  the  thoracico-lumbar  nerves 
{abdominal  splanchnic).  They  convey  to  the  pelvic  viscera — (1)  motor  and 
inhibitory  fibres  for  rectum,  uterus,  and  bladder,  (2)  vaso-dilator  fibres  for  the 
genitals,  and  (3)  secretory  fibres  for  the  prostate  gland. 

This  portion  of  the  cord  is  placed  in  front  of  the  sacrum,  internal  to  the  anterior 
sacral  foramina.  It  is  connected  above  by  a  commissural  cord  with  the  lumbar 
portion  of  the  sympathetic,  and  below  it  ends  in  a  plexiform  union  over  the  coccyx 
with  the  cord  of  the  other  side,  the  two  being  frequently  connected  by  the 
ganglion  impar  or  coccygeal  ganglion.     The  number  of  ganglia  is  variable ;  there  are 


712  THE  NERVOUS  SYSTEM. 

commonly  four.  Thev  are  of  small  size,  gradually  diminishing  from  above  down- 
wards. 

Central  communicating  branches  arise  irregularly  in  the  form  of  gray  rami 
communicantes  from  the  sacral  ganglia,  and  join  the  anterior  primary  divisions  of 
the  sacral  and  coccygeal  nerves. 

Peripheral  Branches  of  Distribution. — (1)  Visceral  branches  of  small  size  arise 
from  the  upper  part  of  the  gangliated  cord,  and  pass  inwards  to  join  the  pelvic 
plexus  (see  below). 

(2)  Parietal  branches,  also  of  small  size,  ramify  over  the  front  of  the  sacrum,  and 
form,  in  relation  to  the  middle  sacral  artery,  a  plexiform  union  with  branches  from 
the  gangliated  cord  of  the  other  side. 

SYMPATHETIC  PLEXUSES. 

It  has  already  been  seen  that  the  peripheral  branches  of  the  sympathetic 
gangliated  cord  throughout  its  length  are  characterised  by  forming  or  joining 
plexuses  in  their  neighbourhood. 

The  cervical  sympathetic  ganglia  and  nerves  give  rise  to  the  carotid  and 
cavernous  plexuses ;  the  external  carotid,  pharyngeal,  thyroid,  vertebral,  and 
subclavian  plexuses ;  and  they  send  important  branches  to  the  cardiac  plexuses 
(described  along  with  the  pneumogastric  nerve). 

The  thoracic  ganglia  send  branches  to  join  the  pulmonary  and  cesophageal 
plexuses  (described  along  with  the  pneumogastric  nerve).  They  form  plexuses  on 
the  thoracic  aorta,  and  by  means  of  the  splanchnic  nerves  they  form  the  chief 
source  of  the  solar  plexus. 

The  Solar  and  Pelvic  Plexuses. 

These  great  plexuses  serve  to  distribute  nerves  to  the  viscera  and  vessels  of  the 
abdominal  and  pelvic  cavities.  Taken  together  they  include  three  plexuses — the 
solar  plexus,  hypogastric  plexus,  and  the  pelvic  plexuses.  They  ariC  constituted 
by  peripheral  branches  of  the  lower  thoracic,  lumbar,  and  upper  sacral  parts  of  the 
gangliated  cord  of  the  sympathetic ;  and  they  are  related  to  the  central  nervous 
system  by  means  of  the  visceral  branches  (white  rami  communicantes)  of  the  lower 
thoracic  and  upper  lumbar  nerves  on  the  one  hand,  and  by  the  visceral  branches 
of  the  second  and  third,  or  third  and  fourth  sacral  nerves,  on  the  other  hand.  The 
thoracico-lumbar  series  join  the  sympathetic  cord,  and  reach  the  solar  plexus 
mainly  through  the  splanchnic  nerves,  and  to  a  lesser  extent  through  the  lumbar 
gangliated  cord.  The  sacral  series  enter  the  pelvic  plexus  without  connexion  with 
the  sympathetic  cord.  The  hypogastric  plexus  serves  as  a  connecting  link  between 
the  solar  and  pelvic  plexuses. 

The  solar  plexus  lies  on  the  posterior  abdominal  wall  in  relation  to  the 
abdominal  aorta  and  behind  the  stomach.  It  is  composed  of  three  elements  :  the 
cceliac  plexus  surrounding  the  origin  of  the  coeliac  axis  between  the  crura  of  the 
diaphragm,  and  two  semilunar  ganglia,  each  lying  on  the  corresponding  crus  of 
the  diaphragm,  and  overlapped  by  the  suprarenal  capsule,  and  on  the  right  side 
Vjy  the  inferior  vena  cava.  The  plexus  is  continuous  with  subordinate  plexuses, 
diaphragmatic,  suprarenal,  renal,  superior  mesenteric  and  aortic ;  and  by  means  of 
the  hypogastric  nerves  the  aortic  plexus  becomes  continued  into  the  hypogastric 
plexus,  which  again  forms  the  chief  origin  of  the  pelvic  plexuses. 

The  semilunar  ganglia  constitute  the  chief  ganglionic  centres  in  the  solar 
plexus.  They  are  irregular  in  form.  They  are  often  partially  subdivided,  and  one 
detached  portion  at  the  lower  end  is  named  the  aortico-renal  ganglion.  Other  small 
scattered  masses  of  cells  are  present  in  the  cceliac  plexus  (ganglia  coeliaca).  At 
the  uj)per  end  the  semilunar  ganglion  receives  the  great  splanchnic  nerve.  The 
aortico-renal  ganglion  at  its  lower  end  receives  the  smaller  splanchnic  nerve. 
Branches  from  the  ganglion  radiate  in  all  directions — inwards  to  join  the  coeliac 
plexus,  upwards  to  form  the  diaj)hragmatic  plexus,  outwards  to  the  suprarenal 
plexus,  downwards  to  the  renal,  superior  mesenteric,  and  aortic  plexuses. 


THE  SOLAE  AND  PELVIC  PLEXUSES. 


713 


The  coeliac  plexus  forms  a  considerable 
plexiform  mass  surrounding  the  coeliac  axis.  It 
•consists  of  a  dense  meshwork  of  fibres  with 
ganglia  intermingled  (g.  coeliaca),  joined  by 
numerous  branches  from  the  semilunar  ganglion 
on  each  side,  and  by  branches  from  the  right 
pneumogastric  nerve.  It  is  continuous  below 
with  the  superior  mesenteric  and  aortic  plexuses. 
Investing  the  cceliac  axis,  it  forms  subsidiary 
plexuses  which  accompany  the  branches  of 
the  artery.  The  coronary  plexus  supplies 
branches  to  the  oesophagus  and  stomach ;  the 
hepatic  plexus  supplies  branches  to  the  liver  and 
gall-bladder,  stomach,  duodenum,  and  pancreas  ; 
and  the  splenic  plexus  sends  offsets  to  the  spleen, 
pancreas,  and  stomach. 

Subordinate  plexuses  are  formed  on  the 
aorta  and  its  branches  by  nerves  derived  from 
the  solar  plexus  (semilunar  ganglia  and  coeliac 
plexus). 

a.  The  diaphragmatic  plexus  consists  of 
fibres  arising  from  the  semilunar  ganglion,  and 
accompanies  the  inferior  phrenic  artery.  Besides 
supplying  the  diaphragm,  it  gives  branches  to 
the  suprarenal  plexus,  and  (on  the  right  side) 
to  the  inferior  vena  cava,  (on  the  left  side)  to 
the  oesophagus.  It  communicates  on  each  side 
with  the  phrenic  nerve.  At  the  junction  of  the 
plexus  and  the  phrenic  nerve  of  the  right  side 
a  ganglion  is  formed  (diaphragmatic  ganglion). 

h.  The  suprarenal  plexus  is  of  most  con- 
siderable size.  It  is  mainly  derived,  from 
branches  of  the  semilunar  ganglion,  reinforced 
by  nerves  from  the  lower  part  of  the  solar  plexus 
which  stream  outwards  on  the  capsular  arteries. 
It  is  joined  by  branches  from  the  diaphragmatic 
plexus  above  and  from  the  renal  plexus  below. 
The  nerves  enter  the  substance  of  the  suprarenal 
capsule. 

c.  Therenalplexusisderivedfrom(l)  branches 
of  the  semilunar  ganglion,  and  (2)  fibres  from 
the  aortic  plexus,  extending  outwards  along  the 
renal  artery  to  the  hilum  of  the  kidney.  It 
receives  also  the  least  splanchnic  nerve,  and  is 
connected  by  numerous  branches  to  the  supra- 
renal plexus. 

d.  The  superior  mesenteric  plexus  is  insepar- 
able above  from  the  cceliac  plexus,  and  is  joined 
on  either   side  by  fibres  from  the   semilunar  j..^^,     ^^^^___-^^^    Ahraxgement  '  ..f    the 

ganglion.        It    is    continuous    below    with    the  Sympathetic  System  in  the   Thorax, 

aortic  plexus.     A  separate  detached  ganglionic         abdomen,  and  Pelvis. 

mass  (superior  mesenteric  ganglion)  is  present  in  '^•^■\^'.  h^'^}  ^-.^'^  '  Co.  Anterior  primary 

^  '        ^  divisions  01  spinal  nerves,  coiniectea  to  tlie 

gangliated  cord  of  the  sympathetic  by 
rami  communicantes,  white  (double  lines)  and  gray  (single  lines)  ;  Oes,  ffisophagus  and  esophageal 
lile.xus  ;  Ao,  Aorta  and  aortic  plexus  ;  Va,  Vagus  nerve  joining  oesophageal  plexus  ;  S.  1,  Great  splanchnic 
nerve  ;  X,  Great  splanchnic  ganglion  ;  S.  2,  Small  splanchnic  nerve  ;  S.3,  Least  splanchnic  nerve  ;  Co, 
Coronary  artery  and  plexus  ;  Spl,  Splenic  artery  and  plexus  ;  H,  Hepatic  artery  and  plexus  ;  S.L,  Semi- 
lunar ganglion  ;  Di,  Diaphragm  ;  S.R,  Suprarenal  capsule  ;  Re,  Renal  artery  and  plexus  ;  S.M,  Superior 
mesenteric  artery  and  plexus  ;  Sp,  Spermatic  artery  and  plexus  ;  I.M,  Inferior  mesenteric  artery  and 
plexus  ;  Hy,  Hypogastric  nerves  and  plexus  ;  Rec,  Rectal  plexus  ;  Ut,  Uterine  plexus  ;  Ves,  Vesical 
plexus  ;  V.V.V,  Visceral  branches  from  sacral  nerves. 


714  THE  NERVOUS  SYSTEM. 

the  plexus.  Accompanying  the  superior  mesenteric  artery  the  plexus  forms 
subordinate  plexuses  around  the  branches  of  the  vessel.  The  plexuses  in  the 
mesentery  at  first  surround  the  intestinal  arteries,  but  near  the  intestine  they 
form  fine  plexuses  between  the  layers  of  the  mesentery,  from  which  branches  pass 
to  the  wall  of  the  gut.  This  plexus  supplies  the  small  intestine,  caecum,  vermiform 
appendix,  ascending  and  transverse  portions  of  the  colon. 

e.  The  aortic  plexus  is  the  continuation  downwards  of  the  solar  plexus  around 
the  abdominal  aorta.  It  is  continuous  above  with  the  superior  mesenteric  and 
solar  plexuses ;  it  is  reinforced  by  the  peripheral  branches  of  the  lumbar  gangliated 
cord  of  the  sympathetic ;  and  it  is  connected  with  the  hypogastric  plexus  below 
by  the  hypogastric  nerves.  Besides  investing  and  supplying  the  aorta,  the  plexus 
contributes  to  various  subordinate  plexuses  on  the  branches  of  the  artery.  It 
contributes  to  the  suprarenal  and  renal  plexuses,  and  it  gives  rise  to  the  spermatic 
or  ovarian  and  the  inferior  mesenteric  plexuses. 

The  spermatic  plexus  invests  and  accompanies  the  spermatic  artery.  It  is 
derived  from  the  aortic  plexus,  and  receives  a  contribution  from  the  renal  plexus. 
It  supplies  the  spermatic  cord  and  testicle. 

The  ovarian  plexus  in  the  female  arises  like  the  spermatic  plexus.  It  accom- 
panies the  ovarian  artery  to  the  pelvis,  and  supplies  the  ovary,  broad  ligament,  and 
Fallopian  tube.  It  forms  communications  in  the  broad  ligament  with  the  uterine 
plexus  (from  the  pelvic  plexus),  and  sends  fibres  to  the  uterus. 

The  inferior  mesenteric  plexus  is  a  derivative  from  the  aortic  plexus,  prolonged 
along  the  inferior  mesenteric  artery.  It  forms  subordinate  plexuses  on  the 
branches  of  the  artery  (colic,  sigmoid,  and  superior  hsemorrhoidal),  and  is  dis- 
tributed to  the  descending  colon,  iliac  colon,  pelvic  colon,  and  upper  part  of  the 
rectum. 

The  hypogastric  nerves  form  the  continuation  of  the  aortic  plexus  into  the 
pelvic  cavity.  They  consist  of  numerous  plexiform  bundles  of  nerve-fibres  which 
descend  along  the  front  and  back  of  the  bifurcation  of  the  aorta  and  the  origiii_of 
the  common  iliac  arteries,  and  over  the  sacral  promontory,  where,  becoming  in- 
extricably mingled,  they  constitute  the  hypogastric  plexus. 

The  hypogastric  plexus  is  continued  downwards  in  front  of  the  sacrum  on  either 
side  of  the  rectum,  and  ends  in  the  pelvic  plexuses. 

The  pelvic  plexuses  are  formed  by  the  separation  of  the  hypogastric  plexus 
into  two  halves  on  either  side  of  the  recturh.  Each  is  joined  by  fibres  from  the 
upper  part  of  the  sacral  portion  of  the  gangliated  cord  of  the  sympathetic,  and  by 
the  visceral  branches  (white  rami  communicantes)  from  the  second  and  third  or 
third  and  fourth  sacral  nerves.  Accompanying  the  internal  iliac  artery  and  its 
branches  each  pelvic  plexus  gives  off  subordinate  plexuses  for  the  pelvic  viscera. 

a.  The  hsemorrhoidal  plexus  supplies  the  rectum,  and  joins  the  superior  hsemor- 
rhoidal plexus  from  the  inferior  mesenteric  plexus. 

h.  The  vesical  plexus  accompanies  the  vesical  arteries  to  the  bladder-wall. 
Besides  supplying  the  muscular  wall  and  mucous  membrane  of  the  bladder,  it 
forms  subordinate  plexuses  for  the  lower  part  of  the  ureter,  the  vesicula  seminalis, 
and  the  vas  deferens. 

c.  The  prostatic  plexus  is  of  considerable  size.  It  is  placed  on  either  side  of 
the  gland,  and  in  addition  to  supi)lying  its  substance  and  the  prostatic  urethra,  it 
sends  offsets  to  the  neck  of  the  bladder  and  the  vesicula  seminalis.  It  is  continued 
forwards  on  each  side  to  form  the  cavernous  plexus  of  the  penis  (plex.  cavernosus 
penis).  Bundles  of  nerves  pierce  the  layers  of  the  triangular  ligament,  and  after 
supplying  the  membranous  urethra  at  the  root  of  the  penis,  give  off  branches  which 
enter  and  supply  the  corpus  cavernosum.  The  cavernous  nerves  communicate  with 
branches  of  the  pudic  nerve,  and  give  offsets  to  the  corpus  spongiosum  and  the 
spongy  portion  of  the  urethra. 

d.  The  uterine  plexus  passes  upwards  for  a  short  distance  with  the  uterine  artery 
between  the  layers  of  the  broad  ligament,  and  is  then  distributed  to  the  surfaces 
and  suljstance  of  the  organ.  It  communicates  between  the  layers  of  the  broad 
ligament  with  the  ovarian  plexus. 

The  vaginal  plexus  is  formed  mainly  by  the  visceral  branches  of  the  sacral 


DEVELOPMENT  OF  THE  SYMPATHETIC  SYSTEM. 


715 


nerves  entering  the  pelvic  plexus.  It  supplies  the  wall  and  mucous  membrane 
of  the  vagina  and  urethra,  and  provides  a  cavernous  plexus  i'or  the  clitoris  (plex. 
cavernosus  clitoridis).  The  uterine  and  vaginal  plexuses  of  the  female  correspond 
to  the  prostatic  plexus  of  the  male. 


DEVELOPMENT  OF  THE  SYMPATHETIC  SYSTEM. 

There  are  two  diametrically  opposite  views  of  the  mode  of  development  of  the  sym- 
pathetic system. 

In  birds  and  mammals  the  first  rudiment  of  tlie  sympathetic  cord  occurs  in  the 
formation  of  a  longitudinal  unsegmented  column  of  mesoblastic  cells  (which  stain  more 
deeply  than  the  mesoblast  in  which  they  lie)  on  either  side  of  the  aorta,  and  coterminous 
with  it.  This  column  of  cells  becomes  joined  at 
an  early  stage  by  the  visceral  branches  of  the 
spinal  nerves  which  grow  inwards  from  the  main 
nerve  trunks  into  the  splanchnic  area,  and  result 
from  the  division  of  the  nerve  into  somatic  and 
visceral  parts.  These  visceral  branches  constitute 
the  white  rami  communicantes.  They  receive 
contributions  usually  from  both  dorsal  and  ventral 
roots,  and  gradually  approaching  the  above-men- 
tioned column  of  mesoblastic  cells,  they  become 
intimately  associated  with  the  cells.  In  some 
cases  fibres  of  the  visceral  nerves  pass  over  the 
cellular  column  into  the  splanchnic  area  without 
connexion  with  it  (Fig.  548).  By  the  junction  of 
these  visceral  nerves  with  the  cells  of  the  column, 
certain  cells  persist  and  produce  the  ganglia. 
The  intervening  portions  of  the  column,  by 
changes  in  the  cells,  and  by  the  addition  possibly 
of  fibres  belonging  to  the  visceral  nerves,  give 
rise  to  the  commissural  cords.  The  cellular 
column,  besides  producing  the  gangiiated  cord, 
by  the  further  growth  of  its  cells  and  their  ex- 
tension centrally  and  peripherally,  produces  the 
gray  rami  communicantes,  parts  of  the  peripheral 
branches,  and  the  peripheral  (collateral  and 
terminal)  ganglia,  as  well  as  the  medullary 
portion  of  the  suprarenal  capsule.  The  cervical, 
lower  lumbar,  and  sacral  portions  of  the  sym- 
pathetic gangiiated  cord  are  secondary  extensions 
from  the  more  primitive  condition,  gradually 
growing  upwards  and  downwards  along  the  main 
vessels.  These  portions  of  the  system  are  not 
])rovided  with  white  rami  commxmicantes.  The 
ganglia  of  the  sympathetic  assume  their  seg-  Sy, 
men  ted  appearance  (1)  from  the  persistence  of 
the  primitive  cells  and  their  connexion  with  the 
spinal  nerves  by  means  of  the  white  and  gray 
rami  communicantes,  and  (2)  from  the  way  in  which  the  primitive  column  is  moulded 
by  the  surrounding  structures  (bones,  segmental  arteries,  etc.) 

Another  account  of  the  development  of  the  sympathetic  system,  supported  by  high 
authority,  describes  the  gangiiated  cord  as  an  outgrowth  of  the  dorsal  ganglia  of  the 
spinal  nerves,  /[t  is  said  that  each  ganglion  gives  off  a  bud  at  its  lower  end,  which, 
growing  inwards  into  the  splanchnic  area,  becomes  attached  to  the  trunk  of  the  spinal 
nerve  just  beyond  the  union  of  the  dorsal  and  ventral  roots.  The  bud  still  extending 
inwards  into  the  splanchnic  area,  remains  associated  with  the  nerve  by  an  attenuated 
stalk.  These  buds,  it  is  said,  become  the  ganglia,  which,  after  reaching  their  permanent 
place  in  the  splanchnic  area,  are  supposed  to  extend  upwards  and  downwards  so  as  to 
coalesce  and  form  a  beaded  chain  of  ganglia.  The  stalks  connecting  the  ganglia  with  the 
spinal  nerves  become  the  white  rami  communicantes.  This  mode  of  development  does 
not  satisfactorily  account  for  several  important  featvires  of  the  sympathetic  system — the 
development  of  those  parts  of  the   gangiiated   cord  which  possess  no   white    rami,   the 


Fig.   547. — The  Developmknt  op  the 
Sympathetic  Gangliated  Cord. 

Sympathetic  cord  ;  Spl,  Splanchnic  branches 
of  spinal  nerves  (white  rami  communi- 
cantes) ;  V.  S,  Vertebral  segments  ;  D.G, 
Dorsal  ganglia. 


16 


THE  NEEVOUS  SYSTEM. 


absence  of  a  real  segmental  character  in  the  cord  (remai'kably  shown  in  the  foetus),  and 
the  constancy  of  continuit}'  in  the  gangliated  cord.     No  instance  is  recorded  of  a  hiatus 

between  two  ganglia.  It  is  a 
tempting  view  on  the  other  hand, 
as  it  ascribes  to  the  one  germinal 
layer  (epiblast)  the  formation  of  all 
the  elements  of  the  nervous  system, 
and  it  brings  the  sympathetic 
ganglia  into  serial  homology  with 
isolated  ganglia  on  the  cranial  nerves 
(e.g.  the  ciliary,  spheno-palatine,  and 
otic,  on  the  trigeminal  nerve). 

The  Morphology  of  the  Sym- 
pathetic System, 

From  a  consideration  of  its  struc- 
ture, functions,  and  development,  there 
appear  to  be  two  separate  structures 
represented  in  the  sympathetic  nervous 
system — the  spinal  and  the  sympathetic 
elements.  The  structure  of  the  system 
presents  a  union  of  two  distinct  elements 
— fibres  of  cerebro-sj)inal  origin  and 
"  sympathetic  "  cells  and  fibres.  While 
the  function  of  the  gangliated  cord  and 
its  branches  seems  to  be  absolutely  de- 
j)endentuponthecerebro-spinalnervous 

uis  connnunieans  (Spl)  ;  (a)  a  portion  of  the  ramus  join-  '^'^^"'',11  ''  ^^^t^^'l.  ^1'^^  ^^t  '''^^'  ^"""^ 
mg  the  ganglion;  (/3)  fibres  passhig  over  the  cord,  acconi-  fibres  of  the  sympathetic  system  possess 
pauiecl  by  a  stream  of  cells  ;  (7)  continuous  with  those  of  ^  ^^.^^^  activity  apart  from  their  con- 
the  gaugliou  ;  (Ao)  Aorta.  nexionwdth  the  central  nervous  system. 

In  the  development  of  the  sympathetic 
it  is  at  least  highly  probable  that  a  mesoblastic  rudiment  or  precursor  forms  the  basis  of  the 
sympathetic  system,  which  is  secondarily  joined  by  nerve-fibres  from  the  roots  of  the  spinal 
nerves. 

Morphologically  this  part  of  the  nervous  system  is  essentially  a  longitudinal  cord  or  column, 
associated  with  involuntary  muscles  and  glandular  tissues,  and  particularly  related  to  the  organs 
in  the  splanchnic  area.  Like  other  longitudinal  structures  in  the  body,  and  especially  like  the 
organs  of  the  splanchnic  area,  tlie  symi^athetic  system  is  not  truly  segmental.  The  gangliated 
cord  is  only  quasi-segmental,  the  segmentation  being  attriliutable  to  its  junction  with  the 
visceral  brandies  of  the  spinal  nerves.  The  peripheral  branches  from  the  gangliated  cord  are 
not  segmental  ;  even  the  gray  rami  are  not  properly  metameric,  but,  like  the  ganglia,  assume  a 
segmental  character  in  consequence  of  their  connexions  with  the  spinal  nerves. 

The  phylogenetic  relation  of  the  sympathetic  and  the  cerebro-spinal  elements  in  the  system 
it  is  impossible  to  determine.  It  may  Ije  that  the  .symi^athetic  system  is  the  representative  of 
an  ancient  architecture  independent  of  the  cerebro-spinal  nervous  system,  the  materials  of  which 
are  utilised  for  a  more  modern  nervous  system  ;  or  it  may  be  that  the  correlation  of  spinal 
nerves  and  sympathetic  are  both  the  consequences  of  the  formation  of  new  organs  and  structures 
in  the  splanchnic  area.  Examined  in  every  light,  it  possesses  features  w^hich  effectually  differ- 
entiate it  from  the  cerebro-spinal  system,  although  it  has  become  inextricably  united  with  it 
and  subservient  to  it. 


Showiuo 


-Section  through  the  Sympathetic  Gangliated 
Cord  of  an  Embryo. 
the    connexion   with    the    ganglion    (Sy)    of   the   white 


THE   ORGANS   OF   SENSE   AND   THE 
INTEGUMENT. 

By  Robert  Howden. 

THE  NOSE. 

The  nose  constitutes  the  peripheral  part  of  the  organ  of  smell  (organon  olfactus), 
since  to  the  upper  portion  of  its  mucous  lining  the  branches  of  the  olfactory  nerve 
are  distributed.  It  consists  of  an  external  portion,  the  outer  nose,  which  projects 
from  the  face,  and  of  an  internal  part,  or  cavum  nasi,  which  is  divided  by  a  vertical 
septum  into  right  and  left  cavities  or  fossa?. 

The  outer  nose,  or  nasus  exteruus,  forms  a  more  or  less  triangular  pyramid,  of 
which  the  upper  angle  is  termed  the  root  (radix  nasi),  and  is  usually  separated  from 
the  glabella  by  a  depression,  while  its  base  (basis  nasi),  directed  downwards,  is  per- 
forated by  the  apertures  of  the  nostrils  (anterior  nares).  Its  free  angle  is  named 
the  point  (apex  nasi),  and  the  anterior  border,  joining  root  and  point,  is  termed  the 
dorsum  nasi ;  the  vipper  part  of  the  dorsum  is  supported  by  the  nasal  bones,  and  is 
named  the  bridge.  The  lateral  aspects  of  the  nose  are  continuous  with  the  eyelids 
above  and  with  the  cheeks  below,  forming  with  the  latter  a  varying  angle.  Each 
lateral  surface  ends  inferiorly  in  a  mobile  and  expanded  portion,  the  ala  nasi,  which 
forms  the  outer  boundary  of  the  anterior  nares,  and  is  limited  above  by  a  furrow, 
the  alar  sulcus.  The  skin  covering  the  nose  is  thin  and  movable  over  the  root,  but 
thick  and  adherent  over  the  point  and  ake,  where  it  contains  numerous  large 
sebaceous  glands. 

The  arterial  supply  of  the  outer  nose  is  derived  from  the  facial  and  ophthalmic  arteries,  and 
its  veins  drain  themselves  into  the  facial  and  ophthalmic  trunks.  Its  principal  lymphatic  vessels 
follow  the  course  of  the  facial  vein  and  open  into  the  submaxillary  lymphatic  glands.  From  the 
root  of  the  nose  one  or  two  vessels  curve  lack  wards  above  the  orbit  to  reach  the  upper  parotid 
glands,  Avhile  a  third  groui)  runs  below  the  orbit  to  the  lower  parotid  glands.  The  facial  nerve 
supplies  its  muscles,  while  the  sensory  nerves  for  the  skin  are  the  infratrochlear  and  nasal  branches 
of  the  ophthalmic  nerve  and  the  infraorbital  branch  of  the  sujjerior  maxillary  nerve. 

The  nose  presents  great  variety  as  to  its  size  and  shape,  and  certain  well-detined  tyj^es,  such  as 
aqiiiliue,  Grecian,  etc.,  are  described.  The  relation  which  its  breadth,  measured  across  the  alae, 
bears  to  its  length,  measured  from  root  to  point,  is  termed  the  nasal  index,  and  is  expressed  thus  : 

greatest  breadth  x  100 
greatest  length. 

In  white  races  this  index  is  below  70  (leptorhines) ;  in  yellow  races,  between  78  and  85 
(mesorhines) ;  and  in  black  races,  aljove  85  (platyrhines). 

CAETILACIES  OF  THE  NOSE. 

In  addition  to  the  bony  skeleton  of  the  nose  there  are  five  chief  cartilages 
(cartilagiues  nasi)  which  contribute  to  the  production  and  maintenance  of  its 
shape.  These  are  named — (a)  the  cartilage  of  the  septum,  and  (b)  the  upper  and 
lower  lateral  cartilages  on  each  side. 

The  cartilage  of  the  septum  (cartilago  septi  nasi.  Fig.  549)  is  of  an  irregularly 
quadrilateral  form.  Its  postero-superior  edge  is  attached  to  the  mesethmoid ;  its 
postero-inferior  margin  to  the  vomer  and  intermaxillary  crest.     Its  antero-superior 

717 


■18 


THE  OEGANS  OF  SENSE. 


border  is  thick,  and  is  fixed  above  to  the  back  of  the  internasal  suture ;  below  the 
level  of  the  nasal  bones  it  is  continued,  on  either  side,  into  the  upper  lateral 
cartilages,  which  may  be  looked  upon  as  its  wing-like  expansions.     The  lower  part 


Frontal  air-sinus 


Cartilage  of  septum- 


Palate  bone 


Fig.  549. — Lateral  View  op  Nasal  Septum. 

of  this  ,  border  is  separated  by  a  fissure  from  the  upper  lateral  cartilages,  and 
extends  downwards  between  the  inferior  lateral  cartilages,  to  which  it  is  attached 
by  fibrous  tissue.  In  this  fibrous  tissue  a  small  sesamoid  cartilage  is  usually 
seen  on  each  side  of  the  middle  line.  Its  antero-inferior  border  is  short,  and  is 
attached  by  fibrous  tissue  to  the  mesial  plates  of  the  lower  lateral  cartilages, 
while  its  anterior  angle  is  rounded  and  does  not  reach  as  far  as  the  point  of  the 
nose.  The  lowest  part  of  the  nasal  septum  is  not  formed  by  the  septal  cartilage, 
but  by  the  mesial  plates  of  the  lower  lateral  cartilages  and  by  the  integument,  and, 
being  freely  movable,  is  termed  the  septum  mobile  nasi.  The  cartilage  of  the  septum 
may  be  prolonged  backwards  (especially  in  children)  as  a  tongue-like  process  into 
the  angle  between  the  vomer  and  ethmoid.  This  process,  varying  in  width  from 
4-6  mm.,  is  named  the  processus  sphenoidalis  septi  cartilaginei,  and  sometimes  reaches 
as  far  as  the  body  of  the  sphenoid. 

Lying  along  the  lower  edge  of  the  cartilage  of  the  septum,  and  best  seen  on 
making  a  coronal  section  of  the  nose,  are  a  couple  of  elongated  cartilaginous  strips. 
Each  measures  from  6-12  mm.  in  length,  is  attached  to  the  vomer,  and  is  named 
the  vomerine  cartilage  Tcartilago  vomeronasalis,  Jacobsoni). 

The  upper  lateral  cartilage  (cartilago  nasi  lateralis,  Figs.  550,  551)  is  triangular 
in  shape  and  situated  immediately  below  the  nasal  bone,  to  which  and  to  the 
superior  maxilla  its  thin  posterior  border  is  attached.  Its  anterior  edge  is  thick 
and  its  upper  part  is  directly  continuous  with  the  cartilage  of  the  septum.  Its  lower 
margin  is  joined  by  fibrous  tissue  to  the  upper  edge  of  the  lower  lateral  cartilage. 

The  lower  lateral  cartilage  (cartilago  ularis  major,  Figs.  550,  551,  552)  encircles 
the  anterior  part  of  the  nostril  and  assists  in  keeping  it  open.  It  consists  of  two 
plates,  outer  and  inner,  which  are  continuous  with  each  other  in  a  rounded  angle 
at  the  point  of  the  nose.  The  outer  plate,  or  crus  laterale,  is  oval  in  shape  and.  is 
attached  to  the  upper  lateral  cartilage  and  to  the  superior  maxilla  by  fibrous  tissue. 


NASAL  FOSSiE. 


719 


Continuous  with  its  postero-superior 
angle  are  two  or  three  small  carti- 
laginous pieces  (cartilagines  alares 
minores),  while  sometimes  a  horizon- 
tal furrow  cuts  off  a  narrow  linear 
part  from  its  upper  aspect.  The 
lower  edge  of  the  outer  plate  does 
not  descend  as  far  as  the  lateral 
boundary  of  the  nostril,  the  ala  being 
devoid  of  cartilage  and  composed  f^^^l^^'^ 
merely  of  fatty  and  connective 
tissue  covered  by  skin.  The  inner 
plate,  or  crus  mediale  (Fig.  552), 
bounds  the  inner  aspect  of  the  nostril 
and  lies  in  the  septum  mobile  nasi, 
below  the  anterior  part  of  the  carti- 
lage of  the  septum.  The  mesial 
plates  of  the  two  cartilages  are  separ- 
ated in  front  by  a  notch  which 
corresponds  with  the  point  of  the 
nose,  and  each  curves  slightly  out- 
wards posteriorly  and  ends  in  a 
rounded  extremity. 

NASAL  FOSS^. 


I 


Fig. 


550. — Profile  View  of  the  Bony  and  Carti- 
laginous Skeleton  of  the  Nose. 


The   nasal  fossae  (Fig.  553)  are 

two  in  number  and  are  placed  one  on 

either  side  of  the  middle  line.     They 

extend   from    the   anterior   to    the 

posterior  nares  or  choanpe,  and    open  through  the  latter  into  the    naso-pharynx. 

Their  bony  boundaries  are  described  in    the  section  on  Osteology  (p.  173).     On 
--  -.,,  the  lateral  wall  of  each  are  found 

the  orifices  of  the  frontal,  eth- 
moidal, sphenoidal,  and  maxillary 
sinuses,  together  with  that  of  the 
nasal  duct. 

Immediately  above  the  aperture 
of  the  nostril  is  a  shghtly  ex- 
panded area,  the  vestibule  (vesti- 
bulum  nasi).  This  is  bounded 
externally  by  the  lower  lateral 
cartilage,  and,  internally,  by  the 
lower  part  of  the  septum,  and  is 
prolonged  towards  the  tip  of  the 
nose  as  a  small  pouch,  termed  the 
ventricle.  Partly  subdivided  by  a 
curved  ridge,  the  vestibule  is  lined 
by  skin  and  contains  hairs  and 
sebaceous  glands.  The  hairs,  or 
vibrissee,  springing  from  its  lower 
half,  are  stout  and  curved  down- 
wards to  guard  the  entrance  to  the 
nostril.  The  upper  part  of  the 
vestibule  is  smooth,  and  is  limited 
above  and  behind  by  a  slightly- 
marked  arched  prominence,  the 
limen  nasi,  beyond  which  the  fossa 


—  Xasal  bone 

N  asal  process  of 
suppi'ior  maxilla 


Uiiper  lateral 
cartilage 
C  irtila.ne  of 
septuiu 

Sesamoid 
caitilage 
Lower  lateral 
cartilage 
Crus  laterale 
Cms  mediale 


720 


THE  OEGANS  OF  SENSE. 


-  Ci  Us  mediiile 


y lateral 
j  cartilag 


Lower  edge  of 
— cartilage  of 
septum 


>_ Fatty  tissue  of 

ala  nasi 


Fig.  552. — Cartilages  of  Nose  from  Below. 


The  nasal  fossa  above  and  behind  the  vestibule  is  divided  into  two  parts,  viz, 
an  upper  or  olfactory,  and  a  lower  or  respiratory  region.  The  olfactory  part,  or  regio 
olfactoria,  is  a  narrow,  slit-like  cavity,  and  comprises  the  region  of  the  superior 

turbinated  bone,  together  with  a  correspond- 
ing portion  of  the  septum.  The  respiratory 
part,  or  regio  respiratoria,  is  expanded,  and 
includes  the  lower  and  remaining  parts  of 
the  fossa. 

Inner  Wall  or  Septum  Nasi  (Fig.  549). 
— Where  the  bony  septum  is  deficient, 
below  and  in  front,  the  gap  is  filled  by  the 
septal  cartilage.  Until  the  seventh  year 
the  nasal  septum  lies,  as  a  rule,  in  the 
mesial  plane,  but  after  this  age  is  very 
often  deflected  to  one  or  other  side — more 
frequently  to  the  right — the  deflection  being 
usually  greatest  along  the  line  of  junction  of  the  vomer  and  mesethmoid.  Deflec- 
tion of  the  septum  is  more  common  in  European  than  in  non-European  skulls — 
occurring  in  about  53  per  cent  of  the  former  and  in  about  28  per  cent  of  the  latter 
(Zuckerkandl,  Anatomic  der  Nasenhohle,  1892).  Associated  with,  or  apart  from, 
this  deviation,  lateral  crests  or  spurs  of  bone  are  found,  in  about  20  per  cent  of 
skulls,  projecting  from  the  septum  into  one  or  other  nasal  fossa.  In  the  floor  of 
the  fossa,  close  to  the  lower  edge  of  the  septal  cartilage  and  immediately^over  the 
incisive  foramen,  a  slight  depression,  the  recessus  naso-palatinus,  may  be  seen.  It 
is  directed  downwards  and  forwards,  and  indicates  the  position  of  the  communication 
which  originally 
existed  between 
the  nasal  and 
buccal  cavities. 
In  the  septum, 
a  little  above 
and  in  front 
of  this  depres- 
sion, is  a  minute 
orifice,  not  always 
rec  ognisable, 
from  which  a 
blind  pouch  ex- 
tends upwards 
and  backwards 
for  a  distance  of 
from  2  to  9  mm. 
This  is  the  rudi- 
mentary organ  of 
Jacobson  (oiga- 
non  vomero- 
nasale)  and  is 
supported  by  the 
vomerine  carti- 
lage. In  many  of  ^^"-  ^^3. 
the  lower  animals 

this  organ  is  well  developed  (Fig.  554),  and  probably  plays  a  part  in  tlie  sense  of 
smell,  being  lined  by  epithelium  similar  to  that  in  the  olfactory  part  of  the  nose 
and  snpp]i(;d  by  branches  of  tlie  olfactory  nerve. 

Outer  Wall  (Fig.  455). — Above  the  superior  turbinated  bone  is  a  narrowrece8s,the 
recessus  spheno-ethmoidalis,  into  the  posterior  part  of  which  the  sphenoidal  air- sinus 
opens.  The  superior  meatus  (meatus  nasi  superior)  is  a  short  oltlique  fissure,  directed 
downwards  and  backwards  under  cover  of  the  su])crior  turbinated  bone  ;  into  its 
antero-superior  portion  the  posterior  ethmoidal  cells  open  by  one  or  more  orifices. 


-Coronal  Section  through  Nasal  Foss/e  ; 
Viewed  from  Behind. 


Anterior  Half  of  Section 


NASAL  rOSS^. 


721 


The  narrow  slit-like  interval  between  the  nasal  septum  and  the  inner  aspect  of  the 
middle  turbinated  bone  is  named  the  olfactory  cleft  or  sulcus.  The  middle  meatus 
(meatus  nasi  medius),  situated  below  and  to  the  outer  side  of  the  middle  turbinated 
bone,  is  a  roomy  passage,  and  is  continued 
forwards  into  a  slightly  depressed  area 
termed  the  atrium  meatus  nasi,  which  lies 
immediately  above  the  vestibule.  The 
atrium  is  limited  above  and  in  front  by  a 
low  ridge,  the  agger  nasi,  the  representa- 
tive of  the  naso-turbinal  found  in  many 
animals.  On  raising  or  removing  the  middle 
turbinated  bone  a  rounded  elevation,  bulla 
ethmoidalis,  caused  by  the  middle  ethmoidal 
air-cells,  is  seen.  This  varies  in  size  and 
is  directed  downwards  and  forwards,  whilst 
opening  either  on  it  or  above  it  are  the 
orifices  of  the  middle  ethmoidal  cells.  Curv- 
ing upwards  and  forwards,  below  and  in  front 
of  the  bulla  ethmoidalis,  is  a  deep,  narrow 
groove,  the  hiatus  semilunaris,  into  which  the  anterior  ethmoidal  cells  and  the 
antrum  of  Highmore  open.  The  opening  from  the  antrum  (ostium  maxillare)  is 
situated   near  the  lower  and  back   part   of  the  hiatus,  and  is   placed   near   the 


Ortraiis  of  Jacobsou 


Fig.  554. — Section  through  Nose  of  Kitten, 
showing  position  of  Jacobson's  organ. 


Frontal  air-sinus. 

Bristle  passed 

from  it  into 

infundibuluni 


Opening  of  middle  ethmoidal  cells 

Openings  of  posterior  ethmoidal  cells 
Recessus  spheno-ethmoidalis 

Sphenoidal  aii  binu'5 


Cut  edge  of  mferioi  turbinated  bone 
''  Bristle  passed  into  opening  of  na^al  duct 


Fig.  555.- -View  of  the  Outer  Wall  of  the  Nose — the  Turbinated  Bones  having  been  removed. 


1.  Vestibule. 

2.  Opening  of  antrum  of  Highmore. 

3.  Hiatus  semilunaris. 


4.  Bulla  ethmoidalis. 

5.  Agger  nasi. 

6.  Opening  of  anterior  ethmoidal  cells 


7.  Cut  edge  of  superior  turbinated  bone. 
S.  Cut  edge  of  middle  turbinated  bone. 
0.  Pharyngeal  orifice  of  Eustachian  tube. 


roof  of  the  antral  cavity.  A  second  opening  (ostium  accessorium)  is  not  infrequently 
seen  in  the  middle  meatus  above  the  posterior  part  of  the  inferior  turbinated  bone. 
The  middle  meatus  extends  upwards  and  forwards,  and,  becoming  narrowed,  is 
continued  into  the  infundibulum  or  channel  leading  into  the  frontal  air-sinus. 
The  inferior  meatus  (meatus  nasi  inferior)  lies  below  the  inferior  turbinated  bone., 
50 


722 


THE  OEGANS  OF  SENSE. 


Fig.  556. — Section  through  the  Olfactory  Mucous  Membrane. 


under  cover  of  the  anterior  part  of  which  is  found  the  slit-like  orifice  of  the  nasal 

duct  (see  p.  741). 

Mucous    Membrane  (membrana  mucosa  nasi). — The    Schneiderian    or   nasal 

mucous  membrane 
is  thick,  highly 
vascular,  and  firmly 
bound  to  the  sub- 
jacent periosteum 
and  perichondrium. 
It  is  continuous, 
through  thechoanpe, 
with  the  mucous 
lining  of  the  naso- 
pharynx ;  through 
the  nasal  duct  and 
lachrymal  canals, 
with  the  conjunc- 
tiva ;  and,  through 
the  apertures  lead- 
ing into  the  air- 
sinuses,  with  the 
delicate  lining  of 
these  cavities. 

Throughout  the 

respiratory  region    it   is   covered  by  columnar,   ciliated   epithelium,   interspersed 

amongst  which  are  goblet  or  mucin  cells,  whilst  between  the  bases  of  the  columnar 

cells  smaller  pyramidal  cells  are  interpolated.     It  contains  a  freely  anastomosing 

venous     plexus,     which 

in    some  parts,  e.g.  over 

the   inferior    turbinated 

bones,  forms   a  kind  of 

cavernous  tissue  (plexus 

cavernosus    concharum). 

Many    acinous     glands, 

secreting  a  watery  fluid, 

are  embedded  in  it,  and 

are  especially  large  and 

numerous  in  the  posterior 

half  of  the  nasal  fossee, 

while  in  children  it  con- 
tains     a      considerable 

amount     of     adenoid 

tissue. 

In     the    olfactory 

region  the  mucous  mem- 
brane   is    yellowish    in 

colour,  more  delicate,  and 

covered   by   non-ciliated 

columnar        epithelium 

(Figs.   556,   557).     Em- 
bedded initarenumerous 

tubular      and      often 

branched  glands,  the 

glands  of  Bowman  (gl.  olfactoriue) ;  these  are  lined  by  polygonal  cells  and  open  by 

fine    ducts    on    its   free  surface.      The  epithelium   covering   the   olfactory  region 

consists  of:  (1)  8upi)orting  cells,  (2)  olfactory  cells,  and  (3)  basal  cells. 

1.  Supporting  Cells. — The  outer  part  of  these  cells  is  columnar  in  shape  and 

contains  fine  granules  of  yellow  pigment,  whilst  the  deeper  portion  is  attenuated 

and  frequently  branched.     They  contain  elliptical  or  oval  nuclei,  which  are  situated 


_01factory 
liairs 


Body  of 
"cell 


-Xucleiis 


_Ceritral 
proce.ss 


Fig.  55? 

A.    Frog 
]i.    Huriiau 


— Olkactouy  and  suppoRTiNCi  Cells. 
M.  SdiulUc-  ^-  Human  (V.  Bruim). 


THE  EYE.  723 

at  the  deep  ends  of  the  columnar  parts  of  the  cells,  and  form  what  is  termed  the 
zone  of  oval  nuclei. 

2.  Olfactory  Cells. — They  are  spindle-shaped  and  lie  between  the  deeper, 
attenuated  parts  of  the  supporting  cells ;  their  nuclei  are  circular  and  form  the 
zone  of  round  nuclei.  Each  cell  gives  off  a  peripheral  and  a  central  process,  the 
former  of  which  is  rod-like  and  ends  on  a  level  with  the  free  extremities  of  the 
supporting  cells,  where  it  is  surmounted  by  a  pencil  of  short  filaments,  termed  the 
olfactory  hairs.  A  fine  membrane,  the  membrana  limitans  externa,  covers  in  many 
animals  the  free  surface  of  the  epithelium,  and  is  pierced  by  the  olfactory  hairs  and 
by  the  ducts  of  Bowman's  glands. 

The  central  process  is  a  very  delicate  varicose  filament,  which  passes  inwards 
and  is  continuous  with  a  fibril  of  the  olfactory  nerve.  Each  of  these  nerve  fibrils 
probably  retains  its  independence  from  its  point  of  origin  in  an  olfactory  cell  to  its 
termination  in  the  olfactory  bulb,  in  the  glomerular  layer  of  which  it  forms  a  free 
arborisation. 

3.  Basal  Cells. — These  cells  are  branched,  and  lie  on  a  basement  membrane 
between  the  deep  extremities  of  the  supporting  and  olfactory  cells. 

Olfactory  Nerves. — These  nerves  arise  from  the  under  aspect  of  the  olfactory 
bulb  and  are  transmitted  through  the  foramina  in  the  cribriform  plate  of  the 
ethmoid  bone.  They  are  at  first  lodged  in  the  bony  canals  or  grooves  situated  on 
the  inner  and  outer  walls  of  the  olfactory  area,  and,  reaching  the  deep  surface  of 
the  mucous  membrane,  are  continued  into  the  central  processes  of  the  olfactory 
cells.     The  olfactory  nerves  possess  no  medullary  sheath. 

The  fifth  cranial  nerve  supplies  branches  of  ordinary  sensation  to  the  nasal  nuicons  membrane 
as  follows  :  The  septum  is  chiefly  supplied  by  the  naso-palatine  nerve,  but  its  jaosterior  part 
receives  some  filaments  from  Meckel's  ganglion  and  tlie  Vidian  nerve,  and  its  anterior  jDortion 
from  the  nasal  branch  of  the  ophthalmic.  The  outer  wall  is  suj^jjlied — (1)  by  the  upjaer  nasal 
branches  of  the  Vidian  nerve  and  Meckel's  ganglion  ;  (2)  by  the  lower  nasal  branches  derived  from 
the  anterior  palatine ;  and  in  front  l)y  (3)  the  outer  division  of  the  nasal  branch  of  the  ophthalmic. 
The  floor  and  anterior  part  of  the  inferior  meatus  are  supplied  by  a  nasal  branch  of  the  anterior 
superior  dental  nerve. 

Blood-vessels. — Arteries. — The  chief  artery  of  the  nose  is  the  spheno-palatine  branch  of  the 
internal  maxillary  artery.  This  reaches  the  nasal  cavity  through  the  spheno-palatine  foramen,  and 
divides  into — («)  posterior  nasal,  which  ramifies  over  the  turbinated  bones  and  sends  branches  to 
the  antrum  and  to  the  frontal  and  ethmoidal  cells ;  and  (b)  naso-palatine,  the  artery  of  the 
septum.  Twigs  are  given  to  the  upper  portion  of  the  cavity  by  the  anterior  and  posterior 
ethmoidal  arteries,  while  its  jjosterior  part  receives  some  small  branches  from  the  descending 
palatine  vessel.  The  nostrils  are  suj^plied  by  the  lateral  nasal  branch  of  the  facial,  and  by  the 
septal  artery  of  the  sujierior  coronary.  The  antrum  is  partly  supplied  by  the  infraorbital  artery, 
whilst  the  sphenoidal  sinus  gets  its  chief  supply  from  the  j)terygo-palatine  vessel.  The  veins 
form  a  dense  jilexus  almost  resembling  cavernous  tissue  in  structure.  This  condition  is  well  seen 
in  the  resjjiratory  region,  and  esjaecially  so  over  the  middle  and  inferior  turbinated  bones  and  on 
the  lower  part  of  the  septum.  The  venous  blood  is  carried  in  three  chief  directions,  viz. 
forivards  into  the  facial  vein,  backwards  into  the  spheno-palatine  vein,  and  upwards  into  the 
ethmoidal  veins.  The  ethmoidal  veins  communicate  with  the  ophthalmic  veins  and  the  veins  of 
the  dura  mater  ;  further,  an  ethmoidal  vein  passes  iip  through  the  cribriform  j^late  of  the 
ethmoid,  and  either  opens  into  the  venous  plexus  of  the  olfactory  bulb  or  directly  into  one  of  the 
veins  of  the  orbital  part  of  the  frontal  lobe  of  the  brain.  The  lymphatics  form  an  irregular  net- 
work in  the  superficial  part  of  the  mucous  membrane,  and  can  be  injected  from  the  subdural  or 
subarachnoid  space.  The  larger  vessels  are  directed  backwards  towards  the  choanal,  and  are 
collected  into  two  trunks,  of  which  the  larger  passes  to  a  lymphatic  gland  in  front  of  the 
axis  vertebra,  and  the  smaller  to  one  or  two  glands  situated  near  the  great  cornu  of  the  hyoid 
bone. 

The  development  of  the  nose  is  described  in  the  section  which  deals  with 
"  General  Embryology  "  (p.  38). 


THE   EYE. 

The  eyeball  or  globe  of  the  eye  (bulbus  oculi)  constitutes 'the  chief  part  of  the 
organ    of   sight    (organon    visus) ;    but,    associated    with    its    description,    certain 
accessory  structures,  such  as  the  eyelids  and  the  lachrymal  apparatus,  fall  to  be 
considered. 
50  a 


724 


THE  OKGANS  OF  SENSE. 


THE  EYEBALL. 

Situated  in  the  anterior  part  of  the  orbital  cavity,  the  eyeball  is  protected  in 
front  by  the  eyelids  and  by  their  mucous  lining,  the  conjunctiva,  and  is  pierced 
behind  by  the  optic  nerve,  or  nerve  of  sight,  which  spreads  out  to  form  its  innermost 
tunic,  the  retina.  The  tendons  of  the  ocular  muscles  are  attached  to  its  outer 
surface  a  short  distance  in  front  of  its  equator,  while  its  posterior  two-thirds  are 


Canal  of  Schleinm 

Suspensory  ligamen 
Len 


Cornea' 

Anterior  chamber 

Iris 

r(jsteiioi  cliamber 
-S^ — ^ Ciliary  piocess 

Canal  of  Petit 

Tendon  of 

internal 

lectns 


Optic  axis 


Vitreous 


Chorioid 


Retina 


Fovea  centralis 


Lamina  cribrosa  sclerse 
Arteria  centralis  retinse 
Optic  nerve 


Fig.  558. — Diagram  of  a  Horizontal  Section  through  left  Eyeball  and  Optic  Nerve 

(four  times  enlarged). 

enveloped  by  a  loose  membrane,  termed  the  capsule  of  Tenon,  or  fascia  bulbi,  which 
separates  it  from  the  surrounding  orbital  fat. 

The  eyeball  is  not  quite  spherical,  being  composed  of  the  segments  of  two 
spheres,  viz.  an  anterior,  transparent,  corneal  segment,  possessing  a  radius  of  7  or 
8  mm.,  and  a  posterior,  opaque,  scleral  segment,  with  a  radius  of  about  12  mm, 
(Fig.  558).  The  anterior  or  corneal  segment,  in  consequence  of  its  shorter  radius, 
projects  as  a  dome  in  front  of  the  scleral  portion,  the  union  of  the  two  parts 
being  indicated  externally  by  a  slight  groove,  the  sulcus  scler^e.  The  central 
points  of  the  anterior  and  posterior  curvatures  of  the  eyeball  constitute 
respectively  its  anterior  and  posterior  poles,  while  a  straight  line  joining  the  two 
poles  is  termed  its  sagittal  axis  (axis  optica).  The  axes  of  the  two  eyeballs  are 
almost  parallel,  diverging  only  slightly  in  front ;  but  the  axes  of  the  optic  nerves 
converge  behind,  and,  if  prolonged  backwards,  would  meet  in  the  region  of  the 
dorsum  sellte  of  the  sphenoid.  An  imaginary  line  encircling  the  globe  midway 
between  its  two  poles  is  named  its  equator,  and  meridional  lines  (meridiani)  may  be 
drawn  from  pole  to  pole  at  right  angles  to  the  ecjuator.  Its  sagittal  and  transverse 
diameters  are  nearly  equal — about  24  mm.;  its  vertical  diameter  is  about  23'5  mm. 
All  three  diameters  are  rather  less  in  the  female  than  in  the  male,  but  the  size  of 
the  eyeball  is  fairly  constant  in  the  same  sex.  What  are  popularly  described  as 
large  eyes  owe  their  apparent  increase  in  size  to  a  greater  prominence  of  the  globe 
and  to  a  wider  fissure  between  the  eyelids. 


SCLEEA.  725 

At  birth  the  eyeball  is  nearly  spherical  and  has  a  diameter  of  about  17 '5  mm.  By 
the  age  of  puberty  this  has  increased  to  20  or  21  mm.,  after  which  it  rapidly  reaches  its 
adult  size. 

The  eyeball  (Fig.  558)  consists  of  three  concentric  tunics  or  coats,  contained 
within  which  are  three  transparent  refracting  media.  The  three  tunics  are  :  (1)  an 
outer  fibrous  coat,  the  sclero-cornea,  consisting  of  an  opaque  posterior  part,  the 
sclera,  and  a  transparent  anterior  portion,  the  cornea;  (2)  an  intermediate 
vascular,  pigmented,  and  partly  muscular  tunic,  the  tunica  vasculosa  oculi,  com- 
prising from  behind  forward  the  chorioid,  the  ciliary  body,  and  the  iris ;  (3)  an 
internal  nervous  tunic,  the  retina.  The  three  refracting  media  are  named, 
from  before  backwards,  the  aqueous  humour,  the  crystalline  lens,  and  the  vitreous 
body 

SCLEEA. 

The  sclera,  sclerotic  coat,  or  white  of  the  eye,  is  a  firm,  opaque  membrane,  which 
forms  something  like  the  posterior  five-sixths  of  the  outer  tunic.  Thickest 
posteriorly  (about  1  mm.),  it  thins  at  the  equator  to  0"4  mm.-0'5  mm.,  and  again 
increases  to  0*6  mm.  near  the  sulcus  sclerae.  In  the  child  it  is  thinner  than  in  the 
adult,  and  presents  a  bluish  appearance,  caused  by  the  pigment  of  the  chorioid 
shining  through  it,  while  in  old  age  it  assumes  a  yellowish  tinge.  Its  outer  surface 
is  covered  by  a  layer  of  endothelium  and  is  in  contact  with  the  capsule  of  Tenon — 
a  lymph  space,  the  suprascleral  Isrmphatic  space,  only  intervening.  In  front  of  the 
equator  it  is  roughened  by  the  attachment  of  the  tendons  of  the  ocular  muscles, 
while  its  anterior  part  is  covered  by  mucous  membrane,  the  conjunctiva.  Its  deep 
surface  presents  a  brownish  colour,  and  is  loosely  attached  to  the  chorioid,  except  at 
the  optic  entrance  and  in  the  neighbourhood  of  the  sulcus  sclera.  It  is  pierced  behind 
by  the  optic  nerve,  the  entrance  for  which  is  funnel-shaped,  wide  behind  and  narrow 
in  front,  and  is  situated  1  mm.  below  and  3  mm.  to  the  nasal  side  of  the  posterior 
pole  of  the  eyeball.  The  fibrous  sheath  of  the  nerve  blends  with  the  outer  part  of 
the  sclera,  while  the  nerve  bundles  pass  through  a  series  of  orifices ;  this  perforated 
portion  is  named  the  lamina  cribrosa  sclerae.  Around  the  entrance  of  the  optic  nerve 
are  some  fifteen  or  twenty  small  apertures  for  the  passage  of  the  ciliary  nerves  and 
short  ciliary  arteries.  The  two  long  posterior  cihary  arteries  pierce  it,  one  on 
either  side,  some  little  distance  from  the  optic  entrance ;  while  a  little  behind  the 
equator  are  four  openings,  two  above  and  two  below,  for  the  exit  of  veins,  called 
venae  vorticosae.  Near  the  sulcus  sclera  it  is  perforated  by  the  anterior  ciliary 
arteries.  Its  inner  surface  is  lined  by  flattened  endothelial  cells  ;  and  between  it 
and  the  chorioid  is  an  extensive  lymph  space,  the  spatium  perichorioideale,  which 
is  traversed  by  the  ciliary  nerves  and  arteries  just  mentioned,  and  by  an  irregular 
meshwork  of  fine,  pigmented,  connective  tissue,  the  lamina  fusca,  which  loosely 
attaches  the  sclera  to  the  chorioid.  At  the  corneo-scleral  junction  the  fibrous 
tissue  of  the  sclera  passes  continuously  into  that  of  the  cornea,  and  in  the  deeper 
part  of  this  junction  there  is  a  circular  canal,  the  sinus  venosus  sclera,  or  canal  of 
Schlemm,  which  communicates  externally  with  the  scleral  veins,  and  internally, 
through  numerous  small  openings,  with  the  anterior  chamber  of  the  eyeball. 

The  sclera  consists  of  bundles  of  white  fibrous  tissue,  together  with  some  fine 
elastic  fibres,  the  bundles  forming  equatorial  and  meridional  layers,  which  inter- 
lace with  each  other.  Numerous  spaces  containing  connective  tissue  cells  and 
migratory  cells  exist  between  the  fibres.  Pigmented  cells  are  plentiful  in  the 
lamina  fusca,  and  a  few  are  also  found  in  the  tissue  of  the  sclera,  near  the  optic 
entrance  and  in  the  region  of  the  corneo-scleral  junction.  The  sclera  receives 
its  blood-supply  from  the  short  posterior  ciliary  and  anterior  ciliary  arteries,  while 
its  veins  open  into  the  vente  vorticosae  and  anterior  ciliary  veins.  The  cell  spaces 
play  the  part  of  lymphatics,  and  communicate  with  the  perichorioidal  and  supra- 
scleral lymph  spaces.  Its  nerves  are  derived  from  the  ciliary  nerves,  which,  after 
losing  their  medullary  sheath,  pass  between  the  fibrous  bundles ;  their  exact  mode 
of  ending  is  not  accurately  known. 


726 


THE  OEGANS  OF  SENSE. 


COENEA. 

The  cornea  forms  the  anterior  sixth  of  the  outer  tunic  and  is  transparent,  in 
order  to  admit  light  into  the  interior  of  the  eyeball ;  its  index  of  refraction  is 
from  1'33  to  1"35.  Its  anterior  surface  (facies  anterior)  is  covered  by  a  stratified 
epithelium,  continuous  with  that  which  lines  the  conjunctiva  ;  its  posterior  surface 
(facies  posterior)  is  directed  towards  the  anterior  chamber  of  the  eyeball  and  is  in 
contact  with  the  aqueous  humour.  Its  degree  of  curvature  varies  in  different 
individuals ;  it  is  always  greater  in  youth  than  in  old  age,  and  is,  as  a  rule,  slightly 
greater  in  the  vertical  than  in  the  horizontal  plane.  It  diminishes  also  from  its 
centre  to  its  periphery,  and  is  less  on  the  nasal  than  on  the  temporal  side  of  the 
anterior  pole.     The  anterior  surface  of  the  cornea  is  almost,  but  not  quite,  circular, 

measuring    11    mm.    vertically 

:    Istratified 
yjj^r^^     epitlieliuin 
rjejOiSf^  ^Anterior 

"elastic 

I  lamina 


and  11 '9  mm.  transversely,  while 
its  posterior  surface  is  circular 
and  has  a  diameter  of  13  mm. 
Its  periphery  is  overlapped  by 
the  tissue  of  the  sclera  as  the 
glass  of  a  watch  is  overlapped 
by  the  metal  rim,  with,  however, 
this  essential  difference,  that  the 
tissue  of  the  cornea  is  directly 
continuous  with  that  of  the 
sclera. 

The  cornea  consists,  from 
before  backwards,  of  the  follow- 
ing strata,  viz,  (Fig.  559) : — 

1.  A  layer  of  stratified  epi- 

thelium. 

2.  An  anterior  elastic  lamina. 

3.  The  substantia  propria. 

4.  A  posterior  elastic  lamina. 

5.  A  layer  of  endothelium. 


Posterior 
elastic  lamina 
Endothelium 


Fig.  559. — Vertical  Section  of  Cornea  (magnified). 


1.  The  layer  of  stratified  epi- 
thelium (epithelium  cornese)  is 
continuous    with     that    which 


covers  the  free  surface  of  the  conjunctiva  and  consists  of  six  or  eight  strata 
of  nucleated  cells.  Deepest  of  all  is  a  single  layer  of  perpendicularly  arranged 
columnar  cells,  the  flattened  and  often-expanded  bases  of  which  rest  on  the  anterior 
elastic  lamina,  while  their  opposite  ends  are  rounded  and  contain  the  nuclei. 
Superficial  to  this  layer  are  three  or  four  strata  of  nucleated,  polygonal  cells,  the 
majority  of  which  exhibit  finger-like  processes  which  join  with  the  corresponding 
processes  of  neighbouring  cells.  The  more  superficial  layers  assume  the  form  of 
nucleated  squames.  The  entire  thickness  of  this  stratified  epithelium  is  about  45  jx- 
at  the  centre  and  about  (SO  /a  at  the  peripliery  of  the  cornea. 

2.  The  anterior  elastic  lamina  (lamina  elastica  anterior,  Bowmani)  is  from 
19-20  j).  thick,  and  may  Ite  regarded  merely  as  a  diClerentiation  of  the  outer  part  of 
the  substantia  propria  from  which  it  is  with  difficulty  separated.  It  is  not  stained 
yellow  Ijy  picrocariiiine,  thus  differing  from  true  elastic  tissue,  and  its  degree  of 
development  varies  in  different  animals. 

3.  The  substantia  propria  presents,  in  a  fresh  condition,  a  homogeneous  appear- 
ance ;  but,  witli  the  assistance  of  reagents,  it  is  seen  to  consist  of  modified  con- 
nective tissue,  with  some  few  elastic  fibres.  An  amor])hous  interstitial  substance 
binds  the  fibres  into  bundles,  and,  in  turn,  cements  the  bundles  into  lamellae,  which 
are  directly  continuous  with  the  fil)rou8  tissue  of  the  sclera.  The  fibres  of  any 
one  lamella  cross  those  of  adjacent  lamellae  almost  at  right  angles,  while  the 
superimposed  lamellte  are  joined  jjy  siitural  fila-es  and  l)y  amorphous  substance. 
Between  the  lamellae  are  found  the  cell  spaces  or  lacunae  of  the  cornea — irregu- 


VASCULAE  AND  PIGMENTED  TUNIC  OF  THE  EYE. 


727 


larly  stellate  in  shape,  and  communicating  freely  witli  each  other  by  means  of  fine 
canaliculi.  The  corneal  cells  or  corpuscles  are  contained  in  these  lacuna3,  without, 
however,  completely  filling  them,  the  remainder  of  the  cavities  being  occupied  by 
lymph.  These  cells  are  nucleated,  tiatteued,  and  star-like,  and  their  branched  pro- 
cesses join  those  of  neighliouring  cells  in  the  canaliculi.  Migratory  or  lympli  cells 
are  also  found  in  cell  spaces. 

In  old  age  a  grayish  ojiaque  ring,  li  to  2  nini.  in  breadth,  is  frequently  seen  near  the  peri- 
jjhery  of  the  cornea  ;  it  is  termed  the  arcus  senilis,  and  results  from  a  deposit  of  fat  granules  in 
the  lamellae  and  corneal  corjmscles. 

4.  The  posterior  elastic  lamina  (lamina  elastica  posterior,  Demoursi,  Descemeti) 
is  a  clear,  structureless  membrane,  covering  the  posterior  aspect  of  the  substantia 
propria  and  possessing  a  thickness  of  6-8  fx  at  the  centre  and  10-12  ^  at  the  peri- 
phery of  the  cornea.  Less  firmly  attached  than  the  anterior  elastic  lamina,  it  may 
he,  stripped  off,  when  it  will  be  found  to  roll  up  with  its  attached  surface  inwards. 
Between  the  ages  of  twenty  and  thirty  small  wart-like  projections  appear  on  its  deep 
surface,  near  its  periphery,  and  these  increase  in  size  and  number  as  years  advance, 
so  that  in  old  age  the  membrane  may  attain  a  thickness  of  20  /x.  Towards  the 
periphery  of  the  cornea  the  lamina  divides  into  three  sets  of  fibres — anterior, 
middle,  and  posterior.  The  anterior  fibres  pass  behind  the  canal  of  Schlemm  into 
the  sclera,  the  middle  give  attachment  to  the  ciliary  muscle,  while  the  posterior  are 
continued  as  radiating  and  anastomosing  fibres  into  the  substance  of  the  iris,  and 
constitute  the  ligamentum  pectinatum  irrdis,  A  number  of  irregular  spaces,  the 
spaces  of  Fontana,  or  spatia  anguli  iridis,  exist  between  the  fibres  of  this  pectinate 
ligament.  Better  developed  in  the  horse  and  ox  than  in  man,  these  spaces  are 
lined  by  a  prolongation  of  the  corneal  endothelium,  and  communicate  internally 
with  the  anterior  chamber  and  the  lymph  spaces  of  the  iris,  and  externally  with 
the  canal  of  Schlemm. 

5.  The  layer  of  endothelium  (endothelium  camera  anterioris)  consists  of  a  single 
stratum  of  nucleated,  flattened,  polygonal  cells,  which  present  a  fibrillar  structure 
and  are  continued  as  a  lining  to  the  spaces  of  Fontana  ;  this  layer  of  endothelium 
is  also  reflected  on  to  the  anterior  surface  of  the  iris. 

Vascular  and  Nervous  Supply  of  the  Cornea. — In  the  fcetus  the  cornea  is  traversed,  almost 
as  far  as  its  centre,  by  capillaries  ;  biit  in  the  adult  it  is  devoid  of  blood-vessels,  excejit  near  its 
margin.  The  capillaries  of  the  conjunctiva  and  >clera  pa.ss  into  this  marginal  area  for  a  distance 
of  about  1  mm.,  where  they  terminate  in  loops.  All  the  remainder  of  the  cornea  is  nourished  by 
the  lymph  which  circulates  in  its  cell  spaces  and  canaliculi. 

The  nerves  of  the  cornea,  discovered  liy  Schlemm,  are  derived  from  the  ciliary  nerves. 
Around  its  periphery  they  form  a  plexus,  the  plexus  annularis,  from  which  fibres  pass  into  the 
cornea,  where,  after  a  distance  of  I  or  2  mm.,  they  lose  their  medullary  sheaths  and  ramify  in  the 
substantia  propria,  forming  what  is  termed  the  fundamental  or  stroma  plexus.  Perforating  fibres 
(fibrte  perforantes)  extend  from  this  plexus  through  the  anterior  elastic  lamina  and  form  a  sub- 
epithelial i^lexus,  from  which  fine  filaments  ramify  between  the  epithelial  cells  as  far  as  the  super- 
ficial layers.  From  the  an- 
nular and  stroma  plexuses 
fibrils  pass  to  the  substantia 
propria  and  come  into  close 
relation  with  the  corneal 
corpuscles. 


Membrane  of  Biuc)i 
Lamin.a 


VASCULAR 
MENTED 


AND     PIG- 
TUNIC. 


The  middle,  vascular, 
and  pigmented  tunic 
(tunica  vasculosa  oculi) 
comprises,  from  behind 
forwards,  the  chorioid, 
the  ciliary  body,  and  the 
iris  (Fig.  558). 

The  chorioid  (chorioidea)  intervenes  between  the  sclera  and  the  retina,  reaching 
as  far  forwards  as  the  ora  serrata  of  the  latter  (p.  731).     Dark  brown  or  black  in 
colour,  it  is  pierced  posteriorly  by  the  optic  nerve,  and  is  here  firmly  attached 
50  <^ 


Fig.  560.- 


-Vebtical  Section  of  Chokioid  axd  Inner  Part 
OF  Sclera. 


728 


THE  OEGANS  OF  SENSE. 


Cornea 


Canal  of  Schlemm 

Circulus  arteriosus 
major 


Conjunctival  vessels 
Recurrent  artery 
of  chorioid 

Anterior 

ciliary 

vessels 


to  the  sclera.  Thicker  behind  than  in  front,  its  outer  surface  is  fiocculent  and 
is  connected  to  the  sclera  by  the  ciliary  vessels  and  nerves,  and  by  the  loose  lamina 
fusca.  Its  inner  surface  is  smooth  and  adheres  to  the  outermost  or  pigmented 
layer  of  the  retina. 

The  chorioid  consists  of  blood-vessels  and  branched  pigment  cells  embedded  in 
a  loose  connective  tissue,  and  presents  from  without  inwards  three  layers,  viz. : 
(a):  the  lamina  suprachorioidea ;  (b)  the  proper  tissue  of  the  chorioid ;  and  (c)  a 
thin  transparent  membrane,  the  lamina  basalis  or  membrane  of  Bruch  (Fig.  560). 

1.  The  lamina  supra-chorioidea  resembles  the,  lamina  fusca  of  the  sclera,  and 
consists  of  a  series  of  line  non-vascular  lamellae,  each  containing  a  delicate  network 

of  elastic  fibres, 
amongst  which  are 
stellate,  pigmented 
cells,  together  with 
amoeboid  cells.  The 
spaces  between  the 
laminae  are  lined  with 
endothelium,  and  to- 
gether form  the 
spatium  perichorio- 
ideale,  already  referred 
to  (p.  725). 

The  proper  tissue  of 
the  chorioid  consists  of 
blood-vessels  and 
numerous  pigmented 
cells,  supported  by 
connective  tissue  and 
elastic  fibres,  together 
with  some  smooth 
muscular  fibres.  Its 
outer  part  contains  the 
larger  blood  -  vessels, 
and  is  named  the 
lamina  vasculosa,  while 
its  inner  portion  is 
composed  of  a  network 
of  fine  capillaries, 
and  is  termed  the 
lamina  choriocapillaris ; 
these  two  laminae  are 
joined  by  a  thin  inter- 
mediate stratum.  The 
arteries  of  the  chorioid 
are  derived  from  the- 
short  posterior  ciliary 
vessels,  which  pierce 
the  sclera  around  the 
optic  entrance  and  form  a  wide -meshed  plexus  in  the  lamina  vasculosa.  Their 
circular  muscular  coat  is  well  developed,  and  longitudinal  muscular  fibres  are  also 
present  in  the  larger  branches.  The  veins,  destitute  of  muscular  tissue,  are  super- 
ficial to  the  arteries;  they  are  surrounded  by  peri -vascular  lymphatic  sheaths 
and  converge  to  form  whorls,  which  open  into  the  venae  vorticosae.  In  the 
tissue  between  the  blood-vessels  are  numerous  stellate,  flattened,  and  pigmented 
ceUs. 

The  lamina  chorio-capillaris,  or  membrane  of  liuyscli,  is  composed  essentially  of 
small  capillaries,  which  form  an  exceedingly  close  network,  embedded  in  a  finely 
granular  or  almost  homogeneous  tissue.  The  intermediate  stratum  between  the 
malina  vasculosa  and  lamina  chorio-capillaris  consists  of  a  network  of  delicate 


Suprascleral  vessels 


Vena  vorticosa 


— Long  posterior  ciliary  artery 
Short  posterior  ciliary  artery 


r  Outer  and 

(inner  vessels  of  optic  sheath 

Optic  nerve 

Central  artery  and  vein  of  retina 
Diagram  of  the  Circulation  in  the  Eve  (Leber). 


VASCULAK  AND  PIGMENTED  TUNIC  OF  THE  EYE. 


729 


Pais  iiidica  retinsB 


Anterior  chamber 


Canal  of  Schlemni 
Spaces  of  Fontana 


Conjunctiva' 


Ciliary  process 
Ligamentuin 
pectinatinn  iridis 
Circular  fibres 
of  ciliary  uiuscle 


Radial  fibres  of 
ciliary  muscle 


Pars  ciliaris  retiufe 


elastic  fibres  and  contains  almost  no  pigment  cells ;  it  is  lined  next  the  lamina 
chorio-capillaris  by  a  continuous  layer  of  endothelium. 

The  lamina  basalis,  or  membrane  of  Bruch,  is  transparent  and  nearly  structure- 
less. Its  outer  surface  presents  a  trellis-like  network  of  fibres  which  unite  it  to 
the  membrane  of  Kuysch,  while  its  inner  surface  is  smooth  and  is  in  contact  with 
the  pigmented  layer  of  the  retina. 

Tapetum. — In  many  animals  a  brilliant  iridescent  appearance  is  seen  on  the  postero-external 
part  of  the  chorioid  to  which  the  name  tapetum  is  applied.  Absent  in  man,  it  may  be  due,  as 
in  the  horse,  to  a  markedly  fibrous  condition  of  the  stratum  intermedium  (tapetum  fibrosum),  or 
as  in  the  seal,  to  the  presence  of  some  five  or  six  layers  of  flattened  iridescent  cells  lying  imme- 
diately outside  the  lamina  chorio-capillaris  (tapetum  cellulosum). 

The  ciliary  body  (corpus  ciliare)  connects  the  chorioid  to  the  circumference  of 
the  iris  (Fig.  562),  and 
presents  the  following 
three  zones,  viz. :  (a)  the 
orbiculus  ciliaris,  (h)  the 
ciliary  processes,  and  (c) 
the  ciliary  muscle. 

The  orbiculus  ciliaris 
forms  a  zone  of  about 
4  mm.  in  width  im- 
mediately adjoining  the 
chorioid,  and  exhibits 
numerous  radially- 
arranged  ridges. 

The  ciliary  processes 
(processus  ciliares),  about 
seventy  in  number,  form 
a  circle  of  radial  thicken- 
ings, each  of  a  somewhat 
triangular  shape.  The 
base  of  the  triangle  is  di- 
rected forwards  towards 
the  equator  of  the  lens, 
while  the  apex  is  con- 
tinuous behind  with  some 
three  or  four  ridges  of  the 
orbiculus  ciliaris.  They 
vary  in  size,  the  largest 
having  a  length  of 
2-0  mm.  The  structure  of 
the  orbiculus  ciliaris  and 
ciliary  processes  is  similar 
to  that  of  the  chorioid, 
but  the  capillaries  are 
larger  and  more  tortuous, 
and  there  is  no  lamina 

chorio-capillaris.  The  deep  aspect  of  the  ciliary  processes  is  covered  by  two  strata 
of  columnar  epithelium,  the  anterior  layer  of  which  is  pigmented ;  these  two  strata 
form  a  direct  continuation  forwards  of  the  retina  and  constitute  the  pars  ciliaris 
retinae.  This  epithelium  is  invaginated  to  form  more  or  less  tubular  glands,  which 
may  take  a  share  in  the  secretion  of  the  aqueous  humour. 

The  ciliary  muscle  (m.  ciliaris)  is  triangular  on  antero -posterior  section,  and 
consists  of  two  sets  of  fibres— radial  and  circular  (Fig.  562).  The  radial  fibres 
(fibrte  meridionales,  Bruckei)  spring  from  the  corneo-scleral  junction  behind  the 
canal  of  Schlemm  and  from  the  ligamentum  pectinatum  iridis,  and  radiate  back- 
wards, to  be  attached  to  the  ciliary  processes  and  orbiculus  ciliaris.  When  they 
contract  the  chorioid  is  drawn  forwards  and  the  lens  becomes  more  convex,  owing 
to  the  relaxation  of  its  suspensory  ligament  (see  p.  736).     The  circular  fibres  (fibree 


Penchorioidal  lymph  si)ac 


Zonule  of  Zinn 


Fig.  562.— Section  through  Ciliary  Region  of  Eyeball. 


730 


THE  OEGANS  OF  SENSE. 


circulares,  Millleri)  form  a  triangular  zone  behind  the  ligamentum  pectinatum 
iridis,  close  to  the  periphery  of  the  iris,  and  also  extend  backwards  under  the  radial 
fibres.  Considerable  individual  differences  are  found  as  to  the  degree  of  develop- 
ment of  these  two  portions  of  the  ciliary  muscle.  The  radial  fibres  are  always  more 
numerous  than  the  circular  fibres,  the  latter  being  absent  or  rudimentary  in  myopic 
eyes,  but  well  developed,  as  a  rule,  in  hypermetropic  eyes. 

The  iris  forms  a  contractile  diaphragm  in  front  of  the  lens,  and  is  pierced  a 
little  to  the  nasal  side  of  its  centre  by  an  almost  circular  aperture,  the  pupil 
(pupilla),  which,  during  life,  is  continually  varying  in  size  in  order  to  regulate 
the  amount  of  light  admitted  into  tlie  interior  of  the  globe.  It  divides  the  space 
between  the  cornea  and  lens  into  two  parts,  which  are  filled  by  the  aqueous  humour, 
and  named  respectively  the  anterior  and  posterior  chambers  of  the  eyeball.  Its 
peripheral  border,  or  margo  ciliaris,  is  directly  continuous  with  the  ciliary  body,  and, 
through  the  medium  of  the  Hgameutum  pectinatum  iridis,  with  the  posterior  elastic 
lamina  of  the  cornea.  Its  free  edge,  or  margo  pupillaris,  forms  the  circumference  of 
the  pupil,  and  rests  upon,  but  is  not  attached  to  the  anterior  siirface  of  the  capsule 
of  the  lens. 

The  distinctive  colour  of  the  eye,  in  different  individuals,  depends  on  the  arrangement 
of  the  pigment  in  the  iris ;  in  the  blue  eye  this  is  limited  to  the  posterior  surface  of  the 
iris,  but  in  the  brown  or  black  eye  it  is  also  scattered  throughout  its  stroma.  In  the  albino 
the  pigment  is  entirely  absent,  and  the  red  appearance  of  the  eye  in  such  a  case  is  pro- 
duced by  the  network  of  blood-vessels  in  the  iris. 

The  pupil  is  closed,  during'  the  greater  part  of  foetal  life,  by  a  thin  transparent 
vascular  membrane,  the  membrana  pupillaris,  continuous  with  the  pupillary  margin  of 
the  iris.  Its  vessels,  derived  partly  from  the  vessels  of  the  iris  and  partly  from  those  of 
the  capsule  of  the  lens,  convei-ge  towards  the  middle  of  the  membrane,  near  which  they 
form  loops  so  as  to  leave  the  central  part  non-vascular.  About  the  seventh  month  the 
vessels  begin  to  be  obliterated  from  the  centre  towards  the  circumference,  and  this  is 
followed  bj'  a  thinning  and  absorption  of  the  membrane,  which  becomes  perforated  by  the 
aperture  of  the  pupil.  This  perforation  gradually  enlarges,  and  at  birth  the  membrane 
has  entirely  disappeared,  although  in  exceptional  cases  it  persists. 

On   the  anterior  surface  (facies  anterior)  of  the  iris  is  a  layer  of  flattened 
.  ,  .     .,.  endothelium,    placed    on    a 

Anterior  ciliary  arteries  t  ,  -■-   , 

basement  membrane,  and 
continuous  with  that  which 
lines  the  spaces  of  Fontana 
and  covers  the  back  of  the 
cornea.  Depressions  or  crypts 
are  here  and  there  seen  in 
which  the  endothelium  and 
basement  membrane  are  ab- 
sent, and  are,  by  some,  re- 
garded as  stomata,  through 
which  the  lymphatics  of  the 
iris  communicate  with  the- 
ca^'ity  of  the  anterior  cham- 
ber. Its  posterior  surface 
(facies  posterior)  is  covered 
by  a  basement  membrane,  on 
which  are  placed  two  layers 
of  columnar,  pigmented  epi- 
thelium, continuous  with  the 
pars  ciliaris  retinas  fand 
termed  tlie  pars  iridica  retinae. 
The  i)roper  tissue  of  the  iris, 
,.  .  or  stroma   iridis,  consists  of 

deucate  connective  tissue  and  elastic  fibres,  with  pigmented  cells,  blood-vessels 

nerves,  and  non-striped  muscle. 

The  blood-vessels  of  the  iris  (Fig.  563)  are  derived  from  the  long  and  anterior 


Veins  of  chorioid 


Aperture  of 
./pupil 


Long 
ciliary 

artery 


Circnlus 
iiiajor 


Fig. 


V 

Anterior  ciliary  arteries 

563. — Blood- VE.S8EL3  of  Iris  and  Anterior  Part  of 
Chorioid,  viewed  from  the  front  (Arnold). 


THE  EETINA.  731 

ciliary  arteries.  The  long  ciliary  arteries,  two  iu  number,  pierce  the  sclera  on  the 
inner  and  outer  side  of  the  optic  nerve  respectively,  and  extend  forwards  between 
the  sclera  and  chorioid  towards  the  ciliary  margin  of  the  iris.  Here  each  divides 
into  an  upper  and  a  lower  branch,  and  the  resulting  four  1  tranches  anastomose  in 
the  form  of  a  circle,  termed  the  circulus  arteriosus  major.  This  circle  is  joined  by  a 
varying  number  of  anterior  ciliary  arteries  derived  from  the  lachrymal  and 
muscular  branches  of  the  ophthalmic  artery,  and,  after  supplying  the  ciliary 
muscle,  sends  converging  branches  inwards  towards  the  aperture  of  the  pupil, 
around  which  a  second  circle,  the  circulus  arteriosus  minor,  is  formed.  The  veins 
proceed  towards  its  ciliary  margin,  and  communicate  with  the  veins  of  the  ciliary 
processes  and  with  the  canal  of  Schlemm.  The  convergence  of  the  Ijlood- vessels 
towards  the  aperture  of  the  pupil  gives  to  the  anterior  surface  of  the  iris  a  striated 
appearance. 

The  non-striped  muscular  fibres  are  arranged  in  two  sets :  (a)  circular,  (6)  radial. 
The  circular  fibres  form  a  band  around  the  pupillary  aperture,  l)y  the  contraction  of 
which  its  size  is  lessened,  and  hence  it  is  termed  the  m.  sphincter  pupillse.  The 
radial  fibres  extend  outwards  from  the  sphincter  to  the  ciliary  margin  and  constitute 
the  m.  dilatator  pupillae.  Many  anatomists  regard  the  radial  fibres,  in  man  and 
most  mammals,  as  being  elastic  and  not  muscular.  In  animals,  where  the  radial 
fibres  are  muscular,  the  degree  of  their  development  varies  considerably ;  they  are 
feebly  marked  in  the  rabbit,  l:)ut  well  developed  in  the  bird,  and  still  more  so  in  the 
otter. 

The  nerves  of  the  chorioid  and  iris  are  derived  from  the  long  and  short 
ciliary  nerves.  The  former,  two  or  three  in  number,  are  branches  of  the  nasal 
nerve ;  the  latter,  varying  from  eight  to  fourteen,  are  derived  from  the  ciliary 
ganglion.  Piercing  the  sclera  around  the  optic  entrance  the  nerves  traverse  the 
perichorioidal  lymph  space,  where  they  form  a  plexus,  rich  in  nerve-cells,  from  which 
filaments  are  supplied  to  the  blood-vessels  of  the  chorioid.  In  front  of  the  ciliary 
muscle  a  second  plexus,  also  rich  in  nerve-cells,  is  formed,  which  supplies  the  muscle 
itself,  and  sends  filaments  into  the  iris  as  far  as  its  pupillary  margin,  for  the  supply 
of  its  muscular  fibres  and  blood-vessels.  The  sphincter  pupillas  is  supplied  by  the 
third  cranial  nerve,  whilst  filaments  from  the  sympathetic  are  distributed  to  the 
dilatator  pupillte. 

THE  RETINA. 

The  retina,  or  nervous  tunic  of  the  eyeball,  is  a  soft,  delicate  membrane,  in  which 
the  fibres  of  the  optic  nerve  are  spread  out.  It  consists  of  two  strata,  viz. :  (a)  an 
outer,  pigmented  layer  (stratum  pigmenti),  attached  to  the  chorioid ;  and  (b)  an 
inner  nervous  lamina,  the  retina  proper,  in  contact  with  the  hyaloid  membrane  of 
the  vitreous  body,  but  only  attached  to  it  at  the  optic  entrance  and  in  the  region 
of  the  ciliary  processes.  Expanding  from  the  entrance  of  the  optic  nerve  the 
retina  appears  to  end,  a  short  distance  Itehind  the  ciliary  body,  in  a  wavy  border, 
the  ora  serrata.  Here  its  nervous  elements  cease  and  the  membrane  becomes 
suddenly  thinned,  but  a  delicate  continuation  of  it  is  prolonged  over  the  posterior 
aspect  of  the  ciliary  body  and  iris.  This  continuation  consists  of  the  stratum  pig- 
menti, together  with  a  layer  of  columnar  epithelium,  and  constitutes  the  pars  ciliaris 
retinae  and  pars  iridica  retinse  already  referred  to  (pp.  729  and  730).  The  portion 
behind  the  ora  serrata  is  termed  the  "  physiological  retina,"  or  pars  optica  retinae, 
and  its  thickness  gradually  diminishes  from  0*4  mm.,  near  the  optic  entrance,  to 
0"1  mm.  at  the  ora  serrata.  Viewed  from  the  front  it  presents,  at  the  posterior 
pole  of  the  eyeball,  and  therefore  directly  in  the  axis  of  the  globe,  a  small  yellowish 
spot,  the  macula  lutea.  Somewhat  oval  in  shape,  the  greatest  or.  transverse 
diameter  of  the  macula  measures  from  2-3  mm. ;  its  central  part  is  depressed  and 
named  the  fovea  centralis.  About  3  mm.  to  the  nasal  side  of  the  posterior  pole 
and  about  1  mm.  below  its  level  is  a  whitish,  circular  disc,  the  optic  disc,  or  porus 
opticus,  which  corresponds  with  the  entrance  of  the  optic  nerve  and  has  a  diameter 
of  about  1*5  mm.  The  circumference  of  the  optic  disc  is  slightly  raised  and  is 
named  the  colliculus  nervi  optici,  while  its  depressed  central  portion  is  termed  the 
optic  cup,  or  excavatio  papillae  nervi  optici.    The  optic  disc  consists  merely  of  nerve- 


732 


THE  ORGANS  OF  SENSE. 


1. 
nearly 


stratum 
pigmenti 


fibres,  the  other  layers  of  the  retina  being  absent,  and  constitutes  the  "  blind  spot " 
of  physiologists. 

The  nervous  layer  of  the  retina  is  transparent  during  life,  but  becomes  opaque 
and  of  a  o-rayish  colour  soon  after  death.  If  an  animal  be  kept  in  the  dark  before 
the  removal  of  its  eyeball,  the  retina  presents  a  purple  tinge,  due  to  the  presence  of 
a  colouring  matter  named  rhodopsin  or  visual  purple,  which,  however,  becomes 
rapidly  bleached  on  exposure  to  sunlight.  This  colouring  matter  is  absent  from 
the  macula  lutea,  and  also  over  a  narrow  zone,  3-4  mm.  in  width,  near  the  ora 
serrata. 

Structure  of  the  Retina  (Figs.  564,  565,  566). — The  nervous  elements  of  the 
retina  are  supported  by  non-nervous  or  sustentacular  fibres,  and  are  arranged  in  seven 
layers,  to  which  must  be  added  the  stratum  pigmenti. 

Our  conception  of  the  minute  structure  of  the  retina,  as  of  all^nervous  tissues,  has  of 
late  years  been  greatly  advanced  by  the  discoveries  of  Ramon  y  Cajal,  on  whose  observa- 
tions the  following  description  is  based  (Fig.  565) : — • 

The  layers  from  within  outwards,  i.e.  fi'om  vitreous  body  to  chorioid,  are  : 
1.   Layer  of  nerve-fibres  (stratum  opticum). 
Layer  of  nerve-cells  (ganglionic  layer). 
Inner  molecular  or  inner  plexiform  layer. 
Inner  nuclear  layer  or  layer  of  inner  granules. 
Outer  molecular  or  outer  plexiform  layer. 
Outer  nuclear  layer  or  layer  of  outer  granules. 

7.  Layer  of  rods  and  cones  (bacillary  layer). 

8.  Layer  of  pigmented  epithelium  (stratum  pigmenti). 

Layer  of  nerve-fibres  or  stratum  opticum. — The  fibres  of  this  stratum  are 
all   centripetal,  and  are  mostly  continuations  of  the  non-medullated  axons  of  the 

cells  in  the  ganglionic  layer.  Some,  however,  are 
centrifugal  and  end  in  branched  clubbed  extremities 
in  the  inner  molecular  or  inner  nuclear  layers. 

2.  Ganglionic  or  nerve-ceil  layer. — The  cells 
of  this  stratum  vary  in  size,  are  oval  or  pyriform  in 
shape,  and  form  a  single  layer,  except  at  the  macula 
lutea,  where  several  strata  are  present.  Each  cell 
contains  a  large  nucleus,  and  gives  off,  from  its 
inner  aspect,  an  axon  which  is  continued  as  a  fibre 
of  the  nerve-fibre  layer.  From  the  outer  surface 
of  each  cell  numerous  dendrites  arise,  which  form 
arborisations  in  the  inner  molecular  layer.  The  cells 
may  be  divided  into  unistratified,  multistratified,  and 
dift'use,  according  as  their  dendrites  ramify  in  one 
or  in  several  strata  of  the  inner  molecular  layer,  or 
extend  throughout  nearly  its  whole  thickness. 

3.  Inner  molecular  orinnerplexiform  layer. 
— This  is  chiefly  constituted  by  the  interlacement  of 
the  dendritic  arborisations  of  the  cells  of  the  gan- 
glionic layer  with  those  of  the  inner  nuclear  layer, 
and  has  been  divided  by  Ramon  y  Cajal  into  five' 
strata.  It  sometimes  contains  horizontal  cells  or 
spongioblasts,  whose  branched  processes  ramify  in  it. 

4.  Inner  nuclear  layer  or  layer  of  inner 

granules. --This  is  the  most  complicated  of  the 
retinal  strata,  and  consists  of  numerous  cells  which 
may  be  divided  into  three  groups,  viz.  :  (a)  bipolar 
cells,  (/>)  horizontal  cells,  and  (c)  spongioblasts, 
or  amacrine  cells. 

[a)  The  bipolar  cells,  by  far  the  most  numerous 
are  fusiform  and  nucleated,  and  each  gives  off  an  external  and  an  internal  process.  The 
internal  ])rocesses  terminate  in  flattened  tufts  at  different  levels  in  the  inner  molecular 
layer,  while  the  external  produce  an  abundant  ramification  in  the  external  zone  of  the 
outer  molecular  layer.  These  bipolar  cells  are  divided  into  rod  bipolars,  cone  bipolars, 
and  giant  bipolars.  The  rod  bipolars  end  peripherally  in  vertical  arborisations  around  the 
button-like  ends  or  .spherules  of  tiie  rod  fibres,  and,  centrally,  in  branched    extremities 


1  stratum 
I  opticum 

Mttiiibiaiia  liriiitans  interna 

Fig.  564. — Diagrammatic  Section  ok  the 
Human  Retina  (modiaed  from  Schultze). 


THE  KETINA. 


733 


which  mostly  become  applied  to  the  cells   of    the  ganglionic  layer.      The  cone  bipolars 
end  peripherally  in  flattened  arborisations  in  the  outer  molecular  layer  in  contact  with 


Fio.  565. — Perpendicular  Sections  of  Mammalian  Retina  (Cajal). 

A,  Layer  of  rods  and  cones  ;  B,  Outer  nuclear  layer  ;  C,  Outer  molecular  layer  ;  D,  Inner  nuclear  layer  ;  E, 
Inner  molecular  layer  ;  F,  Ganglionic  layer  ;  G,  Stratum  opticuni  ;  /■,  rods  ;  c,  cones,  r.g,  rod  granules  ; 
eg,  cone  granules;  r.h,  rod  Ijipolars  ;  c.b,  cone  bipolars;  c.r,  contact  of  rod  bipolars  with  the 
spherules  of  the  rod  fibres  ;  c.c,  contact  of  cone  bipolars  with  the  branches  of  the  cone  fibres  ;  ar, 
internal  arborisation  of  cone  bipolars  ;  ar ,  internal  arborisation  of  rod  bipolars  ;  c.n,  centrifugal  nerve 
fibre  :  h,  horizontal  cells  ;  s.s,  stratified  spongioblasts  ;  d.s,  diffiise  spongioblasts  ;  s.g,  stratified 
ganglion  cell  ;  M,  Sustentacular  fibre  of  Mtiller. 

the  ramifications  of  the  foot-plates  of  the  cone  fibres,  and,  centrally,  ramify  in  some  one  of 
the  five  strata  of  the  inner  molecular  layer.  The  giant  bipolars  form,  peripherally,  an 
extensive  horizontally  arranged  arborisation  in  the  outer  mole- 
cular layer;  centrally,  they  ramify  in  one  or  other  of  the  strata 
of  the  inner  molecular  layer. 

(h)  The  horizontal  cells  are  of  two  varieties:  (1)  small, 
flattened,  star-like  cells,  lying  immediately  below  the  outer 
molecular  layer,  and  sending  a  tuft  of  dendrites  outwards 
towards  the  bases  of  the  cone  fibres,  while  their  axons  are 
directed  horizontally  for  a  variable  distance  ;  (2)  large,  irregular 
cells,  lying  internal  to  the  above  and  ending  in  finger-like 
ramifications  in  the  outer  molecular  layer.  Their  axons  run 
horizontally  for  some  distance,  and  end  in  extensive  varicose 
arborisations  under  the  spherules  of  the  rod  fibres. 

(c)  The  spongioblasts  are  situated  in  the  innermost  part 
of  the  inner  granular  layer  and  have  not  yet  been  sho"\vn  to 
possess  axons.  Their  dendi-ites  ramify  in  the  inner  molecular 
layer,  it  may  be  in  one  stratum  (stratified  spongioblasts)  or 
in  several  strata  (diftuse  spongioblasts). 

5.  Outer  molecular  or  outer  plexiform  layer. — 
This  is  constituted  by  the  interlacement  of  the  dendrites  of 
the  bipolar  and  horizontal  cells,  just  described,  with  the 
spherules  of  the  rod  fibres  and  the  ramifications  of  the  foot- 
plates of  the  cone  fibres.  It  is  divided  into  two  strata  :  (a) 
external,  indicating  the  contact  of  the  rod  bipolars  with  the 
spherules  of  the  rod  fibres ;  (6)  interiial,  the  line  of  contact 
between  the  cone  bipolars  and  the  branches  of  the  cone  fibres. 

6.  Outer  nuclear  layer  or  layer  of  outer  granules. — 
This  is  made  up  of  clear  granules  somewhat  resembling  those 
of  the  inner  nuclear  layei',  and  are  divisible  into  two  kinds  :  (a) 
cone  granules,  {h)  rod  granules.  The  cone  granules  are  the 
larger,  and  each  contains  an  oval  nucleus  ;  they  lie  inmiediately 
inside  the  outer  limiting  membrane,  through  which  they  are 
continuous  with  the  cones  of  the  next  layer.  Each  is  prolonged 
internally  as  a  straight  fibre,  which,  on  reaching  the  outer  mole- 
cular layer,  expands  to  form  a  foot-plate,  from  which  several 
horizontal  fibrils  are  given  off.  The  rod  granules  are  far  more  numerous  than  the 
cone    granules,  and  each  contains  a  small  oval  nucleus,  which  is  transversely   striated. 


Fig.  56G. 

A,  A  cone  and  two  rods  from  the 
human  retina  (modified  from 
Max  Schultze)  ;  B,  Outer 
part   of   rod   separated  into 

discs. 


734 


THE  OKGANS  OF  SENSE. 


Fig.  568. — Section  through  outer 
Layers  op  Retina  (semi-diagram- 
matic). 


Their  outer  processes  are  continuous,  through  the  outer  limiting  membrane,  with  the 
rods  of  the  next  layer,,  while  their  inner  processes  pass  into  the  outer  molecular  layer 
and  end  in  free,  unbranchcd  spherules  amongst  the  arborisations  of  the  rod  bipolars. 

7.  Layer  of  rods  and  cones. — This  consists  of  two  sets  of  structures,  viz.  rods 
and  cones.  Except  at  the  macula  lutea  the  rods  are  far  more  numerous  than  the  cones 
and  assume  the  form  of  elongated  cylinders,  w'hile  the  cones  are  shorter  than  the  rods 
and  taper  externally  to  fine  points.     Each  rod  and  cone  consists  of  two  segments — inner 

and  outer.  The  inner  segment  of  the  rod  only  slightly  exceeds  in 
diameter  its  outer  segment,  whejeas 
the  inner  segment  of  the  cone  greatly 
exceeds  its  outer  part.  The  inner 
segments  of  both  rods  and  cones  have 
an  aflSnity  for  staining  reagents,  and 
consist  of  a  basal  homogeneous  portion 
and  an  outer  longitudinally  striated 
part,  the  proportion  of  the  latter  to 
the  former  being  greater  in  the  cones 
than  in  the  rods.  The  outer  seg- 
ments have  not  the  same  affinity  for 

MAN  Retina  (viewed   tersely  nito  numerous  discs  (l^ig.  566, 

from  the  surface).  B).  The  colouring  matter,  rhodopsin, 
already  referred  to,  is  found  only  in 
the  outer  segments  of  the  rods,  the  terminal  parts  of 
which  extend  into  the  layer  of  pigmented  epithelium. 

8.  Layer  of  pigmented  epithelium  (stratum  pigmenti). — This  consists  of  a  single 
stratum  of  cells  which,  on  surface  view,  are  hexagonal  (Fig.  567),  their  outer  flattened 
surfaces  being  firmly  attached  to  the  chorioid.  When  seen  in  profile  the  outer  part  of 
each  cell  contains  a  large  oval  nucleus  and  is  devoid  of  pigment,  while  the  inner  portion 
is  filled  with  pigment  and  extends  as  a  series  of  thread-like  processes  amongst  the  outer 
segments  of  the  rods  and  cones.  When  the  eye  is  kept  in  the  dark  the  pigment 
accumulates  near  the  outer  part  of  the  cell,  but  when  exposed  to  light  it  streams  in 
between  the  rods  and  cones  (Fig.  568). 

It  will  be  seen  from  the  foregoing  description  that  there  is  no  direct  continuity 
between  the  nervous  elements  which  form  the  different  layers  of  the  retina.  In  the  inner 
molecular  layer  there  is  merely  an  interlacement  between  the  dendrites  of  the  ganglionic 
layer  and  the  arborisations  of  the  cells  of  the  inner  granular  layer,  and  a  similar  inter- 
lacement in  the  outer  molecular  layer  between  the  rod  and  cone  elements  and  the 
processes  of  the  outer  granules. 

Sustentacular  fibres  of  the  retina  (fibrte  Miilleri). — These  support  the  nervous 
structures  and  extend  from  within  outwards  through  the  thickness  of  the  retina  as  far  as 
the  bases  of  the  rods  and  cones  (Fig.  565,  M).  They  begin  at  the  inner  surface  of  the 
nerve-fibre  layer  in  single  or  forked  expanded  bases,  by  the  apposition  of  which  a  delicate 
membrane,  the  membrana  limitans  interna,  is  formed.  In  the  ganglionic  layer  they  give 
off  a  few  lateral  branches,  and,  on  passing  through  the  inner  nuclear  layer,  supply  lateral 
ramifications  amongst  the  inner  granules  for  their  support ;  in  this  part  of  each  fibre 
there  is  seen  an  oval  nucleus.  In  the  outer  nuclear  layer  they  break  up  into  a  network 
of  fibrils  which  surround  the  rod  and  cone  fibres,  and  end  externally  at  the  bases  of  the 
rods  and  cones  in  a  delicate  membrane,  the  membrana  limitans  externa. 

Structure  of  the  macula  lutea  and  fovea  centralis. — The  yellow  colour 
of  the  macula  is  due  to  the  presence  of  pigment  in  the  inner  layers  of  the  retina.  At  the 
circumference  of  the  macula  the  nerve-fibre  layer  is  greatly  thinned  and  the  rods  are  few 
in  number;  the  ganglionic  layer,  on  the  other  hand,  is  thickened  and  may  contain 
from  seven  to  nine  strata  of  cells,  while  the  outer  granular  layer  is  also  thicker  and  its 
bipolar  cells  have  an  oblique  direction.  At  the  fovea  centralis  the  retina  is  much  thinned, 
since  here  its  nerve-fibre  and  ganglionic  layers  are  absent  and  its  other  strata  greatl}' 
attenuated.  The  stratum  pigmenti,  on  the  other  hand,  is  thicker  and  its  pigmentation 
more  pronounced.  The  cone  nuclei  are  situated  some  distance  internal  to  the  outer 
limiting  membrane,  and  thus  the  thin  inner  and  outer  granular  layers  are  in  apposition. 
There  are  no  rods,  and  the  cones,  closely  crowded  together,  are  narrower  and  their 
outer  segments  more  elongated  than  elsewhere,  so  that  the  line  of  their  bases,  indicated 
by  the  membrana  limitans  externa,  pi-esents  a  convexity  directed  forwards.  The  fovea 
centralis  and  macula  lutea  are  spoken  of  by  the  physiologist  as  the  "region  of  distinct  vision." 


EEFEACTING  MEDIA  OF  THE  EYEBALL. 


735 


Structure  of  the  ora  serrata. — Here  the  nervous  layers  of  the  retina  suddenly 
cease  ;  the  layer  of  rods  and  cones  first  failing,  to  be  immediately  followed  by  the  disappear- 
ance of  the  other  nervous  strata.  In  front  of  the  ora  serrata  the  retina  is  prolonged  over  the 
ciliary  processes  in  the  form  of  two  layers  of  cells  :  (a)  an  inner  layer  of  columnar  epithelium, 
and  (6)  an  outer,  consisting  of  the  stratum  pigmenti,  the  two  forming  the  pars  ciliaris 
retina>.  The  same  two  layers  are  prolonged  over  the  back  of  the  iris,  where  both  are 
pigmented  and  form  the  pars  iridica  retinae. 

Vessels  of  the  retina  (Fig.  569). — The  retina  is  supplied  by  the  arteria  centralis 
retinae,  a  branch  of  the  ophthalmic  artery,  which  pierces  the  sheath  of  the  optic  nerve  about 
three-fjuarters  of  an  inch  behind  the  eyeball,  and  makes  its  appearance  in  the  centre  of  the 
optic  disc.  Here  it  divides  into  an  upper  and  a  lower  branch,  and  each  of  these  again  bifur- 
cates into  an  internal  or  nasal,  and  an  external  or  temporal,  branch.  The  resulting  four 
branches  ramify  towards  the  periphery  of  the  retina,  and  are  named  the  superior  and 
inferior  temporal  and  the  superior  and  inferior  nasal  arteries.  The  temporal  arteries 
pass  outwards  above  and  below  the  macula  lutea,  to  which   they  give  small   branches  ; 


Upper  nasal  brancli 
Optic  disc 

Lower  nasal  branch 


Upper  temporal  branch 

Upper  and  lower  macular 
arteries 

— r  Macula  lutea 

Lower  temporal  branch 


Fig.  569. — Blood-vessels  of  the  Retina. 

these  do  not,  however,  extend  as  far  as  the  fovea  centralis,  which  is  devoid  of  blood-vessels. 
The  macula  also  receives  two  small  arteries  (superior  and  inferior  macular)  directly  from 
the  porus  opticus.  The  larger  vessels  run  in  the  nerve-fibre  layer  near  the  membrana 
limitans  interna  and  form  two  capillary  networks — an  inner,  in  the  nerve-fibre  layer,  and 
an  outer,  in  the  inner  nuclear  layer.  The  inner  network  arises  directly  from  the  arteries 
and  sends  numerous  small  branches  to  the  outer  network,  from  Avhich  the  veins  take 
origin.  The  vessels  do  not  penetrate  deeper  than  the  inner  granular  layer,  nor  do  the 
arteries  anastomose  except  through  the  capillary  plexuses.  The  veins  follow  the  course  of 
the  arteries  ;  they  have  no  muscular  coats,  but  consist  merely  of  a  layer  of  endothelial  cells, 
outside  which  is  a  perivascular  lymphatic  sheath,  surrounded  by  delicate  retiform  tissue. 


EEFEACTING  MEDIA  OF  THE  EYEBALL. 

The  vitreous  body  (corpus  vitreum)  is  a  transparent,  jelly-like  substance  situated 
between  the  crystalline  lens  and  the  retina,  and  occupying  the  posterior  four-fifths 
of  the  globe  (Fig.  558).  In  front  it  presents  a  deep  concavity,  the  fossa  patellaris,  for 
the  reception  of  the  posterior  convexity  of  the  lens.  It  is  enclosed  within  a  thin 
transparent  membrane,  the  membrana  hyaloidea,  which  is  in  contact  with  the 
membrana  limitan.s  interna  of  the  retina  and  adherent  to  it  at  the  optic  entrance. 
The  portion  of  the  membrana  hyaloidea  in  front  of  the  ora  serrata  is  thickened 
and  strengthened  by  radial  fibres,  and  is  termed  the  zonule  of  Zinn,  or  zonula  ciliaris. 
Situated  liehind  the  ciliary  body  the  zonula  is  radially  folded  and  presents  a  series 
of  alternating  furrows  and  elevations.  The  ciliary  processes  are  received  into,  and 
are  firmly  adherent  to,  the  furrows,  with  the  result  that,  if  removed,  some  of  their 
pigment  remains  attached  to  the  zonula.  The  elevations  of  the  zonula  are  not 
attached  to  the  interciliary.  depressions,  but  are  separated  by  a  series  of  lymph 
spaces  (recessus  camene  posterioris) ;  these  may  be  regarded  as  diverticula  of  the 


736 


THE  OEGANS  OF  SENSE. 


Fig, 

AND 


posterior  chamber  with  which  they  communicate.  As  the  zonula  approaches  the 
equator  of  the  lens  it  splits  into  two  chief  layers,  viz. :  (a)  a  thin  posterior  lamina, 
which  covers  that  portion  of  the  membrana  hyaloidea  which  lines  the  fossa  patellaris; 
and  (b)  a  thicker  anterior  layer,  termed  the  suspensory  ligament  of  the  lens  (Fig. 
558),  which  blends  with  the  front  of  the  lens  capsule  a  short  distance  from  its 
equator.  Scattered  fibres  of  this  ligament  are  also  attached  to  the  equator  itself 
and  to  the  regions  immediately  anterior  and  posterior  to  it.  By  this  suspensory 
Ligament  the  lens  is  retained  in  position,  and  its  convexity  varies  inversely  with 
the  degree  of  tension  of  the  ligament.  The  radial  fibres  of  the  ciliary  muscle,  by 
pulling  forward  the  ciliary  processes  and  the  attached  zonule  of  Zinn,  relax  the 
ligament,  and  thus  allow  the  lens  to  become  more  convex.  Behind  the  suspensory 
ligament  a  sacculated  lymph  space  surrounds  the  equator  of  the  lens ;  it  is  named 
the  canal  of  Petit,  and  may  easily  be  inflated  on  introducing  a  fine  blow-pipe 
through  the  suspensory  ligament  (Fig.  570).     In  the  foetus  a  blood-vessel,  termed 

the  arteria  hyaloidea,  is  continued  from  the  arteria 
centralis  retinee  forwards  through  the  vitreous 
body  for  the  supply  of  the  capsule  of  the  lens. 
Its  position,  in  the  adult,  is  represented  by  a  lymph 
channel,  termed  the  canalis  hyaloideus  of  Stilling 
(Fig.  558),  the  presence  of  which  may  be  de- 
monstrated by  shaking  up  the  vitreous  body  in  a 
solution  of  picrocarmine,  when  some  of  the  pig- 
ment may  be  seen  to  extend  along  the  canal 
(Anderson  Stuart). 

When  the  vitreous  body  is  treated  by  a  weak 
solution  of  chromic  acid  it  presents  a  series  of 

iSTo'XxHBFSx'SSS)":  «™r'""'  P«"Phe-Uy  arranged  Btria.,  together 

With  numerous  radial  strise  converging  towards 
its  centre.  Between  these  the  more  fluid  part  lies,  and  it  frequently  contains 
vacuolated  amoeboid  cells  scattered  through  it.  The  vitreous  body  consists  of  9 8 "4 
per  cent  of  water,  having  in  solution  about  1-4  per  cent  of  sodium  chloride  and 
traces  of  extractives  and  albumen. 

The  crystalline  lens  (lens  crystallina)  lies  in  front  of  the  vitreous  body  and 
behind  the  iris,  and  is  a  biconvex,  transparent  body  (Fig.  558).  It  is  enclosed  in 
a  thin,  transparent,  homogeneous  capsule,  the  capsule  of  the  lens  (capsula  lentis). 
The  central  points  of  its  anterior  and  posterior  surfaces  are  termed  respectively  its 
anterior  and  posterior  poles,  a  line  joining  which  is  known  as  its  axis  (axis  lentis) ; 
its  peripheral  circumference  is  named  the  equator  (sequator  lentis).  Its  axial 
measurement  is  4  mm.,  and  its  transverse 
diameter  from  9-10  mm.  Its  anterior  surface 
(facies  anterior  lentis)  is  less  curved  than 
the  posterior,  and  its  central  part  corresponds 
with  the  aperture  of  the  pupil  and  is  directed 
towards  the  anterior  chamber.  Around  the 
aperture  of  the  pupil  the  pupillary  margin 
of  the  iris  rests  upon  the  lens,  but  its  peri- 
pheral part  is  separated  from  it  by  the 
aqueous  humour  of  the  posterior  chamber. 
Its  posterior  surface  (facies  posterior  lentis), 
more  convex  than  the  anterior,  occupies  the 
fossa  patellaris  of  the  vitreous  body.  The 
relations  of  its  equator  to  the  suspensory 
ligament  and  the  canal  of  Petit  have  already 
been  referred  to.  The  superficial  part  of  tlie  lens  possesses  a  refractive  index  of 
•  about  1'4,  and  its  central  part  or  nucleus  one  of  about  1*45.  The  curvatures  of 
its  surfaces,  especially  that  of  the  anterior,  are  constantly  varying  during  life  for 
the  purpose  of  focusing  rays  i'rom  near  or  distant  objects  on  the  retina. 

The  lens  substance  Tsubstantia  lentis)  consists  of  a  soft  outer  part,  the  substantia 
corticalis,  easily  crushed  between  the  finger  and  thumb,  and  of  a  dense  central  part. 


Nucleus 
lentis 


Fig.  571. — Lens  hardened  in  Formalin  and 
dissected  to  show  its  concentuic  laminie 
(enlarged). 


EEFEACTING  MEDIA  OF  THE  EYEBALL. 


737 


Fui.  572.- 


-DlAGEAMMATIC    RePRI' SENTATION 

Lentis  of  the  Foltal  Lens. 


THE    UaDII 


A,  Seen  from  the  front  ;  B,  From  behind. 


the  nucleus  lentis.  Faint  lines  (radii  lentis)  radiate  from  its  anterior  and  posterior 
poles  towards  its  equator.  In  the  foetus  they  are  three  in  number,  and  form  with 
each  other  angles  of  120°  (Fig.  572).  From  the  anterior  pole  one  ray  ascends 
vertically  and  the  other  two  diverge  downwards,  while  from  the  posterior  pole  one 
ray  descends  vertically  and  the 
other  two  diverge  upwards.  In 
the  adult  the  rays  may  be  increased 
to  six  or  more.  They  represent 
the  free  edges  of  a  corresponding- 
number  of  septa  which  dip  into 
the  substance  of  the  lens,  and 
along  which  the  extremities  of  the 
different  groups  of  lens  fibres  come 
into  contact,  and  are  attached 
by  a  clear,  amorphous  substance. 
The  lens,  when  hardened,  exhibits 
a  series  of  concentrically  arranged 
laminte  (Fig.  571),  superimposed  like  the  coats  of  an  onion  and  attached  to  each 
other  by  a  clear,  amorphous  substance.  Each  lamina  is  split  along  the  radiating 
lines,  and  consists  of  a  series  of  hexagonal,  riband-like  fibres,  the  fibrse  lentis, 
which  are  adherent  to  each  other  by  their  margins ;  those  of  the  deeper  laminse 
are  smaller  and  serrated,  but  non-nucleated ;  while  those  of 
the  superficial  coats  are  larger  and  nucleated,  but  non-serrated. 
The  fibres  extend  in  a  curved  manner  from  the  rays  on 
the  anterior  surface  to  the  rays  on  the  posterior  surface,  but 
no  fibre  extends  from  pole  to  pole.  Fibres  which  start  at  or 
near  one  pole  end  at  or  near  the  equator  on  the  opposite 
surface,  and  vice  versa,  while  the  intervening  fibres  take  up 
intermediate  positions.  Between  the  substantia  lentis  and  the 
anterior  part  of  the  capsule  there  is  a  layer  of  nucleated 
columnar  epithelial  cells,  the  epithelium  lentis.  On  being 
traced  towards  the  equator  its  cells  become  gradually  elongated 
and  transformed  into  lens  fibres,  which,  when  fully  formed, 
lose  all  trace  of  their  nuclei,  except  in  the  more  superficial 
laininse.  Each  lens  fibre  represents,  therefore,  a  greatly 
elongated  columnar  cell  (Fig.  573). 

In  the  foetus  the  lens  is  soft,  of  a  pinkish  colour,  and  nearly 
spherical ;  while  in  old  age  it  becomes  more  flattened  than  in 
the  adult,  and,  losing  its  transparency,  assumes  a  yellowish 
tint. 

Chambers  of  the  Eye  and  Aqueous  Humour  (Fig.  558). — 
As  already  stated  (p.  730),  the  space  between  the  cornea  and 
the  lens  is  divided  by  the  iris  into  two  unequal  parts,  viz.  the 
anterior  chamber  in  front  and  the  posterior  chamber  behind. 
These  are  filled  by  the  aqueous  humour,  and,  in  the  adult, 
communicate  freely  through  the  aperture  of  the  pupil,  but  in 
the  fffitus  are  separated  from  each  other  by  the  pupillary 
membrane.  The  anterior  chamber  (camera  oculi  anterior)  is 
bounded  in  front  by  the  cornea,  behind  by  the  iris  and  lens, 
whilst  peripherally  it  communicates  with  the  spaces  of  Fontana. 
Section  thkough  the  The  posterior  chamber  (camera  oculi  posterior)  is  triangular 
Equator  of  the  Lens.  ^^  section,  and  is  bounded  in  front  by  the  iris,  behind  by 
the  circumferential  part  of  the  lens  and  its  suspensory  liga- 
ment ;  the  base  of  the  triangle,  situated  externally,  corresponds 
with  the  thick,  anterior  extremities  of  the  ciliary  processes.  It 
communicates  with  the  recessus  camerge  posterior  and  canal 
of  Petit.  The  aqueous  humour  has  a  refractive  index  of  about  1"336,  and  consists 
of  about  98  per  cent  of  water,  with  1-4  per  cent  of  sodium  chloride  and  traces  of 
albumen. 
51 


Fig.  573. 


Showing  the  gradual  tran- 
sition of  the  epithelium 
into  lens  fibres  (after 
Babuchin). 


738 


THE  ORGANS  OF  SENSE. 


EYELIDS. 

The  eyelids  or  palpebrse  are  two  movable  cutaneous  curtains  situated  in  front 
of  the  eyeball,  and  named,  from  their  position,  upper  and  lower.  The  upper  is  the 
larger  and  more  movable,  being  provided  with  a  special  elevator  muscle,  the  m. 
levator  palpebrae  superioris.  The  interval  between  the  lids  is  termed  the  palpebral 
fissure  (rima  palpebrarum),  and  measures  transversely  about  30  mm.,  but  varies 
considerably  in  different  individuals  and  in  different  races.  When  the  eye  is  open 
the  fissure  is  elliptical  in  shape,  but  when  closed  it  assumes  the  form  of  a  transverse 
slit,  which  lies  on  a  level  with  the  lower  margin  of  the  cornea.  The  two  lids  meet 
at  the  extremities  of  the  fissure,  and  form  the  outer  and  inner  angles,  or  cantM. 
Their  free  margins  are  flattened  and  are  surmounted  by  eyelashes  from  the  external 


\Va^'l  \ 


n 


Meibomian  gland  in  tarsal 
plate 


Tendon  of  levator  palpebraj 
^  superioris 


Muscle  of  Riolan 


Orbicularis  palpebraiiim 


Eyelashes 


Fig.  .574. — Vertical  Section  through  Upper  Eyelid. 


canthus  to  a  point  about  5  mm.  from  the  inner  canthus — a  point  indicated  by  a 
small  papilla,  the  papilla  lacrimalis.  Internal  to  this  papilla  the  margins  are 
rounded  and  destitute  of  eyelashes,  and  form  the  upper  and  lower  boundaries 
of  a  triangular  space,  termed  the  lacus  lacrimalis,  which  is  occupied  by  a  small 
pale-red  body,  the  caruncula  lacrimalis.  This  caruncula  consists  of  a  minute 
island  of  modified  skin,  and  contains  sweat  glands,  sebaceous  glands,  and  fine  hairs. 
Posteriorly  the  lids  are  lined  by  a  mucous  membrane,  the  conjunctiva,  and  are  in 
contact  with  the  eyeball,  except  near  the  inner  canthus,  where,  Ijetween  the  eyeball 
and  the  caruncula  lacrimalis,  there  intervenes  a  vertical  fold  of  conjunctiva,  the  plica 
semilunaris  conjunctivse.  This,  which  in  many  animals  contains  a  plate  of  cartilage, 
is  the  representative  of  the  membrana  nictitans,  or  third  eyelid  of  birds,  etc. 

In  each  lid  there  exists  a  framework  of  condensed  fibrous  tissue,  which  gives 
consistence  and  shape  to  the  lid,  and  is  termed  the  tarsal  plate  or  tarsus.  In  front 
of   the   tarsus   are   the    fibres   of   the   orbicularis   palpebrarum   muscle   and    the 


EYELIDS.  739 

integument,  while  embedded  in  its  posterior  surface,  and  covered  by  the  conjunctiva, 
are  numerous  modified  sebaceous  glands  named  the  tarsal  or  Meibomian  glands. 
The  superior  tarsal  plate  (tarsus  superior)  is  larger  than  the  inferior  and  of  a  half 
oval  shape,  with  its  greatest  vertical  diameter  measuring  about  10  or  11  mm.  Its 
upper  margin  is  thin  and  convex,  and  is  continuous  with  the  tendon  of  the  levator 
palpebrte  superioris  muscle,  while  its  lower  edge  is  thick  and  straight.  The  inferior 
tarsal  plate  (tarsus  inferior)  is  a  thin,  narrow  strip,  with  a  nearly  uniform  vertical 
diameter  of  about  5  mm.  The  extremities  of  the  two  plates  are  continuous 
with  the  external  and  internal  tarsal  ligaments.  The  external  tarsal  ligaDient  is  a 
narrow  band  attached  to  the  malar  bone ;  it  divides,  at  the  outer  canthus,  into 
upper  and  lower  pieces  which  are  fixed  to  the  margins  of  the  respective  tarsal 
plates.  The  internal  tarsal  ligament  is  a  strong  band  attached  to  the  nasal  process 
of  the  superior  maxillary  bone  directly  in  front  of  the  lachrymal  groove ;  it  divides 
at  the  inner  canthus  into  two  slips,  one  for  either  tarsal  plate. 

The  eyelids  are  further  strengthened  by  membranous  expansions,  termed  the 
superior  and  inferior  palpebral  ligaments,  which  extend  into  them  from  the  margin 
of  the  orbit.  The  superior  ligament  is  continuous,  along  the  upper  margin  of  the 
orbit,  with  the  pericranium  and  with  the  periosteal  lining  of  the  orbit,  and  blends 
below  with  the  tendon  of  the  levator  palpebrte  superioris.  The  inferior  ligament  is 
prolonged  from  the  under  edge  of  the  inferior  tarsal  plate  to  the  lower  margin  of 
the  orbit,  where  it  is  continuous  with  the  periosteum  of  the  face  and  orbital  floor. 
Externally  the  two  palpebral  ligaments  fuse  to  form  the  external  tarsal  ligament, 
while  internally  they  become  thinned,  and,  separating  from  the  internal  tarsal 
ligament,  are  attached  to  the  lachrymal  bone  behind  the  lachrymal  sac.  These  two 
palpebral  ligaments  form  a  kind  of  septum  or  diaphragm,  the  septum  orbitale, 
between  the  superficial  and  deep  structures  of  the  eyelids;  this  septum  is  perforated 
by  the  vessels  and  nerves,  which  extend  from  the  orbital  cavity  to  the  face  or 
scalp. 

The  skin  covering  the  lids  is  thin  and  delicate,  and  is  continuous,  at  their  margins, 
with  their  conjunctival  lining.  It  contains  numerous  small  sweat  glands  and  fine 
hairs,  the  latter  being  provided  with  sebaceous  follicles.  Branched  pigment  cells 
are  present  in  the  cutis,  and  pigment  also  exists  in  the  deep  layers  of  the  epidermis. 
The  subcutaneous  tissue  is  loose  and  devoid  of  fat,  and  in  it  are  found  the  fibres  of 
the  orbicularis  palpebrarum  muscle — a  small  separate  bundle  of  which,  termed  the 
muscle  of  Riolan,  occupies  the  margin  of  the  lids  behind  the  eyelashes.  The 
Meibomian  glands,  or  glandulse  tarsales,  are  elongated  sebaceous  glands  with 
numerous  lateral  offshoots  ;  they  are  embedded  in  the  tarsal  plates  and  filled  with 
cubical  epithelium.  There  are  from  twenty-five  to  thirty  in  the  upper  lid,  and  from 
twenty  to  twenty-five  in  the  lower ;  they  open  by  small  ducts,  about  1  mm.  in 
length,  along  the  lid  margins  behind  the  eyelashes  ;  the  ducts  are  lined  by  stratified 
epithelium  placed  on  a  basement  membrane.  Between  the  eyelashes  and  the 
muscle  of  Eiolan  are  two  or  three  rows  of  modified  sweat  glands,  termed  the  glands 
of  Moll ;  the  blocking  of  a  duct  of  one  of  these  glands  frequently  gives  rise  to  a  stye. 

H.  Miiller  described  a  layer  of  non-striped  muscle  in  each  lid  :  in  tlie  upjjer  extending  from 
the  tendon  of  the  levator  palpebrse  superioris  to  the  upper  tarsal  plate,  and  in  the  lower 
connecting  the  inferior  tarsal  plate  with  the  inferior  oblicj^ue  muscle. 

The  tendon  of  the  levator  palpebrse  superioris  divides  into  three  parts — an 
anterior,  passing  between  the  bundles  of  the  orbicularis  to  the  deep  surface  of  the 
skin ;  a  middle,  attached  to  the  superior  tarsal  plate ;  and  a  posterior,  to  the  fornix 
conjunctivee :  there  is  no  corresponding  muscle  in  the  lower  lid.  The  eyelashes  are 
curved,  silky  hairs  which  project  from  the  free  margins  of  the  lids ;  in  the  upper 
lid  they  are  longer  and  more  numerous  than  in  the  lower,  and  are  curved  upwards, 
while  those  of  the  lower  lid  are  bent  downwards. 

Conjunctiva. — This  is  the  name  applied  to  the  mucous  membrane  which  Lines 
the  back  of  the  lids  (tunica  conjunctiva  palpebrarum),  and  is  continued  on  to  the 
front  of  the  eyeball  (tunica  conjunctiva  bulbi).  The  line  along  which  it  is  reflected 
from  the  lids  on  to  the  globe  of  the  eye  is  termed  the  fornix  conjunctivae.  The 
palpebral  portion  adheres  intimately  to  the  tarsal  plate  and  presents  numerous 
papillae.  It  is  covered  by  a  layer  of  columnar  epithelial  cells,  beneath  the  bases 
51  a 


740  THE  OKGANS  OF  SENSE. 

of  which  are  small  flattened  cells.  Near  the  fornix  a  number  of  acino-tubular 
glands,  much  more  plentiful  in  the  upper  than  in  the  lower  hd,  open  on  its  free 
surface.  The  conjunctiva  bulbi  is  thinner  than  that  lining  the  lids,  and  is  loosely 
attached  to  the  sclera  by  submucous  tissue.  The  plica  semilunaris  conjunctivae  has 
already  been  referred  to  (p.  738).  On  the  cornea  the  conjunctiva  is  represented 
merely  by  the  stratified  epithelium  already  described  (p.  726). 

Vessels  and  Nerves. — Tlie  cliief  arteries  of  the  eyelids  are  the  superior  and  inferior  palpe- 
bral branches  of  the  ophtlialmic,  which  jDiei-ce  the  septnm  orbitale  above  and  below  the  internal 
tarsal  ligament,  and  run  tortuously  outwards  in  the  corresponding  lid  near  its  free  margin.  On 
reaching  the  region  of  the  outer  canthus  they  anastomose  with  each  other  and  with  twigs  from 
the  lachrymal,  superficial  temjaoral,  and  transverse  facial  arteries,  and  in  this  way  an  arch  is 
formed  in  each  lid.  (upper  and  lower  tarsal  arches).  Secondary  smaller  arches  are  found,  one 
above  the  primary  arch  in  the  upper  lid,  and  another  below  that  of  the  lower  lid,  while  the  upper 
lid  also  receives  branches  from  the  supraorbital  and  frontal  arteries.  The  veins  are  arranged  in 
two  sets  :  (a)  subconjunctival  or  retrotarsal,  oj^eninginto  the  muscular  tributaries  of  the  ophthalmic 
vein,  and  (6)  pretarsal,  into  the  angular  and  superficial  temporal  veins.  The  lymphatics, 
like  the  veins,  form  pre-  and  retrotarsal  networks,  which  communicate  with  each  other  through 
the  tarsal  plates.  The  lymph  is  chiefly  drained  into  the  perauricular  and  parotid  lymphatic 
glands,  but  partly,  by  vessels  which  accompany  the  facial  vein,  into  the  submaxillary  lymphatic 
glands.  The  sensory  nerves  of  the  eyelids  are  supplied  by  the  fifth  cranial  nerve — the  upper 
lid  chiefly  by  the  sujH'aorbital  and  sujDratrochlear  branches  of  the  ophthalmic ;  the  lower,  by 
the  infraorbital  branch  of  the  superior  maxillary.  The  region  of  the  outer  canthus  receives 
some  filaments  from  the  lachrymal  nerve,  that  of  the  inner  from  the  infratrochlear.  These 
sensory  nerves  form  a  marginal  plexus  l^ehind  the  orbicularis  palpebrarum  muscle.  The  levator 
palpebrte  muscle  is  supplied  by  the  third  cranial  nerve  and  the  non-striped  fibres  of  the  lids  by 
the  sympathetic. 

LACHEYMAL  APPARATUS. 

The  lachrymal  apparatus  (apparatus  lacrimalis)  consists  of :  (1)  the  lachrymal 
gland,  which  secretes  the  tears  ;  (2)  the  lachrymal  canals,  by  which  they  are  drained 
from  the  front  of  the  globe  ;  and  (3)  the  lachrymal  sac  and  nasal  duct,  which  convey 
them  into  the  nasal  cavity. 

The  lachrymal  gland  is  a  flattened,  oval  body  situated  in  the  upper  and  outer 
part  of  the  orbital  cavity,  and  consists  of  two  portions — orbital  and  palpebral — 
imperfectly  separated  from  each  other  by  the  expansion  of  the  tendon  of  the  levator 
palpebrse  superioris  muscle.  The  orbital  portion,  or  glandula  lacrimalis  superior, 
is  firm  and  much  larger  than  the  palpebral  part ;  it  measures  transversely  about 
20  mm.,  and  sagittally  from  12-14  mm.  It  occupies  the  fossa  lacrimalis  on  the  inner 
aspect  of  the  external  angular  process  of  the  frontal  bone,  and  is  fixed  by  fibrous 
bands  to  its  periosteum,  while  its  inferior  surface  is  in  contact  with  the  levator 
palpebrae  superioris  and  external  recti  muscles  which  intervene  between  it  and  the 
globe  of  the  eye.  The  smaller,  palpebral  portion,  or  glandula  lacrimalis  inferior, 
consists  of  small,  loosely  aggregated  lobules.  It  lies  below  and  in  front  of  the  orbital 
portion,  and  projects  into  the  posterior  part  of  the  upper  eyelid,  where  its  deep 
surface  is  in  contact  with  the  conjunctiva.  The  ducts  which  drain  the  orbital 
portion  are  from  three  to  five  in  number ;  they  pass  between  the  lobules  of  the 
palpebral  portion,  and  open  at  the  upper  and  outer  part  of  the  fornix  conjunctivae. 
The  ducts  of  the  palpebral  portion  number  from  three  to  nine  ;  some  of  them  join 
those  from  the  orbital  part,  while  others  open  separately  at  the  fornix  conjunctivae. 
The  lachrymal  gland  has  a  structure  similar  to  that  of  the  parotid,  and  is  supplied 
by  the  sympathetic  and  lachrymal  nerves  and  by  the  lachrymal  artery,  while  its 
veins  are  drained  into  the  ophthalmic  vein. 

The  lachrymal  canals  (ductus  lacrimales)  commence  by  minute  orifices,  termed 
the  prmcta  lacrimalia,  at  the  apices  of  the  papillse  lacrimales  already  referred  to  (p. 
738).  The  upper  canal  is  the  smaller  of  the  two,  and  at  first  ascends  for  a  short 
distance,  and  then  runs  inwards  and  slightly  downwards  ;  the  lower  descends  for  a 
short  distance  and  then  runs  horizontally  inwards.  At  the  angle  where  they 
change  their  direction  each  is  dilated  into  an  ampulla  (ampulla  ductus  lacrimalis). 
They  occupy  the  margins  of  the  lids,  where  these  bound  the  lacus  lacrimalis,  and 
the  two  canals  open  close  together  into  the  outer  and  fore-part  of  the  lachrymal 
sac,  a  little  below  its  middle ;  sometimes  they  open  separately  into  a  pouch-like 
dilatation    of  the   sac,  termed  the  sinus  of  Maier.      Each  canal  is  lined  by  a 


DEVELOPMENT  OF  THE  EYE. 


741 


stratified  epithelium  placed  on  a  tunica  propria,  outside  which  is  a  layer  of 
striped  muscular  fibres  derived  from  the  tensor  tarsi  muscle.  These  muscular 
fibres  are  arranged  somewhat  spirally  around  the  canals,  but  at  the  bases  of 
the  papillae  they  are  circular  in  direction  and  form  a  species  of  sphincter.  On 
contraction  they  serve  to  empty  the  contents  of  the  lachrymal  canals  into  the 
lachrymal  sac. 

The  lachrymal  sac  and  nasal  duct  together  form  the  passage  by  which  the  tears 
are  conveyed  from  the  lachrymal  canals  to  the  nose. 

The  lachrymal  sac  (saccus  lacrimalis)  is  the  upper  expanded  part  of  the  passage, 
and  measures  from  12-15  mm.  in  length,  about  7  mm.  antero-posteriorly,  and 
from  4-5  mm.  transversely.  It  lies  in  the  groove  formed  by  the  lacln-ynial  bone 
and  nasal  process  of  the  superior  maxilla,  and  ends  above  in  a  rounded,  blind 
extremity  or  fundus,  while  it  narrows  below  into  the  nasal  duct.  Here  a  fold  of 
mucous  membrane,  named  the  valve  of  Beraud,  together  with  a  laterally  directed 
pouch,  the  sinus  of  Arlt,  are  sometimes  present.  Near  its  superior  extremity  it 
is  crossed  m  front  by  the  internal  tarsal  ligament,  from  the  upper  and  lower 
edges  of  which  the  orbicularis  palpebrarum  takes  origin,  while  behind  it  is  the 
tensor  tarsi  muscle,  or  muscle  of  Horner. 

The  nasal  duct  (ductus  naso-lacrimalis)  averages  about  18  mm.  in  length,  and 
has  a  diameter  of  from  .3-4  mm.  Eather  narrower  near  its  middle  than  at  its  upper 
and  lower  extremities,  it  is  directed  downwards  and  slightly  backwards,  and  opens 
into  the  inferior  meatus  of  the  nose  at  the  junction  of  its  anterior  with  its  posterior 
three-fourths,  i.e.  a  distance  of  30-35  mm.  from  the  posterior  boundary  of  the 
nostril.  Its  lower  orifice  is  somewhat  variable  in  form  and  position,  and  is 
occasionally  duplicated.  It  is  frequently  guarded  by  a  fold  of  mucous  membrane, 
termed  the  valve  or  plica  lacrimalis  of  Hasner.  Through  this  orifice  the  mucous  lining 
of  the  duct  is  continuous  with  that  of  the  nose.  The  mucous  membrane  of  the  duct 
is  thrown  into  inconstant  folds,  several  of  which  have  been  described  as  valves. 
Its  epithelium  is  columnar  and  in  part  ciliated  ;  opening  into  the  lower  part  of  the 
duct  are  numerous  glands  similar  to  those  in  the  nasal  mucous  membrane.  The 
nerves  of  the  lachrymal  canals  and  sac  are  derived  from  the  infratrochlear  branch 
of  the  nasal ;  their  arteries  from  the  inferior  palpebral  and  nasal.  The  veins  of  the 
nasal  duct  are  large  and  numerous,  forming  a  sort  of  erectile  tissue  similar  tn  that 
in  the  nose. 

Development  of  the  Eye. 

The  retina  and  ojitic  nerve  are  developed  from  a  hollow  outgrowth  of  the  fore-brain,  termed 
tlie  optic  vesicle  (see  pp.  178  and  595).     This  extends  towards  the  side  of  the  head,  and  its 


Lens  rudiment 
Optio  cup 
Optic  stalk 


Optic 

vesicle 

becoming 

cupped 


-Outer  layer  of  optic  cup 
-Inner  layer  of  optic  cup 

Lens 


Optic  stalk 
Chorioidal  fissure 


Fig.  575.— 

of 


-Sections  through  Portions  of  the  Heads  of  Fcetal  Rabbits,  to  illustrate  tlie  connexion 
the  optic  cup  with  the  fore-brain,  and  the  invagination  of  the  ectoderm  to  form  the  lens. 


connexion  with  the  brain  is  gradually  elongated  to  form  the  optic  stalk.     The  ectodenii 
overlying  the  optic  vesicle  becomes  thickened,  invaginated,  and  finallv  cut  off  as  a  hollow 
51& 


742  ■     THE  OKGANS  OF  SENSE. 

island  of  cells,  which  is  developed  into  the  lens  and  is  named  the  lens  vesicle.  This  lens 
rudiment  indents  the  outer  and  lower  part  of  the  optic  vesicle,  which  now  assumes  the  form 
of  a  cup  (optic  cup),  lined  by  two  layers  of  cells  continuous  with  each  other  at  the  margin 
of  the  cup.  The  inner  of  these  strata,  thicker  than  the  outer,  is  named  the  retinal  layer, 
and  becomes  differentiated  into  the  nervous  and  supporting  elements  of  the  retina ;  while 
the  outer,  named  the  pigmentary  layer,  forms  its  pigmented  epithelium.  The  edge  of  the 
optic  cup  extends  in  front  of  the  equator  of  the  lens,  and  bounds  the  future  aperture  of 
the  pupil.  In  front  of  the  lens,  and  also  opposite  its  equator,  the  retinal  layer  is  thin, 
and  represented  only  by  a  stratum  of  columnar  cells  which  becomes  closely  applied  to 
the  pigmentary  layer,  the  two  foi'ming  the  pars  ciliai'is  and  pars  iridica  retinae.  The  in- 
dentation of  the  optic  cup  extends  as  a  groove  for  some  distance  along  the  postero-inferior 
aspect  of  the  optic  stalk,  forming  what  is  termed  the  chorioidal  fissure  (Fig.  576).  Through 
this  fissure  the  mesoderm  passes  inwards  between  the  lens  and  the  retina  to  form  the  vitreous 
body,  while  the  arteria  centralis  retinae  also  becomes  enclosed  in  it  and  so  gains  its  future 
position  in  the  centre  of  the  optic  nerve.  The  arteria  centralis  is  prolonged  forwards 
from  the  porus  opticus  through  the  vitreous  body,  as  a  cone  of  branches,  as  far  as  the 
back  of  the  lens.  By  the  fifth  or  sixth  month  all  these  branches  have  disappeared  except 
one,  the  arteria  hyaloidea,  which  persists  until  the  last  month  of  foetal  life,  when  it  also 
atrophies,  leaving  only  the  canalis  hyaloideus  to  indicate  its  position. 

The  lens  rudiment,  at  first  in  contact  with  the  ectoderm,  from  which  it  is  derived, 
soon  becomes  separated  from  it  by  mesoderm,  and  then  consists  of  a  rounded  vesicle  lined 

by  epithelium.     The  epithelium  w^hich  lines  the  anterior 

Qpart  of  the  vesicle  remains  as  a  single  layer  of  cells — 
TN  -V  f  t  th^  anterior  lens  epithelium  of  the  adult.  The  cells 
^\  "    lining  the  posterior  part  of  the  vesicle  become  elongated 

^^°*cViitraUs  "^^"^  lens  fibres,  and  by  the  forward  growth  of  these  the 
fW  Chorioidal  cavity  of  the  vesicle  is  obliterated.  This  elongation  into 
^      fissure  lens  fibres  is  greatest  at  the  centre  of  the  lens,  while 

"----^Lgjig  near  the  equator  the  fibres  are  shorter,  and  here  the 

gradual  transition  between  the  anterior  epithelium  and 
Fig.  576. — Optic  Cdp  and  Lens  viewed   the  lens  fibres  is  seen  (Fig.  573).     The   lens  becomes 
FROM  Behind  and  Below,  to  show   enveloped  in  a  vascular  tunic,  which  receives  its  vessels 
formation  of  chorioidal    fissure  and  ^^  ^^.^^^..^  centralis  retina  and  from  the  vessels 

enclosure  of  the  arteria  centralis  re-  .   .  pi.  •      p  i 

tina;  (from  model  by  Ziegler).  of  the  iris.      i  he  front   part  ot  this  tunic   forms   the 

membrana     pupillaris,     and     this,    like     the    rest    of 
the  tunic,  disapjDears  before  birth. 

The  hollow  stalk  of  the  optic  cup  becomes  solid  by  the  thickening  of  its  walls  and  the 
obliteration  of  its  cavity,  and,  acquiring  nerve-fibres,  becomes  the  optic  nerve.  These  nerve- 
fibres  are  mostly  centripetal,  and  are  derived  from  the  nerve-cells  of  the  retina  :  but  a  few 
are  centrifugal  and  have  their  origin  in  the  brain.  The  further  development  of  the  retina 
resembles,  in  certain  respects,  that  of  the  spinal  cord. 

Cameron  states  ("The  Development  of  the  Retina  in  Amphibia,"  Journ.  Anat.  and  Physiol, 
London,  vol.  xxxix.)  that  in  the  early  stages  of  the  development  of  the  inner  or  retinal  layer  of 
the  optic  cup  all  the  structures,  described  by  His  as  being  present  in  the  spinal  cord  of  the 
human  embryo,  are  to  be  found,  viz.  (a)  spongiol)lasts,  (b)  germinal  cells,  and  (c)  neuroblasts. 

The  spongioblasts  undergo  ramification  and  form  a  network  or  myelospongium,  and  also  give 
rise  to  the  inner  and  outer  limiting  membranes  ;  the  latter  is  next  the  original  cavity  of  the  optic 
vesicle,  and  therefore  corresponds  to  the  inner  limiting  membrane  of  the  spinal  cord.     The  ' 
spongioblasts  also  form  the  groundwork  of  the  inner  and  outer  molecular  layers  into  which  the 
processes  of  the  neuroblasts  grow  and  arborise. 

The  germinal  cells  are  always  situated  beneath  tlie  external  limiting  membrane,  and  by  their 
division  give  rise  to  the  neuroblasts.  The  first-formed  neuroblasts  are  larger  than  those  of 
succeeding  generations,  and  are  found  in  tlie  site  of  the  future  ganglionic  layer.  The  germinal 
ceUs  in  the  middle  of  the  convexity  of  the  retinal  cup  cease  to  divide  at  an  early  stage  of 
development,  and  become  directly  transformed  into  the  rod  and  cone  cells  from  which  the  rods 
and  cones  develop  as  processes  ;  hence  these  structures  appear  first  over  the  middle  of  the 
convexity  of  the  retina,  and  gradually  extend  towards  the  inarghi  of  the  retinal  cup. 

The  nuclei  of  the  retinal  neuroblasts  undergo  a  progressive  diminution  in  size — in  some 
cases  to  one-fourth  of  that  of  their  earlier  stages.  Cameron,  after  a  careful  study  of  the  neuro- 
blasts, not  only  in  the  retina,  but  in  the  wall  of  the  cerebival  vesicle  and  spinal  cord,  is  of  opinion 
that  the  neurohlastic  nuclei  are  destitute  of  a  protoplasmic;  investment,  and  that  what  has  been 
described  as  a  zone  of  "clear  protoplasm  "  surrounding  these  nuclei  during  the  process  of  karyo- 
kinesis  is  simply  the  achromatic  nuclear  substance  set  free  Ijy  the  disappearance  of  the  nuclear 
membrane  ;  and,  further,  that  the  processes  which  grow  out  from  the  neuroblasts  in  reality  issue 
from  the  substance  of  the  nuclei  and  thus  cause  the  gradual  diminution  in  size  of  the  latter, 
"  The  processes  of  the  retinal  'ganglion-cells '  and  of  the  cells  of  tlie  inner  nuclear  layer  first  show 


THE  EXTEENAL  EAE.  743 

themselves  as  i^rotrusions  of  the  nuclear  contents,  while  tlie  rods  and  cones  are  at  first  also 
protrusions  of  the  nuclei  of  tlie  external  nuclear  layer.  The  rod  and  cone  elements,  when  they 
first  ajjjjear,  do  so  as  jierfectly  clear  sjiherical  globules  consisting  of  nothing  more  than  nuclear 
achromatin.  The  axis-cylinders  of  the  optic  nerve  arise  as  processes  of  the  nuclei  in  the 
ganglionic  layer,  and  the  great  difficulty  which  is  experienced  in  staining  the  individual  fibres 
of  the  retinal  nerve-fibre  layer  is  due  to  the  fact  that  tliey  are  composed  of  the  achromatic 
nuclear  substance  of  the  ganglionic  nuclei.  The  origin  of  the  axis-cylinders  from  these  nuclei 
sujjports  the  contention  of  those  who  insist  on  tlie  fact  that  the  axis-cylinder  jirocess  of  a  nerve- 
cell  can  be  traced  right  into  the  nucleus  of  that  cell." 

The  molecular  layers  make  their  appearance  as  plexuses  of  myelospongium.  Tlie  internal 
molecular  layer  is  first  developed  at  the  centre  of  the  retinal  cup,  and  gradually  extends  towards 
the  cup  margin,  and  into  it  the  jirocesses  from  tlie  nuclei  on  either  side  grow  and  ramify.  The 
rod  and  cone  fibres,  and  the  outer  processes  of  the  internal  nuclear  layer,  grow  into  and  arborise 
within  the  external  molecular  layer. 

The  most  interesting  points  with  reference  to  the  development  of  the  nuclear  layers  are, 
(1)  the  extrusion  of  the  various  processes  from  the  nuclei  as  already  described,  and  (2)  the  free 
manner  m  which  these  nuclei  multiply  by  direct  division  during  the  metamori^hosis.  It  is 
interesting  to  note  that  the  retinal  nuclei  are  formed  during  the  early  stages  by  mitotic  or 
indirect  clivision  of  the  germinal  cells,  while  later  they  ajjpear  ca2:)able  of  multiplying  by 
amitotic  or  direct  division  only. 

The  first  evidences  of  the  rods  and  cones  are  in  the  form  of  clear,  absolutely  achromatic 
globules,  which  lie  between  the  nuclei  of  the  external  nuclear  layer  and  the  outer  limiting 
membrane.  Whenever  these  are  protruded  beyond  this  membrane  they  grow  with  gi'eat 
rapidity,  and  exert  an  influence  on  the  retinal  jjigment  cells,  causing  them  to  protrude  their 
processes,  the  pigment  of  which  they  seem  to  digest  and  absorb,  since  they  now  stain  deeply 
with  iron -alum -hfematoxylin.  This  gives  us  a  clue  to  the  mode  by  which  the  rhodopsin 
function  of  the  rods  in  the  adult  is  conducted,  for  these  structures  actually  owe  their  growth  and 
development  to  the  ingestion  of  pigment  from  the  piguient-cell  processes. 

The  condensed  mesoderQi  surrounding  the  optic  cup  becomes  the  sclera  and  chorioid. 
In  the  portion  of  the  mesoderm  which  lies  in  front  of  the  lens  a  cleft-like  fissure  appears, 
and  divides  it  into  a  thick  anterior  and  a  thin  postei'ior  layer.  The  former  becomes  the 
substantia  propria  of  the  cornea ;  the  latter,  the  stroma  of  the  iris  and  anterior  part  of  the 
vascular  tunic  of  the  lens.  The  fissure  represents  the  future  anterior  chamber,  and  its 
lining  cells  form  the  layer  of  endothelium  on  the  back  of  the  cornea  and  front  of  the 
iris. 

The  eyelids  arise  as  two  integumentary  folds  above  and  below  the  cornea,  each  being- 
covered  on  both  its  surfaces  by  the  ectoderm.  By  the  third  month  the  folds  meet  and 
unite  with  each  other  at  their  edges,  the  eyelids  being  only  permanently  opened  shortly 
before  birth  ;  in  many  animals  they  are  not  opened  until  after  birth.  The  ectoderm 
forms  the  epithelium  of  the  conjunctiva  and  the  stratified  epithelium  of  the  cornea.  It 
is  also  invaginated  at  the  lid  margins  to  foi'm  the  hair  follicles  and  the  lining  cells  of  the 
Meibomian  glands  and  glands  of  Moll,  and,  at  the  fornix  conjunctivc'e,  to  form  the  lining 
of  the  alveoli  and  ducts  of  the  lachrymal  gland. 

The  nasal  duct,  lachrymal  sac,  and  canals  represent  the  remains  of  the  furrow  which 
extends  from  the  inner  angle  of  the  eye  to  the  nasal  cavity  between  the  superior  maxillary 
and  lateral  nasal  processes  (p.  40).  It  is  at  first  filled  by  a  solid  rod  of  cells,  which 
becomes  hollowed  out  to  form  the  duct  and  canals. 

THE  EAR. 

The  ear  or  organ  of  hearing  (organon  auditus,  Fig.  577)  consists  of  three  portions 
— external,  middle,  and  internal — the  last  constituting  its  essential  part,  as  within 
it  are  distributed  the  peripheral  terminations  of  the  auditory  nerve. 

EXTEENAL  EAE. 

The  external  ear  ^  includes — {a)  the  pinna  or  auricula,  attached  to  and  pro- 
jecting from  the  side  of  the  head ;  and  (6)  the  passage  or  external  auditory  meatus 
(meatus  acusticus  externus),  leading  inwards  from  the  most  depressed  part  of  the 
pinna  as  far  as  the  tympanic  membrane  or  outer  wall  of  the  middle  ear. 

The  Pinna. 

The  pinna  or  auricula  (Fig.  578)  presents  two  surfaces,  outer  and  inner,  the 
latter  forming  an  angle  (cephalo-auricitlar  angle)  of  about  30°,  with  the  side  of  the 

^  Although  it  is  usual  to  speak  of  the  external,  middle,  and  internal  ear,  it  would  be  more  correct  to  use 
the  terms  external,  middle,  and  internal  pm'tions  of  the  ear. 

51c 


744 


THE  ORGANS  OF  SENSE. 


Tympanic  cavity,  with  chain  of  ossicles 
Seniicuculai  canal 
Utiicle 
Ductus  endolymphaticus 
Saccule 

Cochlea 


head.     The  outer  surface  is  irregularly  concave,  but  presents  several  well-marked 
elevations  and  depressions.     The  deepest  of  the  depressions  is  situated  near  its 

middle,  and  is  named 
the  concha  (concha  auri- 
culee).  It  is  divided 
by  an  almost  transverse 
ridge,  the  crus  helicis, 
into  an  upper,  smaller, 
and  a  lower,  larger  por- 
tion :  the  former  is 
termed  the  cymba  con- 
chse ;  the  latter,  which 
leads  into  the  meatus, 
the  cavum  conchse.  An- 
teriorly, the  crus  helicis 
is  continuous  with  the 
margin  of  the  pinna  or 
helix,  which  is  folded 
over,  in  the  greater  part 
of  its  extent,  like  the  rim 
of  a  hat,  and  is  directed  at 
first  upwards,  and  then 
backwards  and  down- 
wards, to  become  gradu- 
ally lost  a  little  below 
the  middle  of  the  pinna.  Near  the  point  where  the  helix  begins  to  turn  down- 
wards a  small  tubercle,  the  tuberculum  superius  (Darwini),  is  often  seen ;  it  will  be 
again  referred  to.  In  front  of  the  descending  part  of  the  helix  is  a  second 
elevation,  the  antihelix.  Single  below,  it  divides  superiorly  into  two  limbs,  termed 
the  crura  antihelicis,  between  which 
is  a  triangular  depression,  the  fossa 
of  the  antihelix,  or  fossa  triangularis. 
The  elongated  furrow  between  the 
helix  and  antihelix  is  named  the  cms-  antiheiicis  superior 
fossa  of  the  helix  or  scapha.  The 
concavity  of  the  concha  is  over- 
lapped in  front  by  a  tongue-like 
process,  the  tragus,  and  behind  by 
a  *triangular  projection,  the  anti- 
tragus ;  the  notch,  directed  down- 
wards and  forwards  between  these 
two  processes,  is  named  the  incisura 
intertragica.  The  tragus  really 
consists  of  two  tubercles,  the 
upper  of  wliich  constitutes  the 
tuberculum    supratragicum   of   His, 


Eustachian  tube 

Membrana  tympani 

Recessus  epitympanicus 

External  auditory  meatus 


Fig.  577. — Diagrammatic  View  of  the  Organ  of  Hearing. 


Fossa  triangularis — Tjwg 

Crus  antihelicis  inferior ^ 

Cymba  conchaj 

Crus  helicis 

Tiagus 


Incisura  intertiagica 


Tuberculum 
superius 


Antitragus 


Lobule 


Fig.  578.- 


ViEw  OF  Outer  Surface  of  Left  Pinna 
(lialf  natural  size). 


and  is  separated  from  the  helix  by  a  groove,  the  sulcus  auris  anterior.  The  lobule 
(lobulus  auriculse)  is  situated  below  the  incisura  intertragica,  and  is  the  most 
dependent  part  of  the  pinna. 

The  inner  or  cranial  surface  is  also  irregular,  and  presents  elevations  corre- 
sponding to  the  depressions  on  its  outer  surface,  e.g.  eminentia  conchse,  eminentia 
triangularis,  etc. 

The  pinna  is  usually  smalltn'  and  more  finely  modelled  in  the  female  than  in  the  male,  but 
presents  great  variations  in  size,  and  .shape  in  diflVrent  individuals.  In  the  newly -born  child  its 
length  is  aljout  one-third  of  tliat  (;f  tlie  adult,  wliile  it  increases  sliglitly  in  length  and  breadth 
in  old  age. 

The  relation  of  the  width  to  the  height  is  termed  the  auricular  index,  and  is  expressed  as 
follows  : — 

width  of  pinna  X  100  ^  ^^^^^^j^^  .^^^^ 
length  of  pmna 


THE  PINNA. 


745 


M.  helicis  major 


Spina  helicis 
M.  helicis  minor 


°  I 

Fissure  of  | 

Santorini_l\ 
Isthmus  cartila-    * 
ginis  auris 


Incisura  terminalis 
auris 

JI.  antitragicus 


■T^ — Fissura  antitragolielicina 
tf"         Cauda  helicis 


Fig.  579. — Outer  Surface  of  Cartilage  of  Pinna 
(one-half  natural  size). 


This  index  is  less  in  white  than  in  dark  races. 

The  cephalo-auricular  angle  may  be  practically  absent,  as  in  those  cases  where  the  si<in  of  the 
head  passes  directly  on  to  the  outer  surface  of  the  pinna,  or  it  may  be  increased  to  nearly  a  right 
angle,  so  that  tlie  outer  surface  of  the  pinna  looks  directly  forwards.  The  tuberculum  superius, 
the  significance  of  which  was  recognised  by  Darwin,  is  a  somewhat  triangular  prominenrii  which 
projects  forwards  when  the  helix  is  well  rolled  over,  Init  backwards  and  upwards  wlien  the 
incurving  of  the  helix  has  been  arrested.  More  frequently  present  in  men  than  in  women,  it  is 
of  develojimental  interest  since  it  has  been  shown  to  be  well  marked  at  the  sixth  month  of  foetal 
life,  the  entire  jiinna,  at  this  stage,  resemljling  in  apjiearance  that  of  the  adult  macaque. 

The  lobule  may  be  small  ancl  sessile  or  considerably  elongated  ;  it  may  adhere  to  the  skin  of 
the  cheek  (i.e.  webbed),  or  may  tend  to  bifurcate  at  its  lower  extremity. 

Structure  of  the  Pinna. — The  greater  part  of  the  pinna  consists  of  a  lamella 
of  yellow  fibro-cartilage,  the  cartilage  auriculae ;  the  cartilage  is,  however,  absent 
from  the  lobule,  which  is  composed  of  fat  and  connective  tissue.  When  laid  bare, 
the  cartilaginous  lamella  (Figs.  579,  580)  presents,  in  an  exaggerated  condition,  all 
the  inequalities  of  the  pinna,  and 
is  seen  to  be  prolonged  inwards,  to 
form  a  considerable  portion  of  the 
external  auditory  meatus.  The 
cartilage  of  the  helix  projects  an- 
teriorly as  a  conical  eminence,  the 
spina  helicis,  whilst  its  inferior  ex- 
tremity extends  downwards  as  a 
tail-like  process,  the  cauda  helicis, 
which  is  separated  from  the  lower 
part  of  the  antitragus  by  a  fissure, 
termed  the  fissura  antitragohelicina. 
The  cartilage  of  the  pinna  is  con- 
tinuous with  that  of  the  meatus  by 
a  narrow  isthmus  (isthmus  cartila- 
ginis  auris)  measuring  from  8-9  mm. 
in  breadth.  This  isthmus  corresponds  externally  with  the  deepest  part  of  the 
incisura  intertragica,  and  internally  it  forms  the  outer  boundary  of  a  deep  fissure, 
the  incisura  terminalis  auris,  which  separates  the  cartilage  of  the  meatus  from 
that  of  the  concha.  The  upper  edge  of  the  tragus  fits  into  an  angle  below  the 
crus  helicis. 

If  the  incisura  terminalis  auris,  together  with  the  isthmus  and  the  incisura  intertragica,  be 
taken  as  representing  the  boundary  laetween  the  cartilage  of  the  pinna  and  that  of  the  meatus,  it 
follows  that  the  tragus  really  forms  a  part  of  the  meatal  cartilage. 

On  the  cranial  aspect  of  the  cartilage  (Fig.  580)  the  eminences  produced  by  the 
concha  and  fossa  triangularis  are  separated  by  a  transverse  furrow,  the  sulcus  anti- 
helicis  transversus,  corresponding  with  the  crus  antihelicis  inferior;  further,  the 

eminentia  conch  ee  is  crossed  horizontally 
by  a  groove,  the  sulcus  cruris  helicis,  and 
almost  vertically  by  a  slight  ridge,  the 
ponticulus :  the  latter  indicates  the 
attachment  of  the  M.  auricularis  pos- 
terior. 

In  addition  to  the  fissures  described. 
Cartilage  of  others,  termed  the  fissures  of  Santorini, 
tragus  g^j,Q  found,  usually  one  in  the  tragus 
tenninTlis  ^^d  "'lie  Or  uiorc  in  the  cartilage  of  the 
auris  meatus. 

Ligaments  of  the  Pinna. — The 
cartilage  of  the  pinna  is  attached  to 
the  skull  by  two  fibrous  bands  which 
form  its  extrinsic  ligaments,  viz. :  an 
anterio7\  stretching  from  the  zygoma  to  the  spina  helicis  and  tragus ;  and  a  posterior, 
passing  from  the  eminentia  conchae  and  upper  wall  of  the  meatus  to  the  mastoid 


M.  transversus- 


Pouticulus 


Cauda  helicis 


M.  obliquus 

Sulcus  antihelicis 
tiansversus 
Spina  helicis 


Cartilage  of 
meatus 


Fig. 


>80. — Inner  Surface  of  Cartilage  of  Pinna 
(one-half  natural  size). 


746  THE  OEGANS  OF  SENSE. 

process.     Small  ligamentous  bands  pass  between  individual  parts  of  the  pinna,  and 
form  what  are  termed  its  intrinsic  ligaments. 

Muscles  of  the  Pinna  (Figs.  579,  580).— The  muscles  of  the  pinna  are  divided 
into  two  groups,  extrinsic  and  intrinsic.  The  extrinsic  muscles  pass  from  the  pinna 
to  the  skull  or  scalp,  and  are  described  in  the  section  on  Myology.  The  intrinsic 
muscles,  on  the  other  hand,  are  confined  to  the  pinna  and  are  six  in  number,  four 
on  its  outer  and  two  on  its  cranial  aspect. 

(a)  On  the  outer  surface  (Fig.  579) — 

1.  M.  helicis  major,  passes  upwards  from  the  spina  helicis  along  the  ascending 
part  of  the  helix.  2.  M.  helicis  minor,  covers  the  crus  helicis.  3.  M.  tragicus, 
quadrangular  in  shape,  consists  of  fibres  running  vertically  over  the  greater 
part  of  the  tragus.  Some  of  its  fibres  are  prolonged  upwards  to  the  spina  helicis 
and  constitute  the  m.  pyramidalis.  4.  M.  antitragicus,  covers  the  antitragus 
and  passes  obliquely  upwards  and  backwards  as  far  as  the  antihelix  and  cauda 
helicis. 

(&)  On  the  cranial  surface  (Fig.  580) — 

1.  M.  transversus  auriculae,  consists  of  scattered  fibres,  which  stretch  from  the 
eminentia  conchse  to  the  convexity  of  the  helix.  2.  M.  obliduus  auriculae  (Tod), 
comprises  a  few  fasciculi,  which  run  obliquely  or  vertically  across  the  furrow  corre- 
sponding with  the  crus  antihelicis  inferior.  A  small  muscle,  the  stylo-auricularis, 
sometimes  extends  from  the  root  of  the  styloid  process  to  the  cartilage  of  the 
meatus. 

Skin  of  the  Pinna. — The  skin  covering  the  pinna  is  thin  and  smooth,  and  is 
prolonged  inwards,  in  the  form  of  a  tube,  as  a  lining  to  the  external  auditory 
meatus.  It  adheres  firmly,  on  the  outer  surface  of  the  pinna,  to  the  subjacent 
perichondrium.  Hairs  are  well  developed  on  the  tragus  and  antitragus,  and  also  in 
the  incisura  intertragica,  forming  the  barbula  Mrci,  which  guard  the  entrance  to  the 
concha.  Soft  downy  hairs  are  found  over  the  greater  part  of  the  pinna  and  point 
towards  Darwin's  tubercle.  Sebaceous  glands,  present  on  both  surfaces  of  the  pinna, 
are  most  numerous  in  the  concha  and  fossa  triangularis.  Sweat  glands  are  found 
on  both  surfaces,  but  are  much  more  numerous  on  the  cranial  aspect. 

Vessels  of  the  Pinna. — The  arteries  for  the  pinna  are  derived — (a)  from  the  superficial  tem- 
poral, which  sends  two  or  three  branches  to  the  onter  surface  ;  and  (6)  from  the  posterior  auricular, 
which  gives  three  or  four  branches  to  the  cranial  surface.  From  the  latter  two  sets  of  twigs  are 
prolonged  to  the  outer  surface,  one  turning  round  the  free  margin  of  the  helix,  and  the  other 
passing  through  small  fissures  in  the  cartilage.  The  veins  from  the  outer  surface  open  into  the 
superficial  temporal  vein  ;  those  from  the  cranial  surface  chiefly  join  the  posterior  auricular  vein, 
but  some  communicate  with  the  mastoid  emissary  vein.  The  lymphatics  take  three  directions, 
viz. :  (a)  forwards  to  the  parotid  lymphatic  glands,  and  especially  to  the  preauricular  gland  in 
front  of  the  tragus;  (b)  downwards  to  the  lymphatic  glands  which  accompany  the  external  jugular 
vein,  and  to  the  glands  under  the  sternomastoid ;  and  (c)  backwards  to  the  mastoid  lymphatic 
glands. 

Nerves  of  the  Pinna. — The  muscles  of  the  pinna  are  supplied  by  the  seventh  cranial  nerve. 
The  skin  receives  its  sensory  nerves  from — (a)  the  great  auricular,  which  supplies  nearly  the 
whole  of  the  cranial  surface,  and  sends  filaments  in  company  with  the  branches  of  the  posterior 
auricular  artery  to  the  outer  surface  ;  (IS)  the  auriculo-temporal,  which  supplies  the  tragus  and 
ascending  part  of  the  helix  ;  (c)  tlie  small  occipital,  which  sends  a  branch  to  the  uj)per  part  of  the 
cranial  surface. 

External  Auditory  Meatus. 

The  external  auditory  meatus  (meatus  acusticus  externus)  (Figs.  580,  581)  is 
the  passage  leading  inwards  from  the  concha  as  far  as  the  membrana  tympani.  Its 
averao-e  length,  measured  from  the  bottom  of  the  concha,  is  about  one  inch 
(24  mm.),  but,  if  measured  from  the  level  of  the  tragus,  nearly  one  inch  and  a 
half  (35  mm.)  On  account  of  the  obliquity  of  the  membrana  tympani  its  anterior 
and  inferior  walls  are  longer  than  the  posterior  and  superior.  The  tube  consists  of 
two  parts,  viz. :  {a)  an  external  fibro-cartilaginous  portion,  the  pars  cartilaginea, 
having  a  length  of  about  8  mm. ;  and  (h)  an  internal  osseous  portion,  the  pars  ossea, 
measuring  about  16  mm.,  and  formed  by  a  portion  of  the  temporal  bone.  The 
entire  meatus  forms  a  somewhat  S-shaped  bend  (Fig.  582),  and  may  be  divided  into 


EXTERNAL  AUDITORY  MEATUS. 


747 


:  (1)   pars    externa,    directed   inwards,   forwards,  and    slightly 
7  mm. ;  (2)  pars   media,  inclining  inwards  and   backwards  for 


Pars  ossca  ol'  external  aiulitory  meatus 


Recessu.s 

epityinpaiiicus 

Malleus 

Cochlea 

Cavum  tyinpani 

Meiiibrana 

tympani 

lutenial  carotid 
artery 


Crus  antihelicis  inferior 
yinba  concliie 


rns  helicis 


Pars  cartilaginea  of 
external  auditory  meatus 
Cavum  conchpe 


Lower  boundary  of 
incisiira  intertragica 


Fig.  581. 


-Vertical  Transverse  Section  of  Right  Ear  ;  Anterior  Half 
OF  Section,  viewed  from  behiud  (natural  size). 


three  portions,  viz. 
upwards  for  about 
about  5  mm. ;  (3) 
pars  interna,  the 
longest  of  the  three, 
passing  forwards,  in- 
wards, and  slightly 
downwards.  On 
transverse  section 
the  canal  is  seen  to 
be  elliptical,  its 
greatest  diameter 
having  an  inclina- 
tion down  wards  and 
backwards.  Widest 
at  its  outer  ex- 
tremity, it  becomes 
somewhat  narrower 
at  the  inner  end  of 
the  pars  cartila- 
ginea ;  once  more 
expanding    in    the 

outer  part  of  the  pars  ossea,  it  is  again  constricted  near  the  inner  end  of  the  latter, 
where  its  narrowest  part,  or  isthmus,  is  found  at  a  distance  of  about  19  mm.  from 
the  bottom  of  the  concha.  The  inner  extremity  of  the  meatus  is  nearly  circular 
and  is  closed  by  the  membrana  tympani. 

Bezold  gives  the  diameters  of  the  meatus  as  follows  : — 

At  the  commencement  of  the  pars  cartilaginea. 
At  the  end  ,,  ,,  ,, 

At  the  commencement  of  the  pars  ossea 
At  the  end  ,,  „       „ 

The  lumen  of  the  pars  cartilaginea  is  influenced  by  the  movements  of  the 
lower  jaw,  being  increased  when  the  jaw  is  depressed.     This  can  be  easily  verified  by 

inserting  a  finger  into 
themeatus,and  then  al- 
ternately opening  and 
shutting  the  mouth. 

The  condyle  of  the 
jaw  lies  in  front  of  the 
pars  ossea,  while  be- 
tween the  jaw  and  the 
pars  cartilaginea  there 
intervenes  a  portion  of 
the  parotid  gland.  Be- 
low the  meatus  is  the 
retro-mandibular  part 
of  the  parotid  gland. 
Behind  the  pars  ossea, 
and  separated  from  it 
by  a  thin  plate  of  bone, 
are  the  mastoid  air- 
cells. 

Structure  of  the  Meatus. — The  cartilage  of  the  meatus,  directly  continuous 
with  that  of  the  pinna,  is  folded  on  itself  to  form  a  groove,  opening  upwards  and 
backwards,  the  margins  of  which  are  connected  by  fibrous  tissue.  The  inner  end  of 
the  cartilage  is  firmly  fixed  to  the  outer  margin  of  the  bony  meatus,  whilst  its  outer 
extremity  is  continuous  with  the  cartilage  of  the  tragus  {vide  p.  745).     A  couple  of 


Greatest. 

Least. 

9-08  mm. 

6-54  mm 

7-79  mm. 

5-99  mm 

8*67  mm. 

6-07  mm 

8"13  mm. 

4-60  mm 

Condyle  of  jaw. 
Parotid  gland 

Tragus 

Concha 


Antihelix 


Fig.  582. 


Bony  part  of 
Eustachian  tube 

Internal  carotid 

artery 

Membrana  tympani 

First  turn  of 

cochlea 

Cavum  tympani 


Mastoid  air-cells 


Lateral  sinus 


Horizontal  Section  through  Right  Ear  : 
Section   seen  from  below  (natural  size) 


Upper  Half  of 


748  THE  OEGANS  OF  SENSE. 

fissures,  the  fissures  of  Santorini,  exist  in  the  anterior  portion  of  the  cartilage  of  the 
meatus,  and  are  filled  by  fibrous  tissue.  In  the  outer  part  of  the  meatus  the  cartilage 
forms  about  three-fourths  of  its  circumference  ;  but,  on  passing  inwards,  the  propor- 
tion of  cartilage  to  fibrous  tissue  diminishes,  with  the  result  that  near  the  inner 
end  of  the  pars  cartilaginea  the  cartilage  forms  merely  a  part  of  the  anterior  and 
lower  boundaries  of  the  canal. 

The  osseous  portion  (pars  ossea)  of  the  meatus  is  described  on  p.  117  ;  but  it  may  be 
well  to  state  here  that  in  the  newly-bom  child  it  is  represented  only  by  an  incomplete 
ring  of  bone,  tlie  annulus  tympanicus,  together  with  a  small  portion  of  the  squamous 
temporal,  which  articulates  with,  and  bridges  over  the  interval  between,  the  extremities  of  the 
ring  superiorly.  In  tlie  coucavitj  of  the  amiulus  is  a  well-defined  groove,  the  sulcus  tympanicus, 
in  which  the  circumference  of  the  memT)rana  tympani  is  fixed.  On  the  inner  aspect  of  the 
anterior  part  of  the  annulus,  a  little  below  its  free  extremity,  a  groove,  the  sulcus  malleolaris,  is 
directed  downwards  and  forwards.  It  transmits  the  processus  gracilis  and  anterior  ligament 
of  the  malleus,  the  tympanic  artery  and  the  chorda  tympani  nerve.  It  is  limited  above  by  a 
well-marked  ridge,  the  crista  spinarum  of  Henle,  which  ends  in  front  and  behind  in  a  spinous 
process  (spina  tympanica  anterior  and  posterior).  Below  the  sulcus  malleolaris  there  is  a  second, 
less  prominent  ridge,  the  crista  tympanica  of  Gruber,  Avhich  subsequently  unites  with  a  process 
of  the  tegmen  tympani,  and  so  shuts  oft'  the  canalis  musculo -tubarius  from  the  Glaserian  fissure. 
A  fibrous  plate,  the  tympanic  fibrous  plate  (Symington),  intervenes  between  the  annulus 
tympanicus  and  the  inner  end  of  the  cartilage  of  the  meatus,  and  into  this  plate  the  bony  ring 
extends.  The  bony  outgrowth  does  not,  however,  proceed  uniformly  throughout  its  circum- 
ference, but  occurs  most  rapidly  in  the  anterior  and  posterior  parts  of  the  ring.  These  outgrowths 
fuse  about  the  end  of  the  second  year  of  life,  so  as  to  surround  a  foramen  in  the  floor  of  the 
ineatus  (foramen  of  Buschke),  which  is  usually  closed  hj  the  fifth  year,  but  persists  until  adult 
life  in  some  19  per  cent  of  skulls  (Blirkner). 

The  lumen  of  tlie  meatus  in  the  newly-bom  child  is  extremely  small :  its  outer  part  is  funnel- 
shaped  ;  its  inner  a  mere  si  it,  bounded  below  by  the  tympanic  fibrous  plate  and  above  by  the 
obliquely-placed  membrana  tympani. 

The  skin  which  envelopes  the  pinna  lines  the  entire  meatus,  and  covers  also  the 
outer  surface  of  the  tympanic  membrane.  It  is  thick  in  the  pars  cartilaginea,  and 
contains  fine  hairs  and  sebaceous  glands,  the  latter  extending  inwards  for  some 
distance  along  the  postero-superior  wall  of  the  pars  ossea.  The  sweat  glands 
are  enlarged  and  of  a  brownish  colour ;  they  constitute  the  glandulse  ceruminosse 
and  secrete  the  ear  wax  or  cerumen. 

Vascular  and  Nervous  Supply  of  the  Meatus. — The  meatus  receives  its  blood-supply  from 
the  posterior  auricular  and  superficial  temj^oral  arteries,  and  also  from  the  deep  auricular  branch 
of  the  internal  maxillary  artery,  the  last  distributiug  some  minute  branches  to  the  membrana 
tympani.  The  veins  ojjeii  into  the  external  jugular  and  internal  maxillary  veins,  and  also  into 
the  pterygoid  plexus,  while  the  lymphatics  have  a  similar  mode  of  termination  to  those  of  the 
pinna.  Sensory  nerves  are  supplied  to  the  meatus  Ijy  the  auriculo-temporal  branch  of  the  fifth 
and  by  the  auricular  brancli  of  tlie  vagus. 


MIDDLE  EAR  OE  TYMPANIC  CAVITY. 

The  tympanic  cavity  (cavum  tympani)  is  a  small  air  chamber  in  the  temporal 
bone,  which  intervenes  between  the  membrana  tympani  and  the  outer  wall  of  the 
internal  ear  or  labyrinth  (Figs.  5(S1,  582).  Lined  by  mucous  membrane,  it  contains 
a  chain  of  ossicles  (onsicula  auditus)  which  reaches  from  its  outer  to  its  inner  wall, 
and  by  means  of  which  the  vibrations  of  the  membrana  tympani  are  transmitted 
acro.ss  the  cavity  to  the  internal  ear.  Attached  to  the  ossicles  are  several  ligaments, 
together  with  a  pair  of  small  muscles,  while  certain  nerves  are  either  distributed 
to  the  cavity  or  pass  through  it. 

The  tympanic  cavity  consists  of  two  portions:  (1)  The  tympanum  proper,  or 
atrium,  lying  immediately  to  the  inner  aspect  of  the  membrana  tympani ;  and  (2) 
the  recessus  epitympanicus,  lying  aljove  the  level  of  the  membrane  and  containing 
the  greater  part  of  the  incus  and  the  upper  half  of  the  malleus.  Including  this 
recess,  the  vertical  and  antero-posterior  diameters  of  the  tympanic  cavity  are 
rather  more  than  half  an  inch  (15  mm.)  The  distance  between  its  outer  and 
inner  walls  is  about  6  mm.  above  and  4  mm.  below,  while  at  its  central  part, 
owing  to  the  bulging  of  the  two  walls  towards  the  cavity,  it  measures  only 
from  li  to  2  mm. 


MIDDLE  EAK  OE  TYMPANIC  CAVITY. 


749 


The  tympanic  cavity  presents  for  examination  a  roof,  a  floor,  and  four  walls,  viz. 
anterior,  posterior,  external,  and  internal. 

The  roof  (Fig.  583)  (paries  tegmentalis)  is  formed  by  a  thin  plate  of  bone,  the 
tegmen  tympani,  constituting  a  portion  of  the  upper  surface  of  the  petrous-temporal. 
It  extends  backwards  so  as  to  cover  in  the  mastoid  antrum,  and  forwards,  to  form 


Antrum  mastoidenm 
Recessus  eint\  mp  vnic  us 
Piommentia  c  -xinlis  lioialis  \ 


Tegmt  n  tjiiipi'n 


Fenestia  o\alis 
Canal  for  tensor  tympani 

Processus  coclileariformi 

Promontory  witli 

grooves  for 

tympanic  plexus 

Osseous  part  of 

Eustachian  tube 

Bristle  introduced  into  the 

foramen  for  Jacobson's  nerve 


Pyramid 

Sinus  tympani 
Mastoid  air-cells 


Possiila  rotunda 


Course  of  canalis  facialis 


Fig.  583. — Section  through  Left  Temporal  Bone,  showing  inner  wall  of  tympanic  cavity,  etc. 

the  roof  of  the  canal  for  the  tensor  tympani  muscle.  It  separates  the  tympanum 
and  antrum  from  the  cranial  cavity,  and  may  contain  a  few  air-cells,  whilst  occasion- 
ally it  is  partly  deficient.  In  the  child  its  outer  edge  corresponds  with  the  petro- 
squamous suture.  The  floor  (fundus  tympani  seu  paries  jugularis)  is  narrower  than 
the  roof,  and  consists  of  a  thin  plate  of  bone  which  separates  the  cavity  from  the 
fossa  jugularis ;  anteriorly,  it  extends  upwards  and  becomes  continuous  with  the 
posterior  wall  of  the  carotid  canal.  The  inner  orifice  for  Jacobson's  nerve,  or 
tympanic  branch  of 


Recessus  epitympaiucus 
■  ■/•■<. 


the  glosso- pharyn- 
geal, is  seen  near  the 
junction  of  the  floor 
with  the  inner  wall. 
The  posterior 
wall  (paries  mas- 
toidea)  presents, 
from  above  down- 
wards :  (1)  A 
rounded  or  triangu- 
lar opening,  which 
extends  backwards 
from  the  recessus 
epitympanicus  and 
leads  into  the 
mastoid  antrum 
(Fig.  583);  the  latter 
will  be  again  referred 
to  (p.  752).  (2)  A 
depression,  the  fossa 

incudis  (Fig.  584),  which  lodges  the  extremity  of  the  short  process  of  the  incus  ;  this 
fossa  is  situated  in  the  postero-inferior  part  of  the  recessus  epitympanicus.  (3)  A 
minute  conical  bony  projection,  the  pyramid  or  eminentia  pyraniidalis  (Fig.  583),  the 
summit  of  which  is  perforated  by  a  round  aperture  for  the  passage  of  the  tendon  of 
the  stapedius  muscle.  This  aperture  is  continued  downwards  and  backwards  as  a  canal 
in  front  of  the  Fallopian  aqueduct,  and  frequently  opens,  by  a  minute  orifice,  on  the 


Memlirana  flaccida 
(Shrapnell) 


Anterior  and  posterior 
tympano-malleolar  folds 
Tendon  of  tensor 
tympani  muscle  (cut) 

Manubrium  mallei 


Menibrana  tensa 


Sulcus  tympanicus 


Fig.  .584.— Left  Membrana  Tympani  and  Recessus  Epitympanicus,  viewed 
from  within.  The  head  and  neck  of  the  malleus  have  been  removed  to 
show  the  membrana  flaccida  and  the  tympano-malleolar  folds.      x  3. 


750  THE  OEGANS  OF  SENSE. 

base  of  the  skull  iu  front  of  the  stylo-mastoid  foramen.  It  communicates  with  the 
Eallopian  aqueduct  by  one  or  two  small  foramina,  through  which  the  vessels  and  nerve 
pass  to  reach  the  stapedius  muscle.  A  minute  spicule  of  bone  often  extends  from  the 
pyramid  to  the  promontory  on  the  inner  wall  of  the  tympanum.  (4)  A  small  aperture, 
the  apertura  tympanica  canaliculi  chordae  (Fig.  58-4),  which  is  situated  immediately 
internal  to  the  posterior  edge  of  the  membrana  tympani,  nearly  on  a  level  with  the 
upper  end  of  the  manubrium  mallei,  and  transmits  the  chorda  tympani  nerve.  (5) 
A  rounded  eminence,  the  prominentia  styloidea,  is  sometimes  seen  below  the  last ; 
it  is  caused  by  the  upward  and  forward  prolongation  of  the  styloid  process. 

The  anterior  wall  (paries  carotica)  is  narrowed  in  its  transverse  diameter  by 
the  approximation  of  the  outer  and  inner  boundaries  of  the  cavity,  and  in  its 
vertical  diameter  by  the  descent  of  the  roof  and  ascent  of  the  c-irotid  canaL  It 
presents  (Fig.  583)  two  parallel  canals,  one  above  the  other,  separated  by  a  thin 
lamella  of  bone,  the  processus  cochleariformis  (septum  canalis  musculo-tubarii). 
These  run  forwards  on  the  outer  wall  of  the  carotid  canal  and  open  in  the  angle 
between  the  petrous  and  squamous  parts  of  the  temporal  bone.  The  higher  and 
smaller  of  the  two  is  termed  the  canal  for  the  tensor  tympani  muscle  (semicanalis 
m.  tensoris  tympani),  and  lies  immediately  below  the  tegmen  tympani.  It  has  a 
diameter  of  about  2  mm.,  and  extends  on  to  the  inner  wall  of  the  tympanic  cavity 
above  the  anterior  part  of  the  fenestra  ovalis.  The  lower  and  larger  canal  gradu- 
ally increases  in  size  from  before  backwards,  and  forms  the  bony  part  of  the 
Eustachian  tube  (semicanalis  tubte  auditivse).  It  opens  on  the  anterior  wall  of  the 
tympanic  cavity  opposite  the  orifice  leading  into  the  mastoid  antrum.  Below  the 
orifice  of  the  Eustacliian  tube  the  anterior  part  of  the  tympanic  cavity  is  separated 
from  the  ascendiug  portion  of  the  carotid  canal  by  a  thin  plate  of  bone  in  which 
there  are  sometimes  gaps  or  deficiencies.  It  is  perforated  by  a  small  canal,  the 
carotico-tympanic  canal,  which  transmits  the  small,  deep  petrosal  nerve  from  the 
sympathetic  plexus  of  the  carotid  artery  to  the  tympanic  plexus.  The  Eustachian 
tube  is  described  on  p.  753. 

The  outer  wall  (paries  membranaeea)  is  formed  almost  entirely  by  the  mem- 
brana tympani  (Fig.  584),  which  closes  the  inner  extremity  of  the  external  auditory 
meatus,  and  is  fixed  throughout  the  greater  part  of  its  circumference  in  a  groove, 
the  sulcus  tympanicus.  The  bony  ring  containing  this  sulcus  is  deficient  superiorly 
where  it  exhibits  a  distinct  notch,  the  notch  of  Rivinus.  On  a  level  with  the  upper 
edge  of  the  membrane,  and  in  front  of  the  ring  of  bone  in  which  it  is  fixed,  is  the 
inner  end  of  the  Glaserian  fissure,  or  remnant  of  the  fissura  petro -tympanica.  This 
transmits  the  tympanic  branch  of  the  internal  maxillary  artery,  and  lodges  the 
processus  gracilis  and  anterior  ligament  of  the  malleus.  Close  to  the  inner 
extremity  of  the  fissure  is  the  canal  of  Huguier,  or  iter  chordae  anterius  through 
which  the  chorda  tympani  nerv^e  leaves  the  tympanum. 

Membrana  Tympani. — This  is  an  elliptical  disc,  its  greatest  diameter,  9  to 
10  mm.,  being  directed  from  above  and  behind,  downwards  and  forwards,  whilst 
its  least  diameter  is  from  8  to  9  mm.  Its  antero-inferior  portion  inclines  markedly 
inwards,  and  thus  the  membrane  is  placed  very  obliquely,  forming  an  angle  of 
about  55"  with  the  lower  and  anterior  walls  of  the  external  auditory  meatus ;  its' 
antero-inferior  part  is,  therefore,  most  distant  from  the  outer  orifice  of  the  meatus. 
The  meml^rane  is  said  to  be  more  oblique  in  cretins  and  deaf  mutes,  and  more  per- 
pendicular in  musicians. 

The  circumference  of  that  yjortion  of  the  membrane  which  is  fixed  in  the  sulcus 
tympanicus  is  considerably  thickened,  and  is  named  the  annulus  fibro-cartilagineus. 
It  is  prolonged  from  the  anterior  and  posterior  extremities  of  the  notch  of  Rivinus 
to  the  short  process  of  the  malleus  in  the  form  of  two  ligamentous  bands,  the 
anterior  and  posterior  malleolar  folds  or  ligaments  (plica  malleolaris  anterior  et 
posterior;.  The  small  triangular  portion  of  the  membrane  (Fig.  584)  situated  above 
the.?e  folds  is  thin  and  lax,  and  constitutes  the  pars  flaccida  or  membrane  of 
Shrapnell ;  the  main  portion  of  the  membrane  is,  on  the  other  hand,  tightly 
stretched  and  termed  the  pars  tensa.  A  small  orifice,  sometimes  seen  in  the  pars 
flaccida,  is  probably  either  a  pathological  condition  or  has  been  artificially  pro- 
duced during  manipulation.     The  handle  of  the  malleus  is  firmly  fixed  to  the  inner 


MIDDLE  EAK  OR  TYMPANIC  CAVITY. 


751 


surface  of  the  membrana  tympani  aud  draws  its  central  portion  inwards,  rendering 
its  outer  aspect  concave.  The  deepest  part  of  this  concavity  corresponds  with  the 
lower  extremity  of  the  handle  of  the  malleus,  and  is  named  the  umbo  membranse 
tympanae  or  navel. 

The  membrane  tympani  consists  of  three  layers :  (1)  external,  integumentary 
(stratum  cutaneum) ;  (2)  middle,  fibrous  (membrana  propria) ;  (3)  internal,  mucous 
(stratum  mucosum). 

The  external  layer  (stratum  cutaneum)  is  continuous  with  the  integumentary 
lining  of  the  meatus,  and  consists  of  a  thin  layer  of  cutis  covered  by  epidermis. 
The  cutis  is  thickest  near  the  circumference ;  the  epidermis,  on  the  other  hand,  is 
thickest  near  the  centre  of  the  membrane. 

The  middle  layer  (membrana  propria)  consists  of  two  sets  of  fibres :  {a)  external 
or  radial  (stratum  radiatum),  situated  immediately  under  the  integument,  and 
radiating  from  the  handle  of  the  malleus  to  the  annulus  fibro-cartilagineus ; 
(h)  internal  or  circular  (stratum  circulare),  the  fibres  of  which  are  numerous 
near  the  circumference,  but  scattered  and  few  in  number  near  the  centre  of 
the  membrane  (Fig.  584).  Both  radial  and  circular  fibres  are  absent  from  the  pars 
flaccida,  which  is  constituted  merely  by  the  apposition  of  the  cutaneous  and  mucous 
layers.  Gruber  pointed  out  that,  in  addition  to  the  radial  and  circular  fibres,  there 
exists,  next  the  stratum  mucosum,  a  series  of  dendritic  or  branched  fibres,  which 
are  best  developed  in  the  posterior  part  of  the  membrane. 

The  internal  layer  (stratum  mucosum)  is  continuous  with  the  general  mucous 
lining  of  the  tympanum.  It  is  thicker  over  the  upper  part  of  the  membrane  than 
near  its  centre,  and  is  covered  by  pavement  epithelium. 

Otoscopic  Examination  of  the  Tympanic  Membrane  (Fig.  585).— The  membrane,  in  the 
living,  is  of  a  "  pearl-gray  "  colour,  but  may  jDresent  a  reddish  or  yellowish  tinge,  depending  upon 
the  condition  of  its  mucous  lining  and  on  the  condition  of  the  cutaneous  lining  of  the  meatus  ;  the 
posterior  segment  is  usually  clearer 

Po.sterioitympaiio- 

luallcolar  fold 

Sliort  process  of 

malleus 

I^ong  process  of 

incus 


Membrana  Haccida 

Anterior  tympano-. 

malleolar  fold 


than  the  anterior.  At  the  antero- 
superior  part,  close  to  its  periphery, 
a  whitish  point  appears  as  if  pro- 
jecting towards  the  meatus  ;  this  is 
the  short  process  of  the  malleus. 
Passing  downwards  and  backwards 
from  this  jDoint  to  the  umbo  is  a 
ridge  caused  by  the  handle  of  the  Handle  of  malleus 
malleus,  the  lower  extremity  of 
which  api^ears  rounded.  Two 
ridges,  corresponding  with  the  tym- 
pano-malleolar  folds,  extend  from 
the  short  process  of  the  malleus,  one 
forwards  and  upwards,  the  other 
backwards  and  upwards.  Behind, 
and  near  the  lower  extremity  of  the 
handle  of  the  malleus,  is  a  reddish 


Antero-superior- 
quadrant 


Antero-inferioi 
quadrant 


Postero-superior 
([uadrant 

Postero-inferior 
i|ua(lrant 

—    (  one  of  light 


Fig.  585. — Lekt  Tympanic  Membrane  (as  viewed  from  the  external 
auditory  meatus).      x  .3. 


or  yellowish  sjjot,  due  to  the  promontory  of  the  inner  tynq^anic  wall  shining  through.  If  the 
membrane  be  very  transparent,  the  long  process  of  the  incus  may  be  visible  behind  the  upper 
part  of  the  handle  of  the  malleus,  and  reaching  downwards  as  far  as  its  middle.  From  the  lower 
end  of  the  handle  of  the  malleus,  the  "  cone  of  light "  or  "  luminous  triangle "  extends  down- 
wards and  forwards,  its  apex  being  directed  towards  the  handle ;  this  triangle  varies  in  size  in 
different  people.  A  line  jjrolonging  the  handle  downwards  divides  the  membrane  into  two  parts, 
while  another,  drawn  at  right  angles  to  this  through  the  umbo,  will  suljdivide  it  into  four  quad- 
rants, viz.  postero-superior,  postero-infericr,  antero-superior,  and  antero-inferior  ;  this  subdivision 
is  useful  in  enabling  the  otologist  to  localise  and  describe  accurately  the  seat  of  lesions  in  the 
membrane. 

Vascular  and  Nervous  Supply  of  the  Membrana  Tympani.— The  arteries  are  arranged  in 
two  sets,  one  on  the  cutaneous  and  another  on  the  mucous  surface.  These  anastomose  by  means 
of  small  branches  which  pierce  the  membrane,  especially  near  its  ijeriphery.  The  first  set  is 
chiefly  derived  from  the  deep  auricular  branch  of  the  internal  maxillary,  whilst  those  on  the 
mucous  surface  are  small  and  proceed  from  the  tympanic  branch  of  the  internal  maxillary,  and 
from  the  stylo-mastoid  branch  of  the  posterior  auricular.  The  veins  from  the  cutaneous  surface 
open  into  the  external  jugular ;  those  from  the  inner  surface  partly  into  the  venous  plexus  on 
the  Eustachian  tube,  and  partly  into  the  lateral  sinus  and  veins  of  the  dura  mater.  The  outer 
surface  of  the  membrane  receives  its  nerves  from  the  auiiculo-temporal  branch  of  the  fifth  and 
from  the  auricular  branch  of  the  vagus ;  the  inner  surface,  from  the  nerve  of  Jacobson  (tympanic 
branch  of  the  glosso-pharyngeal).     The  lymphatics,  like  the  blood-vessels,  are  arranged  in  two 


752  THE  OEGANS  OF  SENSE. 

sets,  cutaneous  and  mucous,  which,  however,  communicate  freely  with  each  other.     Kessel  has 
described  as  lymphatics  the  spaces  between  the  branches  of  Gruber's  dendritic  fibres. 

The  inner  wall  of  the  tympanic  cavity  (paries  labyrinthica)  is  formed  by  the 
outer  surface  of  the  internal  ear  or  labyrinth  (Fig.  583).     It  presents — (1)  a  rounded 
eminence,  the  promontory  (promontorium),  which  is  caused  by  the  first  coil  of  the 
cochlea,  and  is  grooved  for  the  tympanic  plexus  of  nerves.     (2)  An  oval  or  some- 
what reniform  opening,  the  fenestra  ovalis  seu  vestibuli,  which  is  situated  above 
and  behind  the  promontory,  with  its  long  axis  directed  from  before  backwards. 
It  measures  3  mm.  in  length  and  1|  mm.  from  above  downwards,  and  lies  at  the 
bottom  of  a  funnel-shaped  recess,  the  fossula  fenestras  vestibuli.     In  the  macerated 
bone  it  leads  into  the  vestibule  of  the  labyrinth,  but  is  closed  in  the  recent  state 
by  the  foot  of  the  stapes,  surrounded  by  its  ligamentum  annulare.     (3)  An  elevation, 
the  prominentia  canalis  facialis,  which  is  situated  above  the  fenestra  ovalis,  in  the 
recessus  epitympanicus.     This  indicates  the  position  of  the  upper  part  of  the 
aqueduct  of  Fallopius,  which  contains  the  facial  nerve  and  is  continued  backwards 
and    downwards    behind    the    tympanic    cavity,   to    end    at    the    stylo  -  mastoid 
foramen.     (4)  The  processus  cochleariformis,  or   septum  canalis  musculo-tubarii ; 
this  process  extends  backwards,  above  the  anterior  end  of  the  fenestra  ovaHs,  where 
it  makes  a  sharp  outward  curve,  and  forms  a  pulley  over  which  the  tendon  of  the 
tensor  tympani  muscle  plays.     (5)  A  funnel-shaped  recess,  the  fossula  fenestras 
cochleae,  which  is  situated  behind  and  below  the  promontory,  and  almost  hidden  by 
its  overhanging  edge.     It  leads  forwards,  upwards,  and  inwards  to  an  irregularly 
oval  opening,  termed  the  fenestra  rotunda  seu  cocMeae,  which  in  the  macerated  bone 
communicates  with  the  cochlea,  but  in  the  recent  state  is  closed  by  a  membrane, 
the  membrana  tympani  secundaria.     This  membrane  appears  angularly  bent  along  a 
line   joining   its  antero-inferior  two-thirds  with   the  postero-superior   third.     It 
consists  of  three  layers :  (a)  external,  continuous  with  the  mucous  lining  of  the 
tympanum   and  containing  a  network  of  capillaries;   (Jb)   middle,   or  substantia 
propria,  the  fibres  of  which  radiate  chiefly  towards  the  periphery  of  the  membrane 
— some  branched,  dendritic  fibres  are  also  present ;  (c)  internal,  continuous  with 
the  epithelial  lining  of  the  labyrinth.     (6)  Between  the  fenestra  ovalis  above  and 
the  fossula  rotunda  below  is  a  small  circular  depression,  the  sinus  tympani,  which  is 
perforated  by  one  or  two  minute  foramina  for  blood-vessels,  and  indicates  the 
position  of  the  ampullated  extremity  of  the  posterior  semicircular  canal. 

Mastoid  Antkum  and  Mastoid  Aik-cells. 

The  mastoid  antrum  (antrum  mastoideum  seu  tympanicum)  is  seen  in  the  tem- 
poral bone  at  birth  as  a  cavity,  having  a  vertical  measurement  of  7-9  mm.  and  a 
transverse  of  9-11  mm.,  and  is  nearly  as  large  in  the  newly-born  child  as  in  the 
adult.     Eoofed  in  by  the  tegmen  tympani,  its  floor  and  inner  wall  are  formed  by 
the  petro-mastoid,  while  externally  it  is  closed  by  the  junction  of  the  thin  outer 
part  of  the  squama  with  the  pars  mastoidea.     It  communicates  with  the  epitympanic 
recess  by  a  triangular  or  rounded  opening,  on  the  inner  wall  of  which,  immediately 
above  and  behind  the  canalis  facialis,  is  a  smooth,  convex  area  of  bone  indicating  the 
position  of  the  ampullated  extremities  of  the  superior  and  external  semicircular 
canals.     At  birth  its  outer  wall  has  a  thickness  of  only  1-2  mm.,  but  by  the  ninth 
year  this  has  increased  to  about  10  mm.     Coincident  with  the  growth  of  the 
mastoid  process  the  mastoid  air-cells  are  developed  downwards  and  backwards  as 
diverticula  from  the  antrum,  and  present  the  greatest  possible  variations  in  different 
skulls.     They  may  be  large,  comparatively  few  in  number,  and  involve  the  whole 
process,  in  which  case  the  compact  bone  which  surrounds  them  is  extremely  thin, 
and  the  innermost  cells  are  only  separated  by  a  transparent  lamella  from  the  lateral 
sinus — a  lamella  which,  in  some  instances,  is  partly  deficient.     In  other  cases  the 
cells  may  be  small  and  numerous,  only  invading  a  portion  of  the  process,  the  remainder 
consistin<j-  of  diploiitic  tissue.     No  definite  conclusion  can  be  come  to  as  to  their 
condition  by  external  percussion  or  examination.     A  solid  process  is  occasionally 
seen.     The  air-cells  are  not  limited  to  the  mastoid  process,  but  extend  forwards 
over  the  roof  of  the  meatus,  upwards  towards  the  squama,  and  inwards  towards  the 


EUSTACHIAN  TUBE. 


753 


temporo-occipital  suture,  whilst  in  a  few  cases  they  are  seeu  to  iuvade  the  pars 
jugularis  of  the  occipital  bone.  They,  together  with  the  antrum,  are  lined  by  thin 
mucous  membrane  continuous  with  that  of  the  tympanic  cavity ;  the  deep  surface 
of  the  mucous  membrane  is  firmly  fixed  to  the  periosteum,  while  its  free  surface  is 
covered  by  a  layer  of  flattened,  non-ciliated  epithelium. 


Fascia 
salpingo 


Eustachian  Tube. 

The  Eustachian  tube  (tuba  auditiva  Eustachii)  leads  from  the  tympanic  cavity  to 
the  naso-pharynx,  and  transmits  air  to  the  former,  in  order  that  the  pressure  on  the 
inner  and  outer  surfaces  of  the  membrana  tympani  may  be  equalised ;  it  may  also 
serve  to  convey  mucous  secretion  away  from  the  tympanic  cavity.  Its  outer 
extremity,  the  ostium  tympanicum  tubae  auditivae  (Fig.  583),  opens  into  the  anterior 
part  of  the  tympanic  cavity  below  the  canal  for  the  tensor  tympani  muscle. 
Directed  downwards  and  inwards,  the  tube  ends  on  the  upper  part  of  the  naso- 
pharynx by  a  wide  orifice,  the  ostium  pharyngeum  tubae  auditivae  (Fig.  555).  It 
measures  about  an  inch  and  a  half  (36  mm.) 
in  length,  and  forms  with  the  horizontal 
plane  an  angle  of  30°  to  40°,  with  the  sagittal 
plane  an  angle  of  about  45°,  and  with  the 
bony  part  of  the  external  meatus  one  of 
135°  to  140°.     It  consists  of  two  portions : 

(a)  an  antero-internal,  fibro-cartilaginous 
part,  the  pars  cartilaginea  tubae  auditivae, 
having  a  length  of  about  one  inch ;    and 

(b)  a  postero-external,  osseous  part,  the 
pars  ossea  tubae  auditivae,  measuring  half 
an  inch  in  length.  The  two  portions  are 
not  in  the  same  plane,  the  cartilaginous 
part  inclining  downwards  a  little  more 
than  the  osseous  portion,  and  forming  with  p''»'"y"g<'* 
it  a  wide  angle.  Its  lumen  is  widest  at 
the  ostium  pharyngeum,  narrowest  at  the 
junction  of  the  bony  and  cartilaginous 
portions,  forming  here  the  isthmus,  and 
again  expanding  towards  the  tympanic 
cavity ;  hence  it  presents,  on  longitudinal 
section,  somewhat  the  appearance  of  an 
hour-glass.  The  pars  ossea  occupies  the 
angle  between  the  squamous  and  petrous  parts  of  ihe  temporal  bone,  and  is  separated 
by  the  processus  cochleariformis  from  the  canal  containing  the  tensor  tympani  muscle, 
whilst  immediately  to  its  inner  side  is  the  carotid  canal.  The  pars  cartilaginea  con- 
sists partly  of  cartilage  and  partly  of  fibrous  membrane.  The  cartilage  (cartilago 
tubai  auditive)  presents  the  form  of  an  elongated  triangular  plate,  of  which  the  apex 
is  firmly  attached  to  the  inner  end  of  the  pars  ossea,  while  the  base  is  free,  and  forms 
a  projection  on  the  upper  and  posterior  aspects  of  the  pharyngeal  orifice.  The 
upper  edge  of  this  cartilaginous  plate  is  bent  outwards  in  the  form  of  a  hook,  and 
so  produces  a  furrow  open  below  and  externally,  the  furrow  being  converted  into 
a  complete  canal  by  the  fibrous  part  of  the  tube.  On  transverse  section  (Fig.  586) 
the  cartilage  presents  two  laminae  continuous  with  each  other  superiorly :  (a) 
lamina  medialis,  broad  and  thick ;  and  (b)  lamina  lateralis,  thin  and  hook-shaped. 
At  the  ostium  pharyngeum  the  lamina  medialis  forms  the  entire  inner  wall  of  the 
tube,  but  it  gradually  diminishes  in  breadth  on  approaching  the  isthmus  tubae. 
Fissures  are  often  seen  in  the  cartilage ;  sometimes  it  is  completely  separated  into 
several  pieces,  or  accessory  islands  may  be  observed  in  the  roof,  floor,  or  membranous 
part. 

The  upper  and  inner  aspects  of  the  cartilage  are  firmly  fixed  to  the  base  of  the 
skull,  where  it  lies  in  a  groove,  the  sulcus  tubae  auditivae,  situated  between  the  great 
wing  of  the  sphenoid  and  the  petrous-temporal.     Extending  forwards  on  to  the 
52 


Mucous 
glands 


Fig.  586. — Transverse  Section  of  the 
Cartilaginous  Part  of  the  Eustachian  Tube. 


754  THE  OEGANS  OF  SENSE. 

root  of  the  pterygoid  process  this  sulcus  ends  at  a  projection,  the  processus  tubarius, 
on  the  middle  of  the  internal  pterygoid  plate.  The  tensor  palati  muscle  lies  to 
the  outer  side  of  the  tube  and  receives  some  fibres  of  origin  from  its  lamina 
lateralis;  these  fibres  constitute  the  dilator  tubse  muscle  of  Eiidinger.  To  the 
inner  side  of  the  cartilage  are  found  the  levator  palati  and  the  mucous  membrane 
of  the  pharynx.  The  membranous  part  (lamina  membranacea)  consists  of  a  strong 
fibrous  membrane,  stretching  between  the  two  edges  of  the  cartilage,  and  so  com- 
pleting the  under  and  outer  parts  of  the  canal.  Thin  above,  it  becomes  thickened 
below  and  forms  the  fascia  salpingo-pharyngea  of  Troltsch,  which  gives  origin  to 
some  of  the  fibres  of  the  tensor  palati  muscle.  Between  this  fascia  and  the  mucous 
lining  of  the  tube  is  a  layer  of  adipose  tissue. 

The  pharyngeal  orifice  of  the  Eustachian  tube  (ostium  pharyngeum  tubae),  tri- 
angular or  oval  in  shape,  is  situated  on  the  lateral  wall  of  the  naso-pharynx,,  the 
centre  of  the  opening  being  on  a  level  with  the  posterior  end  of  the  inferior  tur- 
binated bone.  It  is  bounded  above  and  behind  by  a  pad  or  cushion  produced  by 
the  inner  end  of  the  cartilage,  which  here  abuts  against  the  mucous  membrane. 
The  posterior  part  of  this  cushion  is  very  prominent  and  forms  the  anterior  boundary 
of  the  fossa  of  Rosenmiiller.  Prolonged  downwards  from  it  is  an  elevation 
of  the  mucous  membrane,  termed  the  plica  salpingo-pharyngea,  which  covers  the 
small  salpingo-pharyngeus  muscle.  From  the  upper  part  of  the  cushion  an  indis- 
tinct fold,  the  plica  salpingo -palatina,  extends  to  the  palate. 

The  mucous  lining  of  the  tube  is  continuous  behind  with  that  of  the  tympanic 
cavity,  and  in  front  with  that  of  the  naso-pharynx.  It  is  thin  in  the  pars  ossea, 
contains  few,  if  any,  mucous  glands,  and  is  firmly  fixed  to  the  bony  wall ;  whilst  in 
the  pars  cartilaginea  it  is  loose  and  thrown  into  longitudinal  folds.  Numerous 
mucous  glands  open  into  the  tube  near  its  pharyngeal  orifice,  and  here  also  there 
exists  a  considerable  amount  of  adenoid  tissue,  which  constitutes  the  "  tube-tonsil " 
of  Gerlach.  This  adenoid  tissue  is  continuous  with  that  of  the  naso-pharynx,  and, 
like  it,  is  especially  well  developed  in  children.  The  lumen  of  the  tube  is  lined 
with  ciliated  columnar  epithelium. 

The  tube  is  opened,  during  deglutition,  by  the  dilator  tubse  and  salpingo- 
pharyngeus  muscles.  The  former  springs  superiorly  from  the  cartilaginous  hook  of 
the  tube,  and  blends  inferiorly  with  the  tensor  palati.  When  the  dilator  tubse 
contracts,  the  cartilaginous  hook  and  membranous  part  of  the  tube  are  drawn  out- 
wards and  forwards.  Some  anatomists  are  inclined  to  the  view  that  the  entire 
tensor  palati  acts  chiefly  as  a  dilator  of  the  tube,  and  Eiidinger  has  named  it  the 
abductor  tubse.  The  salpingo-pharyngeus  muscle  draws  downwards  and  back- 
wards the  inner  cartilaginous  plate,  increasing  the  angle  between  it  and  the  outer 
plate.  Some  difference  of  opinion  exists  as  to  the  precise  action  of  the  levator 
palati ;  probably  it  assists  in  opening  the  tube. 

The  Eustachian  tuhe  receives  its  blood-supply  from  the  ascending  pharyugeal  artery  and 
from  the  middle  meningeal  and  Vidian  branches  of  the  internal  maxillary  artery.  Its  veins 
form  a  network  which  opens  into  the  pterygoid  venous  plexus.  The  sensory  nerves  of  the  tube 
are  derived  from  the  tympanic  plexus  and  from  the  pharyngeal  branches  of  the  second  division  of. 
the  fifth  cranial  nerve. 

The  tube  of  the  child  differs  considerably  from  that  of  the  adult ;  its  lumen  is  relatively 
wider,  its  direction  more  horizontal,  and  its  pars  ossea  relatively  shorter.  Kunkel  states  that  its 
pharyngeal  orifice  is  below  the  level  of  the  hard  palate  in  the  foetus  ;  at  birth  it  is  on  the 
same  level  as  the  palate,  whilst  at  the  fourth  year  it  is  3  to  4  mm.,  and  in  the  adult  10  mm.,  above 
it.  The  pharyngeal  orifice  forms  a  narrow  fissure,  and  its  cartilage  projects  less  towards  the 
middle  line. 

Tympanic  Ossicles. 

The  tympanic  ossicles  (ossicula  auditus)  form  an  articulated  column  connect- 
ing the  outer  with  the  inner  wall  of  the  tympanic  cavity,  and  are  named,  from 
without  inwards,  the  malleus  or  hammer,  the  incus  or  anvil,  and  the  stapes  or 
stirrup.  The  first  is  attached  to  the  inner  surface  of  the  membrana  tympani;  the 
last  is  fixed  witliin  the  circumference  of  the  oval  fenestra. 

The  malleus  (Fig.  587,  B,  D),  the  largest  of  the  three  ossicles,  has  a  length  of 
8  to  9  mm.,  and  consists  of  a  head  (capitulum  mallei),  a  neck  (coUum  mallei),  and  a 


TYMPANIC  OSSICLES. 


ioo 


handle  (niauubrium  mallei),  together  with  two  processes,  viz.  :  (a)  processus  lougus 
seu  anterior,  (b)  processus  brevis  seu  lateralis.  The  head  and  neck  are  situated  in 
the  epitympanic  recess;  the  processus  brevis  and  manubrium  are  fixed  to  the  inner 
surface  of  the  membrana  tympani ;  whilst  the  processus  lougus  is  directed  forwards 
towards  the  Glaserian  fissure,  to  which,  in  the  adult,  it  is  connected  by  ligamentous 


Fk;.  587. 


SB  C  15  D  E 

-Tympanic  Ossicles  ok  Left  Ear  (enlarged  about  tliree  times). 


A,  Incus,  seen  from  the  front  ;  B,  Malleus,  viewed  from  behind  ;  C,  Incus,  and  D,  Malleus,  seen  from  inner 

asiiect  ;  E,  Stapes. 


1.  Boily  of  incus,  with  articular 

surface  for  head  of  malleus. 

2.  Processus  longus. 

3.  Processus  lentioularis. 

4.  Articular  surface  for  incus. 

5.  Head. 
().  Xeck. 


7.   Processus  brevis. 
S.  Manubrium. 
9.   Body. 

10.  Short  process. 

11.  Long  process. 

12.  Processus  longus. 

13.  Head. 


14.  Facet  for  incus. 

15.  Manubrium. 
It;.  Head. 

17.  Xeck. 

18.  Crus  anterius. 
10.  Crus  posterius. 
20.  Foot-plate. 


fibres.  The  head,  somewhat  rounded,  is  smooth  and  convex  above  and  in  front,  and 
presents,  on  its  posterior  aspect,  a  facet  for  articulation  with  the  body  of  the  incus. 
This  facet  is  directed  obliquely  downwards  and  inwards,  and  reaches  slio-htlv  on  to 
its  mesial  surface.  More  or  less  elliptical  in  form,  it  is  constricted  near  the 'middle 
so  as  to  resemble,  somewhat,  the  figure  8 ;  an  oblique  ridge,  correspondino-  with  the 
constriction,  divides  the  facet  into  tw^o  parts — an  upper  and  larger,  directed  back- 

Reccssus  epitympanicus 
Body  of  incus 


.Short  process  of  incus 
Ligament  of  incu 


Chorda  tympaiii  nerve 

Pyramid,  with  tendon 

of  stapedius  muscle 

issuing  from  it 


Sujierior  ligament  of  malleus 
Head  of  malleus 


Foot  of  stape: 


.\nterior  ligament  of  malleus 


—  Handle  of  malli'us 


Tensor  tympani  muscle 

Processus 
cochlea  riformis 

Osseous  part  of 
Eustachian  tube 


Fig.  588. — Left  Me.mbraxa  Ty.mpaxi  and  Chain  of  Tympanic  Ossicles  (seen  from  inner  aspect),    x  3. 


wards,  and  a  lower  and  lesser,  directed  inwards.  Opposite  the  lower  part  of  the 
constriction  the  inferior  edge  of  the  facet  is  very  prominent,  and  is  continued  up- 
wards into  the  oblique  ridge  just  referred  to ;  it  forms  a  tootli-like  process,  the  spur 
or  cog-tooth  of  the  malleus.  On  the  back  of  the  head,  below  this  spur,  is  an  oblique 
crest,  the  crista  mallei,  to  which  is  attached  the  external  ligament  of  the  malleus. 
The  neck  is  the  shghtly  constricted  portion  immediately  below  the  head.  Flattened 
from  l^efore  backwards,  its  outer  surface  is  directed  towards  the  membrana  flaccida, 


756  THE  OEGANS  OF  SENSE. 

whilst  its  inner  is  crossed  by  the  chorda  tympani  nerve.  The  handle  is  directed 
downwards,  inwards,  and  backwards  from  the  neck,  forming  with  the  long  axis  of 
the  head  an  angle,  opening  inwards,  of  126°  to  150°.  Its  upper  part  is  flattened 
from  before  backwards,  but  towards  the  lower  end  it  is  twisted  on  itself,  so  that  its 
surfaces  look  outwards  and  inwards ;  moreover,  the  lower  end  is  slightly  curved, 
the  concavity  being  directed  forwards  and  outwards.  It  is  fixed,  along  its  entire 
length,  to  the  membrana  propria  of  the  tympanic  membrane  by  its  periosteum  and 
by  a  layer  of  cartilage  (Gruber).  This  latter  intervenes  between  the  handle  and 
the  membrane,  and  must  be  regarded  as  a  residue  of  that  stage  of  development  when 
the  entire  malleus  was  cartilaginous.  On  the  inner  aspect  of  the  handle,  near  its 
upper  extremity,  a  slight  projection  for  the  attachment  of  the  tendon  of  the  tensor 
tympani  muscle  may  be  seen.  The  long  process  is  a  slender  spicule  springing  from 
the  fore-part  of  the  neck  and  directed  forwards  towards  the  Glaserian  fissure.  In 
the  fcetus  it  constitutes  the  longest  process  of  the  malleus  and  is  directly  continuous 
with  Meckel's  cartilage.  In  the  adult  it  usually  assumes  the  form  of  a  small  pro- 
jection, since  its  anterior  part  is  represented  merely  by  fibrous  tissue.  The  short 
process  may  be  looked  upon  as  the  upper  extremity  of  the  handle  projected  out- 
wards ;  it  is  fixed  to  the  upper  part  of  the  membrana  tympani  by  the  cartilaginous 
layer  already  referred  to,  and  to  the  extremities  of  the  notch  of  Pdvinus  by  the 
anterior  and  posterior  malleolar  folds. 

The  incus  (Fig.  587,  A,  C)  is  best  likened  to  a  bicuspid  tooth  with  widely 
divergent  fangs.  It  consists  of  a  body  (corpus  incudis),  a  long  process  (cms  longum), 
and  a  short  process  (crus  breve) ;  the  two  processes  form  with  each  other  an  angle  of 
90°  to  100°.  The  body  and  short  process  are  situated  in  the  epitympanic  recess. 
The  body  presents  a  more  or  less  saddle-shaped  surface  for  articulation  with  the 
head  of  the  malleus.  This  surface  is  directed  forwards,  and  its  lower  part  is 
hollowed  out  for  the  accommodation  of  the  cog-tooth  of  the  malleus.  In  front  of 
this  hollow  it  is  prominent  and  spur-like.  The  short  process  is  thick,  triangular 
in  shape,  and  projects  horizontally  backwards ;  its  conical  extremity,  covered  with 
cartilage,  articulates  with  the  fossa  incudis  in  the  postero-inferior  part  of  the 
epitympanic  recess.  The  long  process  projects,  almost  perpendicularly,  downwards 
from  the  body  into  the  tympanic  cavity,  where  it  lies  parallel  with,  but  1;^  mm. 
behind  and  internal  to,  the  handle  of  the  malleus.  Its  lower  end  is  bent  inwards 
and  narrowed  to  form  a  short  neck,  on  the  inner  extremity  of  which  is  a  small  knob 
of  bone,  the  processus  lenticularis,  for  articulation  with  the  head  of  the  stapes. 
Until  the  sixth  month  of  foetal  life  this  process  exists  as  a  separate  ossicle,  termed 
the  OS  orbiculare. 

The  stapes  (Fig.  587,  E)  presents  a  head  (capitulum  stapedis),  a  neck  (coUum 
stapedis),  two  crura  (crus  anterius  et  posterius),  and  a  base  or  foot-plate  (basis 
stapedis).  The  head,  directed  outwards,  is  concave  externally  for  articulation 
with  the  processus  lenticularis  of  the  incus.  The  neck  is  the  slightly  constricted 
part  immediately  internal  to  the  head,  and  from  it  the  two  crura  spring ;  the 
tendon  of  the  stapedius  muscle  is  inserted  into  the  posterior  aspect  of  the  neck.  The 
anterior  crus  is  shorter  and  less  curved  than  the  posterior.  Diverging  from  each 
other,  the  crura  are  directed  inwards  and  are  attached — one  near  the  anterior,  the 
other  near  the  posterior  end  of  the  foot-plate.  The  foot-plate  almost  completely 
fills  the  oval  fenestra,  and,  like  it,  is  somewhat  oval  or  reniform,  its  anterior  end 
being  the  more  pointed.  In  the  recent  condition  a  membrane  fills  the  arch  formed 
by  the  crura  and  the  foot-plate,  the  crura  being  grooved  for  its  reception.  In  the 
child  the  crura  of  the  stapes  are  less  curved  than  in  the  adult,  and  the  opening 
bounded  by  them  and  the  foot-plate  is  nearly  triangular. 

Articulations  of  the  Tympanic  Ossicles. — The  joint  between  the  head  of  the 
malleus  and  the  body  of  the  incus  (articulatio  incudomalleolaris)  is  diarthrodial, 
and  may  be  described  as  one  of  reciprocal  reception.  It  is  surrounded  by  a  capsular 
ligament,  from  the  inner  surface  of  which  a  wedge-shaped  meniscus  projects  into  the 
joint  cavity  and  incompletely  divides  it.  The  articulation  of  the  processus  lenti- 
cularis and  the  capitulum  stapedis  (articulatio  incudostapedia)  is  of  the  nature  of 
an  enarthrosis  and  is  surrounded  by  a  capsular  ligament.  An  interarticular  carti- 
lage has  been  described  as  occurring  in  this  joint,  while  some  observers  deny  the 


TYMPANIC  OSSICLES.  757 

presence  of  a  synovial  cavity  and  regard  the  articulation  as  a  syndesmosis,  the 
articular  surfaces  being  held  together  merely  by  fibrous  tissue. 

Ligaments  binding  the  Ossicles  to  the  Walls  of  the  Tympanic  Cavity  (lig. 
ossiculorum  auditus). — The  malleus  is  attached  to  the  walls  of  the  tympanum  by 
three  ligaments  (Fig.  588),  viz.  anterior,  superior,  and  external.  The  anterior  liga- 
ment (lig.  mallei  anterius)  consists  of  two  portions  :  (a)  the  band  of  Meckel,  which  is 
attached  to  the  base  of  the  processus  longus,  and  passes  forwards  through  the 
Glaserian  fissure  to  reach  the  spine  of  the  sphenoid ;  it  represents  the  remnant  of  a 
portion  of  Meckel's  cartilage,  and  was  formerly  described  as  the  laxator  tympani 
muscle ;  (b)  a  firm  bundle  of  fibres,  the  lig.  mallei  anterius  of  Helmlioltz,  which 
extends  from  the  spina  tympanica  posterior  at  the  anterior  boundary  of  the  notch 
of  Rivinus  to  the  anterior  aspect  of  the  malleus,  above  the  base  of  the  processus 
longus.  The  superior  ligament  (lig.  mallei  superius)  extends,  almost  vertically, 
from  the  head  of  the  malleus  to  the  roof  of  the  epitympanic  recess.  The  external 
ligament  (lig.  mallei  laterale)  is  short  and  fan-shaped ;  its  fibres  converge  from  the 
posterior  half  of  the  notch  of  Eivinus  to  the  crista  mallei.  The  posterior  part  of 
this  ligament  is  strong  and  constitutes  the  ligamentum  mallei  posticum  of  Helm- 
lioltz. It  forms,  together  with  the  ligamentum  mallei  anterius,  the  axis  around 
which  the  malleus  rotates,  and  the  two  constitute  what  Helmholtz  has  termed  the 
"  axis-ligament  "  of  the  malleus. 

The  posterior  extremity  of  the  crus  breve  of  the  incus  is  tipped  with  cartilage 
and  fixed  by  means  of  a  hgament,  the  ligamentum  incudis  posterius  (Fig.  588),  to  the 
fossa  incudis.  Some  observers  describe  this  as  a  diarthrodial  joint.  A  superior 
ligament,  the  ligamentum  incudis  superius,  is  sometimes  present,  but  consists  mainly 
of  a  fold  of  mucous  membrane.  The  vestibular  surface  and  the  circumference  of 
the  foot  of  the  stapes  are  covered  by  hyaline  cartilage,  and  a  similar  layer  lines 
the  opening  of  the  fenestra  ovalis ;  that  encircling  the  base  of  the  stapes  is  joined 
to  that  which  lines  the  fenestra  by  a  dense  ring  of  elastic  fibres,  named  the 
ligamentum  annulare  baseos  stapedis.  The  posterior  fibres  of  this  annular  hgament 
are  thicker  and  shorter  than  the  anterior,  and  thus  the  anterior  end  of  the  foot- 
plate is  free  to  make  greater  excursions,  during  the  movements  of  the  Ijone,  than 
the  posterior. 

Development  of  the  Tympanic  Ossicles. — It  is  generally  maintained  that  the 
malleus  and  incus  are  developed  from  the  upper  end  of  Meckel's  cartilage,  and  that  the 
stapes  arises  from  the  mesoblast  in  the  region  of  the  fenestra  ovalis  where  it  is  developed 
around  a  small  artery,  the  stapedial  artery,  which  ati'ophies  in  man,  but  persists  in  many 
mammals.  On  the  other  hand,  Gadow  (Fhil.  Tiuns.,  London,  vol.  clxxix.)  says  "the  whole 
system  of  the  one  to  four  elements  of  the  middle  ear,  which  have  all  the  same  function, 
is  to  be  looked  upon  as  otie  organ,  of  one  common  origin,  viz.  a  modification  of  the  hyo- 
mandibula,  the  proximal  paramere  of  the  second  visceral  arch." 

Muscles  of  the  Tympanic  Cavity. — These  are  two  in  number,  viz.  m.  tensor 
tympani  and  m.  stapedius. 

The  m.  tensor  tympani  is  the  larger,  and  takes  origin  from  the  roof  of  the  carti- 
laginous part  of  the  Eustachian  tube  and  from  the  adjacent  part  of  the  great  wing  of 
the  sphenoid.  It  also  receives  some  fibres  from  the  bony  canal  in  which  it  lies,  and 
ends  in  a  tendon  which  bends  outwards,  nearly  at  a  right  angle  to  the  belly  of  the 
muscle,  round  the  pulley-like,  posterior  extremity  of  the  processus  cochleariformis. 
Passing  across  the  cavity  of  the  tympanum  this  tendon  is  inserted  into  the 
inner  edge  and  anterior  surface  of  the  manubrium  mallei,  near  its  upper  end. 
When  the  muscle  contracts  it  draws  inwards  the  handle  of  the  malleus,  and  so 
renders  tense  the  membrana  tympani ;  it  probably  also  slightly  rotates  the  malleus 
around  its  long  axis.  It  receives  its  nerve  from  the  motor  division  of  the  fifth 
cranial  nerve  through  the  otic  ganglion. 

The  m.  stapedius  arises  within  the  pyramid,  and  from  the  canal  which  prolongs 
the  hollow  of  the  pyramid  downwards.  Its  tendon  emerges  from  the  apex  of  the 
pyramid  and  is  inserted  into  the  posterior  surface  of  the  neck  of  the  stapes. 
On  contraction  it  draws  back  the  head  of  the  stapes,  and  so  tilts  the  anterior  end  of 
the  foot-plate  outwards  towards  the  tympanic  cavity  and  the  posterior  end  inwards 


758  THE  OEGANS  OF  SENSE. 

towards  the  labyrinth,  thus  rendering  tense  the  ligamentum  annulare — the  outward 
movement  of  the  anterior  end  of  the  foot-plate  being  greater  than  the  inward  move- 
ment of  its  posterior  end.     The  muscle  is  supplied  by  the  facial  nerve. 

Movements  of  the  Tympanic  Ossicles. — The  manubrium  mallei  follows  all  the 
movements  of  the  membrana  tympani,  while  the  malleus  and  incus  move  together  around 
au  axis  extending  forwards  through  the  short  process  of  the  incus  and  the  anterior 
ligament  of  the  malleus.  When  the  membrana  tympani  moves  inwards  it  carries  with  it 
the  handle  of  the  malleus,  and  the  incus,  moving  iuwards  at  the  same  time,  forces  the  foot 
of  the  stapes  towards  the  labyrinth.  This  inward  movement  is  communicated  to  the  fluid 
(perih'mph)  in  the  labyrinth,  and  causes  an  outward  bulging  of  the  secondary  tympanic 
membrane,  which  closes  the  fenestra  rotunda.  These  movements  are  reversed  when  the 
membrana  tympani  is  relaxed,  unless  the  outward  movement  of  the  membrane  be  excessive. 
In  such  a  condition  the  incus  does  not  follow  the  full  outward  movement  of  the  malleus, 
but  merely  glides  on  this  bone  at  the  incudo-malleolar  joint,  and  thus  the  forcible 
dragging  of  the  foot  of  the  stapes  out  of  the  fenestra  ovalis  is  prevented.  The  cog-tooth 
arrangement,  already  described,  on  the  head  of  the  malleus  and  body  of  the  incus,  causes 
the  incudo-malleolar  joint  to  become  locked  during  the  inward  movements  of  the  handle 
of  the  malleus,  the  joint  becoming  unlocked  during  its  outward  movements. 

Mucous  Lining  of  the  Tympanic  Cavity  (tunica  mucosa  tympanica). — This  is 
continuous,  through  the  Eustachian  tube,  with  that  of  the  naso-pharynx ;  it  also 
extends  backwards  and  lines  the  mastoid  antrum  and  air-cells.  Thin,  transparent, 
and  closely  united  with  the  subjacent  periosteum,  it  covers  the  inner  aspect  of  the 
membrana  tympani  and  is  reflected  over  the  ossicles  and  their  ligaments.  It  also 
supplies  sheaths  for  the  tendons  of  the  tensor  tympani  and  stapedius  muscles,  and 
forms  the  following  mucous  folds,  viz. :  (a)  one  from  the  roof  of  the  epitympanic 
recess  to  the  head  of  the  malleus  and  body  of  the  incus ;  (&)  one  enveloping  the 
chorda  tympani  nerve  and  long  process  of  the  incus ;  (c)  two  extending  from  the 
short  process  of  the  malleus — one  to  the  anterior,  the  other  to  the  posterior  margin 
of  the  notch  of  Eivinus.  A  recess,  the  pouch  of  Prussak,  is  situated  between  the 
membrana  flaccida  and  the  neck  of  the  malleus.  Communicating  behind  with  the 
tympanic  cavity,  this  pouch  may  serve  as  a  reservoir  to  confine  pus  or  other  fluid, 
since  its  opening  into  the  tympanum  is  above  the  level  of  its  floor,  a  condition 
analogous  to  the  opening  from  the  antrum  of  Highmore  into  the  nasal  cavity.  The 
fold  of  mucous  membrane  which  extends  downwards  to  envelop  the  chorda  tympani 
nerve  gives  rise  to  two  pouches,  one  in  front  of,  and  the  other  behind,  the  handle 
of  the  malleus ;  these  are  named  the  anterior  and  posterior  recesses  of  Troltsch. 
The  epithelium  which  lines  the  mucous  membrane  is  flattened  over  the  membrana 
tympani,  promontory,  and  ossicles,  but  ciliated  and  columnar  over  the  greater 
portion  of  the  rest  of  the  cavity. 

The  chorda  tympani  branch  of  the  facial  nerve  passes  from  behind,  upwards, 
and  forwards  through  the  tympanic  cavity.     Its  course  is  described  on  p.  687. 

Vessels  and  Nerves  of  the  Tympanic  Cavity. — The  arteries  whicli  supply  the  tympanic 
cavity  aie  :  (1)  The  tympanic  artery,  a  branch  of  internal  maxillary,  whicli  reaches  the  cavity  by 
way  of  the  Glaserian  fissure.  (2)  The  stylo-mastoid  branch  of  posterior  auricular,  which  passes 
through  the  stylo-mastoid  foramen  and  aqueduct  of  Fallopius  ;  it  sui)plies  branches  to  the  mastoixl 
antrum  and  air-cells,  to  the  stapedius  muscle,  to  the  floor  and  iimer  wall  of  the  tympanic  cavity, 
and  forms  an  anastomotic  circle,  around  the  membrana  tympani,  with  the  tympanic  artery.  (3) 
The  middle  meningeal  artery  sends  a  branch  to  the  tensor  tympani  muscle,  and,  after  entering 
the  skull,  gives  off  its  petrosal  artery,  which  is  conducted  to  the  tympanum  along  the  hiatus 
Fallopii ;  some  twigs  from  the  posterior  division  of  the  middle  meningeal  reach  the  antrum  and 
epitympanic  recess  through  the  petro-squamous  fissure.  (4)  The  internal  carotid  artery,  in  its 
passage  thi-ough  the  canal  in  the  temporal  bone,  gives  off  one  or  two  tympanic  twigs,  while  (5)  a 
branch  from  the  ascending  pliaryngeal  accompanies  the  nerve  of  Jacobson.  The  veins  drain 
their  contents  into  the  pterygoid  plexus,  the  middle  meningeal  vein,  and  superior  petrosal  sinus. 
The  nerves  which  supply  the  nuiscles  of  the  tympanic  cavity  have  already  been  referred  to  (pp. 
757,  758).  The  mucous  membrane  receives  its  nerves  from  the  tymjianic  plexus,  which  is  described 
on  p.  690. 

Early  Condition  of  Tympanic  Cavity.— During  the  greater  part  of  intrauterine  existence 
the  tympanic  cavity  is  almo.st  completely  filled  by  a  soft,  reddish,  jelly-like  embryonic  tissue. 
The  narrow,  slit-like  space  is  lined  l)y  epithelium,  which  is  ciliated  over  the  promontory,  but 
squamous  elsewhere.  Towards  the  end  of  foetal  life  the  gelatinous  tissue  becomes  thinned  and 
the  cavity  corre.spondingly  enlarged.  At  birth  it  is  filled  with  fluid  which  becomes  absorbed, 
coincident  with  the  passage  of  air  from  the  naso-pharynx  througli  the  Eustachian  tube. 


OSSEOUS  LA15YRINTH. 


759 


INTERNAL  EAR. 

The  iunerinost,  and,  at  the  same  time,  tlie  essential  part  of  thi;  organ  of  hearing 
is  situated  in  the  substance  of  the  petrous-temporal  l)oiie,  and  consists  of  two  sets 
of  structures,  viz. :  (1)  a  series  of  cavities  hollowed  out  of  tlie  bone  and  constituting 
tlie  bony  labyrinth  (labyrinthus  osseus) ;  these  cavities  are  continuous  with  each 


Superior  semicircular  caiuil 
Ampulla  of  superior       I 
semicircular  canal 
Canalis  facialis 


Recessus  ellipticus 
Crista  vestibuli 
Rt'cessus  splui'ricus 


Fenestra  ovalis 
Aui])ulla  of  posterior  semi- 
circular canal 
Airipulla  of  external  semi- 
circular canal 
External  semicircular  canal 


canal 
Crus  commune 


Scala  tympani 
Lamina  spiralis  ossea 

Scala  vestibuli 
Opening  of  aqueductus 
cochleii' 
Fenestra  rotunda 
Recessus  coclileari 


Opening  of  crus  commune 
Opening  of  aqueductus  vestibuli 


Fkj.  589. — Left  Bony  LABTiiiNTH  (viewed  from 
the  outer  aspect). 


Fig.  590. — Interior  op  Left  Bony  Labyrinth 
(viewed  from  outer  aspect). 


other,  and  are  named  from  before  backwards  the  cochlea,  vestibule,  and  semicircular 
canals  (Eigs.  589,  590) ;  (2)  a  complex  arrangement  of  membranous  channels  (Fig. 
592),  situated  within,  but  not  nearly  filling,  the  bony  labyrinth  and  forming  the 
membranous  labyrinth  (labyrinthus  membranaceus).  These  channels  are  named  the 
ductus  cochlearis,  utricle,  saccule,  and  membranous  semicircular  canals ;  the  utricle 
and  saccule  are  lodged  within  the  bony  vestibule. 


OSSEOUS   LABYRINTH. 

Vestibule. — The  vestibule  forms  the  central  portion  of  the  osseous  labyrinth,  and 
communicates  behind  with  the  semicircular  canals  and  in  front  with  the  cochlea.  It 
is  somewhat  ovoid  in  shape,  its  long  axis  being  directed  forwards  and  outwards.  It 
measures  about  6  mm.  antero-posteriorly,  4-5  mm.  from  roof  to  floor,  and  about  3  mm. 
from  without  inwards.  Its  outer  wall  is  directed  towards  the  tympanic  cavity,  and 
in  it  is  seen  the  fenestra  ovalis,  which,  in  the  recent  state,  is  closed  by  the  foot  of 
the  stapes.  Its  inner  wall  corresponds  with  the  bottom  of  the  internal  auditory 
meatus,  and  presents,  at  its  antero-inferior  part,  a  rounded  depression,  the  recessus 
sphsericus,  which  lodges  the  saccule.  This  recess  is  perforated  by  some  twelve  or 
fifteen  small  foramina,  which  constitute  the  macula  cribrosa  media,  and  transmit  the 
filaments  of  the  auditory  nerve  for  the  supply  of  the  saccule.  The  recessus 
sphtericus  is  limited  above  and  behind  by  an  oblique  ridge,  the  crista  vestibuli,  the 
anterior  extremity  of  which  is  triangular  in  shape  and  named  the  pyramid  (pyramis 
vestibuli).  Posteriorly  this  crista  divides  into  two  limbs,  between  which  is  a  small 
depression,  the  recessus  cochlearis  of  Reichert,  perforated  by  some  eight  small  fora- 
mina, which  give  passage  to  the  nervous  filaments  for  the  supply  of  the  posterior 
extremity  of  the  ductus  cochlearis.  Above  and  behind  the  crista  vestibuli,  in  the 
roof  and  inner  wall  of  the  vestibule,  is  an  oval  depression,  the  recessus  ellipticus, 
which  lodges  the  utricle.  The  pyramid  and  adjacent  part  of  the  recessus  ellipticus 
are  perforated  by  some  25-30  small  apertures,  which  constitute  the  macula  cribrosa 
superior  seu  major.  The  foramina  in  the  pyramid  transmit  the  nerves  to  the 
utricle ;  those  in  the  recessus,  the  nerves  to  the  ampullary  ends  of  the  superior 
and  external  semicircular  canals.  Behind  and  below  the  recessus  ellipticus  is  a 
furrow,  gradually  deepening  to  form  a  canal,  the  aqueductus  vestibuli,  which  passes 
backwards  through  the  petrous  bone,  and  opens,  as  a  slit-like  fissure,  about  midway 
between  the  internal  auditory  meatus  and  the  groove  for  the  lateral  sinus.     This 


760  THE  ORGANS  OF  SENSE. 

aqueduct  measures  8-10  mm.  in  length,  and  gives  passage  to  the  ductus  endo- 
Ijmphaticus  and  a  small  vein.  The  posterior  part  of  the  vestibule  receives  the 
five  rounded  apertures  of  the  bony  semicircular  canals ;  its  anterior  part  leads,  by 
an  elliptical  opening,  into  the  scala  vestibuli  of  the  cochlea.  This  opening  is 
bounded  inferiorly  by  a  thin  osseous  lamella,  the  lamina  spiralis  ossea,  which 
springs  from  the  floor  of  the  vestibule  immediately  to  the  outer  side  of  the  recessus 
sphtericus,  and  forms,  in  the  cochlea,  the  bony  part  of  the  septum  between  the  scala 
tympani  below  and  the  scala  vestibuli  above.  From  the  anterior  part  of  the  floor 
of  the  vestibule  a  narrow  cleft,  the  fissura  vestibuli,  extends  forwards  into  the  bony 
canal  of  the  cochlea.  It  is  bounded  internally  by  the  lamina  spiralis  ossea  just 
referred  to,  and  externally  by  a  second,  smaller  lamina,  the  lamina  spiralis 
secundaria,  which  projects  inwards  from  the  outer  wall  of  the  cochlea.  These  two 
lamina  are  continuous  with  each  other  around  the  posterior  extremity  of  the 
fissure. 

Semicircular  Canals  (canales  semicirculares  ossei). — The  semicircular  canals 
(Figs.  589,  590),  three  in  number,  are  situated  above  and  behind  the  vestibule. 
They  are  distinguished  from  each  other  by  their  position,  and  are  named  superior, 
posterior,  and  external.  They  open  into  the  vestibule  by  five  apertures,  since  the 
inner  extremity  of  the  superior  and  the  upper  extremity  of  the  posterior  join  to 
form  a  common  canal  or  crus  commune.  Differing  slightly  in  length,  each  forms 
about  two-thirds  of  a  circle,  one  extremity  of  which  is  dilated  and  termed  the 
ampulla  (ampulla  ossea).  Somewhat  compressed  laterally,  their  greatest  internal 
diameter  is  from  1  to  1'5  mm.,  whilst  the  diameter  of  the  ampulla  is  about  2  mm. 

The  superior  semicircular  canal  (canalis  semicircularis  superior),  15-20  mm.  in 
length,  is  vertical  and  placed  transversely  to  the  long  axis  of  the  petrous  bone. 
Its  convexity  is  directed  upwards,  and  its  position  is  indicated  on  the  anterior  sur- 
face of  the  petrous-temporal  by  an  eminence.  Its  ampullated  end  (ampulla  ossea 
superior)  is  anterior  and  external,  and  opens  into  the  vestibule  immediately  above 
that  of  the  external  canal.  Its  opposite  extremity  joins  the  non-ampullated  end 
of  the  posterior  canal  to  form  the  crus  commune,  which  is  about  4  mm.  in  length, 
and  opens  into  the  upper  and  inner  part  of  the  vestibule.  The  posterior  semicircular 
canal  (canalis  semicircularis  posterior)  is  the  longest  of  the  three  and  measures  from 
18-22  mm.  Its  ampullary  end  (ampulla  ossea  posterior)  is  placed  inferiorly,  and 
opens  into  the  lower  and  back  part  of  the  vestibule,  where  may  be  seen  some 
six  or  eight  small  apertures,  forming  the  macula  cribrosa  inferior,  for  the  trans- 
mission of  the  nerves  to  this  ampulla.  Its  upper  extremity  ends  in  the  crus  commune. 
The  external  canal  (canalis  semicircularis  lateralis)  is  the  shortest.  It  measures 
from  12  to  15  mm.,  and  arches  nearly  horizontally  outwards.  Of  its  two  extremities 
the  external  is  ampullated  (ampulla  ossea  lateralis),  and  opens  into  the  vestibule 
immediately  above  the  fenestra  ovalis  and  in  close  relationship  to  the  ampullary 
end  of  the  superior  canal. 

Although  the  three  canals  ai-e  generally  regarded  as  opening  into  the  vestibule  by  five  orifices, 
some  observers  incline  to  the  view  that  the  ampullary  ends  of  the  sujDerior  and  external  canals 
form  a  common  orifice,  and  that,  consequently,  there  are  oidy  four  openings  for  the  three  canals.  • 

Crum  Brown  {Journ.  Anat.  and  Physiol.,  London,  vol.  viii.)  pointed  out  "that  the 
exterior  canal  of  one  ear  is  very  nearly  in  the  same  jslane  as  that  of  the  other  ;  while  the  superior 
canal  of  one  ear  is  nearly  parallel  to  the  posterior  canal  of  the  other." 

Cochlea.^ — When  freed  from  its  surroundings  the  cochlea  assumes  the  form  of 
a  short  cone  (Fig.  591);  the  central  part  of  its  base  (basis  cochleae)  corresponds 
with  the  bottom  of  the  internal  auditory  meatus,  whilst  its  apex  or  cupola  is 
directed  forwards  and  outwards,  and  comes  into  close  relation  with  the  canal  for  the 
tensor  tympani  muscle.  It  measures  about  9  mm.  across  the  base  and  about 
5  mm.  from  base  to  apex,  and  consists  of  a  spirally  arranged  tube,  which  forms  from 
2\  to  2|  coils  around  a  central  pillar  termed  the  modiolus.  The  length  of  the  tube 
is  from  28  to  30  mm.,  and  its  diameter,  near  the  base  of  the  cochlea,  2  mm.  Its 
coils  are  distinguished  by  the  terms  basal,  central,  and  apical ;  the  first,  or  basal 
coil,  gives  rise  to  the  promontory  on  the  inner  wall  of  the  tympanum. 

'    In  the  followiug  description  tlie  cochlea  is  supposed  to  be  placed  on  its  liase. 


OSSEOUS  LABYRINTH. 


761 


The  modiolus  is  about  3  mm.  in  height,  and  diminishes  rapidly  in  diameter  from 
base  to  apex,  while  its  tapered  extremity  fails  to  reach  the  cupola  by  a  distance  of 
1  mm.  Its  base  (basis  modioli)  corresponds  with  the  area  cochleae  on  the  fundus 
of  the  internal  auditory  meatus,  and  exhibits  the  tractus  spiralis  foraminosus,  which 
transmits  the  nerves  for  the  basal  and  central  coils  of  the  cochlea  and  the  foramen 
centrale,  which  gives  passage  to  the  nerves  for  the  apical  coil.  The  foramina  of  the 
tractus  spiralis  foraminosus  traverse  the  modiolus,  at  first  parallel  to  its  long  axis, 
but,  after  a  varying  distance,  they  bend  outwards  to  reach  the  attached  edge  of  the 
lamina  spiralis  ossea,  where  they  become  expanded  and  form  by  their  apposition  a 
spiral  canal,  the  canalis  spiralis  modioli  of  Rosenthal,  which  lodges  the  ganglion  of 
Corti,  or  ganglion  spirale  cochleae.  From  this  spiral  canal  numerous  small  foramina, 
for  the  transmission  of  vessels  and  nerves,  pass  outwards  to  the  free  edge  of  the 
lamina  spiralis.  The  lamina  spiralis  ossea,  a  thin,  Hat  shelf  of  bone,  winds  round  the 
modiolus  like  the  thread  of  a  screw,  and,  projecting  about  half-way  into  the  cochlear 
tube,  incompletely  divides  it  into  two  passages,  of  which  the  upper  is  named  the 
scala  vestibuli ;  the  lower,  the  scala  tympani.  The  lamina  spiralis  ossea  commences 
at  the  floor  of  the  vestibule,  near  the  fenestra  rotunda,  and  ends  close  to  the  apex 
of  the  cochlea  in  a  sickle-shaped  process,  the  hamulus,  which  assists  to  form  an 


Cupola 
Hamulus 


Section  through  promontory' 
Laiuina  spiralis 
ossea  secundaria 

Fissura  vestibuli 
Liniina  spiralis  ossea 


Recessus  cochlearis  of  vestibule  Internal  auditory  meatus 

J'lG.  591. — Section  of  Bony  Cochlea. 


Canalis  feiitralis 
Canalis  spiralis  modioli 


Modiolus 

Scala  vestibuli 

Lamina  spiralis  ossea 
Scala  tymijani 


actus  spiralis 
aminosus 


aperture  named  the  helicotrema.  In  the  basil  coil  the  upper  surface  of  the  spiral 
lamina  forms  almost  a  right  angle  with  the  modiolus,  but  the  angle  becomes  more 
and  more  acute  on  ascending  the  tube.  In  the  lower  half  of  the  basil  coil  a  second 
smaller  Ijony  plate,  the  lamina  spiralis  secundaria,  projects  inwards  from  the  outer 
wall  of  the  cochlea  towards  the  lamina  spiralis  ossea,  without,  however,  reaching  it. 
If  viewed  from  the  vestibule  the  slit-like  fissura  vestibuli,  already  referred  to 
(p.  760),  is  seen  between  the  two  osseous  spiral  laminae.  A  membrane,  the  mem- 
brana  basilaris,  stretches  from  the  free  edge  of  the  lamina  spiralis  ossea  to  the  outer 
wall  of  the  cochlea,  and  completes  the  septum  between  the  scala  vestibuli  and 
scala  tympani,  but  the  two  scalse  communicate  with  each  other  through  the 
opening  of  the  helicotrema  at  the  apex  of  the  cochlea.  The  scala  tympani  begins 
at  the  fenestra  rotunda,  through  which,  in  the  macerated  bone,  it  communicates 
with  the  tympanic  cavity ;  in  the  recent  condition  the  fenestra  is  closed  by  the 
secondary  tympanic  membrane  (vide  p.  752).  At  the  commencement  of  the  scala 
tympani  a  crest,  termed  the  crista  semilunaris,  stretches  from  the  attached  margin 
of  the  lamina  spiralis  ossea  towards  the  orifice  of  the  fenestra  rotunda.  Close  to  this 
crest  is  seen  the  inner  orifice  of  the  aqueductus  cochleae,  a  canal  measuring  from  10 
to  12  mm.  in  length,  and  opening  on  the  under  aspect  of  the  petrous  bone  internal  to 
the  fossa  jugularis.  Through  it  there  is  established  a  communication  between  the 
scala  tympani  and  the  subarachnoid  space,  and  through  it,  also,  a  small  vein  passes 
to  join  the  inferior  petrosal  sinus.  The  scala  vestibuli,  the  higher  of  the  two 
passages,  begins  in  the  vestibule  ;  its  diameter  in  the  basal  coil  is  less  than  that  of 
the  scala  tympani,  but  in  the  upper  coils  it  exceeds  that  of  the  latter. 

Internal  Auditory   Meatus. — It  is  convenient,  at   this  stage,  to  study  the 


762 


THE  OEGANS  OF  SENSE. 


fundus  of  the  internal  auditory  meatus,  which  has  been  referred  to  as  forming  the 
inner  wall  of  the  vestibule  and  the  bas3  of  the  modiolus.  It  is  divided  by  a  trans- 
verse ridge,  the  crista  transversa,  into  two  parts — an  upper  or  fossula  superior  and  a 
lower  or  fossula  inferior.  The  anterior  part  of  the  fossula  superior  is  termed  the 
area  facialis  and  exhibits  a  single  large  opening,  the  commencement  of  the  aque- 
duct of  Fallopius,  for  the  transmission  of  the  facial  nerAe.  Its  posterior  part  is 
named  the  area  vestibularis  superior,  and  is  perforated  by  the  nerves  for  utricle  and. 
ampullar  of  the  superior  and  external  semicircular  canals.  The  anterior  part  of 
the  fossula  inferior  is  termed  the  area  cochleae,  and  consists  of  the  canalis  centralis 
and  the  surrounding  tractus  spiralis  foraminosus,  for  the  passage  of  the  nerves  to 
the  cochlea.  Behind  the  area  cochlear,  and  separated  from  it  by  a  ridge,  is  the 
area  vestibularis  inferior,  which  transmits  the  nerves  to  the  saccule,  whilst  at  the 
posterior  part  of  the  f  jssula  inferior  is  seen  a  single  foramen,  the  foramen  singulare, 
which  gives  passage  to  the  nerves  for  the  ampulla  of  the  posterior  semicircular 
canal. 

MEMBEANOUS   LABYEINTH. 

The  membranous  labyrinth  (labyrinthus  membranaceus)  assumes,  more  or  less 
closely  (Fig.  592),  the  form  of  the  bony  labyrinth  in  which  it  is  situated,  but  does 
not  nearly  fill  it.  It  contains  a  fluid  termed  endolymph,  while  the  interval  between 
it  and  the  bony  labyrinth  is  named  the  perilymphatic  space,  and  is  occupied  by  a 
fluid  termed  perilymph.  The  perilymphatic  space  in  the  vestibule  measures  about 
3  mm.  from  without  inwards,  and  about  3'5  mm.  from  before  backwards.     It  is 

continuous  behind  with  the 

Recessus  utriculi  ■-,  ■,      ,■  f.  . , 

perilymphatic  space  oi  the 
semicircular  canals,  and 
opens  in  front  into  the  scala 
vestibuli.  At  the  apex  of 
the  cochlea  it  is  continuous 
through  the  helicotrema 
with  the  scala  tympani, 
which  is  shut  off  from  the 
tympanum  by  the  secondary 
tympanic  membrane.  It  is 
also  prolonged  into  the 
aqueductus  cochleae,  at  the 
extremity  of  which  it  communicates  with  the  subarachnoid  space.  The 
membranous  semicircular  canals  and  the  membranous  canal  of  the  cochlea  follow 
the  course  of  their  bony  tubes  and  lie  along  the  inner  aspect  of  their  outer  walls. 
The  bony  vestibule,  on  the  other  hand,  contains  two  chief  membranous  structures, 
the  utricle  and  saccule.  The  former  receives  the  extremities  of  the  membranous 
semicircular  canals,  whilst  the  latter  communicates  with  the  membranous  canal 
of  the  cochlea.  Moreover,  the  cavities  of  the  utricle  and  saccule  are  indirectly 
connected,  and  thus  all  parts  of  the  membranous  labyrintli  communicate  with 
each  other,  and  the  contained  endolymph  is  free  to  move  from  one  portion  to 
another.  The  vestibule,  also,  contains  the  ductus  endolymphaticus  and  the  com- 
mencement of  the  ductus  cochlearis. 

The  utricle  (utriculus),  the  larger  of  the  two  sacs  (Fig.  592),  occupies  the 
postero-superior  portion  of  the  bony  vestibule.  Its  highest  part,  or  recessus  utriculi, 
lies  in  the  recessus  ellipticus  and  receives  the  ampullae  of  the  superior  and  external 
membranous  semicircular  canals.  Its  central  part  receives  on  its  lateral  aspect  the 
non-ampullated  end  of  the  external  canal,  and  is  prolonged  upwards  and  backwards 
as  the  sinus  superior,  into  which  the  crus  commune  of  the  superior  and  posterior 
membranous  canals  open.  The  ampulla  of  the  posterior  membranous  canal  opens 
into  its  lower  and  inner  part,  or  sinus  inferior.  The  floor  and  anterior  wall  of  the 
recessus  utriculi  are  thickened  to  form  the  macula  acustica  utriculi,  to  which  are 
distributed  the  utricular  fibres  of  the  auditory  nerve.  Whitish  in  colour,  and  of 
an  oval  or  nearly  rhombic  shape,  this  macula  measures  3  mm.  in  length  and  2-3 
mm.  in  its  greatest  breadth. 


Saccule 


Ductu; 

cochleari 

Ductus  reunieris — 

Ductus 

eudolyiiiijhaticus 

AiMiJulla  of  posterior  canal 

Saccus  endolyii.phaticus 
Fig.  592. 


Ampulla  of  superior 
semicircular  canal 
Ampulla  of  external 
canal 


Sinus  superior 
Ductus 

utriculosaccularis 
Sinus  inferior 


-Diagrammatic  Representation  op  the  Different 
Parts  on  the  Membranous  Labyrinth. 


MEMBRANOUS  LABYEINTH. 


703 


The  saccule  (sacculus)  occupies  the  recessus  sphairicus,  in  the  lower  and  fore-part 
of  the  vestibule  (Fig.  590).  Smaller  than  the  utricle,  it  is  of  an  oval  shape  and 
measures  3  mm.  in  its  longest,  and  about  2  mm.  in  its  shortest  diameter.  It  presents 
anteriorly  an  oval,  whitish  thickening,  the  macula  acustica  sacciili.  This  has  a 
breadth  of  about  1"5  mm.,  and  to  it  are  distributed  the  saccular  fibres  of  the  auditory 
nerve.  The  superior  extremity  of  the  saccule  is  directed  upwards  and  backwards, 
and  forms  the  sinus  utricularis  sacculi,  which  abuts  against,  but  does  not  fuse 
with,  the  wall  of  the  utricle.  From  the  lower  part  of  the  saccule  a  short  canal, 
the  ductus  reuniens  of  Heusen,  opens  into  the  ductus  cochlearis,  a  short  distance 
in  front  of  its  vestibular  or  blind  extremity.  A  second  small  channel,  the  ductus 
endolymphaticus,  is  contiuued  from  the  posterior  part  of  the  saccide,  and,  passing 
between  the  utricle  and  the  inner  wall  of  the  vestibule,  is  joined  by  a  small  canal, 
the  ductus  utriculosaccularis,  which  arises  from  the  inner  aspect  of  the  utricle.  It 
then  enters  and  traverses  the  aqueductus  vestibuli  and  ends,  under  the  dura  mater 
on  the  posterior  surface  of  the  petrous  bone,  in  a  dilated  bhnd  extremity,  termed 
the  recessus  Cotugnii,  or  saccus  endolymphaticus ;  this,  according  to  Eiidinger,  is 
perforated  by  minute  foramina,  through  which  the  endolymph  may  pass  into  the 
meningeal  lymphatics. 

The  vestibule  also  contains  the  blind  extremity  (cajcum  vestibulare)  of  the 
ductus  cochlearis,  which  lies  immediately  below  the  saccule  in  the  recessus 
cochlearis  of  Eeichert ;  from  here  it  passes  forwards  into  the  spiral  tube  of 
the  cochlea. 

The  walls  of  the  utricle  and  saccule  are  composed  of  connective  tissue  which 
blends,  along  their  attached  surfaces,  with  the  periosteal  lining  of  the  vestibule.  It 
is  modified  internally  to  form  a  homogeneous  membrana  propria,  which  is  covered 
by  a  layer  of  pavement  epithelium  and  is  thickened  at  the  maculte  acusticie. 
Towards  the  periphery  of  the  macular  the  epithelium  is  cubical,  while  on  them 
it  is  columnar. 

The  structure  of  the  maculse  in  the  utricle  and  saccule  is  practically  the 
same  ;  two  kinds  of  cells  are  found,  viz.  (a)  supporting  cells,  and  (b)  hair  cells.  The 
supporting  cells  are  some  - 
what  fusiform,  each  con- 
taining, near  its  middle, 
a  nucleus.  Their 
branched,  deep  extremi- 
ties are  attached  to  the 
membrana  propria;  their 
free  ends  lie  between  the 
hair  cells  and  form  a  thin 
inner  hmiting  cuticle. 
The  hair  cells  are  fiask- 
shaped  and  do  not  reach 
the  membrana  propria, 
but  end  in  rounded  ex- 
tremities which  he  be- 
tween the  supporting- 
cells.  Each  contains,  at 
its  deepest  part,  a  large 
nucleus,  the  rest  of  the 
cell  being  granular  and 
pigmented.  From  the 
free  end  of  each  there 
projects  a  stiff,  hair-like 
process,  which,  on  the 
apphcation  of  reagents, 

sphts  into  several  finer  filaments.  The  nerve-fibres  pierce  the  membrana  propria, 
and  end  in  arborisations  around  the  deep  extremities  of  the  hair  cells.  A  collection 
of  small,  rhombic  crystals  of  carbonate  of  hme,  termed  otoconia,  adheres  to  each  of 
the  macular. 


Wall  of 
bony  canal 


Fig.  593. 


-Transverse  Section  of  Human  Se.micikc'ular 
Canal  (Riidinger). 


764 


THE  OKGANS  OF  SENSE. 


The  membranous  semicircular  canals  (ductus  semicirculares)  are  elliptical  on 
transverse  section  (Fig.  593),  and  are  attached  to  the  greater  circumference  of  the 
bony  tubes.  The  peripheral  portion  of  the  ellipse  is  fixed  to  the  periosteal  lining 
of  the  bony  canal,  whilst  the  opposite  part  is  free,  except  that  it  is  connected  by 
irregular  bands,  the  ligamenta  labyrintM  canaliculorum,  which  pass  through  the  peri- 
lymphatic space  to  the  bony  wall.  Like  the  bony  canals,  each  of  the  membranous 
canals  is  dilated  at  one  extremity  into  an  ampulla  (ampulla  membranacea),  which 
is  especially  developed  towards  the  concave  aspect  of  the  tube.  While  the  mem- 
branous ampullae  nearly  fill  the  corresponding  portions  of  the  bony  tubes,  the 
calibre  of  the  remaining  parts  of  the  membranous  canals  is  only  equal  to  about 
one-fourth  of  that  of  the  osseous  canals. 

Each  membranous  canal  consists  of  three  layers,  viz. :  (a)  an  outer  fibrous 
stratum  which  contains  blood-vessels,  together  with  some  pigment,  and  fixes  the 
tube  to  the  bony  wall ;  (h)  an  intermediate,  transparent  tunica  propria,  presenting 
a  numljer  of  papilliform  elevations  which  project  towards  the  lumen.  The  fibrous 
layer  and  tunica  propria  are  thinnest  along  the  attached  surface  of  the  tube,  and 
in  this  region  also  the  papilliform  elevations  are  absent ;  (c)  an  internal  epithelial 
layer,  composed  of  pavement  cells.  In  the  ampullse  the  tunica  propria  is  much 
thickened,  and  projects  into  the  cavity  as  a  transverse  elevation,  termed  the  septum 
transversum,  which,  when  seen  from  above,  is  somewhat  fiddle-shaped;  its  most 
prominent  part  is  covered  by  auditory  epithelium  forming  the  crista  acustica,  at 
each  end  of  which  is  a  half-moon-shaped  border  of  small  columnar  cells,  the  planum 
semilimatum.  The  cells  covering  the  crista  acustica  consist  of  supporting  cells  and 
hair  cells,  and  are  similar  in  their  arrangement  to  those  in  the  maculae  of  the 
utricle  and  saccule.  The  hairs  of  the  hair  cells  are,  however,  considerably  longer, 
and  project  as  far  as  the  middle  of  the  ampullary  lumen.  In  fresh  specimens  they 
appear  to  end  free,  but  in  hardened  preparations  are  seen  to  terminate  in  a  soft, 
clear,  dome-like  structure,  the  cupola  terminalis,  which  is  striated,  the  striae  converg- 
ing towards  its  concavity.  The  nerves  form  arborisations  around  the  bases  of  the 
hair  cells. 

The  membranous  cochlea  (ductus  cochlearis  or  scala  media)  commences  in  the 


SCALA    VESTIBULI 


Reissnei's  mcuibraiie 


Membrana  tectoria 

Sulcus  spiralis 
internus 


Limbas  laininit; 
spiralis 


Section  across  the  Ductus  Cochlearis  (Retzius). 


recessus  cochlearis  of  the  vestibule  by  a  blind  extremity  (caecum  vestibulare),  close 
to  which  it  receives  the  ductus  reuniens  of  Hensen  (vide  p.  763).  It  forms  a 
spirally  arranged  canal  inside  the  bony  cochlea,  and  ends  at  the  apex  of  the  latter 
in  a  second  blind  extremity,  the  lagena,  or  ctecum  cupulare,  which  is  fixed  to  the 
cupola  and  partly  Vjounds  the  helicotrema.  As  already  stated  (^oide  p.  761),  the  mem- 
brana basilaris  extends  from  the  free  edge  of  the  lamina  spiralis  ossea  to  the  outer 


MEMBRANOUS  LABYRINTH. 


765 


Outer  attachment  of 
Ueissner's  membrane 


wall  of  the  cochlea.  A  second,  more  delicate  membrane,  the  membrane  of  Reissner,  or 
membrana  vestibularis,  stretches  from  the  thickened  periosteum  covering  the  upper 
surface  of  the  lamina  spiralis  ossea  to  the  outer  cochlear  wall,  some  little  distance 
above  the  external  attachment  of  the  membrana  basilaris.  A  canal  is  thus  enclosed 
between  the  underlying  scala  tympani  and  the  overlying  scala  vestibuli,  and  con- 
stitutes the  membranous  cochlea  or  ductus  cochlearis.  Triangular  on  transverse 
section,  it  possesses  a  roof,  an  outer  wall,  and  a  floor,  and  is  lined  throughout  with 
epithelium  and  filled  with  endolymph.  On  its  floor  the  epithehum  is  greatly  modified, 
and  here  are  found  the  endings  of  the  cochlear  division  of  the  auditory  nerve. 

The  roof  or  vestibular  wall  of  the  ductus  cochlearis  is  formed  by  the  mem- 
brane of  Reissner,  which  consists  of  a  delicate,  nearly  homogeneous  membrane, 
covered  on  its  two  surfaces  by  a  layer  of  epithelium.  Its  entire  thickness  is 
about  3  jx. 

The  outer  wall  of  the  ductus  cochlearis  (Fig.  595)  consists  of  the  periosteal 
lining  of  the  Ijony  cochlea,  which,  however,  is  much  thickened  and  greatly  modified 
to  form  what  is  termed  the  ligamentum  spirale  cochleae.  Occupying  the  whole  outer 
wall,  this  ligament  projects  inwards  inferiorly  as  a  triangular  prominence,  the  crista 
basilaris,  to  whicli  the  outer  edge  of  the 
membrana  basilaris  is  attached.  The 
fibres  of  the  membrane  radiate  into  the 
ligament  in  the  form  of  a  series  of  bundles 
analogous  to  the  ligamentum  pectinatum 
iridis.  In  the  upper  part  of  the  ligamentum 
spirale  the  periosteum  is  of  a  reddish 
yellow  colour,  and  contains,  immediately 
under  its  epithelial  lining, numerous  small 
blood-vessels  and  capillary  loops,  forming 
the  stria  vascularis.  The  lower  limit  of 
this  stria  is  bounded  by  a  prominence, 
the  prominentia  spiralis,  in  which  is  seen 
a  vessel,  the  vas  prominens,  and  between 
this  prominence  and  the  crista  basilaris 
is  a  concavity,  the  sulcus  spiralis  extemus. 
The  height  of  the  outer  wall  diminishes 
towards  the  apex  of  the  cochlea. 

The  floor  or  tympanal  wall  of  the 
ductus  cochlearis  is  formed  by  the  peri- 
osteum covering  that  portion  of  the 
lamina  spiralis  ossea  which  is  situated  to 
the  outer  side  of  Reissner's  membrane, 
and  by  the  membrana  basilaris,  which 
stretches  from  the  free  edge  of  the  lamina 
spiralis  ossea  to  the  crista  basilaris.  On 
the  inner  part  of  the  membrana  basilaris 
the  complicated  structure  termed  the 
organ  of  Corti  is  situated.  The  lamina 
spiralis  ossea  consists  of  two  plates  of 
bone,  between  which  are  placed  the  canals 
for  the  branches  of  the  cochlear  nerve. 
On  the  upper  plate  the  periosteum  is 
thickened  and  modified  to  form  the  limbus 
laminae  spiralis,  the  outer  extremity  of 
which  forms  a  C- shaped  concavity,  the 
sulcus  spiralis  intemus.  The  portions  of 
the  limbus  which  project  outwards,  above 
and  below  this,  concavity,  are  termed 
respectively  the  labium  vestibulare  and  labium  tympanicum.  The  latter  is  perforated 
by  some  4000  small  apertures,  the  foramina  nervosa,  or  habenula  perforata,  for  the 
transmission  of  the  cochlear  nerves.     Externally  it  becomes  continuous  with  the 


Fig.  595. — Transverse  Section  through  Outer 
Wall  of  Ductus  Cochlearis  (Schwalbe). 


■66 


THE  OEGANS  OF  SENSE. 


inembrana  basilaris.  The  upper  surface  of  the  labium  vestibulare  presents  a 
number  of  furrows  crossing  each  other  nearly  at  right  angles,  and  intersecting  a 
series  of  elevations  which,  at  the  free  margin  of  the  lat)ium,  form  a  row  of  tooth-like 
structures,  some  7000  in  number,  the  auditory  teeth  of  Huschke.  Covering  the 
limbus  is  a  layer  of  apparently  squamous  epithelium;  the  deeper  protoplasmic 
portions  of  the  cells,  however,  with  their  contained  nuclei,  fill  up  the  intervals 
between  the  elevations  and  auditory  teeth.  This  layer  of  epithelium  is  continuous 
with  that  covering  the  under  surface  of  Eeissner's  membrane  and  with  that  which 
lines  the  sulcus  spiralis  internus. 

Membrana  Basilaris. — The  inner  part  of  this  membrane  is  thin,  and  supports 
the  organ  of  Corti ;  it  is  named  the  zona  arcuata,  and  reaches  as  far  as  the  foot- 
plate of  the  outer  rod  of  Corti.  Its  outer  part,  extending  from  the  foot-plate  of 
the  outer  rod  of  Corti  to  the  crista  basilaris,  is  thicker  and  distinctly  striated, 
and  is  termed  the  zona  pectinata.  The  substantia  propria  of  the  membrane  is 
almost  homogeneous,  but  exhibits,  in  its  deeper  part,  numerous  fibres.  These  fibres 
are  most  distinct  in  the  zona  pectinata,  and  number,  according  to  Eetzius,  about 
24,000.  Covering  the  under  surface  of  the  membrana  basilaris  is  a  layer  of  con- 
nective tissue,  which  contains,  in  its  inner  part,  small  blood-vessels,  one  of  which, 
larger  than  the  rest,  lies  below  the  tunnel  of  Corti  and  is  named  the  vas  spirale. 
The  ^vidth  of  the  membrana  basilaris  increases  from  210  /x  in  the  basil  coil  to  360  /* 
in  the  apical  coil. 

Organ  of  Corti  (Fig.  596). — Placed  upon  the  inner  portion  of  the  membrana 
basilaris,  the  organ  of  Corti  consists  of  an  ej^ithelial  eminence  which  extends  along  the 
entire  length  of  the  ductus  cochlearis,  and  comprises  the  following  structures,  viz.  : 
(1)  Corti's  rods  or  pillars,  (2)  hair  cells  (inner  and  outer),  (3)  supporting  cells  of  Deiters, 
(4)  the  cells  of  Hensen  and  Claudius,  (5)  the  lamina  reticularis,  and  (6)  a  cuticular 
membrane,  the  membrana  tectoria. 

The  rods  of  Corti  form  two  rows,  inner  and  outer,  of  stiff,  pillar-like  structures,  and 
each  rod  presents  a  base  or  foot-plate,  an  intermediate  elongated  portion,  and  an  upper 
end  or  head.  The  bases  of  the  two  rows  are  planted  on  the  membrana  basilaris  some 
little  distance  apart.     The  intermediate  portions  incline  towards  each  other  and  the  heads 


Outer  rod  of  Corti 


Liiiibu; 


Inner  rod  of  Corti 
Inner  hair  cell 
Hensen's  stripe 

Membrana  tectoria 
Sulcus  spiralis 
laminw     iuteriiu 
spiralis 


Outer  hair  cells 


Cells  of  Hensen 

Alenibrana  basilaris 

Cells  of  Claudius 


Inner  spiral 
c  fasciculus 

2  Vas  spirale       j     Space  of  Nuel 

Tunnel  nf  Corti 
Fk;.  596. — TuANSVEiisE  Section  of  Couti's  Organ  from  the  Centrat,  Con,  ok  Cochlea  (Retzius). 

come  into  contact,  so  that,  between  the  two  rows  above  and  the  membrana  basilaris  below, 
there  is  enclosed  a  triangular  tunnel,  the  tunnel  of  Corti  ;  this  tunnel  increases  both  in 
height  and  width  on  passing  towards  the  apex  of  the  cochlea.  The  inner  rods  number 
nearly  6000,  and  the  head  of  each  resembles  somewhat  the  upper  end  of  the  ulna,  pre- 
senting a  deep  concavity,  externally,  for  the  reception  of  a  corrcsponrling  convexity  on  the 
head  of  the  outer  rod.  The  part  of  the  head  which  overhangs  this  concavity  is  prolonged 
outwards,  under  the  name  of  the  head-plate,  and  overlaps  the  head  of  the  outer  rod.  The 
expanded  bases  of  the  inner  rods  are  situated  on  the  innermost  portion  of  the  membrana 
basilaris,  immediately  to  the  outer  side  of  the  foramina  nervosa  of  the  labium  tympanicum. 
The   intermediate   parts   of   the   inner  rods  arc   sinuously   curved,    and    form,   with   the 


MEMBRANOUS  LABYRINTH.  767 

membrana  basilaris,  an  angle  of  about  60°.  The  outer  rods  number  about  4000,  and  are 
longer  than  the  innci",  especially  in  the  upper  part  of  the  cochlea.  They  are  more  inclined 
towards  the  membrana  basilaris,  and  form  witli  it  an  angle  of  about  40°.  The  head  of 
each  is  convex  internally,  to  fit  the  concavity  on  the  head  of  the  inner  rod,  and  is  prolonged 
outwards  as  a  plate,  the  phalangeal  process,  which  becomes  connected  with  the  lamina 
reticularis.  In  the  head  is  an  oval  body  which  has  an  affinity  for  certain  reagents.  The 
main  part  of  each  rod  consists  of  a  nearly  homogeneous  material,  which  is  finely  striated. 
At  tlie  bases  of  the  rods,  on  the  side  next  the  tuimel,  is  a  nucleated  mass  of  protoplasm 
which  reaches  as  far  as  the  heads  of  the  rods,  and  covers  also  the  greater  part  of  the 
tunnel  floor.  This  may  be  regarded  as  the  undifferentiated  pai't  of  the  cell  from  which 
the  rod  was  developed.  Slit-like  intervals,  for  the  transmission  of  nerves,  exist  between 
the  intermediate  portions  of  adjacent  rods. 

Hair  Cells. — Tliese,  like  Corti's  rods,  form  two  sets,  inner  and  outer.  The  former 
consists  of  a  single  row  lying  immediately  internal  to  the  inner  rods — the  latter  of  three, 
or,  it  may  be,  four  rows  placed  to  the  outer  side  of  the  external  rods.  The  inner  hair 
cells  are  about  3500  in  number,  and  have  a  greater  diameter  than  the  inner  rods,  and  so 
each  is  supported  by  more  than  one  rod.  Somewhat  oval  in  shape,  their  free  extremities 
are  surmounted  by  about  twenty  fine  hair-like  processes,  arranged  in  the  form  of  a 
crescent,  with  its  concavity  dii'ected  inwards.  The  deep  end  of  the  cell  is  rounded,  and 
contains  a  large  nucleus.  It  reaches  only  about  half-way  down  the  rod,  and  in  contact 
with  it  are  the  arborisations  of  the  nerve  terminations.  To  the  inner  side  of  this  row  of 
hair  cells  are  two  or  tlu-ee  rows  of  elongated  cohnnnar  cells,  which  act  as  supporting  cells, 
and  are  continuous  with  the  low  columnar  cells  lining  the  sulcus  spiralis  internus.  The 
outer  hair  cells  number  about  12,000,  and  form  three  rows  in  the  basal  coil  and  four 
rows  in  the  upper  two  coils,  although  in  the  higher  coils  the  rows  are  not  so  regularly 
arranged.  Their  rounded  free  extremities  support  some  twenty  hairlets  arranged  in  the 
form  of  a  crescent,  opening  inwards.  Their  deep  extremities  reach  about  half-way  to  the 
membi-ana  basilaris,  and  are  in  contact  with  the  nerve  arborisations. 

Alternating  with  the  rows  of  the  outer  hair  cells  are  the  rows  of  Deiters'  supporting 
cells,  the  lower  extremities  of  which  are  expanded  on  the  membrana  basilaris,  whilst  their 
upper  ends  are  tapered  ;  the  nucleus  is  placed  near  the  middle  of  each  cell,  and,  in  addition, 
each  cell  contains  a  bright,  thread-like  structure  called  the  supporting  fibre.  This  fibi-e 
is  attached  by  a  club-shaped  base  to  the  membrana  basilaris,  and  expands,  at  the  free 
end  of  the  cell,  to  form  a  phalangeal  process  of  the  membrana  reticularis. 

The  cells  of  Hensen,  or  outer  supporting  cells,  consist  of  about  half  a  dozen  rows, 
immediately  outside  Deiters'  cells,  and  form  a  well-marked  elevation  on  the  floor  of  the 
ductus  cochlearis.  Their  deep  extremities  ai"e  narrow  and  attached  to  the  membrana 
basilaris,  while  their  free  ends  are  expanded  ;  each  cell  contains  a  distinct  nucleus  and 
some  pigment  granules.  The  columnar  cells,  situated  externally  to  the  cells  of  Hensen, 
cover  the  outer  part  of  the  zona  pectinata,  and  are  named  the  cells  of  Claudius.  A  space, 
the  space  of  Nuel,  exists  between  the  outer  rods  of  Corti  and  the  neighbouring  row  of 
hair  cells.  It  communicates  internally  with  Corti's  tunnel,  and  extends  outwards  between 
the  outer  hair  cells  as  far  as  Hensen's  cells. 

The  lamina  reticularis  is  a  thin  cuticular  structure  which  lies  over  Corti's  organ, 
and  extends  fi'om  the  heads  of  the  outer  rods  as  far  as  Hensen's  cells,  where  it  ends  in  a 
row  of  quadrilateral  areas  which  form  its  outer  border.  On  looking  at  it  from  above  it  is 
seen  to  consist  of  two  or  three  rows  of  structures,  named  phalanges,  which  are  elongated 
cuticular  plates  resembling  in  shape  the  digital  phalanges.  The  innermost  row  is  formed 
by  the  phalangeal  processes  of  the  heads  of  the  outer  row  of  Corti's  rods  ;  the  succeeding 
row,  or  rows,  represent  the  expanded  upper  ends  of  Deiters'  supporting  cells.  The  number 
of  rows  of  phalanges,  therefore,  varies  with  the  number  of  rows  of  outer  hair  cells  and  the 
alternating  cells  of  Deiters.  The  phalanges  separate  the  free  ends  of  the  hair  cells  from 
each  other,  since  these  are  seen  to  occupy  the  somewhat  circvilar  apertures  between  their 
constricted  middle  portions. 

The  membrana  tectoria  (Fig.  596)  is  an  elastic  membrane  overlying  the  sulcus  spiralis 
internus  and  the  organ  of  Corti.  Attached,  by  its  inner  end,  to  the  limbus  laminae  spiralis, 
near  the  lower  edge  of  Reissner's  membrane,  it  reaches  outwards  as  far  as  the  outer  row 
of  hair  cells.  Its  inner  portion  is  thin  and  overlies  the  auditory  teeth  of  Huschke.  Its 
outer  part  is,  at  first,  much  thickened,  but  becomes  attenuated  near  its  external  border, 
which,  according  to  Retzius,  is  attached  to  the  outer  row  of  Deiters'  cells.  Its  lower  edge 
presents  a  firm,  homogeneous  border,  and  opposite  the  inner  row  of  hair  cells  contains  a 
clear,  spirally  arranged  band,  named  Hensen's  stripe.  Probably  the  membrana  tectoria 
acts  as  a  damper  comparable  to  the  otoconia  in  the  utricle  and  saccule. 


768 


THE  OEGANS  OF  SENSE. 


Auditory  Nerve  (Fig.  597). — The  auditory  nerve  consists  of  two  main  parts, 
the  ramus  vestibularis  and  the  ramus  cochlearis  ;  as  the  former  traverses  the  internal 
auditory  meatus  it  presents  a  gangliform  swelling,  the  ganglion  of  Scarpa.     The 


Sinus  superior 
Ampulla  of  external  canal 
Ampulla  of  superior  canal 
Macula  acustica  utriculi 


Macula  acustica  sacculi 
Kamus  vestibularis 
Nervus  facialis 
Ramus  cochlearis         , 


Superior  semicircular  canal 


External  semicircular  canal 
Posterior  semicircular  canal 


Ligamentum 
spirale 
Membrana  basilaris 

Brandies  of  ramus  coch 
learis  to  Corti's  organ 

Branch  of  ramus 
cochlearis  to  ampulla  of  posterior  canal 


Ampulla  of  posterior  canal 
Sinus  inferior 
Ductus  endolymphaticus 


Spiral  fibres 
Ganglion  spirale 


Nerve-libres  which  pass  out 
between  the  two  layers  of  the 
lamina  spiralis  ossea 


Ductus  reuniens 

Fig.  597. — Membranous  Labyrinth  of  a  Five  Months'  Fcetus,  viewed  from  its  postero-mesial 

aspect  (Retzius). 

ramus  vestibularis  divides  into  three  branches,  the  filaments  of  which  pass  through 
the  foramina  in  the  area  vestibularis  superior,  and  are  distributed  to  the  macula 
acustica  utriculi  and  the  ampullee  of  the  superior  and  external  semicircular  canals. 
The  ramus  cochlearis  gives  off  a  branch  to  the  macula  acustica  sacculi  and  another 
to  the  ampulla  of  the  posterior  semicircular  canal.  The  former  exhibits  a  gangli- 
form swelling  beyond  which  its  filaments  pass  through  the  foramina  in  the  area 

vestibularis  inferior ;  the  latter  is  trans- 
mitted through  the  foramen  singulare, 
and  in  this  part  of  its  course  the  nerve 
possesses  two  gangliform  enlargements. 
The  remainder  of  the  ramus  cochlearis 
is  distributed  to  the  hair  cells  of  Corti's 
organ,  the  branches  for  the  basal  and 
middle  coils  entering  the  foramina  in 
the  tractus  spiralis  foraminosus,  those 
for  the  apical  coil  passing  up  through 
the  canalis  centralis  of  the  modiolus. 
Extending  upwards,  in  the  bony  canals 
of  the  modiolus,  the  nerve-fibres  radiate 
outwards  between  the  lamellae  of  the 
lamina  spiralis  ossea.  Contained  in  the 
spiral  canal  of  the  modiolus,  near  the  attached  margin  of  the  lamina,  is  a  ganglion 
which  winds  spirally  round  the  modiolus,  and  is  named  the  ganglion  spirale  or 
ganglion  of  Corti  (Fig.  598).  It  consists  of  bipolar  nerve-cells,  and  each  nerve 
fibre,  probably,  has  its  continuity  interrupted  by  one  of  these  cells.  Beyond  the 
ganglion  spirale  the  nerve-fibres  extend  outwards,  at  first  in  bundles,  and  then 
in  a  more  or  less  continuous  sheet,  from  the  outer  edge  of  which  they  are  again 
collected  into  bundles,  whicli  pass  through  the  foramina  nervosa  of  the  labium 
tympanicura.  Beyond  this  they  appear  as  naked  axis -cylinders,  and,  turning 
in  a  spiral  manner   (inner   or   first  spiral   fasciculus),  send   fibrilhe   towards   the 


Fifi.  .098. 


-Part  of  Cochlear  Nekvk,  liiglily 
magnified  (Henle). 


DEVELOPMENT  OF  LABYRINTH. 


769 


inner  row  of  hair  cells.  Other  fibrils  pass  outwards  between  the  inner  rods 
and  form  a  second  spiral  fasciculus  in  Corti's  tunnel,  from  which  fibrils  extend 
outwards  across  the  tunnel,  and,  passing  between  the  outer  rods,  enter  Nuel's 
space.  They  form  a  spiral  fasciculus  on  tlie  inner  aspect  of  each  row  of  Deiters' 
cells,  and  from  these  fasciculi  fibrillse  pass  towards  the  bases  of  the  outer  hair  cells. 

Schwalbe  divides  the  auditory  nerve  into  tliree  portions,  viz.  :  (1)  ramus  utriculo-ampullaris, 
corresjionding  witli  the  ramus  vestilmlaris  already  described  ;  (2)  ramus  sacculo-ampullaris,  for 
tlie  sarcuki  and  i)osterior  ampulla  ;  and  (3)  ramus  cochlearis,  for  the  ductus  cochlearis. 

Vessels  of  the  Internal  Ear. — Tlie  auditory  artery,  a  branch  of  the  basilar,  enters  the  internal 
auditory  meatus  and  divides  into  vestibular  and  cochlear  branches.  The  vestiljular  branch  sup- 
plies the  soft  tissues  in  the  vestibule  and  semicircular  canals,  each  canal  receiving  two  arteries, 
which,  starting  from  opposite  extremities  of  the  canal,  anastomose  on  the  suuunit  of  the  arch. 
The  cochlear  lu-anch  divides  into  numerous  twigs,  which  enter  the  foramina  in  the  tractus 
spiralis  foraminosus,  and  run  outwards  in  the  lauuna  spiralis  ossea  to  reach  the  soft  structures  ; 
the  largest  of  these  arteries  runs  in  the  canalis  centralis.  The  stylo-mastoid  artery  also  supplies 
some  minute  branches  to  the  cochlea.  Siebenmann  describes  the  auditory  artery  as  dividing  into 
three  branches,  viz.  :  (1)  anterior  vestibular,  (2)  cochlear  proper,  and  (3)  vestibulo-cochlear.  The 
veins  from  the  cochlea  and  vestibule  unite  at  the  bottom  of  the  meatus  with  the  veins  from  the 
semicircular  canals  to  form  the  internal  auditory  vein,  which  may  either  open  into  the  posterior 
part  of  the  inferior  petrosal  sinus  or  into  the  lateral  sinus.  Small  veins  also  pass  through  the 
aqueductus  cochlea  and  aqueductus  vestibuli,  the  former  opening  into  the  inferior  petrosal  sinus 
or  into  the  internal  jugular  vein,  the  latter  into  the  superior  petrosal  sinus. 


Development  of  Labykinth. 

The  epithelial  lining  of  the  labyrinth  is  derived  from  an  invagination  of  the  cephalic 
ectoderm,  termed  the  auditory  pit,  which  appears  opposite  the  hind  brain  immediately 
above  the  first 
visceral  cleft. 
The  mouth  of 
tlie  pit  is  closed 
by  the  growing 
together  of  its 
margins,  and  it 
then  assumes  the 
form  of  a  hollow 
vesicle,  the  otic 
vesicle,  lined  by 
epithelium ;  the 
vesicle  sinks  into 
the  subjacent 
mesoderm,  and 
is  met  by  the 
auditory  nerve 
growing  out 
from  the  neural 
crest.  The  vesi- 
cle soon  becomes 
pear-shaped  ;  its 
upper 


otic  vesicle 


Rudiment  of  ductus  coclilearis 


Fig.  599. 


Sections  through  the  Region  of  the  Hind  Brain  of  Fcetal  Rabbits 
(to  illustrate  the  development  of  the  labyriuthine  epithelium). 

^  t  I"  A  the  ectoderm  is  iuvaginated  to  form  the  auditory  pit  ;  in  B  the  auditory  pit  is  closed 

and  detached  from  the  ectoderm,  forming  the  otic  vesicle  ;  while  C  shows  a  further 
stage  in  the  development  of  the  vesicle. 


part  is  named  the 
recessus  laby  - 
rintM,  and  forms 

the  future  ductus  endoljmphaticus.  About  the  fifth  week,  the  lower  part  of  the  vesicle 
is  prolonged  forwards  as  a  tubular  elongation,  the  future  ductus  cochlearis.  This  is  at 
first  straight,  but  soon  becomes  curved  on  itself,  so  that  at  the  twelfth  week  all  three  coils 
are  difterentiated.  From  the  upper  part  of  the  vesicle  the  semicircular  canals  are  developed, 
and  appear  as  hollow,  disc-like  evaginations,  the  central  parts  of  the  two  walls  of  which 
coalesce  and  disappear,  leaving  only  the  peripheral  rings  or  canals.  The  three  canals  are 
free  about  the  beginning  of  the  second  month,  and  are  developed  in  the  following  order, 
viz.  :  superior,  posterior,  and  external.  The  intermediate  part  of  the  otic  vesicle  represents 
the  vestibule,  and  is  divided  by  a  constriction  into  an  anterior  part,  the  saccule,  communi- 
cating with  the  ductus  cochlearis,  and  a  posterior  portion,  the  utricle,  receiving  the  ex- 
tremities of  the  semicircular  canals.  The  constriction  extends  for  some  distance  into 
53 


770 


THE  OEGANS  OF  SENSE. 


the  ductus  eudolymphaticus,  and  thus  the  utricle  and  saccule  are  only  indirectly  connected 
by   a  Y-shaped    tube.      Another  constriction  makes  its  appearance  between  the  saccule 

and  the  ductus  cochlearis  near  its 
commencement,  and  forms  the 
canalis  reuniens  of  Hensen.  The 
epithelial  lining  is  at  first  columnai', 
but  becomes  cubical  throughout  the 
\yhole  labyrinth,  except  opposite  the 
terminations  of  the  auditory  nerve, 
where  it  forms  the  columnar  epi- 
thelium of  the  maculae  of  the  utricle 
and  saccule,  of  the  cristse  ampullae, 
and  of  the  organ  of  Corti.  On  the 
floor  of  the  ductus  cochlearis  two 
ridges  appear,  of  which  the  inner 
forms  the  limbus  laminae  spiralis, 
whilst  the  cells  of  the  outer  become 
modified  to  foi'm  the  rods  of  Corti, 
the  hair  cells,  and  the  supporting 
cells  of  Deiters  and  Hensen. 

The  mesoderm  surrounding  the 
otic  vesicle  is  differentiated  into  : 
(1)  a  fibrous  layer,  the  wall  of  the 
membranous  labyrinth ;  (2)  a 
cartilaginous  external  capsule,  the 
future  petrous  bone ;  and  (3)  an 
intervening  layer  of  gelatinous  tissue,  which  is  ultimately  absorbed  to  form  the  peri- 
lymphatic space  between  the  bony  and  membranous  labyrinths. 


Cochlear 
part- 


Cochlea 


Saccule 


Fig.  600. 

Left  labyrinth  of  a  human  embryo  of  about  foivc  weeks  ;  B, 
Left  labyrinth  of  a  human  embryo  of  about  five  weeks  (from 
W.  His,  jun. ) 


ORGANS  OF  TASTE. 

The  peripheral  organs  of  the  sense  of  taste  (organon  gustus)  consist  of  groups  of 
modified  epithelial  cells,  termed  the  taste  buds,  which  are  found  on  certain  parts  of 
the  tongue  and  its  immediate  neighbourheod. 

Taste  buds  are  present  in  large  numbers  around  the  circumference  of  the 
IDapillse  vallat£e,  while  some  are  also  found  on  their  opposing  walls  (Fig.  601).     They 


Fig.  601. 


A,  Section  through  a  papilla  vallata  of  human  tongue.  B,  Section  through  a  part  of  the  papilla  foliata 

of  a  rabbit. 
1.  Paiiilla.  2.  Vallum.  3.  Taste  buds.  4.  Papillii'.  :,.  Tasti- Imds.  c.    Duct  of  serous  gland. 

are  very  numerous  over  the  fimbriai  linguaj,  which  correspond  with  the  papillae  foliatse 
of  the  tongue  of  the  rabbit,  and  are  also  found  over  the  posterior  part  and  sides  of 
the  tongue,  either  on  the  papilhe  fungiformes  or  throughout  the  stratified  epithelium. 
They  exist,  also,  on  the  buccal  surface  of  the  soft  palate  and  on  the  posterior  aspect 
of  the  epiglottis. 


ORGANS  or  TASTE. 


771 


Structure  of  Taste  Buds  (Fig.  602). — They  are  oval  or  flask -shaped,  and 
occupy  nests  in  the  stratified  epithelium  of  the  regions  mentioned.  The  deep 
extremity  of  each  is  somewhat  expanded  and  rests  upon  the  corium ;  the  free  end 
is  perforated  by  a  minute  pore,  termed  the  gustatory  pore.  They  consist  of  modified 
epithelial  cells,  which  are  grouped  under  the  two  varieties  of — (a)  supporting  cells, 

Gu-statory  liairs  i  C' ^    ui      .-  •/iv   ^ .^    ___ , —      ..x- 


Fig.  602. 


A,  Three-quarter  surface  view  of  taste  bud  from  the 
papilla  foliata  of  a  rabbit  (highly  maguitied). 


B,  Vertical  section  of  taste  bud  from  the  papilla 
foliata  of  a  rabbit  (highly  maguitied). 


and  (b)  gustatory  cells  (Fig.  603).  The  supporting  cells  are  elongated,  nucleated 
spindles,  and  are  mostly  arranged  like  cask  staves  to  form  the  outer  envelope  of 
the  bud.  Some  are,  however,  found  in  the  interior  of  the  bud,  amongst  the  gustatory- 
cells.  The  latter  occupy  the  centre  of  the  bud,  and  present  a  nucleated  cell-body, 
which  is  prolonged  into  a  peripheral  and  a  central  process.  The  peripheral  process 
is  rod-like  and  almost  hyaline,  and  terminates  at  the  gustatory  pore  in  a  hair- 
like filament,  gustatory  hair.  The  central 
process  passes  inwards  towards  the  deep 
extremity  of  the  bud,  where  it  ends  free, 
either  in  a  single  varicose  filament  or  by 
becoming  bifurcated  or  branched. 

Nerves  of  Taste.  —  The  nerve  which 
supplies  the  taste  buds  over  the  anterior 
part  of  the  tongue  is  probably  the  chorda 
tympani,  which,  although  a  branch  of  the 
facial  nerve,  is  generally  regarded  as  being- 
continuous  with  the  pars  intermedia  of 
Wrisberg  ;  that  for  the  posterior  part  is  the 
glosso- pharyngeal.  The  internal  laryngeal 
branch  of  the  vagus  nerve  supplies  the 
epiglottis,  together  with  a  small  area  of  the 
tongue  immediately  in  front  of  it.  The  nerve 
fibrils,  having  lost  their  medullary  sheaths,  ramify  partly  between  the  gustatory 
cells  and  partly  amongst  the  cells  of  the  bud  capsule.  It  was  formerly  thought 
that  the  nerve-fibrils  were  directly  continuous  with  the  central  ends  of  the 
gustatory  cells,  but  this  view  is  no  longer  entertained. 

The  ducts  of  Ebner's  glands  open  into  the  bottom  of  the  valleys  surrounding 
the  papillae  vallatte,  and  the  serous-like  secretion  of  these  glands  probably  washes 
the  free  hair-like  extremities  of  the  gustatory  cells,  and  so  renders  them  ready  to 
be  stimulated  by  successive  substances.  It  should  be  added  that  there  is  a  close 
association  between  the  senses  of  smell  and  taste.  This  can  be  best  appreciated  by 
considering  the  defective  taste  perceptions  resulting  from  inflammatory  conditions 
of  the  nasal  mucous  membrane,  or  the  common  practice  of  holding  the  nose  in 
order  to  minimise  the  taste  of  nauseous  drugs. 


Fig.  60-3. — Isolated  Cells  from  Taste  Buu 

OF  Rabbit  (Eugelmaun). 

(I,  Supporting  cells.  b,  Gustatory  cells. 


772 


THE  SKIN  OE  INTEGUMENT. 


THE  SKIN  OR  INTEGUMENT. 


ORGANS  OF  TOUCH. 


Duct  of 
sweat  glan 


Papillse  of 
coimiii 


The  Skin. 

The  skin  (integumentum  commune)  covers  the  body,  and  is  continuous,  at  the 
orifices  on  its  surface,  with  the  mucous  lining  of  its  alimentary  and  other  canals.  It 
contains  the  peripheral  terminations  of  the  sensory  nerves,  and  serves  as  an  organ 
of  protection  to  the  deeper  tissues.  It  is  the  chief  factor  in  the  regulation  of  the 
body  temperature,  and  by  means  of  the  sweat  and  sebaceous  glands,  which  open  on 
its  free  surface,  constitutes  an  important  excretory  structure.     Its  superficial  layers 

are  modified  to 
form  appendages 
in  the  shape  of 
hairs  and  nails. 

The  superficial 
area  of  the  skin 
averages  about  one 
and  a  half  square 
metres,  whilst  its 
thickness  varies 
from  0'5  to  4  mm., 
being  greatest  on 
the  palms  of  the 
hands  and  soles  of 
the  feet,  and  on  the 
back  of  the  neck 
and  shoulders,  and 
least  on  the  eyelids 
and  penis.  It  is 
very  elastic  and 
resistant,  and  its 
colour,  determined 
partly  by  its  own 
pigment  .  and 
partly  by  that  of 
the  blood,  is 
deeper  on  exposed 
parts  and  in  the 
regions  of  the  geni- 
tals, axillffi,  and 
mammary  areolae, 
than  elsewhere. 

The  colour  also  varies  with  race  and  age,  the  diflerent  races  of  the  world  being 
roughly  classified,  according  to  the  colour  of  their  skin,  into  the  three  groups 
of  white,  yellow,  and  black.  Pinkish  in  colour  in  childliood,  the  skin  assumes  a 
yellowish  tinge  in  old  age,  while  in  certain  diseases  {e.g.  icterus  and  melasma 
Addisonii)  it  undergoes  marked  alteration. 

The  surface  of  the  skin  is  perforated  by  the  hair  follicles  and  by  the  ducts  of  the 
sweat  and  sebaceous  glands,  and  on  the  palms,  soles,  and  flexor  aspect  of  the  digits 
it  presents  numerous  permanent  ridges  (cristte  cutis)  wliich  correspond  with  rows 
of  underlying  papilke.  Over  tlie  terminal  phalanges  these  ridges  form  distinctive 
patterns,  which  are  retained  from  youth  to  old  age,  and  are  utilised  for  purposes  of 
identification.  Folds  of  the  skin  (retinacula  cutis)  are  seen  in  the  neighbourhood 
of  the  joints,  and  it  can  be  thrown  into  wrinkles  by  the  contraction  of  the  sub- 
cutaneous muscles,  where  these  exist.     Over  the  greater  part  of  the  body  it  is  freely 


Fig.  604. 


Papilla  of  liair 
-Vertical  Section  of  the  Skin  (schematic) 


Oblique  section  through 
a  Pacinian  corpuscle 


STEUCTUEE  OF  THE  SKIN. 


773 


movable ;  but  on  the  scalp  and  outer  surface  of  the  pinna,  as  well  as  on  the  palms 
and  soles,  it  is  bound  down  to  the  subjacent  tissues. 

The  skin  consists  of  two  strata,  viz. :  a  deep,  termed  the  dermis  or  corium,  and 
a  superficial,  named  the  epidermis  (Fig.  604). 

The  corium  gives  elasticity  and  sensibility  to  the  skin,  and  consists  essentially 
of  a  felted  interlacement  of  connective  tissue  and  elastic  fibres.  In  its  deeper  part, 
or  stratum  reticulare,  the  fibrous  bundles  are  coarse  and  form  an  open  network,  in 
the  meshes  of  which  are  vessels,  nerves,  pellets  of  fat,  hair  follicles,  and  glands. 
This  reticular  stratum  passes,  as  a  rule,  without  any  line  of  demarcation,  into  the 
panniculus  adiposus  or  subcutaneous  fatty  tissue,  but  in  some  parts  it  rests  upon  a 
layer  of  striped  or  unstriped  muscular  fibres — the  latter  in  the  case  of  the  scrotum. 
In  the  superficial  layer,  or  stratum  papillare,  of  the  corium,  the  connective  tissue- 
bundles  are  finer  and 
form  a  close  network. 
Projecting  from  its  free 
surface  are  numerous 
finger -like,  single,  or 
branched  elevations, 
termed  papillae  (Fig. 
605),  the  free  ends  of 
which  are  received  into 
corresponding  depres- 
sions on  the  under  sur-  | 
face  of  the  epidermis.  I 
These  papilhe  vary  in  ; 
size,  being  small  on  the  f_ 
eyelids,  but  large  on  the  - 
palms  and  soles,  where  | 
they  may  attain  a  length  t 
of  225  fx,  and  produce 
the  permanent  curved 
ridges  already  alluded 
to.  Each  ridge  usually 
contains  two  rows  of 
papillae,  between  which 
the  ducts  of  the  sweat 
glands  pass  to  reach 
the  surface.  The 
papillie  consist  of  fine 
connective    tissue    and 


—  stratum  lucidum 
stratum 
Kianulosiuu 


btialuiii 
luucosum 


Stratum 
ireiminativwu 


Blood-vessels 
and  nerves 


Fig.  605. — Vehtical  Section  of  Epidermis  and  Papilla  of  Cobium 
(highly  luagnitied). 


elastic  fibres,  mostly  arranged  parallel  to  the  long  axis  of  the  papilla.  The 
majority  contain  capillary  loops,  but  some  the  terminations  of  nerves.  The 
superficial  surface  of  the  corium  is  covered  by  a  thin,  homogeneous  basement 
membrane. 

The  epidermis  covers  the  corium ;  it  is  non-vascular  and  consists  of  stratified 
epithelium.  Its  superficial  layers  are  modified  to  form  the  stratum  comeum,  or  horny- 
layer  of  the  skin,  which  may  be  separated  by  maceration  or  blistering  from  the  deeper, 
softer  portion,  or  stratum  mucosum  (Malpighi).  The  epidermis  consists  from  within 
outwards  of  the  following  five  strata  (Fig.  605) : — 

1.  The  basilar  layer,  or  stratum  germinativum,  which  comprises  a  single  stratum 
of  nucleated  columnar  cells  planted  by  denticulated  extremities  on  the  basement 
membrane  of  the  corium. 

2.  The  stratum  mucosum,  which  consists  of  six  or  eight  layers  of  polygonal, 
nucleated  "  prickle  "  or  "  finger  "  cells,  the  processes  of  which  join  those  of  adjacent 
cells.  Between  the  cells  of  this  layer  are  minute  channels,  in  which  leucocytes  or 
pigment  granules  may  be  seen.  The  cells  of  the  stratum  mucosum  are  charac- 
terised by  the  presence  of  numerous  epidermic  fibrils,  which  are  coloured  violet  by 
hsematoxylin  and  red  by  carmine.  These  fibrils  are  unaffected  by  boiling,  but 
swell  up  under  the  action  of  acids  and  alkalies,  and  form  the  filaments  of  union 

53  a 


774  THE  SKIN  OE  INTEGUMENT. 

between  adjacent  cells.  On  account  of  their  presence,  L.  Kanvier  {Compt.  rend., 
Paris,  Jan.  1899,  tome  cxxviii.)  has  named  this  layer  the  stratum  filamentosum. 
The  dark  colour  of  the  negro's  skin  is  caused  by  the  presence  of  numerous  pigment 
granules  in  the  deeper  layers  of  this  stratum  ;  the  pigment — of  whicli  melanin 
forms  an  important  constituent — is  absent  I'rom  the  more  superficial  layers  of  the 
epidermis. 

3.  The  stratum  granulosum,  which  comprises  two  or  three  layers  of  horizontally 
arranged,  tlattened  cells,  scattered  around  the  nuclei  of  which  are  elliptical  or 
spherical  granules  of  eleidin,  a  substance  staining  deeply  with  carmine,  and  probably 
represeutiug  an  intermediate  stage  between  the  protoplasm  of  the  deeper  cells  and 
the  keratin  of  the  superficial  layers. 

4.  The  stratum  lucidum,  which  is  an  apparently  homogeneous  layer,  but  is  in 
reality  made  up  of  several  strata  of  flattened  or  irregular  squames,  some  of  which 
may  contain  eleidin  granules. 

5.  The  stratum  comeum,  which  comprises  several  layers  of  flattened  non- 
nucleated  squames,  the  more  superficial  of  which  are  from  time  to  time  removed 
by  friction,  and  may  be  seen  partly  detached  on  the  surface.  Hanvier  named  these 
partly  detaciied  squames  the  stratum  disjunctum.  The  deeper  cells  contain  granules 
of  a  fatty  material  which  has  the  consistency  and  plasticity  of  beeswax,  and  stains 
with  osmic  acid.  The  peripheral  parts  of  the  cells  consist  of  keratin,  a  highly 
resistant  substance  which  is  unaffected  by  mineral  acids,  and  is  indigestible  in 
pep.sin-hydrochloric  acid.  Macleod  (Proceedings  of  the  Anatomical  Society  of 
Great  Britain  and  Ireland,  May,  1902)  found  that  after  digestion  of  the  stratum 
comeum  in  the  latter  fluid  the  cells  "presented  the  appearance  of  a  fine  network, 
like  a  honeycomb,  the  contents  of  which  had  completely  gone.  The  periphery  of 
the  cell  alone  resisted  the  action  of  the  pepsin  and  had  become  keratinised." 

L.  Ranvier  {op.  cit.)  lias  pointed  out  tliat  the  stratum  lucidum  is  really  double,  and  lias  named 
the  deeper  of  its  two  layers  the  stratum  intermedium  ;  tliis  he  describes  as  consisting  of  two  or 
three  layers  of  clear  cells  T\^th  atroiDhied  nuclei,  while  in  the  cell-waUs  the  ejaidermic  fibrils  "are 
rolled  up  like  the  threads  of  a  cocoon.'"' 

Regeneration  of  the  epidermis  is  generally  regarded  as  taking  place  by  cell  ijroliferation  in 
the  .stratum  gerruiuativum,  the  young  cells  gradually  passing  through  the  polyhedral  and 
gi-anular  stages,  and  ultimately  becoming  the  horny  squames  of  the  stratum  comeum.  Professor 
Thomson  of  Oxford  con.siders  that,  altliough  this  view  meets  all  the  recjuirements  in  white  races, 
a  difficulty  is  met  with  if  it  is  applied  to  coloured  races,  where  most  pigment  is  found  in  the 
deeper  cells  of  the  stratum  mucosum,  while  the  superficial  layers  are  free  from  colour.  If  the 
deeper  cells  arlvance  to  the  surface,  it  is  only  reasonable  to  suppose  that  they  would  carry  their 
pjigment  with  them.  This  theory,  therefore,  necessitates  a  satisfactory  explanation  of  the 
disappearance  of  the  pigment  from  the  superficial  layers.  He  suggests  that  j^ossiljly  the  growth 
of  the  epidermis  is  analogous  to  the  growtli  of  t)ie  cork  camljium  of  plants,  the  stratum  mucosum 
corresponding  to  the  green  cells,  and  the  stratum  corneum  to  the  corky  layer  of  the  cambium.  If 
such  be  the  case — and  he  insists  that  tliere  is  much  evidence  in  su2J])oit  of  it — the  deeper  cells 
would  advance  inwards  towards  the  corium,  and  the  superficial  cells  would  grow  outwards  towards 
the  surface.  Under  this  view  the  active  layers  would  be  the  stratum  granulosum  and  stratum 
lucidum,  and  by  it  many  of  the  difficulties  would  l)e  exjjlained,  including  the  mysterious  dis- 
appearance of  the  pigment  from  the  superficial  layers ;  it  would  also  afibrd  a  reasonable  explanation 
of  how  it  happens  that,  in  old  age,  a  negro's  hair  becomes  white,  wliile  his  skin  retains  its 
blackness. 

Vessels  and  Nerves  of  the  Skin. — The  arteries  form  a  plexus  in  the  sub- 
cutaneous tissue  from  which  branches  extend  into  the  corium,  where  they  supply 
the  hair  follicles  and  glands,  and  form  a  second  ]il(!xus  under  the  papilke,  to  which 
small  loops  are  given.  The  veins  and  lymphatics  commence  in  the  papillte,  and, 
after  forming  a  subp  ipillary  plexus,  open  into  their  respective  subcutaneous  vessels. 

The  nerves  of  the  skin  vary  in  number  in  different  parts  of  the  body,  being 
extremely  numerous  where  the  sense  of  touch  is  acute,  e.g.  on  the  palmar  aspect 
of  the  terminal  phalanges,  while  in  the  skin  of  the  back,  where  the  sensibility  is 
less,  they  are  fewer  in  number.  They  form  a  plexus  in  the  corium,  and  either 
terminate  amongst  the  cells  of  the  epidermis,  or  in  special  end  organs  named 
tactile  corpuscles.  Those  ending  in  the  epidermis  form  a  rich  subepithelird  plexus, 
from  which  delicate  fibrils  pass  between  the  cells  of  the  rete  mucosum,  where  they 
Vjecome  beaded,  and  end  in  rounded  swellings  on  flattened  discs — the  tactile  discs 
of  Kanvier. 


APPENDAGES  OF  THE  SKIN. 


775 


The  special  end  organs  are  of  three  chief  varieties  (Fig.  606) :  («)  Corpuscula 
bulboidea  (Krausii),  found  on  the  lips,  glans  penis,  etc.,  and  consisting  of  a  connective 
tissue  capsule  enclosing  a  core  of  elongated  and  polygonal  cells, amongst  which  the 
axis-cylinder  of  the  nerve  fibril  becomes  branched  and  its  ramifications  end  in 
clubbed  extremities,  (b)  Corpuscula  lamellosa  (Vateri  and  Pacini).  These  are 
small,  oval  bodies,  with  a  long  diameter  of  2  to  3  mm.,  and  are  found  in  the 
subcutaneous  tissue  attached  to  the  nerve  trunks.  They  are  very  numerous  on 
the  digital  nerves,  but  are  present  in  many  other  situations,  e.(/.  in  the  mesentery. 
Each  possesses  a  sheath,  consisting  of  a  number  of  concentrically  arranged  connective 
tissue  lamellffi,  covered  by  endothelium  continuous  with  the  perineurium.  The 
central  part  of  each  corpuscle  consists  of  a  soft,  almost  homogeneous  core.  The 
nerve-fibre  passes  along  the 
centre  of  the  stalk  of  the 
corpuscle, and, reaching  the 
core,  loses  its  medullary 
sheath,  whilst  its  axis- 
cylinder  passes  into  the 
core  and  becomes  branched 
near  its  distal  extremity, 
the  branches  ending  in 
bulbous  enlargements,  (c) 
Corpuscula  tactus  (Meis- 
sneri).  These  are  very 
numerous  on  the  flexor 
aspect  of  the  hands  and 
feet,  and  especially  so  in 
the  skin  over  the  terminal 
phalanges ;  but  they  also 
exist  in  other  parts  of  the 
body.  They  occupy  certain 
of  the  papillae  of  the  corium, 

and  are  oval  in  shape,  their  long  diameter  in  the  hand  being  from  110^  to  160 /x. 
They  consist  of  a  connective  tissue  capsule,  which  sends  imperfect  septa  into  the 
interior  of  the  corpuscle.  One  or  two  nerve-fibres  perforate  the  capsule,  either 
directly  or  after  taking  a  spiral  course  around  it ;  and  losing,  as  a  general  rule, 
their  medullary  sheath,  their  axis-cylinders  break  up  into  fibrils,  which  end  in 
globular  or  discoid  enlargements. 

Ruffini  has  described  a  special  variety  of  terminal  corpuscle  in  the  human  finger.  They  are 
termed  Kuffini's  endings,  and  are  situated  either  at  the  junction  of  the  corium  and  subcutaneous 
tissue,  or  are  embedded  in  the  latter.  Of  an  oval  shape,  they  consist  of  a  connective  capsule 
within  whicli  the  axis-cylinder  divides  into  varicose  filaments,  and  these  terminate  in  small 
knobs. 


Fig.  606. — Tactile  Corpuscles. 


A,  Eud  bulb  (Kiause). 

B,  Corpuscle  of  Pacini 


C,  Corpuscle  of  Meissner   / 


(after  Ranvier) 


Appendages  of  the  Skin. 

The  appendages  of  the  skin  comprise  the  nails,  the  hairs,  the  sebaceous,  and  the 
sudoriparous  or  sweat  glands. 

Nails. — The  nails  or  ungues  (Figs.  607,  608)  are  epidermal  structures,  and,  in 
man,  represent  the  hoofs  and  claws  of  the  lower  animals.  The  root  of  tlie  nail,  or 
radix  unguis,  is  hidden  from  view  and  embedded  in  a  fold  of  skin  ;  the  body  (corpus 
unguis),  or  uncovered  part,  rests  on  the  corium  and  ends  in  a  free  edge  (margo 
liber).  The  greater  part  of  the  lateral  margins  is  overlapped  by  a  duplicature 
of  skin,  termed  the  nail-wall  or  vallum  unguis.  The  nails  are  pink  in  colour,  with 
the  exception  of  a  small  semilunar  area  near  the  root,  which  is  more  opaque  than 
the  rest,  and  is  named  the  lunula.  The  lunulas  diminish  in  size  from  the  thumb 
towards  the  little  finger,  while  the  thickness  of  the  nail  diminishes  towards  its  root 
and  lateral  margins.  The  corium  under  the  nail  is  highly  vascular  and  sensitive, 
and  presents,  especially  under  the  anterior  part  of  the  body,  numerous  longitudin- 
ally arranged  papillae.  The  part  of  the  corium  under  tlie  body  is  termed  the  nail 
bed :  that  under  the  root,  the  nail  matrix.     The  deep  part  of  the  nail  consists  of 


76 


THE  SKIN  OK  mTEGUMENT. 


the  stratum  germinativum  and  stratum  mucosum,  while  its  superficial  horny  portion 
is  constituted  by  a  greatly  thickened  stratum  lucidum,  and  consists  of  nucleated, 
keratinised  squames.  The  stratum  corneum  is  represented  by  the  thin  cuticular 
fold  overlapping  the  lunula,  and  termed  the  eponychium,  while  the  stratum  granu- 
losum  can  only  be  traced  as  far  forwards  as  the  nail  root. 


Horny  part  of  nail 

Stratum.mucosum 
Nail  bed 


Vallum 


Fig.  607. — Transverse  Section  of  a  Nail. 

Hairs. — Hairs  (pili)  are  well  developed  on  the  scalp,  pubes,  and  margins  of  the 
eyelids,  in  the  axilla,  the  vestibule  of  the  nose,  and  at  the  entrance  to  the  concha, 
and  also  on  the  face  of  the  male.  Those  on  the  genitals  and  face  appear  about 
puberty.  Eudimentary  over  the  greater  part  of  the  body,  they  are  entirely  absent 
on  the  flexor  surfaces  of  the  hands  and  feet,  over  the  dorsal  aspect  of  the  terminal 


Root  of  nail 


Eponycliiuiii 

Homy  part  of 

nail 

Stratum 

miicosuni 


Fig.  608. — Longitudinal  Section  through  Koot  of  Nail. 

phalanges,  the  glans  penis,  the  inner  surface  of  the  prepuce,  and  inner  aspect  of  the 
labia.  Marked  variations,  individual  and  racial,  exist  as  to  the  colour  of  the  hair, 
and  also  as  to  the  manner  of  its  growth ;  hence  the  terms  straight,  curly,  woolly, 
etc.  are  used  to  designate  it.  Straight  hairs  are  coarser  than  curly  ones,  and  have, 
moreover,  a  circular  or  oval  outline  on  transverse  section,  curly  hairs  being  flat 
and  riband-like. 

The  root  of  the  hair  (radix  ])ili)  is  embedded  in  a  depression  of  the  skin,  termed 
the  hair  follicle  (Fig.  604);  while  the  free  portion  is  named  the  stem  or  shaft,  and 
consists  from  without  inwards  of  three  parts,  viz.  cuticle,  cortex,  and  medulla.  The 
cuticle  is  formed  by  a  layer  of  imbricated  scales  which  overlap  one  another  from 
below  upwards.  The  cortex  consists  of  longitudinally  arranged  fibres  made  up  of 
elongated,  closely  applied,  fusiform  cells,  which  contain  pigment  and  sometimes  air 
.spaces,  the  latter  especially  in  wliite  hairs.  Tlie  medulla,  absent  i'rom  the  fine 
hairs  of  the  body  generally  and  irom  the  hairs  of  young  children,  forms  a  central 
core,  which  appears  black  by  transmitted,  and  white  by  reflected  light,  and  is 
composed  of  polyhedral  nucleated  cells  containing  pigment,  fat  granules,  and  air 
spaces. 

The  hair  follicle  (folliculus  pill)  consists  of  an  oblique  or  curved — the  latter  in 


APPENDAGES  OF  THE  SKIN. 


777 


curly  hairs — invagination  of  the  epidermis  and  corium,  which  in  the  case  of  large 
hairs  extends  into  the  subcutaneous  tissue  (Fig.  604) ;  some  little  distance  below  its 
orifice  the  ducts  of  the  sebaceous  glands  open  into  it.  The  portion  of  the  follicle 
derived  from  the  corium  (dermic  coat)  consists  of  a  fibrous  sheath  of  external  longi- 
tudinal and  internal  circular  connective  tissue  fibres,  the  latter  being  lined  by  a 
hyaline  layer  directly  continuous  with  the  basement  membrane  of  the  corium.  The 
parts  of  the  folhcle  derived  from  the  epidermis  are  named  the  inner  and  outer  root 
sheaths.  Below  the  orifices  of  the  sebaceous  gland  ducts  the  outer  root  sheath  is 
formed  by  the  stratum  germinativum  and  stratum  mucosum,  while  above  them  all 
the  epidermal  strata  contribute  to  it.  The  inner  root  sheath  surrounds  the  cuticle 
of  the  hair,  and  consists  from  without  inwards  of —  (a)  Henle's  layer,  a  single  stratum 
of  nucleated,  cubical  cells ;  {h)  Huxley  s  layer,  a  single  or  double  layer  of  polyhedral 
nucleated  cells  ;  and  (c)  a  ddicate  cuticle,  consisting  of  a  single  layer  of  flattened 

Fibrous  slieatli  |^  Deriveil  from 

/      Basement  meiiibrane  )  the  corium 

/     /  Stiatum  germinativum  -j  Outer  root 

Sl'-^S"^^  ■»-  ^   /      y^tratum  iiiucosum     /  slieath 


,    .  ^^  Henle's  layer   ~j 

^  i-'^  -  I  Inner  root 


Fig.  609. — Transverse  Section  of  Hair  Follicle  with  contained  Hair  (liighly  magmtieil). 


imbricated  cells,  with  atrophied  nuclei.  The  bottom  of  the  hair  follicle  is  indented 
by  a  vascular  papilla  (papilla  pili),  derived  from  the  corium  and  capped  by  the 
bulb  (bulbus  pili)  or  expanded  part  of  the  hak  root.  The  cells  of  the  bulb  are 
continuous  with  those  of  the  outer  root  sheath,  and  form  the  different  parts  of  the 
hair,  as  well  as  its  inner  root  sheath.  The  vessels  form  capillary  loops  in  the  papilla 
of  the  hair,  and  send  twigs  into  the  outer  layer  of  its  fibrous  sheath ;  the  inner 
and  outer  root  sheaths  and  the  different  parts  of  the  hair  are  non-vascular.  The 
nerves  terminate  in  longitudinal  and  annular  fibrils  below  the  level  of  the  sebaceous 
glands  and  outside  the  hyaline  layer  of  the  follicle. 

Sebaceous  glands  (glandulse  sebaceae)  exist  wherever  there  are  hairs,  and  their 
ducts  open  into  the  superficial  part  of  the  hair  follicles  (Fig.  604) ;  the  number  of 
glands  associated  with  each  follicle  varies  from  one  to  four.  On  the  labia  minora 
and  mammary  areolae  they  open  on  the  surface  of  the  skin  independently  of  hair 
follicles,  and  in  the  latter  situation  undergo  great  enlargement  during  pregnancy. 
The  deep  extremity  of  each  gland  expands  into  a  cluster  of  oval  or  flask-shaped 
alveoli,  which  are  surrounded  by  a  basement  membrane,  and  filled  with  polyhedral 
cells  containing  oil  droplets.  By  the  breaking  down  of  the  superficial  cells,  then- 
oily  contents  are  liberated  as  the  sehum  cutaneum  and  discharged  into  the  hair 
follicle,  whilst  the  deeper  cells  undergo  proHferation.     The  size  of  the  gland  bears 


778  THE  SKIN  OE  INTEGUMENT. 

no  proportion  to  that  of  the  hairs,  since  they  are  very  large  in  the  minute  hair 
follicles  of  the  fostus  and  newly  born  child,  and  also  in  the  follicles  of  the  rudimen- 
tary hairs  of  tlie  nose  and  certain  parts  of  the  face. 

Bundles  of  non-striped  muscular  fibre  are  associated  with  the  hair  follicles,  and 
are  named  the  mm.  arrectores  pilorum.  Attached  to  the  deep  part  of  the  hair  follicle, 
and  forming  with  it  an  acute  angle,  they  pass  outwards  close  to  the  sebaceous 
glands,  to  end  in  the  papillary  layer  of  the  corium.  Situated  on  the  side  of  the 
hair  towards  which  it  slopes,  they,  on  contraction,  diminish  the  obliquity  of 
the  hair  follicle  and  render  the  hair  more  erect,,  and,  at  the  same  time,  com- 
press the  sebaceous  glands  and  expel  their  contents.  The  condition  of  "goose- 
skin  "  is  caused  by  the  contraction  of  these  slender  muscles. 

Thomson  suggests  that  the  condition  of  curly  hair  is  produced  by  the  contraction  of  these 
small  muscles.  Straight  hair  is  thick  and  rounded  ;  curlj^  hair  is  flat  and  ribbon-like.  When 
the  erector  muscle  contracts,  the  thick  rounded  hair  resists  the  tendency  of  the  muscle  to  bend  it, 
while  the  flat  hair,  not  sufiiciently  strong  to  resist  the  strain  of  the  muscle,  becomes  bent,  and 
this  is  i^robably  the  explanation  why  the  follicle  assumes  the  curved  form  characteristic  of  the 
scalj)  of  a  bushman.  The  sebaceous  gland  lies  in  the  concavity  of  the  bend  between  the  follicle 
and  the  muscle,  and  forms  a  mass  of  greater  resistance,  around  which  the  follicle  may  be  curved 
by  the  contraction  of  the  muscle.  The  cells  at  the  root  of  the  hair  accommodate  themselves  to 
the  curved  follicle,  and,  becoming  more  horny  as  they  advance  to  the  surface,  retain  the  form 
of  the  follicle  in  which  they  are  moulded. 

The  sudoriparous  or  sweat  glands  (glandulse  sudoriferse)  are  relatively  few  in 
number  on  the  back  of  the  trunk,  but  are  very  plentiful  on  the  palms  and  soles, 
where  they  open  on  the  summits  of  the  curved  ridges.  Each  consists  of  an  elongated 
tube,  the  deeper  portion  of  which  forms  its  secretory  part,  and  is  coiled  in  the  sub- 
cutaneous tissue  or  deep  part  of  the  corium  in  the  form  of  an  ovoid  or  spherical  ball, 
termed  the  glomerulus  or  corpus  glandulse  sudoriferse  (Fig.  604).  The  superficial  part 
of  the  tube,  or  ductus  sudoriferus,  extends  through  the  corium  and  epidermis, 
and  opens  on  the  surface  by  a  funnel-shaped  orifice,  the  porus  sudoriferus ;  where 
the  epidermis  is  thick  the  duct  is  spirally  coiled.  The  glomeruli,  as  a  rule,  vary  in 
diameter  from  O'l  to  0-5  mm.,  but  in  the  axillae  they  are  much  larger,  and  may 
measure  from  1  to  4  mm.  Each  is  surrounded  by  a  capillary  network  and  by  a 
capsule  of  connective  tissue,  inside  which  is  a  homogeneous  basement  membrane. 
The  lumen  of  the  tube  is  lined  by  a  layer  of  nucleated,  granular,  and  striated, 
columnar,  or  prismatic  epithelium,  between  the  deep  extremities  of  which  and  the 
basement  membrane  is  a  layer  of  non-striped  muscular  fibres,  the  long  axis  of  which 
is  more  or  less  parallel  with  that  of  the  tube.  The  excretory  ducts  are  devoid  of 
muscular  fibres,  and  consist  of  a  basement  membrane  lined  by  two  or  three  layers 
of  polyhedral  cells,  which  are  covered,  next  the  lumen  of  the  tube,  by  a  thin 
cuticle. 

The  glands  of  Moll  (glandula;  ciliares),  opening  at  the  margins  of  the  eyelids,  and 
the  glandulse  ceruminosae  of  the  external  auditory  meatus,  are  modified  sudoriparous 
glands ;  the-  former  are,  however,  not  coiled  up  to  form  glomeruli,  while  the  cell 
protoplasm  of  the  latter  contains  yellowish  pigment,  and  their  gland  ducts,  in  the 
foetus,  open  into  liair  follicles. 

Development  of  the  Skin  and  its  Appendages. 

Skin. — The  vascular  and  sensitive  corium  is  developed  from  the  mesoderm,  the  cells 
of  which,  immediately  underlying  the  ectoderm,  have,  by  the  second  month  of  foetal  life, 
become  aggregated  together  and  flattened  parallel  to  the  surface  of  the  embryo.  By  the 
third  month  they  are  seen  to  form  two  layers,  the  superficial  of  which  becomes  the 
corium,  and  the  deeper  the  subcutaneous  tissue ;  the  papillae  of  the  corium  make  their 
appearance  in  the  fourth  month.  The  epidermis,  nails,  hairs,  sweat  and  sebaceous  glands 
are  all  of  ectodermal  origin. 

The  epidermis  at  first  consists  of  a  single  layer  of  cells,  but  by  the  end  of  the  second 
month  it  is  duplicated,  and  then  exhiVjits  a  superficial  layer  of  irregular  cells  and  a  deeper 
layer  of  more  or  less  cubical  cells.  By  the  third  month  three  strata  are  seen  :  (a)  a  deep 
layer,  consisting  of  a  single  stratum  of  cubical  cells — the  future  stratum  germinativum ; 
(6)  a  middle  layer,  comprising  two  or  three  strata  of  irregular  cells — the  future  stratum 


DEVELOPMENT  OF  THE  SKIN  AND  ITS  APPENDAGES.        779 

mucosum ;  and  (c)  an  outer  layer,  a  double  stratum  of  large  cells.  This  outer  layer 
appears  to  be  homologous  with  a  thin  membrane,  termed  the  epitrkhium,  first  described 
as  covering  the  embryo  of  the  sloth  and  overlying  its  liairs,  but  since  shown  to  be  present 
in  birds  and  mammals.  Over  the  hairy  parts  of  the  body  it  disappears  about  the  sixth 
month ;  but  over  the  free  edge  and  root  of  the  nails,  and  on  the  palms  and  soles,  it 
develops  into  several  layers  of  cells,  wliich,  in  these  parts,  probably  persist  to  form  the 
thick  stratum  corneum.  The  part  which  persists  over  the  root  of  the  nail  is  termed 
the  eponychium,  and  covers  the  proximal  part  of  the  lunula  {vide  p.  776).  The  stratum 
lucid um  is  diftereutiated  from  the  cells  of  the  epitrichium,  and,  where  the  latter  is  lost, 
possibly  forms  the  superficial  layer  of  the  epidermis  as  it  does  the  horny  part  of  the  nails. 

Nails. — The  first  rudiment  of  the  nails  is  seen  about  the  beginning  of  the  third 
montli  of  embryonic  life,  and  consists  of  a  thickening  of  the  epitrichium  over  the  extremity 
of  the  digits.  Owing  to  the  growth  of  the  palmar  aspect  of  the  digits,  the  nail  rudiment 
comes  to  be  placed  dorsally,  and,  at  its  proximal  edge,  an  ingrowth  of  the  stratum 
mucosum  occurs  to  form  its  root,  while  the  future  nail  becomes  limited  behind  and  later- 
ally by  a  groove.  The  superficial  cells  of  the  stratum  mucosum  become  keratinised  to 
form  a  thick  stratum  lucid  um,  the  future  nail  proper,  over  the  greater  part  of  which  the 
epitrichium  disajjpears.  The  latter  persists  in  the  adult  as  the  perionyx  across  the  root 
of  the  nail,  and,  until  fifth  month,  also  forms  a  thick  mass  over  the  extremity  of  the  nail, 
and  is  continued  into  the  stratum  corneum  over  the  end  of  the  digit.  The  future  distal 
edge  of  the  nail,  at  this  stage,  is  continuous  with  the  stratum  lucidum  in  front  of  it ;  but 
this  continuity  is  lost,  and  by  the  seventh  month  tlie  nail  presents  a  free  border.  The 
nails  grow  in  length,  and  are  renewed,  in  case  of  removal,  by  a  proliferation  of  the  cells 
of  the  stratum  mucosimi  at  the  root  of  the  nail,  while  an  increase  in  their  thickness  takes 
place  from  the  part  of  the  same  stratum  which  underlies  the  lunula. 

Hairs. — The  hair  rudiments  appear  about  the  third  month  of  embryonic  life  as  solid 
downgrowths  of  the  stratum  mucosum,  which  pass  obliquely  into  the  subjacent  corium. 
The  deep  end  of  this  column  of  cells  becomes  expanded  to  form  the  hair  bulb,  and  rests 
on  a  papilla  derived  from  the  corium,  the  epidermis  immediately  overlying  which  becomes 
diftereutiated  into  the  hair  and  its  inner  root  sheath,  while  the  peripheral  cells  form  its 
outer  root  sheath.  The  surrounding  corium  becomes  condensed  to  form  the  fibrous  sheath 
of  the  hair  follicle,  the  hyaline  layer  of  which  is  continuous  with  the  basement  membrane 
covering  the  corium.  The  hair  gradually  elongates,  and,  reaching  the  neck  of  the  follicle, 
its  extremity  lies  at  first  under  the  epitrichium,  but  becomes  free  on  the  disappearance  of 
the  latter.  This  takes  place  about  the  fifth  month,  and  the  first  crop  of  hairs  constitutes 
the  lanugo,  which  is  well  developed  by  the  seventh  month.  The  lanugo  consists  of  very 
delicate  hairs,  some  of  which  are  shed  before,  the  remainder  shortly  after  birth — the  last 
to  drop  out  being  those  of  the  eyelashes  and  scalp — and  are  replaced  by  stronger  hairs. 
Shedding  and  renewal  of  the  hairs  take  place  during  life,  the  renewal  being,  of  course,  absent 
in  the  case  of  baldness.  Prior  to  the  shedding  of  a  hair  active  growth  and  proliferation 
of  the  cells  of  the  hair  bulb  cease,  and  the  papilla  becomes  atrophied,  while  the  hair  root, 
gradually  approaching  the  surface,  at  last  drops  out.  New  hairs  arise  from  epidermic 
buds,  which  extend  downwards  from  the  follicle,  and  their  development  is  identical  with 
that  of  the  original  hairs. 

Sebaceous  Glands. — These  appear  about  the  fifth  month  as  solid  outgrowths  from 
the  sides  of  the  hair  follicles,  and  consist  of  epidermal  oftshoots  continued  from  the  cells 
of  the  outer  root  sheath.  Their  deep  ends  become  enlarged  and  lobulated,  to  form  the 
secreting  part  of  the  gland,  while  the  narrow  neck  coiuiecting  this  with  the  follicle  forms 
its  duct.  The  sebaceous  secretion,  together  with  the  cast-oft"  epidermal  cells,  is  collected 
on  the  surface  of  the  body  during  the  last  months  of  intrauterine  life,  and  forms  a  layer 
of  varying  thickness,  termed  the  vernix  caseosa  or  smegma  einhri/oniim. 

Sweat  Glands. — These,  like  the  hairs,  arise  as  solid  downgrowths  of  the  stratum 
mucosum.  They  descend,  however,  perpendicularly,  instead  of  obliquely,  and  are  of  a 
yellowish  colour  ;  they  appear  on  the  palms  and  soles  early  in  the  fifth  month,  but  much 
later  over  the  hairy  parts  of  the  body.  The  downgrowths  extend  through  the  corium,  and, 
on  reaching  the  subcutaneous  tissue,  become  coiled  up  to  form  the  secreting  part  of  the 
gland.     The  lumen  of  the  gland  does  not  open  on  the  surface  until  the  seventh  month. 


THE   VASCULAR   SYSTEM. 

By  Alfred  H.  Young  and  Arthur  Eobinson. 

The  vascular  system  consists  of  a  series  of  tubular  vessels,  with  more  or  less 
distinct  walls,  which  run  through  all  parts  of  the  body.  Some  contain  blood,  others 
are  filled  with  a  colourless  fluid  called  lymph ;  hence  the  distinction  between  the 
blood- vascular  system  and  the  lymph-vascular  system.  The  two  systems  differ,  not 
only  as  regards  their  contents,  but  also  in  their  relations  to  the  tissues  amongst 
which  they  lie ;  for  whilst  the  vessels  of  the  former  system,  with  the  possible 
exception  of  the  splenic  vessels,  are  closed,  those  of  the  latter  communicate  freely 
with  intercellular  spaces  and  serous  sacs. 

The  blood- vascular  system  is  tubular  throughout ;  the  tubes  or  vessels  possess 
distinct  walls ;  they  vary  in  size  and  in  the  structure  of  their  walls,  but  all  con- 
tain blood,  which  is  conveyed  through  them  to  and  from  the  tissue  elements  of  the 
body.  The  blood  is  propelled  along  the  vessels  cliietiy  by  a  central  propulsive 
oro-an — the  heart.  The  outgoing  vessels  from  the  heart,  along  which  blood  is 
transmitted  to  the  tissues,  are  termed  arteries ;  the  vessels  which  return  blood  from 
the  tissues  to  the  heart  are  known  as  veins;  whilst  the  smallest  tubes — those  which 
connect  the  arteries  and  veins  together,  constituting  at  once  the  terminations  of 
the  arteries  and  the  commencements  of  the  veins — are  called  capillaries. 

Blood  cayjillaries  are  very  small  (hair-like)  vessels  with  exceedingly  thin  walls, 
which  permit  of  the  easy  passage  outwards  of  the  nutritive  plasma  from  the  blood 
to  the  tissues,  and,  in  the  opposite  direction,  of  some  of  the  products  of  tissue  changes 
and  of  modified  food  material  from  the  alimentary  canal. 

Arteries  and  veins  are  simply  conducting  passages;  structurally  they  differ 
from  capillaries  in  the  greater  complexity  of  their  walls.  They  vary  greatly  in  size, 
}jut  are  always  larger  than  capillaries.  The  calibres  of  the  arteries  and  veins 
increase  progressively  from  the  periphery  up  to  the  heart,  where  the  vessels  reach 
their  greatest  size.  With  the  increase  in  calibre  there  is  a  corresponding  increase 
in  the  thickness  and  complexity' of  their  walls. 

Structure  of  Blood  Capillaries. — Capillaries  measure  from  ^^^  to  -a^Vrr  of  an- 
inch  in  diameter,  and  about  .^\,  to  ttV  of  an  inch  in  length.  Their  walls  are 
simple,  and,  in  the  smallest  capillaries,  consist  principally  of  elongated  elastic  endo- 
thelial cells,  with  .sinuous  edges,  pointed  extremities,  and  oval  nuclei.  Tlie  cells  are 
cemented  to  one  another  along  their  margins  by  intercellular  cement,  which  readily 
stains  with  nitrate  of  silver.  Here  and  there  the  cement  substance  appears  to  accu- 
mulate, forming  minute  spots  indicative  of  the  less  perfect  apposition  of  the  edges 
of  the  cells.  These  spots,  when  small,  form  the  so-called  stigmata;  when  larger 
they  are  known  as  stomata. 

The  larger  cai)illaries  are  invested  by  a  connective  tissue  sheath  consisting  of 
branched  cells  which  are  united  together  and  to  the  endothelial  cells  of  the  capillary 
wall.     Tiiis  sheath  is  termed  tin-  adventitia  capillaris. 

Capillaries  are  arranged  in  networks,  the  nature  and  character  of  which  differ 
in  different  tissues.  The  small  arteries  which  end  in  them  are  known  as  capillary 
arterioles,  and  the  venous  radicles  which  commence  from  them  are  appropriately 
termed  capillary  veins. 

780 


STRUCTUEE  OF  AETERIES. 


781 


Structure  of  arteries  and  veins. — The  delicate  elastic  endothelial  membrane 
forming  the  wall  of  the  simplest  capillaries  extends  as  a  continuous  lining  through- 
out the  whole  of  the  blood-vascular  system.  The  constituent  cells  are  fusiform, 
narrow,  and  pointed  in  the  arteries,  whilst  in  the  veins  they  are  somewhat  shorter 
and  broader. 

The  most  essential  structural  difference  between  capillaries  and  the  arteries  and 
veins  which  they  unite  together,  is  to  be  found  in  the  presence,  in  both  of  the  latter, 
of  involuntary  muscular  fibres  inter- 
posed between  the  endothelial  lining  "i'-  e^terua^,, 
and    the     outer    connective    tissue 


sheath.  In  small  vessels,  e.g.  capil- 
lary arterioles,  the  muscle  cells  are 
few  in  number  and  more  or  less 
scattered.  In  larger  vessels  the 
walls  become  stronger  and  thicker, 
muscular  tibres  increase  and  form 
a  continuous  layer,  whilst  yellow 
elastic  and  ordinary  white  connec- 
tive tissue  are  added  in  varying  proportions 


T.  iiitinia 


Fig.  610. 


c  B  ~^^  A2  Ai 

Structure  of  Blood- Vessels  (diagram matic). 
Ai,  Capillary— with  simple  endothelial  walls.  A'',  Larger  capillary 
—with  connective  tissue  sheath,  "  adventitia  capillaris.  '  B, 
Capillary  arteriole— showing  muscle  cells  of  middle  coat,  lew 
and  scattered.  C.  Artery— muscular  elements  ol  the  tunica 
media  forming  a  continuous  layer. 


The  walls  of  the  vessels  thus  become 
more  complex,  and  numerous  strata  may  be  distinguished ;  these,  however,  are  for 
convenience  regarded  as  forming  three  layers,  which  are  known  as  the  inner, 
middle,  and  outer  coats,  superadded  to  which  is  the  investing  common  sheath. 

Structure  of  Arteries.^ — The  walls  of  arteries  are  stronger  and  thicker  than 
those  of  veins  of  corresponding  size,  tlie  inner  and  middle  coats  being  particularly 
rich  in  elastic  and  muscular  elements. 

Inner  coat  (tunica  intima). — The  simple  endothelial  layer  of  the  arterioles  is 
strengthened  by  the  addition  of  yellow  elastic  tissue,  the   fibres   of  which    are 

arranged  in  such  a  manner  as  to  simulate  a  fene- 
strated membrane.  In  arteries  of  medium  size  the 
elastic  lamina  is  separated  from  the  endothelium  by 
a  layer  of  connective  tissue  consisting  of  branched 
cells  and  numerous  fibrils.  In  the  larger  arteries 
the  sub-endothelial  connective  tissue  is  considerably 
increased,  and  delicate  elastic  fibres  appear  which 
connect  it  with  the  more  externally  situated  fene- 
strated elastic  layer. 

The  middle  coat  (tunica  media)  in  the  capil- 
lary arterioles  consists  solely  of  scattered  unstriped 
muscle  fibres;  the  individual  fibres  are  circularly 
disposed,  but  do  not  entirely  surround  the  vessel. 
In  small  arteries  the  muscle  cells  are  so  far  increased 
in  amount  that  they  form  a  continuous  though  thin 
layer.  As  the  arteries  increase  in  size  additional 
layers  of  muscle  cells  are  added,  and  the  greater 
thickness  of  the  arterial  wall  is  mainly  due  to  this 
increase  of  the  muscular  elements  of  the  middle  coat. 
In  the  larger  vessels  delicate  laminae  of  elastic  tissue 
alternate  with  the  layers  of  muscular  fibres,  and  in 
the  aorta  and  the  carotid  arteries,  as  well  as  in  some  of 
Fig.  611.— Transverse  Section  ^^'^  branches  of  the  latter,  the  elastic  elements  largely 
THROUGH  THE  Wall  OF  A  Large  preponderate.  In  the  first  part  of  the  aorta,  in  the 
^^i'^^^^'-  pulmonary  artery,  and  in  the  arteries  of  the  retina,  the 

muscular  fibres  are  entirely  replaced  by  elastic 
tissue. 

The  external  coat  (tunica  externa)  of  an  artery  consists  almost  entirely  of 
fibrillated  connective  tissue,  with  connective  tissue  corpuscles  lying  in  corre- 
sponding spaces.  In  all  but  the  smallest  arteries  numerous  elastic  fibres  are  also 
present.  The  elastic  element  is  specially  strong  near  the  middle  coat  in  small 
and    medium    sized    vessels,  and  is  sometimes  described  as  the  external  elastic 


A,  Tunica  intima.     B,  Tunica  media. 
C,  Tunica  externa. 


782  THE  VASCULAE  SYSTEM. 

membrane  of  Henle.     In  some  arteries  longitudinally  arranged  unstriped  muscular 
fibres  are  also  found  in  the  external  coat. 

The  sheath  of  an  artery  (vagina  vasis). — In  addition  to  the  three  coats 
above  described,  arteries  are  enclosed  in  a  sheath  of  the  surrounding  connective 
tissue,  and  are  more  or  less  connected  with  it  by  fine  strands  of  fibrillated 
connective  tissue. 

Structure  of  Veins. — The  walls  of  veins  are  similar  in  structure  to  those 
of  arteries ;  they  are,  however,  thinner,  so  much  so,  that,  although  veins  are 
cylindrical  tubes  when  full  of  blood,  they  collapse  when  empty,  and  their  lumina 
almost  disappear.  The  structural  details  of  the  three  coats  vary  somewhat  in 
different  veins  ;  in  most  the  inner  coat  is  marked  by  folds  which  constitute  valves. 
Like  the  arteries,  the  veins  are  enclosed  in  connective  tissue  sheaths. 

The  inner  coat  (tunica  intima). — In  the  majority  of  the  veins  the  inner  coat 
includes  an  internal  endothelial  layer,  a  middle  layer  of  sub-endothelial  connective 
tissue,  and  an  outer  layer  of  elastic  tissue.     The  inner  coat  of  a  vein  is  less  brittle 

than  the  inner  coat  of  an  artery,  and  is  more  easily 
peeled  off  from  the  middle  coat.  The  sub-endothelial 
tissue  is  a  fine  fibrillated  connective  tissue,  less  abund- 
ant than  in  the  arteries,  and  indeed  in  many  cases  it  is 
absent.  The  elastic  layer  consists  of  lamellae  of 
elastic  fibres  which  are  arranged  longitudinally,  and 
it  rarely  forms  a  fenestrated  membrane. 

One  of  the  chief  peculiarities  of  the  inner  coat 
is  the  presence  of  folds  of  its  substance  which  con- 
stitute valves.  The  valves  are  of  semilunar  shape, 
and  they  are  usually  arranged  in  pairs.  Their 
convex  borders  are  continuous  with  the  vessel  wall, 
and  their  free  borders  are  turned  towards  the  heart ; 
whilst,  therefore,  they  do  not  interfere  with  the  free 
flow  of  blood  onwards,  they  prevent  any  backward 
flow  towards  the  periphery,  and  they  help  to  sustain 
Fig.  (ji2.— Transverse  Section  of  the  column  of  blood  in  all  vessels  in  which  there  is  an 
THE  Wall  of  a  Vein.  upward  flow.     Each  valve  consists  of  a  fold  of  the 

A,  Tunica  intima.   B,  Tunica  media,      inner  Or  endothelial  layer,  strengthened  by  a  little 

C,  Tunica  externa,  .         ..  .       ''  -,    "  -,       ,,  nf.i 

connective  tissue.  As  a  general  rule,  the  wall  of  the 
vein  is  dilated  above  each  valve  into  a  shallow  pouch  or  sinus ;  consequently,  when 
the  veins  are  distended  they  assume  a  nodulated  appearance.  The  valves  are  more 
numerous  in  the  deep  than  in  the  superficial  veins,  and  in  the  veins  of  children 
than  in  the  veins  of  adults. 

The  middle  coat  (tunica  media)  is  much  thinner  than  the  corresponding  coat 
of  an  artery,  and  it  contains  a  smaller  amount  of  muscular  and  a  larger  amount 
of  ordinary  connective  tissue ;  indeed,  so  much  does  the  latter  preponderate  that  it 
separates  the  muscular  fibres  into  a  number  of  Ijands  isolated  from  each  other  by 
strands  of  connective  tissue,  and  the  muscle  fibres  do  not  form  a  continuous  layer.. 
In  some  of  the  veins  the  more  internal  muscular  fibres  do  not  retain  the  transverse 
direction  which  is  usually  met  with  both  in  arteries  and  veins ;  on  the  contrary, 
they  run  longitudinally.  This  condition  is  met  with  in  the  branches  of  the 
mesenteric  veins,  in  tlie  femoral  and  iliac  veins,  and  in  the  umbilical  veins.  The 
middle  coat  is  absent  in  the  thoracic  part  of  the  inferior  vena  cava;  it  is  but 
slightly  developed  in  many  of  the  larger  veins,  whilst  in  the  jugular  veins  its 
muscular  tissue  is  veiy  small  in  amount. 

The  external  coat(tunicaexterna). — This  coat  consists  of  white  fibrous  and  elastic 
tissue.  In  many  of  the  larger  veins  a  considerable  amount  of  muscular  tissue  is  also 
present ;  this  is  the  case  in  the  iliac  and  axillary  veins,  the  abdominal  part  of  the 
inferior  vena  cava,  the  azygos  veins,  and  in  the  renal,  spermatic,  splenic,  superior 
mesenteric,  portal,  and  hepatic  veins.  The  stri])ed  muscle  fibres  of  the  heart  are  pro- 
longed into  it  at  the  terminations  of  the  vense  cav».  The  external  coat  is  frequently 
thicker  than  the  middle  coat,  and  the  two  are  not  easily  separable  from  one  another. 

Vascular  and  Nervous  Supply  of  Arteries  and  Veins. — Blood-vessels. — The 


THE  HEART.  783 

walls  of  the  blood-vessels  are  supplied  by  numerous  small  arteries,  called  vasa 
vasorum,  which  are  distributed  to  the  outer  and  middle  coats.  They  arise  either 
from  the  vessels  they  supply  or  from  adjacent  arteries,  and  after  a  short  course 
enter  the  walls  of  the  vessels  in  which  they  end.  The  blood  is  returned  by  small 
vente  vasorum. 

Lymphatics. — Although  the  cell  spaces  in  the  middle  and  inner  coats  may  be 
regarded  as  the  commencement  of  lymphatics,  definite  lymphatic  vessels  are  limited 
to  the  outer  coat. 

Nerves. — ^Arteries  and  veins  are  well  supplied  witli  both  meduUated  and  non- 
medullated  nerve-fibres.  The  fibres  form  dense  plexuses  on  the  outer  surfaces  of 
the  vessels,  from  which  filaments  pass  to  the  middle  coat  to  be  distributed  almost 
entirely  to  its  muscular  fibres. 

Divisions  of  the  Blood- Vascular  System. — Blood-vessels  convey  blood  to  or 
from  the  tissues  of  the  body  generally,  or  to  and  from  the  lungs.  The  former 
constitute  the  systemic  vessels  or  general  system ;  the  latter  form  tlie  pulmonary 
system.     These  two  systems  are  connected  together  by  the  heart. 

The  venous  trunks  passing  to  the  liver  form  a  subsidiary  part  of  the  general 
systemic  group  of  vessels,  which  is  known  as  the  portal  system. 

THE   HEART. 

The  heart  (cor)  is  a  hollow  muscular  organ,  and  is  enclosed  in  a  fibro-serous 
sac  known  as  the  pericardium.  It  receives  blood  from  the  veins,  and  propels  it 
into  and  along  the  arteries.  The  cavity  of  the  fully  developed  heart  is  completely 
separated  into  right  and  left  halves  by  an  obliquely  placed  longitudinal  septum, 
and  each  half  is  divided  into  an  upper  receiving  chamber,  the  auricle,  and  a  lower 
ejecting  chamber,  the  ventricle.  The  separation  of  the  auricle  from  the  ventricle, 
however,  is  not  complete.  Externally  a  comparatively  shallow  constriction, 
running  transversely  to  the  long  axis  of  the  organ,  indicates  the  distinction 
between  the  auricles  and  ventricles  ;  internally  a  wide  aperture  is  left  between 
the  auricle  and  ventricle  of  each  side.  Each  auriculo- ventricular  aperture  is 
provided  with  a  valve  which  allows  the  free  passage  of  blood  from  the  auricle  to  the 
ventricle,  but  effectually  prevents  its  return. 

It  lias  already  been  pointed  out  that  tlie  delicate  walls  of  the  blood  capillaries  allow  of  the 
free  passage  outwards  of  nutritive  plasma  from  the  blood.  It  j^asses  into  spaces,  or  intercellular 
channels,  in  which  the  tissue  elements  lie  ;  thus  the  latter  are  directly  bathed  in  blood  plasma. 
The  intercellular  spaces  form  the  commencement  of  the  lymjjli  -vascular  system.  They  commimi- 
cate  together,  and  open  into  lymj)h -vessels  wliicli  carry  the  used  plasma  back  to  the  blood -vascular 
system,  but  in  addition  they  also  convey  new  nutritive  material,  tlie  product  of  digestive 
processes,  from  the  alimentary  canal. 

Lymph -vessels,  in  other  words,  convey  material  from  the  tissues.  Blood-vessels  convey 
material  both  to  and  from  the  tissues. 

The  removal  of  waste  products  from  the  Ijlood  is  jirovided  for  by  special  organs,  some  of  which 
are  simj^ly  interposed  in  the  course  of  the  general  circulation — e.g.  the  liver,  the  kidneys,  and  the 
skin.  The  lungs,  however,  where  the  impure  or  venous  blood  receives  its  main  supply  of  oxygen 
and  gives  up  most  of  its  carbonic  oxide,  etc.,  do  not  lie  in  the  course  of  the  genei'al  or  systemic 
circulation ;  from  them  a  secondary  or  pulmonary  circulation  is  established,  by  which  venous 
blood  is  conveyed  from  the  heart  to  the  lungs  by  the  jiulmonary  artery  and  its  branches,  and,  after 
passing  through  the  iiulmonary  capillaries,  is  returned  again  to  the  heart  as  pure  arterial  blood 
by  the  pulmonary  veins. 

The  heart,  anatomically  a  single  organ,  is  correspondingly  modified,  and,  as  described  above, 
it  is  divided  by  a  sejitum  into  a  right  and  a  left  jiart.  Tlie  right  side  receives  the  blood  from 
the  systemic  A^eins,  and  ejects  it  into  the  pulmonary  artery  ;  whilst  the  left  side  receives  blood 
from  the  pulmonary  veins,  and  ejects  it  into  the  main  systemic  artery — the  aorta. 

The  shape  of  the  heart  is  that  of  an  irregular  and  somewhat  flattened  cone  ;  and 
a  base,  an  apex,  two  surfaces  (inferior  and  antero-superior),  and  two  borders  (right 
and  left)  are  distinguishable. 

An  oblique  groove — the  auriculo-ventricular  groove  (sulcus  coronarius) — runs 
transversely  to  the  long  axis  of  the  organ,  and  separates  the  upper  auricular 
portion  from  the  lower  ventricular  part.  The  separation  of  the  auricular  portion 
into  right  and  left  chambers  is  only  marked  externally  at  the  base  of  the  heart. 


784 


THE  VASCULAR  SYSTEM. 


where  an  indistinct  interauricular  groove  exists.  The  division  of  the  lower  part 
into  right  and  left  ventricles  is  more  definitely  marked  on  the  surface  by  anterior 
and  interior  interventricular  sulci  (sulci  longitudinales). 

The  heart  lies  in  the  middle  mediastinum.  It  is  enclosed  in  the  pericardium, 
and  this  latter  accordingly  intervenes  between  it  and  the  neighbouring  structures. 
It  rests  below  on  the  diaphragm.  Its  long  axis,  from  base  to  apex,  runs  obliquely 
from  behind  forwards,  downwards,  and  to  tlie  left. 

The  base  (basis  cordis),  formed  entirely  by  the  auricles,  and  almost  entirely  by 
the  left  auricle,  is  directed  upwards,  backwards,  and  to  the  right.  It  lies  in  front 
of  the  descending  thoracic  aorta,  the  oesophagus,  and  the  lower  right  pulmonary 
vein,  which  separate  it  from  the  bodies  of  the  sixth,  seventh,  and  eighth  dorsal 
vertebrae. 

On  the  whole  the  base  is  somewhat  flattened,  and  is  irregularly  quadrilateral 


LiL'aiiieiituin  artei'iosum 


Left  pulmonary  arterj\ 


Vestigial  fold 
of  Marshal  1 


Right  pulmonarj'  artery 
Suijerior  vena  cava 


Left  pulmonary  vein; 


Right  pulmonary  veins 


Sulcus  terminalis 


Transverse  branch  of. 
left  coronary  artery 


Left  marginal  artery 


Inferior  vena  cava 


t  ventricle 


Left  ventricle 


Fig.  613. 


Coronary  sinus 

-The  Base  akd  Inferior  Surface  of  the  Heart,  sliowiug  the  openings  of  the  great  vessels 
and  the  line  of  reflection  of  the  serous  pericariliuni. 


in  form.  It  presents  the  orifices  of  the  superior  and  inferior  venae  cavse  and  the  four 
pulmonary  veins.  The  opening  of  the  superior  vena  cava  is  situated  at  the  upper 
right  angle,  that  of  the  inferior  cava  occupies  the  lower  angle  on  the  right  side  ; 
between  and  a  little  to  the  left  of  these  openings  are  the  orifices  of  the  two  right 
pulmonary  veins,  and  immediately  to  the  right  of  the  latter  is  the  indistinct 
posterior  interauricular  sulcus,  which  descends  to  the  left  of  the  orifice  of  the 
inferior  vena  cava.  The.  openings  of  the  two  left  pulmonary  veins  are  situated 
near  the  left  border  of  the  base ;  and  the  portion  of  the  surface  which  lies  between 
the  right  and  left  pulmonary  veins  forms  the  anterior  b*oundary  of  the  great 
oblique  sinus  of  the  pericardium. 

The  base  is  limited  below  by  the  lower  part  of  the  auriculo-ventricular  groove, 
in  which  the  coronary  sinus  lies ;  its  upper  border  is  in  relation  with  the  bifur- 
cation of  the  pulmonary  artery.  A  fold  of  pericardium,  the  vestigial  fold  of 
Marsliall  (ligamentum  v.  cavse  sinistrse)  descends,  near  the  left  border  of  the  base, 


THE  HEART. 


785 


from  the  left  branch  of  the  pulmonary  artery  above  to  the  left  superior  -pulmonary 
vein  below ;  and  from  the  lower  end  of  this  fold,  crossing  obliquely  below  the  left 
pulmonary  vein  to  reach  the  coronary  sinus,  is  the  small  oblique  vein  of  Marshall 
(v.  obliqua  atrii  sinistri  [Marshalli]).  Further,  it  is  from  the  base  that  the 
visceral  layer  of  the  pericardium,  which  elsewhere  completely  invests  the  heart, 
is  reflected,  the  lines  of  reflection  corresponding  with  the  orifices  of  the  great 
vessels.^ 

The  apex  (apex  cordis),  bluntly  rounded,  is  formed  entirely  by  the  left  ventricle. 
It  is  directed  downwards,  forwards,  and  to  the  left,  and  is  situated,  under  cover 
of  the  anterior  border  of  the  left  lung  and  pleura,  behind  the  fifth  left  intercostal 
space,  three  and  a  quarter  inches  from  the  anterior  mesial  line. 

The  inferior  surface  (facies  diaphragmatica)  is  formed  by  the  ventricular  part 


Left  auricle 

Puliuonarv  arteiT 


Siii)erior  vena 

r 

l|H 

cava  ' 

---___ 

d 

^^ 

Right  coronary 
artery  ~ 

4 

j 

WS: 

u 

1 

>r^^ 

Right  auricular 
appendix " 

i 

w 

— 

Right  coronary 

I 

A 

artery " 

^\  ^ 

fr 

'  m 

Anterior  ventri- 
cular artery 

-Vi 

Left  auricular  appendix 


Transverse  branch  of  left 
coronary  artery 


Interventricular  branch  of  left 
oronarv  arterv 


Right  marginal 
arterv 


Right  ventricl 


Fig.  614. — The  Anteko-Superior  Surface  of  the  Heart. 


of  the  heart.  It  rests  upon  the  diaphragm,  chiefly  on  the  central  tendon,  but  upon 
the  left  side,  on  a  small  portion  of  the  muscular  substance  also,  and  it  is  divided 
into  two  areas — a  smaller  to  the  right  side  and  a  larger  to  the  left  side — by  an 
oblique  antero-posterior  groove,  the  inferior  interventricular  sulcus.  It  is  separated 
from  the  base  by  the  posterior  or  inferior  portion  of  the  auriculo-ventricular  sulcus. 
The  a.ntero-superior  surface  (facies  sterno-costalis)  is  directed  upwards,  for- 
wards, and  to  the  left.  It  lies  behind  the  body  of  the  sternum  and"  the  inner 
extremities  of  the  cartilages  of  the  third,  fourth,  fifth,  and  sixth  ribs  on  the  right 
side,  and  a  greater  extent  of  the  corresponding  cartilages  on  the  left  side. 
This  surface  is  separated  into  upper  and  lower  sections  by  the  anterior  portion 
of  the  auriculo  -  ventricular  groove,  which  runs  obliquely  from  above  down- 
wards, and  from  left  to  right,  from  the  level  of  the  third  left  to  that  of  the  sixth 
right  costal  cartilage.     The  upper  section  of  the  surface,  which  is  concave,  is  formed 

^  In  the  fcettis  aud  youug  child  the  auricular  portion  of  the  heart  forms  not  only  the  base,  but  also  the 
posterior  part  of  the  inferior  or  diaphragmatic  surface. 

54 


786 


THE  VASCULAE  SYSTEM. 


by  the  auricles ;  it  is  separated  from  the  sternum  by  the  roots  of  the  aorta  and  the 
pulmonary  artery,  and  is  continuous  laterally  with  the  auricular  appendices  which, 
projecting  forwards,  embrace  the  great  vessels.  The  lower  section  of  the  antero- 
superior  surface  is  convex ;  it  is  formed  by  the  ventricular  part  of  the  heart,  and  is 
divided  by  an  anterior  interventricular  sulcus  into  a  smaller  left  and  a  larger  right 
part.  At  the  junction  of  the  auricular  and  ventricular  parts  of  this  surface  are 
the  orifices  of  the  pulmonary  artery  and  the  aorta,  the  former  lying  in  front  of 
the  latter. 

The  right  margin  of  the  heart  consists  of  an  upper  auricular  part  and 
a  lower  ventricular  part.  The  former  is  almost  vertical;  it  lies  behind 
the   cartilages   of    the    third,    fourth,    fifth,    and   sixth   ribs   on    the    right   side 

about  half  an  inch  from  the  margin 
of  the  sternum ;  it  is  in  relation  with 
the  right  pleura  and  lung,  the  phrenic 
nerve  with  its  accompanying  vessels 
intervening,  and  it  is  marked  by  a 
shallow  groove — the  sulcus  terminalis 
— which  passes  from  the  front  of  the 
superior  vena  cava  to  the  front  of  the 
inferior  vena  cava.  The  lower  part 
of  the  right  margin  (margo  acutus)  is 
sharp,  thin,  and  usually  concave,  corre- 
sponding with  the  curvature  of  the 
anterior  part  of  the  diaphragm ;  it  is 
formed  by  the  right  ventricle,  and  it 
lies  almost  horizontally  in  the  angle 
between  the  diaphragm  and  the  an- 
terior wall  of  the  thorax,  passing  from 
the  sixth  right  costal  cartilage  behind 
the  lower  part  of  the  body  of  the 
sternum,  or  the  ensiform  cartilage,  and 
behind  the  cartilages  of  the  sixth  and 
seventh  ribs  on  the  left  side  to  the  apex 
of  the  heart. 

The  left  margin  (margo  obtusus)  is 
formed  mainly  by  the  left  ventricle,  and  only  to  a  small  extent  by  the  left 
auricle.  It  is  thick  and  rounded.  It  lies  in  relation  with  the  left  pleura  and 
lung,  the  phrenic  nerve  and  its  accompanying  vessels  intervening,  and  it  passes 
from  just  above  the  third  left  costal  cartilage,  about  an  inch  from  the  sternum,  to 
the  apex  of  the  heart,  descending  obliquely  and  with  a  convexity  to  the  left. 


Fig.  6l5. — The  Relation  of  the  Heart  to  the 
Anterior  Wall  of  the  Thorax. 

I,  II,  III,  IV,- V,  VI,  the  iijiper  six  costal  cartilages. 


THE  CHAMBERS  OF  THE  HEART. 

Auricles  (auricula  cordis). — The  auricular  or  basal  portion  of  the  heart  is 
cuboidal  in  form.  Its  long  axis,  which  lies  transversely,  is  curved,  with  the  con- 
cavity of  the  curve  forwards.  It  is  divided  into  two  chambers — the  right  and 
left  auricles — by  a  septum  which  runs  from  the  front  backwards  and  to  the  right, 
80  obliquely  that  the  right  auricle  lies  in  front  and  to  the  right,  and  the  left  auricle 
behind  and  to  the  left. 

Each  auricle  is  also  somewhat  cuboidal  in  form,  the  long  axes  of  both  being 
vertical,  and  each  chamljer  possesses  a  well-marked  ear-shaped,  forward  prolongation, 
whicti  ])rojects  from  the  anterior  and  upper  angle,  and  is  known  as  the  auricular 
appendix. 

The  right  auricle  (atrium  dextrum)  receives,  posteriorly,  the  superior  vena  cava 
above  and  the  inferior  vena  cava  below.  Between  tliese,  and  a  little  above  its 
middle,  it  is  crossed  posteriorly  by  the  lower  right  pulmonary  vein.  It  is  continuous 
below  and  in  front  with  the  right  ventricle  at  tlie  auriculo-ventricular  aperture. 
Above  and  in  front  it  is  in  relation  with  the  ascending  aorta,  and  from  the  junc- 
tion of  this  aspect  with  the  right  lateral  boundary  the  right  auricular  appendix 


THE  CHAMBEKS  OF  THE  HEART. 


787 


is  prolonged  forwards.  On  the  right  side  it  forms  the  upper  portion  of  the  right 
margin  of  the  heart,  and  is  in  relation  with  the  right  phrenic  nerve  and  its  accom- 
panying vessels,  and  with  the  right  pleura  and  lung,  the  pericardium  intervening. 
On  the  left  the  auricle  is  limited  by  the  oblique  septum  whicli  separates  it  from 
the  left  auricle.  The  sulcus  terminalis  is  a  shallow  groove  on  the  surface  of  the 
right  auricle,  which  passes  from  the  front  of  the  superior  vena  cava  to  the  front  of 
the  inferior  vena  cava,  and  indicates  the  junction  of  the  primitive  sinus  venosus 
with  the  auricle  proper. 

The  interior  of  the  auricle  is  lined  with  a  glistening  meml)rane,  the  endo- 
cardium; its  walls  are  smooth,  except  anteriorly  and  in  the  auricular  appendix 
where   muscular   ]»undles,  the   musculi   pectinati,  form  a   series  of  small   vertical 


Vena  cava  superior 


Upper  right tl! 

pulmonary  veil 


Lower  rit;ht 
■jjiilnionary  vein 

Musculi  pectinati 

Annulus  ovalis 

Fossa  ovalis 


Eustacliian  \alve 


Aorta 
Pulmonary  artery 


Right  auricular  appendix 
Conus  arteriosus 


Anterior  cusp  of 
tricuspid  valve 


Cliordse  tendine 


Moderator  band 


Vena  cava  inferior 

Coronary  (Thebesian)  valve 

Musculi  papillares 
Fig.  616.— The  Cavities  of  the  Richt  Auricle  and  Right  Ventricle  of  the  Heart. 

columns.     These  terminate  above  in  a  crest,  the  crista  terminalis,  which  corresponds 
in  position  with  the  sulcus  terminalis  externally. 

At  the  upper  and  back  part  of  the  cavity  is  the  opening  of  the  superior  vena 
cava,  devoid  of  a  valve.  At  the  lower  and  back  part  is  the  orifice  of  the  inferior 
vena  cava,  bounded  in  front  by  the  rudimentary  Eustachian  valve :  and  immedi- 
ately in  front  and  to  the  left  of  the  Eustachian  valve,  between  it  and  the  auriculo- 
ventricular  orifice,  is  the  opening  of  the  coronary  sinus,  guarded  by  the  Thebesian 
valve.  The  auriculo-ventricular  aperture,  guarded  by  a  tricuspid  valve,  is  known 
as  the  tricuspid  orifice.  It  is  situated  in  the  inferior  part  of  the  anterior  boundary, 
and  admits  three  fingers.  A  number  of  small  fossee,  foramina  Thebesii  (foramina 
venarum  minimarum),  are  scattered  over  the  walls,  and  into  some  of  these  the 
venae  minimi  cordis  open.  In  the  septal  wall  is  an  oval  depression,  the  fossa  ovalis, 
bounded  above  and  in  front  by  a  raised  margin,  the  annulus  ovalis  (limbus  fossse 
ovalis),  which  is  continuous  inferiorly  with  the  Eustachian  valve ;  this  fossa  is 
the  remains  of  an  aperture,  the  foramen  ovale,  through  which  the  two  auricles 
communicated  with  each  other  before  birth,  and  even  in  the  adult  a  portion  of  the 
aperture  persists  at  the  upper  part  of  the  fossa  in  about  one  in  five  cases.  Between 
the  apertures  of  the  superior  and  inferior  venfe  cav£e,  and  behind  the  upper  part 
54  a 


788 


THE  VASCULAR  SYSTEM. 


of  the  fossa  ovalis,  a  small  eminence  may  be  distinguished,  which  is  called  the 
tubercle  of  Lower  (tiiberculum  intervenosum) ;  in  the  fcetns  it  probably  directs  the 
blood  from  the  superior  vena  cava  to  the  tricuspid  orifice. 

The  Eustachian  valve  (valvula  vense  cavse  inferioris)  is  a  thin  and  sometimes 
fenestrated  fold  of  endocardium  and  sub-endocardial  tissue,  which  extends  from 
the  anterior  and  lower  margin  of  the  orifice  of  the  inferior  vena  cava  to  the 
anterior  part  of  the  annulus  ovalis.  Varying  very  much  in  size,  it  is  usually  of 
falciform  shape,  its  apex  being  attached  to  the  annulus  and  its  base  to  the  margin 
of  the  inferior  caval  orifice.  It  is  an  important  structure  in  the  fcetus,  directing 
the  blood  from  the  inferior  vena  cava  through  the  foramen  ovale  into  the  left 
auricle. 

The  Thebesian  valve  (valvula  sinus  coronarii)  is  usually  a  single  fold  of  endo- 
cardium which  is  placed  at  the  orifice  of  the  coronary  sinus  ;  occasionally  it  consists 
of  two  cusps.      It  is  almost  invariably  incompetent. 

The  left  auricle  (atrium  sinistrum)  is  in  relation  behind  with  the  descending 
thoracic  aorta  and  the  oesophagus.  Below  and  in  front  it  is  continuous  with  the 
left  ventricle.  Its  antero-superior  surface  is  concave,  and  lies  in  close  relation  to 
the  roots  of  the  ascending  aorta,  the  pulmonary  artery,  and  the  left  coronary 


Left  anterior  ousp  of 
pulmonary  valve' 

Left  posterior  cusp 
of  pulmonary  valve 


Left  posterior  cusp 

of  aortic  valve 

Left  coronary  artery 


Anterior  cu.sp  of 
mitral  valve 


Posterior  cusp  of 
mitral  valve 


Left  ventricle 


Con  us  arteriosus 


Right  anterior  cusp  of 
pulmonary  valve 

Right  coronary  artery 

Anterior  cusp  of  aortic 
valve 

Right  posterior  cusp  of 
am-tic  valve 
Anterior  (infundibular) 
cusp  of  tricuspid  valve 

Right  (marginal)  cusp 
of  tricuspid  valve 

Posterior  (septal)  cusp 
of  tricuspid  valve 


Right  ventricle 


¥io.  617. — The  Bases  of  the  Ventktcles  of  the  Heart,  showing  tlie  auriculo-ventricular,  aortic, 
anil  pulmonary  orifices  and  their  valves. 

artery.  Its  right  side,  formed  by  the  interauricular  septum,  is  directed  forwards 
and  to  the  right.  Its  left  side  forms  a  very  small  portion  of  the  left  margin  of 
the  heart,  and  from  its  junction  with  the  antero-superior  surface  the  long  and 
narrow  auricular  appendix  is  prolonged  forwards  round  the  left  side  of  the 
ascending  portion  of  the  aorta  and  the  trunk  of  the  pulmonary  artery. 

The  four  pulmonary  veins  enter  the  upper  part  of  the  posterior  surface,  two  on 
each  side. 

The  interior  of  the  left  auricle  is  lined  witli  endocardium,  and  its  walls  are 
smooth,  except  in  the  auricular  appendix  where  musculi  pectinati  are  present,  and 
on  the  septum,  in  a  position  corresponding  with  the  upper  part  of  the  fossa  ovalis 
on  the  right  side,  where  there  are  several  musculo-fibrous  bundles  radiating  for- 
wards and  upwards.  These  septal  bundles  are  separated  at  their  Ijases  by  small 
semilunar  depressions,  in  the  largest  of  which  remains  of  the  foramen  ovale  may 
be  found.  Foramina  Thebesii,  and  the  ajertures  of  venae  minimi  cordis,  are 
scattered  irregularly  over  the  inner  aspect,  whilst  in  the  inferior  part  of  the 
anterior  boundary  is  the  auriculo-ventricular  aperture.  The  latter  is  oval  in 
form ;  its  long  axis  is  jilaced  obliquely  from  before  backwards,  and  from  left  to 
right,  and  is  capaVjle  of  admitting  two  fingers.  It  is  guarded  })y  a  valve  formed  of 
two  large  cusps,  and  is  known  as  the  mitral  orifice.    , 

Ventricles.  —  The  ventricular  portion  of  the  heart  is  conical  and  somewhat 


THE  CHAMBEES  OF  THE  HEAET. 


789 


flattened.  The  base,  directed  upwards  and  backwards,  is  partly  continuous  with 
the  auricular  portion  and  partly  free.  It  is  perforated  by  four  orifices,  the  two 
auriculo- ventricular,  the  aortic,  and  the  pulmonary.  The  auriculo- ventricular 
orifices  are  placed  one  on  each  side  below  and  Ijehind ;  in  front  and  between 
them  is  the  aortic  orifice,  whilst  the  orifice  of  the  pvilmonary  artery  is  still  farther 
forward,  and  slightly  to  the  left  of  the  aortic. 

In  the  triangle  (trigona  fibrosa)  between  the  auriculo-ventricular  and  the  aortic 
orifices  is  embedded  the  central  fibro-cartilage,  a  mass  of  fibro-cartilaginous  tissue 
which  is  the  re])reseutative  of  the  os  cordis  of  the  ox.  It  is  continuous  with  the 
upper  part  of  the  interventricular  septum,  and  with  fibrous  rings  which  surround 
the  apertures  at  the  bases  of  the  ventricles. 

The  inferior  surfaces  and  the  antero-superior  surfaces  of  the  ventricles  constitute 
respectively  the  greater  portions  of  the  corresponding  surfaces  of  the  heart ;  the 
former  rest  upon  the  diaphragm,  whilst  the  latter  are  directed  upwards  and 
forwards  towards  the  sternum  and  the  costal  cartilages  of  the  left  side.  The  apex 
of  the  left  ventricle  forms  the  apex  of  the  heart. 

The  right  margin,  which  is  thin,  forms  the  horizontal  portion  of  the  right 
margin  of  the  heart ;  and  the  left  margin,  which  is  thick  and  rounded,  forms 
almost  the  whole  of  the  left  margin  of  the  heart. 

The  ventricular  portion  of  the  heart  is  divided  into  right  and  left  chambers. 
The  interventricular  septum  (septum  ventriculorum)  is  placed  obliquely,  with  one 
surface  directed  forwards  and  to  the  right,  and  the  other  backwards  and  to  the 
left ;  it  bulges  into  the  right  ventricle,  and  its  lower  margin  lies  to  the  right  of 
the  apex  of  the  heart,  which  is,  there- 
fore, formed  entirely  by  the  left  ven- 
tricle. The  margins  of  the  septum  are 
indicated  on  the  surfaces  by  anterior 
and  inferior  interventricular  sulci. 

The  right  ventricle  (ventriculus 
dexter)  is  triangular  in  form.  Its 
base  is  directed  upwards  and  to  the 
right,  and  in  the  greater  part  of  its 
extent  it  is  continuous  with  the  right 
auricle,  with  which  it  communicates 
by  the  auriculo  -  ventricular  orifice  ; 
but  its  left  and  anterior  angle  projects 
in  front  of  the  auricle,  and  gives  origin 
to  the  pulmonary  artery.  Its  inferior 
wall  rests  upon  the  diaphragm.  The 
antero-superior  wall  lies  behind  the 
lower  part  of  the  left  half  of  the 
sternum  and  the  cartilages  of  the 
fourth,  fifth,  and  sixth  ribs  of  the  left 
side.  The  left  or  septal  wall,  which  is 
directed  backwards  and  to  the  left, 
bulges  into  its  interior,  and  on  this 
account  the  transverse  section  of  the 
cavity  has  a  semilunar  outline.  The 
cavity  itself  is  a  bent  tube  consisting 
of  an  inferior  portion  or  body  into 
which  the  auriculo-ventricular  orifice 
opens,  and  of  an  antero-superior  part, 
the  infundibulum  or  conus  arteriosus, 
which  terminates  in  the  pulmonary 
artery.     The  angle  between  the  two  limbs  is  formed  by  a  thick  ledge  of  muscle. 

The  right  auriculo-ventricular  orifice  is  guarded  by  a  tricuspid  valve  (valvula 

tricuspidalis).      The   three  cusps  of  this  valve  are  a  right  or  marginal  (cuspis 

medialis),  a  left  or  infundibular  (cuspis  anterior),  which  intervenes  between  the 

auriculo-ventricular  orifice  and  the  infundibulum,  and  a  posterior  or  septal  (cuspis 

54  ft 


Fk; 


618. — The  Relations  ok  the  Heart  and  the 
Auriculo -Vextuicolar,  Aortic,  and  Pulmonary 
Orifices  to  the  Anterior  Thoracic  Wall. 


I  to  VII.  Costal  cartilages. 

A,  Aortic  orifice. 

Ao,  Aorta. 

C,  Clavicle. 

LA,  Left  auricle. 

LV,  Left  ventricle. 


M,  Mitral  orifice. 
P,  Pulmonary  orifice. 
RA,  Right  auricle. 
RV,  Right  \entricle. 
SVc,  Superior  vena  cava. 
T,  Tricuspid  orilice. 


790  THE  VASCULAE  SYSTEM. 

posterior).  Each  cusp  consists  of  a  fold  of  endocardium,  strengthened  by  a  little 
intermediate  fibrous  tissue,  and  the  bases  of  the  cusps  are  generally  continuous 
with  each  other  at  the  auriculo- ventricular  orifice,  where  they  are  attached  to  a 
fibrous  ring,  but  they  may  be  separated  by  small  intermediate  cusps  which  fill  the 
angles  between  the  main  segments.  The  apices  of  the  cusps  hang  down  into  the 
ventricle.  The  margins,  which  are  thinner  than  the  central  portions,  are  notched 
and  irregular.  The  auricular  surfaces  are  smooth.  The  ventricular  surfaces  are 
roughened,  and,  like  the  margins  and  apices,  they  give  attachment  to  fine  tendinous 
cords,  the  chordae  tendineae,  the  opposite  extremities  of  which  are  attached  to 
muscular  bundles,  the  musculi  papillares,  which  project  from  the  wall  into  the 
cavity  of  the  ventricle. 

The  pulmonary  orifice,  which  lies  in  front  and  to  the  left  of  the  tricuspid  orifice, 
is  guarded  by  a  pulmonary  valve  composed  of  three  semilunar  segments  (valvulse 
semilunares  a.  pulmonalis),  two  of  which  are  placed  anteriorly  and  one  posteriorly. 
The  convexity  or  outer  border  of  each  semilunar  segment  is  attached  to  the  wall  of 
the  pulmonary  artery.  The  inner  border  is  free,  and  it  presents  at  its  centre  a  small 
nodule,  the  corpus  Arantii  (nodulus  valvules  semilunaris),  and  on  each  side  of 
this  body  a  small,  thin  marginal  segment  of  semilunar  form,  the  lunule  (lunula 
valvulse  semilunaris).  Each  segment  of  the  valve  is  formed  by  a  layer  of  endo- 
cardium on  its  ventricular  surface,  an  endothelial  layer  of  the  inner  coat  of  the 
artery  on  its  arterial  surface,  and  an  intermediate  stratum  of  fibrous  tissue.  Both 
the  attached  and  the  free  margins  of  the  cusps  are  strengthened  by  tendinous 
bands,  and  strands  of  condensed  fibrous  tissue  radiate  from  the  outer  borders  to 
the  corpora  Arantii,  but  they  do  not  enter  the  lunulse.  When  the  valve  closes  the 
corpora  Arantii  are  closely  apposed,  the  lunulee  of  the  adjacent  segments  of  the 
valve  are  pressed  together,  and  they  project  vertically  upwards  into  the  interior  of 
the  artery. 

The  cavity  of  the  right  ventricle  is  lined  by  endocardium ;  the  walls  are 
smooth  in  the  conus  arteriosus,  but  are  rendered  rugose  and  sponge-like  in  the 
body  by  the  inward  projection  of  numerous  muscular  bundles,  the  columnse 
cameae  (trabecules  carnege).  These  bundles  are  of  three  kinds ;  the  simplest  are 
merely  columns  raised  in  relief  on  the  wall  of  the  ventricle ;  those  of  the  second 
class  are  rounded  bundles,  free  in  the  middle,  but  attached  at  each  end  to  the  wall 
of  the  ventricle.  One  special  bundle  of  this  group,  called  the  moderator  band,  is 
attached  by  one  extremity  to  the  septum,  and  by  the  other  to  the  antero-superior 
wall,  at  the  base  of  the  anterior  papillary  muscle ;  it  tends  to  prevent  over-distension 
of  the  cavity.  The  third  group  of  columnee  carneee  are  the  musculi  papillares, 
conical  bundles  continuous  at  their  bases  with  the  muscular ywall  of  the  ventricle, 
and  terminating  at  their  apices  in  numerous  chordae  tendineee  which  are  attached  to 
the  apices,  the  borders,  and  ventricular  surfaces  of  the  cusps  of  the  tricuspid  valve. 
The  musculi  papillares  of  the  right  ventricle  are — (1)  a  large  anterior  muscle, 
from  which  the  chord*  pass  to  the  infundibular  and  marginal  segments  of  the 
valve ;  (2)  a  smaller  and  more  irregular  posterior  muscle,  sometimes  represented  by 
two  or  more  segments,  from  which  chordee  pass  to  the  marginal  and  septal  cusps  ;■ 
and  (3)  a  group  of  muscular  bundles,  varying  in  size  and  number,  which  spring 
from  the  septum  and  are  united  by  chordee  to  the  infundibular  and  septal  cusps. 

The  walls  of  the  right  ventricle,  the  septal  excepted,  are  much  thinner  than 
those  of  the  left,  but  the  columnee  carnese  of  the  first  and  second  classes  are  coarser 
and  less  numerous  in  the  right  than  in  the  left  ventricle. 

The  left  ventricle  (ventriculus  sinister)  is  a  conical  chamber,  and  its  cavity  is 
oval  in  transverse  section.  The  base  is  directed  upwards  and  backwards,  and  in  the 
greater  part  of  its  extent  it  is  continuous  with  the  corresponding  auricle  with 
which  it  communicates  through  the  mitral  orifice,  but  in  front  and  to  the  right  of 
its  communication  with  the  auricle  it  is  continued  into  the  ascending  aorta. 

The  mitral  orifice  is  oval ;  its  long  axis  runs  obliquely  from  above  and  to  the 
left  downwards  and  to  the  right,  and  it  is  guarded  by  a  valve  consisting  of 
two  cusps,  which  is  known  as  the  mitral  valve  (valvula  Ijicuspidalis).  The  two 
cusps  of  the  valve  are  triangular  and  of  unequal  size.  The  smaller  of  the  two, 
placed  to  the  left  and  behind,  is  named  the  marginal,  and  the  larger,  placed  to  the 


STEUCTUEE  OF  THE  HEAET.  791 

right  and  in  front,  between  the  mitral  and  aortic  oritices,  is  known  as  the  aortic 
cusp.  The  bases  of  the  cusps  are  either  continuous  with  each  other  at  their 
attachments  to  the  fibrous  ring  round  the  mitral  orifice,  or  they  are  separated  by- 
small  intermediate  cusps  of  irregular  form  and  size.  The  apices  of  the  cusps  hang 
down  into  the  cavity  of  the  ventricle.  The  auricular  surfaces  are  smooth ;  the 
ventricular  surfaces  are  roughened  hj  the  attachments  of  the  chord*  tendinese, 
which  are  also  connected  with  the  irregular  and  notched  margins  and  with  the 
apices.  The  structure  is  the  same  as  that  of  the  cusps  of  the  tricuspid  valve, 
but  the  veutricvilar  surface  of  the  anterior  (or  aortic)  cusp  is  relatively  smooth ; 
therefore  the  blood  flow  into  the  aorta  is  facilitated. 

The  aortic  orifice  is  circular ;  it  lies  immediately  in  front  and  to  the  right  of 
the  mitral  orifice,  from  which  it  is  separated  by  the  anterior  cusp  of  the  mitral 
valve,  and  it  is  guarded  by  the  aortic  valve,  formed  of  three  semilunar  segments 
(valvule  semilunares  aortas),  one  of  which  is  placed  anteriorly  and  the  other  two 
posteriorly.  The  structure  of  these  cusps  and  their  attachments  are  similar  to 
those  of  the  cusps  of  the  pulmonary  valve. 

The  cavity  of  the  left  ventricle  is  separable,  like  that  of  the  right,  into  two 
portions,  the  body  and  the  aortic  vestibule ;  the  latter  is  a  small  section  placed 
immediately  below  the  aortic  orifice,  and  its  walls  are  non-contractile,  consisting  of 
fibrous  and  fibro-cartilaginous  tissue.  The  cavity  is  Hned  by  endocardium.  The 
inferior  wall  and  the  apex  are  rendered  sponge-like  by  numerous  fine  columnse 
carneee  of  the  first  and  second  classes,  whilst  the  upper  part  of  the  antero-superior 
wall  and  the  septum  are  relatively  smooth. 

There  are  two  papillary  muscles  of  much  larger  size  than  those  met  with  in  the 
right  ventricle — an  anterior  and  a  posterior  ;  each  is  connected  by  chordce  tendinese 
with  both  cusps  of  the  mitral  valve. 

The  walls  of  the  left  ventricle,  with  the  exception  of  the  septum,  are  three 
times  as  thick  as  those  of  the  right  ventricle,  and  they  are  thickest  in  the  region  of 
the  widest  portion  of  the  cavity,  which  is  situated  about  a  fourth  of  its  length  from 
the  base.  The  muscular  portion  of  the  wall  attains  its  minimum  thickness  at  the 
apex,  but  the  thinnest  portion  of  the  boundary  is  at  the  upper  part  of  the  septum, 
which  consists  entirely  of  fibrous  tissue ;  here  it  is  occasionally  deficient,  and  an 
aperture  is  left  through  wliich  the  cavities  of  the  two  ventricles  communicate. 

The  interventricular  septum  (septum  ventriculorum)  is  a  musculo-membranous 
partition.  It  is  placed  obhquely,  one  surface  looking  forwards  and  to  the  right, 
and  bulcring  into  the  riyht  ventricle,  and  the  other  backwards  and  to  the  left 
towards  the  left  ventricle.  Its  antero-superior  and  inferior  margins  correspond 
respectively  with  the  anterior  and  inferior  portions  of  the  interventricular  sulcus, 
and  it  extends  from  the  right  of  the  apex  to  the  interval  between  the  pulmonary 
and  aortic  orifices.  In  the  main  part  of  its  extent  it  is  muscular  (septum  musculare 
ventriculorum),  and  this  portion  is  developed  from  the  wall  of  the  ventricular  part 
of  the  heart ;  but  its  upper  and  posterior  portion,  the  pars  membranacea  (septum 
membranaceum  ventriculorum),  which  is  developed  from  the  septum  of  the  aortic 
bulb,  is  entirely  fibrous,  and  constitutes  the  thinnest  portion  of  the  ventricular 
walls.  The  pars  membranacea  lies  between  the  aortic  vestibule  on  the  left  and 
the  upper  part  of  the  right  ventricle,  as  well  as  the  lower  and  left  part  of  the  right 
auricle,  on  the  right. 

Structuee  of  the  Heart. 

The  walls  of  the  heart  consist  mainly  of  peculiar  strijied  muscle,  the  myocardium,  which  is 
enclosed  between  the  visceral  layer  of  the  jiericardium,  or  epicardium,  externally,  and  the 
endocardium  internally.  The  muscular  fibres  differ  from  those  of  ordinary  voluntary  striped 
muscle  in  several  ways  :  they  are  shorter,  many  of  them  being  oblong  cells  with  forked  ex- 
tremities which  are  closely  cemented  to  similar  processes  of  adjacent  cells  ;  they  form  a  reticulum, 
and  the  nuclei  lie  in  the  centres  of  the  cells.  Moreover,  in  some  of  the  lower  mammals,  in  the 
yoimg  child  up  to  the  end  of  the  first  year,  and  occasionally  in  the  human  adidt  also,  still  more 
peculiar  fibres,  the  fibres  of  Purkinje,  are  foimd  immediately  beneath  the  sub -endocardial 
tissue.  These  are  large  cells  which  unite  with  each  other  at  their  extremities ;  their  central 
portions  consist  of  granular  protoplasm,  in  which  sometimes  one,  but  more  frequently  two  nuclei 
are  embedded,  and  the  peripheral  portion  of  each  cell  is  transversely  striated.  These  cells,  in  short, 
present  in  a  permanent  form  a  condition  which  is  transitory  in  all  other  striped  muscle  cells. 


792  THE  VASCULAK  SYSTEM. 

The  reticulating  cardiac  muscle  cells  are  grouped  iu  sheets  and  strands  which  have  a  more  or 
less  characteristic  and  definite  arrangement  in  different  parts  of  the  heart ;  by  careful  dis- 
section, and  after  special  methods  of  preparation,  it  is  possible  to  recognise  many  layers  and 
bundles,  some  of  which  are,  however,  probably  artificially  produced. 

In  the  auricles  the  muscular  fasciculi  fall  naturally  into  two  groups,  those  special  to  each 
auricle,  and  those  common  to  both  auricles ;  the  former  are  situated  deeply  under  cover  of 
the  latter. 

The  deep  special  fibres  are — (a)  Looped  fibres  which  pass  over  the  auricles  from  before  back- 
wards or  from  side  to  side ;  their  extremities  are  attached  to  the  filjrous  rings  which  surround 
the  auriculo-ventricular  orifices,  (b)  Annular  fibres  which  surround  (1)  the  extremities  of  the 
large  vessels  which  open  into  the  auricle,  (2)  the  auricular  appendices,  and  (3)  the  fossa  ovalis. 

The  superficial  fibres,  which  are  common  to  both  auricles,  for  the  most  part  run  transversely 
across  the  auricles,  but  a  few  of  them  turn  into  the  interauricular  septum.  They  are  most 
numerous  on  the  anterior  aspect. 

In  the  ventricles,  also,  two  main  groups  of  fasciculi,  a  superficial  and  a  deep,  have  been 
described,  but  it  is  in  this  region  especially  that  there  is  doubt  regarding  the  individuality  of 
many  of  the  muscular  l^undles  which  have  been  noted,  for  it  appears  probable  that  many  of 
them  are  artificial  products  due  to  the  method  adojated  by  the  dissector.  There  is  no  doubt  that 
in  the  middle  of  the  thickness  of  the  ventricular  walls  the  arrangement  of  the  fibres  is  mainly 
circular,  some  surrounding  one  and  some  both  ventricles.  Near  the  surfaces  the  fasciculi 
assume  an  oblique  direction,  and  it  is  not  improbable  that  many  of  the  bundles  are  arranged  in 
figure  of  8  loops,  whose  upper  extremities  are  attached  to  the  fibrous  rings  round  the  auriculo- 
ventricular  orifices. 

The  superficial  fibres  of  the  ventricles  are  attached  above  to  the  fibrous  rings  at  the  base,  and 
from  this  attachment  they  jsass  obliquely  downwards  to  the  apex,  those  on  the  anterior  surface 
trending  towards  the  left,  and  those  on  the  inferior  surface  towards  the  right.  On  the  inferior 
surface  almost  all  the  fasciculi  appear  to  pass  across  the  septum,  but  on  the  anterior  surface  the 
middle  fasciculi  dip  into  it,  and  only  those  near  the  base  and  apex  cross  from  right  to  left.  All 
the  superficial  fibres  which  reach  the  apex  are  coiled  there  into  a  whorl  or  vortex,  through  which 
they  pass  upwards  into  the  substance  of  the  left  ventricle,  those  descending  from  the  front  and 
left  side  entering  the  base  of  the  posterior  papillary  muscle,  whilst  those  from  the  back  and  right 
side  terminate  in  the  anterior  papillary  muscle.  The  muscular  fasciculi  which  enter  the  papillary 
muscles  are  continued,  by  means  of  the  chordae  tendinese,  to  the  flaps  of  the  mitral  valve  and 
so  to  the  fibrous  ring  round  the  mitral  orifice ;  obviously,  therefore,  many  of  the  superficial 
fasciculi  of  the  ventricles  form  simple  oblique  looj^s  which  commence  externally  at  the  fibrous 
rings  round  the  right  and  left  auriculo-ventricular  orifices,  and  terminate  internally  by  gaining 
attachment  to  the  ring  round  the  left  of  these  orifices  (mitral). 

The  deep  fasciculi  of  the  ventricles  may  be  subdivided  into  two  main  grouj)s — (1)  Those 
common  to  both  ventricles,  and  (2)  those  special  to  each  ventricle. 

The  fasciculi  common  to  both  ventricles  include — {a)  Fibres  which  commence  above  from  the 
posterior  sections  of  the  fibrous  ring  at  the  base  of  the  right  ventricle;  either  directly  or  by 
means  of  the  chord  se  tendinese  of  the  posterior  papillary  muscle  they  pass  obliquely  downwards 
to  the  septum,  traverse  it,  and  ascend  to  the  front  of  the  fibrous  ring  at  the  base  of  the  left 
ventricle,  (b)  Fibres  from  the  anterior  portions  of  the  fibrous  ring  at  the  base  of  the  right 
ventricle,  which  pass  obliquely  downwards  and  assume  a  transverse  course  in  the  j)osterior  wall 
of  the  left  ventricle,     (c)  Annular  filjres  which  encircle  both  ventricles. 

The  deep  special  fibres  of  the  left  ventricle  are  {a)  V-''?liaped  loops  which  commence  at  the 
fibrous  ring  at  the  base,  and  descend  to  tlie  apex,  where  they  turn  upwards  in  the  septum,  and 
terminate  by  joining  the  central  filjro-cartilage ;  (6)  fibres  which  descend  from  the  base,  enter 
the  lower  and  front  part  of  the  septum,  and,  passing  through  it,  assume  an  annular  course  in  the 
posterior  walL 

The  deep  special  fibres  of  tlie  right  ventricle  are  {a)  looped  fibres  which  pass  downwards  in 
the  external  wall  from  the  filjrous  rings  to  the  apex,  where  tliey  enter  the  septum  and  ascend  to 
the  central  fibro-cartilage ;  (b)  circular  fibres  round  the  pulmonary  orifice  ;  and  (c)  radiating  fasci- 
culi from  the  base  of  the  anterior  papillary  mu.scle  to  the  front  part  of  the  pulmonary  orifice. 

The  epicardium,  or  visceral  jjortion  of  the  pericardium,  consists  of  white  connective  and 

of  elastic  tissue,  the  latter  forming  a  distinct  reticulum  in  the  deeper  part.     The  surface  which 

looks  towards  the  pericardial  cavity  is  covered  with  fiat  polygonal  endothelial  plates,  which  are 

-partially  separated  liere  and  there  by  stomata  through  which  tlicperii'ardial  cavity  communicates 

witli  the  lymphatics  of  the  epicardium. 

The  endocardium  lines  the  cardiac  cavities  and  is  continuous  witli  the  inner  coats  of  the 
vessels  wliich  enter  and  leave  the  heart.  It  consists,  like  the  epicardium,  of  white  connective 
tissue  and  elastic  fil;ri-,s,  but  it  is  much  tliinner  than  tlie  epicardium,  and  its  elastic  fibres  are  in 
some  places  blended  into  a  fenestrated  membrane.  Its  inner  surface  is  covered  with  endothelial 
cells,  and  it  rests  externally  upon  the  sub-endocardial  tissue,  in  which  there  are  blood-vessels  and 
nerves  ;  the  fiidoianlium  itself  is  entirely  devoid  of  vessels. 

Size  of  the  Heart.— The  heart  is  al)out  five  inches  (125  min.)  long,  three  and  a  half  inches  (87 
mm.)  broad ;  its  gi-eatest  depth  from  its  antero-superior  to  its  inferior  surface  is  two  and  a  half  inches 
(62  mm.),  and  it  is  rouglily  estimated  as  being  aljout  tlie  same  size  as  the  closed  fist.  The  size, 
however,  is  varialjle,  the  volume  increasing  at  fii-st  rajudly,  and  then  gi'adually,  with  increasing 
age,  from  22  cc.  at  birth  to  155  cc.  at  the  fifteenth  year,  and  to  250  cc.  by  the  twentieth  year. 
From  this  period  to  the  fiftieth  year,  when  the  maximum  volume  (280  cc.)  is  attained,  the  in- 


THE  PEEICAKDIUM.  793 

crease  is  much  more  giadual,  and  alter  fifty  a  .slight  decrease  sets  in.     The  volume  is  the  same 
in  both  sexes  up  to  the  period  of  puberty,  but  thereafter  it  preponderates  in  the  male. 

Weight. — The  average  weight  of  the  heart  m  the  male  adult  is  11  ounces  (310  gi'ms.),  and  in 
the  female  adult  9  ounces  (255  grms.)  ;  but  the  weight  varies  greatly,  alway.s,  however,  in  definite 
relation  to  the  weight  of  the  body,  the  relative  proportions  changing  at  different  periods  of  life. 
Thus  at  birth  the  heart  weighs  13^  drachms  (24  gnus.),  and  its  relation  to  the  body  weight 
is  as  1  to  130,  whilst  in  the  adidt  the  relative  proiiortion  is  as  1  to  205.  The  heart  is  said  to 
increase  rapidly  in  weight  up  to  the  seventh  year,  then  more  slowly  up  to  the  age  of  puberty, 
when  a  second  acceleration  sets  in  ;  but  after  the  attainment  of  adult  life  the  increase,  which 
continues  till  the  seventieth  year,  is  very  gradual. 

The  above  changes  atfect  the  whole  heart,  but  the  several  parts  also  vary  in  their  relation  to 
each  other  at  different  periods  of  life.  During  foetal  life  the  right  auricle  is  heavier  than  the  left ; 
in  the  first  month  after  birth  the  two  become  equal,  and  at  the  second  year  the  right  again  begins 
to  preponderate,  and  it  is  heavier  than  the  left  during  the  remainder  of  life.  In  the  latter  part 
of  foetal  life  the  two  ventricles  are  equal ;  after  birth  the  left  grows  more  rapidly  than  the  right, 
until,  at  the  end  of  the  second  year,  a  position  of  stability  is  gained,  when  the  right  is  to  the  left 
as  1  to  2,  and  this  proportion  is  maintained  until  death. 

Capacity. — During  life  the  capacity  of  the  ventricles  is  probably  the  same,  and  each  is  capable 
of  containing  about  four  ounces  of  blood,  whilst  the  auricles  are  a  little  less  capacioas.  After 
death  the  cavity  of  the  right  ventricle  appears  larger  than  that  of  the  left. 

Vascular  Supply  of  the  Heart. — The  walls  of  the  heart  are  supplied  by  the  coronary  arteries 
(p.  800),  the  branches  of  which  pass  through  the  interstitial  tissue  to  all  parts  of  the  muscular 
substance  and  to  the  sub-endocardial  and  sub-epicardial  tissues  ;  the  endocardium  and  the  valves 
are  devoid  of  vessels.  The  capillaries,  which  are  numerous,  form  a  close-meshed  network  around 
the  muscular  fibres.  Sometimes  the  valves  contain  a  few  muscular  fibres,  and  in  the.se  cases  they 
also  receive  some  minute  vessels.  The  majority  of  the  veins  of  the  heart  end  in  the  coronary 
siniLs,  which  opens  into  the  lower  part  of  the  right  auricle  ;  some  few  very  small  veins,  how- 
ever, open  directly  into  the  right  auricle,  and  others  are  said  to  end  in  the  left  auricle,  and 
in  the  cavities  of  the  ventricles. 

Lymphatics  of  the  Heart. — Lymphatic  vessels  are  freely  distributed  throughout  the  whole 
substance  of  the  heart,  but  they  are  most  numerous  in  the  sub-endocardial  and  the  sub-pericardial 
tissues,  and  the  vessels  which  lie  in  the  latter  situation  commimicate  through  stomata  with  the 
pericardial  cavity.  The  smaller  lymphatic  vessels  accompany  the  blood-vessels  ;  ultimately  they 
converge  to  two  main  trunks — an  anterior  and  an  inferior — which  lie  respectively,  at  their  com- 
mencements, in  the  anterior  and  the  inferior  auriculo-ventricular  sulci.  Each  is  formed  by  one 
or  more  tributaries  which  collect  lymj^h  from  the  ventricles  and  auricles.  The  inferior  trunk 
accompanies  the  right  and  the  anterior  trunk  the  left  coronary  artery.  At  the  ujjper  part  of  the 
heart  the  trunks  pass  backwards,  at  the  sides  of  the  pulmonary  artery,  pierce  the  pericardium,  and 
they  terminate  iu  the  glauds  which  lie  round  the  bifiucation  of  the  trachea. 

Nerves  of  the  Heart. — The  heart  receives  its  nerves  from  the  superficial  and  deep  cardiac 
plexuses  which  lie  beneath  the  arch  of  the  aorta,  and  through  them  it  is  connected  with  the 
vagus,  the  spinal  accessory  (through  the  vagus),  and  the  sympathetic  nerves.  After  leaving  the 
plexuses  uiany  of  the  nerve-fibres  enter  the  walls  of  the  auricles,  and  anastomose  together  in  the 
sub-epicardial  tissue,  forming  a  plexus  in  which  many  ganglion  cells  are  embedded,  especially 
near  the  terminations  of  the  inferior  vena  cava  and  the  puhuonary  veins.  From  the  sub- 
epicardial auricular  plexus,  nerve  filaments,  on  which  nerve  ganglion  cells  have  been  found,  pass 
into  the  substance  of  the  auricular  walls. 

Other  fibres  from  the  cardiac  plexuses  accompany  the  coronary  arteries  to  the  ventricles,  and 
upon  these  also  ganglion  cells  are  found  in  the  region  immediately  below  the  auriculo-ventricular 
sulcus. 

The  nerve-fibres  which  issue  from  the  ganglionated  plexuses  of  the  heart  are  non-medullated. 
They  form  fine  plexuses  round  the  muscle  fibres,  and  they  terminate  either  in  fine  fibrils  on  the 
surfaces  of  the  muscle  fibres,  or  in  nodulated  ends  which  lie  in  contact  with  the  muscle  cells. 


THE   PEEICAEDIUM. 

The  pericardium  is  a  fibro-serous  sac  vvhich  surrounds  the  heart.  It  lies  in  the 
middle  mediastinum,  and  is  attached  below  to  the  diaphragm,  and  above  and  behind 
to  the  roots  of  the  great  vessels.  Anteriorly  and  posteriorly  it  is  in  relation  with 
adjacent  structures ;  laterally  it  is  in  close  apposition  with  the  pleural  sacs. 

The  fibrous  pericardium  is  a  strong  tibrous  sac  of  conical  form;  its  base  is 
attached  to  the  central  tendun  and  to  a  part  of  the  muscular  substance  of  the 
diaphmgm,  and  it  is  pi.rced  by  the  inferior  vena  cava.  At  its  apex  and  posteriorly 
it  is  gradually  lost  u].on  the  great  vessels  which  enter  and  emerge  from  the  heart, 
giving  sheaths  to  ihe  aorta,  the  two  branches  of  the  pulmonary  artery,  the  superior 
vena  cava,  the  four  pulmonary  veins,  and  the  ligamentuin  arti.riosum.  Its 
anterior  suiface  forms  the  yo-terior  boundary  of  the  anterior  mediastinum,  and  it 
gives  attachment,  above  and  below,  to  the  superior  and  inferior  sterno-pericardial 


794 


THE  VASCULAR  SYSTEM. 


ligaments 


xxgcx^v^xxu^.  In  the  greater  part  of  its  extent  it  is  separated  from  the  anterior  wall 
of  the  thorax  bj  the  anterior  margins  of  the  lungs  and  pleural  sacs,  but  it  is  in  direct 
relation  with  the  left  half  of  the  lower  portion  of  the  body  of  the  sternum  and,  in 
many  cases,  with  the  inner  ends  of  the  cartilages  of  the  fourth,  fifth,  and  sixth  ribs 
of  the  left  side.  Its  posterior  surface  forms  the  anterior  boundary  of  the  posterior 
mediastinum ;  it  is  in  relation  with  the  oesophagus  and  the  descending  aorta,  both 
of  which  it  separates  from  the  back  of  the  left  auricle.  Each  lateral  aspect  is  in 
close  contact  with  the  mediastinal  portion  of  the  parietal  pleura,  the  phrenic  nerve 
and  its  accompanying  vessels  intervening.  The  inner  surface  of  the  fibrous  sac  is 
lined  by  the  serous  pericardium,  which  is  closely  attached  to  it. 


Left  phrenic  nerve 
Left  vaiius  nerve 


Right  phrenic  nerve 

Superior  vena  cava 

Aorta 

Pulmonary  artery 
Superior  vena  ca\  a 


Left  pulmonary  artery 


onchus 

Left  pulmonary  veins  in  root  of 
luns 


Right  pulmon- 
ary veins 


Left  pulmonary  veins 
Pel  icai  dium 


Diaplira] 


Fig.  619. — Posterior  Wall  of  the  Pericardium  after  removal  of  the  Heart,  showing  the  relation  of 
the  serous  pericardium  to  the  great  vessels.     From  a  formalin  preparation  made  by  Professor  Birmingham. 

The  serous  pericardium  is  a  closed  sac  containing  a  little  fluid  (liquor  peri- 
cardii). It  is  surrounded  by  the  fibrous  pericardium  and  invaginated  by  the  heart. 
It  is,  therefore,  separable  into  two  portions — the  parietal,  which  lines  the  inner  sur- 
face of  the  fibrous  sac,  and  the  visceral,  which  enslieaths,  or  partially  ensheaths,  the 
heart  and  the  great  vessels  ;  but  the  two  portions  are,  of  course,  continuous  with 
each  other  where  the  serous  layer  is  reflected  on  to  the  great  vessels  as  they  pierce 
the  fibrous  layer.  The  majority  of  the  great  vessels  receive  only  partial  coverings 
from  the  visceral  layer :  thus  the  superior  vena  cava  is  covered  in  front  and 
laterally ;  the  pulmonary  veins  in  front,  above,  and  below ;  and  the  inferior  vena 
cava,  for  a  very  short  distance,  in  front  and  laterally.  The  aorta  and  the 
pulmonary  artery  are  enclosed  together  in  a  complete  sheath  of  the  visceral  layer  ; 
and  when  the  pericardial  sac  is  opened  from  the  front  it  is  possible  to  pass 
the  fingers  behind  them  and  in  front  of  the  auricles,  from  the  right  to  the  left 
side,  through  a  passage  called  the  great  transverse  sinus  of  the  pericardium.     The 


THE  PULMONAKY  AETERY.  795 

spaces  or  pouches  which  intervene  between  the  vessels  which  receive  partial  coverings 
from  the  serous  pericardium  are  also  called  sinuses ;  and  the  largest  of  them,  which 
is  bounded  below  and  on  the  right  by  the  inferior  vena  cava,  and  above  and  on  the 
left  by  the  left  inferior  pulmonary  vein,  is  known  as  the  great  oblique  sinus.  It 
passes  upwards  and  to  the  right  behind  the  left  auricle,  and  lies  in  front  of  the 
oesophagus  and  the  descending  thoracic  aorta. 

A  small  fold  of  the  serous  pericardium,  the  vestigial  fold  of  Marshall  (liga- 
mentum  v.  cavse  sinistra),  passes  from  the  left  pulmonary  artery  to  the  left  superior 
pulmonary  vein  behind  the  left  extremity  of  the  transverse  sinus.  It  merits 
special  attention  because  it  encloses  the  remains  of  the  left  superior  vena  cava, 
which  atrophies  at  an  early  period  of  foetal  life. 

Structure. — The  fibrous  pericardium  consists  of  ordinary  connective  tissue  fibres  felted 
together  into  a  dense,  unyielding  membrane.  The  serous  pericardium  is  covered  on  its  inner 
aspect  by  a  layer  of  flat  endothelial  cells  which  rest  upon  a  basis  of  mixed  white  and  elastic  fibres 
in  which  run  numerous  blood-vessels,  lymphatics,  and  nerves. 

THE   ARTERIES. 
THE  PULMOi^TARY  ARTERY. 

The  pulmonary  artery  (a.  pulmonalis)  springs  from  the  anterior  and  left  angle 
of  the  base  of  the  rii^ht  ventricle,  at  the  termination  of  the  infundibulum.  It 
is  slightly  larger  at  its  commencement  than  the  aorta,  and  is  dilated  immediately 
above  the  valves  into  three  pouches,  the  sinuses  of  Valsalva.  It  runs  upwards  and 
backwards  towards  the  concavity  of  the  aortic  arch,  curving  from  the  front  round 
the  left  side  of  the  ascending  aorta  to  reach  a  plane  posterior  to  the  latter ;  and  it 
terminates,  by  dividing  into  right  and  left  branches,  opposite  the  sixth  dorsal 
vertebrfe.     Its  length  is  a  little  more  than  two  inches. 

Relations. — The  pulmonary  artery  is  enclosed  within  the  fibrous  pericardium, 
and  enveloped  along  with  the  ascending  aorta  in  a  common  sheath  of  the  visceral 
layer  of  the  serous  pericardium.  It  lies  behind  the  inner  extremity  of  the  second 
left  intercostal  space,  from  which  it  is  separated  by  the  anterior  margins  of  the  left 
lung  and  pleural  sac. 

Its  posterior  relations  are  the  root  of  the  aorta,  the  anterior  wall  of  the  left 
auricle,  and  the  first  part  of  the  left  coronary  artery.  To  the  right  it  is  in  relation 
with  the  right  coronary  artery  and  the  right  auricular  appendix,  and  to  the 
left  with  the  left  coronary  artery  and  the  left  auricular  appendix.  Immediately 
above  its  bifurcation,  between  it  and  the  aortic  arch,  is  the  superficial  cardiac 
plexus. 

The  right  branch  of  the  pulmonary  artery  is  longer  and  larger  than  the 
left.  It  passes  to  the  hilum  of  the  right  lung,  forming  one  of  the  constituents  of 
its  root,  and,  enterino-  the  luno-,  descends  with  the  main  bronchus  to  the  lower 
extremity  of  the  organ. 

Relations. — Before  it  enters  the  lung  the  right  pulmonary  artery  passes  behind  the 
ascending  aorta,  the  superior  vena  cava,  and  the  upper  right  pulmonary  vein.  At  first 
it  lies  below  the  arch  of  the  aorta  and  the  right  bronchus,  in  front  of  the  oesophagus,  and 
above  the  left  auricle  and  the  lower  right  pulmonaiy  vein  ;  then  it  crosses  in  front  of  the 
right  bronchus  immediately  below  the  eparterial  branch,  and  reaches  the  hilum  of  the 
lung.  After  entering  the  lung  the  artery  descends,  behind  and  to  the  outer  side  of 
the  main  bronchus  and  between  its  ventral  and  dorsal  branches. 

Branches. — Before  entering  the  hilum  it  gives  off  a  large  branch  to  the  upper  lobe 
which  accompanies  the  eparterial  bronchus,  and  in  the  substance  of  the  lung  it  gives 
ofi"  numerous  branches  which  correspond  with  and  accompany  the  dorsal,  ventral,  and 
accessory  branches  of  the  right  bronchus. 

The  left  branch  of  the  pulmonary  artery,  shorter,  smaller,  and  somewhat 
higher  in  position  than  the  right,  passes  outwards  and  backwards  from  the  bifurca- 
tion of  the  pulmonary  stem,  and  runs  in  the  root  of  the  left  lung  to  the  hilum ;  it 
then  descends  in  company  with  the  main  bronchus  to  the  lower  end  of  the  lung. 


796 


THE  VASCULAE  SYSTEM. 


Relations. — Before  it  enters  the  lung  it  is  crossed  in  front  by  the  upper  left 
pulmonary  vein  ;  hehiiuJ  it,  is  the  left  bronchus  and  the  descending  aorta ;  above,  the 
aortic  arch,  to  which  it  is  connected  by  the  ligamentum  arteriosum,  and  the  left  recurrent 


Fig.  620. — Thk  Pilmoxakv  Aktehies  and  Veins  and  thkih  Relations. 
Parts  of  the  ascending  aorta  ami  superior  vena  cava  have  bt'tu  removed. 


1. 

Aorta. 

11. 

2. 

Buperior  vena  cava. 

12. 

3. 

Upper    right    pulmonary 

13. 

vein. 

14. 

4. 

Rigtit  pulmonary  artery. 

15. 

5. 

Superior  vena  cava. 

Ki. 

6. 

Left  innominate  vein. 

17. 

7. 

Innominate  aitery. 

18. 

8. 

Right  innominate  vein. 

lit. 

9. 

Subclavius  niUHCle. 

20. 

10. 

Clavicle. 

21. 

Internal  niammarj- artery.  22. 

Hubclavian  vein.  2a. 

Suprascapular  artery.  24. 

Transverse  cervical  artery.  25. 

Vertctjral  artery.  20. 

Inferior  thyroid  artery.  27. 

Internal  jugular  vein.  2S. 

Common  carotid  artery.  2i>. 

iSui>erior  thyroid  artery.  30. 

Sterno-thyroid  muHcle.  .'U. 

Omo-hyoid  mu.scle.  H2. 


StHrno-liyoid  niuscli-. 
I'latysniu. 

Sterno-hyoid  muscle. 
Sterno-tliyroid  muscle. 
Sterno-masioid  muscle. 
Phrenic  nerve. 
Vagus  nerve. 
.Veitehral  artery. 
Inferior  thyroid  artery. 
Thoracic  duct. 
Left  suliclavian  artery. 


33.  Subclavius  muscle. 

34.  1st  rib. 

35.  Left    common    carotid 

artery. 
3G.  Aorta. 

37.  Ligamentum  arteriosum. 

38.  Left  pulmonary  artery. 

39.  Ui)per     left     pulmonary 

vein. 

40.  Pulmonary  artery. 


laryngeal  nerve ;  below,  it  is  in  relation  with  the  lower  left  pulmonary  vein.  After  enter- 
ing the  lung  it  descends,  like  the  right  pulmonary  artery,  behind  and  on  the  outer  side  of 
the  stem  Vironchu-s,  and  between  its  ventral  and  dorsal  branches. 

Branches. — Just  before  passing  throngh  the  hihnn  it  gives  off  a  branch  to  the 
upper  lobe,  and  in  the  substance  of  the  lung  its  branches  correspond  with  the  ventral, 
dorsal,  and  accessorv  branches  of  the  bronchial  tube. 


THE  THOEACIC  AORTA.  797 

THE  SYSTEMIC  ARTERIES. 
THE  AORTA. 

The  aorta  is  the  main  trunk  of  the  arterial  system.  It  commences  at  the  base 
of  the  left  ventricle  and  ascends,  with  an  inclination  to  the  right,  to  the  level  of 
the  second  right  costal  cartilage  ;  then  curving  backwards  and  to  the  left,  it 
reaches  the  left  side  of  the  lower  border  of  the  fourtli  dorsal  vertebra,  and  finally 
descends  through  the  thorax  into  the  abdomen,  where  it  terminates,  on  the  left  of  the 
mesial  plane,  at  the  level  of  the  fourth  lumbar  vertebra,  by  bifurcating  into  the  two 
common  iliac  arteries.  The  portion  of  the  aorta  which  is  situated  in  the  thorax  is, 
for  convenience,  termed  the  thoracic  aorta,  and  the  rest  of  the  vessel  is  known  as 
the  abdominal  aorta. 

THE  THORACIC  AORTA. 

The  thoracic  aorta  is  subdivided  into  the  ascending  portion,  the  arch,  and  the 
descending  portion. 

The  ascending  aorta  (aorta  ascendens)  lies  in  the  middle  mediastinum.  It 
springs  from  the  base  of  the  left  ventricle,  behind  the  left  margin  of  the 
sternum,  opposite  the  lower  border  of  the  third  left  costal  cartilage  and  the 
body  of  the  sixth  dorsal  vertebra.  From  its  origin  it  passes  upwards,  forwards, 
and  to  the  right,  and  it  terminates  in  the  arch  of  the  aorta,  behind  the  ri^ht 
margin  of  the  sternum,  at  the  level  of  the  second  costal  cartilage.  Its  length 
is  from  2  to  2\  inches  (50  to  57  mm.),  and  its  breadth  is  1|  inches  (28  mm.) 
In  the  adult  it  is  a  little  narrower  at  its  commencement  than  the  pulmonary 
artery  is,  but  in  old  age  it  enlarges  and  exceeds  the  latter  vessel  in  size.  The 
diameter,  however,  is  not  uuiform  throughout  the  whole  length  of  the  ascendino- 
aorta  ;  four  distinct  dilatations  are  present.  Three  of  these,  small  and  pouch-like', 
are  known  as  the  sinuses  of  Valsalva  (sinus  aortse).  They  are  situated  at  the 
origin  of  the  aorta,  immediately  above  the  semilunar  cusps  of  the  valve  which 
guards  the  aperture  of  communication  with  the  left  ventricle ;  one  is  anterior  in 
position,  and  two  are  situated  posteriorly.  The  fourth  dilatation  is  formed  by 
a  diffuse  bulging  of  the  right  wall,  and  is  known  as  the  great  sinus  of  the 
aorta. 

Relations. — The  ascending  aorta  is  completely  enclosed  within  the  fibrous  peri- 
cardium which  blends  above  with  the  sheath  of  the  vessel.  It  is  enveloped,  too-ether 
with  the  stem  of  the  pulmonary  artery,  in  a  tubular  prolongation  of  the  serous  pericar- 
dium, and  at  its  origin  has  the  pulmonary  artery  in  front,  the  anterior  wall  of  the  left 
auricle  behind,  and  the  right  auricular  appendix  on  its  right  side.  In  the  upper  part  of 
its  course  the  ascending  aorta  is  overlapped  by  the  anterior  margins  of  the  right  lung  and 
right  pleural  sac,  whilst  behind  it  ai'e  the  right  auricle,  tlie  right  branch  of  tlie  pulmonary 
artery,  the  right  bronchus,  and  the  left  margin  of  the  superior  vena  cava.  The  superior 
vena  cava  lies  on  the  right  side,  and  partly  behind  the  upper  part  of  the  ascending  aorta, 
whilst  the  pulmonary  artery  is  at  first  in  front  of  it  and  then,  at  a  higher  level,  on  its  left 
side. 

Branches. — Two  branches  arise  from  the  ascending  aorta,  viz.  the  right  and  the  left 
coronary  arteries.  The  former  springs  from  the  anterior,  and  the  latter  from  the  left 
posterior  sinus  of  Valsalva  (p.  800). 

The  arch  of  the  aorta  (arcus  aortae)  lies  in  the  superior  mediastinum  behind 
the  lower  part  of  the  manubrium  sterni,  and  connects  the  ascending  with  the 
descending  aorta.  It  commences  behind  the  right  margin  of  the  sternum,  on  a 
level  with  the  second  costal  cartilage,  and  extends  to  the  lower  border  of  the  fourth 
dorsal  vertebra.  As  its  name  implies,  it  forms  an  arch ;  in  this  there  are  two 
curvatures,  one  with  the  convexity  upwards,  and  the  other  with  the  convexity 
forwards  and  to  the  left.  From  its  origin  it  runs  for  a  sliort  distance  upwards, 
backwards,  and  to  the  left,  in  front  of  the  trachea ;  then  it  passes  backwards, 
round  the  left  side  of  the  trachea  to  the  left  side  of  the  body  of  the  fourth  dorsal 
vertebra,  and  finally  turns  downwards  to  become  continuous  with  the  descending 
aorta. 


798  THE  VASCULAR  SYSTEM. 

At  its  commencement  it  has  the  same  diameter  as  the  ascending  aorta,  1^ 
inches  (28  mm.),  but  after  giving  off  three  large  branches,  the  diameter  is  reduced 
to  a  little  less  than  one  inch  (23  mm.) 

Relations. — It  is  overlapped  in  front  and  on  the  left  side  by  the  right  and  left  lungs 
and  pleural  sacs,  but  much  more  by  the  latter  than  the  former,  and  in  the  interval 
between  and  behind  the  pleural  sacs  it  is  covered  by  the  remains  of  the  thymus  gland. 
As  it  turns  backwards  it  is  crossed  vertically  on  the  left  side  by  four  nerves  in  the 
following  order  from  before  backwards  : — the  left  phrenic,  the  inferior  cervical  cardiac 
branch  of  the  left  vagus,  the  superior  cardiac  branch  of  the  left  sympathetic,  and  the 
trunk  of  the  left  vagus,  and  the  left  superior  intei'costal  vein  passes  obliquely  upwards 
and  to  the  right  between  the  vagus  and  phi-enic  nerves. 

Behind  and  to  the  right  side  of  tlie  arch  are  the  trachea,  deep  cardiac  plexus,  the  left 
recurrent  lai-yngeal  nerve,  the  left  border  of  the  oesophagus,  and  the  thoracic  duct.  Above 
are  its  thi'ee  large  branches — the  innominate,  the  left  common  carotid,  and  the  left 
subclavian  arteries — and  crossing  in  front  of  the  roots  of  these  is  the  left  innominate  vein. 
Below  is  the  bifurcation  of  the  pulmonary  artery  and  the  root  of  the  left  lung ;  the 
ligamentum  arteriosum,  which  is  also  below,  attaches  it  to  the  commencement  of  the 
left  pulmonary  artery,  whilst  to  the  right  of  the  ligament  is  the  superficial  cardiac 
plexus,  and  to  its  left  is  the  left  recurrent  laryngeal  nerve. 

Branches. — The  three  great  vessels  which  supply  the  head  and  neck,  part  of  the 
thoracic  wall,  and  the  upper  extremities — viz.  the  innominate,  the  left  common  carotid, 
and  the  left  subclavian  arteries — arise  from  the  aortic  ai'ch. 

The  descending  aorta  (aorta  descendens). — The  thoracic  portion  of  the  de- 
scending aorta  lies  in  the  posterior  mediastinum ;  it  extends  from  the  termination 
of  the  arch,  at  the  lower  border  of  the  left  side  of  the  fourth  dorsal  vertebra,  to 
the  aortic  opening  in  the  diaphragm,  where,  opposite  the  twelfth  dorsal  vertebra, 
it  becomes  continuous  with  the  abdominal  portion.  Its  length  is  from  seven  to 
eight  inches  (17'5  to  20  cm.),  and  its  diameter  diminishes  from  23  mm.  at  its 
commencement  to  21  mm.  at  its  termination. 

Relations. — Immediately  hehiTid  it  is  the  vertebral  column  and  the  anterior 
common  ligament.  It  rests  also  on  the  vena  azygos  minor  superior  and  the  vena 
azygos  minor  inferioi",  whilst  from  its  posterior  aspect  the  aortic  intercostal  branches  are 
given  ofl'. 

In  front  it  is  in  relation,  from  above  downwards,  with  the  root  of  the  left  lung,  the  peri- 
cardivmi  which  separates  it  from  the  back  of  the  left  auricle,  the  oesophagus  with  the  oeso- 
phageal plexus  of  nerves,  and  the  crura  of  the  diaphragm  which  separate  it  from  the  Spigelian 
lobe  of  the  liver.  On  the  left  side  are  the  left  lung  and  pleura.  On  the  i^ight  side  the 
thoracic  duct  and  the  vena  azygos  major  form  immediate  relations  along  its  whole  length. 
The  oesophagus  also  lies  to  the  right  of  the  upper  part  of  the  descending  aorta,  whilst  the 
right  lung  and  pleura  are  in  close  I'elation  below. 

Branches. — Nine  pairs  of  aortic  intercostal  arteries,  two  left  bronchial  arteries,  four 
or  five  oesophageal,  some  small  pericardial,  and  a  few  posterior  mediastinal  branches, 
usually  arise  from  the  descending  aorta. 


THE  ABDOMINAL  AORTA. 

The  abdominal  portion  of  the  descending  aorta  lies  in  the  epigastric  and 
umbilical  regions  of  the  abdomen.  It  extends  from  the  middle  of  the  lower 
border  of  the  last  dorsal  vertebra  to  the  left  side  of  the  body  of  the  fourth  lumbar 
vertebra,  where  it  bifurcates  into  the  right  and  left  common  iliac  arteries.  The 
point  of  division  is  a  little  below  and  to  the  left  of  the  umbilicus,  opposite  a  line 
drawn  transversely  across  the  abdomen  on  a  level  with  the  highest  points  of  the 
iliac  crests. 

At  its  commencement  it  is  21  mm.  in  diameter,  but  after  the  origin  of  two 
large  branches,  the  coeliac  axis  and  the  suijcrior  mesenteric  arteries,  it  diminishes 
considerably,  and  then  retains  a  fairly  uniform  diameter  to  its  termination. 

Relations. —  Behind,    it  is   in  contact  with  the    upper  four    lumbar    vertebrae    and 


THE  ABDOMINAL  AOETA. 


799 


intervening  intervertebral  discs,  the  anterior  common  ligament,  and  the  left  lumbar  veins  • 
the  Inmbar  and  the  middle  sacral  arteries  spring  from  this  aspect  of  the  vessel.  In  front 
and  in  close  relation  with  it,  there  are  from  above  downwards  the  following  structures : 
the  coeliac  axis  and  solar  plexus,  the  pancreas  and  splenic  vein,  the  superior  mesenteric 
arterv,  the  left  renal  vein,  the  third  part  of  the  duodenum,  the  root  of  the  mesentery,  the 
aortic  plexus,  the  inferior  mesenteric  artery,  the  peritoneum  and  coils  of  small  intestine. 
More  superficially  the  stomach,  the  transverse  colon,  and  the  great  and  small  omenta,  are 
in  front.     On  the  mght  side,  in  the  upper  part  of  its  extent,  are  the  thoracic  duct  and 


Hepatic  veins 


Inferior  phrenic  artery 

Suprarenal  body 
Inferior  vena  cava 

Renal  artery 
Renal  vein 

Right  ovarian  vein 
Ovarian  artery 

Ureter 
Psoas  muscle 


Ascending  colon 
Common  iliac  vein 
Common  iliac  artery 
Middle  sacral  artery 
Ileum 

Csecum 


External  iliac 
artery 
External  iliac 
vein 


Urachiis 


CEsophagus 


Crus  of  diaphragm 

inferior  phrenic 
artery 

Suprarenal  body 
Cceliac  axis 
Suprarenal  vein 
Superior 

mesenteric  artery 
Renal  artery 

nal  vein 
Lumbar  arteries 

Ureter 

Left  colic  artery 

Ovarian  artery 
Inferior  mesenteric 
artery 

escending  colon 

soas  muscle 
Common  iliac  artery 
Sigmoid  artery 

Common  iliac  vein 
Superior  hemor- 
rhoidal artery 

Iliac  colon 

Pelvic  colon 

External  iliac 

artery 

External  iliac  vein 

',  \ 

/If 
JjA    Fallopian  tube 

1 

.  1    Uterus 


Bladder 


Fig.  621. — The  Abdominal  Aorta  and  its  Branches. 


receptaculum  chyli,  the  vena  azygos  major,  and  the  right  crus  of  the  diaphragm,  the 
latter  separating  it  from  the  right  semilunar  ganglion  and  from  the  upper  part  of  the 
inferior  vena  cava.  In  its  lower  part  it  is  in  direct  relation  with  the  inferior  vena  cava. 
On  the  left  side,  the  left  crus  of  the  diaphragm  with  the  left  semilunar  ganglion,  and  the 
fourth  part  of  the  duodenum,  are  in  close  relation  with  its  upper  part,  whilst  in  the  lower 
portion  of  its  extent  the  peritoneum  and  some  coils  of  the  small  intestine  are  in  contact 
with  it. 

Branches. — The  branches  form  two  groups,  visceral  and   parietal,  and   each  group 
consists  of  paired  and  unpaired  vessels,  as  follows  :  — ■ 


800 


THE  VASCULAE  SYSTEM. 


1 

Visceral. 

Parietal. 

Unpaired.                        Paired. 

1           Unpaired. 

Paired. 

Coeliac  axis                    Suprarenal 
Superior    mesen-          Reual 

teric 
Inferior     mesen-          Spermatic      or 

teric                               ovarian 

1 

'     Middle  sacral 

1 

Inferior  phrenic 
Lumbar  (four  pairs) 
Common  iliac 

BRANCHES  OF  THE  ASCENDING  AORTA. 
CoRONAKY  Arteries. 

The  coronary  arteries  are  two  in  number,  a  right  and  a  left ;  they  are  distributed 
almost  entirely  to  the  heart,  but  give  also  some  small  branches  to  the  roots  of  the 
great  vessels,  and  to  the  pericardium  (Figs.  613,  614,  and  617). 

The  right  coronary  artery  (a.  coronaria  dextra)  springs  from  the  anterior 
sinus  of  Valsalva.  It  runs  forwards,  between  the  root  of  the  puhnonary  artery 
and  the  right  auricular  appendix,  to  the  auriculo-ventricular  sulcus,  in  which  it 
passes  to  the  right,  and  then,  turning  round  the  margin  of  the  heart,  is  continued  to 
the  left  as  far  as  the  posterior  end  of  the  inferior  interventricular  sulcus,  where  it 
ends  by  dividing  into  two  terminal  branches.  It  is  accompanied  by  branches 
from  the  cardiac  plexus,  and  is  in  relation  with  the  right  coronary  vein. 

Branches. — Of  the  two  terminal  branches,  one,  the  transverse  (ramus  circumflexus),  is  of 
small  size ;  it  is  simply  the  continuation  of  the  main  trunk  which  runs  farther  to  the  left  to 
anastomose  with  the  transverse  l^ranch  of  the  left  coronary  artery.  The  other,  the  interventricular 
(ramus  descendens),  is  much  larger  than  the  transverse  branch.  It  runs  forwards  in  the  inferior, 
interventricular  sulcus,  supplies  both  ventricles,  and  anastomoses,  at  the  apex  of  the  heart,  with 
the  interventricular  branch  of  the  left  coronary  artery. 

In  addition  to  the  terminal  branches  small  aortic  and  pulmonary  twigs  are  distributed  to  the 
roots  of  the  aorta  and  pulmonary  artery  respectively.  A  right  auricular  branch  passes  upwards 
on  the  anterior  surface  of  the  right  auricle,  between  it  and  the  ascending  aorta ;  one  or  more 
preventricular  Ijranches,  of  small  size,  descend  on  the  anterior  surface  of  the  right  ventricle ;  a 
branch  of  larger  size,  the  marginal  artery,  descends  along  the  right  margin  and  gives  branches  to 
both  surfaces  of  the  right  ventricle. 

The  left  coronary  artery  (a.  coronaria  sinistra)  arises  from  the  left  posterior 
sinus  of  Valsalva.  In  its  course  and  distribution  it  resembles  in  many  respects 
the  right  coronary  artery,  the  chief  difference  being  that  it  divides  much  sooner 
into  its  two  terminal  branches  ;  the  trunk  of  the  artery  is  therefore  correspondingly 
short.  From  its  origin  it  runs  forwards  between  the  root  of  the  pulmonary  artery 
and  the  left  auricular  appendix,  and,  reaching  the  auriculo-ventricular  sulcus  at  the 
upper  end  of  the  anterior  interventricular  groove,  divides  immediately  into  trans- 
verse and  interventricular  terminal  branches. 

Branches. — Tla-  transverse  terminal  branch  (ramus  circumflexus)  runs  to  the  left  margin  of 
the  heart,  and  there  turns  to  the  inferior  surface  where  it  comes  into  relation  with  the  coronary 
sinus;  it  ends  by  anastomosing  with  the  transverse  branch  of  the  right  coronary  artery.  It 
supplies  the  left  auricle,  the  left  margin  (jf  the  heart,  and  the  posterior  part  of  the  lower  surface 
of  the  left  ventricle.  The  interventricular  terminal  branch  (ramus  descendens  anterior)  passes 
down  the  anterior  interventricular  sulcus  to  llie  apex  of  the  heart,  where  it  anastomoses  with 
the  interventricular  branch  from  the  right  coronary ;  it  sujjjjlies  both  ventricles,  and  is  accom- 
panied Vjy  cardiac  nerves  and  by  the  great  cardiac  vein. 

A  left  auricular  branch,  or  branches  of  small  size,  j)ass  to  the  wall  of  the  left  auricle,  and  small 
aortic  and  pulmonary  branches  are  also  given  to  the  roots  of  the  aorta  and  pulmonary  artery. 


BKANCHES  OF  THE  ARCH  OF  THE  AORTA. 

The  branches  which  arise  from  the  arch  of  the  aorta  supply  the  head  and  neck, 
the  upper  extremities,  and  part  of  the  body  wall. 

They  are  three  in  number,  viz.   the   innominate,  the   left  common  carotid,  and 


THE  COMMON  CAEOTID  AETEEIES.  801 

the  left  subclavian  arteries.  The  iunominate  is  a  short  truuk  from  the  termination 
of  which  the  right  common  carotid  and  the  right  subclavian  arteries  spring  (Figs. 
620  and  624) ;  thus  there  is  at  first  a  difference  between  the  stem  vessels  of  opposite 
sides,  but  bejond  this  the  subsequent  course  and  the  ultimate  distribution  of  these 
vessels  closely  correspond. 

THE  INNOMINATE  ARTERY. 

The  innominate  artery  (a.  anonyma,  Fig.  620)  arises  behind  the  middle  of  the 
lower  part  of  the  manubrium  sterni,  from  the  convexity  of  the  arch  of  the  aorta 
near  its  right  or  anterior  extremity,  and  terminates  opposite  the  right  sterno- 
clavicular articulation,  where  it  divides  into  the  right  subclavian  and  right  common 
carotid  arteries. 

Course. — The  trunk,  which  measures  from  one  and  a  half  to  two  inches  (37  to 
50  mm.)  in  length,  runs  upwards,  backwards,  and  outwards  in  the  superior 
mediastinum. 

Relations. — Posterior. — It  is  in  contact  behind,  with  the  trachea  below  and  with 
the  right  pleural  sac  above. 

Anterior. — The  left  innominate  vein  crosses  in  front  of  the  lower  part  of  the  arter}'^, 
and  above  this  the  sterno-thjroid  muscle  separates  it  from  the  sterno-hyoid  and  the  right 
stemo-clavicular  joint.  The  remains  of  the  thymus  gland,  which  separate  it  from  the 
manubrium  sterni,  are  also  in  front. 

Lateral. — The  right  innominate  vein  and  the  upper  part  of  the  superior  vena  cava 
are  on  the  right  side  of  the  artery.  On  its  left  side  is  the  origin  of  the  left  common 
carotid  artery,  whilst  at  a  higher  level  the  trachea  is  in  contact  with  it. 

Branches. — As  a  rule  the  innominate  artery  does  not  give  off  any  branches  except 
its  two  terminals,  but  occasionally  it  furnishes  an  additional  branch,  the  thyroidea  ima. 

The  thyroidea  ima  is  an  inconstant  and  slender  vessel.  When  present  it 
sometimes  arises  from  the  arch  of  the  aorta,  but  it  usually  springs  from  the  lower 
part  of  the  innominate.  It  passes  upwards  in  front  of  the  trachea,  through  the 
anterior  part  of  the  superior  mediastinum  and  the  lower  part  of  the  neck,  and  gives  oti' 
branches  to  the  lateral  lobes  and  isthmus  of  the  thyroid  body  and  to  the  trachea. 

THE  AETEEIES  OF  THE  HEAD  AND  NECK. 

The  vessels  distributed  to  the  head  and  neck  are  chiefly  derived  from  the 
carotid  trunks ;  there  are,  however,  in  addition,  other  vessels  which  arise  from  the 
main  arterial  stems  of  the  upper  extremities,  and  it  will  be  advantageous  to 
describe  the  most  important  of  these,  viz.  the  vertebral  arteries,  with  the  carotid 
system.  The  smaller  additional  branches  will  be  considered  along  with  the 
remaining  ]:)ranches  of  the  subclavian  arteries. 

The  carotid  system  of  arteries  consists  on  each  side  of  a  common  carotid  trunk, 
which  divides  into  internal  and  external  carotid  arteries,  from  which  numerous 
branches  are  given  off. 

The  internal  carotid  arteries  are  distributed  almost  entirely  to  the  contents  of 
the  cranial  cavity  internal  to  the  dura  mater,  and  to  the  structures  in  the  cavity 
of  the  orbit.  The  external  carotid  arteries,  on  the  other  hand,  supply  structures  of 
the  head  and  neck  more  externally  situated. 

It  is  to  be  observed,  however,  that  the  vascular  supply  of  the  brain  is  not  wholly 
derived  from  the  internal  carotid  A'essels,  but  that  the  vertebral  arteries  also 
contribute  largely  to  it. 

THE  COMMON  CAROTID  ARTERIES. 

The  right  and  the  left  common  carotid  arteries  are  of  unequal  length.  The 
right  common  carotid  commences  at  the  bifurcation  of  the  innominate  artery, 
behind  the  right  sterno-clavicular  articulation;  the  left  arises  in  the  superior 
mediastinum  from  the  arch  of  the  aorta,  but  each  terminates  at  the  level  of 
the  upper  border  of  the  thyroid  cartilage ;  the  left  artery  has  thus  a  short  intra- 
55 


802  THE  VASCULAK  SYSTEM. 

thoracic  course,  and  so  far  its  relations  call  lor  separate  consideration ;  whilst  in 
the  rest  of  its  course  it  passes,  like  the  right  common  carotid,  upwards  in  the  neck 
and  has  almost  similar  relations. 

Thoracic  Portion  of  the  Left  Common  Carotid. — The  thoracic  or  mediastinal 
portion  of  the  left  common  carotid  artery  (a.  carotis  communis  sinistra)  extends 
trom  the  upper  aspect  of  the  aortic  arch,  a  little  behind  and  to  the  left  of  the 
origin  of  the  innominate  artery,  to  the  left  sterno-clavicular  articulation,  where 
the  cervical  portion  commences.  It  is  about  one  or  one  and  a  half  inches  in 
length  (25  to  37  mm.),  and  it  runs  upwards  and  slightly  outwards  through  the 
upper  part  of  the  superior  mediastinum,  lying  farther  back  than  the  innominate 
artery. 

Relations. — Posterior. — The  vessel  is  in  contact  behind  and  from  below  upwards  with 
the  trachea,  the  left  recurrent  laryngeal  nerve,  the  oesophagus,  and  the  thoracic  duct. 

Anterior. — The  left  innominate  vein  runs  obliquely  across  the  front  of  the  artery,  upon 
which  cardiac  branches  from  the  left  vagus  and  sympathetic  descend  vertically.  These 
structures,  together  with  the  remains  of  the  thymus  gland  and  the  anterior  margins  of  the 
left  lung  and  pleura,  separate  the  artery  from  the  manubrium  sterni,  and  from  the  origins 
of  the  sterno-hyoid  and  sterno-thyroid  muscles. 

Lateral. — The  innominate  artery  below  and  the  trachea  above  are  on  the  right  side. 
The  left  pleura,  and,  on  a  posterior  plane,  the  left  phrenic  and  vagus  nerves  and  the  left 
subclavian  artery  are  on  its  left  side. 

Cervical  Portion  of  the  Left  Common  Carotid  Artery.— The  cervical  part 
of  the  left  common  carotid  artery  is  about  three  and  a  half  inches  long  ;  it  extends 
from  the  left  sterno-clavicular  articulation  to  the  level  of  the  upper  border  of  the 
thyroid  cartilage  and  the  lower  border  of  the  third  cervical  vertebra,  where  it  ends 
by  dividing  into  the  external   and  internal  carotid  arteries. 

Course. — It  runs  upwards,  outwards,  and  backwards,  through  the  muscular  and 
the  lower  part  of  the  carotid  divisions  of  the  anterior  triangle  of  the  neck.  In  the 
lower  part  of  its  extent  it  is  separated  from  its  fellow  of  the  opposite  side  by  the 
trachea  and  the  oesophagus,  and  in  the  upper  part  by  the  relatively  wide  pharynx. 

Relations. — It  is  enclosed,  together  with  the  internal  jugular  vein  and  the  vagus 
nerve,  in  a  sheath  of  deep  cervical  fascia — the  carotid  sheath. 

Posterior. — The  longus  colli  and  scalenus  anticus  below,  and  the  rectus  capitis  anticus 
major  above,  are  separated  from  the  posterior  surface  of  the  artery  and  sheath  by  the 
prevertebral  fascia  and  the  sympathetic  cord.  The  inferior  thyroid  artery  crosses  close 
behind  the  vessel  about  the  level  of  the  first  ring  of  the  trachea  ;  lower  down  the  vertebral 
artery  and  the  thoi-acic  duct  are  posterior  to  it,  and  the  vagus  nerve  lies  behind  and  to  its  - 
outer  side. 

Anterior. — The  descendens  cervicis  nerve  descends  superficial  to  the  artery,  usually 
outside  the  sheath,  but  sometimes  enclosed  in  it.  Opposite  the  sixth  cervical  vertebra  the 
omo-hyoid  muscle  and  the  sterno-mastoid  brancla  of  the  superior  thyroid  artery  cross  the 
carotid  artery,  which  is  overlapped,  above  the  omo-hyoid  muscle,  by  the  anterior  border  of 
the  sterno-mastoid,  and  it  is  fx'equently  crossed,  in  this  part  of  its  extent,  by  the  superior 
thyroid  vein.  Below  the  omo-hyoid  the  artery  is  covered  by  the  sterno-thyroid,  the  sterno- " 
hyoid,  and  the  sterno-mastoid  muscles,  and  it  may  be  overlapped  by  the  lateral  lobe  of  the 
thyroid  body ;  it  is  also  crossed  beneath  the  muscles  by  the  middle  thyroid  vein,  whilst 
occasionally  a  communication  Vjctween  the  common  facial  and  anterior  jugular  veins 
descends  in  front  of  the  artery  along  the  anterior  border  of  the  sterno-mastoid.  Just 
above  the  sternum  the  anterior  jugular  vein  is  in  front  of  the  arter^^,  but  separated  from 
it  by  the  sterno-hyoid  and  sterno-thyroid  muscles. 

Lateral. — The  trachea  and  oesophagus,  with  the  recuiTent  laryngeal  nerve  in  the  angle 
between  them,  are  internal  to  the  lower  part  of  the  artery ;  the  pharynx  and  larynx  are 
internal  to  its  upper  part.  The  carotid  gland  lies  immediately  to  the  inner  side  of  the 
termination  of  the  artery. 

The  internal  jugular  vein  occupies  the  outer  part  of  the  carotid  sheath,  and  lies  not 
only  to  the  outer  side  of  the  artery,  but  also  overlaps  it  in  front,  especially  in  the  lower 
part  of  its  extent. 

Branches. — As  a  rule  no  branches  are  given  off  from  either  of  the  common  carotid 
arteries  except  the  terminal  branches  and  some  minute  twigs  from  each  to  the  correspond- 
ing carotid  sheath  and  carotid  body. 


THE  EXTEENAL  CAEOTID  AETEEY. 


803 


The  right  common  carotid  artery,  as  already  stated,  differs  as  regards  origin 
from  the  left  common  carotid.  In  length  and  general  position  it  corresponds  with 
the  cervical  portion  of  the  left  common  carotid,  and  its  relations  also  are  very 
similar.  Such  differences  as  exist  may  be  briefly  summarised  as  follows : — The 
internal  jugular  vera  on  both  sides  lies  external  to  the  artery ;  on  the  left  side  it 
runs  well  in  front  of  the  carotid  artery  in  the  lower  part  of  the  neck,  whilst  on  the 
right  side  the  vein  is  separated  from  the  outer  surface  of  the  artery  at  its  lower  end 
by  a  well-marked  interval  in  which  the  vagus  nerve  appears.  The  thoracic  duct 
does  not  come  into  relation  with  the  right  common  carotid,  and  there  is  also  a 


Anterior  superficial  temporal  artery 


Tr'ins\prse  facial  arterv 


Posterior  superficial 
temporal  arter 


Superficial  temporal  _ 
artery 

Internal  maxillary 
artery 

Posterior  auricular 
artery 

Posterior  belly  of 
digastric  muscle 


Occipital  artery 
Internal  carotid  artery  - 
External  carotid  artery  - 


Angular  artery 

Lateral  nasal 
arterv 


Septal  artery 
Superior 
coronary  artery 
Inferior 

coronary  artery 
Inferior  labial 
arterv 


Subnient-al 
artery 
Facial  arterv 


Lingual  artery 
Superior  thyroid  artery 

<     liiiMon  carotid  artery 


Subclavian  arterj" 
Suprascapular  artery 


Fig.  6-22. — The  Carotid  and  Subclavian  Arterie.s  and  their'Branches. 

difference  in  the  relations  of  the  recurrent  laryngeal  nerves  to  the  arteries  on  the 
two  sides.  On  the  left  side  the  nerve  crosses  behind  the  mediastinal  part  of  the 
left  artery,  and  lies  internal  to  its  cervical  part,  whilst  the  corresponding  nerve  on 
the  right  side  passes  behind  the  lower  part  of  the  carotid  artery  in  the  neck  to  reach 
its  inner  side,  and  the  oesophagus  has  a  less  intimate  relation  with  the  right  than 
^vith  the  left  common  carotid  artery. 


THE  EXTERNAL  CAROTID  ARTERY. 

The  external  carotid  artery  (a.  carotis  externa,  Eig.  623)  is  the  smaller  of  the  two 
terminal  branches  of  the  common  carotid  •  its  length  is  about  two  and  a  half  inches 
55  « 


804  THE  VASCULAR  SYSTEM. 

(62  mm.)  It  extends  from  the  upper  border  of  the  thyroid  cartilage  to  the  back 
of  the  neck  of  the  mandible,  where  it  terminates  by  dividing  into  the  superficial 
temporal  and  the  internal  maxillary  arteries. 

Course. —  It  commences  in  the  carotid  triangle,  passes  upwards  internal  to  the 
posterior  belly  of  the  digastric  and  the  stylo-hyoid  muscles  to  enter  the  posterior 
part  of  the  submaxillary  triangle,  where  it  disappears  behind  the  lower  part  of  the 
parotid  gland,  and  it  terminates  under  cover,  or  in  the  substance,  of  the  upper  part 
of  the  gland. 

At  its  commencement  it  lies  somewhat  in  front  of  and  to  the  inner  side  of  the 
internal  carotid  artery,  but,  inclining  slightly  backwards  as  it  ascends,  it  becomes 
superficial  to  the  latter  vessel,  and  its  course  is  indicated  by  a  line  drawn  from  the 
lobule  of  the  ear  to  the  posterior  extremity  of  the  great  cornu  of  the  hyoid  bone. 

Relations. — Posterior. — In  the  lower  part  of  its  extent  it  is  in  close  relation  with  the 
internal  carotid,  and  in  the  upper  part  of  its  course  with  the  cartilaginous  portion  of  the 
external  auditory  meatus. 

Lateral. — At  its  commencement  the  fibres  of  the  inferior  constrictor  muscle  are  in  con- 
tact with  its  inner  side,  but  at  a  higher  level  the  structures  which  intervene  between  it 
and  the  internal  carotid — viz.  the  stylo-pharyngeus  muscle,  the  tip  of  the  styloid  process, 
the  stylo-glossus  muscle,  the  glosso-pharyngeal  nerve,  and  the  pharyngeal  branch  of  the 
vagus — -separate  it  from  the  wall  of  the  pharynx  ;  whilst  internal  both  to  it  and  to  the 
internal  carotid  artery  are  the  external  and  internal  laryngeal  branches  of  the  superior 
laryngeal  nerve. 

Superficial. — In  the  carotid  triangle  the  lingual,  ranine,  common  facial,  and  superior 
thyroid  veins  are  superficial  to  it,  and  the  hypoglossal  nerve  crosses  the  artery  immediately 
below  the  origin  of  its  occipital  branch.  On  the  boundary  line  between  the  carotid  and 
the  submaxillary  triangles  the  posterior  belly  of  the  digastric  and  the  stylo-hyoid  muscles 
cover  the  artery,  and  from  the  tip  of  the  mastoid  process  downwards  it  is  overlapped  by 
the  anterior  border  of  the  sterno-mastoid  muscle.  Above  the  posterior  belly  of  the 
digastric  the  parotid  gland  is  superficial  to  the  artery,  while  still  more  superficially  are 
the  superficial  fascia  and  the  skin.  In  the  substance  of  the  parotid  gland  the  temporo- 
maxillary  vein  descends  on  the  outer  side  of  the  artery,  and  the  facial  nerve  crosses  on 
the  outer  side  of  the  vein  at  a  right  angle  to  it. 

Branches. — Eight  branches  arise  fx'om  the  external  carotid  artery  ;  of  these  three — the 
superior  thyroid,  the  lingual,  and  the  facial — spring  from  its  anterior  aspect  in  the  carotid 
triangle ;  two  arise  from  its  posterior  aspect,  viz.  the  occipital  and  the  posterior 
auricular,  the  former  commencing  below  the  posterior  belly  of  the  digastric  and  the  latter 
above  it  ;  one  from  its  inner  side,  viz.  the  ascending  pharyngeal,  which  rises  in  the 
carotid  triangle  ;  and  two  from  its  termination,  viz.  the  superficial  temporal  and  the 
internal  maxillary. 

Branches  of  the  External  Carotid  Artery. 

(1)  Superior  Thyroid  Artery  (a.  thyroidea  superior,  Figs.  622  and  624). — This 
vessel  springs  from  the  front  of  the  lower  part  of  the  external  carotid  artery,  just 
below  the  tip  of  the  great  cornu  of  the  hyoid  bone,  and  terminates  at  the  upper  ex- 
tremity of  the  lateral  lobe  of  the  thyroid  body  by  dividing  into  its  terminal  branches. 

Course. — From  its  commencimient  in  the  carotid  triangle  the  artery  runs  at 
first  forwards  and  a  little  upwards  ;  it  then  turns  downwards  to  its  termination. 

Relations. — Internally  it  is  in  relation  with  the  inferior  constrictor  muscle  and  the 
external  laryngeal  branch  of  the  superior  laryngeal  nerve. 

Superficially  it  is  covered  at  its  origin  by  the  anterior  ])order  of  the  sterno-mastoid; 
afterwards,  for  a  short  distance,  by  fascia,  platysma,  and  skin,  and  in  the  lower  part  of  its 
extent  by  the  omo-hyoid,  the  sterno-hyoid,  and  the  sterno-thyroid  muscles,  and  it  is  over- 
lapped by  an  accompanying  vein. 

Branches. — (1)  In  the  carotid  triangle  (a)  an  infrahyoid  branch  (ramus  hyoideus) 
runs  along  tlie  lower  border  of  the  great  corim  of  the  hyoid  bone,  under  cover  of  the 
thyro-hyoid  muscle,  to  anastomose  with  its  fellow  of  the  opposite  side  and  with  the  supra- 
hyoid branch  of  the  lingual  artery.      It  supplies  the  thyrohyoid  muscle  and  membrane. 

{h)  A  laryngeal  branch  ('a.  laryngea  superior)  runs  forwards  beneath  the  thyro-hyoid 
muscle.  It  pierces  the  thyro-hyoid  membrane  in  company  with  the  internal  laryngeal 
nerve,   supplies   the    muscles,    ligaments,    and   mucous   membrane   of   the    larynx,    and 


BEANCHES  OF  THE  EXTERNAL  CAROTID  ARTERY.     805 

anastomoses  with  its  fellow  of  the  opposite  side,  with  branches  of  the  crico-thyroid  artery, 
and  with  tlie  teriiiiiial  branches  of  the  inferior  thyroid  artery. 

(c)  The  sterno-mastoid  branch  (ramus  sterno-cleidomastoideus)  passes  downwards  and 
backwards  along  the  upper  border  of  the  anterior  belly  of  the  omohyoid  muscle,  and  across 
the  common  carotid  artery  to  the  under  surface  of  the  sterno-mastoid  muscle.  It  anasto- 
moses, in  the  sterno-mastoid,  with  branches  of  the  occipital  and  suprascapular  arteries. 

(2)  In  the  muscular  triangle  (d)  a  crico-thyroid  branch  (ramus  crico-thyroideus)  runs 
forwards,  either  over  or  under  the  sternothyroid,  and  crosses  the  cricothyroid  muscle  to 
anastomose  in  front  of  the  crico-thyroid  membrane  with  its  fellow  of  the  opposite  side,  and, 
by  branches  which  perforate  the  crico-thyroid  membrane,  with  laryngeal  branches  of  the 
superior  and  inferior  thyroid  arteries.     It  supplies  the  adjacent  muscles  and  membrane. 

(e)  The  terminal  branches  are  anterior  and  posterior  respectively. 

The  anterior  terminal  branch  (ramus  anterior),  often  much  larger  than  the  crico- 
thyroid artery,  descends  along  the  anterior  border  of  the  lateral  lobe  of  the  thyroid  body, 
and,  extending  on  to  the  upper  border  of  the  thyroid  isthmus,  anastomoses  with  its  fellow 
of  the  opposite  side.  The  posterior  branch  (ramus  posterior)  descends  along  the  posterior 
border  of  the  lateral  lobe,  and  both  terminal  branches  supply  the  thyroid  body  (rami 
glandulares).  They  anastomose  with  each  other  and  with  branches  from  the  inferior 
thyroid  artery. 

(2)  Lingual  Artery. — The  lingual  artery  (a.  lingualis,  Figs.  622  and  624)  springs 
from  the  front  of  the  external  carotid,  opposite  the  tip  of  the  great  cornu  of  the 
hyoid  bone,  and  terminates,  as  the  ranine  artery,  beneath  the  tip  of  the  tongue, 
where  it  anastomoses  with  its  fellow  of  the  opposite  side. 

Course. — From  its  commencement,  and  whilst  in  the  carotid  triangle,  the  first 
part  of  the  artery  forms  a  loop  with  the  convexity  upwards.  A  second  part  passes 
forwards,  internal  to  the  hyo-glossus  muscle,  immediately  above  the  great  cornu  of 
the  hyoid  bone,  to  the  anterior  border  of  the  muscle,  where  it  gives  off  a  sublingual 
branch.  A  third  part  passes  obliquely  forwards  and  upwards  under  cover  of  the 
anterior  border  of  the  hyo-glossus,  and  a  fourth  part  runs  directly  forwards  on  the 
under  surface  of  the  tongue  to  the  tip.  The  third  and  fourth  parts  are  frequently 
described  together  as  the  ranine  artery  (a.  profunda  linguae). 

Relations. — The  first  part  of  the  lingual  ai'tery  is  crossed  superficially  by  the  hypo- 
glossal nerve,  but  besides  this  it  is  only  covered  by  skin,  fascia,  and  the  platysma;  it  rests 
internally  against  the  middle  constrictor  of  the  pharynx.  In  the  rest  of  its  course  the 
artery  is  for  the  most  part  more  deeply  placed.  The  second  part,  remaining  in  contact 
internally  with  the  middle  constrictor,  passes  internal  to  the  hyo-glossus  muscle,  by  which 
it  is  separated  from  the  hypoglossal  nerve,  the  ranine  vein,  and  the  lower  part  of  the  sub- 
maxillary gland.  The  third  part  ascends  almost  vertically,  parallel  with  and  under  the 
anterior  fibres  of  the  hyo-glossus,  which  is  here  covered  by  the  mylo-hyoid,  and  between  it 
and  the  genio-hyo-glossus.  The  fourth  part  runs  forwards  between  the  inferior  lingualis 
and  the  genio-hyo-glossus  muscles,  and  is  only  covered  on  its  lower  surface  by  the  mucous 
membrane  of  the  tongue.  Thus  the  lingual  artery  at  its  termination,  near  the  frsenum 
linguae,  is  again  comparatively  superficial. 

Branches. — (a)  The  supra-hyoid  (ramus  hyoideus),  a  small  branch  which  arises  in 
the  carotid  triangle  and  runs  along  the  upper  border  of  the  great  cornu  of  the  hyoid  bone. 
It  anastomoses  with  its  fellow  of  the  opposite  side  and  with  the  infra-hyoid  branch  of  the 
superior  thyroid  artery. 

(b)  The  dorsalis  linguae  (ramus  dorsalis  linguee)  is  a  branch  of  moderate  size  which 
arises  from  the  second  part  of  the  ai-tery.  It  ascends  external  to  the  genio-hyo-glossus  to 
the  dorsum  of  the  tongue,  where  it  branches  and  anastomoses  with  its  fellow  of  the  opposite 
side  round  the  foramen  caecum.  It  supplies  the  posterior  part  of  the  tongue  as  far  back 
as  the  epiglottis,  and  sends  branches  backwards  to  the  tonsil  which  anastomose  with  the 
tonsillar  branches  of  the  ascending  palatine  branch  of  the  facial  and  with  the  ascending 
pharyngeal  artery. 

(c)  A  sublingual  branch  (a.  sublingualis)  arises  at  the  lower  part  of  the  anterior  border 
of  the  hyo-glossus  muscle  and  runs  forwards  and  upwax-ds,  between  the  mylo-hyoid  and 
the  genio-hyo-glossus,  to  the  sublingual  gland,  which  it  supplies;  it  also  supplies  the  mylo- 
hyoid, the  genio-hyo-glossus,  and  the  genio-hyoid  muscles,  and  it  anastomoses  with  its 
fellow  of  the  opposite  side,  with  the  continuation  of  the  lingual  by  a  branch  whith  it 
sends  along  the  fraeuum  linguae,  and  through  the  mylo-hyoid  muscle  with  the  submental 
branch  of  the  facial. 

55  & 


80G  THE  VASCULAR  SYSTEM. 

(3)  Facial  Artery. — The  facial  or  external  maxillary  artery  (a.  maxillaris 
externa,  Fig.  622)  springs  from  tlie  front  of  the  external  carotid  immediately  above 
the  lingual,  and  terminates  at  the  side  of  the  nose,  where  it  divides  into  lateral 
nasal  and  angular  branches. 

Course. — It  commences  in  the  carotid  triangle  and  passes  upwards  internal  to 
the  posterior  belly  of  the  digastric  and  the  stylo-hyoid  muscles.  It  turns  over  the 
upper  border  of  the  digastric,  and  runs  forwards  and  downwards  in  a  groove  in  the 
submaxillary  gland  to  the  anterior  border  of  the  lower  margiu  of  the  ramus  of  the 
mandible,  then  it  turns  round  the  lower  border  of  the  body  of  the  mandible,  and  is 
continued  upwards  and  inwards,  in  the  face,  to  its  termination. 

Relations. — In  the  carotid  triangle  the  artery  is  comparatively  superficial,  except 
just  at  its  origin,  which  is  beneath  the  anterior  fibres  of  the  stei'no-mastoid  muscle.  Its 
deep  surface  rests  on  the  middle  and  superior  constrictor  muscles  which  separate  it  from 
the  lower  part  of  the  tonsil.  As  it  passes  into  the  submaxillary  triangle  it  is  crossed  by 
the  stylo-hyoid  muscle  and  by  the  posterior  belly  of  the  digastric.  In  the  submaxillary 
triangle  it  is  embedded  in  a  groove  in  the  posterior  part  of  the  submaxillary  gland,  and  it  is 
separated  by  the  gland  from  the  more  superficially  situated  facial  vein.  In  the  upper  part 
of  the  submaxillary  region  the  artery  is  just  under  cover  of  the  ramus  of  the  lov/er  jaw. 

Turning  round  the  lower  border  of  the  body  of  the  jaw,  which  it  grooves  slightly,  the 
artery  becomes  more  superficial  than  in  any  other  part  of  its  course,  being  covered  only  by 
platysma,  fascia,  and  skin.  At  this  point  the  facial  vein  is  close  behind  the  artery,  and 
lies  on  the  surface  of  the  masseter.  On  the  face  the  artery  lies  between  the  platysma, 
the  risorius,  the  zygomaticus  major,  and  the  levator  labii  superioris,  which,  with  skin 
and  fascia,  are  superficial  to  it,  and  the  buccinator  and  levator  anguli  oris,  which  are 
deeper.  The  termination  of  the  artery  is  in  the  substance  of  the  levator  labii  superioris 
et  alte  nasi. 

The  facial  vein,  though  still  posterior  to  the  arteiy  in  the  face,  runs  a  somewhat 
straighter  course,  and  is  situated  at  some  little  distance  from  it. 

Branches. — -Four  named  branches  are  given  off  in  the  neck,  and  seven  in  the  face. 

In  the  Neck. — («)  The  ascending  palatine  (a.  palatina  ascendens.  Fig.  624)  is  a  small 
artery  which  arises  from  the  facial  as  it  enters  the  submaxillary  triangle.  It  ascei>ds 
internal  to  the  internal  pterygoid  and  upon  the  superior  constrictor,  and,  passing  between 
the  stylo-glossus  and  the  stylo-pharyngeus  muscles,  reaches  the  apex  of  the  petrous  portion 
of  the  temporal  bone,  where  it  turns  downwards  accompanying  the  levator  palati  muscle, 
pierces  the  pharyngeal  aponeurosis,  and  enters  the  soft  palate. 

It  supplies  the  lateral  wall  of  the  upper  part  of  the  pharynx,  the  soft  palate,  the 
tonsils,  and  the  Eustachian  tube,  and  it  anastomoses  with  the  tonsillar  branch  of  the  facial, 
the  dorsalis  linguae,  the  posterior  palatine  branch  of  the  internal  maxillary,  and  with  the 
ascending  pharyngeal  artery  which  sometimes  replaces  it. 

(6)  The  tonsillar  (ramus  tonsillaris),  a  small  artery  which  arises  close  to  the  ascending- 
palatine.  It  passes  upwards  between  the  internal  pterygoid  and  the  stylo-glossus,  pierces 
the  superior  constrictor,  and  terminates  in  the  tonsil.  It  supplies  the  middle  and  superior 
constrictor  muscles,  and  it  anastomoses  with  the  dorsalis  linguae,  with  the  ascending 
palatine  branch,  and  with  the  ascendhig  pharyngeal  artery. 

(c)  The  submaxillary  or  glandular  branch  is  frequently  represented  by  two  or  three 
small  twigs  (rami  glandulares)  which  pass  directly  from  the  facial  trunk  into  the  substance 
of  the  suVjmaxillary  gland. 

(ci)  The  submental  branch  (a.  submentalis)  arises  from  the  facial  just  as  the  latter 
vessel  turns  round  the  inferior  V)order  of  the  body  of  the  jaw.  It  is  the  largest  branch 
given  off  in  the  neck,  and  it  runs  forwards,  on  the  outer  surface  of  the  mylo-hyoid  muscle, 
and  internal  to  the  upper  part  of  the  suVjmaxillary  gland,  to  the  symphysis  menti,  where 
it  turns  upwards  round  the  margin  of  the  jaw,  and  terminates  by  anastomosing  with 
branches  of  the  mental  and  inferior  labial  arteries.  In  the  neck  the  submental  artery 
supplies  the  mylo-hyoid  muscle,  and  the  submaxillary  and  sublingual  glands,  the  latter 
by  a  branch  v/hich  perforates  the  mylo-hyoid  muscle.  It  anastomoses  with  the  mylo- 
hyoid branch  of  the  inferior  dental  and  with  the  sublingual  artery.  In  the  face  it 
supplies  the  structures  of  the  lower  lip,  and  anastomoses  with  the  mental  branch  of 
the  inferior  dental,  and  with  the  infei'ior  labial  and  inferior  coronary  branches  of  the 
facial  artery. 

In  the  Face.  —  (e)  The  inferior  labial  branch  (a.  labialis  inferior)  arises  from 
the  front  of  the  facial  artery  immediately  above  the  lower  border  of  the  mandible. 
ft   runs  forwards  beneath   the   depressor   muscles   of   the   angle   of   the   mouth   and  the 


BKANCHES  OF  THE  EXTEENAL  CAROTID  ARTERY.     807 

lower  lip,  supplying  the  skin,  muscles,  and  mucous  membrane,  and  anastomoses  with  the 
mental  branch  of  the  inferior  dental,  with  the  inferior  coronary,  with  the  submental,  and 
with  its  fellow  of  the  opposite  side. 

(/)  The  inferior  coronary  springs  from  the  front  of  the  facial  artery,  either 
together  with  or  directly  above  the  inferior  labial  branch.  It  runs  forwards  beneath  the 
depressor  anguli  oris,  and  between  the  fibres  of  the  orbicularis  oris  and  the  mucous 
membrane  of  the  lip.  It  supplies  the  adjacent  parts,  and  anastomoses  with  its  fellow  of 
the  opposite  side,  and  with  the  mental,  inferior  labial,  and  submental  arteries. 

ig)  The  superior  coronary  (a.  labialis  superior)  springs  from  the  front  of  the  facial 
beneath  the  zygomaticus  major,  and  runs  forwards  and  inwards  between  the  orbicidaris 
oris  and  the  mucous  membrane  of  the  upper  lip  to  the  middle  line.  It  supplies 
the  skin,  muscles,  and  mucous  membrane  of  the  upper  lip,  and  by  a  septal  hranck  the 
lower  and  front  part  of  the  septum  of  the  nose.  It  anastomoses  with  its  fellow  of  the 
opposite  side,  with  the  lateral  nasal,  and,  on  the  septum  nasi,  with  the  naso-palatine 
branch  of  the  spheno-palatine  artery. 

{h)  The  masseteric  branch,  sometimes  represented  by  several  twigs,  arises  from  the 
posterior  aspect  of  the  facial  trunk  a  short  distance  above  the  lower  margin  of  the  jaw.  It 
passes  upwards  and  backwards  across  the  masseter,  and  anastomoses  with  the  transverse 
facial  artery. 

(i)  The  buccal  is  an  inconstant  branch  which,  when  present,  arises  from  the  back  of 
the  facial  artery  above  the  masseteric  branch,  and  runs  upwards  and  backwards,  across  the 
buccinator  muscle,  to  anastomose  with  the  buccal  branch  of  the  internal  maxillary  artery. 

(k)  The  lateral  nasal,  one  of  the  terminal  branches  of  the  facial  artery,  is  usually 
small.  It  ramifies  on  the  ala  of  the  nose,  supplying  the  skin,  muscles,  and  lower 
lateral  cartilages,  and  anastomosing  with  the  angular  branch,  with  the  nasal  branch  of  the 
ophthalmic,  and  with  branches  of  the  spheno-palatine  artery. 

(/)  The  angular  (a.  angularis),  the  other  terminal  branch  of  the  facial,  continues 
the  dii'ection  of  the  main  trunk  along  the  side  of  the  nose  to  the  inner  angle  of  the 
orbit.  It  supplies  the  skin  and  muscles  of  the  side  of  the  nose,  and  anastomoses  with  the 
lateral  nasal,  and  with  the  nasal  and  palpebral  branches  of  the  ophthalmic  artery. 

(4)  Occipital  Artery  (a.  occipitalis,  Figs.  622,  623,  and  650). — This  vessel  arises 
from  the  back  of  the  external  carotid  artery,  below  the  posterior  belly  of  the 
digastric  muscle,  and  terminates  near  the  inner  end  of  the  superior  curved  line 
of  the  occipital  bone  by  dividing  into  internal  and  external  terminal  branches. 

Course. — It  commences  in  the  carotid  triangle  and  runs  upwards  and  back- 
wards, parallel  with  and  under  cover  of  the  posterior  belly  of  the  digastric,  to  the 
interval  between  the  transverse  process  of  the  atlas  and  the  base  of  the  skull,  where 
it  turns  backwards  in  a  groove  on  the  under  surface  of  the  mastoid  portion  of  the 
temporal  bone ;  as  it  leaves  the  groove  it  alters  its  direction  and  runs  upwards 
and  inwards  on  the  superior  oblique  muscle  to  the  junction  of  the  inner  and 
middle  thirds  of  the  superior  curved  line  of  the  occipital  bone,  where  it  enters  the 
superficial  fascia  of  the  scalp. 

Relations. — In  the  first  or  ascending  part  of  its  course  the  occipital  artery  crosses 
successively  the  internal  carotid  artery,  the  liypoglossal  nerve,  the  vagus  nerve,  the  internal 
jugular  vein,  and  the  spinal  accessory  nerve ;  it  is  covered  by  the  lower  fibres  of  the 
posterior  belly  of  the  digastric  and  the  anterior  part  of  the  sterno-mastoid  muscle,  and, 
close  to  its  origin,  it  is  crossed  by  the  hypoglossal  nerve.  In  the  second,  or  more 
horizontal  part  of  its  course,  it  is  still  under  cover  of  the  sterno-mastoid  and  digastric, 
and  lies  internally  against  the  rectus  capitis  latei'alis,  which  separates  it  from  the 
vertebral  artery.  In  the  third  part  of  its  course  it  rests  upon  the  superior  oblique 
and  complexus,  and  is  under  cover  of  the  sterno-mastoid,  the  splenius  capitis,  and  the 
trachelo-mastoid  muscles.  At  its  termination  it  is  crossed  by  the  great  occipital  nerve  ; 
it  passes  either  through  the  trapezius  or  between  the  trapezius  and  the  sterno-mastoid, 
and  pierces  the  deep  fascia  of  the  neck  before  it  enters  the  superficial  fascia  of  the  scalp. 

Branches. — {a)  Muscular  branches  (rami  musculares)  go  to  the  surrounding  muscles. 
The  sterno-mastoid  branch  (a.  sternocleido-mastoidea)  is  the  most  important  of  this  group  ; 
it  springs  from  the  commencement  of  the  occipital,  is  looped  downwards  across  the  hypo- 
glossal nerve,  and  is  continued  downwards  and  backwards,  below  and  in  front  of  the 
spinal  accessory  nerve,  into  the  sterno-mastoid  muscle  where  it  anastomoses  with  the 
sterno-mastoid  branch  of  the  superior  thyroid  artery. 

(6)  The  meningeal  are  irregular  branches  (rami  meningei)  given  oft'  from  the  occipital 
.     55c 


808  THE  VASCULAR  SYSTEM. 

behind  the  mastoid  process.  They  enter  the  posterior  fossa  of  the  skull  through  the  anterior 
condyloid  foramen,  or  through  the  foramen  lacerum  posterius  ;  they  supply  the  upper  part 
of  the  internal  jugular  vein,  the  lateral  sinus,  and  the  dura  mater  in  the  posterior  fossa  of 
the  skull,  and  they  anastomose  with  the  middle  meningeal  and  with  meningeal  branches 
of  the  ascending  pharyngeal  artery. 

(c)  The  mastoid,  a  small  and  irregular  branch  (ramus  mastoideus)  given  off  from  the 
occipital  behind  the  mastoid  process.  It  enters  the  posterior  fossa  of  the  skull  through 
the  mastoid  foramen,  supplies  the  dura  mater,  and  anastomoses  with  branches  of  the 
middle  meningeal  artery. 

(d)  The  princeps  cervicis  (ramus  descendens)  is  a  large  branch  given  off  from  the 
occipital  upon  the  surface  of  the  superior  oblique.  It  passes  inwards  to  the  outer  border 
of  the  complexus,  where  it  divides  into  superficial  and  deep  branches.  The  superficial 
branch  runs  over  the  complexus,  between  it  and  the  trapezius,  and  anastomoses  with  the 
superficial  cervical  artery.  The  deep  branch  runs  between  the  complexus  and  the  under- 
lying semispinalis  colli,  and  anastomoses  with  branches  of  the  vertebral  and  profunda 
cervicis  arteries. 

(e)  The  auricular  (ramus  auricularis)  is  an  inconstant  branch  which,  as  a  rule,  is 
only  given  oft'  from  the  occipital  when  the  posterior  auricular  artery  is  absent.  It 
ramifies  over  the  mastoid  process,  and  supplies  the  inner  surface  of  the  pinna. 

(/)  The  terminal  branches  (rami  occipitales)  are  internal  and  external.  They  ramify 
in  the  superficial  fascia  of  the  posterior  part  of  the  scalp,  anastomosing  with  the  posterior 
auricular  and  superficial  temporal  arteries.  They  are  both  accompanied  by  branches  of 
the  great  occipital  nerve,  and  the  internal  branch  gives  off  a  parietal  twig,  which  passes 
into  the  skull  through  the  parietal  foramen  to  supply  the  walls  of  the  superior  longitudinal 
sinus,  and  to  anastomose  with  the  middle  meningeal  artery. 

(5)  Posterior  Auricular  Artery  (a.  auricularis  posterior,  Figs.  622,  623). — The 
posterior  aviricular  artery  springs  from  the  back  of  the  external  carotid,  iniT 
mediately  above  the  posterior  belly  of  the  digastric  muscle,  and  terminates  between 
the  mastoid  process  and  the  back  of  the  pinna  by  dividing  into  mastoid  and 
auricular  branches. 

Course  and.  Relations. — Commencing  in  the  posterior  part  of  the  submaxil- 
lary triangle,  it  runs  upwards  and  backwards,  under  cover  of  the  posterior  part  of 
the  parotid  gland,  to  the  interval  between  the  mastoid  process  and  the  external 
auditory  meatus.  It  is  accompanied  in  the  terminal  part  of  its  course  by  the 
posterior  auricular  branch  of  the  facial  nerve. 

Branches, — (a)  Muscular  "branches  are  given  to  the  sterno-mastoid,  the  digastric, 
and  the  styloid  group  of  muscles. 

(b)  Parotid  hranches  pass  to  the  lower  and  posterior  part  of  the  parotid  gland. 

(c)  A  stylomastoid  branch  (a.  stylomastoidea)  is  given  off"  at  the  lower  border  of  the 
external  auditory  meatus.  It  runs  upwards  by  the  side  of  the  facial  nerve,  enters  the 
stylo-mastoid  foramen,  and  ascends,  in  the  aqueduct  of  Fallopius,  to  the  upper  part  of  the 
inner  wall  of  the  tympanum  where  it  terminates  by  anastomosing  with  the  petrosal 
branch  of  the  middle  meningeal  artery.  It  supplies  branches  to  the  external  auditory 
meatu.s,  the  mastoid  cells,  the  vestibule,  and  semicircular  canals,  the  stapedius  muscle,  and 
the  tympanic  cavity  (a.  tympanica  posterior).  One  of  the  latter  branches,  anastomosing 
with  the  tympanic  branch  of  the  internal  maxillary,  forms,  in  young  subjects,  a  vascular 
circle  round  the  membrana  tympani ;  other  branches  anastomose  with  tympanic  branches 
from  the  internal  carotid  and  the  ascending  pharyngeal  arteries,  and  with  the  auditory 
brancli  of  the  basilar. 

(d)  The  auricular,  or  anterior  terminal  branch  (ramus  auricularis),  ascends  beneath 
the  retrahens  aurem  muscle.  It  gives  branches  to  the  scalp  in  the  posterior  part  of  the 
temporal  region,  which  anastomose  with  the  superficial  temporal  and  occipital  arteries, 
and  to  the  pinna.  The  latter  branches  supply  both  surfaces  of  the  pinna,  piercing  or 
turning  round  the  margins  of  the  cartilage  to  gain  the  outer  surface,  and  they  anasto 
mose  with  the  auricular  branches  of  the  superficial  temporal  artery. 

(e)  The  mastoid,  or  posterior  terminal  branch  (ramus  occipitalis),  runs  upwards  and 
backwards  along  the  insertion  of  the  sterno-mastoid  muscle.  It  su})plies  the  sterno- 
ma.stoid,  the  occipito  -  frontalis,  and  the  skin,  and  it  anastomoses  with  the  occipital 
artery. 

(6)  Ascending  Pharyngeal  Artery  (a.  pharyngea  ascendens,  Fig.  624). — This 


BKANCHES  OF  THE  EXTERNAL  CAROTID  ARTERY.  809 

arises  from  the  iuner  surface  of  the  lower  part  of  the  external  carotid,  and  terminates 
in  the  wall  of  the  pharynx  and  in  the  soft  palate. 

Course. — Commencing  in  the  carotid  triangle,  usually  as  the  first  or  second 
branch  of  the  external  carotid,  it  ascends  on  the  wall  of  the  pharynx  to  the  apex 
of  the  petrous  portion  of  the  temporal  bone. 

Relations. — Internally  it  is  in  relation  with  the  constrictor  muscles  of  the  pharynx. 
Behind  it  are  the  transverse  processes  of  the  cervical  vertebrae,  the  sympathetic  cord, 
and  the  rectus  capitis  anticus  major.  Externally  it  is  in  relation  with  the  internal 
carotid  artery,  and  it  is  crossed  by  the  stylo-pharyngeus  muscle,  the  glosso-pharyngeal 
nerve,  and  the  pharyngeal  branch  of  the  vagus. 

Branches. — The  bi-anches  of  this  artery  are  very  irregular  and  inconstant,  but  the 
following  have  received  names  : — 

(a)  Pharyngeal  Branches  (rami  pharyngei). — Small  twigs  which  ramify  on  the  walls 
of  the  pharynx  and  supply  the  middle  and  superior  constrictor  musxles,  the  tonsil,  and 
the  lower  part  of  the  Eustachian  tube.  They  anastomose  with  branches  of  the  superior 
thyroid,  lingual,  and  facial  arteries. 

(b)  Prevertebral. — Small  bi-anches  distributed  to  the  prevertebral  muscles  and  fascia, 
the  deep  cervical  glands,  and  the  large  nerve  trunks.  They  anastomose  with  the  ascending 
cervical  and  vertebral  arteries. 

(c)  Meningeal  (a.  meningea  posterior),  one  or  more  small  branches  which  enter  the 
cranium  by  the  anterior  condyloid,  the  posterior  lacerate,  or  the  middle  lacerate  foramen, 
and  supply  the  dura  mater.  They  anastomose  with  branches  of  the  middle  meningeal  and 
vertebral  arteries. 

((/)  Tympanic  (a.  tympanica  inferior),  a  small  artery  which  accompanies  the  tympanic 
branch  of  the  glosso-pharyngeal  nerve  to  the  tympanic  cavity,  where  it  anastomoses  with 
the  other  tympanic  arteries. 

(e)  Palatine. — A  very  variable  artery  which  sometimes  replaces  the  ascending  palatine 
branch  of  the  facial  artery.  When  present  it  springs  from  the  upper  part  of  the  ascend- 
ing phai'yngeal  artery,  pierces  the  pharyngeal  aponeurosis  above  the  upper  border  of 
the  superior  constrictor'muscle,  and  descends  into  the  soft  palate  with  the  levator  palati 
muscle.  It  supplies  the  mucous  membrane  of  the  supero-lateral  part  of  the  pharyngeal 
wall  and  the  tissues  of  the  soft  palate,  and  it  anastomoses  with  the  palatine  branches  of 
the  internal  maxillary,  the  facial,  and  the  lingual  arteries. 

(7)  Superficial  Temporal  Artery  (a.  temporalis  superticialis,  Fig.  622). — This 
artery,  one  of  the  terminal  branches  of  the  external  carotid,  commences  in  the 
upper  part  of  the  parotid  gland,  behind  the  neck  of  the  mandible,  and  terminates 
in  the  scalp,  from  one  to  two  inches  (25  to  50  mm.)  above  the  zygoma,  by  dividing 
into  an  anterior  and  a  posterior  terminal  branch. 

Course. — The  artery  ascends  over  the  posterior  root  of  the  zygoma,  and  passes 
into  the  superficial  fascia  of  the  temporal  region.  It  is  accompanied  by  the 
auriculo-temporal  nerve  and  by  the  superficial  temporal  vein  which  usually  lies 
posterior  to  it.  As  it  crosses  the  zygoma  it  lies  immediately  beneath  the  skin,  and 
it  may  be  easily  compres-ed  against  the  subjacent  bone. 

Branches. — («)  Parotid,  small  branches  (rami  parotidei)  to  the  upper  part  of  the 
parotid  gland 

(b)  Articular,  to  the  temporo-mandibular  articulation. 

(c)  Auricular. — Small  branches  (rami  auriculares  auteriores)  to  the  outer  surface  of 
the  pinna  and  to  the  external  auditory  meatus.  They  anastomose  on  the  surface  of  the 
pinna  with  branches  of  the  posterior  auricular  artery,  and  in  the  external  meatus  with 
branches  of  the  internal  maxillary  artery. 

(d)  Transverse  Facial  (a.  transversa  faciei). — A  branch  of  moderate  size  which  rises  in 
the  substance  of  the  parotid  gland.  It  emerges  from  the  upper  part  of  the  anterior 
border  of  the  gland,  runs  forwards  across  the  masseter,  below  the  zygoma  and  above 
Stenson's  duct,  accompianied  by  the  infra-orbital  branches  of  the  facial  nerve  which  may 
lie  either  above  or  below  it.  It  is  distributed  to  the  parotid  gland,  the  masseter,  Stenson's 
duct,  and  the  skin,  and  it  terminates  in  branches  which  anastomose  with  the  infra -orbital 
and  buccal  branches  of  the  internal  maxillaiy  artery,  and  with  the  buccal  and  masseteric 
branches  of  the  facial  arteiy. 

(e)  Middle  Temporal  (a.  temporalis  media). — A  branch  which  usually  springs  fi'om  the 
superficial  temporal   in  the  parotid   gland.     It   crosses  the  zygoma,  pierces  the  temporal 


810 


THE  VASCULAK  SYSTEM. 


fascia  and  the  temporal  muscle,  and  terminates  in  the  temporal  fossa  by  anastomosing 
with  the  deep  temporal  branches  of  the  internal  maxillary  ai-tery. 

{f)  Orbital  (a.  zygomatico-orbitalis).  —  This  branch  may  spring  directly  from  the 
superficial  temporal,  but  it  is  frequently  a  branch  of  the  middle  temporal.  It  runs 
forwards  above  the  zygoma  between  the  two  layers  of  the  temporal  fascia.  It  supplies 
branches  to  the  orbiculai-is  palebrarum,  and  anastomoses,  through  the  malar  bone  and 
round  the  outer  margin  of  the  orbit,  with  the  lachrymal  and  palpebral  bx-anches  of  the 
ophthalmic  artery. 

ig)  The  anterior  terminal  branch  (rauuis  frontalis)  runs  forwards  and  upwards,  in  a 
tortuous  course,  through  the  superficial  fascia  of  the  scalp  towards  the  frontal  eminence, 
lying  at  first  upon  the  temporal  fascia,  and  then  upon  the  epicranial  aponeurosis.  It 
supplies  the  frontalis  and  the  orbicularis  palpebrarum,  and  anastomoses  with  the  lachrygnal 


Posterior  brand 
of  mid<lle  men-  - 

ingeal  artery 

Suiierftcial  teni-, 

poral  artery 

Internal  maxil- 
lary artery 

Occipital  artery 

Inferior  dental 
artery 

.Mj'lo-hyoid  arteiy  — 

Posterior  auricular 
artery 

Stenio-inastoid  muscle  — 

Levator  anguli 

scapulie  muscle 

Trapezius  muscle     - 

Occipital  artery-  -- 

External  carotid  artery 
Facial  artery- 
Lingual  artery 
Internal  carotid  artery 
Scalenus  medius  muscle 

Superior  thyroid  artery 

Common  carotid  artery 

Fiu.  623.— The  E.xternal  Carotid,  Internal  Ma.\ii,lahv,  and 


Anterior  meningeal 

artery 
Anterior  branch  of 
middle  meningeal 
artery 

Deep  temporal 
'^arteries 

Infraorbital 
artery 

Middle  menin- 
V"  geal  artery 

\     Small  nienin- 
\   g6al  artery 


Posterior  superior 
eiital  artery 

Buccal  artery 


Mental  artery 


Submental  artery 


Meningeal  Arteries. 


and  supraorbital  branches  of  the  ophthalmic  artery,  with  the  ])Osterior  terminal  branch  of 
the  superficial  tciiiporal,  and  with  its  fellow  of  the  op|)osite  side. 

(A)  Tiie  posterior  terminal  branch  (ramus  ])arietalis),  less  tortuous  than  the  anterior, 
runs  upwards  and  backwards  in  tiie  superficial  fascia  of  the  scalp.  It  anastomoses, 
anteriorly,  with  the  anterior  terminal  branch,  posteriorly  with  the  posterior  auricular 
and  occipital  arteries,  and,  across  the  middle  line,  with  its  fellow  of  the  opposite  side.  It 
supplies  the  skin  and  fascia,  and  tlie  attraliens  and  attolleus  aurem  muscles. 

(8)  Internal  Maxillary  Artery  (a.  inaxillaris  interna). — The  internal  maxillary 
arti'ry  commences  in  the  jtarotid  gland  behind  IIk;  ueck  of  the  lower  jaw,  and 
terminates  in  tlie  spheno-maxillary  fossa. 

Course  and  Relations. — Although  tlie  internal  maxilbiry  artery  is  only  a 
short  trunk  it  has  many  important  relations,  in  the  consideration  of  which  it  is 
convenient  to  arbitrarily  divide  the  vessel  int(j  three  parts.  The  first  part  extends 
from  the  back  of  the  neck  of  the  mandible  forwards  into  the  zygomatic  fossa  as 


BEANCHES  OF  THE  EXTEENAL  CAEOTID  AETEEY.  811 

far  as  the  lower  border  of  the  external  pterygoid  muscle.  It  lies  between  the 
spheuo-mandibular  Hgameut  and  the  neck  of  the  jaw,  along  with  the  auriculo- 
temporal nerve  and  the  internal  maxillary  veiu.  The  second  part  is  in  the  zygo- 
matic fossa,  and  ascends  upwards  and  forwards.  It  may  lie  superficial  to,  or  under 
cover  of,  the  lower  head  of  the  external  pterygoid  muscle.  In  the  former  case  it 
is  situated  between  the  temporal  and  external  pterygoid  muscles,  and  in  the  latter 
between  the  external  pterygoid  muscle  and  the  branches  of  the  third  division  of 
the  fifth  nerve.  The  third  part  passes  between  the  upper  and  the  lower  heads 
of  the  external  pterygoid,  through  the  pterygo-maxillary  fissure  and  into  the 
spheno-maxillary  fossa. 

Branches. — From  the  first  part.z—{a)  Deep  auricular  (a.  auricularis  profunda),  a 
small  branch  which  rises  in  the  parotid  gland  and  passes  upwards  to  enter  the  external 
auditory  meatus.  It  supplies  the  temporo-rnandibular  joint,  the  parotid  gland,  and  the 
external  meatus,  and  anastomoses  with  branches  of  the  superficial  temporal  and  posterior 
auricular  arteries 

{b)  The  tympanic  (a.  tympanica  anterior),  a  variable  and  small  branch  which  com- 
mences in  the  parotid  gland.  It  runs  upwards  and  backwards,  traverses  the  Glasserian 
fissure,  and  enters  the  tympanum  through  its  outer  wall.  In  the  tympanic  cavity  it 
anastomoses  with  tympanic  branches  from  the  intei'nal  carotid  and  the  ascending 
pharyngeal  arteries,  and  with  the  stylo-mastoid  branch  of  the  posterior  auricular,  forming 
with  the  latter,  in  young  subjects,  a  circular  anastomosis  round  the  tympanic  membrane. 

(c)  Middle  Meningeal  (a.  meningea  media). — The  largest  branch  of  the  internal 
maxillary.  It  ascends  between  the  external  pterygoid  muscle  and  the  spheno-mandibular 
ligament,  and  passes  between  the  two  roots  of  the  auriculo-temporal  nerve  and  throiigh 
the  foramen  spinosum,  to  enter  the  middle  fossa  of  the  cranial  cavity.  Before  it  enters 
the  skull  it  lies  behind  the  third  division  of  the  fifth  nei've,  and  is  accompanied  by 
two  venee  comites  which  also  pass  through  the  foramen  spinosum.  In  the  middle  cranial 
fossa  it  passes  forward,  and  upwards  for  a  short  distance,  in  a  groove  on  the  great  wing  of 
the  sphenoid,  between  the  dura  mater  and  the  bone,  and  divides  into  anterior  and 
posterior  terminal  branches. 

Branches. — (i.)  Petrosal  (ramus  petrosus  superficialis). — A  small  branch  which  arises  from  the 
middle  meningeal  t^ooii  after  it  enters  the  cranium.  It  passes  through  the  hiatus  Fallojiii  and 
anastomoses  with  the  stylo-mastoid  branch  of  the  posterior  auricular  artery  ;  it  also  sends  some 
small  branches  into  the  tympanic  cavity 

(ii.)  Gasserian. — Minute  branches  which  supply  the  Gasserian  ganglion  and  the  roots  of  the 
fifth  cranial  nerve. 

(iii.)  Tympanic  (a.  tympanica  superior). — A  small  twig  which  reaches  the  tympanic  cavity 
through  the  canal  for  the  tensor  tympani  muscle,  or  through  the  petro-scpiamous  suture. 

(iv.)  Orbital — An  anastomosing  branch  which  occasionally  arises  from  the  anterior  terminal 
branch.  It  jjasses  through  the  foramen  lacerum  anterius  into  the  orbit,  and  anastomoses  with  the 
lachrymal  artery. 

(v.)  Anterior  terminal,  the  larger  of  the  two  terminal  branches,  jjasses  upwards  along  the 
great  wing  of  the  sphenoid  to  the  antero-inferior  angle  of  the  j^arietal  bone,  where  it  is  sometimes 
enclosed  in  a  distinct  bony  canal ;  it  is  continued  upwards  a  short  distance  behind  the  anterior 
border  of  the  parietal  bone  almost  to  the  vertex  of  the  skull,  sending  branches  forwards  into  the 
anterior,  and  backwards  towards  the  posterior  cranial  fossa. 

(vi.)  The  posterior  terminal  branch  passes  backwards  from  the  great  wing  of  the  sphenoid  to 
the  scpiamous  part  of  the  temporal  bone,  beyond  which  it  ascends  to  the  middle  of  the  inner 
surface  of  the  parietal  bone.  It  sends  branches  upwards  to  the  vertex,  and  backwards  towards 
the  posterior  cranial  fossa. 

By  means  of  its  various  branches  the  middle  meningeal  artery  anastomoses  wdth  its  fellow  of 
the  opposite  side,  with  meningeal  branches  from  the  occipital,  ascending  pharyngeal,  ophthalmic, 
and  lachrymal  arteries ;  also  with  the  stylo-mastoid  branch  of  the  posterior  auricular,  the  small 
meningeal  artery,  with  the  deep  temporal  arteries  through  the  substance  of  the  temporal  bone, 
and  with  its  fellow^  of  the  opposite  side. 

(d)  A  small  meningeal  branch  (ramus  meiringeus  accessorius)  may  arise  either 
directly  from  the  first  part  of  the  internal  maxillary  or  from  its  middle  meningeal  branch. 
It  passes  upwards,  on  the  inner  side  of  the  external  pterygoid  muscle,  enters  the  middle 
fossa  of  the  skull  through  the  foramen  ovale,  supplies  the  Gasserian  ganglion  and  the 
dura  mater,  and  terminates  by  anastomosing  with  branches  of  the  middle  meningeal  and 
internal  carotid  arteries. 

(e)  The  inferior  dental  (a.  alveolaris  inferior)  is  a  branch  of  moderate  size  which 
passes  downwards  between  the  spheno-mandibular  ligament  and  the  mandible  to  the 
mandibular  foramen.      It  is  accompanied  by  the  inferior  dental  nerve  which  lies  in  front 


812  THE  VASCULAR  SYSTEM. 

After  entering  the  foramen  it  descends  in  the  mandibular  canal,  and  terminates  at  the 
mental  foramen  by  dividing  into  mental  and  incisive  branches. 

Branches. — Before  it  euter.s  tlie  mandibular  foramen  it  gives  off  two  brandies. 

(i.)  The  lingual,  a  small  twig  to  the  buccal  mucous  membrane  which  accompanies  the  lingual 
nerve,  (ii.)  The  mylo-hyoid  (ramus  mj'lohoideus),  a  small  branch  which  is  given  off  immediately 
above  the  mandibular  foramen.  It  jnerces  the  spheno-mandilnilar  ligament,  and  descends  in  the 
mylo-hyoid  groove,  in  company  with  the  mylo-hyoid  nerve,  to  the  floor  of  the  mouth,  where  it 
anastomoses,  on  the  superficiarsurface  of  the  mylo-hyoid  muscle,  with  the  submental  branch  of 
the  facial  artery. 

In  the  maudiljular  canal  the  following  branches  are  given  off : — 

(i.)  Molar  branches  to  the  molar  teeth,  (ii.)  Bicuspid  branches  to  the  bicuspid  teeth,  (iii.)  The 
incisive  terminal  branch,  which  supplies  the  incisor  teeth  and  anastomoses  Avith  its  fellow  of  the 
opposite  side,  (iv.)  The  mental  terminal  branch  (a.  mentalis),  which  passes  through  the  mental 
foramen,  emerges  beneath  the  depressor  labii  inferioris,  and  anastomoses  with  its  fellow  of  the 
opposite  side,  with  the  inferior  coronary,  the  inferior  labial,  and  with  the  submental  arteries. 

From  the  second  part. — {a)  The  masseteric  (a.  masseterica),  a  small  branch  which 
passes  directly  outwards,  through  the  sigmoid  notch,  to  the  deep  surface  of  the  masseter 
muscle.  It  anastomoses  in  the  substance  of  the  muscle  with  branches  of  the  transverse 
facial  and  with  the  masseteric  branches  of  the  facial  artery. 

(6)  Deep  Temporal. — Two  in  number,  anterior  (a.  temporalis  profunda  anterior) 
and  posterior  (a.  temporalis  profunda  posterior).  They  ascend  between  the  temporal 
muscle  and  the  squamous  portion  of  the  temporal  bone,  supplying  the  muscle  and 
anastomosing  with  the  temporal  and  lachrymal  arteries,  and,  through  the  substance  of 
the  temporal  bone,  with  the  middle  meningeal  artery. 

(c)  Small  pterygoid  branches  (rami  pterygoidei)  supply  the  internal  and  external 
pterygoid  muscles. 

(d)  The  buccal  (a.  buccinatoria),  a  long,  slender  branch  Avhich  passes  obliquely  forwards 
and  downwards  with  the  long  buccal  nerve.  It  supplies  the  buccinator  muscle,' the  skin 
and  mucous  membrane  of  the  cheek,  and  anastomoses  with  the  buccal  branch  of  the 
facial  artery. 

From  the  third  part. — (a)  A  posterior  superior  dental  branch  (a.  alveolaris  superior 
posterior)  descends  in  the  zygomatic  fossa,  on  the  posterior  surface  of  the  superior 
maxilla,  and  ends  in  branches  which  supply  the  molar  and  bicuspid  teeth  and  the  mucous 
membrane  of  the  antrum,  they  also  give  twigs  to  the  gums  and  to  the  buccinator  muscle. 

Ih)  An  infra-orbital  branch  (a.  infra-orbitalis)  commences  in  the  spheno-maxillary  fossa. 
It  enters  the  orbit  through  the  spheno-maxillary  fissure,  and  runs  forwards  in  the  infra- 
orbital groove  and  canal  to  the  infra-orbital  foramen,  through  which  it  passes  to  emerge  on 
the  face  beneath  the  levator  labii  superioris.  Whilst  in  the  infra-orbital  groove  it  gives 
branches  to  the  inferior  rectus,  the  inferior  oblique  and  the  lachrymal  gland.  In  the  infra- 
orbital canal  it  gives  small  twigs  to  the  incisor  and  canine  teeth  (aa.  alveolares  superiores 
anteriores)  and  to  the  antrum.  In  the  face  it  sends  branches  upwards  to  the  lower 
eyelid,  to  the  lachrymal  sac,  and  to  the  nasal  process  of  the  superior  maxilla,  which 
anastomose  with  branches  of  the  ophthalmic  and  facial  arteries  ;  other  branches  run 
downwards  to  the  upper  lip,  where  they  anastomose  with  the  superior  coronary  artery  ; 
lastly,  some  branches  run  outwards  into  the  cheek  to  unite  with  the  transverse  facial  and 
the  buccal  arteries. 

(c)  The  posterior  or  descending  palatine  (a.  palatina  descendens)  runs  downwards 
through  the  spheno-maxillary  fossa,  passes  through  the  posterior  palatine  canal,  and  reaches 
the  mucous  membrane  of  the  roof  of  the  mouth,  where  it  runs  forwards,  internal  to  the 
alveolar  process,  to  terminate  in  a  small  branch  which  ascends  through  the  anterior 
palatine  fossa  and  Stensen's  canal  and  anastomoses  with  the  spheno-palatine  branch  of 
the  internal  maxillary  artery.  As  it  descends  it  gives  off  several  small  twigs  which  pass 
through  the  accessory  palatine  canals  to  supply  the  soft  palate,  and  to  anastomose  with 
the  ascending  palatine  and  tonsillar  branches  of  the  facial  and  with  the  ascending 
pharvngcal  artery.  In  its  course  forwards  in  the  roof  of  the  mouth  it  supplies  the  gums 
and  the  mucous  membrane  of  the  hard  palate,  and  also  the  ])alate  and  superior  maxillary 
bones. 

(d)  The  Vidian  (a.  canalis  pterygoidei)  is  a  long,  slender  branch  which  runs  back- 
wards through  the  Vidian  canal  with  the  Vidian  nerve.  It  supplies  branches  to  the 
upper  part  of  the  pharynx,  to  the  levator  and  tensor  palati  muscles,  and  to  the  Eustachian 
tuVje.  One  of  the  latter  branches  passes  along  the  wall  of  the  Eustachian  tube  to  the 
tympanic  cavity,  where  it  anastomoses  with  the  other  tympanic  arteries. 

(e)  The  pterygopalatine  is  a  small  artery  which  runs  backwards,  with  the  pharyngeal 
branch  of  Meckel's  ganglion,  to  the  roof  of  the  pharynx.     It  supplies  the  upper  and  back 


THE  INTERNAL  CAROTID  ARTERY. 


813 


part  of  the  roof  of  the  nose,  the  roof  of  the  pharynx,  the  sphenoidal  sinus,  and  the  lower 
part  of  the  Eustachian  tube,  and  anastomoses  with  the  Vidian  branch  of  the  internal 
carotid. 

{/)  The  spheno-palatine  branch  (a.  spheno-palatina)  springs  from  the  termination  of 
the  internal  maxillary  artery.  It  passes  inwards  through  the  spheno-palatine  foramen 
into  the  nasal  cavity,  where  it  divides  into  many  branches.  One  of  these,  the  internal 
nasal  or  naso-palatine,  which  is  sometimes  looked  upon  as  the  continuation  of  the  artery, 
crosses  the  back  part  of  the  roof  of  the  nose,  and  descends  in  a  groove  on  the  vomer  to 
the  incisive  foramen,  where  it  anastomoses  with  the  termination  of  the  posterior  palatine 
artery  and  with  the  septal  branch  of  the  superior  coronary.  The  outer  or  external  nasal 
branches  of  the  spheno-palatine  artery  supply  the  greater  part  of  the  outer  wall  of  the 
nasal  fossa  and  the  cavity  of  the  antrum,  anastomosing  with  branches  of  the  infraorbital, 
ethmoidal,  and  lateral  nasal  arteries.  Branches  are  also  distributed  to  the  ethmoidal  cells, 
to  the  sphenoidal  sinus,  and  to  the  upper  part  of  the  pharynx. 

THE  INTERNAL  CAROTID  ARTERY. 

The  internal  carotid  artery  (a.  carotis  interna,  Figs.  622,  624,  and  627)  com- 
mences at  tlie  termination  of  the  common  carotid,  opposite  the  upper  border  of  the 


Common 


Vertebral  artery 

Profunda 
cenicis  artery" 
Superior  inter 
costal  artery- 


Anastomosis 
with  first 
aortic  inter- 
costal artery 


Vertebral  arteri«'s 

Internal  carotid  artery^  _ 

Ascending  pharyngeal 
artery 
Ascending  palatine  artery — 
Stylo-glossus  muscle  ~_ 
Stylo-pharyngeus  muscle  - 
Posterior  auricular  artery. 


Frontal  artery 
Nasal  artery 
Ciliarv  arteries 


acial  arterj' 


Occipital  artery 
Facial  artery- 
Lingual  artery 
External  carotid  artery 
Superior  thyroid  arterj- 


t-arotid 
arterv 


—   Thyroid  axis  artery 

Subclavian  artery 

—    Internal  mammary  artery 

Innominate  artery 


624.— The  Carotid,  Subclavian,  and  Vektebhal  Arteries  and  their  Main  Branches. 

thyroid  cartilage,  and  terminates  in  the  middle  fossa  of  the  skull,  close  to  the 
commencement  of  the  fissure  of  Sylvius,  where  it  divides  into  the  middle  and 
anterior  cerebral  arteries. 

Course.— It  passes  through  the  carotid  and  submaxillary  triangles,  traverses 
the  carotid  canal  of  the  temporal  bone,  crosses  the  upper  part  of  the  foramen  lacerum 
medium,  and  runs  in  the  outer  wall  of  the  cavernous  sinus  in  the  middle  fossa  of  the 
skull. 

At  its  origin  it  hes  behind  and  to  the  outer  side  of  the  external  carotid,  but  as 


814  THE  VASCULAR  SYSTEM. 

it  asceuds  internal  to  the  posterior  belly  of  the  digastric  aud  the  stylo-hyoid  it  gets 
to  the  inner  side  of  that  vessel.  After  entering  the  submaxillary  triangle  it  ascends, 
in  relation  with  the  posterior  surface  of  the  parotid  gland,  to  the  carotid  canal  in 
the  temporal  bone,  through  which  it  passes  to  the  apex  of  the  petrous  portion  of 
the  temporal  bone,  where  it  turns  upwards,  through  the  upper  part  of  the  foramen 
lacerum  medium,  into  the  middle  cranial  fossa.  It  then  runs  forwards  in  the  outer 
wall  of  the  cavernous  sinus  to  the  lower  root  of  the  small  wing  of  the  sphenoid, 
there  it  turns  upwards  and  then  backwards  and  outwards  to  its  termination. 

Relations. — Tlie  relations  of  the  various  parts  of  the  artery  require  separate 
consideration. 

In  the  Xtch. — Foaterior. — The  rectus  capitis  anticus  major,  the  prevertebral  fascia,  and 
the  sympatlietic  cord,  separate  it  fi'om  the  transverse  processes  of  the  cervical  vertebrae, 
and  somewhat  to  its  outer  side  are  the  internal  jugular  vein  aud  the  vagus  nerve.  The 
spinal  accessory  and  the  glosso-pharyngeal  nerves  are  also  behind  and  to  the  outer  side  of 
the  artery  for  a  short  distance  in  the  upper  part  of  the  neck,  and  they  intervene  between 
it  and  the  internal  jugular  vein.  Internal  or  deep  to  the  internal  carotid  is  the  external 
carotid  artery  for  a  short  distance  below,  and  afterwards  the  wall  of  the  pharynx,  the 
ascending  pharyngeal  artery,  the  pharyngeal  plexus  of  veins,  and  the  external  and  internal 
laryngeal  nerves.  Just  before  it  enters  the  temporal  bone  the  levator  palati  muscle  is  to 
its  inner  side.  External  or  superficial  to  it  are  the  sterno-mastoid,  skin,  and  fascia,  and 
it  is  crossed  beneath  the  sterno-mastoid  from  below  upwards  by  the  hypoglossal  nerve, 
the  occipital  artery,  and  the  posterior  auricular  artery.  It  is  also  crossed  more  super- 
ficially by  the  digastric  and  stylo-hyoid  muscles,  and  in  the  upper  part  of  its  extent  it  is 
covered  by  tlie  posterior  part  of  the  parotid  gland.  Passing  obliquely  across  its  anterior 
and  outer  surface,  and  separating  it  from  the  external  carotid  artery,  are  the  following 
structures,  viz.  :  the  stylo-pharyngeus,  the  tip  of  the  styloid  process  or  the  stylo-glossus 
muscle,  and  the  stylo-hyoid  ligament,  the  glosso-pharyngeal  nerve,  the  pharyngeal  branch 
of  the  vagus,  and  some  sympathetic  twigs. 

In  the  Carotid  Canal. — The  artery,  as  it  passes  upwards  and  inwards,  is  in  front  of  and 
below  the  cochlea  and  the  tympanum  ;  behind  and  internal  to  the  canals  for  the  Eustachian 
tube  and  the  tensor  tympani ;  and  below  the  Gasserian  ganglion.  The  thin  lamina  of  bone 
which  separates  it  from  the  tympanum  is  frequently  perforated,  and  that  between  it  and 
the  Gasserian  ganglion  is  not  infrequently  absent.  In  its  course  through  the  canal  it  is 
accompanied  by  small  veins  and  nerves.  The  veins  are  tributaries  from  the  tympanum, 
which  commmiicate  above  with  the  cavernous  sinus  and  below  with  the  internal  jugular 
vein.  The  nerves  are  the  upward  continuations  of  the  sympathetic  cord  ;  they  form  two 
plexuses — one  on  the  outer  side  of  the  artery,  the  carotid  plexus,  and  one  on  the  inner 
side,  the  cavernous  plexus. 

As  it  enters  the  cavity  of  the  cranium  the  internal  carotid  artery  pierces  the  external 
layer  of  the  dui-a  mater  and  passes  between  the  lingula  and  the  sixth  cranial  nerve 
externally,  and  the  posterior  petrosal  process  of  the  body  of  the  sphenoid  internally. 

In  the  Cranial  Cavity. — The  artery  runs  forwards  in  the  oxiterwallof  the  cavernous  sinus 
in  relation  with  the  third,  fourth,  the  ophthalmic  division  of  the  fifth,  and  the  sixth  cranial 
nerves  externally,  and  with  the  endothelial  wall  of  tlie  sinus  internally.  When  it  reaches 
the  lower  root  of  the  small  wing  of  the  sphenoid  it  turns  upwards  to  the  inner  side  of 
the  anterior  clinoid  process,  pierces  the  inner  layer  of  the  dura  mater,  and  comes  into 
close  relation  with  the  under  sui'face  of  the  optic  nerve  immediately  behind  the  optic 
foramen.  It  then  turns  abruptly  backwards  beneath  the  optic  nerve,  and  on  the  inner  side 
of  the  anterior  clinoid  process  which  it  frequently  grooves ;  inclining  outwards,  it  runs 
between  the  second  and  third  nerves,  and  beneath  the  anterior  perforated  space,  to  the 
inner  end  of  the  stem  of  the  Sylvian  fissure,  where  it  turns  upwards,  at  some  distance 
from  the  outer  side  of  the  optic  chiasma,  and,  after  piercing  the  arachnoid,  divides  into 
its  two  terminal  branches,  the  anterior  and  middle  cerebral  arteries. 

Branches  of  the  Internal  Carotid  Artery. 

Branches  are  given  off  from  the  internal  carotid  in  the  temporal  bone  and  in 
the  cranium,  but,  as  a  rule,  no  branches  are  given  off  in  the  neck. 

In  the  Temporal  Bone. — (1)  A  tympanic  branch  (ramus  carotico-tympanicus),  very 
small,  perforates  the  posterior  wall  of  the  can)tid  canal,  and  anastomoses  in  the  tympanum 
with  the  stylo-mastoid  artery  and  with  the  tympanic  branches  of  the  internal  maxillary 
and  ascending  phaiyngeal  arteries. 


BKANCHES  OP  THE  INTEENAL  CAEOTID  AETEEY. 


815 


(2)  The  Vidian  is  a  small  and  inconstant  branch  which  accompanies  the  great 
deep  petrosal  nerve  in  the  Vidian  canal  ;  it  anastomoses  with  the  Vidian  branch  of  the 
internal  maxillary  artery. 

hi  the  Cranium. — (1)  Cavernous,  small  branches  to  the  walls  of  the  cavernous  sinus 
and  to  the  third,  fourth,  fifth,  and  sixth  nerves. 

(2)  Gasserian,  minute  twigs  which  sujjply  the  Gasserian  ganglion. 

(3)  Pituitary  branches  pass  to  the  pituitary  body. 

(4)  Meningeal  branches  ramify  in  the  dura  mater  of  the  middle  cranial  fossa,  anasto- 
mosing with  the  branches  of  the  middle  and  small  meningeal  arteries. 

(5)  Ophthalmic  Artery  (a.  ophthalmica,  Eig.  624).  —  This  artery  springs 
from  the  front  and  inner  side  of  the  internal  carotid  as  it  turns  upwards  on  the 
inner  side  of  the  anterior  clinoid  process.  It  passes  forwards  and  outwards,  beneath 
the  optic  nerve  and  through  the  optic  foramen  into  the  orbital  cavity.  In  the 
orbit  it  runs  forwards  for  a  short  distance  on  the  outer  side  of  the  optic  nerve,  and 
it  is  in  relation  externally  with  the  lenticular  ganglion  and  the  external  rectus 
muscle ;   turning  upwards  and  inwards,  it  crosses  between  the  optic  nerve  and 


Middle  internal  frontal  artery      Corpus  callosum    Septum  lucidum 


Posterior  internal  frontal  artery 


eto-occipital 
rtery 


Internal  orbital 
artery 


Anterior  cerebral 
artery 


External  orbital  arterj 


Middle  cerebral  aitei> 
Temporal  branch  of  middle  cerebral 


Calcarine  artery 
Temporal  branches  of  posterior  cerebral 


Posterior  cer-     Crus 
ebral  artery      cerebri 

Fig.  625. — Distribution  of  the  Cerebral  Arteries  on  the  Mesial,  Tentorial,  and  Inferior 
Surfaces  of  the  Cerebral  Hemlspheres. 

The  auterior  cerebral  artery  is  coloured  green,  the  middle  cerebral  artery  red,  and  the 
posterior  cerebral  artery  orange. 

the  superior  rectus  to  the  inner  wall  of  the  orbit,  where  it  turns  forwards  to 
terminate  at  the  inner  and  front  part  of  the  orbital  cavity  by  dividing  into  frontal 
and  nasal  branches.  It  is  accompanied  at  first  by  the  nasal  nerve,  and  in  the 
terminal  part  of  its  course  by  the  infra-trochlear  nerve. 

Branches. — The  branches  of  the  ophthalmic  artery  are  numerous,  (a)  The  posterior  ciliary, 
usually  six  to  eight  in  number,  run  forwards  at  the  sides  of  the  optic  nerve  ;  they  soon  divide 
into  numerous  branches  which  pierce  the  back  part  of  the  sclerotic  coat ;  the  majority  terminate 
in  the  choroid  coat  of  the  eye  as  the  short  ciliary  arteries  (aa.  ciliares  posteriores  breves),  but  two 
of  larger  size,  the  loncj  ciliary  arteries  (aa.  ciliares  posteriores  longte),  run  forwards,  one  on  each 
side,  almost  in  the  horizontal  plane  of  the  eyeball,  between  the  sclerotic  and  the  choroid  coats,  to 
the  base  of  the  iris,  where  they  divide.  The  resulting  branches  anastomose  together  and  form  a 
circle  at  the  outer  periphery  of  the  iris,  from  w^hich  secondary  branches  run  inwards  and  anasto- 
mose together  in  a  second  circle  near  the  inner  margin  of  the  iris. 

(b)  The  central  artery  of  the  retina  (a.  centralis  retinse)  arises  near  to,  or  in  common  with,  the 
preceding  vessels.  It  pierces  the  inner  and  imder  side  of  the  optic  nerve,  about  half  an  inch  (12 
mm.)  behind  the  sclera,  and  runs  in  its  centre  to  the  retina,  where  it  breaks  up  into  terminal 
branches. 

(c)  Recurrent  (a.  meningea  anterior). — A  small  branch  which  passes  backwards  through  the 
sphenoidal  fissure  into  the  middle  fossa  of  the  cranium,  where  it  anastomoses  with  the  middle  and 
small  meningeal  arteries,  and  with  the  meningeal  branches  of  the  internal  carotid  and  lachrymal 
arteries. 


816 


THE  VASCULAE  SYSTEM. 


(d)  The  lachrymal  artery  (a.  lacrimalis)  arises  from  tlie  oplitlialmic  on  the  outer  side  of 
the  optic  nerve.  It  runs  forwards  along  the  upper  horder  of  the  external  rectus  to  the  upper  and 
outer  angle  of  the  orbit,  and  in  its  course  gives  off  branches  to  the  lachrymal  gland,  muscular 
branches  to  the  external  and  superior  recti,  palpebral  branches  to  the  upi^er  eyelid  and  the  upper 
and  outer  pai't  of  the  forehead,  tem^^oral  and  mahir  l^ranches,  which  accomjiany  the  temporal  and 
malar  branches  of  tlie  temjioro -malar  nerve,  to  the  face  and  the  temporal  fossa  respectively; 
anterior  ciliary  hunches  (aa.  ciliares  anteriores),  which  perforate  the  sclera  behind  the  corneo- 
scleral junction  and  anastomose  with  the  posterior  ciliary  arteries ;  and  a  recurrent  meningeal 
branch,  which  passes  backwards  through  the  outer  jaart  of  the  sphenoidal  fissure  to  anastomose  in 
the  middle  fossa  of  the  skull  with  tlie  middle  meningeal  artery. 

(e)  Muscular. — These  branches  are  usually  arranged  in  two  sets,  outer  and  inner.  The  former 
supply  the  upper  and  outer,  and  the  latter  the  lower  and  inner  orbital  muscles.  They  anastomose 
with  muscular  liranches  from  the  lachrymal  and  the  supra-orbital  vessels,  and  they  give  off 
anterior  ciliary  hranches. 

(J)  The  supra-orbital  branch  (a.  supra-orbitalis)  is  given  off  as  the  oijhthalmic  artery  crosses 
above  the  optic  nerve.  It  jiasses  round  the  inner  borders  of  the  sujDerior  rectus  and  levator 
palpebras  muscles,  and  runs  forwards  between  the  latter  and  the  periosteum  to  the  supra-orbital 
notch,  accompanying  tlie  fi'ontal  and  supra-orliital  nerves.  Passing  through  the  notch  it  reaches 
the  scalj),  and,  perforating  the  frontalis  muscle,  anastomoses  with  the  superficial,  temporal,  and 
frontal  arteries. 

ig)  Ethmoidal  branches,  anterior  (a.  ethmoidalis  anterior)  and  posterior  (a.  ethmoidalis 
posterior),  arise  from  the  ophthalmic  as  it  runs  forwards  along  the  inner  Ijoundary  of  the  orbital 


Ascending  parietal  artery 


Ascending  frontal  arteries 


Parieto-occipital 

arteiy 


Inferior  external 
frontal  artery 


Calcarine  arten 


E\teinal  oibital  artery 


Parieto-temporal  artery  Temporal  brandies  of  middle  cerebral 

Fig.  626. — Distribution  of  Cerebral  Arteries  on  the  Outer  Surface  of  the  Cerebrum. 
Anterior  cereViral  artery  is  coloured  green,  the  middle  cerebral  red,  and  the  posterior  cerebral  orange. 

cavity.  Tliey  pass  inwards  between  the  superior  oblique  and  the  internal  rectus.  The  posterior, 
which  is  much  tlie  smaller  of  the  two,  traverses  the  posterior  ethmoidal  canal,  and  supplies 
the  posterior  ethmoidal  cells  and  the  jiosterior  and  upper  part  of  the  outer  wall  of  the  nasal  cavity. 
The  anterior  ethmoidal  artery  passes  through  the  anterior  ethmoidal  canal  with  the  nasal  nerve, 
enters  the  anterior  fossa  of  the  skull,  and  crosses  the  cribriform  plate  of  the  ethmoid  to  the 
nasal  notch,  through  which  it  reaches  tlie  uasal  cavity,  where  it  descends  with  the  nasal  nerve  in 
a  groove  on  the  l)a(;k  of  the  nasal  bone,  and  finally  passes  between  the  ujjjier  lateral  cartilage  and 
the  lower  border  of  the  nasal  bone  to  the  ti]i  of  the  nose.  It  supplies  biTinches  to  the  membranes 
of  the  brain  in  tlie  anterior  cranial  fossa  as  well  as  to  the  anterior  ethmoidal  cells,  the  frontal 
sinus,  the  antei'ior  aud  upper  ])art  of  the  nasal  mucous  membrane,  and  the  skin  on  the  dorsum 
of  the  nose. 

(h)  Palpebral  branches  (ua.  i)al])cbrales),  u])))cr  and  lower,  are  given  off  near  the  termination 
of  the  ophthalmic.  They  are  distriljuted  to  the  iijjper  and  lower  eyelids,  and  they  anastomose  with 
the  lachrymal,  supra-orbital,  and  infra-ori)ital  arteries. 

{%)  The  nasal  terminal  branch  (a.  dorsalis  nasi)  ])asses  out  of  the  orbit  above  the  internal  tarsal 
ligament.  It  pierces  llie  paljiebral  fascia,  and  terminates  on  the  side  of  the  nose  by  anastomosing 
with  the  angubir  biaiicli  of  the  facial  artery. 

(7c)  The  frontal  terminal  branch  (a.  frontalis)  ])ie,rces  the  pal])ebi'al  fascia  at  the  upper  and 
inner  part  of  the  orbit,  and  ascends,  with  the  suimi-lrochlear  nerve,  in  the  sujierficial  fascia  of 
the  anterior  and  mesial  part  of  the  scalp,  anastomosing  with  its  fellow  of  the  opposite  side  and 
with  the  supra -orljital  artery. 

(6)  The  posterior  communicating  artery  (a.  communicans  posterior)  rises  from  the 
internal  carotid  near  its  termination.      \t  nins  backwards  below  the  optic  ti'act  and  in 


BKANCHES  OF  THE  INTEENAL  CAEOTID  AETEEY.  817 

front  of  the  crus  cerebi'i,  and  passing  above  the  third  nerve,  joins  the  posterior  cerebral 
artery  forming  jDart  of  the  circle  of  Willis.  It  gives  branches  to  the  optic  tract,  the  crus 
cerebri,  the  interpeduncular  x'egion,  and  the  uncinate  convolution  of  the  brain.  The 
posterior  communicating  artery  varies  much  in  size ;  it  may  be  small  on  one  or  both 
sides,  sometimes  it  is  very  large  on  one  side  ;  occasionally  it  replaces  the  posterior 
cerebral  arteiy,  and  it  sometimes  arises  from  the  middle  cerebral  artery. 

(7)  The  anterior  choroidal  (a.  choroidea)  is  a  small  branch,  which  also  rises  near  the 
termination  of  the  internal  carotid  ;  it  passes  backwards  and  outwards,  between  the  crus 
cerebri  and  the  uncinate  convolution,  to  the  lower  and  front  part  of  the  choroidal  fissui'e 
which  it  enters,  and  it  terminates  in  the  choroidal  plexus  in  the  descending  cornu  of  the 
lateral  ventricle.  It  supplies  the  optic  tract,  the  crus  cerebri,  the  uncinate  convolution, 
and  the  posterior  part  of  the  internal  capsule. 

(8)  Anterior  Cerebral  Artery  (a.  cerebri  anterior).  This  is  the  smaller 
of  the  two  terminal  l^rauches  of  the  internal  carotid.  It  passes  forwards  and  in- 
wards, above  the  optic  chiasma  and  immediately  in  front  of  the  lamina  cinerea,  to 
the  commencement  of  the  great  longitudinal  fissure,  where  it  turns  round  the  genu 
of  the  corpus  callosum,  and  runs  backwards  to  the  parietal  lobe  of  the  brain.  At 
the  commencement  of  the  great  longitudinal  fissure  it  is  closely  connected  with  its 
fellow  of  the  opposite  side  by  a  wide  but  short  anterior  conununicating  artery  (a. 
communicans  anterior),  and  in  the  remainder  of  its  course  it  is  closely  accompanied 
by  its  fellow  artery  of  the  opposite  side. 

Branches. — Branches  of  all  the  cerebral  arteries  are  distributed  both  to  the  basal 
ganglionic  masses  of  the  brain  and  to  the  cerebral  cortex  ;  they  therefore  form  two  dis- 
tinct groups — (a)  central  or  ganglionic  ;  {h)  cortical. 

The  branches  of  the  anterior  cerebral  include  : 

(a)  Central  or  ganglionic  branches. — The  antero-mesial  arteries,  a  small  group  of 
vessels,  constitute  the  central  branches  of  the  anterior  cerebral  artery  ;  they  pass  upwards 
into  the  base  of  the  brain  in  front  of  the  optic  chiasma,  and  supply  the  rostrum  of 
the  corpus  callosum,  the  lamina  cinerea,  and  the  septum  lucidum. 

{h)  Cortical  branches.  —  (b^)  Internal  orbital,  one  or  more  small  branches  which 
supply  the  internal  orbital  convolution,  the  gyrus  rectus,  and  the  olfactory  lobe. 

(6-)  Anterior  internal  frontal,  one  or  more  branches  which  are  distributed  to  the 
anterior  and  lower  part  of  the  marginal  convolution,  and  to  the  anterior  portions  of  the 
superior  and  middle  frontal  convolutions. 

{b'^)  A  middle  internal  frontal  is  distributed  to  the  posterior  part  of  the  marginal 
convolution,  and  to  the  upper  portions  of  the  superior  and  ascending  frontal  and  ascend- 
ing parietal  convolutions. 

(b*)  The  posterior  internal  frontal  runs  backwards  to  the  quadrate  lobule.  It 
supplies  the  corpus  callosum,  the  quadrate  lobe,  and  the  upjjer  part  of  the  superior 
parietal  lobule. 

(9)  Middle  Cerebral  Artery  (a.  cerebri  media). — The  middle  cerel^ral  is  the 
larger  of  the  two  terminal  branches,  and  the  more  direct  continuation  of  the 
internal  carotid  artery.  It  passes  outwards  in  the  fissure  of  Sylvius  to  the  outer 
surface  of  the  island  of  Eeil,  which  it  crosses;  and  divides,  in  the  posterior 
limiting  sulcus  of  Eeil,  into  parieto-temporal  and  temporal  terminal  branches. 

Branches. — (a)  Central  or  ganglionic. — Numerous  and  very  variable  in  size.  These 
branches  are  given  off  at  the  base  of  the  brain,  in  the  region  of  the  anterior  perforated 
space.    Two  sets,  known  as  the  internal  and  the  external  striate  arteries,  are  distinguishable. 

(a^)  The  internal  striate  arteries  pass  upwards  through  the  two  inner  segments  of 
the  lenticular  nucleus  (globus  pallidus)  and  the  internal  capsule  to  terminate  in  the 
caudate  nucleus.  They  supply  the  anterior  portions  of  the  lenticular  and  caudate  nuclei 
and  of  the  internal  capsule. 

(a-)  The  external  striate  arteries  pass  upwards  through  the  outer  segment  (puta- 
men)  of  the  lenticular  nucleus,  or  between  it  and  the  external  capsule,  and  the}'  form  two 
sets  :  an  anterior,  the  lenticulo-striate,  and  a  posterior,  the  lenticulo-optic  ;  both  sets 
traverse  the  lenticular  nucleus  and  the  internal  capsule,  but  the  lenticulo-striate  arteries 
terminate  in  the  caudate  nucleus,  and  the  lenticulo-optic  in  the  optic  thalamus.  One  of 
the  lenticulo-striate  arteries,  which  passes  in  the  first  instance  round  the  outer  side  of  the 
lenticular  nucleus,  and  afterwards  through  its  substance,  is  larger  than  its  companions ;  it 
frequently  ruptures,  and  is  known  as  the  artery  of  cerebral  hsemorrhage. 
56 


818  THE  VASCULAK  SYSTEM. 

(b)  Cortical  branches  are  given  off  as  the  middle  cerebral  artery  passes  over  the  surface 
of  the  island  of  Reil  at  the  bottom  of  the  Sylvian  fissure,  as  follows  : — 

{b^)  The  inferior  external  orbital  runs  forwards  and  outwards,  and  is  distributed  to 
the  outer  part  of  the  orbital  surface  of  the  frontal  lobe  and  to  the  inferior  frontal  con- 
volution. 

(6-)  The  ascending  frontal  branch  turns  round  the  upper  margin  of  the  Sylvian 
fissure,  and  is  distributed  to  the  ascending  frontal  convolution  and  to  the  posterior  part 
of  the  middle  frontal  convolution. 

(Jj^)  The  ascending  parietal  branch  emerges  from  the  Sylvian  fissure  and  passes 
upwards  along  the  posterior  border  of  the  ascending  parietal  convolution,  supplying  that 
convolution  and  the  superior  parietal  lobule. 

(h^)  The  temporal  branch  passes  out  of  the  Sylvian  fissure,  and  turns  downwards  to 
supply  the  superior  and  middle  temporal  convolutions. 

{b^)  The  parieto-temporal  branch  continues  backwards,  in  the  direction  of  the  main 
stem,  and  emerges  from  the  posterior  end  of  the  Sylvian  fissure  ;  it  supplies  the  inferior 
parietal  lobule,  the  external  occipital  convolutions,  and  the  posterior  part  of  the  temporo- 
sphenoidal  lobe. 

Vertebral  Artery. 

The  vertebral  artery  (a.  vertebralis,  Figs.  624  and  627)  is  the  first  branch 
given  off  from  the  subclavian  trunk ;  it  arises  from  the  upper  and  back  part  of  the 
parent  stem,  opposite  the  interval  between  the  anterior  scalene  and  the  longus 
colli  muscles,  and  terminates  at  the  lower  border  of  the  pons  Varolii  by  uniting 
with  its  fellow  of  the  opposite  side  to  form  the  basilar  artery. 

Course  and  Relations. — -The  vertebral  artery  is  divisible  into  four  parts. 

The  first  part  runs  upwards  and  backwards,  between  the  scalenus  anticus  and 
the  outer  border  of  the  longus  colli,  to  the  foramen  in  the  transverse  process  of  the 
sixth  cervical  vertebra.  It  is  surrounded  by  a  plexus  of  sympathetic  nerve  fibres, 
covered  anteriorly  by  the  vertebral  and  internal  jugular  veins,  and  crossed  in  front 
by  the  inferior  thyroid  artery.  On  the  left  side  the  terminal  part  of  the  thoracic 
duct  also  passes  in  front  of  it.  The  second  part  runs  upwards  through  the  foramina 
in  the  transverse  processes  of  the  upper  six  cervical  vertebrae.  As  far  as  the 
second  cervical  vertebra  its  course  is  almost  vertical ;  as  it  passes  through  the 
transverse  process  of  the  axis,  however,  it  is  directed  obliquely  upwards  and 
outwards  to  the  atlas.  It  is  surrounded  by  a  plexus  of  sympathetic  nerve  fibres, 
and  also  by  a  plexus  of  veins.  The  artery  Lies  in  front  of  the  trunks  of  the 
cervical  nerves,  and  internal  to  the  intertransverse  muscles.  The  third  part  emerges 
from  the  foramen  in  the  transverse  process  of  the  atlas,  between  the  anterior  primary 
division  of  the  sub-occipital  nerve  internally  and  the  rectus  capitis  lateralis  exter- 
nally, and  runs  almost  horizontally  backwards  and  inwards  round  the  outer  side 
and  back  of  the  superior  articular  process  of  the  atlas.  In  this  course  it  enters 
the  sub-occipital  triangle,  where  it  lies  in  the  groove  on  the  upper  surface  of  the 
posterior  arch  of  the  atlas  (sulcus  arteri^e  vertebralis).  It  is  separated  from  the 
bone  by  the  sub-occipital  nerve,  and  is  overlapped  superficially  by  the  adjacent 
borders  of  the  superior  and  inferior  oblique  muscles.  Finally,  this  part  of  the 
artery  passes  beneath  the  oblique  ligament  of  the  atlas  and  enters  the  spinal  canal. 

The  fourth  .part  pierces  the  spinal  dura  mater  and  runs  upwards  into  the  cranial 
cavity.  It  passes  between  the  roots  of  the  hypoglossal  nerve  above  and  the  first 
dentation  of  the  ligamentum  denticulatum  below,pierces  the  arachnoid, and, gradvially 
inclining  inwards  in  front  of  the  meduUa,  reaches  the  lower  border  of  the  pons 
Varolii,  where  it  unites  with  its  fellow  of  the  opposite  side  to  form  the  basilar  artery. 

Branches. — From  the  first  part. — As  a  rule  there  are  only  a  few  small  muscular 
twigs  from  thi.s  portion  of  the  artery. 

From  the  second  part. — (1)  Muscular  branches  which  vary  in  number  and  size.  They 
supply  the  deep  muscles  of  the  neck,  and  anastomose  with  the  profunda  cervicis,  the 
ascending  cervical,  and  tlie  occipital  arteries. 

(2)  Spinal  branches  (rami  s[)inales)  pass  from  the  inner  side  of  the  second  part  of  the 
vertebral  artery  through  the  intervertebral  foramina  into  the  spinal  canal,  where  they 
give  off  twigs  which  pass  along  the  roots  of  the  spinal  nerves  to  reinforce  the  anterior  and 


VERTEBEAL  AETERY. 


819 


posterior  spinal  arteries;  they  supply  the  hodies  of  the  vertebrae  and  the  intervertebral 
discs,  and  they  anastomose  with  corresponding  arteries  above  and  below. 

From  the  third  jyirt. — (1)  Muscular  branches  to  the  sub-occipital  muscles. 

(2)  Anastomotic  branches  which  unite  with  the  princeps  cervicis  branch  of  the  occi- 
pital and  with  the  profunda  cervicis  artery. 

Frotu  the  fourth  part. — (1)  Meningeal  (rami  meningei). — One  or  two  small  branches 
given  off  l)efore  the  vertebral  artery  pierces  the  dura  mater.  They  ascend  into  the  pos- 
terior fossa  of  the  skull,  where  they  anastomose  with  meningeal  branches  of  the  occipital 
and  ascending  pharyngeal  arteries,  and  occasionally  with  branches  of  the  middle  meningeal 
artery. 

(2)  Posterior  Spinal  (a.  spinalis  posterior). — The  posterior  si)inal  branch  springs  from 


Anterior  comiiniiiicatiiif,'  artery 


Olfactory  tract 


Anterior  cerebral  artery 


Optic  cliiasma 


Infundibuhim 


3rd  cranial  nerve  ^ 


4th  cranial 
nerve 


8th  cranial 
nerve 


Oth  cranial 
nerve 


10th  cranial  nerve 
11th  cranial  nerve 


Middle 
cei-ebral  artery 

Internal 
'  carotid  artery 
Anterior 
choroidal 
artery 

Posterior  com- 
municating 
artery 
Posterior 
cerebral  artery 

Superior  cere- 
bellar artery 
Transverse 

pontine 
arteries 

Basilar  artery 

Anterior 
inferior  cere- 
bellar artery 


Posterior  inferior 
cerebellar  artery 


Vertebral  artery 


12th  cranial  nerve  Anterior  spinal  artery 

Fig.  627.— The  Arteries  of  the  Base  of  the  Brain.     The  Circle  of  Wilus. 

the  vertebral  directly  after  it  has  pierced  the  dura  mater.  It  runs  downwards  upon  the 
side  of  the  medulla  and  the  spinal  cord  in  front  of  the  posterior  nerve  roots.  It  is  a 
slender  artery,  which  is  continued  to  the  lower  part  of  the  cord  by  means  of  reuiforce-^ 
ments  from  the  spinal  branches  of  the  vertebral  and  intercostal  arteries.  It  gives  off 
branches  to  the  pia  mater,  which  form  more  or  less  regular  anastomoses  on  the  inner 
sides  of  the  posterior  nerve  roots,  and  it  terminates  below  by  joining  the  anterior  spinal 
artery. 

(3)  The  anterior  spinal  branch  (a.  spinalis  anterior)  arises  near  the  termination  of  the 
vertebral.  It  runs  obliquely  downwards  and  inwards,  in  front  of  the  medullti,  and  unites 
with  its  fellow  of  the  opposite  side  to  form  a  single  anterior  spinal  artery,  which  descends 
in  front  of  the  anterior  fissure  of  the  spinal  cord,  and  is  continued  as  a  fine  vessel  along 
the  filum  terminale.     The  anterior  spinal  artery  is  reinforced  as  it  descends  by  anastomos- 


820  THE  VASCULAE  SYSTEM. 

ino-  twigs  from  the  spinal  branches  of  the  vertebral,  intercostal,  and  lumbar  arteries.  It 
gives  off  branches  which  pierce  the  pia  mater  and  supply  the  cord,  and  it  unites  below 
with  the  posterior  spinal  arteries. 

(4)  The  posterior  inferior  cerebellar  (a.  cerebelli  inferior  posterior)  is  the  largest 
branch  of  the  vertebral  artery.  It  arises  a  short  distance  below  the  pons  and  passes 
obliquely  backwards  round  the  medulla,  at  first  between  the  roots  of  the  hypoglossal 
nerve,  and  then  between  the  roots  of  the  spinal  accessory  and  vagus  nerves,  into  the 
vallecula  of  the  cerebellum,  where  it  divides  into  external  and  internal  terminal  branches. 

The  trunk  of  the  artery  gives  branches  to  the  medulla  and  to  the  choroid  plexus  of 
the  fourth  ventricle.  The  internal  terminal,  or  vermiform  branch,  runs  backwards 
between  the  inferior  vermiform  process  and  the  lateral  lobe  of  the  cerebellum ;  it  supplies 
principally  the  former  structure,  and  anastomoses  with  its  fellow  of  the  opposite  side.  The 
external  or  hemispheric  branch  passes  outwards  on  the  lower  surface  of  the  hemisphere 
and  anastomoses  with  the  superior  cerebellar  artery. 

Basilar  Artery  (a.  basilaris). — This  artery  is  formed  by  the  junction  of 
the  two  vertebral  arteries ;  it  commences  at  the  lower  border  and  terminates  at  the 
upper  border  of  the  pons  Varolii,  bifurcating  at  its  termination  into  the  two 
posterior  cerebral  arteries. 

Course  and  Relations. — It  runs  upwards  in  a  shallow  groove  on  the  front  of 
the  pons  Varolii,  behind  the  sphenoidal  section  of  the  basi-cranial  axis  and  between 
the  sixth  nerves. 

Branches.— (1)  The  transverse,  a  series  of  small  arteries  which  pass  round  the  sides 
of  the  pons,  supplying  it  (rami  ad  pontem),  the  middle  peduncles  of  the  cerebellum,  and 
the  roots  of  the  fifth  cranial  nerve. 

(2)  The  auditory  (a.  auditiva  interna),  a  pair  of  long  but  slender  branches  which 
accompany  the  eighth  cranial  nerve.  Each  enters  the  corresponding  internal  auditory 
meatus  with  the  seventh  and  eighth  nerves,  and,  passing  through  the  lamina  cribrosa,  is 
distributed  to  the  internal  ear. 

(3)  The  anterior  inferior  cerebellar  (a.  cerebelli  inferior  anterior),  two  branches  which 
arise,  one  on  each  side,  from  the  middle  of  the  basilar  artery.  They  pass  backwards  on  the 
anterior  parts  of  the  lower  surfaces  of  the  lateral  lobes  of  the  -cerebellum,  and  anastomose 
with  the  posterior  inferior  cerebellar  bx'anches  of  the  vertebral  arteries. 

(4)  The  superior  cerebellar  (aa.  cerebelli  superiores)  branches,  two  in  number,  arise  near 
the  termination  of  the  basilar.  Each  passes  outwards  at  the  upper  border  of  the  pons, 
directly  below  the  third  nerve  of  the  same  side,  and  turning  round  the  outer  side  of  the 
crus  cerebri  below  the  fourth  nerve,  reaches  the  upper  surface  of  the  cerebellum,  w^here  it 
divides  into  an  internal  and  an  external  branch.  The  internal  branch  supplies  the  upper 
surface  of  the  vermiform  process  and  the  valve  of  Vieussens.  The  external  branch  is 
distributed  over  the  upper  surface  of  the  lateral  hemisphere,  anastomosing  at  its  margin 
with  the  inferior  cerebellar  arteries. 

(5)  Posterior  Cerebral  Arteries  (aa.  cerebri  posteriores.  Figs.  625  and  627). — 
These  are  the  two  terminal  branches  of  the  basilar.  They  run  backwards  and 
upwards,  between  the  crura  cerebri  and  the  uncinate  convolutions  and  parallel 
to  the  superior  cerebellar  arteries,  from  which  they  are  separated  by  the  third 
and  fourth  cranial  nerves.  Each  posterior  cerebral  artery  is  connected  with  the 
internal  carotid  by  the  posterior  communicating  artery ;  it  gives  branches  to  the 
tentorial  surface  of  the  cerebrum,  and  is  continued  backwards,  beneath  the  splenium 
of  the  corpus  callosum,  to  the  calcarine  fissure,  where  it  divides  into  calcarine  and 
parieto-occipital  branches,  which  pass  to  the  outer  surface  of  the  occipital  lobe  and 
supply  the  inner  and  tentorial  surfaces  of  the  occipital  lobe  and  the  posterior  part 
of  its  outer  surface. 

Branches. — (A)  Central  or  f/anf/lionic. — This  group  includes  (n^)  A  postero-mesial 
set  of  small  vessels  which  pass  on  the  iinier  side  of  the  crus  cerebri  to  the  posterior 
perforated  space.  They  supply  the  crus,  the  posterior  part  of  the  optic  thalamus,  the 
corpora  albicantia,  and  the  walls  of  the  third  vcnti-iclc. 

(a-)  A  postero-lateral  set  of  small  vessels  which  pass  romid  the  outer  side  of  the  crus 
cerebri.  They  supply  the  corpora  quadrigcinina,  the  brachia,  the  pineal  body,  the  crus, 
the  posterior  part  of  the  optic  thalamus,  and  the  corpora  geniculata. 

(a^)  A  posterior  choroidal  set  of  small  branches  which  pass  through  the  upper  part  of 


THE  SUBCLAVIAN  AETEKIES.  821 

the  choroidal  fissxire,  and,  after  entering  the  posterior  part  of  the  velum  interpositum,  end 
in  the  choroid  plexus  in  the  body  of  the  lateral  ventricle  and  the  upper  part  of  its 
descending  cornu. 

(B)  Cortical. — {h^)  The  anterior  temporal,  frequently  a  single  branch  of  variable  size, 
is  not  uncommonly  replaced  by  several  small  branches.  It  supplies  the  anterior  parts  of 
the  uncinate  and  the  occipito-temporal  convolutions. 

{h-)  The  posterior  temporal  is  a  larger  branch  than  the  anterior.  It  supplies  the 
posterior  part  of  the  uncinate  gyrus,  the  greater  part  of  the  occipito-temporal  convolution, 
and  the  lingual  lobule. 

{b^)  The  calcarine  branch  is  the  continuation  of  the  posterior  cerebral  artery  along 
the  calcarine  fissure.  It  supplies  the  cuneate  lobe,  the  lingual  lobule,  and  the  posteri<jr 
part  of  the  outer  surface  of  the  occipital  lobe. 

(6^)  The  parieto- occipital  branch,  smaller  than  the  calcarine,  passes  along  the 
corresponding  fissure  to  the  cuneus  and  precuneus. 

Circle  of  Willis  (Fig.  627). — The  cerebral  arteries  of  opposite  sides  are  intimately 
connected  together  at  the  base  of  the  brain  by  anastomosing  channels.  Thus  the 
two  anterior  cerebral  arteries  are  connected  with  one  another  by  the  anterior 
communicating  artery,  whilst  the  two  posterior  cerebrals  are  in  continuity  through 
the  basilar  artery  from  which  they  rise.  There  is  also  a  free  anastomosis  on  each 
side  between  the  carotid  system  of  cerebral  arteries  and  the  vertebral  system  by 
means  of  the  posterior  communicating  arteries,  which  connect  the  internal  carotid 
trunks  and  posterior  cerebral  arteries. 

The  vessels  referred  to  form  the  so-called  circle  of  Willis  (circulus  arteriosus 
[WiUisi]).  This  is  situated  at  the  base  of  the  brain,  in  the  region  of  the  inter- 
peduncular space,  and  encloses  the  following  structures :  the  posterior  perforated 
space,  the  corpora  albicantia,  the  tuber  cinereum,  the  infundibulum,  and 
the  optic  commissure.  The  "  circle "  is  irregularly  polygonal  in  outline,  and  is 
formed  posteriorly  by  the  termination  of  the  basilar  and  by  the  two  posterior 
cerebral  arteries,  postero-laterally  by  the  posterior  communicating  arteries  and  the 
internal  carotids,  antero-laterally  by  the  anterior  cerebral  arteries,  and  in  front  by 
the  anterior  communicating  artery. 

It  is  stated  that  this  free  anastomosis  equalises  the  flow  of  blood  to  the  various 
parts  of  the  cerebrum,  and  provides  for  the  continuation  of  a  regular  blood-supply 
if  one  or  more  of  the  main  trunks  of  the  basal  vessels  should  be  obstructed. 

AETEEIES  OF  THE  UPPEK  EXTEEMITY. 

The  main  arterial  stem  of  each  upper  extremity  passes  through  the  root  of  the 
neck,  traverses  the  axillary  space,  and  is  continued  through  the  upper  arm  to  the 
forearm.  In  the  latter  it  only  runs  a  short  distance,  terminating  just  below  the 
bend  of  the  elbow  by  bifurcating  into  the  radial  and  ulnar  arteries  which  descend 
through  the  forearm  to  the  hand.  That  portion  of  the  common  trunk  which  lies 
in  the  root  of  the  neck  is  known  as  the  subclavian  artery,  the  part  in  the  axillary 
space  is  termed  the  axillary  artery,  whilst  the  remaining  part  is  called  the  brachial 
axtery. 

THE  SUBCLAVIAX  ARTERIES. 

On  the  right  side  the  subclavian  artery  (a.  subclavia,  Figs.  620  and  622)  com- 
mences at  the  termination  of  the  innominate  artery  behind  the  sterno-clavicular 
articulation,  whilst  that  on  the  left  side  arises  from  the  arch  of  the  aorta  behind 
the  lower  part  of  the  manubrium  sterni. 

The  right  artery  is  about  three  inches  long  (75  mm.),  and  it  lies  in  the  root  of 
the  neck.  The  left  artery  is  about  four  inches  (100  mm.)  long,  and  is  situated  not 
only  in  the  root  of  the  neck,  but  also  in  the  superior  mediastinal  part  of  the  thorax. 
In  the  root  of  the  neck  each  artery  arches  outwards  across  the  apex  of  the  lung  and 
behind  the  anterior  scalene  muscle,  and  is  divided  into  three  parts,  which  lie 
respectively  to  the  inner  side,  behind,  and  to  the  outer  side  of  the  muscle.  The 
extent  to  which  the  arch  rises  above  the  level  of  the  clavicle  varies  considerably, 
and  not  uncommonly  it  reaches  the  level  of  the  lower  part  of  the  thyroid  body. 
56a 


822  THE  VASCULAR  SYSTEM. 

The  first  parts  of  the  subclavian  arteries  differ  materially  from  each  other  both  in 
extent  and  relations.  The  relations  of  the  second  and  third  parts  are  similar  on 
both  sides. 

The  first  part  of  the  left  subclavian  artery  springs  from  the  arch  of  the 
aorta  to  the  left  of  and  behind  the  commencement  of  the  left  common  carotid  and 
on  the  left  side  of  the  trachea.  It  ascends,  almost  vertically,  in  the  superior 
mediastinum  to  the  root  of  the  neck,  where  it  arches  upwards  and  outwards  to  the 
inner  border  of  the  scalenus  anticus. 

Relations. — Posterior. — In  the  superior  mediastinum,  from  below  upwards,  it  is  in 
relatiou  behind  and  ou  its  inner  side  with  the  left  margin  of  the  oesophagus,  the  thoracic 
duct,  and  the  left  longus  coUi  muscle,  whilst  the  outer  part  of  its  posterior  surface  is 
covered  by  pleura. 

Anterior. — In  front  and  to  the  right  of  the  artery  are  the  vagus,  the  left  superior 
cardiac  branch  of  the  sympathetic,  the  left  inferior  cardiac  branch  of  the  vagus,  the  lef 
phrenic  nerve,  and  the  left  common  carotid  artery.     It  is  also  crossed  obliquely  by  the 
left  innominate  vein  above  and  by  the  left  vagus  nerve  below,  and  it  is  overlapped  on 
the  left  side  by  the  left  lung  and  pleura. 

Lateral. — Internally  it  is  in  relation,  from  below  upwards,  with  the  trachea,  the  left 
recurrent  laryngeal  nerve,  the  oesophagus,  and  the  thoracic  duct. 

Externally  it  is  closely  invested  by  the  left  pleura,  and  it  ascends  in  a  groove  on  the 
inner  aspect  of  the  left  lung. 

As  it  turns  outwards  at  the  I'oot  of  the  neck  it  lies  behind  the  terminations  of  the 
internal  jugular,  vertebral,  and  subclavian  veins,  the  phrenic  nerve,  the  sterno- thyroid  and 
sterno-hyoid  muscles,  the  anterior  jugular  vein,  and  more  superficially  the  sterno-mastoid 
muscle,  aiid  the  deep  cervical  fascia ;  the  thoracic  duct  arches  obliquely  over  it,  and  it 
lies  in  front  of  the  apex  of  the  pleural  sac. 

The  first  part  of  the  right  subclavian  artery  (Fig.  620)  extends  from  the 
back,  of  the  right  sterno-clavicular  articulation  to  the  inner  border  of  the  scalenus 
anticus.     It  is  thus  limited  to  the  root  of  the  neck. 

Relations. — Posterior. — Behind  this  part  of  the  artery,  and  intervening  between  it 
and  the  upper  two  dorsal  vertebrae,  are  tiie  recurrent  laryngeal  nerve,  the  posterior  part 
of  the  annulus  Vieusseni,  and  the  apex  of  the  right  pleural  sac.  Anterior. — In  front  it  is 
in  relation  with  the  right  vagus,  the  cardiac  branches  of  the  vagus  and  the  sympathetic, 
the  anterior  portion  of  the  annulus  Vieusseni,  the  internal  jugular  and  vertebral  veins, 
and  more  superficially  the  sterno-hyoid  and  sterno-thyroid  muscles,  the  anterior  jugular 
vein,  the  sternal  end  of  the  clavicle,  the  sterno-clavicular  ligaments,  and  the  sterno- 
mastoid  muscle.  The  recurrent  laryngeal  nerve  passes  below  it  and  intervenes  between  it 
and  the  apex  of  the  pleural  sac. 

The  second  part  of  the  subclavian  artery,  on  each  side,  extends  from  the 
inner  to  the  outer  border  of  the  scalenus  anticus,  behind  which  it  hes. 

Relations. — JJekind  and  beloiv  it  is  in  relation  with  the  pleural  sac.  In  front  it  is 
covered  by  the  anterior  scalene  and  the  sterno-mastoid  muscles.  The  anterior  scalene 
separates  it  from  the  subclavian  vein,  which  also  lies  at  a  slightly  lower  level,  from  the 
transverse  cervical  and  suprascapular  arteries,  from  the  anterior  jugular  vein,  and,  on  the 
right  side,  from  the  phrenic  nerve. 

The  third  part  of  the  subclavian  artery  is  the  most  superficial  portion. 
It  extends  from  the  outer  border  of  the  anterior  scalene  to  the  outer  border  of 
the  first  rib,  lying  partly  in  the  clavicular  portion  of -the  posterior  triangle  and 
partly  behind  the  clavicle  and  the  subclavius  muscle. 

Relations. — It  rests  upon  the  upper  surface  of  the  first  rib.  Immediately  behind  it 
is  the  Ifjwost  trunk  of  the  brachial  plexus,  which  separates  it  from  the  middle  scalene. 
In  front  of  it  and  at  a  slightly  lower  level  lies  the  subclavian  vein.  The  external 
jugular  vein  crosses  the  inner  part  of  this  portion  of  the  artery  in  its  course  to  the  sub- 
clavian vein,  and  just  before  its  termination  receives  the  transverse  cervical  and  supra- 
scapular veins;  these  vessels  also  pass  superficial  to  the  artery,  which  is  thus  covered  by 
venous  trunks  ;  it  is  also  crossed  vertically,  behind  the  veins,  by  the  nerve  to  the  subclavius 
muscle.  The  outer  section  of  this  part  of  the  artery  lies  behind  the  clavicle  and  the 
subclavius  muscle,  and  it  is  crossed  from  within  outwards  by  the  suprascapular  artery, 


BEANCHES  OF  THE  SUBCLAVIAN  AETEEY.  823 

which  is  separated  from  it  by  the  layer  of  deep  cervical  fascia  which  binds  the  posterior 
belly  of  the  omo-hyoid  to  the  posterior  border  of  the  subclavian  groove.  More  superficially 
the  third  part  of  the  artery  is  covered  by  the  superficial  layer  of  the  deep  fascia,  the 
descending  clavicular  branches  of  the  cervical  nerves,  the  platysma,  and  the  skin. 

Beanches  of  the  Subclavian  Artery. 

(1)  The  vertebral  artery  is  distributed  almost  entirely  to  the  head  and  neck, 
and  its  chief  function  is  to  supply  the  posterior  part  of  the  brain.  Its  description 
has  therefore  been  given  with  that  of  the  other  cerebral  arteries  (see  p.  SLS). 

(2)  Thyroid  Axis  (truncus  thyreo-cervicalis,  Figs.  620  and  622). — This  branch 
arises  close  to  the  inner  border  of  the  scalenus  anticus,  and  directly  above  the  origin 
of  the  internal  mammary  artery,  from  the  upper  and  front  part  of  the  subclavian 
artery.  After  a  short  upward  course  of  about  two  lines  (4  mm.),  it  ends  under 
cover  of  the  internal  jugular  vein  by  dividing  into  three  branches — viz.  the  inferior 
thyroid,  the  transverse  cervical,  and  the  suprascapular. 

(A)  The  inferior  thyroid  artery  (a.  thyreoidea  inferior.  Fig.  620)  ascends 
along  the  anterior  border  of  the  scalenus  anticus,  and  turns  inwards  opposite  the 
cricoid  cartilage  to  the  middle  of  the  posterior  border  of  the  lateral  lobe  of  the 
thyroid  body ;  it  then  curves  inwards  and  downwards,  and  descends  to  the  lower 
end  of  the  lobe,  where  it  divides  into  ascending  and  inferior  terminal  branches. 

Relations. — Behind  it  is  the  vertebral  artery  externally  and  the  longus  colli  muscle 
internally ;  the  recurrent  laryngeal  nerve  passes  either  in  front  of  or  behind  the  vessel, 
opposite  the  lower  border  of  the  thyroid  body.  It  is  covered  in  front  by  the  carotid 
sheath,  which  contains  the  common  carotid  artery,  the  internal  jugular  vein,  and  the 
vagus  nerve ;  the  middle  cervical  ganglion  of  the  sympathetic  lies  in  front  of  the  artery 
as  it  bends  inwards,  and  on  the  left  side  the  thoracic  duct  also  passes  in  front  of  it. 

Branches. — It  gives  off  the  following  branches  : — 

(a)  Muscular. — Numerous  small  branches  pass  to  the  scalenus  anticus,  the  longus 
colli,  the  infra-hyoid  muscles,  and  the  inferior  constrictor  of  the  pharynx. 

(6)  The  ascending  cervical  branch  (a.  cervicalis  ascendens)  usually  springs  from  the 
inferior  thyroid  near  its  origin,  though  not  uncommonly  it  rises  separately  from  the  thyroid 
axis.  It  ascends  parallel  with  and  internal  to  the  phrenic  nerve,  in  the  angle  between  the 
rectus  capitis  anticus  major  and  the  scalenus  anticus,  to  both  of  which  it  gives  branches. 
It  also  gives  ofl^  spinal  branches  which  pass  through  the  intervertebral  foramina  to  the 
spinal  canal,  and  it  anastomoses  with  branches  of  the  vertebral,  occipital,  ascending 
pharyngeal,  and  deep  cervical  arteries. 

(c)  (Esophageal  (rami  oesophagei)  are  small  branches  given  to  the  walls  of  the 
oesophagus,  which  anastomose  with  the  cesophageal  branches  of  the  thoracic  aorta. 

{d)  Tracheal  branches  (rami  tracheales)  ar«  distributed  to  the  trachea ;  they  anasto- 
mose with  branches  of  the  superior  thyroid  and  with  the  bronchial  arteries. 

(e)  An  inferior  laryngeal  branch  (a.  laryngea  inferior)  accompanies  the  recurrent 
laryngeal  nerve  to  the  lower  part  of  the  larynx.  It  enters  the  larynx,  beneath  the  lower 
border  of  the  inferior  constrictor,  gives  branches  to  its  muscles  and  mucous  membrane, 
and  anastomoses  with  the  laryngeal  branch  of  the  superior  thyroid. 

(/■)  The  ascending  terminal  branch  supplies  the  posterior  and  lower  part  of  the 
thyroid  body,  and  anastomoses  with  branches  of  the  superior  thyroid  artery. 

{g)  The  inferior  terminal  branch  is  distributed  to  the  lower  and  inner  part  of  the 
thyroid  body.  It  anastomoses  with  its  fellow  of  the  opposite  side  and  with  branches  of 
the  superior  thyroid  artery. 

(B)  The  transverse  cervical  artery  (a.  transversa  colli,  Figs.  620  and  622) 
runs  upwards,  outwards,  and  backwards  from  the  thyroid  axis  across  the  posterior 
triangle  of  the  neck  to  the  anterior  border  of  the  trapezius,  where  it  divides  into 
superficial  cervical  (ramus  ascendens)  and  posterior  scapular  (ramus  descendens) 
branches.  It  is  very  variable  in  size,  and  not  infrequently  the  posterior  scapular 
arises  separately  from  the  third  part  of  the  subclavian. 

Immediately  after  its  origin,  under  cover  of  the  internal  jugular  vein,  it  crosses 

the  scalenus  anticns,  lying  superficial  to  the  phrenic  nerve  and  under  cover  of  the 

sterno-mastoid  muscle;  on  the  left  side  it  is  also  crossed  superficially  by  the  terminal 

part  of  the  thoracic  duct.     Passing  from  beneath  the  sterno-mastoid,  it  enters  the 

56  5 


824 


THE  VASOULAK  SYSTEM. 


lower  part  of  the  posterior  triangle  of  the  neck,  where  it  lies  upon  the  trunks  of 
the  brachial  plexus,  and,  as  it  runs  upwards  and  backwards  to  its  termination,  it 
passes  beneath  the  posterior  belly  of  the  omo-hyoid. 

Branches. — (a)  Small  muscular  branches  to  the  surrounding  muscles. 
(6)  The   superficial    cervical    artery    (a.    cervicalis    superficial  is),    usually   a    slender 
branch,  passes  beneath  the  trapezius ;  it  runs  upwards  over  the  levator  anguli  scapulae 


Levator  anguli  scapulte 


posterior  scapular  artery 
Trapezius 


Suprascapular  artery 


Rhomboideus  minor  — ^ 


Posterior  scapular 
artery 


Rhomboideus  major 

Infraspinatus  — V 
Long  head  of  triceps 

Teres  major 

Latissimus  dorsi 


-—   Infraspinatus 
'  -Deltoid 
-Teres  minor 


Circumflex  nerve 
Posterior  circumflex 
artery 


JDorsalis  scapulie 
artery 

Triceps  (ext.  head) 
Superior  profunda 
artery 
Musculo-spiral  nerve 


—  Triceps  (ext.  head) 


Bracliialis  anticus 


Fig.   628. — Di.ssectio.v  ok  the  Back  ok  thk  Shouldeh  and  UrrEK  Akm,  showing  the  anastomosing 
vessels  on  the  dorsum  of  the  scapula,  and  the  posterior  circumHex  and  superior  jirofunda  arteries. 

and  upon  the  splenius,  and  anastomoses  with  tlie  arteria  princeps  cervicis,  a  branch  of 
the  occipital  artery,  and  it  sends  branches  downwards  which  accompany  the  spinal 
accessory  nerve  and  anastomose  with  the  posterior  scapular  and  suprascapular  arteries. 

(c)  The  posterior  scapular  artery  descends  in  front  of  the  levator  anguli  scapulae  and 
the  rhomboid  muscles,  close  to  the  posterior  border  of  the  scapula.  It  runs  parallel 
with,  and  a  short  distance  away  from,  the  nerve  to  the  rhomboid  muscles,  and  it  sends 
branches    into    the    supraspinous,    the    infraspinous,   and    the    subscapular  fossse,    which 


BRANCHES  OF  THE  SUBCLAVIAN  AKTERY.  825 

anastomose  witli  branches  of  the  sviprascapiilar  and  subscapular  arteries.  It  also  sends 
branches  backwards  through  and  between  the  rhomboid  muscles,  which  anastomose  with 
the  superficial  cervical  artery  and  with  the  dorsal  branches  of  the  intercostal  arteries. 

(C)  The  suprascapular  artery  (a.  transversa  scapulee)  springs  from  the  thyroid 
axis,  and  terminates  in  the  infraspinous  fossa  of  the  scapula.  As  a  rule  it  is 
smaller  than  the  transverse  cervical  artery. 

Commencing  behind  the  internal  jugular  vein,  it  crosses  tlie  scalenus  anticus 
and  phrenic  nerve,  and  is  covered  in  front  by  the  sterno-mastoid  and  the  anterior 
jugular  vein;  on  the  left  side  it  lies  behind  the  termination  of  the  thoracic 
duct  also.  Continuing  outwards  and  backwards  behind  the  clavicle,  and  crossing 
superficially  to  the  third  part  of  the  subclavian  artery  and  the  cords  of  the  brachial 
plexus,  it  reaches  the  suprascapular  notch  and  passes  over  the  suprascapular  liga- 
ment. From  this  point  it  descends  with  the  suprascapular  nerve  through  the 
supraspinous  fossa  and  beneath  the  supraspinatus  muscle,  and  passing  through 
the  great  scapular  notch  in  front  of  the  spino-glenoid  ligament,  enters  the  infra- 
spinous fossa,  where  it  anastomoses  with  the  dorsal  branch  of  the  subscapular  and 
with  branches  of  the  posterior  scapular  arteries. 

Branches. — («)  Muscular,  to  the  sterno-mastoid,  the  subclavius,  and  the  muscles  on 
the  dorsum  of  the  scapula. 

(6)  The  medullary,  a  small  branch  to  the  clavicle. 

(c)  The  suprasternal,  to  the  sternal  end  of  the  clavicle  and  the  sterno-clavicular 
joint. 

((/)  Acromial  branches,  which  ramify  over  the  acromion  process,  anastomosing  with 
the  acromial  branches  of  the  acromio-thoracic  and  the  posterior  circumflex  arteries. 

(e)  Articular,  to  the  acromio-clavicular  and  shoulder-joints. 

(/)  The  subscapular,  which  is  given  oflt'  as  the  artery,  passes  over  the  suprascapular 
ligament.  It  passes  down  into  the  subscapular  fossa,  gives  branches  to  the  subscapularis, 
and  anastomoses  with  the  branches  of  the  subscapular  and  posterior  scapular  arteries. 

{g)  Supraspinous,  which  ramify  in  the  supraspinous  fossa,  supplying  the  muscle,  and 
anastomosing  with  the  posterior  scapular. 

(A)  Terminal  branches  ramify  in  the  infraspinous  fossa,  and  anastomose  with  the 
dorsalis  scapulae  and  with  branches  of  the  posterior  scapular  artery. 

(3)  Internal  Mammary  Artery  (a.  mammaria  interna.  Fig.  620). — This  arises 
from  the  lower  and  front  part  of  the  subclavian  at  the  inner  border  of  the  scalenus 
anticus  and  immediately  below  the  origin  of  the  thyroid  axis.  It  terminates 
behind  the  inner  extremity  of  the  sixth  intercostal  space  by  dividing  into  the 
musculo-phrenic  and  the  superior  epigastric  arteries. 

The  artery  passes  at  first  downwards,  forwards,  and  inwards,  lying  upon  the 
pleura,  and  behind  the  subclavian  vein,  the  sternal  end  of  the  clavicle,  and  the 
cartilage  of  the  first  rib :  it  is  crossed  obliquely  from  without  inwards  by  the 
phrenic  nerve,  which  usually  passes  in  front  of  it.  From  the  cartilage  of  the  first 
rib  it  descends  vertically,  about  half-an-inch  from  the  border  of  the  sternum,  and 
lies  in  the  upper  part  of  its  course  in  front  of  the  pleura,  and  in  the  lower  part  in 
front  of  the  triangularis  sterni.  It  is  covered  anteriorly  by  the  cartilages  of  the 
upper  six  ribs,  the  intervening  intercostal  muscles,  and  the  terminal  portions  of  the 
intercostal  nerves,  and  it  is  accompanied  by  two  vense  comites,  which  unite 
together  above  and  on  its  inner  side  to  form  a  single  trunk  which  terminates  in  the 
innominate  vein. 

Branches. — {a)  The  comes  nervi  phrenici  (a.  pericardiaco-phrenica),  or  superior 
phrenic  artery,  is  a  long  slender  branch  which  is  given  off  from  the  upper  part  of  the 
internal  mammary.  It  accompanies  the  phrenic  nerve  through  the  superior  and  middle 
mediastinal  spaces  to  the  diaphragm,  where  it  anastomoses  with  the  inferior  phrenic  and 
musculo-phrenic  arteries.  In  its  course  downwards  the  artery  gives  off"  numerous  small 
branches  to  the  pleura  and  pericardium,  which  anastomose  with  off"sets  of  the  mediastinal 
and  pericardial  branches  of  the  aorta  and  internal  mammary  arteries,  and  also  with  the 
bronchial  arteries,  forming  the  wide-meshed  subpleural  plexus  of  Turner. 

(b)  Mediastinal  branches  (aa.  mediastinales  anteriores),  small  and  numerous,  pass  to 
the  areolar  tissue  of  the  anterior  mediastinal  space  and  supply  the  remains  of  the  thymus 
gland  and  the  sternum. 


826  THE  VASCULAE  SYSTEM.    . 

(c)  Pericardial. — These  are  several  small  branches  which  ramify  on  the  anterior  aspect 
of  the  pericardium. 

(d)  The  anterior  intercostal  (rami  intercostales)  are  two  in  number  in  each  of  the 
upper  six  intercostal  spaces.  They  pass  outwards  for  a  short  distance  either  between  the 
pleura  or  the  triangularis  sterni  and  the  internal  intercostal  muscles ;  they  then  pierce 
the  internal  intercostal  muscles,  and  ramify  between  them  and  the  external  intercostal 
muscles,  anastomosing  with  the  aortic  and  superior  intercostal  arteries  and  their  collateral 
branches. 

(e)  The  anterior  perforating  branches  (rami  perforantes),  one  in  each  of  the  upper  six 
intercostal  spaces,  are  small  vessels  which  pass  forwards  with  the  intei'costal  nerves, 
piercing  the  internal  intercostal  muscle,  the  anterior  intercostal  membrane,  and  the 
pectoralis  major,  to  terminate  in  the  skin  and  subcutaneous  tissue.  They  supply  twigs 
to  the  sternum,  and  those  in  the  third  and  fourth  spaces,  usually  the  largest  of  the  series, 
give  off  branches  to  the  mammary  gland. 

(/)  The  musculo-phrenic  (a.  musculo-phrenica),  or  external  terminal  branch  of  the 
internal  mammary  artery,  runs  dow-nwards  and  outwards  from  the  sixth  intercostal  space 
to  the  tenth  costal  cartilage.  In  the  \ipper  part  of  its  course  it  lies  upon  the  thoracic 
surface  of  the  diaphragm,  but  it  pierces  the  muscle  about  the  level  of  the  eighth  costal 
cartilage,  and  terminates  on  its  abdominal  surface.     Its  branches  are  : — 

(i.)  Muscular,  which  supply  the  diaphragm  and  anastomose  with  the  superior  and  inferior 
phrenic  arteries. 

(ii.)  Anterior  intercostal  "branches,  two  in  each  of  the  seventh,  eighth  and  ninth  intercostal 
spaces  ;  they  are  distributed  in  the  same  manner  as  the  corresponding  branches  of  the  internal 
mammary  artery,  and  terminate  by  anastomosing  with  the  aortic  intercostals  and  their  collateral 
branches. 

(-7)  The  superior  epigastric  (a.  epigastrica  superior),  or  internal  terminal  branch  of  the 
internal  mammary  artery,  descends  into  the  anterior  wall  of  the  abdomen.  It  leaves  the 
thorax,  between  the  sternal  and  costal  origins  of  the  diaphragm,  and  enters  the  sheath  of 
the  rectus,  lying  first  behind,  and  then  in  the  substance  of  the  rectus  muscle.  It  termi- 
nates by  anastomosing  with  branches  of  the  deep  epigastric  arteiy.     Its  branches  are : — 

(i.)  Muscular,  to  the  rectus,  to  the  flat  muscles  of  the  abdominal  w^all,  and  to  the  diaphragm. 

(ii.)  Anterior  Cutaneous. — These  branches  pierce  the  rectus  and  the  anterior  portion  of  its 
sheath.  They  accompany  the  anterior  terminal  branches  of  the  lower  intercostal  nerves,  and 
terminate  in  the  subcutaneous  tissues  and  skin  of  the  middle  portion  of  the  anterior  abdominal 
walL 

(iii.)  Ensiform,  a  small  branch  which  crosses  the  front  of  the  ensiform  process  to  anastomose 
with  its  fellow  of  the  opposite  side.     It  supplies  the  adjacent  muscles  and  skin. 

(iv.)  Hepatic  branches  of  small  size  pass  backwards  in  the  falciform  ligament  to  the  liver, 
where  they  anastomose  with  branches  of  the  hepatic  artery. 

(4)  Superior  Intercostal  Artery  (truncus  costo-cervicalis..  Fig.  624). — The 
superior  intercostal  artery  springs  from  the  back  of  the  second  part  of  the  sub- 
clavian artery  on  the  right  side  and  from  the  first  part  on  the  left  side.  It  runs 
upwards  and  backwards  from  its  origin,  over  the  apex  of  the  pleural  sac,  to  the 
neck  of  the  first  rib  .in  front  of  which  it  descends,  between  the  first  thoracic 
cranf^Kon  of  the  sympathetic  cord  and  the  first  dorsal  nerve,  to  the  first  intercostal 
space,  where  it  divides  into  two  branches  which  are  distributed  to  the  upper  two 
intercostal  spaces. 

Branches. — (a)  The  profunda  cervicis  (a.  cervicalis  profunda). — This  branch  some- 
times arises  from  the  subclavian  artery  directly ;  but  more  commonly  it  springs  from  the 
superior  intercostal  at  the  upper  border  of  the  neck  of  the  first  rib.  It  runs  backwards, 
like  the  dorsal  branch  of  an  intercostal  artery,  passes  between  the  first  dorsal  and  last 
cervical  nerves,  and  between  the  transverse  jjrocess  of  the  last  cervical  vertebra  and  the 
neck  of  the  first  rib  to  the  back  of  the  neck,  where  it  ascends  between  the  complexus 
and  the  semispinalis  colli  muscle  to  terminate  by  anastomosing  with  the  deep  branch  of 
the  princeps  cervicis  artery.  It  also  anastomoses  with  branches  of  the  ascending  cervical 
and  vertebral  arteries,  suppHes  the  adjacent  muscles,  and  sends  a  spinal  branch,  through 
the  intervertebral  foramen  between  the  last  cervical  and  the  first  dorsal  vertebrae,  into  the 
spinal  canal,  where  it  anastomoses  with  the  spinal  branches  of  the  vertebral  and  inter- 
costal arteries. 

(6)  Terminal. — The  two  terminal  branches  run  outwards — one  in  the  first  and  one 
iu  the  second  intercostal  space.  Each  runs  near  the  upper  border  of  its  space,  passing  at 
first  between  the  pleura  and  the  posterior  intercostal   membrane,  and  then  between  the 


THE  AXILLARY  ARTEEY. 


827 


internal  and  external  intercostal  muscles.  The  branches  terminate  by  anastomosing  with 
anterior  intercostal  branches  of  the  internal  mammary  artery.  Each  gives  off  muscular 
branches  to  the  intercostal  muscles — a  nutrient  branch  to  the  rib  below  which  it  lies,  and 
a  collateral  branch  which  runs  along  the  lower  border  of  the  space  and  terminates  by 
anastomosing  with  an  anterior  intercostal  branch  of  the  internal  mammary  artery. 

THE   AXILLARY   ARTERY. 

The  axillary  artery  (a.  axillaris)  lies  in  the  axillary  space.  It  is  the  direct 
continuation  of  the  subclavian  artery,  and  it  becomes  the  brachial  artery. 

The  axillary  artery  commences  at  the  outer  border  of  the  first  rib,  at  the  apex 
of  the  axillary  space.     It  descends,  with  an  outward  inclination,  along  the  external 


Biacliial  plexu.> 


Deltoid 
Cephalic  vein 

Pectoralis  ramoi 


Axillary 

artery 
Acroinio- 
thoracic  artery 


v^-^xillary  vein 
Ulnar  nerve 


Long  thoracic 
artery 


Long  subscapular 
nerve 


_  Dorsalis  scapula; 
artery 


,atissimus  dorsi 


Fig.  629. — The  Axuxary  Artery  and  its  Branches  and  Relations. 

wall  of  the  space,  i.e.  to  the  inner  side  of  the  shoulder-joint  and  the  humerus,  to 
the  lower  border  of  the  teres  major,  where  it  becomes  the  brachial  artery.  A  line 
drawn  from  the  middle  of  the  clavicle  to  the  inner  border  of  the  prominence  of  the 
coraco-brachialis  and  biceps  muscles,  when  the  arm  is  abducted  until  it  is  at  right 
angles  with  the  side,  indicates  the  position  and  direction  of  the  artery. 

The  position  and  direction,  however,  and  to  a  certain  extent  the  relations  also 
of  the  axillary  artery,  are  modified  by  changes  in  the  position  of  the  upper 
extremity.  "With  the  arm  hanging  by  the  side  the  axillary  artery  describes  a 
curve  with  the  concavity  directed  downwards  and  inwards,  and  the  vein  is  to  its 
inner  side.  When  the  arm  is  at  right  angles  with  the  side,  the  axillary  artery  is 
almost  straight,  it  lies  closer  to  the  outer  wall  of  the  axilla,  and  the  vein  overlaps 
it  in  front  and  on  the  inner  side.     When  the  arm  is  raised  above  the  level  of  the 


828  THE  VASCULAE  SYSTEM. 

shoulder  the  axillary  artery  is  curved  over  the  head  of  the  humerus,  and  the  vein 
lies  still  more  in  front  of  it. 

Eor  descriptive  purposes  the  artery  is  divided  into  three  parts :  the  first  part 
lies  above,  the  second  behind,  and  the  third  part  below  the  pectoralis  minor 
muscle. 

Though  we  have  followed  the  usual  custom  in  describing  three  parts  of  the 
axillary  artery, — a  division  which  is  perhaps  of  practical  interest  in  so  far  as  it 
emphasises  the  fact  that  the  axillary  artery  is  surgically  accessible  above  the 
pectoralis  minor, — it  is  to  be  noted  that  the  upper  border  of  the  pectoralis  minor  is 
usually  exactly  opposite  the  outer  border  of  the  first  rib,  at  the  point  where  the 
axillary  artery  begins.  In  the  strict  sense,  therefore,  no  part  of  the  artery  is  above 
the  pectoralis  minor. 

Relations  of  the  first  part. — Posterior. — The  first  part  of  the  artery  is  enclosed, 
together  with  the  vein  and  the  cords  of  the  brachial  plexus,  in  a  prolongation  of  the 
cervical  fascia  known  as  the  axillary  sheath,  behind  which  is  tlie  upper  serration  of  the 
serratus  magnus  muscle,  the  contents  of  the  first  intercostal  space,  the  inner  cord  of  the 
brachial  plexus,  the  internal  anterior  thoracic  and  the  posterior  thoracic  nerves,  the  latter 
descending  vertically  between  the  artery  and  the  serratus  magnus.  Anterior. — It  is 
covered  in  front  by  the  costo-coracoid  membrane,  the  upper  part  of  which  splits  to  enclose 
the  subclavius  muscle.  The  membrane  intervenes  between  the  artery  and  the  cephalic 
vein,  the  branches  of  the  external  anterior  thoracic  nerve,  the  branches  of  the  acromio- 
thoracic  artery  with  their  accompanying  veins,  and  the  clavicular  part  of  the  pectoralis 
major  muscle,  superficial  to  which  are  the  deep  fascia,  the  platysma,  the  descending- 
clavicular  branches  of  the  cervical  plexus,  and  the  superficial  fascia  and  the  skin.  Behind 
the  costo-coracoid  membrane  the  arteiy  is  crossed  by  a  loop  of  communication  between 
the  external  and  internal  anterior  thoracic  nerves.  Lateral. — Above  and  to  the  outer 
side  are  the  outer  and  posterior  cords  of  the  brachial  j)lexus  and  the  external  anterior 
thoracic  nerve.  Below  and  to  the  inner  side  is  the  axillary  vein,  the  internal  anterior 
thoracic  nerve  intervening. 

Relations  of  the  second  part. — Posterior. — Behind  this  portion  of  the  artery  is 
the  posterior  cord  of  the  brachial  plexus  and  a  layer  of  fascia  which  separates  it  from  the 
subscapularis  muscle.  Anterior. — In  front  is  the  pectoralis  minor,  and  more  superficially 
the  pectoralis  majoi",  the  fasciae  and  skin.  Lateral. — To  the  outer  side  lies  the  outer  cord 
of  the  bi'achial  plexus.  On  the  inner  side  the  inner  cord  of  the  plexus  lies  in  close  relation 
to  the  artery,  and  intervenes  between  it  and  the  axillary  vein. 

Relations  of  the  third  part. — Posterior.  —  The  third  part  of  the  artery  rests 
posteriorly  upon  the  lower  border  of  the  subscapularis,  the  latissimus  dorsi,  and  the 
teres  major.  It  is  separated  from  the  fibi'es  of  the  subscapularis  by  the  circumflex  and 
musculo-spiral  nerves,  and  from  the  latissimus  dorsi  and  teres  major  by  the  musculo- 
spiral  nerve  alone.  Anterior. — It  is  crossed  in  front  by  the  inner  head  of  the  median 
nerve.  In  its  upper  half  it  lies  under  cover  of  the  lower  part  of  the  pectoralis  major, 
the  fascia  and  skin,  whilst  its  lower  part,  which  is  superficial,  is  covered  by  skin  and 
fascia  only.  Lateral. — To  the  outer  side  lie  the  median  and  musculo-cutaneous  nerves 
and  the  coraco-brachialis  muscle.  To  the  inner  side  is  the  axillary  vein.  The  two  vessels 
are,  however,  separated  by  two  of  the  chief  branches  of  the  inner  cord  of  the  brachial  plexus. 
In  the  angle  between  the  vein  and  the  artery,  and  somewhat  in  front  of  the  latter,  lies 
the  internal  cutaneous  nerve  ;  in  the  angle  behind  is  the  ulnar  nerve.  The  lesser  internal 
cutaneous  nerve  lies  internal  to  the  vein,  and  the  venfjo  comites  of  the  brachial  artery 
ascend  along  the  inner  side,  to  terminate  in  the  axillary  vein  at  the  lower  border  of  the 
subscapularis  muscle. 

Branches  of  the  Axillary  Artery. 

(1)  The  superior  thoracic  (a.  thoracalis  suprema.  Fig.  629),  a  small  branch 
which  arises  from  the  first  part  of  the  axillary  at  the  lower  border  of  the  sub- 
clavius. It  runs  downwards  and  inwards  across  the  first  intercostal  space,  pierces 
the  inner  part  of  the  costo-coracoid  membrane,  and  supplies  Ijranches  to  the  sub- 
clavius, the  pectoralis  major  and  minor,  and  to  the  serratus  magnus  and  the  inter- 
costal muscles ;  it  anastomoses  with  branches  of  the  suprascapular,  the  internal 
mammary,  and  the  acromio-tlioracic  arteries. 

(2)  The  acromio-thoracic  (a.  thoraco-acromialis.  Fig.  029)  arises  near  the  upper 
border  of  the  pectoralis  minor,  from  the  second  part  of  the  axillary  artery.     It  is  a 


BRANCHES  OF  THE  AXILLARY  ARTERY.  829 

very  short  trunk,  of  considerable  size,  which  passes  forwards,  pierces  the  costo- 
coracoid  membrane,  and  terminates  beneath  the  clavicular  portion  of  the  pectoralis 
major  by  dividing  into  four  terminal  branches — clavicular,  pectoral,  humeral,  and 
acromial. 

(a)  The  clavicular  branch  (ramus  clavicularis)  is  a  long  slender  arteiy  whicli  runs 
upwards  and  iuwai-ds  to  the  sterno-clavicular  joint,  anastomosing  with  the  superior  thoracic, 
with  branches  of  the  suprascapular,  and  with  the  first  perforating  Ijranch  of  the  internal 
mammary  artery.     It  supplies  the  adjacent  muscles  and  the  sterno-clavicular  articulation. 

(b)  The  pectoral  (ramus  pectoralis),  or  thoracic,  is  a  large  branch  which  descends 
between  the  two  pectoral  muscles,  to  both  of  which  it  gives  branches,  and  it  anastomoses 
with  the  intercostal  and  long  thoracic  arteries. 

(c)  The  humeral  branch  (ramus  deltoideus)  runs  outwards  to  the  groove  between  the 
pectoi'alis  major  and  tiie  deltoid,  in  which  it  descends  by  the  side  of  the  cephalic  vein 
to  the  insertion  of  the  deltoid.  It  anastomoses  witli  the  acromial  branch  and  with  the 
anterior  circumflex  artery,  and  it  gives  branches  to  the  pectoralis  major  and  deltoid 
muscles  and  to  the  skin. 

(d)  The  acromial  branch  (ramus  acromialis)  runs  upwards  and  outwards  across  the  tip 
of  the  coracoid  process  to  the  acromion,  where  it  anastomoses  with  the  last-described 
branch,  with  the  aci'omial  branches  of  the  suprascajDular,  and  with  the  posterior  circimiflex 
arteries.     It  gives  branches  to  the  deltoid. 

(3)  The  long  thoracic  (a.  thoracalis  lateralis)  arises  from  the  second  part  of 
the  axillary,  and  descends  along  the  lower  border  of  the  pectoralis  minor  to 
anastomose  with  the  intercostal  and  subscapular  arteries,  and  with  the  pectoral 
branch  of  the  acromio  -  thoracic.  It  supplies  the  adjacent  muscles,  and  sends 
branches  to  the  outer  part  of  the  mammary  gland ;  hence  it  is  not  infrequently 
called  the  external  mammary  artery. 

(4)  The  alar  thoracic  is  only  occasionally  present  as  a  distinct  branch,  but  it 
is  frequently  represented  by  a  number  of  small  irregular  branches,  which  may 
either  arise  from  the  axillary  or  from  the  thoracic  and  subscapular  branches.  It  is 
distributed  to  the  glands  and  areolar  tissue  in  the  axilla. 

(5)  The  subscapular  artery  (a.  subscapularis)  is  the  largest  branch  of  the 
axillary  artery.  It  arises  from  the  third  part  of  the  artery,  opposite  the  lower 
border  of  the  subscapularis,  along  which  it  descends  to  the  lower  angle  of  the 
scapula  and  to  the  inner  wall  of  the  axillary  space.  It  is  accompanied  by  the 
second  or  long  subscapular  nerve ;  it  supplies  the  adjacent  muscles,  and  it  anasto- 
moses with  the  posterior  scapular,  the  suprascapular,  the  long  thoracic,  and  the 
lateral  branches  of  the  intercostal  arteries,  and  gives  off  one  named  branch,  the 
dorsalis  scapulae. 

The  dorsalis  scapulae  artery  (a.  circumflexa  scapulse)  is  frequently  larger  than  the 
continuation  of  the  subscapular  arteiy.  It  arises  about  one  and  a  half  inches  (37  mm.) 
from  the  commencement  of  the  subscapular  trunk,  and  passes  backwards  into  the 
triangular  space  between  the  subscapularis  above,  the  teres  major  below,  and  the  long 
head  of  the  triceps  externally.  Turning  round,  and  usually  grooving  the  axillary  border 
of  the  scapula,  under  cover  of  the  teres  minor,  it  enters  the  infraspinous  fossa,  where  it 
breaks  up  into  branches  which  anastomose  wdtli  branches  of  the  posterior  scapular  and 
suprascapular  arteries.  Whilst  it  is  in  the  triangular  space  the  dorsal  artery  gives  off  an 
infrascapu/ar  brmtch  which  passes  into  the  subscapidai"  fossa  beneath  the  subscapularis, 
and  terminates  by  anastomosing  with  the  branches  of  the  posterior  and  suprascapular 
arteries.  It  also  gives  off  in  the  same  situation  a  descending  branch,  which  runs  down- 
wards to  the  lower  angle  of  the  scapula  between  the  teres  major  and  minor  muscles,  and 
small  branches  are  given  to  the  deltoid  and  scapular  head  of  triceps. 

(6)  The  posterior  circumflex  (a.  circumflexa  humeri  posterior)  arises  from  the 
third  part  of  the  axillary  artery  and  passes  backwards,  accompanied  liy  the  circum- 
flex nerve,  through  an  intermuscular  cleft,  the  so-called  quadrilateral  space,  which 
is  bounded  by  the  teres  minor  and  subscapularis  above,  the  teres  major  below,  the 
long  head  of  the  triceps  internally,  and  the  humerus  externally.  It  turns  round 
the  surgical  neck  of  the  humerus  under  cover  of  the  deltoid  muscle,  and  terminates 
in  numerous  branches  which  supply  the  deltoid.  As  a  rule  it  is  an  artery  of  large 
size,  only  slightly  smaller  than  the  subscapular. 


830 


THE  VASCULAE  SYSTEM. 


Branches. — (a)  Muscular  to  the  teres  major  and  minor,  the  triceps  heads,  long 
and  external,  and  the  deltoid ;  (b)  An  acromial  branch,  Avhich  ascends  to  the 
acromial  process,  where  it  anastomoses  with  the  acromial  branches  of  the  suprascapular 
and  the  acromio-thoracic  arteries ;  (c)  A  descending  branch,  which  runs  downwards  along 

the  external  head  of  the  triceps  to  anastomose 
with     the     superior     profunda     artery ;      (d) 
Articular  to  the  shoulder-joint ;  (e)    Nutrient 
tUlifJIlilf'it mill^^  to  the  head  of  the  humerus  ;    (/)  Terminal, 

which  supply  a  large  portion  of  the  deltoid,  and 
anastomose  with  the  anterior  circumflex  and 
acromio-thoracic  arteries. 

(7)  The  anterior  circumflex  artery  (a. 

circumflexahumeriauterior)  isa  small  branch 
which  is  giYen  off  from  the  third  part  of  the 
axillary  close  to,  or  in  common  with,  the 
posterior  circumflex.  It  passes  outwards 
behind  the  coraco-brachialis  and  the  two 
heads  of  the  biceps,  round  the  front  of  the 
surgical  neck  of  the  humerus,  and  terminates 
by  anastomosing  with  the  posterior  circum- 
flex. At  the  bicipital  groove  it  gives  a  well- 
marked  ascending  bicipital  branch  which 
ascends  along  the  long  head  of  the  biceps, 
supplying  the  sheath  of  the  tendon,  and 
giving  branches  to  the  shoulder -joint.  It 
also  gives  muscular  branches  to  the  adjacent 
muscles,  one  of  which  descends  along  the 
tendon  of  insertion  of  the  pectoralis  major. 

THE  BRACHIAL  ARTEEY. 

The  brachial  artery  (a.  brachialis,  is 
the  direct  continuation  of  the  axillary.  It 
commences  at  the  lower  border  of  the  teres 
major,  and  terminates  in  the  ante-cubital 
fossa  at  the  level  of  the  neck  of  the  radius, 
by  dividing  into  the  radial  and  ulnar  arteries. 

The  general  course  of  the  brachial  artery 
is  downwards  and  outwards,  along  the  inner 
side  of  the  arm.  Its  position  may  be  in- 
dicated on  the  surface  by  a  line  drawn  from 
the  lower  part  of  the  axillary  space  at  the 
junction  of  its  anterior  and  middle  thirds  to 
the  centre  of  the  bend  of  the  elbow. 


Anastomotic 
artery 

Bracliialis 
anticus 

Pronator 

teres 

Bicipital 
fascia 

Supinator 
lonfrus 


Fig. 


630. — The  Brachial  Artery  and  its 
Branches. 


Relations.— /*o.s^e?7,V>r. — Itliessuccessively 
in  front  of  the  long  head  of  the  triceps,  the 
musculo-spiral  nerve  and  the  superior  profunda 
artery  intervening,  the  internal  head  of  the 
triceps,  the  insertion  of  the  coraco-brachialis 
and  the  brachialis  anticus.  Anterior. — It  is  overlapped  in  front  by  the  inner  border  of  the 
biceps,  is  crossed  at  its  centre  by  the  median  nerve,  and  in  addition  is  covered  by  deep  and 
superficial  fascia  and  by  skin.  In  the  ante-cubital  fossa  a  thickened  portion  of  the  deep 
fascia,  the  semilunar  or  bicipital  fascia,  separates  it  from  the  median  basilic  vein  and  the 
anterior  branch  of  the  internal  cutaneous  nerve,  both  of  which  lie  in  the  superficial  fascia. 
Lateral. — To  the  outer  side  it  is  in  relation  a])Ove  with  the  median  nerve,  and  below  with 
the  biceps.  To  the  inner  side  it  is  in  relation  in  the  upper  part  of  its  extent  with  the 
basilic  vein,  the  internal  cutaneous,  lesser  internal  cutaneous,  and  ulnar  nerves,  and  in 
the  lower  part  with  the  median  nerve.  Two  vena;  comites,  one  on  each  side,  accompany 
the  artery,  and  communications  between  these  pass  across  the  vessel. 


THE  EADIAL  AKTEKY.  831 

Branches  of  the  Brachial  Artery. 

(1)  The  superior  profunda  (a.  profunda  brachii)  is  a  large  branch  which 
arises  from  the  inner  and  back  part  of  the  brachial  soon  after  its  commence  uient. 
It  runs  downwards  and  outwards,  with  the  musculo-spiral  nerve,  in  the  nuisculo- 
spiral  groove,  and  divides  at  the  back  of  the  humerus  into  two  terminal  ])ranches, 
the  anterior  and  the  posterior.  Not  infrequently  this  division  takes  place  at  a 
higher  level,  and  the  artery  appears  double.  The  anterior  terminal  Itranch 
accompanies  the  musculo-spiral  nerve  through  the  external  intermuscular  septum, 
and  descends  between  the  supinator  longus  and  the  brachialis  anticus  to  the  front 
of  the  external  condyle,  where  it  anastomoses  wdth  the  radial  recurrent  artery. 
The  posterior  terminal  branch  descends  behind  the  external  intermuscular  septum, 
and  anastomoses  behind  the  external  condyle  with  the  posterior  interosseous 
recurrent  artery  and  with  the  anastomotic  artery. 

Wliilst  they  are  lying  at  the  back  of  the  humerus  one  of  the  terminal  branches 
gives  off — (a)  a  slender  twig,  which  descends  in  the  substance  of  the  internal  head 
of  the  triceps  to  the  back  of  the  elbow,  where  it  anastomoses  with  the  anastomotic 
artery  ;  (h)  a  nutrient  branch,  which  enters  a  foramen  on  the  posterior  surface  of  the 
humerus ;  and  (c)  an  ascending  branch,  which  anastomoses  with  the  descending 
branch  of  the  posterior  circumflex  artery. 

(2)  Muscular  branches  are  given  to  the  biceps,  coraco-brachialis,  brachialis 
anticus,  triceps,  and  pronator  radii  teres. 

(3)  Nutrient. — A  small  artery  which  arises  from  the  middle  of  the  brachial  and 
enters  the  nutrient  foramen  on  the  inner  side  of  the  shaft  of  the  humerus. 

(4)  The  inferior  profunda  (a.  collateralis  ulnaris  superior)  is  smaller 
than  the  superior  profunda,  with  which  it  sometimes  rises  by  a  common  trunk  ; 
usually,  however,  it  springs  from  the  inner  and  back  part  of  the  middle  of  the 
brachial.  It  runs  downwards  and  backwards,  with  the  ulnar  nerve,  through  the 
internal  intermuscular  septum,  and  then,  descending  more  vertically,  reaches  the 
back  of  the  internal  condyle  of  the  humerus,  where  it  terminates  by  anastomosing 
with  the  posterior  and  anterior  ulnar  recurrent  and  anastomotic  arteries. 

(5)  The  anastomotic  (a.  collateralis  ulnaris  inferior)  rises  from  the  inner 
side  of  the  brachial  artery  about  two  inches  (50  mm.)  above  its  termination. 
It  runs  inwards  behind  the  median  nerve  and  in  front  of  the  brachialis  anticus,  it 
then  pierces  the  internal  intermuscular  septum,  and  turns  outwards  between  the 
inner  head  of  the  triceps  and  the  posterior  surface  of  the  bone  to  the  external  con- 
dyle. It  supplies  the  adjacent  muscles  and  anastomoses,  in  front  of  the  internal 
condyle,  with  the  anterior  ulnar  recurrent,  behind  the  internal  condyle  witli  the 
posterior  ulnar  recurrent  and  the  inferior  profunda,  at  the  middle  of  the  back  of  the 
humerus  with  a  branch  of  the  superior  profunda,  and  behind  the  external  condyle 
with  the  posterior  terminal  branch  of  the  superior  profunda  and  the  posterior  inter- 
osseous recurrent  artery. 

The  Eadial  Artery. 

The  radial  artery  (a.  radiaHs,  Figs.  631,  632,  and  633)  is  the  smaller  of  the 
two  terminal  branches  of  the  brachial  artery,  but  it  is  the  more  direct  continuation 
of  the  parent  trunk.  It  commences  in  the  ante-cubital  fossa  opposite  the  neck  of 
the  radius,  and  terminates  in  the  palm  of  the  hand,  by  anastomosing  with  the 
deep  branch  of  the  ulnar  artery,  and  thus  completing  the  deep  palmar  arch. 

The  trunk  is  divisible  into  three  parts. 

The  Jirst  part  Lies  on  the  front  of  the  forearm.  It  runs  downwards  aud  some- 
what outwards  to  the  apex  of  the  styloid  process  of  the  radius.  The  second  part 
curves  round  the  outer  side  of  the  wrist  and  across  the  back  of  the  trapezium  to 
reach  the  proximal  end  of  the  first  interosseus  space.  The  third  piart  passes 
forwards  through  the  first  interosseous  space  to  the  palm  of  the  hand,  where  it 
joins  the  deep  branch  of  the  ulnar  artery. 

Relations  of  the  first  part. — Posterior. — It  passes  successively  in  front  of  the 
following  structures  :  the  tendon  of  insertion  of  the  biceps,  the  supinator  brevis,  the 
pronator  radii  teres,  the  radial  portion  of  the  flexor  sublimis  digitorum,  the  flexor  longus 
pollicis,  the  pronator  quadratus,  and  the  anterior  ligament  of  the  wrist-joint.     Anterior. — 


832 


THE  VASCULAE  SYSTEM. 


Biceps  — 
Bracliial  artery  ~ 


Median  nerve 

Musculo-sijiral_ 
nerve 

Radial  recurrent 

artery 

Bracliialis 

anticns 

Supinator 

longiis 

Supinator  l)revis 

Radial  recurrent 

artery 

Supinator  brevis 


Flexor  sublimis 
digitorum 

Radial  artery 


The  artery  is  overlapped  in  the  upper  half  by  the  anterior  border  of  the  supinator  longus ; 
in  the  remainder  of  its  extent  it  is  covered  only  by  skin  and  fascia.  Lateral. — To  the 
outer  side  is  the  brachio-radialis,  or  supinator  longus,  and  the  radial  nerve.     This  latter 

lies  quite  near  to  the  artery  in  its  middle 
third.  To  the  inner  side  is  the  pronator 
radii  teres  above  and  the  flexor  carpi 
radialis  below.  Two  vense  comites,  one 
on  each  side,  accompany  the  artery. 

Branches  of  the  first  part. — 
(1)  The  radial  recurrent  (a.  recurrens 
radialis)  arises  in  the  ante-cubital  fossa. 
It  springs  from  the  outer  side  of  the 
radial  in  front  of  the  supinator  brevis. 
It  runs  outwards,  passes  between  the 
radial  and  posterior  interosseous  nerves, 
and  then  ascends  to  the  external  con- 
dyle of  the  humerus,  where  it  anasto- 
moses with  the  anterior  terminal  branch 
of  the  superior  profunda.  The  radial 
recurrent  supplies  numerovis  muscular 
branches  to  the  supinator  longus,  the 
supinator  brevis,  the  extensor  carpi 
radialis  longior,  and  the  extensor  carpi 
radialis  brevior. 

(2)  Muscular  branches  (rami  mus- 
culares)  to  the  muscles  on  the  radial  side 
of  the  anterior  aspect  of  the  forearm. 

(3)  The  superficialis  volse  (ramus 
volaris  superficialis.  Fig.  631)  is  a 
slender  vessel  which  arises  a  short 
distance  above  the  wrist  and  runs 
downwards  across  the  ball,  of  the 
thumb.  It  usually  pierces  the  super- 
ficial muscles  of  the  thenar  eminence, 
and  terminates  either  in  their  sub- 
stance or  by  uniting  with  the  ulnar 
artery  and  completing  the  superficial 
palmar  arch  of  the  hand. 

(4)  An  anterior  radial  carpal 
branch  (ramus  carpeus  volaris)  passes 
inwai'ds  beneath  the  flexor  tendons  and 
their  synovial  sheaths,  and  crosses  the 
anterior  carpal  ligaments.  It  anasto- 
moses with  the  anterior  cai'pal  branch 
of  the  ulnar  artery  to  form  the  anterior 
carpal  arch,  and  it  receives  conmavmi- . 
cations  from  the  anterior  interosseous 
artery  and  from  the  deep  palmar  arch. 

Relations  of  the  second  part. 

— As  it  curves  roiuid  the  outer  side 
and  the  back  of  the  wrist,  the  radial 
artery  lies  upon  the  external  lateral 
ligament  of  the  intercarpal  joint  and 
upon  the  back  of  the  trapezium.  It 
is  crossed  by  the  extensor  ossis  meta- 
carpi  pollicis,  the  extensor  brevis 
pollicis,  and  the  extensor  longus  pol- 
licis ;  moi-e  superficially  it  is  covered 
by  fascia,  in  which  are  some  fila- 
ments of  tlio  radial  nerve  and  tin;  conimenccmcnt  of  tlic  radial  vein,  and  by  skin. 

Branches  of  the  second  part.  -( 1 )  Dorsales  Pollicis. — Two  small  arteries  which 
run  along  the  borders  of  the  dorsal  aspect  of  the  thuml) ;  they  supply  the  skin,  tendons, 
and  joints,  and  anastomose  with  the  palmar  digital  arteries. 


Radialis  indicis 
artery 


Flexor  longus  pollicis— 


Superficiali 


Fkj.  6.31.— Superficial  Dissection  of  the  Fiuint  ok 
THE  FoKEAKM  AND  Hand,  sliowiug  tlie  radial  and 
ulnar  arteries  and  the  superficial  palmar  arch  with  its 
branches. 


THE  EADIAL  AETERY. 


833 


Biceps 


Radial 

recurrent 

artery 

Orbicular 
ligament 

Supinator 

longiis 

Muscular 

branch  of 

artery 

Radial  artery 


Pronator  teres 


Flexor  longus 
pollicis 


Brachial 

artery 

Anastomotic 
artery 

Brachialis 

anticus 

Pronator 

teres 


Ulnar 

recuiTent 

artery 


Flexor ' 

profundus 

digitorum 


Ulnar  artery 


Anterior 

interosseous 

arteiy 


(2)  Dorsalis  Indicis. — A  slender  arteiy  which  runs  downwards  on  the  uhiar  head  of 
the  first  dorsal  interosseous  muscle  and  along  the  dorsal  aspect  of  the  radial  border  of  the 
index-finger. 

(3)  and  (4)  The  metacarpal  or  first 
dorsal  interosseous  and  posterior  radial 
carpal  arise  by  a  common  trunk  which 
crosses  beneath  the  extensor  longus 
pollicis. 

(a)  The  metacarpal  branch  (a.  metacarpea 
dorsalis)  descends  on  the  dorsal  aspect  of  the 
second  dorsal  interosseous  muscle,  and  divides 
opposite  the  heads  of  the  metacarpal  bones 
into  two  digital  branches  which  supply  the 
adjacent  sides  of  the  index  and  middle 
fingers.  (6)  The  posterior  carpal  branch 
(ramus  carjjeus  dorsalis)  runs  inwards  on  the 
dorsal  carpal  ligaments,  and  in  front  of  the 
extensor  tendons,  to  anastomose  with  the 
jjosterior  carjjal  branoli  of  the  ulnar  artery, 
and  to  complete  the  dorsal  carpal  arch,  which 
receives  the  terminations  of  the  anterior 
and  posterior  interosseous  arteries.  The 
dorsal  cardial  arch  gives  oft'  the  second  and 
third  dorsal  interosseous  arteries  (aa.  meta- 
carpte  dorsales),  which  descend  on  the  dorsal 
aspects  of  the  third  and  fourth  dorsal  in- 
terosseous muscles  as  far  as  the  heads  of 
the  metacarpal  bones,  where  each  divides 
into  two  branches  (aa.  digitales  dorsales),  for 
the  adjacent  sides  of  the  third  and  fourth 
and  the  fourth  and  fifth  fingers  respectively. 

Each  dorsal  interosseous  artery  is  con- 
nected with  the  deep  palmar  arch  by  a 
superior  perforating  branch  which  passes 
through  the  ujiper  jjart  of  the  correspond- 
ing interosseous  space,  and  with  a  digital 
branch  from  the  superficial  j^almar  arch  by 
an  inferior  perforating  branch  which  passes 
through  tlie  lower  part  of  the  space. 

Relations  of  the  third  part. — 

The  third  part  of  the  radial  artery  passes 
forwai'ds  between  the  two  heads  of  the 
first  dorsal  interosseous  muscle  to  reach 
the  palm,  where  it  turns  inwards  beneath 
the  upper  part  of  the  oblicpie  adductor 
muscle  of  the  thumb,  and,  after  passing 
through  the  upper  fibres  of  the  tranverse 
adductor,  or  between  the  adjacent  borders 
of  the  oblique  and  transverse  adductors,  it 
unites  with  the  deep  branch  of  the  ulnar 
artery,  completing  the  deep  palmar  arch. 

Branches  of  the  third  part. — 
(1)  The  princeps  pollicis  (a.  princeps 
pollicis)  branch  is  given  off  as  soon  as  the 
radial  artery  enters  the  palm.  It  runs 
downwards  in  front  of  the  first  metacarpal 
bone,  between  the  oblique  adductor  and 
the  opponens  pollicis,  and  under  cover  of  Fig.  632.  —  Deep  Dissection  of  the  Front  of  the 
the  long  flexor  tendon,  and  divides  near  Forearm   and  Hand,  showing  the  radial  and  ulnar 

the  lower  end  of  the  bone  into  collateral 
branches  which  run  along  the  sides  of 
the  thumb  and  anastomose  with  the  dorsales  pollicis  arteries. 

(2)  The  radialis  indicis  (a.  volaris  indicis  radialis)  is  a  branch  which  descends 
between  the  ulnar  head  of  the  first  dorsal  interosseous  muscle  and  the  transverse  adductor 
of  the  thumb.  It  runs  along  the  radial  side  of  the  index-finger  to  its  tip,  supplying  the 
adjacent  tissues  ;  not  uncommonly  it  anastomoses  with  the  superficial  palmar  arch. 

57 


Princeps 
pollicis 


Radialis 
indicis 


Flexor  carpi 


Superficial 


Anterior 
—  communioating 
artery 


Deep  branch 
of  ulnar  artery 


Deep  palmar 
"  arch 

Palmar 
_  interosseous 
arteries 
Digital 
artery 


arteries  and  their 
and  its  branches. 


)ranches  and  the  deep  palmar  arch 


834  THE  VASCULAR  SYSTEM. 

The  Ulnar  Aetery. 

The  ulnar  artery  (a.  ulnaris,  Figs.  631  and  632)  is  the  larger  terminal  branch,  but 
the  less  direct  continuation  of  the  brachial  artery.  It  commences  in  the  ante-cubital 
fossa,  opposite  the  neck  of  the  radius,  and  terminates  in  the  palm  of  the  hand, 
where  it  anastomoses  with  the  superficiahs  vola3  to  form  the  superficial  palmar  arch. 

From  its  origin  it  runs  obliquely  downwards  and  inwards,  beneath  the  muscles 
arising  from  the  internal  condyle,  to  the  junction  of  the  upper  and  middle  thirds  of 
the  forearm,  where  it  comes  into  relation  with  the  ulnar  nerve ;  it  then  descends 
vertically,  on  the  radial  side  of  the  ulnar  nerve,  to  the  wrist,  crosses  in  front  of  the 
main  part  of  the  annular  ligament  to  the  radial  side  of  the  pisiform  bone,  and 
enters  the  palm  of  the  hand  to  form  the  main  part  of  the  superficial  palmar  arch. 

Relations. — Posterior. — From  above  downwards  it  lies  in  front  of  the  lower  part  of 
the  brachialis  anticus,  the  flexor  profundus  digitorum,  and  the  deep  portion  of  the  anterior 
annular  ligament.  Anterior. — In  front  it  is  crossed,  in  the  oblique  part  of  its  course,  by 
the  pronator  radii  teres,  the  median  nerve,  which  is  separated  from  the  artery  by  the  deep 
head  of  the  pronatoi",  the  flexor  sublimis  digitorum,  the  flexor  carpi  radialis,  and  the 
palmaris  longus.  In  the  middle  third  of  the  forearm  it  is  overlapped  by  the  anterior 
border  of  the  flexor  carpi  ulnaris,  and  in  the  lower  third  it  is  covered  by  skin  and  fascia 
only.  A  short  distance  above  the  wrist  the  palmar  cutaneous  branch  of  the  median  nerve 
lies  in  front  of  it,  and  as  it  crosses  the  anterior  annular  ligament,  it  is  bound  down  by  a 
fascial  expansion  from  the  tendon  of  the  flexor  carpi  vdnaris.  Two  vense  comites,  which 
frequently  communicate  with  one  another,  lie  one  on  either  side  of  the  artery.  Lateral. — 
On  the  radial  side  there  is  also,  in  its  lower  two-thirds,  the  flexor  sublimis  digitorum. 
On  its  ulnar  side  there  are  the  flexor  carpi  ulnaris  and  the  ulnar  nerve. 

Branches. — (1)  The  anterior  ulnar  recurrent  is  a  small  branch  which  arises  in  the 
ante-cubital  fossa,  frequently  in  common  with  the  posterior  ulnar  recurrent.  It  passes 
upwards  to  the  front  of  the  internal  condyle,  luider  cover  of  the  pronator  radii  teres,  and 
anastomoses  with  branches  of  the  anastomotic  and  inferior  profunda  arteries. 

(2)  The  posterior  ulnar  recurrent  branch,  larger  than  the  anterior,  arises  in  the 
ante-cubital  fossa,  from  the  inner  side  of  the  ulnar  artery,  and  ascends  on  the  brachialis 
anticus,  and  under  cover  of  the  muscles  which  rise  from  the  internal  condyle  to  the  back 
of  that  prominence,  where  it  passes  between  the  humeral  and  olecranoid  heads  of  the 
flexor  carpi  ulnaris,  and  anastomoses  with  the  inferior  profunda  and  anastomotic  arteries. 
It  gives  branches  to  the  adjacent  muscles  and  to  the  elbow-joint. 

(3)  The  common  interosseous  artery  (a.  interossea  communis),  a  short  trunk  which 
springs  from  the  outer  and  back  part  of  the  iilnar  artery  in  the  lower  part  of  the  ante- 
cubital  fossa.  It  passes  backwards  towards  the  upper  border  of  the  interosseous  membrane, 
and  divides  into  anterior  and  posterior  interosseous  branches. 

(3a)  The  anterior  interosseous  artery  (a.  interossea  volaris)  descends  in  front  of  the 
interosseous  membrane,  between  the  adjacent  borders  of  the  flexor  longus  pollicis  and  the 
flexor  profundus  digitorum,  to  the  upper  border  of  the  pronator  quadratus,  where  it  pierces 
the  interosseous  membrane,  and  continues  its  descent,  first  on  the  posterior  surface  of  the 
membrane,  under  cover  of  the  extensor  longus  pollicis  and  extensor  indicis,  and  then  on 
the  radius,  in  the  groove  for  the  extensor  commvmis  digitorum,  and  it  terminates  on  the 
back  of  the  carpus  in  the  posterior  carpal  arch.  It  is  accompanied  whilst  in  front  of  the 
interosseous  membrane  by  the  anterior  interosseous  nerve,  and  after  it  has  pierced  the 
membrane,  by  the  posterior  interosseous  nerve. 

Branches.  — («)  Nutrient  to  tlic  ladiii.s  and  uhia ;   (h)  Muscular  to  the  adjacent  muscles; 

(c)  Tlic  anterior  communicating,  a  slender  l)raaK'h  wliicli  descends  boliiiid  tlie  pronator  quadratus 
and    in    front   of  tlie   interosseous   mernlaane   to   anastomose   with    the  anterior  carpal   arch ; 

(d)  Small  anastomotic  branches  are  given  off  at  tin-  Lack  of  the  forearm  to  anastomose  with  the 
posterior  interosseous  artery  ;  (c)  Tlie  comes  nervi  mediani  (a.  mediana)  is  a  long  slender  branch 
which  rises  from  the  upper  part  of  the  artery  and  descends  in  the  front  of  the  median  nerve  to 
the  palm,  where  it  anastomoses  with  recurrent  brandies  of  tlie  superiicial  palmar  arch. 

(Sb)  The  posterior  interosseous  trunk  (a.  interossea  dorsalis)  is  usually  smaller  tlian 
the  anterior  intei-osseous.  It  yiasses  backwards  between  the  upper  border  of  the  inter- 
osseous membrane  and  the  oblique  ligament,  and  then  between  the  supinator  brevis  and 
the  extensor  ossis  metacarpi  pollicis,  after  which  it  descends  Itetween  the  superficial  and 
deep  muscles  on  the  back  of  the  forearm  to  the  wrist,  where  it  anastomoses  with  the 
anterior  interosseous  artery  and   with   the    posterior  carpal    arch.      As    it   crosses    the 


THE  AKTEKIAL  AKCHES  OF  THE  WKIST  AND  HAND. 


835 


Triceps 


extensor  ossis  metacarpi  pollicis  it  is  accompauied  by  the  postei'ior  interosseous  nerve, 
but  in  the  remainder  of  its  course  it  is  separated  from  the  nerve  by  the  deep  muscles. 

Branches. — («)  A  posterior  interosseous  recurrent  (a.  iuterossea  recurrens)  branch  is  given  off 
as  soon  as  tlie  posterior  interosseous 
artery  has  passed  beneath  the  lower 
border  of  the  supinator  brevis.  It 
ascends  on  the  posterior  surface  of 
the  supinator  brevis,  under  cover 
of  the  anconeus,  to  the  back  of  the 
external  condyle  of  the  humerus, 
where  it  anastomoses  with  the 
posterior  terminal  branch  of  the 
superior  profunda  and  with 
branches  of  the  anastomotic  artery. 
(b)  Muscular  branches  to  both  super- 
ficial and  deep  muscles  on  the  back 
of  the  forearm,  (c)  Cutaneous 
branches  to  the  skin  on  the  Ijack  of 
the  forearm  and  the  back  of  the 
wrist. 


Anconeu 


(4)  The  anterior  ulnar  carpal 
(ramus  carpeus  volaris),  a  small 
branch  given  off  above  the  an- 
terior annular  ligament ;  it  passes 
outwards  beneath  the  flexor  ten- 
dons and  their  sheaths  on  the 
anterior  surface  of  the  carpal 
ligaments,  and  anastomoses  with 
the  anterior  carpal  branch  of  the 
radial  to  form  the  anterior  carpal 
arch. 

(5)  The  posterior  ulnar  carpal 
branch  (ramus  carpeus  dorsalis) 
arises  from  the  back  of  the  inner 
side  of  the  ulnar  artery  just 
above  the  pisiform  bone.  It 
passes  backwards  under  cover 
of  the  flexor  and  extensor  carpi 
ulnaris  muscles  to  the  back  of 
the  carpus,  where  it  unites  with 
the  posterior  carpal  branch  of 
the  radial  to  form  the  posterior 
carpal  arch. 

(6)  Profunda  (ramus  volaris 
profundus). — This  branch  de- 
scends between  the  abductor  and 
flexor  brevis  minimi  digiti,  and, 
turning  outwards  beneath  the 
flexor  brevis,  theopponens  minimi 
digiti,  and  the  flexor  tendons  and 
their  sheaths,  joins  the  termina- 
tion of  the  radial  artery  to  com- 
plete the  deep  palmar  arch. 


The  Arterial  Arches  of 
THE  Wrist  and  Hand. 


Suijinator  brevis 

Posterior  inter- 
osseous recurrent 
artery 

Posterior  inter- 
osseous artery- 
Flexor  (.-arpi 
ulnaris 


Extensor  carpi 
ulnaris 


Anterior  inter- 
osseous artery 

Posterior  inter- 
osseous artery 


Posterior  carpal 
arch 


Superior  per- 
forating artery 

Dorsal  inter- 
osseous arteries 


Supinator  longus 


Extensor  carpi 
radialis  lonaior 


_  Extensor  carpi 
ulnaris 

_  Extensor  communis 
digitoruin 


Extensor  carpi 
radialis  brevior 

Posterior 
interosseous  nerve 


Pronator  radii  teres 


Extensor  ossis 
metacarpi  pollicis 


Extensor  longus 
pollicis 

Extensor  brevis 
Ijollicis 


Extensor  indicis 


Radial  arterj- 


Dorsalis  pollicis 
arteries 


Dorsalis  indicis 


Fig.  633. — The  Posterior  Interosseous  Artery  and  the 
Second  Part  of  the  Radial  Artery,  with  their  Branches. 


Anterior     Carpal    Arch 

(Fig.  632).  — The  anterior 
carpal  arch  lies  on  the  front  of  the  carpus  behind  the  flexor  tendons  and  their 
synovial  sheaths.  It  is  formed  by  the  union  of  the  anterior  carpal  branches  of  the 
radial  and  ulnar  arteries,  and  it  receives  the  communicating  branch  from  the 
anterior  interosseous  artery  above  and  recurrent  branches  from  the  deep  palmar 


836  THE  VASCULAE  SYSTEM. 

arch  below.  The  branches  of  distribution  which  pass  from  it  supply  the  ligaments 
and  synovial  membranes  of  the  wrist  and  of  the  intercarpal  and  carpo-metacarpal 
joints. 

Posterior  or  Dorsal  Carpal  Arch  (Fig.  633). — This  arch  lies  on  the  posterior 
carpal  ligaments  under  cover  of  the  extensor  tendons  and  their  sheaths.  It  is 
formed  by  the  union  of  the  dorsal  carpal  branches  of  the  radial  and  ulnar  arteries, 
and  receives  the  terminations  of  the  anterior  and  posterior  interosseous  arteries. 

Branches. — (a)  Articular  to  the  adjacent  articulations.  (6)  Dorsal  interosseous, 
two  slender  branches  which  run  downwards  on  the  third  and  fourth  dorsal  interosseous 
muscles  to  the  clefts  of  the  fingers,  where  each  divides  into  collateral  branches.  They 
communicate  near  their  origins  with  the  deep  palmar  arch  by  the  superior  perforating 
arteries,  and  near  their  terminations  with  the  palmar  digital  vessels  through  the  inferior 
perforating  arteries.  Their  collateral  terminal  branches  run  downwards  on  the  dorso- 
lateral aspects  of  the  fingers  Avhich  bound  the  third  and  fourth  interosseous  spaces,  and 
they  anastomose  with  the  collateral  digital  branches  of  the  palmar  digital  arteries. 

Superficial  Palmar  Arch  (arcus  volaris  superficialis,  Fig.  631). — This  arterial 
arch  includes  the  terminal  portion  of  the  ulnar  artery,  and  is  usually  completed 
externally  by  the  superficialis  volse,  or  sometimes  by  the  radialis  indicis,  or  the 
princeps  pollicis.  It  extends  from  the  ball  of  the  little  finger  to  the  inner  border 
of  the  superficial  head  of  the  flexor  brevis  pollicis,  and  reaches  as  low  down  as  a 
line  drawn  across  the  palm  at  the  level  of  the  lower  border  of  the  fully  abducted 
thumb.  It  is  covered  by  the  integuments  and  the  central  portion  of  the  palmar 
fascia,  and,  on  the  ulnar  side  of  the  palm,  by  the  palmaris  brevis,  and  it  is 
accompanied  by  venae  comites.  It  is  in  contact  behind  with  the  flexor  brevis  and 
opponens  minimi  digiti,  and  with  the  digital  branches  of  the  ulnar  and  median 
nerves,  as  well  as  with  the  flexor  tendons  and  the  lumbrical  muscles. 

Branches. — Four  digital  arteries  (aa.  digitales  volares  communes)  arise  from  the 
convexity  of  the  arch.  The  innermost  descends  along  the  ulnar  border  of  the  little  finger, 
accompanied  by  the  internal  digital  branch  of  the  ulnar  nerve ;  the  outer  three  pass  down- 
wards superficial  to  the  digital  nerves,  along  the  middle  of  the  three  inner  interosseous 
spaces  towards  the  interdigital  clefts,  just  above  which  each  digital  artery  divides  into 
two  collateral  digital  arteries  (aa.  digitales  volares  propriee),  which  supply  the 
contiguous  sides  of  the  fingers  bounding  the  cleft.  As  the  collateral  digital  branches 
descend  along  the  sides  of  the  fingers  they  lie  superficial  to  the  corresponding  digital 
nerves,  and  supply  branches  to  the  joints,  to  the  flexor  tendons  with  their  sheaths,  and  to 
the  skin  and  subcutaneous  tissues  on  the  palmar  surface  ;  they  also  send  backwards  dorsal 
branches  which  anastomose  with  the  dorsal  digital  arteries  and  supply  the  tissues  on  the' 
dorsal  aspects  of  the  second  and  terminal  phalanges.  Some  of  the  backwardly-directed 
branches  form  a  plexus  in  the  matrix  of  the  nail.  In  the  pulp  of  the  finger-tips  anasto- 
mosing twigs  join  to  form  arches  from  which  numerous  branches  are  given  oS  to  the  skin 
and  subcutaneous  fat. 

Each  of  the  outer  three  digital  arteries  is  joined  immediately  above  its  division  by  a 
palmar  interosseous  branch  from  the  deep  palmar  arch  and  an  inferior  communicating 
artery  from  a  dorsal  interosseous  artery.  The  innermost  digital  artery  is  joined  by  a 
branch  which  comes  either  from  the  inner  palmar  interosseous  artery  or  from  the  deep 
palmar  arch 

Deep  Palmar  Arch  (arcus  volaris  profundus.  Fig.  632). — The  deep  palmar 
arch  extends  from  the  base  of  the  metacarpal  bone  of  the  little  finger  to  the  upper 
end  of  the  first  interosseous  space,  and  is  formed  by  the  terminal  part  of  the  radial 
artery,  anastomosing  with  the  deep  branch  of  the  ulnar.  It  is  from  half  to  three 
quarters  of  an  inch  (12  to  18  mm.)  above  the  level  of  the  superficial  palmar  arch,  and 
it  Hes  deeply  in  the  palm,  in  contact  with  the  bases  of  the  metacarpal  bones  and 
their  ligaments  and  on  the  origin  of  the  interossei  muscles  ;  it  is  under  cover  of  the 
flexor  tendons  and  their  synovial  sheaths. 

Branches. — («)  The  superior  perforating  (rami  perforantes) ;  three  small  arteries 
which  pass  backwards  through  the  inner  three  interosseous  spaces,  and  between  the  origins 
of  the  dorsal  interossei  muscles.  They  anastomose  on  the  dorsum  of  the  hand  with  the 
dorsal  interosseous  arteries. 


PAEIETAL  BEANCHES  OF  DESCENDING  THOEACIC  AOETA.     837 

(b)  Small  irregular  recurrent  branches  pass  upwards  and  unite  with  the  anterior 
carpal  arch. 

(c)  The  articular  to  the  adjacent  articulations. 

(d)  The  palmar  interosseous  arteries  (aa.  metacarpese  volares)  are  three  vessels  which 
pass  downwards  on  the  interosseous  muscles  of  the  three  inner  spaces.and  under  cover  of 
the  flexor  tendons.  They  terminate  by  anastomosing  with  the  palmar  digital  arteries  just 
befoi'e  the  latter  vessels  divide  into  collatei'al  branches. 

((?)  The  communicating,  a  small  irregular  branch  which  passes  inwards  between  the 
flexor  tendons  and  the  short  muscles  of  the  little  finger  to  anastomose  with  the  innermost 
palmar  digital  artery. 

BRANCHES  OF  THE  DESCENDING  THORACIC  AORTA. 

The  branches  given  off  from  the  thoracic  portion  of  the  descending  aorta  are 
distributed  chiefly  to  the  walls  of  the  thorax  and  to  the  thoracic  viscera.  They 
contribute  also  to  the  supply  of  the  spinal  cord  and  its  membranes,  and  to  that 
of  the  vertebral  column  and  of  the  upper  part  of  the  abdominal  wall.  The 
branches,  which  are  numerous  and  for  the  most  part  arranged  in  pairs,  are  as 
follows : — 

rintercostal.  TBronchial. 

Parietal  i  Subcostal.  Visceral   i  Esophageal. 

Diaphragmatic.  1  ericardial. 

[The  vas  aberrans.  I^Mediastinal. 

Pakietal  Bkanches  of  the  Descending  Thoracic  Aorta. 

1.  Intercostal  Arteries  (a.  intercostales).  —  There  are  nine  pairs  of  aortic 
intercostal  arteries.  They  usually  arise  separately,  though  not  uncommonly 
a  pair  may  take  origin  by  a  common  trunk  from  the  back  of  the  aorta,  and 
are  distributed  to  the  lower  nine  intercostal  spaces,  to  the  spinal  column,  to 
the  contents  of  the  spinal  canal,  and  to  the  muscles  and  skin  of  the  back. 
The  first  three  on  each  side  also  give  branches  to  the  mammary  gland. 
The  arteries  of  opposite  sides  closely  correspond,  but,  since  the  aorta  in  the 
thoracic  region  lies  on  the  left  side  of  the  spinal  column,  the  right  intercostal 
arteries  cross  the  front  of  the  vertebral  column,  behind  the  oesophagus,  the  thoracic 
duct,  and  the  vena  azygos  major,  and  are  longer  than  the  left  arteries.  In  other 
respects  the  course  of  all  the  aortic  intercostal  arteries  is  almost  identical.  They 
run  outwards  and  backwards  on  the  sides  of  the  bodies  of  the  vertebra?  to  the  inter- 
costal spaces,  passing  behind  the  pleura,  and  being  crossed,  opposite  the  heads  of 
the  ribs,  by  the  sympathetic  cord.  The  lower  arteries  are  also  crossed  by  the 
splanchnic  nerves,  and  those  on  the  left  side  are  in  addition  .crossed  by  the  smaller 
azygos  veins.  On  reaching  an  intercostal  space  each  artery  runs  upwards,  some- 
times behind,  sometimes  in  front  of  the  corresponding  intercostal  nerve,  to  the 
upper  border  of  the  space,  along  which  it  is  continued  in  the  subcostal  groove.  It 
lies  at  first  between  the  pleura  and  the  posterior  intercostal  membrane,  immediately 
below  the  intercostal  nerA'e ;  it  then  pierces  the  intercostal  membrane,  and  runs 
between  it  and  the  external  intercostal  muscle  as  far  as  the  angle  of  the  rib, 
beyond  which  it  is  continued  forward  between  the  internal  and  external  intercostal 
muscles.  In  the  subcostal  groove  the  artery  lies  between  the  corresponding  vein 
above  and  the  intercostal  nerve  below,  and  it  terminates  in  front  by  anastomosing 
\\-ith  an  anterior  intercostal  branch  of  the  r'nternal  mammary  or  of  the  musculo- 
phrenic artery.  The  lower  two  intercostal  arteries  on  each  side  extend  beyond 
their  spaces  to  the  abdominal  wall,  and  anastomose  with  branches  of  the  superior 
epigastric,  subcostal,  and  lumbar  arteries. 

Branches. — (a)  Dorsal  (ramus  posterior). — As  each  artery  enters  its  intercostal 
space  it  gives  oft'  a  posterior  or  dorsal  branch  which  passes  backwards,  accompanied  by 
the  posterior  primary  division  of  a  spinal  nerve,  internal  to  the  superior  costo-transvei-se 
hgament,  between  the  necks  of  the  ribs  which  bound  the  space,  and  between  the 
adjacent  transverse  processes,  to  the  vertebral  groove,  where  it  divides  into  internal  and 
external  terminal  branches.     The  internal  branch  (ramus  cutaneus  medialis)  passes  back- 

57  « 


838  THE  VASCULAE  SYSTEM. 

wards  and  inwards  either  over  or  through  the  multifidus  spinte,  giving  branches  to  the 
muscles  between  which  it  passes  and  to  the  vertebral  column.  The  external  branch  (ramus 
cutaneus  lateralis)  runs  outwards  under  cover  of  the  longissimus  dorsi  to  the  interval 
between  it  and  the  musculus  accessorius.  It  terminates  in  the  skin  of  the  back,  after  giving 
branches  to  the  adjacent  muscles.  A  spinal  branch  (ramus  spinalis)  from  each  dorsal  artery 
passes  through  the  corresponding  intervertebral  foramen,  and  enters  the  spinal  canal,  to 
the  contents  and  walls  of  which  it  is  distributed.  It  divides  into  three  branches — neural, 
post-central,  and  pre-laminar.  The  neural  branch  divides  into  two  branches  which  run 
inwards  on  the  roots  of  the  spinal  nerve,  pierce  the  dura  mater  and  arachnoid,  and  divide 
into  branches  some  of  which  pass  to  the  membranes  of  the  cord,  whilst  others  are  continued 
on  to  reinforce  the  dorsal  and  ventral  spinal  arteries.  The  jjcM-central  branch  divides  into 
ascending  and  descending  branches  which,  anastomosing  with  similar  branches  above  and 
below,  form  a  series  of  vertical  arches  on  the  back  of  the  bodies  of  the  vertebrae.  The 
arches  of  opposite  sides  are  connected  by  short  transverse  anastomoses.  The  pre-laminar 
branch  is  small,  and  its  ascending  and  descending  branches  are  distributed  in  a  similar 
though  less  i-egular  manner  on  the  posterior  wall  of  the  spinal  canal. 

(6)  A  collateral  brancli  springs  from  the  trunk  of  each  intercostal  artery  near  the 
angle  of  the  rib.  It  descends  to  the  lower  border  of  the  intercostal  space,  along  which  it 
iiins  forwards  to  anastomose  in  front,  like  the  intercostal  artery  itself,  with  a  separate 
anterior  intercostal  branch  of  the  internal  mammary  or  musculo-phrenic  artery.  The 
collateral  branches  of  the  lower  two  intercostal  arteries  on  each  side  are  inconstant ; 
when  present  they  are  small,  and  terminate  in  the  abdominal  wall. 

(c)  Muscular  branches  (rami  musculares)  to  the  adjacent  muscles  are  given  off  both 
by  the  main  trunk  and  its  collateral  branch. 

id)  A  lateral  cutaneous  (ramus  cutaneus  lateralis)  offset  from  the  intercostal  artery 
accompanies  the  lateral  cutaneous  branch  of  the  intercostal  nerve. 

In  addition  to  the  above-named  branches  the  first  aortic  intercostal  on  each  side 
anastomoses  with  the  superior  intercostal,  and  may  supply  the  whole  or  the  greater  part  of 
the  second  intercostal  space,  and  the  first  right  aortic  intercostal  frequently  gives  origin  to 
the  right  bronchial  artery.  The  upper  three  or  four  aortic  intercostals  on  each  side  give 
branches  to  the  mammary  gland  which  anastomose  with  branches  of  the  long  thoracic  and 
internal  mammary  arteries.  Longitudinal  anastomoses  between  adjacent  intercostal  arteries 
and  their  dorsal  branches  sometimes  exist  near  the  necks  of  the  ribs,  or  near  the  transverse 
processes.      These  longitudinal  anastomoses  are  of  considerable  morphological  interest. 

2.  The  subcostal  arteries  are  the  last  pair  of  parietal  branches  given  off  from  the 
thoracic  aorta.  They  are  in  series  with  and  are  very  similar  to  the  aortic  intercostal 
arteries,  but  are  situated  below  the  last  ribs.  Each  runs  along  the  lower  border  of 
the  twelfth  rib  in  company  with  the  last  dorsal  nerve.  It  passes  beneath  the  liga- 
mentum  arcuatum  externum  to  the  abdomen,  and  there  crosses  in  front  of  the  quad- 
ratus  lumborum,  and  behind  the  kidney  and  the  adjacent  part  of  the  colon.  It 
next  x^ierces  the  aponeurosis  of  origin  of  the  transversalis  abdominis,  and  runs 
between  the  transversalis  and  the  internal  oblique  muscles,  anastomosing  with  the 
lower  intercostal  arteries,  with  the  lumbar  arteries,  and  with  branches  of  the 
superior  epigastric  artery. 

3.  Diaphrag'matic  branches  (aa.  phrenicae  superiores)  are  given  off  from  the 
lower  part  of  the  thoracic  aorta.  They  are  small  vessels  which  ramify  on  the 
upper  surface  of  the  diaphragm,  and  anastomose  with  branches  of  the  superior 
phrenic  and  musculo-phrenic  arteries. 

4.  The  vas  aberrans  is  a  variable  and  inconstant  branch  of  the  thoracic  aorta ; 
it  represents  the  dorsal  roots  of  the  fourth  and  fifth  right  aortic  arches  of  the 
embryo.  When  present  it  arises  from  the  front  and  right  side  of  the  upper  part  of 
the  main  trunk  near  the  ujjper  bronchial  artery,  and  passes  upwards  and  to  the 
right  behind  the  cesophagus;  it  frequently  anastomoses  with  the  right  superior 
intercostal  artery,  and  it  may  be  enlarged  and  form  the  first  part  of  the  right 
subclavian  artery. 

Visceral  Branches  of  the  Descending  Thoracic  Aorta. 

1.  The  bronchial  branches  (aa.  bronchiales)  of  the  thoracic  aortas  are  usually 
two  in  number — an  upper  and  a  lower — and  both  pass  to  the  left  lung.  The  upper 
left  bronchial  artery  arises  from  the  front  of  the  main  trunk  opposite  the  fifth 


PAKIETAL  BEANCHES  OF  THE  ABDOMINAL  AOETA.    839 

dorsal  vertebra;  the  inferior  left  hroncldal  artery  usually  takes  origin  near  the 
lower  border  of  the  left  bronchus.  Both  vessels  are  directed  downwards  and  out- 
wards to  the  back  of  the  bronchus,  which  they  accompany,  and,  dividing  similarly, 
they  follow  its  ramifications  in  the  lung.  They  not  only  supply  the  walls  of  the 
bronchial  tubes  and  the  substance  of  the  lungs,  but  also  give  branches  to  the 
bronchial  glands,  the  pulmonary  vessels,  the  pericardium,  and  the  oesophagus. 

As  a  rule  there  is  only  one  right  bronchial  artery,  and  it  arises  from  the  first 
right  aortic  intercostal  artery ;  but  it  not  uncommonly  arises  from  the  upper  left 
bronchial  artery,  and  more  rarely  it  springs  directly  from  the  aorta.  In  its  course 
and  distriljution  it  corresponds  to  the  bronchial  arteries  of  the  left  side. 

2.  The  (Esophageal  branches  (aa.  oesophagea3)  are  variable;  usually  four  or 
five  small  branches  spring  from  the  front  of  the  aorta  and  pass  forwards  to  the 
oesophagus,  in  the  walls  of  which  they  ramify,  anastomosing  above  with  branches 
of  the  left  bronchial  and  inferior  thyroid  arteries,  and  below  with  oesophageal 
branches  of  the  coronary  and  phrenic  arteries. 

3.  The  pericardial  branches  (rami  pericardiac!)  consist  of  three  or  four  small 
irregular  vessels  which  are  distributed  on  the  surface  of  the  pericardium. 

4.  Small  mediastinal  branches  (rami  mediastinales)  pass  to  the  areolar  tissue 
and  glands  in  the  posterior  mediastinal  space,  and  to  the  posterior  part  of  the 
diaphragm. 

BRANCHES  OF  THE  ABDOMINAL  AORTA. 

The  branches  of  the  abdominal  portion  of  the  aorta  are  distributed  almost 
entirely  to  the  walls  and  contents  of  the  abdominal  cavity,  but  some  also  supply 
small  branches  to  the  vertebral  column,  and  to  the  contents  of  the  spinal  canal,  and 
others  are  prolonged  into  the  pelvis.  They  are  divisible  into  parietal  and  visceral 
groups,  both  of  which  include  paired  and  single  (unpaired)  vessels. 


(I  Inferior  phrenic. 
Paired.-,  Lumbar.  Visceral 

I^Common  iliac. 
Single.    Middle  sacral. 


[  r  Suprarenal. 

Paired.    Renal. 

'  Spermatic  or  ovarian, 
j  Coeliac  axis. 
Single.  -|  Superior  mesenteric. 
I  Liferior  mesenteric. 


Parietal  Beanches  of  the  Abdominal  Aorta. 

1.  The  inferior  phrenic  arteries  (aa.  phrenicee  inferiores.  Fig.  634)  are  two 
in  number,  and  are  of  small  size ;  they  arise,  either  separately  or  by  a  common 
trunk,  from  the  aorta,  immediately  below  the  diaphragm  on  the  under  surface 
of  which  they  are  distributed.  Diverging  from  its  fellow,  each  artery  runs 
upwards  and  outwards  on  the  corresponding  crus  of  the  diaphragm — that  on  the 
right  side  passing  behind  the  inferior  vena  cava,  that  on  the  left  behind  the  oeso- 
phagus— and  just  before  reaching  the  central  tendon  of  the  diaphragm  it  divides 
into  internal  and  external  terminal  branches.  The  interiial  branch  of  each  artery 
runs  forward  and  anastomoses  with  its  fellow  of  the  opposite  side,  forming  an  arch, 
convex  forwards,  along  the  front  of  the  central  tendon  of  the  diaphragm.  Offsets 
from  this  arch  anastomose  with  the  superior  phrenic,  musculo-phrenic,  and  internal 
mammary  arteries.  The  external  branch,  passes  outwards  towards  the  lower  ribs, 
and  anastomoses  with  the  musculo-phrenic  and  lower  intercostal  arteries. 

In  addition  to  supplying  the  diaphragm  each  inferior  phrenic  artery  frequently 
gives  a  superior  capsular  branch  to  the  suprarenal  body  of  its  own  side,  and  occasion- 
ally small  hepatic  branches  pass  through  the  coronary  ligament  to  the  liver. 
Further,  the  left  artery  gives  branches  to  the  oesophagus  which  anastomose  with 
oesophageal  branches  of  the  aorta  and  of  the  coronary  artery,  whilst  from  the  artery 
of  the  right  side  minute  branches  pass  to  the  inferior  vena  cava. 

2.  The  lumbar  arteries  (aa.  lumbales)  correspond  to  the  intercostal  branches  of 
the  thoracic  aorta.  They  are  in  series  with  them,  their  distribution  is  very  similar, 
and,  like  the  intercostals,  they  arise,  either  separately  or  by  common  trunks,  from 
the  back  of  the  aorta. 

57  & 


840 


THE  VASCULAE  SYSTEM. 


There  are  usually  four  pairs  of  lumbar  arteries,  but  occasionally  a  fifth  pair 
arises  from  or  in  common  with  the  middle  sacral  artery. 

From  their  origins  the  lumbar  arteries  pass  backwards  and  outwards  on  the 
front  and  sides  of  the  bodies  of  the  upper  four  lumbar  vertebrae  to  the  intervals 
between  the  adjacent  transverse  processes,  beyond  which  they  are  continued  in  the 
abdominal  wall. 

They  lie  on  the  bodies  of  the  corresponding  lumbar  vertebrae.     In  their  back- 


Hepatic  veins 


Inferior  phrenic  artei  y 

Suprarenal  bocty 
Inferior  vena  cava 


Right  ovarian  vein 

Ovarian  artery 

Ureter 


Ascending  colon 

Common  iliac  veiiT 

Common  iliac  artery 
Middle  sacral  artery 


External  ilian 
arterv 


External  iliac" 
vein 


ffisophagus 


Crus  of  diaphragm 
Inferior  phrenic 
artery 

Suprarenal  body 
Coeliac  axis 
Suprarenal  vein 
Superior 
mesenteric  artery 

Renal  artery 
Renal  vein 
Lumbar  arteries 


Left  colic  artery 

Ovarian  artery 
Inferior  mesenteric 
aiteiy 

—  Descending  colon 

—  Psoas  muscle 
Common  iliac  artery 

, Sigmoid  artery 

Common  iliac  vein 

Superior  hseinor- 
rhoidal  artery 

Iliac  colon 

Pelvic  colon 

External  iliac 
mm        artery 

External  iliac  vein 


Fallopian  tube 


Fio.  634.— Thk  AiiDOMiNAL  Aorta  and  fts  Bhanches. 

ward  course,  and  while  still  in  relation  with  the  vertebral  bodies,  each  artery  is 
crossed  by  the  sympathetic  cord,  and  then,  after  passing  internal  to  and  being  pro- 
tected by  the  fibrous  arches  from  which  the  muscle  arises,  it  runs  behind  the'psoas 
muscle  and  the  lumbar  plexus.  The  upper  two  arteries  on  each  side  also  pass  behind 
the  crura  of  the  diaphragm.  Beyond  the  interval  between  the  transverse  processes  of 
the  vertebrae  each  artery  turns  outwards  and  crosses  the  quadratus  lumborum— the 
last  usually  passing  in  front  of,  and  the  others  behind  the  muscle ;  it  then  pierces 
the  aponeurosis  of  origin  of  the  transversalis,  and  proceeds  forwards  in  the  lateral 
abdominal  wall  in  the  interval   between  the  transversalis  and   internal   oblique 


COMMON  ILIAC  AETEEIES.  841 

muscles.  The  lumbar  arteries  anastomose  with  one  another,  with  the  lower  inter- 
costal and  subcostal  arteries,  and  with  branches  of  the  superior  and  deep  epigastric 
and  of  the  deep  circumflex  iliac  and  ilio-lumbar  arteries. 

Fine  twigs  also  pass  from  the  lumbar  arteries  to  the  extra-peritoneal  fat,  and 
anastomose  with  corresponding  branches  from  the  inferior  phrenic  and  ilio-lumbar 
arteries,  and  with  small  branches  from  the  hepatic,  renal,  and  coUc  arteries,  to  form 
the  subperitoneal  plexus  of  Turner. 

The  abdominal  aorta  lies  but  little  to  the  left  of  the  middle  line,  and  con- 
sequently the  right  lumbar  arteries  are  scarcely  longer  than  the  left.  On  the  right 
side  the  arteries,  which  near  their  origins  lie  more  in  front  of  the  vertebral  bodies, 
pass  behind  the  inferior  vena  cava,  the  upper  two  arteries  being  separated  from  this 
vessel  by  the  right  crus  of  the  diaphragm.  The  upper  two  right  arteries  also  pass 
behind  the  receptaculum  chyli  and  the  lower  end  of  the  large  azygos  vein. 

Branches. — Dorsal  (ramus  dorsalis).  —  Each  lumbar  artery  gives  off,  opposite  the 
interval  between  the  vertebi'al  transverse  processes,  a  dorsal  branch  of  considerable  size. 
It  is  analogous  with  and  distributed  like  the  corresponding  branch  of  an  aortic  intercostal 
artery  (p.  837).  Muscular  branches  are  given  off,  both  from  the  main  trunk  and  its 
dorsal  branch,  to  the  adjacent  muscles. 

3.  The  middle  sacral  artery  (a.  sacralis  media,  Fig.  634)  is  a  single  median 
vessel.  It  is  commonly  regarded  as  a  caudal  aorta  and  as  the  direct  continuation 
of  the  abdominal  aorta.  It  is,  however,  of  small  size,  and  almost  invariably  arises 
from  the  back  of  the  aorta  about  half-an-inch  above  its  bifurcation.  It  descends 
in  front  of  the  two  lower  lumbar  vertebra  and  of  the  sacrum  and  coccyx,  and  ends 
opposite  the  tip  of  the  last-named  bone  by  anastomosing  with  the  lateral  sacral  arteries 
to  form  a  loop  from  which  branches  pass  to  the  coccygeal  body.  In  its  course  it 
passes  at  first  behind  the  lower  part  of  the  abdominal  aorta.  Opposite  the  fifth 
lumbar  vertebra  it  is  crossed  by  the  left  common  iliac  vein,  below  which  it  is 
covered  by  peritoneum  and  coils  of  small  intestine  as  far  as  the  third  sacral  seg- 
ment, and  in  the  rest  of  its  extent  by  the  rectum.  It  is  accompanied  below  by 
venae  comites,  which,  however,  unite  above  to  form  a  single  middle  sacral  vein. 

Small  parietal  branches  pass  transversely  outwards  on  each  side  to  the  last 
lumbar  vertebra  and  to  the  sacrum.  They  anastomose  with  the  lateral  sacral 
arteries,  and  they  usually  give  off  small  spinal  offsets  which  enter  the  anterior 
sacral  foramina.  Small  and  irregular  visceral  branches  pass  to  the  rectum  and 
anastomose  with  the  superior  and  middle  hoemorrhoidal  arteries. 

COMMON  ILIAC  ARTEEIES. 

4.  The  common  iliac  arteries  (aa.  iliacse  communes,  Figs.  634  and  640)  are 
the  terminal  branches  of  the  abdominal  aorta.  They  are  formed  by  the  bifurcation 
of  the  main  trunk,  and  commence  opposite  the  middle  of  the  body  of  the  fourth 
lumbar  vertebra  a  Kttle  to  the  left  of  the  middle  line.  Each  artery  passes  down- 
wards and  outwards  across  the  bodies  of  the  fourth  and  fifth  lumbar  vertebrae 
and  the  intervening  intervertebral  disc,  and  terminates  at  the  level  of  the  lumbo- 
sacral articulation  and  in  front  of  the  corresponding  sacro-iliac  joint  by  dividing 
into  the  internal  and  external  iliac  arteries. 

The  direction  of  each  common  iliac  is  well  indicated  by  a  line  drawn  from  the 
bifurcation  of  the  aorta  to  a  point  midway  between  the  symphysis  pubes  and  the 
anterior  superior  spine  of  the  ilium. 

The  angle  included  between  the  two  diverging  trunks  is  about  60"  in  the  male 
and  about  68^  in  the  female. 

The  right  artery  is,  for  obvious  reasons,  a  little  longer  than  the  left ;  the  former 
is  about  two  inches,  and  the  latter  one  and  three-quarter  inches  in  length. 

Relations. — Anterior. — Both  arteries  are  covered  anteriorly  by  peritoneum,  and  are 
separated  by  it  from  coils  of  the  small  intestine.  Communicating  branches  between  the 
aortic  and  hypogastric  plexuses  of  the  sympathetic  pass  in  front  of  the  arteries,  each  of  which 
is  also  crossed  anteriorly  near  its  termination  by  the  corresponding  ureter. 

The  left  ai-tery  is  in  addition  crossed  in  front  by  the  superior  haemon-hoidal  vessels. 


842  THE  VASCULAE  SYSTEM. 

Posterior. — Behind  the  artery  of  each  side  are  the  bodies  of  the  fourth  and  fifth 
lumbar  vertebrie,  with  the  intervertebral  disc  above  the  latter,  the  psoas  mxiscle,  the 
sympathetic  cord.  These  relationships,  however,  are  much  closer  on  the  left  side  than 
on  the  right.  The  right  common  iliac,  except  at  its  lower  end,  where  it  is  in  contact  with 
the  psoas,  is  separated  from  the  structures  named  by  the  terminations  of  the  right  and 
left  common  iliac  veins  and  the  commencement  of  the  inferior  vena  cava.  The  left 
common  iliac,  wliich  is  not  so  separated,  lies  on  the  inner  border  of  tlie  psoas.  Somewhat 
deeply  placed  in  the  areolar  tissue  between  the  psoas  and  the  lumbar  vertebree,  the 
obturator  nerve,  the  lumbo-sacral  cord,  and  the  ilio-lumbar  artery  form  posterior  relations 
to  the  artery  of  the  corresponding  side. 

Lateral. — On  both  sides  of  each  artery  are  coils  of  small  intestine.  The  commence- 
ment of  the  inferior  vena  cava  lies  to  the  outer  side  of  the  upper  part  of  the  right  artery, 
and  on  the  inner  side  of  this  vessel  are  the  right  common  iliac  vein  below  and  the  left 
common  iliac  vein  above.     The  last-named  vein  lies  on  the  inner  side  of  the  left  artery. 

The  Paired  Visceral  Branches  of  the  Abdominal  Aorta. 

1.  Suprarenal  or  Capsular  Arteries  (aa.  suprarenales,  Fig.  634). — There  are 
three  sets  of  suprarenal  arteries — the  superior,  middle,  and  inferior.  Of  these  the 
middle  only  arise  from  the  aorta  direct ;  the  superior  spring  from  the  inferior 
phrenic,  and  the  inferior  from  the  renal  arteries. 

The  middle  suprarenal  arteries  are  two  small  branches  which  arise,  behind  the 
pancreas,  from  the  sides  of  the  aorta,  close  to  the  origin  of  the  superior  mesenteric 
artery.  They  run,  one  on  each  side,  outwards  and  upwards  upon  the  crura  of  the 
diaphragm,  and  just  above  the  renal  arteries,  to  the  suprarenal  bodies  to  which  they 
are  distributed,  and  they  anastomose  with  the  superior  and  inferior  suprarenal 
arteries. 

2.  Renal  Arteries  (aa.  renales,  Fig.  634). — The  renal  arteries  arise,  one  on 
each  side,  from  the  aorta,  about  half-an-inch  below  the  origin  of  the  superior 
mesenteric  artery  and  opposite  the  second  lumbar  vertebra. 

Both  arteries  are  of  large  size,  and  the  right,  which  is  a  little  longer  than  the 
left,  is  frequently  shghtly  lower  in  position.  Each  artery  runs  almost  transversely 
outwards  to  the  hilum  of  the  corresponding  kidney.  It  passes  in  front  of  the  crus 
of  the  diaphragm  and  of  the  upper  part  of  the  psoas  muscle.  The  left  artery  lies 
behind  the  pancreas;  the  right  vessel  passes  behind  the  inferior  vena  cava,  the 
head  of  the  pancreas,  and  the  second  part  of  the  duodenum.  The  renal  vein 
usually  lies  below  and  in  front  of  the  artery,  but  near  the  kidney  the  vein  not  un- 
frequently  occupies  a  posterior  position. 

On  reaching  the  hilum  of  the  kidney  each  artery  divides  into  three  branches, 
two  of  which  pass  in  front  of  the  pelvis  of  the  ureter,  and  between  it  and  the  renal 
vein,  and  the  third  behind  the  pelvis.  In  the  renal  sinus  these  primary  branches 
break  up  into  numerous  secondary  branches  which  enter  the  kidney  substance 
between  the  pyramids. 

Branches. — The  foUowing  branches  are  given  oft"  by  each  renal  artery,  in  addition  to  the 
terminal  branches  : — 

(a)  Inferior  suprarenal  (a.  suprarenalis  inferior),  whidi  passes  upwards  to  the  lower  part  of 
the  supi'arenal  body. 

(6)  Ureteral. — Small  branches  to  the  upper  part  of  the  ureter,  which  anastomose  with  branches 
of  the  spermatic  or  ovarian  arteries. 

(c)  Peri-renaL — Small  branches  to  the  fatty  capsule  of  the  kidney,  whicli  anastomose  with  the 
lumbar  arteries. 

((T)  Glandular  offsets,  either  from  the  main  tnmk  or  from  some  of  its  Ijranches,  pass  to  the 
renal  and  lumbar  glands. 

3.  Spermatic  Arteries  (aa.  spermaticse  internae). — The  spermatic  arteries  in 
the  male,  and  the  corresponding  ovarian  arteries  (aa.  ovaricce)  in  the  female,  are  two 
long  slender  vessels,  one  on  the  right  side  and  one  on  the  left,  which  arise  from  the 
front  of  the  abdominal  aorta,  a  short  distance  below  the  origins  of  the  renal  arteries. 

Each  spermatic  artery  runs  downwards  and  outw^ards  to  the  internal  abdominal 
ring ;  it  then  traverses  the  inguinal  canal,  and  consequently  takes  a  downward  and 
inward  course.  On  emerging  from  the  canal,  through  the  external  abdominal  ring, 
it  enters  the  scrotum,  in  which  it  descends,  almost  vertically,  but  in  a  tortuous 


VISCEEAL  BEANCHES  OF  THE  ABDOMINAL  AOETA.  843 

manner,  to  end  immediately  above  the  testicle  by  dividing  into  testicular  and 
epididymal  branches. 

Relations. — In  the  abdominal  cavity  the  arteries  lie  behind  the  peritoneum,  to 
which  they  are  closely  attached,  and  in  front  of  the  psoas  muscles.  The  right  artery  is 
also  in  front  of  the  inferior  vena  cava.  Each  artery  descends  in  front  of  the  ureter,  the 
genito-crural  nerve,  and  the  lower  end  of  the  external  iliac  artery  of  its  own  side,  and  is 
accompanied  by  two  sjjermatic  veins  which  unite  above  into  a  sinojle  trunk.  The  anterior 
relations  differ  on  the  two  sides.  The  right  arteiy  lies  behind,  and  is  crossed,  by  the  ileo- 
colic, the  right  colic,  and  the  terminal  branches  of  the  superior  mesenteric  artery,  and  by 
the  third  part  of  the  duodenum,  the  termination  of  the  ileum,  and  the  vermiform  appendix. 
The  left  artery  is  crossed  in  front  by  the  left  colic  and  sigmoid  branches  of  the  inferior 
mesenteric  artery  and  by  the  iliac  colon. 

At  the  internal  abdominal  ring  the  spermatic  artery  comes  into  relation,  at  its  inner 
side,  with  the  vas  deferens.  The  two  structures  run  together  round  the  outer  and  anterior 
aspects  of  the  deep  epigastric  artery  to  the  inguinal  canal.  " 

In  the  inguinal  canal  the  spermatic  artery,  along  with  the  other  constituents  of  the 
spermatic  cord,  is  enclosed  in  the  infundibular  and  cremasteric  fasciae,  the  intercolumnar 
fascia  being  added  at  the  external  abdominal  ring.  In  this  part  of  its  course  the  artery 
lies  in  front  of  the  vas  deferens,  and  behind  the  anterior  part  of  the  pampiniform  plexus 
and  the  spermatic  veins  which  aiise  from  it. 

Branches. — («)  Ureteral  bra,nclies,  small  in  size,  are  distributed  to  the  middle  part  of  the 
ureter,  anastomosing  above  with  branches  from  the  renal  and  below  with  branches  from  the 
vesical  arteries. 

(b)  Cremasteric  branches,  given  off  in  the  inguinal  canal  and  upper  part  of  the  scrotum, 
supply  the  cremaster  muscle,  and  anastomose  wdth  the  cremasteric  branch  of  the  deep  epigastric. 

(c)  Terminal  Branches. — (i.)  The  epididymal  branch  runs  downwards  to  the  epididymis,  which 
it  supplies.  It  also  gives  twigs  to  the  vas  aberrans,  the  coni  vasculosi,  and  the  tunica  vaginalis, 
and  anastomoses  with  the  artery  of  the  vas  deferens,  (ii.)  The  testicular  branch  descends  on  the 
upper  and  back  part  of  the  testicle,  and  breaks  up  into  numerous  peripheral  and  central  branches. 
The  peripheral  branches  pass  through  the  tunica  albuginea  and  ramify  on  its  inner  surface  ;  they 
anastomose  with  one  another  and  wdtli  the  central  branches.  The  central  branches  pass  through 
the  mediastinum  testis  and  along  the  surfaces  of  the  septa. 

3a-  The  ovarian  arteries  (aa.  ovaricte,  Eig.  634)  in  the  female  closely  corre- 
spond to  the  spermatic  arteries  in  the  male.  They  are,  however,  much  shorter, 
and,  instead  of  passing  through  the  abdominal  wall,  descend  into  the  pelvis,  where 
they  run  between  the  layers  of  the  broad  ligament  to  terminate  between  the  ovaries 
and  the  uterus  by  anastomosing  with  the  uterine  arteries. 

Relations. — In  the  upper  part  of  its  course  the  relations  of  each  ovarian  artery  are 
like  those  of  the  corresponding  spermatic  artery,  but  about  the  level  of  the  anterior 
superior  spine  of  the  ilium  each  ovarian  artery  turns  inwards,  and,  crossing  the  upper  part 
of  the  external  iliac  vessels  (artery  and  vein),  descends  in  the  anterior  border  of  the  fossa 
ovarii,  on  the  lateral  wall  of  the  pelvis,  to  the  broad  ligament,  where  it  is  placed  below 
the  Fallopian  tube. 

Branches.  —  («)  Ureteral,  to  the  middle  part  of  the  ureter. 

(b)  Tubal,  to  tlie  Fallopian  tube,  which  anastomose  with  branches  of  the  uterine. 

(c)  Ligamentous,  to  the  round  ligament,  as  far  as  the  inguinal  canal. 

(d)  Ovarian  branches,  numerous,  pass  to  the  liilum  of  the  ovary,  and  thence  to  the  substance 
of  the  organ. 

(e)  A  uterine  branch  is  formed  by  the  continuation  of  the  trunk  to  its  anastomosis  with  the 
uterine  branch  of  the  internal  iliac. 

The  Unpaired  or  Single  Visceral  Branches  of  the  Abdominal  Aorta. 

1.  The  cceliac  artery  or  cceliac  axis  (a.  coeliaca,  Figs.  634  and  635)  arises  from  the 
front  of  the  abdominal  aorta,  immediately  below  the  aortic  orifice  of  the  diaphragm 
and  between  its  crura.  It  is  a  short  but  wide  vessel  which  runs  almost  horizontally 
forwards  for  a  distance  of  about  half-an-inch,  and  then  terminates  by  dividing  into 
three  large  branches — the  coronary  or  gastric,  the  hepatic,  and  the  splenic- 
Relations. — The  short  trunk  extends  from  the  aorta  behind  the  lesser  sac  of 
peritoneum,  by  which  it  is  separated  from  the  stomach,   or  from  the  small   omentum. 


844 


THE  VASCULAR  SYSTEM. 


in  front.  It  runs  below  the  Spigelian  lobe  of  the  liver,  and  above  the  upper  border  of  the 
pancreas  and  the  splenic  vein,  and  it  is  surrounded  by  the  solar  and  cosliac  plexuses  of  the 
sympathetic;  the  right  semilunar  ganglion  is  to  its  right  side,  and  the  left  semikmar 
ganglion  and  cardiac  end  of  the  stomach  are  on  its  left  side. 

Branches. — (a)  The  coronary  or  gastric  artery  (a.  gastrica  sinistra)  is  the 
smallest  branch  of  the  coeliac  axis.  It  runs  obliquely  upwards  and  to  the  left, 
and  reaches  the  smaller  curvature  of  the  stomach  close  to  the  oesophagus.  It  then 
turns  sharply  forwards,  downwards,  and  to  the  right,  and  runs  towards  the  pyloric 
end  of  the  stomach  to  anastomose  with  the  pyloric  branch  of  the  hepatic  artery. 
In  the  first  part  of  its  course  the  artery  lies  behind  the  lesser  sac  of  the  peritoneum  ; 
it  then  passes  into  the  left  pancreatico-gastric  fold,  and  is  continued  between  the 
layers  of  the  small  omentum. 

Branches. — (i.)  (Esophageal  (rami  cesoijliagei). — When  the  artery  readies  tlie  stomach  a  large 


Inferior 
•phrenic 
arteries 


Cystic  arterj 

Superior  pancreatico- 
duodenal artery       / 
Gastro-duodenal  artery- 
Right  gastro-epiploic  artery 

Fig.  635. 


Left  gasti'o- 
\  \  epiploic  artery 

\  Splenic  artery 

Coronary  artery  -  Vv.^.^.  a  y^^  ^^ 


Hepatic  artery      ^  ,    .     , 
Pyloric  artery  ■.  '    m   I'-'-j-'''' 

The  Cceliac  Axis  and  its  Branches. 


oesophageal  branch  is  given  off,  whicli  passes  upwards  on  the  a3sophagus,  and  gives  offsets  to  it 
which  anastomose  with  oesophageal  branches  of  the  thoracic  aorta  and  wdth  branches  of  the 
inferior  phrenic,  (ii.)  Gastric  branches  are  distributed  to  both  surfaces  of  the  stomach.  They 
anastoniose  witli  brandies  of  the  vasa  brevia  of  the  splenic,  and  with  branches  of  the  gastro- 
epiploic arterial  arch  on  the  greater  curvature  of  the  stomach. 

_  (h)  The  splenic  artery  (a.  lienalis,  Fig.  635)  is  the  largest  branch  of  the 
coBliac  axis.  It  runs  a  more  or  less  tortuous  course  behind  the  stomach  and  the 
lesser  sac  of  the  peritoneum,  and  along  the  upper  border  of  the  pancreas.  It  lies  in 
front  of  the  left  suprarenal  capsule  and  the  upper  end  of  the  left  kidney,  and 
passes  forwards  between  the  two  layers  of  the  lieno-renal  ligament,  where  it  divides 
into  from  five  to  eight  terminal  iDranches  (rami  lienales)  which  enter  the  hilum  of  the 
spleen  and  supply  the  splenic  substance.  It  is  accompanied  liy  the  splenic  vein, 
which  lies  below  it. 

Branches. — (i.)  Pancreatic  (rami  i^ancreatici). — Numerous  small  branches  (pancreaticse 
parvtuj  arc  given  off  to  the  pancreas.  One  large  bi'anch  (pancreatica  magna),  occasionally 
present,  enters  the  upper  border  of  the  pancreas,  about  tlie  junction  of  its  middle  and 
left  thirds,  and  runs  from  left  to  right  in  the  substance  of  the  pancreas,  a  little  above  and 
behind  the  pancreatic  duct.  Both  the  small  and  large  arteries  supply  the  substance  of 
the  pancreas,  and  anastomose  with  one  another  and  with  branches  of  the  pancreatico- 
duodenal arteries. 


VISCERAL  BEANCHES  OF  THE  ABDOMINAL  AORTA.  845 

(ii.)  The  vasa  brevia  (aa.  gastric^e  breves),  or  sliort  gastric  branches,  four  or  five  in 
numbei",  are  given  oft'  either  from  the  end  of  the  main  vessel  or,  more  commonly,  from 
some  of  its  terminal  branches.  They  pass  between  the  layers  of  the  gastro-splenic 
omentum  to  the  left  end  of  great  curvature  of  the  stomach,  and  anastomose  with  the 
oesophageal,  the  gastric,  and  the  left  gastro-epiploic  arteries. 

(iii.)  The  left  gastro-epiploic  branch  (a.  gastro-epiploica  sinistra)  arises  from  the 
front  of  the  splenic,  close  to  its  termination,  and  passes  forwai'ds  between  the  layers  of  the 
gastro-splenic  omentima  to  the  left  end  of  the  great  curvature  of  the  stomach,  along  which 
it  is  continued,  from  left  to  right,  between  the  layers  of  the  gastro-colic  or  great  omentum. 
It  ends  by  anastomosing  with  the  right  gastro-epiploic  artery,  and  it  gives  off  numerous 
gastric  branches  to  both  surfaces  of  the  stomach,  which  anastomose  with  the  vasa  brevia 
and  with  branches  of  the  coronary  and  pyloric  arteries.  Long  slender  omental  branches 
pass  to  the  omentum  and  anastomose  with  branches  of  the  colic  arteries. 

(c)  The  hepatic  artery  (a.  hepatica,  Fig.  635)  runs  along  the  upper  border  of 
the  head  of  the  pancreas  to  the  right  pancreatico-gastric  fold  of  peritoueum,  in 
which  it  turns  forwards  to  the  upper  border  of  the  first  part  of  the  duodenum.  It 
then  passes  upwards,  between  the  layers  of  the  small  omentum,  in  front  of  the 
portal  vein  and  to  the  left  of  the  common  bile  duct,  and  reaches  the  transverse 
fissure  of  the  liver,  where  it  divides  into  right  and  left  branches. 

Branches. — (i.)  The  pyloric  artery  (a.  gastrica  dextra)  is  a  small  branch  which 
arises  opposite  the  upper  border  of  the  first  part  of  the  ~duodenum.  It  descends  to 
the  pylorus,  running  between  the  layers  of  the  small  omentum,  and  then  turns  to  the  left 
along  the  smaller  curvature  of  the  stomach.  It  gives  branches  to  both  surfaces  of  the 
stomach,  and  terminates  by  anastomosing  with  the  coronary  artery. 

(ii.)  The  gastro-duodenal  artery  (a.  gastro-duodenalis). — This  branch  of  the  hepatic 
arises  just  above  the  upper  border,  descends  behind,  and  terminates  opposite  the  lower 
border  of  the  first  part  of  the  duodenum.  In  its  course  it  lies  between  the  neck  of 
the  pancreas  and  the  first  part  of  the  duodenum,  and  it  is  in  front  of  the  portal  vein.  The 
common  bile  duct  is  on  its  right  side.  The  vessel  ends  by  dividing  into  the  right  gastro- 
epiploic and  the  superior  pancreatico-duodenal  arteries.  The  right  gastro-epiploic  artery 
(a.  gastro-epiploica  dextra)  is  the  larger  of  the  two  terminal  branches  of  the  gastro- 
duodenal  ;  it  passes  from  right  to  left  along  the  greater  curvature  of  the  stomach,  between 
the  layers  of  the  gastro-colic  omentum,  and  luiites  ^yith  the  left  gastro-epiploic  branch 
of  the  splenic  -artery.  From  the  arterial  arch  so  formed  branches  pass  upwards  on  both 
surfaces  of  the  stomach,  and  anastomose  with  branches  of  the  pyloric  and  coronary  arteries. 
Other  branches  pass  downwards  to  the  omentum,  and  anastomose  with  branches  of  the 
colic  arteries.  The  superior  pancreatico-duodenal  artery  (a.  pancreatico-duodenalis 
superior)  runs  a  short  course  to  the  right,  between  the  duodenum  and  the  head  of  the 
pancreas,  and  divides  into  anterior  and  posterior  terminal  branches  which  descend,  the 
former  in  front  of  and  the  latter  behind  the  head  of  the  pancreas,  to  anastomose  with 
similar  branches  of  the  inferior  pancreatico-duodenal  artery.  They  suppl}^  the  head 
of  the  pancreas,  anastomosing  in  it  with  the  pancreatic  branches  of  the  splenic  artery ; 
branches  are  also  given  to  the  second  part  of  the  duodenum  and  to  the  common  bile  duct. 

(iii.)  Terminal  branches. — The  right  hepatic  artery  (ramus  dexter)  passes  either  in 
front  of  or  behind  the  hepatic  duct  and  behind  the  cystic  duct,  to  the  right  end  of  the 
transverse  fissure  of  the  liver,  where  it  divides  into  two  or  more  branches  which  enter  the 
substance  of  the  liver  and  accompany  the  bi'anches  of  the  portal  vein  and  the  hepatic 
duct.  As  it  crosses  just  above  the  junction  of  the  hepatic  and  cystic  ducts,  the  right 
hepatic  artery  gives  off  a  cystic  branch.  The  cystic  artery  (a.  cystica)  runs  downwards 
and  forwards  along  the  cystic  duct  to  the  gall-bladder,  where  it  divides  into  upper  and 
lower  branches  ;  the  upper  passes  downwards  between  the  gall-bladder  and  the  under 
surface  of  the  liver,  to  both  of  which  it  gives  offsets ;  the  lower  branch  is  distributed  on 
the  under  surface  of  the  gall-bladder,  between  it  and  the  peritoneum.  The  left  hepatic 
artery  (ramus  sinister)  is  longer  and  narrower  than  the  right.  It  runs  to  the  left  end 
of  the  transverse  fissure,  gives  one  or  two  branches  to  the  Spigelian  lobe,  crosses  the 
longitudinal  fissure,  and  breaks  up  into  branches  which  terminate  in  the  substance  of  the 
left  lobe  of  the  liver. 

2.  The  superior  mesenteric  artery  (a.  mesenterica  superior,  Figs.  634,  636, 
and  659)  springs  from  the  front  of  the  aorta,  about  half-an-inch  below  the  origin 
of  the  coeliac  axis  and  opposite  the  first  lumbar  vertebra. 

It  passes  obliquely  downwards  and  forwards,  crossing  in  front  of  the  left  renal 


846 


THE  VASCULAR  SYSTEM. 


vein,  the  lower  part  of  the  head  of  the  pancreas,  and  the  third  part  of  the  duo- 
denum; opposite  the  latter  it  enters  the  root  of  the  mesentery,  in  which  it 
continues  to  descend,  curving  obliquely  from  above  downwards  and  to  the  right,  to 
the  right  iliac  fossa,  and  crossing  in  this  part  of  its  course  obliquely  in  front  of  the 
aorta,  the  lower  part  of  the  inferior  vena  cava,  the  right  ureter,  and  the  right  psoas 
muscle.  At  its  origin  it  lies  behind  the  neck  of  the  pancreas  and  the  splenic  vein ; 
where  it  passes  in  front  of  the  duodenum  it  is  crossed  anteriorly  by  the  transverse 
colon,  and  in  the  lower  part  of  its  extent  it  is  concealed  by  coils  of  small  intestine. 


Middle  colic  artery 


Inferior  pancreatico 
duodenal  artery 


Right  colic  arter 


Ueo-colic  artery 


Termination  o 
superior  mesen- 
teric artery 


Duodeno- 
jejunal flexure 


Rami  intestini 
tenuis 


Fici.  636. — The  Sai'EuroK  Mesenteric  Aktehv  and  its  BraiN'ches. 

Branches. — Ft  gives  off  numerous  branches  wliicli  supply  tlie  duodenum*  and  the 
pancreas  in  part,  the  whole  of  the  small  intestine  Ijclow  the  duodenum,  and  the  lar^e 
intestine  nearly  as  far  as  the  splenic  flexure.  ° 

'^I'he  branches  are  as  fallows  : — 

{(i)  Rami  intestini  tenuis  (aa.  intestinales),  or  Ijvanches  to  the  small  intestine, 
varying  from  ten  to  sixteen  in  number ;  they  spring  from  the  convexity  of  the  superior 
mesenteric  artery,  and  pass  obliquely  forwards  and  downwards  between  the  layers  of  the 
mesentery,  each  dividing  into  two  branches  which  anastomose  with  adjacent  branches  to 
form  a  series  of  arcades  from  which  secondary  branches  are  given  off.  This  process  of 
division  and  union  is  repeated  three  or  four  times ;  -thus  four  or  five  tiers  of  arches  are 


VISCEEAL  BEANCHES  OF  THE  ABDOMINAL  AOETA.  847 

formed,  from  the  most  distal  of  which  terminal  branches  are  given  off  to  the  walls  of  the 
jejunum  and  ileum.  Branches  from  the  successive  arcades  are  also  given  oft'  to  the 
mesenteric  glands.  The  terminal  branches  anastomose  together  in  the  walls  of  the  gut, 
forming  a  vascular  network  which  communicates  above  with  the  inferior  pancreatico- 
duodenal artery  and  below  with  the  terminal  branch  of  the  superior  mesenteric  trunk. 
The  vascular  loops  and  branches  are  accompanied  by  corresponding  veins,  lymphatics,  and 
nerves. 

(6)  The  inferior  pancreatico- duodenal  artery  (a.  pancreatico-duodenalis  inferior).  It 
arises  either  from  the  trunk  of  the  superior  mesenteric,  at  the  upper  border  of  the  third  part 
of  the  duodenum,  or  from  the  first  of  the  rami  intestini.  It  runs  to  the  right,  between 
the  head  of  the  pancreas  and  the  third  part  of  the  duodenum,  and  terminates  by  dividing 
into  two  branches,  anterior  cxnd  posterior,  which  ascend,  the  former  in  front  and  the  latter 
behind  the  head  of  the  pancreas ;  they  supply  the  head  of  the  pancreas,  the  second  and 
third  parts  of  the  duodenum,  and  they  anastomose  with  the  similar  branches  of  the 
superior  pancreatico-duodenal  artery. 

(c)  The  middle  colic  artery  (a.  colica  media)  is  a  large  branch  which  springs  from  the 
front  of  the  superior  mesenteric  as  it  enters  the  root  of  the  mesentery.  It  runs  down- 
wards and  forwards  in  the  transverse  mesocolon,  and  terminates  by  dividing  into  two 
branches,  right  and  left,  which  anastomose  respectively  with  the  right  and  left  colic 
arteries,  forming  arcades  from  Avhich  secondary  and  tertiary  loops  are  derived,  the  terminal 
branches  being  distributed  to  the  walls  of  the  transverse  colon. 

(d)  The  right  colic  artery  (a.  colica  dextra)  springs  from  the  right  or  concave  side  of 
the  superior  mesenteric,  either  alone  or  in  the  form  of  a  common  trunk  which  divides 
into  right  and  ileo-colic  branches.  It  runs  to  the  right,  behind  the  peritoneum  on  the 
posterior  wall  of  the  abdomen,  and  in  front  of  the  right  psoas,  the  ureter,  and  the 
spermatic  or  ovarian  vessels,  towards  the  ascending  colon,  near  which  it  divides  into  an 
ascending  and  a  descending  branch.  The  former  passes  upwards,  and  anastomoses  in  the 
transverse  mesocolon  with  the  middle  colic  artery.  The  latter  descends  to  anastomose 
with  the  upper  branch  of  the  ileo-colic,  and  from  the  loops  thus  formed  branches  are  dis- 
tributed to  the  walls  of  the  ascending  colon  and  the  beginning  of  the  transverse  colon. 

(e)  The  ileo-colic  artery  (a.  ileo-colica)  arises  by  a  common  trunk  with  the  right  colic, 
or  separately  from  the  right  side  of  the  superior  mesenteric,  and  passes  downwards  and 
outwards,  behind  the  peritoneum,  towards  the  lower  part  of  the  ascending  colon,  where 
it  terminates  by  dividing  into  an  ascending  branch  which  anastomoses  with  the  lower 
branch  of  the  right  colic,  and  a  descending  branch  which  communicates  with  the  colic 
terminal  branches  of  the  superior  mesenteric  trunk. 

(/)  Terminal. — ^The  lower  end  of  the  superior  mesenteric  artery  divides  into  five 
branches — (i.)  ileal,  (ii.)  appendicular,  (iii.)  anterior  ileo-caecal,  (iv.)  postei'ior  ileo-ctecal, 
and  (v.)  colic. 

The  ileal  branch  (a.  ilea)  turns  upwards  and  to  the  left  in  the  lowest  part  of  the  mesentery, 
and  anastomoses  with  the  rami  intestini.  The  appendicular  branch  (a.  ai^pendicularis)  passes 
behind  the  terminal  portion  of  the  ileum,  and  through  the  meso-appendix  to  the  vermiform  i>ro- 
cess,  upon  which  it  ends.  The  anterior  ileo-csecal  crosses  the  front  of  the  ileo-ctecal  junction  in 
a  fold  of  peritoneum  ;  the  posterior  ileo-caecal  crosses  the  ileo-caecal  junction  jjosteriorly,  and  the 
colic  runs  upwards  to  the  ascending  colon.  The  ileo-caecal  branches  supjjly  the  walls  of  the 
caecum,  and,  like  the  colic  branch,  anastomose  with  branches  of  the  ileo-colic  artery. 

3.  The  inferior  mesenteric  artery  (a.  mesenterica  inferior,  Fig.  634)  arises 
from  the  front  and  towards  the  left  side  of  the  aorta  an  inch  and  a  half  above  the 
bifurcation ;  it  passes  downwards  and  slightly  outwards,  lying  behind  the  perito- 
neum and  on  the  front  of  the  left  psoas  muscle,  to  the  upper  and  outer  border  of 
the  left  common  iliac  artery,  where  it  becomes  the  superior  hsemorrhoidal. 

Branches. — (a)  The  left  colic  artery  (a.  colica  sinistra)  arises  from  the  left  side  of 
the  inferior  mesenteric  near  its  origin.  It  runs  upwards  and  to  the  left  towards  the  splenic 
flexure  of  the  colon,  where  it  divides  into  ascending  and  descending  branches.  The 
ascending  branch  crosses  in  front  of  the  lower  end  of  the  left  kidney,  passes  between  the 
layers  of  the  transverse  mesocolon,  and,  turning  inwards,  terminates  by  joining  the  left 
branch  of  the  middle  colic  artery.  The  descending  branch  passes  downwards  behind  the 
peritoneum  to  the  inner  side  of  the  descending  colon  to  unite  with  the  superior  sigmoid 
artery,  and  from  the  loops  thus  formed  branches  are  distributed  to  the  descending  colon. 

In  the  whole  of  its  course  the  left  colic  artery  lies  behind  the  peritoneum,  and  on  the 
posterior  abdominal  wall ;  it  crosses  in  front  of  the  left  psoas  and  the  left  ureter. 


848  THE  VASCULAE  SYSTEM. 

(l>)  The  sigmoid  branches  (aa.  sigmoidese),  usually  two  in  number,  arise  from  the 
convexity  of  the  inferior  mesenteric,  and  pass  downwards  and  outwards  to  the  iliac 
colon.  They  lie  behind  the  peritoneum,  and  in  front  of  the  psoas,  the  ureter,  and  the 
upper  part  of  the  iliacus.  They  terminate  by  dividing  into  branches  which  anastomose 
with  the  left  colic  above  and  with  branches  of  the  superior  hsemorrhoidal  below,  forming 
a  series  of  arches  from  which  branches  are  distributed  to  the  lower  part  of  the  descending 
colon,  the  iliac  coloii,  and  the  pelvic  colon. 

(c)  The  superior  hsemorrhoidal  artery  (a.  heemorrhoidalis  superior)  is  the  direct 
continuation  of  the  inferior  mesenteric.  It  enters  the  mesentery  of  the  pelvic  colon, 
crosses  the  front  of  the  left  common  iliac  artery,  descends  into  the  pelvis  as  far  as  the 
third  piece  of  the  sacrum,  or  in  other  words  the  junction  between  the  pelvic  colon  and 
the  rectum,  and  divides  into  two  branches  which  pass  downwards  on  the  sides  of  the 
rectum.  Half-way  down  the  rectum  each  of  the  two  terminal  branches  of  the  superior 
hajmorrhoidal  artery  divides  into  two  or  more  branches  which  pass  through  the  muscular 
coats  and  terminate  in  the  submucous  tissue,  where  they  divide  into  numerous  small  branches 
which  pass  vertically  downwards,  anastomosing  Avith  each  other,  with  offsets  from  the  middle 
hcemorrhoidal  branches  of  the  internal  iliac  arteries,  the  inferior  hsemorrhoidal  branches 
of  the  internal  pudic  arteries,  and  with  branches  from  the  middle  sacral  artery. 

The  superior  hsemorrhoidal  artery  supplies  the  mucous  membrane  of  the  pelvic  colon 
and  the  rectum  and  the  muscular  coats  of  the  pelvic  colon. 

THE  INTERNAL  ILIAC  ARTERY. 

The  internal  iliac  or  hypogastric  artery  (a.  hypogastrica,  Figs.  634,  637,  and 
640)  in  the  fcetus  is  the  direct  continuation  of  the  common  iliac  trunk.  It 
supplies  numerous  branches  to  the  pelvis,  runs  upvs^ards  on  the  anterior  abdominal 
wall  to  the  umbilicus,  and  is  prolonged  as  the  umbilical  artery  to  the  placenta. 
One  of  its  pelvic  branches — the  sciatic — is  at  first  the  main  artery  of  the  inferior 
extremity,  but  subsequently  another  branch  is  given  off  which  becomes  the  chief 
arterial  trunk  of  the  lower  limb.  This  branch  is  the  external  iliac  artery ;  it  soon 
equals  and  ultimately  exceeds  the  internal  iliac  in  size,  and  it  is  into  these  two 
vessels  that  the  common  iliac  appears  to  bifurcate. 

When  the  placental  circulation  ceases  and  the  umbilical  cord  is  severed,  the 
part  of  the  internal  iliac  trunk  which  extends  from  the  pelvis  to  the  umbilicus 
atrophies,  and  is  afterwards  represented  almost  entirely  by  a  fibrous  cord,  known 
as  the  obliterated  hypogastric  artery.  It  is  only  at  its  proximal  end  that  the 
atrophied  part  remains  pervious,  and  here  it  forms  the  commencement  of  the 
superior  vesical  artery ;  accordingly,  the  permanent  internal  iliac  artery  is  a  com- 
paratively short  vessel.  Owing  to  the  arrangement  of  some  of  its  branches  it 
appears  to  end  in  an  anterior  and  a  posterior  division,  the  former  of  which  is  to 
be  regarded  as  the  continuation  of  the  vessel  to  the  obliterated  hypogastric,  whilst 
the  latter  is  simply  a  common  stem  of  origin  for  some  of  the  branches. 

"With  this  explanation  the  internal  iliac  artery  may  be  described  in  the  usual 
manner. 

It  arises  from  the  common  iliac  opposite  the  lumbo-sacral  articulation,  and 
descends  into  the  pelvis,  to  terminate,  as  a  rule,  opposite  the  upper  border  of  the 
great  sciatic  notch,  in  two  divisions — anterior  and  posterior — from  each  of  which 
branches  of  distribution  are  given  off.  The  artery  measures  about  one  and  a  half 
inches  in  length,  and  is  the  inner  of  the  two  terminal  branches  of  the  common 
ihac  artery. 

Relations. — Antei^ior. — The  artery  on  each  side  is  covered  in  front  and  internally 
by  peritoneum,  under  wliich  the  corresponding  lu-eter  descends  along  the  anterior  border 
of  the  artery.  The  ilio-pelvic  colon  crosses  from  the  front  to  the  inner  side  of  the  left 
artery,  and  the  terminal  part  of  the  ileum  bears  the  same  relation  to  the  right  artery. 

Postfivior  to  it  are  the  internal  iliac  vein  and  the  commencement  of  the  common  iliac 
vein  ;  behind  these  is  the  lumbo-sacral  cord  and  the  sacrum. 

Lateral. — On  its  outer  side  the  external  iliac  vein  separates  it  from  the  psoas  muscle 
above,  whilst  below  this  is  the  obturator  nerve,  embedded  in  a  mass  of  fat  which  intervenes 
between  the  internal  iliac  artery  and  the  side  wall  of  the  pelvis.  On  its  inner  side  it  is 
crossed  by  some  of  the  tributaries  of  the  internal  iliac  vein,  and  is  covered  by  peritonevxm. 


BKANCHES  OF  THE  INTERNAL  ILIAC  AETERY. 


849 


Branches. — The  internal  iliac  artery  supplies  the  greater  part  of  the  pelvic 
wall  and  viscera,  and  its  branches  are  also  distributed  to  the  bvittock  and  thigh 
and  to  the  external  organs  of  generation. 

All  the  branches  may  be  given  off  separately  frora  a  single  undivided  parent 


Internal  iliac  arter; 

Lateral  sacral  artery- 
External  iliac  artery  — 


External  iliac  vein- 
Psoas  muscle  — 
Hypogastric  artei  v_  .^     , 
Deep  circumflex  iluc  \  \\ 
artery    \\A 
Superior  vesical  ai  ter\  \ 

Obturator  \ein 

Deep  epigastric  aitei\ 

Round  ligament 

Obturator  nerve 

Obturatoi  arterv 


Dorsal  artery  oi  clitoris 

Artery  to  coipus 
cavernosum 


Sympathetic  conl 

Lateral  sacral  artery 
Internal  iliac  vein 

Gluteal  artery 

Sciatic  artery 

Internal  pudic 
artery 

Sacral  plexus 


Fig.  637.— The  Internal  Iliac  Artery  and  its  Branches  in  the  Female. 


1.  Great  sacro-sciatic  ligament. 

2.  Uterine  artery. 

3.  Vaginal  artery. 

4.  Inferior  liEemorrlioidal  nerve. 

5.  Inferior  htBraorrlioidal  arterv. 


6.  Dorsal  nerve  of  clitoris. 

7.  Internal  pudic  artery. 

8.  Perineal  nerve. 

9.  Superficial  perineal  artery. 
10.  Artery  to  bulb. 


trunk,  but  as  a  rule  they  arise  in  two  groups  corresponding  to  the  two  divisions  in 
which  the  artery  under  these  circumstances  appears  to  end. 


Anterior  division 


j'llio-lumbar 
Posterior  division   |   parietal     Lateral  sacral 

[Gluteal 
/'Obturator 
f  parietal    '.  Sciatic 

I  Internal  pudic 
'Superior  vesical 

(Obliterated  hypogastric) 
visceral    '  Middle  vesical 
Inferior  vesical 
V Middle  heemorrhoidal. 

In  the  female  the  inferior  vesical  is  replaced  by  a  vaginal  branch,  and  an 
additional  branch,  the  uterine,  is  given  off 
58 


850  THE  VASCULAE  SYSTEM. 

Branches  of  the  Posterior  Division. 

The  posterior  terminal  division  gives  off  the  ilio-lumbar  and  lateral  sacral 
arteries,  and  is  continued  as  the  gluteal  artery.  No  visceral  branches  are  derived 
from  this  division. 

1.  Ilio-lumbar  Artery  (a.  ilio-lumbalis). — This  vessel  runs  upwards  and  outwards 
across  the  brim  of  the  pelvis  to  the  iliac  fossa.  It  passes  in  front  of  the  sacro-iliac 
articulation,  between  the  lumbo-sacral  cord  and  the  obturator  nerve,  and  behind 
either  the  lower  part  of  the  common  or  the  upper  part  of  the  external  iliac  vessels 
and  the  psoas  and  iliacus  muscles. 

In  the  iliac  fossa  it  anastomoses  with  branches  of  the  deep  circumflex  iliac  and 
obturator  arteries.  It  also  gives  off  offsets  to  the  iliacus,  and  supplies  a  large 
nutrient  branch  to  the  ilium.  A  lumbar  branch  (ramus  lumbalis)  ascends  behind  the 
psoas  to  the  crest  of  the  ilium.  It  supplies  the  psoas  and  quadratus  lumborum, 
and  anastomoses  with  the  lumbar  and  deep  circumflex  iliac  arteries ;  it  also  gives 
off  a  spinal  branch  which  enters  the  intervertebral  foramen  between  the  fifth 
lumbar  vertebra  and  the  sacrum,  and  is  distributed  like  the  spinal  branches  of  the 
lumbar  and  aortic  intercostal  arteries. 

2.  Lateral  Sacral  Arteries  (aa.  sacrales  laterales).  —  There  is  sometimes 
only  a  single  lateral  sacral  artery  on  each  side ;  more  commonly  there  are  two, 
superior  and  inferior. 

Both  branches  run  downwards  and  inwards  on  the  front  of  the  sacrum.  The 
inferior  passes  in  front  of  the  pyriformis  and  the  sacral  nerves,  and  descends  on 
the  outer  side  of  the  sympathetic  cord  to  the  coccyx  where  it  terminates  by 
anastomosing  with  the  middle  sacral.  The  superior  branch  only  reaches  as  far  as 
the  first  or  the  second  anterior  sacral  foramen,  and  then  it  enters  the  sacral  canal. 
It  anastomoses  with  the  lower  branch  and  with  the  middle  sacral  artery.  Transverse 
branches  are  given  off  by  the  lateral  sacral  arteries  to  the  pyriformis,  and  to  the 
sacral  nerves.  Spinal  offsets  are  also  given  off,  which  pass  through  the  anterior 
sacral  foramina  to  the  sacral  canal ;  they  supply  the  membranes  of  the  cord,  the  roots 
of  the  sacral  nerves,  and  the  filum  terminale,  and  anastomose  with  other  spinal 
arteries.  They  then  pass  backwards  through  the  posterior  sacral  foramina,  and 
anastomose  on  the  back  of  tlie  sacrum  with  branches  of  the  gluteal  and  sciatic 
arteries. 

3.  Gluteal  Artery  (a.  gluta^a  superior.  Figs.  637  and  643). — After  giving  off  the 
ilio-lumbar  and  lateral  sacral  branches,  the  posterior  division  of  the  internal  iliac  is 
continued  as  the  gluteal  artery.  This  is  a  large  vessel  which  pierces  the  pelvic 
fascia,  passes  backwards  between  the  lumbo-sacral  cord  and  the  first  sacral  nerve, 
and  leaves  the  pelvis  through  the  upper  part  of  the  great  sciatic  foramen.  It  runs 
above  the  pyriformis  muscle  to  the  buttock,  immediately  on  reaching  which  it 
terminates,  between  the  adjacent  borders  of  the  pyriformis  and  gluteus  medius 
muscles  and  beneath  the  gluteus  maximus,  by  dividing  into  superficial  and  deep 
branches. 

(a)  The  superficial  branch  divides  at  once  into  numerous  branches,  some  of  which  supply 
the  gluteus  niaxiinus,  wliilst  otliers  pass  through  it,  near  its  origin,  to  the  overlying  skin. 
The  branches  freely  anastomose  with  branches  of  the  sciatic,  internal  pudic,  internal 
circumflex,  deep  circumflex  iliac,  and  lateral  sacral  arteries. 

(h)  The  deep  terminal  branch,  accompanied  by  the  superior  gluteal  nerve,  runs  forwards 
between  the  gluteus  medius  and  minimus,  and,  after  giving  a  nuti'ient  branch  to  the  ilium, 
subdivides  into  upper  and  lower  branches.  The  iij^per  branch,  running  forwards  along 
the  origin  of  the  gluteus  minimus  from  the  middle  curved  line  of  the  ilium,  passes 
beyond  the  anterior  margins  of  the  gluteus  medius  and  minimus  to  anastomose,  under 
cover  of  the  tensor  fascicc  femoris,  with  the  ascending  branch  of  the  external  circumflex 
artery.  It  also  anastomoses  with  the  circumflex  iliac  artery,  and  it  supplies  muscular 
branches  to  the  adjacent  muscles.  The  lower  branch  passes  more  directly  forwards, 
across  the  gluteus  minimus,  towards  the  trochanter  major,  along  with  the  branch  of  the 
superior  gluteal  nerve  which  supplies  the  tensor  fasciai  femoris.  It  supplies  the  glutei 
muscles,  and  anastomoses  with  the  ascending  l)ranch  of  the  external  circumflex  artery. 

Before  leaving  the  pelvis  the  gluteal  artery  gives  muscular  branches  to  the  pelvic 


BKANCHES  OF  THE  INTERNAL  ILIAC  ARTERY.  851 

diaphragm  and  the  obturator  internus,  small  neural  branches  to  the  roots  of  the  sacral 
plexus,  and  nutrient  branches  to  the  hip-bone. 

Branches  of  the  Anterior  Division  of  the  Internal  Iliac  Artery. 

The  anterior  division  gives  off  both  parietal  and  visceral  branches,  and  is 
continued  as  the  hypogastric  artery,  which  for  the  greater  part  of  its  extent  is 
obliterated.  The  parietal  branches  are  the  obturator,  the  pudic,  and  the  sciatic. 
The  visceral  branches  include  the  superior,  middle  and  inferior  vesical,  and  the 
middle  htemorrhoidal  arteries  in  the  male.  Similar  visceral  branches  are  also 
given  oft'  in  the  female,  but  the  inferior  vesical  is  replaced  by  the  vaginal  artery, 
and  an  additional  branch,  the  uterine  artery,  is  also  given  oft". 

Visceral  Branches. 

1.  The  superior  vesical  artery  (a.  vesicaKs  superior)  arises  from  the  anterior 
division  of  the  internal  iliac.  It  divides  into  numerous  branches  which  supply 
the  upper  part  of  the  bladder,  anastomosing  with  the  other  vesical  arteries,  and  it 
also  gives  small  branches  to  the  urachus,  and  often  to  the  lower  part  of  the 
ureter.  It  may  in  addition  give  off  the  middle  vesical  artery,  and  not  un- 
frequently  the  long  slender  artery  to  the  vas  deferens  arises  from  one  of  its 
branches. 

2.  Obliterated  Hypogastric  Artery. — Atrophy  of  that  portion  of  the  internal 
iliac  artery,  which  extends  from  the  side  of  the  bladder  to  the  umbilicus  (a.  umbili- 
calis),  has  already  been  referred  to.  It  is  complete  between  the  umbihcus  and 
the  true  origin  of  the  superior  vesical  artery,  but  between  this  origin  and  the 
apparent  ending  of  the  internal  iliac  in  its  two  divisions  the  atrophy  is  incomplete, 
and  the  lumen  of  the  vessel,  though  greatly  diminished  in  size,  remains,  and  is 
looked  upon  as  the  first  part  of  the  superior  vesical  artery.  Strictly  speaking,  the 
first  of  these  two  parts  only  constitutes  the  "  obliterated  hypogastric  "  (ligamentum 
umbihcale  laterale).  It  is  a  fibrous  cord  which  runs  forwards  and  upwards 
towards  the  apex  of  the  bladder,  whence  it  ascends  on  the  posterior  surface  of 
the  anterior  abdominal  wall  and  on  the  outer  side  of  the  urachus  to  the  umbilicus. 
As  it  passes  along  the  wall  of  the  pelvis  it  is  under  cover  of  the  peritoneum,  and  it 
is  crossed  by  the  vas  deferens  in  the  male,  and  by  the  round  ligament  in  the  female. 

3.  The  middle  vesical  artery  is  usually  given  off  behind  the  superior  vesical. 
It  is  distributed  to  the  posterior  surface  of  the  bladder  as  low  down  as  the  base ; 
and  to  the  vesiculae  seminales. 

-i.  The  inferior  vesical  artery  (a.  vesicalis  inferior)  is  a  very  constant  branch 
which  runs  inwards  upon  the  upper  surface  of  the  levator  ani  to  the  base  of  the 
bladder.  It  also  gives  branches  to  the  seminal,  vesicles,  the  vas  deferens,  the  lower 
part  of  the  ureter  and  the  prostate,  and  it  anastomoses  with  its  fellow  of  the 
opposite  side,  wdth  the  other  vesical  arteries,  and  with  the  middle  htemorrhoidal 
artery. 

The  axtery  to  the  vas  (a.  deferentiahs),  which  not  unfrequently  arises  from  the 
superior  vesical,  is  a  long  slender  vessel  which  runs  downwards  to  the  vas  and 
vesicula  seminales,  and  is  then  continued  with  the  vas  deferens  to  the  testicle, 
where  it  anastomoses  with  the  spermatic  artery.  It  also  anastomoses  with  the 
cremasteric  brancli  of  the  deep  epigastric  artery. 

5.  The  middle  haemorrhoidal  artery  (a.  hamorrhoidalis  media)  is  an  irregular 
branch  w^hich  arises  either  directly  from  the  anterior  division  of  the  internal  iliac  or 
from  the  inferior  vesical  branch ;  more  rarely  it  springs  from  the  internal  pudic 
artery.  It  runs  inwards,  and  is  distributed  to  the  muscular  coats  of  the  rectum ; 
it  also  gives  branches  to  the  prostate,  the  seminal  vesicle,  and  the  vas  deferens,  and  it 
anastomoses  with  its  fellow  of  the  opposite  side,  with  the  inferior  vesical,  and  with 
the  superior  and  inferior  hiemorrhoidal  arteries. 

6.  The  vaginal  artery  (a.  vaginahs)  in  the  female  usually  corresponds  to 
the  inferior  vesical  in  the  male ;  in  which  case  it  arises  from  the  anterior  division 
of  the  internal  ihac,  either  independently  or  in  common  with  the  uterine  artery. 


852  THE  VASCULAE  SYSTEM. 

Occasionally  both  inferior  vesical  and  uterine  vessels  are  present,  and  not  un- 
commonly the  vaginal  artery  is  represented  by  several  branches. 

The  vaginal  arteries  run  downwards  and  inwards  on  the  floor  of  the  pelvis 
to  the  sides  of  the  vagina,  and  divide  into  numerous  branches  which  ramify 
on  its  anterior  and  posterior  walls.  The  corresponding  branches  of  opposite 
sides  anastomose  and  form  anterior  and  posterior  longitudinal  vessels,  the  so-called 
azygos  arteries.  They  also  anastomose  above  with  the  cervical  branches  of  the 
uterine  artery,  and  below  with  the  perineal  branches  of  the  internal  pudic.  In 
addition  to  supplying  the  vagina,  small  branches  are  given  to  the  bulb  of  the 
vestibule,  to  the  base  of  the  bladder,  and  to  the  rectum. 

7.  The  uterine  artery  (a.  uterina)  arises  from  the  anterior  division 
of  the  internal  ihac,  either  separately  or  in  common  with  the  vaginal  or  middle 
hsemorrhoidal  arteries.  It  runs  inwards  and  slightly  forwards,  upon  the  upper 
surface  of  the  levator  ani,  to  the  lower  border  of  the  broad  ligament,  between  the 
two  layers  of  which  it  passes  inwards,  and  arches  above  the  ureter  about  three- 
quarters  of  an  inch  from  the  uterus.  It  passes  above  the  lateral  fornix  of  the 
vagina  to  the  side  of  the  neck  of  the  uterus,  and  is  then  directed  upwards,  until 
it  almost  reaches  the  fundus,  just  below  which,  however,  it  turns  outwards  beneath 
the  isthmus  of  the  Fallopian  tube  and  anastomoses  with  the  ovarian  artery. 
It  supplies  the  uterus,  the  upper  part  of  the  vagina,  the  inner  part  of  the 
Fallopian  tube,  and  gives  branches  to  the  round  ligament  of  the  uterus.  It 
anastomoses  with  its  fellow  of  the  opposite  side,  and  with  the  vaginal,  the  ovarian, 
and  the  deep  epigastric  arteries. 

Paeietal  Branches  of  the  Anterior  Division  of  the  Internal  Iliac. 

1.  The  obturator  artery  (a.  obturatoria.  Figs.  637  and  640)  runs  forwards  and 
downwards  along  the  lateral  wall  of  the  true  pelvis,  just  below  its  brim,  to  the 
obturator  foramen,  through  the  upper  part  of  which  it  passes.  It  terminates  im- 
mediately on  entering  the  thigh  by  dividing  into  internal  and  external  terminal 
branches,  which  skirt  round  the  margin  of  the  obturator  foramen  beneath  the 
obturator  externus  muscle.  It  is  accompanied  in  the  whole  of  its  course  by  the 
obturator  nerve  and  vein,  the  former  being  above  it  and  the  latter  below. 

To  its  outer  side  is  the  pelvic  fascia,  which  intervenes  between  it  and  the  upper 
part  of  the  obturator  internus  muscle,  whilst  on  its  inner  side  it  is  covered  by 
peritoneum ;  between  the  peritoneum  and  the  artery  is  the  ureter.  When  the 
bladder  is  distended  it  also  comes  into  close  relation  with  the  anterior  part  of  the 
artery.  In  the  female  the  ovarian  vessels  and  the  broad  ligament  are  on  the  inner 
side  of  the  obturator  artery. 

Branches. — All  the  branches  except  the  terminal  are  given  off  before  the  artery 
leaves  the  pelvis.  They  include  : — (a)  Muscular  branches  to  the  obturator  internus, 
levator  aui  and  iliopsoas  muscles.  (6)  A  nutrient  branch  to  the  ilium,  which  passes 
beneath  the  ilio-psoas  muscle,  supplies  the  bone,  and  anastomoses  with  the  ilio-lumbar 
artery,  (c)  A  vesical  branch,  or  branches,  pass  inwards  to  the  bladder  beneath  the 
lateral  false  ligament,  {d)  A  pubic  branch  (ramus  pubicus),  which  ascends  on' the  back 
of  the  pubes,  and  anastomoses  with  its  fellow  of  the  opposite  side  and  Avith  the  pubic 
branch  of  the  deep  epigastric,  is  given  off  just  before  the  artery  leaves  the  pelvis.  In 
its  upward  course  it  may  pass  either  on  the  outer  or  inner  side  of  the  exten^al  iliac  vein, 
whilst  not  unfrcqucntly  it  runs  on  the  inner  side  of  the  crural  ring.  In  the  latter  case 
it  is  important  in  relation  to  femoral  hernia ;  and  this  importance  is  emphasised  when, 
as  sometimes  happens,  the  obturator  artery  arises  as  an  enlarged  pubic  branch  of  the 
deep  epigastric  artery  instead  of  from  the  internal  iliac,  (e)  Terminal. — The  internal 
terminal  branch  (ramus  anterior)  runs  forwards,  and  the  external  (ramus  posterior) 
backwards  round  the  margin  of  the  obturator  foramen.  They  lie  on  the  obturator 
membrane,  and  under  cover  of  the  obturator  externus.  They  anastomose  together  at 
the  lower  margin  of  the  foramen,  and  both  give  off  ofTsets  which  anastomose  with  the 
internal  circumflex  artery,  and  twigs  of  supply  to  the  adjacent  muscles.  The  external 
branch  also  gives  an  acetabular  branch  to  the  hip-joint,  which  passes  upwards,  through 
the  cotyloid  notch  on  the  inner  side  of  the  transverse  ligament,  to  supply  the  ligamentum 
teres  and  the  head  of  the  femur. 


BRANCHES  OF  THE  INTERNAL  ILIAC  ARTERY. 


853 


2.  Internal  Pudic  Artery  (a.  pudenda  interna,  Figs.  637  and  638). — The 
internal  pudic  artery  arises  from  the  anterior  division  of  the  internal  iliac  close  to 
the  origin  of  the  sciatic  artery,  which  slightly  exceeds  it  in  size.  It  runs  down- 
wards and  backwards  in  front  of  the  pyriformis  muscle  and  the  sacral  plexus,  from 
both  of  which  it  is  separated  by  the  pelvic  fascia,  and  on  the  outer  side  of  the 
rectum  to  the  lower  part  of  the  great  sciatic  foramen.  In  this  course  it  pierces 
the  pelvic  fascia,  passes  between  the  pyriformis  and  coccygeus  muscles,  and  leaves 
the  pelvis  to  enter  the  buttock  in  company  with  the  corresponding  veins,  the 
sciatic  vessels  and  nerves,  the  pudic  nerve,  and  the  nerve  to  the  obturator  internus. 
In  the  buttock  it  lies,  under  cover  of  the  gluteus  maximus,  on  the  spine  of  the 
ischium,  between  the  pudic  nerve  and  the  nerve  to  the  obturator  internus,  the 
former  being  internal   to  it.     It  next  passes  through  the  small  sciatic  foramen 


Crus-peiiis 


Superficial  perineal 
artery 


Traiisversus  periiiHi 
muscle 


Internal  pudic  arterj 


Inferior  hsemor 
rhoidal  arterj 


C  rus  penis 

Dorsal  artery  of  penis 
md  artery  to  corpus 
tavernosuni 

Bulb  of  penis 

C  onipressor  urethr<e 

Aitery  to  bulb 

Superficial  perineal 
11  tery 

1 1  msverse  perineal 
11  tery 

Internal  pudic  artery 

Inferior  hsemor- 
ihoidal  artery 


Gluteus  maximus 


Fig.  638. — The  Perineal  Distribution  of  the  Intern.\l  Pudic  Artery  in  the  Male. 

and  enters  the  perineum,  in  the  anterior  part  of  which  it  terminates  by  dividing 
into  the  artery  of  the  corpus  cavernosum  and  the  dorsal  artery  of  the  penis. 

In  the  first  part  of  its  course  in  the  perineum  the  artery  lies  in  the  outer 
fascial  wall  of  the  ischio-rectal  fossa,  where  it  is  enclosed  in  the  space  known  as 
Alcock's  canal.  This,  which  is  situated  about  one  and  a  half  inches  above  the 
lower  margin  of  the  tuberosity  of  the  ischium,  contains  also  the  pudic  veins  and 
the  terminal  parts  of  the  pudic  nerve,  viz.  the  dorsal  nerve  of  the  penis  which  lies 
above  the  artery,  and  the  perineal  division  which  lies  below  the  vessel.  From  the 
ischio-rectal  fossa  the  internal  pudic  is  continued  forwards  between  the  two  layers 
of  the  triangular  ligament  of  the  urethra,  and  close  to  the  ramus  of  the  pubis.  About 
half-an-inch  below  the  subpubic  ligament  it  turns  somewhat  abruptly  forwards, 
pierces  the  anterior  layer  of  the  triangular  ligament,  and  immediately  divides  into 
its  terminal  branches,  viz.  the  artery  of  the  corpus  cavernosum  and  the  dorsal 
artery  of  the  penis.  The  division  sometimes  takes  place  whilst  the  artery  is  still 
between  the  layers  of  the  triangular  ligament. 

Branches. — In  the  pelvis  it  gives  small  branches  to  the  neighbouring  muscles  and  to 
the  roots  of  the  sacral  plexus. 


854  THE  VASCULAR  SYSTEM. 

In  the  buttock. — {a)  Muscular  branches  are  given  to  the  adjacent  muscles.  (6) 
Anastomotic  branches  unite  with  branches  of  the  gluteal,  sciatic  and  internal  circumflex 
arteries. 

In  the  ischio-rectal  fossa. — (c)  The  inferior  hsemorrhoidal  artery  (a.  hsemorrhoidalis 
inferior)  pierces  the  inner  wall  of  Alcock's  canal,  and  runs  obliquely  forwards  and  inwards. 
It  soon  divides  into  two  or  three  main  branches,  which,  sometimes  arising  separately,  pass 
across  the  space  to  the  anal  passage.  The  artery  anastomoses  in  the  walls  of  the  anal 
passage  with  its  fellow  of  the  opposite  side,  and  with  the  middle  and  superior  hsemor- 
rhoidal arteries ;  it  also  anastomoses  with  the  transverse  perineal  arteries,  and  it  supplies 
cutaneous  twigs  to  the  region  of  the  anus,  and  others  which  turn  round  the  lower  border 
of  the  gluteus  maximus  to  supply  the  lower  part  of  the  buttock. 

(d)  The  superficial  perineal  artery  (a.  perinei)  arises  in  the  anterior  part  of  the  ischio- 
rectal fossa,  pierces  the  base  of  the  triangular  ligament,  and  divides  into  long  slender 
branches  (aa.  scrotales  posteriores  in  the  male,  labiales  posteriores  in  the  female)  which 
are  continued  forwards  in  the  urethral  triangle,  beneath  the  superficial  perineal  fascia, 
to  the  scrotum.  It  anastomoses  with  its  fellow  of  the  opposite  side,  with  the  transverse 
perineal  and  the  external  pudic  arteries,  and  it  supplies  the  muscles  and  subcutaneous 
structures  of  the  urethral  triangle. 

(e)  The  transverse  perineal  artery  is  a  small  branch  which  arises  either  from  the  internal 
pudic  or  fi'om  its  superficial  perineal  branch.  It  runs  inwards  along  the  base  of  the 
triangular  ligament  to  the  central  point  of  the  perineum,  where  it  anastomoses  with  its 
fellow  of  the  opposite  side,  with  the  superficial  perineal  branch,  and  with  the  inferior 
hfemorrhoidal  arteries.  It  supplies  the  sphincter  ani,  the  bulbo-cavernosus  or  sphincter 
vaginae,  and  the  anterior  fibres  of  the  levator  ani. 

In  the  urethral  triangle. — (/)  The  artery  to  the  bulb  (a.  bulbi  urethree),  a  branch 
which  is  usually  of  relatively  large  size,  is  given  off  between  the  layers  of  the  triangular 
ligament.  It  runs  transversely  inwards  along  the  posterior  border  of  the  compressor 
urethrse,  and  then  turning  forwards  a  short  distance  from  the  outer  side  of  the  urethra, 
it  pierces  the  anterior  layer  of  the  triangular  ligament  and  enters  the  substance  of  the 
bulb.  It  passes  onwards  in  the  corpus  spongiosum  to  the  glans,  where  it  anastomoses 
with  its  fellow  and  with  the  dorsal  arteries  of  the  penis. 

It  supplies  the  compi-essor  urethrse  muscle,  Cowper's  gland,  the  corpus  spongiosum, 
and  the  penile  part  of  the  urethra.  In  the  female  this  artery  supplies  the  bulb  of  the 
vestibule. 

ig)  The  artery  of  the  corpus  cavernosum  (a.  profunda  penis  in  the  male ;  a.  pro- 
funda clitoridis  in  the  female)  is  usually  the  larger  of  the  two  terminal  branches. 
Immediately  after  its  origin  it  enters  the  crus  penis,  and  runs  forwards  in  the  corpus 
cavernosum,  which  it  supplies. 

(A)  The  dorsal  artery  of  the  penis  (a.  dorsalis  penis  in  the  male ;  a.  dorsalis  clitoridis 
in  the  female)  passes  forwards  between  the  la3'ers  of  the  suspensory  ligament,  and  runs 
along  the  dorsal  surface  of  the  penis  with  the  dorsal  nerve  immediately  to  its  outer  side, 
whilst  it  is  separated  from  its  fellow  of  the  opposite  side  by  the  median  deep  dorsal  vein. 
It  supplies  the  superficial  tissues  on  the  dorsal  aspect  of  the  penis,  sends  branches  into 
the  corpus  cavernosum  to  anastomose  with  the  artery  to  the  corpus  cavernosum,  and  its 
terminal  branches  enter  the  glans  penis,  where  they  anastomose  with  the  arteries  to  the 
bulb.      It  also  anastomoses  with  the  external  pudic  branches  of  the  femoral. 

3  Sciatic  Artery  (a.  glutaa  inferior,  Figs.  637  and  639). — The  sciatic  artery 
arises,  usually  distinct  from  the  pudic  artery,  but  sometimes  in  common  with  it, 
from  the  anterior  division  of  the  internal  iliac.  It  descends  a  little  behind  and 
external  to  the  pudic  vessels,  pierces  the  pelvic  fascia,  runs  backwaijds  between 
the  first  and  second,  or  second  and  third  sacral  nerves,  and  passing  betweejQ  the 
pyriformis  and  coccygeus  muscles,  leaves  the  pelvis  through  the  lower  part  of  the 
great  sciatic  foramen,  and  enters  the  buttock  just  below  the  pyriformis.  In  the 
buttock  it  descends  behind  and  to  the  inner  side  of  the  great  sciatic  nerve  beneath 
the  gluteus  maximus,  and  behind  the  obturator  internus,  the  two  gemelli,  the 
quadratus  femoris,  and  upper  part  of  the  adductor  magnus  muscles,  to  the  upper 
part  of  the  thigh. 

Below  the  lower  border  of  the  gluteus  maximus  the  artery  is  comparatively 
superficial,  and  having  given  off  its  largest  branches,  it  descends  as  a  long  slender 
vessel  with  the  small  sciatic  nerve. 

Branches. — In  the  pelvis. — Small  and  irregular  branches  supply  the  adjacent  viscera 


BRANCHES  OF  THE  INTERNAL  ILIAC  ARTERY. 


855 


and  muscles  and  the  sacral  nerves ;  they  anastomose  with  branches  of   the  internal  pudic 
and  lateral  sacral  arteries. 

In  the  buttock. — (a)  Muscular  branches  are  given  off  to  the  nmscles  of  the  buttock 
and  to  the  upper 
parts  of  the  hamstring 
muscles.  They  an- 
astomose with  the 
pudic,  internal  cir- 
cumflex, and  obtin-- 
ator  arteries,  {h)  The 
coccygeal  branch 
arises  immediately 
after  the  artery  leaves  Great  sciatic 
the  pelvis.      It  runs 


Gluteus  ma\iniu 


Comes  nerv  i 


Biceps  aiK 
semitendiiiosu 


Adductor  magnus 


Muscular  branch 
of  profunda  arteiy 


Popliteal  ai  tery 

Superior  internal 
articular  artery 

Semitendmosus 
Gastrocnemius 

Musculai  aiteij 


Fig.  639.- 


Gluteus  medius 


Gluteus  minimus 

Deep  branch  of 
gluteal  artery 


Pyriformis 


ligament 

inwards,    pierces   the     p^jic'artery 
great  sacro-sciatic 

ligament     and     the     Sciatic  artery 

gluteus  maximus,  and 
ends  in  the  soft  tissues 
over  the  back  of  the 
lower  part  of  the 
sacrum    and    of    the 

coccyx.         It     gives    Semimembranos 

several  branches  to  • 
the  gluteus  maximus, 
and  anastomoses  with 
branches of  the  gluteal 
and  lateral  sacral 
arteries,  (c)  An  an- 
astomotic branch 
passes  transversely 
outwards,  over  or 
under  the  great  sciatic 
nerve,  towards  the 
great  trochanter  of 
the  femur.  It  anas- 
tomoses with  branches 
of  the  gluteal,  pudic, 
internal  and  external 
circumflex,  and  the 
first  perforating 
arteries,  taking  part 
in  the  formation  of 
the  so-called  "  crucial 
anastomosis."  {d) 
Cutaneous  branches, 
accompanying  twigs 
of  the  small  sciatic 
nerve,  pass  round  the 
lower  border  of  the 
glutevis  maximus 
muscle  to  the  integu- 
ment, (e)  The  comes 
nervi  ischiatici  (a. 
comitans  n.  ischiadic!) 
is  a  long  slender 
branch  which  runs 
down  on  the  surface, 

or  in  the  substance  of  the  great  sciatic  nerve.     It  supplies  the  nerve,  and  anastomoses 
with  the  perforating  arteries  and  with  the  termination  of  the  profunda. 


Obturator  iiiternus 
and  gemelli 
Ascending  branch 
of  internal 
circumflex  artery 

Quadratus  femoris 

Transverse  branch 
of  internal' 
circumflex  artery 


1st  perforating 
artery 


'2nd  perforating 
artery 


3rd  perforating 
artery 


Termination  of 
profunda  artci'y 
(4th  perforating) 


iShoit  head  of  biceps 


Long  head  of  biceps 


Popliteal  vein 


lor  external  articular 


Gastiocnemius 


-The  Arteries  of  the  Buttock  and  the  Back  of  the 
Thigh  and  Knee. 


856  THE  VASCULAE  SYSTEM. 

AKTEKIES  OF  THE  LOWER  EXTEEMITY. 

The  main  artery  of  each  lower  limb  is  continued  from  the  corresponding  com- 
mon iliac  artery.  It  descends  as  a  single  trunk  as  far  as  the  lower  border  of  the 
popliteus,  and  ends  there  by  dividing  into  the  anterior  and  posterior  tibial  arteries. 
Distinctive  names  are,  however,  applied  to  different  parts  of  the  artery,  correspond- 
ing to  the  several  regions  through  which  it  passes.  Thus  in  the  abdomen  it  is 
called  the  external  iliac  artery,  in  the  upper  two-thirds  of  the  thigh  it  receives  the 
name  of  the  femoral  artery,  whilst  its  lower  part,  which  is  situated  on  the  flexor 
aspect  of  the  knee,  is  termed  the  popliteal  artery. 

THE  EXTERNAL  ILIAC  ARTERY. 

The  external  iliac  artery  (a.  iliaca  externa)  extends  from  a  point  opposite  the 
sacro-iliac  joint  at  the  leVel  of  the  lumbo-sacral  articulation  to  a  point  beneath 
Poupart's  ligament,  midway  between  the  anterior  superior  spine  of  the  ilium  and 
the  symphysis  pubis,  where  it  becomes  the  femoral  artery.  Its  length  is  about 
three  and  a  half  inches  (87  to  100  mm.),  and  in  the  adult  it  is  usually  somewhat 
larger  than  the  internal  ihac  artery. 

It  runs  downwards,  outwards,  and  forwards  along  the  brim  of  the  pelvis,  rest- 
ing upon  the  iliac  fascia,  which  separates  it  above  from  the  inner  border,  and 
below  from  the  anterior  surface  of  the  psoas  muscle,  and  it  is  enclosed  with  its 
accompanying  vein  in  a  thin  fascial  sheath. 

Relations. — Anterior. — It  is  covered  in  front  by  peritoneum,  which  separates  it  on 
the  left  side  from  the  pelvic  colon,  iliac  colon,  and  coils  of  small  intestine,  and  on  the  right 
side  from  the  terminal  portion  of  the  ileum,  and  sometimes  from  the  vermiform  appendix. 
The  ureter,  descending  beliind  the  peritoneum,  sometimes  crosses  the  front  of  the  artery 
near  its  origin,  and  in  the  female  the  ovarian  vessels  cross  the  upper  part  of  the  artery. 
Near  its  lower  end  the  artery  is  crossed  anteriorly  by  the  genital  branch  of  the  genito- 
crural  nerve  and  by  the  deep  circumflex  iliac  vein.  In  the  male  this  part  of  the  artery  is 
also  crossed  by  the  vas  deferens,  and  in  the  female  by  the  round  ligament  of  the  uterus. 
Several  iliac  lymphatic  glands  lie  in  front  and  at  the  sides  of  the  external  iliac  artery,  and 
almost  invariably  one  of  these  is  directly  in  front  of  its  termination. 

Posterior. — The  iliac  fascia  and  psoas  muscle  lie  behind  the  artery.  Near  its  upper 
end  the  obturator  nerve  is  also  posterior  to  the  vessel. 

Lateral. — Externally  is  the  genito-crural  nerve  ;  internally,  and  on  a  somewhat  posterior 
plane,  is  the  external  iliac  vein. 

Branches. — In  addition  to  small  branches  to  the  psoas  muscle  and  to  the 
lymphatic  glands,  two  named  branches  of  considerable  size  spring  from  the  external 
iliac  artery,  viz.  the  deep  epigastric  and  the  deep  circumflex  iliac. 

(1)  The  deep  epigastric  artery  (a.  epigastrica  inferior,  Figs.  637  and  640)  arises 
immediately  above  Poupart's  ligament  from  the  front  of  the  external  iliac.  Curving 
forward  from  its  origin  it  lies  in  the  extra-peritoneal  fat,  it  turns  round  the  lower 
border  of  the  peritoneal  sac,  and  runs  upwards  and  inwards  along  the  inner  side  of 
the  internal  abdominal  ring  and  along  the  outer  border  of  Hesselbach's  triangle;  it 
then  pierces  the  transversalis  fascia,  passes  over  the  semilunar  fold  of  Douglas  and 
enters  the  sheath  of  the  rectus  abdominis.  For  a  short  distance  it  ascends  behind 
the  rectus,  but  it  soon  penetrates  the  substance  of  the  muscle,  and  breaks  up  into 
branches  which  anastomose  with  terminal  offsets  of  the  superior  epigastric  liranch 
of  the  internal  mammary  artery  and  with  the  lower  intercostal  arteries.  At  the 
internal  abdominal  ring  in  the  male  the  vas  deferens,  the  spermatic  vessels,  and  the 
genital  branch  of  the  genito-crural  nerve  hook  round  the  front  and  outer  side  of 
the  artery,  the  vas  deferens  turning  inwards  behind  it ;  whilst  in  the  female  the 
round  ligament  of  the  uterus  and  the  genital  l»ranch  of  the  genito-crural  nerve 
occupy  the  corresponding  positions. 

Branches. — (a)  Muscular  branches  which  spring  mainly  from  the  outer  side  of  the 
artery  supply  the  rectus,  the  pyrumidalis,  tlie  transversalis,  and  the  oblique  muscles  of 
the   abdominal    wall,   and    anastomose  with   bnuiches  of   the    deep   circumflex   iliac,   the 


THE  EXTEKNAL  ILIAC  AETERY. 


857 


Psoas  muscle 

Ureter 

Genito-erural 

nerve 

External  cutaneous  t 

erve 

"r 

11 

lo-inguinal  nerve 

7 

Uc 

-lumbar 

/ 

'~Z/ 

artery 

lumbar,  and  the  lower  iutercostararteries.  (6)  Cutaneous  branches  which  pass  from  the 
front  of  the  deep  epigastric  pierce  the  rectus  abdominis  and  the  front  part  of  its  sheath, 
and  terminate  in  the  subcutaneous  tissues  of  the  anterior  abdominal  wall,  where  they 
anastomose  with  corresponding  branches  of  the  opposite  side  and  with  branches  of  the 
superficial  epigastric  artery,  (c)  The  cremasteric  branch  (a.  spermatica  externa  in  the 
male,  a.  ligamenti  teretis  uteri  in  the  female)  is  small.  It  descends  through  the  inguinal 
canal  and  anastomoses  with  the  external  pudic  and  superficial  perineal  arteries,  and  in  the 
male  with  the  spermatic  artery  also.  In  the  male  it  accompanies  the  spermatic  cord, 
supplying  its  coverings,  including  the  cremaster.     In  the  female  it  runs  with  the  round 


Inferior  vena  cava 

Common  iliac  artery 
Left  common  iliac  vein 


Kight  common 
iliac  vein 


internal  iliac  vein 

ntenial  iliac 
artery 

Telvic  colon 
Ureter 
Uterine  artery 

OA-ary 

terns 
Falloi^ian  tube 

bturator  artery 

Superior  vesical 
lirtery 

Bladder 

obliterated  hypo- 
fiastric  artery 
Urethra 

mlihysis 


Anterior  crural 
nerve ' 

Iliacus  mi-.scle 


Psoas  muscle  - 

External  iliac 

arterj' 

Deep  circumflex 

iliac  artery 

External  iliac  vein 


Deep  epigastric 
artery 

Round  ligament 


Fig.  640.— The  Iliac  Ahteries  and  Veins  in  the  Female. 

ligament,  (d)  The  pubic  branch  (ramus  pubicus)  descends  either  on  the  outer  or  the  inner 
side  of  the  crural  ring  to  anastomose  with  the  pubic  branch  of  the  obturator  artery  ;  it  also 
anastomoses  with  its  fellow  of  the  opposite  side.  Sometimes  when  the  obturator  branch 
of  the  internal  iliac  artery  is  absent,  the  pubic  branch  of  the  deep  epigastric  artery 
enlarges  and  becomes  the  obturator  artery,  which  descends  to  the  obturator  foramen 
either  on  the  outer  or  the  inner  side  of  the  crural  ring.  In  the  latter  case  the  artery  may 
be  injured  in  the  operation  for  the  relief  of  a  strangulated  femoral  hernia. 

(2)  The  deep  circumflex  iliac  artery  (a.  circumflexa  ilium  profunda,  Figs.  637 
and  6-iO)  springs  from  the  outer  side  of  the  external  iliac  artery,  usually  a  little 
below  the  deep  epigastric,  and  immediately  above  Poupart's  ligament.  It  runs 
outwards  and  upwards  to  the  anterior  superior  spine  of  the  ilium.  In  this  part  ot 
its  course  it  Lies  just  above  the  lower  border  of  Poupart's  ligament,  and  is  enclosed 
in  a  fibrous  canal  formed  by  the  union  of  the  transversalis  and  ihac  fascise.  A 
httle  beyond  the  anterior  superior  spine  it  pierces  the  transversalis  abdominis,  and 


858 


THE  VASCULAK  SYSTEM. 


is  continued  backwards  between  the  transversalis  and  the  internal  oblique,  to 
terminate  by  anastomosing  with  branches  of  the  ilio-lumbar  artery. 

Branches.  —  (a) 


Tensor  fascia' 
femoris 

Rectus  feinoris 
Psoas  and 

iliacus 


External  cir- 
cumflex artery 

First  perforat- 
ing arterj 

Second  perfor- 
ating artery 


Vastus  externu'5 


Vastus  internus 


Crureus- 


Rectus  femoris 


Superior  external 
articular  artery 


Anterior  tibial  recurrent 
artery 


Muscular    to 
upper  parts    of 


Pectineus 


Adductor  brevis 


Common  femoral 
ai  tery 
Adductor  longus 

Internal  circum- 
flex artery 
Superficial  femoral 
aitery 


Piofunda  artery 


Anastomotic  artery 


Sartorius 


Anastomotic  artery 


the 
the 
sartorius     and     the 
tensor  fascice  femoris, 
and  to  the  muscles  of 
the  abdominal  wall. 
One  of  the  latter 
branches    is    fre- 
quently of  consider- 
able size ;    it  pierces 
the    transversalis 
muscle  a   short  dis- 
tance in  front  of  the 
anterior    superior 
spine    of   the    ilium, 
and     ascends    verti- 
cally    between     the 
transversalis  and  the 
internal  oblique,  an- 
astomosing with  the 
lumbar     and    epi- 
gastric arteries,     (h) 
Cutaneous  branches 
pierce    the    internal 
and  external  oblique 
muscles.      They  ter- 
minate   in    the   skin 
over  the  crest  of  the 
ilium,  and  they  anas- 
tomose   with    the 
gluteal,    the    super- 
ficial circumflex  iliac 
and   the  ilio-lumbar 
arteries. 

THE   FEMORAL 
ARTERY. 


or  internal  articular 


artery 


ior  internal  articular 


The  femoral 
artery  (a.  femoralis, 
Figs.  641  and  642) 
continues  the  ex- 
ternal iliac  into  the 
thigh.  It  com- 
mences at  the  lower 
border  of  Poupart  s 
ligament,  and,  de- 
scending through 
the  upper  two- 
thirds  of  tlie  thigh, 
terminates   at   the 

opening  in  the  adductor  rnagnus.  At  one  time  it  was  customary  to  speak  of  the 
first  one  and  a  half  inches,  as  far  as  the  origin  of  the  profunda  branch,  as  the 
common  femoral,  and  to  say  that  it  divided  into  the  superficial  and  deep  femoral 
branches,  of  which  the  former  was  the  direct  continuation  of  the  common  trunk. 
The  morphology  and  development  of  the  vessel  gives  no  support  for  such  terminology, 
and  it  should  be  discontinued. 

Course. — Its  general  direction  is  indicated  by  a  line  drawn  from  the  point  of 


Fk;.  641. — The  Femoral  Artery  and  its  Branches. 


THE  FEMOEAL  AETEEY.  859 

origin  midway  between  the  anterior  superior  spine  of  the  ilium  and  the  symphysis 
pubis  to  the  adductor  tubercle,  the  thigh  being  flexed  and  rotated  outwards. 

In  its  upper  half  the  femoral  artery  lies  in  Scarpa's  triangle,  and  is  comparatively 
superticial;  at  the  apex  of  the  triangle  it  passes  beneath  the  sartorius,  enters 
Hunter's  canal,  and  is  thus  more  deeply  placed. 

At  its  entry  into  Scarpa's  triangle  both  the  artery  and  its  vein  are  enclosed,  for 
a  distance  of  one  and  a  quarter  inches,  in  a  funnel-shaped  fascial  sheath  formed  of 
the  fascia  transversalis  in  front  and  the  iliac  fascia  behind.  This  is  called  the 
femoral  sheath;  it  is  di^'ided  by  septa,  running  from  front  to  back,  into  three 
compartments,  the  outer  of  which  is  occupied  by  the  femoral  artery  and  genito- 
crural  nerve.  The  middle  contains  the  femoral  vein,  and  the  internal  compartment 
constitutes  the  crural  canal. 

Relations. — In  Scarjja's  triangle  the  femoral  artery  is  covered  by  skin  aud  fascia, 
by  siiperticial  iuguinal  lymphatic  glands  aud  small  superficial  vessels.  The  anterior 
part  of  the  femoral  sheath  aud  the  cribriform  fascia  are  in  front  of  the  upper  part  of  the 
artery,  and  the  fascia  lata  is  in  front  of  the  lower  part.  Near  the  apex  of  the  ti'iaugle 
the  artery  is  crossed  by  the  internal  cutaneous  nerve,  and  not  infrequently  by  a  tributary 
of  the  internal  saphenous  vein.  Behind,  it  is  in  relation,  from  above  downwards,  with  the 
posterior  part  of  the  femoral  sheath,  the  pubic  portion  of  the  fascia  lata  and  the  psoas, 
the  pectineus,  and  the  upper  part  of  the  adductor  longus  muscles.  The  nerve  to  the 
pectineiis  passes  between  the  artery  and  the  psoas  ;  the  femoral  vein  and  the  profunda 
artery  and  vein  intervene  between  it  and  the  pectineus,  and  the  femoral  vein  also  separates 
it  from  the  adductor  longus. 

The  femoral  vein  which  lies  behind  the  artery  in  the  lower  part  of  Scarpa's  triangle 
passes  to  its  inner  side  above,  but  is  separated  from  the  artery  by  the  outer  septum  of 
the  femoral  sheath.  On  the  outer  side  of  the  artery  is  the  anterior  crural  nerve  above ; 
lower  down  the  internal  saphenous  nerve  and  the  nerve  to  the  vastus  internus  are 
continued  on  the  outer  side.  The  crural  branch  of  the  genito-crural  nerve  is  in  fi-ont  and 
to  the  outer  side  above,  and  runs  for  a  short  distance  in  the  femoral  sheath. 

In  Hiintei-'s  canal  the  artery  has  behind  it  tlie  adductor  longus  and  the  adductor 
magnus,  whilst  in  front  and  to  the  outer  side  is  the  vastus  internus.  The  femoral  vein  is 
also  behind  the  artery,  hut  lies  to  its  outer  side  below  and  to  its  inner  side  above. 
Superficial  to  the  artery  is  the  fascial  roof  of  the  canal,  upon  which  is  the  sub-sartorial 
plexus  of  nei'ves  and  the  sartorius  muscle.  The  internal  or  long  saphenous  nerve  enters 
Hunter's  canal  with  the  artery,  and  runs  first  on  its  outer  side,  then  Jn  front,  and  lastly 
on  its  inner  side. 

Branches. — The  femoral  artery  gives  off  the  following  branches  : — 

(1)  Superficial  branches. 

(rt)  The  superficial  external  pudic. 

(b)  The  superficial  epigastric. 

(o)  The  supei-ficial  circumflex  iliac. 

(2)  Muscular. 

(3)  The  deep  external  pudic. 
(•i)  The  pi-ofunda. 

(5)  The  anastomotica  magna. 

(rt)  The  superficial  circumflex  iliac  (a:  circumflexa  ilium  superficialis)  springs 
from  the  front  of  the  femoral  artery  just  below  Poupart's  ligament.  It  pierces 
the  femoral  sheath  and  the  fascia  lata,  external  to  the  saphenous  opening,  and 
runs  in  the  superficial  fascia  as  far  as  the  anterior  superior  spine  of  the  ilium. 
It  supplies  the  outer  set  of  inguinal  glands  and  the  skin  of  the  groin,  and  it  sends 
branches  through  the  fascia  lata  which  anastomose  with  the  deep  circumflex  iliac 
and  supply  the  upper  parts  of  the  sartorius  and  tensor  fascite  femoris  muscles. 

(b)  The  superficial  epigastric  artery  (a.  epigastrica  superficialis)  arises  near 
the  preceding.  It  pierces  the  femoral  sheath  and  the  cribriform  fascia,  and 
passes  upwards  and  inwards  between  the  superficial  and  deep  layers  of  the  super- 
ficial fascia  of  the  abdominal  wall  towards  the  umbilicus.  It  supplies  the  inguinal 
glands  and  the  integument,  and  anastomoses  with  its  fellow  of  the  opposite  side, 
with  the  deep  epigastric,  and  with  the  superficial  circumflex  iliac  and  superficial 
external  pudic  arteries. 

(c)  The  superficial  external  pudic  artery  (a.  pudenda  externa  superficialis)  also 


860 


THE  VASCULAR  SYSTEM. 


springs  from  the  front  of  the  femoral  artery,  and,  after  piercing  the  femoral  sheath 
and  the  cribriform  fascia,  runs  upwards  and  inwards  towards  the  spine  of  the 
pubis,  where  it  crosses  superficial  to  the  spermatic  cord.  It  supplies  the  integument 
of  the  lower  part  of  the  abdominal  wall,  the  root  of  the  dorsum  of  the  penis  in  the 
male,  and  the  region  of  the  mons  Veneris  in  the  female,  and  it  anastomoses  with 
its  fellow  of  the  opposite  side,  the  deep  external  pudic,  the  dorsal  artery  of  the 
penis,  and  the  superficial  epigastric  arteries. 

(2)   Muscular   branches    are    distributed    to    the   pectineus   and    the   adductor 


Sartorius- 


Tensor  fasciie 
femoris 


Superficial  cir- 
cumflex iliac 
artery 

Rectus  femoris- 
Psoas  and  iliacus 


Profunda  artery_ 

External  cir- 
cumflex artery 


Vastus  extern us 


Vastus  internus 


Femoral  artery 
Femoral  vein 
Crural  canal 


Superficial  ex- 
tt  nial  pudic 
utery 


Deep  external  pudic 
artery 


Long  saphenous  vein 
Adductor  longus 
Gracilis 


Kii;.  012.     'J'mo   Kkmcikai.  Vksski.s   in  Scari'a'h  '1'rtangle.  * 

muscles  on  the  inner  side,  and  to  tlie  sartorius  and  tlie  vastus  internus   on   the 
outer  side. 

(3)  The  deep  external  pudic  artery  (a.  pudenda  externa  profunda)  rises  from  the 
inner  side  of  the  femoral.  It  runs  inwards,  across  the  front  of  the  pectineus,  and  in 
front  of  or  behind  the  adductor  longus,  to  the  inner  side  of  the  thigh  ;  it  then 
pierces  the  deep  fascia,  and  terminates  in  the  scrotum,  where  it  anastomoses  with 
the  superficial  perineal  and  superficial  external  pmlic  arteries,  and  with  the 
cremasteric  branch  of  the  deep  epigastric  artery. 

(4)  The  profunda  artery  (a.  profunda  femoris.  Fig.  640)  is  the  largest  branch 
of  the  femoral  artery.  It  arises  about  an  inch  and  a  half  below  Poupart's  ligament, 
from  the  outer  side  of  the  femoral  artery.  Curving  l)ackwards  and  inwards,  it 
passes  behind  the  latter  vessel,  and  runs  downwards,  close  to  the  inner  aspect  of 


THE  FEMOEAL  AKTEKY.  861 

the  femur,  to  the  lower  third  of  the  thigh,  where  it  perforates  the  adductor  magnus 
and  passes  to  the  back  of  the  thigh.  Its  termination  is  known  as  the  fourth 
perforating  artery.  As  the  profunda  descends  it  lies  in  front  of  the  ihacus,  the 
pectineus,  the  adductor  brevis,  and  the  adductor  magnus.  It  is  separated  from 
the  femoral  artery  by  its  own  vein,  by  the  femoral  vein,  and  by  the  adductor  longus 
muscle  behind  which  it  passes. 

Branches. — {<t)  Muscular  branches  are  given  off  from  the  profunda  both  in  Scarpa's 
triangle,  and  whilst  it  lies  l)etween  the  adductor  muscles ;  many  of  them  terminate  in  the 
adductors,  others  pass  through  the  adductor  magnus,  and  terminate  in  the  hamstrings, 
where  they  anastomose  with  the  transverse  branch  of  the  internal  circumflex  and  with 
the  upper  mviscvdar  branches  of  the  popliteal  artery. 

(b)  The  external  circumflex  artery  (a.  circumflexa  femoris  lateralis,  Figs.  641  and  642) 
springs  from  the  outer  side  of  the  profunda,  or  occasionally  from  the  femoral  artery 
above  the  origin  of  the  profunda.  It  runs  outwards  across  the  front  of  the  iliacus,  and 
between  the  superficial  and  deep  branches  of  the  anterior  crural  nerve,  to  the  outer  boixler 
of  Scarpa's  triangle;  then,  passing  behind  the  sai'torius  and  the  rectus  femoris,  it  terminates 
by  dividing  into  three  terminal  branches — the  ascending,  the  transverse,  and  the  descend- 
ing. Before  its  termination  it  supplies  branches  to  the  muscles  mentioned  and  to  the 
upper  part  of  the  crureus. 

(i.)  The  ascending  terminal  branch,  (ramus  ascendens)  runs  upwards  and  outwards,  behind  the 
rectus  femoris  and  'the  tensor  I'ascise  femoris,  along  the  anterior  intertrochanteric  line,  to  the 
anterior  borders  of  the  gluteus  medius  and  minimus,  between  which  it  j^asses  to  anastomose  with 
the  deep  branches  of  the  gluteal  artery.  It  sujiplies  twigs  to  the  neighbouring  muscles,  anasto- 
moses with  the  gluteal,  the  deep  circumflex  iliac,  and  the  transverse  branch  of  the  external 
circumflex  arteries,  and,  as  it  ascends  along  the  anterior  intertrochanteric  line,  gives  oft'  a  brancli 
which  passes  between  the  two  limbs  of  the  Y-shaped  ligament  into  the  hip-joint,  (ii.)  The 
transverse  terminal  brancli  is  small  ;  it  runs  outwards  between  the  crureus  and  the  rectus  femoris, 
passes  into  the  substance  of  the  vastus  externus,  winds  round  the  femur,  and  anastomoses  with 
the  ascending  and  descending  branches,  with  the  perforating  branches  of  the  profunda,  and  with 
the  sciatic  and  internal  circumflex  arteries.  (iii.)  The  descending  terminal  branch  (ramus 
descendens)  runs  downwards  behind  the  rectus  and  along  the  anterior  border  of  the  vastus 
externus  accompanied  by  the  nerve  to  the  latter  muscle.  It  anastomoses  with  the  transverse 
branch,  with  twigs  of  the  inferior  perforating  arteries,  with  the  anastomotic  branch  of  the  femoral, 
and  with  the  superior  external  articular  branch  of  the  popliteal  artery. 

(c)  The  internal  circumflex  artery  (a.  circumflexa  femoris  medialis.  Fig.  641)  springs 
from  the  inner  and  back  part  of  the  profunda,  at  the  same  level  as  the  external  circumflex, 
and  runs  backwards,  through  the  floor  of  Scarpa's  triangle,  passing  between  the  psoas  and 
the  pectineus ;  crossing  the  upper  border  of  the  adductor  brevis  it  is  continued  backwards 
beneath  the  neck  of  the  femur,  and  passes  between  the  adjacent  borders  of  the  obturator 
externus  and  the  adductor  brevis  to  the  upper  border  of  the  adductor  magnus,  where  it 
divides  into  two  terminal  branches,  a  transverse  and  an  ascending. 

Branch.es. — (i.)  An  articular  branch,  (ramus  acetabuli)  is  given  oft'  as  the  artery  passes 
beneath  the  neck  of  the  femur.  It  ascends  to  the  cotyloid  notch  where  it  anastomoses  with 
twigs  from  the  posterior  branch  of  the  obturator  artery,  and  it  sends  branches  into  the  cotyloid 
cavity  and  along  the  ligamentum  teres  to  the  head  of  the  femur,  (ii.)  Muscular  branches  are 
given  off  to  the  neighbouring  muscles.  The  largest  of  these  branches  usually  rises  immediately 
before  the  termination  of  the  artery,  it  descends  on  the  anterior  aspect  of  the  adductor  magnus 
and  anastomoses  with  the  muscular  branches  of  the  profunda  artery,  (iii.)  The  ascending  terminal 
branch  (ramus  profundus)  passes  upwards  and  outwards,  between  the  obturator  externus  and  the 
quadratus  femoris  to  the  digital  fossa  of  the  femur,  where  it  anastomoses  with  branches  of  the 
gluteal  and  the  sciatic  arteries,  (iv.)  The  transverse  terminal  branch  (ramus  superficialis)  runs 
backwards  between  the  lower  border  of  the  quadratus  femoris  and  the  ujaper  border  of  the 
adductor  magnus  to  the  hamstring  muscles.  It  anastomoses  in  front  of  the  lower  jiart  of  the 
gluteus  maximus  with  the  sciatic  and  first  perforating  arteries  and  with  the  transverse  branch 
of  the  external  circumflex,  and  in  the  substance  of  the  hamstrings  with  the  muscular  branches 
of  the  profunda. 

(d)  The  perforating  arteries  (Fig.  643),  including  the  terminal  branch  of  tlie  profunda, 
are  four  in  number.  They  curve  backwards  and  outwards  round  the  postez-ior  aspect  of 
the  femur,  lying  close  to  the  bone,  in  front  of  well-marked  tendinous  arches,  which 
interrupt  the  continuity  of  muscular  attachments ;  their  terminal  branches  enter  the 
vastus  externus  and  anastomose  in  its  substance  with  each  other,  with  the  descending 
branch  of  the  external  circumflex,  with  the  anastomotic,  and  with  the  superior  external 
articular  branch  of  the  popliteal. 


862 


THE  VASOULAE  SYSTEM. 


The  first  perforating  artery  (a.  perforans  prima)  pierces  the  insertions  of  the  adductors  brevis 
and  magnus,  and  some  of  its  branches  anastomose  in  front  of  the  gluteus  maximus  with  the 
sciatic,  witli  the  transverse  branch  of  the  internal  circumflex,  and  with  the  transverse  branch 
of  the  external  circumflex,  forming  what  is  known  as  the  crucial  anastomosis. 

The  second  perforating  artery  (a.  perforans  secunda)  pierces  the  adductors  brevis  and  magnus, 

and    then  passes    be- 


Glateus  maximus— 


A<lductor  magnus 


—  Gluteus  medius 


Gluteus  minimus 

Deep  branch  of 
gluteal  artery- 


Muscular  branch 
of  profunda  artery 


tween  the  gluteus 
maximus  and  the  short 
head  of  the  biceps  into 
the  vastus  externus.  It 
anastomoses  with  its 
fellows  above  and  be- 
low, and  with  the  in- 
ternal circumflex  and 
the  upper  muscular 
branches  of  the  pop- 
liteal artery. 

The    third   (a.    per- 
forans   tertia)    and 
Obturator internus   fourth  perforating 
and  gemeiii  arteries  pass   through 

-Vscending  branch  the  adductor  magnus 
and  the  short  head  of 
the  biceps  into  the 
vastus  externus.  Their 
anastomoses  are  simi- 
lar to  those  of  the 
second  perforating. 

A  nutrient  branch 
(a.  nutricia  femoris)  to 
the  femur  is  given  off 
either  from  the  second 
or  third  perforating 
artery,  usually  the 
former ;  an  additional 
nutrient  branch  may 
also  be  supplied  by  the 
first  or  fourth  per- 
forating arteries. 


P}  riformis 


of  internal 
ciicumflex  artery 

Quadratus  femoris 


Tiansverse  brancli 
of  internal 
ciicumflex  artery 


1st  perforating 
aitery 


2nd  perforating 
artery 


(5)  The  anas- 
tomotic (a.  genu 
suprema)  arises 
near  the  termina- 
tion of  the  femora] 
artery  in  the  lower 
part  of  Hunter's 
canal,  and  divides 
almost  immediately 
into  a  superficial 
and  a  deep  branch  ; 
indeed,  very  fre- 
quently the  two 
branches  arise 
separately  from  the 
femoral  trunk. 

(a)  The  super- 
ficial branch  (ramus 
saphenus)  passes 
through  the  lower 
end  of  Hunter's  canal 
with  the  long  saphen- 
ous nerve,  and  appears  superficially  on  the  inner  side  of  the  knee  between  the  gracilis 
and  the  sartorius.  It  gives  twigs  to  the  integument  of  the  upper  and  ;""er  part  of 
the  leg  and  it  anastomoses  with  the  inferior  internal  articular  artery.  (h)  The  deep 
branch '(ramus  musculo -articularis)  descends  in  the  substance  of  the  vastus  mternus 
along  the  anterior  aspect  of  the  tendon  of  the  adductor  magnus.     It  anastomoses  with 


Gracilis 


Popliteal  artery 


.Superior  internal 
articular  artery 

Seinitendinosus 
Ga.strocneinius 


Muscular  artery 


3rd  perforating 
artery 


Termination  of 
piofunda  artery 
(4th  perforating) 

•^hoit  head  of  biceps 


i^jong  head  of  biceps 


Popliteal  vein 

Superior  external  articular 
artery 


aslrocneinius 


Fig.  643. 


-The  Arteries  of  the  Buttock  and  the  15.\ck  ok  the 
Thigh  and  Knee. 


THE  POPLITEAL  AETEKY.  863 

the  superior  internal  articular  artery,  and  it  seuSs  branches  outwards,  one  on  the  surface 
of  the  femur  and  another  along  the  upper  border  of  the  patella,  to  anastomose  with  the 
descending  branch  of  the  external  circumflex,  the  inferior  perforating  artery,  the  superior 
external  articular,  and  the  anterior  tibial  recurrent. 

THE   POPLITEAL   ARTERY. 

The  popliteal  artery  (a.  poplitea)  is  the  direct  continuation  of  the  femoral.  It 
commences  at  the  upper  ai>d  inner  part  of  the  popliteal  space,  under  cover  of  the 
semimembranosus,  and  terminates  at  the  lower  border  of  the  popliteus  muscle,  and 
on  a  level  with  the  lower  part  of  the  tubercle  of  the  tibia,  bv  dividing  into  the 
anterior  and  the  posterior  tibial  arteries. 

From  its  origin  the  artery  descends,  with  an  outward  inclination,  to  the  inter- 
space between  the  condyles  of  the  femur,  whence  it  is  continued  vertically  down- 
wards to  its  termination. 

Relations. — Anterior. — It  is  in  contact  in  front  and  from  above  downwards  with  the 
popliteal  surface  of  the  femur,  the  posterior  ligament  of  the  knee-joint,  and  the  fascia 
covering  the  posterior  surface  of  the  popliteus. 

Posterior. — The  artery  is  overlapped  behind  by  the  outer  border  of  the  semi- 
membranosus above ;  it  is  crossed  about  its  middle  by  the  popliteal  vein  and  the  internal 
popliteal  nerve,  the  vein  intervening  between  the  artery  and  the  nerve ;  whilst  in  the 
lower  part  of  its  extent  it  is  overlapped  by  the  adjacent  borders  of  the  two  heads  of  the 
gastrocnemius,  and  is  crossed  by  the  nerves  to  the  soleus  and  popliteus  and  by  the 
plantaris  muscle. 

Lateral. — On  its  outer  side  it  is  in  relation  above  with  the  internal  popliteal  nei-ve  and 
the  popliteal  vein,  then  with  the  outer  condyle  of  the  femur,  and  below  with  the  outer 
head  of  the  gastrocnemius  and  with  the  plantaris. 

On  the  inner  side  it  is  in  relation  above  with  the  semimembranosus,  in  the  middle 
with  the  inner  condyle  of  the  femur,  and  below  with  the  internal  popliteal  nen-e,  the 
popliteal  vein,  and  the  internal  head  of  the  gastrocnemius.  Popliteal  lymphatic  glands 
are  arranged  irregularly  around  the  artery. 

Branches. — (1)  Muscular  branches  are  given  off  in  two  sets,  upper  and  lower. 

The  upper  muscular  branches  are  distributed  to  the  lower  parts  of  the  hamstring 
muscles,  in  which  they  anastomose  with  branches  of  the  profunda  artery. 

The  lower  muscular,  or  sural,  arteries  (aa.  surales)  enter  the  upper  parts  of  the  gastro- 
cnemius, the  plantaris,  the  soleus,  and  the  popliteus  muscles,  and  they  anastomose  with 
branches  of  the  posterior  tibial  artery  and  the  lower  ai'ticular  arteries. 

(2)  The  articular  branches  are  five  in  number — viz.  upper  and  lower  external,  upper 
and  lower  internal,  and  an  azygos  branch, 

(a)  The  superior  external  articular  artery  (a.  genu  superior  lateralis)  passes  outwards 
above  the  external  condyle,  behind  the  femur  and  in  front  of  the  biceps  tendon,  into  the 
vastus  externus,  where  it  anastomoses  with  the  anastomotic,  the  descending  branch  of  the 
external  circumflex,  and  the  lowest  perforating  artery ;  it  also  sends  branches  downwards 
to  anastomose  with  the  inferior  external  articular  and  with  the  anterior  tibial  recurrent. 

(6)  The  superior  internal  articular  artery  (a.  genu  superior  medialis)  passes  inwards 
above  the  internal  condyle,  behind  the  femur,  and  in  front  of  the  tendon  of  the  adductor 
magnus,  into  the  vastus  internus.  It  anastomoses  with  branches  of  the  anastomotic  and 
of  the  superior  external  articular  artery. 

{c)  The  inf^ior  external  articular  artery  (a.  genu  inferior  lateralis)  runs  outwards 
across  the  popliteus  muscle  and  in  front  of  the  plantaris  and  the  external  head  of  the 
gastrocnemius ;  then  turning  forwards,  it  is  joined  by  the  inferior  external  articular  nerve, 
and  passes  to  the  inner  side  of  the  external  lateral  ligament.  It  terminates  by  anasto- 
mosing with  its  fellow  of  the  opposite  side  and  with  the  superior  external  articular  and 
anterior  tibial  recurrent  arteries. 

{d)  The  inferior  internal  articular  artery  (a.  genu  inferior  medialis)  passes  inwards 
below  the  inner  tuberosity  of  the  tibia,  along  the  upper  border  of  the  popliteus  and  in 
front  of  the  internal  head  of  the  gastrocnemius,  to  the  inner  side  of  the  knee,  where  it 
turns  forwards  between  the  bone  and  the  internal  lateral  ligament,  and  terminates 
anteriorly  by  anastomosing  with  its  fellow  of  the  opposite  side,  with  the  recurrent  branch 
of  the  anterior  tibial  artery,  and  with  the  superior  internal  articular  artery. 

(e)  The  azygos  articular  artery  (a.  genu  media)  passes  directly  forwards  from  the  front 


864: 


THE  VASCULAE  SYSTEM. 


of  the  popliteal  artery,  pierces  the  central  part  of  the  posterior  ligament  of  the  knee-joint, 
and  enters  the  intercondylar  space.  It  supplies  branches  to  the  crucial  ligaments  and  to 
the  synovial  membrane,  and  is  accompanied  by  the  azygos  articular  branch  of  the  internal 
popliteal  nerve,  and  sometimes  by  the  genicular  branch  of  the  obturator  nerve. 

(3)  Cutaneous  branches  are  distributed  to  the  skin  over  the  popliteal  space.     One  of 

these,  the  siipei-ficial  sural  artery, 
descends  in    the  middle    line   of 

Semimembranosus       »^  I    /.//7/iK\        fHH^  /  ^^^  back  of  the  calf  along  with 

the  external  saphenous  nerve. 

Semitendinosus 

Superior  internal 
articular  artery 

Muscular  artery 


Inferior  internal 
articular  artery 


Popliteu: 


Soleus 
Posterior  tibial 


Nutrient  artery 


_Biceps 

Superior  external 
-  articular  artery- 
Muscular  arterv 


Popliteal  artery 

Inferior  external 
articular  arter\- 


Posterior  tibial 
artery 


Flexor  longus 
digitorum 


Communicating; 

artery 


Calcaneau  arterv 


The 


posterioe 
Arteey. 


Tibial 


The  posterior  tibial  artery 

(a.  tibialis  posterior),  the  larger 
of  the  two  terminal  branches 
of  the  popliteal,  commences  ab 
the  lower  border  of  the  pop- 
liteus  and.  terminates  midway 
between  the  tip  of  the  inner 
malleolus  and  the  most  pro- 
minent part  of  the  heel,  at  the 
lower  border  of  the  internal 
annular  ligament.  It  ends  by 
dividing  into  the  internal  and 
the  external  plantar  arteries, 
which  pass  onwards  to  the  sole 
of  the  foot. 

The  artery  runs  downwards 
and  inwards  on  the  back  of 
the  leg  between  the  superficial 
and  deep  layers  of  muscles,  and 
covered  by  the  deep  inter- 
muscular fascia  which  inter- 
venes between  them. 


Posterior  jjeroneal  artery 


Relations. — Anterior. — It  is 
in  contact  in  front,  and  from 
above  downwards,  with  the  tibialis 
posticus,  the  flexor  longus  digit- 
orum, the  posterior  surface  of  the 
tibia,  and  the  posterior  ligament 
of  the  ankle-joint. 

Posterior.  —  The      artery      is 
crossed  about  an  inch  and  a  half 
below  its  origin  by  the  postei'ior 
tibial  nerve.     Elsewhere  it  is  in 
contact  with    the   intei'muscular 
fascia,  which  binds  down  the  deep 
layer   of    muscles.     More   super- 
ficially   the    upper    half    of    the 
artery   is  covered   by  the  fleshy 
parts  of  the  soleus  and   gastro- 
cnemius muscles,  between  which 
is  the  plantaris ;   the  lower  half 
of  the  artery  is  much  nearer  the  surface,  and  is  only  covered  by  skin  and  fascia,  except 
at  its  termination,  where  it  lies  beneath  the  internal  aninilar  ligament  and  the  origin  of 
the  abductor  hallucis. 

Lateral. — The  artery  is  accompanied  by  two  vemc  comites,  one  on  either  side.  The 
posterior  tibial  nerve  lies  at  first  on  the  inner  side  of  the  vessel,  then  crosses  behind  it,  and 
is  continued  down  on  its  outer  side.      In  the  last  part  of  its  course  the  artery  is  separated 


F'iG.  644. 


-The    POI'LITEAL    AND    POSTKUIOK    TIBIAL    AUTKIilES 
AND   THKIK    BLANCHES. 


PLANTAE  ARTEEIES.  865 

from  the  internal  malleolus  by  the  tendons  of  the  tibialis  posticus  and  the  flexor  lono-us 
digitorum,  whilst  the  tendon  of  the  flexor  longus  hallucis  lies  behind  and  external  to  it. 

Branches. — The  posterior  tibial  gives  off  numerous  branches,  the  largest  of  which, 
the  peroneal,  forms  one  of  the  chief  arteries  of  the  leg.     The  branches  include — 

(1)  Two  large  muscular  branches  which  are  distributed  to  the  soleus,  the  tibialis 
posticus,  the  flexor  longus  digitorum,  and  the  flexor  longus  hallucis.  They  anastomose 
with  the  deep  sural  branches  of  the  popliteal  artery  and  the  lower  internal  articular  artery. 

(2)  The  medullary  branch  (a.  nutricia  tibiae),  the  largest  of  the  medullary  group 
of  arteries,  springs  from  the  upper  part  of  the  posterior  tibial,  pierces  the  tibialis 
posticus,  and  enters  the  medullary  foramen  on  the  posterior  surface  of  the  tibia.  In  the 
interior  of  the  bone  it  divides  into  ascending  and  descending  branches,  the  former  passing 
upwards  towards  the  liead  of  the  bone,  and  the  latter  downwards  towards  the  lower 
extremity.     Before  entering  the  tibia  the  medullary  artery  gives  small  muscular  Ijranches. 

(3)  A  communicating  branch  (ramus  communicans)  unites  the  posterior  tibial  to 
the  peroneal  artery  about  an  inch  above  the  inferior  tibio-fibular  articulation.  It  passes 
behind  the  shaft  of  the  tibia  and  in  front  of  the  flexor  longus  hallucis. 

(4)  Cutaneous  branches  are  distributed  to  the  skin  of  the  inner  and  posterior  part  of 
the  leg. 

(5)  An  internal  malleolar  branch  (a.  malleolaris  posterior  medialis)  is  distributed 
to  the  internal  surface  of  the  inner  malleolus,  anastomosing  with  a  corresponding  branch 
of  the  anterior  tibial  artery. 

(6)  The  peroneal  artery  (a.  peronaea,  Fig.  644)  is  the  largest  branch  of  the  posterior 
tibial.  It  arises  about  an  inch  below  the  lower  border  of  the  popliteus,  curves  outwards 
across  the  upper  part  of  the  tibialis  posticus  to  the  postero-internal  border  of  the  fibula, 
along  which  it  descends  to  the  lower  part  of  the  interosseous  space,  and  it  terminates  about 
an  inch  above  the  ankle-joint  by  dividing  into  anterior  and  posterior  terminal  branches. 

As  the  peroneal  artery  passes  outwards  from  its  origin  it  lies  behind  the  tibialis 
posticus,  and  is  covered  posteriorly  by  the  deep  intermuscular  fascia  and  b}-  the  soleus. 
As  it  descends  along  the  postero-internal  border  of  the  fibula  it  lies  in  a  fibrous 
canal  between  the  tibialis  posticus  in  front  and  the  flexor  longus  hallucis  behind.  The 
peroneal  artery  is  accompanied  by  two  vense  comites,  and  is  crossed  in  front  and  behind 
by  communicating  branches  between  them. 

Branches. — (a)  Muscular  branches  are  distributed  to  the  soleus,  tibialis  posticus,  flexor  longus 
hallucis,  and  peroneal  muscles.  Some  pass  tlirough  the  interosseous  membrane  and  supply  the 
anterior  muscles  of  the  leg. 

(6)  A  medullary  branch  (a.  mitricia  fibulas)  enters  the  medullary  foramen  of  the  fibula. 

(c)  A  communicating  branch  (a.  communicans)  passes  across  the  back  of  the  lower  end  of  the 
shaft  of  the  tibia,  about  an  inch  above  the  inferior  tibio-fibular  articulation,  to  anastomose  with 
the  posterior  tibial  artery. 

(d)  The  terminal  branches  are  :  (i.)  The  anterior  terminal  branch  or  anterior  x>6roneal  artery 
(ramus  perforans),  which  passes  forwards  between  the  lower  border  of  the  interosseous  membrane 
and  the  interosseous  inferior  tibio-fibular  ligament,  and  runs  in  front  of  the  ankle  to  the  dorsum 
of  the  foot,  where  it  anastomoses  with  the  external  malleolar  branch  of  the  anterior  tibial  artery 
and  with  the  tarsal  branch  of  the  dorsalis  pedis ;  it  also  supplies  branches  to  the  inferior  tibio- 
fibular articulation,  to  the  ankle-joint,  and  to  the  peroneus  tertius. 

(ii.)  The  posterior  terminal  branch  (ramus  calcaneus  lateralis),  ov  jiosterior  ])eroneal  artery,  passes 
downwards  behind  the  inferior  tibio-fibular  articulation  and  external  malleolus  to  the  outer  side 
of  the  heel  and  the  foot.  It  supplies  the  ankle,  the  inferior  tibio-fibular  articulation,  and  the 
calcaneo-astragaloid  joint,  and  anastomoses  with  the  internal  calcaneal  branch  of  the  external 
plantar  artery,  and  with  the  tarsal  and  metatarsal  branches  of  the  dorsalis  pedis.  "V 

Plantar  Arteries. 

(7)  The  internal  and  external  plantar  arteries  are  the  terminal  branches  of  the 
posterior  tibial  artery.  They  arise  beneath  the  origin  of  the  abductor  hallucis 
muscle,  midway  between  the  tip  of  the  internal  malleolus  and  the  most  prominent 
part  of  the  inner  side  of  the  os  calcis. 

Internal  Plantar  Artery  (a.  plantaris  medialis). — This  is  the  smaller  of  the  two 
terminal  branches  of  the  posterior  tibial  artery.  It  passes  forwards  along  the 
inner  side  of  the  foot,  in  the  interval  between  the  abductor  hallucis  and  the  flexor 
bre\is  digitorum,  to  the  head  of  the  first  metatarsal  bone,  where  it  terminates  by 
uniting  with  the  plantar  digital  branch  of  the  dorsalis  hallucis,  which  is  distributed 
to  the  inner  side  of  the  great  toe.  In  its  course  forwards  it  gives  branches  to  the 
adjacent  muscles  and  articulations,  and  to  the  subjacent  skin :  it  also  gives  three 
59 


866 


THE  VASCULAE  SYSTEM. 


digital  branches  which  anastomose  at  the  roots  of  the  inner  three  interdigital  clefts, 
with  the  princeps  hallucis  branch  of  the  dorsalis  pedis  and  with  the  inner  two  digital 
branches  from  the  plantar  arch.  Some  of  the  cutaneous  branches  of  the  internal 
plantar  artery  anastomose,  round  the  inner  border  of  the  foot,  with  the  inner 
cutaneous  branches  of  the  dorsalis  pedis  artery. 

External  Plantar  Artery  (a.  plantaris  lateralis). — This  artery,  the  larger  of  the 
two  terminal  branches  of  the  posterior  tibial  artery,  runs  forwards  and  outwards, 
first  between   the  flexor  brevis  digitorum  and  the  accessorius  and  then  in  the 

interval  between  the 
flexor  brevis  digitorum 
and  the  abductor  minimi 
digiti,  to  the  inner  side 
of  the  base  of  the  fifth 
metatarsal  bone,  where  it 
turns  abruptly  inwards ; 


Calcaneal  branch  of 
posterior  tibial  artery 

Posterior  tibial  artery 

Internal  plantar 

artery 

External  plantar 

artery 


Flexor  longus 

digitorum j 

tendon 


Flexor  longus 
liallucis  tendon 


Flexor  brevis 
hallucis  muscle 


Arteria  magna 
liallucis 


Long  calcaneo- 
cuboid ligament 


Flexor  accessorius 
muscle 


Abductor  minimi 
digiti  muscle 


Internal  calcaneal      •,      ,i  .i 

ranch  of  external     it    thCU  paSSeS  aCrOSS    the 
plantar  artery 


(,>l)lique  adductor 
allucis 


Digital  arteries 


bases  of  the  metatarsal 
bones  and  the  origins  of 
the  interossei,  and  above 
the  oblique  adductor  of 
the  great  toe,  to  the  outer 
side  of  the  base  of  the 
first  metatarsal  bone, 
where  it  terminates  by 
anastomosing  with  the 
dorsalis  pedis  artery.  The 
last  part  of  the  artery  is 
convex  forwards  and 
forms  the  plantar  arch, 
which  is  completed  by  the 
dorsalis  pedis. 


Branches.  —  Between 
its  origin  and  the  base  of 
the  fifth  metatarsal  the  ex- 
ternal plantar  artery  gives 
off  (a)  the  internal  calcaneal 
branch,  which  is  distributed 
to  the  skin  and  the  sub- 
cutaneous tissue  of  the  heel. 
(6)  Muscular  branches 
to  the  abductor  halhicis, 
flexor  brevis  digitorum,  ac- 
cessorius, and  abductor 
minimi  digiti. 

(c)  Cutaneous  branches 
to  the  skin  of  the  outer  side 
of  the  foot. 

Between  the  base  of  the 
fifth  metatarsal  bone  and  the  first  interosseous  space  it  forms  the  plantar  arch  (arcus 
plantaris),  and  gives  oft'  {d)  four  digital  branches  (aa.  metatarsie  plantares) ;  (e)  three 
posterior  perforating  arteries  (rami  jjcrforantes)  to  the  dorsal  interosseous  arteries ;  and 
(/)  articular  branches  to  tlie  tarsal  joints. 

The  outermost  digital  branch  runs  along  the  outer  side  of  the  little  toe,  supplying 
the  skin,  joints,  and  the  flexor  tendons  with  tlieir  synovial  sheaths.  The  inner  three 
digital  branches  run  forwards  on  the  plantar  surfaces  of  the  interossei,  the  inner  two 
lying  dorsal  to  the  oblique  adductor  of  the  great  toe,  and  all  three  passing  dorsal  to  the 
transverse  adductor.  At  the  bases  of  the  interdigital  clefts  the  tliree  inner  digital  arteries 
divide  into  collateral  branches  (aa.  digitales  plantares)  which  run  along  the  plantar  aspect 
of  adjacent  toes,  and  sjipply  skin,  joints,  and  the  ftexor  tendons  and  sheaths.  Opposite 
the  last  phalanx  of  eacfl  toe  the  digital  arteries  anastomose. 


Fig.  645. — The  Plantar  Arteries  and  their  Branches. 


THE  ANTEEIOR  TIBIAL  AETERY. 


867 


The  posterior  perforating  arteries  are  three  in  number  ;  they  pass  doi-salwards  through 
the  three  outer  interosseous  spaces,  between  the  heads  of  the  dorsal  interosseous  muscles, 
and  terminate  bv  uniting  with  the  dorsal  interosseous  branches  of  the  metatarsal  artery. 
Anterior         perforating 
brandies  winch  comnumicate 
with  the  dorsal  interosseous 
arteries   are   given   off  from 
two  or  three  of  the  digital 
arteries     just     before     they 
divide. 

The    articular    branches 
are  numerous  and  irregular  ; 
they   supply  the  joints    and 
■  ligaments  of  the  tarsus  on  its 
plantar  aspect. 


Superior  external 
articular  arteiy 


Inlerior  external 
articular  artery 


Anterior  tibial 
recurrent  artery 


Anastomotic 
artery 


Superior  internal 
articular  arterv 


Inferior  internal 
articular  arterj' 


Anterior  tibial 
arterv 


Tibialis  anticus 


Gastrocnemius 


Anterior  tibial 
nerve 


Peroneus  brevi& 

Extensor  longus 
digitorum 

Extensor  longus 
hallucis" 


Anterior  peroneal 
artery 

External 
malleolar  artery 


Tarsal  artery 


Digital  artery 

Digital  artery 


The  Anterior  Tibial 
Artery. 

The  anterior  tibial 
artery  (a.  tibialis  anterior), 
the  smaller  of  the  two  ter- 
minal divisions  of  the  pop- 
liteal, commences  opposite 
the  lower  border  of  the 
popliteus  muscle,  and  ter- 
minates in  front  of  the 
ankle,  where  it  is  continued 
into  the  dorsal  artery  of 
the  foot. 

Course  and  Relations. 
— Erom  its  origin  at  the 
back  of  the  leg  the  artery 
passes  forwards  to  the  front, 
between  the  two  uppermost 
slips  of  the  tibialis  posticus 
and  above  the  upper  border 
of  the  interosseous  mem- 
brane. It  then  descends 
resting,  in  the  upper  two- 
thirds  of  its  course,  upon  the 
anterior  surface  of  the  in- 
terosseous membrane  and, 
subsequently,  on  the  shaft 
of  the  tibia  and  the  anterior 
ligament  of  the  ankle-joint. 
In  the  upper  third  of  the 
anterior  compartment  of 
the  leg  it  lies  between  the 
extensor  longus  digitorum 
externally  and  the  tibialis 
anticus  internally ;  in  the 
middle  third  it  is  between 
the  extensor  longus  hallucis 
and  the  tibialis  anticus ; 
in  the  lower  third  the  extensor  longus  hallucis  crosses  in  front  of  the  artery  and 
reaches  its  inner  side,  and  the  last  part  of  the  vessel  lies  between  the  tendon  of  the 
extensor  longus  hallucis  and  the  innermost  tendon  of  the  extensor  longus  digitorum. 

The  anterior  tibial  nerve  is  at  first  well  to  the  outer  side  of  the  artery,  but  it 
soon  passes  in  front  of  the  vessel,  and  it  lies  in  front  of  the  artery  in  its  middle 
59  a 


Cutaneous  branch 
Extensor  brevis 
dicitoruni 


Fig.  646.— The  Anterior  Tibial  Artery  and  its  Branches. 


868  THE  VASCULAE  SYSTEM. 

third ;  lower  down  the  nerve  is  usually  found  on  the  outer  side  again,  and  at  the 
ankle  it  intervenes  between  the  artery  and  the  innermost  tendon  of  the  extensor 
longus  digitorum. 

Two  venffi  comites,  with  numerous  intercommunications,  accompany  the  artery. 

Obviously  the  anterior  tibial  artery  is,  at  least  in  its  upper  part,  deeply  placed ; 
moreover,  its  lateral  muscular  boundaries  overlap  it.  In  the  greater  part  of  its 
extent  it  is,  however,  easily  accessible  from  the  surface  ;  and  beyond  being  crossed 
by  the  nerve  and  tendon,  as  already  described,  is  only  covered,  in  addition,  by  skin, 
fascia,  and  the  anterior  annular  ligament. 

Branches. — Close  to  its  origin  the  artery  gives  off  superior  fibular  and  posterior 
tibial  recurrent  branches ;  after  it  reaches  the  front  of  the  leg  it  gives  off  anterior  tibial 
recurrent,  muscular,  cutaneous,  internal  malleolar,  and  external  malleolar  branches. 

(1)  The  superior  fibular  branch  is  a  small  vessel  which  may  arise  separately  from  the 
anterior  tibial  artery,  or  by  a  common  stem  with  the  posterior  tibial  recurrent ;  occasion- 
ally it  springs  from  the  lower  end  of  the  popliteal  artery,  or  from  the  posterior  tibial. 
It  runs  upwards  and  outwards  behind  the  neck  of  the  fibula  and  through  the  fibres  of 
the  soleus,  and  it  terminates  in  branches  which  supply  the  soleus,  the  peroneus  longus, 
and  the  skin  of  tlie  upper  and  outer  part  of  the  leg.  It  anastomoses  with  the  inferior 
external  articular  artery. 

(2)  The  posterior  tibial . recurrent  branch  (a.  recurrens  tibialis  posterior),  also  small, 
and  not  always  present,  runs  upwards  in  front  of  the  popliteus  muscle  to  the  back  of  the 
knee-joint.  It  aiiastomoses  with  the  inferior  articular  branches  of  the  popliteal,  and 
gives  branches  to  the  popliteus  muscle  and  the  superior  tibio-fibular  articulation. 

(3)  The  anterior  tibial  recurrent  branch  (a.  recurrens  tibialis  anterior)  arises  from  the 
anterior  tibial  artery  in  front  of  the  interosseous  membrane.  It  runs  upwards  and  inwards, 
between  the  upper  part  of  the  tibialis  anticus  and  the  outer  tuberosity  of  the  tibia, 
accompanied  by  the  recurrent  articular  branch  of  the  external  popliteal  nerve,  and  after 
supplying  the  tibialis  anticus  and  the  superior  tibio-fibular  articulation  it  pierces  the 
deep  fascia  of  the  leg  ;  it  is  connected  with  the  anastomoses  round  the  knee-joint  formed 
by  the  articular  branches  of  the  popliteal  artery,  the  descending  branch  of  the  external 
circumflex  artery,  and  the  anastomotic  artery. 

(4)  The  muscular  branches  are  distributed  to  the  muscles  of  the  front  of  the  leg, 
and  a  few  small  branches  also  pass  backwards  to  the  deep  surface  of  the  tibialis  posticus 
muscle. 

(5)  The  cutaneous  branches  supply  the  skin  of  the  front  of  the  leg. 

(6)  The  internal  malleolar  branch  (a.  malleolaris  anterior  medialis)  arises  from  the 
lower  pai't  of  the  anterior  tibial  artery,  and  is  smaller  than  its  companion  on  the  outer 
side.  It  runs  inwards,  beneath  the  tibialis  anticus  tendon,  ramifies  over  the  internal 
malleolus,  anastomosing  with  branches  of  the  posterior  tibial  artery,  and  is  distributed  to 
the  skin  and  to  the  ankle-joint. 

(7)  The  external  malleolar  branch  (a.  malleolaris  anterior  lateralis),  more  constant 
and  laro'er  than  the  internal,  passes  outwards  beneath  the  extensor  longus  digitorum 
and  peroneus  tertius  towards  the  external  malleolus.  It  anastomoses  with  the  anterior 
peroneal  and  tai-sal  arteries,  and  supplies  the  ankle-joint  and  the  adjacent  articulations. 

Dorsalis  Pedis  Artery  (a.  dorsalis  pedis). — The  dorsal  artery  of  the  foot  is  ■ 
the  direct  continuation  of  the  anterior  tibial ;  it  commences  opposite  the  front  of 
the  ankle-joint,  and  extends  to  the  posterior  extremity  of  the  first  interosseous 
space,  where  it  passes  to  the  plantar  aspect  of  the  foot,  and,  anastomosing  with  the 
termination  of  the  external  plantar  artery,  completes  the  plantar  arch. 

It  is  covered  superficially  by  skin  and  fascia,  including  the  inferior  part  of  the 
anterior  annular  ligament,  and  it  is  crossed,  just  before  it  reaches  the  first  inter- 
osseous space,  by  the  innermost  tendon  of  the  extensor  brevis  digitorum.  It  rests 
upon  the  anterior  ligament  of  the  ankle,  the  head  of  the  astragalus,  the  astragalo- 
navicular  ligament,  the  dorsum  of  the  navicular  bone,  the  dorsal  naviculo- 
cuneiform  and  the  inter-cuneiform  ligaments  between  the  internal  and  middle 
cuneiform  bones.  On  its  outer  side  is  the  internal  terminal  branch  of  the  anterior 
tibial  nerve,  which  intervenes  between  it  and  the  extensor  brevis  digitorum  and 
innermost  tendon  of  the  extensor  longus  digitorum.  On  its  inner  side  it  is  in 
relation  with  the  tendon  of  the  extensor  proprius  liallucis.  Two  venoe  comites, 
one  on  each  side,  accompany  the  artery. 


THE  ANTERIOE  TIBIAL  ARTERY. 


869 


Peroneus  brevis 

Extensor  longus 

diKitoruiii 


Anterior  peroneal 

artery 

External  malleolar 

artery 


Anterior  tibial 
artery 

Extensor  Inngus 
hallucis 

Tibialis  anticus 

Internal 
malleolar  artery 


Extensor 

brevis 

digitorum 


Tarsal  artery — 


Arteria  dorsalis 
hallucis 


As  it  passes  through  the  base  of  the  first  interosseous  space  it  lies  between  the 
two  heads  of  the  first  dorsal  interosseous  muscle,  and  in  the  sole  of  the  foot  it  is 
dorsal  to  the  flexor  brevis  hallucis. 

Branches. — On  the  dorsum  of  the  foot  the  dorsalis  pedis  artery  gives  off  cutaneous 
branches,  the  tarsal  branch,  the  metatarsal  branch,  and  the  dorsalis  hallucis  or  first  dorsal 
interosseous.  In  the  sole 
of  the  foot,  and  before  it 
unites  with  the  external 
plantar  artery,  it  gives  off 
the  princeps  hallucis. 

(1)  Cutaneous  branches, 
two  or  three  in  number,  are 
distributed  to  the  skin  on 
the  dorsum  and  inner  side 
of  che  foot ;  they  anastomose 
with  branches  of  the  internal 
plantar  artery. 

(2)  The  tarsal  branch 
(a.  tarsea  lateralis)  is  given 
off  opposite  the  head  of  the 
astragalus;  it  runs  outwards 
beneath  the  extensor  brevis 
digitorum,  supplying  that 
muscle  and  the  tarsal  joints, 
and  anastomoses  with 
branches  of  the  anterior 
peroneal,  metatarsal,  and 
external  plantar  arteries, 
and  with  the  external 
malleolar  artery. 

(3)  The  metatarsal 
artery  (a.  arcuata)  arises 
opposite  the  internal  cunei- 
form bone.  It  runs  out- 
wards on  the  bases  of  the 
metatarsal  bones,  beneath 
the  long  and  short  extensor 
tendons,  supplies  the  ex- 
tensor brevis,  and  anasto- 
moses with  branches  of 
the  tarsal  and  external 
plantar  arteries.  It  gives  off 
three  dorsal  interosseous 
arteries  (aa.  metatarseae 
dorsales)  which  run  down- 
wards on  the  muscles  which 
occupy  the  three  outer  inter- 
osseous spaces  to  the  clefts 
of    the     toes,    where     each 

divides  into  two  collateral  digital  branches  (aa.  digitales  dorsales)  for  the  adjacent  sides 
of  the  toes  bounding  the  cleft  to  which  it  goes.  The  outer  side  of  the  little  toe  receives 
a  branch  from  the  outermost  dorsal  interosseous  artery.  Each  dorsal  interosseous  artery 
gives  off  a  posterior  perforating  branch  which  passes  through  the  posterior  part  of  the 
interosseous  space,  between  the  heads  of  the  dorsal  interosseous  muscle,  to  anastomose 
with  the  plantar  arch,  and  an  anterior  'perforating  branch,  which  descends  through  the 
anterior  part  of  the  space  to  anastomose  with  the  corresponding  plantar  digital  artery. 

(4)  The  dorsalis  hallucis  artery  (first  dorsal  interosseous)  is  continued  forwards 
from  the  dorsal  artery  of  the  foot,  and  runs  on  the  dorsal  surface  of  the  first  dorsal 
interosseous  muscle.  It  ends  by  dividing  into  collateral  dorsal  digital  branches  for  the 
adjacent  sides  of  the  first  and  second  toes.  Before  it  divides  it  usually  gives  off  a  dorsal 
digital  branch  which  passes  beneath  the  tendon  of  the  extensor  hallucis  to  the  inner  side 
of  the  great  toe. 

(5)  The   princeps  hallucis  (plantar  digital   artery)  springs  from   the  termination  of 
59  & 


Metatarsal 
artery 


Dorsal 

interosseous 

arteries 


Fig.  647. — The  Dorsalis  Pedis  Artery  and  its  Branches. 


870  THE  VASCULAK  SYSTEM. 

the  dorsalis  pedis  in  the  sole  of  the  foot ;  it  runs  forwards  in  the  plantar  part  of  the 
first  interosseous  space,  and  divides,  at  the  interdigital  cleft,  into  collateral  digital 
branches  for  the  supply  of  the  adjacent  sides  of  the  first  and  second  toes  on  their  plantar 
aspects.  Before  its  division  it  supplies  a  plantar  digital  branch  to  the  inner  side  of 
the  great  toe. 

THE  VEINS. 

Veins  commence  at  the  terminatioias  of  the  capillaries.  They  converge  towards 
the  heart,  and  unite  with  one  another  to  form  larger  and  still  larger  vessels,  until 
finally  seven  large  trunks  are  formed  which  open  into  the  auricles  of  the  heart. 
Three  of  these,  the  superior  vena  cava,  the  inferior  vena  cava,  and  the  coronary  sinus, 
belong  to  the  systemic  circulation ;  they  contain  venous  blood,  and  open  into  the 
right  auricle.  The  remaining  four  belong  to  the  2^ulmo7iari/  circulation ;  they  return 
arterialised  blood  from  the  lungs,  and  open  into  the  left  auricle. 

In  addition  to  the  systemic  and  pulmonary  veins,  there  is  also  a  third  group  of 
veins,  constituting  the  portal  system,  in  which  blood  from  the  abdominal  part  of 
the  alimentary  canal,  and  from  the  spleen  and  pancreas,  is  conveyed  to  the  liver. 
The  portal  system  is  further  peculiar  in  that  it  both  begins  and  ends  in  capillaries. 
Erom  its  terminal  capillaries  in  the  liver  the  hepatic  veins  arise,  and  as  these  open 
into  the  inferior  vena  cava  the  blood  of  the  portal  system  is  finally  poured  into  the 
general  systemic  circulation.  The  hepatic  veins  also  receive  blood  supplied  to  the 
liver  by  the  hepatic  arteries. 

PULMONARY  VEINS. 

The  terminal  pulmonary  veins  (v.  pulmonales.  Figs.  613  and  620),  two  on  each  side, 
open  into  the  left  auricle  of  the  heart.  Their  tributaries  arise  in  capillary  plexuses 
in  the  walls  of  the  pulmonary  alveoli.  By  the  union  of  the  smaller  veins  larger  vessels 
are  formed  which  run  along  the  anterior  aspects  of  the  bronchial  tubes,  and,  uniting 
together,  ultimately  form  a  single  efferent  vessel  in  each  lobe,  which  passes  into  the 
root  of  the  lung.  Thus  there  are  five  main  pulmonary  veins,  but,  immediately 
after  entering  the  root  of  the  lung,  the  vessels  from  the  upper  and  middle  lobes  of 
the  "right  lung  join  together,  and  so  only  four  terminal  pulmonary  veins  open  into 
the  left  auricle  of  the  heart.  Neither  the  main  stems  nor  their  tributaries  possess 
valves. 

Relations. — In  the  root  of  the  lung  the  upper  pulmonarj'^  vein  on  each  side  lies 
below  and  in  front  of  the  pulmonary  arter3^  The  lower  pulmonar}^  vein  on  each 
side  is  in  the  lowest  part  of  the  root,  and  it  is  placed  much  farther  back  than  the 
upper  vein. 

On  the  right  side  the  upper  pulmonary  vein  passes  behind  the  superior  vena  cava,  and 
the  lower  behind  the  right  auricle.  They  both  terminate  in  the  upper  and  back  part  of 
the  left  auricle  close  to  the  interauricular  septum. 

On  the  left  side  both  upper  and  lower  pulmonary  veins  cross  the  front  of  the  descend- 
ing aorta,  and  they  terminate  in  the  upper  and  back  part  of  the  left  auricle  near  its  left 
border. 

All  four  pulmonary  veins  pei-forate  the  fibrous  layer  of  the  pericardium,  and  receive 
partial  coverings  of  the  serous  layer  before  they  enter  the  auricle. 

SYSTEMIC  VEINS. 

The  systemic  veins  return  Itlood  to  the  right  auricle;  of  the  heart  through  the 
superior  vena  cava,  the  inferior  vena  cava,  and  the  coronary  sinus.  The  two  first- 
named  receive  blood  from  the  veins  of  the  body  and  limbs  and  from  most  of  the 
abdominal  and  pelvic  viscera.  The  coronary  sinus  receives  })lood  from  the  veins  of 
the  walls  of  the  heart  alone. 

General  arrangement. — Tlu;  veins  of  the  body  wall  and  limbs  form  two  groups 
— (1)  the  superficial  veins ;  (2)  the  deep  veins. 

The  superficial  veins,  which  commence  in  the  capillaries  of  the  skin  and  sub- 
cutaneous tissues,  lie  in   the  superficial  fascia,  and  are  very  numerous.      They 


THE  SUPEEIOR  VENA  CAVA  AND  ITS  TRIBUTAEIES.         871 

frequently  anastomose  with  one  another,  and  they  also  communicate  with  the  deep 
veins,  in  which,  after  piercing  the  deep  fascia,  they  terminate.  They  may  or  may 
not  accompany  superficial  arteries. 

The  deep  veins  accompany  arteries,  and  are  known  as  vence  comites.  The  large 
arteries  have  only  one  accompanying  vein,  but  with  the  medium-sized  and  small 
arteries  there  are  usually  two  vente  comites,  which  freely  anastomose  with  each 
other  by  short  transverse  branches  of  communication. 

Visceral  veins  usually  accompany  the  arteries  which  supply  viscera  in  the 
head,  neck,  thorax,  and  abdomen.  As  a  rule  there  is  only  one  vein  with  each 
visceral  artery,  and,  with  the  exception  of  those  which  enter  into  the  formation  of 
the  portal  system,  they  terminate  in  the  deep  systemic  veins. 

THE  CORONARY  SINUS  AND  THE  VEINS  OF  THE  HEART. 

The  coronary  sinus  (sinus  coronarius,  Fig.  613)  is  a  short,  but  relatively  wide, 
venous  trunk  which  receives  the  majority  of  the  veins  of  the  heart.  It  lies  in  the 
inferior  portion  of  the  auriculo- ventricular  sulcus,  between  the  left  auricle  and 
the  left  ventricle,  and  it  is  covered  superficially  by  some  of  the  muscular  fibres  of 
the  auricle. 

It  terminates  in  the  lower  and  back  part  of  the  right  auricle,  between  the  orifice 
of  the  inferior  vena  cava  on  the  right,  and  the  right  auriculo-ventricular  orifice  in 
front ;  an  imperfect  valve,  consisting  of  one  or  two  cusps,  called  the  valve  of 
Thebesius,  is  situated  at  the  opening  of  the  sinus  into  the  auricle. 

The  apertures  of  all  the  tributaries  of  the  coronary  sinus,  except  that  of  the 
oblique  vein,  are  provided  with  valves,  which,  however,  are  frequently  incompetent. 

Tributaries. — (1)  The  great  cardiac  or  left  coronary  vein  (v.  cordis  magna,  Fig.  614) 
commences  at  the  apex  of  the  heart.  It  ascends  in  the  anterior  interventricular  sulcus 
to  the  auriculo-ventricular  groove  ;  it  then  turns  to  the  left,  and,  passing  round  the  left 
margin  of  the  heart  into  the  postero- inferior  part  of  the  auriculo-ventricular  groove, 
terminates  in  the  left  extremity  of  the  coronary  sinus.  It  receives  tributaries  from  the 
walls  of  both  ventricles  and  from  the  wall  of  the  left  auricle.  It  also  receives  the  left 
marginal  vein,  which  commences  at  the  lower  extremity  of  the  left  margin  of  the  heart, 
along  which  it  ascends  to  its  termination. 

(2)  Small  cardiac  or  right  coronary  vein  (v.  cordis  parva). — This  vein  is  very  vari- 
able ;  as  a  rule  it  commences  at  the  right  margin  of  the  heart  in  the  auriculo-ventricular 
sulcus,  passes  to  the  left,  and  terminates  in  the  coronary  sinus  near  its  right  end.  It 
receives  tributaries  from  the  walls  of  the  right  auricle  and  the  right  ventricle  ;  one  from 
the  latter,  the  right  marginal  vein,  ascends  along  the  right  margin  of  the  heart,  and 
sometimes  opens  directly  into  the  right  auricle. 

(3)  The  oblique  vein  of  Marshall  (v.  obliqua  atrii  sinistri,  Fig.  613)  is  a  small  venous 
channel  which  descends  obliquely  on  the  posterior  wall  of  the  left  auricle  and  terminates 
in  the  coronary  sinus.  Its  orifice  is  not  provided  with  a  valve.  It  is  of  special  interest, 
inasmuch  as  it  represents  the  left  superior  vena  cava  of  some  other  mammals,  and  is 
developed  from  the  left  dvict  of  Cuvier. 

(4)  The  inferior  interventricular,  inferior  cardiac,  or  middle  cardiac  vein  (v.  cordis 
media),  commences  at  the  apex  of  the  heart,  and,  passing  backwards  in  the  inferior 
interventricular  sulcus,  terminates  in  the  right  end  of  the  coronary  sinus.  It  receives 
tributaries  from  the  inferior  parts  of  the  walls  of  both  ventricles. 

Veins  of  the  heart  which  do  not  end  in  the  coronary  sinus. — (a)  The  anterior 
cardiac  veins  (vv.  cordis  anteriores)  are  two  or  three  small  vessels  which  ascend  on  the 
anterior  wall  of  the  right  ventricle  to  the  auriculo-ventricular  groove,  where  they 
either  end  separately  in  the  right  auricle  or  terminate  in  the  commencement  of  the 
small  cardiac  vein.  {b)  The  vence  minimce  cordis. — A  number  of  small  veins  which 
commence  in  the  substance  of  the  walls  of  the  heart,  and  terminate  directly  in  its  cavities, 
principally  in  the  auricles ;  some  few,  however,  open  into  the  ventricles. 

THE  SUPERIOR  VENA  CAVA  AND  ITS  TRIBUTARIES. 

The  superior  vena  cava  (Figs.  619  and  620)  returns  the  blood  from  the  head 
and  neck,  the  upper  extremities,  the  thoracic  wall,  and  a  portion  of  the  upper  part 
59  c 


872  THE  VASCULAE  SYSTEM. 

of  the  posterior  wall  of  the  abdomen.  It  is  formed,  at  the  lower  border  of  the  first 
right  costal  cartilage,  by  the  union  of  the  two  innominate  veins,  and  it  descends, 
with  a  slight  convexity  to  the  right,  to  the  level  of  the  third  right  costal  cartilage, 
where  it  opens  into  the  upper  and  back  part  of  the  right  auricle.  It  is  about 
three  inches  (7*5  cm.)  long ;  in  the  lower  half  of  its  extent  it  is  enclosed  within 
the  fibrous  layer  of  the  pericardium,  and  it  is  covered  in  front  and  laterally  by  the 
serous  layer. 

Relations. — It  is  overlapped  in  front  by  the  margins  of  the  right  lung  and  pleural 
sac  and  by  the  ascending  aorta.  The  lung  and  pleura  intervene  between  it  and  the 
second  and  third  costal  cartilages,  the  intei'nal  intez'costal  muscles  in  the  first  and  second 
intercostal  spaces,  and  the  internal  mammary  vessels.  It  is  in  relation  behind  with  the 
right  vagus  nerve,  the  vena  azygos  major,  the  right  bi'onchus,  the  right  pulmonary  artery, 
and  the  upper  right  pulmonary  vein.  On  its  left  side  are  the  commencement  of  the 
innominate  artery  and  the  ascending  portion  of  the  aorta,  whilst  on  the  right  side  it  is 
in  close  relation  with  the  right  pleura,  the  phrenic  nerve  and  comes  nervi  phrenici 
vessels  intervening. 

Tributaries. — In  addition  to  the  two  innominate  veins,  by  the  union  of  which  it  is 
formed,  the  superior  vena  cava  only  receives  one  large  tributary,  viz.  the  vena  azygos 
major ;  but  several  small  pericardial  and  mediastinal  veins  open  into  it. 

The  Azygos  Veins. 

The  vena  azygos  major  (v.  azygos,  Fig.  660)  commences  either  from  the  back  of 
the  inferior  vena  cava,  at  the  level  of  the  right  renal  vein,  or  as  the  direct  upward 
continuation  of  an  anastomosing  channel  which  connects  together  the  lumbar 
veins  of  the  right  side,  and  which  is  known  as  the  right  ascending  lumhar  vein. 
The  great  azygos  vein  ascends  through  the  aortic  orifice  of  the  diaphragm,  and 
is  continued  upwards  through  the  posterior  mediastinum.  In  the  upper  part  of 
its  course,  it  first  passes  behind  and  then  arches  forwards  above  the  root  of  the 
right  lung  to  its  termination  in  the  posterior  part  of  the  superior  vena  cava, 
immediately  before  the  latter  vessel  pierces  the  pericardium.  It  frequently 
possesses  imperfect  valves. 

Relations. — In  the  abdomen  it  lies  on  the  bodies  of  the  upper  lumbar  vertebne, 
behind  the  right  cms  of  the  diaphragm  and  the  inferior  vena  cava,  and  to  the  right  side 
of  the  thoracic  duct. 

In  the  thorax  it  lies  on  the  bodies  of  the  lower  eight  dorsal  vertebrse,  the  intervening- 
discs,  and  the  anterior  common  ligaiuent,  and  it  crosses  in  front  of  the  right  aortic  inter- 
costal arteries.  In  the  lower  part  of  the  posterior  mediastinum  it  is  covered  in  front  by  the 
right  pleura  and  lung;  at  a  higher  level  it  is  overlapped  by  the  right  margin  of  the  oeso- 
phagus, and  immediately  before  its  termination  it  is  crossed  by  the  root  of  the  right  lung. 

On  its  riglit  side  it  receives  the  right  posterior  intercostal  veins.  On  its  left  side  it  is 
in  relation,  in  the  greater  part  of  its  extent,  with  the  thoracic  duct  and,  as  it  arches  for- 
wards over  the  root  of  the  lung,  with  the  right  vagus  nerve.  About  the  level  of  the  seventh 
dorsal  vertebi-a  it  receives  the  vena  azygos  minor  su})erior,  whilst  at  the  level  of  the 
eighth  dorsal  vertebra  the  vena  azygos  minor  inferior  opens  into  it. 

In  addition  to  tlie  left  azygos  veins  it  receives  the  riglit  posterior  intercostal  veins, 
except  that  from  the  first  space  but  including  the  right  superior  intercostal  vein,  the 
right  .subcostal  vein,  and,  through  the  ascending  lumbar  vein,  the  upper  right  lumbar 
veins.  It  also  receives  the  right  bronchial  veins  and  some  smiill  oesophageal,  pericardial, 
and  mediastinal  tributaries. 

The  vena  azygos  minor  superior  (v.  hemi-azygos  accessoria)  is  formed  by  the  union  of 
the  fourth,  fifth,  sixth,  uiid  .seventii  left  posterior  intercostal  veins.  It  lies  in  the  posterior 
mediastinum  on  the  left  sides  of  the  Vjodies  of  the  fifth,  sixth,  and  seventh  dorsal  vertebra^, 
and  crosses  the  spine  from  left  to  right  opposite  the  body  of  the  seventh  dorsal  vertebra, 
passing  behind  the  aorta,  a'sophagus,  and  thoracic  duct ;  it  terminates  in  the  vena  azygos 
major.  It  receives  the  left  bronchial  veins,  some  small  posterior  mediastinal  veins  also 
open  into  it,  and  it  communicates  with  the  left  superior  intercostal  vein. 

The  vena  azygos  minor  inferior  (v.  hemi-azygos)  commences  in  the  epigastric  region. 
At  its  origin  it  is  connected  either  with  the  left  ascending  lumbar  vein  or  with  the  left  renal 
vein.     After  piercing  the  left  cms  of  the  diaphragm  it  ascends  on  the  left  sides  of  the 


THE  INNOMINATE  VEINS.  873 

bodies  of  the  lower  dorsal  vertebno,  and  opposite  the  eighth  dorsal  vertebra  it  turns  to  the 
right,  crosses  the  front  of  the  spine  behind  the  aorta,  a>sophagus,  and  thoracic  duct,  and 
terminates  in  the  vena  azygos  major.  As  it  ascends  in  the  postei-ior  mediastinum  it 
lies  internal  to  the  sympathetic  cord,  behind  the  roots  of  the  splanchnic  nerves,  and 
superficial  to  the  lower  left  intercostal  arteries.  Through  the  left  ascending  lumbar 
vein  it  receives  blood  from  the  upper  lumbar  veins  of  the  left  side ;  the  lower  four 
posterior  intercostal  veins,  the  left  subcostal  vein,  and  small  mediastinal  tributaries  also 
terminate  in  it. 

Not  infrequently  the  upper  and  lower  minor  azygos  veins  unite,  opposite  the  seventh 
or  eighth  dorsal  vertebra,  to  form  a  common  trunk  which  terminates  in  the  azygos  major. 

The  bronchial  veins  do  not  quite  correspond  to  the  bronchial  arteries,  and  they  are 
not  fo\md  on  the  walls  of  the  smallest  bronchi.  On  each  side  the  tributaries  run  in  front 
of  and  behind  the  bronchial  tubes  to  the  root  of  the  lung,  where  they  unite,  as  a  rule, 
into  two  small  trunks ;  those  of  the  right  side  open  into  the  vena  azygos  major,  and  those 
of  the  left  into  the  vena  azygos  minor  superior,  or  into  the  left  superior  intercostal  vein. 
On  both  sides  they  are  joined  by  tracheal  and  posterior  mediastinal  veins.  Some  few 
small  bronchial  veins,  including  most  of  those  from  the  smaller  tubes,  open  into  the 
pulmonary  veins. 

Intercostal  Veins. — There  are  two  sets  of  intercostal  veins  (vv.  intercostales),  the 
anterior  and  the  posterior. 

The  anterior  intercostal  veins  are  tributaries  of  the  internal  mammary  or  of  the 
musculo-phrenic  veins,  and  are  described  with  those  vessels  (p.  874). 

The  posterior  intercostal  veins  (Fig.  660)  are  eleven  in  number  on  each  side.  A 
single  vein  runs  in  each  intercostal  space  ;  it  is  situated  in  the  subcostal  groove  above  the 
corresponding  artery. 

On  the  right  side  the  posterior  intercostal  vein  of  the  first  space  accompanies  the 
superior  intei'costal  artery  across  the  front  of  the  neck  of  the  first  rib,  and  terminates 
in  the  vertebral  or  innominate  vein.  The  second,  third,  and  fourth  intercostal  veins  of 
the  right  side  unite  together  to  form  a  common  trunk,  the  right  superior  intercostal  vein 
(v.  intercostalis  suprema  dextra),  which  terminates  by  joining  the  vena  azygos  major.  The 
fifth  to  the  eleventh  posterior  intercostal  veins  of  the  right  side  open  separately  in  the 
vena  azygos  major. 

On  the  left  side  the  first  posterior  intercostal  vein  follows  a  course  similar  to  that 
taken  by  the  corresponding  vein  on  the  right  side,  and  terminates  in  the  left  vertebral  or 
innominate  vein.  The  second,  third,  and  fourth  posterior  intercostal  veins  of  the  left  side 
unite  to  form  the  left  superior  intercostal  vein  (v.  intercostalis  suprema  sinistra),  which 
runs  from  behind  forwards  along  the  left  and  anterior  aspect  of  the  aortic  arch.  It  passes 
obliquely  between  the  left  vagus  and  phrenic  nerves,  crosses  the  root  of  the  left 
subclavian  artery,  and  ends  in  the  lower  part  of  the  left  innominate  vein.  The  fifth, 
sixth,  seventh,  and  eighth  posterior  intercostal  veins  of  the  left  side  terminate  in  the 
vena  azygos  minor  superior,  and  the  ninth,  tenth,  and  eleventh  in  the  vena  azygos  minor 
inferior. 

Each  posterior  intercostal  vein  is  provided  with  valves,  both  at  its  termination  and 
along  its  course,  which  prevent  the  blood  flowing  towards  the  anterior  aspect  of  the 
thoracic  wall.  Its  tributaries  are  derived  from  the  adjacent  muscles  and  bones,  and  a 
short  distance  from  its  termination  it  receives  a  dorsal  tributary  which  passes  forwai'ds 
to  it  between  the  transverse  processes  of  the  vertebrae.  This  dorsal  vessel  is  formed  by 
the  union  of  small  veins  which  issue  from  the  muscles  of  the  back,  from  the  anterior  and 
posterior  spinal  plexuses  which  lie  respectively  in  front  of  the  bodies  and  behind  the 
arches  of  the  vertebrae,  and  by  venous  channels  which  issue  through  the  intervertebral 
foramina ;  the  latter  vessels  commence  in  the  spinal  canal,  where  they  are  connected  with 
the  anterior  and  posterior  spinal  veins. 

The  Innominate  Veins. 

The  innominate  or  brachio-cephalic  veins  (vv.  anonymte  dextra  et  sinistra 
Figs.  619  and  620),  two  in  number,  right  and  left,  return  blood  from  the  head  and 
neck,  the  upper  extremities,  the  upper  part  of  the  posterior  wall  of  the  thorax,  the 
anterior  wall  of  the  thorax,  and  the  upper  part  of  the  anterior  wall  of  the  abdomen. 
Each  innominate  vein  commences  behind  the  sternal  end  of  the  clavicle  of  the 
corresponding  side,  and  is  formed  by  the  union  of  the  internal  jugular  and  sub- 
clavian veins ;  the  two  innominate  veins  terminate  by  uniting  together,  at  the 
lower  border  of  the  cartilage  of  the  first  rib  on  the  right  side,  to  form  the  superior 


874  THE  VASCULAR  SYSTEM. 

veua  cava.  To  reach  this  point  the  left  vein  has  to  pass  from  left  to  right  behind 
the  manubrium  sterui,  and  it  is  therefore  about  three  times  as  long  as  the  right 
vein.     The  innominate  veins  do  not  possess  valves. 

The  right  innominate  vein  is  a  little  more  than  one  inch  (3  cm.)  in  length. 
It  descends  almost  vertically  to  the  lower  border  of  the  first  costal  cartilage,  and 
terminates  in  the  superior  vena  cava. 

Relations. — It  is  in  relation  in  front  with  the  sternal  end  of  the  clavicle  and  the 
stei'uo-hjoid  and  sterno-thja-oid  muscles.  It  partl}^  overlaps  the  innominate  artery,  which 
lies  to  its  left  side,  and  it  is  in  front  of  the  right  vagus  nerve  and  the  posterior  part  of  the 
upper  end  of  the  right  pleural  sac.  The  phrenic  nerve  and  the  accompanying  vessels  run 
along  its  right  side,  and  intervene  between  it  and  the  right  pleural  sac. 

Tributaries. — In  addition  to  the  veins  by  the  union  of  which  it  is  formed,  the  right 
innominate  vein  receives  the  right  vertebral  and  internal  mammary  veins,  and  sometimes 
the  right  inferior  thyroid  vein  and  the  first  right  posterior  intercostal  vein.  The  right 
lymphatic  duct  also  opens  into  it. 

The  left  innominate  vein  passes  from  left  to  right,  with  a  slight  obliquity 
downwards,  behind  the  upper  part  of  the  manulirium  sterni,  to  the  lower  border 
of  the  first  right  costal  cartilage,  where  it  terminates  in  the  superior  vena  cava. 
It  is  a  little  less  than  three  inches  long  (6  to  7*5  cm.) 

Relations. — It  is  covered  in  front,  in  the  greater  part  of  its  extent,  by  the  sterno- 
hyoid and  sterno-thyroid  muscles,  but  at  its  right  extremity  it  is  slightly  overlapped  by 
the  right  pleura,  and  in  the  middle  line  the  remains  of  the  thymus  gland  intervene 
between  it  and  the  posterior  surface  of  the  sternum.  It  rests  posteriorly  upon  the  left 
subclavian  artery,  the  left  phrenic,  and  the  left  vagus  }ierves,  the  left  supeinor  cardiac 
branch  of  the  sympathetic,  the  inferior  cervical  branch  of  the  left  vagus,  the  left  common 
carotid  artery,  the  trachea,  and  the  innominate  artery. 

Its  lower  border  is  in  relation  with  the  arch  of  the  aorta,  and  on  its  upper  border  it 
receives  the  inferior  thyroid  vein  of  one  or  both  sides. 

Tributaries. — It  receives  the  vertebral,  internal  mammary,  inferior  thyroid,  and 
superior  intercostal  veins  of  its  own  side,  the  first  left  posterior  intercostal  vein,  and 
some  pericardial,  tliymic,  anterior  bronchial,  and  anterior  mediastinal  veins.  Sometimes 
the  right  inferior  thyroid  vein  joins  it,  but  usually  this  vessel  terminates  in  the  right 
innominate  vein  or  in  the  commencement  of  the  superior  vena  cava. 

The  thoracic  duct  opens  into  it  just  at  the  angle  of  junction  of  the  internal  jugular 
and  subclavian  veins. 

Internal  mammary  veins  (w.  mammari;e  internee). — Each  internal  mammary 
artery  is  accompanied  by  venaj  comites ;  they  commence  by  the  union  of  the  venae 
comites  of  the  superior  epigastric  and  musculo-phrenic  arteries,  between  the  sixth  costal 
cartilage  and  the  triangularis  sterni,  and  at  the  upper  part  of  the  thorax  they  fuse  into  a 
single  vessel  which  enters  the  superior  mediastiiunu  and  ends  in  the  innominate  vein  of  the 
same  side. 

The  tributaries  of  the  internal  mauuuary  veins  are — (a)  The  venae  comites  of  the 
superior  epigastric  and  musculo-phrenic  arteries,  which  in  their  turn  receive  tributaries 
which  correspond  with  the  branches  of  the  arteries  they  accompany,  (b)  Six  anterior 
perforating  veins  which  accompany  the  corresponding  arteries,  one  lying  in  each  of  the 
upper  six  intercostal  spaces,  (c)  Twelve  anterior  intercostal  veins  from  the  upper  six 
intercostal  spaces,  two  veins  lying  in  each  space  witli  the  coi-responding  branches  of  the 
internal  mammary  artery,  (d)  Small  and  irregular  pleural,  muscular,  mediastinal,  and 
sternal  veins. 

The  internal  mammary  veins  are  provided  witli  numerous  valves  which  prevent  the 
blood  from  flowing  downwaj'ds. 

Superior  epigastric  veins  (w.  epigastricfe  superiores). — The  vense  comites  of  the 
superior  epigastric  artery  receive  tributaries  from  the  substance  of  the  rectus  abdominis, 
the  sheath  of  the  muscle,  and  the  superjacent  skin  and  fascia ;  they  pass  with  the  artery, 
between  the  sternal  and  costal  origins  of  the  diaphragm,  and  terminate  in  the  internal 
manmiary  veins. 

Musculo-phrenic  veins. — The  vena)  comites  of  the  musculo-phrenic  artery  com- 
mence in  the  abdomen,  pass  through  the  diaphragm  witli  the  artery,  and  terminate  in 
the  internal  mammar}-  veins.  They  receive  as  tributaries  the  anterior  intercostal  veins  of 
the  seventh,  eighth,  and  ninth  intercostal  spaces,  and  small  venules  from  the  substance  of 
the  diaphragm. 


VEINS  OF  THE  HEAD  AND  NECK.  875 

Vertebral  Veins  (w.  vertebrales). — These  correspond  ouly  to  the  extra-cranial 
parts  of  the  vertebral  arteries.  Each  commences  by  the  union  of  offsets  from 
the  intraspinal  venous  plexuses,  and,  issuing  from  the  spinal  canal,  passes  across 
the  posterior  arch  of  the  atlas  \vith  the  vertebral  artery  to  the  foramen  in  the 
transverse  process  of  the  atlas.  It  then  descends  through  the  foramina  in  the 
cervical  transverse  processes,  and  breaks  up  into  a  plexus  of  venous  channels  which 
surround  the  artery.  At  the  lower  part  of  the  neck  these  channels  unite  to  form 
a  single  trunk  which  issues  from  the  foramen  in  the  transverse  process  of  the 
sixth  cervical  vertebra,  and  descends,  in  the  interval  between  the  longus  colli  and 
scalenus  anticus  muscles,  to  terminate  in  the  upper  and  back  part  of  the  innominate 
vein,  where  it  possesses  a  uni-  or  bi-cuspidate  valve. 

Relations. — In  the  first  part  of  its  coui'se  the  vein  lies  in  the  suboccipital  triangle. 
The  second,  plexiform  portion,  is  in  the  canal  formed  by  the  foramina  in  the  transverse 
processes  of  the  cervical  vertebrae,  and,  with  the  artery  which  it  surrounds,  lies  in  front  of 
the  trunks  of  the  cervical  spinal  nei-ves.  The  third  part,  in  the  root  of  the  neck,  is 
between  the  longus  colli  and  scalenus  anticus  muscles,  in  front  of  the  fir.st  part  of  the 
vertebral  artery,  and  behind  the  internal  jugular  vein. 

Tributaries. — In  addition  to  the  offsets  from  the  intraspinal  venous  plexuses  by  the 
union  of  which  it  is  formed,  each  vertebral  vein  i-eceives  the  following  tributaries : — (a) 
Small  vessels  which  issue  from  the  muscles,  ligaments,  and  bones  of  the  deeper  parts  of  the 
neck,  and  the  lower  and  back  part  of  the  head,  (b)  Offsets  from  the  intraspinal  venous 
plexuses  which  pass  out  of  the  .spinal  canal  by  the  intervertebral  foramina.  (c)  The 
anterior  deep  cervical  or  anterior  vertebral  vein,  a  vessel  which  is  formed  by  the  union  of 
tributaries  which  issue  from  a  venous  plexus  which  lies  in  front  of  the  bodies  and 
on  the  roots  of  the  transverse  processes  of  the  cervical  vertebra;.  This  vessel  accompanies 
the  ascending  cervical  artery,  and  terminates  in  the  lower  part  of  the  vertebral  vein, 
immediately  after  the  latter  has  issued  from  the  foramen  in  the  sixth  cervical  transverse 
process,  (d)  The  posterior  deep  cervical  (v.  cervicalis  profunda)  or  posterior  vertebral 
vein ;  this  commences  in  the  suboccipital  triangle  from  a  venous  plexiis  with  which 
the  vertebral  and  occipital  veins  communicate.  It  descends  behind  the  transverse 
processes  of  the  cervical  vertebrae  in  company  with  the  pi'ofunda  cervicis  artery,  tiu'us 
forwards  at  the  root  of  the  neck,  between  the  transverse  processes  of  the  sixth  and 
seventh  cervical  vertebrae  or  between  the  latter  and  the  neck  of  the  first  rib,  and  opens 
into  the  vertebral  vein.  It  receives  blood  from  the  muscles,  ligaments,  and  bones  of  the 
back  of  the  neck,  (e)  The  posterior  intercostal  vein  from  the  first  intercostal  space  some- 
times opens  into  it. 

Occasionally  the  venous  plexus  round  the  vertebral  artery  ends  below  in  two  terminal 
trunks,  anterior  and  posterior,  instead  of  one.  In  these  cases  the  second  terminal  vessel 
lies  behind  the  lower  part  of  the  vertebral  artery,  passes  through  the  foramen  in  the 
transverse  process  of  the  seventh  cervical  vertebra,  and  turns  forwards  on  the  outer  side 
of  the  artery  to  join  the  anterior  trunk,  thus  forming  a  common  terminal  vein  which 
ends  in  the  usual  manner. 

Inferior  Thyroid  Veins  (w.  thyreoidea3  inferiores). — Each  inferior  thyroid 
vein  commences  by  the  union  of  a  series  of  tributaries  which  issue  from  the 
isthmus  and  the  corresponding  lateral  lobe  of  the  thyroid  body.  The  two  veins 
descend  along  the  front  of  the  trachea  into  the  superior  mediastinum,  where  the 
right  inferior  thyroid  vein  terminates  in  the  junction  of  the  two  innominate  veins, 
and  the  left  in  the  upper  part  of  the  left  innominate  vein :  or  the  two  veins  unite 
to  form  a  single  trunk,  which  usually  ends  in  the  left  innominate  vein,  but  occa- 
sionally in  the  right.  In  their  descent  through  the  neck  the  inferior  thyroid  veins 
frequently  anastomose  together,  and  sometimes  these  anastomoses  are  so  frequent 
and  irregular  thai  a  venous  plexus  is  formed  in  front  of  the  lower  cervical  portion 
of  the  trachea. 

VEINS    OF   THE   HEAD   AND    NECK. 

Internal  jugular  veins  (Figs.  620  and  650). — Each  internal  jugular  vein  (v. 
jugularis  interna)  commences  in  the  posterior  compartment  of  the  jugular  foramen, 
as  the  direct  continuation  of  the  lateral  sinus,  and  terminates  behind  the  sternal 
part  of  the  clavicle  by  uniting  with  the  subclavian  vein  of  the  same  side  to  form 
the  innominate  vein. 


876  THE  VASCULAR  SYSTEM. 

At  its  commencement  it  is  dilated,  forming  the  bulb  of  the  jugular  vein,  and 
in  this  situation  it  lies  behind  and  somewhat  to  the  outer  side  of  the  internal 
carotid  artery  and  the  last  four  cranial  nerves.  As  it  descends  it  accompanies 
first  the  internal  and  then  the  common  carotid  artery ;  incHning  forwards  during 
its  descent,  it  gradually  passes  from  its  original  position,  behind  and  to  the  outer 
side  of  the  internal  carotid  artery,  and  lies  more  completely  to  the  outer  side  of  the 
internal  and  common  carotid  arteries,  and  indeed  somewhat  overlaps  the  latter  in 
front.  This  is  more  especially  the  case  on  the  left  side,  for  both  internal  jugular 
veins  trend  slightly  towards  the  right  as  they  descend ;  consequently  at  the  root 
of  the  neck  the  right  vein  is  separated  from  the  right  common  carotid  artery  by  a 
small  interval  filled  by  areolar  tissue,  whilst  the  left  vein  is  more  directly  in  front 
of  the  corresponding  common  carotid  artery. 

Within  an  inch  of  its  lower  extremity  each  internal  jugular  vein  is  pro- 
vided with  a  valve,  which,  however,  is  frequently  incompetent.  It  consists  of  one, 
two,  or  three  cusps. 

Relations. — The  vein  lies  in  fi'ont  of  the  transverse  processes  of  the  cervical  verte- 
brae, the  rectus  capitis  lateralis,  rectus  capitis  anticus  major,  and  scalenus  anticus  muscles, 
the  ascending  cervical  artery,  which  runs  upwards  in  the  interval  between  the  attach- 
ments of  the  two  latter  muscles,  and  the  phrenic  nerve  ;  the  suprascapular  and  the 
transverse  cervical  arteries  intervene  between  it  and  the  scalenus  anticus.  At  the  root  of 
the  neck  the  vein  lies  in  front  of  the  first  part  of  the  subclavian  artery  and  the  origins 
of  the  vertebral  artery  and  the  thyroid  axis,  and  on  the  left  side  it  is  in  front  of  the 
terminal  part  of  the  thoracic  duct. 

On  the  inner  side  of  the  internal  jugular  vein,  immediately  below  the  skull,  are  the 
internal  carotid  artery  and  the  last  four  cranial  nerves ;  in  the  rest  of  its  extent  it  is  in 
relation  internally  either  with  the  internal  or  the  common  carotid  artery,  whilst  to  its 
inner  side  and  somewhat  posteriorly,  between  it  and  the  large  arteries,  lies  the  vagus 
nerve. 

Each  internal  jugular  vein  is  covered  in  the  whole  of  its  length  by  the  sterno-mastoid 
muscle;  near  its  upper  end  it  is  crossed  by  the  posterior  belly  of  the  digastric,  whilst  in 
its  lower  half,  in  addition  to  the  sterno-mastoid,  the  omo-hyoid,  the  sterno-hyoid,  and  the 
sterno-thyroid  muscles  are  sujDerficial  to  it.  Just  below  the  transverse  process  of  the  atlas, 
and  under  cover  of  the  sterno-mastoid,  the  vein  is  crossed  on  its  outer  side  by  the  spinal 
accessory  nerve  and  by  the  occipital  artery ;  about  the  middle  of  its  course  it  is  also 
crossed  by  the  communicans  cervicis  nerve,  and  near  its  lower  end  by  the  anterior  jugular 
vein  ;  the  latter  vessel,  however,  is  separated  from  it  by  the  sterno-hyoid  and  sterno- 
thyroid muscles.     Superficial  to  the  vein  are  numerous  deep  cervical  lymphatic  glands. 

Tributaries. — in)  The  inferior  petrosal  sinus,  which  joins  it  near  its  commencement. 
{h)  Pharyngeal  branches  from  the  venous  plexus  on  the  wall  of  the  pharynx,  (c)  The 
common  facial  vein,  which  receives  the  facial  vein  and  its  tributaries.  (cZ)  The  lingual 
veins  (w.  linguales),  small  vente  comites,  which  commence  chiefly  in  the  sublingual 
and  dorsalis  lingufe  veins,  and  accompany  the  first  and  second  parts  of  the  lingual  artery, 
(e)  The  ranine  vein,  which  commences  beneath  the  tip  of  the  tongue,  and  accompanies 
at  first  the  two  terminal  parts  of  the  lingual  artery,  and  afterwards  the  hypoglossal 
nerve.  (/)  The  superior  thsrroid  vein  (v.  thyreoidea  superioris),  which  accompanies  the 
corresponding  artery,  (g)  The  middle  thsrroid  vein,  which  passes  backwards  from  the 
lateral  loV^e  of  the  thyroid  body  and  crosses  the  middle  of  the  outer  aspect  of  the  common 
carotid  artery,  {h)  The  occipital  vein  (v.  occipitalis)  occasionally  terminates  in  the 
internal  jugular  vein.  In  many  cases,  however,  it  ends  in  the  suboccipital  plexus,  which 
is  drained  by  the  vertebral  and  deep  cervical  veins  (see  p.  875). 

The  common  facial  vein  (v.  facialis  comnuuiis)  is  formed  by  the  union  of  the  facial 
vein  (v.  facialis  anterior)  with  the  anterior  division,  or  terminal  branch,  of  a  venous 
trunk  which  lies  in  suljstance  of  the  parotid  gland,  and  which  is  called  the  temporo- 
maxillary  vein  (v.  facialis  posterior).  It  accompanies  the  first  part  of  the  facial  artery 
in  the  carotid  triangle,  passes  l^etween  the  sterno-mastoid,  and  terminates  in  the  antei'ior 
border  of  the  internal  jugiilar  vein.  Just  before  it  disappears  beneath  the  sterno-mastoid, 
the  common  facial  vein  frequently  gives  off  a  large  branch,  which  descends  along  the 
anterior  border  of  the  sterno-mastoid  to  the  suprasternal  fossa,  where  it  joins  the 
anterior  jugidar  vein. 

The  facial  vein  (v.  facialis  anterior,  Fig.  648)  commences  at  the  inner  angle  of  the 
orbit  in  tlie  angular  vein,  which  is  formed  by  the  union  of  the  supra-orbital  and  frontal 


EXTEENAL  JUGULAE  VEIN.  877 

veins.  It  passes  downwards  and  backwards  on  the  face,  from  the  inner  angle  of  the  orbit 
to  the  lower  and  anterior  part  of  the  masseter  muscle,  which  it  crosses,  lying  in  the  same 
plane  as  the  facial  artery,  but  following  a  much  straighter  course.  After  crossing  the 
lower  border  of  the  jaw  it  passes  aci'oss  the  submaxillary  triangle,  supei-ficial  to  the 
submaxillary  gland,  and  separate  from  the  facial  artery,  which  here  lies  in  a  deeper  plane, 
and  it  terminates  a  short  distance  below  the  angle  of  the  jaw  by  uniting  with  the  anterior 
division  of  the  temporo-maxillary  vein  to  form  the  common  facial  vein. 

The  facial  vein  receives  tributaries  corresponding  with  all  the  branches  of  the  facial 
artery,  except  the  ascending  palatine  and  the  tonsillar,  which  have  no  accompanying  veins, 
the  blood  from  the  region  which  they  supply  being  returned  for  the  most  part  through 
the  pharyngeal  plexus.  The  facial  vein  also  communicates  with  the  pterygoid  plexus 
which  surrounds  the  external  pterygoid  muscle  by  means  of  an  anastomosing  channel, 
called  the  deep  facial  vein,  which  passes  backwards  between  the  masseter  and  buccinator 
nuiscles  into  the  zygomatic  fossa. 

The  inferior  thyroid  veins  have  already  been  described  (see  p.  875). 

Subclavian  Veins. — The  subclavian  vein  (v.  subclavia)  of  each  side  is  the 
direct  continuation  of  the  main  vein  of  the  upper  extremity,  the  axillary  vein ;  but 
through  its  tributary,  the  external  jugular  vein,  it  also  receives  blood  both  from 
the  superficial  and  deep  parts  of  the  head  and  neck. 

From  its  commencement  at  the  outer  border  of  the  first  rib  it  runs  inwards 
below  and  in  front  of  the  corresponding  artery,  from  which  it  is  separated  by  the 
lower  part  of  the  scalenus  anticus  muscle,  and  it  terminates  behind  the  sternal 
end  of  the  clavicle,  in  the  innominate  vein  of  the  corresponding  side.  As  it  passes 
inwards  it  forms  a  slight  curve,  the  convexity  of  which  is  directed  upwards. 

Each  subclavian  vein  possesses  a  single  bicuspid  valve  which  is  situated  imme- 
diately on  the  distal  side  of  the  opening  of  the  external  jugular  vein. 

Relations. — The  subclavian  vein  is  in  relation  in  front  with  the  postei'ior  layer  of  the 
costo-coracoid  membrane,  which  separates  it  from  the  subclavius  nuiscle,  and  the  nerve 
to  the  subclavius,  and  with  the  back  of  the  sternal  end  of  the  clavicle,  from  which  it  is 
partly  separated,  however,  by  the  fibres  of  the  sterno-hyoid  and  stern o-thyroid  muscles. 

It  is  closely  attached  in  front  to  the  posterior  surface  of  the  costo-coracoid  membrane, 
consequently  it  is  expanded  when  the  clavicle  is  moved  forwards,  a  condition  of  affairs 
which  constitutes  a  distinct  danger  when  operations  are  being  performed  in  the  neighbour- 
hood of  the  vein,  for  in  the  event  of  the  vessel  being  wounded,  forward  movement  of  the 
clavicle  may  cause  air  to  be  sucked  into  the  vein  with  fatal  results. 

Behind  the  vein,  and  on  a  higher  plane,  are  the  first  and  thii-d  parts  of  the  subclavian 
artery,  but  it  is  separated  from  the  second  part  by  the  scalenus  anticus.  To  the  inner 
side  of  the  anterior  scalene  the  posterior  relations  of  the  vein,  in  addition  to  the  sub- 
clavian artery,  are  the  upper  part  of  the  internal  mammary  artery,  the  phrenic  nerve,  and 
the  cervical  portion  of  the  pleura. 

It  j-ests  upon  the  upper  surface  of  the  first  rib. 

Tributaries. — Whilst  the  subclavian  vein  is  the  direct  continuation  of  the  axillary 
vein,  and  receives  the  blood  from  the  upper  extremity,  it  has,  as  a  general  rule,  only  one 
named  tributary,  viz.  the  external  jugular  vein. 

The  external  jugular  vein  (v.  jugularis  externa,  Fig.  648)  is  formed  on  the 
superficial  surface  of  the  sterno-mastoid  muscle,  a  little  below  and  behind  the  angle 
of  the  jaw,  by  the  union  of  the  posterior  auricular  vein  with  the  posterior  terminal 
branch  of  the  temporo-maxillary  vein.  After  its  formation  the  external  jugular 
vein  descends,  with  a  slight  obliquity  backwards,  to  the  anterior  part  of  the 
subclavian  portion  of  the  posterior  triangle  of  the  neck,  where  it  pierces  the  deep 
fascia,  and,  after  crossing  in  front  of  the  third  part  of  the  subclavian  artery, 
terminates  in  the  subclavian  vein. 

Whilst  on  the  surface  of  the  sterno-mastoid  muscle  it  is  covered  by  the  super- 
ficial fascia  and  platysma  muscle,  and  it  lies  parallel  with,  and  slightly  in  front  of, 
the  great  auricular  nerve  :  after  crossing  the  transverse  cervical  nerve  it  reaches 
the  posterior  border  of  the  sterno-mastoid,  where  it  receives  a  tributary  called  the 
posterior  external  jugular  vein,  which  commences  in  the  superficial  tissues  of  the 
upper  and  back  part  of  the  neck,  and  runs  downwards  and  forwards  across  the  roof 


878 


THE  VASCULAE  SYSTEM. 


of  the  upper  part  of  the  posterior  cervical  triangle  to  its  termination  in  the  external 
jugular  vein. 

As  the  external  jugular  vein  pierces  the  deep  cervical  fascia  in  the  subclavian 
triangle,  its  wall  is  closely  attached  to  the  margin  of  the  opening  through  which 
it  passes,  and  as  it  is  crossing  in  front  of  the  third  part  of  the  subclavian  artery  it 
is  joined  by  the  suprascapular,  transverse  cervical,  and  anterior  jugular  veins. 

There  are  usually  two  valves  in  the  lower  part  of  the  vein — -one,  which  is 
generally  incompetent,  at  its  termination,  and  a  second  at  a  higher  level. 

Tributaries. — lu  addition  to  the  posterior  auricular  vein  and  the  posterior  division 


Superficial  tempoi-al  vein 

Occipital  vein 
Internal  maxillary  veins 

Temporo-niaxillary  vein 
Posterior  auricular  vein 


Anterior  division  of 
temporo-niaxillavy  vein 


Posterior  external 
.jugular  vein 


Transverse  cervical  vf  ii 


Supra-orbital  vein 
Angular  vein 

Lateral  nasal  vein 

Superior  coronary  vein 

Inferior  coronary  vein 
Facial  vein 

Inferior  labial  vein 

Anastomosis  between 
common  facial  and 
anterior  jugular  veins 

Anterior  jugular  vein 
External  jugular  vein 


Fig.  648. — Superficial  Veins  of  the  Heab  and  Neck. 


of  the  temporo-naa.\illary  vein  by  which  it  is  formed,  tlie  external  jugailar  vein  receives 
the  posterior  external  jugular  vein,  which  has  already  been  described,  the  transverse 
cervical  and  suprascapular  veins  from  the  region  of  the  shoulder,  and  the  anterior 
jugular  vein.     Occasionally  the  cephalic  vein  also  opens  into  it. 

The  posterior  auricular  vein  (v.  auricularis  posterior.  Fig.  648)  receives  tributaries 
from  the  po.sterior  parts  of  tlie  parietal  and  temporal  regions  and  from  the  inner  surface 
of  the  pimia.  It  is  considerably  larger  than  the  posterior  auricular  artery,  which  it  only 
accompanies  in  the  scalp.  At  the  base  of  the  scalp  it  leaves  the  artery  and  descends  in 
the  superficial  fascia,  over  the  upper  part  of  the  sterno-mastoid,  to  open  into  the  commence- 
ment of  the  external  jugular  vein. 

The  posterior  division  of  the  temporo-maxillary  vein  (see  p.  880). 


VEINS  OF  THE  SCALP.  879 

The  transverse  cervical  and  suprascapular  veins  accompany  the  corresponding 
arteries ;  not  infrequently  they  open  directly  into  the  subclavian  vein. 

The  anterior  jugular  vein  (v.  jugularis  anterior)  commences  over  the  anterior  belly  of 
the  digastric  muscle,  and  is  formed  by  the  union  of  small  veins  from  the  lower  lip  and  the 
submental  region.  It  descends  in  the  superficial  fascia,  at  a  variable  distance  from  the 
middle  line,  and  perforates  the  superficial  layer  of  the  deep  fascia  just  above  the  inner 
end  of  the  clavicle.  It  there  enters  the  space  above  the  manubrium  stcrni,  which  lies 
between  the  first  and  second  layers  of  the  deep  cervical  fascia,  and  which  is  called  Burns's 
space,  where,  after  anastomosing  with  its  fellow  of  the  opposite  side  and  receiving  a 
commiuiication  from  the  facial  vein,  it  turns  outwards,  between  the  sterno-mastoid  super- 
ficially and  the  sterno-hyoid,  sterno-tliyroid,  and  scalenus  anticus  nuiscles  deeply,  to 
terminate  at  the  outer  border  of  the  latter  muscle  in  the  external  jugular  vein. 

The  Veins  of  the  Scalp. 

The  veins  which  drain  the  blood  from  the  superficial  parts  of  the  scalp  are  the 
frontal,  the  supra-orbital,  the  superficial  temporal,  the  posterior  auricular,  and  the 
occipital.  The  blood  from  the  deeper  part  of  the  scalp,  in  the  region  of  the 
temporal  fossa  on  each  side,  passes  into  the  deep  temporal  veins,  which  are 
tributaries  of  the  pterygoid  plexus. 

The  frontal  (v.  frontalis)  and  supra-orbital  veins  (v.  supra-orbitalis)  receive  blood 
from  the  inner  and  front  part  of  the  scalp.  They  unite  together,  near  the  upper 
and  inner  angle  of  the  orbit,  to  form  the  angular  vein ;  before  the  union  is 
effected  the  supra-orbital  vein  sends  a  branch  backwards  through  the  supra-orbital 
notch  into  the  orbital  cavity,  where  it  terminates  in  the  ophthalmic  vein,  and  as 
this  branch  passes  through  the  notch  it  receives  the  frontal  diploic  vein  (p.  881). 

The  superficial  temporal  vein  (v.  temporalis  superficialis)  receives  tributaries 
from  the  outer  part  of  the  frontal  region,  from  the  greater  part  of  the  super- 
ficial area  of  the  temporal  region,  and  from  the  anterior  part  of  the  parietal 
region.  It  passes  downwards,  across  the  posterior  root  of  the  zygoma,  into  the 
parotid  gland,  where  it  unites  with  the  internal  maxillary  vein  to  form  the  temporo- 
maxillary  trunk. 

The  posterior  auricular  vein  (v.  auricularis  posterior)  drains  the  posterior 
portions  of  the  temporal  and  parietal  areas  of  the  scalp.  It  runs  downwards 
across  the  mastoid  portion  of  the  temporal  bone,  and  terminates  in  the  external 
jugular  vein. 

The  occipital  vein  (v.  occipitalis,  Fig.  648)  receives  tributaries  from  the  inner 
and  posterior  part  of  the  parietal  region  and  from  the  occipital  region.  As  a  rule 
it  pierces  the  occipital  origin  of  the  trapezius,  and,  passing  deeply  into  the  sub- 
occipital triangle,  terminates  in  a  plexus  of  veins  which  is  drained  by  the  vertebral 
and  deep  cervical  veins.  It  sometimes  communicates  with  the  external  jugular 
vein,  and  occasionally  an  offset  from  it  accompanies  the  corresponding  artery  and 
ends  in  the  internal  jugular  vein. 

It  generally  receives  the  mastoid  emissary  vein ;  one  of  its  tributaries  receives 
the  parietal  emissary  vein,  and  occasionally  an  emissary  vein  from  the  torcular 
Herophili  opens  into  it. 

The  Veins  of  the  Orbit,  the  Nose,  and  the  Pterygo-maxillaey  Eegion. 

The  veins  of  these  three  regions  are  closely  associated  together ;  for  although 
the  orbital  blood  is  returned  for  the  most  part  to  the  cavernous  sinus  by  the 
ophthalmic  vein,  the  latter  vein  is  closely  connected  with  the  pterygoid  plexus 
which  lies  in  the  pterygo-maxillary  region. 

Veins  of  the  Orbit. — The  veins  of  the  orbit  correspond,  with  the  exception  of 
the  frontal  vein,  with  the  branches  of  the  ophthalmic  artery,  and  they  gradually 
converge,  as  they  pass  backwards  in  the  orbit,  until  they  form  two  main  trunks,  an 
upper  (v.  ophthalmica  superior)  and  a  lower  (v.  ophthalmica  inferior) ;  these 
terminate,  separately  or  by 'a  single  trunk,  in  the  anterior  end  of  the  cavernous 
sinus,  to  which  they  pass  through  the  foramen  lacerum  anterius,  and  between  the 
two  heads  of  the  external  rectus  muscle. 

The  superior  ophthalmic  vein  communicates,  at  the  internal  angle  of  the  orbit. 


880  THE  VASCULAE  SYSTEM. 

with  the  angular  vein,  and  the  inferior  ophthalmic  vein  communicates  through  the 
spheno-maxillary  fissure  with  the  pterygoid  plexus. 

Veins  of  the  Nose. — The  veins  of  the  walls  of  the  nasal  cavity  end  partly,  in 
the  ethmoidal  tributaries  of  the  superior  ophthalmic  A'cin,  partly  in  the  septal 
affluent  of  the  superior  coronary  and  in  the  lateral  nasal  veins,  both  of  which  are 
tributaries  of  the  facial  vein ;  but  the  majority  of  the  veins  of  the  nose,  both  from 
the  septal  and  outer  walls,  join  together  to  form  a  spheuo-palatine  vein  which 
passes  through  the  spheno-palatine  foramen  and  the  spheno-maxillary  fossa,  and 
terminates  in  the  pterygoid  plexus. 

Pterygoid  Plexus  and  the  Internal  Maxillary  Vein. — The  pterygoid  plexus 
(plexus  pterygoideus)  of  veins  lies  in  the  zygomatic  and  pterygoid  fossas.  It  covers 
the  inner  surface  of  the  internal  pterygoid  muscle,  and  surrounds  the  external 
pterygoid.  It  receives  tributaries  which  correspond  with  and  accompany  the 
branches  of  the  internal  maxillary  artery — viz.  spheno-palatine,  pterygo-palatine, 
vidian,  infra-orbital,  posterior  superior  dental,  posterior  palatine,  buccal,  two  or  three 
deep  temporal,  pterygoid,  masseteric,  and  inferior  dental  veins,  and  the  vena 
comites  of  the  middle  meningeal  artery.  It  communicates  superiorly  with  the 
cavernous  sinus  through  the  foramen  ovale,  anteriorly  with  the  inferior  ophthalmic 
vein  through  the  spheno-maxillary  fissure,  and  between  the  masseter  and  the 
buccinator  with  the  facial  vein  by  the  deep  facial  anastomosing  branch.  It  also 
communicates  posteriorly  and  internally,  on  the  inner  side  of  the  internal  pterygoid, 
with  the  pharyngeal  plexus,  and  it  terminates  posteriorly  in  the  internal  maxillary 
vein. 

The  internal  maxillary  vein  is  a  short  vessel  which  accompanies  the  first  part  of 
the  internal  maxillary  artery,  between  the  spheno-mandibular  ligament  and  the 
neck  of  the  lower  jaw ;  it  enters  the  parotid  gland,  and  terminates  by  uniting  with 
the  superficial  temporal  vein  to  form  the  temporo-maxillary  trunk.  Occasionally 
the  internal  maxillary  vein  is  double. 

The  temporo-maxillary  vein  (v.  facialis  posterior)  is  a  short  trunk  which  is 
formed  in  the  upper  part  of  the  parotid  gland,  behind  the  neck  of  the  jaw, 
by  the  union  of  the  superficial  temporal  and  internal  maxillary  veins.  As  it 
descends  it  hes  superficial  to  the  external  carotid  artery,  and  it  is  crossed  by  the 
cervico-  and  temporo-facial  branches  of  the  facial  nerve.  It  terminates  at  the 
lower  part  of  the  parotid  gland  by  dividing  into  posterior  and  anterior  divisions. 
The  posterior  division  passes  backwards,  perforates  the  deep  cervical  fascia,  and 
unites  on  the  upper  part  of  the  sterno-mastoid  muscle  with  the  posterior  auricular 
vein  to  form  the  external  jugular  vein.  The  anterior  division  passes  downwards 
and  forwards  into  the  carotid  triangle,  where  it  terminates  in  the  common  facial 
vein. 

VENOUS  SINUSES  AND  VEINS  OF  THE  CRANIUM  AND  OF  ITS 

CONTENTS. 

The  venous  channels  met  with  in  the  cranial  walls  and  cranial  cavity  are : —    • 

(1)  The  diploic  veins  (vv.  diploicse),  which  lie  in  the  cancellous  tissue  between 
the  outer  and  inner  tables  of  the  cranial  bones. 

(2)  The  meningeal  veins,  which  accompany  the  meningeal  arteries  in  the  outer 
layer  of  the  dura  mater. 

(3)  The  veins  of  the  brain,  which  lie  between  the  folds  of  pia  mater  and  in  the 
subarachnoid  space. 

(4)  The  cranial  venous  sinuses,  channels  which  are  situated  between  the  outer 
and  inner  layers  of  the  dura  mater;  they  receive  the  blood  from  the  terminal 
cerebral  veins. 

Diploic  and  Meningeal  Veins. 

The  diploic  veins  (vv.  diploicte)  are  anastomosing  spaces  in  the  cancellous 
tissue  of  the  fiat  bones  of  the  skull ;  they  are  lined  by  endothelium.  The  number 
of  efferent  vessels  which  emerge  from  these  spaces  is  not  constant,  but  usually 
there  are  at  least  four — viz.  a  frontal,  two  temporal,  anterior  and  posterior,  and  an 
occipital. 


VEINS  OF  THE  BRAIN. 


881 


The  frontal  diploic  vein  (v.  diploica  frontalis)  is  one  of  the  most  constant ;  it 
drains  the  anterior  part  of  the  frontal  bone,  and,  passing  through  a  small  aperture 
in  the  upper  margin  of  the  s\ipraorl)ital  notch,  terminates  in  the  supraorbital  vein. 

The  anterior  temporal  diploic  vein  (v.  diploica  temporalis  anterior)  drains  the 
posterior  part  of  the  frontal  bone  and  the  anterior  part  of  the  parietal  bone ;  it 
pierces  the  great  wing  of  the  sphenoid,  and  terminates  either  in  the  spheno-parietal 
sinus  or  in  the  anterior  deep  temporal  vein. 

The  posterior  temporal  diploic  vein  (v.  diploica  temporalis  posterior)  drains  the 
posterior  part  of  the  parietal  bone;  it  runs  downwards  to  the  posterior  inferior 
angle  of  the  parietal  bone,  and  terminates  in  the  lateral  sinus,  to  which  it  passes 
either  through  a  foramen  in  the  inner  table  of  the  parietal  bone  or  through  the 
mastoid  foramen. 

The  occipital  diploic  vein  (v.  diploica  occipitalis)  is  usually  the  largest  of  the 


Posterior  temporal 
diploic  \  eiu 


Occipital  diploic <? 

vein      ^^ 


Anterior  temporal  diploic  vein 


Fiontal  diploic  vein 


Fio.  649. — The  Veins  of  the  Diploe. 

series  ;  it  drains  the  occipital  bone,  and  terminates  either  externally  in  the  occipital 
vein  or  internally  in  the  lateral  sinus. 

The  meningeal  veins  (v.  meningese)  commence  in  two  capillary  plexuses,  a 
deep  and  a  superjScial.  The  deep  plexus  is  a  wide-meshed  network  in  the  inner 
layer  of  the  dura  mater.  Its  efferent  vessels  terminate  in  the  superficial  plexus. 
The  superficial  plexus  lies  in  the  outer  layer  of  the  dura  mater.  It  consists  of 
numerous  vessels  of  uniform  calibre  which  frequently  anastomose  together,  and 
terminate  in  two  sets  of  efferents ;  of  these,  one  set  ends  in  the  cranial  blood  sinuses, 
and  the  other  accompanies  the  meningeal  arteries.  The  efferent  meningeal  veins 
are  peculiar,  inasmuch  as  they  do  not  increase  in  size  as  they  approach  their 
terminations,  and  they  are  irregular  in  their  relations  to  the  arteries ;  as  a  rule  the 
middle  meningeal  arteries  alone  possess  two  venae  comites,  the  other  meningeal 
arteries  usually  having  only  one  accompanying  vein. 


Veins  of  the  Brain. 

The  veins  of  the  brain  include  the  veins  of  tl  e  cerebrum,  of  the  mid-brain,  of 
the  cerebellum,  of  the  pons,  and  of  the  medulla  oblongata.  They  do  not  possess 
valves. 

60 


882  THE  VASCULAR  SYSTEM. 

Veins  of  the  Cerebrum  (w.  cerebri). — The  cerebral  veins  are  arranged  in 
two  groups,  (a)  the  deep  and  (b)  the  superficial. 

The  deep  veins  issue  from  the  substance  of  the  brain.  The  superficial  veins  lie 
upon  its  surface  in  the  pia  mater  and  the  subarachnoid  space.  The  terminal 
trunks  of  both  sets  pierce  the  arachnoid  membrane  and  the  inner  layer  of  the  dura 
mater,  and  open  into  the  cranial  venous  sinuses. 

(a)  The  deep  cerebral  veins  are  the  choroid  veins,  the  veins  of  the  corpora 
striata,  the  veins  of  Galen,  and  the  inferior  striate  veins. 

Each  choroid  vein  (v.  chorioidea)  is  formed  by  the  union  of  tributaries  which 
issue  from  the  choroid  plexus  in  the  descending  horn  of  a  lateral  ventricle.  It 
ascends  along  the  lateral  border  of  the  velum  interpositum,  and  passes  forwards  in 
the  outer  border  of  that  fold  of  pia  mater  to  the  foramen  of  Monro,  where  it 
receives  efferents  from  the  choroid  plexus  of  the  third  ventricle,  and  ends  by  unit- 
ing with  the  vein  of  the  corpus  striatum  to  form  the  vein  of  Galen. 

The  vein  of  the  corpus  striatum,  on  each  side,  is  formed  by  the  union  of  tributaries 
which  issue  from  the  corpus  striatum  and  from  the  optic  thalamus.  It  runs  for- 
wards between  these  bodies,  in  a  groove  in  the  floor  of  the  lateral  ventricle,  and, 
after  receiving  tributaries  from  the  walls  of  the  anterior  horn  of  the  ventricle, 
including  the  septum  lucidum,  it  terminates  at  the  apex  of  the  velum  interpositum, 
where  it  joins  the  choroid  vein  to  form  the  vein  of  Galen. 

The  veins  of  Galen  are  three  in  number — a  right  and  a  left  vein,  and  the  vena 
magna  Galeni. 

Each  lateral  vein  of  Galen  commences  at  the  apex  of  the  velum  interpositum, 
near  the  foramen  of  Monro,  by  the  union  of  the  vein  of  the  corpus  striatum  with 
the  choroid  vein.  The  two  veins  run  backwards  between  the  layers  of  the  velum, 
and  terminate  beneath  the  splenium  of  the  corpus  callosum  by  uniting  to  form  the 
vena  magna  Galeni. 

The  tributaries  which  enter  each  vein,  after  its  formation,  are  the  basilar  vein,  the 
efferent  veins  from  the  choroid  plexus  of  the  third  ventricle,  and  veins  from  the  posterior 
part  of  the  corpus  callosum,  the  pineal  body,  the  corpora  quadrigemina,  and  the  walls  of 
the  posterior  cornu  of  the  lateral  ventricle. 

The  vena  magna  Galeni  (v.  cerebri  magna  [Galeni])  passes  backwards  and 
slightly  upwards  from  its  origin,  and  end§  in  the  anterior  extremity  of  the  straight 
sinus.  In  addition  to  the  two  veins  of  Galen,  by  the  union  of  which  it  is  formed, 
it  receives  tributaries  from  the  posterior  parts  of  the  callosal  convolutions,  from  the 
inner  and  tentorial  surfaces  of  the  occipital  lobes  of  the  brain,  and  from  the  upper 
surface  of  the  cerebellum. 

An  inferior  striate  vein  descends  on  each  side  from  the  substance  of  the  corpus 
striatum,  and,  after  passing  through  the  anterior  perforated  space,  ends  in  the 
basilar  vein  (p.  883),  which,  as  already  stated,  is  a  tributary  of  the  corresponding 
lateral  vein  of  Galen. 

(b)  The  superficial  cerebral  veins  are  more  numerous  and  of  larger  calibre . 
than  the  cerebral  arteries.     They  lie  upon  the  surface  of  the  cerebrum,  they  drain 
blood  from  the  cerebral  cortex,  and  they  are  divisible  into  two  sets,  the  superior 
and  the  inferior. 

The  superior  cerebral  veins  (vv.  cerebri  superiores),  twelve  or  more  in  number, 
lie  in  the  yia  mater  and  subarachnoid  space  on  the  upper  and  outer  aspect  of  the 
cerebral  hemispheres.  They  run  inwards  to  the  margin  of  the  longitudinal  fissure, 
where  they  receive  tributaries  from  the  inner  surface  of  the  hemispheres,  and  they 
terminate  in  the  superior  longitudinal  sinus.  The  anterior  veins  of  this  set  are 
small  and  run  transversely  inwards,  but  the  posterior  are  large  and  run  obliquely 
forwards  and  inwards  ;  they  are  embedded  ibr  some  distance  in  the  wall  of  the  sinus, 
and  their  orifices  are  directed  forwards  against  the  blood  stream. 

The  inferior  cerebral  veins  (vv.  cerebri  inferiores)  lie  on  the  lower  and  outer 
aspects  of  tlie  cerel»ral  liemispheres  ;  they  run  downwards  and  inwards,  and  terminate 
in  the  sinuses  which  lie  at  the  Ijase  of  the  skull — viz.  tlie  cavernous,  the  superior 
petrosal,  and  the  lateral  sinuses.  One  of  these  veins,  the  superficial  Sylvian  vein, 
runs  along  the  posterior  liorizontal  limlj  and  stem  of  the  fissure  of  Sylvius  to  the 


BLOOD  SINUSES  OF  THE  CEANIUM.  883 

cavernous  sinus ;  occasionally  it  is  united  by  an  anastomotic  loop,  known  as  the 
great  anastomotic  vein  of  Trolard,  with  the  superior  longitudinal  sinus,  and  some- 
times by  the  posterior  anastomotic  vein  with  the  lateral  sinus. 

The  anterior  cerebral  vein  of  each  side  lies  in  the  great  longitudinal  fissure,  and 
accompanies  the  corresponding  anterior  cerebral  artery  ;  it  receives  tributaries  from 
the  corpus  callosum  and  the  callosal  convolution.  Turning  downwards  round  the 
genu  of  the  corpus  callosum,  it  reaches  the  liase  of  the  lirain,  and  terminates  in  the 
basilar  vein. 

The  deep  Sylvian  vein  lies  deeply  in  the  fissure  of  Sylvius ;  it  anastomoses  freely 
with  the  superficial  Sylvian  vein,  receives  tributaries  from  the  island  of  Reil  and 
the  adjacent  opercula,  and  terminates  in  the  basilar  vein. 

The  basilar  vein  commences  at  the  anterior  perforated  space  ;  it  is  formed  by  the 
union  of  tlie  anterior  cerebral  vein  with  the  deep  Sylvian  vein  and  with  the  interior 
striate  vein.  Passing  backwards  round  the  crus  cerebri,  it  terminates  in  a  vein 
of  Galen.  Its  tributaries  are  derived  from  the  tuber  cinereum,  the  corpus  albicans, 
the  posterior  perforated  space,  the  uncinate  gyrus,  the  inferior  cornu  of  the  lateral 
ventricle,  and  the  crus  cerebri. 

Veins  of  the  Mid-brain. — The  veins  of  the  mid-brain  terminate  for  the  most 
part  in  the  veins  of  Galen. 

Cerebellar  Veins. — These  veins  also  are  divisible  into  two  groups,  the  super- 
ficial and  the  deep.  The  former  are  quite  independent  of  and  much  more 
numerous  than  the  arteries.     They  form  two  sets,  the  superior  and  the  inferior. 

The  superior  superficial  cerebellar  veins  (vv.  cerebelli  superiores)  terminate  in  a 
single  median  or  vermian  efferent  vessel  which  is  sometimes  double,  and  in  several 
lateral  efferents.  The  superior  vermian  vein  runs  forwards  and  ends  in  the  vena 
magna  Galeui,  and  the  lateral  superior  cerebellar  veins  terminate  in  the  lateral 
sinuses  or  in  the  superior  petrosal  sinuses. 

The  inferior  superficial  cerebellar  veins  (vv.  cerebelli  inferiores)  also  form  a 
small  vermian  and  numerous  lateral  efferents ;  the  former  runs  backwards  and 
joins  either  the  straight  sinus  or  one  of  the  lateral  sinuses,  and  the  latter  end  in 
the  inferior  petrosal  and  occipital  sinuses. 

The  deep  cerebellar  veins  issue  from  the  substance  of  the  cerebellum  and 
terminate  in  the  superficial  veins. 

Veins  of  the  Pons  Varolii. — The  deep  veins  from  the  substance  of  the  pons  pass 
forwards  to  its  anterior  surface,  where  they  become  superficial,  and,  anastomosing 
together,  form  a  plexus  which  is  drained  by  superior  and  inferior  efferent  veins. 
The  superior  efferent  veins  join  the  basilar  vein ;  the  inferior  efferent  veins  either 
unite  with  the  cerel^ellar  veins,  or  they  open  into  the  superior  petrosal  sinus. 

Veins  of  the  Medulla  Oblongata. — Deep  veins  of  the  bull>  issue  from  its  sub- 
stance and  end  in  a  superficial  plexus.  Tliis  plexus  is  drained  by  an  anterior  and 
a  posterior  median  vein  and  by  radicular  veins. 

The  anterior  median  vein  is  continuous  below  with  the  corresponding  vein  of  the 
spinal  cord ;  it  communicates  above  with  the  plexus  on  the  surface  of  the  pons. 

The  posterior  median  vein  is  continuous  below  with  the  posterior  median  vein 
of  the  cord,  from  which  it  ascends  to  the  lower  end  of  the  fourth  ventricle,  where 
it  divides  into  two  branches  which  join  the  inferior  petrosal  or  basilar  sinuses. 

The  radicular  veins  issue  from  the  lateral  parts  of  the  plexus  and  run  with  the 
roots  of  the  last  four  cranial  nerves ;  they  end  in  the  inferior  petrosal  and  occipital 
sinuses. 

Blood  Sinuses  of  the  Cranium. 

The  venous  sinuses  of  the  cranium  are  spaces  between  the  layers  of  the  dura  mater; 
they  are  lined  by  an  endothelium  which  is  continuous  with  the  endothelium  of  the 
veins.  They  receive  the  veins  of  the  brain,  communicate  frequently  with  the 
meningeal  veins  and  with  veins  external  to  the  cranium,  and  terminate  du'ectly  or 
indu'ectly  in  the  internal  jugular  vein.  Some  of  the  cranial  blood  sinuses  are 
unpaired,  others  are  paired. 

Unpaired  Sinuses. — These  are  the  superior  longitudinal,  the  inferior  longi- 
tudinal, the  straight,  the  circular,  and  the  basilar. 
60  a 


884 


THE  VASCULAE  SYSTEM. 


The  superior  longitudinal  sinus  (si)ius  sagittalis  superior)  commences  in  the 
anterior  fossa  of  the  cranium,  at  the  crista  galli,  where  it  communicates  through 
the  foramen  ciecum  witli  the  veins  of  the  nasal  cavity  or  with  the  angular  vein. 
It  passes  upwards,  then  backwards,  and  finally  downwards  in  the  convex  margin  of 
the  falx  cerebri,  grooving  the  frontal,  parietal,  and  upper  part  of  the  occipital 
bones.  As  it  descends  it  passes  slightly  to  the  right  side,  and  it  ends  at  the  level 
of  the  internal  occipital  protuberance  by  becoming  the  right  lateral  sinus.     Instead 


Inferior  longitiulinal  sinus 


Straight  sinus 


Vena  magna  Galeui 


Suiierior  petrosal  sinus 
/ 


Cavernous  sinus 


Facial  ner^'e 


,    Posterior  auricular 
artery 


Lateral  sini 

Occipital  sinus 
Sup.  oblique  muscle 

Occipital  artery  -     - 
Princeps  cerviciS  artery 

Vertebral  arteiy '^■ 

Coniplexus  muscle 

Suboccipital  nerve 

Stemo-mastoid 
muscle 


Splenius  capitis 
muscle 


^'      External  carotid 
isrterj' 

i'arotid  gland 
"tylo-byoid  muscle 

Hypoglossal  nerve 


Internal  carotid  artery 
Digastric  muscle  (posterior  belly) 


Trachelo-  Spinal  Internal        Sterno-mastoid      Conmion  carotid  artery 

mastoid  muscle    accessory  nerve  jugular  vein  artery 

Fig.  650. — Dissection  ok  the  Head  and  Neck,  showing  the  cranial  blood  sinuses  and  the  upper  part  of 

the  internal  jugular  vein. 

of  passing  to  the  right,  it  occasionally  turns  to  the  left,  and  ends  in  the  left  lateral 
sinus.  In  either  case  its  termination  is  associated  with  a  well-marked  dilatation,  the 
torcular  Herophili,  which  marks  a  confluence  of  sinuses,  and  which  is  lodged  in  a 
depression  at  one  side  of  the  internal  occipital  protuberance.  The  torcular  isconnected, 
across  the  protuberance,  by  an  anastomosing  channel  with  a  similar  dilatation,  which 
marks  the  junction  of  the  straight  sinus  with  the  lateral  sinus  of  the  opposite  side. 
Opening  into  the  superior  longitudinal  sinus  are  the  superior  cerebral  veins,  and 
it  communicates  on  each  side  by  small  o]ieiiings  with  a  series  of  spaces  in  the  dura 
mater,  the  lacunae  laterales,  into  which  the  racchioiiian  bodies  (arachnoidal  villi) 
project.  It  also  communicates,  by  emissary  veins  which  pass  through  the  foramen 
Ccecum  and  thi'ough  each  parietal  foramen  (emissarium  parietale),  with  the  veins 
on  the  exterior  of  the  cranium.  Its  cavity,  which  is  triangular  in  transverse  section, 
is  crossed  by  several  fibrous  strands  called  the  chordae  Willisii. 

The  inferior  longitudinal  sinus  (sinus  sagittalis  inferior)  lies  in  the  posterior 
two-thirds  of  the  lower  iree  margin  of  the  faJx  cerebri.     It  terminates  posteriorly 

/ 


BLOOD  SINUSES  OF  THE  CRANIUM. 


885 


by  joining  with  the  vena  magna  Galeni  to  form  the  straight  sinus.  It  is  circular 
in  transverse  section,  and  it  receives  tributaries  from  the  falx  cerebri  and  from  the 
inner  surface  of  the  middle  third  of  each  cerebral  hemisphere. 

The  circular  sinus  (sinus  circularis)  is  situated  in  the  pituitary  fossa,  and  sur- 
rounds the  pituitary  body.  It  is  usually  formed  by  anterior  (sinus  intercavernosus 
anterior)  and  posterior  (sinus  intercavernosus  posterior)  transverse  channels  whicli 
pass  across  the  pituitary  fossa  from  one  cavernous  sinus  to  the  otiier. 


Olfactory  bulh 


Optic  nervp 


Optic  commissure 
Anterior  cerebral 
artery 
Middle  cerebral 
artery 
Posterior 
eommiini- 
cating  artery 
Ocuio-motoi 
nerve 
Posterior  cere 
bral  artery 
Superior  cere- 
bellar artery 
Troclileai 
nerve 
Abducent 
nerve 

Trigeminal 
nerve 
Superior 
petrosal 
sinus 
Facial, 
nerve 

Pars  inter- 
media 
Auditory  ner\e 

Glosso-pliaryn- 
geal  ncMe 
Pneumogastnc 
nene 
.Spinal  acce&boi J  nene 


Infra-trochlear  nerve 

Supra-troclilear  nerve 

Oculo-motor  nerve 

Splieiio-parietal  sinus 
Ophthalmic  vein 

Anterior  clinoiil 
process 

Trochlear  nerve 

Oculo-motor 

nene 

Abducent  nerve 

(  ucul  11  sinus 
( iplitli  il   nerve 

SUpi  11(11 

111  ixiUaiy  nerve 

IliteiK.I 

maxill  11 V  nerve 
einous  sinus 
siUi  sinus 


moid 

mils 


Hypoglossal  nei\e 

Lateral  sinus 
Veitebial  at  ten 

bpmal  coid 


Lateial  smus 


Tentoiium  cerebelli 
(cut) 


Occipital  sinuses 


^Straight  sinus 
loicular  Herojihili 


Openings  of  occipital  sinuses 


Superior  longitudinal  sinus 
Falx  cerebri  (cut) 
Fig.  651. — Basal  Blood  Sinuses  ok  the  Duha  M.\teh. 


The  basilar  sinus  (plexus  basilaris). — The  term  basilar  sinus  is  applied  to  a 
venous  plexus  situated  in  the  dura  mater  on  the  basilar  part  of  the  occipital  bone. 
It  connects  the  posterior  ends  of  the  cavernous  or  the  anterior  ends  of  the  inferior 
petrosal  sinuses  together,  and  communicates  below  with  the  anterior  spinal  veins. 

The  straight  sinus  (sinus  rectus)  is  formed  by  the  union  of  the  inferior  longi- 
tudinal sinus  with  the  great  vein  of  Galen.  It  runs  downwards  and  backwards, 
along  the  line  of  attachment  of  the  falx  cerebri  to  the  tentorium  cerebelli.  As  a 
general  rule  it  turns  to  the  left  at  the  internal  occipital  protuberance,  dilates  some- 
what, and  becomes  continuous  with  the  left  lateral  sinus,  its  dilatation  being  united 


886  THE  VASCULAK  SYSTEM. 

with  the  corresponding  dilatation  on  the  lower  end  of  the  superior  longitudinal 
sinus — the  torcular  Herophili — hj  a  transverse  anastomosing  channel.  Occasion- 
ally the  straight  sinus  terminates  in  the  right  lateral  sinus,  and  in  that  case  the 
superior  longitudinal  sinus  ends  in  the  left  lateral  sinus.  It  receives  some  of  the 
superior  cerebellar  veins  and  a  few  tributaries  from  the  falx  cerebri. 

Paired  Sinuses. — There  are  six  pairs  of  sinuses,  viz.  the  lateral,  the  occipital, 
the  cavernous,  the  superior  petrosal,  the  inferior  petrosal,  and  the  spheno-parietal. 

Lateral  Sinuses. — Each  lateral  sinus  (sinus  transversus)  commences  at  the 
internal  occipital  protuberance,  the  right  usually  as  the  continuation  of  the  superior 
longitudinal,  and  the  left  as  the  continuation  of  the  straight  sinus.  Each  passes 
outwards  in  the  outer  border  of  the  tentorium  cerebelli  and  in  a  groove  in  the 
occipital  bone.  From  the  lateral  angle  of  the  occipital  bone  it  passes  on  to  the 
posterior  inferior  angle  of  the  parietal  bone,  which  it  grooves ;  then  it  leaves  the 
tentorium  and  turns  downwards  on  the  inner  surface  of  the  mastoid  portion  of  the 
temporal  bone  :  from  the  latter  it  passes  to  the  upper  surface  of  the  jugular  process 
of  the  occipital  bone,  and  turns  forwards  and  then  downwards  into  the  jugular 
foramen,  where  it  becomes  continuous  with  the  internal  jugular  vein. 

Its  tributaries  are  some  of  the  superior  and  inferior  cerebellar  veins,  a  posterior 
diploic  vein,  and  the  superior  petrosal  sinus.  It  is  connected  with  the  veins  out- 
side the  cranium  by  emissary  veins  which  pass  through  the  mastoid  and  posterior 
condylar  foramina. 

The  occipital  sinuses  (sinus  occipitales)  he  in  the  attached  border  of  the  falx 
cerebelli  and  in  the  dura  matei-  along  the  postero-lateral  boundaries  of  the  foramen 
magnum ;  frequently  they  unite  above  and  open  by  a  single  channel  into  the  com- 
mencement of  either  the  right  or  the  left  lateral  sinus,  but  their  upper  extremities 
may  remain  separate,  and  then  each  communicates  with  the  commencement  of  the 
lateral  sinus  of  its  own  side.  They  open  below  into  the  terminal  part  of  the  corre- 
sponding lateral  sinuses,  and  they  communicate  with  the  posterior  spinal  veins.  Each 
occipital  sinus  is  an  anastomosing  channel  between  the  upper  and  lower  extremities 
of  the  lateral  sinus  of  the  same  side,  and  each  receives  a  few  inferior  cerebellar  veins. 
The  cavernous  sinuses  lie  at  the  sides  of  the  body  of  the  sphenoid  bone.  Each 
sinus  (sinus  cavernosus)  commences  anteriorly  at  the  inner  end  of  the  sphenoidal 
fissure,  where  it  receives  the  corresponding  ophthalmic  vein,  and  it  terminates  at 
the  apex  of  the  petrous  portion  of  the  temporal  bone  by  dividing  into  the  superior 
and  the  inferior  petrosal  sinuses.  Its  cavity,  which  is  irregular  in  size  and  shape, 
is  so  divided  by  numerous  fibrous  strands  that  it  assumes  the  appearance  of 
cavernous  tissue,  and  in  its  outer  wall  are  embedded  the  internal  carotid  artery 
with  its  sympathetic  plexuses,  the  third,  fourth,  first,  and  second  divisions  of  the 
fifth,  and  the  sixth  cranial  nerves.  Its  tributaries  are  the  spheno-parietal  sinus 
and  the  inferior  cerebral  veins,  including  the  superficial  Sylvian  vein.  It  com- 
municates with  the  opposite  cavernous  sinus  by  means  of  the  circular  sinus ;  ^vith 
the  pterygoid  plexus  in  the  zygomatic  fossa  ].»y  an  emissary  vein  which  passes  either 
through  the  foramen  ovale  or  through  the  foramen  Vesalii ;  with  the  internal  jugular 
vein  by  small  venous  channels  which  accompany  the  internal  carotid  artery  through 
the  carotid  canal,  and  by  the  inferior  petrosal  sinus ;  with  the  lateral  sinus  by  the 
superior  petrosal  sinus,  and  through  tlie  ophthalmic  vein  with  the  angular  vein. 

The  spheno-parietal  sinuses  (s.  spheno-parietales)  are  lodged  in  the  dura  mater 
on  the  under  surfaces  of  tlie  small  wings  of  the  sphenoid  bone  close  to  their  posterior 
borders.  Eacli  sinus  communicates  witli  the  middle  meningeal  veins,  receives  veins 
from  the  dura  mater,  and  terminates  in  the  anterior  part  of  the  corresponding 
cavernous  sinus. 

Superior  Petrosal  Sinuses. — Each  superior  petrosal  sinus  (s.  petrosus  superior) 
connaonces  at  tlie  apex  of  tlie  ])etrous  portion  of  the  temporal  bone  in  the  posterior 
end  of  the  coiTesponding  cavernous  sinus.  It  runs  backwards  and  outwards  in  the 
attached  margin  of  the  tentorium  cerebelli,  above  the  fifth  cranial  nerve,  and  grooves 
the  upper  border  of  the  petrous  portion  of  the  temporal  bone,  at  the  outer  extremity 
of  which  it  terminates  in  the  lateral  sinus  at  the  point  where  the  latter  is  turning 
downwards  on  the  inner  surface  of  the  mastoid  portion  of  the  temporal  bone.  It 
receives  inferior  cerebral,  superior  cerebellar,  tympanic,  and  diploic  veins. 


THE  SPINAL  VEINS.  887 

Inferior  Petrosal  Sinuses. — An  inferior  petrosal  sinus  (s.  petrosus  inferior) 
commences  at  the  posterior  end  of  each  cavernous  sinus ;  it  runs  backwards,  out- 
wards, and  downwards  in  the  posterior  fossa  of  the  cranium,  in  a  groove  along  the 
lower  margin  of  the  petrous  portion  of  the  temporal  bone  and  the  adjacent  border 
of  the  basilar  portion  of  the  occipital  bone,  to  the  anterior  compartment  of  the 
jugular  foramen  of  the  same  side,  througli  which  it  passes.  It  crosses  the  last  four 
cranial  nerves  either  externally  or  internally,  and  it  terminates  in  the  internal 
jugular  vein.  Its  tributaries  include  inferior  cerebellar  veins  and  veins  from  the 
internal  ear,  which  pass  to  it  through  the  internal  auditory  meatus,  the  aqueductus 
cochlea,  and  the  aqueductus  vestibuli. 

The  Spinal  Veins. 
The  spinal  veins  include — 

(1)  The  extra-spinal  veins. 

(a)  The  anterior  spinal  plexus. 

(b)  „     posterior  ,, 

(2)  The  veins  of  the  bodies  of  the  vertebrae. 

(3)  The  intra-spinal  veins. 

(a)  The  anterior  longitudinal  veins. 
(h)     „     Interior  „  „ 

(4)  The  veins  of  the  spinal  cord. 

The  anterior  spinal  plexus  lies  in  front  of  the  bodies  of  the  vertebra?.  It  consists  of  a 
number  of  relatively  small  anastomosing  channels,  "which  communicate  ■with  the  veins  of 
the  bodies  of  the  vertebrae,  and  -which  I'eceive  tributaries  from  the  adjacent  muscles  and 
ligaments.  Its  efferent  vessels  terminate  in  the  cervical  region  in  the  anterior  deep 
cervical  vein,  in  the  dorsal  region  in  intercostal  veins,  in  the  lumbar  region  in  the  lumbar 
veins,  and  in  the  sacral  region  in  the  lateral  sacral  veins. 

The  posterior  spinal  plexus  consists  of  numerous  anastomosing  venous  channels  which 
lie  on  the  laminae  and  round  the  spines  and  the  articular  and  transverse  processes  of  the 
vertebrte.  The  plexus  receives  tributaries  from  the  muscles  and  skin  of  the  back,  and 
communicates,  thi'ough  the  ligamenta  subflava,  with  the  posterior  longitudinal  spinal 
veins  in  the  interior  of  the  spiiial  canal.  Its  efferent  vessels  pass  between  the  transverse 
processes  of  the  vertebrae,  or  through  the  sacral  foramina,  and  terminate  in  the  vertebral, 
the  intercostal,  the  lumbar,  and  the  lateral  sacral  veins  respectively. 

Veins  of  the  Bodies  of  the  Vertebrae. — The  cancellous  tissue  of  the  bodies  of  the 
vertebrae  is  permeated  by  large  venous  channels  which  communicate  anteriorly  with  the 
anterior  spinal  plexus.  These  channels  terminate  posterioi'ly  in  the  vence  basis  vertehrce, 
which  open  into  transverse  anastomosing  vessels  which  connect  the  anterior  longitudinal 
spinal  veins. 

Anterior  Longitudinal  Spinal  Veins. — Two  anterior  longitudinal  spinal  veins  collect 
blood  from  the  bodies  of  the  vertebrae,  from  the  adjacent  ligaments,  and  fi'om  the  spinal 
dura  mater.  They  are  plexiform  vessels  which  extend  from  the  foramen  magnum  to  the 
coccyx,  behind  the  bodies  of  the  vertebrae  and  along  the  margins  of  the  posterior  common 
ligament,  and  they  are  connected  together,  opposite  each  vertebral  body,  by  transverse 
anastomoses  which  lie  between  the  posterior  common  ligament  and  the  bodies  of  the 
vertebrae  ;  these  transverse  anastomoses  are  greatly  dilated  opposite  the  centres  of  the 
bodies  where  they  receive  the  venae  basis  vertebrae.  Each  anterior  longitudinal  spinal 
vein  communicates  round  the  margin  of  the  canal  with  the  corresponding  posterior  vein, 
and  it  gives  off  efferent  vessels  which  pass  through  the  intervertebral  foramina  to 
terminate,  accoi'ding  to  the  region  in  which  they  are  placed,  in  the  vertebral,  intercostal, 
lumbar,  or  latei'al  sacral  veins. 

Superiorly  the  anterior  longitudinal  spinal  veins  give  off  large  offsets,  above  the  arch 
of  the  atlas,  which  form  the  commencement  of  the  vertebral  veins  ;  through  the  foramen 
magnum  they  communicate  with  the  basilar  and  with  the  occipital  sinuses. 

The  posterior  longitudinal  spinal  veins  are  placed,  one  on  each  side,  between  the  dura 
mater  anteriorly  and  the  lamina?  and  ligamenta  subflava  posteriorly.  They  are  plexiform 
vessels  which  extend  along  the  whole  length  of  the  spinal  canal.  They  receive  tributaries 
from  the  laminae,  ligaments,  and  spinal  membranes,  and  from  a  post-spinal  plexus  of  veins 
which  lies  between  the  laminae  of  the  vertebrae  and  the  deep  muscles  of  the  back ;  they 
anastomose  with  each  other  by  transverse  channels  which  pass  across  the  laminae,  with 
the  posterior  spinal  plexus  by  vessels  which  pierce  the  ligamenta  subflava,  and  with  the 
60  & 


888  THE  VASCULAE  SYSTEM. 

anterior  longitudinal  veins  round  the  margins  of  the  canal.  Their  efferent  vessels  unite 
with  those  of  the  anterior  longitudinal  veins,  and  terminate  with  them. 

By  means  of  the  longitudinal  spinal  veins  and  the  anastomoses  between  them,  a 
venous  ring  is  formed  within  the  spinal  canal  opposite  each  vertebra.  Commencing  in 
front,  opposite  the  body  of  the  vertebra,  where  it  receives  the  vena  basis  vertebra,  it  passes 
outwards  to  the  anterior  longitudinal  spinal  vein,  turns  backwards  along  the  inner  side 
of  the  pedicle  and  the  inner  surface  of  the  lamina  to  the  posterior  longitudinal  vein,  and 
is  completed  by  the  anastomoses  between  the  posterior  longitudinal  veins.  This  ring 
communicates  through  the  ligamenta  subflava  with  the  posterior  spinal  plexus,  and 
through  the  intervertebral  foramina  with  the  vertebral,  with  the  dorsal  tributaries  of  the 
intercostal  or  lumbar  veins,  or  with  the  lateral  sacral  veins,  according  to  the  region  in 
which  it  lies. 

Superiorly  the  posterior  longitudinal  spinal  veins  communicate  with  the  occipital 
sinuses,  and  as  these  also  communicate  with  the  anterior  spinal  veins,  and  the  latter  with 
the  basilar  sinus,  a  venous  ring  is  completed  round  the  foramen  magnum. 

Veins  of  the  Spinal  Cord. — The  veins  of  the  spinal  cord  issue  from  the 
substance  of  the  cord,  and  terminate  in  a  plexus  in  the  pia  mater.  In  this  plexus 
there  are  six  longitudinal  channels — one  antero-median,  along  the  anterior  fissure, 
two  antero -lateral,  immediately  behind  the  anterior  nerve  roots,  two  poster o-lateral, 
immediately  behind  the  posterior  nerve  roots,  and  one  postero-median,  over  the 
posterior  septum.  Eadicular  efferent  vessels  issue  from  the  plexus,  and  pass  along 
the  nerve  roots  to  communicate  with  the  efferent  vessels  from  the  anterior  and 
posterior  longitudinal  spinal  veins,  and  to  terminate  in  them.  The  veins  of  the 
spinal  cord  vary  very  much  in  size,  but  they  are  largest  on  the  lower  and  on  the 
posterior  portions  of  the  cord. 

The  postero-median  and  antero-median  veins  are  continued  above  into  the 
corresponding  veins  of  the  medulla  oblongata. 

The  antero-lateral  and  postero-lateral  veins  pour  their  blood  partly  into  the 
median  veins  and  partly  into  the  radicular  veins ;  indeed,  the  greater  part  of  the 
blood  from  the  spinal  cord  is  returned  by  the  latter  veins. 

THE  VEINS  OF  THE  UPPER  EXTREMITY. 

The  veins  of  each  upper  extremity  are  divisible  into  two  sets — viz.  superficial 
and  deep.  Both  sets  open  eventually  into  a  common  terminal  trunk  which  is 
known  as  the  axillary  vein.  This  vein  is  therefore  the  chief  efferent  stem  of  the 
upper  extremity.  It  is  continued  as  the  subclavian  vein  to  the  innominate  vein, 
and  its  blood,  together  with  that  of  the  corresponding  side  of  the  head  and  neck, 
reaches  the  superior  vena  cava. 

The  Deep  Veins  of  the  Upper  Extremity. 

The  deep  veins,  with  the  exception  of  the  axillary  vein,  are  arranged  in  pairs 
which  accompany  the  different  arteries  and  are  similarly  named.  So  far  as  these 
veins  (veute  comites)  are  concerned  it  will  be  sufficient  to  state  that  they  are  pro- 
vided with  valves,  that  they  are  situated  one  on  either  side  of  the  artery  with 
which  they  are  associated,  and  that  they  are  usually  united  together  by  numerous 
transverse  anastomoses  which  cross  in  front  of  or  behind  the  artery.  The  axillary 
vein,  however,  requires  more  detailed  consideration. 

The   Axillary  Vein. 

The  axillary  vein  (v.  axillaris,  Fig.  629)  commences  as  the  direct  continuation 
of  the  basilic  vein,  o[)posite  the  lower  border  of  the  teres  major.  It  passes  upwards 
and  inwards  through  the  axilla,  along  the  inner  side  of  the  corresponding  artery, 
and  terminates  at  tlie  outer  border  of  the  first  rib  by  becoming  the  subclavian 
vein.  It  possesses  a  bicuspid  valve  which  is  usually  situated  opposite  the  lower 
border  of  the  subscapularis  muscle. 

Relations. — Its  antei-ior  relations  are  similar  to  those  of  the  axillary  artery,  but,  in 
addition,  the  vein  is  crossed  in  front,  under  cover  of  the  clavicular  part  of  the  pectoralis 


THE  SUPEEFICIAL  VEINS  OF  THE  UPPEK  EXTREMITY.       889 


-Radial  veins 


Cominencenient 
of  median  vein 


major,  by  the  pectoral  branches  of  the  acromio-thoracic  artery,  and  by  branches  of  the 
internal  anterior  thoracic  nerve,  and  it  receives  in  front,  just  above  the  upper  border  of 
the  pectoralis  minor,  the  termination  of  the  cephalic  vein. 

Behind  it  are  the  muscles  which  form  the  posterior  wall  of  the  axilla,  the  axillary  fat, 
and  the  first  ser- 
ration of  the  serra- 
tus  magnus.  The 
long  thoracic  nerve 
intervenes  be- 
tween it  and  the 
serratus  magnus, 
and  the  subscapu- 
lar nerves  and  the 
subscapular  ai'tery 
pass  between  it  and 
the  subscapularis. 

It  is  separated 
from  the  axillary 
artery  on  the  outer 
side,  in  the  lower 
part  of  its  extent 
b)y  the  ulnar  and 
internal  cutaneous 
nerves,  in  the 
middle  of  its  course 
by  the  inner  cord 
of  the  brachial 
plexus,  and  in  the 
upper  part  of  the 
axilla,  behind  the 
costo  -  coracoid 
membrane,  by  the 
internal  anterior 
thoracic  nerve.  To 
its  inner  side  lie 
the  outer  set  of 
axillary  glands, 
and  in  the  lower 
part  of  the  axilla 
the  lesser  intei-nal 
■cutaneous  nerve. 

Tributaries. 
— In  addition  to 
tributaries  corre- 
sponding with  the 
branches  of  the 
axillary  artery,   it 

receives  the  venee  comites  of  the  brachial  artery,  at  tlie  lower  border  of  the  subscapularis, 
and  the  cephalic  vein,  which  joins  it  at  the  upper  border  of  the  small  pectoral  muscle. 

The   Superficial  Veins   of  the   Upper  Extremity. 

The  superficial  veins  of  the  upper  extremity  commence  in  the  superficial  fascia 
of  the  palm  and  dorsum  of  the  hand  and  of  the  fingers. 

The  superficial  veins  of  tne  palmar  aspects  of  the  fingers  terminate  for  the  most 
part  in  dorsal  digital  veins,  which  run  along  the  dorso-lateral  borders  of  the  digits ; 
some,  however,  pass  upwards  into  the  palm  and  join  the  superficial  palmar  veins, 
which,  in  comparison  with  the  superficial  dorsal  veins,  are  relatively  few  and  small. 
The  superficial  veins  of  the  palm  anastomose  together,  forming  a  more  or  less 
polygonal  plexus  from  which  some  efferent  vessels  pass  laterally  round  the  borders 
of  the  palm  to  the  dorsal  plexus  of  the  hand,  whilst  others  ascend  towards  the 
wrist,  where  they  end  either  in  the  median  or  the  anterior  ulnar  superficial  vems 
of  the  forearm. 


Fig.   652. —Superficial  Veins  ox  the  Dorsum  of  the  Hand  and  Digits. 


890 


THE  VASCULAE  SYSTEM. 


the  dorso-lateral  borders  of  the  dii^it. 


■'//// 


Cephalic  vein- 


Basilic  vein- 


Median  cephalic  vein- 
Median  basilic  vein- 
Median  vein- 
Deep  median  vein- 
Posterior  ulnar  vein- 
Radial  veins! 
Anterior  ulnar  vein- 


■^.. 


h. 


The  superficial  veins  on  the  dorsal  aspect  of  each  digit  form  two  longitudinal 
vessels,  the  dorsal  digital  veins  (vv.  digitales  dorsales  proprise),  which  ascend  along 

They  receive  tributaries  from  the  palmar 
aspect  of  the  digit,  from  the  pulp  of  the  tip, 
from  the  subungual  tissues,  and  from  the 
superficial  tissues  of  the  dorsum.  The 
dorsal  digital  veins,  which  run  along  the 
adjacent  borders  of  the  second,  third,  and 
fourth  interdigital  clefts,  unite,  at  the 
apices  of  the  clefts,  to  form  three  dorsal 
interosseous  or  interdigital  veins  (vv.  meta- 
carpse  dorsales),  which  terminate  on  the 
dorsum  of  the  hand  in  a  dorsal  venous 
arch  or  dorsal  venous  plexus ;  the  radial 
or  outer  vein  of  the  index-finger  ends  in 
the  same  arch. 

The  dorsal  venous  arch  of  the  hand 
receives  not  only  the  dorsal  interosseous  or 
interdigital  veins,  and  the  radial  digital 
vein  of  the  index-finger,  but  also  numerous 
tributaries  from  the  superficial  tissues  of 
the  dorsum  of  the  hand,  which  anastomose 
frequently  together  and  form  a  plexiform 
network.  The  arch  lies  opposite  the  lower 
parts  of  the  shafts  of  the  four  inner  meta- 
carpal bones,  and  terminates  at  its  radial 
end  in  the  superiicial  radial  vein,  and  at 
its  ulnar  end  in  the  posterior  or  dorsal 
ulnar  vein ;  the  dorsal  digital  veins  of  the 
thumb  open  into  the  superficial  radial  vein, 
and  the  innermost  or  ulnar  digital  vein  of 
the  little  finger  ends  in  the  posterior 
superficial  ulnar  vein. 

Superficial  Veins  of  the  Forearm. — 
There  are  four  main  superficial  venous 
trunks  in  the  forearm — viz.  the  median, 
the  radial,  and  the  anterior  and  posterior 
ulnar  veins. 

The  median  vein  (v.  mediana  cubiti) 
commences,  as  a  rule,  on  the  dorsal  aspect 
of  the  base  of  the  thumb  by  the  union  of 
a  number  of  efferents  from  the  dorsal 
plexus ;  it  turns  round  the  radial  border 
of  the  forearm,  receives  numerous  tri- 
butaries from  the  radial  and  median 
portions  of  the  palm,  and  ascends  to  the 
middle  of  the  bend  of  the  elbow,  where 
it  is  joined  by  the  deef  median  vein,  a 
large  anastomosing  channel  which  connects 
it  with  the  deep  veins,  and  immediately 
afterwards  terminates  by  dividing  into 
median  cephalic  and  median  basilic 
branches. 

The  median  cephalic  (v.  mediana 
cephalica),  or  outer  branch  of  the  median 
vein,  runs  upwards  and  outwards  in  the  groove  between  the  biceps  and  the 
supinator  longus  muscles.  It  crosses  the  musculo-cutaneous  nerve  superficially, 
and  terminates,  a  short  distance  above  the  external  condyle,  by  uniting  with  the 
radial  vein  to  form  the  cephalic  vein. 


Palmar  plexus- 


.~^< 


Fig. 


653. — SuPEHKiciAL  Vkixs  ox  the  Flkxou 
Aspect  of  the  Upper  Extremity. 


THE  SUPEEFICIAL  VEINS  OF  THE  UPPER  EXTREMITY.       891 


Bracliiali 


Bieei 


Cephalic  veil 


Radial 
recunent  artery 

Musculo- 

cutaii'^ous  nerve 


The  median  basilic  vein  (v.  mediaua  l)asilica)  is  the  inner  branch  of  the 
median  vein.  Running  more  transversely  than  the  median  cephalic  vein,  it  passes 
upwards  and  inwards  along  the  groove  between  the  l»iceps  and  the  pronator  radii  teres. 
It  is  crossed  superficially  by  the  anterior  terminal  brand i  of  the  internal  cutaneous 
nerve;  it  lies  upon  the  bicipital  fascia,  which  separates  it  from  the  brachial  artery, 
and  it  terminates  by  uniting  witli  the  anterior  and  posterior  ulnar  veins  to  form 
the  basilic  vein. 

The  radial  vein  (v.  radialis)  commences  in  the  dorsal  venous  plexus  of  the 
hand,  and,  after  receiA-ing  some  of  the  dorsal  digital  veins  of  the  thumb,  runs  up 
the  radial  border  of  the  forearm  in  relation  with  the  anterior  division  of  the  musculo- 
cutaneous nerve.  It  receives  tributaries  from  the  subcutaneous  tissue  through 
which  it  passes,  and 
terminates  at  the  outer 
side  of  the  bend  of  the 
elbow  by  imiting  with 
the  median  cephalic 
branch  of  the  median 
vein  to  form  the  cephalic 
vein.  It  contains  several 
valves. 

The  anterior  and 
posterior  ulnar  veins 
(vv.  ulnares)  vary  con- 
sidera])ly  in  size,  but  as 
a  rule  the  posterior  is 
the  larger.  Both  are 
provided  with  valves. 

The  anterior  ulnar 
vein  commences  at  the 
base  of  the  little  finger, 
by  the  union  of  tribu- 
taries from  the  ulnar 
part  of  the  dorsal  venous 
plexus  and  from  the 
ulnar  side  of  the  palm  ; 
it  ascends  along  the 
front  of  the  ulnar  side 
of  the  forearm,  and  it 
terminates  in  the  basilic 
branch  of  the  median 
vein. 

The  posterior  ulnar 
vein  commences  in  the 
dorsal  venous  plexus ; 
it  receives  the  ulnar 
dorsal  digital  vein  of  the  little  finger,  and  ascends  along  the  dorsal  side  of  the 
ulnar  aspect  of  the  forearm.  It  terminates  by  joining  the  basilic  brancli  of  the 
median  vein  to  form  the  basilic  vein. 

Superficial  Veins  of  the  Upper  Arm.— Only  two  large  superficial  trunks,  the 
basilic  and  the  cephalic,  are  found  in  the  upper  arm. 

The  basilic  vein  (v.  basilica)  commences  at  the  upper  and  inner  part  of  the 
bend  of  the  elbow  by  the  union  of  the  median  basilic  with  the  posterior  ulnar  vein. 
It  ascends  in  a  groove  along  the  inner  border  of  the  biceps  to  the  middle  of  the 
upper  arm,  where  it  passes  through  an  opening  in  the  deep  fascia,  the  hiatus 
semilunaris,  and  in  the  rest  of  its  course  lies  deeply  along  the  inner  side  of  the 
brachial  artery.  It  terminates  at  the  lower  border  of  the  teres  major  by  becoming 
the  axillarv  vein,  and  it  contains  one  or  more  bicuspid  valves. 

The  cephalic  vein  (v.  cephalica)  is  formed  at  the  upper  and  outer  part  of  the 
bend  of  the  elbow  bv  the  union  of  the  radial  vein  with  the  cephalic  branch  of  the 


•iliaii  cephalic 
vein 


Brachio  radialis 
muscle 


Radial  arterj- 


Median  vein' 


Radial  vein 


Basilic  vein 


Internal 

cutaneous 

nerve 

_Posterior 
ulnar  vein 

Median  nerve 

Bi-achialis 
anticus  muscle 
Brachial 
artery 

Median  basilic 
vein 

Bicipital  fascia 


Anterior  ulnar 
vein 

L'lnar  artery 

Deep  median 
Vfin 


Pronator  radii 
teres  muscle 


Fig.  6f>4.— Superficial  Veins  at  the  Bexd  ok  the  Elbow. 


892  THE  VASCULAK  SYSTEM. 

median  vein.  It  ascends  first  along  the  outer  border  of  the  biceps,  where  it  is 
accompanied  by  the  superior  external  cutaneous  branch  of  the  musculo-spiral  nerve  ; 
then,  after  piercing  the  deep  fascia,  it  is  continued  upwards  between  the  adjacent 
borders  of  the  deltoid  and  pectoralis  major  muscles,  accompanied  by  the  descending 
or  humeral  branch  of  the  acromio-thoracic  axis.  Just  below  the  clavicle  it  turns 
inwards,  crosses  the  pectoralis  minor,  pierces  the  costo  -  coracoid  membrane,  and 
terminates  in  the  upper  or  third  part  of  the  axillary  vein.  It  is  provided  with  a 
bicuspid  valve  at  its  termination.  In  its  primitive  form  it  terminated  in  the 
external  jugular  vein,  to  reach  which  it  passed  either  over  or  through  the  clavicle. 
This  condition  occasionally  persists,  or  is  represented  by  a  small  communicating 
vein. 

THE  INFERIOR  VENA  CAVA  AND  ITS  TRIBUTARIES. 

The  inferior  vena  cava  (Fig.  655)  is  a  large  venous  trunk  which  receives  the 
whole  of  the  blood  from  the  lower  extremities,  and  the  greater  part  of  the  blood 
from  the  walls  and  contents  of  the  abdomen  and  pelvis.  It  commences  opposite 
the  right  side  of  the  body  of  the  fifth  lumbar  vertebra,  behind  and  to  the  right  of 
the  right  common  iliac  artery,  ascends  through  the  abdomen  in  front  and  to  the 
right  of  the  vertebral  column  and  the  right  crus  of  the  diaphragm,  and  pierces 
the  cupola  of  the  diaphragm,  between  the  middle  and  right  sections  of  the  central 
tendinous  leaflet,  at  the  level  of  the  eighth  dorsal  vertebra.  It  then  pierces  the 
fibrous  pericardium,  enters  the  middle  mediastinum,  and  terminates  in  the  lower 
and  back  part  of  the  right  auricle.  Its  intrapericardial  portion  is  very  short,  and 
it  is  covered  on  its  anterior  and  lateral  aspects  by  the  parietal  portion  of  the 
serous  layer.  Attached  to  the  lower  and  front  margin  of  its  auricular  orifice  is 
the  Eustachian  valve,  which  is  a  remnant  of  an  important  fold  of  endocardium  by 
which,  in  the  foetus,  the  blood  from  the  inferior  vena  cava  is  directed,  through  the 
foramen  ovale,  into  the  left  auricle. 

Relations.  —  The  inferior  vena  cava  is  in  relation  behind  with  the  bodies  of  the 
lower  kimbar  vertebrte  and  the  corresponding  part  of  the  anterior  common  ligament,  the 
anterior  portion  of  the  right  psoas  muscle,  the  right  himbar  sympathetic  cord,  the  I'oots 
of  the  right  lumbar  arteries,  the  right  crus  of  the  diaphragm,  the  right  renal  artery,  the 
right  semilunar  ganglion,  the  right  inferior  phi-enic  artery,  and  the  inner  and  upper 
portion  of  the  right  suprarenal  body. 

In  front  of  it,  from  below  upwards,  are  the  following  structures — tlie  right  common 
iliac  arteiy,  the  lower  end  of  the  mesentery  and  the  superior  mesenteric  artery,  the  right 
spermatic  artery  and  the  third  part  of  the  duodenum,  the  head  of  the  pancreas,  the 
portal  vein  and  the  first  part  of  the  duodenum,  the  foramen  of  Winslow,  and  the  posterior 
surface  of  the  liver.  More  superficially  are  coils  of  small  intestine,  the  great  omentum, 
and  the  ti'ansverse  colon  and  mesocolon. 

To  its  left  side  are  the  aorta  and  the  right  crus  of  the  diaphragm. 

On  its  right  side  and  below  is  the  right  ureter,  whilst  at  a  higher  level  tha  right 
kidney  is  only  sepai'ated  from  it  by  a  short  interval. 

Tributaries. — In  addition  to  the  two  common  iliac  veins,  by  the  union  of  wliich  it  is 
formed,  and  through  which  it  receives  blood  from  the  pelvis  and  from  the  lower  extremi- 
ties, the  inferior  vena  cava  receives  tlie  following  tributaries : — The  hepatic  veins,  the 
right  inferior  phrenic  vein,  the  right  suprarenal  vein,  the  right  and  left  renal  veins,  the 
right  spermatic  or  ovarian  vein,  and  the  right  and  left  lumbar  veins. 

Hepatic  Veins  (vv.  hepaticse.  Fig.  655). — These  veins  convey  blood  which  has 
passed  through  the  liver  from  the  portal  veins  and  from  the  hepatic  artery,  and 
they  open  into  that  portion  of  the  inferior  vena  cava  wdiich  lies  immediately  below 
the  diaphragm,  and  behind  the  right  lobe  of  the  liver.  They  form  two  groups,  an 
upper  group  of  two  or  three  large  trunks,  and  a  lower  group  of  smaller  veins. 

The  upper  group  occasionally  consists  of  only  two  veins,  a  right  and  a  left ; 
more  frequently  there  are  three  vessels,  a  right,  a  left,  and  a  middle  vein,  and  in 
the  latter  case  the  middle  vein  issues  from  the  Spigelian  lobe. 

The  veins  of  the  lower  group  vary  in  number  from  six  or  seven  to  twenty ; 
they  return  blood  from  the  right  and  Spigelian  lobes. 

The  hepatic  veins  commence  in   the  interior  of  the  lobules  of  the  liver  as 


THE  INFEEIOE  VENA  CAVA  AND  ITS  TEIBUTAEIES. 


893 


intralobular  veins ;  these  issue  from  the  upper  and  posterior  aspects  of  the  lobules, 
and  unite  together  to  form  suUolndar  veins;  and  the  latter,  uniting  with  one 
another  as  they  converge  towards  the  posterior  surface  of  the  liver,  form  the  larger 
hepatic  veins. 

Inferior  Phrenic  Veins  (vv.  phrenicic  inferiores). — The  ven»  comites  of  the 
inferior  phrenic  arteries  are  formed  by  tributaries  which  issue  from  the  substance 


H'^li'itic  veil 


Infpi-inr  phrenic  arterj 

Suprarenal  boflj 
Inferior  vena  cava 

Renal  ai-tery 
Renal  vein 

Right  ovarian  vein 

Ovarian  arter^ 

Ureter 

Psoas  nmsole 

Ascentling  colon 

Common  iliac  vein 

Common  iliac  artery 

Middle  sacral  arteij 

Ileum 

C-vcum 


External  ilnc     K\r\ 
a  rtei \ 
External  iliac 
vein 


Urachus 


(EsojiliaKus 


Cms  of  diaphragm 

Inferior  phrenic 
artery 

Suprarenal  body 
Cteliac  axis 
Suprarenal  vein 
Sujierior 
mesenteric  artery 

Kerial  artery 
Ri  nal  vein 
Lumbar  arteries 

Ureter 

Left  colic  artery 

Ovarian  artery 
Inferior  mesenteric 
ai  tery 
-  Descending  colon 

Psoas  muscle 
Common  iliac  artery 

-  Sigmoid  artery 

-  Conniirm  iliac  vein 
iSnperiiir  liiemor- 
rlioidal  artery 

~  Iliac  colon 

-  Pelvic  colon 

_  External  iliac 
aitery 

External  iliac  vein 
I'allopiaii  tube 


Fig.  655. — The  Inferior  Vena  Cava  and  its  Tributaries. 

of  the  diaphragm.  The  right  vein  terminates  in  the  upper  part  of  the  inferior 
vena  cava.  Tiie  left  veins  pass  behind  the  oesophagus,  and  usually  end  in  the  left 
suprarenal  vein. 

Suprarenal  Veins. — A  single  suprarenal  vein  (v.  suprarenalis)  issues  from  the 
hilum  on  the  anterior  surface  of  each  suprarenal  body  ;  the  right  vein  terminates  in 
the  inferior  vena  cava;  the  left  usually  ends  in  the  left  renal  vein,  but  sometimes 
it  opens  directly  into  the  inferior  vena  cava. 

Renal  Veins  (vv.  renales). — Each  renal  vein  is  formed  ])y  the  union  of  five  or 
six  tributaries  which  issue  from  the  hilum  of  the  kidney,  where  they  lie  in  front  of 
the  corresponding  arteries. 


894  THE  VASCULAE  SYSTEM. 

The  right  renal  vein  is  about  one  inch  long ;  it  passes  behind  the  second  part  of 
the  duodeuiini,  and  terminates  in  the  right  side  of  the  inferior  vena  cava. 

The  left  renal  vein  crosses  in  front  of  the  left  psoas,  the  left  crus  of  the  diaphragm, 
and  the  aorta  immediately  below  the  superior  mesenteric  artery.  It  lies  behind 
the  pancreas  and  the  fourth  part  of  the  duodenum,  and,  running  above  the  third 
part  of  the  duodenum,  terminates  in  the  left  side  of  the  inferior  vena  cava.  The 
left  spermatic  or  ovarian  vein,  according  to  the  sex,  and  almost  invariably  the  left 
suprarenal  vein,  open  into  it. 

Lumbar  Veins  (vv.  lumbales). — There  are  usually  four  lumbar  veins  on  each 
side,  one  with  each  lumbar  artery;  the  vein  with  the  subcostal  artery  is  not 
included  in  this  number.  The  lumbar  veins  are  formed  by  the  union  of  anterior 
and  posterior  trunks  between  the  transverse  processes  of  the  vertebrpe.  The 
anterior  tributaries  commence  in  the  lateral  walls  of  the  abdominal  cavity,  where 
they  communicate  with  the  superior  and  deep  epigastric  veins.  The  posterior 
tributaries  issue  from  the  muscles  of  the  back  in  the  lumbar  region,  and  receive 
tributaries  from  the  spinal  plexuses.  The  main  stems  pass  forwards  on  the  bodies 
of  the  vertebrae ;  on  each  side  they  run  behind  and  to  the  inner  side  of  the  psoas 
muscle,  whilst  those  of  the  left  side  also  pass  behind  the  aorta.  They  terminate  in 
the  posterior  part  of  the  inferior  vena  cava.  Not  uncommonly  the  corresponding 
veins  of  opposite  sides  unite  together  to  form  a  single  trunk  which  enters  the  back 
of  the  inferior  vena  cava.  All  the  lumbar  veins  of  each  side  are  united  together 
by  a  longitudinal  anastomosing  vessel,  the  ascending  lumbar  vein,  which  passes 
upwards  in  front  of  the  transverse  processes  of  the  lumbar  vertebrae,  and  usually 
ends  above  in  an  azygos  vein,  whilst  below  it  connects  the  lumbar  veins  with  the 
ilio-lumbar  and  lateral  sacral  veins. 

Spermatic  Veins  (vv.  spermaticae). — The  spermatic  veins  on  each  side  issue 
from  the  testicle  and  epididymis  and  form  a  plexus,  the  ]_'>ctmpiniform  ijlexus.  The 
plexus  forms  part  of  the  spermatic  cord,  and  consists  of  from  eight  to  ten  veins, 
most  of  which  lie  in  front  of  the  vas  deferens ;  it  passes  upwards  in  the  inguinal 
canal,  and,  near  the  internal  abdominal  ring,  terminates  in  two  main  trunks  which 
ascend  with  the  corresponding  spermatic  artery  for  some  distance,  receiving 
tributaries  from  the  ureter,  and,  occasionally,  on  the  left  side  from  the  iliac  and 
pelvic  colon ;  ultimately  the  two  veins  unite  together  and  a  single  terminal  vein  is 
formed.  The  terminal  spermatic  vein  on  the  right  side  opens  into  the  inferior 
vena  cava,  that  on  the  left  side  into  the  left  renal  vein.  The  left  spermatic  veins 
are  longer  than  the  right,  the  left  testicle  being  lower  than  the  right,  and  the 
termination  in  the  left  renal  vein  being  at  a  higher  level  than  the  termination  of 
the  right  vein  in  the  inferior  vena  cava.  The  spermatic  veins  on  each  side  lie 
upon  the  psoas  muscle  and  the  ureter.  They  are  covered  by  peritoneum,  and  they 
are  crossed  on  the  right  side  by  the  termination  of  the  ileum  and  the  third  part  of 
the  duodenum,  and  on  the  left  side  by  the  iliac  colon.  They  are  provided  with 
valves  both  in  their  course  and  at  their  terminations,  but  occasionally  the  A^alve  at 
the  orifice  of  the  left  spermatic  vein  is  absent. 

The  ovarian  veins  (vv.  ovaricae),  on  each  side,  issue  from  the  hilum  on  the 
anterior  border  of  the  ovary.  They  pass  between  the  layers  of  the  broad  ligament, 
where  they  anastomose  freely  and  form  the  iiawpiniform  'plexus,,  which  extends 
outwards  towards  the  brim  of  the  pelvis.  From  tlie  plexus  two  veins  are  formed 
which  accompany  the  corresponding  ovarian  artery;  they  pass  in  front  of  the  external 
iliac  artery,  and  then  upwards  behind  the  peritoneum  and  in  front  of  the  psoas 
muscle  and  ureter.  The  veins  of  the  right  side,  like  the  corresponding  spermatic 
veins,  also  pass  behind  the  termination  of  the  ileum  and  the  third  part  of  the 
duodenum;  whilst  the  left  veins,  near  the  brim  of  the  pelvis,  pass  behind  the 
commencement  of  the  pelvic  colon. 

The  two  veins  on  each  side  ultimately  fuse  together  to  form  a  single  terminal 
vein  which  ends,  on  the  right  side  in  the  inferior  vena  cava,  and  on  the  left  side  in 
the  left  renal  vein.  As  the  left  ovarian  veins  ascend  on  the  psoas  they  sometimes 
receive  tributaries  from  the  iliac  and  yjelvic  colon. 


THE  ILIAC  VEINS.  ,  895 

The  Iliac  Veins. 

The  common  iliac  veins  (Figs.  640  and  655),  right  and  left,  are  formed  by  the 
union  of  the  corresponding  external  and  internal  iliac  veins.  Each  commences 
opposite  the  brim  of  the  pelvis,  immediately  behind  the  upper  part  of  the  internal 
iliac  artery  of  its  own  side,  and  both  vessels  pass  upwards  to  the  right  side  of  the 
body  of  the  fifth  lumbar  vertebra,  at  the  upper  part  of  which,  just  behind  and  to 
the  outer  side  of  the  right  common  iliac  artery,  they  unite  together  to  form  the 
inferior  vena  cava. 

The  right  common  iliac  vein  (v.  iliaca  communis  dextra)  is  much  shorter  than 
the  left ;  it  passes  in  front  of  the  obturator  nerve  and  the  ilio-lumbar  artery,  and 
at  first  behind  and  then  somewhat  to  the  outer  side  of  the  corresponding  common 
iliac'  artery. 

The  left  common  iliac  vein  (v.  iliaca  communis  sinistra)  is  much  longer  than 
the  right,  and  is  also  placed  more  obliquely.  It  passes  upwards  and  to  the  right,  in 
front  of  the  body  of  the  fifth  lumbar  vertebra,  and  across  the  middle  sacral  artery. 
For  some  distance  it  runs  along  the  inner  side  of  the  left  common  iliac  artery,  and 
then  passes  behind  the  right  common  iliac  artery.  It  also  passes  behind  the 
mesentery  of  the  pelvic  colon  and  the  superior  h?emorrhoidal  artery. 

Tributaries. — Each  common  iliac  vein  receives  the  corresponding  external  and 
internal  iliac  veins  and  the  ilio-lumbar  veins.  The  left  common  iliac  vein  receives  in 
addition  the  middle  sacral  vein. 

The  ilio-lumbar  veins  (v\^  ilio-lumbales)  receive  tributaries  fx-om  the  iliac  fossa,  from 
the  lower  jDarts  of  the  spinal  muscles,  and  from  the  spinal  canal.  There  is  a  single  vein 
on  each  side  which  accompanies  the  corresponding  artery.  It  passes  behind  the  psoas 
muscle  and  terminates  in  the  common  iliac  vein. 

Middle  Sacral  Veins. — -The  vente  comites  of  the  middle  sacral  artery  commence  by 
the  union  of  tributaries  which  issue  from  the  venous  plexus  in  front  of  the  sacrum, 
through  which  they  communicate  with  the  lateral  sacral  veins  and  receive  blood  from  the 
sacral  part  of  the  spinal  canal.  They  unite  above  into  a  single  stem  (v.  sacralis  media), 
which  terminates  in  the  left  common  iliac  vein. 

The  internal  iliac  vein  (v.  hypogastrica,  Fig.  640)  is  a  short  trunk  formed 
by  the  union  of  tributaries  which  correspond  to  all  the  branches  of  the  internal 
iliac  artery,  with  the  exception  of  the  hypogastric  or  umbilical  and  the  iKo-lumbar 
branches. 

It  commences  at  the  upper  border  of  the  great  sciatic  notch,  and  ascends  to  the 
brim  of  the  pelvis,  where  it  unites  with  the  external  iliac  vein  to  form  the  common 
iliac  vein.  It  lies  immediately  behind  and  slightly  to  the  inner  side  of  the  internal 
iUac  artery,  is  crossed  externally  by  the  obturator  nerve,  and  is  in  relation  internally, 
on  the  left  side  with  the  pelvic  colon,  and  on  the  right  side  with  the  lower  part  of 
the  ileum. 

Tributaries, — The  tributaries,  which  are  numerous,  are  conveniently  divisible  into 
extra-pelvic  and  intra-pelvic  groups. 

The  extra-pelvic  tributaries  are  all  parietal,  and  include  the  obturator,  internal  pudic, 
sciatic,  and  gluteal  veins. 

Obturator  Vein  (v.  obturatoria). — This  vein  is  formed  by  the  union  of  tributaries 
which  issue  from  the  hip-joint  and  from  the  muscles  on  the  upper  and  inner  part  of  the 
thigh.  It  enters  the  pelvis  through  the  obturator  foramen,  runs  backwards  along  the 
lateral  wall  lying  on  the  pelvic  fascia  immediately  below  the  corresponding  artery,  and, 
passing  between  the  internal  iliac  artery  on  the  outside  and  the  ureter  on  the  inside, 
terminates  in  the  internal  iliac  vein. 

Sciatic  Veins  (vv.  glutaefe  inferiores). — The  venae  comites  of  the  sciatic  artery  com- 
mence in  the  subcutaneous  tissues  on  the  back  of  the  thigh ;  they  ascend  with  the  sciatic 
artery,  and  pass  deeply  into  the  buttock  beneath  the  gluteus  maximus,  where  they  receive 
numerous  tributaries  from  the  surrounding  muscles.  Entering  the  pelvis  through  the 
great  sciatic  foramen,  they  unite  into  a  single  vessel,  which  terminates  in  the  lower  and 
anterior  part  of  the  internal  iliac  vein  below  the  termination  of  the  obturator  vein. 

Gluteal  Veins  (w.  glutaete  superiores). — The  vente  comites  of  the  gluteal  artery  are 
formed  by  tributaries  which  issue  from  the  muscles  of  the  buttock.     They  accompany 


896  THE  VASCULAK  SYSTEM. 

the  artery  through  the  great  sciatic  foramen,  and  terminate  in  the  internal  ihac  vein ; 
the}'  frequently  unite  together  before  reaching  their  termination. 

Internal  Pudic  Veins. — The  vense  comites  of  the  internal  pudic  artery  commence  by 
tributaries  Avhich  emerge  from  the  corpus  cavernosum  of  the  penis  (vv.  profimdee  penis) 
or  clitoris  (vv.  profundtc  clitoridis).  They  follow  the  course  of  the  internal  pudic  artery, 
and  usually  join  together  into  a  single  vessel  (v.  pudenda  interna)  which  terminates  in 
the  internal  iliac  vein.  As  tributaries  they  receive  the  veins  from  the  bulb,  the  superficial 
perineal  and  infeiior  htemorrhoidal  veins  (vv.  hsemorrhoidales  inferiores),  and  veins  from 
the  muscles  of  the  buttock. 

The  inferior  hsemorrhoidal  veins,  which  commence  in  the  substance  of  the  external 
sphincter  of  the  anus  and  in  the  walls  of  the  anal  canal,  anastomose  with  the  middle  and 
superior  hpemoiThoidal  veins,  and  consequently  connect  the  portal  and  vena  caval  systems 
together. 

The  intra-jyelvic  tribxitaries  of  the  internal  iliac  vein  are  either  (a)  parietal  or 
(6)  visceral ;  the  former  comprises  the  lateral  sacral  veins,  the  latter  includes  the 
efferent  vessels  from  the  plexuses  around  the  several  pelvic  viscera. 

(a)  Parietal :  Lateral  sacral  veins  (vv.  sacrales  laterales)  accompany  the  corre- 
sponding arteries,  and  terminate  on  each  side  in  the  inner  and  back  part  of  the  internal 
iliac  vein. 

ijj)  Visceral  tributaries  are  derived  from  the  rectum  and  from  the  plexuses  associated 
with  the  uterus,  vagina,  bladder,  and  prostate.  They  include  the  middle  haemorrhoidal, 
the  uterine,  the  vaginal,  and  the  vesical  veins. 

The  middle  hsemorrhoidal  veins  (vv.  hsemorrhoidales  mediales)  are  very  irregular ; 
sometimes  they  cannot  be  distinguished.  When  present  they  are  formed  by  tributaries 
which  commence  in  the  submucous  tissue  of  the  rectum,  where  they  communicate  with 
the  superior  and  inferior  hemorrhoidal  veins ;  they  pass  through  the  muscular  coat, 
and  fuse  together  to  form  two  middle  haemorrhoidal  veins,  right  and  left,  each  of  which 
runs  outwards  beneath  the  peritoneum,  on  the  vipper  surface  of  the  levator  ani,  to 
terminate  in  the  internal  iliac  vein.  In  the  male  each  middle  haemorrhoidal  vein  receives 
tributaries  from  the  seminal  vesicle  and  vas  deferens  of  its  own  side. 

Uterine  Plexuses  and  Veins. — ^The  uterine  plexuses  lie  along  the  lateral  borders 
of  the  uterus ;  they  receive  tributaries,  which  are  entirely  devoid  of  valves,  from  the 
uterus,  and  they  communicate  above  with  the  ovarian,  and  below  with  the  vaginal 
plexuses. 

The  uterine  veins  (vv.  uterina^),  usually  two  on  each  side,  issue  from  the  lower  parts 
of  the  utei'ine  plexuses  above  their  communications  with  the  vaginal  plexuses.  At  first 
the  uterine  veins  on  each  side  lie  in  the  inner  part  of  the  base  of  the  broad  ligament 
above  the  lateral  fornix  of  the  vagina  and  the  ureter ;  they  then  pass  backwards,  accom- 
panying the  corresponding  ai'tery,  in  a  fold  of  peritoneum  which  lies  between  the  back 
of  the  broad  ligament  and  the  recto-uterine  fold ;  finally  they  ascend  in  the  floor  of  the 
ovarian  fossa,  and  terminate  in  the  internal  iliac  vein. 

Vaginal  Plexuses  and  Vaginal  Veins. — The  vaginal  plexuses  lie  at  the  sides 
of  the  vagina.  They  receive  tributaries  from  the  walls  of  the  vagina,  and  communicate 
above  with  the  uterine  plexuses,  below  with  the  veins  of  the  bulb,  in  front  with  the 
vesical  plexus,  and  behind  with  the  veins  which  issue  fi^om  the  middle  and  lower  parts  of. 
the  hajmon-hoidal  plexus.  A  single  vaginal  vein  issues  from  the  upper  part  of  the 
vaginal  plexus  on  each  side ;  it  accompanies  the  corresponding  arteries,  and  terminates 
in  the  internal  iliac  vein. 

Superior  Vesical  Plexus. — The  superior  vesical  plexus  of  veins  lies  on  the  outer 
surface  of  the  muscular  coat  of  the  bladder  at  the  fundus  and  the  sides.  It  receives 
tributaries  from  the  mucous  and  muscular  walls,  and  its  efferent  vessels  terminate  in  the 
prostatico-vesical  jjlexus  in  the  male,  and  in  the  inferior  vesical  plexus  in  the  female. 

Prostatico-vesical  Plexus. — This  plexus  is  distributed  round  the  prostate  and  the 
neck  of  the  bladder,  and  is  enclosed  between  the  proper  fibrous  capsule  of  the  prostate 
and  its  sheath  of  recto-vesical  fascia.  In  front  it  receives  the  dorsal  vein  of  the  penis, 
which  usually  terminates  by  two  branches  ;  behind  and  above  it  communicates  with  the 
superior  vesical  plexus,  and  receives  tributaries  from  the  seminal  vesicles  and  vasa  deferentia. 
One  or  more  efferent  vessels  pass  from  it  on  each  side  and  open  into  the  corresponding 
internal  iliac  vein. 

Tlie  inferior  vesical  plexus  of  the  female,  which  represents  the  prostatico-vesical 
plexus  of  the  male,  surrounds  the  upper  part  of  the  uretlira  and  the  neck  of  the  bladder. 
It  receives  the  dorsal  vein  of  the  clitoris,  and  its  efferent  vessels  terminate  in  the  internal 
iliac  vein. 


THE  DEEP  VEINS  OE  THE  LOWER  EXTREMITY.  897 

Dorsal  Veins  of  the  Penis  (w.  dorsales  peuis). — There  are  two  dorsal  veins  of 
the  penis — the  supertieial  and  the  deep. 

The  superficial  dorsal  vein  receives  tributaries  from  the  prepuce,  and  runs  backwards 
immediately  beneath  tlie  skin  to  the  symphysis,  where  it  divides  into  two  branches  which 
terminate  in  the  superficial  external  pudic  veins. 

The  deep  dorsal  vein  lies  on  the  dorsum  of  the  penis  beneath  the  deep  fascia.  It 
commences  in  the  sulcus  behind  the  glans,  by  the  union  of  numerous  tributaries  from 
the  glans  and  the  anterior  parts  of  the  corpora  cavernosa,  and  runs  backwards  in  the  mid- 
dorsal  line,  in  the  sulcus  between  the  corpora  cavernosa  from  which  it  receives  many 
additional  tributaries.  At  the  root  of  the  penis  the  vein  passes  between  the  two  layers  of 
the  suspensory  ligament,  and  then  between  the  sub-pubic  ligament  and  the  deep  transverse 
ligament  of  the  perineum,  thus  reaching  the  space  between  the  two  layers  of  the  triangular 
ligament,  where  it  lies  above  the  membranous  part  of  the  urethra,  and  is  enclosed  in 
some  of  the  fibres  of  the  compressor  urethne.  Passing  through  the  posterior  layer  of  the 
triangular  ligament,  it  enters  the  pelvis,  and  terminates,  usually  by  two  branches,  in  the 
prostatico-vesical  plexus. 

The  dorsal  vein  of  the  clitoris  in  the  female  has  a  similar  course  to  that  of  the  deep 
dorsal  vein  of  the  penis  in  the  male.     It  terminates  in  tlie  inferior  vesical  plexus. 

THE  VEINS  OF  THE  LOWER  EXTREMITY. 

The  veins  of  the  lower  extremity,  like  those  of  the  upper  extremity,  are  arranged 
in  two  groups,  the  superficial  and  the  deep,  and  in  the  lower  as  in  the  upper  limb 
the  deep  veins  are  associated  with  the  arteries  as  venae  comites,  whilst  the  super- 
ficial veins  which  lie  in  the  subcutaneous  tissues  ultimately  terminate  in  the  deep 
veins.  There  is,  therefore,  a  general  similarity  in  the  arrangement  of  the  veins  of 
the  upper  and  the  lower  limbs,  but  there  are  differences  in  the  details  of  the  arrange- 
ment which  are  of  some  importance.  Thus,  in  the  upper  extremity,  there  are  two 
deep  veins  with  each  artery  from  the  fingers  to  the  root  of  the  limb,  w^here  a  single 
trunk,  the  axillary  vein,  is  formed ;  but  in  the  lower  extremity  each  main  artery 
has  two  venpe  comites  only  as  far  as  the  middle  of  the  limb,  where  a  single  trunk 
is  formed.  This  vessel,  the  popliteal  vein,  is  the  commencement  of  the  main  venous 
stem  of  the  lower  extremity ;  it  is  continued  upwards  through  the  thigh  as  the 
femoral  vein,  and  along  the  brim  of  the  pelvis  as  the  external  iliac  vein,  which 
terminates  by  uniting  with  the  internal  iliac  vein  to  form  the  common  iliac  vein. 

Further,  the  superficial  veins  of  the  upper  hmb  are  more  numerous  than  those 
of  the  lower  limb,  for  in  the  forearm  there  are  four  main  superficial  veins,  and  in 
the  leg  two ;  in  the  arm  two  main  superficial  veins,  and  in  the  thigh  only  one. 

In  the  upper  limb  the  blood  which  passes  through  the  superficial  veins  is  poured 
into  the  efferent  trunk  vein  at  the  root  of  the  limb — that  is,  into  the  axillary  vein  ; 
but  in  the  lower  limb  the  blood  from  the  superficies  of  the  outer  parts  of  the  leg 
and  foot  passes  into  the  commencement  of  the  main  efferent  vein,  the  popliteal 
vein,  at  the  middle  of  the  limb — that  is,  in  the  region  of  the  knee,  whilst  the 
blood  from  the  superficial  parts  of  the  inner  aspect  of  the  lower  limb  is  poured  into 
the  femoral  vein  near  the  root  of  the  limb  in  the  upper  part  of  Scarpa's  triangle. 

In  addition  to  the  above-mentioned  differences  in  the  general  arrangement  of  the 
veins  of  the  upper  and  the  lower  extremities,  it  must  also  be  noted  that  in  the  upper 
extremity  all  the  blood  of  the  Hmb,  both  that  from  the  shoulder-girdle  region  as 
well  as  that  from  the  projecting  portion  of  the  limb,  is  returned  to  the  main 
efferent  venous  trunk  ;  but  in  the  lower  extremity  the  greater  part  of  the  blood  from 
the  region  of  the  pelvic  girdle,  and  a  considerable  portion  from  that  of  the  thigh,  is 
returned  by  the  gluteal,  obturator,  sciatic,  and  pudic  veins  to  the  internal  ihac 
vein,  which  in  the  adult  is  not  the  main  efferent  vein  of  the  lower  extremity. 

The  Deep  Veins  of  the  Lower  Extremity. 

All  the  arteries  of  the  lower  limb  except  the  popliteal  and  femoral  trunks  are 
accompanied  by  two   venm  comites.     They  usually  lie  one  on  each  side  of  the 
artery ;  they  are  connected  with  each  other  by  transverse  channels  wdiich  pass 
in  front  of  or  behind  the  artery,  and  they  are  provided  with  numerous  valves. 
61 


898 


THE  VASCULAE  SYSTEM. 


The  popliteal  vein  (v.  poplitea,  Fig.  643)  is  formed,  at  the  lower  border  of  the 
popliteus  muscle,  by  the  union  of  the  vense  comites  of  the  anterior  and  posterior 
tibial  arteries.  At  its  commencement  it  lies  to  the  inner  side  of  and  somewhat 
superficial  to  the  popliteal  artery,  and  to  the  outer  side  of  the  internal  popliteal 
nerve.  As  it  ascends  through  the  popliteal  space  it  gradually  inclines  towards  the 
outer  side  of  the  artery,  and  in  the  middle  of  the  space  it  is  directly  behind  the 
artery,  separating  the  artery  from  the  internal  popliteal  nerve,  which  is  still  more 
posterior,  whilst  at  the  upper  end  of  the  space  it  is  to  the  outer  side  of  the  artery, 


Sartorius 


Tensor  fascia; 
fenioris 

Superficial  cir- 
cumflex iliac 
artery 

Rectus  femoris 
Psoas  and  iliaciis 


Profunda  artery 

External  cir- 
cumflex artery 


Vastus  externus 


Vastus  internus 


Femoral  artery 
Femoral  vein 
Crural  canal 


Superficial  ex 
^ternal  pudic 


■^  artery 


Deep  external  pudic 
artery 


Long  saphenous  vein 


Adductor  longus 


(rracilis 


Fig.  656. — The  Femokal  Vessels  in  Scarpa's  Triangle. 

and  still  between  it  and  the  internal  popliteal  nerve.     It  then  passes  through  the 
adductor  magnus  muscle  and  becomes  the  femoral  vein. 

The  popliteal  vein,  which  is  provided  with  two  or  three  bicuspid  valves,  is  closely 
bound  to  the  artery  by  a  dense  fascial  sheath.  Not  uncommonly  there  are  one  or 
more  additional  satellite  veins  which  anastomose  with  the  popliteal  vein,  and  in 
these  cases  the  artery  is  more  or  less  completely  surrounded  by  venous  trunks. 

Tributaries. — lu  addition  to  the  vense  comites  of  the  anterior  and  posterior  tibial 
arteries,  it  receives  tributaries  which  correspond  with  the  branches  of  the  popHteal  artery, 
and  it  also  receives  one  of  the  supei*ficial  veins  of  the  leg,  viz.  the  external  or  short 
saphenous  vein. 

The  femoral  vein  (v.  femoralis)  is  the  direct  continuation  of  the  popliteal  vein. 


THE  DEEP  VEINS  OF  THE  LOWER  EXTREMITY. 


899 


It  commences  at  the  junction  of  the  middle  and  lower  thirds  of  the  thigh,  at  the 
opening  in  the  adductor  magnus  muscle.  It  then  ascends  through  Hunter's  canal, 
and  through  Scarpa's  triaugle,  and  terminates  a  little  to  the  inner  side  of  the 
middle  of  Poupart's  ligament  by  l)ecom- 
ing  the  external  iliac  vein. 

In  Hunter's  canal  it  lies  behind,  and 
at  first  to  the  outer  side  of,  the  femoral 
artery,  and  upon  the  adductors  magnus 
and  longus  which  separate  it  from  the 
profunda  vessels.  In  the  lower  part  of 
Scarpa's  triangle  it  is  behind  and  to  the 
inner  side  of  the  artery,  and  immediately 
in  front  of  the  profunda  vein  which 
separates  it  from  the  profunda  artery, 
but  in  the  upper  part  of  Scarpa's  triangle 
it  is  directly  on  the  inner  side  of  the 
femoral  artery.  About  one  and  a-half 
inches  below  Poupart's  ligament  it  enters 
the  middle  compartment  of  the  femoral  \i?^^ 
sheath,  through  which  it  ascends  to  its 
termination,  Ipng  between  the  compart- 
ment for  the  femoral  artery  on  the  outer 
side  and  the  crural  canal  on  the  inner 
side. 

It  usually  contains  two  bicuspid 
valves — one  near  its  termination  and  the 
other  just   above   the    entrance   of    its  ^^  f  ^^ 

profunda  tributary.  f^^l    \   J 


'^M 


Superficial  epigastric  vein 
.  Superficial  circumflex 

iliac  vein 
"Superficial  pudic  vein 

Femoral  vein 

Long  saphenous  vein 


External  superficial 
femoral  vein 

Internal  superficial 
femoral  vein 


Long  saphenous  vein 


Tributaries. — It  receives  tributaries 
(veiue  comites)  which  correspond  with  the 
branches  of  the  femoral  artery  and  the  larger 
of  the  two  superficial  veins  of  the  lower 
extremity,  viz.  the  long  saphenous  vein, 
which  entei's  the  femoral  vein  where  that 
vessel  lies  in  the  middle  compartment  of 
the  femoral  sheath. 

The  external  iliac  vein  (v.  iliaca 
externa,  Eigs.  637,  640,  and  655)  is  the 
upward  continuation  of  the  femoral  vein. 
It  commences  on  the  inner  side  of  the 
termination  of  the  external  iliac  artery, 
immediately  behind  Poupart's  ligament, 
and  ascends  along  the  brim  of  the  p3lvis 
to  a  point  at  the  level  of  the  lumbo-sacral 
articulation  and  opposite  the  sacro-iliac 
joint,  and  immediately  behind  the  in- 
ternal iliac  artery,  wdiere  it  ends  by  join- 
ing the  internal  iliac  vein  to  form  the 
common  iliac  vein.  It  lies  at  first  on 
the  inner  side  of  the  external  iliac 
artery,  but  on  a  somewhat  posterior 
plane,  and  then  directly  behind  the 
artery,  whilst  just  before  its  termination 
it  crosses  the  outer  side  of  the  internal  iUac  artery,  and  separates  that  vessel  from 
the  inner  border  of  the  psoas  muscle.  In  its  whole  course  the  vein  Lies  anterior 
to  the  obturator  nerve.  It  is  usually  provided  with  one  biscupid  valve,  but  some- 
times there  are  two.  Its  tributaries  correspond  to  the  branches  of  the  external 
iliac  artery ;  thus  the  deep  circumflex  iliac  (v.  circumflex  ilium  profunda)  and  deep 


Long  saphenous  vein 


-  Dorsal  venous  arch 


Fig.  057. — The  Internal  or  Long  Saphenous 
Vein  and  its  Tributaries. 


900  THE  VASCULAK  SYSTEM. 

epigastric  (v.  epigastrica  inferior)  veius  open  into  it  close  to  its  origin,  whilst  in 
addition  it  frequently  receives  the  pubic  vein. 

The  pubic  vein  forms  a  communication  between  the  obturator  vein  and  the 
external  iliac  ^■ein.  It  varies  in  size,  and  may  form  the  main  termination  of  the 
obturator  vein  from  which  it  arises.  Commencing  in  the  obturator  foramen,  it 
ascends  at  the  side  of  the  pubic  branch  of  the  deep  epigastric  artery,  and  reaches 
the  external  iliac  vein. 

The  Superficial  Veins  of  the  Lower  Extremity. 

The  superficial  veins  of  the  lower  extremity  terminate  in  two  trunks,  one  of 
which,  the  external  or  short  saphenous  vein,  passes  from  the  foot  to  the  popliteal 
space ;  whilst  the  other,  the  internal  or  long  saphenous  vein,  extends  from  the  foot 
to  the  groin. 

The  superficial  veins  of  the  sole  of  the  foot  form  a  fine  plexus,  immediately 
beneath  the  skin,  from  which  anterior  and  lateral  efferents  pass.  The  anterior 
efferents  terminate  in  a  transverse  arch  which  lies  in  the  furrow  at  the  roots  of  the 
toes,  and  the  lateral  efferents  pass  round  the  sides  of  the  foot  to  the  internal  or 
external  saphenous  veins.  The  transverse  arch  also  receives  small  plantar  digital 
veins  from  the  toes,  and  it  gives  off  interdigital  efferent  branches  to  the  dorsal 
venous  arch. 

The  superficial  veins  on  the  dorsal  aspect  of  each  toe  unite  together  to  form  two 
dorsal  digital  veins  (v.  digitales  pedis  dorsales)  which  run  along  the  borders  of  the 
dorsal  surface.  The  dorsal  digital  veins  of  the  adjacent  borders  of  the  interdigital 
clefts  unite,  at  the  apices  of  the  clefts,  to  form  four  dorsal  interdigital  veins  which 
terminate  in  the  dorsal  venous  arch.  The  dorsal  digital  vein  from  the  inner  side 
of  the  great  toe  ends  in  the  long  saphenous  vein,  and  that  from  the  outer  side  of 
the  little  toe  terminates  in  the  short  saphenous  vein. 

The  dorsal  venous  arch  (arcus  venosus  dorsalis  pedis)  lies  in  the  subcutaneous 
tissue,  between  the  skin  and  the  branches  of  the  musculo-cutaneous  nerve,  opposite 
the  lower  parts  of  the  shafts  of  the  metatarsal  bones.  It  ends  internally  by  unit- 
ing with  the  inner  dorsal  digital  vein  of  the  great  toe  to  form  the  long  saphenous 
vein,  and  externally  by  joining  the  outer  dorsal  digital  vein  of  the  little  toe  to 
form  the  short  saphenous  vein.  The  dorsal  venous  arch  receives  the  dorsal  inter- 
digital veins ;  interdigital  efferents  from  the  plantar  transverse  arch,  and  numerous 
triljutaries  from  the  dorsum  of  the  foot,  which  anastomose  freely  together,  forming 
a  wide-meshed  dorsal  venous  plexus,  open  into  it  behind. 

The  internal  or  long  saphenous  vein  (v.  saphena  magna)  is  formed  by 
the  union  of  the  inner  extremity  of  the  dorsal  venous  arch  with  the  inner 
dorsal  digital  vein  of  the  great  toe.  It  passes  upwards  in  front  of  the  internal 
malleolus,  crosses  the  inner  surface  of  the  lower  part  of  the  shaft  of  the  tibia,  and 
ascends  immediately  Ijehind  the  internal  border  of  that  bone  to  the  knee,  where  it 
lies  just  behind  the  internal  condyle  of  the  femur ;  continuing  upwards,  with  an- 
inclination  forwards  and  outwards,  it  gains  the  upper  part  of  Scarpa's  triangle, 
where  it  perforates  the  cribriform  fascia  and  the  femoral  sheath  to  reach  its  ter- 
mination in  the  femoral  vein.  In  tlie  foot  and  leg  it  is  accompanied  l)y  the  long 
saplienous  nerve,  and  for  a  short  distance  below  the  knee  by  the  superficial  branch 
of  the  anastomotic  artery.  In  the  thigh,  hranches  of  the  internal  cutaneous  nerve 
lie  in  close  relation  with  it.     It  contains  from  eight  to  twenty  bicuspid  valves. 

Tributaries. — It  communicates  freely  through  the  deep  fascia  with  the  deep  inter- 
inuscular  veins.  In  the  foot  it  receives  tribiitaries  fi'om  the  inner  part  of  the  sole  and 
from  the  dorsal  venous  plexus.  As  it  ascends  in  the  leg  it  is  joined  by  tributaries  from 
the  dorsum  of  the  foot,  the  inner  side  and  back  of  the  heel,  the  front  of  the  leg  and  the 
back  of  the  calf,  and  it  anastomoses  freely  with  the  short  saphenous  vein.  In  the  thigh 
it  receives  numerous  tributaries,  some  of  which  usually  converge  to  form  two  superficial 
femoral  veins.  Of  these,  one,  the  external,  ascends  from  the  outer  side  of  the  knee  and 
terminates  in  the  internal  saphenous  vein  about  the  lower  part  of  Scarpa's  triangle ;  the 
other,  the  internal,  receives  a  communication  from  the  external  saplienous  vein,  and 
ascends  from  the  back  of  the  thigh  along  its  inner  side  to  terminate  in  the  long  saphenous 


THE  POETAL  SYSTEM  OF  VEINS. 


901 


vein  almost  opposite  the  termination  of  the  external  su])Ci-ticial  femoral  vein.  The  last 
tributaries  to  enter  the  long  saphenous  vein  are  the  superficial  circumflex  iliac,  epigastric, 
and  pudic  veins.  They  accompany  the  corresponding  arteries,  and  terminate  in  tlie  long 
saphenous  vein  immediately  before  the  latter 
vessels  perforate  the  cribriform  fascia. 

The  suj)erficial  circumflex  iliac  vein  receives 
blood  from  the  lower  and  outer  part  of  the 
abdominal  wall  and  the  upper  and  outer  part  of 
the  thigh.  The  supeiiicial  epigastric  vein  drains 
the  lower  and  inner  part  of  the  abdominal  wall, 
and  the  superficial  pudic  vein  receives  blood  from 
the  doi-sum  of  the  penis  and  the  scrotum  in  the 
male,  and  from  the  labium  majus  in  the  female. 

The  external  or  short  saphenous  vein 

(v.  saphena  parva)  is  formed  by  tlie  union 
of  the  outer  extremity  of  the  dorsal  venous 
arch  with  the  outer  dorsal  digital  vein  of  the 
Httle  toe.  At  first  it  passes  backwards  along 
the  outer  side  of  the  foot  and  below  the 
external  malleolus,  lying  on  the  external 
annular  hgament  in  company  with  the 
external  saphenous  nerve ;  then  it  ascends 
behind  the  external  malleolus,  and  along  the 
outer  border  of  the  tendo  Achillis,  still  in 
company  with  the  external  saphenous  uerve, 
to  the  middle  of  the  calf,  above  which  it  is 
continued  in  the  superficial  fascia,  accom- 
panied by  the  superficial  sural  artery,  to  the 
lower  part  of  the  popliteal  space,  where  it 
pierces  the  deep  fascia,  and  terminates  in  the 
pophteal  vein.  It  communicates  round  the 
inner  side  of  the  leg  with  the  internal 
saphenous  vein,  and  through  the  deep  fascia 
with  the  deep  veins,  and  it  contains  from  six 
to  twelve  bicuspid  valves. 

Tributaries. — It  receives  tributaries  from 
the  outer  side  of  the  foot,  from  the  outer  side 
and  back  of  the  heel,  from  the  back  of  the  leg, 
and  occasionally  a  descending  tributary  from  the 
back  of  the  thigh.  Just  before  it  pierces  the 
popliteal  fascia  it  gives  off  a  small  branch  which 
ascends  round  the  inner  side  of  the  thigh  and 
unites  with  the  internal  supei-ficial  femoral  vein. 

In  this  way  a  communication  is  established  between  the  external  and  internal  saphenous 
veins  ;  this  communication  is  frequently  enlarged,  and  not  uncommonly  constitutes  the 
main  continuation  of  the  external  saphenous  vein. 


Fig. 


658. — The  External  or  Short  Saphenous 
Vein  and  its  Tributaries. 


THE  POETAL  SYSTEM. 

The  portal  system  includes  the  veins  which  convey  blood  from  almost  the 
whole  of  the  abdominal  and  pehdc  parts  of  the  alimentary  canal,  and  from  the 
spleen  and  pancreas,  to  the  hver.     The  tributaries  of  origin  of  these  veins  agree 
closely  with  the  terminal  branches  of  the  corresponding  arteries.     They  are  single 
vessels,  which  for  some  distance  accompany  the  corresponding  arteries,  and  are 
similarly  named.     The  larger  or   terminal  veins,  however,  leave   their  associatedii 
arteries :  the  inferior  mesenteric  vein  joins  the  splenic  vein,  and  the  latter  unites! 
with  the  superior  mesenteric  vein  to  form  the  portal  vein,  which  passes  to  the  liver.  I 
These  veins,  together  with  their    tributaries,  constitute    the  portal    system.     All 
the  vessels  of  this  system  are  devoid  of  valves. 
61a 


902 


THE  VASCULAR  SYSTEM. 


The  portal  vein  (vena  portoe)  is  a  wide  venous  channel,  about  three  inches 
long,  which  conveys  blood  from  the  stomach,  from  the  whole  of  the  intestine, 
except  the  terminal  portion  of  the  rectum,  and  from  the  spleen  and  pancreas  to 
the  Hver.  Unlike  other  veins,  it  ends  like  an  artery  by  breaking  up  into  branches, 
which  ultimately  terminate  in  capillaries  in  the  substance  of  the  liver ;  from  these 
portal  capillaries  the  hepatic  veins  (p.  892),  which  also  receive  the  blood  conveyed 
to  the  liver  by  the  hepatic  artery,  arise  ;  and  as  these  open  into  the  inferior  vena 
cava,  the  portal  blood  ultimately  reaches  the  general  systemic  circulation. 

The  portal  vein  commences  by  the  union  of  the  superior  mesenteric  and  the 


Cvstic  vein  


Pj'loi  ic  vein 


Coronary  vein 


Portal  vein 

IK;?,';,;,   :  [ 

Superior  "' 
mesenteric  vein 

np 

Right  gastro- 
epiploic  vein 
Pancreatico- 
duodenal vein 

'"  ^k"  ~*?.' 

Middle  colic 
vein 

1 

Right  colic 
vein 

Ileo-colic  vein 


Inferior  mesenteric 
vein 

Superior  mesenteric 
artery 


Tributaries 
corresponding 
with  ^•asa 
intestina 
arteries 


Fig.  659.— The  Pohtai.  Vein  and  its  Thibutahies. 

splenic  veins  behind  and  to  the  left  of  the  neck  of  the  pancreas,  and  either  in 
front  of  the  left  border  of  the  inferior  vena  cava,  at  the  level  of  the  body  of  the 
first  lumbar  vertebra,  or  in  front  of  the  upturned  extremity  of  the  lower  portion 
of  the  head  of  the  pancreas.  It  ascends  in  front  of  the  inferior  vena  cava,  and 
behind  the  neck  of  the  pancreas  and  the  first  part  of  the  duodenum,  to  the  lower 
border  of  the  foramen  of  Winslow,  where  it  passes  forwards,  in  the  right  pancreatico- 
gastric  fold  of  peritoneum,  and  enters  the  lower  border  of  the  gastro-hepatic 
omentum ;  continuing  its  upward  course,  it  lies  behind  the  common  bile-duct  and 
hepatic  artery,  and  in  front  of  the  foramen  of  Winslow ;  it  ultimately  reaches  the 
right  end  of  the  transverse  fissure  of  the  liver,  where  it  ends  by  dividino-  into  a 


THE  MESENTERIC  AXD  SPLENIC  VEINS.  903 

short  and  wide  right  and  a  longer  and  narrower  left  branch.  Just  before  its 
termination  it  enlarges,  forming  the  sinus  of  tlie  portal  vein. 

The  right  branch  generally  receives  the  cystic  vein  and  then  enters  the  right  lobe 
of  the  liver,  in  which  it  lireaks  up  into  numerous  ) tranches  which  terminate  in  the 
portal  capillaries  round  the  periphery  and  in  the  substance  of  the  liver  lobules. 

The  left  branch  runs  from  right  to  left  along  the  transverse  fissure,  giving  off 
branches  to  the  Spigelian  and  quadrate  lobes ;  it  crosses  the  longitudinal  fissure, 
and  ends  in  a  siudlar  manner  to  the  right  branch,  but  in  the  substance  of  the 
left  lobe  of  the  liver. 

As  it  crosses  the  longitudinal  fissure,  the  left  branch  of  the  portal  vein  is  joined 
in  front  by  the  round  ligament  of  the  liver,  a  fibrous  cord  which  is  the  remains  of  the 
left  umbilical  vein  of  the  foetus ;  and,  somewhat  to  the  right  of  the  attachment  of 
the  round  ligament  anteriorly,  a  fibrous  cord  springs  from  it  posteriorly  and 
connects  it  with  the  upper  part  of  the  inferior  vena  cava ;  this  cord  is  the  remains 
of  the  ductus  venosus,  a  blood-vessel  of  the  fcetus,  through  which  blood  coming 
from  the  placenta,  by  the  umbilical  vein,  passed  into  the  inferior  vena  cava 
without  going  through  the  liver. 

The  portal  vein  is  accompanied  by  numerous  lymphatic  vessels,  and  it  is 
surrounded  in  the  gastro-hepatic  omentum  by  filaments  of  the  hepatic  plexus 
of  nerves. 

Tributaries. — Soon  after  its  formation  the  jDortal  vein  receives  the  coronary  and 
pyloric  veins,  and  the  cystic  vein  opens  into  its  right  branch. 

The  coronary  vein  (v.  coronaria  ventriculi)  commences  in  the  gastro-hepatic  omentum 
by  the  union  of  tributaries  from  both  surfaces  of  the  stomach.  It  runs  to  the  left 
between  the  layers  of  the  gastro-hepatic  omentum,  and  along  the  lesser  curvature  of  the 
stomach,  -with  the  corresponding  artery,  to  the  oesophagus,  where  it  receives  oesophageal 
tributaries.  It  then  turns  backwards  in  the  left  pancreatico-gastric  fold,  and  reaches  the 
posterior  wall  of  the  abdomen,  where  it  again  changes  its  direction  to  nm  from  left  to 
right,  behind  the  lesser  sac  of  the  peritoneum,  to  the  right  pancreatico-gastric  fold,  at  the 
root  of  which  it  opens  into  the  portal  vein. 

The  pyloric  vein  (v.  pyloi-ica)  is  a  small  vessel  which  is  foi-med  by  the  union  of 
triVmtaries  from  the  upper  parts  of  both  surfaces  of  the  stomach.  It  runs  from  left  to 
right  along  the  righ.t  portion  of  the  lesser  curvature,  between  the  layers  of  the  gastro- 
hepatic  omentum,  and  terminates  in  the  portal  vein,  after  that  vessel  has  entered  the 
gastro-hepatic  omentum. 

The  cystic  vein  (v.  cystica)  is  formed  by  the  union  of  tributaries  which  accompany 
the  branches  of  the  cystic  artery  on  the  upper  and  lower  surfaces  of  the  gall-bladder  :  it 
ascends  along  the  cystic  duct  and,  as  a  rule,  terminates  in  the  right  branch  of  the  portal 
vein. 

The  Mesentekic  and  Splenic  Veins. 

Tlie  superior  mesenteric  vein  (v.  mesenterica  superior)  commences  in  the  right  iliac 
fossa  in  connexion  with  the  lower  part  of  the  ileum.  It  ascends  along  the  right  side  of 
the  superior  mesenteric  artery  in  the  root  of  the  mesentery,  forming  a  curve  with  the 
convexity  to  the  left. 

As  it  ascends  it  passes  in  front  of  the  right  ureter,  the  lower  part  of  the  inferior  vena 
cava,  the  third  part  of  the  duodenum,  and  the  lower  part  of  the  head  of  the  pancreas  ; 
and,  after  passing  behind  the  root  of  the  transverse  mesocolon,  it  terminates  behind 
the  neck  of  the  pancreas  by  uniting  with  the  splenic  vein  to  foi-m  the  portal  vein. 

Its  tributaries  correspond  Avith  the  branches  of  the  superior  mesenteric  artery.  It  is  formed 
by  the  union  of  the  ileo-cpecal  and  appendicular  veins.  In  front  and  towards  the  left  side  the 
tributaries  (vv.  intestinales)  from  between  the  folds  of  the  mesentery  enter  it ;  the  right  colic 
and  ileo-colic  veins  enter  its  right  side  ;  the  middle  colic  vein  joins  it  in  front  at  the  lower  border 
of  the  head  of  the  pancreas,  "and  close  to  its  termination  it'  receives  the  right  gastro-epiploic 
and  the  i^ancreatico-duodenal  veins. 

The  right  gastro-epiploic  vein  (v.  gastro-epijiloica  dextra)  runs  from  left  to  right  along  the 
lower  border  of  the  stomach,  and  between  the  two  anterior  layers  of  the  great  omentum.  It 
receives  tributaries  from  both  surfaces  of  the  stomach,  and  near  the  jwlorus  turns  backwards  in 
the  right  pancreatico-gastric  fold  of  peritoneum,  passes  behind  tlie  neck  of  the  pancreas,  and 
ends  in  the  superior  mesenteric  vein. 

The  pancreatico-duodenal  vein  receives  tributaries  (vv.  pancreatico-duodenalis)  from  the  head 
of  the  pancreas  and  the  adjacent  parts  of  the  duodenum  ;  it  ascends  along  the  superior  pancreatico- 
duodenal arteiv,  and  terminates  in  the  upjjer  part  of  the  superior  mesenteric  vein. 
616    ' 


904  THE  VASCULAE  SYSTEM. 

The  splenic  vein  (v.  lieiialis)  is  formed  by  the  union  of  five  or  six  tributaries  which 
issue  from  the  hilum  on  the  anterior  surface  of  the  spleen.  It  passes  backwards 
and  inwards  in  the  lieno-renal  ligament  to  the  kidney,  then  turning  to  the  right  it  runs 
behind  the  upper  border  of  the  pancreas  and  below  the  splenic  artery  ;  it  crosses  the  front 
of  the  abdominal  aorta,  immediately  below  the  origin  of  the  cccliac  axis,  and  terminates 
behind  the  neck  of  the  pancreas,  by  joining  the  superior  mesenteric  vein  to  form  the 
portal  vein. 

Tributaries. — It  receives  the  vasa  brevia  or  gastric  veins,  the  left  gastro-epiploic  vein, 
the  pancreatic  veins,  and  the  inferior  mesenteric  vein.  Occasionally  the  coronary  vein  ter- 
minates in  it. 

The  vasa  brevia  or  gastric  veins  (vv.  gastricge  breves)  are  a  series  of  small  venous  channels 
which  gather  blood  from  the  region  of  the  left  portion  of  the  great  curvature  of  the  stomach  ; 
they  pass  backwards  towards  the  sjsleen  in  the  gastro-sj^lenic  omentum,  and  terminate  either  in 
the  trunk  of  the  splenic  vein  or  in  one  of  its  main  tributaries. 

The  left  gastro-epiploic  vein  runs  liom  riglit  to  left  along  the  lower  border  of  the  stomach 
between  the  layers  of  the  great  omentum.  At  the  left  extremity  of  the  stomach  it  enters  the 
gastro-splenic  omentum,  through  which  it  passes  towards  the  liilum  of  the  spleen,  and  it  ter- 
minates in  the  commencement  of  the  splenic  vein.  It  receives  tributaries  from  both  surfaces  of 
the  stomach. 

The  pancreatic  veins  issue  from  the  substance  of  the  pancreas,  and  terminate  directly  in  the 
sjjlenic  vein. 

The  inferior  mesenteric  vein  (v.  mesenterica  inferior)  commences,  as  the  superior  htemor- 
rhoidal  vein,  in  the  venous  plexus  which  lies  between  the  muscular  and  mucous  coats  of  the 
rectum.  Tlie  superior  hsemorrhoidal  vein  (v.  hsemorrhoidalis  superior)  drains  the  greater  part  of 
the  blood  from  the  hsemorrhoidal  plexus,  through  wliich  it  communicates  with  the  middle  and 
inferior  hsemorrhoidal  veins.  It  ascends  in  company  with  the  superior  haemorrhoidal  artery,  and 
between  the  layers  of  the  meso-rectum,  to  the  brim  of  the  pelvis,  where  it  jjasses  in  front  of  the 
left  common  iliac  artery  and  becomes  the  inferior  mesenteric  vein. 

The  inferior  mesenteric  vein  runs  upwards  on  the  left  of  the  aorta,  behind  the  jDeritoneum, 
and  in  front  of  the  left  psoas  muscle  and  the  left  spermatic  artery.  Near  its  termination  it 
crosses  in  front  of  the  left  renal  vein,  and,  passing  behind  the  body  of  the  jpancreas,  ends  in  the 
splenic  vein.  Occasionally  it  terminates  in  the  angle  of  union  of  the  suj)erior  mesenteric  and 
splenic  veins. 

Tributaries. — In  addition  to  the  superior  hasmorrlioidal  A'ein,  of  which  it  is  the.  direct  con- 
tinuation, the  inferior  mesenteric  vein  receives  sigmoid  tributaries  {yv.  sigmoidse)  from  the  iliac 
and  pelvic  colon,  and  the  left  colic  vein  from  the  descending  colon  and  splenic  flexure. 


THE   LYMPH   VASCULAR   SYSTEM. 

The  vessels  of  the  lymph  vascular  system  (vasa  lymphatica)  contain  a  colourless 
fluid,  rich  in  white  corpuscles,  called  lymph.  In  many  respects  they  resemble  blood- 
vessels, especially  the  veins ;  but  unlike  veins  they  communicate  with  intercellular 
spaces  and  with  serous  sacs,  and  their  continuity  is  interrupted  by  interposed  nodular 
aggregations  of  lymph  tissue  which  are  known  as  lymph  glands  (lymph oglandules). 

Lymph  is  collected  in  intercellular  spaces  from  which  lymph  capillaries  arise ; 
the   latter   terminate  in  lymphatic  vessels,  which   unite  together,  forming  larger 
vessels;  and  ultimately  two  terminal  trunks — viz.  the  thoracic  duct  and  the  right- 
Isnnphatic  duct — open  into  the  venous  system,  at  the  commencement  respectively 
of  the  left  and  right  innominate  veins. 

There  are  no  outgoing  vessels,  but  it  is  customary  to  speak  of  afferent  (vasa 
afferentia)  and  efferent  (vasa  efferentia)  lymphatics  with  reference  to  vessels  which 
enter  or  leave  the  interposed  lympli-glands. 

Lymph  vessels,  and  the  spaces  in  which  they  commence,  merely  collect  and 
convey  lymph.  The  lymijhatic  glands  act,  in  part  at  least,  as  filters,  and  possibly 
also  some  of  the  white  corpuscles  are  ibrmed  in  tliem. 

The  greater  part,  if  not  the  whole,  of  the  lymph  of  the  body  passes  through  one 
or  more  of  tlic  lym]»h  glands  before  it  reaches  the  blood  vascular  system. 

Lymphatic  spaces.- — Lympli  spaces  are  simply  intervals  or  clefts  in  connective 
tissue.  The  larger  spaces  are  lined  by  a  laycsr  of  flattened  endothelial  cells,  with 
sinuous  outlines,  similar  to  the  cells  of  the  lymphatic  capillaries ;  but  the  smaller 
spaces  have  no  endothelial  lining,  and  they  are  limited  only  by  the  cells  of  the 
tissue  in  which  they  lie.  The  precise  nature  of  the  communications  between 
lymphatic  spaces  and  lymph  capillaries  has  not  been  definitely  ascertained;  but 


THE  LYMPH  VASCULAE  SYSTEM.  905 

undoubtedly  lymph  passes  from  the  spaces  into  the  capillaries,  and  probably  it 
does  so  because  the  spaces  and  vessels  are  directly  continuous. 

As  alternative  explanations,  it  may  be  suggested  either  that  the  passage  is  due 
to  the  existence  of  stomata  in  the  walls  which  separate  spaces  from  the  capillaries, 
or  that  it  may  be  due  to  transudation  through  intervening  tissues. 

Lymph  capillaries. — Lymph  capillaries  are  not  only  much  larger  and  more 
irregular  than  blood  capillaries,  but  they  are  also  larger  than  the  lymphatic  vessels 
into  which  they  open.  They  are  lined  by  a  single  layer  of  endothelial  cells  which 
possess  very  sinuous  outlines ;  apparently  they  are  in  direct  structural  continuity 
with  lymph  spaces,  and  they  anastomose  freely  together,  forming  plexiform 
labyrinths. 

Lymphatic  vessels. — The  smallest  lymphatic  vessels  are  much  narrower  'in 
calibre  than  the  lymph  capillaries  with  which  they  are  continuous.  Their  walls 
consist  of  an  internal  lining  of  endothelial  cells  of  fusiform  shape  and  regular 
outline,  and  an  outer  layer  of  fine  connective  tissue.  They  are  provided  with 
numerous  valves,  and  when  distended  have  a  beaded  appearance. 

The  larger  lymph  vessels  possess  three  coats  —  (1)  An  internal  coat  (tunica 
interna),  formed  by  a  layer  of  endothelial  cells,  of  fusiform  shape,  and  of  regular,  but 
sinuous,  outline.  (2)  A  middle  coat  (tunica  media)  of  unstriped  muscle  fibres, 
arranged  for  the  most  part  circularly,  but  some  of  them  run  obliquely  or  longi- 
tudinally. The  interspaces  between  the  muscle  fibres  are  filled  with  a  fine  con- 
nective tissue.  (3)  An  outer  coat  (tunica  externa)  of  mixed  white  fibrous  and 
elastic  tissue,  which  is  not  sharply  separated  from  the  middle  coat  on  the  inner 
side  or  from  the  surrounding  tissues  on  the  outer  side.  It  may  also  contain  a  few 
unstriped  muscle  fibres.  In  the  largest  vessels  the  two  outer  coats  consist  prin- 
cipally of  muscle ;  they  are,  therefore,  very  friable. 

All  the  large  vessels  are  provided  with  numerous  bicuspid  valves,  which  are 
formed  by  folds  of  the  inner  coat ;  and  as  the  lumina  of  the  vessels  are  enlarged 
just  beyond  the  attachments  of  the  valves,  the  vessels  assume  a  characteristic 
beaded  appearance  when  they  are  distended. 

Lymphatic  vessels  anastomose  freely  together,  and  the  majority  form  communi- 
cating channels  between  different  groups  of  lymphatic  glands,  leaving  the  more 
distal  glands  as  efferent  vessels  and  entering  the  more  proximal  glands  as  afferent 
vessels.  Some  of  the  lymphatic  vessels,  however,  are  afferent  only ;  they  simply 
carry  lymph  from  the  periphery  to  the  nearest  glands ;  w^hilst  others,  which  carry 
lymph  from  the  last  set  of  glands  to  the  terminal  trunks,  are  efferent  only. 

The  lymphatic  vessels,  unlike  the  veins  which  they  usually  accompany,  do  not 
increase  greatly  in  calibre  as  they  converge  towards  their  terminations ;  they  often 
branch,  and  they  frequently  anastomose  together.  In  certain  places,  particularly 
the  central  nervous  system  and  the  spleen,  lymph  capillaries  or  even  lymphatic 
vessels  completely  ensheath  the  smaller  blood  -  vessels,  forming  perivascular 
lymphatic  spaces. 

A  precise  knowledge  of  the  afferent  and  efferent  lymph  vessels,  and  of  the  several 
groups  of  glands  which  are  interposed  between  them,  is  of  the  greatest  practical 
importance ;  both  infective  micro-organisms  from  injured  and  inflammatory  areas 
and  detached  cells  from  malignant  tumour  growths  not  unfrequently  travel  by 
afferent  lymphatics  to  the  nearest  glands  where  they  may  be  arrested,  in  which 
case  micro-organisms  may  excite  secondary  infective  inflammation,  whilst  cells  of 
malignant  growths  may  form  secondary  growths  (metastatic  growths)  of  similar 
nature  in  the  glands. 

It  is  therefore  essential  that  the  pathologist  should  be  well  acquainted  ^vith 
the  anatomy  of  the  pathways  which  convey  lymph,  mth  the  glands  associated 
with  any  given  area,  and  also  with  the  communications  between  adjacent  glands. 

Lymphatic  glands. — Lymphatic  glands  are  globular,  ovoid,  flattened,  or 
irregular  bodies,  and  each  gland  presents  a  localised  depressed  area  which  is  known 
as  the  hilum.  They  vary  considerably  in  size,  some  being  no  larger  than  a  pin's- 
head,  whilst  others  are  as  large  as  a  bean.  In  colour  they  are  usually  grayish  pink, 
but  the  tint  varies  with  the  position,  vascularity,  and  state  of  activity  of  the  gland. 
The  glands  of  the  lung  are  generally  blackened  by  the  deposition  of  carbonaceous 


906  THE  VASCULAE  SYSTEM. 

material  in  their  substance,  and  those  of  the  liver  and  spleen  have  frequently  a 
brownish  hue.  The  glands  of  the  mesentery  are  creamy  or  white  whilst  the  chyle 
is  rapidly  passing  through  them,  but  when  the  absorption  of  food-material  from 
the  intestine  ceases  they  become  a  rosy  pink. 

Structure  of  Lymphatic  Glands.— Lyinpliatic  glands  consist  of  (1)  a  skeleton  or  framework, 
(2)  lymph  sinuses  and  (3)  lymph  follicles  and  cords. 

(i)  The  skeleton  or  framework  consists  of  a  capsule  and  of  primary,  secondary,  and  tertiary 
trabeculsB. 

The  capsuAe  is  formed  of  '.vhite  fibrous  tissue  interspersed  with  elastic  fibres,  and  in  some  cases 
with  unstrijied  muscular  fibres. 

The  primaiy  trahecuhe  spring  from  the  deep  surface  of  the  capsule  ancl  radiate  towards  the 
hilum,  where  they  anastomose  together  and  become  again  continuous  with  the  capsule ;  they 
divide  the  interior  of  the  gland  into  lobes.  Where  they  spring  from  the  capsule  they  are 
flattened,  but  as  they  approach  the  centre  of  the  gland  they  become  rounded  ;  their  structure  is 
the  same  as  that  of  die  capsule,  and  from  their  surfaces  the  secondary  trabeculfe  are  given  off. 
The  secondary  traheculcr,  springing  from  the  surfaces  of  the  primary  trabecule,  cross  the 
lymph  sinuses  and  enter  the  lymph  cords  and  follicles,  where  they  terminate  by  dividing  into 
tertiary  trabeculfe.  As  they  cross  the  lymph  sinuses  they  anastomose  freely  together,  forming  a 
fine  mesh-work  through  which  the  lyniph  passes  in  its  course  from  the  afferent  to  the  efferent 
vessels.  The  secondary  trabeculfe  consist  of  fine  strands  of  fiVjrous  tissue  devoid  of  nuclei,  and 
their  surfaces  are  covered  with  endothelial  cells.  The  tertiary  traheculce  are  finer  and  more 
delicate  than  the  secondary  trabeculfe,  from  the  terminations  of  which  they  spring,  but  they 
have  a  similar  structure.  They  anastomose  together,  forming  a  fine  network  in  the  lymph  cords 
and  follicles,  and  the  spaces  of  the  network  are  filled  with  lymph  corpuscles. 

(2)  The  lymph  sinuses  lie  beneath  the  capsule  and  around  the  primary  trabeculfe  which 
form  their  boundaries  on  one  side,  whilst  on  the  other  they  are  limited  by  the  lymph  cords 
and  follicles.  They  are  traversed  by  the  secondary  trabeculie,  and  their  channels  are  thus 
converted  into  a  kind  of  sponge- work  through  which  the  lym23h  stream  flows.  In  the  peripheral 
or  cortical  parts  (substantia  corticalis)  of  the  glands  they  form  more  or  less  cylindrical  channels, 
but  towards  the  central  or  medullary  parts  (substantia  medullaris)  and  near  the  hilum  they 
become  moniliform.  Afferent  vessels  (vasa  afferentia)  enter  the  sinuses  which  lie  immediately 
beneath  the  capsule  at  various  points,  whilst  the  efferent  A^essels  (vasa  efferentia)  emerge  close 
together  at  the  hilum. 

(3)  The  lymph  follicles  and  cords  are  interposed  between  the  lymph  sinuses.  They  consist 
of  dense  masses  of  lymphoid  cells  embedded  in  a  stroma  formed  by  the  tertiary  trabeculfe.  The 
follicles  and  cords  are  quite  similar  in  structure,  but  the  follicles  are  large  masses  which  inter- 
vene between  the  sinuses  in  the  cortex  of  the  gland,  and  the  cords  are  rounded  and  irregular 
strands  which  lie  between  the  moniliform  sinuses  of  the  medullary  portion  of  the  gland. 

It  is  generally  believed  that  the  lymph  corpuscles  in  the  follicles  and  cords  are  white  blood 
corpuscles  undergoing  proliferation.  If  this  belief  is  well  founded,  Ij^mph  glands  must  be  looked 
upon  as  one  of  the  sources  from  which  white  corpuscles  are  derived. 

The  l3rmph  glands  are  embedded  in  the  connective  tissues,  some  lying  super- 
ficially in  the  sul)Cutaneous  tissues,  but  the  majority  more  deeply  and  usually  at 
the  sides  of  the  great  blood-vessels.  As  a  rule  they  are  arranged  in  groups  of 
from  two  to  fifteen,  but  a  few  of  those  which  lie  in  the  subcutaneous  tissues  are 
solitary. 

They  form  centres  to  which  afferent  lymphatic  vessels  converge,  and  from 
which  efferent  vessels  pass  onwards  to  the  larger  lymph  channels. 

The  student  should  therefore  acquaint  himself  with  the  various  groups  of. 
glands,  with  their  afferents  and  efferents,  and  with  tlie  exact  position  and  relations 
of  the  large  lymphatic  trunks ;  he  will  then  be  in  a  position  to  understand  the 
course  which  minute  organisms  or  particles,  which  have  gained  access  to  the  lymph 
spaces,  may  take  as  they  are  carried  in  the  lymph  stream,  and  he  will  realise  that 
such  structures  may  either  be  entangled  in  the  glands  through  which  the  lymph 
passes,  or,  having  escaped  all  obstructions,  tliat  they  will  finally  enter  the  veins  at 
the  root  of  the  neck.  At  the  same  time,  if  he  bears  in  mind  the  existence  of 
the  numerous  anastomoses  between  the  lymphatic  vessels,  he  will  have  no  difficulty 
in  appreciatmg  that  variations  from  any  regular  course  may  not  infrequently 
occur,  and  his  clinical  experience  at  a  later  period  will  show  that  such  variations 
are  by  do  means  uncommon. 

THE   TERMINAL   LYMPH    VESSELS. 

Tlie  teruiinal  lymj^h  vessels  are  the  thoracic  duct  and  the  right  lymphatic  duct. 
Thoracic  Duct.  —  Tlie   thoracic  duct  (ductus    thoracicus)  is   the   larger   and 


THE  TERMINAL  LYMPH  VESSELS. 


907 


the  longer  of  the  two  terminal  lymph  vessels.  It  commences  in  the  umbilical 
region  of  the  abdomen  as  an  elongated  ovoid  dilation — the  receptaculum  chyli 
(cisterna  chyli) — which  measures  6  to  8  mm.  (^  to  |  in.)  in  its  broadest  diameter, 
and  from  5  to  7"5  cm.  (2  to  3  in.)  in  length.     The  receptaculum  chyli  lies  between 


C3     X     >i  -    - 


Vena 
azygos 
minor 
superior 


Vena  azj^gos  major 


Descending  thoracic 
lymphatic  trunk 


Thoracic  duct 

Receptaculum  cliyli 

Suprarenal  body 

Inferior  vena  cava 

Right  renal  artery 

Left  renal  vein 

Lumbar  veins 


Vena  azygos  minor 
inferior 


CEsophagus 

Descending  thoracic 
lymphatic  trunk 
Inferior  phrenic 
artery 

Suprarenal  body 

Cceliac  axis 

Superior  mesenteric 

artery 

Common  intestinal 

lymphatic  trunk 

Renal  artery 

Renal  vein 


Common  lumbar 
lymphatic  trunks 

Fig.  660. — The  Thoracic  Duct  and  its  Tributaries. 

the  aorta  and  the  lower  part  of  the  vena  azygos  major,  under  cover  of  the  right  crus 
of  the  diaphragm,  and  opposite  the  first  and  second  lumbar  vertebra?.  Passing 
upwards  from  the  receptaculum,  the  thoracic  duct  traverses  the  aortic  opening 
of  the  diaphragm  and  enters  the  posterior  mediastinum,  through  which  it  ascends, 
lying  in  front  of  the  vertebral  column  and  to  the  right  of  the  middle  line,  to  the 
level  of  the  fifth  dorsal  vertebra  ;  it  then  crosses  somewhat  abtruptly  from  the  right 
to  the  left  of  the  median  plane,  and  ascends  through  the  superior  mediastinum  to 


908  THE  VASCULAR  SYSTEM. 

the  root  of  the  neck,  where  it  turns  outwards,  between  the  vertebral  and  common 
carotid  arteries,  to  terminate  at  the  inner  border  of  the  scalenus  anticus  by 
joining  the  commencement  of  the  left  innominate  vein. 

Length  and  diameter. — The  total  length  of  the  duct  averages  about  18  inches 
(45  cm.).  It  is  dilated  both  at  its  origin  and  termination.  As  a  rule  it  is 
narrowest  opposite  the  fifth  dorsal  vertebra,  but  its  calibre  is  very  variable,  and 
sometimes  the  thoracic  portion  is  broken  up  into  a  series  of  anastomosing  channels. 
The  widest  portion  of  the  tube  is  usually  the  receptaculum,  but  occasionally  this 
dilatation  is  entirely  absent.  The  duct  is  provided  with  several  valves,  formed  by 
semilunar  folds  of  the  inner  coat,  arranged  in  pairs,  and  the  most  perfect  of  these 
is  situated  at  the  orifice  of  communication  with  the  innominate  vein. 

Relations. — In  the  abdomen  the  receptaculum  chyli  lies  in  front  of  the  upper  two 
lumbar  vertebrre  and  the  correspouding  lumbar  arteries,  between  the  aorta  on  the  left  and 
the  vena  azygos  major  and  the  right  crus  of  the  diaphragm  on  the  right.  In  the  posterior 
mediastinum  the  thoracic  duct  is  separated  from  the  vertebral  column  and  the  anterior 
common  ligament,  by  the  right  aortic  intercostal  arteries  and  the  transverse  parts  of  the 
small  azygos  veins ;  it  is  covered  in  front  in  the  lower  part  of  its  extent  by  the  right 
pleural  sac,  and  in  the  upper  part  by  the  oesophagus ;  to  its  right  is  the  vena  azygos 
major,  and  to  its  left  the  descending  aorta.  In  the  superior  mediastinum  it  passes  for- 
wards from  the  vertebral  column,  and  it  is  separated  from  the  left  longus  colli  muscle  by 
a  niass  of  fatty  tissue  ;  the  oesophagus  lies  in  front  of  it  in  this  region,  but  the  left  margin 
of  the  duct  projects  beyond  the  oesophagus,  aud  is  in  relation  in  front,  and  from  below 
upwards,  with  the  termination  of  the  arch  of  the  aorta,  the  left  subclavian  artery  and 
the  pleura.  As  the  duct  enters  the  root  of  the  neck  it  passes  behind  the  left  common 
carotid  artery,  whilst  to  its  right  and  somewhat  in  front  is  the  oesophagus,  and  the  left 
pleura  is  still  in  association  with  its  left  border. 

At  the  root  of  the  neck  it  arches  outwards  above  the  apex  of  the  pleural  sac  and  the 
first  part  of  the  left  subclavian  artery.  It  passes  in  front  of  the  vertebral  artery  and 
vein,  the  roots  of  the  inferior  thyroid,  transverse  cervical,  and  suprascapular  arteries,  the 
inner  border  of  the  scalenus  anticus  and  the  phrenic  nerve,  and  behind  the  left  carotid 
sheath  and  its  contents. 

Tributaries. — The  receptaculum  chyli  commonly  receives  six  tributaries. 
(1)  The  common  intestinal  or  pre-aortic  lymphatic  trunk  (truncus  intestinalis),  which 
is  formed  by  the  efferent  of  the  coeliac  and  upper  pre-aortic  glands,  and  conveys 
lymph  from  the  lower  and  anterior  part  of  the  liver,  the  stomach,  the  small 
intestine,  the  spleen,  and  the  pancreas.  (2)  Two  common  lumbar  or  lateral  aortic 
lymphatic  trunks  (trunci  lumbales),  one  on  each  side ;  they  are  formed  by  the 
efferents  of  the  lateral  aortic  glands,  and  are  sometimes  joined  by  efferents  of  the 
retro-aortic  glands ;  they  carry  lymph  from  the  lower  extremities,  from  the  deep 
portions  of  the  abdominal  and  pelvic  walls,  the  large  intestine  and  the  pelvic  viscera, 
and  from  the  kidneys  and  suprarenal  capsules.  (3)  A  retro-aortic  trunk  from 
the  retro -aortic  glands  (see  p.  922) ;  and  (4)  Two  descending  lymphatic 
trunks,  one  on  each  side,  each  of  which  is  formed  by  the  efferent  vessels  from  the 
corresponding  lower  intercostal  glands  ;  these  descend  to  the  receptaculum  through- 
the  aortic  opening  of  the  diaphragm.  Occasionally  they  unite  to  form  a 
single  trunk. 

In  its  course  through  the  posterior  mediastinum  the  thoracic  duct  receives 
efferents  from  the  upper  and  back  part  of  the  liver,  and  from  the  posterior 
mediastinal  and  cesophageal  glands. 

In  the  superior  mediastinum  the  vessels  which  open  into  it  are  derived  from 
the  upper  left  intercostal  glands ,  it  also  receives  lymph  from  the  heart  and  lungs 
by  efferents  from  the,  left  peritracheo-bronchial  glands  and  the  intertracheo- 
bronchial  glands,  though  as  a  rule  the  lymphatics  of  these  glands  unite  with  the 
internal  mammary  lymphatic  to  form  a  common  trunk  which  may  open  either  into 
the  thoracic  duct  or  into  the  innominate  vein. 

At  the  root  of  the  neck,  just  before  its  termination,  it  receives  the  efferents 
from  the  glands  of  the  left  upper  extremity,  which  frequently  unite  to  form  a  com- 
mon trunk  (truncus  subclavius),  and  the  left  common  jugular  lymphatic  (truncus 
jugularis),  which  conveys  the  lymph  from  the  left  side  oi'  the  head  and  neck,  but 
either  or  both  of  these  vessels  may  end  separately  in  the  innominate  vein. 


LYMPHATIC  VESSELS  AND  GLANDS  OF  HEAD  AND  NECK.     909 

Right  Lymphatic  Duct. — The  right  lymphatic  duct  is  not  always  present  (ductus 
lymphaticus  dexter,  Fig.  G64).  It  is  a  short  trunk,  from  half  to  three-quarters  of  an 
inch  (12  to  17  mm.)  in  length,  which  lies  at  the  right  side  of  the  root  of  the  neck  along 
the  inner  border  of  the  scalenus  anticus,  and  it  is  formed  by  the  contiuence  of  the 
right  common  jugular  lymphatic  vessel  and  the  efferent  vessels  from  the  glands  of 
the  right  upper  extremity ;  it  also  receives  efferents  from  the  intercostal  glands  of 
the  upper  intercostal  spaces  on  the  right  side ;  the  internal  mammary  lymphatics 
and  the  right  efferents  from  the  peritracheo-bronchial  glands  on  the  right  side.  It  thus 
receives  lymph  from  the  right  side  of  the  head  and  neck,  the  right  upper  limb  and 
the  right  side  of  the  trunk,  including  the  upper  part  of  the  thoracic  wall,  the  right 
lung  and  pleura,  the  right  half  of  the  heart  and  pericardium,  the  right  side  of  the 
diaphragm,  and  the  upper  surface  of  the  liver.  As  a  rule  the  right  lymphatic  duct 
is  not  present,  and  the  right  jugular  lymphatic  carrying  the  lymph  from  the  head 
and  neck,  the  right  subclavian  lymphatic  bearing  lymph  from  the  right  upper 
extremity,  and  the  trunk  formed  by  the  fusion  of  the  right  internal  mammary 
lymphatic  and  the  right  efferents  from  the  peritracheo  -  bronchial  glands,  end 
separately  in  the  upper  part  of  the  right  innominate  vein,  but  any  two  of  the 
three  main  trunks  of  the  right  side  may  unite  together. 

THE  LYMPHATIC  VESSELS  AND  GLANDS  OF  THE  HEAD  AND  NECK. 

The  lymphatic  vessels  of  the   head  and  neck  form  two  groups — (1)  the 

intracranial  and  (2)  the  extracranial. 

(1)  The  intracranial  lymphatics  are  (a)  the  cerebral  and  (6)  the  meningeal. 

(a)  The  cerebral  lymphatic  vessels  commence  in  the  suljstance  of  the  brain  as 
perivascular  spaces  round  the  Ijranches  of  the  cerebral  arteries ;  they  accompany 
the  cerebral  branches  of  the  internal  carotid  and  the  vertebral  arteries,  and,  leaving 
the  skull  with  the  main  arterial  trunks  and  the  internal  jugular  vein,  terminate  in 
the  upper  deep  cervical  glands. 

(b)  The  meningeal  lymphatic  vessels  commence  in  the  substance  of  the  dura  mater; 
they  accompany  the  meningeal  blood-vessels,  and  they  terminate  in  the  internal 
maxillary  glands  and  in  the  upper  deep  cervical  glands. 

(2)  The  extra-cranial  lymphatics  are  either  (a)  superficial  or  (h)  deep,  and  the 
two  sets  anastomose  freely  together. 

(a)  The  superficial  lymphatic  vessels  commence  in  the  subcutaneous  tissues  and 
superficial  muscles  of  tlie  face  and  scalp. 

(6)  The  deep  lymphatic  vessels  originate  in  the  walls  of  the  nose  and  mouth,  in 
the  tongue,  in  the  walls  of  the  pharynx,  the  oesophagus,  the  larynx  and  trachea,  in 
the  contents  of  the  orbital  and  other  extracranial  fossse,  and  in  the  muscles,  bones, 
and  ligaments  of  the  neck. 

All  the  extracranial  lymphatic  vessels,  both  superficial  and  deep,  are  afterents 
to  some  of  the  glands  of  the  head  or  neck,  and  their  general  distribution  and 
terminations  are  mentioned  in  connexion  with  the  glands  with  which  they 
are  associated. 

The  lymphatic  glands  of  the  head  include  the  following  : — 

The  occipital  glands  (lymphoglanduLii  occipitales),  two  or  three  in  number 
lie  beneath  the  deep  fascia  of  the  neck  upon  the  upper  part  of  the  trapezius  muscle, 
or,  if  the  trapezius  is  small,  upon  the  upper  part  of  the  complexus  muscle.  They 
receive  afferent  vessels  from  the  occipital  region  of  the  scalp  and  from  the  super- 
ficial parts  of  the  upper  and  back  portion  of  the  neck,  and  their  efferents 
terminate  in  the  superficial  and  deep  cervical  glands.  Some  of  the  lymph  vessels 
of  the  occipital  region  pass  directly  to  the  deep  cervical  glands. 

The  mastoid  glands  (lymphoglanduk^e  auriculares  posteriores)  lie  on  the  upper 
part  of  the  sterno-mastoid  muscle  and  on  the  mastoid  portion  of  the  temporal  bone, 
and  they  are  bound  down  by  a  sheathing  of  deep  cervical  fascia.  They  receive 
afferent  vessels  from  the  posterior  part  of  the  parietal  region  of  the  scalp,  and  from 
the  inner  surface  of  the  pinna;  their  efferents  join  the  superficial  and  deep 
cervical  glands. 

The  zygomatic  or  internal  maxillary  glands  (lymphoglandulse  faciales  profundse) 


910 


THE  VASCULAK  SYSTEM. 


are  very  variable  both  iu  number  and  size ;  they  lie,  in  part  in  association  with 
the  internal  maxillary  artery,  extending  from  the  posterior  part  of  the  bucci- 
nator muscle,  across  the  external  pterygoid  muscle,  to  the  anterior  part  of  the 
wall  of  the  pharynx.  Their  afferent  vessels  are  derived  from  the  orbit,  the 
temporal  fossa,  the  zygomatic  fossa,  the  palate,  the  nose,  and  the  cerebral  meninges. 
Their  efferent  vessels  open  into  the  upper  deep  cervical  glands. 

The  parotid  lymphatic  glands  (lymphoglanduU-e  auriculares  anteriores),  which 

are  embedded  in  the 
substance  of  the 
parotid  gland,  some 
superficially  immedi- 
ately beneath  the  fascia 
on  the  external  sur- 
face and  others  deeply. 
The  superficial  receive 
afferents  from  the 
frontal  and  the  tem- 
poral regions  of  the 
scalp,  from  the  eye- 
brow, the  upper  and 
lower  eyelids,  the  upper 
z  part  of  the  cheek,  the 
root  of  the  nose,  and 
the  outer  surface  of 
the  pinna.  Their 
effe rents  pass  to  the 
superficial  and  the 
upper  deep  cervical 
glands.  Tho,  deep  par- 
otid lymphatic  glands 
(lympho  -  glandulee 
parotidefe)  lie  along 
the  course  of  the  upper 
part  of  the  external 
carotid  artery.  They 
receive  afferents  from 
the  external  meatus, 
the  tympanum,  the 
soft  palate,  the  pos- 
terior part  of  the  nose, 
and  the  deeper  por- 
tions of  the  cheek. 
Their  efferents  open 
into  the  upper  deep 
cervical  glands,  and 
they  also  communicate 
with  the  glands  round 


Fig.  661. — Lymphatic  Vessel.s  and  Glands  of  the  Head  and  Neck. 

The  afferent  vessels  are  shown  in  continuous  lines;  the  efferent  and  iutui 
glandular  vessels  are  represented  by  dotted  lines. 

D.C. 

B. 

E.S. 

M. 

0. 

P. 


Deep  cervical  glamls. 

Buccal  <{lands. 

External  suli-sterno-niastoid  glands. 

Ma.stoid  glands. 

Occipital  glands. 

Superficial  parotid  glands. 


P.L.  PriB-laryngeal  glands. 
S.       Sulmiaxillary  glands. 
S.C.  Superficial  cervical  glands. 
S.M.  Submental  glands. 
T.       Pne-tracheal  glands. 
Z.       Zygomatic  glands. 


the   external    jugular 
vein. 

The  Facial  Glands. 

— Several  glands  or  groups  of  glands  have  been  found  Ijy  different  o]»servers  iu 
the  tissues  of  the  face.  Those  most  regularly  present  are  the  mandibular  glands, 
which  lie  close  to  the  facial  artery  as  it  crosses  the  mandiljle  immediately  in 
front  of  the  masseter  muscle.  A  number  of  buccal  glands,  irregular  in  number 
and  size,  are  met  with  on  the  outer  surface  of  the  fascia  covering  the  buccinator 
muscle,  some  near  its  anterior  part  and  others  near  the  point  where  the  buccinator 
is  j)ierced  by  Stensen's  duct.  A  lateral  nasal  gland  is  sometimes  present  in  the 
angle  between  the  ala  of  the  nose  and  the  cheek,  and  an  infraorbital  and  a  malar 
gland  are  described.     These  glands  receive  lymph  from  the  tissues  in  their  im- 


LYMPHATIC  VESSELS  AND  GLANDS  OF  HEAD  AND  NECK.     911 

mediate  ueighbourhood,  and  their  etferents  pass  to  the   suhmaxillaiy  or  parotid 
glands. 

The  lingual  glands  (lyniphoglauduhe  inguales)  lie  between  the  geuio-hyo-glossi 
muscles  and,  on  the  outer  surfaces  of  the  hyo-glossi  and  genio-liyo-glossi  muscles, 
under  cover  of  the  mylo-hyoid  muscles;  they  are  simply  small  lymphatic  nodules 
interposed  in  the  course  of  the  lymphatics  which  are  passing  from  the  tongue  and 
the  floor  of  the  mouth  to  the  deep  cervical  glands. 

The  lymphatic  glands  of  the  neck  include — 

The  superficial  cervical  lymphatic  glands  (lymphoglandulte  cervicales  super- 
ficiales).  These  lie  on  or  are  embedtled  in  the  deep  fascia  along  the  course  of  the 
external  jugular  vein,  superficial  to  the  sterno-mastoid.  They  receive  afferent 
vessels  from  the  superficial  tissues  of  the  neck,  the  mastoid,  the  superficial  parotid, 
and  the  submaxillary  lymphatic  glands.  Their  efferent  vessels  terminate  in  the 
upper  deep  cervical  glands  and  the  supra-clavicular  glands. 

The  submaxillary  lymphatic  glands  (lymphoglandulpe  submaxillares)  vary  in 
number  from  three  to  six.  They  lie  under  cover  of  the  deep  fascia  of  the  neck  in 
the  angle  between  the  lower  border  of  the  mandible  and  the  submaxillary  gland, 
and  the  largest  of  the  series  is  usually  situated  near  the  point  where  the  facial 
artery  turns  round  the  lower  border  of  the  mandible.  Occasionally  some  smaller 
gland  nodules  are  found  on  the  deep  surface  of  the  submaxillary  gland,  but  these 
are  comparatively  rare.  The  afferent  vessels  of  the  submaxillary  lymphatic  glands 
carry  lymph  from  the  side  of  the  nose,  the  upper  lip,  the  outer  part  of  the  lower 
lip,  the  anterior  third  of  the  border  of  the  tongue,  the  gums,  the  submaxillary  and 
sublingual  glands,  and  the  adjacent  parts  of  the  floor  of  the  mouth.  The  etterents 
descend  over  the  superficial  surface  of  the  submaxillary  gland,  and  terminate  in 
the  upper  deep  cervical  glands,  more  particularly  in  those  in.  the  immediate 
neighbourhood  of  the  termination  of  the  common  carotid  artery. 

The  supra-hyoid  or  submental  glands  lie  immediately  beneath  the  chin  superficial 
to  the  mylo-hyoid  muscles  and  between  the  two  anterior  bellies  of  the  digastric 
muscles.  They  are  apt  to  become  enlarged  in  diseased  conditions  of  the  middle  part 
of  the  lower  lip,  the  adjacent  part  of  the  gums,  the  anterior  part  of  the  floor  of  the 
mouth,  the  tip  of  the  tongue,  and  the  skin  beneath  the  chin,  for  their  afferent  vessels 
drain  those  parts.  The  efferents  from  this  group  of  glands  pass  partly  to  the  sub- 
maxillary lymphatic  glands,  and  partly  to  a  deep  cervical  gland  situated  on  the 
siiperficial  surface  of  the  internal  jugular  vein  at  the  level  of  the  cricoid  cartilage. 

The  post-pharyngeal  glands  lie  behind  the  pharynx  and  in  front  of  the  upper 
two  cervical  vertebrae.  Their  afferents  are  derived  from  the  nasal  cavities  and  the 
air  sinuses  communicating  with  them,  the  naso-pharynx,  the  Eustachian  tube  and 
tympanic  cavity,  and  the  adjacent  muscles,  ligaments,  and  bones.  Thus  they 
receive  the  lymph  outflow  from  a  large  area  much  subject  to  inflammatory  condi- 
tions, and  on  this  account  they  not  uncommonly  become  infected  and  form  the  foci 
of  post-pharyngeal  abscesses. 

Their  efferents  terminate  in  the  upper  deep  cervical  glands. 

The  anterior  jugular  glands  are  of  small  size  ;  they  are  very. variable  and  of  little 
importance.  When  they  are  present  they  lie  along  the  course  of  the  anterior 
jugular  vein. 

The  pre  -  laryngeal  glands  are  also  very  variable.  When  present  they  lie  in 
the  crico-thyroid  space  between  the  anterior  borders  of  the  crico-thyroid  muscles. 
Their  afferents  are  derived  from  the  lower  and  middle  parts  of  the  larynx, 
the  upper  part  of  the  trachea,  and  the  thyroid  hodj.  Their  efferents  as  a  rule 
terminate  in  the  lower  deep  cervical  glands,  but  they  also  anastomose  with  the 
afferents  of  the  pre-tracheal  glands,  and  occasionally  they  ascend,  and,  uniting  with 
the  lymphatics  from  the  region  of  the  upper  part  of  the  larynx,  they  terminate  in 
the  upper  deep  cervical  glands  in  the  region  of  the  posterior  belly  of  the  digastric 
muscle. 

The  pre-tracheal  glands  are  generally  present,  but  are  small.  They  lie  upon  the 
surface  of  the  trachea,  receiving  afferents  from  the  trachea,  the  lower  part  of  the 
thyroid  body,  and  occasionally  from  the  pre-laryngeal  glands.  Their  efferents  join 
the  lower  deep  cervical  glands. 


912 


THE  VASCULAE  SYSTEM. 


Fig."  662. — Sfi'EUKiciAL  LyMi-HATic  Vessels  ok  thi 
'Tronk,  and  the  Ly-mphatic  Glands  and  Vessels- 
Superficial  AND  Deep— OF  the  Limbs  (diagram- 
niatic).     All  superficial  lymphatics  are  printed  black 


The     deep     cervical     glands     lie 

under  cover  of  the  sterno -mastoid 
and  in  the  posterior  triangle  of  the 
neck.  The  former  are  designated 
sub -sterno -mastoid  and  the  latter 
supra-clavicular.  They  form  in  reality 
acontinuous  sheet  of  glandular  nodules 
connected  together  by  vessels,  but  it 
is  usual  to  separate  them,  on  account 
of  their  positions,  into  those  which 
are  sub -sterno -mastoid  and  those 
which  lie  in  the  posterior  triangle 
and  are  therefore  supra-clavicular. 

The  sub-sterno-mastoid  glands  are 
separable  into  external  and  internal 
chains. 

The  external  chain  of  sub-sterno- 
mastoid  glands  lies  behind  the  in- 
ternal jugular  vein  under  cover  of 
the  posterior  border  of  the  sterno- 
mastoid  muscle  and  on  the  roots  of 
the  cervical  plexus  of  nerves.  The 
glands  of  this  chain  receive  afferents 
from  the  occipital,  mastoid,  and  ex- 
ternal jugular  glands,  from  the  pinna, 
the  posterior  part  of  the  scalp  and 
the  adjacent  muscles,  and  the  "bones 
and  skin  of  the  neck.  The  group  is 
continuous  below  with  the  supra- 
clavicular* glands,  and  its  efferents 
terminate  either  in  those  glands  or 
in  the  glands  of  the  internal  sub- 
sterno-mastoid  chain.  When  they 
become  enlarged  the  external  sub- 
sterno-mastoid  glands  can  be  felt 
and  even  seen  projecting  from  under 
cover  of  the  posterior  border  of  the 
sterno-mastoid. 

The  internal  chain  of  sub-sterno- 
mastoid  glands  extends  along  the  in- 
ternal jugular  vein  from  the  base  of 
the  cranium  to  the  clavicle,  and  it  is 
not  uncommonly  spoken  of  as  con- 
sisting of  two  groups  of  glands  which 
are  called  the  upper  and  lower  deep 
cervical  glands,  the  former  lying 
above  and  the  latter  below  the  level 
of  the  thyroid  cartilage.  There  is, 
however,  no  distinct  separation  be- 
tween the  two  groups,  and  the  division 
is  made  use  of  merely  for  convenience 
in  indicating  the  higher  or  lower 
terminations  of  the  afferent  vessels. 


the  deep  lymphatics  throughout  are  coloured  red. 


Afferent  vessels  are  represented  by  continuous  lines  ;  efferent  and  interglandular  vessels  by  dotted  lines. 


A.A.  Anterior  axillary  glands. 

A.C.  Ante-cubital  glands. 

A.I.  Anterior  tibial  glands. 

D.F.  Deep  femoral  glands. 


E.A.  External  axillary  glands.  P.A. 

I.  Inguinal  glands.  S.C. 

I.e.  Infra-clavicular  or  subclavian  glands.  S.F. 

P.  Pubic  glands.  U. 


Posterior  axillary  glandf . 
Supra-trochlear  glands. 
Superficial  femoral  glands. 
Urethral  lymphatics. 


LYMPHATIC  GLANDS  AND  VESSELS  OF  UPPEE  EXTEEMITY.     913 

The  upper  group  (lymphoglandulie  cervicales  profundse  superiores)  extends  from 
the  base  of  the  skull  to  the  bifurcation  of  the  common  carotid  artery  at  the  level 
of  the  upper  border  of  the  thyroid  cartilage.  Its  constituent  glands  vary  consider- 
ably in  size,  and  one  of  the  largest,  which  lies  under  cover  of  the  posterior  Ijclly  of 
the  digastric  muscle,  receives  the  majority  of  the  lymphatics  from  the  tongue,  and 
is  therefore  of  great  clinical  importance.  The  glands  of  this  group  are  connected 
with  many  important  regions,  and  are  therefore  liable  to  become  enlarged  as  a  result 
of  diseased  conditions  in  many  of  the  upper  parts  of  the  head  and  neck.  Their 
atferents  are  derived  from  the  interior  of  the  cranium,  the  nose,  the  pharynx,  the 
palate,  the  tonsils,  the  upper  part  of  the  larynx,  the  whole  of  the  tongue,  except 
its  tip  and  the  anterior  third  of  each  lateral  border,  and  the  thyroid  body.  They 
also  receive  as  afferents  the  efferent  vessels  from  the  buccal,  the  internal  maxillary, 
the  retro-pharyngeal,  the  sub-parotid,  and  the  deep  parotid  glands,  and  from  some 
of  the  glands  of  the  external  sub-sterno-mastoid  chain.  They  occasionally  receive 
the  elferents  from  the  pre-laryngeal  glands  carrying  lymph  from  the  lower  part  of 
the  larynx. 

The  lower  glands  of  the  internal  sub-sterno-mastoid  chain  or  the  lower  deep 
cervical  glands  (lymphogiandulre  cervicales  pro  fund  se  inferiores)  lie  along  the  lower 
part  of  the  internal  jugular  vein.  They  receive  the  efferents  from  the  external 
chain  of  sub-sterno-mastoid  glands,  from  the  pre-laryngeal  glands,  and  from  a  group 
of  small  glands  which  lie  in  the  groove  between  the  trachea  and  oesophagus,  along 
the  course  of  the  recurrent  laryngeal  nerve.  These  glands  receive  lymph  from  the 
trachea,  oesophagus,  and  the  lower  part  of  the  thyroid  body. 

The  efferents  of  both  the  upper  and  lower  deep  cervical  glands  unite  together 
at  the  lower  part  of  the  neck  to  form  a  common  jugular  lymphatic  trunk  which 
terminates  on  the  right  side  either  by  uniting  with  the  subclavian  lymphatic  from 
the  upper  limb  to  form  the  right  lymphatic  duct,  or  separately  in  the  commence- 
ment of  the  innominate  vein.  On  the  left  side  the  jugular  lymphatic  trunk 
generally  ends  in  the  thoracic  duct,  but  it  may  end  either  in  the  internal  jugular, 
the  subclavian,  or  innominate  veins. 

The  supra- clavicular  glands  lie  in  the  anterior  part  of  the  posterior  triangle  of  the 
neck  amidst  the  descending  branches  of  the  cervical  plexus  and  on  the  roots  of  the 
brachial  plexus.  The  uppermost  part  of  this  group  is  continuous  with  the  external 
sub-sterno-mastoid  glands,  and  the  lowermost  is  situated  in  the  region  of  the 
termination  of  the  external  jugular  vein.  The'  afferent  vessels  are  derived  from 
the  neck  and  the  posterior  part  of  the  scalp ;  from  the  upper  extremity,  many  of 
the  efferents  of  the  external  axillary  glands  terminating  in  the  supra-clavicular 
glands,  whilst  occasionally  the  lymphatics  which  accompany  the  cephalic  vein 
cross  the  clavicle,  instead  of  dipping  into  the  subclavian  glands,  and  terminate  in 
the  supra-clavicular  glands.  In  addition,  s6me  of  the  lymphatics  on  the  pectoral 
region,  amongst  which  may  be  included  some  occasional  vessels  from  the  mammary 
gland,  also  end  in  the  supra-clavicular  glands. 

It  is  well  known  that  the  supra-clavicular  glands  sometimes  become  enlarged 
subsequent  to  the  appearance  of  malignant  conditions  in  the  abdomen  and  the 
mediastinum,  and  more  particularly  subsequent  to  affections  of  the  oesophageal 
portion  of  the  stomach.  The  course  along  which  the  infective  material  travels  in 
these  cases  is  not  yet  known,  for  as  yet  no  afferent  vessels  have  been  traced  to  the 
supra-clavicular  glands  from  the  mediastinum. 

The  efferents  of  the  supra-clavicular  glands  usually  terminate  in  the  jugular 
lymphatic  trunk. 

LYMPHATIC  GLANDS  AND  VESSELS  OF  THE  UPPER  EXTREMITY. 

The  lymphatic  glands  of  the  upper  extremity  are  divisible  into  (1)  superficial 

and  (2)  deep  sets. 

(1)  The  superficial  glands  lie  in  the  subcutaneous  tissue,  and  form  two  groups, 

a  lower  and  an  upper.     The  loiver  or  ante-cuhital  group  is  frequently  absent ;  when 

present  it  includes  two  or  three  glands  which  lie  in  front  of  the  elbow ;    they 

receive  afferent  vessels  from  the  front  of  the  forearm  and  from  the  median  part  of 

62 


914  THE  VASCULAE  SYSTEM. 

the  palm,  and  occasionally  become  enlarged  subsequent  to  infective  inflammations 
of  those  areas.  They  give  off  efferent  vessels  which  pass  upwards  and  inwards 
along  the  an tero- internal  aspect  of  the  arm.  At  varying  levels  these  efferents 
pierce  the  deep  fascia  and  terminate  in  the  external  axillary  glands.  The  upper 
or  siipra-trochlear  grottp  lies  a  short  distance  above  the  internal  condyle ;  as  a  rule 
it  includes  two  glands  only,  but  the  number  may  be  increased  to  four ;  they  lie 
close  to  the  commencement  of  the  basilic  vein,  and  their  afferent  vessels  are  derived 
from  the  inner  two  or  three  digits,  the  inner  side  of  the  forearm,  and  the  inner 
side  of  the  palm.  Their  efferents  pass  upwards  along  the  basilic  vein,  which  they 
accompany  through  the  opening  in  the  deep  fascia ;  they  then  join  the  deep 
lymphatics,  w"hich  are  ascending  along  the  brachial  artery,  and  accompany  them 
to  the  external  axillary  glands. 

(2)  The  deep  glands  lie  along  the  vessels  in  the  axilla  and,  just  below  the 
clavicle,  in  the  groove  between  the  pectoralis  major  and  the  deltoid  muscles. 
They  are  accordingly  divisible  into  {a)  the  axillary  and  (Jb)  the  infra-clavicular 
or  subclavian  glands. 

One  or  two  small  glands  are  occasionally  found  with  the  arteries  of  the  forearm 
and  a  few  with  the  brachial  artery ;  they  receive  deep  afferent  lymphatics  from 
the  adjacent  muscles,  ligaments,  and  the  bones,  and  they  give  off  efferent  vessels 
which  terminate  in  the  external  axillary  glands. 

(a)  The  axillary  glands  are  arranged  in  four  groups — external,  anterior, 
posterior,  and  central. 

(i.)  The  external  group  (lymphoglandulte  axillares)  consists  of  from  six  or  more 
glands  which  form  a  chain  along  the  antero-internal  aspect  of  the  axillary  vessels, 
extending  from  the  lower  border  of  the  pectoralis  major  to  the  outer  border  of 
the  first  rib.  They  receive  afferent  vessels,  both  superficial  and  deep,  from  the 
whole  of  the  upper  extremity ;  many  of  these  pass  directly  to  the  glands  from  the 
tissues,  the  remainder  include  the  efferents  of  the  superficial  and  deep  glands  of 
the  forearm  and  arm,  and  some  of  the  efferents  of  the  anterior  and  posterior 
axillary  glands.  The  efferents  of  the  external  axillary  glands  pass  along  the 
subclavian  vein,  and  the  majority  either  terminate  in  the  subclavian  glands  or 
unite  with  their  efferents  to  form  a  common  subclavian  trunk,  which  terminate 
on  the  right  side  in  the  right  lymphatic  duct  or  in  the  innominate  vein,  and  on 
the  left  side  in  the  thoracic  duct ;  but  some  of  the  efferents  end  in  the  supra- 
clavicular glands,  and  others  in  the  central  glands. 

(ii.)  The  anterior  axillary  or  pectoral  glands  (lymphoglandulse  pectorales), 
four  or  five  in  number,  lie  at  the  anterior  part  of  the  axilla,  in  the  angle  between 
the  pectoral  muscles  and  the  serratus  magnus.  They  receive  afferent  vessels 
from  the  superficial  parts  of  the  anterior  and  lateral  walls  of  the  body  above  the 
umbiUcus,  and  from  the  outer  two-thirds  of  the  mammary  gland.  Some  of  their 
efferents  pass  to  the  external  axillary  glands,  some  to  the  sul)clavian  glands,  and 
others  end  in  the  glands  of  tl)e  central  group. 

(iii.)  The  posterior  or  subscapular  set  of  axillary  glands  (lymphoglandulse 
subscapulares),  four  or  five  in  number,  lie  along  the  sides  of  the  subscapular 
artery  on  the  posterior  wall  of  the  axilla.  Their  afferents  are  the  superficia. 
lymphatics  of  the  lateral  and  posterior  parts  of  the  body-wall  above  the  umbilicus, 
and  the  superficial  lympliatics  of  the  lower  and  back  part  of  the  neck.  Their 
efferents  generally  join  the  external  and  central  axillary  glands,  but  some  may  end 
in  the  subclavian  glands. 

(iv.)  The  central  group  lies  at  the  Ijase  of  the  axilla  resting  on  the  axillary  fascia 
between  the  other  groups.  It  consists  of  from  three  to  five  glands  which  receive 
afferents  from  the  external,  posterior,  and  anterior  groups  of  glands,  and  its 
efferents  pass  to  the  subclavian  glands. 

(&)  The  infra- clavicular  or  subclavian  glands  lie  in  relation  with  the  upper 
part  of  the  axillary  vein,  and  appear  to  lie  the  upward  extension  of  the  external 
and  anterior  axillary  glands.  They  receive  efferents  from  all  four  groups  of 
axillary  glands,  a  deep  lympliatic  from  the  mamma  which  pierces  the  pectoralis 
major,  and  also  the  lymphatics  which  accompany  the  ceplialic  vein  and  carry 
lymjjh  from   tlie  outer  side  of   the  liand,  forearm,  and  arm.       In  the  course  of 


LYMPHATIC  GLANDS  AND  VESSELS  OF  UPPEE  EXTREMITY.    915 

these  latter  vessels  a  few  small  glauds  are  sometimes  interpolated  in  the  groove 
between  the  deltoid  and  pectoralis  major  muscles. 

The  lymphatic  vessels  of  the  upper  extremity  are,  like  the  glands,  arranged 
in  two  sets,  (1)  the  superficial  and  (2)  the  deep. 

The  superficial  lymphatic  vessels  cummence  in  cutaneous  plexuses  which 
are  linest  and  most  dense  on  the  palmar  aspects  of  the  fingers  and  hand.  The 
efiferents  from  the  palmar  digital  plexuses,  in  each  digit,  converge  to  four  trunks, 
which  lie  two  on  each  side  in  the  subcutaneous  tissue  on  the  lateral  margins  of 
the  dorsal  aspects  of  the  digits.  They  accompany  the  dorsal  digital  veins,  and, 
at  the  roots  of  the  digits,  they  pass  to  the  dorsum  of  the  hand,  where  they 
anastomose  together.  The  plexus  in  the  palm  of  the  hand  is  extremely  fine,  and 
efferents  pass  from  it  not  only  upwards,  but  also  downwards  and  laterally.  The 
upper  efferents,  three  or  four  in  number,  accompany  the  median  vein,  and  terminate 
either  in  the  superficial  glands  at  the  bend  of  the  elbow  or  in  the  supra-trochlear 
glands.  The  lower  efferents  pass  to  the  interdigital  spaces,  and  turn  backwards 
to  the  dorsum  to  join  the  digital  trunks.  The  lateral  efferents  turn  round  the 
borders  of  the  hand,  those  on  the  inner  side  join  the  efferents  from  the  little 
finger,  and  those  on  the  outer  side  the  efferents  from  the  thumb.  Occasionally 
some  of  the  efferents  which  pass  towards  the  outer  side  fuse  to  form  a  fairly  large 


Fig.  663. — Superficial  Lymphatics  of  thk  Digits  and  of  the  Dorsal  Aspect  of  the  Hand. 

trunk,  the  so-called  central  lymphatic,  which  turns  round  the  outer  side  of  the 
second  metacarpal  bone  and  unites  with  the  lymphatic  vessels  of  the  thumb  and 
index-finger. 

The  superficial  lymphatic  vessels  of  the  forearm,  including  those  which  ascend 
from  the  dorsum  and  the  palm  of  the  hand,  are  grouped,  for  the  main  part,  along 
the  radial,  median,  and  ulnar  veins,  the  lateral  vessels  being  joined  at  intervals  by 
tributaries  from  the  dorsum  of  the  limb. 

The  lymphatic  trunks  which  accompany  the  ulnar  veins  terminate  in  the  supra- 
trochlear glands,  and  those  which  accompany  the  median  vein  in  the  glands  at  the 
bend  of  the  elbow,  the  ante-cubital  glands,  or,  if  these  are  not  present,  in  the 
supra-trochlear  glands. 

The  efferent  vessels  of  the  ante-cubital  and  supra-trochlear  glands  have  already 
been  described  (p.  914). 

A  few  of  the  lymphatics  of  the  outer  side  of  the  forearm  and  some  of  those  of 
the  upper  arm  accompany  the  cephalic  vein  and  carry  lymph  to  the  infra-clavicular 
glands,  or  to  some  small  glands  which  lie  in  the  groove  between  the  deltoid  and 
pectoralis  major  muscles  whose  efferents  join  the  infra-clavicular  glands. 

All  the  remaining  superficial  vessels  of  the  upper  arm  and  forearm  pass  towards 
the  axilla.  They  pierce  the  deep  fascia,  and  terminate  in  the  external  set  of 
axillary  glands. 

The  deep  lymphatics  of  the  upper  extremity  commence  in  the  bones, 
periosteum,  hgaments,  muscles,  and  intermuscular  connective  tissue ;  they 
accompany  the  main  vessels,  and  some  of  them  terminate  in  the  deep  glands 
of  the  forearm  and  arm,,  but  the  majority  ascend  to  the  external,  set  of  axillary 
glands. 


916  THE  VASCULAE  SYSTEM. 

THE   LYMPHATIC  GLANDS  AND  VESSELS  OF   THE   LOWER   EXTREMITY. 

Lymphatic  Glands  of  the  Lower  Extremity. — Like  those  of  the  upper 
extremity,  these  glands  are  arranged  in  two  sets,  (1)  superficial  and  (2)  deep. 

(1)  Superficial  Glands. — The  superficial  glands  all  lie  in  the  region  of  the 
groin,  and  form  three  groups — the  superior,  the  inferior,  and  the  internal,  which  are 
all  closely  associated  togetlier  by  numerous  inter-communicating  channels. 

(a)  The  superior  or  inguinal  group  includes  from  four  to  seven  flattened  ovoid 
glands  which  lie  parallel  with  and  just  below  Poupart's  ligament.  They  receive 
afferent  vessels  from  the  back  and  outer  part  of  the  thigh  and  the  buttock,  and 
the  superficial  lymphatics  from  the  body-wall  below  the  level  of  the  umbilicus, 
except  those  from  the  lower  and  anterior  part  which  pass  to  the  internal  group  of 
glands.  Their  efferents  pass  through  the  deep  fascia,  and  terminate  in  either  the 
deep  femoral  or  the  lower  external  iliac  glands. 

(6)  The  inferior  or  superficial  femoral  group  is  formed  by  from  three  to  six  oval 
glands  which  are  disposed  vertically  along  the  upper  part  of  the  internal  or  long 
saphenous  vein.  They  receive  all  the  superficial  lymphatics  of  the  foot  and  leg, 
except  a  few  which  accompany  the  external  saphenous  vein  to  the  popli-teal  glands  ; 
all  the  superficial  lymphatics  of  the  thigh,  except  those  from  the  upper  and  outer 
part,  which  terminate  in  the  superior  set  of  glands,  and  a  few  from  the  upper  and 
inner  part  which  terminate  in  the  inner  group  of  glands.  They  also  occasionally 
receive  lymphatics  from  the  perineum  and  scrotum.  The  efferent  vessels  of  the 
femoral  group  pass  through  the  saphenous  opening,  and  terminate  either  in  the 
deep  femoral  glands  or  in  the  lower  external  iliac  glands. 

(c)  The  internal  or  pubic  group  includes  two,  three,  or  four  rounded  glands 
wliich  lie  internal  to  the  saphenous  opening  and  close  to  the  spine  of  the  pubis. 
They  receive  afferent  vessels  from  the  lower  and  middle  portion  of  the  abdominal 
wall,  from  the  upper  and  inner  part  of  the  thigh,  from  the  skin  of  the  external 
genitals,  including  some  of  the  lymphatics  from  the  lower  third  of  the  vagina  in 
the  female,  and  from  the  perineum,  including  some  of  the  lymphatics  of  the  lowest 
part  of  the  anal  passage  and  anus,  in  both  sexes.  The  vessels  from  the  lower  third 
of  the  vagina  and  the  corresponding  part  of  the  rectum  communicate  not  only 
with  the  inguinal  glands  but  also  with  the  sacral  glands.  The  efferent  vessels  of 
the  pubic  glands  communicate  with  the  efferents  of  the  superior  and  inferior 
groups,  and,  after  passing  through  the  saphenous  opening,  they  terminate  either 
in  the  deep  femoral  or  the  lower  external  iliac  glands.  Although  the  general 
arrangement  of  the  afferent  vessels  of  the  superficial  inguinal  glands  is  that  above 
indicated,  it  must  be  understood  that  it  is  not  constant,  and  that  lymphatics  which 
frequently  terminate  in  one  group  may  in  some  cases  end  in  an  adjacent  group, 
a  fact  which  must  be  kept  in  mind  in  the  investigation  of  diseased  conditions. 

(2)  Deep  Glands. — The  deep  lymphatic  glands  of  the  lower  extremity  are 
found  on  the  upper  yjart  of  the  interosseous  membrane  of  the  leg,  in  the  popliteal 
space,  and  in  Scarpa's  triangle. 

The  anterior  tibial  gland  (lymphoglandula  tibialis  anterior)  is  situated  near  the 
anterior  tibial  artery  on  the  upper  part  of  the  front  of  the  interosseous  membrane. 
It  receives  afferent  vessels  from  the  deep  parts  of  the  sole  and  the  dorsum  of  the 
foot,  and  from  the  deep  parts  of  the  front  of  the  leg.  It  gives  off  two  efferent 
vessels  which  pass  backwards  along  the  anterior  tibial  artery  and  terminate  in  the 
popliteal  glands. 

The  popliteal  glands  (lymphoglanduke  poplitese)  are  four  or  five  in  number ; 
they  lie  in  the  ptjpliteal  space,  generally  round  the  popliteal  artery,  but  occasion- 
ally there  is  one  immediately  beneath  tlie  deep  fascia  near  the  entrance  of  the 
external  saphenous  vein.  They  receive  afferent  vessels  from  the  sole  of  the  foot 
and  the  back  of  the  leg,  from  the  anterior  tibial  gland  and  the  knee-joint ;  they 
also  receive  the  superficial  lymphatics  which  accompany  the  external  saphenous 
vein.  The  majority  of  the  efferent  vessels  join  the  deep  femoral  glands,  but  some 
become  superficial  and  end  in  the  inferior  superficial  femoral  glands,  and  it  is 
stated  that  others  accompany  the  sciatic  nerve  and  end  in  the  lateral  pelvic  glands. 

The  deep  femoral  glands,  three  or  four  in  number,  lie  on  the  inner  side  of  the 


LYMPHATIC  GLANDS  AND  VESSELS  OF  LOWER  EXTREMITY.    917 

femoral  vein,  and  the  largest  of  the  group,  known  as  the  gland  of  Clo(j[uet  or 
Rosenmiiller,  is  embedded  in  the  crural  canal.  Their  afferent  vessels  are  the 
efterents  of  the  popliteal  glands,  some  of  the  etferents  from  the  superficial  glands  of 
the  groin,  the  lymphatics  from  the  glans  penis  and  some  of  the  lymph  vessels 
from  the  penile  portion  of  the  urethra,  and  the  deep  lymphatic  vessels  from  the 
front  and  outer  side  of  the  thigh  and  knee.  Their  efterents  pass  to  the  external 
iliac  glands. 

Lymphatic  Vessels  of  the  Lower  Extremity. — There  are  two  sets  of  these 
vessels,  (1)  the  superficial  and  (2)  the  deep. 

(1)  Superficial  Vessels. — The  superficial  lymphatics  lie  in  the  subcutaneous 
tissues.  They  commence  in  plexuses  which  are  best  marked  on  the  plantar  aspects 
of  the  toes  and  foot.  The  lymphatic  vessels  which  emerge  from  the  plantar  plexus 
in  each  toe  terminate  in  four  digital  vessels  which  are  arranged  in  pairs  along  the 
dorso-lateral  border  of  the  digit,  and  these  end  posteriorly  in  a  plexus  on  the 
dorsum  of  the  foot. 

Some  of  the  vessels  which  drain  the  plexus  in  the  sole  of  the  foot  turn  round 
the  outer  and  inner  borders  of  the  foot  and  join  the  dorsal  plexus,  whilst  others 
pass  up  the  leg  with  the  efferent  vessels  from  the  dorsal  plexus. 

The  efferent  vessels  from  the  dorsal  lymphatic  plexus  of  the  foot  form  two 
groups,  an  inner  and  an  outer.  The  inner  vessels  are  the  more  numerous,  and 
they  are  joined  by  additional  vessels  from  the  inner  part  of  the  sole  and  heel. 
Some  of  them  pass  upwards  in  front  of  and  others  behind  the  internal  malleolus ; 
in  the  leg  they  accompany  the  internal  saphenous  vein,  and  they  terminate  in  the 
lower  or  femoral  set  of  superficial  glands.  The  outer  group  of  vessels  is  reinforced 
by  tributaries  from  the  outer  side  of  the  sole  and  heel :  most  of  the  vessels  of 
this  group  pass  upwards  in  front  of  the  external  malleolus,  but  some  go  behind 
that  prominence  of  bone  ;  they  gradually  turn  inwards  as  they  ascend,  and,  passing 
across  the  front  of  the  leg,  they  join  the  internal  group,  being  first  reinforced 
by  numerous  additional  vessels  from  the  front  and  outer  side  of  the  leg,  and 
they  terminate,  with  the  vessels  of  the  inner  group,  in  the  superficial  femoral 
glands. 

A  few  vessels  of  the  outer  group,  and  one  or  two  large  vessels  which  rise  from 
the  back  of  the  heel  and  the  lower  part  of  the  leg,  ascend  along  the  external 
saphenous  vein,  pierce  the  popliteal  fascia,  and  terminate  in  the  popliteal 
glands. 

The  superficial  lymphatic  vessels  from  the  front,  the  lower  and  outer,  lower 
and  inner,  and  the  back  parts  of  the  thigh  and  knee,  terminate  in  the  superficial 
femoral  glands.  The  vessels  from  the  upper  and  outer  parts  of  the  thigh  and 
from  the  buttock  end  in  the  superficial  inguinal  glands,  and  those  from  the  upper 
portions  of  the  inner  and  back  parts  of  the  thigh  in  the  superficial  pubic 
glands. 

(2)  Deep  Vessels. — The  deep  lymphatics  of  the  lower  extremity  commence  in 
the  bones,  periosteum,  ligaments,  muscles,  and  deep  connective  tissue.  They  follow 
the  main  arteries,  and  they  terminate  in  the  anterior  tibial,  popliteal,  and  deep 
femoral  glands. 

The  vessels  which  terminate  in  the  anterior  tibial  gland  have  already  been 
mentioned  (p.  916). 

The  majority  of  the  deep  vessels  from  the  sole  accompany  the  plantar  arteries ; 
they  ascend  in  the  leg  along  the  posterior  tibial  vessels,  and  are  joined  by  the  deep 
lymphatics  of  the  back  of  the  leg  which  accompany  the  peroneal  and  posterior 
tibial  arteries.  At  the  lower  border  of  the  popliteus  the  deep  vessels  of  the  back 
of  the  leg  meet  the  efferent  vessels  from  the  anterior  tibial  gland  and  ascend  with 
them  to  the  popliteal  glands. 

The  deep  lymphatics  of  the  front  of  the  thigh  and  the  efferents  of  the  popliteal 
glands  end  in  the  deep  femoral  glands ;  those  of  the  upper  part  of  the  back  of  the 
thigh  and  buttock  accompany  the  sciatic  and  gluteal  vessels,  and  terminate  in  the 
lateral  pelvic  glands  ;  the  deep  ^'essels  which  originate  amidst  the  upper  portions 
of  the  adductor  muscles  and  their  surroundings  accompany  the  obturator  vessels, 
and  terudnate  in  the  obturator  or  in  the  lateral  pelvic  glands. 
%2a 


918  THE  VASCULAR  SYSTEM. 

THE  LYMPHATIC  GLANDS  AND  VESSELS  OF  THE  ABDOMEN  AND 

PELVIS. 

The  superficial  lymphatics  of  the  abdominal  wall  have  already  been  sufficiently 
referred  to  as  afferent  vessels  of  the  axillary  glands  and  of  the  superficial  glands  of 
the  groin  (pp.  914  and  916). 

Deep  Lymphatic  Glands  and  Vessels. — The  lymphatic  glands  of  the  abdomen 
and  pelvis  are  arranged  in  two  main  groups,  (1)  the  visceral  glands  and  (2)  the 
parietal  glands.  The  visceral  glands  lie  in  close  relation  with  the  waUs  of  the 
viscera  or  in  the  folds  of  peritoneum,  by  which  the  viscera  are  either  connected 
together  or  attached  to  the  walls  of  the  abdomen  or  pelvis;  they  receive  the 
majority  of  the  lymphatic  vessels  from  the  viscera  with  which  they  are  associated. 
The  parietal  glands  lie  between  the  peritoneum  and  the  walls  of  the  abdomen  and 
pehds ;  they  receive  deep  vessels  from  the  abdominal  and  pelvic  parietes,  and  from 
the  deep  parts  of  the  thigh  and  buttock.  They  also  receive  efferent  lymphatics 
from  the  glands  of  the  lower  extremities,  as  well  as  some  of  the  efferent  vessels 
from  the  visceral  glands,  and  a  few  vessels  which  pass  directly  to  them  from  the 
walls  of  the  viscera. 

(1)  The  visceral  glands  include  the  following  : — 

Gastric  Glands. — The  gastric  glands  are  separable  into  the  coronary,  the  sub- 
pyloric,  and  the  retro-pyloric  groups. 

The  coronary  glands  (lymphoglandulae  gastricse  superiores)  are  situated  in 
relation  with  the  upper  part  of  the  small  curvature  of  the  stomach  between  the 
layers  of  the  gastro-hepatic  omentum,  and  in  the  left  pancreatico-gastric  fold 
immediately  behind  and  to  the  right  of  the  cardiac  orifice.  They  receive  afferents 
from  the  small  curvature,  except  at  the  pyloric  end,  and  from  a  little  more  than 
the  right  halves  of  the  anterior  and  posterior  walls  of  the  vertical  portion  of  the 
stomach.  They  also  receive  afferents  from  the  left  and  posterior  part  of  the  upper 
surface  of  the  liver.  Their  efferents  terminate  in  the  cceliac  group  of  pre-aortic 
glands. 

The  sub-pyloric  glands  lie  in  the  gastro-colic  omentum  near  the  pyloric  end  of  the 
stomach.  Their  afferents  are  derived  from  the  lower  part  of  the  great  curvature  and 
from  the  immediately  adjacent  parts  of  the  anterior  and  posterior  surfaces  of  the 
stomach.     Their  efterents  end  in  the  retro-pyloric  glands. 

The  retro-pyloric  glands  are  very  variable.  They  are  situated  directly  behind 
the  pyloric  end  of  the  stomach  and  the  first  part  of  the  duodenum,  in  close  associa- 
tion with  the  gastro-duodenal  artery  and  in  the  right  pancreatico-gastric  fold. 
They  receive  as  afferents  the  efferents  of  the  sub-pyloric  glands,  and  also  afferent 
vessels  from  the  right  part  of  the  small  curvature  and  from  the  posterior  surface 
of  the  pyloric  portion  of  the  stomach.  Their  efferents  pass  to  the  coeliac  group 
of  pre-aortic  glands. 

In  certain  cases  of  disease  of  the  gastric  glands,  more  particularly  of  the  coronary 
group,  metastatic   deposits   occur   in   the  supra-clavicular  glands,  but   no    direct. 
connexion  between  the  two  groups  of  glands  has  hitherto  been  discovered. 

The  lymphatics  from  the  anterior  and  posterior  walls  of  the  left  half  of  the 
vertical  portion  of  the  stomach  pass  to  the  splenic  glands. 

The  splenic  glands  lie  near  the  hilum  of  the  spleen  in  relation  with  the  tail  of 
the  pancreas,  and  in  the  lieno-renal  ligament ;  they  receive  the  lymph  vessels  from 
the  left  half  of  the  vertical  portion  of  the  stomach,  from  the  capsule  and  the 
substance  of  the  spleen,  and  from  the  pancreas.  Their  efferent  vessels,  accompanied 
by  some  of  the  lymphatics  from  the  left  part  of  tlie  great  curvature  of  the  stomach, 
pass  inwards  in  tli"-.  lieno-renal  ligament  and  teruiinate  in  the  cceliac  glands. 

The  hepatic  glands  lie  in  the  liilum  of  tlie  liver  and  in  the  small  omentum 
beneath  it.  Many  lie  along  the  left  side  of  the  vertical  portion  of  the  portal  vein, 
and  others  along  the  common,  the  hepatic,  and  tlie  cystic  lule  ducts.  The  highest, 
of  the  latter,  which  lies  close  to  the  neck  of  the  gall  Ijladder,  is  known  as  the  cystic 
gland ;  it  constitutes,  however,  but  one  of  the  hepatic  glands.  The  cystic  gland 
receives  afferents  from  the  lateral  and  undcjr  surface  of  the  right  lobe  to  the  right 
of  the  gall  bladder,  and  the  remaining  hepatic  glands  receive  afferents  from,  the 


LYMPHATIC  GLANDS  AND  VESSELS  OF  THE  ABDOMEN.      919 


anterior  surface,  from  the  Spigelian  and  the  quadrate  lobes,  and  from  the  lower  and 
anterior  portion  of  the  deep  substance  of  the  liver.  The  efferents  of  the  hepatic 
glands  pass  to  the 
coeliac  group  of 
pre-aortic  glands. 
The  pancreatic 
glands  (lympho- 
glanduh^  pancre- 
aticae),  which  are 
sometimes  in- 
cluded in  the 
splenic  group,  lie 
along  the  upper 
border  of  the  pan- 
creas behind  the 
small  sac  of  the 
peritoneum;  they 
receive  the  lym- 
phatics    which 

issue     from     the 

pancreas,      and 

efferents  from  the 

splenic  and  from 

the     diaphrag- 
matic     glands. 

Their  efferent  ves- 
sels terminate  in 

the  coeliac  glands. 
The     superior 

mesenteric  glands 

(lymphoglandulae 

mesentericse)   are 

numerous  (100  to 

200) ;     they    are 

scattered  between 

the  layers  of  the 

mesentery  and  in 

the    transverse 

mesocolon,  and 

they   are    most 

numerous  in  that 

portion   of   the 

mesentery  which 

is  connected  with 

the       jejunum. 

They  vary  in  size, 

but  the  largest  are 

rarely  larger  than 

an   almond ;    the 

smaller  glands  lie 

near  the  intestine, 

and     the     larger 

near  the  attached 

border      of      the 

mesentery.    They 

receive  afferent 

vessels    from  the 


Fig.  664.- 


-Deep  Lymphatic  Glands  and  Vessels  of  the  Thorax  and 
Abdomen  (diagrammatic). 


Lateral  lympbatics  are  coloured  black,  and  mesial  red.     Aflerent  vessels  are  repre- 
sented by  continuous  lines,  and  efterent  and  iuterglandular  vessels  by  dotted  lines. 


C. 

C.L 

D.C. 

E.I. 

I. 

LL 

L. 


Common  iliac  glands. 
Common  intestinal  trunk. 
Deep  cervical  glands. 
External  iliac  glands. 
Intercostal  glands  and  vessels. 
Internal  iliac  glands. 
Lateral  aortic  glands. 


M. 

P.A. 

R.C. 

R.L.D. 

S. 

S.A. 

T.D. 


Mediastinal  glands  and  vessels. 

Pre-aortic  glands  and  vessels. 

Eecejitac  Ilium  cbylii. 

Eight  lymphatic  duct. 

Sacral  glands. 

Scalenus  anticus  muscle. 

Thoracic  duct. 


walls  of  the  jejunum  and  ileum,  and  from  the  ascending  colon,  the  ca?cum,  and  the 
transverse  colon.     Their  efterents  terminate  in  the  pre-aortic  glands. 
62& 


920  THE  VASCULAE  SYSTEM. 

The  ileo-caecal  glands,  four  or  five  in  number,  are  a  subsidiary  group  of  the 
mesenteric  glands,  and  are  situated  in  the  lowest  part  of  the  mesentery  near  the 
angle  between  the  ileum  and  the  ascending  colon.  They  receive  afferent  vessels 
from  the  lowest  part  of  the  ileum,  from  the  ctecum,  and  from  the  vermiform 
appendix,  and  their  efferent  vessels  pass,  with  those  of  the  other  mesenteric  glands, 
into  the  pre-aortic  glands.  One  of  them,  the  apj^endicular  gland,  is  occasionally 
separated  from  the  rest,  and  is  placed  in  the  base  of  the  mesentery  of  the  vermi- 
form appendix.  This  gland  is  of  special  interest,  not  only  because  it  receives  the 
lymphatics  of  the  appendix,  but  also  because  in  the  female  some  of  the  lymphatics 
of  the  right  ovary  terminate  in  it. 

The  colic  glands  are  also,  for  the  main  part,  a  subsidiary  group  of  superior 
mesenteric  glands ;  they  He  in  relation  with  the  ascending  portion  of  the  colon  and 
in  the  transverse  mesocolic  fold  of  the  peritoneum.  They  receive  the  lymphatic 
vessels  which  issue  from  the  portion  of  the  gut  in  their  immediate  neighbourhood, 
and  their  efferent  vessels  terminate  in  the  juxta-  and  pre-aortic  glands  and  in  glands 
round  the  root  of  the  superior  mesenteric  artery. 

The  inferior  mesenteric  glands  are  situated  in  the  course  of  the  inferior  mesen- 
teric artery  and  its  branches ;  they  receive  lymph  from  the  ileo-pelvic  and  descending 
colon  and  transmit  it  to  the  juxta-  and  pre-aortic  glands. 

The  rectal  glands  are  a  few  small  glands  which  lie  in  the  meso-rectum  and  the 
areolar  tissue  between  the  rectum  and  the  sacrum  ;  they  are  small,  and  they  receive 
lymphatic  vessels  from  the  upper  part  of  the  rectum.  Their  efferent  vessels 
teriidnate  in  the  juxta-aortic  and  sacral  glands. 

The  coeliac  glands  (lymphoglandulse  cceliacse)  surround  the  cceliac  axis,  and 
lie  in  front  of  the  abdominal  aorta  above  the  origin  of  the  superior  mesenteric 
artery,  and  are  simply  a  group  of  the  upper  pre-aortic  glands.  They  vary  in 
number,  and  are  of  large  size ;  they  receive  the  efferent  vessels  from  the  gastric, 
splenic,  pancreatic,  and  hepatic  glands,  and  their  efferent  trunks  unite  with  the 
efferents  from  the  pre-aortic  glands,  and  form  with  them  a  single  trunk,  the 
common  intestinal  lymphatic  trunk,  which  terminates  in  the  receptaculum  chyli. 

(2)  The  parietal  glands  of  the  abdomen  and  pelvis  are  as  follows : — 

The  external  iliac  glands  are  arranged  in  three  groups,  an  outer,  a  middle,  and 
an  inner,  placed  respectively  to  the  outer  side,  in  front  of,  and  to  the  inner  side  of 
the  external  iliac  artery.  The  inner  group  is  situated  in  the  ca^dty  of  the  pelvis 
between  the  external  iliac  vein  and  the  obturator  nerve,  but  inasmuch  as  it  is 
directly  associated  with  the  efferent  vessels  from  the  deep  crural  glands  it  must  be 
ascribed  to  the  external  iliac  group.  Each  group  forms  a  chain  consisting  of  three 
or  more  glands,  and  the  lowest  gland  of  each  chain,  which  is  situated  immediately 
above  Poujjart's  ligament,  is  known  as  a  retro-crural  gland.  The  internal  chain  of 
external  iliac  glands  receives  afferents  from  the  deep  and  superficial  inguinal  glands, 
from  the  deeper  portions  of  the  abdominal  wall  from  the  region  of  the  umbilicus 
downwards,  from  the  adductor  group  of  muscles  along  the  obturator  nerve  and 
artery,  from  the  neck  of  the  bladder,  from  the  prostate,  from  the  membranous  and 
bulbous  parts  of  the  urethra,  and  also  afferents  from  tlie  glans  penis  or  the  glans 
clitoris  which  have  passed  along  the  crural  canal.  Its  efferents  pass  to  either  the 
common  or  internal  iliac  glands. 

The  middle  chain  is  connected  by  anastomosing  vessels  both  with  the  internal 
and  external  chains,  and  it  also  receives  afferent  vessels  from  the  neck  of  the  uterus 
and  the  upper  part  of  the  vagina  in  the  female,  from  the  prostate  in  the  male,  and 
from  the  bladder  in  both  sexes.     Its  efferents  pass  to  the  common  iliac  glands. 

The  afferents  of  the  external  chain  convey  lymph  from  the  superficial  and  deep 
inguinal  glands  from  the  deeper  parts  of  the  lateral  and  anterior  portions  of  the 
abdominal  wall,  and  a  certain  amount  of  lymph  from  the  glans  penis  or  clitoris 
which  passes  along  vessels  which  traverse  the  inguinal  canal. 

If  the  student  bears  in  mind  what  has  already  been  said  with  regard  to  the 
inguinal  and  external  iliac  glands,  it  will  be  obvious  to  him  that  whilst  the 
lymphatics  of  the  scrotum  and  the  skin  of  the  penis  terminate  entirely,  or  almost 
entirely,  in  the  superficial  inguinal  glands,  those  of  the  glans  pass  to  the  deep  crural 
and  the  retro-crural  glands,  and  it  is  worth  noting  that  some  of  those  which  end  in 


LYMPHATIC  GLANDS  AND  VESSELS  OF  THE  ABDOMEN.      921 

the  retro-crural  glands  pass  to  their  terminations  along  the  crural  and  others  along 
the  inguinal  canal.  It  is  also  a  matter  of  clinical  importance  to  remember  that  the 
lymphatics  from  the  urethra  also  end  partly  in  the  deep  inguinal  glands,  partly  in 
the  external  iliac  glands,  and  partly  in  the  internal  iliac  glands :  those  which 
terminate  in  the  latter  glands  including  some  which  carry  lymph  from  the 
prostatic,  membranous,  and  bulbar  parts  of  the  canal. 

The  efferents  of  the  external  iliac  glands  terminate  in  the  common  iliac  glands. 

The  obturator  gland  is  situated  in  the  pelvis  at  the  upper  end  of  the  obturator 
canal  below  and  behind  the  obturator  nerve.  It  is  not  constant,  but  when  it  is 
present  it  receives  lymph  from  the  deeper  parts  of  the  inner  portion  of  the  thigh, 
and  its  efferent  vessels  end  in  the  inner  chain  of  external  iliac  glands. 

The  deep  glands  of  the  anterior  wall  of  the  abdomen. — These  glands  are  irregular 
both  in  number  and  occurrence,  and  they  are  small  in  size.  When  they  are 
present  they  lie  along  the  deep  circumflex  iliac  and  the  deep  epigastric  arteries, 
and  are  known  as  the  circumflex  iliac  and  epigastric  glands,  in  addition,  however, 
there  are,  at  least  in  the  child,  one  or  two  small  glands  lying  in  relation  with  the 
posterior  surface  of  the  sheath  of  the  rectus  abdominis  above  the  umbilicus,  the 
supra-umbiUcal  glands,  and  there  is  frequently  a  single  infra-umbilical  gland 
situated  to  one  or  the  other  side  of  the  middle  line  below  the  umbilicus.  The 
circumjiex  iliac  and  eiyigastric  glands  receive  afferents  from  the  adjacent  parts  of 
the  abdominal  w"alls,  and  their  efterents  end  in  the  external  iliac  glands.  The 
supra-  and  infra-umhilical  glands  are  connected  with  the  rich  lymphatic  plexuses 
of  the  umbihcal  region.  It  is  probable  that  the  supra-umbilical  glands  are  also 
associated  with  the  lymphatics  of  the  anterior  part  of  the  upper  surface  of  the 
liver ;  and  the  infra- umbilical  gland  wdth  the  lymphatics  of  the  upper  and 
anterior  part  of  the  bladder.  At  aU  events  it  seems  certain  that  the  lymphatics 
of  the  bladder  are  connected  with  those  of  the  umbilical  plexuses,  and  it  is  almost 
certain  that  in  some  cases  at  least  they  are  either  directly  or  indirectly  associated 
with  the  infra-umbilical  gland. 

The  internal  iliac  glands  are  not  in  all  cases  to  be  clearly  defined  from  the  inner 
set  of  external  iliac  glands,  but  if  it  be  accepted  that  all  glands  on  the  side  wall  of 
the  pelvis  above  and  in  front  of  the  obturator  nerve  be  looked  upon  as  external 
iliac  glands, — and  this  is  a  reasonable  view  inasmuch  as  they  are  in  direct  associa- 
tion with  the  deep  crural  glands, — then  all  other  glands  which  lie  in  relation  with 
the  side  wall  of  the  pelvis  may  be  considered  as  internal  ihac  glands.  As  a  general 
rule  it  may  be  said  that  the  larger  glands  of  the  internal  iliac  group  are  situated 
in  the  regions  of  the  origins  of  the  branches  of  the  internal  iliac  artery,  extending 
in  an  irregular  row  from  the  root  of  the  obliterated  hypogastric  artery  in  Iront  to 
the  origin  of  the  gluteal  artery  behind.  They  receive  afferents  from  the  upper 
part  of  the  anal  passage,  and  from  the  lower  part  of  the  rectum ;  from  the  middle 
part  of  the  vagina  and  the  lower  part  of  the  uterus ;  some  lymphatics  from  the 
lower  and  posterior  part  of  the  bladder ;  from  the  prostate,  the  prostatic  and 
membranous  parts  of  the  urethra ;  and  from  the  deeper  parts  of  the  back  of  the 
thigh  and  the  buttock  which  are  suj)plied  by  the  sciatic  and  gluteal  arteries.  The 
efferent  vessels  pass  to  the  posterior  group  of  the  common  iliac  glands. 

The  lateral  sacral  glands  may  be  considered  as  associates  of  the  internal  iliac 
group  of  glands.  They  lie  along  the  front  of  the  sacrum  to  the  inner  sides  of  the 
anterior  sacral  foramina.  They  receive  afferents  from  the  adjacent  bones  and 
ligaments  and  from  the  neck  of  the  uterus,  the  lower  part  of  the  vagina,  and  in 
the  male  from  the  prostate ;  their  efferents  end  either  in  the  internal  or  in  the 
common  iliac  glands. 

The  common  iliac  glands  lie  along  the  common  iliac  artery,  some  to  its  outer 
side,  some  posterior  to  it,  and  some  to  its  inner  side.  The  latter  are  naturally 
close  to  their  fellows  of  the  opposite  side,  and  the  two  groups  of  opposite  sides  are 
sometimes  spoken  of  collectively  as  the  glands  of  the  promontory.  The  number  of 
glands  in  each  set  varies  from  two  to  four.  The  external  and  posterior  glands 
receive  as  afferents  the  efferents  from  the  external  and  internal  ihac  glands,  and 
possibly  a  few  lymphatics  from  the  adjacent  muscles  and  bones.  The  internal 
group  receives  afferents  from  the  base  of  the  bladder  in  both  sexes,  from  the  upper 


922  THE  VASCULAE  SYSTEM. 

and  posterior  part  of  the  prostate  in  the  male,  and  from  the  neck  of  the  uterus 
and  the  lower  part  of  the  va;^ina  in  the  female.  The  efferents  of  the  common  iliac 
glands  terminate  in  the  lateral  aortic  glands. 

The  lumbar  glands  are  of  small  size,  and  they  are  very  irregular  in  occurrence 
and  in  number.  When  they  are  present  they  lie  close  to  the  transverse  processes 
of  the  lumbar  vertebrie  behind  the  psoas  muscle,  and  correspond,  therefore,  in 
position  with  the  posterior  intercostal  glands  of  the  thorax.  They  receive  afferent 
vessels  which  accompany  the  lumbar  arteries  from  the  deeper  parts  of  the 
abdominal  walls.  Their  efferent  vessels  end  either  in  the  lateral  aortic  glands,  or 
they  unite  with  the  efferents  of  those  glands  to  form  the  lateral  aortic  efferents,  or 
common  lumbar  trunks. 

The  aortic  glands  are  situated  in  front  of,  at  the  sides  of,  and  behind  the 
abdominal  part  of  the  aorta,  and  are  therefore  known  as  the  pre-aortic,  the  lateral 
aortic,  and  the  retro-aortic  glands.  The  lateral  aortic  glands  have  usually  been 
known  as  the  mesial  lumlmr  glands,  but  during  the  last  few  years  it  has  been 
becoming  more  customary  to  speak  of  them  as  lateral  aortic  on  account  of  their 
close  association  with  that  great  blood-vessel. 

The  pre-aortic  glands  lie  along  the  anterior  aspect  of  the  abdominal  aorta, 
either  forming  a  continuous  chain  or  arranged  in  three  groups  which  are 
situated  respectively  in  the  regions  of  the  origins  of  the  inferior  and  superior 
mesenteric  arteries  and  round  the  root  of  the  cceliac  axis,  and  the  latter  group 
constitutes  so  distinct  an  entity  that  it  is  most  commonly  spoken  of  as  the 
cceliac  group.  The  afferent  vessels  of  the  pre-aortic  glands  are  derived  from 
the  superior  mesenteric,  the  inferior  mesenteric,  and  the  colic  glands.  The 
cceliac  group  also  receives  afferents  from  the  hepatic,  the  sub-pyloric,  the  retro- 
pyloric,  and  the  coronary,  and  the  pancreatic  and  splenic  glands.  Numerous 
communications  pass  between  the  pre-  and  the  lateral  aortic  glands,  but  speaking 
broadly  it  may  be  said  that  the  pre-aortic  glands  receive  the  greater  part  of  the 
lymph  from  the  abdominal  portion  of  the  alimentary  canal  and  from  the  associated 
glands.  The  afferent  vessels  from  the  lower  glands  of  the  group  either  terminate 
in  the  cceliac  glands  or  join  with  their  efferents  to  a  large  common  intestinal 
lymphatic  trunk  which  is  one  of  the  six  tributaries  of  the  receptaculum  chyli. 

The  lateral  aortic  glands  lie  at  the  sides  of  the  abdominal  aorta,  those  of 
the  right  side  being  situated  both  in  front  of  and  behind  the  inferior  vena  cava. 
They  receive  afferents  from  the  lumbar  glands,  or  if  the  latter  are  absent,  vessels 
which  pass  directly  from  the  abdominal  parietes  along  the  lumbar  arteries.  They 
also  receive  the  lymphatics  of  the  kidneys,  the  testicles  or  ovaries,  the  suprarenal 
bodies,  and  from  the  upper  part  of  the  uterus.  In  addition  they  receive  the 
efferents  of  the  common  iliac  glands.  They  are  connected  by  anastomoses  with 
the  pre-  and  retro-aortic  glands,  and  their  efferents  unite  on  each  side  into  a 
common  lumbar  or  lateral  aortic  trunk  which  joins  the  receptaculum  chyli. 

The  retro-aortic  glands  lie  behind  the  aorta,  in  front  of  the  third  and  fourth 
lumbar  vertebrae.  They  receive  a  few  lymphatics  from  the  adjacent  muscles,  bones, 
and  ligaments,  and  numerous  efferents  from  the  lateral  and  pre-aortic  glands. 
Their  efferents  unite  to  form  a  vessel  of  fair  size  which  ends  in  the  receptaculum 
chyli. 

It  follows  from  what  has  been  already  said  that  the  lymph  from  the  pelvis  and 
the  lower  extremities,  and  that  from  the  pelvic  viscera,  passes  to  the  receptaculum 
through  the  common  iliac  and  the  lateral  aortic  glands,  but  on  account  of  the 
vessels  which  unite  the  lateral  aortic  with  the  pre-  and  retro-aortic  glands  it  is 
obviously  possible  that  infective  material  passing  either  from  the  lower  extremities 
or  from  the  jjelvic  viscera  which  is  not  intercepted  by  the  lateral  glands,  may  pass 
through  them  and  set  uj)  new  foci  of  disease  either  in  the  pre-  or  retro-aortic 
glands,  and  although  the  lateral  aortic  glands  are  the  natural  terminations  of  the 
lymx^hatic  vessels  from  the  kidneys,  testicles,  ovaries,  and  suprarenal  bodies,  never- 
theless infective  material  from  any  of  those  organs  may  pass  through  the  lateral 
into  the  x^re-  or  retro-aortic  glands. 

The  deep  lymphatic  vessels  of  the  abdomen  and  pelvis  have  been  mentioned  so 
frequently  in  association  with  the  gland  groups  in  which  they  terminate  that  no 


LYMPHATIC  GLANDS  AND  LYMPHATIC  VESSELS  OF  THOEAX.    923 

further  account  of  the  vessels  themselves  is  required ;  all  necessary  information 
regarding  them  will  be  found  in  the  accounts  of  the  glands  of  which  they  are  the 
afferents.  It  is,  however,  important  to  bear  in  mind  that  there  is  a  very  rich 
lymphatic  network  in  the  region  of  the  umbilicus.  The  superficial  lymphatics  of 
this  region  terminate  in  the  inguinal  or  pubic  glands,  but  the  deeper  communicate 
with  the  lumbar  and  external  iliac  glands,  and  are  associated  by  anastomoses  with 
the  lymphatics  of  the  upper  part  of  the  bladder  and  the  upper  and  anterior  part  of 
the  surface  of  the  liver.  They  are  also  connected  with  the  supra-  and  infra- 
umbilical  glands,  to  which  reference  has  already  been  made  (p.  921). 


THE  LYMPHATIC  GLANDS  AND  LYMPHATIC  VESSELS  OF  THE  THORAX. 

Most  of  the  superficial  lymphatic  vessels  of  the  thoracic  wall  are  tributaries 
of  the  axillary  glands,  and  they  have  already  been  described,  but  those  of  the 
mamma  are  so  important  from  a  clinical  point  of  view  that  a  more  detailed 
description  of  their  general  arrangement  is  necessary. 

The  lymphatics  of  the  mamma  are  naturally  subdivided  into  cutaneous  and 
glandular.  The  cutmieous  lymphatics  arise  in  the  skin  over  the  gland,  and 
are  separable  into  peripheral  and  central  groups.  The  peripheral  cutaneous  vessels, 
like  the  remainder  of  the  cutaneous  vessels  of  the  thoracic  wall,  pass  to  the  axillary 
glands  without  joining  the  subareolar  plexus  which  lies  immediately  subjacent  to 
the  nipple  and  the  surrounding  areola.  The  central  cutaneous  lymphatics  converge 
to  an  areolar  and  a  mammillary  plexus  from  which  efferent  vessels  pass  to  terminate 
in  a  deeper  or  subareolar  plexus  which  receives  also  the  majority  of  the  glandular 
lymphatics. 

The  glandular  lymphatics  commence  in  the  perilobular  connective  tissue.  The 
majority  follow  the  ducts  of  the  gland  and  end  in  the  subareolar  plexus.  The 
efferent  vessels  of  the  subareolar  plexus  terminate  in  the  anterior  axillary  glands. 
In  addition,  however,  to  this  main  stream  of  lymph,  there  are  three  other  channels 
by  which  lymph  can  pass  from  the  perilobular  lymphatics  of  the  gland.  One  of 
these  channels  runs  from  the  outer  part  of  the  gland  directly  to  the  anterior 
axillary  glands  without  traversing  the  subareolar  plexus.  Another  accompanies 
the  pectoral  branch  of  the  acromio- thoracic  artery,  emerges  from  the  posterior 
surface  of  the  gland,  pierces  the  pectoralis  major,  and  ascends  to  the  subclavian 
glands.  The  third  set  of  accessory  lymphatics  passes  from  the  inner  part  of  the 
gland  along  the  branches  of  the  internal  mammary  artery  which  are  distributed  to 
the  mamma.  These  vessels  pierce  the  great  pectoral  and  end  in  the  internal 
mammary  glands. 

Deep  Lymphatics  of  the  Thorax. — The  glands  associated  with  the  deep 
lymph  vessels  of  the  thorax  may  be  divided  into  the  parietal,  and  the  visceral  or 
mediastinal. 

1.  Parietal  glands  include  the  following  : — 

The  intercostal  glands  (lymphoglandulae  intercostales),  which  lie  in  the  posterior 
parts  of  the  intercostal  spaces  near  the  heads  of  the  ribs,  or  a  little  farther 
out,  between  the  intercostal  muscles.  They  receive  the  lymphatic  vessels  from 
the  deep  parts  of  the  posterior  portions  of  the  thoracic  walls,  including 
the  parietal  pleura,  and  their  efferent  vessels  are  divided  into  ascending  and 
descending  trunks.  The  efferent  vessels  from  the  intercostal  glands  of  the 
upper  five  or  six  spaces  on  the  left  side  pour  their  lymph  into  the  thoracic 
duct,  terminating  separately  in  the  larger  vessel  or  uniting  first  to  form  a 
common  trunk.  The  efferents  from  the  upper  intercostal  glands  on  the  right 
side  may  end  either  in  the  thoracic  duct  or  they  may  join  the  right  broncho- 
mediastinal trunk.  The  efferent  vessels  from  the  intercostal  glands  of  the  lower 
four  or  five  spaces  unite  to  form  a  common  trunk  on  each  side,  which  descends 
through  the  aortic  opening  of  the  diaphragm  and  terminates  in  the  receptaculum 
chyli.  Some  of  them  also  communicate  with  the  thoracic  duct.  In  addition  to 
the  posterior  intercostal  glands,  smaller  lateral  intercostal  glands  are  sometimes 
interposed  in  the  courses  of  the  deep  vessels  of  the  thoracic  wall.     They  have. 


924  THE  VASCULAR  SYSTEM. 

however,  bub  little  practical  importance.     When  they  are  present  they  lie  near  the 
origins  of  the  lateral  branches  of  the  intercostal  arteries. 

The  internal  mammary  or  sternal  glands  (lymphoglanduhe  sternales),  which  lie 
along  the  side  of  the  internal  mammary  artery,  one  or  two,  as  a  rule,,  being  placed 
opposite  the  anterior  end  of  each  intercostal  space.  Their  afferents  are  derived  from 
the  deeper  parts  of  the  anterior  portion  of  the  thoracic  wall,  from  the  deep  part  of  the 
front  of  the  abdominal  wall  by  vessels  which  ascend  along  the  superior  epigastric 
artery,  from  the  inner  portion  of  the  mammary  gland,  and  from  the  anterior  part 
of  the  diaphragm  and  the  anterior  diaphragmatic  glands.  Some  of  their  efferents 
pass  to  the  anterior  mediastinal  glands,  but  the  majority  ascend  to  the  root  of  the 
neck,  where  they  terminate  either  directly  in  the  corresponding  innominate  vein, 
or,  according  to  the  side  on  which  they  lie,  they  end  in  the  thoracic  duct,  or  the 
right  lymphatic  duct  if  it  is  present. 

The  diaphragmatic  glands  are  arranged  in  three  groups — -the  anterior,  middle, 
and  posterior. 

The  anterior  group  lies  behind  the  ensiform  process  and  the  anterior  ends  of 
the  seventh  costal  cartilages.  It  receives  lymph  from  the  anterior  part  of  the 
diaphragm,  and  from  the  anterior  part  of  the  upper  surface  of  the  liver.  Its 
efferents  pass  to  the  internal  mammary  glands. 

The  middle  group  consists  of  two  lateral  portions  which  lie  at  the  sides  of  the 
pericardium  near  the  phrenic  nerves.  On  the  right  side  these  glands  are  closely 
associated  with  the  upper  part  of  the  inferior  vena  cava,  and  some  of  them  lie  on 
the  anterior  wall  of  that  vessel  internal  to  the  fibrous  sac  of  the  pericardium.  The 
afferents  of  the  middle  diaphragmatic  glands  are  derived  from  the  middle  part  of 
the  diaphragm  and  from  the  upper  surface  of  the  liver.  Their  efferents  join  the 
posterior  mediastinal  glands. 

The  posterior  group  has  very  little  importance,  and  practically  constitutes  a 
lower  section  of  the  posterior  mediastinal  glands.  It  lies  between  the  pillars  of 
the  diaphragm  and  the  posterior  wall  of  the  thorax,  and  receives  lymph  from  the 
immediately  adjacent  parts.  Its  efferents  end  in  the  higher  posterior  mediastinal 
glands. 

2.  Visceral  Thoracic  Glands. — Of  these  there  are : — 

The  anterior  mediastinal  glands  (lymphogiandulse  mediastinals  anteriores)  are 
embedded  in  the  loose  tissue  of  the  anterior  mediastinal  region.  They  receive 
afferents  from  the  middle  part  of  the  upper  portion  of  the  liver  which  ascend 
through  the  falciform  ligament,  from  the  anterior  part  of  the  diaphragm,  and 
from  the  lower  sternal  glands.  Their  efferents  pass  upwards  to  the  superior 
mediastinum,  where  some  of  them  enter  tlie  superior  mediastinal  glands,  whilst 
others,  continuing  upwards,  terminate  on  the  right  side  in  the  right  lymphatic 
duct,  and  on  the  left  side  in  the  thoracic  duct. 

The  superior  mediastinal  glands  (lymphoglanduhe  mediastinales  superiores)  are 
grouped  round  the  innominate  veins,  along  the  upper  part  of  the  aortic  arch,  and 
in  front  of  the  thoracic  portion  of  the  trachea.  They  receive  afferents  from 
the  heart,  the  pericardium,  the  thymus,  and  the  anterior  mediastinal  glands. 
Their  efferents  terminate  at  the  root  of  the  neck  in  the  right  lymphatic  and 
thoracic  ducts. 

The  middle  mediastinal  glands  are  situated  round  the  primary  bronchi  and  the 
lower  end  of  the  trachea,  and.they  are  separable  into  the  following  groups : — 

The  bronchial  glands,  which  lie  principally  on  the  anterior  aspects  of  the 
primary  bronchi  and  along  their  upper  borders.  They  receive  lymph  from  the 
lungs  which  lias  previously  passed  through  a  series  of  inter-bronchial  or  pulmonary 
glauds,  which  lie  in  the  angles  of  division  of  the  bronchi  in  the  hilum  and  in  the 
substance  of  the  lungs.  Tlieir  efferents  unite  with  tlie  efferents  of  the  superior 
mediastinal  and  internal  mammary  glands  to  form  a  common  broncho-mediastinal 
trunk  on  each  side.  This  vessel  when  it  is  present  ends  on  the  left  in  the  thoracic 
duct  or  the  innominate  vein,  and  on  the  right  in  the  right  lymphatic  duct  or  in 
one  of  the  large  veins  at  the  root  of  the  neck. 

The  inter-tracheo-bronchial  glands,  which  lie  between  the  primary  bronchi  and 
beneath  the  end  of  the  trachea.     They  receive  afferents  from  the  heart  and  from 


DEVELOPMENT  OF  THE  BLOOD  VASCULAE  SYSTEM.  925 

the  lower  part  of  the  trachea,  and  comimmicating  vessels  connect  them  with  the 
bronchial  glands.  Their  efferents  either  join  the  broncho-mediastinal  trunk  if  it 
is  present,  or  the  thoracic  or  right  lymphatic  duct,  or  tliey  end  directly  in  one  of 
the  great  veins  at  the  root  of  the  neck. 

The  posterior  mediastinal  glands  (lymphoglandvila3  mediastinals  posteriores) 
lie  along  the  aorta  and  the  cesopliagus  in  the  posterior  mediastinum.  They 
receive  afferents  from  the  posterior  part  of  the  pericardium,  the  posterior  part 
of  the  diaphragm,  and  from  the  cesophagus.  Their  efferent  vessels  pass  mainly  to 
the  thoracic  duct,  but  some  of  the  upper  ones  on  the  right  side  end  in  the  right 
lymphatic  duct,  and  a  few  join  the  bronchial  glands. 

The  deep  lymphatic  vessels  of  the  thorax  have  been  included  in  the  description 
of  the  tributaries  of  the  deep  glands.  As  in  the  abdomen  and  pelvis,  the  main 
deep  lympliatic  vessels  accompany  the  blood-vessels  of  the  region. 


DEVELOPMENT  OF  THE  BLOOD  VASCULAR  SYSTEM. 

The  Pericardium,  the  Primitive  Aortjs,  and  the  Heart. 

A  general  accouut  of  the  development  of  the  primitive  vascular  system  and  of  the 
establishment  of  the  foetal  circulation  has  been  given  in  a  previous  chapter  (see  p.  60 
et  se(i.),  and  it  is  there  pointed  out  that  the  earliest  blood-vessels  of  the  developing  ovum 
appear  in  the  vascular  area  of  the  yolk  sac,  i.e.  outside  the  body  of  the  embi-yo  altogether. 
Almost  simultaneously,  however,  two  longitudinal  vessels  appear  in  the  embryo  itself. 
They  are  formed  in  the  splanchnic  mesoderm  of  the  pericardial  area,  and  are  easily 
distinguishable  before  that  area  is  carried  downwards  to  form  the  ventral  wall  of  the 
foregut  during  the  evolution  of  the  headfold. 

V.5  The  two  longitudinal  vessels  are  the  rudiments  of  the  primitive  heart  and  of  the 
principal  blood-vessels.  The  changes  which  take  place  in  them,  and  which  result  in  the 
formation  of  the  fully  developed  heart  and  vessels,  will  be  more  easily  understood  after  the 
development  of  the  pericardial  sac,  together  with  the  alterations  it  undei'goes  both  as 
regards  position  and  relations,  have  been  carcfull}'  studied. 

Development  of  the  Pericardium  and  the  Primitive  Aortae. — The  pericardial 
area  is  recognisable  as  soon  as  the  mesoderm  has  extended  over  the  embryonic  area  of  the 
developing  ovum.  It  is  somewhat  semilunar  in  shape,  it  lies  at  the  extreme  anterior  end 
of  the  embryonic  region,  and  it  limits  the  bucco-pharyngeal  area  or  membi'ane  in  front  and 
at  the  sides  (Figs.  17  and  18).  The  mesoderm  of  the  pericardial  ai'ea  is  continuous  latei'ally 
with  the  general  mesoderm  of  the  embryonic  area,  but  in  those  mammals  in  which  a 
pro-amnion  is  formed  it  is  separated  in  front  from  the  extra-embryonic  mesoderm  by  the 
pro-amniotic  area,  whilst  in  other  mammals  also  it  remains  quite  separate  fi'om  the  extra- 
embiyonic  mesoderm  in  front  though  it  is  more  closely  related  to  it. 

With  the  formation  of  the  ccelom  the  mesoderm  of  the  pericardial  area  is  separated 
into  an  upper  or  somatic  and  a  lower  or  splanchnic  layer,  and  it  is  in  the  latter  that 
the  two  small  tubes  which  constitute  the  first  blood-vessels  of  the  body  of  the  embryo 
appear.  The  two  tubes,  or  primitive  aortfe,  which  run  longitudinally  and  parallel  to 
one  another,  apparently  end  at  first  blindly  both  in  front  and  behind,  but  as  development 
proceeds  they  extend  backwards,  one  on  each  side  of  the  bucco-pharyngeal  membrane, 
and  beneath  the  mesodermal  somites,  to  the  caudal  region,  behind  which  they  pass  on  to 
the  walls  of  the  yolk  sac  to  join  the  blood-vessels  of  the  vascular  area ;  before  ending 
they  give  off  branches  to  the  allantois.  In  the  human  embryo  the  yolk  sac  is  relatively 
small  and  unimportant,  and  accordingly  the  branches  which  go  to  the  allantois,  or  rather 
to  the  chorion  along  the  body  stalk,  appear  to  form  the  more  direct  posterior  continuations 
of  the  primitive  vessels.  The  anterior  end  of  each  primitive  trunk  passes  forwards  to  the 
anterior  margin  of  the  pericardial  area,  and  is  continued  on  to  the  3'olk  sac,  ^\■here  it  also 
joins  the  vessels  of  the  vascular  area. 

During  the  formation  and  evolution  of  the  headfold  the  pericardial  area  increases  in 
size,  its  cavity  enlarges,  and  both  it  and  the  bucco-pharyngeal  area  are  reversed  in  position 
(Figs.  27  and  49).  Both  these  areas  are  carried  forwards  somewhat  with  the  headfold,  in 
which  it  is  to  be  remembered  the  primitive  foregut  is  included,  but  when  the  headfold  is 
completely  formed  the  pericardial  area  lies  ventral  to  the  foregut,  and  its  primitive  upper 
somatic  surface  is  now  its  lower  or  anterior  surface  ;  the  original  lower  or  splanchnic  surface 
is  superior  or  dorsal,  whilst  what  was,  at  first,   the  anterior  border  of  the  pericardial 


926 


THE  VASCULAE  SYSTEM. 


1st  cephalic  aortic  arch 

Anterior  primitive 
ventral  aorta 


Primitive  dorsal  aorta 


Vitelline  vein 


Umbilical  vein 


area  is  converted  into  the  posterior  end  of  the  reversed  area,  and  it  forms  the  anterior 
limit  of  tlie  umbilical  orifice.  In  brief,  the  relative  positions  of  its  several  parts  are 
reversed,  and  at  this  period  the  pericardial  cavity  which,  like  the  area,  is  semilunar  in 
shape,  extends  from  side  to  side  beneath  the  foregut,  and  its  cornua  are  continuous  at  the 
sides  of  the  foregut  with  the  general  body  cavity  of  the  embryo.  Subsequently  this  con- 
tinuity is  obliterated,  and  the  pericardial  cavity  is  separated  from  the  pleuro-peritoneal 
part  of  the  general  body  cavity  or  coelom. 

The  mesoderm  at  the  posterior  end  of  the  reversed  pericardial  region,  where  the 
somatic  and  splanchnic  layers  are  continuous,  i.e.  just  in  front  of  the  umbilicus,  increases 
in  thickness  and  forms  a  semilunar  mass,  the  septum  transversum,  in  which  the  liver  and 
the  ventral  part  of  the  diaphragm  are  formed.  The  latter  extends  mesially  from  the 
anterior  wall  of  the  body  to  the  foregut,  immediately  in  front  of  the  gastric  dilatation,  whilst 
laterally  it  forms  two  falciform  projections  which  encroach  from  wdthout  upon  the  portions 
of  the  coelom  which  lie  at  the  sides  of  the  foregut.  Ultimately  the  lateral  portions  of  the 
diaphragm  pass  inwards,  and,  fusing  with  the  mesentery  of  the  foregut,  they  separate  the 
pleuro-peritoneal  portion  of  the  coeloni  into  three  parts — two  anterior,  one  on  each  side  of 
the  foregut,  thejAeural  sacs,  and  a  posterior,  the  2^eritoneal  cavity. 

When   the   pericardial   region   is   completely  reversed   the  two  vessels   developed    in 

its  splanchnic  layer  lie  side  by  side  in  what  is 
now  its  dorsal  wall.  Posteriorly  they  are  con- 
tinued through  the  septum  transversum  to  the 
wall  of  the  yolk  sac.  Anteriorly  they  are  con- 
tinued, as  the  first  cephalic  aortic  arches,  through 
the  mandibular  arches  which  have  developed  at 
the  sides  of  the  bucco-pharyngeal  membrane,  to 
the  dorsal  Avail  of  the  gut,  where  they  pass 
backwards  beneath  the  paraxial  mesoderm  to 
the  posterior  end  of  the  body,  whence  they  are 
continued,  in  the  human  subject,  along  the  body 
stalk  to  the  placental  portion  of  the  chorion, 
D-iving  off  branches  to  the  walls  of  the  ali- 
mentary  canal  and  yolk  sac. 

These  two  primitive  embryonic  vessels  are  the 
primitive  aortse.  After  the  formation  of  the 
cephalic  and  caudal  folds,  each  primitive  aorta 
may  be  looked  upon  as  consisting  of  three  parts 
united  by  two  arches  : — an  anterior  ventral  part, 
the  anterior  ventral  aorta,  situated  partly  in  the 
septum  transversum  and  partly  in  the  dorsal  wall 
of  the  pei'icardium  and  the  root  of  the  neck ;  a 
dorsal  part,  the  primitive  dorsal  aorta,  which 
extends  beneath  the  paraxial  mesoderm  from 
the  dorsal  end  of  the  mandibular  arch  to  the 
tail  fold  ;  a  posterior  ventral  part,  the  posterior 
ventral  aorta,  which  passes  to  the  yolk  sac ;  the  anterior  part  of  the  posterior  ventral 
aorta  soon  atrophies,  and  the  remainder  of  the  vessel  is  then  prolonged  from  the  posterior 
part  of  the  ventral  wall  of  the  body  to  the  placenta  by  a  new  branch.  The  two  arches 
which  unite  the  tlirec  main  portions  of  each  primitive  aorta  together  are  an  anterior,  the 
first  cephalic  aortic  arch,  which  lies  in  the  mandibular  arch  and  passes  from  the  anterior 
ventral  aorta  to  the  anterior  end  of  the  primitive  dorsal  aorta,  and  a  posterior,  the  primary 
caudal  aortic  arch,  wliich  passes  in  the  tail  fold  and  at  the  side  of  the  hind  gut,  from 
the  primitive  dorsal  aorta  to  the  posterior  portion  of  the  primitive  ventral  aorta. 

As  development  proceeds  a  series  of  transformations  occurs  in  the  various  sections  of 
the  primitive  aorttC.  These  transformations  are,  with  few  exceptions,  alike  on  the  two  sides, 
but  the  transformations  which  occur  in  one  section  are  entirely  different  from  those  met 
with  in  the  other  sections  ;  therefore  each  part  must,  to  a  certain  extent,  be  considered 
separately. 

Each  anterior  ventral  aorta  is  divisible  into  three  parts.  The  posterior  part  lies  in  the 
septum  transversum.  Posteriorly  it  forms  the  terminal  portion  of  the  vitelline  vein,  and 
carries  the  blood  from  the  wall  of  the  yolk  sac.  For  a  long  time  each  vitelline  vein  remains 
separate  from  its  fellow  of  the  opjjosite  side,  but  afterwards  the  two  veins  unite  to  form  a 
common  stem,  which  terminates  at  first  in  the  posterior  part  of  the  heart,  and  subsequently 
in   the  liver.     The  anterior  section  of   the  posterior  part  of  the  anterior  ventral  aorta 


Branches  to  yolk  sac 


Vitelline  artery 

Posterior  primitive 
ventral  aorta 
Primary  candal  arch 

Allantoic  artery 


Placenta 


Fig.  665. — Diagram  of  the  Primitive  Vas- 
cular System  before  the'  Formation  of 
THE  Heart. 


DEVELOPMENT  OF  THE  BLOOD  VASCULAR  SYSTEM. 


927 


Ceplialic  caortic 

arch 

Anterior  ventral  _ 
aorta 

Primitive  dorsal 

aorta 

Vertebral  artery 

Subclavian  artery- 
Primitive  jugular 
vein 
Duct  of  Cuvier 

Cardinal  veil 


1st  cephalic  aortic  arch 

cephalic  aortic  arch 

3rd' cephalic  aortic  arch 

-4th  cephalic  aortic  arch 


■th  cephalic  aortic  arch 
Bulbus  arteriosus 
Ventricle 
Auricle 
Sinus  venosus 


"] 


Umbilical  vein 


rapidly  enlarges  and  unites  with  its  fellow  of  the  opposite  side  to  form  the  sinus  venosus 
or  posterior  chamber  of  the  primi- 
tive heart ;  after  a  time  this  grows 
forwai'ds  out  of  the  septum  into  the 
pericardium,  and  is  absorbed  into 
the  auricular  portion  of  the  heart. 

The  middle  part  of  the  anterior 
ventral  aorta  lies  in  the  dorsal  wall 
of  the  pericai'dium  and  projects 
forwards  into  its  cavity.  It  lies 
close  to  its  fellow  of  the  opposite 
side,  and  as  the  two  vessels  rapidly 
enlarge  their  inner  walls  approach 
each  other,  and,  fusing  together, 
form  a  single  median  vessel  which 
constitutes  the  primitive  heart  (the 
sinus  venosus  being  excepted)  in- 
cluding the  bulbus  arteriosus,  the 
latter  being  afterwards  developed 
into  the  roots  of  the  pulmonary 
and  aortic  vessels. 

The  anterior  portion  of  the  an- 
terior ventral  aorta  is  embedded  in 
the  tissues  at  the  upper  or  anterior 
part  of  the  pericardium,  that  is,  at 
the  root  of  the  neck.  At  first  it  is 
connected  with  the  primitive  dorsal 
aorta  by  a  single  cephalic  aortic 
arch,  but  afterwards  three,  and 
eventually  four,  additional  arches 
connect  it  with  the  anterior  part 
of  the  primitive  dorsal  aorta.  As 
the  neck  lengthens  this  part  of  the 
anterior  ventral  aorta  is  elongated. 
For  the  greater  part  of  its  extent 
it  remains  separate  from  its  fellow  of  the  opposite  side,  and  it  takes  part  in  the  formation 


Branches  to. 
alimentary  canal 


Posterior  ventral, 
aorta 


Caudal  aortic  _ 
arcli 


Hypogastric 
artery 


Fig.  666. — Diagram  of  the  Primitive  Blood-^t:ssels 
after  the  formation  of  the  heart. 


7th  pair  of 
segmental  arteries 


Post-costal 
anastomoses 


1st  pair  of 
segmental  arteries 


Umbilical  vein 
Branches  to  yolk  sac 

Vitelline'artery 


1st  cephalic  aortic  arch 
nd  cephalic  aortic  arch 
3rd  I  cephalic  aortic  arch 
4th  cephalic  aortic  arch 
5 til  cephalic  aortic  arch 
i3ulbus  arteriosus 
Ventricle 


Yolk  sac 


Auricle 
Sinus  venosus 


Vitelline  vein 
Fig.  667.— Diagram  of  the  primitive  Blood-vessels  after  the  formation  of  the  Heart,  bdt 

BEFORE    ITS    SUBDIVISION    BY    SEPTA    INTO    AURICLES    AND    VENTRICLES. 

of  the  great  vessels  of  the  head  and  neck.     Posteriorly,  however,  it  unites  with  its  fellow 
of  the  opposite  side  to  form  the  apex  of  the  bulbus  arteriosus.     After  the  completion  of 


928 


THE  VASCULAR  SYSTEM. 


the  cephalic  aortic  arches  the  portions  of  the  anterior  ventral  aorta  which  lie  between 
their  lower  extremities  are  known  as  the  ventral  roots  of  the  cephalic  aortic  arches. 

The  primitive  dorsal  aorta  may  be  conveniently  divided  into  two  parts.  The  anterior 
part  extends  from  the  dorsal  end  of  the  first  cephalic  aortic  arch  to  the  root  of  the  fore- 
limb.  It  remains  separate  from  its  fellow  of  the  opposite  side,  and  forms  the  dorsal  roots 
of  the  cephalic  aortic  arches  of  its  own  side.  It  takes  part  in  the  formation  of  the  great 
vessels  of  the  head  and  neck  and,  on  the  left  side,  of  part  of  the  aorta  of  the  adult. 

The  remaining  portion  extends  from  the  root  of  the  fore-limb  to  the  pelvic  region ;  it 

passes  inwards,  and  unites  with  its  fellow  of 
the  opposite  side  beneath  the  vei'tebral  column 
to  form  the  greater  part  of  the  permanent 
systemic  aorta. 

The  primary  caudal  arch  connects  the 
primitive  dorsal  with  the  posterior  ventral 
aorta.  As  it  passes  ventrally  it  lies  on  the 
inner  side  of  the  Wolffian  duct.  After  a  time 
it  is  replaced  by  a  secondary  caudal  arch 
which  lies  at  the  outer  side  of  the  Wolffian 
duct,  and  this  subsequently  becomes  the 
common  and  internal  iliac  arteries  and  the 
root  of  the  hypogastric  artery,  the  external 
iliac  being  merely  an  offset  from  it  to  the 
hind-limb. 

The  greater  part  of  the  primitive  posterior 
ventral  aorta  disappears  early,  and  its  secondary 
continuation  to  the  placenta  becomes  the 
remainder  of  the  hypogastric  artery,  Avhich 
passes  from  the  internal  iliac  artery,  by  the 
side  of  the  bladder  and  along  the  ventral  wall 
of  the  abdomen,  to  the  lunbilicus,  whence  it 
is  continued  along  the  umbilical  cord  to  the 
placenta. 

Having  considered  thus  briefly  the  main 
parts  of  the  primitive  aortic  vessels,  and 
having  noted,  shortly,  the  fate  of  each  portion 
in  the  subsequent  phases  of  development,  we 
may  now  turn  to  a  more  detailed  consideration 
of  the  metamorphoses  which  occur  in  those 
parts  of  primitive  vessels,  viz.  the  anterior 
ventral  aortte,  the  cephalic  aortic  arches,  and 
the  anterior  parts  of  the  primitive  dorsal  aortse, 
where  most  strikingandmost  complicated  trans- 
formations result  in  the  formation  of  the 
heart,  the  aorta  in  part,  the  pulmonary  artery 
and  its  primary  branches,  the  chief  arterial, 
trunks  of  the  head  and  neck,  and  the  first 
part  of  the  main  artery  of  the  right  upper 
extremity. 


RV- 


¥i(i.  668. — Development  of  the  Heart. 

Diagram  showing  the  changes  of  form  and  external 
appearances  at  different  stages.  Modified  fioni 
His's  models.  III.B  and  IV.B  are  side  views  ; 
the  other  figures  represent  the  heart  as  seen 
from  the  front. 

A,  Auricle  ;  A.B,  Aortic  bull*  ;  A.C.  Auricular  canal  ; 
A.P,  Auricular  appendix  ;  L.V,  Left  ventricle  ; 
O.A.C,  Opening  of  auricular  canal;  P.V. A, 
Primitive  ventral  aorta  ;  R.V,  Right  ventricle  ; 
S.V,  Sinus  venosus  ;  V,  Ventricle  ;  V.V, 
Vitelline  veins. 

inwards,  their  inner  walls  come  in  contact, 
single  median  tube  is  formed.     Tliis  is  the 


Development  of  the  Heart,  of  the 
first  part  of  the  aorta,  and  of 
THE  Pulmonary  Artery. 

Of  the  three  parts  into  which  each  anterior 
ventral  aorta  is  divisible  the  middle  is  situated 
ill  tlie  splanchnic  mesoderm  of  the  dorsal  wall 
of  the  pericardium.  As  development  proceeds 
the  middle  parts  of  both  anterior  ventral  aortee 
enlarge  and  project  into  the  cavity  of  the  peri- 
cardium, whilst  at  the  same  time  they  grow 
fuse  together,'  and  disappear,  and  so  a  simple 
primitive  heart,  whicli  is  completed  in  front 


DEVELOPMENT  OF  THE  HEAET  AND  AOKTIC  BULB.         929 

and  behind  the  pericardium  by  the  fusion  of  the  adjacent  ends  of  the  anterior  and 
posterior  parts  of  tlie  anterior  ventral  aorta). 

The  simple  tubular  heart,  at  first  straight  and  of  fairly  uniform  calibre,  soon  alters  in 
form  and  in  the  relative  position  of  its  different  parts.  It  becomes  irregularly  enlarged, 
and  a  series  of  four  dilatations,  with  intervening  constrictions,  can  be  distinguished.  The 
dilatations,  from  behind  forwards,  are  as  follows  : — (1)  the  sinus  venosus  or  saccus 
reuniens,  (2)  the  auricle  or  atrium,  (3)  the  ventricle,  and  (4)  the  aortic  bulb  or  bulbus 
arteriosus.  The  short  constriction  between  the  auricle  and  ventricle  is  known  as  the 
auricular  canal,  and  the  less  pronounced  constriction  which  intervenes  between  the 
ventricle  and  the  aortic  bulb  is  termed  the  fretuxn  Halleri.  In  addition  to  this  alteration 
in  form,  the  tubular  heart  elongates,  much  more  so  than  the  pericardium  in  which  it  lies, 
whilst  at  the  same  time  the  anterior  extremity  of  the  aortic  bulb  and  the  sinus  venosus 
are  withdrawn,  from  the  root  of  the  neck  and  the  septum  transversum  respectively,  into 
the  pericardium.  Of  necessity,  therefore,  the  single  heart  is  bent  upon  itself,  and  it 
projects  more  and  more  into  the  pericardium,  pushing  forwards  the  visceral  layer  of 
the  serous  lining  of  this  cavity,  and  carrying  with  it  a  mesentery  of  splanchnic  mesoderm 
which  is  known  as  the  mesocardium. 

The  bending  of  the  heart  results  in  the  formation  of  a  U-shaped  loop,  the  posterior  or 
venous  limb  of  the  loop  lying  to  the  left  and  below,  with  the  body  in  the  erect  posture, 
the  anterior  or  arterial  limb  being  to  the  right  and  above,  whilst  the  intervening  stem  of 
the  loop  runs  from  the  left  and  below  upwards,  forwards,  and  to  the  right.  The  apex 
of  the  aortic  bulb  is  bent  a  little  to  the  left  and  reaches  the  middle  line. 

Subsequently  the  auricle  ascends  behind  the  ventricle,  and  the  ventricular  opening 
of  the  auricular  canal,  the  short  communicating  passage  between  the  auricle  and 
ventricle,  is  seen  as  a  transverse  slit  at  the  upper  part  of  the  left  or  posterior  end  of  the 
ventricle.  As  the  ventricular  chamber  enlarges  its  upper  end  passes  towards  the 
middle  line,  and  the  ventricle  is  no  longer  so  obliquely  directed  from  left  to  right  but 
lies  more  in  the  mesial  plane.  As  the  result  of  these  changes  of  position,  and  the  coin- 
cident modifications  in  size  of  the  different  parts,  the  aortic  bulb  is  eventually  placed 
immediately  in  front  of  the  auricle,  and  the  opening  of  the  auricular  canal  is  nearer 
the  middle  of  the  upper  part  of  the  posterior  wall  of  the  ventricular  chamber.  During 
its  further  growth  the  ventricle  enlarges  principfflly  at  its  anterior  or  ventral  part ;  the 
dorsal  part  is  not  materially  altered  in  position,  and  consequently  the  openings  of  the 
auricular  canal  and  the  aortic  bulb  remain  relatively  close  together.  The  auricle  increases 
in  size  by  lateral  expansion  and  by  forward  extension  of  its  lateral  angles  ;  the  forward 
extensions  embrace  the  sides  of  the  aortic  bulb,  and  constitute  the  rudimentary  auricular 
appendages.  In  the  meantime  the  mesocardium  disappears  and  the  heart  lies  free  in  the 
pericardium  except  at  its  extremities. 

Division  of  the  Heart  into  its  different  Chambers,  and  Division  of 

THE  Aortic  Bulb. 

Whilst  the  changes  in  form,  position,  and  size  of  the  different  sections  of  the  primitive 
heart,  which  have  just  been  described,  are  taking  place,  the  division  of  the  heart  cavity 
into  its  four  permanent  chambers,  and  of  the  aortic  bulb  into  its  aortic  and  pulmonary 
portions  commences.  These  divisions  are  brought  about  by  the  growth  of  septa  in  the 
ventricle,  auiicle,  and  aortic  bulb,  and  by  the  thickening  and  fusion  of  the  middle  portions 
of  the  upper  and  lower  walls  of  the  auricular  canal. 

The  thickenings  of  the  walls  of  the  auricular  canal  are  called  endocardial  cushions  ; 
they  meet  and  fuse  together  mesially  to  form  the  septum  intermedium  b}-  which  the 
central  portion  of  the  canal  is  obliterated,  whilst  the  lateral  portions  are  left  patent  as 
small  triangular  channels  which  still  connect  the  auricular  and  ventricular  chambers. 

The  separation  of  the  ventricular  part  of  the  heart  into  right  and  left  chambers  is 
indicated,  externally,  at  a  very  early  period,  by  a  groove,  well  marked  in  front  and  below, 
but  less  distinct  behind  where  it  runs  upwards  to  the  auricular  canal  ;  whilst  internally, 
in  a  coi-responding  position,  a  ventricular  septum  (s.  inferius)  grows  upwards  from  the 
inferior  part  of  the  ventricular  wall.  The  posterior  part  of  the  upper  border  of  this  septum 
unites  with  the  lower  end  of  the  fused  endocai'dial  cushions  of  the  auricular  canal ;  the 
anterior  part  of  its  upper  border  terminates  a  short  distance  below  the  orifice  of  the  aortic 
bulb,  where  it  unites  with  the  septum  of  the  aortic  bulb  which,  at  a  later  period,  descends 
to  meet  it. 

The  division  of  the  aortic  bulb  commences  at  its  distal  end  between  the  orifices  of 
the  fourth  and  fifth  cephalic  aortic  arches.     It  is  due  to  the  ingrowth  of  two  endocardial 
63 


930 


THE  VASCULAR  SYSTEM. 


thickenings  which  meet  and  fuse  together  from  their  distal  to  their  proximal  ends, 
forming  a  septum  which  divides  the  interior  of  the  aortic  bulb  into  two  parts,  and  then 
projects  downwards  into  the  ventricular  chamber  till  it  meets  and  fuses  with  the  anterior 
part  of  the  upi)er  border  of  the  ventricular  septum.  The  upper  or  distal  part  of  the 
septum  of  the  aortic  bulb  commences  from  the  dorsal  wall  of  the  cavity  between  the 
fourth  and  fifth  cephalic  arches,  and  it  is  placed  transversel}^,  but  its  lower  end  lies 
more  antero-posteriorly,  therefore  it  twists  spirally  as  it  descends,  and  as  a  result  the  right 
part  of  the  ventricle  is  thrown  into  continuity  with  the  fifth  cephalic  aortic  arches,  whilst 
the  left  part  of  the  ventricle  retains  continuity  with  the  remaining  cephalic  aortic  arches. 

After  the  septum  of  the  aortic  bulb  is  completed,  grooves  appear  along  its  margins  on 
the  surface  of  the  bulb  ;  the  grooves  deepen  until  they  divide  the  septum  and  consequently 
the  bulb  into  two  parts ;  the  part  in  connexion  with  the  right  ventricle  and  the  fifth 
aortic  arch  becomes  the  pulmonary  artery,  and  the  part  in  connexion  with  the  left 
ventricle  and  the  remaining  arches  becomes  the  ascending  aorta. 

The  separation  of  the  primitive  auricle  into  right  and  left  portions  is  indicated 
externally  by  the  appearance  of  a  groove  on  the  i^]2£e£_and_posterior  wall ;  opposite  this 

7th  segmental  artery        Dorsal  aorta  Vertebral  artery  Basilar  artery 


Posterior 
cerebral  artery 

/ 
Aorta  ^^ 

arterj'  _, ^ ^        _  /     I  M    / /^F^    J^X         /  ^^\  f     I 

Posterior  com- 
municating 
artery 
Internal 
carotid  artery 
Superior  vena 
caval  blood- 
stream 


Foramen  ovale 


Inferior  vena 
caval  blood- 
stream 


Middle 
'cerebral  artery 


Anterior  cerebral 
artery 


Interaurlcular/ 
septum 


Fig.  669.— Development  of  the  Heart  and  the  Main  Arteries. 
Diagram  of  the  heart,  showing  the  formation  of  its  .septa,  and  of  the  cephalic  portion  of  the  arterial  system. 

groove  an  auricular  septum  grows  downwards  in  the  interior  of  the  auricle.  Its  lower 
border  gradually  approaches  the  endocardial  cushion  in  the  auricular  canal,  and  for  a  time 
a  small  opening  is  left  between  the  upper  ends  of  the  fused  endocardial  cushions  and  the 
lower  edge  of  the  septum.  This  is  the  ostium  primum ;  it  is  closed  by  the  fusion  of  the 
septum  with  the  endocardial  cushions,  but  before  its  closure  is  completed  an  aperture 
appears  in  the  upper  part  of  the  septum ;  this  latter  aperture,  the  ostium  secundum, 
becomes  the  foramen  ovale.  A  second  aui-icular  septum,  the  septum  secumlunt,  grows 
downwards  to  the  right  of  the  first  septum;  its  lower  margin  passes  the  foramen  in  the 
septum  primum  which  is  called  the  foramen  ovale,  but  stops  some  distance  from  the 
posterior  wall  of  the  auricle,  and  this  margin  constitutes  the  limbus  Vieussenii.  The  limbus 
Vieus.senii  forms  the  upper  and  anterior  boundary  of  a  depression  in  the  auricular  septum 
which  is  called  the  fossa  ovalis.  The  floor  of  the  fossa  is  formed  by  the  primary  septum, 
and  the  foramen  ovale  which  lies  at  the  upper  part  of  the  fossa  is  closed  after  birth  by  the 
fusion  of  the  primary  and  secondary  septa. 

The  sinus  venosus,  which  in  the  early  stages  receives  the  vitelline  veins  from  the 
yolk  sac,  the  allantoic  or  umbilical  veins  from  the  placenta,  and  the  ducts  of  Cuvier 
wliich  return  the  blood  from  the  Wolfhan  bodies  and  the  body  of  the  embryo,  is  also 
divided  into  two  parts  by  the  formation  of  a  ledge-like  projection  from  its  posterior  wall 
and  the  lower  end  of  the  septum  secundum  of  the  auricle  crosses  the  ledge  between  the 


DIVISION  OF  THE  HEART  AND  AOETIC  BULB. 


931 


two  parts  and  becomes  continuous  with  the  Eustachian  valve  along  the  anterior  margin  of 
the  inferior  vena  cava.  The  sinus  venosus  lies  at  first  below  and  behind  the  auricle,  with 
which  it  communicates  freely.  It  is  gradually  divided  into  a  large  right  and  a  small  left 
cornu,  and  its  orifice  of  communication  with  the  auricle  is  constricted,  and  ultimately 
it  is  transformed  into  a  cleft  which  opens  from  the  right  end  of  the  sinus  into  the  back  of 


Internal  jugular  vein 
External  jugular  vein 

Vertebral  artery 

Subcla\ian  artery 

Subclavian  ^ein  — ; 

Innominate  veius 

Right  pulmonary  artery 

Superior  vena  cava 

Vena  azygos  major 

Right  auricle 

Right  ventricle 

Hepatic  vein 

Inferior  vena  ca\a 

Intercostal  veins 


Obliterated  portion  of  the 

right  cardinal  vein 

Stem  formed  by  fused 

vitelline  veins 


Lumbar  vein 


Coinmon  iliac  artery 


External  iliac  artery 


Internal  iliac  artery 


1st  cephalic  aortic  arch  (obliterated) 
Internal  carotid  artery 

2nd  cephalic  aortic  arch  (obliterated) 


External  carotid 

3rd  cephalic  aortic  arch  forndng  part  of 

internal  carotid 

^'ertebl■al  artery 

Subclavian  artery 

4th  cephalic  aortic  arch  foninng  arch  of  aorta 
-^ — Left  superior  intercostal  vein 
^^       Ductus  arteriosus  (part  of  the  tifth  aortic 

arch) 

Pulmonary  artery 

Vena  azygos  minor  superior 

-Left  auricle 


Left  ventricle 


-Vena  azygos  minor  inferior 
Ductus  venosus 


Dorsal  aorta 

Obliterated  left  cardinal  vein 


Renal  vein 
Umbilical  vein 


Allantoic  arteries 


Fig.  670.— DiAGRAJt  of  the  Course  of  the  Fcetal  Cikculatiox. 

the  right  part  of  the  auricular  chamber  ;  the  cleft  is  guarded  by  two  lateral  valve-like 
folds  of  endocardium,  the  right  and  left  venous  valves,  which  become  continuous  above 
with  a  transitorv  downward  projection  from  the  roof  of  the  auricle,  known  as  the  septum 
spurium.  The  orifice  of  communication  is  divided  into  two  parts  as  the  right  part  ot  the 
cavitv  is  absorbed  into  the  auricle.  The  left  part  of  the  orifice  becomes  the  opening  ot 
the  coronary  sinus  and  the  right  is  opened  out  as  the  right  part  of  the  smus  is  absorbed 
into  the  auricular  cavitv. 

In  the  early  stages  "the  veins  of  the  two  sides  opened  into  the  corresponding  sections 


932  THE  VASCULAE  SYSTEM. 

of  the  sinus  venosus,  but  numerous  transformations,  which  are  described  in  the  account 
of  the  development  of  the  veins,  occur,  and  finally  all  the  veins,  except  the  left  duct  of 
Cuvier,  open  into  the  right  end  of  the  sinus,  and  ultimately  into  the  auricle  as  the  right 
part  of  the  sinus  is  absorbed  into  it ;  the  left  part  of  the  sinus  becomes  a  mere  appendage  of 
the  right,  and  is  transformed  into  the  coronary  sinus  which  receives  the  blood  from  the 
walls  of  the  adult  heart. 

Thus,  when  the  development  of  the  heart  is  completed,  all  the  large  veins  which  reach 
the  heart,  with  the  exception  of  the  pulmonary  veins,  open  into  the  right  auricle,  and 
into  that  part  of  the  chamber  formed  by  the  absorption  of  the  right  end  of  the  sinus 
venosus.  Indications  of  the  primitive  separation  of  the  auricle  from  the  sinus  venosxis 
are  still  recognisable  in  the  adult,  as  the  sulcus  terminalis  on  the  exterior,  the  corre- 
sponding crista  terminalis  in  the  interioi-,  and  the  Eustachian  and  Thebesian  valves; 
the  Eustachian  valve  is  a  remnant  of  part  of  the  valvular  fold  which  was  situated  at  the 
right  margin  of  the  slit-like  aperture  of  communication  between  the  sinus  venosus  and 
the  auricle,  whilst  the  valve  of  Thebesius  represents  a  fold  of  endocardivim. 

The  valves  which  guard  the  auriculo-ventricular  orifices  are  downgrowths  from  the 
lower  end  of  the  auricular  canal.  The  valves  of  the  pulmonary  and  aortic  apertures  are 
preceded  by  four  endocardial  thickenings  at  the  lower  end  of  the  aortic  bulb — anterior, 
posterior,  and  two  lateral.  As  the  septum  of  the  bulb  descends  it  fuses  with  the  middle 
parts  of  the  lateral  thickenings ;  thus,  when  the  septum  of  the  bulb  has  descended  below 
the  lower  orifice  of  the  bulb,  dividing  it  into  aortic  and  pulmonary  apertures,  three 
endocardial  thickenings  are  found  in  each  aperture,  one  anterior  and  two  posterior  in  the 
pulmonary  aperture,  and  the  reverse  in  the  aortic  orifice.  From  these  thickenings  the 
semilunar  valves  of  the  aortic  and  pulmonary  apertures  are  developed,  and  they  retain 
their  original  positions  until  after  the  sixth  month  of  foetal  life ;  ultimately,  however,  they 
are  twisted  round,  so  that  in  the  adult  the  pulmonary  valves  are  placed  two  in  front  and 
one  behind,  and  the  aortic  one  in  front  and  two  behind. 

The  Aortic  Aeches — Formation  of  the  Chief  Arteries. 

The  aortic  arches  at  the  head  end  of  the  embryo  connect  the  aortic  bulb  and  the 
ventral  aortse  in  front  of  the  bulb  with  the  corresponding  parts  of  the  primitive 
dorsal  aortaj.  The  arches,  ten  in  number,  are  arranged  in  pairs.  There  are,  therefore, 
five  arches  on  each  side,  and  they  are  distinguished  from  before  backAvards  by  their 
numerical  designation.^ 

The  first  is  formed  during  the  development  of  the  head  fold  by  the  bending  of 
the  primitive  aorta ;  it  lies  at  the  side  of  the  bucco-pharyngeal  area,  and  subse- 
quently in  the  substance  of  the  mandibular  arch.  The  remaining  aortic  arches  are 
formed  quite  differently,  and  gi'ow  dorsally  through  the  substance  of  the  remaining 
visceral  arches,  as  these  are  formed  in  regular  succession  in  the  side  wall  of  the  pharyn- 
geal portion  of  the  foregut.  The  second  s^Drings  directly  from  the  anterior  ventral  aorta, 
and  passes  through  the  hyoid  arch  to  the  dorsal  aorta,  but  the  third,  fourth,  and  fifth 
spring  by  a  common  trunk  from  the  apex  of  the  aortic  bulb.  Subsequently,  however,  and 
as  the  neck  grows  forwards,  the  anterior  ventral  aorta  is  elongated,  and  the  third  and 
fourth  arches  arise  separately  from  it.  At  this  later  period,  therefore,  four  vessels,  two 
on  each  side,  spring  from  the  aortic  bulb,  viz.  the  two  fifth  arches  and  the  two 
anterior  ventral  aortse  from  which  the  anterior  four  pairs  of  arches  arise.  When  the 
septum  of  the  aortic  bulb  is  developed,  the  bulb  is  divided  into  two  parts,  one  (the 
pulmonary  artery)  connecting  the  fifth  arclies  with  the  right  ventricle,  and  the  other 
(the  ascending  aorta)  connecting  the  ventral  aortic  stems,  and  through  them  the 
first,  second,  third,  and  fourth  pairs  of  arches,  with  the  left  ventricle.  Each  cephalic 
aortic  arch  is  connected  with  the  arcli  immediately  behind  it  by  a  dorsal  root,  and  in  the 
cases  of  the  first  three  arches  by  a  ventral  root  also ;  but  the  ventral  root  of  the  fourth 
arch  connects  it  with  the  aortic  bulb.  The  dorsal  and  ventral  roots  of  the  arches  are 
simply  portions  of  the  primitive  ventral  and  dorsal  aortse,  which  are  so  named  merely 
for  descriptive  purposes.  From  the  dorsal  roots  a  series  of  segmental  branches  are 
given  off,  which  pass  dorsally,  between  the  rudiments  of  the  transverse  processes  of  the 
cervical  vertebnc,  to  supply  the  spinal  cord  and  its  membranes  and  the  muscles  and 
fasciaj  of  the  back. 

The  five  pairs  of  arches  do  not  all  persist  in  their  entirety,  but  remains  of  each  are 

^  In  some  of  the  lower  forms  six  aortic  arches  have  been  recognised,  and  it  is  possible  that  what  we  know 
as  the  fifth  in  the  human  subject  corresponds  with  the  sixth,  the  fifth  not  being  formed,  or  possessing  only  a 
very  transitory  and  rudimentary  existence. 


THE  BEANCHES  OF  THE  PEIMITIVE  DOESAL  AOETtE.        933 

found  even  in  the  adult.  The  first  and  second  pairs  disappear  almost  entirely ;  from  the 
ventral  ends  of  the  first  arches,  however,  the  superficial  temporal,  the  internal  maxillary, 
the  lingual  and  the  facial  arteries  are  formed ;  whilst  from  the  ventral  ends  of  the  second 
arches  the  ascending  pharyngeal,  posterior  auricular,  and  occipital  arteries  are  derived. 

On  each  side  the  ventral  roots  of  the  first  and  second  arches  persist  as  the  stem  of  the 
corresponding  external  carotid  artery.  The  internal  carotid  is  formed  by  the  third  arch 
together  with  the  dorsal  roots  of  the  second  and  first  arches,  and  is  continued  forwards  to 
the  cerebrum  by  an  outgrowth  from  the  anterior  end  of  the  dorsal  root  of  the  first  arch. 
The  ventral  root  of  the  third  arch  becomes  the  common  cai'otid  artery.  The  dorsal  root 
of  the  third  arch  disappears.  On  the  right  side  the  ventral  root  of  the  fourth  arch  forms 
the  innominate  artery,  and  the  arch  itself  is  converted  into  part  of  the  subclavian  artery, 
whilst  the  dorsal  root  disappears.  On  the  left  side  the  ventral  root  of  the  fourth  arch 
forms  the  small  portion  of  aorta  which  lies  between  the  innominate  and  left  common 
carotid  arteries.  The  left  fourth  arch  itself  and  its  dorsal  root  form  the  arch  of  the  aorta 
from  the  origin  of  the  left  carotid  artery  to  the  attachment  of  the  ductus  arteriosus. 

The  ventral  portion  of  the  fifth  arch  on  each  side  remains  as  the  first  part  of  the  cor- 
responding pulmonary  artery.  The  dorsal  part  disappears  early  on  the  right  side,  but  on 
the  left  side  it  persists  and  remains  patent  up  to  birth  as  the  ductus  arteriosus.  After 
birth  it  is  oblitei-ated  and  transformed  into  a  fibrous  cord. 

The  fate  of  the  primary  caudal  arches,  their  secondary  successors,  and  that  of  the 
posterior  ventral  portions  of  the  primitive  aortte,  has  already  been  fully  considered  (p.  928). 

The  Primitive  Dorsal  Aort.e — Formation  of  the  Descending  Aorta. 

Coincidently  with  the  development  of  the  cephalic  aortic  arches  the  anterior  portions 
of  the  dorsal  sections  of  the  primitive  aortse  are  converted  into  the  dorsal  roots  of  the 
aortic  arches.  As  already  pointed  out,  certain  parts  of  these  disappear  entirely,  whilst 
other  parts  are  utilised  in  the  formation  of  the  permanent  vessels. 

Behind  the  fifth  arches  the  two  primitive  dorsal  aortse  remain  separate  as  far  back  as 
the  root  of  the  fore-limb.  To  this  extent  the  right  vessel  disappears,  whilst  the  left 
remains  and  forms  a  portion  of  the  descending  aorta.  From  the  roots  of  the  fore-limbs 
backwards  to  the  caudal  arches  the  dorsal  aortpe  fuse  together,  beneath  the  vertebral 
column,  to  form  the  remainder  of  the  descending  aorta. 

The  Branches  of  the  Primitive  Dorsal  Aort^. 

Each  primitive  dorsal  aorta  gives  off  from  its  dorsal  surface  a  series  of  somatic  seg- 
mental arteries,  from  its  sides  an  irregular  series  of  intermediate  (visceral)  branches,  and 
from  its  ventral  surface  a  group  of  segmental  splanchnic  branches  to  the  walls  of  the 
alimentary  canal,  see  (Figs.  677  and  678). 

The  somatic  segmental  arteries  divide  into  ventral  and  dorsal  branches  which  accom- 
pany the  posterior  and  anterior  primary  branches  of  the  spinal  nerves  respectively,  and 
the  ventral  branches  give  ofl^  lateral  offsets.  The  various  branches  of  the  somatic  seg- 
mental vessels  anastomose  freely  together. 

The  splanchnic  segmental  arteries  also  anastomose  fi'eely  together.  Ultimately,  from 
the  somatic  vessels  and  their  branches  and  anastomoses  ai'e  developed  the  vertebral,  the 
basilar,  and  the  spinal  arteries  :  part  of  the  right  subclavian  artery,  the  whole  of  the  left 
subclavian  artery,  and  their  continuations  in  the  fore-limbs :  the  intercostal  and  lumbar 
arteries,  and  the  internal  mammary  and  deep  epigastric  arteries;  whilst  from  the  splanchnic 
segmental  arteries  the  majority  of  the  blood-vessels  which  supply  the  alimentary  canal  are 
developed.  The  intermediate  visceral  arteries  supply  the  organs  derived  from  the  inter- 
mediate cell  mass,  viz.  the  suprarenal  capsules,  the  kidney,  and  the  ovaries  or  testicles ; 
but  for  a  full  account  of  the  transformations  which  the  various  vessels  and  anastomoses 
undergo,  reference  must  be  made  to  the  account  of  the  morphology  of  the  arteries. 

The  Arteries  of  the  Limbs. 

Little  is  known  of  the  precise  details  of  the  development  of  the  arteries  of  the  limbs, 
but  there  is  not  much  doubt  that  they  are  formed  almost  entirely  by  prolongations  of  or 
from  somatic  segmental  arteries  or  their  branches. 

The  chief  arterial  stem  of  each  upper  extremity  is  represented  by  the  subclavian,  the 
axillary,  the  brachial,  and  the  anterior  interosseous  arteries;  these  vessels  form  a  con- 
tinuous trunk  which  is  developed,  on  the  left  side  entirely  and  on  the  right  side  mainly, 


934 


THE  VASCULAE  SYSTEM. 


from  the  corresponding  seventh  somatic  segmental  branch  of  the  primitive  aorta,  fi'om  its 
ventral  branch,  and  from  the  lateral  offset  of  the  latter.  It  is  indeed  the  lateral  offset 
of  the  ventral  branch,  growing  outwards  into  the  developing  limb,  which  forms  the 
prolongation  of  the  stem. 

The  root  of  the  right  stem  vessel,  constituted  by  the  right  subclavian  artery  from  its 
origin  almost  as  far  as  the  point  at  which  the  right  vertebral  artery  arises,  is  formed 
by  the  fourth  right  aortic  arch  :  on  the  left  side  the  fourth  arch  takes  no  part  in  the 
formation  of  the  subclavian  artery. 

In  the  lower  limbs  the  primary  main  arterial  stem,  on  each  side,  is  represented  by  the 
sciatic,  the  popliteal,  and  the  peroneal  arteries.  The  sciatic  artery  arises  from  the  caudal 
arch,  and  it,  together  with  its  prolongation  through  the  popliteal  space  and  leg,  is  probably 
formed  from  a  somatic  segmental  vessel,  but  to  which  parts  of  this  it  cori'esponds  is  not 
clear.  The  external  iliac  artery,  prolonged  into  the  limb  as  the  femoral  artery,  is 
developed  at  a  later  period  than  the  sciatic  artery.  It  arises  from  the  caudal  aortic  arch 
above  the  origin  of  the  sciatic  arter}^,  and,  like  the  latter  trunk,  is  probably  a  modified 
somatic  segmental  vessel.  The  femoral  artery  soon  after  its  formation  unites  with  the 
primary  main  stem,  at  the  upper  part  of  the  popliteal  space ;  the  sciatic  artery  then 
atrophies  and  loses  its  coiniexion  with  the  popliteal  artery,  and  ultimately  a  permanent 

chief  stem  vessel  is  formed,  which  includes 
the  external  iliac,  the  femoral,  the  popliteal, 
and  the  peroneal  arteries,  and  obviously  it 
represents  the  two  somatic  segmental  vessels 
by  Avhich  it  is  formed.  Both  in  the  upper 
and  in  the  lower  limb,  branches  which  attain 
a  large  size  are  given  off  from  the  main  stem 
artery  a  short  distance  beyond  the  joint 
between  the  upper  and  middle  sections  of 
the  limb,  i.e.  below  the  elbow  in  the  upper 
limb  and  below  the  knee  in  the  lower  limb, 
and  on  account  of  the  relatively  great  en- 
largement of  these  branches  the  continuity 
of  the  original  stem  is  obsciired.  Thu.s  it  is 
that,  in  the  adult,  the  brachial  artery,  the 
direct  continuation  of  the  stem  which  is 
divided  into  subclavian,  axillary,  and  brachial 
sections,  appears  to  terminate  by  dividing 
into  the  radial  and  ulnar  arteries,  whilst 
originally  it  Avas  continued  through  what, 
in  the  adult,  is  the  upper  part  of  the  ulnar 
artery  to  the  anterior  interosseous  artery ; 
the  posterior  interosseous,  the  radial,  and 
the  ulnar  arteries  being  merely  branches  from 
the  main  stem. 

Similarly,  in  the  lower  extremity  the 
popliteal  artery,  which  is  the  continuation' 
of  the  oi'iginal  stem  artery,  appears  to 
terminate  in  the  adult  by  dividing  into  the 
anterior  and  posterior  tibial  arteries,  both  of 
which  in  reality  are  branches  from  the  sides 
of  the  main  stem  which  was  continued  to 
the  foot  as  the  peroneal  artery. 


Primitive  jugular 
vein 


Internal  jugular  vein 


Subclavian 
vein 

Primitive  jugular 
vein 

Uuct  of  Cuvier 


Cardinal  vein 


Vitelline  vein 


Umljilical  vein 


Renal  vein 


Fig. 


External  iliac  vein 

Cardinal  vein  (internal 

/  "         iliac) 

671. — Development  of  the  Venous  System 
(Diagrammatic). 


DEVELOPMENT  OF  THE  VEINS. 

Simultaneously  with  the  formation  of  the 
arteries  by  which  the  blood  is   distributed 
to  the  embryo  and  to  the  rest  of  the  ovum, 
Stage  I.— The  ducts  of  Cuvier,  the  vitelline  veins,  and   ^'^^  in  a  similar  manner,  a  series  of  vessels  is 
the  umbilical  veins  open  directly  into  the  heart.     "  developed   by   means   of  which   the  blood   is 

returned  to  the  heart.  These  vessels  are  the 
veins,  of  which  there  are  two  main  groups.  One  group  returns  blood  from  the  abdominal 
viscera  and  the  annexa  (the  yolk-sac  and  allantois) ;  the  other  group  includes  the  vessels 
which  return  blood  from  the  Wolffian  bodies,  the  body  wall,  the  head  and  neck,  and  the 
limbs  of  the  embryo.     The  first  group  consists  of  the  vitelline,  allantoic,  and  portal 


DEVELOPMENT  OF  THE  VEINS. 


935 


veins ;  the  second  group  includes  tlie  primitive  jugular  and  the  cardinal  veins  and  the 
ducts  of  Cuvier. 

The  trunks  of  the  vitelline  veins  are  formed  by  the  posterior  parts  of  the  anterior 
primitive  ventral  aorta),  and  necessarily  they  open  into  the  posterior  part  of  the  heart 
(sinus  venosus).  They  collect  blood  from  the  yolk-sac,  and  ascend  along  the  vitello- 
intestinal  duct  to  be  continued  upwards  along  the  sides  of  the  duodenum.  Three 
transverse  anastomoses  soon  form  between  them,  of  which  the  lower  and  the  upper  are  in 
front  of  and  the  middle  is  behind  the  duodeiuuii ;  thus  two  vascular  circles  are  formed 
round  that  portion  of  the  gut.  Whilst  the 
loops  are  being  formed  the  liver  grows 
rapidly,  and  it  interrupts  the  direct  con- 
nexion of  the  vitelline  veins  with  the  heart. 
When  the  upper  vascular  loop  is  established 
the  two  vitelline  veins,  which  appear  to 
be  prolonged  from  its  sides,  enter  the  liver 
and  break  up  into  capillai'ies,  from  which 
two  new  vessels  arise  which  carry  the  blood 
to  the  sinus  venosus.  The  veins  which 
carry  the  blood  to  the  liver  are  now  known 
as  the  venae  advehentes ;  they  become 
the  right  and  left  divisions  of  the  portal 
vein.  The  vessels  which  carry  the  blood 
to  the  sinus  venosus  are  the  venae  reve- 
hentes,  and  they  become  the  hepatic  veins. 

From  the  inferior  part  of  the  lower 
venous  circle  the  vitelline  veins  fuse  into 
a  common  stem  which  receives  the  veins 
from  the  abdominal  portion  of  the  gut, 
and  this,  together  with  the  left  half  of  the 
lower  loop,  becomes  the  superior  mesenteric 
vein,  which  passes  in  front  of  the  third 
part  of  the  duodenum  and  there  receives 
the  splenic  vein.  The  middle  anastomosis 
and  the  right  half  of  the  upper  loop  become 
the  portal  vein.  The  upper  anastomosis 
and  the  left  vena  advehens  become  the 
left  branch  of  the  portal  vein.  The  right 
vena  advehens  forming  the  right  branch, 
and  the  left  half  of  the  upper  and  the  right 
half  of  the  lower  loop  disappeai*. 

The  allantoic  or  umbilical  veins  com- 
mence in  the  placenta  and  fuse  into  a 
single  stem  which  traverses  the  umbilical 
cord  to  reach  the  embryo,  and  divides  at 
the  umbilicus  into  right  and  left  divisions. 
The  two  veins  then  pass  through  the  septum 
transversum,  one  to  the  right  and  the  other 
to  the  left,  and  open  into  the  sinus  venosus. 
After  a  very  short  period  the  communica- 
tions with  the  sinus  are  obliterated,  and 
both  veins  end  in  the  venous  capillaries  of 
the  liver,  the  blood  they  convey  now  pass- 
ing to  the  sinus  venosus  by  the  hepatic  veins 


Lateral  sinus 


External  jugular  vein 
Internal  jugular  vein 

Subclavian  vein 

Transverse  anastomosis 

Lower  part  of  primitive 
jugular  vein 

Duct  of  Cuvier 

Cardinal  vein 
Transverse  anastomosis 
Vena  revehens 
Liver 

Vena  advehens 


—  Umbilical  vein 


Stem  formed  by. fused 
vitelline  veins ' 
~Renal  vein 


Transverse  anastomosis 
External  iliac  vein 


. — Development  of  the  Venous  SvbThM 
(Diagrammatic). 

Stage  II. — The  vitelline  and  umbilical  veins  terminate  in 
the  liver,  and  transverse  anastomoses  have  formed 
between  the  vitelline,  cardinal,  and  primitive  jugular 
veins  of  opposite  sides. 


This  condition  also  is  only  transitory,  for 
the  right  vein  soon  undergoes  complete  atrophy  and  disappears,  whilst  the  left  opens  into 
the  upper  loop  of  the  vitelline  veins.  In  the  meantime,  however,  another  channel,  the 
ductus  venosus,  has  been  developed,  which  passes  directly  from  the  upper  loop  of  the 
vitelline  veins,  or  rather  from  the  left  vena  advehens  to  the  right  hepatic  vein,  and  by 
this  channel  the  greater  part  of  the  placental  blood  passes  to  the  heart  without  traversing 
the  liver  substance.  Some  of  the  placental  blood,  however,  goes  to  the  liver  by  the  left 
vena  advehens.  Finally  the  left  vena  revehens  loses  its  connexion  with  the  sinus  venosus 
and  opens  into  the  right  vena  revehens.  The  left  umbilical  vein  and  the  ductus  venosus 
remain  pervious  until  birth,  when  the  placental  circulation  ceases.  The  two  vessels 
then  rapidly  atrophy,  and  are  subsequently  represented  by  fibrous  cords,  of  which  that 
formed  from  the  left  umbilical  vein  is  known  as  the  round  ligament  of  the  liver. 


936 


THE  VASCULAR  SYSTEM. 


Internal  jugular  vein 
External  jugular  vein 


Subclavian  vein 

Transverse  anastomosis 

Cardinal  vein 
Duct  of  Cuvier 

Heart 


A^ena  revehens 


The  primitive  jugular  and  cardinal  veins,  and  the  ducts  of  Cuvier,  which  constitute  the 
main  veins  of  the  Wolffian  body,  and  of  the  body  wall,  head,  neck,  and  limbs  of  the  embryo, 
are  represented  in  the  adult  by  the  external  jugular  veins,  the  whole  of  the  right  and  part 
of  the  left  innominate  veins,  the  superior  vena  cava,  the  azygos  veins,  the  left  superior 
intercostal  vein,  part  of  the  inferior  vena  cava,  the  right  common  iliac  vein,  a  small  part  of 
the  left  common  iliac  vein,  and  both  right  and  left  internal  iliac  veins. 

The  primitive  jugular  vein  of   each 
Lateral  sinus  gj^jg   returns  blood   fi'om  the    head  and 

neck,  and  coiTCsponding  upper  extremity, 
and  it  terminates  below  by  fusing  with 
the  cardinal  vein  to  form  a  common  trunk, 
the  duct  of  Cuvier,  which  opens  into  the 
sinus  venosus.  Each  cardinal  vein  returns 
blood  from  the  body  wall,  the  Wolffian  body, 
and  the  lower  extremity  of  its  own  side. 
Numerous  transverse  anastomoses  are 
developed  between  the  primitive  jugular 
and  cardinal  veins  of  opposite  sides,  and 
of  these  four  are  specially  important,  one 
between  the  primitive  jugular  veins  and 
Transverse  anastomosis  three  between  the  cardinal  veins ;  the 
former  becomes  the  left  innominate  vein  ; 
of  the  latter,  the  upper  two  become  the 
transverse  parts  of  the  upper  and  lower 
smaller  azygos  veins,  and  the  third  forms 
the  left  common  iliac  vein.  As  these 
transverse  channels  develop  further 
changes  occur  in  the  primitive  jugular 
and  cardinal  trunks.  At  first  the  upper 
extremity  of  the  primitive  jugular  vein 
is  in  direct  continuity  with  the  venous 
sinuses  of  the  cranium  through  an  aper- 
ture, the  post-condyloid  foramen,  in  front 
of  the  external  ear;  but  this  continuity 
is  destroyed,  and  the  aperture  in  the 
skull  closes  as  soon  as  a  new  vessel, 
which  becomes  the  internal  jugular  vein, 
has  grown  upwards  from  a  point  on  the 
inner  side  of  the  primitive  jugular  trunk 
and  has  established  a  communication 
with  the  lateral  sinus  through  the  jugular 
foramen.  This  vessel  rises  behind  the 
sterno-clavicular  joint,  just  opposite  to, 
or  slightly  below,  the  entrance  of  the 
subclavian  vein  into  the  outer  side  of  the 
primitive  jugular  vein. 

With  the  exception  of  its  upper 
extremity,  the  whole  of  the  primitive 
jugular  vein  remains  on  both  sides  in  the 
adult.  On  the  right  side,  above  the 
transverse  anastomosis  between  the  two 
primitive  jugular  veins  which  becomes 
the  left  innominate  vein,  it  forms  the 
external  jugular  vein,  and  that  portion 
of  the  right  subclavian  vein  which  inter- 
venes between  the  external  jugular  and  internal  jiigular  veins,  and  also  the  right  innominate 
vein ;  below  the  anastomosis  it  forms  the  upper  part  of  the  superior  vena  cava,  the  lower 
part  of  the  latter  vessel  from  the  entrance  of  the  vena  azygos  major  downwards  repre- 
senting the  right  duct  of  Cuvier,  which,  though  it  is  placed  transversely  in  the  early 
stages,  becomes  more  vertical  as  the  heart  descends  in  the  thoracic  cavity.  On  the  left 
side  above  the  transverse  anastomosis  it  forms  the  external  jugular  vein,  the  innermost 
part  of  the  subclavian  vein,  and  a  small  part  of  the  left  innominate  vein  ;  the  main  part 
of  the  latter  vessel  being  formed,  as  before  stated,  from  the  transverse  anastomosis.     The 


■Vena  adveliens 


Umbilical  vein 


Splenic  vein 

ior  mesenteric  vein 


V'itellinc  vein 


Transverse  anastomosis 


External  iliac  vein 


Fig.  673. — Development  ok  the  Venous  SystEiM 
(Diagrammatic). 

Stage  III.— The  right  umbilical  vein  has  disappeared,  and 
the  superior  mesenteric  and  splenic  veins  have  joined 
the  fused  vitelline  veins. 


DEVELOPMENT  OF  THE  VEINS. 


937 


Right  innominate 
vein 

Superior  vena  cava 


Vena  azj'gos  major 


Right  hepatic 
vein 


portion  of  the  left  primitive  jugular  vein  which  lies  below  the  anastomosis  is  represented 
in  the  adult  by  the  upper  part  of  the  left  superior  intercostal  vein.^ 

The   portions  of   the  cardinal   veins   lying   below  the   transverse  anastomosis  which 
becomes  the  left  common  iliac 
vein  remain ;  that  on  the  right  />^ 

forms  the  right  internal  and 
common  iliac  veins,  but  the 
left  formsonly  the  left  internal 
iliac  vein  and  a  small  part  of 
the  left  common  iliac  vein,  for 
the  transverse  anastomosis 
commences  on  the  left  side 
almost  opposite  the  point  of 
entrance  of  the  external  iliac  subclavian 
vein,  whilst  it  tei-minates  on  ^®'" 

the    right    side    at   a  higher 
level. 

From  the  left  common 
iliac  vein  to  the  renal  vein 
the  cardinal  vein  of  the  left 
side  disappears ;  that  on  the 
right  side  becomes  the  lower 
part  of  the  inferior  vena  cava, 
to  which  the  blood  passes 
from  the  left  side  of  the  ab- 
dominal wall  by  means  of 
small  transverse  anastomosing 
channels  which  existed  be- 
tween the  cardinal  veins,  and 
which  persist  as  the  terminal 
portions  of  the  left  lumbar 
veins. 

Above  the  renal  veins  part 
of  the  light  cardinal  vein 
persists  as  the  vena  azygos 
major,  and  the  left  forms  the 
upper  and  lower  minor  azygos 
veins  and  the  lower  part  of  the 
left  superior  intei'costal  vein. 
The  azygos  minor  veins  open 
into  the  azygos  major  by  the 
two  transverse  anastomosing 
channels  which  form  between 
the  upper  parts  of  the  cai'dinal 
veins. 

The  upper  part  of  the 
inferior  vena  cava  is  de- 
veloped as  an  outgrowth  from 
the  common  trunk  formed  by 
the  fusion  of  the  ductus 
venosus  with  the  right  hepatic  .  ,^.  ^.  , 

vein.      It   grows    cfownwards,       ^^'^^  674.-Devei.opment  of  the  Venous  system  (Diagrammatic), 
behind  theliver  and  along  the  ^t'-^g^    IV.-The    left  umbilical  has   joined   the  upper  part    of  the  left 
•    i,^       -J         f    ^.v,  ii      1  vitelline  vein  ;  the  ductus  venosus  and  the  upper  part  ot  the  interior 

rignt    Siae    ot    the    vertebral  ^.g,,^  ^^^.^  l^^^.g  appeared,  and  portions  of  the  primitive  jugular  and 

column,   to    the    interval    be-  cardinal  veins  have  atrophied. 

tween  the  kidneys,  where  it 
divides  into  two  branches,  of  which  the  right  anastomoses  with  the  right  cardinal  vein 

1  The  account  which  has  been  given  of  the  prunitive  jugular  veins  is  that  which  has  been  generally  accepted 
for  many  years,  but  in  1895  Salza's  observations  on  the  guinea-pig  led  him  to  dispute  the  correctness  of  the 
description,  and  Mall's  recent  investigations  on  human  embryos  confirm  Salza's  work.  From  the  results  of 
the  investigations  of  these  observers  it  appears  that  the  external  jugular  vein  is  a  secondary  vein,  and  the 
internal  jugular  is  part  of  the  primitive  jugular  which  originally  extended  forwards  to  the  anterior  end  of  the 
superior  longitudinal  sinus.  Its  connection  with  the  sinus  is  soon  lost,  and  the  only  intracranial  remainder  of 
the  primitive  vein  is  the  cavernous  sinus. 


Kiglit  branch  of 
portal  vein 


Inferior  vena  cava 


I^ateral  sinus 


Intenial  jugular  vein 
External  jugular  vein 


Subclavian 
vein 
Left  innominate  vein' 
Left  superior  intercostal 


.        Oblique  vein  of  Marshall 
I  \  I —  Vena  azygos  minor  sujierior 


Heart 

Vena  azygos  minor  inferior 

Left  hepatic  vein 

Ductus  venosus 
Left  branch  of 
portal  vein 

Umbilical  vein 
Portal  vein 


Suprarenal  vein 


Renal  vein 


Spermatic  vein 


Inferior  vena  cava 


Riirht  common 


Right  externa 


Right  internal  iUac  vein 


Spermatic  vein 


Left  common  iliac  vein 


Left  external  iliac  vein 
Left  internal  iliac  vein 
Middle  sacral  vein 


938  THE  VASCULAE  SYSTEM. 

at  the  level  of  the  renal  vein  ;  it  receives  the  suprarenal  vein,  and  it  terminates  in  a 
tapering  extremity  which  is  said  to  become  the  spermatic  vein  of  the  right  side.  The 
left  branch  passes  across  the  front  of  the  aorta  l)elow  the  superior  mesenteric  artery,  and 
unites  with  the  left  cardinal  vein  at  the  point  of  the  entrance  of  the  renal  vein.  It  gives 
off  an  upper  branch  which  becomes  the  left  suprarenal  vein,  and  a  lower  which  becomes 
the  left  spemiatic  vein.  As  before  pointed  out,  the  left  cardinal  vein"  disappears  between 
the  renal  vein  and  the  left  common  iliac  vein,  wliilst  the  right  remains  as  the  lower  part 
of  the  inferior  vena  cava.  The  left  division  of  the  upper  part  of  the  inferior  vena  cava, 
which  crosses  the  aorta  below  the  superior  mesenteric  arteiy,  remains  as  the  inner  portion 
of  the  left  renal  vein,  which  therefore  receives  the  left  spermatic  and  left  suprarenal  veins 
as  tributaries. 

The  Veins  of  the  Limbs. 

Two  sets  of  veins  are  developed  in  each  limb,  the  superficial  and  the  deep ;  the  former 
are  the  primai-y  vessels,  and  as  a  rule  they  are  quite  apart  from  the  limb  arteries ;  the 
deep  veins  are  secondary,  and  they  accompany  the  arteries  of  the  limb. 

At  the  peripheral  extremity  of  each  limb  a  venous  arch  is  developed,  which  is  subse- 
quently connected  with  the  digital  veins.  In  the  upper  extremity  the  arch  terminates  on 
the  ulnar  (post-axial)  side  of  the  limb  in  a  tnnik  which  afterwards  becomes  the  posterior 
ulnar,  basilic,  axillaiy,  and  subclavian  veins.  At  a  latter  period  additional  supei'ficial 
vessels  are  formed,  and  of  these  a  median  vein  which  drains  the  palm,  and  a  radial  which 
commences  on  the  radial  side  of  the  dorsum  of  the  hand,  are  the  most  important.  The 
radial  passes  up  the  preaxial  border  of  the  limb,  becomes  the  cephalic,  and  for  a  time 
terminates  in  the  primitive  jugular  vein ;  ^  this  connexion  is  usually  lost,-  and  a  new  com- 
mvmication  is  formed  with  the  axillaiy  vein.  Tlie  median  vein  ends  in  an  anastomosing 
ves.sel  between  the  basilic  and  cephalic  veins  at  the  elbow,  and  through  which  it  also 
communicates  with  the  deep  veins. 

In  the  lower  extremity  the  peripheral  venous  arch  terminates  in  a  fibular  or  post-axial 
trunk,  which  remains  in  the  adult  as  the  external  saphenous  vein  ;  its  connexion  with  the 
sciatic  vein,  which  was  its  original  continuation  upwards,  is  soon  lost,  and  a  new  com- 
munication is  formed  with  the  popliteal  vein. 

The  internal  saphenous  vein  is  a  later  development  which  appears  on  the  pre-axial 
border  of  the  limb,  and  terminates  in  the  femoral  vein. 

The  deep  veins  appear  as  a  series  of  anastomosing  channels  at  the  sides  of  the 
arteries. 

The  Pulmonary  Veins. 

The  pulrnonaiy  veins  develop  simultaneously  with  the  lungs,  and  at  first  the  veins 
from  both  lungs  unite  to  form  a  single  trunk,  which  enters  the  left  auricle  posteriorly, 
close  to  the  auricular  septum  ;  subsequently  the  single  trunk  is  absorbed,  and  two  veins, 
one  from  each  lung,  enter  the  left  auricle,  and  eventually,  as  the  result  of  further 
absorption,  two  veins  from  each  lung  terminate  in  that  cavit}^ 

The  Lymphatic  Vessels. — The  lymph  vessels  commence  as  outgrowths  from  the 
large  veins  at  tlie  root  of  tlie  neck  and  gradually  extend  throughout  the  body  by  a  pro- 
cess of  budding,  at  least  this  appears  to  be  the  case  in  the  pig.  The  growth  therefore  is 
from  the  centre  to  the  periphery,  and  the  communications  with  the  large  serous  cavities 
must  be  formed  secondarily. 

MORPHOLOGY  OF  THE  VASCULAR  SYSTEM. 

In  conformity  with  th(!  general  plan  of  tlie  vertel)rate  body,  the  vascular  system  is  essentially 
segmental  in  character.  Tliis  i.s  o>)vioiLS,  even  in  the  adult,  in  the  intercostal  and  lumbar  vessels. 
It  i.s  di.«tinguishab]e,  though  l&«s  obviou.o,  in  the  vessels  of  the  head  and  neck  and  of  the  pelvis. 

Tlie  .aegnifntal  ai-t^-rifes  and  vf-ins  form  a  series  of  bilaterally  symmetrical  vessels,  each  of 
which  i.s  united  to  the  vci^st-h  of  a^ljaoent  segments  by  intersegmental  channek,  which  anastomose 
with  one  another,  through  the  portion.s  of  tlie  segmental  vessels  which  they  connect  together, 
and  thiLS  form  longitudinal  trunks.  The  longitudinal  trunks  are  mainly,  though  not  exclusively, 
intersegmental-  From  tliem  the  main  stem  vessels  of  the  individual  are  formed,  and  from  or  to 
the.se  latter  the  .segmental  ve.s.seLs  appear  to  proceed  as  liranches  or  trilnitarics. 

In  the  course  of  development  the  longitudinal  trunks  become  the  most  important  trunks  in 
tlie  individual,  and  they  are  formefl  before  the  segmental  vessels  make  their  appearance. 

'  See  note  on  page  937. 

*  In  certain  cases  it  remains,  and  then  the  cephalic  vein  crosses  the  front  of  the  clavicle  and  terminates 
in  the  external  jugular  Tein. 


MOEPHOLOGY  OF  THE  AETERIES. 


939 


The  Segmental  Arteries  and  their  Anastomoses. 

The  main  longitudinal  trunks  are  the  primitive  aortte.     The  descending  aorta  is  formed,  in 


So.SA.  1 


CAA.I 


'^±\  i' 


Fig.  675. — Diagram  of  the  Cephalic  Aortic  Arches,  and  of  the  Segmental  and  Intersegmental 
Arteries  in  the  Region  in  Front  op  the  Umbilicus. 


C.A.A.  I,  II,  III,  IV 
Co 


D.D. 

D.Sp, 
L.B. 


L.E.D. 
P.D.A. 
Po.C. 


V.  The  cephalic  aortic  arches.  Po.T. 

Auastomosing  vessel    between   the    primitive  Pr.C. 

ventral    aorta     and    the    ventral    somatic  P.V.A. 

anastomosis.  So.S.A. 
Dorsal  division  of  a  somatic  segmental  artery. 

Dorsal  splanchnic  anastomosis.  Sp.S.A. 

Lateral  branch  of  ventral  division  of  somatic  V.D. 

segmental  artery.  V.E.D. 

Branch  to  lateral  enteric  diverticiihim.  V.V. 

Primitive  dorsal  aorta.  V.So. 

Post-costal  anastomosis.  V.Sp. 


Post-transverse  anastomosis. 
Pre-costal  anastomosis. 
Primitive  ventral  aorta. 
1,    2,   3,    4,   5,   6,    7,    8.    Somatic   segmental 

arteries.  , 

Splanchnic  segmental  arteries. 
Ventral  division  of  a  somatic  segmental  artery. 
Branch  to  ventral  enteric  diverticulum. 
Vitelline  vessels. 
Ventral  somatic  anastomosis. 
Ventral  splanchnic  anastomosis. 


the  greater  part  of  its  extent,  by  the  fusion  of  the  dorsal  parts  of  the  primitive  aortae,  and  from  it 
the  segmental  arteries  arise  in  jaairs. 

In  a  typical  segment  of  the  body  ^  "  ^-^ 

of  the  embryo  there  are  three  seg- 
mental arteries  on  each  side.  One 
rises  from  the  dorsal  surface  of  the 
primitive  dorsal  aorta,  i.e.  from  the 
dorsal  longitudinal  trunk,  and  runs 
outwards  in  the  tissues  developed 
from  the  somatic  mesoderm  ;  it  is 
distributed  to  the  body  wall,  in- 
cluding the  sj^inal  column  and  its 
contents,  and  is  termed  a  somatic 
segmental  artery.  A  second  vessel 
rises  from  the  side  of  the  primitive 
dorsal  aorta ;  it  is  distributed  to 
the  structures  developed  from  the 
intermediate  cell  mass,  viz.  the 
suprarenal  body,  the  kidney,  and 
the  ovary  or  testicle,  and  it  is  ac- 
cordingly termed  the  intermediate 
visceral  artery.  The  third  artery, 
which  is  known  as  the  splanchnic 
segmental  artery,  springs  from  the 
ventral  surface  of  the  descending 
aorta.  It  runs  in  the  tissues  de- 
veloped from  the  splanchnic  meso- 
derm, and  supplies  the  wall  of  the 
alimentary  canal. 

The  somatic  segmental  arteries  form  in  the  early  embryo  a  regular  series  of  paired  vessels 
throughout  the  cervical,  dorsal,  lumbar,  and  sacral  regions.  It  is,  however,  only  in  the  dorsal  and 
lumbar  regions  that  their  original  characters  are  retained.     The  paired  vessels  pa.ss  backwards 


VEDiHy) 


Fig.  676. — Diagram  ok  the  Caudal  Aortic  Arch,  and  of  the 
Segmental  and  Intersegmental  Arteries  in  the  Region 
behind  the  Umbilicus. 


Cd.A.A. 

Caudal  aortic  arch. 

So.S.A.     Somatic     segmental 

D.Sp. 

Dorsal    splanchnic    ana- 

arteries. 

stomosis. 

Sp.S..\.    Splanchnic     segmental 

M.S. 

Middle  sacral  artery. 

arteries. 

Pa.C. 

Parietal     branch     from 

V.E.D.  (Hy).  Branch  to  a  ventral 

caudal  arch. 

enteric  diverticulum. 

P.D.A. 

Primitive  dorsal  aorta. 

Vi.C.        Visceral  branch  from  the 

P.V.A. 

Primitive  ventral  aorta. 

caudal  arch. 

V.V.   Vitell 

ine  vessels. 

940 


THE  VASCULAE  SYSTEM. 


PrL 


PrN 


by  the  sides  of  the  vertebrt^,  and  divide  into  dorsal  and  ventral  branches  which  accompany  the 
corresiJonding  anterior  and  posterior  primary  divisions  of  the  spinal  nerves. 

The  ventral  branches  run  outwards  l^etween  the  ribs  in  the  dorsal  region,  and  in  correspond- 
ing positions  in  the  lumbar  region.  They  are  connected  together,  near  their  commencements,  by 
a  series  of  precostal  anastomoses  which  pass  in  front  of  the  necks  of  the  ribs,  and  they  are  also 
connected  together  near  their  terminations  by  ventral  anastomosing  channels  which  run  in  the 
thoracic  region  behind  the  costal  cartilages,  and  in  the  lumbar  region  behind  or  in  the  substance 
of  the  rectus  abdominis  muscle.  Each  ventral  branch  gives  off  a  lateral  offset  which  is  distributed 
like  the  lateral  cutaneous  branch  of  a  spinal  nerve. 

The  dorsal  branches  run  backwards  between  the  transverse  processes  of  the  vertebrae  ;  they  are 
connected  behind  the  necks  of  the  ribs  by  jDost-costal  anastomoses,  and  again  behind  the  transverse 

processes  of  the  vertebrae  by 
post-transverse  anastomosing 
channels.  Moreover,  each 
dorsal  branch,  as  it  j)asses  by 
the  corresponding  interverte- 
bral foramen,  gives  off  a  spinal 
offset  which  enters  the  spinal 
canal  along  the  corresponding 
nerve-root,  and  divides  into  a 
dorsal,  a  ventral,  and  a  neural 
branch.  The  dorsal  branches 
of  these  spinal  arteries  are  con- 
nected together  along  the 
ventral  surfaces  of  the  laminae 
by  pre-laminar  anastomoses, 
and  the  ventral  branches  are 
united  on  the  dorsal  surfaces 
of  the  vertebral  centra  with 
their  fellows  above  and  below 
by  post-central  anastomoses ; 
they  are  also  united  with 
their  fellows  of  the  opjDosite 
side  by  transverse  communi- 
cating channels.  The  neural 
branches  of  the  spinal  arteries 
divide  similarly  into  dorsal 
and  ventral  branches ;  the 
dorsal  branches  of  each  side 
are  connected  together  by  post- 
neural  anastomoses,  and  the 
ventral  branches  unite  in  the 
middle  line  both  with  their 
fellows  above  and  below  and 
with  those  of  the  opposite  side, 
forming  a  single  longitudinal 
l^re-neural  trunk. 

In  the  dorsal  and  lumbar 
regions  of  the  body  the  somatic 
segmental  arteries  persist  and 
form  the  intercostal  and  lum-  " 
bar  arteries.  These  vessels 
spring  from  the  dorsal  aspect 


Fig.  677. — Dt.vgram  showing  the  Arrangement  and  Communications 
OF  THE  Segmental  and  Intersegmental  Arteries  at  an  early 
Stage  ok  Development. 

C,  Ccelom  ;  D.Sp,  Dorsal  splancLnic  anastomosis  ;  In,  Intestine  ;  I.V,  Inter- 
mediate visceral  artery  ;  L.  B,  Lateral  branch  of  the  ventral  division  of 
a  somatic  segmental  artery  ;  P.C,  Post-central  anastomosis  ;  P.D.A, 
Primitive  dorsal  aorta  ;  Po.C,  Post-costal  anastomosis  ;  Po.N,  Post- 
neural  anastomosis  ;  Po.T,  Post-transverse  anastomosis  ;  Pr.  C,  Pre- 
costal  anastomosis;  Pr.L,  Pre-laminar  anastomosis  ;  Pr.N,  Pre-neural 
anastomosis  ;  So.S.A,  Somatic  segmental  artery  ;  Sp.S.A,  Splanchnic 
segmental  artery  ;  V.E.D,   Branch  to  a  ventral  enteric  diverticulum  ; 

V.So,   Ventral   somatic  anastomosis  ;    V.Sp,  Ventral  splanchnic  ana-    of  thedescendingaorta, usually 
stomosis.  in  pairs.     The  corresponding 

vessels  of  opposite  sides,  how- 
ever, occasionally  fuse  together  at  their  origins,  simultaneously  with  the  fusion  of  the  dorsal 
longitudinal  trunks  to  form  the  descending  aorta,  and  then  they  arise  by  common  stems. 

The  precostal  anastomoses  between  the  ventral  branches  of  the  somatic  segmental  arteries 
are  only  representerl  in  the  dorsal  region  l)y  the  superior  intercostal  arteries ;  in  the  lumbar 
region  they  disappear  entirely.  Tlie_  anastomoses  Itetween  the  anterior  ends  of  the  ventral 
branches  of  the  somatic  segmental  arteries  persist  as  the  internal  mammary  and  deep  epigastric 
arteries. 

The  lateral  offsets  of  the  ventral  branches  are  represented  by  the  cutaneous  arteries  which 
accompany  the  lateral  cutaneous  Ijranches  of  the  spinal  nerves. 

The  post-costal  and  post-transverse  anastomoses  usually  disappear  in  the  dorsal  and  lumbar 
regions,  but  the  post-costal  anastomoses  occasionally  jjersist  in  the  ujjper  dorsal  region,  and  take 
part  in  the  formation  of  the  vertebral  artery,  which  in  such  cases  arises  from  the  first  or  second 
intercostal  artery.  In  some  carnivores  the  post-costal  longitudinal  vessels  persist  in  the  upper 
dorsal  region,  and  form,  on  each  side,  a  trunk  which  is  connected  with  tin;  first  aortic  intercostal, 
and  which  supplies  the  five  anterior  intercostal  spaces. 

The  pre-laminar,  the  post-central,  and  the  pre-  and  post-neural  anastomoses  persist,  the  two 


MORPHOLOGY  OF  THE  ARTERIES. 


941 


latter  aiding  in  the  formation  of 
the  dorsal  and  lumliar  portions  of 
the  pre-  and  post-spinal  arteries 
respectively. 

It  is  in  the  cervical  region,  how- 
ever, that  the  most  interesting 
changes  occur.  The  first  six  pairs 
of  somatic  segmental  arteries  lose 
their  connexions  Avith  the  dorsal 
roots  of  the  aortic  arches,  i.e.,  in  other 
Avords,  with  the  longitudinal  anasto- 
mosing channels  in  this  region.  The 
seventh  pair,  however,  persist  in 
their  entirety  ;  and  from  them  are 
formed,  on  the  right  side,  a  portion 
of  the  subclavian  trunk,  and  on  the 
left  side  the  whole  of  the  subclavian 
stem  from  its  commencement  up  to 
the  origin  of  the  vertebral  artery. 
On  each  side  the  ventral  branch  of 
the  seventh  segmental  artery  forms 
that  portion  of  the  subclavian  artery 
which  lies  between  the  origins  of  the 
vertebral  and  internal  mammary 
arteries,  and  also  the  trunk  of  the 
internal  mammary  artery  as  far  as 
the  upper  border  of  the  first  costal 
cartilage.  The  remainder  of  the  in- 
ternal mammary  artery  represents  Fig.  678.— Diagram  of  the  Segmental  and  Intersegmental 
the  ventral  longitudinal  anastomoses  Arteries   at   a  later    Period   of    Development    than   in 

between  the  ventral  branches  of  the  Fig.  677. 

seventh  and  the  following  somatic  c,  Ccelom  ;  D.A,  Dorsal  aorta  ;  D.Sp,  Dorsal  splanclniic  auastoniosis ; 
segmental  arteries.      The  coutinua-  j^,  intestine  ;  V.E.D,  Branch  to  ventral  enteric  diverticulum  ; 

tion  ot  the  subclavian  artery,  beyond  y.Sp,  Ventral  splanchnic  anastomosis. 

the  inner  margin  of  the  first  rib,  is 

the  persistent  and  enlarged  lateral  oft'set  of  the  ventral  branch  of  the  seventh  somatic  segmental 
artery,  which  is  continued  outwards  into  the  upper  limb  behind,  or  postaxial  to  the  shoulder  girdle. 
The  thyroid  axis  and  the  superior  intercostal  artery,  both  branches  of  the  subclavian  artery,  are 

persistent   pre-costal  anastomoses,  and 


PrL  pv,N 


SoSA 


PDA 


the  ascending  cervical  artery  belongs  to 
the  same  series  of  vessels.  The  verte- 
bral artery,  which  appears  as  a  branch 
of  the  subclavian  in  the  adult,  is  mor- 
phologically somewhat  complex.  The 
first  part  represents  the  dorsal  branch 
of  the  seventh  somatic  segmental  artery ; 
the  second  part,  that  passing  through 
the  cervical  transverse  processes,  con- 
sists of  the  jjersistent  post-costal  an- 
astomoses between  the  first  seven  seg- 
mental arteries ;  a  third  part,  that 
lying  on  the  arch  of  the  atlas,  is  the 
spinal  branch  of  the  first  somatic  seg- 
mental artery  and  its  neural  continua- 
tion ;  whilst  finally  the  upper  part  of 
the  vertebral  artery,  that  in  the  cranial 
cavity,  apj^ears  to  represent  a  prolonga- 
tion of  the  jjreneural  anastomoses, 
which  still  farther  upwards  are  prob- 
ably represented  by  the  basilar  artery. 
As  already  stated,  the  post -costal  an- 
FiG.  679.— Diagram  showing  the  Arrangement  and  Com-  astomoses  below  the  seventh  segmental 
munications  of  the  Segmental  Arteries  in  the  artery  occasionally  persist,  and  in  such 
Region  of  the  Cephalic  Aortic  Arches.  cases  the  vertebral   may  lose  its  con- 

^,  .    .    ^,    ,    ,.         ^.        ,      ^     ^         .        ^  ^   ^  ,        ,    nexion  with  the  subclavian,  and  spring 

C.A.A  Cephalic  aortic  arch  ;  In,  Intestine  ;  I.B,  Lateral  branch  f^.^^^^  ^^^  ^^  ^tj^^^.  ^f  ^^^  ^^^^4^^  branches 
of  a  somatic  segmental  artery  ;  L.E.D,  Branch  to  a  lateral      .  .,  intercostal  qrteries 

enteric  diverticulum  ;  P.C,  Post-central  anastomosis  ;  P.D.A,  °^  ^^^  uppei  intercostal  aiteiies. 
Primitive  dorsal  aorta  ;  Po.C.  Post-costal  anastomosis  ;  Po.N,  ,      ^he  profunda  cervicis  artery 
Post-neural  anastomosis  ;  Po.T,  Post-transverse  anastomosis ;  "^e  regarded  as  a  remnant  of  the  post- 
Pr.C.  Pre-costal  anastomosis :  Pr.L,  Pre-laminar  anastomosis ;  transverse  longitudinal  anastomoses. 
Pr.X,  Pre-neural  anastomosis;  P.  V.  A,  Primitive  ventral  aorta;         The  origin  of  the  seventh  somatic 
So.S.A,  Somatic  segmental  artery ;  V.E.D,  Branch  to  a  ventral  segmental  artery  from  the  dorsal  longi- 
enteric  diverticulum  ;  V.So,  Ventral  somatic  anastomosis.       tudinal  trunk  is  at  first  some  distance 


VED 


IS  to 


942  THE  VASCULAE  SYSTEM. 

behind  the  fifth  aortic  arch,  but,  simultaneously  with  the  elongation  of  the  neck  and  the  retrac- 
tion of  the  heart  into  the  thoracic  region,  it  is  shifted  forward  until  it  is  opposite  the  dorsal 
end  of  the  fourth  aortic  arch. 

The  middle  .sacral  artery  i.s  formed  by  the  fusion  of  two  vessels,  each  of  which  springs  from 
the  primitive  aorta  in  exactly  the  same  manner  as  a  somatic  segmental  artery ;  it  may  therefore 
be  looked  ui^on  as  consisting  of  fused  somatic  segmental  vessels  which  have  been  prolonged 
backward  for  the  supply  of  the  caudal  appendage.  It  is,  however,  commonly  regarded  as  the 
direct  continuation  of  the  descending  aorta,  and  consequently  as  being  mainly  intersegmental. 
Its  mode  of  origin  and  general  nature  do  not  lend  much  supjjort  to  the  latter  view. 

The  intermediate  visceral  arteries  suj^ply  the  organs  derived  from  the  intermediate  cell 
mass.  They  form  a  somewhat  irregular  series  of  vessels  in  the  adult,  but  presumably  in  the 
primitive  condition  there  was  a  pair  in  each  segment  of  the  body ;  many  of  these  disappear, 
however,  and  the  series  is  only  represented  in  the  adult  l)y  the  suprarenal,  the  renal,  and  the 
spermatic  or  ovarian  arteries — jjossibly,  also,  by  some  of  the  branches  of  the  internal  iliac  arteries. 

The  splanchnic  segmental  arteries  arise  in  the  embryo  from  the  ventral  aspects  of  the 
Ijrimitive  dorsal  aortse,  and  are  distributed  to  the  walls  of  the  alimentary  canal.  They  anasto- 
mose with  their  fellows  in  front  and  behind  in  the  dorsal  wall  of  the  gut ;  those  in  front  of 
the  umbilicus  also  communicate  together  on  the  ventral  wall  of  the  gut,  whilst  those  behind  the 
umbilicus  terminate  ventrally  in  the  posterior  sections  of  the  ventral  aortse. 

After  the  fusion  of  the  dorsal  longitudinal  trunks  to  form  the  descending  aorta,  the  origins  of 
the  splanchnic  arteries  in  each  segment  fuse  into  a  common  stem,  or  either  the  right  or  left  artery 
altogether  disappears,  whilst  at  a  later  period  the  majority  of  the  splanchnic  segmental  arteries 
lose  their  direct  comiexion  with  the  descending  aorta ;  those  which  retain  their  connexion  are 
the  left  bronchial  arteries,  the  oesophageal  branches  of  the  aorta,  the  coeliac  axis,  and  the  superior 
and  inferior  mesenteric  arteries,  the  three  latter  vessels  greatly  increasing  in  size. 

The  coronary  or  gastric  branch  of  the  coeliac  axis,  as  it  j)asses  from  its  origin  to  the  small 
curvatui'e  of  the  stomach,  represents  a  right  S2:)lanchnic  artery ;  the  remainder  of  the  coronary 
artery  and  the  pyloric  branch  of  the  hejjatic  are  remnants  of  the  ventral  anastomoses  between  the 
splanchnic  arteries  in  front  of  the  umbilicus. 

The  sj^lenic  artery  is  a  branch  given  off  from  a  splanchnic  artery  to  an  organ  develoj)ed  in  the 
gastric  mesentery,  and  the  hepatic  is  a  branch  from  the  ventral  splanchnic  anastomoses  to  the 
heijatic  diverticulum  from  the  wall  of  the  duodenal  portion  of  the  fore-gut. 

The  superior  and  inferior  mesenteric  arteries  represent  at  their  origins  sjDlanchnic  branches, 
and  in  the  remainder  of  their  extent  the  dorsal  anastomoses  on  the  gut  wall. 

The  Aorta,  Pulmonary  Artery,  and  other  Chief  Stem  Vessels. 

The  heart  and  the  majority  of  the  great  arterial  trunks  of  tlie  body,  including  the  aorta,  the 
innominate,  part  of  the  right  subclavian,  the  common,  external,  and  greater  parts  of  the  internal 
carotids,  the  common  and  internal  iliacs,  and  the  pulmonary  arteries,  are  all  modified  jjortions 
either  of  the  primitive  aortai  or  of  the  aortic  arches.  The  developmental  changes,  which  result 
in  the  formation  of  the  -^-essels  named,  are  described  in  the  preceding  chapter,  and  the  morphology 
of  these  vessels  is  ob^dously  the  same  as  that  of  the  trunks  from  which  they  are  derived. 

It  will  be  suflicient,  therefore,  to  jjoint  out  that  the  primitive  aort*  are  to  be  regarded 
as  the  greatly  enlarged  pre-central  or  pre-A'ertebral  longitudinal  anastomoses  between  the 
successive  segmental  arteries  of  each  side ;  obviously,  therefore,  each  primitive  aorta,  like 
the  rest  of  the  longitudinal  anastomoses,  consists  chiefly  of  intersegmental  elements.  The  origins 
of  the  segmental  vessels  only  enter  into  its  formation  in  so  far  as  they  connect  the  inter- 
segmental vessels  together,  and  so  comjjlete  the  longitudinal  anastomoses. 

The  first  cephalic  aortic  arches  and  the  primary  caudal  arches  are  simply  j)ortions  of  the 
primitive  aortce.  The  other  aortic  arches  have  possibly  a  different  morphological  significance, 
l)Ut  their  exact  nature  is  not  definitely  settled. 

The  second,  third,  fourth,  and  fifth  cephalic  aortic  arches  of  each  side  are  developed  in  the  un- 
divided mesoderm  of  the  head  region  behind  the  first  arch.  They  sjning  from  the  anterior  part  of 
the  primitive  aorta  which,  after  the  head  fold  is  formed,  lies  on  the  ventral  asj)ect  of  the  fore-gut, 
and  they  extend  at  the  side  of  the  pliarjmgeal  part  of  tlie  fore-gut  to  the  dorsal  aorta.  Thus  in 
some  respects  they  resemble  segmental  vessels.  Behind  the  umbilicus  some  of  the  segmental 
splanchnic  arteries  jjass  from  the  dorsal  to  tlie  ventral  aorta  in  the  splanchnic  mesoderm  on  the 
wall  of  the  alimentary  canal.  In  addition  to  the  vessels  already  mentioned,  there  ai'e  given  off 
from  the  ventral  aortic  and  the  aortic  arches  a  series  of  branches  wliich  sui^jjly  ventral  and  lateral 
diverticula  from  the  alimentary  canal ;  these  are  represented  in  the  adult  by  the  suj)erior 
tliyroid,  the  thyioidca  ima,  and  the  terminal  branches  of  the  hypogastric  arteries. 

"  Iliac  Arteries  and  their  Branches. — The  common  iliac  arteries  are  undoubtedly  formed 
from  the  primitive  aortic  longitudinal  vessels ;  they  are  simply  those  portions  of  the  right 
and  left  primitive  aortte  respectively  whicli  lie  immediately  beyond  or  caudal  to  the  per- 
manent descending  aorta.  The  direct  continuation  of  each  is  the  primary  caudal  arch, 
which  forms  the  origin  of  the  .superior  A'esical  artery,  and  is  prolonged  as  the  hypogastric 
artery ;  these  continuous  channels  are  for  the  most  part  made  up  of  intersegmental  vessels. 
So  also  are  the  permanent  vessels  into  which  they  are  transformed.  Reference  has  already  been 
made  to  the  fact  that  the  primary  caudal  arch  almost  entirely  disappears,  and  that  a  secondary 
caudal  arch  is  developed  in  lieu  of  it  (j).  928)- 

The  internal  iliac  arteries  arc  almost  entirely  formed  from  the  secondary  caudal  arches.     The 


MOKPHOLOGY  OF  THE  VEINS.  943 

primary  caudal  arch,  beyond  doubt,  is  nut  a  .segiueutal  vessel ;  the  secondary  arch  may  be,  but 
this  is  still  unproved.  The  branches  of  the  internal  iliac  artery  which  rejjresent  oft'sets  of  the 
"  caudal  arch '"'  portion  of  the  primitive  aortae  are  arranged  in  two  groups — (1)  a  visceral  set 
which  supplies  the  walls  of  the  hind -gut  and  the  genital  organs,  and  (2)  a  parietal  set  which  is 
distributed  to  the  body  wall  and  to  the  hind-limbs.  The  branches  distributed  to  the  gut  prob- 
ably represent  the  segmental  splanchnic  vessels  given  off  from  the  dorsal  longitudinal  vessels ; 
those  to  the  genital  organs  appear  to  correspond  with  the  intermediate  visceral  branches,  for  they 
are  distributed  to  organs  derived  from  the  intermediate  cell  mass. 

The  jDarietal  set  are  to  be  regarded  as  modified  somatic  segmental  branches  of  the  dorsal 
longitudinal  trunks.  The  lateral  sacral  arteries  which  belong  to  tliis  group  represent,  in  the 
greater  parts  of  their  extent  at  least,  the  jire-costal  anastomoses. 

The  Limb  Aktekies. 

In  all  probability  the  vessels  of  both  the  anterior  and  the  posterior  extremities  are  derived 
from  several  somatic  segmental  arteries,  the  majority  of  which,  however,  in  the  course  of  phylo- 
genetic  development,  have  atrophied.  The  upper  limb  is  supplied  in  man  by  the  lateral  offset 
from  the  ventral  branch  of  the  seventh  somatic  segmental  artery.  It  passes  out  into  the 
extremity  behind  the  shoulder  girdle,  courses  through  the  upj^er  arm,  enters  the  antecubital 
fossa,  and  is  continued  through  the  forearm,  in  the  early  stages,  as  the  anterior  interosseous 
artery,  to  the  deep  part  of  the  palm,  where  it  terminates  in  the  deep  palmar  arch.  At  a  later 
period  a  median  artery  is  given  off  from  the  jjarent  stem,  and  it  terminates  in  a  superficial 
palmar  arch ;  still  later  the  radial  and  ulnar  branches  are  given  oft".  The  latter  grow 
raj)idly,  soon  exceeding  in  size  the  parent  stem,  and  they  terminate  in  the  superficial  and 
deep  palmar  arches.  The  interosseous  and  median  arteries  decrease,  and  generally  lose  their 
direct  connexions  with  the  palmar  arches.  The  posterior  interosseous  artery  is  also  a 
secondary  branch  from  the  parent  stem,  and  the  digital  arteries  are  offsets  from  the  jDalmar 
arterial  arches. 

The  chief  arteries  of  the  lower  extremities  spring  directly  from  the  caudal  arches,  and  may  be 
looked  iqion  as  being  essentially  segmental ;  whether  they  represent  the  whole  or  only  parts  of 
typical  somatic  segmental  arteries,  however,  is  not  clear. 

The  arteries  of  the  hind-limbs  certainly  show  no  very  obvious  indications  of  division  into 
dorsal  and  ventral  branches,  though  such  indications  are  not  entirely  wanting.  In  their  com- 
parative absence  it  is  sup^josed  that  the  dorsal  branches  have  been  either  suppressed  or  incor- 
porated with  the  common  stems ;  that  similarly  the  ventral  branches  and  their  lateral  offsets 
are  indistinguishably  fused,  and  that  probably  both  are  represented  in  a  limb  artery. 

The  original  stem  vessel  of  the  lower  limb  is  the  sciatic  artery,  which  is  continued  down- 
wards behind  the  pelvic  girdle  into  the  poijliteal  and  peroneal  arteries,  and  so  to  the  plantar 
arch.  Subsequently  the  external  iliac  artery  is  given  off  from  the  caudal  arch  above  the  origin 
of  the  sciatic,  and,  passing  into  the  limb  in  front  of  the  jjelvic  girdle,  it  becomes  the  femoral 
artery.  This  vessel  ultimately  unites  with  the  upper  part  of  the  popliteal  artery,  and  after  this 
communication  is  established  the  lower  j)art  of  the  sciatic  ati'ophies  and  loses  its  connexion 
with  the  popliteal,  which  henceforth  apjjears  to  be  the  direct  continuation  of  the  femoral  trunk  ; 
therefore,  whilst  the  main  artery  of  the  ujDj^er  limb  is  formed  by  the  prolongation  of  the  lateral 
branch  of  one  segmental  artery,  the  corresponding  vessel  of  the  lower  extremity  is  developed 
from  representatives  of  two  somatic  segmental  arteries,  the  external  iliac  and  femoral  trunks 
Ijeing  the  representatives  of  one,  whilst  the  popliteal  and  its  continuation,  the  peroneal,  are 
pai-ts  of  another. 

The  first  main  artery  of  the  leg  is  the  peroneal,  which  is  continued  into  the  plantar  arch  ; 
after  a  time,  however,  the  posterior  and  anterior  tibial  branches  are  given  oft'  from  the  stem, 
over  which,  as  a  rule,  they  soon  jj^ej^onderate  in  size,  and  they  terminate  in  the  jslantar  arch, 
whilst  the  parent  trunk  diminishes  and  loses  its  direct  connexion  with  the  arch. 

The  peroneal  artery  corresponds  in  position  and  develojiment  with  the  interosseous  trunk 
and  the  anterior  interosseous  artery  in  the  forearm.  The  posterior  tibial  apparently  corre- 
sponds with  the  median  artery ;  it  develops  in  a  similar  way,  and  has  similar  relations  to 
homologous  nerves,  the  posterior  tibial  nerve  representing  the  combined  median  and  ulnar 
nerves  of  the  upper  extremity. 

The  anterior  tibial  artery  represents  the  posterior  interosseous,  whilst  the  radial  and  ulnar 
arteries  of  the  upper  extremity  are  not  represented  in  the  lower  limb. 

MORPHOLOGY   OF   THE   VEINS. 

^Two  dorsal  longitudinal  vessels,  one  on  each  side,  connect  the  successive  segmental  veins 
together.  They  do  not,  however,  in  any  j^art  of  their  course,  fuse  together  to  form  a  single 
vessel  comparable  to  the  descending  aorta. 

Of  these  dorsal  longitudinal  vessels,  that  on  the  right  side  greatly  enlarges,  and  from  it  the 
main  stem  vessels  which  return  blood  from  the  body  walls,  the  head  and  neck,  and  the  limbs,  are 
almost  entirely  formed.  The  left  dorsal  longitudinal  vessel  remains  relatively  small — in  parts, 
indeed,  it  altogether  disappears — and  the  blood  conveyed  to  it  by  the  corresponding  segmental 
veins  is  transmitted  across  the  middle  line  to  the  chief  functional  stem  by  later  develoj)ed  and 
superadded  transverse  communicating  channels,  which  are  formed  between  the  more  primitive 
longitudinal  anastomoses. 


944  THE  VASCULAE  SYSTEM. 

The  ijrimitive  dorsal  longitudinal  anastomosing  channels  include  on  each  side  (1)  the  primi- 
tive jugular  vein,  (2)  the  primitive  cardinal  vein,  and  (3)  the  duct  of  Cuvier ;  the  last-named 
vessel,  however,  is  not  so  much  a  longitudinal  anastomosis  as  a  communicating  channel  between 
the  longitudinal  anastomoses  and  the  heart,  for  it  is  formed  by  the  junction  of  the  primitive 
jugidar  and  cardinal  veins,  and  opens  into  the  sinus  venosus  of  the  primitive  heart. 

From  these  vessels,  and  from  the  transverse  communications  which  are  established  between 
the  primitive  jugular  and  cardinal  veins  of  opposite  sides,  the  chief  veins  of  the  head  and  neck 
and  the  body  are  formed  ;  there  are  in  addition,  however,  three  later-formed  vessels  from  which 
some,  or  portions  of  some,  of  the  main  stem  vessels  of  the  body  are  evolved.  These  later-formed 
vessels  are  the  two  internal  jugular  veins,i  and  the  upper  part  of  the  inferior  vena  cava,  whilst 
from  the  latter  of  these  portions  of  the  renal  veins,  the  suprarenal  veins  and  the  spermatic 
or  ovarian  veins  are  possibly  developed  as  offsets ;  moreover,  it  must  not  be  forgotten  that  the 
veins  of  the  extremities  are,  like  the  extremities  themselves,  secondary  structures,  and  that  they 
are  developed  at  a  later  period  than  the  veins  of  the  trunk,  with  which,  however,  they  ultimately 
communicate. 

In  the  light  of  these  facts  the  morphology  of  the  chief  veins  of  the  trunk  and  limbs  may 
now  be  considered. 

The  external  jugular  vein  is  obviously  a  portion  of  an  intersegmental  anastomosis,  for  it  is  part 
of  the  primitive  jugular  vein,  which  originally  extended  from  the  internal  occipital  protuberance 
to  the  post-condyloid  foramen,  and  thence  to  the  duct  of  Cuvier.  During  the  course  of  develop- 
ment the  intracranial  part  of  the  primitive  jugular,  on  each  side,  is  converted  into  the  horizontal 
portion  of  the  lateral  sinus  and  the  occasionally  persistent  squamo-petrosal  sinus ;  outside  the 
cranium  the  trunk  of  the  temporo-maxillary  vein,  the  whole  of  the  external  jugular  vein,  and 
that  portion  of  the  subclavian  vein  which  intervenes  between  the  external  and  internal  jugular 
veins,  are  formed  from  the  primitive  jugular.  On  the  right  side  the  right  innominate  vein 
and  the  upper  part  of  the  superior  vena  cava  are  also  formed  from  the  primitive  jugular  vein, 
whilst  on  the  left  side  the  lower  portion  of  the  vessel  becomes  the  upper  part  of  the  left  superior 
intercostal  vein.^ 

After  the  formation  of  the  limbs  the  primitive  jugular  receives  the  pre-axial  and  post-axial 
veins  of  the  fore-limb  of  the  same  side,  which  pass  respectively  along  the  radial  and  ulnar 
borders  of  the  limb ;  both  join  the  primitive  jugular  vein,  the  former  above  and  the  latter 
below  the  clavicle.^  Subsequently,  however,  the  pre-axial  vein  of  the  fore-limb  loses  its  connexion 
with  the  primitive  jugular  vein,  and  opens  below  the  clavicle  into  the  post-axial  vein,  and  the 
upper  part  of  that  vessel  becomes  the  outer  part  of  the  subclavian  vein,  i.e.  that  portion  of  the  sub- 
clavian vein  which  extends  from  the  outer  border  of  the  first  rib  to  the  entrance  of  the  external 
jugular  vein,  the  remainder  of  the  subclavian  being  formed  by  the  portion  of  the  primitive 
jugular  vein  which  intervenes  between  the  entrance  of  the  pre-axial  vein  and  the  junction  with 
the  internal  jugular  vein. 

The  internal  jugular  vein  is  a  newly  formed  anastomosing  vessel  which  commences  from  the 
primitive  jugular  vein  at  the  root  of  the  neck  and  grows  upwards  to  the  base  of  the  skull, 
where  it  passes  through  the  jugular  foramen,  and  ascends  along  the  inner  surface  of  the  mastoid 
portion  of  the  temporal  bone  to  join  the  lateral  sinus,  of  which  it  becomes  the  sigmoid  portion. 
It  probably  represents  a  dorsal  sj^lanchnic  intersegmental  venous  anastomosis.^ 

The  innominate  vein  of  the  left  side  is  an  enlarged  transverse  anastomosis  between  the  two 
primitive  jugular  veins,  and  the  corresponding  vessel  on  the  right  side  is  the  portion  of  the 
right  primitive  jugular  vein  which  lies  between  the  origin  of  the  right  internal  jugular  vein  and 
the  transverse  anastomosis  between  the  two  primitive  jugular  veins. 

The  superior  vena  cava  is  also  formed  from  the  primitive  longitudinal  anastomosis  on  the 
right  side ;  the  upper  portion,  which  lies  above  the  entrance  of  the  azygos  vein,  being  the  lower 
part  of  the  right  primitive  jugular  vein,  and  the  lower  portion,  which  is  enclosed  within  the  peri- 
cardium, is  the  persistent  right  duct  of  Cuvier. 

The  only  other  vein  formed  from  the  jugular  jDortion  of  the  dorsal  longitudinal  anastomosis 
is  the  upper  part  of  the  left  superior  intercostal  vein,  which  represents  the  part  of  the  left 
primitive  jugular  vein  lying  below  the  transverse  anastomosis  which  becomes  the  left  innomi- 
nate vein  ;  occasionally  tliis  part  of  the  left  primitive  jugular  vein  becomes  enlarged,  and  forms 
a  vertical  left  innominate  vein  which  terminates  in  a  left  superior  vena  cava,  the  latter  being 
formed  from  the  left  duct  of  Cuvier.  This  arrangement  is  the  regular  and  normal  condition  in 
many  mammals. 

The  internal  iliac  veins,  the  right  common  iliac  vein,  the  lower  part  of  the  inferior  vena 
cava,  the  vena  azygos  major,  and  the  vertical  portions  of  the  ujjper  and  lower  left  azygos  veins,, 
and  part  of  the  left  superior  intercostal  vein,  are  all  2jarts  of  the  primitive  cardinal  veins.  They 
represent,  therefore,  portions  of  the  dorsal  longitudinal  intersegmental  anastomoses. 

The  internal  iliac  veins  are  the  persistent  lower  sections  of  the  cardinal  veins,  and  their 
visceral  and  parietal  tributaries  probaT^ly  rej^resent  more  or  less  modified  splanchnic  and  somatic 
.segmental  veins. 

The  left  common  iliac  vein  may,  in  the  lower  part  of  its  extent,  represent  the  part  of  the  left 
cardinal  vein  immediately  above  the  junction  of  the  pre-axial  hind-limb  vein  with  the  latter 
vessel,  but  the  greater  part  of  it  is  an  enlarged  transverse  anastomosis  between  the  cardinal  veins 
at  the  level  of  the  pelvic  Ijrim.     The  right  common  iliac  vein,  on  the  other  hand,  is  the  portion 

1  See  note  on  p.  937.  "'^  Ibid- 

3  If  the  observations  recorded  on  \>.  937  are  correct,  tlien  the  external  jugular  vein  is-  not  the  priraitiva 
jugular  vein  but  a  newly-ibrmed  vessel  into  which  the  pre-axial  vein  opens. 


MOEPHOLOGY  OF  THE  VEINS.  945 

of  tlie  right  cardinal  vein  which  lies  between  the  entrance  of  the  limb  vein  and  the  transverse 
anastomosis  which  becomes  the  left  common  iliac  vein.  The  inferior  vena  cava,  from  its  com- 
mencement to  the  entrance  of  the  renal  veins,  is  a  jjortiou  of  the  right  cardinal  vein,  and  the 
right  lumbar  veins  whicli  terminate  in  it  are  the  somatic  segmental  veins  of  the  right  side  of  the 
lumbar  region  ;  whilst  the  left  lumbar  tributaries  are  the  left  lumbar  segmental  veins,  which  have 
been  transmitted  across  the  middle  line  by  transverse  anastomosing  channels  which  connected 
the  lumbar  sections  of  the  cardinal  veins  together. 

The  upper  part  of  the  inferior  vena  cava  is  a  new  anastomosing  channel  formed  between  the 
upper  end  of  the  right  hepatic  vein  and  the  right  cardinal  vein.  This  section  of  the  inferior 
vena  cava  grows  do\\'nwards  from  the  right  hepatic  vein. 

The  right  and  left  renal  veins  originally  terminated  in  the  corresponding  cardinal  veins, 
and  are  therefore  pi-obably  intermediate  visceral  segmental  veins,  but  that  part  of  the  left  renal 
vein  which  crosses  the  middle  line  is  either  an  enlarged  transverse  anastomosis  between  the 
cardinal  veins,  or  an  outgrowth  from  the  lower  end  of  the  upper  part  of  the  inferior  vena  cava  ; 
api^areutly  the  latter,  for  as  the  ujjper  section  of  the  inferior  vena  cava  grows  downwards  from 
the  right  hepatic  vein  it  divides  into  two  branches,  right  and  left,  eacli  of  which  joins  the 
corresj^onding  cardinal  vein  close  to  the  termination  of  the  renal  vein.  Before  it  fuses  with  the 
cardinal  vein  of  its  own  side,  each  of  the  terminal  branches  of  the  upper  section  of  the  inferior 
vena  cava  gives  oft'  branches  which  ultimately  become  the  suprarenal  and  spermatic  veins ;  there 
can  be  no  doubt,  however,  that  both  the  suprarenal  and  spermatic  veins  are  intermediate  visceral 
segmental  veins,  and  in  all  probability  they  originally  terminated  in  the  corresponding  cardinal 
veins,  their  development  from  the  upper  section  of  the  inferior  vena  cava  Ijeing  due  to  the 
jjroduction  in  the  embryo  of  a  condition  which  has  been  secondarily  acquired  during  the 
development  of  the  species.  If  this  is  the  case,  it  is  extremely  probable  that  the  left  sjjermatic 
vein  rejjresents  not  only  an  elongated  intermediate  visceral  segmental  vein,  but  also  a  portion  of 
the  left  cardinal  into  which  it  ojjened. 

The  vena  azygos  major  is  the  jjersistent  upper  portion  of  the  left  cardinal  vein,  a  fact 
which  is  emphasised  by  its  frequent  connexion  with  the  inferior  vena  cava  at  the  level  of  the 
right  renal  vein.  The  right  intercostal  veins  which  open  into  the  vena  azygos  major  are  somatic 
segmental  veins,  the  ujjper  three  or  four  of  which  liave  united  together  by  pre-costal  anastomoses 
10  form  a  right  superior  intercostal  vein. 

The  vertical  portions  of  the  left  az3gos  veins  are  remnants  of  the  left  primitive  cardinal 
vein,  and  their  transverse  portions  are  enlarged  transverse  anastomoses  comparable  to  the  left 
innominate  and  left  common  iliac  veins.  The  left,  like  the  right  intercostal  veins,  are  segmental 
somatic  veins  ;  Ijut  whilst  the  right  sujjerior  intercostal  vein  is  formed  by  pre-costal  anastomoses 
between  the  upper  three  or  four  dorsal  somatic  segmental  veins,  the  left  superior  intercostal  vein 
(Fig.  674)  represents  the  upper  part  of  the  left  cardinal  vein  and  the  part  of  the  left  primitive 
jugular  vein  below  the  transverse  anastomosis,  which  becomes  the  left  innominate  vein ; 
moreover,  the  left  superior  intercostal  vein  frequently  retains  in  the  adult  a  connexion  with  the 
oblique  vein  of  Marshall,  which  represents  the  left  duct  of  Cuvier,  by  means  of  which  both  the 
left  i^rimitive  jugular  and  the  left  cardinal  veins  originally  communicated  witli  the  heart. 

Visceral  Veins. — The  portal  vein  represents  portions  of  the  ventral  longitudinal  anastomosing 
vessels,  being  derived  from  the  vitelline  veins. 

The  pyloric  vein  is  a  sj^lanchnic  intersegmental  ventral  longitudinal  anastomosing  vein.  The 
coronary  vein  is  partly  a  ventral  and  partly  a  dorsal  splanchnic  intersegmental  longitudinal 
anastomosis,  and  the  sujierior  and  inferior  mesenteric  veins  are  dorsal  splanchnic  longitudinal 
intersegmental  venous  anastomoses,  the  splenic  vein  being  merely  a  tributary  from  a  lymphoid 
organ  develojjed  in  the  dorsal  mesentery. 

The  facial  vein  is  a  combination  of  somatic  and  splanchnic  veins  of  several  segments,  and  the 
internal  maxillary  vein  is  probably  of  similar  nature.  The  thyroid  and  bronchial  veins  return 
blood  from  organs  developed  from  diverticula  from  the  walls  of  the  alimentary  canal ;  they  are, 
therefore,  more  or  less  modified  segmental  splanchnic  veins  ;  so  also  apparently  are  the  vesical  and 
the  middle  and  inferior  htemorrhoidal  veins. 

The  cardiac  veins  are  simply  "  vasa  vasorum,"  and  they  belong  therefore  to  the  splanchnic 
group  of  vessels,  but  it  is  imjjossible  to  say  whether  they  are  segmental  or  intersegmental.  The 
coronary  sinus  into  which  they  open  is  a  jiortion  of  the  sinus  venosus  of  the  heart,  and  therefore 
of  an  originally  intersegmental  vessel. 

The  hepatic  and  pulmonary  veins  are  new  vessels  which  return  blood  to  the  heart  after  the 
liver  and  lungs  ha\e  been  interposed  in  the  vascular  system. 

It  is  noteworthy  that  some  jjarts  of  the  splanchnic  venous  system,  i.e.  the  portal  vein  and  the 
coronary  sinus,  are  portions  of  the  most  primitive  vascular  system,  and  that  others,  i.e.  the 
thyroid,  bronchial,  mesenteric,  vesical,  and  hemorrhoidal  veins,  appear  to  belong  to  a  somewhat 
secondary  group  of  splanchnic  veins  of  combined  segmental  and  intersegmental  character  ;  more- 
over, some  of  the  secondary  group  of  A'eins  open  into  the  primary  splanchnic  veins,  e.g.  the 
superior  and  inferior  mesenteric  into  the  portal  vein  ;  some  open  into  the  dorsal  longitudinal 
anastomosing  veins,  e.g.  the  vesical  and  hgemorrhoidal  veins  open  into  the  cardinal  veins,  which 
are  intersegmental  anastomoses ;  others  again  open  into  an  entirely  new  vein,  viz.  the  internal 
jugular,^  which  is  developed  along  the  dorso-lateral  border  of  the  fore-gut,  and  which  is  therefore 
comparable  to  the  dorsal  venous  splanchnic  intersegmental  anastomosis,  which  in  the  abdominal 
region  becomes  converted,  after  fusion  of  the  vessels  of  opposite  sides,  into  the  greater  parts  of  the 
superior  and  inferior  mesenteric  veins  ;  the  latter,  however,  open  into  a  ventral  longitudinal 

'  See  note  on  p.  937. 

64 


946  THE  VASCULAE  SYSTEM. 

anastomosing  vessel,  tlie  portal  vein,  whilst  the  former  joins  a  dorsal  longitudinal  anastomosing 
trunk. 

Veins  of  the  Limbs. — The  veins  of  the  limbs,  like  the  arteries,  were  j^robably  at  one  time 
segmental  in  character,  but  we  have  no  absolute  proof  that  this  was  tlie  case.  Looked  at  from 
an  embryological  standpoint,  the  most  primitive  limb  veins  are  a  superficial  distal  arch  and 
a  post-axial  trunk  vein  in  each  extremity  ;  at  a  later  period  digital  veins  aje  connected  with  the 
distal  arch,  and  a  pre-axial  trunk  is  formed.  In  the  upper  extremity  the  distal  arch  and  its 
tribiitaries  remain  as  the  dorsal  venous  arch  and  the  digital  veins,  and  the  post-axial  vein  becomes 
the  posterior  idnar,  the  basalic  and  axillary  veins,  and  also  that  jiart  of  the  subclavian  vein  which 
lies  external  to  the  termination  of  the  external  jugular  vein,  the  remainder  of  the  subclavian 
vein  being  formed  from  the  primitive  jugular  vein  itself  The  pre-axial  vein  of  the  upper 
extremity  is  represented  in  the  adult  by  the  radial  and  cej^halic  veins  ;  the  latter  vessel  originally 
terminated  in  the  external  jugular  vein  above  the  clavicle,  the  union  with  the  axillary  portion  of 
the  post-axial  vessel  being  a  secondary  condition  ;  tlie  j^rimary  condition  is,  however,  frequently 
retained  in  man,  and  is  constant  in  many  monkeys.  The  anastomosis  between  the  j^re-axial 
and  post -axial  veins  in  the  region  of  the  elbow,  and  the  connexion  of  the  anastomosing 
channels,  is  lirought  about  liy  newly-formed  vessels  of  secondary  character. 

The  distal  arch  in  the  lower  extremity  and  the  tributaries  connected  with  it  remain  in  the 
adult  as  the  dorsal  venous  arch  of  the  foot  and  the  digital  A-eins.  The  post-axial  vein  becomes 
the  external  saphenous  A^ein,  which  was  originally  continued  upwards  as  the  sciatic  vein  to  the 
internal  iliac  portion  of  the  cardinal  vein  ;  its  connexion  with  the  popliteal  vein,  and  its  more 
occasional  connexion  with  the  internal  saphenous  vein,  being  brought  about  by  the  formation  ot 
secondary  anastomoses. 

The  j^re-axial  vein  of  the  lower  limb  becomes  the  long  saphenous  A^ein,  Avhich  is  continued 
ujjwards  to  the  cardinal  portion  of  the  left  common  iliac  vein  as  the  upper  part  of  the  femoral 
and  the  external  iliac  veins. 

The  veuEe  comites  of  the  arteries  in  both  the  upper  and  lower  extremities  are  secondarily 
developed  vessels  which  become  connected  with  the  upper  portions  of  the  pre-axial  venous 
trunks. 


ABNORMALITIES  OR  VARIATIONS  OF  THE  VASCULAR 

SYSTEM. 

Abnormalities  are  of  special  interest  to  the  anatomist  because  ot  their  morphological  signifi- 
cance, and  the  vascular  system  is,  perhaps  more  than  any  other,  rich  in  such  abnormalities,  many 
of  which  are  of  great  practical  imiaortance. 

With  the  exception  of  those  irregularities  which  are  directly  due  to  the  effect  of  morbid 
conditions  and  external  influences,  all  abnormalities  are  the  result  of  modifications  of  normal 
developmental  processes.  The  exceptions  referred  to  are,  however,  very  numerous ;  thus  disease 
and  external  influences  may  lead  to  the  obliteration  of  vessels,  a  condition  which  is  invariably 
associated  with  the  enlargement  of  collateral  vessels,  and  it  Avill  be  obvious  that  abnormalities 
so  produced  may  occur  in  almost  any  situation. 

Abnormalities  which  are  determined  by,  or  are  dej^endent  upon,  modifications  of  the  usual 
developmental  processes  are  of  greater  interest.  In  the  human  subject  they  are  generally 
due  either  to  the  retention  of  conditions  which  normally  are  only  transitory,  or  to  the  acquire- 
ment of  conditions  which,  though  not  as  a  rule  present  at  any  time  in  man,  occur  normally  in 
other  animals. 

There  are  in  addition  otlier  variations  from  the  normal,  such  as  the  division  of  the  axillary 
artery  into  radial  and  ulnar  branches ;  the  higher  or  lower  division  of  the  brachial  artery ;  the 
formation  of  "  vasa  aberrantia,"  e.g.  of  long  slender  vessels  connecting  the  axillary  or  brachial-  to 
the  radial,  ulnar,  or  interosseous  arteries ;  the  altered  position  of  certain  vessels,  as  e.g.  the  trans- 
ference of  the  subclavian  artery  to  the  front  of  the  scalenus  anticus,  or  of  the  ulnar  artery  to  the 
front  of  the  superficial  flexor  muscles ;  all  of  which,  though  undoubtedly  due  to  alterations  of 
ordinary  developmental  proce.sses,  still  do  not  rej^resent  conditions  met  with,  either  temporarily 
or  permanently,  in  man  or  in  other  animals.  Their  occurrence  cannot  at  present  be  adequately 
explained,  and  their  retention  is  entirely  dependent  upon  their  utility. 

To  the  first  and  last  of  these  different  groups  of  abnormalities  it  is  not  necessary  to  refer 
furth(!r,  whilst  with  regard  to  the  rest  it  will  be  suflicient  to  indicate  those  of  greatest 
importance.  Tliey  can  only,  however,  be  fully  understood  and  explained  on  the  basis  of  a 
comprehen.-^ivc  knowledge  of  the  development  and  inorphology  of  the  vascular  system,  to  the 
chapters  on  which  the  reader  is  referred. 

ABNORMALITIES  OF  THE  HEART. 

The  heart  may  be  transposed  from  the  left  to  the  right  side  of  the  body,  a  condition  which 
is  usually  associated  with  general  transposition  of  the  viscera,  and  with  the  presence  of  a  right 
instead  of  a  left  aortic  arch. 

The  external  form  of  the  heart  does  not  as  a  rule  vary  much,  but  occasionally  the  apex  is 
slightly  bifid,  a  character  it  normally  possesses  at  an  early  stage  of  its  development,  and  which  is 


ABNOKMALITIES  OF  ARTERIES.  947 

retained  in  the  adult  in  many  cetaceans  and  sirenians.  The  internal  conformation  of  the  heart 
deviates  from  the  normal  much  more  frequently  ;  more  particularly  is  this  the  case  with  regard 
to  the  septa  which  separate  the  right  from  the  left  chambers.  The  interauricular  septum  may 
be  entirely  absent,  as  in  fishes ;  it  may  be  fenestrated  and  incomplete,  as  in  some  amphibians  ;  or 
the  foramen  ovale  may  remain  patent,  as  in  amphibians  and  rejitiles. 

The  interventricular  septum  may  be  absent,  as  in  fishes  and  amphibians,  or  incomplete,  as  in 
reptiles  ;  when  incomplete,  it  is  usually  the  "  pars  membranacea  septi "  whicli  is  deficient. 

ABNORMALITIES  OF  ARTERIES. 

The  pulmonary  artery  and  the  aorta  may  arise  by  a  common  stem,  as  in  fishes  and  some 
amphil)ians,  and  the  common  stem  may  spring  either  from  the  right  or  the  left  ventricle,  or  from 
both.  In  these  cases  the  aortic  bulb  has  remained  undivided,  and  the  normal  jjosition  of  the 
interventricular  septum  in  relation  to  the  lower  orifice  of  the  aortic  bulb  has  been  altered. 

Again,  owing  to  malposition  of  the  aortic  sejituni,  the  pulmonary  artery  may  spring  from  the 
left  ventricle  and  the  aorta  from  the  right  ventricle.  In  some  cases  the  root  of  the  jiulmonary 
artery  is  obliterated,  and  the  blood  passes  to  the  lungs  along  the  patent  ductus  arteriosus. 

Occasionally  the  arch  of  the  aorta  is  on  the  right  side  instead  of  the  left,  a  condition  whicli  is 
normal  in  birds.  More  rarely  there  are  two  permanent  aortic  arches,  right  and  left,  as  in  reptiles ; 
tlie  oesoi^hagus  and  trachea  in  these  cases  are  enclosed  in  a  vascular  collar,  the  two  arches  unite 
dorsally,  and  the  beginning  of  the  descending  aorta  is  double.  Quite  independent  of  this  condi- 
tion, however,  the  two  primitive  dorsal  aortre  sometimes  fail,  either  altogether  or  partially,  to 
unite  together,  and  the  descending  aorta  is  accordingly  represented,  to  a  corresponding  extent,  bj^ 
two  tubes.  A  more  common,  though  still  rare,  form  of  double  aorta  is  that  due  to  the  persistence, 
in  whole  or  in  part,  of  the  septum  formed  by  the  fused  walls  of  the  isrimitive  dorsal  aortae 
from  which  the  descending  aorta  is  developed. 

The  length  of  the  descending  aorta  is  determined  largely  by  the  extent  to  which  fusion  of  the 
two  primitive  aortre  takes  place.  Accordingly,  when  this  deviates  from  the  normal,  the  termi- 
nation of  the  descending  aorta  is  at  a  correspondingly  higher  or  lower  level  than  usual,  and 
resulting  from  this  the  lengths  of  the  common  iliac  arteries  are  almost  invariably  proportionately 
modified.  The  bifurcation  ^  of  the  aorta  may  be  as  low  as  the  fifth  lumbar  vertebra,  less 
frequently  it  is  higher  than  usual ;  it  is  rare,  however,  to  find  it  higher  than  the  third  or  second 
lumbar  vertebra. 

The  aorta,  instead  of  bifurcating  into  two  common  iliac  arteries,  may  terminate  in  a  common 
iliac  artery  on  one  side  and  an  internal  iliac  artery  on  the  opposite  side,  the  external  iliac  artery 
on  the  irregular  side  arising,  at  a  higher  level,  as  a  branch  of  the  aortic  stem.  This  arrangement 
approaches  the  condition  met  with  in  carnivores  and  many  other  mammals,  in  which  the  aorta 
bifurcates  into  two  internal  iliac  arteries,  the  external  iliacs  arising  from  the  aorta  at  a  higher 
level  as  lateral  branches  ;  it  is  due  either  to  a  more  extensive  fusion  than  usual  of  the  primitive 
dorsal  aortie,  or  to  the  origin  of  the  external  iliac  arteries  from  the  primitive  dorsal  aortae  being 
at  a  higher  level  than  is  ordinarily  the  case  ;  if  tlie  condition  is  due  to  the  latter  cause,  it  may 
be  that  the  external  iliac  arteries  in  carnivores,  and  the  external  iliac  arteries  which  occasionally 
rise  from  the  aorta  in  man,  are  somatic  segmental  arteries  of  a  higher  segment  than  the  normal 
external  iliac  arteries  of  the  human  subject. 

The  Branches  of  the  Aorta. 

The  coronary  or  cardiac  arteries  may  arise  by  a  single  stem.  Wlien  arising  sejjarately 
both  may  spring  from  the  same  sinus  of  \  alsalva  ;  or  again,  their  interventricular  and  transverse 
branches  may  all  arise  as  distinct  vessels  from  a  single  sinus  of  Valsalva.  This  variability  is  not  so 
remarkable,  seeing  that  the  arteries  in  question  are  merely  enlarged  "  vasa  vasorum  "  raised  to  a 
position  of  special  importance  by  the  development  of  the  heart. 

The  branches  of  the  arch  of  the  aorta  are  sometimes  increased  and  sometimes  decreased  in 
number. 

The  highest  number  recorded  is  six,  viz.,  right  subclavian,  right  vertebral,  right  common 
carotid,  left  common  carotid,  left  vertebral,  and  left  subclavian.  Apparently  this  condition  is  the 
result  of  the  absorption  of  the  innominate  artery  and  of  the  roots  of  the  subclavian  arteries, 
to  points  beyond  the  origins  of  the  vertebrals,  into  the  arch.  By  variations  of  this  process  of 
absorption  other  combinations  may  be  jsroduced  ;  thus,  instead  of  the  roots  of  the  subclavian 
arteries  being  absorbed,  the  right  common  carotid  and  innominate  arteries  may  alone  be  absorbed, 
in  which  case  the  five  following  branches  sj^ring  separately  fx'om  the  arch  of  the  aorta  :  right 
subclavian,  right  external  carotid,  right  internal  carotid,  left  common  carotid,  and  left 
subclavian.  The  trunk  most  commonly  absorbed  is  the  initial  part  of  the  left  subclavian  ;  the 
number  of  branches  then  arising  from  the  arch  of  the  aorta  is  four,  the  additional  vessel 
being  the  left  vertebral,  which  arises  between  the  left  common  carotid  and  the  left  subclavian. 
Occasionally  the  usual  three  branches  from  the  arch  are  increased  to  four  by  the  formation  of  a 
new  vessel,  the  "  thyroidea  iiua."  This  may  be  placed  between  the  innominate  and  left  carotid 
trunks,  in  which  case  it  represents  a  persistent  ventral  visceral  branch  from  the  ventral  root  of  the 
f(jurth  left  aortic  arch  ;  in  other  cases  the  thyroidea  ima  springs  from  the  innominate  artery  and 

^  It  is  to  be  observed  that  tlie  exact  i)oint  of  liifurcation  of  the  aorta,  in  relation  to  the  vertebral 
column,  is  not  entii-ely  determined  bv  the  length  of  the  descending  aorta. 

64  « 


948  THE  VASCULAE  SYSTEM. 

represents  a  ventral  visceral  branch  of  tlie  ventral  root  of  the  fourth  right  arch.  Very  rarely 
the  right  vertebral  artery  arises  separately,  and  forms  a  fourth  branch  of  the  arch  of  the  aorta, 
the  rest  of  the  branches  being  normal.  This  condition  cannot  be  accounted  for  by  any  modifica- 
tion of  the  ordinary  developmental  processes.  It  may  possibly  be  due  to  the  persistence  of  an 
irregular  or  unimportant  anastomosis  between  the  ventral  root  of  an  aortic  arch  and  the  seventh 
somatic  segmental  artery. 

Decrease  in  the  number  of  branches  from  the  arch  of  the  aorta  is  most  frequently  due  to 
fusion  of  the  ventral  roots  of  the  fourth  aortic  arches,  the  result  being  that  a  stem  is  formed 
common  to  the  right  subclavian  and  the  right  and  left  common  carotid  arteries  ;  whilst  the  left 
subclavian,  arising  se2:)arately,  is  the  only  other  branch  which  springs  from  the  arch  of  the  aorta. 

If  the  fusion  of  the  ventral  roots  proceeds  further  and  includes  those  of  the  third  arches,  the 
result  as  regards  the  branches  given  off  from  the  arch  of  tlie  aorta  is  the  same,  viz.  there  is  a 
common  stem  for  the  right  subclavian  and  both  carotids,  and  a  separate  left  subclavian  trunk  ;  but 
the  common  stem  now  gives  off  the  right  subclavian  artery,  and  then  continues  as  a  single  vessel 
for  some  distance  before  it  divides  into  the  two  common  carotids,  of  which  the  left  crosses  in 
front  of  the  trachea.  This  arrangement  is  common  in  many  quadrumana  and  in  some  other 
mammals. 

It  is  only  very  occasionally  when  the  number  of  branches  from  the  arch  of  the  aorta  is 
reduced  to  two,  that  these  consist  of  a  right  subclavian  artery  and  of  a  single  stem  common  to 
the  two  carotids  and  the  left  subclavian  arteries.  In  sucli  cases,  however,  the  right  common 
carotid  crosses  m  front  of  the  trachea,  and  the  variation  is  one  of  practical  importance.  It  does 
not  appear  to  exist  as  a  normal  condition  in  any  mammal.  Probably  it  is  due  to  fusion  of  the 
ventral  roots  of  tlie  fourth  aortic  arches,  with  absorption  of  the  left  fourth  arch  and  the  left  sub- 
clavian into  the  stem  so  formed,  whilst  the  right  subclavian  is  relatively  displaced.  The  two 
common  carotids  may  arise  by  a  common  stem,  and  the  left  subclavian  arise  separately  from 
the  arch  of  the  aorta,  whilst  the  right  subclavian  sj^rings  from  the  descending  aorta.  This 
arrangement  probably  results  from  the  disappearance  of  the  fourth  right  arch  and  the.  fusion  of 
the  ventral  roots  of  the  fourth  arches  of  opposite  sides. 

Sometimes  two  innominate  arteries,  right  and  left,  replace  the  three  usual  branches  of  the 
arch  of  the  aorta.  This  is  the  normal  arrangement  in  bats,  moles,  and  hedgehogs.  It  is 
obviously  the  result  of  the  disapisearance  of  that  portion  of  the  arch  which  intervenes  between 
the  left  carotid  and  left  subclavian  arteries,  and  the  consecpient  fusion  of  these  two  vessels. 

In  a  similar  way  may  be  explained  the  rarer  condition  in  which  the  three  ordinary 
branches  of  the  arch  arise  by  one  single  stem,  which  divides  into  right  and  left  innominate 
arteries.     In  most  ruminants,  in  the  horse  and  in  the  tapir,  this  arrangement  is  constant. 

It  will  be  evident  that  other  combinations  and  modifications  may  be  met  with  in  the  branches 
of  the  arch  of  the  aorta  as  the  result  of  fusions  and  a1)sorption. 

The  bronchial  arteries  obviously  correspond  to  splanchnic  segmental  arteries  and  their 
continuations  to  diverticula  from  the  walls  of  the  gut,  therefore  the  usual  origin  of  tlie 
right  bronchial  artery  from  the  first  right  aortic  intercostal  artery  must  result  from  the 
persistence  of  an  anastomosis  between  a  sj^lanchnic  segmental  arterj'  and  the  first  part  of  a 
somatic  segmental  artery  ;  the  origin  of  the  right  from  the  ujjper  left  bronchial  artery,  which 
sometimes  occurs,  is  due  to  the  fusion  of  the  roots  of  two  sjjlanchnic  segmental  arteries.  The 
occasional  origin  of  a  bronchial  vessel  from  an  internal  mammary  artery  can  only  result  from 
the  persistence  and  enlargement  of  an  anastomosis  between  a  splanchnic  segmental  artery  and 
the  ventral  Ijrancli  of  a  somatic  segmental  artery.  Tlie  origin  of  a  Ijronchial  branch  from  a 
subclavian  artery  may  have  the  same  or  a  different  significance  on  opposite  sides  of  the  liody. 
A  bronchial  artery  arising  from  the  left  subclavian  artery  corresponds  with  the  origin  of  the 
right  Ijronchial  artery  from  the  first  aortic  intercostal  artery ;  it  is  due  to  the  persistence  of  an 
anastomosis  between  a  splanchnic  segmental  artery  and  the  root  of  a  somatic  segmental  artery, 
and  the  origin  of  a  bronchial  artery  from  a  right  subclavian  artery  may  be  due  to  a  similar  cause. 
It  may,  on  the  other  hand,  be  due  to  the  enlargement  of  an  anastomosis  between  a  splanchnic 
branch  of  the  descending  aorta  and  a  siDlanchnic  branch  of  the  fourth  right  aortic  arch.  When, 
as  occasionally  hap])ens,  the  bronchial  artery  arises  from  the  inferior  thyroid,  it  is  due  to  the 
persisti'iicc;  and  enlargement  of  an  anastomosis  between  splanchnic  arteries. 

Intercostal  Arteries. — Variations  of  the  intercostal  arteries  are  not  very  common,  but 
they  are  significant  and  interesting.  Corres])onding  vessels  of  opposite  sides  may  arise  from  a 
common  stem  which  has  been  formed  l)y  the  fusion  of  the  roots  of  two  somatic  segmental  arteries 
after  or  simultaneously  with  the  fusion  of  the  primitive  dorsal  aortte.  The  number  of  intercostal 
arteries  may  be  reduced,  one  artery  supplying  two  or  more  intercostal  spaces  ;  in  these  cases  the 
roots  of  oi-igin  of  some  of  the  somatic  segmental  arteries  in  the  dorsal  region  have  disappeared, 
and  the  precostal  anastomoses  between  their  ventral  branches  have  persisted. 

Occasionally  tin;  numl)er  of  the  aortic  intercostal  arteries  is  increased,  an  additional  artery 
being  given  to  the  second  intercostal  space,  which  is  usually  supplied  by  the  superior  intercostal 
arteiy  ;  this  is  brought  about  by  tlie  pereistence  of  the  root  of  the  tenth  somatic  segmental  artery 
and  the  disappearance  of  tlie  precostal  anastomosis  betwee-n  the  ventral  Ijranchesof  the  ninth  and 
tenth  somatic  segmental  arteries.  Very  rarely  the  first  aortic  intercostal  artery  sends  a  branch 
upwards  between  the  necks  of  the  ribs  and  thc^  transverse  processes  of  the  upper  dorsal  region; 
this  l^ranch  supplies  the  upper  intercostal  sj)aces,  the  superior  intercostal  artery  being  small  or 
absent,  and  it  terminates  by  becoming  the  ])rofunda  cervicis  artery.  It  is  due  to  the  persistence 
of  the  postcostal  anii-stomoses  in  the  uppei-  doi-sal  region,  and  is  a  repetition  of  a  condition  regularly 
present  in  some  caniivore,«. 


ABNORMALITIES  OF  ARTERIES.  949 

There  are  no  very  important  variations  of  the  oesophageal,  pericardial,  and  mediastinal 
arteries. 

Lumbar  Arteries.  —  Variations  of  the  lumbar  arteries  are  very  similar  to  those  of  the 
intercostal  arteries,  and  they  are  due  to  similar  causes.  The  lumbar  arteries  of  opposite  sides 
may  arise  by  common  stems  from  the  back  of  the  aorta  ;  and  the  last  pair  of  lumbar  arteries 
may  arise  in  common  with  the  middle  sacral  artery.  Further,  a  lumbar  artery  may  have  its 
area  of  distribution  increased  to  the  adjacent  segment. 

The  inferior  phrenic  arteries  are  very  variable ;  they  may  arise  by  a  common  trunk  either 
from  the  coeliac  axis  or  from  the  aorta  ;  they  may  arise  sej^arately  either  from  the  aorta  or  from 
the  coeliac  axis,  and  more  commonly  from  the  latter  vessel ;  or  again,  one  may  spring  from  the 
aorta  or  coeliac  axis,  and  the  other  from  the  coronary,  renal,  or  even  from  the  superior  mesenteric 
artery. 

The  middle  sacral  artery  usually  springs  from  the  back  of  the  aorta  above  its  bifurcation  ; 
it  may  be  considerably  above,  or  more  rarely  it  may  spring  directly  from  the  bifurcation.  Not 
infrequently  it  arises  from  the  last  lumbar  artery  or  from  a  stem  common  to  the  two  last 
lumbar  arteries,  and  occasionally  it  arises  from  a  common  or  internal  iliac  artery.  Some- 
times it  apparently  gives  off  the  last  j^air  of  lumbar  arteries,  and  very  occasionally  an  accessory, 
renal,  or  a  hajmorrhoidal  branch  arises  from  it.  The  vessel  is  not  always  present,  it  may  be 
double,  entirely  or  in  part,  and  it  may  bifurcate  at  its  termination. 

The  renal  arteries  frequently  deviate  from  the  normal  arrangement.  The  arteries  of 
opposite  sides  may  sjiring  from  a  common  stem,  or  there  may  be  two  or  more  renal  arteries  on 
one  or  both  sides.  The  accessory  arteries  are  more  common  on  the  left  than  on  the  right  side, 
and  an  accessory  artery  rising  below  the  ordinary  vessel  is  more  common  than  one  rising 
above  it. 

Accessory  renal  arteries  may  be  derived  not  only  from  the  aorta,  but  also  from  the  common 
or  internal  iliac  arteries  ;  they  have  also  been  described  as  arising  from  the  inferior  phrenic, 
spermatic,  lumbar,  or  middle  sacral  arteries,  and  even  from  the  external  iliac  artery.  As  the 
kidney  is  developed  in  the  region  of  the  first  sacral  vertebra,  and  afterwards  ascends  to  its  perma- 
nent position,  it  is  not  surjarising  that  it  occasionally  receives  arteries  from  the  main  stem  of 
more  than  one  of  the  segments  of  the  body  through  which  it  has  passed,  and  it  is  usually  found 
that  the  lower  the  position  of  the  kidney  in  the  abdomen  the  more  likely  it  is  to  receive  its 
arteries  from  the  lower  part  of  the  aorta  or  from  the  common  iliac  arteries.  The  accessory  renal 
arteries  which  spring  from  the  inferior  phrenic,  the  spermatic,  and  lumbar  arteries  can  only  be 
the  result  of  the  persistence  and  enlargement  of  anastomosing  channels  between  the  renal  and 
either  another  intermediate  visceral,  or  a  somatic  artery. 

The  spermatic  or  ovarian  arteries  may  be  double  on  one  or  both  sides  ;  the  arteries  of  oppo- 
site sides  may  spring  from  a  common  trunk,  or  they  may  rise  from  the  renal  or  suprarenal 
arteries.  The  right  artery  may  pass  behind  instead  of  in  front  of  the  inferior  vena  cava.  The 
spermatic  and  ovarian  arteries  arise  from  the  upper  lumbar  portion  of  the  aorta,  because  the 
testicles  and  ovaries  are  developed  in  and  obtain  their  arterial  supply  in  that  region,  and  the 
vessels  are  elongated  as  the  testicles  and  ovaries  descend  to  their  permanent  positions.  The 
occurrence  of  two  spermatic  arteries  on  one  side  is  probably  an  indication  that  the  testicle  was 
developed  in  at  least  two  segments  of  the  body,  and  the  origin  of  a  spermatic  artery  from  a  renal 
or  suprarenal  artery  is  due  to  the  obliteration  of  the  root  of  the  original  vessel  and  the  enlarge- 
ment of  an  anastomosis  between  the  intermediate  visceral  arteries  of  adjacent  segments. 

The  coeliac  axis  may  be  absent,  its  branches  arising  separately  from  the  aorta  or  from  some 
other  source.  Sometimes  it  gives  off  only  two  branches,  usually  the  coronary  and  splenic,  and 
occasionally  it  gives  four  branches,  the  additional  branch  being  either  a  second  coronary  artery 
or  a  separate  gastro -duodenal  artery. 

The  hepatic  artery  may  spring  directly  from  the  aorta  or  from  the  superior  mesenteric 
artery,  and  the  left  hepatic  artery  occasionally  arises  from  the  coronary  artery.  Accessory  hepatic 
arteries  are  not  uncommon,  and  they  originate  either  from  the  coronary,  superior  mesenteric,  renal, 
or  inferior  mesenteric  artery. 

The  coronary  artery  is  occasionally  double ;  it  may  spring  directly  from  the  aorta,  and  it 
may  give  off  the  left  hepatic  or  an  accessory  hepatic  artery. 

The  splenic  artery  may  arise  from  the  middle  colic,  from  the  left  hepatic,  or  from  the 
inferior  mesenteric  artery. 

The  superior  mesenteric  artery  may  be  double,  and  it  may  supply  the  whole  of  the 
alimentary  canal  from  the  second  part  of  the  duodenum  to  the  end  of  the  rectum,  the  inferior 
mesenteric  artery  being  absent.  In  addition  to  its  ordinary  branches  it  may  give  off  a  hepatic, 
a  splenic,  a  pancreatic,  a  gastric,  a  gastro-epiploic  or  a  gastro-duodenal  branch.  Very  rarely 
it  gives  off  an  omphalo-mesenteric  branch,  which  passes  to  the  region  of  the  umbilicus  and 
becomes  connected  with  capillary  vessels  m  the  falciform  ligament  of  the  liver. 
■-  The  inferior  mesenteric  artery  may  give  hepatic,  renal,  or  middle  colic  branches  ;  occasion- 
ally it  is  absent,  being  replaced  by  branches  of  the  superior  mesenteric,  and  sometimes,  as  in 
ruminants  and  some  rodents,  its  left  colic  branch  does  not  anastomose  with  the  middle 
colic  artery. 

All  these  variations  of  the  unpaired  visceral  branches  of  the  abdominal  aorta  are  merely  due 
to  modifications  of  the  usual  processes  by  which  these  vessels  are  developed. 

The  origin  of  the  branches  which  usually  rise  from  the  coeliac  axis,  from  the  trunk  of  the 
aorta  is  the  result  of  the  retention  of  a  greater  number  of  the  splanchnic  segmental  arteries 
than  usual.     A  double  superior  mesenteric  arterv  results  from  the  persistence  of  both  the  right 

64  & 


950  THE  VASCULAE  SYSTEM. 

and  left  splanchnic  vessels  from  whicli  tlie  superior  mesenteric  artery  is  formed,  these  remaining 
separate  instead  of  fusing  together.  All  the  other  variations  are  the  results  of  the  obliteration 
of  the  usual  channels,  combined  with  the  enlargement  of  anastomoses  which  exist  both 
between  the  splanchnic  arteries  of  adjacent  segments  and  tlie  splanchnic  and  intermediate 
visceral  arteries. 

The  Arteries  of  the  Head  and  Neck. 

Innominate  Artery. — From  what  has  abeady  been  said  with  reference  to  the  branches 
of  the  arch  of  the  aorta,  it  will  be  seen  that  the  innominate  artery  may  be  absent.  On  the  other 
hand  there  may  be  two  innominate  arteries,  a  right  and  a  left,  each  ending  in  corresponding 
common  carotid  and  subclavian  trunks,  and  the  two  vessels  may  themselves  arise  by  a  common 
stem. 

The  branches  given  off  by  the  innominate  artery  may  be  increased  in  number,  or  the  innomi- 
nate may  only  vary  from  the  normal  as  regards  length.  As  a  consequence  of  such  modifications 
m  length,  the  origins  of  the  right  common  carotid  and  riglit  subclavian  arteries  may  be  situated 
at  a  higher  or  lower  level  than  usual,  whilst,  in  the'  absence  of  the  innominate  artery,  both  these 
branches  may  arise  directly  from  the  aorta. 

Common  Carotid  Arteries. — When  the  right  common  carotid  artery  arises  separately  from 
the  arch  of  the  aorta,  it  may  be  the  first,  or  mucli  more  rarely  the  second  branch.  In  the 
former  case  the  fourth  right  aortic  arch  has  been  olaliterated,  and  the  right  subclavian  artery 
springs  from  the  descending  aorta ;  in  the  latter  case  either  the  innominate  stem  has  been 
absorljed  into  tlie  arch  of  the  aorta,  or  the  ventral  root  of  the  fourth  right  aortic  arch  has  fused 
with  jaart  of  an  elongated  fourth  left  arcli. 

Whether  arising  as  the  first  or  second  branch,  the  origin  may  be  to  the  left  of  the  mesial  plane, 
and  the  trunk  may  pass  in  front  of  the  trachea,  or  behind  the  oesophagus,  before  it  ascends  in  the 
neck. 

The  left  common  carotid  artery  varies  as  regards  its  origin  much  more  frequently  than  the 
right  vessel ;  not  uncommonly,  and  apparently  because  of  the  fusion  of  the  ventral  roots  of  the 
fourth  aortic  arches,  it  arises  from  a  stem  common  to  it  and  to  the  right  common  carotid  and 
right  subclavian  arteries. 

Both  common  carotids  may  vary  as  regards  their  termination.  They  may  divide  at  a  higher 
or  lower  level  than  usual,  the  former  more  commonly  than  the  latter  ;  whilst  in  a  few  excej)tionaI 
cases  the  common  carotid  does  not  divide,  but  is  continued  directly  into  the  internal  carotid,  and 
from  this  the  branches  usually  given  off  by  the  external  carotid  are  derived. 

This  arrangement  is  probably  due  to  obliteration  of  the  ventral  roots  of  the  first  and  second 
aortic  arches,  the  arches  persisting  and  being  divided  into  the  branches  which  generally  arise 
from  their  ventral  extremities. 

Usually  the  common  carotids  give  off  no  branches,  but  not  infrequently  one  or  more  of  the 
branches  of  the  external  carotids  arise  from  them. 

The  external  carotid  artery  may  be  absent,  or  it  may,  in  rare  cases,  arise  directly  from  the 
arch  of  the  aorta.  The  number  of  its  branches  may  be  diminished  either  by  fusion  of  their  roots 
or  by  transference  to  the  internal  or  common  carotid  arteries.  On  the  other  hand,  the  number  of 
its  branches  may  be  increased  ;  thus  the  sterno-mastoid  artery,  the  liyoid  branch  usually  given  oft' 
by  the  superior  thyroid  artery,  or  the  ascending  palatine  Ijranch  of  the  facial,  may  arise  from  it. 
Sometimes  the  Ijranches  may  arise  in  the  usual  way,  but  may  deviate  from  the  course  generally 
taken  ;  more  particularly  is  this  the  case  with  the  internal  maxillary  artery,  which  may  pass 
either  between  the  heads  or  entirely  external  or  internal  to  both  heads  of  the  external 
pterygoid  muscle. 

The  internal  carotid  artery  is  rarely  absent.  Occasionally  it  sjarings  from  the  arch  of  the 
aorta,  and  in  its  course  through  the  neck  it  may  vary  somewhat  in  length  and  in  tortuosity.  One 
or  more  of  tlie  branches  usually  derived  from  the  external  carotid  artery  may  arise  from  it,  and  it 
sometimes  gives  off  a  large  meningeal  branch  to  the  posterior  fossa  of  the  skull.  Its  posterior 
communicating  branch  may  replace  the  posterior  cerebral  artery  ;  on  the  other  hand,  the  upper 
part  of  the  internal  carotid  may  lie  aljsent,  and  the  posterior  communicating  artery  may  become 
the  middle  cerebral  artery.  The  anterior  cerebral  liranch  of  the  internal  carotid  may  be  absent, 
or  rather  it  may  arise  from  the  corresijonding  artery  of  the  opposite  side  ;  or  there  may  be  three 
anterior  cerebral  arteries,  the  third  arising  from  the  anterior  communicating  artery  which  connects 
the  two  anterior  cerebrals  together.  The  ophthalmic  artery,  as  it  traverses  the  orbit,  may  pass 
either  (;ver  or  under  the  optic  nerve.  It  is  occasionally  replaced  by  a  branch  of  the  middle 
raeniiig<;al  ai-tery. 

The  vertebral  artery  may  have  a  doulile  origin — one  fiom  tlie  subclavian,  and  one  from  the 
inferior  tliyioid  ai-lciy  or  from  the  aorta. 

The  right  ^-ertebral  may  arise  from  the  common  carotid  or  from  the  arch  of  the  aorta. 
Occasionally  it  springs  from  the  des(;(!nding  aorta,  an  arrangement  associated  with  the  persistence 
of  the  dorsal  roots  of  tlie  fourth  and  fifth  riglit  arches. 

The  left  verteln-al  artery  not  infnnpuaitly  spi'ings  from  the  arch  of  the  aorta,  arising  between 
the  left  common  (carotid  and  left  suljclavian  arteries  ;  this  is  evidently  due  to  the  absorption  of 
the  stem  of  the  seventh  segmental  artery  into  the  aortic  arch.  Very  exceptionally  the  left 
vertebral  is  a  liranch  of  an  intercostal  artery. 

In  its  course  upwards  either  vertebral  arteiy  may  enter  the  vertebrarterial  foTvamen  of  any  of 
the  lower  six  cervical  vertebra. 


ABNORMALITIES  OF  ARTEEIES.  951 

The  cases  iii  which  it  does  not  enter  one  of  the  lowest  of  these  are  apparently  associated  with 
it*  formation  in  part  from  the  precostal  instead  of  from  the  postcostal  anastomosing  channels. 

The  artery  may  enter  the  spinal  canal  with  the  second  instead  of  with  the  first  cervical  nerve, 
or,  after  leaving  tlie  foramen  in  the  transverse  process  of  the  third  vertebra,  it  may  divide  into 
two  branches,  one  of  which  accompanies  the  second  and  the  otlier  the  first  cervical  nerve  ;  the  two 
Inanches  unite  together  again  in  the  spinal  canal  to  form  a  single  trunk. 

Sometimes,  thougli  rarely,  it  gives  off  superior  intercostal  and  inferior  thyroid  branches.  The 
upper  end  of  one  of  the  vekelirals  is  sometimes  very  small,  or  it  may  be  entirely  wanting;  in 
the  latter  case  the  basilar  artery  is  formed  by  the  direct  continuation  of  the  opposite  verteljral. 

The  basilar  artery  may  be  double  in  part  or  the  whole  of  its  extent,  or  its  caA-ity  may  be 
divided  by  a  more  or  less  complete  septum.  It  may  terminate  in  one  instead  of  two  posterior 
cerebral  arteries,  the  missing  vessel  being  supplied  by  the  enlargement  of  the  postei'ior  com- 
municating branch  of  the  internal  carotid. 

The  Arteries  of  the  Upper  Limb. 

Subclavian  Arteries. — The  variations,  so  far  as  regards  the  origins  of  the  subclavian 
arteries,  have  aheady  been  mentioned  {p.  947).  Other  interesting  modifications  are  met  with  in 
respect  of  its  position  and  branches. 

The  subclavian  artery  may  reach  as  high  as  one  or  even  one-and-a-half  inches  above  the 
clavicle,  thougli  as  a  rule  it  does  not  reach  higher  than  three-quarters  of  an  inch  above  that 
tone.  On  the  other  hand,  it  may  not  rise  even  to  the  level  of  the  upper  border  of  the  clavicle. 
These  differences  appear  to  be  associated  with  the  descent  of  the  clavicle  and  sternum,  which 
occui-s  as  age  increases. 

The  artery  may  pass  in  front  of  or  through  the  scalenus  anticus  instead  of  behind  it,  or 
the  A"eiii  may  accompany  it  behind  the  muscle. 

The  branches  of  the  subclavian  artery  may  be  modified  with  reference  to  their  points  of  origin; 
thus  those  of  the  first  part  may  be  further  in  or  out  than  usual,  the  suprascapular  or  some  other 
branch  of  the  thyroid  axis  may  arise  separately  from  the  third  part  of  the  artery,  and  not 
imcommonly  the  posterior  scapular  artery  is  a  brancli  of  this  part.  The  abnormalities  of  the 
vertebral  branch  have  already  been  described  ;  those  of  the  thyroid  axis  and  its  branches  are 
numerous  but  not  important. 

Tlie  internal  mammary  artery,  usually  a  branch  of  the  first  part  of  the  subcla^-ian,  is  very 
variable  as  regards  its  origin.  It  may  arise  from  the  second  or  third  parts,  or  from  the  thyroid 
axis,  or  it  may  spring  from  the  aorta,  or  from  the  innominate  or  axillary  arteries.  All  these 
variations  are'  due  to  obliteration  of  the  normal  origin  and  the  opening  up  of  anastomoses. 
The  internal  mammary  artery  sometimes  descends  in  front  of  the  cartilages  of  one  or  more  of 
the  lower  true  ribs,  and  occasionally  it  gives  oft"  a  large  lateral  branch  (a.  mammaria  lateralis) 
which  descends  on  the  inner  side  of  the  chest  wall  nearly  in  the  mid-axiUary  line,  a  point  of 
importance  in  paracentesis. 

A  few  cases  have  also  been  noticed  in  which  a  bronchial  artery  has  arisen  from  the  internal 
mammary. 

Tlie  superior  intercostal  branch  of  the  subclavian  may  be  absent.  In  any  case  its  deep 
cervical  branch  may  rise  directly  from  the  subclavian  trunk.  The  superior  intercostal  is  some- 
times formed  from  a  postcostal  instead  of  a  precostal  jjrimitive  channel,  and  in  this  case  it  passes 
between  the  necks  of  the  ribs  and  the  transverse  processes  of  the  verteliraj  instead  of,  as  usual,  in 
fi-ont  of  the  necks  of  the  ribs. 

The  axillary  artery  does  not  vary  much  as  regards  its  origin  or  course.  Its  relations  may  be 
modified  by  the  existence  of  a  muscular  or  tendinous  "  axillary  arch,"  wliich,  passing  from  the 
latissimus  dorsi  to  tlie  pectoralis  major,  crosses  the  lower  part  of  the  artery  superficially  ;  and 
a  further  interesting  modification  is  associated  with  an  anomalous  arrangement  of  its  Ijranches. 
Occasionally  the  sub-scapular,  circumflex,  and  sujierior  and  inferior  profunda  arteries  arise  from 
the  axillary  by  a  common  stem.  In  these  cases  the  cliief  branches  of  the  brachial  plexus  are 
gi-ouped  round  the  common  stem  instead  of  round  the  main  trunk,  and  it  is  suggested  that  the 
common  stem  in  question  was  originally  the  trunk  artery  of  the  upper  limb,  the  lower  part  of 
which  has  been  obliterated,  the  circulation  being  carried  on  by  a  vas  aberrans  which  anastomoses 
below  either  with  the  brachial  artery  or  with  one  of  the  arteries  of  the  forearm.  It  is  also 
said  that  a  rudiment  of  this  artery  exists  in  a  muscular  branch  which  jxa.sses  between  the  heads 
of  the  median  nerve. 

Sometimes  the  axillary  artery  divides  into  the  radial  and  ulnar  arteries,  and  more  rarely  the 
interosseous  artery  may  sjjring  from  it. 

Obviously  when  the  radial  and  ulnar  arteries  are  formed  by  the  division  of  the  axillary,  there 
is  no  brachial  artery  ;  its  place  is  taken  by  the  two  abnormal  vessels  which,  as  a  rule,  are 
separated  by  the  median  nerve  as  they  run  through  the  upper  arm  ;  the  radial  is  usually  more 
superficial  than  the  ulnar,  and  crosses  outwards  in  front  of  it  at  the  bend  of  the  elbow. 

The  brachial  artery  is  rarely  prolonged  beyond  its  usual  point  of  1  lifurcation,  not  uncommonly, 
however,  it  bifurcates  at  a  higher  level.  Of  tlie  two  terminal  branches  of  the  brachial,  one  may 
divide  into  radial  and  interosseous,  the  other  forming  the  ulnar  ;  or  one  may  divide  into  radial 
and  ulnar,  whilst  the  other  is  the  interosseous  artery.  Occasionally  the  brachial  artery  ter- 
minates by  dividing  into  three  branches — viz.  the  raclial,  the  ulnar,  and  the  interosseous.  In 
any  case,  the  l:>ranch  whicli  gives  origin  to  or  becomes  the  interosseous  was  in  all  probaljility  the 
original  trunk. 


952  THE  VASCULAR  SYSTEM. 

Division  of  the  brachial  artery  at  a  higher  level  than  nsual  occurs  most  commonly  in  the 
upper  third  of  the  arm,  and  least  commonly  in  the  lower  third  ;  the  resulting  trunks  are  often 
united  near  the  bend  of  the  elbow  by  a  more  or  less  oblique  anastomosis. 

In  cases  of  liigh  division  of  the  brachial  artery  the  radial  branch  may  pierce  the  deep  fascia 
of  the  arm  near  the  bend  of  the  elbow,  and  descend  in  the  forearm  immediately  beneath  the 
skin ;  in  other  cases  the  radial  runs  deeper,  and  passes  behind  the  tendon  of  the  biceps.  The 
ulnar  branch  sometimes  runs,  on  the  internal  intermuscular  septiim,  towards  the  inner  condyle, 
and  then  outwards  towards  the  middle  of  the  bend  of  the  elbow  under  a  band  of  fascia,  from 
which  the  upper  fibres  of  the  jjronator  teres  arise,  or  round  the  supracondylar  process  of  the 
humerus  if  it  is  present.  More  commonly  the  ulnar  branch  descends  towards  the  inner  condyle, 
and  crosses  sujjerficial  to  the  flexor  muscles  or  beneath  the  palmaris  longus  ;  and  in  a  few  cases  it 
is  subcutaneous.  Very  occasionally  the  uhiar  artery  accompanies  the  ulnar  nerve  behind  the 
inner  condyle ;  in  these  cases  it  has  obviously  been  formed  by  enlargement  of  the  ordinary 
inferior  profunda  and  posterior  iilnar  recurrent  arteries. 

Iiistead  of  following  its  usual  course  along  the  brachialis  anticus,  the  brachial  artery  may 
accomjjany  the  median  nerve  behind  a  supracondylar  or  ej)icondylic  process,  or  ligament,  as  in 
many  carnivores  ;  it  may  pass  in  front  of  the  median  nerve  instead  of  behind  it.  It  may  give 
off  a  "  vas  aberrans  "  or  a  median  artery,  and  any  of  its  ordinary  branches  may  be  absent. 

The  vas  aberrans  given  off  from  the  brachial  artery  usually  ends  in  the  radial  artery,  some- 
times in  the  radial  recurrent,  and  rarely  in  the  ulnar  artery. 

The  ulnar  artery  may  be  absent,  being  replaced  by  the  "comes  nervi  mediani"  or  the  inter- 
osseous artery,  and  it  may  terminate  in  the  deep  instead  of  in  the  superficial  palmar  arch.  It 
rarely  rises  at  a  lower  level  than  usual,  and  when  it  rises  at  a  higher  level  it  most  commonly 
passes  superficial  to  the  muscles  which  spring  from  the  internal  ej^icondyle.  Moreover,  in  these 
cases  it  frequently  has  no  interosseous  branch,  the  latter  vessel  springing  from  the  radial  artery, 
and  in  all  probability  variations  of  this  description  are  produced  by  the  ulnar  artery  taking 
origin  from  the  main  trunk,  which  is  represented  by  the  radio-interosseous  vessel,  at  a  higher 
level  than  usual.  Even  when  it  commences  in  the  usual  way  the  ulnar  artery  may  pass  super- 
ficial to  the  muscles  from  the  internal  epicondyle,  and  m  these  cases  its  interosseous  and  recurrent 
branches  spring  from  the  radial  artery. 

The  anterior  and  posterior  interosseous  arteries  may  arise  separately  from  the  ulnar  instead  of 
by  a  common  interosseous  trunk.  The  recurrent  branches  of  the  ulnar  may  spring  from  the 
interosseous,  and  the  interosseous  itself  may  be  a  branch  of  the  radial. 

The  small  median  artery,  the  companion  artery  of  the  median  nerve,  usually  a  branch  of  the 
anterior  interosseous,  may  sjaring  from  the  axillary,  brachial,  or  ulnar  arteries  ;  it  may  be  much 
larger  than  iisual,  and  terminate  either  by  breaking  wp  into  digital  branches,  or  by  joining  one 
or  more  digital  branches  of  the  superficial  palmar  arch  or  the  palmar  arch  itself. 

The  radial  artery  may  be  absent,  its  place  being  taken  by  branches  of  the  ulnar  or  inter- 
osseous arteries  ;  it  may  arise  from  the  axillary,  or,  higher  than  usual,  from  the  brachial.  It 
may  terminate  in  muscular  branches  in  the  front  of  the  forearm,  or  in  the  superficialis  volse, 
or  in  carpal  branches ;  the  lower  portion  of  the  artery,  in  these  cases,  is  usually  replaced  by 
branches  of  the  ulnar  or  interosseous  arteries.  Occasionally  the  radial  divides  some  distance 
above  the  wrist  into  two  terminal  branches,  one  of  which  gives  off  the  cardial  bi*anches,  and 
becomes  the  suj^erficialis  volae,  whilst  the  other  crosses  superficial  to  the  extensor  tendons  and 
passes  to  the  back  of  the  wrist. 

The  radial  artery  may  run  a  superficial  course,  or,  and  esi^ecially  when  it  commences  at  a 
lower  level  than  usual,  it  may  pass  beneath  the  pronator  radii  teres  and  the  radial  origin  of  the 
flexor  sublimis  digitorum.  In  some  cases  it  passes  to  the  back  of  the  wrist  across  the  supinator 
longus,  and  in  others  it  lies  upon,  instead  of  beneath,  the  extensor  tendons  of  the  thumb. 

Its  branches  may  be  diminished  or  increased  in  number.  The  radial  recurrent  may  spring 
from  the  brachial  or  ulnar  arteries,  or  may  be  represented  by  several  branches  from  the  upper 
part  of  the  radial.  The  dorsalis  indicis  may  be  large,  and  may  replace  the  princeps  pollicis  and 
the  radialis  indicis.  On  tlie  contrary,  the.  dorsal  carjial  artery  and  dorsal  digital  branches  of  the 
radial  may  be  small,  or  the  former  may  be  replaced  by  branches  of  the  interosseous  arteries,  and 
the  latter  by  llie  sujxjrior  perforating  brandies  of  the  deejj  jxilmar  arch. 

The  princeps  pollicis  and  radialis  indicis  arteries  may  be  absent,  their  places  being  taken 
either  by  brandies  of  the  supi^rficial  jialmar  arch  or  by  the  dorsalis  indicis  artery 

The  superficial  palmar  arch  is  sometimes  absent ;  its  branches  are  then  given  oft'  from  the 
deep  arch.  Conversely,  it  may  be  larger  tlian  normal,  and  it  may  be  completed  on  the  xdnar 
side  by  the  radialis  indicis,  the  princeps  pollicis,  or  tlie  comes  nervi  mediani  arteries. 

Tlie  deep  palmar  arch  is  much  more  rarely  absent  tlian  .the  superficial  arch.  When  absent 
its  branches  are  su])plic'd  by  the  superfi(;ial  arch,  tlie  superior  perforating  arteries,  or  the  palmar 
carjjal  arcli. 

The  Iliac  Arteries  and  their  Branches. 

The  common  iliac  artery  may  be  longer  or  shorter  than  usual,  a  modification  which  is 
largely  though  not  altogether  determined  by  the  point  at  which  the  bifurcation  of  the  aorta 
takes  place.  If  exceptionally  long,  it  is  usually  tortuous.  In  rare  cases  in  man  the  artery  is 
absent.  It  occa.sionally  gives  ott'  the  middle  or  a  lateral  sacral  artery,  and  ilio-lumbar,  spiermatic, 
or  accessory  renal  brandies  may  arise  from  it. 

The  internal  iliac  artery  varies  as  regards  length.  It  is  usually  longer,  and  rises  at  a 
higher  level  when  the  conimoii  iliac  is  sliort.     In  ran;  cases  it  has  been  found  to  arise  from  the 


ABNOKMALITIES  OF  AETERIES.  953 

aorta  without  the  intervention  of  a  common  iliac.  Frequently  it  does  not,  even  in  appearance, 
end  in  anterior  and  posterior  divisions,  but  obviously  forms  a  single  trunk,  as  in  the  foetus,  from 
which  the  several  branches  are  given  off. 

The  visceral  branches  vary  much  in  number  and  size,  and  the  middle  heemorrhoidal  may  not 
be  present,  its  place  being  taken  by  branches  from  the  vesical  arteries.  A  renal  branch  some- 
times arises  from  the  internal  iliac. 

The  ilio-lumbar  branch  may  rise  from  the  common  instead  of  from  the  internal  iliac ;  the 
gluteal  and  sciatic  may  rise  by  a  common  stem,  or  the  gluteal  may  be  absent,  and  its  place  taken 
by  a  branch  from  the  femoral  artery  ;  the  sciatic  artery  may,  as  in  the  foetus,  constitute  the  main 
artery  of  the  hind  limb,  and  run  down  to  become  continuous  with  the  popliteal  artery.  Probably 
the  "  comes  nervi  ischiadici "  rej^resents  the  original  continuity  of  these  two  vessels.  Occasionally 
the  lateral  sacral  arteries  do  not  arise  from  the  internal  iliac  trunks. 

In  some  few  instances  the  obturator  artery  arises  from  the  deep  epigastric  artery  instead  of 
from  the  internal  iliac.  The  condition  is  apparently  due  to  obliteration  of  the  usual  origin  of  the 
obturator  artery  and  to  the  subsequent  enlargement  of  the  anastomosing  pubic  branches  of 
the  obturator  and  deep  epigastric  arteries.  The  course  of  the  abnormal  obturator  artery  is  of 
importance.  From  its  origin  it  descends  into  the  pelvis  on  the  inner  side  of  the  external  iliac 
vein,  and  in  the  majority  of  cases  on  the  outer  side  of  the  crural  ring,  but  in  three-tenths  of  the 
cases,  and  more  frequently  in  males  than  in  females,  it  descends  on  the  inner  side  of  the  ring. 

The  obturator  artery  sometimes  gives  off  an  accessory  pudic  branch  which  passes  along  the 
side  of  the  prostate,  jjierces  the  triangular  ligament,  and  terminates  by  dividing  into  the  artery 
of  the  corpus  caveruosum  and  the  dorsal  artery  of  the  penis.  When  this  occurs  the  pudic  arterv 
is  small,  and  it  terminates  in  the  artery  to  the  bulb.  Occasionally  the  accessory  pudic  arises  from 
the  pudic  artery  in  the  pelvis,  or  from  one  of  the  vesical  arteries. 

The  external  iliac  artery  may  be  much  smaller  than  usual,  especially  if  the  sciatic  artery 
persists  as  the  main  vessel  of  the  lower  limb.  It  may  give  off  two  deep  circumflex  iliac  branches, 
a  dorsal  artery  of  the  penis,  an  internal  circumflex  artery  of  the  thigh,  or  a  vas  aberrans,  and  its 
deep  circumflex  iliac  and  deep  epigastric  branches  may  arise  at  higher  or  lower  levels  than  usual. 

The  Arteries  of  the  Lower  Limb. 

The  femoral  artery  is  small,  and  ends  in  the  profunda  and  circumflex  branches,  when  the 
sciatic  artery  forms  the  principal  vessel  of  the  lower  limb.  The  profunda  branch,  which  usually 
arises  from  the  outer  side  of  the  femoral  trunk,  about  one-and-a-half  inches  below  Poupart's  liga- 
ment, may  commence  at  a  higher  or  a  lower  level,  and  from  the  back  or  the  inner  side  of  the 
femoral  trunk.  Absence  of  the  profunda  has  been  noted,  and  in  these  cases  the  branches  usually 
given  oft'  by  it  spring  directly  from  the  femoral  artery. 

The  femoral  artery  may  be  double  for  a  portion  of  its  extent,  or  it  may  be  joined  by  a  vas 
aberrans  given  off  from  the  external  iliac  artery.  In  addition  to  its  ordinary  branches,  it  may 
furnish  one  or  both  of  the  circumflex  arteries  of  the  thigh,  and  sometimes  it  gives  off,  near  the 
origin  of  the  profunda,  a  great  saphenous  artery,  such  as  exists  normally  in  many  mammals. 
This  vessel  descends  through  Scarpa's  triangle  and  Hunter's  canal,  and  accompanies  the  internal 
saphenous  nerve  to  the  inner  side  of  the  foot. 

The  deep  circumflex  iliac,  the  obturator,  and  the  deep  epigastric  arteries  are  occasionally 
given  off  from  the  femoral. 

The  popliteal  artery  may  exceptionally  form  the  direct  continuation  of  the  sciatic  artery.  It 
sometimes  divides  at  a  higher  or  lower  level  than  usual,  and  the  division  may  be  into  either  two 
or  three  branches ;  if  three  terminal  branches  are  present,  they  are  the  anterior  and  posterior 
tibial  and  the  peroneal  arteries,  and  if  only  two,  either  the  anterior  and  posterior  tibial,  or  the 
anterior  tibial  and  the  peroneal  arteries. 

Occasionally  the  artery  is  double  for  a  short  portion  of  its  course,  and  it  has  been  found  to 
cross  first  behind  the  inner  head  of  the  gastrocnemius  to  the  inner  side  of  the  knee,  and  then  in 
front  of  the  inner  head  of  the  gastrocnemius  to  regain  tlie  pojiliteal  s^Dace.  The  number  of  its 
branches  may  be  reduced,  or  they  may  be  increased  by  the  addition  of  a  vas  aberrans  which 
connects  it  with  the  joosterior  tibial  artery.  Its  superficial  sural  braiicli  may  enlarge  to  form  a 
well-marked  small  saphenous  artery. 

The  posterior  tibial  artery  may  be  small  or  altogether  absent,  its  place  being  taken  by 
branches  of  the  peroneal  artery  ;  again,  it  may  be  longer  or  shorter  than  usual,  in  conformity  with 
the  higher  or  lower  division  of  the  popliteal  trunk.  The  peroneal  artery  is  large  if  either  the 
anterior  or  posterior  tibial  arteries  are  small  The  anterior  terminal  branch  of  the  peroneal  is 
almost  invariably  large  when  the  anterior  tibial  artery  is  small ;  in  some  cases,  indeed,  it  replaces 
the  whole  of  the  dorsalis  pedis  continuation  of  the  latter  vessel ;  in  others,  however,  only  the 
tarsal  and  metatarsal  branches  are  so  rej)laced.  The  peroneal  sometimes  arises  from  a  stem 
common  to  it  and  the  anterior  tibial  artery. 

The  anterior  tibial  artery  may  be  absent,  its  place  being  taken  by  branches  of  the  posterior 
tibial  and  peroneal  arteries.  It  is  longer  than  normal  when  the  popliteal  artery  divides  at  a 
higher  level  than  usual,  and  in  these  cases  it  may  pass  either  behind  or  in  front  of  the  pojjliteus 
muscle.  Occasionally  the  anterior  tibial  artery  and  its  dorsalis  pedis  continuation  are  larger 
than  normal,  and  the  terminal  part  of  the  dorsalis  pedis  takes  the  place,  more  or  less  completely, 
of  the  external  plantar  artery. 

The  internal  plantar  artery  is  sometimes  very  small,  and  it  may  be  absent ;  its  place  is 


954  THE  YASCULAE  SYSTEM. 

taken  by  branclies  of  the  doi-salis  pedi:?  or  external  plantar  arteries.     The  external  plantar 
artery  ako  may  be  small  or  alisent,  the  plantar  arch  lieing  formed  entirely  by  the  dorsalis  pedis. 


ABXOEMALITIES  OF  YEINS. 

Abnormalities  or  variations  of  veins  are  as  freqnently  met  with  as  those  of  arteries,  and  they 
are  dne  to  similar  causes. 

The  Supeeiok  Yexa  Cava. 

The  superior  vena  cava  may  develop  on  the  left  side  instead  of  the  right.  This  peculiarity 
is  due  to  the  persistence  of  the  left  duct  of  Cuvier  instead  of  that  on  the  right  side,  and  it  is- 
associated  with  absence  of  the  coronary  sinus,  which  is  replaced  by  the  lower  part  of  the  left 
superior  vena  cava.  An  exceptional  case  is  recorded  in  which  the  opening  of  the  coronary  sinus 
into  the  heart  was  obliterated,  and  the  cardiac  veins  terminated  in  a  trunk  which  passed  upwards 
to  the  left  innominate  vein.  This  trunk  was  obviously  formed  by  enlargement  of  the  left  duct  of 
Cuvier  and  the  lower  j^art  of  the  left  primitive  jugular  vein.  Not  very  uncommonly,  as  the 
result  of  the  persistence  of  both  ducts  of  Cuvier,  there  are  two  superior  vena;  cavse,  the  transverse 
anastomosis  which  usually  forms  the  left  innominate  vein  being  small  or  entirely  absent.  In 
these  cases  the  left  innominate  vein  descends  m  the  left  jiart  of  the  superior  mediastinum,  crosses 
the  aortic  arch,  is  joined  by  the  left  superior  intercostal  vein,  and  becomes  the  left  superior 
vena  cava  ;  this  latter  vessel  descends  in  front  of  the  root  of  the  left  lung,  and  terminates  in  the 
lower  and  back  part  of  the  right  auricle.  It  receives  the  great  cardiac  vein,  and,  turning  to  the 
back  of  the  heart,  replaces  the  coronary  sinus.  This  arrangement  is  normal  in  many  mammals. 
Occasionally  in  man  the  left  superior  vena  cava  terminates  in  the  left  auricle,  and  the  coronary 
sintis,  which  represents  a  part  of  the  sinus  venosus,  has  been  seen  to  ha^-e  a  similar  ending ;  both 
these  abnormal  endings  must  be  the  result  of  malposition  of  the  interauricular  sejatum. 

The  vena  azygos  major  may  be  formed  on  the  left  side  ;  it  then  arches  over  the  root  of  t]ie 
left  lung,  and  terminates  in  the  left  end  of  the  coronary  sinus.  This  is  the  normal  arrangement 
in  some  mammals,  and  it  is  due  to  the  persistence  of  the  left  cardinal  vein  and  the  left  duct  of 
Cuvier. 

The  azygos  veins  may  be  reduced  or  increased  in  number.  In  the  former  case  there  may  be 
only  one  azygos  vein  which  receives  the  intercostal  veins  of  both  sides,  or  there  may  be  two 
azygos  veins,  a  right  and  a  left,  the  left  usually  being  diA-ided  into  itpj^er  and  lower  sections 
which  are  connected  by  a  smaller  intermediate  portion,  and  united  to  the  right  vein  by  one  or 
more  transverse  anastomoses,  or  it  may  terminate  by  joining  either  the  left  innominate  vein  or 
the  left  superior  vena  cava.  The  small  intermediate  section  on  the  left  side  may  form  a  sejoarate 
vessel,  and  then  the  number  of  the  azygos  veins  is  increased  to  four,  each  of  the  three  left  veins 
terminating  in  the  right  vein.  When  there  is  only  one  azygos  vein  the  portion  of  the  left 
cardinal  vein,  from  which,  usually,  the  vertical  portions  of  the  left  azygos  veins  are  formed,  has 
disappeared,  and  the  left  intercostal  A^eins  open  into  the  right  azygos  A-ein  by  separate  transA^erse 
anastomoses,  as  in  the  case  of  the  left  lumbar  A-eins  and  the  inferior  A'ena  cava.  On  the  other 
hand,  when  there  is  only  one  left  azygos  vein  the  intermediate  sections  of  the  thoracic  part  of  the 
left  cai-dinal  vein  and  one  or  more  of  the  transverse  anastomoses  have  i^ersisted,  whilst,  when  the 
left  azygos  terminates  in  the  left  innominate  vein,  tlie  traiisA'erse  anastomoses  haA'e  disappeared, 
and  the  lower  part  of  the  left  primitive  jugular  A'ein  has  remained  jjatent. 

Occasionally  the  A^ena  azygos  major  takes  the  place  of  the  upper  part  of  the  inferior  vena 
caA-a,  and  the  whole  of  the  left  cardinal  A'ein  is  enlarged  ;  in  these  cases  the  upper  portion  of  the 
normal  inferior  A-ena  caA-a  is  absent  or  exceptionally  small. 

The  internal  jugular  vein  is  sometimes  smaller  or  larger  than  normal.  In  either  case  com- 
pensatory changes  in  size  occur  in  the  lateral  sinus  and  internal  jugular  A-ein  of  the  opposite 
.side,  or  in  the  external  and  anterior  jugular  A^eins  of  the  same  side. 

The  external  jugular  vein  is  sometimes  absent,  or  it  may  be  smaller  than  usual ;  in  both 
cases  either  the  anterior  or  internal  jugular  veins  are  enlarged.  In  some  of  the  cases  in  which 
the  external  jugular  vein  is  small  it  receiA'es  no  communication  from  the  temjDoro-maxillary 
v^ein,  but  is  merely  the  continuation  of  the  posterior  auricular  vein.  On  the  other  hand,  it  may 
be  enlarged,  and  receiAX-  the  Avhole  of  the  temporo-maxillarj'  vein. 

The  anterior  jugular  vein  may  be  absent,  or  it  may  be  unusually  large,  especiall}'  in  the 
lower  part  of  its  extent,  and  after  it  has  receiA^ed  an  occasional  tributary  from  the  common  facial 
vein. 

The  tempore -maxillary  vein  may  terminate  entirely  in  the  common  facial  vein,  or  in  the 
external  or  tJit-  internal  jugular  vein.     It  may  Ije  A-ery  small,  and  occasionally  it  is  absent. 

VariatioiLs  of  tin-  cranial  blood  sinuses  are  not  luimerous.  One  lateral  sinus  may  be 
absent  or  very  small  Avhen,  as  a  rule,  that  of  the  opposite  side  is  enlarged.  The  inferior  longi- 
tudinal, the  occipital,  or  the  spheno-jjarietal  sinuses  may  be  absent,  and  there  may  be  an  additional 
petro-squamous  iriljutary  to  the  lateral  sinus.  The  petro-squamous  sinus,  Avhen  present,  is  the 
remains  of  that  portion  of  the  primitive  lateral  sinus  Avhich  crossed  the  temporal  bone,  passed 
through  the  jx>st -condyloid  foramen  and  terminated  in  the  primitive  jugular  vein.  Very  occasion- 
ally in  the  human  adult  it  still  pierces  the  skuU  beliind  the  condyle  of  the  jaw,  and  terminates 
in  the  temporo-maxillary  vein,  and  this  is  the  normal  arrangement  in  some  mammals. 


ABNOEMALITIES  OF  THE  LYMPHATICS.  955 

The  Veins  of  the  Upper  Extremity, 

The  superficial  veins  of  tlie  forearm  are  extremely  variable ;  any  of  tliem  may  be  absent, 
but  most  commonly  it  is  the  median  or  the  radial  vein  which  is  wanting.  The  median  cejihalic 
And  the  cephalic  veins  may  be  small  or  absent,  and  on  the  other  liand  the  cephalic  vein  may  be 
larger  than  usual.  Moreover  the  cephalic  vein  may  end  in  the  external  jugular  vein,  its  original 
termination  ;  or  it  may  be  connected  with  the  external  jugular  vein  by  an  anastomosing  channel 
which  sometimes  passes  over  the  clavicle  and  sometimes  through  that  bone. 

The  basilic  vein  is  sometimes  larger  and  sometimes  smaller  than  usual,  and  it  may  pierce  the 
fascia  of  the  arm  at  a  higher  or  at  a  lower  level  than  is  customary. 

The  venae  comites  of  the  arteries  of  the  upper  extremity  generally  terminate  at  the  lower 
border  of  the  subscapularis,  where  they  join  the  axillary  vein,  but  they  may  end  above  or  lielow 
the  position  of  their  usual  termination. 

The  subclavian  vein  sometimes  passes  behind  instead  of  in  front  of  the  scalenus  anticus 
muscle,  and  it  has  been  seen  passing  between  the  clavicle  and  the  subclavius  muscle. 

The  Inferior  Vena  Cava. 

The  lower  part  of  the  inferior  vena  cava  is  sometimes  absent,  in  which  case  the  common  iliac 
N-eins  ascend,  one  on  the  right  and  the  other  on  the  left  of  the  aorta,  to  the  level  of  the  second 
lumbar  vertebra,  where  the  left  common  iliac  vein  receives  the  left  renal  vein,  and  then  crosses  in 
front  of  or  Ijehind  the  aorta  to  fuse  with  the  right  corresponding  vein  ;  in  these  cases,  therefore,  the 
inferior  vena  cava  commences  at  the  level  of  the  second  lumbar  verteln-a,  and  it  represents  only 
the  upper  and  last-formed  part  of  the  ordinary  vessel ;  the  common  iliac  veins,  each  of  which 
receives  the  lumljar  veins  of  its  own  side,  are  exceptionally  long,  and  they  may  or  may  not  be 
united  at  the  j^elvic  l)rim  l)y  a  small  transverse  anastomosing  channel. 

Occasionally  the  inferior  vena  cava  does  not  terminate  m  the  right  auricle,  but  is  continuous 
with  the  vena  azygos  major,  which  is  much  enlarged,  all  the  inferior  caval  blood  being  then 
carried  to  the  sujjerior  vena  cava.  In  these  cases  the  liepatic  veins  ojien  directly  into  tlie  right 
auricle  without  communicating  with  the  inferior  vena  cava. 

The  lower  part  of  the  inferior  vena  cava  sometimes  lies  to  the  left  instead  of  to  the  right  of 
the  aorta  ;  this  condition  is  associated  with  a  long  right  common  iliac  vein,  which  crosses  obliquely 
from  right  to  left  to  join  the  shorter  left  common  iliac  vein.  After  receiving  the  left  renal  vein 
the  misplaced  inferior  vena  cava  crosses  in  front  of  the  aorta,  reaching  the  right  side  at  the  level  of 
the  second  or  first  lumbar  vertebra.  In  other  cases,  however,  the  left  inferior  vena  cava  continues 
upwards  through  the  left  crus  of  the  diaphragm,  usuri^ing  the  place  of  a  greater  or  smaller  part 
of  the  left  azygos  vein  ;  having  entered  the  thorax,  it  may  cross  to  the  ojjposite  side  and  terminate 
in  the  vena  azygos  major,  or  it  may  continue  upwards  on  the  same  side,  and  after  arching  over 
the  root  of  the  left  lung,  descend  behind  the  left  auricle,  to  terminate  in  the  right  auricle  in  the 
situation  of  the  coronary  sinus.  In  this  group  of  cases  also  the  hepatic  veins  open  separately  into 
the  right  auricle. 

The  tributaries  of  the  inferior  vena  cava  are  also  subject  to  variation.  Additional  renal, 
spermatic,  ovarian,  or  suprarenal  veins  may  be  j^resent.  Two  or  three  luml^ar  veins  of  one  or 
both  sides  may  unite  into  a  common  trunk  which  terminates  in  the  inferior  vena  cava,  and  the 
hejjatic  veins  may  open  separately,  or  after  fusing  into  a  common  trunk,  into  the  right  auricle 
near  the  o^jening  of  the  inferior  vena  cava. 

No  explanation  of  the  variations  of  the  inferior  vena  cava  and  its  tributaries  is  necessary, 
Ijeyond  the  statement  that  they  are  due  to  jsersistence  of  portions  of  the  cardinal  veins  which 
usually  disaj^pear,  and  to  the  persistence  of  transverse  anastomoses  and  tributaries  which  usually 
atrojihy,  or  to  modifications  of  those  which  ordinarily  take  part  in  the  formation  of  the 
inferior  vena  caval  system. 

The  left  common  iliac  vein  is  short  and  the  right  long  when  the  inferior  vena  cava  lies  on 
the  left  side.  Tlie  common  iliac  veins  may  be  absent,  the  internal  iliac  veins  uniting  to  form  the 
commencement  of  the  inferior  vena  cava,  into  Avhich  the  external  iliac  veins  oijen  as  lateral 
tributaries. 

The   Veins   of   the   Lower   Extremity. 

The  long  saphenous  vein  is  not  sulsject  to  much  variation,  but  the  short  saphenous  vein 

may  terminate  by  joining  the  long  sajjhenous,  or,  after  jjiercing  the  deep  fascia  in  the  lower  part 
of  the  thigh,  it  may  ascend  and  join  the  sciatic  vein  or  one  of  the  tributaries  of  the  profunda 
vein. 

The  venae  comites  are  generally  described  as  terminating  in  the  lower  extremity,  at  the 
lower  part  of  tlie  poj^liteal  space,  but  they  may  ascend  as  far  as  Scarpa's  triangle  ;  as  a  matter 
of  fact,  although  as  a  rule  there  is  only  one  large  popliteal  and  one  large  femoral  vein,  one  or 
more  small  additional  veins  usually  accompany  the  poj^liteal  and  femoral  arteries. 

in  a  few  cases  the  popliteal  vein  does  not  j^ierce  tlie  lower  part  of  the  aljductor  magnus,  but 
ascends  behind  that  muscle  and  becomes  continuous  with  the  profunda  vein,  the  femoi'al  artery 
being  unaccompanied  liy  any  large  vein  during  its  jiassage  through  Hunter's  canal. 

ABNORMALITIES    OF   THE   LYMPHATICS. 

Variations  of  the  glands  and  smaller  vessels  of  the  lymphatic  system  are  so  common  that 
they   can  hardly  be  regarded  as  abnormalities  ;  variations  of  the  larger  vessels,  however,  are 


956  THE  VASCULAE  SYSTEM. 

comparatively  rare.  This  is  especially  the  case  with  respect  to  the  two  terminal  trunks,  the  thoracic 
duct  and  the  right  lymphatic  duct,  the  abnormalities  of  which  are  interesting  and  important. 

When  the  arch  of  the  aorta  is  on  the  right  instead  of  on  the  left  side,  the  thoracic  duct 
usually  terminates  in  the  right  innominate  vein,  in  which  case  it  receives  the  tributaries  which 
usually  open  into  the  right  lymphatic  duct,  whilst  the  corresponding  area  on  the  left  side  is 
drained  by  lymphatics  terminating  in  a  left  lymphatic  duct  which  oj^ens  into  the  commencement 
of  the  left  innominate  vein.  A  similar  arrangement  of  the  terminal  lymphatic  trunks  sometimes 
occurs  even  when  the  arch  of  the  aorta  is  in  its  normal  position  on  the  left  side.  In  either  case 
the  thoracic  duct  may  commence  in  the  usual  way,  and  after  reaching  the  level  of  the  fifth  dorsal 
vertebra  continue  upwards  on  the  right  side,  instead  of  crossing  to  the  left  side,  of  the  vertebral 
column  ;  more  rarely  it  commences  on  the  left  side  and  crosses  over  to  the  right  at  a  higher  level. 

In  one  case  in  which  the  thoracic  duct  opened  into  the  right  innominate  vein,  instead  of  the 
left,  no  trace  of  a  lymphatic  duct  was  discovered  on  the  left  side. 

Occasionally  the  thoracic  duct  commences  and  terminates  in  the  usual  manner,  but  crosses  the 
vertebral  column  immediately  after  its  origin  and  ascends  on  the  left  side. 

Not  uncommonly  there  is  no  distinct  receptaculum  chyli,  in  which  case  the  terminal 
lymphatic  vessels  of  the  abdomen  merely  unite  to  form  a  larger  vessel  which  does  not  present 
any  obvious  dilatation,  and  from  which  the  thoracic  duct  is  continued.  The  terminal  lymphatic 
trunk  may  open  into  the  internal  jugular  vein  previous  to  its  junction  with  the  subclavian, 
instead  of  into  the  commencement  of  the  innominate  vein. 

Occasionally  the  thoracic  duct  is  double,  either  on  the  whole  or  in  part  of  its  extent,  and 
sometimes  it  breaks  up  into  a  j)lexus  of  vessels  which  may  reunite  into  a  single  trunk  in  the 
upper  part  of  the  thorax.  Both  the  thoracic  duct  and  the  right  lymphatic  duct  may  before 
terminating  divide  into  branches  which,  though  sometimes  reuniting  on  each  side  into  a  single 
trunk,  not  infrequently  oj)en  separately  into  the  great  veins  at  the  root  of  the  neck. 

As  a  rule  the  thoracic  duct  joins  the  commencement  of  the  left  innominate  vein,  but  it  may 
end  in  the  internal  jugular,  vertebral,  or  subclavian  veins  of  the  left  side ;  whilst  very  rarely,  it 
opens  into  the  vena  azygos  major. 


THE   EESPIRATOKY   SYSTEM. 

THE  ORGANS  OF  RESPIRATION  AND  VOICE 

By  D.  J.  Cunningham. 

The  organs  of  respiration  are  the  larynx  and  trachea,  which  together  constitute  a 
median  air-passage ;  the  two  bronchi  or  branches  into  which  the  lower  end  of  the 
trachea  divides ;  and  the  two  lungs  to  which  the  bronchi  conduct  the  air.  In 
connexion  with  the  lungs  we  have  likewise  to  consider  the  pleural  membranes — 
two  serous  sacs  which  line  the  portions  of  the  thoracic  cavity  which  contain  the 
lungs,  and  at  the  same  time  give  a  thin  coating  to  these  organs. 

The  larynx  opens  above  into  the  lower  part  of  the  pharynx,  and  the  air  which 
passes  in  and  out  from  the  air-passages  likewise  traverses  the  pharynx,  the  nasal 
fossse,  and  also  the  buccal  cavity  if  the  mouth  is  open.  This  connexion  between 
the  digestive  and  respiratory  systems  is  explained  by  the  fact  that  the  respiratory 
apparatus  is  secondarily  developed  as  an  outgrowth  from  the  front  aspect  of  the 
primitive  fore-gut  of  the  embryo.  In  most  mammals  the  upper  aperture  of  the 
larynx  opens  into  the  part  of  the  pharynx  which  lies  behind  the  nasal  chambers. 
In  man,  however,  the  upper  opening  of  the  larynx  is  placed  lower  down,  below  the 
communication  between  the  mouth  and  pharynx,  and  both  nasal  and  buccal 
breathing  may  be  carried  on  with  very  nearly  equal  ease. 

THE  LARYNX  OE  ORGAN  OF  VOICE. 

The  larynx  is  the  upper  part  of  the  air-passage,  specially  modified  for  the  pro- 
duction of  the  voice.  Above,  it  opens  into  the  pharynx,  whilst  below,  its  cavity 
becomes  continuous  with  the  lumen  of  the  trachea  or  windpipe. 

Position  and  Relations  of  the  Larynx. — In  the  natural  position  of  the  neck, 
and  whilst  the  organ  is  at  rest,  the  larynx  is  placed  in  front  of  the  bodies  of  the 
fourth,  fifth,  and  sixth  cervical  vertebras.  Its  highest  point,  represented  by  the 
tip  of  the  epiglottis,  reaches  as  high  as  the  lower  border  of  the  body  of  the  third 
cervical  vertebra,  whilst  its  lower  limit,  or  the  lower  border  of  the  cricoid  cartilage 
usually  corresponds  to  the  lower  border  of  the  body  of  the  sixth  cervical  vertebra. 
From  the  vertebral  column  the  larynx  is  separated,  not  only  by  the  prevertebral 
muscles  and  prevertebral  layer  of  cervical  fascia,  but  also  by  the  posterior  wall 
of  the  pharynx — indeed  the  posterior  surface  of  the  larynx  forms  the  lower  part  of 
the  anterior  wall  of  the  pharynx,  and  is  covered  })y  the  lining  mucous  membrane 
of  that  section  of  the  alimentary  canal. 

The  larynx  lies  below  the  hyoid  bone  and  the  tongue,  and  in  the  interval 
between  the  great  vessels  of  the  neck.  It  forms  a  more  or  less  marked  projection 
on  the  front  of  the  neck,  and  in  the  median  line  it  approaches  very  close  to  the 
surface,  being  merely  covered  by  skin  and  the  two  layers  of  fascia.  Laterally  it  is 
more  deeply  placed.  Thus  it  is  overlapped  by  the  sterno-mastoid  muscle,  covered 
by  the  two  strata  of  thin  ribbon-like  muscles  which  are  attached  to  the  thyroid 
cartilage  and  the  hyoid  bone,  and  hidden  to  some  extent  by  the  upward  prolonga- 
tions of  the  lateral  lobes  of  the  thyroid  body. 

The  position  of  the  larnyx  is  influenced  by  movements  of  the  head  and  neck.  Thus 
it  is  elevated  when  the   head  is  thrown  back,  and  depressed  when  the  chin  is  carried 

957 


958  THE  RESPIEATOEY  SYSTEM. 

downwards  towards  the  chest.  Again,  if  the  finger  is  placed  upon  it  during  deglutition,  it 
will  be  seen  that  the  larynx  moves  to  a  very  considerable  extent.  The  pharyngeal  muscles 
attached  to  it,  and  more  especially  the  stylo-pharyngeal  muscles,  are  chiefly  responsible 
for  bringing  about  these  movements.  During  singing,  changes  in  the  position  of  the 
larynx  may  also  be  noted,  a  high  note  being  accompanied  by  a  slight  elevation,  and  a  low 
note  by  a  slight  depression  of  the  organ. 

The  position  of  the  larynx  is  not  the  same  at  all  periods  of  development  and  growth. 
In  the  foetus,  shortly  before  birth,  it  lies  much  higher  up  in  the  neck.  Thus  its  lower 
border  corresponds  to  the  lower  border  of  the  fourth  cervical  vertebra.  Its  permanent 
position  is  not  reached  until  the  period  of  puberty  is  attained  (Symington).  This  descent 
of  the  larynx  has  been  stated  to  be  due  to  the  rapid  and  striking  growth  of  the  facial  part 
of  the  skull  Avhich  lies  above  it  (Symington).  It  is  very  doubtful,  however,  if  the  facial 
growth  has  any  influence  in  this  direction.  In  the  anthropoid  ape,  in  which  the  face  forms 
a  much  greater  part  of  the  skull  than  in  man,  and  in  which,  in  the  transition  from  the 
infantile  to  the  adult  condition,  the  facial  growth  is  even  more  striking  than  it  is  in  man, 
the  larynx  occupies  a  relatively  higher  position  in  the  neck.  In  the  early  stages  of 
gi'owth  all  the  thoracic  viscera  undergo  a  gradual  subsidence.  The  larynx  in  its  descent 
follows  these.  Indeed  it  cannot  do  otherwise,  seeing  that  the  bifurcation  of  the  trachea 
between  infancy  and  puberty  moves  downwards  more  than  the  depth  of  one  thoracic 
vertebra. 

General  Construction  of  the  Larynx. — The  wall  of  the  larynx  is  constructed 
upon  a  somewhat  complicated  plan.  There  is  a  frame-work  composed  of  several 
cartilages.  These  are  connected  together  at  certain  points  by  distinct  joints  and 
also  by  elastic  membranes.  Two  elastic  cords,  which  stretch  in  an  antero-posterior 
direction  from  the  front  to  the  back  wall  of  the  larynx,  form  the  ground-work  of 
the  true  vocal  cords.  Numerous  muscles  are  likewise  present.  These  operate 
upon  the  cartilages  of  the  larynx,  and  tliereby  not  only  bring  about  changes  in 
the  relative  position  of  the  true  vocal  cords,  but  also  produce  different  degrees  of 
tension  of  these  cords.  The  cavity  of  the  larynx  is  lined  with  mucous  membrane, 
under  which,  in  certain  localities,  are  collected  masses  of  mucous  glands. 

CARTILAGES  OF  THE  LARYNX. 

There  are  three  single  cartilages  and  three  pairs  of  cartilages  entering  into  the 
construction  of  the  laryngeal  wall.     They  are  named  as  follows : — 

,  rpi     .  •  1  f  Arytenoid. 

o-     1  , -1  I  ri  •     •  1  T)  ■     1        i.-i  )  Cornicula  larvngis,  or  the 

hmgle  cartilages  '   Cricoid.  raired  cartila^'es  <  ^..  "p  ^     . 

°  I  P   ■  1  tf  '  )       cartilages  of  Santormi. 

^  °         ' '  (  Cuneiform  cartilages. 

Thyroid  Cartilage  (cartilage  thyreoidea). — The  thyroid  cartilage,  the  largest 
of  the  laryngeal  cartilages,  is  formed  of  two  quadrilateral  plates  termed  the  alse, 
which  meet  in  front  at  an  angle,  and  become  fused  along  the  mesial  plane.  Behind, 
the  ahe  diverge  from  each  other,  and  enclose  a  wide  angular  space  which  is  open 
behind.  The  anterior  borders  of  the  alfe  are  only  fused  in  their  lower  parts.  Above 
they  are  separated  by  a  deep,  narrow  V-shaped  median  notch,  called  the  incisura 
thyroidea.  In  the  adult  male  the  angle  formed  by  the  meeting  of  the  anterior 
borders  of  the  two  ahe,  especially  in  its  upper  part,  is  very  projecting,  and  with  the 
margins  of  the  thyroid  notch,  which  lies  above,  constitutes  a  marked  subcutaneous 
prominence  in  the  neck,  which  receives  the  name  of  the  pomum  Adami. 

The  anglft  which  is  formed  by  the  meeting  of  the  two  alai  of  the  thyroid  cartilage  varies  to 
some  extent  in  different  individuals  of  the  same  sex,  and  shows  marked  differences  in  the  two 
sexes  and  at  different  periods  of  lite.  In  the  adult  male  the  average  angle  is  said  to  be  90° :  in 
the  adult  female  it  is  120^ ;  whilst  in  the  infant  the  ahe  meet  in  tlie  form  of  a  gentle  curve 
convex  to  tlie  front. 

The  posterior  hoarder  of  each  ala  of  the  tliyroid  cartilage  is  thick  and  rounded, 
and  is  prolonged  beyond  the  superior  and  inferior  borders  in  the  form  of  two  slender 
cylindrical  processes,  termed  cornua.  Tlie  superior  cornu  is  longer  than  the  inferior 
cornu.  It  is  directed  upwards,  with  a  slight  inclination  inwards  and  backwards, 
and  it  ends  in  a  rounded  extremity,  which  is  joined  to  the  tip  of  the  great  cornu  of 


CAETILAGES  OF  THE  LARYNX. 


959 


the  hyoid  bone  by  the  lateral  thyro-hyoid  ligament.     The  inferior  cornu  is  shorter 


As  it  pi'oceeds  downwards  it  curves  slightly 

Hyoid  bone        Epiglottis 


Cartilago  tiiticea 

Tliyro-hyoid 
irifiubranf-  -7 
Superior  cornu  of  / 
tliyroid  cartilage "7" 


Thyroid  uotcl 


Crico-tliyroid 
membrane 


Inferior  cornu  of 
tliyroid  cartilage' 


Cricoid  cartila: 


Fig. 


680. — The  Cartilages  and  Ligaments  of  the 
Larynx  viewed  from  the  Front. 


and  stouter  than  the  superior  cornu. 

inwards,  and  upon  the  inner  face  of 

its  extremity  it  shows  a  circular  flat 

facet,  by  means  of  which  it  articulates 

with  a  similar  facet  on  the  lateral 

aspect  of  the  cricoid  cartilage.     The 

superior  border  of  the  ala  is  for  the 

most   part    slightly  convex,   and   in 

front  it  dips  suddenly  down  to  become 

continuous  with   the  margin  of  the 

thyroid  notch.     Posteriorly,  where  it 

joius  the  superior  cornu,  it  exhibits 

a  shallow  notch  or  concavity.     The 

inferior  border  is  to  all  intents  and 

purposes  horizontal,  but  it  is  marked 

off  by  a  projection,  termed  the  inferior 

tubercle,  into  a  short   posterior  part, 

which  shows  a  shallow  concavity  in 

front    of   the  inferior  cornu,  and    a 

longer  part  which  lies  in  front  of  the 

tubercle,  which  is  also  concave,  but  to 

a  less  degree.     The  external  surface 

of  the  ala  is  divided  into  two  unequal 

areas    by   an   oblique    line   or   ridge. 

This  line  begins  above  at  the  superior 

tubercle,  a  prominence  situated  im- 
mediately below  the  superior  border,  and  a  short  distance  in  front  of  the  root  of 

the  superior  cornu.     From  this  the  oblique  line  proceeds  downwards  and  forwards, 

to  end  inferior ly  in  the  inferior  tubercle  on  the  lower  border  of  the  ala.     The  area 

which  lies  behind  the  oblique  line  is  much  smaller  than  that  which  lies  in  front. 

It  is  covered  by  the  inferior  constrictor  muscle 
of  the  pharynx.  The  larger  anterior  area  is  for 
the  most  part  covered  by  the  thyro-hyoid 
muscle.  To  the  oblique  line  are  attached  the 
sterno-thyroid  and  thyro-hyoid  muscles.  The 
i7iner  surface  of  the  ala  of  the  thyroid  cartilage 
is  smooth  and  slightly  concave. 

Cricoid  Cartilage  (cartilago  cricoidea). — 

-^ — ^- »^^ — — ■:-•  -  The  cricoid  cartilage  is  shaped  like  a  signet- 

^  \^     ^y^  ^  '^''''    '^^^      ring.     Behind,  there  is  a  broad,  thick  plate 

somewhat  quadrilateral  in  form  and  termed 
the  posterior  lamina  ;  whilst  in  front  and  later- 
ally, the  circumference  of  the  ring  is  com- 
pleted by  a  curved  band,  called  the  anterior 
arch.  The  lumen  of  the  ring  enclosed  by 
these  parts  is  circular  below,  but  above  the 
ring  is  compressed  laterally,  so  that  the  lumen 
becomes  elliptical.  The  superior  border  of 
the  posterior  lamina  presents  a  faintly-marked 
median  notch.  On  either  side  of  this  there  is 
an  oval  convex  facet  which  looks  more  out- 
wards than  upwards,  and  which  articulates 
with  the  base  of  the  arytenoid  cartilage.  The 
681.— Profile  View  of  the  Cartilages  posterior  surface  of  the  lamina  is  divided  by 
AND  Ligaments  of  the  Larynx.  an  elevated  median  ridge  into  two  depressed 

areas  which  give  attachment  to  the  posterior 

crico-arytenoid  muscles.     The  front  part  of  the  anterior  arch  of  the  cricoid  is  in 

the  form  of  a  narrow  band,  but  as  it  proceeds  backwards  towards  the  posterior 


Epiglottis 


Hyoid  bone 


Inferior  tubercle 
Inferior  cornu  of 
thyroid  cartilage 
Crico-thyroid 
membrane 
Cricoid  cartilage 


960 


THE  KESPIEATOKY  SYSTEM. 


lamina  its  superior  border  rises  rapidly,  and  in  consequence  the  arch  becomes  much 
broader.  The  inferior  border  of  the  cricoid  is  nearly  horizontal,  although  it 
frequently  presents  a  median  projection  in  front,  and  a  lateral  projection  on 
eitlier  side.  It  is  joined  to  the  tirst  ring  of  the  trachea  by  an  intervening  elastic 
membrane.  On  the  outer  surface  of  the  cricoid  cartilage,  at  the  place  where  the 
anterior  arch  joins  the  posterior  lamina,  a  vertical  ridge  descends  from  the 
arytenoid  articular  facet.  On  this,  a  shoi-t  distance  from  the  lower  border  of  the 
cartilage,  a  prominent  circular  articular  facet  is  visible  for  articulation  with  the 
inferior  cornu  of  the  thyroid  cartilage  (Fig.  683,  p.  963).  The  inner  surface '  of 
the  cricoid  cartilage  is  smooth,  and  is  lined  by  mucous  membrane. 

The  narrow  band-like  part  of  the  anterior  arch  of  the  cricoid  cartilage  lies 
below  the  lower  border  of  the  thyroid  cartilage,  whilst  the  posterior  lamina  is 
received  into  the  interval  between  the  posterior  portions  of  the  ahe  of  the  thyroid 
cartilage. 

Arytenoid  Cartilages  (cartilagines  arytsenoidese). — The  arytenoid  cartilages  are 
placed  one  on  either  side  of  the  mesial  plane,  and  rest  upon  the  u])per  border  of  the 

posterior  lamina  of  the  cricoid 
cartilage,  in  the  interval  between 
the  posterior  portions  of  the  alae  of 
the  thyroid  cartilage.  They  pre- 
sent a  somewhat  pyramidal  form. 
The  pointed  apex  or  summit  of  each 
is  directed  upwards,  and  at  the  same 
time  curves  backwards  and  inwards. 
It  supports  thecorniculumlaryngis. 
Of  the  three  surfaces,  one  looks 
directly  inwards  towards  the  cor- 
responding surface  of  the  opposite 
cartilage,  from  which  it  is  separated 
by  a  narrow  interval ;  another  looks 
backwards ;  whilst  the  third  is 
directed  outwards  and  forwards. 
The  internal  surface,  which  is  the 
smallest  of  the  three,  is  triangular 
in  outline.  It  is  narrow,  vertical, 
and  even,  and  is  clothed  by  the 
lining  mucous  membrane  of  the 
larynx.  The  posterior  surface  is 
smooth  and  concave  from  above 
downwards ;  it  lodges  and  gives 
attachment  to  the  arytenoideus 
transversus  muscle.  The  antero- 
external  surface  is  the  most  exten- 
sive of  the  three  (Fig.  683,  p.  963). 
Its  middle  part  is  marked  by  a  deep  depression  in  which  is  lodged  a  mass  of 
mucous  glands.  Upon  this  surface  of  the  arytenoid  cartilage  the  powerful  thyro- 
arytenoid muscle  is  inserted,  whilst  a  small  tubercle  a  short  distance  above  the 
base  gives  attachment  to  the  superior  thyro-arytenoid  ligament — the  feeble  sup- 
porting ligament  of  the  false  vocal  cord.  The  three  surfaces  of  the  arytenoid 
cartilage  are  separated  from  each  other  by  an  anterior,  a  posterior,  and  an  external 
border.  The  external  border  is  the  longest,  and  it  pursues,  as  it  is  traced  from  the 
apex  to  the  base,  a  sinuous  course.  Reaching  the  base  of  the  cartilage,  it  is  pro- 
longed outwards  and  Ijackwards  in  the  form  of  a  stout  prominent  angle  or  process, 
termed  the  processus  muscularis.  Into  the  front  of  this  process  is  inserted  the  crico- 
arytenoideus  lateralis  muscle  :  whilst  into  its  posterior  aspect  the  crico-arytenoideus 
posticus  muscle  is  inserted.  A  small  nodule  of  yellow  elastic  cartilage,  called 
the  sesamoid  cartilage,  is  frequently  found  on  the  external  border  of  the  arytenoid 
cartilage,  where  it  is  held  in  position  by  the  investing  perichondrium.  The 
anterior  border  of  the  arytenoid  is  vertical,  and  at  the  base  of  the  cartilage  is 


Cartilago  triticea 

Tliyro-epiglottideaii 
ligament 

Superior  cornu  of 
thyroid  cartilage 


Curtilage  of  Sautoriiii 
Arytenoid  cartilage 
Muscular  process  of 
arytenoid  cartilage 


Inferior  curuu  of 
thyroid  cartilage 


Fig.  682.- 


-Cautilages  and  Ligaments  of  Larynx, 
as  seen  from  beliind. 


JOINTS  AND  LIGAMENTS  OF  THE  LAEYNX.  961 

prolonged  horizontally  forwards  into  a  small  sharp-pointed  process  called  the  processus 
vocalis.  It  receives  this  name  because  it  gives  attachment  to  the  inferior  thyro- 
arytenoid ligament  or  supporting  band  of  the  true  vocal  cord.  The  base  of  the 
arytenoid  cartilage  presents  on  its  under  surface,  and  more  particularly  on  the 
under  surface  of  the  processus  muscularis,  an  elongated  concave  facet  for  articulation 
with  the  upper  border  of  the  posterior  lamina  of  the  cricoid  cartilage. 

Cartilages  of  Santorini  (cartilagines  corniculatse). — The  cartilages  of  Santorini, 
or  tlie  cornicula  laryngis,  are  two  minute  conical  nodules  of  yellow  elastic, cartilage 
which  surmount  the  apices  of  the  arytenoids,  and  prolong  the  upper  curved  ends  of 
these  cartilages  in  a  backward  and  inward  direction.  Each  cartilage  of  Santorini 
is  enclosed  within  the  posterior  part  of  the  corresponding  aryteno-epiglottidean 
fold  of  mucous  membrane. 

Cuneiform  Cartilages  (cartilagines  cuneiformes). — The  cuneiform  cartilages 
are  not  invariably  present.  They  are  two  minute  rod-shaped  pieces  of  yellow 
elastic  cartilage,  each  of  which  occupies  a  place  in  the  corresponding  aryteno- 
epiglottidean  fold  of  mucous  membrane  immediately  in  front  of  the  arytenoid 
cartilage  and  the  cartilage  of  Santorini.  On  the  superficial  surface  of  each  a 
collection  of  mucous  glands  is  present,  and  this  tends  to  make  the  cartilage  stand 
out  in  relief  under  the  mucous  membrane. 

Epiglottidean  Cartilage  (cartilago  epiglottica). — The  epiglottis  is  supported 
by  a  thin  leaf- like  lamina  of  yellow  fibro-cartilage  which  is  placed  behind  the 
root  of  the  tongue  and  the  body  of  the  hyoid  bone,  and  in  front  of  the  superior 
aperture  of  the  larynx.  When  divested  of  the  mucous  membrane,  which  covers  it 
behind  and  also  to  some  extent  in  front,  the  epiglottidean  cartilage  is  seen  to 
present  the  outline  of  a  bicycle- saddle,  and  to  be  indented  by  pits  and  pierced  by 
numerous  perforations.  In  the  former,  glands  are  lodged,  whilst  through  the  latter, 
blood-vessels  and  in  some  cases  nerves  pass.  The  broad  end  of  the  cartilage  is 
directed  upwards,  and  is  free.  Its  margins  are,  to  a  large  extent,  enclosed  within  the 
aryteno-epiglottidean  folds  of  mucous  membrane.  The  anterior  surface  is  only  free 
in  its  upper  part.  This  part  is  covered  with  mucous  membrane,  and  looks  towards 
the  pharyngeal  part  of  the  tongue.  The  posterior  surface  is  covered  throughout  its 
whole  extent  by  the  lining  mucous  membrane  of  the  laryngeal  cavity.  The  lower 
pointed  extremity  of  the  cartilage  is  carried  downwards  in  the  form  of  a  strong 
fibrous  band,  termed  the  thyro-epiglottidean  ligament. 

Ossification  of  the  Cartilages  of  the  Larynx. — The  thyroid  and  cricoid 
cartilages  and  the  greater  part  of  the  arytenoid  cartilages  are  composed  of  the  hyaline 
variety  of  cartilage.  The  apical  parts,  and  also  the  vocal  processes  of  the  arytenoid 
cartilages,  the  cartilages  of  Santorini,  the  cuneiform  cartilages,  and  the  epiglottis,  are 
formed  of  yellow  iibro-cartilage,  and  at  no  period  of  life  do  they  exhibit  any  tendency 
towards  the  ossific  change.  The  thyroid,  cricoid,  and  basal  portions  of  the  ai'vtenoids,  as 
life  advances,  become  more  or  less  completely  transformed  into  bone.  In  males  over 
twenty  years  of  age,  and  in  females  over  twenty-two  years  of  age,  the  process  wall  usually 
be  found  to  have  begun  (Chievitz).  It  is  impossible,  however,  by  an  examination  of  the 
laryngeal  cartilages,  to  form  an  estimate  of  the  age  of  the  individual,  although  in  old  age 
it  is  usual  to  find  the  thyroid,  cricoid,  and  the  hyaline  part  of  the  arytenoid  completely 
ossified.  It  would  appear  that  the  process  is  somewhat  slower  in  the  female  than  in  the 
male.  The  thyroid  is  the  first  to  show  the  change ;  then,  but  almost  at  the  same  time, 
the  cricoid,  and  lastly,  a  few  years  later,  the  arytenoid. 

JOINTS,  LIGAMENTS,  AND  MEMBRANES  OF  THE  LARYNX. 

Crico-thyroid  Joints  (articulationes  cricothyreoideffi). — These  are  diarthrodial 
joints,  and  are  formed  by  the  apposition  of  the  circular  facets  on  the  tips  of  the 
inferior  cornua  of  the  thyroid  cartilage  with  the  elevated  circular  facets  on  the 
sides  of  the  cricoid  cartilage.  A  capsular  hgament  is  thrown  around  each  articula- 
tion, and  this  is  lined  by  synovial  membrane.  On  the  posterior  aspect  of  the  joint 
a  strengthening  band  is  present  in  the  capsule.  The  movements  which  take  place 
at  th  ■  crico-thyroid  joints  are  of  a  twofold  character,  viz.  gliding  and  rotatory.  In 
the  first  case  the  thyroid  facets  glide  upon  the  cricoid  surfaces  in  different  directions. 
65 


962  THE  RESPIEATORY  SYSTEM. 

The  rotatory  movement  is  one  iu  which  the  thyroid  cartilage  rotates  to  a  slight 
extent  around  a  transverse  axis  which  passes  through  the  centre  of  the  two  joints. 

Crico- arytenoid  Joints  (articulationes  cricouryta^noideas). — These  also  are 
diarthrodial  articulations.  In  each  case  there  is  a  joint  cavity  surrounded  by  a 
capsular  ligament,  which  is  lined  by  a  synovial  membrane.  The  cricoid  articular 
surface  is  convex,  whilst  that  of  the  arytenoid  is  concave ;  both  are  elongated  or 
elliptical  in  form,  and  they  are  applied  to  each  other,  so  that  the  long  axis  of  the  one 
intersects  or  crosses  that  of  the  other  at  an  acute  angle.  In  no  position  of  the  joint 
do  the  two  surfaces  accurately  coincide — a  portion  of  the  cricoid  facet  is  always  left 
uncovered.  The  capsule  of  the  joint  is  strengthened  behind  by  a  band  which  is 
inserted  into  the  inner  and  back  part  of  the  base  of  the  arytenoid  cartilage,  and  plays 
a  somewhat  important  part  in  the  mechanism  of  the  joint ;  it  arrests  effectually 
excessive  forward  movement  of  the  arytenoid  cartilage. 

The  movements  which  take  place  at  the  crico-arytenoid  joint  are  of  a  twofold 
kind,  "siz.  gliding  and  rotatory.  The  ordinary  position  of  the  arytenoid  during  easy, 
quiet  breathing  is  one  in  which  it  rests  upon  the  outer  part  of  the  cricoid  facet. 
By  a  gliding  movement  it  can  ascend  upon  the  cricoid  facet,  and  advance  towards 
the  median  plane  and  its  fellow  of  the  opposite  side.  The  ghding  movements, 
therefore,  are  of  such  a  character  that  the  two  arytenoid  cartilages  approach  or 
retreat  from  each  other  and  the  mesial  plane.  In  the  rotatory  movement  the 
arytenoid  cartilage  revolves  around  a  vertical  axis.  By  this  movement  the  vocal 
process  is  swung  outwards  or  inwards,  so  as  to  open  or  close  the  rima  giottidis. 

The  joint  between  the  arytenoid  and  the  cartilage  of  Santorini  may  either 
partake  of  the  nature  of  an  amphiarthrosis  or  of  a  diarthrosis.  The  tips  of  the  two 
cornicula  laryngis  can  generally  be  made  out  to  be  connected  to  the  upper  border  of 
the  posterior  lamina  of  the  cricoid  cartilage  by  a  dehcate  Y-shaped  ligament  termed 
the  ligamentum  jugale. 

Thyro-hyoid  Membrane  (membrana  hyothyreoidea).^ — ^This  is  a  broad  mem- 
branous and  somewhat  elastic  sheet  which  occupies  the  interval  between  the  hyoid 
bone  and  the  thyroid  cartilage.  It  is  not  equally  strong  throughout.  It  presents 
a  central  thick  portion  and  a  cord-like  right  and  left  margin,  whilst  in  the  intervals 
between  these  it  is  thin  and  weak  (Figs.  680  and  681,  p.  959).  The  central  thickened 
part  (ligamentum  thyro-hyoideum  medium)  is  largely  composed  of  elastic  fibres. 
Below,  it  is  attached  to  the  margins  of  the  thyroid  notch,  whilst  above,  it  is  fixed 
to  the  posterior  aspect  of  the  upper  margin  of  the  body  of  the  hyoid  bone.  The 
upper  part,  therefore,  of  its  anterior  surface  is  placed  behind  the  j)osterior  hollowed- 
out  surface  of  the  body  of  the  hyoid  bone ;  a  synovial  bursa  of  variable  extent  is 
placed  between  them,  and  in  certain  movements  of  the  head  and  larynx  the  upper 
border  of  the  thyroid  cartilage  slips  upwards  behind  the  hyoid  bone.  On  either 
side  of  the  strong  central  part,  the  thyro-hyoid  membrane  is  thin  and  loose.  It  is 
attached  below  to  the  upper  border  of  the  thyroid  cartilage,  and  above  to  the 
posterior  aspect  of  the  great  cornu  of  the  hyoid  bone.  It  is  pierced  by  the  internal 
laryngeal  nerve  and  the  superior  laryngeal  vessels.  The  posterior  border  of  the 
thyro-hyoid  membrane  on  each  side  is  thickened,  round,  and  cord-like,  and  is  chiefly 
composed  of  elastic  fibres.  It  is  termed  the  ligamentum  thyro-hyoideum  laterale, 
and  extends  from  the  tip  of  the  great  cornu  of  the  hyoid  bone  to  the  extremity  of 
the  superior  cornu  of  the  thyroid  cartilage.  In  this  ligament  there  is  usually 
developed  a  small  oval  cartilaginous  or  bony  nodule  which  receives  the  name  of  the 
cartilage  triticea.  The  deep  surface  of  the  lateral  part  of  the  thyro-hyoid  membrane 
is  covered  by  the  pliaryngeal  mucous  membrane.  Behind  its  central  part  lies  the 
epiglottis,  but  separated  from  it  by  a  mass  of  adipose  tissue  (Fig.  686,  p.  966). 

Crico-thyroid  Membrane  (membrana  cricothyreoidea). — This  is  a  very  important 
structure,  which  must  be  considered  in  three  parts,  viz.  a  central  and  two  lateral, 
all  of  which  are  directly  continuous  with  each  other,  and  differ  only  in  the  nature 
of  their  superior  connexions.  The  central  part  of  the  crico-thyroid  membrane  i& 
strong,  tense,  and  elastic.  It  is  triangular  in  shape,  and  is  attached  by  its  broad 
Imse  10  the  upper  border  of  the  anterior  arch  of  cricoid  cartilage,  whilst  above,  it  is 
fixed  to  the  middle  part  of  the  lower  border  of  the  thyroid  cartilage  (Fig.  680,  p.  959). 
It  is  pierced  by  minute  apertures,  and  is  crossed  superficially  by  the  crico-thyroid 


JOINTS  AND  LIGAMENTS  OF  THE  LARYNX. 


963 


Arytenoid  cartilage 

M  uscular  process 


Vocal  process 


Riiiia  Klottidis 


I-igaiiieiit  of  true 

vocal  cord 

Lateral  part  of  crico- 

tliyroid  membrane 
Facet  on  cricoid  for  inferior 
cornu  of  thyroid  cartilage 


Cricoid  cartilage 


branch  of  the  superior  laryngeal  artery.  The  central  part  of  the  crico-thyroid  mem- 
brane, therefore,  closes  in  front  the  interval  between  the  cricoid  and  thyroid  cartilages. 
Tlie  lateral  part  on  each  side  presents  very  different  connexions.  It  is  not  attached 
to  the  lower  border  of  the  thyroid  cartilage,  but  slopes  upwards  and  inwards  within 
the  thyroid  ala,  and  thus  diminishes  materially  the  transverse  width  of  the  lower 
subdivision  of  the  laryngeal  cavity.  Its 
attachments  are  very  definite.  Below,  it 
is  fixed  to  the  upper  border  of  the  cricoid 
cartilage,  immediately  subjacent  to  the 
lining  mucous  membrane  of  the  larynx  ; 
above,  it  is  directly  continuous  with  the 
inferior  thyro-arytenoid  ligament  or  sup- 
porting band  of  the  true  vocal  cord.  This 
ligament,  indeed,  may  be  looked  upon 
as  constituting  the  upper  thickened  free 
border  of  the  lateral  part  of  the  crico- 
thyroid membrane.  In  front,  the  lateral 
part  of  the  crico-thyroid  membrane  is 
attached  to  the  lower  half  of  the  inner 
surface  of  the  ala  of  the  thyroid  cartilage, 
close  to  the  angle,  and  heliind,  to  the 
lower  border  of  the  processus  vocalis  of 
the  arytenoid  cartilage.  In  contact  with 
the  outer  surface  of  the  lateral  part  of  Fig.  683.— Dissectiox  to  show  the  Lateral  Part 
the  crico-thyroid  membrane,  and  separat-  o^  the  Crico-thyroid  Membrane.     The  right 

ing  it  from  the  thyroid  ala,  are  the  lateral         "^''^  °^  *^^"  '^'^^^'^^  '^'"^^■**^"-'^  ^'^' '""'''  '•"™°^'"'^- 
crico-aryteuoid  and  the  thyro-arytenoid  muscles ;  the  inner  surface  is  clothed  by 
the  lining  mucous  membrane  of  the  larynx. 

Inferior  Thyro-arytenoid  Ligament  (ligamentum  vocale).— This  is  formed 
in  connexion  with  the  upper  border  of  the  lateral  part  of  the  crico-thyroid 
membrane,  and  it  constitutes  the  supporting  ligament  of  the  true  vocal  cord.  It 
is  attached  in  front,  close  to  its  fellow  of  the  opposite  side,  to  the  middle  of  the 
angular  depression  between  the  two  al£e  of  the  thyroid  cartilage.  From  this  it 
stretches  backwards,  and  becomes  incorporated  with  the  tip  and  upper  border  of  the 
processus  vocalis  which  projects  forwards  from  the  base  of  the  arytenoid  cartilage. 
The  inferior  thyro-arytenoid  ligament  is  composed  of  yellow  elastic  fibres,  and 
embedded  in  its  anterior  extremity  there  is  frequently  a  minute  nodule  of  elastic 
cartilage.  Its  inner  border  is  sharp  and  free,  and  is  clothed  by  mucous  membrane, 
which  in  this  position  is  very  thin  and  tightly  bound  down  to  the  ligament. 

The  superior  thyro-arytenoid  ligament  (ligamentum  ventriculare)  supports 
the  false  vocal  cord.  It  is  weak  and  indefinite,  but  somewhat  longer  than  the 
preceding  ligament.  In  front  it  is  attached  to  the  angular  depression  between  the 
two  alee  of  the  thyroid  cartilage,  above  the  true  vocal  hgaments  and  close  to  the 
attachment  of  the  thyro-epiglottidean  hgament,  and  it  extends  backwards  to  be  fixed 
to  a  tubercle  on  the  antero-external  surface  of  the  arytenoid  cartilage,  a  short  dis- 
tance above  the  processus  vocahs.  It  is  composed  of  connective  tissue  and  elastic 
fibres  which  are  continuous  with  the  fibrous  tissue  in  the  aryteno-epiglottidean  fold. 

Epiglottidean  Ligaments. — The  epiglottis  is  bound  by  ligaments  to  the  base 
of  the  tongue,  to  the  wall  of  the  pharynx,  to  the  hyoid  bone,  and  to  the  thyroid 
cartilage.  The  glosso-epiglottidean  ligament  (plica  glosso-epiglottica  mediana)  is 
a  prominent  mesial  fold  of  mucous  membrane  which  proceeds  from  the  middle 
of  the  anterior  free  surface  of  the  epiglottis  to  the  base  of  the  tongue.  The 
pharyngo-epiglottidean  ligaments  or  folds  (plicae  glosso-epiglotticse  laterales)  are 
similar  mucous  folds  which  proceed  from  the  margins  of  the  epiglottis  in  an  upward 
direction  on  the  side  wall  of  the  pharynx.  Between  the  two  layers  of  mucous 
membrane  which  form  the  glosso-epiglottidean  and  pharyngo-epiglottidean  folds 
there  is  a  certain  amount  of  elastic  tissue.  By  the  three  folds  the  depression 
between  the  root  of  the  tongue  and  the  epiglottis  is  marked  off  into  two  fossae 
termed  the  valleculae. 
65  a 


964 


THE  EESPIEATOEY  SYSTEM. 


The  hyo-epiglottidean  ligament  (ligamentimi  hyoepigiotticum)  is  a  short,  broad 
elastic  Land,  someNyhat  broken  up  by  adipose  tissue,  which  connects  the  anterior 
face  of  the  epiglottis  to  the  upper  border  of  the  hyoid  bone  (Fig.  686,  p.  966).  The 
thyro-epiglottidean  ligament  (ligamentnm  thyreoepiglotticum)  is  strong  and  thick 
(Fig.  682,  p.  960).  Composed  mainly  of  elastic  tissue,  it  proceeds  downwards  from 
the  lower  pointed  extremity  of  the  epiglottis,  and  is  attached  to  the  angular 
depression  between  the  two  alas  of  the  thyroid  cartilage  below  and  behind  the 
median  notch. 

A  triangular  interval  is  left  between  the  anterior  face  of  the  epiglottis  and  the 
thyro-hyoid  membrane.  This  is  imperfectly  closed  above  by  the  hyo-epiglottidean 
ligament,  and  contains  a  pad  of  soft  fat  (Fig.  686,  p.  966). 

INTERIOR  OF  THE  LARYNX. 


The  cavity  of  the  larynx  is  smaller  than  might  be  expected  from  an  inspection 
of  its  exterior.  On  looking  into  its  interior  through  the  superior  aperture  it  is 
seen  to  be  subdivided  into  three  portions  by  two  elevated  folds  of  mucous  membrane 
which  extend  from  before  backwards,  and  project  inwards  from  each  side-wall  of  the 
cavity.  The  upper  pair  of  folds  are  the  false  vocal  cords  ;  the  lower,  more  definite 
pair,  are  the  true  vocal  cords  (Fig.  684).  The  latter  are  the  chief  agents  in  the 
production  of  the  voice,  and  the  larynx  is  so  constructed  that  changes  in  their 
relative  position  and  in  their  degree  of  tension  are  brought  about  by  the  action  of 
the  muscles  and  the  recoil  of  the  elastic  ligaments. 

Superior  Aperture  of  the  Larynx  (aditus  laryngis). — This  is  a  large  obliquely- 
placed  opening  which  slopes  rapidly  from  above  downwards  and  backwards  and 
looks  backwards  into  the  upper  part  of  the  laryngeal  portion  of  the  pharynx.  Some- 
what triangular  in  outhne, 
the  basal  part  of  the  aper- 
ture, placed  above  and  in 
front,  is  formed  by  the  free 
border  of  the  epiglottis. 
Behind,  the  opening  rapidly 
narrows,  and  finally  ends 
in  the  interval  between  the 
two  arytenoid  cartilages. 
The  sides  of  the  aperture 
are  formed  by  two  sharp 
and  prominent  folds  of 
mucous  membrane  called 
the  aryteno  -  epiglottidean 
Cuneiform  tubercle  folds  (pHcai  aryepiglotticse), 
which  stretch  between  the 
lateral  margins  of  the  epi- 
glottis in  front  and  the 
arytenoid  cartilages  behind. 
The  aryteno  -  epiglot- 
tidean folds  enclose  between 
the  two  layers  of  mucous 
membrane    which   compose 

Fig.   684.— Supkiuor  Aperture  op  Larynx,    exposed  by  laying  open  ^^Jjqjj^      some     connective 
the  pharynx  from  behind.  ,  .  i  r>i  i 

tissue,  muscular  fibres  be- 
longing to  the  aryteno-epiglottidean  muscles,  and  in  their  posterior  parts  the 
cuneiform  cartilages  and  the  cornicula  laryngis  which  surmount  the  arytenoid 
cartilages.  These  small  nodules  of  cartilage  raise  the  hinder  part  of  the  aryteno- 
epiglottidean  fold  in  the  form  of  two  rounded  eminences,  termed  respectively  the 
cuneiform  tubercle  (tuberculum  cuneiforme)  and  the  tubercle  of  Santorini  (tuberculum 
corniculatum). 

On  either  side  of  the  posterior  and  lower  part  of  the  laryngeal  opening  there  is, 
in  the  pharynx,  a  small  downwardly-directed  recess  which  presents  a  wide  entrance. 


Riiiia 
glottidis 
Pyriforiu 
sinus 
Superior 
cornu  of 
tliyroid 

Pharyngeal 
wall  (cut) 


Glosso- 

epiglottideau 

lieament 


Vallecula 

Pliaryngo- 
epiglottideau 
ligament 
Epiglottis 

Cushion  of  epiglotti 

Ai-j'teno- 
epiglottideau  fold 
Laryngeal  sinus 

False  vocal  cord 


Tubercle  of 
Santorini 


Posterior  aspect  of 
ciicoid  cartilage 


INTERIOR  OF  THE  LARYNX. 


9G5 


Hyoid  bone 


True  vocal 
cord 
Thyro- 
arytenoid 
muscle 

tUicoid 
fartilage 


but  rapidly  narrows  towards  the  bottom.  It  is  termed  the  sinus  pyriformis,  and  is  of 
importance  to  the  surgeon,  because  foreign  bodies  introduced  into  the  pharynx  are 
Hable  to  be  caught  in  this  little  pocket.  On  the  inner  side  the  sinus  pyriformis,  is 
bounded  by  the  arytenoid  cartilage  and  the  aryteno-epiglottidean  fold,  whilst  on 
the  outer  side  it  is  limited  by  the  inner  surface  of  the  ala  of  the  thyroid  cartilage, 
clothed  by  the  pharyngeal  mucous  membrane. 

Upper  Subdivision  of  the  Laryngeal  Cavity  (vestibulum  laryngis). — The 
upper  subdivision  of  the  laryngeal  cavity  extends  from  the  superior  opening  of  the 
larynx  down  to  the  false  vocal  cords.  In  its 
lower  part  it  exhibits  a  marked  lateral  com- 
pression. Its  width,  therefore,  diminishes  from 
above  downwards,  whilst,  owing  to  the  obliquity 
of  the  upper  aperture  of  the  larynx,  its  depth 
rapidly  diminishes  from  before  backwards.  In 
front  it  is  bounded  by  the  posterior  surface  of 
the  epiglottis,  clothed  by  mucous  membrane. 
This  wall  descends  obliquely  from  above  down- 
wards and  forwards,  and  becomes  narrower  as  it 
approaches  the  anterior  ends  of  the  false  vocal 
cords.  The  upper  part  of  the  posterior  surface 
of  the  epiglottis  is  convex,  owing  to  the  manner 
in  which  the  upper  margin  is  curved  forwards 
towards  the  tongue ;  below  this  there  is  a 
slight  concavity,  and  still  lower  a  marked  bulg- 
ing or  convexity  over  the  upper  part  of  the 
thyro-epiglottidean  ligament.  This  swelling  is 
called  the  cushion  or  tubercle  of  the  epiglottis 
(tuberculum  epigiotticum),  and  it  forms  a  con- 
spicuous object  in  laryngoscopic  examinations 
of  the  larynx.  The  lateral  vjall  of  the  upper 
compartment  or  vestibule  of  the  larynx  is  formed 
by  the  inner  surface  of  the  aryteno-epiglottidean 
fold.  For  the  most  part  it  is  smooth  and 
slightly  concave,  and  it  diminishes  considerably 
in  vertical  depth  as  it  passes  backwards.  In  its 
posterior  part  the  mucous  membrane  stands  out  in  two  elongated  vertical  elevations 
placed  one  behind  the  other  (Fig.  686,  p.  966).  The  anterior  elevation  is  formed 
by  the  subjacent  cuneiform  cartilage  with  the  mass  of  glands  associated  with 
it ;  the  posterior  elevation  is  produced  by  the  anterior  margin  of  the  arytenoid 
cartilage  and  the  cartilage  of  Santorini.  A  shallow  groove  (philtrum  ventriculi  of 
Merkel)  descends  between  these  rounded  elevations,  and  terminates  below  by 
running  into  the  interval  between  the  false  and  true  vocal  cords.  The  anterior 
elevation  comes  to  an  end  below  in  the  posterior  extremity  of  the  false  vocal  cord ; 
the  arytenoid  or  posterior  elevation,  in  its  inferior  part,  bends  round  the  hinder  end 
of  the  ventricle  of  the  larynx  and  becomes  lost  in  the  true  vocal  cord.  The  posterior 
wall  of  the  laryngeal  vestibule  is  narrow,  and  corresponds  to  the  interval  between 
the  upper  parts  of  the  two  arytenoid  cartilages.  Its  width,  to  a  large  extent,, 
depends  on  the  position  of  these  cartilages,  and  when  they  are  placed  near  each  othei 
the  mucous  membrane  which  covers  this  wall  is  thrown  into  longitudinal  folds. 

Middle  Subdivision  of  the  Laryngeal  Cavity. — The  middle  compartment  of 
the  larynx  is  much  the  smallest  of  the  three.  It  is  bounded  above  by  the  false 
vocal  cords  and  below  by  the  true  vocal  cords,  whilst  it  communicates  between 
these  folds  with  the  vestibule  on  the  one  hand  and  the  inferior  compartment  of 
the  larynx  on  the  other. 

The  false  vocal  cords  (plicse  ventriculares)  are  two  prominent  mucous  folds 
which  extend  from  before  backwards  on  the  side  walls  of  the  laryngeal  cavity.  In 
front  they  reach  the  angle  between  the  two  alas  of  the  thyroid  cartilage,  but  behind 
they  do  not  extend  so  far  as  the  posterior  wall  of  the  larynx.  They  come  to  an 
end  on  each  side  at  the  lower  end  of  the  elongated  swelling  produced  by  cuneiform 
65  & 


Fig.  685. — Coronal   Section  through 
Larynx,  to  show  its  three  compartments. 


966 


THE  RESPIEATORY  SYSTEM. 


cartilage.     The  false  vocal  cord  is  soft  and  somewhat  tiaccid,  aud  presents  a  tree 
border  which  is  slightly  arched— the  concavity  looking  downwards.     Within  the 

fold  of  mucous  membrane  which  forms  this 
cord  are  contained  :  (1)  the  feeble  superior 
thyro-arytenoid  hgament ;  (2)  numerous 
glands  which  are  chieliy  aggregated  in  its 
middle  part ;  and  (3)  a  few  muscle  fibres. 

The  interval  between  the  false  vocal 
cords  is  sometimes  termed  the  false  glottis 
(glottis  spuria),  and  is  considerably  wider 
than  the  interval  between  the  true  vocal 
cords,  which  is  called  the  true  glottis  (glottis 
vera)  or  rima  glottidis.  It  follows  from  this 
that  when  the  cavity  of  the  larynx  is 
examined  from  above  the  four  cords  are 
distinctly  visible,  but  when  examined  from 
below  the  true  vocal  cords  alone  can  be 


Hyoid  boue 

Hyo-epiglottidean  ligament 


Cartilage  of  epiglottis 
Fatty  pad 
Tbyro-liyoid  membrane 


Thyroid  cartilage 
^  Elevation  produced  by 
'  cuneifonn  cartilage 

False  vocal  cord 

Philtrum  ventriculi 
Elevation  produced 
by  arytenoid  cartilage 
Laryngeal  sinus 

True  vocal  cord 

Arytenoid  muscle 

Processus  vocalis 


seen. 


Cricoid  cartilage 
Cricoid  cartilage 


Fig.  686.— Mesial  Section  through  Larynx 
to  show  the  outer  wall  of  the  right  half. 


The  true  vocal  cords  (plicae  vocales), 
placed  below  the  false  cords,  extend  from 
the  angle  between  the  alse  of  the  thyroid 
cartilage  in  front  to  the  vocal  processes  of 
the  arytenoid  cartilages  behind.  The  true 
vocal  cord  is  sharp  and  prominent,  and  the 
mucous  membrane  which  is  stretched  over 
it  is  very  thin  and  firmly  bound  down  to 
the  subjacent  ligament.  In  colour  it  is 
pale,  almost  pearly  white,  whilst  posteriorly 
the  point  of  the  processus  vocalis  of  the 
arytenoid,  which  stands  out  clearly  in  relief, 
presents  a  yellowish  tinge.  In  cross-section 
the  true  vocal  cord  is  prismatic  in  form,  and 
its  free  border  looks  upwards  as  weU  as  inwards. 

The  true  vocal  cords  are  the  agents  by  means  of  which  the  voice  is  produced. 
The  false  vocal  cords  are  of  little  import- 
ance in  this  respect;    indeed,  they  can  />7y2iV<X/'''''yi'oid cartilage 
in  great  part  be  destroyed  and  no  ap- 
preciable difference  in  the  voice  result. 

Glottis  vera  (rima  glottidis).— This 
name  is  applied  to  the  elongated  fissure  by 
means  of  which  the  middle  compartment 
of  the  larynx  communicates  with  the 
lower  compartment.  It  is  placed  some- 
what below  the  middle  of  the  laryngeal 
cavity,  of  which  it  constitutes  the  nar- 
rowest part.  In  front  it  corresponds  to 
the  interval  between  the  true  vocal 
cords ;  behind,  it  corresponds  to  the 
interval  between  the  bases  and  vocal 
processes  of  the  arytenoid  cartilages.  It 
is  composed,  therefore,  of  two  distinct 
parts:  (1)  a  narrow  anterior  portion, 
between  the  true  vocal  cords,  involving 
more  than  half  of  its  length,  and  called  the 
glottis  vocalis  (pars  intermembranacea) ; 

f2)    a    broader,    shorter    portion,    between    a.  Duriug  ordimiry  easy  breatliing 

the  arytenoid  cartilages,  and  t(irmed  the 
glottis  respiratoria  (pars  intercartilaginea).     By  changes  in  the  position  of  the  ary- 
tenoid cartilages  the  form  of  the  rima  glottidis  undergoes  constant  alterations.     In 


Inferior  thyro- 
arytenoid ligament 


Vocal  process 
of  arytenoid  " 
cartilage 


Fig.  687. — Diagram  of  IIi.ma  Glottidis. 


B.  Widely  open. 


IXTEEIOR  or  THE  LARYNX.  967 

ordinary  easy  breathing  it  is  somewhat  lanceolate  in  outline.  The  glottis  vocalis 
presents  under  these  conditions  the  form  of  an  elongated  triangle  with  the  base 
directed  backwards,  and  corresponding  to  an  imaginary  line  drawn  between  the 
points  of  the  vocal  processes  of  the  arytenoid  cartilages,  wiiilst  the  glottis  respira- 
toria  is  somewhat  quadrangular.  When  the  glottis  is  opened  widely  the  broadest 
part  of  the  fissure  is  at  the  extremities  of  the  vocal  processes  of  the  arytenoids, 
and  here  the  side  of  the  rima  presents  a  marked  angle.  The  two  vocal  cords,  on 
the  other  hand,  may  be  approximated  to  each  other  so  closely,  as  in  singing  a  high 
note,  that  the  glottis  vocalis  is  reduced  to  a  linear  chink. 

The  length  of  the  rinia  glottidis  differs  very  con-siderably  in  the  two  sexes,  and  upon  this 
depends  the  different  character  of  the  voice  in  the  male  and  female.  According  to  Moura,  the 
following  are  the  average  measurements  in  the  quiescent  condition  of  the  rima  : — 

Male — Length  of  entire  rima  glottidis,  (  glottis  vocalis,  15'5  mm. 

23  mm. \  glottis  respiratoria,  7'5  mm. 

Female — Length  of  entire  rima  glottidis,  j  glottis  vocalis,  11'5  mm. 

17  mm. \  glottis  respiratoria,  5'5  mm. 

By  stretching  the  vocal  cords,  however,  the  length  of  the  liraa  glottidis  in  the  male  may 
be  increased  to  27'5  mm.,  and  in  the  female  to  20  mm. 

The  position  of  the  rima  glottidis  may  be  indicated  on  the  surface  by  marking  a  point  on  the 
middle  line  of  the  neck  8-5  mm.  below  the  bottom  of  the  thyroid  notch  in  the  male  and  6"5  mm. 
in  the  female.     This  is  the  average  position  (Taguchi). 

Laryngeal  Sinus  (ventriculus  laryngis). — The  side  wall  of  the  larnyx,  in  the 
interval  between  the  false  and  the  true  vocal  cords,  exhiljits  a  marked  pocket-like 
depression  or  recess  called  the  laryngeal  sinus.  The  recess  passes  upwards  so  as 
to  undermine  somewhat  the  false  vocal  cord,  and  its  mouth  is  somewhat  narrower 
than  its  cavity.  In  front  it  reaches  forwards  to  the  angle  between  the  alee  of  the 
thyroid  cartilage,  whilst  behind  it  ends  at  the  anterior  border  of  the  arytenoid 
cartilage. 

Under  cover  of  the  forepart  of  tlie  false  vocal  cord  a  small  slit-like  aperture 
may  be  detected  ;  this  leads  upwards  from  the  laryngeal  sinus  into  a  small  diverti- 
culum of  mucous  membrane,  termed  the  laryngeal  saccule  (appendix  ventriculi) 
which  ascends  between  the  false  vocal  cord  and  the  ala  of  the  thyroid  cartilage. 
The  laryngeal  saccule  is  of  variable  extent,  but  as 
a  rule  it  ends  blindly  at  the  level  of  the  upper 
border  of  the  thyroid  cartilage. 

Sometimes  the  saccule  extends  much  higher,  and  may 
even  reach  the  hinder  part  of  the  great  coruu  of  the 
hyoid  bone.  This  is  of  interest  when  considered  in 
connexion  with  the  extensive  larnygeal  pouches  of  the 
anthropoid  apes. 

Lower  Compartment  of  the  Laryngeal  Cavity. 

— This  leads  directly  downwards  into  the  trachea. 

Above  it  is  narrow  and  compressed  laterally,  but 

it  gradually  widens  out  until,  in  its  lowest  part,  it 

becomes  circular,  in  correspondence  with  the  trachea 

with  which  it  is  continuous.     It  is  bounded  by  the  Fig.  688.— specimen  showing  a  great 

sloping  inner  surfaces  of  the  crico-thyroid  membrane       Extension  of  the  Saccule  of  the 

and  by  the  inner  aspect  of  the  cricoid  cartilage — 

both  covered  by  smooth  mucous  membrane.     In  the  operation  of  laryngotomy  the 

opening  is  made  through  the  anterior  wall  of  this  compartment. 

Mucous  Membrane  of  the  Larynx. — The  mucous  membrane  which  Lines  the 
larynx  is  continuous  above  with  that  lining  the  pharynx,  and  below  with  mucous 
membrane  of  the  trachea.  Over  the  posterior  surface  of  the  epiglottis  it  is  closely 
adherent,  but  elsewhere,  above  the  level  of  the  true  vocal  cords,  it  is  loosely 
attached  by  submucous  tissue  which  extends  into  the  aryteno-epiglottidean  folds. 
As  it  passes  over  the  true  vocal  cords  the  mucous  membrane  is  very  thin,  and  is 
tightly  bound  down. 

It  is  important  to  bear  these  facts  in  mind,  because  in  certain  inflammatory  conditions  the  lax 
submucous  tissue  in  the  upper  jiart  of  the  lar^Tix  is  liable  to  become  infiltrated  with  fluid,  pro- 


968 


THE  EESPIRATOKY  SYSTEM. 


ducing  what  is  known  as  oedema  glottidis.  This  may  proceed  so  far  as  to  cause  occlusion  of  the 
upper  part  of  the  cavity.  The  close  adhesion  of  the  mucous  membrane  to  the  true  vocal  cords, 
however,  prevents  the  oedema  extending  beyond  the  level  of  the  rima  glottidis,  and  the  surgeon 
is  thus  able  to  relieve  the  patient  by  making  an  opening  through  the  front  part  of  the  crico- 
thyroid membrane  into  the  lower  compartment  of  the  larynx. 

Above  the  level  of  the  rima  glottidis  the  laryngeal  mucous  membrane  is 
extremely  sensitive,  and  when  touched  by  a  foreign  body  there  is  an  immediate 
response  in  the  shape  of  an  explosive  cough.  In  the  lower  compartment  of  the 
larynx  the  mucous  membrane  is  lined  by  columnar  ciliated  epithelium.  Over  the 
true  vocal  cords  this  is  replaced  by  squamous  epithelium.  In  the  middle  compart- 
ment and  in  the  lower  part  of  the  vestibule  of  the  larynx  the  columnar  ciliated 
epithelium  again  reappears.  The  upper  part  of  the  epiglottis  and  the  upper  parts 
of  the  side  walls  of  the  vestibule  are  covered  by  squamous  epithelium  similar  to 
that  present  in  the  mouth  and  pharynx. 

The  mucous  membrane  of  the  larynx  has  a  plentiful  supply  of  acinose  glands, 
and  in  only  one  place,  viz.  over  the  surface  of  the  true  vocal  cords,  are  these  com- 
pletely absent.  For  the  most  part  the  glands  are  aggregated  in  groups.  The 
following  are  the  localities  in  which  these  groups  are  especially  noticeable  : — (1)  On 
the  dorsal  surface  of  the  epiglottis,  many  of  the  glands  piercing  the  cartilage ;  (2) 
around  the  cuneiform  cartilage,  where  they  are  chiefly  responsible  for  the  elongated 
elevation  seen  in  this  part  of  the  wall  of  the  vestibule ;  (3)  in  the  false  vocal  cord, 
and  over  the  wall  of  the  laryngeal  sinus  and  the  laryngeal  saccule. 


LARYNGEAL  MUSCLES. 

Under  this  heading  we  do  not  include  all  the  muscles  which  are  attached  to 
the  cartilages  of  the  larynx.  Thus  the  inferior  constrictor  muscles  of  the  pharynx, 
although  attached  to  both  cricoid  and  thyroid  cartilages,  and  the  stylo-pharyngeus 
muscle  on  each  side,  although  inserted  in  part  into  the  thyroid  cartilage,  properly 
belong  to  the  pharynx.  Of  the  laryngeal  muscles  proper  two  are  attached  to  the 
oblique  line  of  the  thyroid  cartilage  (viz.  the  sterno-thyroid  and  thyro-hyoid),  and 
are  concerned  in  producing  movements  of  the  larynx  as  a  whole.  These  are  termed 
the  extrinsic  muscles  of  the  larynx,  and  have  been  already  described  (p.  412).  The 
intrinsic  muscles  of  the  larynx  are  a  group  of  small  muscles  which  help  to  build  up 
the  laryngeal  wall,  and  which,  by  their  contraction,  move  the  laryngeal  cartilages 
on  each  other.  One  passes  between  the  cricoid  and  thyroid  cartilages — the  crico- 
thyroid muscle ;  two  pass  between  the  cricoid  and  arytenoid  cartilages — the  crico- 
arytenoideus  posticus  and  crico-arytenoideus  lateralis  :  one,  in  each  lateral  wall  of  the 
larynx,  under  cover  of  the  ala  of  the  thyroid  cartilage,  passes  between  the  thyroid  and 
the  arytenoid  cartilages— the  thyro-arytenoid.     These  muscles  are  in  pairs.     One 

muscle  only,  which  connects  the  two  arytenoid 
cartilages,  and  which  is  termed  in  consequence  the 
arytenoideus,  is  single.  In  addition  to  these,  some 
muscular  fibres  which  enter  the  aryteno-epiglotti- 
dean  fold  and  reach  the  epiglottis  require  to  be 
considered.  These  constitute  the  thyro-ary-epi- 
glottidean  muscle. 

The  crico  -  thyroid  muscle  (musculus  crico- 
thyreoideus)  is  placed  on  the  cricoid  cartilage,  and 
bridges  over  the  crico-thyroid  interval.  Taking 
origin  from  the  lower  border  and  outer  surface  of 
the  anterior  arch  of  the  cricoid  cartilage,  its  fibres 
spread  out  in  an  upward  and  backward  direction, 
and  are  inserted  into  the  inner  surface  and  lower 
margin  of  the  thyroid  cartilage,  and  also  into  the 
anterior  aspect  of  its  inferior  cornu.  As  a  general 
rule  it  is  divided  into  two  parts,  viz. :  (1)  an  anterior 
or  oblique  part,  composed  of  those  fibres  which  are 
inserted  into  the  ala  of  the  thyroid  cartilage ;  and 
(2)  a  posterior  or  horizontal  part  formed  of  those  fibres  which  are  inserted  into  the 


Obliqui 


Horizontal 


Fig. 


).— The  Crico-Thykoid  Musclk. 


LAKYNGEAL  MUSCLES. 


969 


inferior  cornu  of  the  thyroid  cartilage.  It  is  closely  associated  with  the  inferior 
constrictor  muscle  of  the  pharynx,  and  sometimes  shows  a  certain  amount  of  con- 
tinuity with  it. 

The  posterior  crico-arytenoid  muscle  (musculus  cricoarytaenoideus  posterior) 
is  somewhat  fan-shaped  (Fig.  691,  p.  970).  It  springs  by  a  broad  origin  from  the 
depression  which  is  present  on  the  posterior  lamina  of  the  cricoid  cartilage  on  each 
side  of  the  mesial  ridge,  and  its  fibres  converge  to  be  inserted  into  the  posterior 
surface  of  the  processus  muscularis  of  the  arytenoid  cartilage.  In  pursuing  its 
upward  and  outward  course  on  the  back  of  the  cricoid  cartilage  its  fibres  show 
different  degrees  of  obliquity.  The  uppermost  fibres  are  short  and  nearly  horizontal ; 
the  intermediate  fibres  are  the  longest,  and  are  very  oblique ;  whilst  the  lowest 
fibres  are  almost  vertical  in  their  direction. 

The  lateral  crico-arytenoid  muscle  (musculus  cricoarytsenoideus  lateralis)  is 
triangular  in  form  and  smaller  than  the  preceding  muscle  (Fig.  690).  It  springs 
from  the  upper  border  of  the  lateral  part  of  the  anterior  arch  of  the  cricoid  as  far 
back  as  the  facet  which  supports  the  base  of  the  arytenoid  cartilage.  A  few  of  its 
fibres  also  take  origin  from  the  lateral  part  of  the  crico-thyroid  membrane,  to  which 
its  deep  surface  is  applied.  From  this  attachment  its  fibres  run  backwards  and 
upwards,  and  converge  to  be  inserted  into  the  anterior  surface  of  the  processus 
muscularis  of  the  arytenoid  cartilage.  The  superficial  or  outer  surface  of  this 
muscle  is  covered  by  the  lower  jiart  of  the  ala  of  the  thyroid  cartilage  and  by  the 
upper  part  of  the  crico-thyroid  muscle. 

The  thyro-arytenoid  muscle  (musculus  thyi-eoarytsenoideus)  is  placed  in  the 
lateral  wall  of  the  larynx  under  cover  of  the  ala  of  the  thyroid  cartilage  (Fig.  690). 
Its  lower  border  is  contiguous  with,  and  generally  inseparably  blended  with, 
the  upper  margin  of  the  lateral  crico-arytenoid  muscles,  so  that  the  two  muscles 
form  a  more  or  less  continuous  sheet.  The  thyro-arytenoid  muscle  is  usually 
described  as  consisting  of  a  superficial  and  a  deep  part,  termed  respectively  the 
thyro-arytenoideus  externus  and  the  thyro-arytenoideus  internus.  As  a  rule  these 
parts  are  more  or  less  completely  united,  and  can  only  be  isolated  from  each 
other  by  artificial  means. 

The  thyro-arytenoideus  externus  is  a  broad  muscular  layer  which  Hes  immediately 
subjacent  to  the  ala  of  the  thyroid  ^  .^j    .^ 

cartilage.    ItslowerborderisinCOn-  ^^^.     "  Arj-teno-epiglottidean  muscle 

tact  with  the  lateral  crico-arytenoid 
muscle,  whilst  its  upper  border  is 
placed  at  a  higher  level  than  the 
true  vocal  cord.  The  upper  part 
of  the  muscle  is  therefore  in  rela- 
tion to  the  wall  of  the  sinus  of  the 
larynx.  The  thyro-arytenoideus 
externus  arises  in  front  from  the 
lower  half  of  the  inner  surface  of 
the  ala  of  the  thyroid  cartilage, 
close  to  the  angle,  and  also  from 
the  lateral  part  of  the  crico- 
thyroid membrane,  on  which  it  to 
some  extent  lies.  Its  fibres  pass 
backwards,  and  are  inserted  into 
the  outer  border  and  muscular 
process  of  the  arytenoid  cartilage, 
a  certain  number,  however,  turning 
round  this  cartilage,  and  becom- 
ing continuous  with  the  transverse 
fibres  of  the  arytenoideus  muscle. 
A  considerable  number  of  the 
uppermost  fibres  of  the  thp-o- 
arytenoideus  externus,  as  they  pro- 
ceed  backwards,  curve  upwards  so  as    to  form  a  thin  band  which   reaches  the 


Hyoid 

Cuneiform  cartilage 


Thyro-epiglottidean  muscle 
Thyro-hyoid  membrane 

Saccule  of  larj'nx 
Muscular  process  of 
arytenoid  cartilage 

Thyro-arytenoid  muscle 
Thyroid  cartilage 


Crico-arytenoideus  lateralis 


— Crico-arytenoideus  posticus 
Crico-thvroid  membrane 


Cricoid  cartilage 


Fig.  690. — Dissection  of  the  Muscles  in  the  Lateral 

W^ALL    OF    THE    LARTNX. 

The  right  ala  of  the  th-SToid  cartilage  has  been  removed. 


970 


THE  EESPIEATOEY  SYSTEM. 


aryteno-epiglottidean    fold  aud  the  margin  of   the    epiglottis.     These   constitute 
the  thyro-epiglottidean  muscle. 

The  thyro-arytenoideus  internus  is  a  slender,  three-sided,  muscular  band  which 
is  applied  to  the  outer  aspect  of  the  true  vocal  cord,  and  receives  its  prismatic  form 
from  this  adaptation.  It  arises  in  front  from  the  angular  depression  between  the 
two  alee  of  the  thyroid  cartilage,  and  is  inserted  behind  into  the  outer  aspect  of  the 
processus  vocalis  and  also  into  the  adjoining  depressed  part  of  the  antero-external 
surface  of  the  arytenoid  cartilage.  The  thyro-arytenoideus  internus  is  somewhat 
thicker  behind  than  in  front.  This  is  due  to  the  fact  that,  whilst  all  the  fibres 
which  compose  it  are  attached  to  the  arytenoid  cartilage,  only  a  certain  proportion 
obtain  attachment  in  front  to  the  thyroid  cartilage.  A  large  number  of  the  deeper 
fibres  are  directly  fixed  at  different  points  to  the  outer  side  of  the  true  vocal  cord. 
These  constitute  the  ary- vocalis  muscle  (Ludwig). 

The  tliyro-arytenoideus  is  a  complicated  muscle,  and  the  above  description  can  only  be 
regarded  as  conveying  in  a  general  way  what  may  be  regarded  as  the  more  nsual  arrangement 
of  its  fibres.  It  is  subject  to  much  variation  and  to  very  different  degrees  of  development  in 
different  individuals.  As  a  rule  it  is  possible  to  trace  from  both  parts  of  the  muscle  fibres 
A\'hich  are  carried  obliquely  upwards  over  the  larjaigeal  sinus,  and  to  some  extent  also  over  the 
sacculus  laryngis.  Further  an  additional  part,  termed  the  small  or  superior  thyro-arytenoideus, 
is  as  a  rule  i^resent  (93  per  cent  according  to  Sewell).  This  is  a  slender  band  which  arises  from  the 
inner  asjject  of  the  ala  of  the  thyroid  cartilage  close  to  the  notch,  and  joasses  backwards  and 
downwards  to  find  insertion  into  the  lateral  border  of  the  arytenoid  cartilage  immediately  above 
the  processus  muscularis. 

The  arytenoideus  muscle  is  composed  of  two  portions — a  superficial  part, 
termed  the  arytenoideus  obliquus,  and  a  deeper  part,  called  the  arytenoideus 
transversus. 

The  arytenoideus  obliquus  consists  of  two  Jumdles  of  muscular  fibres,  each  of 
which  springs  from  the  posterior  aspect  of  the  muscular  process  of  the  arytenoid 
cartilage.  From  these  points  the  two  fleshy  slips  proceed  upwards  and  inwards, 
and  cross  each  other  in  the  mesial  plane  like  the  two  limbs  of  the  letter  X. 
Eeaching  the  summit  of  the  arytenoid  cartilage  on  each  side,  many  of  the  fibres  are 
inserted  into  it,  whilst  the  remainder  are  prolonged  round  it  into  the  aryteno- 
epiglottidean  fold.  Here  they  receive  the 
name  of  the  aryteno-epiglottidean  muscle, 
and  as  they  approach  the  epiglottis  they 
are  joined  'by  the  fibres  of  the  thyro- 
epiglottidean  muscle.  The  oblique  ary- 
tenoid muscles  may  therefore  be  regarded 
as  forming  a  rudimentary  sphincter  muscle 
for  the  superior  aperture  of  the  larynx. 
Each  bundle,  starting  from  the  base  of  one 
(jf  tlie  arytenoid  cartilages,  is  prolonged 
into  the  aryteno-epiglottidean  fold  of  the 
opposite  side,  and  within  this  to  the 
margin  of  the  epiglottis. 

The  arytenoideus  tranversus  is  an  un- 
l)aired  muscle.  It  is  composed  of  trans- 
verse fibres  which  bridge  across  the  interval 
between  the  two  arytenoid  cartilages,  and 
occupy  their  posterior  concave  surfaces. 
To  a  large  extent  these  fibres  are  inserted 
into  the  posterior  aspect  of  the  outer  border 
of  each  arytenoid  cartilage,  but  many  turn 
round  this  border  and  become  continuous 
with  the  fibres  of  the  thyro-arytenoid 
muscle.  It  follows  from  this  that  the  arytenoideus  transversus  and  the  two  thyro- 
ai-ytenoid  muscles  are  sometimes  spoken  of  as  tlie  sphincter  of  the  glottis. 

Action  of  the  Laryngeal  Muscles. — J^y  the  action  of  the  laryngeal  muscles  the 
position  and  tension  of  the  true  vocal  cords  are  so  influenced  tliat,  during  the  passage  of 


Epiglotti 


Arytf-no-epiglottidean 
folrt' 


Cartilage  of  Saiitorin 
Arytenoideus  oblifiims. 

Arytenoideris_ 

transver.sus" 

Muscular  process  of 

arytenoid  cartilage" 


Crico-arytenoideus 

j)osticus 

Facet  for  iMfcrioi 

coniu  of  tliyroii 

cart  Hug 

Crico-arytenoideu 

posticus 


FlO.   691. — DiSSKCTION    OF   THE    MUSCLES    ON    THE 

PosTERioii  Aspect  of  the  Larynx. 


LARYNGEAL  MUSCLES.  971 

air  through  the  larynx,  the  tone  and  the  pitch  of  the  voice  is  determined.  Tension  of  the 
true  vocal  cords  is  produced  by  the  contraction  of  the  two  crico-th.yroid  muscles.  The 
anterior  or  oblique  portions  of  the  muscles  pull  the  lower  border  of  the  tiiyroid  cartilage 
downwards,  whilst  the  posterior  horizontal  portions,  through  their  insertion  into  the 
inferior  cornua,  draw  the  thyroid  cartilage  forwards,  thereby  increasing  the  distance 
between  the  angle  of  the  thyroid  cartilage  and  the  vocal  processes  of  the  arytenoid  car- 
tilages. When  the  crico-thyroid  muscles  cease  to  contract,  the  relaxation  of  the  cords  is 
brought  about  by  the  elasticity  of  the  ligaments.  The  thyro-arytenoid  muscles  must  be 
regarded  as  antagonistic  to  the  crico-thyroid  muscles.  When  they  contract  they  approxi- 
mate the  angle  of  the  thyroid  cartilage  to  the  arytenoid  cartilages,  and  still  further  relax 
the  true  vocal  cords ;  and  when  they  cease  to  act  the  elasticity  of  the  ligaments  of  the 
larynx  again  restore  the  state  of  equilibrium.  The  ary-vocales  muscles,  by  the  insertion 
of  their  fibres  into  the  true  vocal  cords,  may  tighten  portions  of  these  cords,  whilst  they 
relax  at  the  same  time  the  parts  behind. 

The  width  of  the  rima  rjlottidis  is  regulated  by  the  arytenoideus  muscle,  which  draws 
together  the  two  arytenoid  cartilages,  and  this  may  be  done  so  effectually  that  the  inner 
surfaces  of  these  cartilages  come  into  contact ;  tlie  glottis  respiratoria  is  thus  completely 
closed.  The  lateral  and  posterior  crico-arytenoid  muscles  also  modify  the  width  of  the 
rima  glottidis.  When  they  act  together  they  assist  the  arytenoideus  muscle  in  closing 
the  glottis,  but  when  the}'  act  independently  they  are  antagonistic  muscles.  Thus  the 
posterior  crico-arytenoid  muscles,  by  drawing  the  muscular  processes  of  the  arytenoid 
cartilages  outwards  and  backwards,  swing  the  processus  vocales  and  the  vocal  cords  out- 
wards, and  thereby  open  the  rima.  The  lateral  crico-arytenoid  muscles  act  in  exactly  the 
opposite  manner.  By  drawing  the  muscular  processes  of  the  arytenoid  cartilages  forwards 
and  inwards,  they  approximate  the  processus  vocales  and  close  the  rima. 

Closure  of  the  Larynx  during  Deglutition. — But  the  muscles  of  the  larynx 
have  another  function  to  perform  besides  vocalisation  and  regulating  the  amount  of  air 
passing  to  and  fro  through  the  glottis.  During  deglutition  it  is  requisite  that  t?ie  com- 
munication between  the  pharynx  and  larynx  should  be  closed,  so  as  to  prevent  the 
fluid  or  solid  parts  of  the  food  entering  the  respiratory  passages.  Formei'ly  it  was  believed 
that  this  was  eff"ected  by  the  folding  back  of  the  epiglottis ;  that  in  fact  the  epiglottis, 
during  the  passage  of  the  food,  is  applied  like  a  lid  over  the  entrance  into  the  vestibule  of 
the  laiynx.  The  observations  of  Professor  xA.nderson  Stuart  would  seem  to  indicate  that 
this  view  is  incorrect.  According  to  Professor  Stuart  it  is  not  the  anterior  wall  of  the 
vestibule  which  moves ;  the  epiglottis  stands  erect,  whilst  the  posterior  wall  formed  by 
the  arytenoids  is  carried  forwards.  In  the  process  of  closing  the  laryngeal  entrance  the 
arytenoid  cartilages  are  closely  approximated,  glide  forwards,  and  are  then  inclined  towards 
the  epiglottis.  The  result  of  this  is  that  the  laryngeal  opening  is  converted  into  a 
T-shaped  fissure.  The  mesial  limb  of  the  T  is  formed  by  the  interval  between  the  closely- 
applied  arytenoid  cartilages,  whilst  the  cross  limb,  which  lies  in  front,  is  bounded  anteriorly 
by  the  epiglottis  and  behind  by  the  aryteno-epiglottidean  folds.  The  apices  of  the 
arytenoid  cartilages,  with  the  cartilages  of  Santorini,  are  pressed  against  the  cushion  of 
the  epiglottis,  whilst  the  lateral  margins  of  the  epiglottis  are  pulled  backwards  so  as  to 
make  the  transverse  limb  of  the  fissure  distinctly  concave  in  a  backward  direction.  The 
muscles  chiefly  concex'ned  in  producing  these  movements  are  the  external  thyro-arytenoid 
and  the  transverse  arytenoid  muscles.  These  form  a  true  sphincter  vestibuli.  The  thyro- 
ai-y-epiglottidean  muscles  also  come  into  play.  They  pull  upon  the  epiglottis  so  as  to 
produce  tight  application  of  its  cushion  to  the  arytenoid  cartilages  and  the  cartilages  of 
Santorini,  and  they  also  curve  its  margins  backwards  so  as  to  increase  its  posterior 
concavity. 

Vessels  and  Nerves  of  the  Larynx. — Two  branches  of  the  vagus  nerve,  viz.  the  superior 
larpigeal  and  the  recurrent  larjmgeal  nerves,  supply  the  larpix.  The  superior  laryngeal  divides 
into  the  internal  and  external  larpigeal  branches.  The  external  laryngeal  nerve  supj^lies  the 
crico-thyroid  muscle  ;  whilst  the  internal  laryngeal  nerve  enters  the  larynx  by  piercing  the 
lateral  part  of  the  thyro-hyoid  membrane  to  sujiply  the  laryngeal  mucous  membrane.  The  re- 
current laryngeal  nerve  reaches  the  larynx  from  below,  and  supplies  all  the  intrinsic  larpigeal 
muscles  with  tlie  exception  of  the  crico-thyroid. 

The  superior  laryngeal  artery,  a  branch  of  the  sujaerior  thyroid,  accompanies  the  internal 
larpigeal  nerve  ;  whilst  the  inferior  laryngeal  artery,  which  springs  from  the  inferior  thyroid, 
accompanies  the  recurrent  laryngeal  nerve.  These  two  vessels  ramify  in  the  laryngeal  wall  and 
supply  the  mucous  membrane,  the  glands,  and  muscles. 

Growth-Alterations  and  Sexual  Differences  in  the  Larynx. — A  considerable 
amount  of  variation  may  be  noticed  in  the  size  of  the  larynx  in  difl^erent  individuals. 
This  is  quite  independent  of  statiire,  and  explains  to  a  great  extent  the  difference  in  the 


972 


THE  EESPIEATOEY  SYSTEM. 


pitch  of  the  voice  which  is  observable  in  different  persons.  But  quite  apart  from  these 
individual  variations,  there  is  a  marked  sexual  difterence  in  the  size  of  the  larjaax.  The 
male  larynx  is  not  only  absolutely  but  also  relatively  lai-ger  than  the  female  larynx.  This 
is  noticeable  in  all  its  diameters,  but  more  particularly  in  the  antero-posterior  diameter, 
and  to  a  large  extent  the  increase  in  the  latter  direction  is  produced  by  the  strong  develop- 
ment of  the  laryngeal  angle  or  pomum  Adami  in  the  male.  The  great  antero-posterior 
diameter  of  the  male  larj-nx  necessaril}'  implies  a  greater  length  of  the  vocal  cords  and  a 
lower  or  deeper  tone  of  the  voice  than  in  the  female. 

In  the  newly-born  child  the  larynx,  in  comparison  with  the  rest  of  the  body,  is  some- 
what large  (C.  L.  Merker),  and  it  continues  to  grow  slowly  and  uniformly  up  to  the  sixth 
year  of  childhood.  At  this  period  thei-e  is  a  cessation  of  growth,  which  persists  until 
puberty  is  reached,  and  then  a  stage  of  active  growth  supervenes.  Up  to  this  time  the 
larynx  in  both  sexes  is  similar  in  its  characters,  and  although  the  growth  which  now 
occurs  affects  botli  the  male  and  the  female  larynx,  it  is  much  more  rapid  and  much  more 
accentuated  in  the  male  than  in  the  female.  As  a  result  of  this  the  voice  of  the  male 
breaks  and  assumes  its  deep  tone. 

It  is  interesting  to  note  that  the  growth  activity  of  the  larynx  at  puberty  is  intimately 
connected  with  the  development  of  the  sexual  organs.  In  an  individual  who  has  been 
castrated  when  young  the  larynx  attains  a  size  which  exceeds  that  of  the  female  only  to 
a  very  small  degree,  and  the  high  pitch  of  the  voice  is  retained. 

Appearance  presented  by  the  Interior  of  the  Larynx  when  examined  by  the  Laryngo- 
scope.— When  the  cavity  of  the  larynx  is  illuminated  and  examined  by  the  laryngoscopic  mirror 
the  parts  which  surround  the  suiDerior  aperture  of  the  larynx,  as  well  as  the  interior  of  the  organ, 

come  into  view. 
Not  only  this,  but 
when  the  vocal 
cords  are  widely 
separated  it  is  pos- 
11  sible  to  inspect  the 
interior  of  the 
ij  trachea  as  low 
down  as  its  bifur- 
cation. 

In  such  an  exa- 
mination the 
arched  upper 
border  of  the  epi- 
glottis constitutes 
a  conspicuous 
object,  whilst, 
behind  this,  the 
bulging  on  the 
anterior  wall  of  the 
vestiljule,  formed 
by  the  cushion  of 
the  ejjiglottis,  may 
constitute  a  feature 
of  the  picture. 
The  middle  glos.so-epiglottidean  ligauieut,  with  the  vallecular  fossa  on  either  side  of  it,  can  also 
be  inspected  in  the  interval  between  the  epiglottis  and  the  base  of  the  tongue.  The  sharp  ary- 
epiglottidean  folds  are  clearly  visible,  and  in  the  back  portion  of  each  of  these  can  be  seen  the 
two  prominent  tuljercles  which  are  formed  by  the  enclosed  cuneiform  cartilage  and  the  cartilage 
of  Santorini.  Behind  tliese  tubercles  is  the  jiosterior  wall  of  the  pharynx,  whilst  to  their  outer 
side  the  deep  sinus  pyriforniis  may  be  seen.  In  the  interior  of  the  larynx  the  false  and  the  true 
vocal  cords  are  easily  recognised,  and  the  interval  between  the  false  and  the  true  cord,  or,  in 
other  words,  tlie  entrance  into  the  laryngeal  sinus,  appears  as  a  dark  line  on  the  side  wall  of  the 
larynx.  The  false  vocal  cords  are  red  and  tieshy-loi»king  ;  the  ti'ue  vocal  cords  during  phonation 
are  tightly  stretched  and  pearly  wliite— the  wliite  colour  being  usually  more  apparent  in  the 
female  than  in  the  male.  The  outline  and  yellowisli  tinge  of  the  processus  vocalis  at  its  attach- 
ment to  the  true  vocal  cord,  as  well  as,  to  a  slight  extent,  the  outline  of  the  fore  part  of  the  base 
of  the  arvtenoid  cartilage,  can  in  a  successful  laryngoscopic  exaiuinatioji  be  made  out.  The  true 
vocal  cords  during  ordinary  inspiration  are  seldom  at  I'cst,  and  with  the  laryngoscope  their  move- 
ments may  be  studied.  It  should  T»e  borne  in  mind  that  the  picture  afforded  by  the  laryngoscope 
does  not  give  a  true  idea  of  the  level  at  which  the  different  jjarts  lie.  The  cavity  appears  greatly 
shortened,  and  its  depth  diminished. 

THE  trachp:a. 

The  trachea  or  windpipe  in  a  wide  tube  which  is  kept  permanently  patent  by 


A  B 

P'iG.   692. — Cavity  of  the  Larynx,  as  seen  by  means  of  the  laryngoscope. 
A.  The  rima  glottidis  closed.  B.  The  rima  glottidis  widely  open. 

Laryngeal  sinus. 

Vallecula. 

True  voc?!l  cord. 

Cushion  of  ei)i<,'lottis. 

Middle  glosso-epiglottideaii  fold 


1.  Rings  of  the  trachea. 
•2.  Processus  vocalis  of  the 
arytenoid  cartilage. 

3.  Aryteno-e])iglottidpan  fold, 

4.  Sinus  pyriformis. 


(i. 


10.  Base  of  tongue. 

11.  Epiglottis. 
VI.  Fal.se  vocal  cord. 
1.3.  Cuneiform  tubei'cle. 
14.  Tubercle  of  Santorini. 


THE  TKACHEA. 


973 


Thyroid  cartilage 


Crico-thyroid  iiieinbraiie 


Cricoid  cartilage 


Part  of  tracliea  covered  by 
istlimus  of  thyroid  body 


Common  carotid  artery 


a  series  of  cartilaginous  rings  embedded  in  its  wall.  These  rings  are  deficient 
posteriorly,  and  consequently  the  tube  is  not  completely  cylindrical :  its  hinder 
wall  is  fiattened.  The  trachea  begins  above  at  the  lower  Ijorder  of  the  cricoid 
cartilage,  and  opposite  the  lower  margin  of  the  sixth  cervical  verteljra.  From  this 
it  extends  downwards  through  the  lower  part  of  the  neck  into  the  superior  media- 
stinum of  the  thorax,  in  which  it  ends  at  the  level  of  the  upper  border  of  the  fifth 
dorsal  vertebra  by  dividing  into  the  right  and  left  l^ronchus.  The  length  of  the 
trachea  in  the  male  is  from  four  to  four  and  a  half  inches,  and  in  the  female  from 
three  and  a  half  to  four  inches,  but  even  in  the  same  individual  it  varies  consider- 
ably in  length  with  the  movements  of  the  head  and  neck. 

The  lower  end  of  the  trachea  is  fixed  in  position.  This  is  a  necessary  provision  to 
prevent  dragging  on  the  roots  of  the  lungs  during  movements  of  the  head  and  neck. 
The  remainder  of  the  tube 
is  surrounded  by  a  quantity 
of  loose  areolar  tissue,  and 
possesses  a  considerable  amoiuit 
of  mobility.  Further,  its  wall 
is  highly  elastic,  and  thus 
when  the  head  is  thrown  back 
the  tube  elongates  through 
stretching,  and  when  the  chin 
is  depressed  its  length  is 
diminished  by  the  recoil  of  its 
wall. 

The  trachea  does  not 
present  an  absolutely  uni- 
form calibre  throughout  its 
whole  length.  About  its 
middle  it  exhibits  a  slight 
expansion  or  dilatation,  and 
from  this  the  calibre  dimin- 
ishes in  an  upward  and  a 
downward  direction.  Close 
to  the  bifurcation  it  is  again 
slightly  expanded  (Braune 
and  Stahel). 

These  differences  in  the 
calibre  of  the  tube  are  de- 
termined by  the  surroundings 
of  the  trachea.  The  upper 
part  is  narrowed  through  its 
being  clasped  by  the  thyroid 
body.  Further,  a  short  dis- 
tance above  the  bifurcation 
an  impression,  sometimes 
strongly  marked,  is  usually 
seen  on  the  left  side  of  the 
trachea.  This  is  due  to  the 
close  contact  of  the  aortic 
arch  as  it  passes  backwards 
against  this  part  of  the  tube. 
It  is  evident  therefore  that 
the  second  slight  diminution 
in  calibre  which  is  described 
by  Braune  and  Stahel  is  pro- 
duced by  the  proximity  of 
the  aorta.  Lejars  gives  the 
average  antero- posterior  dia- 
meter   of  the   trachea   in   the 

living  person  as  11  mm.,  and  the  transverse  diameter  as  12*5  mm 
the  lumen  of  the  tube  is  considerably  greater. 


Pulmonary  artery 
Fig.  693. — The  Trachea  and  Bronchi. 
The  thyroid  body  is  indicated  by  a  dotted  line  and  a  purple  tint. 

In  the  dead  subject 


974 


THE  KESPIEATORY  SYSTEM. 


Common  carotid  artery 

Inferior  tliyroi<l  artery 
■RHciirrent  laryngeal  nerve 
^^!i^(Esopliagns 


Left  comnKjn 
carotid  artery 

Vaf'ns  nerve  ' 


Left  subclavian  artery 

Thoracic  iluct  \ 


Left  common 
carotid  arterv 


Vagus  nerve  X; 
subclavian  artery ' 
Left  recun-ent 
laryngeal  nerve 


The  trachea  adheres  rigorously  to  the  median  liue  except  towards  its  lower  end, 
where  it  de\nates  very  slightly  to  the  riglit.  As  it  descends  it  recedes  rapidly 
from  the  surface.  This  is  due  to  its  following  the  curvature  of  the  vertebral 
column,  from  which  it  is  separated  by  the  cesophagus  alone. 

Relations  of  the  Trachea. 

^Thyroid  body 
Trachea 


— In  the  study  of  the  rela- 
tions of  the  trachea  it  is  con- 
venient to  consider  it  in  the 
two  stages  of  cervical  and 
thoracic. 

When  the  chin  is  held  so 
that  the  face  looks  forwards 
the  cervical  part  of  the 
trachea  measures  from  2  to 
2h  inches  in  length ;  but 
when  the  head  is  thrown 
back  the  length  is  consider- 
ably increased.  In  its  upper 
part  the  trachea  is  clasped  by 
the  thyroid  body,  the  isthmus 
of  which  is  applied  to  its 
anterior  surface,  and  covers 
the  second,  third,  and  fourth 
rings,  whilst  on  each  side 
the  lateral  lobe  of  the  same 
body  is  applied  to  its  lateral 
surface,  and  extends  down- 
wards as  low  as  the  fifth  ring. 
On  either  side  of  the  cervical 
trachea  is  the  common  carotid 
artery,  whilst  the  recurrent 
laryngeal  nerve  ascends  in 
the  groove  between  the 
trachea  and  the  oesophagus. 
Posteriorly  the  trachea  is  in 
relation  to  the  oesophagus, 
which  intervenes  between  it 
and  the  bodies  of  the  verte- 
brae, and  deviates  somewhat 
to  the  left  as  it  descends. 

In  addition  to  the  isthmus 
of  the  thyroid  body  two  thin 
muscular  strata,  composed  of 
the  sterno-hyoid  and  sterno- 
thyroid muscles,  and  also  the 
deep  fascia  and  integument, 
separate  the  cervical  trachea 
from  the  surface.  In  the 
middle  line  of  the  neck  there 
is  a  narrow  diamond-shaped 
space  between  the  inner 
margins  of  these  muscles, 
within  which  the  trachea  is 
merely  covered  by  the  integu- 
ments and  fasciae.  It  is  important  to  note  that  in  the  lower  part  of  the  neck 
the  deep  cervical  fascia  is  in  two  layers — viz.  a  strong  stratum  applied  to  the  anterior 
surface  of  the  sterno-hyoid  and  sterno-thyroid  muscles,  and  a  weaker  superficial  layer 
stretching  across  between  the  two  sterno-mastoid  muscles.  Beneath  these  muscular 
and  fascial  layers  the  inferior  thyroid  veins  descend  on  the  surface  of  the  trachea, 


nujraeic  duct 


Ejiarterial  bronchus 
Vagus  nerve 
Bronchial'arteiy 
Vena  azygos  major 
(Jisophagus 


Fig.  694. — Tkansvkhse  Sections  through  the  trachea  and  its  imme- 
diate surroundings  at  the  level  of  each  of  the  upper  five  dorsal 
vertebrae. 


THE  BEONCHI.  975 

and  sometimes  the  occasioual  thyroidea  ima  artery  passes  upwards  iii  front  of  the 
tube.  At  the  upper  border  of  the  manubrium  sterni  the  innominate  artery  may 
be  seen  crossing  the  trachea  obliquely. 

The  thoracic  part  of  the  trachea  is  situated  in  the  back  part  of  the  superior 
mediastinum,  being  separated  from  the  bodies  of  the  vertebrae  by  the  cesophagus 
alone.  Immediately  above  its  bifurcation  the  deep  cardiac  plexus  of  nerves  is 
placed  in  front  and  on  either  side  of  the  trachea.  At  the  level  of  the  fourth  dorsal 
vertebra  the  aortic  arch  is  very  intimately  related  to  it.  At  first  in  front  of  the 
tube,  the  aortic  arch  passes  backwards  in  close  contact  with  its  left  side.  The 
three  great  vessels  which  spring  from  the  aortic  arch  are  also  placed  in  close  proximity 
to  the  trachea.  ,  The  innominate  and  left  common  carotid  arteries,  at  first  in  front, 
gradually  diverge  as  they  proceed  upwards  and  come  to  lie  on  either  side  of  the 
tube — the  innominate  to  the  right,  and  the  left  common  carotid  to  the  left.  In 
front  of  these  vessels  are  the  left  innominate  vein  and  the  remains  of  the  thymus 
body.  On  the  right  side  the  thoracic  part  of  the  trachea  is  in  relation  to  the  right 
vagus  nerve,  and  is  clothed  by  the  right  mediastinal  pleura ;  on  the  left  side  are 
the  left  subclavian  artery  and  the  left  recurrent  laryngeal  nerve. 

Structure  of  the  Wall  of  the  Trachea. — The  wall  of  the  trachea  and  bronchi  is 
composed  of  (1)  a  fibro-elastic  membrane  in  which  the  cartilaginous  rings  are  embedded  ; 
(2)  within  this,  and  on  the  posterior  aspect  of  the  tube,  a  layer  of  muscular  tissue,  termed 
the  musculus  trachealis ;  and  (3)  the  lining  mucous  membrane. 

The  fibro-elastic  membrane  is  strong  and  dense,  and,  passing  round  the  whole  circum- 
ference of  the  tube,  it  becomes  continuous  superiorly  with  the  perichondrium  which 
invests  tiie  cricoid  cartilage.  Embedded  in  its  substance  are  the  series  of  cartilaginous 
rings.  These  vary  in  number  from  15  to  20,  and  are  composed  of  h^-aline  cartilage. 
They  are  horseshoe-shaped,  the  posterior  fourth  of  the  circumference  being  deficient,  so 
that  behind,  each  ring  ends  in  two  rounded  extremities.  The  external  surface  of  a  tracheal 
ring  is  flat  and  even,  and  does  not  project  much  beyond  the  level  of  the  membrane  in 
which  it  is  embedded ;  the  inner  surface,  however,  is  convex  in  the  vertical  direction,  and 
consequently  it  bulges  slightly  into  the  lumen  of  the  trachea.  The  intervals  between  the 
rings  are  somewhat  narrower  than  the  rings  themselves,  and  neighbouring  rings  frequently 
show  a  more  or  less  complete  fusion,  whilst  others  present  other  irregularities,  such  as  a 
tendency  to  bifurcate.  The  lowest  ring  is  specially  adapted  to  the  tracheal  bifurcation. 
In  the  middle  line  in  front  it  inclines  downwards,  and  from  this  median  peak,  a  cartilaginous 
strip  is  carried  backwards  in  the  fork  between  the  two  bronchi. 

The  musculus  trachealis  is  a  continuous  layer  of  involuntary  muscular  tissue  placed 
in  the  posterior  part  of  the  wall  in  front  of  the  fibro-elastic  membrane.  The  muscular 
bundles  ai-e  arranged  transversely,  and  are  attached  to  the  extremities  of  the  rings,  and 
also  to  the  deep  surface  of  the  rings  for  a  short  distance  beyond  their  extremities.  In  the 
intervals  between  the  rings  the  transverse  muscular  bundles  are  attached  to  the  fibro- 
elastic  membrane.  It  is  evident  that,  by  its  conti'action,  this  muscle  will  reduce  in  a 
marked  degree  the  lumen  of  the  tube. 

The  mucous  membrane  is  laid  smoothly  over  the  interior  of  the  tube  upon  a  layer  of 
submucous  areolar  tissue.  L^miphoid  tissue  enters  largely  into  the  composition  of  the 
tracheal  mucous  membrane,  and  its  inner  surface  is  lined  by  columnar  ciliated  epithelial 
cells.  The  action  of  the  cilia  exercises  an  important  influence  in  producing  an  upward 
movement  of  the  mucus  which  is  present  on  the  surface  of  the  mucous  membrane. 

Numerous  longitudinal  bundles  of  elastic  tissue  are  present  in  the  posterior  wall  of 
the  trachea,  more  particulai-ly  in  its  lower  part,  between  the  mucous  membrane  and  the 
musculus  trachealis. 

In  connexion  with  the  mucous  membrane  there  is  a  plentiful  supply  of  acinose  mucous 
glands.  These  are  placed  in  the  submucous  tissue,  and  also  on  the  posterior  aspect  of  the 
tube  on  the  exterior  of  the  musculus  trachealis  as  well  as  amidst  its  muscular  bundles. 
They  send  their  ducts  to  the  surface  of  the  mucous  membi'ane,  where  they  open  by 
trumpet-shaped  mouths. 

THE  BRONCHI. 

The  two  bronchi  proceed  obliquely  downwards  and  outwards  from  the  termina- 
tion of  the  trachea,  each  towards  the  hilum  of  the  corresponding  lung.  Like  the 
trachea  they  are  kept  permanently  patent  by  the  presence  of  cartilaginous  rings  in 
their  walls.     These  rings  are  deficient  posteriorly,  so  that  the  bronchi  exhibit  a 


976  THE  EESPIEATOEY  SYSTEM. 

flattened  posterior  surface  in  every  respect  similar  to  the  trachea.  The  two 
bronchi  ditfer  from  each  other,  not  only  in  the  relations  which  they  present  to  sur- 
rounding structures,  but  also  in  length,  in  width,  and  in  the  direction  which  they 
pursue  (Fig.  693,  p.  973). 

The  first  collateral  branch  arises  from  the  right  bronchus,  much  nearer  the 
trachea  than  in  the  case  of  the  left  bronchus.  It  is  this  which  determines  the 
length  of  these  primary  divisions  of  the  trachea,  and  although  there  is  much  varia- 
tion in  this  matter,  it  may  be  said  that,  as  a  rule,  the  left  bronchus  is  at  least  twice 
as  long  as  the  right  bronchus.  According  to  Henle  there  are  from  six  to  eight 
rings  in  the  right  and  from  nine  to  twelve  rings  in  the  left  bronchus.  A  marked 
difference  is  also  noticeable  in  the  calibre  of  the  two  tubes.  The  right  bronchus 
is  wider  than  the  left  in  the  proportion  of  100  :  78 "4  (Braune  and  Stahel),  and  this 
asymmetry  is  clearly  due  to  the  fact  that  the  right  lung  is  more  bulky  than  the 
left.  The  right  bronchus,  as  it  passes  towards  the  hilum  of  the  right  lung,  takes 
a  more  vertical  course  than  the  left  bronchus.  It  therefore  lies  more  in  the  line 
of  the  trachea,  and  to  this,  as  well  as  to  its  greater  width,  is  due  the  greater 
tendency  which  foreign  bodies  exhibit,  when  introduced  into  the  trachea,  to  drop 
into  the  right  in  preference  to  the  left  bronchus.  The  average  angle  which  the 
right  bronchus  forms  with  the  median  plane  is  24"8°,  whilst  the  angle  formed  by 
the  left  bronchus  with  the  median  plane  is  45 "6°.  The  more  horizontal  course  of 
the  left  bronchus  is  probably  determined  by  the  marked  projection  of  the  heart  to 
the  left  side  of  the  mesial  plane  (Merkel). 

Relations  of  the  Bronchi. — Arching  forwards  over  the  right  bronchus  is  the 
vena  a^ygos  major,  whilst  arching  backwards  over  the  left  bronchus  there  is 
the  aroh  of  the  aorta.  Occupying  the  interval  between  the  bronchi  there  is  a 
cluster  ^of  bronchial  lymphatic  glands,  and  an  irregular  chain  of  similar  glands  is 
carried  along  each  tube  towards  the  hilum  of  the  lung.  On  the  posterior  aspect  of 
each  bronchus  the  vagus  nerve  breaks  up  into  the  posterior  pulmonary  plexus,  whilst 
the  left  bronchus,  as  it  proceeds  downwards  and  outwards,  crosses  in  front  of  the 
oesophagus  and  the  descending  thoracic  aorta.  But  perhaps  the  most  interesting 
relation  is  that  presented  on  each  side  by  the  corresponding  pulmonary  artery.  On 
the  left  side  the  pulmonary  artery  crosses  in  front  of  the  left  bronchus  above  the 
level  of  its  first  collateral  branch,  and  then  turns  round  its  outer  side  to  gain  its 
posterior  aspect.  All  the  left  bronchial  Ijranches,  therefore,  are  jjlaced  below  the 
left  pulmonary  artery,  and  are  in  consequence  termed  hyparterial.  The  right 
pulmonary  artery,  on  the  other  hand,  crosses  in  front  of  the  continuation  of  the 
right  bronchus  below  its  first  collateral  branch.  This  branch  is  therefore  termed 
the  eparterial  bronchus,  whilst  all  the  others  are  classified  as  hyparterial. 

Structure  of  the  Walls  of  the  Bronchi. — The  walls  of  the  bronchi  present  a 
structure  similar  to  that  seeu  in  the  trachea. 

THE  THOEACIC  CAVITY. 

A  central  vertical  partition,  termed  the  mediastinum  thoracis,  which  extends 
from  the  vertebral  column  Ijehind  to  the  anterior  thoracic  wall  in  front,  subdivides 
the  thoracic  cavity  into  two  large  lateral  chambers  which  contain  the  lungs.  From 
the  fact  of  each  of  these  chambers  being  lined  by  an  extensive  and  separate  serous 
membrane  called  the  pleura,  they  receive  the  name  of  the  pleural  cavities. 

The  mediastinum  or  intervening  partition  is  built  up  of  several  structures 
which  lie  in  or  in  close  proximity  to  the  mesial  plane.  The  more  important  of 
these  are  the  heart,  enveloiied  in  its  Yjericardium,  the  thoracic  aorta,  with  the  great 
vessels  which  spring  from  its  arch,  the  pulmonary  artery,  and  the  great  veins  in 
the  neighbourhood  of  the  heart,  the  thynius  RUnd  or  its  remains,  the  trachea, 
oesophagus,  and  thoracic  duct,  and  the  pneurift{^f?tric  and  phrenic  nerves. 

The  i»leural  cavities  in  which  the  two  lungs  lie  comprise  much  the  largest  part 
of  the  thoracic  cavity.  Each  is  bounded  below  by  the  corresponding  cupola  of  the 
diaphragm ;  and  as  the  right  cupola  rises  to  a  higher  level  than  the  left,  the  right 
pleural  cavity  presents  a  smaller  vertical  depth  than  the  left.  In  front,  the  wall 
of  each  pleural  chamber  is  formed  by  the  costal   cartilages  and  the   sternum ; 


THE  PLEUEAL  MEMBKANES. 


977 


laterally,  hy  the  shafts  of  the  ribs  aud  the  intercostal  muscles  as  far  back  as  the 
angles  of  the  ribs ;  leliind,  by  the  portions  of  the  ribs,  with  the  interveniu<'-  inter- 
costal muscles,  which  lie  internal  to  the  costal  angles ;  and  internally,  by  the  bodies 
of  the  vertebrye  and  the  mediastinal  partition  which  completely  shut  off  the  one 
chamber  from  the  other. 

The  mediastinum  is  not  median  in  position.  Owing  to  the  marked  projection 
of  the  heart  to  the  left  side,  and  to  the  position  of  the  descending  thoracic  aorta  on 
the  left  side  of  the  mesial  plane,  the  left  pleural  chamber,  although  it  is  deeper 
than  the  right,  is  greatly  reduced  in  width.  The  two  pleural  cavities,  therefore, 
are  very  far  from  being  symmetrical  in  form. 

Each  pleural  cavity  is  completely  lined  by  a  separate  serous  membrane  termed 
the  pleura.  The  portion  of  this  membrane  which  clothes  the  mediastinum  or 
intervening  partition  forms  the  lateral  boundary  of  a  space  termed  the  mediastinal 
or  interpleural  space,  within  which  the  parts  which  build  up  the  mediastinum  are 
placed. 

THE  TWO  PLEUEAL  MEMBEANES. 

The  pleura  or  pleural  membrane  of  each  side  not  only  lines  the  corresponding 
pleural  cavity,  but  at  the  pulmonary  root  it  is  prolonged  on  to  the  lung  so  as  to 
give  it  a  complete  investment.  It  is  customary,  therefore,  to  recognise  a  visceral 
or  investing  part  (pleura  visceralis)  and  a  parietal  or  lining  part  (pleura  parietalis). 
The  inner  surface  of  the  membrane  {i.e.  that  surface  which  is  turned  towards  the 
interior  of  the  cavity)  is  coated  with  squamous  endothelium,  and  presents  a  smooth, 
glistening,  and  polished  appearance ;  further,  it  is  moistened  by  a  small  amount  of 
serous  fluid.  In  consequence  of  this  the  surface  of  the  lung  covered  by  visceral 
pleura  can  glide  on  the  wall  of  the  cavity,  lined  as  it  is  by  parietal  pleura,  with  the 
least  possible  degree  of  friction.  In  the  pathological  condition  known  as  pleurisy 
the  surface  of  the  membrane  becomes  roughened  by  inflammatory  exudation,  and 
the  so-called  "  friction  sounds  "  become 

evident  when  the  ear  is  applied  to  the      visceral.    /V^iii*— «s~^— ii:>^\     Parietai 
chest. 

Visceral  Pleura.  —  The  visceral 
pleura  is  very  thin,  and  is  so  firmly 
bound  down  to  the  surface  of  the  lung 
that  it  cannot  be  detached  without 
laceration  of  the  pulmonary  substance, 
and  then  only  in  small  pieces.  It 
dips  into  the  fissures  of  the  lungs, 
lines  them  down  to  the  very  bottom, 
and  thus  completely  separates  the  dif- 
ferent lobes  of  the  lungs  from  each  other. 
The  visceral  pleura  becomes  continuous 
with  the  mediastinal  part  of  the  parietal 
pleura  over  the  root  of  the  lung,  and 
also  through  the  ligameutum  latum 
pulmonis. 

Parietal  Pleura. — Different  names 
are  applied  to  the  parietal  pleura  as  it  lines  the  different  parts  of  the  wall  of  the 
cavity  in  which  the  lung  lies.  Thus  there  is  the  costal  pleura,  the  diaphragmatic 
pleura,  the  mediastinal  pleura,  and  the  cervical  pleura  ;  but  it  must  be  borne  in 
mind  that  these  terms  are  merely  used  for  convenience  in  description,  and  the 
portions  of  the  membrane  so  designated  are  all  directly  continuous  with  each 
other. 

The  cervical  pleura  rises  up  into  the  root  of  the  neck,  through  the  superior 
aperture  of  the  thorax,  and  forms  a  dome-shaped  roof  for  the  pleural  cavity.  Its 
summit  or  highest  point  reaches  the  level  of  the  lower  border  of  the  neck  of  the 
first  rib ;  but  owing  to  the  great  obliquity  of  the  first  costal  arch,  this  point  is 
placed  from  one  to  two  inches  above  the  anterior  extremity  of  the  first  rib,  and 
from  a  half  to  one  and  a  half  inches  above  the  clavicle.  The  cervical  dome  of 
66 


Fig.   695. — Diagram  showing  Arrangement  of 
Pleural  Sacs,  as  seen  in  transverse  section. 


978 


THE  EESPIEATOEY  SYSTEM. 


Right  vagus  nerve      Tracliea 


ffisophagus  Left  subclavian  artery 


pleura  is  supported  on  the  outer  side  by  the  scalenus  anticiis  and  scalenus  medius 
muscles,  whilst  the  subclavian  artery  arches  over  it,  and  lies  in  a  groove  on  its  inner 
and  anterior  aspect  a  short  distance  below  its  summit.  At  a  lower  level  the 
innominate  and  subclavian  veins  also  lie  upon  its  inner  and  anterior  aspects. 

The  cervical  cul  de  sac  of  pleura  is  strengthened  and  held  in  place  by  an  aponeurotic 
expansion,  first  described  by  Sibson,  which  is  spread  over  it,  and  is  attached  to  the  inner 
concave  margin  of  the  first  rib.     This  fascia  is  derived  from  a  small  muscular  slip  which 

takes  origin  from 
the  transverse  pro- 
cess of  the  seventh 
cervical  vertebra. 

The    costal 
pleura     is     the 

strongest  and 
thickest  part  of 
the  parietal 
pleura.  It  lines 
the  deep  surface 
of  the  costal 
arches  and  of  the 


bulcus  sut)cla\  iiib 

Lett  Mgus  nei\e 
Left  common 
riirtid  irtery 
Left  mno- 
unnate  ^ein 


intervening 


in- 


tercostal muscles. 
Infront  itreaches 
the  back  of  the 
sternum,  whilst 
behind  it  is 
carried  forwards 
on  the  bodies  of 
the  vertebrae.  It 
is  easily  detached 
from  the  parts 
which  it  covers, 
except  as  it  passes 
from  the  heads 
of  the  ribs  on  to 
the  vertebral 
column.  Here  it 
is  somewhat 
tightly  bound 
down. 

The  diaphragm- 
atic pleura  covers 
the  portion  of 
the  upper  surface 
of  the  diaphragm 
which  lies  to  the 
\^>\      J^  ^s^  .jj^/  outer  side  of  the 

^y^^-^^  X_x^  l^ase  of  the  peri- 

69(5._I)I.S.SKCTI()N  OK  A  SUIUECT  HARDENED  BY   FOUMALIN-INJ  ECTION,   tO    sllOW  tlie  CardlUUl,       DUt      it 

relations  of  tVie  two  i)leural  sacs  as  viewed  from  tlie  front.  The  anterior  and  doCS  not  dipdowU 
diaphragmatic,  lines  of  pleural  reflection  are  exhibited  by  black  dotted  lines,  whilst  ^^  ^^^  bottom  of 
the  outlines  of  the  lungs  ami  their  fissures  are  indicated  by  the  blue  lines;  ^^^      narrOW     in- 

terval between  the  thoracic  wall  and  the  diaphragm.      In  other  words,  a  strip  of  the 
upper  surface  of  the  diaphragm  adjoining  its  costal  attachment  is  left  uncovered. 

The  mediastinal  pleura  extends  backwards  from  the  posterior  surface  of  the 
anterior  thoracic  wall  to  the  vertebral  column,  and  it  clothes  the  side  of  the 
mediastinum  or  partition  intervening  between  the  two  pleural  cavities.  It  is 
continuous  with  the  pleura  costalis  of  its  own  side,  both  in  front  and  behind,  along 
two  lines  which  are  respectively  termed  the  anterior  and  posterior  lines  of  pleural 


Fig 


THE  PLEURAL  MEMBRANES. 


979 


reflection;  whilst  below  it  becomes  continuous  with  the  diaphragmatic  pleura  of 
its  own  side  at  the  base  of  the  pericardium. 

Above  the  level  of  the  root  of  the  lung  the  mediastinal  pleura  passes  directly 
backwards  from  the  sternum  to  the  vertebral  column.  In  this  region  the  left 
mediastinal  pleura  is  applied  to  the  arch  of  the  aorta  and  the  phrenic  and  vagus 
nerves ;  to  the  left  innominate  vein,  the  left  superior  intercostal  vein,  and  the  left 
common  carotid  and  left  subclavian  arteries ;  to  the  cesophagus  and  tlie  thoracic 
duct.  The  right  mediastinal  pleura, 
on  the  other  hand,  is  applied,  above 
the  level  of  the  root  ot  the  lung,  to 
the  upper  part  of  the  superior  vena 
cava  and  right  innominate  vein  ;  to 
the  right  innominate  artery  ;  to  the 
vena  azygos  major,  as  it  hooks 
forwards  above  the  bronchus ;  to 
the  vagus  and  phrenic  nerves  ;  and 
to  the  right  side  of  the  trachea. 

Opposite  the  root  of  the  lung, 
as  well  as  in  the  region  below  it, 
the  mediastinal  pleura  clothes  the 
corresponding  aspect  of  the  peri- 
cardium, and  is  somewhat  firmly 
attached  to  it.  As  the  phrenic 
nerve  passes  downwards  upon  the 
pericardium  it  is  likewise  covered 
over  by  the  pleura.  In  the  region 
corresponding  to  the  upper  lateral 
aspect  of  the  pericardium  the 
mediastinal  pleura  is  prolonged 
outwards,  so  as  to  form  an  invest- 
ment for  the  root  of  the  lung,  and 
become  continuous  around  the 
hilum  of  the  lung  with  the  visceral 
pleura.  Below  the  root  of  the 
lung  the  two  layers  of  pleura  which 
invest  it  come  into  apposition  with 
each  other,  and  are  prolonged  down- 
wards as  a  distinct  fold,  termed 
the  ligamentum  latum  pulmonis. 
This  fold  stretches  between  the 
pericardium  and  the  lower  part  of 
the  inner  surface  of  the  lung,  and 
ends  below  in  a  free  border. 

Behind  the  root  off  the  lung 
and  the  ligamentum  latum  pul- 
monis the  mediastinal  pleura  on 
the  right  side  is  carried  backwards 
to  the  vertebral  column  on  the 
oesophagus ,  whilst  on  the  left  side 
it  is  carried  backwards  over  the 
descending  aorta,  and  to  a  small 
extent,  in  the  region  immediately  above  the  diaphragm  and  in  front  of  the  aorta, 
over  the  lower  end  of  the  oesophagus. 


Fi«.  697. — Lateral  View  of  the  Right  Pleukal  Sac  in 
A  Subject  hardened  by  Formalin  -  injection.  The 
blue  lines  indicate  the  outline  of  the  right  lung,  and  also 
the  position  of  its  fissures. 


Lines  of  Pleural  Reflection. — These  are  three  in  number — viz.  the  anterior  or 
sternal,  the  posterior  or  vertebral,  and  the  lower  or  diaphragmatic.  The  pleural  cavities 
are  not  symmetrical.  The  left  is  longer  and  narrower  than  the  right,  and  it  thus  happens 
that  the  lines  of  pleural  reflection  do  not  accurately  correspond  on  the  two  sides  of  the 
body.     Further,  although  the  posterior  line  of  reflection  is  fairly  constant,  the  other  two 


980 


THE  KESPIKATOEY  SYSTEM. 


CEsophagTis 
Left  subclavian  [artery 
Left  comiiiou  carotid  artery 
Left  suxjerior  intercostal  vein 
Lsft  innominate  vein 


reflection-lines  are  subject  to  marked  variations  in  different  subjects.     Consequently  the 
following  description  must  be  regarded  as  merely  giving  the  average  condition. 

The  posterior  or  vertebral  line  of  pleural  reflection  is  that  along  which  the  costal  pleura 
is  continued  forwards  from  the  vertebral  column  to  become  the  mediastinal  pleura.  On 
the  right  side,  above  the  root  of  the  lung,  the  pleura  passes  from  the  bodies  of  the  vertebrae 
on  to'  the  right  side  of  the  trachea ;  whilst  below  this  level,  and  behind  the  peri- 
cardium, it  passes  from  the  vertebral  bodies  on  to  the  oesophagus.  On  the  left  side,  and 
above  the  arch  of  the  aorta  the  pleura  along  this  line  of  reflection  is  carried  from  the 
vertebral  column  on  to  the  oesophagus  and  thoracic  duct ;  below  that  level  it  passes  on 
to  the  descending  thoracic  aorta.  In  the  upper  part  of  the  chest  the  right  and  left 
lines  of  reflection  are  placed  well  apart  from  each  other,  and  about  equidistant  from  the 

mesial  plane.  As  they  are 
traced  downwai'ds  they 
approach  more  closely  to 
each  other  and  deviate  to 
the  left,  so  that  whilst  the 
reflection  on  the  right  side 
takes  place  from  the  front 
aspect  of  the  vertebral 
bodies,  on  the  left  side  it 
takes  place  from  the  left 
aspect  of  the  vertebral 
column.  This  is  due  to 
the  position  of  the  descend- 
ing thoracic  aorta. 

The   anterior   line    of 
pleural   reflection  is  that 
along    which     tiie     costal 
pleura  leaves  the  anterior 
thoracic  wall  to  become  the 
mediastinal   i:)leura.      The 
line    differs    somewhat    on 
the  two  sides,  and  in  both 
cases  shows  a  tendency  to 
deviate  to  the  left  (Fig.  696, 
p.  978).     Behind  the  upper 
part    of    the    manubrium 
stemi  the  two  pleural  sacs 
are    separated    from    each 
other  by  an  angular  inter- 
val.    The  lines  of  reflection 
at  the  inlet  of  the  thorax 
correspond  to   the   sterno- 
clavicular    joints.      From 
these  points,   as  they  are 
traced    downwards,     they 
converge  on  the  back  of  the 
manubrium,  until  at  last 
they  meet  a  short  distance 
above  the  upper  end  of  the 
gladiolus.     Here  the    two 
sacs  come  into  contact  with 
each  other,  and  the  lines  of 
reflection  coincide.     From 
this    they   proceed    down- 
698.— Lekt  i'LEiKAi,  Sac  in  a  Sibject  hahdened  «v   Fokmai.in-  wards  on  the  back  of  the 
INJECTION,  ojiened  into  by  the  removal  of  the  co.stal  part  of  the  purietal  sternum    with  a  slio-ht  de- 
pleura.     The  lung  lias  also  been  reniove<l  so  a,s  to  display  the  media-  yij^^j^j^   [^  ^^le   left^f  the 
stinal  pleura.  .    , 

mesial  plane,  until  a  point 

immediately  above  the  level  of  the  sternal  attiichments  of  the  fourth  costal  cartilages  is 
reached,  and  here  the  two  sacs  part  company.  The  line  of  reflection  of  the  right  jy/eura  is 
continued  downwards  in  a  straiglit  line  behind  the  sternum  until  the  back  of  the  ensiform 
cartilage  is  reached,  and  here  the  sternal  reflection-line  passes  into  the  right  diaphragmatic 


Diaphragm 


THE  PLEURAL  MEMBEANES. 


981 


reflection-line.  Opposite  the  sternal  attachment  of  the  fourth  costal  cartilage  the  reflection 
line  of  the  left  jAeura  deviates  outwards  on  the  back  of  the  sternum,  and  is  continued 
downwards  at  a  variable  distance  from  the  riglit  pleura.  A  small  triangular  area  of 
pericardium  is  thus  left  uncovered  by  pleura,  and  therefore  in  direct  contact  with  the 
anterior  chest-wall.  Leaving  the  sternum,  the  reflection-line  of  the  left  pleura  descends 
parallel  and  close  to  the  left  margin  of  the  sternum  behind  the  fourth  intercostal 
space,  the  fifth  costal  cartilage  and  the  fifth  intercostal  space,  to  the  back  of  the  sixth 
costal  cartilaeje.   Here 


it  turns  outwards  and 
downwards,  and 
passes  into  the  dia- 
phragmatic reflec- 
tion-line of  the  left 
side. 

From  the  back  of 
the  sternum  the  riciht 
pleura  is  reflected  in 
the  upper  part  of  the 
chest  on  to  the  re- 
mains of  the  thymus, 
the  right  innominate 
vein  and  the  superior 
vena  cava,  and  below 
this  directly  on  to 
the  front  of  the  peri- 
cardium. The  left 
pleura  is  reflected 
from  the  back  of  the 
manubrium  sterni  on 
to  the  left  innominate 
vein  and  the  aortic 
arch,  and  below  this 
directly  on  to  the 
front  of  the  peri- 
cardium. 

The  diaphragma- 
tic line  of  reflection 
is  that  along  which 
the  pleura  leaves  the 
thoracic  wall  and  is 
reflected  on  to  the 
upper  surface  of  the 
diaphragm.  This 
reflection  takes  place 
along  a  curved  line, 
which,  except  behind 
as  it  approaches  the 
vertebral  column,  is 
placed  a  short  dis- 
tance above  the  lower 
border  of  the  thoracic 
wall.  It  differs  some- 
what on  the  two  sides 
of  the  body. 

On  the  left  side  the  diaphragmatic  line  of  reflection  pi-oceeds  downwards  behind  the 
, ascending  part  of  the  sixth  costal  cartilage,  crosses  behind  the  anterior  end  of  the  sixth 
intercostal  space  and  the  descending  part  of  the  cartilage  of  the  seventh  rib  (Fig.  698). 
Still  continuing  to  descend,  it  passes  behind  the  eighth  costal  arch  at  the  junction  between 
its  cartilaginous  and  bony  portions.  This  is  a  fairly  constant  relation  on  both  sides  of  the 
body,  and  it  should  be  noted  that  a  vertical  line  drawn  downwards  from  the  nipple  (mam- 
millary  line)  intersects  the  line  of  pleural  reflection  close  to  the  point  where  it  presents  this 
relation  to  the  eighth  costal  arch.  Beyond  this  point  the  line  of  diaphragmatic  reflec- 
tion is  carried  downwards  and  outwards  across  the  extremities  of  the  bony  portions 
66  a 


Fig.  699. — Dissection-  of  the  Pleural  Sacs  from  Behind. 
The  blue  lines  indicate  the  outlines  and  the  fissures  of  the  lungs. 


982  THE  EESPIEATOKY  SYSTEM. 

of  the  ninth  and  tenth  ribs.  As  it  passes  under  cover  of  the  tenth  rib,  or  it  may  be  as 
it  proceeds  across  the  tenth  intercostal  space,  the  hne  of  pleural  reflection  reaches  its 
lowest  point,  and  it  is  important  to  observe  that  this  point  lies  in  the  mid-lateral  line  {i.e. 
a  vertical  line  drawn  downwards  on  the  side  of  the  chest  midway  between  spine  and 
sternum).  From  this  it  ascends  slightly  as  it  curves  backwards  towards  the  spine.  Thus 
it  cuts  across  the  eleventh  rib  and  reaches  the  twelfth  rib.  The  relation  which  it  presents 
to  the  twelfth  rib  varies  in  accordance  with  the  length  of  that  rib.  When  the  last  rib  is 
not  abnormall}^  short  the  pleura  clothes  its  inner  half,  and  the  line  of  reflection  falls 
below  this  portion  of  the  rib  so  as  to  reach  the  spine  midway  between  the  head  of  the  last 
rib  and  the  transverse  pi'ocess  of  the  first  lumbar  vertebra  (Fig.  699).  Here,  therefore, 
the  line  of  diaphragmatic  reflection  falls  below  the  lower  border  of  the  thoracic  wall, 
and  this  is  a  point  of  high  practical  importance.  In  operations  upon  the  kidney  the 
incision  cannot  be  carried  above  the  level  of  the  transverse  process  of  the  first  lumbar 
vertebra  and  the  ligamentum  arcuatum  externum  without  the  risk  of  wounding  the  pleura. 

On  the  right  side  the  line  of  diaphragmatic  pleural  reflection  differs  from  that  on  the 
left  chiefly  in  front  (Fig.  697,  p.  979).  Here  it  descends  to  a  lower  level.  Thus  it  pro- 
ceeds outwards  and  downwards  from  the  back  of  the  ensiform  cartilage  along  the 
posterior  aspect  of  the  ascending  part  of  the  seventh  costal  cartilage,  and  it  passes  beneath 
the  eighth  costal  arch,  as  a  rule,  at  the  same  point  as  on  the  left  side,  viz.  at  the  junction 
of  its  cartilaginous  and  bony  parts.  From  this  backwards  to  the  spine  the  relations  are 
so  similar  to  those  of  the  left  side  that  a  separate  description  is  unnecessary. 

It  is  commonly  stated  that  the  left  pleural  sac  reaches  a  lower  level  than  the  right. 
In  certain  cases  there  is  no  doubt  that  it  does,  but  this  condition  is  by  no  means  the  rule. 
In  those  cases  where  the  two  pleural  sacs  do  not  reach  the  same  level  at  their  lowest 
points,  it  is  sometimes  the  right  and  sometimes  the  left  pleura  wliich  oversteps  the  mark. 

As  already  stated,  the  lowest  point  to  which  the  pleura  descends  is  usually  found,  on 
both  sides,  in  the  mid-lateral  line  where  the  diaphragmatic  reflection-line  crosses  the  tenth 
rib  or  the  tenth  intercostal  space.  This  point  can  be  very  readily  ascertained  on  the 
surface  by  drawing  a  horizontal  line  round  the  trunk  at  the  level  of  the  lower  part  of  the 
e.Ktremity  of  the  spinous  process  of  the  first  lumbar  vertebra,  and  noting  where  it  is 
intersected  by  the  mid-lateral  line.  In  the  majority  of  cases  the  point  of  intersection  will 
correspond  with  the  lowest  part  of  the  pleural  sac.  Another  horizontal  line  opposite  the 
spine  of  the  last  dorsal  vertebra  will  give  the  level  of  the  diaphragmatic  pleural  reflection 
in  the  mammillary  line.^ 

Along  the  line  of  the  diaphragmatic  reflection  a  strong  fascia  passes  from  the 
lower  uncovered  part  of  the  diaphragm,  and  from  the  costal  cartilages  to  the  surface 
of  the  costal  pleura,  so  as  to  hold  it  firmly  in  its  place.  It  may  be  termed  the  phrenico- 
pleural  fascia. 

MEDIASTINAL  OR  INTERPLEURAL  SPACE. 

The  term  mediastinal  space  is  applied  to  the  interval  between  the  mediastinal 
portions  of  the  two  pleural  sacs.  In  front  it  is  liounded  by  the  sternum,  and 
behind  by  the  vertebral  column.  It  is  customary  to  subdivide  this  space  in  a 
purely  arbitrary  manner  into  four  portions,  termed  respectively  superior,  anterior, 
middle,  and  posterior,  according  to  the  relations  which  they  present  to  the 
pericardium. 

The  superior  mediastinum  is  the  part  of  tlie  general  space  which  lies  above  the 
level  of  the  pericardium.  Its  boundaries  arc  the  following: — In  front,  the  manu- 
brium sterni,  to  the  posterior  aspect  of  whicli  are  the  attached  lower  ends  of  the 
sterno-hyoid  and  sterno-thyroid  muscles  ;  hehind,  the  bodies  of  the  upper  four  dorsal 
yertebrie ;  below,  an  imaginary  and  oblique  plane,  which  extends  from  the  lower 
border  of  the  manubrium  sterni  backwards  and  upwards  to  the  lower  border  of  the 
fourth  dorsal  vertebra ;  laterally,  the  mediastinal  ph/ura. 

Within  the  superior  mediastinal  space  are  placed  (1)  the  aortic  arch  and  the 
three  great  arteries  which  siiring  I'rom  it;  (2)  the  innominate  veins  and  the  upper 
part  of  the  superior  vena  cava ;  (3)  the  trachea,  gullet,  and  thoracic  duct ;  (4)  tlie 
phrenic,  pneumogastric,  left  recurrent  laryngeal  and  cardiac  nerves ;  (5)  the 
thymus  gland. 

'  The  above  description  represents  the  average  results  whicli  have  been  obtained  from  the  study  of 
the  i)leura  in  a  large  number  of  subjects,  eight  of  which  were  specially  hardened  by  formalin  or  other 
re-agents  for  the  purpose.  For  many  of  the  disaectious  I  have  to  thank  my  former  assistant,  Dr.  H. 
St.  J,  Brooks,  and  for  others  I  am  indebted  to  Professor  C.  J.  Patten  of  Sliellield. 


THE  LUXGS.  .  983 

The  middle  mediastinum  is  the  wide  part  of  the  space  which  contains  the 
pericardium,  and  lies  below  the  superior  mediastinum.  In  addition  to  the  peri- 
cardium and  its  contents  the  middle  mediastinum  contains  the  phrenic  nerv^es  and 
their  accompanying  vessels. 

The  anterior  mediastinum  is  that  part  of  the  interpleural  space  which  lies 
between  the  pericardium  liehind  and  the  sternum  in  front.  In  its  upper  part  this 
space  can  liardly  be  said  to  exist,  seeing  that  here  the  two  pleural  sacs  come  into 
contact  with  each  other  on  the  anterior  aspect  of  the  pericardium ;  but  below  the 
level  of  the  sternal  ends  of  the  fourth  costal  cartilages  the  left  pleura  falls  short 
of  the  right  pleura,  and  an  interval  is  apparent.  The  only  contents  to  he  noticed 
in  the  anterior  mediastinum  are  a  few  lymphatic  glands  and  some  areolar  tissue, 
in  which  ramify  some  lymphatic  vessels,  and  some  minute  twigs  from  the  internal 
mammary  artery. 

The  posterior  mediastinum  is  that  part  of  the  interpleural  space  which  is 
situated  behind  the  pericardium.  It  may  be  regarded  as  the  continuation  down- 
wards of  the  posterior  part  of  the  superior  mediastinum,  and  many  of  the  structures 
in  the  one  are  prolonged  downwards  into  the  other.  The  arbitrary  upper  limit  of 
the  posterior  mediastinum  is  the  lower  border  of  the  fourth  dorsal  vertebra.  In 
front  it  is  bounded  by  the  pericardium,  except  in  its  lowest  portion,  where  the 
anterior  wall  is  formed  by  the  back  of  the  diaphragm.  Behind  it  is  limited  by  the 
bodies  of  the  eight  lower  dorsal  vertebrae,  and  on  each  side  by  the  mediastinal  pleura. 
It  contains  the  descending  thoracic  aorta  with  the  left  aortic  intercostal  arteries, 
the  azygos  veins,  the  thoracic  duct  and  the  oesophagus,  with  the  two  pneumogastric 
nerves. 

Structure  of  the  Pleura. — The  pleura  on  each  side  is  a  closed  sac,  and,  like  other 
serovis  membranes,  it  is  attached  by  its  outer  surface  to  the  wall  of  the  cavity  which  it 
lines  and  to  the  surface  of  the  viscus  which  it  covers.  It  is  composed  of  a  thin  con- 
nective-tissue stratum  in  which  bundles  of  fibres  cross  each  other  in  various  directions, 
and  intermixed  with  which  there  is  a  considerable  quantity  of  elastic  tissue.  On  the  inner 
surface  of  this  there  is  a  continuous  coating  of  thin  endothelial  cells  placed  edge  to  edge. 
The  pleura  so  formed  is  attached  to  the  parts  it  lines  and  invests  by  a  small  amount  of 
areolar  tissue  which  forms  a  subserous  layer.  In  the  case  of  the  visceral  pleura  the  sub- 
serous tissue  is  continuous  with  the  areolar  tissue  in  the  substance  of  the  lung,  and  this 
accounts  for  the  tight  manner  in  which  the  membi"ane  is  bomid  down. 

The  pleura  is  plentifully  supplied  with  blood.  This  is  conveyed  to  it  by  minute  twigs 
from  the  intercostal  arteries,  the  internal  mammary  artery,  and  the  bronchial  arteries. 
Lymphatic  vessels  also  are  particularly  abundant  in  the  pleura  and  in  the  subserous 
layer,  and  it  is  by  these  that  excess  of  fluid  is  conveyed  from  its  cavity.  Many  lymphatic 
vessels  commimicate  directly  with  the  cavity  by  means  of  excessively  minute  orifices 
termed  stomata.  Dybkowsky  has  shown  that  the  lymphatics  and  stomata  of  the  pleura 
are  not  equally  distributed  throughout  the  membrane.  Over  the  ribs  and  on  the 
mediastinal  pleui'a  they  are  absent. 

THE  LUNGS. 

"\Mien  healthy  and  sound  each  lung  lies  free  within  the  corresponding  pleural 
chamber,  and  is  only  attached  by  its  root  and  the  ligamentum  latum  pulmonis.  It 
is  not  common,  however,  to  meet  with  a  perfectly  healthy  lung.  Adhesions  between 
the  visceral  and  parietal  layers  of  pleura,  due  to  pleurisy,  are  generally  present. 

Like  the  cavities  in  wliich  they  are  placed,  the  two  lungs  are  not  precisely 
alike.  The  right  lung  is  slightly  larger  than  the  left,  in  the  proportion  of  about 
11  to  10.  The  right  lung  Is  also  shorter  and  wider  than  the  left  lung.  This 
difference  is  due  to  the  great  bulk  of  the  right  lobe  of  the  liver,  which  elevates  the 
right  cupola  of  the  diaphragm  to  a  higher  level  than  the  left  cupola,  and  likewise 
to  the  heart  and  pericardium  projecting  more  to  the  left  than  to  the  right,  and 
thus  diminishing  the  width  of  the  left  lung. 

The  lung  is  light,  soft,  and  spongy  in  texture ;   when  pressed  between  the 

finger  and  thumb  it  crepitates,  and  when  placed  in  water  it  floats.     The  elasticity 

of  "the  pulmonary  tissue  is  very  remarkable.     A  striking  demonstration  of  this  is 

afforded  when  the  thoracic  cavity  is  opened,  and  the  atmospheric  pressure  acting 

66  6 


984 


THE  EESPIEATORY  SYSTEM. 


upon  the  interior  and  exterior  of  the  lung  is  equalised.  Immediately  the  organ 
collapses  to  aliout  one-third  of  its  original  bulk,  and  it  becomes  impossible  in  such 
a  specimen  to  study  its  proper  form  and  dimensions. 

The  surface  of  the  adult  lung  presents  a  mottled  appearance.  The  ground 
colour  is  a  light  slate -blue,  but  scattered  over  this  there  are  numerous  dark 
patches  of  various  sizes,  and  also  fine  dark  intersecting  lines.     The  coloration  of 


Recurrent  laryngpal  nei  \  e 
Inferior  tliyioid  \em 

Right  \  agus  ner\  e 

Bifurcation  of  mn 
minate  art^i  \ 


Sterno-hj  oid  muscle 
Stemo  tin  101(1  muscle 
Stemo  mastoid  muscle 
Thyroid  body 
Internal  jugular  \  em 
Phrenic  nerve 

Scalenus  anticus 

-'iubclavian  arteiy  (left) 
Left  -^  agus  nerve 


Subcla\  lan  vein  (left) 

Common  carotid  artery 
T  eft  innominate  vein 


Left  lobe  ok 
thymus  oland 


Middle  lobe  J  -  HM^      *^- 
of  right  lun-     I     'V    V  ^ 

Basal  lobe  of 
right  lull- 


Pulmonary  fissure 


Pericardium 


Fig.  700.— Dissection  of  Thorax  and  root  op  the  Neck  from  the  front  to  show  the  ■  relations 
OF  the  LuNCis,   Pericardium  and  Thymus  Gland. 

the  lung  differs  considerably  at  different  periods  of  life.  In  early  childhood  the 
lung  is  rosy-pink,  and  the  darker  colour  and  the  mottling  of  the  surface  which 
appear  later  are  due  to  the  pulmonary  substance,  and  chiefly  the  interstitial  areolar 
tissue  becoming  impregnated  more  or  less  completely  with  atmospheric  i  dust  and 
minute  particles  of  soot. 

At  every  breath  foreign  matter  of  this  kind  is  iulialed,  l)ut  only  a  .small  proportion  of  it 
reaches  the  lung  tissue.  The  greater  part  of  it  becomes  entangled  in  the  slimy  mucus  which 
coats  the  mucous  membrane  of  the  larger  air-pa.ssages,  and  is  gradually  got  rid  of  along  with 
the  mucus  through  the  activity  of  the  cilia  attached  to  the  lining  ei)ithcliuni.  By  the  constant 
upward  sweep  of  these  a  current  towards  the  pharynx  is  (^stablislu-d.  The  tine  dust  and  soot 
particles  which  reach  the  finer  recesses  of  the  lungs,  and  ultimately  the  interstitial  issue,  is 
partly  conveyed  away  by  the  lymphatic  vessels  to  the  bronchial  glands,  which  in  consequence 
become  in  many  cases  absolutely  black.     The  colour  of  the  lung,  therefore,  depends  to  some 


THE  LUXGS. 


985 


extent  upon  the  purity  of  the  atmosphere  which  is  inhaled,  and  it  thus  happens  tliat  in  coal- 
miners  the  surface  of  the  lung  may  be  verj^  nearly  uniformly  black. 

The  fcetal  lung  differs  in  a  marked  degree  from  the  lung  in  an  individual  who 
has  breathed.  After  respiration  is  fully  established,  the  lung  soon  comes  to  occupy 
almost  the  whole  space  allotted  to  it  in  the  pleural  cavity ;  in  the  fcetus,  on  the 
other  hand,  the  lung  is  packed  away  at  the  back,  and  occupies  a  relatively  much 
smaller  amount  of  space  in  the  thoracic  cavity.  Further,  it  is  firm  to  the  touch, 
and  sinks  in  water.  It  is  only  when  air  and  an  increased  supply  of  blood  are 
introduced  into  the  lung  that  it  assumes  the  soft  spongy  and  buoyant  quahties 
which  are  characteristic  of  the  adult  lung. 

Form  of  the  Lungs.— The  lungs  are  accurately  adapted  to  the  walls  of  the 
pleural  chambers  in  which  they  are  placed,  and  in  the  natural  state  ^hey  bear  on 


Pulmonary  \eiii 


1. 

Base. 

7. 

Groove  for  vena  azygos  major 

2. 

Fissure. 

8. 

Eparterial  bronchus. 

3. 

Cardiac  depression. 

9. 

Pulmonary  arterj-  (right). 

4. 

Groove  for  innominate  vein. 

10. 

Fissure. 

5. 

Groove  for  innominate  artery. 

11. 

Groove  for  aorta. 

6. 

Apex  pnlmonis. 

12. 

Bronchus. 

Fig.  701. — Mediastinal  Surfaces  of  the  two  Luxgs  of  a  Subject  hardened  by  Formalin-injection. 

A,  Right  luug.  B,  Left  luiig. 

13.  Puluionaiy  artery  (left). 
1-1.  Apex  pulmonis. 

15.  Groove  for  left  subclavian  artery. 

16.  Groove  for  left  innominate  vein. 

17.  Cardiac  depression. 
IS.  Fissure.  It>.  Base. 

the  surface  impressions  and  elevations  which  are  an  exact  counterpart  of  the 
irregularities  on  the  walls  of  the  cavity  in  which  they  lie. 

When  care  has  been  taken  to  harden  it  in  situ,  each  lung  presents  an  apex 
and  a  base,  an  inner  and  an  outer  surface,  and  an  anterior  and  a  posterior 
border. 

The  apex  pulmonis  is  blunt  and  rounded,  and  rises  above  the  level  of  the 
oblique  first  costal  arch  to  the  full  height  of  the  cervical  dome  of  pleura.  It 
therefore  protrudes  upwards  through  the  thoracic  inlet  into  the  root  of  the  neck. 
The  subclavian  artery  arches  outwards  on  its  inner  and  anterior  aspects  a  short 
distance  below  its  summit,  and  a  groove  (sulcus  subclavius)  corresponding  to  the 
vessel  is  apparent  vipon  it.  At  a  lower  level  on  the  apex  pulmonis  a  shallower  and 
wider  groove  upon  its  inner  and  anterior  aspects  marks  the  position  of  the  innomi- 
nate and  subclavian  veins.  Although  these  vessels  impress  the  lung  they  are 
separated  from  it  by  the  cervical  pleura. 

The  basis  pulmonis  presents  a  semilunar  outline,  being  curved  around  the  base  of 
the  pericardium.  It  is  adapted  to  the  upper  surface  of  the  diaphragm,  and  conse- 
quently it  is  deeply  hollowed  out.  As  the  right  cupola  of  the  diaphragm  ascends 
higher  than  the  left,  the  basal  concavity  of  the  right  lung  is  deeper  than  that  of 


986 


THE  EESPIEATORY  SYSTEM. 


the  left  lung.  Laterally  and  behind,  the  base  of  each  lung  is  limited  by  a  salient 
thin  margin  which  descends  for  some  distance  in  the  narrow  pleural  recess  (sinus 
phrenico-costalis)  between  the  diaphragm  and  the  chest  wall.  This  basal  margin 
of  the  lung  extends  lower  down  on  the  outer  side  and  behind  than  it  does  in  front, 
but  it  falls  considerably  short  of  the  bottom  of  the  phrenico-costal  sinus  of  pleura. 
Thus,  after  expiration,  it  reaches  in  the  mammillary  line  the  lower  border  of  the 
sixth  rib;  in  the  axillary  or  mid -lateral  line  the  eighth  rib;  whilst  behind  it  pro- 
ceeds inwards  along  a  straight  horizontal  line  so  as  to  reach  the  vertebral  column 
at  the  level  of  the  extremity  of  the  spine  of  the  tenth  dorsal  vertebra.  During 
respiration  the  thin  basal  margin  rises  and  falls  in  the  phrenico-costal  sinus  of  the 
pleura,  but  even  after  the  deepest  breath  it  never  reaches  the  lowest  limit  of  this 
recess. 

The  bases  of  the  lungs  establish  important  relations  with  certain  of  the  viscera  which 
occupy  the  costal  zone  of  the  abdominal  cavity,  the  diaphragm  alone  intervening.     Thus 


LAVIAN      ARTERY 


Fig.  702. — Outer  or  Costal  Sukb^aces  of  the  two  Lungs. 
A,  Right  lung.  B,  Left  lung. 

the  base  of  the  right  lung  rests  upon  the  right  lobe  of  the  liver ;  whilst  the  base  of  the 
left  lung  is  in  relation  to  the  left  lobe  of  the  liver,  the  fundus  of  the  stomach,  the  spleen, 
and  in  some  cases  to  the  splenic  fle.xure  of  the  colon. 

The  outer  surface  of  the  lung  (facies  costalis  pulmonis)  is  extensive  and  convex. 
It  is  accurately  adapted  to  that  part  of  the  wall  of  the  pleural  cavity  which  is 
formed  by  the  costal  arches  and  the  intervening  intercostal  muscles,  and  it  presents 
markings  corresponding  to  these.  Thus  the  imprint  of  the  ribs  appear  as  shallow 
oblique  grooves,  while  the  intercostal  spaces  show  as  elongated  intervening 
bulgings. 

The  inner  or  mediastinal  surface  of  the  lung  (facies  mediastinalis  pulmonis) 
presents  a  smaller  area  than  the  outer  surface.  It  is  applied  to  the  mediastinal 
septum,  and  presents  markings  in  accordance  with  the  inequalities  upon  this  (Fig. 
701,  p.  985).  Thus  it  is  deeply  hollowed  out  in  adaptation  to  the  pericardium  upon 
which  it  fits.  This  pt^ricardial  concavity  comprises  the  greater  part  of  the  media- 
stinal surface,  and  owing  to  the  greater  projection  of  the  heart  to  the  left  side,  it  is 
much  deeper  and  more  extensive  in  the  left  lung  tlian  in  the  right  lung.  Above 
and  behind  the  pericardial  hollow  is  the  hilum  of  the  lung.  This  is  a  wedge-shaped 
depressed  area,  within  which  the  vessels,  nerves,  and  lymphatics,  together  with  the 


THE  LUNGS. 


987 


bronchus,  enter  and  leave  the  organ.  Amidst  these  structures  also  are  some 
bronchial  cdands.  The  hilum  is  surrounded  by  the  reflection  of  the  pleura  from 
the  surface" of  the  lung  on  to  the  pulmonary  root.  Behind  the  hiluni  and  peri- 
cardial  area  there 

^Trapezius 

Supra-spinatus 


Clavicular  part  of 
pectoralis  major' 

Coracoi 


Cephalic  vein 

Sternal  part  o 
pectoralis  majo 

Axillary  arterj 
Brachial  nerves- 
Axillary  V 


Pectorali 
minor 


Spine  of  scapula 


Subscapularis 


Rhomboideus 
'r\ — I'l'ijor 


area  tnere  is 
on  each  lung  a  narrow 
strip  of  the  inner  sur- 
face of  the  lung  which 
is  in  relation  to  the 
lateral  wall  of  the  pos- 
terior mediastinum. 
On  the  right  lung  this 
part  of  the  surface  is 
depressed,  and  corre- 
sponds to  the  oeso- 
phagus ;  on  the  left 
lung  it  presents  a 
broad  longitudinal 
groove,  which  is  pro- 
duced by  the  contact 
of  the  lung  with  de- 
scending thoracic 
aorta,  and  also,  close 
to  the  base,  a  small 
flattened  area  in  front 
of  this  which  is  ap- 
plied to  the  oesophagus 
where  it  pierces  the 
diaphragm. 

The  portion  of  the 
inner  surface  of  the 
lung  which  lies  above 
the  hilum  and  peri- 
cardiac hollow  is  ap- 
plied to  the  lateral 
aspect  of  the  superior 
mediastinum,  and  the 
markings  are  accordingly  somewhat  different  on  the  two  sides.  On  the  left  lung  a 
broad  deep  groove,  produced  by  the  aortic  arch,  curves  backwards  over  the  hilum, 
and  becomes  continuous  with  the  aortic  groove  on  the  posterior  mediastinal 
surface.  From  this  a  narrower,  deeper,  and  much  more  sharply-marked  groove 
ascends,  and  turns  outwards  over  the  apex  pulmonis  a  short  distance  from  the 
summit.  This  is  the  sulcus  subclavius,  and  it  contains  the  left  subcla\dan  artery 
when  the  lung  is  in  place.  In  front  of  this  a  shallow  wide  groove,  also  leading 
up  to  the  front  aspect  of  the  apex,  corresponds  to  the  left  innominate  vein.  In 
the  right  lu7ig  the  hilum  is  also  circumscribed  above  by  a  curved  groove,  but  this 
is  narrow  and  more  distinctly  curved  than  the  aortic  groove  on  the  left  side.  It 
lodges  the  vena  azygos  major  as  it  turns  forwards  to  join  the  superior  vena  cava. 
From  the  anterior  end  of  the  azygos  sulcus  a  wide  shallow  groove  extends  upwards 
to  the  lower  part  of  the  front  of  the  apex  pulmonis.  This  is  produced  by  the 
apposition  of  the  lung  with  the  vena  cava  superior  and  the  right  innominate  vein. 
Close  to  the  summit  of  the  apex  there  is  also,  on  its  inner  aspect,  a  sulcus  for  the 
upper  end  of  the  innominate  artery. 

In  addition  to  the  hilum,  it  must  now  be  evident  that  the  inner  surface  of  each 
lung  presents  three  areas  which  correspond  respectively  with  (1)  the  middle 
mediastinum  {i.e.  the  pericardial  hollow) ;  (2)  the  posterior  mediastinum  ;  and  (3)  the 
superior  mediastinum ;  and  that  in  each  of  these  districts  impressions  correspond- 
ing to  structures  contained  within  these  portions  of  the  interpleural  space  may  be 
noticed. 

The  posterior  border  of  the  lung  is  thick,  long,  and  rounded.     It  forms  the  most 


-Diaphragm 


Fic;.  703, — Sagittal  Section  throcgh  Lekt  Shouldek  and  Left  Lung. 


988 


THE  EESPIEATOEY  SYSTEM. 


Omo 
Cla%  ic 

Scalenus  ineJius^ 
Brachial  nerves 

SubcLivius 
Subcla\  lan 
aitciy 

Subcla%  lan 
\ein 


Trappzins 
Seiiatus  magnus 
Supra-spinatus 

Subscapularis 

Br«'-\      scapula 
\  \       ^  Infra- 
spinatus 


bulky  part  of  the  organ,  and  occupies  the  deep  hollow  in  the  thoracic  cavity  which 
is  placed  on  either  side  of  the  spine.  Indeed  the  term  "  border "  is  somewhat 
inappropriate,  ;is  it  forms  in  reality  a  somewhat  extensive  surlace  deeply  impressed 

by  the  ribs,  and  not  in 
any  way  marked  off  from 
the  outer  surface  of  the 
lung. 

The  anterior  border  of 
the  lung  is  short  and  ex- 
ceedingly thin  and  sharp. 
It  begins  abruptly  above, 
immediately  below  the 
groove  on  the  apex  for 
the  innominate  vein,  and 
extends  down  to  the  base, 
where  it  becomes  con- 
tinuous with  the  sharp 
basal  border.  The  thin 
anterior  part  of  the  lung 
is  carried  forwards  and 
inwards  in  front  of  the 
pericardium  into  the 
narrow  pleural  recess  be- 
hind the  sternum  and 
costal  cartilages  (sinus 
costo-mediastinalis).  The 
anterior  border  of  the 
right  lung  fills  up  this 
recess  completely,  and  in 
the  upper  partof  the  chest 
is  only  separated  from 
the  corresponding  border 
of  the  left  lung  by  the 
two  layers  of  mediastinal 
pleura  which  are  reflected 
backwards  from  the  ster- 
num to  the  pericardium.  The  anterior  border  of  the  left  lung,  in  its  lower  part, 
shows  a  marked  deficiency  or  notch  (incisura  cardiaca)  corresponding  to  the  apex  of 
the  heart,  and  where  this  exists  the  lung  margin  leaves  a  considerable  portion  of 
the  pericardium  uncovered,  and  fails  to  completely  fill  up  the  costo-mediastinal 
sinus  of  the  pleural  cavity.  During  respiration  the  anterior  margin  of  the  left 
lung  at  the  incisura  cardiaca  advances  and  retreats  to  a  small  extent  in  this  pleural . 
sinus  in  front  of  the  pericardium. 

Fissures  and  Lobes  of  the  Lungs. — The  left  lung  is  divided  into  two  lobes 
by  a  long  deep  fissure  which  penetrates  its  substance  to  within  a  short  distance  of 
the  hilum.  Above  and  below  the  hilum  this  fissure  cuts  right  through  the  lung 
and  appears  upon  the  mediastinal  or  inner  surface.  Viewed  from  the  outer  aspect 
of  the  organ,  it  begins  at  the  posterior  border  about  two  and  a  half  inches  below  the 
summit  of  the  apex,  about  the  level  of  the  vertebral  end  of  the  third  rib,  and  is 
continued  downwards  and  forwards  in  a  somewhat  spiral  direction  to  the  base  of  the 
lung,  which  it  reaches  a  short  distance  behind  its  anterior  end.  The  upper  lobe  of 
the  lung  (iobus  superior)  lies  above  and  in  front  of  this  cleft.  It  is  conical  in 
form,  with  an  oldique  base,  and  the  apex  and  the  whole  of  the  anterior  border  of 
the  lung  belong  to  it.  The  lower  lobe  (Iobus  inferior)  lies  below  and  behind  the 
fissure.  It  is  tlie  more  bulky  of  the  two,  and  includes  almost  the  entire  base  and 
the  greater  part  of  the  thick  posterior  border. 

In  the  right  lung  there  are  two  fissures  subdividing  it  into  three  lobes.  One 
of  these  fissures  is  very  similar  in  its  position  and  relations  to  the  fissure  in  the  left 
lung.    It  is,  however,  rather  more  vertical  in  its  direction,  and  ends  below  somewhat 


Diaphragm 


Reflection 
of  pleura 


704. — Sagittal  Section  through  the  Left  Shoulder, 
Lung,  and  Apex  of  the  Heart. 


EOOT  OF  THE  LUNG.  989 

further  outwards.  It  separates  the  lower  lobe  from  the  upper  and  middle  lobes. 
The  second  cleft  begins  in  the  main  fissure  at  the  posterior  border  of  the  lung,  and 
proceeds  horizontally  forwards,  to  end  at  the  anterior  border  of  the  lung  at  the 
level  of  the  fourth  costal  cartilage.  The  middle  or  intermediate  lobe  of  the  right 
lung  is  triangular  or  wedge-shaped  in  outline. 

Variations. — Variations  in  the  i)uhnonaiy  fissures  are  fairly  common.  Tims  it  .sometimes 
happens  that  the  middle  lobe  of  tlie  right  lung  is  imperfectly  cut  off  from  the  upper  lobe. 
Supernumerary  fissures  also  are  not  infrequent,  and  in  this  way  the  left  lung  may  be  cut  into 
three  lobes,  and  the  right  lung  into  four  or  even  more  lobes.  The  occurrence  of  a  lobus  azygos 
in  the  right  lung  is  a  variation  of  some  interest,  seeing  that  such  a  lobe  is  constant  in  certain 
mammals.  It  is  a  small  accessory  loVje,  pyramidal  in  form,  which  makes  its  appearance  on  the 
lower  part  of  the  inner  asjaect  of  the  right  lung.  In  certain  cases  the  vena  azygos  major  is 
enclosed  within  a  fold  of  pleura,  and  is  sunk  so  deeply  in  the  pulmonary  substance  of  the  right 
lung  that  it  marks  off  a  small  accessory  lobe. 

ROOT  OF  THE  LUNG. 

The  term  root  of  the  lung  (radix  pulmonis)  is  applied  to  a  number  of  structures 
which  enter  and  leave  the  lung  at  the  hilum  on  its  inner  surface.  They  are  held 
together  by  an  investment  of  pleura,  and  constitute  a  pedicle  which  attaches  the 
lung  to  the  mediastinal  wall  of  the  pleural  cavity.  The  phrenic  nerve  descends  a 
short  distance  in  front  of  the  pulmonary  root,  whilst  the  vagus  nerve  breaks  up 
into  the  posterior  pulmonary  plexus  on  its  posterior  aspect  under  cover  of  the 
investing  pleura.  The  delicate  anterior  pulmonary  plexus  is  placed  in  front  of  the 
root  of  the  lung  beneath  the  pleura,  whilst  from  the  lower  border  of  the  root  of  the 
lung  the  ligamentum  latum  pulmonis  extends  downwards.  These  are  the  relations 
which  are  common  to  the  pulmonary  root  on  both  sides  of  the  body,  but  there  are 
others  which  are  peculiar  to  each  side.  On  the  right  side  the  superior  vena  cava 
lies  in  front  of  the  pulmonary  root,  whilst  the  vena  azygos  major  arches  over  its 
upper  aspect.  On  the  left  side  the  aorta  arches  over  the  root  of  the  lung,  whilst 
the  descending  thoracic  aorta  passes  down  behind  it. 

Constituent  Parts  of  the  Pulmonary  Root. — The  most  important  structures 
which  enter  into  the  formation  of  the  pulmonary  root  are  (1)  the  two  pulmonary 
veins ;  (2)  the  pulmonary  artery ;  (3)  the  bronchus.  But  in  addition  to  these 
there  are  one  or  more  small  bronchial  arteries  and  veins,  the  pulmonary  nerves 
and  the  pulmonary  lymphatic  vessels,  and  some  bronchial  glands. 

The  pulmonary  nerves  come  from  the  vagus  nerve  and  also  from  the  sympathetic  system. 
They  enter  the  lung  and  follow  the  air-tubes  through  the  organ.  Tlie  bronchial  arteries  are 
small  vessels  which  carry  blood  for  the  sujiply  of  the  lung  tissue.  They  arise  from  the  aorta  or 
from  an  intercostal  artery,  and  vary  in  number  from  one  to  three  for  each  lung.  In  the  root  of 
the  lung  they  lie  on  the  jiosterior  aspect  of  the  bronchus,  and  they  follow  the  air-tubes  through 
the  organ.  Part  of  the  blood  conveyed  to  the  lung  by  the  bronchial  arteries  is  returned  by  the 
pulmonary  veins  ;  the  remainder  is  returned  by  sjjecial  bronchial  veins  which  ojaen  on  the  right 
side  into  the  vena  azygos  major,  and  on  the  left  side  into  the  vena  azygos  minor  superior. 

The  lymphatic  vessels  of  the  lung,  as  they  emerge  from  the  hilum,  unite  into  a  small  number 
of  trunks,  which,  placed  behind  the  large  pulmonary  vessels,  open  into  the  bronchial  glands. 

The  bronchus  in  the  root  of  the  lung  lies  behind  the  great  pulmonary  vessels. 
The  pulmonary  artery  occupies  a  different  position  on  the  two  sides  in  relation  to  the 
main  or  undivided  part  of  the  bronchus.  On  the  right  side  it  is  placed  below 
it,  whilst  on  the  left  side  it  crosses  the  bronchus  and  occupies  a  higher  level  in  the 
pulmonary  root.  The  tw^o  pulmonary  veins  on  both  sides  lie  at  a  lower  level  in  the 
root  of  the  lung  than  the  pulmonary  artery  and  bronchus,  whilst  the  upper  of  the 
two  veins  occupies  a  plane  in  front  of  the  pulmonary  artery  (Fig.  701,  p.  985). 

Distribution  of  the  Bronchial  Tubes  within  the  Lungs. — The  two  lungs  are 
iiot  symmetrical;  the  right  lung  is  subdivided  into  three  lobes,  and  the  left  lung  is 
cleft  into  two  lobes.  The  bronchi  exhibit  a  corresponding  want  of  symmetry.  The 
right  bronchus,  as  it  approaches  the  pulmonary  hilum,  gives  off  two  branches  for  the 
upper  and  middle  lobes  of  the  right  lung  respectively,  and  then  the  main  stem  of  the 
tube  enters  the  lower  lobe.  The  left  Ironchus  sends  off  a  large  branch  to  the  upper 
lobe  of  the  left  lung,  and  then  sinks  into  the  lower  lobe.  The  first  branch  of  the 
right  bronchus  for  the  upper  right  pulmonary  lobe  leaves  the  main  stem  about  one 


990  THE  EESPIRATOEY  SYSTEM. 

inch  from  the  trachea.  The  first  branch  of  the  left  bronchus,  on  the  other  hand, 
takes  origin  about  twice  that  distance  from  the  trachea. 

The  relation  of  the  pulmonary  artery  to  the  bronchial  subdivisions  is  different 
on  the  two  sides.  On  the  right  side  it  turns  backwards  to  reach  the  posterior 
aspect  of  the  bronchus  below  the  first  and  above  the  second  bronchial  branch.  On 
the  left  side  the  pulmonary  artery  turns  backwards  above  the  level  of  the  first 
bronchial  branch.  On  the  right  side,  therefore,  the  first  bronchial  branch  is  placed 
above  the  pulmonary  artery,  and  in  consequence  it  is  termed  the  eparterial  bronclius  ; 
all  the  others  lie  below  the  artery,  and  are  termed  hyparterial  broncM.  On  the 
left  side  there  is  no  eparterial  branch ;  they  are  all  hyparterial. 

When  the  main  stem  of  the  bronchus  is  followed  into  the  inferior  lobe  of  each 
lung,  it  is  seen  to  travel  downwards  and  backwards  in  the  pulmonary  substance 
until  it  reaches  the  thin  back  part  of  the  base  of  the  lung  which  lies  between  the 
diaphragm  and  the  thoracic  wall,  and  there  it  ends.  As  it  proceeds  through  the 
inferior  lobe  it  gives  off  a  series  of  large  ventral  and  a  series  of  smaller  dorsal 
branches.  As  a  rule  these  are  three  in  number  in  each  case,  and  the  dorsal  and 
ventral  branches  do  not  arise  opposite  to  each  other,  but  alternately,  one  from  the 
back,  and  then  another,  after  a  slight  interval,  from  the  front  of  the  tube.  The 
first  hyparterial  division  on  each  side  {i.e.  the  Ijranch  to  the  middle  lobe  of  the  right 
lung  and  the  branch  to  the  upper  lobe  of  the  left  side)  is  generally  regarded  as  the 
first  member  of  the  ventral  group. 

It  was  Aeby  who  first  recognised  tbe  existence  in  each,  lung  of  a  main  or  stem  bronchus 
giving  off  a  ventral  and  dorsal  series  of  branches,  and  who  drew  the  distinction  between  the 
eparterial  and  hyparterial  bronchial  branches.  A  consideration  of  these  relations  led  this  author 
to  conclude  that  the  eparterial  bronchus  and  the  upper  lobe  of  the  right  lung  have  no  morpholo- 
gical equivalents  on  the  left  side  of  the  body.  In  other  words,  he  was  led  to  believe  that  the 
middle  lobe  of  the  right  lung  is  the  homologue  of  the  upper  lobe  of  the  left  lung.  Hasse,  who 
has  also  investigated  the  subject,  endorsed  this  view,  with  certain  modifications  and  additions, 
and  the  hypothesis,  either  in  its  original  state  as  j^resented  by  Aeby,  or  as  subsequently  modified 
by  Hasse,  has  been,  until  lately,  very  generally  accepted  by  anatomists.  More  recent  research, 
however,  has  seriously  a ft'ected  the  stability  of  this  conclusion.  Narath  contends  that  the  distinc- 
tion between  the  eparterial  bronchus  of  the  right  side  and  the  hyparterial  bronchi  of  both  sides 
is  not  one  of  fundamental  importance,  and  further,  that  a  branch  which  arises  from  the  first 
hyparterial  bronchus  on  the  left  side  and  turns  upwards  into  tlie  apex  of  the  left  lung  is  the  direct 
equivalent  of  the  ej^arterial  bronchus  of  the  right  side.  This  he  terms  the  apical  bronchus,  and 
he  believes  that  it  represents  the  first  dorsal  branch  of  the  left  stem-bronchus.  Huntington,  in  a 
very  convincing  paper,  strongly  supports  the  contention  of  Narath,  and  holds  that,  except  "  for 
purposes  of  topography,  we  should  abandon  the  distinction  between  eparterial  and  hyparterial 
bronchi."  With  Narath  he  regards  the  ejjarterial  bronchus  as  a  secondary  branch  which  has 
migrated  in  an  upward  direction  on  the  main  stem.  According  to  Huntington,  therefore,  Aeby's 
proposition  should  be  amended  as  follows  : — 

Right  side.  Left  side. 

Upper         +         middle  lobe  =  Upper  lobe. 

Lower  -I-         cardiac  lobe  =  Lower  lobe. 

The  cardiac  lobe  mentioned  in  this  table  is  the  occasional  azygos  lobe  to  which  reference  has 
already  been  made,  and  it  is  interesting  to  note  that,  whilst  tlie  lobe  in  question  as  a  separate 
entity  is  rarely  seen  in  the  human  lung,  the  bronchus  which  corresponds  to  it  is  always 
jjresent  in  the  pidmonary  substance  as  an  accessory  branch,  which  proceeds  from  the  main  stem 
as  it  traverses  the  lower  lobe  of  the  right  side.     It  receives  the  name  of  the  cardiac  bronclius. 

Structure  of  the  Lung. 

The  lung  is  constructed  so  that  the  blood  which  reaches  it  through  the  pulmouaiy 
artery  is  brought  into  the  most  intimate  relation  with  the  air  which  enters  it  through  the 
trachea  and  bronchi.  An  interchange  of  materials  between  the  blood  and  the  air  is  thus 
rendered  possible,  and  the  object  of  respiration  is  attained.  As  a  result  of  this  inter- 
change the  dark  impure  blood  which  flows  into  the  lung  through  the  pulmonary  artery  is 
rendered  bright  red  and  arterial. 

Lobules  of  the  Lung. — A  thin  layer  of  suljpleural  connective  tissues  lies  subjacent 
to  the  continuous  coating  whicli  the  lung  receives  from  the  visceral  pleura.  From  the 
deep  surface  of  this  subplcural  layer  fine  septal  processes  penetrate  into  the  substance  of 
the  lung,  and  these,  with  the  connective  tissue  which  enters  at  the  hilum  upon  the  vessels 
and  bronchi,  constitute  a  supporting  framework  for  the  organ.  The  lung  is  lobular,  and 
on  the  svirface  the  small  polygonal  areas  which  represent  the  lobules  are  indicated  by  the 


STRUCTUEE  OF  THE  LUNG.  991 

pigment  present  in  the  connective  tissue  septa  which  intervene  between  them.  Although 
no  pigment  is  present,  the  lobular  character  of  the  lung  is  particularly  well  marked  in  the 
foetus,  and  with  a  little  care  the  surface  lobules  in  the  foetal  lung  can  be  separated  from 
each  other  by  gently  tearing  through  the  intervening  connective  tissue.  The  lobules  thus 
isolated  are  pyriform  or  pyramidal  in  form.  The  broad  bases  of  these  lobules  abut  against 
the  subpleural  layer,  whilst  each  of  the  deep  narrow  ends  receives  a  minute  division  from 
the  bronchial  system  of  tubes.  The  lobules  which  lie  more  deeply  in  the  substance  of 
the  organ  are  not  so  large,  and  are  irregularly  polygonal  in  form. 

Alveolar  Ducts,  Infundibula,  and  Air-cells. — The  larger  branches  of  the 
bronchi,  as  they  traverse  the  lung,  give  off  numerous  divisions  which,  by  repeated 
branching,  ultimately  form  a  system  of  tubes  which  pervade  the  entire  organ.  At 
first  the  bronchial  divisions  come  oft'  at  very  acute  angles,  but  as  the  finer  ramifications 
are  reached  this  character  becomes  much  less  apparent.  There  is  no  anastomosis  between 
the  bronchial  branches. 

Within  the  various  lobules  the  finer  bronchioles  send  ott'  further  branches,  which  pro- 
ceed at  right  angles  from  them.  Soon  the  ultimate  tubes  are  reached.  These  are  not 
cylindrical,  but  have  their  walls  pouched  out  by  numerous  hemispherical  diverticula. 
Such  a  bronchiole  is  called  an  alveolar  duct,  and  the  diverticula  are  the  air-cells  or  alveoli. 
Finally  the  alveolar  duct  divides  into  two,  three,  or  more  terminal  parts,  which  become 
expanded  and  form  the  club-shaped,  blind  terminations  of  the  bronchial  system  of  tubes. 
These  csecal  endings  are  the  infundibula,  and  the  walls  of  each  are  thickly  covered  by 
alveoli  or  air-cells,  all  of  which  open  into  the  infundibulum  as  into  a  corridor. 

Structure  of  the  Bronchi, — When  the  large  bronchi  enter  the  lung  they  become 
cylindrical,  and  lose  the  flattening  on  the  posterior  aspect  which  is  characteristic  of  the 
primary  bronchi  outside  the  lung.  They  possess  the  same  coats  as  are  present  in  the  case 
of  the  trachea  and  primary  bronchi,  but  as  the  tubes  become  smaller  by  repeated  division, 
these  coats  become  correspondingly  thinner  and  finer.  Certain  marked  ditfereuces  also  in 
the  manner  in  which  the  constituents  of  these  coats  are  arranged  become  apparent. 

In  the  external  fibro-cartilaginous  coat  the  cartilage  is  no  longer  present  in  the  form 
of  incomplete  rings,  but  in  irregular  plates  or  flakes  deposited  at  vai'ious  points  around 
the  wall.  As  the  tubes  diminish  these  cartilaginous  deposits  show  a  corresponding  reduc- 
tion in  size,  until  at  last,  in  bronchi  of  1  mm.  in  diameter,  they  disappear  altogether.  The 
glands  in  relation  to  the  tubes  for  the  most  part  cease  to  exist  about  the  same  point. 
The  muscular  or  middle  coat,  which  in  the  trachea  and  primary  bronchi  is  confined  to 
the  back  wall  of  the  tube,  forms  a  continuous  layer  of  circularly-arranged  bundles  in  the 
bronchi  as  they  ramif}^  within  the  lung.  Spasmodic  contraction  of  the  muscular  coat  gives 
rise  to  the  serious  symptoms  which  accompany  asthmatic  atlections.  The  muscular  fibres 
of  the  middle  coat  may  be  traced  as  far  as  the  infundibula,  on  the  walls  of  which  they  are 
present  in  considerable  numbers.  The  mucous  lining  of  the  tubes  becomes  greatly  thinned 
as  it  is  followed  into  the  smaller  bronchioles.  It  contains  a  large  number  of  longitudinally- 
arranged  elastic  fibres,  and  is  disposed  in  longitudinal  folds,  so  that  when  the  tube  is  cut 
across  the  lumen  presents  a  stellate  appearance.  The  mucous  membrane  is  lined  by 
ciliated  columnar  epithelium. 

Structure  of  the  Infundibula  and  Alveoli. — The  walls  of  the  infundibula  and 
alveoli  are  exceedingly  fine  and  delicate,  but  nevertheless  constituents  continuous  with 
those  observed  in  the  three  coats  of  a  bronchus  are  found  entering  into  their  construction. 
The  epithelium  is  reduced  to  a  single  layer.  Further,  it  is  no  longer  columnar  and 
ciliated,  but  it  has  become  flat  and  pavement-like.  Two  kinds  of  epithelial  cells  may  be 
recognised — (1)  a  few  small  granular  polygonal  cells,  arranged  singly  or  in  groups  of  two 
or  three ;  (2)  moi'e  numerous  thin  cells  of  large  size,  and  somewhat  irregular  in  outline. 
Outside  the  epithelium  is  a  delicate  layer  of  faintlj'-fibrillated  connective  tissue.  This  is 
strengthened  by  a  network  of  elastic  fibres  which  is  specially  well  marked  around  the 
mouths  of  the  alveoli,  and  is  also  to  some  extent  carried  over  the  walls  of  the  air-cells. 
Muscular  fibres  are  likewise  present  on  the  walls  of  the  infundibula,  but  it  is  questionable 
if  any  are  pi'olonged  over  the  air-cells. 

Pulmonary  Vessels. — The  pulmonary  artery,  as  it  traverses  the  lung,  divides  with 
the  bronchi,  and  closely  accompanies  these  tubes.  The  resultant  branches  do  not  anasto- 
mose, and  for  the  most  part  they  lie  above  and  behind  the  corresponding  bronchi.  The 
fine  terminal  divisions  of  the  artery  join  a  dense  capillary  plexus  which  is  spread  over  the 
alveoli  or  air-cells.  This  vascular  network  is  so  close  that  the  meshes  are  barely  wider 
than  the  capillaries  which  form  them.  In  the  partitions  between  adjacent  alveoli  there 
is  only  one  layer  of  the  capillary  netwoi-k,  and  thus  the  blood  flowing  through  these 
vessels  is  exposed  on  both  aspects  to  the  action  of  the  air  in  the  air-cells.     The  radicles 


992  THE  EESPIEATOEY  SYSTEM. 

of  the  pulmonary  vein  arise  in,  and  carry  the  blood  from,  the  pulmonary  capillary  plexus. 
Each  afterent  arteriole  supplies  the  blood  which  flows  through  the  capillaries  spread  over 
a  number  of  neighbouring  alveoli,  atid  in  like  manner  each  efterent  venous  radicle  drains 
au  area  corresponding  to  several  adjoining  air-cells.  At  first  the  veins  run  apart  from 
the  arteries,  but  after  they  have  attained  a  certain  size  they  join  them  and  the  bronchi. 
As  a  rule  the  pulmonary  veins  are  placed  on  the  lower  and  front  aspect  of  the  corre- 
sponding bronchi. 

Development  of  the  Eespikatory  Appaeatus. 

The  larynx,  the  trachea,  the  bronchi,  and  the  lungs  arise  as  an  outgrowth  from  the 
ventral  aspect  of  the  foregut.  The  first  indication  of  a  respiratory  tract  occurs  in  the 
human  embryo  when  it  has  attained  a  length  of  3 "2  mm.,  on  or  about  the  fifteenth  day 
of  development.  A  median  longitudinal  groove  makes  its  appearance  within  the  foregut 
on  its  ventral  wall.  This  extends  from  the  pharynx  in  front  to  the  region  of  the  stomach 
behind,  and  it  gradually  deepens  as  it  passes  backwards.  The  hinder  or  gastric  end  of 
the  pulmonary  groove  ends  in  a  blind  diverticulum  or  pocket,  which  freely  communicates 
with  the  cavity  of  the  foregut,  and  forms  a  hollow  median  protrusion  on  the  ventral 
aspect  of  this  portion  of  the  primitive  alimentary  canal.  The  opposite  end  of  the  groove 
is  bounded  by  the  furcula  (see  p.  35).  Further,  it  is  lined  with  endoderm  or  hypoblast 
continuous  with  the  endodermal  lining  of  the  foregut. 

Trachea  and  Larynx. — The  pulmonaiy  groove  on  the  ventral  aspect  of  the  foregut 
becomes  first  partially  and  then  completely  separated  from  the  part  of  the  foregut  which 
lies  on  its  dorsal  aspect  by  two  lateral  ridges  which  grow  inwards  and  finally  meet.  Two 
tubes  are  thus  formed — viz.  one  behind,  the  oesophagus,  and  the  other  in  front,  the 
trachea  and  larynx.  At  their  cephalic  ends  a  communication  between  the  two  tubes  is 
preserved  as  the  permanent  communication  between  the  larynx  and  pharynx. 

The  cephalic  end  of  the  air-tube  which  is  thus  separated  off"  from  the  foregut  becomes 
enlarged  to  form  the  larynx,  whilst  the  remainder  is  developed  into  the  trachea.  The 
cai-tilages  of  the  larynx  do  not  make  their  appearance  until  the  eighth  or  ninth  week. 
The  thyroid  cartilage  is  believed  to  be  formed  out  of  the  ventral  jDortions  of  the  cartilages 
which  support  the  4th  and  5th  visceral  arches  of  the  two  sides  united  in  the  median  plane. 
The  epiglottis  takes  form  in  the  upper  or  front  part  of  the  furcula  (see  chapter  on  Embryo- 
logy, p.  35),  whilst  the  aryteno-epiglottidean  folds  and  the  ar3^tenoid  cartilages  are 
developed  in  its  lateral  portions.  The  cricoid  cartilage  and  the  tracheal  rings  are  formed 
in  the  mesoderm  of  the  air-tube. 

Lungs  and  Bronchi. — The  endodermic  diverticulum,  or  pocket  in  which  the  gastric 
end  of  the  primitive  respiratory  groove  terminates,  very  early  bifurcates  into  two  vesi- 
cular portions,  which  represent  the  primitive  right  and  left  bronchi  and  lungs.  From  the 
first  the  right  pulmonary  vesicle  is  slightl}^  the  larger  of  the  two.  Both  elongate,  and 
almost  immediately  each  part  undergoes  a  subdivision — the  right  into  three  vesicles,  and 
the  left  into  two  vesicles — thus  early  indicating  the  three  lobes  of  the  right  lung  and  the 
two  lobes  of  the  left  lung.  The  endodermal  cells  form  the  epithelial  lining  of  the  air- 
passages,  whilst  from  the  mesoderm  are  derived  the  blood-vessels  and  the  other  tissues 
which  build  up  the  lung.  The  hypoblastic  or  endodermal  subdivisions  thus  formed  are 
embedded  within  the  surrounding  mesoderm.  The  main  endodermal  subdivisions  continue 
to  branch  and  rebranch,  pushing  their  way  into  the  pulmonary  mesoblast,  until  the 
complete  bronchial  tree  is  formed.  The  method  of  subdivision  is  very  characteristic,  and 
from  the  first  the  various  branches  are  bulbous  or  flask-shaped  at  their  extremities. 
These  bifurcate,  and  although  at  first  the  two  subdivisions  in  each  case  appear  of  equal 
importance,  one  grows  out  as  the  continuation  of  the  main  bronchial  stem,  whilst  the 
other  remains  as  a  lateral  branch.  When  the  ramification  of  the  endodermal  tubes  into 
the  lung  mesoderm  is  complete,  the  small  terminal  flask-shaped  extremities  of  the  various 
branches  represent  the  infundibula.  At  first  these  are  devoid  of  air-cells,  but  between 
the  sixth  month  and  the  termination  of  gestation  the  alveolar  diverticula  make  their 
appearance  on  the  alveolar  ducts  and  on  the  infundibula.  It  is  thus  seen  that  the 
epithelial  lining  of  the  entire  system  of  bronchial  tubes,  infundibula  and  alveoli,  is 
originally  derived  from  the  endodermal  lining  of  the  foregut.  The  other  constituents 
which  enter  into  the  constitution  of  the  lungs  and  bronchi  are  derived  from  the  mesoblast. 
The  rudiments  of  the  lungs  grow  backwards  on  either  side  of  the  oesophagus  into  the 
fissure-like  portion  of  the  coelom  which  occupies  the  thoracic  region.  They  push  before 
them  the  epithelial  lining  of  the  latter,  and  thus  acquire  their  covering  of  visceral  pleura. 
By  the  development  of  the  diaphragm  and  the  pericardium  the  pleural  portions  of  the 
coelom  become  cut  off  from  the  peritoneal  cavity  and  from  each  other. 


THE  DIGESTIVE  SYSTEM. 

By  Ambrose  Birmingham. 

Under  this  head  will  be  described  the  parts  which  are  connected  with  the 
reception  and  mastication  of  the  food,  and  its  digestion  and  passage  through  the 
body.  As  the  greater  part  of  the  digestive  system  is  placed  within  the  abdomen, 
the  description  of  this  cavity  as  a  whole,  with  that  of  its  lining  membrane  the 
peritoneum,  will  be  included. 

The  different  parts  of  the  digestive  system  may  be  grouped  under  the  following 
heads,  viz : — 

1.  The  Alimentary  Canal  or  Digestive  Tube. 

2.  The  Digestive  Glands. 

3.  Accessory  Parts. 

Alimentary  Canal. — The  alimentary  canal,  taken  as  a  whole,  measures  about 
30  feet  in  length  (Fig.  705),  and  consists  of  the  following  parts  in  order : — mouth, 
pharynx,  oesophagus,  stomach,  small  and  large  intestines.  The  mouth  is  the  first 
division  of  the  tube.  It  is  separated  from  the  nasal  cavities  above  by  the  palate, 
and  opens  behind  into  the  pharynx.  This  latter  is  an  expanded  portion  of  the 
canal  lying  behind  both  the  mouth  and  the  nasal  cavity,  the  former  opening  into 
it  through  the  isthmus  of  the  fauces,  the  latter  through  the  posterior  nares ;  whilst 
lower  down,  immediately  below  the  base  of  the  tongue,  the  aperture  of  the  larynx 
is  found  on  its  anterior  wall.  Opposite  the  lower  border  of  the  larynx,  the  pharynx 
is  succeeded  by  the  oesophagus,  a  long  and  comparatively  straight  portion  of  the 
digestive  tube,  leading  through  the  neck  and  thorax  to  the  abdomen,  wliich  it 
reaches  by  piercing  the  diaphragm.  Immediately  after  entering  the  abdomen  the 
tube  expands  into  a  pear-shaped  dilatation,  the  stomach.  This  is  followed  by  over 
20  feet  of  small  intestine,  the  junction  of  the  two  being  marked  by  a  constriction, 
the  pylorus.  The  small  intestine  presents  three  more  or  less  arbitrary  divisions — 
namely,  (a)  the  duodenum,  a  part  about  10  inches  in  length,  cur^■ed  somewhat  hke 
a  horse-shoe,  and  closely  united  to  the  posterior  abdominal  wall ;  (b)  the  jejunum, 
which  includes  the  upper  two-fifths,  and  (c)  the  ileum,  the  lower  three-fifths  of  the 
smaU  intestine  beyond  the  duodenum.  The  jejunum  and  ileum  are  movably 
suspended  from  the  posterior  abdominal  wall  by  tlie  mesentery,  a  fan- shaped  fold 
of  the  peritoneum  or  lining  membrane  of  the  abdominal  cavity.  The  terminal  part 
of  the  ileum  opens  into  the  side  of  the  large  intestine,  a  few  inches  (2^)  from  the 
blind  commencement  of  the  latter.  There  is  thus  formed  at  the  beginning  of  the 
great  intestine  a  cul-de-sac,  the  csecum,  in  connexion  with  which  is  found  a  small 
worm-shaped  diverticulum,  the  vermiform  appendix. 

The  orifice  through  which  the  ileum  opens  into  the  large  intestine  is  guarded 
by  the  ileo-caecal  valve,  which  prevents  any  return  of  its  contents  from  the  large  into 
the  small  bowel.  After  the  ctecum  comes  the  ascending  colon,  which  runs  up  in 
the  right  side  of  the  abdomen.  This  is  succeeded  in  order  by  the  transverse  colon 
crossing  from  right  to  left,  the  descending  colon  running  down  on  the  left  side,  the 
sigmoid  flexure  of  the  colon  (which  includes  the  iliac  and  greater  part  of  the  pelvic 
colons  of  the  text),  and  finally  the  rectum,  which  opens  on  the  surface  at  the  anus. 

Digestive    Glands. — AVhilst    the   greater   part   of    the   alimentary   canal   is 
furnished    with    numerous   minute    glands   contained    entirely    within    its   w^alls, 
67  993 


994 


THE  DIGESTIVE  SYSTEM. 


there  are  in  addition  certain  special  accumulations  of  glandular   tissue,  namely, 
the  liver,  the  pancreas,  and  the  salivary  glands,  which,  although  developed  in  the 


Xaso-pliaryiix 

Cavity  of  mouth 
Pharynx 

Opening  of  larynx 


Transverse  colon  (cut)  > 


Hepatic  flexure  of  cole 


Common  orifice  of  bile  and 
pancreatic  ducts 


Uuodenui 


Pancreatic  duct 


Splenix  flexure  of  colon 


Fio.  705. — Geneual  View  of  the  JJicestive  System  (diagrammatic). 

The  transverse  colon  has  been  cut  to  show  the  duodenum,  but  its  course  is  Indicated  by  dotted  lines.  The 
vermiform  appendix  is  seen  hanging  down  from  the  Ciecum.  The  loop  of  large  intestine  which  precedes 
the  rectum  is  marked  "sigmoid  flexure,"  and  includes  tlie  iliac  colon  and  the  gi-eater'part  of  the  pelvic 
colon. 

embryo  as  outgrowths  of  its  wall,  lie  entirely  outside  the  tube  in  the  adult, 
and  are  connected  with  it  by  special  ducts  through  which  the  gland-secretions 
pass.     The  largest  of  these,  the  liver,  is  placed  in  the  upper  and  right  portion  of 


THE  MOUTH.  995 

the  abdominal  cavity,  immediately  beneath  the  diaphragm,  and  its  secretion — 
the  bile — ^is  conveyed  into  the  duodenum  by  the  bile  duct.  The  pancreas,  next  in 
size,  lies  across  the  front  of  the  vertebral  column,  with  its  right  end  or  head  resting 
in  the  concavity  of  the  duodenum,  into  which  its  secretion  flows  through  the 
pancreatic  duct.  The  salivary  glands,  of  which  there  are  three  chief  pairs — parotid, 
submaxillary,  and  sublingual — are  placed  about  the  face,  and  their  ducts,  which 
convey  the  saliva,  open  into  the  mouth.  Whilst  the  secretion  of  these  latter 
undoubtedly  possesses  some  digestive  action,  and  they  must  consequently  be  classed 
as  digestive  glands,  nevertheless  the  saliva  is  to  be  looked  upon  as  a  mechanical 
lubricant,  which  facilitates  swallowing  and  the  movements  of  the  tongue  in  speaking 
and  masticating,  rather  than  as  an  aid  to  the  digestive  process. 

Accessory  Parts. — Under  this  heading  we  group  the  teeth,  tongue,  gums, 
palate,  and  tonsils.  The  teeth,  32  in  number  in  the  adult,  are  embedded  in  the 
jaws  and  surrounded  by  the  gums.  The  tongue  is  a  muscular  organ,  useful  alike 
in  masticating,  swallowing,  speaking,  and  in  tlie  exercise  of  the  sense  of  taste, 
which  specially  resides  in  its  modified  epithelium  ;  it  occupies  the  greater  portion 
of  the  floor  of  the  mouth,  whilst  the  roof  of  that  cavity  is  formed  by  the  hard 
palate  anteriorly,  and  by  the  soft  palate  behind,  finally,  the  tonsils  (Fig.  707)  are 
two  large  masses  of  lymphoid  tissue,  found  on  the  side-walls  of  the  oral  portion  of 
the  pharynx,  just  behind  the  mouth. 

THE  MOUTH. 

The  mouth  is  the  expanded  upper  portion  of  the  digestive  tube,  specially 
modified  for  the  reception  and  mastication  of  the  food.  In  it  we  distinguish :  the 
aperture  of  the  mouth  placed  between  the  lips ;  the  vestibule,  the  slit-like  space 
which  intervenes  between  the  teeth  and  gums  internally,  and  the  lips  and  cheeks 
externally  (Fig.  706) ;  and  the  cavity  of  the  mouth,  which  lies  within  the  round  of 
the  dental  arches,  and  opens  behind  into  the  pharynx  through  the  isthmus  of  the 
fauces  (Fig.  707). 

The  aperture  of  the  mouth  (rima  oris)  is  the  upper  or  anterior  opening  of  the 
alimentary  canal,  and  is  bounded  above  and  below  by  the  corresponding  lips, 
which,  by  their  junction  at  the  sides,  form  the  angles  of  the  mouth  (commissurae 
labiorum).  In  a  state  of  rest,  with  the  lips  in  apposition,  the  rima  appears  as  a 
slightly  curved  hue,  corresponding  in  length  to  the  interval  between  the  first 
premolar  teeth,  and  in  level  to  a  line  drawn  across  just  below  the  middle  of  the 
upper  incisor  crowns.  The  shape  of  the  rima  varies  with  every  movement  of  the 
lips,  from  the  resting  Unear  form,  curved  like  the  conventional  bow,  to  a  circular 
or  oval  shape  when  the  mouth  is  widely  open,  or  tbe  "  pursed  up  "  condition  pro- 
duced by  the  contraction  of  the  orbicularis  oris. 

The  vestibule  (vestibulum  oris.  Fig.  706)  lies  immediately  within  the  aperture 
of  the  mouth.  In  the  normal  resting  condition  its  cavity  is  practically  obliterated 
by  the  meeting  of  its  walls,  which  reduces  it  to  a  slit-like  space.  It  is  limited  on 
the  one  hand  by  the  deep  surface  of  the  lips  and  cheeks,  and  on  the  other  by  the 
dental  arches  and  gums.  Its  narrow  roof  and  floor  are  formed  respectively  by  the 
reflection  of  the  mucous  membrane,  from  the  deep  surface  of  the  lips  and  cheeks  to 
the  corresponding  gum.  This  reflection  is  interrupted  in  the  middle  hue  by  a 
small  but  prominent  fold  of  the  mucous  membrane,  the  frenulum,  which  connects 
the  back  of  each  lip  to  the  front  of  the  gum.  The  upper  frenulum  is  the  better 
developed,  and  is  readily  brought  into  view  by  everting  the  lip. 

On  the  outer  wall  of  the  vestibule,  opposite  the  crown  of  the  middle  upper 
molar,  is  seen,  upon  a  variably  developed  eminence  (Fig.  716),  the  small  opening  of 
Stenson's  duct,  which  conveys  the  saliva  from  the  parotid  gland  to  the  mouth. 

When  the  teeth  are  in  contact  the  vestibule  communicates  with  the  cavity  of 
the  mouth,  only  through  the  small  and  irregular  spaces  left  between  the  opposing 
teeth,  and  posteriorly  by  a  wider  but  variable  aperture  behind  the  last  molars. 

Advantage  is  sometimes  taken  of  the  presence  of  this  aperture,  which  lies  between  the 
wisdom  teeth  and  the  ramus  of  the  jaw,  for  the  introduction  of  liquid  food  in  certain  cases— 
trismus,  anchylosis,  etc. — in  wliich  the  mouth  is  rigidly  closed. 


996 


THE  DIGESTIVE  SYSTEM. 


The  anterior  border  of  the  masseter  can  be  distinctly  felt  with  the  finger,  on  the  outer  wall 
of  the  vestibule,  when  the  muscle  is  thrown  into  a  state  of  contraction.  Still  further  back,  the 
front  of  the  coronoid  process,  bearing  the  lower  part  of  the  insertion  of  the  temporal  muscle,  can 
be  easily  made  out.  Whilst  the  pterygo-maxillary  ligament,  which  corresponds  to,  and  is  felt 
along  with,  tlie  anterior  border  of  the  internal  pterygoid,  is  distinguishable  as  a  pliant  ridge 
when  the  finger  is  carried  from  the  front  of  the  coronoid  process  inwards  behind  the  wisdom 
teeth  to  the  cavity  of  the  mouth. 

In  addition  to  Stenson's  duct,  the  ducts  of  numerous  small  glands  which  are  embedded  in  the 
li23S  and  cheeks  open  into  the  vestibule. 

Under  normal  conditions,  as  pointed  out  above,  the  lips  and  cheeks  lie  against  the  teeth  and 
gums,  obliterating  the  cavity  of  the  vestibule,  and  helping,  with  the  aid  of  the  tongue,  to  keep 
the  food  between  the  grinding  surfaces  of  the  molar  teeth  during  mastication.  In  facial  palsy, 
however,  owing  to  the  paralysis  of  their  muscles,  the  lips  and  cheeks  fall  away  from  the  dental 
arches,  and  allow  the  food  to  pass  out  from  between  the  teeth  and  to  accumulate  in  the  vestibule. 

Lips  (labia  oris,  Fig.  708). — These  are  the  two  movable  folds,  covered  superfici- 
ally by  skin,  and  on  their  deep  surface  by  mucous  membrane,  which  surround  the 
rima  oris.     Laterally  the  two  meet  at  the  angles  of  the  mouth,  and  beyond  this  are 


— Palatine  glands 


Buccinator 


Genio-hyoid 


Mylo-liyoid 


Digastric 
Platysma 


Fig.  706. — Coronal  Section  through  the  closed  Mouth. 

The  slit-like  character  of  the  vestibule,  the  manner  in  which  the  tongue  fills  up  the  mouth  cavity,  the 
close  apposition  of  the  teeth,  the  relations  of  the  roots  of  the  upper  molars  to  tlie  antrum  of  High- 
more,  the  plica  sublingualis  over  the  sublingual  gland,  and  the  position  of  the  rauine  artery  shonld 
be  noted. 

prolonged  into  the  cheeks,  with  which  they  are  continuous.  The  upper  lip  presents 
on  its  superficial  surface  a  well-marked  vertical  groove,  the  philtrum,  bounded  by 
two  distinct  ridges  descending  from  the  columella  nasi  (Fig.  71:^);  inferiorly  the- 
groove  widens  out,  and  terminates  opposite  a  slight  projection — the  labial  tubercle 
— on  the  free  edge  of  the  upper  lip.  This  tubercle  is  particularly  well  developed 
in  children,  and  is  chiefly  responsible  for  the  characteristic  curve  of  the  rima  oris. 
The  lower  is  usually  longer  and  more  movable  than  the  upper  lip. 

In  passing  from  before  backwards  the  following  structures  are  found  in  the 
lips : — (1)  The  skin,  which  is  closely  beset  with  hairs,  small  and  fine  in  the  child 
and  female,  long  and  stout  in  the  adult  male.  (2)  A  layer  of  fatty  superficial  fascia 
continuous  with  the  fascia  of  the  face  generally.  (3)  The  orbicularis  oris  muscle, 
continuous  at  its  periphery  with  the  various  muscles  converging  towards  the  mouth. 
A  number  of  its  fibres,  or  tliose  of  the  muscles  joining  it,  pass  through  the  super- 
ficial fascia  and  are  attached  to  the  skin,  thus  establisliing  a  close  connexion 
between  the  latter  and  the  muscle.  (4)  The  submucous  tissue,  which  is  occupied 
by  an  almost  continuous  layer  of  racemose  glands — the  labial  glands  (glandulee 
labiales).  These  open  into  the  vestibule,  and  their  secretion  is  said  to  be 
mucous.  (5)  The  mucous  membrane  of  the  mouth,  covered  by  stratified  squamous 
epithelium.     Between  the  orbicularis  and  mucous  membrane,  but  nearer  to  the 


THE  MOUTH.  997 

former,  that  is,  in  the  deeper  part  of  the  submucosa,  the  coronary  artery  is 
found  a  short  distance  from  the  free  margin  of  the  Hp,  running  to  meet  its  fellow 
of  the  opposite  side. 

The  free  margin  of  the  lip  is  covered  by  a  dry  and  otherwise  modified  mucous  membrane. 
It  begins  where  the  integument  changes  colour  at  the  outer  edge  of  the  lij),  and  ends  posteriorly 
just  behind  the  line  along  which  the  two  lips  meet  when  closed,  where  it  passes  into  the  ordinary 
moist  mucous  membrane  of  the  vestibule.  It  presents  numerous  simple  vascular  papillue,  and 
its  nerves  (which  are  derived  from  the  infra-orbital  in  the  upper  lip,  from  the  long  buccal  at  the 
angles,  and  from  the  mental  branch  of  the  inferior  dental  in  the  lower  lip)  terminate  in  special 
end  organs,  hence  the  acute  sensitiveness  of  this  part.  In  tlie  child,  at  birth,  the  margin  of  the 
lip  is  divided  by  a  very  pronounced  groove  or  fissure  into  an  outer  and  an  inner  zone,  differing 
consideralily  in  their  appearance. 

When  the  tongue  is  invssed  firmly  against  the  back  of  the  lijxs  and  moved  about,  the  labial 
glands  can  be  distinctly  felt  through  the  mucous  membrane,  giving  the  impression  of  a  knobby 
or  irregular  surface.  The  glands,  which  are  about  the  size  of  hemp-.seeds  and  can  be  readily 
displayed  by  removing  the  mucous  membrane,  are  more  numerous  in  the  lower  than  in  the 
upper  lip.  Stoppage  of  their  ducts,  with  the  resulting  distension  of  the  glands,  gives  rise  to 
"  mucous  cysts,"  a  well-known  pathological  condition. 

It  should  be  remembered,  in  connexion  with  epithelioma  of  this  part,  that  the  lymphatics  of 
both  lips  pass  down  to  join  the  submaxillary  lymijhatic  glands. 

Cheeks  (buccne). — The  cheeks  resemble  the  lips  in  structure,  being  formed  of  cor- 
responding layers.  Superficially  is  the  skin.  Under  this  lies  the  fatty  superficial 
fascia  of  the  face,  through  which  Stenson's  duct  runs  inwards  to  pierce  the 
buccinator ;  in  it  also,  near  the  end  of  the  duct,  are  found  four  or  five  mucous 
glands,  as  large  as  hemp-seeds.  These  are  known  as  the  molar  glands  (glandul* 
molares);  their  ducts  pierce  the  cheek  and  open  into  the  vestibule.  Beneath 
this  superficial  fascia  lies  the  buccinator  muscle,  covered  by  the  thin  bucco- 
pharyngeal aponeurosis.  Deeper  still  is  the  submucosa,  which,  like  that  of 
the  lips,  contains  numerous  racemose  buccal  glands  (glandul^e  buccales).  And 
finally  the  mucous  membrane  is  reached  (Fig.  709). 

An  important  constituent  of  the  cheek  of  the  infant  is  the  sucking  pad  (corjjus  adiposum 
buccae),  an  encapsuled  mass  of  fat,  distinct  from  the  surrounding  superficial  fascia,  which  lies  on 
the  outer  side  of  the  buccinator,  and  passes  backwards  into  the  large  recess  between  that  muscle 
and  the  overlying  anterior  part  of  the  masseter.  This  fatty  mass,  which  is  relatively  more 
developed  in  the  child  than  in  the  adult,  strengthens  the  cheek,  and  helps  it  to  resist  the  effects 
of  atmospheric  pressvu'e  during  the  act  of  sucking.  In  the  adult  the  remains  of  the  pad  can  be 
distinctly  made  out  under  the  anterior  border  of  the  masseter. 

Cavity  of  the  Mouth  Proper  (cavum  oris  proprium). — This  is  the  space 
situated  within  the  dental  arches.  The  latter,  with  the  gums,  separate  it  from 
the  vestibule  (Fig.  706),  so  that  the  two  communicate,  when  the  teeth  are  in 
contact,  only  by  the  irregular  interdental  spaces,  and  through  the  passages  behind 
the  wisdom  teeth  already  referred  to. 

Posteriorly  the  cavity  of  the  mouth  opens,  through  the  isthmus  of  the  fauces, 
into  the  pharynx  (Fig.  707). 

Its  roof  is  formed  by  the  hard  and  the  greater  part  of  the  soft  palate ;  whilst 
its  floor,  in  the  ordinary  resting  condition,  is  entirely  occupied  by  the  tongue 
(Fig.  709).  If,  however,  the  tip  and  marginal  parts  of  the  tongue  be  raised,  there 
is  exposed  a  hmited  surface  to  which  the  term  "  floor  of  the  mouth  "  or  sublingual 
region  is  more  usually  apphed  (Fig.  712). 

The  sublingual  region  (Fig.  712)  is  covered  by  the  oral  mucous  membrane  which 
is  carried  across  from  the  deep  surface  of  the  gum  to  the  inferior  aspect  of  the 
tongue,  with  the  mucous  membrane  of  which  it  becomes  continuous.  When  the 
tip  of  the  tongue  is  raised  the  membrane  forms  in  the  middle  line  a  prominent 
fold,  the  frenum  linguae,  stretching  from  the  floor  of  the  mouth  to  the  under  surface 
of  the  tongue.  On  each  side  of  the  frenum,  near  its  junction  with  the  floor,  there 
can  be  readily  made  out  a  prominent  soft  papilla  (caruncula  sublingualis),  on 
which  the'  opening  of  Wharton's  duct  (of  the  submaxillary  gland)  may  be  seen 
(Fig.  712).  Eunning  outwards  and  backwards  on  each  side  from  this,  and  occupy- 
ing the  greater  part  of  the  floor  of  the  mouth,  there  is  a  well-marked  ridge  (plica 
sublingualis)  due  to  the  projection  of  the  underlying  sublingual  gland,  most  of  the 
ducts  of  which  open  near  the  crest  of  the  ridge. 


998  THE  DIGESTIVE  SYSTEM. 

"When  the  moiitli  is  closed,  and  respiration  is  carried  on  througli  the  nose,  the  cavum  oris 
is  reduced  to  a  slit-like  space,  and  practically  obliterated  by  the  tongue  coming  in  contact 
with  the  palate  above,  and  with  the  gums  and  teeth  laterally  and  in  front  (Fig.  706).  When  the 
mouth  is  slightly  oj^en  and  the  teeth  nearly  in  contact,  the  tongue  becomes  somewhat  concave 
or  grooved  along  tlie  middle  line,  and  leaves  a  channel-like  space  between  it  and  the  palate,  while 
it  remains  in  contact  with  the  roof  and  gums  laterally.  By  depressing  the  hyoid  bone  with  the 
root  of  the  tongue,  the  cavum  oris  can  be  increased  to  a  considerable  size  even  when  the  teeth  are 
in  contact.  Finally,  by  the  simultaneous  descent  of  the  lower  jaw  and  hyoid  bone  with  the  tongue, 
and  the  ascent  of  the  soft  palate,  the  cavity  is  increased  to  its  greatest  dimensions  (Fig.  707). 

Gums  (gingivae). — This  term  is  applied  to  the  red  firm  tissue,  continuous  with 
the  mucous  membrane  of  the  vestibule  on  the  one  hand,  and  with  that  of  the 
palate  or  floor  of  the  mouth  on  the  other  (Fig.  706),  which  covers  the  alveolar 
borders  of  the  maxilla  and  mandible,  and  surrounds  the  necks  of  the  teeth. 
The  gums  are  composed  of  dense  fibrous  tissue,  inseparably  united  to  the  periosteum 
and  covered  by  mucous  membrane.  They  are  richly  supplied  with  blood-vessels, 
but  sparsely  with  nerves,  and  are  covered  by  stratified  squamous  epithelium. 
Around  the  neck — or  more  correctly  the  base  of  the  crown — of  each  tooth,  the  gum 
forms  a  free  overlapping  collar,  and  at  this  part  particularly  it  is  closely  beset  with 
small  papillae,  visible  to  the  naked  eye.  In  thickness  it  usually  measures  from  1 
to  2  mm. 

THE  PALATE  AND  ISTHMUS  FAUCIUM. 

The  palate  (palatum)  is  the  term  applied  to  the  strongly-arched  structure  which 
forms  the  roof  of  the  mouth,  and  projects  posteriorly  into  the  pharynx  as  a  pliant 
fold,  imperfectly  dividing  that  cavity  into  two  (Figs.  708  and  710).  Its  anterior  half 
or  more  has  a  foundation  of  bone,  and  separates  the  nasal  fossae  from  the  mouth. 
This  part  is  known  as  the  hard  palate.  The  posterior  portion,  which  is  free  from 
bone,  separates  the  naso-pharynx  above,  from  the  mouth  and  oral  pharynx  below, 
and  is  known  as  the  soft  palate. 

The  hard  palate  (palatum  durum.  Fig.  708)  occupies  the  space  within  the 
upper  dental  arch,  and  is  continuous  with  the  gums  in  front  and  laterally,  whilst 
behind  it  passes  into  the  soft  palate.  It  is  formed  by  the  palatal  processes  of  the 
superior  maxillary  and  palate  bones  (Fig.  721),  covered  by  periosteum,  and  by  a 
layer  of  firm  mucous  membrane.  Beneath  this  mucous  membrane,  particularly  at 
the  sides  and  in  front,  is  found  a  considerable  quantity  of  dense  fibrous  tissue, 
firmly  united  to  the  periosteum  on  the  one  hand  and  to  the  mucous  membrane  on 
the  other.  This  dense  tissue  forms  an  effective  protection  for  the  palate,  and,  in 
addition  to  the  palatine  vessels  and  nerves,  it  contains  in  its  posterior  half  a  large 
number  of  racemose  (palatine)  glands. 

Traversing  the  middle  of  the  palate  is  seen  a  faint  central  ridge  or  raphe  (Fig.  707),  indicating 
its  original  development  from  two  lateral  halves.  Behind,  this  raphe  is  continued  along  the  soft 
palate  to  the  base  of  the  uvula,  and  in  front  it  ends  in  a  slight  elevation,  the  incisive  pad  or 
papilla  palatina.  From  the  anterior  end  of  the  raphe  a  series  of  transverse  ridges  of  mucous 
membrane,  about  six  in  number,  run  outwards,  just  behind  the  incisor  teeth  ;  they  are  known  as. 
the  palatine  rugse,  and  are  composed  of  dense  fibrous  tissue.  Sometimes  a  small  pit,  which  will, 
admit  tlie  point  of  a  pin,  is  seen  on  each  side  immediately  behind  the  central  incisor  teeth,  and 
about  2  mm.  from  the  middle  line.  These  pits  correspond  to  the  lower  openings  of  Stenson's 
canals,  with  which  they  are  occasionally  continuous. 

The  soft  palate  (palatum  molle,  or  velum  pendulum  palati.  Fig.  708)  is  a 
movaljle  valve-like  fold  which  runs  obliquely  downwards  and  backwards,  like  the 
"  tongue "  of  a  whistle,  across  the  cavity  of  the  pharynx  almost  as  far  as  its 
posterior  wall.  Whilst  it  is  attached  to  the  hard  palate  in  front,  and  blends  with 
the  pharyngeal  walls  laterally,  its  posterior  border  is  free,  and  between  it  and  the 
posterior  wall  of  the  pharynx  is  left  a  valvular  passage — the  isthmus  of  the 
pharynx — through  which  the  naso-pharynx  and  the  oral  pharynx  communicate 
with  one  another. 

The  soft  palate  is  composed  of  two  layers  of  mucous  membrane  between  which 
are  contained  the  palatine  muscles,  vessels,  nerves,  and  connective  tissue,  the 
aponeurosis  of  the  palate,  and,  in  addition,  a  very  large  number  of  racemose  glands. 
These  glands  are  arranged  in  a  thick  continuous  layer  on  the  inferior  surface  beneath 
the  mucous  membrane,  and  form  quite  one-half  of  the  mass  of  the  soft  palate 


THE  PALATE  AND  ISTHMUS  FAUCIUM. 


999 


The  pliilliLim 


Raphe  of  palate 


Tongue 


Fig.  707.— Open  Mouth  showing  Palate  and  Tonsils. 

It  also  shows  the  two  palatine  arches,  and  the  pharyngeal 
isthmus  through  which  the  naso-pharynx  above  com- 
municates with  the  oral  portion  of  the  pharynx 
below. 


generally,  whilst  in  its  anterior  part,  where  muscular  fibres  are  wanting,  they 
constitute  almost  its  entire  thickness. 

Its  upper  surface,  which  is  convex,  forms  a  continuation  backwards  and 
downwards  of  the  floor  of  the  nasal  fossie  (Fig.  708),  and  is  covered  hy  a  pro- 
longation of  the  nasal  mucous  mem- 
brane— ciKated  in  its  upper  half  or 
more.  The  under  surface  is  arched, 
and  prolongs  backwards  the  roof  of  the 
mouth,  towards  the  cavity  of  which  it 
looks.  In  front  the  soft  palate  is 
attached  to  the  posterior  edge  of  the 
hard  palate.  Laterally  it  blends  with 
the  side  wall  of  the  pharynx  along  a 
very  oblique  line  as  it  slopes  down- 
wards and  backwards  (Fig.  708).  Its 
posterior  margin  is  thin  and  free :  it 
presents  in  the  middle  line  an  elongated 
conical  projection,  the  uvula  (Fig.  707), 
and  at  each  side  of  this  a  sharp  con- 
cave edge  arches  outwards,  and  passing 
downwards  and  slightly  backwards 
becomes  continuous  with  a  ridge  on 
the  side  wall  of  the  pharynx  termed 
the  posterior  palatine  arch  (posterior 
pillar  of  fauces).  From  the  under 
surface  of  the  soft  palate,  7  or  8  mm. 
further  forwards,  and  near  the  base 
of  the  uvula,  spring  another  pair  of 
ridges,  the  anterior  palatine  arches 
(anterior  pillars  of  fauces),  which 
pass  downwards  and  slightly  forward  to  the  sides  of  the  tongue  (Fig.  707). 

The  anterior  part  of  the  soft  palate  for  8  or  10  mm.  {\  inch)  contains  practically  no 
muscular  fibres ;  it  is  composed  of  the  palatine  aponeurosis,  covered  by  an  extremely 
thick  layer  of  glands  on  the  under  surface  and  by  mucous  membrane  on  both  surfaces. 
This  anterior  portion  is  much  less  movable  than  the  rest  of  the  soft  palate,  and  forms  a 
relatively  horizontal  continuation  backwards  of  the  hard  palate,  stretching  across  between 
the  two  internal  pterygoid  plates.  It  is  upon  this  portion  chiefly  that  the  tensor  palati 
acts.  The  posterior  and  larger  part  contains  muscular  fibres  in  abundance,  slopes  strongly 
downwards,  and  is  freely  movable,  being  the  portion  upon  which  the  remaining  palatine 
•muscles  act. 

The  palatine  aponeurosis,  which  is  confined  to  the  anterior  part  of  the  soft  palate,  is  in 
the  form  of  a  thin  flat  sheet,  constituting,  as  it  were,  a  kind  of  common  tendon  for  the 
palatine  muscles  which  are  attached  to  (or  blended  with)  its  posterior  margin ;  whilst  its 
anterior  margin  is  united  to  the  posterior  edge  of  the  palatal  processes  of  the  palate  bone. 
With  the  exception  of  the  aponeurosis  of  the  tensor  palati  which  passes  into  its  lateral 
part,  the  muscles  do  not,  as  a  rule,  reach  further  forwards  than  to  within  8  or  10  mm.  of 
the  postei'ior  edge  of  the  hard  palate. 

The  uvula,  already  referred  to,  is  a  conical  projection,  very  variable  in  length,  which 
is  continued  downwards  and  backwards  from  the  middle  of  the  soft  palate.  It  is 
composed  chiefly  of  a  mass  of  racemose  glands  and  connective  tissue  covered  by  mucous 
membrane,  and  containing  a  slender  prolongation  of  the  azygos  uvuhe  muscle  in  its 
upper  part. 

The  mucous  membrane  of  the  palate,  which  is  covered  by  stratified  squamous  epithelium,  is 
firmer  and  more  closely  adherent  in  front,  near  the  ruga?,  than  behind,  near  the  soft  palate. 

Mucous  glands,  the  orifices  of  which  can  be  seen  as  dots  with  the  naked  eye,  are  extremely 
abundant  in  the  soft  palate,  and  in  the  posterior  half  of  the  hard  palate,  except  near  the  raphe. 
They  are  wanting  in  the  anterior  part  of  the  palate,  where  the  mucous  membrane  is  particularly 
dense. 

The  palatine  rugse  (which  correspond  to  more  strongly  developed  ridges  in  carnivora,  etc.)  are 
very  well  marked  in  the  child  at  birth,  although,  perhaps,  relatively  less  distinct  in  the  fcetus  of 
five  or  six  months;  in  old  age  they  become  more  or  less  obliterated  and  irregular.     At  birth, 


1000  THE  DIGESTIVE  SYSTEM. 

also,  and  in  the  fcetus,  the  incisive  pad  at  the  anterior  end  of  the  raphe  is  continued  over  the 
edge  of  the  gum  into  the  frenuhim  of  the  upper  lip. 

The  vessels  of  the  palate  are  derived  from  the  posterior  palatine  artery,  which  runs  forwards 
on  the  hard  palate  close  to  the  alveolar  border,  and  from  the  ascending  palatine  branch,  of  the 
facial,  which  accompanies  the  levator  palati  to  the  soft  palate. 

The  nerves — all  branches  of  Meckel's  ganglion — are :  the  large  posterior  palatine,  which 
descends  through  the  posterior  palatine  canal  and  runs  forward  on  the  hard  palate  with  the 
posterior  palatine  artery  ;  the  naso-palatine,  which  passes  down  through  the  foramen  of  Scarpa 
and  reaches  the  front  of  the  hard  palate  ;  and.  the  small  posterior  and  accessory  posterior  palatine 
nerves,  which  run  through  the  accessory  palatine  canals  and  supply  the  soft  palate. 

Fauces  or  Isthmus  of  the  Fauces  (isthmus  faucium). — This  is  the  aperture 
through  which  the  mouth  communicates  with  the  pharynx  (Fig.  707).  It  is 
bounded  at  the  sides  by  the  anterior  palatine  arches,  above  by  the  under  surface  of 
the  soft  palate,  and  below  by  the  dorsum  of  the  tongue ;  in  width  it  corresponds 
pretty  closely  to  the  cavum  oris. 

The  anterior  palatine  arches  (arcus  giosso-palatinus),  often  known  as  the  anterior 
pillars  of  tlie  fauces,  are  two  prominent  folds  of  mucous  membrane,  containing  the 
palato-glossus  muscles  in  their  interior,  which  bound  the  isthmus  of  the  fauces 
laterally  (Fig.  707).  Springing  above  from  the  under  surface  of  the  soft  palate,  a 
little  way  (about  8  mm.)  in  front  of  its  free  edge,  and  near  the  base  of  the  uvula, 
they  pass  downwards  and  slightly  forwards  to  join  the  tongue  a  little  behind  the 
middle  of  its  lateral  border. 

The  posterior  palatine  arch  is  described  with  the  pharynx  (p.  1034). 

THE  TONGUE. 

The  tongue  (lingua)  is  a  large  mobile  mass  composed  chiefly  of  muscular 
tissue,  and  covered  by  mucous  membrane,  which  occupies  the  floor  of  the  mouth 
and  forms  the  anterior  wall  of  the  oral  pharynx  (Fig.  708). 

AVhilst  the  sense  of  taste  resides  chiefly  in  its  modified  epithelium,  the  tongue 
is  also  an  important  organ  of  speech,  and,  in  addition,  it  assists  in  the  mastication 
and  deglutition  of  the  food — functions  which  it  is  well  fitted  to  perform;  owing  to 
its  muscular  structure  and  great  mobility.  In  length  it  measures,  when  at  rest, 
about  three  and  a  half  inches,  but  both  its  length  and  width  are  constantly 
varying  with  every  change  in  the  condition  of  the  organ,  an  increase  in  length 
being  always  accompanied  by  a  diminution  in  width,  and  vice  versa. 

In  describing  the  tongue  we  distinguish  the  following  parts :  the  body  (corpus 
lingua),  made  up  chiefly  of  striped  muscle,  and  forming  the  mass  of  the  organ  ;  the 
dorsum  (Fig.  709),  which  looks  towards  the  palate  and  pharynx,  and  is  free  in  its 
whole  extent;  the  base,  the  posterior  wide  end  which  is  attached  to  the  hyoid 
bone ;  the  apex  or  tip,  the  pointed  and  free  anterior  extremity ;  the  margin,  which  is 
free  in  its  anterior  half  or  more,  i.e.  in  front  of  the  attachment  of  the  anterior  palatine 
arch  (Fig.  709).  Finally,  the  unattached  portion  on  the  inferior  aspect,  seen  when 
the  apex  is  turned  strongly  upwards  (Fig.  712),  constitutes  the  inferior  surface ; 
whilst  the  attached  portion,  fixed  by  muscles  and  mucous  membrane  to  the  hyoid. 
bone  and  mandible,  is  known  as  the  root. 

The  dorsum  of  the  tongue  (dorsum  lingute),  when  the  organ  is  at  rest,  is 
strongly  arched  from  before  backwards  in  its  whole  length  (Fig.  708),  the  greatest 
convexity  corresponding  to  the  attachment  of  the  anterior  palatine  folds.  When 
removed  from  the  body  the  tongue,  unless  previously  hardened  i^i  situ,  loses  its 
natural  shape,  and  appears  as  a  flat,  elongated  oval  structure,  which  gives  a  very 
erroneous  idea  of  its  true  form  and  connexions. 

The  dorsum  is  naturally  divided  into  two  areas — an  anterior  or  oral  part,  which 
lies  nearly  horizontally  on  the  floor  of  the  mouth,  and  constitutes  about  two-thirds 
of  the  length  of  the  whole  tongue  (Fig.  709j ;  and  a  posterior  or  ijliaryngeal  imrt, 
the  remaining  third  of  the  organ,  which  is  placed  nearly  vertically,  and  forms  the 
anterior  wall  of  the  oral  pharynx  (Fig.  710).  The  separation  between  these  two 
parts,  which  differ  in  appearance  as  well  as  in  direction,  is  indicated  by  a  distinct 
V-shaped  groove,  called  the  sulcus  terminalis  (Fig.  710),  the  apex  of  which  is 
directed  backwards,  and  corresponds  to  a  blind  depression  on  the  surface  of  the 
tongue,  the  foramen  caecum,  whilst  its  diverging  limbs  pass  outwards  and  forwards 


THE  TONGUE. 


1001 


towards  the  attachments  of  the  anterior  palatine  arches.  The  foramen  ctecum  is 
the  remains  of  a  tubular  down-growth  formed  early  in  embryonic  life,  in  the  re'don 
of  the  dorsum  of  the  tongue,  from  which  the  isthmus  of  the  thyroid  gland  is 
developed  (see  page  38). 

The  posterior  or  pharyngeal  portion  of  the  dorsum  linguae  (Fig.  708),  nearly 
vertical  in  direction,  forms  the  greater  portion  of  the  anterior  wall  of  the  oral 
pharynx  (Fig.  710).     Its  surface  is  free  from  evident  papilla?,  but  is  thickly  studded 


Middle  turbinated  bone 
Middle  meatus  of  nose  \ 


Inferior  meatus 
of  nose 


Superior  meatus  of  nose 


Sphenoidal  sinus 

lufeuor  turbinated  bone 


Posterior  edge  of  nasal  septunj 
Oritice  of  Eustachian 

be 


ursa  pharyngea 


Part  of  the 
l)liaryngeal  tonsil 

Lateral  recess  of 
pharynx 

Levator  cushion 

Salpingo- 
pharyngeal fold 

Glands  in  soft 

palate 
Anterior 

palatine  arch 
Supratonsillar 

fossa 

~  Plica  triangularis 

-   Tonsil 

Posterior  palatine 
arch 


Epiglottis 


Aryteuo- 
epiglottic  fold 


Cricoid  cartilage 


Genin-glossus 

Genio-hyoid 

Lymphoid  follicle 

Hyoid  bone 

Fig.  708. — Sagittal  Section  through  Mouth,  ToxGirE,  Lauvnx,  Pharynx,  and  Nasal  Cavity. 

The  section  was  slightly  oblique,  and  the  posterior  edge  of  the  nasal  septum  has  been  preserved. 
The  specimen  is  viewed  sliglitly  from  lielow,  hence  the  apparently  low  position  of  the  inferior 
turbinated  bone.; 

with  rounded  projections,  each  presenting,  as  a  rule,  a  little  pit,  visible  to  the 
naked  eye,  at  its  centre ;  the  great  majority  of  these  are  lymphoid  follicles  (folliculi 
tonsillares  linguales.  Fig.  713,  C)  similar  to  those  found  in  the  tonsils;  some  few 
are  said  to  be  mucous  glands ;  all  are  covered  by  a  smooth  mucous  membrane, 
and  they  combine  to  give  to  this  region  a  characteristic  nodular  appearance. 

The  mucous  membrane  of  this  portion  of  the  tongue  is  separated  from  the 
muscular  substance  by  a  submucous  layer  in  which  the  lymphoid  follicles  and 
the  mucous  glands  lie  embedded  (Fig.  708).  At  the  sides  it  is  continuous 
wdth  that  covering  the  tonsils  and  the  side  wall  of  the  pharynx ;  whilst  behind 


1002 


THE  DIGESTIVE  SYSTEM. 


it  is  reflected  on  to  the  front  of  the  epiglottis,  forming  in  the  middle  line  a 
prominent  fold,  the  frenulum  epiglottidis  or  middle  glosso  -  epiglottic  fold  (phca 
glosso-epiglottica  media.  Fig.  709),  at  each  side  of  which  is  a  wide  depression, 
the  vallecula. 

Two  lateral  glosso-epiglottic  folds  have  been  described,  but  these  pass  from  the  side 
of  the  epiglottis,  not  to  the  tongue,  but  upwards  along  the  wall  of  the  pharynx,  upon 
which  they  are  soon  lost ;  consequently  the  term  phaiyngo-epiglottic  is  more  applicable 
to  them. 

The  anterior  or  oral  portion  of  the  dorsum  linguae,  namely,  the  part  in  front 
of  the  sulcus  terminalis  (Eig.  709),  is  convex,  both  from  before  backwards  and 

Internal  jugular  vein    Hypoglossal  nerve 


Spinal  accessory  nerve 
Digastric  muscle 


Stylohyoid 
Glosso- 
pharyngeal ner\e 
Parotid  gland 
Temporo- 
maxillary  vein 
External  carotid 
artery 
Styloglossus 
Ascending 
palatine  artery 

Internal  pterygoid 

Epiglottis 

Frenulum 
epiglottidis 

Masseter 

Pharyngeal  portion 
of  tongue 


Internal  carotid  artery 
I     Pneumogastric  nerve 

Sympathetic 

Ascending  pharyngeal  artery 

Odontoid  process 


Fungiform  papilla 
Buccinator 


Post-pharyngeal 
lymphatic  gland 

Superior 
constrictor  muscle 

Posterior  palatine 
arch 

Tonsil 

Pharyngo-epiglottic 
fold 

Anterior  palatine 
arch 

Gircunivallate 
papillaj 


Raphe  of  tongue 


Conical  papillae 


Fungiform  papilla 


Fig.   709. — Horizontal  Skction  throuoh  Mouth  and  Pharynx  at  the  Level  of  the  Tonsils. 

The  stylopharyngeus,  which  i.s  shov/n  immediately  to  the  inner  side  of  the  external  carotid  artery,  and  the 
prevertebral  muscles,  are  not  indicated  by  reference  lines. 

from  side  to  side  in  the  resting  condition  of  the  organ  (Fig.  706).  It  usually 
presents  also  a  slight  median  depression,  along  the  centre  of  which  may  be  seen 
some  indication  of  a  median  raphe  in  the  form  of  an  irregular  crease,  which  ends 
posteriorly  near  the  foramen  caecum.  The  mucous  membrane  of  this  portion  of 
the  dorsum  is  thickly  covered  with  the  prominent  and  numerous  papillae  (papillte 
linguales)  which  give  the  tongue  its  most  characteristic  appearance. 

On  the  pharyngeal  part  of  the  tongue  there  are  also  small  papillary  projections  of  the 
corium,  Vjut  the  epithelium  fills  up  all  the  intervals  Ijetween  the  jiapillse,  and,  as  it  were,  levels 
off  the  surface,  so  that  none  are  visible  to  the  eye  as  projections  above  the  general  leveL  Over 
the  anterior  part  of  the  tongue,  on  the  contrary,  the  i^rojections  of  the  corium  are  large  and 
prominent,  and  the  intervals  between  them,  while  they  are  covered,  yet  are  not  filled  up,  by  the 
epithelium,  so  that  the  projections  stand  out  distinctly  and  independently,  and  in  places  attain  a 
height  of  nearly  2  mm.  above  the  general  surface. 


THE  TONGUE. 


1003 


Papillae  of  the  Tongue  (Fig.  709). — These  are  formed  by  variously-shaped 
projections  of  the  corium  of  the  mucous  membrane,  covered  by  thick  caps  of  epithe- 
lium. They  are  of  three  different  varieties  : — 1,  Conical  or  filiform  (papillae  conicte, 
p.     filiformes) ;  ,  .      , 

^  ~       '  >^^B)  '     /^ Internal  carotid  artery 

v^^^^  '        '■.•^<a'>'2»''*co-»'«--L  ^ — =>,- — Foramen  lacenim  medium 
Q\  ^ —^      /■  /    ♦JA»*'f,:^"    "W^ — <S^/?jV Cartilage  of  Eustachian  tube 


2,  Fungiform 
(papillae  fungi- 
formes  et  p.  lenti- 
culares) ;     and 

3,  Circumvallate 
(papillai  vallatte). 

The  conical  or 
filiform  papillae 
(Fig.  711)  are 
the  smallest  and 
most  numerous, 
forming  as  they 
do  a  dense  crop 
of  minute  pro- 
jections all  over 
the  anterior  two- 
thirds  of  the 
dorsum,  and  also 
upon  the  upper 
part  of  the  margin 
and  tip,  of  the 
tongue.  Pos- 
teriorly they 
are  arranged  in 
divergent  rows 
running  out- 
wards and  for- 
wards from  the 
raphe,  parallel  to 
the  limbs  of  the 
sulcus  terminalis. 
More  anteriorly, 
the  rows  become 
nearly  trans- 
verse, and  near 
the  tip  irregular. 
Each  papilla  is 
composed  of  a 
conical  projection 
of  the  corium, 
beset  with  micro- 
scopic papillse 
like  those  of  the 


Cavity  of  Eustachian  tube 

Levator  palati 

Inferior  turbinated  bone 

Lateral  recess  of  pharynx 

Levator  cushion 

Superior  constrictor  muscle 
Glands  in  soft  palate 
Uvula 

Palatopliaryngeus 
Circumvallate  papillae 
Sulcus  terminalis 
Glossopharyngeal  nerve 
Foramen  ciecum 
Lymphoid  follicle 

Middle  constrictor  muscle 
Epiglottis 

Pliarj-ngo-epiglottic  fold 

Lingual  artery 
Hyoglossus  muscle 
Hyoid  bone 
Superior  laryngeal  artery 

^Internal  laryngeal  nerve 
^Aryteno-epiglottic  fold 
Sinus  pyriformis 

Superior  aperture  of  larynx 
Inferior  constrictor  muscle 
Top  of  cricoid  cartilage 


?i  Vn 


Fig.  710.— The  Anterior  Wall  of  the  Pharynx  with  its  Orifices,  seen 

from  behind. 

aC\T,  "^Qrirl  nnvcrprl    The  specimen  from  which  the  drawing  was  made  was  obtained  from  a  formalin-hardened 
bKin,dUUCU\eieu  ^^^^  removin-  the  posterior  wall  of  the  pharynx  while  leaving  the  anterior 

by  a   thick  long  "  .    .  •    - ,     ,,  ,       ..,    .i, f,.of  ,.-iritv,  ^f 

cap  of  stratified 
squamous  epithe- 


'lium. 


wall  undisturbed.      The  following  points  should  be  noted  :  the  greatest  width  of 
the  pharynx,  above,  at  the  lateral  recesses  ;  the  posterior  nares,  with  the  inferior 
turbinated  bones  seen  through  them  ;    the  levator  cushion 
portion  of  the  tongue. 


and  the  pharyngeal 


Often,  however,  the  cap  of  epithelium  is  broken  up  into  several  long  slender  hair-like 
processes,  giving  rise  to  the  variety  known  as  filiform  papillae.  The  cap  of  epithelium  is 
being  constantly  shed  and  renewed,  and  an  excessive  or  diminished  rate  of  shedding  or 
renewal,  coupled  with  the  presence  of  various  fungi,  gives  rise  to  the  several  varieties  of 
"  tongue  "  found  in  different  diseases. 

The  conical  and  filiform  papillte  are  probably  of  a  prehensible  or  tactile  nature,  and 
are  highly  developed,  and  horny,  in  carnivora. 


1004 


THE  DIGESTIVE  SYSTEM. 


Fungiform  papilla 


Conical  and  fungiform  papillaj.     x30. 


Secondarj'  papillae 


Taste-buds 


The  fungiform  papillae  (Fig.  711)  are  larger  and  redder,  but  less  numerous  than 
the  last  variety,  and  they  are  found  chiefly  near  the  tip  and  margins  of  the  tongue, 
comparatively  few  being  present  over  the  dorsum  generally.     Each  is  in  shape  like 

a  "  puff-ball  "  fungus  (Halhburton), 

pa^piih^^''^        consisting  of  an  enlarged  rounded 

Conical papiite         ^^as^^^       /'     '  head,    attached    by    a    somewhat 

narrower  base.  As  in  the  case  of 
the  conical  papillae,  the  corium 
is  studded  over  with  microscopic 
papillfe,  which  are  buried  in  the 
covering  of  squamous  epithelium 
and  do  not  appear  on  the  surface. 
Most  of  the  fungiform  papillae,  if 
not  all,  appear  to  be  furnished  with 
taste-buds,  and  they  are  probably 
intimately  connected  with  the  sense 
of  taste. 

The  circumvallate  papillae 
(Fig.  711),  much  the  largest  of 
all  the  papillse  of  the  tongue,  are 
confined  to  the  region  immediately 
in  front  of  the  sulcus  terminalis 
and  foramen  Ccccum.  Usually  about 
ten  in  number,  they  are  arranged 
in  the  form  of  the  letter  V,  with 
the  apex  backwards,  just  in  front 
of  and  parallel  to  the  sulcus  ter- 
minalis. One  or  two  of  the  papillae 
are  usually  placed  at  the  apex  of 
the  V,  immediately  anterior  to  the 
In  appearance  a 
circumvallate  papilla  resembles  very 
closely  the  impression  left  by  press- 
ing the  barrel  of  a  small  pen  on  soft  wax  (Fig.  710).  Each  is  composed  of  a 
cylindrical  central  part  (1  to  2-5  mm.  wide),  slightly  tapering  towards  its  base,  and 
flattened  on  its  crown,  which  projects  a  little  above  the  general  surface  of  the  tongue. 
This  is  surrounded  by  a  deep,  narrow,  circular  trench  or  fossa,  the  outer  wall  of 
which  is  known  as  the  vallum.  The  vallum  appears  in  the  form  of  an  encircling 
collar  very  slightly  raised  above  the  adjacent  surface  (Fig.  709). 

As  in  the  case  of  the  other  forms,  the  circumvallate  papillae  are  made  up  of  a 
central  mass  of  corium,  beset  with  numerous  microscopic  papillae  on  the  crowns, 
but  not  on  the  sides,  and  covered  over,  as  are  the  surfaces  of  the  fossa  and  vallum, 
by  stratified  squamous  epithelium.  Into  the  fossas  open  the  ducts  of  some  small 
serous  glands  (Fig.  711). 

On  the  sides  of  the  circumvallate  papilke,  as  well  as  upon  the  opposed  surface 
of  the  vallum,  are  found,  in  considerable  numbers,  the  structures  known  as  taste- 
buds,  the  special  end-organs  of  the  nerves  of  taste. 

The  apex  (apex  linguae),  and  the  margin  (margo  lateralis)  of  the  tongue  in 
front  of  the  attachment  of  the  anterior  palatine  arch,  are  free,  and  lie  in  contact 
with  the  teeth  when  the  tongue  is  at  rest. 

On  the  upper  half  or  more  of  the  margin  and  aj^e-x,  papillii;  are  present  as  on  the  dorsum  ; 
but  on  the  lower  part  they  are  aVjsent,  and  the  siu'face  is  covered  by  smooth  mucous  membrane. 

Just  in  front  of  the  anterior  palatine  arch,  on  the  margin,  are  usually  seen  about  five  or  six 
distinct  vertical  folds,  forming  the  folia  linguae,  which  are  beset  with  taste-bud.s,  and  correspond 
to  a  well-defined  area  (the  pa])ilhe  foliatai)  on  the  side  of  the  tongue  in  certain  animals  (rabbit, 
hare,  etc.),  in  which  it  forms  an  important  part  of  the  organ  of  taste. 

The  inferior  surface  (facies  inferior)  of  the  tongue,  which  is  exposed  by  turning 
the  apex  of  the  organ  upwards,  is  limited  in  extent  (Fig.  712),  and  is  free  from 
visible  papilke,  the  surface  being  covered  by  a  smooth  mucous  membrane.     Eunning 


A  circumvallate  papilla.     xl2. 

Fig.  711. — The  Paph^l^  of  Tongue. 

The  upper  illustration  shows  conical  and  fungiform  papillae 

the    lower    a    circumvallate    papilla.       C,     Corium,    and    fQ-rarngii    Ccecum 
E,    Epithelium   of  the    mucous  membrane.       The  wavy 
dark  lines  represent  arteries. 


THE  TONGUE. 


1005 


along  its  middle,  except  near  the  tip,  is  a  depression,  from  which  a  fold  of  mucous 
membrane,  the  frenulum  linguae,  passes  down  to  the  floor  of  the  mouth,  and  on 


towards  the  back  of  the  mandilde. 
distance  from  it,  the  large  ranine 
vein  is  distinctly  seen  through  the 
mucous  membrane.  Further  out 
still  are  situated  two  indistinct, 
fringed  folds  of  mucous  membrane, 
the  plicae  fimbriatae,  wdiich  converge 
somewhat  as  they  are  followed 
forward  towards  the  tip,  near  which 
they  are  lost. 

From  the  inferior  surface  of 
the  tongue  the  mucous  membrane 
passes  across  the  floor  of  the  mouth 
to  the  inner  surface  of  the  gum, 
with  the  mucous  covering  of  which 
it  becomes  continuous. 

The  plicae  fimbriatse  correspond  pretty 
closely  to  tlie  course  of  the  ranine  arteries 
as  they  run  towards  tlie  tip  ;  the  arteries, 
however,  are  deeply  ijlaced  in  the  sub- 
stance of  the  tongue,  at  a  distance  of  3 
to  6  mm.  from  the  inferior  surface.  The 
jjlicte,  which  are  more  distinct  at  birth 
and  in  the  I'cEtus,  are  said  to  correspond 
to  the  under  tongue  found  in  the  lemurs. 

The  root  of  the  tongue  (radix 
linguaj)  is  the  portion  of  the 
inferior  aspect  which  is  connected 
by  muscles  and  mucous  membrane 
to  the  mandible  and  hyoid  bone. 
It  is  of  very  considerable  extent, 
and  is,  with  the  base,  the  most 
fixed  part  of  the  organ.  It  is  also 
the  situation  at  which  the  vessels 
and  nerves  as  well  as  the  extrinsic 
muscles  enter. 


At  each  side  of  the  frenulum,  and  a  short 


The  pliiltrmn 


Apical  gland  of 

toiigvie 

Layer  of  muscle  cut 
to  show  the  gland 

Plicie  ftmbriat* 


]__  Frenulum  linguas 


Wliarton's  duct 

Openings  of 
Wharton's  ducts 

Sublingual  gland 


Plica  sublingualis, 
with  ojienings  of 
ducts  of  sublingual 
gland 


Fig.  712. — Open  Mouth  with  Tongue  baised,  and  the 
Sublingual  and  Apical  Glands  exposed. 

The  sublingual  gland  of  the  left  side  has  been  laid  bare  by 
removing  the  mucous  membrane  ;  to  expose  the  ajiical 
gland  of  the  right  side  a  tliin  layer  of  muscle,  in  addition 
to  the  mucous  membrane,  has  been  removed.  A  branch 
of  the  lingual  nerve  is  seen  running  on  the  inner  aspect 
of  the  gland.  The  ranine  vein  is  faintly  indicated  on 
this  side  also. 


Structure  of  the  Tongue. — The  tongue  is  chiefly  composed  of  striped  muscular 
tissue,  in  connexion  with  which  are  found  a  considei'able  admixture  of  fine  fat  and  a 
median  septum  of  connective  tissue  occupying  the  central  part  of  the  organ.  In  addition, 
there  are  vessels,  nerves,  glands,  and  lymphoid  tissue,  the  whole  being  covered  over  by 
mucous  membrane,  except  at  the  root  (Fig.  713). 

The  muscular  tissue  is  derived  partly  from  the  terminations  of  the  extrinsic  muscles 
— namely,  the  hyoglossus,  styloglossus,  genioglossus,  palatoglossus,  and  chondroglossus ; 
but  also  largely  from  the  intrinsic  muscles — namely,  the  superior  liiigualis,  inferior 
lingualis,  the  transverse,  and  the  vertical  lingual  muscles.  These  are  so  arranged  that 
they  form  a  cortical  portion,  made  up  chiefly  of  longitudinal  fibres — derived  above  from 
the  superior  lingualis  and  the  hyoglossus,  at  the  sides  from  the  styloglossus,  and  below 
from  the  inferior  lingualis.  This  cortex  surrounds  a  central  or  medullary  portion,  divided 
into  two  lateral  halves  by  the  septum,  and  formed  in  great  part  by  the  transverse  and 
vertical  fibres,  and  also  by  the  fibres  of  the  genioglossi  ascending  to  the  dorsum.  The 
Tnuscular  fibres  derived  from  these  various  sources  end  by  being  inserted  into  the  deep 
surface  of  the  mucous  membrane. 

The  detailed  description  of  the  extrinsic  and  intrinsic  muscles  will  be  found  on 
page  414. 

The  septum  is  a  median  fibrous  partition  found  in  the  medullary  portion  only,  and 
easily  exposed  by  separating  the  two  genioglossi  on  the  under  surface  of  the  tongue. 
Anteriorly  it  usually  extends  to  the  apex  ;  whilst  posteriorly  it  grows  gradually  narrower, 
and  expanding  transversely  at  the  same  time,  it  passes  into  a  broad  sheet  (the  hyoglossal 


1006 


THE  DIGESTIVE  SYSTEM. 


membrane)  which  is  united  to  the  upper  border  of  the  hyoid  bone,  and  gives  attachment 
to  the  posterior  fibres  of  the  genioglossus.  From  the  sides  of  tlie  septum  the  transverse 
fibres  of  the  tongue  arise. 

The  mucous  membrane  on  the  anterior  two-thirds  of  the  dorsum,  and  on  the  free 
margins,  is  firm  and  closely  adherent  to  the  underlying  muscular  substance,  the  fibres 
of  which  are  inserted  into  it.  On  the  posterior  third  of  the  dorsum,  and  on  the  inferior 
surface,  it  is  neither  so  firm  nor  so  closely  united  to  the  muscular  substance,  from  which 
it  is  separated  in  both  of  these  situations  by  a  layer  of  submucous  tissue. 

The  mucous  membrane  of  the  tongue,  like  that  of  the  rest  of  the  mouth,  is  covered 
by  stratified  squamous  epithelium. 

Glands  of  the  Tongue. — Numerous  small  racemose  glands  are  found  scattered  beneath  the 
mucous  memljrane  of  the  posterior  third  of  the  tongue  ;  and  a  small  collection  of  similar  glands 
is  present  at  the  margin,  opposite  the  circumvallate  papillte.  Small  serous  glands  are  also 
found  embedded  in  the  dorsum  near  the  circumvallate  papillae,  into  the  fossae  of  which  their 
ducts  open  (Fig.  711). 

The  chief  collections  of  glandular  tissue  in  the  tongue,  however,  are  found  embedded  in  the 
muscle  of  the  under  surface,  a  little  way  behind  the  apex,  on  each  side  of  the  middle  line  (Fig. 
712).     They  are  known  as  the  apical  glands  (glandulae  linguales  anteriores  of  Nuhn  or  Blandin). 

These  apical  glands  are  displayed  by  removing  the  mucous  membrane  and  also  a  layer  of 


Transverse        Vertical 
fibres  fibres 


Nodules  of 
Epithelium     lymphoid  tissue 


Hanine  artei 


Mucous  „landb 


iSeptum 


Inferior  lingualis 


Fat 


Fig.  713. — A,  Transverse,  and  B,  Longitudinal  Vertical  Section  through  the  Tongue  (Krause)  ; 
C,  A  Lymphoid  Follicle  from  Back  Part  ok  Tongue  (Macalister,  slightly  modified). 

muscular  fibres  (derived  from  the  united  inferior  lingualis  and  styloglossus)  about  2  mm.  in 
thickness  from  the  under  surface  of  the  tongue  a  little  distance  behind  the  apex.  .They  are  oval  in 
shape,  often  partly  broken  up  by  muscular  fibres,  and  they  measure  from  i  to  |  in.  (12  to  19  mm.) 
in  length.  They  are  mixed  serous  and  mucous  glands,  and  they  open  by  three  or  four  very 
small  ducts  on  the  inferior  surface  of  the  tongue. 

Vessels. — The  chief  artery  is  the  lingual.  Tliis  vessel  passes  forwards  on  each  side  beneath 
the  hyoglossus  muscle,  and  then  is  continued  on  to  tlie  apex — between  the  genioglossus  on  the 
inner  side  and  the  inferior  lingualis  externally — under  the  name  of  the  ranine  artery.  Anteriorly 
it  is  covered  by  the  fibres  of  the  inferior  lingualis,  and  lies  \  to  j  inch  from  the  surface.  Near 
the  apex  the  arteries  of  opposite  sides  are  connected  by  a  branch  which  pierces  the  septum,  but 
otherwise,  with  the  exception  of  capillary  anastomosis,  they  do  not  communicate.  The  dorsalis 
linguae  branch  of  the  lingual  is  distributed  to  the  pharyngeal  part  of  the  tongue,  whilst  some 
twigs  of  tlie  tonsillar  branch  of  the  facial  are  also  distributed  in  the  same  region. 

The  veins  are  :  the  ranine,  the  chief  vein,  which  lies  beneath  the  mucous  membrane  at  the 
side  of  the  frenurn,  and  runs  backwards  over  the  hyoglossus  muscle  with  the  hyj)oglossal  nerve  ; 
two  vense  comites,  which  accompany  the  lingual  artery  ;  and  a  dorsalis  linguae  vein  from  the  back 
of  the  tongue.  Tliese  eitlier  unite  and  form  a  common  trunk,  or  open  separately  into  the  internal 
jugular  vein. 

Nerves. — The  nerves  whicli  supply  the  tongue  are  :  (1)  The  hypoglossal,  the  motor  nerve  of 
the  tongue,  which  enters  the  genioglossus  and  passes  up  in  its  substance  to  the  intrinsic  muscles, 
in  which  it  ends.  (2)  The  lingnial,  a  branch  of  the  inferior  maxillary  nerve,  which  is  accom- 
panied by  the  chorda  tympani  branch  of  the  facial.  The  lingual,  after  crossing  the  hyoglossus 
muscle,  breaks  up  and  entei's  the  inferior  lingualis  and  genioglossus,  and  thus  makes  its  way 
upwards  to  the  nmcous  membrane  of  tlie  anterior  two-thirds  of  the  tongue — the  lingual  itself 
conferring  common  sensation  on   this  part,  the  chorda  tympani  probably  carrying  to  it  taste 


GLANDS.  1007 

fibres.  (3)  The  glossopharyngeal  nerve  passes  forwards  beneath  the  uj^per  piirt  of  the  hyoglossus, 
and  sends  its  terminal  branches  to  the  niucous  membrane  of  the  posterior  tliird  of  the  tongue, 
supplying  the  circumvallate  paj^illse,  and  the  part  of  the  tongue  behind  these,  with  both  gustatory 
and  common  sensory  fibres.  (4)  The  internal  laryngeal  nerve  also  distributes  a  few  filn'es  to  the 
posterior  part  of  the  base  of  the  tongue,  near  the  epiglottis. 

The  lymphatics  of  the  anterior  Jialf  of  the  tongue  pass  down  thrcnigh  the  floor  of  tlie  mouth 
and  join  the  submaxillary  lymphatic  glands.  Those  from  tlie  posterior  half  run  with  tlie  ranine 
vein  across  the  hyoglossus  muscle  (whei'e  they  are  connected  with  some  small  lingual  glands)  and 
join  the  deep  cervical  glands. 

GLANDS. 

Various  organs,  differing  widely  both  in  structure  and  function,  are  commonly 
included  under  the  general  term  glands.  It  is  made  to  embrace :  (a)  the  glands 
vjith  ducts,  such  as  the  digestive  glands  (liver,  pancreas,  salivary  glands,  etc.),  the 
sweat  and  sebaceous  glands  of  the  skin,  the  testes,  etc.,  and  the  small  glands 
embedded  in  the  walls  of  the  digestive  and  respiratory  tracts;  (b)  the  so-called 
ductless  glands  (spleen,  thyroid,  suprarenals,  etc.),  which  possess  no  ducts,  but 
throw  their  secretions  into  the  blood  or  lymph  passing  through  them.  We  shall 
here  consider  only  the  true  glands — namely,  those  included  in  the  first  group 
mentioned  above,  which  are  all  characterised  by  the  possession  of  ducts ;  and  what 
follows  refers  to  them  alone. 

A  gland  may  be  defined  as  an  epithelial  organ  which  separates  or  elaborates  from  the  blood 
some  substance  which  is  either  to  be  discharged  from  the  body  or  used  further  in  the  economy. 
The  product  of  the  activity  of  the  gland  is  knovm  as  its  secretion,  and  the  secretion  is  conveyed 
to  its  destination  in  all  true  glands,  as  explained  above,  by  the  gland  duct. 

Every  gland  is  primarily  an  outgrowth  of  the  epithelium  from  the  surface  to  which  the  secre- 
tion of  the  gland  is  to  be  subsequently  conveyed.  This  outgrowth  may  remain  undivided,  con- 
stituting a  simple  gland.  On  the  other  hand,  it  may  break  up  into  two  or  more  branches,  giving 
rise  to  a  compound  gland.  We  thus  arrive  at  the  two  great  classes  of  glands — simple  and 
compound. 

A  simple  gland  may  remain  tubular,  when  it  is  known  as  a  simple  tubular  gland,  of  which 
Lieberkuhn's  follicles  in  the  wall  of  the  small  intestine  and  the  sweat  glands  are  examples.  Or 
it  may  be  dilated  at  its  extremity,  the  enlargement  being  known  as  an  acinus  {aKivos,  a  grape  or 
grape-stone)  or  alveolus,  thus  constituting  a  simple  acinous  or  alveolar  gland,  of  which  there  are 
few  examples  in  man  (viz.  some  sebaceous  glands),  though  they  are  numerous  in  the  skin  of  the 
frog,  etc.     This  gives  us  two  varieties  of  simple  glands — tubular  and  acinous  or  alveolar. 

Similarly  a  compound  gland  may  remain  tubular,  constitutmg  a  compound  tubular  gland,  such 
as  the  kidney,  testicle,  and  the  majority  of  the  gastric  glands.  Or,  on  the  other  hand,  the 
terminal  branches  of  its  ducts  may  be  beset  with  clilatations  {i.e.  acini  or  alveoli),  giving  rise  to 
a  compound  acinous  or  alveolar  gland,  which  latter,  owing  to  a  remote  resemblance  presented  by 
its  clustering  lobules  to  a  miniature  bunch  of  grapes,  is  often  known  as  a  racemose  gland  (racemus,  a 
cluster).  Must  of  the  glands  of  the  body  are  examples  of  this  variety — e.g.  the  salivary  glands,  the 
small  glands  of  the  mouth,  tongue,  pharynx,  oesophagus,  respiratory  passages,  eyelids,  etc.  Thus 
we  arrive  at  two  varieties  of  compound  glands  also — tubular  and  acinous  or  alveolar. 

A  compound  acinous  (racemose)  gland  is  composed  of  a  main  duct  which  branches  and 
re-branches  more  or  less  freely  according  to  the  size  of  the  gland,  and  the  terminal  divisions  of 
which  end  finally  in  specialised  secreting  parts,  the  acini  or  alveoli,  quite  distinguishable  from 
the  ducts  or  conducting  parts.  In  true  acinous  glands  the  acini  or  alveoli  are  distinctly  saccular  ; 
in  other  glands,  such  as  the  pancreas,  this  is  not  the  case,  the  acini  being  long  and  narrow. 
Accordingly,  the  term  acino-tubular  has  been  introduced  and  applied  to  glands  of  this  latter 
type,  which  is  usually  made  to  include  the  pancreas,  the  prostate,  and  Brunner's  glands,  i 

It  should  be  added  that  the  term  acino-tubular  is  by  some  authors  used  exclusively  instead 
of  acinous  for  all  racemose  glands. 

There  is  one  gland,  however,  which  cannot  be  included  in  any  of  the  above  varieties,  and 
which  must  be  placed  in  a  class  by  itself  This  is  the  liver.  It  is  composed  of  an  enormous 
number  of  small  secreting  lobules,  between  which  run  the  branches  of  the  bile-duct.  These 
lobules  in  the  mammalian  liver  cannot  in  any  way  be  compared  to  acini,  or  to  collections  of  acini, 
as  their  cells  are  not  arranged  around  a  central  lumen,  but  form  a  practically  solid  mass,  M'itli 
minute  bile  capillaries  running  everywhere  between  them.  It  might  in  mammals,  for  want  of  a 
loetter  term,  be  classed  as  a  solid  gland. 

The  foregoing  may  be  summarised  in  tabular  form  thus  : — 

I.  Simple  glands. — Duct  undivided. 

(a)  Simple  tubular.  —Undilated  at  end— e.g.  Lieberkuhn's  follicles,  sweat,  and  many  gastric 

glands. 
(6)  Simple  acinous  (alveolar  or  saccular).— Dilated  at  end— e.^.  some  .sebaceous  glands  (rare) 

1  Some  authorities  consider  the  glands  of  Brunner  to  belong  to  the  class  of  compound  tubular  glands 
(Heidenhain,  Watney,  Jonnesco,  etc.). 


1008 


THE  DIGESTIVE  SYSTEM. 


Small  duct  from  an  alveolu 
Laree  duct 


II.  Compound  glands. — Duct  divided. 

(«.)  Compound   tubular. — Branched    elongated    tubes,  no   acini — e.g.   testes,  kidney,  most 

gastric  glands. 
(b)  Compound  acinous  or  alveolar  (racemose  glands),  branched  duct  with  saccular  acini  on 
terminal  brandies — e.g.  salivary,  sebaceous,  and  Meibomian  glands  ;  the  mucous  glands 
of  the  mo\ith,  tongue,  jialate,  j^harynx,  nose,  oesophagus,  and  respiratory  tube. 
((•)  Acino-tubular. — Branched  duct,  with  elongated  narrow  acini  on  terminal  branches — e.g. 
jjaucreas,  Brunner's  glands,  jirostate. 
III.  Solid  gland.— The  liver. 

To  save  confusion  it  may  be  pointed  out  that  instead  of  acinus  the  term  alveolus  (and  also 
saccule  and  follicle)  is  often  used,  and  also  that  the  term  "  racemose  gland  "  is  often  conveniently 
used  instead  of  compound  acinous  gland. 

General  Structure  of  Glands. — Whilst  the  small  glands,  such  as  those  of  the 
mouth  and  pharynx,  are  placed  in  the  mucosa  or  submucosa  immediately  beneath  the 
point  at  which  their  ducts  open  on  the  surface,  the  large  glands  foi-m  distinct  masses, 
generally  surrounded  by  special  capsules,  and  often  lie  at  a  considerable  distance  from  the 
points  at  which  their  ducts  open. 

One  of  these  large  glands  of  the  acinous  type,  such  as  the  parotid  or  submaxillary, 
presents  the  following  general  arrangement.  The  gland  is  made  up,  as  can  be  seen  with 
the  unaided  eye,  of  a  number  of  masses,  often  as  large  as  peas,  which  are  surrounded  and 
held  together  by  connective  tissue.  These  are  known  as  lobes,  and  to  each  a  branch  of 
the  duct  passes.  The  lobes  are  in  turn  made  up  of  a  number  of  smaller  masses — lobules 
— each  having  a  special  branch  of  the  lobar  duct.  These  again  are  composed  of  smaller 
lobules,  and  so  on  to  a  varying  degree.  Finally,  the  smallest  are  made  up  of  a  terminal 
branch  of  the  duct,  with  a  cluster  of  acini  or  alveoli  developed  upon  it, 

•  The  acini  or  alveoli,  the  special  secreting  portions  of  the  gland,  are  composed  of  a 
basement  membrane,  often  fenestrated  or  basket-like,  formed  of  flattened  cells,  on  the 
outer  side  of  which  the  blood  and  lymph  vessels  lie.  The  inner  surface  of  this  membrane 
is  lined  by  the  secreting  epithelial  cells,  usually  polygonal  in  shape,  which  almost  com- 
pletely fill  the  alveolus.     A  small  lumen,  however,  is  left,  into  which  the  secretion  of  the 

cells  is  shed,  whence  it 
passes  into  the  duct  of 
the  lobule,  and  thus  to 
the  main  duct. 

The  blood-vessels  and 
lymphatics,  on  entering 
the  gland,  break  up  and 
run,  branching  as  they 
go,  in  the  connective 
tissue  which  conveys 
them  to  all  parts  of  the 
gland. 

Mucous  and  Serous 
Glands.  —  Two  distinct 
varieties  of  salivary 
glands  are  found,  the 
serous  and  the  mucous,- 
differing  not  only  in  the 
nature  of  their  secretion, 
but  also  in  the  character 
of  the  epitlielium  lining 
their  alveoli.  In  those 
of  the  mucous  type 
(Fig.  714)  the  epithe- 
lial cells  are  large,  clear, 
or  faintly  granular,  and 
the  nucleus  lies  as  a  rule  near  the  base  of  tlic  cell,  in  addition,  many  mucous  o-lands, 
but  not  all,  have  small  flattened  or  crcscentic  cells,  distinctly  granular,  which  stain  strongly 
with  ordinary'  stains,  lying  between  the  basement  membrane  and  the  bases  of  the  chief 
cells.     'J'hese  are  the  crescents  or  demilimcs  of  (jianuzzi. 

In  the  acini  or  alveoli  of  serous  glands,  on  the  other  hand  (Fig.  714),  the  epithelial 
cells  arc  distinctly  granular,  the  granules  staining  well  with  ordinary  stains;  the  nuclei 
are  rounded  and  lie  near  the  centre  of  the  cells,  and  no  demilunes  are  present. 

In  man  the  parotid  and  the  small  glands  which  open  into  the  fossae  of  the  circum- 


Cre.sceiit  of  Giauuzzi 
An  alvf-'olus  with  .secreting  cell 

Connective  tissue 

Fi<;.   714.— Section  ok  a  Skuous  Gland  on  the  i.ekt,  a  Micous  Gland 
ON  THE  KioHT  SIDE  (Bfilun  and  V.  Davido/r). 

In  the  serous  gland  the  granular  secreting  cells  and  the  ccntrally-]>laced  nucleus 
should  be  noted.  Tbe  relatively  clear  cells,  with  tlie  dark  crescents  of 
Gianuzzi,  are  distinctive  in  the  mucous  gland. 


SALIVAEY  GLANDS. 


1009 


vallate  papillae  alone  are  serous.  The  sxibniaxillaiy  and  the  apical  gland  of  the  tongue 
are  mixed,  the  serous  alveoli  being  the  more  numerous ;  whilst  the  sublingual,  labial, 
buccal,  and  all  other  glands  of  the  mouthy  tongue,  and  palate  are  said  to  be  imicous. 


Salivary  Glands. 


This  term  is  generally  understood  to  include  only  the  three  large  masses  of 
glandular  tissue  found  on  each  side  of  the  face — namely,  the  parotid,  submaxillary, 
and  sublingual  glands.     But,  as  previously  pointed  out,  numerous  other  small  glands 


Internal  jugular  veiu    Hypoglossal  nerve 
Spinal  accessory  nerve        I      I     Internal  carotid  artery 
Digastric  muscle       I  '     j     Pneumogastric  nerve 

/     _    \       \        ^     \    \  Sympathetic 

\    \    \      (       Ascentling  pharyngeal  artery 

Stylohyoid^/   ^^A^i^-^.-'"-^'-^-     \     I"  Odont, id  process 


Glosso 

pharyngeal  nerve' 

Parotid  gland 


Temporo-    |    f--- 
maxillary  vein-- — L-^ 

External  carotid. 

artery 

Styloglossus 

Ascending 

palatine  artery 

Internal  pterygoid —  ~^^^, 

Epiglottis- 

Frenuluni 
epiglottidis 

Masseter — 

Pharyngeal  portion, 
of  tongue 


Fungiform  { ai  ilU 
Buci  inator 


Post-pharyngeal 
lymphatic  gland 

Superior 
onstrictor  muscle 
Posterior  palatine 
irch 

--  t'onsil 

Pharvngo-epiglottic 
^fold  ' 

interior  jsalatine 
Tch 


Circumvallate 

\     papillai 


W-""'-  ■  ■  J  s.  Raphe  of  tongue 
Conical  papillae 


Fungiform  pipiUa- 


Fig.  715.^ — Horizontal  Section  through  Mouth  and  Pharynx  at  the  Level  of  the  Tonsils. 

The  stylopharyugeus,  whicli  is  shown  immediately  to  the  inner  side  of  the  external  carotid  artery,  and  the 
prevertebral  muscles,  are  not  indicated  by  reference  lines. 

of  a  similar  nature  are  found  in  the  lips,  cheeks,  palate,  tongue,  etc.     These  have 
already  been  sufficiently  described,  and  require  no  further  mention. 

Parotid  Gland  (glandula  parotis).— This,  the  largest  of  the  salivary  glands,  is 
a  distinctly  lobulated  mass  of  a  yellowish  or  light  reddish-brown  colour,  which  is 
placed  in  a  deep  recess  (the  parotid  recess)  at  the  side  of  the  head,  below  and  in 
front  of  the  ear  (Fig.  716).  It  extends  up  to  the  zygoma,  down  to  the  angle  of 
the  jaw  or  even  to  a  lower  level,  and  backwards  to  the  sterno-mastoid  muscle. 
Internally  it  lies  on  the  styloid  process,  and  anteriorly  its  facial  process  is  continued 
for  a  variable  distance  over  the  surface  of  the  masseter. 

When  the  gland  is  carefully  removed  without  disturbing  the  surrounding  parts,  the 

recess    which    it    occupies    is   seen    to   be   a   considerable   space,   between    the  ramus  of 

the   jaw  in   front  and  the  sterno-mastoid   muscle   behind,   with  a   floor  formed   of  two 

sloping  walls,  an  anterior  and  a  posterior,  which  meet  at  an  angle  corresponding  pretty 

68 


1010 


THE  DIGESTIVE  SYSTEM. 


closely  to  the  styloid  process.  Tlius  the  recess  is  three-sided  (Fig.  715),  the  third 
side  corresponding  to  the  parotid  fascia  covering  the  gland.  Into  this  ^aro^i'c^  recess  the 
greater  part  of  the  parotid  gland  fits  closely.  From  its  anterior  part,  however,  the 
variably-developed  facial  process  is  continued  forward  over  the  masseter  muscle. 

Parotid  Fascia. — The  parotid  recess  is  covered  over  on  the  one  hand,  and  lined  on  the 
other,  by  fascia.  The  covering  layer  is  specially  known  as  the  parotid  fascia,  and  both  it 
and  the  lining  layer  are  derived  from  the  deep  cervical  fascia,  which  divides  below  to 
enclose  the  gland.  The  parotid  fascia  proper  is  connected  above  to  the  zygoma  ;  behind,  to 
the  auditory  meatus  and  anterior  border  of  the  sterno-mastoid ;  below,  it  is  continuous 
with  the  deep  cervical  fascia,  and  in  front  it  passes  forwards  over  the  masseter,  and  blends 
with  the  fascia  of  that  muscle.  The  layer  of  fascia  beneath  the  gland  forms  a  lining  for 
the  recess,  and  is  united  above  to  the  periosteum  over  the  auditory  meatus  and  back 
part  of  the  glenoid  fossa ;  internally  it  is  connected  to  the  styloid  process ;  whilst  below  it 

joins  the  deep  cervical 
fascia.  Taken  together, 
the  two  layers  form  a 
definite  capsule  which 
completely  encloses  the 
gland.  In  connexion 
with  the  lower  and 
anterior  part  of  this 
capsule  is  developed  a 
special  flat  band,  the 
stylomandibular  liga- 
ment, which  passes 
downwards  and  out- 
wards from  the  styloid 
process  to  the  angle  of 
the  jaw.  It  separates 
the  anterior  part  of  the 
parotid  gland  from  the 
back  of  the  internal 
pterygoid  muscle ;  per- 
haps occasionally,  also, 
from  the  upper  and 
posterior  part  of  the 
submaxillary  gland 

Shape    and  Rela- 
ijuctofBaithoiin(rare)  tions  of  the  Parotid 

Gland.— Like  the 
recess  in  which  it 
lies,  the  main  mass 
of  the  parotid  gland 
is  three -sided  (Fig.- 
715),       the       three 


Stenson's  duct 
Orifice  of  duct 
Parotid  gland 

Masseter  (cut) 

Mucous  membrane 

(cut) 

Deep  process  of 

submaxillary  gland 

Mylohyoid  muscle 
(cut) 

Submaxillary  gland 

Lower  border  of 
mandible 

Mylohyoid  muscle 

Anterior  belly  of__ 

digastric" 

Hyoid  bone^' 


M  barton's  duct 
i)uct  of  sublingual  gland 
Sublingual  gland 


Fig.  716.— The  Salivary  Glaxds  and  their  Ducts. 


The  greater  portion  of  tlie  body  of  the  maudible  has  been  removed  to  expose  the 
sublingual  and  the  deeper  parts  of  the  submaxillary  glands.  Four  ducts  of 
the  sublingual  gland  are  shown  opening  on  the  floor  of  the  mouth  over  the  SUrfaCCS  being  SUpcr- 
gland,  a  fiftli  is  shown  opening  into  the  anterior  end  of  Wharton's  duct,  ficial  anterior  and 
The  course  of  Wharton's  duct  is  shown  by  a  dotted  line.  i-inQtprinr 

The  swperficial  surface  is  closely  covered  by  the  parotid  fascia,  and  its  lower 
part  is  also  crossed  by  the  highest  fibres  of  the  platysma.  The  anterior  surface,, 
approximately  flat,  lies  in  contact  with  the  wide  posterior  surface  of  the  in- 
ternal pterygoid  muscle ;  it  is  also  related  to  the  posterior  border  of  the  mandible 
and  the  masseter  muscle,  whilst  from  its  superficial  part  the  facial  process  is 
continued  forwards  over  that  muscle.  The  ^posterior  surface  lies  from  without 
inwards  against  (1)  the  anterior  border  of  the  sterno-mastoid  and  the  auditory 
meatus,  (2)  the  posterior  belly  of  the  digastric  and  the  occipital  artery,  and  (.3)  the 
spinal  accessory  nerve  and  carotid  sheath — the  internal  jugular  vein  within  the 
sheath  being  in  very  close  relation.  The  inner  angle  formed  by  the  meeting 
of  the  anterior  and  posterior  surfaces  corresponds  to  the  styloid  process  and  the 
styloid  muscles  (Fig.  715).  Above,  the  gland  is  hmited  superficially  by  the 
zygoma;  more  deeply  a  thin  process  runs  up  into  the  posterior  part  of  the  glenoid 


SALIVAEY  GLANDS.  1011 

fossa.  Inferiorly  it  usually  reaches  a  little  distance  below  a  line  prolonged  hori- 
zontally backwards  from  the  angle  of  the  jaw,  but  its  limit  in  this  direction  is 
variable. 

Occasionally  the  parotid  gland  passes  down  a  considerable  distance  below  the  angle  of  the 
mandible,  lying  here  superficial  to  the  posterior  part  of  the  submaxillary  gland,  from  which  it 
is  separated  by  a  thickened  band  of  the  deep  cervical  fascia,  passing  from  the  angle  of  the  jaw  to 
the  fascia  of  the  sterno-mastoid.     At  other  times  it  does  not  quite  reach  the  angle. 

The  facial  process  of  the  gland — often  of  considerable  size — is  a  flat  and  some- 
what triangular  portion  which  runs  forwards  from  the  upper  part  of  the  gland,  and 
overlaps  the  masseter  muscle  to  a  varying  extent ;  from  its  most  anterior  part 
the  parotid  duct  emerges,  and  a  separated  portion  of  this  process,  often  found  lying 
immediately  above  the  duct,  is  known  as  the  socia  parotidis  (glandula  parotis 
accessoria). 

Traversing  the  substance  of  the  gland  (Fig.  715)  are  found : — (1)  the  temporo- 
maxillary  vein ;  (2)  on  a  deeper  plane,  the  branches  of  the  facial  nerve  passing 
forwards;  and  (3)  more  deeply  still,  the  external  carotid  artery  which  lies  beneath 
the  lower  part  of  the  gland,  but  is  embedded  in  its  deep  surface  above.  Just 
before  it  emerges,  the  artery  divides  into  its  two  terminal  branches  in  the  gland 
substance. 

The  parotid  or  Stenson's  duct  (ductus  parotideus)  leaves  the  anterior  border 
of  the  gland  at  its  most  prominent  part  (Fig.  716).  It  first  runs  forwards  across 
the  masseter,  usually  accompanied  by  the  socia  parotidis  which  lies  above  it, 
and  also  by  branches  of  the  facial  nerve ;  whilst  the  transverse  facial  artery 
is  commonly  some  distance  above,  though  its  relation  is  variable.  Having  crossed 
the  masseter,  it  turns  abruptly  round  the  anterior  border  of  this  muscle  and  runs 
inwards  through  the  fat  of  the  cheek,  practically  at  right  angles  to  the  first  part  of 
its  course,  to  reach  the  buccinator,  which  it  pierces.  Then  passing  for  some  distance 
(5  to  10  mm.)  between  the  buccinator  and  mucous  membrane,  it  opens  into  the 
vestibule  of  the  mouth  by  a  very  small  orifice,  on  a  variably-developed  papilla, 
opposite  the  crown  of  the  second  upper  molar  tooth. 

The  course  of  the  duct,  which  is  fairly  constant,  can  be  marked  on  the  side  of 
the  face  by  drawing  a  line  from  the  lower  edge  of  the  auditory  meatus  to  a  point 
midway  between  the  ala  of  the  nose  and  the  red  of  the  lip;  the  middle  third 
of  this  line  corresponds  fairly  accurately  on  the  surface,  to  the  course  pursued 
by  the  duct. 

The  gland  varies  in  weight  from  half  an  ounce  to  an  ounce  or  more.  Several  small  lobes  or 
processes  are  found  in  connexion  with  it — viz.  one  running  backwards  between  the  sterno-mastoid 
and  the  digastric ;  a  glenoid  lobe  of  very  small  size,  which  lies  in  the  posterior  part  of  the 
glenoid  cavity  ;  a  pharyngeal  process  (Fig.  715),  which  runs  forwards  and  inwards  between  the 
styloid  process  and  the  external  carotid  artery  towards  the  pharynx.  A  pterygoid  extension 
running  forwards  between  the  two  pterygoid  muscles,  although  described,  cannot  properly  be  said 
to  exist. 

Stenson's  duct  measures  from  1|  to  2^  inches  (38  to  62  mm.)  in  length,  and  |-  inch  (3  to  4  mm.) 
in  diameter.  The  calibre  of  the  duct  is  very  much  greater  than  that  of  its  orifice,  which  only 
admits  a  fine  bristle,  and  for  this  reason  the  duct  may,  to  some  extent,  be  looked  upon  as  a 
reservoir  for  the  saliva,  as  well  as  a  duct  for  its  conveyance.  In  the  child  it  pierces  the  "  sucking 
pad  "  on  its  way  to  the  mouth. 

Vessels  and  Nerves. — The  arteries  which  supply  the  gland  arise  from  the  external  carotid, 
and  from  the  branches  of  this  artery  in  relation  to  the  gland. 

The  veins  join  the  temj)oro-maxillary  and  its  tributaries.  The  lymphatics  pass  to  both  the 
■superficial  and  the  deep  cervical  glands ;  there  are  also  a  few  small  parotid  lymphatic  glands, 
which  lie  on  the  surface  of  the  upper  and  lower  part  of  the  parotid  beneath  the  capsule.  Some 
are  said  to  be  embedded  in  the  substance  of  the  jjarotid  itself. 

The  nerves  are  derived  (a)  from  the  auriculo-temporal,  and  (b)  from  the  symjjathetic  on  the 
external  carotid.  The  fibres  of  the  sympathetic  are  mainly  vaso-constrictor.  Those  of  the 
auriculo-temporal  convey  to  the  gland  secretory  fibres  from  the  glosso-j)haryngeal. 

Submaxillary  Gland. — The  submaxillary  gland  is  next  in  size  to  the  parotid, 

and  resembles  it  in  its  lobulation  and  colour.  It  is  placed  partly  in  the  sub- 
maxillary triangle  and  partly  under  cover  of  the  posterior  part  of  the  mandible 
near  its  angle  (Fig.  716). 

In  size  and  shape  it  may  be  compared  to  a  small  walnut  with  three  flattened 


1012  THE  DIGESTIVE  SYSTEM. 

sides.  It  is  enclosed  in  a  complete  capsule  derived  from  the  deep  cervical  fascia : 
embedded  in  this  capsule,  and  superficial  to  the  gland,  are  found  a  few  submaxillary 
lymphatic  glands,  which  are  of  importance  owing  to  their  connexion  with  the 
lymphatics  of  the  lips  and  of  the  anterior  half  of  the  tongue. 

In  considering  the  relations  of  the  gland,  it  is  well  to  remark  tliat  there  is  in  this  region  a 
three-sided  space  bounded  externally  by  the  inner  surface  of  the  mandible  below  the  mylohyoid 
ridge,  internally  and  above  by  the  mylohyoid  muscle  running  inwards  and  downwards,  and  below 
by  the  skin  and  fascia  passing  from  the  margin  of  the  jaw  obliquely  inwards  and  doAvn wards  to  join 
the  side  of  the  neck.  In  tliis  space  the  gland  lies  with  external,  internal,  and  inferior  surfaces 
corresponding  to  the  walls  of  the  sj^ace. 

The  su])erficial  or  inferior  surface  looks  downwards  and  outwards ;  it  is  covered 
by  the  deep  cervical  fascia  and  the  platysma,  and  is  crossed  by  the  facial  vein, 
which  lies  superficial  to  the  gland,  whilst  the  artery  passes  in  part  beneath  it.  The 
external  surface  rests  against  the  inner  aspect  of  the  lower  jaw  (submaxillary  fossa) 
for  an  inch  and  a  half  forward  from  the  angle,  to  which  latter  it  usually  reaches 
behind.  The  deep  or  internal  surface  lies  on  the  posterior  part  of  the  mylohyoid 
muscle,  and  behind  this,  on  the  hyoglossus  and  the  posterior  belly  of  the  digastric 
with  the  stylohyoid ;  for  the  gland  is  not  contained  within  the  limits  of  the  sub- 
maxillary triangle  inferiorly,  but  passes  down  some  little  distance  over  the  digastric 
muscle.  From  the  deep  surface,  anterior  to  its  middle,  a  narrow  tongue-like  deep 
process  (Fig.  716)  is  continued  forwards  beneath  the  mylohyoid  muscle  along  with 
the  duct. 

The  230sterior  end  of  the  gland,  which  is  its  most  bulky  portion,  either  abuts 
against,  or  lies  very  close  to,  the  sterno-mastoid,  and  is  often  overlapped  by  the 
lower  end  of  the  parotid  gland.  The  facial  artery,  on  its  way  to  the  border  of  the 
mandible,  lies  in  a  groove  in  the  upper  and  back  part  of  the  gland. 

The  submaxillary  or  Wharton's  duct  leaves  the  deep  surface  of  the  gland 
about  its  middle,  and  runs  forwards  beneath  the  mylohyoid  muscle  with  the  deep 
process,  along  the  upper  and  inner  aspect  of  which  it  is  placed  (Figs.  716  and  712). 
Pursuing  its  course  forwards  beneath  the  floor  of  the  mouth,  on  the  inner  side  of 
the  sublingual  gland,  the  duct  crosses  the  hyoglossus  and  the  genioglossus  muscles, 
and  finally  opens  on  the  floor  of  the  mouth  at  the  side  of  the  frenulum  linguae, 
where  its  small  orifice  is  placed  on  the  summit  of  a  soft  papilla  (caruncula  sub- 
lingualis) close  to  its  fellow  of  the  opposite  side. 

While  running  forward  beneath  the  floor  of  the  mouth  the  duct,  which  is  about  two  inches  long 
(50  mm.),  is  crossed  on  its  inferior  aspect  by  the  lingual  nerve  near  the  anterior  border  of  the 
hyoglossus,  that  is  opi^osite  the  2nd  molar  tootli.  The  nerve  at  the  time  is  arching  from  the 
posterior  end  of  the  mylohyoid  ridge  (against  which  it  lies)  inwards  and  forwards  in  order  to 
reach  the  under  surface  of  the  tongue,  and  in  this  course  it  passes  Ijeneath  the  duct  at  the  point 
indicated.  As  in  the  case  of  Stenson's  duct,  the  calibre  of  Wharton's  duct  is  much  greater  than 
that  of  the  orifice  by  which  it  opens  ;  for  this  reason  it  may  likewise  be  looked  upon  as  forming, 
to  some  extent,  a  reservoir  for  the  saliva  secreted  by  the  gland. 

Vessels  and  Nerves. — The  arteries  come  chiefly  from  the  facial  and  its  submental  branch  : 
the  veins  are  similarly  disposed.  Tlie  nerves  are  derived  from  the  submaxillary  ganglion  (which 
lies  aljove  the  deej)  process  of  the  gland),  and  are  composed  of  fibres  from  the  cliorda  tympani, 
from  the  lingual,  and  from  the  sympathetic  on  the  facial  artery.  The  lyiiiphatics  pass  to  the 
submaxillary  lymphatic  glands. 

Sublingual  Gland. — This  is  an  elongated  almond-shaped  mass,  flattened  from 
side  to  side,  and  much  wider  (from  above  downwards)  in  front  than  behind,  which 
lies  on  the  floor  of  the  mouth  beneath  the  plica  sublingualis — a  ridge  of  the  mucous 
membrane  produced  by  the  prominent  upper  border  of  the  gland.  It  is  usually 
from  1^  to  12  inches  (37  to  45  mm.)  in  length,  whilst  its  bulk  is  about  equal  to 
that  of  two  or  three  almonds. 

It  is  placed  Ijetween  the  mandible  externally,  the  genioglossus  internally,  the 
mylohyoid  muscle  below,  and  tlie  mucous  memljrane  of  the  mouth  above  (Fig.  706). 

Its  detailed  relations  ai'c  as  follows  : — Its  outer  surface  rests  against  the  inner  aspect 
of  the  body  of  the  mandible  above  the  mylohyoid  ridge.  Its  hiner  surface  is  in  contact 
with  the  genioglossus  and  the  liyoglossus  muscles,  as  well  as  with  Wharton's  duct,  which 
runs  forwards  between  the  gland  and  the  muscles.  Below,  it  rests  on  the  mylohyoid,  and 
at  its  posterior  part  on  the  deep  process  of  the  submaxillary  gland ;    whilst  its  ux>per 


DEVELOPMENT  OF  SALIVAEY  OLANDS,  PALATE,  AND  TONGUE.    1013 

prominent  border  is  covered  only  by  the  mucous  membrane  of  the  mouth,  here  raised  up 
by  the  gland  to  form  the  plica  sublingualis  (Fig.  712).  The  anterior  portion  of  the  gland 
is  much  deeper  and  more  bulky  than  the  posterior  half,  and  it  meets  its  fellow  in  the 
middle  line  beneath  the  frenulum  linguie.  The  posterior  extremity  gi'ows  gradually  more 
slender,  and  ends  near  the  posterior  part  of  the  mylohyoid  ridge,  where  it  lies  above  the 
deep  process  of  the  submaxillary  gland. 

Its  ducts,  generally  known  as  the  ducts  of  Rivinus  (ductus  sublinguales  minores), 
are  numerous  and  of  small  size  ;  they  leave  the  upper  part  of  the  gland,  and,  after  a 
short  course,  open  on  a  series  of  papillaj,  visible  to  the  naked  eye,  which  are  placed 
along  the  summit  of  the  plica  sublingualis. 

The  gland  is  not  enclosed  in  a  distinct  capsule,  thus  differing  from  the  jiarotid  and  suljmaxil- 
lary  glands  ;  but  its  numerous  lobules,  which  are  smaller  than  those  of  the  glands  just  mentioned, 
are  held  together  by  fine  connective  tissue,  loosely,  but  still  in  such  a  manner  as  to  make  one 
more  or  less  consolidated  mass  out  of  what  was,  in  the  embryo,  a  number  of  separate  glands. 

As  a  rule  all  the  ducts  open  sejjarately  on  the  summit  of  the  \A\ca  sublingualis,  and  appar- 
ently none  of  them  join  Wharton's  duct.  Frequently  some  of  those  from  the  anterior  and  more 
bulky  part  of  the  gland  are  larger  than  the  others,  but  the  j^resence  of  a  large  duct  running 
alongside  of  Wharton's  duct,  and  opening  with  or  beside  it  (ductus  major  Rivini,  duct  of 
Bartholin),  is  very  rare,  and  must  be  considered  as  an  exceptional  condition  in  man,  although 
normal  in  the  ox,  sheep,  and  goat.  The  same  may  also  be  said  of  ducts  from  the  sublingual, 
which  are  described  as  opening  into  the  duct  of  Wharton. 

Vessels  and  Nerves. — The  arteries  are  derived  from  the  sublingual  branch  of  the  lingual 
and  from  the  submental  branch  of  the  facial.  The  nerves  come  from  the  lingual,  the  chorda 
tympani,  and  the  sympathetic,  through  a  branch  of  the  submaxillary  ganglion  which  joins  the 
lingual,  and  is  conveyed  by  it  to  the  gland. 

The  apical  gland  of  the  tongue  (Nuhn's)  is  described  with  the  tongue,  p.  1006. 
Development  of  the  Salivaey  Glands,  Palate,  and  Tongue. 

The  general  development  of  the  lips,  mouth,  palate,  and  tongue  is  described  on  pages 
37  to  42,  and  reference  wiF  be  made  here  only  to  a  few  special  points  bearing  upon  this 
matter. 

Several  explanations  of  the  formation  of  the  philtrum  or  groove  on  the  front  of  the 
upper  lip  have  been  put  forward  ;  most  probably  it  is  produced  by  the  union  of  the  median 
fronto-nasal  process  with  the  two  maxillaiy  processes  (see  p.  39),  the  floor  of  the  groove 
being  formed  by  the  fronto-nasal  process,  and  the  ridges  bounding  the  groove  at  the  sides 
corresponding  to  the  line  of  meeting  of  the  fronto-nasal  with  the  maxillary  processes. 

The  salivary  glands  are  developed  as  solid  outgi-owths  of  the  buccal  epithelium,  one 
each  for  the  submaxillary  (the  first  developed)  and  the  parotid,  several  for  the  sublingual 
gland.  The  outgi'owths  are  at  first  simple ;  they  subsequently  divide,  and  finally  develop 
alveolar  enlargements  on  their  exti-emities.  By  a  separation  of  the  lining  cells,  the  ducts, 
and  later  on  (about  the  22nd  week)  the  alveoli,  become  hollowed  out,  and  present  a  lumen 
as  in  the  adult. 

The  development  of  the  palate  is  given  at  page  40  ;  but  it  should  be  mentioned 
that,  in  oi'der  to  account  for  the  position  which  the  fissure  in  cleft  palate  usually  occupies, 
viz.  between  the  central  and  lateral  incisors,  the  theory  has  been  advanced  by  Albrecht, 
that  each  premaxilla  is  made  up  of  two  separate  segments,  an  inner  (or  endo-gnathion), 
containing  the  central  incisor,  and  an  outer  (or  meso-gnathion),  containing  the  lateral 
incisor  (the  rest  of  the  maxilla  constituting  the  exo-gnathion).  Between  these  two 
segments  of  the  premaxilla  (endo-  and  meso-gnathion)  the  cleft  is  said  to  run,  and  not 
between  the  premaxilla  and  maxilla  as  usually  held. 

Tongue. — The  tongue  is  developed  in  the  embryo,  not  on  the  floor  of  the  primitive 
mouth,  but  upon  the  anterior  wall  of  the  pharynx,  and  in  two  parts,  which  are  at  first 
distinct  but  soon  unite.  The  anterior  two-thirds  of  the  organ  is  formed  from  the 
tuberculum  impar,  a  single  median  elevation,  developed  on  the  ventral  wall  of  the  pharynx, 
Immediately  behind  the  first,  or  mandibular,  visceral  arch.  Behind  the  tuberculum  impar, 
at  first,  lies  a  prominent  elevation — the  furcula,  from  the  anterior  part  of  which  the 
epiglottis  is  formed — the  two  being  separated  by  a  distinct  sulcus,  the  sinus  arcuatus 
(see  p.  37).  Soon,  however,  the  ventral  extremities  of  the  second  and  third  visceral 
arches,  growing  downwards,  unite  across  the  middle  line.  The  tuberculum  is  thus 
separated  fi-om  the  furcula,  and  the  middle  portion  of  the  sinus  arcuatus  is  divided  into 
an  anterior  and  a  posterior  part.  The  venti'al  ends  of  the  two  arches  having  fused, 
develop,  after  a  little  time,  into  a  prominent  semilunar  ridge,  the  rudiment  of  the  posterior 
68  a 


1014 


THE  DIGESTIVE  SYSTEM. 


third  of  the  tongue.  This  ridge  embraces  the  back  of  the  tubercukim  impar,  but  it  is 
separated  from  it  in  part  by  the  anterior  division  of  the  sinus  arcuatus,  which  persists 
even  in  the  adult  as  the  foramen  csecum,  with  the  sulcus  terminalis  running  forwards  and 
outwards  on  each  side  from  it.  Finally,  the  two  rudiments  of  the  tongue — the  tuberculum 
impar  and  the  semilunar  ridge — become  blended,  the  only  indication  of  the  original 
separation  being  the  foramen  ceecum,  the  sulcus  terminalis,  and  the  different  characters 
which  the  mucous  membrane  presents  on  the  two  divisions  of  the  organ.  At  the  foramen 
ciecum  the  downgrowth  which  gives  rise  to  the  isthmus  of  the  thyroid  gland  takes  place, 
and  a  part  of  the  thyro-glossal  duct  which  in  the  early  condition  connects  the  two  may  in 
rare  cases  persist  in  the  adult  in  connexion  with  the  foramen. 


Permanent  canine 
1st  permanent  premolar 
2nd  permanent  premolar 


1st  permanent  molar 


2nd  permanent 
molar 


Permanent 

lateral 

incisor 


,  central 
incisor 


THE  TEETH. 

The  teeth  are  highly  modified  portions  of  the  mucous  membrane  of  the  mouth, 
specially  developed  to  perform  the  important  function  of  mastication,  that  is,  the 
division  and  trituration  of  the  food  which  takes  place  in  the  mouth  before  the  lolus, 

as    the    resulting 
""^  'f\  mass  is   called,  can 

be  sw^allowed.  Each 
tooth  is  a  calcified 
papilla  of  the  mucous 
membrane  of  the 
mouth,  and  consists 
like  that  membrane 

Permanent     of  tWO  chicf  portionS 

— namely,  the  den- 
tine derived  from  the 
connective  tissue, 
and  the  enamel  from 
the  epithelial  layer 
of  the  mucous  mem- 
brane. The  dentine 
constitutes  the  chief 
mass  of  the  tooth, 
whilst  the  enamel 
forms  a  cap  for 
the  portion  which 
projects  above  the 
gum.  There  is  also 
found  in  the  teeth 
another  special 
tissue  —  the  cemen- 
tum  or  crustapetrosa, 
a  form  of  modified 
bone — which    en- 


2\i<\  !nilk  molar 

1st  milk  molar 

Mental  foramen 


Fig.  717. — Teeth  of  a  Child  over  Seven  Yeaiis  old  (modified  from  Testut). 

By  removing  the  bony  outer  wall  of  the  alveoli,  the  roots  of  the  teeth  which  have 
been  erupted,  and  the   permanent  teeth  which    are  still    embedded    in  the 
mandible  and  maxilla,  have  been  e.xposed.      The  milk  teeth  are  coloured  blue, 
the  permanent  teeth  yellow.      It  will  be  seen  that  the  first  permanent  molars 
have  appeared,  the  central  and  lateral  milk  incisors  have  been  replaced  by  the 
coiTesponding  permanent  teeth  in  the  upper  jaw,  but  the  milk  canine  and 
molars  have  not  yet  been  shed.     In  the  lower  jaw  the  central  milk  incisor  has    CaSCS  the  rOOtS,  these 
been  replaced  by  the  permanent  central ;  the  lateral  has  not  j'et  been  shed,  but    latter    beino"    formed 
its  permanent  successor  is  making  its  way  up  to  the  surface  on  its  lingual  side.    pi-,4Qfl,     „f  j^    j.- 
In  addition,  the  canine  and  two  molars  of  the  milk  set  persist.      The  position    Cnieny  01^  Qentme. 
of  the  crowns  of  the  permanent  teeth  between  the  roots  of  the  milk  molars,  JjCntme         and 

and  the  deep  situation  occupied  by  the  permanent  canines,  should  be  noted,    enamel   but  particu- 
Observe  also  the  absorption  of  the  root  of  the  lower  lateral  incisor.  lovl  v   tl'  o  1    tf 

the  hardest  and  most  resistant  structures  in  the  body,  and  are  thus  specially  fitted 
for  the  functions  which  they  have  to  jjerform. 

Temporary  and  Permanent  Teeth.. — The  mouth  of  the  infant  at  birth  contains 
no  teeth,  although  a  number,  partly  developed,  lie  embedded  in  the  jaws  beneath 
the  gum.  Some  six  months  later  teeth  begin  to  appear,  and  by  the  end  of  the 
second  year  a  set,  known  as  the  milk  teeth,  twenty  in  number,  has  been  "  cut." 
Then  follows  a  pause  of  about  four  years,  during  which  no  visible  change  takes 
place  in  the  mouth,  although  in  reality  an  active  preparation  for  further  develop- 
ment is  going  on  beneath  the  gum. 


THE  TEETH. 


1015 


At  the  end  of  this  period,  namely,  about  the  sixth  year,  the  next  stage  in  the 
production  of  the  adult  condition  begins.  It  consists  in  the  eruption  of  ibur  new 
teeth — the  hrst  permanent  molars — one  on  each  side,  above  and  below,  behind  those 
of  the  milk  set.  This  is  followed  by  the  gradual  falling  out  of  the  twenty  teeth 
which  have  occupied  the  mouth  since  the  second  year  (Fig.  717),  and  the  sub- 
stitution for  them  of  twenty  new  teeth,  which  take  up,  one  by  one,  the  vacancies 
created  by  the  dropping  out  of  each  of  the  milk  set.  Finally,  the  adult  condition 
is  attained  by  the  eruption  of  eight  additional  teeth — the  2nd  and  3rd  molars — 
two  on  each  side,  above  and  below,  behind  those  which  have  already  appeared.  All 
of  these — the  permanent  set — have  appeared  by  the  end  of  the  twelfth  or  thirteenth 
year,  except  the  four  wisdom  teeth,  which  are  usually  cut  between  the  seventeenth 
and  twenty-tifth  year,  but  are  often  delayed  until  a  very  much  later  period,  and 
occasionally  never  appear. 

The  set  of  teeth  which,  as  indicated  above,  begin  to  appear  in  the  infant  about 
the  sixth  month,  are  known  as  the  deciduous,  temporary,  or  milk  teeth  (dentes 
decidui),  whilst  those  which  succeed  them  and  form  the  adult  equipment  are  the 
permanent  teeth  (dentes  permanentes). 

The  milk  teeth  are  twenty  in  number,  and  are  named  as  follows  in  each  jaw, 
beginning  at  the  middle  line : — central  incisor,  lateral  incisor,  canine,  first  molar 
and  second  molar  ;  or  more  briefly,  two  incisors,  one  canine,  two  molars.  This  is  con- 
veniently expressed  by  the  "  dental  formula  "  for  the  deciduous  teeth  in  man,  which 
shows  the  number  of  each  class  of  teeth  above 
and  below  on  one  side  of  the  mouth,  viz. : — 
i.  f ,  c.  \,  m.  f . 

The  permanent  teeth,  thirty  -  two  in 
number,  are  named  in  each  jaw,  Iteginning 
at  the  middle  line: — central  incisor,  lateral  crowi 
incisor,  canine,  1st  premolar  (or  bicuspid), 
2nd  premolar  (or  bicuspid),  1st  molar,  2nd 
molar,  and  3rd  molar  or  wisdom  tooth 
(dens  serotinus).  The  dental  formula  for 
the  permanent  set  in  man  is  thus : — 

i.  f,  c.  \,  pvi.  -|,  m.  |. 

General  Form  and  Structure. — A  tooth  ^'''■^ 
consists  (Fig.  718)  of  (1)  the  crown  (corona 
dentis),  the  portion  projecting  above  the 
gum,  which  varies  in  shape  in  the  different 
teeth,  and  in  all,  except  the  incisors  and 
canines,  bears  on  its  grinding  surface  a 
number  of  tubercles  or  cusps  (tubercula 
corouie),  varying  in  number  from  two  to  five  Root 
in  the  different  teeth  ;  (2)  the  neck  (collum 
dentis),  the  faintly  constricted  part  which  is 
surrounded  collar  -  wise  by  the  gum,  and 
which  connects  the  crown  with  (3)  the  root 
(radix  dentis),  the  portion  of  the  tooth 
which  is  embedded  in  the  alveolus  of  the 
maxilla  or  the  mandible.  In  the  majority 
of  teeth,  namely,  in  aU  except  the  molars, 
the  root,  as  a  rule,  is  single,  or  nearly  so, 
and  consists  of  a  long,  tapering,  conical,  or 
flattened  piece,  perfectly  adapted  to  the 
alveolus  in  which  it  lies.  In  the  molar  teeth  (and  in  some  of  the  others  occasion- 
ally) the  root  is  divided  into  two  or  three  tapering  or  flattened  roots  or  fangs. 
At  the  apex  of  each  root  there  can  be  made  out,  even  with  the  naked  eye, 
a  minute  opening  (foramen  apicis)  through  which  the  vessels  and  nerves  enter  the 
tooth. 

On  making  a  section  of  a  tooth  (Fig.  718),  it  will  be  seen  that  the  interior  of 
68  & 


Bone 
Cement  or  crusta  petrosa 

Alveolar  periosteum  or  root-membrane 
Fio.  718.— Vertical  Section  of  Canine  Tooth 
to  illustrate  its  various  parts,  and  its  structure. 


1016  THE  DIGESTIVE  SYSTEM. 

the  body  is  occupied  by  a  cavity  of  some  size,  generally  called  the  pulp  cavity 
(cavum  dentis),  owing  to  the  fact  that  it  is  filled  in  the  natural  state  by  the  soft 
and  sensitive  tissue  known  as  the  pulp.  This  pulp  cavity  gradually  narrows 
below,  and  is  prolonged  into  each  root  of  the  tooth  as  a  slender  tapering  passage, 
the  root  canal  (canalis  radicis),  which  opens  at  the  apical  foramen  already  referred 
to.  Through  these  root-canals,  w^hich  also  contain  some  pulp,  the  vessels  and 
nerves,  which  enter  at  the  apex,  pass  to  the  interior  of  the  tooth. 

Short  diverticula  of  the  pulp  cavity  are  prolonged  into  the  bases  of  the  cusps  in 
the  molar  and  premolar  teeth,  and  in  the  incisors  also  there  are  similar  slight  pro- 
longations of  the  cavity  towards  the  angles  of  the  crown. 

The  roots  of  the  teeth  are  embedded  in  the  sockets  or  alveoli  of  the  jaws,  to 
which  they  are  accurately  adapted,  and  firmly  united  (Fig.  718)  by  a  highly 
vascular  layer  of  connective  tissue — the  alveolar  periosteum  (alveolo-dental  perios- 
teum or  root-membrane).  This  is  attached  to  the  wall  of  the  alveolus  on  the  one 
hand  and  to  the  root  of  the  tooth  on  the  other,  whilst  above  it  is  continuous  with 
the  connective  tissues  of  the  gum. 

So  accurately  are  the  root  and  the  alveolus  adapted  to  each  other  over  their 
whole  extent,  and  so  firmly  does  the  periosteum  bind  them  together,  that,  under 
normal  conditions,  the  tooth  is  quite  firmly  fixed  in  the  bone,  and  no  movement 
of  the  root  within  the  alveolus  can  take  place ;  the  vessels  and  nerves  entering  at 
the  apex  are  thus  secured  against  pressure  or  strain. 

When,  lio-svever,  the  alveolar  periosteum  is  inflamed  it  becomes  swollen  and  exquisitely  sensi- 
tive ;  the  tooth,  as  a  result  of  the  swelling,  is  pushed  partly  out  of  its  socket,  its  crown  projects 
above  those  of  its  neighbours,  and  strikes  against  the  opposing  tooth  when  the  mouth  is  closed, 
giving  rise  to  much  pain  and  discomfort. 

The  neck,  although  a  useful  term,  can  scarcely  be  recognised  as  a  distinct  constriction  in  the 
permanent  teeth  ;  it  corresponds  to  the  line  along  which  the  gum  and  alveolar  periosteum  meet, 
or  along  which  the  gum  is  united  to  the  tooth ;  biit,  as  already  pointed  out,  the  gum  does  not 
stop  at  the  neck,  but  forms  a  free  fold  which  surrounds  the  base  of  the  crown  collar-wise  for  a 
short  distance.  The  oiitline  of  the  margin  of  the  giun  opposite  the  labial  and  lingiial  surfaces  of 
the  crown  is  usually  concave,  but  opposite  the  proximal  and  distal  sides  of  the  tooth  it  is  convex, 
and  reaches  much  nearer  to  the  edge  of  the  cro^\^a  than  on  the  other  surfaces. 

In  the  incisors  and  canines  the  pulp  cavity,  which  is  about  |  to  j  the  diameter  of  the  tooth, 
passes  very  gradually  into  the  root  canal  (Fig.  718),  so  that  it  is  difficult  to  say  where  one  ends 
and  the  other  begins"^  The  reverse  is  the  case  in  the  molars,  whilst  the  premolars  are  somewhat 
variable  in  this  respect. 

Tartar  is  a  hard  calcareous  deposit  from  the  saliva  (salivary  calculus),  often  found  on  the  teeth 
near  their  necks.  It  is  composed  of  lime  salts,  and  its  deposit  is  largely  determined  by  the 
presence  of  organisms  (leptothrix,  etc.)  in  the  mouth. 

THE  PERMANENT  TEETH. 

The  permanent  teeth  (Figs.  719  and  724)  are  thirty-two  in  number,  sixteen  above 
and  sixteen  below,  or  eight  in  each  half  of  either  jaw ;  and,  although  we  can  group 
them  under  four  heads — incisors,  canines,  premolars,  and  molars — the  individual 
teeth  differ  so  much  in  their  characters  that  each  tooth  will  require  a  separate 
description. 

Descriptive  Terms. — Before  describing  the  permanent  teeth,  it  is  requisite  that 
certain  terms  which  are  employed  to  denote  the  surfaces  of  the  teeth  should  be  defined. 
This  is  a  matter  of  some  importance,  seeing  that  the  terms  inner  and  outer,  anterior  and 
posterior,  cannot,  owing  to  the  curvature  of  the  dental  arches,  be  properly  applied  to  all 
the  teeth  in  the  same  sense.  The  terms  given  below  have  been  adopted  seeing  that  they 
are  free  from  the  danger  of  misconception. 

The  part  of  a  tooth  which  comes  in  contact  with  the  teeth  of  the  opposite  jaw  is  known 
as  the  grinding  or  masticating  surface  (facies  masticatoria.  Fig.  721).  The  surface  in 
contact  with  or  looking  towards  its  predecessor  in  the  row  is  known  as  the  proximal 
surface  {fades  medialis  in  incisors  and  canines,  facies  anterior  in  premolars  and  molars) ; 
the  opposite  surface,  namely,  that  wliich  looks  towards  its  successor  in  the  row,  is  known 
as  the  distal  surface  (facies  lateralis  in  incisors  and  canines,  facies  posterior  in  molars  and 
premolars).  The  surface  which  looks  towards  the  tongue  is  the  lingual  surface  (facies 
lingualis),  and  that  looking  in  the  opposite  direction,  i.e.  towards  the  lips  and  cheek,  the 
labial  surface  (facies  labialis).  The  portion  of  a  tooth  which  touches  its  neighbour  in  the 
same  row  is  known  as  the  contact  surface  (facies  contactus). 


THE  TEETH. 


1017 


Incisor  Teeth  (dentes  incisivi,  Figs.  719  and  720). — These  teeth,  four  in  number 
in  each  jaw,  are  used  specially  for  cutting  the  food,  hence  their  name.  The  crown 
of  each  is  chisel-shaped,  and  presents  an  anterior  or  labial  surface  which  is  convex 
in  all  directions,  a  posterior  concave  surface,  and  a  chisel-like  edge,  which,  when 
first  cut,  is  surmounted  by  three  small  tubercles  separated  by  two  grooves.  These 
tubercles,  however,  are  soon  worn  down,  and  the  edge  becomes  straight  or  nearly 
so.  Owing  to  the  fact  that  the  upper  incisors  overlap  those  in  the  lower  jaw,  the 
cutting  edge  is  worn  away,  or  becomes  bevelled,  on  the  posterior  aspect  in  the 
former,  but  on  the  anterior  aspect  or  summit  in  the  latter.  The  upper,  but 
particularly  the  upper  central  incisors,  are  of  large  size,  and  slope  somewhat  forwards  ; 


3nd  molar 


3rcl  molar 


2nd  viremolar  Canine  Central  incisor 

Ist  molar  I         1st  premolar     tv  Lateral  incisor 


3rd  molar 


1st  molar 


1st  premolar     Y'        Lateral  incisor 
2nd  premolar  Canine  Central  incisor 


2nd  molar 

Fig.  719. — The  Permanent  Teeth  of  the  Right  Side,  Outer  or  Labial  Aspect. 

The  upper  row  shows  the  upper  teeth,  the  lower  row,  the  lower  teeth.      The  wide  vertical  "labial  ridge  "  is 
distinct  on  the  upper  canine  and  premolar  teeth. 

whilst  the  lower  incisors,  which  are  all  nearly  equal  in  size,  are  much  smaller — being 
the  smallest  of  all  the  teeth — and  are  placed  vertically.  The  roots  of  the  incisors 
are  single,  though  a  groove  is  occasionally  seen  on  each  side,  suggesting  a  division. 

The  central  upper  incisors  are  very  much  larger  than  the  upper  lateral  incisors  (Fig.  719),  but  in 
the  lower  jaw  the  opposite  is  the  case,  the  lateral  incisors  being  slightly  the  larger.  In  all  incisors 
the  outer  (distal)  angle  of  the  crown  is  more  rounded  than  the  ijroximal.  The  posterior  concave 
surface  of  the  crown  in  the  upper  incisors  is  usually  limited  towards  the  gum  by  a  a -shaped 
ridge  (Fig.  720),  known  as  the  basal  ridge  or  cingulum.  The  two  limbs  of  the  A  are  continued 
up  along  the  sides  of  the  jwsterior  surface,  whilst  the  apex  is  turned  towards  the  gum  ;  and  here, 
particularly  in  the  lateral  incisor,  there  is  often  developed  a  small  lingual  cusp  (Fig.  720).  The 
cingulum  is  rarely  found  on  the  lower  incisors. 

The  roots  of  the  upper  incisors  and  canines  are  conical  and  rounded  (the  laterals  and  canines 
not  so  distinctly  as  the  centrals,  Fig.  723),  whilst  those  of  the  lower  jaw  are  flattened  from  side  to 
side  (j)roximo-distaUy). 

Canine  Teeth. — In  the  four  canine  teeth  (dentes  canini),  which  succeed  the 
incisors  in  each  row  (Figs.  719  and  720),  the  crown  is  large  and  conical,  corresponding 
closely  in  general  form  to  a  very  large  central  incisor  with  its  angles  cut  away, 
so  that  the  crown  assumes  a  pointed  or  conical  shape.  The  labial  surface  is 
convex,  the  lingual  usually  somewhat  concave.  The  root  is  single  and  long,  par- 
ticularly in  the  upper  canine,  the  root  of  which  is  longer  than  that  of  any  other 
tooth,  and  produces  the  canine  eminence  on  the  anterior  surface  of  the  upper  jaw. 
The  upper  canines  are  larger  than  the  corresponding  lower  teeth,  behind  which 
they  bite ;  and  they  are  sometimes  known  as  the  "  eye  teeth." 

The  upper  canine  presents  on  its  lingual  surface  a  well-marked  cingulum,  and  often  a  distinct 
lingual  cusp  ;  in  addition,  there  is  usually  a  median  ridge  running  from  the  point  of  the  cro-wn 
to  the  apex  of  the  cingulum,  which  is  separated  from  the  lateral  part  of  the  cingulum  on  each 
side  by  a  slight  depression.  These  points  are  neither  so  well  marked,  nor  so  constant,  in  the 
lower  as  in  the  upper  canine. 


1018 


THE  DIGESTIVE  SYSTEM. 


Of  the  two  margins  sloping  away  from  the  apex  of  the  crown,  the  lateral  is  the  longer  in  both 
teeth.    After  it  has  been  a  little  worn  the  lower  canine  is  less  distinctly  pointed  than  the  upj)er  ; 

Central  incisor  Canine  Snd  premolar  2nil  inolar 

Lateral  incisor  /\      1st  premolar        |  1st  molar  |  3rd  molar 


Lateral  incisor 
Central  incisor 


1st  premolar      I  1st  molar  3rd  molar 

Canine  2nd  premolar  2nd  molar 


Fig.   720. — The  PERMA^"ENT  Teeth  of  the  Right  Side,  Inner  or  Lingual  Aspect. 

The  upper  row  shows  the  upper  teeth,  the  lower  row  the  lower  teeth.     The  cingulum  is  distinct  on  the  upper 
incisors  and  hoth  canines,  the  lingual  cusp  on  the  upper  lateral  incisor  and  the  upper  canine. 

its  root  is  also  more  flattened.  On  the  labial  surface  of  the  crown,  of  both  canines  and  premolars, 
a  wide  low  vertical  ridge  (labial  ridge)  can  generally  be  made  out  (Fig.  719) ;  it  is  most  dis- 
tinct on  the  canine  and  first  upper  premolar. 

Premolar  or  Bicuspid  Teeth  (dentes  premolares,  Figs.  719  and  720). — Eight  in 
number,  two  in  each  jaw  above  and  below,  the  premolar  teeth  are  placed  behind  the 

canines,  and  in  front  of  the  molars  as  indi- 
cated bj  the  term  "  premolar."  The  crown 
which,  unlike  that  of  the  incisors  and 
canines,  is  flattened  from  before  backwards 
(proximo-distally),  is  characterised  by  the 
presence  of  two  cusps  (Fig.  721),  hence 
the  term  bicuspid  often  applied  to  these 
teeth.  One  of  the  cusps,  the  larger,  is 
placed  on  the  outer  or  labial,  the  other 
on  the  inner  or  lingual  side.  The  labial 
and  hngual  surfaces  are  both  convex. 
The  root  is  single,  but  it  is,  as  a  rule, 
flattened  from  before  backwards  (proximo- 
distally)  and  grooved,  showing  in  this  a 
tendency  to  division,  wliich  often  actually 
takes  place  in  the  first  upper  premolar. 
The  upper  premolars  are  easily  distin- 
FiG.  721.— The  Upi-er  Pek.manent  Teeth,  viewed  guished  by  the  fact  that  their  two  cusps 
froiri  below.  q^q   large   and   are    separated    from    one 

The  cu.sps  of  the  premolars  and  molars  of  the  right  another    by   a    distinct    antero- posterior 

.side  (left  of  picture)  are  particularly  well  .shown,  n   „  /-c:^     itoin  i  -i   i.     •        i-iT       ^ 

Tlie    ridge    from   the    inner    anterior    (proximo-  ^^^^^    (^Ig-    ^21) ;    whllst    in    the    loWCr 

lingual)  to  the  outer  posterior  (labio-distai)  cusp  premolars,  on  the  other  hand,  the  separa- 

is  also  di.stinct  in  the  first  and  second  molars,  tion  between  the  two  CUSpS  is  not  effected 

The   second    molars   .show   four    cu.sps,    one    of  r  ^    ^    ^^„4-,-    ,,,    ,    n  •       xi 

them  small,  although  tliree  only  are  frequently  '^7   ^   Continuous    fissure   aS   m    the    upper 

found.  teeth,  but  by  two  dimple-like  depressions 

separated  by  a  ridge,  which  joins  the  two 
cusps  (Fig.  722).  In  the  upper  premolars,  therefore,  the  two  cusps  are  separated 
by  a  fissure,  in  the  lower  they  are  united  by  a  ridge. 

The  first  upper  premolar  is  often  slightly  larger  than  the  second  ;  the  reverse  is  the  case  in 
the  lower  jaw.     The  outer  or  labial  surface  of  the  crown  is  usually  somewhat  larger  than  the 


THE  TEETH.  1019 

inner  or  lingual  surface  in  all  pi-emolais.  The  upper  are  distinguished  from  tlie  lower  bicuspids, 
as  pointed  out  above,  by  the  fact  that  in  the  upper  the  two  cusps  are  separated  by  a  groove,  in  the 
lower  they  are  united  by  a  ridge  ;  in  the  latter  also  the  crowns  are  more  circular  (Figs.  715  and  722). 
It  will  further  usually  l>e  found  that  the  outer  or  labial  surface  of  the  crown  is  strongly  sloped 
(bevelled)  inwards,  near  the  grinding  surface,  in  the  lower  premolars.  The  first  can  usually  be 
distinguished  from  the  second  by  the  fact,  that,  while  the  lingual  cusp  and  surface  are  smaller 
than  the  labial  in  the  first  premolar,  they  are  nearly  of  the  same  size  in  the  second.  In  addition, 
the  i-oot  of  the  fii-st  upper  premolar  is  bifid  or  nearly  so,  and  its  labial  ridge  is  fairly  distinct,  but 
is  indistinct  in  the  second.  In  the  first  lower  premolar  tlie  lingual  cusp  and  surface  are  very 
small,  in  fact  the  cusp  is  quite  rudimentary.  It  should,  however,  be  added  that  it  is  often 
extremely  difficult  to  identify  the  various  bicuspids.  The  differences  may  be  expressed  in 
tabular  form  thus  : — 

Premolars. 


Boot.  Cusp  and  Surface. 


Upper    have  two  Hst  premolar    bifid,  or  nearly  so  Lingual  smaller  than  labial. 

cusps  separated^ , 

by  a  groove)       [2nd      „  1  single  Lingua]  nearly  as  large  as  labial. 


Lower   'have  two  f  1st  premolar    single  Lingual  much  smaller  than  labial. 

cusps  united  by- 

aridgei  1 2nd       ,,  ,,  Lingual  nearly  as  large  as  labial. 

Molar  Teeth  (denies  molares;. — The  molar  teeth,  also  known  as  the  grinders  or 
multicuspidati,  are  twelve  in  number — three  on  each  side  above  and  below — and 
are  distinguished  as  hrst,  second,  and  third  molars.  The  latter  is  also  known  as 
the  wisdom  tooth,  owing  to  its  late  eruption.  All  the  molars  are  characterised  bv 
the  large  size  of  the  cro^Ti  and  the  possession  of  three  or  more  trihedral  cusps  oia 
the  masticating  surface  (Figs.  721  and  722).  They  are  the  largest  of  all  the  teeth, 
but  they  diminish  in  size  from  the  first  to  the  third,  the  last  being,  as  a  rule, 
the  smallest  of  the  three.  In  shape  the  crown  is  more  or  less  quadrangular, 
with  convex  labial  and  lingual  surfaces.  The  roots  are  either  two  or  three 
in  number,  but  frequently  in  the  wisdom  teeth  they  are  united  to  a  varying 
degree. 

The  molars  of  the  upper  and  lower  jaws  differ  so  considerably  in  their  further 
details  that  they  must  be  considered  separately.  They  may  be  most  readily  dis- 
tinguished from  one  another  by  the  fact  that  normally  the  upper  molars  possess 
three  roots  (Figs.  719  and  720),  whilst  the  lower  molars  have  two  at  most.  The 
number  of  cusps,  though  not  so  reliable  a  guide  as  the  form  of  the  root,  is  also 
generally  sufficient  to  distinguish  them.  In  the  upper  molars  there  are  either 
three  or  four  cusps,  whilst  in  the  lower  the  number  is  most  commonly  five  (see, 
however,  page  1021). 

In  the  upper  molars,  the  crown,  viewed  from  the  grinding  surface  (Fig.  721),  is 
rhomboidal  in  shape  [i.e.  quadrangular  with  the  angles  not  right  angles).  The  outer 
(labial)  and  the  inner  (lingual)  surfaces  are  convex.  The  number  of  cusps  is  either 
four  or  three.  On  the  Jirst  there  are  invariably  four — two  on  the  labial  and  two 
on  the  lingual  side — the  antero-internal  (proximo-lingual)  of  these  being  connected 
with  the  postero-external  (labio-distal)  by  an  oblique  ridge  (Fig.  721),  which  is 
also  found  on  the  second  and  third  molars  when  these  bear  four  distinct  cusps. 
The  second  upper  molar  has  either  four  or  three  cusps  in  about  an  equal  proportion 
of  European  skulls,  whilst  in  the  third  the  number  is  much  more  freciuently  three 
than  four.  The  roots  in  the  upper  molars  are  three  in  number  (except,  occasionally, 
when  the  three  roots  of  the  wisdom  tooth  are  confluent),  two  being  external  or 
labial,  and  the  third  internal  or  palatal  (Figs.  719,  720,  and  723). 

In  the  lower  molars,  the  crown,  viewed  from  above  (Fig.  722),  is  somewhat 
cubical.  The  outer  and  inner  surfaces  are  convex,  as  in  the  upper  molars.  The 
Jirst,  as  a  rule,  bears  five  cusps,  two  being  on  the  outer  side,  two  on  the  inner,  and 
the  fifth  behind  and  external,  that  is,  between  the  two  posterior  cusps  and  somewhat 
to  the  outer  side.  The  second  has  usually  only  four  cusps ;  a  fifth,  however,  is 
sometimes  present.  The  third  has  either  four  or  five,  the  former  number  more 
frequently  than  the  latter. 

The   roots   of  the  lower  molars   are   two  in  number,  each  wide,  grooved,  and 


1020 


THE  DIGESTIVE  SYSTEM. 


flattened  from  before  backwards.     One  is  placed  anteriorly,  the  other  posteriorly, 
and  both  are  usually  recurved  in  their  lower  portions  (Fig.  719).     As  in  the  corre- 


Gentral  incisor 

Lateral  incisor 


/Canine 


1st  premolar 

■3ud  premolar 

1st  molar 


lid  molar 

Sill  molar 


Fig.   722. — The  Lower  Permanent  Teeth,  viewed  from  above. 


spending  teeth  of  the  upper  jaw,  the  roots  of  the  lower  wisdom  teeth  are  often  more 
or  less  united  into  a  single  mass. 

The  chief  characters  of  the  upper  and  lower  molars  may  be  summarised  thus  : — 

Molars. 


Upper 


Lower 


The  molars  diminish  in  size  from  before  backwards.  This  remark  applies  particularly  to  the 
wisdom  teeth,  which  are  extremely  variable  in  form  and  position  among  civilised  races.  The 
long  axis  of  the  upper  molars  has  a  general  direction  downwards  and  outwards  ;  wdiilst  that  of 
the  lower  molars,  which  the  former  i)artly  overlap,  slopes  upwards  and  inwards,  with  the  result 
that  the  outer  cusps  of  the  lower  molars  lie  in  the  groove  separating  the  inner  from  the  outer 
cusps  of  the  upper  teetli  (Fig.  706,  p.  996).  As  a  furtlier  result  of  this  overlapping,  the  outer 
edge  of  the  crown  is  sliarp  and  the  inner  edge  rounded  in  the  upper  molars ;  whilst  the  inner 
edge  is  sharp  and  the  outer  edge  rounded  in  the  lower  set.  The  cause  of  this  is  obvious.  The 
outer  margins  of  the  upjjer  molars  overlap  their  fellows  on  the  Iniccal  side,  whilst  the  inner 
margins  of  the  lower  molars  overlap  their  fellows  on  the  lingual  side  ;  these  margins,  therefore, 
are  subject  to  comparatively  little  attrition,  and  consequently  remain  sharp.  The  other  margin 
of  each  tooth,  on  the  other  hand,  strikes  against  the  gi'oove  on  the  crown  of  the  opposing  tooth, 
and  consequently  becomes  worn  and  round. 

The  fissures  which  separate  the  cusps  on  the  grinding  surfaces  of  tlie  molar  teeth  are  generally 
continued  as  faint  grooves  on  the  labial  and  lingual  surfaces. 

Upper  Molars. — The  crowns,  as  already  stated,  ai'c  rhomljoidal  in  shape,  and  when  viewing 
their  grinding  surface.s,  as  in  Fig.  721,  if  the  planes  of  separation  between  them  be  prolonged, 
they  would  strike  the  middle  line  near  the  back  part  of  the  hard  palate  ;  in  other  words,  their 


I    1st  Upper. 

2nd  Upper. 

3rd  Upper. 

Cusps    . 

4 

3  or  4 

3  or  4 

3  (or  1) 

Roots    . 

3 

3 

Ist  Lower. 

2nd  Lower. 

3rd  Lower. 

Cusps    . 

r, 

4  or  5 

4  or  5 

Roots    . 

2 

2 

2  (or  1) 

THE  TEETH. 


1021 


proximal  and  distal  surfaces  are  not  in  transverse  but  in  oblique  planes,  sloping  strongly  back- 
wards and  inwai-ds,  and  converging  somewhat  internally.  A  knowledge  of  this  is  useful  in 
determining  the  side  to  which  an  upjier  molar  belongs,  as  is  the  fact  that  the  anterior  labial  root 
is  broader  than  the  posterior  (Fig.  723). 

As  regards  the  number  of  cus2)s  (Fig.  721) : — The  first  upper  molar  has  four  cusps  in 
practically  all  skulls  (99  jier  cent) ;  occasionally,  indeed,  another,  but  very  rudimentary,  cusp  is 
present  on  the  lingual  side  of  the  antero-internal  (i^roximo-lingual)  cusp.  The  second  molar  has 
either  three  or  four  in  an  almost  equal  proportion  of  Eurojieans,  but  more  frequently  four  taking  the 
teeth  of  all  nations  together.  (According  to  Topinard,  four  cusps  are  present  in  66  per  cent  of  all 
races,  and  in  58  per  cent  of  European,  Semitic,  and  Egyptian  skulls  ;  according  to  Zuckerkandl,  in 
73'5  per  cent  of  the  lower  races  and  45-6  percent  of  Europeans.)  The  third  upper  molar  has  three 
cusps  much  more  frequentlv  than  four  amongst  Europeans  (four  cusps  only  in  36  per  cent,  although 
it  has  four  cusps  more  frequently  in  certain  lower  races).  It  should  be  remarked  that,  while  thex-e 
are  practically  always  four  cusps  in  tlie  first  molar,  still  there  is  a  tendency  to  the  disappearance 
of  the  postero-internal  (disto  -  lingual)  cusp,  which  tendency  grows  more  pronounced  as  we 
pass  Ijackwards  to  the  second  and  third 
molai-s.  The  other  cusps  are  practically 
constant. 

The  three  roots  of  the  ujjper  molars 
(Figs.  719,  720,  and  723)  are  a  large  inner 
or  palatal,  sub-CA'lindrical  in  shajie,  and 
two  external  or  labial  roots,  smaller  and 
flattened  from  before  backwards.  The 
palatal  fang,  which  is  placed  opposite 
the  posterior  labial  root,  is  often  united 
to  one  of  the  othei-s.  The  lower  part 
of  the  antrum  of  Highmore  generally 
extends  down  between  the  jjalatal  and 
the  two  labial  fangs  (Fig.  706,  p.  996), 
but  the  latter  i^roject  on  its  floor  more 
frequently  than  the  palatal  root.  In 
the  wisdom  tooth  the  three  roots  are 
frequently  more  or  less  united  into  a 
single  conical  jirocess  (Fig.  723). 

Lower  Molars. — The  crowns  are 
more  massive  than  those  of  the  upi)er 
molars,  and  are  elongated  antero-pos- 
teriorly  (Fig.  722).  A  crucial  groove 
separates  the  four  chief  cusps  from  one 
another ;  this  bifurcates  behind  to  en- 
close the  fifth  cusp,  which  lies  slightly 
to  the  outer  side  of  the  middle  of  the 
tooth.  The  numbei-  of  cusps  present  in 
the  lower  molars  is  as  follows  : — The 
first  has  usually  five  cusps  (62  per  cent 
of  all  races,  61  per  cent  of  Eiu'opeans) ; 
the  second  has  four  cusps,  as  a  rule  (five 
cusps  in  only  2-4  per  cent  of  all  skulls)  ; 
the  lower  wisdom  tooth  has  four  cusps 
a  little  more  fx'equently  than  five  (five 
in  46  per  cent  of  all  skulls),  but  like 
the  upper  wisdom  tooth  it  is  extremely 
variable. 

The    roots    of    th.e    lower    molars 
(Fig.  719),  two  in  number,  are  flattened 
from  before  backwards,  and  very  wide, 
but  one  (Fig.  723). 
two  are  united 


Fig. 


723. — Horizontal  Sections  through  both  the  Upper 
AND  Lower  Jaws  to  show  the  roots  of  the  teeth.  The 
sections  were  carried  through  the  bones  a  short  distance 
from  the  edge  of  their  alveolar  borders.  The  upper  figure 
shows  the  upper  teeth,  the  lower  figure  the  lower  teeth. 
Note  the  flattened  roots  of  the  lower  incisors,  the  two 
root  canals  in  the  anterior  root  of  each  lower  molar,  and 
the  confluence  of  the  three  roots  of  the  upper  wisdom 
teeth. 


The  anterior  of  these  has  two  root  canals  ;  the  jjosterior 
The  wisdom  tooth  has  commonly  two  roots  like  its  fellows  ;  occasionally  the 
in  determining  the  side  to  which  a  lower  molar  belongs,  it  should  be  remembered 
that  the  lower  part  of  the  root  is  generally  curved  backwards,  and  also  that  the  blunter  margin 
of  the  crowQ  (see  above)  and  the  fifth  cusj),  if  present,  are  on  the  outer  side. 

Arrangement  of  the  Teeth  in  the  Jaws. — The  teeth  are  arranged  in  each  jaw 
in  a  curved  row — the  dental  arch  (arcus  d.entalis) — of  approximately  a  semi-oval 
form  (Figs.  721  and  722).  The  curve  formed  by  the  upper  teeth,  however,  is  wider 
than  that  formed  by  the  lower  set,  so  that  when  the  two  are  brought  in  contact 
the  upper  incisors  and  canines  overlap  their  feUows  in  front,  and  the  outer  cusps 
of  the  upper  premolars  and  molars  overlap  the  corresponding  cusps  of  the  lower 
teeth  (Fig.  706,  p.  996).  It  ^^ill  also  be  seen  that,  as  a  rule,  the  teeth  in  one 
jaw  are  not  placed  exactly  opposite  their  fellows,  but  rather  opposite  the  interval 
between  two  teeth,  in  the  other  jaw  (Fig.  724).  This  arrangement  is  brought 
about  largely  by  the  great  width  of  the  upper  central  incisors  as  compared  with 


1022 


THE  DIGESTIVE  SYSTEM. 


their  feUows  of  the  lower  jaw,  which  throws  the  upper  canines  and  the  succeeding 
teeth  into  a  position  behind  (distal  to)  that  of  the  same  named  teeth  of  the  lower 

set.  But  as  the  lower  molars  are 
larger  in  their  antero  -  posterior 
diameter  than  those  of  the  upper 
row — and  this  remark  applies  par- 
ticularly to  the  wisdom  teeth — 
the  two  dental  arches  terminate 
behind  at  approximately  the  same 
point. 

The  upper  dental  arcli  is  said  to  form 
an  elliptical,  the  lower  a  parabolic  curve 
(Figs.  721  and  722).  The  line  formed  by 
the  grinding  surfaces  of  the  upper  teeth, 
as  seen  on  profile  view  (Fig.  724),  is 
usually  somewhat  convex,  owing  largely 
to  the  failure  of  the  wisdom  tooth  to 
descend  into  line  with  the  others. 
Similarly  the  line  of  the  lower  teeth  is 
as  a  rule  concave. 

In  both  jaws  the  cro^vns  of  the  front 
teeth  are  higher  (longer)  than  those  of 
the  molars. 


Fig, 


724. — To  show  the  relation  of  the  upper  to  the  lower 
teeth  when  the  mouth  is  closed.  The  manner  in  which  a 
tooth  of  one  row  usually  strikes  against  two  teeth  of  the 
opposite  row,  and  the  resulting  interlocking  of  the  teeth, 
is  to  be  noted. 


Period  of  Eruption  of  the  Per- 
manent Teetli. — Although  there  is 
considerable  variety  in  the  dates 
at  which  the  various  permanent 
teeth  appear  above  the  gums,  the 
order  of  eruption  is  practically  constant  in  different  individuals,  and  is  as 
follows : — Before  any  of  the  temporary  teeth  are  lost  the  first  permanent  molars 
appear  behind  the  2nd  milk  molars.  Next  the  central  milk  incisors  fall  out,  and 
their  places  are  taken  by  the  permanent  teeth  of  the  same  name ;  then  follow  the 
remaining  teeth  in  the  following  order :  Lateral  incisors,  1st  premolars,  2nd 
premolars,  canines,  2nd  molars,  and  3rd  molars.  It  will  be  observed  that  the 
eruption  of  the  canine  is  delayed  until  the  two  premolars,  which  succeed  it  in  the 
row,  are  cut,  so  that  it  breaks  the  otherwise  regular  order  of  eruption.  The  1st 
molar  is  sometimes  popularly  known,  owing  to  the  date  of  its  eruption,  as  the  "  six- 
year-old  tooth,"  and  the  2nd  molar  as  "  the  twelve-year-old  tooth." 

The  dates  at  which  the  eruption  usually  takes  place  may  be  simply  stated  as 
follows  for  the  lower  teeth  ;  those  of  the  upper  jaw  appear  a  little  later  : — 

1st  molars  appear  soon  after  the  6th  year. 
Central  incisors  appear  soon  after  the  7th  year. 


Lateral         „ 

8th 

1st  premolar 

9th 

2nd 

10th 

Canine     ,, 

11th 

2nd  molar 

12th 

3rd       „ 

fr 

om  the 

17th 

to 

Variations  in  the  Number  of  the  Teeth. — The  presence  of  an  additional  tooth  is  by  no 
means  uncommon.  It  may  appear  in  connexion  with  the  incisor,  premolar,  or  the  molar  groups. 
Windle  very  properly  draws  a  distinction  between  "  supernumerary  "  or  imperfect  additions  to 
the  dentition  and  "supplemental"  teeth  which  correspond  in  size  with  those  with  which  they 
are  associated.  When  a  supplemental  incisor  appears  it  has  an  interesting  bearing  upon  the 
solution  of  the  much -debated  point  as  to  whicli  incisor  has  disappeared  from  the  primate 
dentition.  The  addition  of  a  third  premolar  may  be  looked  upon  as  a  reversion  to  the  condition 
present  in  the  New  World  Apes  and  the  Lemurs.  The  })resence  of  a  fourth  molar  has  not 
infrequently  been  observed,  and  recently  it  has  formed  the  subject  of  an  instructive  and  sugges- 
tive paper  by  J.  T.  Wilson  (Journ.  Anat.  and  Phys.,  vol.  xxxix.  part  ii.). 


The  Milk  Teeth. 

The  deciduous,  temporary,  or  milk  teeth  (dentes  decidui)  are  twenty  in  number, 
ten  above  and  ten  below,  or  five  in  each  half  of  each  jaw — namely,  two  incisors,  one 


STEUCTUEE  OF  THE  TEETH. 


1023 


canine,  and  two  molars.  They  may  be  distinguished  from  the  permanent  teeth 
by  their  smaller  size,  their  well-marked  and  constricted  necks,  and,  in  the  case  of 
the  molars,  by  the  wide  divergence  of  their  roots  (Fig.  725).  Otherwise  they 
correspond  so  closely  to  the  same  named  teeth  of  the  permanent  set,  that  they 
require  no  separate  description,  except  in  the  case  of  the  molars.  The  first  upper 
molar  has  but  three  cusps  on  its  crown — two  external  and  one  internal ;  the 
first    lower    molar    has    four —  istmniar 

two  external  and  two  internal, 
and    the   crowns   of    both 


are 


Canine 


\ 


&&h 


flattened  from  side  to  side.  Lateral  incisor 
The  second  molars  of  the  upper  central  iucisoi-  \ 
jaw    have    four,    those   of    the  ^ 

lower  jaw  five  cusps  each.  In 
every  case  the  second  are  much 
larger  than  the  first  molars. 
The  cusps  are  sharper  and  are 
separated  by  deeper  fissures 
or  fossse  than  those  of  the 
permanent  teeth,  whilst  the 
roots  of  the  milk  molars, 
except  for  their  greater  di- 
vergence, agree  with  those  of 
the  permanent  set. 

The  marked   constriction  at   the 
neck  of  the  milk  teeth  (Fig.  725)  is 

due  to  a  great  thickening  of  the  cap  ,  ,  , 

of    enamel    on    the    crown,    and    its  Tt^  masticating  surfaces  of  the  two  upper  molars  are  shown  above 

In  the  second  row  the  upper  teeth  are  viewed  Irom  the  outer 
or  labial  side.  In  the  third  row  the  lower  teeth  are  shown 
in  a  similar  manner  ;  and  below  are  the  masticating  surfaces 
of  the  two  lower  molars.  In  the  specimen  from  which  the 
first  upper  molar  was  drawn  the  two  outer  or  buccal  cusps 
were  not  distinctly  separated,  as  is  often  the  case. 


Central  incisor 
Lateral  incisor 


Fig.  725. 


•2nfl  molar 
crown 


-2nd  molar 


-2nd  molar 


2nd  molar 
crown 


1st  molar 
-The  Milk  Teeth  of  the  Left  Side. 


abrupt  termination  as  the  neck  is 
reached.  The  enamel,  too,  is  much 
whiter  as  a  rule  than  in  the  per- 
manent teeth.  It  should  be  added 
that  the  labial  surface  of  the  canines 


and  molars  departs   very  markedly 

from  the  vertical  ;   it  slopes  strongly  inwards  towards  the  mouth  cavity  as  it  approaches  the 

grinding  surface  of  the  crown,  whichlatter  is,  as  a  result,  much  reduced  in  width. 

The  divergence  of  the  fangs  in  the  milk  molars  allows  the  crowms  of  the  permanent  premolars 
to  fit  in  between  them  before  the  milk  molars  are  shed. 


Structure  of  the  Teeth. 

As  mentioned  above,  the  teeth  are  composed  of  three  special  tissues,  enamel,  dentine, 
and  crusta  petrosa,  in  addition  to  the  pulp  which  occupies  the  tooth  cavity.  The  chief 
mass  of  the  tooth  is  formed  of  dentine,  which  surrounds  the  pulp  cavity  and  extends  from 
crown  to  root ;  outside  this  is  a  covering  of  enamel  on  the  crown,  and  a  layer  of  crusta 
petrosa  or  cement  on  the  root. 

The  enamel  (substantia  adamantina)  is  the  dense,  white,  glistening  layer  which 
forms  a  cap,  thickest  over  the  cusps,  for  the  portion  of  each  tooth  projecting  above  the 
gum  (Fig.  718).  At  the  neck  it  ceases  gradually,  being  here  slightly  overlapped  by  the 
crusta  petrosa. 

It  is  composed  chiefly  of  phosphate  and  carbonate  of  lime  (phosphate  of  calcium  89-82  per 
cent,  carbonate  of  calcium  4-37  per  cent,  magnesium  phosphate  1-34  per  cent,  a  trace  of  calcium 
fluoride,  other  salts  -88  per  cent),  and  has  generally  been  considered  to  contain  about  3-6  per  cent 
of  organic  substance;  but  this  Tomes  has  recently  shown  to  be  inaccurate :"  That  which  has 
heretofore  been  set  down  as  organic  matter  is  simply  water  combined  with  the  lime  salts. 
Enamel  is  to  be  regarded  as  an  inorganic  substance  composed  of  lime  salts,  which  have  been 
deposited  in  particular  patterns  and  formed  under  the  influence  of  organic  tissues,  which  have 
themselves  disappeared  during  its  formation." 

Enamel  consists  of  calcified  microscopic  prisms  (prismata  adamantina),  radiating  from 
the  surface  of  the  dentine,  on  which  their  inner  ends  lie,  to  the  surface  of  the  crown, 
oil  which  they  terminate  by  free  ends.  These  prisms  are  hexagonal  in  shape,  solid,  and 
of  considerable  length,  for  most  of  them  reach  from  the  dentine  to  the  surface  of  the  crown 
without  interruption.  The  prisms,  which  are  calcified  themselves,  are  held  together  by  the 
smallest  possible  amount  of  calcified  matrix  (Tomes).     In  old  teeth  the  cap  of  enamel  is 


1024 


THE  DIGESTIVE  SYSTEM. 


often  worn  away  over  the  cusps,  the  dentine  is  then  exposed,  and  is  easily  recognised  by 
its  yellowish  colour,  which  contrasts  strongly  with  the  whiteness  of  the  enamel. 

Whilst  adjacent  enamel  prisms  are  in  general  parallel  to  one  another,  they  do  not 
usually  take  a  straight,  but  rather  a  wavy  course,  and  in  alternate  layers  they  are  often 
inclined  in  opposite  directions,  thus  giving  rise  to  certain  radial  striations  seen  by 
reilected  light  (Schi'eger's  lines).  Certain  other  pigmented  lines,  more  or  less  parallel  to 
tlie  surface,  are  also  seen  in  the  enamel  (brown  strife  of  Retzius).  They  are  due  to  true 
pigmentation  (Williams),  and  mark  the  lines  of  deposit  of  the  enamel  during  its  develop- 
ment. The  enamel  prisms  are  more  or  less  tubular  in  certain  animals — viz.  in  all 
marsupials  except  the  wombat,  in  the  hyrax,  certain  insectivora,  and  certain  rodents. 

Nasmyth's  membrane  (enamel  cuticle)  is  an  extremely  thin  {-^o^ou  oi  an  inch) 
cuticular  layer  which  covers  the  enamel  of  recently-cut  teeth,  and  is  very  indestructible, 
resisting  almost  all  reagents.  Two  chief  views  are  held  as  to  its  origin.  One  that  it  is 
the  last  formed  layer  of  enamel,  which  has  not  yet  been  calcified,  and  therefore  the  final 
product  of  the  enamel  cells.  The  other  that  it  is  produced  by  the  outer  layer  of  cells  of 
the  enamel  organ.     This  latter  seems  to  be  the  more  probable  view. 

Dentine  (substantia  eburnea)  is  the  hard  and  highly  elastic  substance,  yellowish 
white  in   colour,  which  forms  the  greater  part  of  the  mass  of  every  tooth  (Fig.  726). 

Like  the  enamel  it  is  highly  calcified,  but  it 
differs  from  enamel  in  containing  a  very  con- 
siderable amount  of  organic  matter  and 
Avater  incorporated  Avith  its  salts,  w-hich  are 
chiefly  phosphate  and  carbonate  of  lime. 


Enamel 


Dentine 


Crown 


Pulp 
cavity 


Neck 


Fresli  human  dentine  contains  10  per  cent  of 
water,  28  jier  cent  of  organic  and  62  per  cent  of 
inorganic  material.  The  organic  matter  is  com- 
posed cliiefly  of  collagen,  and  to  a  less  extent  of 
elastin.  The  organic  matter  consists  of  (1) 
calcium  phosphate  (with  a  trace  of  fluoride),  (2) 
calcium  carbonate,  and  (3)  magnesium  jjliospliate, 
the  percentages  present  in  dried  dentine  being 
66-72,  3-36,  1-08  respectively.* 


^Dentine  consists  of  a  highly  calcified 
organic  matrix,  Avhich  is  itself  practically 
structureless,  although  everywhere  traversed 
by  tubes — the  dentinal  tubes — which  give 
to  this  tissue  a  finely  striated  appearance, 
the  strise  usually  running  in  wavy  lines. 
The  dentinal  tubes  begin  by  open  mouths  on 
the  w^all  of  the  pulp  cavity,  whence  they  run 
an  undulating,  and  at  the  same  time  a  some- 
W'hat  spiral  course,  towards  the  periphery  of 
the  dentine.  They  give  off  fine  anastomosing 
branches,  and  occasionally  divide  into  two. 
SomcAvliat  reduced  in  size,  they  usually  end  in 
the  outer  part  of  the  dentine. 

The  tubules  are  generally  described  as 
l)eing  lined  by  special  sheaths  (dentinal  sheaths 
of  Neumann)  which  are  composed  of  a  most 
resistant  material,  and  possibly  are  calcified. 
It  should  be  mentioned  that  the  presence 
of    these    sheaths    as    separate    structures    is 

doubted  by  some  authorities,  who  hold  that  the  part  described  as  the  sheath  is  only  a 

modified  portion  of  the  dentinal  matrix  surrounding  the  tubules. 

The  dentinal  tubules  are  occupied  by  processes,  prolonged  from  the  outermost  cells  of 

the  pulp — the  odontoblasts.     These  processes  are  called  after  their  discoverer.   Tomes' 

fibrils  (dentinal  fibrils),  and  they  are  probably  sensory  in  function. 

The  concentric  lines  of  Schreger,  frefpicntly  seen  in  tlie  dentine,  are  due  to  bends  in  successive 
dentinal  tubes  taking  jilace  aloTig  regular  lines  parallel  to  tlie  periplnjry  of  the  dentine.  Other 
lines  (the  incremental  lines  of  Salter),  due  to  inii>erfect  calcification,  are  found  arching  across  the 
substance  of  the  dentine,  chiefly  in  tlie  crown.  There  nuist  also  be  mentioned  the  interglobular 
spaces,  intervals  left  in  the  dentine,  as  a  result  of  imperfect  calcification,  bounded  by  the  fully 
calcified  surrounding  dentine,  the  contour  of  wliich  is  in  the  form  of  a  niimber  of  small  projecting 


Cement  or  crusta  petrosa 
Alveolar  periosteum  or  root-membrane 
Fig.  726. — Vertical  Section  ok  Canine  Tooth, 
to  illu.strate  its  various  parts,  and  its  structure. 


DEVELOPMENT  OF  THE  TEETH. 


1025 


globules  of  dentine.  These  interglobular  spaces  are  very  numerous  in  the  outer  or  "  granular 
layer"  of  the  dentine,  particularly  beneath  the  cementum  (see  Fig.  726). 

The  crusta  petrosa  or  cementum  (substantia  ossea)  is  a  layer  of  modified  bone 
which  encases  the  whole  of  the  tooth  except  its  crown.  It  begins  as  a  very  thin  stratum, 
slightly  overlapping  the  enamel  at  the  neck.  From  tliis  it  is  continued,  increasing  in 
amount,  towards  the  apex,  which  latter  is  formed  entirely  of  this  substance.  It  is  relatively 
less  in  amount  in  the  child,  and  increases  during  life.  In  places  the  dentine  seems  to 
pass  imperceptibly  into  the  crusta  petrosa  (the  "granular  layer"  of  dentine  marking  the 
junction  of  the  two,  see  Fig.  726),  and  some  of  the  dentinal  tubes  are  continuous  with 
the  lacunse  of  the  cementum.  Like  true  bone,  it  is  laminated,  it  possesses  lacuna3, 
canaliculi,  and,  when  in  large  masses,  it  may  even  contain  a  fevs'  Havei'sian  canals. 

The  tooth  pulp  occupies  the  pulp  cavity  and  the  root  canals  of  the  teeth.  It  is 
composed  of  a  number  of  branched  connective  tissue  cells,  the  anastomosing  processes 
of  which  form  a  fine  connective  tissue  network,  containing  in  its  meshes  a  jelly-like 
material,  in  addition  to  numerous  vessels  and  nerves,  but  no  lymphatics.  The  most 
superficial  of  these  cells  form  in  the  young  tooth  a  continuous  layer  of  columnar, 
epithelium-like  cells,  lying  on  the  surface  of  the  pulp  against  the  dentine;  they  are 
known  as  odontoblasts,  for  they  are  the  active  agents  in  the  formation  of  dentine.  From 
the  outer  ends  of  the  odontoblasts  processes  are  continued  into  the  dentinal  tubes,  where 
they  have  been  already  I'eferred  to  as  Tomes'  fibrils.  The  vessels  of  the  pulp  are 
numerous,  and  form  a  capillary  plexus  immediately  within  the  odontoblasts.  The  nerves 
form  rich  plexuses  throughout  the  pulp,  but  their  exact  mode  of  ending  is  unknown. 

The  alveolar  periosteum  (alveolo- dental  periosteum  or  root-membrane)  is  a  layer 
of  connective  tissue  free  from  elastic  fibres,  but  well  supplied  both  with  blood-vessels  and 
nerves,  which  fixes  the  root  of  the  tooth  in  the  alveolus,  being  firmly  united  by  perforat- 
ing fibres  of  Sharpey,  to  the  crusta  petrosa  on  the  one  hand,  and  to  the  bone  of  the 
alveolus  on  the  other.  It  establishes  a  communication  between  the  bone  of  the  jaw 
and  the  cementum,  and  above  it  is  continuous  with  the  tissue  of  the  gum.  Its  blood 
comes  chiefly  from  the  arteries,  which  subsequently  enter  the  apical  canals  for  the 
supply  of  the  pulp,  but  in  part  also  from  the  vessels  of  the  bone  and  those  of  the  gum 
(hence  the  relief  obtained  in  dental  periostitis  by  lancing  the  gum). 


Development  of  the  Teeth. 

At  the  beginning  of  this  chapter  a  tooth  was  described  as  a  calcified  papilla  of  the 
mucous  membrane,  composed  of  two  chief  parts — 
namely,  the  enamel  formed  by  the  epithelial  layer, 
and  the  dentine  by  the  connective  tissue  layer  of  the 
mucous  membrane.  The  details  of  the  process  by 
which  such  a  tooth  is  developed  from  the  two  layers 
of  the  mucous  membrane  are  both  numerous  and 
intricate,  and  can  be  but  briefly  described  here. 

In  lower  vertebrates  (sharks,  rays,  etc.),  teeth 
which  correspond  essentially,  both  in  structure  and 
development,  to  those  of  mammals,  are  found  on  the 
surface  of  the  body,  and  are  known  as  dermal  teeth. 
The  following  outline  of  the  development  of  the  dermal 
tooth  of  a  shark  may  assist  in  rendering  the  de- 
velopment of  the  human  teeth  more  intelligible  : — 

First,  a  papilla  is  formed  from  the  corium  or  con- 
nective tissue  layer  of  the  skin  (Fig.  727,  B),  which 
papilla  is  covei'ed  over  by  the  ej)ithelial  layer. 

Next  the  superficial  (connective  tissue)  cells  of 
the  papilla  begin  to  form  a  laj'er  of  dentine  on  the 
surface  of  the  papilla  (Fig.  727,  C),  which  it  soon 
encases,  the  remains  of  the  papilla  persisting  in  the 
interior  as  the  future  pulp.  At  the  same  time  the 
deepest  cells  of  the  epithelium  deposit  a  layer  of 
enamel,  outside  the  dentine,  over  the  summit  of  the 
papilla  (Fig.  727,  C),  and  subsequently  the  two — 
enamel  and  dentine — become  inseparably  united,  thus 
giving  rise  to  the  substance  of  the  tooth. 

At  a  later  period  the  epithelium  covering  the  summit  disappears  and  the  tooth  comes 
to  the  surface ;  this  constitutes  its  eruption  (Fig.  727,  D). 
69 


A,  Section  of  skin 
showing  epithelium 
e,  basement  mem- 
brane b,  and  connec- 
tive tissue  layer  c. 

B  shows  the  papilla  of 
the  connective  tissue 
layer  growing  up 
covered  by  the  epi- 
thelial layer. 


In  C  the  superficial  cells 
of  the  papilla  z  begin 
to  deposit  dentine  d 
over  the  papilla,  and 
at  the  same  time  the 
deepest  cells  of  the 
epithelium  deposit 
enamel  a. 


D  shows  the  tooth 
breaking  through 
the  epithelium  and 
reaching  the  surface. 


727. — Diagram  to  illustrate  thk 
Development  of  a  Dermal  Tooth 
IN  the  Shark. 

In  all  figures — a,  enamel ;  b,  tesement  mem- 
brane ;  c.  connective  tissue  layer  of  skin  ; 
cl,  dentine  ;  «,  epithelium  ;  and  z,  superficial 
cells  of  papilla. 


Fig, 


1026 


THE  DIGESTIVE  SYSTEM. 


^Jss.^ 


In  the  case  of  the  mammaliau  tooth  a  similar  process  takes  place,  not,  however,  on  the 
surface,  but  deep  down  in  the  substance  of  the  gum,  into  which  a  downgrowth  of  epithel- 
ium has  previously  taken  place.  This  epithelial  downgrowth  spreads  out  in  the  substance 
of  the  jaw,  and  into  it  the  papilla  grows  up,  and  goes  through  the  other  changes  described 
above,  as  if  the  whole  process  took  place  on  the  surface. 

Development  of  Human  Teeth. — The  following  is  a  brief  summary  of  the  chief 
^^^_^^^_^  events  in  the  development  of  a  h\iman 


tooth.  For  convenience  ui  expression 
and  terms,  the  description  refers  to  the 
development  of  a  lower  tooth.  The 
upper  teeth  ai'e  of  course  developed  in  a 
manner  exactly  similar. 

1.  The  first  distinct  evidence  of  the 
development  of  the  teeth  is  to  be  found 
in  a  thickening  of  the  mouth  epithelium, 
at  the  site  of  the  future  gum,  and  a  re- 
sulting downgrowth  of  its  deeper  portion 
into  the  substance  of  the  primitive  jaw 
(Fig.  728,  L).  This  epithelial  down- 
growth  is  continued  along  the  whole 
length  of  the  gum,  and  is  known  as  the 
dental  lamina  or  tootli-band  (Zahnleiste). 
On  the  under  surface  of  the  dental  lamina 
there  soon  appears  a  series  of  knob-like 
projections — one  for  each  of  the  milk 
teeth  (Fig.  728,  II.) — which  are  known 
as  enamel  germs  or  enamel  organs. 
These  enamel  organs  are  connected  with 
the  epithelium  of  the  dental  lamina  by  a 
constricted  part,  and  although  at  first 
knob-like,  they  soon  become  bell-shaped 
owing  to  the  invagination  of  the  lower 
surface  of  the  knobs,  so  that  each  may 
now  be  compared  to  an  inverted  egg-cup. 

2.  As  soon  as  the  enamel  organs 
begin  to  assume  a  cup-like  shape,  the 
cellular  connective  tissue  of  the  jaw 
beneath  grows  up  and  projects  into  the 
cavity  of  the  cup  (Fig.  728,  III.)  in  the 
form  of  a  papilla — the  dentine  papilla 
(papilla  dentis).  The  arrangement, 
pursuing  our  simile,  may  now  be  com- 
pared to  an  egg  fitting  into  its  cup — the 
dentine  papilla  representing  the  egg,  and 
the  enamel  organ  the  cup  (Fig.  728,  III.). 

3.  The  two  layers  of  cells  which  are 
thus  bi'ought  in  contact,  namely,  the 
epithelial  cells  lining  the  conca\'ity  of 
the  enamel  organ,  and  the  superficial 
cells  of  the  dentine  papilla,  become 
elongated    or    columnar,    and    undergo 


I.  Shows  tlie  downgrowth  of 
the  dental  lamina  D.L  from 
the  surface  epithelium  E 
and  the  beginning  of  the 
enamel  germ  E.G. 


II.  Shows  the  further  growth 
of  the  enamel  germ  and  its 
invagination. 


III.  The  enamel  germ  is  more 
invaginated,  and  its  inner 
layer  of  cells  becomes 
columnar.  A,  the  dental 
lamina,  grows  thinner,  but 
near  its  posterior  or  lingual 
edge  there  is  an  enlarge- 
ment R.Ci  which  is  the  re- 
serve germ  for  a  permanent 
tooth.  The  superficial  cells 
of  the  dentine  papilla  P  are 
becoming  colunjnar. 


IV.  The  inner  columnar  cells 
of  the  enamel  germ  (called 
enamel  cells)  A  have  formed 
a  cap  of  enamel  En,  inside 
which  the  superficial  cells 
of  the  papilla,  the  odonto- 
blasts O,  have  formed  a 
layer  of  dentine  D. 


V.  Shows  a  more  advanced 
stage  still.  The  deposit  of 
dentine  is  extending  down- 
wards, and  enclosing  the 
papilla  to  form  the  future 
pulp,  in  which  a  vessel  V 
is  seen. 


Fui.  728. 


-DiAGKAM    TO 
OF    A 


ILM'STKATE    De VKI.OPM  ENT 

Tooth. 


A,  Inner  layer  of  enamel  germ  ;  B,  Outer  layer :  C,  Remains  of    Other   changes,    preliminary    tO   the    pro- 


inte.rmediate  cells;  I),  Dentine;  D.L,  Dental  lamina;  E, 
Epithelium  ;  E.G,  Enamel  germ  ;  E.v,  Enamel  ;  F,  Dental 
furrow;  L.D,  Labio-dental  furrow;  M,  Connective  tissue 
cells;  O,  Odontoblasts;  P,  Dentine  papilla;  R.G,  Reserve 
germ  ;  V,  Blood-vessel. 


d action  of  the  enamel  by  the  former- 
which  are  now  called  enamel  cells  or 
ameloblasts — and  the  dentine  by  the 
latter,  which  are  known  as  odontoblasts. 

4.  The  odontoblasts,  that  is  the  layer  of  columnar-shaped  connective  tissue  cells 
lying  on  the  surface  of  the  dentine  papilla,  begin  to  form  at  their  outer  ends  a  la3'er  of 
dentine  (Fig.  728,  IV.).  Similarly,  the  enamel  cells  lining  the  cup  begin  to  form  at  their 
inner  surface  a  layer  of  enamel  on  the  top  of  the  layer  of  dentine  (Fig.  728,  IV.),  to  which 
it  adheres :  in  each  case  the  deposit  taking  place  first  at  the  summit  of  the  tooth. 

5.  The  formation  of  dentine  and  enamel  proceeds  apace,  the  dentine  increasing  at  the 
expense  of  the  papilla,  the  enamel  similarly  encroaching  on  the  cup  or  enamel  organ  ; 


DEVELOPMENT  OF  THE  TEETH.  1027 

and  in  each  case  the  two  layers  of  cells — odontoblasts  and  enamel  cells — which  produced 
the  deposits,  retiring  gradually  fi'om  one  another,  as  the  space  between  them  becomes 
occupied  by  the  newly-formed  dentine  and  enamel  respectively  (Fig.  728,  V.). 

The  I'emains  of  the  dentine  papilla  persist  as  the  pulp  of  the  tooth,  which  is  covered 
even  in  the  adult  by  the  odontoblasts,  and  occupies  the  pulp  cavity,  i.e.  the  central  part 
of  the  tooth  to  which  the  dentine  formation  has  not  extended. 

6.  Turning  now  to  the  jaw  itself :  The  connective  tissue  of  the  gum  surrounding  the 
tooth  germ  (as  the  developing  tooth  with  its  enamel  organ  and  dentine  papilla  are  called) 
early  becomes  condensed  and  vascular  (Fig.  728,  V.),  and  later  on  forms  a  membranous 
bag — the  tooth-sac  or  follicle — which  completely  shuts  off  the  developing  tooth  from  the 
surrounding  structures.  On  the  floor  of  this  sac  the  tooth  germ  sits,  the  base  of  its 
dentine  papilla  being  continuous  with  the  tissue  of  the  floor  of  the  sac,  and  the  young 
tooth  being  enclosed  by  the  sac,  as  a  kernel  is  enclosed  by  its  shell. 

7.  Reverting  to  the  tooth  :  When  the  crown  is  completed  the  deposit  of  dentine,  but 
not  of  enamel,  is  continued  downwards  to  form  the  root.  This  latter  is  composed  chiefly 
of  dentine  continuous  above  with  that  of  the  crown,  and  like  it  formed  by  the  odontoblasts 
of  the  dentine  papilla.  As  the  dentine  is  deposited,  and  the  root  is  being  built  up,  the 
connective  tissue  of  the  tooth-sac  comes  to  surround  the  root  more  closely,  and  deposits 
on  its  surface,  after  the  manner  of  a  periosteum,  a  layer  of  bone,  the  cementum  or  crusta 
petrosa.  The  cementum  having  been  formed,  the  connective  tissue  of  the  sac  then  per- 
sists as  the  alveolar  periosteum.  The  development  of  the  root  takes  place  very  slowly, 
and  its  lower  end  is  not  completed  as  a  rule  for  some  time  after  the  eruption  of  the  tooth 
has  taken  place. 

8.  During  the  development  of  the  teeth  the  ossification  of  the  jaw  has  been  going  on, 
and  as  it  grows  up  on  each  side,  the  young  teeth,  enclosed  in  their  tooth-sacs,  come  to  lie 
in  an  open  bony  groove,  which  is  subsequently  divided  by  septa  into  compartments — the 
alveoli — for  the  individual  tooth-sacs.  The  bone  continuing  to  grow  after  birth,  these 
compartments  become  more  perfect,  but  are  never  entirely  closed  in  over  the  crowns  of 
the  teeth.  During  the  eruption  of  the  teeth  the  upper  and  anterior  part  of  these  bony 
cells  is  absorbed  ;  subsequently,  however,  it  is  reformed  around  each  tooth  when  it  has 
taken  its  final  position. 

9.  Eruption. — Long  before  the  root  is  completed,  the  crown,  by  some  force  which  is 
not  properly  understood,  but  which  does  not  seem  to  depend  on  additions  to  the  root,  is 
pushed  through  the  top  of  the  tooth  sac,  and — the  upper  and  anterior  wall  of  the  roomy 
alveolus  having  been  absorbed  at  the  same  time — onwards  through  the  gum  until  the 
mouth  is  reached.  Later  on,  when  the  tooth  has  assumed  its  final  position,  the  alveolus, 
as  already  stated,  is  re-formed,  and  closely  embraces  the  completed  root. 

10.  After  the  enamel  organs  of  the  milk  teeth  have  been  formed  on  the  inferior  aspect 
of  the  dental  lamina,  as  described  above,  the  neck  of  epithelium  by  which  the  lamina  is 
still  connected  with  the  surface  becomes  broken  up  into  a  cribriform  sheet.  Its  free 
posterior  border,  on  the  other  hand,  continues  to  grow  backwards  in  the  tissue  of  the 
gum  towards  the  cavity  of  the  mouth  (Fig.  728,  III.  and  IV.),  and  at  a  later  date  there 
appear  on  its  under  surface,  near  the  free  edge,  and  behind  the  several  developing  milk 
teeth,  the  enamel  organs — or  so-called  "reserve  germs  " — for  the  corresponding  permanent 
teeth,  which  are  developed  from  these  in  exactly  the  same  manner  as  the  milk  teeth 
described  above. 

In  connexion  with  the  development  of  the  permanent  molars,  which  have  no  corre- 
sponding teeth  in  the  milk  set,  there  takes  place  a  prolongation  backwards  of  the  posterior 
extremity  of  the  dental  lamina  into  the  tissue  of  the  jaw,  behind  the  last  milk  molar.  On 
the  inferior  aspect  of  this  prolongation,  which  has  no  direct  connexion  with  the  surface 
epithelium,  enamel  organs  are  formed  for  the  permanent  molars,  and  their  further 
development  goes  on  in  the  manner  described  for  the  other  teeth. 

The  dates  at  which  some  of  the  chief  events  in  the  development  of  the  teeth  occur 
may  be  briefly  given  : — The  thickening  of  the  epithelium,  the  first  sign  of  the  future 
teeth,  begins  about  the  sixth  week  of  foetal  life,  and  the  dental  lamina  is  completed  by 
the  end  of  the  seventh  week. 

The  dentine  papilke  for  the  eight  front  teeth  appear  and  become  surrounded  by  their 
enamel  organs  about  the  tenth  week,  and  the  papilla  for  the  first  permanent  molar  about 
the  seventeenth  week. 

The  first  traces  of  calcification,  and  the  formation  of  the  tooth-sacs,  take  place  about 
the  fifth  month  of  foetal  life. 

Eruption  of  Deciduous  Teeth. — The  period  at  which  the  eruption  of  the  milk  teeth 
takes  place  is  extremely  variable,  and  no  two  observers  seem  to  agree  upon  the  question. 
69  a 


1028  THE  DIGESTIVE  SYSTEM. 

The  following,  according  to  Tomes,  may  be  taken  as  representing  the  average.  The 
lower  central  incisors  appear  first,  usually  between  the  sixth  and  ninth  months ;  then 
follows  a  rest  of  a  few  months.  Next  come  the  four  upper  incisors,  followed  by  a  rest  of 
a  few  months.  Then  the  lower  lateral  incisors  and  the  four  first  molars  erupt,  succeeded 
by  a  rest  of  a  few  months.  Next  appear  the  canines,  and  finally  the  four  second  molars, 
which  are  all  cut  by  the  end  of  the  second  year. 

The  following  statement  is  simple,  and  perhaps  is  sufficient  for  all  ordinary  purposes. 
The  temporary  teeth  usually  appear  in  the  following  order : — Central  incisors,  lateral 
incisors,  first  molars,  canines  and  second  molars ;  the  eruption  commences  between  the 
sixth  and  the  ninth  month,  and  is  usually  completed  by  the  twenty-fourth — the  lower 
teeth,  as  a  rule,  preceding  the  upper. 

Formation  of  Enamel  and  Dentine. — Different  opinions  are  held  as  to  the  method  in  which 
thf  enamel  is  produced  by  the  enamel  cells.  One  view  maintains  that  it  is  secreted  and  shed 
ont  liy  the  enamel  cells  (Kcilliker).  According  to  the  other  view,  part  of  the  substance  of  the 
cells  is  actually'  converted  or  transformed  into  enamel  (Tomes).  In  connexion  with  this  latter 
view,  which  seems  to  receive  more  support  at  jjresent,  Tomes  has  discovered  that  there  j)rojects 
from  the  base  of  each  enamel  cell,  towards  or  into  the  most  recently  formed  enamel,  a  fibrillar 
process,  which  has  received  the  name  of  Tomes'  process,  and  he  holds  that  the  enamel  is  formed 
hj  calcification  taking  place  in  or  around  the  process. 

Similarly,  two  views  are  held  as  to  the  production  of  dentine  by  the  odontoblasts ;  one,  that 
the  odontoblasts  secrete  the  matrix  of  the  dentine,  and  the  other,  that  their  substance  is  actually 
conA'erted  into  the  matrix.  The  odontoblasts,  when  active,  are  Isranched  columnar-shaped  cells, 
and  from  their  outer  ends  one  or  more  processes  extend  towards  and  into  the  dentine  ;  between 
these  processes  a  matrix  appears — i^roduced  probably  by  the  odontoblasts — and  soon  this  matrix 
becomes  calcified.  In  this  way  the  dentine  is  formed,  and  the  process  is  repeated  until  its  full 
thickness  is  attained.  The  branches  of  the  odontoblasts,  encased  in  dentine,  just  mentioned,  are 
the  Tomes'  fibrils  already  described  ;  the  canals  in  which  they  lie  are  the  dentinal  tubes  ;  and  the 
fibrils  themseh'es  are  concerned  in  the  j^roduction  of  the  sheaths  of  Neumann  which  line  the  tubes. 

The  tooth-sacs,  when  fully  developed,  are  large  and  distinct  fibrous  bags  which  lie 
in  the  alveoli  of  the  maxilla  and  mandible,  and  are  continuous  above  with  the  tissue  of 
the  gum.  On  the  lingual  side  of  the  sacs  of  the  milk  teeth  are  found  the  germs  of  the 
permanent  teeth,  surrounded  by  their  own  sacs.  These  latter  are  at  first  very  small,  and 
are  partly  embedded  in  the  posterior  wall  of  the  temporary  tooth-sacs,  but  subsequently 
they  come  to  lie  in  distinct  but  incomplete  bony  cavities  of  their  own.  The  bone  sur- 
rounding the  tooth-sacs,  tempoi'ary  and  permanent,  is  always  wanting  over  the  summit  of 
the  sac,  and  the  band  of  connective  tissue  by  which  the  sac  is  connected  with  the  over- 
lying gum  tissue,  through  the  deficiency,  is  known  as  the  gubernaculum  dentis. 

These  points  are  easily  demonstrated  on  the  lower  jaw  of  a  child  at  birth,  particularly 
when  the  tissues  have  been  allowed  to  soften  a  little.  If,  in  such  a  specimen,  the  gum 
and  periosteum  be  reflected  upwards  from  the  outer  and  inner  surfaces  of  the  mandible, 
and  freed  as  far  as  the  upper  border  of  the  jaw,  the  gum,  with  the  tooth-sacs  depending 
from  it  like  small  bags,  can  be  pulled  aw^ay  out  of  the  bony  groove  of  the  jaw ;  and  if  the 
operation  has  been  successfully  performed,  the  tooth-sacs  of  the  three  front  permanent 
teeth  may  be  seen,  varying  in  size  from  a  small  pin's-head  to  a  hemp-seed,  hanging  down 
behind  the  upper  part  of  the  corresponding  temporary  sacs.  As  already  explained, 
the  tooth-sacs  are  produced  simply  by  a  condensation  of  the  connective  tissue  around 
the  developing  tooth,  the  condensation  going  on  to  the  formation  of  a  distinct  mem- 
branous bag. 

Formation  of  Alveoli  and  Eruption. — At  first  the  developing  teeth  lie  in  an  open 
bony  groove  or  channel  between  the  outer  and  inner  plates  of  the  young  jaw.  This 
groove  is  subsequently  divided  up  into  separate  compartments  for  the  sacs  of  each  of  the 
temporary  teeth.  As  development  proceeds  these  compartments  or  alveoli  surround  the 
sacs  more  completely,  but  never  actually  close  over  the  summit.  When  the  eruption  of 
the  temporary  teeth  is  about  to  take  place,  the  anterior  wall  and  I'oof  of  the  alveolus  are 
absorbed  ;  the  tooth  yjasses  through  the  sac  and  appears  above  the  gum,  and  then  the 
alveolus,  which  up  to  this  was  much  too  large  to  give  actual  support,  is  re-formed  more 
closely  around  the  tooth.  Meanwhile  the  root,  which  was  only  partly  formed  at  the  time 
of  the  eruption,  continues  to  be  added  to,  possibly  for  a  few  years  moi-e,  and,  as  it  grows, 
the  alveolus  is  completed  around  it.  When  the  permanent  tooth,  or  as  much  of  it  as 
is  then  formed,  is  about  to  be  erupted,  it  makes  its  way  from  its  own  bony  cell  through 
the  posterior  wall  of  the  alveolus  of  its  temporary  predecessor ;  the  root  of  the  temporary 
tooth  undergoes  absorption  at  the  same  time,  but  quite  independently  of  pressure  from 
the  permanent  tooth.  The  alveolus,  now  occupied  by  both  teeth,  is  again  much  enlarged 
by  absorption,  particularly  in  front ;  what  remains  of  the  temporary  tooth  is  shed ;  the 


THE  PHARYNX.  1029 

permanent  tooth  passes  onwards  through  the  enlarged  alveolus,  and,  making  its  way  to 
the  surface,  appears  above  the  gum.  After  some  time,  when  the  tooth  has  taken  its  final 
position,  the  alveolus  is  again  re-formed,  first  around  its  neck,  and  later  on,  as  the  root  is 
built  up,  around  it  also,  and  thus  the  tooth  is  permanently  fixed. 

What  the  force  is  which  causes  the  eruption,  is  a  question  that  has  not  been  answered 
satisfactorily.  That  the  growth  of  the  root  pushes  up  the  crown  was  formerly  the 
favourite  explanation.  For  several  reasons,  unnecessary  to  detail,  this  view  is  now  dis- 
carded, and  a  theory  which  attributes  the  impelling  force  to  the  blood  pressure  is  looked 
upon  with  more  favour,  although  even  this  is  not  altogether  satisfactory.  (See  Tomes' 
Dental  Anatomy,  5th  Edition,  page  211.) 

MOKPHOLOGY   OF   THE    TeETH. 

In  most  vertebrates  below  mammals  all  the  teeth  are  alike  in  form  ;  such  a  dentition  is  said 
to  be  homodont.  In  the  majority  of  mammals,  on  the  other  hand,  the  teeth  are  arranged  in 
groups  of  different  size  and  form  ;  such  a  dentition  is  heterodont. 

Again,  mammals  have,  neglecting  exceptional  cases,  but  two  functional  sets  of  teeth  ;  they  are 
consequently  said  to  be  diphyodont.  Most  vertebrates  below  mammals,  on  the  other  hand,  "have 
a  continuous  succession  of  teeth  throughout  life,  and  hence  are  said  to  be  polyphyodont. 

Seeing  that  practically  all  lower  vertebrates  are  provided  with  simple  conical  teeth,  the  evolu- 
tion of  the  many-cusped  mammalian  molar  has  given  rise  to  much  speculation.  The  jaws  of  the 
earliest  fossil  mammals  found  are  furnished  with  tri-tubercular  teeth,  the  three  tubercles  being 
placed  in  an  antero-posterior  line  ;  by  a  rotation  of  two  of  the  cusps  out  or  in,  as  the  case  may 
be  (a  condition  found  in  certain  other  fossil  skulls),  we  arrive  at  a  tri-tubercular  form,  from  which 
the  transition  to  an  ordinary  mammalian  molar  is  not  dilficult.  As  to  how  the  tri-tubercular 
tooth  arose  from  the  sim^jle  cone,  two  different  views  are  advanced  :  one,  that  it  was  formed  by  the 
imion  of  several  conical  teeth  as  a  residt  of  the  shortening  of  the  jaw  and  the  crowding  of  the 
teeth  together ;  the  other,  that  the  single  conical  tooth  developed  on  its  crown  two  subsidiary 
cusjjs,  one  in  front  and  the  other  behind,  and  that  these  cusps  growing  larger,  the  tooth  assumed 
the  tri-tubercular  form. 

The  complete  or  typical  mammalian  dentition,  in  its  highest  development,  as  in  the  horse,  is 
represented  by  the  following  formula  :  i,  f,  c.  \,  pm.  f,  m.  f  =  44.  In  the  dentition  of  man,  there- 
fore, one  incisor  and  two  premolars  are  wanting.  Different  views  are  held  as  to  which  teeth 
have  been  suppressed — most  probably  they  are  the  second  incisors,  and  the  first  and  second  or  first 
and  last  premolars. 

In  general  it  may  be  said  that  the  dentition  of  the  lower  races  differs  from  that  of  the 
higher,  in  that  the  dental  arches  are  scpiarer  in  front,  the  teeth  larger  and  more  regular,  the 
canines  stronger,  the  wisdom  teeth  better  developed,  and  the  cusps  on  the  molars  more  perfect,  in 
the  lower  than  in  the  more  civilised  races.  It  may  be  mentioned,  however,  that  the  teeth  of  a 
savage  man,  if  seen  in  the  mouth  of  a  Euroi)ean,  would  be  looked  upon  as  an  "exceedingly 
perfectly-formed  set  of  teeth  "  (Tomes). 

To  express  the  j^roportionate  size  of  the  crowms  of  the  premolars  and  molars  to  that  of  the 
skull  in  diffei'ent  races.  Flower  compared  the  distance  from  the  front  of  the  first  premolar  to  the 
back  of  the  last  molar,  in  situ,  with  the  distance  from  the  front  of  the  foramen  magnum  to  the 
naso-frontal  suture  (basi-nasal  length),  in  the  form  of  a  "  dental  index  " — 

„,  Length  of  teeth  \  100     .^         ,  .    , 

i  bus  :       T^    ^ rn n —  =  Dental  index, 

Easi -nasal  length 

and  by  this  means  he  has  divided  the  various  races  into  microdont  (index  42  to  43,  Europeans, 
Egyptians,  etc.),  mesodont  (index  43  to  44,  Chinese,  American  Indians,  Negroes,  etc.),  and  macro- 
dont  (index  44  and  upwards,  Australians,  Melanesians,  etc.). 

THE  PHARYNX. 

The  pharynx  is  the  expanded,  upper  portion  of  the  digestive  tube  which  lies 
behind,  and  communicates  with,  the  mouth,  the  larynx,  and  the  nasal  cavities 
(Fig.  729).  It  serves  for  the  passage  of  both  air  and  food,  conveying  the  former  to 
the  larynx  and  the  latter  to  the  oesophagus. 

It  extends  from  the  base  of  the  skull  above  to  the  level  of  the  sixth  cervical 
vertebra  below  (Fig.  730),  where,  opposite  the  lower  border  of  the  cricoid  cartilage, 
it  passes  into  the  oesophagus;  its  total  length  varies  from  5  to  5i  inches  (12-5 
to  14-0  cm.). 

When  in  its  natural  state  within  the  body,  the  pharynx  is  expanded  laterally 
and  compressed  in  the  opposite  direction,  so  that  its  anterior  and  posterior  walls 
approach  one  another,  and  its  sides  are  reduced  to  little  more  than  mere  borders. 
Although  its  cavity  is  much  reduced  by  this  approximation  of  the  anterior  and 
posterior  walls,  there  is  always  left,  above  the  orifice  of  the  larynx,  a  sufficient 
69  6 


1030 


THE  DIGESTIVE  SYSTEM. 


Internal  carotid  artery 
Foramen  lacerum  medium 
Cartilage  of  Eustachian  tube 
Cavity  of  Eustachian  tube 

Levator  palati 

Inferior  turbinated  bone 
Lateral  recess  of  pharynx 

I>evator  cushion 


space  for  the  entrance  of  air  to  the  lungs.  Below  the  laryngeal  orifice,  on  the 
other  hand,  the  anterior  and  posterior  walls  are  in  contact,  and  the  cavity,  except 
during  the  passage  of  food,  is  reduced  to  a  transverse  slit  (Fig.  730). 

As  usually  seen  in  tlie  dissecting-room,  when  distended  for  dissection,  tlie  pharynx  is  of  an 
elongated  oval  form,  tapering  rapidly  below.  This  form,  however,  is  due  entirely  to  the  arti- 
ficial conditions  under  which  it  is  placed. 

Taken  as  a  whole,  the  pharynx  is  a  tube,  the  anterior  wall  of  which  is  wanting. 

The  place  of  this 
wall  is  occupied 
by  the  nasal,  oral, 
and  laryngeal 
cavities,  as  well 
as  by  the  base  of 
the  tongue  ;  and 
to  the  lateral 
boundaries  of  all 
these  parts  the 
sides  of  the  tube 

Superior  constrictor  muscle     are    COnnCCtcd. 

In  this  way  it 
comes  to  be  at- 
tached from 
above  downwards 
to  the  following 
more  or  less  fixed 
points :— (1)  The 
Eustachian  tube 
and  internal 
pterygoid  plate ; 
(2)  the  pterygo- 
maxillary  liga- 
ment, the  pos- 
terior end  of  the 
mylohyoid  ridge 
on  the  inner  as- 
pect of  the  lower 
jaw,  and  the 
mucous  mem- 
brane of  the 
mouth  ;  (3)  the 
baseof  the  tongue 
and  the  hyoid 
bone ;  and  (4) 
the  thyroid  and 
cricoid  cartilages 
of  the  larynx. 
Above,it  is  firmly 
fixed  by  its  apo- 
neurosis to  the 
periosteum  of  the 
basi-occipitaland 

Tlie  specimen  from  which  the  drawing  wa.s  made  was  obtained  from  a  formalin-hardened  -i-,gH.Qii  g      DOrtion 
body,  by  removing  the  posterior  wall  of  the  pharynx  while  leaving  the  anterior  ■'^f.    , ,         ,  •'^  i 

wall  undisturbed.  The  following  points  should  be  noted  :  the  greatest  width  of  01  the  temporal 
the  pharynx,  above,  at  the  lateral  recesses  ;  the  posterior  nares,  w-ith  the  inferior  boneS  j  and  in 
turbinated  bones  seen  through  theni  ;  the  levator  cushion;  and  the  pharyngeal  orjrJ-jfiQTi  the 
portion  of  the  tongue,  ,  „  ,, 

raphe  ot  the  con- 
strictors is  attached  to  the  pharyngeal  tubercle  of  the  occipital  bone.  Below  it 
becomes  continuous  with  the  resophagus.  Behind  and  at  the  sides,  the  pharynx 
is  connected  merely  by  loose  areolar  tissue  to  the  surrounding  parts. 


Glands  in  soft  palate 
Uvula 

Palatopharyngeus 
Circumvallate  papillte 
Sulcus  terminalis 

Glossopharyngeal  nerve 
Foramen  csecum 
Lymphoid  follicle 

Middle  constrictor  muscle 
Epiglottis 

Pharyngo-epiglottic  fold 

Lingual  artery 
Hyoglossus  muscle 
Hyoid  bone 
Superior  laryngeal  artery 

Internal  laryngeal  nerve 
Aryteno-epiglottic  fold 
Sinus  pyriformis 
Sujierior  aperture  of  larynx 
Inferior  constrictor  muscle 
Top  of  cricoid  cartilage 


Fk). 


J29. — Thk  Anteuioh  Wall  ok  the  Pharynx  with  its  Orifices,  seen 

FROM    BEHIND. 


THE  PHAEYNX. 


1031 


Tlie  pharynx  presents  the  following  relations: — In  front,  as  already  described, 
are  the  nasal  cavities,  the  mouth,  base  of  tongue,  and  larynx,  all  of  which  are  seen 
on  its  anterior  wall  (Fig.  729).  Behind,  it  is  separated  by  loose  areolar  tissue  (known 
as  the  retro-pharyngeal  space)  from  the  prevertebral  fascia  and  muscles,  which  inter- 
vene between  it  and  the  six  upper  cervical  vertebrae.  At  the  sides  are  placed  the 
carotid  sheaths  with  their  contents,  whilst  the  styloid  process  with  its  muscles, 
and  the  glosso-pharyngeal  nerve,  running  downwards  and  forwards,  form  lateral 


Middle  turbinated  bone 
Middle  meatus  of  nose 


Inferior  meatus 
of  nosi' 


Superior  meatus  of  nose 


Splienoidal  sinus 

Inferior  turbinated  bone 


Posterior  edge  of  nasal  septum 
Orifice  of  Eustachian 
tube 


liarvngea 


Genio-'lobsu 


Part  of  the 
pharyngeal  tonsil 

Lateral  recess  of 
pharynx 

Levator  cushion 

Salpingo- 
pharyngeal fold 

Glands  in  soft 
lalatc 
Anterior 
palatine  arch 
Supra  tonsillar 
fossa 

Plica  triangularis 

Tonsil 

Posterior  ijalatine 
arch 

Epiglottis 

Aryteno- 
epiglottic  fold 


Cricoid  cartilage 


Geniohyoid 
Lymphoid  follicle 

Hyoid  boue 


Fig.  730. — Sagittal  Section  through  Mouth,  Tongue,   Larynx,  Pharynx,  and  Nasal  Cavity. 

The  section  is  slightly  oljlique,  and  the  posterior  edge  of  the  nasal  septum  has  been  preserved.  The 
specimen  is  viewed  slightly  from  below,  hence  in  part  the  low  position  of  the  inferior  turbinated 
bone. 

relations  in  its  upper  part.  Above,  the  pharynx  is  united  to  the  basi-occipital  and 
the  petrous  portion  of  the  temporal  bones,  as  already  described  ;  and  below,  it  joins 
tlie  oesophagus. 

The  cavity  of  the  pharynx  is  widest  above  in  the  naso-pharynx,  immediately 
behind  the  Eustachian  tubes  (Fig.  729),  where  it  extends  out  on  each  side,  over 
the  upper  border  of  the  superior  constrictor,  in  the  form  of  a  pouch — the  lateral 
recess.  Its  width  is  also  considerable  opposite  the  upper  part  of  the  thyroid  carti- 
lage, but  it  rapidly  diminishes  below  the  laryngeal  orifice,  and  is  narrowest  at  its 
termination  in  the  oesophagus. 

The  cavity  is  interrupted  above  by  the  soft  palate,  a  movable  muscular  sheet 


1032 


THE  DIGESTIVE  SYSTEM. 


which  is  attached  in  frout  to  the  hard  palate,  and  laterally  to  the  side  walls  of  the 
pharynx.  This  sheet,  sloping  obliquely  backwards  and  downwards,  cuts  into  the 
cavity  of  the  pharynx  (Fig.  730),  and,  falling  short  of  the  posterior  wall,  incom- 
pletely divides  it  into  two,  namely,  an  upper  part  or  naso-pharynx  (pars  nasalis),  and  a 
lower  part  or  pharynx  proper,  which  is  further  subdivided — perhaps  unnecessarily — 
into  the  oral  pharynx  (pars  oralis)  lying  behind  the  mouth  and  tongue,  and  the 
laryngeal  pharynx  (pars  laryngea)  behind  the  larynx. 

The   aperture   left   behind    the    soft    palate   and   the   posterior  wall   of  the 
pharynx,  through  which  the  naso-pharynx  communicates  with  the  lower  divisions 


Posterior  end  of 

middle  turbinated 

bone 


Pharyngeal  tonsil 


Antrum  of  Higlimore  — 

Posterior  end  of 
inferior  turbinated  - 
bone 


Uvula 


Orbit 


Posterior  edge  of 
nasal  septum 

Eustachian  cushion 


Orifice  of  Eustachian 
tube 


Anterior  palatine 
arch 


Tonsil 
Buccinator  (cut) 


Posterior  palatine 
arch 

Pharyngeal  isthmus 


Tongue 


Fig.  731. — The  Naso-pharynx  from  the  Front. 

A  coronal  section  was  made  through  the  upper  part  of  the  head;  this  passed  immediately  in  front  of 
the  posterior  edge  of  the  nasal  septum,  and  extended  into  the  month  Ijelow.  Through  the  posterior 
nares  tlie  naso-pliarynx  is  seen.  The  prominence  of  the  posterior  margin  of  the  Eustachian  orifice, 
and  the  lymphoid  nodules  constituting  the  pharyngeal  tonsil,  should  be  noted.  The  palatine  arches, 
the  tonsils,  and  an  unusually  wide  pharyngeal  isthmus,  are  also  seen. 

of  the  cavity,  may  conveniently  be  called  the  pharyngeal  isthmus  (isthmus 
pharyngo-nasalis). 

The  pharynx  presents  seven  openings  through  which  it  communicates  with 
neighbouring  cavities  (Fig.  729).  These  are  the  two  posterior  nares  (choanse) 
on  the  anterior  wall,  and  the  two  Eustachian  tubes  on  the  sides,  of  the  naso- 
pharynx ;  the  isthmus  of  the  fauces  leading  into  the  mouth  from  the  oral  pharynx ; 
the  orifice  of  the  larynx  on  the  anterior  wall  of  the  laryngeal  portion  of  the 
cavity ;  and  finally,  the  opening  of  the  oesophagus  at  its  lower  end. 

Naso-pharynx  (Figs.  730  and  731).— Although  described  asa  part  of  the  pharynx, 
this  portion  of  the  cavity  should  be  regarded  as  an  annex  to  the  respiratory  portion 
of  the  nasal  cavities  rather  than  as  a  subdivision  of  the  pharynx  proper,  for,  both 


THE  PHAKYNX.  1033 

anatomically  and  functionally,  it  is  all  but  completely  marked  oft"  from  the 
digestive  tube.  It  differs  from  the  rest  of  the  pharynx  in  that  its  cavity  remains, 
under  all  conditions,  a  distinct  open  chamber  incapable  of  obliteration,  owing  to 
the  fact  that  all  its  walls,  with  the  single  exception  of  the  floor,  are  practically 
immovable. 

The  chamber  of  the  naso-pharynx  is  irregular  in  shape,  and  is  enclosed  by  six 
walls — namely,  anterior,  posterior,  two  lateral,  and  a  floor — together  with  a  roof  or 
vault  formed  above  by  the  approximation  of  the  anterior  and  posterior  walls. 

The  anterior  loall,  which  slopes  upwards  and  backwards,  is  entirely  occupied  by 
the  two  posterior  nares,  with  the  nasal  septum  between  them  (Fig.  729). 

The  posterior  wall  is  inclined  upwards  and  forwards,  and  forms  the  vault  of  the 
pharynx  (fornix  pharyngis)  above  by  meeting  the  anterior  wall  at  a  rounded  angle. 
On  the  upper  part  of  the  posterior  wall,  at  and  above  the  level  of  the  Eustachian 
orifices,  there  is  seen,  particularly  in  early  life,  a  considerable  accumulation  of 
lymphoid  tissue,  associated  with  a  thickened  and  folded  condition  of  the  mucous 
membrane  in  the  child.  This  is  the  pharyngeal  tonsil  (tonsilla  pharyngea,  Figs. 
730  and  731).  In  old  age  it  becomes  very  indistinct,  or  completely  disappears ; 
whilst  in  the  child  it  is  often  increased  in  size,  and  occasionally,  when  greatly 
hypertrophied,  blocks  up  the  naso-pharynx  almost  completely. 

In  connexion  with  the  lower  part  of  tlie  pharyngeal  tonsil,  there  is  found,  constantly 
in  the  child  and  occasionally  in  the  adult,  a  small  median  recess  which  runs  upwards  and 
backwards  in  the  wall  of  the  pharynx  for  some  distance,  and  is  known  as  the  bursa 
pharyngea  (Fig.  730). 

Three  leading  views  are  held  as  to  the  nature  of  the  bursa  pharyngea,  namely — 
1.  That  it  is  the  remains  of  Rathke's  pouch,  from  which  the  antei'ior  lobe  of  the  pituitary 
body  is  formed.  2.  That  it  is  a  crypt  connected  with  the  formation  of  the  pharyngeal 
tonsil.  3.  That  it  is  an  independent  outgrowth  of  the  mucous  membrane.  The  last  view 
is  perhaps  most  generally  accepted. 

The  floor  of  the  naso-pharynx  is  formed  by  the  upper  surface  of  the  soft  palate 
(Fig.  730),  which  in  its  anterior  part  is  a  direct  continuation  backwards  of  the  floor 
of  the  nasal  cavity,  whilst  posteriorly  it  slopes  strongly  downwards  and  backwards. 
Between  the  floor  and  the  posterior  wall  is  left  the  aperture  referred  to  above  as 
the  pharyngeal  isthmus,  through  which  the  naso-pharynx  communicates  with  the 
rest  of  the  pharyngeal  cavity.  By  the  action  of  the  palatal  muscles  the  floor  can 
be  raised  or  depressed,  and  these  changes  of  position  are  accompanied  by  corresponding 
alterations  in  the  size  and  shape  of  the  cavity. 

Each  lateral  loall  of  the  naso-pharynx  (Fig.  730)  is  occupied  in  the  greater  part 
of  its  extent  by  the  opening  of  the  Eustachian  tube,  behind  which  is  seen  a 
vertical  slit-like  depression  leading  into  a  recess,  the  lateral  recess  of  the  pharynx, 
or  fossa  of  Rosenmuller. 

The  pharyngeal  orifice  of  the  Eustachian  tube  (ostium  pharyngeum)  is  a  considerable 
opening,  usually  of  a  somewhat  triangular  form,  with  a  characteristic  infundibular 
or  funnel-like  appearance  (Fig.  730).  It  is  bounded  above  and  behind  by  a 
prominent  rounded  ridge,  the  Eustachian  cushion  (torus  tuberius).  This  ridge 
is  due  to  the  projection  of  the  cartilage,  which  surrounds  the  Eustachian 
passage  above  and  behind,  but  is  absent  below  and  in  front.  The  prominence 
of  the  posterior,  as  contrasted  with  the  anterior  margin  of  the  orifice,  and  the 
direction  of  the  tube  itself,  which  runs  strongly  forwards  as  well  as  inwards 
(traced  from  the  tympanum),  greatly  facilitate  the  introduction  of  a  Eustachian 
catheter. 

The  exact  position  of  the  orifice  is  of  importance  in  connexion  with  this  latter 
operation.  It  is  situated  on  the  side-wall  of  the  naso-pharynx,  a  short  distance 
(about  IT  to  i-  inch)  behind  the  posterior  end  of  the  inferior  turbinated  bone,  and 
immediately  above  the  level  of  the  hard  palate  (Figs.  730  and  731). 

A  slight  ridge  of  the  mucous  membrane  descends  from  the  lower  end  of  the  Eustachian 
cushion  on  the  side-wall  of  the  pharynx,  and  gradually  becomes  lost.  This  is  known  as 
the  salpingo-pharyngeal  fold  (plica  salpingo-pharyngea).  Another  less  developed  ridge, 
the  salpingo-palatine  fold  (plica  salpingo-palatina),  passes  from  the  anterior  border  of 


1034 


THE  DIGESTIVE  SYSTEM. 


the  Eustachian  orifice  downwards  and  forwards  to  join  the  palate.  In  front  of  the  latter 
lies  an  indistinct  groove,  the  naso-pharyngeal  groove,  which  indicates  the  separation  of 
the  nasal  cavity  from  the  naso-pharynx. 

The  levator  palati  muscle  in  descending  runs  parallel  to  the  Eustachian  tube,  and  along 
its  lower  border.  As  it  enters  the  palate,  it  produces,  particularly  when  in  a  state  of 
contraction,  an  elevation  just  below^  the  Eustachian  orifice,  known  as  the  levator 
cushion  (torus  levatorius,  Figs.  729  and  730),  which  in  its  outer  portion  abuts  against 
the  lower  part  of  the  orifice,  and  forms  its  base  when  that  opening  assumes  its  usual 
triangular  shape. 

Occasionally  the  Eustachian  orifice  is  of  an  oval  or  slit-like  form,  Avith  sloping  edges, 
but  the  triangular  shape  described  above  is  much  more  commonly  found. 

Immediately  behind  each  Eustachian  orifice  is  seen  the  lateral  recess  of  the 
pharynx  (recessus  pharyngeus,  fossa  of  Eosenmiiller),  a  nearly  vertical,  slit-like 
depression  of  considerable  depth  (Figs.  729  and  730),  which  runs  outwards  in  the 
form  of  a  flattened  pouch  or  diverticulum. 

The  lateral  recesses  project  out  over  the  iipper  margin  of  the  su]3erior  constrictor,  and 
beneath  the  petrous  portion  of  the  temporal  bone,  corresponding  to  the  position  of  the  sinus  of 
Morgagni  on  each  side.  The  recess  is  the  remains  of  the  inner  or  i^haryngeal  j)ortion  of  the 
second  -\-isceral  cleft,  the  lower  part  of  which  is  represented  in  the  supratonsillar  fossa. 

Oral  Pharynx  (pars  oralis). — This  is  the  portion  of  the  pharyngeal  cavity  which 
lies  behind  the  mouth,  and  intervenes  between  the  soft  palate  above  and  the 
superior  aperture  of  the  larynx  below.  Its  anterior  wall  is  occupied  by  the 
isthmus  of  the  fauces,  leading  into  the  mouth ;  and  below  this  by  the  pharyngeal 
portion  of  the  tongue,  almost  vertical  in  direction.  Its  lateral  wall  (Fig,  730) 
presents  a  triangular  area  (sinus  tonsillaris),  bounded  in  front  by  the  anterior 
palatine  arch,  behind  by  the  posterior  palatine  arch,  and  below  by  the  sides  of  the 
tongue  in  its  pharyngeal  portion.     This  area  is  occupied  in  the  greater  part  of  its 

extent  by  the  tonsil,  above  which  is 

The  philtrum  p  ^  ^  -A  ^         •■•■, 

lound  a  depression,  the  supratonsillar 
fossa  (Fig.  730),  which  is  of  consider- 
able interest  clinically. 

The  posterior  palatine  arch  (arcus 
pharyngo-palatinus,  posterior  pillar  of 
the  fauces)  is  a  prominent  fold  of 
mucous  membrane,  containing  the 
palato- pharyngeus  muscle  in  its  in- 
terior, which  springs  above  from  the 
posterior  edge  of  the  soft  palate,  and, 
passing  downwards  and  shghtly  back- 
wards, ends  below  on  the  side-wall  of 
the  pharynx  (Fig.  730).  The  two 
posterior  palatine  arches  form  the 
lateral  boundaries  of  the  pharyngeal 
isthmus,which  passage  they  can  modify 
both  in  size  and  shape  by  the  con- 
traction of  their  contained  muscles. 

The  anterior  palatine  arch  is  de- 
scribed on  page  1000. 

The  pharyngeal  isthmus  (isthmus 
pharyngo-nasalis)  is  the  very  oblique 
and  somewhat  triangular  orifice 
through  which  the  oral  pharynx  com- 
municates with  the  naso-pharynx  (Fig. 
732).  It  differs  consideral^ly  in  size 
and  shape  in  different  indi\iduals,  being  in  some  so  small  that  the  naso-pharynx 
can  be  explored  from  the  mouth  only  with  very  great  difficulty ;  whilst  in  others 
it  is  of  much  larger  dimensions  (Fig.  731)  and  affords  ample  space  for  the 
rhinoscopic  examination  of  the  naso-pharynx  and  the  back  part  of  the  nasal 
cavities. 


Raijhe  of  palate 


Fig.  732. — Oi'EN  Mouth  showing  Palate  and  Tonsils. 

It  also  .shows  the  two  palatine  arches,  and  the  pharyngeal 
isthmus  through  which  the  naso-pharynx  above  com- 
municates with  the  oral  portion  of  the  pharynx 
below. 


THE  PHAEYNX. 


1035 


In  general  it  may  be  described  as  triangular  in  shape,  the  sides  corre- 
sponding to  the  posterior  palatine  arches,  and  the  base,  which  is  behind, 
being  formed  by  the  posterior  wall  of  the  pharynx.  The  apex  of  the  triangle  is 
directed  towards  the  soft  palate,  and  is  encroached  upon,  and  overlapped  from  below 
by,  the  uvula,  which  assists  in  the  closure  of  the  orifice  (Fig.  732). 

Bv  the  contraction  of  the  palato-pharyngei  muscles,  which  are  enclosed  within  the 
palatine  arches,  the  sides  of  the  isthmus  can  be  approximated,  like  two  curtains,  and  its 
size  correspond iugly  diminished.  When,  at  the  same  time,  the  uvula  and  soft  palate  are 
elevated,  and  the  whole  pharynx  in  this  region  is  narrowed  by  the  contraction  of  the 
superior  constrictor,  the  aperture  can  be  completely  closed,  and  the  oral  separated  from 
the  nasal  pharynx,  as  in  the  acts  of  swallowing  and  vomiting. 


Internal  jugular  vein    Hypoglossal  nen'e 


Spinal  accessory  nerve 
Digastric  muscle 


Stylohyoid 
Glosso- 
pharyngeal nerve 
Parotid  gland 
Temporo- 
maxillary  vein 

External  carotid 

arlerj- 

Styloglossus 

Ascendin; 

palatine  artery 

Internal  pterygoid 

Epiglottis  Y^ 

Frenulum_V_k 
epiglottidis 

Masseter- 

Pharyngeal  portion 
of  tongue 


Fungiform  papilla 
Buccinator 


Internal  carotid  artery 
Pneumogastric  nerve 
Sympathetic 

Ascending  pharyngeal  artery 

odontoid  process 


Post-pharyngeal 
lymiiliatic  gland 


Sujit'rior 

constrictor  muscle 
Posterior  palatine 
arch 


Pliaivngo-epiglottic 
fold  " 

Anterior  palatine' 
irch 


Raphe  of  tongue 


Conical  papillie 


Fungiform  papilla 


Fig.  733. — Horizontal  Section-  theocgh  Mouth  and  Phakynx  at  the  Level  of  the  Tonsils. 

The  stylopharvDgeus,  which  is  shown  immetliately  to  the  inner  side  of  the  external  carotid  artery,  and  the 

prevertebral  muscles,  are  not  indicated  by  reference  lines. 

The  tonsils  (tonsillge  palatin8e,  amygdalae)  are  two  large,  oval  masses  of  lymphoid 
tissue  which  are  embedded  in  the  lateral  walls  of  the  oral  pharynx,  between  the 
anterior  and  posterior  palatine  arches  (Fig.  730).  As  already  pointed  out,  there  is 
in  this  region  a  triangular  interval  (the  sinus  tonsillaris),  situated  between  the  two 
palatine  arches  and  the  side  of  the  tongue.  The  greater  part  of  this  interval  is 
occupied  by  the  tonsil.  In  its  upper  part,  however,  above  the  tonsil,  there  is 
usually  found  a  variably-developed  depression  already  referred  to  as  the  supra- 
tonsillar  fossa. 

The  tonsil  lies  under  cover  of  the  ramus  of  the  jaw,  and  corresponds  in  position 
to  a  point  a  little  above  and  in  front  of  its  angle.  Its  inner  or  'pharyngeal  surface 
is  prominent,  and  closely  beset  with    numerous  deep,  pit -like  depressions — the 


1036  THE  DIGESTIVE  SYSTEM. 

crypts  of  the  tonsil.     These  crypts  are  most  numerous  in  the  upper  part  of  the  mass, 
where,  in  particular,  they  form  a  series  of  irregular  inter-communicating  passages. 

The  outer  or  attached  surface  is  enclosed  in  a  distinct  fibrous  capsule  connected 
with  the  pharyngeal  aponeurosis,  outside  which  lie  the  superior  constrictor  of  the 
pharynx  and  the  internal  pterygoid  muscles  (Fig.  733). 

The  ascending  palatine  artery,  running  upwards  and  backwards  between  the  stylo- 
glossus and  stylo-pharyngeus,  lies  in  close  relation  to  the  outer  surface  of  the  tonsil — 
separated  only  by  its  capsule  and  the  superior  constrictor — as  does  also  the  tonsillar 
artery,  which  is  often  represented  by  a  branch  of  the  last.  More  external  still  lies  the 
internal  pterygoid  and  the  ramus  of  the  jaw ;  whilst  the  internal  carotid  artery,  with  the 
large  cranial  nerve  trunks,  is  placed  f  to  1  inch  behind  and  to  its  outer  side  (Fig.  733). 

The  size  of  the  tonsils  is  extremely  variable,  but  as  a  rule,  in  early  life,  they 
measure  something  under  1  inch  (20  to  22  mm.)  from  above  downwards,  about  f  inch 
(18  to  20  mm.)  antero-posteriorly,  and  I  inch  (12  to  15  mm.)  from  within  out. 

In  tlie  child  and  young  adult  there  is  usually  seen  a  thin  triangular  fold  of  mucous  mem- 
brane, the  plica  triangularis  (His),  which  stretches  from  the  anterior  palatine  arch  backwards  for 
a  varialjle  distance  over  the  tonsil  (Fig.  730).  Its  apex  is  directed  upwards  towards  the  soft 
palate,  its  base  towards  the  tongue,  and  its  free  margin  crosses  the  tonsil,  to  which  it  often 
adheres  in  later  life.  In  this  latter  condition  the  plica  encloses  a  more  or  less  distinct  space 
situated  between  itself  and  the  tonsil,  in  which  diseased  processes  are  often  set  up. 

Above  the  tonsil,  as  already  mentioned,  is  found  a  variably-developed  depression,  the  supra- 
tonsillar  fossa,  which  occasionally  is  of  considerable  size,  and  then  extends  either  upwards  into 
the  soft  palate  or  forwards  and  downwards  beneath  the  jslica  triangularis.  This  fossa  is  frequently 
the  seat  of  suppurative  changes,  and  is  consequently  of  considerable  clinical  importance. 

The  supratonsillar  fossa,  like  the  lateral  recess  of  the  pharynx,  is  the  remains  of  the  pharyn- 
geal portion  of  the  second  visceral  cleft.  The  palate  in  its  growth  backwards  crosses  the  cleft, 
which  it  divides  into  two  parts — namely,  the  pharyngeal  recess  above,  and  the  supratonsillar 
recess  below  the  soft  palate. 

In  the  severe  heemorrhage  which  has  been  kno-WTi  to  follow  excision  of  an  enlarged  tonsil,  and 
which  has  been  erroneously  attributed  to  the  wounding  of  the  internal  carotid  artery,  the  blood  is 
derived  chiefly  from  enlarged  branches  of  the  ascending  palatine,  tonsillar,  or  ascending  pharyn- 
geal vessels. 

The  arteries  of  the  tonsil  are  derived  from  the  ascending  palatine  and  tonsillar  branches  of 
the  facial,  the  ascending  pharyngeal  of  the  external  carotid,  and  the  dorsalis  linguae  of  the 
lingual  The  veins  pass  to  the  tonsillar  plexus,  on  the  outer  side  of  the  tonsil,  which  is  an 
offshoot  of  the  pharyngeal  venous  plexus. 

Nerves. — The  tonsil  receives  a  special  branch  from  the  glosso-pharyngeal ;  this  unites  with 
branches  from  the  pharyngeal  plexus  in  a  small  plexus  tonsillaris  which  supplies  the  organ. 

The  lymphatics  are  extremely  numerous,  and  pass  down  to  join  some  of  the  submaxillary 
lymjjhatic  glands  near  the  angle  of  the  jaw. 

Laryngeal  Portion  of  the  Pharynx  (pars  laryngea). — This  division  of  the 
pharyngeal  cavity  lies  behind  the  larynx  (Fig.  729).  It  is  wide  above,  where  it  is 
continuous  with  the  oral  portion,  and  maintains  a  considerable  width  until  within 
about  an  inch  of  its  termination,  when  behind  the  cricoid  cartilage  it  narrows 
rapidly  and  passes  down  to  join  the  oesophagus.  Except  during  the  passage  of  food, 
the  anterior  and  posterior  walls  of  this  latter  part  are  in  contact,  and  its  cavity  is 
reduced  to  a  mere  transverse  slit  (Fig.  730). 

The  anterior  tuall  of  the  laryngeal  portion  of  the  pharynx  is  formed  in  its  whole 
extent  by  the  back  of  the  larynx,  of  which  the  following  parts  are  seen  within  the 
pharyngeal  cavity  (Fig.  729) : — The  epiglottis  above ;  below  this  the  superior 
aperture  of  the  larynx,  bounded  at  the  sides  by  the  aryteno- epiglottic  folds; 
outside  these  folds  is  seen  on  each  side  a  deep  recess,  the  sinus  pyriformis  (recessus 
piriformis,  Fig.  729 j.  Lower  down  still,  the  back  of  the  arytenoid  and  cricoid  carti- 
lage, covered  by  muscles  and  mucous  membrane,  are  visible. 

Its  posterior  and  lateral  walls  are  directly  continuous  with  the  corresponding 
walls  of  the  oral  pharynx,  and  present  no  features  which  require  special  notice. 

A  prominent  fold  of  the  mucous  membrane,  extending  from  the  side  of  the  epiglottis,  runs  up 
along  tlie  lateral  waU,  upon  which  it  ends  near  the  posterior  palatine  arcli.  This,  the  pharyngo- 
epiglottic  fold,  is  often  described  as  a  lateral  glosso-epiglottic  fold  (see  p.  1002). 

The  sinus  pjrriformis  is  a  deep  depression,  seen  on  each  side  between  the  aryteno- 
epiglottic  fold  and  the  ala  of  the  thyroid  cartilage.     When  viewed  from  above,  as 


DEVELOPMENT  OF  THE  PHARYNX.  1037 

iu  larjngoscopic  examinations,  it  appears  of  a  pyriform  shape,  the  wider  end  being 
directed  upwards  and  forwards.  When  viewed  from  behind,  the  recess  is  boat- 
shaped  and  elongated  in  the  vertical  direction.  Its  outer  wall  is  formed  by  the 
thyroid  cartilage  and  thyro-hyoid  membrane,  covered  by  mucous  membrane  ;  its 
inner  wall  by  the  aryteno-epiglottic  fold,  and  slightly  below  by  the  upper  part  ot 
the  cricoid  cartilage. 

Vessels  and  Nerves  of  the  Pharynx. — Tlie  arteries  of  the  pliaryiix  are  derived  from — 1, 

tlie  ascending  pliarpigeal  ;  2,  the  ascending  palatine  branch  of  facial  ;  3,  the  posterior  palatine, 
from  the  internal  maxillary,  with  a  few  twigs  from  the  dorsalis  lingua;,  tonsillar  (of  facial), 
vidian,  and  pterygo-palatine  of  the  internal  maxillaiy.  The  veins  go  to  the  pharyngeal  venous 
plexus,  which  is  found  between  the  constrictors  and  the  hucco-pharyngeal  aponeurosi.s.  The 
plexus  communicates  with  the  pterygoid  jjlexus  above  and  with  the  internal  jugular  or  facial 
vein  below. 

The  lymphatics  of  the  pliarynx  pass  chiefly  to  the  up^aer  set  (jf  deep  cervical  glands.  Those 
from  the  upper  prrt  of  the  posterior  wall  join  a  few  post-pharyngeal  glands  which  are  found  on 
each  side  between  the  pharynx  and  the  rectus  anticus  major  muscle.  These  latter  glands,  which 
are  large  in  the  child,  small  in  the  adult,  but  apparently  always  present  (Fig.  733),  are  of  con- 
siderable clinical  interest,  as  they  often  form  the  starting-point  of  post-pharyngeal  abscess. 

The  nerves  of  the  jiharynx,  both  motor  and  sensory,  are  derived  chiefly  from  the  phar}Tigeal 
plexus,  which  is  formed  by  branches  of  the  vagus,  glosso-pharyngeal,  and  sympathetic.  The 
.soft  jjalate  and  the  neighbourhood  of  the  tonsil  are  sujaplied  by  the  posterior  and  external 
palatine  branches  of  Meckel's  ganglion.  The  tonsil  receives  a  branch  from  the  glosso-pharyngeal 
direct.  The  vault  of  the  jsharynx,  and  the  region  around  the  Eustachian  orifice,  as  well  as  the 
orifice  itself,  are  su23plied  by  the  pharyiigeal  branch  of  Meckel's  ganglion.  Finally,  the  superior 
laryngeal  nerve  supplies  tlie  mucous  membrane  of  the  back  of  the  larynx,  where  it  forms  the 
anterior  wall  of  the  laryngeal  portion  of  the  pharynx. 

Structure  of  the  Pharyngeal  Wall.  —  The  pharyngeal  wall  is  made  up  of 
the  following  layers  : — (1)  The  thick  mucous  membrane,  which  is  plentifully  supplied 
with  racemose  mucous  glands  and  lymphoid  tissue,  and  is  lined  by  stratified  squamous 
epithelium,  except  in  the  naso-pharynx,  where  the  epithelium  is  columnar  and  ciliated. 
(2)  Outside  the  mucous  membrane  lies  a  layer  of  firm  connective  tissue,  the  pharyngeal 
aponeurosis,  which  is  closely  associated  with  the  muscles,  and  receives  the  insertions  of 
many  of  their  fibres.  This  layer  blends  with  the  periosteum  of  the  base  of  the  skull 
superiorly,  and  is  united  to  the  Eustachian  tube,  the  margins  of  the  posterior  nares,  and 
the  other  fixed  points  to  which  the  pharynx  is  connected  anteriorly.  It  is  thickest  above, 
at  the  sinuses  of  Morgagni,  where  the  muscular  coat  is  wanting,  and  where  it  forms  the 
chief  constituent  of  the  pharyngeal  wall.  Below,  it  gradually  grows  thinner  as  the  lower 
end  of  the  pharynx  is  approached.  (3)  External  to  the  pharyngeal  aponeurosis  lies  the 
muscular  coat,  formed  of  the  three  constrictors  with  the  stylo-  and  palato-pharyngeus. 
The  muscular  coat  is  covered  externally  by  (4)  the  bucco-pharyugeal  fascia,  a  thin  and,  in 
places,  ill-defined  layer  of  fascia  which  surrounds  the  constrictors  of  the  pharynx,  and  passes 
forwai'd  above  to  cover  the  outer  surface  of  the  buccinator.  It  is  connected  behind  to  the  pre- 
vertebral fascia  by  loose  connective  tissue  (the  retro-pharyngeal  space),  and  it  is  similarly 
connected  by  areolar  tissue  to  the  other  structures  with  which  the  pharynx  comes  in  contact. 

The  racemose  glands  of  the  mucous  membrane,  which  are  of  the  mucous  type,  are 
very  numerous  in  the  walls  of  the  naso-pharynx  and  in  the  soft  palate,  where  they  form 
a  thick  continuous  layer.  They  are  also  numerous  about  the  aryteno-epiglottic  folds  and 
on  the  back  of  the  arytenoid  muscles  in  the  laryngeal  portion  of  the  pharynx.  Over  the 
rest  of  this  cavity,  though  numerous,  they  are  not  so  thickly  placed  as  in  the  regions  just 
mentioned.  The  lymphoid  tissue,  either  in  a  diffuse  form  or  collected  into  lymphoid 
follicles,  is  found  throughout  the  whole  of  the  mucous  membrane.  As  already  pointed 
out,  it  is  particularly  abundant  on  the  upper  portion  of  the  posterior  wall  of  the  naso- 
pharynx, where  it  forms  the  pharyngeal  tonsil. 

The  pharyngeal  aponeurosis,  which  is  thick  above  and  thin  below,  and  the  bucco- 
pharyngeal fascia,  which  is  thin  above  and  stouter  below,  are  practically  blended  into  one 
layer  above,  near  the  base  of  the  skull,  where  the  muscular  coat  is  absent.  Lower 
down  they  are  separated  by  the  constrictoi-s,  and  become  two  distinct  sheets.  They 
are  strengthened  in  the  middle  line  posteriorly  by  a  fibrous  band  descending  from  the 
pharyngeal  tubercle. 

Development  of  the  Pharynx  and  Tonsil. 

For  the  development  of  the  pharynx  from  the  anterior  portion  of  the  foregut,  and  the 
formation  and  fate  of  the  visceral  arches  and  clefts  which  are  found  in  its  wall,  the  reader 
is  referred  to  the  chapter  on  General  Embryology,  p.  34. 


1038 


THE  DIGESTIVE  SYSTEM. 


The  anterior  palatine  arch  is  derived  from  the  second  visceral  arch,  behind  which,  in 
the  embryo,  lies  the  pharyngeal  portion  of  the  second  visceral  cleft.  This  cleft  is  crossed 
by  the  palate  in  its  growth  backwards  ;  the  part  above  the  palate  is  represented  in  the  adult 
by  the  lateral  recess  of  the  pharynx  and  the  part  below  it  by  the  sinus  tonsillaris.  From 
the  lower  and  greater  part  of  the  sinus  tonsillaris  the  tonsil  is  developed ;  the  upper  part 
of  the  sinus  persists,  however,  as  the  supratonsillar  fossa.  The  tonsil  at  first  is  a  smooth 
depression  of  the  mucous  membrane.  About  the  fourth  month  of  foetal  life  downgrowths 
of  the  epithelium  take  place,  which  are  afterwards  converted  into  the  tonsillar  crypts. 
Subsequently  lymphoid  cells  accumulate  around  the  downgrowths  and  form  the  lymphoid 
tissue,  which  constitutes  the  mass  of  the  organ. 

The  upper  and  anterior  part  of  the  naso-pharynx  is  derived  from  the  stomatodeum, 
the  remainder  of  the  cavity  from  the  foregut. 


THE   (ESOPHAGUS. 


Hj-oid  bone 


— Thyroid  cartilage 


Cricoid  cartilage 
Trachea  QS^,,^ 
Oesophagus 


-Aortic  arch 


Left  bronchus 


The  oesophagus  or  gullet  is  the  portion  of  the  digestive  canal  which  intervenes 
between  the  pharynx  above  and  the  stomach  below.     With  the  exception  of  the 

pylorus,  it  is  the  narrowest,  and  at  the  same 
time  one  of  the  most  muscular  parts  of  the 
whole  alimentary  tube. 

It  extends  from  the  termination  of  the 
pharynx,  at  the  lower  border  of  the  cricoid 
cartilage  and  opposite  the  sixth  cervical 
vertebra,  to  the  cardiac  orifice  of  the  stomach, 
opposite  the  eleventh  dorsal  vertebra.  Be- 
tween these  two  points  it  traverses  the  lower 
part  of  the  neck,  the  whole  length  of  the 
thorax,  and,  having  pierced  the  diaphragm, 
it  enters  the  abdomen,  and  immediately 
afterwards  joins  the  stomach.  In  this 
course  it  does  not  adhere  to  the  mesial 
plane  of  the  body,  but  twice  leaves  it,  and 
curves  to  the  left.  The  first  of  these  curva- 
tures corresponds  to  the  lower  part  of  the 
neck  and  the  upper  part  of  the  thorax,  where 
the  oesophagus  projects  beyond  the  left 
margin  of  the  trachea  to  the  extent  of  ^ 
or  I  inch  (4  to  6  mm.).  It  returns  to  the 
middle  hne  about  the  level  of  the  aortic 
arch.  Lower  down,  behind  the  pericardium, 
it  again  passes  to  the  left,  and  at  the  same 
time  forwards,  in  order  to  reach  the  oeso- 
phageal opening  in  the  diaphragm  (which 
is  placed  in  front  and  to  the  left  of  the 
aortic  opening),  and  it  maintains  this  direc- 
tion until  the  stomach  is  reached. 

In  addition  to  the  curvatures  just  de- 
scribed, it  is  also  curved  in  the  antero- 
posterior direction,  in  correspondence  with 
the  form  of  the  vertebral  column  upon 
which  it,  in  great  part,  lies. 

In  length  it  usually  measures  about  ten 
inches  (25  cm.). 

Its  hreadth,  where  the  tube  is  widest, 
varies  between  half  an  inch  (13  mm.)  in  the 
empty  contracted  condition  and  an  inch  or  more  (25  to  30  mm.)  in  the  fully 
distended  state. 

When  seen  in  sections  of  the  frozen  body  (Fig.  735),  the  cesophagus  usually 


Thoracic  duct 

Dorsal  vertebra  xii. 
Abdominal  aorta 


Fig.  734. — Diagram  to  show  the  Couksk 

OF   THK    CESOPHAOrS. 


THE  (ESOPHAGUS. 


1039 


appears  either  as  a  flattened  tube  with  a 
transverse  slit-like  cavity,  or  as  an  oval  or 
rounded  canal  with  a  more  or  less  stellate 
lumen.  The  former  condition  is  more 
common  in  the  neck,  owing  to  the  pressure 
of  the  trachea,  and  the  latter  in  the  thorax. 

When  exposed  in  the  ordinary  post- 
mortem examination  soon  after  death,  it  has 
rather  the  appearance  of  a  solid  muscular 
rod  or  band  than  of  a  hollow  tube. 

The  cesophagus  presents  two  distinct  con- 
strictions, one  situated  at  its  beginning,  the 
other  at  the  point  where  it  is  crossed  by  the 
left  bronchus.  Both  constrictions  are  of 
the  same  size,  and  will  admit  without  injury 
an  instrument  with  a  ma.ximum  diameter  of 
A  inch  (20  mm.).  At  each  of  these  points 
the  tube  is  flattened  from  before  backwards. 

The  a3sopliagus  varies  in  len^'tli  in  different  in- 
dividuals, from  8  to  14  inches  (20  to  35  mm.).  The 
distance  from  the  upper  incisors  to  the  beginning 
of  the  cesophagus  averages  about  6  inches  (15  cm.). 

During  life  the  cervical  portion  is  said,  under 
ordinary  circumstances,  to  be  closed  and  flattened 
from  before  backwards  by  outside  pressure,  whilst 
the  thoracic  j^ortion  may  Ije  open  owing  to  the 
negative  pressure  in  the  thorax.  The  passage  into 
the  stomach  is  also  said  to  be  oj)en  (Mickulicz),  but 
this  is  doubtful. 

The  size  at  the  two  constrictions,  when  the  tube  is 
fully  distended,  is  23  mm.  transversely,  and  17  mm. 
antero  -  posteriorly.  The  other  parts  vary  in 
diameter  between  26  and  30  mm.  (Jonnesco). 

In  its  first  curvature  to  the  left  the  divergence 
is  greatest  opposite  the  third  dorsal  vertebra. 
The  second  inclination  to  this  side  begins  about  the 
seventh  dorsal  vertebra,  and  continues  to  the  end  of 
the  cesophagus,  being  considerably  increased  as  the 
diaphragm  is  approached. 

Relations    of    the    CEsophagus.  —  The 

relations  (Fig.  735)  differ  so  widely  in  the 
neck  and  thorax  that  they  must  be  described 
separately  for  each  of  these  regions. 

In  the  neck. — In  front  lies  the  trachea 
—  to  the  posterior  membranous  wall  of 
which  the  oesophagus  is  loosely  connected 
by  areolar  tissue — and  in  the  groove  at  each 
side,  between  the  two,  the  recurrent  laryngeal 
nerve  ascends  to  the  larynx  (Fig.  735,  A). 
Behind  lie  the  vertebral  column  and  the 
longus  colli  muscles,  from  which  the  ceso- 
phagus is  separated  by  the  prevertebral 
layer  of  the  cervical  fascia.  At  the  sides 
are  placed  the  carotid  sheaths  with  their 
contained  vessels,  and  the  lateral  lobes  of 
the  thyroid  l)ody.  Owing  to  the  deviation 
of  the  tube  to  the  left  in  the  lower  part  of 
the  neck,  its  relation  to  the  carotid  sheath 
and  thyroid  body  is  much  more  intimate  on 
this  than  on  the  right  side. 

In  the  thorax. — -The  oesophagus  passes 
successively  through  the  superior  and  pos- 


Fi^;.  A  is  at  level 
of  the  up])er 
part  Ist  dorsal 
vert((V)ra,  and 
shows  the  cliief 
yH  relations  of  the 
o-'sophagus  in 
the  neck  and 
also  its  diver- 
gence to  the 
left. 


I^T  DORSAL  V. 


Fig.  B,  at  the  3rd 
dorsal  verte- 
lira,  shows  the 
thoracic  duct 
ying  on  left 
side  of  the  oeso- 
hagus. 


3^''  DORSAL  V. 


In  Fig.  C,  at  the 
evel  of  the  5tli 
dorsal  vertebra, 
the  left  bron- 
chus is  seen  in 
relation  to  the 
front  of  the 
ffisophagus. 


Fig.  D  is  at  level 
of  Sth  dorsal 
v(!rtebra,  and 
shows  the  x>eri- 
cardium  lying 
on  front  of  ceso- 
phagus. 


DORSAL  V. 


Fig.  735. — Tracings  from  Frozen  Sections  to 
SHOW  THE  Relations  of  the  (Esophagus 
at  the  levels  of  the  1st,  3rd,  Sth,  Sth,  and 
9th  dorsal  vertebras  respectively. 

A,  Aorta ;  C,  Common  carotid  artery  ;  D,  Diaphragm  ; 
L.B,  Left  bronchus  ;  L.C,  Left  subclavian  artery  ; 
L.R,  Left  recurrent  nerve;  L.V,  Left  vagus  ;  Oe, 
OEsophagus  ;  P,  Pleura  ;  Pc,  Pericardium  ;  R.B, 
Right  bronchus;  R.R,  Right  recurrent  nerve; 
R.V,  Right  vagus;  T,  Trachea;  T.D,  Thoracic 
duct ;  v.  A,  Vena  azygos  major. 


1040  THE  DIGESTIVE  SYSTEM. 

terior  mediastina,  in  the  former  lying  close  to  the  vertebral  column,  but  in  the 
latter  advancing  somewhat  into  the  thoracic  cavity  and  coming  into  contact  with 
the  back  of  the  pericardium.  The  trachea  still  lies  in  front  as  far  as  its  bifurcation. 
Immediately  below  this  the  cesophagus  is  crossed  by  the  left  bronchus  (Fig.  735,  C), 
and  in  the  rest  of  its  thoracic  course  it  lies  in  the  closest  relation  to  the  back  of  the 
pericardium.  Behind,  it  rests  on  the  longus  colli  muscle  and  the  vertebral  column 
in  the  upper  part  of  the  thorax  ;  but  below  the  bifurcation  of  the  trachea,  as  already 
explained,  it  advances  into  the  cavity  of  the  posterior  mediastinum,  and  is  soon 
separated  from  the  spine  by  the  vena  azygos  major,  the  thoracic  duct,  the  upper  six 
aortic  intercostal  arteries  of  the  left  side,  and  in  its  lower  part  by  the  aorta  as  well. 

On  its  left  side  lie  the  thoracic  duct,  the  pleura,  and  the  left  subclavian  artery 
in  the  upper  part  of  the  thorax ;  the  aorta  in  the  middle  region,  and  lower  down 
the  pleura  again,  for  a  little  way,  before  the  oesophagus  pierces  the  diaphragm.  On 
the  right  side  the  tube  comes  into  relation  with  the  arch  of  the  azygos  vein,  whilst 
below  this  the  pleura  clothes  it. 

The  two  pneumogastric  nerves,  after  forming  the  posterior  pulmonary  plexuses 
behind  the  roots  of  the  lungs,  descend  to  the  oesophagus,  where  they  form,  by  unit- 
ing with  one  another  and  with  the  branches  of  the  sympathetic,  the  plexus  guise  or 
oesophageal  plexus.  Lower  down  the  left  nerve  winds  round  to  the  front,  whilst  the 
right  turns  to  the  back,  and  in  this  relation  they  pass  with  the  tube  through  the 
diaphragm  to  reach  the  stomach. 

Relation  of  the  Aorta  to  the  CEsophagus. — The  arch  of  the  aorta,  passing  back  to  reach 
the  vertebral  column,  lies  in  relation  to  the  left  side  of  the  oesophagus ;  consequently  the 
descending  tlioracic  aorta  lies  at  first  to  its  left ;  lower  down,  however,  as  the  aorta  passes  on  to 
the  front  of  the  vertebral  column,  and  the  gullet  inclines  forwards  and  to  the  left,  the  oesophagus 
comes  to  lie  at  first  in  front,  and  then,  as  the  diaphragm  is  approached,  it  lies  not  only  in  front, 
but  also  somewhat  to  the  left  of  the  artery  (Figs.  734  and  735). 

Relation  of  the  Thoracic  Duct  to  the  CEsophagus. — The  thoracic  duct,  lying  to  the  right 
of  the  aorta  below,  is  not  directly  related  to  the  cesophagus  (Fig.  735,  E) ;  but  higher  up 
(Fig.  735,  D  and  E)  it  lies  behind  it.  About  the  level  of  the  aortic  arch  the  duct  jjasses  to  the  left, 
and  above  this  (Fig.  735,  B  and  A)  will  be  found  resting  against  the  left  side  of  the  cesophagus, 
which  it  accompanies  into  the  neck. 

Relation  of  the  Pleural  Sacs  to  the  CEsophagus. — Above  the  level  of  the  aortic  arch  and 
the  arch  of  the  vena  azygos  major,  between  which  the  tube  descends,  the  pleurae,  though  not  lying 
in  immediate  contact  with  the  oesophagus,  are  sej)arated  from  it  only  by  a  little  connective  tissue, 
and  on  the  left  side  also,  behind  the  subclavian  artery,  by  the  thoracic  duct  (Fig.  735,  B).  Here, 
in  thin  bodies,  the  pleura  is  very  close  to  the  cesophagus,  and  the  thoracic  duct,  lying  on  its  left 
side,  may  occasionally  be  seen  through  the  pleural  membrane.  Below  the  arch  of  the  azygos 
vein  the  pleura  clothes  the  right  side  of  the  cesophagus — and  very  often  even  a  considerable 
portion  of  its  posterior  surface  too,  thus  forming  a  deep  recess  behind  it — almost  as  low  down  as 
the  opening  in  the  diaphragm.  On  the  left  side,  below  the  level  of  the  aortic  arch,  the  pleura 
comes  in  contact  with  the  guUet,  only  for  a  short  distance,  just  above  the  diaphragm  (Fig.  735,  E). 

Divisions. — Both  a  diaphragmatic  (Jonnesco)  and  an  abdominal  part  of  the  oesoj^hagus  are 
described.  The  diaphragmatic  portion,  said  to  be  about  half  an  inch  in  length  (1  to  1-5  cm.), 
corresponds  to  tlie  portion  of  the  tube  which  lies  in  the  oesophageal  orifice  (or  canal)  of  the 
diaphragm.  The  plane  of  this  orifice  is  very  oblique  or  almost  vertical,  and  its  abdominal 
opening  looks  forwards  and  to  the  left,  and  but  little  downwards.  Above  and  in  front,  where  it  is 
bounded  either  Ijy  the  posterior  edge  of  the  central  tendon  or  by  a  few  decussating  fibres  of  the 
muscular  portion  of  the  diaphragm,  which  meet  behind  the  tendon,  the  oesophageal  orifice  has 
practically  no  length,  and  consequently  the  oesophagus  here  passes  into  the  abdominal  cavity 
immediately  after  leaving  the  thorax.  At  the  sides  and  behind,  on  the  other  hand,  the  decus- 
sating bands  from  the  two  crura,  which  embrace  the  orifice,  are  so  arranged  that  they  turn  a  flat 
surface  (not  an  edge)  towards  the  opening,  and  thus,  posteriorly  and  laterally,  the  orifice  or  canal 
is  of  some  lengtli ;  and  on  these  aspects  there  is  a  portion  of  the  tube  in  contact  with  the 
diapliragm  for  a  distance  of  1  to  1^  cm.  But  this  contact  takes  place  not  around  a  horizontal 
line,  but  in  a  very  oljlique  plane  corresponding  to  that  of  the  orifice.  On  the  whole,  it  is  perhajjs 
more  satisfactory  not  to  describe  a  sej^arate  diaphragmatic  portion,  but  to  say  that  the  oesophagus 
pierces  the  diaphragm  very  obliquely,  and  that  at  the  sides  and  behind  it  is  in  contact  with  the 
walls  of  the  orifice  for  a  distance  of  half  an  inch  or  more. 

The  oesophagus,  in  passing  through  the  orifice,  is  connected  to  its  boundaries  by  a  considerable 
amount  of  strong  connective  tissue,  but  it  is  extremely  diflicult,  or  impossible,  to  demonstrate  any 
direct  naked-eye  connexion  between  the  oesophageal  muscular  filjres  and  those  of  the  diaphragm. 
The  anterior  or  right  boundary  of  the  oesophageal  orifice,  formed  of  fibres  derived  from  both 
crura  of  the  diaphragm,  is  strongly  developed  and  prominent,  and  usually  lies  in  the  oesophageal 
groove,  on  the  back  of  the  left  lobe  of  the  liver,  which  groove  is  rarely  due  to  the  pressure  of  the 
cesophagus  alone. 

The  abdominal  portion  of  the  cesophagus  is  very  short,  for  immediately  after  piercing  the 


THE  (ESOPHAGUS. 


1041 


diaphragm  the  tube  expands  into  tlie  stomach.  However,  wlicn  tlie  empty  stomach  is  drawn 
forcil)ly  downwards,  a  portion  of  the  front  and  left  side  of  the  tul)e,  about  lialf  an  inch  in  h^ngth 
(1  to  1-5  cm.),  is  seen,  to  wliicli  tlie  aljove  term  is  applied.  This  part  is  covered  with  peritoneum, 
derived  from  the  great  sac  in  front  and  on  the  left,  whilst  its  right  and  posterior  surfaces  are 
uncovered.  It  is  generally  described  as  lying  against  the  wsopliageal  groov(!  and  the  left  lateral 
ligament  of  the  liver  in  front,  Imt  it  never  actually  comes  in  contact  with  the  latter  of  these 
structures,  whicli  is  attached  to  the  upper  surface  of  the  left  lol)e  of  the  liver  by  one  edge,  and 
to  the  diaphragm,  over  an  inch  in  front  of  the  oesophagus,  by  tlie  other.  As  regards  the  former, 
the  oesophageal  groove  of  the  liver  is  generally  occupied  by  the  prominent  right  margin  of  the 
oesophageal  orifice  of  the  diaphragm  and  occasionally  by  the  oesophagus  as  well.  Possibly  this 
margin  is  so  strongly  developed  and  so  prominent  in  order  that  it  may  bear  the  2)ressure  of  the  liver 
off  the  gullet,  which  otherwise  might  be  interfered  with  in  its  dilatation  during  tlie  jmssage  of  food. 

When  the  stomach  is  fully  distended  the  abdominal  part  of  the  oesophagus  almost  disappears, 
being  absorbed  into  the  stomach  in  its  distension. 

Variations. — The  chief  anomalies  found  in  the  oesophagus  are  :  (1)  Annular  or  tubular  con- 
strictions ;  (2)  diverticula,  of  whicli  the  most  interesting — known  as  "  pressure  pouches  " are 

usually  situated  on  the  posterior  wall  close  to  its  junction  with  the  pharynx,  and  these  some- 
times require  surgical  interference  ;  (3)  doubling  in  jjart  of  its  course  ;  and  (4)  communications 
between  the  trachea  and  oesophagus. 

Structure  of  the  CEsophagus  (Fig.  738).— The  oesophageal  wall  is  composed  of 
three  proper  coats — (1)  muscular,  (2)  submucous,  and  (3)  mucous.  In  addition,  it  is  sur- 
rounded by  an  outer  covez'ing  of  areolar  tissue  (tunica 
adventitia),  by  which  it  is  loosely  connected  to  the 
various  structures  related  to  it  in  its  course.  This 
loose  covering  permits  of  its  free  movement  and  of 
its  increase  in  size,  or  of  its  diminution,  during  the 
act  of  swallowing. 

The  muscular  coat  (tunica  muscularis)  is  com- 
posed of  two  layers — an  outer  of  longitudinal,  and  an 
inner  of  circular  fibres.  The  longitudinal  layer  is 
highly  developed,  and,  unlike  the  condition  usually 
found  in  the  digestive  tube,  it  is  as  stout  as,  or  in 
places  stouter  than,  the  cii'cular  layei*.  Its  fibres  form 
along  the  greater  length  of  the  tube  an  even  covering 
outside  the  circular  layer,  and  below  they  are  con- 
tinued into  the  longitudinal  fibres  of  the  stomach. 
Above,  near  the  upper  end  of  the  oesophagus,  the 
longitudinal  fibres  of  each  side,  separating  at  the  back, 
pass  round  towards  the  anterior  aspect  and  form  two 
longitudinal  bands  (Fig.  736),  which  run  up  on  tlie 
front  of  the  tube,  and  are  attached  by  a  tendinous 
band  to  the  upper  part  of  the  back  of  the  cricoid 
cartilage  (Fig.  737). 

The  circular  -muscular  fibres,  though  not  forming 
such  a  thick  layer  as  the  longitudinal  fibres,  are  nevei'- 
theless  well  developed.  Below  they  are  continued  into 
both  the  circular  and  oblique  fibres  of  the  stomach. 
Above  they  pass  into  the  lower  fibres  of  the  inferior 
constrictor  of  the  pharynx. 

The  muscular  fibres  are  entirely  of  the  striated 
variety  at  the  upper  end  of  the  oesophagus.  Soon 
unstriped  fibres  begin  to  appear,  increasing  in  number 
as  we  descend.  In  the  lower  half  or  two-thirds,  only 
unstriped  muscle  is  found. 

The  longitudinal  fibres  for  about  the  upper  fifth  of  the  tube  are  entirely  striped  ;  in 
the  second  fifth  striped  and  unstriped  are  mixed  ;  whilst  in  the  lower  three-fifths  unstriped 
fibres  alone  are  present.  The  circular  fibres  are  entirely  striated  for  the  first  inch  ;  after 
this  unstriped  fibi'es  appear ;  and  in  the  lower  two-thirds,  only  unstriped  muscle  fibres 
are  found  (D.  J.  Coffey). 

The  longitudinal  fibres  are  often  joined  by  slips  of  imstriped  muscle,  or  elastic  fibres, 
which  spring  from  various  sources,  including  the  left  pleura  (constant,  Cunningham),  the 
bronchi,  back  of  trachea,  pericardium,  aorta,  etc.  These  slips  assist  in  fixing  the  oesophagus 
to  the  surrounding  structures  in  its  passage  through  the  thorax,  and  have  been  aptly 
compared  to  the  tendrils  of  a  climbing  plant  (Treitz). 

The  submucous  coat,  composed  of  areolar  tissue,  is  of  very  considerable  thickness,  in 

70 


Trachea 


Longitudinal , 
fibres  diverging 

Fig.  736.  —  Dissection  to  show  the 
arrangement  of  the  muscular  fibres 
on  the  back  of  the  oesophagus  and 
pharynx.  Traced  upwards,  the  lon- 
gitudinal muscular  fibres  of  the 
oesophagus  are  seen  to  separate 
behind  ;  passing  round  to  the  sides, 
they  form  two  longitudinal  bands 
which  meet  in  front  above,  and  are 
united  to  the  cricoid  cartilage,  as 
shown  in  the  next  figure. 


1042 


THE  DIGESTIVE  SYSTEM. 


^Inferior 
constrictor 


-3 — Tendinous  band 


Circular  fibres 
of  cesophagns 


Fig. 


Longitudinal  bands 

737. — The  Lower  Part  of  the  Pharynx 
AND  THE  Upper  Part  of  the  CEsophagus 
have  been  slit  w])  from  behind,  and  the  mucous 
membrane  removed  to  show  the  muscular  fibres. 
The  two  longitudinal  bands  are  seen  coming 
round  to  the  front  to  be  attached  by  a  common 
tendon  to  the  upper  border  of  the  cricoid  car- 
tilage.    See  explanation  of  last  figure. 


order  to  allow  of  the  expansion  of  the  tube  during  swallowing.     It  connects  the  mucous 
membrane  loosely  to  the  muscular  coat,  and  admits  of  the  former  being  thrown  into  folds 

when  empty.  In  this  coat  are  contained  the 
numerous  racemose  mucous  glands  which 
open  into  the  cavity  of  the  oesophagus  (Fig. 
738). 

The  mucous  membrane  is  of  a  greyish 
pink  colovu',  much  paler  than  that  of  the 
pharynx,  and  of  a  firm  and  resistant  texture. 
It  is  covered  by  a  thick  stratified,  squamous 
epithelium,  on  the  surface  of  which  the  open- 
ings of  numerous  glands  are  found.  Below, 
its  junction  with  the  gastric  mucous  mem- 
-SidSage  brane  is  indicated  by  a  distinct,  irregularly 
dentated  or  crenated  line,  which  runs  trans- 
versely round  the  tube.  In  carefully  preserved 
specimens  the  smooth  mucous  membrane  of 
the  oesophagus  above  this  line  contrasts 
strongly  with  the  mammillated  gastric  mucous 
membrane  below. 

Owing  to  the  inelasticity  of  this  coat,  and 
the  fact  that  it  is  but  loosely  connected  to 
the  muscular  coat  by  the  submucosa,  it  is 
thrown  into  a  series  of  longitudinal  folds  when 
the  oesophagus  is  empty  and  contracted  ;  hence 
the  stellate  lumen  often  seen  in  sections  of 
the  gullet. 

Glands.  —  Numerous  racemose  mucous 
glands,  large  enough  to  be  distinctly  seen  with 
the  naked  eye,  are  found  in  the  submucosa. 
They  are  pretty  evenly  distributed  over  the 

whole  tube,  and  do  not  appear  to  be  more  numerous  towards  either  end   (Coffey).       In 

addition  to   these,  other    glands,  resembling 

closely  those  of  the  cardiac  end  of  the  stomach, 

are    found     in    the    mucous    membrane    of 

certain  portions  of  the  oesophagus.     They  are 

entirely  confined  to  the  mucosa,  and  do  not 

extend  beyond  the  musciilaris  mucoste.  These 

glands   are    specially  numerous  at  both  the 

upper  and   lower  ends  of   the  tube  (Coffey, 

Schafer). 
Vessels  and  Nerves.— Its  arteries  consist  of 

numerous  small  branches  derived,  in  the  neck, 

from  the  inferior  thyroid,  in  the  thorax,  from 

the  bronchial  arteries  and  thoracic  aorta,  and  in 

the  abdomen,   from  the  coronary  artery  of  the 

stomach,  and  also  from  the  left  phrenic. 

Tlie  veins  form  a  plexus  on  the  exterior  of  the 

ocsopliagus,  from  wliicli  branches   pass,    in  the 

lower  part  of  the  tul>e,  to  the  coronary  vein  of 

the  stomach,  and,  higher  up,  to  the  azygos,  and 

thyroid  veins.     There  is  thus  established  on  the 

lower  ])art  of  the  oeso])hagus  a  free  connuunica- 

tiou  between  thi;  portal  and  systemic  veins. 

The  lymphatics  pass  to  the  inferior  set  of  deep 

cervical  glands  in  the  neck,  and  to  the  posterior 

mediastinal  glands,  many  of  which,  of  large  size, 

are  seen  around  the  tube,  in  the  thorax. 

The  nerves  are  derived  from    the  recurrent 

laryngeal,  and  from  the  cervical  sympathetic  in 

the  neck,  from  the  pneumogastrics  and  sympathetic  in  the  thorax. 

Development  of  the  CEsophagus. 

The  oesophagus  is  developed    from  the  foregut    lying  between   the  pharynx  and  the 
dilatation  which  represents  the  future  stomach.     At  first,  owing  to  the  flexure  of  the  head 


Vreolar  coat 


Fig.  738. — Structure  of  the  CEsophagus, 
transverse  section  (after  Horsley). 


THE  ABDOMINAL  CAVITY.  1043 

on  the  trunk  in  the  early  embryo,  it  is  relatively  short,  but,  as  the  neck  is  developed,   it 
gradually  becomes  elongated  and  more  or  less  cylindrical. 

The  superficial  epithelial  cells  are  ciliated  and  somewhat  cylindrical  between  the 
fourth  and  eighth  months  of  foetal  life  (Neumann) ;  subsequently  the  adult  condition  is 
established. 

THE   ABDOMINAL   CAVITY. 

As  the  remaining  parts  of  the  digestive  system  lie  within  the  abdomen  it  will 
be  necessary  to  describe  that  cavity  as  a  whole,  and  to  refer  briefly  to  its  Hninf^ 
membrane — the  peritoneum — before  passing  on  to  the  consideration  of  the  viscera 
which  are  contained  within  it. 

The  abdomen  is  that  portion  of  the  cavity  of  the  trunk  which  lies  below  the 
diaphragm.  It  is  the  largest  of  all  the  cavities  of  the  body,  and  contains  the 
greater  part  of  the  digestive,  urinary,  and  generative  systems  of  organs,  in  addition 
to  numerous  vessels,  nerves,  and  other  structures. 

Shape. — In  general,  the  abdominal  cavity  is  of  a  somewhat  oval  form,  with  the 
long  axis  directed  vertically,  and  the  wide  end  upwards.  It  is  strongly  flattened 
from  before  backwards,  and  is  encroached  upon  in  the  middle  line  posteriorly  by 
the  projection  forwards  of  the  vertebral  column,  on  each  side  of  which  it  presents 
the  appearance  of  a  deep  wide  groove. 

Boundaries. — ^The  cavity  is  limited  above  by  the  concave  vault  of  the  diaphragm, 
which  is  dome-shaped  and  divided  into  a  right  and  a  left  cupola  by  an  intervenino- 
depression.  Into  the  right  cupola  fits  the  greater  part  of  the  hver ;  in  the  left  lie 
the  stomach  and  spleen.  On  the  upper  surface  of  each  cupola  is  placed  the  base 
of  the  corresponding  lung,  whilst  between  them,  on  the  depression,  rests  the  under 
surface  of  the  heart. 

During  expiration,  the  right  cupola  ascends  almost  to  the  level  of  the  rio-ht 
nipple ;  it  is  highest  at  a  point  about  one  inch  internal  to  the  nipple  line,  and  here 
it  reaches  the  upper  border  of  the  fifth  rib,  or  even  the  middle  of  the  fourth  inter- 
costal space.  On  the  left  side  it  is  one-half  to  one  inch  (12-25  mm.)  lower,  and 
in  the  middle  line  it  crosses  the  inferior  extremity  of  the  gladiolus  about  the  level 
of  the  sixth  rib  cartilage. 

Beloiu,  the  cavity  is  limited  by  the  pelvic  floor,  formed  by  the  levatores  ani, 
and  coccygei  muscles,  covered  on  their  upper  surface  by  the  pelvic  fascia.  The 
anterior  loall  is  formed  by  the  aponeuroses  of  the  three  flat  abdominal  muscles, 
together  witli  the  two  recti,  which  latter  constitute  powerful  braces  for  the  wall, 
on  each  side  of  the  middle  line.  The  lateral  tvalls  are  formed  by  the  muscular 
portions  of  the  obliqui  and  transversales  muscles,  and  below  by  the  iliac  bones  with 
the  iliacus  muscles. 

Finally,  the  cavity  is  Limited  behind  by  the  lumbar  portion  of  the  vertebral 
column  with  the  psoas  muscle  on  each  side,  and  the  quadratus  lumborum  still 
further  out.  The  iliac  bones  also  enter  into  the  formation  of  the  lower  portion  of 
the  posterior  wall. 

The  upper  portion  of  the  cavity  lies  under  cover  of  the  ribs,  which  attbrd  con- 
siderable protection  to  this  part  of  the  abdomen,  particularly  at  the  sides  and 
behind,  in  which  latter  position  the  cavity  is  further  protected  by  the  vertebral 
column.  Anteriorly,  on  the  other  hand,  the  ribs  are  wanting  below  the  sternum, 
and  here,  the  abdominal  wall  is  formed  only  of  aponeuroses  and  muscles.  But  e\'en 
at  the  sides  and  back  there  is  a  considerable  zone,  usually  one  to  two  inches  wide 
(Cunningham),  between  the  lower  ribs  above  and  the  crest  of  the  ihum  below, 
which  has  no  bony  support  except  that  afforded  by  the  vertebral  column. 

.  Whilst  the  circumference  of  the  diaphragm  is  attached  to  the  lower  part  of 
the  thoracic  framework  in  front  and  at  the  sides,  and  to  the  lumbar  vertebrae 
behind,  the  central  portion  of  the  dome,  on  the  other  hand,  namely,  the  central 
tendon,  is  placed  high  up,  under  cover  of  the  ribs,  and  in  a  more  or  less  horizontal 
plane.  As  a  result,  the  peripheral  muscular  part  slopes  almost  vertically  upwards 
from  the  circumference  of  the  thoracic  framework  to  the  central  tendon,  and  lies 
for  a  considerable  distance  in  contact  with  the  deep  surface  of  the  ribs ;  thus  the 
diaphragm  comes  to  form,  not  only  the  roof  of  the  cavity,  but  it  also  enters  into 
70  a 


1044 


THE  DIGESTIVE  SYSTEM. 


the  formation  of  the  lateral,  posterior,  and,  to  a  less  extent,  of  the  anterior  walls ; 
and  almost  as  much  of  the  cavity  of  the  abdomen  as  of  the  thorax  lies  under 
shelter  of  the  ribs. 

Owintr  to  the  fact  that  the  boundaries  of  the  abdomen  are  formed  chiefly  of 
muscles,  it  follows  that  its  walls  are  capable  of  contraction  to  a  very  considerable 
extent,  and  the  size  of  the  cavity  can  consequently  be  altered  in  all  directions.  Its 
chief  changes  in  form  are  due  to  the  descent  or  elevation  of  the  diaphragm,  the 
contraction  or  relaxation  of  the  anterior  and  lateral  walls,  and  the  raising  or 
lowering  of  the  pelvic  floor. 

Within  the  muscles  forming  its  walls,  the  abdomen  is  lined  by  an  envelope  of 


Diaphragm- 


Attachment  of_ 
falciform  ligament 


Right  lobe  of  liver- 


Gall-bladder- 


Transverse  colon  - 
Small  intestine- 


Ascending  colon 


Anterior  superior  

spine      ^^ 

Csecnni  - 


-Outline  of  liver 


^Stomach 


-Great  omentum  (cut) 

Transverse  mesocolon 
-with  jejunum 


SCALE  IN  INCHES 


SCALE  IN  CENTIMETRES 


F,-.  739  —The  Abdominal  Vi.sceka  in  situ,  as  seen  when  the  abilomeu  is  laid  open  and  the  great  omentum 
"  removed  (drawn  to  scale  from  a  photo.qraph  of  a  male  body  aged  56,  hardened  by  formalin  injections). 

The  ribs  on  the  right  side  are  indicated  by  Roman  numerals  ;  it  will  be  observed  that  the  eighth  costal  cartilage 
articulated  with  the  sternum  on  both  sides.  The  subcostal,  intertubercular,  and  right  and  left  Foupart 
lines  are  drawn  in  black,  and  the  mesial  plane  is  indicated  by  a  dotted  line.  The  intercostal  muscles  and 
part  of  the  diaphrac^m  have  been  removed,  to  show  the  liver  and  stomach  extending  up  l)eneath  the  rio.". 
The  stomach  is  moderately  distended,  and  the  intestines  are  particularly  regular  in  their  arrangement. 

fascia  which  separate  the  muscles  from  the  extraperitoneal  connective  tissue  and 
peritoneum.  This  aponeurotic  layer  is  distinguished  in  different  locahties  as  :— 
(1)  the  transversalis  fascia  on  the  anterior  and  lateral  walls,  linmg  the  deep 
surface  of  the  transversahs  muscle  and  continuous  above  with  the  fascia  clothing 
the  under  surface  of  the  diaphragm ;  (2)  the  iliac  fascia  on  the  posterior  wall, 
coverincr   the   psoas   and   iliacus   muscles;  (3)  the  anterior  layer  of  the  lumbar 


SUBDIVISION  OF  THE  ABDOMINAL  CAVITY.  1045 

aponeurosis,  also  ou  the  posterior  wall  covering  the  frout  of  the  quadratus 
lumborum ;  and  (4)  the  pelvic  fascia,  lining  the  pelvis. 

Apertures. — Certain  apertures  are  found  in  the  walls  of  the  abdomen,  some  of 
which  lead  to  a  weakening  of  the  parietes.  These  are :  the  three  openings  in  the 
diaphragm  for  the  passage  of  the  inferior  vena  cava,  the  a3soplmgus,  and  the  aorta 
respectively ;  the  apertures  in  the  pelvic  floor,  through  which  the  rectum,  the 
urethra,  and  the  vagina  in  the  female,  reach  the  surface  ;  the  inguinal  canal, 
through  which  the  spermatic  cord  (or  round  ligament)  passes,  in  leaving  the 
abdominal  cavity ;  and  lastly,  the  crural  canal,  a  small  passage  which  runs  down 
from  the  abdomen  along  the  inner  side  of  the  femoral  vessels.  The  two  latter  con- 
stitute on  each  side  weak  points  in  the  abdominal  wall,  through  which  a  piece  of 
intestine  occasionally  makes  its  way,  giving  rise  to  inguinal  or  femoral  hernia 
respectively. 

Extraperitoneal  or  Subperitoneal  Connective  Tissue  (tela  subserosa). — Between 
the  fascia  which  covers  the  deep  surfaces  of  the  abdominal  muscles,  and  the  peri- 
toneum which  lines  the  ca'ST.ty,  there  is  found  a  considerable  quantity  of  connective 
tissue,  generally  more  or  less  loaded  with  fat,  which  is  known  as  the  extraperitoneal 
or  subperitoneal  connective  tissue.  This  is  part  of  an  extensive  fascial  system 
which  lines  the  whole  of  the  body  cavity,  outside  its  various  serous  sacs,  and  is 
continued  on  the  several  vessels,  nerves,  and  other  structures  which  pass  from  these 
cavities  into  the  limbs  and  neck. 

In  the  abdomen  it  is  divisible  into  a  parietal  and  a  visceral  portion,  both  com- 
posed of  loose  connective  tissue.  The  former  lines  the  cavity,  whilst  the  latter 
passes  forwards  between  the  mesenteries  and  other  peritoneal  folds  to  the  viscera. 
These  two  portions  of  the  extraperitoneal  tissue  are  perfectly  continuous  with  one 
another,  and  contain  in  their  whole  extent  a  vascular  plexus,  through  which  a  com- 
munication is  established  between  the  vessels  of  the  abdominal  wall,  on  the  one 
hand,  and  those  of  the  contained  viscera  on  the  other. 

The  imrietal  portion  is  thin  and  comparatively  free  from  fat  over  the  roof  and 
anterior  wall  of  the  abdomen,  and  here  the  peritoneum  is  more  firmly  attached 
than  where  the  tissue  is  fatty  and  large  in  amount.  In  the  pelvis,  on  the  other 
hand,  the  tissue  is  loose  and  fatty,  and,  as  such,  it  is  continued  up  for  some  inches 
on  the  anterior  abdominal  wall  above  the  pubes,  to  permit  of  the  ascent  of  the 
bladder  during  its  distension,  and  the  attendant  stripping  of  the  peritoneum  off  this 
portion  of  the  anterior  abdominal  wall.  Here  also  the  urachus  and  the  obliterated 
hypogastric  arteries  will  be  found  passing  up  in  its  substance.  On  the  posterior 
wall  the  tissue  is  large  in  amount  and  fatty,  particularly  where  it  surrounds  the 
great  vessels  and  kidneys. 

From  this  latter  portion  especially  the  visceral  expa7isions  are  derived  in  the 
form  of  prolongations  around  the  various  branches  of  the  aorta.  These  expansions 
are  connected  with  the  areolar  coats  of  the  blood-vessels  and  are  conducted  by 
them  into  the  mesenteries  and  other  folds  of  the  peritoneum,  and  thus  reach  the 
viscera. 

The  chief  uses  of  this  tissue  are :  (1)  to  unite  the  layers  of  the  abdominal  wall 
together  ;  (2)  to  connect  the  viscera  to  these  walls  and  to  one  another  in  such  a 
loose  manner  that  their  distension  or  relaxation  may  not  be  interfered  with,  which 
would  not  be  the  case  if  the  connecting  medium  were  firm  or  rigid  ;  (3)  in  addition, 
it  is  a  storehouse  of  fat,  forms  sheaths  for  the  vessels  and  nerves,  and  establishes, 
through  its  vascular  plexus,  communication  between  the  parietal  vessels  and  those 
distributed  to  the  abdominal  viscera. 

Subdivision  of  the  Abdominal  Cavity. 

The  abdomen  is  divided  naturally  by  the  pelvic  brim  into  two  parts,  the 
abdomen  proper,  and  the  ca\ity  of  the  pelvis.  The  former  of  these  is  further  sub- 
divided, artijicially ,  into  nine  regions. 

The  pelvic  brim  (Figs.  166  and  167,  p.  221),  which  separates  the  two  natural 
divisions  of  the  cavity,  is  formed  behind  by  the  base  of  the  sacrum,  at  the  sides  by 
the  iliopectineal  lines  of  the  innominate  bones,  and  in  front  by  the  pubic  crests  and 
70  & 


1046 


THE  DIGESTIVE  SYSTEM. 


the  symphysis  pubis.  In  the  erect  position  it  usually  makes  an  angle  of  about  55 
to  60  degrees  with  the  horizontal.  The  two  portions  of  the  abdominal  cavity 
which  the  brim  separates  meet  at  an  angle,  the  abdomen  proper  running  almost 


SCALE    IN    INCHES  SCALE    IN    CENTIMETRES 

Fl(i.  740. The  Front  of  the  Body,  sliowing  the  subdivisions  of  tlie  alidoiuiiial  cavity  and  the  position  of 

tlie  chief  viscera.  (From  a  photograph  of  the  body  represented  in  tlie  preceding  figure.)  The  viscera  in 
Fig.  739  liave  been  traced  in  red  on  this  figure.  The  photograplis  for  these  two  figures  and  for  Fig.  744 
were  taken  from  the  same  body,  under  precisely  similar  conditions;  consequently  the  relations  of  the 
deeper  parts  to  the  surface  are  correctly  obtained  by  superimposing  the  pictures  as  in  this  illustration. 
The  liver  occupies  a  slightly  lower  position  than  usual. 

vertically  upwards  from  it,  whilst  the  pelvic  cavity  slopes  backwards  and  slightly 
downwards. 

The  pelvic  cavity  is  bounded  in  front  and  at  the  sides  by  the  portionis  of  the  in- 
nominate bones  below  the  level  of  the  iliopectineal  line.  These  bony  walls  are  partly 
clothed,  in  front  and  laterally,  by  the  obturator  internus  nuisclcs,  and  internal  to  these 
by  the  parietal  portion  of  the  pelvic  fascia,  as  low  down  as  the  white  line.     The  posterior 


THE  ABDOMINAL  CAVITY.  1047 

wall  is  formed  by  the  front  of  the  sacrum,  covered  on  each  side  l)y  the  pyriformis 
muscle.  This  wall  (as  represented  by  the  pyriformis  muscles)  meets  the  lateral  wall 
at  the  anterior  border  of  the  great  sciatic  foramen ;  through  this  foramen  the  pyriformis 
passes  out,  thus  closing  up  what  would  otherwise  be  a  large  aperture  in  the  parietes  of 
the  cavity.  The  floor  is  composed  of  the  two  pairs  of  muscles  which  form  the  pelvic 
diaphragm,  namely,  the  levatores  ani  and  coccygei — covered  by  the  visceral  layer  of  the 
pelvic  fascia.  These  muscles  pass  on  each  side,  from  the  lateral  wall  of  the  pelvis,  down- 
wards and  inwards  towards  the  middle  line,  and  present  a  concave  upper  surface  towards 
the  pelvic  cavity. 

Subdivision  of  the  Abdomen  Proper. — Owing  to  the  large  size  of  the  cavity, 
and  in  order  to  localise  more  correctly  the  position  of  the  various  organs  contained 
within  it,  the  abdomen  proper  is  artificially  subdivided  by  two  horizontal  and  two 
vertical  hnes  (Fig.  7-iO)  drawn  on  its  anterior  wall.  From  these  lines  imaginary 
planes  are  supposed  to  be  continued  backwards,  wliich  divide  up  the  cavity  into 
nine  regions. 

Of  the  two  liorizontal  lines,  one  is  drawn  around  the  trunk  at  the  level  of  the 
lower  border  of  the  tenth  costal  cartilage ;  this  is  known  as  the  subcostal  line, 
and  the  imaginary  plane  corresponding  to  it,  as  the  subcostal  plane.  The 
second  horizontal  line  is  drawn  at  the  level  of  the  highest  point  of  each  diac  crest, 
visible  from  the  front ;  this  point  corresponds  to  the  tubercle  seen  on  the  outer  lip 
of  the  crest,  about  two  inches  behind  the  anterior  superior  spine,  and  can  be  easily 
located ;  the  line  and  plane  are  consequently  known  as  the  intertubercular  line  and 
plane  respectively. 

The  vertical  lines  are  drawn,  one  on  each  side,  perpendicularly  upwards  from  a 
p)oint  on  Poupart's  ligament  midway  between  the  anterior  superior  spine  and  the 
symphysis  pubis.  These  lines  and  the  corresponding  planes  are  known  as  the 
Poupart  lines  and  planes  respectively. 

By  the  two  horizontal  lines  the  abdomen  is  divided  into  tliree  zones,  an  upper 
or  costal,  a  middle  or  umbilical,  and  a  lower  or  hypogastric  zone.  By  the  two 
perpendicular  lines  each  of  these  is  subdivided  into  three  parts,  a  central  and  two 
lateral.  Thus,  in  the  upper  zone,  we  get  a  hypocliondriac  region  or  hypochondrium 
on  each  side,  and  an  epigastric  region  or  epigastrium  in  the  centre.  Similarly,  the 
umbiHcal  zone  is  divided  into  right  and  left  lumbar  regions,  with  an  umbilical  region 
between.  And  the  hypogastric  zone  has  a  hypogastric  region  or  hypogastrium  in  the 
centre,  with  right  and  left  iliac  regions  at  the  sides. 

In  addition,  the  portion  of  the  abdominal  wall  above  the  pubis  is  known  as 
the  suprapuhic  region,  and  that  immediately  above  Poupart's  ligaments,  as  the 
inguinal  region. 

The  three  central  divisions,  namely,  the  epigastric,  umbilical,  and  hypogastric 
regions,  can  conveniently  be  further  subdivided  by  the  mesial  plane,  passing  through 
the  middle  of  the  body,  into  right  and  left  halves. 

The  upper  horizontal,  or  subcostal,  plane  joasses  behind,  through  the  upper  part  of  the  third 
lumtiar  vertebra,  or  the  disc  between  the  second  and  third  lumbar  vertebra;.  The  intertubercular 
plane  cuts  through  the  middle  or  uj^per  part  of  the  fifth  lumbar  vertebra. 

The  lower  margin  of  the  tenth  costal  cartilage  frequently  corresponds  to  the  most  dependent 
part  of  the  thoracic  framework.  Often,  however,  the  eleventh  costal  cartilage  descends  j  to  ^ 
inch  lower.  Nevertheless,  the  tenth  cartilage  is  selected  in  drawing  the  subcastal  plane,  for  two 
chief  reasons,  namely,  it  is  visible  from  the  front  as  a  rule,  and  it  is  comparatively  fixed,  whilst 
the  eleventh,  being  a  floating  rib,  is  much  more  movable,  is  variable  in  length,  and  more 
difficult  to  locate. 

Contents  of  the  Abdomen. — The  following  structures  are  found  within  the 
abdominal  cavity : — 

1.  The  greater  part  of  the  alimentary  canal,  viz.  stomach,  small  intestine,  and  large  intestine. 
-^  2.  Digestive  glands:  the  liver  and  pancreas. 

3.  Ductless  glands:  the  spleen  and  the  two  suprarenal  bodies. 

4.  Urinary  apparatus:  the  kidneys,  ureters,  bladder,  and  part  of  urethra. 

5.  The  internal  generative  organs  according  to  the  sex. 

6.  Blood  and  lymph  vessels,  and  lymphatic  glands. 

7.  The  aMominal  jjortion  of  the  cerebro-spinal  and  sympathetic  nervous  systems. 

8.  Certain /ff^rtZ  remains. 

9.  The  peritoneum — the  serous  membrane  which  lines  the  cavity,  and  is  reflected  over  most  of 
its  contained  viscera. 

70  c 


1048 


THE  DIGESTIVE  SYSTEM. 


C^i 


THE  PEEITONEUM. 

The  arrangement  of  the  peritoneum  is  so  complicated,  and  its  relations  to  the 
abdominal  contents  so  intricate  and  detailed,  that  it  wjll  be  expedient  to  postpone 
its  complete  description  until  the  various  organs,  with  their  special  peritoneal 
relations,  have  been  separately  considered.  Nevertheless,  it  will  be  necessary  to 
give  here  a  general  account  of  the  disposition  of  the  membrane,  and  to  refer  to 
the  three  varieties  of  folds  which  it  forms  in  passing  from  organ  to  organ,  or  from 
these  to  the  abdominal  wall. 

The  peritoneum  (tunica  serosa)  is  the  serous  sac  which  lines  the  abdominal 
cavity  and  invests  most  of  the  abdominal  viscera,  to  a  greater  or  less  degree.  Like 
the  pleuree,  the  tunica  vaginalis  of  the  testicle,  and  other  serous  sacs,  its  walls  are 
composed  of  a  thin  layer  of  fibrous  tissue,  containing  numerous  elastic  fibres,  and 
covered  over  on  the  side  turned  towards  the  cavity  of  the  sac  by  flattened 
endothelial  cells.  Like  them,  too,  the  peritoneum  in  the  male  is  a  completely 
closed  bag,  but  in  the  female  this  is  not  the  case,  for  the  abdominal  end  of  each 
Fallopian  tube  opens  into  the  sac,  whilst  the  other  end  of  that  tube  communicates 
with  the  interior  of  the  uterus,  and  thus,  indirectly,  with  the  exterior.  Normally 
the  membrane  secretes  only  sufficient  moisture  to  lubricate  its  surface,  otherwise 
the  sac  is  perfectly  empty,  and  its  opposing  walls  lie  in  contact,  thus  practically 
obliterating  its  cavity. 

The  use  of  these  lubricated  and  highly  polished  serous  linings,  found  in  the 

abdomen  and  certain  other  cavities, 
^  is  to  facilitate  the  movements  of 

the  contained  viscera  during  any 
changes  in  size  or  form  which  they 
or  their  containing  cavity  may 
undergo.  As  a  result  of  this 
arrangement,  notwithstanding  the 
tonic  pressure  of  the  abdominal 
wall  on  its  contents,  the  stomach 
and  intestines  are  free  to  move 
with  the  greatest  ease  and  the 
least  degree  of  friction,  when  any 
change  takes  place  either  in  the 
organs  themselves  or  in  their 
surroundings. 

The  peritoneum  is  a  thin 
glistening  membrane,  which  may 
aptly  be  compared  to  a  coat  of 
varnish  applied  to  the  inner  aspect 
of  the  abdominal  walls,  and  to  the 
surface  of  the  contained  viscera, 
except  where  these  are  directly 
applied  to  the  walls  or  to  one 
another.  It  forms  throughout  its 
entire  extent  a  continuous  and 
distinct  sheet,  but  it  is  united  so 
intimately  to  the  viscera,  and 
follows  the  irregularities  of  their 
Fig.  741 -Diagrammatic  Mesiai  Section  OF  Female  Body,  ^y^ns  SO  closely,  that  it  appears 
to  show  the  jjentoiieutn  on  vertical  tracing.     The  great  sac       ,     n      .       •    i  i.    I      k  a    •    1 

of   the    peritoneum   is    black   and  is   represented  as  Ijeing    ^^1    IirSt    Sight    tO    DC    a    SUpernCial 


Small  .sac 
Foramen  of 
Winslow,  with 
arrow  passed 
through  it 

Pancreas 

Third  part  of 
duodenum 

Transverse 
colon 


The  mesentery 


Uterus 


Bladder 


Rectum 


Pouch  of 
Douglas 


much  larger  than  in  nature  ;  the  small  sac  is  very  darkly 
shaded  ;  the  jieritoneuni  on  section  is  shown  as  a  white 
line  ;  and  a  white  arrow  is  passed  through  the  foramen  of 
Winslow  from  the  great  into  the  small  sac. 


layer  of  these  walls,  rather  than 
a  separate  membrane.  Outside 
the  peritoneum  lies  the  extra- 
peritoneal connective  tissue — al- 
ready described — which  connects  it  more  or  less  intimately  to  the  fascial  lining 
of  the  abdominal  walls  and  to  the  abdominal  viscera. 

If  we  trace  the  peritoneum  as  a  continuous  layer,  beginning  in  front,  we  find 


THE  PEEITONEUM. 


1049 


Falciform  ligament 
Foramen  of  Wiiislow 


Round  liirament  of  liver 


Lesser  omentum  (cut) 
Portal  vein 


Lieno-renal 
lisrament 


Small  intestine 


liight  kidney 


The  mesentery 


that  it  lines  the  deep  surface  of  the  anterior  abdominal  wall,  and  is  continued 
upwards  to  the  under  surface  of  the  diaphragm  (Fig.  741),  the  greater  portion 
of  which  it  covers.  From  the  posterior  part  of  the  diaphragm  it  is  reflected  or 
carried  forwards  on  to  the  upper  surface  of  the  liver,  and  then  down  over  the 
stomach,  intestines,  and  other  abdominal  viscera — clothing  them  all — to  the  pelvis. 
In  like  manner,  when  traced  laterally  from  the  anterior  wall,  the  membrane  will  be 
found  to  line  the 
sides  of  the  cavity, 
and  passing  back- 
wards to  clothe  the 
posterior  abdominal 
wall,  and  the  viscera 
lying  upon  it  (Fig. 
742,  B).  It  should 
be  pointed  out  that 
all  the  abdominal 
viscera  are  either 
directly  fixed  by  con- 
nective tissue  to  the 
posterior  abdominal 
wall,  or  suspended  by 
blood-vessels  from  it. 
In  the  former  case  the 


peritoneum  is  re  - 
fleeted  directly  from 
the  wall  on  to  the 
viscera ;  in  the  latter 
it  runs  along  the 
blood-vessels  to  reach 
the  viscera,  which  it 
clothes,  and  then 
returns  to  the  wall 
on  the  opposite  sides 
of  the  vessels,  which 
it  thus  encloses  in 
a  fold. 

Whilst  the  main 
sac  of  the  peritoneum 
lies  in  front  of  the 
various  abdominal 
viscera,  covering 
them  over  and  dip- 
ping down  between 
them,  it  should  be 
mentioned  that  there 
is  a  special  diverti- 
culum derived  from 
this  "great  sac," 
which  turns  in  behind 

the  stomach,  and  covers  its  posterior  surface ;  this  is  known  as  the  lesser  or 
smaller  sac,  and  it  will  be  described  in  detail  later  on.  The  aperture  through 
which  one  sac  communicates  with  the  other  is  termed  the  foramen  of  Winslow. 

In  passing  from  organ  to  organ,  or  from  these  to  the  abdominal  wall,  the 
peritoneum  forms  numerous  folds,  which  are  divided  according  to  their  connexions 
into  three  classes : — 

(a)  Omenta  are  folds  of  peritoneum  which  pass  from  the  stomach  to  other 
abdominal  organs.  They  are  three  in  number,  namely :  (1)  The  great  or  gastro- 
colic omentum,  which  hangs  down  like  an  apron  from  the  great  curvature  of 
the  stomach,  and  passes  to  the  transverse  colon,  connecting  this  latter,  very  loosely. 


Ascending  colon 


Descending  colon 


Fig.  742. — Diagrammatic  Transverse  Sections  of  Abdomen,  to  slaow  the 
peritoneiun  on  trausverse  tracing.  A,  at  level  of  foramen  of  Winslow  ; 
B,  lower  down.  In  A  note,  one  of  the  vasa  brevia  arteries  passing  to 
the  stomach  between  the  layers  of  the  gastro-spleuic  omentum,  and  also 
the  foramen  of  Winslow  leading  into  the  lesser  sac  which  lies  liehind  the 
stomach. 


1050 


THE  DIGESTIVE  SYSTEM. 


however,  to  the  stomach 

Fundus 


Superior  or 
parietal  surface 


Antrum  pylori 


(2)  the  lesser  or  gastro-hepatic  omentum,  which  extends 
from  the  lesser  curvature  of  the 
stomach  to  the  hver ;  and  (3)  the 
^<xs?^ro-s23^ewicomew^Mm,  which  passes 
from  the  stomach  to  the  spleen. 

(&)  Mesenteries  are  folds  of  peri- 
toneum which  unite  portions  of  the 
intestine  to  the  posterior  abdominal 
wall,  and  convey  to  them  their 
vessels  and  nerves.  There  are 
several  mesenteries,  e.g.,  the  mesen- 
tery jprofer,  which  connects  the 
jejunum  and  ileum  to  the  posterior 
abdominal  wall,  \h<d  transverse  meso- 
colon, the  pelvic  (or  "siginoid") 
mesocolon,  and  occasionally  others. 

(c)  Ligaments  are  peritoneal  folds 
which  pass  between  abdominal 
viscera  other  than  portions  of  the 
digestive  tube,  or  connect  them  to 
the  abdominal  wall.  As  examples 
of  these  may  be  mentioned  most  of 
the  ligaments  of  the  liver,  the  so- 
called  "  false  ligaments "  of  the 
bladder,  and  the  broad  ligaments 
of  the  uterus. 

This  term  is  also  applied  to  several 
small  folds  which  connect  portions  of 
the  intestinal  tube  to  the  parietes,  but 
do  not  convey  to  them  their  vessels 
and  nerves.  The  gastro- phrenic  and 
phreno-colic  ligaments  are  examples  of 
these. 

THE   STOMACH. 

The  stomach  (ventriculus)  is  the 
large  dilatation  found  on  the  diges- 
tive tube  immediately  after  it  enters 
the  abdomen  (Figs.  743  and  744). 
It  constitutes  a  receptacle  in  which 
the  food  accumulates  after  its  pass- 
age through  the  oesophagus,  and  in 
it  take  place  some  of  the  earlier 
processes  of  digestion,  resulting  in 
the  conversion  of  the  food  into  a 
viscid  soup-like  mixture,  known  as 
chyme.  The  chyme  as  it  is  formed 
is  allowed  to  escape  intermittently 
through  the  pylorus,  into  the  small 
intestine,  where  the  digestive  pro- 
cesses are  continued. 

Although  tb  e  form  of  the  stomach 
varies  considerably  under  different 
conditions,  in  general  it  is  of  an 
irregularly  pyriform  shape,  with  a 
wide  or  cardiac  end  directed  back- 
wards and  to  the  left,  and  a  narrow 
pyloric  end  which  runs  to  the  right  to  join  the  duodenum.  In  addition  to  (a) 
its   two  ends,  the  stomach  presents  for  examination  the  following  parts :  (h)  two 


Great 
omentum  (cut) 

Cardia 

Gastro-phrenie 
ligament 

Gastro-splenic 
omentum  (cut) 

Uncovered  area 

Superior  or 
parietal  surface 

Inferior  or 
visceral  surface 

Lesser 
omentum  (cut)' 

Pylorus 


Superior  or 
parietal  surface 


Great 
omentum  (cut) 


Inferior  or 
visceral  surface 


Fig.  743. — Modekatei.i  L»i^.texued  Stomach,  viewed,  A, 
from  front ;  B,  from  inuer  or  right  side  ;  and  C,  from 
the  outer  or  left  side.  (From  pliotographs  of  the 
stomach  shown  in  Fig.s.  739  and  744.  The  contents  of  the 
stomach  were  carefully  removed  through  an  artificial 
opening,  and  replaced  with  gelatine,  the  stomach  remain- 
ing ill  situ  throughout  the  operation.  After  the  jelly 
hardened,  its  exact  orientation  was  carefully  noted,  and 
pins  indicating  the  vertical,  horizontal,  and  transverse 
j)lanes  having  been  inserted,  the  organ  was  removed 
and  photographed.) 


THE  STOMACH. 


1051 


curvatures,  greater  and  lesser,  separating  (c)  hvo  surfaces,  superior  and  inferior ; 
and  (d)  two  orifices,  the  oesophageal  orifice  or  cardia,  and  the  pyloric  orifice  or 
pylorus  (Fig.  743). 

Position  and  Form  of  the  Stomach. —  When  empty,  or  nearly  so,  the  stomach 
lies  in  the  left  hypochondrium  and  left  part  of  the  epigastrium,  with  its  wide  end 
or  fundus  directed  backwards  towards  the  diaphragm,  its  long  axis  lying  almost 
in  a  horizontal  plane,  and  its  pyloric  portion  running  to  the  right  to  join  the 
duodenum.  In  this  state  the  whole  organ  is  narrow  and  attenuated,  particularly 
the  pyloric  portion,  which  is  contracted,  and  resembles  a  piece  of  thick-walled  small 
intestine. 

When  distended,  the  organ  assumes  the  form  of  an  irregular  pear,  and  both 


stomach 


Attacliment  of 
faleifonn  ligament 


Hepatic  flexurp 


T^i\ Splenic  flexur 


Spleen  (anterior 
angle) 


Transverse  mesocolon, 
with  stoniacli  resting 
on  it 


Apex  of  vermifi>rni 
appendix 

Terminal  part  of  ileum 


Caecum 


Tenninal  part  of 
luodenuni 


Descending  colon 
Root  of  mesentery  (cut) 


Pelvic  (sigmoid) 
niesocolou 


Pelvic  colon  (sigmoid 
flexure) 


SCALE  IN  INCHES 


SCALE  IN  CENTIMETRES 


Fk;.  744. — Thc  ABDO^[I.VAL  Viscera  after  the  Removal  of  the  Jejunum  and  Ileum  (from  a  photograph 
of  the  same  body  as  Fig.  739).  The  transverse'colon  is  much  more  regular  than  usual.  Both  the  liver 
and  ciecum  extend  lower  down  than  normal.  The  subdivisions  of  the  abdominal  cavity  are  indicated 
by  dark  lines.  ~ 

the  (Cardiac  and  pyloric  portions  become  full  and  rounded  (Fig.  743).  It  still  lies 
within  the  hypochondriac  and  epigastric  regions ;  but  in  extreme  distension,  or  in 
exceptional  cases,  it  may  pass  down  below  the  subcostal  plane  and  reach  into  the 
umbilical  and  left  lumbar  regions.  As  a  result  of  the  general  increase  in  length 
which  takes  place  during  distension,  the  pylorus  is  moved  a  variable  distance  to 
the  right  beneath  the  quadrate  lobe  of  the  Hver,  and  at  the  same  time  the  long 
axis  of  the  whole  organ  becomes  much  more  oblique,  running  forwards,  downwards, 
and  to  the  right.  Finally  there  is  developed  a  special  dilatation  of  the  pyloric 
portion,  known  as  the  antrum  pylori,  which  in  extreme  distension  is  carried  so  far 
to  the  right  that  it  may  even  reach  into  the  hypochondrium. 

In  brief,  it  may  be  said  that  the  stomach  when  empty  is  contracted,  not 
collapsed ;  that  it  assumes  a  narrow,  attenuated  shape,  its  cavity  being  practically 
obliterated,  and  its  pyloric  portion  contracted  to  the  size  of  small  intestine ;  and  in 


1052  THE  DIGESTIVE  SYSTEM. 

addition,  that  its  long  axis  lies  in  an  almost  horizontal  plane.  With  distension 
there  comes  a  general  enlargement  of  the  various  diameters,  an  elongation  of  the 
whole  organ,  with  a  consequent  passage  of  its  pyloric  portion  to  the  right  beneath 
the  liver,  the  development  of  the  antrum  pylori,  and  an  inclination  of  its  axis  from 
behind  downwards  and  forwards,  without  any  rotation. 

Natural  Form  of  the  Stomach. — As  seen  in  male  bodies  the  viscera  of  wliicli  liave  been 
liai'dened  by  the  intravascular  injection  of  formalin,  the  empty  stomach,  as  already  stated,  j^resents 
an  attenuated  or  slender  pear-shaped  appearance,  and  is  sharply  bent  on  itself,  particularly  at 
the  junction  of  the  cardiac  and  pyloric  portions.  As  a  rule  it  is  somewhat  flattened  from  above 
downwards  in  its  cardiac  portion,  but  preserves  in  its  whole  length,  more  or  less,  an  irregularly 
rounded  or  cylindrical  form.  Its  long  axis  is  directed,  in  the  cardiac  portion,  from  behind 
forwards  and  to  the  right  with  a  slight  inclination  downwai'ds  ;  then  it  bends  almost  at  a  right 
angle,  and  in  the  pyloric  portion  runs  to  the  right  towards  the  pylorus. 

Even  in  the  empty  condition,  the  cardiac  portion  retains,  as  a  rule,  an  appearance  of 
rotundity,  and  never  assumes  a  completely  collapsed  and  flattened  form  ;  although  it  sometimes 
is  very  much  contracted,  and  aj)j) roaches  the  tubular  form  of  the  pyloric  portion. 

The  collapsed,  flat-walled,  and  flaccid  bag,  often  pictured  as  the  empty  stomach,  does  not 
represent  its  true  condition  during  life,  but  is  rather  the  result  of  i^ost-mortem  softening,  re- 
laxation, and  pressure.  The  stomach,  like  the  bladder,  and  like  other  hollow  viscera  with 
muscular  walls,  is  not  an  inert  bag,  but  an  extensile  living  organ  capable  of  exjjansion  and 
contraction,  which  adapts  the  size  of  its  cavity  to  the  amount  of  its  contents.  When  food  enters, 
it  expands,  the  expansion  being  proportionate  to  the  amount  of  food  that  enters  ;  and  when  the 
food  passes  away  or  is  absorbed,  it  contracts,  until  its  cavity  is  reduced  to  little  more  than  a 
stellate  lumen. 

In  the  gradual  passage  of  the  stomach  from  the  empty  to  the  distended  condition  we  may 
recognise  three  stages.  First  stage. — This  commences  with  an  enlargement  of  the  fundus,  and  is 
followed  by  an  expansion  of  the  whole  cardiac  portion,  which  passes  upwards  and  also  to  the 
left  towards  the  diaphragm,  displacing  the  coils  of  the  transverse  colon,  which  lie  here  when 
the  stomach  is  empty.  The  pyloric  portion  for  3  or  4  inches  still  remains  contracted  and 
cylindrical.  In  this  condition  the  stomach  is  frequently  found  after  death.  Second  stage. — As 
distension  goes  on  the  lesser  curvature  opens  out,  the  pyloric  portion  (with  the  exception  of  its 
last  inch)  expands,  but  its  junction  with  the  cardiac  portion  usually  remains  distinct,  until  disten- 
sion is  almost  complete.  TJiird  stage. — A  further  general  expansion  of  the  whole  stomach  takes 
place  ;  the  diameters  of  both  cardiac  and  pyloric  j)ortions,  as  well  as  the  length  of  the  organ,  are 
increased  ;  and  the  great  curvature  presses  forwards  against  the  anterior  abdominal  wall  in  front, 
where  the  restraining  influence  of  the  ribs  is  absent.  The  pyloric  end  for  about  1  inch  (2-5  cm.) 
from  the  pylorus  remains  narrow  (constituting  the  pyloric  canal  of  Jonnesco),  but  to  the  left  of 
this  it  bulges  forward,  forming  the  antrum  pylori,  which  is  most  distinct  at  the  great  curvature. 
By  the  increase  of  the  organ  in  length  the  antrum  is  carried  a  considerable  distance  to  the  right 
beneath  the  liver — even  further  than  the  pylorus  itself — so  that  the  terminal  part  of  the  stomach 
is  bent  backwards  and  to  the  left,  in  order  to  reach  the  pylorus,  which  latter  very  rarely  passes 
more  than  one  and  a  half  or  two  inches  to  the  right  of  its  normal  position,  namely,  in  the  empty 
condition,  within  half-an-inch  (12  mm.)  of  the  middle  line.  Finally,  as  it  fills,  the  stomach 
becomes  gradually  more  oblique,  so  that  in  the  distended  state  the  long  axis  of  the  posterior 
two-thirds  of  the  organ  is  directed  forwards,  downwards,  and  to  the  right,  and  forms  an  angle 
of  about  40"  to  45"  with  both  the  horizontal  and  sagittal  planes  (Fig.  743),  whilst  its  anterior 
third  is  still  more  oblique. 

There  is,  however  (as  pointed  out  by  Jonnesco),  no  distinct  rotation  of  the  organ  on  its  long 
axis — no  turning  of  the  great  curvature  more  forwards,  nor  of  the  so-called  anterior  surface  more 
upwards. 

In  the  change  from  the  distended  to  the  empty  state  these  stages  are  reversed ;  the  whole 
stomach  is  contracted,  or  drawn  in,  from  all  directions  towards  the  lesser  curvature  ;  this  latter 
is  bent  upon  itself  to  an  acute  angle,  and  the  long  axis  of  the  organ,  becoming  less  oblique, 
aj)proaches  the  horizontal. 

Although  this  description  of  the  shape  and  direction  of  the  stomach  is  at  variance  with  the 
generally  accej)ted  accounts,  it  is  Ijased  upon  tlie  examination  of  a  considerable  number  of 
specially-hardened  bodies,  and  has  been  found  to  apply  .so  generally,  that  it  is  advanced  here  as 
the  condition  most  frequently  found  in  the  male  immediately  after  death,  and  as,  in  all  probability, 
giving  a  near  approximation  to  the  conditions  present  during  life.  It  must,  however,  be 
admitted  that,  in  the  female,  as  a  result  of  tight  lacing,  the  stomach  is  often  found  to  assume 
an  abnormal  vertical  position  ;  Init  this  condition  is  associated  with  displacement  of  other 
abdominal  organs  in  the  neighbourhood,  and  cannot  be  looked  upon  as  normal. 

[In  the  present  edition  it  has  Ijcen  tliought  riglit  to  leave  the  above  description  of  the  stomach 
as  it  was  originally  written  by  Professor  Birmingliam.  Subsequtait  investigation  has  served  to 
show  the  accuracy  of  his  views  in  so  far  as  the  various  stomach  forms  which  he  describes  are  con- 
cerned, and  the  sliape  which  he  ascribes  to  tlie  empty  condition  of  the  organ,  and  which  he  was 
the  first  to  describe  has  been  proved  beyond  dispute  to  be  frequently  met  with  in  properly 
prepared  subjects.  The  question,  however,  which  is  being  at  present  discussed  is  whether  this 
stomach-form,  in  which  the  cardiac  part  forms  a  more  oi'  less  cajtacious  sac,  and  the  pyloric  part 
is  tubidar  and  thick-walled,  is  not  rather  to  be  associated  witli  a  particular  stage  in  the  digestive 
act.     From  investigations  on  the  cat  by  means  of  RiJntgen  rays,  Cannon  has  sliown  tliat  during 


THE  STOMACH. 


1053 


digestion  tlie  stomacli  becoiiifs  divided  into  a  cardiac  saccular  reservoir  in  wliich  no  peristaltic 
movement  can  be  detected,  and  a  long  tnbular  jjyloric  portion  along  which  successive  constriction 
waves  are  seen  to  be  constantly  passing.  In  the  latter  the  food  is  tritui'ated  and  mixed  with  the 
gastric  juices,  and  when  fully  prei)ai'ed  it  is  sepiirted  at  irri^gular  intervals  through  the  pyloric 
orifice  into  the  duodenum. — Ed.] 

Size  and  Capacity  of  the  Stomach. — Probably  no  organ  in  the  body  varies  more 
in  size  within  the  limits  of  health  than  the  stomach.  Moreover,  as  its  tissues  change  so 
rapidly  after  death,  measurements  made  on  softened  and  relaxed  organs  are  not  only 
worthless  but  quite  misleading.  Consequently  it  is  difficult,  perhaps  impossible,  to  arrive 
at  a  correct  estimate  of  its  size  and  capacity. 

The  length  of  the  stomach  in  the  fully  distended  condition  is  about  10  to  11  inches 
(25  to  27'5  cm.),  and.  its  greatest  diameter  not  more  than  4  to  4 J-  inches  (10  to  11-2  cm.) ; 
whilst  its  capacity  in  the  average  state  rarely  exceeds  40  ounces,  or  1  quart. 

The  length  has  been  estimated  by  different  authorities  at  from  10  to  13i  inches  (26  to  34 
cm.) ;  its  diameter,  from  3j  to  6  inches  (8  to  15  cm.)  ;  and  its  cajjacity  from  l|  to  5  pints.  The 
measurements  of  the  capacity  given  by  Dr.  Sidney  Martin  are  j^robably  the  most  accurate  :  he 
states  that  the  capacity  varies  between  9  and  59  oz.,  with  an  average  of  from  35  to  40,  or  a  little 
over  a  litre. 

The  distance  in  a  direct  line  from  the  cardiac  to  the  pyloric  orifice  varies  from  3  to  5  inches 
(7*5  to  12-5  cm.),  and  that  from  the  cardia  to  the  summit  of  the  fundus  from  2^  to  4  inches 
(6-2  to  10-0  cm.). 

As  regards  the  loeight,  1  have  found  the  average  of  twelve  wet  specimens  freed  from  their 
omenta  to  be  4|  oz.  (135  grms.),  with  a  maximum  of  7  oz.  (198-45  grms.)  and  a  minimum  of 
3^  oz.  (99 "22  grms.).     Glendenning  gives  the  weight  as  4^  ounces. 

Relations  and  Connexions  of  the  Stomach. — The  relations  will  be  much 
more  readily  understood  if  we  briefly  consider  the  disposition  of  the  portion  of 
the  abdominal  cavity  in  which  the  stomach  lies,  a  portion  which  has  such  con- 
stant and  definite  surrovmdings  that  it  perhaps  merits  the  title  of  "  stomach 
chamber." 

The  stomachi  chamber  (Figs.  745  and  746)  is  a  space  in  the  upper  and  left  jjortion  of  the 
abdominal  cavity  which  is 
comjjletely  occupied  by  the 
stomach  when  that  organ  is 
distended,  but  into  which  the 
transverse  colon  also  j^asses, 
doubling  up  over  the  stomach, 
when  tliis  latter  is  empty. 

The  chamber  presents  an 
arched  roof,  an  irregularly 
slojjing  floor,  and  an  anterior 
wall.  The  '  roof  is  formed 
partly  by  the  visceral  surface 
of  the  left  lobe  of  the  liver, 
and  in  the  rest  of  its  extent 
by  the  left  cupola  of  the 
diaphragm,  which  arches 
gradually  downwards  behind 
and  on  the  left  to  meet  the 
floor. 

The  floor  or  '■'■stomach  bed  " 
(Fig.  745)  is  a  sloping  shelf 
on  which  the  under  surface 
of  the  stomach  rests,  and  by 
which  it  is  supported.  The 
bed  is  formed  Ijehind  by  the 
top  of  the  left  kidney  (with 

its  suprarenal  capsule)  and  the  gastric  surface  of  the  spleen  ;  in  front  of  this,  by  the  wide 
upper  surface  of  the  pancreas  ;  and  more  anteriorly  still,  by  the  transverse  mesocolon  running 
forwards  above  the  small  intestine,  from  the  anterior  edge  of  the  pancreas  to  the  colon  (Fig. 
745),  •which  latter  completes  the  floor  anteriorly. 

Finally,  the  anterior  wall  of  the  stomach  chamber  is  formed  by  the  abdominal  wall,  between 
the  ribs  on  the  left  and  the  liver  on  the  right  side. 

This  chamber  is  completely  filled  by  the  stomach,  when  that  organ  is  distended.  When,  on 
the  other  hand,  the  stomach  is  empty  and  contracted,  it  still  rests  on  the  floor,  or  stomach  bed, 
but  occupies  only  the  lower  portion  of  the  chamber,  whilst  the  rest  of  the  space  is  filled  by  the 
transverse  colon,  which  turns  gradually  ujjwards  as  the  stomach  retracts,  and  finally  comes  to 
lie  both  above  and  in  front  of  that  organ  and  immediately  beneath  the  diaphragm — a  fact  to  be 
remembered  in  clinical  examinations  of  this  region. 


Gall-bladder 


Liver 


Duodenum 


Fig.  745. — The  Stomach  Chamber  and  Stomach  Bed. 

From  the  same  body  as  the  preceding  figure,  after  the  stomach  had  been 
removed. 


1054 


THE  DIGESTIVE  SYSTEM. 


The  upper  (or  parietal)  surface  of  the  stomach  is  more  convex  and  more  extensive 
than  the  lower.  It  lies,  when  the  organ  is  distended,  in  contact  with  the  roof  and 
anterior  wall  of  the  stomach  chamber,  and  thus  comes  into  relation  with  the  under 
surface  of  the  left  lobe  of  the  liver  on  the  right,  the  vault  of  the  diaphragm  on  the 
left,  and  the  anterior  abdominal  wall  in  front  (Fig.  739).     When  the  stomach  is 


Fossa  for  Spigelian  lobe 
Right  phrenic  vessels 

Vena  cava 
Hepatic  vein     , 
Hepatic  artery 
Portal  vein 
Pylorub 

Bile  duct 


Oesophagus 

Coronary  artery 
Diaphragm 


Left  suprarenal  body 
Splenic  artery 
Kidney 


Right  suprarenal  body 


Upper  surface  of  pancreas 
Gastric  surface  of  spleen 


nder  surface 
^  of  pancreas 
^Attachment  of 

transverse 

mesocolon 

Duodeno- 
ejunal  flexure 
Gastro-rtuodenal 
artery  and  neck 
of  pancreas 
Superior  mesen- 
teric artery 

Duodenum 


Spermatic  vein 

Ureter  - 

Right  common  iliac 
vein ' 

Right  common  iliac 
artery 
Left  common  iliac 
vein 


Colon 


Flo.  746. — The  Viscera  and  Vessels  on  the  Posterior  Abdominal  Wall. 

The  stomach,  liver,  and  most  of  the  intestines  have  been  removed.  Tlie  peritoneum  has  been  preserved  on  the 
right  kidney,  and  also  the  fossa  for  the  Spigelian  lobe.  In  taking  out  the  liver,  the  vena  cava  was  left 
behind.     The  stomach  bed  is  well  shown.     (From  a  body  hardened  by  chromic  acid  injections.) 

empty,  on  the  other  hand,  the  transverse  colon,  as  just  explained,  doubles  up  over 
it,  and  separates  this  surface  from  the  roof  of  the  chamber. 

The  lower  (or  visceral)  surface,  more  flattened  than  the  upper,  rests  upon  the 
stomach  bed,  and  comes  into  relation  with  the  following  parts : — Behind,  at  the 
fundus,  with  the  diaphragm  and  gastric  surface  of  the  spleen  ;  in  front  of  this  with 


THE  STOMACH.  1055 

the  left  kidney,  the  suprarenal,  and  the  upper  surface  of  the  pancreas,  and,  more 
anteriorly  still,  with  the  transverse  mesocolon  and  colon.  From  all  of  these  the 
stomach  is  separated  by  the  small  sac  of  the  peritoneum  (the  anterior  layer  of 
which  clothes  this  surface),  except  below  and  to  the  left  of  the  cardia,  where  the 
peritoneum  is  absent,  over  an  irregularly  triangular  area  (Fig.  743),  and  here  the 
stomach  lies  in  direct  contact  with  the  diaphragm  (sometimes  also  with  the  top  of 
the  left  kidney  and  suprarenal  capsule). 

It  should  be  pointed  out  that  the  under  surface  of  the  stomach  is  separated  from  the 
duodeno-jejunal  flexure  and  the  beginning  of  the  jejunum  by  the  transverse  mesocolon  only.  By 
cutting  through  this,  the  surgeon  is  enabled  to  bring  the  stomach  and  duodenum  together  in  the 
operation  of  gastro-intestinal  anastomosis. 

The  cardiac  end  or  fundus  (fundus  ventricnli)  is,  in  the  distended  condition,  a 
large  rounded  cul-de-sac,  which  projects  backwards  and  upwards  against  the  left 
cupola  of  the  diaphragm ;  opposite  the  oesophageal  orifice  it  passes  into  the  body 
of  the  stomach.  Its  surfaces  are  merely  prolongations  of  the  upper  and  lower 
surfaces  of  the  organ,  and  accordingly  its  relations  are  similar. 

Thus  the  upper  surface  lies  against  the  left  cupola  of  the  diaphragm  (and  occasionally  the 
left  lobe  of  the  liver,  when  this  extends  further  than  usual  to  the  side) ;  whilst  the  lower  surface 
rests  chiefly  on  the  gastric  surface  of  the  spleen,  and  also  on  the  left  kidney. 

The  highest  part  of  the  fundus  reaches  to  the  level  of  a  point  on  the  chest  wall  about  half-an- 
inch  (12  mm.)  internal  to  the  apex  point  of  the  heart. 

The  narrow  or  pyloric  end,  when  the  stomach  is  empty,  is  contracted  and 
cylindrical,  and  runs  transversely  to  the  right,  lying  as  a  rule  beneath  the  left  lobe 
of  the  liver.  During  distension  it  is  carried  to  the  right  beneath  the  quadrate  lobe, 
and  its  terminal  part  is  there  directed  backwards  in  order  to  reach  the  duodenum. 
Even  in  this  condition  its  last  inch  remains  comparatively  undistended. 

The  lesser  curvature  (curvatura  ventriculi  minor)  is  directed  towards  the  liver, 
and  corresponds  to  the  line  along  which  the  lesser  omentum  is  attached  to  the 
stomach,  between  the  pyloric  and  oesophageal  orifices  (Fig.  743).  It  is  connected 
to  the  liver  by  the  lesser  omentum,  between  the  layers  of  which  the  gastric  and 
pyloric  vessels  run  along  the  curvature. 

This  curvature,  when  the  stomach  is  empty,  presents  a  sharp  bend  at  the  junction  of  the 
cardiac  and  pyloric  portions,  but  when  fully  distended  it  forms  an  open  curve  except  near  its 
pyloric  end,  where  it  becomes  convex,  corresponding  to  the  S-shaped  form  of  this  portion  of  the 
organ  (see  below).  On  viewing  a  distended  stomach  from  the  right  side  (Fig.  743,  B),  it  will  be 
observed  that  the  line  of  the  lesser  curvature  turns  slightly  on  to  the  upper  asj^ect  in  order  to 
reach  the  cardia,  which  is  situated  rather  on  the  upper  surface  than  on  the  border  of  the  stomach. 

The  great  curvature  (curvatura  ventriculi  major),  which  is  usually  over  three 
times  as  long  as  the  lesser  curvature,  corresponds  to  a  line  drawn  from,  the  cardia 
over  the  summit  of  the  fundus  (Fig.  743),  and  then  along  the  line  of  attachment 
of  the  great  omentum  as  far  as  the  pylorus.  In  general,  it  is  directed  to  the  left 
and  forwards,  but  at  its  beginning,  near  the  cardia,  it  of  course  looks  in  the 
opposite  direction.  The  great  curvature  corresponds  in  the  greater  part  of  its 
length  to  the  attachment  of  the  great  omentum ;  and  in  close  relation  to  it,  but 
between  the  layers  of  the  omentum,  run  the  right  and  left  gastro-epiploic  vessels. 

Antrum  Pylori — This  is  a  prominence  of  the  great  curvature  in  the  distended  stomach,  situated 
a  short  distance  from  the  pylorus.  When  the  stomach  is  distended,  the  pyloric  portion,  near  its 
right  extremity,  becomes  curved  somewhat  like  the  letter  S  placed  horizontally.  The  first  curve  of 
the  S  is  convex  downiwards  and  forwards,  and  this  becoming  more  prominent  with  distension, 
forms  a  projection  of  the  great  curvature  known  as  the  antrum  pylori.  The  terminal  part  of  the 
S  extends  to  the  pylorus  ;  it  is  about  one  inch  (2'5  cm.)  in  length,  and  it  ajjpears  never  to  become 
distended  to  any  noticeable  extent.  This  latter  is  the  part  described  by  Jonnesco  as  the  pyloric 
canal. 

The  terms  cardiac  and  pyloric  portions  are  often  employed  to  indicate  the  wider  and  narrower 
portions  of  the  stomach  respectively.  The  cardiac  portion  includes  about  two-thirds  of  the 
length  of  the  whole  organ ;  the  pyloric  portion  the  remaining  third.  Except  in  complete  dis- 
tension, the  junction  of  the  two  is  usually  indicated  by  a  slight  constriction,  and  occasionally 
there  is  a  thickening  of  the  muscular  fibres  (apparently  those  of  the  oblique  layer),  corresponding 
in  part  to  the  constriction. 

The  oesophageal  orifice  or  cardia  is  the  aperture  at  which  the  gullet  opens  into  the 


1056 


THE  DIGESTIVE  SYSTEM. 


stomach.  It  is  situated  at  the  upper  end  of  the  lesser  curvature,  to  the  right  of  the 
fundus,  and  nearer  the  upper  than  the  lower  surface  of  the  stomach  (Fig.  743,  B). 
The  cardia  is  very  deeply  placed,  and  lies  about  four  inches  behind  the  sternal  end 
of  the  seventh  left  costal  cartilage,  at  a  point  one  inch  from  its  junction  with  the 
sternum.     Posteriorly  it  corresponds  to  the  level  of  the  eleventh  dorsal  vertebra. 

Owing  to  the  fixation  of  the  oesophagus  by  its  passage  through  the  diaphragm,  and  the  close 
connexion  between  the  stomach  and  the  diaphragm,  near  the  cardia  where  the  peritoneum  is 
absent,  this  is  the  most  fixed  part  of  the  whole  organ.  The  object  of  this  immobility  is 
evidently  to  maintain  a  clear  passage  for  the  food  entering  the  stomach.  The  orifice  is  oval 
rather  than  round,  with  its  long  axis  very  oblique ;  and  although  the  presence  of  a  valvular 
arrangement  at  the  cardia  has  been  advocated  by  several  authorities,  it  is  difficult  to  find  satis- 
factory proof  of  its  existence  in  hardened  bodies.  It  seems  more  probable,  on  the  whole,  that 
no  such  arrangement  naturally  exists  here.  On  the  other  hand,  the  muscular  margins  of  the 
(Esophageal  opening  in  the  diaphragm,  and  the  circular  fibres  of  the  lower  end  of  the  CESophagus, 
which  are  particularly  well  developed,  aftord,  by  their  simultaneous  contraction,  an  effective 
means  of  closing  the  cEsoj)hagus  immediately  above  the  cardia,  and  thus  of  preventing  regurgita- 
tion of  the  contents  of  the  stomach. 

The  pyloric  orifice  or  pylorus  is  the  aperture  through  which  the  stomach  com- 
municates with  the  duodenum.  It  is  marked  on  the  surface  by  a  slight  constriction, 
most  evident  at  the  curvatures ;  and  in  the  interior  by  a  prominent  thickening  of 
the  wall — the  pyloric  valve  (valvula  pylori) — produced  by  a  special  development  of 


Pyloric  sphincter 
Longitudinal  muscular  coat 


Circular  muscle 
fibres  of  the  duodenum 

Briinner's  glands 


Longitudinal  muscular  coat 
(duodenum) 


iliicous  membrane 
ol'  the  duodenum 


Duodenum 


Submucous 
coat 


Pyloric  canal  ;  I  i  •  I 

Longitudinal  muscular  coat        I  ]  I  ' 

Mucous  coat        i  i  1 

Pyloric  spliincter        !  ' 

Pyloric  orifice    i 

Briinner's  glands 

Fio.  747.— Longitudinal  Section  through  the  Pyloric  Canal  akd  Commencement  of  the 
Duodenum  in  a  New-born  Child.     (From  Stiles.) 

the  circular  muscular  fibres,  known  as  the  pyloric  sphincter  (musculus  sphincter 
pylori).  When  examined  post-mortem  in  the  ordinary  way,  the  aperture,  viewed 
from  the  duodenal  side,  is  somewhat  oval  in  form,  and  closely  resembles  the  external 
OS  uteri  (Cunningham).  When  seen  from  the  opposite  side,  it  presents  an  irregular 
or  stellate  appearance,  owing  to  the  fact  that  the  rugse  of  the  gastric  mucous 
membrane  are  continued  up  to  the  orifice. 

The  pylorus  rests  on  the  neck  of  the  pancreas  below  and  behind,  and  is  over- 
lapped by  the  liver  above  and  in  front.  Its  average  position  can  be  marked  on  the 
surface  of  the  body  by  tbe  intersection  of  two  lines ;  one  drawn  horizontally  half- 
way between  the  top  of  the  sternum  and  the  pubic  crest  (Addison),  the  other  drawn 
vertically  a  little  way  (^  inch,  12  mm.)  to  the  right  of  the  middle  line. 

During  the  earlier  stages  of  gastric  dig(;stion  the  sphincter  pylori  is  strongly  contracted 
and  the  aperture  firmly  closed,  but  it  opens  intermittently  to  allow  of  the  passage  of  properly 
digested  x^ortions  of  the  food.  As  digestion  advances  the  sphincter  probably  relaxes  somewhat ; 
but  in  hardened  bodies  a  really  patent  pylorus  is  rarely  or  never  found,  which  would  seem  to 


THE  STOMACH. 


1057 


indicate  that  the  pyloriis  is  normally  closed,  or  nearly  so,  and  that  its  opening  is  an  active  rather 
than  a  passive  condition,  as  in  the  case  of  the  anal  canal. 

As  regards  its  size,  the  pylorus  is  stated  to  be  about  i  inch  (12-5  mm.)  in  diameter,  but  there 
is  no  doubt  that  this  represents  neither  its  full  size  nor'  the  calibre  of  the  valve  when  at  rest. 
Foreign  bodies  with  a  diameter  of  ^ 
to  1  inch  have  been  kno^Ti  to  pass 
through  the  pylorus  without  giving 
rise  to  trouble,  even  in  children.  On 
the  other  hand,  when  at  rest,  with  an 
empty  stomach  and  duodenum,  the 
aperture,  as  seen  in  formalin-hardened 
bodies,  is  practically  clo.sed,  and  pre- 
sents a  stellate  or  purse-mouth  appear- 
ance, viewed  from  either  asjject.  In 
hardened  bodies  with  distended  stomach 
and  duodenum,  the  aperture,  which  is 
somewhat  oval,  is  practically  closed,  and 
from  the  duodenal  side  resembles,  as 
Cunningham  has  shown,  the  external 
OS  uteri.  But  both  in  the  empty  and 
the  distended  condition  of  the  stomach 
the  pylorus  seems  to  be  rather  a  tubular 
narrowing,  extending  over  at  least  h  to 
1  inch  of  the  canal,  than  a  sudden  con- 
striction. 

"When  the  stomach  is  empty  the 
pylorus  is  iisually  placed  near  {i.e. 
within  h  inch,  12  mm.  of)  the  middle 
line,  beneath  the  left  or  sometimes  the 
quadrate  lobe  of  the  liver,  and  at  the 
level  of  the  first  lumbar  vertebra,  or 
the  disc  between  this  and  the  second 
lumbar.  During  distension  it  is  pushed 
over  beneath  the  quadrate  lobe  for  a 
variable  distance,  but  very  rarely  more 
than  1^  or  2  inches  to  the  right  of  the 
middle  line  ;  and  its  orifice,  instead 
of  looking  towards   the   right,  is   then  The   liver  is   much  enlarged,  and   extends  on   the   left  side   to 


SCALE   IN  INCHES 


SCALE   IN  CENTIMETRES 


Fig.   748.- 


-Abdomen  of  Female,  showing  Displacements 

RESULTING    FROM    TiGHT    LaCING. 


the  ribs,  where  it  was  folded  back  on  itself  for  over  an 
inch.  The  pyloric  end  of  the  stomach  and  the  beginning 
of  the  duodenum  are  quite  superficial  below  the  liver,  and 
all  the  viscera  are  displaced  downwards.  (From  a  photo- 
graph of  a  body  hardened  by  injections  of  formalin.) 


directed  backwards,  for,  as  already  ex- 
plained, the  antrum  in  distension  is 
carried  to  the  right  in  front  of  the 
pylorus,  or  even  beyond  it. 

Peritoneal  Relations.  —  The 
stomach  is  almost  completely  covered  by  peritoneum — the  anterior  surface  being 
clothed  by  the  posterior  layer  of  the  great  sac,  and  the  posterior  surface  by  the 
anterior  layer  of  the  small  sac.  From  the  lesser  curvature  the  lesser  omentum 
extends  to  the  liver,  whilst  from  the  great  curvature  the  great  omentum  passes 
down  to  the  transverse  colon.  Higher  up  still,  on  the  left,  the  continuation  of  the 
great  omentum,  namely,  the  gastro-splenic  omentum,  passes  off  (from  the  inferior 
surface,  a  little  below  the  great  curvature)  to  the  spleen.  Finally,  a  small  peri- 
toneal fold,  known  as  the  gastro-phrenic  ligament,  is  found  running  from  the 
stomach  up  to  the  diaphragm  along  the  left  side  of  the  oesophagus. 

A  small,  irregularly  triangular,  area  (Fig.  744),  about  2  inches  wide  and  \\  inches  from  above 
downwards,  during  moderate  distension  of  the  stomach,  on  the  inferior  surface  below  and  to  the 
left  of  the  cardia,  is  uncovered  by  peritoneum,  and  over  it  the  organ  is  in  direct  contact  with 
the  diaphragm,  occasionally  also  with  the  top  of  the  left  kidney  and  suprarenal.  From  the  left 
angle  of  this  "  uncovered  area  "  the  attachment  of  the  great  omentum  (gastro-splenic  part)  starts  ; 
and  at  the  right  angle  the  coronary  artery  passes  on  to  the  stomach. 

In  the  child  at  birth  the  stomach  is  scarcely  as  large  as  a  small  hen-egg,  and  its 
capacity  is  about  one  ounce  (28-3  grammes).  In  shape  it  coiTesponds  pretty  closely  to 
that  of  the  adult,  and  tlie  fundus  is  well  developed. 

In  the  female  (Fig.  748),  as  a  result  of  tight  lacing,  the  stomach  is  often  displaced 
ill  position  and  distorted  in  shape,  so  that  instead  of  running  obliquely  forwards,  down- 
wards, and  to  the  right,  it  is  placed  nearly  vertically  along  the  left  side  of  the  vertebral 
column,  in  which  direction  it  has  a  very  considerable  length.  Its  lower  part  bends  rather 
suddenly,  and  runs  upwards  and  to  the  right  to  join  the  pylorus,  which  is  often  placed 
quite  supei-ficiallv  below  the  liver.  As  a  result  of  the  displacement,  the  left  extremity  of  the 
71 


1058 


THE  DIGESTIVE  SYSTEM. 


pancreas  is  pushed  downwards  from  the  horizontal  until  it  almost  assumes  a  vertical  position. 
The  narrowing  and  inversion  of  the  lower  margin  of  the  thoracic  framework  at  the  same 
time  constricts  the  stomach  about  its  middle,  and  often  leads  to  a  bilocular  condition. 

Hour-glass  or  Bilocular  Stomach. — This  is  a  condition  of  the  organ,  by  no  means  rare, 
in  whicli  the  stomach  is  more  or  less  completely  separated  into  two  divisions — a  cardiac  and 
a  pyloric — the  normal  arrangement  in  certain  rodents  and  other  animals.  As  a  rule  the  former 
division  is  the  larger,  but  occasionally  the  two  are  nearly  equal,  or  the  pyloric  portion  may 
exceed  the  cardiac  in  size.  Sometimes  the  condition  is  temporary,  and  the  result  of  a  vigorous 
contraction  of  the  circular  muscular  fibres  at  the  seat  of  constriction.  In  other  cases  it  is  per- 
manent, and  may  be  due  to  cicatricial  contraction  after  gastric  ulcer,  or  to  some  other  pathological 
condition.  The  condition  is  more  frequent  in  the  female  than  the  male,  and  is  rarely  found  in 
the  foetus  or  child. 


Gland  moutlis 


Structuee  of  the  Stomach. 

The  stomach  wall  is  composed  of  four  coats — namely,  from  without  inwards  :  (1) 
peritoneal,  (2)  muscular,  (3)  submucous,  and  (4)  mucous  (Fig.  749). 

Peritoneal  or  Serous  Coat  (tunica  serosa).— This 
coat  is  formed  of  the  peritoneum,  the  relations  of 
which  to  the  stomach  have  already  been  described. 
It  is  closely  attached  to  the  subjacent  muscular 
coat,  except  near  the  curvatures,  where  the  con- 
nexion is  more  lax ;  and  it  confers  on  the  stomach 
its  smooth  and  glistening  appearance. 

Muscular  Coat. — The  muscular  coat,  which  is 
composed  of  unstriped  muscle,  is  thinnest  in  the 
fundus  and  body,  much  thicker  in  the  pyloric 
portion,  and  very  highly  developed  at  the  pylorus. 
It  is  made  up  of  three  incomplete  layers — an 
external  of  longitudinal,  a  middle  of  circular,  and  an 
internal  of  oblique  muscular  fibres. 

The  exteo'iial  layer  (stratum  longitudinale)  con 
sists  of  longitudinal  fibres,  continuous  with  those  of 
the  oesophagus,  on  the  one  hand,  and  those  of  the 
duodenum  on  the  other  (Fig.  750,  A).  They  are 
most  easily  demonstrated  on  the  lesser  curvature, 
where  they  can  be  traced  down  from  the  right  side 
of  the  oesophagus.  Over  the  great  curvature  and 
on  the  two  surfaces  they  are  present  as  an  extremely 
thin  and  irregular  sheet.  Towards  the  pylorus  the 
longitudinal  fibres  grow  much  thicker,  and  also 
Fig.  749.— Section  through  Wall  of  much  tougher  and  more  closely  united,  but  they 
^^«?.'f  ?V  ^^^^^f  ^omioTii  (slighbly  (Jq  ^q^  t^jjg  ^^^  j,^  ^l^g  formation  of  the  pyloric 

modified  from  Stohr).  ■, 

valve. 

A  .specially-condensed  band  of  these  can  be  often  made  out  both  on  the  front  and  back 
at  the  antrum  pylori,  the  form  of  which  is  said  to  be  due  to  their  presence.  These  bands  are 
known  as  the  pyloric  ligaments  (ligamenta  pylori). 

The  middle  layer  (stratum  circulare)  is  composed  mainly  of  circular  fibres,  continuous 
with  the  more  superficial  of  the  circular  fibres  at  the  lower  end  of  the  oesophagus  (Fig. 
750,  B).  They  do  not  commence  as  a  series  of  circular  bundles  surrounding  the  fundus, 
as  usually  described.  On  the  contrary,  they  begin  as  a  set  of  U-shaped  bundles  which 
loop  over  the  lesser  curvature  at  the  right  of  the  cardia,  and  pass  downwards  and  to  the 
left  on  both  surfaces.  Further  to  the  right  these  looped  fibres  are  succeeded  by  circles 
which  surround  the  organ  completely.  Traced  towards  the  narrow  end  of  the  stomach, 
the  circular  bundles  grow  thicker,  and  at  the  pylorus  they  undergo  a  further  increase, 
giving  rise  to  the  pyloric  sphincter  which  surrounds  the  orifice  as  a  thick  muscular  ring. 

On  the  gastric  side  the  pyloric  sphincter  jmsses  gradually  into  the  thick  circular  fibres 
of  the  pyloric  portion  of  the  stomach.  On  the  opposite  side  it  ceases  abruptly,  only  its 
outer  part  being  continued  into  the  circular  fibres  of  the  duodenum  (Fig.  751). 

The  intermd  layer  (fibrse  oblique)  is  composed  of  fibres  which  are  arranged  on  the 
fundus  and  adjacent  parts  of  the  stomach,  in  much  the  same  manner  as  those  of  the 
middle  layer  are  on  the  body  and  pyloric  portion  of  the  organ  (Fig.  750,  C).  Continuous 
above  with  the  deeper  circular  fibres  of  the  lower  end  of  the  oesophagus,  they  begin  as 


Oblique 
muscular  fibres 


Circular 
muscular  fibres 


Longitudinal 

)nuscular  fibres 

Peritoneum 


STEI7CTUEE  OF  THE  STOMACH. 


1059 


U-shaped  bundles  which  loop  over  the  stomach  immediately  to  the  left  of  the  cardia, 
and  run  very  obliquely  downwards  and  to  the  right  for  a  considerable  distance  on  both 
surfaces  of  the  organ.  These  looped  fibres,  as  we  pass  to  the  left,  gradually  become  less 
oblique,  and  finally  form  circles  which  surround  the  wide  end  of  the  stomach  completely, 
even  as  far  as  the  summit  of  the 
fundus.  The  oblique  fibres  can  be 
most  readily  shown  by  removing  the 
circular  fibres  on  either  surface  below 
the  cardia.  When  traced  towards 
the  right,  they  will  be  found  to 
terminate  by  turning  down  and  join 
ing  the  fibres  of  the  circular  layer. 

Submucous  Coat  (tela  submucosa). 
— The  submucous  coat  is  a  layer  of 
strong  but  loose  connective  tissue, 
which  lies  between,  and  unites  the 
muscular  and  mucous  coats  (Fig.  749). 
It  is  more  loosely  attached  to  the 
former  and  more  closely  to  the  latter 
coat,  and  it  forms  a  bed  in  which  the 
vessels  and  nerves  break  up  before 
entering  the  mucous  membrane. 

Mucous  Coat  (tunica  mucosa). — 
If  examined  in  the  fresh  state  soon 
after  death,  the  mucous  coat  is  of  a 
reddish-gray  colour  and  of  moderate 
consistence.  When  examined  some 
time  after  death,  the  colour  turns  to  a 
darker  gray,  and  the  whole  membrane 
becomes  softer  and  more  pulpy.  It 
is  thicker  (over  2  mm.)  and  firmer 
in  the  pyloric  than  in  the  cardiac 
portion,  and  is  thinnest  at  the  fundus, 
where  it  often  shows  signs  of  post- 
mortem digestion.  When  the  stomach 
is  empty  all  three  outer  coats,  which 
are  extensile,  contract ;  whilst  the 
inextensile  mucous  coat,  as  a  result 
of  its  want  of  elasticity,  is  thrown 
into  numerous  prominent  folds  or 
rugce,  which  project  into  the  interior 
and,  as  it  were,  occupy  the  cavity  of 
the  contracted  organ.  These  are,  in 
general,  longitudinal  in  direction, 
with  numerous  cross  branches,  and 
they  ai-e  largest  and  most  numerous 
along  the  great  curvature.  They  dis- 
appear when  the  stomach  is  distended. 

When  the  surface  of  the  mucous 
coat  is  examined  in  Si  fresh  stomach, 
it  is  seen  to  be  marked  out  into  a 
number  of  small,  slightly  elevated, 
polygonal  areas  (areee  gastricse)  by 
numerous  linear  depressions ;  the 
mucous  membrane  is  consequently 
said  to  be  mammillated  (Fig.  752,  A). 
These  little  areas,  which  measure  from  1  to  6  mm.  in  diameter,  are  beset  with  numerous  small 
pits  (foveolee  gastricse,  about  -2  mm.  wide),  which  are  the  mouths  of  the  gastric  glands,  and 
they  are  so  closely  placed  that  the  amount  of  surface  separating  them  is  reduced  (particularly 
in  the  pyloric  portion,  where  the  gland  mouths  are  widest)  to  a  series  of  elevated  ridges  (plicae 
villosse)  resembling  villi  on  section.  Although  the  gland  mouths  cannot  be  seen  with  the 
naked  eye,  a  very  slight  magnification  is  sufficient  to  show  them  clearly  ;  it  is  also  possible 
to  see  the  gland  tubes  leading  off  from  the  bottom  of  each  (Fig.  752,  B). 


Fig.  750. — The  Three  Layers  of  the  Muscular  Coat  of 
THE  Stomach.  A,  Outer  or  longitudinal  layer  ;  B,  Middle 
or  circular  layer  ;  C,  Internal  or  oblique  layer,  a,  Longi- 
tudinal fibres  of  cesophagus  ;  h.  Superficial  circular  fibres 
of  oesophagus  passing  into  circular  fibres  of  stomach  in  B  ; 
c.  Deep  circular  fibres  of  oesophagus  passing  into  oblique 
fibres  of  stomach  in  C  ;  d,  Oblique  fibres  forming  rings  at 
the  fundus  ;  e,  Submucosa. 


1060 


THE  DIGESTIVE  SYSTEM. 


p^'LOR'js  r 


Blood-vessels. — The  arteries  of  tlie  stomach  are  all  derived  ultimately  from  the  coeliac  axis. 
Tlie  corollary  arises  from  this  trunk  direct.  Having  reached  the  lesser  curvature  and  given  off 
an  (Esophageal  branch,  it  divides  into  two  large  branches,  which  run,  one  on  each  side,  along  this 

curvature,  and  join   below   with   two  similarly   disposed   arteries 

derived   from   the  i^yloric  branch  of  the   hepatic.     From  the  two 

arches  thus  formed,  four  or  five  laige  branches  jiass  to  each  surface 

of  the  stomach,  and  soon  pierce  the  muscular  coat.     Along  the  great 

curvature  several  smaller  branches  reach  the  stomach  from  the  right 

and  left  gastro -epiploic  arteries,  which  are  branches  respectively  of  the 

gastro-  duodenal  and  the  splenic,  and  run  in  the  great  omentum  close 

to  its  attachment  to  the  stomach.     Finally,  four  or  five  vasa  brevia, 

branches  of  the  splenic,  are  distributed  to  the  fundus  of  the  stomach, 

Fig.  751.  —  Diagram  to  show  which  they  reach  by  j^assing  forwards  between  the  layers  of  the 

Formation     of     Pylorus,  gastro-sjilenic  omentum.     At  first  the  arteries  lie  beneath  the  peri- 

P,    Peritoneum ;    L,    Loiigi-  toneum  ;  very  soon,  however,  they  pierce  the  muscular  coat,  which 

tudinal  layer    of    muscular  they  supply,  and  reaching  the  submucosa,  break  up  to  form  a  close 

fibres ;    C,    Circular   layer ;  network  of  vessels.      From  these  arise  numerous  small   branches, 

which  enter  the  mucous   membrane   and   form   capillary  plexuses 


M,   Mucous  membrane 
Villi. 


It  will  be  seen  that  a^-Qund  the  glands  as  far  as  the  surface. 


tlie  pyloric  narrowing  is  due 
practically     entirely  '  to 


The  veins  begin  in  the  capillary  plexuses  around  the  glands ; 

thickening    of  "the  ^-''-i^^ting,  they  form  a  network  in  the  submucosa,  from  which  arise 

muscular      fibres, 


Rngfe-^ 


circular  muscular  "fibres^  hranches  that  pierce  the  muscular  coat,  and  finally  end  in  the 
which  stops  abruptly  at  the  following  veins  :  the  right  gastro-epiploic,  which  joins  the  superior 
pyloric  orifice.  mesenteric;   the    left  gastro-epiploic,  and   four  or  five  veins  corre- 

sponding to  the  vasa  brevia  arteries,  which  join  the  splenic  ;   the 

coronary  or  gastric  vein,  which  runs  along  the  lesser  curvature  towards  the  cardia,  receives  an 

oesophageal  branch,  and  then  turns  down  and  runs  beside  the  coronary  artery  to  join  the  portal 

trunk ;  and  the  pijloric  vein,  corresponding  to  the  same  named  artery,  which  also  joins  the  j)ortal. 

These  veins  contain  numerous  valves, 

which,  though  competent  to  prevent 

the  return  of  blood  in  the  child,  are 

rarely  so  in  the  adult. 

The    lymphatics    arise    in     the 

mucous  membrane  arotmd  the  gastric 

glands ;    they   then    join    a   plexus 

of     vaived     vessels     in     the     sub  - 

mucosa,  from  which  the  chief  trunks 

pass  with   the   blood-vessels   to  the 

curvatures,  being  joined  on  the  way 

by  the  efferent  vessels  of  a  subperi- 
toneal lymphatic  plexus.     They  are 

connected  with  the  superior  gastric 

glands  along  the  lesser  curvatures, 

the  inferior  gastric  glands  along  the 

great    curvature,    and    the    splenic 

glands,  which  they  reach  with  the 

vasa   brevia.     Finally,  the   efferent 

vessels  of  all  these  join  the  coeliac 

glands. 

The  nerves  are  derived  from  the 

two pjneumogastrics  and  from  the  solar 

plexus    of    the    sympathetic.      The 

pneurnogastric     nerves    pass    down 

through    the   diaphragm   with    the 

oesophagus,  the  left  lying  on  its  front, 

the  right  on  its  back ;  in  this  way 

they   reach    the    upper  and    lower 

surfaces  of  the  stomach  resjjectively. 

Here  they  im.itewith  thesympathetic 

fibres  from  the  cojliac  plexus  (an  off- 
shoot of  the  solar  plexas),  which  pass 

to  the  stomach  with  the  branches  of 

the  coeliac  axi.s.     The  nerve  fibres, 

wliich   are  chiefly  non-medullated, 

form  two  gangliated  plexuses,  those  of  Auerbach  and  Meisssner,  in  the  muscular  and  submucous 

coats  respectively. 

The  development  of  the  stomach  is  described  with  that  of  the  intestines  on  p.  110.5. 

INTESTINES. 

As  the  coat.s  of  the  remaining  portions  of  the  digestive  tube  agree  in  many- 
particulars,  it  will  be  convenient  to  describe  the  general  structure  of  the  intestines 


Mouths  of 

gastric  glands, 

witli  gland 

tubes  at 

bottom 

Depression 

between  two 

manimillse 


'jfxm 


^SffS 


w^m 


Fig.  752. — The  Mucous  Membua.ne  of  Stomach.  A,  Natural 
size  ;  B,  Magnified  25  iliameters.  In  A  the  rugte  and  the 
mammillated  surface  are  shown.  In  B  the  gland  mouths 
(foveola;  gastricw),  with  the  gland  tubes  leading  off  from  some 
of  them,  and  the  ridges  separating  the  mouths  (plicae  villosffi) 
are  seen. 


STEUCTUKE  OF  THE  INTESTINES. 


1061 


here.     Subsequently,  any  peculiarities  of  structure  in  particular  regions  will  be 
described  with  the  corresponding  division  of  the  tube. 


Stkucture  of  the  Intestines. 

The  wall  of  the  intestines,  like  that  of  the  stomach,  is  made  up  of  four  coats,  which 
are  named  from  without  inwards — serous  or  peritoneal,  muscular,  suljinucous,  and  mucous 
(Figs.  753  and  754). 

1.  Serous  Coat  (tunica  serosa). — This  is  formed  of  peritoneum,  and  confers  on  the 
nitestines  their  smooth  and  glossy  appeai-auce.  It  varies  in  the  extent  to  which  it  clothes 
the  different  divisions  of  the  tube,  giving  the  duodenum,  the  ascending,  descending,  and 

Two  mesenteric  lymphatic  gland 
Mesentery 

-  Lymphatic 


Peritoneal  coat 


Circular 
muscular  fibres 


Longitudinal  muscular  fibres 


Fig.  753. ^A  Portion  of  Small  Intestine,  with  Mesentery  and  Vessels.     The  peritoneal  coat  has  been 
removed  from  the  right  half,  and  the  two  layers  of  the  muscular  coat  exposed. 

iliac  colons,  and  the  rectum  only  a  partial  covering ;  whilst  it  clothes  the  jejunum  and 
ileum,  the  ciecum,  the  transverse  and  the  pelvic  colons  completely.  The  detailed 
arrangement  of  this  coat  will  be  given  with  the  description  of  each  division  of  the 
intestinal  tube. 

2.  Muscular  Coat  (tunica  muscularis). — This  consists  of  unstriped  muscle  arranged 
m  two  layers — an  outer,  in  which  the  fibres  run  longitudinally,  and  an  inner,  in  which 
they  are  circularly  disposed.  The  muscular  coat  is  thicker  in  the  duodenum  than  in  anv 
other  part  of  the  small  intestine,  and  it  gradually  diminishes  in  thickness  until  the  end 
of  the  ileum  is  reached.  On  the  other  hand,  in  the  large  intestine,  it  is  thickest  in  the 
rectum  and  thinner  towards  the  beginning  of  the  colon. 

The  longitudinal  layer  (stratum  longitudinale)  of  this  coat  is  much  thinner  than  the 
underlying  circular  layer.  In  the  small  intestines  it  forms  a  complete  sheet,  continuous 
all  round  the  gut  (Fig.  753),  but  thickest  at  its  free  margin  ;  whilst  in  the  large  intestine 
it  is  divided  up  into  three  longitudinal  bands  (Fig.  762),  known  as  the  tcenke  cod,  which 
will  be  more  fully  described  in  connexion  with  the  colon. 

The  circular  layer  (stratum  circulare),  much  thicker  than  the  longitudinal  layer,  is 
composed  of  bundles  of  muscular  fibres  arranged  circularly  round  the  tube  (Fig.  753), 
and  forming  in  all  parts  a  continuous  sheet.  Unlike  the  longitudinal  fibres,  those  of  the 
circular  layer  take  part  in  the  formation  of  the  pyloric  and  ileo-caecal  valves. 

3.  Submucous  Coat  (tela  submucosa). — This  is  a  loose  but  strong  layer  of  areolar 
tissue  connecting  the  muscular  and  mucous  coats,  on  which  chiefly  depends  the  streno-th 
of  the  intestinal  w;dl.  In  addition  to  forming  a  bed  in  which  the  vessels  break  up  before 
entering  the  mucous  coat,  it  contains  the  glands  of  Brunner  in  the  duodenum  (Fig.  754), 
and  in  both  small  and  large  intestine  the  bases  of  the  solitary  glands  lie  in  it  (Fig.  754). 

4.  Mucous  Coat  (tunica  mucosa). — The  mucous  membrane  constitutes  the  inner 
coat  of  the  intestine,  on  which  its  digestive  functions  depend.  It  is  everywhere  composed 
(Fig.  754)  of  the  following  parts: — (1)  A  layer  of  striated,  columnar,  epithelial  cells 
resting  on  (2)  a  basement  membrane.  Outside  this  lies  (3)  a  layer  of  retiform  tissue, 
containing  a  considerable  number  of  scattered  lymphoid  cells.  This  layer  is  limited 
towards    the    submucosa    by    (4)    an    extremelv    thin    sheet   of    unstriped    muscle,    the 

71a 


1062 


THE  DIGESTIVE  SYSTEM. 


LIEBERKUHNS   G 


Submucosa 


Circular 
muscular  fibres 

Longitudinal 

muscular  fibres 

Peritoneum 


Lieberkiihn's 
eland 


Submucosa 


Circulai 
muscular  fibre? 

Longitudinal     ^ 
muscular  fibres — ^ 

Peritoneum 


Villi 

Lieberkiihn's 

gland 

Muscularis 

mucosae 

Brunner's 

glands 


Circular 
muscular  fibres 

^_ Longitudinal 

=\   nmscular  fibres  able 


muscularis  mucosa,  which  is  not  visible  to  the  naked  eye.     The  mucous  membrane  is 
very  vasculai*,  particularly  in  the  small  intestine.     It  is  thicker  in  the  duodenum  than 

in  the  jejunum,  and 
thicker  in  this  latter 
than  in  the  ileum. 

Throughout  both 
the  small  and  large 
intestines  the  sub- 
stance of  the  mucous 
membrane  is  closely 
beset  with  innumer- 
small  (micro- 
scopic) tubular 
glands,  known  as  the 
glands  or  follicles  of 
Lieberkiihn  (gland- 
ulse  intestinales).  In 
shape  they  are  minute 
straight  tubes — like 
diminutive  test-tubes 
— with  their  mouths 
opening  on  the  sur- 
face, their  closed  ends 
lying  in  the  deeper 
part  of.  the  mucous 
coat,  and  their  cavities 
lined  by  columnar 
epithelium.  They 
open  on  the  surface 
between   the   villi  of 

the  small  intestine,  and  are  present  also  on  the  valvulse  conniventes.      In  the  large  gut 
their  orifices  are  found  all  over  the  surface  of  the  mucous  membrane 


Blood-vessels 
forming  net- 
work in  sub- 
mucosa 


Blood-vessel 


SMALL     INTESTINE 


Fig.  754. — Diagram  to  show  the  structure  of  the  small  and  large  intestine 
and  the  duodenum. 


Certain  special  developments  of  the  mucous  coat,  found  in  particular  regions  of 
the  intestinal  tube,  must  next  be  considered :  these  are  the  (1)  villi ;  (2)  valvulse 
conniventes  ;  (3)  solitary  glands ;  and  (4)  agminated  glands,  or  Peyer's  patches. 

Villi  (villi  intestinales). — If  the  mucous  membrane  of  any  part  of  the  small 
intestine  be  examined,  it  is  seen  to  present  a  soft,  velvety,  or  fleecy  appearance 
(Fig.  755,  B) ;  this  is  due  to  the  presence  of  an  enormous  number  of  minute  pro- 
cesses, known  as  villi,  which  cover  its  surface. 

Villi  are  minute  cylindrical  or  finger-like  projections  of  the  mucous  membrane 
(Fig.  754),  about  -^V^h  or  -jVth  of  an  inch  (1-2  to  1'6  mm.)  in  height,  and  barely 
visible  to  the  naked  eye,  which  are  closely  set  all  over  the  surface  of  the  mucous 
membrane  of  the  small  intestine.  Beginning  at  the  edge  of  the  pyloric  valve,  they 
are  said  to  be  broader  but  shorter  in  the  duodenum,  and  to  grow  narrower  as  they 
are  followed  down  through  the  intestine  to  the  ileo-caecal  valve,  at  the  edge  of 
which  they  cease.  They  are  found,  not  only  on  the  general  surface  of  the  mucous 
membrane,  but  also  upon  the  valvulte  conniventes,  and,  while  they  are  not  present 
over  the  solitary  glands,  they  are  found  in  the  intervals  between  the  individual 
nodules  of  the  Peyer's  patches. 

They  are  connected  with  the  absorption  of  the  products  of  digestion  which 
takes  place  in  the  small  intestine. 

Valvulae  Conniventes  (plicae  circulares). — When  the  intestine  is  empty  and 
contracted,  its  mucous  membrane  may  in  places  be  thrown  into  effaceable  i'olds  or 
rugse,  which  disappear  on  distension.  But  in  addition  to  these,  there  are  found 
in  certain  x^ortions  of  the  small  intestine  a  series  of  large,  permanent  folds,  which 
are  not  effaceable ;  these  are  known  as  valvulse  conniventes  (Fig.  755).  They  are 
usually  more  or  less  crescentic  in  shape,  and  resemble  a  series  of  closely-placed 
shelves  running  transversely  around  the  gut.  They  rarely  form  more  than  two- 
thirds  of  a  circle ;  sometimes,  however,  they  present  a  circular  or  even  a  spiral 
arrangement,  the  spiral  extending  little  more  than  once  round  the  tube,  as  a  rule. 


STEUCTUEE  OF  THE  INTESTINES. 


1063 


Fk;.  755. — Valvul-e  Conniventes  (uatural  .size). 

A,  as  seen  in  a  bit  of  jejunum  which  has  been  filled  with  alcohol  and  hardened  ; 
B,  a  portion  of  fresh  intestine  spread  out  under  water. 


Occasionally  they  bifurcate  at  one  or  both  ends ;  sometimes,  too,  short  irregularly 
directed  branches  pass  off  from  them.  They  are  usually  about  2  to  3  inches  (5  to 
7"5  cm.)  in  length, 
and  their  breadth, 
that  is  their  pro- 
jection into  the 
cavity,  may  be  as 
much  as  ^rd  of  an 
inch  (8  mm.), 
whilst  in  thick- 
ness, as  seen  when 
cut  across,  they 
measure  about  -^th 
inch  (3  mm.). 

They  are  com- 
posed of  two  layers 
of  mucous  mem- 
brane, placed  back- 
to  back,  with  a 
little  submucosa 
between,  to  bind 
the  two  together, 
and  are  covered 
with  villi  and 
Lieberkilhn's 
glands.  Their 
use  is  to  increase  the  amount  of  surface  available  for  secretion  and  absorption. 

Valvul?e  conniventes  are  not  Ibund  in  the  upper  part  of  the  duodenum.  They 
begin  at  a  distance  varying  from  1  to  2  inches  (2-5  to  5  cm.)  from  the  pylorus. 
At  first  they  are  small,  irregular,  and  scattered ;  but  they  grow  gradually  larger  as 
we  pass  down,  and  when  the  opening  of  the  bile-duct  is  reached  (4  inches  from  the 
pylorus)  they  have  become  distinct  and  prominent.  In  the  rest  of  the  duodenum, 
and  in  the  upper  half  of  the  jejunum,  they  are  highly  developed,  being  large, 
broad,  and  closely  set.  In  the  lower  half  of  the  jejunum  they  become  gradually 
smaller  and  fewer.  Passing  down*  into  the  ileum,  they  become  still  smaller  and 
more  irregular,  and,  as  a  rule,  they  practically  cease  a  little  below  the  middle  of 
the  ileum. 

The  mucous  membrane  covering  the  folds  possesses  villi,  solitary  glands,  and 
Lieberkilhn's  glands,  like  the  mucous  membrane  of  the  general  surface  between  the 
valves. 

Often  patclie.s  of  valvulaj  conniventes,  much  rediiced  in  size,  can  be  traced  to  witliin  a  short 
distance  of  the  ileo-csecal  valve.  According  to  Sappey,  Luschka,  and  otliers,  they  usually  reach 
to  within  two  or  three  feet  of  the  end  of  the  ileum. 

Solitary  Glands  (noduli  lymphatici  solitarii). — These  are  minute  nodules  of  lym- 
phoid tissue,  opaque  and  of  a  whitish  colour,  found  projecting  on  the  surface  of  the 
mucous  membrane  throughout  the  whole  length  of  both  the  small  and  large  intestines. 

Isolated  lymphoid  cells  are  found  in  abundance  scattered  through  the  connec- 
tive tissue  layer  of  the  intestinal  mucous  membrane  generally ;  in  places  these 
cells  are  gathered  together  to  form  little  nodules,  supported  by  a  framework  of  reti- 
form  tissue,  and  surrounded  by  a  lymphatic  space  which  communicates  below  with 
the  lymphatics  of  the  submucosa.  Such  a  collection  of  lymphoid  cells  constitutes 
a  solitary  gland.  They  are  usually  of  a  rounded  or  oval  shape  (Eig.  754),  the  wide 
end  resting  in  the  submucosa,  the  nodule  itself  piercing  the  muscularis  mucosse, 
and  the  narrow  end  projecting  slightly  above  the  surface  of  the  mucous  membrane. 
In  size  they  vary  from  J^-th  to  ^th  of  an  inch  ('6  to  3-0  mm.),  but  their  average 
bulk  is  about  that  of  a  small  grain  of  sago,  to  which  they  bear  some  resemblance. 

As  already  mentioned,  they  are  present  throughout  the  small  and  large 
intestines,  being  particularly  abundant  in  the  vermiform  appendix  and  caecum.  In 
'71& 


1064 


THE  DIGESTIVE  SYSTEM. 


Two  solitaiT  f^lands 


Peycr's  patch 


the  small  intestine  they  are  found  on  the  valvule  conniventes,  as  well  as  upon  the 

general  surface  of  the  mucous  membrane  between  them. 

Peyer's   Patches,   or  Agminated   Glands   (noduli   lymphatici  aggregati,   tonsillse 

intestinales).  —  A  Peyer's  patch  consists  of  a  large 
number  of  lymphoid  nodules  grouped  closely  together 
so  as  to  form  a  slightly  elevated  area,  usually  of  an 
oblong  form,  on  the  surface  of  the  mucous  membrane 
(Fig.  756).  In  length  they  vary  from  half  an  inch 
(12  mm.)  or  less  to  three  or  four  inches  (100  mm.),  and 
in  width  they  commonly  measure  from  a  third  to  half 
an  inch  (8  to  12  mm.).  Their  number  is  variable,  but 
in  the  average  condition  about  30  or  40  are  found. 
They  are  best  marked  in  young  subjects,  where  they 
form  considerable  elevations  above  the  general  surface, 
and  may  be  as  many  as  45  in  number.  After  middle 
life  they  atrophy,  and  in  old  age,  although  usually  to 
be  found,  they  are  indistinct,  occasionally  being  marked 
by  little  more  than  a  dark  discoloration  of  the  mucous 
membrane.  They  are  invariably  situated  along  the 
free  surface  of  the  intestine  opposite  the  line  of  mesen- 
teric attachment,  with  their  long  axis  corresponding 
to  that  of  the  bowel.  Consequently,  in  order  to 
display  them,  the  tube  must  be  slit  up  along  its  attached 
or  mesenteric  border. 

Peyer's  patches  are  entirely  confined  to  the  small 
intestine,  being  largest  and  most  numerous  in  the  ileum, 

Solitary  gland  Intermediate  forn>  particukrly   in   its   lowcr   part,   wherc    they    usually 

Fig.  756.— Peyer's  Patch  and  assume  an  oblong  shape ;  in  the  lower  half  of  the 
Solitary  Glands,  from  intestine  jejunum  they  are  small,  circular,  and  few  in  number ; 
of  child  two  years  old  (natural  in  its  upper  part  they  are  rare ;   and,  although  their 

presence  has  been  noted  in  the  lower  portion  of  the 
duodenum,  they  may  be  said  to  be  as  a  general  rule 
absent  from  this  division  of  the  intestine. 


size). 


Near  the  lower  bonier  are  seen  a 
few  small  patches  made  up  of 
two  or  three  Ij'mphatic  nodules  ; 
they  are  marked  "  intermediate 
form." 


The  valvulse  conniventes  stop  at  the  margins  of  Peyer's 
patches,  and  are  not  c(5ntinued  across  them  ;  but  villi  are  found 
on  the  surface  of  the  patches,  in  the  intervals  between  the  lymphoid  nodules. 

The  chief  bowel  lesion  in  typhoid  fever  is  found  in  Peyer's  patches  and  the  solitary  glands. 

Wlien  the  surface  of  a  Peyer's  patch  from  a  child's  intestine  (in  which  these  structures  are 
particularly  well  developed)  is  carefully  examined,  it  is  seen  to  he  made  up,  not  of  a  series  of 
separate,  rounded  nodules  grouped  together,  but  rather  of  a  number  of  wavy,  irregular,  and 
branching  ridges  connected  with  one  another  by  cross  branches  (Fig.  756),  the  whole  recalling  in 
miniature  the  appearance  of  a  raised  map  of  a  A^ery  mountainous  district  in  which  the  chief 
chains  run  irregular  courses,  and  are  joined  to  one  another  by  connecting  ridges. 

Small  patches,  intermediate  in  form  between  solitary  glands  and  Peyer's  jjatches,  and  consist- 
ing of  two  or  three  lyinphoid  nodules,  are  also  tisually  present. 

THE  SMALL  INTESTINE. 

The  small  intestine  is  the  portion  of  the  digestive  tube  which  is  placed 
between  the  stomach  and  the  beginning  of  the  large  intestine.  It  commences  at 
the  pylorus,  where  it  is  continuous  with  the  stomach,  and  ends  at  the  ileo-c£ecal 
valve  by  joining  the  large  intestine.  It  occupies  the  greater  portion  of  the 
abdominal  cavity  below  the  liver  and  stomach  (Pig.  740),  and  is  found  in  the 
umbilical,  hypogastric,  and  both  lumbar  regions ;  also,  but  to  a  less  extent,  in  the 
other  regions  of  the  abdomen,  and  in  the  pelvic  cavity. 

In  length,  the  small  intestine  usually  measures  over  20  feet.  According  to 
Treves,  it  is  22|  ft.  in  the  male,  2.'3  in  the  female,  whilst  Jonnesco  gives  the  average 
length  at  24  ft.  7  ins.,  or  Ih  metres.  In  form  it  is  cylindrical,  with  a  diameter 
varying  from  nearly  two  inches  (47  mm.)  in  the  duodenum  to  a  little  over  an  inch 
(27  mm.)  at  the  end  of  the  ileum ;  there  is  thus  a  gradual  diminution  in  its  size 
from  the  pylorus  to  the  ileo-ctecal  valve. 


STRUCTUEE  OF  THE  INTESTINES.  1065 

This  portion  of  the  digestive  tube  is  divided  more  or  less  arbitrarily  into  three 
parts  (Fig.  705) — namely,  the  duodenum,  constituting  the  first  eleven  inches,  dis- 
tinctly marked  off  from  the  rest  by  its  fixation  and  the  absence  of  a  mesentery  ;  the 
jejunum,  which  comprises  the  upper  two-fifths,  and  the  ileum,  the  lower  three-fifths 
of  the  remainder.  The  two  latter  parts  pass  imperceptibly  into  one  another,  and 
the  line  of  division  drawn  between  them  is  entirely  artificial ;  however,  if  typical 
parts  of  the  two — namely,  the  beginning  of  the  jejunum  and  the  end  of  the  ileum 
— be  selected,  they  differ  so  much  in  size  and  in  the  appearance  presented  by  their 
lining  mucous  membrane,  that  they  can  be  distinguished  from  one  another  without 
difficulty. 

Both  the  jejunum  and  ileum  are  irregularly  disposed  in  the  form  of  crowded 
loops  or  coils  (Fig.  739)  which  are  connected  to  the  posterior  abdominal  wall  by  a 
great  fan -shaped  fold  of  peritoneum,  containing  their  vessels  and  nerves,  and 
known  as  the  mesentery.  This  is  of  such  a  length  that  the  coils  are  able  to  move 
about  freely  in  the  abdominal  cavity,  and  consequently  the  position  occupied  by 
any  portion  of  the  tube,  with  the  exception  of  the  beginning  of  the  jejunum  and 
the  ending  of  the  ileum,  can  never  be  stated  with  certainty.  Nevertheless,  it  may 
be  said  that,  in  general,  the  jejunum  occupies  the  upper  and  left  portions  of  the 
cavity  below  the  stomach,  the  ileum  the  lower  and  right  divisions,  its  terminal 
part  almost  always  lying  in  the  pelvis,  just  before  it  joins  the  large  gut. 

,  The  small  intestine  is  relatively  longer  in  the  child  than  in  the  adult ;  at  birth  it  is  to  the  total 
height  of  the  child  as  7  to  1,  whilst  in  tlie  adidt  the  proportion  is  as  4  to  1.  Notwithstanding 
Treves'  results,  it  is  generally  held  that  the  small  gut  is  relatively  longer  in  the  male  than  the 
female. 

It  should  perhaps  be  added  that  in  formalin-hardened  bodies  the  small  bowel  rarely  measures 
more  than  12  or  13  feet  in  length.  Similarly  its  diameter  is  often  reduced  in  places  to  ^  or  | 
inch  (12"5  to  18*7  mm.),  although  the  greater  part  of  the  gut  may  retain  its  usual  width  :  these 
narrow  parts  have  apparently  been  fixed  in  a  state  of  contraction. 

THE  DUODENUM. 

The  duodenum,  the  portion  of  the  digestive  tube  which  immediately  succeeds 
the  stomach,  is  the  first  part  of  the  small  intestine,  and  differs  from  the  rest  of 
that  tube  in  having  no  mesentery,  and  also  in  being  closely  fixed  to  the  posterior 
abdominal  wall — conditions  which  are  evidently  associated  with  its  relation  to  the 
bile  and  pancreatic  ducts,  both  of  which  open  into  its  cavity. 

Shape  and  Divisions. — The  duodenum  begins  at  the  pylorus,  about  the  level 
of  the  first  lumbar  vertebra,  and  ends,  after  a  somewhat  C-shaped  course,  at  the 
left  side  of  the  first  or  second  lumbar  vertebra  (Fig.  757).  It  is  generally  described 
as  being  made  up  of  three  parts,  namely : — (1)  The  first  or  superior  portion,  which 
begins  at  the  pylorus,  passes  backwards  and  to  the  right  beneath  the  liver,  and 
ends  at  the  neck  of  the  gall-bladder,  by  turning  down  and  joining  (2)  the  second 
or  descending  portion.  This  begins  at  the  neck  of  the  gall-bladder,  runs  down 
behind  the  transverse  colon  (Fig.  758),  and  ends  opposite  the  third  or  fourth 
lumbar  vertebra  by  turning  to  the  left,  and  passing  into  (3)  the  third  or  inferior 
portion.  This  at  first  runs  more  or  less  transversely  to  the  left,  across  the  vena 
cava,  and  then  ascends,  in  front  of  the  aorta,  as  far  as  the  under  surface  of  the 
pancreas,  where,  at  the  level  of  the  first  or  second  lumbar  vertebra,  it  bends 
abruptly  forwards,  forming  the  duodeno-jejunal  flexure  (Fig.  757),  and  passes  into 
the  jejunum. 

Taking  the  whole  of  the  duodenum  together,  it  forms  an  irregularly  C-shaped 
curve,  with  the  opening  of  the  C  directed  upwards  and  to  the  left,  and  the 
ends  reaching  to  within  about  two  inches  of  one  another.  "Within  the  concavity 
of  the  curve  the  head  of  the  pancreas  is  placed. 

The  incomplete  ring  which  the  duodenum  makes  does  not  all  He  in  the  same 
plane ;  for,  whilst  its  greater  part  is  placed  in  a  transverse-vertical  plane,  the 
middle  portion  bends  strongly  backwards,  round  the  right  side  of  the  vena  cava, 
and  lies  almost  in  a  sagittal  plane  (Fig.  757). 

Position  and  Size. — As  a  rule,  a  little  more  than  half  of  the  duodenum  lies 
in  the  epigastrium,  the  remainder,  namely,  about  the  lower  third  of  the  descending 


1066 


THE  DIGESTIVE  SYSTEM. 


portion  and  the  adjoining  two-thirds  of  the  inferior  or  third  portion,  are  placed  in 
the  umbilical  region.  With  the  exception  of  the  terminal  ascending  portion  of  the 
third  part,  the  whole  of  the  duodenum  lies  to  the  right  of  the  middle  line. 

Its  length  is  usually  about  11  inches  (27"5  cm.),  its  first  portion  being  the  shortest 
and  its  third  portion  the  longest.     Its  diameter  varies  considerably,  and  may  be 


Fossa  for  Spigelian  lol?e 
Riglit  phrenic  vessels 
Vena  cava       \^ 
Hepatic  veii| 


Hepatic  aitery 
Portal  vein 


PyloriiH 
Bile  duct 
Right  suprarenal  body 


(Esophagus 
/         poronary  artery 
Diaphragm 
Left  suprarenal  body 

Splenic  artery 
/  Kidnev 


UppPi  sui  face  of  pancreas 
Gastnc  smface  of  spleen 


Ureter 
Inferior  mesen- 
teric artery 

Si)erinatic  vein 

Ureter 

Right  common  iliac 
vein 

Right  common  iliac 
artery 
r.eft  common  iliac 
vein 


Uiiiler  surface 
^    of  pancreas 
Attachment  of 
tians\eise 
mesocolon 

Duodeno 
lejunal  fle\ure 
Gastio-duodenal 
niteiy  and  neck 
of  pancreas 
supeiioi  mesen- 
teric aiter> 

'  Duodeninn 


_  Colon 


Fig.  757. — Thk  Visceka  and  Vesskls  ox  tiik   1'osti:i{I(»u  Abdominal  Wall. 

The  .stomach,  liver,  and  mo.st  of  the  intestines  have  been  removed.  The  peritonetuu  has  been  preserved  on  the 
right  kidney,  and  the  fossa  for  the  Spigelian  lobe.  In  taking  out  the  liver,  the  vena  cava  was  left 
behind.     The  stomach-bed  is  well  shown.     (From  a  body  hardened  by  injection  of  chromic  acid.) 

stated  to  average  about  Ih  inches  when  empty,  but  it  may  be  as  much  as  two 
inches  when  distended. 

Relations. — Tlie  first  or  superior  portion  (^pars  sux^erior)  begins  at  the  pylorus 
opposite  the  first  lumbar  vertebra.  From  this  it  runs  to  the  right,  and  then 
backwards,  Jjeueath  the  liver  when  the  stomach  is  empty,  but  directly  backwards 


THE  DUODENUM. 


1067 


when  it  is  full ;  and  ends  at  the  neck  of  the  gall-bladder  by  turning  downwards 
and  passing  into  the  second  part.  Its  length  varies  from  about  li  to  2  inches 
(3-7  to  5-0  cm.),  and  is  said  to  be  greater  when  the  stomach  is  empty  than  when 
distended. 

Its  relations  (Figs.  757  and  758)  are  as  follows :— Above  and  in  front  lies  the 
quadrate  lobe  of  the  liver,  which  hangs  downwards  and  to  the  right  over  the  tube. 
Beloic,  it  rests  on  the  head  and  neck  of  the  pancreas  (the  latter  running  up  behind 
it  for  a  little  way).  Behind  it,  close  to  the  pylorus,  the  portet-v«in  ascends  to  the 
liver,  and  the  bile-dwe^-mth  the  gastro-duodenal  artery  passes  downwards.  Further 
to  the  right,  as  it  bends  backwards,  it  lies  against  the  right  side  of  the  vefla_caya^ 

Its  peritoneal  relations  for  about  an  inch  from  the  pylorus  are  the  same  as  those 
of  the  pyloric  end  of  the  stomach,  that  is  to  say,  both  the  anterior  and  posterior 


Toil  of  small  sa'^ 


Inferior  vena  cava 


Lesser  onientuin  (cut) 

\ 
Right  lateral  ligament 
of  liver 


Left  lateral  ligament  of  liver 
/  Oesophageal  opening  in  diaphragm 

/         Gastro-plirenic  ligament 

/  /  Corresponds  to  'uncovered  area'  of  stomach 

/  /  /  Oastro-splenic  omentum  (cut) 


Transverse  colon  crossing  duodenum 


Phreno-colic  ligament 


Head  of  pancreas 
Great  omentum  (cut) 

Part  of  small  sac 


Left  end  of  transverse  mesocolon 
Splenic  flexure  of  colon 
Transverse  mesocolon  (cut) 
Root  of  mesentery  (cut) 
Fig.  758.— The  Peritoneal  Relations  of  the  DuoDENrji,  Pancreas,  Spleen,  Kidneys,  etc. 

From  a  body  hardened  by  injections  of  formaliu.     In  removing  the  liver,  stomach,  and  intestines  the  lines  of 
the  peritoneal  reflexions  were  carefully  preserved.     The  peritonenm  is  coloured  blue. 

^surfaces  are  covered,  and  the  lesser  and  great  omenta  are  attached  to  its  upper 
and  lower  borders  respectively  (Fig.  758).  Beyond  this,  however,  only  the  anterior 
surface  has  a  serous  coat. 

The  peritoneal  covering  of  the  jfirst  half  of  the  posterior  surface  is  derived  from  a  diver- 
ticulum of  the  small  sac  which  runs  to  the  right  behind  the  duodenum  for  the  distance 
mentioned. 

When  the  stomach  is  distended,  the  first  inch  of  the  duodenum — which  is  movable  on  account 
of  its  complete  peritoneal  covering — is  carried  to  the  right  with  the  pylorus,  and  thus  brought 


1068  THE  DIGESTIVE  SYSTEM. 

into  line  with  tlie  second  or  terminal  half,  whujli  is  always  directed  backwards.     Hence  the 
whole  of  the  first  portion  of  the  dnodennm  is  directed  backwards  when  the  stomach  is  full. 

The  second  or  descending  portion  (pars  descendens)  begins  at  the  neck  of  the  gall- 
bladder, passes  down  behind  the  transverse  colon,  and  ends  at  the  right  side  of 
the  third  or  fourth  lumbar  vertebra.  In  length  it  measures  oh  or  4  inches  (8"7  to 
10  cm.). 

In  front,  it  is  crossed  about  its  middle  by  the  beginning  of  the  transverse  colon 
(Fig.  758).  Above  the  colon,  it  is  in  contact  with  the  narrow  end  of  the  gall-bladder 
and  below  it  with  the  coils  of  the  small  intestine.  Behind,  it  is  connected  by  areolar 
tissue  to  the  inner  part  of  the  right  kidney,  with  its  ureter  and  renal  vessels ;  it 
is  also  related,  as  a  rule,  to  the  riglH„43soas__muscle  below  the  kidney  (Fig.  757). 
To  its  otUer  or  right  sifle  lies  the  liver  (here  presenting  the  duodenal  impression) 
above,  and  often  the  ascending  colon  below.  To  its  inner  side  are  the  inferior 
vena  cava  and  the  head  of  the  pancreas,  this  latter  overlapping  it  somewhat  in  front. 

The  common  bile  duct,  after  passing  down  behind  the  first  portion  of  the 
duodenum,  descends  between  the  head  of  the  pancreas  and  the  second  portion, 
nearly  as  far  as  its  middle ;  here  it  is  joined  by  the  pancreatic  duct,  and  the  two, 
piercing  the  wall  of  the  duodenum  obliquely,  open  by  a  common  orifice  on  its 
inner  aspect,  about  Sh  to  4  ii^ches  (8-7  to  10  cm.)  beyond  the  pylorus. 

Peritoneal  relations. — There  is  no  peritoneum  on  the  posterior  or  deep  surface 
of  this  part,  whilst  its  superficial  or  anterior  surface  is  covered,  except  where  it  is 
crossed  by  the  colon  (Fig.  758). 

When  the  beginning  of  the  transverse  colon  is  completely  covered  by  peritoneum,  and  has  a 
mesentery  (a  condition  which  often  seems  to  be  determined  by  a  liver  large  in  the  vertical  direc- 
tion), the  whole  of  the  anterior  surface,  with  the  exception  of  the  insignificant  area  between  the 
two  layers  of  the  transverse  mesocolon,  is  covered  by  the  peritoneum. 

On  the  other  hand,  when  this  part  of  the  colon  has  no  mesentery,  it  lifts  the  peritoneum  oft' 
the  front  of  the  duodenum,  and  leaves  a  considerable  "uncovered  area,"  which  is  united  by 
areolar  tissue  to  the  back  of  the  colon. 

The  tMrd  or  inferior  portion  (pars  inferior)  begins  at  the  right  side  of  the  third 
or  fourth  lumbar  vertebra.  From  this  it  first  runs  more  or  less  transversely  to  the 
left  across  the  vena  cava  (Fig.  757)  for  one  or  two  inches,  and  then  passes  very 
obliquely,  or  even  vertically,  upwards  in  front  of  the  aorta  and  left  psoas  muscle. 
Finally,  having  reached  the  lower  surface  of  the  pancreas,  it  bends  forwards,  and 
passes  into  the  jejunum.  Owing  to  the  different  directions  which  they  take,  we 
can  recognise  two  divisions,  a  transverse  and  an  ascending  terminal,  in  this  portion 
of  the  duodenum  (Fig.  757). 

In  front,  it  is  crossed  (about  the  junction  of  its  two  divisions)  by  the  superior 
mesenteric  vessels,  and  also  by  the  root  of  the  mesentery  (Fig.  758).  On  each 
side  of  this  it  is  covered  by  coils  of  small  intestine.  .Behind,  its  horizontal  portion 
lies  on  the  vena  cava ;  its  ascending  portion  on  the  aort^-,  the  left  renal  vessels, 
and  the  left  psoas  muscle,  all  of  which  separate  it  from  the  vertebfal  column. 
Above,  it  is  closely  applied  in  its  whole  extent  to  the  head  of  the  pancreas.  The- 
left  side  of  the  ascending  terminal  fart,  whicli  is  free,  lies  in  contact  with  some  coils 
of  the  small  intestine. 

Peritoneal  relations. — The  third  portion  of  the  duodenum  is  covered  by  peri- 
toneum on  its  anterior  surface  throughout,  except  where  it  is  crossed  by  the 
superior  mesenteric  vessels  and  the  root  of  the  mesentery  which  contains  them 
(Fig.  758).  h\  addition,  its  ascending  terminal  portion  is  also  clothed  by  this 
membrane  on  its  left  side ;  and  here  are  usually  found  one  or  two  small  peritoneal 
pouches  known  as  the  duodenal  fossae. 

The  attachment  of  the  root  of  tin;  mesentery  begins  above  quite  close  to  the  duodeno-jejunal 
flexure,  on  the  front  of  the  duodenum  ;  from  this  it  runs  down  on  the  anterior  aspect  of  the 
ascending  terminal  part,  and  finally  leaves  the  duodenum  about  the  union  of  the  two  divisions 
of  its  third  ]>ortion. 

Duodenal  Fossae.  —  In  the  neighbourhood  of  the  ascending  part  of  the  third 
portion  of  the  duodenum  are  found  thi-ee  well-known  fo«s;e  of  the  peritoneum  which  are 
of  some  surgical  interest ;  these  are  the  superior  and  inferior  duodenal  and  the  paraduo- 
denal fossae  (Fig.  759).     Other  rarer  forms  are  occasionally  present. 


THE  DUODENUM. 


1069 


Transversa  meso- 
colon 


When  tlie  ascending  terminal  part  of  tlie  duodenum  is  drawn  over  to  tlie  right, 
and  the  angle  between  its  left  side  and  the  posterior  abdominal  wall  examined,  one  or 
two  triangular  folds  of  peritoneum  will  generally  be  found  crossing  over  this  angle  from 
the  duodenum  to  the  abdominal  wall.  Each  fold  has  one  edge  attached  to  the  duodenum, 
another    to    the   parietal   peri- 

Tnuisverse  cok 


toneum  at  the  left  of  the  duo- 
denum, whilst  the  third  is  free, 
and  bounds  the  opening  of  a 
small  pouch  which  lies  behind 
the  fold.  One  of  these,  the 
superior  duodenal  fold,  is  situ- 
ated near  the  termination  of 
the  duodenum,  with  its  apex 
directed  up  and  its  free  margin 
down.  It  sometimes  contains 
between  its  two  layers  the 
termination  of  the  inferior 
mesenteric  vein.  Behind  it  lies 
the   superior  duodenal   fossa, 


Diiodenun 

Superior 
duodenal  fossa 

Inferior 


the     opening     of      which     looks     duodenal  fossa 


downwards,  and  will  usiially 
admit  the  tip  of  a  finger  (Fig. 
759).     The  second,   known  as 


The  mesentei\  (cut) 


lufenoi  mesenteric  vein 
Infeiioi  mebenteiic  aitery 


Fig.  759. — The  Duodenal  Fossae  and  Folds. 


the  inferior  duodenal ^f old,  is  The  transverse  colon  and  niesocolon  have  been  thrown  up,  and  the 
placed  lower  down,  at   the  side  mesentery  has  been  turned  to  the  right  and  cut.     The  paraduodenal 

of  the   same    part   of    the   duo-  fossa   (of  Landzert)   is   situated  to  the  inner  side  of  the  inferior 

1  Ti       j>  11-  mesenteric  vein,  between  it  and  the  terminal  part  of  the  duodenum. 

denum.       Its    free    border    is  it  is  not  shown  in  the  illustration, 

directed    upwards,    as    is    the 

mouth  of  the  inferior  duodenal  fossa,  which  lies  behind  it.  This  latter  is  larger  and 
more  constant  than  the  superior  duodenal  fossa,  and  is  present  in  75  per  cent  of  bodies, 
whilst  the  superior  is  present  in  50  per  cent  (Jonnesco). 

Paraduodenal  Fossa  (fossa  of  Landzert). — This  fossa,  which  is  best  seen  in  the 
infant,  is  placed  some  distance  to  the  left  of  the  terminal  part  of  the  duodenum.  It  is 
produced  by  the  inferior  mesenteric  vein  raising  up  a  fold  of  peritoneimi,  as  it  runs 
along  the  outer  side  of  the  fossa,  and  then  inwards  above  it  (see  Fig.  759,  where  the  vein, 
but  not  the  fossa,  is  shown).  It  is  limited  below  by  a  special  fold  (the  mesenterico-meso- 
colic  fold).  According  to  Moynihan,  this  is  the  only  fossa  to  the  left  of  the  duodenum 
capable  of  developing  into  the  sac  of  a  hernia ;  and  when  this  occurs,  the  inferior 
mesenteric  vein  always  lies  in  the  anterior  margin  of  the  orifice  of  the  sac  (accompanied 
for  some  distance  by  the  ascending  branch  of  the  left  colic  artery). 

In  addition  to  the  above,  a  duodeno-jejunal  fossa  at  the  front  of  the  duodeno- 
jejunal flexure,  and  five  other  fossae,  have — perhaps  unnecessarily — been  described  in 
this  region. 

Peritoneal  Relations  of  the  Duodenum. — Whilst   the  relations  of  the   peritoneum   to   the 

second  and  third  portions  of  the  duodenum  are 
usually  described  as  in  the  foregoing  account,  it 
should  perhaps  be  pointed  out,  that  it  is  not  really 
the  front,  but  the  right  half  of  the  circumference 
of  the  descending  portion  which  has  a  serous  coat. 
Similarly,  it  is  the  lower  and  anterior  half  of  the 
circumference  of  the  transverse  part  of  the  third 
portion  which  is  clothed  by  j^eritoneum,  whilst 
considerably  more  than  half  of  the  circumference  of 
its  ascending  terminal  part  is  covered  ;  for  the 
Ijeritoneum  forms  a  fold  running  in  behind  this 
part,  m  addition  to  covering  its  left  side  and  half 
its  anterior  aspect. 

Interior  of  Duodenum. — No  valvulse 
conniventes  are  found  in  the  duodenum  for 
an  inch  or  two  beyond  the  pylorus.  Here 
they  begin ;  at  first  as  low,  scattered,  and 
irregular  folds;  further  down,  they  gradually 
become  larger,  more  regular,  and  more  numerous ;  and  by  the  time  the  middle  of 
the   descending    stage    is    reached   they   have   attained   a   considerable   develop- 


Hood-like 

valvula 

connivens 

Bile  papilla 
Common  open- 
ing of  bile  and 
pancreatic  duct 

Frenulum 


Fig.  760. — The  Bile  Papilla  in  the 
Interior  of  the  Duodenum. 


1070  THE  DIGESTIVE  SYSTEM. 

ment.       In    the    lower   part   of  the  duodenum    the   folds   are   large,   prominent, 
and  closely  set. 

On  the  inner  aspect  of  the  descending  portion,  about  its  middle — namely,  3^ 
or  4  inches  (8"7  to  10  cm.)  beyond  the  pylorus — is  seen  a  prominent  papilla,  on 
which  the  bile  and  pancreatic  ducts  open  by  a  common  orifice  (Fig.  760).  This  is 
known  as  the  bile  papilla  (papilla  duodeni ;  caruncula  major  of  Santorini). 

The  bile  papilla  is  placed  beneatli,  and  protected  by,  a  prominent,  hood-like  valvula  con- 
nivens,  which  is  situated  immediately  above  it.  From  its  lower  margin  a  firm  ridge  of  the 
mucous  membrane  (the  plica  longitudinalis  duodeni)  descends  for  a  considerable  distance,  and 
acts  as  a  frenum,  which  fixes  the  papilla  and  directs  its  apex  somewhat  downwards  (Fig.  760). 
The  papilla  is  prominent,  and  nipple  or  dome-shaped,  and  at  its  summit  is  placed  the  small 
orifice,  which  will  usually  admit  the  point  of  a  pencil ;  the  whole  bears  a  close  resemblance  to 
the  nozzle  of  a  perfume-spray. 

Nearly  an  inch  higher  up,  and  invariably  on  the  ventral  side  of  the  bile  papilla  (sometimes 
as  much  as  a  ^  to  f  inch  distant),  is  seen  a  second  and  smaller  papilla  (the  caruncula  minor  of 
Santorini),  at  the  point  of  which  is  placed  the  very  small  orifice  of  the  accessory  pancreatic 
duct.  This  second  papilla  seems  to  be  constantly  present,  although  sometimes  so  small  that  it 
may  easily  escape  detection  unless  carefully  sought  for.  When  well  developed,  it  may  have  a 
hood-like  valvula  connivens  and  a  little  frenulum,  like  those  of  the  bile  papilla. 

Structure  of  the  Duodenum. — The  peritoneal  coat,  which  is  incomplete,  has 
already  been  described  in  detail,  in  connexion  with  each  division  of  the  duodenum. 

The  muscular  coat  is  well  developed,  and  is  pierced  by  the  bile  and  pancreatic  ducts, 
but  otherwise  calls  for  no  special  description. 

The  submucosa  differs  from  that  of  the  rest  of  the  small  intestine,  in  that  it  con- 
tains, especially  in  the  upper  half  of  the  duodenum,  the  glands  of  Brunner  (glandules 
duodenales).  These  are  small  acinotubular  glands,  closely  resembling  the  pyloric  glands 
of  the  stomach,  which  Me  in  the  submucous  coat,  and  send  their  ducts  through  the 
muscularis  mucosae  to  open  on  the  surface  between  Lieberkiihn's  glands,  or  sometimes  into 
these  glands  themselves  (Fig.  754).  They  can  be  exposed  by  removing  the  peritoneal 
and  muscular  coats,  and  also  some  of  the  submucosa,  when  they  appear  as  little  round 
or  flattened  masses  of  a  reddish  gi'ay  colour,  varying  in  size  from  Joth  to  ^^^th  of  an  inch 
in  diameter  ('5  to  2-0  mm.).  They  form  an  almost  continuous  layer  as  far  as  the  opening 
of  the  bile  duct ;  beyond  this  they  diminish  progressively,  and  completely  disappear  near 
the  duodeno-jejunal  flexure. 

The  mucous  membrane,  which  is  thicker  in  the  duodenum  than  in  any  other  part  of 
the  small  intestine,  is  covered  throughout  with  broad  short  villi.  Its  other  character- 
istics have  been  already  fully  described. 

Various  Forms  of  Duodenum. — Three  diflerent  types  of  duodenum  have  been  described — 
(1)  The  annular,  in  which  the  curves  separating  the  various  portions  are  open,  and  the  two 
extremities  come  fairly  close  to  one  another.  (2)  The  U-shaped,  in  which  the  transverse  part  of 
the  third  portion  is  very  long,  and  the  ascending  portion  nearly  vertical ;  and  (3)  the  V-shaped 
duodenum,  in  which  the  transverse  part  of  the  third  portion  is  very  short  or  alisent. 

Duodenal  Pouch. — A  diverticulum  of  the  duodenum,  arising  from  its  left  side  just  above  the 
opening  of  tlie  bile  duct,  and  running  into  the  substance  of  the  pancreas,  is  occasionally  found. 
It  is  possibly  connected  with  one  of  the  outgrowths  of  the  duodenum  from  which  the  pancreas 
is  developed  in  the  embryo. 

Vessels  and  Nerves. — The  duodenum  receives  its  blood  from  the  suj^erior  and  inferior 
pancreatico-duodenal  arteries,  branches  of  the  gastro-duodenal  and  superior  mesenteric  arteries 
respectively.  The  blood  is  returned  by  the  corresponding  veins,  the  suiDerior  of  which  opens  into 
the  superior  mesenteric,  and  the  inferior  into  the  beginning  of  the  portal  vein. 

The  lymphatics  pass  to  a  set  of  glands  placed  along  the  pancreatico-duodenal  arteries,  and 
thence  to  the  coeliac  glands. 

The  nerves  come  from  the  .solar  plexus  of  the  sympathetic. 

Duodeno-jejunal  Flexure. — When  the  ascending  terminal  portion  of  the 
duodenum  reaches  the  under  surface  of  the  pancreas,  at  a  point  opposite  the  left 
side  of  the  first  or  second  lumbar  vertebra,  it  turns  abruptly  forwards,  downwards, 
and  to  the  left,  and  passes  into  the  jejunum.  This  abrupt  bend  is  known  as  the 
duodeno-jejunal  flexure.  Unlike  the  rest  of  the  duodenum,  which  is  subject  to 
considerable  variations  in  position  in  different  individuals,  the  duodeno-jejunal 
flexure  is  fixed  by  a  thin  band  of  unstriped  muscle,  which  is  attached  above  to  the 
strong  connective  tissue  around  the  cceliac  axis,  as  well  as  to  the  left  cms  of  the 
diaphragm,  and  below  joins  the  muscular  coat  of  the  duodenum  at  the  flexure. 
This  band  is  known  as  the  suspensory  muscle  of  the  duodenum  (musculus  sus- 
pensorius  duodeni — Treitz). 


THE  JEJUNUM  AND  ILEUM. 


1071 


The  course  taken  by  the  gut  at  the  duodeno-jejunal  flexure  is  variable  :  the  chief  directions 
in  their  order  of  frequency  are — (1)  dowTiwards,  forwards,  and  to  the  left ;  (2)  directly  forwards 
and  do^-nwards  ;  (3)  to  the  left,  and  then  downwards ;  (4)  forwards  and  to  the  right  (Harman). 

Some  of  the  fibres  of  the  suspensory  muscle  are  said  by  Lockwood  to  pass  into  the  mesen- 
tery, and  he  consequently  calls  it  "the  suspensory  muscle  of  the  duodenum  and  mesentery 
proper." 

THE   JEJUNUM   AND    ILEUM. 

The  upper  two-fifths,  that  is,  about  8  feet  of  the  small  intestine  beyond  the 
duodenum,  are  known  as  the  jejunum  (intestinum  jejunum).  The  succeeding  three- 
fifths,  which  usually  measures  about  12  feet,  constitute  the  ileum.  The  ileum 
opens  into  the  large  intestine  at  the  junction  of  the  caecum  and  ascending  colon, 
where  its  orifice  is  guarded  by  the  ileo-csecal  valve. 

Both  the  jejunum  and  ileum  are  connected  to  the  parietes  by  a  large  fold  of 


Stoniacli 


Attachment  of 
falciform  ligament' 


Hepatic  flexure 


Spleen  (anterior 
angle) 

Splenic  flexuie 

Transverse  inesocolon, 
■with  stomach  resting 
ou  it 


Terminal  part  of 
luodfiiuni 


De.seen<]ini'  colon 


Root  of  mesentery  (cut) 


Apex  of  verraifonn    {      YfVtV  ^ 


appendix 
Terminal  part  of  ileum 


Csecum 


Pelvic  (sifrmoi(l) 

mesocolon 


J^Pclvic  colon  (sigmoid 
rtexure) 


Bladder 

Fig.  761. — The  Abdominal  Viscera  after  the  Removal  of  the  Jejunum  and  Ileum  (from  a  photograph 
of  the  same  body  as  depicted  in  Fig.  739).  The  transverse  colon  is  much  more  regular  than  usual. 
Both  the  liver  and  csecum  extend  lower  down  than  normal.  The  subdivisions  of  the  abdominal  cavity 
are  indicated  by  dark  lines. 

peritoneum — the  mesentery — which  conveys  vessels  and  nerves  from  the  posterior 
abdominal  wall  to  these  divisions  of  the  intestine. 

The  part  of  the  tube  to  which  the  mesentery  is  connected  is  known  as  the 
mesenteric  or  attached  border ;  the  opposite  side  is  the  free  border. 

The  mesentery  (mesenterium)  is  a  broad  fan-shaped  fold,  composed  of  two 
layers  of  peritoneum,  which  connects  the  small  intestine  to  the  back  of  the  abdomen. 
One  border  of  the  fold  is  wide  and  contains  the  intestine  within  it  (Fig.  753). 
The  other,  known  as  the  root  of  the  mesentery  (radix  mesenterii),  is  compara- 
tively narrow,  being  only  6  or  7  inches  wide,  but  it  is  much  thicker  than  the 
part  near  the  gut,  for  it  contains  between  its  layers  a  considerable  amount  of 
fatty  subperitoneal  tissue,  in  addition  to   the  large  vascular  trunks  passing  to 


1072  THE  DIGESTIVE  SYSTEM. 

the  intestine.  The  root  is  attached  to  the  posterior  abdominal  wall  along 
an  oblique  line,  extending  approximately  from  the  left  side  of  the  second 
lumbar  vertebra  to  the  right  iliac  fossa  (Fig.  761).  In  this  course  its  Une 
of  attachment  passes  from  the  duodeno-jejunal  flexure  down  over  the  front  of 
the  terminal  part  of  the  duodenum,  then  obhquely  across  the  aorta,  the  inferior 
vena  cava,  the  ureter,  and  psoas  muscle,  to  reach  the  right  iliac  region. 

The  opposite  border  of  the  mesentery  is  frilled  out  to  an  enormous  degree,  so 
that,  while  the  root  measures  but  6  or  7  inches,  the  free  border  is  extended  to 
some  20  feet,  thus  resembhng  a  fan,  one  border  of  which  may  be  twenty  or  thirty 
times  as  long  as  the  other.  The  length  of  the  mesentery,  measured  from  its  root 
to  the  attached  edge  of  the  intestine  directly  opposite,  usually  measures  at  its 
longest  part  about  6  inches  (8  or  9  inches,  Treves  and  Lockwood). 

Behceen  the  two  layers  of  the  mesentery  (Fig.  753)  are  contained  (a)  the 
intestinal  branches  of  the  superior  mesenteric  vessels,  accompanied  by  the  mesenteric 
nerves  and  lymphatics ;  (h)  the  mesenteric  lymphatic  glands,  which  vary  from  40 
to  150  in  number ;  (c)  a  considerable  amount  of  fatty  connective  tissue,  continuous 
with  the  extra-peritoneal  areolar  tissue ;  and  (d)  the  intestine  itself. 

The  peritoneum  from  the  right  side  of  the  mesentery  passes  out  on  the  posterior  abdominal 
wall  to  clothe  the  ascending  colon,  and,  above,  it  is  connected  by  a  fold  with  the  transverse  meso- 
colon. That  of  the  left  side,  similarly,  passes  across  the  parietes  to  the  descending  and  iliac 
colons. 

The  mesentery  begins  above,  immediately  beyond  the  ending  of  the  duodenum — that  is,  in 
the  angle  of  the  duodeno-jejunal  flexure — and  it  ends  below  in  the  angle  between  the  ileum  and 
ascending  colon.  It  is  very  short  at  each  end,  but  soon  attains  the  average  length.  Its  longest 
part  goes  to  the  portion  of  the  small  intestine  situated  between  two  points,  one  six  feet,  the  other 
eleven  feet  from  the  duodenum  (Treves). 

Whilst  the  root  of  the  mesentery  pursues  at  its  attachment  an  almost  straight  line  from  one  end 
to  the  other,  if  cut  across  a  very  short  distance  from  the  posterior  abdominal  wall,  it  will  here  be 
found  to  form  a  wavy  or  undulating  line.  Further  out  still  this  condition  becomes  more  and  more 
marked  ;  and  finally,  if  the  bowel  be  removed  by  cutting  through  the  mesentery  close  to  its  attach- 
ment to  the  intestinal  wall,  it  will  be  seen  that  its  free  edge  is  not  only  undulating,  but  is  frilled  or 
plaited  to  an  extreme  degree.  When  shown  in  this  way,  it  is  found  that  the  plaiting  or  folding 
Ls  not  quite  indiscriminate,  but  that  the  main  folds,  of  which  there  are  usually  six,  run  alter- 
nately to  the  right  and  left.  As  a  rule,  the  first  fold  runs  to  the  left  from  the  duodeno-jejunal 
flexure,  and  goes  to  a  coil  of  jejunum  which  lies  under  the  transverse  mesocolon,  and  helps  to 
support  the  stomach  (this  coil  has  Ijeen  already  referred  to,  page  1053).  The  second  fold  passes 
to  the  right,  the  third  to  the  left,  and  so  on  uja  to  the  fifth  and  sixth,  which  are  usually  small 
From  the  margins  of  these  primary  folds  secondary  folds  project  in  all  directions,  and  from  these 
again  even  a  third  series  may  be  formed. 

This  order  is  of  course  by  no  means  constant,  but  if  the  intestine  be  removed  from  a  hardened 
body  in  the  way  suggested,  without  disturbing  the  mesentery,  it  will  be  found  to  be  arranged 
with  more  or  less  regularity,  on  some  such  plan  as  that  indicated. 

Arrangement  of  Coils  of  Small  Intestine. — Although  the  greatest  variety  is 
found  in  the  disposition  of  the  small  intestine,  and  it  is  impossible  to  state  in  what 
regions  of  the  abdomen  the  different  parts  of  the  tube  will  be  found,  still  it  may 
be  said  that  in  general  the  jejunum  (as  might  be  expected  from  the  position  at 
which  it  begins)  is  placed  above  and  to  the  left,  in  reference  to  the  ileum,  which 
latter  lies  below  and  to  the  right.  Again,  the  upper  part  of  the  jejunum  is  usually 
situated  to  the  left  of  the  duodeno-jejunal  flexure,  in  contact  with  the  under 
surface  of  the  pancreas  and  transverse  mesocolon ;  and,  similarly,  the  terminal  part 
of  the  ileum  almost  always  lies  in  the  pelvis,  from  which  it  passes  up  over  the 
right  side  of  the  jjelvic  brim  to  reach  the  ileo-ctecal  orifice.  Another  portion  of 
the  small  intestine  is  not  uncommonly  found  in  the  pelvis ;  this  is  the  part  with 
the  longest  mesentery,  and  lies  between  two  points,  six  and  eleven  feet  respectively 
from  the  duodenum  (Treves). 

Differences  between  Jejunum  and  Ileum.— If  the  small  intestine  be  followed 
down  from  the  duodenum  to  the  caecum  no  noticeable  change  in  appearance  will 
be  found  at  any  one  part  of  its  course,  to  indicate  the  transition  from  jejunum  to 
ileum  ;  for  the  one  passes  insensibly  into  the  other.  Nevertheless,  a  gradual  change 
takes  place,  and  if  typical  parts  of  the  two,  namely,  the  upper  portion  of  the 
jejunum  and  the  lower  portion  of  the  ileum,  be  examined,  they  will  be  found  to 
present  characteristic  differences,  which  are  set  forth  in  the  following  table : — 


THE  JEJUNUM  AND  ILEUM.  1073 


Jejunum.  Ileum. 


Wider,  1|  to  1|  inch  in  diameter.  Narrower,  1|  to  1  inch  in  diameter. 

Wall,  thicker  and  heavier.  Wall,  thinner  and  ligliter. 

Redder  and  more  vascular.  Paler  and  less  vascular. 

Valvulaj  conniventes  well  develojied.  Valvulae  conniventes  absent  or  very  small. 

Fever's  jmtches,  few  and  small.  Fever's  patches,  large  and  numerous. 


The  villi  are  also  said  to  be  shorter  and  broader  in  the  jejunum,  more  slender 
and  filiform  in  the  ileum  (Eauber). 

The  terminal  portion  of  the  ileum,  after  crossing  the  brim  of  the  pelvis,  runs 
upwards,  and  also  slightly  backwards  and  to  the  right,  in  close  contact  with  the 
caecum,  until  the  ileo-ctecal  orifice  is  reached. 

Meckel's  Diverticulum  (diverticulum  ilei). — This  is  a  short  wide  protrusion  which  is  found 
springing  from  the  lower  part  of  the  ileum  in  a  little  over  2  jjer  cent  of  the  bodies  examined. 
It  is  usually  about  2  inches  long,  and  of  the  same  width  as  the  intestine  from  which  it 
comes  off.  Most  commonly  it  is  found  about  2|  feet  from  the  ileo-cascal  valve,  and  opposite 
the  termination  of  the  superior  mesenteric  artery.  As  a  rule,  it  runs  at  right  angles  to 
the  gut,  and  its  end  is  free ;  but  occasionally  it  is  adherent  either  to  the  abdominal  wall, 
the  adjacent  viscera,  or  the  mesentery,  when  it  may  be  the  cause  of  strangulation  of  the 
intestine. 

The  diverticidum  is  due  to  the  persistence  of  the  proximal  portion  of  the  vitelline  (or  vitello- 
intestinal)  duct,  which  connects  the  primitive  intestine  of  the  embryo  -with  the  yolk  sac.  In 
shape  it  may  be  cylindrical,  conical,  or  cord-like,  and  it  may  present  secondary  diverticula  near 
its  tip.  It  arises  most  frequently  from  the  free  border  of  the  intestine,  but  it  sometimes  comes 
off  from  the  side.  It  runs  at  right  angles  to  the  gut  most  commonly,  but  it  may  assume  any 
direction,  and  it  often  is  provided  with  a  mesentery.  In  3302  bodies  .specially  examined  with 
reference  to  its  existence,  it  was  present  in  73,  or  2-2  per  cent,  and  it  appeared  to  be  more  common 
in  the  male  than  in  the  female.  In  59  out  of  the  73  cases  its  position  with  reference  to  the  end 
of  the  ileum  was  examined  :  its  average  distance  from  the  ileo-csecal  valve  was  32i  inches 
measured  along  the  gut,  the  greatest  distance  being  12  feet,  and  the  smallest  6  inches.  In 
52  specimens  the  average  length  was  2-1  inches,  the  longest  being  Sj  inches,  the  shortest  ^  inch. 
The  diameter  usually  equals  that  of  the  intestine  from  which  it  springs ;  but  occasionally  it 
is  cord-like,  and  pervious  only  for  a  short  way ;  on  the  other  hand,  it  may  attain  a  diameter  of 
3|  inches.  (The  foregoing  results  have  been  compiled  from  the  reports  of  The  Collective 
Investigation  of  the  Anatomical  Society  of  Great  Britain  and  Ireland — L.  J.  Mitchell,  Kelynack, 
Rogie,  and  Augier.) 

Vessels  and  Nerves  of  the  Jejunum  and  Ileum. — The  arteries  for  both  the  jejunum  and 
ileum — the  vasa  intestini  tenuis — come  from  the  superior  mesenteric,  and  are  contained  between 
the  two  layers  of  the  mesentery.  After  breaking  up  and  forming  three  tiers  of  arches,  the  ter- 
minal branches  (Fig.  753)  reach  the  intestine,  where  they  bifurcate,  giving  a  branch  to  each  side 
of  the  gut.  These  latter  run  transversely  I'ound  the  intestines,  at  first  under  the  peritoneal  coat ; 
soon,  however,  they  pierce  the  muscular  coat  and  form  a  plexus  in  the  submuco.sa,  from  which 
numerous  branches  pass  to  the  mucous  membrane,  where  some  form  plexuses  around  the  glands 
of  Lieberkiihn,  whilst  others  pass  to  the  villi.  The  veins  are  similarly  disposed,  and  the 
blood  from  the  whole  of  the  small  intestine  l^eyond  the  duodenum  is  returned  by  the  superior 
mesenteric  vein,  which  joins  with  the  splenic  to  form  the  jJortal  vein. 

The  lymphatics  of  the  small  intestine  (known  as  lacteals)  begin  in  the  villi,  and  also  as 
lymphatic  sinuses  surrounding  the  bases  of  the  solitary  glands ;  a  large  jjlexus  is  formed  in  the 
submuco.sa,  a  second  between  the  two  layers  of  the  muscular  coat,  and  a  third  beneath  the 
peritoneum.  The  vessels  from  all  these  pass  up  in  the  mesentery,  being  connected  on  the  way 
with  the  numerous  (from  40  to  150;  mesenteric  glands,  and  finally  unite  to  form  one,  or  a  few, 
intestinal  lymi^hatic  trunks,  which  open  into  the  receptaculum  chyli. 

The  nerves  come  from  the  solar  plexus,  through  the  sujjerior  mesenteric,  which  latter 
accompanies  the  superior  mesenteric  artery  betAveen  the  layei-s  of  the  mesentery,  and  thus 
reaches  the  intestine.  Some  of  the  fibres  are  derived  ultimately  from  the  right  vagus.  The 
nerve-fibres  are  non-medullated,  and  form,  as  in  other  parts  of  the  canal,  two  gaugliated 
plexuses — that  of  Auerbach  in  the  muscular  coat,  and  the  plexus  of  Meissner  in  the  sub- 
mucosa. 

Structure. — The  serous  coat  is  complete  in  all  parts  of  the  jejunum  and  ileum. 
The  muscular  coat  is  thicker  in  the  jejunum,  and  grows  gi-adually  thinner  as  it  is  traced 
down  along  the  ileum.  The  submucosa  contains  the  bases  of  the  solitary  glands  (Fig.  754), 
but  otherwise  calls  for  no  special  remark.  The  mucous  coat  is  thicker  and  redder  above, 
in  the  jejunum,  thinner  and  paler  in  the  ileum.  It  is  covered  throughout  by  villi,  which 
are  shorter  and  broader  in  the  jejunum,  longer  and  naiTower  in  the  ileum.  In  its  whole 
extent  it  is  closelv  beset  with  Lieberkuhn's  follicles,  and  numerous  solitary  glands  are 
72 


1074  THE  DIGESTIVE  SYSTEM. 

seeu  projecting  on  its  surface.  Peyer's  patches  are  particularly  large  and  numerous  in 
the  ileum;  they  are  fewer,  smaller,  and  usually  circular,  in  the  jejunum.  Finally,  the 
mucous  membrane  forms  valvuhe  conniventes,  which  are  much  more  prominent  in  the 
jejinium  ;  they  are  smaller  and  fewer  in  the  upper  part  of  the  ileum,  and  usually  disappear 
a  little  below  its  middle. 

THE  LAEGE  INTESTINE. 

The  ileum  is  succeeded  by  the  large  intestine  (intestinum  crassum),  which 
begins  on  the  right  side,  some  2h  inches  below  the  ileo-ctecal  junction,  and  com- 
prises the  following  parts  :— 

1.  The  csecum,  a  wide,  short  cul-de-sac,  consisting  of  the  portion  of  the  large 
bowel  below  the  ileo-caecal  junction.  It  lies  in  the  right  iliac  region,  and  from 
its  inner  and  back  part  a  worm-shaped  outgrowth,  the  vermiform  process,  is  pro- 
longed (Fig.  7G1). 

2.  The  ascending  colon  extends  from  the  csecum,  up  in  the  right  side  of  the 
abdomen,  to  the  li^^er :  here  the  gut  bends  to  the  left,  forming  the  hepatic  flexure, 
which  connects  the  ascending  colon  to  the  transverse  colon. 

3.  The  transverse  colon  is  a  long  loop  of  intestine  which  arches  across  the 
abdominal  cavity  in  an  irregular  manner.  It  ends  at  the  lower  extremity  of  the 
spleen,  wdiere  it  turns  downward,  forming  the  splenic  flexure,  and  passes  into  the 
descending  colon. 

4.  The  descending  colon  runs  down  on  the  left  side,  from  the  splenic  flexure 
to  the  iliac  crest. 

5.  The  iliac  colon  extends  from  the  crest  of  the  ilium  to  the  brim  of  the  pelvis, 
where  it  is  succeeded  by  the  pelvic  colon. 

6.  The  pelvic  colon  is  a  large  loop  of  intestine  which  is  usually  found  in  the 
pelvis.  The  iliac  and  pelvic  portions  of  the  colon  taken  together  are  commonly 
described  as  the  sigmoid  flexure  of  the  colon. 

7.  The  rectum,  the  terminal  part  of  the  large  bowel,  succeeds  the  pelvic  colon, 
and  ends  at  the  anal  orifice. 

In  its  course  the  large  bowel  is  arranged  in  an  arched  manner  around  the 
small  intestine,  which  lies  within  the  concavity  of  its  curve  (Fig.  739). 

In  length,  the  great  intestine  is  equal  to  about  one-fifth  of  the  whole  intestinal 


iSacculatioiis  'Jitniacoli 

Appendices  cpiploicse 
Fig.  762. — Large  Intestine. 

A  piece  of  transverse  colon  from  a  cliild  two  years  old.     The  three  cliief  characteristics  of  the  large  intestine — 
sacculations,  tsenise,  and  appendices  epiploicse — are  shown. 

canal,  and  usually  measures  between  5  and  6h  feet  (180  to  195  cm.).  Its  breadth 
is  greatest  at  the  ctecum,  and  from  this — with  the  exception  of  a  dilation  at  the 
rectum — it  gradually  decreases  to  the  anus.  At  the  crecum  it  measures,  when 
distended,  about  3  inches  (75  mm.)  in  diameter;  beyond  this  it  gradually 
diminishes,  and  measures  only  Ih  inch  (37  mm.)  or  less  in  the  descending  and 
iliac  divisions  of  the  colon. 

The  large  intestine,  with  the  exception  of  the  rectum  and  vermiform  appendix, 
may  be  easily  distinguished  from  the  regularly  cylindrical  small  intestine  by  (a) 
the  presence  of  three  longitudinal  bands — the  taeniae  coli — running  along  its  surface 
(Fig.  762) ;  (h)  by  the  fact  that  its  walls  are  sacculated ;  and  (c)  by  the  presence 
of  numerous  little  peritoneal  processes,  known  as  appendices  epiploicse,  projecting 


THE  LAKGE  INTESTINE.  1075 

from  its  serous  coat.  In  addition,  the  larger  intestine  is  usually  wider  than  the 
small,  but  too  much  reliance  cannot  be  placed  on  this  character,  for  the  jejunum  is 
often — indeed,  generally — wider  than  the  empty  and  contracted  descending  colon. 

Taeniae  Coll. — In  the  large  bowel,  unlike  the  small,  the  longitudinal  fibres  of 
the  muscular  coat  do  not  form  a  complete  layer,  continuous  all  round  the  tube, 
but,  on  the  contrary,  are  broken  up  (Fig.  762)  into  three  bauds,  known  as  the 
taeniae  coll.  These  bands,  which  are  about  l  inch  (6  mm.)  wide,  begin  at  the  base 
of  the  vermiform  appendix,  and  run  along  the  surface  of  the  gut  at  nearly  equal 
distances  from  one  another  until  the  rectum  is  reached.  Here  they  spread  out 
and  form  a  layer  of  longitudinal  muscular  fibres,  which  is  continuous  all  round  the 
tube  (see  p.  1087).  The  bands  are  about  one-sixth  shorter  than  the  intestine  to 
which  they  belong ;  consequently,  in  order  to  accommodate  the  Itowel  to  the  length 
of  the  tieniffi,  the  gut  is  tucked  up,  giving  rise  to  a  sacculated  condition  (Fig.  762). 
Three  rows  of  pouches  or  saccules  are  thus  produced,  along  the  length  of  the  tube, 
between  the  tsenite.  If  the  t?enise  be  dissected  off,  the  sacculations  disappear, 
the  intestine  becomes  cylindrical,  and  at  the  same  time  about  one-sixth  longer. 

The  appendices  epiploicae  (Fig.  762)  are  little  processes  or  pouches  of  peritoneum, 
generally  more  or  less  distended  with  fat,  except  in  emaciated  subjects,  which 
project  from  the  serous  coat  along  the  whole  length  of  the  large  intestine,  mth  the 
exception  of  the  rectum  proper. 

When  the  interior  of  a  piece  of  distended  and  dried  large  intestine  is  examined,  its 
saccules  appear  as  rounded  pouches  (haustra),  separated  by  crescentic  folds  (pHcaj 
semilunares  coli),  corresponding  to  the  creases  on  the  exterior  separating  the  saccules 
from  one  another. 

The  position  of  the  three  tfenise  on  the  intestines  is  as  follows  : — On  the  ascending,  descending, 
and  iliac  colons  one  taenia  lies  on  the  anterior  aspect  of  tlie  gut,  and  two  behind,  namely,  one  to 
the  outer  (postero-extemal),  the  other  to  the  inner  side  (postero-internal).  It  is  chiefly  along 
the  first  of  these  (the  anterior)  that  tlie  a2Dpendices  epiploicae  are  found.  On  the  transverse 
colon  their  arrangement  is  different,  but  is  rendered  exactly  similar  by  turning  the  great 
omentum,  with  the  colon,  up  over  the  thorax.  On  the  transverse  colon  in  the  natural  position, 
the  anterior  taenia  of  the  ascending  and  descending  colons  becomes  the  j^osterior  (or  postero- 
inferior,  taenia  libera),  the  postero-extemal  becomes  the  anterior  (or  omental),  and  the  j^ostero- 
internal  the  superior  or  mesocolic.  The  anterior  and  postero-extemal  tfenire  of  the  iliac  colon 
pass  below  on  to  the  front  of  the  pelvic  colon  and  rectum. 

In  formalin-hardened  bodies  portions  of  the  large  inte.stine,  but  particularly  of  the  descending 
and  sigmoid  colons,  are  often  found  fixed  in  what  appears  to  be  a  state  of  contraction,  when 
they  are  reduced  to  a  diameter  of  about  f  or  ^  of  an  inch  (16  to  19  mm.).  Under  similar  con- 
ditions parts  of  the  small  intestine  are  found  correspondingly  reduced. 

The  appendices  epiploicae,  although  generally  said  to  be  absent  in  the  foetus,  can  be  distinctly 
seen  as  early  as  the  seventh  month,  but  at  this  time  they  contain  no  fat. 

Structure  of  the  Large  Intestine.  —  The  serous  coat  is  complete  on  the 
vermiform  appendix,  csecum,  transverse  colon,  and  pelvic  colon ;  incomplete  on  the 
ascending,  descending,  and  iliac  divisions  of  the  colon  and  on  the  rectum.  It  will  be 
described  in  detail  with  each  of  these  portions  of  the  intestine. 

The  mucous  coat  is  of  a  pale,  or  yellowish,  ash  colour  in  the  colon,  but  becomes  much 
redder  in  the  rectum.  Unlike  that  of  the  small  intestine,  its  surface  is  smooth,  owing  to 
the  absence  of  villi,  but  it  is  closely  studded  with  the  orifices  of  numerous  large 
Lieberkiihn's  glands.  Solitary  glands  are  also  numerous,  particularly  in  the  vermiform 
process  (Fig.  767). 

Vessels  and  Nerves. — The  caecum  and  vermiform  aj^i^endix  receive  their  blood  from  the 
ileo-colic  artery ;  the  ascending  colon  from  the  right  colic ;  and  the  transverse  colon  from  the 
middle  colic  which  lies  in  the  transverse  mesocolon.  These  are  all  branches  of  the  superior 
mesenteric  artery.  The  descending  colon  is  supplied  hx  the  left  colic,  and  the  iliac  and  pelvic 
colons  by  the  sigmoid  arteries,  branches  of  the  inferior  mesenteric.  The  rectum  derives  its  blood 
from  the  three  haemorrhoidal  arteries,  which  will  be  described  with  that  division  of  the  gut. 

The  veins  correspond  to  the  arteries,  and  join  the  inferior  and  superior  mesenteric  vessels, 
which  send  their  blood  into  the  portal  vein. 

The  lymphatics  begin  in  the  mucous  membrane,  and  form  a  large  plexus  in  the  submucosa  ; 
leaving  the  gut,  those  of  the  caecum,  ascending,  transverse,  and  upper  half  of  the  descending  colon, 
pass  to  the  mesocolic  glands,  which  lie  behind  the  ascending  and  descending  divisions  of  the  colon 
and  between  the  layers  of  the  transverse  mesocolon.  The  lymphatics  from  the  lower  half  of 
the  descending,  and  from  the  iliac  and  pelvic  colons,  join  the  left  lymphatic  trunk  of  the  lumbar 
glands.  Those  of  the  rectum  will  be  described  later. 
72  a 


1076 


THE  DIGESTIVE  SYSTEM. 


Nerves. — The  nerves  come  from  the  superior  mesenteric  plexus,  an  offshoot  of  the  solar 
plexus,  and  from  the  inferior  mesenteric,  a  derivation  of  the  aortic  plexus.  The  arrangement  is 
similar  to  that  of  the  nerves  of  the  small  intestine. 


Frenulum 

of  ileo--__^' 
colic  valve 


Tseuite  coli' 
Orifice  of  appendix 


\utPiioi'  tasnia  coli 


Upper  segment  of 
ileo-colic  valve 

Fi  enulum  of  the 
\ahe 

Oufice  of  valve 
Inferior 
segment 


THE  CiECUM  AND  APPENDIX. 

Csecum. — After  leaving  the  pelvic  cavity,  as  already  described,  the  terminal 
portion  of  the  small  intestine  passes  upwards,  backwards,  and  to  the  right,  and 
opens,  by  the  ileo-caecal  orifice,  into  the  large  intestine  some  2|  inches  from  its 

lower  end.  '  The  portion  of  the 
large  gut  which  lies  below  the 
level  of  this  orifice  is  known  as 
the  caecum  (caput  csecum  coli). 
In  shape  (Fig.  763)  it  is  a  wide, 
unsymmetrical,  or  lop-sided  cul- 
de-sac,  furnished  with  the  tsenise 
and  sacculations  usually  found  in 
the  large  intestine.  Its  lower  end 
ox  fundus  is  directed  downwards 
partoTnlum  and  inwards,  and  usually  rests 
on  the  front  of  the  right  psoas 
muscle,  close  to  the  brim  of  the 
pelvis ;  whilst  the  opposite  end 
is  directed  upwards  and  out- 
wards, and  is  continued  into  the 
ascending  colon. 

Fig.  763.— CjiCDM  showing  Ileo-c^cal  Valve.  j^-g  unsymmetrical  form  is  due  to 

The  cEecum  lias  been  distended  witli  air  and  dried,  and  a  portion    the    fact    that    the    outer    and    inner 
of  its  anterior  wall  has  been  removed.  portions  of  the  organ  undergo  an  un- 

equal development  in  the  child.  The 
inner  (or  inner  and  posterior)  section  lags  behind,  whilst  the  outer  (or  outer  and  anterior) 
division  grows  much  more  rapidly,  and,  projecting  downwards,  soon  comes  to  form  the  lower 
end  or  fundus  of  the  CEecum.  As  a  result  the  original  extremity  of  the  gut,  with  the  vermi- 
form process  springing  from  it,  is  hidden  away  behind  and  to  the  inner  side  of  the  fundus. 

In  length  the  distended  csecum  usually  measures  about  2|  inches  (60  mm.) ; 
whilst  its  Ireadth  is  usually  more,  and  averages  about  3  inches  (75  mm.). 

Position. — It  is  situated,  when  normal,  almost  entirely  within  the  right  iliac 
region  of  the  abdomen,  immediately  above  Poupart's  ligament ;  but  its  lower  end 
projects  inwards  in  front  of  the  psoas  and  reaches  the  hypogastrium  (Fig.  769). 
On  the  other  hand,  it  is  sometimes  found,  even  when  quite  healthy,  high  up  in 
the  right  lumbar  region  (owing  to  the  persistence  of  the  foetal  position),  or  hanging 
over  the  pelvic  brim  and  dipping  into  the  pelvic  cavity  to  varying  extents. 

In  the  great  majority  of  cases  the  csecum  is  completely  covered  by  peri- 
toneum on  all  aspects,  and  lies  quite  free  in  the  abdominal  cavity.  In  .a 
small  proportion,  namely,  about  6  or  7  per  cent  of  bodies,  the  posterior  surface 
(probably  as  a  result  of  adhesions)  is  not  completely  covered,  but  over  a 
greater  or  less  portion  of  its  extent  is  bound  down  to  the  posterior  abdominal 
wall  by  connective  tissue. 

Relations. — Behind,  the  csecum  rests  on  the  ilio-psoas  muscle ;  generally,  too, 
on  its  own  vermiform  process  and  the  external  iliac  artery.  In  front,  it 
usually  lies  in  contact  with  the  anterior  abdominal  wall ;  sometimes,  however, 
when  the  csecum  is  empty,  the  small  intestine  intervenes.  Its  outer  side  is 
placed  immediately  above  the  outer  half  of  Poupart's  ligament  (Fig.  769),  whilst 
the  inner  side  has  the  termination  of  the  ileum  lying  in  contact  with  it.  On  the 
inner  and  posterior  aspect,  but  more  on  the  former  than  the  latter,  the  small 
intestine  joins  the  csecum.  On  the  same  aspect,  and  usually  about  1^  inches 
(31  mm.)  lower  down,  the  venniform  process  comes  off. 

The  interior  of  the  csecum  corresponds  in  general  appearance  to  that  of 
the  large  intestine ;  but  it  presents  two  special  features  on  the  posterior 
part  of  its  inner  wall,  namely,  the   ileo-csecal   orifice,  guarded   by  the   ileo-caecal 


THE  C^CUM  AND  APPENDIX. 


1077 


valve,  aud  below  this  the  small  opening  of  the  vermiform  appendix,  both  of  which 
call  for  further  notice. 

Ileo-caecal  Valve  (valvula  coli). — Where  the  ileum  enters  the  large  in- 
testine, the  end  of  the  small  gut  is, 
as  it  were,  thrust  through  the  wall  of 
the  large  bowel,  carrying  with  it  certain 
layers  of  that  wall,  which  project  into 
the  caecum  in  the  form  of  two  folds, 
lying  respectively  above  and  below  its 
orifice,  and  constituting  the  two  seg- 
ments of  the  ileo-caecal  valve  (Fig.  765). 
The  condition  may  be  compared  to  a 
partial  inversion  or  telescoping  of  the 
small  into  the  large  intestine :  it  must 
be  added  that  the  peritoneum  and 
longitudinal  muscular  fibres  of  the 
bowel  take  no  part  in  this  infolding ; 
on  the  contrary,  they  are  stretched 
tightly  across  the  crease  produced  on 
the  exterior  by  the  inversion,  and  thus 
serve  to  preserve  the  fold  and  the 
formation  of  the  valve. 

As  seen  from  the  interior,  in  speci- 
mens which  have  been  distended  and 
dried  (Fig.  763),  the  valve  is  made  up 
of  two  crescentic  segments — an  upper, 
in  a  more  or  less  horizontal  place, 
forming  the  superior  margin  of  the 
aperture ;  and  a  lower,  which  is  also 


Upper 
segment- 
of  valve 

Orifice  of. 
valve 

Lower  JjL^iS 
segment  '^i' 

Prenuluin- 
of  valve 

Bristle 

passed 

through 

orifice  of 

appendix 


<:^ 


Fig.  764.- 
bodies 


Three  Forms  op  iLEo-CiECAL  Valve,  from 
hardened    by    intravascular    injections    of 


larger,  placed  in  an  oblique  plane,  aud 
sloping  upwards  and  inwards  (i.e. 
towards  the  cavity  of  the  caecum). 
Between  the  two  segments  is  situated 
the  slit -shaped  opening,  which  runs 
in  an  almost  antera4Kiale¥io^--dTre^ion, 
with  a  rounded  anterior  and  a  pointed 
posterior  extremity  (Fig.  763).  At  each 
end  of  the  orifice  the  two  segments  of 
the  valve  meet,  unite,  and  are  then 
prolonged  around  the  wall  of  the  cavity 
as  two  prominent  folds — the  frenula 
(frenula  valvulae  coli).  It  is  thought 
that  when  the  caecum  is  distended, 
and  its  circumference  thereby  increased, 
these  frenula  are  put  on  the  stretch, 
and,  pulling  upon  the  two  segments  of 
the  valve,  they  bring  them  into  apposi- 
tion, and  effect  the  closure  of  the  orifice. 

The  position  of  the  ileo-caecal  orifice,  in  the  average  condition,  may  be  indicated 
on  the  surface  of  the  body  by  the  point  of  intersection  of  the  intertubercular  and 
Poupart  lines.  A  point  1  to  Ih  inches  (2-5  to  3'7  cm.)  lower  down  would  correspond 
tO-  the  orifice  of  the  vermiform  process. 

Ill  bodies  hardened  in  situ  with  formalin,  the  valve  and  orifice  j^reseut  an  entirely  different 
appearance  (see  Fig.  764,  in  which  three  different  forms  of  hardened  valves  are  shown),  suggesting, 
much  more  closely  than  in  the  dried  state,  the  appearance  of  telescoping  or  inversion  mentioned 
above.  In  them  also  the  two  segments  of  the  valve  are  much  thicker  and  shorter,  but  they  can 
always  be  distinguished,  and  are  found  to  bear  the  same  relation  to  one  another  as  in  the  dried 
condition,  although  this  may  be  obscured  by  foldings  or  rugse.  The  aperture  may  be  slit-like  or 
rounded,  with  sloj)ing  or  infundibuliform  edges  ;  the  frenula  are  not  so  prominent  at  times  ;  but 
the  whole  valve  projects  much  more  abruptly  into  the  cavity  of  the  caecum  than  in  the  distended 
and  dried  specimen. 

72  & 


formalin. 

The  hardening  was  not  so  complete  in  the  case  of  the 
highest  of  the  three  valves  represented.  In  each 
a  bristle  is  passed  through  the  orifice  of  the  vermi- 
form appendix. 


1078 


THE  DIGESTIVE  SYSTEM. 


PERITONEUM 


Structure  of  the  Ileo-caecal  Valve. — Each  segment  of  the  valve  is  formed  of  an 
infolding  of  all  the  coats  of  the  gut,  except  the  peritoneum  and  the  longitudinal  muscular 
fibres,  and  consequently  it   consists  of  two  la^z^aia-J^f-^tttteotts-Hagterrrbrane,  with  the   sub- 

mucosa  and  the  circular  muscular  fibres  between,  all  of 
which  are  continuous  with  those  of  the  ileum  on  the  one 
hand  and  of  the  large  intestine  on  the  other.  The  surface 
of  each  segment  turned  towards  the  small  intestine  is 
covered  with  villi,  and  conforms  in  the  structure  of  its 
'^^"  mucous  membrane  to  that  of  the  ileum ;  whilst  the 
ANE  mucous  membrane  of  the  opposite  side  resembles  the 
mucous  coat  of  the  large  bowel. 

In  the  dried  specimen  the  upper  segment  usually  projects 
further  into  the  cavity  of  the  caecum  than  the  lower,  so  that 
the  aperture  appears  to  be  placed  betM^een  the  edge  of  the 
lower  segment  and  the  under  surface  of  the  upper. 

There  is  little  doubt,  as  pointed  out  by  Symington,  that 
the  efficiency  of  the  ileo-caecal  valve  is  largely  due  to  the 
oblique  manner  in  which  the  ileum  enters  or  invaginates  the 
csecum ;  this  oblique  passage  alone,  as  in  the  case  of  the 
ureter  piercing  the  wall  of  the  bladder,  would  probably  be 
sufficient  to  j^revent  a  return  of  the  ctecal  contents.  In  the 
great  majority  of  cases,  when  in  position  within  the  body,  the 

■pjy    jgg  Diagrammatic  Section    ileum  is  perfectly  protected  from  such  a  return,  although  when 

THROUGH  THE  JUNCTION  OF  ILEUM  the  parts  are  removed,  and  then  distended  with  fluid,  this  often 
WITH  CiEcuM,  TO  SHOW  THE  passes  througli  the  valve,  and  reaches  the  small  intestine. 
Formation  of  the  Ii-eo-c^cal  Still,  the  efficiency  of  such  a  test,  applied  when  the 
Yalye.  parts  are  deprived  of  their  natural  supports,  cannot  be  relied 

upon. 
The  size  of  the  segments  of  the  valve,  as  seen  in  the  dried  condition,  varies  considerably ; 
they  are  sometimes  very  im23erfect ;  and  even  the  absence  of  both  has  been  recorded.     But  here 
again  there  is  danger  of  falling  into  error,  through  examining  the  parts  under  such  artificial 
conditions. 

Development  of  Csecum  and  Appendix. — The  caecum  first  appears  in  the  embryo,  at  about 
the  fifth  week,  as  a  small  outgrowth  of  the  wall  of  the  j)rimitive  gut  (mid -gut),  not  yet 
dift'erentiated  into  small  and  large  intestines.  At  this  time  the  outgrowth  is  of  the  same  size 
throughout,  and  is  practically  equal  to  the  intestines  in  diameter.  About  the  eleventh  week, 
whilst  the  large  and  small  bowels  are  still  of  the  same  Avidth,  it  has  increased  very  considerably 
in  length  (being  equal  to  about  five  times  the  diameter  of  the  small  intestine,  and  thus  being 
relatively  as  long  as  in  the  adult) ;  but  even  at  this  early  date  the  basal  portion,  for  about  one- 
fifth  of  its  length,  is  quite  as  wide  as  the  intestine,  whilst  the  remaining  four-fifths  of  the  out- 
growth— the  future  appendix — is  only  about  one-half  or  one-third  the  diameter  of  the  gut. 
From  this  it  is  seen  that  the  distal  portion  of  the  outgrowth,  which  subsequently  becomes  the 
vermiform  process,  begins  to  lag  behind  even  at  this  eai'ly  j^eriod  of  its  development. 

The  basal  portion  continues  to  expand  with  the  gut ;  the  distal  part  grows  rapidly  enough 
in  leiigtli,  but  otherwise  enlarges  very  slowly,  so  that,  towards  the  end  of  foetal  life,  the  caecum 
has  attained  a  conical  shape,  the  wider  end  joining  the  ascending  colon,  the  narrow  end  tapering 
gradually  and  passing  into  the  vermiform  process.  This  form,  known  as  the  infantile  type  of 
ceecum,  is  retained  for  some  time  after  birth,  or  even  may  (in  2  or  3  -per  cent  of  cases)  persist 
throughout  lii'e. 

As  early  as  the  sixth  or  seventh  month  of  foetal  life  the  wall  of  the  terminal  jjortion  of  the 
small  intestine  adlieres  to  the  inner  side  of  the  caecum  for  some  distance  below  the  ileo-caecal 
orifice.  And  this  connexion,  which  is  rendered  more  intimate  by  tlie  passage  of  two  folds  of 
peritoneum,  one  on  the  front,  the  other  on  the  back,  between  the  two  parts,  profoundly  modifies 
the  subsequent  growth  of  the  Ciscura,  and  determines  very  largely  its  adult  form.  For,  when  the 
csecum  Ijegins  to  expand,  the  inner  aspect  is  prevented,  l)y  its  connexion  with  the  termination 
of  the  ileum,  from  eidarging  as  freely  as  the  rest  of  the  wall ;  in  consequence  of  this  the  outer 
part  grows  and  expands  much  more  ra^jidly,  producing  the  lojj-sided  appearance  already  referred 
to,  and  .soon  comes  to  form  the  lowest  jtart  or  fundus  of  the  caecum,  and  the  greater  part  of  its 
sac ;  whilst  the  original  apex,  with  the  vermiform  appendix  springing  from  it,  anchored,  as  it 
were,  to  the  end  of  the  ileum,  is  thrust  to  one  side,  and  finally  lies  on  the  inner  and  posterior 
aspect  of  the  caecum,  a  little  way  .below,  and  usually  posterior  to,  the  end  of  the  ileum. 

The  position  of  the  caecum  varies  at  different  periods  of  fcctal  life.  About  the  eleventh  or 
twelfth  week  it  lies  immediately  beneath  the  liver,  and  to  the  left  of  the  middle  line ;  it  then 
gradually  travels  to  the  right,  crossing  the  descending  duodenum,  and  is  found  lying  on  the 
right  side,  just  beneath  tlie  liver,  at  the  fourth  month.  From  this  it  descends  slowly  to  its 
adult  position,  which  it  usually  ajjjiroaches  towards  the  end  of  foetal  life,  but  it  may  not  actually 
reach  it  until  some  time  after  birth.  An  imperfect  descent  gives  rise  to  the  lumbar  position  of 
the  ctecum,  or  an  excess  in  this  direction  to  the  pelvic  position  (referred  to  on  p.  1076). 

Types  of  Caecum. — Three  chief  types  of  caecum  may  be  distiuguished — the/ceteZ  tyjje,  conical 
in  shape  and  nearly  symmetrical,  with  the  lower  end  gradually  passing  into  the  vermiform 


THE  C^CUM  AND  APPENDIX. 


1079 


appendix  ;  tlie  infantile,  in  which  the  passage  from  the  caecum  to  the  vermiform  process  becomes 
more  abrupt,  the  outer  Avail  more  prominent,  and  tlie  whole  sac  more  unsymmetrical ;  and  the  lop- 
sided adult  form,  as  described  above,  which  is  the  condition  found  in  93  or  94  per  cent  of  adults. 

Structure. — Nothing  in  the  arrangement  of  the  mucous  and  submucous  coats  calls 
for  special  notice.  Tlie  ttenia;  or  longitudinal  bands  of  the  muscular  coat  all  spring 
from  the  base  of  the  vermiform  appendix  (Fig.  766)  ;  the  anterior  runs  up  on  the  front, 
internal  to  the  main  prominence  of  the  c.rcum  ;  tlie  postero-external  runs  up  behind  this 
prominence ;  whilst  the  postero-internal  passes  directly  upwards  behind  the  ileum  (Fig. 
766).  Tlie  longitudinal  filires  on  the  upper  aspect  of  the  ileum  partly  join  the  postero- 
internal taenia  :  those  on  the  front  and  back  join  the  circular  fibres  of  the  large  gut. 

The  serous  coat  has,  in  connexion  with  it,  certain  folds  and  fossa^  which  are  described 
at  p.  1081. 

Vermiform  Process  or  Appendix  Caeci  (Fig.  768). — The  appendix  is  a  worm- 
like tubular  outgrowth  which  springs  from  the  inner  and  back  part  of  the  c?ecum 
about  1  to  1|  inches  (2'5  to  3'75  cm.)  below  the  ileo-ca3cal  orifice.  From  this  it 
generally  runs  in  one  of  three  chief  directions,  namely — (1)  over  the  brim,  into  tbe 
pelvis ;  (2)  upwards  behind  the  Cc^cum ;  or  (3)  upwards  and  inwards,  thus  pointing 


ANT 
CAECAL  A 


Fig.  766. — The  Blood  Scpply  of  thk  C^cni  and  Vermiform  Appendix. 

The  illustration  to  the  left  gives  a  front  view,  in  that  to  the  right  the  ca?cum  is  viewed  from  liehiiul.  In  the 
latter  the  artery  of  the  appendix,  and  three  taeuiaj  coli  springing  from  the  base  of  the  appendix, 
should  be  specially  noted  (modified  from  Jonnesco). 

towards  the  spleen ;  each  of  which  has  been  considered  to  be  the  normal  position 
by  one  or  more  observers.  In  the  first  of  these  situations  it  is  quite  evident  as  it 
hangs  over  the  pelvic  brim  ;  in  order  to  expose  it  in  the  second,  the  csecum  must  be 
turned  upwards ;  whilst,  in  the  third  position,  it  lies  behind  the  end  of  the  ileum 
and  its  mesentery,  and  these  must  be  raised  up  in  order  to  display  it.  In 
addition  to  the  positions  just  mentioned,  it  has  been  found  in  almost  every 
possible  situation  in  the  abdomen  which  its  length  and  the  extent  of  its  mesentery 
would  allow  it  to  attain.  In  every  case  the  anterior  taenia  of  the  ca?cum,  which  is 
always  distinct,  offers  the  surest  guide  to  the  process,  the  base  of  which  can  be 
located  with  certainty  by  following  this  taenia  to  the  liack  of  the  caecum  (Fig.  766). 

Its  size  is  almost  as  variable  as  its  position.  Taking  the  average  of  numerous 
measurements,  its  length  may  be  given  us  about  oh  inches  (92  mm..  Berry),  and  its 
breadth  as  \  inch  (6  mm..  Berry).  On  the  other  hand,  it  has  been  found  as  long  as 
9  inches  (230  mm.),  and  as  short  as  f  inch  (18  mm.).  Even  its  absence  has  been 
recorded  (Fawcett). 

Its  lumen  or  cavity  is  variable  in  its  development,  and  is  found  to  be  totally 
or  partially  occluded  in  at  least  one-fourth  of  all  adult  and  old  bodies  examined. 
This  is  looked  upon  as  a  sign  of  degeneracy  in  the  process,  which  is  by  many 
considered  to  be  undergoing  a  gradvial  obliteration  in  the  human  species.  It 
opens  into  the  cavity  of  the  caecum  on  its  inner,  or  inner  and  posterior  aspect 
(Fig.  763),  at  a  point  1  to  Ih  inches  (2-5  to  3"8  cm.)  below,  and  somewhat  behind 


1080 


THE  DIGESTIVE  SYSTEM. 


the  ileo-Ccecal  orifice.  These  are  the  relative  positions  of  the  two  orifices,  as  seen 
from  the  interior  of  the  caecum  ;  viewed  from  the  exterior,  the  base  of  the  appendix 
is  within  f  inch  of  the  lower  border  of  the  ileum.  This  apparent  difference  is  due 
to  the  fact  that  the  ileum  adheres  to  the  inner  side  of  the  caecum  for  a  distance  of 
nearly  1  inch  before  it  opens  into  it. 

Sometimes  the  orifice  of  the  appendix  has  a  crescentic  fold  or  valve  (valvula 
processus  vermiformis)  placed  at  its  upper  border  ;  but  it  is  probably  of  very  little 
functional  importance  when  present,  for  the  aperture  of  the  appendix  is  usually  so 
small  that  its  cavity  is  not  likely  to  be  invaded  by  the  contents  of  the  caecum. 

The  vermiform  process  is  completely  covered  by  peritoneum,  and  has  a  con- 
siderable mesentery,  the  meso- appendix  (mesenteriolum  processus  vermiformis), 
which  extends  to  its  tip  as  a  rule,  and  connects  the  process  to  the  under  surface  of 
that  part  of  the  mesentery  proper  which  goes  to  the  lower  end  of  the  ileum. 

The  appendix  is  relatively,  to  the  rest  of  the  large  intestine,  longer  in  the  child  at  birth  than 
in  the  adult,  the  proportion  being  about  1  to  16  or  17  at  birth  and  1  to  19  or  20  in  the 
adiilt.  (The  difference  is  certainly  not  as  great  as  stated  by  Eibbert,  who  makes  the  proportion 
1  to  10  at  birth  and  1  to  20  in  the  adult.)  The  process  attains  its  greatest  length  and  diameter 
during  adult  and  middle  age,  and  atrophies  slowly  after  that  time.  It  is  said  to  be  slightly 
longer  in  the  male  than  in  the  female. 

Total  occlusion  of  its  cavity  is  found  in  3  or  4  per  cent  of  bodies ;  it  is  then  converted  into  a 
fibrous  cord.  Partial  occlusion  is  present  in  25  per  cent  of  all  cases,  and  in  more  than  50  per  cent 
of  those  over  60  years  old,  whilst  it  is  unknown  in  the  child.  This  frequency  of  occlusion,  the 
physiological  atrophy  which  takes  place  after  middle  life,  the  great  variations  in  length,  and  other 
signs  of  instability,  have  been  considered  to  point  to  the  retrogressive  character  of  the  appendix. 

A  vermiform  process  is  found  only  in  man,  the  higher  apes,  and  the  wombat,  although  in 
certain  rodents  a  somewhat  similar  arrangement  exists.  In  carnivorous  animals  the  csecum  is  very 
slightly  developed  ;  in  herbivorous  animals  (with  a  simple  stomach)  it  is,  as  a  rule,  extremely  large. 
It  has  been  suggested  that  the  vermiform  process  in  man  is  the  degenerated  remains  of  the 
herbivorous  ceecum,  which  has  been  rejslaced  by  the  carnivorous  form.  Another  and  perhaps 
more  probable  view  regards  the  appendix  as  a  lymphoid  organ,  having  the  same  functions  as 
Peyer's  patches,  and  like  these  undergoing  degeneration  after  middle  life  (Berry). 

In  the  foetus  and  child,  as  well  as  in  the  adult  with  the  infantile  type  of  caecum,  the  appendix 
springs  from  the  true  aj^ex,  not  from  the  inner  and  posterior  aspect. 

Foreign  bodies,  although  reputed  to  find  their  way  very  easily  into  the  appendix,  are  rarely 
found  there  after  death.  On  the  other  hand,  concretions  or  calculi,  formed  of  mucus,  faeces,  and 
various  salts,  are  often  present  (Berry). 

Structure  (Fig.  767). — The  serous  coat  is  complete,  and  forms  a  perfect  investment 
for  the  process.     The  muscular  coat,  unlike  that  of  the  rest  of  the  large  intestine,  has  a 


Fk;.  767. — Stkucturk  df  thk  Vkumikokm  Ai'I'kndi.x. 
A.    From  a  child  two  years  old.  B.   From  a  male,  age  56. 

It  will  be  observed  that  the  .submiico.sa  is  almost  entirely  occupied  by  lymplioid  nodules  and  patches 


muscularis  mucosie  is  very  faint,  and  lies  quite  close  to  the  bases  of  Lieberkiihn's  glands, 
tudinal  layer  of  muscular  fibres  forms  a  continuous  sheet. 


The 
The  longi- 


coutinuous  and  stout  layer  of  longitudinal  fibres,  which  passes  at  the  root  of  the  process 
into  the  three  ttenia;  coli  (Fig.  768).  The  layer  of  circular  fiVn-es  is  well  developed.  The 
submucosa  is  almost  entii'ely  occupied  by  large  masses  of  lymplioid  tissue  surrounded  by 


THE  C^CUM  AND  APPENDIX. 


1081 


sinus-like  lymph  spaces.  Owing  to  the  large  size  of  these  lymphoid  nodules,  the  areolar 
tissue  of  the  submucosa  is  compressed  against  the  inner  surface  of  the  muscular  coat,  and 
forms  a  well-marked  fibrous  ring,  which  sends  processes  at  intervals  between  the  lymphoid 
masses  towards  the  mucous  membrane.  The  inner  portion  of  this  fibrous  ring  seems  to 
have  been  generally  mistaken  for  the  muscularis  mucosae,  which  lattei*,  as  seen  in  Fig. 
767,  lies  internal  to  the  chief  masses  of  lymphoid  tissue,  and  not  outside  it,  as  figured 
by  Testut.  These  lymphoid  nodules,  which  correspond  to  solitary  glands,  have,  owing  to 
their  great  number,  been  almost  completely  crushed  out  of  the  mucosa  (in  which  they 
chiefly  lie  in  the  intestine)  into  the  submucosa. 

The  mucous  coat  corresponds  to  that  of  the  large  intestine  in  its  general  characters, 
but  the  Liebei'kiihn's  glands  are  fewer,  and  irregular  in  their  direction  ;  the  muscularis 
mucosa?  is  thin  and  ill-defined  ;  it  lies  just  internal  to  the  lymphoid  nodules  of  the  sub- 
mucosa, and  immediately  outside  the  base  of  Lieberkuhn's  glands.  Some  few  lymphoid 
nodules  lie  in  the  mucous  coat  also 

Blood-vessels  of  the  Caecum  and  Vermiform  Appendix  (Fig.  766). — These  parts  are 
supplied  with  blood  by  the  ileo-csecal  artery.  This  gives  off,  near  the  upper  angle  formed  by 
the  junction  of  the  ileum  with  the  small  intestine — (o)  an  anterior  ccecal  artery,  which  passes 
down  on  the  front  of  the  ileo-csecal  junction  to  the  ctecuui,  and  breaks  up  into  numerous  branches 
for  the  supply  of  that  part;  (6)  a 2}Osterior  ccecal  artery,  similarly  disjjosed  on  the  back  ;  and  (c) 
the  artery  of  the  ai>pendix.  The  last-named  branch  passes  down  behind  the  ileum  (Fig.  766),  then 
enters  the  mesentery  of  the  appendix,  and  running  along  this  near  its  free  border,  sends  off  several 
branches  across  the  little  mesentery  to  the  appendix,  before  finally  ending  in  it.  The  coiu-se 
of  the  artery  behind  the  ileum  is  said  to  render  it  subject  to  pressure  from  faecal  masses  in  that 
gut,  and  thus  to  predispose  to  an  interference  with  the  suj^jjly  of  the  apjaendix,  and  morbid 
changes  in  the  process.  It  has  also  been  said  that  the  appendix  receives  a  small  branch  from  the 
left  ovarian  artery  in  the  female — a  statement  which  I  have  been  unable  to  verify. 

The  veins  correspond  to  the  arteries.  The  lymphatics  pass  with  the  vessels  to  join  a  few 
small  glands  which  are  found  in  the  mesentery  of  the  appendix  at  its  base,  the  efferent  vessels 
from  which  join  the  mesocolic  glands  behind  the  ascending  colon. 

Caecal  Folds  and  Fossae. — The  peritoneum  forms  in  the  neighbourhood  of  the 
ctecum  certain  fosste,  of  which  the  most  interesting  and  important  are — (a)  the  retro- 
cecal or  retro-colic  fossae ;  {h)  the  ileo-cfecal  fossa  ;  and  (c)  the  ileo-colic  fossa. 


The  C^cal  Folds  a>.d  Foss.e. 


In  A.  tlie  cfecuiu  is  viewed  from  the  front ;  the  mesentery  of  the  appendix  is  distinct,  and  is  attached  above 
to  the  under  surface  of  the  portion  of  the  mesentery  going  to  the  end  of  the  ileum.  lu  B,  the  crecum 
is  turned  upwards  to  show  a  retro-caecal  fossa,  which  lies  behind  it  and  the  beginuiug  of  the  ascending 
colon. 

The  retro-colic  fossae  (Fig.  768,  B)  are  only  occasionally  present,  and  are  exposed  by 
turning  the  ctecum  and  adjacent  part  of  the  ileum  upwards.  Two  forms,  external  and 
internal,  are  described;  the  first  lies  behind  the  outer  part  of  the  ascending  colon, 
immediately  above  the  cfecum  ;  the  second  behind  its  inner  part.  These  fossae  are 
specially  interesting  because,  when  present,  they  frequently  lodge  in  the  vermiform  process 
(see  Fig.  768,  B),  a  condition  which  is  said  to  favour  the  production  of  appendicitis. 

Ileo-caecal  Fossa  and   Fold. — If  the  appendix  be  drawn  down,  and  the  finger  run 


1082  THE  DIGESTIVE  SYSTEM. 

towards  the  ca)cum,  along  the  lower  border  of  the  terminal  part  of  the  ileum,  its  point 
will  generally  run  into  a  fossa  situated  in  the  angle  between  the  ileum  and  CEecum  (Fig. 
768,  A),  which  is  known  as  the  ileo-ctecal  fossa.  The  fold  which  bounds  the  fossa  in  front 
is  the  ileo-csecal  fold  (the  "bloodless  fold  of  Treves").  It  passes  from  the  ileum  to  the 
front  of  the  meso-appendix,  which  latter  forms  the  posterior  wall  of  the  fossa. 

Ileo-colic  Fold  and  Fossa. — Similarly,  if  the  finger  be  run  out  along  the  upjoer  border 
of  the  ileum  towards  the  caecum,  it  will  usually  lodge  in  a  smaller  fossa,  the  ileo-colic,  which 
is  bounded  in  front  by  a  small  peritoneal  process,  the  ileo-colic  fold  (Fig.  768,  A),  containing 
the  anterior  ctecal  arteiy. 

THE  COLON. 

Ascending  Colon  (colon  ascendens).  —  This  section  of  the  great  gut  begins 
about  the  level  of  the  intertubercular  plane,  opposite  the  ileo-caecal  orifice,  where 
it  is  continuous  with  the  csecum.  From  this  it  runs  upwards  and  somewhat  back- 
wards, with  a  slight  concavity  to  the  left,  until  it  reaches  the  under  surface  of  the 
liver,  where  it  bends  forwards  and  to  the  left,  and  passes  into  the  hepatic  flexure 
(Fig.  769).  In  its  course  it  lies  in  the  angle  between  the  quadratus  lumborum 
behind,  and  the  more  prominent  psoas  internally  (Fig.  742). 

It  is  situated  chiefly  in  the  right  lumbar  region,  but  it  extends  slightly  into 
the  hypochondrium  above ;  and,  although  it  usually  begins  about  the  level  of  the 
intertubercular  line,  still  with  a  low  position  of  the  csecum  it  will  extend  further 
down,  and  may  occupy  a  considerable  part  of  the  iliac  region. 

Its  length  is  about  8  inches  (20  cm.),  and  it  is  wider  and  more  prominent  than 
the  descending  colon.  It  generally  presents  several  minor  curves  or  flexures,  and 
it  often  has  the  appearance  of  being  pushed  into  a  space  which  is  too  short  to 
accommodate  it. 

Relations. — In  front,  it  is  usually  in  contact  with  the  abdominal  wall,  but  the 
small  intestine  frequently  intervenes,  particularly  above  (Fig.  739).  To  its  inner 
side  lie  the  coils  of  the  small  bowel  and  the  psoas ;  to  the  outer  side  is  the  lateral 
wall  of  the  abdomen.  Its  2yosterior  surface,  which  is  free  from  peritoneum  as  a 
rule  (Fig.  742),  is  connected  by  areolar  tissue  to  the  iliacus  muscle  as  far  up  as 
the  crest  of  the  ilium,  to  the  quadratus  lumborum  above  this,  and  finally  to  the 
lower  and  outer  part  of  the  right  kidney. 

In  the  great  majority  of  cases  only  the  two  sides  and  the  anterior  surface  are 
covered  by  peritoneum,  the  posterior  surface  being  destitute  of  a  serous  coat  (Fig. 
742).  In  a  small  proportion  of  bodies,  however,  the  ascending  colon  is  provided 
with  a  complete  peritoneal  coat  and  a  mesentery,  but  this  latter  is  so  short  that  it 
admits  of  but  a  slight  amount  of  movement  in  the  gut. 

Like  the  ctecuia,  the  ascending  colon  is  frequently  found  distended  with  gas  or  fa3ces  after 
death,  hence  in  part  its  large  size  and  prominence  as  compared  with  the  descending  colon,  which 
is  generally  empty. 

Hepatic  Flexure  (flexura  coli  dextra). — The  hepatic  flexure  is  the  bent  piece 
of  the  large  intestine  between  the  end  of  the  ascending  colon  and  the  beginning 
of  the  transverse  colon  (Figs.  758  and  769). 

AVhen  the  ascending  colon,  lying  on  the  front  of  the  kidney,  reaches  the  under 
surface  of  the  liver,  it  bends — usually  acutely,  sometimes  obtusely — forwards  and 
to  the  left,  and  on  reaching  the  front  of  the  descending  duodenum,  passes  into  the 
transverse  colon. 

The  fle.xure  is  placed  between  the  descending  duodenum  internally  and  the 
lower  thin  margin  of  the  liver,  or  the  lateral  abdominal  wall,  externally ;  above,  it 
corresponds  to  the  colic  impression  on  the  liver,  and  behind  it  rests  on  the  kidney. 
Its  peritoneal  relations  are  similar  to  those  of  the  ascending  colon. 

Transverse  Colon  (colon  transversum). — This  is  the  long  and  arched  portion  of 
the  large  intestine  which  lies  between  the  hepatic  and  splenic  flexures.  It  begins 
where  the  colon  crosses  the  descending  duodenum  at  the  end  of  the  hepatic  flexure 
(Fig.  769).  From  this  it  runs  transversely  to  the  left,  and  for  the  first  few 
inches  is  comparatively  fixed,  being  united  to  the  front  of  the  descending  duo- 
denum and  the  head  of  the  pancreas  either  by  a  very  short  mesentery  or  by  areolar 
tissue.     Immediately  beyond  this  a  long  mesentery  is  developed,  which  allows  the 


THE  COLON.  1083 

colon  to  hang  down  in  front  of  the  small  intestine,  at  a  considerable  distance  from 
the  posterior  abdominal  wall.  Towards  its  left  extremity  the  mesentery  shortens 
again,  thus  bringing  the  gut  towards  the  tail  of  the  pancreas  (Fig.  758),  along 
which  it  runs  upwards  into  the  left  hypochondrium,  under  cover  of  the  stomach, 
as  far  as  the  lower  end  of  the  spleen,  where  it  passes  into  the  splenic  flexure 
(Fig.  757).  Its  two  ends  lie  in  the  right  and  left  hypochondriac  regions  re- 
spectively, whilst  its  middle  portion  hangs  down  into  the  umbilical,  or  even  the 
hypogastric  region. 

Its  average  length  is  about  19  or  20  inches  (47'5  to  50*0  cm.),  that  is  more 
than  twice  the  distance,  in  a  direct  line,  between  its  two  extremities.  This  great 
length  is  accounted  for  by  the  curved  and  somewhat  irregular  course  wliich  the 
bowel  pursues. 

Relations.  —  The  greater  part  of  the  transverse  colon  lies  behind  the  great 
omentum,  which  must  consequently  be  turned  upwards  in  order  to  expose  it. 
Above,  it  is  in  contact,  from  right  to  left  (Fig.  769),  with  the  liver  and  gall-bladder, 
the  stomach,  and,  near  its  left  end,  with  the  tail  of  the  pancreas  and  lower  end  of  the 
spleen  (Fig.  758).  In  front  are  placed  the  omentum  and  the  anterior  abdominal 
wall ;  towards  its  termination  the  stomach  is  likewise  in  front.  Behind,  it  first  lies 
in  contact  with  the  descending  duodenum  and  head  of  the  pancreas ;  beyond  this, 
W'here  it  hangs  down,  the  small  intestine  is  placed  below  and  behind,  and  it  is  con- 
nected to  the  posterior  abdominal  wall  (more  correctly,  to  the  anterior  border  of  the 
pancreas)  by  the  transverse  mesocolon.  It  is  also  loosely  connected  to  the  stomach 
by  the  great  omentum,  which  is  attached  to  its  anterior  surface.  The  transverse 
mesocolon  and  the  great  omentum  are  described  with  the  peritoneum,  p.  1097. 

The  transverse  colon  is  completely  covered  by  peritoneum,  with  the  exception 
of  the  first  few  inches  of  its  posterior  surface,  which  are  often,  if  not  usuaUy, 
uncovered. 

The  state  of  tlie  peritoneal  covering  on  the  back  of  the  first  part  of  the  transverse  colon 
would  seem  to  depend,  in  some  degree,  on  the  extent  to  which  the  liver  passes  downwards  on 
the  right  side.  With  a  small  high  liver  no  mesentery  is  present,  and  the  posterior  surface  is 
devoid  of  peritoneum  ;  on  the  other  hand,  when  the  liver  is  enlarged  in  the  vertical  direction, 
it  pushes  the  colon  downwards  before  it,  and  brings  the  vipper  line  of  the  peritoneal  reflection 
from  its  back,  into  contact  with  the  lower,  thus  giving  rise  to  the  mesentery.  In  the  foetus  of 
three  or  four  months  every  part  of  the  colon  is  supplied  with  a  long  mesentery ;  subsequently 
this,  as  a  rule,  disappears  at  the  beginning  of  the  transverse  colon,  but  it  may  be  reproduced  in 
tlie  manner  stated. 

Splenic  Flexure  (flexura  coli  sinistra). — The  terminal  portion  of  the  trans- 
verse colon  runs  upwards  (also  backw^ards  and  to  the  left)  until  the  lower  end  or 
base  of  the  spleen  is  reached ;  here  it  bends  sharply,  forming  the  splenic  flexure, 
and  runs  down  into  the  descending  colon.  The  flexure  is  placed  deeply  in  the  left 
hypochondrium,  behind  the  stomach,  and  in  contact  with  the  base  of  the  spleen. 
It  lies  at  a  higher  level  than  the  hepatic  flexure,  and  is  connected  to  the 
abdominal  parietes  by  the  phreno-colic  ligament,  which  helps  to  maintain  it  in 
this  position. 

Phreno-colic  or  Costo-colic  Ligament  (ligamentum  phrenocolicum.  Fig.  758). — 
This  is  a  triangular  fold  of  peritoneum,  with  a  free  anterior  border,  which  is 
attached  internally  to  the  splenic  flexure  and  externally  to  the  diaphragm  opposite 
the  eleventh  rib.  Owing  to  the  fact  that  the  base  of  the  spleen  rests  upon  it,  the 
ligament  has  also  received  the  name  of  sustentaculum  lienis. 

The  phreno-colic  ligament  is  formed  in  the  foetus  from  the  left  margin  of  the  great  omentum 
(Jonnesco  and  Fig.  758). 

The  peritoneal  covering  of  the  splenic  flexure  is  similar  to  that  of  the  descending  colon. 

Descending  Colon  (colon  descendens). — This  is  much  narrower  and  less  obtrusive 
than  the  ascending  colon  :  indeed  in  a  large  number  of  cases  it  is  found  firmly 
contracted.  It  begins  in  the  left  hypochondrium  at  the  splenic  flexure,  passes 
down  on  the  left  side  of  the  abdomen,  and  ends  in  the  lumbar  region,  opposite  the 
crest  of  the  ilium,  by  passing  into  the  iliac  colon.  Its  course  is  not  quite  straight, 
for  it  first  curves  downwards  and  inwards  along  the  outer  side  of  the  left  kidney, 
and  then  descends  almost  vertically  to  the  iliac  crest  (Fig.  769).    . 


1084 


THE  DIGESTIVE  SYSTEM. 


Its  length  is  usually  from  4  to  6  inches  (10  to  15  cm.),  and  its  width,  which  is 
less  than  that  of  the  ascending  colon,  about  Ih  inches  (37  mm.). 

Relations.— The  descending  colon  first  hes  in  contact  with  the  outer  aspect  of 
the  left  kidney;  below  this  it  is  placed,  hke  the  colon  of  the  opposite  side,  in  the  angle 
between  the  psoas  and  quadratus  lumborum  muscles.  Behind,  it  rests  upon  the 
lower  part  of  the  diaphragm  above,  and  on  the  quadratus  lumborum  below.  In 
front  (and  somewhat  to  the  outer  side  also,  except  when  the  bowel  is  distended) 
are  placed  numerous  coils  of  small  intestine,  which  hide  the  colon  completely  from 


Attachment  of_ 
falcifoi'iii  ligament 


Tenninal  part  of  ileum - 


-Stomach 


_Spleeii  (anterior 
angle) 

-Splenic  flexure 

Transverse  mesocolon, 
-with  stomach  resting 
on  it 


Terminal  part  of 
duodenum 


"Descending  colon 


-Root  of  mesentery  (cut) 


Pelvic  (sigmoid) 
mesocolon 


^Pelvic  colon  (sigmoid 

M  fle\ure) 


SCALE  IN  INCHES 


SCALE  IN  CENTIMETRES 


Fig.  769. — The  Abdominal  Viscera  after  the  Removal  of  the  Jejunum  and  Ileum  (from  a  photograph 
of  the  same  body  as  depicted  in  Fig.  739).  The  transverse  colon  is  much  more  regular  than  usual. 
Both  the  liver  and  csecum  extend  lower  down  than  normal.  The  subdivisions  of  the  abdominal  cavity 
are  indicated  by  dark  lines. 

view,  and  compress  it  against  the  posterior  abdominal  wall.     To  its  inner  side  lies 
the  lower  part  of  the  kidney  above,  the  psoas  below. 

In  the  great  majority  of  bodies  only  the  front  and  sides  of  the  descending 
colon  are  covered  by  peritoneum  (Fig.  779) ;  the  posterior  surface,  being  destitute 
of  a  serous  coat,  is  connected  to  the  posterior  wall  of  the  abdomen  by  areolar 
tissue.  In  a  small  proportion  of  cases,  on  the  other  hand,  the  serous  coat  is  com- 
plete, and  the  colon  is  furnished  with  a  short  mesentery. 

Up  to  the  fourtii  or  fifth  month  of  foetal  life  the  descending  colon  has  a  complete  investment 
-of  peritoneum  and  a  long  mesenteiy.  After  the  fifth  month  the  mesentery  adheres  to,  and  soon 
blends  with,  tlie  parietal  peritoneum  on  the  posterior  abdominal  wall,  and  is  com])letely  lost  as 
a  rule.  The  persistence  of  this  mesentery,  in  a  greater  or  less  degree,  exj^lains  the  occasional 
jjresence  of  a  uescending  mesocolon  in  the  adult. 

Sigmoid  Flexure  and  Rectum. — It  was  formerly  customary  to  divide  the  remaining  portion 
of  the  large  intestine  into  .sigmoid  flexure  and  rectum.  Tlie  former  was  said  to  begin  at  the 
crest  of  the  ilium,  to  lie  in  the  iliac  fo.ssa,  and  to  end  at  the  brim  of  tlie  pelvis.  Or,  in  later 
years,  the  ".sigmoid  colon"  was  described  as  "that  part  of  the  colon  which  is  'attached  to  the 
ieft  iliac  foasa,  from  the  iliac  crest  to  the  brim  of  the  true  pelvis  "  (Symington).  Its  upper  part 
<was  said  to  be  covered  by  peritoneum  on  the  anterior  and  lateral  surfaces  only,  its  lower  part 


^QOh^'^'-XS^^^fZCc^ur-') 


to  form  a  large  loop  with  a  complete  serous  coat  and  a  long  mesentery,  which ^ung  down  into 
the  pelvic  cavity  when  tlie  bladder  and  rectum  were  empty,  and  passed  up  out  of  it  when 
these  were  distended. 

The  rectum  was  described  as  beginning  at  the  brim  of  the  pelvis,  opposite  the  left  sacro-iliac 
joint,  and  as  ending  at  tlie  anus.  It  was  divided  into  three  portions,  of  wliicli  the  first  extended 
from  the  brim  of  the  pelvis  to  the  middle  of  the  third  piece  of  the  sacrum,  had  a  complete 
covering  of  jieritoneum,  and  was  connected  to  the  pelvic  wall  by  a  mesentery — the  mesorectum. 
The  second  and  third  jJarts  of  the  rectum  we  may  i)ass  over  for  the  present,  as  they  agree  in 
general  with  the  description  of  the  rectum  given  below. 

Treves  in  1885,  and  Jonnesco  in  1889,  directed  attention  to  the  fact  that  no  such  loop  as  the 
classical  sigmoid  flexure,  lying  in  the  iliac  fossa,  was  to  be  fouiid  in  nature ;  and  also,  that  the 
separation  of  the  first  portion  of  the  rectum  from  the  sigmoid  flexure — so-called — was  both 
artificial  and  inaccurate.  They  pointed  out  that  the  "  first  part  of  the  rectum  "  really  belongs 
to  the  sigmoid  flexure,  with  which  it  has  everything  in  common,  and  that  on  no  grounds  could 
it  be  properly  assigned  to  the  rectum. 

An  unbiassed  study  of  the  parts  concerned,  particularly  in  bodies  the  viscera  of  which  have 
been  hardened  in  situ,  will  leave  little  doubt  on  an  unprejudiced  mind  that  the  old  descriptions 
are  not  only  artificial  but  erroneous.  Consequently,  the  admirable  account  of  this  part  of  the 
intestine,  given  by  Jonnesco,  will  be  followed  in  its  main  features  in  describing  the  divisions  of 
the  bowel  heretofore  known  as  the  sigmoid  flexure  and  first  part  of  the  rectum. 

Jonnesco,  recognising  that  this  portion  of  the  intestine  lies  partly  in  the  iliac  fossa  and 
partly  in  the  pelvis,  very  appropriately  calls  the  former  the  iliac  colon  and  the  later  the  pelvic 
colon.  The  iliac  colon  includes  the  portion  of  the  "  sigmoid  flexure  "  which  extends  from  the 
crest  of  the  ilium  to  the  inner  side  of  the  psoas  muscle  (that  is  practically  the  brim  of  the 
jjelvis),  and  is  usually  destitute  of  a  mesentery.  The  pelvic  colon  embraces  the  remainder  of  the 
"  sigmoid  colon  "  and  the  first  part  of  the  rectum,  both  of  which  are  attached  by  a  continuous 
mesentery,  and  form  one  large  loop  lying  in  the  pelvic  cavity,  and  ending  at  the  level  of  the 
third  sacral  vertebra  by  passing  into  the  rectum  proper.  ^t , 

Iliac  Colon  (colon  iliacum). — This  corresponds  to  the  portion  of  the  "sigmoid 
flexure  "  which  lies  in  the  iliac  fossa,  and  it  has  no  mesentery.  It  is  the  direct 
continuation  of  the  descending  colon,  with  which  it  agrees  in  every  detail,  except 
as  regards  its  relations.  Beginning  at  the  crest  of  the  ilium,  it  passes  downwards 
and  somewhat  inwards,  lying  in  front  of  the  iliacus  muscle.  A  little  way  above 
Poupart's  ligament  it 
turns  inwards  over 
the  psoas,  and  ends 
at  the  inner  border 
of  this  muscle  by 
dipping  into  the 
pelvis  and  becoming 
the  pelvic  colon  (Fig 
769).  It  usually 
measures  about  5  or 
6  inches  (12*5  to  15 
cm.)  in  length,  but  it 
varies  considerably  in 
this  respect. 

Relations.  —  Be- 
hind, it  lies  upon, 
and,  as  a  rule,  is  con- 
nected by  areolar 
tissue  to,  the  front  of 
the  ilio-psoas  muscle. 
In  front,  it  is  usually 
covered  by  coils  of 
small  in  testine,  which 
hi4e  it  from  view;  but 
when  distended,  or 
it  occupies  a 
position  than 
it  comes  into 
contact    with 


Cut  edgp  of 

peritoueuiii' 

Situation  of 

intersigmoid- 

fossa 

Pelvic  colon 

turning  down' 

Pelvic 
mesocolon' 

Beginning  of 
rectum" 


Pelvic  colon 


Bladder 


Fig.  770. — The  Iliac  and  Pelvic  Colons,  from  a  fonnaliu-hardeiied  male 
body,  aged  30. 

The  pelvic  coloii  was  unusually  long  ;  its  course  is  shown,  as  well  as  that  of  the 
beginning  of  the  rectum,  by  dotted  lines.  It  first  runs  across  the  upper 
surface  of  bladder  to  the  right  pelvic  wall,  then  recrosses  the  pelvis  in  a 
line  posterior  to  its  first  crossing  ;  finally  it  returns  towards  the  middle 
line,  and  passes  into  the  rectum.  As  a  rule,  after  crossing  to  the  right 
side  of  the  pelvis,  the  pelvic  colon  turns  backwards  and  inwards  to  reach 
the  middle  line,  where  it  passes  into  the  rectum. 


when 

lower 

usual, 

direct 

the  anterior  abdom 

inal  waD.  As  a  rule  (90  per  cent  of  bodies — Jonnesco),it  is  covered  by  peritoneum  only 


1086  THE  DIGESTIVE  SYSTEM. 

on  its  anterior  and  two  lateral  surfaces.     Occasionally  (10  per  cent  of  cases)  it  is  com- 
pletely covered,  has  a  short  mesentery  (1  inch,  2  to  3  cm.),  and  is  slightly  movable. 

In  its  course  it  passes  down  over  tlie  iliac  fossa  near  its  middle,  generally  forming  a  curve 
■witli  its  concavity  directed  inwards  and  upwards,  and  having  reached  a  point  1^  or  2  inches  (4 
to  5  cm.)  above  Poui^art's  ligament,  it  turns  inwards  across  the  psoas  towards  the  pelvic  cavity. 
Occasionally  the  iliac  colon  occu])ies  a  lower  position  than  usual,  and  runs  along  the  deep  surface 
of  Poupart's  ligament,  immediately  behind  the  anterior  abdominal  wall. 

Pelvic  Colon  (colon  pslvinum).  • —  This  corresponds  to  the  portion  of  the 
"  sigmoid  flexure  "  which  hes  in  the  pelvis,  together  with  the  so-called  "  first  part  of 
the  rectum."  The  pelvic  colon  is  a  large  coil  of  intestine,  which  begins  at  the  inner 
border  of  the  left  psoas  muscle,  where  it  is  continuous  with  the  iliac  colon,  and 
ends  at  the  level  of  the  third  sacral  vertebra  by  passing  into  the  rectum  proper. 
Between  these  two  points  it  has  a  well-developed  mesentery,  and  forms  a  large  and 
variously-shaped  coil,  which  usually  lies  in  the  cavity  of  the  pelvis  (93  per  cent). 

Whilst  the  loop  of  the  pelvic  colon  is  very  irregular  in  form,  the  following  may 
be  given  as  perhaps  its  most  common  arrangement.  Beginning  at  the  inner  margin 
of  the  left  j)Soas,  it  first  plunges  over  the  brim  into  the  pelvis,  and  crosses  this 
cavity  from  left  to  right ;  it  next  bends  backwards  and  then  returns  along  the 
posterior  waU  of  the  peMs  towards  the  middle  line,  where  it  turns  down  and  passes 
into  the  rectum  (Figs.  769  and  770). 

Relations. — In  its  passage  into  the  pelvis  it  crosses  the  external  iliac  vessels ; 
in  running  from  left  to  right  across  the  cavity,  it  rests  on  the  bladder  or  uterus, 
according  to  the  sex  ;  whilst  above  it  lie  the  coils  of  the  smaU  intestine. 

It  is  completely  covered  by  peritoneum,  and  is  furnished  with  an  extensive 
me-sentery — the  pelvic  mesocolon — which  permits  of  considerable  movement. 

Sometimes,  when  longer  than  usual  (Fig.  770),  the  pelvic  colon,  in  returning  from  the  right 
side  of  the  pelvis,  crosses  the  middle  line,  going  even  as  far  as  the  left  wall,  and  then  turns 
bick  a  second  time  towards  the  middle  of  the  sacrum,  where  it  joins  the  rectum  at  the  usual 
level,  thus  making  an  S-shaped  curve  within  the  pehas.  On  the  other  hand,  when  the 
loop  is  short  (a  not  infrequent  occurrence),  all  its  curves  are  abridged,  and  it  fails  to  pass 
over  to  the  right  side,  but  runs  more  or  less  directly  backwards  after  entering  the  pelvis. 

From  what  has  been  said  it  will  be  seen  that  the  loop  of  the  pelvic  colon  is  subject  to 
numerous  and  considerable  variations,  which  are  chiefly  dependent  upon  its  length  and  that  of 
its  mesentery,  and  also  upon  the  state  of  emptiness  or  distension  of  itself  and  of  the  other  pelvic 
viscera.  When  the  intestine  is  long  the  loop  is  more  complex  ;  when  short,  more  simple.  When 
the  bladder  and  rectum  are  distended,  or  when  the  pelvic  colon  itself  is  much  distended,  it  is 
unable  to  find  accommodation  in  the  true  pelvis,  and  consequently  it  passes  up  into  the 
abdominal  cavity,  almost  any  part  of  the  lower  half  of  which  it  may  occupy.  But,  as  already 
stated,  in  the  great  majority  of  cases  (92  per  cent,  according  to  Jonnesco)  it  is  found  after 
death  lying  entirely  within  the  pelvic  cavity. 

In  length,  the  pelvic  colon  generally  measures  about  16  or  17  inches  (40  to 
42'5  cm.),  but  it  may  be  as  short  as  5  inches  (12  cm.),  or  as  long  as  35  inches 
(84  cm.). 

The  pelvic  mesocolon,  which  corres2:)onds  to  both  the  sigmoid  mesocolon  and  the  meso- 
rectum,  is  a  fan-shaped  fold,  short  at  each  extremity,  and  long  in  its  middle  portion  (Figs.  769 
and  770).  Its  root  is  attached  along  an  inverted  V-shaped  line,  one  limb  of  which  runs  up  close 
to  the  inner  border  of  the  left  psoas,  as  high  as  the  bifurcation  of  the  common  iliac  artery  (or 
often  higher) ;  here  it  bends  at  an  acute  angle,  and  the  second  limb  descends  over  the  sacral 
promontory  and  along  the  front  of  the  sacrum  to  the  middle  of  its  third  piece,  where  the 
mesentery  ceases,  and  the  pelvic  colon  passes  into  the  rectum.  Wlien  the  pelvic  colon  ascends 
into  the  abdominal  cavity  this  mesentery  is  doubled  up  on  itself,  the  side  which  was  naturally 
posterior  becoming  anterior. 

Intersigmoid  Fossa  (recessus  intersigmoideus). — When  the  pelvic  colon  with  its  mesentery 
is  raised  upwards,  a  small  orifice  will  usually  be  found  beneath  the  mesentery,  correspond- 
ing to  the  apex  of  the  V-shaped  attachment  of  its  root  to  the  posterior  abdominal  wall. 
This  orifice  leads  into  a  fossa  which  is  directed  upwards,  and  will  often  admit  the  last 
joint  of  the  little  finger.  It  is  kno-HTi  as  the  intersigmoid  fossa,  and  is  due  to  the  imperfect 
blending  of  the  mesentery  of  the  descending  colon  of  the  fa3tus  with  the  parietal  peritoneum. 
In  the  foetus  this  mesentery  is  well  develoj^ed,  and  extends  from  the  region  of  the  vertebral 
column  out  towards  the  descending  colon.  After  a  time  it  begins  to  unite  with  the  underlying 
parietal  peritoneum ;  but  in  the  region  of  the  intersigmoid  fossa  the  union  is  rarely  perfect, 
hence  the  presence  of  the  fossa. 

In  the  child  at  birth  only  the  terminal  part  of  the  pelvic  colon  lies  in  the  pelvis.  This 
is  chiefly  owing  to  the  small  size  of  the  pelvic  cavity  m  the  infant.  Beginning  at  the  end 
of  the   iliac  colon,  the  pelvic  colon   generally  arches   upwards   and   to   the   right   across  the 


i 


THE  EECTUM. 


1087 


abdomen  towaixls  the  right  iliac  fossa,  -wheie  it  fuims  one  or  two  coils,  and  then  passes  down 
over  the  right  side  of  the  pelvic  brim  into  the  pelvic  cavity.  In  cases  of  imjierforate  anus,  it  is 
important  to  remember,  in  connexion  with  the  operation  for  forming  an  artificial  anus,  that, 
whilst  the  iliac  colon  is  found  in  the  left  iliac  region,  the  pelvic  colon  ("sigmoid  flexure")  usually 
lies  on  the  right  side,  and  passes  over  the  right  portion  of  the  brim  to  enter  the  pelvis. 

Structure  of  the  Pelvic  Colon.— Only  the  arrangement  of  the  muscular  coat  need  be  referred 
to.  As  the  taenia?  of  the  descending  colon  are  followed  downi,  it  will  be  found  that  the  postero- 
external band  gradually  passes  on  to  the  front,  and  unites  with  the  anterior  tienia  to  form  a  broad 
band,  which  occupies  nearly  the  whole  width  of  this  bowel  in  its  lower  portion.  The  postero- 
internal tfenia  spreads  out  in  a  similar  manner  on  the  })ack  ;  so  that  in  the  lower  half  of  the 
pelvic  colon  the  longitudinal  layer  of  the  muscular  coat  is  complete,  with  the  exception  of  a 
narrow  part  on  each  side  ;  here  the  circular  fibres  come  to  the  surface,  and  the  intestine  presents 
a  series  of  small  sacculation-s.  These,  however,  disappear,  and  the  longitudinal  fibres,  although 
thicker  in  front  and  behind,  -form  a  continuous  layer  all  round,  as  the  rectum  proper  is 
approached. 

THE  EECTUM. 

The  rectum  (proper  intestinum  rectum  :  second  portion  of  the  rectum  accordincr 
to  the  older  method  of  description)  is  the  comparatively  dilated  portion  of  the  lar^e 
bowel  which  intervenes  between  the  pelvic  colon  al)0ve  and  the  anal  canal — the 


Posterior  superior  spine 


Upper  lateral  inflexion 


Peritoneum  (jiararectal 
fossa)- 


Su  perior' hKiuorrhoidal 
artery 


Rectiun 

Great  sciatic  ligament 
Ischio-rectal  fossa 

Anal  canal 


Third  sacral  vertebra 


Fourth  sacral  vertebra 

(cut) 

fjower  border  of 

pyriformis  (cut) 

.Superior  hemorrhoidal 
artei-v 


Lateral  inflexion 
Goccygeus 

Levator  ani 
External  sphincter 


Fig.  771. — The  Rectum  from  behind. 

The  sacrum  has  beeu  sawu  across  through  the  4th  sacral  vertebra,  aud  its  lower  part  reinoveil  with  the  coccyx. 
The  posterior  portions  of  the  coccygei,  levatores  ani,  and  of  the  external  sphincter  have  been  cut  away. 
The  "  pinching  in  "  of  the  lower  end  of  the  rectum  by  the  inner  edges  of  the  levatores  ani,  resulting  in  the 
formation  of  the  flattened  anal  canal,  is  suggested  in  the  illustration,  which  has  been  made  from  a 
formaliu-hardened  male  body,  aged  thirty.  The  lateral  inflexions  of  the  rectum,  corresponding  to 
Houston's  valves,  are  also  shown. 

sht-like  passage  through  which  it  communicates  with  the  exterior  (Fig.  771).  It 
forms  a  temporary  reservoir  in  which  the  faces  accumulate  a  short  time  before  they 
are  discharged  from  the  body,  but  as  a  result  of  habit  this  temporary  function  may 
be  converted  into  a  more  or  less  permanent  one. 

Unlike  the  portion  of  the  bowel  which  immediately  precedes  it,  the  rectum  has 
but  a  partial  covering  of  peritoneum,  and  is  entirely  destitute  of  a  mesentery  ; 


1088 


THE  DIGESTIVE  SYSTEM. 


sacculations,  too,  which  are  so  characteristic  of  the  large  intestine,  cannot  properly 
be  said  to  be  present. 

The  rectum  begins  at  the  termination  of  the  pelvic  mesocolon,  namely,  about  the 
level  of  the  thiniiaciaL  vertebra,  and  ends,  where  the  bowel  pierces  the  pelvic  floor, 
opposite  the  lower  and  back  part  of  the  prostate  in  the  male,  or  at  a  point  Ih  inches 
(3-7  cm.)  in  front  of,  but  at  a  lower  level  than,  the  tip  of  the  coccyx  in  both  sexes. 
It  first  descends  along  the  front  of  the  sacrum  and  coccyx,  following  the  curve  of 
these  bones;  beyond  the  coccyx,  it  rests,  for  about  1|  inches  (3-7  cm.),  on  the  back 
part  of  the  pelvic  floor,  here  formed  by  the  union  of  the  two  levatores  ani;  and 
finally,  having  reached  the  lower  part  of  the  prostate,  it  bends  rather  abruptly 


Lateral  inflexions 


TTnppr  leetal  \nhp 


Ureter  (cut) 


Vesicula  seminalis 


\  as  deferen 


Piostatic  venous 
plpxus 

^^  lute  line  of  pelvic  fascia 

L6%ator  am 
<  )utlme  of  empt)  bladdei 


Base  of  i)rostate  Urethra 

Fig.  772. — Distended  Rectum  in  situ. 

From  a  fornialin-hardened  male  body,  age  56.  The  peritoneum  and  extra-peritoneal  tissue  have  been  removed^ 
after  sawing  the  pelvis  along  a  plane  passing  through  the  upper  part  of  the  symiihysis  pubis  iu  front 
and  the  lower  part  of  tlie  second  sacral  vertebra  behind.  The  bladder,  which  was  empty  and  contracted, 
has  also  been  removed,  but  its  form  is  shown  by  a  dotted  line.  The  rectum  was  very  much  distended, 
and  almost  completely  occupied  the  jjararectal  fossw. 

backwards  and  downwards,  and,  piercing  the  pelvic  flo(jr,  passes  into  the  anal 
canal  (Fig.  774). 

Its  general  direction  is  downwards,  but  this  varies  at  its  two  extremities,  being 
downwards  and  backwards  above,  downwards  and  strongly  forwards  below. 

Curvatures. — The  rectum  is  far  from  straight,  notwithstanding  its  name, 
whicii  descriijes  its  condition  fairly  accurately  in  most  animals,  but  not  in  man,  in 
whom  it  is  curved  in  both  the  antero -posterior  and  the  transverse  planes. 
Viewed  from  the  side,  it  forms  a  gentle  curve,  with  the  convexity  back- 
wards, which  extends  from  the  beginning  of  the  rectum  to  the  back  of  the 
prostate,  and  fits  into  the  hollow  of  the  sacrum  and  coccyx.  At  the  back  of  the 
prostate  a  second  curve  is  formed  where  the  rectum  joins  the  anal  canal;    this 


THE  EECTUM.  I  1089 

has  its  convexity  directed  forwards,  whilst  its  concavity  embraces  the  ano-coccygeal 
ibody — the  mass  of  muscular  and  connective  tissue  which  lies  between  the  tip  of 
the  coccyx  and  the  anal  canal. 

When  viewed  from  the  front  the  rectum  is  seen  to  be  regularly  folded  from  side 
to  side  in  a  zigzag  fashion,  the  folding  being  slightly  marked  when  the  rectum  is 
empty,  but  becoming  much  more  distinct  with  distension  (Figs.  772  and  773).  In 
other  words,  when  viewed  from  this  aspect  it  presents,  in  the  majority  of  cases,  three 
more  or  less  distinct  lateral  flexures  or  inflexions.  Of  these  the  upper  and  lower 
have  their  concavities  directed  to  the  left  as  a  rule ;  the  third  flexure,  which  is  the 
best  marked,  lies  between  the  other  two,  but  on  the  right  side.  Not  infrequently, 
however,  two  are  found  on  the  right  and  one  on  the  left  side.  The  flexures,  which 
are  marked  on  the  exterior  by  a  crease,  appear  in  the  interior  as  three  prominent 
crescentic  shelves  (Fig.  774),  known  as  the  rectal  valves,  which  help  to  support  the 
fsecal  contents  when  the  rectum  is  distended  (Fig.  772). 

This  folding  is  maintained  by  the  arrangement  of  the  longitudinal  nuiscular  fibres,  the 
majority  of  wliich  are  accumulated  in  the  form  of  two  wide  bands,  one  on  the  front,  tlie  other  on 
the  back  of  the  bowel.  These  two  bands,  which  are  continuous  with,  and  comj^arable  in  their 
functions  to,  the  tteuise  of  the  colon,  are  shorter  than  the  other  coats  of  the  rectum  ;  hence  they 
give  rise,  as  in  the  case  of  the  colon,  to  a  folding  or  sacculation  of  the  tube,  which  can  be  effective 
only  at  the  sides  where  the  longitudinal  fibres  are  fewest,  for  the  front  and  back  are  occupied  by 
the  thickened  longitudinal  bands  (see  p.  1092). 

In  addition  to  supporting  the  faeces,  these  foldings  greatly  increase  the  capacity  of  the  rectum 
without  unduly  dilating  the  tube.  When  the  rectum  is  empty  (Fig.  773)  its  course  is  comparatively 
straight,  its  lateral  flexure  being  but  slightly  marked,  and  its  whole  calibre  very  much  reduced. 
In  this  condition  it  occupies  only  a  small  portion  of  the  posterior  division  of  the  pelvic  cavity 
near  the  mesial  plane,  and  at  each  side,  between  it  and  the  lateral  wall  of  the  jjelvis,  is  a  large 
fossa  of  the  jjeritoneum  (the  j^ararectal  fossa,  p.  1101),  which,  when  the  bowel  is  empty,  contains 
a  mass  of  small  intestine  or  pelvic  colon  (Figs.  771  and  773).  When  the  rectum  is  distended  the 
lateral  flexures  become  much  more  marked,  and  the  gut,  projecting  alternately  to  each  side,  passes 
out  beneath  the  peritoneum,  obliterating  the  pararectal  fossse  (Fig.  772),  and  fills  the  greater  part 
of  the  posterior  division  of  the  pelvis — a  condition  which  could  not  be  brought  about  with  a 
straight  rectum  without  an  enormous  increase  in  all  the  diameters  of  the  tube. 

According  to  Jonnesco,  the  rectum  begins — that  is,  the  pelvic  mesocolon  ceases — most  frequently 
opposite  the  disc  between  the  third  and  fourth  sacral  vertebrae.  It  is  our  experience  that  the 
mesocolon  ends  more  frequently  above  than  below  the  third  sacral  vertebra — often,  indeed,  at  the 
level  of  the  second. 

At  its  upper  end  the  rectum,  following  the  curve  of  the  sacrum,  slopes  downwards  and  at  the 
same  time  slightly  backwards  ;  its  middle  portion  is  practically  vertical,  but  the  terminal  third 
or  more  is  directed  downwards  and  forwards  at  an  angle  varying  from  45°  to  60°  wdth  the  horizontal. 
The  pelvic  floor,  upon  which  this  latter  part  rests,  forms  here  a  similar  angle  with  the  horizontal. 
Tlie  l3end  which  the  bowel  makes  behind  the  lower  end  of  the  prostate,  where  the  rectum  jjasses 
into  the  anal  canal,  is,  as  pointed  out  above,  abrupt,  and  usually  ajjproaches  a  right  angle,  so 
that  the  anal  canal  itself  slopes  downwards  and  backwards  at  an  angle  of  nearly  45°  with  the 
horizontal. 

Not  uncommonly  the  al)rupt  curve,  at  the  junction  of  the  rectum  with  the  anal  canal,  presents 
in  front  a  knuckle-like  projection  (well  seen  on  mesial  section),  immediately  above  the  canal.  It 
is  most  marked  in  females,  and  sometimes  ajapears  as  if  the  bowel  were  doubled  back  upon  itself 
at  this  point.  The  floor  of  the  pouch  thus  formed  may  dip  down  in  front,  even  below  the  level 
of  the  upper  aperture  of  the  anal  canal.  This  condition  is  most  common  in  multiparEe,  and  is 
evidently  due  to  the  relaxed  condition  of  the  pelvic  structures,  and  the  slight  support  afforded 
by  the  perineal  body  to  this  part  of  the  gut  in  these,  and  the  great  capacity  and  shallowness  of 
the  pelvis  in  the  female. 

\n  length  the  rectum  usually  measures  about  5  or  6  inches  (12*5  to  15"0  cm.),  but 
it  may  be  much  longer. 

Its  diameter  is  smallest  above,  near  the  junction  with  the  pelvic  colon,  and  is 
greatest  below,  near  the  anal  canal,  where  there  is  a  special  enlargement  known  as 
the  rectal  ampulla  (ampulla  recti).  When  empty  the  rectum  measures  little  over 
an  inch  (2-5  cm.)  in  diameter,  but  in  a  state  of  extreme  distension  it  may  be  as 
much  as  3  inches  (7"5  cm.)  in  width. 

Peritoneal  Relations  of  the  Rectum  (Figs.  773  and  823). — As  a  rule  the  upper 
two-thirds  of  the  rectum  has  a  partial  covering  of  peritoneum — in  front  and  at 
the  sides  at  first,  later  on  in  front  only — whilst  the  lower  third  has  no  peritoneal 
investment  whatsoever.  When  the  mesocolon  ceases  at  the  end  of  the  pelvic 
colon,  its  two  layers  separate  and  leave  the  back  of  the  rectum  destitute  of 
peritoneum.  Very  soon  the  membrane  quits  its  sides  also,  and  is  then  found  on 
73 


1090 


THE  DIGESTIVE  SYSTEM. 


the  front  only ;  so  that  the  greater  part  of  the  rectum  hes  behind  or  beneath  the 
pelvic  peritoneum,  as  it  were,  and  is  capable  of  expanding  and  contracting  without 
being  in  anj  way  hampered  by  its  partial  peritoneal  coat. 

Erom  the  front  of  the  rectum  the  peritoneum  is  carried  forwards  to  the  base  of 
the  bladder  in  the  male,  forming  the  floor  of  the  recto-vesical  or  recto-genital  pouch 
(excavatio  recto- vesicalis.  Fig.  823).  In  the  female  it  passes  to  the  upper  part 
of  the  posterior  wall  of  the  vagina,  forming  the  floor  of  the  pouch  of  Douglas 
(excavatio  recto-uterina  Douglasi,  Eig.  818).  Whilst  at  each  side,  in  both  sexes, 
it  passes  from  the  front  of  the  rectum  on  to  the  posterior  wall  of  the  pelvis,  forming 
the  bottom  of  a  large  fossa,  seen  at  the  sides  of  the  rectum  when  that  bowel 
is  empty,  and  known  as  the  pararectal  fossa.  With  distension  this  fossa  is 
encroached  upon  by  the  enlarging  bowel,  and  soon  is  obliterated. 

The  level  at  which  the  reflection  of  the  peritoneum  takes  place  from  the  front  of 
the  rectum  is  of  considerable  practical  importance  in  connexion  with  operations  in 
this  region.    As  a  general  rule  this  reflection,  that  is,  the  bottom  of  the  recto-vesical 


Second  sacral  vertebra 


Sacro-iliac  joint 


Ending  of  pelvic  mesocolon 

Sacral  iierves 

''    ,  N       4^/'4\  Pararectal  fossa 


[Jreter  (cut) 
Internal  iliac  artery 
Obturator  nerve 
Ureter 


Uiacus 
External  iliac  artery 
Vas  deferens 
Obliterated  hypogastric  artery 


Bladder 


Deep  epigastiic  arterj 

Ureter 
Paravesical  fossa 
Plica  vesicalis  transversa 

Rectus 

Pyramidalis  Urachus 

Fig.  773. — The  Peritonedm  of  the  Pelvic  Cavity, 

he  pelvis  was  sawn  across  obliquely  iu  a  thin  male  subject  aged  60.  Owing  to  the  absence  of  fat  the  various 
pelvic  organs  are  visible  through  the  peritoneum,  though  not  quite  so  distinctly  as  represented  here. 
The  bladder  and  rectum  are  both  empty  and  contracted  ;  the  paravesical  and  pararectal  fossae  as  a 
result,  are  very  well  marked. 

pouch,  is  placed  at  a  distance  of  1  inch  (2-5  cm.)  aljove  tlie  Ijase  of  the  prostate,  or 
about  3  inches  above  the  anus,  but  the  level  is  subject  to  considerable  variation, 
being  as  a  rule  relatively  much  higher  in  well-developed  muscular  or  fatty  subjects, 
whilst  it  is  usually  lower  in  emaciated  Ijodies,  owing  to  the  thinness  of  the  structures 
forming  the  pelvic  floor. 

The  bottom  of  the  recto-vesical  fossa  may  reach  down  in  an  extreme  case  to  witliin  an  inch 
(2'5  cm.)  of  the  anns,  whilst  it  is  not  at  all  rare  to  find  it  Avithin  2  inches  (5'0  cm.)  of  that  orifice  ; 
on  the  other  hand,  it  may  be  considerably  higher  than  normal,  sometimes  being  placed  at  a  dis- 
tance of  4  or  4^  inches  (lO'O  to  11"2  cm.)  from  the  anus.  It  should  also  be  added  that  the  level  is 
generally  believed  to  be  somewhat  raised  by  distension  of  the  rectum  and  bladder,  and  lowered 
by  emptying  these  viscera,  although  this  is  denied  by  Jonnesco. 

In  the  child  at  birth,  the  peritoneum  extends  down  to  the  base  of  the  prostate  (Symington), 
and  is  thus  lower  in  relation  to  the  bladder ;  but  this  may  be  partly  accounted  for  by  the  high 
position  of  this  organ  in  the  child. 


THE  ANAL  CANAL.  1091 

As  a  rule  it  will  be  found  that  2  inches  (5-0  cm.)  of  the  front  of  the  rectuui,  exclusive  of  the  anal 
canal,  are  entirely  free  from  peritoneum,  and  it  is  this  and  the  adjacent  portion  of  the  bowel  which, 
being  free  from  the  restraining  influence  of  the  peritoneum,  is  most  distensible,  and  is  known  as 
the  rectal  ampulla.  Including  the  anal  canal,  3^  inches  (87  cm.)  of  the  rectum,  measured  along 
the  front  of  the  tube,  have  no  serous  covering.  On  the  other  hand,  the  h)ack  is  free  from  peri- 
toneum for  5  or  6  inches  (12"5  to  150  cm.) — or  sometimes  much  more — above  the  anu.s. 

It  is  also  of  interest  to  notice  that  the  connexion  of  the  peritoneum  to  the  rectum  varies  in 
its  character  at  different  parts  : — Above  and  in  front  it  is  closely  adherent,  and  can  be  removed 
only  with  the  greatest  difficulty  ;  at  the  sides  and  below  the  connexion  is  much  looser.  As  a 
result,  the  peritoneum  can  be  stripped  oft"  the  rectum  in  its  lower  third  or  half  without  much 
difficulty,  whilst  in  its  upper  portion  this  is  not  the  case — an  arrangement  which  admits  of  the 
free  expansion  of  the  rectal  ampulla. 

General  Relations  of  the  Rectum  (Figs.  771  and  772). — Behind,  the  rectum 
rests  on  the  front  of  the  sacrum  and  coccyx,  and  below  these  upon  the  posterior  part 
of  the  pelvic  floor — here  formed  by  the  meeting  of  the  two  levatores  ani  in  the  ano- 
coccygeal raphe.  When  much  distended  it  also  comes  into  relation  on  each  side  with 
the  lower  part  of  the  pyriformis  and  the  sacral  plexus.  The  bowel  is  separated 
from  these  structures  by  a  very  considerable  amount  of  connective  tissue,  arranged 
(apparently  in  several  layers)  around  the  tube.  In  this  tissue  the  two  chief 
branches  of  the  superior  hsemorrhoidal  vessels  lie  behind  the  upper  part  of  the 
bowel,  but  lower  down  they  are  placed  in  relation  to  its  sides. 

At  its  sides  above  are  the  pararectal  fossae  and  their  contents  (pelvic  colon,  or 
ileum) ;  below  this  the  rectum  is  in  contact  with  the  coccygei  and  levatores  ani 
muscles,  which  run  backwards  to  the  coccyx  on  each  side  of  the  bowel.  The 
branches  of  the  superior  hsemorrhoidal  vessels  are  also  found  running  down  on 
its  muscular  coat,  as  far  as  the  middle  of  the  rectum,  where  they  pierce  the  wall 
of  the  boweL 

In  front,  the  rectum  is  separated  from  the  bladder,  to  mthin  an  inch  of  the 
prostate,  by  the  recto- vesical  pouch  of  peritoneum,  which  usually  contains  some 
coils  of  small  intestine.  Below  the  reflection  of  the  peritoneum  the  front  of  the 
bowel  is  in  contact  with  the  base  of  the  bladder,  the  vasa  deferentia,  vesiculae 
seminales,  and  the  back  of  the  prostate  gland  (Fig.  772),  from  all  of  which  it  is 
separated  by  the  recto-vesical  layer  of  the  pelvic  fascia.  In  the  female  (Fig.  777) 
the  rectum  is  separated  from  the  posterior  surface  of  the  uterus  and  the  upper 
end  of  the  vagina  by  the  pouch  of  Douglas  and  the  intestine  which  it  usually 
contains.  Below  the  peritoneal  reflection  it  is  in  direct  contact  with  the  posterior 
vaginal  wall,  to  which  it  is  connected  loosely  above,  but  more  closely  below. 

The  lower  portions  of  the  rectum  and  bladder  in  the  male  are  separated  by  the 
recto-vesical  fascia  only,  over  a  narrow  triangular  area  which  measures  about  an 
inch  (2-5  cm.)  in  vertical  height.  The  base  of  this  triangle  corresponds  to  the 
reflection  of  the  peritoneum  from  one  organ  to  the  other,  and  the  apex  to  the 
base  of  the  prostate,  whilst  the  sides  are  formed  by  the  vasa  deferentia,  which  lie 
very  close  to  one  another  except  above,  near  the  base  of  the  triangle,  where  they 
diverge  rather  abruptly  (Fig.  772).  Through  this  triangle  the  operation  of  tapping 
the  bladder  from  the  rectum  is  performed. 

The  vesiculse  seminales,  unless  when  of  a  small  size,  slope  outwards  and  backwards 
round  the  front  and  sides  of  the  distended  rectum  (Fig.  772),  which  they  thus  embrace, 
as  it  were,  within  their  grasp. 

The  ureters,  as  they  run  inwards  towards  the  base  of  the  bladder,  lie  close  in  front  of 
the  vasa  deferentia,  and  are  not  far  separated  from  the  distended  rectum  (see  Fig.  772). 

The  portion  of  the  rectum  below  the  level  of  the  peritoneal  reflection  is  surrounded 
by  the  rectal  fascia,  a  layer  of  connective  tissue  which  is  derived  from  the  visceral 
layer  of  the  pelvic  fascia. 

In  the  child  the  rectum,  or  at  least  its  upper  part,  is  relatively  larger,  and  it  pursues 
a  mnch  straighter  course  than  in  the  adult.  As  pointed  out  above,  its  peritoneal  covering 
likewise  descends  lower  at  birth,  and  reaches  as  far  as  the  base  of  the  prostate. 

THE  ANAL  CANAL. 

Anal  Canal  (pars  analis  recti — third  part  of  the  rectum  of  the  old  descrip- 
tions).— In  order  to  reach  the  exterior,  it  is  necessary  for  the  lower  end  of  the 
73  a 


1092  THE  DIGESTIVE  SYSTEM. 

bowel  to  pierce  the  floor  of  the  pelvis.  This  it  does  by  passing  through  the  narrow 
interval  left  between  the  mesial  borders  of  the  levatores  ani  muscles  (Fig.  771). 
As  it  passes  between  them,  the  two  muscles  pinch  in  the  tube,  and  by  the  apposi- 
tion of  its  lateral  walls  obliterate  its  cavity,  reducing  it  to  a  mere  slit-like  passage. 
This  passage,  throvigh  which  the  rectum  communicates  with  the  exterior,  is  the 
"  anal  canal "  (Symington). 

Formerly  this  terminal  portion  of  the  tube  was  described  as  the  "  third  part  of  the  rectum," 
and,  like  the  rest  of  that  bowel,  it  was  supposed  to  form  a  reservoir  for  the  retention  of  the 
fcBces.  Symington  pointed  out  that  this  was  not  the  case.  He  showed  that  the  canal  was  not 
of  the  same  nature  as  the  rest  of  the  rectum,  but  that  it  was  a  mere  passage  through  which  the 
bowel  discliarged  its  contents,  the  relation  between  the  two  being  practically  the  same  as  that 
between  the  urethra  and  the  bladder  in  the  female.  It  is  probable,  however,  that,  when  the 
rectum  is  distended,  the  upjjer  part  of  the  anal  canal  is  often,  if  not  usually,  occupied  by  the 
wedge-shaped  lower  end  of  the  contained  faecal  mass,  whilst  the  chief  bulk  of  the  contents  is 
supported  by  the  rectal  valves  and  the  levatores  ani. 

The  anal  canal  begins  where  the  rectum  proper  terminates,  namely,  at  the 
level  of  the  levatores  ani  muscles,  opposite  the  lower  part  of  the  prostate. 
When  the  distended  rectum  is  cut  across  near  its  lower  end,  in  a  hardened  body, 
and  the  cavity  examined  from  the  interior,  a  distinct  projection,  formed  by  the 
inner  border  of  the  levator  ani  (pubo-rectalis,  or  sphincter  recti  portion),  is  seen  on 
each  side,  indicating  the  upper  limit  of  the  canal.  It  is  said  that  these  ridges  can 
also  be  felt  during  life  by  the  finger  introduced  into  the  rectum  (Cripps).  Below, 
the  anal  canal  ends  at  the  anus,  or  anal  orifice,  by  opening  on  the  exterior. 

Its  length  is  usually  from  1  to  Ih  inches  (2-5  to  3'7  cm.),  being  greater  when 
the  bowel  is  empty,  and  less  when  it  is  distended.  Its  antero-posterior  diameter 
when  closed  varies  between  |  and  f  inch  (12  to  19  mm.). 

The  direction  of  the  anal  canal,  as  already  pointed  out,  is  downwards  and  back- 
wards, often  forming  an  angle  of  nearly  45°  with  the  horizontal,  although  it  is 
usually  somewhat  nearer  to  the  vertical. 

Relations.  —  It  is  surrounded  by  both  the  external  and  internal  sphincters, 
and  above  also  by  the  borders  of  the  levatores  ani,  these  muscles  forming  a 
muscular  cylinder  around  it  (Fig.  771).  On  each  side  is  situated  the  ischio- 
rectal fossa  with  its  contained  fat,  which  allows  of  the  distension  of  the  canal 
during  the  passage  of  faeces.  Behind  is  placed  a  mass  of  mixed  connective  and 
muscular  tissue,  known  as  the  ano-coccygeal  body  (Symington),  which  intervenes 
between  it  and  the  coccyx.  Finally,  in  front,  it  lies  close  behind  the  bulb  of  the 
urethra  and  the  base  of  the  triangular  ligament  in  the  male,  and  a  sound  in  the 
urethra  can  be  easily  felt  by  the  finger  introduced  into  the  anal  canal,  particularly 
in  thin  bodies.  In  the  female  it  is  separated  from  the  vagina  by  the  wedge-shaped 
mass  of  fatty  and  muscular  tissue  known  as  the  "  perineal  body." 

Structure  of  the  Rectum  and  Anal  Canal. — The  wall  of  the  rectum  is  made  up 
of  four  coats,  viz.  :  —1.  The  outer  coat,  formed  in  part  of  peritoneum  (already  described  ), 
and,  where  the  peritoneum  is  absent,  of  connective  tissue  wliich  can  be  dissected  off  in 
several  layers.  In  this  connective  tissue  the  hasmorrlioidal  vessels  run  until  they  pierce 
the  wall  of  the  tube.  In  it  also,  at  the  back  and  sides  of  the  rectum,  are  found  embedded 
a  number  of  rectal  lymphatic  glands. 

2.  The  muscular  coat,  wliich  is  much  thicker  than  in  any  other  portion  of  the  intes- 
tine, is  composed  of  two  stout  layers  of  unstriped  muscle — an  outer  longitudinal  and  an 
inner  circular — like  that  of  the  intestine  generally.  The  lo7i(jitudinal  fibres,  although 
present  all  round,  are  chiefly  accumulated  on  the  front  and  back  of  the  tube  (see  p.  1089), 
where  they  form  two  broad  bands ;  at  the  sides  they  are  reduced  to  a  thin  layer,  the 
deepest  fibres  of  which  are  folded  in  and  take  part  in  the  formation  of  the  rectal  valves. 

Where  the  rectum  pierces  the  floor  of  the  pelvis,  the  outer  layisr  of  longitudinal  fibres  is  united 
to  the  deeper  portion  of  the  levator  ani,  partly  by  tendinous  fibi;es  and  partly  by  an  inter- 
change of  muscular  fibres,  between  the  levatores  and  the  muscular  coat  of  the  rectum.  This 
interchange  of  fibres,  however,  is  denied  by  Peter  Thompson  and  Browning.  BeloM',  the  longi- 
tudinal fibres  pass  between  the  external  and  internal  si)hincter  muscles,  or  through  the  latter 
to  join  the  skin  around  the  anus.  The  folding  of  the.  rectum  froin  side  to  side,  described  above^ 
is  brought  about  and  maintained  by  the  shortness  of  the  fibres  of  this  coat  on  the  front  and  back 
of  the  bowel. 

In  saggital  sections  of  the  pelvis  near  the  mesial  plane  there  can  generally  be  seen  a  distinct 
baud  of  red,  longitudinally -arranged,  muscular  fibres,  which  descends  on  each  side  from  the  front 


THE  ANAL  CANAL. 


1093 


of  the  coccyx  to  bleiul  with  the  longitudinal  fibres  on  the  back  of  tlie  rectum.     This  band  is  the 
recto-coccygeus  muscle.     It  is  composed  of  striped  fibres  above,  Ijut  becomes  unstriped  below. 

Some  unstriped  muscular  filn-es  which  are  found  descending  in  the  subcutaneous  tissue  of  the 
lower  part  of  the  anal  canal,  to  join  the  skin  around  the  anus,  have  been  described  by  Ellis  as  the 
corrugator  cutis  ani.  According  to  Roux,  they  are  some  of  tlie  longitudinal  fibres  of  tlie  rectum 
which  have  passed  througli  the  internal  sphincter  to  tlie  sulnnucous  tissue,  and  then  descended 
to  the  skin. 

The  circular  Jihrt^s  form  along  the  whole  length  of  the  tube  a  continuous  layer,  which 
is  doubled  inwards  to  assist  iu  the  formation  of  each  rectal  valve  and  is  thickened 
below  to  form  the  internal  sphincter  of  the  anus.  The  internal  sphincter  (sphincter  ani 
internus),  as  just  f)ointed  out,  is  formed  by  a  great,  and  rather  sudden,  increase  of  the 
circular  muscular  tibres,  which  begins  at  the  upper  end  of  the  anal  canal.  It  surrounds 
the  canal  for  about  an  inch  (2*5  to  3-0  cm.),  and  terminates  \  or  \  inch  (6  or  7  mm.) 
above  its  lower  aperture  (Fig.  775). 

3.  The  submucous  coat  is  composed  of  loose  areolar  tissue,  which  allows  of  a  free 
movement  of  the  mucous  layer  on  the  muscular  coat,  and  which  also  admits,  under 
certain  abnormal  conditions,  of  a  prolapse  of  the  mucous  membrane  throu<>h  tlie  anal 
orifice.     The  hsemorrhoidal  plexus  of  veins  is  contained  in  this  laver. 

4.  The  mucous  coat  must  be  considered  separately  in  the"  rectum  and  anal  canal. 
That  of  the  rectum  is  redder  in  colour  than  the  mucous  membrane  of  the  colon  as  a  result 
of  its  greater  vascularity.  It  is  also  thicker,  and  owing  to  the  looseness  of  the  underlyin^j- 
submucosa,  is  thrown  into  numerous  irregular  rugte  when  the  rectum  is  empty ;  these 
disappear  when  the  bowel  is  distended,  and  there  then  become  evident  thi'ee  (sometimes 
more,  sometimes  less)  crescentic  folds,  which  are  much  less  noticeable  in  the  empty  state, 
and  which  have  been  already  referred  to  as  the  rectal  valves.  Lymphoid  nodules  and 
glands  of  Lieberktihn  are  present ;  but  these  latter  are  not  so  numerous  as  in  the  colon, 
although  their  calibre  is  greater. 

The  imicous  memhrane  of  the  anal  canal  presents  in  its  upper  half  a  number  of 
vertical  ridges  known  as  the  columns  of  Morgagni ;  between  the  lower  ends  of  these  are 
found  a  series  of  small  semilunar  folds  which  are  disposed  horizontally  around  the 
passage  and  are  called  the  anal  valves  (Fig.  775).  Above  the  level  of  the  anal  valves 
the  canal  is  lined  by  a  modified  mucous  membrane  resembling  that  of  the  rectum  :  the 
portion  below  the  valves  {i.e.  the  lower  12  to  16 
mm.  of  the  canal)  is  covered  by  modified  skin,  con- 
tinuous with  that  around  the  anus. 

The  mucous  menibi'ane  of  the  rectum  presents  a 
characteristic  pmictated  appearance,  which  is  due  to  the 
presence  of  a  considerable  number  of  rounded  depres- 
sions, such  as  might  be  made  l)y  firmly  pressing  a  finely- 
pointed  pencil  against  the  membrane.  These  rectal 
pits,  of  whicli  we  can  find  no  previous  description,  are 
tubular  in  form,  and  have  an  accumulation  of  lymphoid 
tissue  at  the  bottom  of  each  ;  the  whole  appearance 
being  such  as  might  be  produced  if  a  small  solitary 
gland  were  drawn  down  from  the  surface  into  the 
intestinal  wall. 

Rectal  Valves,  or  Valves  of  Houston  (plicae 

transversales  recti). — These,  sometimes  termed 
the  valves  of  Kohlrausch,  are  crescentic  shelf- 
like folds  which  project  into  the  cavity  of  the 
rectum  ou  its  lateral  aspects  (Fig.  77-4).  They 
are  composed  of  an  infolding  of  the  mucous, 
submucous,  and  greater  part  of  the  muscular 
coats,  and  their  form  is  preserved  by  the  relative 
shortness  of  the  anterior  and  posterior  bands  of 
longitudinal  muscular  fibres.  They  are  pro- 
duced, as  pointed  out  above,  by  the  projection, 
into  the  interior  of  the  bowel,  of  the  creases 
on  the  exterior  which  result  from  the  lateral  inflections  of  the  rectum.  In  the 
majority  of  cases  three  are  present  (there  may  be  four,  five,  or,  it  is  said,  even 
more),  but  often  the  lowest  of  the  three  is  small  or  absent ;  or  all  the  valves  may 
be  ill-developed  and  indistinct.  When  mesial  sections  of  the  ernvty  rectum  are 
73  6 


Fk;.  774. — DiAGR.\M  of  RECirM,  showing 
Houston's  valves  in  interior. 

The  diagram  is  a  reduced  tracing  of  Fig.  772. 
After  removal  of  the  prostate,  etc.,  an 
aperture  was  made  in  the  anterior  wall 
of  the  rectum,  through  which  two  rectal 
valves  can  be  seen  corresponding  to 
lateral  inflections  on  the  e.xterior.  The 
levator  ani  is  also  shown,  and  its  relation 
to  tiie  beginning  of  the  anal  canal  is 
sugsrested. 


1094 


THE  DIGESTIVE  SYSTEM. 


examined,  the  valvea  are  not  easily  seen,  as  they  then  project  but  slightly, 
and  are  almost  completely  hidden  amongst  the  numerous  rugpe  of  the  mucous 
coat.  They  are  most  evident  in  a  distended  rectum  which  has  been  hardened 
in  situ ;  they  can  also  be  seen  during  life,  ^Jier  anitm,  with  the  aid  of  a  rectal 
speculum. 

As  a  rule  two  valves  are  found  on  the  left  and  one  on  the  right  side ;  this  latter  is 
generally  the  largest,  and  is  situated  a  little  above  the  level  of  the  peritoneal  reflection, 
viz.  3  or  3.V  inches  (7'5  to  8"7  cm.)  above  the  anus ;  the  other  two  valves  are  found  about 

1  to  1|-  inches  (2-5  to  3-7 
cm.)  higher  up  and  lower 
down  respectively.  The  valves 
are  distinctly  marked  in  the 
foetus  (see  Fig.  775),  and  seem 
to  constitute  an  essential  part 
of  the  human  rectum,  their 
use  being  to  'support  the 
contents  of  the  rectum,  which 
they  break  up  into  segments, 
each  supported  by  a  valve 
(see  p.  1089).  They  are  said 
to  interfere  sometimes  with 
the  introduction  of  an  enema 
tube. 


Longitudinal 
fibres  ofx. 
rectum 


Anal  valves 


V     ) 


Fig.  775. 


The  rectum  in  animals 
generally  is  free  from  the 
lateral  inflections  described 
above,  and  the  condition  found 
in  man  is  evidently  an  adapta- 


-The  Interior  of  the  Anal  Canal  and  Lower  Part 

OF  Rectum, 

Showing  the  columns  of  Morgagni  and  the  anal  valves   between  their    tion  to  the  erect  attitude.      In 

lower  ends.      The  columns  were  more  numerous  in   this  specimen    quadrujaeds  the  contents  oi  tne 

than  usual.  rectum  do  not  press  unduly  on 

the  sphincter,  owing  to  the 
horizontal  position  of  the  body.  AVith  the  assumption  of  the  erect  attitude,  on  the  other  liand, 
the  whole  weight  of  the  contents  would  be  thro-mi  on  the  sphincters,  were  it  not  for  the  lateral 
foldings  and  the  resulting  shelves. 

Columns  of  Morgagni  (column^e  recti  Morgagni). — The  mucous  membrane  of 
the  anal  canal  presents,  in  its  upper,  and  part  of  its  middle  thirds,  a  number  (5  to 
10)  oi  permanent  vertical  folds,  separated  by  grooves,  and  known  as  the  columns  of 
Morgagni  (Fig.  775).  They  are  usually  |~  to  h  inch  (8  to  12  mm.)  in  length,  ^  to 
\  inch  (3  to  6  mm.)  in  width,  and  they  extend  down  to  within  J  or  f  inch  (12  to 
7  mm.)  of  the  anal  aperture.  They  are  formed  by  infoldings  of  the  mucous 
membrane,  containing  in 

their   interior   some  un-  \t:/2W:W& 

striped    muscle    derived 

from   the   muscularis 

mucosae,  and   also,  as   a 

rule,  an  artery  and  a  vein. 

Very  often  the  contained 
vein  presents  an  enlarge- 
ment, or  a  kno))dike  tor- 
tuous plexus  in  the  lower 
part  of  the  column  ;  below 
this  the  plexus  is  continued 
down  beneath  the  mucous 
membrane  of  the  lower  zone 
of  the  anal  canal  into  the 
anal  veins  (see  p.  1095).  This  portion  has  accordingly  been  described  as  the  hsemor- 
rhoidal  zone  of  the  anal  canal.  Sometimes  the  columns  of  Morgagni  ai-e  very  indistinct ; 
occasionally  no  trace  of  them  can  be  found,  although  in  the  foetus  (Fig.  776)  they  are 
usually  well  marked. 


Fid.  776. — The  Anal  Canal 


AM)  Lower  Part  of  Kectfm  in  the 
Fcetds. 


aged  4  to  5  months  ;  K,  6  months  ;  and  C,  9  niontlis.  In  each  the  anal 
canal  is  distinctly  marked  off  from  the  rectum  ])roper  ;  the  columns  of 
Morgagni  and  tlie  rectal  valves  are  distinct.      R.V,  Rectal  valves. 


THE  ANAL  CANAL.  1095 

Anal  Valves  (of  Morgagni). — If  a  probe  be  passed  downwards  along  the 
groove  which  separates  two  adjacent  colunms  of  Morgagni  (Fig.  755),  its  point 
will  usually  catch  in  a  small  crescentic  fold  which  joins  the  lower  ends  of  the  two 
columns.  These  little  folds,  which  resemble  in  miniature  the  segments  of  the 
semilunar  valves  of  the  heart,  are  the  anal  valves.  They  project  inwards  and 
upwards,  and  behind  each  is  found  a  little  pocket-like  sinus  (sinus  rectalis). 

These  valves  were  j&rst  described  by  Morgagni.  Recently  the  view  has  been  advanced  by 
Ball  that  tliey  are  the  remains  of  the  embryonic  cloacal  or  anal  membrane  ;  and  he  explains  the 
production  of  "  painful  fissure  of  the  anus  "  by  tin-,  tearing  dowai  of  one  of  them  during  aefascation 
by  hardened  masses  of  fa3ces. 

The  epidermis  is  continued  in  a  tlun  and  modified  form  from  the  exterior  uj)  along  the  anal 
canal  as  far  as  the  margins  of  the  anal  valves  ;  and  the  view  is  pretty  generally  held  that  only 
this  lower  portion  of  the  anal  passage  is  formed  from  the  proctodicum  in  the  embryo.  The 
junction  of  the  skin  with  the  mucous  membrane  is  indicated  by  a  fine  wavy  line  ("white  line" 
of  Hilton — ano-cutaneous  line  of  Hermann)  which  runs  around  the  bowel  at  the  level  of  the 
valves.  The  mucous  membrane  of  tlie  region  immediately  above  the  anal  valves  is  of  a  more  or 
less  transitional  nature  ;  glands  are  absent  from  it,  and  over  the  columns  of  Morgagni  it  is  said 
to  be  covered  with  stratified  ejiithelium,  the  su2:)erficial  cells  of  which  are  flattened,  whilst  in  the 
grooves  between  the  columns  the  epithelium  is  columnar.  In  the  ujoj^er  zone  of  tlie  anal  canal 
the  mucous  membrane  gradually  aj)2)roaches  to  tlie  rectal  type,  but  the  Lieberkiilm's  glands  and 
lymphoid  nodules  are  few  and  scattered. 

Anus  or  Anal  Orifice. — At  the  inferior  aperture  of  the  anal  canal,  the 
modified  skin  of  its  lower  zone  passes  into  the  ordinary  skin.  A  little  way 
outside  the  orifice,  hairs,  sebaceous  glands,  and  large  modified  sweat  -  glands 
(glandular  circumanales)  appear. 

Action  of  the  Sphincters. — In  connexion  with  the  anal  canal  are  found  three  muscles — 
namely,  the  2)aired  levatores  ani,  the  external  sphincter,  and  the  internal  sphincter — the  action 
of  which  may  be  briefly  referred  to  here. 

Levator  Ani. — The  fibres  of  the  levator  which  arise  from  the  pubis  (piibo-coccygeus  or 
sphincter  recti  portion)  pass  backwards  on  each  side  of  the  beginning  of  the  anal  canal,  and,  in 
great  part,  meet  behind  the  jmssage.  These  two  muscular  bands — which  are  but  a  little  distance 
apart  at  their  origin,  and  are  actually  united  behind  the  bowel — are  closely  aj^jjroximated 
during  the  contraction  of  the  muscles,  like  the  limbs  of  a  clamp,  and,  pressing  on  the  sides  of  the 
anal  canal,  they  assist  in  closing  the  upper  part  of  that  passage,  whilst  at  the  same  time  drawing 
it  slightly  towards  the  pubes.  There  is  little  doubt  that  the  levator  ani  in  this  waj^  acts  as  one 
of  the  chief  sphincters  of  the  bowel ;  and  it  should  be  noticed  that  it  is  placed  where  its  action 
would  be  most  effective,  namely,  opposite  the  point  at  which  the  rectum  is  narrowed  or  "pinched 
in  "  to  form  the  anal  canal.  In  addition  to  its  sjjhincter  action  the  muscle  supports  the  expanded 
bowel  immediately  above  the  anal  canal,  and  in  this  way  sustains  the  weight  of  the  faeces  when 
the  rectum  is  distended.  It  is  probably  relaxed  during  defiecation,  except  perhaj^s  at  the  com- 
pletion of  the  act.     The  muscle  is  under  the  control  of  the  will. 

The  external  sphincter  forms  a  muscular  cylinder  around  the  lovvej'  two-thirds  of  the  anal 
canal,  with  (except  in  the  case  of  some  of  its  inner  fibres)  an  anterior  and  a  posterior  attachment. 
When  the  muscle  contiacts,  its  fibres  are  tightly  stretched  between  its  two  attachments,  and  the 
space  between  them  is  reduced  to  a  narrow  antero-posterior  slit.  By  this  action  the  anal  canal  is 
flattened  from  side  to  side  and  closed,  so  that,  whilst  the  levator  ani  is  the  sjihincter  of  the  upper 
aperture  of  the  anal  canal,  the  external  sphincter  closes  its  lower  and  greater  joart.  It  is  under 
the  control  of  the  will,  but  under  ordinary  circumstances  it  is  in  a  state  of  tonic  contraction. 

The  internal  sphincter  is  merely  a  thickening  of  the  circidar  muscular  coat  at  the  lower  end 
of  the  bowel  It  is  continuous  with  the  circular  fibres  of  the  gut,  not  only  in  structure,  but 
jirobably  also  in  action,  its  chief  use  being  to  empty  the  anal  canal  completely,  after  the  jjassage 
of  each  ftecal  mass.  Owing  to  the  fact  that  the  canal  is  an  antero-posterior  slit,  not  a  circular 
orifice,  and  that  the  internal  sphincter  forms  a  muscular  ring  around  it,  acting  alone,  it  is  scarcely 
competent  to  keej)  the  sides  of  the  canal  in  ajjposition,  and  probably  it  acts  rather  as  a  detrusor 
than  a  true  sphincter  of  the  anal  passage. 

Vessels. — The  rectum  and  anal  canal  receive  their  blood  supply  from  three  chief  sources, 
namely,  tlie  three  liaemorrhoidal  arteries  ;  to  these  another  less  important,  though  constant, 
source  may  be  added — the  middle  sacral  artery. 

1.  The  superior  hsemorrhoidal,  the  princijaal  artery  of  the  rectum,  is  the  prolongation  of  the 
inferior  mesenteric  trunk  (Fig.  634,  j).  840).  At  first  it  descends  in  the  root  of  the  jjelvic  meso- 
colon until  the  rectum  is  reached.  Here  it  divides  into  two  chief  branches  which  run  downwards 
and  forwards  around  the  sides  of  the  rectum — the  right,  usually  the  larger,  lying  more  behind, 
the  left  more  to  the  front,  and  the  two,  as  it  were,  embracing  the  bowel  between  tliem  (Fig.  771). 
From  these  two  arteries  come  oft"  secondary  branches  (about  five  to  eight  in  all),  which  pierce  the 
muscular  coat  about  the  middle  of  the  rectum,  and  then  descend  in  the  submucosa  as  a  series  of 
longitudinally-running  "  terminal  branches  "  as  far  as  the  anal  valves,  above  the  level  of  which 
one  is  usually  found  beneath  each  column  of  Morgagni.  These  terminal  branches  give  oft' 
numerous   twigs   in   their   course,  which  form  a  hajmorrhoidal   plexus   in   the   submucosa  by 

73  c 


1096  THE  DIGESTIVE  SYSTEM. 

anastomosing  with  one.  another,  and  also  with  branches  of  the  middle,  and,  in  the  lower  part  of 
the  bowel,  of  the  inferior  htemorrhoidal  arteiy. 

2.  The  middle  hsemorrlioidal  arteries,  two  in  number  —  one  on  each  side  —  are  usually 
branches  of  the  anterior  division  of  the  internal  iliacs ;  they  run  down  on  the  side  wall  of 
the  lower  part  of  the  rectum,  and  after  giving  off  branches  to  the  bladder,  seminal  vesicles, 
prostate  (or  vagina,  according  to  tlie  sex),  each  breaks  up  into  four  or  five  small  branches,  some 
of  which  supply  the  muscular  wall  of  the  lower  part  of  the  rectum,  whilst  the  others  pierce  the 
muscular  coat  near  the  upper  end  of  the  anal  canal,  and  join  in  the  submucosa  with  the  plexus 
formed  by  the  superior  htemorrlioidal  artery  already  described. 

3.  The  inferior  hsemorrlioidal  arteries,  generally  two  or  three  in  number  on  each  side,  arise 
at  variable  levels  from  the  internal  pudic  arteries,  whilst  these  latter  are  situated  on  the  outer 
side  of  the  ischio-rectal  fossae.  They  pass  inwards  and  downwards  through  the  fat  in  the 
fossae,  and,  near  the  wall  of  the  anal  canal,  break  uj)  into  branches,  some  of  which  are  distri- 
buted to  the  levatores  ani  and  the  sphincters,  whilst  others  pierce  the  sphincters  and  break  up  in 
the  submucosa  into  a  close  network  which  supplies  the  lower  part  of  the  anal  canal,  and  com- 
municates above  with  the  plexus  formed  by  the  superior  and  middle  hsemorrhoidal  arteries. 
The  inferior  hsemorrlioidal  artery  is  distributed  chiefly  on  the  back,  and  the  middle  hsemorrhoidal 
chiefly  on  the  front  of  the  lower  part  of  the  bowel. 

4.  One  or  more  small  branches  of  the  middle  sacral  artery  reach  the  back  of  the  rectum, 
where  they  are  distributed  chiefly,  if  not  solely,  to  the  muscular  coat. 

Anastomosis  of  the  Hsemorrhoidal  Arteries. — The  superior  and  middle  heemorrhoidal  arteries 
anastomose  freely,  not  only  in  the  hsemorrhoidal  plexus  of  the  submucosa,  but  also,  as  a  rule,  by 
a  few  lai'ge  branches  on  the  exterior  of  the  bowel :  some  perforating  branches  of  the  middle 
sacral  also  join  the  plexus  in  the  submucous  layer  at  the  lower  part  of  the  rectum,  as  do  numerous 
small  branches  from  the  inferior  hsemorrhoidal  arteries  which  pierce  the  sphincters.  In  addition, 
small  branches  of  these  several  arteries  unite  with  one  another  in  the  muscular  coat.  It  should 
be  remarked  that  the  superior  hsemorrhoidal  artery  supplies  both  the  muscular  and  mucous 
coats  above,  whilst  it  is  confined  to  the  latter  in  the  lower  few  inches  of  the  gut,  the  muscular 
coats  here  being  sujjplied  by  the  middle  and  inferior  haemorrhoidal  vessels. 

Veins  of  the  Rectum  and  Anus. — These  form  two  chief  plexuses  of  large  vessels  devoid  of 
valves,  namely,  the  internal  hsemorrhoidal  plexus  situated  in  the  submucous  coat,  and  the 
external  hsemorrhoidal  plexus  in  the  outer  coat.  The  internal  hsemorrhoidal  plexus  takes  origin 
near  the  margin  of  the  anus  in  a  number  of  small  (anal)  veins,  which  aie  radially  disposed 
beneath  the  skin  of  the  anus,  and  communicate  below  with  the  rootlets  of  the  inferior  hsemor- 
rhoidal vein  over  the  external  spliiucter.  These  anal  veins,  traced  upwards,  join  together,  and 
are  joined  by  others  from  the  surrounding  parts  to  form  larger  and  often  tortuous  vessels,  wliicli 
ascend  in  the  columns  of  Morgagni,  where  they  frequently  present  amjaullary  enlargements, 
varying  in  size  up  to  that  of  a  small  pea,  which  are  said  to  be  the  starting-points  of  hsemorrhoids. 
Passing  upwards,  the  veins  are  known  as  the  "  terminal  veins  "  ;  they  communicate  freely  with 
one  another,  forming  the  plexus,  and  unite  into  still  larger  vessels,  which  pierce  the  muscular 
coat  about  the  middle  of  the  rectum,  and  join  the  two  branches  of  the  superior  hsemorrhoidal  vein. 

From  the  lower  part  of  the  internal  lisemorrhoidal  plexus  numerous  vessels  jsass  through 
the  external  sphincter  to  join  a  venous  network  on  the  outer  surface  of  that  muscle,  from 
which  the  inferior  hsemorrhoidal  veins  arise.  This  network,  as  jjointed  out  above,  also  com- 
municates with  the  internal  hsemorrhoidal  j^lexus,  thi'ough  the  anal  veins  which  descend  from 
the  latter  beneath  the  skin  of  the  anal  canal,  to  the  exterior  of  the  sphincter. 

The  various  veins  which  pass  out  thi'ough  the  walls  of  the  rectum  unite  freely  on  its 
exterior  to  form  a  rich  venous  jjlexus  (external  hsemorrhoidal  plexus),  through  which  the  three 
hsemorrhoidal  vessels  are  brought  into  free  communication  with  one  another.'  Passing  ott'  from 
this  plexus,  tlie  superior  hsemorrhoidal  vein  joins  the  inferior  mesenteric,  which  opens  into  the 
portal  vein  ;  the  middle  hsemorrhoidal  joins  the  internal  iliac,  a  tributary  of  the  vena  cava ; 
and  the  inferior  haimorrhoidal  joins  the  internal  pudic,  a  tributary  of  the  internal  iliac. 
Thus,  on  the  rectum,  a  free  anastomosis  is  established  between  the  veins  of  the  portal  and" 
systemic  circulations. 

Lymphatics. — Most  of  the  lymphatics  of  the  rectum  join  a  number  (four  or  five)  of  rectal 
glands  found  in  the  ccninective  tissue  coat  of  the  bowel  along  the  superior  hsemorrhoidal 
vein  and  its  two  branches,  whence  tliey  pass  to  the  sacral  glands  on  the  front  of  the  sacrum. 
Some  of  those  from  the  lower  part  of  the  anal  canal  join  the  cutaneous  lympliatics  round  the 
anus,  and  pass  with  them  to  the  oblique  set  of  sujjerficial  inguinal  glands.  A  few  of  the 
lymphatics  from  the  lower  portion  of  tlie  rectum  are  said  (by  (^uenu)  to  join  the  internal  iliac 
glands,  but  these  are  inconstant  according  to  Gerota. 

Nerves. — The  nerves  of  tlie  rectum  come  partly  from  the  sympathetic  and  partly  from  the 
cerebro-.spiiial  .system.  The  sympathetic  fibres  are  derived  on  the  one  hand  from  the  inferior 
mesenteric  ple.vus,  and  on  the  other  from  the  right  and  lei't  divisions  of  the  hypogastric  plexus 
{i.e.  the  pelvic  plexuses),  the  former  accoiiqjanyiug  the  superior  hsemorrhoidal,  the  latter  the 
middle  hsemorrhoidal  vessels,  to  the  rectum.  The  cerebro-spinal  fibres  arise  from  the  second, 
third,  and  fourth  sacral  nerves  soon  after  these  leave  the  sacral  foramina  (and  constitute  the 
"pelvic  splanchnics"  of  Gaskell).  They  run  forward  in  the  pelvic  connective  tissue,  and 
joining  the  pelvic  plexuses,  reach  the  side  of  the  rectum.  Fibres  of  the  inferior  hsemorrhoidal 
branch  of  the  internal  i^udic  nerve  (third  and  fourth- sacral)  are  also  distributed  to  the  lower  part 
of  the  anal  canal  as  well  as  to  the  external  sphincter. 

It  has  been  shown  by  experiments  on  animals,  that  the  cerebro-spinal  nerves  (from  the 


THE  PERITONEUM.  1097 

second,  third,  and  fourth  sacral)  convey  motor  iniijulses  to  the  longitudinal  fibres,  but  inhibitory- 
impulses  to  the  circular  muscular  fibres.  In  like  manner  the  branches  from  the  sympathetic 
convey  motor  fibres  (derived  from  some  of  the  lumbar  rami  communicantes)  to  the  circular 
muscle,  and  inhibitory  fibres  to  the  longitudinal  muscle  of  the  rectum. 

The  reflex  centre  which  governs  the  action  of  the  sphincters  and  the  mu.scular  fibres  of  the 
rectum  ("  defiecatiou  centre  ")  is  situated  in  the  lumbar  region  of  the  cord,  and  appears  to  be 
capable  of  carrying  out  the  whole  act  of  deftecation  even  when  separated  from  the  brain. 

Variations. — The  best  known  anomalies  found  in  connexion  with  the  rectum  are  those 
classed  under  the  term  imperforate  anus  or  atresia  ani.  The  atresia  may  be  simply  due  to  a 
partial  or  complete  persistence  of  the  anal  membrane  (see  p.  45),  which  separates  the  procto- 
dseum  from  the  hind-gut  in  the  embryo  (atresia  ani  simplex) ;  or  the  hind-gut  may  be  deficient 
in  its  lower  part,  when  there  is  a  considerable  interval  between  the  proctodieum  and  the  gut 
(defectus  recti  partialis,  vel  totalis) ;  or  the  rectum  may  open  into  the  vagina,  the  uterus,  the 
bladder,  or  the  ureters,  when  usually  no  anus  is  evident ;  or  finally  the  cloaca  may  persist. 
Other  forms  are  also  described,  but  the  foregoing  are  those  most  commonly  found. 

For  the  development  of  the  rectum  and  anus,  see  pp  33  and  45. 

THE  PERITONEUM. 

An  introductory  sketch  of  the  peritoneum  was  given  on  p.  1048  ;  subsequently, 
when  describing  the  abdominal  viscera,  an  account  of  its  detailed  relations  to 
each  of  these  was  included.  We  shall  here  consider  the  membrane  and  its  folds  as 
parts  of  one  continuous  whole ;  and  we  shall  also  describe  its  arrangement  as  seen 
on  horizontal  and  vertical  sections  of  the  abdomen — a  favourite  method  of  studying 
the  peritoneum. 

As  already  explained,  the  peritoneum  is  the  serous  membrane  which,  on  the 
one  hand,  lines  the  abdominal  cavity,  and  on  the  other  forms  a  more  or  less 
complete  covering  for  the  contained  viscera.  The  portion  which  lines  the 
walls  of  the  cavity  is  known  as  the  parietal  peritoneum  (peritoneum  parietale), 
that  which  clothes  the  viscera  as  the  visceral  peritoneum  (peritoneum  viscerale). 
The  membrane  is  connected  to  both  walls  and  viscera  by  a  layer  of  areolar  tissue — 
the  extra  or  subperitoneal  connective  tissue — which  is  considerable  in  amount  in 
certain  regions,  whilst  it  is  reduced  to  a  mere  trace  in  others,  particularly  on  the 
viscera.     ( I'he  subperitoneal  tissue  is  described  at  p.  1045). 

The  peritoneum  is  described  as  consisting  of  two  sacs — a  greater  and  a  lesser. 
The  former  lines  the  greater  portion  of  the  abdominal  cavity,  and  invests  most  of 
the  abdominal  viscera ;  the  latter  lies  chiefly  behind  the  stomach,  and  is  much  more 
restricted  in  its  distribution.  It  must  be  clearly  understood  that  these  two  sacs 
are  not  two  separate  cavities,  but  simply  subdivisions  of  one  great  cavity ;  for  the 
lesser  is  merely  a  recess  of  the  greater  sac,  from  which  it  has  become  partly  shut 
off  by  changes  that  take  place  in  the  position  of  the  adjacent  viscera  during  their 
development.  If  the  great  sac  be  compared  to  a  bag,  the  lesser  sac  might  be  repre- 
sented as  a  pocket  lying  behind,  and  opening  into  it  by  a  narrow  orifice — the  foramen 
of  Winslow — on  its  posterior  wall. 

Speaking  generally,  the  great  sac  lines  the  walls  of  the  abdominal  cavity,  and  it  also 
covers  the  various  organs  which  receive  a  peritoneal  investment,  except  the  back  of 
the  stomach,  the  SpigelianySSk- caudate\lol>e||  of  the  liver,  the  left  suprarenal  capsule, 
the  upper  surface  of  the  pancreas,  and  also  parts  of  the  spleen,  left  kidney,  and  transverse 
colon  ;  all  of  which,  as  well  as  the  parietes  behind  the  Spigelian  lobe,  are  clothed  by  the 
small  sac. 

The  great  sac  of  the  peritoneum  is  placed  between  the  parietes  in  front  and 
the  abdominal  viscera  behind.  It  is  composed  of  two  layers,  an  anterior  which 
lines  the  anterior  abdominal  wall,  and  a  posterior  v\hich  covers  the  viscera;  but 
this  posterior  l.iyer  is  carried  forwards  by  the  viscera,  so  that  the  two  layers  come 
in  contact,  and  the  cavity  of  the  sac  is  practically  obliterated. 

The  anterior  layer  of  the  great  sac  covers  the  anterior  abdominal  wall  com- 
pletely, from  the  diaphragm  above  to  the  pelvis  below.  Over  the  greater  part  of 
its  extent  the  connexion  of  the  peritoneum  to  the  waU  is  by  a  small  amount  of 
fatty  extra-pt  ritoneal  connective  tissue ;  but  below,  near  the  pubic  region,  the 
fat  is  more  abundant,  and  the  connexion  between  the  two  becomes  much  looser. 
This  is  to  allow  of  the  peeling  off  of  the  peritoneum,  which  takes  place  here  during 


1098 


THE  DIGESTIVE  SYSTEM. 


Lesser 
omentum 


distension  of  the  bladder.  As  the  bladder  enlarges  it  passes  up  along  the  anterior 
abdominal  wall,  off  which  it  strips  the  peritoneum,  so  that,  in  the  fully  distended 
condition,  it  may  be  in  contact  with  this  wall,  without  the  interposition  of  peri- 
toneum, for  a  distance  of  two  inches  (5*0  cm.,  or  occasionally  more)  above  the  pubes 
(Fig.  810). 

Running  up  in  this  fatty  tissue  are  found  five  cord-like  structures,  one  placed 
in  the  middle  line,  and  two  at  each  side.  These  are  (a)  the  urachus — the  remains  of 
the  alluntois  of  the  foetus — which  in  the  adult  is  a  slender  -fibrous  band  connected 
to  the  um])ilicus  above,  and  to  the  apex  of  the  bladder  below,  where  it  usually 
becomes  much  stouter.  External  to  the  urachus,  and  some  distance  from  it  (Fig. 
773),  will  1)6  found,  in  the  same  fatty  tissue,  (b)  two  stouter  fibrous  cords,  the 
obliterated  hypogastric  arteries  (arterite  umbilicales).  Traced  upwai'ds,  these  also 
become  more  slender,  and  approach  the  urachus,  along  with  which  they  are  con- 
nected to  the  umbilicus.  Below,  they  grow  thicker,  and  can  be  followed  backwards 
along  the  side  wall  of  the  pelvis  to  the  internal  iliac  arteries,  which  they  join. 
(c)  Further  out  still,  the  deep  epigastric  arteries  are  seen  running  upwards  and 
inwards  from  the  external  ihac  trunk  on  each  side. 

When  the  anterior  abdominal  wall  is  examined  from  behind,  it  will  be  seen 
that  tliese  five  structures  which  lie  on  the  front  of  the  peritoneum  carry  that 
meml:)rane  inwards  towards  the  abdominal  ca^dty  in  the  form  of  five  more  or  less 

distinct  ridges,  in  relation  to 
which  are  found  on  each  side 
three  peritonal  fossee,  known  as 
the  inguinal  pouches  or  fossse  (fovea 
inguinales). 

Tlie  external  inguinal  fossa  (fovea 
ingiiinalis  lateralis)  lies  outside  the 
deep  e^Digastric  arterj^  and  corresponds 
to  the  position  of  the  internal  abdominal 
ling.  At  its  bottom  is  often  found  a 
dimjDle-like  depression  of  the  peri- 
toneum, indicating  the  jjoint  from 
which  the  jjrocessus  vaginalis  jjassed 
down,  in  connexion  with  the  descent  of 
the  testicle.  The  middle  inguinal  fossa 
(fovea  inguinal  is  mesialis)  is  situated 
between  the  deep  epigastric  and  the 
obliterated  hypogastric  arteries  ;  whilst 
tlie  internal  inguinal  fossa  (fovea  in- 
giiinalis interna,  fovea  supravesicalis) 
lies  to  the  inner  side  of  the  obliterated 
hypogastric  artery,  namely,  between 
it  externally  and  the  urachus  inter- 
nally. Seeing  that  the  obliterated 
hypogastric  artery,  in  passing  upwards, 
crosses  Hasselbach's  triangle,  dividing 
it  into  an  outer  and  an  inner  part,  it 
follows  that  the  middle  inguinal  fossa 
corresj)onds  to  the  outer  division  of  the 
triangle,  and  the  inner  fossa  to  its 
inner  division. 

Still  another  fossa  of  the  jjeritoneum 
FIG.  777.-Diac;hammat,c  Mesial  Section  ok  Female  Body,  f '^^''  in  this  region  just  beneath  the 
to  .show  the  peritoneu.a  on  vertical  tracing.  The  great  sac  mner  part  ot  Poupart  s  bgament  corre- 
of  the  peritoneum  is  black  and  is  represented  as  being  spondmg  to  the  position  ol  the  femoral 
much  larger  than  in  nature  ;  the  small  sac  is  very  darkly  or  crural  ring,  and  consequently  known 
shaded  ;  the  peritoneum  in  section  is  shown  as  a  white  as  the  femoral  or  crural  fossa  (fovea 
line:  and  a  white  arrow  is  passed  through  the  foramen  of  femoralis).  It  may  be  added  that  the 
Winslow  from  the  great,  into  the  small  sac.  vas  deferens  crosses   the  outer  jDart  of 

this  latter  fossa,  and  the  obliterated 
hyj)0gastric  artery  its  inner  part.  The  significance  of  those  fossse  is  referred  to  in  connexion 
with  the  applied  anatomy  of  the  inguinal  and  femoral  regions. 

Near  the  middle  line,  above  the  umbilicus,  the  peritoneum  is  earned  back  from 
the  anterior  abdominal  wall  and  diaphragm  to  the  parietal  surface  of  the  liver  in 
the  form  of  a  crescentic  fold,  the  falciform  ligament  of  the  liver  (ligamentum  falci- 


THE  PERITONEUM.  1099 

forme  hepatis,  described  with  the  liver),  which  connects  the  liver  to  the  abdominal 
wall.  This  fold  lies  somewhat  to  the  right  of  the  middle  line,  and  extends  almost 
as  low  down  as  the  umbilicus.  It  consists  of  two  layers  of  peritoneum,  between 
which,  in  the  lower  border  of  the  fold,  runs  the  round  ligament  of  the  liver — the 
remains  of  the  umbilical  vein  of  the  fcetus. 

Posterior  Layer  of  the  Great  Sac. — After  clothing  the  anterior  abdominal  wall,  in 
the  manner  just  described,  the  anterior  layer  of  the  great  sac  is  continued  back  on 
the  under  surface  of  the  diaphragm,  until  this  latter  begins  to  descend  behind  the 
liver,  when  it  is  reflected  from  the  diaphragm  on  ■  to  the  upper  aspect  of  the  liver, 
and  here  the  anterior  passes  into  the  posterior  layer  of  the  great  sac.  The  posterior 
layer  first  clothes  the  upper  aspect  of  the  liver,  then  turns  round  its  anterior  border, 
and  is  continued  back  on  the  under  surface  as  far  as  the  attachment  of  the  lesser 
omentum,  where  it  quits  the  liver  and  passes  down,  as  the  anterior  layer  of  the 
lesser  omentum,  to  the  lesser  curvature  of  the  stomach. 

The  line  of  reflection  from  diajjhragm  to  liver  is  interrupted  near  the  mesial  plane  by  the 
falciform  ligament.  The  portion  lying  to  the  right  of  this  fold  forms  the  upper  layer  of  the 
coronary  ligament ;  that  to  the  left  of  it,  the  upper  layer  of  the  left  lateral  ligament  of  the  liver. 

The  extent  to  which  the  peritoneum  of  the  great  sac  passes  back  on  the  under  surface  of  the 
liver  varies  according  as  it  is  traced  at  the  right,  the  left,  or  the  middle  jDortion  of  the  liver.  It 
clothes  the  right  portion  as  far  back  as  the  lower  edge  of  the  uncovered  area  of  the  liver,  where 
it  is  reflected  on  to  the  posterior  wall  of  the  abdomen  and  the  toji  of  the  right  kidney  (constitut- 
ing the  hej^ato-renal  ligament),  as  the  lower  layer  of  the  coronary  ligament.  On  the  left  portion 
it  is  continued  back  as  far  as  the  posterior  border  of  the  left  lobe — or  even  a  little  way  on  to  its 
upper  surface — whence  it  passes  to  the  diaphragm  as  the  inferior  layer  of  the  left  lateral 
ligament.  The  middle  region  of  the  imder  surface  it  clothes  only  as  far  as  the  portal  fissure  and 
the  fissure  of  the  ductus  venosus  ;  from  these  the  peritoneum  is  carried  down  as  the  anterior  layer 
of  the  les.ser  omentum  to  the  lesser  curvature  of  the  stomach,  where  we  shall  return  to  it  directly. 

The  peritoneum,  which  2msses  back  on  the  under  surface  of  the  diaphragm  to  the  left  of  the 
liver,  is  continued  down  on  the  j^osterior  abdominal  wall,  behind  the  fundus  of  the  stomach  and 
the  spleen,  until  the  left  kidney  is  reached.  It  coA'ers  the  upper  and  outer  part  of  the  kidney, 
and  is  then  carried  forward  as  the  lieno-renal  ligament  to  the  spleen,  around  which  it  passes 
— clothing  its  renal,  jshrenic,  and  gastric  surfaces — as  far  as  the  hilum  (Fig.  779) ;  from  this  it 
is  carried  to  the  stomach  as  the  anterior  layer  of  the  gastro-splenic  omentum.  Similarly,  the 
under  layer  of  the  left  lateral  ligament  is  continued  do^ai  on  the  back  part  of  the  diaphragm  to 
the  oesophagus,  the  anterior  and  left  sides  of  which  it  clothes.  It  also  forms  a  little  fold  at  the 
left  of  the  CESophagus,  known  as  the  gastro-phrenic  ligament  (see  p.  1057  and  Fig.  780). 

At  the  right  side,  the  portion  of  the  peritoneum  which  forms  the  under  layer  of  the 
coronary  ligament  is  carried  down  over  the  riglit  kidney  (and  lower  part  of  the  suprarenal 
capsule)  to  the  duodenum  and  hepatic  flexure,  over  both  of  which  it  passes. 

We  shall  now  follow  down  the  posterior  layer  of  the  great  sac — which  we 
have  already  traced  to  the  stomach — as  seen  in  a  sagittal  section  (Fig.  770). 

Having  reached  the  lesser  curvature  of  the  stomach,  it  passes  down  over  the 
front  of  that  organ,  clothing  it  completely  as  far  as  the  great  curvature.  From 
this  it  descends,  in  front  of  the  transverse  colon  and  small  intestine,  forming  the 
anterior  layer  of  the  great  omentum — a  large  apron-like  fold,  containing  the  lower 
part  of  the  small  sac  in  its  interior,  which  hangs  down  from  the  stomach.  Arrived 
at  the  lower  border  of  the  great  omentum,  the  membrane  returns  on  itself,  and 
passes  upwards  towards  the  posterior  abdominal  wall,  forming  the  posterior  layer 
of  that  omentum.  On  the  way  it  meets  and  passes  behind  the  transverse  colon, 
clothing  its  posterior  aspect  at  the  same  time  (Fig.  777),  and  is  then  continued, 
as  the  posterior  layer  of  the  transverse  mesocolon,  up  to  the  posterior  abdominal 
wall,  which  it  reaches  at  the  anterior  border  of  the  pancreas  (Fig.  777). 

From  the  anterior  border  of  the  pancreas  it  is  continued  downwards  again, 
clothing  first  the  lower  part  of  that  organ,  then  the  front  of  the  third  portion  of 
the  duodenum,  and  below  this  the  posterior  abdominal  wall.  From  this  latter, 
however,  it  is  soon  carried  forwards  again  by  the  branches  of  the  superior  mesen- 
teric vessels,  passing  to  the  small  intestine.  Eunning  out  along  these,  it  forms 
the  upper  (or  more  correctly,  the  right)  layer  of  the  obliquely-placed  mesentery 
(Fig.  777) :  on  reaching  the  small  bowel  at  the  border  of  the  mesentery,  it  invests 
that  tube,  giving  it  its  serous  coat,  and  then  returns — as  the  under,  or  left,  layer 
of  the  mesentery — to  the  posterior  abdominal  wall,  on  which  it  runs  down,  covering 
the  great  vessels  near  the  middle  line,  and  the  psoas  muscles  and  ureters  at  each 
side,  to  enter  the  pelvis.     The  mesentery  is  described  at  p.  1071. 


1100 


THE  DIGESTIVE  SYSTEM. 


Pelvic  Peritoneum. — The  detailed  arrangement  of  the  peritoneum  in  the  pelvic 
cavity  is  somewhat  complicated,  and  is  fully  described  in  connexion  with  the 
several  pelvic  organs.     A  general  account  will  suffice  here. 

Having  passed  over  the  brim  all  round,  it  enters  the  pelvis,  and  covers  its 
walls  as  low  as  the  pelvic  floor,  across  which  it  passes  to  the  various  organs. 
Behind,  it  invests  completely,  and  forms  a  mesentery  (pelvic  mesocolon)  for,  the 
pelvic  colon,  as  far  down  as  the  third  sacral  vertebra.  Here  the  colon  joins  the 
rectum  proper,  and  the  complete  investment  of  the  bowel  ceases. 

As  the  end  of  the  pelvic  colon  is  approached  the  two  layers  of  its  mesocolon 
become  shorter,  and  when  the  rectum  is  reached,  they  separate,  leaving  its  posterior 
surface  uncovered,  whilst  the  bowel  is  clothed  in  front  and  at  the  sides.  Lower 
down,  the  membrane  leaves  the  sides,  and  finally,  at  a  point  which  is  usually  about 
3  inches  (7"5  cm.,  see  p.  1089)  above  the  anus,  it  leaves  the  front  of  the  bowel, 


Second  sacral  \eitpbia 
Sacro  iliac  ]oiiit      / 

Rectum 
Pararectal  fossa 


Ending  of  peUic  mesocolon 

sicral  nerves 


Ureter  (cut) 

Crescentic  fold  ot 
peritoneum  (recto 
genital  fold) 
Seminal  vesicle 

beneath  this    --y>^^ 

External  iliac 

vein 


External  iliac 
artery 


Pararectal  fossa 

^  U'eter  (cut) 

Internal  iliac  artery 
Obturator  nerve  | 

Ureter 


Fossa 

obturatoria 

(Waldeyer) 


Deep  epigastric  artei  s 

Uretei        / 
Paravesical  fossa 
Plica  vesicalis  transversa 

Rectus 


Iliaciis 


External  iliac  arteiy 


Vas  deferens 


^         Obliterated  hypogastric  artery 
ISladder 


Pyramidalis 


Urachus 


Fig.  778. — The  Peritoneum  op  the  Pelvic  Cavity. 

The  pelvis  was  sawn  across  obliqiiely  (as  in  Fig.  772)  in  a  thin  male  subject  aged  60.  Owing  to  the  absence 
of  fat  the  various  pelvic  organs  are  visible  through  the  peritoneum,  though  not  quite  so  distinctly  as 
represented  here.  The  bladder  and  rectum  were  both  empty  and  contracted  ;  the  paravesical  and  para- 
rectal fossse,  as  a  result,  are  very  well  marked. 

and  in  the  male  is  carried  on  to  the  back  part  of  the  bladder  (here  covered  by  the 
seminal  vesicles  and  vasa  deferentia),  forming  the  floor  of  the  recto-vesical  pouch 
(excavatio  recto-vesicalis,  recto-genital  pouch)  found  between  these  organs.  It 
then  covers  the  upper  surface  of  the  bladder,  and  passing  off  from  its  sides  to  the 
walls  of  the  pelvis,  constitutes  the  so-called  false  ligaments  of  that  organ.  From'the 
apex  of  the  bladder  it  is  carried  on  to  the  anterior  abdominal  wall  by  the  urachus, 
thus  forming  the  superior  or  anterior  false  ligament  of  the  bladder  (plica  pubo- 
vesicalis). 

In  the  female  (Fig.  777),  the  peritoneum,  on  leaving  the  rectum,  passes  to  the 
posterior  wall  of  the  vagina,  the  upper  portion  of  which  it  covers.  From  this  it  is 
continued  up  over  the  posterior  surface  and  fundus  of  the  uterus,  and  down  on 
its  anterior  surface  as  far  as  the  junction  of  the  cervix  and  body  (Fig.  853).  Here 
it  passes  from  the  uterus  to  the  bladder,  which  it  partly  covers,  as  in  the  male,  and 
is  then  carried  on  to  the  anterior  abdominal  wall.  Between  the  rectum  behind, 
and  the  uterus  and  vagina  in  front,  is  situated  the  pouch  of  Douglas  Texcavatio 


THE  PERITONEUM. 


1101 


Falciform  ligament 
Foramen  (jf  Winslo 


Stomaoli 


Round  ligament  of  liver 


T.esser  omentum  (cut) 
Portal  vein 


Vpiia  cava 


Hight  kidney 


Small  intestine 


Aorta, 


The  mt'senterv 


recto-utenna  Douglasi,  recto-genital  pouch),  the  entrance  of  which  is  limited  on 
each  side  by  a  fold  passing  from  the  cervix  of  the  uterus  around  the  sides  of  the 
pouch  towards  the  rectum ;  these  are  the  folds  of  Douglas  (plica?  recto-uterinte 
Douglasi,  recto-genital  folds),  and  they  contain  in  their  interior  the  utero- sacral 
ligaments  (musculi  recto-uterini),  two  bands  of  fibrous  tissue  with  plain  muscle 
fibres  intermixed,  which  pass  from  the  cervix  of  the  uterus,  backwards  on  each 
side  ot  the  rectum,  to 
blend  with  the  con- 
nective tissue  on  the 
front  of  the  lower  part 
of  the  sacrum. 

Similarly,  in  front 
of  the  uterus,  between 
it  and  the  bladder,  is 
found  the  much 
smaller  utero  -  vesical 
pouch  (excavatio 
vesico-uterina).  Fin- 
ally, the  peritoneum  is 
prolonged  as  a  wide 
fold  from  each  margin 
of  the  uterus  to  the 
side  wall  of  the  pelvis, 
constituting  the  broad 
ligament  of  the  uterus 
(ligamentum  latum 
uteri),  within  which 
are  contained  the 
Fallopian  tube,  the 
ovary,  the  round  liga- 
ment,  and  other 
structures  (see  p. 
1189). 

When  the  bladder  is 
emi^ty,  there  is  seen  at 
each  side,  between  it  and 
the  pelvic  wall,  a  con- 
siderable peritoneal  de- 
pression— the  paravesical 
fossa  (Fig.  778).  This 
fossa  is  traversed  by  a 
peritoneal  fold — the  plica 
vesicalis  transversa  — 
which  is  found  running 
transversely  outwards 
from  the  upper  surface  of 
the  empty  bladder,  and, 
when  well  marked,  pass- 
ing to  the  neighbourhood 
of  the  internal  abdominal 
ring. 

,.afoln7'l  ^^f  ^'inilf '  °\  ""f  ^  ^^'^'^  °*'  *^^  urachus,  is  found  the  internal  inguinal  fossa  already 
bladder  °^  *^*'^''  ^^^^*  ^^'"^  Practically  obliterated  by  distension  of  the 

Similarly,  there  is  seen  at  each  side  of  the  empty  rectum,  on  the  posterior  pelvic  walLa  large 
depression,  which  may  be  known  as  the  pararectal  fossa  (fossa  para-rectalis,  Fig.  778).  When  t£e 
rectum  is  empty  and  contracted,  these  foss;^  are  filled  by  intestine;  during  distension,  the 
rectum  increasing  m  width,  expels  tlie  intestine  and  practically  obliterates  the  iossee. 

Transverse  Tracing  of  the  Peritoneum.— If  the  peritoneum  be  followed  Irans- 
versely  around  the  abdomen,  just  above  the  level  of  the  iliac  crest,  where  the  com- 
plications produced  by  the  small  sac  are  absent  (Fig.  779,  B),  few  difficulties  will 
be  encountered.  From  the  anterior  abdominal  wall  it  passes  round  on  each  side  to 
the  back,  lining  the  lateral  and  posterior  walls.     Passing  inwards  on  the  posterior 


Descending  colon 


Ascending  colon 


Fig.  779.— Diagrammatic  Transverse  Sections  op  Abdomen,  to  sliow  the 
peritoneum  on  transverse  tracing.  A,  at  level  of  foramen  of  Winslow, 
B,  lower  down.  In  A,  note  one  of  the  vasa  brevia  arteries  passing  to 
the  stomach  between  the  layers  of  the  gastro-splenic  omentum,  and  also 
the  foramen  of  Winslov,-  leading  into  the  lesser  sac  which  lies  behind  the 
stomach. 


1102  THE  DIGESTIVE  SYSTEM. 

wall,  it  meets  the  colon — ascending  on  the  right  side,  descending  on  the  left — over 
which  it  is  carried,  in  each  case  covering  the  bowel  in  front  and  at  the  sides  only, 
and  leaving  the  posterior  surface  bare,  as  a  rule.  Sometimes,  however,  the  covering 
is  complete,  and  a  short  mesentery  is  formed.  It  is  next  continued  inwards  over 
the  psoas  muscles,  the  ureters,  and  the  great  vessels,  on  the  front  of  which  it  meets 
the  superior  mesenteric  artery  and  vein  running  downwards  to  the  intestines. 
From  both  sides  it  passes  forwards  on  these  vessels,  forming  the  right  and  left 
layers  of  the  mesentery ;  and  finally,  having  reached  the  intestine,  it  clothes  it 
completely,  and  the  two  portions  become  continuous  on  the  bowel. 

A  transverse  tracing  at  a  higher  level  would  include  the  small  sac ;  it  will, 
therefore,  be  well  to  study  this  portion  of  the  peritoneum  before  describing  such  a 
tracing. 

Small  Sac  of  the  Peritoneum  (bursa  omentalis). — This,  as  already  pointed 
out,  is  a  diverticulum  of  the  great  sac  which  lies  behind  the  stomach  and  adjacent 
organs,  and  which  communicates  with  the  great  sac  by  a  constricted  passage,  the 
foramen  of  Winslow.  If  the  great  sac  be  compared,  as  already  suggested,  to  a  bag, 
the  anterior  layer  of  which  clothes  the  anterior  and  lateral  walls  of  the  abdomen, 
and  the  posterior  layer  the  viscera  lying  on  the  posterior  wall,  the  small  sac  would 
correspond  to  a  pocket  lying  behind  the  upper  part  of  the  great  sac,  and  opening 
into  its  cavity  by  a  narrow  mouth,  on  the  right  side,  just  below  the  liver.  From 
this  opening  the  pocket  passes  to  the  left  behind  the  lesser  omentum,  as  far  as  the 
spleen,  up  behind  the  Spigelian  lobe  of  the  liver,  and  down  behind  the  stomach, 
and  into  the  great  omentum. 

As  in  the  case  of  the  great  sac,  it  \\ill  of  course  be  understood  that  the  two  walls  of 
the  small  sac  and  the  boundaries  of  the  foramen  of  Winslow  are  normally  in  contact. 
We  shall  first  consider  this  opening,  and  then  trace  the  layers  of  the  small  sac. 

Foramen  of  Winslow  (Fig.  779,  A). — This,  the  constricted  passage  which  leads 
from  the  great  into  the  small  sac  of  the  peritoneum,  is  found  just  below  and  behind  the 
portal  fissure  of  the  liver  by  running  the  finger  along  the  under  surface  of  the  gall- 
bladder towards  its  neck,  when,  with  little  difficulty,  it  passes  behind  the  right 
margin  of  the  lesser  omentum  and  into  the  foramen.  It  is  bounded  in  front  by  the 
free  right  border  of  the  lesser  omentum,  passing  up  from  the  first  part  of  the  duodenum 
to  the  portal  fissure,  and  containing  between  its  two  layers  the  portal  vein,  hepatic 
artery,  and  bile  duct.  Behind,  lies  the  inferior  vena  cava,  covered,  of  course,  by 
peritoneum.  Above,  is  placed  the  caudate  lobe  of  the  Kver.  And  below,  lie  the  first 
part  of  the  duodenum,  and  the  hepatic  artery,  the  latter  running  forwards  and  to  the 
right  beneath  the  foramen,  before  turning  up  into  the  lesser  omentum.  It  should 
be  remembered  that,  normally,  the  various  boundaries  of  the  foramen  lie  in  contact, 
and  that  its  cavity  can  only  be  said  to  exist  as  such  when  its  walls  are  drawn  apart. 

If  we  follow  the  small  sac,  in  through  the  foramen,  it  will  be  found  that  it 
expands  immediately  beyond  this  narrow  opening  (Fig.  777),  its  upper  portion  lying 
behind  the  lesser  omentum,  and  running  up  behind  the  Spigehan  lobe  of  the  liver 
as  far  as  its  upper  end ;  and  its  lower  portion  passing  down  behind  the  stomach 
and  on  into  the  great  omentum,  where  it  lies  in  front  of  the  transverse  colon,  and 
extends  practically  to  the  lower  margin  of  the  omentum — although  this  latter  point 
cannot  as  a  rule  be  demonstrated  in  the  adult. 

As  the  small  sac  is  composed,  like  the  great,  of  two  distinct  layers,  an  anterior 
and  a  posterior,  it  will  be  necessary  to  follow  each  of  these  separately.  Above,  the 
anterior  layer  of  the  small  sac  clothes  the  Spigehan  lobe ;  it  then  passes  down  (from 
the  posterior  margin  of  the  portal  fissure,  and  the  fissure  of  the  ductus  venosus)  to 
the  lesser  curvature  of  the  stomach  as  the  posterior  layer  of  the  lesser  omentum. 
Continued  on  from  this,  it  clothes  the  inferior  (or  visceral)  surface  of  the  stomach 
as  far  as  the  great  curvature,  with  the  exception  of  the  small  "  uncovered  area " 
below  and  to  the  left  of  the  cardia  (Fig.  743,  B),  but  it  does  not  actually  come 
in  contact  with  the  oesophagus  itself,  the  back  and  right  side  of  which  are  un- 
covered. On  the  left,  it  is  reflected  from  the  back  of  the  stomach  to  the  spleen  as 
the  deeper  layer  of  the  gastro-splenic  omentum. 

From  the  great  curvature  of  the  stomach  it  is  continued  down,  forming  the 
posterior  layer  (of  the  anterior  fold)  of  the  great  omentum ;  and  at  the  lower  part 


THE  PEEITONEUM. 


no: 


of  the  omentum  it  meets  and  becomes  continuous  with  the  posterior  layer  of  the 
small  sac. 

The  posterior  layer  of  the  small  sac,  in  passing  through  the  foramen  of  Winslow, 
clothes  the  front  of  the  vena  cava  (Fig.  779,  A) ;  beyond  this,  it  covers  the  coeliac 
axis,  and  passes  up  to  line  the  slight  depression  on  the  posterior  abdominal  wall 
(diaphragm),  against  which  the  Spigehan  lobe  rests.  Then,  passing  over  to  the  left, 
it  covers  the  upper  surface  of  the  pancreas,  the  top  of  the  left  kidney  and  suprarenal 
■capsule,  and  the  inner  part  of  the  gastric  surface  of  the  spleen  (i"ig.  780).  Prom 
the  anterior  border  of  the  pancreas  it  is  prolonged  forwards  and  downwards — as  the 
anterior  or  upper  layer  of  the  transverse  mesocolon — to  the  transverse  colon  (Fig.  777). 


Top  of  small  s:'.c 


Inferior  vena  cava 
I.esser  omentum  (cut) 


Kight  lateral  ligament 
of  liver 


Left  lateral  ligament  of  liver 
'  Q;sophageal  opening  in  diaphragm 

Gastro-phrenic  ligament 
Corresponds  to  '  uncovered  area '  of  stomach 
Gastro-s;)Ie!iic  omentum  (cut) 


Transverse  colon  crossing  duodenum     / 
Head  of  pancreas 
Great  omentum  (cut)         / 
Part  of  small  sac 


Phreno-colic  ligament 


Fig.  780.- 


Leftend  of  transverse  mesocolon 
Splenic  flexure  of  colon 
Transverse  mesocolon  (cut) 
17oot  of  mesenterv  font) 
The  Peritoneal  Relations  of  the  Duodenum,  Pancreas,  Spleen,  Kidneys,  etc. 


It  next  clothes  the  upper  aspect  of  this  gut,  and  is  then  continued  down  as  the  anterior 
layer  of  the  posterior  fold  of  the  great  omentum,  almost  to  its  lower  border,  where 
it  becomes  continuous  with  the  anterior  layer  of  the  small  sac,  already  described. 

The  transverse  tracing  at  the  level  of  the  foramen  of  Winslow  is  shown  in  Fig. 
778,  A,  and  can  be  easily  followed  without  any  further  description  than  is  there 
given. 

The  following  additional  details  may  be  mentioned  : — The  small  sac  is  divided  by  a  constric- 
tion into  two  parts — an  upper,  lying  behind  the  lesser  omentum  and  Spigelian  lobe,  and  a  lower, 
placed  behind  the  stomach  and  within  the  great  omentum.  The  constriction  is  due  to  the  passage 
of  the  coronary  and  hepatic  arteries  forward  around  the  sac  ;  the  former  winds  round  its  left 
side,  the  latter  round  its  right  ;  and  each  raises  up  a  fold  of  peritoneum,  which  projects  strongly 
into  the  sac,  and  partially  divides  it  into  two.  This  can  be  shown  by  cutting  the  lesser  omentum 
along  the  lesser  curvature  of  the  stomach  and  looking  into  the  cavity. 


1104  THE  DIGESTIVE  SYSTEM. 

"Where  the  small  sac  runs  up  behind  the  Spigelian  lobe,  it  forms,  as  pointed  out  at  j)age  1116, 
the  left  boundary  of  the  uncovered  area  of  the  right  lobe,  and,  consequently,  a  third  or  left  layer 
of  the  coronary  ligament. 

A  special  diverticulum  of  the  small  sac  runs  out  to  the  right,  l^ehind  the  beginning  of  the 
duodenum,  to  clothe  the  back  of  that  tube  for  about  an  incli  (Fig.  780). 

The  splenic  artery  reaches  the  sj^leen  by  passing  to  the  left,  behind  the  posterior  layer  of  the 
small  sac,  which  also  extends  to  that  organ  (Fig.  779,  A). 

The  lesser  omentum  is  described  at  page  1116;  it  need  only  be  pointed  out 
now  that  it  is  composed  of  two  layers,  the  anterior  derived  from  the  great  sac, 
and  the  posterior  from  the  small  sac,  both  of  which  are  extremely  thin — some- 
times even  criljriform. 

The  great  omentum  is  a  large  apron-like  fold  of  peritoneum,  usually  more  or 
less  loaded  with  fat,  which  is  suspended  from  the  great  curvature  of  the  stomach, 
and  hangs  down  in  front  of  the  intestines  to  a  variable  extent.  When  the  abdomen 
is  carefully  opened  without  disturbing  the  viscera,  it  is  rare  to  find  the  great 
omentum  evenly  spread  over  the  front  of  the  intestines.  More  commonly  it  is  folded 
in  between  some  of  the  coils  of  intestine,  or  tucked  into  the  left  hypochondrium  ; 
or  perhaps  it  is  carried  upwards  in  front  of  the  stomach  by  a  distended  transverse 
colon.  It  extends  between  the  great  curvature  of  the  stomach  above  and  the 
transverse  colon  below,  not  taking  the  shortest  course  from  one  of  these  to  the  other, 
but  hanging  down  as  a  loose  fold  between  the  two.  The  lower  part  of  the  small 
sac  is  continued  down  within  it  (Fig.  777). 

The  great  omentum  may  be  said  to  consist  of  two  folds,  each  formed  of  two 
layers,  one  derived  from  each  sac  of  the  peritoneum.  The  anterior  or  descending  fold 
begins  at  the  great  curvature  of  the  stomach,  where  it  is  formed  by  the  meeting  of 
the  two  layers  from  the  superior  and  inferior  surfaces  of  that  organ  respectively ; 
from  this  it  descends  to  the  lower  border  of  the  omentum,  where,  turning  back 
upon  itself  (Fig.  777),  it  passes  up  as  the  posterior  or  ascending  fold.  This  runs 
upwards  until  it  meets  the  transverse  colon ;  here  its  two  layers  separate  to  enclose 
and  cover  that  colon — and  the  omentum  properly  so  called  ceases.  Its  two  layers, 
however,  unite  at  the  upper  surface  of  the  colon  (Fig.  777)  to  form  the  transverse 
mesocolon,  which  is  continued  upwards  and  backwards  to  the  anterior  border  of  the 
pancreas.  Here  the  layers  of  the  transverse  mesocolon  again  separate — the  upper, 
derived  from  the  small  sac,  running  backwards  and  upwards  over  the  upper  surface 
of  the  pancreas  to  the  posterior  abdominal  wall ;  the  lower,  derived  from  the  great 
sac,  passing  downwards  along  the  back  of  the  abdomen,  as  already  explained. 

The  great  omentum  is  continued  to  the  right  for  a  short  distance  (25  mm.)  along  the  lower  border 
of  the  duodenum.  At  the  left  end  it  shortens  very  much,  and  is  directly  continued  into  the 
gastro-splenic  omentum  ;  the  spleen,  as  it  were,  being  introduced  between  the  two  layers  instead 
of  the  colon. 

Functions  of  the  Great  Omentum. — Numerous  uses  have  been  assigned  to  the  great 
omentum  ;  the  chief  seem  to  be  :  (1)  To  act  as  a  movable  and  easily  adjustable  packing  material, 
capable  of  filling  all  temporarily-produced  spaces  in  the  abdomen.  In  this  respect  it  may  be  - 
compared  with  the  Haversian  fatty  pads  in  joints.  (2)  It  probably,  to  some  extent,  prevents  the 
passage  of  the  small  intestine  up  into  the  stomach  chamber,  and  heljDS  to  keep  them  froiii 
getting  entangled  there.  (3)  It  is  a  storehouse  of  fat.  (4)  It  is  said  to  be  "  the  great  protector 
against  peritoneal  infectious  invasions."  Being  freely  movable,  it  can  pass  to  almost  any  part  of 
the  abdomen,  and  there  "  build  up  barriers  of  exudations  to  check  infection  "  (Byron  Robinson). 

Mr.  Lockwood  has  made  the  interesting  observation  (in  connexion  with  the  contents  of  hernise) 
that,  in  bodies  under  forty-five  years  of  age,  the  omentum  can  rarely  be  drawn  down  below  the 
level  of  the  pubic  spine  ;  in  older  bodies  the  reverse  is  the  rule. 

The  gastro-splenic  omentum  is  a  short  fold  composed  of  two  layers,  the  anterior 
or  more  superficial  Ijeing  derived  from  the  great  sac,  the  posterior  or  deeper  from  the 
small  sac  (Fig.  779,  A).  It  is  attached  by  one  margin  to  the  wide  end  of  the  stomach 
(^just  below  the  line  of  the  great  curvature),  and  by  the  other  to  the  gastric  surface 
of  the  spleen  just  in  front  of  the  hilum.  Ijetween  its  two  layers  the  vasa  brevia  of 
the  splenic  artery  pass  from  the  spleen  to  the  stomach.  Below  and  in  front,  its 
layers  are  continued  into  the  corresponding  layers  of  the  great  omentum ;  above 
and  behind,  they  separate  at  the  "  uncovered  area  "  of  the  stomach  (Fig.  780). 

Minor  Folds  of  Peritoneum. — The  phreno-colic  ligament,  passing  from  the 
splenic  flexure  of  the  colon  to  the  diaphragm  opposite  the  10th  or  11th  ribs,  has 


DEVELOPMENT  OF  INTESTINAL  CANAL  AND  PERITONEUM.     1105 

been  described  in  connexion  with  the  splenic  flexure.  The  mesentery  of  the 
appendix,  and  the  folds  and  fossae  around  the  ileo-c8ecal  region,  are  included  in  the 
account  of  the  caecum,  as  are  those  around  the  duodenum  in  the  description  of  that 
viscus.  The  lieno-renal  and  hepato-renal  ligaments  have  been  referred  to  incident- 
ally above. 

Development  of  the  Intestinal  Canal  and  Peritoneum. 

As  already  explained  on  p.  32,  when  the  embryo  begins  to  take  definite  shape,  and  to 
be  marked  off  from  the  general  surface  of  the  blastodermic  vesicle  by  an  infolding  of  its 
margins — resulting  in  the  formation  of  the  cephalic  or  head  fold,  the  caudal  or  tail  fold, 
and  the  lateral  folds — a  portion  of  the  cavity  of  the  vesicle  is  cut  oft'  by  these  folds,  and 
more  or  less  completely  enclosed  within  the  body  of  the  embryo,  to  form  the  primitive 
alimentary  canal.  Tiiis  is  simply  an  imperfect  tubular  cavity,  situated  beneath  the 
notochord,  and  bounded  towards  one  end  by  the  head  fold,  at  the  other  by  the  tail  fold, 
and  at  the  sides  by  the  lateral  folds.  The  anterior  portion  of  this  cavity,  situated  within 
the  head  fold,  is  known  as  the  foregut,  and  from  it  are  developed  the  back  part  of  the 
mouth,  the  tongue,  phaiynx,  oesophagus,  stomach,  and  the  greater  jjortion  of  tlie  duodenum, 
together  with  the  organs  formed  as  outgrowths  from  these.  Similarly,  the  posterior  tubular 
portion,  contained  within  the  tail  fold,  constitutes  the  hindgut,  and  from  it  are  formed 
the  rectum,  except  its  anal  end,  and  a  portion  of  the  colon.  The  middle  division,  known 
as  the  midgut,  gives  rise  to  the  rest  of  the  digestive  tube,  and  is  at  first  widely  open 
below,  where  it  is  continuous  with  the  cavity  of  the  yolk  sac.  Soon,  however,  it  is 
gradually  closed  in  by  the  approximation  of  the  four  folds  which  meet  around  the  margins 
of  the  umbilical  orifice,  and  the  communication  between  the  alimentary  canal  and  the  yolk 
sac  is  thus  reduced  to  a  narrow  passage — the  vitelline  or  vitello-intestinal  duct.  This 
duct  joins  that  portion  of  the  primitive  tube  which  subsequently  forms  the  lower  part  of 
the  iletun,  and  a  i;emnant  of  it  is  sometimes  found  in  the  adult,  when  it  is  known  as 
Meckel's  diverticulum  (see  p.  1073). 

At  this  stage  the  primitive  canal  has  the  form  of  a  nearlj'  straight  tube,  blind  at  both 
extremities,  and  communicating  only  with  the  cavity  of  the  yolk  sac.  It  is  lined  through- 
out by  the  endoderm,  the  cells  of  which  form  the  epithelial  lining  of  the  adult  canal ; 
outside  this  it  is  invested  by  the  splanchnopleure,  or  splanchnic  layer  of  the  mesoderm, 
and  is  separated  from  the  somatopleure  or  body  wall  by  the  coelom  or  body  cavity,  Avhich 
later  on  gives  rise  to  the  pleural,  pericardial,  and  peritoneal  cavities  of  the  body.  At  the 
back,  the  splanchnic  mesoderm  which  surrounds  the  canal  passes  dorsalwards,  to  become 
continuous  with  the  general  mesoderm  beneath  the  notochord,  thereby  forming  a  fold 
which  connects  the  primitive  alimentary  tvibe  to  the  dorsal  wall  of  the  embryo,  and 
constitutes  the  primitive  mesentery.  This  is  at  first  of  considerable  thickness.  At  a 
later  period  it  becomes  reduced  to  a  thin  sheet  of  mesodermic  tissue,  covered  on  each  side 
by  a  layer  of  flattened  endothelial  cells,  which  suspends  the  primitive  alimentary  canal 
within  the  body  cavity  of  the  embryo. 

At  each  end  of  the  embryo,  an  ingrowth  of  the  ectoderm  takes  place,  W'hich  meets 
and  finally  becomes  continuous  with  the  corresponding  extremity  of  the  primitive  alimentary 
tube,  giving  rise  to  the  mouth  and  anus  respectively.  The  former  of  these  ingrowths  is 
known  as  the  stomatodaeum,  and  from  it  is  formed  the  epithelial  lining  of  the  vestibule  of 
the  mouth,  of  the  salivary  glands,  the  gums,  and  the  greater  part  of  the  nasal  cavity,  as 
well  as  the  anterior  lobe  of  the  pituitary'  body.  From  the  other  ingrowth — the  proctodseum 
— are  formed  the  anal  aperture  and  probably  the  anal  canal,  below  the  level  of  the  anal 
valves.  An  account  of  the  formation  of  the  mouth  and  the  anus  will  be  found  on  pages 
■34,  38,  and  45. 

At  an  early  date  special  outgrowths  of  the  lining  endoderm  take  yjlace  from  the 
portion  of  tlie  foregut  corresponding  to  the  future  duodenum.  From  these  diverticula 
the  liver  and  pancreas  are  formed  :  the  former  grows  forwards  from  the  gut,  whilst  the 
latter  grows  backwards  into  the  dorsal  mesentery  (see  pages  1122  and  1129  respectively). 

The  primitive  alimentary  canal  is  now  a  tubular  cavity,  suspended  from  the  dorsal 
wall  of  the  embryo,  within  the  coelom,  by  a  simple  mesentery  (Fig.  781).  In  front,  it 
communicates  with  the  exterior  through  the  stomatodteum  or  primitive  mouth,  and  in 
the  region  of  the  future  duodenum  the  liver  appears  as  a  bifid  outgrowth,  followed  soon 
by  outgrowths  for  the  formation  of  the  pancreas.  Finally,  at  a  date  which  has  not  been 
precisely  determined,  the  anal  membrane  disappears,  and  its  posterior  end  communicates 
with  the  exterior  through  the  pi'octodteum. 

Stomach. — As  early  as  the  fourth  week  the  foregut  exhibits  a  fusiform  enlargement 
74 


1106 


THE  DIGESTIVE  SYSTEM. 


CEsophagai 


Stomachs 
Spleeiiv^ 


Small  intestine 
Superior  mesen- 
teric arterj' 

Small 
intestine' 

Vitelline 
duct 

Caecum  — 
Inferior  mesenteric  artery 

Rectuiii 


Ventral  mesentery 
Liver 

Ventral  mesentery 
-Bile  duct 
/     yStomacli 


in  the  region  of  the  developing  heart,  which  is  the  tirst  evidence  of  the  diffei-entiatiou  of 
the  stomach  :  this  enlargement  is  at  first  symmetrical,  and  mesially  placed.  Soon,  how- 
ever, as  the  diaphragm  is  being  formed,  the  stomach  descends  into  the  abdomen,  and  its 
dorsal  wall — the  futui-e  great  curvature — begins  to  grow  more  rapidly  than  the  ventral 
wall.  As  a  result  the  whole  organ  becomes  somewhat  curved,  and  its  lower  end  is 
carried  forwards  from  the  posterior  abdominal  wall,  giving  rise  to  the  cui-vature  of  the 
duodenum.  The  excessive  growth  of  its  posterior  wall  causes  the  stomach  to  turn  over 
on  to  its  right  side,  Avhich  now  becomes  posterior  or  dorsal.  In  this  rotation  its  upper  or 
cardiac  portion  moves  to  the  left  of  the  middle  line,  and  the  whole  organ  assumes  an 
oblique  direction  across  the  abdomen.  Already,  at  the  fifth  or  sixth  week,  the  adult  form 
of  the  stomach  is  clearly  indicated. 

This  rotation  of  the  stomach  around  its  long  axis,  which  is  accompanied  by  a  rotation 
of  the  lower  end  of  the  oesophagus,  explains  the  unsymmetrical  position  of  the  two 
pneumogastric  nerves.  In  the  adult  the  left  nerve  is  found  on  the  front  of  the  stomach, 
which  was  originally  the  left  side  of  the  organ  :  similarly,  the  right  nerve  lies  on  the 
back,  which  was  originally  the  right  side. 

Intestines, — At  first  there  is  no  separation  into  large  and  small  intestines  ;  the 
primitive  canal  simply  forms  a  slender  tube,  with  a  convexity  towards  the  umbilical 
orifice,  through  which  the  vitelline  duct  passes  to  the  yolk  sac.  Later,  the  tube  increases 
in  length,  and  in  embryos  of  11  or  12  mm.  an  outgrowth  of  the  canal  appears,  which 
represents  the  future  ceecum,  and  indicates  the  separation  into  large  and  small  intestines. 
Growing  longer,  the  intestine  forms  a  large  loop  with  the  vitelline  duct  springing  from 
its   apex   (Fig.    781),   and    the   superior  mesenteric    artery   running    down    between    the 

layers  of  its  mesenterj'. 
At  the  same  time  the  two 
extremities  of  the  coil 
approach  one  another, 
and  form  a  narrow  neck 
to  the  loop,  as  shown  in 
Fig.  781.  There  now 
takes  place  a  change 
which  entirety  modifies 
the  position  of  the  parts 
— this  is  a  rotation  of  the 
whole  loop,  with  its 
mesentery,  around  the 
superior  mesenteric  artery 
as  an  axis  (Fig.  782).  The 
result  of  this  rotation  is 
that  the  original  right 
side  of  the  loop  of  gut 
and  mesentery  becomes 
the  left  side ;  and  the 
beginning  of  the  large 
intestine  is  carried  across 

™  ,      ,  ,  .„,...,,  :,  .,      the  duodenum  (Fig.  782), 

The  figure  to  the  right  shows  the  rotation  of  the  mtestinal  loop  round  the      ,  1    ■    ■         i- V, 

superior  mesenteric  arterv.     In  both  figures  the  parts  are  supposed  to  be    ^'^^^  expiaming  tne  pas- 
viewed  from  the  left  side.'  sage    of    the    duodenum 

behind  the  ti-ansverse 
colon  in  the  adult.  At  the  same  time  the  csecum  comes  to  lie  near  the  middle  of  the 
abdomen  below  the  liver,  a  position  in  which  it  will  be  found  during  the  third  month. 
Subsequently,  it  passes  fai-ther  to  the  right :  and  finally,  descending,  comes  to  occupy  its 
adult  position. 

The  small  intestine  continues  to  grow  in  length,  and,  as  a  result,  is  thrown  into  coils, 
which  become  more  and  more  complex  as  the  length  increases,  until  the  adult  condition 
is  attained.  The  terminal  portion  of  the  large  bowel  retains  its  position  on  the  left  side, 
and  passes  down  to  the  anus.  The  development  of  the  caecum  and  appendix  is  described 
at  page  1078. 

Peritoneum. — At  first  the  primitive  alimentary  canal  is  suspended  from  the 
dorsal  wall  of  the  embryo,  along  the  middle  line,  by  a  simple  dorsal  mesentery,  which 
extends  along  the  whole  length  of  the  tube,  and  is  common  to  all  its  divisions — a  condition 
found  in  the  adult  stage  of  many  reptiles.  There  is  also  present,  in  the  upper  part  of  the 
cavity,  after  the  stomach  and  liver  descend  into  the  abdomen,  a  ventral  mesentery  (Fig. 


.Diaphragm 

ll,-  .Sjjleen 

Line  crosses 
mesogastrium 

„    Pancreas 

^ Superior  mesen- 
teric artery 
Duodenum 

Colon 

Inferior  mesen- 
teric arterv 


"Rectum 
The  mesentery 


Fig.  781.— Two  Dl^gra.ms  to  iLLrsTRATE  the  Developmext  of  the 
IXTESTiXAL  Canal. 


DEVELOPMENT  OF  INTESTINAL  CANAL  AND  PERITONEUM.     1107 


Miildli!  lino 


Cii'cuiii 


Mpsoiitery  obliterated 


Transv(!i-.~ 


781),  which  connects  the  stomach  and  duodenum  to  the  back  of  the  liver,  and,  j)assing  on, 
connects   the   front  of  the   liver  to  the  anterior  abdominal   wall.     The  portion  of  this 
ventral  mesentery,   between   the   stomach   and   liver,    becomes  the   lesser  omentum;   its 
anterior  portion,   between 
the  liverand  the  abdominal  stomaci, 

wall,  forms  the  falciform 
limiment  (Fig,  781)  :  and, 
ni  its  lower  margui,  the 
umbilical  vein  runs  from 
the  umbilicus  to  the  liver. 
The  portion  of  the 
dorsal  mesentery  lying  be- 
hind the  stomach  is  known  Cucum 
as  the  mesogastrium.  At 
first  it  is  relatively  short ; 
but  with  the  growth  of 
the  posterior  wall  of  the 
stomach,  and  the  turning  mesentery 
of  that  organ  over  on  its 
right  side,  the  mesogas- 
trium becomes  elongated, 
and  is  folded  on  itself, 
forming  more  or  less  of  a 
pouch,  directed  downwards 
and  to  the  left.  The  wall 
of  this  pouch  becomes  in 
part  the  great  omentum, 
and  within  it  is  developed 


Tlie  niesfiiite 


Rectum^ 
Mesentery  of  descending  colon 

FlO.    782. — Two    DiAfiRAMS    TO    ILLUSTRATE    THE    ])EVEL<)PMENT    OK    THE 

Mesenteries. 

In  the  first  figure  the  rotation  of  the  intestinal  loop  and  the  continuous 
primitive  mesentery  is  shown.  In  the  second  figure  (to  the  right), 
which  shows  a  more  advanced  stage,  the  portions  of  the  primitive 
mesentery  (going  to  tlie  ascending  and  descending  colons)  which  dis- 
appear, through  their  adhesion  to  the  postei'ior  abdominal  wall,  are 
shaded  dai'k  ;  the  portions  which  persist  are  lightly  shaded. 


the  small  sac  of  the  peri- 
toneum. In  the  rotation  of  the  stomach  and  the  accompanying  passage  of  the  lesser 
omentum  from  an  antero-posterior  to  a  more  or  less  transverse  direction,  a  portion  of  the 
cavity  of  the  abdomen  is,  as  it  were,  caught  in  behind  the  stomach  and  lesser  omentum. 
This  portion  of  the  cavity  becomes  the  upper  part  (vestibule)  of  the  small  sac,  and  at 

first  it  communicates  with  the 
general  cavity  by  a  wide 
opening  to  the  right  of  the 
lesser  omentum ;  but  the 
growth  of  the  liver,  encroach- 
ing upon  the  opening,  and  other 
causes,  reduce  it  to  a  relatively 
small  size,  and  it  forms  the 
foramen  of  Winslow  in  the 
adult. 

The  great  omentum  is,  as 
pointed  out  above,  a  bag-like 
gi'owth  of  the  lower  part  of 
the  mesogastrium,  which  passes 
downwards  and  to  the  left  in 
front  of  the  transverse  colon. 
As  shown  in  Fig.  783,  A  and 
B,  it  is  first  entirely  uncon- 
nected with  the  transverse 
colon  and  mesocolon ;  but 
about  the  third  or  fourth 
month  it  becomes  united  to 
both,  and  the  adult  condition 


Fig.  78£ 


B  C 

-Diagrams  to  illustrate  the  Devdloi-mknt  ok  the 
Great  Omentum  (after  Hertwig). 

A,  shows  the  beginning  of  the  great  omentum  and  its  independence  of 
the  transverse  mesocolon  ;  in  B,  the  two  come  in  contact  ;  and  in 

C,  they  have  fused  along  tlie  line  of  contact.  (According  to  Lock- 
wood,  the  two  layers  of  the  fold  shown  in  A,  running  in  between 
the  great  omentum  and  transverse  mesocolon,  instead  of  fusing,  as 
shown  in  B,  are  drawn  out  —  unfolded  —  producing  the  condition 
shown  in  C).     A,  stomach  ;  B,  transverse  colon  ;  C,  small  intestine  ; 

D,  duodenum  ;  E,  pancreas  ;  F,  great  omentum  ;  G,  placed  in  great    is  established  (Fig.  78.3,  C). 
sac  ;  H,  in  small  sac  of  peritoneum. 

It  would  appear  that  the 
growth  of  the  lower  part  of  the  small  sac,  and  of  the  great  omentum,  is  primarily  due  to  a  pro- 
liferation of  the  cells  over  a  limited  area  of  the  mesogastrium,  and  a  resulting  folding  of  this 
layer  downwards  and  to  the  left. 

In  the  upper  part  of  the  mesogastrium  the  spleen  is  developed,  and  the  portion  of 

74  a 


1108  THE  DIGESTIVE  SYSTEM. 

this  fold  which  intervenes  between  the  stomach  and  spleen  forms  the  gastro- splenic 
omentum,  whilst  the  part  behind  the  spleen  becomes  the  lieno-renal  ligament. 

Of  the  primitive  mesentery,  the  portion  connected  with  the  stomach — the  mesogastrium 
■ — becomes  modified  in 'the  manner  just  described.  The  next  division — the  mesoduodenum 
— disappears  completely,  owing  to  the  turning  over  of  the  duodenal  loop  on  to  its  right 
side,  and  its  subsequent  adhesion  to  the  posterior  abdominal  wall,  accompanied  by  the 
absorption  of  its  mesentei'y.  The  mesenteries  of  the  small  and  large  intestine  are  con- 
tinuous at  first  (Fig.  781).  When  the  rotation  of  the  intestinal  loop  takes  place  around 
the  superior  mesenteric  artery  (see  above),  the  beginning  of  the  large  intestine,  with  its 
mesentery,  is  carried  to  the  right  across  the  duodenum,  and  a  fan-shaped  portion  of  the 
general  mesentery,  lying  within  the  concavity  of  the  loop,  is  partially  cut  off;  this,  later 
on,  forms  the  mesentery  proper  in  the  adult.  At  first  it  is  continuous  by  its  right  border 
with  the  mesentery  of  the  ascending  colon,  a  part  of  the  primitive  mesentery  (which  is 
similarly  continued  into  the  mesentery  of  the  ti'ansverse,  descending,  iliac,  and  pelvic 
colons).  Subsequently,  as  shown  by  the  darkly-shaded  parts  in  Fig.  782,  the  back  of  the 
mesenteries  of  the  ascending,  descending,  and  iliac  portions  of  the  colon  adheres  to  the 
posterior  abdominal  wall,  and  these  mesenteries  become  lost ;  whilst  the  mesenteries  of 
the  transverse  and  pelvic  portions  of  the  colon  remain  free,  and  persist  in  the  adult. 

At  the  same  time,  the  mesentery  proper  (which  was  at  first  attached  only  at  its 
narrow  neck,  between  the  duodenum  and  transverse  colon,  and  below  this  was  continuous 
on  the  right  with  the  ascending  mesocolon)  now  acquires  a  new  attachment  to  the 
posterior  abdominal  wall  through  the  absorption  of  the  ascending  mesocolon  (Fig.  782), 
and  the  adult  condition  is  attained. 

THE  LIVEE. 

The  liver  (hepar)  is  a  large  glandular  mass  of  irregular  shape,  which  lies 
under  cover  of  the  ribs  in  the  upper  and  right  portion  of  the  abdominal  cavity, 
immediately  beneath  the  diaphragm  (Fig.  784).  It  is  the  largest  of  all  the 
digestive  glands,  and  plays  an  important  part  in  the  metabolism  of  both  carbo- 
hydrate and  nitrogenous  materials:  in  addition,  it  secretes  the  bile  —  a  fluid 
which  although  chiefly  excretory,  assists  to  some  extent  in  pancreatic  digestion. 
From  the  liver  the  bile  is  conveyed  to  the  duodenum  by  the  bile  duct,  in  con- 
nexion with  which  is  found  a  pear-shaped  diverticulum,  for  the  temporary  storage 
of  the  bile,  known  as  the  gcdl-Uadder  (Fig.  786). 

Form. — The  liver  is  so  irregular,  and  varies  so  considerably  in  size  and  shape 
in  different  bodies,  and  even  in  the  same  body  under  different  conditions,  that  it 
is  difficult  to  convey  a  true  idea  of  its  form.  This,  perhaps,  may  be  most  readily 
realised  from  a  consideration  of  the  portion  of  the  abdomen  in  which  the  liver 
lies,  and  to  the  shape  of  which  its  form  is  chiefly  due. 

The  upper  portion  of  the  abdominal  cavity  is  dome-shaped,  its  anterior,  posterior, 
and  lateral  walls,  as  well  as  its  roof,  being  formed  chiefly  by  the  vaulted  under  surface 
of  the  diaphragm,  which  slopes  down  on  the  inner  aspect  of  the  ribs  as  far  as  the 
lower  l)order  of  the  thoracic  framework.  In  the  right  and  middle  portions  of  the 
dome-shaped  space  thus  formed  the  liver  lies,  like  a  cast  in  its  mould,  and  from  it 
chiefly  its  form  is  derived.  And,  if  an  imaginary  plane  be  passed  backwards  and 
upwards,  from  an  oblique  line  extending  across  the  anterior  abdominal  wall,  from  a 
point  immediately  below  the  right  margin  of  the  ribs  to  a  point  one  inch  below 
the  left  nijjple,  it  will  cut  off  a  segment  of  the  abdominal  cavity  which  corre- 
sponds toleraljly  accurately  to  the  liver,  in  both  size  and  form. 

Accordingly,  the  liver  may  be  described  as  having  two  chief  surfaces  :  a  parietal 
surface,  convex  in  general  outline,  whicli  fits  into  the  arch  of  the  diaphragm;  and 
a  visceral  surface,  irregular  in  form,  which  looks  downwards,  backwards,  and  to  the 
left,  and  rests  upon  the  abdominal  viscera.  These  two  surfaces  are  separated  from 
one  another  by  the  inferior  margin  of  the  liver. 

Symington  has  described  the  liver,  when  hardened  in  situ,  as  a  right-angled  triangular  prism 
with  its  right  angles  rounded  off,  and  as  having  five  surfaces — anterior,  posterior,  superior,  right, 
and  inferior.  The  first  four  of  these  would  be  included  in  the  parietal  surface  described  above, 
and  the  inferior  corresponds  to  the  visceral  surface. 

Previously  His  had  described  three  surfaces  :  an  inferior,  corresponding  to  the  visceral,  and 
a  superior  and  posterior,  which  together  correspond  to  the  parietal  surface. 


I 


THE  LIVER 


1109 


Before  His's  descrii^tion,  which  changed  all  previous  views  on  the  form  of  the  liver,  became 
current,  it  was  described  as  having  two  surfaces,  an  upper  and  a  lower,  and  two  borders,  an 
anterior  thin  and  a  posterior  thick ;  and  this  is  the  shape  of  the  ordinary  soft  dissecting-room 
liver,  which  flattens  out  into  a  cake-like  form  when  removed  from  the  body. 

In  the  body,  on  the  other  hand,  instead  of  being  flattened  out  in  this  way,  it  is  folded,  as  it 
were,  around  its  jjortal  and  longitudinal  fissures  into  a  much  more  compact  mass ;  and  if  hard- 
ened in  situ  before  its  removal,  it  presents  an  appearance  very  different  from  that  of  the  soft  liver 
just  referred  to.  From  a  study  of  such  hardened  specimens  it  will  be  seen  that  the  mass  of  the 
right  lobe  lies  chiefly  in  an  antero-post«rior  direction,  its  posterior  thick  portion  fitting  into  a  wide 
groove  at  the  side  of  the  vertebral  column,  and  its  long  axis  running  from  behind  forwards  and  a 


Diaphragm- 


Attachment  ot 
falciform  liKament" 


Bight  lobe  of  li\  ei  ■ 


GaM  bladdei r'S"?*?*^-  /- 


Transverse  colon - 
Small  intestine- 


Ascending  colon — i      uw 


Anterior  supeiioi 
spine 

Csecuni  - 


— Outline  of  liver 


^■Stomach 


Jreat  omentwm  (cut) 
I'ransverse  inesocolon 
-with  jejunum 
beneath  it 
Tsenia  of  transverse 
colon 


-Internal  oblique 

-  I'osition  of  umbilicus 


SCALE  IN  INCHES 


SCALE  IN  CENTIMETRES 


Fig.  784. — The  Abdominal  Viscera  in  situ,  as  seen  when  the  abdomen  is  laid  open  and  the  gi'eat  omeutum 
removed  (drawn  to  scale  from  a  photograph  of  a  male  body  aged  56,  hardened  by  formalin  injections). 

The  ribs  on  the  right  side  are  indicated  by  Roman  numerals  ;  it  will  be  observed  that  the  eighth  costal  cartilage 
articulated  with  the  sternum  on  both  sides.  The  subcostal,  intertubercular,  and  right  and  left  Poupart 
lines  are  drawn  in  black,  and  the  mesial  plane  is  indicated  by  a  dotted  line.  The  intercostal  muscles  and 
part  of  the  diaphragm  have  been  removed,  to  show  the  liver  and  stomach  extending  up  beneath  the  ribs. 
The  stomach  was  moderately  distended,  and  the  intestines  were  particularly  regular  in  their  aiTangemeut. 

liltle  inwards.  The  left  lobe,  leading  off  from  the  anterior  part  of  the  right  lobe,  is  folded  across 
the  front  of  the  vertebral  column  and  great  vessels,  its  long  axis  running  transversely,  but  it  does 
not  usually  pass  back  at  the  side  of  the  vertebral  column,  like  the  right  lobe,  into  the  vertebral 
groove  ;  so  that  there  is  no  real  notch,  as  usually  described,  at  the  back  of  the  liver  for  the 
vertebral  column,  but  merely  an  angle  formed  by  the  meeting  of  the  two  lobes  coming  from 
different  directions. 

Position. — The  main  mass  of  the  liver  lies  in  the  right  hypochondrium ;  from 
this  it  extends  across  the  upper  part  of  the  epigastrium,  and  usuaUj  reaches 
as  far  as   the   left    Poupart  plane.      Not  uncommonly  it  passes   into    the   left 

746 


1110  THE  DIGESTIVE  SYSTEM. 

hypochondriiim,  where  it  may  extend  eA'en  as  far  as  the  left  lateral  wall  of  the 
abdomen.  Usually,  too,  its  lower  margin  passes  down  on  the  right  side  for  a  little 
distance  (|  inch,  12-5  mm.)  below  the  subcostal  plane,  and  comes  to  lie  in  the 
right  lumbar  region.  Under  ordinary  conditions,  the  anterior  end  of  the  longi- 
tudinal fissure,  which  separates  the  right  from  the  left  lol)e,  lies  one  or  two  inches 
to  the  right  (»f  the  mesial  plane. 

The  limits  even  of  the  normal  liver  are  very  variable,  but,  taking  the  average 
condition  in  the  male,  they  may  be  marked  out  on  the  surface  of  the  body  by  the 
following  method : — Three  points  are  determined — (a)  half  an  inch  (12'5  mm.) 
below  the  right  nipple ;  (b)  half  an  inch  (12-5  mm.)  below^  the  right  margin  of  the 
thorax  (or  below  the  tip  of  the  tenth  rib) ;  and  (c)  one  inch  (25  mm.)  below  the 
left  nipple.  If  these  points  be  joined  by  three  lines,  slightly  concave  towards 
the  liver,  they  will  give  the  outline  of  the  organ  with  sufficient  accuracy  for  all 
ordinary  purposes.     (For  variations  in  position  see  p.  1117.) 

To  state  the  matter  somewhat  more  in  detail : — if  the  two  "  nipple  j)oints  "  (a)  and  (c)  be 
joined  by  a  line,  slightly  convex  upwards  on  each  side,  but  a  little  depressed  at  the  centre  corre- 
sponding to  the  position  of  the  heart,  and  crossing  the  lower  end  of  the  sternum  about  the  level 
of  the  sixth  cartilage,  it  will  mark  the  upper  limit.  A  line,  convex  outwards,  from  the  right 
nipple  point  (a)  to  the  subcostal  point  (b)  will  indicate  the  riglit  limit,  wdiile  the  loM'er  limit  is 
marked  by  a  line,  convex  downwards,  drawn  from  the  subcostal  point  (b)  to  the  left  nipple  point 
(c),  and  passing  through  a  point  half-way  between  the  umbilicus  and  the  lower  end  of  the 
gladiolus,  in  the  middle  line. 

The  line  indicating  the  v/pper  limit  of  the  liver  is  elevated  on  each  side,  corresponding  to  the 
ciipolfe  of  the  diaphragm,  and  depressed  in  the  centre  beneath  the  heart.  On  the  right  side 
where  highest,  namely,  about  one  inch  (25  mm.),  internal  to  the  mammary  line,  it  reaches  during 
expiration  to  the  upper  border  of  the  fifth  rib  ;  on  the  left  side  it  is  one-half  to  three-quarters  of 
an  inch  (12  to  18  mm.)  lower  ;  and  it  crosses  behind  the  sternum  at  the  level  of  the  sixth  sterno- 
costal junction — or  sometimes  lower.  It  must  be  remembered,  however,  that,  Avhilst  the  liver 
reaches  up  to  the  levels  just  given,  it  does  so  only  at  the  highest  part  of  its  convex  parietal  surface, 
and  i.s  separated  from  the  ribs  all  round  by  the  thin  lower  margin  of  the  lung  (which  extends 
dovni  between  the  chest  wall  and  diaphragm  to  the  sixth  rib  in  front,  to  the  eighth  in  the  mid- 
lateral  line,  and  to  the  level  of  the  tip  of  the  spine  of  the  tenth  dorsal  vertebra  behind),  so  that, 
in  percussing  over  the  livei',  its  dulness  is  obscured  by  the  resonance  of  the  lungs  above  these 
points. 

Weight  and  Size. — The  liver  usually  weighs  from  three  to  three  and  a  quarter 
pounds,  or  al»out  J^-th  of  the  body  weight. 

The  average  size  of  the  liver  may  be  briefly  expressed  as  follows  : — It  measures  in  the  trans- 
verse direction  about  seven  inches  (17'5cm.) ;  in  the  vertical,  six  to  seven  inches  (15  to  17'5  cm.) ; 
and  in  the  antero-posterior,  on  the  right  side  where  greatest,  about  six  inches  (15  cm.)  Its 
greatest  width,  measiu-ed  obliquely  from  side  to  side  along  the  inferior  or  visceral  surface,  is  ten 
inclies  (25  cm.) 

Its  weight  ordinarily  varies  betAveen  fifty  and  fifty-five  ounces  in  the  male,  and  between  forty 
three  and  forty-eight  in  the  female,  with  an  aA-erage  for  the  two  sexes  of  about  forty-nine  oimces, 
or  a  little  over  three  pounds.  It  corres23onds  to  about  i'^tli  of  tlie  body  weight  in  the  adult ; 
wliilst  at  birth  it  is  relatively  twice  as  large  (viz.  -jig-th  or  -gVth  of  the  body  weight),  and  in  the 
early  foetus  very  much  largei-. 

The  proportion  of  the  right  to  the  left  lobe  is  very  variable,  but  is  usually  about  as  4  to  1  ; 
at  lu'rth  it  is  about  as  2  or  3  to  1. 

Relations  and  Surfaces. — The  liver,  as  already  pointed  out,  possesses  two  chief 
surfaces,  the  parietal  lying  in  contact  with  the  abdominal,  parietes,  and  the  visceral 
resting  on  the  abdominal  viscera. 

Parietal  Surface. — In  conformity  with  the  shape  of  the  upper  portion  of  the 
abdominal  cavity  which  it  occupies,  the  parietal  surface  ('Fig.  785)  is  convex  in 
general  outline,  and,  taken  as  a  whole,  lies  against  the  diaphragm,  except  below 
and  in  front,  where  it  projects  from  beneath  the  riljs  (Fig.  784),  and  comes  in 
contact  witli  the  anterior  abdominal  wall  for  about  two  or  three  inches  (5*0  to  7'5 
cm.)  below  the  xiphi-sternal  articulation.  It  is  completely  covered  by  peritoneum, 
except  behind  at  the  "  uncovered  area,"  where  it  comes  into  direct  relation  with 
the  diaphragm ;  and  it  is  divided  into  right  and  left  lobe-portions  by  the  attach- 
ment of  the  falciform  ligament — a  fold  of  peritoneum  which  connects  it  to  the 
diaphragm  and  anterior  abdominal  wall. 

As  the  space  which  the  liver  occupies  is  bounded  l»y  the  anterior,  the  right, 


THE  LIVER 


nil 


and  the  posterior  walls  of  the  abdomen,  as  well  as  by  the  roof,  we  can  distinguish 
on  its  parietal  surface,  which  lies  against,  and  takes  its  shape  from,  these  walls, 
four  corresponding  "  areas,"  namely  (a)  the  superi(jr,  (&)  the  anterior,  (c)  the  right, 
and  (d)  the  posterior  areas  of  the  parietal  surface.  Of  these  the  posterior  area  is 
the  most  important,  and  must  be  described  in  greater  detail  than  the  others. 

Posterior  Area  of  the  Parietal  Surface.  —  This  portion  of  the  parietal 
surface  (whicli  corresponds  to  the  posterior  surface  of  His)  is  directed  back- 
wards, and  lies  in  contact  with  the  diaphragm,  as  the  latter  passes  down  on  the 
posterior  al>domnial  wall.  It  is  very  irregular  in  shape,  and  presents  from  right 
to  left  the  following  parts  :— (1)  The  "  uncovered  area  "  of  the  right  lobe  ;  (2)  the 
suprarenal  impression ;  (3)  the  fossa  of  the  vena  cava ;  (4)  the  Spigelian  lobe, 
separated  l)y  the  fissure  of  the  ductus  venosus  from  (5)  the  oesophageal  groove, 
which  belongs  to  the  left  lolie. 

(1)  The  "  uncovered  area  "  of  the  right  lobe  (Fig.  786)  is  a  considerable  portion 

Superior  area  of  parietal  surface 


.Vttacliiueiit  of 
falcifonii  ligaiiieut 


Anterior  area  of 
parietal  surface 


Round  ligament 
Falcifonn  ligament 
Fundus  of  j,'all-bladder 

Fig.  785. — The  Lis-eu   froji  the  kront,  showing  tlie  superior,  right,  ami  anterior  areas  of  the 

parietal  surface. 

of  the  back  of  the  right  lobe — varying  from  Ih  to  2-J-  inches  (3-7  to  6'2  cm.)  in  width, 
and  from  3  to  4  inches  (7'5  to  10  cm.)  in  transverse  measurement — which  corre- 
sponds to  the  interval  Itetween  the  two  layers  of  the  coronary  ligament,  and  is 
devoid  of  peritoneum.  Over  this  uncovered  portion,  which  looks  more  inwards  than 
backwards,  the  liver  and  diaphragm  are  in  direct  contact,  and  are  united  Ijy  areolar 
tissue ;  here  too  is  estaljlished  a  communication  by  small  veins  between  the  portal 
circulation  of  the  liver  and  the  systemic  circulation  of  the  diaphragm. 

(2)  Suprarenal  Impression. — On  the  "  uncovered  area,"  immediately  to  the 
right  of  (and  behind)  the  vena  cava,  is  a  triangular  impression  (impressio  supra- 
renalis.  Fig.  786),  produced  by  the  suprarenal  body,  which,  projecting  upwards  from 
the  top  of  the  right  kidney,  becomes  wedged  in  between  the  diaphragm  and  liver. 

(3)  Fossa  of  the  Vena  Cava  (fossa  veme  cavte). — At  the  left  extremity  of  the 
•''  uncovered  area "  the  inferior  vena  cava  hes  vertically,  embedded  in  a  fossa 
of  the  liver  substance,  between  the  Spigelian  lobe  on  the  left  and  the  adjacent 
part  of  the  uncovered  area  on  the  right,  both  of  which  project  over  the  sides 
of  the  cava,  almost  hiding  it  from  view  (Fig.  786);  sometimes  they  actually 
meet  and  form  a  pons  hepatis  across  the  back  of  the  vein. 


1112 


THE  DIGESTIVE  SYSTEM. 


(4)  Spigelian  Lobe. — To  the  left  of  the  fossa  of  the  cava  lies  the  SpigeKan  lobe 
'globus  caudatus),  a  prominent  oblong  mass  (Fig.  786),  which  is  placed  vertically  on 
the  back  of  the  liver,  between  the  fissure  of  the  ductus  venosus  on  the  left  and  the 
fossa  of  the  vena  cava  on  the  right — the  former  marking  it  off  from  the  left  lobe,  the 
latter  from  the  "  uncovered  area  "  of  the  right  lobe.  The  top  of  the  small  sac  of 
peritoneum  .separates  the  back  of  the  Spigehan  lobe  from  the  diaphragm,  which 
latter,  in  turn,  separates  it  from  the  aorta  just  before  that  vessel  enters  the 
abdomen. 

The  upper  end  of  the  Spigelian  lobe  is  separated  from  the  superior  area  of  the  parietal  surface 
bv  the  meeting  of  the  vena  cava  and  the  fissure  of  the  ductus  venosus  in  front  of  it.     Its  lower 

Veua  cava  in  its  fossa 
Spigelian  lobe 


Fissure  of  ductus  venosu-s 
Omental  tuberosity 
(Esophageal  groove 


End  of  riglit  sujjrarenal  vein 
Suprarenal  impression 

Right  end  of  caudate  lobe 

Uncovered  area  of  right  lobe 
Renal  impression 

Attachment  of  right 
lateral  ligament 


Gastric  impression 


Vl<}. 


Portal  hSHMrn 

L'mbillcal  fissure 


Quadrate  lobe 

Portal  vein 

Gall  bladder 

Duodenal  impression 

Colic  impression 

'86. — The  Livek  kuom  bklow  and  behind,  showing  the  whole  of  the  visceral  surface  and  the  posterior 
area  of  the  parietal  .surface.  The  portal  fissure  has  been  slightly  opened  up  to  show  the  vessels  passing 
through  it ;  the  other  fissures  are  represente4  in  their  natural  condition— closed.  In  this  liver,  which 
was  hardened  in  situ,  the  impressions  of  the  sacculations  of  the  colon  are  distinctly  vi.sible  at  the  colic 
impression.  The  round  ligament  and  the  remains  of  the  ductus  venosus  are  hidden  in  the  depths'.of 
their  fissures. 


end  i.s  free  and  prominent,  and  reaches  to  the  visceral  surface,  where  it  usually  presents  a 
notch  or  fi.ssure  (in  which  the  hepatic  arteiy  lies,  particularly  in  the  fa;tus),  which  marks  off  a 
larger  and  more  prominent  left  part  (the  tulx-rculum  papillare)  projecting  downwards  behind  the 
poi-tal  fi.ssure,  and  a  smaller  right  part  pa.s.sing  out  into  the  processus  caudatus,  or  caudate  lobe 
whi^ch  connects  it  ^Fig.  78b')  with  the  under  or  visceral  surface  of  the  right  lobe. 

The  posterior  surface  of  the  Spigelian  lobe  is  free  ;  it  is  placed  vertically,  and  looks  backwards 
and  Hlightly  inwards.  The  lobe  has  also  another  surface,  which  is  hidden  when  in  the  body  and, 
in  the  hardened  liver  by  the  folding  of  the  left  lobe  across  it.  By  this  folding  there  is  formed  a 
deep  fi-ssure  (fissure  of  the  ductus  venosus),  at  the  bottom  of  which  will  be  found  the  remains  of 
the  ductus  venosus. 

(5)  The  CEsophageal  Groove  is  situated  on  the  back  of  the  left  lobe,  to  the 
left  of  the  upper  end  of  the  Spigelian  lobe,  but  separated  from  it  by  the  fissure  of 
the  ductus  venosus  ffossa  ductus  venosi),  which  on  this  aspect  indicates  the  division 
tetween  the  right  and  left  lobes.     The  groove  leads  down  into  the  gastric  impres- 


THE  LIVER  1113 

sion  on  the  visceral  surface  of  the  left  lobe  (Fig.  786),  and,  when  in  the  bodj,  lies 
in  contact  with  the  prominent  right  or  anterior  margin  of  the  cesophageal  oritice 
of  the  diaphragm  (see  p.  1040  and  Fig.  795),  sometimes  also  with  the  oesophagus 
itself. 

Tlie  superior  area  of  the  parietal  surface  lies  iu  contact  with  the  roof  of  the  abdomen  ;  it  is 
convex  on  each  side,  and  depressed  near  the  middle  line.  The  two  convexities,  of  which  the 
right  is  the  more  prominent,  fit  into  the  two  cupoke  of  the  diaphragm ;  whilst  the  central 
depression  (depressio  cardiaca)  corresjjonds  to  the  position  of  the  heart.  This  area  (with  the 
exception  of  a  small  triangle  at  its  posterior  part,  between  the  separating  layers  of  the  falciform 
ligament)  is  completely  covered  by  peritoneum,  and  on  it  the  division  of  the  liver  into  right  and 
left  lobes  is  indicated  by  the  attachment  of  the  falciform  ligament. 

Tlie  anterior  area  of  the  parietal  surface  is  triangular  in  shape,  and  after  death  is  usually 
flattened,  owing  to  the  falling  in  of  the  anterior  abdominal  wall.  In  part  it  lies  in  contact  with 
the  diaphragm,  which  separates  it  from  the  rib-cartilages  on  each  side,  but  at  the  subcostal 
triangle  it  comes  into  direct  relation  with  the  anterior  wall  of  the  abdomen,  for  a  distance 
usually  of  two  or  three  inches  below  the  xiphi-sternal  articulation.  It  has  a  complete  peritoneal 
covering,  and  gives  attachment  as  far  down  as  the  umbilical  notch,  at  the  inferior  border,  to  the 
falciform  ligament,  which  connects  it  to  the  anterior  abdominal  wall. 

The  anterior  passes  gradually  into  the  upper  and  right  areas,  but  it  is  distinctly  separated 
from  the  visceral  surface  by  the  sharp  inferior  border  of  the  organ.  The  umbilical  notch  is 
often  continued  ujjwards  for  some  distance  on  the  surface  as  a  slit-like  fissure. 

The  right  area  of  the  parietal  surface  is  convex  and  extensive,  and  lies  in  contact  with  the 
diaphragm,  which  separates  it  from  the  inner  surface  of  the  lower  ribs,  and  also  from  the  lower 
margin  of  the  lung  and  pleura  above.  Though  sharply  marked  off  by  the  inferior  border  from 
the  visceral  surface,  it  passes  without  distinct  limits  into  the  other  areas  of  the  parietal  suiiace. 
It  is  completely  covered  by  peritoneum. 

Visceral  or  Inferior  Surface. — This  is  an  irregular,  obliquely  sloping  surface 
(Fig.  786),  which  looks  downwards,  backwards,  and  to  the  left,  and  rests  upon 
the  stomach,  small  omentum,  intestines,  and  right  kidney.  The  division  into 
right  and  left  lobes  is  indicated  on  this  surface  by  the  umbilical  fissure,  which 
passes  from  the  umbilical  notch  at  the  anterior  border  back  to  the  portal  fissure. 

The  visceral  surface  of  the  left  lobe  is  directed  dowuwards  and  backwards,  and 
rests  on  the  upper  surface  of  the  stomach,  in  front  of  the  cardia ;  also  on  the  lesser 
curvature  with  its  attached  lesser  omentum.  The  part  which  rests  upon  the  upper 
surface  of  the  stomach  is  rendered  concave  by  the  pressure  of  that  organ  (Fig.  786), 
and  is  known  as  the  gastric  impression  (impressio  gastrica) ;  whilst  the  portion  to 
the  riglit  of  this,  being  free  from  the  pressure  of  tlie  stomach,  projects  backwards 
over  the  lesser  curvature  against  the  lesser  omentum  in  the  form  of  a  smooth 
rounded  prominence,  and  is  known  as  the  omental  tuberosity  (tuber  omentale). 

The  visceral  surface  of  the  riglit  lobe  may  be  divided  iuto  two  portions  by  the  line 
of  the  gall-bladder,  which  extends  forwards  in  its  fossa  to  the  lower  sharp  margin 
of  the  liver  (Fig.  786). 

(a)  To  the  left  of  the  line  of  the  gall-bladder  are  found  from  before  backwards  : — 
The  quadrate  lobe,  portal  fissure,  and  caudate  lobe,  (i)  The  quadrate  lobe  (lobus 
quadratus)  is  placed  at  the  anterior  part  of  the  under  surface,  between  the  gall- 
bladder aud  tlie  umbilical  fissure,  extending  to  the  inferior  margin  of  the  liver  iu 
frout,  and  to  the  portal  fissure  behind :  it  rests  upon  the  pylorus  or  the  beginning 
of  the  duoilenum.  (2)  The  portal  or  transverse  fissure  is  a  deep  cleft  through  which 
the  portal  vein,  hepatic  artery,  antl  hepatic  duct  enter  the  liver,  and  to  the  margins 
of  which  are  attached  the  two  layers  of  the  lesser  omentum  (Fig.  786).  (o)  The 
caudate  lobe  or  process  (processus  caudatus)  consists  of  a  narrow  ridge  of  liver 
substance  which  runs  across  behind  the  portal  fissure,  and  connects  the  lower  end 
of  the  Spigelian  lol)o  with  the  rest  of  the  right  lobe.  It  forms  the  upper  boundary 
of  the  foramen  of  Winslow,  and  is  felt  when  the  finger  is  introduced  into  that 
passage.  It  is  often  very  narrow  but  can  always  be  distinguished  through  its 
intervening  between  the  portal  vein  and  the  inferior  vena  cava. 

(b)  The  surface  to  the  right  of  the  gall-bladder,  which  is  more  extensive  than 
that  on  its  left,  is  entirely  occupied  by  three  impressions  produced  by  the  under- 
lying viscera — namely:  (1)  The  colic  impression  (impressio  colicu)  lies  in  front  and 
to  the  right  of  the  gall-bladder.  It  rests  up'-n  the  hepatic  tiexure  and  the 
beginning  of  the  tninsverse  colon.  (2)  Behind  th.s  is  the  renal  impression  (im- 
pressio renalis),  larger  than  the  preceding,  which  corresponds  in  size  and  form  to 


1114  THE  DIGESTIVE  SYSTEM. 

the  upper  half  or  two-tliirds  of  the  right  kidney,  against  the  anterior  or  visceral 
surface  of  which  it  lies.  It  is  placed  behind  the  colic  impression  just  as  the  kidney 
itself  is  placed  behind  the  colon.  (3)  To  the  inner  side  of  the  renal  impression,  and 
near  the  neck  of  the  gall-bladder,  is  placed  the  narrow  duodenal  impression  (im- 
pressio  duodenalis),  which  lies  in  contact  with  the  duodenum  (the  second  part,  dow^n 
to  the  point  at  which  it  is  crossed  by  the  colon). 

The  quadrate  lobe  is  of  an  oblong  sliaj^e,  the  autero-j^osterior  diameter  being  the  greatest.  Its 
.•surface  is  generally  concave,  and  is  related  to  the  jjylorus  and  the  adjacent  parts  of  the  stomach 
and  duodenum,  when  the  former  is  distended.  When  the  stomach  is  empty,  however,  the 
pylorus  usually  lies  beneath  the  right  portion  of  the  left  lobe,  and  the  first  part  of  the  duodenum 
lies  beneath  the  quadrate  lobe,  the  transvei-se  colon  also  coming  in  contact  with  it  anteriorlv 
(Fig.  786).  ,  .  .  " 

The  ujjper  end  of  the  renal  impression  is  frequently  uncovered  by  peritoneum  (Fig.  786),  that 
is  to  say,  the  "uncovered  area"  of  the  right  lobe  extends  doAvii  over  the  impression  for  a  little 
way.  This  impression  is  very  deep,  and  accommodates  nearly  the  whole  thickness  of  the  kidney. 
In  many  hardened  specimens  it  would  appear  to  belong  more  to  the  posterior  jDart  of  the 
parietal  than  to  the  inferior  or  A-isceral  surface. 

The  inferior  margin  of  the  liver,  as  already  pointed  out,  separates  the  parietal 
from  the  visceral  surface.  Behind,  it  is  indistinctly  marked  and  corresponds  to  the 
lower  edge  of  the  posterior  area,  or  back,  of  the  parietal  surface :  it  is  in  con- 
tact with  the  right  kidney,  and  runs  along  the  course  of  the  eleventh  rib.  At  the 
rigli  t  side  it  is  stout  but  distinct,  and  usually  corresponds  to,  or  projects  a  little  way 
Ijelow,  the  lower  border  of  the  thoracic  framework.  In  front  (margo  anterior)  it  is 
thin  and  sharp,  and  crosses  the  anterior  abdominal  wall  obliquely,  generally  corre- 
sponding to  a  line  drawn  from  a  point  half  an  inch  (12  mm.)  below  the  margin  of 
the  ribs  (tip  of  tenth  costal  cartilage)  on  the  right  side  to  a  point  an  inch  below  the 
nipple  on  the  left,  and  extending  down  in  the  middle  hne  to  a  point  half-way 
between  the  gladiolus  and  the  umbilicus.  This  portion  of  the  lower  border 
usually,  but  not  invariably,  presents  one  or  two  notches.  The  umbilical  notch 
(incisura  umbilicalis),  the  more  constant  of  the  two  (Fig.  785),  is  situated 
at  the  anterior  end  of  the  umbilical  fissure,  and  corresponds  to  the  lower  part 
of  the  attachment  of  the  falciform  ligament.  It  is  usually  placed  from  one  to 
two  inches  (2-5  to  5'0  cm.)  to  the  right  of  the  middle  line.  The  second  notch,  less 
frequently  present,  corresponds  to  the  fundus  of  the  gall-Jiladder,  and  may  be 
called  the  notch  of  the  gall-bladder  (incisura  vesicic  felleas). 

At  its  left  extremity  the  inferior  margin  passes  backwards  around  the  edge  of 
the  left  lobe,  and  ends  at  the  oesophageal  groove  on  its  back. 

Fissures  of  the  Liver. — Five  fissures  or  fossae  are  usually  described  in  con- 
nexion with  the  liver;  these  are:  (1)  the  umbilical  fissure,  (2)  the  fissure  of  the 
ductus  venosus  ;  (3)  the  portal  fissure  ;  (4)  the  fissure,  or  fossa,  of  the  gall-bladder  ; 
and  (5)  the  fissure,  or  fossa,  of  the  vena  cava. 

Taken  together,  the  five  fissures  are  arranged  somewhat  in  the  form  of  the  letter 
A  (Fig.  786) ;  the  two  lower  divisions  of  the  diverging  limbs  being  formed  by  the 
umbilical  fissure  and  the  fissure  of  the  gall-bladder  respectively,  and  the  cross-piece 
by  the  portal  fissure — all  of  which  are  placed  on  the  inferior  or  visceral  surface: 
The  two  upper  divisions  of  the  limbs  are  represented  by  the  fissure  of  the  ductus 
venosus  and  that  of  the  vena  cava,  which  meet  abo\^e  and  are  both  placed  on 
the  back  or  posterior  area  of  the  parietal  surface.  The  latter  of  these  two — 
namely,  the  fissure  of  the  cava,  represented  by  the  right  upper  division  of  the  A — 
does  not  join  the  cross-piece  (the  portal  fissure),  but  is  separated  from  it  below  by 
a  narrow  ridge  of  liver  sul)stance — the  caudate  lobe  or  process  (Fig.  786). 

(1)  The  umbilical  fissure  (fossa  vense  umbilicalis)  is  a  deep  crevice-like  fissure, 
situated  on  the  visceral  surface  between  the  adjacent  portions  of  the  quadrate  and 
left  lobes.  At  its  bottom  is  seen  a  stout  fibrous  Itand,  the  round  ligament — the 
remains  of  the  umlulical  vein  of  the  foetus.  The  fissure  leads  from  the  umbilical 
notch  at  the  inferior  border  of  the  liver  to  the  left  extremity  of  the  portal  fissure 
(Fig.  786),  and  is  very  often  crossed  by  a  pons  hepatis— a  band  of  liver  substance 
— which  may  even  extend  along  the  whole  length  of  the  fissure,  hiding  the  round 
ligament  completely  from  view. 

(2)  The  fissure  of  the  ductus  venosus  (fossa  ductus  venosi)  lies  on  the  back  of 


THE  LIVER.  1115 

the  parietal  surface  of  the  liver  and  separates  the  Spigelian  from  the  left  lobe 
(Fig.  786).  It  joins  the  portal  fissure  helow,  opposite  the  umbilical  fissure ;  and 
above,  it  meets  the  fissure  of  the  vena  cava.  On  separating  its  sides  there  is  found 
at  its  bottom  a  fibrous  band,  usually  mucli  thinner  than  the  round  ligament :  this 
is  the  remains  of  the  ductus  venosus  of  the  fretus. 

The  umltilical  fissure  and  the  fissure  of  the  ductus  venosus  taken  together  c(jn- 
stitute  the  longitudinal  fissure  of  the  liver  (fossa  longitudinalis  sinistra),  which 
separates  the  right  from  the  left  lobe  on  Ijoth  the  inferior  and  posterior  aspects.  It 
will  be  observed  that  all  other  fissures  and  all  other  lobes  (except  the  left)  lie  to 
the  right  of  the  longitudinal  fissure,  and  therefore  are  situated  on  the  right  lobe. 

(3)  The  portal  or  transverse  fissure  (porta  hepatis)  when  examined  in  the  un- 
hardened  liver  appears  as  a  deep  depression,  bounded  l)y  prominent  lips,  which  runs 
to  the  right,  from  the  middle  of  the  longitudinal  fissure,  lietween  the  quadrate 
lobe  in  front  and  the  caudate  and  Spigelian  lobes  behind  (Fig.  786).  Through  it 
the  portal  vein,  hepatic  artery,  and  hepatic  plexus  of  nerves  enter,  and  the  hepatic 
ducts  and  lymphatic  vessels  leave,  the  liver,  whilst  around  its  margins  are  attached 
the  two  layers  of  the  lesser  omentum.  The  fissure  itself  is  filled,  between  the 
entering  and  issuing  vessels,  by  a  loose  connective  tissue  known  as  Glisson's 
capsule,  which  passes  with  the  portal  vein  into  the  liver  suljstance. 

Wlien  the  liver  is  in  the  Isody,  or  wlien  liardened  before  removal,  these  three  fissures,  instead  of 
appearing  as  wide,  shallow  dejiressions,  have  the  form  of  narrow  clefts,  with  a  depth  of  three- 
quarters  to  one  inch  (18-25  mm.),  or  even  more — a  form  which  results  from  the  folding  together  of 
tlie  portions  of  the  liver  bounding  these  fissures. 

(4)  The  fossa  of  the  gall  bladder  (fossa  vesicae  fellese)  is  a  slight  depression 
which  begins  (often  as  a  notch)  at  or  near  the  inferior  Ijorder  of  the  liver, 
and  runs  backwards  and  to  the  left,  as  far  as  the  portal  fissure  (Fig.  786), 
separating  the  quadrate  from  the  rest  of  the  right  lobe.  Its  surface  is  uncovered 
by  peritoneum  as  a  rule,  and  in  it  lies  the  gall-bladder — the  two  being  united  })y 
areolar  tissue. 

(5)  The  fossa  of  the  vena  cava  (fossa  venae  cavae)  is  a  deep  groove,  on  the 
back  of  the  liver,  between  the  Spigelian  and  right  lobes,  in  which  the  upper 
part  of  the  inferior  vena  cava  is  embedded,  immediately  before  it  pierces  the 
diaphragm.  It  has  been  already  descrilied  in  connexion  with  the  posterior  area  of 
the  parietal  surface  of  the  liver,  page  1111. 

The  depressions  for  the  gall-bladder  and  the  vena  cava  are  called,  almost  indiscriminately, 
fisS'Ures  or  fossae.  In  hardened  specimens,  it  will  be  seen  that  only  three  are  really  fissure  or 
crevice-like,  namely,  the  umbilical  fissure,  the  poi'tal  fissure,  and  the  fissure  of  tlie  ductus  venosus : 
the  remaining  two  are  rather  of  the  nature  of  fosste. 

Lobes  of  the  Liver. — The  liver  is  divisible  into  two  chief  lobes,  right  and 
left,  which  are  separated  by  the  attachment  of  the  falciform  ligament  above  and  in 
front,  and  by  the  two  parts  of  the  longitudinal  fissure  below  and  Ijehind.  The  right 
lobe  forms  aljout  four-fifths  of  the  mass  of  the  liver,  and  on  it  three  secondary  lobes — 
the  quadrate,  Spigelian,  and  caudate,  already  sufficiently  described^are  marked  off 
by  the  five  fissures  referred  to  in  the  preceding  paragraphs.  The  left  lobe  is  much 
smaller  and  more  flattened  than  the  right,  and,  as  a  rule,  it  projects  one  or  two  inches 
(2'5  to  5-0  cm.)  to  the  right  of  the  middle  line.  The  details  of  these  lobes  have  been 
already  given  in  connexion  with  the  surfaces  of  the  liver. 

Peritoneal  Relations  of  the  Liver. — With  the  exception  of  (1)  the  uncovered 
area  at  the  back  of  the  right  lobe,  (2)  a  small  triangular  space  on  the  parietal  surface, 
where  the  two  layei's  of  the  falciform  ligament  separate  posteriorly,  and  (3)  usually,  but 
not  invariably,  the  fossa  of  the  gall-bladder,  the  liver  is  completely  covered  by  peritoneum. 
The  covering  of  the  caudate  and  Spigelian  lobes  is  derived  from  the  small  sac,  that  of  the 
rest  of  the  organ  from  the  great  sac  of  the  peritoneum. 

The  peritoneum  of  the  anterior  abdominal  wall  passes  back  on  the  under  surface  of 
the  diaphragm,  whence  it  is  reflected  on  to  the  upper  aspect  of  the  liver,  but  the  line  of 
reflection  is  broken  by  a  fold  running  down  at  right  angles  from  its  middle  to  the  umbili- 
cal notch  ;  this  is  the  falciform  ligament  already  referred  to.  The  portion  of  the  reflection 
to  the  right  of  this  fold  forms  the  upper  layer  of  the  coronary  ligament,  that  to  the  left 
forms  the  upper  layer  of  the  left  lateral  ligament. 


1116  THE  DIGESTIVE  SYSTEM. 

Having  thus  reached  the  liver  from  the  diaphragm,  the  peritoneum  passes  forwards, 
clothing  its  parietal  surface  as  far  as  the  anterior  margin,  around  which  it  turns  to  gain 
the  lower  or  A'isceral  surface.  This  it  also  covers  as  far  back  as  the  portal  fissure  and  the 
fissure  of  the  ductus  venosus  (Fig.  786),  from  which  it  descends  to  the  stomach  as  the 
anterior  layer  of  the  lesser  omentum. 

As  regards  the  covering  derived  from  the  small  sac  : — Its  peritoneum  passes  iii  through 
the  foramen  of  Winslow,  which  is  placed  immediately  beneath  the  caudate  lobe,  and  thus 
it  clothes  this  lobe  (Fig.  786).  Then  turning  upwards  it  expands  over  the  Spigelian 
lobe,  clothing  its  two  surfaces. 

From  the  right  margin  of  the  Spigelian  lobe  it  is  reflected  to  the  diaphragm,  here 
forming  the  last  boundary  (Fig.  795)  of  the  uncovered  area  of  the  right  lobe,  and  a  third 
layer  of  the  coronary  ligament.  , 

The  detailed  arrangement  of  the  peritoneum  will  be  found  on  p.  1097,  with  the  general 
account  of  the  peritoneal  cavity. 

Ligaments. — Most  of  the  ligaments  of  the  liver,  namely,  the  coronary,  falciform,  and 
two  lateral,  are  formed  by  folds  of  peritoneum ;  the  other  two,  namely,  the  round  ligament 
and  the  ligament  of  the  ductus  venosus,  are  remains  of  foetal  blood-vessels. 

The  coronary  ligament  (ligamentum  coronarium  hepatis)  consists  of  the  folds  of 
peritoneum  which  are  reflected  from  the  liver  to  the  diaphragm  at  the  margins  of  the  un- 
covered area  of  the  right  lobe ;  both  its  upper  and  lower  layers  are  derived  from  the  great 
sac.  The  name  of  right  lateral  ligament  has  been  given,  without  sufficient  reason,  per- 
haps, to  its  pointed  right  extremity  (Fig.  786). 

The  left  lateral  ligament  (ligamentum  triangulare)  is  a  considerable  triangular  fold, 
entirely  unconnected  with  the  coronary  ligament,  which  is  attached  by  one  end  to  the 
upper  or  parietal  surface  of  the  left  lobe  near  its  posterior  border,  and  by  the  other  to  the 
diaphragm,  for  a  distance  of  several  inches  as  a  rule. 

Its  attachment  to  the  diaphragm  lies  nearly  altogether  to  the  left  of  the  oesophageal  orifice, 
and  about  |  inch  (18  mm.)  in  front  of  the  line  of  this  opening.  Sometimes  it  is  directed 
from  the  diaphragm  backwards  to  its  hepatic  attachment. 

Falciform  Ligament  (ligamentum  falciforme  hepatis). — This  is  also  known  as  the 
broad  or  the  suspensory  ligament.  It  is  a  crescentic  fold  of  peritoneum,  which  is 
attached  by  its  convex  border  to  the  under  surface  of  the  diaphragm,  and  to  the  anterior 
abdominal  wall  (an  inch  or  more  to  the  right  of  the  middle  line)  to  within  a  short 
distance  (1  to  2  inches,  2'5  to  5  cm.)  of  the  umbilicus.  Its  concave  border  is  attached 
to  (the  superior  and  anterior  areas  of)  the  parietal  surface  of  the  liver;  below  this  it 
presents  a  free  edge,  stretching  from  near  the  umbilicus  to  the  umbilical  notch  of  the 
liver,  and  containing  within  it  a  stout  fibrous  cord,  the  round  ligament. 

Near  the  back  part  of  the  upper  asjDect  of  the  liver  the  two  layers  of  which  the  falciform 
ligament  is  composed  separate,  and  leave  a  triangular  area  of  liver  substance  in  front  of  the 
upper  end  of  the  vena  cava  uncovered  by  peritoneum.  Traced  backwards,  the  right  layer  passes 
into  the  upper  layer  of  the  coronary  ligament,  the  left  into  that  of  the  left  lateral  ligament.  It 
is  the  remains  of  the  ventral  mesentery  of  the  embryo,  and  has  no  supporting  or  suspensory 
action  on  the  liver  of  the  adult. 

The  lesser  or  gastro- hepatic  omentum  (omentum  minus)  is  a  fold  of  peritoneum 
which  extends  from  the  liver  to  the  lesser  curvature  of  the  stomach.  Of  its  two  layers — 
which  are  largely  blended  together  in  the  adult — the  anterior  is  derived  from  the  great, 
the  posterior  from  the  small  sac. 

It  is  attached  above  to  the  margins  of  the  portal  fissure,  and  also  to  the  bottom  of  the 
fissure  of  the  ductus  venosus.  Below,  it  is  connected  to  the  lesser  curvature  of  the 
stomach,  where  its  two  layers  separate  to  enclose  that  organ,  and  also  to  the  upper  border 
of  the  duodenum  for  an  inch  or  more  beyond  the  pylorus.  Between  its  layers,  close  to 
its  right  or  free  bordei-,  are  contained  the  bile  duct,  the  hepatic  artery,  the  portal  vein,  and 
the  nerves  and  lymphatics  passing  to  the  portal  fissure  (Fig.  788).  It  is  wide  in  the  middle 
and  narrow  at  each  end.  Of  the  two  ends  the  right  is  free,  and  stretches  from  the  liver 
to  the  duodenum,  forming  the  anterior  boimdary  of  the  foramen  of  Winslow.  The  left 
end  is  very  narrow,  and  is  attached  to  the  diaphragm  between  the  oesophageal  and  caval 
openings  (just  to  the  right  of  the  reference  line  in  Fig.  795,  marked  "top  of  small  sac") 

The  portion  of  the  omentum  passing  between  the  liver  and  the  stomach  is  sometimes  known 
as  the  hepato-gastric  ligament  (ligamentum  hepato-gastricum),  that  between  the  liver  and  the 
duodenum  as  the  hepato-duodenal  ligament  (ligamentum  heiiato-duodenale). 

The  round  ligament  (ligamentum  teres  hepatis)  is  a  stout  fibrous  band  which  passes 
from  the  umbilicus  backwai'ds  and  upwards,  within  the  free  margin  of  the  falciform  liga- 


THE  LIVER. 


1117 


ment,  to  the  umbilical  notch  of  the  liver,  and  thence  back  in  the  umbilical  fissure,  to  join 
the  left  branch  of  the  portal  vein.  It  is  the  remains  of  the  umbilical  vein  which,  Ijefore 
birth,  carries  the  arterial  blood  from  the  placenta  to  the  body  of  the  foetus  (Fig.  787). 

The  remains  of  the  ductus  venosus  (ligamentum  venosum  Arantii)  is  a  slender 
fibrous  cord,  which  passes  from  the  left  branch  of  the  portal  vein,  nearly  opposite  the 
attachment  of  the  I'ound  ligament,  backwards  in  the  fissure  bearing  its  name,  to  be  con- 
nected with  the  inferior  vena  cava  as  it  leaves  the  liver.  In  the  foetus  this  structiu-e  is  a 
considerable  vessel,  which  conveys  some  of  the  blood  brought  to  the  portal  fissure  by  the 
umbilical  vein  directly  backwards  to  the  vena  cava.  At  the  time  of  birth  the  ductus 
venosus  and  umbilical  vein  cease  to  carry  blood,  their  cavities  become  obliterated,  and  they 
degenerate  into  fibrous  cords. 

Physical  Characters  of  the  Liver. — The  livei-  is  a  compact  mass,  moderately 
firm  to  the  touch ;  it  is  pliant,  but  not  tough,  and  is  easily  lacerated.  Its  torn 
surface  presents  a  granular  appearance,  due  to  the  fact  that  it  is  made  up  of  small 
lobules  about  the  size  of  a  pin's  head  (xoth  to  oVth  of  an  inch,  1  to  2  mm.).  These 
little  lobules  also  give  its  exterior  a  characteristic  finely-mottled  appearance.  Its 
colour  is  reddish  brown,  and  its  specific  gravity  varies  from  1'05  to  l^OG. 

In  the  Child. — The  liver  of  the  child  differs  from  that  of  the  adult,  in  being  rela- 
tively larger — yV^^  of  the  body  weight  at  l>irth  as  against  t^V^Ii  oi'  iV^^^  i'l  the 
adult — in  occupying  more  of  the  abdominal 
cavity,  and  in  the  fact  that  its  two  lobes 
are  more  nearly  equal  in  size,  the  proportion 
being  as  two  to  one  at  birth  and  as  four  to 
one  in  the  adult. 

Variations  in  Size,  Form,  and  Position.— Few 

organs  w'ill  be  found  to  vary  more  in  size  in  different 
bodies  than  the  liver ;  these  variations,  liow^ever, 
are  very  frequently  to  be  looked  upon  as  pathological. 
But  even  the  normal,  healthy  liver  may  vary  in 
M'eight  from  48  to  58  ounces  in  the  adult  male, 
and  from  40  to  50  ounces  in  the  female. 

Variations  in  form  and  position  doubtlessly  take 
place  physiologically,  as  a  result  of  the  conditions  of 
fulness  or  emptiness  of  the  adjacent  viscera  ;  for, 
tliough  the  liver,  like  the  other  solid  abdominal 
organs,  has  an  intrinsic  shape  of  its  own,  this  is 
capable  of  modification  within  certain  limits  by  the 
varying  pressure  of  the  surrounding  parts.  Thus, 
distension  of  the  stomach,  or  of  a  portion  of  the 
transverse  colon  lying  in  the  stomach  chamber, 
may  push  the  liver  over  to  the  right,  so  that  it  may 
hardly  reach  the  middle  line,  and  at  the  same  time 
it  increases  its  vertical  depth.  On  the  other  hand, 
a  distended  state  of  the  small  intestines,  with  a 
contracted  stomach  and  colon,  may  have  the  opj)Osite  The  large  liver  and  the  large  size  of  its  left  lobe, 
effect,  flattening  it   from  below   upwards   and    en-  at  this  age,  should  be  noted, 

larging  it  in  the  transverse  direction. 

Variations  inform  and  position  due  to  mft^/o?-ma^Jo?is  of  the  thoracic  framework,  either  con- 
genital or  acquired,  are  very  common,  particularly  in  females  as  a  result  of  tight-lacing,  which 
carries  in  the  lower  ribs.  Sometimes  in  these  cases  the  constriction  of  the  waist  lies  chiefly 
below  the  liver.  The  organ  is  then  forced  up  against  the  diaphragm,  filling  its  -whole  vault,  and 
extending  across  to  the  left  abdominal  wall,  where  its  left  margin  may  lie  in  the  interval 
betw^een  the  diaphragm  and  the  spleen.  But  more  conmionly  it  would  seem  that  the  liver  is 
caught  by  the  constriction  :  its  upper  part  is  then  closely  pressed  into  the  vault  of  the  diaphragm, 
which,  owing  to  the  narrowing  of  the  thorax,  is  unable  to  accommodate  the  whole  organ,  so 
that  its  lower  part  is  crushed  down  for  a  considerable  distance  into  the  umbilical  zone  of  the 
abdomen  (Fig.  748,  p.  1057),  i^articularly  on  the  riglit  side.  Often,  too,  a  wide,  tongue-like 
process  (the  so-called  "Reidal's  lobe")  descends  from  the  lower  margin,  external  to  the  gall- 
bkdder.  This  process,  which  when  very  large  may  reach  to  the  iliac  crest,  is  sometimes  found 
in  men,  although  more  common  in  women,  and  is  liable  to  be  mistaken  for  a  tumour.  A  some- 
what similar  process  occasionally  descends  from  the  left  lobe. 

Again,  in  apparently  healthy  bodies  the  liver  may  extend  up  on  the  right  side  almost  tothe 
fourth  rib  ;  whilst  in  other  cases  it  may  be  as  low  as  the  sixth  rib,  or  even  low^er.  Nor  is  it 
rare — i:)articularly  in  females — to  find  the  lower  border  projecting  two  or  three  inches  (5'0  to  7 '5 
cm.)  below  the  margin  of  the  thorax  on  the  right  side  (Fig.  748,  p.  1057). 

Reference  sliould  be  made  here  to  certain  grooves  often  seen  on  the  liver.  Some  of  these  are 
found  running  obliquely  low  down  at  the  right  side  where  the  li^er  is  in  contact  with  the  ribs  ; 


Limp 


Umbilical  vein 
Umbilical  cord 

Urachus 
Hypogastric 
artery 
Bladder 


Fig.   787.— The  Abdominal  and  Thoracic 
Viscera  of  a  Five-Months  Fcetos. 


1118  THE  DIGESTIVE  SYSTEM. 

they  are  particularly  common  in  females,  and  are  due  to  the  pressure  of  the  ribs  resulting  from 
tight-lacing.  Grooves  of  a  different  kind  are  found  at  the  upper  part  of  the  parietal  surface ; 
where  the  liver  is  in  contact  with  the  diaphragm  ;  these  usually  run  radially,  that  is,  in  the 
direction  of  the  muscular  fibres  of  the  diaphragm,  and  are  apparently  i:)roduced  by  a  wrinkling, 
or  irregular  contraction,  of  the  diaphragm.  At  least,  ridges  of  the  diaphragm  are  found  lying  in 
the  grooves,  and  these  ridges  or  wrinkles  would  seem  to  be  responsible  for  the  production  of  the 
grooves. 

Finally,  the  liver  may  present  certain  congenital  irregularities  in  the  direction  of  additional 
fissures  and  lobes,  which  reproduce  the  conditions  found  in  the  higher  apes,  and  are  very 
commonly  present  in  the  foetus  (Thomson).  Or  the  liver  may  be  divided  up  into  a  large  number 
of  distinct  lobes,  as  in  most  other  animals. 

Changes  in  position  have  been  already  referred  to  in  connexion  with  variations  in  form ; 
there  need  only  be  added  here  that  the  liver  ascends  and  descends  at  every  expiration  and  inspira- 
tion respectively,  and  that  it  also  descends,  but  very  slightly,  in  changing  from  the  reclining  to 
the  erect  posture.  Occasionally,  without  any  evident  cause,  the  liver  and  diaphragm  are  found 
to  occupy  a  higher  or  lower  position  than  usual. 

Fixation  of  the  Liver. — At  first  sight  it  is  not  easy  to  understand  the  means  by  which 
the  liver  maintains  its  position  in  the  abdomen  (and  the  same  remark  applies,  perhaps,  to  other 
solid  abdominal  organs).  The  falciform  ligament  gives  it  no  support,  as  it  is  quite  lax  when 
in  the  body.  Nor  can  it  be  said  that  its  vessels,  except  perhaps  the  hepatic  veins,  assist. 
However,  on  considering  the  conditions  under  which  the  viscera  are  placed  in  the  abdominal 
cavity  the  problem  becomes  less  difficult. 

The  abdomen  is  a  closed  cavity,  with  a  firm  framework  to  its  upper  part,  a  tightly  stretched 
diaphragm  for  its  roof,  and  muscular  walls  all  round.  Into  the  concavity  of  this  roof  the  parietal 
surface  of  the  liver  is  fitted  with  perfect  accuracy,  so  that  the  two  are  in  absolute  contact,  and 
cannot  be  separated  without  producing  a  vacimm,  unless  some  other  structure  is  in  a  position  to 
fill  the  space.  But  there  is  hardly  any  other  viscus  movable  enough  to  pass  up  over  the  front 
of  the  liver  into  the  vault  of  the  diaphragm,  so  that  atmospheric  pressure  alone  is  probably 
sufficient  to  retain  the  organ  in  situ,  as  in  the  case  of  the  hip  joint.  In  addition,  the  abdominal 
muscles  are  always  in  a  condition  of  tonic  contraction  or  "  tone,"  which  gives  rise  to  an  intra- 
abdominal pressure.  This  is  effective  in  all  directions,  and  consequently  there  is  a  considerable 
pressure  on  all  the  abdominal  walls.  The  liver,  being  in  absolute  contact  with  the  roof,  may  be 
considered  a  part  of  this  wall,  and  it  is  consequently  affected  by  this  pressure  which  helps  to 
sustain  it.  Add  to  this,  the  support  which  the  organ  receives  from  the  intestines,  the  stomach, 
and  the  pancreas  ;  from  the  coronary  and  lateral  ligaments  ;  from  the  connexion  of  the  back  of 
the  right  lobe  by  areolar  tissue  to  the  diaphragm  ;  and,  finally,  from  the  vena  cava  embedded  in 
the  liver  and  sending  its  hepatic  veins  forwards  to  all  parts  of  the  organ,  just  before  the  cava 
itself  is  firmly  attached  to  the  margins  of  the  caval  orifice  in  the  central  tendon  of  the 
diaphragm,  and  we  will  probably  find  sufficient  cause  for  the  maintenance  of  the  organ  in  its 
position  in  the  abdominal  cavity. 

THE  GALL-BLADDER  AND  BILE-PASSAGES. 

Under  this  heading  we  have  to  consider  the  hepatic  ducts,  the  gall-bladder,  the 
cystic  duct,  and  the  common  bile-duct. 

The  excretory  ducts  of  the  liver  (Fig.  788)  begin  within  the  hepatic  lobules  as  minute 
channels,  running  between  the  hepatic  cells  (Fig.  792),  and  known  as  the  bile  canaliculi 
(ductus  biliferi). 

Outside  the  lobules  these  join  (Fig.  792)  the  interlobular  ducts  (ductus  iuterlobu- 
lares),  which  latter  hy  uniting  form  larger  and  larger  ducts,  and  finally  end  in  two,  or 
more,  chief  hepatic  ducts,  a  larger  from  the  right,  and  a  smaller  from  the  left  lobe,  which 
unite  immediately  after  leaving  the  liver  to  form  the  hepatic  duct. 

As  a  rule,  five  or  six  ducts  leave  the  liver  at  the  bottom  of  the  portal  fissure  ;  these  generally 
unite  into  right  and  loft  main  ducts  ;  sometimes  they  all  converge  towards,  and  unite  at  the 
beginning  of  the  hepatic  duct.  It  is  interesting  to  note  that  the  ducts  from  the  Spigelian  and 
caudate  lobes  join  the  left  main  duct. 

Hepatic  Duct  (ductus  hepaticus). — This  duct  formed  at  the  bottom  of  the  portal 
fissure  by  the  union  of  right  and  left  chief  ducts  (Fig.  788),  passes  downwards,  with 
an  irregular  course,  and,  just  outside  the  mouth  of  the  portal  fissure,  is  joined  by 
the  cystic  duct  (Fig.  788)  to  form  the  commoii  bile-duct.  In  length  it  usually 
measures  about  1  to  1|-  inches  (25  to  31  mm.),  and  in  breadth,  when  flattened 
out,  nearly  }  inch  (6  mm.),  or  about  as  much  as  a  goose  quilL  It  lies,  practically 
altogether,  witldn  the  portal  fissure. 

Gall-bladder  (vesica  fellea). — The  gall-bladder,  with  its  ,cystic  duct,  may  be 
looked  upon  as  a  diverticulum  of  the  bile-duct,  enlarged  at  its  extremity  to  form  a 
reservoir  for  the  bile.     It  is  pear-shaped,  and  lies  obliquely  on  the  under  surface  of 


THE  GALL-BLADDER  AND  BILE-PASSAGES. 


1119 


Hounil  ligament 


Gall-blail<ler 
Cystic  duct 


Quadrate  lobe 
Hepatic  duct         \ 


)mt>iital  tuberosity 
<;astric  impression 
Posterior  layer  of 
sser  oiiifntuin 


Duodenum 


the  liver  (Fig.  788).     The  wide  end,  or  fundus,  usually  reaches  the  inferior  border  of 

the  liver— where  there  is  sometimes  a  notcli  to  receive  it— and  comes  in  contact  with 

the  anterior  abdominal  wall  (Fig.  784).     The  body  (corpus)  runs  backwards,  upwards, 

and  to  the  left,  lying  in  the  fossa  of  the  gall-bladdcn-,  and  ntsar  the  portal  fissure  passes 

ratlier  abruptly  into  the  narrow  neck.     The  neck  (collum)  is  curved  inwards  towards 

the  portal  fissure,  in  the  form  of  the  italic  letter  s,  and  when  distended  it  presents 

the  appearance  of  a  spiral  constriction  which  is  continued  into  the  beginning  of  the 

cystic  duct,  and  is 

due  to  a  series  of 

crescentic  folds 

placed     somewhat 

spirally  round  the 

interior    of    its 

cavity.        Having 

arrived    near    the 

portal  fi  ssure,  much 

reduced  in  size,  it 

passes     into      the 

cystic  duct. 

As  a  rule  the 
gall-bladder  is 
covered  by  the 
peritoneum  of  the 
inferior  surface  of 
the  liver,  except  on 
its  upper  aspect, 
which  is  united  to 
the  fossa  of  the  gall- 
bladder b}^  areolar 
tissue.  Sometimes, 
but  rarely,  this 
surface  is  covered 
also,  and  the  gall- 
bladder    is     then 

suspended  from  the  liver  by  a  short  peritoneal  ligament.  The  fundus  usually 
lies  in  contact  with  the  anterior  abdominal  wall,  at  or  immediately  beneath 
the  point  where  the  right  Poupart  line  strikes  the  low^er  margin  of  the  ribs 
(i.e.  in  the  angle  between  the  outer  border  of  the  right  rectus  muscle  and  the 
lower  margin  of  the  ribs).  Above,  the  gall-bladder  lies  against  the  liver;  and 
below,  it  rests  on  the  transverse  colon  in  front,  and  behind,  near  its  neck  on  the 
duodenum. 

In  some  bodies  the  fundus  of  the  gall-l)ladder  does  not  reach  the  border  of  the  hver  or  the 
abdominal  wall.  In  others  it  may  be  moved  considerably  to  the  right  of  the  Poupart  line — 
possibly  as  a  result  of  distension  of  the  stomach  and  colon — or  as  a  result  of  tiglit -lacing,  it  may  be 
moved  to  the  left,  and  may  then  lie  near  the  middle  line  and  far  below  the  ribs  (Fig.  748,  p.  1057). 

Its  total  absence,  as  well  as  the  presence  of  two  distinct  gall-bladders,  and  several  other 
irregularities  in  form,  have  been  recorded. 

Its  size  is  usually  about  3  inches  (75  mm.)  in  lengtli,  and  1  to  ]|  inch  (25  to  31  mm.)  in 
diameter.      Its  cajiacity  varies  between  1  and  H  fluid  ounces. 

Structure  of  Gall-bladder. — Tlie  wall  of  the  gall-bladder  is  composed  of  an  outer 
coat  of  peritoneum,  usually  incomplete ;  a  middle  coat  of  fibrous  tissue  with  unstriped 
muscle  intermixed  ;  and  an  inner  coat  of  mucous  membrane,  which  is  covered  by  columnar 
epithelium,  and  is  raised  into  a  number  of  small  ridges,  which  confer  on  it  a  reticulated 
appearance.  The  mucous  membrane  is  always  deeply  stained  witli  bile  when  the  gall- 
bladder is  opened  after  death. 

Tlie  cystic  artery  which  supplies  it  with  blood  arises  from  the  hepatic,  or  its  right  division, 
and  divides  into  two  branches,  which  run  on  the  lateral  surfaces  of  the  organ.  The  veins  join 
the  portal  trunk,  and  the  nerves  come  from  the  symjoathetic  on  the  hepatic  artery. 

The  cystic  duct  (ductus  cysticus),  about  half  the  diameter  of  the  hepatic  duct 
(3  mm.),  but  usually  slightly  longer  (1^  to  1|  inch,  31  to  37  mm.),  begins  at  the 


f ortal  vein 
^         Hepatic  artery 
Common  bile-duct  \     /     ^SH/      \     "\       \  "^  Pylorus 

Right  gastro-epiploic  artery 
Superior  pancreatico-duodenal  artery 
Pancreatic  duct 
Fig.  788. — Structures  between  the  Layers  of  the  Lesser  Omentum. 

The  liver  has  been  raised  up,  and  the  anterior  layer  of  the  omentum  removed 
(semi-diagrammatic). 


1120 


THE  DIGESTIVE  SYSTEM. 


M    C  L 


A.D.S. 


ueck  of  the  gaU-bladder,  and  running  an  irregular  course  backwards  and  inwards, 
joins  the  hepatic  duct  at  the  mouth  of  the  portal  fissure,  to  form  the  common  bile- 
duct.  The  spiral  constriction  found  in  the  neck  of  the  gall-bladder  is  continued 
into  the  beginning  of  this  duct. 

Sometimes  the  cystic  duct  joins  tlie  right  hepatic  duct  instead  of  the  hej^atic  duct  projDer. 

Common  Bile-duct  (ductus  choledochus).     This  begins  at  the  mouth  of  the  portal 
fissure,  where  it  is  formed  by  the  union  of  the  hepatic  and  cystic  ducts.     From 

this  it  passes  downwards,  in  front  of  the  foramen  of 
Winslow,  lying  between  the  two  layers  of  the  lesser 
omentum,  with  the  portal  vein  behind  and  the  hepatic 
artery  to  its  left.  It  next  descends  behind  the  first 
part  of  the  duodenum  (Fig.  788),  and  then  between 
the  pancreas  and  descending  duodenum.  Finally,  it 
meets  the  pancreatic  duct,  and  the  two,  running 
together,  pierce  the  inner  wall  of  the  descending 
duodenum  very  obliquely,  and  open  by  a  common  orifice 
on  the  bile  papilla  (papilla  duodenalis),  about  3|  or 
4  inches  (8 '7  to  10  cm.)  beyond  the  pylorus  (see  p. 
1069). 

The  length  of  the  common  bile-duct  is  about  3 
inches  (75  mm.),  and  its  diameter,  which  is  very 
variable,  is  generally  about  I  inch  (6  to  7  mm.). 

Structure  of  Excretory  Ducts. — With  the  exception 
A.D.S,  Accessory  pancreatic  duct   of  the  peritoneal  coat,  which  is  absent,  the  hepatic,  cystic, 
(ofSautorini);  c,  Circular  mus-   ^nd    common   bile-ducts   asree   with    the    gall-bladder    in 

cular   fibres  ;    L,   LongitLidinal  i     j.        j.  ^ 

muscular   fibres;    M,  Mucous    general  Structure. 

coat.  The   bile   and  pancreatic  ducts,  in  piercing  the  wall  of  the 

duodenum,  run  obliquely  through  its  coats  for  about  -^  or  |  of  an 
inch  (12  to  18  mm.),  and,  as  a  rule,  do  not  unite  until  they  have  almost  readied  the  opening  on 
the  bile  papilla  (Fig.  789).  This  orifice  is  very  much  smaller  than  either  duct,  and  the  short 
and  relatively  wide  common  cavity  which  precedes  it  is  sometimes  known  as  the  "  ampulla  of 
Vater."     Occasionally  the  cystic  and  hepatic  ducts  open  into  the  duodenum  separately. 


Fig.  789. — Diagram  showing  the 
Bile  and  Pancreatic  Ducts 
piercing  the  Wall  of  the 
Duodenum  obliquely. 


Vessels  op  the  Liver. 

The  liver  derives  its  blood-supply  from  two  sources,  namely — (1)  the  portal  vein, 
which  conveys  to  it,  for  further  elaboration,  the  blood  from  the  digestive  system, 
laden  with  the  products  of  digestion ;  and  (2)  the  hepatic  artery,  which  supplies  it  with 
blood  for  the  nourishment  of  its  own  tissue.  All  the  blood  is  returned  from  the  liver  to 
the  inferior  vena  cava  by  the  hepatic  veins. 

The  portal  vein  and  the  hepatic  artery  pass  up  to  the  liver  between  the  two  layers 
of  the  lesser  omentum  and  in  front  of  the  foramen  of  Winslow.  Here  they  are  accom- 
panied by  the  hepatic  duct,  which  lies  to  the  right,  whilst  the  artery  is  placed  to  the 
left,  and  the  portal  vein  behind  both.  In  this  order  they  enter  the  portal  fissure,  and 
there  becoming  re-arranged,  so  that  the  vein  lies  behind  the  artery  in  the  middle  and 
the  duct  in  front,  each  breaks  up  into  two  chief  branches — a  right  and  a  left — and  several 
smaller  ones,  which  enter  the  liver  substance,  surrounded  by  a  prolongation  of  the  con- 
nective tissue  coat  of  the  liver,  known  as  Glisson's  capsule.  Within  the  organ  the  three 
vessels  run  and  divide  together,  so  that  every  branch  of  the  portal  vein  is  accompanied 
by  a  corresponding  (but  much  smaller)  branch  of  the  hepatic  artery  and  of  the  hepatic 
duct :  and  the  three,  surrounded  by  a  prolongation  of  Glisson's  capsule,  and  accompanied 
by  branches  of  the  hepatic  nerves  and  lymphatics,  run  in  special  tunnels  of  the  liver 
substance,  which  are  known  as  portal  canals  (Fig.  791,  1>). 

Finally,  the  portal  vein  breaks  up  into  interlobular  veins  (venae  interlobulares)  which 
lie  in  the  spaces  between  the  liver  lobules  (Fig.  792).  The  branches  of  these  enter  the 
lobules  on  all  sides,  and  unite  with  their  cajjillary  network,  which  converges  towards 
the  centre  of  the  lobule,  and  joins  the  intralobular  or  central  vein  (vena  centralis). 

The  hepatic  artery  similarly  divides  into  interlobular  branches  (rami  arteriosi 
interlobulares)  of  a  very  small  size,  which  accompany  the  inteilobular  branches  of  the 
vein,  and  supply  the  tissue  and  the  vessels  between  the  lobules.  In  addition,  the  hepatic 
artery  gives  off  vaginal  branches  to  supply  the  walls  of  the  vessels  and  ducts,  and  the 


STEUCTUKE  OF  THE  LIVER  1121 

connective  tissue  in  the  portal  canals ;  and  capsular  branches,  which  are  distributed  to 
the  hbrous  coat  of  the  liver. 

The  hepatic  veins  are  two  large  and  several  small  veins,  which  converge  from  the 
different  portions  of  the  liver  (Fig.  791,  A)  to  the  vena  cava.  Their  ultimate  radicles  are 
the  intralobular  or  central  veins,  which  run  down  through  the  centre  of  the  liver  lobules,  and 
passing  out  at  the  base,  join  the  sublobular  veins  (Fig.  790) :  these  by  their  union  finally 
form  the  hepatic  veins.  The  two  chief  hepatic  veins,  which  are  of  very  large  size,  open 
into  the  vena  cava,  as  it  leaves  the  liver,  and  immediately  before  it  pierces  the  diaphragm. 
The  smaller  branches  open  into  it  lower  down.  The  branches  of  the  portal  differ  from 
those  of  the  hepatic  vein  in  the  following  points: — (1)  The  branches  of  the  portal  vein 
converge  towards  the  portal  fissure  ;    those  of  the  hepatic  veins  towards  the  vena  cava. 

(2)  On  section  of  the  liver  the  portal  branches  are  always  seen  to  be  accompanied  by 
branches  of  the  hepatic  artery  and  duct,  whilst  those  of  the  hepatic  vein  run  alone ;  and 

(3)  owing  to  the  loose  wrapping  of  connective  tissue  (Glisson's  capsule)  which  surrounds 
the  branches  of  the  portal  vein,  their  walls  fall  away  from  the  liver  substance  when 
empty,  and  collapse,  whilst  the  hepatic  veins,  which  are  destitute  of  this  wrapping,  are 
closely  connected  to  the  liver  substance,  and  consequently  do  not  collapse  so  easily  as  the 
portal  vessels  "^ 

_,Tlie  lymphatics  of  the  liver  are  arranged  in  a  superficial  and  a  deep  set : — 1.  Tlie  superficial 
set  lies  beneath  the  iieritoneum  on  botli  (a)  the  visceral  and  (h)  the  parietal  surfaces  of  the  organ. 
(«)  The  vessels  from  the  visceral  surface  pass  cliiefly  to  the  hepatic  glands,  which  lie  between  the 
layers  of  the  lesser  omentum  ;  but  some  of  them,  from  the  back  part  of  this  surface  on  the  right 
lobe,  join  the  lumbar  glands,  and  others  from  the  back  part  of  the  left  lobe  go  to  the  coiliac  glands. 
(b)  The  vessels  from  the  parietal  surface  pass  in  various  directions.  Those  from  the  adjacent 
parts  of  the  right  and  left  lobes  pass  up  in  the  falciform  ligament,  and  jiierce  the  diaphragm  to 
reach  the  anterior  mediastinal  glands,  and  end  finally  in  the  right  lymphatic  duct.  Those  from 
the  anterior  part  of  this  surface  pass  down  to  the  inferior  aspect,  and  join  the  hepatic  glands 
in  the  lesser  omentum.  The  lymphatics  from  the  back  of  the  right  lobe  pierce  the  diaphragm 
between  the  layers  of  the  coronary  ligament,  and  join  some  glands  in  the  thorax  around  the  upper 
end  of  the  inferior  cava ;  others  run  in  the  right  lateral  ligament,  and  either  pierce  the 
diaphragm  and  end  in  the  anterior  mediastinal  glands,  or,  turning  down,  join  the  cceliac  groui^. 

2.  The  deep  lymphatics  accompany  either  (o)  the  portal  or  (b)  the  hepatic  veins,  (a)  The 
former  set  pass  out  through  the  portal  fissure  and  join  the  hejiatic  glands,  the  efferent  vessels  of 
which  join  the  cceliac  glands,  (b)  Those  which  accompany  the  hejjatic  veins  pierce  the  diaphragm 
with  the  vena  cava,  and  having  formed  connexions  with  the  group  of  glands  at  its  upper  end, 
wuthin  the  thorax,  turn  down  and  join  the  beginning  of  the  thoracic  duct. 

The  nerves,  which  are  chiefly  of  the  non-medulla  ted  vai'iety,  are  derived  from  the  left 
jineuuiogastric  and  the  solar  plexus  of  the  sympathetic.  The  branches  of  the  former  pass  from 
the  front  of  the  stomach  up  between  the  layers  of  the  lesser  omentum  to  the  liver.  Those  of 
the  latter  pass  from  the  cceliac  plexus  along  the  hepatic  artery — forming  the  hepatic  plexus — to 
the  portal  fissure,  where  they  enter  the  liver  with  the  blood-vessels.  They  are  distributed  chiefly 
to  the  walls  of  the  vessels  and  of  the  bile-ducts. 

Structure  of  the  Liver. 

The  liver  is  invested  by  an  outer  serous  coat  (tunica  serosa),  already  described  in 
connexion  with  the  peritoneum.  Within  this  is  a  thin  areolar  coat  (capsula  fibrosa 
Glissonii)  of  delicate  fibrous  tissue,  which  is  most  evident  where  the  serous  coat  is  absent. 
In  the  neighbourhood  of  the  portal  fissure  it  is  particularly  abundant,  and  here,  under 
the  name  of  Glisson's  capsule,  it  surrounds  the  vessels  entering  the  fissure,  and  accom- 
panies them  through  the  portal  canals  in  the  liver  substance.  This  coat  is  continuous 
with  the  fine  areolar  tissue  which  pervades  the  liver,  surrounding  its  lobules  and  holding 
them  together. 

The  liver  substance  proper  is  made  up  of  an  enormous  number  of  small  lobules,  yVth 
to  TT^th  inch  (1  to  2  mm.)  in  diameter,  closely  packed,  and  held  together  by  a  small 
amount  of  connective  tissue.  In  man  the  lobules  are  not  completely  separated  from  one 
another  all  round  their  circumference,  but  coalesce  in  places ;  the  reverse  is  the  case  in 
certain  animals  such  as  the  camel  and  the  pig.  The  lobules  are  arranged  around  the 
branches  of  the  hepatic  veins,  to  form  the  compact  mass  of  the  liver,  in  the  following 
manner : — 

The  hepatic  veins  radiate  from  the  inferior  vena  cava,  at  the  back  of  the  liver,  to  all 
parts  of  the  organ,  dividing  and  re-dividing  until  the  vessels  are  reduced  to  branches  of  a 
very  small  size,  known  as  sublobular  veins — the  whole  arrangement  may  be  aptly  com- 
pared so  far  to  the  branching  of  a  tree  (Fig.  791,  A).  On  all  sides  there  open  into  these 
sublobular  veins  numerous  closely-crowded  vessels — the  intralobular  or  central  veins 
75 


1122 


THE  DIGESTIVE  SYSTEM. 


(which,  following  our  simile,  may  be  compared  to  an  enormous  number  of  thorns  grow- 
ing out  on  all  sides  from  the   sublobular  twigs  of  the  tree).     On  each  of   these   little 


Intralobular  capillary  plexus 


Intralobular 
capillary  plexus 


Intralobular 
vein 


Intralobular  veift 


Sublobular  vein 


Fig.  790. — Liver  of  a  Pig  injected  from  the  Hepatic  Vein  by  T.  A.  Carter.      (Froiu  a^.specimeu  left  in 
the  Anatomy  Department  of  the  Edinburgh  University  by  Sir  William  Turner. )~ 

central  veins  there  is  impaled,  as  it  were,  a  lobule  (which  is  more  or  less  like  a  conical 
bullet  in  shape — Purser).  These  little  conical  lobules,  with  their  intralobular  or  central 
veins    running    through    them,    are    so    numerous    and    so    closely    packed    together, 

that  they  give  rise  to  the  practically  solid 
Liver  lobules  ^  I    .       j    \  Hver  tissue. 

The  lobules  are  surrounded  by  the 
interlobular  branches  of  the  portal  vein, 
from  which  numerous  twigs  enter  the 
lobule  on  all  sides,  and  converging,  join 
the  central  or  intralobular  vein  (Fig. 
792).  This  runs  down  through  the 
centre  of  the  lobule  (Fig.  791,  A),  and 
opens  at  its  base  into  a  sublobular  vein. 
The  sublobular  veins,  uniting  and  grow- 
ing larger  by  constant  additions,  finally 
form  the  hepatic  veins,  which  open  into 
the  vena  cava. 

Hepatic  Cells. — In  the  intervals  be- 
tween the  branches  of  the  capillaries, 
running  from  the  interlobular  to  the 
intralobular  veins  (Fig.  792),  are  placed 
the  pol^^gonal-shaped,  epithelial,  hepatic 
cells.  Between  the  cells  run  the  bile 
canaliculi  (ductus  biliferi)  which,  passing 
out  of  the  lobule  (Fig.  792),  join  the 
interlobular  bile -ducts  (ductus  inter- 
lobiilares),  and  these  uniting,  finally  end 
in  the  hepatic  ducts. 

Development  of  the  Liver. 


Vena  cava 


Fig.  791.- 


-DlAGRAMS    illustrating 

OF  Liver. 


THE  Structure 


A,  Arrangement  of  liver  lobules  around  the  sublobular 
branches  of  the  hepatic  vein  ;  B,  Section  of  a  portal 
canal,  showing  its  contained  branches  of  the  portal 
vein,-  hepatic  artery,  and  bile-duct,  surroumled  by  a 
prolongation  of  Glisson's  capsule. 


In  man,  the  liver  first  appears  as  two 
hollow  outgrowths  from  the  ventral  wall 
of  the  foregut,  in  the  position  of  the  future  duodenum.  These  outgrowths,  which  are 
formed  entirely  of  endoderm  (hypoblast),  pass  forwards  and  upwards  into  a  mass  of 
mesodermic  tissue — called  by  His  the  septum  transversum— which  lies  in  front  of  the 
foregut  just  below  the  heart.     In  addition  to  constituting  the  mesodermic  bed  in  which 


DEVELOPMENT  OF  THE  LIVER 


1123 


the  liver  is  developed,  tliis  mass  also  forms  the  chief  rudiment  of  the  future  diaphragm ; 
through  it,  too,  pass  the  great  foetal  veins  on  their  way  to  the  heart. 

The  two  outgrowths  give  oft'  numerous  solid  b\ids  of  endodermic  cells — known  as 
hepatic  cylinders — which  grow  into  the  tissue  of  the  septum  transversmu,  and  there 
branch  and  anastomose  freely  with   one   another,  forming  a   complicated   network,   the 


Interlobulnr 

veins  ' 
''and  dui-ts 


Veins 


Bile  ducts 


Fig.  792. — Diagram  illustrating  the  arrangement  of  tlie  blood-vessels  (on  left)  and  of  the  hepatic  cells  and 
bile  ducts  (on  right)  within  a  lobule  of  the  liver.  The  first  diagram  shows  the  intei-lobidar  veins 
running  around  the  outside  of  the  lobule,  and  sending  their  capillaries  into  the  lobule  to  join  the  central 
vein.  In  the  second  diagram  the  Viile  capillaries  are  seen,  with  the  hepatic  cells  between  them, 
radiating  to  the  periphery  of  the  lobule,  where  they  join  the  interlobular  bile-ducts. 


(Esophagus  \ 

Stomacli 
Spleen 


Ventral  mesentery 
Liver 

Ventral  mesentery 
Bile  duct 
Stomach 


meshes  of  which  are  occupied  by  blood-vessels.  From  the  sides  of  these  primary  hepatic 
cylinders  come  off  secondary  cell-buds,  which  similarly  branch  and  anastomose ;  and  this 
process  is  continued  until  the  mass  of  the  liver  is  formed. 

The  two  original  outgi'owths  which  open  into  the  foregut  close  together,  are  soon 
succeeded  by  an  eva- 
gination  of  the  wall  of 
the  duodenum,  which 
embraces  the  orifices 
of  both,  and  subse- 
quently forms  the 
common  bile  duct ; 
whilst  the  two  primary 
diverticula,  which  are 
now  connected  with  the 
evagination,  form  the 
right  and  left  hepatic 
ducts. 

The  interlobular 
bile  ducts  and  the  bile 
capillaries  are  formed 
by  a  canalisation  of 
the  primitive  hepatic 
cylinders  which  have 
been  budded  off"  from 
the  original  diverticula. 
And  the  gall-bladder  is 
formed  as  an  outgrowth 
from  the  common  bile 
duct. 

As  the  liver  in- 
creases in  size,  it  begins  to  project  down  from  the  septum  transversum  into  the 
abdominal  cavity,  so  that  now,  instead  of  being  situated  within  the  septum,  it  looks 
like  an  appendage  of  its  under  surface.  In  other  words,  the  septum  begins  to  differentiate 
into  two  parts — a  lower,  the  liver,  and  an  upper,  which  constitutes  the  greater  portion  of 
the  diaphragm,  both  of  these  having  been  at  first  one  continuous  mass.  In  the  course 
75  a 


Suiierior  mesen- 
teric artery 


Cwcum 


,  Diaphragm 

^.    Spleen 

j     Line  crosses 

mesogastrium 

-Pancreas 
Superior  mesen- 
teric artery 
Duodenum 

Colon 


Inferior  mesen- 
teric artery 


Inferior  mesenteric  artery 

Rectum 


Rectum 
The  mesentery 


Fig.  793. 


-Two  Diagrams  to  illustrate  the  Development  of  the 
Intestinal  Canal. 


The  figure  to  the  right  shows  the  rotation  of  the  intestinal  loop  round  the 
stiperior  mesenteric  artery.  In  both  figures  the  parts  are  stipposed  to  he 
viewed  from  the  left  side. 


1124  THE  DIGESTIVE  SYSTEM. 

of  development  the  separation  of  the  two  becomes  more  marked,  and  finally  is  complete 
everywhere  except  at  the  coi'onary  and  lateral  ligaments  behind,  and  at  the  falciform 
ligament  in  front,  where  they  are  still  connected. 

As  the  liver  separates  oft'  from  the  future  diaphragm,  and  descends  into  the  abdomen, 
there  descends  with  it  the  ventral  mesentery — a  fold  which  connects  the  stomach  and 
duodenum  with  the  anterior  abdominal  wall.  This  is  divided  by  the  liver  into  two  parts 
— a  posterior,  stretching  from  the  front  (lesser  curvature)  of  the  stomach  to  the  liver, 
which  becomes  the  lesser  omentum ;  and  an  anterior,  stretching  from  the  liver  to  the 
anterior  wall  of  the  abdomen,  which  forms  the  falciform  ligament. 

In  early  foetal  life  the  liver  is  relatively  of  enormous  size.  Up  to  the  fourth  or  fifth 
month  it  almost  completely  fills  the  abdominal  cavity,  leaving  but  a  small  space  below 
for  the  intestines.  Subsequently  its  relative  size  is  not  so  great ;  but  even  at  birth  it 
still  occupies  nearly  half  of  the  abdomen,  and  forms  about  Ysth  of  the  body  weight,  whilst 
in  the  adult  it  is  reduced  to  -^jjth..  At  first  the  right  and  left  lobes  are  nearly  equal  in 
size ;  subsequently,  the  right  grows  more  rapidly  than  the  left,  so  that  at  birth  it  is  about 
twice,  and  in  the  adult  four  times,  as  large  as  the  left.  In  the  foetus,  and  at  birth,  the 
caudate  and  Spigelian  lobes  are  relatively  larger  than  in  the  adult. 

The  changes  which  take  place  during  development  in  the  vessels  connected  with  the 
liver  are  described  on  p.  934. 

THE   PANCEEAS. 

The  pancreas  is  an  elongated  glandular  mass  which  Hes  transversely  on  the 
posterior  abdominal  wall,  with  its  right  end  resting  in  the  concavity  of  the 
duodenum  (Fig.  794),  and  its  left  end  touching  the  spleen.  It  secretes  a 
digestive  tiuid — the  pancreatic  juice — which  is  conveyed  to  the  duodenum  by 
the  2J((''>^creatic  duct,  and  constitutes  one  of  the  chief  agents  in  proteid  digestion. 

The  absence  of  a  true  capsule,  and  the  resulting  distinct  lobulation  of  the  gland, 
give  the  pancreas  a  very  characteristic  appearance  (Fig.  794). 

Position. — The  greater  part  of  the  gland  lies  in  the  epigastrium,  but  the  tail 
and  adjacent  part  of  the  body  extend  into  the  left  hypochondrium. 

The  head  is  placed  opposite  the  second  and  upper  part  of  the  third  lumbar  vertebra,  whilst 
the  body  rvuis  to  the  left,  about  the  level  of  the  first  lumbar  vertebra.  It  should  be  added,  that 
very  often  the  lower  portion  of  the  head  projects  some  distance  below  the  subcostal  plane,  and 
thus  lies  in  the  umbilical  region. 

In  shape  the  pancreas,  when  hardened  in  situ,  is  very  irregular  (Fig.  794), 
its  right  end  being  flattened  and  hook-like,  whilst  the  rest  of  the  organ  is  pris- 
matic and  three-sided.  It  may,  perhaps,  in  general  form  be  best  compared  to 
the  letter  J  placed  thus  c,  particularly  if  the  stem  and  hook  of  the  letter  be 
thickened. 

The  gland  is  divisible  into  a  head,  a  neck,  and  a  body.  The  head  corresponds 
to  the  hook  of  the  c~,  and  runs  downwards  and  to  the  left  along  the  second 
and  third  portions  of  the  duodenum.  The  stem  of  the  c~  represents  the  body  of 
the  gland,  and  the  narrow  part  connecting  the  two  is  the  neck  (Symington). 

When  removed  from  the  body  without  previous  hardening,  the  pancreas  loses 
its  true  form,  and  becomes  drawn  out  into  a  slender,  elongated,  tongue-shaped 
mass,  with  a  wider  end  turned  towards  the  duodenum,  and  a  narrow  end  corre- 
sponding to  the  tail. 

Its  total  length,  when  fixed  in  situ,  is  about  5  or  6  inches  (12  "5  to  15  em.) ;  after  removal,  if 
not  previously  hardened,  it  is  easily  extended  to  a  length  of  8  inches  (20  cm.). 
Its  weight  is  usually  about  3  oiinc(;s  (87  grammes). 

Relations. — The  general  position  and  relations  of  the  pancreas  may  be  briefly 
expressed  as  follows : — The  head  (Fig.  794)  lies  in  the  concavity  of  the  duodenum, 
with  the  vena  cava  and  aorta  behind  it ;  the  body  crosses  the  left  kidney  and 
suprarenal  capsule ;  and  the  tail  touches  the  lower  part  of  the  spleen.  The 
greater  part  of  the  organ  lies  behind  the  stomach,  which  must  be  detached 
from  the  great  omentum,  and  turned  upwards,  in  order  to  expose  it. 

In  describing  the  detailed  relations,  each  part  of  the  organ  will  require  to 
be  considered  separately. 


THE  PANCEEAS. 


1125 


The  head  (caput  pancreatis)  is  the  large  flattened  and  somewhat  disc-shaped  portion 
of  the  gland  which  lies  in  the  concavity  of  the  duodenum,  extending  along  its  second 
and  third  portions  almost  as  far  as  the  duodenal-jejunal  flexure.  Above,  in  its  right  half, 
it  is  continuous  with  the  neck;  whilst  to  the  left  of  this  it  is  separated  from  the^ieck  by 
a  deep  notch  (incisura  pancreatis),  in  which  lie  the  superior  mesenteric  vessels  (Fig.  794). 


Aorta 


Fossa  for  Spigelian  lobi' 
Right  phrenic  vessels 

Vena  cava 
Hepatic  vein      ^ 
Hepatic  artery 
Portal  vein 
Pylorus 


Bile  duct 
Right  suprarenal  capsule 


(Ksopliagus 

Coronary  artery 
Diaphragm 

Left  suprarenal  capsule 
Splenic  artery 
/   Kidney 

Upper  surface  of  pancreas 
Gastiic  surface  of  spleen 


Ureter 
Inferior  nieseu- 
.teric  artery 

Spermatic  vein 
Ureter 
Right  common  iliac 
vein 

Right  common  iliac 
artery 
Left  coiniaou  iliac 
vein 


Under  surface 
of  pancreas 
Attachment  of 
transverse 
mesocolon 

Duodeno- 
jejunal flexure 
Gastro- duodenal 
artery  and  neck 
of  pancreas 

Superior  mesen- 
teric artery 

Duodenum 


Ureter 


—Colon 


Fig.  794.— The  Viscera  and  Vessels  on  the  Posterior  Abdominal  Wall. 

The  stomach,  liver,  and  most  of  the  intestines  have  been  removed.  The  peritoneum  has  been  preserved  on  the 
right  kidney,  and  the  fossa  for  the  Spigelian  lobe.  In  taking  out  the  liver,  the  vena  cava  was  left 
behind    •  The  stomach-bed  is  well  shown.      (From  a  body  hardened  by  chromic-acid  injections.) 

Its  right  and  lower  borders  are  moulded  on  to  the  side  of  the  duodenum,  which  lies  in  a 
groove  of  the  gland  substance — -the  common  bile  duct  being  interposed  as  far  down 
as  the  middle  of  the  second  portion  of  the  duodenum.  The  2^osterwr  stirface  of  the 
head  is  applied  to  the  front  of  the  inferior  vena  cava ;  it  also  lies  on  the  renal  vessels, 
and,  at  its  left  end,  on  the  aortaas  well-  ..  Its  anterior  siirface  is  in  contact  above  and 
on  the  right  with  the  beginning  of  the  transverse  colon  (Fig.  795),  without  the  inter- 


1126 


THE  DIGESTIVE  SYSTEM. 


position  of  the  peritoneum  as  a  rule.  Below  this  it  is  clothed  by  peritoneum,  and  is 
covered  by  the  small  intestine. 

The  superior  mesenteric  vessels,  after  passing  forward  through  the  pancreatic  notch, 
descend  in  front  of  that  portion  of  the  head  (processus  uncinatus)  which  runs  to  the  left 
along  the  third  part  of  the  duodenum.  The"  superior  pancreatico- duodenal  vessels  run 
downwards,  and  break  up  on  the  front  of  the  head  (Fig.  794). 

The  neck  (Fig.  794)  is  a  comparatively  attenuated  portion  of  the  gland  which  lies 
in  front  of  the  portal  vein,  and  connects  the  head  to  the  body.  Springing  from  the  upper 
and  right  portion  of  the  head,  it  runs  upwards  and  to  the  left  for  about  1  inch  (25  mm.), 
and  then  passes  into  the  body. 

The  neck  is  about  |  inch  (18  mm.)  in  width,  and  less  than  i  inch  (12-5  mm.)  in  thickness.     In 


Top  of  small  sac 


Inferior  vena  cavr. 
Lesser  omentum  (cut ) 


Right  lateral  ligament 
of  livor 


Left  lateral  ligament  of  liver 
/  CEsoijhageal  opening  in  diaphragm 

Gastro-phrenic  ligament 
C jrrpsponds  to  '  uncovered  area '  of  stomach 
Gastro-splenic  omentum  (cut) 


I'hreno-cohc  ligament 


Transverse  colon  crossing  duodr:nuni  / 
Head  of  ])ancreas 
Great  omentum  (cut) 


Part  of  small  .sac 


Left  end  of  transverse  mesocolon 
Splenic  flexure  of  colon 
Transverse  mesocolon  (cut) 
Koot  of  niesenteiy  (cut) 
Fif!.  795. — Thk  Peritoneai.  Relations  of  the  Duodenum,  Pancreas,  Spleen,  Kidneys,  etc. 

fr(yat  and  to  its  right  lie  the  first  part  of  the  duodemun  and  the  pylorus  ;  behind  and  to  the  left  it 
rests  upon  the  beginning  of  tlie  portal  vein,  which  is  formed  under  cover  of  its  lower  border,  by  the 
union  of  the  splenic  and  superior  mesenteric  veins.  It  has  a  partial  covering  of  peritoneum  on  its 
anterior  surface  ;  and  its  Ijegimiing  is  generally  marlced  off  from  the  head  l:iy  the  gastro-duodenal 
artery,  with  its  continuation  the  .superior  pancreatico-duodenal,  which  lies  in  a  groove  of  the 
gland  substance  between  the  head  and  neck. 

The  body  is  of  a  prismatic  form,  largest  where  it  lies  in  front  of  the  left  kidney, 
and  usually  somewhat  tapering  towards  the  tail  (Fig.  795).  Beginning  at  the  termina- 
tion of  the  neck,  it  runs  backwards  and  to  the  left  across  the  front  of  the  left  kidney, 
beyond  which  its  extremity  or  tail  comes  in  contact  with  the  spleen.  When  hardened  m 
situ  it  presents  three  surfaces — su])erior,  inferior,  and  posterior — all  of  which  are  of 
nearly  equal  width  (namely,  aljout  1]  inch  :  31  mm.). 


THE  PANCREAS.  1127 

The  upper  surface  (facies  anterior)  is  widest  towards  the  left  end  ;  it  looks  upwards 
and  forwards  (Fig.  794),  and  forms  a  considerable  portion  of  the  stomach-bed.  This 
surface  is  completely  covered  by  peritoneum,  derived  from  the  posterior  wall  of  the  small 
sac,  which  latter  separates  the  pancreas  fi'om  the  under  surface  of  the  stomach.  Towards 
its  right  extremity  it  presents  an  elevation  or  prominence  where  the  body  joins  the  neck. 
This  projects  against  the  back  of  the  small  omentum  when  the  stomach  is  distended, 
and  is  conseciuently  known  as  the  omental  tuberosity  (tuber  onientale). 

The  inferior  surface  of  the  body,  which,  like  the  superior,  is,  as  a  rule,  widest  towards 
its  left  end,  looks  downwards  and  slightly  forwards.  It  is  completely  covered  by 
peritoneum,  viz.  the  descending  layex",  derived  from  the  transverse  mesocolon  (Fig.  795). 
It  lies  in  contact  with  the  duodeno-jejunal  flexure  towards  its  right  end,  with  the  splenic 
flexure  of  the  colon  near  its  left  end,  and  with  a  mass  of  small  intestine  (jejunum,  which 
is  always  found  packed  in  beneath  it)  in  the  rest  of  its  extent. 

The  posterior  surface  of  the  body  looks  directly  backwards,  and  is  entirely  destitute 
of  peritoneum.  It  is  connected  by  areolar  tissue  to  the  posterior  abdominal  wall  with 
the  organs  lying  upon  it.  From  right  to  left  these  are  :  the  aorta  with  the  origin  of  the 
superior  mesenteric  artery,  the  left  renal  vessels,  the  left  suprarenal  capsule,  and  the  left 
kidney.  In  addition,  the  splenic  artery  runs  its  tortuous  course  to  the  left  behind  the 
upper  border  of  the  pancreas,  whilst  the  splenic  vein  runs,  behind  the  gland,  at  a  lower 
level  than  the  artery. 

The  three  surfaces  of  the  body  of  the  pancreas  are  separated  by  three  borders.  The 
anterior  border  is  the  most  prominent,  and  gives  attachment  to  the  transverse  mesocolon 
(Fig.  795).  It  is,  as  it  were,  squeezed  forward,  by  the  pressure  of  the  stomach  above  and 
the  small  intestine  below,  into  the  interval  between  these  two  sets  of  viscera,  thus  follow- 
ing the  line  of  least  resistance  (Cunningham).  Towards  the  neck  this  border  is  no 
longer  prominent,  but  becomes  rounded  off,  so  that  here  the  upper  and  lower  surfaces  are 
confluent. 

The  coeliac  axis  projects  over  the  upper  border,  and  sends  its  hepatic  branch  to  the 
right,  resting  upon  it,  whilst  the  splenic  artery  runs  to  the  left  behind  it  (Fig.  794).  The 
inferior  border  calls  for  no  special  description. 

The  tail  of  the  pancreas  is  the  somewhat  pointed  left  end  of  the  body,  which  is  in 
contact  with  the  lower  portion  of  the  gastric  surface  of  the  spleen.  It  usually  presents  an 
abrupt,  blunt  ending,  in  which  case  it  is  related  to  the  spleen  in  the  manner  just  described  ; 
or  it  may  be  elongated  and  narrow,  when  it  bends  backwards  around  the  outer  aspect  of 
the  kidney,  and  beneath  the  base  of  the  spleen.  '  In  either  case  it  lies  in  contact  below 
with  the  splenic  flexure  of  the  colon  (Fig.  794). 

Peritoneal  Relations  of  the  Pancreas. — The  posterior  surface  of  the  pancreas 
is  entirely  free  from  peritoneum.  The  otlier  surfaces  derive  their  peritoneal  covering 
from  the  prolongation  of  the  two  layers  of  the  transverse  mesocolon,  which  latter  is 
attached  to  the  anterior  border  of  the  gland,  from  the  tail  to  the  neck.  At  this  border 
the  two  layers  separate  (Fig.  777,  p.  1098),  the  anterior — derived  from  the  small  sac 
— passing  backwards  and  upwards  over  the  superior  surface  ;  the  posterior — derived 
from  the  large  sac — turning  downwards  and  backwards  along  the  inferior  surface. 

As  the  transverse  mesocolon  is  followed  to  the  right  it  ceases,  as  a  rule,  that  is,  its  two  layers 
fail  to  meet  about  the  neck  of  the  pancreas  (Fig.  795).  Beyond  this  the  posterior  surface  of 
the  colon  is  generally  free  from  peritoneum,  and  is  connected  by  areolar  tissue  to  the  front  of  the 
head  of  the  gland.  Below  the  level  of  the  colon  the  head  is  covered  by  the  continuation  down- 
wards of  the  peritoneum  from  the  under  surface  of  that  gut.  Often,  however,  the  tramverse 
mesocolon  is  continued  to  the  right  as  far  as  the  hepatic  flexure,  when  the  anterior  surface  of 
the  head  is  then  completely  covered  by  peritoneum.'.; 

Ducts  of  the  Pancreas. — Almost  invariably  two  ducts  are  found  in  the  interior 
of  the  pancreas — the  pancreatic  duct  proper  and  the  accessory  pancreatic  duct. 

The, pancreatic  duct  (ductus  pancreaticus  Wirsungi)  begins  near  the  tip  of  the 
tail  by  the  union  of  small  ducts  from  the  lobules  forming  that  part  of  the  organ. 
From  this  it  pursues  a  rather  sinuous  or  zigzag  course  (Fig.  796)  through  the  axis 
of  the  gland,  at  first  running  transversely  to  the  right,  until  the  neck  is  reached, 
then  bending  downwards  towards  the  head.  Here  it  approaches  the  second 
portion  of  the  duodenum,  and  meeting  the  bile  duct,  the  two  pierce  the  inner  wall 
of  the  gut  obhquely  (for  |  to  f  of  an 'inch,  12  to  18  mm.),  and  open,  by  a  common 
orifice  on  the  bile  papilla,"about  U  or  4  inches  (8-7  to  10  cm.)  beyond  the  pylorus 
(see  p.  1120). 


1128 


THE  DIGESTIVE  SYSTEM. 


Accessory 
^pancreatic 
^  duct 


In  its  course  through  the  gland  the  duct  receives  numerous  branches,  which 
join  it,  as  a  rule,  at  very  open  angles.  These,  as  well  as  the  main  duct  itself,  are 
easily  recognised  by  the  whiteness  of  their  walls,  as  contrasted  with  the  darker 
colour  of  the  gland  tissue.     The  main  duct  receives  branches  from  all  portions  of 

the  pancreas,  and  to- 
wards its  termination 
has  attained  a  consider- 
able size  (namely,  yV^h 
to  -^th  of  an  inch — 2'5 
to  4  mm. — when  fat- 
tened out,  or  somewhat 
larger  than  a  crow  quill). 

The  accessory  pan- 
creatic duct  (ductus  pan- 
creaticus  accessorius, 
Santorini)  is  a  small  and 
variably  -  developed  duct 
(Fig.  796)  which  opens 
into  the  duodenum  about 
I  of  an  inch  above  and 
somewhat     in    front     of 


Pancreatic  iluct/ 


KJuijerior  mesenteric  vein' 


Head  of  pancreas 


riranch  of 
accessory  duct 


Fig.  796. 


-The  Pancreas  and  Duodenum  from  Behind,  with  the 
pancreatic  duct  exposed. 

The  superior  mesenteric  vessels  are  also  shown  in  section,  passing  forward, 
surrounded  by  the  recurved  portion  of  the  head  of  the  2:iancreas. 

{i.e.  ventral  to)  the  pan- 
creatic duct.  From  the  duodenum  it  runs  to  the  left  and  downwards,  and  soon  divides 
into  two  or  more  branches,  one  of  which  joins  the  pancreatic  duct,  the  others  pass  down 
and  receive  the  ducts  from  the  lower  part  of  the  head.  It  is  generally  supposed  that  the 
current  flows  from  this  into  the  main  duct,  and  not  into  the  duodenum,  as  a  rule,  except 
iu  early  life. 

Physical  Characters  and  Structure  of  the  Pancreas. — The  pancreas  is  of  a 
reddish  cream  colour,  soft  to  the  touch,  and  distinctly  lobulated.  The  lobules 
are  but  loosely  held  together  by  their  small  ducts  and  by  loose  areolar  tissue ; 
for,  as  already  pointed  out,  the  pancreas  is  devoid  of  a  regular  capsule,  and 
possesses  instead  merely  an  adventitious  coat  of  fine  connective  tissue. 

The  gland  belongs  to  the  class  of  acino-tubular  glands,  its  alveoli  or  acini  being 
elongated  like  those  of  Brunner's  glands ;  otherwise  it  corresponds  very  closely  to 
a  serous  salivary  gland,  the  general  structure  of  which  will  be  found  on  p.  1007. 

Variations. — The  chief  variations  found  are  : — (1)  A  separation  of  the  part  of  the  head, 
known  as  the  uncinate  process,  which  then  forms  a  lesser  j)ancreas.  (2)  A  growth  of  the  jjancreas 
around  the  duodenum,  which  it  may  practically  encircle  for  a  short  part  of  its  course.  And  (3) 
an  opening  of  its  duct  into  the  duodenum,  independently  of  the  bile  duct.  An  accessory  pancreas 
(pancreas  accessorium)  is  also  sometimes  found  in  the  wall  of  the  stomach  or  of  the  jejunum. 
Diverticula  of  the  duodenum,  already  described  (p.  1070),  ought  perhaps  to  be  mentioned  in 
this  connexion. 

Vessels. — The  arteries  of  the  pancreas  are  : — (1)  The  superior  pancreatico-duodenal,  a  branch 
of  the  gastro-duodenal  artery,  which  runs  down  on  the  front  of  the  head  (Fig.  794),  sending 
branches  outwards  to  the  duodenum,  as  wcdl  as  numerous  twigs  into  the  substance  of  the 
pancreas.  (2)  The  inferior  pancreatico-duodenal,  a  branch  of  the  ujjper  part  of  the  superior 
mesenteric  artery ;  it  runs  upwards  and  to  the  right  across  the  back  of  the  head,  and 
sends  branches  to  it  and  to  the  duodenum,  one  of  which  runs  between  the  head  and  the 
duodenum.  These  two  pancreatico-duodenal  arteries  anastomose  around  the  inferior  border  of  the 
head.  (3)  Tiie  inferior  pancreatic  branch  of  the  superior  mesenteric  (or  sometimes  of  the  gastro- 
duodenal)  artery,  a  considerable  bi'anch,  which  arises  along  witii,  or  near,  the  last,  and  jams  to  the 
left  along  the  lower  bolder  of  the  pancreas,  often  even  as  far  as  its  tail.  (4)  Pancreatic  branches 
of  the  splenic  artery,  are  several  (3  to  5)  fair-sized  branches  wliich  come  oft'  from  the  splenic 
as  it  runs  Ijcliind  tlie  upper  border  of  the  gland  ;  they  enter  the  pancreas  immediately,  and 
traverse  its  substance  from  above  downwards,  some  sc^ndiiig  l)i'anches  in  both  directions  along 
the  course  of  the  i)ancreatic  duct.  (5)  Small  pancreatic  branches  also  arise  from  the  hepatic 
artery  whilst  it  rests  on  the  upper  part  of  the  gland,  and  outer  it  immediately.  The  pan- 
creatica  magna,  which  is  described  as  accompanying  the  duct  from  left  to  right,  does  not  seem 
to  exist  in  the  majority  of  cases. 

The  veins  are  :  (1)  An  anterior  'pancreatico-duodenal  (Fig.  794),  which  passes  downwards  and 
to  the  left,  on  the  front  of  the  head,  and  joins  the  superior  mesenteric  ;  (2)  a  posterior  pancreatico- 
duodenal, which  crosses  the  back  of  the  head,  and  opens  into  the  portal  vein  ;  (3)  several  small 
jjancreatic  veiiLS  which  join  the  splenic ;  and  (4)  some  from  the  upper  part  of  the  head  and 


THE  PANCREAS.  1129 

neck  join  the  portal,  wliicli  latter  vein  ultimately  receives  all  the  blood  returned  from  the 
f^land. 

The  lymphatics  paf^s  chiefly  with  the  splenic  lymphatics  to  the  cceliac  glands  ;  some  also  are 
connected  with  a  few  glands  which  lie  near  the  upper  end  of  the  superior  mesenteric  vessels.  All 
the  lymphatics  of  the  organ  pass  ultimately  to  the  cceliac  glands. 

The  nerves,  which  are  almost  entirely  non-medullated,  come  from  the  solar  plexus,  through 
the  cceliac,  splenic,  and  sujierior  mesenteric  plexuse.s. 

Development  of  the  Pancreas. 

The  pancreas  is  developed  at  a  very  early  period  in  man  (being  visible  in  embryos  of 
8  mm.)  from  at  least  two  independent  hollow  outgrowths,  one  of  which  takes  place  from  the 
ventral  aspect  of  the  future  duodenum  in  connexion  with  the  diverticula  which  form  the 
liver  ;  the  other  from  the  dorsal  side  of  the  tube.  From  this  latter,  which  springs  from  the 
duodenum  nearer  to  the  pylorus  than  the  ventral  outgrowth,  the  greater  part  of  the  gland 
is  formed,  whilst  the  ventral  diverticulum  gives  rise  to  the  smaller  portion.  About  the 
sixth  week  the  two  outgrowths  meet,  and  they,  as  well  as  their  ducts,  fuse.  At  first  the 
main  duct  of  the  gland  is  connected  with  the  dorsal  outgrowth  ;  later  on,  the  portion  of 
this  duct  between  the  duodenum  and  the  meeting  of  the  two  ducts  lags  behind  in  its 
growth,  whilst  the  corresponding  portion  of  the  ventral  duct  increases  rapidly  in  size  ;  and 
finally,  this  latter  appears  to  be  the  direct  continuation  of  the  main  duct,  whilst  the 
former,  and  now  much  smaller,  dorsal  duct  becomes  the  accessory  pancreatic  duct.  The 
two  ducts  come  to  open  on  the  inner  or  left  side  of  the  gut,  owing  to  the  turning  over  of 
the  duodenum  on  its  right  side,  and  the  unequal  growth  of  different  poi'tions  of  its  wall. 

The  primary  diverticula  give  oft"  hollow  lateral  buds,  which  in  their  turn  give  ofl^ 
others,  and  this  process  is  continued  until  the  mass  of  the  gland  is  formed.  The  terminal 
buds  thus  produced  develop  into  the  gland  acini,  whilst  the  others  form  the  gland  ducts. 

When  first  formed  in  the  embryo,  the  pancreas  runs  upwards  towards  the  head,  behind 
the  stomach  and  between  the  two  layers  of  the  mesogastrium,  so  that  it  possesses  a 
complete  peritoneal  covering.  Subsequently,  as  a  result  of  the  changes  which  take  place 
in  tlie  position  of  the  stomach,  it  turns  over  on  to  its  right  side,  and  becomes  adherent  to 
the  posterior  abdominal  wall,  its  head  occupying  the  concavity  of  the  duodenum,  and  its 
tail  passing  towards  the  spleen.  The  peritoneum  of  its  posterior  surface  is  soon  lost  by 
absorption  ;  but  it  persists  on  its  anterior  aspect. 


76 


THE    URINOGENITAL    SYSTEM 

By  a.  Francis  Dixon, 

THE  UKINARY  ORGANS. 

The  kidneys,  or  glands  which  secrete  the  urine,  are  a  pair  of  ahnost  symmetric- 
ally-placed organs,  situated  in  the  posterior  part  of  the  abdominal  cavity,  one 
on  each  side  of  the  lower  movable  portion  of  the  vertebral  column.  The  fluid 
secreted  by  the  kidneys  is  received  into  the  upper  expanded  portions  of  a  pair  of 
long  tubes,  the  ureters,  by  them  is  conducted  to  the  bladder,  which  is  placed 
within  the  pelvic  cavity.  From  the  bladder  the  urine  is  passed,  during  micturi- 
tion, along  the  urethra  to  the  exterior.  In  the  male  the  urethra  is  a  relatively 
long  passage,  and  traverses  the  prostate  gland  and  the  whole  length  of  the  penis  ;  in 
the  female  it  is  a  short  tube,  and  opens  on  the  surface  just  above  the  vaginal 
orifice. 

THE  KIDNEYS. 

The  kidney,  when  removed  from  a  fresh  subject,  presents  a  bean-shaped  contour. 
It  is  of  a  dark  brown-red  colour,  and  is  surrounded  by  a  thin  glistening  capsule 
(tunica  fibrosa),  which  gives  tO'  the  whole  organ  a  uniformly  smooth  surface. 
The  kidney  is  not  a  solid  body,  but  contains  a  cavity  called  the  renal  sinus, 
the  opening  into  which,  termed  the  Mlum  (hilum  renalis),  is  situated  on  the  inner 
and  anterior  part  of  the  organ.  Each  kidney  measures  about  4|  inches  in 
length,  2  inches  in  width,  and  about  1^  inch  in  thickness,  and  is  placed  so 
that  its  long  axis  is  nearly  vertical.  The  weight  of  the  adult  kidney  is 
about  4^  ounces.  In  the  freshly-removed  kidney  the  upper  and  lower  ends 
are  smoothly  rounded,  and  the  upper  end  (extremitas  superior)  is  usually  a  little 
more  bulky  than  the  lower  (extremitas  inferior).  The  outer  harder  (margo 
lateralis),  which  is  opposite  to  the  hilum,  is  rounded  and  convex,  while  the  inner 
border  (margo  medialis),  on  which  the  hilum  is  placed,  is  concave  from  above  down- 
wards. These  two  borders  separate  the  anterior  surface  (facies  anterior)  from  the 
posterior  surface  (facies  posterior)  of  the  kidney. 

The  capsule,  which  envelops  the  whole  organ,  divides  in  the  region  of  the 
hilum  into  two  layers,  one  of  which  is  continued  over  the  lips  of  the  hilum 
into  the  interior  of  the  kidney,  and  lines  the  walls  of  the  kidney  sinus. 
The  other  layer  is  prolonged  to  form  a  tubular  sheath  for  the  vessels  and  nerves 
of  the  kidney  before  they  pass  through  the  hilum  to  enter  the  sinus,  within 
which  they  break  up  into  branches.  These  branches,  piercing  the  wall  of  the 
sinus,  enter  the  substance  of  the  kidney.  The  upper  expanded  portion  of  the 
ureter  leaves  the  sinus  through  the  hilum  in  company  with  the  blood-vessels  and 
nerves. 

Position  of  the  Kidneys. — The  precise  level  of  the  kidney  in  the  abdominal 
cavity  is  subject  to  a  consideraljle  amount  of  variation,  and  also  it  is  usual  to  find 
a  difference  in  the  levels  of  the  right  and  left  kidneys  of  the  same  individual.  Most 
frequently  the  left  kidney  is  on  a  higher  level  than  the  right,  but  in  many  cases 
the  kidneys  occupy  the  same  level,  or,  the  more  usual  condition  being  reversed,  the 
right  kidney  is  a  little  higher  than  the  left. 

1130 


THE  KIDNEYS. 


1131 


If  a  line  he  drawn  round  the  body  at  the  level  of  the  lowest  part  of  the  thoracic 
wall,  the  whole,  or  almost  the  whole,  of  the  left  kidney  will  be  found  to  lie  above 
the  level  of  the  plane  (subcostal)  so  determined.  It  is,  therefore,  situated  in  tlie 
subcostal  zone  of  the  abdominal  cavity.  The  right  kidney,  however,  although  it 
lies  for  the  most  part  in  the  subcostal  zone,  usually  projects  at  its  lowest  part 
sHghtly  below  the  subcostal  plane,  and  hence  lies  to  a  small  extent  in  the  umbilical 
zone.  It  is  often  stated  that  the  kidneys  are  placed  on  a  somewhat  lower  level 
in  the  female  than  in  the  male. 

By  far  the  greater   part,  usually  two-thirds   or  more,  of   the   kidney  lies  to 


Vetia  cava 
Suprarenal  body  j 

Duodeinnu      j  . 


ffisopliatieal  openiiiij 
of  iliapliTai;iii 


Spleen 


Lumbar  fascia 


Kidney 
Quadratus  luniborttui 

Spermatic  vessel 


kidney 


I.     Uio-hypogastric  nerve 
Ureter        1  j  j  !  llio-iuguinal  nerve 

Psoas  muscle  i  '■  |  Jejunum 

Pancreas  Superior  mesenteric  vessels 

Fig.  797. — Dissection  to  show  the  Position  and  Relationships  of  the  Kidneys.  The  outlines  of  the 
costal  arches  are  indicated,  and  it  will  be  noted  that  in  the  subject  from  which  the  drawing  was 
made  the  lower  ends  of  both  kidneys  lay  below  the  level  of  the  subcostal  zone. 

the  inner  side  of  a  line  drawn  vertically  upwards  through  the  middle  point  of 
Poupart's  ligament. 

The  posterior  aspect  of  the  kidney  is  closely  applied  against  the  muscles 
attached  to  the  bodies  of  the  last  dorsal  and  upper  three  lumbar  vertebrae,  and  is 
placed  in  front  of  the  last  rib  and  of  the  transverse  processes  of  the  upper  three 
lumbar  vertebrae.  In  some  cases,  more  frequently  on  the  left  side  of  the  body, 
the  eleventh  rib  also  lies  behind  the  upper  part  of  the  kidney.  The  relationship 
of  the  kidney  to  the  lower  two  riljs  is,  however,  very  inconstant,  owing  partly  to 
the  great  variability  in  size  and  inclination  of  these  bones  (Fig.  779). 

The  lower  end  of  the  kidney  is  usually  situated  from  1^  to  2  inches  above  the 
highest  part  of  the  crest  of  the  ilium ;  the  interval  Ijetween  the  kidney  and  the 
ilium  being  usually  greater  on  the  left  side  of  the  body. 
76  a 


1132 


THE  UEINOGENITAL  SYSTEM. 


Sometimes  the  lower  end  of  the  kidney  lies  on  the  same  level  as,  or  only  a 
short  distance  above,  the  iliac  crest,  and  this  may  be  due  to  the  crest  rising  to  a 
higher  level  than  usual,  the  kidney  occupying  its  normal  position  in  relation  to 
the  vertebral  column.  It  is  important  to  remember  that  normally  the  kidney 
moves  upwards  and  downwards  during  life,  following  the  respiratory  movements 
of  the  part  of  the  diaphragm  against  w^hich  it  rests. 

The  kidneys  are  placed  behind  the  peritoneum,  and  project  into  the  jjosterior 
part  of  the  abdominal  cavity.  Each  is  surrounded  by  a  considerable  amount  of 
loose  tissue,  often  loaded  with  fat,  the  fatty  tissue  (capsula  adiposa)  being  present 
in  greater  quantity  round  the  margins  of  the  organ,  and  only  to  a  less  extent  in 
front  of  and  behind  the  kidney.  In  this  fat  the  renal  vessels  and  nerves  lie  before 
they  enter  the  organ,  and  the  adipose  tissue  is  continued,  along  with  the  vessels. 


Duodeno-jejunal  flexure 


First  part  of  duodenum 


Neck  of  gall 
bladder 


Second  part  of 
duodenum 


Fatty  tissue 


Tail  of  pancreas 

Lumbar  fascia 

Quadratus  lumborum 


Kidney 


Body  of  vertebra 


Fig.  798. — Transverse  Section  through  the  Abdomen  at  the  level  of  the  Second  Lumbar  Vertebra. 
The  plane  of  the  section  is  somewhat  oblique,  being  lower  behind  than  in  front.  The  costal  arches 
are  numbered  8-11.  On  the  right  side  the  posterior  layer  of  the  renal  fascia  is  indicated.  (From  a 
specimen  in  the  Anatomical  Department,  University  College,  Cardiff.) 

through  the  hilum  into  the  kidney  sinus,  where  it  fills  up  all  the  space  unoccupied 
by  the  vessels  and  nerves. 

The  long  axis  of  each  kidney  is  somewhat  oblique,  as  the  upper  end  of  the  organ 
approaches  nearer  to  the  middle  line  than  the  lower.  The  surface  of  the  kidney,  ■ 
which  is  applied  against  the  muscles  forming  the  posterior  wall  of  the  abdomen, 
looks,  as  a  whole,  backwards  and  inwards,  and  that  which  projects  into  the 
aljdominal  cavity  forwards  and  outwards.  Hence  it  happens  that  the  outer  border 
of  the  kidney  lies  on  a  posterior  plane  to  the  inner  border.  The  kidney  is  rotated 
in  this  manner  on  its  long  axis  to  such  a  degree  that  the  inner  margin  and  hilum 
are  scarcely  viable  from  behind,  and  but  a  limited  view  of  the  outer  border  can 
be  obtained  in  front  (Figs.  SOO  and  803). 

Embedded  in  the  soft  fatty  tissue  surrounding  the  kidney  is  a  layer  of  fibrous 
tissue  to  which  the  term  fascia  renalis  is  applied.  This  fascia  surrounds  the 
kidney  and  a  considerable  amount  of  its  fatty  capsule  in  the  form  of  a  loose 
sheath,  in  which  may  be  distinguished  anterior  and  posterior  walls.  The  sheath 
is  open  below  and  internally,  but  closed  above  and  to  the  outer  side  of  the  kidney 
by  the  apposition  of  its  walls.  Externally  the  anterior  and  posterior  walls  of 
the  sheath  come  into  contact  and  are  connected  with  the  retro-peritoneal  tissue ; 
internally  the  layers  forming  these  walls  remain  distinct  and  the  anterior  one  is 
continued  across  the  middle  line,  in  front  of  the  renal  vessels  and  the  aorta,  to 
join  the  corresponding  layer  of  the  opposite  side,  while  the  posterior  wall  fuses 


THE  KIDNEYS. 


1133 


with  the  fascia  covering  the  psoas  and  quadratus  luniboruni  muscles.  Inferioiiy, 
below  the  level  of  the  kidney,  the  anterior  and  posterior  layers  of  the  renal 
fascia  remain  distinct  and  can  be  traced  downwards  into  the  iliac  fossa.  Above 
the  level  of  the  kidney  and  the  suprarenal  body  the  layers  of  the  renal  fascia 
unite  and  join  the  fascia  covering  the  diaphragm.  It  has  been  suggested  that  the 
terms  "  tunica  adiposa "  and  "  peri-renal  fat "  should  l)e  restricted  to  the  loose 
fatty  tissue  enclosed  along  with  the  kidney  within  the  sheath  of  renal  fascia,  and 
that  the  term  "  para-renal  i  )ody,"  or  fat,  be  applied  to  the  tissue  outside  the  sheath. 
The  fibrous  capsule  of  the  kidney  is  joined  to  the  loose  sheath  formed  by  the  renal 
fascia  by  numerous  connective  tissue  strands,  which  traverse  the  peri-renal  fat  and 
undoubtedly  assist  in  fixing  the  kidney.     The  para-renal  fat  is  present  in  greatest 


12th  rib 

Crus  of  I 

diaphragm  ) 

External  'j 

arcuate  .- 

ligament  j 

Diaphragm 

Spleen 

Kidney 


Quadratus 
lumborum 

Small 
intestine 


Iliac  crest 


Fig.  799. 


-The  Posterior  Relationships  of  the  Kidneys.     The  dotted  Hues  indicate  the  contours  of  the 
kidneys.     The  drawing  is  made  from  a  model  prepared  by  Professor  Cunningham. 


quantity  behind  the  lower  part  of  the  kidney,  and  in  this  position  the  layer  of 
fibrous  tissue,  separating  the  two  masses  of  fat  and  forming  the  posterior  layer  of 
the  sheath  of  renal  fascia,  is  usually  well  marked. 

Fixation  of  the  Kidney. — The  kidney  is  not  held  in  its  place  by  any  distinct 
ligaments,  or  special  folds  of  peritoneum,  but  its  fixation  depends,  to  a  large 
extent,  on  the  pressure  and  counter-pressure  which  is  exerted  upon  it  by  neigh- 
bouring structures,  and  on  its  connexions  with  the  renal  fascia  above  described. 

Posterior  Relations  and  the  Posterior  Surface  of  the  Kidney. — The  muscles 
of  the  posterior  abdominal  wall  on  which  the  kidney  rests  are  the  psoas,  the  quadratus 
lumborum,  the  diaphragm,  and  the  tendon  of  the  transversalis  abdominis.  The 
abdominal  surfaces  of  these  muscles  do  not  lie  on  the  same  plane,  but  slope 
towards  one  another,  and  thus  the  bed  on  which  the  kidney  rests  is  not  flat.  The 
posterior  aspect  of  the  kidney,  when  in  situ,  adapts  itself  to  the  inequalities  of  the 
76  & 


1134 


THE  UEINOGENITAL  SYSTEM. 


surface  against  which  it  is  placed,  and  so  we  find  on  a  kidney  which  has  been  care- 
fully fixed  and  hardened  before  it  has  been  disturbed,  areas  marked  off  for  the 
different  planes  of  these  muscles.  When  the  kidney  is  in  position,  slight  ridges  or 
elevations  separating  these  areas  correspond  to  the  angles  along  which  the  different 
muscular  planes  meet.  These  ridges  can  be  observed  in  the  hardened  kidney  after 
its  removal  from  the  body,  but  usually  they  are  not  very  sharply  defined,  the 
angles  between  the  muscular  planes  being  very  obtuse. 

A  kidney  removed  from  the  body  after  having  been  hardened  in  situ  (Fig.  800) 
presents  an  area  near  the  inner  part  of  its  posterior  surface  adapted  to  the  anterior 
aspect  of  the  psoas  muscle.  This  part  of  the  posterior  surface  looks  inwards  and 
slightly  backwards.  Farther  out  there  is  a  larger  area  which  rests  against  the 
quadratus  lumborum  and  looks  more  directly  backwards.  These  two  areas  are 
separated  by  a  rounded  ridge  which  fits  into  the  angle  between  the  muscles  men- 


Area  for 
"diaphragm 


Area  for  crus  of  / 

\    '  — diaphragm  \  / 


^^ ^Area  for 

"^  diaphragm 


Area  for 

transversalis" 

tendon 


Area  for 
quadratns- 
luraborum 


-4 


I  r  ^ 


'    ^ 


-Area  for  psoas 


h '_ 


Area  for  psoas - 


Area  for 

transversalis 

tendon 


v>. 


J     f 


Fig.  800. — The  Kidneys  viewed  from  Behind.     Same  specimen  as^J'ig.  803.     The  dotted  lines  mark  oii.t 
the  areas  in  contact  with  the  various  muscles  forming  the  posterior  abdominal  wall. 

a.   Depression  corresponding  to  the  transverse  process  of  the  first  lumbar  vertebra. 
6.   Depression  corresponding  to  the  transverse  process  of  the  second  lumbar  vertebra, 
c.   Depression  corresponding  to  the  twelfth  rib. 

tioned.     Beyond  the  area  in  contact  with  the  quadratus  lumborum  is  the  thick 
outer  border  of  the  kidney. 

Towards  the  upper  end  of  the  kidney  the  posterior  surface  slopes  forwards  and 
rests  upon  the  diaphragm.  Indeed  the  upper  part  of  the  kidney  is,  as  a  whole, 
bent  slightly  forwards,  following  that  part  of  the  arch  of  the  diaphragm  on  which  it 
rests,  and  thus  a  narrow  interval  is  left,  in  which  the  pleural  cavity  passes  down  behind 
the  upper  end  of  the  kidney  (Fig.  799).  This  relationship  of  the  pleural  cavity  to 
the  kidney  is  of  importance  in  connexion  with  surgical  operations  on  the  organ, 
performed  through  a  lumbar  incision.  The  portions  of  the  diaphragm  to  which 
the  kidney  is  applied  are  the  crus  and  the  parts  arising  from  the  last  rib  and 
arcuate  ligaments. 

In  addition  to  these  surfaces,  or  facets,  for  the  muscles  with  whicli  it  is  in  contact,  the 
posterior  aspect  or  outer  border  of  the  kidney  often  shows  a  groove  for  the  last  rib,  another  for 
the  external  arcuate  ligament,  and  two  or  three  depressions  for  the  tips  of  the  transverse  processes 
of  the  upper  two  or  three  lumbar  vertebrae.  In  some  cases  also  faint  narrow  grooves  are  to  be 
seen  for  tlie  nerves  which  pass  do\niwards  and  outwards  between  the  kidney  and  quadratus 
lumborum — namely,  the  last  dorsal  nerve  and  the  ilio-hypogastric  and  ilio-inguinal  nerves. 

It  is  probable  that  some  at  least  of  the  depressions  on  the  posterior  asj)ect  of  the  kidney  are 
produced  after  death,  and  are  caused  by  the  weight  of  the  other  abdominal  organs  pressing  the 


THE  KIDNEYS. 


1135 


nperior  mesenteric 
vessels; 


Ureter 


Fill.  801. — Rkjht  Kidxey  and  Duodenuji.     (1).  J.  Cuiuiiiigliaiii.) 


—The  anterior 
)ut  also  many 


kidney  backwards  against  the  more  resisting  structures  of  the  abdominal  wall,  at  a  time  when 
the  muscles  behind  the  kidney  have  become  flaccid.  When  uincli  fat  is  i)resi'iit,  the  posterior 
aspect  of  the  kidney  is  more  uniforiuly  convex. 

The  outer  border  in  its  middle  and  lower  part  is  rather  a  surface  than  a 
border,  and  looks  for  the  most  part  directly  Ijackwards.  It  rests  on  the  anterior 
surface  of  the  lumbar  fascia, 
and  lies  to  the  outer  side  of 
the  quadratus  lumborum. 
The  outer  border  is  luirrowest 
above,  and  widest  just  below 
its  middle  point,  correspond- 
ing to  the  greater  thickness 
of  this  part  of  the  kidney. 

In  many  ways  it  would 
be  more  satisfactory  to  apply 
the  term  muscular  surface 
(facies  muscularis)  collec- 
tively to  the  areas  described 
here  as  posterior  surface  and 
outer  border,  and  in  like 
manner  the  term  visceral 
surface (facies  visceralis) 
might  be  suitably  applied  to 
the  so-called  anterior  surface 
of,  the  organ.  The  edge 
separating  the  visceral  from 
the  muscular  surface  is  the  actual  outer  border  of  the  kidney. 

Anterior  Relations  and  the  Anterior  Surface  of  the  Kidney 
relations  of  the  kidneys  not  only  differ  on  the  two  sides  of  the  ]jody, 
of  the  structures  related  to  the  anterior  surface  of  each  kidney  undergo  frequent 

changes  in  position 
during  life. 

A  small  area  on 
the  upper  part  of 
the  anterior  surface 
of  the  right  kidney- 
is  in  relation  to  the 
corresponding  sup- 
rarenal capsule 
(Fig.  803).  The 
rest  of  the  upper 
part  of  the  anterior 
surface  is  in  contact 
with  the  visceral 
surface  of  the  liver, 
which  is  often  hol- 
lowed out  to  form 
a  fossa  for  the  kid- 
ney. The  supra- 
renal capsule  is 
bound  to  the  kid- 
ney by  connective  tissue,  while  the  part  of  the  kidney  in  relation  to  tlie  liver  is, 
like  the  liver  itself,  covered  by  peritoneum,  and  thus  the  two  organs,  although 
closely  applied,  are  really  separated  by  a  part  of  the  general  peritoneal  cavity. 
In  front  of  the  lower  end  of  the  right  kidney  are  usually  found  two  parts  of  the 
alimentary  canal — namely,  the  descending  part  of  the  duodenum  and  the  hepatic 
flexure,  or  the  commencement  of  the  transverse  colon.  The  part  of  the  kidney 
related  to  the  duodenum  lies  to  the  inner  side  of  the  area  which  touches  the  colon, 
but  the  exact  amount  of  the  kidney  in  contact  with  each  of  these  two  parts  of 
76  c 


Fig. 


802. — Left  Kidney,  the  Pancreas,  the  Spleen,  and  the  descending 
Colon.     (D.  J.  Cumunghani.) 


1136 


THE  UKINOGENITAL  SYSTEM. 


intestine  varies  much  in  difterent  subjects.  Frequently  the  colon  and  the  kidney 
are  both  covered  by  peritoneum  where  they  are  in  contact,  but  the  duodenum  is 
bound  down  to  the  kidney  by  the  peritoneum.  In  addition  to  the  structures 
mentioned,  some  portion  of  the  ileum,  or  of  the  jejunum,  is  often  found  in  contact 
with  a  small  part  of  the  right  kidney. 

In  some  cases  the  peritoneal  cavity  does  not  pass  upwards  in  front  of  the  upper 
end  of  the  right  kidney,  and  thus  the  anterior  aspect  of  this  part  of  the  organ  is, 
like  the  suprarenal  body,  bound  by  connective  tissue  to  the  uncovered  area  of  the 
liver. 

In  front  of  the  extreme  upper  and  inner  part  of  the  left  kidney  is  the  inferior 
portion  of  the  left  suprarenal  capsule ;  at  a  lower  level  the  upper  part  of  the 
left  kidney  is  in  contact  with  the  stomach  and  pancreas.  The  suprarenal  capsule 
and  the  pancreas  are  bound  down  to  the  kidney  by  connective  tissue,  but  the 
stomach  is  separated  from  the  part  of  the  kidney  with  which  it  is  in  apposition,  by 
the  lesser  sac  of  the  peritoneum.  The  part  of  the  kidney  in  actual  contact  with 
the  stomach  is  usually  a  small,  somewhat  triangular,  area  situated  above  the  level 
at  which  the  pancreas  crosses  the  organ.  The  renal  surface  of  the  spleen  is 
related  to  the  anterior  surface  of  the  left  kidney  in  its  upper  and  outer  part,  the 
two  organs  being  separated  by  a  portion  of  the  general  peritoneal  cavity,  except 
along  the  area  where  spleen  and  kidney  are  connected  by  the  lieno-renal  ligament. 
The  anterior  surface  of  the  lower  end  of  the  left  kidney  is  related,  towards  the 
inner  side,  to  a  part  of  the  jejunum,  and  towards  the  outer  side  to  a  part  of  the 
splenic  flexure  of  the  colon. 

Suprarenal  area  Suprarenal  area 


1 1  stric  area 


— >I>lenic  area 


Hepatic  arc  i 


Duodenal  area 


Colic  are 


1  lunal  area 


Fio. 


803. — The  Kidneys  and  Giieat  Vessels,  viewed  from  the  front.  The  drawing  was  made,  before 
removal  of  the  organs,  from  a  specimen  in  which  the  viscera  had  heen  hardened  in  situ.  The  dotted 
lines  mark  out  the  areas  which  were  in  contact  with  tlie  various  other  abdominal  viscera. 


The  right  and  left  colic  arteries,  or  their  branches,  as  they  pass  outwards  to  reach  the 
colon,  are  often  related  to  the  anterior  aspects  of  the  corresponding  kidneys.  The  splenic 
vessels  pass  outwards  in  front  of  the  inner  part  of  the  left  kidney  (Fig.  797). 

The  anterior  surface  of  a  kidney,  which  has  been  hardened  i7i  situ,  is,  like  the 
posterior  surface,  not  uniformly  rounded,  but  marked  by  a  series  of  impressions 
corresponding  to  the  different  structures  which  lie  in  contact  with  it.  In  the  case 
of  each  kidney,  the  most  prominent  region  on  the  anterior  surface  lies  below  the 


THE  KIDNEYS. 


1137 


level  of  the  middle  of  the  kidney,  and  corresponds  to  the  thickest  part  of  the 
organ.  From  this  prominence  on  the  anterior  surface  a  series  of  more  or  less 
flattened  planes  slope  away  towards  the  borders  of  the  kidney.  These  flattened 
areas  are  bhe  impressions  formed  by  the  viscera  which  lie  in  front  of  the  kidney. 

In  the  case  of  the  right  kidney,  three  impressions  can  usually  be  distinguished 
on  the  anterior  surface.  One  occupies  the  whole  of  the  upper  part  of  the  oro-an, 
and  is  the  hepatic  impression  (impressio  hepatica) ;  another  stretches  from  the  most 
prominent  point  to  the  lower  end  of  the  kidney,  and  is  related  to  the  colon  ;  while 
the  third  extends  along  the  inner  margin,  below  the  hilum,  and  is  in  contact  with 
the  second  part  of  the  duodenum  (Fig.  803).  The  relative  sizes  of  these  three 
impressions  vary  much  in  different  specimens. 

On  the  left  kidney,  also,  three  more  or  less  marked,  flattened  impressions  slope 
towards  the  borders  of  the  organ  from  the  most  prominent  part  of  the  anterior 
surface.  One  of  these,  on  the  upper  and  outer  part  of  the  kidney,  is  the  splenic 
impression ;  another,  extending  downwards  to  the  lower  end  of  the  kidney,  is  for 
the  colon,  or  for  the  colon  and  jejunum ;  while  the  third,  or  impressio  gastrica, 
corresponds  to  the  position  of  tlie  overlying  stomach.  The  gastric  impression 
occupies  an  area  of  the  anterior  surface  of  the  left  kidney,  above  and  in  the  region 
of  the  hilum.  Only  a  small  portion  of  this  impression  is  in  direct  contact  with 
the  stomach,  since  the  pancreas  and  a  part  of  the  suprarenal  capsule  intervene 
between  the  stomach  and  the  kidney  (Fig.  803). 

It  is  common  to  find  the  left  kidney  thicker  and  less  flattened  antero-posteriorly  than 
the  right,  the  impressions,  or  facets,  upon  its  surface  being  at  the  same  time  better 
marked.  With  this  probably  is  to  be  associated  the  fact  that  floating  kidney  is  more 
rarely  met  with  on  the  left  than  on  the  right  side  of  the  body. 

Extremities  of  the  Kidney. — The  kidney,  fixed  and  hardened  in  situ,  is  usually 
more  pointed  at  its  lower  than  at  its  U23per  end.  The  latter  is  more  flattened  from 
before  backwards,  and  is  wider 
from  side  to  side.  This  flattened 
upper  part  of  the  kidney  rests  upon 
the  diaphragm,  and  is  bent  some- 
what forward. 

Renal  Sinus  (sinus  renalis). — 
The  sinus  of  the  kidney  (Fig.'  80-1), 
into  which  the  hilum  opens,  is  a 
narrow  space,  having  its  long  axis 
corresponding  to  that  of  the  kidney. 
The  thick  walls  of  the  sinus  cavity 
are  formed  by  the  substance  of  the 
kidney,  and  lined  by  a  part  of  the 
fibrous  kidney  capsule  which  enters 
the  sinus  over  the  lips  of  the  hilum. 
The  floor  of  the  sinus  is  not  smooth, 
but  presents  a  series  of  small  pro- 
jecting conical  elevations  called 
renal  papillae  (papilla3  renales), 
which  vary  from  twelve  to  fifteen 
in  number.  Eadiating  from  each 
papilla  are  a  number  of  somewhat 
raised  bars,  or  ridges,  of  kidney 
substance,  separated  by  depressed 
areas.  The  blood-vessels  and  nerves 
enter  and  leave  the  kidney  by 
piercing  the  wall  of  the  sinus 
where  it  is  formed  by  these  little 

depressed  areas  (Fig.  804).  The  summit  of  each  renal  papiUa  is  pierced  by  a 
number  of  minute  openings  called  foramina  papillaria,  which  are  the  terminal 
apertures  of  the  secreting   tubules,   of   which    the  kidney  is   mainly   composed. 


PapiUa 


Papilla 


Pyramid' 

Column  of 

Bertiii' 

Wall  of  sinus- 


Fig.  804. — Lo^'GITDDI^•AL  Section  through  the  Kidney. 

The  vessels  and  fat  have  been  removed  to  give  a  view  of  the 
wall  of  the  kidney  sinus.  The  points  where  the  vessels 
enter  the  kidney  substance  are  seen  as  little  holes  in  the 
sinus  wall  at  a  and  elsewhere. 


1138 


THE  UEINOGENITAL  SYSTEM. 


The  urine  secreted  by  the  kidney  escapes  through  these  foramina  into  the  upper 
part  of  the  ureter. 

Kidney  in  Section. — Sections  (Fig.  804)  through  the  kidney  show  it  to  be, 
for  the  most  part,  composed  of  a  number  of  pyramidal  masses  arranged  with  their 
bases  towards  the  surface,  while  their  apices  project  into  the  sinus  of  the  kidney 
and  form  the  renal  papillse  already  mentioned.  These  are  termed  the  medullary 
PSrramids  (pyramides  renales),  and  together  constitute  the  medulla  (substantia  medul- 
laris)  of  the  kidney.  They  are  more  numerous  than  the  papilla?,  two  or  three  usually 
ending  in  each  papilla  in  the  middle  part  of  the  kidney,  and  sometimes  as  many  as 
six  or  even  more  in  each  papilla  near  the  upper  and  lower  ends  of  the  organ.  The 
bases  of  the  pyramids  do  not  reach  the  surface  of  the  kidney,  but  are  separated 
from  it  by  a  thin  layer  of  kidney  substance  called  the  cortex,  or  cortical  part  of 
the  kidney  (substantia  corticalis).  The  cortical  substance  not  only  covers  over  the 
bases  of  the  pyramids,  but  also  sends  in  prolongations,  called  columns  of  Bertin 
(column te  renales),  between  the  pyramids,  towards  the  sinus.  The  medullary  jart 
of  the  kidney  exhibits  in  section  a  striated  appearance,  while  the  cortical  part  is 
more  granular  and  usually  different  in  colour.  The  outer  part  of  each  pyramid,  or 
the  intermediate  zone  (basis  pyramidis),  as  it  is  termed,  appears  in  section  to  be 
composed  of  alternate  dark  and  light  streaks,  while  the  inner,  or  papillary  part, 
which  is  of  a  lighter  colour,  is  more  uniformly  and  faintly  striated. 

In  sections  of  the  kidney  the  larger  blood-vessels  are  seen,  after  they  have 
entered  the  kidney  substance,  to  He  between  the  pyramids ;  some  of  their  main 
branches  are  also  visible  passing  across  the  bases  of  the  pyramids. 

In  the  foetus  and  young  child,  and  sometimes,  though  much  less  distinctly,  iu  the  adult, 
the  surface  of   the  kidney  is   marked  by  a   number  of  grooves   dividing  it  into  polygonal 

areas.  These  represent  the  lobes 
(lobi  renales)  or  "  Renculi,"  of 
which  the  kidney  is  originally 
composed,  and  each  corresponds 
to  one  papilla  with  its  pyramids 
and  surrounding  cortical  sub- 
stance. 


Medullary  ravs 
/  ,1 


Papillse-  -f  - 


_  Intermediate 
'zone 


;.  Medullar)- 

■ -.-y-rays  (cut 

^--'i,-'    obliquely) 


Column  of  Bertii. 


Medullary  pyramid- 


^^VJ/////^^ 


— ,.s^' 


An  examination,  with  an 
ordinary  pocket  lens,  of  a 
section  through  the  kidney 
shows  that  the  lighter  striae 
of  the  intermediate  zone  are 
continued  into  the  cortex. 
As  they  pass  through  the  cortex 
towards  the  surface  of  the 
kidney  they  become  less  dis- 
tinct, and  appear,  when  cut 
longitudinally,  as  separate  ray- 
like prolongations  carried  out- 
ward from  the  bases  of  the 
pyramids.  These  parts  of  the 
cortex,  which  seem  in  this  way  to  be  continuations  of  the  medulla,  are  called  medullary 
rays  (pars  radiata),  and  the  portions  of  kidney  cortex  which  intervene  between  them 
form  the  labyrinth  (pars  convoluta,  Fig.  806).  The  appearance  presented  by  the 
cortex  of  tho  kidney  in  section  varies  much  according  to  the  plane  in  which  the 
section  has  been  taken.  If  the  section  passes  through,  and  lies  parallel  to  the 
axis  of  a  pyramid,  the  medullary  rays,  met  with,  will  appear  as  isolated  streaks 
directed  from  the  base  of  the  pyramid  towards  the  surface  of  the  kidney  and  separated 
from  one  another  by  narrow  strips  or  intervals  of  labyrinth.  On  the  other  hand,  in 
sections  made  at  right  angles  to  the  axis  of  a  pyramid,  or  cutting  this  axis  obliquely, 
the  labyrinth  portion  of  the  cortex  presents  the  appearance  of  a  continuous  net  the 
meshes  of  which  are  occupied  Ijy  the  medullary  rays,  and  these  latter  now  exhibit 
a  circular  or  oval  outline  (Fig.  805).     In  a  similar  manner  sections  through  the 


Fk;.  805. — Section  Through  a  Poktiox  of  twk  Kidney. 

The   darker    pai-ts   separating   the  medullary  rays,  represent    thi 
labyrinth  portion  of  the  cortex. 


thj:  kidneys. 


1139 


Glomerulus 


intermediate  zone  differ  much  in  the  appearances  they  afford  according  to  the 
plane  in  which  they  are  cut. 

Kidney  Tubules. — The  substance  proper  of  the  kidney  is  composed  of  an  enormous 
number  of  minute  tubules  (tubuli  renales),  each  of  wliicii  has  an  exceedingly  complicated 
course.  The  wall  of  a  uriniferous  tubule  consists  throughout  of  a  basement  membrane 
and  of  an  epithelial  lining,  but  the  diameter  of  the  tubule  and  the  character  of  the 
epithelium  vary  much  in  the  different  parts.  Each  tubule  begins  in  a  thin-walled 
spherical  dilatation,  or  capsule  (capsula  glomeruli),  in  which  a  complicated  loop  of  capillary 
blood-vessels  is  contauied.  The  tuft  of  capillaries  is  covered  by  a  reflection  of  the  delicate 
wall  of  the  capsule,  and  is,  as  it  were,  invaginated  into  the  capsule  (Fig.  806).  Tlje 
capsules  with  their  enclosed  capillaries  are  often  called  Malpighian  corpuscles  (corpuscula 
renis),  and  are  all  placed  in  the  labyrinth  portion  of  the  kidney  cortex,  where  they  may  be 
recognised  as  minute  red  points  just  visible  to  the  unaided  eye  and  best  marked  "when  the 
renal  vessels  are  congested.  The  tubule  leading  from  the  capsule — first  convoluted  tubule 
— is  much  convoluted,  and  lies  within 

the    labyrinth.      I'assing    from    the  La^yrinti,  M.>,iuiiary  ray 

labyrinth,  the  tubule  enters  a  medul- 
lary ray,  in  which  its  course  becomes 
less  complicated,  and  here  it  receives 
the  name  of  spiral  tubule.  From  the 
medullary  ray  the  tubule  enters  the 
intermediate  zone  of  the  pyramid, 
and,  diminishing  in  diameter,  it  pur- 
sues a  straight  course  towards  the 
apex  of  the  pyramid,  forming  the  so- 
called  descending  limb  of  Henle's 
loop.  Within  the  apical  portion  of  the 
pyramid  tlie  tubule  suddenly  bends 
upon  itself,  forming  the  loop  of  Henle, 
and  reversing  its  direction,  it  passes 
back  again  through  the  intermediate 
zone  into  the  medullary  ray  as  the 
ascending  limb  of  Henle's  loop.  This 
ascending  limb  exhibits  a  slight  spii'al 
twisting.  Leaving  the  medullary  ray, 
the  tubule  once  more  enters  the 
labyrinth,  where  its  outline  becomes 
so  uneven  that  the  name  irregular 
tubule  is  applied  to  it.  While  still 
within  the  labyrinth,  its  contour  hav^- 
ing  acquired  a  more  vmiform  appear- 
ance, the  tubule  receives  the  name  of 
second  convoluted  tubule  ;  this  latter 
finally  ends  in  a  short  junctional 
tubule,  which  passes  back  into  a 
medullary  ray  and  joins  a  collecting 
tube.  Each  collecting  tube  receives 
numerous  kidney  tubules,  and  pursues 
a  straight  course  through  a  medullary 
ray  and  pyramid.  Finally,  several  collecting  tubes,  uniting  together,  open  as  an 
excretory  tube,  by  one  of  the  foramina  papillaria,  on  the  surface  of  a  renal  papilla, 
into  a  calyx  of  the  ureter  (Fig.  806).  In  microscopic  sections  the  various  portions  of  the 
kidney  tubule  may  be  distinguished  by  the  position  which  they  occupy  and  by  the 
character  of  the  lining  epithelium. 

Connective  Tissue  of  the  Kidney. — The  tubules  and  the  blood-vessels  foi-ming  the 
substance  of  the  kidney  are  all  united  together  by  a  very  small  amount  of  connective 
tissue,  which  completely  surrounds  each  tubule  and  blood-vessel  and  binds  it  to  its 
neighbours.  It  has  been  found  possible  to  obtain  an  accurate  idea  of  the  arrangement  of 
this  connective  tissue  by  submitting  thin  sections  of  the  kidney  to  the  action  of  certain 
digestive  fluids.  When  this  is  done  the  tubules  and  blood-vessels  are  removed,  and  the 
connective  tissue  stroma  alone  is  left  behind  and  is  seen  to  form  a  continuous  network,  the 
spaces  in  which  faithfully  repi'oduce  the  outlines  and  the  arrangement  of  the  kidney 
tubules.     The  network  of  the  stroma  is  continuous  with  the  capsule  of  the  kidney. 


Loop  of 
Henle 

Efferent 
vessel 

Afferent 
vessel 


Fig, 


Glomerulus 
Capsule 


806. — Diagrammatic  representation  of  the 
Structures  forming  a  Kidney  Lobe. 


In  the  middle  part  of  the  figure  the  course  of  one  of  the  kidney 
tiibnles  is  indicated,  and  in  the  lateral  parts  the  disposition 
of  the  larger  arteries.  A,  Cortex  ;  B,  Intermediate  zone  ; 
C,  Papillary  portion. 

The  diagram  at  the  right-hand  side  of  the  lower  part  of  the 
figure  illustrates  the  connexions  of  the  structures  com- 
posing a  Malpighian  corpuscle. 


1140  THE  UPvINOGENITAL  SYSTEM. 

Vessels  of  the  Kidney. — The  renal  artery  is  very  large  in  proportion  to  the  size  of 
the  organ  to  which  it  conveys  blood.  Its  main  branches,  as  they  approach  the  kidney  to 
enter  the  hilum,  lie  between  the  tributaries  of  the  renal  vein  in  front,  and  the  ureter 
behind.  Within  the  sinus  of  the  kidney  the  branches  of  the  renal  artery  become 
arranged  in  a  dorsal  and  a  ventral  group,  the  dorsal  vessels  lying  behind,  the  ventral  ones 
in  front  of  the  subdivisions  of  the  ureter.  The  ventral  group  of  vessels  supplies  the  part 
of  the  kidney  which  forms  the  anterior  and  outer  walls  of  the  sinus ;  the  distribution  of 
the  dorsal  group  is  for  the  most  part  restricted  to  the  portion  of  the  kidney  which  lies 
behind,  and  to  the  inner  side  of,  the  sinus.  Entering  the  substance  of  the  kidney  in  the 
manner  described  above  (p.  1137),  the  larger  arteries  lie  in  the  intervals  between  the 
pyramids,  and  are  called  the  interlobar  arteries  (arterite  interlobares  renis).  These  vessels 
dividing,  form  a  series  of  incomplete  arterial  arches  (arterire  arciformes),  which  pass  across 
the  bases  of  the  pyramids.  Although  we  speak  of  arterial  arches,  it  must  be  understood 
that  no  anastomosis  between  the  branches  of  the  interlobar  arteries  actually  takes  place, 
but  that  each  artery  which  enters  the  wall  of  the  kidney  siniis  has  an  isolated  distribution 
and  possesses  the  characters  of  an  end  artery.  From  the  arches  two  chief  sets  of 
branches  come  off — those  of  one  set  are  continued  towards  the  periphery  and  enter  the 
labyrinth,  while  those  of  the  second  set  pursue  a  recurrent  course  and  enter  the 
intermediate  zone  of  the  medulla.  The  latter  vessels,  called  arteriolse  rectae,  give  rise  to 
the  coarsely-striated  appearance  which  this  part  of  the  kidney  exhibits  in  section.  Each 
of  these  vessels,  entering  the  medulla,  divides  into  a  number  of  fine  branches  which  run 
nearly  parallel  to  one  another,  and  supply  the  tubules  in  this  region  of  the  kidney.  The 
vessels  directed  outwards,  or  interlobular  arteries  (arterise  interlobulares),  pass  through  the 
labyrinth  towards  the  surface  of  the  kidney.  They  give  off  a  number  of  short  branches, 
termed  vasa  afferentia,  each  of  which  proceeds  to  the  dilated  extremity,  or  capsule,  of  a 
uriniferous  tubule.  Here  the  vas  afFerens  breaks  up  into  a  much  convoluted  capillary  mass, 
called  a  glomerulus,  which  is  contained  within  the  invagination  of  the  capsule.  The  little 
vein  which  issues  from  the  glomerulus,  or  vas  eflferens,  instead  of  running  directly  into  a 
larger  vein  breaks  up,  after  the  manner  of  an  artery,  into  capillaries  which  supply  the 
tubules  of  the  labyrinth  and  medullary  rays.  Hence  almost  all  the  blood  which  supplies 
the  tubules  of  the  cortical  part  of  the  kidney  passes  in  the  first  instance  through  the 
glomeruli.  Some  of  the  tubules  of  the  intermediate  zone  also  receive  their  blood-supply 
through  vasa  efFerentia  derived  from  the  glomeruli  which  lie  near.  These  little  vessels 
passing  from  glomeruli  into  the  intermediate  zone  of  the  medulla  accompany  the  arteriolse 
rectte  and  ai-e  sometimes  spoken  of  as  false  arteriolse  rectse. 

The  fibrous  capsule  of  the  kidney  receives  minute  branches  from  the  interlobidar 
arteries,  some  of  which,  piercing  the  capsule,  communicate  by  capillaries  with  the  vessels  of 
the  tunica  adiposa. 

Veins  corresponding  to  the  interlobular  arteries  and  arteriolse  rectse  collect  the  blood 
from  the  capillaries  surrounding  the  tubules,  and  unite  to  form  a  series  of  complete  arches 
across  the  bases  of  the  jjyramids.  From  these  venous  arcades  vessels  arise,  which  traverse 
the  intervals  between  the  j^yramids  and  reach  the  sinus  of  the  kidney,  where  they  unite 
to  form  the  dorsal  and  ventral  tributaries  of  the  renal  vein.  Some  small  veins  in  the 
superficial  part  of  the  cortex  communicate  through  the  fibrous  capsule  with  minute  veins 
in  the  tunica  adiposa. 

Nerves  of  the  Kidney. — The  nerves  of  the  kidney  accompany  the  branches  of  the 
artery,  and  issue  from  the  renal  plexus. 

From  clinical  evidence  it  would  appear  that  the  nerve  fibres  which  reach  the  kidney  are . 
derived  from  the  tenth,  eleventh,  and  twelfth  thoracic  nerves.     The  minute  branches  of  the- 
nerves  form  regular  net-like  plexuses  on  the  walls  of  the  fine  arteries  and  kidney  tubules, 
and  the  presence  of  nerve  terminations  occurring  among  the  epithelial  cells  lining  the 
tubules  has  recently  been  demonstrated. 

Variations. — A  marked  difference  in  the  size  of  the  two  kidneys  is  sometimes  observed, 
a  small  kidney  on  one  side  of  the  body  being  usually  compensated  for  by  a  large  kidney  on  the 
opposite  side.     Cases  of  complete  absence  of  one  or  other  kidney  are  recorded. 

Traces  of  the  superficial  lobulation  of  the  kidney,  present  in  the  foetus  and  young  child,  are 
often  retained  in  tlie  adult. 

Horse-shoe  kidney  is  not  an  infrequent  abnormality.  In  these  cases  the  two  kidneys  are 
united  at  their  lower  ends,  across  the  middle  line,  by  a  connecting  piece  of  kidney  substance. 
The  amount  of  fusion  between  the  two  kidneys  varies  much  ;  it  is  sometimes  very  complete, 
while  in  other  cases  it  is  but  slight,  the  connexion  being  chiefly  composed  of  fibrous  tissue. 

In  very  rare  cases  the  kidney  appears  to  be  almost  entirely  surrounded  by  peritoneum  and  to 
be  attaclied  to  the  abdominal  wall  by  a  kind  of  mesentery,  enclosing  the  vessels  and  nerves  passing 
to  the  hiluui.     The  condition  is  believed  to  be  congenital. 


THE  DUCT 'OF  THE  KIDNEY. 


lUl 


Not  very  infrequent ly  one  or  both  kidneys  are  found  at  a  much  lower  level  lliau  usual,  and 
occupying  a  position  in  the  iliac  fossa  or  the  pelvic  cavity.  This  condition,  wlien  congciuital,  is 
associated  with  an  arrest  in  the  normal  change  in  position,  relative  to  surrounding  structures, 
which  the  kidney  experiences  during  development.  In  such  cases  the  kidney  does  not 
receive  its  blood  supply  from  usually  placed  renal  arteries,  but  from  vessels  wliich  arise  from 
the  lower  end  of  the  aorta,  or  from  tlie  iliac,  or  the  middle  sacral  artery.  These  congenitally 
abnormally  situated  kidneys  do  not  usually  possess  the  typical  outline  of  the  normal  organ,  but 
vary  much  in  shape,  and  the  hilum  is  often  directed  downwards  and  not  inwards. 

In  some  mammalian  animals,  sucli  as  the  bear,  the  ox,  the  porpoise,  etc.,  the  kidneys  are  com- 
posed of  a  number  of  completely  isolated  lobes,  each  of  whicli  corresponds  to  one  })aj)illa,  its 
pyramids  and  surrounding  cortex  ;  while  in  others,  such  as  the  horse,  the  fusion  of  tlie  lolies  is 
more  complete  even  than  in  the  liuman  kidney,  and  a  single  mass  represents  the  united  jjapillse. 


Interlobar"! 
vessel / 
Pyraniid 

Intermediate 
zone 


Papilla 


The  Duct  of  the  Kidney. 

The  duct  of  the  kitlney  begins  above  in  a  thin-walled  funnel-shaped  expauKion 
called  the  pelvis  (pel\  is  renalis),  placed  partly  within  and  partly  outside  the  sinus 
of  the  kidney.  Towards  t!ie  level  of  the  lower  end  of  the  kidney  the  part  of  the 
pelvis  which  lies  outside  the  sinus  diminishes  in  calibre,  and  I'orm-;  a  tube  termed 
the  ureter  (Fig.  807). 

Pelvis  of  the  Kidney. — Within  the  sinus  of  the  kidney  the  pelvis  lies  for  the 
most  part  behind  the  larger  renal  vessels,  and  is  formed  by  the  junction  of  two,  or 
more  rarely  three,  thin -walled 
tubes  (calyces  majores),  each  of 
which  has  a  number  of  branches. 
These  latter,  called  infundibula, 
or  calyces  (calyces  renales),  are 
short,  and  increase  in  diameter 
as  they  approach  the  sinus  wall. 
Their  wide,  somewhat  funnel- 
like ends  enclose  the  renal 
papilke,the  secretion  from  which 
they  receive  and  conduct  to  the 
pelvis.  The  calyces  are  usually 
about  twelve  in  number,  one 
calyx  sometimes  surrounding- 
two  or  even  three  papilkie.  The 
portion  of  the  pelvis  that  lies 
outside  the  kidney  has  in  front 
of  it,  in  addition  to  the  renal 
vessels,  on  the  right  side  the 
second  part  of  the  duodenum, 
and  on  the  left  side  a  part  of 
the  pancreas  and  sometimes 
the  duodeno- jejunal  flexure 
(Fig.  794). 

Ureter. — The  ureter  is  the  vessel  which  carries  the  urine  from  the  pelvis  of  the 
kidney  to  the  bladder.  It  is  a  pale-coloured  thick-walled  duct  with  a  small  lumen. 
While  in  situ  it  has  a  total  length  of  about  ten  inches,  and  lies  throughout  its 
whole  course  behind  the  peritoneum,  to  which  it  is  closely  connected,  in  the  sub- 
peritoneal tissue.  In  its  upper  part  the  ureter  lies  in  the  abdominal  cavity,  and  in 
its  lower  part  in  the  pelvic  cavity  (Figs.  79^,  794,  and  808). 

Tlie  normal  ureter,  in  the  flaccid  condition,  measures  after  its  removal  from  the  body  eleven 
to  fourteen  inches. 

The, abdominal  portion  of  the  ureter  (pars  abdominalis),  about  five  or  five  and  a 
half  inches  in  length,  is  directed  downwards  and  slightly  inwards,  and  lies  upon  the 
psoas  muscle.  Certain  structures  are  related  to  the  ureters  in  a  similar  manner  on 
each  side  of  the  body ;  for  instance,  the  abdominal  portion  of  each  ureter  is  crossed 
very  obliquely,  on  ]ts  anterior  aspect,  by  the  spermatic  or  ovarian  vessels,  and 
behind  each  duct  the  genito-crural  nerve  passes  downwards  and  outwards.     Other 


—Longitudinal  Section  of  the  Kidney,  opening  c 
THE  Kidney  Sinus. 

The  pelvis  of  the  ureter  and  some  of  its  calj^ces  have  heen  laid 
open  as  they  lie  within  the  sinus. 


1142 


THE  UEINOGENITAL  SYSTEM. 


structures  are  related  to  the  duct  of  the  right  or  left  side  alone ;  on  the  right  side 
the  descending,  or  second,  part  of  the  duodenum  lies  in  front  of  the  upper  part  of  the 
ureter,  and  the  line  of  attachment  of  the  mesentery  crosses  it  lower  down,  just  before 
the  vessel  enters  the  pelvic  cavity.-  On  the  left  side  of  the  body  the  line  of  attach- 
ment of  the  mesentery  of  the  pelvic  colon  crosses  the  ureter. 

Crossing  the  common  iliac,  or  the  external  iliac  artery,  the  ureter  enters  the 
pelvis.  The  left  ureter  more  usually  crosses  the  common  iliac  artery,  the  right 
vessel  in  most  cases  lies  across  the  external  iliac,  but  this  arrangement  is  by  no 
means  constant. 

The  pelvic  portion  of  the  ureter  (pars  pelvina)  is  about  four  or  four  and  a  half 
inches  in  length,  and  passes  downwards  on  the  side  wall  of  the  pelvis,  immediately 
beneath  the  peritoneum,  describing  a  curve  which  is  convex  backwards  and  outwards 
(Fig.   808).       The  most  convex  portion  of  this  curve   lies  close  to  the  deepest 


Obturator  fns'ja 
External  iliac  vessels 
Obturator  nervp 
Obliterated  hypogastric 
arterj 
Vas  deferens! 


Position  of  internal  iliac 
artery. 


Plica  ■) 

iiinbilicalis 

lateralis  J 

Obturator  ) 

vessels  I 

Paravesical  1 

fossa  J 

Plica  1 

vesicalis 

transversa  ) 


Symphysis 
pubis 


^^  / 

Pi  estate 

Opening  of  ureter  into  bladder  / 

Portions  of  vasa  deferentia  cut  in  section 

Fig.  808. — Mesial  Section  of  an  Adult  Male  Pelvis. 

The  coils  of  the  small  intestine  which  lay  within  the  jielvis  have  been  lifted  out  in  order  to  give  a  view  of  the 
side  wall  of  the  pelvic  cavity.  The  peritoneum  is  coloured  blue.  The  separation  of  the  bladder  from 
the  prostate  is  indicated  somewhat  diagrammatically. 

part  of  the  great  sciatic  notch  (Figs.  831  and  854).  In  its  course  within  the 
pelvis  the  ureter  lies  in  front  of  the  internal  iliac  artery,  and  crosses  the  inuer  aspect 
of  the  obturator  nerve  and  vessels  and  of  the  obliterated  hypogastric  artery.  About 
the  level  of  the  ischial  spine  the  ureter  bends  somewhat  inwards  above  the  fascia  of 
the  pelvic  floor,  to  reach  the  bladder,  and  in  this  position  it  is  crossed  on  its  inner 
side  by  the  vas  deferens.  A  little  further  on  in  its  course  the  ureter  comes  into 
relationship  with  the  upper  end  of  the  vesicula  seminalis,  in  front  of  which  it  lies 
as  it  pierces  the  bladder  wall.  The  ureter,  as  it  passes  inwards  to  the  bladder,  is 
placed  on  an  anterior  and  deeper  plane  than  the  vas  deferens,  and  is  surrounded  by 
a  dense  plexus  of  veins,  connecting  the  vesical  and  prostatic  plexuses  with  the 
internal  iliac  vein.  "When  the  right  and  left  ureters  reach  the  bladder  they  are  a 
little  more  than  two  inches  apart  and  they  pierce  the  bladder  wall  very  obliquely, 
lying  embedded  within  its  muscular  tissue  for  nearly  three  quarters  of  an 
inch  of  their  length.     Finally,  they  open  into  the  bladder  by  two  small  slit-lilce 


THE  DUCT  DF  THE  KIDNEY.  1143 

apertures  which  are  of  a  valvular  nature,  and  prevent  a  backward  passage  of  fluid 
from  the  bladder.  It  is  probable,  however,  that  an  exaggerated  idea  of  the 
valvular  nature  of  the  openings  of  the  ureters  into  the  bladder  is  obtained  by  an 
examination  of  the  parts  in  the  dead  subject.  When  the  })ladder  is  empty  the 
openings  of  the  ureters  are  placed  at  about  one  inch  apart,  but  when  that  viscus  is 
distended  they  are  often  two  inches,  or  more,  distant  from  one  another.  As  the 
ureter  pierces  the  bladder- wall  the  muscular  fibres  of  the  bladder  and  ureter  remain 
quite  distinct,  and  so  the  ureter,  remaining  a  thick -walled  tubular  structure, 
appears  to  pass  through  a  gap  in  the  muscular  wall  of  the  bladder.  The  mucous 
coat  alone  of  the  ureter  becomes  continuous  with  that  of  the  bladder. 

The  triangular  district  on  the  side  wall  of  the  pelvis,  which  is  bounded  behind  by  the 
ureter,  below  by  the  vas  deferens,  and  above  by  the  external  iliac  vessels  and  pelvic  brim, 
is  called  the  obturator  fossa. 

The  canal  of  the  ureter  is  not  uniform  throughout  but  is  somewhat  constricted 
in  certain  places,  corresponding  to  the  regions  where  the  ureter  is  most  sharply 
curved,  or  changes  its  direction.  These  more  constricted  parts  of  the  tube  are 
described  as  occurring  one  in  the  middle  of  the  abdominal  portion,  one  at  the 
^"unction  of  abdominal  and  pelvic  portions,  and  one  in  the  pelvic  part  of  the  ureter. 
Also  just  before  the  ureter  joins  the  pelvis  of  the  kidney  and  just  as  it  reaches  the 
bladder  wall  its  lumen  is  usually  somewhat  constricted. 

In  the  female,  the  ureter,  near  its  termination,  passes  beneath  the  lower  part  of 
the  broaiUigament  of  the  uterus  and  lies  to  the  outer  side  of  the  cervix  uteri  and 
upper  part  of  the  lateral  wall  of  the  vagina.  It  is  accompanied  in  the  lower  part  of 
its  course  by  the  uterine  artery,  which  crosses  it  on  its  anterior  aspect  not  far  from 
its  termination.  Higher  up  it  lies  in  the  peritoneal  ridge  which  forms  the  posterior 
and  lower  boundarv  of  the  fossa  ovarica,  a  posterior  subdivision  of  the  obturator 
fossa  (Fig.  824). 

Structure  of  the  Ureter. — The  wall  of  the  ureter  is  thick  and  of  a  whitish 
colour  and  is  composed  of  mucous,  muscular,  and  fibrous  coats.     The  mucous  coat 
(tunica  mucosa)  of  the  ureter  possesses  an  epithelium  composed  of  many  layers  of 
cells,  those  nearest  the  surface  being  of  large  size.     When  the  canal  is  empty  the 
mucous  coat  is  thrown  into  numerous  longitudinal  folds,  and  so  its  lumen  exhibits 
a  stellate  outline  in  transverse  section.      The  submucous  tissue  varies  much  in 
thickness  in  different  parts  of  the  ureter  and  contains  some  elastic  fibres.     The 
unstriated  muscle  fibres  which  compose  the  muscular  coat  (tunica  muscularis)  are 
collected  into  bundles  which  are  separated  by  a  considerable  amount  of  connective 
tissue  and   are  arranged,  some  longitudinally,  some   circularly.      In    the   upper 
part  of  the  ureter  a  relatively  large   amount   of  connnective  tissue   is  present 
deep  to,  and  among  the  bundles  of  muscle  fibres  which  are  arranged  in  three 
distinct   strata — an   inner  longitudinal,  an   intermediate   circular,  and  an  outer 
longitudinal.     In  the  middle  part  of  the  vessel  the  same  layers  may  be  recognised, 
but  the  circularly  disposed  bundle  of  fibres  are  more  numerous  than  higher  up. 
In  the  lower  part  of  the  ureter  the  connective  tissue  is  relatively  scanty  and  the 
inner  longitudinal  fibres  lie  close  to  the  lining  epithelium ;  in  this  region  also  the 
longitudinal  folds  of  the  mucous  coat  become  fewer  and  less  marked.     A  short 
distance  above  the  point  where  it  reaches   the  bladder,  the  wall  of  the  ureter 
becomes   much*  thickened   by  the   addition   of  a   number   of  coarse   bundles   of 
longitudinally  arranged  muscle  fibres,  which  are  applied  to  the  outer  surface  of  the 
muscular  coat.     These  muscle  fibres  form  the  so-called  "  sheath  of  the  ureter,"  and 
are  continued  on  the  superficial  aspect  of  the  vessel  as  it  passes  through  the  bladder 
wall.     In  the  portion  of  the  ureter  which  traverses  the  wall  of  the  bladder  (pars 
intramurahs)  nearly  all  the  fibres  of  the  muscular  coat  are  disposed  longitudinally 
or  in  a  direction  parallel  to  that  of  the  vessel.     The  muscle  fibres  lie  close  beneath 
the  epithelium,  and  end  just  where  the  mucous  coats  of  the  bladder  and  ureter 
become  continuous.     The  outer  fibrous  coat  (tunica  adventitia)  of  the  ureter  varies 
in  thickness  at  different  levels,  and  in  its  lower  part  blends  with  the  connective 
tissue,  which  lies  among  the  muscle  fibres  forming  the  sheath  of  the  ureter  just 
mentioned  above. 


1144  THE  UEINOGENITAL  SYSTEM. 

The  mucous  membrane  of  the  calyces  and  of  the  pelvis  of  the  kidney  possesses  an 
epithelium  resembling  that  of  the  ureter.  Where  each  renal  papilla  projects  into 
one  of  the  calyces  a  deep  circular  recess,  or  fornix,  is  formed  between  the  wall  of 
the  calyx  and  the  sloping  side  of  the  papilla ;  at  the  bottom  of  this  recess  the 
epithelium  of  the  calyx  becomes  continuous  with  that  covering  the  papilla.  At 
the  tormina  papillaria  the  epithelium  joins  that  of  the  kidney  tubules.  The 
muscular  fibres  in  the  wall  of  the  calyces  and  of  the  pelvis  are  collected  into  loosely 
arranged  bundles  separated  by  wide  intervals  occupied  by  fibrous  connective  tissue. 
As  in  the  ureter,  the  outermost  and  innermost  fibres  run  in  a  longitudinal,  the 
intermediate  ones  in  a  circular  direction.  The  circularly  arranged  fibres  alone 
form  a  distinct  layer. 

The  abdominal  part  of  the  ureter  receives  its  blood  supply  from  the  renal  and 
spermatic  arteries ;  the  pelvic  portion  is  supplied  by  the  superior  vesical  and 
middle  hsemorrhoidal  vessels. 

The  nerves  of  the  ureter  reach  it  through  the  renal,  the  spermatic,  and  the 
hypogastric  plexuses. 

Variations. — The  ureter  is  sometimes  represented  by  two  tubes  in  its  upper  portion.     In  rarer 
cases  it  is  double  througliout  the  greater  part  of  its  extent,  or  even  its  whole  length  from  the 
pelvis  of  the  kidney  to  the  bladder.     In  such  cases  there  may  be  two  ojaenings  into  the  bladder.^ 
Asymmetry  as  regards  such  alanormalities  is  very  common. 

Variations  in  the  form  of  the  pelvis  of  the  kidney  are  of  frequent  occurrence.  Most  usually 
the  pelvis  divides  into  two  large  subdivisions,  one  of  wliich  jDasses  in  the  direction  of  the  upper, 
the  other  in  that  of  the  lower  23ole  of  the  kidney.  In  some  cases  these  branches  come  off  directly 
from  the  ureter  without  the  intervention  of  a  pelvis,  or  a  subdivision  may  lead  to  the  formation 
of  two  pelves. 

THE  BLADDER 

The  bladder  (vesica  urinaria)  is  a  hollow  muscular  organ  situated  in  the  anterior 
part  of  the  pelvic  cavity,  behind  the  symphysis  pubis.  It  lies  in  front  of  the 
rectum,  from  which  it  is  separated  i7i  the  male  by  the  seminal  vesicles  and  the 
terminal  portions  of  the  vasa  deferentia,  and  in  the  female  by  the  vagina  and 
uterus.  The  bladder  wall  is  chiefly  composed  of  muscular  tissue,  and  its  thickness 
and  the  size  of  the  contained  cavity  depends  on  the  amount  of  fluid  within  the 
organ.  The  right  and  left  ureters  which  convey  the  fluid  secreted  by  the  kidneys 
open  into  the  lower  and  under  part  of  the  bladder  about  half  an  inch  from  the 
mesial  plane ;  also  the  urethra,  or  canal  by  which  the  urine  reaches  the  surface, 
opens  into  the  bladder,  its  aperture  lying  in  the  middle  line  of  the  under  part  of 
the  bladder  wall,  not  far  from  the  openings  of  the  ureters,  but  on  a  lower  and 
anterior  plane.  The  size  and  shape  of  the  bladder,  and  also  to  a  great  extent  its 
relations,  vary  with  the  amount  of  distension,  or  contraction,  of  the  organ.  When 
the  bladder  is  empty,  or  only  slightly  distended,  it  lies  within  the  pelvic  cavity ; 
as  it  becomes  filled  with  urine  it  rises  above  the  pubis,  and,  crossing  the  pelvic 
brim,  enters  the  abdominal  cavity.  Tliese  changes  affect  chiefly  the  upper  part  of 
the  bladder,  which  becomes  altered  in  shape  and  size,  and  acquires  new  connexions 
and  relations ;  the  lower  portion  varies  but  slightly  with  the  amount  of  distension 
of  the  organ  (see  Figs.  809  and  810).  The  position  occupied  by  the  bladder 
depends,  to  a  certain  extent,  on  the  condition  of  the  rectum,  for  when  the  lower 
part  of  the  rectum  is  distended,  the  bladder  as  a  whole  is  thrust  somewhat  upwards 
and  forwards.  The  upper  part  of  the  bladder  is  covered  by  peritoneum,  which  is 
reflected  on  to  it  from  the  anterior  abdominal  wall  in  front,  from  the  sides  of  the 
pelvis  laterally,  and,  in  the  male,  across  the  seminal  vesicles  and  terminal  parts  of 
the  vasa  deferentia  from  the  rectum  behind.  In  the  female  the  peritoneum  passes 
on  to  the  bladder  posteriorly  from  the  anterior  surface  of  the  uterus.  The 
peritoneum  dips  down  posteriorly  for  a  certain  distance  between  the  bladder  and 
rectum  in  the  male,  forming  the  recto-vesical  or  recto-genital  pouch ;  in  the  female 
a  slit-like  peritoneal  depression,  called  the  utero-vesical  pouch,  intervenes  between 
the  anterior  surface  of  the  uterus  and  the  bladder  (Fig.  818).  The  under  part  of 
the  bladder  whicli  lies  below  the  peritoneum  is  for  the  most  part  directed  towards 
the  pelvic  floor.     In  the  middle  line  it  is  supported  ])y  the  sympliysis  pubis  and  the 


THE  ^LADDER. 


1145 


retro-pubic  pad  of  fat ;  further  back  in  the  male  it  rests  upon  the  prostate  and  on 
the  lower  part  of  the  rectum,  from  which  latter  it  is  separated  by  the  vesicuhe 
seminales  and  the  terminal  parts  of  the  vasa  deferentia.  In  the  female  it  rests 
upon  the  anterior  wall  of  the  vagina.     Laterally  the  bladder  is  supported  by  the 


First  sacral  vertebra 


Symphysis  pubis 
Prostate 


Bulb  of  urethra 


Bulbo-cavernosus 
lauscli 


Recto-vesical 
peritoneal  reflexion 
Cavity  of  bladder 


Vas  deferens 
Rectum 


Compressor  urethra 
External  sphincter  ani 

j-Intemal  sphincter  anl 
Axial  canal 


External  sphincter  ani 


Mesial  Section  through  the  Male  Pelvis. 


The  Ijladder  contains  but  a  small  aniouiit  of  fluid.  The  separation  between  the  bladder  and  prostate  is  shown 
somewhat  diagi-animatically.  Drawn  from  a  preparation  in  the  Anatomical  Department,  Trinity  College, 
Dublin. 

levatores  ani  muscles,  and  further  from  the  middle  line  it  is  in  contact  on  each 
side  with  the  obturator  internus ;  it  is  separated  from  both  of  these  muscles  by  a 
layer  of  the  pelvic  fascia. 

The  opening  of  the  urethra,  or  internal  urethral  orifice  (orificium  urethras 
internum),  is  placed  in  or  near  the  part  of  the  bladder  wall  which  lies  lowest  in 
the  pelvic  cavity.  The  term  neck  or  cervix,  is  often  applied  to  this  region,  the 
bladder  appearing  as  if  it  were  suddenly  constricted  here  to  form  the  urethra.  The 
portion  of  the  bladder  wall  behind  the  urethral  orifice,  which  is  directed  in  the 
male  towards  the  anterior  wall  of  the  rectum  and  lies  below  and  in  front  of  the 
recto-vesical  pouch,  is  called  the  base  of  the  bladder  (fundus  vesicas) ;  it  is  closely 
related  to  the  seminal  vessels  and  ampullae  of  the  vasa  deferentia.  The  correspond- 
ing part  of  the  bladder  in  the  female  rests  against  the  anterior  wall  of  the  vagina. 
The  term  apex,  or  summit  of  the  bladder  (vertex  vesicas)  is  applied  to  the  portion 
which  lies  nearest  to  the  upper  border  of  the  symphysis  when  the  organ  is  empty, 
and  rises  high  above  the  pubis  into  the  abdominal  cavity  when  the  bladder  is 
distended.  Connected  with  the  apex  of  the  bladder  is  a  fibrous  cord  (ligamentum 
umbilicale  medium)  which  passing  upwards,  in  the  middle  line,  on  the  posterior 
aspect  of  the  anterior  abdominal  wall  reaches  the  umbilicus,  and  represents  the 
77 


1146 


THE  URINOGENITAL  SYSTEM. 


urachus,  or  portion  of  the  allantois  retaiued  within  the  body  of  the  developing 
embryo.  The  part  of  the  bladder  connecting  the  apex  with  the  base,  and  not 
sharply  marked  off  from  either,  is  called  the  body,  or  corpus  vesicae. 

Position  of  the  Urethral  Orifice. — During  the  various  changes  in  shape  and 
size  which  the  bladder  undergoes,  the  region  of  the  urethral  orifice  remains  almost 


External 
sphincter  ani 
Anal  canal 
"^Bulb  of  uretbra 
External 
sphincter  ani 


Fro.  810. — Mksial  Section  of  the  Male  Pelvis. 

The  bla'liler  lias  been  artiticially  distended.      From  a  specimen  in  the  Anatomical  Department, 

Trinity  College,  Dublin. 

fixed  in  position.  The  comparatively  slight  variations  in  the  level  of  the  internal 
urethral  orifice  which  do  occur,  depend  partly  upon  the  quantity  of  fluid  contained 
in  the  bladder,  and  partly  upon  the  amount  of  distension  of  the  lower  portion  of 
the  rectum.  When  the  bladder  is  very  much  distended  this  region  lies  at  a  slightly 
lower  level  in  the  pelvis  than  it  does  when  the  organ  is  empty ;  and,  on  the  other 
hand,  distension  of  the  lower  part  of  the  rectum  raises,  to  some  extent,  the  level  of 
the  urethral  orifice.  The  urethral  orifice  lies  immediately  above  the  prostate,  and 
behind  and  slightly  below  the  level  of  the  upper  margin  of  the  symphysis  pubis, 
from  which  it  is  distant  about  two  to  two  and  a  half  inches.  It  can  be  easily 
reached  by  a  finger  introduced  into  the  bladder  through  the  abdominal  wall  above 
the  symphysis  pubis.  It  is  usually  placed  half  an  inch  to  one  inch  above  the  level 
of  a  plane  passing  through  the  lower  margin  of  the  symphysis  and  the  lower  end 
of  the  sacrum,  but  in  some  cases  it  is  found  to  be  somewhat  lower.  In  the  female 
it  normally  occupies  a  lower  level  than  in  the  male.  Since  the  position  of  the 
internal  urethral  orifice  varies,  in  the  manner  above  described,  with  the  condition 
of  the  rectum  and  of  the  bladder  itself,  it  follows  that  it  lies  at  its  lowest  limit 


THE  BLADDEK. 


1147 


Bladder  apex 


when  the  bladder  is  full  and  the  rectum  empty,  and  at  its  highest  level  when  the 
bladder  is  empty  and  the  rectum  distended. 

Under  Aspect  of  the  Bladder. — The  lower  part  of  the  bladder,  which  is  directed 
towards  the  pelvic  floor,  changes,  as  we  have  seen,  but  slightly  with  the  varying 
amount  of  distension  of  the  viscus.  When  the  organ  has  been  carefully  hardened 
before  its  removal  from  the  body,  it  is  possible  to  map  out  on  its  under  aspect  three 
convex  triangular  areas,  which  may  be 
distinguished  from  one  another  by  the 
directions  in  which  they  look.  The 
three  areas  approach  one  another  in 
the  region  of  the  urethral  orifice,  where, 
in  the  male,  a  portion  of  the  under 
aspect  of  the  bladder  wall  is  structurally 
continuous  with  the  upper  part  of  the 
prostate.  Behind  the  urethral  orifice 
is  a  triangular  district,  directed  down- 
wards and  backwards,  and  related,  in 
the  male,  to  the  seminal  vesicles  and 
the  terminal  portions  of  the  vasa  de- 
ferentia  which,  together  with  the  recto- 
vesical layer  of  the  pelvic  fascia,  inter- 


— Lateral  border 


Infero-lateral 
area 


Area  continuous 
with  prostate 


Base  of  bladder 


Fl<; 


Inferorlateral 
areS: 


811. — Under  Aspect  ok  the  empty  Male  Bladdku 
from  a  subject  in  which  the  viscera  had  been  har- 
dened 111  situ. 
vene  in  tllis position  between  the  bladder    The  prostate  has  been  severed  from  the  bladder,  and  the 

and  the  rectum.     This  triangular  area         ^t"'  T\  '""  *!>« /'■^^^^^g  indicates  the  position 

o  where  the  two  structures  were  continuous. 

ot  the  bladder  wall  is  known  as  the  base, 

or  postero- inferior  surface  of  the  bladder,  and  in  the  female  it  is  directed  against  the 
anterior  wall  of  the  vagina.  The  rest  of  the  under  aspect  of  the  bladder  is  formed 
by  two  infero-lateral  areas,  or  surfaces,  which  meet  in  the  middle  line  in  front  of  the 
urethral  orifice,  and  are  directed  for  the  most  part  downwards  and  outwards 
(see    Fig.   811).      Each    of  these   areas   extends   backwards  to  join    the  postero- 

„,  , ,  inferior  surface, or  base,alonc^  a  rounded 

Bladder  apex  i   •    i      i-  ^  ^     i 

border  which  lies  between  the  point 
where  the  ureter  reaches  the  bladder 
and  the  urethral  orifice.  The  infero- 
lateral  part  of  the  bladder  wall  rests 
against  the  fascia  covering  the  levator 
ani  and  the  obturator  internus  muscles, 
and,  nearer  the  middle  line,  upon  the 
pubes  and  retro- pubic  pad  of  fat. 

The  three  rounded  borders  which 
mark  off  the  three  triangular  areas  on 
the  under  aspect  of  the  bladder,  just 
described,  extend  from  the  region  of- 
the  urethral  orifice  to  the  bladder 
apex,  and  to  the  points  where  the 
ureters  reach  the  bladder  wall  (see 
Fig.  811). 

Shape  and  Relations  of  the  Empty 
Bladder. — When  the  bladder  is  empty, 
or  nearly so,it  has,roughlyspeaking,the 
shape  of  an  inverted  tetrahedron,  w^hose 
apex  corresponds  to  the  point  where  the  urethra  leaves  the  organ,  while  the  base 
of  the  tetrahedron  is  formed  by  the  superior  surface  of  the  bladder.  The  three 
basal  angles  of  the  tetrahedron  correspond  to  the  bladder  apex  and  to  the  two 
lateral  angles  of  the  bladder,  or  points  where  the  ureters  join  the  organ.  The  three 
surfaces,  which  meet  inferiorly  at  the  urethral  orifice,  are  only  marked  off  from  one 
another  by  rounded  borders,  but  as  long  as  the  organ  is  empty,  or  nearly  so,  they 
are  separated  by  distinct  borders  from  the  superior  surface.  These  three  areas 
have  been  already  described  as  the  infero-lateral  surfaces  and  the  base  of  the 
bladder  (Figs.  811  and   812).     Their   relations   have   also   been    indicated.     The 


Posterior  surface  of  prostate 

Seminal  vesicle 
Fig.  812; — ^The  Bladder,  Prostate,  and  Seminal 
Vesicles,  viewed  from  below. 

Taken  from  a  subject  in  which  the  viscera  were  hardened 
in  situ.  Same  specimen  as  figure  813,  A.  The 
bladder  contained  but  a  small  amount  of  fluid. 


1148 


THE  UEINOGENITAL  SYSTEM. 


superior  surface  of  the  empty  bladder  looks  upwards  into  the  pelvic  cavity ;  it  is 
convex  when  the  organ  is  contracted,  concave  when  relaxed.  This  surface  is  covered 
by  peritoneum,  and  its  outline,  which  is  approximately  triangular,  is  determined 
by  lateral  and  posterior  borders  (Fig.  829;.  The  lateral  borders  of  the  empty 
bladder  are  sharply  marked,  and  extend  from  the  bladder  apex  to  the  lateral  angles 
of  the  bladder,  or  points  where  the  ureters  join  the  organ.  They  separate  the 
superior  surface  from  the  infero-lateral  portions  of  the  under  aspect  of  the  bladder 
wall  (Fig.  813,  A).  The  posterior  border  stretches  across  between  the  lateral  angles 
of  the  bladder,  and  separates  the  superior  from  the  basal  surface  of  the  viscus.  The 
superior  surface  is  related  in  the  male  to  coils  of  intestine;  in  the  female  it  is 
also  related  to  the  anterior  surface  of  the  uterus.  The  lateral  border  of  the  empty 
bladder  lies  against  the  pelvic  fascia  just  above,  or  at  the  level  of  the  upper  limit 
of  the  levator  ani  muscle.     The  vas  deferens  crosses  the  side  wall  of  the  pelvis 


hiis 


Lateral  aspect 
of  prostate 


Infero-lateral 
area  of  bladder 


Fig.  813. — The  Bladder,  Prostate,  and  Seminal  Vesicle,  viewed  from  the  Outer  Side. 

Drawn  from  specimens  in  which  the  viscera  were  hardened  before  removal  from  the  body.  In  A  the  bladder 
contained  but  a  very  small  quantity  of  fliuid  ;  in  B  the  quantity  was  somewhat  greater.  In  A  the 
peritoneum  is  shown  covering  the  upper  surface  of  the  bladder,  and  its  cut  edge  is  seen  where  it  is 
reflected  along  the  lateral  border  of  the  organ.  In  B  the  level  of  the  jjeritoneal  reflexion  is  indicated 
by  a  dotted  line. 

parallel  to  it,  but  at  a  considerably  higher  level;  In  mesial  section  the  cavity  of 
the  empty  and  relaxed  bladder  often  presents  the  appearance  of  a  Y-shaped  chink, 
the  stem  of  the  Y  being  represented  by  the  urethra  as  it  leaves  the  organ,  and  the  two 
limbs  by  the  narrow  intervals  between  the  superior  surface  and  the  under  parts  of 
the  bladder  wall  which  lie  in  front  of  and  behind  the  urethral  orifice.  This  relaxed 
form  is  sometimes  described  as  the  diastolic  condition  of  the  empty  bladder,  and  is 
found  associated  with  a  bladder  wall  of  but  little  thickness,  and  a  concave  upper 
surface.  The  condition  is  usually  the  result  of  an  escape  of  fluid  after  death, 
when  the  bladder  wall  has  lost  the  power  of  contracting.  It  certainly  does  not 
represent  a  normal  condition  of  the  organ  in  the  living.  The  normal  empty 
bladder  is  strongly  contracted,  and  its  wall  is  thick  and  firm.  A  distinctly 
Y-shaped  appearance  is  not  presented  by  its  cavity  in  mesial  section,  but  the 
interior  of  the  organ  is  seen  as  a  simple  narrow  interval  continuous  with  the  canal 
of  the  urethra. 

Distended  Bladder. — As  the  bladder  fills  with  fluid  the  superior  wall  is 
raised  upwards  from  the  intero-lateral  and  basal  walls,  and,  at  the  same  time,  the 
borders  separating  the  superior  from  the  other  surfaces  of  the  bladder  become  at 
first  more  rounded  and  then  obliterated.  The  lateral  borders  of  the  bladder, 
becoming  in  this  manner  opened  out,  give  rise  to  so-called  lateral  surfaces  in 
the  distended  organ.  These  surfaces,  however,  are  not  sharply  marked  off, 
and  are  directly  continuous  with  the  superior  surface.  During  distension, 
also,  the  angles  present  in  the  empty  condition  of  the  organ  become  rounded 
as  the  entire  bladder  wall  becomes  more  uniformly  convex.  The  general 
shape  of  the  bladder  becomes  altered  during  distensioii  —  from  the  tetrahedral 
form  of  the  empty  organ,  already  descril^ed,  the  bladder  as  it  becomes  filled  assumes 
first  a  somewhat  spherical,  then  an  oval  contour.     During  distension  the  enlarging 


THE  BLADDER. 


1149 


bladder  comes  to  occupy  more  and  more  of  the  pelvic  cavity,  displacing  upwards 
the  portions  of  the  colon  and  small  intestine  which  may  lie  in  the  pelvis  when  the 
organ  is  empty.  Until  all  the  available  pelvic  space  has  been  filled  up,  the  form 
of  "the  distended  bladder  is  oval,  with  the  larger  end  directed  downwards  and  back- 


Peritoneal-covered 
surface  of  bladder 


Vas  deferens 


Ureter 


Seminal  vesicle      — 


Obliterated  hypo- 
gasti'ic  artery 

-  Uraelius 


Muscular  coat  of 
bladder 


Prostate 
Cowper's  gland 
Bulb  of  urethra 


Corijus  spongiosum 


Glans  penis 


Fig.  814. — Thk  Bladder    and  the  Structures  traversed  by  the  Urethra  in  the  Male, 
viewed  from  the  outer  side.      The  bladder  has  been  artificially  distended. 

wards ;  but  when  the  pelvic  wall  prevents  further  expansion,  the  portion  lying  above 
the  pelvic  brim  being  more  free  to  enlarge,  the  outline  of  the  organ  may  become 
an  oval  with  the  larger  end  directed  upwards  and  forwards  into  the  aljdominal 
cavity  (compare  Figs.  815,  810).  The  higliest  part  of  the  distended  bladder  lies  at 
some  distance  above  the  pelvic  brim,  and  does  not  correspond  to  the  attachment  of 
the  urachus  at  the  apex,  but  to  a  point  further  back  (Fig.  814).  As  the  superior 
wall  of  the  bladder  is  raised  up  during  distension  it  carries  with  it  the  peritoneum, 
and  thus  the  reflexion  of  that  membrane,  from  the  anterior  abdominal  wall  on  to 
the  apex  of  the  bladder,  comes  to  lie  one  and  a  half  inches,  or  even  higher,  above  the 
upper  margin  of  the  symphysis  pubis  (Fig.  810).  It  is,  therefore,  possible  to  puncture, 
or  open  into  the  distended  bladder,  through  the  anterior  abdominal  wall  above  the 
symphysis  pubis,  without  at  the  same  time  opening  into  the  peritoneal  cavity. 
In  a  similar  manner  the  line  of  reflexion  of  the  peritoneum,  from  the  side  wall  of 
the  pelvis  on  to  the  lateral  aspect  of  the  bladder,  is  raised  higher  during  distension, 
and  may  come  to  correspond,  in  part,  to  the  level  of  the  vas  deferens,  or  to  that  of 
the  obliterated  hypogastric  artery  (Figs.  814  and  816).  On  the  other  hand,  the  level 
of  the  reflexion  of  the  peritoneum  from  the  rectum  towards  the  basal  aspect  of  the. 


1150 


THE  UEINOGENITAL  SYSTEM. 


bladder  does  not  appear  to  vary  much  with  the  distension,  or  contraction,  of  the  organ 
(compare  Figs.  809  and  810),  and  thus  the  fossa  between  the  bladder  and  rectum 


Seminal 
vesicle 


—  Urethra 

Fig.   815. — Lateral  Aspect  of  Bladder  containing  ten  ounces  of  Fluid.     (Normally  distended. ) 
Tlie  dotted  line  indicates  the  line  along  which  the  peritoneum  was  reflected  from  the  organ. 

becomes  relatively  very  deep  when  the  bladder  is  full.     The  bladder  in  normal 
distension  may  contain  as  much  as  one  pint,  but  in  most  cases  the  organ  is  emptied 


Pubic  spine 


Obliterated  hypo- 
gastric artery 
Deep  exMgastric  artery 

Va.s  deferens- 


Coloi 


Uretei 


Pectineal  eminence 
Deep  epigastric  artery 

Vas  deferens 


—  Bladder  (highest  point) 


Sacral  promontory 
Ureter 


Fig.  "816.— View  lookinc  into  the  Pelvis  from  above  and  somewhat  behind. 
The  bladder  has  been  artificially  distended. 

when  its  contents  reach  from  six  to  ten  ounces.     Under  abnormal,  or  pathological, 
conditions  the  bladder  capacity  may  be  much  increased. 


THE  BLADDER 


1151 


Folds  in 
mucous  coat 


L'lum. 
•  ureteris 


Pig.  817. 


Ridge  connecting  ureters  (torus  uretericus) 
—View  of  the  Interior  of  the  Bladdeh  in  the 
Region  of  the  Urethral  Orifice. 


Varying  Relationships,  according  to  the  degree  of  Distension  of  the  Bladder. 

— When  the  bladder  is  distended  the  obliterated  hypogastric  artery  may  cross 
forwards  against  its  side,  when  empty  the  obliterated  vessel  where  nearest 
often  lies  as  much  as  one  and  a  quarter  inches  above  the  lateral  border  of  the 
organ  (Figs.  808  and  814).  The  vas  deferens,  during  a  part  of  its  course,  is  in  contact 
with  the  side  wall  of  the  distended  bladder,  but  lies  when  the  organ  is  empty 
above  and  parallel  to  the  lateral  border,  only  coming  into  relationship  with  the 
basal  surface  of  the  bladder  beyond  the  point  where  it  crosses  the  ureter.  The  side 
wall  of  the  distended  bladder  is  closely  related  to  the  obturator  vessels  and  nerves. 

Interior  of  the  Bladder.  —  The  mucous  membrane  lining  the  bladder  is 
loosely  connected  to  the  muscular  coat,  and  when  the  bladder  is  contracted  the 
mucous  lining  is  thrown  into  a  number  of  prominent  wrinkles  or  folds  (Fig.  817). 
At  one  place  only  the  mucous 
membrane  is  firmly  connected  to 
the  subjacent  muscular  coat,  and 
the  inner  surface  of  this  part  of 
the  bladder  wall  is  smooth  and 
free  from  wrinkles.  This  smooth 
area,  called  the  trigonum  vesicae, 
corresponds  to  a  triangular  surface 
behind  the  urethral  orifice  and 
to  the  part  of  the  bladder  wall  0,1^^. 
which  immediately  surrounds  the 
opening.  The  apex  lies  at  the 
beginning  of  the  urethra,  and  the 
base  of  the  triangle  is  formed  by 
a  line  drawn  between  the  open- 
ings of  the  ureters  into  the 
bladder.  Just  behind  the  urethral  opening  the  bladder  wall  sometimes  bulges 
slightly  into  the  cavity,  owing  to  the  presence  beneath  it  of  the  middle  lobe 
of  the  prostate.  When  well  marked,  as  it  often  is  in  old  people,  this  elevation 
is  termed  the  uvula  vesicae.  Stretching  across  between  the  openings  of  the 
ureters  there  is  usually  to  be  seen  a  smooth  ridge,  which  is  due  to  the  presence 
of  a  bundle  of  transversely-disposed  muscle  fibres,  within  this  part  of  the  bladder 
wall,  beneath  the  mucous  membrane.  This  ridge,  which  may  be  deficient  near  the 
middle  line,  has  been  called  the  "  torus  uretericus,"  and  curved  so  as  to  be  convex 
forwards.  The  lateral  portions  of  the  ridge  which  lie  outside  the  openings  of  the 
ureters  are  called  the  plicae  uretericae,  and  are  produced  by  the  terminal  parts  of  the 
ureters  as  they  traverse  the  bladder  wall  and  lie  beneath  the  mucous  coat  of  the 
bladder  (Fig.  817).  In  old  people  the  region  behind  the  trigonum  is  usually 
distinctly  depressed  and  forms  a  shallow  fossa,  sometimes  called  the  retro-ureteric 
fossa.  A  less  distinct  shallow  depression  may  sometimes  be  observed  on  each  side 
of  the  trigone.  Eound  the  urethral  orifice  are  a  number  of  minute  radially-disposed 
folds  which,  disappearing  into  the  urethra,  become  continuous  with  the  longitudinal 
folds  of  the  mucous  membrane  of  the  first  part  of  that  canal.  The  ureters  pierce 
the  bladder  wall  very  obliquely,  and  so  tiie  minute  opening  (orificium  ureteris)  of 
each  has  an  elliptical  outline.  The  outer  boundary  of  each  opening  is  formed  by  a 
thin,  crescentic  fold,  which,  when  the  bladder  is  artificially  distended  in  the  dead 
subject,  acts  as  a  valve  in  preventing  water  or  air  from  entering  the  ureter.  Hence 
the  term  "valvula  ureteris"  is  sometimes  used  to  designate  the  fold.  In  the 
empty  bladder  the  urethral  orifice  and  the  openings  of  the  two  ureters  lie  at  the 
angles  of  an  approximately  equilateral  triangle,  whose  sides  are  about  one  inch  in 
length.  When  the  bladder  is  distended,  the  distance  between  the  openings  may 
be  increased  to  one  and  a  half  inches  or  more. 

Bladder  in  the  Female.  — In  the  female  the  bladder  is  related  behind  to 
the  uterus  and  upper  part  of  the  vagina.  The  anterior  surface  of  the  uterus  in  its 
upper  part  is  separated  from  the  upper  surface  of  the  bladder  by  the  shallow  utero- 
vesical  pouch  of  peritoneum,  but  the  two  organs  are  nevertheless  normally  in 
apposition.     So  close  is  this  relationship  that  the  upper  surface  of  the  bladder  very 


1152  THE  URINOGENITAL  SYSTEM. 

often  shows  a  slight  concavity,  due  to  contact  with  the  convex  anterior  wall  of  the 


Cavitv  of  uterub 


Labium  anteiius 
(cervix  uteii)' 

Symphysis  pubi 


Labium  posterius 
(cervix  uteri) 


Labium  minus 


Sphincter  aiii 


Mesial  Sfx'tion  of  the  Pelvis  in  an  Adult  Female. 


The  cavity  of  the  uterus  is  iudicated  diagrammatically      From  a  specimen  in  the  Anatomical  Department, 

Trinity  College,  Dublin. 


uterus. 


Uraclius 


Ureter 


Vas  deferens 


The  lower  part  of  the  uterus  and  upper  part  of  the  vagina  are  not 

separated  by  peritoneum  from  the  basal 
surface  of  the  bladder,  but  are  in  actual 
apposition  with  it  (Eig.  818).  Thus, 
below  the  level  of  the  utero- vesical 
pouch,  the  female  bladder  is  related  in 
much  the  same  manner  to  the  uterus' 
and  anterior  wall  of  the  vagina  as  the 
male  bladder  is  related  to  the  vesiculae 
seminales  and  vasa  deferentia.  The 
apex  of  the  bladder,  where  the  urachus 
is  attached,  often  lies  on  a  lower  level 
than  in  the  male,  so  that  the  organ, 
even  when  distended,  rises  less  freely 
into  the  abdomen.  The  bladder  as  a 
whole  is  placed  deeper  in  the  pelvis 
than  in  the  male,  and  the  internal 
urethral  oritice  lies  just  above  or  just 
Ijelow  a  line  drawn  from  the  lower  margin  of  the  symphysis  to  the  lower  end  of  the 
sacrum  (p.  1146).     The  lower  level  of  the  internal  urethral  orifice  is  probably  corre- 


Prostate 


Musculus  pubo-vesicalis 


Urethra 


Fig.  819. — The  Bladder  of  a  newly-born  Male 

(Jhild,  viewed  from  the  outer  .side. 

The  drawing  is  from  a  specimen  which  had  been 

hardened  in  situ. 


THE  BLADDER 


1153 


Bladder 


Symphysis 


Corpus  cavernosuur 

Bulb  of  urethra-T 
Bulbo-caveniosus^ 
muscle 


Internal  sphincter  aiii 
External  sphincter  ani 
Anal  canal 

External  sphincter  ani 


la  ted  with  the  absence  of  the  prostate  in  the  female.  It  is  probable  that  as  regards 
capacity  no  difference  exists  between  the  bladder  in  the  male  and  in  the 
female ;  the  conflicting  results  arrived  at  by  different  observers  are  probably  due 
to  the  faulty  methods  which  have  been  employed  in  estimating  the  capacity  of  the 
organ. 

Bladder  in  the  Newly-born  Infant  and  in  the  Child. — At  birth  the  empty 
bladder  is  spindle- 
or  torpedo  -  shaped, 
and  its  long  axis, 
which  extends  from 
the  point  of  attach- 
ment of  the  urachus 
to  the  internal 
urethral  orifice,  is 
directed  downwards 
and  backwards  (Fig. 
819).  The  lateral 
and  posterior  bor- 
ders seen  in  the 
adult  organ  cannot 
be  recognised  at 
birth,  nor  is  there 
any  part  of  the 
bladder  wall  di- 
rected downwards 
and  backwards,  as 
is  the  basal  surface 
of  the  adult  organ. 
In  the  fcetus  and 
young  child  the 
bladder  occupies  re- 
latively a  much 
liigher  level  than  it 
does  in  the  adult, 
and,  even  when 
empty,  it  extends 
upwards  into  the 
abdominal  cavity. 
Its  anterior  aspect 
is  in  contact  with 
the  posteriorsurface 
of  the  anterior  ab- 
dominal wall.  At 
birth  the  peri- 
toneum forming  the 
recto -vesical  pouch 
covers  the  whole  of 
the  posteriorsurface 


Bladder 


Symphysis  pubis 


Carina  urethral! 


Labium  niinu 


Uterus 


Internal  sphincter  ani 
-External  sphincter  ani 
Anal  canal 

External  sphincter  ani 


Fig.  820. — Mesial  Sectiux  through  the  Pelvis  of  newly-born  Child. 

A,  Male,  and  B,  Female.     From  preparations  in  the  Anatomical  Department, 
Trinity  College,  Dublin. 


of  the  bladder,  and  reaches  as  low  as  the  upper  limit  of  the  prostate.  The  internal 
urethral  orifice  is  placed  at  a  high  level,  and  sinks  gradually  after  birth  (Fig. 
820,  A).  In  the  newly-born  child  this  opening  lies  on  a  level  with  the  upper  margin 
of  the  symphysis  pubis,  and  the  openings  of  the  ureters  lie  almost  on  a  level  with 
the  plane  of  the  pehdc  brim.  The  obliterated  hypogastric  arteries  are  more  in- 
timately related  to  the  bladder  in  the  fcetus  and  child  than  in  the  adult,  and  lie 
close  against  its  sides  as  they  pass  upwards  towards  the  umbilicus  (Fig.  821). 

Peritoneal  Relations  and  Connexions  of  the  Bladder. — We  have  already 

seen  that  the  superior  surface  of  the  empty  bladder  is  covered  by  peritoneum,  which 

leaves  it  along  the  lateral  border  on  each  side  to  reach  the  pelvic  wall  at  about  the 

level  of  the  white  line  (arcus  tendineus)  of  the  pelvic  fascia.     To  this  peritoneal 

78 


1154 


THE  UEINOGENITAL  SYSTEM. 


Internal 
abdominal  rinff 


H  ypogastric  artery 


Epididyiiiis 


Giibernaculum 


Mesorchliim 


Vas  defermis 


reflection  the  term  lateral 
false  (or  peritoneal)  liga- 
ment is  often  applied. 
The  lateral  ligaments  of 
opposite  sides  are  con- 
tinuous in  front  at  the 
bladder  apex,  in  which 
position  the  peritoneum 
is  conducted  over  the 
fibrous  cord  of  the 
urachus  to  reach  the  an- 
terior abdominal  wall, 
forming  the  so  -  called 
anterior  false  (or  peri- 
toneal) ligament.  When 
the  bladder  is  empty  the 
level  of  this  anterior  re- 
flection lies  just  behind, 
or  just  below,  the  upper 
margin  of  the  symphysis 
pubis.  When  the  bladder 
becomes  filled  the  level  of  the  peritoneal  reflection  forming  the  anterior  false  liga- 

Uraclius 


Psoas 


Rectum 


Fig.  821. — View  looking  from  above  into  the  Pelvis  and  Lower 
Part  of  the  Abdominal  Cavity  in  a  Fcetus  of  about  the 
Se\tenth  Month. 

On  tlie  left  side,  which  represents  a  slightly  more  advanced  condition  than 
the  right,  the  testis  has  entered  the  inguinal  canal ;  on  the  right  side 
the  testis  is  still  within  the  abdominal  cavity. 


Bladder 


Obliterated  hypogastric  artery 
Pectineal  eminence 


Deep  epigastric 
artery 


Plica  vesicalis 
transversa 


— —    Vas  deferens 
Vesical  artery 

Ureter 


Jruter 

Iliac  vessels 
Sacral  promontory 
Cut  edge  of  peritoneum 

Fio.  822. — View  looking  into  the  Male  Pelvls  fkom  above  and  somewhat  behind. 

From  a  specimen  in  which  the  bladder  was  firmly  contracted  and  contained  but  a  small  amount  of  fluid.  The 
paravesical  fossa  is  seen  on  each  side  of  tlie  bladder.  Tlie  deep  peritoneal  pouch  in  front  of  the  rectum 
is  liounded  by  marked  crescentic  folds  (sacro-genital  or  posterior  false  ligaments  of  the  bladder),  which 
meet  together  some  distance  behind  the  posterior  border  of  tlie  bladder. 

ment  is  raised  upwards,  and  may  reach  a  point  two  inches,  or  more,  above  the  upper 


THE  'BLADDER. 


1155 


margin  of  the  symphysis  pubis.  Similarly,  the  line  along  which  the  lateral  peri- 
toneal ligament  reaches  the  pelvic  wall  is  also  carried  upwards  in  distension  of  the 
bladder,  aud  may  reach  the  level  of  the  vas  deferens  and  of  the  obliterated  hypo- 
gastric artery. 

When  the  bladder  is  empty  the  peritoneum  is  carried  downwards  upon  the  side 
wall  of  the  pelvis  as  low  as  tlie  lateral  border  of  the  organ,  and  lines  a  shallow 
depression  which  receives  the  name  of  paravesical  fossa.  This  peritoneal  fossa 
lies  below  the  level  of  the  so-called  obturator  fossa,  from  which  it  is  separated  by 
the  vas  deferens.  As  the  bladder  fills  the  peritoneum  is  raised  off  this  part  of  the 
pelvic  wall,  and  certain  structures,  such  as  the  obturator  vessels  and  nerve  and 
the  vas  deferens,  which  lie  on  the  side  wall  of  the  pelvis,  come  into  direct  relation- 
ship with  the  lateral  aspect  of  the  distended  bladder. 

Posteriorly  the  peritoneum  leaves  the  upper  surface  of  the  empty  bladder  at  its 
posterior  border,  and  is  carried  backwards,  forming  a  kind  of  horizontal  shelf,  or 
fold,  for  a  distance  of  about  half  an  inch,  giving  at  the  same  time  a  partial  cover- 
ing to  the  vasa  deferentia  and  upper  ends  of  the  seminal  vesicles.  The  peritoneum 
then  suddenly  dips  downwards  to  reach  the  bottom  of  the  recto-genital  (or  recto- 


Obturator  vessel: 
Vas  deferciis 


Uri;ter 


Sciatic  artery 


Gluteal  artery 

/  Nfr\e  cord  from  hypogastric  plexus 


Obliterated  hypogastric 


Plica  vesicalis  transversa 
Plica  umbUicalis  lateralis     \ 


Septum 
pectinifonne 


Membranous  uretlira  i 

Bulb  of  urethra  i 

luterual  urethral  orifice 


baero-genital  fold 
j         \  Vasa  deferentia 

V       E.jaeulatory  duct 
Prostate  (middle  lobe) 

Fig.  823. — Mesial  Section  of  the  Pelvis  in  an  Adult  Male.' 
The  coils  of  small  intestine  which  lay  within  the  pelvis  have  been  lifted  out  in  order  to  give  a  view  of  the  side 
wall  of  the  pelvic  cavity.     The  peritoneum  is  coloured  blue. 

vesical)  pouch,  where  it  is  reflected  on  to  the  anterior  surface  of  the  rectum 
(Fig.  823).     As  a  rule,  no  part  of  the  basal  surface  of  the  contracted  and  empty 
bladder   receives   a   covering  from   the    peritoneum,   since    the   seminal    vesicles 
78  a 


1156  THE  URINOGENITAL  SYSTEM. 

and  terminal  portions  of  the  vasa  deferentia  intervene  as  they  lie  in  the  anterior 
wall  of  the  recto-genital  pouch.  When  the  bladder  is  distended  the  posterior 
border,  separating  the  upper  and  basal  surfaces,  is  rounded  out,  and  the  peritoneum 
forming  the  horizontal  shelf,  just  described,  is  taken  up  (compare  Figs.  810  and  823). 
It  is  to  be  specially  noted  that  the  level  of  the  peritoneal  reflection,  forming  the 
bottom  of  the  recto-genital  pouch,  does  not  alter  to  any  considerable  extent  in  dis- 
tension of  the  bladder  (Figs.  809  and  810). 

An  examination  of  mesial  sections  of  the  pelvis  sliows  the  great  danger  run  by  the  ampullae 
of  the  vasa  deferentia  in  any  operation  for  reaching  the  bladder  through  the  anterior  wall  of  the 
rectum,  and  the  difficulty  in  avoiding  injury  to  the  peritoneum. 

The  term  "  posterior  false  (or  peritoneal)  ligament "  is  often  applied  to  the  some- 
what variable  crescentic  fold  of  peritoneum  which  bounds  on  each  side  the 
entrance  to  the  recto-genital  pouch,  and  which  often  unites  with  the  fold  of  the 
opposite  side  across  the  middle  line,  behind  the  posterior  border  of  the  bladder  and 
the  vasa  deferentia.  These  folds  represent  the  folds  of  Douglas  in  the  female,  and 
are  to  be  regarded  as  connexions  of  the  vasa  deferentia  rather  than  of  the  bladder, 
lience  the  term  sacro-genital  folds  is  applicable  to  these  structures  in  both  sexes. 
The  folds  are  seen  in  Figs.  822  and  823. 

In  the  female  the  peritoneum  is  reflected  posteriorly  from  the  upper  surface  of 
the  bladder  on  to  the  anterior  aspect  of  the  uterus. 

The  peritoneum  covering  the  upper  surface  of  the  empty,  or  partly  distended,  bladder 
often  exhibits  a  transversely-disposed  fold  or  wrinkle,  to  which  the  term  plica  vesicalis 
transversa  has  been  applied.  This  fold,  Avhen  well  developed,  can  be  traced  on  to  the 
side  wall  of  the  pelvis,  where  it  traverses  the  paravesical  fossa,  and  in  some  cases  it  is 
found  to  cross  the  pelvic  brim  and  to  be  directed  towards  the  internal  abdominal  ring 
(Figs.  822  and  823). 

Fixation  of  the  Bladder. — When  the  fibrous  cord  of  the  urachus  (ligamentum 
umbilicale  medium),  which  binds  the  bladder  apex  to  the  anterior  abdominal  wall, 
and  the  peritoneal  folds,  already  described  as  the  false  ligaments,  are  severed,  the 
bladder  is  easily  moved  about,  except  in  its  lower  and  basal  parts.  Anteriorly  it 
is  connected  to  the  pubis,  and  laterally  to  the  fascial  lining  of  the  pelvis  by  loose 
areolar  tissue  only,  which  permits  free  movement  during  expansion  and  contraction. 
The  lower  fixed  part  of  the  bladder  is  chiefly  held  in  place  by  processes  of  the 
pelvic  fascia,  continuous  with  those  forming  the  capsule  of  the  prostate.  The 
fascial  connexions  constitute  the  true  ligaments  of  the  bladder,  and  are  described 
as  puho-prostatic  or  anterior  ligaments,  reaching  the  bladder  from  the  pubis  in  front, 
and  lateral  ligaments,  reaching  the  bladder  from  the  fascial  lining  of  the  side  wall 
of  the  pelvis. 

In  addition  to  the  urachus  and  the  peritoneal  and  true  ligaments  already 
mentioned,  the  bladder  is  supported  and  fixed  in  position,  in  the  region  of  its 
basal  surface,  by  the  dense  fibrous  and  unstriped  muscular  tissue  which  surrounds 
the  seminal  vesicles,  the  terminal  portions  of  the  vasa  deferentia  and  the  ureters. 

Laterally  the  strands  of  connective  tissue  and  the  bundles  of  musclefibres  forming  this  sup- 
port pass  backwards  to  gain  attachment  to  the  fascia  in  connexion  with  the  rectum,  and  the 
front  of  the  sacrum.  Muscle  fibres  connected  with  the  bladder  waU  are  also  found  within  the 
pubo-prostatic  ligaments,  through  which  they  are  attached  to  the  pubis. 

In  the  female  the  basal  part  of  the  bladder  wall  is  supported  and  held  in  place 
by  its  connexion  with  the  anterior  wall  of  the  vagina.  The  region  of  the  urethral 
orifice  is  the  most  firmly  fixed  part  of  the  bladder  wall  in  both  sexes. 

Structure  of  the  Bladder  Wall. — The  wall  of  the  bladder  from  without  inwards 
is  composed  of  a  serous,  a  muscular,  a  submucous,  and  a  mucous  coat.  The  serous  coat 
(tunica  serosa),  formed  by  peritoneum,  is  incomplete,  and  covers  only  the  upper  and 
posterior  parts  of  the  distended  bladder  (Fig.  814). 

A  considerable  amount  of  fibrous  connective  tissue  surrounds  the  muscular  coat,  and 
penetrating  it  divides  it  into  numerous  coarse  bundles  of  muscle  fibres.  All  the  muscle 
fibres  are  of  the  smooth  variety,  and  the  bundles  formed  by  them  are  arranged  in  three 
very  impei-fectly  separated   strata  called  external,  middle,  and  internal.     The  external 


THE  URETHEA.  1157 

stratum  (stratum  externum)  is  for  the  most  part  made  up  of  fibres  which  are  directed 
longitudinally,  and  it  is  best  marked  near  the  middle  line  on  the  upper  and  under  aspects 
of  the  bladder.  Farther  from  the  middle  line,  on  the  sides  of  the  bladder,  the  fibres 
composing  the  external  stratum  run  more  obliquely,  and  their  directions  frequently  cross 
one  another.  In  the  male,  many  of  the  fibres  of  the  external  stratum  are  attached  both 
anteriorly  and  posteriorly  to  the  prostate,  and  in  the  female  the  corresponding  fibres  join 
the  dense  tissue  which  in  this  sex  surrounds  the  upper  part  of  the  urethra.  Other  fibres 
of  this  stratum  on  each  side  of  the  body  join  the  lower  part  of  the  symphysis  pubis  and 
constitute  the  musculus  pubo-vesicalis,  which  lies  in  the  substance  of  pubo-prostatic 
ligament.  Lastly  some  fibres  of  the  external  stratum  blend  posteriorly  with  the  anterior 
aspect  of  the  rectum  and  receive  the  name  of  musculus  recto-vesicalis.  The  middle 
stratum  (stratum  medium)  is  composed  of  fibres  which  for  the  most  part  run  circularly, 
and  forms  the  greater  part  of  the  thickness  of  the  muscular  coat.  In  the  region  of,  and 
behind,  the  urethral  orifice  the  bundles  of  fibres  are  finer  and  more  densely  arranged  and 
suri'ound  the  opening  in  a  plane  which  is  directed  obliquely  downwards  and  forwards. 
This  part  of  the  middle  stratum  is  often  spoken  of  as  the  sphincter  vesicae.  Inferiorl}'' 
the  fibres  of  the  sphincter  vesicae  ai'e  continuous  with  the  muscular  tissue  of  the  prostate 
in  the  male,  and  with  the  muscular  wall  of  the  urethra  in  the  female.  In  other  parts  of  the 
bladder  the  fibres  of  the  middle  stratiun  are  coarser  and  separated  by  intervals  filled  by 
connective  tissue.  The  inner  stratum  (stratum  internum)  is  a  thin  layer  of  fibres 
directed  for  the  most  part  longitudinally. 

The  submucous  coat  (tela  submucosa)  is  composed  of  areolar  tissue,  but  contains 
numerous  fine  elastic  fibres. 

The  mucous  coat  (tunica  mucosa)  is  loosely  attached,  by  means  of  the  submucous 
layer,  to  the  subjacent  muscular  coat,  except  in  the  region  of  the  trigonum  vesicae,  where 
the  muscular  fibi'es  lie  close  beneath,  and  are  firmly  adherent  to  the  mucous 
membrane.  Over  the  trigonum  the  mucous  coat  is  always  smooth  and  flat ;  elsewhere  it  is 
thrown  into  folds  when  the  bladder  is  empty.  The  mucous  membrane  of  the  bladder  is 
continuous  with  that  of  the  ureters  and  urethra.  The  epithelium,  covering  it,  varies 
much  in  appearance  in  different  conditions  of  the  organ,  and  is  of  the  variety  known  as 
transitional  stratified  epithelium. 

Vessels  and  Nerves  of  the  Bladder. — The  1  ladder  receives  its  blood  supj^ly  on  each  side 
from  the  superior  and  inferior  vesical  arteries.  The  superior  vesical  artery  arises  from  the 
pervious  part  of  the  hypogastric  artery,  and  the  inferior  vesical  from  the  internal  iliac.  The 
largest  veins  are  found  just  above  the  prostate,  and  in  the  region  where  the  ureter  reaches  the 
bladder.  They  form  a  dense  plexus  which  pours  its  blood  into  tributaries  of  the  internal  iliac 
vein,  and  communicates  below  Avitli  the  prostatic  plexus.  The  lymphatics  from  the  bladder  join 
the  iliac  group  of  glands. 

The  nerve  supply  of  the  bladder  is  derived  on  each  side  from  the  vesical  plexus,  the  fibres  of 
which  come  from  two  sources,  namely  (1)  from  the  upper  lumbar  nerves  through  the  hypogastric 
plexus,  and  (2)  from  the  third  and  fourth,  sacral  nerves.  The  fibres  from  the  latter  sources  join 
the  vesical  plexus  directly. 

THE   URETHRA. 

The  urethra  is  the  channel  which  serves  to  convey  the  iirme  from  the  bladder 
to  the  exterior.  In  the  male  it  consists  of  two  portions,  a  proximal  part,  less  than 
one  inch  in  length,  extending  from  the  bladder  to  the  points  where  the  ducts  of 
the  reproductive  glands  join  the  canal,  and  a  much  longer  distal  portion  which 
serves  as  a  common  passage  for  the  secretion  of  the  kidneys  and  for  the  generative 
products.  An  account  of  the  male  urethra  follows  the  description  of  the  male 
reproductive  glands  and  passages  (see  p.  1177).  In  ihe  female  the  urethra  is  more 
simple  in  its  arrangement,  and  represents  only  the  proximal  part  of  the  male 
canal.  It  is  a  short  passage  leading  from  the  bladder  to  the  external  urethral 
orifice — an  aperture  placed  within  the  urinogenital  cleft  immediately  above  and  in 
front  of  the  opening  of  the  vagina. 

Female  Urethra.-^The  female  urethra  (urethra  muliebris)  is  a  canal  of  about 
one  to  one  and  a  half  inches  in  length,  which  follows  a  slightly  curved  direction 
downwards  and  forwards,  below  and  behind  the  lower  border  of  the  symphysis 
pubis.  As  it  leavea  the  pelvis  the  urethra  pierces  the  triangular  ligament,  and 
the  part  of  the  passage  which  lies  between  the  deep  and  superficial  layers  of  this 
ligament  is  surrounded  hj  the  fibres  of  the  compressor  urethrcB  muscle.  Except 
78  & 


1168 


THE  UEINOGENITAL  SYSTEM. 


during  the  passage  of  fluid  the  canal  is  closed  by  the  apposition  of  its  anterior  and 
posterior  walls.  The  external  orifice  (orificium  urethrpe  externum)  is  placed  between 
the  labia  minora,  immediately  in  front  of  the  opening  of  the  vagina,  and  lies  about 
one  inch  below  and  behind  the  clitoris  (Fig.  855).  The  opening  is  sLt-like,  and  is 
bounded  by  slightly  marked  lateral  lips.     The  posterior  wall  of  the  urethra,  except 


Ileum 


Suspensory  _j | 

ligament" 


Caecum 
Venniforii 
iippenri 


um  -  t — ^1 
'lix     I    1 


Ovary 

Fallopian  tube 

Deep  epigastric  -  -  »- 

Round  ligament r 

Fundus  uteri  -'' 


Obliterated . 
hypogastric 


Bladdpr--- 


Uretlira 


Vagina 


Labium  minus- 
r.abinm  majoi  - 


Via.  824. — Mesiat,  Secttox  throcgh  the  Female  Pelvis;     Drawn  for  tlie  most  part  from  a  model 

of  a  dissection  by  Dr.  E.  H.  Taylor. 

in  its  upper  part,  is  very  intimately  connected  with  the  anterior  wall  of  the  vagina. 
The  mucous  lining  of  the  canal  is  raised  into  a  number  of  slightly  marked  longi- 
tudinal folds,  one  of  which,  more  distinct  than  the  others,  and  placed  upon  the 
posterior  wall  of  the  passage,  receives  the  name  of  crista  urethralis. 

Structure. — The  wall  of  the  female  urethra  is  thick  and  contains  much  fibrous 
tissue,  especially  in  its  outer  part,  and  this  passes  without  any  sharp  line  of  demarkation 
into  the  surrounding  mass  of  connective  tissue.  The  muscular  coat  of  the  urethra  (tunica 
muscularis)  is  continuous  above  with  that  of  the  bladder,  and  is  composed  of  layers  of 
circularly  and  longitudinally  disposed  smooth  muscle  fibres  an-anged  to  form  outer  and 
inner  strata.  Within  the  muscular  coat  the  wall  of  the  urethra  is  very  vascular,  and  the 
canal  itself  is  lined  by  a  pale  mucous  membrane  which  is  thrown  into  longitudinally- 
directed  folds,  one  of  which  is  the  crista  urethralis  mentioned  above.  The  epithelium  of 
the  canal,  in  its  upper  part,  is  of  the  transitional  variety,  like  that  of  the  bladder;  in 
its  lower  part  it  becomes  scaly.  Numerous  minute  glands  (glandula)  urethrales) 
and  pit  like  depressions  (lacunae  urethrales)  open  into  the  urethral  canal.  One  group  of 
these  glands  possesses  a  minute  common  duct  (ductus  paraurethralis),  which  opens  into 
the  urinogcnital  cleft  by  the  side  of  the  urethral  orifice.  It  is  believed  that  these  latter 
glands  represent  the  prostatic  glands  of  the  male  subject.  The  vascular  layer  which  lies 
between  the  muscular  coat  and  the  mucous  membrane  contains  elastic  fibres,  and  in 
appearance  resembles  erectile  tissue.     Striped   muscle  fiVn-es  are  present  on   the  outer 


THE  MALE  KEPEODUCTIVE  ORGANS. 


L159 


aspect  of  the  muscular  coat  of  the  urethra.  In  the  upper  part  of  the  canal  these  tibres 
form  a  complete  ring-like  sphincter,  but  in  the  middle  and  lower  parts  the  striped  muscle 
fibres  though  present  in  front  are  absent  in  the  posterior  wall  of  the  urethra,  as  at  this 
level  they  pass  backwards  on  the  outer  aspect  of  the  vagina,  and  enclose  this  latter 
passage  together  with  the  urethra  in  a  single  loop  of  muscle  tissue.  The  lower  fibres, 
therefore,  form  a  urinogeuital  sphincter. 


THE  MALE  KEPEODUCTIVE  OKGANS. 


We  have  here  to  describe  (1;  the  testes  or  essential  reproductive  glands  of  the 
male,  together  with  their  (2)  coverings  and  (3)  ducts,  (4)  the  prostate,  (5j  Cowper's 
glands,  (6)  the  external  genital  organs,  and  (7)  ihe  male  urethra. 

The  reproductive  glands  of  the  male,  or  testes,  are  a  pair  of  nearly  symmetrical 
oval-shaped  bodies  situated  in  the  scrotum.  The  duct  of  each  gland,  at  first 
much  twisted  and  intertwined,  forms  a  structure  known  as  the  epididymis,  which 
is  applied  against  the  posterior  and  outer  part  of  the  testis.  From  the  epi- 
didymis the  e.xcretory  duct,  or  vas  deferens,  passes  upwards  towards  the  lower  part 
of  the  anterior  abdominal  wall,  which  it  piercts  very  obliquely,  to  enter  the 
abdominal  cavity.  Here  each  vas  deferens  is  covered  by  the  peritoneum,  and 
almost  at  once  crossing  the  pelvic  biim,  enters  the  pehis.  The  vas  now  runs  on 
the  side  wall  of  the  pelvis  towards  the  base  of  the  bladder,  where  it  omes  into 
rehition  with  a  branched  tubular  structure  termed  the  vesicula  seminalis.  Joined 
by  the  duct  of  the  vesicula  seminalis,  the  vas  deferens  forms  a  short  canal  called 
the  common  ejaculatory  duct,  which  terminates  by  opening  in:  o  the  prostatic  part 
of  the  urethra.  The  prostate,  a  partly  glandular,  part'y  muscular  structure, 
surrounding  the  first  part  of  the  urethra,  and  also  a  pair  of  small  glandular  bodies 
called  Cowper's  glands,  are  accessory  organs  conuected  with  the  male  reproductive 
system.  The  ducts  of  Cowper's  glands  and  those  of  the  prostate,  like  the  common 
ejaculatory  ducts,  open  into  the 
urethra,  which  thus  serves  not  only 
as  a  passage  for  urine,  but  also  for 
the  generative  products.  The  ex- 
ternal genitals  are  the  penis  and 
scrotum. 

THE  TESTIS. 

The  male  reproductive  glands,  the 
testicles  or  testes,  are  a  pair  of  some- 
what oval,  slightly  flattened  bodies  of 
a  whitish  colour,  measuring  about 
an  inch  an,d  a  half  in  length,  one 
inch  from  before  backwards,  and 
rather  less  in  thickness.  Each  testis 
is  placed  within  the  cavity  of  the 
scrotum  in  such  a  manner  that  its 
long  axis  is  directed  upwards,  slightly  fiu.  S25. 

forwards,  and  outwards,  and    usually    a.    The  right  testis  and  epididymi.s,  seen  witliiii  the  tunica 

the  left  gland  occupies   a  lower   level  vaginalis,  which  has  been  opened  up. 

.1  i.u        ■    Ui.        rrii:     J.     i-     /!'•       oocN    B.    The  riffht  testis  and  eiiididvinis  seen  troni  behind,  after 

than  the  right.  The  testis  (tig.  825)  ^^^^^^^^^^  ^^„^^^.^^i  J^^^^  ^^^^-^^^^  ^„^,^^^^  .c  ^he  lunic;^ 
has  two  somewhat  flattened  surlaces,  vagindis. 
one  of  which,  called  the  outer  surface 
(facies  lateralis)  looks  outwards  and 
backwards ;  the  other,  or  inner  sur- 
face (facies  medialis),  looks  inwards 
and  forwards,  and  is  usually  the  more  flattened.  The  two  surfaces  are  separated  by 
two  rounded  borders,  of  which  the  anterior  (margo  anterior)  is  the  more  convex, 
and  is  free,  while  the  posterior  (margo  posterior)  is  less  rounded,  and  is  the  one  by 
which  the  organ  is  suspended  within  tlie  scrotum.     A  structure  called  the  epididymis 


I-.  Epididymis. 
;/.»!.  Gl  'lius  major. 
'j.m'.  Globus  minor. 

h.  Hydatids. 
s.c.  Spermatic  cord. 


I.  Testis. 
/.(-.  Tmiica  vaginalis. 
t.v'.  Cut  ed'.'e  of  tunica  \aginalis. 
c.d.  Vas  deferens. 


1160 


THE  UEINOGENITAL  SYSTEM. 


and  the  lowest  portion  of  the  spermatic  cord  are  attached  to  the  posterior  border 
of  the  testis.  Each  border  ends  above  in  the  upper,  and  below  in  the  lower  extremity 
of  the  testis  (extremitas  superior  et  extremitas  inferior).  Owing  to  the  obliquity 
of  the  long  axis  of  the  gland,  the  vipper  extremity  of  the  testis  lies  on  an  anterior 
and  external  plane  to  the  lower  one. 

Epididymis. — The  epididymis  is  a  somewhat  crescentic  structure;  which  is  curved 
round  the  posterior  border  of  the  testis  and  overlaps  to  some  extent  the  posterior 
part  of  the  outer  surface  of  that  organ.  The  upper,  somewhat  swollen  part  of  the 
epididymis,  is  called  the  globus  major  (caput  epididymidis),  and  overhangs  the  upper 
end  of  the  testis,  to  which  it  is  directly  connected  by  numerous  emerging  ducts,  by 
connective  tissue,  and  by  the  serous  covering  of  the  organ.  The  lower  and  smaller 
end  is  termed  globus  minor  (cauda  epididymidis),  and  is  attached  by  loose  areolar 
tissue  and  by  the  serous  covering  to  the  lower  end  of  the  testis.  The  intermediate 
part,  or  body  (corpus  epididymidis),  is  applied  against,  but  is  separated  from,  the 
posterior  part  of  the  outer  surface  of  the  testis  by  an  involution  of  the  serous 
covering  of  the  organ,  which  forms  an  intervening  pocket  termed  the  digital  fossa 
(sinus  epididymidis). 

The  main  mass  of  the  epididymis  is  composed  of  an  irregularly  twisted  canal, 
the  canal  of  epididymis,  which  forms  the  first  part  of  the  duct  of  the  testis. 

Minute  sessile,  or  pedunculated,  bodies  are  often  found  attached  to  the  globus  major 
or  to  the  upper  end  of  the  testis.  These  are  called  appendices  of  the  epididymis  and 
testis  (appendices  testis),  or  hydatids  of  Morgagni,  and  have  a  developmental  interest. 
The  minute  body  which  lies  on  the  upper  end  of  the  testis  represents  the  free  end  of 
Mliller's  duct  in  the  embryo  and  the  fimbriated  end  of  the  Fallopian  tube  of  the  female  ;  it 
is  usually  sessile.  Above  the  globus  major,  and  in  front  of  the  lower  part  of  the  spermatic 
cord,  there  may  also  be  present  a  small  rudimentary  body  called  the  organ  of  Giraldes  or 
paradidymis.     This  is  rai-ely  seen  in  the  adult  and  is  best  marked  in  young  children. 

Tunica  Vaginalis. — The  cavity  within  which  the  testis  and  epididymis  are 
placed   is   lined   by  a  smooth   serous   membrane — the    tunica   vaginalis— which 

resembles  in  appearance  and  structure 
the  peritoneum  from  which  it  is  origin- 
ally derived.  The  cavity  is  considerably 
larger  than  the  contained  structures, 
and  extends  not  only  down  to  a  lower 
level  than  the  testis,  but  also  reaches 
upwards  to  a  higher  level  than  the  gland. 
The  sac,  or  cavity,  tapers  as  it  is  traced 
upwards,  and  above  the  level  of  the  testis 
the  spermatic  cord  bulges  forwards  into 
its  posterior  part.  The  tunica  vaginalis 
lines  the  cavity  for  the  testis,  and  is 
reflected  from  the  posterior  wall  of  the 
scrotal  chamber  over  the  testis  and 
epididymis,  giving  a  covering  to  each. 
The  part  of  the  membrane  lining  the 
cavity  is  called  the  parietal  portion  (lamina" 
parietalis)  of  the  tunica  vaginalis,  while 
the  part  clothing  the  testis  and  epididy- 
mis is  termed  the  visceral  portion  (lamina 

,,      „„,.     ,,        „,  ,„  ,.  visceralis).     Between  the  outer  surface 

Pit;.   826. — Right  'Iestjs  within   Tl'mca  Vaginalis.       „     ,  ■'    . 

In    the    region    of    the   globus    major    the    tunica    Ot    the    teStlS    and    the    body  ol    the  Cpi- 

vaginaiis  has  been  cut  througii  and  tiie  globus  didymis,  the  visceral  part  of  the  tunica 
major  of  the  epididymis  has  been  raised  to  show  vaginalis  dips  in  and   lines  a    narrow 

the  vasa  enerentia  and  com  vasculosi.  .f  ,         iii,i         ,...,„  ,. 

interval  called  the  digital  fossa  (sinus 
epididymidis).  The  entrance  to  the  fossa  is  limited  above  and  below  by  short 
crescentic  folds  of  the  tunica  vaginalis,  which  pass  from  the  testis  to  the  globus 
major  and  minor  of  the  epididymis.  These  folds  are  spoken  of  as  the  superior 
and  inferior  ligaments  of  the  epididymis.  In  three  positions  the  surface  of  the 
testis  receives  no  covering  I'rom  the  tunica  vaginalis, — superiorly  where  the  globus 


Spermatic  cord  _  _ 


Coni  vasculosi,  . 
Vasa  efferentia,. 

Appendix  testis 
Superior  ligament 
of  epididymis  ~ 
Cut  edge  of  _ 
tunica  vaginalis 

Epididymis  _ 
Sinus  epididymidis    - 


Inferior  ligament 
of  epididymis 


THK  TESTIS.  1161 

major  is  attached,  inferiorly  where  the  globus  minor  is  iu  contact,  and  posteriorly 

where  the  blood-vessels  and  nerves  enter  the  organ  from  the  spermatic  cord. 

Structure  of  the  Testis  and  Epididymis.— Beneath  the  serous  tunica  vaginalis 
the  testis  is  invested  by  an  external  coat,  composed  of  dense  white  inelastic  fibrous 
tissue  called  the  tunica  albuginea,  from  the 

deep  surface  of  which  a  number  of  slender  ,'' sinus  ei.ididymidis 

fibrous  bands  or  septa   dip  into    the  gland.  •'     ^r Veins 

These — the  septula  testis — imperfectly  divide  lttAs'^\ Vas  deferens 

the  organ  into  a  number  of  wedge-sbaped 

parts  called  lobes,  or   lobules  (lobuli    testis,  %'B^^^^^HP  _, -Corpus  uigiimoii 

Fig.  825).     All  the  septa  end  posteriorly  in  -.iv,***  v.^^j 

a  mass  of  fibrous  tissue  which  is  directly  con-  ^ '^ii/t'Hf^^^^^^^       Epididymis 

tinuous  with  the  tunica  albuginea,  and  which  uHM^^^^^^KV-^^eptuia  testis 

projects  forwards  into  the    testis   along   its  ^^^^^^^^^^ 

posterior    border.      This    structure    receives  '^^^^^^^^■------Lobuies 

the    name   of  mediastinum  testis,   or  corpus 
Highmori,  and  is  traversed  by  an  exceedingly 
complicated  network  of  fine  canals,  into  which 

the  minute  tubules  which  compose  the  sub-  A- 
stance  proper  of  the  testis  open.     The  medi- 
astinum is  also  pierced  by  the  arteries,  veins, 

and  lymphatics  of  the  testis.     These  vessels  -"-""""■^    ~     ""^-^^....-^.--.skiu 

enter  the  posterior  border  of  the  organ,  and  ."Tt^^  superticiai 

traversing  the  mediastinum,  spread  out  on  ...:                         .          External sper- 

the  fibrous  septa  which  radiate  towards  all  ,^^^Eg."\rV."^""      *'.r~  l'nf"nd?b^^^^ 

parts  of  the  deep  surface  of  the  tunica  albu-  "^^ShIIBJ^^*  "         form  fascia 

ginea.     In   this  way  a  delicate  network  of  ! /^^I^j^^j^v , 

vessels  (tunica  vasculosa)  is  formed  on  the  //'         ^5^*^^^- ;;~<^^  venous 

deep  surface  of  the  tunica  albuginea  and  on  ^.  .  •'              \   1    'v          ""^'^e^'^'aster 

the  sides  of  the  septa.  '""   Vas  deferens    ;     deferens" ''"*'  """'^^ 

The  mediastinum,  the  septa,  and  the  tunica  spermatic  artery 

albuginea   form    a    framework   enclosing    a 
number  of  imperfectly  isolated  spaces  which  ^^'■^-  ^^"• 

are    filled    by    a    loosely    packed    substance    of  ^-   '^''-ausverse  section  of  testis  aud  epididymis. 
„    i-^i^-     -i     ^  1  n    J    ii  1  B.   Transverse  section  of  spermatic  cord  below 

a  light-brown  colour  called  the  parenchyma  external  abdominal  ring. 

of  the  testis  (parenchyma  testis). 

The  parenchyma  is  composed  of  enormous  numbers  of  much-convoluted  semini- 
ferous tubules  (tubuH  seminiferi  contorti),  and  completely  fills  up  the  intervals 
between  the  septa.  The  minute  tubules  look  hke  fine  threads  to  the  unaided  eye, 
and  are  but  loosely  held  together  by  a  small  amount  of  connective  tissue.  Usually 
three  or  four  tubules  are  found  in  each  lobule  of  the  gland,  and  the  total  number 
in  the  testis  has  been  estimated  at  about  600.  The  seminiferous  tubules,  after  a 
course  of  abofit  two  feet  in  length,  pass  towards  the  mediastinum  testis,  and  unite, 
at  acute  angles,  to  form  a  smaller  number  of  slender  tubes  which  run  a  straight 
course.  These  latter  are  called  tubuli  recti,  and  open  into  a  complicated  network 
of  fine  canals  situated  in  the  substance  of  the  mediastinum,  called  the  rete  testis. 
The  tubules  are  much  more  twisted  and  convoluted  in  the  cortical  part  of  the 
gland,  near  the  tunica  vaginalis,  than  in  the  region  of  the  mediastinum,  and  often 
in  this  position  give  off  side  branches  which,  according  to  some  observers,  may 
effect  anastomoses  between  the  tubules.  It  appears  doubtful,  however,  if  the 
tubules  of  the  testis  do  really  anastomose. 

Microscopic  sections  show  that  the  walls  of  the  seminiferous  tubules  are  composed  of 
a  basement  membrane  and  of  an  epithelial  lining,  formed  of  several  layers  of  cells. 
Certain  cells  of  this  epithelium  are,  in  the  adult,  constantly  undergoing  transformation 
into  spermatozoa,  and  the  appearance  of  the  tubules  in  section  varies  much,  according  to 
age  and  to  the  greater  or  less  activity  of  the  epithelial  cells. 

The  secretion  of  the  seminiferous  tubules  is  carried  through  the  tubuli  recti 
into  the  rete  testis,  and  leaves  the  latter,  to  reach  the  canal  of  the  epididymis, 


1162 


THE  UKINOGENITAL  SYSTEM. 


through  from  tifteeu  to  twenty  minute  tubules  called  vasa  efferentia  (ductuli 
efferentes  testis).  These  latter  pierce  the  tunica  albuginea  and  enter  the  globus 
major,  where  it  is  in  direct  contact  with  the  upper  end  of  the  testis.  Each  vas 
efferens  is  at  first  straight,  but  soon  becomes  much  convoluted,  and  forms  a  little 
conical  mass  of  twisted  tuljule  called  a  conus  vasculosus  (lobulus  epididymidis). 

Within  the  globus  major  the  little  canals  finally  open 
into  the  single  much-convoluted  tube  which  consti- 
tutes the  chief  bulk  of  the  epididymis,  and  is  called 
the  canal  of  the  epididymis  (ductus  epididymidis). 
This  canal,  which  is  not  less  than  19  or  20  feet  in 
length,  may  be  said  to  begin  in  the  globus  major,  and 
to  end,  after  an  extraordinarily  tortuous  course,  at  the 
globus  minor  by  becoming  the  vas  deferens  (ductus 
deferens,  Fig.  828). 

In  most  cases  cue  or  move  slender  convokited  diverticula 

from  the  canal  of  the  epididymis  may  be  found  near  its 

lower  end.     These  receive  the  name  of  vasa  aberxantia 

Fig.  828.  (ductuli  aberrantes),  and  one  of  them  which  is  very  con- 

DiAGKAM  to  illustrate  the  .■itructure  of  stantly  present  often  measures  a  foot  or  more  in  length. 

the  testis  and  e])ididymis.  MinutC    StruCturC- — The   canal  of   the   epididymis 

and  the  vasa  efferentia  are  lined  by  a  ciliated  epithelium, 
the  cilia  of  which  maintain  a  constant  current  towards 
the  vas  deferens.  The  canal  of  the  epididymis  possesses 
a  muscular  coat  composed  of  an  inner  stratum  of  trans- 
versely and  an  outer  sti'atum  of  longitudinally  directed  fibres.  The  wall,  at  first  thin, 
becomes  much  thicker  as  the  canal  approaches  the  vas  deferens. 

Vessels  and  Nerves  of  the  Testis. — The  testis  is  supplied  by  the  spermatic  artery,  a  branch 
uf  the  aorta.  This  slender  vessel,  after  a  long  course,  reaches  the  posterior  border  of  the  testis, 
where  it  breaks  uj)  into  branches  which  enter  the  mediastinum  testis,  and  are  distributed  along 
the  sejita  and  on  the  deep  surface  of  the  tunica  albuginea.  The  veins  issuing  from  the  posterior 
border  of  the  testis  form  a  dense  plexus,  called  the  plexus  pampiniformis,  which  finally  poius  its 
blood  through  the  spermatic  vein,  on  the  right  side,  into  the  inferior  vena  cava ;  on  the  left  side  the 
spermatic  vein  joins  the  left  renal  vein.  The  nerves  for  the  testis  accompany  the  spermatic 
artery,  and  are  derived  through  the  aortic  and  renal  plexuses  from  the  tenth  thoracic  segment  of 
the  spinal  cord.  The  afferent  filares  from  the  epididymis  appear  to  reach  the  spinal  cord  througli 
the  jjosterior  roots  of  the  eleventh  and  twelfth  thoracic  and  first  lumbar  nerves.  The  arteries  and 
nerves  of  the  testis  communicate  with  those  on  the  lower  part  of  the  vasdefereus,  namely,  with 
the  artery  of  the  vas  and  with  twigs  from  the  hypogastric  plexus.  The  lymphatic  vessels  of  the 
testis  pass  upwards  in  the  spermatic  cord,  and  end  in  the  lumbar  lymphatic  glands. 


c.i;.   Coni  vasculosi 
i;       Globus  major. 
ij.m'-  Globus  minor. 
/-.!•.   Rete  testis. 
J*.       Septula  testis. 


f.     Seminiferous 

tubule. 
d.  Vas  deferens. 
c.    Vas  efferens. 
/■.   Tubuli  recti. 


THE  VAS  DEFERENS. 

The  vas  deferens  (ductus  deferens)  is  the  direct  continuation  of  the  canal  of  the 
epididymis.  Beginning  at  the  lower  extremity  of  the  epididymis,  it  ends,  after  a 
course  of  nearly  18  inches,  by  opening  as  the  common  ejaculatory  duct  into  the 
prostatic  or  first  part  of  the  urethra.  The  duct  in  parts  of  its  course  is  somewhat 
convoluted,  and  the  actual  distance  traversed  by  it  is  not  more  than  12  inches. 
Placed  in  the  first  instance  outside  the  abdominal  cavity,  the  vas  deferens  ascends 
within  the  scrotum  towards  the  lower  part  of  the  anterior  abdominal  wall,  which  it 
reaches  not  far  from  the  middle  line.  During  this  part  of  its  course  the  duct, 
together  with  the  vessels  and  nerves  of  the  testis,  is  surrounded  by  a  number  of 
loose  coverings  derived  from  certain  layers  of  the  abdominal  wall,  and  the  cord-like 
structure  so  formed  is  termed  the  spermatic  cord.  The  vas  deferens,  together  with 
the  accompanying  vessels  and  nerves,  now  passes  through  the  abdominal  wall  in  an 
oblique  passage,  to  which  the  name  inguinal  canal  is  applied.  Within  the  abdomen 
the  vas  Lies  immediately  beneath  the  peritoneum,  and  soon  crossing  over  the  pelvic 
brim,  it  enters  the  pelvis,  on  the  side  wall  of  which  it  proceeds  backwards  towards 
the  base  of  the  bladder.  Here,  near  the  middle  line,  the  vas  deferens  is  joined  by 
the  duct  of  the  corresponding  vesicula  seminalis,  and  the  common  ejaculatory  duct, 
thus  formed,  having  traversed  the  prostate,  opens  into  the  urethra. 

At  first  the  vas  deferens,  like  the  canal  from  which  it  takes  its  origin,  is  very 


THE  VAS  DEFEKENS. 


1163 


tortuous,  but  soon  increasing  in  thickness,  the  duct  becomes  less  twisted,  and  passes 
upwards  along  the  inner  side  of  the  epididymis,  behind  the  testis,  to  enter  the 
spermatic  cord  (Fig.  828).  Its  course  is  now  almost  vertically  upwards  towards 
the  spine  of  the  pubis,  near  which,  crossing  the  inner  part  of  Poupart's  ligament, 
the  vas  enters  the  inguinal  canal  by  the  external  abdominal  ring.  Of  the  structures 
composing  the  spermatic  cord  the  vas  is  the  most  posterior,  and  it  can  be  readily 


niaddor    Urachus 


Vas  deferens 
Obliterated  hypoga.'itric  artery       i 

Deep  epigastric  artery 
External  iliac  vessels 


Plica  vesicalis  transversa 
i    Median  portion  of  middle  peritoneal  fossa 
Paravesical  fossa 

Trigonnm  fi^morale 


Uljtiuator  nerve 
Obliterated  liypogastrie  artery 


IJretei-  ; 

Third  sacral  vertebra 


;    i     Obturator  fossa 

■  Lateral  portion  of  the  midille  peritoneal  fossa 

iSacro-senital  fold 


Pararectal  fossa 
Rtctuni 


Lower  part  of  pelvic  mesocolon 


Fio.  829. — The  Peritoneum  of  the  Pelvic  Cavity.     The  upper  part  of  tlie  posterior  wall  of  the  pelvis  has 
been  removed  to  show  more  clearly  the  disposition  of  the  peritoneum.     (Birmingham.^ 


distinguished,  even  in  the  undissected  subject,  by  its  hard  firm  feel  when  it  is  taken 
between  the  finger  and  thumb.  In  the  inguinal  canal  the  vas  is  directed  outwards, 
upwards,  and  a  little  backwards  to  the  internal  abdominal  ring,  where,  at  a  point 
half  an  inch  above  Poupart's  ligament,  and  midway  between  the  symphysis  pubis 
and  the  anterior  superior  iliac  spine,  it  enters  the  abdomen.  The  distance  between 
the  point  where  the  cord  enters  the  inguinal  canal  to  the  point  where  it  leaves  it 
to  enter  the  abdomen  is  about  one  and  a  half  inches.  While  passing  from  the 
external  to  the  internal  abdominal  ring  the  vas  deferens,  together  with  the  other 
structures  of  the  spermatic  cord,  rests  upon  tlie  upper  grooved  surface  of  Poupart's 
ligament,  and  is  placed  behind  the  aponeurosis  of  the  external  oblique  and  some  of 
the  lower  fibres  of  the  internal  oblique  muscle.  From  before  backwards  the  vas 
rests,  in  the  first  instance,  upon  the  conjoined  tendon  of  the  internal  oblique  and 
transversalis  muscles,  and  farther  outwards  upon  the  transversalis  fascia.  Above  the 
cord  are  some  arching  fibres  of  the  internal  oblique  muscle,  which  enter  the  conjoined 
tendon.  As  the  vas  deferens  leaves  the  inguinal  canal  by  the  internal  abdominal 
ring,  it  turns  round  the  deep  epigastric  artery  on  its  outer  and  posterior  aspect. 
Completely  changing  the  direction  of  its  course,  the  duct  now  runs  for  a  short 
distance  backwards,  inwards,  and  upwards,  beneath  the  peritoneum  to  a  point  one  and 
a  half  to  two  inches  from  the  spine  of  the  pubis,  where  it  crosses  the  ilio-pectineal 
Kne  and  enters  the  pelvis.  In  this  part  of  its  course  the  duct  usually  at  first  lies  in 
front  of  the  external  iliac  vessels,  and  then  in  the  floor  of  a  little  triangular  fossa 


1164 


THE  URINOCtENITAL  SYSTEM. 


Ureter 


^1 Internal  uretliral  orifice 

4 Trigonuni  vesicns 

^^— Ureter 


(trigonuni  femorale)  between  these  vessels  and  the  pelvic  brim.  On  the  side  wall 
of  the  pelvis  the  vas  is  continued  backwards,  and  a  little  downwards  and  inwards, 
in  the  direction  of  the  ischial  spine,  and  lies  immediately  beneath  the  peritoneum, 
through  which  it  can  usually  be  seen  shining.  In  the  pelvic  part  of  its  course  the 
vas  deferens  crosses  on  the  inner  side  of  (1)  the  obliterated  hypogastric  artery,  (2) 
the  obturator  nerve  and  vessels,  (3)  the  vesical  vessels,  and  (4)  the  ureter  (Fig.  823). 
Beyond  the  ureter  tlie  vas  takes  a  somewhat  sudden  bend,  and  passes  down- 
wards and  inwards  towards  the  middle  line,  beneath  the  peritoneum  of  the  pelvic 

floor.  Eeaching  the  interval 
between  the  base  of  the 
bladder  in  front  and  the 
rectum  behind,  the  vasa 
deferentia  of  opposite  sides 
occupy  the  angle  formed 
between  the  vesiculse  semi- 
nales  (Eig.  831).  As  they 
approach  one  another  each 
vas  becomes  somewhat  tor- 
tuous, sacculated,  and  di- 
lated, and  assumes  a  general 
resemblance  in  structure  to 
a  portion  of  the  vesicula 
seminalis.  This  dilated  part 
of  the  vas  deferens  is  termed 
the  ampulla  (ampulla  ductus 
deferentis).  As  it  turns  in- 
wards the  vas  lies  a  short 
distance  behind  the  ureter, 


-Vas  deferens 


Fig.    830. 


HOUI/OM  \1       blOiioN      THROauH     THE      ReCTUM     AND 


Bladder  at  the  Level  at  which  the  Ureters  pierce  the 
Bladder  Wall. 

From  a  specimen  in  the  Surgical  Museum,  Trinity  College,  Dublin. 


and  immediately  in  front  of  the  free  edge  of  the  peritoneal  fold  (sacro-genital)  which 
bounds  the  recto-genital  pouch  of  the  peritoneum.  Just  above  the  base  of  the 
prostate  the  vas  deferens  becomes  once  more  a  narrow  canal,  and  in  this  position 
it  is  joined  by  the  duct  of  the  corresponding  seminal  vesicle  to  form  .the  common 
ejaculatory  duct,  which,  after  a  short  course  downwards,  forwards,  and  inwards 
through  the  prostate,  opens  into  the  urethra. 

In  some  cases  the  vas  deferens  crosses  the  obliterated  liypogastric  artery  before  it  enters  the 
pelvic  cavity  ;  it  normally  does  so  in  the  foetus. 

Common  Ejaculatory  Duct  (ductus  ejaculatorius). — This  minute  duct,  formed 
by  the  union  of  the  vas  deferens  with  the  duct  of  the  corresponding  seminal  vesicle, 
is  less  than  one  inch  in  length,  and  lies  very  close  to  its  fellow  of  the  opposite  side 
as  it  passes  through  the  prostate  behind  its  mesial  lobe.  The  ducts  open  by  slit-like 
apertures  into  the  first  part  of  the  urethra,  one  on  each  side  of  the  sinus  pocularis 
(utriculus  prostaticus). 

The  mucous  membrane  of  the  duct  is  thrown  into  numerous  complicated  folds,  and  in 
connexion  with  it  are  a  number  of  remarkable  minute  diverticula  which  are  enclosed 
within  the  muscular  coat  of  the  duct. 

Seminal  Vesicles. — The  vesiculse  seminales,  or  seminal  vesicles,  are  a  pair  of 
hollow  sacculated  structures  placed  in  front  of  the  rectum  and  behind  the  bladder 
(Fig.  831).  Each  vesicula  seminalis  is  usually  about  two  inches  in  length,  and  has 
its  long  axis  directed  downwards,  inwards,  and  somewhat  forwards.  The  upper 
extremity  of  the  vesicle,  which  is  partly  covered  by  peritoneum,  is  large  and 
rounded,  and  lies  at  a  consideraVjle  distance  from  the  middle  line,  behind  the  lower 
end  of  the  ureter.  The  peritoneum  of  the  recto-genital  pouch  separates  the  upper 
end  of  the  seminal  vesicle  from  the  rectum ;  below  the  peritoneal  cavity  the  vesicle 
and  rectum  are  more  intimately  related.  The  vesicle  tapers  towards  its  lower  end, 
which  is  placed  close  to  the  middle  line  and  immediately  above  the  prostate. 
Inferiorly,  the  vesicle  becomes  constricted  to  form  a  short  duct  (ductus  excretorius), 
which  joins  the  outer  side  of  the  corresponding  vas  deferens  at  an  acute  angle  to 


THE  VAS  DEFEEENS. 


1165 


form  the  common  ejaculatory  duct.  The  inner  side  of  each  vesicle  is  related  to 
the  vas  deferens,  and  the  outer  side,  when  the  bladder  is  empty,  lies  close  to  the 
sloping  pelvic  lloor.  The  seminal  vesicle  often  assumes  a  more  vertical  position 
when  the  bladder  is  distended,  a  more  horizontal  one  when  the  bladder  is  empty. 
Its  upper  end  is  sometimes  found  to  be  curved  backwards  against  the  side  of  the 
rectum.  The  seminal  vesicles  are  in  some  cases  much  smaller  than  usual,  and  may 
be  less  than  one  inch  in  length.  Frequently  they  are  unsymmetrical  as  regards 
size  and  shape.     The  seminal  vesicles  are  more  intimately  related  to  the  wall  of 


Posterior  superior 
iliac  spine 


Gluteus    ^.g 
uiaximus 


Posterior  superior 
iliac  spine 


Ureter 
Jreat  sciatic  notcL 

Vas  deferens 

Spine  of  ischium 

Vas  deferens- 

Seminal  vesicle___i^i£  Jl      '  1K_  ^ 

Bladder  waU_.^E^_  _  '.i  Ll^ 


Levator  ani 

Prostate 

Ischio-rectal  fossa       w3B 
Tuberosity  of  ^ 
ischium  / 


Cut  end  of  rectum 
Apex  of  sacrum 
Great  sciatic  notch 
Ureter 
Peritoneum 
Spine  of  ischium 
Bladiler  wall 


Seminal  vesicle 

J_ Ampulla  of  vas  deferens 
(  Cut  end  of  great  sacro- 
I  sciatic  ligament 
Common  ejaculatory  duct 

Levator  ani 

Tuberosity  of  ischium 

Ischio-rectal  fossa 

Cut  end  of  rectum 
External  sphincter  ani 
Gluteus  maximus 


Fig.  831. — View  of  the  Base  of  the  Bladder,  Prostate,  Seminal  Vesicles,  and  Vasa 

Deferentia  from  BEHFN'D. 

The  coccyx  and  the  sacro-sciatic  ligameuts,  together  with  the  muscles  attached  to  them,  have  been  removed. 
Tlie  levatores  ani  have  been  separated  along  the  median  raphe,  and  drawn  outwards.  A  considerable 
portion  of  the  rectum  and  the  upper  part  of  the  right  seminal  vesicle  have  been  taken  away.  The 
peritoneum  is  coloured  blue. 

the  bladder  than  to  that  of  the  rectum — their  upper  ends  are,  as  we  have  seen, 
separated  from  the  rectum  by  a  portion  of  the  recto-genital  pouch  of  peritoneum, 
and  lower  down  the  septum  of  fascia  which  intervenes  between  the  vesiculse 
seminales  and  the  rectum  is  denser  than  that  which  separates  them  from  the 
bladder. 

The  vfisicula  seminalis  is  in  reality  a  tube  bent  in  a  tortuous  manner  on  itself, 
and  if  the  dense  connective  tissue  which  envelops  it  be  taken  away,  the  length  of 
the  tube  when  untwisted  may  be  found  to  be  as  much  as  five  inches.  The  tube  is 
closed  above,  and  a  variable  number  of  short  tortuous  branches  come  off  it  at 
different  levels.  The  blind  end  of  the  tube  usually  lies  at  the  upper  and  outer 
extremity  of  the  seminal  vesicle,  but  in  some  cases  the  tubular  vesicle  is  so  bent 


1166 


THE  URINOGENITAL  SYSTEM. 


upon  itself  that  the  blind  terminal  part  lies  against  the  side  of  the  issuing  duct. 
The  development  of  the  vesiculse  seminales  shows  that  they  are  to  be  looked  upon 
as  diverticula  of  the  vasa  deferentia,  from  which  they  originally  arise  as  small 
pouches. 


Lateral  aspect 
of  prostate 


Uraclius 


Infero-lateral 
area  of  bladder 


Urethra 


Fig.  8-32. — The  Bladder,  Prostate,  and  Seminal  Vesicle  viewed  from  the  Side. 
Drawn  from  specimens  hardened  in  situ. 

In  A  the  bladder  contained  but  a  small  anjount  of  fluid  ;  in  B  the  quantity  was  somewhat  greater. 

The  dense  tissue  in  which  the  seminal  vesicles  are  embedded  contains  much  nnstriped  muscle 
tissue,  which,  sweeping  round  in  the  side  wall  of  the  recto-genital  pouch,  gains  an  attachment 
to  the  fascia  in  front  of  the  sacrum  and  to  the  rectum.  Inferiorly  this  tissue  is  attached  to 
the  capside  of  the  prostate.  The  large  veins  coming  from  the  prostatic  and  vesical  plexuses  are 
closely  related  to  the  seminal  vesicles. 

Structure  of  the  Vas  Deferens  and  of  the  Vesicula  Seminalis. — Except  near 
its  termination,  where  it  is  dilated  to  form  the  ampulla,  the  vas  deferens  is  a  thick- 
walled  tube  with  relatively  a  very  small  lumen.     The  hard  cord-like  sensation  which 


Coininoii 
ejaciilatory  duct 


^Seminal 
vesicle 

1-  ---.Vas 

deferens 


V£'L^  ^Cominon  ejacu- 
^y      latory  duct 


Si'iuiiial  vesic 


A  and  B.   Drawings  illustrating  the  seminal  vesicle  and  the  ampulla  of  vas  deferens  taken  from  two  different 

subjects. 
C  The  seminal  vesicle  and  vas  deferens  have  been  cut  into  to  show  the  pitted  structure  of  their  walls. 

the  vas  deferens  conveys  to  the  touch  is  due  to  the  thickness  and  toughness  of  its 
wall,  which  is  composed  of  three  layers — an  outer  fibrous  (tunica  adventitia),  an 
intermediate  muscular  (tunica  muscularis),  and  an  inner  mucous  coat  (tunica 
mucosa).  The  thickness  of  the  wall  is  due  to  the  great  development  of  the  middle 
or  muscular  coat,  which  is  composed  of  an  intermediate  layer  of  circularly  and 
an  inner  and  outer  layer  of  longitudinally  directed  unstriped  muscular  fibres.  Of 
these  layers  the  middle  one  is  by  far  the  thickest  and  forms  the  chief  part  of  the 


DESCENT  OF  THE  TESTIS. 


1167 


thickness  of  the  wall  of  the  vas  deferens.  The  mucous  membrane  of  the  vas 
exhibits  a  number  of  slight  longitudinal  folds  and  possesses  a  ciliated  epithelium. 
The  ampulla,  or  terminal  part,  possesses  a  much  thinner  wall,  and,  as  the  surface  of 
its  mucous  membrane  has  a  number  of  ridges  separating  depressed  areas,  the  lining 
of  this  part  of  the  tube  presents  a  pitted  or  honeycombed  appearance.  The  wall 
of  the  vesicula  seminalis  resembles  that  of  the  ampulla  in  being  thin,  and  in 
having  a  mucous  lining  with  uneven  honeycomb-Uke  ridges  and  depressions.  In 
it  the  same  coats  are  to  be  recognised  as  in  the  ^'as,  but  the  muscular  layer  is  much 
thinner,  and  the  strata  composing  it  less  regularly  arranged. 

The  seminal  vesicles  are  not  present  in  all  mammals,  and  in  tliose  in  which  they 
do  occur  their  relative  size  and  form  vary  much.  Among  the  carnivora,  marsupials, 
and  some  other  groups  of  mammals,  the  seminal  vesicles  do  not  occur ;  in  some  other 
animals,  such,  for  instance,  as  the  hedgehog,  they  are  relatively  of  enormous  size. 

Vessels  and  Nerves  of  the  Vas  Deferens  and  of  the  Vesicula  Seminalis. — The  vas 

ri'ceivi'S  its  arterial  supjily  from  the  superior  or  inferior  vesical  artery.  The  artery  to  the 
vas  accompanies  that  structure,  sujiplying  it  as  far  as  the  testis,  where  it  ends  by  anastomosing 
with  branches  of  the  spermatic  artery.  The  vesicula  seminalis  is  sui)plied  by  the  inferior  vesical 
artery.  The  nerves  of  the  vas  and  vesicula  seminalis  are  derived  from  the  hypogastric  ple.\us. 
In  lower  animals  the  nerves  for  the  seminal  vesicles  leave  the  spinal  cord  Ijy  the  nerve  roots  of 
the  second,  third,  and  fourth  lumbar  nerves. 


Descent  of  the  Testis. 

The  peculiar  course  pursued  by  the  vas  deferens  in  the  adult,  and  the  manner  in  which 
it  is  related  to  the  anterior  abdominal  wall,  are  rendered  clear  by  a  study  of  the  arrange- 
ment of  the  parts  that  obtains  in  the  foitus.  The  testes  until  nearly  the  end  of  intra- 
uterine life  are  placed  in  the  abdominal  cavity.  Lying  at  first  on  the  posterior  wall  of 
the  abdomen  at  the  level  of  the  two  upper  lumbar  vertebra^  and  just  below  the  level 
assumed  l)y  the  permanent  kidney,  the  testis  is  held  in  place  by  a  fold  of  peritoneum  or 
mesentery,  called  the  mesorchium.  As  growth  goes  on  the  testis  is  found  to  occupy  a 
lower  level  in  the  abdominal  cavity  ;  in  the  third  month  it  lies  in  the  iliac  fossa,  and  in 
the  seventh  it  is  situated  near  the  internal  abdominal  ring.  Meanwhile  a  blind  pouch  or 
diverticulum    of    the    peri- 

Bladiler        Hyi)Ogastric  artery 
Internal  2v— ==?:: ^^~~7C 


t<nieal  membrane,  termed 
the  processus  vaginalis,  has 
grown  downwards  and  in- 
wards through  the  anterior 
abdominal  wall  towards  the 
scrotum,  deriving  as  it  goes 
a  covering  from  each  of  the 
layers  of  the  abdominal  wall 
through  which  it  passes.  The 
testis  with  its  mesorchium 
enters  the  diverticulum  of 
the  abdominal  cavity,  and 
descends  Avithin  it  until  the 
sci-otiun  is  reached.  At  a 
later  stage,  the  connexion 
between  the  part  of  the 
processus  vaginalis  that  lies 
in  the  scrotum  and  the 
])eritoueal  lining  of  the  ab- 
domen becomes  lost  by  the 
obliteration  of  the  upper 
part  of  the  pouch.  Thus 
the    part    of    the  processus 


abdominal 


Eijitlidyiuis 


Gubernaciihim 


Mesorchium 


Vas  deferens 


Psoas 
Kectum 


Fig.  834. — View  lookinc;  fuo.m  above  into  the  Pelvis  and  Lower 
Part  of  the  Abdominal  Cavity  in  a  FolTUs  of  about  the 
Seventh  Month. 

On  the  left  side,  which  represents  ;i  slightly  more  advanced  condition  than 
the  right,  the  testis  has  entered  the  inguinal  canal  ;  on  the  right  side 
the  testis  is  still  within  the  abdominal  cavity. 


vaginalis  tliat  persists  in  the  scrotum  becomes  the  parietal  portion  of  the  tunica  vaginalis ; 
while  the  visceral  part  of  that  membrane  is  the  primitive  peritoneal  covering  of  the  testis 
and  epididymis  (Figs.  834  and  835). 

Often  a  small  fibrous  band— the  ligamentum  vaginale — may  be  found  in  the  adult 
passing  through  the  inguinal  canal  and  joining  the  peritoneum  superiorly  in  the  region  of 
the  internal. abdonainal  ring.     Sometimes  the  ligament  is  connected  below  with  the  tunica 


1168 


THE  UEINOGENITAL  SYSTEM. 


Fig, 


835. — Diagram  to  illustrate  the  descent  of  the 
testis  and  the  manner  in  which  the  tunica  vaginalis 
is  derived. 

a.c.  Abdominal  cavity.  s.     Scrotum. 

p.v.  Processus  vaginalis.  t.v.  Tunica  vaginalis. 

X.     Ligamentum  vaginale. 


t.      Testis. 


vaginalis,  but  more  often  it  does  not  reach  so  far  downwards.     When  present  it  represents 
the  obHterated  portion  of  the  processus  vaginahs  (rudimentum  processus  vaginahs). 

In  other  rare  cases  the  processus  vaginalis  may  persist  after  birth  as  a  channel  freely 
open  to  the  abdominal  cavity  above,  or  the  passage,  becoming  closed  at  intervals,  may 
give  rise  to  one  or  more  cysts  within  the  coverings  of  the  spermatic  cord. 

It  sometimes  happens  that  the  descent 
of  the  testis  is  arrested,  and  then,  either 
failing  to  enter  the  processus  vaginalis, 
the  testis  remains  within  the  abdominal 
cavity  ;  or  entering  the  processus  vaginalis, 
it  fails  to  reach  the  scrotum,  and  lies  in 
the  inguinal  canal.  The  term  cryptorchism 
is  frequently  applied  to  such  cases. 

In  connexion  with  the  descent  of  the 
testis  a  remarkable  cord-like  structure — 
the  gubernaculum  testis — must  be  men- 
tioned. The  gubernaculum  arises  for  the 
most  part  within  a  peritoneal  fold  which, 
at  an  early  time  in  the  development  of 
the  foetus,  may  be  seen  stretching  from 
the  inguinal  region  to  the  Wolffian  duct  (future  duct  of  testis)  and  lower  end  of 
mesonephros  (primitive  kidney).  This  peritoneal  fold,  termed  the  plica  inguinalis 
(or  plica  inguino-mesonephrica),  is  joined  from  above  by  a  less  marked  fold  (the  plica 
testis  inferior)  which  extends  downwards  from  the  lower  end  of  the  testis, — at  this 
time  situated  in  the  abdomen  close  to  the  inner  aspect  of  the  mesonephros.  Within  both 
these  folds  smooth  muscular  and  fibrous  tissue  arises  and  gives  origin  to  a  continuous 
band  or  ligament  —  the  gubernaculum  testis.  The  gubernaculum  is,  therefore,  to  be 
regarded  as  originally  composed  of  two  portions,  —  a  part  developed  within  the  plica 
inguinalis  and  a  part  formed  within  the  plica  testis  inferior.  It  is  interesting  to  note 
that  the  representatives  of  these  two  parts  of  the  gubernaculum  remain  separate  in  the  female 
throughout  life,  and  are  the  round  ligament  of  the  uterus  and  the  ligament  of  the  ovary. 
The  gubernaculum,  when  it  is  at  its  greatest  development  (about  the  sixth  month),  is 
I'ounded  and  cord-like,  and  is  attached  above  to  the  lower  end  of  the  testis,  while  inferiorly 
it  is  fixed  near  the  inguinal  region.  In  the  lower  part  of  its  course  it  is  closely  related  to, 
and  is  partly  covered  by,  the  peritoneum  of  the  processus  vaginalis.  Striped  muscular 
fibres  are  present  in  the  lower  part  of  the  gubernaculum,  and  these  have  their  origin  from 
the  muscles  of  the  inguinal  part  of  the  anterior  abdominal  wall.  As  the  testis  enters  the 
processus  vaginalis  the  gubernaculum  atrophies,  but  at  birth  a  short  part  of  the  guber- 
naculum may  still  be  found  passing  downwards  towards  the  lower  part  of  the  scrotum  and 
lying  below  the  level  of  the  tunica  vaginalis.  It  is  considered  by  some  anatomists  that 
the  movement  downwards  of  the  testis  may  be  pai'tly  due  to  a  pull  caused  by  the  shrink- 
ing of  the  gubernaculum  as  it  atrophies. 

In  some  mammals,  such  as  the  elephant,  the  testes  remain  permanently  within  the 
abdominal  cavity ;  while  in  others,  such  as  the  rabbit  and  the  hedgehog,  the  peritoneal 
pouches  remain  widely  open  throughout  life,  and  the  testes  are  periodically  withdrawn 
into  the  abdomen. 

The  Spermatic  Cord. 

The  testis  in  its  course  downwards  through  the  abdominal  wall  into  the 
scrotum  takes  with  it  its  duct  (vas  deferens),  blood-vessels,  lymphatics,  and  nerves 
of  supply.  All  these  lie  together  in  the  inguinal  canal  as  they  traverse  the 
abdominal  wall,  and  when  they  leave  the  canal  by  the  external  abdominal  ring 
they  extend  downwards  to  the  posterior  border  of  the  testis.  The  vas  deferens, 
the  spermatic  vessels,  and  the  nerves  and  lymphatics  of  the  testis,  loosely  connected 
together,  form  the  spermatic  cord  (funiculus  spermaticus).  At  the  internal 
abdominal  ring  the  constituent  parts  of  the  cord  separate  from  one  another,  and 
the  cord  may  therefore  be  considered  to  extend  from  the  internal  abdominal  ring 
to  the  posterior  border  of  the  testis.  The  structures  whicli  form  the  cord  are  enclosed 
within  a  numljer  of  coverings  derived  from  the  layers  of  the  anterior  abdominal 
wall,  and  these,  when  the  constituents  of  the  cord  reach  the  posterior  border  of  the 
testis,  surround  the  tunica  vaginalis,  and  so  form  a  part  of  the  wall  of  the  scrotum. 
The  sheaths  or  coverings  of  the  cord  derived  from  the  abdominal  wall  -are  three  in 


THE  SPERMATIC  CORD. 


1169 


number,  and  are  named  intercolumnar  fascia, 
cremasteric  fascia,  and  infundiijuliform 
fascia.  The  intercolumnar  fascia''is  the  most 
superficial  of  the  three  sheaths  and  is  derived 
from  the  aponeurosis  of  the  external  oblique 
muscle,  with  which  it  is  continuous  round 
the  mary;ins  of  the  external  abdominal  rincr. 
The  cremasteric  fascia  consists  partly  of  mus- 
cular fibres  derived  from  the  lower  part  of 
the  internal  oblique  muscle,  and  partly  of 
delicate  connective  tissue.  The  muscular 
fibres  pass  down  over  the  cord,  and  form  a 
series  of  loops  round  the  testis  aud  tunica 
vaginalis.  The  infundibuliform  fascia  is  de- 
rived from  the  fascia  transversalis  of  the 
abdomen.  It  passes  downwards  over  the 
cord  and  encloses  its  various  structures,  to- 
gether with  a  certain  amount  of  areolar 
tissue  derived  from  th43  sub -peritoneal 
tissue  of  the  abdominal  wall  and  some 
smooth  muscle  fibres,  in  a  continuous 
sheath. 

In  addition  to  tlie  structiu'es  enumerated  above, 
the  artery  to  the  vas,  the  cremasteric  artery,  and  the 
genital  branch  of  the  genito-crural  nerve,  accom- 
pany the  structures  forming  tlie  spermatic  cord. 

The  Sceotum. 


I Sinus  epididymidis 


-Veins 


Vas  deferens 


_  ,  .  Coi  pus  Highraori 

Epididymis 

i-.»-.Septula  testis 

.""-.^■l.obule.s 


Vein 


.Skin 

Superficial 
".     fascia 

External  sper- 

niatir  fascia 
Infundibuli- 

form  fascia 


Venous 
^-J^-Ijlexus 

,  ':^        t  "^Cremaster 

.     Artery  to  vas  muscle 

^  as  deferens    :     deferens 

Spennatic  artery 

B 

Fig.  836. 


The     scrotum,     in     which     the     testes    are    a.   Trausverse  .section  of  testis  aud  epididymis. 
■,         -,  .  '       .  ■       Tnn  "•    transverse  section  of  spermatic  cord  below 

placed,  varies  much  in  appearance  m  dinerent  external  abdominal  ring. 

subjects,  and  even  in  the 
same  individual,  at  differ- 
ent times.  As  the  result 
of  cold  or  of  exercise,  the 
wall  of  the  scrotum  becomes 
contracted  and  firm,  and 
the  skin  covering  it 
wrinkled ;  at  other  times 
the  wall  may  be  relaxed 
and  flaccid,  the  scrotum 
then  assuming  the  appear- 
ance of  a  pendulous  bag. 
The  left  side  of  the  scrotum 
reaches  to  a  lower  level 
than  the  right,  in  corre- 
spondence with  the  lower 
level  of  the  testis  on  that 
side  of  the  body.  The  skin 
covering  the  scrotum  is  of 
a  darker  colour  than  the 
general  skin  of  the  body, 
and  is  covered  by  hair. 
It  is  marked  in  the  middle 
line  by  a  median  raphe 
(raphe    scroti),    which    is 

The  external  and  the  iuternal  oblique  muscles  have  been  reflected  to  .show  continued     backwards     tO- 
the  whole  length  of  the  inguinal  canal,  and  the  cord  enclosed  withm  t        i  j    f 

the  infundibuliform  fascia  is  seen  cut  across.     (From  Cunningham.)      WarCtS    the    ailUS,    anCl    lOr- 

79 


Deep  Dissectiox  of  the  Inguixal  Region. 


1170  THE  UEINOaENITAL  SYSTEM. 

wards  ou  to  the  under,  or  urethral,  surface  of  the  penis.  The  difference  in  the 
appearance  of  the  scrotum  at  different  times  is  due  to  the  amount  of  contraction, 
or  relaxation  of  a  layer  of  muscular  fibres,  constituting  the  dartos  muscle,  situated 
in  the  superficial  fascia.  When  this  muscular  layer  is  contracted,  the  scrotum 
becomes  smaller  and  somewhat  globular,  and  the  skin  is  thrown  into  folds  or 
^vrinkles  called  rugae ;  when  it  is  relaxed,  the  scrotum  is  flaccid  and  pendulous, 
and  the  skin  becomes  more  smooth  and  even.  The  layer  of  fascia  which  con- 
tains the  smooth  muscle  fibres  of  the  dartos  muscle  is  often  spoken  of  as  the 
tunica  dartos.  It  can  be  shown  to  be  continuous  superiorly  with  the  superficial 
fascia  of  the  penis,  and  with  the  deep  layer  of  the  superficial  fascia  of  the 
abdomen,  and  to  be  attached  laterally  to  the  bones  forming  the  pubic  arch.  The 
muscle  fibres  are  arranged  in  a  thick  layer  of  interlacing  bundles,  and  many 
of  the  deeper  fibres  are  continued  into  a  septum  (septum  scroti)  which  divides 
the  scrotum  into  two  cavities,  one  for  each  testis.  The  wall  of  each  of  these 
cavities  is  formed  by  the  corresponding  tunica  vaginalis,  infundibuliform  fascia, 
cremasteric  fascia,  and  intercolumnar  fascia,  while  the  skin,  the  superficial 
fascia,  and  the  superficial  part  of  the  dartos  muscle  form  coverings  which  are 
common  to  the  whole  scrotum,  and  enclose  both  cavities.  The  layer  of  tissue 
immediately  beneath  the  dartos  tunic  is  made  up  of  exceedingly  loose  and  easily 
stretched  areolar  connective  tissue,  and  in  it  as  throughout  in  the  superficial  fascia 
of  the  scrotum  there  is  an  entire  absence  of  fat. 

The  scrotum  in  the  fa3tus  contains  no  cavity,  but,  like  the  labia  majora  in  the  female,  it  is 
composed  entirely  of  vascular  connective  tissue. 

Vessels  and  Nerves  of  the  Scrotum. — The  scrotum  receives  its  vascular  supply  from  the 
superficial  perineal  branches  of  the  iiiternal  pudic  artei'ies  Avhich  reach  it  from  behind,  and 
from  the  external  pudic  branches  of  the  femoral  artery  which  reach  its  ujjper  and  anterior  part. 
The  nerves  of  the  scrotum  are  derived  from  the  superficial  perineal  branches  of  the  internal 
j)udic,  from  the  perineal  branch  of  the  small  sciatic,  and  from  the  ilio-inguinal  nerve.  The 
branches  from  the  internal  pudic  and  sciatic  nerves  reach  the  scrotum  from  behind,  while  the 
ilio-inguinal  supplies  its  ujoper  and  anterior  part.  The  nerve  fibres  for  the  dartos  muscle  fibres 
are  believed  to  come  from  the  ]iyj)ogastric  plexus. 

THE  PENIS. 

The  penis  is  composed  chiefly  of  erectile  tissue,  and  is  traversed  by  the  canal 
of  the  urethra.  The  surface  nearest  to  which  the  canal  of  the  urethra  lies  is 
called  the  under  or  urethral  surface  (facies  urethralis) ;  the  opposite  and  more 
extensive  aspect  is  the  dorsum  penis.  The  erectile  tissue  is  for  the  most  part 
disposed  in  three  longitudinal  columns,  which  in  the  body  of  the  organ  are  placed 
side  by  side,  while  at  the  root  of  the  penis  they  separate  from  one  another,  and 
become  attached  to  the  triangular  ligament  and  the  pubic  arch.  Two  of  these 
masses  of  erectile  tissue,  placed  one  on  each  side  of  the  middle  line,  and  forming  the 
dorsum  and  sides  of  the  penis,  are  called  the  corpora  cavernosa  (corpora  cavernosa 
penis),  while  the  third,  which  is  called  the  corpus  spongiosum  (corpus  cavernosum 
urethree),  is  situated  mesially  near  the  urethral  surface.  The  corpus  spongiosum  is 
the  part  of  the  penis  which  is  traversed  by  the  urethra,  and  it  is  considerably 
smaller  than  the  corpora  cavernosa  which  form  the  chief  bulk  of  the  organ. 

In  the  body  of  the  penis  (corpus  penis)  each  corpus  cavernosum  is  placed  close 
to  the  mesial  plane,  and  presents  a  rounded  surface,  except  where  it  is  flattened 
by  contact  with  its  fellow  of  the  opposite  side.  The  corpora  cavernosa  are  separ- 
ated on  the  anterior  (dorsal)  surface  by  a  shallow  groove,  and  on  the  posterior 
(urethral)  aspect  by  a  deeper  and  wider  furrow,  in  which  lies  the  corpus  spongiosum 
(Fig.  839).  Towards  the  distal  end  of  the  penis  the  corpus  spongiosum  appears  to 
expand,  and,  spreading  towards  the  dorsal  surface  of  the  organ,  it  forms  a  kind  of 
conical  cap,  the  glans  penis,  which  covers  over  the  blunt  rounded  termination  of 
the  corpora  cavernosa.  The  prominent  margin  of  the  glans,  called  the  corona 
glandis,  projects  dorsally  and  laterally  beyond  the  extremities  of  the  corpora 
cavernosa.  Like  the  corpus  spongiosum  the  glans  is  traversed  by  the  urethra, 
which  ends  near  the  summit  of  the  glans  in  a  slit-like  opening  called  the  meatus 
urinarius,  or  external  urethral  orifice.     The  united  corpora  cavernosa  end  in  a  blunt 


THE  PENIS. 


1171 


conical  extremity,  tlie  apex  of  which  is  received  into  a  hollow  in  the  base  of  the 
glans.  The  skin  covering  the  body  of  the  penis  is  thin,  delicate,  and  freely 
movable,  and,  except  near  the  root  of  the  organ,  is  free  from  hairs ;  on  the  urethral 
aspect  of  the  penis  the  skin  is  marked  by  a  median  raphe,  continuous  with  the 
raphe  of  the  scrotum.  Traced  towards  the  base  of  the  glans,  the  skin  forms  a  free 
fold  called  the  prepuce  (praeputium),  which  overlaps  the  glans  to  a  variable  extent. 
From  the  deep  surface  of  the  prepuce  the  skin  is  reflected  on  to  the  terminal  part 
of  the  penis,  just  above  the  level  of  the  corona  glandis,  and  is  continued  over  the 


(.'ovpus  oavernosui 
Corpus  siioiij;iosuni 

Crus  ppnis 

Miillms  iiivthr.' 

TubiT  iscliii 


Fk;.  838.- -Dissection  to  illustrate  the  Component  Parts  of  the  Penis. 

On  tlie  ritfht  side  of  tlie  figure  the  muscles  of  the  thigh  have  been  reflected  down  to  the  plane  of  the  ohturator 
exteruus.     The  letters  TL  are  placed  upon  the  triangular  ligament. 

entire  glans  to  the  meatus  urinarius.  A  small  median  fold,  the  frenulum  praeputii, 
passes  to  the  deep  surface  of  the  prepuce  from  a  point  just  below  the  meatus 
urinarius.  The  skin  covering  the  glans  is  firmly  attached  to  the  underlying 
erectile  tissue,  and  here,  as  well  as  on  the  deep  surface  of  the  prepuce,  it  presents 
some  resemblance  to  mucous  membrane. 

Sometimes  minute  sebaceous  glands  (glandul^e  prfeputiales)  are  found  in  very  variable 
numbers  on  the  glans  and  inner  surface  of  the  prepuce  ;  the  secretion  from  these  when 
they  are  present  may  help  to  form  the  smegma  praeputii,  which  tends  to  collect  in  the 
groove  between  the  glans  and  the  prepuce.  The  main  source  of  the  smegma  is  to  be 
found  in  the  desquamated  and  broken-down  epithelial  cells  derived  from  the  surface  of 
the  glans  and  prepuce. 

At  the  root  of  the  penis  (radix  penis)  the  three  component  parts  of  the  organ 
separate  from  one  another  (Fig.  838).  The  corpora  cavernosa,  diverging  from  each 
other  laterally,  at  first  become  somewhat  swollen,  and  then,  gradually  tapering  off, 
gain  a  firm,  fibrous  attachment  to  the  periosteum  on  the  inner  part  of  the  pubic 
arch.  These  diverging  parts  of  the  corpora  cavernosa  are  called  the  crura  penis,  and 
each  is  covered  by  the  corresponding  ischio-cavernosus  muscle.  The  corpus 
spongiosum  lying  between  the  crura  becomes  enlarged,  and  forms  a  somewhat 
spherical  mass  which  receives  the  name  bulb  of  the  urethra  (bulbus  urethrse).  The 
bulb  varies  much  in  size  in  different  individuals,  and  is  attached  to  the  under 
surface  of  the  triangular  ligament,  against  wdiich  it  rests.  The  posterior  part  and 
under  surface  of  the  bulb  usually  show  a  median  notch  or  groove,  which  is  an  indi- 
cation that  the  bulb  is  originally  composed  of  two  symmetrical  portions,  which  during 
79  a 


1172 


THE  UEINOGENITAL  SYSTEM. 


development  have  become  fused  in  the  middle  line.  These  two  portions  are  termed 
the  hemispheria  bulbi  urethrse,  and  are  best  seen  in  subjects  whose  tissues  have  been 
hardened  by  intra-vascular  injection.  A  slightly  marked  median  septum,  situated 
within  the  bulb  tissue,  indicates  on  a  deeper  plane  the  line  along  which  fusion  has 
taken  place.  The  canal  of  the  urethra,  piercing  the  triangular  ligament,  enters 
the  bulb  obliquely  a  short  distance  in  front  of  its  posterior  extrenuty  (Fig.  844). 
Covering  the  superficial  surface  of  the  bulb  is  the  bulbo-cavernosus  muscle. 

A  somewhat   triangular  band  of  strong  fibrous  tissue,  called  the  suspensory 

ligament   of  the   penis,   is 
'^    —      ?  attached   to  the  front  of 

the  symphysis  pubis,  and 
extends  to  the  fibrous 
capsule  of  the  penis,  with 
which  it  becomes  con- 
tinuous. 

Structure  of  the 
Penis.  —  Each  corpus  cav- 
ernosum  penis  is  enclosed  by 
a  dense  white  fibrous  coat 
or  tunica  albuginea  (tunica 
albuginea  corporum  cavern- 
osorum),  which,  fusing  with 
the  corresponding  coat  of  the 
opposite  side,  forms  a  mesial 


Fio.  8-39. — A  Longitudinal  Section  of  the  Terjiinal  Portion  of 
THE  Penis,  and  a  Transverse  Section  throitgh  the  Body  of 
the  Organ. 


a.  Corpus  cavernosuiii. 
h.  Corpus  spongiosum. 
c.  Urethral  canal. 


d.  Glaus  penis. 

e.  Fossa  iiavicnlaris. 

/.  Part  of  septum  pectiniforme. 


Dorsal  vein. 
Dorsal  artery. 
Dorsal  nerve. 


septum  (septum  penis).  The  septum  is  very  incomplete,  especially  near  the  terminal  part 
of  the  penis,  where  it  is  interrupted  by  a  number  of  nearly  parallel  slit-like  perforations, 
hence  the  term  septum  pectiniforme  is  often  applied  to  it  (Figs.  839  and  845).  Through 
these  openings  the  erectile  tissue  of  the  corpora  cavernosa  of  opposite  sides  is  continuous. 

The  fibrous  coat  contains  some  elastic  fibres,  and  may  be  divided  into  an  outer  layer 
of  longitudinally  directed  fibres  and  an  inner  layer  of  circular  fibres,  some  of  which  latter 
are  continued  into  the  septum.  Numerous  fibrous  strands,  called  trabeculse  (trabeculse 
corporum  cavernosorum),  proceed  from  the  deep  surface  of  the  tunica  albuginea,  and 
stretching  across  the  interior  of  the  corpus  cavernosum,  form  a  fine  sponge-like  framework 
whose  interspaces  communicate  freely  with  one  another,  and  'are  filled  with  blood. 
These  blood-containing  spaces  lead  directly  into  the  veins  of  the  penis,  and  like  the  veins 
have  a  lining  of  flat  endothelial  cells.  The  size  of  the  penis  varies  with  the  amount  of 
blood  in  this  cavernous  tissue.  The  structure  of  the  corpus  spongiosum  resembles  that 
of  the  corpora  cavernosa,  but  the  fibrous  coat  is  much  thinner  and  more  elastic,  and  the 
trabeculie  are  finer  (Fig.  839). 

The  glans  penis  is  also  composed  of  cavernous  tissue  which  communicates  by  a  rich 
venous  plexus,  situated  on  the  ventral  aspect  of  the  urethra,  with  the  corpus  spongiosum 
urethr^e.  No  strongly  marked  tunica  albuginea  is  present,  and  the  erectile  tissue  is 
practically  bounded  by  the  firmly  adherent  skin.  Surrounding  the  urethra,  which  in  this 
part  of  the  penis  is  represented  by  a  laterally  compressed  slit-like  passage,  is  a  mass  of 
fibro-elastic  tissue  which  forms  a  kind  of  median  septum  within  the  glans.  This  septum 
is  continued  backwards  to  join  the  sheath  of  the  conical  end  of  the  corpora  cavernosa,  and 
ventrally  it  gives  attachment  to  the  frenulum  of  the  prepuce.  It  imperfectly  divides  the 
erectile  tissue  of  the  glans  into  right  and  left  portions,  which,  however,  freely  communicate 
dorsally.     From  the  septum  trabecular  pass  out  in  all  directions  into  the  tissue  of  the  glans. 

Loosely  surrounding  the  coi'pora  cavernosa  and  the  corpus  spongiosum  is  a  fibrous 
sheath  containing  numerous  elastic  tissue  fibres.  This  sheath  is  termed  the  fascia  penis 
and  reaches  as  far  as  the  base  of  the  glans,  where  it  becomes  fixed  to  the  floor  of  the 
groove  limited  by  the  corona  gland  is.  In  its  proximal  part  the  sheath  gives  insertion  to 
many  of  the  fibres  of  the  bulbo-cavernosus  and  ischio-cavernosus  muscles. 

Superficial  to  the  fascia  penis  is  a  layer  of  extremely  lax  areolar  tissue,  and  more 
superficial  still  is  a  prolongation  of  the  dartos  muscle  of  the  scrotum  (dartos  penis)  and 
the  delicate  skin  of  the  penis.  Numerous  sebaceous  glands  are  present  in  the  skin, 
especially  on  the  iirethral  aspect  of  the  penis. 

In  some  mammals,  such  as  the  walrus,  dog,  hear,  baboon,  etc.,  a  Ijone  called  the  os  penis  is 
developed  in  the  septum  which  intervenes  between  the  corpora  cavernosa. 

Vessels  and  Nerves  of  the  Penis. — The  penis  receives  its  arterial  supply  from  branches  of 


THE  PEOSTATE. 


1173 


the  iuteriial  piidic  artery.  The  erectile  tissue  of  the  corpora  cavernosa  is  siipjilied  chiefly  by  the 
deep  arteries  of  the  penis,  while  that  of  the  corpus  spongiosum  receives  its  arterial  supply  from 
the  artery  to  the  bulb.  Branches  of  the  dorsal  artery  ui'  the  penis  piercing  the  fibrous  coat  of 
the  corpora  cavernosa  furnisli  additional  twigs  to  the  erectile  tissue  of  these  structures.  The 
glans  receives  its  chief  blood  supjily  from  branches  of  the  dorsal  artery.  The  small  branches  of 
these  arteries  run  in  the  trabeculse  of  the  erectile  tissue,  and  the  capillaries,  into  Avhich  they 
lead,  open  directly  into  the  cavernous  venous  spaces.  As  tlu-y  lie  in  the  finer  trabecuhe  the 
smaller  branches  often  jjresent  a  peculiar  twisted  ajjpearance,  and  hence  the  name  helicine 
arteries  (arteria;  helicinte)  is  sometimes  aj^plied  to  them. 

The  veins  with  which  the  cavernous  spaces  communicate  carry  tlie  blood,  for  the  most  part, 
I'itlier  directly  into  the  prostatic  plexus,  or  into  the  dorsal  vein,  and  so  to  the  prostatic  plexus. 
The  dorsal  vein  of  the  jienis  begins  in  tril)utaries  from  the  glans  and  j)re2?uce,  and  lies  in  the 
groove  between  the  corpora  cavernosa  as  it  ascends  to  pass  beneath  the  sub-puljic  ligament  and 
join  the  prostatic  plexus.  On  each  side  of  it  lies  the  dorsal  artery,  and  still  farther  from  the 
middle  line  the  dorsal  nerve  (Fig.  839). 

Tlie  lymphatics  of  the  penis  aj-e  arranged  in  a  deep  and  superficial  series  and  end  in  the 
inner  glands  of  tlie  inguinal  group. 

The  nerve-su2)ply  of  the  penis  is  derived  from  the  internal  jiudic  nerve  and  from  the  hypo- 
gastric and  pelvic  plexuses.  The  branches  of  the  internal  pudic  are  the  dorsal  nerve  of  the 
jienis,  and  branches  from  the  superficial  perineal  nerves.  These  supply  the  cutaneous  structures 
of  the  jjenis,  while  the  sympathetic  filaments  from  the  hypogastric  and  pelvic  ])lexuses,  whicli 
reach  the  penis  through  the  prostatic  plexus,  end  in  the  erectile  tissue. 

THE  PROSTATE. 

The  prostate  (prostata)  is  a  partly  glandular,  partly  muscular  organ  of  a  dark 
Itrown-red  colour  whicli  surrounds  the  beginninij-  of  the  urethra  in  the  male.  It 
lies  within  the  pelvis  behind  the  pubes,  and  is  enclosed  by  a  dense  capsule  derived 
from  the  pelvic  fascia.  Through  the  various  connexions  of  this  capsule  the 
prostate  is  firmly  fixed  w^ithin  the  pelvic  cavity.  The  common  ejaculatory  ducts 
traverse  the  prostate  in  their  course  downwards  and  forwards  to  join  the  urethra 
as  it  descends  through  the  gland  (Fig.  831).  The  size  of  the  prostate  varies 
considerably  in  different  individuals,  but  its  transverse  or  longest  diameter  is 
usually  from  one  and  a  quarter  to  one  and  a  half  inches;  its  antero- posterior 
diameter  about  three-quarters  of  an  inch  ;  and  its  vertical  diameter  about  one  and  a 


Crethra 
A  B 

Fiu.  8^0.— Bladder,  Pkostate,  and  Sejiinal  Vesicles  viewed  i-kom  the  Outer  Side. 

Drawn  from  specimens  hardened  in  situ. 

quarter  inches.  Superficially  the  prostate  is  separated  from  the  bladder  by  deep 
wide  lateral  grooves  directed  downwards  and  forwards,  and  liy  a  narrow  posterior 
groove  which  is  horizontal. 

In  connexion  with  the  prostate  we  descril»e  an  apex  which  is  directed  down- 
wards, a  base  looking  upwards,  a  posterior,  and  two  lateral  surfaces.  The  general 
outline  of  the  organ  has  Ijeen  often  compared  with  that  of  a  Spanish  chestnut. 
The  upper  surface,  or  base  of  the  prostate  (basis  prostatee)  is  directed  upwards 
against  the  under  aspect  of  the  bladder,  in  the  neighbourhood  of  its  urethral  open- 
ing. The  greater  part  of  this  surface  is  structurally  continuous  with  the  bladder 
waU,  only  a  narrow  portion  remains  free  on  each  side,  and  forms  the  lower  limit 
of  the  deep   groove  which   marks    the   separation  of   the  bladder   and   prostate 


1174 


THE  UEINOaENITAL  SYSTEM. 


BladdcT 


lateral 


1  j'retw- 


(Fig.  840).  The  lateral  surface  of  the  prostate  is  convex  and  prominent,  especially 
in  its  posterior  and  upper  portion,  and  rests  against  the  fascia  covering  the  levator 
ani  muscle.  The  lateral  surfaces  are  directed  for  the  most  part  outwards,  down- 
wards, and  somewhat  forwards,  and  meet  together  in  front  in  a  rounded  anterior 
border,  often  called  the  "anterior  surface"  (facies  anterior)  of  the  prostate. 
Posteriorly  the  prostate  presents  a  flattened  somewhat  triangular  area,  directed 
backwards  and  downwards  against  the  anterior  wall  of  the  rectum,  from  which  it 
is  separated  by  a  layer  of  the  pelvic  fascia.  This  flattened  posterior  surface  (facies 
posterior)  is  separated  on  each  side  from  the  lateral  surface  by  a  rounded  border 
which,  beginning  above  at  the  prominent  lateral  part  of  the  prostate,  ends  below 
at  the  apex  of  the  organ.  The  apex  of  the  prostate  (apex  prostatas)  points  down- 
wards, and  is  in  relation  to  the  compressor  urethrae  muscle,  from  which  it  is  separ- 
ated by  the  pelvic  fascia.  From  the  apex  the  rounded  anterior  border,  which 
separates  the  lateral  surfaces,  passes  upwards  in  the  middle  line  behind  the 
symphysis  pubis  and  retro-pubic  pad  of  fat.  This  border  is  interrupted  in  its  lower 
part  by  the  passage  of  the  urethra. 

When  the  capsule  formed  by  the  pelvic  fascia  is  stripped  off  the  prostate  the 
organ  has  a  more  rounded  outline,  and  the  surfaces  just  described  are  not  so 

clearly  defined.  The  anterior  border 
may  now  appear  to  be  rather  a  surface 
than  a  border,  and  the  antero-posterior 
diameter  of  the  whole  organ  is  con- 
siderably reduced. 

The  urethra  enters  the  prostate 
at  a  point  near  the  middle  of  its  upper 
surface,  and  leaves  it  at  a  point  situated 
on  its  anterior  border,  just  above  and 
in  front  of  the  apex.  As  it  descends, 
the  urethra  describes  a  curve  which  is 
concave  forwards,  and  in  mesial  section 
it  is  seen  to  lie  on  the  whole  nearer 
to  the  posterior  surface  than  to  the 
anterior  border  of  the  gland. 

The  common  ejaculatory  ducts,  en- 
tering a  slit-like  interval  or  hilum  situ- 
ated just  in  front  of  the  border  which 
Tiie  latera]  separates  the  base  from  the  posterior 

.surfaces  of  tlie  prostate  are  seen  cue  on  each  side  of  ^,      p  f> .  i  ,    ,  i  j 

the  urethra  and  in  front  of  the  posterior  sm-face.  ^^^^face  of  the  prOState,  ruU  doWUWards, 

inwards,  and  forwards,  to  open  into 
the  prostatic  portion  of  the  urethra  very  close  to  one  another.  The  somewhat 
wedge-shaped  portion  of  the  prostate,  which  lies  between  these  ducts  and  the 
posterior  aspect  of  the  urethra,  receives  the  name  of  middle  Idhe  (lobus  medius,  Fig. 
845).  The  base  of  this  middle  lobe  projects  upwards  against  the  bladder,  and  is 
continuous  with  the  part  of  the  Ijladder  wall  lying  immediately  behind  the  urethral 
orifice.  When  hypertrophied  (as  it  often  is  in  old  people)  the  middle  lobe  of  the 
prostate  may  cause  a  considerable  elevation  in  the  cavity  of  the  bladder,  to  which 
the  term  uvula  vesicae  is  applied,  and  which  possesses  considerable  surgical  interest. 
The  rest  of  the  ^jrostate  is  described  as  being  composed  of  two  large  lateral  portions 
or  lateral  lobes,  which  are,  however,  not  marked  off  from  one  another  superficially. 

In  front  of  the  prostate,  between  it  and  the  pubis,  is  a  rich  venous  plexus  in  which 
the  dorsal  vein  of  the  penis  terminates.  This  plexus  is  continued  backwards,  on  each 
side,  round  the  lateral  aspect  of  the  prostate  and  joins  the  large  thin-walled  veins 
which  are  collected  for  the  most  part  in  the  deep  sulcus  between  the  bladder  wall 
and  the  prostate,  and  form  the  prostatico-vesical  plexus.  Most  of  the  veins  forming 
this  plexus  lie  partly  within  and  partly  outside  the  dense  fibrous  capsule  of  the 
prostate,  which  is  derived  from  the  visceral  pelvic  fascia  (Figs.  842  and  848). 

The  fibrous  capsule  of  the  prostate  is  formed  by  tlie  visceral  pelvic  fascia,  and 
closely  invests  the  gland  on  its  lateral  and  posterior  aspects.  Inferiorly  at  the 
apex  of  the  jirostate  this  capsule  becomes  continuous  with  the  layer  of  fascia  which 


Poste 

Seminal  Vt'siclfi 

841. — Pkostatk,  Bladder,  and  Seminal 
Vesicles  seen  fkom  below. 

Drawn  from   a  specimen  hardened  in  situ. 


Fic, 


THE  PROSTATE. 


1175 


lies  above  the  compressor  urethne  muscle,  aud  is  attached  to  the  pelvic  arch.  lu 
front  two  thickened  bands  pass  forwards  irom  the  anterior  aspect  of  the  capsule, 
one  on  each  side  of  the  middle  line,  to  reach  the  back  of  the  lower  part  of  the  pubis 
where  they  are  attached  to  the  periosteum.  These  constitute  the  pubo-prostatic 
ligaments,  and  contain  smooth  muscle  fibres  as  well  as  dense  connective  tissue. 
Some  of  the  muscle  fibres  in  connexion  with  the  pubo-prostatic  ligaments  passing 
upwards  as  well  as  backwards,  gain  the  bladder  wall  and  are  spoken  of  as  the  pubo- 
vesical muscles.     Below  the  pubo-prostatic  ligaments  the  inner  edges  of  the  levatr>res 


y^ 


f  ^ 


Veins  of  piostatico- 
.  "1  vesical  plexus 


* ^     B^—    ''"^''tt)'"  I'll 
'<  'i    I 


Glandular  tissue 


Ejaculatory  ducts 


Fig.  842. — Transverse  Sectiox  through  the  Prostate,  just  below  its  junction  witli  the  bladder. 

About  twice  natural  size. 

ani  muscles  pass  inwards  and  meet  together  in  front  of  the  apex  of  the  prostate. 
When  followed  backwards,  the  inner  edges  of  these  muscles  are  seen  to  closely 
embrace  the  apex  of  the  prostate. 

Between  the  pubo-prostatic  ligaments  there  is  a  shallow  fossa,  or  depression,  the 
floor  of  which  is  formed  by  a  thin  layer  of  fascia  connecting  the  anterior  aspect  of 
the  capsule  of  the  prostate  with  the  back  of  the  pubis.  When  the  fibrous  capsule 
of  the  prostate  is  traced  upwards  beyond  the  level  of  the  upper  margin  of  the  gland 
it  becomes  thinned  out  and  joins  the  facial  covering  of  the  bladder.  Posteriorly 
the  upward  prolongation  of  the  capsule  is  continuous  with  the  facial  layers  which 
enclose  the  ampullae  of  the  vasa  deferentia  and  the  seminal  vesicles,  and  it  is 
adherent  to  the  peritoneum  of  the  recto-genital  pouch.  In  this  position  it  is  often 
spoken  of  as  the  recto-vesical  fascia. 

Structure  of  the  Prostate. — Beneath  the  fibrous  capsule  of  the  gland  the  super- 
ficial part  of  the  prostate  is  seen  to  be  largely  composed  of  matted  interlacing 
bundles  of  smooth  muscle  and  connective  tissue  fibres,  which  form  a  kind  of  sheath 
for  the  deeper  parts  of  the  organ.  This  layer  or  sheath  is  not  sharply  defined,  but 
from  its  deep  aspect  filn-ous  and  muscular  strands  pass  inwards,  converging  towards 
the  posterior  wall  of  the  urethra,  to  become  continuous  with  the  mass  of  smooth 
muscular  tissue  w^hich  surrounds  this  canal  as  it  traverses  the  prostate.  These 
somewhat  radially  arranged  strands  divide  the  prostate  into  a  number  of  incom- 
pletely defined  lobules  of  which  there  appear  to  be  about  fifty.  The  yellowish- 
coloured  glandular  tissue  (corpus  glandulare)  which  forms  these  lobules  is  composed 
of  minute,  slightly  branched  tubules,  the  walls  of  which  in  certain  places  show 
numerous  saccular  dilatations.  In  the  upper  portion  of  the  gland  the  tubules  are 
slightly  dilated  and  shorter  than  in  the  lower  part,  where  they  are  longer  and  more 
convoluted.  The  glandular  tubules  lead  into  the  minute  prostatic  ducts,  which 
open  into  the  urethral  canal  as  it  traverses  the  prostate.  These  ducts  (ductus 
prostatici)  number  about  twenty  or  thirty,  and  open  for  the  most  part  into  a  groove 
on  each  side  of  the  median  elevation  (crista  urethralis)  in  the  posterior  wall  of  the 
urethra  (Fig.  846). 

The  bulk  of  the  glandular  tissue  is  situated  at  the  sides  of  and  behind  the 
79  & 


1176 


THE  UEINOGENITAL  SYSTEM. 


urethra.  In  front  of  the  upper  part  of  the  prostatic  portion  of  the  urethra  there 
is  a  mass  of  smooth  muscular  fibres,  which  is  continued  upwards  and  backwards  on 
the  sides  of  the  urethra  to  form  a  part  of  the  sphincter  vesicae.  At  a  lower  level 
striped  muscular  tissue,  which  is  continuous  with  the  deep  part  of  the  compressor 
urethrte  muscle,  occupies  a  position  in  front  of  the  urethral  canal. 


Pubo-prostatic  ligaiiiPiits 

^ 

/     \ 


~  -7  Levator  aui  muscle 


Veins  of  prostatico- 
vesical  plexus ' 


Crista  urethrse 
Strands  of  muscular  tissue 
Fig.  84-3. — Tkaxsverse  Section  through  the  Prostate,  about  half-way  between  its  apex  and  base. 


The  muscular  tissue  of  the  prostate  may  be  regarded  as  the  thickened  muscular 
layer  of  the  wall  of  the  urethra,  which  has  become  broken  up  and  invaded  by  the 
prostatic  glands,  which  arise  and  are  developed  from  the  lining  layer  of  the  canal 
during  embryonic  life. 

In  old  age  the  prostate  frequently  undergoes  an  hypertrophy,  which. may  affect 
chiefly  the  glandular  tissue,  or  the  entire  organ.  Not  infrequently  calcareous  con- 
cretions are  found  embedded  in  the  prostate. 

Vessels  and  Nerves  of  tlie  Prostate. — The  prostate  receives  its  blood-supply  from  branches 
of  the  hsemorrhoidal  and  inferior  vesical  arteries,  while  the  large  plexus  of  veins  which  surrounds 
it,  and  into  which  the  veins  of  the  penis  open,  communicates  with  the  vesical  plexus,  and  drains 
into  the  internal  iliac  veins.  In  old  people  the  veins  of  the  prostatic  plexus  usually  become 
much  enlai'ged.     Tlie  nerves  of  the  prostate  are  derived  from  the  hypogastric  plexus. 


COWPER'S  GLANDS. 

Cowper's  glands  (glandulte  bulbo-urethrales)  are  a  pair  of  small  bodies  placed  in 
relation  to  the  second,  or  membranous,  part  of  the  urethra.  They  are  each  about 
the  size  of  a  pea,  and  are  of  a  yellowish-brown  colour.  Situated  in  the  space 
between  the  two  layers  of  the  triangular  ligament,  they  lie  below  the  level  of  the 
apex  of  the  prostate,  and  above  that  of  the  bulb  of  the  corpus  spongiosum  (Figs. 
844  aud  846).  The  gland  is  made  up  of  a  number  of  closely  applied  lobes  or 
lobules,  and  is  of  the  compound  racemose  type.  The  ductules  of  each  gland  unite 
to  form  a  single  duct  (ductus  excretorius),  which  pierces  the  bulb  of  the  corpus 
spongiosum,  aud,  after  a  relatively  long  course,  ends  by  opening  into  the  spongy 
portion  of  the  urethra  by  a  minute  aperture.  The  secreting  acini  are  lined  by 
columnar  epithelium. 

The  glands  receive  their  arterial  supply  from  the  artery  to  the  bulb. 

In  old  age  these  glands  are  often  difficult  to  find. 


THE  MALE  UEETHEA. 


1177 


THE   MALE   UEETHEA. 

The  urethra  in  the  male  is  a  channel  of  about  eight  inches  in  length  leading 
from  the  bladder  to  the  external  urethral  orifice  at  the  extremity  of  the  glans 
penis.  The  canal  serves  not  only  for  the  passage  of  urine,  but  it  also  aflbrds  an 
exit  for  the  seminal  products  which  enter  by  the  common  ejaculatory  ducts,  and 
for  the  secretion  of  the  prostatic  and  Cowper's  glands.  In  addition,  numerous 
minute  glands  (glandulie  urethrales)  pour  their  secretion  into  the  urethra. 

As  it  passes   from   the   internal   urethral   orifice,  to  its  external  opening,  the 


Peritoneal-covered 
surface  of  bladder 


Va.s  deferens 


Ureter 


Seminal  vesicle 


Obliterated  hypo- 
gastric artery 

Uraclius 


Muscular  coat  of 
bladder 


Cowper's  gland 
Bulb  of  urethra 


Corpus  spongiosum 


Glans  penis 


Fig.  844. — The  Bladder  and  the  Structures  traversed  by  the  Urethra,  seen  from  the  outer  side 
after  removal  from  the  body.      The  bladder  has  been  artiticially  distended. 

urethra  describes  a  somewhat  (f)  shaped  course,  and  it  is  customary  to  divide  it  into 
certain  sections  which  have  received  distinctive  names.  The  first  part  of  the 
urethra  lies  within  the  pelvic  cavity,  and  has  an  almost  vertical  course  as  it  traverses 
the  prostate.  Turning  more  forwards,  the  urethra  passes  below  the  pubic  arch, 
and  pierces  the  fibrous  layers  which  form  the  pelvic  wall  in  this  region.  Leaving 
the  pelvic  cavity,  the  canal  enters  the  bulb  of  the  corpus  spongiosum,  where  the 
latter  is  attached  to  the  triangular  ligament,  and  throughout  the  rest  of  its  course 
it  lies  in  the  erectile  tissue  of  the  corpus  spongiosum  and  glans  penis.  The  part  of 
the  urethra  which  lies  embedded  in  the  prostate  is  called  the  prostatic  portion  ;  the 
short  portion  which  pierces  the  pelvic  wall  is  called  the  membranous  portion,  and 
the  part  surrounded  by  the  corpus  spongiosum  receives  the  name  of  spongy  portion. 
Of  these  three  sections  of  the  urethra  the  spongy  portion  is  much  the  longest,  and 
the  membranous  is  the  shortest. 


1178 


THE  UEINOCtENITAL  SYSTEM. 


\  euical  artcii 
External  iliac  \es»el& 
Obturator  uei\e 
Obliterated  hj  po^astric 

aitei\  \  \ 

Vas  deferen-. 


1  list  bacral  \eitel)ia 


Position  ot  lutenial  iliac 
aiterj 


Pio.>tatt 

Opening  of  ureter  into  bladder  / 

Portions  of  vasa  deferentia  cut  in  section 
Fig.  845. — Mesial   Section  of  an 


Rectum 


Adult   Male   Pelvis. 


Tlie  coils  of  the  small 
to  give  a 


intestme  and  of  the  pelvic  colon  v^fhich  lay  within  the  pelvis  have  been  lifted  out  in  order 
view  of  the  side  wall  of  the  pelvic  cavity.     The  peritoneum  is  coloured  blue. 


Bulbils  uretlir<i; 


Developmentally  the  spongy  portion  of  the  urethra  has  a  different  origin  from 

the  other  subdivisions,  as  it  is  derived  from 
the  ectodermal  cloacal  fossa,  while  the 
prostatic  and  membranous  portions  owe 
their  origin  to  the  urinogenital  canal, — a 
derivative  of  the  endodermal  cloaca. 

Prostatic  Portion  of  the  Urethra. — 
The  prostatic  part  (pars  prostatica)  of 
the  urethra  descends  through  the  prostate 
from  the  base  towards  the  apex,  describing 
a  slight  curve  which  is  concave  forwards. 
It  is  about  one  inch  in  length,  and  is 
narrower  above  and  below  than  in  its 
middle  portion,  which  is  indeed  the  widest 
part  of  the  whole  urethral  canal.  Except 
while  fluid  is  passing,  the  canal  is  collapsed,- 
and  the  mucous  membrane  of  the  anterior 
and  posterior  walls  is  in  contact,  and  thrown 
into  a  series  of  longitudinal  folds.  When 
distended,  the  middle,  or  widest  pa.rt  of  the 
canal,  may  normally  have  a  diameter  of 
about  one-third  of  an  inch.  The  posterior 
wall,  often  termed  the  "  floor  "  of  the  pro- 
static urethra,  presents  a  distinct  mesial- 
ridge  or  elevation  called  the  crista  urethrse 
(crista  urethralis)  or  verumontanum  (Fig. 
846).  This  projects  forwards  into  the 
urethra  to  such  an  extent  that  the  canal 
in  transverse  section  presents  a  somewhat  crescentiC  outline.      Tn    the   depres- 


Pars  caverno.sa 
urethra- 


Fig.  846. — Thk  Pjiostatic,  Membranous,  and  the 
Upper  Portion  of  the  Spongy  Urethra. 
opened  from  in  front  and  above  to  show  the 
posterior  wall  or  floor.  The  minute  openings 
of  the  common  ejaculatory  ducts  and  tlie  orifice 
of  the  sinus  pocularis  are  seen  upon  the  crista 
urethrae. 


THE  MALE  URETHKA.  1179 

sioiis  or  grooves  on  each  side  of  the  crista  urethne  tiie  numerous  ducts  of  the 
prostatic  glands  open  )»y  minute  apertures.  Some  few  ducts  from  the  middlti 
part  of  the  gland  open  nearer  the  middle  line,  on  the  sides  of  the  urethral 
crest.  On  the  summit  of  the  crista  urethrte  is  a  slit-like  opening  whicli  leads 
backwards  and  upwards  for  a  distance  of  about  a  quarter  of  an  inch,  as  a  })lind 
pouch,  in  the  substance  of  the  prostate.  This  little  cavity  is  the  prostatic 
utricle  (utriculus  prostaticus)  or  sinus  pocularis,  and  represents  the  fused  posterior 
ends  of  the  Miillerian  ducts  from  which  the  uterus  and  vagina  of  the  female 
are  developed.  ;The  term  uterus  masculinus  is  therefore  sometimes  applied  to 
this  little  pouch.  On  each  side  of  the  mouth  of  the  utricle  is  the  much 
more  minute  opening  of  the  common  ejaculatory  duct.  When  traced  upwards 
towards  the  bladder,  the  urethral  crest,  diminishing  in  height,  becomes  indistinct, 
Init  in  it  can  often  be  traced  as  a  slight  median  ridge  as  far  as  the  uvula  vesicfe. 
When  followed  in  the  opposite  direction  the  ridge  becomes  less  marked,  and  can 
lie  followed  on  the  urethral  wall  into  the  mem] >ranous  portion  of  the  canal,  where  it 
divides  into  a  pair  of  inconspicuous  folds  or  elevations,  which  gradually  fade  out 
into  the  urethral  wall  (Fig.  846). 

The  curvature  and,  to  a  less  degree,  the  length  of  the  prostatic  urethra  depends 
upon  the  amount  of  distension  of  the  bladder  and  of  the  rectum. 

Membranous  Part  of  the  Urethra.— The  second  or  membranous  portion 
(pars  membranacea)  of  the  urethra  leads  downwards  and  forwards  from  the  apex  of 
the  prostate  to  the  bulb  of  the  coqjus  spongiosum,  and  is  the  shortest  and  narrowest 
of  the  three  subdivisions  of  the  canal,  its  length  being  somewhat  less  than  half 
an  inch.  It  begins  at  the  deep  layer  of  the  triangular  ligament,  a  layer  of  pelvic 
fascia  which  lies  above  the  compressor  urethras  muscle,  where  it  is  continuous 
with  the  prostatic  portion,  and  ends,  having  pierced  the  superficial  layer,  by  be- 
coming continuous  with  the  spongy  portion  of  the  urethra.  Placed  in  front  of  the 
rectum,  it  lies  about  one  inch  behind  and  below  the  sub-pubic  ligament,  and  is 
surrounded  by  fibres  of  the  compressor  urethrse  muscle.  Behind  it,  on  each  side 
of  the  mesial  plane,  are  Cowper's  glands.  The  posterior  part  of  the  bulbus  urethrte 
projects  backwards  and  overlaps  to  a  considerable  extent  the  posterior  wall  of  the 
second,  or  membranous,  part  of  the  urethra. 

The  membranous  portion  of  the  urethra  is  the  most  firmly  fixed  and  least 
dilatable  part  of  the  passage. 

A  slight  median  elevation,  which  is  continuous  above  with  the  crista  urethrse, 
projects  into  the  canal  from  its  posterior  wall,  and  becoming  less  marked  as  it  is 
traced  downwards,  is  often  seen  to  divide  into  two  faint  ridges.  When  the  canal 
is  empty  other  longitudinal  folds  or  ridges  are  usually  to  be  seen  on  the  mucous 
membrane,  but  these  become  obliterated  when  the  passage  is  distended.  The 
lumen  of  the  empty  tube,  in  transverse  section,  presents  a  stellate  outline. 

The  terminal  portion  of  the  meuibrauous  urethra,  where  it  is  overlapped  posteriorly  by 
the  urethral  bulb,  lies  in  front  of  the  triangular  ligament.  It  is  considerably  wider  than 
the  upper  part  of  this  subdivision  of  the  canal,  and  is  very  thin-walled  (Figs.  Si-i  and  845) 

Spongy  Portion  of  the  Urethra.— The  third  or  spougy  portion  (pars 
cavernosa)  of  the  urethra  is  much  the  longest  of  the  three  subdivisions.  It  begins 
at  a  point  about  half  an  inch  in  front  of  the  posterior  end  of  the  bulb,  and  ends  at 
the  external  orifice  on  the  gians  penis.  Its  proximal  or  perineal  portion  has  a 
fixed  position  and  direction,  while  its  distal  part  varies  with  the  position  of  the 
penis.  The  canal  is  about  six  inches  in  length,  and  is  related  throughout  its 
whole  extent  to  the  erectile  tissue  of  the  corpus  spongiosum  and  glans. 
Directed  at  first  forwards  through  the  bulb  of  the  corpus  spongiosum,  the  canal 
turns  downwards  and  forwards  at  the  point  where  it  comes  to  lie  in  front  of  the 
lower  part  of  the  symphysis  pubis  (Fig.  845).  This  bend  in  the  direction  of  the 
canal,  roughly  speaking,  corresponds  to  the  place  of  attachment  of  the  suspensory 
ligament  to  the  dorsum  of  the  penis.  When  the  penis  is  drawn  upwards  towards 
the  front  of  the  abdomen,  the  direction  of  the  terminal  half  of  the  canal  is  of  course 
changed,  and  at  the  same  time  the  whole  length  of  this  subdivision  of  the  iu:ethra 
becomes  more  uniformly  curved.     The  urethra  passing  obhquely  downwards  and 


1180 


THE  URINOGENITAL  SYSTEM. 


forwards  enters  the  Lulb  at  a  point  nearly  half  an  inch  from  its  posterior  extremity. 
Immediately  after  the  canal  has  pierced  the  triangular  ligament  its  posterior 
aspect  becomes  surrounded  by  the  erectile  tissue  of  the  bulb,  but  the  anterior  wall 
remains  uncovered  for  a  distance  of  about  a  quarter  of  an  inch  (Figs.  844  and  845). 
The  wall  of  the  urethra  is  here  very  thin,  and  the  passage  is  more  readily  dilatable 
than  in  other  parts.  In  this  region  the  urethral  wall  may  readily  be  torn  through, 
if  undue  force  is  used,  or  if  the  handle  is  depressed  too  soon  when  attempting  to 
pass  an  instrument  into  the  narrower  more  fixed  membranous  part  of  the  canal. 
The  urethra  lies  at  first  in  the  upper  part  of  the  erectile  tissue,  but  as  it  passes 
forwards  it  sinks  deeper,  and  comes  to  occupy  the  middle  part  of  the  corpus 
spongiosum  (Fig.  845).  In  the  glans,  on  the  other  hand,  the  erectile  tissue  lies  on 
the  dorsal  and  lateral  aspects  of  the  urethra.  Like  the  other  parts  of  the  urethra 
the  canal  is  closed  except  during  the  passage  of  fluid,  the  closure  being  effected  by 
the  apposition  of  its  dorsal  and  ventral  walls  except  in  the  part  of  the  canal  which 
lies  in  the  glans  penis,  where  the  lateral  walls  of  the  canal  come  into  contact 
(Fig.  847).     Thus    the    lumen  of   the  first   part   of  the    canal,  when   empty,   is 

represented  in  cross  sec- 
tion by  a  transverse  slit, 
and  that  of  the  terminal 
part  by  a  vertical  slit. 
The  spongy  part  of  the 
urethra  does  not  present 
a  uniform  calibre  through- 
out, but  is  narrower  in  its 
intermediate  part,  where 
it  traverses  the  corpus 
spongiosum,  than  it  is  in 
those  portions  of  its  course 
which  are  surrounded  by 
the  bulb  and  the  glans. 
The  terminal  dilated  part 
of  the  passage  is  termed 
the  fossa  navicularis  urethrse,  and  opens  on  the  surl'ace  by  the  vertically-placed 
slit-hke  external  urethral  orifice  (orificium  urethras  externum),  which  is  bounded 
by  lateral  lips,  and  is  the  narrowest  and  least  dilatable  part  of  the  whole  urethral 
canal. 

The  ducts  of  Cowper's  glands  open  by  very  minute  apertures  in  the  under 
wall  of  the  proximal  part  of  the  spongy  portion  of  the  urethra.  Before  opening 
into  the  canal,  they  lie  for  some  distance  immediately  beneath  its  mucous  mem- 
brane. A  number  of  little  pit-like  recesses,  called  the  lacunse  urethrales,  also  open 
into  the  spongy  part  of  the  urethra,  and  are  so  disposed  that  their  openings  lead 
for  the  most  part  obliquely  into  the  canal  in  the  direction  of  its  external  orifice. 

lu  some  cases  a  somewlial.  Aalvu-like  fold  (valvula  fossa  navicularis)  of  tlie  mucous  membrane 
is  found  in  the  upper  wall  of  the  urethra  in  the  region  of  the  fossa  navicularis.  The  free  edge  of 
tliis  fold  is  directed  towards  the  external  urethral  orifice,  and  may  engage  the  point  of  a  fine 
instrument  introduced  into  the  urethra. 


Fui.  847. — A   Longitudinal    Sjection   ok    the    Terminal  Portion 


THE  Penis,  and 
THE  Organ. 

a.  Corpus  cavernosuni. 
h.  Corpus  spongiosum. 
c.   Urethral  caual. 


Transverse  Section  through  the.  Body 


of 

OF 


Glaus  penis. 

Fossa  navicularis. 

Part  of  septum  pectiniforiue. 


Dofsal  vein. 
Dorsal  artery. 
Dorsal  nerve. 


Structure. — The  mucous  membrane  of  the  urethra  contains  numerous  elastic  fibres 
and  varies  in  thickness  in  different  parts  of  the  canal.  In  many  positions  it  shows 
distinct  longitudinal  folds  and  also  minute  depressions  or  pits, — the  lacuuce  already 
mentioned.  The  lining  epithelium  is  composed  of  many  layers  of  cells,  and  is  continuous 
through  the  internal  urethral  orifice  with  the  epithelium  of  the  bladder,  which  at  first  it 
closely  resembles.  At  the  fossa  navicularis  the  lining  cells,  which  throughout  the  spongy 
portion  of  the  canal  arc  of  a  colunniar  type,   l)Ccome  fiat  and  scaly. 

Numerous  minute  glands,  glands  of  Littr^  (glandulfc  urethrales)  open  into  the 
urethra.  Tliese  are  most  plentiful  in  the  upper  or  anterior  wall,  but  they  also  occur  in 
smaller  numbers  in  the  floor  and  side  walls.  They  ai-e  most  numerous  in  the  anterior 
half  of  the  spongy  portion  of  the  canal,  and  in  the  membranous  subdivision  of  the  urethra. 

The  larger  glands  are  deeply  i)laced  beneath  the  mucous  coat,  and  communicate  with 
the  ui'ethra  by  long  slender  obliquely-placed  In-anched  ducts.     The  smaller  glands  lie  in 


THE  FEMALE  REFRODUCTIVE  OEGANS. 


1181 


the  mucoiis  coat  and  form  Hask-like  depressions  with  very  short  ducts.  The  ducts  of  some 
of  the  glands  open  into  the  laeunje,  but  many  of  the  hitter  have  no  connexion  with  the 
urethral  glands. 

Frequently  two  or  more  elongate  ducts  belonging  to  some  of  the  larger  glands  open 
into  the  urethra  quite  close  to  its  termination.  These  are  sometimes  spoken  of  as  para- 
urethral ducts  and  may  be  traced  backwards  for  some  distance  beneath  the  mucous 
membrane  forming  the  roof  of  the  urethra.  Morphologically  they  do  not  correspond  to 
the  ducts  which  in  the  female  have  received  the  same  name. 

The  muscular  wall  in  the  upper  part  of  the  urethra  consists  of  smooth  muscle  fibres 
directed  for  the  most  part  longitudinally,  but  some  circularly  arranged  fibres  are  also 
present.  It  is  probable  that  throughout  the  greater  [)art  of  the  spongy  urethra  a  muscular 
coat  is  not  represented. 

Round  the  l)eginning  of  the  urethra  there  is  an  obliqucly-placcd  band  of  circularly- 
arranged  smooth  muscle  fibres,  which  is  continued  downwards  and  forwaixls  from  ))elow 
the  anterior  part  of  the  trigone  of  the  bladder.  The  lower  and  anterior  fibres  of  this 
band  lie  in  the  anterior  wall  of  the  upper  part  of  the  prostatic  urethra.  The  band  is 
sometimes  spoken  of  as  the  sphincter  vesicas  internus.  At  a  lower  level,  in  front  of  the 
prostatic  urethra,  is  a  band  of  striped  muscular  fibres  which  is  continuous  inferiorly  with 
the  inner  circidarly-disposcd  part  of  the  compressor  urethne. 

Like  the  latter  it  is  probably  to  be  regarded  as  a  part  of  a  primitive  voluntary 
urinogenital  sphincter  muscle,  such  as  is  represented  also  in  the  female  subject. 


THE  FEMALE  REPRODUCTIVE  ORGANS. 

The  reproductive  glands  in  the  female  are  a  pair  of  ovaries  placed  laterally  in 


Ileum 


Suspenson- 
ligament 

Cieeuni 

Veriiiifonii 

appendix 

Ovary 
Fallopian  tub^ 
Deep  epii;asti'ic  -  - 

Round  liganient-- 
Fundus  uteri  '' 


Obliterated 
liypogastrie 

Bladder 


Urethra 


liabium  minus 
Labium  niajor- 


Ureter 


Fig.  848. — Mesial  Section  through  the  Female  Pelvis.     Drawn  lor  the  most  part  from  a  model  made 

from  a  dissection  liy  Dr.  E.  H.  Taylor. 

the  cavity  of  the  pelvis.      In  connexion  with  each  ovary  is  an  elongated  passage 
or  tube — the  Fallopian  tube — which  leads  to  the  uterus  and  opens  into  its  canity. 


1182  THE  URINOGENITAL  SYSTEM. 

There  is  no  direct  continuity  between  the  ovary  and  the  Fallopian  tube,  such  as 
exists  between  the  other  glands  of  the  body  and  their  ducts,  but  the  ova  when 
shed  from  the  ovary  pass  into  the  open  end  of  the  tube,  and  are  thus  conducted  to 
the  uterine  cavity.  The  uterus,  or  womb,  is  a  hollow  muscular  organ  which  occupies 
a  nearly  median  position  in  the  pelvis  ;  it  is  joined  by  the  Fallopian  tubes  above, 
and  it  communicates  with  the  upper  part  of  the  vagina  below.  The  ovum,  having 
passed  through  the  Fallopian  tube,  reaches  the  cavity  of  the  uterus,  and  in  it,  if 
fertilisation  has  taken  place,  the  ovum  undergoes  its  development  into  the  embryo 
and  fcetus.  The  vagina  is  the  passage  which  leads  from  the  uterus  to  the  exterior,  and 
lias  its  external  opening  behind  that  of  the  urethra,  witliin  the  urinogenital  space. 
In  connexion  with  the  urinogenital  space  are  a  number  of  structures  which  are 
included  under  the  term  external  genital  organs,  and  which  represent  in  the 
female  the  various  parts  of  the  penis  and  scrotum  in  the  male.  These  are  the 
labia  majora  and  the  mons  Veneris,  the  labia  minora,  the  clitoris,  and  the  bulbus 
vestibuli.  The  glands  of  Bartholin,  placed  one  on  each  side  of  the  lower  part 
of  the  vagina,  are  accessory  organs  of  the  female  reproductive  system,  and  are 
represented  by  Cowper's  glands  in  the  male. 

THE  OVAEY. 

The  ovary  (ovarium)  is  a  solid  body,  flattened  from  side  to  side,  and  about  the 
size  and  shape  of  a  large  almond.  Its  length  is  usually  between  one  and  one  and  a 
half  inches,  and  the  thickness  from  side  to  side  between  a  quarter  and  half-an-inch. 
In  the  adult  the  ovary  is  placed  against  the  side  wall  of  the  pelvic  cavity,  and  is 
connected  by  peritoneal  folds  with  the  broad  ligament  of  the  uterus  and  with  the 
lateral  wall  of  the  pelvis.  The  position  occupied  by  the  ovary  within  the  pelvic 
cavity  is  fairly  constant,  although  these  ligaments  do  not  hold  the  organ  firmly 
fixed  in  any  definite  place. 

In  the  ovary  we  recognise  two  poles  or  extremities — an  upper  pole,  larger  and 
more  rounded,  and  a  loioer  pole,  somewhat  pointed.  The  term  tubal  pole  (extre- 
mitas  tubaria)  is  applied  to  the  upper  end  of  the  ovary,  as  it  is  most  intimately 
connected  with  the  Fallopian  tube ;  the  term  uterine  pole  (extremitas-  uterina)  is 
used  with  reference  to  the  lower  extremity,  since  this  part  of  the  ovary  is  con- 
nected with  the  uterus  by  a  fibrous  cord,  termed  the  ligament  of  the  ovary.  The 
flattened  surfaces  of  the  ovary  are  called  internal  (facies  medialis)  and  external 
(facies  lateralis),  and  the  lorders  separating  them  anterior  (margo  mesovaricus)  and 
'posterior  (margo  liber).  The  posterior  border  is  convex  and  free ;  while  the 
anterior  one,  which  is  straighter  and  narrower,  is  connected  by  a  very  short  peri- 
toneal fold  (mesovarium)  with  the  posterior  layer  of  the  broad  ligament  of  the 
uterus.  The  vessels  and  nerves  enter  the  ovary  by  this  anterior  border,  which  is 
therefore  often  termed  the  Mlum  of  the  ovary. 

Position  and  Relations  of  the  Ovary. — ^When  the  ovary  occupies  its  most 
usual  or  typical  position  the  long  axis  of  the  gland  is  vertical.  Its  outer  or  lateral 
surface  lies  against  the  side  wall  of  the  pelvis,  and  its  inner  surface  looks  inwards 
towards  the  pelvic  cavity.  The  peritoneum  of  the  pelvic  wall,  where  the  ovary 
lies  against  it,  is  depressed  to  form  a  little  fossa  termed  tlie  fossa  ovarica,  within 
which  the  ovary  is  placed.  In  the  floor  of  this  fossa  are  the  obturator  nerve  and 
vessels.  The  upper  pole  of  the  ovary  lies  below  the  level  of  the  external  iliac 
vessels,  and  its  lower  end  is  placed  just  above  the  level  of  the  peritoneum  covering 
the  pelvic  floor.  The  fossa  ovarica,  in  which  the  ovary  lies,  extends  as  far  forwards 
as  the  obliterated  hypogastric  artery,  and  backwards  as  far  as  the  ureter  and 
uterine  vessels.  Thus  the  anterior  border  of  the  ovary  lies  just  behind  the  line  of 
the  obliterated  hypogastric  artery,  and  the  posterior  border  is  on  a  plane  anterior 
to  the  ureter  (Fig.  849).  The  inner  surface  of  the  ovary  is  almost  completely 
covered  by  the  Fallopian  tube,  which,  passing  upwards  on  it  near  its  anterior 
border,  arches  over  the  upper  pole,  and  then  turns  downwards  in  relation  to  the 
]josterior  border  and  posterior  part  of  the  inner  surface  (Fig.  849). 

In  some  cases  the  ovary  is  found  to  lie  behind,  oi'  more  rarely  in  front,  of  the  fossa  described 


THE  OVAEY. 


1183 


above,  and  its  lung  axis  may  be  oblique  instead  of  vertical.  The  above  descrijition,  however, 
corresi^onds  to  the  typical  j^sition  of  the  organ  in  Avonien  wlio  have  not  borne  children.  When 
the  uterus  is  much  iuclined  towards  the  riglit  side  of  the  body  the  left  ovary  lias  its  long  axis 
directed  obliquely  downwards  and  inwards,  the  right  glaud  remaining  vertical. 


External  iliac  artery 

— .External  iliac  vein 
Internal  iliac  artery 


Sacrum 


Pyriforniis-f 


Su 

ligament  ufn  ,     .1  ^,;;y/M^<t 
the  ovary  j      |l..ijSy    '^* 


Levator  an,-j-— 

Obturator  |  \ 

interiuis 


: il  U  reter 

////// External 
iliac 
artery 


External 
iliac 

'I   /'"I  1/         vein 


'^i     '',     /    Hypogastric 


Round  ligament 
of  uterus 


Superior  vesical 
artery 


Pubic  lamus 


-Obturator  externus 


Fig.  S19. — Side  Wall  of  the  Female  Pelvis,  showing  the  position  of  the  ovary  and  its  relation  to  the 
Fallopian  tube.  The  pelvis  has  been  cut  in  section  parallel  to,  but  at  some  distance  from,  the  mesial 
plane.     Drawn  from  a  specimen  in  the  Anatomical  Department,  Trinity  College,  Dublin. 

Connexions  of  the  Ovary. — When  the  ovary  is  in  position  a  small  somewhat 
triangular  peritoneal  fold  passes  upwards  from  its  upper  pole,  and  becomes  lost  in 


Parovarium  Ligament 

Fallopian  tube  \      Ovary      ut  o\  iiv  rtPTU^i 


Lateral  angle 
of  uterus 


Hydatid 


Fimbriated  end  of  tube 

Round  ligament' 


Broad 
ligament 


Vaginal  cavity 
A  B 

Fk;.  850. — A.   The  Uterus  and  Broad  Ligament  seen  from  behind  (the  broad  ligament  has  been 

spread  out). 

a,  b,  and  c,  the  isthmus  tuba?,  the  ligament  of  the  ovary,  and  the  rouml  ligament  of  the  right  side  cut  short. 
B.   Diagrammatic  Representation  of  the  Uterine  Cavity  opened  up  from  in  front. 

the  peritoneum  covering  the  external  iliac  vessels  and  the  psoas  muscle  (Fig.  849). 
This  fold  has  received  the  name  of  suspensory  ligament  of  the  ovary  (or  ovario- 


1184  THE  UKINOGENITAL  SYSTEM. 

pelvic  ligament),  and  is  a  portion  of  the  upper  and  outer  part  of  the  broad  ligament 
of  the  ,  uterus,  which  here  contains  between  its  two  layers  the  ovarian  vessels  and 
nerves  as  they  pass  down  into  the  pelvis  to  reach  the  hilum  of  the  ovary.  The 
vessels  and  nerves  entering  the  ovary  along  its  anterior  border  are  enclosed  in  a 
sheath  of  peritoneum  derived  from  the  posterior  layer  of  the  broad  ligament.  In 
this  way  the  ovary  is  connected  along  the  whole  length  of  its  anterior  border  by  a 
very  short  mesentery,  or  mesovarium,  to  the  posterior  aspect  of  the  broad  ligament 
(Fig.  850).  The  lower  pole  of  the  ovary  is  connected  with  the  lateral  angle  of  the 
uterus  by  a  ligament  cliHed  1;he  ligament  of  the  ovary  (ligamentum~OTam  proprium). 
This  has  the  form  of  a  rounded  cord  enclosed  between  the  peritoneal  folds  of  the 
broad  ligament,  and  is  attached  to  the  uterus,  behind  and  below  the  point  of 
entrance  of  the  Fallopian  tube.  It  is  chiefly  composed  of  smooth  muscle  fibres 
continuous  with  those  of  the  uterus.  The  upper  pole  of  the  ovary  is  usually 
directly  connected  with  one  of  the  largest  of  tlie-  fimbriae  surrounding  the 
abdominal  end  of  the  Fallopian  tube,  which  receives  the  name  ovarian  fimbria  of 
the  tul)e  (Fig.  850). 

Descent  of  the  Ovary. — Like  the  testes,  the  ovaries  at  first  lie  in  the  abdominal 

cavity,  and  only  later  assume  a  lower  position.  At  birth  the  ovary  lies  partly  in  the 
abdominal,  and  partly  in  the  pelvic  cavity ;  soon,  however,  it  takes  up  a  position  entirely 
within  the  pelvis.  As  in  the  male  a  gubernaculum  is  present  in  the  early  stages  of 
development.  The  ligament  of  the  ovary  represents  the  upper  part  of  the  gubernaculum 
which  is  developed  within  the  plica  testis  inferior  in  the  male,  and  the  round  ligament  of 
the  uterus  represents  the  lower  part,  which  is  formed  within  the  plica  inguinalis  (see  p.  1168). 
It  is  a  rare  abnormality  for  the  ovary,  instead  of  entering  the  pelvis,  to  take  a  course  similar 
to  that  of  the  testis,  and  pass  through  the  inguinal  canal  into  the  tissue  of  the  labium  majus. 

Structure  of  the  Ovary. — The  ovary  is  for  the  most  part  composed  of  a  connective 
tissue  stroma  (stroma  ovarii),  richly  supplied  by  blood-vessels  aiid  nerves.  The  stroma 
contains  very  numerous  spindle-shaped  connective  tissue  libres,  and  some  elastic  tissue. 
The  surface  of  the  ovary  is  covered  by  a  layer  of  epithelium,  which  is  composed  of 
columnar  cubical  cells,  and  is  continuous  with  the  epithelium  of  the  peritoneum 
forming  the  mesovarium.  The  ovarian  epithelium  is  a  persistent  portion  of  the 
germinal  epithelium  of  the  embrj'o  which  covers  the  genital  ridges,  and  from  which  the 
ova  and  other  cells  of  the  Graafian  follicles  are  derived.  The  position  in  Avhich  it  be- 
comes continuous  with  the  peritoneum  can  usually  be  distinguished  as  a  fine  white  line 
near  the  hilum  of  the  ovary.  Shining  through  the  epithelium  of  the  fresh  ovary  (except 
in  old  age),  are  usually  to  be  seen  a  variable  number  of  small  vesicles — the  G-raafian 
follicles  (folliculi  oophori  vesicidosi),  in  which  the  ova  are  contained.  The  number  of 
follicles  visible,  and  also  the  size  which  each  follicle  reaches  before  it  ruptures  and  sheds 
its  contents,  is  by  no  means  constant.  When  a  follicle  ruptures  and  discharges  the  ovum 
its  walls  at  first  collapse,  but  later  the  cavity  becomes  filled  with  exti'avasated  blood  and 
cellular  tissue  of  a  yellowish  colour.  The  resulting  structure,  called  a  corpus  luteum, 
slowly  degenerates  unless  impregnation  has  taken  place,  in  which  case  it  develops  and 
becomes  larger  during  pregnancy.  As  it  atrophies  the  cells  of  the  corpus  luteum 
disappear,  and  the  structure,  losing  its  yellow  colour,  receives  the  name  of  corpus  albicans. 
After  a  time  the  corpus  albicans  completely  disappears.  Owing  to  the  periodic  rupture 
of  the  Graafian  follicles,  the  surface  of  the  ovary,  which  is  at  first  smooth  and  even, 
becomes  in  old  age  dimpled  and  puckered. 

A  section  through  the  ovary,  esi)ecially  in  young  children,  presents  in  its  superficial 
part  a  somewhat  granular  appearance,  which  is  due  to  the  presence  of  enormous  numbers 
of  small  follicles,  or  collections  of  epithelial  cells,  embedded  in  the  connective  tissue 
near  the  surface  of  the  ovary.  The  larger  follicles  lie  deeper  in  the  stroma,  but  when 
they  become  fully  developed  they  pass  towards  the  surface,  where  the  ripe  follicles  ai'e 
often  seen  slightly  projecting  and  ready  to  Inu'st.  In  the  deepest  part  of  the  ovary  the 
blood-vessels  are  most  numerous,  and  here  also  some  smooth  muscle  fibres  are  to  be  found. 

The  ova  and  the  other  colls  that  compose  the  Graafian  follicles  are  dei'ived  originally 
from  the  germinul  epithelium  which  covers  the  developing  ovary  in  the  embryo.  The 
epithelium,  at  first  simple,  grows  down  into  the  underlying  tissue  in  the  foi'm  of  branching 
tube-like  processes,  or  "egg  tubes."  This  takes  place  during  foetal  development,  and  the 
branching  cellular  processes  .so  formed  become  broken  up,  within  the  stroma,  into  little 
nests  or  clumps  of  cells,  each  of  which  becomes  a  Graafian  follicle.  From  the  beginning 
some  cells  of  the  egg  tubes  are  larger  than  the  others ;  these  become  the  future  ova 


THE  FALLOP'IAN  TUBES. 


1185 


wliile  the  cells  round  them  become  the  investing  cells  of  the  follicle.  The  investing  cells, 
at  first  flattened,  form  u  single  layer  round  each  ovum.  Later  becoming  columnar,  as  the 
follicle  increases  in  size  and  sinks  more  deeply  in  the  stroma,  these  cells  divide  in  such  a 
manner  that  the  ovum  becomes  surrounded  by  a  double  layer  of  cells.  Fluid — liquor 
folliculi — accumulates  between  the  two  celUdar  layers,  except  at  one  place  where  the 
inner  cells  surrounding  the  ovum  remain  attached  to  the  outer  layer  or  stratum  granu- 
losum.  To  the  inner  cellular  mass  enclosing  the  ovum  (ovulum)  the  term  discus 
proligerus  (cumulus  oophorus)  is  applied  (Fig.  S.")l).     Tiie  ripe  follicle  contains  a  rela- 


Uowngrowths  of  eiiiUieliuiu 
Germinal  epithelium 


Ovum  with  its  iuxcstiiii:  cells 


Stratum  iiraniilosuii 


'       ]'. 


/  I       Liquor  folliculi 

Xests  of  epithelial  cells        Ovarian  stroma         Graafian  follicle  Ovum  Discus  proligerus 

Fig.  851. — A.  Diagrammatic  Representation  of  the  Manner  in  which  the  Graafian  Follicles  arise 

DURING    THE    DEVELOPMENT    OF    THE    OVARY.       B.     DIAGRAM    ILLUSTRATING    THE    STRUCTTTRE  OF  A  RiPB 

Graafian  Follicle. 

tively  large  amount  of  fluid,  and  the  surrounding  stroma  becomes  difterentiated  to  form 
for  each  a  capsule  (theca  folliculi).  This  capsule  is  composed  of  an  inner  more  vasndar 
layer  (tunica  interna),  and  an  outer  more  fibrous  layer  (tunica  externa).  There  is 
reason  to  believe  that  in  the  hiunan  embryo  the  formation  of  ova  and  follicles  ceases  at 
birth,  and  that  the  appearances  which  have  led  to  the  belief  that  they  may  originate 
during  the  first  j^ears  of  extrauterine  life  have  been  due  to  pathological  conditions.  In 
the  young  child  there  are  enormous  numbers  of  small  follicles  in  the  supei^ficial  parts  of 
the  ovary,  but  in  old  age  none  are  found  in  this  situation. 

The  appearance  and  structure  of  the  ripe  ova  have  been  described  on  p.  10. 

Vessels  and  Nerves  of  the  Ovary. — The  ovarian  arteries,  corresponding  to  the  speimatic 
arteries  of  the  male,  ai'e  a  pair  of  long  slender  vessels  which  spring  from  the  anterior  asjiect  of 
the  aorta,  below  the  level  of  origin  of  the  renal  vessels.  Each  gains  the  jielvis  in  the  fold  of 
peritoneum  forming  the  suspensory  ligament  of  the  ovary,  and  enters  the  ovary  at  its  anterior 
Ijorder  or  liilum.  These  ovarian  arteries  anastomose  freely  near  the  liiluiu  with  other  vessels 
derived  from  the  uterine  arteries.  The  blood  is  returned  by  a  series  of  communicating  veins, 
similar  to  the  pampiniform  plexus  in  the  male.  The  nerves  of  the  ovary  are  derived  chiefly 
from  a  plexus  which  accomjiaiiies  the  ovarian  artery,  and  •which  is  continuous  aliove  with  the  renal 
plexus.  Other  fibres  are  derived  from  the  lower  part  of  the  aortic  plexus,  and  join  the  plexus 
on  the  ovarian  artery  (plexus  arterite  ovaricpe).  The  afferent  impulses  from  the  ovary  reach  the 
central  nervous  system  through  the  posteiior  root  fibres  of  the  tenth  thoracic  nerve.  The 
lymphatics  of  the  ovary  join  with  those  from  the  uj^per  part  of  the  uterus,  and  end  in  the 
lumbar  lymphatic  glands. 

THE  FALLOPIAN  TUBES. 

The  Fallopian  tubes  (tubse  uterinse)  are  a  pair  of  ducts  or  passages  which  convey 
the  ova,  discharged  from  the  Graafian  follicles  of  the  ovaries,  to  the  cavity  of  the 
uterus.  Each  tube  is  about  four  and  a  quarter  inches  in  length,  and  opens  at  one 
end  into  the  pelvic  cavity  near  the  ovary,  and  at  the  other  end  by  a  smaller  opening 
into  the  lateral  part  of  the  uterine  cavity.  The  tube  is  enclosed  in  a  fold  of  peri- 
tonevim  called  the  mesosalphinx,  which  is  a  portion  of  the  broad  ligament  of  the 
uterus. 

The  opening  of  the  tube  into  the  pelvic  cavity — or  ostium  abdominale — is  of 
small  size,  being  only  about  2  mm.  in  diameter  when  its  walls  are  relaxed,  and 
80 


1186  THE  UEINOGENITAL  SYSTEM. 

much  narrower  when  the  muscular  coat  of  the  tube  is  contracted.  This  opening  is 
placed  at  the  bottom  of  a  funnel-like  expansion  of  the  tube  called  the  infundibulum 
(infundibulum  tubii?  uterinte),  the  margins  of  which  are  produced  into  a  number  of 
irregular  processes  or  fimbrise  (fimbriae  tuba^).  The  presence  of  these  fimbriae,  many 
of  which  are  branched  or  fringed,  has  given  the  name  fimbriated  extremity  to  this 
end  of  the  Fallopian  tube.  The  surface  of  the  fimbriae  which  looks  into  the  cavity 
of  the  infundibulum  is  covered  by  a  mucous  membrane  continuous  with  that  lining 
the  tube,  while  the  outer  surface  is  clothed  by  peritoneum.  The  mucous  surfaces 
of  the  larger  fimbria  present  ridges  and  grooves  which  are  continued  into  the  folds 
and  furrow^s  of  the  mucous  coat  of  the  tube.  One  of  the  fimbriee,  usually  much 
larger  than  the  rest,  is  connected  either  directly  or  indirectly  with  the  upper  or 
tubal  pole  of  the  ovary,  and  to  it  the  name  ovarian  fimbria  (fimbria  ovarica)  is 
applied.  The  part  of  the  tube  continuous  with  the  infundibulum,  and  into  which 
the  ostium  abdominale  leads,  is  called  the  ampulla  (ampulla  tuhse.  uterine).  This, 
the  widest  and  longest  portion  of  the  Fallopian  tube,  is  usually  tortuous  and  of 
varying  diameter,  being  in  some  places  slightly  constricted,  and  in  others  dis- 
tended. The  wide,  thin-walled  ampulla  ends  in  the  narrower,  thicker- walled,  and 
much  shorter  isthmus  (isthmus  tubas  uterinas)  which  joins  the  lateral  angle  of  the 
uterus.  The  last  portion  of  the  canal,  or  pars  uterina,  is  embedded  in  the  substance 
of  the  uterine  wall,  which  it  traverses  to  reach  the  cavity  of  the  uterus  (Fig.  852,  B). 
The  opening  into  the  uterus  (ostium  uterinum  tubte)  is  smaller  than  the  ostium 
abdominale,  being  about  1  mm.  in  diameter.  The  lumen  of  the  canal  gradually 
increases  in  width  as  it  is  traced  outwards  from  the  uterus  towards  the  ovary. 

Course  of  the  Fallopian  Tube. — Traced  from  the  lateral  angle  of  the  uterus 
the  Fallopian  tube  is  directed  at  first  horizontally  outwards  towards  the  lower,  or 
uterine,  pole  of  the  ovary.  It  then  passes  upwards  in  relation  to  the  inner  side  of 
the  anterior  border  of  the  ovary,  until  it  reaches  the  upper  or  tubal  pole,  where, 
arching  backwards,  it  descends  along  the  posterior  border,  resting  against  the  inner 
surface  of  the  gland  (Fig.  852).  As  the  Fallopian  tube  describes  this  loop  it  often 
covers  almost  the  entire  inner  surface  of  the  ovary.  The  fimbriated  end  of  the 
tube  lies  against  the  lower  part  of  the  inner  surface  of  the  ovary,  and  from  it  the 
ovarian  fimbria  passes  upwards  to  gain  attachment  to  the  tubal  pole. 

The  fimbriated  end  of  the  Falloiiian  tube  lies  in  the  abdomnial  cavity  until  the  ovary  in  its 
descent  has  entered  the  pelvis. 

Structure  of  the  Fallopian  Tubes. — The  wall  of  each  tube,  which  is  surrounded 
by  a  covering  of  peritoneum  (tunica  serosa),  is  composed  of  a  number  of  concentric  layers, 
or  coats.  Immediately  beneath  the  peritoneum  is  a  layer  of  loose  connective  tissue  in 
which  lie  many  vessels  and  nerves  (tunica  adventitia).  Beneath  this  is  the  muscular  coat 
(tunica  muscularis)  composed  of  two  strata  of  smooth  muscle  fibres, — a  more  superficial 
thin  stratum  of  longitudinally  arranged  fibres  (stratum  longitudinale),  and  a  deeper 
thicker  layer,  the  fibres  of  which  are  circularly  disposed  (stratum  circulare).  Deeper  is  a 
submucous  layer  (tela  submucosa),  and  then  the  lining  membrane  or  mucous  coat  (tunica 
mucosa).  In  the  part  of  the  tube  near  the  uterus  the  muscular  layer  is  thicker  than 
towards  the  other  end,  and  in  the  isthmus  it  forms  the  chief  part  of  the  wall.  The 
mucous  membrane,  on  the  contrary,  is  thickest  towards  the  fimbriated  end,  and  here  it 
forms  the  chief  part  of  the  tube  wall.  The  stratum  of  circular  muscle  fibres  is  especially 
well  developed  near  the  uterus.  The  mucous  membrane  is  thi'own  into  numerous  longi- 
tudinal folds  (pliCfC  tubarifc),  which  in  the  ampulla  are  exceedingly  complex,  the  larger 
ones  being  beset  on  the  surface  by  smaller  folds.  In  transverse  sections  of  this  part  of 
the  tuVje  the  folds  of  the  nmcous  menrbrane  look  like  large  branching  processes  projecting 
into,  and  almost  completely  tilling  up,  the  lumen  of  the  tube.  The  mucous  membrane  is 
covered  by  a  ciliated  epithelium,  the  cilia  of  which  tend  to  drive  the  contents  of  the  tube 
towards  the  uterus.  The  epithelivun  is  continuous  with  that  of  the  uterus,  and  at  the 
fimbriated  end  joins  the  peritoneum. 

Vessels  and  Nerves  of  the  Fallopian  Tube.  Tin-  Fallojiian  tube  receives  its  chief  blood- 
supply  fioiii  a  biaiiih  ol'  the  uterine  artery  (Taiuus  tubarius),  but  it  also  receives  small  branches 
derived  from  the  ovarian  artery.  'Jlic  v(;iiis  of  Ihe  tube  pour  their  blood  jjartly  into  tlie  uterine 
and  j^artly  into  tlie  <jvariaii  veins.  Tim  nerves  are  derived  fi-om  the  j'lexus  that  su2")plies  the 
ovary,  and  also  froia  tlie  ])]exus  in  couucixion  witli  the  uterus.  Tlie  afferent  fibres  ajjpear  to 
belong  to  the  eleventh  and  twelfth  thoracic  and  tlie  first  lumbar  nerves.  The  lymphatics  join 
the  lumbar  gi'oup  of  glands. 


THE  UTEKUS.  1187 

Epoophoron  and  Paroophoron. — These  are  two  rudiuientary  structures  found 
between  the  layers  of  the  broad  ligament. 

The  epoophoron,  or  parovarium  (sometimes  called  the  organ  of  Kosenmlillerj,  lies 
in  the  mesosalpinx  between  the  Fallopian  tube  and  the  ovary.  In  the  adult  it 
consists  of  a  number  of  small  rudimentary  blind  tubules  lined  !)y  an  epithelium. 
One  of  these  tubules,  called  the  duct  of  Gartner  (ductus  epoophori  longitudmalis), 
lies  close  to,  and  runs  nearly  parallel  with,  the  Fallopian  tube.  It  is  joined  by  a 
number  of  the  other  tubules  (ductuli  transversi)  which  enter  it  at  right  angles 
from  the  neighbourhood  of  the  ovary.  The  duct  of  Gartner  is  a  persistent  portion 
of  the  Wolffian  duct,  and  represents  the  canal  of  the  epididymis  in  the  male,  while 
the  tubules  whicli  join  it  are  derived  from  the  mesonephros  and  represent  the  vasa 
efferentia  and  coni  vasculosi  of  the  testis  (and  probably  also  the  ductuli  aberrantes 
of  the  canal  of  the  epididymis).  The  epoophoron  is  best  seen  by  holding  up  to 
the  light  the  part  of  the  broad  ligament  in  which  it  lies. 

One  or  more  small  pedunculated  cystic  structures,  called  hydatids  of  Morgagni 
(appendices  vesiculosi),  are  often  seen  near  the  infundibulum  of  the  Fallo[)ian  tube. 
These  are  usually  supposed  to  represent  portions  of  the  upper  end  of  the  Wolffian 
duct. 

The  paroophoron  is  a  collection  of  rudimentary  tubules  also  enclosed  by  the  layers 
of  the  mesosalpinx,  but  lying  nearer  the  uterus  than  the  epoophoron.  These  very 
rudimentary  tubules  represent  the  paradidymis  or  organ  of  Giraldes,  in  the  male, 
and  are  derived  from  the  part  of  the  mesonephros  which  lies  nearer  the  caudal  end 
of  the  body  of  the  embryo.  Though  sometimes  visible  in  the  child  at  birth,  the 
paroopheron  in  the  adult  can  only  be  made  out  with  the  aid  of  a  lens. 

THE   UTEEUS. 

The  uterus  or  v/omb  is  a  hollow,  thick-walled,  muscular  organ  placed  within  the 
pelvis  between  the  bladder  in  front  and  the  rectum  behind.  The  ova  discharged 
from  the  ovary  enter  the  uterus  through  the  Fallopian  tubes,  and,  if  fertilisation  has 
taken  place,  undergo  their  development  within  it.  In  form  the  viterus  is  somewhat 
pear-shaped,  the  wide  upper  end  of  the  organ  projecting  freely  upwards  and  for- 
wards into  the  pelvic  cavity,  while  the  lower  more  constricted  part  is  connected 
with  the  vagina.  The  usual  length  of  the  adult  uterus  (when  non-pregnant)  is 
three  inches,  its  greatest  breadth  is  nearly  two  inches,  and  its  maximum  thickness 
is  about  one  inch. 

In  the  description  of  the  uterus  we  distinguish  between  an  upper  larger  portion, 
somewhat  flattened  from  before  backwards,  composed  of  fundus  and  body,  and  a 
lower  more  cylindrical  part  called  the  "cervix  (Fig.  852).  The  part  of  the  uterus 
that  lies  above  the  level  of  a  line  joining  the  points  of  entrance  of  the  Fallopian 
tubes  is  called  the  fundus  (fundus  uteri).  The  fundus  is  convex  from  before  back- 
wards and  from  side  to  side,  its  anterior  and  posterior  aspects  being  directly  con- 
tinuous with  the  anterior  and  posterior  surfaces  of  the  body  of  the  organ.  The 
body  of  tlie  uterus  (corpus  uteri),  when  seen  from  in  front  or  from  behind,  has  a 
somewhat  triangular  outline,  and  lies  below  the  fundus,  with  which  it  is  con- 
tinuous. The  base  of  the  triangle  is  directed  upwards  and  is  formed  by  a  line  joining 
the  lateral  angles  of  the  uterus,  or  points  of  entrance  of  the  Fallopian  tubes,  and 
the  sides  of  the  triangle  correspond  to  the  lateral  borders  of  the  uterus,  which 
extend  on  each  side  from  the  lateral  angle  to  the  cervix.  The  lateral  harder  (margo 
lateralis)  separates  on  each  side  the  anterior  surface  (facies  vesicalis)  from  the 
posterior  surface  (facies  intestinalis)  of  the  body.  Both  these  surfaces  are  rounded, 
but  the  posterior  is  much  the  more  convex.  The  anterior  surface  rests  against  the 
upper  aspect  of  the  bladder,  from  which  usually  it  is  separated  only  by  the  layers 
of  peritoneum  forming  the  utero-vesical  pouch.  The  posterior  surface  forms  the 
chief  part  of  the  anterior  wall  of  the  deep  recess  situated  between  the  uterus  and 
rectum,  and  is  usually  in  contact  with  some  part  of  the  small  intestine  or  the  pelvic 
colon. 

The  broad  ligament  passes  outwards  on  each  side  of  the  uterus  from  the  lateral 
border  of  the  organ. 


1188 


THE  UKINOGENITAL  SYSTEM. 


The  neck,  or  cervix  uteri,  is  cylindrical,  and  at  its  commencement  it  is  sometimes 
marked  off  from  the  body  by  a  slight  constriction.  Its  length  is  about  one  inch,  and 
its  lower  end,  tapering  somewhat,  enters  the  upper  part  of  the  vagina.  The  cervix  is 
attached  to  the  margin  of  the  opening  in  the  vaginal  wall,  through  which  it  passes, 
and  in  this  way  a  supravaginal  portion  (portio  supra  vaginalis)  is  marked  off  from  a 
vaginal  portion  (portio  vaginalis)  of  the  cervix.  In  the  vaginal  portion  of  the  cervix 
there  is  an  opening — the  external  os  uteri  (orificium  externum  uteri) — through  which 
the  cavity  of  the  uterus  communicates  with  that  of  the  vagina.  In  the  uterus  which 
has  never  been  pregnant  this  opening  is  nearly  circular,  but  in  women  who  have 
borne  children  it  is  usually  a  transverse  slit  with  a  somewhat  irregular  outline.  In 
front  of  and  behind  this  opening  the  cervix  forms  two  lips,  an  anterior  and  a 
Ijosterior  (labium  anterius  et  labium  posterius).  The  anterior  lip  is  thicker,  and 
slightly  more  rounded ;  it  is  placed  upon  a  lower  level  than  the  posterior  lip,  which 
is  slightly  longer  and  thinner  The  cervix  enters  the  vagina  through  the  upper 
part  of  its  anterior  wall  in  such  a  manner  that  the  external  os  uteri  is  directed 
backwards  and  downwards  against  the  upper  part  of  the  posterior  vaginal  wall 
(Fig.  853). 


Parovarium  Ligament 

Fallopian  tube  |      Ovary     of  ovary  Uterus 


Lateral  angle 
of  uterus 


Hydatid 


Fimbriated  end  of  tube  V, 

Round  ligament         Broad 
ligament 


Fig.  852. — A.  Thk  Uterus  and  Broad  Ligament  seen  from  behind  (the  broad  ligament  has  iDseu 

spread  out). 

a,  h,  and  c,  the  isthmus  tubee,  the  ligament  of  the  ovary,  and  the  round  ligament  of  the  right  side  cut  short. 

B.  Diagrammatic  Representation  of  the  Uterine  Cavity  opened  up  from  in  front. 

Cavity  of  the  Uterus. — In  comparison  with  the  size  of  the  organ,  the  cavity  of 
the  uterus  (cavum  uteri)  is  of  small  size  owing  to  the  great  thickness  of  the  uterine 
wall.  In  the  body,  or  corpus  uteri,  the  cavity  is  merely  a  narrow  chink  between  the 
anterior  and  posterior  walls,  which  are  almost  in  contact  (Fig.  853).  When,  how- 
ever, the  organ  is  opened  from  above  downwards  in  coronal  section  the  cavity  of 
the  body  has  a  triangular  outline  (Fig.  852).  The  base  of  the  triangle  is  directed 
upwards,  and  corresponds  to  a  line  drawn  Ijetween  the  opeiiings  of  the  Fallopian 
tubes,  while  the  apex  is  directed  downwards  towards  the  cervix.  The  sides  of  the 
triangle  are  convex  inwards  towards  the  cavity.  The  cavity  of  the  body  becomes 
continuous  with  that  of  the  neck,  or  cervix,  by  an  opening  called  the  internal  os 
uteri  (orificium  internum  uteri),  which  is  a  little  smaller  and  more  circular  than 
the  external  os  uteri.  The  cavity  of  the  cervix,  or  cervical  canal  (canalis  cervicis 
uteri),  extends  from  the  internal  os  uteri,  where  it  joins  the  cavity  of  the  body,  to 
the  external  os  uteri,  where  it  opens  into  the  vagina.  It  is  a  somewhat  spindle- 
shaped  passage,  wliich  is  narrower  above  and  below  than  in  its  middle  part ;  also 
sections  show  that  its  antero-posterior  diameter  is  shorter  than  its  transverse  one, 
owing  to  an  approximation  of  its  anterior  and  posterior  walls.  In  the  body  of  the 
uterus  the  walls  of  the  cavity  are  smooth  and  even,  but  in  the  cervical  canal  the 
mucous  membrane  forms  a  remarkal)le  series  of  folds,  called  the  arbor  vitse  uterinse 
or  plicae  palmatse.  These  consist  of  an  anterior  and  a  posterior  longitudinally, 
directed  fold  or  ridge,  from  wliich  a  large  number  of  secondary  folds,  or  rugae, 
branch  off  obliquely  upwards  and  outwards  (Fig.  852). 


THE  UTERUS.  1189 

Connexions  of  the  Uterus  and  its  Relations  to  the  Peritoneum.— I u  addition 
to  the  Fallopian  tubes  at  its  upper  lateral  angles,  and  the  vagina  below,  the  uterus 
possesses  other  important  connexions.  Some  of  these  are  simply  peritoneal  iolds 
passing  from  the  uterus  to  neighbouring  structures;  others  contain  librous  con- 
nective tissue,  or  smooth  muscle  fibres. 

Tlie  peritoneum  covering  the  fundus  of  the  uterus  is  continued  down  over  tlie 
anterior  surface  as  far  as  the  junction  of  the  body  and  cervix,  where  it  leaves  the 
uterus  to  be  reflected  on  to  the  bladder,  forming  the  utero-vesical  fold,  or  "  anterior 
ligament  of  the  uterus."  The  peritoneal  recess  between  the  bladder  and  tbe  uterus 
is  called  the  utero-vesical  pouch  (excavatio  vesico-uterina).  Below  the  level  of  the 
floor  of  this  pouch  the  anterior  aspect  of  the  cervix  is  connected  by  loose  tissue 
with  tlie  posterior,  or  basal,  part  of  the  bladder.  Posteriorly  the  peritoneum  covers 
the  whole  of  the  uterus,  except  tbe  small  portion  of  the  cervix  which  projects  into 
the  upper  part  of  the  vagina.  The  peritoneum  covering  the  posterior  surface  of 
the  uterus  is  continued  to  such  a  depth  that  it  invests  a  small  portion  of  the  upper 
part  of  the  posterior  wall  of  the  vagina  before  it  is  reflected  on  to  the  rectum, 
to  form  the  recto-vaginal  fold  (Fig.  853).  The  deep  pouch  between  the  uterus  and 
vagina  in  front  and  the  rectum  behind  is  called  the  pouch  of  Douglas  (excavatio 
recto-uterina  or  recto-genital  pouch),  and  its  entrance  is  bounded  on  each  side  by 
a  crescentic  peritoneal  fold,  which  passes  from  the  posterior  surface  of  the  cervix 
uteri  to  the  posterior  wall  of  the  pelvis,  and  ends  near  the  side  of  the  rectum. 
These  crescentic  folds  are  called  the  recto-uterine  folds  (plicse  recto- uterinie,  recto- 
genital  folds),  or  folds  of  Douglas,  and  each  contains  between  its  layers  a  consider- 
able amount  of  fibrous  and  smooth  muscular  tissue.  Some  of  these  fibres,  which 
are  continuous  with  the  uterine  wall,  pass  backwards  to  reach  the  rectum  and 
constitute  the  recto-uterine  muscle  (musculus  recto-uterinus) ;  others,  gaining  an 
attachment  to  the  front  of  the  sacrum,  form  the  utero-sacral  ligament.  In  many 
cases  the  recto-uterine  folds  become  continuous  with  one  another  across  the  middle 
line  behind  the  cervix  uteri,  and  form,  in  this  position,  a  transverse  ridge  termed 
the  torus  uterinus.  The  pouch  of  Douglas,  or  recto-genital  pouch  of  the  female, 
represents  the  recto-vesical,  or  recto-genital  pouch  of  the  male,  and  the  folds  which 
bound  it  laterally,  namely,  the  recto-uterine  folds,  correspond  to  the  sacro-genital 
folds  (sometimes  called  posterior  false  hgaments  of  the  bladder)  in  the  male  sex. 
The  peritoneum  of  the  anterior  and  posterior  surfaces,  leaving  the  uterus  along 
each  lateral  border  to  reach  the  side  wall  of  the  pelvis,  forms  the  broad  ligament 
of  the  uterus. 

The  broad  ligament  (ligamentum  latum  uteri)  is  a  wide  peritoneal  fold  which 
passes  from  the  lateral  border  of  the  uterus  to  the  pelvic  wall,  and  contains  between 
its  layers  several  important  structures  (Fig.  852).  The  plane  of  the  inner  part  of 
the  ligament  is  determined  by  the  position  of  the  uterus.  When  the  uterus  is 
normally  placed,  the  ligament  has  an  anterior  surface  which  looks  downwards  as 
well  as  forwards,  and  a  posterior  one  which  looks  upwards  and  backwards.  Near 
its  attachment  to  the  pelvis  the  ligament  is  placed  more  vertically.  The  free  edge 
of  the  ligament  contains  the  Fallopian  tube,  and  follows  the  course  pursued 
by  that  structure.  Thus,  in  the  undisturbed  condition  of  parts,  it  at  first  passes 
horizontally  outwards  towards  the  lov/er  end  of  the  ovary,  where  it  ascends 
to  arch  over  the  upper  pole  of  the  ovary  on  its  inner  side.  Owing  to  the  course 
pursued  by  the  Fallopian  tube  round  the  ovary,  the  broad  ligament  forms  a  kind 
of  curtain  over  the  gland,  and  the  ovary  lies  in  a  little  pocket  formed  by  the  broad 
ligament,  to  which  the  name  of  bursa  ovarii  is  applied  (Figs.  848  and  849).  This; 
bursa  ovarii  is  not  to  be  confused  with  the  fossa  ovarica,  or  depression  on  the  side 
wall  of  the  pelvis,  against  which  the  ovary  is  usually  placed. 

The  various  structures  in  connexion  with  the  broad  ligament  are  most  easily 
demonstrated  when  the  ligament  is  spread  out  as  flat  as  possible. 

The  ovary  is  connected  with  the  posterior  layer  of  the  broad  ligament  by  a 
very  short  mesentery,  called  the  mesovarium,  which,  passing  to  the  hilum,  encloses 
the  ovarian  vessels  and  nerves  as  they  reach  the  ovary.  The  part  of  the  broad 
ligament  which  slings  the  Fallopian  tube  is  called  the  mesosalpinx.  When  the 
ligament  is  spread  out,  the  mesosalpinx  has  the  form  of  a  narrow  triangle,  the 
80  a 


1190  THE  UEINOGENITAL  SYSTEM. 

■apex  of  which  is  at  the  lateral  angle  of  the  uterus,  while  the  upper  side  is  formed 
by  the  Fallopian  tube,  and  the  lower  one  by  the  ligament  of  the  ovary  and  the 
ovary  itself.  The  narrow  base  of  the  triangle  is  directed  outwards.  Between  the 
layers  of  this  part  of  the  broad  ligament  are  situated  the  parovarium  (epoophoron) 
and  the  paroophoron  (Fig.  852).  The  part  of  the  broad  ligament  below  the  level 
of  the  mesosalpinx  is  termed  mesometrium,  and  contains,  especially  in  its  lower 
part,  a  considerable  amount  of  fatty  connective  tissue  (parametrium)  and  unstriped 
muscle  fibres.  The  ureter  and  the  uterine  vessels  lie  in  the  lowest  part  of  the 
broad  ligament  where  it  joins  the  pelvic  floor. 

The  highest  part  of  the  attached  lateral  portion  of  the  broad  ligament  forms  the 
suspensory  ligament  of  the  ovary  and  contains  between  its  layers  the  ovarian 
vessels  and  nerves,  as  they  enter  or  leave  the  pelvis. 

The  ligament  of  tlie  ovary  (ligamentum  ovarii  proprium)  is  a  rounded  fibrous 
cord,  of  about  one  to  one  and  a  half  inches  in  length,  which  is  attached  by  its  outer 
end  to  the  lower  pole  of  the  ovary,  and  by  its  inner  end  to  the  lateral  angle  of  the 
uterus  immediately  below  and  behind  the  entrance  of  the  Fallopian  tube.  This 
ligament,  which  is  largely  composed  of  unstriped  muscle  fibres  continuous  with 
those  of  the  uterus,  is  enclosed  in  a  slight  fold  derived  from  the  posterior  layer  of 
the  broad  ligament. 

The  ligament  of  tlie  ovary  represents  the  u^Dper  portion  of  the  gubernaculum  which  ajDpears 
in  tlie  emlaryo. 

The  round  ligament  of  the  uterus  (ligamentum  teres  uteri)  is  a  narrow  flat 
band  attached  to  the  uterus  just  in  front  of  and  a  little  below  the  opening  of  the 
Fallopian  tube.  Near  the  uterus  it  contains  numerous  smooth  muscle  fibres,  which 
are  continuous  with  those  of  the  uterus ;  further  on  it  is  chiefly  composed  of 
fibrous  connective  tissue.  Lying  in  the  anterior  part  of  the  broad  ligament,  it 
reaches  the  pelvic  wall,  and  is  then  directed  forwards  and  slightly  upwards  to  cross 
the  obHterated  hypogastric  artery  and  the  pelvic  brim.  After  it  has  reached  the 
pelvic  wall  its  course  is  comparable  to  that  of  the  vas  deferens  in  the  male,  and, 
Like  the  latter,  it  leaves  the  abdomen  to  traverse  the  inguinal  canal  (Figs.  845  and 
848).  It  finally  ends  in  the  subcutaneous  tissue  and  skin  of  the  labium  majus.  Its 
terminal  part  is  composed  of  connective  tissue  only. 

In  some  cases  a  small  diverticulum  of  the  peritoneal  cavity  can  be  traced  accompanying  the 
round  ligament  through  the  abdominal  wall.  This  is  called  the  canal  of  Nuck  (processus 
vaginalis  i^eritonaii),  and  corresponds  to  the  processus  vaginalis  of  tlie  male  {-p.  1167). 

The  round  ligament  of  the  uterus  represents  the  lower  portion  of  the  gubernaculum  testis 
which  appears  in  the  male  embryo  (see  pp.  1168  and  1184). 

Position  and  Relations  of  the  Uterus. — The  position  occupied  by  the 
uterus  in  the  pelvis  is  not  always  the  same,  but  varies  with  the  conditions  of  the 
neighbouring  organs.  The  lower  cervical  part  is,  however,  much  more  firmly  fixed 
in  place  than  the  body  and  fundus,  which  possess  a  considerable  amount  of  mobility. 
Usually  the  level  of  the  external  os  uteri  will  be  found  to. correspond  to  that  of  a 
horizontal  plane  passing  through  the  upper  margin  of  the  symphysis  pubis.  The  . 
uterus  rarely  lies  exactly  in  the  mesial  plane  of  the  body,  but  usually  bends  to  one 
or  other  side,  most  frequently  towards  the  right.  The  anterior  surface  of  the  uterus 
rests  against  the  bladder,  and  follows  the  rising  or  falling  of  its  superior  wall  as 
that  organ  becomes  filled  or  emptied.  Wlien  the  bladder  is  empty  the  long  axis  of 
the  uterus  points  forwards  and  upwards,  and  the  organ  is  said  to  be  in  an  anteverted 
position.  Also  the  long  axis  of  the  uterus  is  bent  on  itself  where  the  body  joins  the 
cervix,  and  so  the  organ  is  said  to  be  antefiexed.  The  anteflexion  is  due  to  the  fact 
that  the  more  rigid  cervix  is  fixed,  while  the  movable  upper  part  of  the  uterus  sinks 
forwards,  following  the  bladder  wall.  With  the  empty  condition  of  the  bladder 
the  angle  formed  between  the  long  axis  of  the  uterus  and  that  of  the  vagina  is 
about  a  right  angle.  When  the  bladder  becomes  filled,  the  anteversion  and 
anteflexion  of  the  uterus  become  less  marked,  owing  to  the  body  and  fundus 
being  pushed  backwards.  Finally,  if  the  rectum  be  empty  and  -the  bladder  very 
much  distended,  the  uterus  is  pushed  so  mucli  backwards  that  tbe  long  axis  of  the 
organ  may  nearly  correspond  to  that  of  the  vagina.     The  uterus  is  then  said  to  be 


THE  UTERUS.  1191 

retroverted.  Superiorly  a  part  of  the  peritoneal  cavity  interveues  between  the  anterior 
surface  of  the  uterus  and  the  bladder,  but  lower  down  the  two  organs  are  separated 
merely  by  a  small  quantity  of  connective  tissue.  The  posterior  surface  of  the 
uterus  looks  into  the  pouch  of  Douglas,  and  is  usually,  like  the  fundus,  in  relation 
to  some  loops  of  intestine.  Laterally  the  uterus  is  related  to  the  broad  ligaments. 
The  terminal  parts  of  the  ureters  pass  downwards,  inwards,  and  a  little  forwards  on 
each  side  of  the  cervix,  but  are  separated  from  it  by  an  interval  of  about  three- 
quarters  of  an  inch.  The  lowest  part  of  the  cervix  is,  as  we  have  seen,  enclosed 
within  the  cavity  of  the  vagina. 

On  each  side  of  the  cervix  uteri  and  upper  part  of  the  vagina  there  is  an 
interval  in  which  lie  numerous  large  vessels.  These  are  surrounded  by  loose  fatty 
tissue,  which  is  continued  upwards  for  a  considerable  distance  between  the  layers 
of  the  broad  ligament.  This  loose  tissue,  which  is  of  surgical  importance,  lias 
received  the  name  parametrium. 

Structure  of  the  Uterus. — The  thick  uterine  wall  is  composed  of  three  chief  layers, 
which  are  termed  respectively  the  serous,  the  muscular,  and  the  mucous  coats. 

The  serous  coat  or  perimetrium  (tunica  serosa)  is  derived  from  the  peritoneum,  and 
covers  the  whole  organ  except  the  anterior  surface  of  the  cervix,  and  the  part  of  the 
cervix  which  projects  into  the  vagina.  At  the  lateral  borders  it  is  continued  into  the 
broad  ligaments.  Over  the  fundus  and  body  of  the  uterus  the  serous  coat  is  very  firmly 
adherent  to  the  deeper  layers,  and  cannot  be  easily  peeled  off  without  tearing  either  it  or 
the  underlying  muscular  tissue.  Near  the  lateral  borders  the  peritoneum  is  less  firmly 
attached,  and  over  the  posterior  aspect  of  the  cervix  it  may  readily  be  stripped  off  without 
injury  to  the  underlying  structures. 

The  muscular  coat  (tunica  muscularis)  is  composed  of  unstriped  fibres,  and  forms  the 
chief  part  of  the  uterine  wall.  Inferiorly  the  muscular  coat  of  the  uterus  becomes  con- 
tinuous with  that  of  the  vagina.  The  more  superficial  layer  of  the  muscular  coat  sends 
prolongations  into  the  recto-uterine  folds,  into  the  round  and  broad  ligaments  of  the  uterus, 
and  into  the  ovarian  ligaments.  Other  fibres  join  the  walls  of  the  Fallopian  tubes.  The 
main  branches  of  the  blood-vessels  and  nerves  of  the  uterus  lie  among  the  muscle  fibres.  In 
the  deeper  layers  of  the  muscular  coat  a  considex'able  amount  of  connective  tissue  and  some 
elastic  fibres  are  to  be  found.  The  muscular  coat  of  the  cervix  (tunica  muscularis  cervicis) 
contains  more  connective  and  elastic  tissue  than  that  of  the  body,  and  hence  the  greater 
firmness  and  rigidity  of  the  cervical  part  of  the  uterus. 

The  deeper  and  thicker  part  of  the  muscular  tissue  of  the  uterus  is  considered  by  some 
anatomists  to  represent  a  muscularis  mucosae,  and  is  therefore  described  as  part  of  the 
mucous  coat.  The  deep  and  supei-ficial  portions  of  the  muscular  coat  are,  however,  quite 
continuous,  and  there  is  no  representative  of  a  submucous  vascular  layer  of  tissue  such 
as  in  the  alimentary  canal  separates  the  muscular  coat  from  the  muscularis  mucosae.  In 
the  uterus  the  blood-vessels  lie  in  the  muscular  coat. 

The  mucous  coat  (tunica  mucosa)  in  the  body  of  the  uterus  is  smooth  and  soft,  and 
covei-ed  by  columnar  ciliated  epithelium.  Simple  tubular  glands  (glandulae  uterinse), 
also  lined  by  a  ciliated  epithelium,  are  present  in  the  mucous  membrane,  and  penetrate 
in  their  deeper  parts  into  the  muscular  coat.  In  the  cervix  of  the  uterus  the  mucous 
coat  is  firmer  and  more  fibrous  than  in  the  body,  and  its  surface  is  not  smooth,  but 
pi'esents  a  number  of  peculiarly  disposed  ridges,  which  have  been  already  described. 
Like  the  mucous  membrane  of  the  body  of  the  uterus,  that  of  the  cervix  is  covered  by  a 
ciliated  epithelium  which  passes  into  squamous  epithelium  just  inside  the  external  os  uteri. 
The  cervix  uteri  possesses,  in  addition  to  unbranched  tubular  glands,  resembling  those 
present  in  the  body,  numerous  somewhat  branched  glands  (glandulte  cervicales  uteri). 
Both  kinds  of  glands  are  lined  by  ciliated  epithelium.  In  many  cases  little  clear 
retention  cysts,  ovules  of  Naboth,  are  to  be  seen  in  the  cervical  mucous  membrane, 
which  arise  as  a  result  of  obstruction  at  the  mouths  of  the  glands. 

Difference  in  the  Uterus  at  Different  Ages. — At  birth  the  cervix  uteri  is 
relatively  larger  than  in  the  adult  organ,  and  its  cavity  is  not  distinctly  marked 
off  from  the  interior  of  the  body  by  an  internal  os  uteri.  At  this  time  also  the 
arbor  vitas  extends  throughout  the  whole  length  of  the  uterus.  The  organ  grows 
slowly  until  just  before  puberty,  when  its  growth  is  rapid  for  a  time.  As  the 
body  increases  in  size  the  mucous  membrane  becomes  smooth  and  the  arbor  vitse 
becomes  restricted  to  the  cervix.  In  women  who  have  borne  children  the  canity 
80  6 


1192  THE  UKINOGENITAL  SYSTEM. 

remains  permanently  somewhat  wider  and  larger  than  in  cases  where  the  uterus 
has  never  been  pregnant. 

In  old  age  the  uterine  wall  becomes  harder  and  has  a  paler  colour  than  it 
possesses  in  the  young  subject. 

Variations. — In  rare  cases  the  uterus  may  be  divided  by  a  septum  into  two  distinct  cavities, 
or  its  lateral  angles  may  be  in-oduced  into  straight  or  curved  processes,  called  "  liorns  "  or  comua. 
The  latter  abnormality  recalls  the  appearance  of  the  bicornuate  uteri  of  some  animals.  Both  the 
above  conditions  arise  from  an  arrest  in  the  fusion  of  tlie  two  separate  tubes — the  Miillerian 
ducts — which  normally  unite  to  form  the  uterus. 

Periodic  Changes  in  the  Uterine  Wall.— At  each  menstrual  period  a  remark- 
able series  of  changes  occurs  which  results  in  a  periodic  shedding  of  the  super- 
ficial parts  of  the  uterine  mucous  membrane.  For  a  few  days  before  menstruation 
begins,  the  mucous  membrane  gradually  thickens  and  becomes  more  vascular,  while 
at  the  same  time  its  surface  becomes  uneven.  Soon  the  superficial  parts  of  the 
mucous  membrane  disintegrate  and  haemorrhage  takes  place  from  the  small  super- 
ficial blood-vessels.  In  this  way  a  hemorrhagic  discharge  is  caused,  and  the 
superficial  parts  of  the  uterine  mucous  membrane  are  shed  at  each  period.  When 
menstruation  is  over  the  mucous  membrane  is  rapidly  regenerated. 

Pregnant  Uterus. — The  pregnant  uterus  increases  rapidly  in  size  and  weight, 
so  that  from  being  three  inches  in  length  and  one  ounce  in  weight,  it  becomes  by 
the  eighth  month  about  seven  or  eight  inches  in  length  and  sometimes  as  much 
as  two  pounds  in  weight.  In  shape  the  uterus  is  now  oval  or  rounded,  wdth  a  thick 
wall  composed  chiefly  of  muscle  fibres  arranged  in  distinct  layers.  The  rounded 
fundus  is  very  prominent.  The  round  ligaments  are  stronger  and  better  marked, 
and  the  layers  of  the  broad  ligament  become  separated  in  their  inner  parts  by  the 
growth  of  the  uterus  between  them.  The  blood-vessels,  especially  the  arteries,  are 
very  large  and  tortuous.  The  changes  which  occur  in  the  mucous  membrane  of 
the  pregnant  uterus  are  intimately  connected  with  the  manner  in  which  the 
developing  fcetus  receives  its  nutrition,  and  have  been  noticed  on  p.  53. 

Vessels  and  Nerves  of  the  Uterus.— The  uterus  receives  its  arterial  supply  from  the 
uterine  arteries,  wliich  are  branches  of  the  internal  iliac  arteries,  and  also  from  the  ovarian  arteries, 
branches  of  the  aorta.  The  vessels  derived  from  these  two  sources  communicate  freely  with  one 
another.  Each  uterine  artery,  reaching  the  side  of  the  lower  part  of  the  uterus,  divides  into  a 
large  branch  which  passes  upwards  to  supply  the  body  and  fundus,  and  a  much  smaller  branch 
which  passes  dowmwards  to  supply  the  cervix.  The  vessels  distributed  to  the  body  and  fundus 
have  an  exceedingly  tortuous  course.  The  branches  of  the  uterine  artery,  having  entered  the 
muscular  coat,  break  up  within  its  deeper  layers  into  smaller  twigs  which  supply  the  muscular 
tissue  and  the  mucous  coat.  The  small  uterine  branch  from  the  ovarian  artery  reaches  the 
uterxis  in  the  region  of  the  lateral  angle.  During  pregnancy  the  arteries  become  enormously 
enlarged. 

The  thin-walled  veins  form  a  plexus  wliicli  pours  its  blood  into  the  tributaries  of  the  internal 
iliac  vein. 

The  nerves  of  the  uterus  are  derived  chiefly  from  a  plexus  placed  in  the  neighbourhood  of 
the  cervix  uteri,  to  which  the  term  cervical  ganglion  or  plexus  utero-vaginalis  is  applied. 
Superiorly  this  plexus  is  continuous  with  the  hypogasti'ic  plexus,  but  it  also  receives  fibres  from 
the  third  and  fourth  sacral  nerves.  In  addition  to  fibres  from  the  plexus  utero-vaginalis,  the 
uterus  receives  fibres  directly  from  the  hypogastric  plexus,  and  also  from  the  vesical  plexus. 

Clinical  observations  indicate  that  afferent  impulses  reach  the  central  nervous  system  from  the- 
uterus  througli  the  posterior  roots  of  the  tenth,  eleventh,  and  twelfth  thoracic  nerves,  the  first 
lumbar,  and  the  second,  third,  and  fourtli  sacral  nerves. 

The  numerous  lymphatic  vessels  comiug  from  the  body  of  the  uterus  join  those  from  the  ovary 
and  end  for  the  most  ])art  in  the  lumViar  lymphatic  glands.  Along  the  course  of  the  round 
ligament  of  the  uterus  there  are  a  few  lymphatic  vessels  which  establish  a  connexion  between  the 
lymphatic  network  suiTOunding  tlie  uterus  and  the  inguinal  lymphatic  glands.  The 
lymphatics  from  the  cervix  uteri  end  in  the  gland  placed  near  the  bifuication  of  tlie  common 
iliac  artery. 

THE    VAGINA. 

The  vagina  is  a  passage  about  three  inches  in  length,  open  at  its  lower 
end,  and  communicating  above  with  the  cavity  of  the  uterus.  The  passage  is 
directed  downwards  and  forwards,  describing  a  slight  curve  which  is  convex  back- 
wards.    The  axis  of  the  vagina  forms  with  that  of  the  uterus  an  angle  which  is 


THE  VAGINA. 


1193 


open  forwards.  This  angle  is  usually  somewhat  greater  than  a  right  angle,  but  varies 
with  the  condition  of  the  neighbouring  viscera  (p.  1190).  The  vagina  is  wider  in  its 
middle  part  than  it  is  at  either  end,  and  normally  its  anterior  and  posterior  walls 
are  in  contact.  In  transverse  section  the  lower  part  is  usually  an  H -shaped  cleft, 
the  middle  part  a  simple  transverse  slit,  while  the  lumen  of  the  upper  portion,  into 
which  the  cervix  uteri  projects,  is  more  open.  The  lower  part  of  the  cervix  uteri  has 
the  appearance  of  entering  the  vagina  through  the  upper  portion  of  its  anterior 
wall  (Fig.  853).     As  more  of  the  posterior  than  of  the  anterior  part  of  the  cervix 


Cavity  of  uterii.' 


Cavity  of 

bladder 

LaViiuiii  anterius 

(cervix  uteri)' 

Symphysis  pubi 


Uretliri 


Labium  miiiu 


Labium  posterius 
(cervix  uteri) 


Anal  canal 
Sphincter  ani 


Fig.  853. — Meslvl  Sectidn  of  thk  Pelvis  in  .-vn  Adclt  Female. 

The  cavity  of  the  uterus  is  iiulicateil  iliagrammatieally.      From  a  specimen  in  the  Anatomica) 
Department,  Trinity  College,  Dublin. 

projects  into  the  vagina,  a  deeper  recess  is  formed  between  the  vaginal  wall  and 
the  cervix  behind,  than  in  front  or  laterally.  The  term  anterior  fornix  is  often 
applied  to  the  angle  or  recess  in  front,  posterior  fornix  to  the  deeper  angle  behind,  and 
lateral  fornix  to  the  recess  on  each  side  of  the  cervix  uteri,  between  it  and  the  w^all 
of  the  vagina.  The  anterior  vaginal  wall  (paries  anterior)  is  shorter  than  the 
posterior  (paries  posterior),  the  former  being  about  three  inches  in  length,  the 
latter  about  three  and  a  half  inches.  At  its  lower  end  the  vagina  opens  into  the 
urinogenital  cleft,  the  opening  being  situated  behind  the  orifice  of  the  urethra  and 
the  clitoris,  and  between  the  labia  minora.  The  opening  is  partly  closed  in  the 
virgin  by  a  thin  crescentic  or  annular  fold,  called  the  hymen,  torn  fragments  of 
which  persist  round  the  opening,  as  the  carunculse  hymenales,  after  the  fold  itself 
has  been  ruptured. 

Relations  of  the  Vagina. — The  anterior  w-all  of  the  vagina  in  its  upper  part 


1194 


THE  UEINOGENITAL  SYSTEM. 


lies  against  the  base  of  the  bladder,  but  is  separated  from  it  by  loose  connective 
tissue.  Lower  down,  the  anterior  wall  iu  the  mesial  line  is  intimately  connected 
with  the  urethra  (Fig.  853).  Near  the  middle  line  the  posterior  wall,  in  its  upper 
portion,  is  covered  for  a  distance  of  about  a  quarter  of  an  inch  by  the  peritoneum, 
which  here  forms  the  anterior  boundary  of   the  deepest   part  of  the   pouch   of 


Posterior  superior 
iliac  spine 


Apex  of  sacrum 


Great  sciatic  notch 

Rectuui 
Peritoneum 

Ureter 

Ischial  spine 
Uterine  artery 

Bladder  wall 

Ureter 

Levator  ani 

Sacro-sciatic 

ligament 

Isehio-rectal  fossa 
Tuber  ischii 
Gluteus  maximus 


Resto-vaginal  pouch 

Vaginal  wall 

Fig.  854.— The  Vagina,  the  Base  of  Bladder,  and  the  Recto-vaginal  Pouch  of  Peritoneum,  seen 

from  behinil. 

The  coccyx  aud  the  sacro-sciatic  ligaments,  together  with  the  muscles  att/iched-  to  them,  have  been  removed. 
The  levatores  ani  have  been  separated  along  the  median  raphe,  and  drawn  outwards.  A  considerable 
portion  of  the  rectum  has  been  removed,  but  the  position  which  it  occupied  is  indicated  by  the  dotted 
lines.  The  peritoneum  is  imlicated  by  a  blue  colour.  The  recto-vaginal  pouch  is  probably  not  quite  so 
deep  as  usual. 

Douglas.  The  depth  to  which  the  peritoneum  of  this  pouch  descends  practically 
corresponds  to  the  level  of  the  ischial  spines.  Lower  down,  the  posterior  wall 
Hes  close  against  the  rectum,  from  which  it  is  separated  by  a  layer  of  the  pelvic 
fascia.  As,  however,  the  orifice  of  the  vagina  is  approached,  the  rectum  and  vagina 
become  separated  by  a  considerable  interval,  which  is  occupied  by  a  mass  of  fibrous 
and  fatty  tissue,  often  called  the  "  perineum  "  or  "  perineal  body."  At  the  sides 
the  vagina  is  su^jported  by  the  levatores  ani  muscles.  The  terminal  part  of  the 
ureter  lies  not  far  from  the  side  wall  of  the  upper  part  of  the  vagina,  as  it  passes 
from  above  and  behind  downwards,  inwards,  and  a  little  forwards  to  reach  the 
bladder.  Near  its  termination  the  vagina  pierces  the  triangular  ligament,  and  is 
related  laterally  to  the  bulbus  vestibuli,  the  gland  of  Bartholin,  and  the  sphincter 
vaginae  muscle. 


THE  FEMALE  EXTERNAL  GENITAL  ORGANS.  1195 

Structure  of  the  Vagina. — The  vaginal  wall  has  a  distinct  muscular  coat  (tunica 
muscularis),  composed  of  unstriped  muscle  fibres,  most  of  which  are  longitudinally  dis- 
posed. Towards  the  lower  end  of  the  passage  circularly-disposed  bundles  of  striped  muscle 
fibres,  some  of  which  are  continuous  with  those  forming  a  part  of  the  urethral  wall,  are 
found  in  the  muscular  coat.  The  thick  mucous  membrane  (tunica  mucosa),  which  has  a 
stratified  scaly  epithelium,  is  corrugated,  and  presents  a  number  of  transverse  ridges  or 
elevations  called  rugae  vaginales.  In  addition  to  these  transverse  ruga),  a  slightly  marked 
longitudinal  ridge,  or  colunm,  is  to  be  seen  on  the  anterior  and  on  the  posterior  wall  of 
the  vagina.  These  receive  the  name  columnae  rugarum,  and,  like  the  transverse  ruga;, 
are  best  seen  in  young  subjects  and  in  the  lower  part  of  the  vagina.  The  urethral  canal 
lies  in  close  relationship  to  the  anterior  column  of  the  vagina  in  its  lower  part,  and  hence 
this  portion  of  the  anterior  column  is  sometimes  called  the  carina  urethralis  (Fi(>s  820  i' 
and  853). 

Within  the  mucous  coat  are  to  be  found  small  collections,  or  nodules,  of  ]ymi)hoid 
tissue. 

The  vaginal  wall  is  surrounded  by  a  layer  of  loose  vascular  connective  tissue  containing 
numerous  large  communicating  veins. 

Variation. — In  rare  cases  the  vagina  has  been  found  divided  by  an  incomplete  septum  into 
two  passages.  Such  abnormality  is  due  to  an  incomplete  fusion  of  the  lower  portions  of  the 
Miillerian  ducts  from  which  the  vagina  is  developed  in  the  embryo. 

Vessels  and  Nerves  of  the  Vagina.— Tlie  blood -supply  of  the  vagina  is  for  the  most  part 
derived  from  branches  of  tlie  vesico-vaginal  artery,  the  vaginal  branch  of  the  uterine  artery,  tlie 
vaginal  branches  of  the  middle  haemorrhoidal  artery,  and  from  tlie  branches  of  the  internal  pudic. 
The  veins  form  a  plexus  surrounding  tlie  vaginal  wall,  and  drain  their  blood  into  the  tributaries 
of  the  internal  iliac.  The  lymphatics  from  the  upper  part  of  the  vagina  join  the  internal  iliac 
group  of  glands,  while  those  from  the  lower  part  end  in  the  superficial  inguinal  glands.  The 
nerves  of  the  vagina  are  derived  from  the  plexus  utero-vaginalis,  and  from  the  plexus  vesicalis. 
Other  fibres  are  derived  directly  from  the  third  and  fourth  sacral  nerves. 

THE  FEMALE  EXTERNAL  GENITAL  ORGANS. 

The  term  vulva,  or  pudendum  (pudendum  muliebre),  is  often  applied  collectively 
to  the  female  external  genital  organs,  i.e.  to  the  labia  majora  and  the  structures 
which  lie  between  them. 

Labia  Majora. — The  labia  majora  represent  the  scrotum  in  the  male,  and 
form  the  largest  part  of  the  female  external  genital  organs.  They  form  the  lateral 
boundaries  of  the  urinogenital  cleft  (rima  pudendi),  into  which  the  urethra  and 
vagina  open.  Each  labium  is  a  prominent  rounded  fold  of  skin,  narrow  behind 
where  it  approaches  the  anus,  but  increasing  in  size  as  it  passes  forwards  and 
upwards  to  end  in  a  median  elevation,  the  mons  pubis  or  Veneris.  The  mons  Veneris, 
also  called  the  anterior  commissure  (commissura  labiorum  anterior),  lies  over  the 
symphysis  pubis,  and,  like  the  labia  majora,  it  is  composed  chiefly  of  fatty  and 
areolar  tissue,  and  is  covered  by  hair.  The  outer  convex  surface  of  each  labium 
majus  is  covered  by  skin  containing  numerous  sebaceous  glands  and  resembling 
that  of  the  scrotum  in  the  male,  but  the  inner  flatter  surface  is  smooth,  and  presents 
a  more  delicate  integumentary  covering.  In  some  cases  the  posterior  narrow  ends 
of  the  labia  majora  are  connected  across  the  middle  line  in  front  of  the  anus  by  a 
slight  transverse  fold — the  posterior  commissure  (commissura  labiorum  posterior). 

Usually,  especially  in  young  subjects,  the  labia  majora  are  the  only  visible  parts 
of  the  external  genital  organs,  since  they  are  in  contact  with  one  another,  and 
completely  enclose  the  structures  within  the  urinogenital  cleft. 

The  round  ligament  of  the  uterus  ends  in  the  fatty  tissue  of  the  labium  majus.  The 
supei-ficial  subcutaneous  tissue  resembles  that  of  the  scrotum,  but  contains  no  muscular 
fibres.  The  nerve  supply  corresponds  with  that  of  the  scrotum,  the  anterior  part  of  each 
labium  being  supplied  by  the  branches  of  the  ilio-inguilial  nerve,  and  the  posterior  part 
by  branches  fronr  the  internal  pudic,  and  by  the  perineal  branch  of  the  small  sciatic 
nerve.  The  blood-vessels  of  the  labia  majora  are  derived  from  the  superficial  pudic 
arteries  and  from  the  perineal  branches  of  the  internal  pudic  vessels. 

Labia  Minora.  —  The  labia  minora,  or  nymphte  (labia  minora  pudendi), 
are   a  pair  of  much  smaller  and  narrower  longitudinal   folds,  usually  completely 


1196 


THE  UEINOGENITAL  SYSTEM. 


^^smzii^c^ 


.Glans  olitoridis 
Freiiuluiii  clitoridis 


Labium  niajus 

Labium  minus 
Orificium  uretlirw 
externum 


_Commissiira 
posterior 


enclosed  withiu  the  cleft  between  the  labia  majora.  Diminishing  m  size,  and 
becoming  less  marked  in  their  posterior  parts,  the  labia  minora  end  by  gradually 
joining  the  inner  surfaces  of  the  labia  majora.  In  the  young  subject,  a  shghtly 
raised^transverse  fold  is  usually  seen  connecting  the  posterior  ends  of  the  labia 

minora ;     to    this 
fold  the  term  frenu- 
lum     (frenulum 
labiorum    puden- 
di),  or  fourchette, 
is  applied.   Traced 
forwards,     each 
labium      minus 
divides    into   two 
portions,  an  outer 
and  an  inner.   The 
outer   portions  of 
the  two  labia  unite 
over   the   glans 
clitoridis,  and  form 
a  fold  or  covering 
for  it,  called   the 
praeputium      clito- 
ridis.     The  inner 
portions,    uniting 
at  an  acute  angle, 
join  the  glans  and 
form  the  frenulum 
clitoridis.      The 
skin  of  the  labia 
minora   resembles 
the  integument  on 
the  inner  or  deep 
surface  of  the  labia 
majora,      being 
smooth,  moist,  and 
pink  in  colour. 
The     inner     sur- 
FiG.  855.— Female  External  Glmt.vl  Organ.-,.  faces   of   the  labia 

The  fourchette  is  seen  stretching  across  liehiud  the  fossa  naviciUaris  ami  in  front  of  minora  are  in  COn- 
the  posterior  commissure.  The  ducts  of  Bartholin's  glands  open  in  the  intervals  ^^^^^  with  OUC  ail- 
between  the  vaginal  oritice  and  the  inner  edges  of  the  labia  minora. 

other ;  their  outer 
surfaces  are  applied  against  the  inner  aspects  of  the  labia  majora. 

The  openings  of  the  urethra  and  vagina  are  placed  in  the  middle  line,  in  the 
interval  between  the  labia  minora,  which  must  be  separated  to  bring  them  into 

view. 

The  vestibule  (vestibulum  vaginse)  is  the  name  apphed  to  the  cleft  that  lies 
between  the  labia  minora  and  behind  the  glans  clitoridis.  In  its  floor  are  the 
openings  of  the  urethra,  the  vagina  and  the  minute  ducts  of  Bartholin's  glands. 

The  fossa  navicularis  is  the  part  of  the  vestibule  placed  behind  the  vaginal 
opening  and  in  front  of  tin;  fourchette. 

Tlie  external  urethral  orifice  lies  immediately  in  front  of  that  of  the  vaguia,  and 
is  about  one  inch  behind  the  glans  clitoridis.  The  opening  has  the  appearance  of 
a  vertical  slit,  or  of  an  inverted  V-shaped  cleft,  the  slightly  prominent  margins  of 
which  are  in  contact.  On  each  side  of  the  urethral  orifice  there  may  sometimes  be 
seen  the  minute  opening  of  the  para-urethral  duct  (see  page  1158). 

The  vaginal  opening  (orilicium  vaginse)  lies  further  back  and  below  the  orifice 
of  the  urethra.  The  appearance  of  the  opening  varies  with  the  condition  of  the 
hymen— a  membrane  wliich  in  the  young  subject  partly  closes  the  aperture.  When 
the  liymen  is  intact  the  opening  is  small,  and  is  only  seen  when  tlie  membrane  is 


THE  FEMALE  EXTEENAL  GENITAL  OEGANS. 


1197 


put  on  the  stretch.  When  the  hymen  has  been  ruptured  the  opening  is  much 
larger,  and  round  its  margins  are  often  seen  small  projections  carunculae  hymenales 
— which  are  to  be  looked  upon  as  persistent  portions  of  the  hymen. 

The  hymen  is  a  thin  membranous  fold,  partially  closing  the  lower  end  of  the 
vagina,  and  usually  perforated  somewhat  in  front  of  its  middle  point.  The  posi- 
tion of  the  opening  gives  the  fold,  when  stretched,  a  crescentic  appearance.  The 
opening  in  the  hymen  is  sometimes  cleanly  cut,  sometimes  fringed.  The  membrane 
is  not  stretched  tightly  across  the  lower  end  of  the  vagina,  but  is  so  ample 
that  it  projects  downwards  into  the  urinogenital  fissure,  and  the  parts  of  its  upper 
surface  are  in  contact  with  one  another  on  each  side  of  the  opening.  The 
opening  is  thus  a  mesial  slit  whose  margins  are  normally  in  contact.  The  upper 
surface  of  the  hymen  is  directly  continuous  with  the  vaginal  wall,  and  on  it  are 
to  be  seen  slight  ridges  continuous  with  the  vaginal  ruga;. 

Developmen  tally  the  hymen  appears  to  be  a  portion  of  the  vagina. 

On  each  side  of  the  vaginal  opening,  and  close  against  the  inner  side  of  the 
attached  margin  of  the  laljium  minus,  is  the  nunute  opening  of  the  duct  of  Bar- 
tholin's gland.     This  is  usually  just  large  enough  to  be  visible  to  the  unaided  eye. 

Numerous  minute  mucous  glauds  (glaiidulte  vestibuli  minores)  open  on  tlie  surface  of  tlie 
mucous  membrane  of  tlie  vestibule,  between  the  urethral  and  vaginal  orifices.  The  ojjening  of 
the  ductus  jmra-urethralis  at  the  side  of  the  urethral  orifice  has  been  already  noted,  pp.  1196 
and  1158. 

'  Clitoris. — The  clitoris  is  the  morphological  equivalent  of  the  penis,  and  is 
composed  of  a  body  and  two  crura.  Upon  the  sunnnit  of  the  body  is  a  minute 
glans.  Unlike  the 
penis,  the  clitoris  is 
not  traversed  by 
the  urethra. 

The  body  of  the 
clitoris  (corpus 
clitoridis)  is  com- 
posed for  the  most 
part  of  erectile 
tissue  resembling 
that  of  the  penis 
in  the  male.  It  is 
about  an  inch  or  an 
inch  and  a  half  in 
length,  and  is  bent 
upon  itself,  form- 
ing an  angle  open 
downwards.  The 
body  of  the  clitoris 
tapers  towards  its 
distal  end,  which 
is   covered   by  the 

glans  clitoridis.  The  organ  is  enclosed  in  a  dense  fibrous  coat,  and  is  divided 
by  an  incomplete  septum  (septum  corporum  cavernosorum)  into  two  symmetrical 
and  somewhat  cylindrical  portions,  the  corpora  cavernosa  clitoridis.  These  represent 
the  corpora  cavernosa  of  the  male,  and  diverge  from  one  another  at  the  root  of  the 
clitoris  to  form  the  crura  clitoridis.  A  suspensory  ligament  (ligamentum  suspen- 
sorium  clitoridis)  passes  from  the  fibrous  coat  of  the  body  of  the  clitoris  to  the 
symphysis  pubis. 

The  glans  clitoridis  is  a  small  mass  of  erectile  tissue  which  is  fitted  over  the 
pointed  end  of  the  body.  It  possesses,  like  the  glans  penis  which  it  represents,  a 
very  sensitive  epitheUum.  The  prepuce,  or  fold  of  skin  which  covers  it,  and  the 
frenulum  which  is  attached  to  it  interiorly,  are  continuous  with  the  labia  minora 
(Fig.  855). 

The  crura  clitoridis  diverge  from  the  body  posteriorly,  and  are  attached  to  the 
sides  of  the  pubic  arch.     Each  is  continuous  with  one  of  the  corpora  cavernosa,  and 


Fig.  856. —Dissection  of  the  Female  External  Genital  Organs. 

The  suspensory  ligament  is  seen  passing  upwards  towards  the  symphysis  pubis. 


1198 


THE  UEINOGENITAL  SYSTEM. 


has  a  firm  fibrous  sheath,  which  is  covered  by  the  corresponding  ischio-cavernosus 
or  erector  clitoridis  muscle.  In  structure  the  crura  and  body  of  the  clitoris 
resemble  the  corpora  cavernosa  penis,  while  the  gians  more  closely  resembles  the 
bulbus  vestibuli,  with  which  it  is  continuous  through  a  structure  known  as  the 
pars  intermedia. 

In  the  seal  and  some  other  animals,  a  bone,  wliich  represents  the  os  penis  of  the  male,  is 
devekiped  in  tlie  septum  of  the  clitoris.     Tliis  bone  receives  the  name  OS  clitoridis. 

Arteries  and  Nerves  of  the  Clitoris. — Each  cms  receives  a  branch  (arteria  profunda  clito- 
ridis) from  the  internal  pudic  artery,  ^vlnle  the  glans  is  supplied  by  branches  of  the  dorsal  arteries 
of  the  clitoris  (arteri;i3  dorsalis  clitoridis).  The  nerve  supj^ly  of  the  clitoris  is  derived  partly  from 
tlie  hypogastric  sympathetic  plexus  and  partly  from  the  dorsal  nerves  of  the  clitoris. 

Bulbus  Vestibuli. — The  bulbus  vestibuli  is  a  mass  of  erectile  tissue,  in  the 
female,  which  corresponds  developmentally  to  the  corpus  spongiosum  urethrse  of 
the  male.  In  the  female  the  fusion  of  the  two  halves  of  this  structure  is  not 
nearly  so  complete  as  in  the  male,  for  the  vagina  and  urethra  separate  the  bulbus 
vestibuli  into  two  lateral  portions  which  are  only  slightly  connected  in  front  by  a 
narrow  median  part  called  the  pars  intermedia.  Each  lateral  portion  of  the  bulb  is 
thick  and  massive  posteriorly,  and  more  pointed  in  front  where  it  joins  the  pars 
intermedia.  It  rests  against  the  side  wall  of  the  vagina,  and  upon  the  superficial 
aspect  of  the  triangular  ligament.  Superficially  it  is  covered  by  the  bulbo- 
cavernosus  muscle.  The  pars  intermedia  lies  above  the  urethra,  and  becomes  con- 
tinuous with  the  tissue  of  the  glans  clitoridis.  It  represents  one-half  of  the  corpus 
spongiosum  urethrie  of  the  male. 

The  bulbus  vestibuli  is  for  the  most  part  composed  of  minute  convoluted  blood- 
vessels, held  together  by  a  very  small  amount  of  connective  tissue.  These  vessels 
frequently  anastomose  with  one  another,  and  those  of  each  lateral  half  com- 
municate with  the  vessels  of  the  pars  intermedia  and  the  glans  clitoridis. 

The  blood-supply  of  the  bulb  is  derived  on  each  side  from  a  branch  (arteria  bulbi 
vestibuli)  of  the  internal  pudic. 


The  Glands  of  Baktholin. 

The  glands  of  Bartholin  (glanduhe  vestibulares  majores)  are  placed  one  on  each 
side  of  the  lower  part  of  the  vagina,  and  represent  Cowper's  glands  in  the  male. 

They  are  often  overlapped  by  the 
posterior  ends  of  the  bulbus 
vestibuli,  and  are  covered  by  the 
bulbo -cavern osus  muscle.  Each 
is  about  the  size  and  shape  of  a 
small  bean,  and  possesses  a  long 
slender  duct  which  opens  into  the 
urinogenital  cleft  in  the  angle 
between  the  attached  border  of 
the  labium  minus  and  the  vaginal 
^^-    opening. 


TRI/ilNGULAR 

^  ligT 


DEVELOPMENT  OF  THE 
URINOGENITAL  ORGANS. 


Fio, 


In  tracing  the  developmental 
history  of  the  urinogenital  system 
we  may  for  convenience  begin  with 
an  embryo  of  fifteen  days  old. 
About  this  time  a  duct,  which  runs 
in  ji  longitudinal  direction,  and 
occiipies  a  position  on  the  outer  side 
of  the  protovertebral  somites,  begins  to  develop  on  each  side  of  the  body.  With  the 
exception  of  the  anterior  portion  of  the  ck)aca  and  the  proximal  part  of  the  allantois,  this 
duct,  which  has  received  the  name  of  WolflO.an  duct,  is  the  earliest  formed  structure  from 
which,  or  in  connexion  with  which,  the  parts  of  the  advdt  urinogenital  system  arise. 


Central  point  of  i)Rriiieum 
857. — Dissection   of   Female   Peuineum    to   show  the 
Clitoris,  the  Bulb  ok  the  Vestibule,  and  Bartholin's 
Glands  (D.  J.  Cunniiigham). 


DEVELOPMENT  OF  THE  URINOGENITAL  ORGANS. 


1199 


The  Wolffian  duct  serves  as  the  canal,  or  duct,  for  the  primitive  secretory  organ  or 
mesonephros  of  the  embryo.  With  the  atrophy  of  the  mesonephros  the  duct  suffers 
modification,  yet  both  sexes  in  the  ^idult  possess  structures  which  have  their  embryonic 
origin  from  the  Wolffian.  In  the  male  the  canal  of  the  epididymis,  the  vas  deferens, 
and  the  common  ejaculatory  duct,  are  to  be  looked  upon  as  dii-ectly  developed  from  the 
Wolffian  duct  of  the  embryo  ;  while  in  the  female  the  longitudinal  duct  of  the  par- 
ovarium and  the  hydatids  of  Morgagni  are  rudimentary  structures  having  a  like  origin. 
?'urther,  the  ureter  and  its  pelvis,  together  probably  with  the  complicated  system  of 


Fig.  858. — Development  of  the  Bladder,  Ureter,  and  Kidney.     From  the  models  by  Professor  Keibel. 

A.  Caudal  portion  of  an  embryo  of  15  to  18  days  old.     The  cloaca  is  relatively  very  large,  and  is  not  yet  joiued 

by  the  Wolffian  ducts  ;  an  indication  is  present  of  the  separation  of  the  cloaca  into  dorsal  or  rectal,  and 
ventral  or  urinogeuital,  subdivisions. 

B.  The  cloaca  of  an  older  embryo — 25  to  27  days  old.     The  subdivision  of  the  cloaca  is  more  clearly  marked. 

The  Woltfian  duct  is  seen  joining  the  anterior  subdivision,  and  from  the  lower  part  of  the  duct  an  out- 
growth is  present,  which  gives  origin  to  the  ureter  and  the  kidney. 

C.  Still  older  stage  (36  to  37  days  old).      The  ureter  has  acquired  a  separate  opening  into  the  developing  bladder 

which  is  placed  upon  the  same  level  as  that  of  the  Wolffian  duct.     The  kidney  is  much  more  advanced, 
and  the  rectum  is  becoming  separated  from  the  urinogenital  canal. 

D.  Female  embryo  8i  to  9  weeks  old.     The  openings  of  the  ureter  and  genital  ducts  have  become  separated  by 

a  considerable  interval.     The  urinogenital  canal  and  i-ectum  have  acquired  separate  openings. 
1,  Spinal  cord  ;  2,  Notochord  ;  3,  Pubic  symphysis  ;   4,  Cloacal  membrane,  forndng  the  tioor  of  the  ectodermal 
cloacal  fossa  ;  [>,  Allantoic  canal  ;  6,  Rectum,  or  rectal  subdivision  of  cloaca  ;  7,  Urinogenital  subdivision 
of  cloaca  ;  8,  Bladder  ;  9,  Urinogenital  canal  ;  10,  Wolffian  duct ;  11,  Ureter  (or  ureter  and  developing 
kidney)  ;  12,  Miillerian  duct  ;  13,  Genital  eminence. 

kidney  tubules  which  open  into  it,  arise  in  both  sexes  as  an  outgrowth  from  the  Wolffian 
duct.  In  the  male  tlie  vesicula  seminalis  also  arises  as  a  diverticulum  of  the  Wolffian 
duct  (Fig.  860). 

The  primitive  secretory  organ,  the  mesonephros,  or  Wolffian  body  develops  in 
connexion  with  the  anterior  part  of  the  Wolffian  duct  (p.  32),  and  is,  during  the  early  life 
of  the  embryo,  a  most  important  structure.  With  the  development  of  the  permanent 
kidney  the  mesonephros  atrophies,  yet  some  of  its  tubules  persist  in  the  adult.  The 
vasa  efferentia,  the  ductuli  aberrantes,  and  the  rudimentary  paradidymis  (organ  of 
Giraldes)  in  the  male,  and  the  rudimentary  tubules  of  the  parovarium  (epoophoron)  and 
of  the  paroophoron  in  the  female,  are  structures  which  owe  their  origin  to  tubules  of  the 
mesonephros. 

Soon  after  the  formation  of  the  Wolffian  ducts  two  other  longitudinally-disposed  canals, 
called  the  Miillerian  ducts,  are  developed.  These  open  at  their  cephalic  ends  into  the 
body  cavity,  and  at  their  caudal  ends,  unlike  the  Wolffian  ducts,  they  unite  with  one 
another  in  the  middle  line.  From  them  are  formed,  in  the  female — the  Fallopian  tubes, 
the  uterus,  and  the  vagina ;  and  in  the  male — tlie  hydatids  of  the  testis  and  the 
utriculus  prostaticus. 

The  AVolffian  and   Miillerian   ducts   open   at   their   caudal   ends  into   the  ventral   or 


1200 


THE  UEINOGENITAL  SYSTEM. 


urinogenital  part  of  the  cloaca,  which  in  the  course  of  development  becomes  transformed 
into  the  bladder  and  the  urinogenital  canal  of  the  embryo  (Figs.  858  and  860).  The 
developing  ureter  at  first  arises  as  a  diverticulum  from  the  Wolffian  duct,  at  a  short 
distance  from  the  point  where  the  latter  joins  the  cloaca.  Soon,  however,  the  ureters 
acquire  independent  openings  into  the  cloaca,  which  become  gradually  shifted  further 
from  one  another  and  from  those  of  the  Wolffian  ducts.  The  ureters  are  now  found  to 
open  into  the  anterior  portion  of  the  cloaca  which  lies  nearer  to  the  head  of  the  embryo 
than  the  part  with  which  the  Wolffian  ducts  are  connected.  This  cephalic  portion  receiv- 
ing the  ureters  becomes,  in  the  male,  the  bladder  and  the  upper  part  of  the  prostatic 
urethra;  in  the  female,  the  bladder  and  the  entire  urethra  (Fig.  861).  The  caudal  part, 
lying  below  the  level  of  the  enti-ance  of  the  Wolffian  ducts,  is  the  urinogenital  canal,  and 
is  represented  in  the  adult  male  by  the  lower  part  of  the  prostatic  and  by  the  membranous 
portions  of  the  urethra ;  in  the  female  by  the  part  of  the  urinogenital  fissure  which 
immediately  surrounds  the  openings  of  the  urethra  and  vagina  (Fig.  861).  The  united 
Miillerian  ducts  open  into  the  lower  part  of  the  cloaca  or  lu'inogenital  canal,  between  the 
Wolffian  ducts  of  opposite  sides.  In  the  male  the  position  of  this  ojDcning,  which  is 
represented  in  the  adult  by  the  opening  of  the  uterus  masculinus,  remains  almost  un- 
changed ;  in  the  female,  on  the  other  hand,  the  urinogenital  canal  becomes  relatively 
shorter  during  development,  and  thus  the  opening,  which  in  this  sex  is  represented  by 
the  orifice  of  the  vagina,  comes  to  the  surface  at  the  bottom  of  the  urinogenital  fissure 
(Fig.  861).  The  cavity  of  the  developing  bladder  is  directly  continuous  above  with  that 
of  the  allantois,  and  by  some  authorities  the  bladder  is  described  as  arising  as  a  dilatation 
of  the  proximal  part  of  the  allantois. 

When  the  ectodermal  cloacal  fossa  is  formed,  after  the  complete  separation  of  the 
cloaca  into  anterior  or  urinogenital,  and  posterior  or  rectal  parts,  it  communicates  at  first 
with  the  rectum  behind  and  later  on  with  the  urinogenital  canal  in  front  (p.  45).  The 
fossa  is  bounded  laterally  by  well-marked  skin  folds,  the  labio-scrotal  folds,  and  at  its 
anterior  end  is  situated  the  genital  eminence.  This  eminence  becomes  the  main 
portion  of  the  penis  or  of  the  clitoris,  and  its  posterior  surface  is  grooved  longitudinally 
in  such  a  manner  that  the  proximal  end  of  the  groove  lies  near  the  opening  of  the  virino- 
genital  canal  into  the  cloacal  fossa. 

In  the  male  the  lips  of  this  groove  on  the  genital  eminence,  meeting  together,  form  a 
canal  which,  in  the  adult,  traverses  the  penis  as  the  terminal  part  of  the  urethra.  The 
latei-al  margins  of  the  cloacal  fossa,  behind  the  genital  eminence,  meet  togethei',  and  fusing 
in  the  middle  line,  convert  the  fossa  into  a  canal,  which  completes  the  spongy  portion  of 
the  adult  urethra.  In  this  way  all  the  cloacal  fossa  lying  in  front  of  the  rectum,  and  the 
groove  on  the  genital  eminence,  become  closed  over  to  form  the  third  part  of  the  urethra. 
The  spongy  part  of  the  urethra  is  thus  derived  from  the  ectodermal  cloacal  fossa  and  the 
groove  on  the  genital  eminence,  while  the  prostatic  and  membranous  parts  owe  their 
origin  to  the  endodermal  cloaca. 

In  the  female  the  margins  of  the  ectodermal  cloacal  fossa  remain  separate  throughout 
life,  and  the  fossa  persists  as  the  urinogenital  cleft.  The  groove  on  the  genital  eminence 
closes  over,  but  does  not  form  a  canal  as  in  the  male.  The  urinogenital  canal,  at 
first  like  that  of  the  male,  becomes  relatively  shorter  and  shorter  during  develop- 
ment, and,  as  a  result,  the  lower  end  of  the  fused  portions  of  the  Miillerian  ducts,  which 

opens  into  the  canal,  and  from 
whicl)  the  vagina  is  formed, 
appears  in  the  adult  to  open 
directly  into  the  fossa  (urino- 
genital space)  behind  the 
Bo.iy  cavity  channel  leading  from  the 
bladder.  From  the  latter 
channel  is  formed  the  female 
urethra  (Fig.  861). 

Wolffian  Duct  and 
Embryonic  Secretory 
Organ. — The  Wolffian  duct 
arises  in  the  mesoblast,  about 
the  fifteenth  day,  as  a  solid 
cord  of  cells  occupying  a 
position  immediately  to  the 
outer  side  of  the  mesoblastic 
When  first  recognised  the  duct  lies 


Xotofhor'i 


Neural  tube 

Somite 


Wolffian  duct 
and  niesonepliros 


Intermediate  cell  mass 


Mesonephros  and 
Wolffian  duct 


— Transverse  Section  through  the  Body  of  a 
Fowl  Embryo. 


somites  and  to  the  inner  side  of  the  body  cavity 


DEVELOPMENT  OF  THE  UEINOGENITAL  OEGANS. 


1201 


immediateh'  beneath  the  epiblast,  and  as  it  grows  backwards  to  reach  the  cloaca  it  is 
often  found  to  be  intimately  connected  with  the  epiblast.  This  close  connexion  of  the 
duct  with  the  epiblast,  in  the  early  stages,  is  by  some  authorities  supposed  to  indicate 
a  primitive  epiblastic  origin  of  the  canal,  but  by  others,  and  apparently  with  more 
reason,  to  be  a  trace  of  the  opening  of  ducts  on  the 
surface  of  the  body,  such  as  exists  in  connexion  with 
the  excretory  organs  of  lower  animals.  During  the 
third  week  the  cellular  cord  Avhich  represents  the 
Wolffian  duct  acquires  a  lumen,  and  about  the  end 
of  the  same  week  the  duct  in  its  growth  reaches  the 
cloaca.  As  soon  as  the  cloaca  has  become  divided  into 
dorsal  and  ventral  subdivisions,  the  Woltfian  duct  is 
seen  to  end  in  the  caudal  part  of  the  ventral  sub- 
division, which  becomes  the  urinogenital  canal  (Fig.  860). 

The  Wolffian  body  or  mesonephros  is  developed  in 
the  mesoblast  of  the  "intermediate  cell  mass,"  immedi- 
ately adjoining  the  Woltfian  duct,  and  consists  of  a 
number  of  transversely-arranged  canals  or  tubviles,  each 
of  which  opens  by  one  end  into  the  Woltfian  duct, 
while  its  other  extremity  ends  blindly.  These  trans- 
verse tubules,  like  the  canal  into  which  they  open,  are 
at  fii'st  solid  cellular  sti'uctures,  and  only  later  acquire 
a  distinct  lumen.  Increasing  rapidly  in  size  and 
number,  the  tubules  become  twisted  and  tortuous,  and 
the  blind  end  of  each  dilates  to  form  a  capsule  in- 
vaginated  upon  itself  and  containing  a  bunch  of  capil- 
lary blood-vessels  similar  to  the  glomeruli  of  the  adult 
kidney.  It  would  appear  that  primitively  one  tubule 
is  developed  in  the  portion  of  the  intermediate  cell 
mass  (nephrotome)  corresponding  to  each  mesoblastic 
somite,  but,  in  higher  vertebrates  at  all  events,  such  a 
con-espondence  between  the  number  of  somites  and 
the  number  of  tubules  cannot  be  deiiionstrated.  In 
the  posterior  part  of  the  Wolffian  body  the  number  of 
tubules  is  very  numerous,  and  probably  far  greater 
than  the  number  of  segments  in  this  region.  The 
tubules  when  formed  appear  to  increase  by  a  kind  of 
budding.  The  tubules  in  the  anterior  part  atrophy 
and  disappear  at  a  very  early  time,  even  while  others 
are  being  formed  towards  the  hind  end  of  the  embryo. 
When  at  its  greatest  development  (fifth  to  eighth  week)  Fig.  860. — Diagram  to  illustrate  the 
the  mesonephros  forms  a  relatively  large  glandular  Manner  in  which  the  Ureter,  the 
mass,  composed  of  tubules  resembling  in  a  general 
way  those  of  the  adult  kidney,  which  projects  into 
the  dorsal  part  of  the  body  cavity,  and  extends  from 
the  region  of  the  liver  to  the  caudal  end  of  the  body 
cavity.     Along  its  outer  side  lies  the  Wolffian  duct. 

In    anamniate    vei'tebrates,   fishes,    and    amphibia,  The  manner  in  whicli  the  rectum  and 

the  mesonephros  pei'sists  as  the  secretory  organ  of  bladder  become  separated  and  acquire 
the  adult  "  openings    into    the    ectodernial    cloacal 

fossa  is  shown  in   II.  and   III.  (A.  H. 
Pronephros. — From  what  is  know^^  regarding  the  de-       Young  and  A.  Robinson). 
veloiime](jt  of  lower   animals,  it  seems   certain   that   the   i^      AUantois.  R.     Rectum. 

Woltfian  duct  originallv  served  as  the  duct  of  a  still  earlier  B.     Biadrier.  UR.  Urinogenital  duct, 

secretory  organ  called  the  Pronephros.     The  pronephros  is  g-^^^  ^^^^^  „f         V'b.  Vaf  deferens. 
lormed  nearer  to  the  head  end  ot  the  embryo  than  the  later  cloacal  fossa.      VS.    Seminal  vesicle, 

appearing  mesonephros,  and  its  tubules,  "which  in  many  K.     Pelvis  of  Kidney.  WD.  Wolffian  duct, 
ways  resemble  those  of  the  mesonephros,  differ  from  them 

in  that  they  open  directly  into  the  body  cavity,  and  in  being  derived  from  the  lining  mesoblast 
of  the  body  cavity.  It  is  i^ossible  that  some  of  the  tubules  whicli  in  man  lie  far  forwards  at  the 
anterior  end  of  the  mesonephros,  and  which  do  not  appear  to  be  functional  even  during  embryonic 
life,  may  represent  the  prone2:)hros  of  lower  vertebrates.  Tubules  occur  in  all  segments  from 
the  sixth  cervical  to  the  last  lumbar. 

As  the  permanent  kidney  is  developed   the  mesonephros  atrophies  ;  a  portion  of  it, 
however,  is  retained  in  the  male,  and  forms  the  excretory  apparatus  of  the  testis.      The 
81 


Vas    Deferens,    and    the    Bladder 
ARISE  in  the  Embryo. 

The  structures  developed  from  the  cloaca 
ai-e  indicated  in  blue,  those  from  the 
Wolffian  duct  in  red,  and  the  ectoderm 
in  black. 


1202 


THE  UEINOGENITAL  SYSTEM. 


•lUr-etcr 


Wolrtiau  duct  becomes  the  canal  of  the  epididymis  and  the  vas  deferens  of  the  adult  (see 
p.  1204).     In  the  female,  when  the  permanent  kidney  is  formed,  the  mesonephros  and  its 

duct  undergo  atrophy  to  a  greater  extent  than 
in  the  male,  and  they  are  only  represented 
in  the  adult  by  the  rudimentary  structures 
present  in  the  broad  ligament  of  the  uterus 
(see  p.  1205). 

Ureter  and  Permanent  Kidney. — 
The  kidney  and  ureter  arise  as  a  tubular 
diverticulum  from  the  Wolffian  duct  close  to 
the  point  where  the  latter  joins  the  cloaca. 
Tills  diverticulum  is  seen  first  during  the  fourth 
week,  and  grows  from  behind  forwards,  dorsal 
to  the  body  cavity.  Even  ni  its  very  early 
condition  the  portion  of  the  outgrowth  which 
lies  nearest  to  the  Wolffian  duct,  and  from 
which  the  adult  ureter  is  developed,  is  more 
slender  than  the  distal  part,  which  becomes 
branched,  and  grows  out  to  form  the  pelvis 
and  calyces  of  the  tireter.  The  uriniferous 
tubules  of  the  kidney  appear  to  arise  as  branch- 
ing tubular  outgrowths  from  the  calyces.  The 
blind  distal  end  of  each  tubule  soon  dilates 
to  form  a  capsule  which,  becoming  invaginated 
on  itself,  encloses  a  tuft  of  capillary  blood- 
vessels. The  Malpighian  corpuscles  arising  in 
this  manner  are  found  in  the  human  kidney 
as  early  as  the  eighth  week. 

Accoi'ding  to  many  embryologists  it  is  only 
the  collecting  tubules  that  are  formed  in  this 
manner,  and  the  other  tubules  of  the  kidney 
have  a  mesoblastic  origin  similar  to  that  of 
the  tubules  of  the  mesonephros  and  inde- 
pendent of  the  outgrowth  Avhich  gives  origin 
to  the  ureter  and  its  pelvis.  These  authorities 
state  that  the  kidney  tubules  arising  in  the 
mesoblast,  only  later  acquire  connexions  with 
the  outgrowths  from  the  ureter. 

It  is  possible  that  the  tubules  which  give 
rise  to  the  permanent  kidney  really  lie  in  series 
with  those  which  form  the  mesonephros,  and 
hence  begin  where  the  latter  cease  to  be  formed, 
namely  at  the  first  sacral  segment. 

As  the  ureter  increases  in  length,   it  be- 
comes separated  from  the  Wolflian  duct,  and 
acquires  a  distinct  opening  into  the  anterior 
part  of    the    cloaca    nearer    the  head   of    the 
In  each  case  the  hypoblast  is  indicated  Ly  a  thick  embryo  than  that  of  the  Wolffian  duct.      This 
black  line,  while  the  einblast  is  sliowni  by  a  double  part  of    the   cloaca  receiving    the   ureters  bc- 
line  with  cross  shading.  comes  the  bladder.     The  kidney  is  at  first  a 

A.  Rejiresents  a  stage  passed  tlirougli  by  both  sexes,  distinctly  lobulated  body,  and  shows  at  birth, 
and  illustrates  the  connexions  of  the  uiinogenital  .^,^^  sometimes  even  in  the  adult,  traces  of 
duets  and  of  the  rectum  with  the  ectodermal  cloacal    .  ...        ,    ,.    .   .        .  i    i     i 

fossa;  (/(^,  indicates  the  position  where  the  Wolffian  ^^s  original  subdivision  mto  lobule 


Fig.  861. — Diagrammatic  Representation  and 
Comparison  of  the  Manner  in  which  the  Urino- 
GENiTAL  Passages  arise  in  the  two  Sexes. 


and  Miillerian  ducts  open  into  theurinogenital  canal ; 
ge,  genital  eminence  ;  'U(js,  urinogenital  canal. 


Bladder. — The  bladder  is  formed  from 


B 


Male  condition.  The  greater  portion  of  the  urethral  canal  is  ectodermal  in  origin,  and  is  derived  from 
the  ectodermal  cloacal  fossa  an<l  the  groove  on  the  genital  eminence  Ijy  the  meeting  of  their  lateral 
boundaries.  (The  portion  of  tlie  canal  wliich  is  usually  tlie  last  to  be  closed  in  is  indicated  at  x.)  The 
upper  ]iart  of  the  urethra  is  endoderiual  in  origin.  The  jiosition  where  the  genital  ducts  (in  the  male 
represented  by  the  vasa  deferentia  and  uterus  masculinus)  join  the  urinogenital  canal  is  indicated  at  vcl  ; 
s,  symphysis  jmbis. 
C.  Female  condition.  Owing  to  the  shortening  of  the  urinogenital  canal  {v/js,  in  A)  and  tlie  rapid  growth  of 
the  vagina  the  urethral  and  genital  openings  come  to  lie  in  tlie  bottom  of  the  urinogenital  fissure.  The 
deepest  jiart  of  this  fissure,  immediately  surrounding  the  <')]ieniiigs,  is  formed  by  endoderm  lerived  from 
the  urinogenital  canal. 


DEVELOPMENT  OF  THE  UKINOGENITAL  OKGANS. 


1203 


the  upper  part  of  the  anterior  subdivision  of  the  cloaca  (Figs.  SfiS  and  860),  which  hi- 
creases  in  width  as  the  openings  of  the  ureters  become  shifted  further  from  one  anotlier. 
Inferiorly  the  anterior  part  of  the  cloaca  remains  narrow,  and  forms  the  urinogenital 
canal.  At  a  very  early  stage  the  triangular  surface,  known  in  the  adult  as  the  trigonum 
vesicae,  is  to  be  recognised.  From  the  cephalic  end  of  the  developing  bladder  the 
allantoic  canal  extends  to  the  umbilicus ;  but  the  allantois  loses  its  lumen  in  the  fifth 
week,  and  the  portion  enclosed  within  the  body  of  the  embryo,  known  as  the  urachus, 
becomes  converted  into  the  fibrous  cord  found  in  the  adult  connected  with  the  bladder  apex. 

The  cavity  of  the  allantois  is  sometimes  not  lost  so  early,  and  in  rare  cases  it  has  been 
found  persisting  in  the  child  or  adult  as  a  pervious  channel  extending  from  the  apex  of 
the  bladder  to  the  umbilicus.     Here  it  may  open  on  the  surface  of  the  body. 

By  some  authorities  the  bladder  is  stated  to  arise  as  a  dilatation  of  the  proximal  part  of 
the  allantois  rather  than  from  the  cloaca  itself.  The  distinction,  however,  does  not  seem 
to  be  important,  and  probably  both  the  cloaca  and  the  allantois  share  in  its  formation. 

Male  Urethra. — The  urethra  in  the  male  is  composed  of  two  parts  which  are 
developmentally  distinct.  One  of  these  corresponds  to  the  prostatic  and  membranous 
portions  of  the  adult,  and  owes  its  origin  to  the  endodermal  cloaca,  while  the  other  part 
corresponds  to  the  spongy  portion  of  the  adult,  and  arises  in  connexion  with  the  ectodermal 
cloacal  fossa  and  genital  eminence  (Fig.  861).  The  upper  part  of  the  prostatic  urethra 
has  an  origin  similar  to  that  of  the  bladder,  and  is  derived  from  the  upper  portion  of  the 
urinogenital  subdivision  of  the  cloaca ;  the  lower  prostatic  and  the  membranous  parts  are 
formed  from  the  urinogenital  canal  of  the  embryo.  The  spongy  portion  of  the  adult 
urethra  is  developed  superficial  to  the  cloacal  membrane  which  separates  the  ectodermal 
cloacal  fossa  from  the  endodermal  cloaca.  This  ectodermal  part  of  the  urethral  canal  is 
formed  by  the  meeting  of  the  lateral  boundaries  of  the  anterior  part  of  the  cloacal  fossa, 
where  they  lie  in  front  of  the  anal  opening,  and  also  by  the  closing  of  the  lips  of  a  groove 
which  appears  on  the  genital  eminence.  In  the  early  stages  the  position  of  the  greater 
part  of  the  future  urethra  is  indicated  by  a  solid  cord -like  mass  of  epithelial  cells,  which 
forms  the  so-called  "  urethral  septum."  This  becomes  broken  down  later  on  to  form  the 
groove  or  gutter  which  is  converted  into  the  urethral  canal  (see  p.  1206).  The  median 
raphe,  extending  from  the  anus  forwards  along  the  urethral  surface  of  the  penis  in  the 
adult,  indicates  the  line  of  fusion  along  which  the  spongy  part  of  the  urethra  has  been 
closed  in  and  converted  into  a  canal.  The  last  portion  of  the  groove  to  be  closed  over 
is  the  extreme  anterior  part  which  lies  behind  the  base  of  the  glans  penis.  In  some  rare 
cases  failure  of  the  margins  of  the  groove  to  unite  in  this  situation  causes  the  urethra  to 
appear  to  terminate  at  this  point.  In  other  cases  a  greater  arrest  of  development  leaves 
the  cloacal  fossa  open,  and  we  have  a  condition  retained  which  resembles  to  a  certain 
extent  the  normal  arrangement  of  the  parts  in  the  female.  To  such  abnormalities  of  the 
xirethra  the  term  hypospadias  is  applied. 

Female  Urethra. — In  the  female  the  urethra  is  developed  from  the  part  of  the 
anterior  portion  of  the  cloaca 
which  lies  below  the  de- 
veloping bladder,  and  above 
the  openings  of  the  Mlillerian 
and  Wolffian  ducts.  The 
part  below  these  openings, 
the  urinogenital  canal,  dur- 
ing the  course  of  develop- 
ment becomes  relatively 
shorter  and  shorter,  and 
finally  forms  the  epithelium 
at  the  bottom  of  the  urino- 
genital cleft  immediately 
surrounding  the  urethral  and 
vaginal  openings  of  the  adult. 
Thus  in  the  adult  the  ui-ethra, 
which  originally  led  into  the 
urinogenital  canal,  opens  into 
the  urinogenital  fissure. 

In  some  mammals,  such 
as  the  hedgehog,  the  shorten-  ,     ,     .        ,       ,  ^        j 

ing  of  the  urinogenital  canal  does  not  take  place  in  the  female  durmg  development,  and 
in  these  animals  a  single  aperture  exists  for  the  urinary  and  genital   systems. 
81a 


Neural  tube. -yi 


Mesentery 


Blood-vessel 


Fk;.  862 


Transverse  Section  thhoucih  the  Body  uf  a  Rat  Embryo. 
The  position  where  the  germinal  epithelium  arises  is  indicated  at  a. 


The 


1204  THE  UEINOGENITAL  SYSTEM. 

hynieu  is  placed  where  the  fused  Miillerian  ducts  (vagina)  open  into  the  uvinogenital 
canal. 

Sexual  Glands. — In  the  development  of  the  sexual  glands,  male  and  female,  a 
differentiated  thickened  portion  of  the  peritoneal  epithelium  is  first  recognised.  This 
specialised  epithelium,  which  has  received  the  name  of  germinal  epithelium,  is  situated  to 
the  inner  side  of  the  mesonephros  and  of  the  Wolffian  and  Miillerian  ducts.  Here  it 
covers  a  longitudinally-disposed  ridge  or  elevation  called  the  genital  ridge.  The  germinal 
epithelium  is  not  strictly  limited  to  this  ridge,  but  extends  to  some  extent  beyond  its 
limits.  The  genital  ridge  is  soon  found  to  have  numerous  epithelial  cells  embedded  in 
its  conuective-tissue  stroma  which  appear  to  originate,  in  both  sexes,  by  a  proliferation 
from  the  deep  surface  of  the  germinal  epithelium  covering  the  ridge.  From  these 
epithelial  cells  the  seminiferous  tubules  of  the  male,  and  Graafian  follicles  with  their  con- 
tained ova  of  the  female  are  developed. 

In  the  male,  as  early  as  the  thirty-third  day,  the  epithelial  cells  embedded  in  the 
stroma  of  the  developing  testis  have  become  ai-ranged  into  a  network  of  anastomosing 
cords  within  which  certain  larger  cells  are  seen  to  be  irregularly  scattered.  These  larger 
cells  have  received  the  name  of  primitive  sperm  cells,  and  are  relatively  few  in  number. 
They  undergo  frequent  division,  and  in  the  later  stages  are  not  to  be  distinguished' 
from  the  other  cells  of  the  cords.  The  cellular  cords  undergo  direct  transformation  into 
the  seminiferous  tubules  of  the  testis,  but  the  excretory  apparatus,  including  the  rete  testis 
and  tubuli  recti,  is  derived  by  outgrowths  from  the  anterior  tubiiles  of  the  mesonephros. 
At  a  very  early  stage  the  superficial  part  of  the  stroma  of  the  developing  testis,  becomes 
denser,  and  gives  origin  to  the  tunica  albuginea. 

It  has  been  stated  that  the  sexual  epithelium  of  the  testis,  unlike  that  of  the  ovaiy, 
is  not  derived  from  the  germinal  epithelium,  but  that  it  has  its  origin  in  an  outgrowth  of 
the  mesonephros.  The  course  of  the  development  of  the  sexual  glands  is  without  doubt 
extremely  difficult  to  follow. 

In  the  female  large  epithelial  cells  are  found  in  the  stroma  of  the  developing  ovary, 
beneath  the  germinal  epithelium,  as  early  as  the  thirty-third  day.  These  primitive  ova 
are  much  more  numerous  than  the  primitive  sperm  cells  of  the  male,  and  form  a  very 
characteristic  feature  of  the  developing  ovary.  At  first  they  lie  isolated,  but  later — about 
the  fifth  week — they  become  surrounded  by  other  smaller  cells  having  a  like  origin  from 
the  germinal  epithelium.  Each  primitive  ovum  surrounded  by  its  cells  becomes  a 
primitive  follicle,  the  further  development  of  which  has  already  been  described  (p.  1184). 
The  pi'oliferation  of  cells  from  the  germinal  epithelium  goes  on  until  the  seventh  month, 
and  during  the  later  stages  the  epithelium  has  the  appearance  of  growing  down  into  the 
stroma  in  the  form  of  long  branching  cellular  processes  w^hich  break  up  into  little  nests  of 
cells  to  form  the  future  follicles  (p.  851).  It  is  extremely  doubtful  if  any  new  ova  arise 
after  birth. 

Generative  Ducts. — As  has  been  already  stated,  the  male  ducts  arise  from  the 
Wolffian,  and  the  female  from  the  Miillerian  ducts  of  the  embryo.  Both  sexes  at  first 
possess  well-developed  Wolffian  and  Miillerian  ducts,  which  are  arranged  in  a  very  definite 
manner.  The  Wolffian  ducts  communicating  directly  with  the  tubules  of  the  mesonephros 
lie  at  first  parallel  to,  and  at  a  considerable  distance  from  one  another.  As  they  pass 
backwards  towai'ds  the  caudal  end  of  the  embryo  they  approach  one  another,  and  each 
becomes  enclosed  in  a  fold  of  peritoneum  called  the  plica  urogenitalis.  More  caudally 
the  ducts  become  closely  approximated  to  each  other,  are  embedded  in  a  cord-like  mass  of 
connective  tissue,  to  which  the  term  genital  cord  is  applied.  They  finally  open  into  the 
lower  part  of  the  anterior  subdivision  of  the  cloaca. 

The  Miillerian  ducts,  opening  freely  into  the  body  cavity  at  their  cephalic  ends,  lie  to 
the  outer  side  of  the  Wolffian  ducts.  As  they  are  traced  caudally  they  cross  the  Wolffian 
ducts  and  enter  the  genital  cord,  within  which  they  unite  and  form  a  canal,  which  occupies 
the  mesial  plane,  and  opens  into  the  lower  part  of  the  anterior  subdivision  of  the  cloaca, 
between  the  Wolffian  ducts.  The  manner  in  which  the  ureters  become  separated  from 
the  Wolffian  ducts  has  already  been  described. 

Ducts  in  the  Male.— The  seminiferous  tubules  of  the  testis  become  comiected  with 
the  Wolffian  duct  through  a  fusion  with  the  anterior  canals  of  the  mesonephros. 
At  the  place  where  this  fusion  occurs  the  rete  testis  and  the  tubuli  recti  are  formed. 
The  connexion  is  definitely  established  in  the  third  month.  The  number  of  tubules 
taking  part  varies  considerably,  but  corresponds  to  the  number  of  vasa  efferentia  found 
in  the  adult.  The  connecting  tubules  becoming  much  convoluted,  just  as  they  join 
the  Wolffian  duct,  form  the  coni  vasculosi.  The  canal  of  the  epididymis  is  directly 
formed  from  the  anterior  part  of  the  Wolffian  duct,  and  the  vas  deferens  from  the  more 


DEVELOPMENT  OF  THE  UEINOGENITAL  OEGANS. 


1205 


postei-ior  portion.  The  ductuli  aberrantes  and  the  rudimentary  tubules  of  the  organ  of 
Griraldes  are  to  be  looked  upon  as  persistent  tubules,  of  a  more  posterior  portion  of  the 
Wolffian  body,  which  have  failed  to  become  connected  with  the  tubules  of  the  testis. 
The  seminal  vesicles  are  developed  in  the  third  month  as  evaginations  which  arise  from 


C 


D 


Fig.   863. 


\ 


-Development  of  the  External  Genital  Organs. 
From  the  figures  of  Professor  Herzog. 

A.  Embryo  of  20  mm.  long.     So-called  indiiferent  stage. 
Conical    genital    eminence    with    shallow  furrow    on    its    under  aspect, 

and  well-rnarked  labio- scrotal  fold  on  each  side.  The  uriuogenital 
canal  does  not  yet  open  on  the  surface,  but  the  opening  of  the  rectum 
is  seen  in  a  transverse  furrow  behind  the  genital  eminence. 

B.  Embryo  28  mm.  long.     Male. 
The   uriuogenital  canal  opens  into  and  is  continuous  with  a  gutter-iike 

groove  (formed  Ijy  a  cleft  in  the  urethral  septum)'on  the  posterior  two- 
thirds  of  genital  eminence.  The  opening  of  rectum  lies  behind  the 
opening  of  the  uriuogenital  canal  into  the  ectodermal  cloaca. 

C.  Embryo  31  mm.  long.      Female. 
The  \xrinogenital   canal    oj^ens    into    the   extodermal   cloaca  ;    a  groove 

is  continued  on  to  under  aspect  of  the  clitoris. 

D.  Embryo  45  mm.  long.     Male. 

Formation  of  scrotum.  The  labio-scrotal  folds,  formerly  best  marked  at  sides  of  genital  eminence,  have 
grown  backwards  and  united  behind  to  form  the  raphe  scroti.  The  scrotum  embraces  the  base  of  the 
genital  eminence  or  penis.  The  glans  is  very  prominent,  and  the  cleft  to  form  the  iirethra  does  not  yet 
reach  as  far  as  the  base  of  the  glans. 

E.  Embryo  60  mm.  long.     Male. 

Behind  the  glans  penis  the  urethra  opens  in  a  diamond-shaped  fossa  in  the  posterior  wall  of  which  the 
median  raphe  ends.  The  prepuce  is  formed  behind  the  constriction  which  marks  off  the  glands,  and  as 
it  grows  forwards  the  constriction  disappears. 

In  each  case  a  little  horn-like  process  of  epithelium  is  present  on  the  summit  of  the  genital  eminence. 


E 


the  Wolffian  ducts,  near  their  caudal  extremities.  Each  at  first  has  the  appearance  of  a 
longitudinal  groove  in  the  wall  of  the  vas  deferens,  which  closes  over  and  becomes  cut  off 
from  the  main  tube  except  at  the  point  where  later  on  the  duct  of  the  seminal  vesicle 
joins  the  vas  deferens.  From  the  part  of  the  cloaca  into  which  the  Wolffian  ducts  open 
the  prostatic  urethra  of  the  adult  is  derived.  The  Miillerian  ducts  atrophy  in  the  male 
embryo,  but  the  hydatids  of  the  testis  are  rudimentary  remains  of  their  anterior  portions, 
while  the  sinus  pocularis  represents  the  lower  fused  portions  which,  in  the  embryo,  occupy 
the  genital  cord. 

Ducts  in  the  Female. — The  Miillerian  ducts  in  the  female  retain  their  openings  into 
the  body  cavity,  and  their  anterior  portions  become  the  Fallopian  tubes.  Their  fused 
posterior  parts,  which  at  first  join  the  uriuogenital  canal,  give  rise  to  the  uterus  and 
vagina.  The  manner  in  which  the  original  position  of  the  opening  of  the  Miillerian  ducts 
becomes  shifted,  by  the  shortening  of  the  uriuogenital  canal,  so  as  to  appear  at  the  bottom 
of  the  uriuogenital  fissure,  has  already  been  described. 

The  vaginal  portion  of  the  fused  Miilleiian  ducts  is  at  first  relatively  very  short,  and 
at  the  point  where  it  opens  into  the  uriuogenital  canal  a  slight  fold  appears,  which  is  the 
future  hymen.  The  vagina  increases  rapidly  in  length  as  its  opening  moves  downwards 
towards  the  uriuogenital  cleft.  In  the  human  embryo  during  the  third  month  the 
closely-applied  Miillerian  ducts,  which  higher  up  have  fused  to  form  the  uterus,  are  repre- 
sented at  their  lower  ends  by  a  pair  of  rapidly-elongating  solid  cellular  cords,  which  at 
a  later  stage  break  down  to  form  the  vagina. 

The  Wolfliian  ducts  and  the  mesonephros  atrophy  in  the  female,  but  traces  of  them  are 
to  be  found  in  the  parovarium  and  paroophoron  of  the  adult.  In  the  foetus  the  Wolffian 
duct  can  be  traced  along  each  side  of  the  uterus  as  far  as  the  upper  end  of  the  vagina. 

Prostate. — The  glandular  portion  of  the  prostate  arises  as  a  series  of  solid  outgrowths 
from  the  epithelium  of  the  uriuogenital  canal  during  the  third  month.     The  outgrowths 
81h 


1206 


THE  UEINOGENITAL  SYSTEM. 


which  are  at  first  simple,  become  branched  and  finally  acquire  a  lumen.  They  are 
arranged  in  tlu'ee  gi'oups — an  upper  and  a  lower  dorsal,  and  a  ventral  group.  The  glands 
of  the  ventral  group  soon  become  reduced  in  number  and  often  completely  disappear ; 
those  of  the  ujjper  dorsal  group  form  the  chief  part  of  the  gland. 

Cowper's  glands  arise  in  the  third  month,  and  appear  to  be  developed  from  the 
epithelium  of  the  urinogenital  canal.  Since  in  the  Echidna  these  glands  have  been  shown 
to  have  an  ectodermal  origin,  and  as  in  man  their  ducts  are  connected  with  a  part  of  the 
urethra  which  is  ectodermal  in  its  origin,  it  is  possible  that  further  investigation  will 
show  that  Cowper's  glands  arise  superficial  to  the  cloacal  membrane  and  form  the  ectodei'm 
in  the  human  embryo. 

The  glands  of  Bartholin  arise  as  epithelial  outgrowths  in  the  same  manner  as 
Cowper's  glands. 

External  Genital  Organs. — The  external  genital  organs  are  developed  in  the 
region  of  the  ectodermal  cloacal  fossa,  and  those  of  the  male  and  female  cannot  be 
distinguished  from  one  another  in  the  earlier  stages.  The  ectodermal  cloacal  fossa,  at 
first  very  narrow,  is  completely  filled  by  a  wedge-shaped  mass  of  ectodermal  cells.  At  its 
anterior  end  lies  the  genital  eminence,  a  somewhat  conical  projection  which  represents  the 
future  penis  or  clitoris.  The  genital  eminence  appears  very  early,  even  before  the 
endodermal  cloaca  has  become  divided  into  urinog-enital  and  rectal  subdivision.     On  each 


A  B 

Fig.    864. — External  Genital  Or(;ans  in  Male  Fcetus.     From  tigures  of  Professor  Herzog. 

The  prepuce  has  grown  forwards  so  as  to  cover  glans  completely.  The  urethra  has  l3een  contiuued  forwards 
to  the  apex  of  the  glans.  As  in  the  body  of  the  penis  the  portion  of  the  urethra,  which  traverses  the 
glans,  is  at  first  represented  Ijy  a  cleft  in  the  "  urethral  septum." 


side  of  it  is  a  prominent  fold-like  projection — labio-scrotal  fold — which  is  continued 
backwards  to  bound  the  ectodermal  cloacal  fossa  laterally  (see  Fig.  863).  An  opening  of 
the  rectum  on  the  surface  of  the  body  is  established  at  an  earlier  date  than  that  at  which 
the  communication  between  the  urinogenital  canal  and  the  ectodermal  fossa  is  formed.  As- 
the  later  opening  becomes  established,  the  wedge-shaped  mass  of  ectoderm,  which  fills  all 
the  anterior  part  of  the  fossa,  and  is  continued  as  a  kind  of  septum  into  the  substance  of 
the  genital  eminence,  becomes  converted  into  a  groove  or  gutter.  At  a  later  time  the 
margins  of  this  groove,  meeting  in  the  middle  line,  give  rise  to  a  canal  which  is  the  repre- 
sentative of  the  spongy  portion  of  the  urethra.  The  mass  of  ectoderm  which  becomes  cleft 
to  form  the  groove,  and  later  on  forms  the  lining  of  the  spongy  portion  of  the  urethra, 
has  been  termed  the  urethral  septum.  The  septum  is  cleft  from  behind  forwards,  and  the 
groove  which  results  is  closed  in  gradually  from  behind  forwards  to  form  the  urethra.  The 
part  of  the  septum  which  extends  forwards  into  the  glans  penis  remains  solid,  after  the  rest 
of  the  canal  has  been  formed,  hence  the  urethra  for  some  time  appears  to  end  in  a  little 
diamond-shaped  fossa  situated  at  the  base  of  the  glans  which  at  the  time  forms  a  prominent 
knob-like  projection  on  the  apex  of  the  genital  eminence  (Fig.  863,  E).  At  a  later  time  the 
septum  within  the  glans  is  cleft  and  converted  into  a  canal,  and  the  urethra  is  then  con- 
tinued to  the  end  of  the  penis.  The  glans  is  at  first  uncovered  and  marked  off  from  the 
rest  of  the  penis  by  a  circular  constriction  behind  which  the  prepuce  takes  origin.  As  the 
prepuce  grows  forwards  the  groove  disappears  and  the  glans  becomes  covered.     While  the 


THE  MAMMARY  GLANDS. 


1207 


spongy  portion  of  the  urethra  is  being  formed,  the  labio-scrotal  folds  grow  backwards  and 
meet  together  in  the  middle  line  behind  the  penis  and  in  front  of  the  anus.  From  them  is 
formed  the  scrotum  of  the  adult,  and  the  line  along  which  they  meet  is  the  raphe  scroti. 

In  the  female  the  labio-scrotal  folds  do  not  fuse  together,  but  become  tlie  labia  majora, 
and  the  interval  between  them  the  urinogenital  cleft  of  the  adult.  A  groove  arises  on 
the  genital  eminence,  but  it  closes  in  again  without  forming  a  canal,  and  hence  when  the 
urinogenital  canal,  which  forms  the  urethra,  opens  into  the  ectodermal  fossa  it  is  not  con- 
tinued into  the  clitoris. 


THE  MAMMARY  GLANDS. 

The  mammary  glands  (maminse)  or  breasts  are  accessory  organs  connected  with 
the  female  reproductive  system.  Each  gland  is  situated  in  the  superficial  fascia 
covering  the  anterior  aspect  of  the  thorax,  and  usually  extends  from  the  level  of  the 
second  or  third  to  that  of  the  sixth  rib.  The  hemispherical  projection  formed  by 
the  gland  lies  upon  the  superficial  aspect  of  the  pectoralis  major  and  to  a  less  extent 
upon  the  serratus  magnus  muscle.  Near  the  summit  of  each  mammary  elevation, 
and  usually  at  the  level  of  the  fourth  or  fifth  rib,  is  placed  the  wart-like  nipple 
(papilla  mammse),  which  is  pierced  by  the  minute  openings  of  the  lactiferous  ducts 
and  is  surrounded  by  a  coloured  circular  area  of  skin  called  the  areola.  The  skin 
covering  the  nipple  is  thrown  into  numerous  wrinkles,  and  on  the  areola  exhibits 
many  minute  rounded  projections  due  to  the  presence  of  underlying  cutaneous 
glands.  These  have  received  the  name  of  Montgomery's  glands  or  glandulae  areolares, 
and  are  considered  to  represent  rudimentary  portions  of  the  mammary  gland.  The 
colour  of  the  nipple  and  areola  varies  with  the  complexion  of  the  individual,  but 
in  young  subjects  they  are  usually  of  a  somewhat  rosy-pink  colour,  which  changes 
to  a  deep  brown  during  the  second  and  third  months  of  first  pregnancy.  Also 
during  pregnancy  the  areola  increases  in  size  and  its  glands  become  more  marked. 
The  nipple  contains  a  considerable  number  of  unstriped  muscle  fibres,  and  becomes 
firmer  and  more  prominent  as  a  result  of  mechanical  stimulation. 

The  size  and  appearance  of  the  mammary  glands  vary  much,  not  only  in  the 
different  races  of  mankind,  but  also  in  the  same  individual  under  different  con- 
ditions.    In  the  young  child  the  mamm£e  are  small,  and  there  is  little  difference 
between  those  of  the  male  and  female.     Their  growth  is  slow  until  the  approach 
of  puberty,  and   then    the   female   mammae   increase   rapidly  in    size.     At   each 
pregnancy  the  mammae  become 
large,   and    they   attain   their 
greatest    development   during 
lactation.      The    size    of    the 

mamma  depends  partly  on  the  ^^ 

amount  of  superficial  fat  and 
partly  on  the  amount  of 
glandular  tissue  present. 

Structure  of  the  Mamma.  /    '^^--^^     >  ^ 

— The  mamma  is  composed  of  Ampuiia- 
a  mass  of  glandular  tissue 
traversed  and  supported  by 
strands  of  fibrous  connective 
tissue,  and  covered  by  a  thick 
layer  of  fat.  The  glandular 
tissue,  to  which  the  term  corpus 
mammae  is  applied,  forms  a 
somewhat  conical  mass  whose 
apex  corresponds  to  the  position 
of  the  nipple  while  its  base  is 
loosely  connected  to  the  fascia  covering  the  pectoralis  major  and  serratus  magnus 
muscles.  In  section  the  corpus  mammse  is  readily  distinguished  from  the  sur- 
rounding fat  by  its  firmer  consistency  and  by  its  pinkish-white  colour.  The  corpus 
mammse  is  composed  of  lobes  and   lobules,  and  its  superficial  aspect  and  edges 


Dissection  of  the  Mammary  Gland. 


1208 


THE  UKINOGENITAL  SYSTEM. 


Processes  radiating  out 
from  the  corpus  iiHium* 


Ampulla 
Ductus  lactiferi 


are  very  uneven,  the  inequalities  of  its  surface  being  filled  up  by  processes  of 
the  fatty  tissue  which  forms  a  covering  for  the  gland.  This  fatty  covering  is 
incomplete   beneath   the    areola,   and   here    the  lactiferous   ducts   pass   into   the 

nipple.  The  gland  is  composed  of  fifteen 
to  twenty  lobes  (lobi  mammae)  which 
radiate  from  the  nipple,  each  lobe  being 
quite  distinct  from  the  others  and  possess- 
ing its  own  duct.  The  lobes  are  sub- 
divided into  secondary  lobes  and  lobules, 
bound  together  and  supported  by  a  con- 
siderable amount  of  connective  tissue  which 
forms  the  stroma  of  the  gland. 

The  alveoli  of  the  gland  and  the 
secretory  epithelium  lining  them  vary  much 
under  different  conditions.  At  puberty 
the  corpus  mammae  is  chiefly  composed  of 
connective  tissue  stroma  and  the  ducts  of 
the  gland.  At  this  time  the  alveoli  are 
small  and  few  in  number.  During  lacta- 
tion, when  the  gland  is  fully  functional, 
the  alveoli  are  enlarged,  distended  with 
fluid,  and  much  more  numerous.  The 
epithelial  cells  are  cubical  and  filled  with 
fat  globules.  When  the  gland  is  not 
secreting,  the  alveoh  become  small  and 
reduced  in  number,  while  the  cells  of  the 
lining  epithelium,  which  are  now  small 
and  glandular,  do  not  contain  fat  globules. 
The  duct  (ductus  lactiferi)  of  each  lobe, 
passing  towards  the  nipple,  becomes  en- 
larged to  form  a  small  spindle-shaped 
dilatation,  called  an  ampulla,  or  sinus  lacti- 
feri ;  then  becoming  once  more  constricted,  each  duct  passes,  without  communicating 
with  its  neighbours,  to  the  summit  of  the  nipple,  where  it  opens. 

In  the  male  subject  the  various  parts  of  the  mamma  are  represented  in  a  rudi- 
mentary condition. 

The  presence  of  milk-glands  is  characteristic  of  the  class  mammalia,  and  the 
number  of  pairs  of  glands  in  each  group  of  animals  bears  some  relation  to  the 
number  of  young  usually  produced  at  each  birth. 

Variations. — Asymmetry  in  the  development  of  the  mammae  is  very  common — the  left 
mamma  being  very  often  larger  than  the  right.  Absence  of  one  or  both  mammse  is  a  very 
rare  abnormality,  which  may  or  may  not  be  associated  with  absence  of  the  nipples.  When  one 
nipple  only  is  present  it  is  usually  the  left.  The  presence  of  supernumerary  glands  or  nipples  is 
not  very  imcommon,  and  a  large  number  of  examples  are  recorded.  The  term  polymasty  has 
been  applied  to  cases  in  which  more  than  the  normal  number  of  mammte  are  present,  and  poly- 
thely  to  those  in  which  additional  glands,  in  a  rudimentary  condition,  are  represented  by  accessory 
nipples.  Usually  the  accessory  glands,  or  nipples,  are  present  on  the  ventral  aspect  of  the  thorax, 
and  in  most  instances  they  occur  below  and  a  little  to  the  inner  side  of  the  normal  site.  When 
the  abnormal  glands  are  found  above  the  normal  site  they  generally  lie  further  from  the  middle 
line.  Much  more  rarely  accessory  glands  have  been  found  on  the  abdomen,  in  the  axilla,  or  in 
some  other  situation,  including  even  tlie  dorsal  aspect  of  tlie  trunk.  As  many  as  three  extra  pairs 
of  mammaj  have  been  found  in  the  same  individual,  and  cases  in  which  tlie  probable  representa- 
tives of  mammary  glands  were  even  more  numeroushave  been  recorded.  Asymmetry  is  very  common 
in  these  abnormal  structures.  It  is  interesting  to  note  that  examples  of  polymasty  and  polythely 
occur  in  the  male  rather  more  frequently  than  in  the  female.  In  some  women  the  accessory 
breasts  have  yielded  milk  during  lactation  ;  in  other  cases  the  abnormal  organs  have  been  very 
rudimentary,  and  represented  only  by  a  minute  nipple  or  pigmented  areola.  These  cases  of  i^oly- 
masty  and  polythely  are  supposed  to  represent  a  reversion  to  an  ancestral  condition,  in  which 
more  than  two  mammary  glands  were  normally  present,  and  in  which  probably  many  young  were 
produced  at  each  birth.  In  this  connexion  it  is  interesting  to  observe  that  usually  the  accessory 
glands  occur  in  positions  normally  occupied  by  mammai  in  lower  animals.  In  the  course  of  the 
development  of  the  mammary  glands  in  man,  specialised  areas  of  the  epidermis,  similar  to  those 
which  give  origin  to  the  mammary  glands,  have  been  observed  both  above  and  below  the  region 


Fat  lobule 


Fig.  866. — Section  through  a  Mammary  Gland. 
Prepared  after  immersion  in  nitric  acid  as  recom- 
mended by  Mr.  Harold  Stiles.    (D.  J.  Cunningham. ) 


DEVELOPMENT  OF  THE  MAMM^.  1209 

in  which  the  adult  mammary  glands  are  developed.  These  areas  appear  to  be  present  normally, 
but  in  most  cases  they  disappear  at  an  early  stage  in  the  history  of  the  embryo.  In  some  other 
mammals  rudimentary  mammary  glands  may  occur,  as,  for  instance,  in  lemurs  and  in  some  cows. 

A  slight  functional  activity  of  the  mammary  glands  of  the  male  at  birth  and  about  the  time 
of  puberty  is  stated  to  be  not  a  very  uncommon  occurrence. 

Vessels  and  Nerves  of  the  Mamma.— The  breast  receives  its  arterial  supply  from  tlie  per- 
forating branches  of  the  internal  mammary  artery  and  from  the  external  mammary  branch  of  the 
long  thoracic.  Additional  supply  is  sometimes  derived  from  some  of  the  intercostal  ve.ssels.  The 
veins  coming  from  the  gland  pour  their  blood  into  the  axillary  and  internal  mammary  veins. 
Some  small  superficial  veins  from  the  breast  join  tributaries  of  the  external  jugular.  The 
lymphatics  of  the  breast  are  very  numerous,  and  form  extensive  lymph  spaces  round  the  alveoli  of 
the  gland.  The  lymphatic  vessels  coming  from  the  mamma  for  the  most  part  join  the  lymphatic 
glands  of  the  axilla,  but  some  vessels  from  the  inner  part  of  the  breast,  following  the  course  pur- 
sued by  the  perforating  arteries,  join  the  lymphatic  glands  situated  along  the  course  of  the  internal 
mammary  artery.  The  nerve  supply  of  the  gland  is  derived  from  the  intercostal  nerves  of  the 
fourth,  fifth,  and  sixth  intercostal  spaces.  Along  the  course  of  these  nerves  sympathetic  filaments 
reach  the  breast  from  the  dorsal  part  of  the  sympathetic  cord. 

DEVELOPMENT  OF  THE  MAMM.^. 

The  mammary  glands  are  developed  as  downgrowths  of  the  ectoderm  into  the  under- 
lying mesoblastic  tissue.  In  the  human  embryo  a  thickened  raised  area  of  the  ectoderm 
is  to  be  recognised  in  the  region  of  the  future  mammary  gland  at  the  end  of  the  fourth 
week.  This  thickened  ectoderm  becomes  depressed  in  the  underlying  mesoblast,  and  thus 
the  mammary  area  soon  becomes  fiat,  and  finally  sunk  below  the  level  of  the  surrounding 
epidermis.  The  mesoblast,  where  it  is  in  contact  with  this  downgrowth  of  the  ectoderm, 
is  compressed,  and  its  elements  become  arranged  in  concentric  layers,  which,  at  a  later 
stage,  give  rise  to  the  connective  tissue  stroma  of  the  gland.  The  depressed  mass  of  ecto- 
derm cells  soon  becomes  somewhat  flask-shaped,  and  grows  out  into  the  surrounding 
mesoblast  as  a  number  of  solid  processes,  which  represent  the  future  ducts  of  the  gland. 
These  processes,  by  dividing  and  branching,  give  rise  to  the  future  lobes  and  lobules,  and 
much  later  to  the  alveoli.  The  mammary  area  becomes  gradually  raised  again  in  its 
central  part  to  form  the  nipple.  A  lumen  is  only  formed  in  the  different  parts  of  this 
branching  system  of  cellular  processes  at  birth,  and  with  its  establishment  is  associated 
the  secretion  of  a  fluid  resembling  milk,  which  often  takes  place  at  this  time.  The 
ampullae  appear  as  thickenings  on  the  developing  ducts  before  birth. 

In  those  animals  which  possess  a  number  of  mammary  glands — such  as  the  cat,  pig, 
etc. — the  thickening  of  the  ectoderm,  which  is  the  first  indication  of  the  development  of 
these  structures,  takes  the  form  of  a  pair  of  ridges  extending  from  the  level  of  the  fore- 
limb  towards  the  inguinal  region.  These  converge  posteriorly,  and  at  their  terminations 
lie  not  far  from  the  middle  line.  By  the  absorption  of  the  intermediate  portions  the 
ridges  become  divided  up  into  a  number  of  isolated  areas,  in  connexion  with  which  the 
future  glands  arise.  Such  linear  thickenings  of  the  ectoderm  have  not  yet  been  shown  to 
occur  in  the  human  embryo,  but  the  usual  positions  assumed  by  the  accessory  glands  when 
present,  leads  one  to  suspect  that  in  all  probability  the  ancestors  of  man  possessed 
numerous  mammary  glands  arranged,  as  in  lower  animals,  in  lines  converging  towards  the 
inguinal  region. 


THJ]    DUCTLESS    GLANDS. 

By  D.  J.  Cunningham. 

Under  this  title  we  include  a  heterogeneous  group  of  organs,  the  common  feature 
of  which  is  that  the  products  of  their  activity  are  not  conveyed  from  them  by 
means  of  ducts,  but  are  discharged  directly  into  the  vascular  system  through  the 
veins  or  lymphatic  vessels  which  take  origin  ^vithin  them.  This  physiological 
process  is  termed  internal  secretion,  and  in  the  case  of  certain  of  these  organs  the 
secretion  has  been  shown  to  exert  a  profound  influence  upon  the  nutritive  changes 
of  the  body. 

The  ductless  glands  include  the  lymphatic  glands,- which  have  been  already 
described  with  the  vascular  system ;  the  pineal  and  pituitary  bodies,  which  have 
been  referred  to  in  the  account  which  has  been  given  of  the  brain ;  and  the  spleen, 
the  suprarenal  capsules,  the  thyroid  body,  the  parathyroids,  the  thymus  body,  the 
coccygeal  body,  the  carotid  body — all  of  which  still  remain  to  be  studied, 

THE  SPLEEN. 

The  spleen  (lien)  is  the  largest  of  the  ductless  glands.  It  varies  greatly  in  size 
in  different  individuals,  and  also  in  the  same  individual  under  different  conditions, 
consequently  it  is  difiicult  to  give  its  average  dimensions.  Eoughly  speaking,  it  may 
be  said  to  be  as  a  rule  about  five  inches  in  length  and  three  inches  in  width  at  its 
widest  part.  It  is  a  soft  yielding  organ,  very  vascular,  and  somewhat  purple  in 
colour.  It  lies  far  back  in  the  abdominal  cavity  between  the  stomach  and  the 
diaphragm,  and  its  position  is  such  that,  whilst  the  greater  part  of  the  organ  is 
situated  m  the  left  hypochondrium,  its  upper  end  extends  inwards  beyond  the  left 
Poupart  plane,  and  thus  comes  to  lie  in  the  epigastric  region.  It  is  placed  very 
obliquely,  and  its  long  axis  corresponds  closely  in  its  direction  to  that  of  the 
back  jjart  of  the  tenth  rib. 

Form  and  Relations  of  the  Spleen. — The  spleen  has  the  shape  of  an  irregular 
tetrahedron.  The  upper  end  (extremitas  superior)  points  inwards  and  backwards, 
and  is  curved  to  some  extent  forwards  on  itself.  Of  the  four  surfaces  the  most 
extensive  is  the  diaphragmatic  (facies  diaphragmatica),  which  looks  backwards 
and  outwards.  It  rests  upon  the  back  part  of  the  diaphragm,  to  the  curvature 
of  which  it  is  accurately  adayjted.  By  the  diaphragm  it  is  separated  from  the  ninth, 
tenth,  and  eleventh  ribs.  It  is  necessary  also  to  rememljer  that  the  pleura  descends 
between  this  portion  of  the  chest  wall  and  the  diaphragm,  and  thus  comes  to  lie 
superficially  to  the  greater  part  of  this  diaphragmatic  surface  of  the  spleen.  The 
thin  basal  margin  of  the  lung,  which  occupies  the  upper  part  of  the  pleural  recess, 
likewise  intervenes  between  the  upper  part  of  the  spleen  and  the  surface  of  the 
body. 

In  the  foetus  and  infant,  in  which  the  liver  is  relatively  very  large,  the  left  lobe  of  that  organ 
extends  to  the  left  so  far  that  it  comes  as  a  rule  to  intervene  between  a  portion  of  the  spleen  and 
the  diaphragm.  Such  a  relation  is  sometimes  seen  in  the  adult,  but,  except  in  childhood,  it  is 
usual  for  the  liver  to  fall  short  of  the  spleen. 

1210 


THE  SPLEEN. 


1211 


The  remaining  three  surfaces  of  the  spleen  are  turned  towards  the  cavity  of  the 
abdomen,  and  are  closely  applied  to  the  viscera  which  support  the  organ  in  its 
place.  These  three  surfaces,  which  may  be  grouped  together  under  the  one  term 
of  visceral  aspect  of  the  organ,  are  separated  from  each  other  by  three  ridges  which 
radiate  from  a  blunt  and  often  inconspicuous  prominence  which  may  be  termed 
the  intermediate  angle  and  represents  the  apex  of  the  tetrahedron.  One  of  these 
ridges,  a  salient  and  prominent  border  (margo  intermedins),  extends  to  the  upper 
end  of  the  spleen,  and  separates  an  extensive  anterior  gastric  area  from  a  narrower 
posterior  renal  area.  A  second  short  border  passes  backwards  to  the  posterior  angle, 
and  intervenes  between  the  renal  and  colic  surfaces ;  whilst  the  third  ridge,  often 
obscurely  marked,  proceeds  forwards  to  the  anterior  angle  and  separates  the  gastric 


Rib  IX 


Rib  XI 

Descending  colon 


Rib  IX 


-Rib  XI 


Ascending  colon 


Fig. 


-Dissection  of  the   Spleen,  Liver,  and  Kidneys  from  behind,  in  a  Subject  hardened  by 

PYjrmalin-injection. 


and  the  colic  surfaces  from  each  other.  The  term  colic  surface  is  applied  to  a 
triangular  area  which  is  mapped  out  by  the  two  last-named  ridges  together  with  the 
lower  border  of  the  organ. 

The  gastric  surface  (facies  gastrica)  is  the  most  extensive  of  the  three  visceral 
districts.  It  is  deeply  concave,  and  is  moulded  on  the  fundus  of  the  stomach. 
Within  its  area,  and  about  an  inch  or  so  in  front  of  the  margo  intermedins,  is  the 
hilum  of  the  organ.  This  is  a  slit,  frequently  broken  up  into  two  or  more  pieces, 
which  gives  passage  to  the  vessels  and  nerves  which  enter  and  leave  the  spleen. 
Behind  the  hilum,  and  immediately  in  front  of  the  intermediate  angle,  there  is  a 
depression  of  variable  extent  and  depth  into  which  the  tail  of  the  pancreas  is 
received. 

The  renal  surface  (facies  renalis)  is  flat  and  even.  It  is  applied  to  the  anterior 
surface  of  the  upper  part  of  the  kidney,  close  to  its  outer  border.  Sometimes  the 
part  of  this  surface  which  adjoins  the  upper  end  of  the  organ  is  applied  to  the  left 
suprarenal  capsule,  but  as  a  rule  it  falls  short  of  that  structure. 


1212 


THE  DUCTLESS  GLANDS. 


ANTERfOR 


Hihuii 


Pancreatic  impression 

Intermediattt  a 


ile 


Posterior  angle 


The  colic  surface  (fades  basalis)  is  the  smallest  of  the  three  visceral  areas.  It 
is  triangular  in  form,  and  looks  downwards  and  inwards,  and  is  in  contact  with  the 
splenic  flexure  of  the  colon  and  the  costo-colic  ligament  (vide  p.  1083). 

The  anterior  border  (margo  anterior)  of  the  spleen  is  sharp  and  prominent,  and 
intervenes  between  the  gastric  and  diaphragmatic  surfaces.  Its  leading  character- 
istic is  that  it  is 
irregularly  notched. 
The  posterior  border 
(margo  posterior) 
separates  the  renal 
r  from  the  diaphrag- 
matic surface.  It 
is  important  to 
know  that,  if  in  the 
living  subject  the 
finger  is  drawn 
along  the  last  in- 
tercostal space,  it 
will  indicate  with 
tolerable  accuracy 
on  the  surface  of 
the  body  the  posi- 
tion and  direction 
of  the  posterior 
border.  The  in- 
ferior border  (margo 
inferior)  of  the 
spleen  intervenes 
between  the  dia- 
phragmatic surface 
and  the  colic  sur- 
face. The  other  margins  of  the  spleen  are  those  which  separate  the  visceral  areas 
from  each  other,  and  they  have  been  already  noticed. 

A  marked  feature  of  the  typically-formed  spleen  is  the  great  prominence  of  the 
anterior  angle.     It  forms  the  most  anteriorly-placed  part  of  the  organ. 

The  form  of  tlie  spleen  varies  much  in  accordance  with  the  changing  conditions  of  the 
neighbouring  hollow  viscera.  Shepherd  has  shown  that  there  are  two  extreme  forms,  viz.  the 
tetrahedral,  which  is  described  above,  and  the  orange-segment  type.  In  the  case  of  the  former 
the  colon  is  distended,  and  the  stomach  as  a  rule  more  or  less  empty  :  the  colon  displaces  the 
stomach  from  contact  with  the  lower  part  of  the  visceral  surface  of  the  spleen,  and  by  its 
pressure  produces  the  colic  impression. 

When  the  spleen  presents  a  form  similar  to  that  of  the  segment  of  an  orange  its  lower  end 
becomes  pointed,  and  the  entire  visceral  surface  is  occupied  by  the  renal,  gastric,  and  pancreatic 
impressions  or  areas.  The  colon  is  as  a  rule  empty  and  exerts  no  pressure  on  the  spleen,  whilst 
the  stomach  is  in  all  probability  distended.  As  Shepherd  has  shown,  every  intermediate  form 
of  spleen  between  the  two  extreme  types  are  met  with,  and  may  occur  with  varying  conditions 
of  the  hollow  viscera,  at  different  times,  in  the  same  individual 

Notches  and  Fissures. — The  usual  number  of  notches  on  the  anterior  border  of  the  spleen  is 
two,  although  in  exceptional  cases  there  may  be  as  many  as  six  or  even  seven.  It  is  not  un- 
common to  find  one  or  more  fissures  on  the  posterior  border  and  also  on  the  parietal  surface 
of  the  organ  (Parsons). 

Peritoneal  Relations  of  the  Spleen. — The  spleen  is  almost  completely  enveloped 
by  peritoneum,  and  two  folds  of  peritoneum,  viz.  the  gastro-splenic  omentum  and 
the  lieno-renal  ligament,  pass  from  it.  Both  of  these  folds  are  attached  in  the 
neighbourhood  of  the  hilum.  The  lieno-renal  ligament  proceeds  backwards  to  the 
anterior  surface  of  the  left  kidney  (p.  1099) ;  the  gastro-splenic  omentum  connects 
the  spleen  with  the  i««4«8  of  the  stomach  (p.  1104). 

Accessory  Spleens. — Small  globular  masses  of  splenic  tissue  are  not  infrequently  found  in 
the  neif,dibourljood  of  tlie  spleen.     Tliose  arc  termed  accessory  spleens. 

Blood-vessels,  Lymphatics,  and  Nerves  of  the  Spleen. — The  large  splenic  artery  gains  the 
spleen  by  passing  between  tlie  two  layers  of  the  lieno-renal  ligament.     It  breaks  uji  into  several 


Fig.  868. — The  Spleen — Visceral  Aspect. 


THE  SUPEAEENAL  CAPSULES.  1213 

brandies  whicli  enter  the  organ  tlirough  the  hihun.  Some  twigs  pi'oceed  from  the  splenic  artery 
to  the  stomach,  whicli  they  gain  by  insinuating  themselves  between  the  two  layers  of  the  gastro- 
splenic  omentum.  The  splenic  vein  is  formed  in  the  lieno-renal  ligament  by  the  union  of  the 
branches  which  emerge  from  the  hiluni  of  the  organ.  It  joins  the  superior  mesenteric  vein  to 
form  the  vena  port£e. 

The  splenic  plexus  of  nerves  is  an  offset  from  the  cceliac  part  of  the  solar  plexus,  and  accom- 
2>anies  the  arteries  into  the  spleen. 

Tilt'  lymphatic  vessels  leave  the  spleen  at  the  liilum,  and  accompany  the  great  vessels.  There 
are  no  lymphatic  channels  within  the  spleen,  although  they  are  present  in  its  capsule  (Mall). 

Structure  of  the  Spleen. — In  our  study  of  the  structure  of  the  spleen  we  have  to 
consider — (1)  the  tunica  propria,  (2)  the  trabecular  framework,  (3)  the  spleen  pulp, 
and  (4)  the  distribution  of  the  blood-vessels  and  the  Malpighian  corpuscles. 

Tunica  propria  (tunica  albuginea). — Subjacent  to  the  serous  coating  furnished  by  tlie 
peritoneum  the  spleen  is  provided  with  a  strong  capsule  termed  the  tunica  propria.  'I'his 
is  formed  of  fibrous  tissue,  with  a  large  proportion  of  elastic  fibres  and  a  certain  amount  of 
involuntary  muscular  tissue.  It  is  therefore  highly  distensible,  and  perhaps  feebly  con- 
tractile.    To  the  outer  surface  of  this  capsule  the  peritoneum  is  inseparably  attached. 

Trabecular  Framework  (trabecule  lienis).  —  From  the  deep  surface  of  the  tunica 
propria  numerous  processes  or  trabeculte  are  given  off,  and  these  penetrate  into  the  sub- 
stance of  the  spleen.  Some  are  cord-like,  others  are  in  the  form  of  flattened  bands,  and  all 
are  composed  of  fibrous  tissue  and  involuntary  muscular  fibres.  Within  the  spleen  the 
trabecuhe  branch  and  re-branch,  and  join  with  each  other  to  form  a  supporting  framew(jrk 
for  the  organ.  The  blood-vessels,  as  they  enter  at  the  hilum,  carry  in  with  them  connec- 
tive tissue  sheaths,  and  these  also  take  part  in  the  formation  of  the  trabecular  framework 

Spleen  Pulp  (pulpa  lienis). — The  interstices  between  the  sti'ands  of  the  trabecular 
framework  are  filled  with  spleen  pulp.  This  is  supported  by  a  delicate  reticulum  foi'med 
by  branching  cells.  The  spaces  of  the  network  freely  communicate,  and  are  occupied  by 
blood  in  which  there  are  lai'ge  numbei's  of  leucocytes,  and  also  large  cells  special  to  the 
spleen.  These  are  termed  splenic  cells,  and  contain  pigment,  and  not  infrequently  red 
blood  corpuscles,  in  their  interior. 

Blood-vessels  and  Malpigliian  Corpuscles. — The  splenic  arteries,  as  they  traverse  the 
spleen,  run  in  the  trabeculee.  The  small  branches  ultimately  leave  these  and  enter  the 
spleen  pulp.  As  they  do  so  they  become  ensheathed  in  a  coating  of  adenoid  tissue.  At 
certain  points  in  the  course  of  the  arteries  this  sheath  suddenly  increases  in  thickness,  and 
forms  small  round  or  oval  masses  of  adenoid  tissue  upon  the  vessel.  In  sections  through 
the  spleen  these  small  nodular  masses  are  visible  to  the  naked  eye  as  minute  white  spots. 
They  are  called  Malpighian  corpuscles  (noduli  lymphatic!  lienales).  The  artery  rarely 
passes  through  the  centre  of  such  a  coi'puscle.  As  a  rule  the  adenoid  tissue  is  massed 
chiefly  upon  one  side  of  the  vessel,  and  a  plentiful  supply  of  blood  is  given  to  the  nodule 
by  means  of  a  capillai-y  network  in  connexion  with  the  artery  on  which  the  Malpighian 
corpuscle  is  developed. 

The  manner  in  which  the  minute  terminal  arteries  end  in  the  spleen  pulp  is  peculiar. 
The  wall  becomes  reduced  to  the  endothelial  lining,  and  the  cells  forming  this  gradually 
separate  from  each  other  and  become  continuous  with  those  of  the  reticulum  of  the  spleen 
pulp.  The  blood  therefore  flows  directly  into  the  meshes  of  the  reticulum  of  the  pulp. 
The  minute  radicles  of  the  veins  begin  in  the  same  way  as  the  arteries  end.  The  walls 
are  gradually  built  up  by  the  union  of  cells  continuous  with  the  open  reticulum,  and  the 
blood  flowing  into  the  vessels  so  formed  is  led  away  towards  the  larger  veins  which  occupy 
the  trabecuhe. 

Development  of  the  Spleen. — It  is  not  until  the  second  month  of  intrauterine 
development  that  the  spleen  begins  to  develop.  It  is  formed  from  mesoderm,  and  appears 
in  the  dorsal  mesogastrium  in  the  neighbourhood  of  the  pancreas.  After  a  short  time  it 
becomes  invaded  by  blood-vessels,  but  the  Malpighian  corpuscles  are  somewhat  late  in 
making  their  appearance.  The  spleen  grows  to  the  left  in  the  direction  of  least  resistance, 
protruding  the  left  layer  of  the  mesogastrium  before  it,  and  its  form  is  determined  by 
the  pressure  to  Avhich  it  is  subjected  by  the  neighbouring  viscera  and  the  abdominal  wall. 

THE  SUPEAEENAL  CAPSULES. 

The  suprarenal  capsules  (glandule  suprarenales)  are  two  small  flattened  organs 
which  lie  iu  the  epigastric  region,  one  on  either  side  of  the  spine,  and  in  intimate 
relation  to  the  upper  end  of  the  corresponding  kidney. 

The  right  suprarenal  capsule  is,  as  a  rule,  triangular  in  form,  and  rests  by  its 
baaajipon  the  anterior  and  inner  aspect  of  the  upper  end  of  the  right  kidney.     It 


1214 


THE  DUCTLESS  GLANDS 


is  placed  between  the  posterior  surface  of  the  right  lobe  of  the  liver  and  that  portion 
of  the  diaphrao-m  which  covers  the  side  of  the  spine. 

The  anterior  surface,  which  looks  outwards  as  well  as  forwards,  presents  two 
impressions— (1)  The  one  is  a  narrow  flattened  strip  adjoining  the  anterior  border 
of  the  capsule  which  is  overlapped  by  the  inferior  vena  cava;  (2)  the  second 
impression  comprises  the  remainder  of  tlie  anterior  surface,  and  is  in  contact  with 


Uaiisular  \eiii 


Surface  in  contact 
with  liver 


Surface  covered 
by  inferior  cava 


Surface  covi^red  by 
l)eritoueiuii 


Fig.  869. 

A.  Anterior  siulaee  of  right  .suprarenal  cap-sule.      B.  Anterior  surface  of  left  suprarenal  capsule. 

Tlie  upper  and  inner  parts  of  each  kidney  are  indicated  in  outline.     On  the  right  capsule  the  dotted  line 

indicates  the  upper  limit  of  the  peritoneal  covering. 

the  liver.  Only  a  small  and  variable  part  of  the  lower  portion  of  the  anterior 
surface  of  the  right  suprarenal  capsule  is  covered  by  peritoneum.  On  the  upper 
part  of  the  impression  for  the  vena  cava,  not  far  from  the  apex  of  the  capsule,  a 
short  fissure  termed  the  hilum  may  be  observed.  From  this  issues  a  short  wide 
vein  which  immediately  enters  the  vena  cava  infer.ior.  The  posterior  surface  of 
the  right  suprarenal  capsule  is  divided  by  a  salient  curved  ridge  into  an  upper  flat 


Surface  in  relation 

to  iliapliragiii       ^ 


Surface  in  relation 
A    to  kidney 

Fk;.  .s70. 
A.    I'osterior  .surface  of  riglit  sujniuenal  capsule.       U 


Surface  in  relation  to 
left'  crus  of  diaphragm 


Surface  in  relation 
to  kidney 


stcrior  surface  of  left  suprarenal  capsule. 


part,  which   is  applied   to   the   diaphragm,  and    a  concave  lower  part,  which   is 
occupied  by  fat  and  rests  upon  the  kidney. 

The  left  suprarenal  capsule  i»resents  a  swnilunar  form,  and  as  a  rule  is  slightly 
Iftfgef-than  the  light  capsiik'.  Its  position  on  tluTlrilliley  is  also  somewhat  different. 
It  is  usually  placed  on  its  inner  border  immcidiately  above  the  hilum.  The 
anterior  surface  presents,  not  far  from  its  lower  end,  a  very  obvious  slit  or  hilum 
with  a  large  emerging  vein.     The  greater  part  of  this  surface  is  in  relation  to  the 


THE  SUPEAEEXAL  CAPSULES. 


1215 


posterior  aspect  of  the  stomach,  and  forms  a  portion  of  the  bed  on  which  that  organ 
Hes.  This  gastric  area  of  the  suprarenal  capsule  is  clothed  bj  peritoneum  derived 
from  the  loeoor  oac.  The  lower  portion  of  the  anterior  surface  is  covei'ed  by  the 
pancreas  and  crossed  by  the  splenic  vessels,  and  is  not  in  relation  to  the  peritoneum. 
Sometimes  the  spleen  extends  inwards  so  as  to  lie  in  relation  to  the  upper  part  of 
the  anterior  surface  of  the  left  suprarenal  capsule,  but  this  cannot  be  said  to  be  the 
rule.  The  i^osterior  surface  is  subdivided  into  two  areas,  as  on  the  right  side,  byli 
curved  ridge.  The  upper  area  is  flat,  and  applied  to  the  Ifti^t-cms!  nf  f.hp  rlinphragr"  ; 
the  lower  area  is  hollowed  out,  and  is  in  relation  to  the  kidney,  a  considerable 
amount  of  fat  intervening. 

In  the  fojtus  the  suiirarenal  capsules  are  relatively  very  iniicli  larger  than  in  the  adult. 
Indeed,  on  the  left  side  the  capsule  extends  downwards  on  the  kidney  so  far  that  the  spleen  is 
completely  shut  out  l)y  it  from  that  organ. 

Vessels  of  the  Suprarenal  Bodies. — Each  capsule  receives  three  arteries — viz.  from  the  iufeHt^ 
plireiiKL^Jrpiu  the  aorta,  and  from  the  renal  artery.     One  large  vein,  emerging  from  the  hilum  on 


Medulla  of  suprarenal  capsule 


Cortex  of  suprarenal  capsule 


rmBfi  \     1^     ,.---  Left  crus  of  diaphr 


Intervertebral  disc 


f-^\ ^Spinal  cord 


Fig.  871.- 


-Transverse  Section  through  the  Suprarenal  Capsule  of  a  New-born  Child 

IX  SITU. 


the  anterior  surface,  as  a  rule  conveys  all  the  blood  from  the  organ.     On  the  right  side  it  opens  at 
once  into  the  inferior  vena  cava,  and  on  the  left  side  into  the  left  renal  vein. 

The  nerves  of  the  suprarenal  bodies  are  very  numerous.  They  come  from  the  solar  plexus, 
and  constitute  the  suprarenal  jilexus. 

Structure  of  the  Suprarenal  Capsule. — The  suprarenal  capsule  is  surrounded  by  a 
thin  connective  tissue  sheath,  from  the  deep  surface  of  which  hue  processes  are  given  oft  \vhich 
enter  the  substance  of  the  organ,  and  form  within  it  a  supporting  stroma  or  framework. 

The  gland-substance  is  composed  of — (1)  an  external  corticd'V  portion,  firm  in  con- 
sistence, of  a  yellowish  hue,  and  forming  tlie  chief  bulk  of  the  organ  j  and  (2)  an  internal 
medullary  part,  very  soft  and  pulpy,  and  dark  bi-own  in  colour.  In  the  bulky  orgair  of 
the  foetus  the  appearance  presented  by  these  constituent  parts  is  j~Qry  different.  The 
cortex  is  dark  purple  in  colour,  whilst  the  medulla  presents  a  light  y^rfdw  tint  (Fig.  871). 

The  cortical  substance  (substantia  corticalis)  consists  of  groups  of  cells  occupying  the 
interstices  of  the  stroma.  These  cell-groups  present  diff"erent  forms  at  different  levels 
from  the  surface.  Thus,  subjacent  to  the  connective  tissue  sheath,  there  is  a  thin  stratum, 
termed  the  zona  glomertdosa,  in  which  the  cell-masses  ar'e  more  or  less  rounded  ;  next 
comes  the  zona  fasciculata,  which  constitutes  the  chief  part  of  the  cortex,  and  in  which 
the  cells  are  grouped  in  long  columns  which  are  arranged  radially  with  reference  to  the 
surface  ;  and  lastly,  there  is  the  deepest  layer,  the  zona  reticularis,  in  which  the  cells  are 
disposed  in  a  reticular  manner  amidst  the  stroma. 

The  medullary  part  (substantia  medullaris)  is  also  pervaded  by  a  fibrous  stroma 
continuous  with  that  of  the  cortex.  This  forms  an  irregular  meshwork,  the  spaces  of  which 
are  occupied  by  cells  of  very  variable  shape.  When  treated  with  chromic  salts  they  assume 
a  dark  brown  colour,  and  have  consequently  been  termed  chromaffin  or  chromogenic  cells. 

The  arteries  enter  the  cortex  and  break  up  into  capillaries  which  ai*e  arranged  around 
the  cell-groups.  In  the  medulla  there  are  large  thin-walled  capillaries  into  which  the 
whole  blood  of  the  organ  passes.  These  capillaries  are  closely  surrounded  by  the  medullary 
cells.     Proceeding  from  them  are  the  radicles  of  the  capsular  vein. 


1216 


THE  DUCTLESS  GLANDS. 


Development  of  the  Suprarenal  Capsule. — It  would  appear  that  the  cortical 
and  medullary  parts  of  the  suprarenal  body  have  a  totally  different  origin.  The  medulla 
is  derived  as  a  mass  of  cells  which  grows  out  from  the  ganglia  of  the  sympathetic  cord, 
and  becomes  in  the  process  of  deA'elopment  encapsulated  within  the  cortex.  It  is  important 
to  note  in  this  connexion  that  a  certain  number  of  chromaffin  cells  are  found  within  the 
sympathetic  ganglia.  Although  nervous  in  its  origin,  the  medulla  of  the  suprarenal  becomes 
glandular  and  gives  to  the  blood  an  internal  secretion  whicli  exercises  a  most  potent 
physiological  action. 

The  cortical  part  of  the  suprarenal  body  is  formed  from  a  mass  of  mesodermic  cells 
which  on  the  right  side  become  grouped  together  in  the  immediate  vicinity  of  the  inferior 
vena  cava  soon  after  that  vessel  is  formed.  The  cells  thus  accumulated  together  are  said 
to  be  derived  directly  or  indirectly  from  the  epithelial  cells  which  line  the  body  cavity  in 
the  region  of  the  Wolffian  ridge. 

As  we  ascend  the  scale  of  vertebrates,  the  suprarenal  bodies  show  an  interesting  series 
of  evolutionai-y  stages.  "  In  fishes  the  two  constituents  («'.e.  medulla  and  cortex)  are  quite 
separate ;  in  amphibians  they  come  into  contact ;  in  reptiles  they  are  beginning  to  be 
intermixed  ;  in  birds  the  cortex  and  medulla  interlace ;  whilst  in  mammals  the  medulla 
is  surrounded  by  the  cortex  "  (Swale  Vincent). 


Crico-tliyroid 
iiiembraue 


THE  THYEOID  BODY. 

The  thyroid  body  (glandnla  thyreoidea)  is  a  highly  vascular,  pliant  structure 
which  clasps  the  upper  part  of  the  trachea  and  extends  upwards  for  some  distance 

upon  each  side  of  the  larynx. 
Thyroid  cartilage  In  sizc  it  varics  greatly  in 
different  individuals,  and  in 
the  female  and  child  it  is 
always  relatively  larger  than 
in  the  adult  male.  It  consists 
of  three  well  -  marked  sub- 
divisions —  viz.  two  lateral 
lobes,  joined  across  the  middle 
line  by  the  isthmus. 

Each  lateral  lobe  is  conical 
in  form.  Its  base  extends 
downwards  upon  the  side  of 
the  trachea  as  far  as  the  fifth 
or  sixUh  tracheal  ring,  whilst 
its  apex  rests  upon  the  ala  of 
the  thyroid  cartilage.  Its 
superficial  surface  is  somewhat 
flattened,  and  is  clothed  by  the 
pretracheal  layer  of  cervical 
fascia,  from  which  the  organ 
derives  a  sheath,  and  also  by 
the  sterno  -  thyroid,  sterno- 
hyoid, and  omo-hyoid  muscles. 
It  is  .also  overlapped  by  the 
sterno -mastoid  muscle.  Its 
deep  surface  is  adapted  to  the 
parts  upon  which  it  lies — viz. 
to  the  side  of  the  trachea,  to  the  cricoid  cartilage,  and  to  the  inferior  cornu  and 
adjoining  part  of  the  surface  of  the  ala  of  the  thyroid  cartilage  ;  whilst  its  posterior 
border  extends  backwards  so  as  to  touch  the  cesophagus  and  pharynx  and  overlap 
the  common  carotid  artery  (Fig.  694,  p.  974). 

The  isthmus  of  the  thyroid  body  is  a  narrow  Ijand  of  varying  width  which  lies 
in  front  of  the  second,  third,  and  fourth  rings  of  the  trachea,  and  unites  the  bases 
or  lower  cuds  of  the  two  lateral  lobes. 

A  third  lobe  is  frequently  found  in  connexion  with  tlie  thyroid  body.  This  is 
the  pyramidal  or  middle  lobe  (Fig.  873).     When  present  it  assumes  the  form  of  an. 


Innoiiiiiiatc  artery 

Fio.  872. — Dissection  of  the  Thvkoid  Body  and  of  the  F.vkts 

IN    IMMBDIATK    RELATION    TO    IT. 


THE  THYKOID  BODY.  1217 

elongated  slender  process  which  springs  from  the  upper  border  of  the  isthmus  on 
one  or  other  side  of  the  mesial  plane  (more  usually  on  the  left  side)  and  extends 
upwards  for  a  variable  distance  towards  the  hyoid  bone  upon  the  cricoid  and  thyroid 
cartilages.  A  strand  of  lil)rous  tissue,  or  perhaps  a  narrow  slip  composed  of  muscular 
fibres  (levator  giandula;  thyreoideae),  connects  it  to  the  body  of  the  hyoid  bone. 

The  thyroid  body  is  firmly  attached  to  the  parts  on  wliich  it  lies,  and  therefore 
follows  the  larynx  in  all  its  movemeuts. 

Variations. — Small  detaclied  portions  of  the  thyroid  tissue  placed  in  the  neighljourhuod  of 
the  lateral  lobes  or  in  the  \iciuitv  of  the  hyoid  bone  are  not  imconmion.  Such  glandular  masses 
are  termed  accessory  thyroid  bodies.  The  isthmus  is  the  part  of  the  organ  which  is  most  sub- 
ject to  variation.  Its  size  differs  greatly  in  different  individuals,  and  it  not  infrequeiUiy  happens 
that  it  is  absent. 

Blood-vessels.—  Four  large  arteries,  and  occasionally  a  fifth  smaller  vessel,  convey  blood  to  the 
tliyroid  l)ody.  Two  superior  thyroid  branches  spring  from  the  external  carotid  arteries.  Eacji 
nf  these  divides  at  the  apex  of  the  lateral  lobe  into  three  branches  for  its  supply.  Tw(j 
inferior  thyroid  branches  from  the  tliyroid  axes  of  the  subclavian  arteries  distribute  their  terminal 
In'anches  to  the  ba.sal  portions  and  deep  surfaces  of  the  lateral  lolx'.s  The  occasional  artery  is  the 
thyroidea  ima,  a  lnvuicli  of  the  innominate,  wdiich  ascends  upon  the  trachea  to  reach  the  isthmus 
of  the  thyroid  body.     The  thyroid  arteries  anastomose  freely  with  each  other. 

The  veins  which  drain  the  blood  from  the  thyroid  body  are  still  more  numerous.  They  are 
three  in  number  on  each  side  \'iz.  the  superior  and  middle  thyroid  veins,  which  join  the  internal 
jugular  ;  and  the  inferior  thyroid,  which  descends  in  front  of  tlie  trachea  and  joins  its  fellow  of 
the  opposite  side  to  form  a  large  conunon  stem  which  ojjens  into  the  left  innominate  vein. 
Numerous  large  veins  ramify  on  the  surface  of  the  organ  and  lie  in  grooves  in  its  substance. 
It  is  from  this  j'lexus  that  the  inferior  thyroid  veins  take  origin. 

The  nerves  which  go  to  the  thyroid  body  accompany  the  vessels.  They  are  deriveil  from 
the  middle  and  inferior  cervical  ganglia  of  the  sympathetic. 

Structure  of  the  Thyroid  Body. — The  thyroid  body  is  enveloped  by  a  clusely- 
applied  thiu  capsule  of  connective  tissue.  From  the  deep  surface  of  this  numerous 
processes  penetrate  into  the  substance  of  the  organ,  and  divide  it  into  lobes  and  lobules. 
From  the  septa  which  separate  the  lobules  fine  lamelke  proceed  which  form  the  boundaries 
of  vast  uumbei's  of  closed  vesicles  or  alveoli  of  dift'erent  sizes  and  shapes.  Some  of  the 
vesicles  are  spherical  or  polyhedral,  whilst  others  are  oval  or  flattened  and  branching.  All 
are  lined  by  a  layer  of  cubical  or  columnar  epithelial  cells,  and  most  of  them  contain  a 
viscid  semi-fluid  colloid  material. 

The  blood-vessels  traverse  the  organ  in  the  fibrous-tissue  septa,  whilst  the  capillarv 
network  is  disposed  on  the  outer  surface  of  the  various  vesicles.  Numerous  lymphatic 
vessels  ai'ise  external  to  the  alveoli,  and  Baber  has  shown  that  they  frequently  contain 
colloid  material  similar  to  that  in  the  interior  of  the  vesicles. 

Development  of  the  Thyroid  Body. — The  thyroid  body  is  formed  from  three 
originally  separate  and  distinct  rudiments  which  arise  independently  of  each  other — viz. 
a  median  rudiment  and  two  lateral  rudiments. 

The  median  thyroid  rudiment  arises  as  a  hypoblastic  outgrowth  from  the  floor  or 
ventral  wall  of  the  pharynx  (Fig.  30,  F.O,  p.  36).  The  point  at  which  this  occurs  is  in  front 
of  the  second  visceral  arches,  at  the  junction  between  the  basal  portion  of  the  tongue  and 
that  part  of  the  organ  which  is  developed  from  the  tuberculum  impar  (see  pp.  37  and 
1013).  The  foramen  Ccecum  on  the  dorsum  of  the  adult  tongue  represents  the  upper 
jjersistent  part  of  the  median  thyroid  diverticulum.  The  median  thyroid  rudiment 
extends  downwards  towards  the  front  of  the  larynx.  It  rapidly  elongates,  and  its  distal 
extremity  bifurcates  and  comes  to  lie  in  front  of  the  upper  part  of  the  trachea.  This 
bifurcated  extremity  forms  the  isthmus  of  the  thyroid  body,  and  also  a  portion  of  each 
lateral  lobe. 

The  portion  of  the  diverticulum  which  intervenes  between  the  dorsum  of  the  tongue 
and  the  isthmus  is  termed  the  thyro-glossal  duct.  As  already  explained,  its  upper  end 
persists  as  the  foramen  cceaan  of  the  tongue.  Its  opposite  extremity  is  usually  retained 
as  the  pyramidal  lohe  of  the  thyroid  body,  whilst  the  intervening  portion  disappears. 
Such  is  the  usual  course  of  development,  V)ut  in  certain  cases  more  or  less  extensive 
sections  of  the  tbyx'O-glossal  duct  may  persist.  The  rare  occurrence  of  a  lingual  duct 
which  extends  dowmwards  througli  the  tongue  towards  the  hyoid  bone  is  accounted  for  in 
this  manner.  Thyro-glossal  cysts  situated  in  any  part  of  the  path  of  the  duct  owe  their 
origin  to  a  similar  cause. 

The  lateral  tliyroid  rudiment  of  each  side  arises  as  a  saccular  hypoblastic  diverticulum 
from  the  pharyngeal  side  of  the  fourth  visceral  cleft  (see  p.  35).  It  comes  into  relation 
with  the  lateral  aspect  of  the  larynx,  and  becoming  cut  off' from  the  cavitv  of  the  pharynx, 
82 


1218 


THE  DUCTLESS  GLANDS. 


it  joins  Avith  the  isthmus  or  median  rudiment  to  form  the  greater  part  of  the  lateral  lobe 
of  the  thyroid  body. 

'J'he  thyroid  body  in  its  primitive  condition,  and  in  each  of  its  three  parts,  is  epithelial. 
Soon  it  is  invaded  by  connective  tissue  and  blood-vessels,  but  the  hypoblastic  epithelium 
is  retained  as  the  cellular  linins;  of  its  constituent  vesicles. 


Inli-'iiial  jugular  vein 

Vagus  ueive 

C'jiiinioii  carotid  artery 

lunoiuiiiate  artery 
.Subclaviai 

Subcla\iaii  \eiii 

Iniioiiiiiidt> 
vein 


.ali'ral  lobe  ul'  thyroid 
body 


Istliiiuis  of  tliyroiii 
body 


(  uiiiiuoii  caiutid  artery 
Internal  jugular  vein 
Hand  connecting 
tliymus  with  thyroid 
N'agus  nerve 

Subclavian  arteiy 

Subclavian  vein 
Innomiuule  vein 


Parathyroids. 

The  parathyroid  glands  are  two  minute  structures  which  lie  in  more  or  less  close 
relation  to  each  lateral  lobe  of  the  thyroid  body.  They  are  apt  to  be  mistaken  for 
accessory  thyroids,  but  in  structure  they  are  different.  One,  more  constant  in 
position  than  the  other,  is  situated  on  the  posterior  aspect  of  the  oesophagus  at 
the  level  of  the  lower  border  of  the  cricoid  cartilage,  and  in  more  or  less  intimate 
relation  to  the  posterior  border  of  the  lateral  lobe  of  the  thyroid  body.  The 
second  parathyroid  body  is  placed  either  in  close  apposition  witli  the  lower  border 
of  the  lateral  lobe  of  the  thyroid,  or  on  the  trachea  at  a  varying  distance  below  it. 
The  inferior  thyroid  artery  intervenes  between  the  two  parathyroid  bodies  (Welsh). 

The  parathyroid 
bodies  are  composed  of 
reticulating  rows  of  cells, 
with  blood-vessels 
arranged  between  them. 
In  structure  they  bear  a 
close  resemblance  to  that 
of  the  anterior  lobe  of  the 
pituitary  body.  The 
upper  parathyroid  body 
is  derived  as  a  hypoblastic 
bud,  which  grows  out 
from  the  bottom  of  the 
pharyngeal  side  of  the 
third  visceral,  cleft ;  the 
lower  body  has  a  similar 
origin  from  the  fourth 
visceral  cleft. 

It  has  been  shown 
that  the  removal  of  the 
four  parathyroids  from 
the  cat  is  followed  by 
very  severe  symptoms, 
and  in  two  cases  out  of 
three  death  ensued  in 
the  course  of  a  few  days 
(Welsh). 

THYMUS  GLAND. 

The  thymus  gland 
can  only  be  studied  to 
advantage  in  the  later 
period  of  foetal  life  or  in 
early  childhood.  It 
attains  its  maximum 
developmeut  towards  the  end  of  the  secuud-^ear,  and  from  this  time  on  it  dwindles 
away  until  only  a  comparatively  small  portion  of  it  is  left.  In  the  new-born 
child  it  is  of  a  pinkish  colour,  and  is  composed  of  two  lateral  lobes,  very  seldom 
of  equal  size,  and  sc^purated  by  an  intervening  fissure.  The  main  portion  of  the 
gland  is  placed  within  the  tliorax,  but  the  two  lobes  end  above  in  two  blunt 
prolongations  which  are  carried  upwards  for  a  varying  distance  into  the  neck. 


Fi.;.  873. 


-THYMCS    (iLANO    I.N    A    FULL-TI.ME    FOiTUS    HAUDKNKU    liY 
FOK.MALIN-INJECTION. 


THYMUS  GLAND. 


1219 


The  thoracic  portion  of  the  thymus  gland,  in  its  fully-developed  condition,  is 
placed  in  the  superior  and  anterior  mediastinal  spaces,  and  as  a  rule  it  extends 
downwards  as  far  as  the  level  of  the  fourth  costal  cartilages.  The  mediastinal 
pleura  and  the  lung  are  applied  to  it  on  either  side,  whilst  the  sternum  and  costal 
cartilages  are  in  close  relation  to  it  in  front.  The  deep  surface  of  the  thymus  is 
moulded  upon  the  pericardium  and  upon  the  vessels  in  the  front  part  of  the 
superior  mediastinum.  Thus,  when  it  is  hardened  in  situ  and  removed,  it 
presents  on  its  posterior  surface  a  deep  pericardial  concavity,  with  impressions 
on  the  upper  part  of  this  hollow  corresponding  to  the  pulmonary  artery  and  vena 


Reeunent  laryngeal  nerv 
Inferior  tliyrokl  vein  -       ^^   f 

Right  vagus  nerve  ^  y 
Bifurcation  of  iiuui- 
ininate  arti'r\ 

Right  subclaviai 

vessel- 

Internal  niammai 
artei 


Right  lobe  of 
thymus  gland 


Sterno-hyoid  muscle 
•Sterno-thyroid  muscle 
Sterno-mastoid  muscle 
Thyroid  body 
Internal  jugular  vein 
Phrenic  nerve 

Scalenus  anticus 


I'lilmonary  fissure 


I'erlcaixlium 


Fio.  874.  — Dissection  to  show  the  Thymus  Gland  in  an  Auli.t  Female. 


cava  superior  (Fig.  875).  Aljove  the  pericardial  surface  deep  grooves  indicate 
the  intimate  manner  in  which  it  is  adapted  to  the  two  innominate  veins.  Above 
the  left  innominate  vein  the  two  lobes  of  the  thymus  ascend  to  an  unequal  height 
into  the,  neck.  They  are  placed  in  front  of  the  trachea,  and  extend  outwards 
so  as  to  overlap  the  termination  of  the  innominate  artery  on  the  right  side  and 
the  left  common  carotid  artery  on  the  left  side.  One  or  other  of  the  lobes  may 
rise  as  high  as  the  thyroid  gland,  but  as  a  rule  both  fall  somewhat  short  of 
this  organ,  and  the  lobe  which  ascends  highest  is  usually  attached  to  the  corre- 
sponding lateral  lobe  of  the  thyroid  body  by  a  strand  of  connective  tissue. 
82  a. 


1220 


THE  DUCTLESS  GLANDS. 


After  the  second  year  the  thymus  gland  remains  stationary,  or  it  begins  slowly 
to  diminish  in  size,  but  when  puberty  is  reached  a  rapid  degeneration  sets  in.  Its 
lobules  become  intiltrated  with  tat  and  loose  strands  of  connective  tissue.  Waldeyer 
has  shown,  however,  that  throughout  the  whole  of  life  it  not  only  retains  something 
of  its  old  form,  but  also  that  tlie  degeneration  is  never  complete.  Preserved  within 
its  substance  (either  uniformly  diffused  through  it  or  in  distinct  masses)  there  may 
always  be  found  remains  of  the  original  thymus-tissue.  Indeed,  more  of  the  gland 
is  retained  in  the  adult  than  is  generally  supposed.  It  is  easy  to  demonstrate 
in  subjects  hardened  by  formalin-injection  that  as  a  rule  both  lobes  are  present  in 
the  front  part  of  the  superior  mediastinum  in  the  form  of  two  elongated  finger- 
like bodies. 

Blood-vessels  and  Nerves. — The  arteries  Avliidi  cany  blood  to  tlie  thymus  come  from  the 
inferior  thyroid,  the  internal  mammary,  and  perhaps  also  from  other  sources.  The  veins  join 
the  neiglibouring  venous  trunks— viz.  the  inferior  thyroid,  the  iirternal  mammary,  and  the  two 
innominate  veins. 

The  nerves  to  the  tliymus  are  derived  from  the  vagus  and  sympathetic  trunks. 

The  lymphatic  vessels  are  of  large  size,  and  accompany  the  blood-vessels. 

Structure  of  the  Thymus. — The  thymus  is  composed  of  a  large  number  of  small 
polyhedral  lobules.  The  sheath  which  envelops  the  organ  sends  oif  f rom  its  deep  surface 
fine  partitions  or  septa  which  pass  into  the  gland  and  separate  the  different  lobules  from 
each  other. 

Each  lobule  is  composed  of  clusters  of  lymphoid  follicles,  with  a  small  amount  of 
delicate  connective  tissue  intervening  between  them.  A  follicle  consists  of  an  outer 
cortical  and  an  inner  or  central  medullary  portion.  Both  are  formed  of  adenoid  tissue, 
but  in  the  cortex  tlie  lymphoid  cells  are  packed  much  more  closely,  whilst  in  the  medulla 
the  retifornr  matrix  is  coarser  and  the  lymphoid  cells  less  numerous.  Further,  the  medulla 
contains  the  concentric  corpumles.  of  liassall.  These  are  curious  bodies,  composed  of 
flattened  cells  arranged  concentrically  around  a  granular  nucleated  corpuscle. 

The  blood-vessels  form  a  fine  plexus  around  the  various  follicles,  and  from  this 
capillaries  penetrate  into  the  central  medulla. 

Development  of  the  Thymus  Body. — The  thymus  gland  is  derived  from  the 
hypoblastic  lining  of  the  pharynx.  It  takes  oiigin  as  a  tubular  diverticulum  from  the 
dorsal  part  of  the  pharyngeal  aspect  of  the  third  visceral  cleft  on  each  side  (see  p.  35). 
This  diverticulum  has  thick  epithelial  walls,  and  it  grows  by  rapid  proliferation  of  its  cells. 
It  extends  downwards  on  the  side  of  the  trachea  towards  the  pericardium,  and  coming 
into  contact  with  the  corresponding  h3^poblastic  outgrowth  of  the  opposite  side,  the  two 

lobes  of  the  organ  are  formed — one  from  each 
latei'al  diverticulum.  The  narrow  upper  part 
of  the  outgrowth  remains  for  a  time  tubular, 
and  connected  with  the  phai-yngeal  cleft  from 
which  it  originates.  Ultimately  this  connexion 
is  broken  through,  and  the  expanded  lowef  end 
sends  out  solid  bud-like  branches  after  the 
manner  of  an  acinous  gland.  The  connective 
tissue  sheath  and  framework  of  the  thymus 
are  derived  from  the  surrounding  mesoblast. 

Originally  epithelial  in  its  composition,  the 
thymus  becomes  lymphoid  by  the  rapid  pro- 
liferation of  its  cells.  The  products  of  this 
division  become  the  lymphoid  cells  of  the 
follicles  of  the  gland.  The  corpuscles  of 
Hassall  were  formerly  believed  to  be  epithelial 
remnants,  but  this  is  now  known  not  to  be  the  case,  as  the  transformation  of  the  original 
elements  of  the  organ  into  lymj)hoid  cells  is  complete.  The  corpuscles  of  Hassall  are 
derived  from  the  repeated  divisions  of  one  cell,  the  products  of  wdiich  remain  attached  to 
each  other. 

THE  CAKOTID  AND  COCCYGEAL  BODIES. 

The  carotid  body  i.s  a  minute  oval  reddisl)-l)rown  structure  placed  on  the  deep 
aspect  of  the  common  carotid  artery  at  the  })oint  where  it  bifurcates  into  its  two 
terminal  branches.  It  is  closely  coniujcted  with  the  sympatbetic  nerve  filaments 
which    twine   around    the   carotid   vessels,  and    nuuHirous  minute  arterial  twig? 


Groove  foi 
pulmonary  arte  r\ 


(iroove  for  left 
Miiiiate  vein 
Groove  for 
vena  cava 
superior 

Mediastinal 
surface 


Tericarclial  surface 
Fig.  87.5.— Deep  Surface   of  Thymus   Glanu, 

TAKEN     FROM     A    FuiTOS     HARDENED    BY     FoK- 
MALIN-INJBCTION. 


THE  CAROTID  AXD  COCCYGEAL  BODIES. 


1221 


enter  it.     In  structure  the  carotid  body  is  composed  of  nodular  masses  of  poly- 

CHiitral  blood -spac-  Capillaries 


Capillarif 


■I'apillaries 


From   J.  W.  Thomson  Walker. 


terial  branches 


'  iod-space 

Fig.  876. — Section  throi-gh  C(hxv(;eal  Body  (highly  magiiified). 

hedral  epithelial-like  cells,  separated    from  each   other  by  strands  of  connective 
tissue.     Wide,  thin -walled   tortuous 
capillaries  are  brought  into  intimate 
relation  with  the  cells. 

The  carotid  body  contains  chrom- 
affin cells,  and  Swale  Vincent  believes 
that  it  should  be  associated  as  regards 
both  origin  and  function  with  the 
medulla  of  the  suprarenal  capsule. 

The  coccygeal  body  is  a  small 
structure  placed  in  front  of  the  tip 
of  the  coccyx.  Branches  from  the 
middle  sacral  artery  enter  it,  and  its 
structure  is  similar  to  that  of  the 
carotid  body. 

Thomson  Walker,  who  has  made 
an  exhaustive  investigation  into  the 
constitution  of  the  coccygeal  gland, 
has  shown,  by  means  of  serial  sections 
through  the  region,  that  in  addition 
to  the  main  body  usually  described, 
there  are  numerous  other  minute  out- 
lying subsidiary  portions  of  the  gland 
grouped  around  the  middle  sacral 
artery  and  its  branches.  In  structure 
the  gland,  as  well  as  its  accessory  parts, 
consists  of  collections  of  round  or  poly- 
hedral cells  with  large  nuclei  arranged 
around  a  central  blood-space  (Archiv 
f.  mUcroscop.  Anatomie,  Bd.  Ixiv.). 
82  & 


Arterial  bi-aiiche: 


Accessory  coccygeal 
bodies 


Accessory  coccysea 
bodie; 


Entrance  of  artery 

into  main  carotid 

body. 

Accessory 
coccygeal  bodies 


Main  carotid  bodv— -(- 


Accessory 
coccygeal  bodies" 


Fig.  877.— Schema  ok  the  uelatiox  presented  by  the 
Coccygeal  Body  and  its  accessory  outlying  tarts 
TO  THE  Branches  ok  the  Middle  Sacral  Artery. 
(Reconstructed  from  serial  sections  through  the  region.) 
From  J.  W.  Thomson  Walker. 


SURFACE   AND   SURGICAL   ANATOMY. 

By  Harold  J.  Stiles. 

THE  HEAD  AXD  NECK. 

THE  CRANIUM. 

Scalp. — The  first  and  third  layers  of  the  scalp,  namely,  the  skin  and  the  occipito- 
frontalis  muscle,  are  firmly  united  by  fibrous  processes  which  pass  from  the  one  to 
the  other  through  the  second  or  subcutaneous  fatty  layer.  Intervening  between 
these  three  layers  and  the  pericranium  is  a  loose  cellular  layer  which  supports  the 
small  vessels  passing  between  the  scalp  proper  and  pericranium.  The  thin  peri- 
cranium, although  regarded  anatomically  as  periosteum,  possesses  very  limited 
bone-forming  properties ;  over  the  vertex  it  is  readily  separated  from  the  skull-cap, 
except  along  the  lines  of  the  sutures,  where  it  gives  off  intersutural  processes  to 
join  the  endosteal  layer  of  the  dura. 

The  free  blood-supply  of  the  scalp  is  for  the  purpose  of  nourishing  its  abundant 
hair  follicles  and  glands.  The  main  vessels  lie  in  the  dense  subcutaneous  tissue, 
and  are  superficial,  therefore,  to  the  occipito- frontalis  (Fig.  878).  The  arteries 
supplying  the  frontal  region  are  derived  from  the  internal  carotid,  while  those  for 
the  remainder  of  the  scalp  spring  from  the  external  carotid.  These  two  sets  of 
vessels  anastomose  freely  with  one  another,  and  freely  also  across  the  mesial  plane ; 
hence  the  failure  of  ligature  of  the  external  carotid  to  cure  cirsoid  aneurysm  of  the 
temporal  artery. 

"Wounds  of  the  scalp  bleed  freely,  and  the  vessels  fire  difficult  .to  ligature  on  account  of  the 
adhesion  of  tlieir  Avails  to  the  dense  subcutaneous  tissue.  In  extensive  flap  wounds  and  in  diffuse 
supjiuration  Ijeueath  tlie  occipito -frontalis  there  is  little  danger  of  sloughing  of  the  scalp. 
Abscesses  and  haemorrhages  superficial  to  tlie  occipito-frontalis  are  usually  limited  on  account  of 
the  density  of  the  subcutaneous  tissue.  Hjeinorrhage  beneath  the  occipito-frontalis  is  seldom 
extensive  on  account  of  the  small  size  of  the  vessels,  but  suppuration  in  this  situation  may 
rapidly  undermiin*.  the  whole  muscle  ;  incisions  to  evacuate  the  pus  should  be  made  early,  and 
parallel  to  the  main  vessels  of  the  scalp.  Extravasation  of  bloocl  beneath  the  pericranium  leads 
to  a  lia-matoma  wliich  is  limited  by  the  sutures. 

The  veins  of  the  scalp  communicate  with  the  intra-cranial  venous  sinuses—^ 
(1)  directly  through  their  anastomoses  with  the  large  emissary  veins,  namely,  the 
parietal,  which  opens  into  the  superior  longitudinal  sinus,  and  the  mastoid  and 
posterior  condyloid,  which  open  into  the  lateral  sinus ;  (2)  through  the  anastomoses 
of  the  frontal  and  supra-orbital  veins  with  the  ophthalmic  vein,  which  opens  into 
the  cavernous  sinus;  (3j  through  the  veins  of  the  diploe,  which  connect  the  veins 
of  the  scalp  and  the  pericranium  on  the  one  hand  with  those  of  the  dura  mater 
and  the  venous  sinuses  on  the  other;  (4)  through  small  veins  which  pass  from  the 
pericranium  through  the  bones  and  the  intersutural  membranes  to  the  dura.  It  is 
along  these  various  channels  that  pyogenic  infection  may  extend,  from  the  scalp 
and  pericranium,  through  the  bone  to  the  dura  mater  and  venous  sinuses,  and  from 
the  latter  to  the  cerebral  veins,  the  pia-arachnoid,  and  the  substance  of  the  brain. 
More  rarely  the  infection  spreads  from  the  cranial  cavity  along  the  emissary  veins 
to  the  scalp. 

1222 


THE  CKANIUM. 


1223 


The  lymphatics  of  the  auterior  part  of  the  scalp  join  tlie  facial  lymphatics  ;  those 
of  the  temporal  and  parietal  regions  open  into  the  pre-auricnlar  and  parotid 
lymphatic  glands,  situated  in  front  of  and  below  the  ear,  and  into  the  post-auricular 


:^))j'Jr--'|.^.\!--'J->?-pi»:-^'7i"'M'i  ^'p'"  '•'  suiierfifial  fascia 


Epicranial  aponeurosis. 

Lax  connective  tissue — - —  L-I^^l^ 

Pericranium — siu.  "  i   "^^ t' 

Outer  table  of  cranial  wall .. .  .1   .       \  . 


Anastomosis  between  arteries 
scalp  and  those  of  the  dura  mater 
Inner  table  of  cranial  wall- 
Dura  mater- 
Parasinoidal  sinus- 
Cerebral  vein  opening  into 
superior  longitudinal  sinus 


Jries  of     'A*>«?yv^B^/  f'^,>iSv^*  »  ?  S  41 


Inli'gument 

Artery  in  suiKjrticial  fascia 


Vein  of  the  diploe  connecting 
tilt;  veins  of  the  scalp  with  those 
of  the  dura  mater 

Vein  in  dura  mater 

Arachnoid  mater 
Pia  mater 
Pacchionian  hody 
Cortex  cerebri 

Superior  longitudinal  sinus 

Vein  in  pia-arachnoid 

Sub-arachnoid  space 


Fig.  S7S. — Diaghammatic  Representation  of  a  Coronal  Section  through  the  Scalp,  Cranium, 
Meninges,  and  Cortex  Cerebri  (moditied  Irom  Cunningham). 

or  mastoid  glands,  situated  upon  the  insertion  of  the  steruo-mastoid  muscle.  The 
lymphatics  of  the  occipital  region  open  into  the  occipital  glands,  which  lie  close  to 
the  occipital  artery  where  it  becomes  superficial  in  the  scalp. 

Bony  Landmarks  of  the  Cranium. — At  the  root  of  the  nose  is  the  ironto- 
nasal  suture  (nasion) ;  a  little  above  it  is  the  glabella,  a  slight  prominence  which 
connects  the  superciliary  ridges.  About  1  in.  below  the  posterior  pole  of  the 
cranium,  and  2  in.  above  the  spine  of  the  axis,  is  the  external  occipital  protuber- 
ance (inion).  In  the  child  the  protuberance  is  not  developed ;  its  position  may  be 
defined  by  taking  a  point  at  the  junction  of  the  upper  and  middle  thirds  of  a  line 
extending  from  the  posterior  pole  of  the  skull  to  the  spine  of  the  axis.  About  a 
third  of  the  distance  from  the  nasion  to  the  inion  is  the  bregma  or  junction  of  the 
coronal  and  sagittal  sutures ;  with  the  head  in  the  natural  erect  posture  the  bregma 
corresponds  to  the  middle  of  a  line  carried  across  the  vertex  between  the  pre-auri- 
cular  points  of  the  zygomatic  arches. 

At  birth  the  position  of  the  bregma  is  occupied  by  the  anterior  fontanelle,  a 
rhomboidal  membranous  area  which  generally  becomes  ossified  at  abi;)ut  the 
eighteenth  month.  The  size  and  date  of  closure  of  the  fontanelle,  as  well  as  its 
tension  and  pulsation,  are  all  points  to  be  carefully  noted  in  the  clinical  examina- 
tion of  children. 

The  lambda,  or  junction  of  the  sagittal  and  lanibdoidal  sutures,  situated  1\  in. 
above  the  inion,  can  generally  be  felt  through  the  scalp ;  a  line  drawn  from  it  to 
the  posterior  border  of  the  root  of  the  mastoid  process  corresponds  to  the  lambdoidal 
suture.  In  the  adult  the  -par ieto- occipital  fissure  of  the  brain  lies  opposite,  or  a  few 
millimetres  in  front  of,  the  lambda ;  in  the  child,  however,  the  fissure  may  be  as 
much  as  1  in.  in  front  of  it. 

Crossing  the  supra-orbital  margin  close  to  its  inner  angle,  a  finger's-breadth 
from  the  middle  line,  are  the  supra-trochlear  nerve  and  the  frontal  branch  of  the 
ophthalmic  artery ;  the  latter  nourishes  the  tiap  in  the  operation  of  rhinoplasty. 
At  the  junction  of  the  inner  and  middle  thirds  of  the  supra-orbital  margin,  1  in. 


1224:  SUKFACE  AND  SUEGICAL  ANATOMY. 

from  the  middle  line,  is  the  supra-orbital  notch  or  foramen,  the  guide  to  the  supra- 
orbital vessels  and  nerves.  A  little  above  the  level  of  the  outer  canthus  of  the  eye- 
lid is  the  fronto-malar  suture,  immediately  above  which  is  the  external  angular 
process  of  the  froutal  bone.  At  the  posterior  end  of  the  suture  the  temporal  branch 
of  the  orbital  nerve  pierces  the  temporal  fascia  to  reach  the  scalp.  Half  an  inch 
above  the  suture  is  the  lower  margin  of  the  cerebral  hemisphere ;  while  half  an  inch 
below  the  suture  is  a  small  tubercle  on  the  posterior  border  of  the  malar  bone ;  a 
line  drawn  from  this  tubercle  to  the  lambda  gives  the  line  of  the  parallel  fissure 
and  of  the  descending  comu  of  the  lateral  ventricle. 

The  zygomatic  arch,  an  important  landmark,  is  horizontal  when  the  head  is  in 
the  natural  position,  and  is  on  the  same  level  as  the  lower  margin  of  the  orbit  and 
the  inion ;  its  upper  border  is  at,  or  not  infrequently  a  little  above,  the  level  of 
the  lower  lateral  margin  of  the  hemisphere.  The  upper  border  of  the  zygoma  may 
be  traced  backwards  immediately  above  the  tragus  and  the  external  auditory  meatus 
to  become  continuous  with  the  ridge  formed  by  the  supra-mastoid  portion  of  the 
temporal  crest.  The  part  of  the  posterior  root  of  the  zygoma  which  lies  immed- 
iately in  front  of  the  upper  end  of  the  tragus  constitutes  a  valuable  landmark  which 
may  with  advantage  be  termed  the  pre-auricular  point  of  the  zygoma,  while  by  the 
term  post-auricular  point  is  understood  that  point  upon  the  supra-mastoid  crest 
which  lies  immediately  behind,  and  a  finger's-breadth  below,  the  upper  attachment 
of  the  auricle.  The  temporal  vessels  and  the  auriculo-temporal  nerve  cross  the 
zygoma  at  the  pre-auriclar  point,  and  it  is  here  that  the  pulsations  of  the  temporal 
artery  may  be  felt  during  the  administration  of  an  ansesthetic,  or  the  vessel 
compressed  for  the  purpose  of  checking  bleeding  from  the  temporal  region  of  the 
scalp.  The  termination  of  the  auriculo-temporal  nerve  in  the  neighbourhood 
of  the  parietal  eminence  is  often  the  seat  of  a  neuralgic  pain  in  irritative  condi- 
tions about  the  external  auditory  meatus,  the  latter  being  supplied  by  this  nerve. 

Two  inches  vertically  above  the  pre-auricular  point  is  the  lower  end  of  the 
fissure  of  Rolando.  Two  inches  vertically  above  the  middle  of  the  zygomatic  arch 
is  the  pterion  (spheno-parietal  suture),  a  point  which  cannot  be  felt,  but  which  is 
nevertheless  of  topographical  importance,  as  it  overlies  the  Sylvian  point  (the  point 
where  the  Sylvian  fissure  breaks  up  into  its  three  branches)  and  the  anterior  branch 
of  the  middle  meningeal  artery.  A  point  three  fingers'-breadth  vertically  above  the 
middle  of  the  zygomatic  arch,  on  the  left  side,  will  mark  the  position  of  the  centre 
of  Broca's  convolution  (posterior  extremity  of  the  left  inferior  frontal  convolution). 

The  frontal  eminence  (better  marked  in  the  child)  overlies  the  middle  frontal 
convolution.  The  parietal  eminence,  which  varies  considerably  in  the  definiteness 
with  which  it  can  be  recognised,  overlies  the  termination  of  the  posterior  hori- 
zontal limb  of  the  fissure  of  Sylvius,  and  therefore  also  the  supra-marginal  convolution, 
which  is  named  by  Turner  the  convolution  of  the  parietal  eminence.  The  part  of 
the  temporal  crest  which  intervenes  between  the  external  angular  process  and  the 
coronal  suture  lies  a  little  above  the  level  of  the  inferior  frontal  sulcus.  The 
highest  part  of  the  temporal  crest  crosses  the  Eolandic  area  at  the  junction  of  its 
middle  and  lower  thirds,  that  is  to  say,  at  the  junction  of  the  motor  areas  for  the 
arm  and  face.  In  the  child,  the  temporal  muscle,  which  is  relatively  much  smaller 
than  in  the  adult,  reaches  only  a  short  distance  above  the  squamous  suture,  and. 
therefore,  only  as  far  as  the  level  of  the  lower  end  of  the  fissure  of  Kolando. 

The  tliickncss  of  tlie  skull-cap  varies  at  different  parts  and  in  different  individuals.  The 
inner  table  is  only  half  the  tliickness  of  the  outer  table,  but  l)oth  possess  the  same  degree  of  elas- 
ticity. When  the  vault  is  fractured  from  direct  violence,  tlie  inner  table  is  more  extensively 
fissured  than  the  outer  table,  because  tlie  elements  of  the  latter  are  compressed,  while  those  of  the 
former  are  stretched  apart.  Tlie  weak  an^as  at  the  base  of  the  skull  through  which  fractures  arc 
liable  to  extend  ar<; :  in  tlie  anterior  cranial  fossa,  the  orbital  plates  of  the  frontal  bone,  and  the 
cribriform  ])late  of  the  ethmoid  ;  in  the  middle  cranial  fossa,  the  region  of  the  glenoid  fossa  of 
the  temi)oral  ix>ne,  aiul  of  the  foramen  ovale  of  the  s])henoid  ;  in  the  posterior  fossa,  the  cerebellar 
fossa;  of  the  occipital  Vjone.  The  strong  petrous  temi)oral  is  weakened  by  the  tympanic  cavity 
and  by  the  deep  jugular  fossa. 

Cranio-Cerebral  Topography.  —  Of  the  many  methods  which  have  been 
devi.scd  for  mai)piiig  out  the  ndatifms  of  the  cranial  contents  to  the  scalp,  that 
introduced    by    Professor   Chiene   is,   probably,   the  most   useful   from  a  clinical 


THE  CEANIUM.  1225 

point  of  view ;  no  figures  or  angles  liave  to  be  remembered,  aiul  the  primary 
surface  lines  are  drawn  from  bony  points  which  are  not  variable,  whilst  the 
secondary  lines  are  drawn,  for  the  most  part,  between  mid-points  of  the  primary 
lines.     The  method  is  as  follows  (Figs.  879  and  881) : — 

"  The  head  being  shaved,  find  in  the  mesial  line  of  the  skull  between  the 
glabella  (G)  and  the  external  occipital  protuberance  (0)  the  following  points : — 

"  First,  the  mid-point  (M) ;  second,  the  three-quarter  point  (T);  third,  the  seven- 
eighth  point  (S). 

"  Find  also  the  external  angular  2yrocess  (E),  and  the  root  of  the  zygoma  (pre- 
auricular point)  (P),  immediately  above  .and  in  front  of  the  external  auditory 
meatus.  Having  found  these  five  points,  join  EP,  PS,  and  ET.  Bisect  EP  and 
PS  at  N  and  Ft. "  Join  MN  and  MR.  Bisect  also  AB  at  C,  and  draw  CD  parallel 
to  AM." 

The  line  MA  corresponds  to  the  superior  and  inferior  precentral  sulci,  and  may 
therefore  be  termed  the  pre-central  line.  The  07-igins  of  the  superior  and  inferior 
frontal  sulci  may  be  indicated  by  trisecting  MA  at  the  points  K  and  L,  the  latter 
point  being  at  the  level  of  the  temporal  crest. 

Tlie  line  ET,  termed  the  oblique  or  Sylvian  line,  intersects  the  pre-central  line  at 
the  point  A,  which  overlies  the  pterion,  and  corresponds  therefore  to  the  Sylvian 
point  of  the  fissure  of  Sylvius  and  to  the  anterior  division  of  the  middle  meningeal 
artery.  AC  overlies  the  posterior  horizontal  limb  of  the  fissure  of  Sylvius,  which 
terminates  at  the  level  of  the  temporal  crest,  in  the  lower  part  of  the  triangle  HCB. 
This  triangle  contains  the  parietal  eminence,  and  may,  therefore,  be  termed  the 
supra-marginal  triangle.  The  termination  of  the  Sylvian  line,  at  the  three-quarter 
sagittal  point  T,  overlies  the  parieto- occipital  fissure. 

By  joining  TR,  EG.,  a  triangle  is  mapped  out  which  delimits  the  outer  surface 
of  the  occipital  lobe  ;  the  line  TE  corresponds  to  the  lambdoidal  suture,  while  EG 
corresponds  to,  or  lies  a  -little  above,  the  tentorium  and  the  upper  border  of  the 
lateral  sinus. 

CD,  the  post-central  line,  corresponds  to  the  superior  postcentral  sulcus,  and  lies  a 
little  behind  the  inferior  postcentral  sulcus. 

The  parallelogram  AMDC  overlies  the  Rolandic  area,  i.e.  the  ascending  frontal 
and  the  ascending  parietal  convolutions,  separated  by  the  fissure  of  Eolando. 

The  pentagon  ABEPN  maps  out  the  temporal  lobe,  with  the  exception  of  its 
apex,  which  is  directed  downwards,  forwards,  and  inwards,  a  finger's-breadth  in 
front  of  the  point  N. 

A  finger's-breadth  below  AB  is  the  parallel  sulcus,  the  posterior  extremity  of 
which  turns  upwards  to  terminate  at  B,  the  point  which  indicates,  therefore,  the 
position  of  the  angular  gyrus. 

The  fissure  of  Rolando  may  be  mapped  out  upon  the  scalp  by  drawing  a  line 
downwards  and  forwards  for  a  distance  of  3|  in.  from  a  point  half  an  inch  behind 
the  mid-sagittal  point  M  at  an  angle  of  67°  to  the  sagittal  line  (Hare).  This 
angle  may  readily  be  found  by  Chiene's  plan  of  folding  a  sheet  of  paper  first  to 
half  a  right  angle  and  again  to  a  quarter  of  a  right  angle  (45°  +  22-5^  =  67"5'). 
According  to  Cunningham,  the  average  angle  which  the  fissure  makes  with  the 
sagittal  line  is  70°. 

The  topographical  distribution  of  function  in  the  cerebral  cortex  is  shown  in 
Fig.  879,  in  which  the  areas  worked  out  by  Grlinbaum  and  Sherrington  in  the 
anthropoid  apes  have  been  transferred  to  the  human  brain.  The  above  observers 
have  shown  that,  while  the  motor  area  occupies  the  whole  length  of  the  pre-central 
convolution  and  of  the  fissure  of  Eolando  (with  the  exception  of  its  very  extremities), 
it  nowhere  extends  on  to  the  exposed  surface  of  the  post-central  gyrus ;  nor  does  it 
extend  as  far  down  on  the  mesial  surface  of  the  hemisphere  as  the  calloso-marginal 
fissure.  Extirpation  of  the  hand  area,  for  example,  is  followed  by  severe  paralysis 
of  the  hand,  but  the  use  and  power  of  the  hand  is  regained  in  a  few  weeks ;  abla- 
tions, on  the  other  hand,  of  even  large  portions  of  the  post-central  gyrus  do  not 
give  rise  even  to  transient  paralysis. 

In  some  of  the  animals  experimented  on,  the  motor  area  was  lound  to  extend 
to  the  deeper  part  of  the  posterior  wall  of  the  fissure  of  Eolando.     Anteriorly  it 


1226 


SURFACE  AKD  SURGICAL  ANATOMY, 


extended  into  the  pre-central  sulci  as  well  as  into  the  occasional  sulci  which  cross 
the  pre-central  gyrus  ;  indeed  the  hidden  part  of  the  motor  area  fully  equals  in 
extent  that  contVibuting  to  the  free  surface  of  the  hemisphere.  The  motor  areas 
extend  a  little  in  front  of  the  superior  and  inferior  pre-central  sulci,  which  cannot 
therefore  be  regarded  as  physiological  boundaries. 

Reference  to  Fig.  879  shows  that  of  the  main  areas  that  for  the  lower  extremity 
occupies  the  upper  third  of  the  motor  region,  that  for  the  upper  extremity  the 


Fig.  879. — Cuankj-Ckkkbkal  Topogkaphy. 
Shows  relation.s  of  the  motor  and  seii.snry  areas  to  tlie  convolutions,  and  to  Chiene's  lines. 


G.   Glabella. 

O.    Inion. 

M.    Mid-point  between  G  and  0. 

T.    Mid-point  Vjetween  M  and  O. 

S.     Mid-point  between  T  and  O. 

E.    External  angular  process. 

P.    Fvoot  of  zygoma  (pre-auricular  point). 

N.    Mid-point  of  EF. 

R.    Mid-point  of  FS. 


C.  Mid-point  of  AB. 

CD  is  drawn  p.irallel  to  AM. 

Z.  Post-auricular  point. 

VW.  Guide  to  anterior  limit  of  lateral  sinus. 

Y.  Mastoid  antrum. 

*'.  Site  at  wliicli  subaracliuoid  space  may  be  opened. 

*-.  Site  for  draining  lateral  ventricle  (Kocher). 

*^.  Site  for  draining  lateral  ventricle  (Keen). 


middle  third,  wiiile  the  iace  occupies  the  lower  third.  The  relatiye  topography  of 
the  chief  siib-divisions  of  these  main  areas  is  shown  in  Fig.  880.  It  must  be 
remembered,  liowever,  that  there  exists  mucli  oyerlapping  of  the  adjacent  areas. 

The  lateral  ventricle  may  be  tapped  or  drained  from  above,  by  traversing  brain 
tissue  for  a  depth  of  4  to  5  cm.  througli  the  superior  frontal  sulcus,  1|  in.  (two 
fingers'-breadth;  in  front  of  the  ])oint  K,  the  instrument  being  directed  downw;ard8 
and  backwards  (Kocher;. 

Keen  drains  the  ventricles  through  an  opening  1;^  in.  behind   the  external 


THE  CRANIUM. 


1227 


ANUS    &    VAGINA 


MASTICATION 


.  880. — Scheme  .showing  Relative  Topogkaphv  ok  the  Chief 
SuBDivisiON.s  OF  THE  MoTOR  Area  (ailaptcfl  from  Gninbaum  and 
Sherrington). 


auditory  meatus  and  the  same  distance  above  Reid's  base  line  (a  line  drawn 
backwards  from  the  lower  margin  of  the  f>rl>it  tliroiigh  the  centre  of  the  external 
auditory  meatus),  the  in- 
strument being  passed  into 
the  brain  towards  the  sum- 
mit of  the  opposite  auricle. 
If  the  ventricle  be  not  dis- 
tended it  will  be  reached  at 
a  depth  of  two  inches  from 
the  surface. 

To  open  the  subarachnoid 
space,  the  pin  of  a  small 
trephine  is  placed  over  the 
mid-point  of  the  line  EA  ; 
the  dura  is  incised  as  it 
crosses  the  stem  of  the 
fissure  of  Sylvius  from  the 
frontal  lobe  to  the  anterior 
extremity  of  the  temporal 
lobe.  Care  must  be  taken 
to  keep  in  front  of  the  ^''ig 
middle  meningeal  artery. 

The  cisterna  magna,  situ- 
ated between  the  back  part  of  the  under  surface  of  the  cerebellum  and  the 
medulla  oblongata,  may  be  reached  by  turning  down  a  flap  of  soft  parts,  and 
removing  a  circle  of  bone  a  little  above  the  foramen  magnum,  and  immediately 
to  one  side  of  the  middle  line  so  as  to  avoid  the  occipital  sinus.  The  fourth 
ventricle  may  be  opened  up  by  making  a  somewhat  larger  trephine  opening  in 
the  mesial  plane  and  separating  the  posterior  extremities  of  the  tonsillar  lobes 
of  the  cerebellum. 

To  expose  the  lateral  hemisphere  of  the  cerebellum,  trephine  over  the  centre  of 
a  line  drawn  from  the  tip  of  the  mastoid  process  to  the  external  occipital  pro- 
tuberance. The  occipital  artery  and  the  mastoid  emissary  vein  will  be  divided 
in  turning  down  the  flap. 

Meningeal  Arteries. — When  the  calvarium  is  removed  the  meningeal  arteries 
are  found  to  adhere  firmly  to  the  dura.  Of  these  vessels  the  middle  meningeal 
artery  is  the  only  one  of  surgical  importance.  It  is  frequently  lacerated  in 
fractures  of  the  skull ;  the  blood  is  generally  extravasated  between  the  dura  and 
the  bone,  and  the  bleeding  point  lies  beneath  the  clot.  After  entering  the  cranial 
cavity  through  the  foramen  spinosum,  the  main  trunk,  which  is  usually  about 
11  in.  in  length,  runs  outward  and  slightly  forwards  to  bifurcate  into  anterior  and 
posterior  divisions  at  a  point  a  finger's-breadth  above  the  middle  of  the  zygomatic 
arch,  viz.  at  or  close  behind  the  point  N.  When  the  main  trunk  is  short  the 
Ijifurcation  takes  place  opposite  the  middle  of  the  zygomatic  arch. 

The  anterior  and  larger  division  passes  upwards,  with  a  slight  forward  con- 
vexity, a  little  behind  the  spheno  -  squamous  suture  and  across  the  pterion  to 
the  anterior  inferior  angle  of  the  parietal  bone.  From  this  point  the  vessel  is 
continued  upwards  and  slightly  backwards  behind  the  coronal  suture ;  it  gives 
off  branches  which  ascend  over  the  motor  area.  The  position  and  general 
direction  of  the  anterior  branch  may  be  said  to  correspond  to  the  line  LN ;  it 
follows,  therefore,  that  the  artery  will  be  encountered  in  trephining  over  the  lower 
and  anterior  part  of  the  Eolandic  area,  especially  over  the  motor  centres  for  the 
tongue  and  face. 

Tlie  posterior  division  passes  almost  horizontally  backwards  towards  the 
posterior  inferior  angle  of  the  parietal  bone. 

To  expose  the  trunk  of  the  vessel  and  its  bifurcation,  the  trephine  is  applied 
immediately  above  the  middle  of  the  zygomatic  arch.  To  expose  the  anterior 
division  the  pin  of  the  trephine  may  be  applied  at  the  point  A,  which  strikes  the 
artery  as  it  crosses  the  pterion  and  grooves  the  anterior  inferior  angle  of  the  parietal 


1228 


SUKFACE  AND  SUEGICAL  ANATOMY. 


bone.  The  lower  segment  of  the  disc  of  bone  removed  is  much  thicker  than  the  upper, 
as  it  involves  the  prominent  ridge  which  passes  from  the  tip  of  the  great  wing  of  the 
sphenoid  on  to  the  anterior  inferior  angle  of  the  parietal  bone.  At  the  anterior 
inferior  angle  of  the  parietal  bone,  the  artery  frequently  runs  in  a  canal  for  a 
distance  of  half  an  inch.  It  follows,  therefore,  that  a  considerable  thickness  of 
bone  has  to  be  sawn  through  at  the  lower  segment  of  the  circle  before  the  disc  can 


Guiding  lines  (Cliiene 

G.    Glabella. 

0.    Inion. 

M.   Mid-point  biitween  G  and  0. 

T.    Mid-point  between  M  and  O. 

H.     Mid-point  between  T  and  0. 

E.    External  anguliir  jiroce.s.s. 

P.     Root  of  zygoma  (pre-aurieular  point). 

N.    Mid- point  of  EP. 

R.    Mid-point  of  PS. 


ChaiMO-Ckuebual  Topography. 

hie  ;  sutures,  green  ;  meningeal  arteries,  red  ;  sulci,  black. 


C.      Mid-point  of  AB, 

MA  is  divided  into  thirds  at  K  and  L. 

CD    is  drawn  parallel  to  AM. 

Z.      Post-auricular  point. 

V\V.  Guide  to  anterior  limit  of  lateral  sinus. 

V.      Mastoid  antrum. 

*'.      Site  at  which  subarachnoid  space  may  be  opened. 

*-.      Site  for  draining  lateral  ventricle  (Kocher). 

*•'.      Site  for  draining  lateral  ventricle  (Keen). 


be  removed,  and  during  the  removal  l)leeding  may  occur  from  the  artery  as  it  lies 
in  the  canal. 

Vogt  localises  the  anterior  division  at  a  point  a  thumb's-breadth  behind  the 
tubercle  on  the  posterior  border  of  the  malar  bone  and  two  fingers'-breadth  above 
the  zygoma.  Kronlein  trephines  at  a  point  1^  in.  behind  the  external  angular 
process,  on  a  line  drawn  from  the  supra-orbital  margin  backwards  parallel  to 
Reid's  base  line.     If  the  centre  of  the  trephine  be  placed  at  tlie  mid-point  of  the 


THE  CEANIUM.  1229 

line  LA,  the  anterior  division  will  be  reached  above  the  canal  and  the  ridge  at  the 
anterior  inferior  angle  of  the  parietal ;  should  the  bleeding-point  be  lower  down, 
the  trephine  opening  may  be  enlarged  downwards  along  the  line  LN. 

The  course  of  the  posterior  division  may  be  indicated  upon  the  surface  by  draw- 
ing a  line  backwards  from  the  point  N  parallel  to  PE,  that  is  to  say,  a  finger's- 
breadth  above  the  zygoma  and  the  supra-mastoid  crest. 

When  the  frontal  branch  of  tlie  anterior  divisiou  is  injured,  the  clot  is  in  tlie  fronto-temporal 
region, and  involves  moie  especially  the  motor  area  for  the  face,  and,  on  the  leftside,  Broca's  con- 
volution ;  wlien  the  anterior  division  is  wounded,  the  clot,  which  is  larger,  involves  the  jjarieto- 
temporal  region,  and  the  motor  symptoms  are  due  to  j^ressure  upon  the  centres  for  the  arm  and 
face;  in  injuries  to  the  posterior  division  the  clot  overlies  the  parieto-occipital  region,  and  the 
localising  symptoms  are  sensory  /Kronlein).  In  more  extensive  meningeal  haemorrhage  the  clot 
may  cover  the  greater  part  of  the  hemisphere. 

The  superior  longitudinal  sinus,  which  enlarges  as  it  extends  backwards,  occupies 
the  mesial  plane  of  the  vertex  from  the  glabella  to  the  internal  occipital  pro- 
tuberance, where  it  opens  into  the  torcular  Herophili,  and  becomes  continuous 
usually  with  the  right  lateral  sinus.  Opening  into  the  sinus,  especially  in  the 
posterior  part  of  the  parietal  region,  are  the  para-sinoidal  sinuses,  into  which 
Pacchionian  glands  project.  In  opening  the  skull  over  the  posterior  part  of  the 
vertex,  the  edge  of  the  trephine  should  be  kept  at  least  three-quarters  of  an  inch 
from  the  mesial  plane. 

The  lateral  sinus  may  be  mapped  out  on  the  surface  by  drawing  a  line,  slightly 
convex  upwards,  from  a  point  a  little  above  the  level  of  the  external  occipital 
protuberance  to  the  asterion  (1^  in.  behind  and  1  in.  above  the  centre  of  the 
external  auditory  meatus)  at,  or  a  little  in  front  of,  the  point  E,  which 
forms  the  highest  imrt  of  the  arch  of  the  sinus ;  from  this  point  the  iipper  border 
of  the  sinus  follows  the  line  PE  for  a  distance  of  one  inch,  and  then  curves  down- 
wards and  forwards  to  a  point  three-quarters  of  an  inch  below  and  behind  the 
centre  of  the  external  auditory  meatus,  where  it  finally  curves  inwards  and 
forwards  to  open  into  the  jugular  bulb,  which  occupies  the  jugular  foramen. 
According  to  Moorhead  the  highest  part  of  the  sinus  lies  a  finger's-breadth  above 
the  middle  of  a  line  extending  from  the  inion  to  the  middle  of  the  external  auditory 
meatus.  The  anterior  horder  of  the  descending  or  mastoid  'jyortion  of  the  sinus  may 
be  mapped  out  by  drawing  a  line  VW  from  a  point  a  finger's-breadth  behind  the 
post-auricular  point  of  the  temporal  crest  to  the  anterior  border  of  the  tip  of  the 
mastoid  process.  In  wounds  of  the  sinus  the  haemorrhage  is  very  free,  owing  to 
the  inability  of  its  walls  to  collapse,  but  the  bleeding  is  easily  controlled  by 
plugging. 

Of  the  cerebral  .arteries,  the  middle  supplies  almost  the  whole  of  the  motor  area, 
and  one  of  its  lenticulo-striate  branches,  which  enters  the  brain  at  the  anterior 
perforated  space,  is  called  "  the  artery  of  cerebral  hcemorrhage  "  from  the  frequency 
of  its  rupture  in  apoplexy.  The  extravasated  blood  involves  the  motor  part  of  the 
internal  capsule.  The  postero-mesial  central  branches  of  the  posterior  cerebral 
artery,  which  enter  the  brain  at  the  posterior  perforated  spot,  supply  the  optic 
thalamus  and  walls  of  the  third  ventricle ;  hcemorrhage  from  one  of  these 
branches  is  apt  to  rupture  into  the  ventricle.  The  postero-lateral  central  branches 
of  the  posterior  cerebral  artery  supply  the  optic  thalamus,  and  when  one  of  these 
vessels  ruptures  the  haemorrhage  is  apt  to  invade  the  posterior  or  sensory  part  of 
the  internal  capsule. 

Ear. — The  skin  covering  the  outer  surface  of  the  auricle  is  tightly  Ijound 
down  to  the  perichondrium,  hence  inflammations  of  it  are  attended  with  little 
swelling  but  much  pain.  The  posterior  auricular  artery,  which  ascends  along  the 
groove  at  the  posterior  attachment  of  the  auricle,  is  immediately  anterior  to  the 
incision  for  opening  the  mastoid  antrum. 

The  external  auditory  canal,  the  general  direction  of  which  is  inwards,  forwards, 
upwards,  and  downwards,  possesses  various  curves  of  practical  importance.  The 
highest  part  of  the  upward  convexity,  which  is  also  the  narrowest  part  of  the  canal, 
is  situated  at  the  centre  of  its  osseous  portion  ;  beyond  this  the  floor  sinks  to  form  a 
recess  in  which  foreign  bodies  are  liable  to  be  imprisoned.     Of  the  two  horizontal 


1230 


SUEFACE  AND  SUEGICAL  ANATOMY. 


curves  the  outer  is  convex  forwards,  the  inner  concave  forwards.  The  skin  of  the 
osseous  portion  of  the  canal  is  thin  and  fused  with  the  periosteum,  hence  when 
chronically  inflamed  it  is  liable  to  give  rise  to  secondary  periostitis  and  osseous 
narrowing  of  the  canal. 

The  relations  of  the  osseous  walls  of  the  canal  are  of  importance  to  the  surgeon. 


Roof  of  mastoid  antrum 
Posterior  part  of  middle  fossa  of  slcull 


Posterior  branch  of  middle  meningeal  artery 

Anterior  branch  of  middle  meningeal  artery 


Portion  of  cerebellar  fossri 

forming  posterior  ^\all  of 

mastoid  antrum 

Interior  of  lateral  sinuS' 


Anterior  limit  of  lateral  smus 

Mastoid  antrum 


Spheno-temporal  sinus 
Trunk  of  middle  meningeal  artery 


Incus 

Membrana  tympani 


\  Tegmen  tympani 

Chorda  tympani  nerve 


Fig.  882. 


Head  of  malleus 
-View  of  the  Outer  Wall  of  the  Middle  Ear. 


Section  through  the  left  temporal  bone  of  a  child,  to  show  the  relations  of  the  middle  ear  and  mastoid  antrum 
to  the  middle  and  posterior  fossae  of  the  skull. 

The  whole  of  the  upper  wall  and  the  upper  half  of  the  posterior  wall,  developed 
from  the  squamous  portion  of  the  temporal  bone,  consist  of  two  layers  of 
compact  bone,  an  upper  and  a  lower,  which  are  continuous,  the  former  with  the 
inner  table,  the  latter  with  the  outer  table  of  the  skull.  The  upper  plate  passes 
inwards  to  the  petro-squamous  suture,  where  it  becomes  continuous  witli  the  outer 
edge  of  the  tegmen  tympani,  which  roofs  over  the  tympanic  attic  and  the  mastoid 
antrum :  the  lower  plate  bends  downwards  and  inwards  at  its  deepest  part  to  form 

the  lower  and  outer  wall  of 
the  tympanic  attic  and  the 
anterior  part  of  the  outer 
wall  of  the  antrum  (Traut- 
mann).  It  follows,  there- 
fore, that  when  the  mastoid 
antrum  is  abnormally  small, 
due  to  sclerosis  of  the  bone, 
or  when  it  is  encroached 
upon  by  a  far-forward  lateral 
sinus,  it,  along  with  the 
tympanic  attic,  can  be 
opened  by  perforating  the 
junction  of  the  upper  and 
posterior  walls  of  the  os- 
seous canal,  the  instrument  being  directed  inwards  and  slightly  upwards.  Upon 
the  upjter  and  posterior  segment  of  the  external  auditory  process  is  the  supra- 
meatal  spine  ;  this  small  Init  important  jjrocess,  developed  from  the  squamous  portion, 
can  usually  be  distinctly  made  out  in  the  living  suljject  by  pressing  upwards  and 
backwards  with  the  forefinger  placed  in  the  external  auditory  meatus. 

The  lower  half  of  the  posterior  wall  of  the  osseous  canal  (posterior  part  of  the 
tympanic  plate)  is  fused  with  the  anterior  part  of  the  mastoid  process,  and  closes  the 
lower  and  anterior  set  of  mastoid  cells  fborder  cells). 

Anteriorly  and  inferiorly  the  osseous  canal  is  related  respectively  to  thetemporo- 
maxillary  articulation  and  the  parotid  gland  ;  hence  it  follows  that  blows  upon  the 
chin  may  fracture  the  tympanic  plate  as  well  as  the  base  of  the  skull,  that  pain  on 


Membrana  flaccid; 


Anterior  tympano-, 
malleolar  fold 


Handle  of  malleu; 


Antero-superior 
quadrant 


Antero-inferior. 
quadrant 


Posterior  tympaiio- 

malleolar  fold 

Short  process  of 

malleus 

Long  process  of 

incus 

Postero-superior 
quadrant 


Postero-inferior 
quadrant 
(.'one  of  li^dit 


Fig.  88.3. 


-Left  Tympanic  Meiibuank  (as  viewed  from  the  external 
auditory  meatus),     x  3.    (From  Howden.) 


THE  CEANIUM. 


1231 


masticatiou  is  usually  complained  of  iu  acute  inflammatory  affections  of  the  meatus 
and  middle  ear,  and  that  in  young  children,  iu  whom  the  tympanic  plate  is  incom- 
pletely ossified,  suppurative  inHammation  is  liable  to  extend  from  tiie  ear  to  the 
parotid  region. 

Clinically,  to  obtain  a  view  of  the  membrana  tympani  ;i  spcculuui  and  a  retiectiug 
mirror  arc  employed  :  tlie  auricle  is  pulled  upwardrs,  bacivwards,  and  outwards,  in  order  to 


Middlf  fossa  of  skull 
Tensor  tyiiiiiuni  muscle 


I'locwssus  cochk'arifoiniis 
I       Eiuitience  of  external 


Ku.-.tai.liiaii  III 


Ketro-iiliaryii: 


al  sinus 

riur  fossa  of  skull 

toiil  jiroccss 


Stapes 
Promontory 
Fig.  884. — View  of  the  Inner  Wall  uk  ihl  iliDDi.K  Eak. 


Internal  carotid  artery 

Internal  jugular  vein 


Stctioii  through  the  left  temporal  boue  of  a  child,  to  show  the  relations  of  the  niiildle  ear  and  mastoid  antrum 
to  the  middle  aud  posteiior  fossae  of  the  skull. 

straighten  the  cartilaginous  part  ol"  the  canal.  The  healthy  membrane  is  pearly  gray,  semi- 
opaque,  slightly  concave  outwards,  and  obliquely  placed,  being  inclined  outwards,  especially 
above  and  behind. 

The  handle  and  short  process  of  the  malleus,  both  embedded  in  the  meiubrana  tympani, 
are  the  only  objects  distinctly  seen  when  the  healthy  ear  is  examined  with  the  sj)eciilum. 


Groove  for  i>osterior  branch  of  middle  meningeal  artery 

A'-*^'--  ■•  ',  antrum 


Mastoid  antrum 
Lateral  sinu 


iVIiddle  cranial  fossa 

Tegmen  tympani 


lyiiiiiaiiic  attic 


^.('hoi'da  tympani  nerve 
.Tensor  tympani  nmscle 


-  Handle  of  malleus 
-(  arotid  canal 
-Tympanic  membrane 


Jmiular  fossa 


L. Styloid  process 
Mastoid  process  j 

Stylo-mastoid  foramen 

Fk;.  885. — Section  thuocgh  Left  Temporal  Bonk,  showjni;  Octkk  Wall  of  Tympanic  CAvnv,  etc. 

The  short  process  of  the  malleus  projects  outwards,  and  presents  itself,  therefore,  as  u 
distinct  knob-like  projection  at  the  upper  part  of  the  membrane  ;  passing  forwards  and 
backwards  from  this  process  are  the  anterior  and  posterior  folds  of  the  membrana 
tympani  ;  they  form  the  lower  limit  of  Shrapnell's  membrane,  and  correspond  to  the  line 
of  the  chorda  tvmpani  nerve.  The  handle  of  the  malleus,  situated  at  the  junction  of  the 
two  upper  quadrants,  is  seen  passing  downwards  and  backwards  to  the  point  of  maximum 
concavity  of  the  membrane  (umbo),  situated  a  little  below  its  centre  (Fig.  883);  passing 


1232 


SURFACE  AND  SURGICAL  ANATOMY. 


downwards  and  forwards  from  the  umbo  is  the  trianyular  cone  of  reflected  light,  to  which 
too  much  importance  must  not  be  attached,  since  its  appearances  vary  considerably  in 
healthy  ears.  Normally,  the  long  process  of  the  incus  is  but  faintly  visible,  and  still  less 
so  are  the  promontory  and  foramen  rotund um ;  in  the  condition  of  Eustachian  obstruction, 
however,  in  which  the  membrane  is  indrawn,  these  structures,  along  with  the  folds  of  the 
drum,  become  more  distinct. 

In  performing  the  operation  of  'parace)itesis  of  the  tympcudc  membrane  the  postero- 
inferior  quadrant  is  the  site  chosen  for  making  the  puncture,  as,  in  addition  to  providing 
good  drainage,  it  is  farthest  removed  from  important  structures,  especially  the  chorda 
tympani  nerve. 

In  order  to  understand  the  clinical  importance  of  the  parts  seen  through  the  trans- 
lucent membrane,  it  is  necessary  to  study  the  relative  position  of  the  structure  of  the 
"  »ieso-ti/mjKiHii/H,"  that  is  to  say,  that  part  of  the  tympanum  which  lies  opposite  the 
tympanic  membrane.  If  the  tympanic  plate  and  the  tympanic  membrane  be  carefully 
removed  so  as  to  leave  the  ossicles  and  chorda  tympani  nerve  in  position,  it  will  be  seen 
that  the  head  of  the  malleus  and  the  l)ody  and  short  j)rocess  of  the  incus  are  altogether 
above  the  tympanic  membrane,  and  that  they  occupy  the  tympanic  attic  or  epitympanic 
space  (Fig.  J^'By).  At  the  junction  of  the  two  upper  quadrants  of  the  membrane  is  the  handle 
of  the  malleus,  which  is  directed  downwards,  backwards,  and  inwards.  The  short  process 
of  the  malleus  is  directed  outwards  a  little  below  the  deepest  part  of  the  roof  of  the 
osseous  external  auditory  canal.  Opposite  the  postero-superior  quadrant  are  the  long 
process  of  the  incus,  which  descends  behind  and  almost  parallel  to  the  handle  of  the 
malleus,  and  the  stapes,  which  is  directed  inwards  and  slightly  backwards  to  the  foramen 
ovale.  The  chorda  tympani  nerve  runs  from  behind  forwards  between  the  outer  surface 
of  the  upper  part  of  the  long  process  of  the  incus  and  the  inner  surface  of  the  neck  of 
the  malleus.  At  the  deepest  part  of  the  roof  of  the  osseous  canal  above  the  chorda 
tympani  nerve  and  the  short  process  of  the  malleus  is  a  notch  {notch  of  Rivini),  which 
is  occupied  by  the  flaccid  and  highest  portion  of  the  membrana  tympani  {ShrajmeH's 
vieinbrmie).  Opposite  the  postero-inferior  quadrant  of  the  drum-head  is  the  promontory 
of  the  cochlea,  below  and  behind  which  is  the  foramen  rotundum.  Opposite  the  antero- 
superior  quadrant  are  the  processus  cochleariformis,  the  tendon  of  the  tensor  tympani,  and 
the  passage  leading  towards  the  Eustachian  tube. 

The  inner  ivall  of  the  tympanic  cavity  is  related  to  the  internal  ear.     The  upper  ivall 


Roof  of  luasloid  uutniiu 


MiiJiUu  ciauial  fossa 


-Mastoid  aiitrum 


Gioo\  u  for  lateral  sinus 


Uroovi;  for 
iiiirldlc  iiieiiiu-^. 

goal  arteiy     7<^' 

Head  of^    '   /  X?.  V  '. 
malleus 


Body  of  iucus- 
I'aiial  for  Iriisor  tyiiijiaMi  ijiusc 


I'ortioii  of  i.'xtcrnal  .seiui- 
circular  canal, 


Elevation  caused  by 
;iqueduct  of  Fallopius 


Carotid  canal 

Menibiana  tj  njijani 

Styloid  process 

Facial  nerve 
I'oslcrior  margin  of  jugular  foramen 

Fllj.   886.— hjKCTlON    THKUUGU    I'KTUOUS   POKTION    OF    TkMI'UUAI.    BuNE    OK   ADULT. 

Sliowiiig  tlic  relation  of  tlie  middle  ear  to  the  iniildle  anil  posterioi-  foss;r  of  tlie  skull. 


is  separated  from  the  middle  fossa  of  the  skull  and  the  under  surface  of  the  temporal 
lobe!   of   the   brain   by  the  tegmen  tympani — a  thin  plate  of  bone,    which   is   continued 


THE  OeANIUM.  1233 

anteriorly  to  form  the  roof  of  the  osseous  portion  of  the  Eustachian  tube,  while  posteriorly 
it  roofs  over  the  mastoid  antrum.  Externally  tlic  tegmen  is  limited  by  the  petro- 
squamous suture,  which  may  remain  unossified  for  some  years  after  birth,  thus 
aiibrding  a  channel  along  whicli  pyogenic  infection  may  spread  from  the  middle  ear  to  the 
meninges  and  brain.  Infection  may  also  spread  along  the  small  veins  which  convey  blood 
from  the  tympanum  to  the  superior  petrosal  and  lateral  sinuses. 

The  Jloor  of  the  tympanum  is  formed  mainly  by  the  bone  forming  the  jugular  fossa, 
which  is  occupied  by  the  bulb  of  the  internal  jugular  vein.  When  the  lateral  sinus  is 
lai'ge  and  unusually  far  forward  the  bulb  is  likewise  large,  and  the  fossa,  which  is  con- 
sequently deeper,  may  arch  up  into  the  floor  of  the  tympanic  cavity,  from  which  it  may 
be  separated  merely  by  a  thin  and  translucent  plate  of  bone  which  occasionally  shows  an 
osseous  deficiency.  In  cases  where  this  condition  existed  the  jugular  bulb  has  been 
wounded  in  the  operation  of  paracentesis  of  the  tympanic  membrane. 

Anteriorly  the  tympanic  cavity  leads  into  the  Eustachian  tube,  which  brings  it  into 
communication  with  the  naso-pharynx.  In  the  child  the  Eustachian  tube  is  shorter, 
wider,  and  more  horizontal  than  in  the  adult,  hence  inflanniiations  are  more  liable  to 
spread  along  it  to  the  tympanum. 

Above  the  level  of  the  membrana  tympani  is  the  tympanic  attic  or  epitympanic  space, 
which  communicates  posteriorly  bj^  means  of  a  triangular  opening  {aditus  ad  antmvi) 
with  the  mastoid  antrum ;  the  base  of  the  ti'iangle,  directed  upwards,  is  formed  by  the 
tegmen  tympani ;  its  apex,  directed  downwards,  is  formed  by  the  meeting  of  the  inner  and 
outer  walls.  The  opening  will  admit  an  instrument  half  a  cm.  in  diameter.  The  tympanic 
attic  contains  from  before  backwards  the  head  of  the  malleus,  the  body  and  short  process 
of  the  incus,  the  latter  projecting  backwards  into  the  aditus.  When  these  structures 
are  covered  with  inflamed  mucous  membrane  or  granulations,  drainage  from  the 
mastoid  antrum  into  the  tympanum  proper  is  interfered  with.  The  houndarieis  of  the 
aditus,  important  surgically,  are  as  follows  :  superiorly,  the  tegmen  tyiiipani ;  internally,  an 
eminence  of  compact  bone,  containing  the  external  semicircular  canal,  below  and  in  front  of 
which  is  a  second  smaller  prominence,  corresponding  to  that  portion  of  the  aqueduct  of 
Fallopius  which  curves  immediately  above  and  behind  the  foramen  ovale.  The  wall  of  the 
aqueduct  is  hei-e  thin  and  not  infrequently  deficient,  in  which  case  inflammation  may  readily 
spread  from  the  tympanum  to  the  facial  nerve.  The  outer  wall  of  the  aditus  is  formed  by 
tlie  deepest  part  of  the  upper  and  outer  wall  of  the  osseous  external  auditory  canal. 

The  posterior  wall  of  the  tympanum,  below  the  aditus  ad  antrum,  is  formed  by  diploic 
bone  which  contains  the  descending  portion  of  the  aqueduct  of  Fallopius 

The  mastoid  antrum  is  to  be  considered,  developmen tally  as  well  as  anatomically, 
as  an  extension  upwards  and  backwards  of  the  tympanum  (Fig.  885).  Its  ana- 
tomy and  relations  will  be  best  understood  by  studying  it  in  the  child,  in  whom  it 
is  relatively  larger  than  in  the  adult.  Situated  above  and  behind  the  tympanic 
cavity  proper,  its  cmter  v:aU  is  formed  by  a  triangular  plate  of  bone  which  descends 
behind  the  external  auditory  process  from  the  squamous  portion.  Posteriorly, 
this  triangular  plate  is  separated  from  the  pebro-mastoid  element  by  the  petro- 
mastoid  suture,  which  overlies  the  posterior  part  of  the  antrum  and  transmits 
small  veins  to  the  surface.  The  suture  does  not  become  completely  ossified  until 
a  year  or  two  after  birth,  and  remains  of  it  may  frequently  be  detected  in  the 
adult  bone.  The  anterior  and  upper  portion  of  the  triangular  plate  turns  inwards 
at  an  angle  to  form  the  upper  and  posterior  wall  of  the  rudimentary  osseous  canal, 
as  well  as  the  floor  of  the  tympanic  attic. 

In  the  adult  the  outer  wall  of  the  mastoid  antrum  is  formed  by  a  plate  of  bone, 
from  i  to  f  in.  in  thickness,  which  occupies  the  triangular  and  somewhat  depressed 
area  between  the  ridge  extending  backwards  and  slightly  upwards  from  the 
posterior  root  of  the  zygoma  (supra -mastoid  portion  of  temporal  crest),  and 
the  upper  and  posterior  quadrant  of  the  osseous  external  auditory  meatus;  upon 
the  latter  is  the  supra -meatal  spine,  immediately  behind  which,  upon  the  floor 
of  the  above  triangle,  is  a  crescentic  depression,  the  fossa  mastoidea.  The  outer 
wall  of -the  antrum  is  felt  through  the  skin  as  a  slight  depression  immediately 
behind  the  auricle,  and  immediately  below  the  ridge  formed  by  the  supra-mastoid 
crest;  below  the  depression  is  the  prominence  corresponding  to  the  insertion  of 
the  sterno-mastoid  muscle.  Trautmann  has  pointed  out,  however,  that  the  supra- 
mastoid  crest,  which  varies  considerably  in  its  obliquity,  is  sometimes  situated  a 
little  above  the  level  of  the  roof  of  the  antrum,  and  that  it  is  safer,  therefore,  to 
83 


1234 


SUKFACE  AND  SUEGICAL  ANATOMY. 


take  the  level  of  the  upper  border  of  the  osseous  meatus  as  the  guide  in  order  to 
avoid  opening  the  middle  fossa  of  the  skull.  In  children  the  supra-mastoid  crest 
is  not  developed,  so  that  if  the  operator  mistake  the  posterior  root  of  the  zygoma 
for  the  crest,  he  will  open  into  the  middle  fossa  of  the  skull  immediately  in  front 
of  the  attic.  The  upper  and  posterior  quadrant  of  the  osseous  meatus  is,  therefore, 
the  only  reliable  guide  to  the  antrum  in  the  child. 

The  inner  vxdl  is  formed  by  a  thick  plate  of  spongy  bone  which  separates  the 
antrum  from  that  portion  of  the  posterior  fossa  lying  between  the  aqueduct  of 
the  vestibule  and  the  groove  for  the  sigmoid  portion  of  the  lateral  sinus,  and  which 
contains  the  posterior  semicircular  canal. 

The  roof,  which  slopes  downwards  and  forwards,  is  formed  by  the  posterior  and 
thinnest  part  of  the  tegmen  tympani. 

The  fioor  is  on  a  lower  level  than  the  aditus,  and  is  therefore  unfavourably 
placed  for  natural  drainage. 

The  mastoid  process  begins  to  develop  in  the  second  year.     As  development 


Fig,     888.  —  A     Large 

Right     Frontal 

Sixus    WITH    Septum 

OBLIQUE       to     the 

Left  (Logan  Turner). 

Fig.  887. — Frontal  Sinuses  of  Average 
Dimensions,  with  a  Mesial  Septum  (Logan 
Turner). 

advances  the  diploe  surrounding  the  antrum  in  the  child  becomes  excavated  to 
form  the  mastoid  cells,  which  radiate  from  the  antrum,  and  either  directly  or 
indirectly  communicate  with  it  by  small  openings.  In  the  pneumatic  type  of 
mastoid  the  whole  of  the  process  is  excavated  by  these  cells,  which  extend 
upwards  into  the  squamous  portion,  forwards  to  the  posterior  wall  of  the  osseous 
meatus  (border-cells),  and  backwards  into  the  occipital  bone.  Pus  retained  within 
the  "harder-cells"  may  bulge  into,  and  rupture  through,  the  posterior  wall  of  the 
osseous  meatus.  Less  frequently  the  mastoid  cells  are  absent,  the  bone  consisting 
either  of  osseous  tissue  similar  to  that  of  the  diploe,  or  of  dense  bone  (sclerosed 

The  mastoid  process  is  grooved  upon  its  inner  surface  by  the  sigmoid  portion  of 
the  lateral  sinus.  The  average  distance  of  the  foremost  part  of  the  sinus  from  the 
supra-meatal  spine  is  1  cm.  The  right  sinus  usually  receives  the  superior 
longitudinal  sinus,  and  when  this  is  the  case  it  is  larger  and  farther  forward  than 
the  left ;  in  extreme  cases  it  may  reach  to  within  2  or  3  mm.  of  the  meatus.  The 
average  minimum  distance  of  the  lateral  sinus  from  the  oicter  surface  of  the 
mastoid  is  about  1  cm.,  but  when  the  sinus  is  large  and  far  forward  the  thickness 
may  be  reduced  to  1  or  2  mm. 

The  facial  nerve,  after  entering  the  aqueduct  of  Fallopius  at  the  bottom  of  the 
internal  auditory  meatus,  lies  immediately  above  and  behind  the  foramen  ovale, 
between  it  and  the  prominence  of  the   external  semicircular  canal ;    thence   it 


THE  CRANIUM. 


1235 


Fk;.  889.  —  Right  Fkontal  Sinos  of 
very  laroe  dimensions  ;  left  sinus 
UNOPENED  (Logan  Turner). 


descends  almost  vertically  in  the  posterior  wall  of  the  tympanum  J  in.  behind  and 
internal  to  the  lower  halt"  of  the  deepest  part  of  the  posterior  wall  of  the  external 
osseous  canal,  and  emerges  through  the  stylo- 
mastoid foramen  (Fig.  583). 

In  the  infant,  in  consequence  of  the  absence 
of  the  mastoid  process,  the  exit  of  the  facial 
nerve  from  the  stylo-mastoid  foramen  is  unpro- 
tected and  exposed  upon  the  lateral  rather  than 
upon  the  basal  surface  of  the  skull  at  a  point 
immediately  behind  the  posterior  segment  of 
the  tympanic  horse-shoe.  It  follows,  therefore, 
tliat,  in  infancy,  the  incision  to  expose  the  antrum 
should  not  be  curved  too  far  downwards  and 
forwards,  otherwise  the  facial  nerve  may  be  di- 
vided. In  the  infant  the  position  of  the  mastoid 
antrum  is  relatively  higher  than  in  the  adult, 
because  in  the  former  the  upper  wall  of  the 
osseous  canal  inclines  towards  the  vertical  plane 
instead  of  being  horizontal.  The  lymphatics  from 
the  auricle  and  external  auditory  meatus  open 
into  the  mastoid  and  parotid  lymphatic  glands, 
the  latter  receiving  also  the  lymphatics  from 
the  middle  ear.  The  efferent  vessels  from  these 
glands  open  into  the  superior  sub-sternomastoid 
glands ;  hence  it  is  that  these  groups  of  glands 
are  so  frequently  found  to  be  diseased  secondary  to  tuberculosis  of  the  middle  ear ; 
and  care  must  be  taken  not  to  mistake  an  abscess  in  one  of  the  mastoid  glands 
for  sub-periosteal  mastoid  suppuration  associated  with  middle-ear  disease. 

To  open  the  mastoid  antrum  the  surgeon  makes  a  curved  incision  a  little  behind  the 
attachment  of  the  auricle,  and  chisels  or  drills  away  the  bone  immediatel}'  above  and 
behind  the  postero-superior  quadrant  of  the  external  osseous  meatus.  In  this  operation 
the  middle  fossa  of  the  skull  is  avoided  by  keeping  below  the  supra-mastoid  crest,  the 
lateral  sinus  by  keeping  close  to  the  external  auditor}-  canal  and  by  chiselHng  obliquely  to 
the  surface  in  opening  the  mastoid  cells,  the  descending  portion  of  the  facial  nerve  is 
avoided  by  not  encroaching  upon  the  lower  half  of  the  deepest  part  of  the  posterior  wall 
of  the  osseous  canal.  In  extending  the  operation  from  the  mastoid  antrum  through  the 
aditus  into  the  tympanic  attic,  the  external  semicircular  canal  and  the  curve  of  the  facial 
nerve,  which  lie  in  relation  to  the  inner  wall  of  the  aditus,  are  liable  to  iujury,  and  must 
be  protected  either  by  a  curved  probe,  or  better  by  Stacke's  protector,  passed  from  the 
antrum  through  the  aditus  into  the  tympanic  cavity. 

The  frontal  air  sinuses  are  two  cavities  situated  immediately  above  the  root  of 
the  nose  between  the  two  tables  of  the  frontal  bone.  Each  sinus  at  its  most 
dependent  part  communicates,  by  means  of  the  naso-frontal  duct,  either  directly 
with  the  middle  meatus  of  the  nose,  or  indirectly  with  that  channel  through  its 
inf undibulum.  A  bony  septum,  rarely  incomplete,  separates  the  two  sinuses ;  it 
is  usually  mesial  in  position  below,  but  it  may  deviate  to  one  or  other  side  above 
(Figs.  887  and  888). 

The  sinuses  vary  considerably  in  their  size  and  shape,  independently  of  the 
degree  of  development  of  the  glabella  and  superciliary  ridges  (Fig.  889).  According 
to  Logan  Turner,  the  dimensions  of  an  average-sized  sinus  are :  height,  1\  in.,  from 
the  lower  end  of  the  fron to-maxillary  suture  vertically  upwards ;  breadth,  1  in., 
from  the  mesial  septum  horizontally  outwards  ;  depth,  |  in.,  from  the  anterior  wall 
backwards  along  the  orbital  roof.  The  sinus  may  exist  merely  as  recesses  limited 
to  a  small  area  of  bone  above  the  nose,  or  it  may  extend  upwards  on  to  the  fore- 
head for  more  than  two  inches;  externally  it  may  be  Hmited  by  the  bony 
wall  of  the  temporal  fossa,  while  posteriorly  it  may  reach  as  far  back  as  the  optic 
foramen.  The  anterior  wall  is  thickest,  but  the  thickness  may  vary  frona  1  to 
5  mm.  The  floor  is  the  thinnest  wall,  hence  when  pus  is  retained  within  the 
83  a 


1236 


SUEFACE  AND  SUEGICAL  ANATOMY. 


cavity,  it  tends  to  point  at  the  upper  and  inner  angle  of  the  orbit.     Intracranial 
suppuration  mar  arise  in  connexion  with  sinus  disease  by  extension  through  the 


Sepjum  of  frontal  simisps 
Right  frontal  sinus 


Crista  Cnlll        T.cft  frontal  sinus 

Floor  nf  anterior  fossa  of  skull 

AntPrior  part  of  roof  of  orbit 


Anterifir  fxtreinit)  ofmuldlf    _ 
Turbinnl 


flartilagc  of  nasal  sepLuui- 


.Anterior  Pxtrf-mity  of  inferior 
turbinal 


Nasal  process  of 
superior  maxilla 


Fi<;.  890. — Vkrtic.\l  Coronal  Section  thkough  the  Nose  and  Frontal  Sinuses. 

l)Osterior  wall.     The  niuco-periosteal  lining,  which  readily  strips  from  the  bone,  is 
thin  and  pale,  and  provided  with  mucous-secreting  glands. 

In  many  individuals,  by  the  aid  of  trans-illumination,  the  extent  of  the  sinuses  and  the 
position  of  the  intervening  septtun  may  be  mapped  out  upon  the  forehead.  For  this 
purpose  a  small  electric  lamp  is  placed  against  the  floor  of  the  sim;s,  beneath  the  inner 
third  of  the  supra-orbital  margin.  In  exploring  the  sinus,  the  opening  in  the  bone  shoxdd 
be  made  close  to  the  mesial  plane,  immediatelj-  above  the  root  of  the  nose.  In  marked 
cases  of  deviation  of  the  septum  one  sinus  may  extend  so  far  across  the  mesial  plane  of 
the  forehead  as  to  reduce  the  other  to  a  mere  slit ;  in  such  cases  the  surgeon  may  fail  to 
open  the  diseased  simis  when  the  operation  is  performed  through  the  anterior  wall.  The 
sinus  frequently  contains  incomplete  partitions,  which  give  rise  to  the  formation  of  pockets 
and  recesses  usually  found  towards  the  external  angle  of  the  sinus ;  when  dealing  with 
clu'onic  suppuration  of  the  sinuses,  special  attention  should  be  paid  to  these  recesses  as 
well  as  to  the  backward  extension  of  the  cavity  along  the  orbital  roof.  The  anterior 
ethmoidal  cells  are  closely  related  to  the  thin  inner  or  nasal  portion  of  the  floor  of  the 
sinus  and  its  duct  of  exit;  hence  suppuration  very  frequently  co-exists  in  both  cavities.. 
In  some  cases  pus  flows  directly  from  the  fi'ontal  sinus  and  infundibulum  along  the 
hiatus  semilunaris  into  the  maxillary  antrum,  which  opens  into  the  back  part  of  the 
hiatus.  Killian's  operation  for  the  cure  of  chronic  suppuration  in  the  sinus  consists  in 
the  removal  of  its  anterior  and  inferior  walls,  the  supra-orbital  margin  being  left  to 
prevent  the  falling  in  of  the  eyebrow.  By  removing  the  frontal  process  of  the  superior 
maxilla  good  access  may  at  the  same  time  be  obtained  to  the  ethmoidal  cells  and  free 
drainage  established  l)etween  the  frontal  sinus  and  the  nasal  cavity. 


THE  FACE. 

The  skin  of  the  face  is  thin,  vascular,  and  rich  in  sebaceous  and  sweat  glands ; 
It  IS  intimately  connected  with  the  subcutaneous  tissue,  in  which  are  imbedded  the 
facial  muscles  as  well  as  the  main  blood-vessels.  Owing  to  its  elasticity  and  to 
the  presence  of  the  main  blood-vessels  in  the  lax  subcutaneous  tissue,  the  face  is  an 


THE  FACE.  1237 

admirable  site  for  plastic  operations,  as  the  flaps  do  not  necrose  in  spite  of  consider- 
a])le  tension.  The  laxity  of  the  tissues  accounts  for  the  marked  swelling  which 
attends  cedematous  and  inflammatory  conditions  about  the  face.  Whenever  pos- 
sible, incisions  shoidd  be  made  along  the  line  of  the  natural  furrows  and  creases  of 
the  skin,  so  as  to  render  the  resulting  cicatrix  less  noticealile. 

The  bony  landmarks  of  the  face  which  may  be  readily  palpated  are :  the 
superciliary  ridges  and  the  glabella,  the  nasion  (fronto-nasal  junction),  the  bridge  of 
the  nose,  the  osseous  anterior  nares  and  the  nasal  spine,  the  supra-  and  infra-orbital 
margins,  the  external  antl  internal  angular  processes,  the  anterior  part  of  tht-  temporal 
crest,  the  malar  bone,  the  zygomatic  arch,  and  the  region  of  the  canine  fossa  of  the 
upper  jaw. 

Immediately  below  the  root  of  the  zygoma,  and  in  front  of  the  upper  part  of 
the  tragus,  is  the  condyle  of  the  jaw.  By  pressing  w^ith  the  point  of  the  flnger 
upon  the  condyle  while  the  mouth  is  being  widely  opened,  the  bone  will  be  felt  to 
glide  forward,  while  the  flnger  sinks  deeply  into  the  hollow  corresponding  to  tht- 
glenoid  cavity.  The  close  relation  of  the  first  part  of  the  internal  maxillary  artery 
to  the  inner  aspect  of  the  neck  of  the  jaw  must  be  kept  in  mind  in  operations 
calling  for  disarticulation  or  excision  of  the  condyle.  The  ascending  ramus  of  the 
jaw  is  sandwiched  between  the  masseter  and  the  pterygoid  muscles,  and  can  be 
removed  without  opening  into  the  mouth.  Passing  downwards  from  the  condyle, 
one  can  palpate  the  anterior  and  posterior  borders  of  the  ascending  ramus  and  the 
angle  antl  body  of  the  mandible.  The  anterior  border  of  the  coronoid  process  is 
felt  in  front  of  the  upper  part  of  the  anterior  border  of  the  masseter,  inmiediately 
below  the  anterior  part  of  the  zygomatic  arch. 

The  pulsation  of  the  facial  artery  may  be  felt  as  the  vessel  crosses  the  lower 
margin  of  the  mandible  at  the  anterior  border  of  the  masseter,  1^  in.  in  front  of 
the  angle  of  the  jaw.  To  map  out  the  course  of  the  artery  upon  the  face,  draw  a 
line  from  this  point  to  a  point  ^  in.  external  to  the  angle  of  the  mouth,  and 
thence  to  a  point  a  little  behind  the  ala  nasi  and  along  the  side  of  the  nose  to 
the  inner  angle  of  the  orbit.  The  facial  vein  lies  behind  the  facial  artery,  and 
takes  a  straighter  course  from  the  inner  canthus  to  the  anterior  inferior  angle  of 
the  masseter.  The  vessel  is  devoid  of  valves,  hence  infective  phlebitis  and  throm- 
bosis are  liable  to  spread  along  it  to  the  cavernous  sinus  by  way  of  the  ophthalmic 
and  pterygoid  veins. 

A  line  projected  downwards  from  the  supra-orbital  notch  (junction  of  inner 
and  middle  thirds  of  the  supra-orbital  margin)  to  the  lower  border  of  the 
mandible  opposite  the  interval  between  the  two  lower  bicuspid  teeth,  will  cross 
the  infra-orbital  and  mental  foramina,  the  former  ^  in.  below  the  infra-orbital 
margin,  the  latter  midway  between  the  upper  and  lower  borders  of  the  lower  jaw. 
In  performing  the  operation  of  neurectomy  for  the  relief  of  trigeminal  neuralgia, 
these  foramina  furnish  the  guides  to  the  correspondingly-named  branches  of  the  fiftli 
nerve.  It  should  be  remembered  that  the  nerves  in  question,  after  emerging  from 
their  respective  foramina,  lie,  in  the  first  instance,  beneath  the  facial  muscles.  The 
supra-orbital  and  infra-orbital  nerves  are  uot  infrequently  represented  each  by  two 
liranches,  one  of  which  passes  through  an  accessory  foramen  situated  external  to 
the  normal  opening.  Neurectomy  of  the  inferior  pental  nerve  is  performed  by 
trephining  the  ascending  ramus  of  the  jaw  midway  between  its  anterior  and  pos- 
terior borders,  on  a  level  with  the  crown  of  the  last  molar  tooth,  the  nerve  being 
reached  as  it  enters  the  inferior  dental  canal :  the  lingual  nerve,  which  lies  a  little 
anterior  to  the  inferior  dental,  can  be  exposed  through  tlie  same  opening. 

The  facial  nerve,  after  emerging  from  the  stylo-mastoid  foramen,  is  imbedded 
in  the  parotid  gland  where  it  is  superficial  to  the  external  carotid  artery ;  the 
nerve  can  be  rolled  under  the  finger  as  it  crosses  the  posterior  border  of  the  ascend- 
ing ramus  of  the  jaw  at  the  level  of  the  lower  margin  of  the  tragus ;  incisions  con- 
tinued along  the  ramus  above  this  point  should  be  only  skin  deep  if  the  nerve  is 
to  be  avoided.  To  expose  the  trunk  of  the  nerve  an  incision  is  made  from  the 
anterior  border  of  the  mastoid  process  to  the  angle  of  the  jaw.  Incisions  upon  the 
cheek  should,  whenever  possible,  be  planned  so  as  to  run  parallel  with  the  branches 
of  the  nerve ;  these  radiate  from  the  lower  end  of  the  tragus.  The  nerve  may 
83  5 


1238  SUEFACE  AND  SUKGICAL  ANATOMY. 

be  paralysed  by  wounds  of  the  cheek  and  by  malignant  tumovirs  of  the  parotid,  as 
also  by  intracranial  and  middle-ear  lesions. 

The  parotid  gland  is  surrounded  by  a  fascial  envelope,  the  strongest  portion  of 
which  is  continued  from  the  deep  cervical  fascia  over  its  superficial  aspect  to 
become  attached  to  the  zygoma  (Fig.  716) ;  hence  abscesses  in  the  parotid  tend 
to  burrow  deeply  towards  the  pterygo-maxillary  space  and  the  upper  part  of  the 
pharynx  (Fig.  897) ;  the  pus  should  therefore  be  evacuated  by  Hilton's  method, 
through  an  early  incision  over  the  angle  of  the  jaw.  A  study  of  the  relations  of 
the  gland  explains  the  surgical  difficulties  which  attend  its  complete  removal. 

The  parotid  duct  can  he  rolled  beneath  the  finger  as  it  crosses  the  masseter, 
rather  less  than  a  finger's  breadth  below  the  zygoma.  After  winding  over  the 
anterior  border  of  the  muscle  it  soon  pierces  the  buccinator,  and  opens  into  the 
mouth  opposite  to  the  second  molar  tooth  of  the  upper  jaw.  The  duct  corresponds 
to  the  middle  third  of  a  line  drawn  from  the  lower  margin  of  the  concha  to  a  point 
midway  between  the  ala  nasi  and  the  margin  of  the  upper  lip. 

Superficial  to  the  parotid  and  a  little  in  front  of  the  tragus  is  the  pre-auricular 
lymphatic  gland,  which  is  frequently  found  to  be  inflamed  in  children  suffering  from 
eczematous  conditions  of  the  eyelids,  face,  scalp,  and  external  ear.  In  opening 
an  abscess  connected  with  this  gland  care  must  be  taken  to  make  the  incision  as 
low  down  as  possible,  so  as  to  avoid  the  parotid  duct. 

Eyelids. — The  skin  of  the  eyelids,  more  especially  of  the  upper,  is  very  thin  and 
connected  with  the  orbicularis  muscle  by  delicate  and  lax  subcutaneous  tissue 
destitute  of  fat ;  hence  the  marked  swelling  which  occurs  in  a  "  black  eye  "  and  in 
oedema  of  the  lids.  Along  the  anterior  edge  of  the  free  margins  of  the  lids  are  the 
eyelashes  and  the  orifices  of  the  sebaceous  glands,  suppurative  inflammation  of 
which  gives  rise  to  a  "  stye " ;  along  the  sharp  posterior  edge  of  the  free  margins 
are  the  minute  orifices  of  the  Meibomian  glands.  These  glands,  imbedded  in  the 
deep  surface  of  the  tarsal  plates,  are  seen  through  the  palpebral  conjunctiva  as  a 
row  of  parallel,  yellowish,  granular-looking  streaks.  From  the  deep  position  of  the 
glands  it  follows  that  the  skin  over  a  Meibomian  cyst  is  freely  movable,  and  that 
to  reach  the  cyst  an  incision  should  be  made  through  the  conjunctival  surface  of 
the  lid. 

The  palpebral  conjunctiva  is  closely  adherent  to  the  ocular  surface  of  the  tarsal 
plates ;  at  the  fornix  it  is  loose  and  contains  small  lymphoid  follicles,  which 
become  hypertrophied  in  the  condition  known  as  granular  conjunctivitis.  The 
ocular  conjunctiva  is  thin,  transparent,  and  loosely  attached  to  the  sclerotic,  so  that 
in  operating  upon  the  eye  a  fold  of  the  membrane  can  be  picked  up  with  forceps 
to  steady  the  eyeball. 

In  inflammatory  affections  of  the  eye  the  state  of  those  vessels  which  are  visible  gives 
important  information  as  to  the  seat  of  the  mischief.  For  example,  in  inflammation  of 
the  conjunctiva  the  posterior  conjunctival  vessels  (derived  from  the  palpebral  arteries), 
scarcely  visible  normally,  appear  as  a  close  network  which  fades  away  towards  the  corneal 
margin  ;  these  vessels  move  freely  with  the  conjunctiva,  and  do  not  di&appear  under  pres- 
sure. In  superfcial  inflammations  of  the  cornea  the  anterior  conjunctival  vessels  (the 
most  superficial  of  the  terminal  branches  of  the  anterior  ciliary  arteries)  are  seen  to 
spread  in  a  freely  branching  manner  into  its  superficial  layers.  In  ^V^^^s  and  deep  inflam- 
mations of  the  cornea  there  is  a  pink  circumcorneal  zone  of  vascular  dilatation  consisting 
of  delicate  straight  vessels  which  disappear  under  pressure  and  do  not  move  with  the  con- 
junctiva ;  they  are  the  subconjunctival  (episclerotic)  terminations  of  the  anterior  ciliary 
arteries  ;  in  health  they  are  invisible. 

Lachrymal  Apparatus.  The  lachrymal  gland,  situated  behind  the  outer  part 
of  the  supra-orbital  margin,  cannot  be  felt  unless  enlarged.  By  everting  and 
raising  the  upper  eyelid,  the  accessory  (palpebral)  portion  of  the  gland  is  seen  to 
project  Vjeneath  the  outer  third  of  the  fornix,  in  which  situation  also  the  minute 
orifices  of  the  lachrymal  ducts  may  be  detected.  V)j  gently  drawing  downwards 
the  lower  lid,  the  small  punctum  lachrymale  is  seen  situated  upon  a  slight  papillary 
alevation  of  its  margin  about  4  mm.  from  the  inner  canthus ;  the  corresponding 
orifice  of  the  upper  lid  is  placed  a  little  nearer   the  canthus.       Normally   the 


THE  FACE.  1239 

puucta  are  directed  towards,  aud  accurately  applied  to,  the  ocular  conjunctiva 
immediately  external  to  the  caruncle.  By  drawing  the  lids  outwards  the  internal 
palpebral  ligament  it;  put  upon  the  stretch,  and  can  be  felt  as  a  narrow  tense  band 
passing  transversely  inwards  to  be  attached  to  the  nasal  process  of  the  superior 
maxilla.  The  ligament  is  a  guide  to  the  position  of  tiie  lachrymal  sac,  wliich  it 
crosses  a  little  above  its  centre.  Continuous  with  the  lower  end  of  the  laclirymal 
sac  is  the  nasal  duct,  wliich  passes  downwards  and  slightly  backwards  aud  outwards, 
to  open  into  the  inferior  meatus  of  the  nose,  under  cover  of  the  anterior  end  of  the 
inferior  turbinal.  The  lachrymal  sac  and  duct  each  measure  about  .1  in.  in  length  ; 
the  latter  is  slightly  contracted  at  its  commencement  and  termination,  and  it  is  in 
these  situations  that  pathological  strictures  of  the  duct  are  commonest.  Spon- 
taneous rupture  of  an  abscess  of  the  lachrymal  sac  almost  invariably  occuz-s  just 
below  the  tendo  palpebrarum ;  it  is  in  this  situation  that  the  abscess  should  be 
opened,  the  incision  being  made  a  Little  external  to  the  angular  termination  of  the 
facial  artery. 

The  canaliculi  lachrymales,  which  convey  the  tears  from  the  puncta  to  the  lach- 
rymal sac,  run  for  the  hrst  1-2  mm.  almost  vertically  to  the  free  margins  of  the 
lids,  and  thence  parallel  to  them.  Between  the  canaliculi  is  the  lachrymal  caruncle. 
In  the  various  morbid  conditions  which  give  rise  either  to  misdirection  of  the 
puucta  or  to  stricture  at  any  part  of  the  lachrymal  drainage  apparatus,  overflow 
of  the  tears  {epiph&ra)  is  the  chief  symptom.  In  passing  a  probe  along  a 
canaliculus  the  instrument,  in  consequence  of  the  bend  upon  the  duct,  is 
passed  at  first  vertically  to  the  margin  of  the  lid,  and  afterwards  parallel  to  it, 
until  the  point  is  felt  to  strike  against  the  inner  wall  of  the  lachrymal  sac ;  to 
pass  the  instrument  onwards  along  the  nasal  duct  the  handle  is  rotated  forwards 
and  upwards  through  a  quarter  of  a  circle,  and  then  pushed  gently  downwards  and 
slightly  backwards  and  outwards  into  the  inferior  meatus  of  the  nose. 

The  tarsal  "  cartilages  "  are  attached  to  the  periosteum  of  the  orbital  margins  by 
the  orbito-tarsal  ligaments  which  shut  off  the  communication  between  the  subcuta- 
neous tissue  of  the  eyelids  and  the  fatty  tissue  of  the  orbital  cavity.  In  fracture 
of  the  anterior  fossa  of  the  base  of  the  skull  involving  the  orbital  plate,  the  blood 
extends  forwards  between  the  periosteum  and  the  musculo-fascial  envelope  of  the 
orbit  and  appears  under  the  conjunctiva. 

To  obtain  free  access  to  the  cavity  of  the  orbit,  the  surgeon  first  enlarges  the 
palpebral  fissure  by  making  a  horizontal  incision  from  the  outer  canthus  to  the 
outer  margin  of  the  orbit,  and  then,  after  everting  the  eyelid,  divides  the  conjunc- 
tiva along  the  fornix  of  the  upper  or  lower  lid,  or  of  both,  as  may  be  desired. 

Nose. — To  examine  the  anterior  uares  {anterior  rhinoscopy)  a  strong  light  is 
reflected  into  the  nostril,  which  is  dilated  by  means  of  a  nasal  speculum.  The 
anterior  extremity  of  the  inferior  turbinal  appears  as  a  rounded  body  projecting 
from  the  outer  wall  of  the  nose  ;  in  turgescence  of  its  erectile  tissue  it  is  hable  to 
come  in  contact  with  the  nasal  septum  aud  so  occlude  the  nostril.  The  inferior 
meatus,  situated  between  the  inferior  turbinated  body  and  the  floor  of  the  nasal 
fossa,  is  brought  into  view  by  tilting  forwards  the  head.  The  lower  aperture  of  the 
nasal  duct  is  concealed  from  view  by  the  anterior  part  of  the  inferior  turbinal. 
The  floor  of  the  nose  is  horizontal  and  placed  on  a  slightly  lower  level  than  the 
anterior  nares.  The  septum,  generally  more  or  less  deviated  to  one  or  other  side, 
is  seen  when  the  head  is  slightly  rotated  away  from  the  side  to  be  examined.  The 
anterior  extremity  of  the  middle  turbinal,  which  lies  a  little  behind  and  internal  to 
the  lower-internal  angle  of  the  orbital  margin,  is  seen  when  the  patient's  head  is 
thrown  well  back ;  between  it  and  the  septum  is  a  sht-Iike  interval  (olfactory  cleft]. 
By  rotating  the  patient's  head  towards  the  corresponding  shoulder  the  anterior  part 
of  the  middle  meatus  is  brought  into  view ;  pus  in  this  situation  may  originate  from 
the  frontal,  the  anterior  ethmoidal,  or  the  maxillary  sinuses,  all  of  which  open  into 
the  hiatus  semilunaris  of  the  middle  meatus  (Fig.  555). 

To  make  a  satisfactory  digital  exploration  of  the  anterior  part  of  the  nasal 

cavities,  it  is  necessary  to  divide  the  columella  aud  the  cartilaginous  septum  with 

a  strong  pair  of  scissors,  one  blade  bein^j  introduced  into  each  nostril  (Kocher) ; 

blood  spurts  from  the  small  arteries  of  the  septum,  but  the  bleeding  soon  ceases. 

83  c 


1240 


SUEFACE  AND  SUKGICAL  ANATOMY. 


When  these  vessels,  which  are  derived  from  the  superior  coronary  arteries,  are  the 
source  of  the  haemorrhage  in  epistaxis,  the  bleeding  can  be  arrested  either  by  com- 
pressing the  coronary  arteries,  by  plugging  the  anterior  nares,  or  by  grasping  the 
cartilaginous  part  of  the  nose  firmly  between  the  finger  and  thumb. 

The  maxillary  sinus  or  antrum  of  Highmore,  situated  in  the  upper  jaw,  is  a 
pyramidal  cavity  with  its  base  formed  by  the  outer  wall  of  the  nose  and  its  apex 
directed  towards  the  malar  bone  (Fig.  126).  The  cavity  is  lined  by  a  thin  muco- 
periosteal  membrane,  easily  separable  from  the  bone ;  in  the  mucous  layer  are 
numerous  mucous  glands  from  which  cysts  may  develop.  The  floor  of  the  antrum, 
which  is  at  or  a  little  below  the  level  of  the  floor  of  the  nose,  is  separated  from 
the  roots  of  the  bicuspid  and  molar  teeth  by  a  plate  of  bone  of  varying  thickness. 
When  this  plate  is  thin  and  devoid  of  spongiosa,  the  floor  of  the  antrum  sinks  below 
the  level  of  the  floor  of  the  nose,  and  suppuration  at  the  roots  of  one  of  the  teeth 
above  mentioned  is  in  these  circumstances  very  liable  to  extend  to  the  antrum.  In 
an  antrum  of  average  dimensions  the  line  of  union  of  the  nasal  and  facial  walls  of 
the  cavity  corresponds  externally  to  the  outer  edge  of  the  canine  ridge  (Logan 
Turner).  The  antral  orifice  is  situated  at  the  highest  part  of  the  antrum,  and 
is  therefore  unfavourably  placed  for  natural  drainage ;  it  opens  into  the  posterior 
and  lower  part  of  the  infundibulum,  which  in  its  turn  communicates  with  the 
middle  meatus  of  the  nose  through  the  hiatus  semilunaris.  In  old  age  there  is 
frequently  a  second  communication  between  the  antrum  and  middle  meatus,  the 
opening  being  situated  behind  and  below  the  normal  orifice ;  when  this  accessory 
osteum  exists,  pus  from  the  antrum  may  drain  backwards  into  the  naso-pharynx 
(Logan  Turner).  In  empyema  of  the  antrum  the  opening  to  evacuate  and  drain 
the  cavity  may  be  made  (1)  through  the  alveolus  of  the  second  bicuspid  or  of  the 
first  or  second  molar  tooth,  the  first  molar  being  the  site  of  election ;  (2)  through 
the  canine  fossa,  external  to  the  prominence  caused  by  the  root  of  the  canine  tooth ; 
or  (3)  through  the  outer  wall  of  the  inferior  meatus  of  the  nose. 

Lips. — In  compressing  the  coronary  arteries,  it  must  be  remembered  that  they 
run  beneath  the  mucous  surface  of  the  lips  a  short  distance  from  their  free  margins. 
The  lips  are  abundantly  supplied  with  mucous  glands  which  can  be  felt  immediately 
■  beneath  the  mucous  membrane  nearer  their  attached  than  their  free  borders ;  the 
glands  are  a  frequent  source  of  mucous  cysts ;  occasionally  they  are  enlarged 
congenitally,  giving  rise  to  one  form  of  hypertrophy  of  the  lip. 

Hare-lip  is  due  to  failure  of  the  union  of  the  superficial  parts  of  the  internal  nasal  sub- 
division of  the  fronto-nasal  process  with  the 
maxillary  process  (Fig.  891).  The  deformity  is 
spoken  of  as  complete  or  incomplete  according 
as  the  cleft  extends  into  the  nostril  or  merely 
involves  a  portion  of  the  lip.  The  fissure  may 
involve  the  lip  only,  or  it  may  include  the 
alveolar  process  of  the  jaw  ;  in  the  latter  case 
the  cleft  may  or  may  not  be  associated  with  a 
cleft  of  the  palate.  Lastly,  the  hare-lip  may  be 
single  or  double,  according  as  the  deficiency  has 
occurred  on  one  (usually  the  left)  or  both  sides. 
Fig.  892,  taken  from  a  coronal  section 
through  the  head  of  a  human  embryo  at  the 
seventh  week,  shows  how  the  mouth  is  shut 
off  from  the  nasal  cavities  by  the  growth 
ii:iwards  from  the  deep  aspect  of  the  maxillary 

process    of     two    horizontal    plates     (palatal 
tui.   891. — Hkad  of  Human  Embryo  about   29  \      i  •  i,        -4.     •     j.i         -jji     t  -j-i 

n»v>.  r.rr,  cT, «,.,;„„ +!,.,  ,ii,M..;.,„  , f  +i  i  "^^  "':  processes)  which  unite  in  the  middle  line  with 
DAYS  OLD,  snowing  the  division  oi  tlie  lower  part  *•,  ,'  i-iii 

of  the  mesial  frontal  ].rocess  into  the  two  gloljular  each  other  and  With  the  lower  border  ot  the 

processes,  the  intervention  of  the  olfactory  pits  septum  of  the  nose  ;  the  latter,  which  develops 
between  the  mesial  and  lateral  nasal  processes,  as  a  downgrowth  from  the  primitive  basis 
and  the  approximation  of  the  maxillary  and  ^^.^^^jj  ■  continuous  anteriorly  with  the  two 
lateral    nasal     processes,    -which,     however,     are  .  '  i  •   i      ,. 

separated  by  the  oculo-nasal  sulcus  (from  His),      internal  nasal  processes  which  form  the  pre- 

maxillte  and  the  middle  portion  of  the  upper 
lip.     The  various  degrees  of   deft  palate  are  due  to  the  more  or   less  complete  failure 


Olubulai  inocebb 


Mesial  nasal 
process 


THE  FACE. 


1241 


Xasal  si>i)tmii 
Anteiior  cranial  fossa  i 


MM^lIr 


Infcriiir  turbinal 


Xasal  cavitv- 


Buccal  cavity 


Lower  jaw  - 
.^Icckels  ca 


Fk;    892. 


-CUUONAL    Skc'TIUX    THROUGH   THE    FacK    OF 

AT  TUK  Seventh  Week. 


1  y>lalliiiH  lens 
)t'  tin.'  eyeball 


--  I'alatal  luocess 
Dental  lamina 


roumip 
Dental  lamina 


Human  Embhyo 


of  union  of  the   palatal  j^rocesses  with  each  other  and  with  the  preniaxillary  part  of  the 

internal   nasal  processes.     The  cleft  in  the  soft  palate,  which  is  always  mesial,  may  be 

either  partial  or  com-  " 

plete,  and  may  or  may 

not    extend    i'orwards 

into  the  hard  palate. 

The  cleft  in  the  latter 

is  spoken  of  as  single 

or    double    according 

to  whether  the  palatal 

processes  have    failed 

to  unite  with  the  lower 

edge  of  the  nasal  sejj- 

tum  on  one,or  on  both, 

sides.    When  the  cleft 

extends      forwards 

tiirough   the    alveolar 

process      to      become 

continuous  with  a  cleft 

of  the  lip,    the   inner 

(premaxillary)  edge  of 

the    cleft    is    usually 

projected   forwards    in   advance   of    the  outer    (maxillary)    edge.      Before    proceeding    to 

repair  the  cleft   in  the  lip,   the  projecting    premaxillary  edge   is    forced  back    into    line 

with   the   maxillary 
edge. 

In  what  is  known 
as  a  complete  double 
cleft  palate,  the 
palatal  processes  fail 
to  join  the  nasal 
septum  and  the  pre- 
maxillie  on  both 
sides  ;  the  result  is 
a  wide  median  cleft 
which  comniun  icates 
with  both  nasal 
cavities.  The  free 
lower  border  of  the 
vomer  extends  along 
the  middle  of  the 
cleft  to  be  continuous 
anteriorly  with  the 
rounded  premaxil- 
lary mass  ;  the  latter, 
along  with  the  cen- 
tral portion  of  the 
upper  lip,  is  pro- 
jected forwards  be- 
tween the  two  labial 
clefts,  often  to  such 
an  extent  that  it 
appears  to  spring 
from  the  tip  of  the 
nose  (Fig.  893).  In 
operating  on  such  a 
double  hare-lip  the 
first   step  is   to  get 

rid  of  the  premaxillary  projection.      This  is  done,  not  by  removing  it  altogether,  but  by 

removing  a  triangular  portion  of  the  septum  of  the  nose  behind  it,  so  as  to  allow  of  its 

being  bent  back  into  line  with  the  alveolar  processes  of  the  superior  maxillfe.     The  base 

of  the  triangular  piece  of  bone  should  not  be  taken  from  the  constricted  portion  of  neck 

of  the  premaxillary  projection,  but  should  consist  of  the  olive-shaped  thickening  situated 


Ala  nasi 

Anterior  extremity  nf 

inferior  turbinal 

Centi-al  portion  of 

upper  lip 


Premaxilla 

Left  nasal  cavity 

Outer  edye  of  left 

labial  cleft 

Riglit  nasal  cavity 

Nasal  septum 

Palatal  process  of  right 

superior  maxilla 

Tongue 
Lower  lip 


Fig.  893. — Fiioji  a  Photograph  showing  Double  Co.miletk  llAiiE-Lir 
AND  Cleet  Palate. 


1242 


SUKFACE  AND  SUKGICAL  ANATOMY. 


immediately  behind  the  neck.      This  thickening   is  crossed   by   the    transverse   suture 
uniting  the  premaxilla  with  the  anterior  extremity  of  the  vomer  (Fig.  894).     If  the  pre- 

maxillary  projection   be  re- 


,Fi-eiiiaxilla 


Suture  bulweeu  preniaxilhi  and  vunifr 


moved  altogether,  there  is 
nothing  left  to  support  the 
upper  lip,  and  the  result  is 
an  ugly  deformity,  due  to 
the  comparative  protrusion 
and  redundancy  of  the  lower 
lip. 


I'alaUil  inuccss  ul' 
suiK'iiijr  maxilla 


.Horizontal  plate  of 
palate  bone 


Fig.  894.  —  Shows   Aukaxgement  of   Bones  in  Double  Cleft  Palate 
(Handbook  of  Practical  Surgerij,  Bergmann,  Brtxns,  itnd  Mikulicz). 


__  [.fit  nasal  cavity 

Nasal  septuni 

Teeth. — The  milk  teeth 

Ijegin  to  appear  from  the 
sixth  to  the  eighth  month, 
the  first  to  emerge  being 
the  lower  central  incisors. 
The  first  dentition  is  com- 
pleted about  the  thirtieth 
month.  Delayed  dentition 
is  generally  due  to  rickets. 
Of  the  permanent  set  the 
first  to  erupt  are  the  first 
molars,  which  appear  at 
the  end  of  the  sixth  or 
seventh  year;  the  third  molars  (wisdom  teeth),  the  last  to  appear,  may  erupt 
any  time  between  the  eighteenth  and  the  twenty-fifth  year,  or  even  later.  As 
the  permanent  teeth  push  their  way  towards  the  surface,  absorption  of  the  roots 
of  the  first  set  takes  place,  which  either  fall  out  of  their  own  accord  or  are  easily 
removed.  Loss  of  the  permanent  teeth  is  followed  by  absorption  of  the  alveolar 
margin  of  the  jaw.  The  tooth  sockets  are  lined  by  a  thin  periosteum,  which  is 
anatomically  continuous  with  the  jjulp  tissue  of  the  teeth  on  the  one  hand  and  the 
dense  fibrous  tissue  of  the  deep  layer  of  the  gum  on  the  other. 

The  upper  incisors  and  canines  and  the  lower  bicuspids  have  cylindrical  roots, 
lience  in  extracting  these  teeth  they  should  be  first  loosened  by  a  slight  rotatory 
movement ;  the  roots  of  the  lower  incisors  and  canines  and  of  the  upper  bicuspids 
are  flattened,  so  that  they  must  be  loosened  by  a  lateral  movement.  The  roots  of 
the  wisdom  teeth  are  convergent,  generally  welded  together  and  curved  backwards, 
especially  in  the  lower  jaw.  The  first  and  second  upper  molars  have  three  roots 
which  are  often  divergent  (Figs.  719  and  720). 

Tongue. — For  practical  purposes,  as  well  as  on  developmental  and  structural 
grounds,  it  is  convenient  to  divide  the  tongue  into  an  anterior  two-thirds — the 
oro-glossus,  and  a  posterior  third — the  pharyngo-glossus  (Wingrave),  Fig.  897.  At 
the  junction  of  the  two  portions,  immediately  behind  the  median  circum vallate 
papilla,  is  the  foramen  caecum,  which  represents  the  remains  of  the  upper  or  pharyn- 
geal extremity  of  the  thyro-glossal  tract.  Congenital  cysts  and  fistulce  which  develop 
from  persistent  remains  of  this  tract  are  always  mesial ;  those  arising  from  the. 
upper  or  lingual  portion  of  the  tract  are  situated  above  the  hyoid  bone,  whereas 
those  developed  from  the  lower  or  thyroid  portion  are  situated  below  the  hyoid 
bone.  The  liability  of  these  cysts  and  fistuke  to  recur  after  operation  is  probably 
due  to  the  fact  that  part  of  the  epithehal  tract  lies  in  the  substance  of  the  hyoid 
bone. 

The  mucous  membrane  covering  the  pharyngo-glossus  is  much  more  sensitive 
than  that  covering  the  oro-glossus,  hence  in  using  a  tongue  depressor  the  instru- 
ment should,  except  under  special  circumstances,  rest  only  upon  the  latter  region, 
otherwise  a  reflex  arching  of  the  tongue  will  be  set  up,  which  prevents  the  operator 
from  obtaining  a  satisfactory  view  of  the  throat.  Scattered  over  the  pharyngo- 
glossus  are  clusters  of  lymphoid  follicles  (lingual  tonsils),  which  appear  on  the 
surface  as  a  number  of  nodular  umbilicated  elevations  provided  with  little  crypts 
into  which  mucous  glands  open  (Fig.  710).  The  lingual  tonsils  are  liable  to 
chronic  inflammation  and  hypertrophy,  conditions  whicli  are  often  accompanied  by 


THE  FACE. 


1243 


a  varicose  condition  of  the  veins  wliich  lie  immediately  beneath  the  mucous  nieni- 

Iiiferior  turbiiial 
Internal  pterygoid  Soft  ](alat« 

External  pterygoid 


m 

Stylo-glossiis  -^JJ^^VJ 


Inferior  dental 

vessels  and  nerve 

Lingual  nerve 


Facial  artery 
Superttcial  part  of 


Tongue 


Inferior  dental 
vessels  and  nerve 


'^-Vt  M— Facial  artery 


submaxillary  gland  ?^^^X^.A%i\ 
Wharton's  <luct  ^V^^vVf^ 'I 
Deep  part  of  X'^Qx^"'.  \. 
submaxillary  gland       x^ 
Hypoglossal  nerve 

Lingual  artery 

Hyoglossns 

Mylo-hyoid 
Digastric  tendon 

Genio-liyoi 


Fig. 


Jlylo-hyoid 

Lingual  nerve 
Deep  part  of  submaxillary  gland 
Wharton's  duct 
Hypoglossal  nerve 
Lingual  artery 
Digastric 
Hyoglossns 
Genio-hyoid 

895. — Coronal  Sectiox  through  the  Tongue  and  Submaxillary  Region  in  a  Plane  behlnu 
THE  Molar  Teeth  (from  Cunningliani). 


brane  containing  the  palato-glossus 
lingual  tonsils  in  the  living  subject 
the  laiyngoscopic  mirror  must  be 
employed. 

The  pair  of  mucous  glands  situ- 
ated on  the  under  surface  of  the 
tongue  a  little  behind  its  tip  and 
known  as  the  "  apical "  glands,  are 
of  interest  in  that  they  occasionally 
give  rise  to  mucous  cysts  similar  to 
those  -which  develop  in  connexion 
with  the  labial  glands  (Fig.  896). 

The  muscular  bundles  of  the 
tongue  are  separated  by  a  quantity 
of  loose  connective  tissue,  rich  in 
blood-vessels  and  lymphatics  (Fig. 
713) ;  hence  acute  inflammatory 
oedema  of  the  substance  of  the 
tongue  may  be  attended  with  a 
degree  of  swelling  sufficient  to  ob- 
struct the  respiratory  passage. 

The  main  blood-vessels  of  the 
tongue  run  from  behind  forwards, 
nearer  its  under  than  its  upper  sur- 
face (Fig.  895);  incisions  into  the 
substance  of  the  tongue  to  reduce 
svvelHng  and  tension  should,  there- 
fore, be  made  longitudinally  upon 
the  dorsum.  Bleeding  from  the 
lingual  artery,  divided  in  the  sub- 
stance of  the  tongue,  is  temporarily 
arrested  by  passing  the  finger  be- 
hind the  base  of  the  tongue  and 
hooking  it  well   forward,  so   as  to 


muscle.     To  obtain  a  satisfactory  view  of  the 


ilL ^— The  philtruni 


Apical  gland  of 
tongue 


Layer  of  muscle  cut 
';3^^^  to  show  the  gland 

'i^l^^      _PIica^  fimbriat» 


Frenuiu  linguie 
Wharton's  duct 


•v^^^^-i__ Openings  of 

^^7  Wharton's  ducts 

-Sublingual  gland 


Plica  sublingualis, 
with  oi)enings  of 
ducts  of  sublingual 
gland 


Fig.  896. — Oi'en  Mouth  with  Tongue  raised  and  the 
Sublingual  and  Apical  Glands  exposed. 
The  sublingual  glaud  of  the  left  side  has  been  laid  bare  by 
removing  the  mucous  membrane  ;  to  expose  the  apical 
gland  of  the  right  siile  a  thin  layer  of  muscle,  in  addition 
to  the  mucous  membrane,  has  been  removed.  A  branch 
of  the  lingual  nerve  is  seen  running  on  the  inner  aspect 
of  the  gland.  The  rauine  vein  is  faintly  indicated  on 
this  side  also  (from  Birmingham). 


1244  SURFACE  AND  SURGICAL  ANATOMY. 

compress  the  vessel  against  the  inner  surface  of  the  lower  jaw.  On  account  of 
the  very  slender  anastomosis  between  the  vessels  of  the  two  halves  of  the  tongue 
scarcely  any  bleeding  occurs  when  the  organ  is  split  mesially. 

According  to  Poirier  the  collecting  trunks  which  arise  from  the  lymphatic  net- 
works in  the  mucous  membrane  and  muscular  substance  of  the  tongue  may  be 
divided  into  four  groups :— (1)  Apical  trunks  which  open  partly  into  the  submental 
glands  and  partly  into  a  gland  of  the  internal  jugular  chain  lying  immediately 
above  the  anterior  belly  of  the  omohyoid  muscle.  (2)  Marginal  trunks  which  pass, 
some  external  to  the  sulilingual  gland  and  through  the  mylohyoid  muscle  to  join 
the  most  anterior  of  the  submaxillary  lymphatic  glands ;  others  pass  internal  to 
the  subhngual  gland,  in  front  of  and  behind  the  hyoglossus  muscle  to  join  the  glands 
of  the  internal  jugular  chain.  The  more  anterior  their  lingual  origin  the  loicer  in 
the  chain  is  the  gland  to  which  they  pass.  (3)  The  basal  trunks,  from  the  posterior 
third  of  the  tongue,  pass  from  before  backwards  towards  the  lower  extremity  of  the 
tonsils,  where  they  pierce  the  superior  and  middle  constrictors  of  the  pharynx,  and, 
after  surrounding  the  lingual  artery,  open  into  a  gland  placed  on  the  internal 
jugular  vein  immediately  below  the  posterior  belly  of  the  digastric.  (4)  The  central 
trunks,  which  descend  in  the  middle  line  between  the  genio-hyo-glossi,  pass  beneath 
the  hyoglossus  and  mylohyoid  muscles  into  the  submaxillary  space,  and  thence 
in  front  of  the  hyoid  bone  (having  embraced  the  tendon  of  the  digastric)  to  join 
the  glands  of  the  internal  jugular  chain. 

Between  the  tongue  and  the  inner  surface  of  the  gums  is  the  alveolo-glossal 
sulcus,  crossed  in  the  middle  line  by  the  frenum  linguse,  which  passes  upwards  to 
the  under  surface  of  the  tongue  (Fig.  896).  Immediately  on  either  side  of  the 
lower  part  of  the  frenum  is  the  orifice  of  Wharton's  duct.  A  little  external  to  the 
frenum  the  ranine  veins  are  seen  lying  immediately  under  the  thin  mucous  mem- 
brane ;  to  the  outer  side  of  the  veins  are  the  ranine  arteries  and  the  lingual  nerves, 
both  of  which  lie  deeper  than  the  veins,  and  are  therefore  not  visible. 

The  mucous  membrane  at  the  anterior  part  of  the  floor  of  the  alveolo-glossal 
sulcus  is  thrown  into  a  slight  elevation,  which  overlies,  and  is  caused  by,  the 
sublingual  salivary  gland.  The  duct  of  the  submaxillary  gland  (Wharton's  duct) 
and  the  Ungual  nerve  lie  beneath  and  to  the  inner  side  of  the  sublingual  gland. 

In  dividing  a  shortened  frenum  for  "  tongue-tie  "  the  ranine  vessels  and  the  orifices  of 
Wharton's  ducts  must  be  avoided.  Behind  the  frenum  linguee  are  the  anterior  borders  of 
the  genio-hyo-glossi,  which  descend  to  the  upper  genial  tubercles.  In  operations  necessitat- 
ing the  removal  of  the  region  of  the  symphysis  of  the  jaw,  or  the  separation  of  the  origins 
of  the  genio-hyo-glossi,  the  tongue  must  be  kept  forward,  otherwise  the  patient  will  be 
suffocated  by  the  organ  falling  backwards  over  the  entrance  to  the  larynx.  In  removing 
a  small  salivary  calculus  from  the  floor  of  the  mouth  the  calculus  should  be  fixed  with  the 
finger  against  the  inner  surface  of  the  jaw  before  catting  down  upon  it. 

When  the  teeth  are  clenched  the  vestibule  of  the  mouth  communicates  behind 
the  last  molars  with  the  oral  cavity  proper  through  an  opening  which  barely 
admits  a  medium-sized  catheter.  Hence,  when  the  jaws  cannot  be  separated  it  is 
generally  necessary  to  feed  the  patient  through  a  tube  passed  along  the  floor  of  the 
nose. 

By  opening  the  mouth  widely  and  taking  a  deep  inspiration,  the  soft  palate  is 
elevated,  and  the  anterior  and  posterior  pillars  of  the  fauces  are  rendered  prominent 
(Fig.  707).  The  anterior  pillars  are  seen  to  spring  from  the  anterior  surface  of  the 
soft  palate,  close  to  the  base  of  the  uvula,  and  to  arch  downwards  and  outwards  in 
front  of  the  tonsils  to  end  at  the  posterior  extremity  of  the  lateral  border  of  the 
tongue.  The  posterior  pillars  are  really  the  continuation  of  the  lower  free  border  of 
the  soft  palate  downwards  behind  the  tonsils  to  become  attached  to,  and  lost  upon, 
the  postero-lateral  wall  of  the  pharynx.  Together  with  the  lower  edge  of  the  soft 
palate  and  the  base  of  the  tongue  they  bound  a  hemispherical  opening  (isthmus 
faucium),  through  which  is  visil)le  the  oral  portion  of  the  mucous  membrane  cover- 
ing the  posterior  wall  of  the  ])harynx. 

The  faucial  tonsils  (Fig.  897)  lie  one  on  each  side  of  the  isthmus,  between  the 
anterior  and  posterior  pillars  of  the  fauces ;  they  are  situated  opposite  the  angle 


THE  FACE. 


1245 


r)f  the  jaw,  but  they  cannot  be  felt  froiu  the  outside.  Eacli  tonsil  is  covered  on  its 
tree  surface  by  mucous  membrane  upon  which  are  seen  the  orifices  of  the  tonsillar 
crypts  ;  the  outer  or  deep  surface  is  covered  by  a  layer  of  fibrous  tissue  which  forms 
an  imperfect  capsule  to  the  organ.  According  to  Merkel,  the  internal  carotid 
artery  is  situated  1-5  cm.  behind  the  outer  margin  of  the  tonsil,  which  is 
separated  from  the  superior  constrictor  by  a  quantity  of  loose  cellular  tissue 
and  fat,  so  that  the  gland  can  be  grasped  with  a  volsellum  and  pulled  forward 
without  dragging  the  vessel  with  it.  The  tonsil  receives  its  blood -■'nijoj^h/ 
mainly   from  a  sniall  vessel  derived  from   the   anterior   palatine   artery ;   when 

Hyi)oglossal  nervp 
liiternal,ju^;iilar  vein    |    Inti^rnal  oarotiil  artery 


Spinal  accossory  nerv: 
PiRastrio  tiinscle 


Styloliyoi 

Glos.so- 

l)liaiyii>;cal  iiovm' 

I'arntid  glaii'l 

Teinpom- 

Miaxillary  voiii 

Kxtenial  caroti  " 

artpiy 

Styloglossus 

Ascending 
]ialatinp  arten 

Iiitonial  ptory^niil— 1 

Epiglottit 

Frennlnii 
ppiglottifli- 

?.[asspte 

rhaiynsoal  portim 
of  tniicrni 


Pimumogastric  ner\p 

I      Synipathptio 
,  1        Asceiidiiig  pliaryngpal  artery 

\    \    \      I       I  Odontoid  procps: 


l'iist.])liarynni'al 
■yini)liatic  gland 


Superior 

constrictor  inusili' 
I'osterior  palatini- 
arch 

Tonsil 

I'haryngo-ppijrlottic 
fold 

Anterior  palatini' 
arch 

Circnmvallati' 
papilla- 


Raplip  of  tongue 
CoiMPal  jiai>ill;i- 


I-'ungiforni  papilla  _ 
nupcinatnr 


Fungiform  papilla 


Fici.  897.  — HoiiizoxTAL  Section  thuduoh  Mouth  axd  PHARi'Nx  at  thk  Lkvei.  or  thi;  Tnxsir.s. 

The  stylopharj'ngeu.s,  which  i.s  sliown  immediately  to  the  inner  side  of  the  external  carotid  ,ut<-rj-,  and  tlie 
prevertebral  muscles,  are  not  indicated  by  reference  lines  (from  Birmingham). 

this  branch  is  larger  than  usual  and  adherent  to  the  capsule  of  the  tonsil  the 
lileeding  which  attends  the  operation  of  removal  of  the  tonsils  may  be  consider- 
able. The  haemorrhage  can  be  arrested  by  pressing  the  bleeding  point  outwards 
against  the  internal  pterygoid  and  the  ramus  of  tlie  jaw.  If  the  bleeding  be  from 
a  spurting  vessel  of  larger  size,  its  source,  according  to  Merkel,  is  probably  the 
facial  artery,  which  has  been  wounded  as  it  arches  upwards  beneath  the  digastric 
and  stylo-hyoid  muscles  to  within  a  short  distance  from  the  outer  surface  of  the 
tonsil.  In  children  and  adolescents  the  tonsils  are  frequently  hypertrophied  ;  the 
enlargement  may  be  either  general,  more  towards  the  middle  line,  downwards  along 
the  pharynx,  or  upwards  behind  the  soft  palate ;  to  expose  and  thoroughly  remove 
the  last-mentioned  variety  of  enlargement  the  upper  part  of  the  anterior  pillar  of 
tVie  fauces  must  be  divided. 

The  mucous  membrane  and  the  periosteum  of  the  haxd  palate  are  so  closely 


1246  SUEFACE  AND  SURGICAL  ANATOMY. 


united  as  to  form  practically  one  membrane.  The  posterior  palatine  arteries,  after 
leaving  the  posterior  palatine  foramina,  run  forward  in  shallow  grooves  in  the 
hard  palate,  close  to  its  alveolar  margin.  In  the  operation  for  cleft  palate 
(staphylorraphy),  in  order  to  secure  nourishment  for  the  muco-periosteal  flaps,  the 
lateral  incisions  should  be  made  external  to  these  vessels. 

Secondary  hfemorrhage  after  the  operation  for  cleft  palate  is  treated  by  plugging  the 
posterior  palatine  foramen,  which  lies  a  little  internal  to  the  last  molar  tooth  about 
i  in.  in  front  of  the  hamular  process,  which  can  be  felt  at  the  upper  extremity  of  the  fold 
of  mucous  membrane  containing  the  pterygo-maxillary  ligament.  In  the  closure  of 
a  wide  cleft  of  the  soft  palate  the  tension  of  the  tensor  palati  muscle  is  got  rid  of 
by  chipping  off  the  hamular  process  with  a  small  chisel  introduced  at  the  posterior 
extremity  of  the  lateral  rehef  incisions. 

Naso-pharynx. — To  explore  the  upper  or  nasal  division  of  the  pharynx  the 
finger  should  be  hooked  upwards  behind  the  soft  palate.  Anteriorly,  the  finger 
readily  detects  the  sharp  posterior  border  of  the  vomer,  the  posterior  nares,  and  the 
posterior  extremity  of  the  middle  and  inferior  turbinals.  The  roof  of  the  space  is 
formed  by  the  basilar  process  of  the  occipital  bone,  while  upon  the  posterior  wall  is 
a  transverse  bony  ridge  caused  by  the  projection  of  the  anterior  arch  of  the  atlas. 
Upon  the  lateral  toalls  of  the  naso-pharynx  are  the  openings  of  the  Eustachian 
tubes,  situated  -h  in.  behind  the  posterior  extremities  of  the  inferior  turbinals  (Fig. 
708).  The  orifices,  bounded  superiorly  and  posteriorly  by  a  prominent  margin,  are 
directed  downwards  and  forwards,  and,  therefore,  in  a  direction  favourable  to  the 
passage  of  the  Eustachian  catheter.  Behind  the  prominent  posterior  margin  of  the 
orifice  is  a  lateral  recess  of  the  pharynx  known  as  the  fossa  of  Rosenmiiller,  in  which 
the  point  of  the  Eustachian  catheter  is  apt  to  become  engaged.  Upon  the  roof  and 
posterior  wall  of  the  pharynx,  down  to  the  level  of  the  anterior  arch  of  the  atlas, 
and  extending  laterally  as  far  as  the  Eustachian  orifices,  is  a  collection  of  adenoid 
tissue,  the  pharyngeal  tonsil.  Hypertrophy  of  this  tissue  constitutes  the  condition 
known  as  "  adenoids,"  the  harmful  effects  of  which  are  due  to  their  interference 
with  nasal  respiration.  Upon  the  centre  of  the  pha.ryngeal  tonsil  is  an  orifice 
leading  into  a  small  recess  into  which  numerous  mucous  glands  open.  The 
structures  felt  in  the  post-nasal  space  may  be  rendered  visible  by  reflecting  the 
light  upon  a  small  mirror  placed  immediately  behind  and  below  the  soft  palate 
(posterior  rhinoscojjy).  The  lower  part  of  the  inferior  turbinal  is  obscured  from 
view  by  the  bulging  of  the  upper  surface  of  the  soft  palate. 

In  plugging  the  posterior  nares,  it  is  imrjortant  to  remember  that  these  openings 
measure  nearly  one  inch  in  the  vertical  and  half  an  inch  in  the  transverse  direction. 
In  the  child,  owing  to  the  small  size  of  the  face,  the  vertical  diameter  of  the  naso- 
pharynx is  relatively  much  smaller  than  in  the  adult. 

The  lymphatics  from  the  nasal  fossfe  and  pharynx,  including  the  faucial  and 
pharyngeal  tonsils,  join  the  sub-parotid  and  upper  deep  cervical  glands,  one  of 
which  lies  internal  to  the  carotid  vessel  between  the  lateral  recess  of  the  pharynx 
and  the  prevertebral  fascia.  In  children  suppuration  originating  in  this  gland  is 
the  commonest  cause  of  a  retro-pharyngeal  abscess. 

In  the  adult  the  four  upper  cervical  vertebrae  can  be  explored  from  the  mouth, 
while  in  the  cliild  the  finger  can  also  reach  as  far  down  as  the  sixth  vertebra  and  the 
Imck  of  the  cricoid  cartilage. 

THE   NECK. 

The  general  envelope  of  deep  cervical  fascia,  along  with  the  processes  and  partitions 
which  proceed  from  its  deep  surface,  subdivides  the  neck  into  compartments  which 
limit  and  determine  the  spread  of  pus.  The  most  important  compartment  is  the 
central  or  visceral  compartment,  bounded  anteriorly  by  the  pretracheal  fascia,  pos- 
teriorly by  the  prevertebral  fascia,  and  laterally  by  the  fascia  forming  the  vascular 
compartment.  Posteriorly,  this  compartment  extends  from  the  base  of  the  skull 
downwards  into  the  posterior  mediastinum  ;  anteriorly,  it  extends  from  the  hyoid 
bone  into  the  anterior  part  of  the  superior  mediastinum.     Abscesses  in  the  visceral 


'ter  V 


THE  NECK. 


1247 


compartment  are  either  secondary  to  disease  of  the  organs  it  contains,  or  the  result 
of  a  primary  suppurative  cellulitis.  A  tubercular  abscess  originating  in  one  of  the 
retropharyngeal  lymphatic  glands  (Fig.  897)  lies  in  front  of  the  prevertebral  fascia, 
and  points  towards  the  posterior  wall  of  the  pharynx ;  a})scesses  secondary  to 
disease  of  the  cervical  vertebras  lie  behind  the  prevertebral  fascia,  and  spread 
laterally  behind  the  vascular  compartment ;  they  point  behind  the  sterno-mastoid, 
and  should  be  opened  through  an  incision  at  the  posterior  border  of  the  muscle,  the 
surgeon  keeping  to  the  anterior  aspect  of  the  transverse  j)rocesses  in  order  to  avoid 
the  structures  in  the  vascular  compartment  (Chiene). 

In  front  of  the  visceral  compartment  is  a  small  muscular  compartment  containing 
the  depressor  muscles  of  the  hyoid  bone ;  anterior  to  it  again,  in  the  region  of  the 
supra-sternal  notch,  is  tlie  small  supra-sternal  compartment,  containing  the  lower 


Facial  artery 
Submaxillary  gland 

Bifiu'catioii  of  common  carotid  artery 


Brachial  plexu 
Subclavian  aitery 
Acromial  end  of  clax  ic\e 
Lesser  tubei  osity  of    \ 
humei  u 
Tendon  of  bicepi 
Greater  tubeiobit; 
of  humeius  / 

/ 
# 


Anterior  belly  of  digastric 
Tlyoid  boTie 

liyroid  cartilage  (pomum  Adami) 
Crico-thyroid  meinbrane 

External  jugular  vein 
!ricoid  cartilage 

tlimus  of  thyroid  gland 

internal  head  of  sterno-mastoid 
— t;iavicular  head  of  sterno-mastoid 

no-ela\  leular  articulation 
Ti'i  1  st  part  axi  llary  artery 
,'oracoid  process 


noiiaiy  valve 
Tiicnspid  valve  /      '  Aortic  valve 

Mitial  vahe 
Fi(!.  898.— Anterior  Aspect  of  Neck  and  Shoulders. 

part  of  the  anterior  jugular  veins,  along  with   their  transverse  communicating 
branch,  a  little  fat,  and  one  or  two  lymphatic  glands. 

The  vascular  compartment,  triangular  in  section,  is  bounded  anteriorly  by  the 
general  fascial  envelope,  which  splits  at  the  omo-hyoid  to  enclose  the  depressors  of 
the  hyoid  bone ;  posteriorly  by  the  prevertebral  fascia ;  internally  by  the  visceral 
compartment ;  externally  by  the  meeting  of  the  prevertebral  fascia  and  the  pos- 
terior layer  of  the  sterno-mastoid  sheath.  This  compartment  contains  the  carotid 
vessels,  and  the  internal  jugular  vein,  and  the  following  nerves,  viz. :  the  vagus, 
the  first  part  of  the  hypoglossal,  the  descendens  hypoglossi,  and  the  upper  part  of 
the  spinal  accessory.  The  carotid  chain  of  lymphatic  glands  lies  in  the  cellular 
tissue  which  connects  the  various  structures  in  the  compartment ;  normally  they 
may  be  readily  separated  from  the  sheath  of  the  internal  jugular  vein,  to  which, 
however,  they  become  adherent  when  inflamed.     A  glandular  abscess  in  this  com- 


1248 


SUEFACE  AND  SUEGICAL  ANATOMY. 


partment  usually  points  upon  the  surface,  adhesions  being  formed,  first,  between 
the  gland  and  the  fascia,  and,  subsequently,  between  the  latter  and  the  cutaneous 
structures.  In  diffuse  suppurative  cellulitis  of  this  compartment  the  pus  burrows 
towards  the  root  of  the  neck,  and  may  reach  either  the  mediastinum  or  the  axilla. 

Middle  Line  of  the  Neck. — The  body  of  the  hyoid  bone  divides  the  middle  line 
of  the  neck  into  supra-  and  infra-hyoid  portions.  Above  the  hyoid  bone  is  the  sub- 
mental triangle,  with  its  apex  at  the  lower  border  of  the  symphysis  menti  and  its 
sides  formed  by  the  anterior  bellies  of  the  digastrics.  In  the  floor  of  the  triangle 
are  the  anterior  portions  of  the  mylo-hyoid  muscles,  separated  by  the  median 
raphe  (Fig.  79).  The  most  important  structures  in  the  triangle  are  the  submental 
lymphatic  glands,  which  can  usually  be  felt  a  little  above  the  body  of  the  hyoid 
bone.  They  are  a  frequent  seat  of  abscess  secondary  to  impetigo  of  the  lower  lip 
and  chin.  About  1  in.  below  the  hyoid  bone  is  the  pomum  Adami,  more  prominent 
in  the  male  than  in  the  female.  On  either  side  of  the  pomum  Adami  are  the  alae 
of  the  thyroid  cartilage,  while  between  the  latter  and  the  hyoid  bone  is  the  thyro- 
hyoid membrane.  In  the  operation  of  sul-hyoid  ;pharyngotomy  the  epiglottis  and 
the  superior  opening  of  the  larynx  are  reached  by  passing  through  the  anterior 
wall  of  the  pharynx  at  the  level  of  the  thyro-hyoid  membrane.  The  structures 
divided  from  without  inwards  are :  the  integuments,  the  sterno-hyoid,  omo-hyoid, 
and  thyro-hyoid  muscles,  the  middle  portion  of  the  thyro-hyoid  membrane,  along 
with  a  layer  of  fat  between  it  and  the  lower  part  of  the  epiglottis,  and,  finally, 
the  glosso-epiglottidean  ligament  and  fold  of  mucous  membrane.     The  incision 


Anterior  belly  of  digastric 
Mylo-hyoid 


Submaxillary  gland 


Thyro-hyoid  membrane 


Thyroid  cartilage 

Superior  thyroid  artery 
Crico-thyroid  membrane 

Cricoid  cartilage 

Lateral  lobe  of  thyroid 
Common  carotid 

Phrenic  nerv 
Inferior  thyroid 
Transver.salis  colli 
Vertebral  artery 

Subclavian  artery 
Suprascapular  artery 

Common  carotid  artery 
Internal  mammary  artery 
Innominate  artery 
Inferior  thyroid  vein 


Anterior  belly  of  digastric 
M  i^io-hyoid 


Submaxillary  gland 

Omo-hyoid 
Sterno-hyoid 

Internal  jugular  vein 
Superior  thyroid  vein 

_  Common  carotid  artery 

-  Sterno-mastoid 

-  Crico-thyroid  muscle 

Lateral  lobe  of  thyroid-  bodj- 
Isthmus  of  thyroid 
Scalenus  anticus 

Scalenus  medius 
Subclavian  artery 


First  rib 


Trachea 


Fig.  899. — Dissfxtion  ok  the  Front  ok  thk  Neck.  'ITie  lower  portions  of  the  steruo-mastoid  muscles 
have  been  removed,  and  the  lower  part  of  the  right  common  carotid  artery  cut  away  to  show  the  deeper 
parts  (from  Cunningham). 


must  not  be  extended  too  far  on  either  side  of  the  mesial  plane  for  fear  of 
wounding  the  superior  laryngeal  vessels  and  nerve  which  pierce  the  thin  lateral 
portions  of  the  thyro-hyoid  membrane. 

Tlie  •wound  in  suicidal  cut-throat  is  generally  at  this  level.  The  more  important  structures 
Avhich  are  usually  divided  are  :  more  or  less  of  tlie  left  sterno-mastoid  muscle,  the  superior 
thyroid  vessels,  the  thyro-hyoid  memhrane,  the  base  of  the  epiglottis,  and,  less  frequently,  the 
carotid  ve.sseb,  the  intenial  jugular  vein,  and  the  superior  laryngeal  nerve.     When  the  wound. 


THE  NECK.  1249 

is  above  the  hyoid  bone,  tlie  lingual  and  facial  vessels  and  the  muscles  of  the  tongue  are  the 
more  important  structures  injured. 

At  the  level  of  the  middle  of  the  anterior  border  of  the  thyroid  cartilage  is  the 
rima  glottidis.  A  little  more  tlian  au  inch  below  the  pomum  Adami  is  the 
anterior  arch  of  the  cricoid  cartilage,  which  may  be  readily  felt,  and,  when  the  neck 
is  extended,  often  seen ;  it  lies  a  little  below  a  point  midway  between  the  lower 
margin  of  the  chin  and  the  upper  border  of  the  sternum.  Above  the  cricoid  is  the 
crico-thyroid  membrane ;  in  the  operation  of  laryngotomy  only  the  middle  portion 
of  the  membrane  is  divided,  in  order  to  avoid  injury  to  the  crico-thyroid  muscles. 
The  small  crico-thyroid  branch  of  the  superior  thyroid  artery  lies  close  to  the 
lower  border  of  the  thyroid  cartilage.  Below  the  cricoid  cartilage  is  the  trachea, 
which  recedes  as  it  descends,  so  that  it  lies  Ih  in.  from  the  surface  at  the  level  of 
the  upper  border  of  the  sternum.  The  isthmus  of  the  thyroid  gland  lies  in  front  of 
the  second,  third,  and  fourth  rings  of  the  trachea  (Fig.  872) ;  not  infrequently, 
however,  it  reaches  up  to  the  cricoid.  Immediately  in  front  of  the  trachea,  Ijelow 
the  isthmus  of  the  thyroid,  is  the  pretracheal  fat,  containing  one  or  two  lymphatic 
glands  and  the  inferior  thyroid  veins,  each  represented  by  one  or  more  branches  which 
converge  as  they  descend.  The  pretracheal  lymphatic  glands  receive  afferent  vessels 
from  the  larynx  and  thyroid  body,  while  their  efferent  vessels  open  into  the  inferior 
carotid  glands.  In  the  adult  the  innominate  artery  crosses  the  front  of  the  trachea 
at  the  level  of  the  upper  border  of  the  sternum  ;  in  the  child,  however,  it  not 
infrequently  crosses  half  an  inch  higher,  a  relation  which  must  be  remembered  in 
performing  the  operation  of  low  tracheotomy. 

In  the  operation  of  high  tracheotomy  the  upper  three  rings  of  the  trachea  are  divided. 
The  incision,  which  should  be  mesial,  divides  the  integuments,  the  tributaries  of  the 
anterior  jugular  veins,  the  general  envelope  of  deep  cervical  fascia,  and,  after  passing 
between  the  depressor  muscles  of  the  hyoid  bone,  the  pretracheal  fascia,  which  descends 
from  the  cricoid  to  enclose  the  isthmus  of  the  thyi'oid  gland.  By  dividing  this  fascia 
transversely  below  the  cricoid,  the  isthmus  may  be  pulled  dowaiwards  and  the  upper  rings 
of  the  trachea  exposed.  In  some  cases  it  is  necessary  either  to  divide  the  isthmus  or  to 
extend  the  incision  upwards  through  the  cricoid  cartilage.  In  opening  the  trachea,  the 
edge  of  the  knife  should  be  dii'ected  upwards  so  as  to  avoid  injuring  the  vessels  at  the 
upper  border  of  the  isthmus.  The  anterior  jugular  veins  are  in  danger  of  being  wounded 
if  the  skin  incision  is  not  strictly  mesial.  In  low  tracheotomy  the  trachea  below  the 
isthmus  is  opened  ;  it  is  a  more  troublesome  operation  on  account  of  the  depth  of  the 
trachea  and  the  presence  in  front  of  it  of  the  large  inferior  thyroid  veins  and  of  the  trans- 
verse anterior  jugular  vein.  In  children  the  difficulty  is  increased  by  the  higher  position 
of  the  innominate  artery  and  left  innominate  vein,  by  the  presence  of  the  thymus  gland, 
and  by  the  shortness  of  the  neck. 

Triangles  of  the  Neck. — The  lateral  aspect  of  the  neck  may  be  divided  into 
an  anterior  and  a  posterior  triangle  by  the  sterno-mastoid  muscle ;  the  former 
is  further  subdivided  into  digastric,  carotid,  and  muscular  triangles  by  the  digastric 
and  omo-hyoid  muscles.  The  posterior  triangle  is  subdivided  into  occipital  and 
clavicular  portions  by  the  posterior  belly  of  the  omo-hyoid. 

The  sterno-mastoid  muscle  forms  one  of  the  most  important  superficial  land- 
marks of  the  neck.  The  anterior  border  of  the  muscle,  the  more  distinct  of  the 
two,  may  be  felt  along  its  whole  extent.  Between  the  prominent  sternal  origin 
and  the  broad  ribbon-like  clavicular  origin  is  a  sUght  triangular  depression  which 
overlies  the  lower  part  of  the  internal  jugular  vein. 

Digastric  Triangle. — This  triangle  is  subdivided  into  an  anterior  or  sub- 
maxillary portion  and  a  posterior  or  parotid  portion  by  the  stylo-maxillary  liga- 
ment. In  the  anterior  portion  is  the  submaxillary  gland,  which  extends  from  the 
posterior  half  of  the  lower  border  of  the  mandible  to  the  great  cornu  of  the  hyoid 
bone.  The  facial  vein  passes  downwards  and  backwards  superficial  to  the  gland, 
while  the  facial  artery,  imbedded  in  its  deep  surface,  arches  upwards  under  cover 
of  the  angle  of  the  jaw,  where,  according  to  Merkel,  it  approaches  the  tonsil,  being 
separated  from  it,  however,  by  the  superior  constrictor  of  the  pharynx.  The 
lingual  artery  may  be  ligatured  in  the  digastric  triangle,  where  it  lies  behind  the 
84 


1250 


SUEFACE  AND  SUEGICAL  ANATOMY. 


hyo-glossus  a  little  above  the  great  cornu  of  the  hyoid  bone  ;  the  superficial  guides 
to  the  vessel  are  the  lower  border  of  the  submaxillary  gland,  and  the  hypoglossal 


Apex  of  mastoid  process \ 


Hypoglossal  nerve 

Bifurcation  of  common 
carotid  artery 

Stemo-mastoid 

Carotid  tubercle 

Apex  of  lung 

Brachial  plexus 

Subclavian  artery 
1st  part  axillary  artery 
Coracoid  process 

Acromio- 
clavicular joint 


-External  angular  process 
JZygoma 

-Temporal  artery 

'acial  nerve 
Transverse  process  of  atlas 
acial  artery 
Submaxillary  gland 

— ; Anterior  belly  of  digastric 
-Tip  of  greater  cornu  ot  hyoid  bone 

Tip  of  superior  cornu  of  thyroid 

cartilage 

Body  of  hyoid  bone 

Poniuin  Adanii 
'ricoid  cartilage 
.sthmus  of  thyroid  gland 

Clavicular  head  of  steruo-mastoid 
Sternal  head  of  stemo-mastoid 

?^5„„, Bifurcation  of 

innominate  artery 

^nfra-clavicular  fossa 

Upper  border  of 
manubrium  sterni 


Greater  tuberositj 
of  Imnieru-) 


Lesser  tuberosity  of 
humerus 
Bicipital  groove 


Fig.  900. — Lateral  Aspect  of  Neck. 


nerve  and  lingual  vein,  wliich  lie  upon  the  hyo-glossus,  the  latter  being  .recognised 
by  the  vertical  direction  of  its  fibres.  The  fioor  of  the  digastric  triangle  is  formed, 
from  before  backwards,  by  the  mylo-hyoid,  hyo-glossus,  and  superior  constrictor 
of  the  pharynx.  The  lymphatic  glands  of  this  space  receive  their  lymphatics  from 
the  face,  lips,  teeth  and  gums,  tongue,  and  floor  of  the  mouth.  Suppurative 
cellulitis  of  the  connective  tissue  of  this  space  is  called  angina  Ludovici. 

Carotid  Triangle. — The  central  landmark  of  this  triangle  is  the  great  cornu  of 
the  hyoid  bone,  the  tip  of  which,  when  the  fascia  is  relaxed,  may  be  readily  felt 
immediately  in  front  of  the  anterior  border  of  the  stemo-mastoid,  at  a  point  corre- 
sponding to  the  centre  of  a  line  drawn  from  the  tip  of  the  mastoid  process  to  the 
pomum  Adami.  The  deep  cervical  fascia  holds  the  upper  part  of  the  sterno- 
mastoid  forwards  towards  the  angle  of  the  jaw,  so  that,  with  the  fascia  undivided, 
the  anterior  border  of  the  sterno-mastoid  overlaps  the  internal  jugular  vein  and 
the  bifurcation  of  the  common  carotid  artery. 

The  course  of  the  carotid  vessels  is  indicated  upon  the  surface  by  a  line  extending 
from  the  upper  end  of  the  sterno-clavicular  articulation  to  a  point  midway  between 
the  angle  of  the  jaw  and  the  tip  of  the  mastoid  process ;  a  point  upon  this  line, 
at  the  level  of  the  upper  border  of  the  thyroid  cartilage,  overlies  the  bifurcation 
of  the  common  carotid.  The  anterior  belly  of  the  omo-hyoid  crosses  the  common 
carotid  at  the  level  of  the  cricoid  cartilage.  The  pulsations  of  the  carotid  vessels 
may  be  felt  in  the  hollow  between  the  larynx  and  the  anterior  border  of  the  sterno- 
mastoid.  In  the  carotid  triangle  the  external  carotid  lies  internal  and  anterior 
to  the  internal  carotid.  The  seat  of  election  for  ligation  of  the  external  carotid 
is  between  its  superior  thyroid  and  lingual  branches,  a  finger's-breadth  below  the 
tip  of  the  great  cornu  of  the  hyoid  bone  ;  the  difficulty  in  the  operation  is  due  to 
the  plexus  of  veins  (formed  by  the  common  facial,  lingual,  and  superior  thyroid 
veins)  which  overhes  the  artery.  The  lingual  and  facial  arteries  frequently  arise 
from  a  common  trunk  which  must  not  be  mistaken  for  the  external  carotid.     The 


THE  NECK.  1251 

superior  thyroid  artery  arises  opposite  the  upper  cornu  of  the  thyroid  cartilage,  which 
may  be  distinctly  felt  1  in.  below  the  tip  of  the  great  cornu  of  the  hyoid  bone. 
The  vessel  and  its  companion  vein  are  common  sources  of  haemorrhage  in  cut-throat. 
The  guide  to  the  lingual  artery,  in  the  carotid  triangle,  is  the  tip  of  the  great  cornu 
of  the  hyoid  bone,  above  which  it  forms  an  arch,  crossed  by  the  hypoglossal  nerve. 
The  vessel  enters  the  digastric  triangle  by  passing  beneath  the  tendons  of  the 
stylo-hyoid  and  digastric  muscles.  When  ligation  of  the  artery  is  called  for,  it  is, 
as  a  rule,  preferable  to  secure  it  in  the  carotid  rather  than  the  digastric  triangle. 

From  a  surgical  point  of  view  the  internal  jugular  vein  is  the  most  important 
structure  in  the  anterior  triangle.  In  the  carotid  division  of  the  triangle  it  over- 
laps the  carotid  vessels,  and  its  sheath  lies  close  beneath  the  general  envelope  of 
deep  cervical  fascia.  About  the  level  of  the  hyoid  bone  it  receives  the  large  common 
facial  vein,  and  it  is  the  glands  in  the  neighbourhood  of  those  which  overlie  the 
junction  of  this  vein  with  the  internal  jugular  that  are  most  frequently  the  seat 
of  tubercular  disease,  because  they  receive  efferent  vessels  from  so  many  regions  of 
the  head  and  neck. 

The  deep  cervical  chain  of  lymphatic  glands  descends  beneath  the  sterno-mastoid 
muscle  from  the  subparotid  glands  above  to  the  subclavian  glands  below.  While 
the  majority  are  related  to  the  anterior  and  external  aspects  of  the  sheath  of  the 
internal  jugular  vein,  there  are  others  (receiving  cutaneous  lymphatics  from  the 
posterior  part  of  the  head  and  neck)  which  lie  more  posteriorly,  in  the  fibro-fatty 
tissue  which  surrounds  the  upper  part  of  the  spinal  accessory  nerve  and  the  branches 
of  the  cervical  plexus. 

The  hypoglossal  nerve  curves  forwards  across  the  carotid  vessels  at  the  level  of 
the  lower  border  of  the  posterior  belly  of  the  digastric.  The  vagus  nerve  descends 
vertically  behind  and  between  the  carotid  vessels  and  the  internal  jugular  vein ; 
care  must  be  taken  not  to  include  it  when  ligaturing  the  common  carotid  or 
internal  jugular.  Surgically,  the  spinal  accessory  is  the  most  important  nerve  in 
the  anterior  triangle ;  it  enters  the  substance  of  the  sterno-mastoid  muscle  Ih  in. 
below  the  tip  of  the  mastoid  process.  A  portion  of  the  nerve  is  resected  in  the 
treatment  of  spasmodic  wry-neck,  and  it  is  almost  always  exposed  in  the  removal 
of  the  upper  carotid  group  of  deep  cervical  glands.  The  course  of  the  nerve 
may  be  mapped  out  upon  the  surface  by  drawing  a  line  from  a  point  midway 
between  the  tip  of  the  mastoid  process  and  the  angle  of  the  jaw  to  the  middle  of 
the  posterior  border  of  the  sterno-mastoid  muscle,  and  thence  across  the  posterior 
triangle  to  the  anterior  border  of  the  trapezius,  beneath  which  it  passes  at  the 
level  of  the  seventh  cervical  spine.  The  deeper  guides  to  the  nerve  are  the 
posterior  belly  of  the  digastric,  the  internal  jugular  vein,  and  the  transverse 
process  of  the  atlas,  which  is  felt  as  a  distinct  bony  landmark  midway  between 
the  tip  of  the  mastoid  and  the  angle  of  the  jaw.  The  cervical  sympathetic  lies 
in  the  posterior  wall  of  the  vascular  compartment  of  the  neck,  and  may  be 
reached  by  an  incision  along  the  posterior  border  of  the  sterno-mastoid:  the 
anterior  surfaces  of  the  roots  of  the  transverse  processes  of  the  vertebra  are  the 
deep  guides  to  the  nerve.  The  cervical  plexus,  which  lies  behind  the  upper  half 
of  the  sterno-mastoid  upon  the  levator  anguli  scapula;  and  scalenus  medius 
muscles,  may  be  exposed  through  an  incision  along  the  posterior  border  of  the 
upper  half  of  the  sterno-mastoid  muscle.  The  phrenic  nerve,  the  most  important 
branch  of  the  cervical  plexus,  arises  one  inch  above  the  carotid  tubercle  and 
descends  almost  vertically  upon  the  scalenus  anticus ;  it  is  overlapped  by  the 
outer  margin  of  the  internal  jugular  vein. 

The  muscular  or  lower  carotid,  triangle  is  an  important  triangular  inter- 
muscular space  bounded  by  the  anterior  liorder  of  the  sterno-mastoid,  the  anterior 
belly  of  the  omo-hyoid  and  the  sterno-hyoid.  By  making  an  incision  along  the 
anterior  border  of  the  left  sterno-mastoid  muscle,  and  passing  through  this  triangle, 
the  surgeon  reaches,  in  order  from  before  backwards,  the  internal  jugular  vein,  the 
common  carotid  artery,  the  vagus,  the  thoracic  duct  (on  the  left  side),  the  middle 
cervical  ganglion  of  the  sympathetic,  the  inferior  thyroid  artery,  the  vertebral 
vessels,  the  recurrent  laryngeal  nerve,  and  the  oesophagus.  The  most  important 
bony  landmark  in  this  triangle  is  the  prominent  anterior  tubercle  of  the  transverse 


1252  SURFACE  AND  SUEGICAL  ANATOMY. 

process  of  the  sixth  cervical  vertebra.  The  common  carotid  artery  may  be  com- 
pressed against  this  tubercle,  which  is  therefore  termed  the  "  carotid  tubercle."  As 
it  is  the  most  important  guide  to  the  vertebral  artery,  which  enters  the  foramen  in 
its  transverse  process,  it  is  often  referred  to  as  the  "  vertebral  arterial  tubercle^ 

In  operations  in  this  region,  on  the  left  side,  it  is  important  to  avoid  the 
thoracic  duct,  which  extends  upwards  into  the  neck  one  inch  vertically  above  the 
inner  end  of  the  clavicle,  and,  after  arching  outwards  behind  the  common  carotid, 
descends  behind  the  lower  inch  of  the  internal  jugular  vein. 

The  cervical  portion  of  the  oesophagus,  which  begins  at  the  level  of  the  cricoid 
cartilage,  descends  behind,  and  a  little  to  the  left  of,  the  trachea.  To  expose  it,  the 
surgeon,  after  passing  through  the  above-mentioned  muscular  triangle,  passes 
between  the  trachea  and  the  carotid  sheath ;  or  it  may  be  exposed  through  an 
incision  in  the  middle  line,  the  trachea,  which  is  freely  movable,  being  displaced  to. 
the  right  side.  In  opening  the  oesophagus  care  must  be  taken  not  to  injure  the 
recurrent  laryngeal  nerve  which  ascends  in  the  groove  between  it  and  the  trachea, 
and  also  that  the  loose  submucous  cellular  interval  must  not  be  mistaken  for  the 
lumen  of  the  tube.  The  recurrent  laryngeal  nerve  must  be  avoided  also  in 
operations  connected  with  the  thyroid  gland ;  it  is  most  liable  to  be  injured  during 
the  application  of  a  ligature  to  the  inferior  thyroid  artery,  which  arches  inwards  in 
front  of  the  nerve  to  reach  the  posterior  surface  of  the  gland.  Adjacent  to  the 
lateral  aspects  of  the  cervical  portions  of  the  trachea  and  oesophagus  are  a  few  small 
lymphatic  glands  which  receive  their  efferent  vessels  from  the  larynx,  trachea, 
oesophagus,  and  thyroid  body.  The  efferent  vessels  from  this  chain  join  either  the 
inferior  carotid  or  subclavian  glands. 

The  Posterior  Triangle. — Imbedded  in  the  deep  cervical  fascia  at  the  posterior 
border  of  the  sterno-mastoid  muscle,  is  a  chain  of  lymphatic  glands  which  lies  in 
close  relation  to  the  spinal  accessory  nerve  and  to  the  branches  of  the  cervical 
plexus ;  these  glands  are  a  frequent  source  of  abscess  in  pediculosis  and  impetigo  of 
the  scalp.  The  posterior  belly  of  the  omo-hyoid,  which  forms  the  upper  boundary 
of  the  supraclavicular  division  of  the  posterior  triangle,  passes  beneath  the  posterior 
border  of  the  sterno-mastoid  at  a  point  about  one  inch  above  the  clavicle.  The 
external  jugular  vein,  usually  visible  through  the  skin,  runs  in  a  line  from  the  angle 
of  the  jaw  to  the  middle  of  the  clavicle  ;  it  is  the  vessel  which  is  generally  opened 
to  relieve  the  right  side  of  the  heart  in  asphyxia.  The  lumen  of  the  vein  is  kept 
patent  where  it  pierces  the  fascia  of  the  subclavian  triangle ;  hence  a  wound  of  the 
vein  in  this  situation  is  liable  to  be  followed  by  the  suction  of  air  into  the  circula- 
tion during  inspiration.  The  third  part  of  the  subclavian  artery  can  be  compressed 
against  the  first  rib  by  pressing  downwards  and  backwards  inimediately  above  the 
clavicle,  a  little  behind  the  posterior  border  of  the  sterno-mastoid  muscle.  To  map 
out  the  course  of  the  subclavian  artery  in  the  neck,  draw  a  line,  convex  upwards, 
from  the  upper  border  of  the  sterno-clavicular  articulation  to  the  middle  of  the 
clavicle,  the  highest  part  of  the  arch  to  reach  from  |  to  1  in.  above  the  bone.  To 
ligature  the  vessel  in  the  third  part  of  its  course,  an  angular  incision  is  made  along 
the  middle  of  the  upper  border  of  the  clavicle  and  the  lower  part  of  the  posterior 
border  of  the  sterno-mastoid  muscle.  The  most  important  guides  to  the  vessel  are 
the  posterior  belly  of  the  omo-hyoid,  the  outer  border  of  the  scalenus  anticus,  and 
the  scalene  tubercle  of  the  first  rib.  The  close  relation  of  the  vessel  to  the  lowest 
trunk  of  the  brachial  plexus  and  to  the  cervical  pleura  must  be  kept  in  mind.  In 
the  rare  instances  in  which  a  cervical  rib  is  present  the  subclavian  artery  lies  either 
in  front  of  it,  or  arches  above  it,  according  to  the  degree  of  development  of  the  rib. 
The  subclavian  vein  lies  below,  and  anterior  to,  the  artery,  altogether  under  cover  of 
the  clavicle. 

Entering  the  posterior  triangle  from  behind  the  outer  border  of  the  scalenus 
anticus  are  the  trunks  of  the  brachial  plexus.  They  lie^pon  the  scalenus  medius, 
and  can  be  felt  through  tlie  skin  immediately  above  and  behind  the  third  part  of 
the  subclavian  artery.  The  anterior  primary  division  of  the  fifth  cervical  nerve 
supplies  the  rhomboids,  the  abductors  and  external  rotators  of  the  arm,  and  the 
fiexors  and  supinators  of  the  forearm ;  that  of  the  sixth  the  serratus,  the  adductors 
and  internal  rotators  of  the  arm,  and  the  extensors  and  pronators  of  the  forearm  ; 


THE  THOEAX.  1253 

that  of  the  seventh  the  tlexors  and  extensors  of  the  wrist ;  that  of  the  eighth  the 
tiexors  and  extensors  of  the  tingers ;  that  of  the  first  dorsal  all  the  small  muscles 
of  the  hand.  Tlie  carotid  tubercle  lies  between  the  anterior  primary  divisions  of 
the  sixth  and  seventh  cervical  nerves.  The  fifth  and  sixth  cervical  nerves  are  those 
which  suffer  most  when  the  plexus  is  injured  by  forcible  depression  of  the  shoulder 
while  the  head  is  bent  to  the  opposite  side,  such  as  occurs,  for  instance,  in  the 
"  Obstetrical  Paralyses  "  of  Duchenne. 

To  expose  the  trunks  of  tlie  brachial  plexus  an  incision  is  made  from  the 
junction  of  the  middle  and  lower  thirds  of  the  posterior  border  of  the  sterno-mastoid 
downwards  and  outwards  to  the  junction  of  the  outer  and  middle  thirds  of  the 
clavicle. 

In  the  middle  line  of  the  neck  posteriorly  is  the  nuchal  furrow,  at  the  bottom 
of  which  are  the  cervical  spines  and  the  ligamentum  nuchie.  At  the  upper  part  of 
the  furrow,  about  two  inches  below  the  external  occipital  protuberance,  is  the  large 
spine  of  the  axis,  which  can  be  distinctly  felt ;  a  line  drawn  from  it  outwards  and 
slightly  upwards  to  the  transverse  process  of  the  atlas  corresponds  to  the  position  of 
the  inferior  oblique  muscle  and,  therefore,  to  the  lower  margin  of  the  sub-occipital 
triangle.  The  course  of  the  deep  part  of  the  great  occipital  nerve  may  be  mapped 
out  by  drawing  a  line  from  the  centre  of  the  above-mentioned  line  to  a  point  one 
inch  external  to  the  external  occipital  protuberance.  At  the  floor  of  the  sub- 
occipital triangle  is  the  posterior  arch  of  the  atlas  upon  which  the  vertebral  artery- 
lies. 

THE   THOEAX. 

For  the  convenience  of  topographical  description,  clinicians,  by  the  use  of 
vertical  and  transverse  lines,  have  arbitrarily  divided  the  surface  of  the  chest  into 
certain  definite  regions  or  areas.  The  vertical  lines  are :  the  mid-sternal,  the 
lateral  sternal,  the  'parasternal,  the  'tiianiniary  or  mid-clavicular,  the  anterior,  inid, 
and  posterior  axillary,  and  the  scapular.  The  position  of  the  mid  and  lateral 
sternal  lines  is  sufficiently  indicated  by  their  names. 

The  mammary,  better  termed  the  mid-clavicular,  is  drawn  vertically  down  from 
the  centre  of  the  clavicles,  or,  what  comes  to  practically  the  same  thing,  from  a  point 
midway  between  the  centre  of  the  supra-clavicular  notch  and  the  tip  of  the  acromion 
process.  In  the  male  this  line  usually  lies  i  to  |  in.  internal  to  the  centre  of  the 
nipple,  which  is  usually  placed  over  the  fourth  interspace,  or  fifth  rib,  four  inches 
from  the  middle  line.  In  the  child  the  nipple  may  be  as  high  as  the  lower  border 
of  the  third  rib.  In  the  female  the  position  of  the  nipple  is  so  variable  that  it  is 
of  no  topographical  value.  In  a  well-proportioned  subject,  the  mid-clavicular  line, 
if  prolonged  downwards,  will  be  found  to  be  continuous  with  the  vertical  Poupart 
line,  which  crosses  the  costal  margin  at  the  tip  of  the  ninth  costal  cartilage. 

The  para-sternal  line,  drawn  midway  between  the  lateral  sternal  and  mid- 
clavicular, crosses  the  costal  margin  opposite  the  tip  of  the  eighth  costal  cartilage. 

The  anterior,  the  mid,  and  the  posterior  axillary  lines  are  respectively  drawn 
downwards  from  the  anterior  fold,  the  apex,  and  the  posterior  fold  of  the  axilla. 

The  scapular  line  is  drawn  perpendicularly  through  the  inferior  angle  of  the 
scapula. 

Of  the  tu'o  transverse  lines,  the  upper,  which  separates  the  infra-clavicular  and 
supra-sternal  regions  from  the  mammary  and  infra-sternal  regions,  is  drawn  at  the 
level  of  the  third  chondrq-sterual  articulation  ;  the  lower,  which  separates  the 
mammary  and  infra-mammary  regions,  is  drawn  at  the  level  of  the  sixth  chondro- 
sternal  articulation. 

The  lateral  area  of  the  chest  is  divided  into  an  upper,  or  axillary,  and  a  lower,  or 
infra-axillary  region,  by  as"  horizontal  line  drawn  at  the  level  of  the  sixth  rib. 

In  muscular  subjects  there  is  a  well-marked  mesial  furrow,  the  sternal  furrow, 
between  the  sternal  origins  of  the  pectoralis  major  muscles.  The  inner  part  of  the 
lower  border  of  these  muscles  forms  a  curved  prominence  which,  overlying  the 
fifth  rib,  corresponds  to  the  junction  of  the  mammary  and  infra-mammary  regions. 
Below  this  prominence  is  the  infra-mammary  region,  which  forms  a  somewhat  flat 
84  a 


1254 


SUEFACE  AND  SURGICAL  ANATOMY. 


Fig.  901. — Anterior  Aspect  of  Trunk,  showing  Surface  Topography  of  Visceka. 


M.C. 

Mid-clavicular  line. 

T. 

Tricuspid  orifice. 

A.C. 

Ascending  colon. 

P.R. 

Para-sternal  line. 

R.L. 

Rif,dit  lung. 

T.C. 

Transverse  colon. 

P. 

Poupart  vertical  line. 

L.L. 

Left  lung. 

D.C. 

Descending  colon. 

I.e. 

Infracostal  line. 

PI. 

Pleura. 

11.  C. 

Iliac  colon. 

T. 

Inteitubercular  line. 

L. 

Liver. 

P.O. 

Pelvic  colon. 

Pv. 

Transpyloric  line  of  Addison. 

0. 

CEsopliagus. 

R. 

Rectum. 

A. 

Aorta. 

St. 

Stomach. 

C.L 

Common  iliac  artery 

H. 

Heart. 

Py- 

Pylorus. 

E.I. 

External  iliac  artery. 

P. 

Pulmonary  orifice. 

D. 

Duodenum. 

I.V.C 

Inl'erior  vena  cava. 

A. 

Aortic  orifice. 

I. 

Ileum. 

U. 

Umbilicus. 

M. 

Mitral  orifice. 

V. 

Ileo-cajcal  valve. 

THE  LUNGS.  1255 

surface  corresponding  to  the  upper  part  of  the  rectus  muscle.  In  the  axillary  and 
infra -axillary  regions  are  the  prominences  caused  by  the  digitations  of  origin  of  the 
serratus  magnus,  the  first  to  appear  below  the  pectoralis  major  y)eing  that  which 
springs  from  the  fifth  ril). 

The  upper  border  of  the  sternum  lies  in  the  same  horizontal  plane  as  the  lower 
border  of  the  liody  of  the  second  dorsal  vertebra,  the  distance  between  the  two  being 
about  two  inches.  The  junction  of  the  manubrium  and  the  body  of  the  sternum 
forms  a  slight  prominence  or  angle,  known  as  the  angulus  Ludovici,  which, 
although  not  usually  visible,  may  always  be  felt.  The  angulus  lies  in  the  same 
plane  as  the  body  of  the  fifth  dorsal  vertebra. 

The  xiphi-stemal  junction  corresponds  to  the  disc  between  the  ninth  and  tenth 
dorsal  vertebne.  Immediately  below  the  xiphi-sternal  articulation  is  the  infra- 
sternal  notch,  formed  by  the  junction  of  the  seventh  costal  cartilages  with  the 
sternum.  Below  the  notch  is  the  epigastric  fossa  or  triangle,  bounded  laterally  by 
the  seventh  costal  cartilages.  The  apex  of  the  triangle  forms  an  angle  which  varies 
considerably  according  to  the  shape  of  the  chest,  the  average  being  about  70°.  Not 
infrequently  the  eighth  costal  cartilage  articulates  ^\ith  the  sternum. 

Fracture  of  the  sternum  is  rare,  and  generally  occurs  at  or  close  to  the  junction  of  the  manu- 
brium and  the  body  ;  it  may  occur  either  from  direct  violence,  or  indirectly  along  with  fracture 
of  the  spine.  Unlike  that  of  the  ribs,  the  periosteum  covering  the  sternum  is  tirmly  adherent 
to  the  bona 

The  ribs,  which  in  well-nourished  subjects  cause  no  surface  prominences,  are 
readily  visible  in  thin  persons ;  in  the  obese  they  are  very  difficult  to  feel.  In 
counting  the  ribs  from  the  front,  the  second  may  always  be  identified  by  its  relation 
to  the  angulus  Ludovici.  The  Jirst  rib  is  to  a  large  extent  under  cover  of  the  clavicle. 
The  lower  border  of  the  pectoralis  major  and  the  first  ^^sible  digitation  of  the 
serratus  magnus  afford  reliable  guides  to  the  Jifth  rib.  The  infra-sternal  notch  is 
the  guide  to  the  inner  end  of  the  seventh  costal  cartilage.  The  second  and  third 
costal  cartilages  are  almost  horizontal ;  below  this  the  cartilages  ascend  with 
increasing  obliquity,  that  of  the  sixth  being  the  first  to  present  a  distinct  angle. 
The  inner  end  of  the  second  intercostal  space  is  the  widest,  while  those  of  the  fifth 
and  sixth  are  very  narrow. 

The  costo-chondral  junctions  may  be  indicated  on  the  surface  by  a  line  drawn 
from  the  upper  end  of  the  para-sternal  line  to  a  point  a  finger 's-breadth  behind  the 
angle  of  the  tenth  costal  cartilage. 

The  internal  mammary  artery  crosses  behind  the  inner  ends  of  the  upper  five 
intercostal  spaces  about  half  an  inch  from  tlie  edge  of  the  sternum ;  as  it  descends  it 
approaches  a  little  nearer  to  the  sternum.  The  vessel  is  accompanied  by  two  veins 
which  unite  to  form  a  single  vein  opposite  the  second  interspace. 

This  artery  is  occasionally  injured  in  punctured  wounds  of  the  chest.  At  the  second  or  third 
intercostal  space  it  is  easily  ligatured  through  a  transverse  incision,  but  at  a  lower  level  it  is 
generally  necessary  to  resect  a  portion  of  one  of  the  costal  cartilages. 

THE  LUXGS. 

The  apex  of  the  lung  extends  upwards  into  the  root  of  the  neck  for  a  distance 
of  one  to  two  inches  above  the  anterior  extremity  of  the  first  rib,  and  is  mapped  out 
by  a  curved  line  drawn  from  the  upper  border  of  the  sterno-clavicular  articulation 
across  the  sterno-mastoid  to  the  junction  of  the  inner  and  middle  thirds  of  the 
clavicle,  the  highest  part  of  the  curve  reaching  from  h  to  Ih  in.  above  the  clavicle. 
The  apex  of  the  right  lung  reaches  half  an  inch  higher  than  that  of  the  left  lung. 
Intimately  related  to  the  apex  of  the  cervical  pleura  are  the  subclavian  artery  and 
the  inferior  cervical  ganglion  of  the  sympathetic. 

Both  the  cervical  pleura  and  the  subclavian  artery  may  be  injured  by  one  of  the  fragments  in 
a  fracture  of  the  clavicle ;  the  scaleni  muscles,  however,  atfording  considerable  protection  to  the 
former.  In  ligaturing  the  third  part  of  the  subclavian  artery,  care  must  be  taken  not  to  injure 
the  cervical  pleura. 

To  delineate  the  anterior  border  of  the  right  lung,  draw  a  line  from  the  upper 


1256 


SUKFACE  AND  SUEGICAL  ANATOMY. 


border  of  the  sterno-clavicular  articulatiou  to  the  centre  of  the  manubrium  sterni, 
and  from  thence  vertically  downwards,  in  or  slightly  to  the  left  of  the  middle  line, 
to  the  level  of  the  sixth  or  seventh  costal  cartilage,  or  it  may  be  even  to  the  infra- 
sternal  notch  (Fig.  902). 

The  anterior  border  of  the  left  lung  is  mapped  out  by  a  corresponding  line  as 


Right  vagus  nerve      Trachea 


CEsophagiii^ 


Right  subclavian 
artery 

Rii;ht 
nnominate  ^em 
Innominate 

artery    //'/// 


Left  suoclavian  artery 

Sulcus  subclavius 


Fic    902  —Dissection  ok  a  Subject  hardened  by  Formalin-injection,  to  show  the  relations  of  the  two 
"  pleural  sacs  as  viewed  from  the  front.     The  anterior  and  diapliragniatic  lines  of  pleural  rellection  are 
exhibited  by  black  dotted  lines,  whilst  the  outlines  of  the  lungs  and  their  fissures  are  indicated  by  the 
blue  lines  (from  Cunningham). 

far  as  the  fourth  costal  cartilage ;  thence  it  is  directed  outwards  along  the  lower 
border  of  the  fourth  costal  cartilage  to  the  para-sternal  line ;  it  then  passes  down- 
wards and  slightly  outwards  across  the  fourth  interspace,  and  curves  mwards 
behind  the  fifth  costal  cartilage  and  fifth  interspace  to  reach  the  upper  border  of 
the  sixth  costal  cartilage  in  the  para-sternal  line.  The  lower  part,  therefore,  of  the 
anterior  surface  of  the  right  ventricle  is  uncovered  by  lung  and  gives  a  completely 
dull  note  on  percussion  ;  this  area  is  si)oken  of  as  the  area  oi"  sujoerficial  or  absolute 
cardiac  dulness." 


THE  LUNGS. 


1257 


Fig.  903. — Anterior  Aspect  of  Trunk,  showing  Surface  Topography  of  Viscera. 


M.C. 

Mid-clavicxilar  line. 

L.L. 

Left  luug. 

Q.L. 

P.S. 

Para-sternal  line. 

PI. 

Pleura. 

P.S. 

P. 

Poupart  vertical  line. 

0. 

(Esophagus. 

R.U. 

I.e. 

Infracostal  line. 

R.K. 

Right  kidney. 

L.U. 

T. 

Intertubercular  line. 

L.K. 

Left  kidney. 

C.L 

Pv. 

Transpyloric  line. 

Sp. 

Spleen. 

E.I. 

T. 

Trachea. 

S.R. 

Suprarenal  capsule. 

I.V.( 

A. 

Aorta. 

Pa. 

Pancreas. 

U. 

R.L. 

Right  lung. 

D. 

Duodenum. 

Quadratus  lumborum. 
Psoas. 

Right  ureter. 
Left  ureter. 
Common  iliac  artery. 
E.xternal  iliac  artery. 
I.V.C.  Inferior  vena  cava. 
Umbilicus. 


1258 


SUEFAOE  AND  SUEGICAL  ANATOMY. 


The  level  of  the  lower  border  of  the  lung  is  practically  the  same  on  both  sides ; 
it  is  mapped  out  by  a  line  extending  outwards  from  the  lower  extremity  of  the 
anterior  border  to  the  sixth  costal  cartilage  in  the  mid-clavicular  line,  and  thence 

in  a  slightly  curved  direction,  with 
the  convexity  downwards,  across 
the  lateral  aspect  of  the  chest  to 
the  tenth  dorsal  spine.  This  line 
crosses  the  eighth  rib  in  the  mid- 
axillary  line  and  the  tenth  rib  in 
the  scapular  line  (Figs.  904  and 
905). 

To  indicate  the  position  of  the 
oblique  fissures  a  line  is  drawn  from 
the  second  dorsal  spine  across  the 
interscapular  region  to  the  root  of 
the  spine  of  the  scapula,  and  thence 
downwards  and  outwards  across 
the  infraspinous  fossa,  to  end  at 
the  lower  border  of  the  lung 
opposite  the  sixth  costal  cartilage, 
a  little  internal  to  the  mammary 
line.  When  the  arm  is  raised 
above  the  level  of  the  shoulder,  and 
the  hand  placed  on  the  back  of 
the  head,  the  inferior  angle  of  the 
scapula  is  rotated  upwards  and 
forwards  so  that  the  vertebral 
border  practically  corresponds  with 
the  line  of  the  oblique  fissure. 

The  transverse  fissure  of  the 
right  lung  is  mapped  out  by 
drawing  a  line  from  the  anterior 
border  of  the  lung,  at  the  level  of 
the  fourth  costal  cartilage,  outwards 
and  slightly  upwards  to  join  the 
middle  of  the  oblique  fissure. 

Pleura. — The  line  of  reflection 
of  the  right  pleura  from  the  back 
of  the  sternum  may  be  said  to 
correspond  to  the  anterior  border 
of  the  right  lung. 

On  the  left  side,  the  pleural  re- 
flection corresponds  to  the  anterior 
border  of  the  left  lung  as  far  as 
the  lower  edge  of  the  fourth 
chrondro  -  sternal  junction,  from 
which  point  it  diverges  slightly 
and  descends  behind  the  left  border 
of  the  sternum  to  the  sixth  costal  cartilage  (Fig.  902).  It  is  only  occasionally 
that  the  inner  extremities  of  the  fifth  and  sixth  interspaces  are  uncovered 
by  pleura. 

The  right  costo-diaphragmatic  reflection  (see  Figs.  903  and  907)  is  indicated  on 
the  surface  by  a  line  drawn  from  the  sixth  or  seventh  chondro-sternal  junction  (some- 
times the  infra-sternal  notch)  downwards  and  outwards  to  a  point  two  inches  verti- 
cally above  the  angle  of  the  tenth  costal  cartilage  ;  from  this  point  the  line  is  carried 
with  a  slightly  downward  curve  across  the  lateral  aspect  of  the  chest  to  the 
twelfth  rib  at  the  outer  margin  of  the  erector  spinw. ;  thence  it  passes  below  the 
twelfth  rib  and  reaches  the  ■  vertebral  column  at  the  level  of  the  upper  border 
of  the  twelfth  dorsal  spine.     The  relation  of  the  costo-diaphragmatic  reflection  to 


Fig.  904. — Lateral  View  of  the  Right  Pleural  Sac  in 
A  Surtect  hardened  by  Formalin-injection.  The  Vjlue 
lines  indicate  the  outline  of  the  right  lung,  and  also  the 
position  of  its  fissures  (from  Cunningham). 


THE  LUNGS. 


1259 


the  seventh,  eighth,  and  ninth  costal  arches  may  be  conveniently  expressed  by 
stating  that  it  lies  a  little  in  front  of  the  costo-chondral  junction  of  the  seventh, 
opposite  that  of  the  eighth,  and  a  little  behind  that  of  the  ninth. 

The  left  costo-diaphragmatic  reflection  is  indicated  by  a  line  drawn  from  a  point 
opposite  the  sixth  costal  cartilage,  a  tinger's-breadth  from  its  junction  with  the 
sternum,  to  a  point  one  and  a  half  inches  vertically  above  the  angle  of  the  tenth 
costal  cartilage, 
and  thence  to  the 
spine,  as  on  the 
right  side,  but  at 
a  slightly  lower 
level. 

The  costo-dia- 
phragmatic re- 
flection reaches  its 
loioest  limit  a 
little  behind  the 
mid -axillary  line 
two  inches  verti- 
cally above  the 
tip  of  the  eleventh 
costal  cartilage,  a 
level  which  may 
1)6  readily  indi- 
cated, according 
to  Cunningham, 
b}'  a  point  in  the 
mid-axillary  line 
intersected  by  a 
horizontal  line 
drawn  round  the 
trunk  at  the  level 
of  the  lowest  part 
of  the  extremity 
of  the  first  lum- 
bar spine  (Fig. 
904).  The  same 
author  localises 
the  level  of  the 
diaphragmatic 
pleural  reflection 
in  the  mammary 
line  at  the  point 
where  this  line  is 
intersected  by 
another  horizontal 
line  at  the  level 
of  the  spine  of 
the  last  dorsal 
vertebra. 

The  relations  of  the  pleura  to  the  twelfth  rib  are  of  importance  to  the  surgeon, 
especially  in  connexion  with  operations  on  the  kidney  (Figs.  905  and  906).  When  this  rib 
is  not  abnormally  short,  the  pleural  reflection  crosses  it  opposite  the  outer  border  of  the 
erector  spina?  muscle,  hence  an  incision  may  be  carried  deeply  as  far  as  the  apex  of  the 
angle  formed  by  the  twelfth  rib  and  the  outer  border  of  the  erector  spinre  without  entering 
the  pleura.  When,  however,  the  twelfth  rib  does  not  reach  the  outer  border  of  the  erector 
spina?,  an  incision  carried  upwards  into  the  apex  of  the  augle  between  this  muscle  and  the 
eleventh  rib  is  certain  to  wound  the  pleura  (Melsome).  It  is  important,  therefore,  to 
count  the  ribs  from  above  downwards,  in  order  not  to  mistake  the  eleventh  for  the  twelfth, 
when  the  latter  is  rudimentary. 


Fig.  905. —Dissection  of  the  Pleural  Sacs  from  Behind. 
The  blue  liues  indicate  the  outlines  and  the  fissures  of  the  lungs  (from  Cunningham), 


1260 


SUKFACE  AND  SUEGICAL  ANATOMY. 


Internal  to  the  outer  edge  of  the  erector  spinte  the  pleural  reflection  lies  below  the 
level  of  the  twelfth  rib,  and  not  infrequently  descends  as  far  as  the  transverse  process 
of  the  first  lumbar  vertebra. 

On  the  right  side  the  posterior  mediastinal  pleura,  as  it  passes  from  the  posterior 
aspect  of  the  pericardium  backwards  to  the  front  of  the  vertebral  column  sweeps  over  the 


J 


Crus  of  diap}iragin 


Crus  of  diapliragin 


Ligamentuiii  arcuatuiii 
extemuiu 


Diaj^hiagiii 


Spleen 


Intestine  JV 


Ligainentum  arcuatuni 
^externum 


Ascending  colon 


Fig.  906. — ^^Dissectiox  from  behind  to  show  the  relation  of  the  two  Pleural  Sacs  to  the  Kidneys. 
Outline  of  upper  portions  of  kidneys  indicated  by  dotted  lines  (from  Cunningham). 

right  side  of  the  oesophagus  ;  hence  malignant  ulcers  of  the  oesophagus  are  more  likely 
to  invade  the  right  pleura  than  the  left.  On  the  left  side  the  posterior  mediastinal  pleura 
passes  from  the  lateral  aspect  of  the  bodies  of  the  vertebra3  on  to  the  left  side  of  the 
aorta.  Hence,  to  evacuate  pus  from  the  posterior  mediastinum,  there  is  less  risk  of 
opening  the  pleura  if  the  space  be  entered  from  the  left  side  of  the  vertebral  column. 

The  seat  of  election  for  tapping  the  pAeura  {paracentesis  pleurcB)  is  the  sixth  or  seventh 
costal  interspace  a  little  in  front  of  the  posterior  axillary  fold.  To  allow  of  the  introduc- 
tion of  a  tube  to  drain  away  the  pus  from  the  pleural  cavity  in  empyema,  a  portion  of  one 
of  the  ribs  (sixth  to  ninth)  is  resected.  The  intercostal  vessels  and  nerves,  which  lie  in  the 
groove  at  the  lower  border  of  the  rib,  are  avoided  by  removing  the  portion  of  bone  sub- 
periosteally.  If  the  chest  is  opened  in  the  scapular  line  care  must  be  taken  not  to  resect 
either  the  seventh  or  the  eighth  ribs,  which  are  exposed  when  the  arm  is  elevated,  but 
overlapped  by  the  angle  of  the  scapula  when  the  arm  is  lowered. 


Anteriorly,  the  bifurcation  of  the  trachea  lies  at  or  a  little  below  the  angulus 
Ludovici,  while  jjosteriorly  it  lies  a  little  below  the  level  of  the  root  of  the  spine 
of  the  scajjula,  opposite  the  fourth  dorsal  spine.  The  bifurcation  takes  place  one 
vertebra  higher  in  the  infant  than  in  the  adult  (Symington). 

The  septum  between  the  right  and  left  bronchi  lies  a  little  to  the  left  of  the 
middle  of  the  trachea,  and  the  right  bronchus  is  wider  and  more  nearly  in  a  line 
with  the  trachea  than  the  left  bronchus,  hence  the  greater  tendency  of  foreign 
bodies  to  enter  the  former. 

The  roots  of  the  lungs  are  situated  opposite  the  fourth,  fifth,  and  sixth  dorsal 
spines,  midway  between  them  and  the  vertebral  borders  of  the  scapulae. 

The  lower  end  of  tlie  trachea,  the  hroDclii,  the  vagi,  and  the  left  recurrent  laryngeal  nerve, 
are  all  more  or  less  surrounded  by  lymjjhatic  glands,  which,  when  enlarged,  may  exert  injuxious 
pressure  upon  them. 


THE  LUNGS. 


1261 


Fig.  907. — Posterior  Aspect  of  Trunk,  showing  Surface  Topography  of  Viscera. 


T.       Trachea. 
A.       Aorta. 
L.L.   Left  lung. 
R.L.   Right  lung. 
St.       Stomach. 


Sp.  Spleen. 

L.  Liver. 

S.R.  Suprarenal  body. 

L.K.  Left  kidney. 

R.K.  Ridit  kidney. 


P.  Pancreas. 

PI.  Pleura. 

D.C.  Descending  colon. 

A.C.  Ascending  colon. 

R.  Rectum. 


1262  SUEFACE  AND  SUEGICAL  ANATOMY. 

THE  HEART  AND  GREAT  VESSELS. 

Viewed  from  the  front,  the  outline  of  the  precordial  area,  like  that  of  the  peri- 
cardial sac,  is  roughly  triangular,  the  base  of  the  triangle  being  below  and  the  apex 
above.     The  boundaries  are  delineated  upon  the  surface  as  follows : — 

The  right  side  of  the  triangle,  formed  by  the  right  auricle,  is  indicated  by 
drawing  a  line  slightly  convex  outwards  from  the  upper  end  of  the  third  to  the 
sixth  costal  cartilage  a  fingers-breadth  from  the  edge  of  the  sternum ;  the  curve 
attains  its  maximum  opposite  the  fourth  intercostal  space,  where  it  reaches  one 
and  a  half  inch  from  the  middle  line. 

The  hase  of  the  triangle,  formed  by  the  margo  acutus  of  the  right  ventricle  and 
to  a  very  slight  extent  by  the  apical  portion  of  the  left  ventricle,  is  almost 
horizontal,  and  corresponds  to  a  line  drawn  from  the  lower  extremity  of  the  right 
side  of  the  triangle  to  the  apex  of  the  left  ventricle,  which  lies  behind  the  fifth  left 
intercostal  space,  three  and  a  half  inches  from  the  middle  line  and  half  an  inch 
internal  to  the  mid-clavicular  line.  The  base  line  crosses  the  xiphoid  cartilage 
at  its  junction  with  the  body  of  the  sternum. 

The  left  side  of  the  triangle,  formed  by  the  margo  ohtusus  of  the  left  ventricle,  is 
indicated  by  a  slightly  curved  line  extending  from  the  apex  of  the  heart  upwards 
to  the  lower  edge  of  the  second  interspace,  a  fingers-breadth  from  the  sternum,  the 
convexity  of  the  curve  being  directed  outwards  and  slightly  upwards. 

The  truncated  apex  of  the  triangle,  which  lies  behind  the  sternum  at  the  level 
of  the  second  intercostal  space,  corresponds  to  the  highest  part  of  the  heart, 
namely,  where  the  auricular  appendices  embrace  the  aorta  and  puhxionary  artery. 

The  anterior  part  of  the  right  auriculo-ventricular  groove  is  mapped  out  by  a 
line  drawn  from  the  middle  line,  opposite  the  lower  border  of  the  third  right  costal 
cartilage,  downwards  and  outwards  to  the  sixth  right  chondro-sternal  junction ; 
the  line  should  be  slightly  convex  upwards  and  to  the  right.  The  right  auricular 
appendix  lies  at,  or  a  little  to  the  left  of,  the  middle  line,  at  the  level  of  the  second 
intercostal  space  and  the  upper  border  of  the  third  costal  cartilage.  The  left 
auricular  appendix  lies  behind  the  second  left  intercostal  space,  close  to  the  edge  of 
the  sternum. 

The  inferior  surface  of  the  heart  (facies  diaphragmatica)  rests  upon  the  diaphrag- 
matic or  basal  part  of  the  pericardium.  The  true  ^oosterior  surface  of  the  heart  is 
formed  mainly  by  the  left  auricle,  which  is  moulded  posteriorly  upon  the  oesophagus, 
the  aorta,  the  bronchi,  and  the  bronchial  glmds,  the  pericardium  intervening. 
The  left  auricle  extends  behind  the  right  auricle  for  a  considerable  distance  to  the 
right  of  the  mesial  plane. 

In  determining  the  position  of  the  cardiac  orifices  and  their  valves  it  is  to  be 
remembered  that  they  are  all  situated  to  the  left  of  the  right  auriculo-ventricular 
groove,  and  that  they  lie  in  the  following  order  from  above  downwards — viz.  pul- 
monary, aortic,  mitral,  and  tricuspid.  When  delineated  on  the  surface  they  will 
be  seen  to  lie  within  an  ellipse  whose  long  axis  extends  from  the  upper  border  of 
the  third  left  to  the  sixth  right  chondro-sternal  junction. 

The  pulmonary  orifice,  directed  upwards  and  slightly  backwards  and  to  the  left, 
lies  opposite  the  upper  border  of  the  third  left  chondro-sternal  junction  ;  the  aortia 
orifice,  directed  upwards,  backwards,  and  to  the  right,  lies  further  from  the  surface, 
behind  the  left  half  of  the  sternum,  opposite  the  lower  border  of  the  third  costal 
cartilage  ;  the  mitral  orifice  lies  at  a  lower  level  behind  the  left  half  of  the  sternum, 
opposite  the  fourth  rib ;  the  orifice  of  the  opening  is  directed  downwards,  forwards, 
and  to  the  left.  The  tricuspid  orifice,  situated  nearer  the  anterior  wall  of  the  chest 
than  the  mitral,  lies  very  obliquely  Ijehind  the  right  half  of  the  sternum  at  the 
level  of  the  fourth  and  fifth  cartilages  and  intervening  space. 

Although  the  first  and  second  sounds  of  the  heart  are  heard  all  over  the  cardiac  area,  the 
sounds  produced  by  the  individual  valves  are  heard  most  distinctly,  not  directly  over  their  ana- 
tomical situation,  but  over  the  area  where  tlie  cavity  in  which  the  valve  lies  approaches  nearest 
to  the  surface.  Hence  tlie  mitral  sound  is  best  heard  over  the  apex  (mitral  area),  the  tricuspid 
over  the  k>wer  part  of  the  body  of  the  sternum  (tricuspid  area),  tlie  aortic  over  the  second  right 
costal  cartilage  (aortic  area),  and  the  pulmonary  over  the  second  left  intercostal  space  (pulmonary 
area). 


THE  HEAET  AND  GKEAT  VESSELS. 


1263 


Fig.  908. 


Fig.  909. 


Fig.  910. 


Fig.  911. 


From  photographs  of  a  formalin -hardened  subject,  with  the  heart  dissected  in  situ,  to  show  the  relations  of  its 
cavities  and  valves  to  the  anterior  wall  of  the  thorax. 

Tn  Fig.  908  the  anterior  wall  of  the  right  ventricle  has  been  removed  and  the  pulmonary  artery  opened. 

lu  Fig.  909  the  anterior  walls  of  the  ascending  aorta  and  of  the  right  auricle  have  been   removed  ;  also  tlie 

anterior  cusp  of  the  tricuspid  valve. 
In  Fig.  910  the  greater  part  of   interventricular  septum  has  been  removed,  exposing  anterior  cusp  of  mitral 

valve. 
In  Fig.  911  the  ascending  aorta,  anterior  cusp  of  mitral  valve,  trunk  of  pulmonary  artery,  and  interauricular 
septum  have  been  removed  ;    the  cavities  of  left   auricle  and   left  ventricle  are  exposed,  also  the  left 
auricular  appendix  and  posterior  cusjj  of  mitral  valve. 
K.A.        Right  auricle.  P.A.  Pulmonary  artery.  M.V.         Mitral  valve. 

R.V.       Right  ventricle.  P.V.  Pulmonary  valve.  S.V.C.       Superior  vena  cava. 

L.A.        Lett  auricle.  A.      Aortic  arch.  P.V.  Pulmonary  vein  (in  Fig.  911). 

L.A.A.    Left  auricular  appendix.       A.V.  Aortic  valve.  M.  Moderator  band. 

S.V.        Interventricular  septum.       T.V.  Tricuspid  valve. 


1264  SUEFACE  AND  SUEGICAL  ANATOMY. 

Ill  tapping  the  pericardium  (jjaracentesis  pericardii)  the  pleura  will  be  avoided  by  making 
the  puncture  through  the  fifth  or  sixth  left  intercostal  space  as  close  as  jDossible  to  the  edge  of  the 
sternum.  When,  however,  the  pericardial  sac  is  distended  with  fluid,  the  pleura  is  pushed  out- 
wards, and  will  therefore  escape  injury  if  the  puncture  be  made  at  a  safe  distance  external  to  the 
internal  mammary  vessels,  viz.  one  inch  external  to  the  left  border  of  the  sternum. 

To  establish  free  drainage  in  suj)i3urative  pericarditis,  the  sixth  left  costal  cartilage  must  be 
resected  and  the  internal  mammary  vessels  ligatured ;  the  triangularis  sterni  and  the  pleural 
reflection  are  then  pushed  aside  and  the  jjericardium  exposed  and  incised. 

The  ascending  aorta  lies  behind  the  sternum,  opposite  the  second  and  third  ribs, 
and,  unless  dilated,  does  not  project  beyond  its  right  border.  The  upper  border  of 
the  aortic  arch  lies  at  or  a  little  above  the  centre  of  the  manubrium  sterni ;  in  the 
child  the  vessel  may  reach  as  high  as  the  upper  border  of  the  manubrium. 

The  innominate  and  left  common  carotid  arteries  diverge  from  either  side  of  the 
mesial  plane  between  the  upper  part  of  the  manuVjrium  sterni  and  the  front  of  the 
trachea.  A  pin  pushed  directly  backwards  immediately  above  the  middle  of  the 
supra-sternal  notch  will  strike  the  inner  border  of  the  innominate  artery  a  little 
below  its  bifurcation. 

The  pulmonary  artery  lies  behind  the  left  border  of  the  sternum  opposite  the 
second  interspace  and  the  second  costal  cartilage. 

The  left  innominate  vein  lies  behind  the  upper  part  of  the  manubrium  sterni, 
the  right  behind  the  inner  end  of  the  right  clavicle.  The  superior  vena  cava  lies 
immediately  to  the  right  of  the  margin  of  the  sternum,  opposite  the  first 
and  second  interspaces  and  the  intervening  second  rib ;  its  opening  into  the  right 
auricle,  behind  the  third  chondro-sternal  articulation,  corresponds  to  the  centre  of 
the  root  of  the  right  lung. 

(Esophagus. — The  average  length  of  the  oesophagus  in  the  adult  is  10  in. 
(25  cm.) ;  the  distance  from  the  incisor  teeth  to  its  commencement  is  6  in. ;  to  the 
point  or  level  where  it  is  crossed  by  the  left  bronchus,  9  in. ;  to  the  oesophageal 
opening  of  the  diaphragm,  14  to  15  in. ;  to  the  cardiac  orifice  of  the  stomach,  16  in. 
These  measurements,  which  are  of  great  importance  in  diagnosing  the  seat  of 
oesophageal  obstructions,  should  be  marked  off  from  below  upwards  upon  all 
oesophageal  bougies  and  probangs.  Posteriorly,  the  oesophagus  extends  from  the 
level  of  the  sixth  cervical  spine  to  that  of  the  tenth  dorsal,  a  little  to  the  left  of 
which  is  the  situation  at  which  the  stethoscope  is  placed  in  order  to  hear  the  sound 
produced  by  the  passage  of  fluid  into  the  stomach. 

Clinically  it  is  important  to  bear  in  mind  the  relation  of  the  oesophagus  to  the  trachea  and 
left  bronchus,  to  the  left  recurrent  laryngeal  nerve,  to  the  bronchial  and  posterior  medias- 
tinal glands,  to  the  descending  thoracic  aorta,  and  to  the  right  posterior  mediastinal  pleura. 
Ulcers  of  the  oesophagus  are  liable  to  open  into  either  the  trachea,  the  left  bronchus,  or  the 
right  pleura. 

The  veins  of  the  lower  end  of  the  oesoj^hagus  open  partly  into  the  systemic  veins  and  partly 
into  the  portal  system ;  like  those  at  the  lower  end  of  the  rectum  they  are  liable  to  become 
varicose  in  conditions  which  give  rise  to  chronic  interference  with  the  portal  circulation. 

The  lyraxihatics  of  the  upper  part  of  the  oesophagus  oj)en  into  the  lower  carotid  glands,  the 
remainder  into  the  posterior  mediastinal  glands. 

The  oesophagus  is  very  distensible  in  the  transverse  but  not  in  the  antero -posterior  direction, 
hence  the  most  useful  forceps  for  removing  foreign  Ijodies  from  the  oesophagus  are  those  which  open 
laterally. 

THE  ABDOMEN. 

THE  ANTERIOR  ABDOMINAL   WALL. 

The  configuration  of  the  abdomen  varies  with  the  age,  sex,  obesity,  and  muscular 
development  of  the  individual.  In  the  child  it  is  wider  above  than  below,  while 
the  converse  is  the  case  in  the  adult  female.  It  is  most  prominent  in  the  region  of 
the  umbilicus,  which  is  situated,  normally,  below  the  mid-point  between  the  infra- 
sternal  notch  and  the  symphysis  pubis,  usually  a  little  below  the  level  of  the  highest 
part  of  the  iliac  crest,  and  opposite  the  middle  of  the  body  of  the  fourth  lumbar 
vertebra.  In  the  obese,  and  especially  when  the  abdominal  muscles  have  lost  their 
tone,  the  umbilical  region  becomes  prominent  and  more  or  less  pendulous,  so  that 
the  umbilicus  may  come  to  lie  considerably  below  the  normal  level.     In  the  child , 


THE  ABDOMEN. 


1265 


it  is  relatively  lower  than  in  the  adult,  in  consequence  of  the  undeveloped  state  of 
the  pelvis. 

In  spare  su])jects  tlie  lower  end  of  the  ])ody  of  the  sternum,  the  xiphoid  carti- 
lage, and  the  costal  margin,  can  readily  he  traced.  The  slight  depression  or  notcli 
formed  Ity  the  seventh  costal  cartilages  and  tlie  lower  ))order  of  the  hody  of  the 
sternum  is  termed  the  infrasternal  notch.  Below  the  notch,  and  l)ounded  on  either 
side  hy  the  seventh,  eighth,  and  ninth  costal  cartilages,  is  the  infracostal  angle, 
which  varies  considerably  according  to  the  shape  of  the  chest ;  it  is  relativel}-  widei- 
in  the  child  than  in  the  adult.  The  lower  border  of  the  curve  of  the  tenth  costal 
cartilage  is  easily  recognisa])le,  and  has  been  selected  by  Cunningham  as  the  level 
of  the  plane  of  separation  (infracostal  plane)  between  the  u])])cr  aud  middle  abdo- 
minal zones. 

The  anterior  abdominal  wall  is  limited  below  by  the  fold  of  the  groin  and  the 
crest  of  the  pubes.  In  a  spare  muscular  subject  the  recti,  the  furrows  corre- 
sponding to  the  linese  transversae,  and  the  supra-umbilical  portion  of  the  linea  alba, 
can  be  readily  made  out.  When  the  outline  of  the  rectus  is  not  visible  the  outer 
border  may  be  indicated  by  a  line  drawn  from  the  tip  of  the  ninth  costal  cartilage 
to  the  mid-point  of  a  line  joining  the  umbilicus  and  the  anterior  superior  iliac 
spine,  and  from  thence  to  the  pubic  spine.  In  the  angle  between  the  outer  border 
of  the  rectus  and  the  ninth  costal  cartilage,  on  the  right  side,  is  a  slight  triangular 
depression  which  overlies  the  fundus  of  the  gall-bladder.  Between  the  lower  part 
of  the  outer  border  of  the  rectus  and  the  prominence  above  the  anterior  part  of  the 
iliac  crest,  caused  by  the  lower  muscular  fibres  of  the  external  ol)lique,  is  another 
slight  triangular  depression,  which  corresponds  to  the  lower  and  narrow  part  of 
the  aponeurosis  of  the  external  oblique  muscle. 


Obliquus  externus 

Obliquus  internus   — 

Obliqnus  internus  (cut)  — 
Deep  circumflex  iliac  artery  — 

Internal  abdominal  ring  and 
infundibuliforni  fascia 

Cremnster  muscle     ,   .  , 
Obliquus  externus  ^  " 

Spermatic  cord  passing  __  -  ■ 
through  cremaster  nuiscle 


Obliiiuiis  I'xtcnius 

<  >bli(|uns  intiTims  (eat) 

Transversalis  muscle 
Over  deep  epigastric  artery 

Fascia  transversalis 
Deep  epigastric  artery 
Conjoint  tendon 

Over  outer  border  of  rectus  abdominis 
Spermatic  cord 
-Triangular  fascia 


Fig.  912. — The  Groin.     The  structures  seen  on  reflexion  of  part  of  the  oblifjuus  internu.s  (A.  M.  Paterson). 

Close  above,  and  almost  parallel  to,  the  inner  half  of  Poupart's  ligament  is  the 
inguinal  canal,  traversed  by  the  spermatic  cord  (Fig.  912);  the  latter  can  be  felt 
to  emerge  at  the  external  abdominal  ring  immediately  above  the  pubic  spine. 
The  external  and  internal  abdominal  rings  have  been  fully  described  elsewhere ;  the 
former  is  triangular  in  shape,  with  its  apex  directed  upwards  and  outwards,  and  its 
base  immediately  above  the  pubic  crest.  By  invaginating  the  skin  of  the  scrotum 
the  little  finger  may  readily  be  passed  through  the  ring  into  the  canal.  It  is 
to  be  noted  that  the  neck  of  an  inguinal  hernia  lies  above  the  pubic  spine, 
whereas  the  neck  of  a.  femoral  hernia  emerges  below  the  inner  end  of  Poupart's 
ligament,  external  to  the  pubic  spine.  The  internal  abdominal  ring,  an  opening 
in  the  fascia  transversalis,  lies  half  an  inch  above  a  point  a  little  internal  to  the 
85 


1266  SUEFAGE  AND  SUEGICAL  ANATOMY. 

middle  of  Poupart's  ligament.  The  deep  epigastric  artery  may  be  mapped  out  by 
drawing  a  line  from  a  point  midway  between  the  anterior  superior  iliac  spine  and 
the  symphysis  pubis  towards  the  umbilicus.  The  vessel,,  together  with  the  inner 
third  of  l^oupart's  ligament  and  the  lower  part  of  the  outer  border  of  the  rectus, 
bounds  a  triangle  known  as  Hesselbach's  triangle.  As  the  deep  epigastric  artery 
passes  upwards  and  inwards  to  disappear  behind  the  conjoined  tendon  and  the 
outer  border  of  the  rectus,  it  lies  behind  the  spermatic  cord  immediately  internal 
to,  and  below,  the  internal  abdominal  ring.  The  floor  of  Hesselbach's  triangle  is 
formed  throughout  by  the  fascia  transversalis,  superficial  to  which,  over  the  inner 
half  or  so  of  the  triangle,  is  the  conjoined  tendon.  An  oblictue  inguinal  hernia  leaves 
the  abdomen  at  the  internal  abdominal  ring  and  traverses  the  whole  length  of 
the  inguinal  canal ;  its  coverings  are  therefore  the  same  as  those  of  the  spermatic 
cord,  and  the  neck  of  the  sac  lies  external  to  the  deep  epigastric  artery,  hence  this 
variety  of  hernia  is  also  termed  an  external  inguinal  hernia.  A  direct  inguinal 
hernia,  on  the  other  hand,  instead  of  traversing  the  whole  length  of  the  inguinal 
canal,  pushes  before  it  that  part  of  its  posterior  wall  which  is  formed  by  the  floor 
of  Hesselbach's  triangle.  The  neck  of  the  sac,  therefore,  lies  internal  to  the  deep 
epigastric  artery,  and  this  variety  of  hernia  may  be  termed  an  internal  inguinal 
hernia.  If  a  direct  hernia  makes  its  way  through  the  inner  part  of  Hesselbach's 
triangle,  it  derives  a  covering  from  the  conjoined  tendon  as  well  as  from  the  fascia 
transversalis ;  if  through  the  outer  part  of  the  triangle,  the  outer  edge  of  the  con- 
joined tendon  curves  round  the  inner  side  of  the  neck  of  the  sac.  To  relieve  the 
constriction  at  the  neck  of  the  sac,  in  the  case  of  an  oblique  inguinal  hernia,  the  edge 
of  the  knife  is  directed  upwards  and  outwards  to  avoid  the  deep  epigastric  artery, 
while  in  a  direct  hernia  the  artery  is  avoided  by  dividing  the  constriction  in  an 
upward  and  inward  direction.  In  an  oUique  inguinal  hernia  the  sac  lies  within 
the  infundibuliform  fascia  (fascia  propria  of  the  hernia),  whereas  in  a  direct  hernia 
the  fascia  propria  is  derived  from  the  fascia  transversalis  of  Hesselbach's  triangle. 
The  extra-peritoneal  fat  whicli  covers  the  outer  surface  of  the  hernial  sac  is  some- 
times hypertrophied  to  such  an  extent  as  to  amount  to  a  fatty  tumour. 

In  a  large  proportion  of  children  at  birth  the  funicular  process  of  peritoneum, 
which  connects  the  tunica  vaginalis  testis  with  the  abdominal  peritoneum, 
especially  on  the  right  side,  is  still  patent.  Should  the  bowel  force  its  way 
along  the  patent  process  a  congenital  inguinal  hernia  arises.  In  the  majority  of 
the  cases  of  congenital  inguinal  hernia  it  will  be  found  that  the  tunica  vaginalis 
testis  has  been  shut  off  by  closure  of  the  lower  part  of  the  funicular  process,  only 
the  upper  part  remaining  patent  and  forming  the  sac  of  the  hernia.  In  regard  to 
the  operation  for  the  cure  of  inguinal  hernia,  it  should  be  borne  in  mind  that  in 
the  acquired  form  the  liernia  -produces  the  sac,  whereas  in  the  congenital  variety 
the  sac  is  the  cause  of  the  hernia ;  it  follows,  therefore,  that  in  the  operation  for 
acquired  hernia  the  closure  of  the  canal  is  as  important  as  the  removal  or  oblitera- 
tion of  the  sac,  while  in  a  congenital  hernia  the  most  essential  part  of  the  operation 
is  the  closure  of  the  neck  of  the  sac,  and  as  the  muscular  and  fascial  apparatus 
forming  the  walls  of  the  canal  are  well  developed,  they  should  be  interfered  with 
as  little  as  possible.  A  patent  funicular  process  may  persist  during  adult  life 
without  any  bowel  descending  into  it ;  on  the  other  hand,  years  after  birth,  bowel 
may  suddenly  enter  it.  In  practically  all  oblique  inguinal  hernire,  which  develop 
suddenly  in  children  as  well  as  in  adolescents  and  young  adults,  the  sac  is  of 
congenital  origin. 

In  the  ordinary  form  of  liydrocelc  the  fluid  is  confined  to  the  tunica  vaginalis  testis, 
but  when  the  funicular  portion  of  the  processus  vaginalis  remains  patent,  the  hydrocele 
may  extend  upwards  into  the  inguinal  canal,  and  may  or  may  not  communicate  with  the 
general  peritoneal  cavity.  In  the  condition  l<nown  as  encysted  liydrocele  of  the  cord  the 
patent  funicular  process  is  shut  off  both  from  the  tunica  vaginalis  testis  and  from  the 
peritoneal  cavity 

Parallel  to  and  ai  the  level  of  the  outer  half  of  Poupart's  ligament  is  the  deep 
circumflex  iliac  artery.  In  dividing  the  abdominal  wall  to  reach  the  structures  in 
the  iliac  fossae,  the  incision  should  be  made  in  the  angle  between  this  vessel  and  the, 


THE  ABDOMINAL  CAVITY.  1267 

deep  epigastric  artery.  To  lessen  the  risk  of  ventral  hernia  the  muscles  sliould  be 
split  in  the  direction  of  their  fibres — the  aponeurosis  of  the  external  obHque  from 
above  downwards  and  inwards,  the  muscular  fibres  of  the  internal  o})lique  and 
transversalis  horizontally.  An  incision  through  the  abdominal  wall  parallel  to  the 
outer  border  of  the  rectus  has  the  great  disadvantage  of  dividing  the  abdominal 
terminations  of  the  lower  intercostal  nerves. 

The  middle  line  is  the  site  usually  selected  by  the  surgeon  to  open  the  abdomen. 
The  points  of  surgical  importance  to  be  noted  in  connexion  with  the  linea  alba  are : 
(1)  that  its  blood  supply  is  scanty ;  (2)  that  it  is  considerably  wider  above  than 
below  the  umbilicus,  where  the  two  edges  of  the  recti  lie  in  close  apposition ;  (3) 
that  above  the  umbiUcus  the  fascia  transversalis  and  linea  alba  are  adherent,  so 
that  the  two  form  practically  one  membrane ;  (4)  that  the  extra-peritoneal  fat  is 
more  abundant  beneath  the  linea  alba  than  to  either  side  of  it ;  (5)  that  above  the 
pubes  the  fascia  transversalis  recedes  from  the  linea  alba,  leaving  a  triangular  space 
occupied  by  fat  which  must  not  be  mistaken  for  the  extra-peritoneal  fat. 

The  posterior  layer  of  the  rectal  sheath  ceases  at  the  fold  of  Douglas,  which  is 
situated  one-third  of  the  distance  from  the  umbilicus  to  the  pubes.  The  fleshy  fibres 
of  the  transversalis  muscles  extend  inwards  for  a  considerable  distance  Vjehind  the 
upper- part  of  the  recti. 

THE  ABDOMINAL  CAVITY. 

To  simplify  the  topography  of  the  abdominal  viscera  the  abdomen  is  arbitrarily 
divided  into  nine  regions  by  two  horizontal  and  two  vertical  planes.  Of  the  two 
horizontal  planes,  the  upper  (infracostal)  plane  is  at  the  level  of  the  low"est  part  of 
the  tenth  costal  cartilages ;  the  lower  (intertubercular)  plane  is  at  the  level  of  the 
tubercular  points  of  the  iliac  crests.  The  two  vertical  planes  correspond  upon  the 
surface  to  a  line  drawn  vertically  upwards  on  either  side  from  a  point  midway 
between  the  anterior  superior  iliac  spine  and  the  pubic  symphysis.  Superiorly, 
these  vertical  planes  generally  strike  the  tip  of  the  ninth  costal  cartilages.  The 
subdivisions  of  the  upper  zone  are  termed  the  eiyigasiric  and  right  and  left  hypo- 
chondriac regions,  of  the  middle  zone  the  umbilical  and  right  and  left  lumbar  regions, 
of  the  lower  zone  the  hypogastric  and  right  and  left  iliac  regions.  The  epigastric, 
umbilical,  and  hypogastric  regions  may  be  further  divided  into  right  and  left 
halves  by  the  median  plane.  The  xiphisternal  junction  is  on  a  level  with  the  disc 
between  the  ninth  and  tenth  dorsal  vertebrae.  The  infracostal  plane  passes  through 
the  upper  part  of  the  third  lumbar  vertebra ;  the  intertubercular  plane  through  the 
fifth  lumbar  vertebra,  about  one  inch  above  the  sacral  promontory.  The  umbilicus 
is  usually  situated  from  one  to  two  inches  above  the  intertubercular  line. 

In  the  method  of  surface  topography  employed  by  Addison  the  plane  of  separa- 
tion between  the  superior  and  middle  abdominal  zones  is  placed  midway  between 
the  suprasternal  notch  and  the  upper  border  of  the  pubic  symphysis.  It  will  be 
found  to  lie  at  or  near  the  mid-point  between  the  xiphisternal  junction  and  the 
umbilicus.  Posteriorly,  this  plane  strikes  the  lower  border  of  the  first  lumbar 
vertebra,  and  it  so  constantly  passes  through  the  pylorus  that  it  may  with  advantage 
he  termed  the  transpyloric  plane. 

The  peritoneal  cavity  may  be  regarded  as  a  large  and  complicated  lymph  sac 
which  is  intimately  related  to  the  abdominal  viscera,  and  more  especially  to  the 
gastro-intestinal  canal.  Inflammatory  infections  of  the  peritoneum  are  therefore 
almost  always  secondary  to  lesions  of  the  viscera.  The  peritoneal  lymph  sac  is 
l^rought  into  direct  communication  with  the  subperitoneal  lymphatics  of  the 
diaphragm  through  stomata  which  open  upon  the  peritoneum  covering  the  under 
surface  of  that  muscle.  The  healthy  peritoneum,  in  virtue  of  the  vital  action  of 
its  endothelial  cells,  is  endowed  with  great  absorptive  properties,  and,  when  irritated, 
has  the  power  o£  throwing  out  an  abundant  exudation.  The  reflection  of  the 
peritoneum  and  its  relations  to  the  various  organs  have  been  elsewhere  fully 
described  (p.  1097). 

From  the  surgical  point  of  view  the  peritoneal  cavity  may  be  arbitrarily  divided 
into  four  great  subdivisions :  viz.  (1)  that  between  the  transverse  mesocolon  and  the 
85  a 


1268 


SURFACE  AND  SUEGICAL  ANATOMY, 


Fig.  913. — Anteuiok  Aspect  of  Trunk,  showinc;  Surface  Topography  of  Viscera. 


M.C. 

Mid-clavicular  line. 

P.S. 

Para-sternal  line. 

P. 

Poupart  vertical  line. 

I.e. 

Infracostal  line. 

T. 

Intertubercular  line. 

Py. 

Transpyloric  line  of  Addi.son 

A. 

Aorta. 

H. 

Heart. 

P. 

Pulmonary  orifice. 

A. 

Aortic  orifice. 

M. 

Mitral  orifice. 

T.  Tricuspid  orifice. 

R.L.  Right  lung. 

L.L.  Left  Lung. 

PI.  Pleura. 

L.  Liver. 

O.  CEsophagus. 

St.  Stomach. 

Py.  Pylorus. 

U.  Duodenum. 

T.  Ileum. 

V.  lleo-c£ecal  valve. 


A.C. 

Ascending  colon. 

T.C. 

Tians verse  colon. 

D.C. 

Descending  colon. 

11.  C. 

Iliac  colon. 

P.O. 

Pelvic  colon. 

R. 

Rectum. 

C.L 

Coininon  iliac  artery 

E.L 

External  iliac  artery 

I.V.C 

Inferior  vena  cava. 

U. 

Unjbilicus. 

THE  ABDOMINAL  CAVITY. 


1269 


diaphragm ;  (2)  that  between  the  transverse  mesocolon  and  the  mesentery  of  the 
small  intestine ;  (3)  that  between  the  mesentery  and  the  true  pelvis ;  (4)  that  in 
the  true  pelvis.  The  lesser  sac  of  the  peritoneum  may  be  looked  upon  as  a  diverti- 
culum of  the  first-mentioned  subdivision. 

The  attachment  of  the  transverse  mesocolon  to  the  posterior  abdominal  wall  is 
at  the  level  of  the  second  lumbar  vertebra,  and  lies,  therefore,  a  little  above  the 
infracostal  plane.  The  attachment,  which  ascends  slightly  as  it  passes  from  right 
to  left,  crosses  the  right  kidney,  the  second  part  of  the  duodenum,  and  the  head  of 
the  pancreas,  after  which  its  attachment  foUows  the  anterior  border  of  the  pancreas. 
The  2><"i'itoneal  subdivision  above  this  attachment  is  roofed  in  by  the  diaphragm,  and 
includes  the  upper  part  of  the  greater  sac,  and,  behind  it,  the  larger  portion  of  the 
lesser  sac.  The  organs  related  to 
this  area  of  the  peritoneum  are  the 
liver,  along  with  the  bile  ducts  and 
gaU-bladder,  the  stomach  and  part 
of  the  duodenum,  the  spleen,  the 
pancreas,  the  upper  part  of  the 
kidneys,  and  the  suprarenal  cap- 
sules. Suppuration  connected  with 
any  of  these  organs  is  hable  to  spread 
upwards  under  the  cupola  of  the 
diaphragm, producing  what  is  known 
as  subphrenic  abscess.  The  routes 
followed  to  drain  this  region  of  th* 
peritoneal  cavity  are  either  (1 ) 
through  the  anterior  abdominal  wall 
and  the  gastro-hepatic  or  gastro- 
colic omenta ;  (2)  through  the  loins 
l)elow  the  twelfth  ribs  ;  (3)  througli 
the  chest  wall,  tlie  lower  part  of  the 
pleural  cavity,  and  the  diaphragm, 
steps  having  been  previously  taken 
to  shut  off  the  drainage-track  from 
the  pleural  cavity.  This  subdivision 
of  the  peritoneal  cavity  may  become 
shut  off  from  the  rest  of  the  space 
by  adhesion  of  the  great  omentum 
to  the  peritoneum  of  the  anterior 
abdominal  wall. 

The  attachment  of  the  mesentery 
of  the  small  intestine  extends  from 
the  left  side  of  the  second  lumbar 
vertebra  downwards  to  the  right 
iliac  fossa  (Fig.  744,  p.  1051).  The 
attachment  may  be  mapped  out  on 
the  surface  by  drawing  a  line  from 
a  point  on  the  transpyloric  line,  one 
inch  to  the  left  of  the  middle  line, 
to  the  mid-point  of  a  line  drawn  Fig.  914.— Lateral  Aspect  of  Trunk,  showing  Surface 
horizontals  between  the  right  an-  Topographv  of  Viscera. 

terior  superior  iliac  spine  and  the  f-L-  Right  lung.  r.k.  R;gbt  ^dney. 

•  1  Ti     1-  mi-  7   7-     •    •        T   i  L.        Liver.  F.L.    FJeura. 

middle  line.  The  subdivision  betiveen 

the  transverse  mesocolon  and  the  mesentery  proper  is  related  more  particularly  to  the 
small  intestine,  the  csecum  and  vermiform  appendix,  the  ascending  colon,  the  right 
ureter,  and  part  of  the  right  kidney.  Suppuration  in  connexion  with  the  organs  in 
this  area  involves  more  especially  the  right  lumbar  region,  and  may  extend  upwards 
along  the  colon  into  the  subdiaphragmatic  region,  or  downwards  into  the  true  pelvis. 
To  drain  this  region  a  tube  is  introduced  into  the  right  lumbar  region  either 
through  the  anterior  abdominal  wall  or  through  the  right  loin. 


1270  SUEFACE  AND  SURGICAL  ANATOMY. 

The  peritoneal  siibdivision  belovj  the  mesentenj  corresponds  to  the  left  umbilical, 
left  lumbar,  and  left  iliac  regions,  and  is  related  to  the  duodeno-jejunal  junction, 
the  greater  part  of  the  small  intestine,  part  of  the  transverse  colon,  the  splenic 
flexure,  the  descending  colon,  tlie  ihac  colon,  the  lower  part  of  the  left  kidney,  the 
left  ureter,  the  lower  part  of  the  abdominal  aorta,  and  the  common  iliac  arteries. 
Suppuration  in  this  division  is  very  liable  to  extend  downwards  into  the  pelvis. 
Drainage  may  be  established  by  the  introduction  of  a  tube  either  through  the 
anterior  abdominal  wall  or  through  the  left  lumbar  region.  If  suppuration  occur 
in  the  pelvis,  drainage  may  be  carried  out  through  the  anterior  abdominal  wall  or, 
in  the  case  of  the  female,  through  the  vagina. 

Liver. — The  loiver  horcler  of  the  liver,  as  it  crosses  the  costal  angle,  can  readily 
be  determined  by  palpation  and  light  percussion ;  it  passes  from  the  eighth  left  to 
the  tip  of  the  tenth  right  costal  cartilage,  and  crosses  the  mesial  plane  at  the  level 
of  the  transpyloric  line.  In  the  mid-axillary  line  it  reaches  down  to  a  point  a 
little  below  the  lowest  part  of  the  tenth  right  costal  cartilage.  Above  the  left 
costal  margin  the  lower  border  passes  upwards  and  to  the  left  to  join  the  left 
extremity  of  the  liver  at  the  fifth  interspace  in  the  mammary  line.  The  highest 
part  of  the  liver,  which  corresponds  also  to  the  highest  part  of  the  right  arch  of  the 
diaphragm,  reaches,  during  expiration,  to  the  level  of  the  fourth  intercostal  space  in 
the  mammary  line.  To  the  right  of  the  mesial  plane  the  upper  border  of  the  liver 
is  too  far  removed  from  the  anterior  wall  of  the  chest,  and  overlapped  by  too  thick 
a  layer  of  lung  substance,  to  be  accurately  determined  by  percussion.  Behind  the 
sternum  the  upper  border  reaches  to  the  level  of  the  sixth  chondro-sternal  junctions. 
To  the  left  of  the  mesial  plane  the  upper  limit  of  the  liver  cannot  be  determined 
by  percussion  as  it  merges  into  the  cardiac  dulness.  The  falciform  ligament  of  the 
liver  lies,  as  a  rule,  a  little  to  the  right  of  the  mesial  plane. 

The  anterior  surface  of  the  liver  may  be  reached  through  a  mesial  incision 
extending  downwards  from  the  ensiform  cartilage,  or  by  an  oblique  incision  a  finger's 
breadth  below  and  parallel  to  the  right  costal  margin.  To  obtain  free  access  to  the 
upper  surface  the  eighth  and  ninth  costal  cartilages  must  be  resected ;  the  seventh 
cartilage  should,  if  possible,  be  avoided,  otherwise  the  pleural,  and  even  the  peri- 
cardial cavity,  may  be  opened.  Division  of  the  round  and  falciform  ligaments 
allows  of  greater  downward  displacement  of  the  liver.  To  reach  the  centre  of  the 
lateral  surface  of  the  right  lobe  portions  of  the  seventh  and  eighth  ribs  should  be 
resected  in  the  mid-axillary  line,  and  both  the  pleural  and  peritoneal  cavities  must 
be  traversed. 

The  relation  of  the  fundus  of  the  gall-liladder  to  the  surface  is  subject  to  consider- 
able variation.  Normally  it  is  situated  opposite  the  angle  between  the  ninth  costal 
cartilage  and  the  outer  border  of  the  rectus ;  exceptionally  it  is  pendulous  and 
suspended  from  the  liver  by  a  more  or  less  distinct  mesentery ;  or  it  may  be 
elongated  and  drawn  downwards  by  adhesion  to  the  duodenum  or  colon.  When 
displaced  downwards  it  is  liable  to  be  mistaken  for  a  floating  kidney,  but  may  be 
distinguished  from  it  by  the  fact  that  although  it  may  be  pushed  backwards  into 
the  lumbar  region  it  returns  at  once  to  its  habitual  position  immediately  behind 
the  anterior  abdominal  wall  as  soon  as  it  ceases  to  be  manipulated.  The  cystic  duct,_ 
which  is  about  an  inch  and  a  half  in  length,  is  sharply  bent  upon  itself  close  to  its 
origin  at  the  neck  of  the  gall-bladder.  It  joins  the  hepatic  duct  at  a  very  acute 
angle.  The  passage  of  a  probe  along  the  normal  duct  is  rendered  difficult  by  the 
marked  flexure  at  its  commencement,  as  well  as  by  the  folded  condition  of  its  mucous 
membrane ;  hence  also  the  frequency  with  which  calculi  become  impacted  at  the 
neck  of  the  gall-bladder.  In  excising  the  gall-bladder,  it  is  an  advantage  to  ligature 
and  divide  the  cystic  artery  and  duct  before  proceeding  to  detach  the  organ  from 
the  under  surface  of  the  liver.  The  common  bile-dicct,  about  three  and  a  half  inches 
in  length,  lies,  in  its  upper  third,  close  to  the  right  free  border  of  the  gastro-hepatic 
omentum.  When  cutting  into  this,  the  most  accessible  part  of  the  duct,  it  should 
be  drawn  forward  by  the  finger  introduced  behind  it,  through  the  foramen  of 
Winslow ;  the  portal  vein,  which  must  be  avoided,  lies  behind  and  a  little  to  the 
left  of  the  duct.  The  middle  third  of  the  common  duct  lies  a  little  to  the  right  of 
the  commencement  of  the  gastro-hepatic  artery  behind  the  first  part  of  the  duodenum 


THE  ABDOMINAL  CAVITY.  1271 

about  a  finger's  breadth  I'roni  the  pylorus.  The  lower  third  of  the  duct  which  passes 
downwards  and  to  the  right,  is  intimately  related  to  the  pancreas,,  and  is  usually  so 
embedded  in  the  posterior  aspect  of  its  head  that  it  cannot  be  freed  by  blunt 
dissection.  Close  to  its  termination  the  common  duct  is  joined  by  the  pancreatic 
duct,  the  two  opening  separately,  but  close  together,  at  the  bottom  of  a  diverticulum 
(ampulla  of  ^'arter),  which  pierces  the  wall  of  the  duodenum  obliquely,  and  opens 
at  the  summit  of  a  small  papilla  situated  at  the  lower  part  of  tlie  inner  wall  of  the 
descending  portion  of  the  duodenum,  about  four  inches  from  the  ]>ylorus.  When  a 
calculus  l)ecomes  impacted  in  the  ampulla,  there  is  retention  of  the  pancreatic  as 
well  as  of  tlie  biliary  secretion.  Not  infrequently  there  is  an  accessory  pancreatic 
duct  (duct  of  Santorini)  which  opens  into  the  duodenum  at  a  higher  level  than  the 
main  duct,  which  it  joins  by  its  other  extremity.  A  calculus  in  the  ampulla  may 
be  readied  either  by  opening  the  duodenum  from  the  front  (trans-duodenal  route), 
or  by  freeing  the  duodenum  and  gaining  access  to  the  duodenum  from  behind 
(retro-duodenal  route).  In  the  latter  instance  an  incision  is  made  external  to  the 
outer  bortler  of  the  second  part  of  the  duodenum,  through  that  portion  of  the 
peritoneum  which  ascends  from  the  upper  layer  of  the  transverse  mesocolon  over 
the  anterior  surface  of  the  hepatic  area  of  the  kidney.  By  blunt  dissection  directed 
inwards  behind  the  duodenum,  this  organ,  along  with  the  adjacent  part  of  the  head 
of  the  pancreas,  can  be  separated  from  the  kidney  and  vena  cava  and  folded  over 
towards  tlie  left,  like  a  door  on  its  hinges.  In  freeing  the  bile-duct  from  the 
posterior  aspect  of  the  head  of  the  pancreas  a  vein  of  considerable  size  will  be 
encountered ;  this  vein,  which  returns  the  blood  from  the  pancreatic-duodenal 
system  of  arteries,  lies  close  to  the  bile-duct  as  it  ascends  behind  the  head  of  the 
pancreas  to  open  into  the  commencement  of  the  vena  porta.  Of  the  lymphatic  glands 
related  to  the  bile  passages  it  is  to  be  remembered  that  one  lies  at  the  neck  of  the 
gall-bladder,  another  at  the  junction  of  the  cystic  and  hepatic  ducts,  while  a 
third  lies  close  to  the  termination  of  the  common  duct.  When  these  glands  are 
enlarged  and  indurated,  care  must  be  taken  not  to  mistake  them  for  impacted 
gall-stones. 

Stomach. — The  stomach  lies  almost  entirely  within  the  left  half  of  the  epi- 
gastric and  the  left  hypochondriac  regions.  The  cardiac  orifice,  which  lies  1  in. 
below  and  to  the  left  of  the  cesophageal  opening  in  the  diaphragm,  is  about  4  in. 
from  the  surface,  and  corresponds,  on  the  anterior  surface  of  the  body,  to  a 
point  over  the  seventh  left  costal  cartilage  1  in.  from  the  sternum.  The  pylorus, 
which  is  generally  partly  overlapped  by  the  lower  margin  of  the  liver,  hes,  as  a  rule, 
about  one  inch  to  the  right  of  the  mesial  plane ;  when  the  stomach  is  empty  it 
generally  lies  in  the  mesial  plane,  when  distended  it  may  reach  two,  or  even  three, 
inches  to  the  right  of  the  middle  line.  The  pyloric  portion  of  the  stomach  is  prac- 
tically bisected  by  a  horizontal  plane  which  passes  through  the  abdomen  at  the 
level  of  a  point  midway  between  the  suprasternal  notch  and  pubic  symphysis 
(Addison) ;  it  lies,  therefore,  three  to  four  inches  below  the  infrasternal  notch,  mid- 
way between  it  and  the  umbilicus,  opposite  the  first  lumbar  vertebra.  The 
highest  part  of  the  fundus  of  the  stomach  corresponds  to  the  left  vault  of  the 
diaphragm,  and  lies  at  the  level  of  the  fifth  rib  in  the  mammary  line,  a  little  above 
and  behind  the  apex  of  the  heart.  The  greater  curvature  crosses  behind  the  left 
costal  margin  opposite  the  tip  of  the  ninth  costal  cartilage,  that  is  to  say,  where  the 
transpyloric  line  intersects  the  vertical  Poupart  line.  The  lowest  part  of  the  great 
curvature,  situated  generally  in  the  mesial  plane,  extends  down  to,  or  a  little  above, 
the  infracostal  plane,  about  two  inches  above  the  umbilicus.  The  lesser  curvature  and 
the  adjacent  part  of  the  anterior  wall  of  the  stomach  are  overlapped  by  the  lower 
margin  of  the  liver. 

Overlying  the  stomach  is  an  important  surface  area  known  to  clinicians  as  the 
semilunar  space  of  Traube.  This  space,  which  yields  a  deeply  tympanitic  note  on 
percussion,  is  bounded  above  by  the  lower  margin  of  the  left  lung ;  below,  by  the 
left  costal  margin ;  to  the  right,  by  the  lower  edge  of  the  left  lobe  of  the  liver ; 
behind  and  to  the  left,  by  the  anterior  border  and  anterior  basal  angle  of  the  spleen. 
The  line  of  the  costo-diaphragmatic  pleural  reflection  crosses  the  space  about  mid- 
way between  its  upper  and  lower  limits.  The  tympanitic  area  of  the  space  is 
85  & 


1272  SURFACE  AND  SURGICAL  ANATOMY. 

dimiuished  superiorly  by  pleuritic  effusion,  towards  the  right  by  enlargement  of 
the  liver,  and  towards  the  left  by  enlargement  of  the  spleen. 

I'erforation  of  an  ulcer  on  the  anterior  wall  of  the  stomach  leads  to  extravasa- 
tion into  the  greater  sac  of  the  peritoneum,  while  if  the  perforated  ulcer  be  upon 
the  posterior  wall,  extravasation  takes  place  into  the  lesser  sac.  The  close  relation 
of  the  splenic  artery  and  its  branches  to  the  posterior  wall  of  the  stomach  explains 
the  severe  hemorrhage  which  is  sometimes  caused  by  a  posterior  gastric  ulcer. 
The  surgeon  may  reach  the  posterior  wall  of  the  stomach  through  the  gastro-colic 
omentum,  or,  after  throwing  upwards  the  great  omentum  and  transverse  colon,  by 
traversing  the  transverse  mesocolon ;  by  the  former  route  the  posterior  wall  of  the 
stomach  is  reached  through  the  anterior  wall  of  the  lesser  sac,  in  the  latter  case 
through  its  posterior  wall. 

Duodenum. — The  first  part  of  the  duodenum,  situated  in  the  right  half  of  the 
epigastrium,  hes  behind  the  eighth  costal  cartilage,  immediately  internal  to  the 
gall-bladder,  and  is  overlapped  by  the  quadrate  lobe  of  the  liver.  If  the  finger 
be  passed  above  this  part  of  the  duodenum  and  towards  the  left,  behind  the  right 
free  border  of  the  lesser  omentum,  it  will  occupy  the  foramen  of  Winslow,  which  is 
just  large  enough  to  easily  admit  the  finger.  In  resecting  the  pylorus,  the 
suro-eon  should  remember  that  the  gastro-duodenal  vessels  lie  behind  the  first  part 
of  the  duodenum,  about  one  inch  to  the  right  of  the  pylorus. 

The  second  part  of  the  duodenum  descends  a  little  internal  to  the  right  vertical 
Poupart  plane,  and  is  crossed  about  its  middle,  at  the  level  of  the  infracostal  plane, 
by  the  attachment  of  the  transverse  mesocolon.  It  lies  in  front  of  the  hilum  and 
lower  part  of  the  inner  border  of  the  right  kidney. 

The  transverse  portion  of  the  third  part  of  the  duodenum  occupies  the  upper 
part  of  the  umbilical  region,  and  crosses  the  middle  line  about  one  inch  above  a  line 
joining  the  highest  part  of  the  iliac  crests ;  behind  its  commencement  is  the  upper 
part  of  the  right  ureter. 

The  ascending  portion  of  the  third  part  of  the  duodenum  crosses  the  infra- 
costal plane,  and  ascends  upon  the  left  side  of  the  vertebral  column  opposite  the 
second  and  third  lumbar  vertebra. 

The  duodeno -jejunal  flexure,  which  lies  in  the  transpyloric  plane  one  inch  to  the 
left  of  the  mesial  plane,  is  the  landmark  which  the  surgeon  makes  for  when  he 
wishes  to  identify  the  commencement  of  the  jejunum  (Fig.  746,  p.  1054).  To  find 
the  fiexure  the  omentum  and  transverse  colon  should  be  thrown  upwards  and  the 
finc-er  passed  along  the  lower  layer  of  the  transverse  mesocolon  to  the  left  side  of 
the  vertebral  column.  The  flexure  lies  in  the  angle  or  recess  formed  by  the  left  side 
of  the  second  lumbar  vertebra  and  the  under  surface  of  the  body  of  the  pancreas. 
With  the  finger  in  this  recess  the  commencement  of  the  jejunum  may  be  hooked 
forward  a  little  to  the  left  of  the  superior  mesenteric  vessels  at  the  root  of  the 
mesentery.  In  connexion  with  the  duodeno-jejunal  junction  is  the  duodeno -jejunal 
fossa  (inferior  duodenal  fossa  of  Jonnesco),  formed  Ijy  a  fold  of  peritoneum  which 
stretches  from  the  left  side  of  the  fourth  or  ascending  part  of  the  duodenum 
upwards  to  become  attached  to  the  peritoneum  of  the  posterior  abdominal  wall  close 
to  the  inner  border  of  the  left  kidney.  The  free  edge  of  the  fold  and  the  mouth  of 
the  fossa  look  upwards.  This  is  one  of  the  situations  at  which  an  internal  hernia 
sometimes  develops,  the  sac,  as  it  enlarges,  extending  further  and  further  into  the 
extra-peritoneal  tissue  on  the  posterior  abdominal  wall.  Should  strangulation 
occur,  the  lower  edge  of  the  orifice  must  be  divided  in  a  downward  direction,  in 
order  to  avoid  the  superior  mesenteric  vein  which  curves  round  the  anterior  and 
upper  aspects  of  the  orifice  (Treves). 

Small  Intestine. — The  coils  of  the  small  intestine  dip  downwards  into  the 
pelvis,  overlap  the  ascending  and  descending  portions  of  the  colon,  and  extend 
upwards  to  the  attachment  of  the  transverse  mesocolon.  To  the  left  of  the 
mesentery  they  reach  as  far  as  the  under  surface  of  the  pancreas  and  the  splenic 
flexure  of  the  colon ;  here  they  are  overlapped  by  the  lower  part  of  the  stomach, 
from  which  th&y  are  separated  by  the  transverse  mesocolon.  The  only  certain 
means  which  the  surgeon  has  of  distinguishing  the  upper  from  the  lower  coils  of 
small  intestine  is  by  their  relation  to  the  duodeno-jejunal  flexure  and  the  ileo- 


THE  ABDOMINAL  CAVITY. 


1273 


Ciecal  junction.  Occasionally  the  Peyer's  patches  can  be  seen  from  the  peritoneal 
aspect  and  the  ileum  thereby  identified.  The  terminal  portion  of  the  ileum,  which 
is  attached  by  the  lower  end  of  the  mesentery  to  the  upper  part  of  the  right'  lateral 
wall  of  the  true  pelvis,  crosses  over  its  brim,  and  ascends  along  the  inner  edge  of 
the  caecum  before  opening  into  it.  The  terminal  loop  of  the  ileum  may  be  hooked 
up  by  passing  the  finger  along  the  inner  side  of  the  caecum  downwards  over  the 
inner  border  of  the  psoas  and  the  external  iliac  vessels  into  the  pelvis. 

Meckel's  diverticulum,  which  is  due  to  persistent  patency  of  tlie  proximal  portion  of 
the  vitelline  duct,  is  usually  situated  from  two  to  three  feet  above  the  ilco-Cfecal  valve ;  its 
average  length  is  two  inches.  Springing  from  the  antimeseuteric  border  of  the  ileum,  its 
termination  is  usually  free,  but  it  may  be  adherent  either  to  the  anterior  abdominal  wall, 
to  the  mesentery,  or,  more  rarely,  to  one  of  the  adjacent  viscera.  When  its  termination 
is  fixed  it  may  give  rise  to  strangulation  of  the  intestine. 

Large  Intestine. — The  csecum,  which  occupies  the  right  iliac  region,  comes 
into  contact  with  the  anterior  abdominal  wall  immediately  above  the  outer  third  of 


RETRO-CAECAL  FOSSA 

B 

Fig.  915. — The  C^cal  Folds  and  Foss.e. 

In  A,  the  ciecniu  is  viewed  from  the  front  ;  the  mesentery  of  the  appendix  is  distinct,  and  is  attached  above 
to  the  under  surface  of  the  portion  of  the  mesentery  going  to  the  end  of  the  ileum.  In  B,  the  csecum 
is  turned  upwards  to  show  a  retro-caecal  fossa,  wliich  lies  behind  it,  and  the  beginning  of  the  ascending 
colon  (from  Birmingham). 

I'oupart's  ligament ;  laterally,  it  extends  from  the  anterior  superior  iliac  spine  to 
the  brim  of  the  pelvis.  When  dilated,  it  extends  considerably  beyond  these  limits  ; 
when  empty,  it  is  generally  more  or  less  completely  overlapped  by  small  intestine. 
The  ileo-csecal  valve  lies  at  the  junction  of  the  intertubercular  and  Poupart 
planes  (Fig.  913  V). 

The  orifice  of  the  appendix  opens  upon  the  postero-internal  aspect  of  the  caecum 
about  an  inch  below  the  ileo-coecal  valve,  a  point  which,  according  to  M'Burney, 
may  be  located  on  the  surface  at  the  junction  of  the  outer  and  middle  thirds  of  a 
line  drawn  from  the  umbilicus  to  right  anterior  superior  iliac  spine.  The  appendix 
will  generally  be  found  to  pass  either  upwards  and  inwards  behind  the  lower  end 
of  the  ileum,  or  downwards  and  inwards  so  as  to  overhang  the  external  iliac  vessels 
at  the  brim  of  the  pelvis ;  less  frequently  it  ascends  in  the  pouch  behind  the 
commencement  of  the  ascending  colon.  The  Hood  supply  of  the  appendix  is  derived 
from  a  single  artery  (a  branch  of  the  ileo-colic)  which  occupies  the  small  mesentery 
of  the  appendix  (Fig.  916);  hence  interference  with  the  flow  of  blood  along  this 
vessel,  either  mechanically  or  from  disease,  predisposes  to  gangrene  of  the  appendix. 
In  opening  the  abdomen  to  remove  the  appendix  it  is  usual  either  to  split  the 
three  lateral  abdominal  muscles  in  the  direction  of  their  fibres  ("  gridiron  "  incision) 
or  to  pass  through  the  sheath  of  the  rectus,  in  which  case  the  muscle  itself  is 
either  pulled  inwards  or  its  fibres  separated.     When  the  gridiron  incision  is  made 


1274 


SUEFACE  AND  SURGICAL  ANATOMY. 


ILEO-COLIC  ARTERY 


ILIAC  BRANCH 


FlO.   916.- 


-The  Blood  Supply  of  the  C^.cum  and  Ver- 
MiKORM  Appendix. 


as  long  as  possible,  it  is  necessary  to  divide  both  the  ascending  branch  of  the  deep 
circumflex  ihac  and  the  deep  epigastric  vessels,  the  former  at  the  outer  and  the 
latter  at  the  inner  extremity  of  the  incision.     After  dividing  the  peritoneum,  the 

appendix  is  sought  for  by  passing  the 
finger  behind  the  angle  formed  by  the 
inner  aspect  of  the  caecum  and  the 
lower  end  of  the  ileum.  It  may  be 
necessary  to  bring  the  csecum  out  of 
the  wound,  in  order  that  the  anterior 
longitudinal  band  of  muscular  fibres 
(ttenia  coli)  may  be  traced  downwards 
to  the  root  of  the  appendix  (Fig. 
915,  A). 

The  ascending  colon,  after  crossing 
the  iliac  crest,  lies  deeply  in  the  right 
lumbar  region  upon  the  quadratus 
lumborum  and  the  right  kidney. 

The  hepatic  flexure  reaches  upwards 
beneath  the  tenth  costal  cartilage 
into  the  lowest  part  of  the  right  hypo- 
chondrium,  where  it  lies  immediately 
to  the  right  of  the  gall-bladder,  be- 
The  illustration  gives  a  view  of  the  cseinn  from  behind,  tween  the  liver  and  the  lower  half  of 

The    artery    of    the     appendix,    and    the    three    taenia    the  anterior  SUrface  of  the  kidney, 
coli  springing  from  the  base  of  the  appendix,  should  ^hc    transversa    COlon    CrOSSCS    the 

be    specially    noted    (modified    Ijy    Birmingham    from  ,        n    ,i  n  -t      i 

Jonnesco).  "^  .  o  upper  part  01    the  umbilical  region. 

Not  infrequently  it  forms  a  U-shaped 
or  a  V-shaped  loop  which  reaches  for  a  variable  distance  below  the  level  of  the 
umbilicus ;  when  the  intestines  are  distended  it  may  ascend  in  front  of  the 
stomach. 

The  splenic  flexure  reaches  upwards  behind  the  greater  curvature  of  the 
stomach  into  the  left  hypochondriac  region,  as  far  as  the  lower  extremity  of  the 
spleen,  from  which  it  is  separated  by  the  costocolic  fold  of  peritoneum. 

The  descending  colon  lies  deeply  in  the  left  lumbar  region,  along  the  lower  half 
of  the  outer  border  of  the  left  kidney. 

The  iliac  and  pelvic  portions  of  the  colon  lie  respectively  in  the  left  iliac  fossa 
and  in  the  true  pelvis ;  the  latter  is  provided  with  a  distinct  mesentery  which, 
as  it  crosses  the  left  ureter  and  the  bifurcation  of  the  common  iliac  vessels,  forms 
the  intersigmoid  peritoneal  fossa.  This  fossa  is  sometimes  the  starting-point  of  an 
internal  retroperitoneal  hernia.  The  mouth  of  the  fossa  looks  downwards  and  to 
the  left ;  above  and  to  its  right  is  the  sigmoid  artery.  The  iliac  colon  can  generally 
be  felt  through  the  abdominal  wall  as  it  descends  from  the  crest  of  the  ileum  to 
the  inner  margin  of  the  psoas  muscle.  The  upper  portion  of  the  pelvic  colon  is 
the  part  of  the  bowel  which  is  most  frequently  opened  when  it  is  desired  to  make- 
an  artificial  anus.  It  is  exposed  through  an  oblique  incision,  the  centre  of  which 
is  at  the  junction  of  the  middle  and  outer  thirds  of  a  line  drawn  from  the 
umbilicus  to  the  anterior  superior  iliac  spine. 

Kidneys.^ — The  kidneys,  which  lie  behind  the  peritoneum,  extend  higher  up 
than  is  often  supposed,  and  laterally  they  do  not  extend  so  far  away  from  the 
spine  as  is  almost  invariably  depicted ;  hence  it  is  that,  unless  enlarged,  the  kidneys 
can  seldom  be  felt  through  the  abdominal  wall.  The  right  kidney  as  a  rule  lies  a 
little  lower  than  the  left,  as  well  as  a  little  further  away  from  the  mesial  plane. 
The  hilum  of  the  right  kidney  lies  2  in.  from  the  mesial  plane ;  that  of  the  left 
li  in.  from  the  mesial  plane.  For  practical  purposes  the  hilum  of  the  kidney  may 
Ije  regarded  as  ojjposite  a  point  on  the  anterior  abdominal  wall  a  finger's  breadth 
internal  to  the  tip  of  the  ninth  costal  cartilage  ;  and  a  line  joining  the  two  hili 
crosses  the  vertebral  column  opposite  the  disc  between  the  first  and  second  lumbar 
vertebrse,  that  is  to  say,  on  a  level  with  the  transpyloric  line.  The  hiffhest  ijoint 
of  the  kidney  is  situated  two  inches  from  the  mesial  plane,  on  a  level  with  a 


THE  ABDOMINAL  CAVITY. 


1275 


Fig.  917. — Anterior  Aspect  ov  Trunk,  showin(;  Surface  Topography  of  Viscera. 


M.C. 

Mid-clavicular  line. 

L.L. 

Left  lung. 

Q.L. 

Quadratus  lumboruni 

P.S. 

Para-sternal  line. 

PI. 

Pleura. 

Ps. 

Psoas. 

P. 

Poupart  vertical  line. 

0. 

CEsopliagus. 

R.U. 

Right  ureter. 

I.e. 

Infracostal  line. 

R.K. 

Ricjht  kidney. 

L.U. 

Left  ureter. 

T. 

Intertubercular  line. 

L.K. 

Left  kidney. 

C.L 

Common  iliac  artery. 

Py. 

Transpyloric  line. 

Sp. 

Spleen. 

E.L 

External  iliac  artery. 

T. 

Trachea. 

S.R 

Suprarenal  capsule. 

l.V.C. 

Inferior  vena  cava. 

A. 

Aorta. 

Pa. 

Pancreas. 

U. 

Umbilicus. 

R.L. 

Right  hiug. 

D. 

Duodenum. 

1276  SURFACE  AND  SURGICAL  ANATOMY. 

line  crossing  the  abdomen  midway  between  the  xiphisternal  and  transpyloric 
planes.  The  loioest  point  of  the  kidney  reaches  down  to,  or  a  little  below,  the 
infracostal  plane. 

The  student  should  make  himself  familiar  with  the  feel  of  tlie  parts  in  relation 
to  tlie  kidneys,  as  far  as  they  can  be  made  out  by  introducing  the  hand  through  a 
mesial  abdominal  incision.  The  lower  half  of  the  right  kidney  is  covered  by  the 
hepatic  flexure  of  the  colon ;  the  upper  part  lies  deeply  in  the  hypochondrium,  and 
is  felt  by  thrusting  the  hand  upwards  and  backwards  between  the  liver  and  the 
hepatic  flexure  of  the  colon.  Between  this  part  of  the  kidney  and  the  renal  sur- 
face of  the  liver  is  a  deep  recess  which  receives  its  serous  covering  from  peri- 
toneum continued  upwards  from  the  upper  layer  of  the  transverse  mesocolon. 
Overlapping  the  hilum  and  the  lower  part  of  the  inner  border  is  the  descending 
part  of  the  duodenum,  which  is  crossed  by  the  transverse  colon. 

The  lower  half  of  the  left  kidney,  covered  by  peritoneum  continued  downwards 
from  the  lower  layer  of  the  transverse  mesocolon,  is  easily  felt  in  the  hollow 
between  the  vertebral  column  and  the  upper  part  of  the  descending  colon.  It  is 
overlapped  by  coils  of  small  intestine,  and  passing  transversely  outwards  in  front 
of  it  is  the  left  colic  artery  and  its  branches.  Crossing  the  left  kidney,  a  little 
above  its  middle,  is  the  body  of  the  pancreas,  together  with  the  splenic  vessels. 
To  reach  the  part  of  the  kidney  which  lies  above  the  pancreas,  an  opening  should 
be  made  through  the  gastro-colic  omentum  and  the  hand  passed  upwards  behind 
the  stomach  into  the  lesser  sac  of  the  peritoneum.  Applied  to  the  upper  half  or 
more  of  the  outer  border  of  the  kidney  is  the  renal  surface  of  the  spleen. 

The  posterior  relations  of  the  kidneys  will  be  referred  to  when  dealing  with 
the  back. 

Outside  the  true  capsule  of  the  kidney  is  the  adipose  capsule,  which  is  a 
specialised  thickening  of  the  extra-peritoneal  fat.  It  is  in  this  fat  that  a  peri- 
nephritic  abscess  develops,  the  pus  passing  backwards  into  the  loin,  downwards 
towards  the  iliac  fossa,  or  forwards  into  the  extra-peritoneal  fat  of  the  anterior 
abdominal  wall. 

The  ureters  lie  behind  the  peritoneum  covering  the  psoas  muscles ;  they 
descend  almost  vertically  in  the  umbilical  region  1|  in.  from  the  mesial  plane. 
At  the  level  of  the  intertubercular  plane  they  lie  in  front  of  the  termination  of  the 
common  iliac  arteries,  and  then  pass  down  into  the  true  pelvis  in  front  of  the 
internal  iliac  arteries. 

Pancreas. — The  head  of  the  'pancreas  occupies  the  curve  of  the  duodenum, 
and  Hes  in  the  lowest  part  of  the  right  half  of  the  epigastric  region,  on  a  level  with 
the  second  lumbar  vertebra.  The  neck,  which  crosses  the  mesial  plane  opposite  the 
disc  between  the  first  and  second  lumbar  vertebrae,  lies  in  the  transpyloric  plane, 
while  the  body  lies  immediately  above  that  plane.  The  tail  lies  in  the  left  hypo- 
chondriac region.  The  relations  of  the  pancreas  to  the  transverse  mesocolon  and 
to  the  neighbouring  viscera  have  already  been  sufficiently  referred  to. 

After  opening  the  abdomen  in  the  middle  line,  the  pancreas  is  best  exposed  by 
passing  through  the  gastro-colic  omentum ;  access  to  the  organ  through  either  the 
gastro-hepatic  omentum  or  the  transverse  mesocolon  is  more  limited  and  therefore 
less  satisfactory. 

A  X->ancreatic  cyst  gives  rise  to  a  tumefaction  of  the  abdomen  either  in  the 
epigastric  or  in  the  umbilical  region,  depending  on  whether  it  pushes  the  gastro- 
hepatic  omentum  before  it  and  develops  between  the  liver  and  stomach,  or  whether 
it  extends  forwards  below  the  stomach.  In  severe  contusions  of  the  abdomen  the 
pancreas  may  be  ruptured  against  the  vertebral  column. 

Vessels  of  the  Abdomen. — The  commencement  of  the  abdominal  aorta  and  the 
coeliac  axis  is  situated  two  fingers'  breadth  above  the  transpyloric  plane.  The 
superior  mesenteric  artery  arises  a  finger's  breadth  above  the  transpyloric  plane,  the 
renal  arteries  a  finger's  breadth  below  it.  The  inferior  mesenteric  artery  arises  mid- 
way between  the  transpyloric  and  the  intertubercular  plane — that  is  to  say,  about 
1  in.  above  the  level  of  the  umbilicus.  The  abdominal  aorta  bifurcates  in,  or  a 
little  to  the  left  of,  the  mesial  plane,  on  a  level  with  the  highest  part  of  the  iliac 
crest,  and  about  f  in.  below  the  level  of  the  umbilicus. 


THE  MALE  PEEINEUM. 


1277 


The  inferior  vena  cava  lies  immediately  to  the  right  of  the  aorta;  its  most 
important  surgical  relation  is  the  right  ureter,  which  lies  close  to  its  outer  side. 

The  common  and  external  iliac  arteries  may  be  mapped  out  by  drawing  a  line, 
curved  slightly  outwards,  from  a  point  opposite  the  Ijilurcation  of  the  aorta  to  a 
point  midway  between  the  anterior  superior  iliac  spine  and  the  pubic  symphysis : 
the  upper  third  of  this  Hue  corresponds  to  the  common  iliac,  the  lower  two-thirds 
to  the  external  iliac.  The  common  iliac  veins  lie  mainly  to  the  right  of  the  corre- 
sponding arteries,  the  left  vein,  however,  crossing  behind  the  right  artery  to  join  its 
fellow  to  form  the  inferior  vena  cava.  The  relation  of  the  veins  and  of  the  ureters 
must  be  borne  in  mind  in  ligaturing  the  common  iliac  arteries. 

The  great  vessels  upon  the  posterior  abdominal  wall,  along  with  the  adjacent 
lymphatic  vessels  and  glands,  lie  in  the  extra-peritoneal  fat,  and  therefore  within 
the  general  fascial  envelope  of  the  abdomen.  Abscesses,  originating  from  the 
retro-peritoneal  lymphatic  glands  are,  therefore,  like  perinephritic  abscesses,  extra- 
peritoneal, but  intra-fascial ;  abscesses  of  spinal  origin,  whether  lumbar,  iliac,  or 
psoas,  are,  on  the  other  hand,  extra-fascial.  Abscesses  connected  with  the  vermi- 
form appendix  are  primarily  intra-peritoneal ;  occasionally  they  ulcerate  through 
the  parietal  peritoneum  and  burrow  in  the  extra-peritoneal  fat. 


CORPUS    CAVERNOSUM 
^**"  CORPUS    SPONGIOSUM 
■CORO 


CAVERNOSUM 


F.\SC\A  OF  CO 


THE  MALE  PEEINEUM. 

The  male  perineum  is  a  heart-shaped  space  the  osseous  boundaries  of  which  are 
the  same  as  those  which  form 
the  outlet  of  the  pelvis.  A 
line  drawn  transversely  across 
the  perineum  between  the  an- 
terior part  of  the  tuberosities 
crosses  the  middle  line  immediately 
in  front  of  the  anus,  and  divides 
the  space  into  an  anterior  or  urino- 
genital  triangle  and  a  posterior  or 
rectal  triangle.  The  urinogenital 
triangle  is  subdivided  into  a  super- 
ticial  and  deep  compartment  by  the 
triangular  ligament ;  in  the  super- 
iicial  compartment  is  the  root  of 
the  penis,  which  gives  rise  to  a 
longitudinal  fulness  upon  the  sur- 
face. Anteriorly,  the  surface  of  the 
urinogenital  triangle  is  continued 
on  to  the  scrotum,  whilst  laterally 
a  distinct  groove  separates  it  from 
the  inner  surface  of  the  thighs. 
The  central  point  of  the  perineum 
(common  tendon  of  the  perineal 
muscles)  is  continuous  with  the 
centre  of  the  base  of  the  triangular 
ligament,  and  lies  a  finger's  breadth 
in  front  of  the  anus.  Immediately 
in  front  of  it,  and  about  1  in.  from 
the  centre  of  the  anus,  is  the  pos- 
terior edge  of  the  bulb  of  the  corpus 
spongiosum.  The  superficial  com- 
partment of  the  urinogenital  triangle 

is     bounded    below    by  the    perineal  I^f'^™'- 1>*""'"'^^°">'-^""--^-  inferior  ha^morrholdal  artery 

fascia    of   CoUes    (Fig.  918),    which  ^lo-  918. -Dissection   of  the  Perineum.     Th«  scrotum  and 

.      ,  •   °i  11  the  penis  Lave  been  cut  transversely  across  and  removed 

is  attached  posteriorly  to  the  base        (from  Cunningham). 

of  the    triangular    ligament,    and 

laterally  to  the  margins  of  the  pubic  arch.     Anteriorly,  the  fascia  of  CoUes  passes 


1278  SUEFACE  AND  SUKGICAL  ANATOMY. 

on  to  the  scrotum,  the  penis,  and  spermatic  cord,  to  become  continuous  with  the 
fascia  of  Scarpa  upon  the  front  of  the  abdomen. 

When  the  urethra  is  ruptured  below  the  anterior  layer  of  the  triangular  liga- 
ment, the  course  of  infiltration  of  extra vasated  urine  is  determined  by  these  attach- 
ments ;  at  first,  therefore,  the  urine  is  confined  within  this  compartment,  but 
gradually  travels  forwards  under  the  fascia  of  CoUes  on  to  the  lower  part  of  the 
anterior  abdominal  wall ;  it  is  prevented  from  passing  down  the  front  of  the  thigh 
by  the  attachment  of  Scarpa's  fascia  to  the  fascia  lata,  a  little  below  Poupart's 
ligament. 

The  deep  compartment  of  the  urinogenital  division  of  the  perineum  corresponds  to 
the  interval  between  the  triangular  ligament  proper  and  the  parietal  layer  of  the 
pelvic  fascia  (the  so-called  superior  or  deep  layer  of  the  triangular  ligament). 
The  most  important  structures  which  this  compartment  contains  are  the  membranous 
portion  of  the  urethra,  Cowper's  glands,  the  internal  pudic  vessels,  and  the  artery 
to  the  bulb. 

The  membranous  part  of  the  urethra  lies  one  inch  behind  the  lower  border  of  the 
pubic  symphysis.  When  this  division  of  the  urethra  is  ruptured,  the  extravasated 
urine,  after  filKng  the  deep  compartment,  may  reach  the  superficial  compartment 
by  bursting  through  the  triangular  ligament  where  the  vessels  pierce  it ;  or  it  may 
penetrate  the  parietal  layer  of  the  pelvic  fascia,  infiltrate  the  perivesical  connective 
tissue  and  the  space  of  Eetzius,  and  ultimately  ascend  in  the  anterior  abdominal 
wall  between  the  fascia  transversalis  and  the  parietal  peritoneum. 

Cowper's  glands,  which  lie  immediately  behind  the  membranous  urethra,  are 
overlapped  by  the  bulb  of  the  urethra,  from  which  they  are  separated  by  the  tri- 
angular ligament.  The  internal  pudic  artery  lies  just  within  the  margin  of  the 
pubic  arch.  The  artery  to  the  bulb  runs  transversely  inwards  \  in.  above  the  base 
of  the  triangular  ligament,  i.e.  above  the  level  of  a  line  drawn  from  the  front  of  the 
tuberosities  to  the  central  point  of  the  perineum. 

The  male  urethra  measures  about  eight  inches  from  the  external  to  the  internal 
meatus ;  the  narrowest  portion  is  at  the  external  meatus ;  a  second  narrowing 
occurs  at  the  triangular  ligament.  It  is  behind  these  constrictions  that  a  calculus 
is  liable  to  become  impacted.  The  most  dependent  part  of  the  urethra  is  the 
bulbous  portion,  and  it  is  in  this  situation  that  an  organic  stricture  is  most 
frequently  met  with.  The  membranous  portion  of  the  urethra,  situated  between 
the  two  layers  of  the  triangular  ligament,  is  surrounded  by  the  compressor  urethrse 
muscle,  which,  when  thrown  into  spasm,  may  firmly  grip  an  instrument  as  it  is 
passed  into  the  bladder.  Rupture  of  the  urethra  from  a  fall  on  the  perineum 
generally  involves  the  bulbous  portion.  A  false  'passage  made  during  the  passage 
of  an  instrument  generally  traverses  the  floor  of  the  urethra  at  the  triangular  liga- 
ment; to  prevent  this  the  point  of  the  instrument  should  always  be  directed 
upwards,  and  the  handle  at  the  same  time  depressed  as  soon  as  the  instrument  is  felt 
to  encounter  the  resistance  of  the  triangular  ligament.  When  tYiQ  prostate  is  hyper- 
trophied  the  prostatic  portion  of  the  urethra  is  elongated,  and  the  internal  meatus 
may  look  directly  forwards,  while  if  the  lateral  lobes  are  unequally  enlarged  it 
may  deviate  laterally.  Patients  with  prostatic  hypertrophy  are  seldom  able  to 
completely  empty  the  bladder,  on  account  of  the  dependent  well  which  exists 
behind  the  prostate. 

THE  PKOSTATE. 

The  operation  of  prostatectomy  has  in  recent  years  proved  so  successful  in 
removing  the  urinary  complications  associated  with  enlargement  of  the  prostate 
that  a  fresh  impetus  has  been  given  to  the  study  of  the  anatomy  of  the  gland  from 
the  surgical  point  of  view.  With  the  body  erect  the  hase  of  the  prostate  lies  in  a 
horizontal  plane  at  the  level  of  the  middle  of  the  symphysis  pubis,  while  its  apex 
Lies  ^  in.  liehind  and  below  the  sub-pubic  angle.  It  follows,  therefore,  that  the 
vesical  orifice  and  the  base  of  the  prostate  are  within  easy  reach  of  the  finger  intro- 
duced through  a  supra-pubic  cystotomy  incision.  The  anterior  surface  of  the 
prostate  lies  about  |  in.  behind  the  pubes,  to  which  it  is  connected  by  the  pubo- 
prostatic ligaments.     Above  these  ligaments  is  the  syace  of  Eetzius,  occupied  by 


THE  PEOSTATE.  1279 

fatty  tissue  whicli  passes  upwards  iu  front  of  the  anterior  wall  of  the  bladder  to 
be  continuous  with  the  extra-peritoneal  fat.  The  posterior  surface  of  the  prostate 
is  related  to  that  part  of  the  rectal  ampulla  immediately  above  the  anal  canal,  and 
is  therefore  accessible  to  palpation  per  rectum.  Between  the  rectal  and  the  pelvic 
fascia  covering  this  surface  of  the  prostate  is  a  loose  cellular  interval,  which  is 
taken  advantage  of  in  separating  the  two  organs  in  the  operation  of  excision  of  the 
rectum,  and  in  exposing  the  posterior  surface  ol'  tlie  prostate  in  the  operation  of 
perineal  prostatectomy.  The  lateral  surfaces  of  the  prostate  cannot  be  felt  through 
the  rectum ;  they  are  related  to  the  anterior  or  ■i)u})o-rectal  fibres  of  the  leva  tores 
ani,  from  wiiich  they  are  separated  by  the  lateral  portion  of  the  fascial  envelope  of 
the  gland.  The  prostate  substance  is  made  up  of  branching  tubular  glands 
supported  by  a  fibro-muscular  stroma.  The  gland  tissue  is  most  abundant  in  the 
posterior  and  lateral  aspects  of  the  organ ;  anteriorly  the  stroma  is  more  abundant 
and  extends  backwards  from  the  capsule  to  the  urethra  to  Ibrm  a  sort  of  anterior 
commissure.  By  the  term  "  capsule  "  of  the  prostate  is  understood  the  immediate 
or  proper  envelope  of  the  gland ;  this  envelope  consists  of  parallel  layers  of  fibro- 
nmscular  tissue,  continuous  with,  and  forming  part  of,  the  stroma  of  the  organ.  In 
some  instances  it  is  so  thin  that  the  gland  tissue  reaches  almost  to  its  surface, 
while  in  other  instances  it  is  so  thick  as  to  deserve  to  l)e  regarded  as  forming  the 
cortical  portion  of  the  gland.  Bj  the  term  "  sheath  "  of  the  prostate  is  meant  the 
fibrous  envelope  derived  from  the  pelvic  fascia.  The  veins  of  the  2^'^ostatiG  pil^^us 
lie,  not  between  the  capsule  and  the  sheath,  but  between  the  lamellte  of  the  sheath 
itself.  The  plexus  is  arranged  in  the  form  of  the  letter  Y,  the  stem  occupying  the 
anterior  segment  of  the  sheath,  while  its  limbs  embrace  the  lateral  aspects  of  the 
base  of  the  gland. 

In  what  is  known  as  "  senile  "  hyperiropliy  of  the  prostate  the  organ  may  be  uniformly 
enlarged  or  the  enlargement  may  chiefly  affect  one  or  other  of  the  lateral  lobes,  one  or 
both  of  which  may  enlarge  more  particularly  in  an  upward  direction  so  as  to  project  into 
the  bladder.  This  intra- vesical  overgrowth  may  take  the  form  either  of  a  more  or  less 
pedunculated  projection  situated  immediately  behind  the  vesical  orifice,  or  it  may  surround 
the  latter  to  form  a  prominent  ring-like  elevation.  As  the  intra-vcsical  growth  enlarges 
it  makes  its  way  towards  tlie  bladder  within  the  ring  of  the  sphincter  vesicte,  and,  having 
pushed  ])efore,  or  separated,  tlie  internal  longitudinal  fibres  of  the  bladder,  it  comes 
ultimately  to  be  separated  from  the  cavity  of  the  bladder  by  mucous  membrane  only.  In 
the  operation  of  svpra-ptibic  prostatectomy  the  true  capsule  of  the  prostate  is  at  once 
reached  by  simply  tearing  through  the  mucous  membrane  immediately  beliind  the  vesical 
orifice.  By  keeping  close  to  the  capsule,  the  entire  organ,  including  the  capsule,  may  be 
enuclciited  from  its  sheath.  As  the  latter  is  markedly  thicker  and  denser  in  the  hyper- 
trophied  than  in  the  normal  prostate,  this  enucleation  can  be  accomplished  withoiit  injur- 
ing the  veins  of  the  prostatic  plexus.  As  a  rule,  the  only  part  where  any  difficulty  in  the 
enucleation  is  encountered  is  anteriorly,  where  the  capside  is  more  intimately  connected 
with  the  sheath  by  the  interposition  of  a  layer  of  striated  longitudinal  nmscular  fibres 
which  pass  from  the  urethra  to  be  continuous  with  the  oiiter  longitudinal  fibres  of  the 
bladder,  fn  "  total "  prostatectomy,  practically  the  whole  of  the  prostatic  lu'ethra  is 
removed  along  with  the  gland.  In  some  instances,  instead  of  removing  the  entire  prostate 
and  its  capsule  along  with  the  pi'ostatic  urethra,  the  surgeon,  by  working  within  the 
capsule,  is  able  to  enucleate  each  lateral  glandular  mass  either  separately  or  imited  to  its 
fellow  in  the  form  of  a  horse-shoe  shaped  mass,  the  urethra  and  the  anterior  commissure 
being  left  more  or  less  intact.  The  cavity,  which  is  left  behind  after  the  I'emoval  of  the 
prostate,  at  once  contracts  owing  to  the  approximation  of  the  bladder  and  rectum  antero- 
posteriorly,  and  of  the  levatoi-es  ani  laterally. 

In  perineal  pi'ostatectomy  the  posterior  surface  of  the  prostate  is  exposed  by  making  a 
liorse-shoe  shaped  incision  with  the  convexity  reaching  forwards  to  immediately  behind 
the  bulb ;  laterally  the  incision  sinks  into  the  ischio-rectal  fossa),  its  extremities  ending  at 
the  anterior  part  of  the  ischial  tuberosities  (Fig.  918).  After  reflecting  the  skin  and 
subcutaneous  tissue,  the  incision  is  carried  through  the  central  point  of  the  perineum  and 
outwards  on  either  side  of  it  through  the  base  of  the  lower  layer  of  tiie  triangular 
ligament.  The  bulb,  the  superficial  transverse  perineal  muscles,  and  the  triangular 
ligament  (lower  layer)  are  now  retracted  forwards,  and  the  fibres  of  the  recto-urethral 
muscle  (which  connect  the  anterior  wall  of  the  rectal  ampulla  with  the  constrictor 
urethrse)  are  divided  ;  this  allows  the  anal  canal  and  the  lower  end  of  the  rectum  to  be 


1280 


SUEFACE  AND  SUEGICAL  ANATOMY. 


retracted  backwurd.s.  Tlie  dissectii)n  is  now  carried  between  the  anterior  borders  of  the 
levatores  aui  in  a  forward  direction  towards  the  prostate,  so  as  to  strike  the  loose  non- 
vascular space  which  intervenes  between  the  posterior  part  of  the  prostatic  sheath  and  the 
thin  fascia  outside  the  muscular  wall  of  the  rectum.  The  posterior  surface  of  the 
prostate,  covered  by  its  true  capsule,  is  reached  by  incising  the  sheath.  The  prostate, 
along  with  its  true  capsule  and  the  urethra,  may  either  be  eniicleated  from  the  sheath 
entire,  or  the  true  capsule  may  be  incised  as  well  as  the  sheath,  and  the  adenomatous 
masses  removed  separately.  The  operation  is  facilitated  by  pulling  the  prostate  down 
into  the  wound  by  a  special  retractor  inserted  into  the  bladder  through  a  median  incision 
into  the  floor  of  the  membranous  urethra. 

The  epididymis,  which  can  he  felt  behind  the  testicle  as  an  elongated  curved 
body  applied  vertically  to  its  posterior  surface,  is  especially  involved  in  gonorrhoeal 
and  tubercular  infections  of  the  testicle.  Occupying  the  posterior  part  of  the 
spermatic  cord  is  the  vas  deferens,  which,  when  grasped  between  the  finger  and 
thumb,  feels  like  a  piece  of  whip-cord.  The  spermatic  veins  form  a  plexus  in  the 
substance  of  the  cord,  known  as  the  pampiniform  plexus ;  a  varicose  condition  of 
these  veins  gives  rise  to  the  condition  known  as  varicocele.  In  operating  for 
varicocele  the  veins  are  reached  by  dividing  in  succession  all  the  coverings  of  the 
cord ;  the  deepest  covering,  viz.  the  infundibuliform  fascia,  derived  from  the  fascia 
transversalis,  forms  a  well-marked  fibrous  envelope  which  immediately  surrounds 
the  veins  and  other  constituents  of  the  cord.  Besides  the  spermatic  artery,  the 
testicle  receives  its  blood  supply  from  the  artery  accompanying  the  vas  deferens 
and  from  the  cremasteric  branch  of  the  deep  epigastric. 

The  marked  swelling  which  attends  ceclema  and  hcematoma  of  the  scrotum  is  due 
to  the  loose  and  delicate  character  of  the  cellular  tissue  which  occupies  the  space 
between  the  dartos  muscle  and  the  subjacent  membrane  derived  from  the  inter- 
columnar  fascia. 

The  anus  is  situated  in  the  rectal  division  of  the  perineum  about  1 1  in.  in  front 
of  and  Ijelow  the  tip  of  the  coccyx.     The  skin  around  the  orifice  is  pigmented  and 

thrown  into  radiating 
folds.  The  painful  linear 
crack  or  ulcer,  known  as 
fissure  of  the  anus,  gener- 
ally occupies  one  of  the 
furrows  at  the  posterior 
margin  of  the  anus.  The 
skin  of  the  anus  is  pro- 
vided with  large  sebace- 
ous and  sweat  glands, 
which  are  occasionally 
the  site  of  small  and  very 
painful  anal  abscesses. 

On  making  a  rectal 
examination  it  will  be 
observed  that  the  finger, 
before  it  reaches  the 
cavity  of  the  rectum, 
traverses  the  narrow  or 
sphincteric  portion  of  the 
rectum,  appropriately 
named  by  Symington  the 
anal  canal.  This  canal,  which  is  directed  from  below  upwards  and  forwards,  extends 
from  the  anal  orifice  to  the  ampulla  of  the  rectum,  is  about  1  in.  in  length ;  its 
upper  end  is  on  a  level  witli  the  inner  borders  of  the  pubo-rectal  portions  of  the 
levatores  ani. 

External  hcemorrhoids  are  developed  from  the  anal  folds  situated  outside  the 
white  line  corresponding  to  the  muco-cutaneous  junction ;  internal  piles  are 
developed  from  the  veins  of  the  mucosa  at  the  upper  part  of  the  anal  canal. 

In  the  upper  half  of  the  anal  canal  are  the  columns  of  Morgagni.     According  to 


Longitudinal 
fibres  of 
rectum 


Anal  canal 


Fifi.  919. — Thk    Intekior  ok   the   Anal  Caxal   and  Lower  Part 
OF  Rectum. 

Showing  the  coluuins  of  Morgagni  and  the  anal  valves  between  their 
lower  ends.  The  columns  were  more  numerous  in  this  specimen 
than  usual  (from  Birmingham). 


THE  PEdSTATE.  1281 

Ball,  fissure  of  the  anus  is  generally  caused  by  the  tearing  downwards  of  one  of  the 
posterior  anal  valves  (Fig.  705)  during  the  passage  of  a  scybalous  mass. 

According  to  Birmingham,  the  pubo-coccygeal  fibres  of  the  levator  ani  close  the 
upper  part  of  the  anal  canal,  whilst  tlie  external  sphincter  closes  the  remaining 
part.  The  internal  sphincter,  according  to  the  same  author,  acts  probably  as  a 
detrusor,  its  use  being  to  empty  the  anal  canal  completely  after  the  passage  of 
each  fpecal  mass. 

The  apex  of  the  iscMo-rectal  fossa  (Fig.  918),  formed  by  the  attachment  of  the  anal 
fascia  to  the  obturator  portion  of  the  parietal  pelvic  fascia,  is  directed  upwards 
towards  the  pelvis,  and  lies  2h  in.  from  the  surface.  The  inner  wall  of  the  fossa  is 
bounded  by  the  levator  ani  and  coccygeal  muscles  covered  Ijy  the  anal  fascia  (Fig. 
920) ;  the  outer  wall  by  the  obturator  internus  muscle  covered  by  the  obturator 
fascia.  An  abscess  in  the  ischio-rectal  fossa  should  be  opened  early,  otherwise  it  is 
liable  to  burst  through  the  inner  wall  into  the  rectum  ;  should  it  open  also  upon  the 
skin  surface  a  complete  "fistula  in  ano  "  is  formed.  When  a  "  fistula  in  ano  "  results 
from  the  bursting  of  a  submucous  aliscess  of  the  anal  canal  the  track  of  the  fistula 
runs  either  internal  to  or  through  tlie  fibres  of  the  internal  and  external  sphincter 
muscles,  and  the  external  or  skin  opening  is,  as  a  rule,  close  to  the  anus,  while  the 
internal  opening  is  generally  within  the  upper  end  of  the  anal  canal.  Occasionally 
the  ischio-rectal  abscess  perforates  the  levator  ani  towards  the  apex  of  the  fossa  ; 
it  then  burrows  into  the  peri-rectal  cellular  tissue  of  the  pelvis,  and  opens  into  the 
ampulla  of  the  rectum.  In  other  cases,  again,  the  abscess  starts  in  the  peri-rectal 
tissue  internal  to  the  levator  ani,  and  either  bursts  into  the  rectal  ampulla  or 
through  the  levator  ani  into  the  ischio-rectal  fossa,  and  so  reaches  the  surface.  Or 
the  pus  may  burrow  between  the  rectum  and  coccyx,  whence  it  may  pass  outwards 
through  the  great  sacro-sciatic  foramen  behind  the  parietal  pelvic  fascia  into  the 
buttock  ;  or,  by  piercing  the  visceral  layer  of  the  pelvic  fascia,  may  reach  the  extra- 
peritoneal fatty  tissue  of  the  pelvis  and  ascend  in  it  to  form  an  iliac  abscess. 

The  li/mpJcatics  from  the  skin  of  the  anus  pass  along  the  perineo-crural  folds  to 
the  innermost  glands  of  the  groin,  both  inguinal  and  crural.  According  to  Poirier 
and  Cuneo,  those  from  the  region  of  the  white  line  end  in  the  hypogastric  glands 
which  lie  in  front  of  the  internal  iliac  artery,  while  those  which  issue  from  the 
mucous  membrane  of  the  upper  part  of  the  anal  canal  and  the  rectum  proper 
traverse  a  few  minute  glands  (ano-rectal  glands  of  Gerota)  placed  between  the 
muscular  and  fibrous  coats  of  the  rectum,  alongside  the  main  branches  of  the  superior 
hajmorrhoidal  artery.  After  traversing  these  glands  they  join  the  glands  which  lie 
in  relation  to  the  trunk  of  the  superior  haemorrhoidal  artery  as  it  lies  between  the 
two  layers  of  the  pelvic  mesocolon. 

In  making  a  rectal  examination  the  finger  should  be  carried  forwards  from  the  tip  of 
the  coccyx  so  as  to  enter  the  anus  from  behind.  The  finger  is  then  gently  pressed  upwards 
and  slightly  forwards  through  the  sphincteric  region  in  the  axis  of  the  anal  canal  until  it 
reaches  the  cavity  of  the  rectum,  the  lower  part  of  which  is  dilated  to  form  the  ampulla. 
The  folds  or  valves  of  Houston,  three  in  number,  project  into  the  cavity  of  the  bowel  in 
the  form  of  prominent  crescentic  shelves,  which  are  produced  by  the  three  permanent  or 
true  flexures  into  which  the  rectum  is  thrown  (Birmingham) ;  the  lower  valve,  which  may 
be  sufficiently  prominent  to  impede  the  passage  of  the  finger,  must  not  be  mistaken  for  a 
pathological  condition.  Through  the  anterior  wall  the  finger  can  palpate  from  below  up- 
wards the  bulb  of  the  urethra,  the  membranous  parts  of  the  urethra,  Cowper's  glands  (when 
inflamed  and  enlai'ged),  the  apex  and  lateral  lobes  of  the  prostate,  the  vesicular  seminales 
(when  diseased),  and  the  external  trigone  of  the  bladder.  With  the  left  forefinger  in  the 
rectum,  an  instrument  passed  into  the  bladder  can  be  distinctly  felt  as  it  traverses  the  mem- 
branous urethra ;  as  it  lies  in  the  prostatic  vu-ethra  it  is  separated  from  the  finger  by  the 
pi'ostate.  Hence,  when  &.  false  passage  is  made  through  the  bulbous  or  membranous  portion  of 
the  urethra,  the  instrument,  if  pushed  onwards  towards  the  bladder,  will  be  felt  immediately 
outside  the  rectum  between  it  and  the  prostate.  In  the  child,  o\fing  to  the  rudimentary 
condition  of  the  prostate,  the  instrument  is  distinctly  felt  close  to  the  rectum,  as  it  lies  in 
the  prostatic  as  well  as  in  the  membranous  portion  of  the  urethra.  When  the  prostate  is 
not  enlarged  the  tip  of  the  finger  can  just  reach  the  external  trigone,  which  is  most 
distinctly  felt  when  the  bladder  is  full.  The  vesiculse  seminales,  indistinctly  felt  when 
healthv,  may  be  readily  palpated  when  enlarged  and  indurated  from  disease.  Through 
"  86 


1282 


SUEFACE  AND  SUKaiCAL  ANATOMY. 


the  lateral  wall  of  the  rectum  may  be  palpated  the  ischio-rectal  fossa,  the  bony  wall  of  the 
true  pelvis,  and,  when  enlarged,  the  internal  iliac  lymphatic  glands ;  through  the  posterior 
wall  the  hollow  of  the  sacrum  and  coccyx,  and  the  lymphatic  glands  lying  in  the  retro- 
rectal cellular  tissue. 

In  the  child  rectal  examination  enables  one  to  palpate,  in  addition  to  the  structures  in 
the  cavity  of  the  true  pelvis,  those  which  occupy  the  lower  segment  of  the  abdomen. 
When  the  bladder  is  empty  even  a  small  calculus  can  be  readily  felt  by  recto-abdominal 
palpation. 

The  distance  of  the  apex  of  the  recto-vesical  pouch  of  peritoneum  from  the  anus 
varies  considerably,  according  to  the  degree  of  distension  of  the  bladder  and  rectum  ; 


Posterior  superior  spine 


Upper  lateral  inflexion 


Peritoneum  (pararectal 
fossa)' 


Superior  haimorrlioidal_^ 
artery 


Rectum 

Great  sciatic  ligament 
Ischio-rectal  fossa 

Anal  canal 


Third  sacral  vertebra 


Fourth  sacral  vertebra 
(cut) 

Lower  border  of 
pyi'iformis  (cut) 

Superior  hfemoirhoidal 
artery 


Lateral  inflexion 
Coccygeus 

Levator  ani 
External  sphincter 


Fig.  920. — The  Rectum  from  behind. 

The  sacrum  has  been  sawn  across  through  the  4th  sacral  vertebra,  and  its  lower  part  removed  with  the  coccyx. 
The  posterior  portions  of  the  coccygei,  levatores  ani,  and  of  the  external  sphincter  have  been  cut  away. 
Tlie  "pinching  in  "  of  the  lower  end  of  the  rectum  by  the  inner  edges  of  the  levatores  ani,  i-esulting  in 
the  formation  of  the  flattened  anal  canal,  is  suggested  in  the  illustration,  which  has  been  made  from  a 
formalin-hardened  male  body,  aged  thirty.  The  lateral  inflections  of  the  rectum,  corresponding  to 
Houston's' valves,  are  also  shown  (from  Birmingham). 

when  both  are  empty  it  reaches  to  about  2  in.  from  the  anus ;  -when  both  are  dis- 
tended it  is  at  least  one  inch  higher  (Fig.  920).  As  pointed  out  by  Birmingham,  the 
peritoneum  is  closely  adherent  to  the  rectum  above  and  in  front,  -while  at  the  side 
and  below  the  connexion  is  much  looser,  so  that  by  stripping  the  peritoneum 
upwards  the  greater  part,  or  even  the  whole,  of  the  rectum  may  be  excised  without 
opening  into  the  peritoneal  cavity. 


FEMALE   PELVIS. 

The  external  genitals  are  fully  described  at  page  1195.  The  external  orifice  of 
the  urethra,  surrounded  by  a  slight  annular  prominence  of  the  mucous  membrane, 
is  situated  about  1  in.  behind  the  clitoris,  immediately  above  the  centre  of  the  base 


FEMALE  PELVIS.  1283 

of  the  vestibule — a  smooth  triangular  area  at  the  anterior  part  of  the  vulva,  with  its 
sides  formed  by  the  labia  minora  and  its  base  by  the  anterior  margin  of  the  ostium 
vaginae.  In  passing  the  catheter  the  instrument  is  directed  along  the  forefinger 
(introduced  just  within  the  ostium  vaginae  with  the  palmar  surface  towards  the 
symphysis  pubis)  to  the  base  of  the  smooth  vestibule,  where  it  is  tilted  sliglitly 
upwards  so  as  to  bring  its  point  opposite  the  meatus. 

Bartholin's  glands,  about  the  size  of  a  bean,  are  placed  one  on  either  side  of 
the  posterior  third  of  the  orifice  of  the  vagina,  above  the  triangular  ligament. 
Their  ducts,  nearly  one  inch  in  length,  open  posteriorly  between  the  hymen  and 
the  posterior  commissure  (fossa  navicularis).  Abscesses  and  cysts  not  infrequently 
develop  in  connexion  with  these  glands.  The  bulbs  of  the  vagina  are  two  pyriform 
collections  of  erectile  tissue  situated  one  upon  each  side  of  the  vestibule,  between 
the  sphincter  vaginte  and  the  anterior  layer  of  the  triangular  ligament.  Rupture 
of  these  bodies  gives  rise  to  the  condition  known  as  'pudendal  hcematocele. 

Ill  making  a  vaginal  examination  the  patient  should  be  placed  in  the  dorsal  position, 
with  the  thighs  well  flexed  ;  the  index-finger  of  the  right  hand  is  now  carried  along  the 
fold  of  the  buttock  towards  the  middle  line,  where  it  will  impinge  against  the  posterior 
aspect  of  the  introitus  vaginae,  whence  it  is  inserted  upwards  and  backwards  into  the 
canal  ;  to  render  the  examination  more  thorough  the  middle  finger  may  also  be  intro- 
duced. When  the  uterus  is  in  its  normal  position  the  vaginal  portion  of  the  cervix  uteri 
is  felt  as  a  knob-like  body  projecting  dowuAvards  and  backwards  into  the  upper  part  of 
tiie  canal.  In  nulliparae  the  os  uteri  is  a  small  transverse  slit,  whereas  in  women  who 
have  borne  children  it  is  larger  and  more  or  less  fissured.  Above  and  behind  the  cervix 
is  the  posterior  fornix,  which  is  in  close  proximity  to  the  pouch  of  Douglas ;  this  pouch, 
though  normally  emj^ty,  is  the  frequent  site  of  displaced  abdominal  and  pelvic  organs, 
and  collections  of  intraperitoneal  effusions  and  exudations.  A  loaded  rectum  can  be 
detected  through  the  vagina  by  the  characteristic  way  in  which  the  contents  caii  be  pitted 
by  the  finger.  In  front  of  the  cervix  is  the  shallow  anterior  fornix,  through  which  may 
be  felt  the  body  of  the  uterus  and  the  base  of  the  bladder,  while  through  the  lower  half 
of  the  anterior  vaginal  wall  the  urethra  may  be  detected  as  a  cylindrical,  cord-like 
thickening  which  may  be  rolled  against  the  lower  border  of  the  symphysis.  The  ureter, 
especially  if  enlarged,  can  be  recognised  through  the  antero-lateral  fornix,  by  compressing 
it  against  the  pubic  bone. 

By  the  bimanual  examination  the  pelvic  organs  are  steadied  and  pushed  downwai'ds 
towards  the  pelvic  outlet  by  the  pressure  of  the  left  hand  applied  in  the  hypogastric 
region,  so  that  they  can  be  more  readily  reached  and  palpated  by  the  finger  placed  in  the 
vagina  with  its  palmar  aspect  directed  upwards.  The  ovary  may  be  felt  as  a  firm  body 
about  the  size  of  the  end  of  the  thumb  by  pushing  the  fingers  well  up  into  the  lateral 
fornix  towards  the  lateral  wall  of  the  pelvis.  In  health  the  ovaries  are  freely  movable. 
The  healthy  Fallopian  tubes  cannot,  as  a  rule,  be  felt  per  vaginam. 

The  whole  of  the  interior  of  the  bladder  in  the  female  can  be  readily  seen  by  reflecting 
light  into  it  through  a  speculum  introduced  into  the  empty  bladder  after  dilating  the 
urethra.  The  patient  is  placed  in  the  genu-pectoral  position,  so  that  the  bladder  may 
become  inflated  with  air,  the  coils  of  intestine  being  displaced  upwards.  In  the  distended 
condition  of  the  bladder  the  mucosa  has  a  dull  white  appearance,  except  in  the  region  of 
the  trigone,  which  shows  a  pale  pink  injection ;  when  the  bladder  is  contracted  the 
mucosa  appears  injected  throughout.  The  ureteral  orifices,  placed  about  one  inch  apart 
and  connected  by  a  slight  transverse  ridge  (inter-ureteric  fold),  present  the  appearance 
of  fine  transverse  slits  situated  upon  small  and  somewhat  injected  elevations  of  the 
mucosa.  Every  minute  or  so  a  jet  of  urine  Avill  be  seen  to  issue  from  the  orifice.  Having 
in  this  way  located  the  ureteral  opening,  a  catheter  or  bougie  may  be  passed  into  it 
along  the  speculum. 

By  rectal  examination  the  finger  can  palpate,  from  below  upwards,  the  recto-vaginal 
septum,  the  cervix  uteri,  the  posterior  fornix  of  the  vagina,  the  apex  of  the  pouch  of 
Douglas,  and  the  body  of  the  uterus.  By  washing  out  the  rectum  and  introducing  a 
specukim  -into  the  bowel,  with  the  patient  in  the  genu-pectoral  position,  the  rectum 
becomes  inflated  with  air ;  the  finger  can  now  feel  very  distinctly  the  posterior  surface 
of  the  uterus  and  the  Fallopian  tubes,  and  by  running  the  finger  outwards  along  the  pro- 
minent fold  formed  by  the  utero-ovarian  ligament  the  ovary  is  also  very  distinctly  felt. 

On  opening  the  abdomen  by  a  mesial  incision  extending  from  the  umbilicus  to 
the  pubes,  and  looking  into  the  pelvis  from  above  after  displacing  some  coils  of 


1284  SUKFACE  AND  SUEGICAL  ANATOMY. 

the  small  intestine  upwards,  the  fundus  of  the  uterus,  directed  forwards  and  a 
little  upwards,  is  seen  resting  upon  the  postero-superior  surface  of  the  bladder. 
Behind  the  uterus  is  the  rectum,  and  between  the  two  the  pouch  of  Douglas, 
containing  the  pelvic  colon  and  the  lower  part  of  the  ileum.  The  ovary  lies  a 
little  below  the  level  of  the  brim  of  the  pelvis  upon  a  triangular  shelf,  bounded  in 
front  by  the  broad  ligament,  behind  and  internally  by  the  utero-sacral  ligament, 
and  behind  and  externally  by  the  pelvic  wall.  When  the  vermiform  appendix 
overhangs  the  brim  of  tlie  pelvis  its  tip  may  come  into  close  relation  with  the  right 
ovary,  a  condition  which  often  leads  to  a  difficulty  in  distinguishing  an  inflam- 
mation of  that  ovary  from  appendicitis.  The  round  ligaments  are  seen  passing 
forwards  and  outwards  from  the  anterior  aspect  of  the  cornua  of  the  uterus  to 
the  internal  abdominal  rings,  which  lie  immediately  in  front  and  to  the  inner  side 
of  the  terminations  of  the  external  ihac  arteries.  Below  and  at  the  inner  side  of 
the  round  ligament,  as  it  leaves  the  pelvis,  is  the  deep  epigastric  artery.  By  pulling 
the  uterus  upwards  the  attachments  of  the  broad  ligament  to  the  floor  and  lateral 
walls  of  the  pelvis  are  brought  into  evidence,  as  also  are  the  utero-vesical  and 
recto-vaginal  peritoneal  pouches;  the  former  is  shallow,  while  the  deepest  part  of 
the  latter  covers  the  upper  fourth  of  the  posterior  wall  of  the  vagina,  and  comes 
into  relation,  therefore,  with  the  posterior  fornix. 

The  ureter  crosses  the  brim  of  the  pelvis  in  front  of  the  bifurcation  of  the 
common  iliac  artery  1|  in.  external  to  and  a  little  below  the  centre  of  the  sacral 
promontory.  The  corresponding  point  on  the  anterior  abdominal  wall  is  at  the 
junction  of  the  outer  and  middle  thirds  of  a  line  joining  the  anterior  superior 
spines  of  the  ilium.  After  crossing  the  termination  of  the  common  iliac  artery 
from  without  inwards  the  ureter  curves  downwards  and  forwards  behind  the  perito- 
neum of  the  postero-lateral  wall  of  the  true  pelvis  ;  in  front  of  it  are  the  Fallopian 
tube  and  ovary.  Before  reaching  the  bladder  it  enters  the  parametric  connective 
tissue,  in  which  it  curves  downwards,  forwards,  and  inwards  about  three-quarters  of 
an  inch  external  to  the  lateral  aspect  of  the  cervix  uteri. 

The  uterine  artery  in  the  first  part  of  its  course  runs  downwards  and  forwards 
a  little  external  to  the  ureter ;  at  the  level  of  the  internal  os  it  curves  inwards  in 
front  of  the  ureter  and  then  divides  into  uterine  and  vaginal  branches. . 

In  the  operation  of  hysterectomy  care  must  be  taken  not  to  injure  the  ureter ;  it 
is  important,  therefore,  to  keep  in  mind  its  relation  more  especially  to  the  uterine 
artery  and  to  the  cervix  uteri. 

The  ovarian  artery  enters  the  pelvis  between  the  layers  of  that  portion  of  the 
broad  hgament  known  as  the  infundibulo-pelvic  ligament ;  it  is  here  that  the  vessel 
may  be  most  readily  ligatured  in  abdominal  hysterectomy,  and  in  ovariotomy. 

THE   BACK. 

In  the  middle  line  of  the  back  is  the  spinal  furrow,  which  is  deepest  in  the 
lower  dorsal  and  upper  lumbar  regions,  where  the  erectores  spin*  muscles  are  most 
prominent.  Over  the  upper  sacral  region,  where  the  erectores  spinse  muscles  are 
tendinous,  is  a  flattened  area  forming  an  equilateral  triangle,  the  angles  of  which 
correspond  respectively  to  the  posterior  superior  spines  of  the  two  iliac  bones  and  the 
third  sacral  spine.  The  vertebral  spines  can  be  palpated  at  the  bottom  of  the  spinal 
furrow ;  they  become  more  distinct  when  the  spine  is  flexed,  and,  as  pointed  out 
by  Holden,  they  become  mapped  out  by  reddened  areas  when  friction  is  applied 
along  the  furrow.  The  identification  and  counting  of  the  spines  will  be  facilitated 
if  it  be  remembered  that  the  first  dorsal  is  more  prominent  than  the  vertebra 
prominens  (seventh  cervical),  that  the  third  dorsal  is  on  a  level  with  the  root  of 
the  spine  of  the  scapula,  the  seventh  dorsal  with  its  inferior  angle,  the  fourth 
lumbar  with  the  highest  part  of  the  iliac  crest,  and  the  second  sacral  with  the 
posterior  superior  iliac  spine. 

Above  the  spine  of  the  scapula  is  the  suprascapular  region,  which  is  padded  by  a 
thick  mass  of  muscle  consisting  of  the  supra-spinatus  and  levator  anguli  scapulae, 
covered  by  the  upper  part  of  the  trapezius ;  the  two  latter  muscles  may  be  thrown 
into  relief  by  shrugging  the  shoulders. 


THE  BACK.  1285 

In  the  interscapular  region  are  the  rhomboid  muscles  which  are  thrown  into 
prominence  by  bracing  back  the  shoulders. 

Below  the  inferior  angle  of  the  scapula  the  last  five  ribs  can  readily  be  felt 
external  to  the  erector  spinse  muscle ;  when  the  twelfth  rib  does  not  reach 
beyond  this  muscle,  the  eleventh  rib  will  be  mistaken  for  it,  unless  the  ribs  be 
counted  from  above  downwards. 

The  lower  border  of  the  trapezius  is  indicated  by  a  line  extending  upwards  and 
outwards  from  the  twelfth  dorsal  spine  to  the  root  of  the  syjine  of  the  scapula ;  the 
upper  border  of  the  latissimus  dorsi  by  a  line  extending  from  the  sixth  dorsal  spine 
transversely  outwards  across  the  angle  of  the  scapula.  Between  these  two  muscles 
and  the  lower  part  of  the  vertebral  border  of  the  scapula  is  a  triangular  area,  the 
floor  of  which  is  formed  by  the  rhomboideus  major  muscle  and  the  sixth  costal 
interspace. 

The  outer  border  of  the  erector  spinse  is  indicated  on  the  surface  by  drawing  a 
line  from  a  point  on  the  iliac  crest  3^  in.  (four  fingers'-breadth)  from  the  middle 
line,  upwarcls  and  slightly  outwards  to  the  angles  of  the  ribs.  The  outer  border 
of  the  quadratus  lumborum,  which  passes  upwards  and  slightly  inwards,  lies  a  little 
external  to  that  of  the  erector  spinse  at  the  crest,  and  a  little  internal  to  it  at  the 
twelfth  rib. 

The  anatomy  of  the  muscles  and  fasciae  which  complete  the  abdominal  wall 
between  the  last  rib  and  the  iliac  crest  is  of  great  importance  in  connexion  with 
operations  in  the  region  of  the  loin.  The  space  between  the  last  rib  and  the  iliac 
crest  varies  greatly  according  to  the  length  of  the  former,  and  according  to  the  general 
shape  of  the  chest  and  slope  of  the  ribs.  As  a  rule,  the  tip  of  the  twelfth  rib  lies 
about  two  inches  vertically  above  the  centre  of  the  iliac  crest.  From  a  surgical 
point  of  view  the  costo-iliac  space  may  be  said  to  be  hmited  internally  by  the  outer 
edge  of  the  erector  spinse,  and,  more  deeply,  by  the  tips  of  the  transverse  processes 
of  the  lumbar  vertebrse,  while  externally  it  is  bounded  by  the  posterior  free  border 
of  the  external  oblique,  and,  more  deeply,  by  the  line  of  reflection  of  the  peritoneum 
from  the  colon  on  to  the  lateral  wall  of  the  abdomen.  The  space  is  roofed  over  by 
the  latissimus  dorsi,  except  below,  where  a  narrow  triangular  interval  is  left  between 
its  outer  border  and  the  posterior  boi'der  of  the  external  oblique,  the  base  of  the 
triangle  being  formed  by  the  crest  of  the  ilium,  a  little  behind  its  centre.  This 
triangle  (Fig.  275,  p.  358),  known  as  the  "triangle  of  Petit,"  represents  a  weak  area 
through  which  a  lumbar  abscess  may  come  to  the  surface,  and  through  which  a 
lumbar  hernia  occasionally  develops.  On  removing  the  latissimus  dorsi  and  the 
lower  part  of  the  thin  serratus  posticus  inferior,  another  triangle  will  be  exposed, 
which  constitutes  a  second  weak  area  in  the  loin ;  it  is  bounded  above  by  the  last 
rib,  internally  by  the  outer  border  of  the  erector  spinse,  and  externally  by  the 
posterior  muscular  fibres  of  the  internal  oblique ;  the  floor  of  the  triangle  is  formed 
by  the  aponeurosis  of  origin  of  the  transversalis  abdominis  muscle.  At  the  outer 
border  of  the  quadratus  lumboruru  this  aponeurosis  splits  into  three  layers  to  form 
two  compartments,  the  anterior  enclosing  the  quadratus  lumborum  and  the  posterior 
the  erector  spina. 

Kidneys. — By  retracting  inwards  the  erector  spinse  and  dividing  the  posterior 
fibres  of  the  three  abdominal  muscles,  along  with  the  outer  fibres  of  the  quadratus, 
the  kidney  may  be  exposed,  with  the  colon  lying  vertically  in  front  of  its  outer  border 
(Fig.  921).  The  upper  limit  of  the  kidney  is  indicated  by  a  line  drawn  transversely 
across  the  loin  opposite  the  eleventh  dorsal  spine,  the  lower  limit  by  a  line  on  a  level 
with  the  third  lumbar  spine.  The  upper  extremity  reaches  to  the  eleventh  rib  ;  the 
lower,  which  lies  immediately  external  to  the  tip  of  the  transverse  process  of  the  third 
lumbar  vertebra,  reaches  to  within  Ih  to  2  in.  of  the  crest  of  the  ihum.  About 
a  third  of  the  kidney  lies  above  the  lower  margin  of  the  twelfth  rib.  The  left 
kidney  usually  lies  about  i  in.  higher  than  the  right.  The  most  external  point  of 
the  outer  border  lies  4  in.  from  the  middle  line,  while  the  hilum  lies  1|  in.  external 
to  it  in  front  of  the  interval  between  the  tips  of  the  transverse  processes  of  the 
first  and  second  lumbar  vertebrse. 

The  psoas  muscle  intervenes  between  the  postero-internal  surface  of  the  kidney 
and  the  transverse  processes,  and  protects  the  organ  from  injury  by  a  blow  directed 
86  a 


1286 


SUEFACE  AND  SUEGICAL  ANATOMY. 


from  the  front.  Between  the  upper  end  of  the  kidney  and  the  eleventh  and  twelfth 
ribs  is  the  diaphragm  and  the  posterior  costo-diaphragmatic  reflection  of  the  pleura 
(Fig.  921).  The  relations  of  the  pleura  to  the  last  rib  have  already  been  considered 
(p.  1238). 

Posteriorly  the  course  of  the  upper  part  of  the  ureter  may  be  indicated  by  a 
line  drawn  vertically  upwards  from  the  posterior  superior  ihac  spine  to  the  level  of 
the  second  lumbar  spine  ;  the  deep  guides  are  the  tips  of  the  transverse  processes 
of  the  second,  third,  and  fourth  lumbar  vertebrte,  covered  by  the  psoas  muscle. 

A  needle  passed  through  the  inner  extremity  of  the  eleventh  intercostal  space 
will  transfix  the  suprarenal  body. 

The  pus  of  a  perinephritic  abscess  occupies  the  extraperitoneal  fatty  layer  (peri- 


Rib  IX 


Rib  XI 
Descending  colon 


Rib  XI 


Ascending  colon 


Fig.  921.— Di-ssection  of  the  Splken,  Liver,  and   Kidneys  from  behind,  in  a  Subject  hardened  by 

FORJIAI.IN-INJECTION    (from  Cuiiniughaiii). 


renal  fat),  and  lies,  therefore,  within  the  fascial  envelope  of  the  abdomen  ;  the  pus  in 
a  psoas  abscess,  on  the  other  hand,  lies  external  to  the  fascia.  In  opening  a  psoas 
abscess  from  behind,  a  vertical  incision  is  made  in  the  angle  formed  by  the  outer 
border  of  the  erector  spinte  and  the  crest  of  the  ilium  ;  in  the  deeper  part  of  the 
dissection  the  surgeon  should  keep  close  to  tlie  front  of  the  transverse  process  of 
the  fourth  lumbar  vertebra. 

Diaphragm,  Liver,  Stomach,  and  Large  Intestine. — Posteriorly  the  right 
arch  of  the  diaphragm  and  the  right  lobe  of  the  liver  extend  upwards  to  the  level 
of  the  angle  of  the  scapula  (eighth  rib),  while  the  left  arch  and  the  fundus  of  the 
stomach  lie  one  inch  lower  (eighth  interspace) ;  the  central  tendon  reaches  up  to 
the  eighth  dorsal  spine.  The  right  lobe  of  the  liver  is  covered  posteriorly  by  the 
eighth  to  the  twelfth  rilis,  and  is  overlapped  by  tlie  base  of  the  right  lung  as  far  as 
a  line  drawn  horizontally  outwards  from  the  tenth  dorsal  spine ;  hence,  posteriorly, 


THE  BACK. 


1287 


the  upper  limit  of  the  liver  cannot  be  defined  by  percussion,  and  its  lower  limit 
merges  into  the  dulness  of  the  loin  muscles  and  kidney. 


Fig.  922. — Posterior  Aspect  of  Truxk.  showixg  Surface  Topography  of  Viscera. 

T.  ^  Trachea. 

A.  Aorta. 

L.  L.  Left  lung 

R.L.  Right  luug. 

St.  Stomach. 


Sp.      Spleen. 

L.        Liver. 

S.E.    Suprarenal  body. 

L.K.  Left  kidney. 

R.K.  Right  kidney. 


P.       Pancreas. 

PL     Pleura. 

D.C.  Descending  colou. 

A.C.   Ascending  colon. 

R.       Rectum. 


The  cardiac  orifice  of  the  stomach  lies  one  inch  to  the  left  of  the  ninth  dorsal 
spine.     The  cardiac  portion,  overlapped  by  the  ninth  to  the  twelfth  ribs,  extends 


1288 


SUEFACE  AND  SUEGICAL  ANATOMY. 


upwards  to  the  level  of  the  eighth  dorsal  spine,  one  inch  below  the  angle  of  the 
scapula.  The  pyloric  portion  crosses  the  mesial  plane  opposite  the  twelfth  dorsal  and 
first  lumbar  spines,  the  pylorus  itself  being  situated  one  inch  to  the  right  of  the 
twelfth  dorsal  spine.  The  lesser  curvature  lies  to  the  left  of  and  below  the  tenth  and 
eleventh  dorsal  spines. 

Viewed  from  behind,  the  large  intestine  on  both  sides  overlaps  the  outer  border 
of  the  kidneys  and  lies  parallel  to  the  outer  border  of  the  erectores  spinse  muscles. 
The  peritoneum  is  reflected  from  the  colon  on  to  the  posterior  abdominal  wall  along 
a  line  drawn  vertically  upwards  from  the  centre  of  the  iliac  crest.    The  splenic  flexure, 


Oblique  fissure  of  lung  _. 

Upper  lobe  of  lung  -_ , 

■~— ^ 

Diaphragm  --- 

Liver 

"1 

Diaphragm  _ 

I 

Stomach' 

Cut  surface  of  base  of  lung 


Spleen 


Great  omentum 

Section  of  tenth  rib  opposite  costo- 
diaphragmatic  reflection  of  the  pleura 
(indicated  by  dotted  line) 


Fig.  923. — Dissection  of  the  Left  Hypochondrium  to  show  the  Relations  of  the  Spleen  to  the 
Lateral  Wall  of  the  Chest,  the  Diaphracim,  and  the  Adjacent  Viscera.  In  addition  to  the 
portions  of  ribs,  tliere  has  been  removed  a  part  of  the  base  of  the  left  lung,  and  a  window  has  been  made 
in  the  diaphragm  almost  down  to  the  level  of  the  costo-diaphragmatic  reflection  of  the  pleura. 

which  reaches  up  to  the  level  of  the  twelfth  dorsal  spine  and  the  tenth  rib,  lies 
about  five  inches  above  the  iliac  crest.  The  hepatic  flexure  lies  on  a  level  with  the 
first  lumbar  spine. 

Spleen. — The  spleen,  situated  in  the  left  hypochondrium  behind  the  cardiac  end 
of  the  stomach,  is  overlapped  by  the  ninth,  tenth,  and  eleventh  ribs,  the  long  axis 
of  the  organ  corresponding  approximately  to  that  of  the  tenth  rib.  Between  the 
upper  third  of  the  spleen  and  the  chest  wall  (pleura  and  diaphragm  intervening)  is 
the  base  of  the  left  lung,  the  lower  margin  of  which  crosses  the  organ  horizontally 
at  the  level  of  the  tenth  dorsal  spine.     The  costo-diaphragmatic  reflection  of  the 


THE  BACK. 


1289 


pleura  reaches  down  as  far  as  the  inferior  angle  of  the  spleen.  The  upper  limit  of 
the  organ  cannot  therefore  be  defined  by  percussion ;  and  unless  enlarged,  or 
displaced  downwards,  the  spleen  cannot  be  punctured  from  behind  without  traversing 
the  pleural  as  well  as  the  peritoneal  cavity. 

Of  the  three  angles  of  the  spleen,  the  loosterior  or  vertehral  lies  at  the  same  level 
as  the  lower  margin  of  the  lung,  1^  in.  external  to  the  tenth  dorsal  spine.  The 
inferior  angle  lies  opposite  the  eleventh  intercostal  space  on  a  level  with  the  first 
lumbar  spine,  in  a  line  drawn  vertically  upwards  from  a  point  one  inch  behind  the 
centre  of  the  ihac  crest.  This  angle  is  situated  behind  the  upper  part  of  the 
descending  colon  immediately  external  to  the  middle  of  the  outer  border  of  the 
kidney.  The  anterior  angle  is  at  the  level  of  the  ninth  interspace  in  the  mid- 
axillary  line.  Having  placed  a  mark  on  the  skin  opposite  these  three  angles  the 
organ  is  mapped  out  on  the  surface  as  follows : — The  posterior  or  renal  border  is 
obtained  by  joining  the  posterior  and  inferior  angles ;  this  border,  which  gives  the 
key  to  the  position  of  the  spleen,  will  be  found  to  follow  the  eleventh  intercostal 
space.  The  short  antero-inferior  border  corresponds  to  a  line  joining  the  anterior 
and  the  inferior  angles ;  it  is  related  to  the  splenic  flexure  of  the  colon,  and  may 
therefore  be  termed  the  colic  border.  Commencing  at  the  vertebral  angle,  the  so- 
called  anterior  border  is  at  first  arched  upwards,  the  summit  of  the  arch  reaching 
to  the  level  of  the  upper  border  of  the  ninth  rib  in  the  scapular  line ;  thence  it  is 
continued  downwards  and  forwards  across  the  posterior  axillary  hne  as  the 
"  anterior  crenated  border  "  to  the  anterior  angle.  The  upper  arched  portion  lies 
parallel  to  and  about  one  inch  below  the  highest  part  of  the  fundus  of  the  stomach. 
The  only  parts  of  the  splenic  outline  which  can  be  defined  by  percussion  are  the 
lower  crenated  part  of  the  anterior  border,  the  anterior  angle,  and  the  short  postero- 
inferior  or  colic  border ;  and  it  is  these  parts  which  may  be  felt  below  the  costal 
margin  when  the  organ  is  considerably  enlarged. 

In  excising  the  spleen  it  is  important  to  remember  that  the  splenic  vessels  lie 
between  the  two  layers  of  the  lieno-renal  ligament,  and  not  in  the  gastro-splenic 
omentum,  which  contains  the  vasa  brevia.  In  a  floating  spleen  these  two  peritoneal 
ligaments  are  elongated  to  form  a  distinct  pedicle. 

Pancreas. — The  head  of  the  pancreas  lies  opposite  the  last  dorsal  and  first 
lumbar  spines ;  the  tail  lies  at  the  same  level  as  the  splenic  flexures  of  the  colon,  a 
little  above  the  inferior  basal  angle  of  the  spleen. 

Table  indicating  the  Level  of  the  more  important  Structures  in 

RELATION  TO  THE  SpINES  OF  THE  VeRTEBR^. 


Spines  of  Vertebrae. 


1  Cervical 

2  „ 

3  „ 

4  „ 
5 


1  Dorsal 

2  Dorsal 


Origins  of  Spinal  Nerves. 


2  Cervical 
3  and  4         „ 
5 
6 


1  and  2  Dorsal 

3  „ 

4  Dorsal 


5  and  6 


Level  of  other  Structures. 


Soft  palate. 

Isthmus  of  fauces. 

Upper  part  of  epiglottis. 

Vocal  cords. 

Crico-tliyroid  membrane. 
fArcli  of  thoracic  duct. 
I  Commencement  of  trachea  and  oesophagus. 
C  Lower  end  of  cervical  enlargement  of  cord. 

Inferior  cervical  ganglion. 
I  Apices  of  lung. 

Summit  of  arch  of  subclavian  artery. 
f  Upper  angle  of  scapula. 
I  Just  above  level  of  highest  part  of  arch  of 
I      aorta. 
vEpisternal  notch. 

Root  of  spine  of  scapula. 

Arch  of  vena  azygos  major. 

Highest  part  of  lower  lobes  of  lungs. 

Termination  of  transverse  portion  of  arch 
of  aorta. 

Bifurcation  of  trachea. 

Lower  limit  of  superior  mediastinum. 
'^Angulus  Ludovici. 


1290 


SUEFACE  AND  SUEGICAL  ANATOMY. 


Table  indicating  the  Level  of  the  more  important  Structures  in 
RELATION  TO  THE  Spines  OF  THE  Vertebr.^ — Continued. 


Spines  of  Vertebrae. 

4  Doi-sal 

5       „           .         . 

6       „           .         . 

i     7       „           .        . 

8       „           .         . 

9       „           .         . 

10     „             .         . 

11       „           ■         • 

12       „           .         . 

'     1  Lumbar  . 

12          „         .         . 
3         „         -         . 

Origins  of  Spinal  Nerves. 


6  Dorsal 


10 


11 


12  Dorsal  and  1  Lumbar 


2  Lumbar 


3  and  4 


1,  2,  3  Sacral 


4  and  5 


4 

1  Sacral 

2  „ 

3  „ 


Level  of  other  Structures. 


11 


j' Commencement    of    descending    thoracic 

I      aorta. 

I  Bronchi. 

I  Upper  limit  of  heart. 

/"Centre  of  root  of  lung. 

I  Mitral  orifice. 

Tricusjiid  orifice. 
j'  Lowei'  angle  of  scapula. 
\  Orifice  of  inferior  vena  cava, 
i  Right  arch  of  diaphragm. 
/■Lowest  limit  of  heart. 
I  Left  arch  of  diaj^hragm. 
j  Fundus  of  stomach. 
IXijjhi-sternal  articulation. 

Upper  limit  of  spleen. 
r  Cardiac  oi-ifice  of  stomach. 

Upper  end  of  lumbar  enlargement. 

Lower  border  of  lung,  posteriorly. 

Vertebral  angle  of  spleen  (apex  of  spleen). 

UpjDer  end  of  left  kidney. 

Lesser  curvature  of  stomach. 

Lower  limit  of  j)leura  at  vertebral  column. 

Upi^er  end  of  right  kidney. 

Suprarenal  capsule. 

Body  of  j)ancreas. 
!^ Lesser  curvature  of  stomach. 
/"Level  at  which  jjleura  crosses  twelfth  rib. 

Lower  end  of  spleen, 
-j  Sj)lenic  flexure  of  colon. 

Uj)per  part  of  head  of  jjancreas. 
V  Pylorus  and  pyloric  portion  of  stomach. 
^Conus  meduUaris. 

Lower  limit  of  pleura  (mid -axillary  line). 

Hili  of  kidneys. 

Head  of  j^ancreas. 

Hej^atic  flexure  of  colon. 

Portal  vein. 

Second  part  of  duodenum. 

Greater  curvature  of  stomach. 
I  ^Common  bile  duct. 
J  Commencement  of  ureters. 
\^  Lowest  part  of  head  of  pancreas. 
( Lower  limit  of  cord  in  child. 
J  Lower  ends  of  kidneys. 
\  Third  part  of  duodenum. 

(Highest  part  of  crest  of  ilium. 
Bifurcation  of  aorta. 
Umbilicus. 
/•Common  iliac  arterie.s. 
\Ileo-ca!cal  valve. 
Sacral  promontory. 
Lower  end  of  subdural  space. 
( Ui^jJer  end  of  gluteal  cleft. 
-'Lower    limit   of  sub -arachnoid  and  sub- 
\     dural  spaces. 


Spinal  Cord.— The  spinal  cord  ends  opposite  the  lower  border  of  the  first 
lumbar  spine;  in  the  infant  it  reaches  to  the  interval  ])etween  the  second  and 
third  lumbar  spines.  The  cervical  eyilargement  which  corresponds  to  the  lower  four 
cervical  and  the  first  two  dorsal  segments  ends  opposite  the  seventh  cervical  spine. 
The  lumbar  enlargemeyit  lies  opposite  the  last  three  dorsal  spines.  The  five  lumbar 
segments  are  opposite  the  ninth,  tenth,  and  eleventh  dorsal  spines,  while  the  five. 


THE  UPPER  EXTEEMITY.  1291 

sacral  segments  extend  from  the  lower  border  of  the  eleventh  dorsal  to  the  lower 
border  of  the  first  lumbar  spine. 

Tlie  sub-dural  space  extends  down  to  the  level  of  the  second  sacral  spine.  In 
performing  the  operation  of  lumbar  i^uncture  (Quincke)  a  fine  trochar  and  cannula 
is  introduced  into  the  sub-araclinoid  space  below  the  level  of  the  cord,  the  puncture 
being  made  \  to  \  in.  to  one  side  of  the  interspinous  ligament  in  the  interval 
between  the  third  and  fourth  or  fourth  and  fifth  lumbar  spines.  The  instrument 
should  be  directed  inwards  towards  the  mesial  plane  and  very  slightly  upwards. 
In  the  adult  the  distance  of  tlie  thecal  sac  from  the  surface  is  about  2  in.,  in  the 
infant  ^  in. 

Fracture-dislocations  of  the  spine  are  commonest  in  the  lower  cervical  and  dorso- 
lumbar  regions ;  that  is  to  say,  where  the  movable  cervical  and  lumbar  regions 
join  the  more  fixed  dorsal  region.  The  spinal  column  above  the  injury  is  generally 
displaced  forwards,  so  that  the  spinal  cord  is  often  severely  lacerated  or  completely 
torn  across  by  the  upper  end  of  the  portion  of  the  column  below  the  fracture.  It 
is  important  to  remember  that  in  consequence  of  the  shortness  of  the  cord  as  com- 
pared with  the  spine,  the  origins  of  the  spinal  nerves  are  at  a  higher  level  than 
their  exits  from  the  spinal  canal.  The  distance  between  their  origins  from  the 
cord  and  their  exits  through  the  intervertebral  foramina  becomes  greater  the 
further  down  we  descend,  the  lowest  nerve  trunks  running  almost  vertically  down- 
wards. The  cervical  nerves  leave  the  spinal  canal  ahove  the  vertebrae  after  which 
they  are  named ;  the  dorsal,  lumbar,  and  sacral  nerves,  on  the  other  hand,  leave 
the  canal  helow  the  correspondingly  named  vertebrae. 

To  understand  the  effect  of  lesions  of  the  cord,  it  is  necessary  to  be  familiar  with  the 
sensory  and  motor  distributions  of  the  various  spinal  segments  (see  Figs.  487,  p.  611,  and 
489,  p.  615).  Transverse  lesions  of  the  cord  above  the  fifth  cervical  spine  (that  is,  above 
the  disc  between  the  fourth  and  fifth  cervical  vertebrae)  are  qviickly  fatal  from  paralysis 
of  respii-ation,  as  the  phi-enic  nerve  arises  mainly  from  tlie  fourth  segment.  In  transverse 
lesions  of  the  cervical  enlargement  the  cutaneous  insensibiliti/  does  not  extend  higher  than 
a  transverse  line  at  the  level  of  the  second  intercostal  space.  The  diagnosis  of  the  par- 
ticular segment  involved  is  arrived  at  by  testing  the  motor  and  sensory  functions  of  each 
segment.  The  sensoiy  areas  corresponding  to  the  loioer  four  cervical  and  the  first  ttvo 
dorsal  segments  occupy  the  upper  extremities,  and  are  placed  in  numerical  order  from  the 
radial  to  the  ulnar  side  of  the  limb.  The  sensory  area  corresponding  to  the  second,  third, 
and  fourth  cervical  segments  occupy  tlie  occipital  region  of  the  scalp,  the  back  of  the 
auricle,  and  the  masseteric  region,  the  whole  of  the  neck,  and  the  shoulders  and  upper 
part  of  the  chest  down  to  a  horizontal  line  at  the  level  of  the  anterior  end  of  the  third 
intercostal  space.  In  total  transverse  lesion  of  the  cord  in  the  dorsal  region,  the  upper 
limit  of  the  anaesthesia  is  horizontal,  and  reaches  to  the  level  of  the  terminations  of  the 
anterior  primary  divisions  of  the  spinal  nerves  which  arise  from  the  spinal  segment 
opposite  the  vertebral  injury.  Hence  the  upper  limit  of  the  anaesthesia  is  at  a  much 
lower  level  than  that  of  the  injured  vertebra.  For  example,  a  fracture-dislocation  at  the 
level  of  the  eighth  dorsal  vertebra  involves  the  origin  of  the  tenth  dorsal  nerve  which  ends 
at  the  level  of  the  umbilicus.  The  sensory  zone  corresponding  to  the  fifth  dorsal  segment 
is  at  the  level  of  the  nipples,  that  of  the  seveyith  dorsal  segment  is  at  the  level  of  the  ensi- 
form  cartilage,  that  of  the  tenth  at  the  level  of  the  umbilicus,  while  that  of  the  twelfth 
reaches  down  anteriorly  to  the  upper  border  of  the  symphysis.  The  sensory  areas 
corresponding  to  the  lumbar  and  sacral  segments  are  seen  in  Figs.  487  and  489. 

THE  UPPER  EXTREMITY. 

THE  SHOULDER. 

The  bony  landmarks  of  the  shoulder  must  be  systematically  examined  in  all 
injuries  about  this  region.  The  inner  extremity  of  the  clavicle  is  prominent ;  its 
articulation  with  the  sternum  forms  essentially  a  weak  joint  which  is  liable  to  be 
dislocated,  especially  from  blows  upon  the  outer  part  of  the  shoulder  which  drive 
the  inner  end  of  the  clavicle  forwards  against  the  weak  anterior  sterno-clavicular 
ligament.  The  shaft  of  the  clavicle,  subcutaneous  throughout,  is  weakest  at  the 
junction  of  its  two  curves ;    it  is  in  this  region  that  the  bone  is  so  frequently 


1292  SUEFACE  AND  SURGICAL  ANATOMY. 

fractured  as  the  result  of  force  transmitted  through  it  to  the  trunk.  The  dis- 
placement of  the  outer  fragment  varies  according  to  whether  the  break  takes  place 
internal  or  external  to  the  coraco-clavicular  ligament ;  in  the  former  case  the  weight 
of  the  upper  extremity,  acting  through  the  coraco-clavicular  ligament,  pulls  the 
outer  fragment  downwards ;  when  the  fracture  is  external  to  the  ligament,  the  outer 
end  of  the  clavicle  rotates  forwards,  but  there  is  no  downward  displacement.  The 
outer  end  of  the  clavicle  is  on  a  plane  posterior  to  its  inner  end,  so  that  the  shoulder 
is  braced  backwards  away  from  the  thorax ;  hence  in  fractures  of  the  clavicle,  both 
inside  and  outside  the  coraco-clavicular  ligament,  the  point  of  the  shoulder  rotates 
forwards  and  inwards.  The  acromio-clavicular  articulation  is  somewhat  difficult  to 
feel ;  the  groove  which  corresponds  to  it  runs  in  the  sagittal  direction,  and  lies 
1:^  in.  internal  to  the  outer  border  of  the  acromion,  and  immediately  external  to  a 
slight  prominence  upon  the  outer  extremity  of  the  clavicle.  When  this  joint  is 
dislocated  the  clavicle  almost  invariably  overrides  the  acromion,  and  the  summit 
of  the  shoulder  presents  a  somewhat  conical  or  "  sugar-loaf  "  appearance. 

The  tip  of  the  acromion  looks  directly  forwards,  and  lies  a  fingers-breadth 
external  to  and  a  little  in  front  of  the  outer  extremity  of  the  clavicle.  The  outer 
border  of  the  acromion  can  readily  be  followed  to  its  junction  with  the  spine  of  the 
scapula,  and  the  latter  to  its  root,  which  is  situated  on  a  level  with  the  third  dorsal 
spine.  The  inner  border  of  the  acromion  and  the  posterior  border  of  the  outer  end 
of  the  clavicle  meet  at  an  angle  into  which  the  point  of  the  finger  can  be  pressed. 
The  upper  angle  of  the  scapula,  covered  by  the  trapezius  and  the  supraspinatus 
muscles,  is  too  deeply  placed  to  be  palpated  distinctly.  The  inferior  angle,  and 
the  internal  border,  from  the  root  of  the  spine  downwards,  form  visible  prominences 
which  are  readily  felt ;  the  former  overlies  the  seventh  intercostal  space  on  a  level 
with  the  seventh  dorsal  spine,  while  the  latter  lies  a  little  internal  to  the  angles  of 
the  ribs 

To  elicit  crepitus  in  a  transverse  fracture  of  the  scapula  below  the  spine,  the  surgeon 
stands  behind  the  patient  and  grasps  the  upper  fragment  by  placing  the  forefinger  upon 
the  coracoid  and  the  thumb  upon  the  spine,  while  with  the  other  hand  he  grasps  the 
inferior  angle  ;  the  two  fragments  are  then  moved  the  one  upon  the  other. 

The  tip  of  the  coracoid  process  may  be  felt  by  pressing  the  finger  firmly  upon  the 
anterior  border  of  the  deltoid  at  a  point  one  inch  below  the  junction  of  the  middle 
and  outer  thirds  of  the  clavicle.  Internal  to  the  coracoid  is  a  triangular  depres- 
sion which  corresponds  to  the  upper  end  of  the  interval  between  the  clavicular 
fibres  of  the  pectoralis  major  and  deltoid  muscles.  Behind  this  triangular  depres- 
sion are  the  termination  of  the  cephalic  vein,  a  lymphatic  gland,  the  first  part  of 
the  axillary  vessels,  and  the  cords  of  the  brachial  plexus.  By  firm  pressure  in  this 
situation  the  pulsation  of  the  axillary  artery  can  be  felt,  and  by  further  pressure 
the  circulation  in  the  vessel  can  be  arrested  by  compressing  the  artery  against  the 
second  rib.  The  first  part  of  the  axillary  artery  may  be  cut  down  upon  either  by 
a  transverse  incision  through  the  clavicular  origin  of  the  pectoralis  major,  or  by  a 
longitudinal  incision  in  the  interval  between  this  muscular  slip  and  the  deltoid. 
The  companion  vein  lies  in  front  of,  as  well  as  to  the  thoracic  side  of,  the  artery, 
thus  adding  to  the  difficulty  of  exposing  the  vessel.  In  fractures  of  the  middle 
third  of  the  clavicle  the  subclavian  vessels  are  protected  by  the  soft  pad  formed  by 
the  subclavius  muscle. 

The  upper  end  of  the  humerus  covered  by  the  deltoid  gives  rotundity  to  the 
shoulder.  The  greater  tuberosity  projects  beyond  the  acromion,  and  constitutes  the 
most  external  bony  landmark  of  the  shoulder.  When  the  head  of  the  bone  is  dis- 
located, the  outer  border  of  the  acromion  then  becomes  the  most  external  bony 
landmark,  and  the  shoulder  presents  a  square  contour.  The  lesser  tuberosity,  small 
but  conical,  can  be  felt  through  the  deltoid.  Pointing  directly  forwards,  it  lies  one 
inch  external  to  and  a  little  below  the  level  of  the  tip  of  the  coracoid  process.  In 
examining  the  upper  end  of  the  humerus  for  fracture,  the  tuberosities  should  be 
grasped  between  the  finger  and  thumb  of  one  hand,  while  the  flexed  elbow  is 
rotated  with  the  other  hand.  The  head  of  the  humerus  has  the  same  direction  as 
the  internal  condyle ;  its  lower  part  can  be  palpated  through  the  axilla,  the  arm. 


THE  AXILLA.  1293 

being  meanwhile  abducted,  to  bring  the  head  in  contact  with  the  under  surface  of 
the  capsule.  It  is  through  this,  the  weakest  part  of  the  capsule,  that  the  head  is 
driven  in  the  common  varieties  of  dislocation  of  the  shoulder,  viz.  those  due  to 
forcible  abduction.  The  upper  epiphysis  of  the  humerus  includes  the  head  and  the 
greater  part  of  the  tuberosities.  The  capsule  is  mainly  attached  to  the  ejjiphysis ; 
hence,  in  children,  we  find  that  separation  of  the  upper  epiphysis  takes  the  i)lace  of 
dislocation.  Disease  in  the  upper  end  of  tlie  diaphysis  does  not  necessarily  involve 
the  cavity  of  the  joint.  The  bicipital  groove  of  the  humerus,  which  lies  imme- 
diately external  to  the  lesser  tuberosity,  may  be  mapped  out  upon  the  surface  by 
drawing  a  line,  two  inches  in  length,  downwards  along  the  axis  of  the  humerus 
from  the  tip  of  the  acromion.  When  there  is  effusion  into  the  joint,  the  arm  be- 
comes slightly  abducted,  and  there  is  fulness  in  front,  along  the  line  of  the  long 
tendon  of  the  biceps.  With  the  elbow  at  the  side  the  inferior  part  of  the  capsule 
of  the  shoulder-joint  is  loose  and  folded  upon  itself  to  form  a  dependent  pocket ; 
if,  after  an  injury,  the  arm  be  retained  too  long  in  this  position,  the  patient  may  be 
unable  to  abduct  the  arm  in  consequence  of  the  formation  of  adhesions  in  and 
around  the  pouch.  To  evacuate  pus  from  the  shoulder -joint,  the  integuments, 
deltoid,  and  capsule  should  be  cut  into  by  an  incision  passing  vertically  downwards 
from  the  tip  of  the  acromion. 

THE  AXILLA. 

The  anterior  fold  of  the  axilla,  formed  by  the  lov/er  border  of  the  pectoralis 
major,  extends  from  the  fifth  rib  to  the  middle  of  the  anterior  border  of  the  deltoid. 
With  the  arm  abducted,  the  interval  between  the  sternal  and  clavicular  fibres  of 
the  pectoralis  major  is  indicated  by  a  slight  groove  extending  downwards  and  out- 
wards from  the  inner  end  of  the  clavicle.  The  sternal  fibres,  along  with  the 
pectoralis  minor,  are  removed  in  a  complete  operation  for  malignant  disease  of  the 
breast,  the  pectoral  branches  of  the  thoracic  axis  artery  being  secured  as  they 
cross  the  interval  between  the  sternal  and  clavicular  portions  of  the  greater  pectoral. 
The  posterior  fold  of  the  axilla,  formed  by  the  latissimus  dorsi  and  the  teres  major 
muscles,  is  on  a  lower  level  than  the  anterior  fold,  and  leaves  the  chest  a  little  in 
front  of  the  inferior  angle  of  the  scapula.  Between  the  two  folds,  and  running  in 
the  long  axis  of  the  limb,  from  the  axilla  to  the  middle  of  the  upper  arm,  is  the 
prominence  of  the  coraco-brachialis  muscle.  The  pulsations  of  the  third  part  of 
the  axillary  artery  may  be  felt  in  the  furrow  immediately  behind  this  prominence 
at  the  junction  of  the  anterior  and  middle  thirds  of  the  outer  wall  of  the  axilla. 

Female  Mamma. — The  breast  tissue  proper  is  arranged  to  form  a  central 
portion,  the  carious  mammce,  and  a  peripheral  portion,  made  up  of  branching 
processes  which  radiate  into  the  paramammary  fat  and  become  continuous 
ultimately  with  the  connective  tissue  septa  of  the  subcutaneous  fatty  tissue.  The 
mamma,  therefore,  has  no  distinct  capsule.  In  the  young  adult  nullipara,  the 
corpus  mamma;  is  compact  and  well  defined,  and  contains  but  Httle  intramammary 
fat,  while  the  peripheral  processes  are  relatively  small.  In  multipara,  the  corpus 
mammse  contains  more  fat,  and  the  peripheral  processes  extend  more  widely  into 
the  paramammary  fat. 

Tlie  arrangement  and  extent  of  the  parenchyma  can  be  well  seen  by  treating  the  breast  with 
a  5  "per  cent  solution  of  nitric  acid.  If  slices  of  the  fresh  organ  be  placed  in  this  solution  for  a 
few  minutes  and  then  washed  under  running  water,  the  albumen  of  tlie  eijithelial  cells  of  the 
parenchyma  is  coagulated,  while  the  connective  tissiie  is  rendered  translucent  and  somewhat 
gelatinous.  The  ultimate  lobules  of  the  2}arenchyma  now  appear  as  little  (1  to  2  mm.),  dull,  opaque, 
white,  sago-like  bodies,  arranged  in  grape-like  clusters  aroimd  the  finer  branches  of  the  ducts. 

The  parenchyma  is  prolonged  into  the  peripheral  processes,  into  the  suspensory 
ligaments  of  Cooper,  and  into  the  loose  retromammary  cellular  tissue  and  pectoral 
fascia.  The  breast  tissue,  therefore,  has  a  much  wider  distribution  than  was 
formerly  supposed.  Vertically,  it  extends  from  the  second  rib  to  the  sixth  costal 
cartilage  at  the  angle  where  it  begins  to  ascend  towards  the  sternum ;  horizontally, 
from  a  little  within  the  lateral  border  of  the  sternum,  opposite  the  fourth  rib,  to 
the  fifth  rilj  in  the  midaxillary  line.     The  innei'  hemisphere  of  the  mamma  rests 


11^94 


SUEFACE  AND  SUEGICAL  ANATOMY. 


almost  entirely  on  the  pectoralis  major ;  at  its  lowest  part  it  slightly  overlies  the 
upper  part  of  the  aponeurosis  covering  the  rectus  abdominis  muscle.  The  upper 
quadrant  of  the  outer  hemisphere  rests  upon  the  greater  pectoral,  on  the  edge  of 
the  lesser  pectoral,  and  to  a  slight  extent  on  the  serratus  magnus,  upon  which 
it  extends  upwards  into  the  axilla  ("  axillary  tail "  of  Spence)  as  high  as  the  third 
rib,  where  it  comes  into  relation  with  the  thoracic  group  of  axillary  lymphatic 
glands.  The  remainder  of  the  outer  hemisphere  rests  almost  entirely  upon  the 
serratus  magnus,  except  the  lowest  part,  which  overlaps  the  digitations  of  the 
external  oblique  arising  from  the  fifth  and  sixth  ribs.  It  follows,  therefore,  that 
fully  one-third  of  the  whole  mamma  lies  inferior  and  external  to  the  axillary 
horder  of  the  pectoralis  major  muscle.  The  surgeon  must  cut  beyond  the  above 
limits  if  he  wishes  to  remove  the  whole  of  the  mammary  tissue. 

The  axillary  fascia  resists  the  spontaneous  rapture  of  an  axillary  abscess,  which, 
therefore,  tends  to  spread  upwards  beneath  the  pectorals,  and  towards  the  root  of  the 
neck.  To  open  the  abscess  the  incision  should  be  made  upon  the  inner  wall,  behind, 
and  parallel  to,  the  long  thoracic  artery,   which  runs  under  cover  of  the  anterior  fold. 


'>^^Z7fjr,,, 


Brachial  artery 
Biceps  tendon  f 

Supinator  longus 


Clavicle 
Anterior  axillary  fol^  I 

Coraco-braehialis      Deltoid     ; 


Flexor  muscles 

Bicipital  fascia 

Internal  condyle 

Bracliialis  anticus 

Ulnar  nerve' 
Internal  intermuscular  sejjtuni 

Median  nervd 
Inner  head  of  tricejjfe 

Long  head  of  tricepi^ 
Lower  border  of  teres  major 

Posterior  axillary  fold 

Fir;.  924. — Axilla.  Inner  Aspect  of  Upper  Arm  and  Elbow. 


m 


The  axillary  lymphatic  glands  vary  greatly  in  size  and  number;  many  are  no  larger 
than  a  pin's  head.  In  the  female  some  of  them  undergo  an  adipose  functional  involu- 
tion, whereby  they  come  to  resemble  fat  lobules.  In  health  one  or  two  glands  can  usually 
be  felt  by  thrusting  the  fingers  upwards  and  inwards  beneath  the  anterior  fold,  the  arm 
being  only  slightly  abducted,  so  as  not  to  stretch  the  axillary  fascia.  The  central  group 
(Leaf),  embedded  in  the  fat  immediately  beneath  the  axillary  fascia,  become  inflamed  in 
poisoned  wounds  of  the  upper  extremity.  The  same  group,  along  with  the  pectoral  groiip 
(related  to  the  inner  wall  of  the  axilla,  at  the  lower  border  of  the  pectoralis  minor),  are 
usually  the  first  to  become  diseased  in  malignant  affections  of  the  breast.  When  the 
disease  is  more  advanced  the  posterior  (subscapular)  and  the  apical  (subclavicular)  groups 
are  generally  affected  as  well ;  and  Rotter  has  shown  that  in  a  considerable  porportion  of 
cases  diseased  glands  are  to  be  found  in  the  retro-i^ectoral  fascia,  i.e.  between  the  pectoralis 
major  and  minor  and  above  the  latter  muscle  on  the  first  intercostal  space  in  relation  to 
the  small  superior  thoracic  artery.  In  operating  for  malignant  disease  of  the  breast,  the 
surgeon  removes,  in  addition  to  the  whole  breast  and  the  greater  part  of  the  skin  over  it, 
both  pectoral  muscles  (with  the  exception  of  the  clavicular  fibres  of  the  pectoralis  major), 
all  the  axillary  lymphatic  glands,  and,  as  far  as  possible,  all  the  fat  and  fascia,  including  the 
sheath  of  the  axillary  vein.  It  must  be  remembered  that  the  lower  part  of  the  axillary 
vein  lies  immediately  underneath  the  deep  fascia  of  the  outer  wall  of  the  axilla ;  in  clean- 
ing the  inner  wall  the  long  thoracic  nerve  must  not  be  injured ;  and  in  removing  the 
posterior  group  of  lymphatic  glands  the  long  subscapular  nerve,  which  accompanies  the 
subscapular  vessels,  must  be  avoided,  as  it  is  doubly  important  to  retain  the  action  of  the 
latissimus  dorsi  after  removing  the  pectorals.  The  writer  has  so  frequently  met  with 
disease  in  these  retro-pectoral  glands,  that  he  is  convinced  of  the  necessity  of  removing 
the  ])ectoral  muscles. 


THE  UPPER  AEM. 


1295 


THE  UPPER  ARM. 

The  anterior  and  posterior  borders  of  the  deltoid  may  be  traced  from  the 
shoulder  girdle  to  the  insertion  of  that  muscle.  The  surface  relations  of  the  anterior 
border  have  already  been  referred  to ;  the  posterior  border  forms  a  well-marked 
and  important  landmark  as  it  crosses  the  angle  between  the  axillary  border  of  the 
scapula  and  the  upper  part  of  the  shaft  of  the  humerus.  By  making  an  incision 
along  this  part  of  the  posterior  border  of  the  deltoid,  and  retracting  the  edge  of  the 
muscle  upwards  and  outwards,  we  expose  the  surgical  neck  of  the  humerus,  the 
quadrilateral  opening  in  the  posterior  wall  of  the  axilla  transmitting  the  posterior 
circumflex  artery  and  the  circumflex  nerve ;  a  little  lower  down  is  the  musculo- 
spiral  nerve.  The  coraco-brachialis,  the  guide  to  the  upper  half  of  the  brachial 
artery,  forms  a  prominence  occupying  the  upper  half  of  the  internal  bicipital  ftirrow. 
Traced  downwards  the  internal  bicipital  furrow  widens  out  into  an  elongated 
triangle.  This  triangle,  which  may  be  termed  the  internal  supracondi/loid  triangle, 
becomes  continuous  below  with  the  inner  part  of  the  triangle  in  front  of  the  bend 
of  the  elbow,  and  is  limited  posteriorly  by  the  internal  intermuscular  septum,  which 
may  be  felt  as  a  cord-like  band  extending  upwards  from  the  internal  condyle ;  the 


Head  of  radiu$ 
External  condyle 
Extensor  carpi  radialis  longior 
Musculo-spiral  ner\e 
External  Intermuscular  septum  Biceps 

Circumflex  nerve 


jExtensor  carpi  radialis  brevier 
Posterior  interosseous  nerve 

Extensor  ossis  metacarpi  pollicis 
JUddle  thecal  tubercle 
Styloid  process  of 
third  metacarpal 


Head  of  ulna 


Infraspinatus 


Trii-pps  tendon 
i       Outer  head  of  triceps 
Posterior  border  of  deltoid 
Long  head  of  triceps 
I     Teres  major 
Latissimus  dorsi 


Posterior  border  of  ulna 
Flexor  carpi  ulnaris 
Extensor  carpi  ulnaris 
I  Extensor  communis  digitornm 

I      Anconeus 
Tip  of  olecranon  process 


Fig.  925. — Extensor  Aspect  of  Upper  Limb. 


floor  of  the  space  is  formed  by  the  inner  part  of  the  brachialis  anticus.  Within 
the  triangle  are  the  following  important  structures,  enumerated  from  without  in- 
wards, viz. :  the  brachial  artery,  the  median  nerve,  the  lower  part  of  the  basilic 
vein,  the  internal  cutaneous  nerve  and  the  supracondyloid  lymphatic  glands,  two 
or  three  in  number.  Extending  upwards  from  the  external  condyle  to  the  insertion 
of  the  deltoid  is  the  external  intermuscular  septum,  which  is  pierced  at  the 
junction  of  its  upper  and  middle  thirds  by  the  musculo-spiral  nerve.  Between  the 
external  intermuscular  septum  and  the  outer  edge  of  the  biceps  is  the  ill-defined 
external  bicipital  furrow,  the  floor  of  which  is  formed  by  a  strip  of  the  brachialis 
anticus,  and,  nearer  the  elbow,  by  the  supinator  longus  and  extensor  carpi  radialis 
longior. 

The  posterior  compartment  of  the  upper  arm  is  occupied  by  the  triceps,  the  long 
head  of  which  can  be  traced  upwards  to  the  axillary  border  of  the  scapula  in  front 
of  the  posterior  border  of  the  deltoid  and  behind  the  posterior  fold  of  the  axilla. 
The  outer  head  of  the  triceps,  after  emerging  from  under  cover  of  the  lower  part 
of  the  posterior  border  of  the  deltoid,  is  continued  obliquely  down  the  outer  aspect 
of  the  upper  arm  as  a  well-marked  muscular  elevation.  Above  the  olecranon  is 
the  strap-like  tendon  of  insertion  of  the  triceps,  which,  when  the  elbow  is  fully 
flexed,  forms  an  admirable  posterior  splint  in  supracondyloid  fractures  of  the 
humerus. 

The  brachial  artery,  slightly  overlapped  in  the  upper  half  of  the  arm  by  the 
coraco-brachialis  and  in  the  lower  half  by  the  biceps,  can  be  felt  pulsating  through- 
out the  whole  length  of  the  anterior  part  of  the  internal  bicipital  furrow.     The 


1296  SUEFACE  AND  SUEGICAL  ANATOMY. 

course  of  the  vessel  may  be  mapped  out  upon  the  surface  by  drawing  a  line  from 
the  inner  border  of  the  coraeo-brachialis,  at  the  level  of  the  posterior  fold  of  the 
axilla,  downwards  to  a  point  (opposite  the  neck  of  the  radius)  |  in.  below  the 
middle  of  the  bend  of  the  elbow.  In  hgaturing  the  vessel,  the  edges  of  the 
coraeo-brachialis  and  biceps  muscles,  together  with  the  median  nerve,  furnish  valu- 
able guides  to  the  artery,  the  mobility  of  which  is  often  a  source  of  trouble  in 
performing  the  operation. 

The  basilic  vein,  which  is  superficial  to  the  deep  fascia  in  the  lower  third  of  the 
upper  arm,  is  visible  in  the  internal  supracondyloid  triangle  and  the  lower  part  of 
the  internal  bicipital  groove.  The  cephalic  vein  ascends  a  httle  internal  to  the 
outer  edge  of  the  triceps  to  reach  the  interval  between  the  deltoid  and  pectoralis 
major. 

The  surface  guide  for  the  median  nerve  is  the  same  as  that  for  the  brachial 
artery.  The  ulnar  nerve  is  indicated  superficially  by  a  line  extending  from  the 
outer  wall  of  the  axilla  immediately  behind  the  prominence  of  the  coraeo-brachialis, 
to  the  back  of  the  internal  condyle ;  in  the  upper  half  of  the  arm  the  nerve  lies 
close  behind  the  brachial  artery  under  cover  of  the  basilic  vein,  while  in  the  lower 
half  it  lies  a  little  behind  the  internal  intermuscular  septum,  partially  embedded 
in  the  fibres  of  the  inner  head  of  the  triceps.  To  map  out  the  course  of  the  musculo- 
spiral  nerve,  first  mark  the  point  where  it  pierces  the  external  intermuscular 
septum,  viz.  the  junction  of  the  upper  and  middle  thirds  of  a  line  extending  from 
the  insertion  of  the  deltoid  to  the  external  condyle ;  from  tliis  point  draw  a  line 
obliquely  downwards  and  forwards  to  the  front  of  the  external  condyle,  where  the 
nerve  divides  into  its  radial  and  posterior  interosseous  branches.  To  map  out  the 
nerve  as  it  lies  in  the  musculo-spiral  groove,  draw  a  line  from  the  same  point 
obliquely  upwards  across  the  prominence  formed  by  the  outer  head  of  the  triceps  to 
the  junction  of  the  posterior  fold  of  the  axilla  with  the  upper  arm.  In  fractures  of 
the  humerus  in  the  neighbourhood  of  the  insertion  of  the  deltoid,  the  nerve  is  not 
infrequently  lacerated,  or  so  involved  in  the  callus  as  to  produce  the  condition 
known  as  "  drop-wrist,"  the  result  of  paralysis  of  the  extensor  muscles  of  the 
forearm.  To  cut  down  upon  the  nerve,  commence  the  incision  a  little  below  the 
point  where  it  pierces  the  external  intermuscular  septum,  and  carry  it  obliquely 
upwards  and  slightly  backwards  through  the  outer  head  of  the  triceps. 

The  shaft  of  the  humerus,  nowhere  subcutaneous,  is  most  readily  manipulated 
in  the  region  of  the  insertion  of  the  deltoid,  upwards  along  the  outer  head  of  the 
triceps,  and  downwards  behind  the  external  supracondyloid  ridge.  The  surgical 
neck,  situated  between  the  tuberosities  and  the  attachments  of  the  muscles  inserted 
into  the  region  of  the  bicipital  groove,  is  related  to  the  outer  wall  of  the  axilla,  and 
is  on  a  level  with  the  junction  of  the  upper  and  middle  thirds  of  the  deltoid ;  at 
the  same  level  are  the  circumflex  vessels  and  nerves. 

The  shaft  may  be  cut  down  upon  with  least  injury  to  soft  parts:  (1)  in  its  iipper 
third,  anteriorly,  by  an  incision  extending  downwards  through  the  anterior  fibres  of  the 
deltoid,  parallel,  and  a  little  external,  to  the  bicipital  groove  ;  the  sheath  of  the  biceps 
will  thus  be  avoided,  and  the  small  anterior  circumflex  artery  will  be  the  only  vessel 
divided.  (2)  In  the  upjier  third,  posteriorly,  by  an  incision  through  the  posterior  fibres 
of  the  deltoid,  the  bone  being  reached  just  external  to  the  origin  of  the  outer  head  of  the- 
triceps,  thus  avoiding  the  musculo-spiral  nerve  ;  the  circumflex  vessels  and  nerves  will  be 
exposed  at  the  upper  part  of  the  wound.  (3)  In  the  lower  third,  by  an  incision  extending 
upwards  from  the  back  of  the  external  condyle  a  little  to  the  inner  side  of  the  external 
intermuscular  septum. 

THE  ELBOW. 

In  injuries  about  the  elbow  the  diagnosis  rests  mainly  upon  the  relative 
positions  of  the  bony  points,  which  are,  therefore,  of  great  importance.  The 
epicondylar  processes  of  the  humerus  are  both  subcutaneous  and  upon  the  same 
level,  the  internal  being  the  more  prominent.  In  the  extended  position  of  the 
elbow  the  tip  of  the  olecranon  is  on  a  level  with  a  line  joining  the  epicondyles ; 
when   the  forearm  is  flexed    the  olecranon  descends,  and  when  full    flexion   is. 


THE  ELBOW. 


1297 


reached  it  lies  1  iu.  below  the  condyles,  and  in  a  plane  anterior  to  the  posterior 
surface  of  the  lower  end  of  the  humerus.  The  head  of  the  radius,  which  lies  nearly 
1  in.  below  the  external  epicondyle,  is  best  manipulated  from  behiud  by  placin-^' 
the  thumb  upon  it,  while  the  semi-flexed  forearm  is  being  alternately  pronated 
and  supinated.  Upon  the  outer  part  of  the  posterior  aspect  of  the  extended 
elbow  is  a  distinct  dimple,  which  overlies  the  radio -humeral  articulation;  this 
dimple,  aloncj  with  the  hollows  on  either  side  of  the  olecranon,  becouies  etfaced  in 
synovial  thickenings  and  effusions  into  the  joint.  The  coronoid  process  is  situated 
too  deeply  to  be  distinctly  felt.  The  lower  epiphysis  of  the  humerus  includes  the 
articular  portion  of  the  lower  extremity  and  the  external  condyle;  it  is,  therefore, 
small  and  almost  entirely  intra-articular,  so  that  foci  of  disease  in  its  neighbour- 
hood soon  invade  the  cavity  of  the  joint.     The  internal  epicondyle  ossifies  as  a 


Vena  comes  of  brachial  artery 

Musculo-cutaneous  nerve 
Tendon  of  biceps 
Median  cephalic  vein 


Brachial  artery 

Metliau-basilic  vein 
'  /  Vena  conies  of  brachial  artery 

Pronator  radii  teres 


Supinator  longus- 


Musculo-spiral      // 
nerve      fj- 


Radial  extensors  - 


Articular  surface  of  humerus 


Median  nerve 
Brachialis  anticus 


Common  origin  of 
rtexor  muscles 


Internal  condyle 


Ulnar  nerve 


\Inferior  profunda 
artery 


External  condj  le 


Olecranon 


Fig.  926. 


Anconeus  Olecranon  fossa  of  humerus 

-Traxsyeese  Sectiox  through  the  Bend  of  the  Elbow. 


separate  epiphysis  which  unites  with  the  lower  end  of  the  diaphysis.  In  inter- 
preting skiagrams  of  the  elbow  of  children  about  six  years  of  age  and  upwards,  care 
must  be  taken  not  to  mistake  the  centre  of  ossification  in  the  radial  portion  of  the 
lower  epiphysis  of  the  humerus  for  a  fracture.  In  the  commonest  dislocation  of 
the  elbow,  viz.  with  backward  displacement  of  both  bones  of  the  forearm,  the 
normal  relative  position  of  the  bony  points  is  lost,  whereas  in  a  transverse  supra- 
condyloid  fracture  the  normal  relations  are  maintained.  In  the  child  the  head 
of  the  radius  is  relatively  smaller,  and  less  firmly  kept  in  position  by  the 
orbicular  ligament  than  in  the  adult,  so  that  it  is  liable  to  be  partially  dislo- 
cated, giving  rise  to  the  condition  kno^vn  as  "pulled  elhoiv."  To  evacuate  pus 
from  the  elbow-joint  a  vertical  incision  should  be  made  over  the  dorsal  aspect  of 
the  joint,  immediately  external  to  the  olecranon. 

The  median  vein  is  seen  to  bifurcate  into  median  basilic  and  median  cephalic 
h  in.  below  the  middle  of  the  Ijend  of  the  elbow ;  opposite  the  same  point,  but 
beneath  the  deep  fascia,  is  the  bifurcation  of  the  brachial  artery.  The  median  basilic 
^nd  median  cephalic  veins  diverge  a?  they  ascend  one  on  either  side  of  the  biceps 
tendon  ;  the  larger  of  the  two  veins,  viz.  the  median  basilic,  is  usually  selected  for 
the  operations  of  venesection  and  transfusion.  When  the  elbow  is  flexed  the  biceps 
tendon  can  be  traced  vertically  through  the  centre  of  the  bend  of  the  elbow  almost  to 
its  insertion.  Passing  downwards  and  inwards  from  the  inner  edge  of  the  tendon  is 
the  bicipital  fascia,  which  separates  the  median  basilic  vein  from  the  l^rachial  artery. 
If  the  fin!j;er  nail  be  insinuated  beneath  the  inner  edge  of  the  fascia  the  point  of  the 


1298 


SUEFACE  AND  SUEGICAL  ANATOMY. 


finger  will  rest  upon,  and  feel  the  pulsations  of,  the  brachial  artery.  The  median 
nerve  descends  through  the  space  a  little  internal  to  the  brachial  artery.  The 
bifurcation  of  the  musculo -spiral  nerve  takes  place  in  front  of  the  external  condyle 
under  cover  of  the  supinator  longus.  The  ulnar  nerve  can  be  rolled  beneath  the 
finger  upon  the  back  of  the  internal  condyle  ;  its  position  renders  it  liable  to  injury 

in  severe  fractures  about  the 
elbow,  and  in  excising  the  joint 
care  must  be  taken  not  to  injure 
the  nerve. 


Biacliialis  anticus 

Cephalic  vein. 

Biceps 


-Brachial  artery 


Median  cephalic  vein 

Tendon  of  biceps 
Musculo-spiral  nerve. 


Posterior  interosseous 
nerve 


Supinator  longus 


—  Basilic  vein 

—  Brachialis  anticus 


Median  basilic 
vein 

■Bicipital  fascia 


Radial  nerve 


Radial  artery 


-  -  Ulnar  artery 


Tendon  of  flexor  carpi 

radialis 

Base  of  styloid  process 


Radial  artery 


THE  FOREARM  AND  HAND. 

The  upper  half  of  the  radius 
is  deeply  placed;  the  lower  half 
is,  however,  easily  palpated. 
The  anterior  border  of  its  lower 
extremity  is  felt  as  a  prominent 
transverse  ridge,  situated  1  in. 
above  the  thenar  eminence ; 
immediately  below  the  ridge 
is  the  radio-carpal  articulation. 
The  tip  of  the  styloid  process, 
situated  nearly  \  in.  lower  than 
that  of  the  ulna,  is  deeply 
placed  at  the  outer  side  of  the 
wrist,  in  the  hollow  between 
the  extensor  tendons  of  the 
first  and  second  phalanges  of 
the  thumb.  Upon  the  middle 
of  the  posterior  surface  of  the 
lower  end  of  the  radius  is  the 
dorsal  radial  tubercle  which 
intervenes  between  the  extensor 
of  the  second  phalanx  of  the 
thumb  and  the  short  radial 
extensor  of  the  wrist ;  the 
tubercle  can  be  distinctly  felt, 
and  may  be  taken  as  a  guide 
to  the  upper  end  of  Lister's 
dorso-radial  incision  for  excision 
of  the  wrist.  The  posterior 
border  of  the  ulna  is  sub- 
cutaneous throughout,  and  may 
be  felt  along  the  interval  be- 
tween the  flexor  and  extensor 
carpi  ulnaris  muscles.  Upon- 
the  ulnar  side  of  the  dorsal 
aspect  of  the  wrist  is  a  well- 
marked  rounded  prominence 
formed  by  the  lower  extremity 
of  the  ulna,  anterior  to  which  is  the  styloid  process,  the  deep  groove  between  the 
two  being  occupied  by  the  tendon  of  the  extensor  carpi  ulnaris. 

The  carpal  bones  are  Iniilt  up  so  as  to  form  an  arch,  converted  by  the  anterior 
annular  ligament  into  a  tunnel  for  the  transmission  of  the  flexor  tendons.  At  each 
extremity  of  the  arch  the  two  bony  points  to  which  the  ligament  is  attached 
furnish  important  landmarks.  These  bony  points  are  :  externally,  the  tubercle  of  the 
scaphoid  and  the  ridge  of  the  trapezium  ;  internally,  the  pisiform  and  the  hook  of 
the  unciform.  The  tubercle  of  the  scaphoid  is  felt  immediately  above  the  root  of 
the  thenar  eminence,  midway  between  the  tendons  of  the  extensor  ossis  metacarpi 


Median  uerve 


Plexor  carpi 

ulnaris 

Flexor  sublimis 

digitorum 

Pisiform  bone 

Anterior  annular 
ligament 


Deep  palmar  arch 


Fig.  927.- 


-Bend  of  Elbow,  Front  of 
OF  Hand. 


FOKEARM.    AND    PaLM 


THE  FOREAEM  AND  HAND. 


1299 


pollicis  aud  the  flexor  carpi  radialis  ;  h  in.  below  the  tubercle  of  the  scaphoid  is 
the  ridge  of  the  trapezium,  felt  deeply  beneath  the  inner  part  of  the  thenar 
eminence.  At  the  root  of  the  hypothenar  eminence,  and  crossed  by  the  crease 
which  separates  the  forearm  from  the  hand,  is  the  pisiform  bone,  above  which  is  the 
tendon  of  the  Hex  or  carpi  ulnaris,  passing  to  be  inserted  into  it.  The  hook  of  the 
unciform  is  felt  deeply  beneath  the  radial  side  of  the  hypothenar  eminence,  and  a 
i'ull  finger's  breadth  below  and  external  to  the  pisiform. 


Suiierticial  palmar  arel 


Deep  branch  of  ulnar 
artery 

Hook  of  unciform  bone 

Deep  branch  of  ulnar  nerve- 

Ulnar  nerve 
Pisiform  bone 

Paluiaris  longus 
Styloid  process  of  ulna 

Ulnar  artery 


Deep  palmar  arch 

Anterior  annular  ligament 
Riiige  of  trapezium 
Radial  artery 

Median  nerve 
Styloid  process  of  radius 
—Radial  artery 

-  Flexor  carpi  radialis 


Fig.  928. — Palm  of  Hand. 

The  bases  of  the  first,  third,  and  fifth  metacarpals,  all  of  which  can  Ije  readily 
identified  on  the  dorsal  aspect,  furnish  a  sufficient  guide  to  the  line  of  the  carpo- 
metacarpal articulations.  At  the  base  of  the  third  metacarpal  is  a  tuljercle,  which 
can  be  felt  projecting  from  its  dorsal  aspect  at  a  point  If  in.  vertically  below  the 
tubercle  upon  the  back  of  the  lower  end  of  the  radius.  This  metacarpal  tubercle 
marks  the  insertion  of  the  extensor  carpi  radialis  brevior,  the  favourite  site  for 
the  development  of  a  "ganglion,"  which  may  frequently  be  ruptured  by  pressmg 
it  firmly  against  the  tubercle.  Anteriorly,  the  carpo- metacarpal  articulations 
correspond  to  the  lower  border  of  the  anterior  annular  ligament. 

The  ijrojiiinences  of  the  knuckles  are  formed  entirely  by  the  heads  of  the 
metacarpal  bones.  Anteriorly,  the  metacarpo-phalangeal  articulations  are  situated 
I  in.  above  the  level  of  the  web  of  the  fingers  ;  posteriorly,  the  joints  may  be  felt 


1300 


SUKFACE  AND  SUKGICAL  ANATOMY. 


as  a  groove  immediately  above  the  projecting  ridge  at  the  base  of  the  first 
phalanges.  A  well-marked  crease  crosses  obliquely  over  the  anterior  aspect  of  the 
metaearpo-phalangeal  joint  of  the  thumb.  To  cut  into  the  first  interphalangeal 
joints  from  the  front,  incise  along  the  highest  of  the  creases  in  front  of  the  joints ; 
whereas  to  cut  into  the  terminal  joints,  incise  along  the  loioesi  of  the  creases  in 
front  of  the  joints.  Posteriorly,  the  first  and  terminal  interphalangeal  articu- 
lations are  opposite  the  distal  of  the  various  creases  overlying  the  joints. 

The  most  important  muscular  landmarks  upon  the  front  of  the  forearm  are  the 
supinator   lougus,    the  flexor   carpi   radialis   and  the  pronator  radii   teres.     The 


Styloiil  process  of  third  metacarpal 

ItaJial  artery 
Extensor  longus  pollicis 
Extensor  carpi  radialis  longior 
Extensor  carpi  radialis  bre\') 


Base  of  fifth  metacarpal 


Styloid  process  of  ulna 


Extensor  communis  digitorum 


Extensor  minimi  digiti 
Extensor  carpi  ulnaris 


Extensor  brevis  pollicis^ 

Fig.  929.— Dorsal  Aspect  of  Hand. 

supinator  longus  is  thrown  into  prominence  by  flexing  the  semi-prone  forearm 
against  resistance.  At  the  junction  of  the  upyjer  and  middle  thirds  of  the  forearm 
the  pronator  radii  teres  passes  beneath  the  supinator  longus ;  between  the  two  is 
the  radial  artery.  The  tendon  of  the  flexor  carpi  radialis  forms  a  prominent 
landmark  descending  along  the  middle  of  the  anterior  aspect  of  the  forearm 
towards  the  ridge  of  the  trapezium;  the  tendon  of  tlie  palmaris  longus,  when 
present,  is  seen  to  its  inner  side. 

At  the  back  of  the  forearm  the  intermuscular  septum  between  tlie  radial  and 
common  extensors  corresponds  to  the  upper  part  of  a  line  extending  from  the 
external  epicondyle  of  the  humerus  to  the  tubercle  on  the  back  of  the  lower  end  of 
the  radius.     The  posterior  interosseous  nerve,  at  the  point  at  which  it  emerges  from 


THE  FOEEAKM  AND  HAND.  1301 

the  substance  of  the  supinator  brevis,  will  be  found  at  the  bottom  of  this  septum, 
2  in.  below  the  head  of  the  radius ;  below  this  point  the  septum  is  the  best  line 
along  which  to  cut  down  upon  the  posterior  surface  of  the  radius.  "Winding  across 
the  lower  third  of  this  surface  is  an  oblique  prominence  caused  Ijy  the  extensors 
of  the  metacarpal  bone  and  first  phalanx  of  the  thumb. 

The  flexor  sheaths  of  the  palm  and  of  the  digits  are  of  surgical  importance  in 
consequence  of  their  liability  to  suppurative  inflammation.  The  common  flexor  sheath 
begins  li  in.  above  the  annular  ligament,  under  which  it  extends  to  a  little 
below  the  middle  of  the  palm.  The  digital  flexor  sheaths  extend  from  the  bases  of 
the  terminal  phalanges  to  the  level  of  the  distal  transverse  crease  of  the  palm, 
opposite  the  necks  of  the  metacarpal  bones,  with  the  exception  of  the  sheath  of  the 
little  finger,  which  is  continuous  with  the  common  flexor  sheath  of  the  palm.  The 
sheath  of  the  flexor  longus  pollicis  extends  from  the  base  of  the  terminal  phalanx 
upwards  to  a  point  about  1  in.  above  the  annular  ligament ;  it  frequently  com- 
municates with  the  common  flexor  sheath.  From  this  anatomical  arrangement 
it  follows  that  suppuration  in  the  sheaths  of  the  little  finger  and  thumb  is 
specially  liable  to  spread  upwards  into  the  palm,  and  thence  underneath  the 
annular  ligament  into  the  forearm. 

The  pulsations  of  the  radial  artery  can  readily  be  felt  in  the  lower  third  of  the 
forearm,  midway  between  the  outer  border  of  the  radius  and  the  tendon  of  the 
flexor  carpi  radialis.  The  course  of  the  vessel  is  indicated  upon  the  surface  by 
a  line  extending  from  the  bifurcation  of  the  brachial  {h  in.  below  the  middle  of 
the  bend  of  the  elbow)  to  the  tubercle  of  the  scaphoid,  around  which,  and  below 
the  tip  of  the  styloid  process,  the  artery  winds  to  the  back  of  the  radial  side  of  the 
wrist ;  in  the  latter  situation  the  vessel,  after  passing  beneath  the  extensor  tendons 
of  the  thumb,  dips  into  the  palm  through  the  proximal  extremity  of  the  first  inter- 
osseous space.  Incisions  for  opening  or  resecting  the  wrist  are  planned  so  as  to 
avoid  the  vessel. 

The  upper  third  of  the  ulnar  artery  is  deeply  placed,  and  takes  a  curved  course 
from  the  bifurcation  of  the  brachial  towards  the  inner  part  of  the  anterior  surface  of 
the  forearm ;  the  lower  two-thirds  of  the  vessel  correspond  to  the  lower  two-thirds 
of  aline  drawn  from  the  front  of  the  internal  condyle  to  the  inner  border  of  the  pisiform 
bone.     The  course  of  the  ulnar  nerve  corresponds  to  the  whole  of  the  above  line. 

The  median  nerve  in  the  forearm  may  be  mapped  out  by  a  line  extending  from 
a  point  midway  between  the  centre  of  the  bend  of  the  elbow  and  the  internal  epi- 
condyle,  to  a  point  midway  between  the  styloid  processes ;  in  the  lower  third  of 
the  forearm  the  line  follows  the  inner  border  of  the  tendon  of  the  flexor  carpi 
radialis.  To  evacuate  pus  spreading  deeply  up  the  front  of  the  forearm,  the 
incisions  should  be  made  on  either  side  of  the  line  corresponding  to  the  median 
nerve.  The  radial  nerve  winds  to  the  back  of  the  forearm  round  the  outer  border 
of  the  radius  beneath  the  tendon  of  the  supinator  longus,  at  the  junction  of  the 
middle  and  lower  thirds  of  the  forearm.  The  summit,  or  most  distal  part  of  the 
superficial  palmar  arch,  corresponds  to  the  mid-point  of  a  line  extending  from  the 
middle  of  the  lowest  transverse  crease  of  the  wrist  to  the  root  of  the  middle 
finger ;  a  line  drawn  from  the  outer  border  of  the  pisiform  bone  across  the  hook 
of  the  unciform,  and  thence  in  a  curved  direction  downwards  and  outwards  to  this 
point,  corresponds  to  the  main  or  proximal  part  of  the  arch ;  the  first  and  fourth 
digital  branches  overlie  the  fifth  and  third  metacarpal  bones  respectively,  while 
the  second  and  third  overlie  the  fourth  and  third  interspaces  respectively.  The 
deep  arch  lies  almost  transversely,  midway  between  the  lower  border  of  the  anterior 
annular  ligament  and  the  superficial  arch.  The  radialis  indicis  corresponds  to  the 
radial  border  of  the  index -finger. 

The  ulnar  nerve  and  the  commencement  of  its  two  divisions  lie  immediately  to 
the  inner  side  of  the  superficial  palmar  arch,  so  that  the  pisiform  and  the  hook  of 
the  unciform  are  the  guides  to  the  nerve.  The  median  nerve  emerges  from  beneath 
the  annular  ligament  opposite  the  inner  edge  of  the  thenar  eminence,  while  the 
digital  branches  to  the  thumb  follow  its  lower  margin.  Incisions  for  the  removal 
of  foreign  bodies  may  therefore  be  made  into  the  thenar  with  greater  freedom 
than  into  the  hypo-thenar  eminence. 


1302  SUKFACE  AND  SUEGICAL  ANATOMY. 

Incisions  to  evacuate  deep-seated  pus  in  the  palm  may  be  made  in  one  or  more  of 
the  following  situations :  (1)  over  the  lower  two-thirds  of  the  second  metacarpal  bone  ;  (2) 
over  the  distal  half  of  the  fourth  metacarpal  bone ;  (3)  from  the  proximal  part  of  the  first 
incision  an  opening  may  be  made  through  the  first  interosseous  space  on  to  the  dorsum, 
care  being  taken  to  keep  below  the  radial  artei-y  ;  (4)  a  longitudinal  incision  between  the 
median  and  ulnar  nerves,  on  the  pi'oximal  side  of  the  superficial  palmar  arch.  At  the 
wrist  a  longitudinal  incision  may  be  made  immediately  internal  to  the  palmaris  longus 
tendon,  thus  falling  between  the  line  of  the  median  nerve  and  the  ulnar  artery.  To  open 
the  digital  flexor  sheaths,  incisions  are  made  along  the  middle  of  the  palmar  surface  of  the 
fingers  opposite  the  first  and  second  phalanges.  The  collateral  digital  vessels  and  nerves 
descend  along  the  lateral  aspects  of  the  fingers,  nearer  the  flexor  than  the  extensor 
surfaces.  In  cutting  down  upon  the  dorsal  aspects  of  the  phalanges,  the  incisions  should 
be  made  to  one  or  other  side  of  the  extensor  tendon,  preferably  upon  the  ulnar  side,  to  avoid 
division  of  the  insertions  of  lumbrical  muscles.  The  subcutaneous  tissue  of  the  palmar 
aspect  of  the  terminal  phalanges  is  connected  by  fibrous  processes  with  the  periosteum ; 
hence  the  frequency  of  necrosis  of  the  terminal  phalanx  in  suppurative  inflammations 
in  this  region. 

THE   LOWEE  EXTEEMITY. 
THE  BUTTOCK. 

The  region  of  the  hip  or  buttock  extends  from  the  crest  of  the  ilium  above  to 
the  gluteal  fold  below.  The  highest  point  of  the  iliac  crest,  situated  a  little  behind 
its  middle,  is  on  a  level  with  the  fourth  lumbar  spine ;  the  anterior  superior  spine 
of  the  ilium  is  directed  forwards,  and  belongs  to  the  groin,  which  it  limits  exter- 
nally ;  the  posterior  superior  spine,  situated  at  the  bottom  of  a  dimple  or  small 
depression,  is  on  a  level  with  the  second  sacral  spine,  and  corresponds,  therefore,  to 
the  middle  of  the  sacro-iliac  joint.  Two  and  a  half  inches  behind  the  anterior 
superior  spine  is  a  prominence  upon  the  outer  lip  of  the  iUac  crest ;  this  pro- 
minence, which  is  termed  the  tubercular  point,  is  the  most  external  part  of  the  crest, 
and  have  been  referred  to  in  dealing  with  the  surface  anatomy  of  the  abdomen. 
A  hand's  breadth  below  the  tubercle  of  the  crest  is  the  great  trochanter  of  the 
femur,  the  most  external  bony  landmark  of  the  hip ;  its  anterior  and  posterior 
borders  are  best  felt  between  the  fingers  and  thumb,  while  the  limb  is  slightly 
abducted  to  relax  the  ilio-tibial  band,  and  if  the  thigh  be  now  rotated,  it  will  be 
noted  that  the  trochanter  rotates  around  the  segment  of  a  circle,  the  radius  of 
which  is  formed  by  the  head  and  neck  of  the  femur ;  in  non-impacted  fractures  of 
the  neck  of  the  femur  the  trochanter  rotates  around  the  segment  of  a  much 
smaller  circle.  Nelatons  line,  drawn  from  the  anterior  superior  spine  to  the  most 
prominent  part  of  the  ischial  tuberosity,  crosses  the  hip  at  the  level  of  the  upper 
border  of  the  great  trochanter ;  this  line  is  employed  to  ascertain  the  presence 
or  absence  of  upward  displacement  of  the  trochanter.  Chiene  demonstrates  the 
relative  height  of  the  trochanters  by  stretching  two  tapes  across  the  front  of 
the  pelvis,  one  between  the  anterior  superior  spines,  and  the  other  between  the 
upper  borders  of  the  trochanters ;  the  lower  tape  will  converge  towards  the  upper 
on  the  side  of  the  upward  displacement.  A  line  prolonging  the  anterior  border  of 
the  great  trochanter  vertically  upwards  touches  the  iliac  crest  at  the  tubercular 
point.  The  ischial  tuberosity,  in  the  erect  posture,  is  overlapped  by  the  lower 
border  of  the  gluteus  inaximus;  its  most  prominent  part  is  felt  a  little  above  the 
inner  part  of  the  gluteal  fold.  If  the  hip  be  rotated  inwards,  the  lesser  trochanter 
of  the  femur  may  be  felt  by  deep  palpation  above  the  outer  end  of  the  gluteal 
fold ;  it  corresponds  to  the  interval  between  the  lower  border  of  the  quadratus 
femoris  and  the  upper  border  of  the  adductor  magnus,  and  therefore,  also,  to  the 
level  of  the  internal  circumflex  artery. 

The  lower  border  of  the  gluteus  maximus  lies  a  little  above  the  gluteal  fold  inter- 
nally, crosses  it  about  its  middle,  and  is  continued  downwards  and  outwards  to 
meei  the  upper  end  of  the  furrow  of  the  external  intermuscular  septum,  at  the 
junction  of  the  upper  and  middle  thirds  of  the  femur.  The  inner  borders  of  the 
two  great  gluteal  muscles  are  separated  by  the  deep  gluteal  cleft,  which  extends 
upwards  and  backwards  from  the  perineum  to  the  level  of  the  fourth  sacral  spine, 


THE  BACK  OF  THE  THIGH. 


1303 


\yhere  it  opens  out  into  the  triangle  upon  the  back  of  the  sacrum.  Anteriorly  the 
buttock  is  limited  by  the  prominence  of  the  tensor  fasciae  femoris  muscle,  which 
extends  downwards  and  somewhat  backwards  from  the  anterior  end  of  the  crest,  to 
join  the  ili'j-tibial  band  below  the  root  of  the  great  trochanter. 

The  gluteal  artery  reaches  the  buttock  immediately  below  the  upper  border  of 
the  great  sacro-sciatic  foramen,  opposite  a  point  corresponding  to  the  junction  of 
the  upper  and  middle  thirds  of  a  line  drawn  from  the  posterior  superior  iliac  spine 
to  the  up];>er  border  of  the  great  trochanter.  To  expose  the  vessel,  the  incision 
should  be  made  along  tliis  line,  which  has  the  advantage  of  running  parallel  to  the 
ribres  of  the  gluteus  rnaximus,  as  well  as  parallel  to  the  interval  between  the 
gluteus  medius  and  pyriformis  muscles. 

The  great  sciatic  nerve  enters  the  buttock  at  a  point  corresponding  to  the  junc- 
tion of  the  upper  and  middle  thirds  of  a  line  drawn  from  the  posterior  superior 
iliac  spine  to  the  iscliial  tul>erosity ;  from  this  point  the  nerve  passes  downwards 
and  slightly  outwards  upon  the  ischium  to  a  point  midway  between  its  tuberosity 
and  the  great  trochanter.  The  spine  of  the  ischium  and  the  pudic  vessels  are 
situated  opposite  the  junction  of  the  lower  and  middle  thirds  of  the  above  hne.  The 
vessels  and  ner\-es  which  enter  the  buttock  through  the  great  sacro-sciatic  foramen 
beloic  the  pyriformis,  may  be  exposed  through  an  incision  below  and  parallel  to 
that  above  described  for  exposing  the  gluteal  artery,  viz.  an  incision  corresponding 
to  the  middle  two-fourths  of  a  line  extending  from  the  upper  end  of  the  gluteal 
cleft  to  the  root  of  the  great  trochanter ;  the  deep  landmarks  are  the  lower  border 
of  the  pyriformis  and  the  root  of  the  ischial  spine. 


THE  BACK  OF  THE  THIGH. 

The  hamstring  muscles,  and  especially  the  tendon   of  the  biceps  and  semi- 
Femur         Rectus  femoris 

Vastus  intern  as 

'  Nerve  to  vastus  intemus 

Internal  saphenous  nerve 
f      Sartorius 

Femoral  vein 

Femoral  artery 

Adductor  longus 

Internal  saphenous  vein 


Gracilis 


Vastus  extemus 


External  intermuscular  septum 

Great  sciatic  nerve      Biceps 


.\dfluctor  magnus 
Profunda  artery 
Semitendinosus 
Semimembranosus 


Adductor  brevis 
Fig.  930. — SECxioy  xHRorcH  Thigh  at  the  Level  of  the  Upper  Part  of  Hunter's  Canal. 

tendinosus    are  thrown  into  prominence  either  by  standing  on  tiptoes  with  the 


1304 


SUEFACE  AND  SURGICAL  ANATOMY. 


knees  slightly  liexed,  or  ]jy  flexing  the  leg  against  resistance.  By  throwing  the 
hamstrings  into  action,  the  line  of  the  external  intermuscular  septum  of  the  thigh  is 
indicated  by  a  well-marked  furrow,  extending  from  the  lower  edge  of  the  insertion 
of  the  gluteus  maximus  to  the  outer  aspect  of  the  knee ;  behind  this  furrow  is  the 
biceps,  and  in  front  of  it  is  the  large  vastus  externus,  covered  by  the  strong  ilio- 
tibial  portion  of  the  fascia  lata.  The  shaft  of  the  femur  may  be  cut  down  upon 
along  the  whole  length  of  this  furrow  with  least  injury  to  the  soft  parts  ;  the  trigone 
of  the  femur  and  deep-seated  popliteal  abscesses  are  most  conveniently  reached 
through  the  lower  part  of  the  same  incision.  The  course  of  the  great  sciatic  nerve 
corresponds  to  the  upper  half  of  a  line  extendiug  from  a  point  midway  between 
the  tuberosity  of  the  ischium  and  the  great  trochanter  to  the  centre  of  the  popliteal 
space.  The  nerve  enters  the  thigh  under  cover  of  the  outer  border  of  the  biceps, 
whereas  the  small  sciatic,  which  takes  the  same  line,  descends  superficial  to  the 


Siibsj-novial  fat 


stus  internus 


Adductor  tubercle 


Deep  branch  of 

anasto;iiotica  magna 

artery 

Tendon  of  adductor 

mat^nus 


Sartorius 


Quadriceps  extensor  tend^m 


Synovial  jjouch  of  kne^ 


Vastus  externus — , 
nio-tibial  band 


Superior  external 
articular  artery 


Popliteal  arter} 

Biceps 

Popliteal  vein 
External  popliteal  ner\  e\ 

Internal  popliteal  nei\( 

Lymjihatic  gland 


Gracilis 
Semimembranosus  Seniitendinosus 

Fig.  931.— Section  throuoh  the  Thigh  immediately  above  the  Patella. 

biceps,  between  it  and  the  fascia  lata.  In  the  operation  of  stretching  the  great 
sciatic  the  nerve  is  cut  down  upon  immediately  below  the  lower  border  of  the 
gluteus  maximus.  The  surgeon,  standing  on  the  side  of  the  patient  opposite  to 
the  leg  to  be  operated  upon  (Chiene),  makes  an  incision  in  the  line  of  the  nerve 
through  the  integuments  and  fascia  lata,  and,  sweeping  the  index  -  finger 
round  the  outer  border  of  the  biceps,  hooks  up  the  nerve  as  it  lies  between  that 
muscle  and  the  adductor  magnus.  The  external  popliteal  nerve  may  be  rolled  under 
the  finger  as  it  descends  immediately  behind  the  tendon  of  the  biceps  and  the  head 
of  the  fibula ;  so  close  is  the  nerve  to  the  tendon  that  the  latter  should  be  divided,  in 
cases  where  this  is  necessary,  by  the  open  method  rather  than  subcutaneously. 

Absces.ses  may  reacli  the  flexor  compartment  of  the  tliigh  from  various  sources,  viz.  :  (1)  from 
the  posterior  a.spect  of  the  hip-joint :  (2)  from  the  pelvis  tlirough  the  great  sacro-sciatic  foramen  ; 
(3)  from  one  or  other  of  the  burste  under  the  gluteus  maximus  ;  (4)  from  the  front  of  the  hip-joint 
by  passing  backwards  under  the  tensoi-  fasciie  femoris  ;  or  by  winding  Vjackwards  beneath  the  neck 
of  the  femur,  and  through  the  interval  between  the  quadratus  femoris  and  the  adductor  magnus  ; 
(5)  from  the  iliac  fossa  under  Poupart's  ligament  into  Scarpa's  triangle,  and  thence  to  the  back  of 


THE  FRONT  OF  THE  THIGH. 


1305 


the  thigh  by  one  or  other  of  the  routes  already  mentioned  ;  (6)  the  pus  may  spread  upwards  from 
the  trigone  of  the  femur,  the  knee,  a  popliteal  gland,  or  from  a  bursa. 


THE   POPLITEAL   SPACE. 

When  the  knee  is  extended  the  popliteal  fascia  is  put  upon  the  stretch,  and 
obliterates  the  hollow  of  the  pophteal  space;  by  flexing  the  knee  the  fascia  is 
relaxed,  and  the  fingers  may  be  pressed  deeply  into  the  upper  or  femoral  division 
of  the  space  ;  as  a  rule,  the  pulsations  of  the  popliteal  artery  can  be  felt.  Beneath 
the  semitendinosus  is  the  fleshy  semimembranosus,  which  bulges  into  the  space  and 
overlaps  the  upper  part  of  the  popliteal  artery.  Between  the  semimembranosus  and 
the  inner  head  of  the  gastrocnemius  is  the  most  important  bursa  in  the  popliteal 
region  ;  it  not  infrequently  liecomes  distended  with  fluid,  and  then  presents  usually 

Gluteu.s  medius 

Tubpiclc  of  iliac  crest     I 

Anterior  superior  iliac  spine  I 

Linea  semilunaris 


Sartorius 
Rectus  femorisi 
Tensor  fascise.  fenioris  | 
Femoral  artery  at  apex  of  Scarpa's  tri.Tnsle 
RectU'.  femori-. 
Lower  end  of  femoral  arttTj 

Vastus  internus 


Internal  semi- 
lunar cartilage 


Tensor  fasciee 

femoris 
Vastus  externus 
Sartorius 
ntenial  abdominal  ring 


Fk;.  9.32.— The  Thk.h  and  Gh(ii.n. 

a  more  or  less  sausage-shaped  outline ;  according  to  Holden,  the  bursa  communi- 
cates with  the  cavity  of  the  knee-joint  in  one  subject  out  of  five. 

To  map  out  the  line  of  the  popliteal  vessels  and  the  internal  popliteal  nerve,  draw 
a  Une  from  a  point  a  little  internal  to  the  upper  angle  of  the  space  to  a  point  mid- 
way between  the  condyles  of  the  femur,  and  thence  down  the  middle  of  the  space 
to  the  level  of  the  lower  part  of  the  tubercle  of  the  tibia.  The  internal  popliteal 
nerve  lies  immediately  beneath  the  deep  fascia  ;  the  artery  is  separated  from  the 
trigone  of  the  femur  by  a  quantity  of  fat.  The  popliteal  lymphatic  glands  lie 
beneath  the  popliteal  fascia,  one  upon  the  internal  popliteal  nerve,  the  others  deeply 
in  the  space  (Leaf). 

THE   FRONT    OF    THE   THIGH. 

Between  the  front  of  the  thigh  and  the  abdomen  is  the  fold  of  the  groiii,  at  the 
bottom  of  which  Poupart's  ligament  can  be  felt  as  a  tense  band,  stretching  from  the 
anterior  superior  spine  of  the  ilium  to  the  spine  of  the  pubis.     The  anterior  superior 


1306  SUKFACE  AND  SUEGIOAL  ANATOMY. 

spine  looks  directly  forwards ;  comparative  measurements  of  the  lower  extremities 
are  made  by  stretching  a  tape  from  it  to  the  tip  of  one  or  other  of  the  malleoli,  care 
being  taken  that  the  pelvis  is  horizontal,  and  the  limbs  in  corresponding  positions. 
The  pubic  spine  is  felt  nnder  the  upper  and  outer  part  of  the  mons  Veneris  and  at 
a  corresponding  point  in  the  male ;  between  the  spine  and  the  symphysis  is  the 
crest  of  the  pubis,  the  two  crests  together  forming  a  rounded  subcutaneous  bony 
ridge.  A  line  extending  from  the  pubic  spine  horizontally  outwards  across  the  front 
of  the  thigh  crosses  the  front  of  the  hip-joint  at  the  level  of  the  lower  part  of  the  head 
of  the  femur.  The  cord-like  tendon  of  the  adductor  longus  is  readily  felt,  and  a 
point  about  1  in.  below  the  pubic  spine  is  selected  for  performing  the  operation 
of  subcutaneous  tenotomy  of  the  tendon. 

The  centre  of  the  saphenous  opening  is  situated  Ih  in.  below  and  external 
to  the  pubic  spine ;  it  overhes  the  inner  (hernial)  and  middle  (venous)  com- 
partments of  the  femoral  sheath ;  behind  the  outer  border  of  the  opening  is  the 
arterial  compartment  of  the  sheath ;  crossing  over  the  lower  border  is  the  termina- 
tion of  the  long  saphenous  vein.  A  femoral  hernia  makes  its  way  into  the  thigh 
beneath  the  upper  edge  of  the  opening.  The  course  of  the  long  saphenous  vein  in 
the  thigh  is  indicated  by  a  line  extending  from  the  adductor  tubercle  of  the  internal 
condyle  of  the  femur  to  the  lower  part  of  the  saphenous  opening. 

The  horizontal  or  inguinal  chain  of  lymphatic  glands  can  usually  be  felt  along,  and 
a  little  below,  the  line  of  Poupart's  ligament ;  when  the  glands  are  inflamed  the 
surgeon  should  not  neglect  to  examine  the  buttocks  and  anus  as  well  as  the 
external  genitals.  The  vertical  or  femoral  chain  lies  in  close  relation  to  the  upper 
end  of  the  long  saphenous  vein.  Deeper  glands  also  are  met  with  beneath  the 
cribriform  fascia,  close  to  the  inner  side  of  the  femoral  vein,  and  there  is  generally 
one  in  the  crural  canal.  To  clear  out  the  glands  in  the  groin  an  incision  should 
be  made  parallel  to,  and  a  finger's  breadth  below,  the  whole  length  of  Poupart's 
ligament. 

To  map  out  the  course  of  the  femoral  artery,  the  thigh  being  slightly  flexed  and 
rotated  outwards,  draw  a  line  from  the  mid-point  between  the  anterior  superior 
iliac  spine  and  the  symphysis  pubis  to  the  adductor  tubercle  at  the  upper  and  back 
part  of  the  internal  condyle ;  rather  less  than  the  upper  third  of  this  line  corre- 
sponds to  the  femoral  artery  in  Scarpa's  triangle,  while  rather  more  than  its  middle 
third  corresponds  to  the  artery  as  it  lies  in  Hunter's  canal.  The  seat  of  election 
for  ligature  of  the  vessel  is  at  the  apex  of  Scarpa's  triangle.  To  compress  the 
common  femoral,  pressure  should  be  made  directly  backwards  against  the  pubic 
eminence,  and  not  against  the  head  of  the  femur ;  to  compress  the  femoral  in 
Hunter's  canal,  pressure  should  be  made  outwards  against  the  inner  surface  of  the 
shaft  of  the  femur. 

On  the  outer  aspect  of  the  thigh  the  fascia  lata  is  thick,  aponeurotic,  and 
loosely  attached  to  the  vastus  externus ;  hence  the  tendency  of  abscesses  to  travel 
downwards  beneath  it  towards  the  knee.  The  sartorius,  which  forms  the  most  im- 
portant muscular  landmark  of  the  thigh,  may  be  thrown  into  prominence  by  main- 
taining the  thigh  unsupported,  flexed,  and  slightly  rotated  outwards.  Observe  that 
in  the  uyjper  third  of  the  thigh  it  forms  the  outer  boundary  of  Scarpa's  triangle  ;  in 
the  middle  third  it  is  placed  over  Hunter's  canal ;  while  in  the  lower  third  it 
lies  in  front  of  the  inner  hamstrings.  External  and  adjacent  to  the  upper  part  of 
the  sartorius  is  the  prominence  of  the  tensor  fasciae  femoris,  which,  as  it  descends, 
diverges  from  the  sartorius ;  in  the  angle  between  the  two  the  tendon  of  the  rectus 
may  be  felt  as  it  overlies  the  lower  part  of  the  anterior  aspect  of  the  capsule  of  the 
hip -joint. 

The  inner  aspect  of  the  lowei-  half  of  the  shaft  of  the  femur  may  be  conveniently  cut  down 
upon  through  the  vastus  internus,  where  it  comes  to  the  surface  T)etween  the  sartorius  and  rectus 
muscles ;  the  incision  should  be  made  in  the  direction  of  a  line  extending  from  a  point  midway 
between  the  inner  border  of  the  patella  and  the  adductor  tubercle,  to  the  anterior  superior  iliac 
spine. 

The  front  of  the  hip-joint  may  be  reached  through  an  incision  downwards  from  the  anterior 
superior  iliac  spine,  either  along  the  inner  or  the  outer  border  of  the  sartorius  ;  in  the  former 
case  the  deeper  part  of  the  dissection  passes  between  the  iliacus  and  the  inner  border  of  the  rectus, 
while  in  the  latter  case  the  joint  is  reached  external  to  the  rectus  tendon,  between  it  and  the 


THE  l^NEE. 


1307 


anterior  borders  of  the  gluteus  meclius  and  mininuis  muscles.  The  ascending  branch  of  the 
external  circumflex  artery  crosses  the  capsule  parallel  to,  and  inmiediately  above,  the  anterior 
intertrochanteric  line.  The  ilio-psoas  crosses  the  anterior  and  the  inner  jjart  of  the  cajisule  ; 
between  the  two  is  a  bursa,  which  frequently  communicates  with  the  joint  througli  the  tliin  ])art 
of  the  capsule  internal  to  the  ilio-femoral  band  ;  it  is  by  way  of  this  communication  that  a  jjsoas 
abscess  occasionally  gives  rise  to  secondary  tubercular  disease  of  tlie  liip-joint.  One  of  the 
commonest  situations  to  meet  with  an  abscess  in  hip-joint  disease  is  in  the  cellular  tissue  and  fat 
under  the  tensor  fascite  femoris  ;  or  the  pus  may  pass  below  and  to  the  inner  side;  of  the  neck  of 
the  femur,  and  thence  along  the  course  of  the  internal  circumflex  artery  to  the  liack  of  the 
thigh.  To  tap  or  explore  the  hip-joint,  the  i^uncture  should  be  made  in  the  interval  between  the 
sartorius  and  the  tensor  fascife  femoris,  2  to  3  in.  l)elow  the  anterior  superior  iliac  S2:)ine  ;  if 
the  instrument  is  then  pushed  upwards,  inwards,  and  backwards  Ijeneath  the  tendon  of  the  rectus, 
it  will  pass  througli  tlie  capsule  a  little  above  the  anterior  intertrochanteric  line.  Regarded 
from  the  point  of  view  of  dislocation,  the  regions  of  the  cotyloid  notch  and  of  the  inferior  jiart 
of  the  capsule  are  the  weak  points  in  the  joint ;  it  follows,  therefore,  that  abduction  favours 
dislocation  by  bringing  the  head  of  the  femur  into  relation  with  these  two  weak  areas. 


THE  KNEE. 

With  the  knee  extended  and  the  quadriceps  relaxed,  the  patella  can  be  readily 
outlined  and  moved  from  side  to  side 
upon  the  femoral  condyles.  On 
contracting  the  quadriceps  its  tendon 
springs  forwards  and  is  felt  as  a 
tense  band  above  the  patella  ;  while 
the  patellar  ligament,  which  has  be- 
come tense  and  prominent,  may  be 
traced  to  the  lower  part  of  the 
tubercle  of  the  tibia.  In  front  of 
the  lower  part  of  the  patella  and  of 
the  upper  part  of  the  patellar  liga- 
ment is  the  pre-patellar  bursa,  into 
which  effusion  takes  place  in  the 
condition  known  as  housemaid'sknee. 
Beneath  and  on  either  side  of  the 
patellar  ligament  is  a  well-circum- 
scribed pad  of  fat,  palpation  of  which 
gives  rise  to  a  feeling  closely  re- 
sembling true  fluctuation.  In  ex- 
tension, only  the  lower  pair  of 
articular  facets  of  the  patella  are 
in  contact  with  the  trochlear  surface 
of  the  femur.  In  semiflexion  the 
middle  pair  of  facets  rests  upon  the 
trochlea ;  in  this  position  the  inner 
margin  of  the  internal  condyle,  the 
upper  border  of  the  inner  tuberosity 
of  the  tibia,  and  the  low^er  part  of 
the  patella  are  all  distinctly  visible, 
and  together  bound  a  triangular  de- 
pression, which  overlies  the  line  of 
the  joint  and  contains  the  anterior 
part  of  the  internal  semilunar  car- 
tilage ;  it  is  in  this  triangle  that  the 
surgeon  searches  for  a  displaced  or 
thickened  internal  semilunar  car- 
tilage, for  a  loose  body,  and  for 
"  lipping  "  of  the  edge  of  the  articular 
cartilage  in  chronic  osteo- arthritis. 
A  similar,  but  less  well  defined, 
triangle  may  be  felt  immediately 
external  to  the  lower  edge  of  the  patella 


Gracilis 

Rectus  femoris 
Sartorius 

Vastus  externus 
Vastus  interims 


Quadriceps  extensor 

tendon 

Upper  border  of 

patella 

Patella 

Uio-tibial  band 

Internal  condyle 
Internal  semilunar 
cartilage 
Ligamentuui  jjatellse 

Pad  of  fat 
Internal  tuberosity 
of  tibia 

Head  of  fibula 
Tubercle  of  tibia 


—  Inner  border  of  tibia 


Crest  of  tibia 
Gastrocnemius 


Soleus 


Fig.  933. — Anterior  Aspect  of  Knee. 


When  the  quadriceps  is  thrown  into 


1308  SURFACE  AND  SURGICAL  ANATOMY. 

suddeu  or  violent  contraction,  as  in  preventing  oneself  from  falling  backwards,  the 
patella  may  be  transversely  fractured  at  the  moment  of  partial  flexion.  In  full 
flexion  almost  the  whole  of  the  trochlear  surface  of  the  condyles  is  exposed  to 
palpation,  covered,  however,  by  the  stretched  quadriceps  tendon. 

The  upper  part  of  the  inner  surface  of  the  internal  condyle  is  overlapped  by  the 
muscular  prominence  of  the  lower  fibres  of  the  vastus  internus.  Leading  upwards 
from  the  internal  condyle  is  a  sKght  furrow,  corresponding  to  the  interval  between 
the  lower  part  of  the  vastus  internus  and  the  sartorius ;  at  the  bottom  of  the  furrow 
the  cord-like  tendon  of  the  adductor  magnus  may  readily  be  felt,  and  followed  down 
to  its  insertion  into  the  adductor  tubercle  :  the  latter,  situated  at  the  junction  of  the 
internal  supracondyloid  ridge  with  the  upper  and  back  part  of  the  internal  condyle, 
marks  the  level  of  the  epiphysial  cartilage.  Anteriorly  and  posteriorly  the  epi- 
physial cartilage  lies  immediately  above  the  highest  part  of  the  articular  cartilage. 

Disease  of  the  lower  end  of  the  diaphysis  of  the  femur  generally  invades  the  trigone  of  the 
femur  and  the  popliteal  space  rather  than  the  cavity  of  the  knee-joint.  In  Macetven's  operation 
for  hiocJi-Jmee,  the  incision  (through  which  the  osteotome  is  introduced  to  divide  the  femur)  is 
carried  dovTX  to  the  bone  through  the  vastus  internus  a  little  above  the  internal  condyle,  a  finger's 
breadth  above  the  summit  of  the  trochlea,  to  avoid  injury  to  the  epiphysial  cartilage,  and  the 
same  distance  in  front  of  the  adductor  tendon,  to  avoid  injury  to  the  deep  branch  of  the  anasto- 
motic artery. 

Below  the  internal  condyle  is  the  subcutaneous  inner  tuberosity  of  the  tibia 
across  which  the  tendons  of  the  sartorius,  gracilis,  and  semitendinosus  pass  to  their 
insertion.  Between  the  above  tendons  and  the  inner  head  of  the  gastrocnemius  is 
a  groove  which  winds  downwards  and  forwards  from  the  popliteal  space  ;  an  incision 
along  this  groove  will  expose  the  long  saphenous  vein  and  nerve  and  the  superficial 
branch  of  the  anastomotic  artery. 

On  the  outer  side  of  the  knee  is  the  ilio-tibial  band,  which,  after  crossing  and 
obscuring  the  line  of  the  joint,  is  attached  to  the  outer  tuberosity  of  the  tibia.  By 
semiflexion  of  the  knee  the  posterior  border  of  the  band  is  thrown  into  relief,  and  a 
well-marked  furrow  intervenes  between  it  and  the  prominent  tendon  of  the  biceps ; 
the  lower  part  of  the  shaft  of  the  femur  and  the  trigone  may  be  reached  through 
an  incision  along  this  furrow.  Under  cover  of  the  ilio-tibial  band,  as  it  crosses  the 
line  of  the  joint,  are  the  external  semilunar  cartilage,  the  inferior  external  articular 
artery,  and  the  external  lateral  ligament.  The  head  of  the  fibula,  with  the  tendon  of 
the  biceps  passing  to  be  inserted  into  it,  are  rendered  distinctly  visible  by  semi- 
flexing  the  knee  ;  the  former  lies  on  a  level  with  the  tubercle  of  the  tibia,  1|-  in. 
behind  and  a  little  below  the  most  prominent  part  of  the  outer  tuberosity 
of  the  tibia.  Immediately  below  the  head  of  the  fibula  is  the  termination  of  the 
external  popliteal  nerve,  which  is  liable  to  be  contused  from  blows,  and  in 
fractures  of  the  neck  of  the  fibula. 

The  synovial  membrane  of  the  knee-joint  extends  downwards  anteriorly  as  far  as  the 
level  of  the  upper  border  of  the  tibia ;  posteriorly,  it  dips  downwards  for  a  short  distance 
behind  the  popliteal  notch  of  the  tibia,  to  form  a  small  cul-de-sac,  the  close  relation  of 
which  to  the  popliteal  artery  must  be  borne  in  mind  in  performing  the  operation  of 
excision  of  the  knee.  Anteriorly,  the  synovial  cavity  extends  upwards  beneath  the  quadri- 
ceps in  the  form  of  a  pouch,  wliich  reaches  neai'ly  two  inches  above  the  articular  surface 
of  the  femur;  posteriorly,  there  is  no  extension  of  the  synovial  cavity  upwards  above  the" 
condyles ;  laterally,  the  synovial  membrane  covers  the  anterior  third  of  the  outer  surface 
of  each  condyle. 

In  effusion  into  the  knee-joint  the  hollows  become  obliterated,  the  patella  is  floated  up,  and 
fluctuation  may  be  obtained  above,  below,  and  to  either  side  of  tlie  patella. 

To  pass  a  tube  through  the  knee-joint  for  drainage,  two  short  vertical  incisions  should 
be  made — one  on  each  side  of  the  joint  at  the  Ittvel  of  tlie  upper  part  of  the  patella,  and 
a  finger's  breadth  behind  its  lateral  edges.  In  arthrectomy  of  tlie  knee  for  tubercular  disease,  the 
subsynovial  fat  facilitates  the  separation  of  tlie  sujuapatellaT  i)ou(h  from  tlie  lower  and  anterior 
part  of  the  shaft  of  the  femur  ;  to  expose  the  pouches  behind  the  condyles,  the  crucial  ligaments 
must  be  divided. 

THE  LEG 

The  inner  surface  of  the  tibia  is  subcutaneous  throughout,  hence  the  seat  of  a 
fracture  of  the  shaft  is,  as  a  rule,  easily  felt,  and  the  lower  extremity  of  the  upper 


THE  LEG. 


1309 


Ilio-tibial  band 


Biceps  tendon 


External  condyle 


Vastus  externus 


Quadriceps  extensor 
u-ndon 


atella 

J-^xlernal  tuberosity 
of  tibia 
I.igamentum  patellip 

Tubercle  of  tibia 


Tibialis  anticus 


fragment  is  liable  to  perforate  the  skin.  The  skin  over  the  lower  half  of  this 
surface  is  the  commonest  seat  of  varicose  and  callous  ulcers,  which  are  frequently 
prevented  from  healing  by  adhesion  of  the  tloor  of  the  ulcer  to  the  periosteum. 

The  shaft  of  the  fibula,  situated  on  a  plane  posterior  to  that  of  the  tibia,  is,  with 
the  exception  of  the  triangular  subcutaneous  surface  above  the  external  malleolus, 
deeply  placed  amongst  the 
muscles.  To  examine  the 
fibula,  the  surgeon  should 
stand  on  the  opposite  side 
of  the  patient  and  manipu- 
late the  bone  along  the  line 
of  the  intermuscular  septum 
between  the  peronei  and  the 
muscles  of  the  calf. 

The  greater  fulness  of 
the  antero- external  surface 
of  the  leg,  as  compared  with 
its  inner  surface,  is  due  to 
the  presence  of  the  extensor 
and  peroneal  groups  of 
muscles.  When  these 
groups  are  thrown  into 
action,  the  individual 
muscles  are  mapped  out 
upon  the  surface  by  the 
grooves  corresponding  to 
their  intermuscular  septa. 
The  posterior  peroneal  sep- 
tum is  seen  as  a  well-marked 
furrow,  extending  from  the 
posterior  aspect  of  the  head 
of  the  fibula  to  the  hollow 
behind  the  external  mal- 
leolus ;  in  front  of  it  are 
the  peronei  muscles,  the 
long  us  giving  rise  to  a  pro- 
minence on  the  upper  half 
of  the  leg,  while  the  Irevis 
is  prominent  on  the  lower 
half:  behind  the  septum  is 
a  prominence  formed  by 
the  outer  border  of  the 
soleus,  which  projects 
beyond  that  of  the  gastro- 
cnemius. 

It  is  along  the  line  of 
the  posterior  peroneal  inter- 
muscular septum  that  in- 
cisions should  be  made  to 
expose  the  fibula;  to  avoid  the  musculo -cutaneous  nerve,  however,  the  incision 
must  not  extend  higher  than  1  in.  below  the  head  of  the  fibula. 

The  furrow  between  the  extensors  and  the  two  peronei,  the  anterior  peroneal 
septum,  is  much  less  distinct,  and  runs  in  a  line  from  the  anterior  border  uf  the 
head  of  the  fibula  to  the  anterior  border  of  the  external  malleolus  :  the  cutaneous 
portion  of  the  musculo-cutaneous  nerve  corresponds  to  the  lower  half  of  this  line. 
At  the  junction  of  the  middle  and  lower  thirds  of  the  leg  the  extensor  muscles 
incline  inwards  over  the  anterior  surface  of  the  tibia. 

The  anterior  tibial  artery  reaches  the  front  of  the  interosseous  membrane  2  in. 
below  the  tubercle  of  the  tibia  ;  in  the  upper  two-thirds  of  its  course  it  lies  upon  the 


Peroueus  tertius 


Fig.  yo4. — Outer  Aspect  of  Knee  and  Lei; 


1310 


SUEFACE  AND  SUEGICAL  ANATOMY. 


iuterosseous  membrane,  while  in  its  lower  third  it  winds  on  to  the  front  of  the  tibia, 
to  terminate  at  a  point  opposite  the  ankle-joint,  midway  between  the  two  malleoli. 
Incisions  to  expose  the  vessel  should  strike  the  outer  Ijorder  of  the  tibialis  anticus, 
which  corresponds  to  a  line  drawn  from  a  point  midway  l^etween  the  external 
tuberosity  of  the  tibia  and  the  head  of  the  fibula,  to  the  termination  of  the  vessel. 

When  the  muscles  of  the  calf  are  thrown  into  action,  a  groove  is  seen  between 
the  two  heads  of  the  gastrocnemius,  the  fleshy  fibres  of  which  extend  a  little  below 
the  middle  of  the  leg.  The  fleshy  fibres  of  the  soleus  extend  to  the  junction 
of  the  middle  and  lower  thirds  of  the  leg,  and  project  l^eyond  the  margins  of  the 
gastrocnemius.  The  narrowest  part  of  the  tendo  AcMUis  is  situated  opposite  the 
bases  of  the  malleoli,  and  it  is  here  that  the  tendon  is  divided  in  the  operation 
of  tenotomy.  The  short  saphenous  vein,  which  lies  a  little  to  the  outer  side  of 
the  tendon,  gradually  reaches  the  middle  of  the  calf,  along  which  it  ascends  to  the 
middle  of  the  popliteal  space.  The  internal  saphenous  vein  and  nerve  lie  along  the 
inner  border  of  the  tibia. 

The  course  of  the  posterior  tibial  artery  is  mapped  out  by  drawing  a  line  from 
the  low^er  angle  of  the  popliteal  space,  at  the  level  of  the  lower  border  of  the 
tubercle  of  the  tibia,  to  a  point  midway  between  the  internal  malleolus  and  the 
tendo  Achillis.  To  expose  the  vessel  in  the  upper  half  of  the  leg,  an  incision  is 
made  parallel  to  and  |  in.  behind  the  inner  border  of  the  tibia  ;  after  retract- 
ing the  inner  border  of  the  gastrocnemius  and  dividing  the  tibial  origin  of  the 
soleus,  the  artery  is  found  lying  on  the  tibialis  posticus.  In  exposing  the  artery 
below  the  soleus,  divide  two  layers  of  deep  fascia  and  keep  the  knife  directed 
towards  the  tibia. 

The  peroneal  artery  is  given  off  3  in.  below  the  head  of  the  fibula ;  incisions 
to  expose  the  vessel  are  made  in  the  direction  of  a  line  extending  from  the 
posterior  border  of  the  head  of  the  fibula  to  a  point  midway  between  the  external 
malleolus  and  the  tendo  Achillis. 


THE  FOOT  AND  ANKLE. 

The  tip  of  the   external  malleolus  is   situated  \   in.   lower  and  f   in.   further 
back  than  that  of  the  internal  malleolus.     Above  the  external  malleolus  is  the 


Extensor  brevi.s  digitorum 


Tendon  of  tiexor  loiign 
digitorum  to  iiftli  to 
Second  metatarso- 
pihalan^'ftal  joint 


Filtli  iji'datarso-ijlialan-i.'al  joint        liase  of  liftli  nn^tatarsal  ,         \ 

Peroneus  brevis      i 
Greater  process  of  os  calcis 


External  malleolus 
^        Peroneal  tubercle 
Peroneus lougus 


Fk;.  93.V. — OrTKi{  Asi'ect  ok  Foot  and  Axkle. 

triangular  subcutaneous  surface  of  the  fibula,  the  apex  of  which  corresponds  to 
tlie  lower  end  of  the  extensor-peroneal  intermuscular  septum. 

Tlie  line  of  the  ankle-joint  can  be  felt  on  either  side  of  tlie  extensor  tendons,  and 
\vh(;ii  th<'  foot  is  extended  the  anterior  jxirt  of  the  superior  articular  surface  of  the 
astragalus  forms  a  visible  prominence  below  the  anterior  border  of  the  lower  end  of 
the  tibia.     The  small  posterior  surface  of  the  astragalus  is  felt  below  and  behind 


THE  FOOT  AND  ANKLE. 


1311 


the  internal  malleolus,  at  the  anterior  part  of  the  hollow  between  it  and  the  heel. 
In  effusions  into  the  anUe-joint  the  hollows  in  front  and  behind  the  malleoli  are 
obhterated,  and  the  extensor  tendons  are  raised  from  the  front  of  the  joint. 

A  finger's  breadth  below  the  tip  of  the  internal  malleolus  is  the  sustentaculum 
tali ;  \\  in.  in  front  of  the  latter,  and  midway  between  tlie  dursal  and  plantar 
margins  of  the  inner  aspect  of  the  foot,  is  the  tubercle  of  the  scaphoid  (tlie  inner 
landmark  in  Chopart's  amputation),  whicli  is  generally  visible,  and  always 
distinctly  palpable.  The  calcaneo - astragaloid  joint  lies  immediately  below  the 
sustentaculum,  while  close  above  it  the  tendon  of  the  tibialis  posticus  may 
be  rendered  visible,  as  it  extends  from  behind  the  tip  of  the  internal  malleolus  to 
the  tubercle  of  the  scaphoid.  An  mch  and  a  half  in  front  of  the  tubercle  of  the 
scaphoid  is  the  joint  between  the  internal  cuneiform  and  the  first  metatarsal ;  the 
ridge  at  the  base  of  the  latter  lione  furnishes  a  good  guide  to  the  articulation.  The 
first  metatarso-phalangeal  joint  lies  a  little  in  front  of  the  middle  of  the  ball  of  tlie 
great  toe. 

A  hnger's  breadth  vertically  below  the  tip  of  the  external  malleolus  is  the 
peroneal  tubercle  of  the  os  calcis,  and  midway  between  the  two  is  the  calcaneo- 
astragaloid  joint ;  the  tubercle  is,  when  present,  a  trustworthy  guide  to  the  level  at 
which  the  two  peronei  tendons  cross  the  outer  surface  of  the  os  calcis.  The  greater 
process  of  the  os  calcis  is  felt  in  the  triangular  interval  l:)etween  the  tendons  cf  the 


Tibialis  posticus 
Anterior  border  of  lower  end  of  tibiii 
Line  of  ankle-joint 

Tibialis  anticus^ 

Head  of  astragalus 
Tubercle  of  scaphoid 

Tarso-metatarsal  articulation 


First  metatarso- 
pbalangeal  articulation 


Posterior  tibial 
artery 

I'lexor  longus 
luUluois 

Internal  malleolus 

'endo  Achillis 

lexor  longus 
igitorum 

-Sustentaculum 
tali 


'^■M. — In^ek  Aspect  uf  Foiu  and  Ankle. 


peroneus  brevis  and  tertius;  the  calcaneo-cuboid  joint — the  outer  landmark  in 
Chopart's  amputation — is  placed  a  little  in  front  of  the  mid-point  between  the  tip 
of  the  external  malleolus  and  the  base  of  the  fifth  metatarsal  bone.  To  open  the 
outer  tarso-metatarsal  articulations,  the  knife,  entered  behind  the  projecting  base  of 
the  fifth  metatarsal  bone,  should  be  directed  forwards  as  well  as  inwards.  On  the 
dorsum  of  the  foot  the  tarsal  joints  are  obscured  by  the  extensor  tendons.  The 
s3movial  membrane  of  the  ankle-joint  is  prolonged  on  to  the  neck  of  the  astragalus, 
and  care  must  be  taken  to  avoid  opening  the  ankle-joint  in  performing  Chopart's 
amputation. 

The  line  of  the  tarso-metatarsal  joints  extends  nearly  1  in.  further  forwards  on 
the  inner  than  on  the  outer  border  of  the  foot ;  between  these  points  the  joint- 
line  takes  a  zigzag  course  on  account  of  the  second  metatarsal  bone  extending 
backwards  between  the  internal  and  external  cuneiform  bones.  The  joint  between 
the  second  metatarsal  and  middle  cuneiform  is  nearly  i  in.  behind  that  between 
the  first  metatarsal  and  internal  cuneiform,  and  nearly  \  in.  behind  that  between 
the  third  metatarsal  and  the  external  cuneiform.  The  strong  transverse  inter- 
osseous Hgament  {Lisfrancs  ligament),  which  connects  the  outer  surface  of  the 
internal  cuneiform  with  the  base  of  the  second  metatarsal,  must  be  divided  in 
the  tarso-metatarsal  amputation  of  Lisfranc.  In  order  to  preserve  the  insertions 
of  the  two  tibial  and  the  three  peroneal  muscles  it  is  advisable,  when  possible, 
instead  of  disarticulating  at  "  Lisfranc's  joint,"  to  saw  through  the  metatarsal  bones 
just  in  front  of  their  bases. 


1312  SUEFACE  AND  SUEGICAL  ANATOMY. 

The  metatarso-phalangeal  articulations  are  situated  1  in.  behind  the  web  of  the 
toes.  In  disarticulating  a  toe,  the  transverse  metatarsal  ligament,  which  unites 
the  heads  of  the  metatarsal  bones,  should  not  be  injured. 

The  tendon  of  the  tibialis  posticus  may  be  felt,  and,  by  inverting  the  foot,  seen, 
as  it  extends  from  behind  the  tip  of  the  internal  malleolus  to  the  tubercle  of  the 
scaphoid ;  it  crosses  the  astragalus  immediately  above  the  sustentaculum  tali. 

In  the  commonest  form  of  club-foot,  viz.  talipes  eqicino- varus,  the  tubercle  of  the 
scaphoid  is  approximated  to  the  internal  malleolus,  so  that  tenotomy  of  the  tendon 
should  be  performed  through  a  puncture  a  little  below  tlae  tip  of  the  internal  malleolus ; 
if  the  knife,  after  dividing  the  tendon,  be  carried  down  to  the  bone,  the  inferior  calcaneo- 
scaphoid  ligament  will  be  divided  and  the  astragalo-scaphoid  joint  opened,  a  procedure 
which  is  called  for  before  the  foot  can  be  brought  into  good  position. 

Crossing  the  front  of  the  ankle-joint,  from  within  outwards,  are  the  following 
tendons :  viz.  the  tibialis  anticus,  the  largest  and  most  prominent ;  the  extensor 
longus  hallucis,  the  extensor  longus  digitorum,  and  the  peroneus  tertius.  The 
extensor  brevis  digitorum  gives  rise  to  a  fleshy  pad  which  overhes  the  dorsal  aspect 
of  the  calcaneo-cuboid  joint.  When  the  foot  is  everted,  the  tendon  of  the  peroneus 
brevis  may  be  seen  extending  from  the  tip  of  the  external  malleolus  to  the  base  of 
the  fifth  metatarsal  bone  ;  immediately  below  it  is  the  tendon  of  the  peroneus  longus, 
which,  as  it  winds  round  the  cuboid,  is  obscured  by  the  fleshy  fibres  of  the  abductor 
minimi  digiti  muscle.  The  abductor  hallucis  muscle,  although  described  along  with 
the  sole,  forms  a  fleshy  pad  along  the  inner  border  of  the  foot  below  the  susten- 
taculum tali. 

An  incision,  extending  from  the  tubercle  of  the  scaphoid  to  the  middle  of  the 
inner  border  of  the  heel,  will  expose  the  various  tendons,  vessels,  and  nerves,  as 
they  pass  from  the  inner  ankle  into  the  sole  beneath  the  abductor  hallucis. 

The  dorsalis  pedis  artery  may  be  mapped  out  on  the  surface  by  drawing  a  line  from 
a  point  opposite  the  ankle-joint,  midway  between  the  tips  of  the  two  malleoli,  to  the 
hinder  end  of  the  first  interosseous  space ;  the  vessel  may  be  compressed  against 
the  inner  column  of  the  tarsal  bones.  The  internal  saphenous  vein  and  nerve  lie 
between  the  anterior  border  of  the  internal  malleolus  and  the  tendon  of  the  tibialis 
anticus ;  the  external  saphenous  vein  and  nerve  take  the  same  course  as  the  tendon 
of  the  peroneus  brevis. 

The  internal  plantar  vessels  and  nerves  lie  along  the  internal  intermuscular 
septum,  which  corresponds  to  a  line  drawn  from  the  under  surface  of  the  inner 
tuberosity  of  the  os  calcis  to  the  interval  between  the  first  and  second  toes.  The 
external  plantar  vessels  and  nerves  may  be  exposed  by  an  incision  along  the 
external  intermuscular  septum,  which  runs  in  a  line  extending  from  the  middle  of 
the  under  surface  of  the  heel  to  the  fourth  toe  (Kocher) ;  to  map  out  the  course 
of  the  plantar  arch,  draw  a  line  across  the  sole  from  the  inner  side  of  the  base  of 
the  fifth  metatarsal  bone  to  the  hinder  end  of  the  first  interosseous  space. 


INDEX 


88 


INDEX 


Note.  —  The  B.N.A.  nomenclature,  wherever  possible  and  exjiedient,  is  included  in  the  index; 
and  cross  references  to  the  English  terms  used  in  the  text  are  given  excej^t  when  the 
B.N.A.  and  the  English  are  identical.  In  the  lists  of  arteries,  muscles,  etc.,  when  the 
B.N.A.  and  the  English  terms  differ  only  in  the  terminal  lettei's  the  B.N.A.  alone  are 
usually  given.  Figures  in  heavy  type  refer  to  the  pages  on  which  structures  are  most 
exhaustively  described. 


Abdomen,  1043 
cavity  of,  1043 
contents  of,  1047 
fascife  of,  420,  1044 
lymphatics  of,  918 
muscles  of,  421 
planes  of,  1267 
regions  of,  1047,  1267 
semilunar  space  of  Traube  of,  1271 
surface  and  surgical  anatomy  of,  1264 
zones  of,  1047,  1267 
AMominal  aorta,  798 

surface  and  surgical  anatomy  of,  1276 
Abdominal  cavity,  1043 
apertures  of,  1045 
boundaries  of,  1043 
fascia  of,  420,  1044 
pelvic  portion  of,  1045 
subdivisions  of,  1045,  1047 
Abdominal  rings.     See  Inguinal  rings 

surface  and  surgical  anatomy  of,  1265 
Abdominal  wall,  fasciae  of,  420,  1044 

muscles  of,  421 
Abducent  nerve,  686 

development  of,  699 
morphology  of,  701 
nucleus  of,  502,  524 
origin  of,  deep,  502,  524 
superficial,  486,  524,  686 
Abduction,  259 

Abductor  digiti  cjuinti  muscle  of  foot,  381 
action  of,  384 
nerve-supply  of,  383 
digiti  quinti  muscle  of  hand,  345 
action  of,  352 
nerve -supply  of,  351 
haUucis  muscle,  381 
action  of,  384 
nerve-supply  of,  383 
surgical  anatomy  of,  1312 
poUicis  brevis  muscle,  343 
action  of,  353 
nerve-supply  of,  351 
longus  muscle,  350.     See  also  Muscle 
Aberrant  arteries,  838,  946,  952 
Abnormalities  of  arteries,  947 
of  heart,  946 
of  lymphatics,  955 
of  veins,  954 


Accessorius  muscle  of  back.  See  Iliocostalis  dorsi 
of  foot,  379.     See  also  ]\Iuscle,  quadratus 
plantse 
Accessory  obturator  nerve,  447 
Accessory  processes  of  vertebrae,  84 
Acetabular  artery,  of  ol^turator,  852  ;  of  internal 

circumflex,  861 
Acetabular  fossa,  218 
Acetabulum,  218,  219 
Achromatic  spindle,  10,  13 

substance,  8,  10 
Acini,  1008 

Acino-tubular  glands,  1007 
Acinous  glands,  1007 
Acromial  angle,  186 
artery,  829 
nerves,  617,  619 
morphology  of,  622 
Acromio-clavicular  joint,  274 
movements  at,  275 
.   surgical  anatomy  of,  1292 
ligament,  274 
Acromio-thoracic  artery,  828 
Acromion  process,  183,  186 

surgical  anatomy  of,  1292 
Acustic  area,  488,  520 

develojjment  of,  527 
Adduction,  259 
Adductor  brevis  muscle,  362 
actions  of,  370,  371,  393 
nerve-supply  of,  370 
hallucis  muscle,  382 
action  of,  384 
nerve-supply  of,  383 
longus  muscle,  362 

actions  of,  370,  371,  393 
nerve-supply  of,  370 
surgical  anatomy  of,  1306 
magnus  muscle,  362 
actions  of,  370,  371,  393 
nerve-supply  of,  370 
surgical  anatomy  of,  1308 
minimus  muscle,  363 
pollicis  obliquus  muscle,  345 
action  of,  353 
nerve -supply  of,  351 
transversus  muscle,  345 
action  of,  353 
nerve-sujiply  of,  351 


1315 


1316 


INDEX. 


Adductor  tubercle  of  femur,  226,  229 

surgical  anatomy  of,  1308 

Aditus  ad  antrum,  Ajppendix  A,  ii 

surgical  anatomy  of,  1233 

laryngis,  964 
Adventitious  ligaments,  261 
^Equator  bulbi  oculi,  724 

lentis,  736 
AffenspaUe,  564 
Agger  nasi,  136,  721 
Agitator  caudse  muscle,  365 
Agminated  glands,  1062,  1064 
Air-cells,     ethmoidal,    128.       See    also    Cells, 
ethmoidal 
surgical  anatomy  of,  1236 

of  lung,  991,  992 

mastoid,  121,  752 

surgical  anatomy  of,  1234 
Air-sinuses,  72 

frontal,  104.     See  also  Frontal  sinus 

maxillary.     See  Antrum,  Maxillary 

sphenoidal,  121,  127,  150,  172 
Akanthion,  Appendix  D,  xvi 
Akrocephalic  skulls.     Aj^jjendix  D,  xvii 
Ala  cinerea,  488 

lobuli     centralis     cerebelli.       See    Alae     of 
cerebellum 

magna    ossis    sphenoidalis.       See   Wing    of 
sphenoid 

nasi,  717 

parva    ossis    sphenoidalis.       See    Wing    of 
sphenoid 

sacralis,  86 

vomeris,  131,  171 
Alse  of  cerebellum,  506,  507 

of  thyroid  cartilage,  958 
Alar  lamina.     See  Neural  tube 

ligaments  of  knee,  302 

odontoid  ligaments,  267 

process  of  ethmoid,  127 

.spine  of  si^henoid,  123,  154,  159,  165 

sulcus,  717 
Albumen  of  ovum,  12 
Alcock's  canal,  853 
Alecithal  ovum,  11 
Alimentary  canal,  993 

development  of,  32,  1105 
Alisphenoids,  126 

development  of.  Appendix  E,  xxi 
Allantoic  arteries,  51 

diverticulum,  50,  51,  65 

stalk,  51,  65 

veins,  62,  934 
Allan tois,  51 
Alveolar  arch,  159 

ducts  of  lungs,  991 

glands,  1007 

index,  Appendix  D,  xviii 

periosteum,  1016,  1025 
development  of,  1027 

point,  Appendix  D,  x\'i 

process,  136,  150 
Alveoli  dentales.     See  A.  of  jaws 

of  glands,  1008 

of  jaws,  136,  142,  1016 

development  of,  1027,  1028 

pulmonum,  991,  992 
Alveolo-dental  periosteum,  1016,  1025 
Alveolo-glossal  sulcus,  1244 
Alveus,  572,  577 
Ameloblasts,  1026 
Amitosis,  9 


Amnion,  48,  59 
false,  59 
fold,  49,  65 
true,  49 
Amniotic  area,  24,  48 
cavity,  48,  49,  50 
fluid,  48 
folds,  27,  49,  65 
Amphiarthrosis,  256,  257 

development  of,  260 
Ampulla  ductus    deferentis.      See    A.   of    vas 
deferens 
of  Fallopian  tube,  1186 
lacrimalis,  740 
of  lactiferous  duct,  1208 
membranacea.     See  A.  of  semicircular  canals 
ossea  lateralis,  posterior,  superior.      See  A.  of 

semicircular  canals 
recti.     See  A.  of  rectum 
of  rectum,  1089,  1091 

of  semicircular  canals,    osseus,    760;    mem- 
branous, 764 
tubee  uterinse.     See  A.  of  Fallopian  tube 
of  vas  deferens,  1164,  1166 
of  Vater,  1120 
Amygdala.     See  Tonsil 

of  cerebellum,  507 
Amygdaloid  nucleus,  576,  579,  582 

tubercle,  576 
Anal  canal,  1091 

columns  of,  1093,  1094 
develoiDment  of,  45 
hemorrhoidal  zone  of,  1094 
orifice  of,  1074,  1092,  1095 
relations  of,  1092 
sinuses  of,  1095 
valves  of,  1093,  1095 

surgical  anatomy  of,  1281 
vessels  of,  1095 
white  line  of,  1095 
veins,  1096 
Analogy,  2 
Anaphase,  10,  13 
Anapophysis,  Appendix  C,  xv 
Anastomoses,  arterial  segmental,  939 
Anastomosis,  855,  862 
Anastomotic  artery  of  brachial,  831 
of  femoral,  862 
of  sciatic,  855 
of  vertebral,  819 
vein  of  Trolard,  883 
Anatomical  neck  of  humerus,  188 
Anatomy,  1 
surgical,  1222 
systematic,  3 
topographical,  4 
Anconajus  muscle,  349 
action  of,  335,  352 
nerve-supply  of,  351 
i\.ngeiology,  3 
Angle,  Augulus — 
acromial,  186 
cephalo-auricular,  743,  745 
costaj.     See  Angle  of  rib 
facial.  Appendix  D,  xvii 
frontalis,  107 

inferior  lateral,  of  sacrum,  87 
inferior  scapuUe,  184 
infracostal,  1265 
infrasternal,  102 
of  jaw,  143 

differences  in,  due  to  age,  145,  181 


INDEX. 


1317 


Angle  of  jaw,  surgical  anatomy  of,  1237 
lateralis  scapulse,  184 
Ludovici,  1255 

mandibulae.     See  Angle  of  jaw 
mastoideus,  108 
medialis  scapulre,  184 
occipitalis,  108 
oculi  lateralis.     See  Cantlii 

medialis.     See  Canthi 
pubis,  217 

of  rib,  97,  98,  99,  100 
Eolaiidic,  558 
sacro-vertebral,  88 

sexual  differences  in,  222 
sphenoidalis,  108 
sterni,  95 
Angular  artery,  807 
gyrus,  563,  564 

surface  anatomy  of,  1225 
processes  of  frontal  bone,  103,  105,  147 
surface   and   surgical    anatomy   of,    1224, 
1237 
vein,  879 
Ankle,  surface  and  surgical  anatomy  of,  1310 
Ankle-joint,  306 
movements  of,  307 

muscles  producing,  384 
nerves  of,  651,  653 
synovial  membrane  of,  307 
surgical  anatomy  of,  1311 
Annectant  gyri  of  calcarine  fissure,  565,  566 
of  internal  parieto-occipital  fissure,   565, 

566 
of  intrajiarietal  sulcus,  563 
gyrus,  deejj,  of  fissure  of  Rolando,  558 
Annular  ligament  of  ankle,  372 
of  stapes,  752,  757 
of  wrist,  336,  337 

surface  anatomy  of,  1298 
Annular  plexus  of  cornea,  727 
Aniruli  fibrosi  cordis,  792 
Annulus  femoralis.     See  Femoral  ring 
fibro-cartilagineus,  750 
fibrosus,  262 
ingninalis  abdominalis.      See  Inguinal  ring, 

abdominal 
ingninalis  subcutaneus.     See  Inguinal  ring, 

superficial 
ovalis,  787 
tympanicus,  748 
Ano-coccygeal  body,  1089,  1092 
Ano-cutaneons  line,  1095 
Ansa  hypoglossi,  621,  622,  697 
lenticularis,  545,  581 
peduncularis,  545 
subclavia  (Vieussenii),  708 
Ante-cubital  lymphatic  glands,  913 
Antbelix.     See  Antihelix 
Antibracliium.     See  Forearm 
Antihelix,  744 

development  of,  37,  43 
fossa  of,  744 
Antithesis  in  muscular  action,  399 
Antitragicus  muscle,  746 
Antitragus,  744 

development  of,  37,  43 
Antrum  of  Highmore,  136,  150.     See  also  A., 
maxillary 
mastoid,  752 
development  of,  44 
formation  of,  121 
relation  of,  to  tympanum,  749 


Antrum,  mastoid,  surface  and  surgical  anatomy 
of,  1233,  1235 
maxillary,  136,  150 

connexion  of,  witli  nasal  fossae,  173,  721 
in  coronal  section  of  .skull,  175 
openings  into,  135,  172,  721 
relation  of  molar  teeth  to,  1021 
surgical  anatomy  of,  1240 
pyloricum,  1051,  1055 

changes  in,  during  digestion,  1052 
tympanicum.     See  Antrum,  mastoid 
Anus,  993,  1092,  1095 
development  of,  45 
imperforate,  1097 

sphincters  of,  431,  433,  439,  1093,  1095 
surgical  anatomy  of,  1280 
Aorta,  797 

abdominalis,  798 
branches  of,  800,  839 
paired  visceral,  842 
parietal,  839 
unpaired  visceral,  843 
surgical  anatomy  of,  1276 
abnormalities  of,  947 
arch  of,  797 

abnormalities  of,  947 
branches  of,  798,  800 

abnormalities  of,  947 
development  of,  933 
surface  anatomy  of,  1264,  1289 
ascendens,  797 

branches  of,  797,  800 
development  of,  930 
surface  anatomy  of,  1264 
ascending.     See  Aorta  ascendens 
bifurcation  of,  797 

surgical  anatomy  of,  1276,  1290 
variations  in,  947 
descendens,  798 

branches  of,  798,  837 

abnormalities  of,  948 
formation  of,  933 
morphology  of,  939 
descending.     See  Aorta  descendens 
development  of,  928 
great  sinus  of,  797 
primitive,  branches  of,  939 
development  of,  925,  926 
formation  of,  61 
morphology  of,  939,  942 
subdivision  of,  62 
relations  of,  797,  798,  1040 
sinuses  of  Valsalva  of,  797 
thoracalis.     See  Aorta,  thoracic,  descending 
thoracic,  797 
descending,  798 
branches  of,  837 
surface  anatomy  of,  1290 
ventral,  926 
Aortic  arches,  caudal,  62 

development  of,  926,  928 
morphology  of,  942 
cephalic,  36,  37,  62 
abnormalities  of,  948 
development  of,  926,  927,  928,  932 
morphology  of,  942 
segmental  branches  of,  932 
area,  1262 

bulb,  abnormalities  of,  947 
division  of,  929 
septum  of,  930,  947 
eusp  of  mitral  valve,  791.     See  also  Heart 


1318 


INDEX. 


Aortic  opening  of  diaphragm,  419 
orifice  of  heart,  789,  791 

surface  anatomy  of,  1262 
plexus,  710,  711,  714 
valve,  791 
vestibule,  791 
Aortico-renal  ganglion,  710,  712 
Apertura  externa  aquaBcluctus  cochlea},  117 
externa  aquseductus  vestibuli,  119 
(lateralis  ventriculi  quarti,  601) 
niedialis    ventriculi    quarti    (Foramen    Ma- 

gendii).     Sec  Foramen  of  Magendie 
pelvis  (minoris)  inferior,  220 

superior,  220 
piriformis.     See  Aperture,  nasal,  anterior 
superior  canaliculi  tymi^ani,  118 
thoracis  infeidor,  101  ;  superior,  102 
tymijanica  canaliculi  chordte,  750 
Aperture,  nasal,  anterior,  146,  150 

measurement  of,  AjJijendix  D,  xviii 
Ajjex  auriculae  (Darwini).    See  Darwin,  tubercle 
of 
cajjituli  fibulae.     See  Styloid  process 
columnpe  jjosterioris.     See  Apex  cornu 
cornu,  456 
of  heart,  785 
ossis  sacri,  87 
patellae,  229 
prostatse.     See  Prostate 
Apical  bronchus,  990 

glands  of  tongue,  1006 
Aponeurosis,  318.     See  also  Fascia 
epicranial,  394,  396 
intercostal,  416 
of  i)alate,  999 

palmaris.     See  Palmar  fascia 
l^haryngeal,  1037 
plantaris.     See  Plantar  fascia 
vertebral,  319,  385 
Apophysis,  submalleolar,  Appendix  B,  xiii 
Apparatus  digestorius.     See  Digestive  system 
lacrimalis,  740 

respiratorius.     See  Eespiratory  system 
urogenitalis.     See  Urogenital  system 
Appendages  of  skin,  775 
Appendices,  auricular,  786,  788 
development  of,  929 
surface  anatomy  of,  1262 
epiploicae,  1074,  1075 
testi.s.     See  Hydatid  of  testis 
vesiculosi  (Morgagni).     See  Hydatid  ol'  ]\Ior- 
gagni 
Appendicidar  artery,  847,  1081 
lymphatic  gland,  920 
muscles,  319 
skeleton,  69,  70 

morphologj'  of,  Ajjpendix  F 
vein,  903 
Appendix  epididymidis,  1160 

ventriculi  laryngis.     See  Saccule,  laryngeal 
vermiform,  1079.     See  also  Venniform  ap- 
pendix 
Aquteductus  cerebri  (Sylvii).     See  Aqueduct  oi' 
Sylvius 
vestibuli.     See  Aqueduct  of  vestiljule 
Aqueduct  of  cochlea,  117,  761 
of  Fallopius,  118,  164,  752,  762 
of  Sylviu-s,  476,  531,  533,  551 

development  of,  478,  542 
of  vestibule,  119,  759 
AqueoiLS  humour,  725,  737 
Arachnoidal  villi,  884 


Arachnoidea  encephali,  600.      See  also  Sj)ace, 
subarachnoid 
Pacchionian  bodies  of,  602 
spinalis,  601 
Arbor  vitse  cerebelli,  510 

uteri,  1188 
Arch,  alveolar,  superior,  159 
anterior,  of  atlas,  79 
aortic,  797.     See  also  Aorta,  arch  of 
branches  of,  798,  800 
caudal,  62.     See  also  Aortic  arches 
cephalic,  36.     See  also  Aortic  arches 
carpal,  anterior,  835 

dorsal,  833,  836 
crural.     See  Arch,  femoral 
dental,  159,  1021 
femoral,  deep,  356 

superficial,  356,  422 
hyoid,  36,  37,  43 

muscles  jjroduced  from,  441 
nerve  of,  702 
mandibular,  36,  38,  43 

muscles  produced  from,  441 
nerve  of,  701 
neural.     See  Arch,  vertebral 
palmar,  deej),  836 

abnormalities  of,  952 
morphology  of,  943 
surgical  anatomy  of,  1301 
sujjerficial,  836 

abnormalities  of,  952 
morj^hology  of,  943 
surgical  anatomy  of,  1301 
plantar,  860 

abnormality  of,  954 
mor^jhology  of,  943 
surgical  anatomy  of,  1312 
posterior,  of  atlas,  79 
pubic,  218,  221 

temporo-maxillary,  Apj)endix  B,  x 
thyro-hyoid,  36,  37 

muscles  produced  from,  441 
nerve  of,  702 
A^enous,  dorsal,  of  foot,  900 
mor2:)liologv  of,  946 
of  hand,  890 " 

moi'jjlaology  of,  946 
transverse  (osseous),  of  foot,  315 

venous,  900 
vertebral,  76 

of  fifth  lumbar,  variation  in, Appendix  B,vi 
ossification  of,  92,  93 
serial  homology  of,  Ajjpendix  C,  xiv 
zygomatic,  154,  159 

surgical  anatomy  of,  1224,  1237 
Ai'chenteron,  19 

Arches,  aortic,  927.     See  also  Aortic  arches 
dorsal  roots  of,  928 
segmental  branches  of,  932 
ventral  roots  of,  928 
arterial,  of  wrist  and  hand,  835 
axillary,  325 

nerve-supply  of,  671 
of  foot,  315 
tarsal,  of  eyelids,  740 
visceral,  35,  36 

muscles  produced  from,  441 
relation  of,  to  cranial  nerves,  701,  703 
Arcuate  eminence,  117,  169 
fibres,  deep,  493,  498,  511 
develo])iiieiit  of.  528 
superficial,  485,  496,  498,  511 


INDEX. 


1319 


Arcuate  fibres,  superficial,  development  of,  528 

ligaments  of  diaphragm,  417,  418 
of  pubis,  292 

nucleus  of  medulla,  490,  498 
development  of,  528 
of  optic  thalamus,  545 
Arcus  anterior  atlantis.     See  Arch,  anterior,  of 
atlas 

aortaa.     See  Aortic  arch 

dentalis    inferior  et    superior.      See  Dental 
arches 

glosso-palatinus.    See  Pillar  of  fauces,  anterior 

lumbo-costalis  lateralis   (Halleri).     See   Ar- 
cuate ligaments 
medialis  (Halleri).     Ut  swpra 

palatini.     See  Palatine  arches 

parieto-occijjitalis,  559 

pharyngo-palatinus.     See    Pillar   of  fauces, 
posterior 

plantaris.     See  Plantar  arch 

posterior  atlantis.    See  Arch,  posterior,  of  atlas 

pubis.     See  Pubic  arch 

senilis,  727 

supcrciliaris.     See  Superciliary  ridge 

tarseus  inferior  et  superior.    See  Afches,  tarsal 

tendineus  m.  levatoris  ani.     See  White  line 

venosus    dorsalis    pedis.     See   Arch,  venous 
dorsal,  of  foot 

vertebrae.     See  Arch,  vertebral 

volaris  profundus.     See  Arch,  palmar,  deep 

volaris  superficialis.    See  Arch,  palmar,  super- 
ficial 

zygomaticus.     See  Zygomatic  arch 
Area  of  absolute  cardiac  dulness,  1265 

acustica.     See  Acustic  area 

amniotic,  24,  48 

bucco-pliaryngeal,  23,  33 

cliorionic,  24,  52 

cochlete,  761,  762 

embryonic,  19,  60,  65 

facialis,  762 

nervi    facialis    fundi    meatus.       See   Area 
facialis 

notochordal,  23 

pericardial,  23,  33 

placental,  24,  48,  52,  54 

postrema,  488 

proamniotic,  23 

vascular,  61 

vestibularis  inferior  et  superior,  762 
Areola  mammse,  1207 
Areolar  coat  of  liver,  1121 
Areolar  glands,  1207 
Arlt,  sinus  of,  741 
Arm,  development  of,  46 

external  bicipital  furrow  of,  1295 

fascise  of,  332 

intermuscular  septa  of,  332 

internal  bicipital  furrow  of,  1295 

internal  supracondyloid  triangle  of,  1295 

lymphatics  of,  913 

muscles  of,  332 

surface  and  surgical  anatomy  of,  1295 

See  also  Limb,  upper 
Arnold,  nerve  of,  692 
Arrectores  pilorum,  778 
Arteria.     See  Artery 
Arterial  arches  of  wrist  and  hand,  835 
Arteriola  (venula)  macularis  inferior  et  superior. 
See  Artery,  macular 

nasalis    retinte    inferior    et    suj^erior.       See 
artery,  nasal,  of  retina 


Arteriola  temporalis  retinae  inferior  et  superior. 

See  Artery,  temj)oral,  of  retina. 
ArteriolfB  rectiu,  1140 
Arterioles,  capillary,  780 

Artery  or  Arteries ;    Arteria  or  Arterise,  780, 
795 
aberrant,  838,  946,  952 
abnormalities  of,  947 
acetabular,  of  internal  circumfle.x,  861 
acetal)uli  (obturator),  852 
acromial,  829 
acromio-tlioracic,  828 
allantoic,  51 
alveolares    superiores    anteriores.       See    A., 

dental,  anterior  superior 
alveolaris  inferior.     See  A.,  dental,  inferior 

superior  posterior.   See  A.,  dental,  posterior 
superior 
anastomotic,  of  brachial,  831 

of  femoral,  862 

of  sciatic,  855 

of  vertebral,  819 
angularis,  807 

auonyma.     See  A.,  innominate 
appendicularis,  847.     See  also  A.  of  appendix 
of  aijpendix,  847,  1081 
arciformes,  1140 
articular,  azygos,  of  popliteal,  863 

of  deeji  palmar  arch,  837 

of  dorsal  carjjal  arch,  836 

of  external  plantar,  866,  867 

external,  of  popliteal,  863 
surgical  anatomy  of,  1308 

of  internal  circumfiex,  861 

internal,  of  popliteal,  863 
auditiva  interna.     See  A.,  auditory 
auditory,  769,  820 
auricular,  deejj,  811 

of  occipital,  808 

posterior,  808 

development  of,  933 
surgical  anatomy  of,  1229 
auricularis    posterior.       See    A.,    auricular, 
posterior 

profundus.       See  A.,   auricular,  deep 
axillaris.     See  A.,  axillary 
axillary,  827 

abnormalities  of,  951 

formation  of,  933 

surgical  anatomy'  of,  1292,  1293 
basilaris,  820 

abnormalities  of,  951 

formation  of,  933 

mor^jhology  of,  941 
bicipital,  830 
bicusi^id,  812 
brachialis,  830 

abnormalities  of,  951 

formation  of,  933 

surgical  anatomv  of,  1295,  1297 
bronchiales,  838,  989 

abnormalities  of,  948 

morphology  of,  942 
buccal,  of  facial,  807 

of  internal  maxillary,  812 
buccinatoria.       See  A.,    buccal,   of   interna. 

maxillary 
bulbi  urethrte,  854,  1173 

surgical  anatomy  of,  1278 

vestibuli  (vaginas),  1198 
cgecal,  1081 
calcaneal,  internal,  866 


1320 


INDEX. 


Artery  or  Arteries — continued 
calcarine,  821 
canalis  pterygoidii  (Vidii).    See  A.,  Vidian,  of 

internal  maxillary 
capsular,  842 

luorpLology  of,  942 
inferior  (sujjrarenal),  842 
of  liver,  1121 
superior,  839 
carotid,  common,  801 

abnormalities  of,  950 
formation  of,  933 
morpliology  of,  942 
surgical  anatomy  of,  1250,  1264 
left,  802 

abnormalities  of,  947,  950 
right,  803 

abnormalities  of,  947,  948,  950 
external,  803 

abnormalities  of,  947,  950 
develoimient  of,  933 
inorjjliology  of,  942 
surgical  anatomy  of,  1250 
internal,  813 

abnormalities  of,  947,  950 
development  of,  933 
morijliology  of,  942 
sheath  of,  802 
carotis  commimis.     See  A.,  carotid,  common 
externa.     See  A.,  carotid,  external 
interna.     See  A.,  carotid,  internal 
carpal,  radial,  anterior,  832 
posterior,  833 
ulnar,  anterior,  835 
posterior,  835 
cavernous,  815 
central,  of  middle  cerebral,  817 

of  posterior  cerebral,  820 
centralis  retinie,  735,  742,  815 
cerebelli  inferior  anterior,  820 
posterior,  820 
superior,  820 
cerebral,  middle,  817 
cerebri  anterior,  817     ' 
abnormalities  of,  950 
media.     See  A.,  cerebral,  middle 
posterior,  820 
surgical  anatomy  of,  1229 
cervical,  ascending,  823 
morjjhology  of,  941 
deep,  826 

morphology  of,  941 
superficial,  824 
transverse,  823 
cervicalis  ascendens.    See  A.,  cervical,  ascend- 
ing 
profunda.     See  A.,  cervical,  deep 
superficialis.     See  A.,  ceivical,  superficial 
chorioidea.     See  A.,  choroidal, 
choroidal,  anterior,  817 

posterior,  820 
ciliares  anteriores  breves  et  longa3.     See  A., 

ciliary 
ciliary,  731,  815 
anterior,  731,  816 
long,  731,  815 
posterior,  728,  815 
short,  728,  815 
circumflex,  anterior,  830 
external,  861 
surgical  anatomy  of,  1307 
iliac,  deep,  857 


Artery  or  Ai'teTies^contmued 

circumflex  iliac,  deej),  surgical  anatomy  of, 
1266 
suijerficial,  859 
internal,  861 
j)osterior,  829 

surgical  anatomy  of,  1295 
circumflexa  femoris  lateralis.     See  A.,  circum- 
flex, external 
medialis.     See  A.,  circumflex,  internal 
humeri    anterior.        See    A.,    circumflex, 
anterior 
posterior.     See  A.,  circumflex,  posterior 
ilium  profunda.     See  A.,  circumflex,  iliac, 
deep 
sujDerficialis.      See  A.,  circumflex,  iliac, 
superficial 
scapulae.     See  A.,  dorsalis  scapulae 
clavicular,  829 
coccygeal,  855 
cceliaca,  843 

abnormalities  of,  949 
morjjhology  of,  942 
surgical  anatomy  of,  1276 
colic,  84';i^  1075 
colica  dextra,  847,  1075 
media,  847,  1075 
sinistra,  847,  1075 
collateral  digital,  of  foot,  869 

of  hand,  836 
collateralis  ulnaris  inferior.     See  A.,  anasto- 
motic, of  brachial 
superior.   See  A.  profunda  brachii  inferior 
comes  nervi  ischiatici,  855 
mediani,  834 
phrenici,  825 
comitans  n.  ischiadici.     See  A.  comes 
communicans  anterior  et  posterior.     See  A., 

communicating 
communicating,  anterior,  817 
of  anterior  interosseous,  834 
of  deej)  i^almar  arch,  837 
peroneal,  865 
posterior,  816 

abnormality  of,  951 
tibial,  865 
coronariee  (cordis)  dextra  et  sinistra.     See  A., 

coronary,  of  heart 
coronary,  of  heart,  793,  800 
abnormalities  of,  947 
of  facial,  807 

surgical  anatomy  of,  1240 
of  stomach,  844,  1060 
abnormalities  of,  949 
morphology  of,  942 
of  corpus  cavemosum,  854 
cremasteric,  of  spermatic,  843 

of  deep  epigastric,  857 
crico-thyroid,  805 
cystica,  845 

deferentialis.     See  Artery  of  vas 
dental,  anterior  superior,  812 
inferior,  811 
posterior  superior,  812 
development  of,  932 
diaphragmatic,  of  aorta,  838 
of  comes  nervi  phrenici,  825 
of  musculoTphrenic,  826 
of  inferior  phrenic,  839 
digital,  of  foot,  866,  869 
of  hand,  833,  836 
morphology  of,  943 


INDEX. 


1S21 


Artery  or  Arteries — continued 

digital,  of  hand,  surgical  anatomy  of,  1302 
digitales  dorsales  (A.  radialis),  833 

(A.    tibialis  anterior).      See   A.,  collateral 

digital 
jjlantares,  866 
volares  communes,  836 
proi^rite,  836 
dorsalis  clitoridis,  854,  1198 
hallucis,  869 
iudicis,  833 

abnormalities  of,  952 
linguai,  805,  1006 
nasi.     See  A.,  nasal 
pedis,  868 

surgical  anatomy  of,  1312 
penis,  854 
pollicis,  832 
scapulte,  829 
elastic  lamina  of,  781 
endothelium  of,  781 
epigastric,  deep,  856,  1098 
formation  of,  933 
morphology  of,  940 
surgical  anatomy  of,  1266,  1284 
superficial,  859 
superior,  826 
epigastrica  inferior.     See  A.,  Epigastric,  deep 
ethmoidalis  anterior,  816 

jjosterior,  816 
facial,  806 

formation  of,  933 

surgical  anatomy  of,  1237,  1245,  1249 
transverse,  809 
femoralis,  858 

abnormalities  of,  953 
formation  of,  934 
morpliology  of,  943 
surgical  anatomy  of,  1306 
fibular,  superior,  868 
I'routal,  of  superficial  temj^oral,  810 
frontalis  (a.  ojjhthalmicae),  816 
surgical  anatomy  of,  1223 
Gasserian,  of  middle  meningeal,  811 

of  internal  carotid,  815 
gastric,  844,  1060 

morjjhology  of,  942 
short,  845 
gastrica  dextra.     See  A.,  pyloric 

sinistra.     See  A. ,  coronary,  of  stomach 
gastricae  breves.     See  A.,  gastric,  short 
gastro-duodenalis,  845 
gastro-epiploica  dextra,  845,  1060 

sinistra,  845,  1060 
genu   inferior  lateralis.      See  A.,   articular, 
external,   of  j)opliteal 
medialis.     See  A.,  articular,  internal,  of 
poiDliteal 
media.    See  A.,  articular,  azygos,  of  j)opliteal 
superior     lateralis.      See     A.,     articular, 
external,  of  popliteal 
medialis.     See  A.,  articular,  internal,  of 
l^opliteal 
suprema.     See  A.,  anastomotic,  of  femoral 
glutsea  inferior.     See  A.,  sciatic 

suj^erior.     See  A.,  gluteal 
gluteal,  850 

surgical  anatomy  of,  1303 
hffimorrhoidalis  inferior,  854,  1095 
media,  851,  1096 
superior,  848,  1096 
of  head  and  neck,  801,  950 


Artery  or  Arteries — continued 
helicinse,  1173 
hepatic,  845,  1120 

abnormalities  of,  949 
morphology  of,  942 
of  inferior  i)hrenic,  839 
hepatica,  hejjatica  propria.     See  A.,  hepatic 
humeral,  829 
hyaloidea,  736,  742 

hypogastric,  obliterated,  848,  851,  1098 
hypogastrica.     See  A.,  iliac,  internal 
ilese.     See  Rami  intestini  tenuis 
ileo-cffical,  847,  1081 
ileo-colica,  847 
iliac,  common,  841 

abnormalities  of,  952 
morphology  of,  942 
surgical  anatomy  of,  1277,  1290 
external,  856 

abnormalities  of,  953 
formation  of,  934 
morphology  of,  943 
surgical  anatomy  of,  1277 
internal,  848 

abnormalities  of,  952 
branches  of,  849 
morjjhology  of,  942 
iliaca  communis,  externa.     See  A.,  iliac 
ilio-lumbalis.     See  A.,  ilio-lumbar 
ilio -lumbar,  850 

abnormality  of,  953 
infra-hyoid,  804 
infra -orbitalis,  812 
infra-scapular,  829 
innominate,  800,  801 

abnormalities  of,  948,  950 
development  of,  933 
morphology  of,  942 
surgical  anatomy  of,  1249,  1264 
intercostal,  837 

abnormalities  of,  948 
formation  of,  933 
morphology  of,  940 
anterior,  826 
superior,  826 

abnormalities  of,  951 
morjDhology  of,  940,  941 
intercostalis   suj^rema.      See   A.,   intercostal, 

superior 
interlobares  renis,  1140 
interlobulares,  1140 
intermediate  visceral,  939,  942 
interossea   communis.     See  A.,  interosseous, 
common 
dorsalis.     See  A.,  interosseous,  posterior 
recurrens.     See  A.,  recurrent,  interosseous, 

posterior 
volaris.     See  A.,  interosseous,  anterior 
interosseous,  of  dorsal  carpal  arcli,  836 
dorsal,  of  foot,  869 
of  hand,  833,  836 
anterior,  834 

abnormalities  of,  952 
formation  of,  934 
morphology  of,  943 
common,  834 
palmar,  837 
posterior,  834 

abnormality  of,  952 
formation  of,  934 
morphology  of,  943 
intersegmental,  938 


1322 


INDEX. 


Artery  or  Arteries — continued 
intesthiales,  846,  1073 
jejunales.     See  Rami  intestiiii  tenuis 
labiales  posteriores  (vulvae),  854 
labialis  inferior,  806 

superior.     See  A.,  coronary,  of  facial 
lacrimalis  =  lachrymal,  816 
laryngea  inferior,  823,  971 

superior,  804,  971 
lienalis.     See  A.,  splenic 
ligament!  teretis  uteri.     See  A.,  cremasteric 
lingual,  of  inferior  dental,  812 
lingualis,  805,  1006 
development  of,  933 
surgical  anatomy  of,  1243,  1249,  1251 
of  lower  limb,  856 

abnormalities  of,  953 
formation  of,  934 
morphology  of,  943 
lumbales.     See  A.,  lumbar 
lumbalis  inia  =  fifth  lumliar,  840 
lumbar,  839 

abnormalities  of,  949 
formation  of,  933 
of  ilio-lumbar,  850 
morjjhology  of,  940 
macular,  735 
malleolar,  external,  868 

internal,  of  anterior  tilnal,  868 
of  posterior  tibial,  865 
malleolaris     anterior     lateralis.        See     A., 
malleolar,  external 
medialis.     See  A.,  malleolar,  internal,  of 
anterior  tibial 
posterior    medialis.       See    A.,    malleolar, 
internal,  of  posterior  tibial 
mammaria    interna.       See    A.,    mammaiy, 

internal 
mammary,  external,  829 
internal,  825 

abnormalities  of,  951 
formation  of,  933 
morphology  of,  940,  941 
surgical  anatomy  of,  1255 
lateral,  951 
masseterica,  812 
mastoid,  of  occipital,  808 

of  posterior  auricular,  808 
maxillaris  externa.     See  A.,  facial 

interna.     See  A.,  maxillary,  internal 
maxillary,  internal,  810 
abnormalities  of,  950 
development  of,  933 
surgical  anatomy  of,  1237 
mediana,  834 

abnormality  of,  952 
morpliology  of,  943 
mediastinal,  of  aorta,  839 
mediastinals  anteriores,  825 
medullary.     See  A.  nutritiic  ossium 
meningea  anterior,  815 

media.     See  meningeal,  middle 
posterior  (asc.  phar.),  809 
meningeal,  of  internal  carotid,  815 
middle,  811 

surgical  anatomy  of,  1224,  1225,  1227 
of  occi])ital,  807 
small,  811 
of  vertebral,  819 
mentalis,  812 
mesenterica  inferior,  847 
abnormalities  of,  949 


Artery  or  Arteries — continued 

mesenterica  inferior,  morphology  of,  942 
surgical  anatomy  of,  1276 
superior,  845,  1126 
abnoi'inalities  of,  949 
morphology  of,  942 
surgical  anatomy  of,  1276 
metacarpeaj  dorsales.    See  A.,  interosseous,  of 
dorsal  carpal  arch 
volares.     See  A.,  interosseous,  palmar 
metacarpal,  833 

metatarsese    dorsales.      See  A.,  interosseous, 
dorsal  of  foot 
plantares.     See  A.,  digital,  of  foot 
metatarsal,  869 
muscle  fibres  of,  781 
inusculo-phrenica,  826 
mylo-hyoid,  812 
nasal,  dorsal,  816 
lateral,  807 
of  retina,  735 
naso-palatine,  813 
nerves  of,  783 
of  nose,  717,  723 

nutritise  ossium  (nutrient,  of  bones),  75 
claviculae,  825 
femoris,  862 
fibuh«,  865 
humeri,  831 
ossis  coxse,  851,  852 
radii,  834 
ulnai,  834 
obturatoria,  852 

abnormalities    of,    953.       See    also    Deej) 
epigastric  artery,  857 
occipital,  of  jaosterior  auricular,  808 
occipitalis,  807 

formation  of,  933 
oesophagese.        See     A.,     oesophageal,     of 

aorta 
oesophageal,  of  aorta,  839 
morphology  of,  942 
of  coronary,  844 
of  inferior  thyroid,  823 
ophthalmica,  815 

abnormalities  of,  950 
orbital,  of  middle  meningeal,  811 

of  superficial  temporal,  810 
ovarian,  843,  1185,  1192 
abnormalities  of,  949 
morphology  of,  942 
surgical  anatomy  of,  1284 
ovarica.     See  A.,  ovarian 
palatina  ascendens,  806,  1000,  1037 

descendens.     See  A.,  palatine,  posterior 
palatine,  of  ascending  j)haryngeal,  809     • 
posterior,  812,  1000,  1037 
surgical  anatomy  of,  1246 
palpebrales,  816 
pancreatic,  844 
of  hepatic,  1128 
of  sjilenic,  1128 
of  superior  mesenteric,  1128 
pancreatica  magna,  844,  1128 
pancreatico-duodenalis  inferior,  847,  1128 

superior,  845,  1126,  1128 
parietal,  of  superficial  temporal,  810 
parieto-occipital,  821 
parotid,  of  posterior  auricular,  808 

of  su])erficial  temporal,  809 
jjectoral,  of  acromio-thoracic,  829 
penis,  854,  1172 


I 


INDEX. 


1323 


Artery  or  Arteries — continued 

perforans   prima,   secuiida,   tertia.      See   A., 

perforating,  of  profunda  fenioris 
perforating,  anterior,  of  foot,  867,  869 
posterior,  866,  869 
inferior,  of  hand,  833 

superior,  833,  836 
of  internal  mammary,  826 
of  peroneal,  865 
of  profunda  fenioris,  861 
pericardiaco-plirenica.      See  A.  comes  iiervi 

phrenici 
pericardial,  of  internal  mammary,  826 

of  aorta,  839 
perineal,  suijerficial,  854,  1170 

transverse,  854 
perinei.     See  A.,  Perineal,  KUi)erticial 
perirenal,  842 
perontea — peroneal,  865 
abnormalities  of,  953 
formation  of,  934 
morijhology  of,  943 
surgical  anatomy  of,  1310 
anterior,  865 
posterior,  865 
pharyngea  ascendens,  808,  1037 

development  of,  933 
jjhrenic,  inferior,  839 
abnormality  of,  949 
suj)erior,  825 
jjhrenicie  superiores.     See  A.,  diaphragmatic, 

of  aorta 
pituitary,  815 
plantar,  external,  865,  866 
internal,  865 

abnormalities  of,  953,  954 
surgical  anatomy  of,  1312 
jdantaris  lateralis.     See  A.,  plantar,  external 

medialis.     iS'ee  A.,  plantar,  internal 
poplitea,  863 

abnormalities  of,  953 
formation  of,  934 
morphology  of,  943     ' 
surgical  anatomy  of,  1305 
prevertebral,  of  ascending  pharjTigeal,  809 
princeps  cervicis,  808 
hallucis,  869 
pollicis,  833 
abnormality  of,  952 
profunda  brachii.    See  A.  prof,  brach.  superior 
inferior,  831 
superior,  831 
clitoridis,  1198 
femoris,  860 

abnormalities  of,  953 
lingiise.     See  A.,  ranine 
penis,  1173 
of  ulnar,  835 
pterygoid,  812 
pterygo-palatine,  812 
pubic,  of  deep  epigastric,  857 

of  obturator,  852 
l^udenda  interna.     See  A.,  pudic,  internal 
pudendte  externse.     See  A.,  pudic,  external, 

superficial,  and  deep 
pudic,  accessory,  953 

external,  deep,  860,  1170 

superficial,  859,  1170 
internal,  853 

surgical  anatomy  of,  1278,  1303 
pulmonalis.     See  A.,  pulmonary 
pulmonary,  795,  989,  991 


Artery  or  Arteries — contimied 
pulmonary,  abnormalities  of,  947 
development  of,  930,  933 
morphology  of,  942 
surface  anatomy  of,  1264 
pyloric,  845,  1060 

morphology  of,  942 
radialis,  831 

abnormalities  of,  952 
formation  of,  934 
morphology  of,  943 
surgical  anatomy  of,  1301 
indicis,  833 

abnormalities  of,  952 
surgical  anatomy  of,  1301 
ranine,  805 

recurrens  radialis,  tibialis.     See  A.,  recurrent 
recurrent,  of  deep  palmar  arch,  837 
interosseous,  posterior,  835 
radial,  832 

al)normalities  of,  952 
tibial,  anterior,  868 

posterior,  868 
ulnar,  834 
renalis,  842,  1140 

abnormalities  of,  949 
morphology  of,  942 
surgical  anatomy  of,  1276 
of  round  ligament,  843 
sacralis  laterali.s,  850 
morphologv  of,  943 
media,  841,  1095 

abnormalities  of,  949 
morjjliology  of,  942 
saphenous,  862 

small,  953 
of  scalp,  1222 
scapular,  dorsal,  829 
posterior,  824 
transverse,  825 
sciatic,  854 

abnormalities  of,  953 
formation  of,  934 
morjDhologj^  of,  943 
scrotales  posteriores,  854 
segmental,  932,  933,  939 
anastomoses  of,  939 
somatic,  933,  939 
splanchnic,  933,  939,  942 
septal,  of  nose,  807 
sheath  of,  782 
sigmoideie,-  848,  1075 
spermatic,  842,  1162 
abnormalities  of,  949 
morj^hology  of,  942 
spermatica  externa.     See  A.,  cremasteric 

interna.     See  A.,  spermatic 
spheno-palatina,  813 
spinal,  formation  of,  933 
of  ilio-lumbar,  850 
of  intercostals,  838 
of  lateral  sacral,  850 
of  vertebra],  818,  819 
spinalis  anterior  et  posterior.     See  A.,  .spinal, 

of  vertebral 
splenic,  844,  1212,  1213 
abnormalities  of,  949 
morphology  of,  942 
stapedial,  757 
sternomastoid,  of  occij^ital,  807 

of  superior  thyroid,  805 
of  stomach,  1060 


1324 


INDEX. 


Artery  or  Arteries — continued 
striate,  external,  817 

internal,  817 
structure  of,  780,  781 
stylo-mastoidea,  808 
subclavia,  821,  822 

abnormalities  of,  947,  948,  951 
branches  of,  823 
development  of,  933,  934 
morjiliology  of,  941,  942 
surgical  anatomy  of,  1252,  1255 
subcostal,  838 
sublingualis,  805 
submaxillary,  806 
submentalis,  806 

subscajjular,  of  suprascapular,  825 
subscapularis,  829 
suj)erficial  jjetrosal,  811 

volar,  832 
sujH'aliyoid,  805 
supraorbitalis,  816 

surgical  anatomy  of,  1224 
suprarenalis  inferior,  842 

media.     See  A.,  capsular 
suprascapular,  825 
supraspinous,  825 
surales,  863,  864 
systemic,  797 
tarsal,  lateral,  869 
temporal,  deej),  anterior,  812 
l^osterior,  812 
middle,  809 

of  posterior  cerebral,  821 
of  retina,  735 
temporalis  media.     See  A.,  tempoi'al,  middle 
profunda  anterior,  et  posterior.      See  A., 

temporal,  deep 
superficialis,  809 
development  of,  933 
surgical  anatomy  of,  1224 
testicularis,  843,  1162 
tlioracic,  alar,  829 
long,  829 
superior,  828 
thoracalis  lateralis.     See  A.,  tlioracic,  long 

suj^rema.     See  A.,  thoracic,  superior 
thoraco-acromialis.     See  A.,  acromio-thoracic 
thyreoidea  ima,  801,  1217,  947 
morphology  of,  942 
inferior,  823,  1217 

surgical  anatomy  of,  1252 
superior,  804,  1217 
mythology  of,  942 
surgical  anatomy  of,  1251 
tibial,  recurrent,  868 
tibialis  anterior,  867 

abnormalities  of,  953 
formation  of,  934 
moi'phology  of,  943 
surgical  anatomy  of,  1309 
posterior,  864 

abnormalities  of,  953 
ibrmation  of,  934 
morpliology  of,  943 
surgical  anatomy  of,  1310 
of  tongue,  1006 
of  tonsil,  1036 

tonsillar,  of  facial,  806,  1006 
tracheal,  823 

transverse,  of  basilar,  820 
transversa  colli.     See  A.,  cervical,  transverse 
faciei.     See  A.,  facial,  transverse 


Artery  or  Arteries — continued 

transversa  scapulae.     See  A.,  suprascapular 

tubal,  843 

tunica  externa  of,  781 

intima  of,  781 

media  of,  781 
tympanic,  of  internal  carotid,  814 
tympanica  anterior  (A.,  max.  int.),  811 

inferior  (A.,  phar.  asc),  809 

posterior  (A.,  stylomas.),  808 

superior  (A.,  mening.  med.),  811 
ulnaris,  834 

abnormalities  of,  952 

formation  of,  934 

morphology  of,  943 

surgical  anatomy  of,  1301 
umbilical,  of  foetus,  51,  848 
umbilicalis.     See  A.,  hypogastric,  obliterated 
of  upper  limb,  821 

abnormalities  of,  951 

formation  of,  933 

morphology  of,  943 
ureteral,  of  renal,  842 

of  spermatic  and  ovarian,  843 
uterina,  852,  1192 

surgical  anatomy  of,  1284 
uterine,  of  ovarian,  843,  1192 
vaginal,  of  liver,  1120 
vaginalis,  851,  1195 
of  vas,  851,  1167 
venfe  comites  of,  abnormalities  of,  955 

morj)hology  of,  946 
vertebralis,  818,  823 

abnormalities  of,  947,  950 

development  of,  933 

morphology  of,  940,  941 

surgical  anatomy  of,  1252 
vesical,  middle,  851 

of  obturator,  852 
vesicales  sujieriores,  851,  1157,  1167 
vesicalis  inferior,  851,  1157,  1167 
vesico-vaginal,  1195 
'    vessels  of,  782 
Vidian,  of  internal  carotid,  815 

of  internal  maxillary,  812 
visceral,  intermediate,  939,  942 
volaris    indicis    radialis.       See    A.    radialis 

indicis 
zygomatico-orbitalis,  810 
Arthrodia,  257 
Arthrology,  3,  255 
Articular  arteries.     See  Artery 
disc,  260,  261 

eminence  of  temporal  bone,  113,  154 
processes  of  atlas,  79 

of  axis,  80 

of  cervical  vertebras,  78 

of  coccyx,  87 

of  dorsal  vertebras,  81 

of  lumbar  vertebrce,  84 

of  sacrum,  85,  86 

serial  homology  of.  Appendix  C,  xiv 

of  twelfth  dorsal  vertebrae,  82 
Articulatio  or  Articulationes.     See  also  Joints 
acromio-clavicularis,  274,  275 

toj^ography  of,  1295 
atlanto-epistrophica.     See  Joint,  atlo-axial 
atlanto-occipitalis.    See  Joint,  occipito-atloid 
calcaneo-cuboidea,  311 

surgical  anatomy  of,  1311 
capitulorum.     See  Joints,  costo-central 
carpo-metacarpea  pollicis,  287 


INDEX. 


1325 


Articulatio  or  Articxilationes — continued 
carpo-metacarpese  digitorum,  287 
costo-transversariae,  270 
costo-vertebrales,  269 
coxae.     See  Joint,  hip 
crico-arytenoidea,  962 
crico-thyreoidea,  961 
cubiti.     See  Joint,  elbow 
cuneo-navicularis.     See  Joint,  scapho-cimei- 

form 
digitorum  manus,  288 

pedis,  314 
genu.     See  Joint,  knee 
humeri.     See  Joint,  shoulder 
humero-radialis,  279 
humero-ulnaris,  279 
incudo-malleolaris,  756 
incudo-stapedia,  756 
intercarpeae,  284  ' 
interchondrales,  279 
intermetacarpeae,  287 

movements  at,  289 
intermetatarseae,  314 
intertarseae,  308 

movements  at,  312 
mandibularis.    See   Joint,    temporo  -  mandi- 
bular 
manus,  284 
metacarpo-phalaugeae,  288 

movements  at,  289,  352 

surgical  anatomy  of,  1300 
metatarso-phalangeae,  314 

movements  at,  315,  384 

surgical  anatomy  of,  1311,  1312 
ossiculorum  auditus,  756 
ossis  pisiformis.     See  Joint,  piso-cuneiform 
pedis.     See  Joints  of  foot 
radiocarpea,  283 

movements  at,  284,  352 

surgical  anatomy  of,  1298 
radio-ulnaris  distalis.    See  Joint,  radio-ulnar, 
inferior 

proximalis.  See  Joint,  radio-ulnar,  superior 
sacro-iliaca,  290,  293 

topography  of,  1302 
sterno-clavicidaris,  273 

movements  at,  275,  327 

surgical  anatomy  of,  1291 
sterno-costales.     See  Joints,  costo-sternal 
talo-calcanea,  308 
talo-calcaneo-navicidaris,  309,  315 
talo-ci'uralis.     See  Joint,  ankle 
talo-navicularis.     See  Joint,  talo-scaphoid 
tarsi  transversa  (Choparti).     See  Joint,  trans- 
verse tarsal 
tarso-metatarseae,  313,  315 

surgical  anatomy  of,  1311 
tibio  -  fibularis.      See     Joint,     tibio  -  fibular, 
superior 
Aryteno-epiglottidean  folds,  964 
development  of,  38 

muscle,  970 
Arytenoid  cartilage,  960 

development  of,  992 

ossification  of,  961 

processus  muscularis  of,  960 
vocalis  of,  961 

sesamoid  of,  960 
muscle,  970 

action  of,  971 
Ary  vocalis  muscle,  970 

action  of,  971 


Ascending  degeneration,  466 

palatine  artery,  806,  1000 
Association  centres,  593 
fibres,  cerebellar,  511 

of  cerebral  hemisj^heres,  589 
of  cord,  468,  470 
of  medulla,  498 
Asterion,  151,  158,  Appendix  D,  xvi 
Astragalo-calcanean  ligaments,  309 
Astragalo-scaphoid  joint,  309 
surgical  anatomy  of,  1312 
ligament,  311 
membrane,  311 
Astragalus,  238 

architecture  of,  Aj^pendix  A,  v 
articiUar  surfaces  of,  306,  309 
homology  of,  Appendix  F,  xxiv 
ossification  of,  249 
Asymmetry,  4 
Atlas,  79 

ossification  of,  92 

serial  homology  of,  Appendix  C,  xiv 
transverse  ligament  of,  265,  267 
transverse  process  of,  relations  of,  165 
surgical  anatomy  of,  1251 
Atlo-axial  joint,  265 

movements  at,  267,  393 
Atresia  ani,  1097 

Atrium  cordis  dextrum.      See  Heart,  auricle, 
right 
sinistrura.     See  Heart,  auricle,  left 
meatus  nasi,  135,  721 
of  primitive  heart,  929 
of  tvmpanic  cavity,  748 
Attic,"^  tympanic,  1232,  1233 
Attollens  aurem  muscle,  396 

nerve-supply  of,  404 
Auditory  area  of  cerebral  cortex,  593 
artery,  769,  820 
labyrinth,  759 

meatus,  external,  115,  154,. 746 
blood-vessels  of,  748 
ceruminous  glands  of,  748,  778 
development  of,  44,  121 
fissures  of  Santorini  of,  748 
foramen  of  Huschke  of,  748 
isthmus  of,  747 
lymphatics  of,  748 
nerves  of,  748 
structure  of,  747 
surgical  anatomy  of,  1229 
variation  in,  Appendix  B,  ix 
internal,  118,  169,  170 

absence  of,  Appendix  B,  ix 
fundus  of,  761 
nerve,  688.     See  also  Nerve 
ossicles,  754 
pit,  66,  769 

radiation,  583,  591,  592 
teeth  of  Huschke,  766 
vesicle,  703 
Auerbach,  plexus  of,  in  stomach,  1060 

in  intestines,  1073 
Auricula.     See  Pinna 

(cordis)     dextra.        See     Heart,      auricular 
appendix,  right 
sinistra.     See   Heart,  auricular  appendix, 
left 
Auricular  artery,  deep,  811 
of  occipital,  808 
posterior,  808 

development  of,  933 


1326 


INDEX. 


Aiiricular     artery,    deep     posterior,     surgical 
anatomy  of,  1229 
canal,  929 
cartilage,  745 
fissure,  114 
index,  744 
nerves,  746 

of  auricido-temjioral,  684 
great,  617,  618 

morpliology  of,  622 
posterior,  687 
of  vagus,  692 
septum,  930 
surface  of  ilium,  214 

of  sacrum,  86 
vein,  posterior,  878 
Auricularis  muscle,  anterior,  396 
posterior,  396 
superior,  396 
Auricles  of  lieart,  786.     See  also  Heart 
Auriculo-temporal  nerve,  684 
surface  anatomy  of,  1224 
Auricido-ventricular  apertures,  783 
mitral,  788,  790 
tricuspid,  787,  789 
groove,  783,  785 

surface  anatomy  of,  1262 
Auris.     See  Ear 

interna.     See  Ear,  internal 
Auscultation,  triangle  of,  320 
Axial  line,  dorsal,  of  limbs,  614,  672 
ventral,  of  limbs,  660,  672 
muscles,   385 

process,  22.     See  also  Axon 
skeleton,  69,  70 
Axilla,  1293 
■  folds  of,  1293 
lymphatic  glands  of,  1294 
surgical  anatomy  of,  1293 
Axillary  arches,  325 

nerve-supply  of,  671 
artery,  827 

abnormalities  of,  951 
formation  of,  933 
surgical  anatomy  of,  1292,  1293 
border  of  scapula,  184 
fascia,  322 
folds,  1293 
lines,  1253 

lymjibatic  glands,  914 
region,  1253 
slieatli,  828 
vein,  888 

development  of,  938 
morphology  of,  946 
surgical  anatomy  of,  1292 
Axis,  basi -cranial,  170 
cceliac,  843 

abnormalities  of,  949 
morphology  of,  942 
surgical  anatomy  of,  1276 
cylinder.     See  Axon 
lenti.s,  736 

ligament  of  malleus,  757 
optica,  724 
pelvis,  221 
thyroid,  artery,  823 
abnormalities  of,  951 
nioi'pliology  of,  941 
vertebra,  80 

devcloi)nu'nt  (jf,  93 
topograpliy  of,  1253 


Axon,  445,  449 

development  of,  22,  448,  472 
Azjrgos  lobe  of  lung,  989 

uvulas  muscle,  412 
nerve-supply  of,  413 

veins,  872.     See  also  Veins 

Bacillary  layer  of  retina,  732,  734 
Back,  fascia  of,  319,  385 
muscles  of,  386 

actions  of,  392,  393 
nerve-supply  of,  392 
superficial,  319 
regions  of,  1284 
spinal  furrow  of,  1284 
surgical  anatomy  of,  1284 
Baillarger,  bands  of,  585,  587 
Balbiani,  body  of,  11 
Ball-and-socket  joint,  257,  259 
Band  of  Baillarger,  585,  587 
of  Bechterew,  587 
ilio-tibial,  355 

surface  anatomy  of,  1308 
of  Meckel,  757 
of  Vicq  d'Azyr,  585 
Bar,  hyoid,  37,  146 
thyreo-hyoid,  146 
Barbula  hirci,  746 
Bartholin,  duct  of,  1013 
glands  of,  1182,  1198 
development  of,  1206 
surgical  anatomy  of,  1283 
Basal  cells  of  olfactory  mucous  membrane,  723 
centre  of  mandible,  145 
ganglia,  579 

lamina.     See  Neural  tube 
layer  of  placenta,  57,  58 
ridge  of  tooth,  1017 
Base  of  cranium,  159 
of  heart,  784 
of  lower  jaw,  142 
Base-line  of  Eeid,  1227 
Basement  membrane,  1008 
Basi-cranial  axis,  170 
Basihyal,  146 

Basilar  artery,  820.     See  also  Ai-tery 
groove.  111 

membrane.     See  Menibrana  basilaris 
process,  108,  111,  159,  163 

development  of,  Appendix  E,  xxi 
sinus,  885 
sulcus  of  pons,  486 
vein,  883  ' 
Basilic  vein,  891.     See  also  Vein 
Basion,  165,  Appendix  D,  xvi 
Basiotic  bone,  112,  Appendix  B,  viii 
Basi-pharyngeal  caiial,  162 
Basi-sphenoid,  126 

Basis  bimdle,  anterior,  470,  483,  491,  494 
development  of,  473 
lateral,  468,  470,  484,  498 
development  of,  473 
cerebri,  475 
cochlefe,  760 

cordis.     See  Base  of  heart 
cranii.     See  Base  of  cranium 
mandibulse.     See  Base  of  lower  jaw 
modioli  cochlete,  761 
ossis  hyoidei.     See  Hyoid  bone,  body  of 
pedunculi.     See  Crura  cerebri,  crusta  of 
stapedis,  756 
Basket-cells,  513 


INl)EX. 


1327 


Becliterew,  band  of,  587 

nucleus  of,  520 
Beraiid,  valve  of,  741 
Bertin,  bones  of,  127 

columns  of,  1138 
Biaxial  joints,  257 
Biceps  bracliii  muscle,  332.     See  also  Muscle 

femoris  muscle,  368.     See  also  Muscle 
Bicipital  artery,  830 
fascia,  334 

surgical  anatomy  of,  1297 
furrow,  1295 
groove,  189,  190 

topography  of,  1293 
tuberosity,  199 
Bicusjjid  arteries,  812 

teeth,  1015,  1018 
Bifurcatio  trache;i3,  1260,  1289 
Bigelow,  Y-shaped  ligament  of,  295 
Bile  canaliculi,  1118,  1122 
Bile  duct,  common,  1120 
develojjment  of,  1123 
level  of,  1290 

relation  of,  to  duodenun),  1068 
termination  of,  1068,  1070 
surgical  anatomy  of,  1270 
papilla,  1070,  1120 
Biasterionic  width.  Appendix  D,  xvii 
Bistephanic  diametei',  Appendix  D,  xvii 
Biventer  cervicis  muscle,  389 
Biventral  lobule,  508 

Bladder,  gall,  1118.     See  also  Gall  bladder 
urinary,  1130,  1144 
capacity  of,  1150 
development  of,  1200,  1202 
distended,  1148 
empty,  1147 
in  female,  1151 
fixation  of,  1156 
in  infant,  1151 
interior  of,  1153 

examination  of,  1283 
ligaments  of,  false,  1100,  1154,  1156 

true,  1156 
neck  of,  1145 
nerves  of,  1157 
peritoneal  relations  of,  1153 
pliciB  uretericae  of,  1151 
sphincter  of,  1157 
structure  of,  1156,  1157 
trigonum  of,  1151,  1203 
urachus  of,  1146,  1156 

develo23ment  of,  1203 
ureteral  orifices  of,  1151 
examination  of,  1283 
urethral  orifice  of,  1145,  1146 
uvula  of,  1151 
vessels  of,  1157 
Blastoderm,  19,  20,  22,  50 
areas  of,  22,  50 
layers  of,  19 
Blastodermic  vesicle,  18,  19,  26,  50 
Blastomere,  17 
Blastopore,  19 
Blastiila,  18,  65 
Blind  spot,  732 
Blood  capillaries,  780 
development  of,  61 
islands,  61 
Blood-vascular  system,  780 
abnormalities  of,  946 
development  of,  60,  925 


Blood -vascular  system,  morj^hology  of,  938 
Blood-vessels.     See  Arteries,  Veins 

development  of,  61 
Body  of  Balbiani,  11 
cavity,  25,  1105 
pituitary,  549 

development  of,  42 
polar,  13,  15 
stalk,  33,  50,  65 
vitelline,  11 
Wolffian,  32,  1201 
Bone  or  Bones,  69 
air-spaces  of,  72 
of  Bertin,  127 

bregmatic.  Appendix  B,  viii 
carpal,  201 
cartilage,  74 

of  skull.  Appendix  E,  xxii 
compact  tissue  of,  71 
composition  of,  70 
descriptive  terms,  70 
diaphysis  of,  73 
diploe,  72 

epactal.     See  Bones,  sutural 
epiphyses  of,  73,  74 
epipteric,  119,  133 
of  face,  103,  133 
fiat,  70,  72 
of  foot,  238 
growth  of,  74 
of  hand,  201 

Haversian  systems  of,  72 
of  head,  103 
hip,  212 
irregular,  70 
long,  70,  71,  72 
of  lower  limb,  212 
lymphatics  of,  75 
marrow  of,  71 
membrane,  73, 

of  skull,  A])pendix  E,  xxii 
metacarpal,  207 
metatarsal,  249 
of  middle  car,  754 
nerves  of,  75 
number  of,  70 
ossification  of,  73 
periosteum  of,  71,  73 
primordial,  A])pendix  E,  xxii 
secondary.  Appendix  E,  xxii 
sesamoid,   of    metacarpo  -  phalangeal  joints, 
212,  288,  344 
of  metatarso-phalangeal  joint,  253,  314, 382 
of  peroneus  longus,  253,  375 
See  also  Patella 
short,  70 
of  skull,  103 
of  spine,  75 
strength  of,  71 
structure  of,  71 
sutural,  133 
tarsal,  238 
thigh,  223 
of  thorax,  94,  101 
of  upper  limb,  181 
vascular  supply  of,  75 
Wormian,  133,  158,  Appendix  B,  viii 
Bowman,  elastic  lamina  of,  726 

glands  of,  722 
Brachial  artery,  830.     See  o.lso  Artery 

plexus,  622.     See  also  Plexus 
Brachialis  muscle,  334 


1328 


INDEX. 


Brachialis  iniiscle,  action  of,  335 

nerve-supply  of,  335 
Bracliio-ceplialic  vein,  873 
Brachio-radialis  muscle,  348 
action  of,  352 
nerve -supply  of,  351 
Brachium  coiijunctivum  cerebelli,  486,  503,  535 

quadrigeminum  inferius  532,  534,  535 
superius,  532,  534,  535 
Brachycephaly,  158,  Apj)endix  D,  xv 
Bracliyfacial  skulls,  Ajjpendix  D,  xvii 
Brachykerkic  limbs.  Appendix  D,  xx 
Bracliy-knemic  limbs.  Appendix  D,  xx 
Bracliyuranic  skulls,  Appendix  D,  xviii 
Brain,  44J,  474 

arteries  of,  813,  818 

development  of,  476.     See  also  Development 

flexures  of,  479 

fore,  476,  478,  542 
development  of,  594 

hind,  476,  481 

development  of,  526 
isthmus  of,  476 

lymphatics  of,  909 

meninges  of,  597 

mid-brain,  531.     See  also  Mid-brain 

nerve-cells  of,  445 

nerve-fibres  of,  444 

neuroglia  of,  451 

veins  of,  881 

weight  of,  597 
Branchial  arches,  36 

muscles  derived  from,  441 

nerves  of,  701,  702,  703 
Breast,  1207 

bone,  94 
Bregma,  158,  Appendix  D,  xvi 

topography  of,  1223 
Bregmatic  bone,  Appendix  B,  viii 

fontanelle,  Appendix  E,  xxii 
Brim  of  pelvis,  221 
Broad  ligament  of  uterus,  1101,  1189 

surgical  anatomy  of,  1284 
Broca's  convolution,  1224 
Bronchi  (dexter  et  sinister),  975,  989 

apical,  990 

cardiac,  990 

cartilaginous  rings  of,  975 

development  of,  992 

eparterial,  976,  990 

hbro-cartilaginous  coat  of,  991 

hyparterial,  976,  990 

mucous  membrane  of,  991 

muscular  coat  of,  991 

relations  of,  976 

in  root  of  lung,  989 

structure  of,  976,  991 

topography  of,  1260,  1290 
Broncliial  arteries,  838,  989 
abnormalities  of,  948 
morpliology  of,  942 

lymphatic  glands,  924 

tu];es  in  lung,  989 

veins,  873,  989 

morpliology  of,  945 
Bronchioli,  991 
Bruch,  membrane  of,  728,  729 
Brunner,  glands  of,  1061,  1070 
Bucc«i.     See  Cheeks 
Buccal  artery  of  facial,  807 
of  internal  maxillary,  812 

glands,  997 


Buccal  lymphatic  glands,  910 
nerve  of  fifth,  684 
nerve  of  seventh,  688 
vein,  880 
Buccinator  muscle,  398 

action  of,  399,  413 

nerve-supply  of,  399 
Bucco-pharyngeal  area,  23,  33 
fascia,  1037 
membrane,  33,  35,  38 
Buds,  taste,  770,  1004 
Bulb,  aortic,  927,  929 

abnormality  of,  947 

septum  of,  930 
of  brain.     See  Medulla  oblongata 
of  cornu,  576 

of  corpus  spongiosum,     See  Bulb  of  urethra 
of  hair  root,  777 
of  jugular  vein,  876 
olfactory,  569.     See  also  Olfactory  bulb 
of  urethra,  1171 

surgical  anatomy  of,  1277 
of  vagina.     See  Bulb  of  vestibule 
of  vestibule,  1182,  1198 

surgical  anatomy  of,  1283 
Bulbo-cavernosus  muscle,  432 
Bulbus  aortse.     See  B.  arteriosus 
arteriosus.     See  Bulb,  aortic 
cornu  posterius.     See  Bulb  of  cornu 
oculi.     See  Globe  of  eye 
olfactorius.     See  Olfactory  bulb 
pili.     See  Bulb  of  hair  root 
urethrae.     See  Bulb  of  urethra 
venee    jugularis    suj^erior.        See    Bulb    of 

jugular  vein 
vestibuli.     See  Bulb  of  vestibule 
Bulla  ethmoidalis,  721 

Bundle,   posterior   longitudinal.       See   Longi- 
tudinal bundle,  posterior    • 
Burdach,  column  of     See  Sjjinal  cord 
Burns,  space  of,  879 
Bursa  or  Burste,  258,  318 

of  coracoclavicular  ligament,  275 
of  eyeball.     See  Capsule  of  Tenon 
of  flexor  carpi  radialis,  339 
under  hyoid  bone,  962 
of  ilio-psoas,  296,  360 

surgical  anatomy  of,  1307 
at  knee-joint,  299,  302,  303 

surgical  anatomy  of,  1305,  1307 
of  muscles  of  arm,  334,  335 

of  back,  superficial,  320, 

of  back  of  forearm,  348 

of  back  of  leg,  377,  378 

of  back  of  thigh,  368,  369,  370 

of  buttock,  365,  366,  367 

of  front  of  leg,  374,  375 

of  front  of  thigh,  358,  359,  360 

of  shoulder,  328,  329 
omentalis.     See  Peritoneum,  small  sac  of 
of  peroneal  muscles,  375,  376 
pharyngea,  1033 
prajpatellaris  subcutanea,  1307 
at" shoulder-joint,  278 
subcutaneous,  258 
Subtendinous,  258 
thecal,  258 
Buttock,  fascige  of,  353 
muscles  of,  364 

actions  of,  370 

nerve-supply  of,  370 
surgical  anatomy  of,  1302 


iiJdex. 


1329 


Caical  artery,  1081 
folds,  1081 
fossee,  1081 
C«cum,  1074,  1076 
development  of,  1078 
dimensions  of,  1076 
foetal,  1078 

ileo-csecal  orifice  of,  1076,  1077,  1078 
infantile,  1079 
position  of,  1076,  1078 
relations  of,  1076 
surgical  anatomy  of,  1273 
types  of,  1078 
vermiform  process  of,  1079 
vessels  of,  1081 
Cfecum  cupulare  cochlea?,  764 

vestibulare,  763,  764 
Calamus  scriptorius,  488 
Calcaneal  artery,  866 
Calcanean  facets,  240,  241 

nerve,  internal,  453 
Calcaneo-astragaloid  joint,  308 
surgical  anatomy  of,  1311 
Calcaneo-cuboid  joint,  311 

surgical  anatomy  of,  1311 
ligaments,  311 
functions  of,  315 
Calcaneo-fibular  ligament,  307 
Calcaneo-metatarsal  ligament,  373 
Calcaneo-scaphoid  ligaments,  309 
function  of,  315 
surgical  anatomy  of,  1312 
Calcaneo-tibial  ligament,  307 
Calcaneus,  243 
Calcar  avis,  576 

femorale.  Appendix  A,  v 
Calcarine  artery,  821 

fissure,  565,  566,  576 
Callosal  gyrus,  568 

svdcus,  568 
Calloso-marginal  fissure,  560 
Calyces  renales,  1141 

develoijment  of,  1202 
Calyculi  gustatorii.     See  Buds,  taste 
Camera  oculi  anterior.     See  Chamber,  anterior, 
of  eye 
posterior.     See  Chamber,  posterior,  of  eye 
Canal ;  Canalis 

adductorius  (Hunteri).     See  Hunter's  canal 
of  Alcock,  853 
alimentary,  993 

primitive,  32,  1105 
anal,  1091.     See  also  Anal  canal 
development  of,  45 
surgical  anatomy  of,  1280 
for  Arnold's   nerve.      See  Canaliculus  mas- 

toideus 
auricular,  929 
basi-pharyngeus,  162 
caroticus,  117,  163,  168 

relation  of,  to  tympanum.  Appendix  A,  ii 
variation  in,  Appendix  B,  ix 
central,  of  medulla,  498 
centralis  cochlete,  762 

medullse  spinalis,  456,  459 
development  of,  473 
cervicis  uteri,  1188 

condyloideus.  See  Foramen,  condylic,  posterior 
cranio-pharpigeus,  123,  163 

closure  of.  Appendix  E,  xxi 
crural.     See  Canal,  femoral 
dental,  inferior,  143,  156 

89 


Canal,  dental,  posterior,  134,  155 

of  epididymis,  1162 

development  of,  1199,  1202,  1205 
ethmoidal,  on  ethmoid,  128 

on  frontal,  104 

in  the  orbit,  147 

in  anterior  cranial  fossa,  166 
Eustachian,  116,  163,  165 
facialis  (Fallopii).    See  Aqueduct  of  Fallopiiis 
femoral,  356 
Haversian,  72 
of  Hugiiier,  113 

relation  of,  to  tympanum,  750 
hyaloideus,  736 

development  of,  742 
hypoglossi.     See  Foramen,  condylic,  anterior 
infraorbitalis,  134,  149,  175 
inguinalis,  428 

surgical  anatomy  of,  1265 
innominatus,  163 
for  Jacobson's  nerve,  117 
lacrimal,  membranous,  740 
development  of,  743 

osseous.     See  Canal  of  nasal  duct 
malar,  141 

mandibulaj.     See  Canal,  dental,  inferior 
musculo-tubarius.     See  Canal,  Eustachian 
of  nasal  duct,  135,  150,  172,  174 
naso-lacrimalis.      See   Groove,    lacrimal,  of 

maxilla 
neural,  76,  90 
neurenteric,  20,  66 
of  Nuck,  1190 
obturatorius,  293 
palatine,  accessory,  139,  161 
superior  openings  of,  157 

anterior,  136,  161,  172 

posterior,  135,  136,  138,  157,  161 
palato-maxillary,  135 
of  Petit,  736 

pharjTigeus.     See  Canal,  pterygo-palatine 
portal,  1120 

pterygoideus  (Vidii).     See  Canal,  Vidian 
pterygo-palatine,  126,  140,  157,  161 
pterygo  -  palatinus.       See    Canal,    palatine, 

posterior 
pyloric,  1052,  1055 
radicis  dentis,  1016 
reuniens,  770 
sacralis,  87 
of  Schlemm,  725 

semicirculares  ossei.     See  Semicircular  canals 
spheno-vomerine.  Appendix  B,  x 
spinalis,  88,  90 
spiralis  modioli,  761 
of  Stenson,  998 
temporal,  141,  153 
for  tensor  tympani  muscle,  116,  750 
urogenital,  1200 
Vidian,  125,  157,  162,  163,  168 
Canaliculus  or  Canaliculi,  bile,  1118,  1122 
of  bone,  72 

carotico-tympanici,  117 
innominatus,  124 
lachrymales,  1239 
mastoideus,  116 
tympanicus,  117 
Canine  teeth,  1015,  1017 
eruption  of,  1022 
fossa,  134,  1237 
Canthi  of  eye,  738 
Capillaries,  780 


1330 


INDEX. 


Capillary  arterioles,  V80 
lymi:)hatics,  905 
veins,  780 
Cai^itellum.     See  Capitulum  humeri 
Capitular  process.  Appendix  C,  xiv 
Capitulum  humeri,  192 

maudibulfe.     See  Condyle  of  jaw 
Capsula  adiposa  of  kidney,  1276 
articularis.     See  Capsule  of  joints 
externa.     See  Capsule,  external 
fibrosa  (Glissoni).     See  Liver,  areolar  coat  of, 

and  Cajisule  of  Glisson 
glomeruli.     See  Capsule,  glomerular 
interna.     See  Capsule,  internal 

pars    frontalis.      See    Capsule,  internal, 

anterior  limb  of 
occij)italis.       See  Capsule  internal,  pos- 
terior limli  of 
Cai^sular  artery,  iiiferior,  842 
of  liver,  1121 
middle,  842 

morjihology  of,  942 
superior,  839 
Capsule,  external,  581,  583 
of  Glisson,  1115,  1120,  1121 
glomerular,  1139 
internal,  543,  582 
anterior  limb  of,  583 
auditory  radiation  fibres  of,  583,  592 
fronto-pontine  fil^res  of,  583,  591 
fronto-thalamic  fibres  of,  583 
genu  of,  583 
lenticular  part  of,  583 
optic  radiation  fibres  of,  553,  583,  592 
posterior  limb  of,  583 
pyramidal  fibres  of,  583,  591 
retro-lenticular  part  of,  583,  592 
strio-thalamic  fibres  of,  581,  583 
tem^Doro-pontine  fibres  of,  583,  591 
thalamo-frontal  fibres  of,  583 
thalamo-striate  fibres  of,  583 
of  joints,  258 
of  lens,  736 

otic,  119  ;  Apjjendix  E,  xxi 
suprarenal.     See  Suprarenal  capsule 
of  Tenon,  405,  724 
Caput    angulare    m.  ([uadrati  labii  sujierioris. 
See  Muscle,  levator  labii  superioris  alseque 
nasi 
epididymidis.     See  Epididymis,  globus  major 

of 
infraorbitale   m,   quadrati    lal^ii    superioris. 

See  Muscle,  levator  labii  superioris 
zygomaticum  m.   quadrati   labii  superioris. 
See  Muscle,  zygomaticus  minor 
Cardia,  1051,  1055 

topography  of,  1271,  1287,  1290 
Carcfiac  bronchus,  990 

ganglion  of  Wrisberg,  693 

lobe  of  lung,  990 

nerves  of  sympathetic,  707,  708 

of  vagus,  692 
notch  of  lung,  989 
plexus.     See  Plexus 
portion  of  stomach,  1050,  1052,  1055 
Cardiac  veins,  871 
Cardinal  veins,  935,  936 

morphology  of,  944,  945 
Carina  urethralis,  1195 
Carotid  arteiy,  common,  801 
almormalities  of,  950 
develo])ment  of,  933 


Carotid  artery,  common,  morphology  of,  942 
surgical  anatomy  of,  1250,  1264 
left,  802 

abnormalities  of,  947,  950 
right,  803 

abnormalities  of,  947,  948,  950 
external,  803 

abnormalities  of,  947,  950 
development  of,  933 
morj^hology  of,  942 
surgical  anatomy  of,  1250 
internal,  813 

abnormalities  of,  947,  950 
development  of,  933 
moriDhology  of,  942 
canal,  117,  163,  168 

relation  of,  to  tympanum,  Appendix  A,  ii 
variation  in.  Appendix  B,  ix 
gland,  1220 
groove,  123,  168 
lymphatic  glands,  1247 
jilexus,  707,  712 
sheath,  395,  802 
triangle,  1250,  1251 
tubercle,  1252 
Carjjal  arch,  anterior,  835 
dorsal,  836 
artery,  anterior  radial,  832 
ulnar,  835 
posterior  radial,  833 
ulnar,  835 
bones,  201 

architecture  of.  Appendix  A,  iii 
ossification  of,  207 
variations  in,  Apj^endix  B,  xi 
joints,  284 

movements  at,  289 
nerves  to,  631 
synovial  membrane  of,  286 
transverse,  285 
Carpale,  os,  Apjoendix  F,  xxiv 
Carpo-metacarpal  joints,  287 
Carims,  201 

ossification  of,  207 
Cartilage  ;  Cartilago,  Cartilagines — 
alares  minores,  719 
alaris  major.     See  Cartilage,   nasal,  lateral, 

lower 
aryteenoidea,  960.  See  also  Arytenoid  cartilage 
auriculge,  745 
bones,  74 

of  skull,  Ajjpendix  E,  xxiv 
corniculatfe    (Santorini).      See   Cartilage   of 

Santorini 
costalis,  100 
joints  of,  271 
topograjahy  of,  1265 
cricoidea,  959 

development  of,  992 
ossification  of,  961 
surgical  anatomy  of,  1249 
cuneiform  es  (Wrisbergi),  961 
ensiform,  94,  96 
ejiiglottica,  961 
laryngis,  958 

devekqiment  of,  992 
meatus  acustici,  746 
of  Meckel,  36,  144 
nasal,  717 

lateral,  lower,  718 

U2)per,  718 
of  sei)tum,  717 


INDEX. 


1331 


Cartilage,    nasal,    processus    sphenoidalis    of, 
718 
vomerine,  718 
nasi.     See  Cartilage,  nasal 

lateralis.       Sec   Cartilage,  nasal,    lateral, 
upper 
parachordal.  Appendix  E,  xxi 
of  pinna,  745 
of  Eeichert,  146 
of  Santorini,  961 
semilunar,  301 

surgical  anatomy  of,  1307,  1308 
septi  nasi,  717 
sesamoid,  of  arytenoid,  960 
sesamoide;e  nasi,  719 
tarsal,  1239 
thyreoidea,  958 
development  of  37,  992 
ossification  of,  961 
surgical  anatomy  of,  1248 
traclieales,  975 
triticea,  962 
vomero-nasalis    (Jacobsoni).     See   Vomerine 

cartilage 
xiphoid,  94,  96 
Cartilaginous  cranium,  Appendix  E,  xx 

vertebral  column,  90 
Caruncula  lacrimalis,  738,  1239 
major  of  Santorini,  1070 
minor  of  Santorini,  1070 
sublingualis,  997,  1012 
Caruncula?  myrtiformes.     See  C.  hymenales 

hymenales,  1193,  1197 
Cauda  epididymidis.     See  Epididymis,  globus 
minor  of 
equina,  454,  609 
helicis,  745 
Caudal  aortic  arches.     See  Aortic  arches 
fold,  27,  49,  66 
nerves,  608,  614 
process,  43 
Caudate  lobe  of  liver,  1113 

nucleus,  574,  575,  579 
Cavernous  arteries,  815 
plexus,  707,  712 
sinus,  886 
Cavitas   glenoidalis.      See   Cavity,  glenoid,  of 

scapula 
Cavity,  amniotic,  48,  49,  50 
glenoid,  of  scapula,  184,  276 
of  temporal  bone,  113,  154 
condition  of,  at  birtli,  121 
topography  of,  1237 
segmentation,  17 

sigmoid,  of  radius.     See  Ulnar  notch 
of  ulna,  194,  195 
Cavum  abdominis.     See  Abdominal  cavity 
articulare.     See  Joint  cavity 
conchse,  744 

dentis.     See  Pulp  cavity  of  tooth 
epidurale.     See  Epidural  space 
Meckelii,  679 

mediastinal  anterius.    See  Mediastinal  space, 
anterior 
posterius.        See        Mediastinal        space, 
posterior 
meduUare.     See  Medullar}'  cavity  of  bone 
nasi.     See  Nasal  cavity 
oris.     See  Mouth,  cavity  of 

proprium.     Sec  Mouth,  cavity  of,  proper 
pelvis.     See  Pelvis,  cavity  of 
peritonaei.     See  Peritoneal  cavity 


Cavum  i:)haryngis.     See  Pharynx,  cavity  of 

pleurae.     See  Pleui-al  cavity 

Retzii,  437.     See  also  Retzius,  space  of 

septi  pellucidi.     See  Ventricle,  fifth 

subarachnoidale.     See  Subarachnoid  space 

subdurale.     See  Siibdural  space 

thoracis.     See  Thoracic  cavity 

tympani.     See  Tympanic  cavity 

Titeri.     See  Uterus,  cavity  of 
Cells,  8 

basal,  of  olfactory  mucous  membrane,  722, 723 

body  of,  8 

ethmoidal,  128,  720,  721 

relation  of,  to  orbit,  144,  150 

to  nasal  fossae,  1 72 
surgical  anatomy  of,  1236 

germinal,  12,  13,  15, 

of  neural  tube,  22,  447,  471 

of  Golgi,  464,  586 

lymj^hoid,  906 

of  marrow,  71 

of  Martinotti,  586 

mastoid,  121,  752 

surgical  anatomy  of,  1234 

nerve.     See  Nerve-cells 

nucleus  of,  8 

olfactory,  722,  723 

of  Rauber,  18 

reproduction  of,  9 

reproductive,  10 

sperm-mother,  14 

sustentacular,  14 
Cell-mass,  inner,  18,  50 

intermediate,  26 
history  of,  32 
Cellulse  ethmoidales.     See  Cells,  ethmoidal 

mastoidea?.     See  Cells,  mastoid 
Cementum,  1014,  1025 

development  of,  1027 
Central  arteries  of  middle  cerebral,  817 
of  posterior  cerebral,  820 
of  retina,  735,  742,  815 

gyri.     See  Gyri 

lobule  of  cerebellum,  506,  507 

lymjihatic  of  hand,  915 

point  of  perineum,  1277 

sulcus  of  insula,  568 
Centrale,  os.  Appendix  F,  xxiv 
Centre,  association,  593 

medullary.     See  IMedullary  centre 

of  ossification,  72,  73 
Centrolecithal  ovum,  11 
Centrosome,  9,  10,  11,  14,  15,  17 
Centrum  tendineum.     See  Diaphragm,  central 
tendon  of 

of  vertebra,  76 
Cephalic  aortic  arches,  36,  37,  62,  926, 927,  928, 
932 
morphology  of,  942 

flexure  of  brain,  479 

fold,  27,  49,  66 

index.  Appendix  D,  xv 

myotomes,  440 

somites,  31,  32 

vein,  891.     See  also  Veins 
Cephalo-auricular  angle,  743 

variations  in,  745 
Cerato-hyal,  146 

Cerebellar  artery,  anterior  inferior,  820 
superior,  820 
posterior  inferior,  820 

tract.     See  Tract 


1332 


INDEX. 


Cerebellar  veins,  883 
Cerebello-olivary  tract,  496,  497,  510 
Cerebellum,  475,  505 
alae  of,  506,  507 
arbor  vitae  of,  510 
association  fibres  of,  511 
clivus  monticuli  of,  506,  507 
commissural  fibres  of,  511 
corpus  dentatum  of,  510 

trapezoides  of,  509 
culmen  monticuli  of,  506 
development  of,  477,  480,  528 
fissures  of,  506,  507,  508,  509 

development  of,  529 
folia  of,  512 

folium  cacuminis  of,  506,  507 
furrowed  band  of,  508 
gi'ay  matter  of,  509,  512 
hemispheres  of,  606 

surgical  anatomy  of,  1227 
lingula  of,  487,  506,  507 
lobes  of,  506 
lobides  of,  506,  507,  508 
medullary  velum  of,  inferior,  511 

superior,  486,  511 
minute  structure  of,  512 
nodide  of,  507,  508 
notches  of,  506 
nucleus  emboliformis  of,  510 

fastigii  of,  510,  511,  521 

globosus  of,  510 
peduncles  of,  510 

inferior,  476,  485,  510 

middle,  476,  486,  500,  501,  510 

superior,  476,  486,  510,  535,  546,  592 
origin  of  fibres  of,  511 
in  sections  of  pons,  503 
pyramid  of,  507,  508 
roof -nucleus  of,  510,  511,  521 
sidci  of,  506,  507 

development  of,  530 
tonsil  of,  507 

tuber  valvulaj  of,  507,  508 
uvula  of,  507,  508 
A'allecula  of,  506 
vermis  of,  506 
white  matter  of,  509,  512 
Cerebral  artery,  anterior,  817 
abnormalities  of,  950 

middle,  817 

l^osterior,  820 

surgical  anatomy  of,  1229 
cortex,  554,  584 

association  centres  of,  593 
fibres  of,  589 

auditory  area  of,  593 

band  of  Baillarger  of,  585,  587 
of  Bechterew  of,  587 
of  Vicq  d'Azyr  of,  585 

cells  of  Golgi  of,  464,  586 
of  Martinotti  of,  586 

commissural  fibres  of,  588 

connexion  of,  with  optic  thalamus,  545 

gray  layers  of,  585 

inter-radial  felt-work  of,  587 

layer  of  polymorphic  cells  of,  585,  586 
of  pyramidal  cells  of,  585 

nerve-fibres  of,  586 

olfactory  area  of,  593 

projection  fibres  of,  591 

somajsthetic  area  of,  593 

stratum  zonale  of,  685 


Cerebral  cortex,  stria  of  Gennari  of,  585 

structure  of,  584 

supra-radial  felt-work  of,  687 

tangential  fibres  of,  585 

thickness  of,  584 

topography  of,  1224 

visual  area  of,  593 

white  layers  of,  585 
hemispheres,  553 

association  fibres  of,  689 

basal  ganglia  of,  579 

borders  of,  554 

claustrum  of,  582 

commissural  fibres  of,  588 

convolutions  of     See  Gyri 

corpus  callosum  of,  670 

cortex  of,  654,  584.    See  also  Cerebral  cortex 

development  of,  478,  480,  481,  556,  595 

fimbria  of,  568,  572,  577 

fissures  of,  653,  554,  855 

form  of,  553 

general  structure  of,  554 

gray  matter  of,  554,  584 

groove  for  lateral  sinus  on,  554 

gyri  of,  554.     See  also  Gyri 

incisura  longitudinalis  of,  696 

internal  capsule  of,  682.     See  also  Capsule, 
internal 

intimate  structure  of,  684 

island  of  Reil  of,  556,  567 

level  of  lower  margin  of,  1224 

limen  insulse  of,  668 

lobes  of,  556 

medullary  centre  of,  554,  584,  588 

morphological  subdivisions  of,  684 

nuclei  of,  579,  582 

operciila  of,  556,  561 

poles  of,  564 

praeoccipital  notch  of,  562 . 

projection  fibres  of,  591 

Rolandic  angle  of,  558 

septum  lucidum  of,  573 
development  of,  597 

sulci  of,  554 

surfaces  of,  563 

surgical  anatomy  of,  1224 

Sylvian  fossa  of,  556,  696 
point  of,  556 

ventricles  of     See  Ventricles 
veins,  882,  883 
vesicles,  22,  66,  476,  481 
Cerebro-spinal  fluid,  453,  601 
nervous  system,  443,  451 

axis  of,  443.     See  also  Brain,  Spinal  cord 

ganglionic  part  of,  448,  461 

gray  matter  of,  443 

medullary  part  of,  461 

nerve-cells  of,  445 

nerve-fibres  of,  444 

nerves  of,  444.     See  also  Nerves,  cranial ; 
Nerves,  spinal 

neuroglia  of,  451 

neurons  of,  448,  449,  461 

white  matter  of,  443 
Cerebrum.     See  Cerebral  hemispheres.  Corpus 

callosum.  Fornix,  Thalamus,  ventricle 
Cerumen,  748 

Ceruminous  glands,  748,  778 
Cervical  artery,  ascending,  823 
morphology  of,  941 

deep,  826 

morphology  of,  941 


INDEX. 


1333 


Cervical  artery,  superficial,  824 
transverse,  823 
fascia,  394 

surgical  anatomy  of,  1246 
flexure  of  neural  tube,  477,  479,  526 
ganglion,  inferior,  706,  708 

surgical  anatomy  of,  1255,  1289 
middle,  706,  708 
superior,  706 
glands  of  uterus,  1191 
lymphatic  glands,  911,  912 

surgical  anatomy  of,  1251,  1252 
nerves,  611.     See  also  Nerves 
pleura,  977 

plexus,  617.     See  also  Plexus 
ribs,  81,  92 

serial  homology  of.  Appendix  C,  xiv 
sympathetic,  706 
development  of,  715 
surgical  anatomy  of,  1251 
veins.     See  Veins 
vertebrae,  76,  78 
Cervicalis  ascendens  muscle,  389 

descendens  nerve,  621 
Cervix  colunmse  posterioris.     See  Sjiinal  cord, 
cornu  posterior,  neck  of 
uteri,  1188 

arbor  vitse  of,  1188 
glands  of,  1191 
mucous  membrane  of,  1191 
muscular  coat  of,  1191 
supra -vaginal  portion  of,  1188 
vaginal  portion  of,  1188 
surgical  anatomy  of,  1283 
Chamtecephalic  skulls.  Appendix  D,  xvii 
Chamaeprosope,  Appendix  D,  xvii 
Chamber,  anterior,  of  eye,  730,  737 
development  of,  743 
endothelium  of,  727 
posterior,  of  eye,  730,  737 
recesses  of,  735 
Check  ligaments,  267 
Cheek  bone,  140,  150 
Cheeks,  997 
glands  of,  997 
sucking-pad  of,  997 
Chest.     See  Thorax 
Chiasma  opticum.     See  Optic  chiasma 
Choante,  159,  162,  719 
Chondro-cranium,  Appendix  E,  xx 
Chondro-epitrochlearis  muscle,  325 
Chondro-glossus  muscle,  409 

action  of,  410 
Chorda  obliqua.     See  Ligament,  oblique  radio- 
ulnar 
tympani  nerve,  687.     See  also  Nerve 
Chordae  tendineae,  790,  791 

Willisii,  884 
Chordal  portion  of  skull.  Appendix  E,  xxi 
Chorioid,  725,  727 
development  of,  743 
lamina  basalis  of,  728,  729 
chorio-capillaris  of,  728 
supra -chorioidea  of,  728 
vasculosa  of,  728 
nerves  of,  731 
pigment  of,  728 
proper  tissue  of,  728 
spatium  perichorioidale  of,  725 
stratum  intermedium  of,  728 
tapetum  of,  729 
Chorioidal  fissure,  742 


Chorioidea.     See  Chorioid 
Chorion,  48,  52 
Chorionic  area,  24,  52 
vesicle,  52 

villi,  52,  54,  55,  58,  65 
Choroid  plexuses  of  fourtli  ventricle,  512 
development  of,  529 
of  lateral  ventricle,  575,  604 
of  descending  horn  of,  578 
development  of,  596 
of  third  ventricle,  550,  604 
Choroidal  artery,  anterior,  817 
posterior,  820 
fissure,  578,  605 

development  of,  596 
veins,  882 
Chromaffin  cells,  1215 
Chromatin,  9 

skein,  10 
Chromogenic  cells,  1215 
Chromosome,  10,  13,  15,  17 
Chyme,  1050 
Chymus.     See  Chyme 
Cilia.     See  Eyelashes 
Ciliary  arteries,  731,  815 
anterior,  731,  816 
long,  731,  815 
posterior,  728,  815 
short,  728,  815 
body,  725,  729 
border  of  iris,  730 

bimdle  of  orbicularis  palpebrarum,  397 
glands,  739,  778 
ganglion,  680 

development  of,  699 
long  root  of,  680,  681 
morphology  of,  701 
short  root  of,  677,  681 
sympathetic  root  of,  681,  708 
Ciliary  muscle,  729 

nerves,  distribution  of,  on  cornea,  727 
in  chorioid  and  iris,  731 
entrance  of,  into  eyeball,  725 
long,  680 
short,  681 
processes,  729 
veins,  731 
Cingulum  of  brain,  590 

extremitatis  inferioris.     See  Girdle,  pelvic 

superioris.     See  Girdle,  i:)ectoral 
of  teeth,  1017 
Circle  of  WilUs,  821 
Circidar  sinus,  855 

sulcus,  556,  567 
Circulation,  foetal,  60,  63,  931 
Circulus   arteriosus   (WiUisii).      See   Circle   of 
WiUis 
major  of  iris,  731 
minor  of  iris,  731 
tonsillaris,  690 
Circum-anal  glands,  1095 
Circumduction,  movement  of,  259 
Circumflex  artery,  anterior,  830 
external,  861 

surgical  anatomy  of,  1307 
internal,  861 
posterior,  829 

surgical  anatomy  of,  1295 
iliac  artery,  deep,  857 

surgical  anatomy  of,  1266 
superficial,  859 
vein,  deep,  899 


1334 


INDEX. 


Circumflex  A^eiu,  superficial,  901 
Circumflex  nerve,  625,  632 

surgical  anatomy  of,  1295 
Circumttexus  palati  muscle.    See  Muscle,  tensor 

palati 
Circumvallate  papillne,  1003,  1004 
Cisterna  basalis,  602 

cerebello-medullaris.     iiee  C.  magna 
cliyli.     See  Receptaculum  chyli 
inter2:)eduncularis.     See  C.  basalis 
magna,  602 

surgical  anatomy  of,  1227 
pontis,  602 
Cisternae  subarachnoidales,  602 
Clarke,  vesicular  column  of,  461,  464,  469 
Claudius,  cells  of,  766,  767 
Claustrum,  582 
Clava,  484,  492 
Clavicle,  181 

architecture  of,  Appendix  A,  ii 
articulations  of,  273 
morphology  of,  Ajjj^endix  F,  xxv 
ossification  of,  183 
surgical  anatomy  of,  1291 
variations  in,  Ajjpendix  B,  x 
Clavicula.     See  Clavicle 
Clavicular  artery,  829 
facet  of  sternum,  94 
nerves,  617,  619 
morphology  of,  622 
Cleft,  gluteal,  1290,  1302 
olfactory,  1239 
palate,  40,  135,  1013,  1240 
urogenital,  1195,  1200,  1207 
visceral,  35,  43 
nerves  of,  701,  703 
stages  of,  at  difterent  ages,  66,  67 
Cleido-mastoid  muscle,  405 
Cleido-occipitalis  muscle,  405 
Clinoid  process,  anterior,  123 
middle,  122 
posterior,  122 
Clitoris,  1182,  1197 
arteries  of,  1198 
bone  of,  1198 
corpora  cavernosa  of,  1197 
crura  of,  1197 
development  of,  1200,  1207 
dorsal  vein  of,  897 
frenulum  of,  1196,  1197 
glans  of,  1197 
prepuce  of,  1196,  1197 
suspensory  ligament  of,  1197 
Clivus  monticuli  cerebelli,  506,  507 
Cloaca,  45,  1200,  1203 
Cloacal  fossa,  45,  1200,  1203,  1206 

membrane,  21,  23,  45 
Co-aptation  in  joints,  259 
Coccygeal  artery,  855 
ganglion,  704,  711 
gland,  1220 
nerves,  613,  655 
plexus,  658 

vertebrae.     See  Coccyx 
Coccyx,  87,  220,  222 
ossification  of,  94 
Cochlea,  760 

membranous,  764 
Cochlear  nerve,  689.     See  also  Nerve 
nucleus,  519,  520 
development  of,  699 
Cochleariform  process,  116,  750,  752,  1232 


Coeliac  arter}',  843 
axis,  843 

abnormalities  of,  949 
morphology  of,  942 
surgical  anatomy  of,  1276 
ganglia,  712 
lymphatic  glands,  920 
plexus,  712,  713 
Coelom,  24,  27,  50,  52,  1105 
Colic  artery,  left,  847,  1095 
middle,  847,  1095 
right,  847,  1095 
impression  of  liver,  1113 
lymphatic  glands,  920 
vein,  left,  904 
middle,  903 
right,  903 
Collar  bone,  181 
Collateral  digital  artery  of  foot,  869 

of  hand,'  836 
Collateral  eminence,  578 
fissure,  559 
nerve-fibres,  468 
Collecting  tubules,  renal,  1139 
CoUes,  perineal  fascia  of,  1277 
Colliculus     (cartilaginis     aryttenoideee).        See 

Cartilage,  sesamoid,  of  arytenoid 
Colliculus  inferior.    See  Corpora  quadrigemina, 
inferior 
nervi  optici,  731 

superior.  See  Corpora  quadrigemina,  sui^erior 
Collum.     See  Neck 
Colon,  1074.     See  also  Intestine 
appendices  epiploicse  of,  1074,  1075 
ascendens.     See  Colon,  ascending 
ascending,  1074,  1082 
topography  of,  1274 
csecum  of,  1074,  1076.    See  also  Caecum 
descendens.     See  Colon,  descending 
descending,  1074,  1083 
topography  of,  1274 
dimensions  of,  1074 
haustra  of,  1075 
hei^atic  flexure  of,  1074,  1082 
level  of,  1288,  1290 
topography  of,  1274 
Uiac,  1074,  1085 

topography  of,  1274 
mesentery  of,  1082,  1086 
nerves  of,  1076 
pelvic,  1074,  1085,  1086 
mesentery  of,  1086 
in  new-bom  child,  1086 
structure  of,  1087 
surgical  anatomy  of,  1274 
plicse  semilunares  of,  1075 
sacculi  of,  1075,  1087 
sigmoid  flexure  of,  1074,  1084 
sigmoideum.     See  Colon,  sigmoid  flexure 
splenic  flexure  of,  1074,  1083 
level  of,  1288,  1290 
topography  of,  1274 
structure  of,  1075 
ttenice  of,  1061,  1074,  1075,  1087 
transverse,  1074,  1082 
toi)ography  of,  1274 
vessels  of,  1075 
Columna  anterior.      See  Spinal  cord,  anterior 
horn  of 
fornicis.     See  Fornix,  anterior  pillar  of 
lateralis.     See  Spinal  cord,  lateral  horn  of 
posterior.     See  Sjjinal  cord,  posterior  horn  of 


INDEX. 


1335 


Columiaa  veiti'bralis.     See  Vertebral  colunni 
Columnse  camese,  790,  791 

griseaj.     See  Spinal  cord,  horns  of 

rectales     (Morgagnii).        See     Columns     of 

Morgagni 
renales  (Bertini).     See  Columns  of  Bertin 
rugarum  vaginai,  1195 
Columns  of  Bertin,  1138 
of  Morgagni,  1093,  1094 
of  spinal  cord.     See  Spinal  coid 
vertebral,  membranous,  30 
Comes  nervi  ischiatici,  855 
mediani,  834 
phrenici,  825 
Comma  tract,  466 

Commissura  anterior  alba.       See  Spinal  cord, 
commissure,  anterior  wliite 
anterior   (cerebri).     See  Commissure,  wliite, 

anterior,  of  brain 
anterior  grisea.    See  Spinal  cord,  commissure, 

gray,  anterior 
halaenularum,  548 

hippocampi.     See  Lyra,  or  Psalterium 
labiorum  anterior.     See  Mons  Veneris 

posterior.       See   Commissure,  posterior  of 
vulva 
palpebrarum  lateralis.     See  Canthi  of  eye 

medialis.     See  Canthi  of  eye 
posterior.       See    Spinal    cord,    commissure, 
posterior 
cerebri.     See  Commissure,  white,  posterior 
of  brain 
Commissural  fibres,  cerebellar,  511 

cerebral,  588 
Commissure  of  cord.     See  Spinal  cord 
gray,  of  third  ventricle,  544,  550 
of  Gudden,  532,  552,  676 
hippocampal,  572,  589 
of  lips,  995 
optic,  475,  551,  676 

development  of,  595,  699 
morphology  of,  703 
posterior,  of  vulva,  1195 
white,  anterioi',  of  brain,  549,  588 
development  of,  597 
jjosterior,  of  brain,  547,^  548 
development  of,  595 
Common  ligaments  of  sj^ine,  263 
Communicating  artery,  anterior,  of  brain,  817 
of  anterior  interosseous,  834 
of  deep  palmar  arch,  837 
peroneal,  865 
posterior,  of  brain,  816 
abnormalities  of,  951 
tibial,  865 
Complexus  muscle,  389 
action  of,  392,  393 
nerve-supply  of,  392 
Compound  glands,  1007 
Compressor  bulbi  muscle,  431 
hemispherium  bulbi,  432 
naris  muscle,  397 
radicis  penis,  431 
urethrte  muscle,  432 
ven£B  dorsalis  penis  muscle,  433 
Concentric  corpuscles  of  Hassall,  1220 
Concha  auricula;,  744 

nasalis  inferior.  See  Turbinated  bone,  inferior 
media.       See     Turbinated     processes     of 

ethmoid 
superior.       See    Turbinated    processes    of 
ethmoid 


Conclue  splienoidales.  See  Sphenoidal  turl)inals 
Condyle  of  femur,  lateral,  227 
medial,  227 
of  humerus.     See  E])icondyle  of  humerus 
of  jaw,  143 

topography  of,  1237 
occii^ital,  109,  164 

third.  Appendix  B,  vi,  viii 
Condylic  foramina,  109,  110,  164,  169 
fossa,  109,  110,  164 
surface  of  tilna,  230 
Condyloid  joints,  257 

Condylus  lateralis   femoris.      See   Condyle   of 
femur,  latciul 
medialis  femoris.  /See  Condyle  of  femur,  medial 
occipitalis.     See  Condyle,  occipital 
Cone  of  attraction,  16 
biijolars  of  retina,  733 
granules  of  retina,  733 
retinal,  734 

development  of,  743 
Confiuens  sinnum.     See  Torcular  Herophili 
Coni  vasculosi,  1162 

development  of,  1204 
Conical  papillte,  1003 
Conjoined  tendon,  425,  426 

suj'gical  anatomy  of,  1266 
Conjugal  ligament  of  ribs,  270 
Conjugata.     See  Conjugate  diameter 
Conjugate  diameter  of  pelvis,  221,  222 
Conjunctiva,  739 
fornix  of,  739 
nerves  of,  740 
ocular,  739 
palpebral,  739 
l^lica  semilunaris  of,  738 
surgical  anatomy  of,  1238 
vessels  of,  740 
Conoid  ligament,  274 
functions  of,  275 
tubercle,  183 
Constrictor  muscles  of  pharjnix,  410 
actions  of,  413 
development  of,  441 
inferior,  411 
middle,  411 
nerve  supply  of,  413 
superior,  410 
of  urethra.     See  Compressor  urethra} 
Conus  arteriosus,  789 
elasticus.     See  Crico-thyroid  membrane 
meduUaris,  452 
level  of,  1290 
structure  of,  458 
vasculosus,  1162 
Convoluted  tubules  of  kidney,  1139 
Convolutions  of  cerebrum.     See  Gyri 
Cor.     See  Heart 
Coraco-acromial  ligament,  275 
Coraco-brachialis  muscle,  332 
action  of,  335 
nerve -supjily  of,  335 
sui)erior  or  brevis,  332 
surgical  anatomy  of,  1293,  1295 
Coraco-clavicular  ligament,  274 
Coraco-glenoid  ligament,  277 
Coraco-humeral  ligament,  277 
Coracoid  process,  185 

morphology  of.  Appendix  F,  x.xv 
topograjjliy  of,  1292 
variations  of.  Appendix  B,  x 
Cord,  gangliated,  of  sympathetic,  703 


1336 


INDEX. 


Cord,  gangliated,  cervical,  706 

development  of,  715 

lumbar,  710 

sacral,  711 

thoracic,  708 
genital,  1204 
lumbo-sacral,  648 
lymphatic,  906 
spermatic,  1162,  1168 

cremasteric  fascia  of,  425,  428,  1169 

infundibuliform  fascia  of,  421,  428,  1169 

intercolumnar  fascia  of,  423,  428,  1169 

surgical  auatomj^  of,  1265 
spinal.     See  Spinal  cord 
umbilical,  51 
vocal,  false,  965 

true,  666.     See  also  Larynx 
Cords  of  brachial  plexus,  623 

branches  of,  625 

formation  of,  624 

morphology  of,  663 
Corium,  773 
papillee  of,  773 
stratum  papillare  of,  773 

reticulare  of,  773 
Cornea,  725,  726 

anterior  elastic  lamina  of,  726 
arcus  senilis  of,  727 
blood-vessels  of,  727 
curvature  of,  726 
develojDment  of,  743 
inflammation  of,  1238 
ligamentum  pectinatum  of,  727 
nerves  of,  727 

posterior  elastic  lamina  of,  727 
spaces  of  Fontana  of,  727 
structure  of,  726 
Cornicula  larjTigis,  961 
Cornu  ammonis.     See  Hippocampus  major 
anterius  ventriculi  lateralis,  574 
inferius  ventriculi  lateralis.      See  Ventricle, 

lateral,  descending  horn  of 
inferius  fossae  ovalis.  See  Saj)henous  opening, 

comua  of 
majus     OSS.     hyoidei.        See     Hyoid     bone, 

comua  of 
minus  oss.  hvoidei.     See  Hyoid  bone,  cornua 

of 
posterius  ventriculi  lateralis,  576 
superius     fosste    ovalis.         See     Saphenous 

Oldening,  cornua  of 
Cornua  coccygea,  87 

of  cord.     See  Spinal  cord 
sacralia,  85 

of  saphenous  opening,  354 
of  thyroid  cartilage,  958,  959 
of  uterus,  1192 
Corona  dentis.     See  Teeth,  crown  of 
glandis,  1170 
radiata,  583,  591 

of  ovum,  12 
Coronal  plane,  5 

suture,  107,  151,  158 

synostosis  of,  181 
Coronary  arteries  of  face,  807 

surgical  anatomy  of,  1240 

of  heart,  793,  800 
abnormalities  of,  947 

of  stomach,  844,  1060  • 

abnormalities  of,  949 
morphology  of,  942 
ligament  of  knee-joint,  302 


Coronary  ligament  of  liver,  1099,  1115,  1116 
plexus,  694 
sinus,  871 

abnormalities  of,  954 
develo]3ment  of,  931 
morphology  of,  945 
opening  of,  787 
veins  of  heart,  871 
.   of  stomach,  903,  1060 
Coronoid  fossa,  192 

process  of  jaw,  143,  156 

surface  anatomy  of,  1237 
of  ulna,  194,  1297 
Corpora  mammillaria,  475,  548 

connexion  of,  with  fornix,  548,  572 
development  of,  478,  595 
relation  of,  to  third  ventricle,  550 
quadrigemina,  476,  531,  534 
brachia  of,  532,  534,  535 
connexion  of,  with  cochlear  nerve,  534 

with  thalamus,  534 
development  of,  477,  542 
fillet-fibres  of,  534,  538 
inferior,  531,  534 

connexion  of,  with  lateral  fillet,  538 
structure  of,  534 
superior,  531,  534 

connexion  of,  with  optic  tract,  552 
with  o])tic  radiation,  553,  592 
Corpus  adiposum  buccae.     See  Suctorial  pad 
albicans  of  ovary,  1184 
Arantii,  790 
callosum,  476,  570,  588 
absence  of,  588,  590 
body  of,  571 
development  of,  597 
forceps  major  of,  571,  576 
genu  of,  571 
gray  matter  of,  571 
gyri  of,  571 
radiation  of,  571,  588 
rostrum  of,  571 
sj)lenium  of,  571 
strise  longitudinales  of,  569,  571 

morphology  of,  573 
tapetum  of,  571 

condition    of,    in     absence     of    corpus 
callosum,  588,  591 
termination  of  fibres  of,  588 
cavernosum  clitoridis,  1197 
penis,  1170,  1172 
urethrse.     See  Corpus  spongiosum 
ciliare.     See  Ciliary  body 
dentatum  cerebelli,  510 
e23ididymidis.     See  Epididymis,  body  of  ■ 
fornicis.     See  Fornix,  body  of 
geniculatum  externum,  531,  544 

connexion  of,  with  optic  radiation,  592 

with  optic  tract,  552 
development  of,  594 
structure  of,  546 
internum,  532 

connexion  of,  with  auditory  radiation,  592 
with  lateral  fillet,  538 
with  mesial  root  of  ojitic  tract,  552 
development  of,  594 
laterale.     See  C.  geniculatum  externum 
mediale.     See  C.  geniculatum  internum 
glandulare  prostatfe,  1175 
Highmori,  1161 
lingute,  1000 
luteum,  1184 


INDEX. 


1337 


Coqjus  mandibulae.     See  Jaw,  lower,  body  of 
luaxillse.     See  Maxilla,  body  of 
ossis  iscliii,  216 

pubis,  217 

splienoidalis,  121 
pineale.     See  Pineal  body 
restifoi'Jiie.     See  Eestifonn  body 
spongiosum  penis,  1170,  1172 
surface  anatomy  of,  1277 
sterni.     See  Gladiolus 
striatum,  554,  580 

connexions  of,  581 

development  of,  596 

morphology  of,  584 

vein  of,  574,  882 
subthalamicum,  546 
trajsezoides  of  cerebellum,  509 

of  pons,  501,  520 
trapezoideum.   See  Corpus  trapezoides  of  pons 
vertebrae.     See  Centrum 
vitreum.     See  Vitreous  body 
Wolffi.     See  WolflSan  body 
Corpuscles,  blood,  61 

concentric,  of  Hassall,  1220 
of  Krause,  775 
lymph,  906 
Malpighian,  of  spleen,  1213 

of  kidney,  1139 
of  Meissner,  775 
of  Pacini,  775 
of  Ruffini,  775 
tactile,  774 
of  Vater,  775 
Corpuscula  bulboidea.  See  Corpuscles  of  Krause 
lamellosa.   See  Corpuscles  of  Vater  and  Pacini 
renis(Malpighii).  See  Corpuscles,  Malpighian, 

of  kidney 
tactus  (Meissneri).  See  Corpuscles  of  Meissner 
Corrugator  cutis  ani  muscle,  431,  1093 
supercilii  muscle,  397 

action  of,  399 
Cortex,  cerebral,  584.     See  also  Cerebral  cortex 

renal,  1138 
Corti,  ganglion  of,  761,  768 
organ  of,  765,  766 

cells  of  Claudius  of,  766,  767 
of  Hensen  of,  766,  767 

development  of,  769 

hair-cells  of,  766,  767 

lamina  reticularis  of,  766,  767 

membrana  tectoria  of,  766,  767 

pillars  of,  766 

rods  of,  766 

space  of  Nuel  of,  767 

supporting  cells  of,  766,  767 
fibres  of,  767 
phalangeal  processes  of,  767 
tunnel  of,  766 
Cortico-pontine  tract,  591 

in  internal  caj)sule,  583 

in  mid-brain,  540 

in  pons,  501 
Costse.     See  Ribs 

spuriae.     See  Ribs,  false 
verae.     See  Ribs,  true 
Costal  cartilages,  100 

joints  of,  271 

topography  of,  1265 
demi-facets  of  dorsal  vertebrae,  81 
pleura,  977,  978 
zone  of  abdomen,  1047 
Costo-central  joints,  269 


Costo-chondral  joints,  271 

topography  of,  1255 
Costo-clavicular  ligament,  274,  275 
Costo-colic  ligament,  1083 
Costo-coracoid  ligament,  323 
membrane,  323,  828 
muscle,  325 
Costo-sternal  joints,  271 
Costo-transverse  joints,  270 

ligaments,  270 
Costo-vertebral  joints,  269 
Cos  to-xiphoid  ligaments,  272 
Cotyloid  cavity,  218 
ligament,  294 
notch,  216,  218 

absence  of.  Appendix  B,  xi 
Cowper,  glands  of,  1159,  1176 
development  of,  1206 
ducts  of,  1180 
surgical  anatomy  of,  1278 
Coxa.     See  Hip 

Cranial  fossa,  anterior,  166,  170,  175,  176 
middle,  166,  170,  177,  178 
posterior,  169,  170 
Cranial  nerves,  674.     See  also  Nerves 
1st.     See  Nerve,  olfactory 
2nd.     See  Nerve,  optic 
3rd.     See  Nerve,  oculo-motor 
4th.     See  Nerve,  trochlear 
5th.     See  Nerve,  trigeminal 
6th.     See  Nerve,  abducent 
7th.     See  Nerve,  facial 
8th.     See  Nerve,  auditory 
9th.     See  Nerve,  glosso-pharyngeal 
10th.     See  Nerve,  vagus 
11th.     See  Nerve,  spinal  accessory 
12th.     See  Nerve,  hyjooglossal 
Cranio-cerebral  topography,  1224 
Craniology,  Appendix  D,  xv 
Craniometry,  Appendix  D,  xv 
Cranio-pharyngeal  canal,  123,  163 

closure  of.  Appendix  D,  xxi 
Cranium,  103.     See  also  Skull 
articulations  of,  with  spine,  266 
bony  landmarks  of,  1223 
capacity  of.  Appendix  D,  xv 
cartilaginous,  Appendix  E,  xx 
cerebrale,  103 

circumference  of.  Appendix  D,  xvii 
height  of.  Appendix  D,  xvii 
membranous.  Appendix  E,  xx 
sinuses  of,  883 

surgical  anatomy  of,  1222,  1224 
thickness  of,  1224 

trabecular  portion  of.  Appendix  E,  xxii 
veins  of,  880,  883 

vertebral  portion  of.  Appendix  E,  xxii 
viscerale,  103 
Cremaster  muscle,  425 
nerve  supply  of,  430 
artery  of  deep  epigastric,  857 

of  spermatic,  843 
fascia,  425,  428,  1169 
Crescents  of  Gianuzzi,  1008 
Crescentic  lobule  of  cerebellum,  506,  507 
Crest,  ethmoidal,  139 
falciform,  118 
frontal,  105,  166 
iliac,  212,  222 

topography  of,  1290,  1302 
incisor,  136 
infra-temporal,  125,  153,  155 


1338 


INDEX. 


Crest,  lacrimal,  131,  150 
malar,  124 
nasal,  of  maxilla,136 

of  nasal  bones,  172 
neural,  21 
obturator,  217 
occipital,  external,  109 

internal,  109,  169 
pubic,  217 

sexual  difference  of,  222 

topograpliy  of,  1306 
sacral,  85 
sphenoidal,  123 
supra -mastoid,  113,  152 
temporal,  151 

of  frontal  bone,  104 

of  parietal,  107 

topography  of,  1224,  1237 
of  tibia,  anterior,  232 
turbinated,  inferior,  of  maxilla,  135 

superior,  of  maxilla,  136 

of  palate,  138 
urethral,  1178 
Cribriform  fascia,  354 
plate,  129 

relation  of,  to  cranial  fossa,  175 
to  nasal  fossie,  170,  175 
Crico-arytenoid  joint,  962 
muscles,  969 

actions  of,  971 
Cricoid  cartilage,  959 

development  of,  992 

ossification  of,  961 

surface  anatomy  of,  1249 
Crico-thyroid  artery,  805 
joint,  961 
membrane,  962 

level  of,  1289 

surgical  anatomy  of,  1249 
muscle,  968 

action  of,  971 

nerve  of,  971 
Crista  or  Cristai — 
acustica,  764 

anterior  tibite.     See  Crest  of  tibia,  anterior 
basilaris  cochleae,  765 
capituli  costie,  97 
colli  costte,  97 

conclialis.     See  Crest,  turbinated,  inferior 
cutis,  772 

ethmoidalis.     See  Crest,  ethmoidal 
frontalis.     See  Crest,  frontal 
galli,  127,  166 
iliaca.     See  Crest,  iliac 
infra-temporalis.     See  Crest,  infra-temporal 
intertrochauterica.  See  Intertrochanteric  line, 

posterior 
lacrimalis  anterior,  135 

posterior.     See  Crest,  lacrimal 
mallei,  755 

nasalis  (maxilbe).     See  Crest,  nasal 
obturatoria.     See  Crest,  oljturator 
occi])italis    externa.      See    Crest,    occipital, 

external 
sacrales  articulares,  85 

laterales,  85 

media,  85 
splienoidalis.     See  Crest,  sphenoidal 
spinarum,  748 
terminalis,  787 

development  of,  932 
transversa,  762 


Crista  or  Cristte — continued 

tuberculi  majoris  et  minoris,  190 
urethralis  muliebris,  1158 

virilis.     See  Verumontanum 
vestibuli,  759 
Crucial  anastomosis,  855,  862 
ligament  of  atlas,  267 
of  knee,  300 

in  movements  of  knee,  303 
Crura  antihelicis,  744 
cerebri,  532 

crusta  of,  532,  539 
development  of,  477,  480,  481,  542 
fronto-pontine  fibres  of,  540,  591 
position  and  connexions  of,  475,  476,  532 
pyramidal  fibres  of,  540,  591 
red  nucleus  of,  535,  536,  546 
tegmental  part  of,  532,  535,  546 
relation  of,  to  thalamus,  543 
to  third  ventricle,  550 
temporo-pontine  fibres  of,  540,  591 
clitoridis,  1197 
of  diaphragm,  417 

fornicis.     See  Fornix,  posterior  jiillars  of 
of  penis,  1171 
Crural  arch,  deep.     See  Femoral  arch,  deep 
superficial.    See  Femoral  arch,  superficial 
canal.     See  Femoral  canal 
fossa,  1098 
nerve,  anterior,  645 

of  genito-crural,  643 
ring.     See  Femoral  ring 
septum.     See  Femoral  septum 
sheath.     See  Femoral  sheath. 
Crureus  muscle.    See  Muscle,  vastus  intermedins 
Crus.     See  Leg 

anterius  stapedis,  756 

breve  incudis.     See  Incus,  short  process  of 

commune  of  semicircular  canals,  760 

helicis,  744 

inferius  (annuli  inguinalis  subcutanei).     See 

Inguinal  ring,  superficial,  outer  pillar  of 
longum  incudis.     See  Incus,  long  process 
mediale  diaphragmatis,  417 
posterius  stapedis,  756 

superius  (annuli  inguinalis  subcutanei).     See 
Inguinal  ring,  suijerficial,  inner  pillar  of 
Crusta  of  crus  cerebri,  532,  539 
petrosa,  1014,  1025 
development  of,  1027 
Cryptorchism,  1168 
Cryptozygous  skulls.  Appendix  D,  xvii 
Crystalline  lens,  736.     See  also  Lens 
Cubitus.     See  Elbow 
Cubo-cuneiform  articulation,  312 
Cuboid  bone,  247 

morijhology  of.  Appendix  F,  xxv 
Cucullaris  muscle.    See  Muscle,  trapezius 
Culmen  monticuli,  506,  507 
Cumulus  oophorus.     See  Discus  laroligerus 
Cuneate  funiculus,  491.     See  also  Funiculus 
gyrus,  665,  566 

nucleus,  492.     See  also  Nucleus 
tubercle,  485,  492 
Cuneiform  bone  of  hand,  203 

morjjhology  of.  Appendix  F,  xxiv 
ossification  of,  207 
of  foot,  first,  245 
second,  246 
tbird,  247 
morphology  of.  Appendix  F,  xxiv,  xxv 
ossification  of,  249 


INDEX. 


1339 


Cuneiform  cartilages,  961 

tuborcle,  964 
Cuiieo-liugual  gyri,  566 
Cuiieo-iuetatarsal  ligaiueiits,  313 
Cmieus,  566 

Cup,  optic,  of  optic  vesicle,  698,  742 
morphology  of,  703 
of  retina,  731 
Cupola  of  cochlea,  760 

terminalis,  764 
Cupula  cochieaj.     Sec  Cupola 
Curvatura    ventriculi    maj(jr.     See    Stomacli, 
greater  curvature  of 
minor.     See  Stomach,  lesser  curvature  of 
Curved  lines  of  ilium,  214 

of  occipital  bone,  108,  109,  153,  158 
Cushion,  endocardial,  929 
of  epiglottis,  965 
Eustachian,  1033 
levator,  1034 
Cusps  of  cardiac  valves,  789,  790,  791 

of  teeth,  1017,  1021 
Cutaneous  lamella,  30,  31 
Cuticula  deutis.     See  Nasmyth,  memljrane  of 
Cutis.     See  Skin 
Cuvier,  duct  of,  935,  936 
abnormalities  of,  954 
morphology  of,  944 
Cylinder,  axis.     Sec  Axon 
Cymba  conch  te,  744 
Cystic  artery,  845 
duct,  1119 

surgical  anatomy  of,  1270 
vein,  903 
Cytolymph,  8 
Cytoplasm,  7,  8,  10 
Cyto-reticulum,  8 

Dacryon,  Appendix  D,  xvi 
Dartos  muscle,  430,  1170 

penis,  1172 
Darwin,  tubercle  of,  744 
Decidua,  53,  56 

basalis,  54,  57,  58 

capsularis,  54,  57 

layers  of,  57,  58 

relation  of  ovum  to,  53 

vera,  54,  57 
Deciduous  teeth,  1015,  1022 

development  of,  1027 
Declive     cerebelli.       See     Cerebellum,    clivus 

monticuli  of 
Decussatio  brachii  conjunctivi.    See  Decussation 
of  superior  cerebellar  peduncles 

lemnisconim.     See  Decussation  of  fillet 

l^yramidum.     See  Decussation  of  2>yramids 
Decussation  of  superior  cerebellar  peduncles,  536 

of  fillet,  493 

of  Forel,  539 

fountain,  539 

of  Mepiert,  539 

in  optic  commissure,  676 

of  pyramids,  482,  483,  490 

sensory,  493 

transverse,  of  pons,  500 
Defsecation  centre,  1097 
Degeneration,  Wallerian,  466 
Deglutition,  movements  in,  413 
Deiters,  nucleus  of,  520,  521 

supporting  cells  of,  766,  777 
Deltoid  eminence,  190 

ligament,  307 


Deltoid  muscle,  328 

action  and  nerve-supply  of,  331 
topograi)liy  of,  1295 
tulHTcte,  182 
Demihuies  of  Gianuzzi,  1008 
Demours,  lamina  of,  727 
Dendrites,  445,  447 

of  cells  of  cerel)ellum,  513 
of  cerebral  cortex,  585 
of  cord,  461 

of  symiiathetic  ganglia,  704 
deAelopment  of,  22 
function  of,  449 
Dens  serotinus.     See  Wisdom  loolli 
Dental  arches,  151,  159,  1021 
artery,  anterior  suijerioi-,  812 
inferior,  811 
l^osterior  superior,  811 
canal,  inferior,  143,  156 

posterior,  134,  155 
foramen,  143,  156 
formula,  1015 

index.  Appendix  D,  xviii  ;  1029 
lamina,  1026 
nerve,  anterior,  682 
inferior,  685 

surgical  anatomy  of,  1237 
middle,  682 
posterior,  681 
veins,  880 
Dentary  centre,  145 
Dentate  fissure,  554,  569 
gyrus,  568 
nucleus,  510,  511 
Deutes.     See  Teeth 

canini.     See  Teeth,  canine 
decidui.     See  Teeth,  milk 
incisivi.     See  Teeth,  incisor 
molares.    See  Teeth,  molar 
2)ermanentes.     See  Teeth,  permanent 
l^r a' molares.     See  Teeth,  l.ncuspid 
Dentinal  fibrils,  1024 

development  of,  1028 
papilla,  1025,  1026 
sheaths,  1024 

development  of,  1028 
tubes,  1024 

development  of  1028 
Dentine,  1014,  1023 

development  of,  1025,  1026 
formation  of,  1028 
structure  of,  1024 
Dentition,  dijihyodont,  1029 
heterodont,  1029 
homodont,  1029 
of  lower  races,  1029 
polyphyodont,  1029 
typical  mammalian,  1029 
Dejjressor  alse  nasi  muscle,  397 
anguli  oris  muscle,  398,  399 
labii  inferioris  muscle,  398,  399 
septi  muscle,  397 
Dermal  teeth,  1025 
Dermic  skull,  Apjiendix  E,  xxii 
Dermis,  773 

Descemet,  lamina  of,  727 
Descendens  hypoglossi  nerve,  621,  697 
Descending  degeneration,  466 

palatine  artery,  812 
Descensus  testis.     See  Testis,  descent  of 
Descrijjtive  terms,  4,  70 
Deutoplasm,  10,  47 


1340 


INDEX. 


Development,  1 

of  alimentary  canal,  32 

of  anal  canal,  45 

of  appendicular  skeleton,  Appendix  F,  xviii 

of  arteries,  932 

of  auditory  ossicles,  757 

of  blood-vascular  system,  60,  925 

of  blood-vessels,  60 

of  brain,  476,  526,  542,  556,  594 

of  cerebeUum,  477,  480,  528 

of  cerebral  bemispheres,  478,  480,  594,  595 

of  chondro-cranium.  Appendix  E,  xx 

of  cranial  nerves,  698 

of  Eustacbian  tube,  43,  44 

of  external  ear,  43,  66 

of  eye,  741 

of  beart,  62,  925,  928 

of  inter-brain,  478 

of  intestine,  1105 

of  joints,  259 

of  labyrintli,  769 

of  larynx,  35,  992 

of  limbs,  46,  66 

of  liver,  1122 

of  mamma,  1209 

of  medulla  oblongata,  477,  480,  526 

of  mid-brain,  476,  477,  542 

of  mouth,  34,  38,  41,  67 

of  neck,  35,  36,  37,  67 

of  nerve-cells,  22,  447,  448,  471 

of  nose,  38,  66 

of  cesopbagus,  1042 

of  palate,  40,  1013 

of  pancreas,  1129 

of  pericardium,  925 

of  peritoneum,  1105 

of  pharynx,  34,  1037 

of  pinna,  43,  66 

of  pituitary  body,  42 

of  placenta,  52 

of  pons  Varolii,  477,  480,  528 

of  quadrigeminal  bodies,  542 

of  respiratory  apparatus,  992 

of  salivary  glands,  1013 

of  skeletal  muscles,  439 

of  skin,  778 

of  spinal  cord,  471 

of  spinal  nerves,  660 

of  spleen,  1213 

of  suprarenal  capsules,  1216 

of  sympathetic  system,  715 

of  teeth,  1025 

of  thymus  gland,  1220 

of  thyroid  gland,  1217 

of  tongue,  35,  37,  1013 

of  tonsil,  1037 

of  tympanic  cavity,  43,  44 

of  urinogenital  organs,  1198 

of  veins,  62,  934 
Diagonal  sulcus,  560,  561 
Diameter  obliqua  pelvis,  221,  222 

transversa  pelvis,  221,  222 
Diaphragm,  417 

anomalies  of,  419 

arch  of,  1286,  1290 

central  tendon  of,  418 

crura  of,  417 

foramina  in,  419 

hernia  of,  419 

relation  of,  to  aMominal  cavity,  1043 
Diaphragma.     See  Diaphragm 
pelvis.     See  Pelvic  dia]jhragm 


Diaphragma  sellce,  599 

urogenitale.      See  Ligament,   triangular,    of 
perinseum 
Diaphragmatic  arteries'  of  aorta,  838 
of  comes  nervi  phrenici,  825 
of  inferior  phrenic,  839 
of  musculo-phrenic,  826 
ganglion,  622,  713 
line  of  pleura,  979,  981 
lymphatic  glands,  924 
pleura,  977 
plexus,  622,  713 
Diaphysis,  73 

Diapophysis,  Appendix  D,  xiv 
Diarthrosis,  257 

development  of,  260 
Diencephalon,  476,  478,  481,  542 
Digastric  fossa,  142 
muscle,  407 
action  of,  410 
development  of,  441 
nerve -supply  of,  409 
triangle,  1249 
Digestive  system,  993 
Digital  arteries  of  foot,  866,  869 
of  hand,  833,  836 
morphology  of,  943 
surgical  anatomy  of,  1302 
depressions,  105,  108 
fossa  of  femur,  225 

of  testis,  1160 
sheaths  of  fingers,  338 

of  toes,  373 
veins  of  foot,  900 
of  hand,  889 
morphology  of,  946 
Digitationes  hippocampi.     See  Pes  hippocampi 
Digitus  post  minimus.  Appendix  F,  xxv 
Dilatator  pupillte,  731 
Dilator  naris  muscle,  397 

tubse  muscle,  754 
Diphyodont  dentition,  1029 
Diploe,  72 
Diploic  veins,  880 
Disc,  interpubic,  292 
intervertebral,  261 
optic,  731 
tactile,  774 
Discus    articularis    acromio-clavicularis.      See 
Fibro  -  cartilage    of    acromio  -  clavicular 
joint 
mandibularis.       See     Fibro-cartilage     of 

temporo-maxillary  joint 
radio-ulnaris  distalis.     See  Fibro-cartilage, 

triangular 
sterno-clavicularis.     See  Fibro-cartilage  of 
sterno-clavicular  joint 
proligerus,  1185 
Diverticulum,  allantoic,  50,  51,  65 

ilei  (Meckel),  1023,  1105 
Dolicho-cephalic  skulls,  158,  Appendix  D,  xv 
Dolicho-facial  skulls.  Appendix  D,  xvii 
Dolicho-hieric  sacrum.  Appendix  D,  xx 
Dolicho-kerkic  limbs.  Appendix  D,  xx 
Dolicho-knemic  limbs,  Appendix  D,  xx 
Dolicho-pellic  pelves.  Appendix  D,  xi.x 
Dolichuranic  skulls.  Appendix  D,  xviii 
Dorsal  axial  line  of  limbs,  614 

vertebrae,  81 
Dorsalis  clitoridis  artery,  854,  1198 
nerve,  660 
hallucis  artery,  869 


INDEX. 


1341 


Dorsalis  indicis  artery,  833 

abnormalities  of,  952 
linguae  artery,  805,  1006 
pedis  artery,  868 

surgical  anatomy  of,  1312 
penis  artery,  854 

nerve,  660 
pollicis  artery,  832 
scapulae  artery,  829 
Dorsitiexion,  308,  315 
Dorso-epitrochlearis  muscle,  325 
Dorsum  sellae,  121,  168 

development  of,  Appendix  E,  xxi 
Douglas,  folds  of,  peritoneal,  1101,  1189 

of  sheath  of  rectus,  428 
topography  of,  1267 
pouch  of,  1090^  1100,  1189 

surgical  anatomy  of,  1283,  1284 
Ductuli  aberrantes.       See  Vasa  aberrantia    of 

epididymis 
alveolares.     See  Ducts,  alveolar,  of  lung 
efferentes  testis.     See  Yasa  eft'erentia  testis 
transversi  (of  epoophoron),  1187 
Duct  or  Ducts,  Ductus — 
alveolar,  of  lung,  991 
arteriosus,  37,  63,  64,  933 

abnormalities  of,  947 
of  Bartholin,  1013 
bile,  common,  1120 

development  of,  1123 

level  of,  1290 

relation  of,  to  duodenum,  1068 

surgical  anatomy  of,  1270 

termination  of,  1068,  1070 
biliferi.     See  CanalicuLi,  bile 
choledochus.     See  Duct,  bile,  common 
cochlearis,  764,  765 

development  of,  769 
of  Cu\-ier,  935,  936 

abnormalities  of,  954 

morphology  of,  944 
cystic,  1119 

surgical  anatomy  of,  1270 
deferens.     See  Yas  deferens 
ejaculatorius,  1159,  1162,  1164 

development  of,  1199 

opening  of,  1179 
endolymphaticus,  763 

development  of,  769 
epididymidis.     See  Canal  of  ejiididymis 
epoophori  longitudinalis  (Gartneri).    See  Duct 

of  Gartner 
excretorius      (Glandular      bulbo-urethralis), 

1176 
of  Gartner,  1187 
hepaticuo,  1118 

development  of,  1123 
interlobulares  hepatis,  1118,  1122 

development  of,  1123 
lacrimales.     See  Lacrimal  canals 
lactiferi  mammje,  1208 
lingualis,  1217 
lymphaticus  dexter,  904,  909 

abnormality  of,  956 
MiieUeri,  1199 

development  of,  1204 
nasal,  741 

development  of,  40,  743 

surgical  anatomy  of,  1239 
naso-lacrimalis.     See  Duct,  nasal 
pancreaticus  (Wirsungi),  1127 

termination  of,  1068,  1070 


Duct  or  Ducts — continued 

pancreaticus  accessorius  (Santorini),  1128 
para-urethrales,  1158,  1196 
parotideus  (Stenonis),  1011 

surgical  anatomy  of,  1238 
prostatici,  1175 
reuniens  (Henseni),  763 

development  of,  770 
of  Rivinus,  1113 
semicircularis  lateralis,    posterior,    superior 

See  Semicircular  canal,  membranous 
of  Stenson.     See  Ductus  parotideus 
sublingualis  major.     See  Duct  of  Bartholin 
sublinguales  minores.     See  Duct  of  Rivinus 
submaxillaris    (Whartoni).        See    Duct    of 

Wharton 
sudoriferus,  778 
thoracicus,  904,  906 

abnormalities  of,  956 

surgical  anatomy  of,  1252,  1289 
thyro-glossal,  37,  1014,  1217 
utriciilo-saccularis,  763 
venosus  (Arantii),  63,  903,  935 

fissure  of,  1112,  1114 

ligament  of,  1117 
vitelline.     See  Duct,  vitello-intestinal 
vitello-intestinal,  33,  48,  51 

remnant  of,  in  adult,  1073,  1105 
of  Wharton,  997,  1012 

surgical  anatomy  of,  1244 
of  Wirsung,  1127 
Wolffi,  1198,  1200,  1204 
Ductless  glands,  1007,  1210 
Duodenal  folds,  1069 
fossae,  1068 
impression,  1114 
pouch,  1070 
Duodeno-jejunal  flexure,  1065,  1070 

surgical  anatomy,  1272 
fossa,  1069,  1272 
Duodenum,  993,  1065.     See  also  Intestine 
carimcula  of,  1070 
diverticulum  of,  1070 
first  part  of,  1065,  1066 
interior  of,  1069 
nerves  of,  1070 
orifice  of  bile-duct  in,  1068 
peritoneal  relations  of,  1067,  1068,  1069 
relations  of,  1065 
second  part  of,  1065,  1068 
structure  of,  1070 
surgical  anatomy  of,  1272 
suspensory  muscle  of,  1070 
third  part  of,  1065,  1068 

level  of,    1290 
uncovered  area  of,  1068 
various  forms  of,  1070 
vessels  of,  1070 
Dura  mater,  597 

cranial,  597 

diaphragma  sellse  of,  599 

encephali.     See  Duia  matei',  cranial 

falx  cerebelli  of,  599 
cerebri  of,  599 

lacunae  laterales  of,  603 

layers  of,  598,  600 

parasinoidal  sinuses  of,  603 

prolongations  of,  on  nerves,  598,  600 

spinalis,  453,  599 

venous  lalood-sinuses  of,  598,  599 

Ear,  743 


1342 


INDEX. 


Ear  capsule,  119,  Appendix  E,  xxi 

external,  743 

development  of,  43,  66,  67 

meatus  of,  743.     See  also  Auditory  meatus 

pinna  of,  743 

internal,  759.     See  also  Labyrintli 

middle,  748,     See  also  Tymimnic  cavity 

muscles  of,  extrinsic,  396 
intrinsic,  746 

surgical  anatomy  of,  1229 
Ebner,  glands  of,  771 
Ectochondral  ossification,  74 
Ectoderm,  18,  19,  28 

neural,  28 

structures  formed  from,  28 

surface,  28 
Ecto-rhinal  fissure,  560,  568 

moi'iihology  of,  564 
Egg-tubes,  1184 
Ejaculator  urinaj  muscle,  431 
Ejaculatory  duct,  1159,  1162,  1164 
deA'elopment  of,  1199 
opening  of,  1179 
Elastic  lamina  of  arteries,  781 
of  cornea,  726,  727 

membrane  of  Henle,  782 
Elbow,  surgical  anatomy  of,  1296 
E11)ow-joint,  279 

fat-pads  of,  281 

movements  at,  281,  335,  352 

muscles  acting  on,  335,  352 

nerves  of,  628 

surgical  anatomy  of,  1296 

synovial  membrane  of,  281 
Embolus  of  cerebellum,  510 
Embryo,  28 

ectoderm  of,  28 

entoderm  of,  28,  29 

external  characters  of,  at  different  periods,  65 

folding  off  of,  from  blastodermic  vesicle,  26 

intermediate  cell-mass  of,  32 

lateral  mesodermic  plates  of,  31 

membranes  of,  48,  59 

mesodermic  somites  of,  30,  31 

nutrition  of,  47,  60 
Embryology,  1,  7 
Embryonic  area,  19,  26 

at  different  periods,  65,  66 
Eminence,  arcuate,  117,  169 

genital,  45,  66,  1200,  1206 

ili(j-])cctincH],  215,  217 
Eiiiiiientia  arcuata.     See  Eminence,  arcuate 

articiilaris,  113,  154 

collateralis,  560,  578 

conch  £e,  744 

fosste  triangularis,  744 

ilio-pectinea.     See  Eminence,  ilio-j)ectineal 

intercondyloidea.     See  Spine  of  tibia 

medialis.     See  Eininentia  teres 

pyramidalis.  See  Pyramid  of  tympanic  cavity 

scap]i;e,  744 

teres,  488,  524,  527 
Emissary  veins,  884,  886, 
Enamel,  1014,  1023 

development  fjf,  1025 
formation  oi',  1028 

cells,  1026,  1028 

cuticle,  1024 

germs,  1026 

organs,  1026 

prisms,  1023 
Enarthrodial  joints,  257 


Encephalon.     See  Brain 
End-bulbs  of  Krause,  775 
Endocardial  cushions,  929 
Endocardium,  787,  788,  790,  791 

structure  of,  792 
Endochondral  ossification,  74 
Endognathion,  1013 
Endolymph,  762 
Endoskeleton,  69 
Ensiform  artery,  826 

cartilage,  96 
Entoderm,  18,  19,  29,  50 
Epactal  bones.     See  Bones,  sutural 
Eparterial  bronchus,  976,  990 
Ependyma,  573,  578 
Ependymal  cells,  451,  459 

layer,  472 
Epiblast,  18 

Epibranchial  organs,  701,  702 
Epicardium,  791,  792 
Ei)icondyle  of  humerus,  lateral,  191 
medial,  191 
ossification  of,  193 
surgical  anatomy  of,  1296 
of  femur,  227 
Epicondylic  lines,  226 

process  of  humerus.  Appendix  B,  xi 

ossification  of,  194 
ridges,  191 
Epicondylus  lateralis  femoris.     See  Tuberosity 
of  femur,  lateral 
humeri.       See    EiJicondyle    of     humerus, 
lateral 
medialis  femoris.     See  Tuberosity  of  femur, 
medial 
humeri.       See    Epicondyle    of     humerus, 
medial 
Epicranial  aponeurosis,  394,  396 
Epidermis,  773 

development  of,  778 
Epididymal  artery,  843 
Epididymis,  1159,  1160 
body  of,  1160 
canal  of,  1162 

development  of,  1199,  1202,  1205 
globus  major  of,  1160 

minor  of,  1160 
hydatids  of,  1160 

development  of,  1205 
sinus  of,  1160 
structure  of,  1161 
surgical  anatomy  of,  1280 
vasa  aberrantia  of,  1162 
development  of,  1199 
Epidural  space,  598,  600 
Epigastric  artery,  deep,  856,  1098 
development  of,  933 
morphology  of,  940 
surgical  anatomy  of,  1266,  1284 
superficial,  859 
superior,  826 
fossa,  1255 
region,  1047,  1267 
vein,  deep,  900 
sujjerficial,  901 
superior,  874 
Epigastrium,  1047 
Epiglottidean  ligaments,  963 
Epiglottis,  961 
cartilage  of,  961 
cushion  of,  965 
in  deglutition,  971 


INDEX. 


1343 


Epiglottic,  development  of,  35,  38,  992 
frenulum  of,  1002 
glands  of,  968 
level  of,  1289 
taste  buds  of,  770 
Epihyal,  146 
Epiotie,  120 
Epiphyses,  73,  74 
Epipteric  ossicles,  119,  133 
Episternal  bones,  A^jpendix  B,  vii 

notch,  level  of,  1289 
Ejjistropheus.     See  Axis  vertebra 
Epithalamus,  542 

d(^V('lopinent  of,  594 
Epithelium,  28 
Epitrichium,  779 
Eijitrochleo-anconeus  muscle,  349 
Epitymjianic  space,  1232,  1233 
Eponychium,  776,  779 
Epooplioron,  1187,  1190 
development  of,  1199 
Erect  position,  4 
Erector  clitoridis  muscle,  432 
penis  muscle,  432 
sijinse  muscles,  387 
actions  of,  392,  393 
surface  anatomy  of,  1285 
Eruption  of  teeth,  i)ermanent,  1022 

temporary,  1025,  1027,  1028 
Erythroblasts,  71 
Ethmoid  bone,  103,  127 
ossification  of,  129 
relation  of,  to  cranial  fossa,  166 
to  nasal  fossae,  170 
to  orbit,  149 
variations  in,  Ajipendix  B,  ix 
Ethmoidal  arteries,  816 
canals,  128.     See  also  Canal 
cells,  128,  149,  150,  172,  720,  721 

surgical  anatomy  of,  1236 
crest,  139 
foramen,  anterior  104,  147,  166 

posterior,  104,  147,  166 
notch,  104 

plate,  Aj^jjendix  E,  xxi 
process,  130 

sinuses.     See  Ethmoidal  cells 
spine,  123 
Ethmo-turbinals,  128 
Ethmo-vomerine  region.  Appendix  E,  xxi 
Eustachian  canal,  116,  163,  165 
cushion,  1033 
tube,  750,  753 
blood-vessels  of,  754 
in  child,  754 
development  of,  43,  44 
dilator  muscle  of,  954 
fascia  salpingo-pharyngea  of,  754 
groove  for,  124,  163 
isthmus  of,  753 
lamina  membranacea  of,  754 
nerves  of,  754 
ostium  pharyngeum  of,  753,  754,  1033 

tympanicum  of,  753 
pars  cartilaginea  of,  753 
ossea  of,  753 

surgical  anatomy  of,  1232,  1233,  1246 
tonsil  of,  754 
valve,  788 

development  of,  932 
Eutelolecithal  ovum,  11 
Eversion  of  foot,  315 


Excavatio  jiapillae  n.  optici.     See  Cn\\  optic, 
of  retina 
recto-uterina.     Sre  Pouch  of  Douglas 
recto-vesicalis.     See  Poucli,  recto-vesical 
vesico-uterina.     See  Pouch,  utero-vesical 
Exoccipitals,  113 

development  of.  Appendix  E,  xxi 
Exognathion,  1013 
Exoskeleton,  69 
Expression,  facial,  399 
Expiration,  419 
Extension,  movement  of,  259 
Extensor  carpi  radialis  brevis  muscle,  348 
action  of,  352 
nerve-supply  of,  351 
longus  muscle,  348 
action  of,  352 
nerve -su2;)ply  of,  351 
ulnaris  muscle,  349 
action  of,  352 
nerve-sujjjjly  of,  352 
digiti  quinti  proprius  muscle,  348 
action  of,  352 
nerve-supjily  of,  352 
digitorum  brevis  muscle,  375 
action  of,  384 
nerve-supi)ly  of,  383 
tojiogiaijliy  of,  1312 
communis  muscle,  348 
action  of,  352 
nerve-sui^jjly  of,  351 
longus  muscle,  374 
action  of,  384 
nerve-supply  of,  383 
topograjjhy  of,  1312 
hallucis  longus  muscle,  375 
action  of,  384 
nerve-supi^ly  of,  383 
indicia  proprius  muscle,  351 
action  of,  352 
nerve-supply  of,  352 
ossis  metacarpi  pollicis  muscle,  350 
action  of,  352,  353 
nerve-sujiply  of,  352 
metatarsi  hallucis  muscle,  375 
pollicis  brevis  muscle,  351 
action  of,  352,  353 
nerve-supply  of,  352 
longus  muscle,  351 

action  of,  352,  353 
nerve-supply  of,  352 
primi  internodii  hallucis  muscle,  375 

pollicis  muscle,  351 
secundi  internodii  pollicis  muscle,  351 
Eye,  723.     See  also  Eye-ball 
development  of,  741 
movements  of,  407 
pineal,  547 
Eyeball,  723,  724 

anterior  chamber  of,  730,  737 

development  of,  743 
coats  of,  725.    See  also  Chorioid,  Retina,  Sclera 
dimensions  of,  724 
equator  of,  724 
meridional  lines  of,  724 
nerves  of     See  Nerves,  ciliary 
nervous  tunic  of,  725,  731 
poles  of,  724 

posterior  chamber  of,  730,  737 
refracting  media  of,  725.     See  also  Aqueous 

humour.  Lens,  Vitreous  body 
sagittal  axis  of,  724 


1344 


INDEX. 


Eyeball,  sclero-cornea  of,  725 
shape  of,  724 
sulcus  sclerse  of,  724 

tunica    vasculosa    of,    725,    727.      See    also 
Chorioid,  Ciliary  body.  Iris 
Eyelashes,  738,  739 
Eyelids,  738 

blood-vessels  of,  740 
canthi  of,  738 
development  of,  743 
in  fcotus,  67,  68 
glands  of  Moll  of,  739,  778 
lacus  lacrimalis  of,  738 
lymphatics  of,  740 

mucous  membrane  of,  738.      See  also   Con- 
junctiva 
muscles  of,  397,  739 

actions  of,  399 
nerves  of,  740 
palpebral  ligament  of,  739 
papilla  lacrimalis  of,  738 
septum  orbitale  of,  739 
skin  of,  739 
tarsal  arches  of,  740 
glands  of,  739,  740 
ligaments  of,  739 
plates  of,  738 
third,  738 
Eye-teeth,  1017 

Face,  bones  of,  103,  133,  150,  159 
bony  landmarks  of,  1236 
measurements  of.  Appendix  D,  xvii 
muscles  of,  397 

actions  and  nerve-supply  of,  399 
development  of,  441 
surgical  anatomy  of,  1236 
Facial  angle.  Appendix  D,  xvii 
artery,  806.     See  also  Artery 
expression,  399 
index.  Appendix  D,  xvii 
nerve,  686.     See  also  Nerve 
veins,  876 
common,  876 

surface  anatomy  of,  1237,  1251 
deep,  877 
Falciform  crest,  118 

ligament  of  saphenous  opening,  355,  356 
of  liver,  1098,  1116 

development  of,  1107,  1124 
topography  of,  1270 
process  of  sacro-sciatic  ligament,  292 
Fallopian  tube,  1181,  1185 

abdominal  ostium  of,  1185 
ampulla  of,  1186 
development  of,  1199 
fimbriae  of,  1186 
hydatids  of,  1187 
infundibulum  of,  1186 
isthmus  of,  1186 
mesosalpinx  of,  1185,  1189 
nerves  of,  1186 

ovarian  fimbria  of,  1184,  1186 
pars  uterina  of,  1186 
plicae  of,  1186 
structure  of,  1186 
surgical  anatomy  of,  1283 
uterine  ostium  of,  1186 
vessels  of,  1186 
Fallopius,  aqueduct  of,  118,  164,  752,  762 
hiatus  of,  117,  168 

condition  of,  at  birtli,  121 


Falx  cerebeUi,  599 
cerebri,  599 

inguinalis.     See  Tendon,  conjoint 
Fangs  of  teeth,  1015 
Fascia  or  Fasciae  of  abdomen,  420,  1044 
antibrachii.     See  Fascia  of  forearm 
of  arm,  332 
axillaris,  322 
of  back,  319,  385 
bicipital,  334 

surgical  anatomy  of,  1297 
brachii.     See  Fascia  of  arm 
bucco-pharyngea,  1037 
bulbi  (Tenoni).     See  Capsule  of  Tenon 
cervical,  deep,  394 

muscular  compartments  of,  1247 
suprasternal  compartment  of,  1247 
surgical  anatomy  of,  1246,  1247 
vascular  compartment  of,  1246 
visceral  compartment  of,  1246 
colli.     See  Fascia,  cervical 
cremasterica  (Cooperi),  425,  428,  1169 
cribriform,  354 

cribrosa.     See  Fascia,  cribriform 
cruris.     See  Fascia  of  leg 
deep,  318 

dentata  hippocampi.     See  Gyrus  dentatus 
diaphragmatis  pelvis   superior.     See   Pelvic 
fascia,  visceral 
urogenitalis  inferior.     See  Triangular  liga- 
ment 
superior.    See  Triangular  ligament,  deep 
layer  of 
of  foot,  371 
of  forearm,  336 
of  groin,  353 
of  hand,  336 
of  head,  394 
iliaca,  1044 

infundibuliform,  421,  428,  1169 
intercolumnar,  423,  428,  1169 
lata  of  thigh,  353 

surgical  anatomy  of,  1306 
of  leg,  371 
of  lower  limb,  353 
lumbar,  319,  385 

lumbo-dorsalis.     See  Fascia,  lumbar 
masseteric,  394 
of  neck,  394 
obturatoria,  434 
of  orbit,  399 
palmar,  338 
parotid,  394,  1010 

pectinea.     See  Pubic  portion  of  fascia  lata 
pectoralis,  322 
pelvis,  434 
penis,  1172 
of  perineum,  430 

surgical  anatomy  of,  1277 
phrenico-pleural,  982 
piriformis,  434 
plantar,  372 
popliteal,  356 

surgical  anatomy  of,  1305 
of  popliteus,  378 
praevertebralis,  395 
prostata}.     See  Prostate,  capsule  of 
rectal,  1091 
recto-vesical,  436 
renalis,  1132 
salpingo-pharyngea,  754 
of  Scarpa,  1278 


INDEX. 


1345 


Fascia,  semilunar.     See  Fascia,  bicipital 
of  shoulder,  327 
spermatic,  423,  428 
superficialis,  318 
temporalis,  394 
of  thigh  and  buttock,  353 
transversalis,  420,  1044 
triangular,  424 
of  upper  limb,  319 
Fasciculus  or  Fasciculi 

anterior     proprius    (Fk-chsigi).      See    Basis 

bundle,  anterior 
antero-lateralis   superficialis  (Govversi).     See 

Gowers,  tract  of 
cerebello-spinalis.    See  Tract,  direct  cerebellar 
cerebro  -  sjjinalis       anterior       (pyramidalis 
anterior).     See  Tract,  pyramidal,  direct 
lateralis  (pyramidalis  lateralis).    See  Tracts, 
pyramidal,  crossed 
cuneatus  (Burdachi).     See  Tract  of  Burdach 
gracilis  (GoUi).     See  Tract  of  Goll 
lateralis  (plexus  brachialis).    See  Cord,  outer, 

of  brachial  plexus 
lateralis     proprius    (Flechsigi).      See    Basis 

bundle,  lateral 
longitudinalis  inferior  (cerebri),  590 

medialis.  See  Longitudinal  bundle,  posterior 
superior  (cerebri),  590 
medialis  (plexus  brachialis).     See  Cord,  inner, 

of  brachial  plexus 
occipito-frontalis,  590 
olfactory,  of  cornu  ammonis,  572 
posterior     (plexus     brachialis).       See    Cord, 

posterior,  of  brachial  plexus 
retroflexus  (Meynerti),  539,  547 
solitarius,  517,  518,  524,  527 
spiralis  of  cochlear  nerve,  768,  769 
thalamo-mammillaris.  See  Fasciculus  of  Vicq 

d'Azyr 
transversi  aponeurosis  palmaris.     See  Trans- 
verse metacarpal  ligament,  superficial 
plantaris.     See  Transverse  metatarsal  liga- 
ment, superficial 
of  Vicq  d'Azyr,  545,  548,  572 
Fat-pads,  synovial,  258 
of  elbow-joint,  281 
of  hip-joint,  295 
of  knee-joint,  302 
Fauces,  1000 

isthmus  of,  993,  995,  1000,  1244 

level  of,  1289 
pillars  of,  999,  1000,  1034 
surgical  anatomy  of,  1244 
Female  pronucleus,  13,  16 
Femoral  arch,  deep,  356 
superficial,  356,  422 
artery,  858.     See  also  Artery 
canal,  356 
fossa,  1098 
hernia,  356 
lymphatic  glands,  916 
ring,  356 
septum,  356 
sheath,  356,  421,  859 
vein,  897.     See  also  Vein 
superfi.cial,  900 
Femur,  223 
architecture  of.  Appendix  A,  iv 
connexions  of,  228 
homology  of.  Appendix  F,  xxiv 
lower  epiphysial  line  of,  1308 
ossification  of,  228 

90 


Femur,  sexual  differences  of,  228 

variations  in,  Appendix  B,  xi 
Fenestra  ovalis  s.  vestibuli,  752,  759 

rotunda  s.  cochlete,  752,  1232 
Fenestrated  membrane,  781 
Fertilisation  of  ovum,  16,  65 
Fibrse  arcuat;e  externae,  485 
internaj,  493 

circulares  Mlilleri,  699,  729 

intercrurales.     See  Fibres,  intercolumnar 

lentis,  737 

meridionales  (Brueckei),  729 

obliqua3  ventriculi,  1058 
Fibres,  intercolumnar,  423 

of  Purkinje,  791 
Fibrils,  dentinal,  1024,  1028 
Fibro-cartilage,  interarticular,  258 

of  acromio-clavicular  joint,  274,  275 

development  of,  260 

of  pubis,  292 

semilunar,  301 

surgical  anatomy  of,  1307,  1308 

of  sterno-clavicular  joint,  274 

of  temporo-maxillary  joint,  268 

triangular,  282,  283 
Fibrocartilagines  intervertebrals,  261 
Fibrous  plate  of  fingers,  289 
of  toes,  315 
tympanic,  748 
Fibula,  234 

architecture  of.  Appendix  A,  v 

connexions  of,  237 

morphology  of,  Apjjendix  F,  xxiv 

ossification  of,  237 

surface  and  surgical  anatomy  of,  1308,  1309 

variations  in.  Appendix  B,  xii. 
Fibular  artery,  superior,  868 
Fibulare,  os,  Appendix  F,  xxiv 
Field,  polar,  9 
Fifth  ventricle,  573 
Filament,  axial,  15 
Filiform  papilla;,  1003 
FiUet,  494,  592 

connexion  of,  with  cochlear  nuclei,  538 
with  geniculate  body,  534,  538 
with  optic  thalamus,  539 
with  quadrigeminal  body,  534,  538 
with  superior  olive,  538 

decussation  of,  493 

interolivary  stratum  of,  496 

lateral,  505,  521,  533,  538 

mesial,  504,  539,  546,  553,  592 

in  mid-brain,  533,  534,  535,  538 

in  pons,  502,  504 
Filtrum  ventriculi  of  Merkel,  965 
Filum  terminale,  452,  459,  599 
Fimbria  (hippocampi),  568,  572,  577 

ovarica,  1184 

tubse  Fallopii,  1184,  1186 
Fimbrio-dentate  sulcus,  569 
Finger-cells,  773 
Fingers,  bones  of,  210 

movements  of,  352 
Fissure  or  Fissures  ;  Fissura 

antitrago-helicina,  745 

auricular,  114 

calcarina,  565,  576 

calloso-marginal,  560 

of  cerebellum,  506 

of  cerebrum,  553,  554 

cerebri  ^lateralis    (Sylvii).      See    Fissure    of 
Sylvius 


1346 


INDEX. 


Fissure,  chorioidal,  742 
choroidal,  578,  605 

development  of,  596 
collateralis,  559 
complete,  554 
of  cord,  454,  460 

development  of,  473 
dentate,  554,  569 
of  ductus  venosus,  1112,  1114 
ecto-rhinal,  560,  568 
morjjliology  of,  584 
floccular,  of  cerebellum,  509 

development  of,  529 
Glaserian,  113,  750 
great  horizontal,  of  cerebellum,  506 
development  of,  531 
longitudinal,  of  cerebrum,  474,  553 
development  of,  596 
hippocampi.     See  Fissure,  dentate 
incomplete,  554 
infrapyramidal,  508 

development  of,  530 
interlobar,  555 
longitudinalis    cerebri.      See    Fissure,    great 

longitudinal 
of  lung,  988 
of  meduUa,  482 

orbitalis    inferior.       See     Fissure,    spheno- 
maxillary 
superior.     See  Fissure,  sphenoidal 
palpebral,  738 
parallel,  567 

topography  of,  1224,  1225 
parapyramidal,  508 

development  of,  530 
parie to-occipital  is,  558,  559,  565 

topography  of,  1223,  1225 
petro-basilar,  117 
petro-occipitalis,  163 
petro-squamosa,  118 
petro-tympanica     (Glaseri).       See     Fissure, 

Glaserian 
portal,  1113,  1115 
post-nodular,  509 

development  of,  530 
post-lunata,  507 

development  of,  530 
prima  of  cerebellum,  530 
pterygoidea.     See  Pterygoid  notch 
pterygo-maxillary,  155,  157 
of  Rolando,  558 

annectant  gyri  of,  558 
development  of,  558,  564 
topography  of,  1224,  1225 
retrotonsillar,  of  cerebellum,  508 

development  of,  530 
of  Santorini,  745 
secunda  of  cerebellum,  508 
sphenoidal,  123,  124,  147,  168 

variations  in.  Appendix  B,  ix 
spheno-maxillary,   125,   134,  149,   153,   156, 
162 
Wormian  bones  in  connexion  witli,  133 
spheno-petrosa,  162,  163 
suprapyramidal,  508 

development  of,  530 
of  Sylvius,  553,  555 

anterior  ascending  ramus  of,  556,  557 
development  of,  556 
horizontal  rami  of,  556,  557 
stem  of,  553,  555 
terminal  piece  of,  556 


Fissure  of  Sylvius,  topography  of,  1224 
vallecuUa  of,  555 
transversa  cerebri,  604,  605 
transverse,  of  liver.     See  Fissure,  portal 
tympano-mastoidea.     See  Fissure,  auricular 
umbilical,  1114 
urogenital,  1200 
vestibuli,  760 
Flat  bones,  70,  72 
Flechsig,  areas  of,  in  medulla,  499 

in  cerebrum,  593 
Flexion,  259 

Flexor  accessorius  muscle,  379.    See  also  Muscu- 
lus,  quadratus  plantae 
carpi  radialis  muscle,  339 
action  of,  352 
nerve-sup23ly  of,  351 
surface  anatomy  of,  1300 
ulnaris  muscle,  339 
action  of,  352 
nerve-supply  of,  351 
caudse  muscle,  438 
digiti  quinti  brevis  of  foot,  382 
action  of,  384 
nerve-supply  of,  383 
of  hand,  346 
action  of,  352 
nerve-supply  of,  351 
digitorum  brevis,  381 
action  of,  384 
nerve-supply  of,  383 
longus  muscle,  378 
action  of,  384 
nerve-supply  of,  383 
profundus,  341 
action  of,  352 
nerve-supply  of,  351 
sublimis  muscle,  341 
action  of,  352 
nerve-suj)ply  of,  351 
hallucis  brevis  muscle,  382 
action  of,  384 
nerve-supply  of,  383 
longus  muscle,  379 
action  of,  384 
nerve-supply  of,  383 
poUicis  brevis  muscle,  344 
action  of,  353 
nerve-supply  of,  351 
longus  muscle,  342 

action  of,  352,  353 
nerve -sujDply  of,  351 
surface  anatomy  of,  1301 
Flexura  coli  dextra.     See  Flexure,  hepatic 

sinistra.     See  Flexure,  sj)lenic 
Flexures  of  brain,  479 
cephalic,  479 
cervical,  477,  479,  526 
pontine,  479 
duodeno-jejunal,  1065,  1070 

topographical  anatomy  of,  1272 
hepatic,  1U82 

level  of,  1288,  1290 

topography  of,  1274 

sigmoid,  993,  1074,  1084 

splenic,  1074,  1083 

level  of,  1288,  1290 

topography  of,  1274 

Floating  ribs,  97 

Floccular  fissure  of  cerebellum,  509 
develojjment  of,  529 
fossa,  119,  121 


INDEX. 


1347 


Flocculus  cerebelli,  508,  509 

development  of,  529 
Foetus,  circulation  of,  60,  63,  931 
estimate  of  age  of,  68 

external  characters  of,  at  different  periods,  65 
membranes  of,  48,  59 
Fold  or  folds,  amnion,  49,  65 
aryteuo-epiglottidean ,  964 

development  of,  38 
axillary,  1293 
caudal,  27,  66 
cephalic,  27,  66 

of  Douglas,  of  sheath  of  rectus,  428 
topography  of,  1267 
of  pelvic  peritoneum,  1101,  1189 
genital,  45,  1206 
glosso-epiglottic,  963,  1002 
gluteal,  1302 

iUo-ctecal  fold,  1081,  1082 
labio-scrotal,  1200,  1206 
lateral  amniotic,  45 
medullary,  21,  66 
perineal,  45 

pharyngo-epiglottic,  963,  1002,  1036 
recto-genital,  1101,  1189 
recto-uterine,  1189 
recto- vaginal,  1189 
sacro-genital,  1156 
salpingo-palatine,  754,  1033 
salpingo-pharyngeal,  754,  1033 
transverse  vesical,  1156 
utero-vesical,  1189 
vestigial,  of  Marshall,  784,  795 
Folia  of  cerebellum,  510,  512 

lingufe,  1004 
Folium  cacuminis,  506,  507 
Follicles,  Graafian,  1184 
development  of,  1204 
of  hair,  776 
of  Lieberkiihn,  1062 
lymphatic,  906 
primitive,  of  ovary,  1204 
of  teeth,  1027,  1028 
Folliculi  oophori  primarii.   See  Follicles,  primi- 
tive, of  ovary 
vesiculosi  (Graafi).     See  Follicles,  Graafian 
Folliculus  pili.     See  Follicles  of  hair 
Fontana,  spaces  of,  727 

Fontaneile,  anterior,  1223  ;  Appendix  E,  xxii 
antero-lateral.  Appendix  E,  xxii 
posterior.  Appendix  E,  xxii 
postero-lateral.  Appendix  E,  xxii 
sagittal.  Appendix  B,  viii 
Fonticulus  frontalis  (major).     See   Fontaneile, 
anterior 
mastoideuy.     See  Fontaneile,  postero-lateral 
occipitalis  (minor).    See  Fontaneile,  posterior 
sphenoidalis.     See  Fontaneile,  antero-lateral 
Foot,  articulations  of,  306 
bones  of,  238 

architecture  of.  Appendix  A,  v 
morphology  of,  Appendix  F,  xxiv 
ossification  of,  249,  251,  252 
variations  in.  Appendix  B,  xii,  xiii 
fasciae  of,  371 
lymphatics  of,  916,  917 
mechanism  of,  315 
muscles  of,  373,  375,  380 

actions  and  nerve-supplies  of,  383,  384 
surgical  anatomy  of,  1310 
Foot-plate  of  stapes,  756 
Foramen  apicis  dentis,  1015 


Foramen  caecum  lingufe  (Morgagnii),  1000, 1242 
development  of,  37,  1014,  1217 
meduUse  oblongata^,  482 
of  skuU,  105,  128,  166 
centrale  cochlete,  761 
condylic,  anterior,  109,  164,  169,  170 

posterior,  110,  164,  169 
dental,  inferior,  143,  156 
diaphragmatis  (sellte),  599 
epiploicum    (Winslowi).       See    Foramen   of 

Winslow 
ethmoidale  auterius,  104,  147,  166 

posterius,  104,  147,  166 
of  Huschke,  748 

incisivum.  See  Foramen  of  Stenson,  or  incisor 
incisor,  136,  161 
infraorbital,  134,  149 

surface  anatomy  of,  1237 
interventriculare  (Monroi).     See  Foramen  of 

Monro 
intervertebrale,  77,  90 

ischiadicum   majus.      See   Foramen,    sciatic, 
greater 
minus.    See  Foramen,  sciatic,  lesser 
jugulare,  110,  116,  164,  169 
lacerum,  163,  168 
magnum,  108,  111,  159,  165,  169 

plane  of,  170 
of  Magendie,  512,  601 

mandibiUare.     See  Foramen,  dental,  inferior 
mastoideum,  116,  154,  169 
mentale,  142 

surface  anatomy  of,  1237 
of  Monro,  476,  544,  551,  573 
development  of,  479,  594 
obturatum,  212,  218 

occipitale  magnum.     See  Foramen  magnum 
opticum,  123,  147,  168 

abnormalities  of,  Appendix  B,  ix 
ovale  of  heart,  63,  787 
development  of,  930 
persistence  of,  947 
ossis  sphenoidalis,  124,  155,  163,  168 
abnormality  of.  Appendix  B,  ix 
palatine,  greater,  or  posterior,  161 
surgical  anatomy  of,  1246 
lesser,  139,  161 
palatinum   majus.     See   Foramen,   palatine, 

greater 
parietale,  107,  157,  166 

origin  of.  Appendix  B,  viii 
quadratum,  419 
rotundum,  124,  156,  168 

abnormality  of.  Appendix  B,  ix 
sacro-sciatic.     See  Foramen,  sciatic 
of  Scarpa,  136,  161 
sciatic,  greater,  220,  292 

lesser,  220,  292 
singulare  cochleae,  762 

sive    incisura    supraorbitalis.       See    Supra- 
orbital notch 
spheno-palatiuum,  139,  156,  172 
spinal,  76,  78,  81,  83 
spinosum,  124,  155,  163,  168 

abnormality  of,  Appendix  B,  ix 
of  Stenson,  136,  161 

development  of,  137 
stylomastoideum,  116,  164,  165 

absence  of.  Appendix  B,  ix 
supraorbital,  103,  147 

surface  anatomy  of,  1224 
supratrochlear,  of  humerus,  Appendix  B,  xi 


1348 


INDEX. 


Foramen,  thyroid.     See  Foramen  obUiratnm 
transversarium,  78 

vena3  cava;.     See  Foramen  quadratum 
vertebrale,  76,  81,  83 
vertebrarterial,  78,  79,  80,  81 

serial  homology  of.  Appendix  C,  xiv 
of  Vesalius,  124,  155,  168 
of  Wiuslow,  1049,  1097,  1102 

development  of,  1107 

surgical  anatomy  of,  1272 
zygomatico-faciale.     See  Malar  canal 
zygomatico-orbitale,  141 
zygomatico-temporale,  141 
Foramina     alveolaria.        See     Dental     canals, 
posterior 
nervosa,  765 

palatina  minora.  See  Foramen,  palatine,  lesser 
papillaria,  1137 
sacralia  anteriora,  84 

posteriora,  85 
veuarum  minimarum  cordis  (Thebesii),  787, 
788 
Forceps  major,  571,  576 
Forearm,  fascias  of,  336 
lymjshatics  of,  915 
muscles  of,  338 
superficial  veins  of,  890 
surgical  anatomy  of,  1298 
Fore -brain,  476,  542 

develoj^ment  of,  478,  594 
Fore-gut,  33,  37,  1105 
Forel,  decussation  of,  539 
Formatio  reticularis  of  medulla,  490,  498,  499 

of  pons,  502,  528 

of  spinal  cord,  457,  460 
Formative  pole,  11 
Fornix  of  cerebrum,  571 

connexion  of,  with  hippocampus  major,  572 

development  of,  597 

lyra  of,  572 

pillars  of,  anterior,  548,  550,  572 
posterior,  568,  572 

tsenia  of,  572 
conjunctivae  inferior,  739 

suj)erior,  739 
pharyngis.     See  Pharynx,  vault  of 

vaginge,  1193,  1283 
Fossa  or  Fossse,  acetabuli,  218 
anterior  palatine,  136,  161 
antihelix,  744 
canina,  134,  1237 
cloacal,  45,  1200,  1203,  1206 
condylic,  110,  164 
condyloidea.     See  Fossa,  condylic 
coronoidea,  192 
cranii,  166 

anterior,  166,  170,  175,  176 

media,  166,  170,  177,  178 

posterior,  169,  170 
crural,  of  peritoneum,  1098 
digastrica  (mandiljuhje),  142 
digital,  of  femur,  225 

of  testis,  1160 
ductus  venosi,  1112,  1114 
duodenal,  inferior,  1068,  1069 

superior,  1068,  1069 
duodeno-jejunal,  1069 

surgical  anatomy  of,  1272 
epigastric,  1255 

femoral,  of  peritoneum.     See  Fossa,  crural 
fioccular,  119,  121 
for  gall  bladder,  1115 


Fossa  or  Fossae,  glandulae  lacrimalis,  105,  149 
glenoid,  of  scajjula,  184,  276 

of  temporal  bone,  113,  154 
condition  of,  at  birth,  121 
surgical  anatomy  of,  1237 
of  helix,  744 

hyaloidea.     See  Fossa  patellaris 
hyjjophyseos.     See  Fossa,  pitiiitary 
]  lypotroch  an terica,  Appendix  B,  xii 
ileo-cascal,  1081 
ileo-colic,  1081,  1082 
iliaca,  215 
incisor,  of  maxilla,  134 

of  mandible,  142 
incudis,  749 

infraspinata.     See  Fossa,  infraspinous 
infraspinous,  185,  187 
infratemporal,  154 
inguinal,  external,  1098 

internal,  1098,  1101 

middle,  1098 
intercondyloidea  (femoris),  227  « 

anterior  (tibias),  231 

posterior  (tibiae),  231 
intersigmoid,  1086 

surgical  anatomy  of,  1274 
ischio-rectalis,  1281 
jugularis,  116 

condition  of,  at  birth,  121 

relation  of,  to  jugular  foramen,  164 
to  tympanum,  1233 
lacrimal,  105 
of  Landzert,  1069 
for  ligamentum  teres  of  hip,  224 
variation  in.  Appendix  B,  xi 
mandibularis.  See  Fossa,  glenoid,  of  temporal 

bone 
mastoid,  1233 
myrtiform,  134 
nasal.     See  Nasal  fossa 
navicularis  urethras  (Morgagni),  1180 
surgical  anatomy  of,  1283 

vestibuli  vaginae,  1196 
obturator,  1143 
olecrani,  192 
orbital,  147 
ovalis  (femoris).     See  Saphenous  opening 

of  heart,  787,  788 
development  of,  930 
ovarica,  1182 
paraduodenal,  1068,  1069 
pararectal,  1090,  1101 
paravesical,  1101,  1155 
patellaris,  735 
pituitary,  121,  170 

development  of,  Ajojjendix  E,  xxi 
pterygoid,  125,  161 
pterygo-palatina,  156 
radialis,  192 
retro-caecal,  1081 
retro-colic,  1081 

retro-mandibularis.     See  Parotid  recess 
rhomboid  alea.     See  Fossa  rhomboidalis 
rhomboidalis,  482,  487 
of  Rosenmiiller,  754,  1033,  1034 

development  of,  35 

surgical  anatomy  of,  1246 
sacci  lacrimalis.     See  Lacrimal  groove 
scaphoid  of  pinna.     See  Scapha 
scaphoidea  (oss.  sjjhenoid.),  125,  161 
spheno-maxillary,  156 
Bubarcuata,  119,  121 


INDEX. 


1349 


Fossa  or  Fossae,  submaxillary,  143 

supraspinata.     See  Fossa,  supraspinous 
supraspinous,  185,  187 
supratonsillar,  1034,  1035 

development  of,  1036,  1038 
of  Sylvius,  556,  596 
temporalis,  154 
triangularis  auricul£e,  744 
trochanterica.     See  Fossa,  digital,  of  femur 
venae  cavse  (inferioris),  1111,  1115 

umbilicalis,  1114 
vermiform.  Appendix  B,  viii 
vesicae  felleae,  1115 
zygomatic,  154,  162 
Fossula  fenestras  cochleae,  117,  752 
vestibuli,  752 
inferior,  of  internal  auditory  meatus,  762 
superior,  of  internal  auditory  meatus,  762 
Fossulae  tonsillares.     See  Tonsil,  crypts  of 
Fountain  decussation,  539 
Fourchette,  1196 

Fourth  ventricle,  487.     See  also  Ventricle 
Fovea   capitis    femoris.      See   Fo-ssa   for  liga- 
mentum  teres 
capituli  radii,  198 
centralis  retinae,  731,  734 
costalis  inferior.    See  Costal  demifacets,  lower 

superior.     See  Costa,!  demifacets,  upper 
dentis,  79 

femoralis.     See  Femoral  fossa 
inferior  of  foiirth  ventricle,  488,  527 
inguinalis    lateralis.      See    Fossa,    inguinal, 
external 
medialis.     See  Fossa,  inguinal,  internal 
pterygoidea,  144 

submaxillaris.     See  Fossa,  submaxillary 
superior  of  fourth  ventricle,  488,  527 
supravesicalis.      See  Fossa,  inguinal,  middle 
trochlearis,  105,  147 
Foveas  articulares  superiores  atlantis,  79 
Foveolae  gastricae,  1059 

granulares  (Pacchioni).     See  Pacchionian  de- 
pressions 
Frenula  valvulae  coli,  1077 
Frenulum  clitoridis,  1196,  1197 
epiglottidis,  1002 
of  Giacomini,  569 
labii  inferioris,  995 

superior  is,  995 
labiorum  pudendi.     See  Fourchette 
linguae,  997,  1005 

surgical  anatomy  of,  1244 
praeputii,  1171 

veli  medullaris  anterioris,  531 
development  of,  542 
Fretum  Halleri,  929 
Frontal  artery  of  ophthalmic,  816 
surface  anatomy  of,  1223 
of  superficial  temporal,  810 
bone,  103 

architecture  of.  Appendix  A,  i 
ossification  of,  106 
sexual  differences  in,  103 
variations  in,  Appendix  B,  viii 
crest,  105,  166 
eminence,  103 

difference  in,  due  to  sex,  180 
relation  of,  to  brain,  1224 
gyrus,  ascending,  560 
inferior,  560,  561 
middle,  560,  561 
superior,  560 


Frontal  gvrus,  topography  of,  1224,  1225 
lobe,  560 
nerve,  679 
plane,  5 
process  of  maxilla,  135,  150 

of  zygomatic  bone,  140 
sinus,  104 

in  coronal  sections,  173 
growth  of,  106 
at  puberty,  181 

relation  of,  to  infundibulum,  129 
to  nose,  173 
to  orbit,  149 
surgical  anatomy  of,  1235 
suture,  147 
vein,  879 
Fronto-marginal  sulcus,  560 
Fronto-nasal  process,  38 
Fronto-pontine  tract,  591 
in  crus,  540 

in  internal  capsule,  583 
Froriep,  ganglion  of,  700,  701 
Fundus  of  caecum,  1076 

meatus  acustici  interni,  762 
of  stomach,  1051,  1052,  1055 
level  of,  1290 
surgical  anatomy  of,  1271 
tympani,  749 
uteri,  1187,  1284 

ventriculi.     See  Fundus  of  stomach 
vesicae,  1145 
Fungiform  papillae,  1003,  1004 
Funicular  process,  1266 
Funiculus  anterior  of  cord,  455 
cuneatus,  455,  484,  491,  492 
constitution  of,  466 
development  of,  473 
in  section  of  medulla,  489 
gracilis,  455,  484,  491,  492 
constitution  of,  466 
development  of,  473 
in  section  of  medulla,  489 
lateralis  of  cord,  455 
posterior  of  cord,  455 
of  Rolando,  485,  491 
separans,  488 

spermaticus.     See  Spermatic  cord 
umbilicalis.     See  Umbilical  cord 
Furcula,  35,  38,  1013 
Furrow,  bicipital,  1295 
nuchal,  1253 
spinal,  1284 
sternal,  1253 
ulnar,  197 

Galea  aponeurotica.    See  Epicranial  aponeurosis 
Galen,  veins  of,  604,  682 
Gall-bladder,  1108,  1118 

development  of,  1123 

duct  of,  1119 

structure  of,  1119 

surgical  anatomy  of,  1265,  1270 

variations  in,  1119 
Gangliated  cord  of  sympathetic,  703.     See  also 

Cord,  gangliated 
Ganglion  or  Ganglia,  aortico-renal,  710,  712 

basal,  of  brain,  579 

of  cardiac  plexuses,  693,  793 

cardiacum    (Wrisbergi).       See    Ganglion    of 
Wrisberg 

cervicale  inferius,  706,  708 

surgical  anatomy  of,  1255,  1289 


1350 


INDEX. 


Ganglion  or  Ganglia,  cervicale  medium,  706, 708 

plexuses  of,  712 

superius,  706 

of  uterus,  1192 
ciliare,  680.     See  also  Ganglion,  lenticular 
coccygeal,  704,  711 
cochlear.     See  Nucleus,  cochlear 
coeliaca,  712 
of  Corti,  761,  768 
of  cranial  nerves,  443 
diaphragmatic,  622,  713 
of  Froriep,  700,  701 
Gasserian,  524,  679 

develojiment  of,  699 

morphology  of,  701,  702 
geniculate,  524,  686 

development  of,  699 

morphology  of,  701,  702 
geniculi.     See  Ganglion,  geniculate 
habenulse,  547 
impar,  704,  711 
interpedunculare,  539 

relation  of,  to  fasciculus  retroflexus,  548 
jugular,  of  ninth  nerve,  689 

development  of,  700 

morphology  of,  701 
jugulare.     See  Ganglion  of  root  of  vagus 
lenticular,  680 

development  of,  699 

long  root  of,  680,  681 

morj)hology  of,  701 

short  root  of,  677,  681 

sympathetic  root  of,  681,  708 
lumbalia.     See  Ganglia,  lumbar 
lumbar,  710 
of  Meckel,  682,  699 

development  of,  699 
mesentericum  superius,  713 
nodosum,  690,  692 

development  of,  700 

morphology  of,  701 
olfactory,  698 

morphology  of,  703 
oticum,  685,  707 

de vel oilmen  t  of,  699 
petrosum,  689 

development  of,  700 

morphology  of,  701 
phrenica.     See  Ganglion,  diaphragmatic 
of  root  of  vagus  (jugulare),  690,  692 
development  of,  700 
morphology  of,  701 
sacralia,  711 
of  Scarpa,  768 
semilunar,  710,  712 

semilunare  (Gasseri).  See  Ganglion,  Gasserian 
spheuo-jjalatinum,  682 

development  of,  699 
spinal,  443,  608 

accessory,  608 

cells  of,  608 

development  of,  661 
spirale  coclilcie,  689,  761,  768 
splauchiiicum,  710 
submaxillare,  685,  687,  707 
superius.     See  Ganglion,  Jugular,  of  ninth 
sympathetic,  443,  704 

cells  of,  704 

collateral,  704,  715 

development  of,  715 

gray  rami  of.     See  Rami  connnunicantes 

terminal,  704,  715 


Ganglion  or  Ganglia,  thoracalia.     See  Ganglia, 
thoracic 
thoracic,  709 

central  branches  of,  710 
first,  706 

peripheral  branches  of,  709,  710 
jjlexuses  of,  712 
trunci  sympathici,  704 
of  trunk  of  vagus.     See  Ganglion,  nodosum 
vestibulare,  689 

development  of,  699,  700 
of  Wrisberg,  693 
Ganglionic  layer  of  retina,  732 
Gasserian  artery  of  internal  carotid,  815 
of  middle  meningeal,  811 
depression,  117,  168 
ganglion,  679.     See  also  Ganglion 
Gastric  artery,  844,  1060.     See  also  Artery 
impression  of  liver,  1113 

of  kidney,  1137 
lymphatic  glands,  918 
veins,  904,  1060 
Gastrocnemius  muscle,  376 
action  of,  384 
nerve-supj)ly  of,  383 
surface  anatomy  of,  1309,  1310 
Gastro-colic  omentum,  1049,  1104 
Gastro-duodenal  artery,  845 
Gastro-epiploic  artery,  845,  1060 

veins,  903,  904,  1060 
Gastro-hepatic  omentum,  1050,  1116 

develoj)ment  of,  1107 
Gastro-phrenic  ligament,  1057,  1099 
Gastro-splenic  omentum,  1050, 1057,  1099, 1104, 
1212 
development  of,  1108 
Gelatinous  marrow,  71 
Gemellus  inferior  muscle,  367 
superior  muscle,  367 
actions  of,  370 
nerve-supplies  of,  370 
General  lumbar  index,  Appendix  D,  xix 
Genial  spines.     See  Mental  Spines 
Geniculate  body,  external,  531.    See  also  Corpus 
geniculatum  externum 
internal,    532.        See    also    Corpus    geni- 
culatum internum 
ganglion,  686.     See  also  Ganglion 
Geniculum  nervi  facialis,  686 
Genio-hyo-glossus  muscle,  408 
action  of,  410 
nerve-supply  of,  409 
surgical  anatomy  of,  1244 
Genio-hyoid  muscle,  408 
action  of,  410 
nerve -supijly  of,  409 
Genital  cord,  1204 

eminence,  45,  66,  1200,  1206 
fold,  45,  1206 
nerve  of  genito-crural,  643 
organs,  development  of,  1206 
female,  1182,  1195 
male,  1159,  1182 
ridge,  1204 
Genito-crural  nerve,  643 
Gennari,  stria  of,  585 
Genu  corjjoris  callosi,  571 
cajasuhe  interna},  583 
of  facial  nerve,  686 
of  fissure  of  Rolando,  558 
Germ  cells,  enamel,  1026 
nerve,  661 


INDEX. 


1351 


Germ  of  tooth,  1027 

Germinal  cells  of  ovary  and  testis,  12,  13,  15 
of  spinal  cord,  22,  447,  471,  661 
epithelium,  1184,  1204 
layers,  8,  19 
spot,  10,  11 
vesicle,  11 
Giacoraini,  frenulum  of,  569 
Gianuzzi,  crescents  of,  1008 
Gimbernat,  ligament  of,  430 
Gingivae.     See  Gums 
Ginglymus,  257 

Girald^s,  organ  of,  1160,  1199,  1205 
Girdle,  pectoral,  187,  254 

pelvic,  212,  254 
Glabella,  103,  147,  170,  Appendix  D,  xvi 

surgical  anatomy  of,  1223,  1237 
Gladiolus,  94 

Glands  or  Glandular,  1007 
acini  of,  1008 
acino-tubular,  1007 
acinous,  1007 
agminated,  1062,  1064 
alveolar,  1007 
alveoli  of,  1008 
apical,  of  tongue,  1006 
areolares  (Montgomerii),  1207 
of  Bartholin,  1182,  1198 
development  of,  1206 
surgical  anatomy  of,  1283 
basement  membrane  of,  1008 
of  Bowman,  722 
of  Brunner,  1061,  1070 
buccales,  997 
bulbo-urethrales   (Cowperi).     See   Glands  of 

Cowper 
carotid,  1220 
ceruminosae,  748,  778 
cervicales  uteri,  1191 
ciliares  (MoUi),  739,  778 
circum-anales,  1095 
coccygeal,  1220 
compound,  1007 
of  Cowper,  1159,  1176,  1179 
development  of,  1206 
ducts  of,  1180 
surgical  anatomy  of,  1278 
digestive,  993 
ductless,  1007,  1210 

duodenales  (Brunneri).  See  Glands  of  Brunner 
of  Ebner,  771 
Haversian,  295 
intestinales  (Lieberkuehni).     See  Glands   of 

Lieberkilhn 
labiales,  996,  997 

lacrimalis  inferior  (  =  palpebral  portion),  740 
superior  (  =  orbital  portion),  740 
surgical  anatomy  of,  1238 
laryngese,  968 
of  Lieberklihn,  1062 
of  small  intestine,  1073 
of  colon,  1075 
of  rectum,  1093 
linguales  anteriores.     See  G.,  apical 
of  Littre,  1180 

lymphatic.     See  Lymphatic  glands 
mammary,  1207.     See  also  Mammary  gland 
Meibomian,  739 

surgical  anatomy  of,  1238 
molares,  997 
of  Moll,  739,  778 
of  Montgomery,  1207 


Glands  or  Glandulee,  mucous,  1008 
olfactorise.     Glands  of  Bowman 
palatinse,  998,  999 
parotis,  1009.     See  also  Parotid  gland 

accessoria.     See  Socia  parotidis 
praeputiales,  1171 
prostate,  1173.     See  also  Prostate 
prostatic,  1175,  1179 
racemose,  1007 
salivary,  1008,  1009,  1013 
sebacete,  77T,  779 
serous,  1008 
simple,  1007 
solid,  1007 
solitary,  of  small  intestine,  1063 

of  large  intestine,  1075 
structure  of,  1008 
sublingxialis,  1012 
development  of,  1013 
surgical  anatomy  of,  1244 
submaxillaris,  1011 
development  of,  1013 
surgical  anatomy  of,  1249 
sudoriferse.     See  Glands,  sudoriparous 
sudoriparous,  778,  779 
suprarenalis,  1213.  /Seeafeo  Suprarenal  capsule 

surgical  anatomy  of,  1286,  1290 
tarsales  (Meibomi).     See  Glands,  Meibomian 
thymus,  1218 
thyreoidea,  1216.     See  also  Thyroid  body 

accessorite,  1217 
of  tongue,  1006 
tubular,  1007 

urethrales  (Littrei).     See  Glands  of  Littrd 
uterinpe,  53,  1191 
vestibulares  minores,  1197 
vestibularis  major  (Bartholini).     See  Glands 
of  Bartholin 
Glaus  clitoridis,  1197 

penis,  1170,  1206 
Glaserian  fissure,  113,  120,  750 
Gleno-humeral  ligament,  277 
Glenoid  cavity  of  scapula,  184,  276 
fossa  of  temporal  bone,  113,  154 
condition  of,  at  birth,  121 
surgical  anatomy  of,  1237 
ligament,  276 
Glisson,  capsule  of,  1115,  1120,  1121 
Globe  of  eye,  723,  724 
Globular  process,  39,  68 
Globus  pallidus,  580,  581 
Glomerulus,  olfactory,  587 
renal,  1140 
of  sweat  glands,  778 
Wolffian,  1201 
Glomus  caroticum.     See  Carotid  gland 

coccygeum.     Sec  Coccygeal  gland 
Glosso-epiglottidean  folds,  963,  1002 

ligament,  963 
Glosso-pharyngeal  nerve,  689.     See  also  Nerve 
Glosso-pharyngeus  muscle,  410 
Glottis  respiratoria,  966 
spuria,  966 
vera,  966 
vocalis,  966 
Glutseus  maximus  muscle,  364 
actions  of,  370,  393 
nerve -supply  of,  370 
surface  anatomy  of,  1302 
medius  muscle,  365 
minimus  muscle,  365 
actions  of,  370,  393 


1352 


INDEX. 


Glutaeus  minimus  muscle,  nerve -supply  of,  370 
Gluteal  artery,  850 

surface  anatomy  of,  1303 
cleft,  1290,  1302 
fold,  1302 
lines,  214 

surface  of  ilium,  214 
veins,  895 
Gnathic  index,  Apj)endix  D,  xvii 
Golgi,  cells  of,  464,  586 
GoU,  column  of,  466,  473 
Gonion,  Appendix  D,  xvi 
Gowers'  tract,  468,  469,  473,  484,  498,  511 
Graafian  follicles,  1184,  1204 
Gracile  funiculus,  491.     See  also  Funiculus 
lobule,  508 

nucleus,  485,  490.     See  also  Nucleus 
Gracilis  muscle,  362 
action  of,  370 
nerve-supply  of,  370 
Granulationes  arachnoideales.    See  Pacchionian 

bodies 
Granule  cells,  514 

layei-s  of  retina,  732,  733 
Gray  matter,  central,  of  mid-brain,  533,  550 
of  cerebellum,  509,  512 
of  cerebral  cortex,  554,  584 
cerebro-spinal,  443 
of  cord,  456,  460 

development  of,  473 
of  medulla,  489,  498 
of  optic  thalamus,  544 
Groin,  1305 

fasciae  of,  353 
Groove,  antero-lateral,  of  medulla,  482 
antero-median,  of  cord,  482 
auriculo-ventricular,  783,  785 

topography  of,  1262 
bicipital,  189,  190 

surface  anatomy  of,  1293 
carotid,  of  sphenoid,  123,  168 
costal,  98,  100 

for  Eustachian  tube,  124,  163, 
for  inferior  petrosal  sinus,  111,  116,  169 
interosseous,  of  astragalus,  239 

of  OS  calcis,  243 
interventricular,  784,  785,  786 
intervertebral,  77 
lacrimal,  of  lacrimal  bone,  131,  150 

of  maxilla,  135,  150 
for  lateral  sinus,  169 

on  cerebral  hemisphere,  554 
on  occipital  bone,  109,  110 
on  parietal,  108 
on  temporal,  115 

partial  absence  of,  Apjjendix  B,  ix 
medullary,  21 

for  meningeal  arteries,  166,  168,  170 
on  frontal  bone,  105 
on  parietal,  108 
on  temporal,  114 
musculo-spiral,  191 
mylo-hyoid,  143 

development  of,  144 
naso-pharyngeal,  1034 
neural,  20,  21,  66 
obturator,  218 

abnormality  of.  Appendix  B,  ii 
for  occipital  sinus,  169 
oesophageal,  of  liver,  1112 

of  lung,  987 
olfactory,  128,  129,  166 


Groove,  optic,  122 
popliteal,  227 

postero-lateral,  of  medulla,  482 
I^rimitive,  20,  66 
pterygo-palatine,  of  palate,  140 

of  sjjhenoid,  126 
sacral,  85 
subclavian,  99 
for  subclavius,  182 
subcostal.     See  Groove,  costal 
for  superficial  petrosal  nerve,  118 
for  superior  longitudinal   sinus,  on  cranial 
vault,  166 
on  frontal,  105 
on  occipital,  109 
on  parietal,  108 
for  superior  j)etrosal  sinus,  116,  169 
vertebral,  of  spinal  column,  88 
of  thorax,  101 
Gubernaculum  dentis,  1028 

testis,  1168 
Gudden,  commissure  of,  532,  552,  676 
Gullet,  1038 
Gums,  995,  998 
Gustatory  cells,  771 
hair,  771 
pore,  771 
Gyrus  or  Gyri,  554 
angularis,  563,  564 

topography  of,  1225 
annectant,  deep,   of  calcarine  and  parieto- 
occipital fissure,  565,  566 
of  intraparietal,  563,  564 
of  Rolandic,  558 
callosal,  568 

.centralis  anterior.    See  Gyrus,  frontal,  ascend- 
ing 
posterior.     See  Gyrus,  parietal,  ascending 
cinguli.     See  Gyrus,  callosal 
cuneate,  565,  566 
cuneo-lingual,  anterior,  566 

posterior,  566 
dentatus,  568 
development  of,  696 
fomicatus.     B.N.A.  =  Limbic  lobe 

English  =  callosal  gyrus 
frontal,  ascending,  560 
frontalis  inferior,  560,  561 
medius,  560,  561 
superior,  560 
topography  of,  1225 
fusiformis.     See  Gyrus,  occiijito-temporal 
hippocampi,  568 

morphology  of,  584 
lingualis,  566 
marginalis,  561 
occipito-temporal,  566,  567 
orbitalis  anterior,  562 
internus,  562 
posterior,  562 
parietal,  ascending,  563,  564 
topography  of,  1225 
inferior,  563,  564 
superior,  563,  564 
postcentralis,  563 
postparietalis,  563,  564 
rectus,  562 
subcallosus  (pedunculus  corporis  callosi),  571, 

573 
supracallosus,  569,  571 
supramarginalis,  563,  564 
topography  of,  1224 


I^DEX. 


1353 


Gyrus  or  Gyri,  temporalis  inferior,  567 

medius,  567 

superior,  567 
temporales  transversi,  567 
transitivi  cerebri.     See  Gyri,  annectant 

Habenula,  commissure  of,  548 
ganglion  of,  547 
perforata,  765 
Hajmorrhoidal  arteries,  inferior,  854,  1095 
middle,  581,  1096 
superior,  848,  1096 
nerve,  inferior,  659 
plexus,  714 

venous,  1096 
veins,  896.     See  also  Vein 
Hair,  776 

develojjment  of,  779 
of  fa3tus,  68 
erector  muscles  of,  778 
follicle  of,  776 
papilla  of,  777 
Hair-cells,  auditory,  763,  764,  766,  767 
Hair-follicles,  776 
Hairs,  gustatory,  771 

olfactory,  723 
Haller,  fretum  of,  929 
Hamstring  muscles,  368 

surgical  anatomy  of,  1303 
Hamular  process  of  pterygoid  plate,  125, 162 
surgical  anatomy  of,  1246 
of  lacrimal,  131 
Hamulus  cochleae,  761 
lacrimalis.     See  Hamular  process  of  lacrimal 
laminge  spiralis,  761 

ossis  hamati.     See  Hamulus  of  unciform 
pterygoideus.        See     Hamular     process     of 

pterygoid 
of  unciform  bone,  205 
Hand,  arterial  arches  of,  835 
articulations  of,  284 
bones  of,  201 

architecture  of.  Appendix  A,  iii 
morphology  of,  Appendix  F,  xxiv 
ossification  of,  207,  210,  211 
variations  in.  Appendix  B,  xi 
fasciae  of,  336 
movements  of,  289 
muscles  of,  336,  343 
surgical  anatomy  of,  1298 
Hard  palate,  159 

relation  of,  to  surface,  150 
in  coronal  section  of  skull,  176 
Hare-lip,  1240 

Harmonia.     See  Suture,  harmonia 
Hasner,  valve  of,  741 
Hassall,  concentric  corpuscles  of,  1220 
Haunch-bone.     See  Innominate  bone 
Haustra  coli,  1075 
Haversian  canals,  72 
gland,  295 
systems,  72 
Head,  arteries  of,  801,  950 
bones  of,  103 
fasciae  of,  394 
lymphatics  of,  909 
mesodermal  somites  of,  31,  32 
movements  of,  393,  410 
muscles  of,  395 

development  of,  441 
nerves  of,  700 
segmental  characters  of,  701  ;  App.  E,  xxii 


Head,  surgical  anatomy  of,  1222 

veins  of,  875 
Head-cap,  15 

Head-fold  of  embryo,  27,  33 
Heart,  783 
abnormalities  of,  946 
annulus  ovalis  of,  787 
aortic  cusp  of,  791 

orifice  of,  791 

topography  of,  1262 

valve  of,  791 

vestibule  of,  791 
apex  of,  785,  789 

abnormalities  of,  946 
arteries  of.     See  Arteries,  coronary 
auricles  of,  786 

development  of,  930 

structure  of,  792 

topography  of,  1262 
auricular  aj)pendices  of,  786,  788 

develojjment  of,  929 
auriculo- ventricular  apertures  of,  783,  787, 

789,  790 
auriculo-ventricular  groove  of,  783,  785 

topography  of,  1262 
base  of,  784 
capacity  of,  793 

central  fibro-cartilage  of,  789,  792 
chambers  of,  786 
chordae  tendineae  of,  790,  791 
columnae  cameae  of,  790,  791 
conus  arteriosus  of,  789 
coronary  sinus  of,  787,  871 

abnormalities  of,  954 

develojjment  of,  931 

morjjhology  of,  945 

ojiening  of,  787 
corpora  Arantii  of,  790 
crista  terminalis  of,  787 
development  of,  62,  925,  928 
endocardium  of,  787,  788,  790,  791 

structure  of,  792 
epicardium  of,  791,  792 
Eustachian  valve  of,  788 

development  of,  932 
fibrous  rings  of,  790,  791,  792 
foramen  ovale  of,  63,  787,  788,  930 

persistence  of,  947 
foramina  Thebesii  of,  787,  788 
fossa  ovalis  of,  787 

development  of,  930 
infundibulum  of,  789 
interauricular  septum  of,  786,  787,  788 

abnormalities  of,  947 

development  of,  930 
interauricular  sulcus  of,  784 
interventricular  septum  of,  789,  791 

abnormalities  of,  947 

development  of,  929 
interventricular  sulcus  of,  784,  785 
lunulae  of  valves  of,  790 
lymphatics  of,  793 
margins  of,  786 

topography  of,  1262 
mitral  orifice  of,  788,  790 
level  of,  1290 
topography  of,  1262 

valve  of,  790 
moderator  band  of,  790 
musculi  papillares  of,  790,  791 

structure  of,  792 
musculi  pectinati  of,  787,  788 


1354 


INDEX. 


Heart,  myocardium  of,  791 
nerves  of,  793 

orifices  of  pulmonary  veins  in,  784,  788 
orifices  of  vense  cavse  in,  787 
pars  membranacea  septi  of,  791 

abnormalities  of,  947 
primitive,  928 

pulmonary  orifice  of,  789,  790 
topography  of,  1262 
valve  of,  790 

development  of,  932 
Purkinje's  fibres  of,  791 
relation  of,  to  wall  of  thorax,  785, 786, 789, 1262 
semilunar  valves  of,  790,  791 

development  of,  932 
shape  of,  783 
size  of,  792 
structure  of,  791 
sulcus  terminalis  of,  787 

developmental  significance  of,  932 
surface  and  surgical  anatomv  of,  1262 
Thebesian  valve  of,  787,  788 

development  of,  932 
transposition  of,  946 
tricuspid  orifice  of,  787,  789 
level  of,  1290  j 
topography  of,  1262 
valve  of,  789 
trigona  fibrosa  of,  789 
tubercle  of  Lower  of,  788 
veins  of,  787,  788,  793,  871 

morphology  of,  945 
venous  valves  of,  931  ' 

ventricles  of,  783,  788,  789,  790 

structure  of,  792 
weight  of,  793 
Helicine  arteries,  1173 
Helicotrema,  761 
Helix,  744 

development  of,  43 
fossa  of,  744 
muscles  of,  746 
spine  of,  745 
tail  of,  745 
Helmholtz,  ligamenta  mallei  of,  757 
Hemisphseria  bulbi  urethrte,  1172 
Hemisphaerium   cerebelli.      See   Hemispheres, 

cerebellar 
Hemispheres,  cerebellar,  506 

cerebral,  553.     See  also  Cerebral  hemispheres 
Henle,  elastic  membrane  of,  782 
layer  of,  777 
loop  of,  11.39 
Hensen,  cells  of,  767 
ductus  reuniens  of,  762 
development  of,  770 
stripe  of,  767 
Hepar.     See  Liver 

Hepatic  artery,  845.     See  also  Artery 
cells,  1122 
cylinders,  1123 
duct,  1118 

development  of,  1123 
flexure  of  colon,  1082 
level  of,  1288,  1290 
topography  of,  1274 
lymphatic  glands,  918 
plexus,  713 

veins,  892.     See  also  Veins 
Hepato-duodenal  ligament,  1116 
Hepato-gastric  ligament,  1116 
Hepato-renal  ligament,  1099 


Hernia,  surgical  anatomy  of,  1265,  1266 
femoral,  356 
inguinal,  429 
Hesselbach,  triangle  of,  429 

surgical  anatomy  of,  1266 
Heterodont  dentition,  1029 
Hiatus  aorticus.     See  Aortic   opening  of  dia- 
phragm 
canalis  facialis.     See  Hiatus  Fallopii 
Fallopii,  117,  168 

condition  of,  at  birth,  121 
interosseus,  283 
maxillaris.        See     Highmore,     antrum     of, 

opening  of 
cesophageus.       See   (Esophageal    opening   of 

diaphragm 
sacralis,  85 
semilunaris,  721 

surgical  anatomy  of,  1239 
tendineus  adductorius,  858 
Highmore,  antrum  of,  136,  150 
opening  of,  135,  172,  721 
relations  of,  173,  721,  1021 
surgical  anatomy  of,  1240 
Highmori,  corpus,  1161 
Hilum  of  corpus  dentatum,  510 
of  kidney,  1130 

topography  of,  1274,  1290 
of  lung,  986 

topography  of,  1260 
of  lymphatic  glands,  905 
of  olivary  nucleus,  495 
of  ovary,  1182 
of  spleen,  1211 
of  suprarenal  capsule,  1214 
Hilus  lienis.     See  Hilum  of  spleen 
nuclei  dentati.    See  Hilum  of  corpus  dentatum 
nuclei  olivaris.    See  Hilum  of  olivary  nucleus 
ovarii.     See  Hilum  of  ovary     . 
pulmonis.     See  Hilum  of  lung 
renalis.     See  Hilum  of  kidney 
Hind-brain,  476 

parts  derived  from,  481 
Hind-gut,  33,  34,  1105 
Hinge-joints,  257 
Hip,  surgical  anatomy  of,  1302 
Hip-bone,  212 
Hip-joint,  293 

movements  at,  296,  370,  371 
nerves  to,  644,  646,  647,  649,  652 
surgical  anatomy  of,  1306 
synovial  membrane  of,  295 
Hippocampal  commissure,  572 

fissure,  554,  568.     See  also  Dentate  fissure 
Hippocampal  gyrus,  568 
Hijipocampus.     See  Hippocampus  major 
Hippocampus  major,  576 

connexion  of,  with  fornix,  572 

with  thalamus,  573 
fimbria  of,  568,  572,  577 
olfactory  bundle  of,  572 
pes  of,  577 
minor.     See  Calcar  avis 
Histology,  4 

Homodont  dentition,  1029 
Homology,  2 

of  limb-bones.  Appendix  F,  xxiii 
serial,  3 

of  vertebras.  Appendix  C,  xiii 
Homoplasy,  3 

Horizontal  fissure  of  cerebellum,  great,  506 
development  of,  531 


i 


INDEX. 


1355 


Horner,  muscle  of,  741.     See  also  Tensor  tarsi 

muscle 
Horse-shoe  kidney,  1140 
Hour-glass  stomacli,  1058 
Houston,  valves  of,  1093 
Huguier,  canal  of,  113 

relation  of,  to  tympanum,  750 
Humeral  artery,  829 
Humero-femoral  index,  Appendix  D,  xx 
Humero-ulnar  joint,  279 
Humerus,  188  ' 

architecture  of,  Appendix  A,  iii 

connexions  of,  193 

epiphyses  of,  193 

morjshology  of.  Appendix  F,  xxiv 

ossification  of,  193 

sexual  differences  of,  193 

surgical  anatomy  of,  1292,  1293,  1295,  1296, 

1297 
variations  in,  Appendix  B,  xi 
Humor  vitreus.     See  Vitreous  body 
Humour,  aqueous,  725,  737 
Huschke,  foramen  of,  748 
Huxley,  layer  of,  777 
Hyaloid  artery,  736 
history  of,  742 
canal,  736 

development  of,  742 
membrane,  735 
Hyaloplasm,  8 
Hydatid  of  Morgagni,  1187,  1199 

of  testis,  1160,  1205 
Hymen,  1193,  1196 

development  of,  1205 
Hyo-epiglottidean  ligament,  964 
Hyo-glossal  membrane,  1005 
Hyo-glossus  muscle,  409 
action  of,  410 
nerve -supply  of,  409 
Hyoid  arch,  36,  37 

muscles  derived  from,  441 
nerve  of,  702 
Hyoid  artery,  804,  805 
bar,  37,  146 
bone,  145 

connexions  of,  146 
cornua  of,  145,  146 
development  of,  37 
movements  of,  409,  413 
ossification  of,  146 
surgical  anatomy  of,  1250 
Hyparterial  bronchus,  976,  990 
Hypochondrium,  1047,  1267 
Hypochordal  bow,  91 

spange,  Appendix  C,  xv 
Hypogastric  artery,  848.     See  also  Artery,  iliac, 
intei'nal 
abnormalities  of,  942 
obliterated,  848,  851 

relation  of,  to  urachus,  1098 
nerves,  642,  712,  714 
plexus,  712,  714 
region,  1267 

vein,  89.5.     See  also  Veins 
zone,  1047 
Hypogastrium,  1047 
Hypoglossal  nerve,  696.     See  also  Nerve 
Hypophysis,  549.     See  also  Pituitary  body 
Hypospadias,  1203 
Hypothalamus,  542,  595 
Hypotrochanteric  fossa.  Appendix  B,  xii 
Hypsicephalic  skulls,  Appendix  D,  xvii 


Idiosome,  14 
Heal  artery,  847 
Ileo-caecal  a;"tery,  847,  1081 
fold,  1081,  1082 
fossa,  1081 
glands,  920 
orifice,  1076,  1078 
valve,  1077 

frenula  of,  1077 
structure  of,  1078 
topography  of,  1273,  1290 
vein,  903 
Ileo-colic  artery,  847 
fossa,  1081,  1082 
veins,  903 
Ileum,  1065,  1071.     See  also  Intestine 

diverticulum    of,    1073.      See  also    Meckel, 

diverticulum  of 
structure  of,  1073 
vessels  and  nerves  of,  1073 
Iliac  arteries,  841.     See  also  Artery    . 
colon,  1085 

topography  of,  1274 
crest,  212,  222 

topography  of,  1290,  1302 
fascia,  1044 
fossa,  215 

lymphatic  glands,  920,  921 
portion  of  fascia  lata,  354 
region,  1047,  1267 
spine,  anterior  inferior,  213 
superior,  212,  222 

surface  anatomy  of,  1302,  1305 
posterior  inferior,  213,  221 
superior,  213,  222 

surface  anatomy  of,  1302 
tuberosity,  214 
veins,  895.     See  also  Veins 
Iliacus  muscle,  361 

action  of,  370,  371,  393 
nerve-supply  of,  370 
minor,  361 
Ilio-capsularis  muscle,  361 
Ilio-coccygeus  muscle,  438 
Ilio-costalis  cervicis  muscle,  389 
dorsi  muscle,  389 
lumborum  muscle,  387 
Ilio-femoral  ligament,  295,  296 
Ilio-hypogastric  nerve,  642 
Ilio-inguinal  nerve,  642 
Ilio-lumbar  artery,  850 
abnormalities  of,  953 
ligament,  291 
inferior,  291 
vein,  895 
Ilio-pectineal  eminence,  215,  217 

line,  215,  220,  222 
Ilio-psoas  muscle,  359 
action  of,  371 
bursa  of,  296,  360 
nerve-supply  of,  370 
surgical  anatomy  of,  1307 
Ilio-sacralis  muscle,  438 
Ilio-sciatic  notch.     See  Notch,  sciatic,  greater 
Ilio-tibial  band,  355 

relation  of,  to  muscles,  357,  364,  365 
surgical  anatomy  of,  1308 
Ilio-trochanteric  ligament,  295 
Ilium,  213 

morphology  of,  A])pendix  F,  xxv 
Immovable  joints,  255,  260 
Impressio  trigemini.     See  Gasserian  depression 


1356 


INDEX. 


Impressiones  digitatae.     See  Digital  depressions 
Incisive  artery,  812 

bundle,  398 

centre,  137 

fossa,  134 

pad  of  palate,  998 

condition  of,  at  birtli,  1000 

suture,  137 
Incisor  crest,  136 

foramen,  136, 161.  See  also  Stenson,  foramen  of 

fossa,  142 

nerve,  685 

teeth,  1015,  1017 
eruption  of,  1022 
Incisura  acetabuli.     See  Cotyloid  notcli 

cardiaca,  988 

cerebelli  anterior,  506 
posterior,  506 

clavicularis.     See  Clavicular  notch 

ethmoidalis,  104 

fibularis,  233 

interarytsenoidea,  964 

intertragica,  744 

ischiadica  major.     See  Sacro-sciatic  notch 
minor.     See  Sacro-sciatic  notch 

jugularis  ossis  occijjitalis.     See  Jugular  notch 
sterni.     See  Suprasternal  notch 

mandibulae.     See  Sigmoid  notch 

mastoidea.     See  Digastric  fossa 

nasalis.     See  Nasal  aperture,  notch  of 

pancreatis,  1125 

parietalis,  114 

radialis.     See  Sigmoid  cavity,  small 

scapulse.     See  Suprascapular  notch 

semilunaris.     See  Sigmoid  cavity,  great 

sjiheno-iDalatina.     See  Spheno-palatine  notch 

supraorbitalis.     See  SuiDraorbital  notch 

temporalis,  560,  568,  584.     See  also  Fissure, 
ecto-rhinal 

tentorii,  531,  599 

terminalis  auris,  745 

thyreoidea  inferior,  959 
superior,  958 

ulnaris.     See  Ulnar  notch 

umbilicalis.     See  Umbilical  notch 

vertebralis  inferior.    See  Intervertebral  notch 
superior.     See  Intervertebral  notch 
Inclinatio  pelvis.     See  Pelvis,  position  of 
Incremental  lines  in  dentine,  1024 
Incudo-malleolar  joint,  756 
Incudo-stapedial  joint,  756 
Incus,  756 

articulations  of,  757 

development  of,  757 

ligaments  of,  757 

movements  of,  758 

processus  lenticularis  of,  756 
Index,  alveolar,  Ajj^jendix  D,  xvii 

auricular,  744 

cephalic.  Appendix  D,  xv 

dental,  1029  ;  Appendix  D,  xviii 

facial,  superior,  Appendix  D,  xvii 
total.  Appendix  D,  xvii 

gnathic,  Appendix  D,  xvii 

nasal,  717  ;  Appendix  D,  xviii 

orVjital,  Appendix  D,  .xviii 

palato-niaxillary.  Appendix  D,  xviii 

vertical,  of  skull,  Appendix  D,  xvii 
Indices  of  skulls.  Appendix  D,  xv 
Infra -axillary  region,  1253 
Infraclavicular  lymphatic  glands,  914 
Infraclavicular  nerves,  625 


Infraclavicular  region,  1253 
Infracostal  angle,  1265 

muscles.     See  Mm.  subcostales 
plane,  1265,  1267 
Infraglenoid  impression,  185 
Infrahyoid  artery,  804 
muscles,  405 

action  of,  410,  419 
nerve -supply  of,  409 
Inframammary  region,  1253 
Infra  mandibular  nerve,  688 
Infraorbital  artery,  812 
canal,  135 

relation  of,  to  orbit,  149 
variations  in.  Appendix  B,  ix 
foramen,  134 

topography  of,  1237 
margin,  134 
nerve,  682 
plexus,  682,  688 
suture,  Appendix  B,  ix 
vein,  880 
Infrapatellar  bursa,  299 

fat-pad,  302 
Infrapyramidal  fissure,  508 
Infrascapular  artery,  829 
Infraspinatus  muscle,  329 
action  of,  331 
nerve-supply  of,  331 
Infraspinous  fossa,  185,  187 
Infrastemal   depression,   96.     See  also   Pit   of 
stomach 
notch,  1255,  1265 
region,  1253 
Infratemporal  crest,  125,  153,  155 

fossa,  154 
Infratrochlear  nerve,  680 
Infundibuliform  fascia,  421,  428,  1169 
Infundibulo-pelvic  ligament,  1284 
Infundibulum  of  brain,  475,  548 
development  of,  595 
relation  of,  to  third  ventricle,  551 
ethmoidale,  129 

relation  of,  to  nasal  fosste,  172,  173 
to  orbit,   150 
of  Fallopian  tube,  1186 
of  heart,  789 

hypothalami.     See  Infundibulum  of  brain 
of  nose,  721 
of  pulmonary  lobules,  991 

development  of,  992 
renal,  1141 

tubse  uterinpe.  See  Infundibulum  of  Fallopian 
tube 
Inguen.     See  Groin 
Inguinal  canal,  428 

surgical  anatomy  of,  1265 
fossa,  external,  1098 
internal,  1098,  1101 
middle,  1098 
glands,  916 

hernia,  surgical  anatomy  of,  1265,  1266 
region,  1047 

ring,  abdominal,  421,  428 
superficial,  422,  428 
Inion,  153.      See  also  Occipital   protuberance, 
external 
topography  of,  1223 
Inner  cell-mass,  18,  50 
Innominate  artery,  801 

abnormalities  of,  948,  950 
development  of,  933 


INDEX. 


1357 


Innominate  artery,  morphology  of,  942 
topography  of,  1249, 1264 
bone,  212 

architecture  of,  Appendix  A,  iv 
connexions  of,  218 
morphology  of,  Appendix  F,  xxv 
ossihcation  of,  219 
variations  in,  Appendix  B,  xi 
vein,  874.     See  also  Vein 
Inscriptiones  tendineaj,  427 
Insertion  of  muscles,  318 
Inspiration,  419 

muscles  of,  327,  331 
Insula.     See  Reil,  island  of. 
Integument,  772 

Integumentum  commune.     See  Skin 
Interarticular   tibro-cartilages,   258 
of  acromio-clavicular  joint,  274 

function  of,  275 
development  of,  260 
of  inferior  radio-ulnar  joint,  282 
semilunar,  301 

of  temporo-mandibular  joint,  268 
ligaments,  258 

of  costo-central  joints,  270 
of  costo-sternal  joints,  272 
development  of,  260 
of  hip-joint,  295 
Interauricular  septum  of  heart,  786,  787,  7) 
abnormalities  of,  947 
development  of,  930 
sulcus  of  heart,  784 
Interbrain,  476.     See  also  Diencephalon 
Intercavernous  sinuses,  885 
Intercentral  articulations,  261 
Interchondral  joints,  271 
Interclavicular  ligament,  274 
function  of,  275 
notch,  95 
Intercoccygeal  joints,  264 
Intercolumnar  fascia,  423,  428,  1169 
Intercondylic  fossa  of  femur,  227 
of  tibia,  231 
notch,  227 
Intercostal  aponeuroses,  416 

arteries.     See  Arteries,  intercostal 
lymphatic  glands,  923 
muscles,  416 
action  of,  419 
nerve -supply  of,  419 
nerves,  635 

surgical  anatomy  of,  1267 
spaces,  101 

veins,  873.     See  also  Veins 
Intercosto-humeral  nerve,  636 

variations  in,  673 
Intercuneiform  joints,  312 
Interdigital  veins  of  foot,  900 

of  hand,  890 
Interglobular  spaces  of  dentine,  1024 
Interlobar  fissure,  555 
Intermaxillary  process,  41 

suture,  136,  150 
Intermediate  cell-mass,  26 
history  of,  32 
visceral  arteries,  939,  942 
Intermedium,  os,  Appendix  F,  xxiv 
Intermetacarpal  articulations,  287 

movements  of,  289 
Intermetatarsal  articulations,  314 
Intermuscular  septa  of  arm,  332 
of  foot,  373 


Intermuscular  septa  of  foot,  topography  of,  1312 
of  leg,  371 
of  tliigli,  355 

topography  of,  1304 
Internal  abdominal  ring,  421,  428 
surgical  anatomy  of,  1265 
capsule,  582.     See  also  Capsule,  internal 
cutaneous  nerve  of  arm,  631 
le.sser,  of  Wrisberg,  632 
of  thigh,  646 
ear,  759.     See  also  Labyrinth 
Internasal  suture,  133 
Interneural  articulations,  263 
Interolivary  stratum,  496 
Interosseous  arteries.     See  Artery 
groove  of  astragalus,  240 

of  OS  calcis,  243 
ligaments,  calcaneo-cuboid,  311 
carpal,  285,  286 
carpo-metacarpal,  287 
cubo-cuneiform,  312 
cuneo-metatar.sal,  313 
intercuneiform,  312 
intermetatarsal,  314 
scapho-cuboid,  311 
talo -calcaneal,  309 
tibio-fibular,  304 
membrane  of  forearm,  283 

of  leg,  304 
muscles  of  foot,  383 
action  of,  384 
nerve-supply  of,  383 
of  hand,  346 
action  of,  352 
nerve-supply  of,  351 
nerves.     See  Nerves 
ridge  of  fibula,  236 

of  tibia,  232 
veins  of  hand,  890 
Interparietal  bone,  111,  112.     See  also  Os  Incse 
Interpeduncular  ganglion,  539 

relation  of,  to  fasciculus  retroflexus,  548 
space,  475 

development  of,  478 
Interphalangeal  joints  of  foot,  314 
movements  at,  315,  384 
of  hand,  288 

movements  at,  289 
surgical  anatomy  of,  1300 
Interpleural  space,  977, 982.  See  also  Mediastinal 

space 
Interpubic  lamina,  292 
Interscapular  region,  1285 
Intersegmental  association  fibres  of  spinal  cord, 
468,  470 
vessels,  938 
Intersigmoid  fossa,  1086 

surgical  anatomy  of,  1274 
Interspinales  muscles,  392 
Interspinous  ligaments,  263 
Intertarsal  joints,  308 
movements  at,  315 
sjTiovial  membranes  of,  312 
Intertransversales  muscles,  392 
Intertransverse  ligaments,  264 
Intertrochanteric  lines,  224 
Intertubercular  line,  1047 

plane,  1047,  1267 
Interventricular  grooves,  784,  785,  786 
septum,  789,  791 

abnormalities  of,  947 
development  of,  929 


1358 


INDEX. 


Intervertebral  discs,  261 
foramen,  77,  87,  90 
groove,  77 
notch,  77 

of  cervical  vertebrae,  78,  80 
of  lumbar  vertebrjB,  83 
of  thoracic  vertebrae,  81 
Intestinal  arteries,  846,  1073 
lymphatic  trunk,  908 
veins,  903,  1073 
Intestine,  1060 
agminated  glands  of,  1064.     See  also  Peyer's 

patches 
basement  membrane  of,  1061 
Brunner's  glands  of,  1070 
development  of,  1105 
epithelium  of,  1061 
large,  993,  1074 

divisions  of,  1074.     See  also  Caecum,  Colon, 

Rectum 
nerves  of,  1075 
structure  of,  1075 
topography  of,  1286,  1288 
vessels  of,  1075 
Lieberkiihn's  glands  of,  1062,  1075,  1093 
mucous  membrane  of,  1061 
of  anal  canal  of,  1093 
of  large,  1075 
of  small,  1070 
structure  of,  1073 
muscular  coat  of,  1061 
of  anal  canal  of,  1092 
of  large,  1075,  1087 
of  rectum,  1089 
of  small,  1070 
structure  of,  1073 
muscularis  mucosae  of,  1062 
Peyer's  patches  of,  1064,  1073,  1074 
re ti  form  tissue  of,  1061 
serous  coat  of,  1061 
of  large,  1075 
of  small,  1070 
structure  of,  1073 
small,  993,  1064 
coils  of,  1072 
divisions   of,    1065.     See   also  Duodenum, 

Ileum,  Jejunum 
duodeno-jejunal  flexure  of,  1065,  1070 

topography  of,  1272 
lacteals  of,  1073 
Meckel's  diverticulum  of,  1073 
mesentery  of,  1065,  1071 
nerves  of,  1070,  1073 
topography  of,  1272 
vessels  of,  1073 
solitary  glands  of,  1063,  1073,  1075 
structure  of,  1061.    See  also  Colon,  Duodenum, 

Ileum,  Jejunum,  Rectum 
submucous  coat  of,  1061,  1070,  1093 
surgical  anatomy  of,  1272 
valvulae  conniventes  of,  1070,  1074 
Intestinum  caecum.     See  Caecum 
crassum.     See  Intestine,  large 
ileum.     See  Ileum 
jejunum.     See  Jejunum 
rectum.     See  Rectum 
tenue.     See  Intestine,  small 
lutrajugular  process,  110 
Intraparietal  sulcus,  563 

Intumescentia  cervicalis.     See  Spinal  cord,  en- 
largements of 
lumbalis.     See  Spinal  cord,  enlargements  of 


Inversion  of  foot,  315 

muscles  producing,  384 
Iris,  730 

blood-vessels  of,  730 

ciliary  margin  of,  730 

ligamentum  pectinatum  of,  727 

nerves  of,  681,  731 

pupil  of,  730 

puijillary  border  of,  730 
membrane  of,  730 

stroma  of,  730 
Irregular  tubules  of  kidney,  1139 
Ischial  spine,  216 

sexual  differences  of,  221 
topography  of,  1303 

tuberosity,  216 

sexual  differences  of,  222 
topography  of,  1302 
Ischio-bulbosus  muscle,  432 
Ischio-capsular  ligament,  295 
Ischio-cavernosus  muscle,  432 
Ischio-coccygeus  muscle.    See  Coccygeus  muscle. 
Ischio-pubicus  muscle,  433 
Ischio-rectal  fossa,  1281 
Ischium,  216 

morphology  of.  Appendix  F,  xxv 

spine  of,  216.     See  also  Ischial  spine 

tuberosity  of,  216.     See  also  Ischial  tuberosity 
Island  of  Reil,  556,  567 

limiting  sulcus  of,  556 

opercula  of,  556 
Isthmus  of  auditory  meatus,  747 

of  brain,  476 

of  callosal  gyrus,  568 

cartilaginis  auris,  745 

of  Eustachian  tube,  753 

of  Fallopian  tube,  1186 

of  fauces,  993,  995,  1000,  1244 
level  of,  1289 

faucium.     See  Isthmus  of  fauces 

glandulae  thyreoideae.    See  Isthmus  of  thjToid 
gland 

gyri  fornicati.     See  Isthmus  of  limbic  lobe 

of  limbic  lobe,  568 

pharyngo-nasal,  932,  934 

of  pharynx,  998 

rhombencephali,  476 

of  thyroid  gland,  1216 
tojDography  of,  1249 

tubae  auditivaj.  See  Isthmus  of  Eustachian  tube 

tubae  uterinae.    See  Isthmus  of  Fallopian  tube 
Iter  chordae  anterius,  687,  750 
posterius,  687 

Jacobson,  nerve  of,  689 

organ  of,  41,  720 
Jaw,  alveoli  of,  136,  142,  1016,  1027 
formation  of,  1028 
lower,  142 
angle  of,  143 
body  of,  142 
condyle  of,  144 
coronoid  process  of,  143 
movements  of,  404 
ramus  of,  143 
toixjgrai)hy  of,  1237 
upper,  133.     See  also  Maxilla 
Jejunum,  993,  1071.     See  also  Intestine 
structure  of,  1073 
vessels  and  nerves  of,  1073 
Jelly  of  Wharton,  51 
Joints,  255.     See  also  Articulationes 


i 


INDEX. 


1359 


Joints,  acromio-clavicular,  274 
movements  at,  275 
topography  of,  1292 
amphiarthrodial,  256,  257 

development  of,  260 
ankle,  306.     See  also  Ankle-joint 

surgical  anatomy  of,  1310 
arthrodial,  257 
astragalo-scapboid,  309 
topography  of,  1312 
atlo-axial,  265 

movements  at,  267,  393 
of  auditory  ossicles,  756 
ball  and  socket,  257,  259.     See  also  Joints, 

enarthrodial 
biaxial,  257 
calcaneo-astragaloid,  308 

topography  of,  1311 
calcaneo-cuboid,  311 

topography  of,  1311 
capsule  of,  258 
carpal,  284.     See  also  Carpal  joints 

movements  at,  289 
carpo-metacarpal,  287 
cavity  of,  257 
classiiication  of,  255 
of  clavicle,  273 
condyloid,  257 
costo-central,  269 
costo-chondral,  271 

topography  of,  1255 
costo-sternal,  271 
costo-transverse,  270 
costo-vertebral,  269 
crico-arytenoid,  962 
crico-thyroid,  961 
cubo-cuneiforni,  312 
development  of,  259 
diarthrodial,  257 

development  of,  260 
elbow,  279.     See  also  Elbow-joint 
enarthrodial,  257 
of  foot,  306 

nerves  of,  651,  654,  655 
hinge,  257 

hip,  293.     See  also  Hip-joint 
humero-ulnar,  279 
immovable,  255 

development  of,  260 
incudo-malleolar,  756 
incudo-staijedial,  756 
intercentral,  261 
intei'chondral,  271 
intercoccygeal,  264 
intercuneiform,  312 
intermetacarpal,  287 
movements  at,  289 
intermeta tarsal,  314 
interneural,  263 

interphalangeal,  of  foot,  314,  315 
movements  at,  384 
of  hand,  288 

movements  at,  289 
topograjjhy  of,  1300 
interpubic,  292,  293 
intertarsal,  308 

synovial  membranes  of,  312 
knee,  297.     See  also  Knee-joint 
of  larynx,  961 
of  lower  extremity,  293 
lumbo-sacral,  290 
metacarpo-phalangeal,  288 


Joints,  metacarpo-phalangeal,  movementsat,  289 
topograpliy  of,  1299 
metatarso-phalangeal,  314 
movements  at  315,  390 
topography  of,  1311,  1312 
movable,  256 

development  of,  260 
movements  at,  259 
multiaxial,  257,  259.      See  also  Joints,  l)all 

and  socket 
occipito-atloid,  266 

movements  at,  393 
of  pelvis,  289,  293 
pisi-cuneiform,  286 
radio-carpal,  283 

topography  of,  1298 
radio-humeral,  279 

topography  of,  1297 
radio-ulnar,  inferior,  282 

superior,  281 
rotatory,  257 
sacro-coccygeal,  264 
sacro-iliac,  290,  293 

topograpliy  of,  1302 
scapho-cuboid,  311 
scapho-cuneiform,  312 
scapulo-clavicular,  274 
shoulder,  276 

of  spine  with  cranium,  266 
sternal,  272 
sterno-clavicular,  273,  275 

movements  at,  327 
structures  forming,  257 
synarthrodial,  255,  257 
talo-calcaneal,  308 
talo-calcaneo-navicular,  309 

movements  at,  315 
tarsal,  308 

movements  at,  315 
tarso-metatarsal,  313 
movements  at,  315 
tojiography  of,  1311 
temporo-mandibular,  267 
of  thorax,  269 
tibio-iibular,  inferior,  304 
superior,  304 

movements  at,  383 
transverse  carjjal,  285 
transverse  tarsal,  311,  315 
uniaxial,  257 
of  upper  extremity,  273 
of  vertebral  column,  261 
wrist,  movements  at,  352 
xiphisternal,  272 

level  of,  1255,  1267,  1290 
Juga  alveolaria,  142 
Jugal  point.  Appendix  D,  xvi 
Jugular  foramen,  116,  169,  170 
fossa,  116 

development  of,  121 
relation  of,  to  jugular  foramen,  164 
to  tympanum,  1233 
ganglion,  689.     See  also  Ganglion 
lymphatic  trunk,  908 
notch,  110 

process,  110,  159,  164 
tubercle,  110 

veins,  875.     See  also  Veins 
primitive,  935,  936 

remains  of,  in  adult,  936,  937 
Junctional  tubules  of  kidney,  1139 
Junctura  ossiiim,     See  Joints 


1360 


INDEX. 


Juncturaj  tendinum  musculi   extensoris   digi- 
toruni  communis,  348 

Karyokinesis,  9 
Karyoplasm,  8 
Keratin,  774 
Kerkring,  ossicle  of,  112 
Kidney,  1130 

anterior  surface  of,  1135 
arteries  of,  1140 
calyces  of,  1141 

development  of,  1202 
capsula  adiposa  of,  1132,  1276 
capsule   of,    1130.     See  also  Kidney,  tunica 

fibrosa  of 
columns  of  Bertin  of,  1138 
connective  tissue  of,  1139 
cortex  of,  1138 
development  of,  1202 
dimensions  of,  1130 
duct  of,  1141 
extremities  of,  1137 
fascia  renalis  of,  1132 
fixation  of,  1133 
foramina  papillaria  of,  1137 
gastric  impression  of,  1137 
glomeruli  of,  1139,  1140 
hepatic  impression  of,  1137 
Mlum  of,  1130,  1137 

topography  of,  1274,  1290 
horse-shoe,  1140 
intermediate  zone  of,  1138 
labyrinth  of,  1138 
lobes  of,  1138 
Malpighian  corpuscles  of,  1139 

development  of,  1202 
medulla  of,  1138 
medullary  rays  of,  1138 
muscular  surface  of,  1135 
nerves  of,  1140 
outer  border  of,  1135 
papillse  of,  1137 
pararenal  fat  of,  1133 
pelvis  of,  1141 

development  of,  1199,  1202 
perirenal  fat  of,  1133 

surgical  anatomy  of,  1286 
position  of,  1130 
posterior  surface  of,  1133 
primitive,  32.     See  also  Wolffian  body 
pyramids  of,  1138 
relations  of,  1131 

anterior,  1135 

posterior,  1133 
sinus  of,  1130,  1137 
splenic  impression  of,  1137 
surface  impressions  of,  1134,  1137 
surgical  anatomy  of,  1274,  1285,  1290 
tubules  of,  1139 

development  of,  1199,  1202 
tunica  fibrosa  of,  1130 
ureter  of,  1141 

development  of,  1199,  1202 
variations  in,  1140 
vasa  afferentia  of,  1140 

efferentia  of,  1140 
development  of,  1199 
veins  of,  1140 
visceral  surface  of,  1135 
Knee-joint,  297 

articular  surfaces  of,  297 

bursae  connected  with,  299,  302,  303 


Knee-joint,  surgicalanatomy  of  bursee,  1305, 1307 
fibro-cartilages  of,  301 

surgical  anatomy  of,  1307,  1308 
ligaments  of,  298 
movements  at,  303 

muscles  producing,  371 
nerves  of,  from  anterior  crural  nerve,  646,  647 
from  great  sciatic  nerve,  650 
from  obturator  nerve,  645 
from  peroneal  nerve,  651 
from  tibial  nerve,  652 
surgical  anatomy  of,  1307 
synovial  membrane  of,  302 
surgical  anatomy  of,  1308 
Knuckles,  1299 
Kohlrausch,  valves  of,  1093.     See  also  Houston, 

valves  of 
Krause,  end-bulbs  of,  775.     See  also  Corpuscula 
bulboidea 

Labia  majora,  1195 

development  of,  1207 
minora,  1195 
oris,  996.     See  also  Lips 
Labial  artery,  branch  of  facial  artery,  806 
branch  of  sujjerficial  perineal  artery,  854 
glands,  996,  997 
nerves,  682 
tubercle,  996 
veins,  877 
Labio-scrotal  folds,  1200,  1206 
Labium  anterius  orificii  externi  uteri.     See  Os 
uteri  externum 
externum  cristas  iliacae.     See  Iliac  crest 
inferius.     See  Lips 

internum  cristas  iliacse.     See  Iliac  crest 
majus  pudendi.     See  Labia  majora 
minus  pudendi.     See  Labia  minora 
posterius  orificii  externi  uteri.'    See  Os  uteri 

externum 
superius.     See  Lips 
tymj)anicum,  765 
vestibulare,  765 
Labrum   glenoidale,   294.      See   also    Cotyloid 

ligament,  Glenoid  ligament 
Labyrinth,  auditory,  759 
auditory  nerve  in,  768 
blood-vessels  of,  769 
cochlea  of,  760 

membranous,  764 
development  of,  769 
endolymph  of,  762 
hair-cells  of  crista  acustica  of,  764 
of  maculas  of,  763 
of  organ  of  Corti  of,  767 
membranous,  762 
organ  of  Corti  of,  765,  766 
osseous,  759 
otoconia  of,  763 
perilymph  of,  762 
saccule  of,  763 
saccus  endolymphaticus  of,  763.     See  also 

Recessus  Cotugnii 
semicircular  canals  of,  760 

membranous,  764 
utricle  of,  762 
vestil^ule  of,  759 
of  ethmoid,  128 
of  kidney,  1138 
Labyrinthus   ethmoidalis.      See   Labyrinth   of 
ethmoid 
membranaceus.     See  Labyrinth,  membranous 


INDEX. 


1361 


Labyrinthus  osseiis.    See  Labyrinth,  osseous 
Lacertus    fibrosus    musculi    bicipitis    bracliii. 

See  Fascia,  bicipital 
Lachrymal.     See  Lacrimal 
Lacrimal  apparatus,  740 

surgical  anatomy  of,  1238 
artery,  816 
bone,  131 

relation  of,  to  nasal  fossae,  170 
to  orbit,  149 
canaliculi,  1239 
canals,  740 

bony  walls  of,  135 
development  of,  743 
caruncle,  1239 
crest,  of  lacrimal  bone,  131 

of  maxilla,  135 
fossa,  105 
gland,  740 
inferior,  740 
orbital  i)ortion  of,  740 
palpebral  portion  of,  740 
superior,  740 
surgical  anatomy  of,  1238 
groove,  of  lacrimal  bone,  131 
relation  of,  to  orbit,  149 
of  maxilla,  135 
nerve,  679 
papillae,  738 
process,  130 
puncta,  740 
sac,  741 

development  of,  40 
surgical  anatomy  of,  1239 
Lacteals,  1073 
Lactiferous  ducts,  1208 
Lacunae  of  bone,  72 

laterales  of  longitudinal  sinus,  603,  884 
urethrales,  1180 
Lacus  lacrimalis,  738 
Lagena  cochleae,  764.     See  also  Ci^cum  cupulare 

of  cochlea 
Lambda,  157,  158 

topography  of,  1223 
Lambdoid  suture,  151 

topography  of,  1223,  1225 
Lamellae,  cutaneous,  30,  31 
fundamental,  72 
interstitial,  72 
osseous,  72 
Lamina  or  Laminae,  alar.     See  Neural  tube 
basal.     See  Neural  tube 
basalis   of  chorioid,    729.      See   also   Bruch, 

membrane  of 
basilaris.     See  Membrana  basilaris  cochleae 
chorio-capillaris,  728 
cinerea,  549 

development  of,  595 
cribrosa  ossis  ethmoidalis,  129 
sclerae,  725 
of  temporal  bone,  118 
dental,  1026 
elastica  anterior  (Bowmani),  726 

posterior  (Demoursi,  Descemeti),  726 
fibro-cartilaginea  interpubica,  292 
fusca,  725 

lateralis  processus  pterygoidei.    See  Pterygoid 
plate,  external  or  lateral 
tubae  auditivae  (Eustachii),  753 
medialis  processus  pterygoidei.   See  Pterygoid 
plate,  internal  or  medial 
tubae  auditivae  (Eustachii),  753 

91 


Lamina  or  Laminae,  medullares  thalami.     See 
Laminae,  medullary,  external  and  in- 
ternal, of  optic  thalamus 
medullary,  external,  of  lenticular  nucleus,  580 
of  optic  thalamus,  543,  544 

internal,  of  lenticular  nucleus,  580 
of  optic  thalamus,  545 
membranacea  tubae  auditivae  (Eustachii),  754 
modioli.     See  Lamina  spiralis  ossea 
nasal,  41 

papyracea.     See  Os  planum  of  ethmoid 
parietalis  (tunicae  vaginalis  propriae  testis), 

1160 
perpendicularis  ossis  ethmoidalis.     See  Ver- 
tical plate  of  ethmoid  bone 
quadrigemina,  533 
reticularis,  767 
septi  pellucidi,  573 
spiralis  ossea,  760,  761 

secundaria,  760,  761 
suprachorioidea,  728 
terminalis,  479 
vasculosa  of  chorioid,  728 
vertebral,  77,  78,  80,  81,  83 
visceralis  (tunicae  vaginalis  propriae  testis), 
1160 
Landzert,  fossa  of,  1069.    See  also  Paraduodenal 
Lanugo,  779  [fossa 

Large  intestine,  1074.     See  also  Intestine,  large 
Laryngeal  arteries,  971.     See  also  Artery 
nerves,  692.     See  also  Nerves 
nucleus,  517 
pharynx,  1032,  1036 

prominence,  958.     See  also  Pomum  Adami 
Larynx,  957  ^ 

action  of  muscles  of,  970 
aryteno-epiglottidean  folds  of,  964 
blood-vessels  of,  971 
cartilages  of,  958 

development  of,  992 
crico-thyroid  membrane  of,  962 
cuneiform  tubercle  of,  964 
in  deglutition,  971 
development  of,  35,  38,  992 
epithelium  of,  968 
general  construction  of,  958 
glands  of,  968 
glottis  respiratoria  of,  966 

spuria  of,  966 

vera  of,  966 

vocalis  of,  966 
growth -alterations  of,  971 
interior  of,  964 

viewed  with  laryngoscope,  972 
joints  of,  961 

larjTigoscopic  examination  of,  972 
ligaments  of,  961 
mucous  glands  of,  968 

membrane  of,  967 
muscles  of,  968 

nerves  of,  971.     See  also  Nerves,  laryngeal 
philtrum  ventriculi  of,  965 
position  and  relations  of,  957 
saccule  of,  967 
sexual  differences  in,  971 
sinus  of,  967 

pyriformis  of,  965 
subhyoid  bursa  of,  962 
superior  aperture  of,  964 
thyro-hyoid  membrane  of,  962 
tubercle  of  Santorini  of,  964 
tuberculum  epiglotticum  of,  965 


1362 


INDEX. 


Larynx,  vallecida  of,  963 
vestibule  of,  965 
vocal  cords  of,  false,  964,  965 
true,  964,  966 

mucous  membrane  of,  968 

relation  of,  to  tliyro-arytenoideus  muscle, 

970 
topography  of,  1289 
Lateral  angle,  inferior,  of  sacrum,  87 
fold,  of  embryo,  27,  49 
ligaments,  of  ankle,  307 
of  elbow,  280 
of  jaw,  268 

relation  of,  to  deej)  cervical  fascia,  395 
of  knee,  300 

surgical  anatomy  of,  1308 
of  liver,  1116 
of  patella,  298 
of  wrist,  283,  284,  286 
line,  sense  organs  of,  701 
mass  of  atlas,  79 
of  etlimoid,  128 

relation  of,  to  nasal  fosste,  170 
of  sacrum,  84 

ossification  of,  94 
nasal  process,  39 
plates,  mesodermic,  26,  30,  31 
recess  of  fourth,  ventricle,  487,  512,  601 
recesses  of  pharjTix,  1031,  1033,  1034 

development  of,  1038 
sinuses,  venous,  886 
abnormalities  of,  954 
grooves  for,  169.    See  also  Groove  for  lateral 

sinus 
morphology  of,  944 
surgical  anatomy  of,  1234,  1235 
ventricles.     See  Ventricle 
Latissimus  dorsi  muscle,  320 
action  of,  331,  393,  419 
nerve-supply  of,  326 
topography  of,  1285 
Layers  of  blastoderm,  18,  19 
germinal,  18,  19 
of  Rauber,  18 
scleratogenous,  30 
Leg,  development  of,  46 
fascise  of,  371 

intermuscular  septa  of,  371 
lymphatics  of,  917 
muscles  of,  373 
action  of,  384 
nerve-supply  of,  383 
surgical  anatomy  of,  1308 
Lemniscus,  494.     See  also  Fillet 

lateralis.     See  Fillet,  lateral 
•    medialis.     See  Fillet 
Lens  crystallina,  736 
axis  of,  733 
cap.sule  of,  736 
cortical  substance  of,  736 
curvatures  of,  736 
development  of,  703,  742 
at  different  ages,  737 
epithelium  of,  737 

history  of,  742 
equator  of,  736 
fibras  of,  737 

history  of,  742 
laminae  of,  737 
nucleus  of,  737 
poles  of,  736 
radii  of,  737 


Lens,  refractive  index  of,  736 
suspensory  ligament  of,  736 
vascular  tunic  of,  742 
vesicle,  742 
Lenticular  ganglion,    680.       See   also    Ciliary 
ganglion 
nucleus,  580 

papillae,  1003.     See  also  Fungiform  papillse 
process  of  incus,  756 
Lenticulo-ojstic  artery,  817 
Lenticulo-striate  artery,  817 
i   Leptoprosope  skulls,  Appendix  D,  xvii 
Leptorhine  skulls,  717  ;  Appendix  D,  xviii 
Levator  anguli  oris  muscle,  398 
action  of,  399 
ani  muscle,  438 

action  of,  1095 
cushion,  1034.     See  also  Torus  tubarius 
glandulee  thyreoidese,  406 
labii  superioris  muscle,  398 
action  of,  399 
alseque  nasi,  397 
action  of,  399 
menti  muscle,  398 
action  of,  399 
palati  muscle,  412 
action  of,  413 
nerve-supply  of,  413 
palpebrge  superioris  muscle,  399 
action  of,  401 
nerve-supply  of,  401 
prostatse  muscle,  439 
scapulae  muscle,  320 
action  of,  327,  393 
nerve-supply  of,  327 
Levatores  costarum  muscles,  416 
action  of,  419 
nerve-supply  of,  419 
Lieberkiihn,  glands  of,  1062,  1075,  1093 
Lien.     See  Spleen 

accessorius.     See  Spleen,  accessory 
Lieno-renal  ligament,  1099,  1212 

development  of,  1108 
Ligament  or  Ligaments  ;  Ligamentum  or  Liga- 
menta,  256,  258,  260 
accessoria  jjlantaria.  See  Ligaments,  plantar 

volaria.     See  Ligaments,  palmar 
acromio-claviculare,  274 
adventitious,  261 
alar,  302 

alaria.     See  Ligaments,  check 
of  ankle-joint,  306 
annular,  of  ankle,  372 
of  stapes,  752,  757 
of  wrist,  336 

surgical  anatomy  of,  1298 
annulare    baseos    stajjedis.      See    Ligament, 
anniilar,  of  stapes 
radii.     See  Ligament,  orbicular 
annularia  digitorum  manus.     See  Ligaments, 

annular,  of  wrist 
apicis  dentis.    See  Ligament,  odontoid,  middle 
arcuate,  of  diaphragm,  417 
arcuatum  pubis,  292 
arteriosum,  796,  798 
astragalo-calcaneal,  309 
astragalo-scaphoid,  311 
atlo-axoid,  265 
of  auditory  ossicles,  756 
auriculare  anterius.     See  Ligaments  of  pinna 
posterius.     See  Ligaments  of  pinna 
superius.     See  Ligaments  of  pinna 


INDEX. 


1363 


Ligament  or  Ligaments — continued 

basium   ossium   metacarpalium.      See   Liga- 
ments, intermetacarpal 
metatarsalium.       See    Ligaments,     inter- 
meta  tarsal 
bifurcatiim.    See  Ligamenta  calcaneo-navicu- 

laria,  calcaneo-cuboidea 
of  Bigelow,  295 
of  bladder,  1100,  1154,  1156 
brevia  of  Hexor  digitoriun  longus,  379 
digitorum  profuudus,  342 
digitorum  sublimis,  341 
broad,  of  uterus,  1101,  1189 
surgical  anatomy  of,  1284 
calcaneo-cuboidea,  311 
calcaneo-fibulare,  307 
calcaneo-metatarsal,  373 
calcaneo-navicularia.     See   Ligaments,   cal- 

caneo-scaphoid 
calcaneo  -  scaphoid,  309 
function  of,  315 

surgical  anatomy  of,  1312 
calcaneo-tibiale,  307 

capituli  costse  interarticulare.  See  Ligaments, 
interarticular,  of  costo-central  joints 
radiatum.     See  Ligaments,  stellate 
fibulaj.     See  Ligaments,  tibio-fibular 
capitulorum  ossium  metacarpalium  transversa. 
See  Ligaments,  transverse  metacarpal 
metatarsalium  transversa.     See  Ligaments, 
transverse  metatarsal 
carpi,  285 

carpo-metacarpea,  287 
check,  267 

collateralia.     See  Latei'al  ligaments 
colli  costae.     See  Ligaments,  costo-transverse 

(middle) 
columnpe  vertebralis  et  cranii.    See  Ligaments 

of  vertebral  column  and  skull 
common,  anterior,  of  spine,  263 

posterior,  of  spine,  263 
conjugal,  of  ribs,  270 
conoideum,  274 

function  of,  275 
coraco-acromiale,  275 
coraco-claviculare,  274 
coraco-glenoid,  277 
coraco-humerale,  277 

relation  of,  to  pectoralis  minor  muscle,  325 
corniculo-pharyngeiim.       See     Ligamentum 

jugale 
coronaria  ot  knee,  302 

coronarium  hepatis.    See  Ligaments,  coronary 
coronary,  1099,  1115,  1116 
costo-claviculare,   274.     See  also   Ligament, 

rhomboid 
costo-colic,  1083.  Seealso  Ligamentum  phreni- 

co-colicum 
costo-coracoid,  323 
costo-sternal,  271 
costo-transversaria,  270 
costo-vertebral,  269 
costo-xiphoidea,  272 
cotyloid,  294 

crico-arytenoideum  posterius,  962 
crico-tliyreoideum.     See  Crico-thyroid  mem- 
brane 
crico-thyroid,  961 
crico-tracheale,  960 
crucial,  of  atlas,  267 
of  knee,  300 

relation  of,  to  movements  at  knee,  303 


Ligament  or  Ligaments — continued 

cruciata  genu.    See  Ligaments,  crucial,  of  knee 

atlantis.     See  Ligament.s,  crucial,  of  atlas 
cruciatum  cruris.     See  Ligaments,  annular,  of 

ankle 
cubo-cuneiform,  312 
cuboideo-navicularia.    See  Ligaments,  scapho- 

cuboid 
cuneo-cuboidea.     See  Ligaments,  cubo-cunei- 
form 
cuneo-metatarsea,  313 
deltoideum,  307 
denticulatum,  453,  602,  605 
of  elbow-joint,  279 
epiglottidean,  963 
falciform,  of  liver,  1098,  1116 
development  of,  1107,  1124 
topography  of,  1270 
falciforme  hepatis.     See  Ligament,  falciform, 

of  liver 
flava.     See  Ligamenta  subflava 
gastro-colicum.     See  Gastro-colic  omentum 
gastro-lienale.     See  Gastro-splenic  omentum 
gastro-phrenic,  1057,  1099 
of  Gimbernat,  422 
gleno-humeral,  277 
glenoid,  276 

glosso-epiglottideau,  963 
hepato-duodenale,  1116 
hepato-gastricum,  1116 
hepato-renale,  1099 
of  hip-joint,  294 
hyo-epiglotticum,  964 

hyo-thyreoidea.    See  Ligaments,  thyro-hyoid 
ilio-femorale,  295,  296 
ilio-lumbale,  291 
ilio-trochanteric,  295 
incudis.     See  Ligaments  of  incus 
of  incus,  756,  757 
infundibulo-pelvic,  1284 
inguinale.     See  Ligament  of  Poupart 

refiexum  (Collesi).     See  Fascia,  triangular 
interarticular,  258 

development  of,  260 

of  costo-central  joints,  270 

of  costo-iternal  joints,  272 

of  hip-joint,  295 

of  sacro-coccygeal  joint,  264 
intercarpea,  285 
interchondral,  271 
interclaviculare,  274,  275 
intercuneiformia  interossea,  312 
intermeta tarsal,  314 
interosseous,  of  carpal  joints,  285,  286 

of  carpo-metacarpal  joints,  286,  287 

of  inter-tarsal  joints,  309,  311 

of  tarso-metatarsal  joints,  312,  313 

of  tibio-fibular  joint,  inferior,  305 
interspinalia,  263 
intertransversaria,  264 
ischio-capsulare,  295 

relation  of,  to  movements  at  hip-joint,  297 
jugale,  962 
of  knee-joint,  298 
laciniatum.        See    Ligaments,    annular,    of 

ankle 
lacunare    (Gimbernati).      See    Ligament    of 

Gimbernat 
of  larynx,  961 
latum  pulmonis,  979 

uteri.     See  Ligament,  broad,  of  uterus 
lieno-renal,  1099,  1212 


1364 


INDEX. 


Ligament  or  Ligaments — continued 
lieno-renal,  development  of,  1108 
of  Lisfranc,  1311 
of  liver,  1116 
longa,  341,  342,  379 
longitudinalia.     See  Ligaments,  common,  of 

spine 
lumbo-costale,  271 
lumbo  -  sacral,  289 
mallei.     See  Ligaments  of  malleus 
malleolar,  305 

malleoli.     See  Ligaments,  malleolar 
of  malleus,  756 
metacarjjo-plialangeal,  288 
nieta,tarso-23lialaugeal,  314 
morphology  of,  261 
mucosum,  302 
naA'iculari  -  cuneifoi^mia.        See     Ligaments, 

scaplio-cuneiform 
nucliee,  264 
oblique,  283 
occipito-atloid,  266 
occipito-axoid,  266 
odontoid,  267 
orbicular,  282 
orbito-tarsal,  1239 
ossiculoruni     auditus.       See     Ligaments    of 

auditory  ossicles 
ovarii  j)roprium.     See  Ligament  of  ovary 
of  ovary,  1184,  1190 
palmar,  285,  287,  288 
pal23ebral,  topography  of,  1239 
jjalj^ebralia,  739 
patellte,  299,  359 

topography  of,  1307 
patellar,  lateral,  298 

relation  of,  to  fascia  lata,  355,  359 
pectinatum  iridis,  727 
of  pelvis,  289 
of  peritoneum,  1050 
l^hrenico-colicum,  1083,  1104 
of  i^inna,  745 
pisi-metacarpal,  286,  346 
pisi-unciform,  286 

l^iso-hamatum.    See  Ligaments,  j^isi-unciform 
piso-metacarpeum,  286,  340       , 
plantar,  314 

plantare  longum.     See  Ligaments,  calcaneo- 
cuboid 
poplitea.     See  Ligaments  of  knee-joint 
jjosticum  Winslowi,  299 
of  Poupart,  422 

topography  of,  1305 
2)terygo-spiiiosum,  269 

relation  of,  to  deep  cervical  fascia,  395 
pubicum,  292 
pubo-capsulare,  295 
pul>o-femoral,  295,  296 
pubo-prostatica,  436,  437,  1156 
pulmonale.    See  Ligamentum  latum  jjulmonis 
pylori,  1058 
radio-carpea,  283 
radio-ulnar,  282 
rhomboid,  274 

relation  of,  to  movements  of  clavicle,  275 
round,  of  liver,  903,  1116 
development  of,  935 

of  uterus,  1190 

surgical  anatomy  of,  1284 
sacro-coccygea,  264 
sacro-iliaca,  290 
sacro-sciatic,  great,  291 


Ligament  or  Ligaments — continued 
sacro-sciatic,  small,  292 
sacro-sjjinosum.     See  Ligament,  sacro-sciatic 

small 
sacro-tuberosum.   See  Ligament,  sacro-sciatic, 

great 
scapho-cuboid,  311 
scapho-cuneiform,  312 
of  scajDula,  275 
of  shoulder-joint,  276 
siDheno-mandibulare,  268 

develojDment  of,  37 
sj)ino-glenoid,  275 
spirale  cochleee,  765 
of  stajjes,  756 
stellate,  269 
sterno-claviculare,  273 

relation  of,  to  movements  of  clavicle,  275 
sterno-costalia.    See  Ligaments,  costo-sternal 
sterno-jDericardiaca,  793 
stylo-hyoideum,  269 

development  of,  37 
stylo-mandibulare,  269,  395 

relation  of,  to  parotid  fascia,  1010 
subflava,  263 
subjDubic,  292 
svijjrascajjular,  275 
suj)rasj)inale,  264 
suspensorium  of  clitoris,  1197 

of  lens,  736 

of  ovary,  1183 

of  penis,  1172 
talo-calcanea,  309 
talo-fibularia,  307 
talo-naviculare.     See    Ligaments,    astragalo- 

scajjhoid 
talo-tibialia,  307 
tarsal,  of  eyelids,  739,  741 
tarso-metatarsea,  313 
temj^oro-mandibulare,  267,  268 
teres  femoris,  295 

relation  of,  to  movements  athi2)-joint,297 

hepatis.     See  Ligament,  round,  of  liver 

uteri.     See  Ligament,  round,  of  uterus 
thyreo-epigiotticum,  964 
thyro-arytenoid,  963 
thyro-hyoid,  962 
tibio-fibular,  304,  305 
tibio-naviculare,  307 
transverse,  of  acetabulum,  294 

of  atlas,  265,  267 

humeral,  277 

of  knee,  302 

metacarpal,  287,  288 
suj)erticial,  338 

metatarsal,  314 
sui)erficial,  373 

perineal,  293 
transversum  acetabuli.     See  Ligament,  trans- 
verse, of  acetabulum 

atlantis.     See  Ligament,  transverse,  of  atlas 

cruris.     See  Ligaments,  annular,  of  ankle 

genu.     See  Ligament,  transverse,  of  knee 

pelvis.     See  Ligamenta  pubo-prostatica 

scapuhe   inferius.      See  Ligament,    spino- 
glenoid 
sui)erius.     See  Ligament,  suprascapular 
trapezoideum,  274 

relation  of,  to  movements  of  clavicle,  275 
triangular,  of  jjcrineum,  292 

relation  of,  to  fascia  of  i)elvis,  435 
triangularia.     See  Lateral  ligaments  of  liver 


INDEX. 


1365 


Ligament  or  Ligaments — continued 
of  tympanic  membrane,  750 
umbilicale  laterale.     See  Obliterated   hypo- 
gastric artery 
utero-sacral,  1189 
of  uterus,  1101,  1189 
vaginal,  338 
vaginale,  1167 

vaginalia  digitorum  manus,  338 
venae  cavai  sinistraj.     See  Fold,  vestigial,  of 

Marshall 
venosum  Arantii,  1117 

ventriculare.    iS'ee  Ligaments,  thyro-arytenoid 
of  vertebral  column  and  skull,  261 
vocale.     See  Ligaments,  thyro-arytenoid 
Ligula,  512 

Limb-girdles,  Appendix  F,  xxv 
Limbic  lobe,  568 
Limbs,  development  of,  46 
dorsal  axial  line  of,  614,  672 
morphology  of,  Appendix  F,  xxiii 
of  muscles  of,  440 
of  nerve-plexuses  of,  662 
nature  of,  662 

post-axial  border  of,  663,  664 
pre-axial  border  of,  663,  664 
segmental  relations  of,  663 
surfaces  of,  663 
ventral  axial  line  of,  660,  672 
Limbus  alveolaris  mandibulse.     See  Mandible, 
(upper  border  of) 
maxillae.     See  Maxilla  (alveolar  border  of) 
fossae  ovalis,  787 
laminae  sjiiralis,  765 
Limen  insulae,  568 

nasi,  719 
Limiting  sulcus  of  Reil,  556 
Line  or  Linea,  alha,  421 

surgical  anatomy  of,  1265,  1267 
ano-cutaneous,  1095 
arcuatae  ossis  iliaci.      See  Lines,  curved,  of 

ilium 
aspera  of  femur,  226 
axillaris.     See  Axillary  line 
base,  of  Reid,  1227 
of  chest.     See  Thorax 
curved,  of  ilium,  214 

of  occipital  bone,  108,  109,  153,  158 
doi-sal  axial,  of  limbs,  614,  672 
epicondylic,  226 

glutaea  anterior.     See  Line,  curved  (middle), 
of  ilium 
inferior.     See   Line,    curved    (inferior),    of 

ilium 
posterior.     See  Line,  curved  (posterior),  of 
ilium 
ilio-pectineal,  215,  217 

relation  of,  to  true  pelvis,  220 
incremental,  1024 
intercondyloidea,  227 
intermedia   cristae   iliacae.      See   Iliac  crest, 

(middle  lij)  of) 
intertrochanterica,  224 
intertubercular,  1047 
lateral,  sense-organs  of,  701 
mammillaris,  981 
mammary,  1253 
median,  5 
mediana  anterior,  5 

posterior,  5 
mid-lateral,  of  thorax,  982 
mylohyoidea,  143,  165 


Line  or  Linea,  of  Nelaton,  1302 
nuclue  inferior,  109 

mediana,  109 

superior,  108,  153,  158 

suprema.     See  Linea  nuchas  superior 
obliqua  mandibuhe,  143,  165 
oblique,  of  tibia,  233 
parasternalis,  1253 
pectinea,  226 
of  pleural  reflection,  979 
poplitea,  233 
post-central,  1225 
Poupart,  1047 
pre-central,  1225 
scapularis,  1253 
of  Schreger,  1024 

semicircularis  (Douglasi).    See  Fold  of  Douglas 
semilunaris,  427 
spiral,  of  femur,  224,  226 
splendens,  605 
sternalis,  1253 
subcostal,  1047 
Sylvian,  1225 
temporalis  inferior.     See  Temporal  ridge 

ossis  frontalis.     See  Temporal  ridge 

superior.     See  Temporal  ridge 
terminalis.     See  Line,  ilio-ijectineal 
transversae.     See  Inscriptiones  tendineae 
ventral  axial,  of  limb.s,  660,  672 
white,  of  anus,  1095 

of  pelvis,  434,  436 
Lingual  artery,  805,  1006 

development  of,  933 

surgical  anatomy  of,  1243,  1249,  1251 
cusps  of  teeth,  1017 
duct,  1217 
glands,  1006 
gyrus,  566 

lymphatic  glands,  911 
nerve,  684.     See  also  Nerve 
septum,  1005 
tonsil,  1001 

surgical  anatomy  of,  1242 
vein,  876 
Lingualis  muscle,  inferior,  409 

superior,  409 
Lingula  cerebelli,  487,  507 

mandibulae,  143 

sphenoidalis,  124 
Linin,  9 

Lip,  rhombic,  527 
Lips,  996 

commissures  of,  995 
development  of,  39,  68 
frenulum  of,  995 
glands  of,  996,  997 

surgical  anatomy  of,  1240 
lymphatics  of,  997 
mucous  membrane  of,  996 
nerves  of,  997 
philtrum  of,  996 

development  of,  39 
structure  of,  996 
surgical  anatomv  of,  1240 
tubercle  of,  996  " 
Liquor  folliculi,  1185 

pericardii,  794 
Lisfranc,  ligament  of,  1311 
Lissauer,  tract  of,  468 
Littre,  glands  of,  1180 
Liver,  1108 

areolar  coat  of,  1121 


1366 


INDEX. 


Liver,  arteries  of,  1120 

bile  caualiciili  of,  1118,  1122 

capsule  of  Glisson  of,  1121 

cardiac  depression  of,  1113 

caudate  lobe  of,  1113 

cells  of,  1122 

in  child,  1117 

colic  impression  of,  1113 

congenital  irregularities  in,  1118 

coronary  ligament  of,  1099,  1115,  1116 

development  of,  1122 

duodenal  im2:)ression  of,  1114 

excretory  ducts  of,  1118,  1122 

development  of,  1123 
falciform  ligament  of,  1098,  1116 
develoj)ment  of,  1107,  1124 
topograjjliy  of,  1270 
fissures  of,  1114 
fixation  of,  1118 
form  of,  1108 

variations  in,  1117 
fossa  of  gall-bladder  of,  1115 

of  vena  cava  of,  1111,  1115 
gastric  impression  of,  1113 
inferior  margin  of,  1114 
interlobular  ducts  of,  1118,  1122 

development  of,  1123 
ligaments  of,  1116 
lobes  of,  1115 

topography  of,  1286 
lobules  of,  1121 
longitudinal  fissure  of,  1115 
lymphatics  of,  1121 
nerves  of,  1121 

notch  of  gall-bladder  of,  1114,  1115 
oesophageal  groove  of,  1112 
omental  tuberosity  of,  1113 
parietal  surface  of,  1110 
peritoneal  relations  of,  1115 
physical  characters  of,  1117 
pons  hepatis  of,  1111,  1114 
portal  canals  of,  1120 

fissure  of,  1113,  1115 
position  of,  1109 

variations  in,  1117 
quadrate  lobe  of,  1113,  1114 
relations  of,  1110 
renal  impression  of,  1113 
Riedel's  lobe  of,  1117 
round  ligament  of,  903,  1116 

develojnnent  of,  935 
serous  coat  of,  1121 
size  of,  1110 

variations  in,  1117 
Spigelian  lobe  of,  1112 
structure  of,  1121 
suprarenal  impression  of,  1111 
surgical  anatomy  of,  1270,  1286 
tuberculuni  painllare  of,  1112 
umbilical  fissure  of,  1114 

notch  of,  1114 
uncovered  area  of,  1111 
variations  in,  1117 
visceral  surface  of,  1113 
veins  of,  1120 

central,  or  intralobular,  1120,  1121 

interlobular,  1120 

sublobular,  1121 
weight  of,  1110,1117 
Lobe  or  Loljus,  azygos  of  lung,  989 
anterior  hypophysis,  549 
cacuminis,  507 


Lobe  or   Lobus,   caudate,  of  liver,  1113.      See 
also  Processus  caudatus 
caudatus.     See  Lobe,  Spigelian,  of  liver 
centralis,  507 
cerebellar,  506 
cerebral,  555 
cerebri,  555 
clivi,  507 
culminis,  507 
frontalis,  560 

hei^atis.     See  Lobes  of  liver 
insular,  556,  567.     See  also  Rail,  island  of 
limbic,  568 
of  liver,  1115 
of  lung,  988 

development  of,  992 
mammae,  1208 
noduli,  508 
occipitalis,  564 

topography  of,  1225 
olfactorius,  569 

development  of,  479,  596 
relation  of,  to  anterior  commissure,  588 
parietalis,  562 
posterior  hypophysis,  549 
of  prostate  gland,  1174 
pyramidalis  of  thyroid  gland,  1216 

development  of,  1217 
pyramidis,  508 
pyriform,  568,  584 
quadratus,  1114 
of  Riedel,  1117 
Spigelian,  of  liver,  1112 
tem]3oralis,  567 

topography  of,  1225 
of  testis,  1161 
of  thyroid  gland,  1216 
tuberis,  508 
uvulee,  508 
Lobular  tubercle,  43 
Lobule  of  ear,  744,  745 

quadrate,  563 
Lobules  of  cerebellum,  506,  507,  508 

of  lung,  990 
Lobulus  or  Lobuli,  auriculte.     See  Lobule  of  ear 
biventer,  507 
centralis,  506 

epididymidis.     See  Conus  vasculosus 
gracilis,  508 

hepatis.     See  Liver,  lobules  of 
mammae,  1208 
pa  racen  trails,  562 

parietalis    inferior.       See    Gyrus,    parietal, 
inferior 
superior.     See  Gyrus,  jparietal,  superior    " 
pulmonum.     See  Lobules  of  lung 
quadraugularis.     See  Lobule,  quadrate 
semilunares.      See    Lobules    of    cerebellum, 

(crescentic) 
testis,  1161 
Locus  cceruleus,  488 

development  of,  527 
perforatus  anticus,  475 

relation  of,  to  olfactory  tract,  570 
posticus,  475,  548 
development  of,  478 
relation  of,  to  third  ventricle,  550 
Long  bones,  70,  71,  73 
Longissimus  capitis  muscle,  389 
cervicis  muscle,  389 
dorsi  muscle,  389 
Longitudinal  bundle,  j^osterior,  537 


INDEX. 


1367 


Longitudinal  bundle,  connexions  of,  with  lower 
visual  centres,  553 
in  medulla,  494 
in  mesencephalon,  535 
in  pons,  502,  504 

relation  of,  to  anterior  basis  bundle,  491 
to  oculo-motor  and  trochlear  nuclei,  541, 

542 
to  sixth  cranial  nerve,  524 
fissure,  great,  553 

development  of,  596 
sinus,  884.     See  aho  Sinus 
Longus  colli  muscle,  415 
Loopof  Henle,  1139 

subclavian,  708 
Lowenthal,  marginal  tract  of,  521 
Lower,  tubercle  of,  788 
Lumbar  aponeurosis,  1044 
arteries,  of  aorta,  839 

abnormalities  of,  949 
development  of,  933 
morphology  of,  940 
of  ilio-lumbar,  850 
fascia,  319,  385 
ganglia,  710 
lymphatic  glands,  922 

trunk,  908 
nerves,  607.     See  also  Nerves 
plexus,  639,  641 
region,  1047,  1267,  1285 
rib,  92  ;  Appendix  B  and  C 
sympathetic,  710 
veins,  894.     See  also  Veins 
vertebrae,  83 
Lumbo-costal  ligament,  271 
Lumbo-sacral  cord,  648 
joint,  289 
ligament,  289 

plexus,  639.     See  also  Plexus 
Lumbricales  muscles  of  foot,  379 
action  of,  384 
nerve-supply  of,  383 
of  hand,  342 
action  of,  352 
nerve-supply  of,  351 
Lung,  983 
air-cells  of,  991 

development  of,  992 
alveolar  ducts  of,  991 
apex  of,  985 
level  of,  1289 
topography  of,  1255 
azygos  lobe  of,  989 

sulcus  of,  987 
blood-vessels  of,  991 
bronchial  tubes  of,  989 
bronchioles  of,  991 
cardiac  lobe  of,  990 

notch  of,  988 
development  of,  992 
fissures  of,  988 

topography  of,  1258 
fcetal,  985 
form  of,  985 
hilum  of,  986 
infundibula  of,  991 

development  of,  992 
ligamentiim  latum  of,  979,  983 
lobules  of,  990 
lower  lobe  of,  988 
lymjjhatics  of,  989 
middle  lobe  of,  989 


Lung,  nerves  of,  989 
root  of,  989 
level  of,  1290 
topography  of,  1260 
structure  of,  990 
sulcus  subclavius  of,  985,  987 
surgical  anatomy  of,  1255 
ujjper  lobe  of,  988 
variations  in,  989 
Lunula  unguis,  775 

Lunulas  valvularum  semiluuarium,  790 
Lymph,  904 

sinuses,  906 
Lymphatic  capillaries,  905 
duct,  right,  904,  909 

abnormalities  of,  956 
glands  or  Lympho-glandul*,  904,  905 
of  abdomen,  918 
ano-rectal,  1281 
.ante-cubital,  913 
anterior  auricular,  910 
jugular,  911 
tibial,  916 
aortic,  922 
aj^pendicular,  920 
auriculares  anteriores,  910 

posteriores,  909.     See  also  LI.,  mastoid 
axillares,  914 

surgical  anatomy  of,  1294 
bronchiales,  924 
buccal,  910 
carotid,  1247 
cervical,  deep,  912 
superficial,  911 

surgical  anatomy  of,  1251,  1252 
cervicales   profundse   inferiores.      See   LI., 
cervical,  deep 
superiores.     See  LL,  cervical,  deep 
superficiales.    See  LI.,  cervical,  superficial 
circumflex  iliac,  921 
cceliacae,  920 
colic,  920 
common  iliac,  921 
cubitales  profundse.     See  LL,  ante-cubital 

superficiales.     See  LL,  ante -cubital 
diaphragmatic,  924 
of  digastric  triangle,  1250 
epigastricje,  921 
external  iliac,  920 
facial,  910 

faciales  profundai,  910 
femoral,  916 

surgical  anatomy  of,  1306 
follicles  of,  906 
gastric,  918,  1060 
gastricse  inferiores,  918 

superiores.      See    LL,   gastric   (coronary 
group) 
of  head  and  neck,  909 
hepatic^,  918 
ileo-csecal,  920 
infra-clavicular,  914 
infra-umbilical,  921 
inguinales,  916 

surgical  anatomy  of,  1306 
intercostales,  923 
internal  iliac,  921 
mammary,  924 
maxillary,  909 
intertracheo-bronchial,  924 
lateral  aortic,  922 
linguales,  911 


1368 


INDEX. 


Ljnipliatic  glands,  of  lower  limb,  916 
lumbales,  922 
mandibular,  910 
mastoid,  909 
mediastinales  anteriores,  924 

posteriores,  92-4 
mesenteric8e,  919,  1073 
mesocolicffi,  1075 
obturator,  921 
occipitales,  909 
pancreatic,  919 
pancreatico-lienales,  919 
parotideae,  910 
pectorales,  914 

surgical  anatomy  of,  1294 
of  pelvis,  918 
popliteffi,  916 

surgical  anatomy  of,  1305 
posterior  auricular,  909 
of  posterior  triangle,  1252 
post-pbaryngeal,  911,  1037 

surgical  anatomy  of,  1246 
pre-aortic,  922 
pre-auricular,  1238 
pre-laryngeal,  911 
pre -tracheal,  911 

surgical  anatomy  of,  1249 
of  the  promontory,  921 
jDubic,  916 
pulmonales,  989 
rectal,  920,  1096 
retro-aortic,  922 
retro-crural,  920 
retro-peritoneal,  1277 
retro -pyloric,  918 
sacrales,  921 
sinuses  of,  906 
splenic,  918,  1060 
stemales,  924 
structure  of,  906 
sub-clavian,  914 
sub- clavicular,  1294 
sub-inguinales  profundee,  916 

superficiales,  916 
sub-maxillares,  911 

surgical  anatomy  of,  1250 
sub-mental,  911 

surgical  anatomy  of,  1248 
sub-pyloric,  918 
sub-scapulares,  914 

surgical  anatomy  of,  1294 
sub-sternomastoid,  912 
supra-clavicular,  913 

supra-condyloid,  1295.     See  also  LL,  ante- 
cubital 
supra-hyoid,  911 

surgical  anatomy  of,  1248 
supra-trochlear,  914 
supra-umbilical,  921 
of  thorax,  923 

tibialis  anterior.     See  L.,  anterior  tibial 
trabeculee  of,  906 
of  upper  limb,  913 
visceral,  of  alxlomen  and  pelvis,  918 

of  thorax,  924 
zygomatic,  909 
spaces,  904 

perivascular,  905 
trunk,  common  intestinal,  908 
common  luml^ar,  908 
descending,  908 
jugular,  908 


Lymjphatic  trunk,  retro-aortic,  908 
subclavian,  908 
vessels,  905 

of  abdomen,  918 

abnormalities  of,  955 

of  anus,  1281 

of  arm,  915 

of  blood-vessels,  783 

of  bones,  75 

of  breast,  923 

of  buttock,  917 

central,  of  hand,  915 

cerebral,  909 

endothelium  of,  904 

extra-cranial,  909 

of  foot,  917 

of  forearm,  915 

of  hand,  915 

of  head  and  neck,  909 

of  heart,  793 

intra -cranial,  909 

lateral  aortic,  908 

of  leg,  917 

of  lower  limb,  916 

of  lung,  989 

meningeal,  909 

of  pelvis,  918 

of  pharynx,  1037 

surgical  anatomy  of,  1246 
of  pleura,  983 
pre-aortic,  908 
of  scalp,  1223 
terminal,  906 
of  thigh,  917 
of  thorax,  923 
of  tongue,  1007 

surgical  anatomy  of,  1244 
tunica  externa  of,  905 

interna  of,  905 

media  of,  905 
of  upper  limb,  913,  915 
valves  of,  905 

visceral,  of  abdomen  and  pelvis,  918 
Lymph -vascular  system,  904 
Lyra,  572 


Macrodont  skulls,  1029.     See  also  Megadont 
Macula  acustica  sacculi,  763 

utriculi,  762 
cribrosa  inferior,  760 

media,  759 

superior,  759 
flava  of  true  vocal  cord,  966 
lutea,  731 

structure  of,  734 
Macular  artery,  735 
Maier,  sinus  of,  740 
Malar  bone,  140 

architecture  of,  Appendix  A,  ii 

connexions  of,  141 

ossification  of,  141 

relation  of,  to  orbit,  147,  149 

surgical  anatomy  of,  1237 

variations  in.  Appendix  B,  x 
canal,  141 
centre,  137 
crest,  124 
nerve,  of  facial,  688 

of  superior  maxillary,  681 
process,  135 
tuberosity,  140 


INDEX. 


1369 


Male  pronucleus,  16 

Malleolar  arteries,  of  anterior  tibial,  868 
of  jjosterior  tibial,  865 
folds  of  tympanic  membrane,  750 
Malleolus,  external.     See  Malleolus  lateralis 
topography  of,  1310 
internal.     See  Malleolus  medialis 

topography  of,  1310 
lateralis,  237 
medialis,  233 
Malleus,  754 

articulations  of,  756 
development  of,  757 
ligaments  of,  757 
movements  of,  758 
surgical  anatomy  of,  1231 
Malpighian  corpuscles,  of  kidney,  1139 
development  of,  1202 
of  spleen,  1213 
layer  of  skin,  773 
Mamma,  1207.      See  also  Mammary  gland 
Mammoe   accessorial.        See    Mammary  gland, 

sui:)ernumerary 
Mammary  artery.     See  Artery 
gland,  1207 

alveoli  of,  1208 
ampulL-B  of,  1208 
areola  of,  1207 
areolar  glands  of,  1207 
development  of,  1209 
lobes  of,  1208 
lymphatics  of,  923,  1209 
nerves  of,  1209 
nipple  of,  1207,  1208 
stroma  of,  1208 
structure  of,  1207 
supernumerary,  1208 
surgical  anatomy  of,  1293 
variations  in,  1208 
vessels  of,  1209 
line,  981,  1253 
lymphatic  glands,  924 
region,  1253 
veins,  874 
Mammillary  bodies,  475,  572 
development  of,  478,  595 
line,  981,  1253 
process  of  vertebrae,  84 
ossification  of,  92 
Mandible,  142,  151,  165 

architecture  of.  Appendix  A,  ii 
body  of,  142 

differences  in,  due  to  age,  181 
movements  of,  268 
ossification  of,  144 
ramus  of,  143,  155 
variations  in.  Appendix  B,  x 
Mandibula.     See  Mandible 
Mandibular  arch,  36,  38,  43 
muscles  derived  from,  441 
nerve  of,  701 
canal,  143,  156 
foramen,  143 
Mantle -layer,  472 
Manubrium  mallei,  755,  756 

sterni,  94 
Marginal  artery  of  heart,  800 
gyrus,  561 
tract,  521 
veins  of  heart,  871 
Margo  ciliaris.     See  Ciliary  border 
falciformis,  354 


Margo  infraorVjitalis.     See  Infraorbital  margin 
liber  of  ovary,  1182 
pupillaris,  730 

supraorbitalis.     See  Supraorbital  margin 
Marrow,  71 
gelatinous,  71 
red,  71 
yellow,  71 
Marrow-cells,  71 
Marshall,  oblique  vein  of,  785,  871 

vestigial  fold  of,  784,  795 
Martinotti,  cells  of,  586 
Massa  lateralis  of  atlas,  79 

intermedia.     See  Commissure,  gray 
Masseter  muscle,  401 
action  of,  404 
nerve-suji^jly  of,  404 
Masseteric  artery,  812 

border  of  zygomatic  bone,  140 
fascia,  394 
nerve,  683 
vein,  880 
Mastication,  muscles  of,  401 
actions  of,  404 
nerve-supply  of,  404 
Mastoid  air-cells,  121,  752 

surgical  anatomy  of,  1234 
angle  of  parietal  bone,  108 
antrum,  752 
aditus  of,  1233 
develoi:)ment  of,  44,  121 
relation  of,  to  supra-meatal  triangle,  154 

to  tympanum,  749 
surgical  anatomy  of,  1233 
artery,  808 
border-cells,  1234 
canaliculus,  116 
foramen,  116,  154,  169 
fossa,  1233 

lymphatic  glands,  909 
process,  115 

growth  of,  121,  752 

ossification  of,  120 

relation  of,  to  transverse  process,  of  atlas, 

165 
sexual  differences  in,  180 
surgical  anatomy  of,  1234 
Matrix  imguis.     See  Nail,  matrix  of 
Maturation  of  ovum,  12 
Maxilla,  133 

antrum  of,  136.     See  also  Maxillary  sinus 
architecture  of.  Appendix  A,  ii 
body  of,  133 
connexions  of,  137 
ossification  of,  137 
processes  of,  133,  135 
relation  of,  to  nasal  fosste,  170 
to  orbit,  149 
to  zygomatic  fossa,  155 
tuberosity  of,  134,  136,  155 
variations  in,  Appendix  B,  ix 
Maxillary  arteries.     See  Artery 
lymphatic  glands,  internal,  909 
nerve,  inferior,  683 

superior,  681 
process,  36,  38,  39,  41,  66,  67 
of  inferior  turbinated  bone,  130 
of  palate  bone,  139 
sinus,  135,  136 

development  of,  137 

relation  of,  to  nasal  fossas,  150,  172,  173, 
175 


1370 


INDEX. 


Maxillary  sinus,  relation  of,  to  orbit,  149 
surgical  anatomy  of,  1240 
vein,  internal,  880 
morphology  of,  945 
Maxillo-turbinal,  131 
Measurements  of  skulls.  Appendix  D,  xv 
Meatus     acusticus     exteruus.        See    Meatus, 
auditory,  external 
internus.     See  Meatus,  auditory,  internal 
auditory,  external,  115,  154,  746 
blood-vessels  of,  748 
ceruminous  glands  of,  748,  778 
development  of,  44,  121 
fissure  of  Santorini  of,  748 
foramen  of  Huschke  of,  748 
isthmus  of,  747 
lymjshatics  of,  748 
nerves  of,  748 
structure  of,  747 
surgical  anatomy  of,  1229 
variations  in,  Aj^pendix  B,  ix 
internal,  118,  169,  170 

absence  of,  Appendix  B,  ix 
fundus  of,  761 
nasi  inferior.     See  Meatus  of  nose,  inferior 
medius.     See  Meatus  of  nose,  middle 
superior.     See  Meatus  of  nose,  superior 
of  nose,  atrium  of,  135,  721 
inferior,  721 
bony,  135,  172 
surgical  anatomy  of,  1239 
middle,  721 

bony,  129,  135,  172 
surgical  anatomy  of,  1239 
superior,  720 
bony,  128,  172 
urinarius,  1170 
Mechanism  of  foot,  315 

of  pelvis,  293 
Meckel,  band  of,  757 
cartilage  of,  36,  144 
diverticulum  of,  1073,  1105 
ganglion  of,  682 

development  of,  699 
Median  artery,  834 

abnormalities  of,  952 
morphology  of,  943 
line,  5 
nerve,  627 

surgical  anatomy  of,  at  elbow,  1298 
in  forearm,  1301 
in  upper  arm,  1295,  1296 
veins,  890.     See  also  Veins 
Median-basilic  vein,  891 

surgical  anatomy  of,  1297 
Median-cephalic  vein,  890 
abnormalities  of,  955 
surgical  anatomy  of,  1297 
Mediastinal  arteries,  of  aorta,  839 
of  internal  mammary,  825 
lymphatic  glands,  924 
pleura,  977,  978,  1260 
space,  977,  982 
veins,  874 
Mediastinum  testis,  1161 
thoracis,  976 
anterior,  983 
middle,  983 
posterior,  983 
superior,  982 
Medulla  of  bone,  71 
of  kidney,  1138 


Medulla  oblongata,  481 

anterior  basis-bundle  of,  483 

relation    of,    to    posterior   longitudinal 
bundle,  491,  494 
antero-lateral  furrow  of,  482 
antero-median  groove  of,  482 
arcuate  fibres  of,  deej),  493.     See  also  Ar- 
cuate fibres 
superficial,  485.    See  also  Arcuate  fibres 
areas  of,  483,  488,  499 

acustic,  488 

development  of,  527 

anterior,  483,  499 

lateral,  483,  499 

posterior,  484,  499 
association  fibi-es  of,  498 
calamus  scriptorius  of,  488 
central  canal  of,  498 
cerebello-olivary  fibres  of,  496 
clava  of,  484 

closed  part  of,  482,  489,  525 
cuneate  tubercle  of,  485 
development  of,  477,  480,  526 
direct  cerebellar  tract  of,  484,  496 

relation  of,  to  restiform  body,  485 
fasciculus  solitarius  of,  517 

development  of,  527 
fillet-fibres  of,  493,  496 
foramen  caecum  of,  482 
formatio  reticularis  of,  490,  498,  499 

development  of,  528 
fovea  inferior  of,  488 

development  of,  527 
funiculus  cuneatus  of,  484,  491,  492 

gracilis  of,  484,  491,  492 

of  Eolando  of,  485,  491 
gray  matter  of,  489,  498 
intercalated  portion  of,  526 
internal  structure  of,  489 
lateral  basis-bundle  of,  484,  498 
nuclei  of     See  Nucleus,  arcuate,  cuneate, 

gracile,  lateralis,  olivary 
olivary  eminence  of,  484 
open  part  of,  482,  487 
origin  of  nerves  from,  514 
position  and  connexions  of,  475,  481 
posterior  longitudinal  bundle  in,  491,  494 
postero-lateral  furrow  of,  482 
postero -median  fissure  of,  482 
.  pyramidal  tract  in,  483,  494 
decussation  of,  490 
development  of,  528 
pyramids  of,  483 
raphe  of,  489 

develojjraent  of,  528 
restiform  body  of,  485,  496 
sections  of,  489 

striae  acusticte  of,  488,  497,  521 
tract  of  Gowers  in,  484,  498 
trigonum  acustici  of,  488 

liypoglossi  of,  488 
development  of,  527 

vagi  of,  488,  517 

develoi^ment  of,  627 
tuberculuni  Rolandi  of,  485,  491 
veins  of,  883 
white  matter  of,  489 
ossium.     See  Marrow 

flava.     See  Marrow,  yellow 
rubra.     See  Marrow,  red 
spinalis.     See  Spinal  cord 
Medullary  arteries.     See  Arteries,  nutrient 


INDEX. 


1371 


MeduUary  cavity,  71 
centre,  554,  584,  588 
corona  radiata  of,  591 
myelinisation  of,  594 
folds,  21 
groove,  21 

lamina,  external,  of  lenticular  nucleus,  580 
of  thalamus,  543,  544 
internal,  of  lenticular  nucleus,  580 
of  thalamus,  545 
rays,  1138 
sheath,  444,  465 
velum,  511.     See  also  Velum 
Megacephalic  skulls.  Appendix  D,  xv 
Megadont  skulls,  Appendix  D,  xviii 
Megaseme  skulls,  Appendix  D,  xviii 
Meibomian  glands,  739 

surgical  anatomy  of,  1238 
Meissner,  corpuscles  of,  775 

plexus  of,  of  small  intestine,  1073 
of  stomach,  1060 
Melanin,  774 

Membraua    atlanto  -  occipitalis    anterior.     See 
Ligament,  occipito-atloid,  anterior 
posterior.     See  Ligament,  occipito-atloid, 
posterior 
basilaris  cochleae,  764,  765,  766 
substantia  propria  of,  766 
vas  spirale  of,  766 
zona  arciiata  of,  766 
pectinata  of,  766 
hyaloidea,  735 

hyothyreoidea.     See  Membrane,  thyro-hyoid 
interossea  antibrachii.     See  Membrane,  inter- 
osseous, of  forearm 
cruris.      See    Membrane,    interosseous,    of 
leg 
limitans  retinae  externa,  734 

interna,  734 
obturatoria.     See  Membrane,  obturator 
pupillaris,  730 

development  of,  742 
stemi,  271,  272 

tectoria,  266.     See  also   Ligament,  occipito- 
axoid,  posterior 
of  organ  of  Corti,  766,  767 
tympani,  750 

annulus  fibro-cartilagineus  of,  750 

blood-vessels  of,  751 

dendritic  fibres  of,  752 

development  of,  43 

folds  of,  1231 

lymphatics  of,  751 

malleolar  folds  of,  750 

membrana  propria  of,  751 

nerves  of,  751 

otoscopic  appearances  of,  751 

paracentesis  of,  1232 

pars  flaccida  of,  750 

tensa  of,  750 
secundaria,  752 
stratum  circulare  of,  751 
cutaneum  of,  751 
mucosum  of,  751 
radiatum  of,  751 
surgical  anatomy  of,  1231 
triangular  cone  of,  1232 
umbo  of,  751 
vestibularis,  765 
Membranee  deciduse,  54 
Membrane,  astragalo-scaphoid,  311 
bones,  73  ;  Appendix  E,  xxii 


Membrane    of  Bruch,  729.      See  also  Lamina 
basalis  of  chorioid 
bucco-pharyngeal,  35,  38 
chorionic,  52.     See  also  Chorion 
cloacal,  21,  23,  45 
costo-coracoid,  323 

relation  of,  to  axillary  artery,  828 
crico-thyroid,  962 

level  of,  1289 

surgical  anatomy  of,  1249 
elastic,  of  Henle,  782 
fenestrated,  782 
hyoglossal,  1005 
interosseous,  of  forearm,  283 

of  leg,  304 
of  Nasmyth,  1024 
nictitating,  738 
nuclear,  8,  9,  10 
obturator,  293 
periosteal,  71 
of  Reissner,  765 
of  Ruysch,  728 
Schneiderian,  722 
of  Shrapnell,  750 

surgical  anatomy  of,  1232 
thyro-hyoid,  962 

surgical  anatomy  of,  1248  * 

tympanic,  750.     See  also  Membrana  tympani 
vitelline,  11 
Membranes,  foetal,  48,  59 

of  spinal  cord,  453,  597,  599,  601,  605 
synovial,  257,  258 

of  ankle-joint,  307 

of  carpo-metacarpal  joints,  288 

development  of,  260 

of  elbow-joint,  281 

of  hip-joint,  295 

of  intercarpal  joints,  286 

of  intertarsal  joints,  312 

of  knee-joint,  302 

of  metacarpo-phalangeal  joints,  288 

of  radio-carpal  joint,  284 

of  radio-ulnar  joint,  282 

of  shoulder-joint,  278 

of  temporo-mandibular  joint,  268 
Membranous  cranium.  Appendix  E,  xx 
labyrinth,  762 
urethra,  1177,  1179,  1203 

surgical  anatomy  of,  1278 
vertebral  column,  30,  90 
Meningeal  arteries.     See  Artery 
lymphatics,  909 
veins,  880,  881 
Meninges,  597.     See  also  Arachnoid,  Dura,  Pia 

Mater 
Meniscus,  258.      See  also  Interarticular  fibro- 

cartilages 
lateralis.     See  Semilunar  cartilage,  external 
medialis.     See  Semilunar  cartilage,  internal 
Mental  artery,  812 
foramen,  142 

topography  of,  1237 
nerve,  685 
protuberance,  142 
spines,  143 
tubercles,  142 
Meridiani,  724 

Merkel,  philtrum  ventriculi  of,  965 
Mesaticephalic  skulls,  Appendix  D,  xv 
Mesencephalic  root  of  trigeminal  nerve,  504 
Mesencephalon,  531.     See  also  Mid-brain 
Mesenteric  arteries.     See  Arteries 


1372 


INDEX. 


Mesenteric  ganglion,  superior,  713 

lymphatic  glands,  919 

plexus,  superior,  713 
inferior,  714 

veins,  901.     See  also  Veins 
Mesenterico-mesocolic  fold,  1069 
Mesenterium.     See  Mesentery 
Mesentery,  1065,  1071 

develojjnient  of,  33,  1106 

dorsal,  1106 

folds  of,  1072 

primitive,  1105 

root  of,  1071,  1072 

structure  of,  1072 

surgical  anatomy  of,  1269 

of  testis,  1167 

ventral,  1106,  1124 

of  vermiform  appendix,  1080,  1105 
Mesial  plane,  4 
Meso-appendix,  1080,  1105 
Mesoblast,  19.     See  also  Mesoderm 
Mesocejjhalic  skulls.  Appendix  D,  xv 
Mesocolic  glands,  1075 
Mesocolon  ascendens,  1082 

descendens,  1084 

development  of,  1108 

pelvic,  1086,  1100 

sigmoideus,  1085,  1086 

transversum,  1083,  1104 

attacliment  of,  1127 

topography  of,  1269 

Mesoderm,  19,  20,  22,  30,  65 

lateral  plates  of,  26,  30,  31 

paraxial,  26 

somatic,  25,  50 

somites  of,  26,  30,  31 

structures  formed  from,  30 
Mesodont  skulls,  1029,  Ajjpendix  D,  xviii 
Mesoduodenum,  1108 
Mescenteriolum     j)rocessus    vermiformis.      See 

Meso-appendix 
Mesogastrium,  1107 
Mesognathion,  1013 

Mesognathous  skulls.  Appendix  D,  xviii 
Mesometrium,  1190 
Mesonephros,    1199,    1201.     See   also   Wolffian 

body 
Mesorchium,  1167 
Mesorectum,  1085,  1086 
Mesorhine  skulls,  717,  Appendix  D,  xviii 
Mesosalpinx,  1185,  1189 
Mesoseme  skulls.  Appendix  D,  xviii 
Mesostemum,  94 
Mesotympanum,  1232 
Mesovarium,  1182,  1189 
Mesuranic  skulls,  Apjjendix  D,  xviii 
Metacarpal  arteries,  883 

bones,  207 

architecture  of,  Appendix  A,  iii 
ossification  of,  210 
surgical  anatomy  of,  1299 
variations  in,  Ap])endix  B,  xi 

ligament,  sujjerficiai  transverse,  338 

tubercle,  1299 
Metacarpo-phalangeal  joints,  288 

topography  of,  1299 
Metacarpus,  207 
Metaphase,  10,  13 
Metastemum,  94 
Metatarsal  artery,  869 

bones,  249 

architecture  of,  Ajjpendix  A,  vi 


Metatarsal  bones,  ossification  of,  251 
variations  in,  Appendix  B,  xiii 
ligaments,  transverse,  314 
superficial,  373 
Metatarso-j)halangeal  joints,  314 
movements  at,  315,  384 
surgical  anatomy  of,  1311,  1312 
Metatarsus,  249 

Metathalamus.     See  Corpus  geniculatum,   ex- 
ternum, internum 
Metencephalon,  477,  481 
Metopic  skulls,  158 

suture,  104,  158 
Metrio-cephalic  skulls.  Appendix  D,  xvii 
Meynert,  decussation  of,  539 
Microcephalic  skulls.  Appendix  D,  xv 
Microdont  skulls,  1029,  Aj^pendix  D,  xviii 
Microseme  skulls.  Appendix  D,  xviii 
Microsome,  8 
Mid-brain,  531 

aqueduct  of  Sylvius  of,  531,  533,  551 

development  of,  542 
corpora    quadrigemina    of,    634.      See    also 

Corpora  quadrigemina 
cortico-pontine  fibres  of,  540 
crura  of,  532.     See  also  Crura  cerebri 
deep  origin  of  nerves  from,  540 
development  of,  477,  542 
fasciculus  retroflexus  of,  539 
fillet  fibres  of,  534,  535,  538 

surface  elevations  of,  533 
fountain  decussation  of,  539 
frenulum  veli  of,  531 

development  of,  542 
ganglion  interpedunculare  of,  539 
internal  structure  of,  533 
lamina  quadrigemina  of,  533 
lateral  sulcus  of,  533 
nuclei  of,  533,  534,  535,  536 
oculo-motor  sulcus  of,  533 
posterior  longitudinal  bundle  of,  535,  537 
j)yramidal  fibres  of,  540 
situation  and  connexions  of,  476,  531 
stratum  griseum  centrale  of,  533 

intermedium  of,  681 
substantia  nigra  of,  533 

in  subthalamic  region,  546,  581 
superior  cerebellar  peduncle  in,  535 
sylvian  grey  matter  of,  533,  540 
veins  of,  883 
Mid-clavicular  line,  1253 
Mid-gut,  33 

relation  of,  to  Meckel's  diverticulum,  1106 
structures  derived  from,  34 
Mid-sternal  line,  1263 
Middle  cutaneous  nerve  of  thigh,  646 
Middle-ear,  748.     See  also  Tympanic  cavity 
Milk-teeth,  1014,  1015,  1022 
eruption  of,  1027 
surgical  anatomy  of,  1242 
Mitochondrial  sheath,  15 
Mitosis,  9 

heterotype,  13,  15 
homotyjje,  13 
Mitral  area,  1262 
orifice,  788,  790 
level  of,  1290 
topography  of,  1262 
valve,  790 
Moderator  band,  790 
Modiolus,  760 
Molar  artery,  812 


INDEX. 


1373 


Molar  glands,  997 
teeth,  1015,  1019 

development  and  eruption  of,  1027 
of  milk  dentition,  1023 
Molecular  layers  of  retina,  732,  733 
Moll,  glands  of,  739,  778 
Monro,  foramen  of,  476,  544,  551,  573 
development  of,  479,  594 
sulcus  of,  551,  594 
Mons  pubis.     See  Mons  Veneris 
Mons  Veneris,  1182,  1195 
Montgomery,  glands  of,  1207 
Monticulus,  506,  507 
Morgagni,  columns  of,  1093,  1094 
surgical  anatomv  of,  1280 
hydatid  of,  1187 
origin  of,  1199 
Morphology,  2 

of  appendicular  skeleton.  Appendix  F,  xxiii 
of  arteries,  939 
of  cervical  plexus,  622 
of  cranial  nerves,  700 
of  head-muscles,  441 
of  ligaments,  261 
of  limb-muscles,  440 
of  limb-plexuses,  662 
of  limbs,  Api^endix  F,  xxiii 
of  posterior  divisions  of  .sjiinal  nerves,  614 
of  primitive  streak,  19 
of  pudendal  plexus,  660 
of  skeletal  muscles,  439 
of  skull.  Appendix  E,  xx 
of  svmpathetic  system,  716 
of  teeth,  1029 

of  vascular  system,  938,  943 
of  veins,  943 
Morula,  17 
Moss-fibres,  514 
Motor  area,  1225 
Mouth,  993,  995 
aperture  of,  995 
buccal  glands  of,  997 
cavity  of,  995 
proper,  997 
develoi^ment  of,  34,  38,  41 
floor  of,  997 

incisive  pad  of,  998,  1000 
labial  glands  of,  996,  997 
molar  glands  of,  997 
mucous  membrane  of,  996 
muscles  of,  397 
plica  sublingualis  of,  997 
primitive,  34.     See  also  Stomatodseum 
roof  of,  997 
sublingual  caruncle  of,  997 

region  of,  997 
sucking-pad  of,  997 
vestibule  of,  995 
Movable  joints,  256 

vertebrte,  76,  78 
Movements  in  leaping,  385 
in  locomotion,  384 
in  respiration,  419 
in  running,  385 
in  swallow'ing,  413 
in  walking,  384 
Mucous  glands,  1008 
Miiller,  fibres  of,  699,  734 

muscle  of,  401 
Mtillerian  duct,  1199 

development  of,  1204 
Multicuspidate  teeth,  1019 


Multifidus  spinae  muscle,  391 
action  of,  392,  393 
nerve-supply  of,  392 
Muscle  or  Muscles  ;  Musculus  or  Musculi,  317 
of  abdominal  wall,  421 
abdominis.     See  Abdomen,  muscles  of 
abductor  digiti  quinti  (manus),  345 
nerve-supply  of,  351 
(pedis),  381 
action  of,  384 
nerve-supply  of,  383 
hallucis,  381 
action  of,  384 
nerve-supply  of,  383 
surgical  anatomy  of,  1312 
minimi   digiti   of  foot.     See  M.  abductor 
digiti  quinti  (pedis) 
of    hand.      See    M.    abductor    digiti 
quinti  (manus) 
pollicis  brevis,  343 
action  of,  353 
nerve-supply  of,  351 
longus,  350 
accessorius  of  back,  389 
of  foot,  379 
action  of,  384 
nerve-supply  of,  383 
adductor  brevis,  362 
action  of,  370,  393 
nerve-supply  of,  370 
hallucis,  caput  obliquum,  382 
action  of,  384 
nerve -sup]  >ly  of,  383 
transvei'sum,  382 
action  of,  384 
nerve-sup>i)ly  of,  383 
longus,  362 

action  of,  370,  393 
nerve-sujiply  of,  370 
surgical  anatomy  of,  1306 
magnus,  362 

action  of,  370,  393 
nerve-supply  of,  370 
surgical  anatomy  of,  1308 
minimus,  363 

obliquus  hallucis.    See  M.  adductor  hallucis, 
caput  obliquum 
poUicis,  345 
action  of,  353 
nerve-supply  of,  351 
poUicis,  caput  obliquum.     See  M.  adductor 
obliquus  pollicis 
cajDut    transversum.      See  M.   adductor 
transversus  pollicis 
transversus    hallucis.       See    M.    adductor 
hallucis,  caput  transversum 
pollicis,  345 
action  of,  353 
nerve -supply  of,  351 
agitator  caudse,  365 
anconeeus,  349 
action  of,  352 
nerve-supply  of,  351 
antitragicus,  746 
ajDpendicular,  319 
of  arm,  332 

arrectores  pilorum,  779 
articularis  genu.     See  M.  subcrureus 
aryepiglotticus.  See  M.,  aryteno-epiglottidean 
arytsenoideus  obliquus,  970 

transversus,  970 
ary-vocalis,  970,  971 


1374 


INDEX. 


Muscle  or  Muscles — continued 
attoUens  aurem,  396 

nerve-suj^ply  of,  399 
attraliens  aurem,  396 

nerve -sujJijly  of,  399 
auricularis  anterior.     See  M.  attrahens  aurem 
posterior.     See  M.  retraliens  aurem 
superior.     See  M.  attollens  aurem 
axial,  385 
azygos  uvulae,  412 

nerve-supply  of,  413 
of  back,  385 
action  of,  392 
nerve-supply  of,  392 
biceps  brachii,  332 

action  of,  335,  352 
nerve -supply  of,  335 
surgical  anatomy  of,  1297 
femoris,  368 

action  of,  370,  371 
nerve-supply  of,  370 
surgical  anatomy  of,  1304,  1308 
biventer  cervicis,  389 
bracliialis,  334 
action  of,  335 
nerve-supply  of,  335 
anticus.     See  M.  bracliialis 
bracliio-radialis,  348 
action  of,  352 
nerve-supply  of,  351 
topography  of,  1300 
buccinator,  398 
action  of,  399 
nerve-supply  of,  399 
bucco-pharyngeus,  41 0 
bulbo-cavernosus,  431 
of  buttock,  364 
actions  of,  370 
nerve-supplies  of,  370 
caninus.     See  M.  levator  anguli  oris 
capitis.     See  Mm.  of  head 
cerato-pharyngeus,  411 
cervicalis  ascendens,  389 
action  of,  392 
nerve-suj^ply  of,  392 
chondro-epitrochlearis,  325 
chondro-glossus,  409 
chondro-i^baryngeus,  411 
ciliaris,  729 

circumflexus  palati.     See  M.  tensor  jjalati 
cleido-mastoid,  405 
cleido-occipitalis,  405 
coccygeus,  438 
colli.     See  Mm.  of  neck 
complexus,  389 
action  of,  392 
nerve-sujiply  of,  392 
compressor  Ijulbi,  431 
hemisi^herium  bulbi,  432 
naris,  397 
radicis  penis,  431 
urethrie,  432 
ven*  dorsalis  penis,  433 
con.strictor  pharyngis  inferior,  41 1 
action  of,  413 
development  of,  441 
nerve-supply  of,  413 
medius,  411 
action  of,  413 
development  of,  441 
nerve-supply  of,  413 
superior,  410 


Muscle  or  Muscles — continued 

constrictor  pharyngis  superior,  action  of,  413 
development  of,  441 
nerve-supply  of,  413 
coraco-brachialis,  332 
action  of,  335 
nerve-sujDply  of,  335 
topography  of,  1293,  1295 
coraco-brachialis  sujaerior,  332 
corrugator  cutis  ani,  431,  1093 
sujDercilii,  397 
action  of,  399 
nerve-supply  of,  399 
costo-coracoideus,  325 
cremaster,  425 
crico-arytsenoidei,  969 

action  of,  971 
crico-pharyngeus,  411 
crico-thyreoideus,  968 
action  of,  971 
nerve -supply  of,  971 
crureus,  359 
action  of,  371 
nerve-supply  of,  370 
cucuUaris.     See  M.  trapezius 
dartos,  430,  1170 
deltoideus,  328 
action  of,  331 
nerve-supply  of,  331 
topograjjhy  of,  1295 
depressor  alas  nasi,  397 
auguli  oris,  398 
action  of,  399 
nerve-supply  of,  399 
labii  inferioris,  398 
action  of,  399 
nerve -supply  of,  399 
septi,  397 
development  of,  439 
diaphragm,  417.     See  also  Diaphragm 
digaatricus,  407 
action  of,  410 
development  of,  441 
nerve-supply  of,  409 
dilatator  pupillse,  731 
dilator  naris,  397 

tubae,  754 
dorsi.     See  Mm.  of  back 
dorso-ejiitrochlearis,  325 
with  double  nerve -sujaply,  671 
of  ear,  extrinsic,  396 

intrinsic,  746 
ejaculator  urinse,  431 
ejiicranius.     See  M.  occipito-frontalis 
eiiitrochleo-anconeus,  349 
erector  clitoridis,  432 
penis,  432 
spinas,  387 

action  of,  392,  393 
nerve-sujjj^ly  of,  392 
topography  of,  1285 
extensor  carpi  radialis  brevis,  348 
action  of,  352 
nerve-siipjjly  of,  351 
longus,  348 
action  of,  352 
nerve-sujiply  of,  351 
ulnaris,  349 
action  of,  352 
nerve-suj^jjly  of,  352 
digiti  quinti  projirius,  348 
action  of,  352 


INDEX. 


1375 


Muscle  or  Muscles — continued 

extensor  digit!  quinti  jjioprius,  nerve-supijly 
of,  352 
digitorum  bruvis,  375 
action  of,  384 
nerve-supply  of,  383 
topography  of,  1312 
communis,  348 
action  of,  352 
nerve-supply  of,  351 
longus,  374 
action  of,  384 
nerve-su])ply  of,  383 
topograjjhy  of,  1312 
hallucis  longus,  375 
action  of,  384 
nerve-supply  of,  383 
topography  of,  1312 
indicis,  351 

action  of,  352 
nerve-supply  of,  352 
proprius.     See  M.  extensor  indicis 
minimi    digiti.      See   M.    extensor    digiti 

quinti  proj^rius 
ossis  raetacarpi  jjollicis,  350 
action  of,  353 
nerve-suj^ply  of,  352 
metatarsi  hallucis,  375 
pollicis  brevis,  351 
action  of,  353 
nerve-supplj-  of,  352 
longus,  351 
action  of,  353 
nerve -supply  of,  352 
primi  internodii  hallucis  longus,  375 
proprius  hallucis.    See  ]\I.  extensor  liallucis 

longus 
quinti  digiti  proprius,  348 
extremitatis  inferioris.  See  Mm.  of  lower  limb 

superioris.     See  Mm.  of  upper  limb 
of  eyeball,  morphology  of,  701 
of  eyelids,  397 
action  of,  399 
nerve-supplv  of,  399 
of  face,  397 

development  of,  441 
fasciculi  of,  317 
flexor  accessorius,  379 
action  of,  384 
nerve-supply  of,  383 
carpi  radialis,  339 
action  of,  352 
nerve-sujjply  of,  351 
topography  of,  1300 
ulnaris,  339 
action  of,  352 
nerve-supjjly  of,  351 
caudse,  438 
digiti  quinti  brevis  (manus),  346 

(pedis),  382 
digitorum  brevis,  381 
action  of,  384 
nerve-supply  of,  383 
longus,  378 
action  of,  384 
nerve-supply  of,  383 
profundus,  341 
action  of,  352 
nerve-supply  of,  351 
sublimis,  341 
action  of,  352 
nerve -supply  of,  351 


Muscle  or  Muscles — continued 
flexor  liallucis  brevis,  382 
action  of,  384 
nerve-supjjly  of,  383 
longus,  379 
action  of,  384 
nerve-supply  of,  383 
minimi  digiti  brevis,  of  foot.    See  M.  flexor 
digiti  quinti  brevis  (pedis) 
of  hand.    See  M.  flexor  digiti  quinti 
(manus) 
pollicis  brevis,  344 
action  of,  353 
nerve-supply  of,  351 
longus,  342 
action  of,  353 
nerve-supply  of,  351 
of  foot,  373 
actions  of,  384 
nerve-su^Ji^lies  of,  383 
of  forearm,  338 
frontalis,  396 
gastrocnemius,  376 
action  of,  384 
nerve-su^jply  of,  383 
topography  of,  1309,  1310 
gemellus  inferior,  367 
action  of,  370 
nerve-supply  of,  370 
superior,  367 
action  of,  370 
nerve-supjjly  of,  370 
genio-glossus,  408 
action  of,  410 
nerve -sujjjJy  of,  409 
surgical  anatomy  of,  1244 
genio-hyo-glossus.     See  M.  genio-glossus 
genio-hyoideus,  408 
action  of,  410 
nerve-supply  of,  409 
glosso-palatinus.     See  M.  jaalato-glossus 
glosso-pharyngeus,  410 
glutteus  maximus,  364 
action  of,  370,  393 
nerve-sujJialy  of,  370 
topography  of,  1302 
medius,  365 

action  of,  370,  393 
nerve-supi^ly  of,  370 
minimus,  365 

action  of,  370,  393 
nerve-.supply  of,  370 
gracilis,  362 
action  of,  370 
nerve-sujjply  of,  370 
hamstring,  368 

topograj^hy  of,  1303 
of  hand,  343 
of  head,  395 
of  heart,  791 
helicis  major,  746 

minor,  746 
of  Horner,  741 
hyo-glossus,  409 
action  of,  410 
nerve-supjjly  of,  409 
of  hyoid  bone,  405 
iliacus,  361 

action  of,  370,  371,  393 
nerve-supj)ly  of,  370 
minor,  361 
ilio-capsularis,  361 


1376 


INDEX. 


Muscle  or  Muscles — continued 
ilio-coccygeus,  438 
ilio-costalis,  387 

cervicis.     See  M.  cervicalis  ascendens 
dorsi.     See  M.  accessorius,  of  back 
lumborum.     See  M.  ilio-costalis 
ilio-psoas,  359 
action  of,  371 
bursa  of,  296,  360 
nerve-supply  of,  370 
surgical  anatomy  of,  1307 
ilio-sacralis,  438 

infracostales.     See  Mm.  subcostales 
infrahyoid,  405 
action  of,  410,  419 
nerve-supply  of,  409 
infraspinatus,  329 
action  of,  331 
nerve-supj)ly  of,  331 
insertion  of,  318 
intercostales  externi,  416 
action  of,  419 
nerve-supply  of,  419 
interni,  416 
action  of,  419 
nerve-supply  of,  419 
interossei  manus,  346 
action  of,  352 
nerve-sujJi^ly  of,  351 
pedis,  383 
action  of,  384 
nerve-sxipply  of,  383 
interspinales,  392 
intertransversarii,  392 
intrinsic,  of  tongue,  409 
ischio-bulbosus,  432 
ischio-cavemosus,  432 
ischio-coccygeus.     See  M.  coccygeus 
iscliio-pubicus,  433 
laryngeal,  968 
latissimus  dorsi,  320 

action  of,  327,  331,  393,  419 
nerve-supply  of,  326 
surgical  anatomy  of,  1285 
of  leg,  373 
action  of,  384 
nerve-supply  of,  383 
levator  anguli  oris,  398 
action  of,  399 
nerve-supply  of,  399 
scapulae.     See  M.  levator  scapulae 
ani,  438,  1095 
glandulse  thyreoidete,  406 
labii  superioris,  398 
action  of,  399 
nerve-supply  of,  399 
alteque  nasi,  397 
action  of,  399 
nerve-supply  of,  399 
menti,  398 
action  of,  399 
nerve-supply  of,  399 
palati,  412 
action  of,  413 
nerve-supply  of,  413 
palpebrse  superioris,  399 
action  of,  401 
nerve-supply  of,  401 
prostatse,  439 
scapulae,  320 

action  of,  327,  393 
nerve-supply  of,  327 


Muscle  or  Muscles — continued 

levator  veli  jjalatini.     See  M.  levator  palati 
levatores  costarura,  416 
action  of,  419 
nerve-supply  of,  419 
linguae.     See  Mm.  of  tongue 
lingualis  inferior,  409 

superior,  409 
of  little  finger,  345 
longissimus  capitis,  389 
cervicis,  389 
dorsi,  389 
longitudiiTalis    inferior.      See    M.    lingualis 
inferior 
superior.     See  M.  lingualis  sujoerior 
longus  capitis.     See  M.  rectus  capitis  anticus 
major 
colli,  415 
of  lower  limb,  353 
lumbricales  of  foot,  379 
action  of,  384 
nerve-supply  of,  383 
of  hand,  342 
action  of,  352 
nerve-sup]3ly  of,  351 
niasseter,  401 
action  of,  404 
nerve-supply  of,  404 
of  mastication,  401 
action  of,  404 
nerve-supply  of,  404 
mentalis.     See  M.  levator  menti 
morphology  of,  439 
of  mouth,  397 
of  Miiller,  401 
multifidus  (spinas),  391 
action  of,  392,  393 
nerve-supply  of,  392 
mylo-hyoideus,  407 
action  of,  410 
nerve -supply  of,  409 
mylo-pharyngeus,  410 
nasalis.     See  M.  compressor  naris 
of  neck,  405 
of  nose,  397 
actions  of,  399 
nerve-supplies  of,  399 
obliquus  auriculae,  746 
capitis  inferior,  391 
action  of,  393 
nerve-supply  of,  392 
superior,  392 
action  of,  393 
nerve-supply  of,  392 
externus  abdominis,  421 
action  of,  430 
nerve-supply  of,  430 
inferior  of  neck.     See  M.  obliquus  capitis 
inferior 
of  orbit,  400 
internus  abdominis,  424 
action  of,  430 
nerve-supply  of,  430 
superior  of  neck.     See  M.  obliquus  capitis 
superior 
of  orbit,  400 
obturator  externus,  363 
action  of,  370,  393 
nerve-supply  of,  370 
internus,  366 

action  of,  370,  393 
nerve -supply  of,  370 


INDEX. 


1377 


Muscle  or  Muscles — continued 
occipitalis,  395 
occipito-froutalis,  395 

action  of,  399 
oculi.     See  Mm.  of  orbit 
omohyoideus,  405 
action  of,  410 
nerve-sujjply  of,  409 
surgical  anatomy  of,  1250 
opponens  digiti  quinti,  346 
action  of,  352 
nerve-supjaly  of,  351 
minimi   digiti.      See   M.    opj^onens   digiti 

quinti 
pollicis,  343 
action  of,  353 
nerve-supply  of,  351 
orbicularis  oculi,  397 
action  of,  399 
nerve -supply  of,  399 
oris,  398 

action  of,  399 
nerve -supjaly  of,  399 
palpebrarum.     See  M.  orbicularis  oculi 
of  orbit,  399 
action  of,  401 
develojDment  of,  441 
nerve-supply  of,  401 
origin  of,  318 
ossiculorum  auditus.     See  Mm.  of  tympanic 

cavity 
ossis  byoidei.     See  Mm.  of  byoid  bone 
palato-glossus,  409 
action  of,  413 
nerve-suj^ply  of,  413 
palato-pharyngeus,  411 
action  of,  413 
nerve-supply  of,  413 
palmaris  brevis,  336 
longus,  339 
action  of,  352 
nerve-supply  of,  351 
topography  of,  1300 
papillares  (of  heart),  790,  791 

structure  of,  792 
pectinati,  787,  788 
pectineus,  361 

action  of,  370,  371 
nerve-suj)j)ly  of,  370 
of  pectoral  region,  323 
pectoralis  major,  323 

action  of^  327,  331,  419 
nerve -supply  of,  327 
topography  of,  1253 
minimus,  325 
minor,  325 

action  of,  327,  331,  419 
nerve-supply  of,  327 
of  pelvis,  438 
perinei,  431 
peronaeo-calcaneus,  380 

extemus,  376 
peronaso-cuboideus,  376 
peronseus  accessorius,  376 
brevis,  375 
action  of,  384 
nerve-supply  of,  383 
topography  of,  1309 

of  tendon  of,  1311,  1312 
digiti  quinti,  376 
longus,  375 
action  of,  384 

92 


Muscle  or  Muscles — continued 

jjeronaeus  longus,  nerve-supply  of,  383 
topograj)hy  of,  1309 

of  tendon  of,  1311,  1312 
tertius,  375 
action  of,  384 
nerve-supply  of,  383 
topography  of,  1312 
pharyngo-palatinus.      See  M.  j)alato-pharyn- 

geus 
of  pharynx,  410 
action  of,  413 
development  of,  441 
nerve-suj^ply  of,  413 
of  pinna,  746 
piriformis,  366 
action  of,  370,  393 
nerve -supi^ly  of,  370 
plantaris,  377 
action  of,  384 
nerve-supply  of,  383 
platysma,  395 

action  of,  399 
development  of,  441 
nerve-supply  of,  399 
popliteus,  378 
action  of,  371 
nerve -supply  of,  383 
minor,  378 
procerus.     See  M.  pyramidalis  nasi 
pronator  quadratus,  343 
action  of,  352 
nerve-supply  of,  351 
radii  teres.     See  M.  pronator  teres 
teres,  338 

action  of,  352 
nerve-sujaply  of,  351 
psoas  magnus,  359 

action  of,  370,  392,  393 
nerve-supply  of,  370 
surgical  anatomy  of,  1285 
major.     See  M.  psoas  magnus 
minor.     See  M.  psoas  parvus 
parvus,  360 

action  of,  392,  393 
nerve -supply  of,  370 
pterygoideus  externus,  403 
action  of,  404 
nerve -supply  of,  404 
internus,  403 
action  of,  404 
nerve-supply  of,  404 
pterygo-pharyngeus,  410 
pubo-cavernosus,  432 
pubo-coccygeus,  438,  1095 
pubo-rectalis,  438 
pubo-vesicalis,  1157 
pyramidalis  abdominis,  427 
auriculfe,  746 

nasi,  397  , 

action  of,  399 
nerve-supply  of,  399 
pyriformis.     See  M.  piriformis 
quadratus  femoris,  367 
action  of,  370 
nerve-sup2)ly  of,  370 
labii   inferioris.      See   M.   depressor  labii 
inferioris 
superioris,  397 
lumborum,  430 

surgical  anatomy  of,  1285 
plantse.     See  M.  flexor  accessorius 


1378 


INDEX. 


Muscle  or  Muscles — continued 
quadriceps  fenioris,  357 
action  of,  371 
nerve-sujjply  of,  370 
recto-coccygeus,  1093 
recto-uteriiius,  1101,  1189 
recto-vesicalis,  1157 
rectus  abdominis,  427 

caj)itis   anterior.     Hec    M.    rectus    caj)itis 
anticus  minor 
anticus  major,  414 

minor,  415 
lateralis,  415 
action  of,  393 
nerve-su232^1y  of,  415 
Ijosterior  major,  392 
minor,  392 
external,  of  orbit.     See  M.  rectus  lateralis 
femoris,  357 

action  of,  370,  393 
nerve-suj^ply  of,  370 
inferior,  400 
action  of,  401 
nerve-sui3j)ly  of,  401 
internal,      of      orbit.        See      M.      rectus 

medialis 
lateralis,  400 
action  of,  401 
nerve-sujiply  of,  401 
medialis,  400 
action  of,  401 
nerve-supi^ly  of,  401 
superior,  400 
action  of,  401 
nerve -su2Dj)ly  of,  401 
of  respiration,  415 
action  of,  419 
nerve-sujjj^ly  of,  419 
retraliens  aurem,  396 
action  of,  399 
nerve-supply  of,  399 
rhomboideus  major,  322 
action  of,  327 
nerve-supply  of,  327 
minor,  322 
action  of,  327 
nerve-supjjly  of,  327 
of  Riolan,  739 
risorius,  398 
action  of,  399 
nerve-sujjply  of,  399 
rotator  humeri,  332 
rotatores  (dorsi),  392 
action  of,  393 
nerve-sup2:)ly  of,  392 
sacro-si^inalis,  387 
salpingo-pliaryngeus,  411 

relation  of,  to   plica  salpingo-pliarynge;i, 
754 
sartoriuH,  356 

action  of,  370,  371,  393 
nerve-supply  (jf,  370 
topograjjhy  of,  1306 
scalenus  anterioi',  413 
action  of,  419 
nerve-sujjply  of,  415 
mediiLS,  414 
action  of,  419 
nerve-sup]  )ly  of,  415 
posterior,  414 
action  of,  419 
nerve-supply  of,  415 


Muscle  or  Muscles — continued 
of  scalp,  395 
action  of,  399 
nerve-suijj^l}'-  of,  399 
semimembranosus,  369 
action  of,  370 
nerve -su2Jj)ly  of,  370 
topograpliy  of,  1305 
semisjomaiis,  391 
capitis,  389 
cervicis,  391 
action  of,  392 
nerve-supj)ly  of,  392 
colli.     See  M.  semisjpinalis  cervicis 
dorsi,  391 
action  of,  392 
nerve-supply  of,  392 
semitendinosus,  369 
action  of,  370,371 
nerve-supply  of,  370 
tojDography  of,  1305 
serratus  anterior,  326.     See  also  M.  serratus 
magnus 
magnus,  326 

action  of,  327,  419 
nerve-sujDply  of,  327 
topography  of,  1255 
posterior  inferior,  387 
action  of,  393,  419 
nerve-sujoply  of,  392 
superior,  386 

action  of,  393,  419 
nerve-supply  of,  392 
of  shoulder,  327 
skeletal,  317 
skeleti.     See  M.  skeletal 
of  soft  palate,  412 

develojDment  of,  441 
soleus,  378 
action  of,  384 
nerve-supply  of,  383 
topography  of,  1309,  1310 
sphincter  ani  externus,  431,  1095 
action  of,  433 
nerve -supply  of,  433 
internus,  1093,  1095 
pupillee,  731 
pylori,  1056,  1058 
recti,  1095 
urethrae  membranaceae.     See  M.  conijjressor 

urethrse 
vaginae,  432 
vesicae,  1157 
spinalis  dorsi,  389 
splenius  capitis,  387 
action  of,  392 
nerve -supply  of,  392 
cervicis,  387 
action  of,  392 
nerve-sujjply  of,  392 
colli.     See  M.  splenius  cervicis 
stapedius,  757 
sternalis,  325 
sterno-clavicularis,  326 

sterno-cleido-mastoideus,   405.     See  also   M., 
sterno-mastoid 
action  of,  393,  419 
nerve-su2)ply  of,  405 
stemo-hyoideus,  406 
action  of,  410 
nerve-supply  of,  409 
sterno-mastoid,  405 


INDEX. 


1379 


Muscle  or  Muscles — continued 

sterno-mastoid,  action  of,  393,  419 
nerve-supply  of,  405 
surgical  anatomy  of,  1249 
stenio-thyreoideus,  406 
action  of,  410 
nerve-supply  of,  409 
stylo-auricularis,  746 
stylo-glossus,  409 
action  of,  410 
nerve-supjjly  of,  409 
stylo-hyoideus,  407 
action  of,  410 
develoj)ment  of,  441 
nerve-supply  of,  409 
stylo-pliarpigeus,  411 
action  of,  413 
development  of,  441 
nerve -supply  of,  413 
subanconeeus,  335 
subclavius,  325 
action  of,  327 
nerve-supply  of,  327 
subcostales,  416 
action  of,  419 
nerve-sujjply  of,  419 
subcrureus,  359 
subscapularis,  331 
action  of,  331 
nerve-supply  of,  331 
minor,  331 
supinator.     See  M.  supinator  radii  brevis 
longus.     See  M.  brachio-radialis 
radii  brevis,  349 
action  of,  352 
nerve-supply  of,  352 
supra-hyoid,  406 
action  of,  410 
nerve-supply  of,  409 
supraspinatus,  329 
action  of,  331 
nerve-supply  of,  331 
suspensorius  duodeni,  1070 
tarsalis  inferior.     See  M.  tensor  tarsi 
temporalis,  402 
action  of,  404 
nerve -svipply  of,  404 
tensor  fasciae  femoris.     See  M.  tensor  fasciae 
latte 
latfe,  365 

action  of,  370,  371 
nerve-supply  of,  370 
topography  of,  1303,  1306 
suralis,  369 
palati.  412 

relation  of,  to  Eustachian  tube,  754 
surgical  anatomy  of,  1246 
tarsi,  397,  741 
action  of,  399 
nerve-supply  of,  399 
tympani,  757 

surgical  anatomy  of,  1232 
veli  palatini.     See  M.  tensor  palati 
teres  major,  330 
action  of,  331 
nerve-supply  of,  331 
minor,  329 
action  of,  331 
nerve-supjjly  of,  331 
of  thigh,  356 
actions  of,  370 
nerve-supplies  of,  370 


Muscle  or  Muscles — continued 
thoracis.     See  Mm.  of  thorax 
of  thorax,  415 
actions  of,  419 
nerve-supplies  of,  419 
of  thumb,  343 
actions  of,  353 
nerve-supplies  of,  351 
thyreo-arytccnoideus,  969 
action  of,  971 
nerve-supply  of,  971 
thyreo-epiglotticus,  970 
thyreo-hyoideus,  406 
action  of,  410 
nerve -su^jply  of,  409 
thyreo-pharyngeus,  411 
thyro-ary-epigiottidean,  968 
action  of,  971 
nerve-supply  of,  971 
tibialis  anterior,  373 
action  of,  384 
nerve-su})ply  of,  383 
topography  of  tendon  of,  1312 
anticus.     See  M.  tibialis  anterior 
posterior,  379 
action  of,  384 
nerve-suj^ply  of,  383 
topography  of,  1311,  1312 
posticus.     See  M.  tibialis  posterior 
tibio-fascialis  anterior,  374 
of  tongue,  408 
action  of,  409 
arrangement  of,  1005 
develojiment  of,  441 
morphology  of,  701 
nerve-su2:)ply  of,  409 
surgical  anatomy  of,  1243 
tracheal,  975 
trachelo-mastoid,  389 
action  of,  393 
nerve-supply  of,  392 
tragicus,  746 

transversalis  abdominis.     See  M.  transversus 
abdominis 
cervicis,  389 
transverse,  of  tongue,  409 
transversus  abdominis,  425 
auriculffi,  746 
linguae,  409,  1005 
perinei  profundus,  433 

superticialis,  431 
thoracis.     See  M.  triangularis  sterni 
vaginte,  433 
trapezius,  319 
action  of,  327 
nerve-supply  of,  326 
topography  of,  1285 
triangularis.     See  M.  depressor  anguli  oris 
sterni,  416 
action  of,  419 
nerve-supply  of,  419 
triceps  brachii,  335 
action  of,  335 
nerve-supply  of,  335 
topography  of,  1295 
surae,  376 
of  tympanic  cavitj^,  757 
of  upj^er  limb,  319 
uvula!.     See  M.  azygos  uvulae 
vastus  externus.     See  M.  vastus  lateralis 
intermedins,  359 
action  of,  371 


1380 


INDEX. 


Muscle  or  Muscles — continued 

vastus  intermedius,  nerve-suj^jily  of,  370 
iutenius.     See  ]\I.  vastus  medialis 
lateralis,  358 
action  of,  371 
nerve-supply  of,  370 
topograpliy  of,  1304 
medialis,  358 
action  of,  371 
nerve-supply  of,  370 
topograj)hy  of,  1308 
verticalis  lingute,  409,  1005 
vocalis.     /S'ee  M.  thyreo-arytasnoideus 
zygomaticus,  397 
action  of,  399 
nerve-supply  of,  399 
major.     Hee  M.  zygomaticus 
minor,  397 
action  of,  399 
nerve-sujjply  of,  399 
Muscle-cells,  317 
Muscle-plate,  30 

Muscular  process  of  aryttenoid  cartilage,  960,  971 
of  vertebrae,  76,  77 
system,  317 

triangle  of  neck,  1249,  1251 
Musculo-cutaneous  nerve,  of  arm,  627.     See  cdso 
Nerve 
of  leg,  651.     See  also  Nerve 
Musculo-iihrenic  artery,  826 

vein,  874 
Musculo-spiral  groove,  191 
nerve,  632 
surgical  anatomy  of,  at  elbow,  1298 

in  ujjper  arm,  1295,  1296 
variations  in,  673 
Myelenceplialon,  477,  481 
Myelin,  444 
Myelinisation,  466 

of  sensory  nerve-fibres,  594 
of  tracts,  470,  473,  537 
Myelocoele,  30 
Myelospongium,  22,  472 
Myloliyoid  artery,  812 
groove,  143 
muscle,  407 
action  of,  410 
nerve-supply  of,  409 
nerve,  685 
ridge,  143,  165 
Myocardium,  791 
Myology,  3,  317 
Myotomes,  30,  318,  440,  Appendix  E,  xxii 

cephalic,  441,  701 
Myrtiform  fossa,  134 

Naboth,  ovules  of,  1191 
Nail,  775 

bed  of,  775 

development  of,  779 

in  fcetus,  47 

lunula  of,  775 

matiix  of,  775 

papilla;  of,  775 

vallum  of,  775 

wall,  775 
Nares.     See  Nares,  anterior 

anterior,  172,  717 

surgical  anatomy  of,  1239 

posterior,  162,  172,  719 
surgical  anatomy  of,  1246 
Nasal  aperture,  anterior,  146,  150 


Nasal  arteries.     See  Artery 
bone,  132 

relation  of,  to  nasal  aperture,  150 
to  nasal  fossae,  170 
cartilages,  717,  718 
cavity,  development  of,  40 
crest,  136 

relation  of,  to  nasal  septum,  172 
duct,  741 

bony  canal  of,  150,  172,  174 
development  of,  40,  743 
surgical  anatomy  of,  1239 
fossa,  170,  179 
agger  nasi  of,  721 
atrium  of,  721 
basal  cells  of,  723 
blood-vessels  of,  723 
Bowman's  glands  of,  722 
bulla  ethmoidalis  of,  721 
cavernous  tissue  of,  722 
development  of,  40 
epithelium  of,  722,  723 
hiatus  semilunaris  of,  721 
inferior  meatus  of,  721 

surgical  anatomy  of,  1239 
infundibulum  of,  721 
inner  wall  of.     See  Nasal  septum 
limen  of,  719 
lymphatics  of,  723 
middle  meatus  of,  721 

surgical  anatomy  of,  1239 
olfactory  cells  of,  723 
part  of,  720 

mucous  membrane  of,  722 
organ  of  Jacobson  of,  720 
orifices  in,  719,  720,  721 
outer  wall  of,  720 
recessus  naso-palatinus  of,  720 

spheno-ethmoidalis  of,  720 
respiratory  part  of,  720 

mucous  membrane  of,  722 
sensory  nerves  of,  723 
superior  meatus  of,  720 
supporting  cells  of,  722 
ventricle  of,  719 
vestibule  of,  719 
iiidex,  717,  Appendix  D,  xviii 
laminee,  41 

nerve,  680.     See  also  Nerve 
notch,  of  frontal  bone,  103 

of  maxilla,  134 
pit,  698,  703 

process,  of  frontal  bone,  103 
lateral,  39 
of  maxilla,  135 
median,  39 
sejitum,  720 
bony,  159,  172 
develojiment  of,  41 
sjiine,  anterior,  134,  136,  150 
topography  of,  1237 
of  frontal  bone,  104 
posterior,  138,  159 
veins,  880 
Nasion,  1223,  1237  ;  Appendix  D,  xvi 
Nasmyth,  memlu'ane  of,  1024 
Naso-frontal  suture,  147 
Naso-labial  Imnd,  398 
Naso-palatine  artery,  813 
nerve,  683 
recess,  720 
Naso-pharyngeal  groove,  1034 


INDEX. 


1381 


Naso-pliarnyx,  1032 
development  of,  1038 
Eustachian  oritice  of,  1033 
fossa  of  Rosenmliller  of,  1033,  1034 
surgical  anatomy  of,  1246 
tonsil  of,  1033 
Nasus.     See  Nose 
Nates.     See  Buttock 
Navicular  bone,  of  foot,  245 

morphology  of.  Appendix  F,  xxiv 
of  hand,  202 
Neck,  anterior  triangle  of,  1249 
development  of,  35,  36,  37 
digastric  triangle  of,  1249 
carotid  triangle  of,  1250 
fascise  of,  394 
infrahyoid  region  of,  1248 
lymi^hatics  of,  909 
middle  line  of,  1248 
muscles  of,  405 
muscular  triangle  of,  1251 
nuchal  furrow  of,  1253 
posterior  triangle  of,  1252 
sub-occipital  triangle  of,  1253 
suprahyoid  region  of,  1248 
surgical  anatomy  of,  1246 
Nelaton,  line  of,  1302 
Neo-pallium,  568,  584 
Nerve  or  Nerves  ;  Nervus  or  Nervi 
abducens,  686 

deep  connexions  of,  524 
development  of,  699 
morj^hology  of,  701 
nucleus  of,  502,  524 

relation    of,   to    posterior    longitudinal 
fasciculus,  537,  538 
origin  of,  deep,  502,  524 
superficial  486,  686 
accessorius.     See  N. ,  spinal  accessory 
accessory  obturator,  647 
acromial  descending,  619 
morphology  of,  622 
acusticus.     See  N.,  auditory 
to  adductor  magnus  muscle,  from  obturator, 
645 
from  great  sciatic,  649 
alveolares  superiores,  682 
alveolaris  inferior.     See  N.,  dental,  inferior 
ampullares.    See  Nn.  to  semicircular  canals 
to  ankle-joint,  from  anterior  tibial,  651 

from  posterior  tibial,  654 
anococcygei.    >S'ee  N.,sacro-coccygeal,  anterior 
anterior  crural,  645 

cutaneous,  of  thorax,  636,  638 
thoracic,  626 
of  Arnold,  692 
to  arteries,  783 

to  articulations  of  foot,  from  anterior  tibial, 
651 
from  external  plantar,  655 
from  internal  plantar,  654 
from  tibial,  653 
auditory,  688 

cochlear  division  of,  689 

termination  of,  768 
development  of,  699 
in  labyrinth,  768 
morphology  of,  702 
nucleus  of,  519.    See  also  Nucleus,  cochlear, 

vestibular 
origin  of,  deep,  519 
superficial,  486,  688 


Nerve  or  Nerves — continued 

auditory,  radix  cochlearis  of,  688 
development  of,  699 
vestibularis  of,  688 
development  of,  699 
ramus  sacculo-ampullaris  of,  769 

utriculo-ampullaris  of,  769 
vestibular  division  of,  689 
termination  of,  768 
auricular,  of  auriculo-temporal,  684 
great,  618 

morj^hology  of,  622 
posterior,  687 

of  vagus,  692.     See  also  N.  of  Arnold 
auriculares  anteriores.     See  N.,  auricular,  of 

auriculo-temporal 
auricularis  magnus.     See  N.,  auricular,  great 

posterior.     See  N.,  auricular,  posterior 
auriculo-temporalis,  684 

toj^ography  of,  1224 
axillaris.     See  N.,  circumflex 
to  azygos  uvulae  muscle,  683 
bigeminus,  639,  647 
of  blood-vessels,  783 
of  bones,  75 
to  brachial  artery,  627 
buccal,  of  inferior  maxillary,  684 

of  facial,  688 
buccinatorius.     See  N.,  buccal 
to  bulb  of  urethra,  659 
calcanean,  internal,  653 
canalis  pterygoidei  (Vidii).      See  N.,  Vidian 
cardiac,  inferior,  of  sympathetic,  708 
of  vagus,  692 
middle,  708 

superior,  of  sympathetic,  707 
of  vagus,  692 
cardiacus    inferior,    medius,    superior.       See 
Nn.,  cardiac,  inferior,  middle,  and 
superior  of  sympathetic 
carotici  externi.    See  Plexus,  carotid,  external 
caroticus  internus,  707 
caudal,  608,  614 
cerebrales.     See  Nn.,  cranial 
cervical,  611 

anterior   primary  divisions   of,   617.      See 

also  Plexus,  cervical,  brachial 
descending,  621 
first,  611 

grey  rami  of,  617 
cervicales.     See  Nn.,  cervical 
cervicalis  descend  ens,  621 
chorda  tympani,  687 

branches  of,  to  sublingual  gland,  1013 

to  submaxillary  gland,  1012 
development  of,  699 
morphology  of,  702 
relation  of,  to  taste,  771 
to  lingual  nerve,  685 
in  tymjjanum,  1232 
ciliares  breves,  681 

longi,  680 
circumflex,  632 

toijography  of,  1295 
clavicxilar,  descending,  619 

morj^bology  of,  622 
clunium  inferiores,  657 
coccygeus,  613 
to  coccygeus  muscle,  657 
cochleae.     See  N.,  cochlear 
cochlear,  689 

deep  origin  of,  519 


1382 


INDEX. 


Nerve  or  Nerves — continued 
coclilear,  spiral  fasciculi  of,  768 

termination  of,  768 
communicans  fibularis,  650 
to    constrictors     of   pliarynx,    from   glosso- 
pharyngeal, 690 
from  vagus,  692 
to  corpus  cavernosum,  660 
cranial,  674 

afferent  roots  of,  development  of,  698 

morphology  of,  701 
connexion  of,  with  superior  cervical  gang- 
lion, 706 
deep  connexions  of,  in  cerebrum,  551 
in  medulla  and  jyons,  514 
in  mesencephalon,  640 
develojiment  of,  698 
efferent  roots  of,  development  of,  698 

mor23hology  of,  701 
ganglia  of,  443 
general  distribution  of,  674 
motor  nuclei  of,  515 
morj)hology  of,  700 
nuclei  of  origin  of,  515 

of  termination  of,  515 
roots  of,  443 

segmental  characters  of,  701 
1st.     See  N.,  olfactory 
2nd.     See  N.,  optic 
3rd.     See  N.,  oculomotor 
4th.     See  N.,  trochlear 
5th.     See  N.,  trigeminal 
6th.     See  N.,  abducent 
7th.     See  N.,  facial 
8th.     See  N.,  auditory 
9th.     See  N.,  glosso-pharyngeal 
10th.     See  N.,  vagus 
11th.     See  N.,  spinal  accessory 
12th.     See  N.,  hypoglossal 
to  cremaster  muscle,  643 
crural,  anterior,  645 

of  genito-crural,  643 
cutaneous,  of  abdomen,  638,  639 
from  ilio-inguinal  nerve,  643 
of  lower  limb,  tables  of,  668,  669,  673 
of  upi^er  limb,  tables  of,  665,  666,  672 
cutaneus  antibrachii  lateralis.     See  N.,  mus- 
culo -  cutaneous,  of  arm  (cutaneous 
branch  of) 
medialis.      See  N.,  internal   cutaneous, 

of  arm 
dorsalis.     See  N.,  musculo-spiral  (lower 
external  cutaneous  branch  of) 
brachii     lateralis.       See     N.,     circumflex 
(cutaneous  branch  of) 
medialis.      See  N.,  internal   cutaneous, 

lesser,  of  arm 
posterior.     See  N.,  musculo-.S])iral  (upper 
external  cutaneous  branch  of) 
colli,  618.     See  also  N.,  cervical,  superficial 
dorsalis    intermedins.      See   N.,    musculo- 
cutaneous,    of     leg     (intermediate 
branch  of  internal  terminal  branch 
oO 
lateralis.        See    N.,     short    saphenous 

(digital  branch  of) 
medialis.      See   N.,    nmsculo- cutaneous, 
of  leg  (internal  branch  of  internal 
terminal  branch  of) 
femoris  lateralis.     See  N.,  external  cutane- 
ous, of  thigh 
posterior.     See  N.,  sciatic,  small 


Nerve  or  Nerves — continued 

cutaneus  sura;  lateralis,  650,  653.     See  also 
N.,  sural 
medialis.     See  N.,  tibial,  communicating 
dental,  anterior,  682 
inferior,  685 

surgical  anatomy  of,  1237 
middle,  682 
jDOsterior,  681 
descendens  hypoglossi,  621,  697 
to  diaphragm,  621,  638 
to  digastric  muscle,  685,  687 
digital,  of  foot,  from  musculo-cutaneous,  653 
from  jDlantar,  655 
from  short  saj)henous,  654 
from  tibial,  anterior,  652 
of  hand,  from  median,  629 
from  radial,  634 
from  ulnar,  630 
digi tales   dorsales.      See   Nn.,    radial,  ulnar 
(dorsal  digital  branches  of) 
dorsales  hallucis  lateralis  et  digiti  secundi 
medialis.      See  N.,   tibial,   anterior 
(internal  terminal  branch  of) 
pedis.      See  N.,   musculo-cutaneous,   of 

leg  (digital  branches  of) 
plantares  communes.     See  Nn.,  plantar, 
external,  internal  (digital  branches 
of) 
volares  communes.    See  Nn.,  median,  ulnar 
(palmar  digital  branches  of) 
to  dilatator  pupillse  muscle,  731 
dorsalis  clitoridis,  660 
penis,  660 

scapulge.     See  N.  to  rhomboids 
of  elbow-joint,  628 

ethmoidalis  anterior.     See  N.,  nasal  (anterior 
ethmoidal  branch  of) 
posterior.  See  N.,  nasal  (posterior  ethmoidal 
branch  of) 
of  Eustachian  tube,  754 
of  external  auditory  meatus,  748 
external  cutaneous,  of  thigh,  643 

respiratory,  of  Bell,  625 
of  eyelid,  740 
facialis,  686 

afferent  root  of,  699,  702 

in  aqueduct  of  Fallopius,  686 

ascending  part  of,  523 

in  auditory  meatus,  686 

branches  of,  686 

central  connexions  of,  523 

cervico-facial  division  of,  688 

communications  of,  686 

deep  origin  of,  523 

development  of,  699 

efferent  root  of,  699,  701,  702 

emergent  pai^t  of,  523 

geniculate    ganglion    of,    686.       See   also 

Ganglion,  geniculate 
geniculum  of,  686 
in  infant,  1235 
intrapontine  course  of,  523 
morphology  of,  702 
in  neck,  687 
nucleus  of,  502,  523 
in  parotid  gland,  687 
pars  intermedia  of,  522 
develojiment  of,  699 
origin  of,  524 

relation  of,  to  cliorda  tympani,  687 
to  geniculate  ganglion,  686 


INDEX. 


1383 


Nerve  or  Nerves — continued 

facialis,  pars  intermedia   of,  relation  of,  to 
vestibular  nerve,  689 
pes  anserinus  of,  687 
radicular  part  of,  523 
roots  of,  502,  522 
surgical  anatomy  of,  1234,  1237 
superficial  origin  of,  486,  522 
temporo-facial  division  of,  687 
to  femoral  artery,  644 
femoralis.     See  N.,  anterior  crural 
to  femur,  646 
to  fibula,  654 

to  flexor  carpi  ulnaris  muscle,  629 
frontalis,  679 
furcalis,  639 

variations  of,  674 
to  gemelli  muscles,  649 
genital,  of  genito-crural,  643 
genito-crural,  643 

geuito-femoralis.     See  N.,  genito-crural 
glosso-pharyngeus,  689 
afferent  fibres  of,  517 

root  of,  700,  702 
communications  of,  689 
deep  origin  of,  517 
development  of,  700 
efferent  fibres  of,  517 

root  of,  700,  701,  702 
in  jugular  foramen,  689 
jugular  ganglion  of,  689 
morphology  of,  702 
in  neck,  690 
nucleus  of,  517 

relation  of,  to  fourth  ventricle,  488 
petrous  ganglion  of,  689 
roots  of,  517,  518 
superficial  origin  of,  689 
in  tongue,  771,  1007 
glutfeus  inferior,  649 

superior,  649 
gluteal,  of  small  sciatic,  657 
hsemorrhoidalis  inferior,  659 
to  hamstring  muscles,  649 
of  heart,  692,  708.     See  also  Nn.,  cardiac 
of  hip-joint,  from  accessory  obturator,  647 
from  anterior  crural,  646 
from  obturator,  644 
from  nerves  of  sacral  plexus,  649,  652 
to  humerus,  627 
hypogastric,  of  ilio -hypogastric,  642 

of  aortic  plexus,  712,  714 
hypoglossus,  696 

ansa  hypoglossi  of,  697 
communications  of,  696 
deep  origin  of,  515 
descending  branch  of,  697 
development  of,  700 
nucleus  of,  515 

relation  of,  to  fourth  ventricle,  488 
superficial  origin  of,  696 
surgical  anatomy  of,  1251 
in  tongue,  1006 
iliac,  of  N.  ilio-hypogastricus,  642 
ilio-hypogastricus,  642 
ilio-inguinalis,  642 
incisor,  685 
infra-clavicular,  625 
to  infra-hyoid  muscles,  617,  621 
infra-mandibular,  of  N.  facialis,  688 
infra-orbital,  of  N.  facialis,  688 
infra-orbitalis  of  N.  trigeminus,  682 


Nerve  or  Nerves — continued 
infra-trochlearis,  680 
intercostal,  635 

surgical  anatomy  of,  1267 
intercosto  ■■  brachialis.      See    N.,    intercosto- 

humeral 
intercosto-humeral,  636 
intermedins.      See   N.    facialis,    pars    inter- 
media of 
internal  cutaneous,  of  arm,  631 
surgical  anatomy  of,  1295 
lesser,  of  Wrisberg,  632 
of  thigh,  646 
to  interossei  muscles  of  foot,  651,  655 

of  hand,  631 
interosseous,  anterior,  628 
of  peroneal,  651 
posterior,  634 

surgical  anatomy  of,  1300 
interosseus    (antibrachii)  dorsalis.      See    N., 
interosseous,  posterior 
volaris.     Sea  N.,  interosseous,  anterior 
ischiadicus.     See  N.,  sciatic,  great 
of  Jacobson,  689 
jugularis,  707 

of  knee-joint,  from  anterior  crural,  646,  647 
from  obturator,  645 
from  peroneal,  651 
from  sciatic,  great,  650 
from  tibial,  652 
labial,  682 
labiales  anteriores,  643 

posteriores,  659 
to  lacrimal  canals,  741 
lacrimalis,  679 
of  large  intestine,  1075 
laryngeal,  external,  692,  971 

inferior,  692,  693.     See  also  N.,  laryngeal, 
morphology  of,  702  [recurrent 

internal,  692,  971 
in  tongue,  1007 
recurrent,  971 

surgical  anatomy  of,  1252 
sujjerior,  692 

morphology  of,  702 
surgical  anatomy  of,  1248 
laryngeus  inferior    .See  N.,  laryngeal,  inferior 

superior.     See  N.,  laryngeal,  superior 
lateral  cutaneous  of  thorax,  616 
to  latissimus  dorsi  muscle,  635 
to  levator  scapulae  muscle,  617,  620 
to  levator  ani  muscle,  from  perineal  nerve,  659 

from  pudendal  plexus,  657 
to  levator  palati  muscle,  683 
lingual,  of  ninth,  690 
morjjhology  of,  702 
of  tenth,  692 
of  twelfth,  698 
lingualis,  684 

surgical  anatomy  of,  1237 
in  tongue,  1006 
long  scrotal,  657.     See  also  N.,  perineal 
to  longus  colli  muscle,  621,  624 
lumbales.     See  Nn.,  lumbar 
lumbar,  607 

anterior  primary  divisions  of,  639,  647 
posterior  primary  divisions  of,  613 
lumbo-inguinalis.     See  N.,  crural,  of  genito- 
crural 
to  lumbricales  muscles,  of  foot,  654,  655 

of  hand,  629,  631 
of  lung,  694.     See  also  Plexus,  pulmonary 


1384 


INDEX. 


Nerve  or  Nerves — continued 
malar,  of  facial,  688 

of  superior  maxillary,  681 
mandibularis.     See  N.,  maxillary,  inferior 
massetericus,  683 
mastoid,  618 

maxillaris.     See  N.,  maxillary,  superior 
maxillary,  inferior,  683 

superior,  681 
meatus  auditorii  externi,  684 
medianus,  627 

surgical  anatomy  of,  at  elbow,  1298 
in  forearm,  1301 
in  upper  arm,  1295,  1296 
of  membrana  tympani,  751 
meningeal,  of  vagus,  692 
meningeus  (medius),  681 
mentalis,  685 

middle  cutaneous,  of  tliigli,  646 
to  muscles  of  abdominal  wall,  430 

of  arm,  335 

of  back,  392 

of  buttock,  370 

of  face,  399 

of  foot,  383 

of  forearm,  351 

of  hand,  351 

of  hyoid  bone,  409 

of  iris,  681 

of  leg,  383 

of  lower  limb,  669,  670 

of  mastication,  404 

of  orbit,  401 

of  pectoral  region,  327 

of  pelvis,  438 

of  perineum,  433 

of  pinna,  687 

prevertebral,  415 

of  thigh,  370 

of  thorax,  419 

of  tongue,  409 

between  trunk  and  upper  limb,  326 

of  shoulder,  331 

of  soft  palate,  692 

of  upper  limb,  667,  671 
musculo-cutaneous,  of  arm,  627 
variations  of,  673 

of  leg,  651 

topography  of,  1309 
musculo-cutaneus.  See  N.,  musculo-cutaneous, 

of  arm 
musculo-spiral,  632 

topograi)hy  of,  at  elljow,  1298 
in  upjjer  arm,  1295,  1296 

variations  of,  673 
myelinisation  of,  466,  470,  473,  537,  594 
mylo-hyoideus,  685 
nasal,  6'80 

external,  680 

inferior,  683 

of  infra -orbital,  682 

internal,  680 

superior,  683 
iiaso-ciliaris.     See  N.,  nasal 
naso-palatinus,  683,  1000 
to  obliqui  aWoniinis  muscles,  638 
obturator,  643 

accessory,  647 
to  obturator  extemus  muscle,  645 

intemus  muscle,  649 
obturatorius,  643 
occipital,  great,  612 


Nerve  or  Nerves — continued 

occipital,  great,  topography  of,  1253 

of  posterior  auricular,  687 

small,  618 

morjDhology  of,  622 

third,  612 
occipitalis  major.     See  N.,  occipital,  great 

minor.     See  N.,  occijoital,  small 

tertius.     See  N.,  occipital,  third 
to  occipito-frontalis  muscle,  687 
oculo-motorias,  676 

deejj  origin  of,  541 

development  of,  699 

morphology  of,  701 

superficial  origin  of,  533 
cesoj^hageal,  from  sympathetic,  710 

from  vagus,  695 
olfactorii.     See  Nn.,  olfactory 
olfactory,  675 

bulb  of,  569 

development  of,  587 
morphology  of,  703 
structure  of,  587 

development  of,  587,  698 

morjjhology  of,  703 

origin  of,  675 

termination  of,  723 

tract  of,  569,  675 
development  of,  587 
ojjhthalmicus,  679 

development  of,  701 
opticus,  675 

development  of,  698,  742 

morphology  of,  703 

origin  of,  552,  675 

retinal  portion  of,  676.     See  also  Eetina 

tract  of,  552.     See  also  Tract,  optic 
orbital,  of  Meckel's  ganglion,  683 

of  superior  maxillary,  681 
palatine,  j)osterior,  accessory,  683,  1000 
large,  683,  1000 
small,  683,  1000 
jDalatini,  1000 

palatinus  anterior.  See  N. ,  palatine,  posterior, 
large 

medius.     See  N.,  palatine,  posterior,  acces- 
sory 

jjosterior.     See  N.,  palatine,  posterior,  small 
j)ali3ebral,  682 
to  parotid  gland,  1011 
patellar,  647 

pathetic,  677.     See  also  N.  trochlearis 
perforans  coccygeus  major,  657 
perforating  cutaneous,  657 
2)ericardiac,  695 
l^erineal,  659 

of  fourth  sacral,  658 

of  small  sciatic,  657 

superficial,  659 
to  i)erinea]  muscles,  659 
])erinei.     See  N.,  perineal 
])eripheral,  607 
jjcroiuTUis  communis.     See  N.,  peroneal 

l)rofundus.     See  N.,  tibial,  anterior 

suj)erficialis.     See  N.,  muscido-cutaneous, 
of  leg 
peroneal,  648,  650 

communicating,  650 
to  peroneus  brevis,  651 

longus,  651 
petrosal,  great  deep,  687,  707 

small  deep,  689,  707 


INDEX. 


1385 


Nerve  or  l>^Gvves— continued 

petrosal,  superficial,  external,  687 
large,  686 
small,  687,  689 
petrosusprofinidus.  (S'et'N., petrosal, great deejj 
superficialis  major.    See  N.,  petrosal,  super- 
ficial, large 
minor.      See    N.,    2)etrosal,    superficial, 
small 
pharyngeal,  1037 

of  Meckel's  ganglion,  683 
of  ninth  nerve,  690 
of  symjjathetic,  707 
of  vagus,  692 
phrenicus,  621 

surgical  anatomy  of,  1251 
of  pinna,  746 
to  piriformis  muscle,  649 
l)lantar,  external,  654 

surgical  anatomy  of,  1312 
internal,  654 

surgical  anatomy  of,  1312 
l^lantaris  lateralis.     See  N.,  plantar,  external 

medialis.     See  N.,  j^lantar,  internal 
pneumogastric,  690.     See  also  N.,  vagus 
popliteal,  external,  648,  650 

surgical  anatomv  of,  1304,  1308 
internal,  648,  652  " 

surgical  anatomy  of,  1305 
to  prevertebral  muscles,  617,  621 
to  psoas  muscle,  642 
pterygoideus  externus,  683 

internus,  683 
pterygo-palatine,  683 
pudendal,  inferior,  657 
pudendus.     See  N.,  pudic 
pudic,  658 
pulmonary,  989 

from  symjDathetic,  709 
from  vagus,  691 
to  2:)yramidalis  abdominis  muscle,  639 
to  quadratus  femoris  muscle,  649,  652 

lumborum  muscle,  642 
radial,  634 

surgical  anatomy  of,  1301 
radialis.     See  N.,  musculo-spiral 
to  radio-carpal  joint,  628 
to  radius,  628 
of  rectum,  1096 
recurrens  (vagi).     See  N.,  vagus  (meningeal 

branch  of) 
to  rhomboids,  625 

sacral,  607.     See  also  Plexus,  lumbar,  sacral 
anterior  primary  divisions  of,    647,    655. 

See  also  Plexus,  sacral,  ^^ndendal 
posterior  primary  divisions  of,  613 
visceral  branches  of,  711,  714 
sacrales,  607 
■  sacro-coccygeal,  anterior,  658 

posterior,  614 
saphenous,  long,  646 

surgical  anatomy  of,  in  foot,  1312 
in  leg,  1310 
in  thigh,  1308 
short,  653 

surgical  anatomy  of,  1312 
saphenus.     See  N.,  saphenous,  long 
to  scaleni  muscles,  617,  620,  621 
to  scalp  muscles,  399 
scapular,    posterior,    625.     See    also    N.,  to 

rhomboids 
sciatic,  great,  647,  648 


Nerve  or  Nerves — continued 

sciatic,  great,  surgical  anatomy  of,  1303,  1304 
small,  655 

surgical  anatomy  of,  1304 
scrotales  anteriores,  643 

posteriores,  659 
segmental,  of  head,  701 
to  semicircular  canals,  689 
to  short  muscles  of  little  finger,  631 

of  thumlj,  629,  631 
to  shoulder-joint,  from  circumflex,  632 

from  su2)rascapular,  625 
of  skin,  774 

of  small  intestine,  1070,  1073 
spermaticus   externus.      See   N.,  genital  ^(of 

geni  to-crural) 
spheno-palatini,  681 
to  sphincter  ani  muscle,  657,  659 

puijillpB  muscle,  731 
spinal  accessory,  695 
accessory  jjart  of,  695 
development  of,  700 
morphology  of,  702 
deep  origin  of,  516 
development  of,  700 
medullary  part  of,  516 
morphology  of,  701,  702 
nucleus  of,  517 
spinal  part  of,  516,  695 
develojsment  of,  700 
morphology  of,  702 
superficial  origin  of,  482,  695 
surgical  anatomy  of,  1251 
spinales,  607  .^ 

anterior  primary  divisions  of,  609,  615 
classification  of,  607 
development  of,  660 
distribution  of,  general,  610,  616 
to  lijnb-muscles,  667,  671 
to  skin  of  limbs,  665,  671 
formation  of,  662 
ganglia  of,  608 
grey  rami  of,  615,  616 
of  brachial  plexus,  623 
of  cervical  plexus,  617,  620 
of  lumbo-sacral  jjlexus,  639 
of  pudendal  plexus,  655 
of  sacral  plexus,  647 
of  thoracic,  636,  637,  638 
morphology  of  primary  divisions  of,  614 
number  of,  608 
origin  of,  455,  461,  608 
posterior  primary  divisions  of,  610,  662 
recurrent  branches  of,  609 
relation  of,  to  meninges,  609 

to  vertebras,  1289 
roots  of,  608.     See  also  Nerve-roots 
dorsal,  608 

development  of,  661 
ventral,  608,  609 
development  of,  661 
segmental  disjjosition  of,  610,  614 
size  of,  608 

somatic  i)ortion  of,  615,  662,  709 
splanchnic  jjortion  of,  615,  662,  709 
visceral  branches  of,  609,  662 
white  rami  of,  609,  615,  704 
development  of,  715 
of  lumbar  and  sacral  nerves,  640,  711 
of  pudendal  j^lexu.?,  655 
of  sacral  jjlexus,  647 
of  thoracic,  637,  638,  709,  710 


1386 


INDEX. 


Nerve  or  Nerves — continued 

spinosus.     See    N.,    maxillary,    inferior    (re- 
current meningeal  branch  of) 
splanclmic,  710 
great,  710 
least,  710 
small,  710 
splanchnicus  imus.     See  N.,  splanchnic,  least. 
major.     See  N.,  splanchnic,  great 
minoi'.     See  N.,  splanchnic,  small 
stapedius,  687,  758 
sternal,  descending,  617,  619 

morphology  of,  622 
to  sterno-mastoid  muscle,  617,  619 

from  spinal  accessory,  696 
of  stomach,  1060 
to  stylo-pharyngeus  muscle,  690 
subclavius,  624 
of  sublingual  gland,  685,  1013 
sublingualis,  685 
of  submaxillary  gland,  1012 
suboccipitalis,  611 
ganglion  of,  608 
morphology  of,  614 
subscapular,  long,  635 
lower,  635 
short,  635 
subscapulares,  625,  635 
supraclavicular,  of  brachial  plexus,  624 

of  cervical  plexus,  618 
supraclaviculares,  618 

anteriores.     See    Nn.,   supraclavicular,    of 
cervical  plexus  (sternal  branches  of) 
medii.     See  Nn.,  supraclavicular,  of  cervi- 
cal plexus  (clavicular  branches  of) 
posteriores.     See  Nn.,  supraclavicular,    of 
cervical  plexus  (acromial  branches 
of) 
supramandibular,  688 
supraorbitalis,  679 

surgical  anatomy  of,  1224 
suprascapularis,  624,  625 

variations  of,  673 
supratroclilearis,  679 

surgical  anatomy  of,  1223 
sural,  of  peroneal,  650 
of  small  sciatic,  657 
suralis.     See  N.,  saphenous,  short 
sympathetic,  703.     See  also  Sympathetic 
of  taste,  771 

temporal,  of  auriculo-temporal,  684 
deep,  683 
of  facial,  687 
of  orbital,  681 

topography  of,  1224 
temporales    profundi.     See    Nn.,    temporal, 

deep 
to  tensor  palati  muscle,  686 
tympani  muscle,  686,  757 
fasciie  lat;e  muscle,  649 
tensoris  tym])ain,  686,  657 

veli  palatini,  686 
tentorii,  679 

to  teres  minor  muscle,  632 
thoracales.     See  Nn.,  thoracic 
thoracalis  longus.     See  N.,  tlunucic,  long 
thoracic,  607 

anterior  primary  divisions  of,  635 
cutaneous  branches  of,  638 
of  first,  636 
of  second,  636 
of  twelfth,  639 


Nerve  or  Nerves — contimied 

thoracic,  communications  of,  636,  638 
external  anterior,  626 
first,  635 

internal  anterior,  626 
long,  625 

muscular  branches  of,  638 
of  first,  635 
of  second,  636 
of  twelfth,  639 
posterior  primary  divisions  of,  613 

cutaneous  branches  of,  613 
second,  636 
twelfth,  638 
thoraco-dorsalis.     See  N.,  subscapular,  long 
to  tibia,  653 
tibial,  648,  650,  652 
anterior,  651 
communicating,  653 
posterior,  652 
recurrent,  650 
tibialis.     See  N.,  tibial 
to  tibio-fibular  joint,  from  peroneal,  651 

from  tibial,  653 
of  tongue,  1006 
of  tonsil,  1036 

to  transversalis  abdominis,  638 
to  trapezius  muscle,  617,  620 
from  spinal  accessory,  696 
to  triangularis  sterni  muscle,  638 
trifacial,  678.  •  See  also  N.,  trigeminal 
trigeminal,  678,  686 
ascending  root  of,  525 
deep  origin  of,  524,  525 
development  of,  699 
divisions  of,  679 
Gasserian  ganglion  of,  679 
mesencephalic  root  of,  526,  540 

in  pons,  504 
morphology  of,  701 
motor  root  of,  504,  678 
development  of,  699 
morphology  of,  701 
nuclei  of,  524 

development  of,  527,  528 
of  mesencephalic  root  of,  540 
in  pons,  503 
sensory  root  of,  504,  524,  678 
development  of,  699 
morjjhology  of,  701 
spinal  root  of,  502,  525 

develoj)ment  of,  528 
superficial  origin  of,  486,  524 
trigeminus.     See  N.,  trigeminal 
trochlearis,  677 

communications  of,  678 
deep  origin  of,  540 
development  of,  699 
morphology  of,  701 
nucleus  of,  541 
superficial  origin  of,  487,  677 
tympanicus,  689,  758 
morphology  of,  702 
to  ulna,  628 
ulnar,  629 

surgical  anatomy  of,  at  elbow,  1298 
in  palm,  1301 
in  upper  arm,  1296 
collateral,  633 
communicating,  629 
to  utricle,  689 
utricularis.     See  N.,  to  utricle 


INDEX. 


1387 


Nerve  or  Nerves — continued 
vagus,  690 

abdominal  branches  of,  693 
afferent  fibres  of,  517 

root  of,  700,  702 
branches  of,  691 
cardio-inhibitory  fibres  of,  696 
communications  of,  692,  693 
deep  origin  of,  517 
development  of,  700 
efferent  fibres  of,  517 

root  of,  700,  701,  702 
ganglion  of  root  of,  692 

of  trunk  of,  692 
in  jugular  foramen,  690 
left,  in  thorax,  691 
morpliologv  of,  702 
in  neck,  690,  692 
nucleus  of,  517,  518 

relation  of,  to  fourth  ventricle,  488 
right,  in  thorax,  691 
roots  of,  517 

development  of,  700 
morphology  of,  701 
superficial  origin  of,  482,  690 
surgical  anatomy  of,  1251 
termination  of,  in  coats  of  stomach,  1060 
in  thorax,  691 
viscero-motor  fibres  of,  696 
vesicales,  714 
vestibuli,  689,  768 

connexion  of,  with  cerebellum,  521 
deep  origin  of,  519,  521 
descending  root  of,  520,  522 
nucleus  of,  519,  521 

relation  of,  to  fourth  ventricle,  488 
Vidian,  origin  of,  687,  707 

termination  of,  682 
zygomatico-facialis,  681 
zygomatico-temporalis,  681 
zygomaticus.     See  N.,  orbital 
Nerve-cells,  445 

axons  of,  445.     See  also  Axon 

bipolar,  448 

cellulipetal  processes  of,  449 

of  cerebellum,  512 

of  cerebral  cortex,  585 

dendrites  of,  447 

develojjment  of,  447,  471 

ganglionic,  448 

of  Golgi,  of  cerebral  cortex,  586 

of  spinal  cord,  464 
processes  of,  445 
of  Purkinje,  512,  514 
radicular,  464 
of  spinal  cord,  445,  461 

ganglia,  608 
of  sympathetic  ganglia,  704 
unipolar,  448 
Nerve -fibres,  444 
afferent,  445,  451 
collateral,  445,  448 
efferent,  445,  451 
myelinisation  of,  466 

order  of  occurrence  of,  in  sjjinal  cord,  473 
of  posterior  longitudinal  fasciculus,  537 
of  pyramidal  tract,  470 
of  sensory,  594 
non-medullated,  444 
primitive  sheath  of,  444 
splanchnic,  afferent,  705,  706,  710 
in  thoracic  region,  709 


Nerve-fibres,  splanchnic,  efferent,  704,  706,  710 
in  thoracic  region,  709 
periplieral,  705 
symjjathetic,  704 
cervical,  706 
destinations  of,  704 
medullated,  704 
non-medullated,  705 
splanchnic,  704,  705,  706 
terminations  of,  444,  448 
Wallerian  degeneration  of,  466 
Nerve-roots,  443 
cranial,  443 
spinal,  454,  608 

development  of,  660 
anterior,  443,  455,  608 
develoi^ment  of,  473,  661 
origin  of,  461 

relation  of,  to  sympathetic,  704 
posterior,  443,  455,  609 
development  of,  473,  661 
in  posterior  column  of  cord,  466 
relation  of,  to  sj-mpathetic,  704 
Nervous  system,  443 

cerebro  -  spinal,    443.      See   also    Cerebro- 
spinal 
sympathetic,  703.     See  also  Sympathetic 
Neural  arch.     See  Vertebral  arch 
arteries,  of  gluteal,  851 

of  iutercostals,  838 
canal,  76,  90 
crest,  21 
ectoderm,  28 
fold,  21 
groove,  20,  21 
tube,  21,  471 

alar  lamina  of,  472,  480 
in  fore- brain,  594 
in  hind-brain,  526,  527 
in  mid -brain,  542 
relation  of,  to  origin  of  nerves,  698 
basal  lamina  of,  472,  480 
in  fore-brain,  594 
in  liind-brain,  526 
in  mid -brain,  542 
relation  of,  to  origin  of  nerves,  698 
cellular  buds  of,  661 
central  canal  of,  471,  472 
development  of  cranial  nerves  from,  698 

of  spinal  nerves  from,  661 
ependymal  layer  of,  472 
flexures  of,  479 
limiting  membrane  of,  external,  471 

internal,  471 
mantle -layer  of,  472 
mid-dorsal  lamina  of,  471,  526 
mid-ventral  lamina  of,  471,  526 
myelospongium  of,  472 
neuroblasts  of,  472,  527,  528 
peripheral  reticular  layer  of,  472 
Neurenteric  canal,  20 
Neuroblasts,  22,  447 
N  euro-central  s\aichondrosis,  92 
Neuro-fibrillse,  449,  468 
Neuroglia,  451,  461,  465 
Neurolemma,  444 
Neurology,  3 
Neuromeres,  22 
Neuron,  22,  448,  449 
Nictitating  membrane,  738 
Nipple,  1207,  1208 
Nodule  of  cerebellum,  507,  508 


1388 


INDEX. 


Nodule  of  cerebellum,  development  of,  530 
Noduli  aggregati  processus  vermiformis,  1081 

lymphatici  aggregati.     See  Peyer's  patches 
intestini  recti,  1093 
lieuales.      See    Malpigliian    corpuscles    of 

spleen 
solitarii.     See  Solitary  glands 

valvularum     semilunarium.        See      Corpus 
Arantii 
Nodulus.     See  Nodule  of  cerebellum 
Norma  basalis,  159 

frontalis,  146 

lateralis,  151 

occiijitalis,  157 

verticalis,  158 
Nose,  717 

ala  of,  717 

alar  sulcus  of,  717 

arteries  of,  717,  723 

bridge  of,  717,  1237 

cartilages  of,  717 

develojiment  of,  38 

floor  of,  1239 

fossae  of,  170,  176,  719.     See  also  Nasal  fossae 

hiatus  semilunaris  of,  1239 

infuudibulum  of,  721 

limen  of,  719 

lymjAatics  of,  717,  723 

meatuses  of,  720.     See  also  Meatus 

mucous  membrane  of,  722 

muscles  of,  397 
action  of,  399 
nerve-supply  of,  399 

nasal  index  of,  717  ;  Appendix  D,  xviii 

nerves  of,  717,  723 

olfactory  part  of,  720,  722 

outer,  717 

respiratory  part  of,  720,  722 

septum  of,  717,  720 

surgical  anatomy  of,  1239 

surgical  anatomy  of,  1239 

veins  of,  879 

ventricle  of,  719 

vestibule  of,  719 

vessels  of,  723 
Nostril,  717 
Notch,  cotyloid,  216,  218 

variations  in.  Appendix  B,  xi 

ethmoidal,  104 

intercondylic,  of  femur,  227 

nasal,  103 

pr* -occipital,  562 

jjterygoid,  126 

of  Rivinus,  750,  1232 

sacro-sciatic,  213,  216 

scapular,  great,  185 

sigmoid,  143 

spheno -palatine,  139 

of  spleen,  1212 

supraorbital,  103 

suprascapular,  184 

suprasternal,  95 

umbilical,  1114 
Notochord,  24,  90,  Appendix  E,  xx 
Notochordal  area,  23 
Nuclial  furrow,  1253 

lines,  108,  153,  158 

plane  of  occipital  Ijone,  109,  153,  158 
Nuck,  canal  of,  1190 
Nuclear  layer  of  retina,  732,  733 

membrane,  8,  9,  10 

juice,  8 


Nucleolus,  8,  9,  10 

Nucleus  or  Nuclei,  of  abducent  nerve,  502,  524 
relation  of,  to  j)osterior  longitudinal  fasci- 
culus, 537,  538 
ambiguus,  518 

amygdalas.     See  Nucleus  amygdaloid 
amygdaloid,  576,  579,  582 
anterior  thalami,  545 
arcuatus,  498 

development  of,  528 
thalami,  545 
of  auditory  nerve,  519.     See  also   Nucleus, 

cochlear,  vestibular 
of  Bechterew,  520 
caudatus,  574,  579 
of  cells,  8 

during  mitosis,  10,  13 
segmentation,  17 
central,  of  Luys,  545,  546.     See  also  Corpus 

subthalamicum 
cochlear,  519,  520 

development  of,  699 
colliculi  inferioris.  See  Corpora  quadrigemina, 

nuclei  of 
corporis  geniculati  lateralis,  546 
medialis,  538 
mamillaris,  548,  572 
cuneate,  492,  494 
development  of,  528 
relation  of,  to  arcuate  fibres,  496 
surface  elevation  of,  485 
of  Deiters,  520 

function  of,  521 
dentatus,    510,   511.      See   also  Corpus  den- 

tatum 
dorsalis.     See  Clarke,  column  of 
emboliformis,  510 
facial,  502,  523 
of  fasciculus  solitarius,  518 
fastigii,  510.     See  also  Nucleus,  roof 
funiculi    cuneati,    492.       See   also    Nucleus, 
cuneate 
gracilis,  492.     See  also  Nucleus,  gracile 
globosus,  510 
glosso-pharyngeal,  517 

relation  of,  to  fourth  ventricle,  488 
gracile,  492 

relation  of,  to  arcuate  fibres,  496 

to  fillet,  494 
surface  elevation  of,  485 
habenula3.     See  Ganglion  habenulse 
hypoglossal,  515 

relation  of,  to  fourth  ventrical,  488 
hypothalamicus.       See   Nucleus,   central,  of 

Luys 
intercalatus,  488 
laryngeal,  517 
lateralis  (of  medulla),  498 

tlialami,  545 
of  lateral  fillet,  505,  521 
lemnisci   lateralis.     See   Nucleus,    of  lateral 

fillet 
lenticular,  580 

lentiformis.     See  Nucleus,  lenticular 
lentis,  737 

medialis  thalami,  545 
of  medulla  oblongata,  490 
dev(!lopment  of,  527 
surface  elevations  of,  488 
of  mesencephalon,  534,  535,  536 
motor,  515 
motorii  nervi  trigemini,  525 


INDEX. 


1389 


Nucleus    or    Nuclei,    nervi    aliducentis.      See 
Nucleus  of  abducent  nerve 
acustici.     See  Nucleus  of  auditory  nerve 
cochlearis.     See  Nucleus,  cochlear 
facialis.     See  Nucleus  of  facial  nerve 
hypoglossi.     See  Nucleus,  hypoglossal 
oculomotorii.     See  Nucleus,  oculomotor 
trochlearis.     See  Nucleus,  trochlear 
vestibularis.     Sec  Nucleus,  vestibular 
oculo-motor,  537,  541 

olivaris    accessorius  dorsalis.       See    Nuclei, 
olivary,  accessory 
medialis.     See  Nuclei,  olivary,  accessory 

inferior,  494 
develoi3nient  of,  528 

relation  of,  to  cerebello-olivary  fibres,  497 
surface  elevation  of,  484 
superior,  502 

pedicle  of,  521,  524 
relation  of,  to  corpus  trapezoides,  520 
to  lateral  fillet,  538 
to  nucleus  of  lateral  fillet,  505 
olivary,  accessory,  495,  498,  526 

inferior,    494.     See  also   Nucleus   olivaris 

inferior 
superior,  502.     See  also   Nucleus   olivaris 
superior 
of  optic  nerve,  552 
of  origin  of  nerves,  515 
development  of,  527 
originis.     See  Nuclei  of  origin  of  nerves 
of  pons,  502,  504 
pontis,  499,  500 

development  of,  528 

relation  of,  to  transverse  fibres  of  pons,  501 
puljjosus,  262 
pyramidal,  490 

radicis  descendentis  nervi  trigemini,  526 
red,  536,  546 
roof,  510 

relation  of,    to   direct    sensory   cerebellar 
tract,  521 
ruber.     See  Nucleus,  red 
salivary,  524 
segmentation,  17 
spinal  accessory,  516 
tegmenti,  535 
terminales,  514,  527 
of  termination  of  nerves,  514,  527 
thalamic,  544 
tractus  solitarii,  517 

spinalis  nervi  trigemini,  525 
trapezoideus,  520 
trigeminal,  504,  524,  525,  540 

develoj)nient  of,  528 
trochlear,  541 

relation  of,  to  posterior  longitudinal  fasci- 
culus, 537 
vagus,  517,  518 

relation  of,  to  fourth  ventricle,  488 
vestibular,  519,  521 

relation  of,  to  fourth  ventricle,  488 
Nuel,  space  of,  767 
Nutrient  arteries.     See  Arteries 
Nutritive  j3ole,  11 
Nymphas,  1195 

Obelion,  158  ;  Appendix  D,  xvi 

Obex,  512 

Oblique  ligament,  283 

line,  anterior,  of  radius,  199 
external,  of  jaw,  142 


Oblique  line  of  tibia,  233 
ridge  of  clavicle,  183 
vei]i  of  Marshall,  785,  871 
Obliquus  extern  us  abdominis  muscle,  421 
inferior  of  neck.       See    Musculus    obliquus 
capitis  inferior 
of  orbit,  400 
internus  abdominis  muscle,  424 
superior  muscle  of  neck.     See  Musculus  ob- 
liquus capitis  superior 
of  orbit,  400 
action  of,  401 
nerve-sujjply  of,  401 
Obliterated  hypogastric  artery,  851 
Obturator  artery,  852 

abnormalities  of,  953 
canal,  293 
crest,  217 

externus  muscle,  363 
action  of,  370,  393 
nerve-sujjply  of,  370 
fascia,  434 
foramen,  212,  218 
fossa,  1143 
gland,  921 
groove,  218 

abnormalities  of,  ApjDendix  B,  xi 
internus  muscle,  366 
action  of,  370,  393 
nerve-supply  of,  370 
membrane,  293 
nerve,  643 

accessory,  647 
plexus,  644,  646 
tubercle,  anterior,  218 

p)Osterior,  218 
vein,  895 
Occijiital  angle  of  parietal  bone,  108 
arteries.     See  Arteries 
bone,  108 

architecture  of,  AjJiJendix  A,  i 
basilar  part  of,  108,  110,  163 

ossification  of.  111 
condylic  parts  of,  108,  109 

ossification  of,  112 
connexions  of.  111 
morphology  of,  Ajjjaendix  E,  xxii. 
ossification  of.  111 
relation  of,  to  sutures,  153,  157 
tabular  part  of,  108 

ossification  of.  111 
variations  in.  Appendix  B,  viii 
condyles,  109,  165 

third,  AjDjiendix  B,  ix 
crest,  external,  109 
internal,  109,  169 
fontanelle,  Ajsi^endix  E,  xxii 
lobe,  564 

tojjography  of,  1225 
lymjihatic  glands,  909 
nerves.     See  Nerves 
plane,  108,  153 
point,  170  ;  Aj^pendix  D,  xvi 
protuberance,  external,  108,  153,  158 

internal,  109,  169 
sinus,  886 

abnormalities  of,  954 
sulcus,  566.     See  also  Sulcus 
triangle,  1253 
vein,  876,  879 
Occijjito-atloid  joint,  266 
movements  at,  393 


1390 


INDEX. 


Occipito-atloid  ligaments,  266 
Occipito-axoid  ligaments,  266 
Occipito-frontal  strand,  590 
Occipito-frontalis  muscle,  395 
action  of,  399 
nerve-supply  of,  399 
Occipito-mastoid  suture,  151,  165 
Occipito-temporal  gyrus,  566,  567 

sulcus,  566,  567 
Oculo-motor  nerve,  676 
deA'elopment  of,  699 
morphology  of,  701 
nucleus  of,  537,  541 
sulcus,  533 
Oculo-nasal  sulci,  39 
OcLilus.     See  Eye 
Odontoblasts,  1025,  1026,  1028 

processes  of,  1024 
Odontoid  ligaments,  267 
process,  80 

ossification  of,  93 
(Esophageal  arteries  of  aorta,  839 
of  coronary,  844 
of  inferior  thyroid,  823 
morphology  of,  942 
groove  of  liver,  1112 

of  lung,  987 
opening  of  diaphragm,  419 
orifice  of  stomach,  1055 
plexus,  691,  695,  1040 
veins,  1042 
(Esophagus,  1038 

abdominal  portion  of,  1040 
cervical  portion  of,  1039 

surgical  anatomy  of,  1252 
constrictions  of,  1039,  1041 
development  of,  1042 
diaphragmatic  division  of,  1040 
glands  of,  1042 
relations  of,  1039,  1040 
structure  of,  1041 
surgical  anatomy  of,  1264 
thoracic  part  of,  1039 
variations  in,  1041 
vessels  of,  1042 
Olecranon.     See  Olecranon  process 
fossa,  192 
process,  194 

topography  of,  1296 
Olfactory  area,  593 
bulb,  569 

development  of,  698 
mor2>ho]ogy  of,  703 
structure  of,  587 
bundle,  572 
ceUs,  698,  722,  723 
cleft,  1239 
ganglion,  698 

morpliology  of,  703 
glands.     See  (jlands  of  Bowman 
groove,  129,  166 
hairs,  723 
lol)e,  569 

deve]o])meiit  of,  479,  596 
relation  of,  to  anterior  commissure,  588 
nerve,  675.     See  also  Nerves 
pits,  38 
sulcus,  562 
tract,  569 

development  of,  698 
structure  of,  587 
tubercle,  670 


Oligolecithal  ovum,  11 
Oliva.     See  Olivary  eminence  of  medulla 
Olivary  eminence  of  medulla,  484 
of  sphenoid,  122,  168 
nucleus,  494.     See  also  Nucleus 
Omental  sac,  1102 

tuberosity  of  liver,  1113 
of  pancreas,  1127 
Omentum,  1049 
gastro-colic,  1049 
gastro-hepatic,  1050,  1116 
gastro-splenic,  1057,  1099,  1104,  1212 
development  of,  1108 
relation  of,  to  lesser  sac,  1102 
great,  1057,  1099,  1104 
development  of,  1107 
relation  of,  to  duodenum,  1067 
to  lesser  sac,  1102 
to  transverse  colon,  1083 
majus.     See  Omentum,  great 
minus.     See  Omentum,  small 
small,  1055,  1057,  1099,  1104,  1116 
development  of,  1107,  1124 
relation  of,  to  lesser  sac,  1102 
Omohyoid  muscle,  405 
action  of,  410 
nerve-supjDly  of,  409 
Ontogeny,  1 
Oocyte,  12 

of  first  order,  12,  15 
of  second  order.  13,  15 
Oogonia,  12,  15 
Oolemma,  11 
Oosperm,  17 

Opercula  insula;,  556,  561 
Ophryon,  Apj)endix  D,  xvi 
Ophthalmic  artery,  815 
abnormalities  of,  950 
nerve,  679 

morphology  of,  701 
veins,  879 
Opisthion,  165  ;  Ajipendix  D,  xvi 
Opponens  digiti  quinti  muscle,  346 
action  of,  352 
nerve-supply  of,  351 
minimi  digiti  muscle.     See  Opponens  digiti 

quinti  muscle 
poUicis  muscle,  343 
action  of,  353 
nerve-supply  of,  351 
Optic  axis,  724 
chiasma,  475,  676 

development  of,  595,  699 
morphology  of,  703 
commissure,  676.     See  also  Optic  chiasma   • 
cup,  698,  703 

of  optic  disc,  731 
disc,  731 
foramen,  123,  147,  168 

abnormalities  of,  Appendix  B,  ix 
groove,  122 
nerve,  675 

deep  connexions  of,  551 
development  of,  595,  698,  742 
morjjhology  of,  703 
in  retina,  731 
radiation,  553,  583,  591 
recess,  551,  595 
stalk,  478,  698,  741 

morphology  of,  703 
thalamus,  542.     See  also  Thalamus 
tract  532.     See  also  Tract 


INDEX. 


1391 


Optic  vesicle,  478,  741 

pigmentary  layer  of,  742 
Ora  serrata,  731 

structure  of,  735 
Oral  pharynx,  1032,  1034 
Orbicular  ligament,  282 
Orbicularis  oris  muscle,  398,  996 
action  of,  399 
nerve-supjjly  of,  399 
jialpebrarum  muscle,  397 
Orbiculus  ciliaris,  729 
Orbit,  147,  175 
fascia  of,  399 
muscles  of,  399 
action  of,  401 
morphology  of,  441 
nerve-supply  of,  401 
veins  of,  879 
Orbita.     See  Orbit 

Orbital  artery  of  middle  meningeal,  811 
of  superficial  temjioral,  810 
canals.     See  Ethmoidal  canals 
fossa,  147 
gyri,  562 

index,  A2)pendix  D,  xviii 
margin,  103 

sexual  differences  in,  180 
nerves,  681,  683 
plate  of  ethmoid  bone,  128,  149 

of  frontal  bone,  104,  147 
process  of  zygomatic  bone,  141 
of  palate  bone,  138,  139,  149 
septum,  739 
sulcus,  562 

wings  of  sphenoid,  123 
Orbito-maxillary  frontal  suture.  Appendix  B,ix 
Orbito-nasal  centre,  137 
Orbito-sphenoids,  126  ;  Appendix  E,  xxi 
Orbito-tarsal  ligaments,  1239 
Organ  of  Corti,  766.     See  also  Corti,  organ  of 
epibranchial,  701,  702 
of  Jacobson,  41,  720 
of  lateral  line,  701 
of  Roseaimiiller,  1187 
Organon  spirale  (Cortii).     See  Organ  of  Corti 
vomero-nasale    (Jacobsoni).       See    Organ   of 
Jacobson 
Orifice,  aortic,  791 

topography  of,  1262 
mitral,  788,  790 
level  of,  1290 
topography  of,  1262 
pulmonary,  789,  790 

topograjjiiy  of,  1262 
tricuspid,  787,  789 
level  of,  1290 
topography  of,  1262 
Orificium  externum  uteri.     See  Os  uteri   ex- 
ternum 
internum  uteri.     See  Os  uteri  internum 
urethrse  externum.     See  Meatus  urinarius 
Origin  of  muscles,  318 
Oro-glossus  muscle,  1242 
Orthocephalic  skulls.  Appendix  D,  xvii 
Orthognathous  skulls.  Appendix  D,  xviii 
Os,  995.     See  also  Mouth 
uteri  externum,  1188 
internum,  1188 
Os  or  ossa,  breve      See  Bone,  short 
calcis.     See  Calcaneus 
capitatum.     See  Os  magnum 
carpale,  Appendix  F,  xxiv 


Os  or  ossa,  carjji.     See  Bones,  carpal 
centrale,  Ajjpendix  B,  xi 

morphology  of.  Appendix  F,  xxiv 
clitoridis,  1198 
coccygis.     See  Coccyx 
cordis,  789 
costale.     See  Ribs 
00X83.     See  Innominate  bone 
cranii.     See  Bones  of  skull 
cuboideum.     See  Cuboid  bone 
cuneiforme  primum.     See  Cuneiform  bone  ol 
foot,  tirst 

secundum.      See  Cuneiform  bone  of  fo(jt, 
second 

tertium.       See    Cuneiform    l)one   of    foot, 
third 
ethmoidale.     See  Ethmoid  bone 
extremitatis  inferioris.     See  Bones  of  lower 
limb 

superioris.     See  Bones  of  ujjper  limb 
faciei.     See  Bones  of  face 
fibulare,  Appendix  F,  xxiv 
frontale.     See  Frontal  bone 
hamatum,  205.     See  also  Unciform  bone 
hyoideum.     See  Hyoid  bone 
ilium.     See  Ilium 
Incse,  Ajjpendix  B,  viii 
intercuneiforme.  Appendix  B,  xiii 
interfrontale.  Appendix  B,  viii 
intermetatarsum,  Appendix  B,  xiii 
interparietale.  Appendix  B,  viii 
ischii.     See  Ischium 
Japonicum,  Ajjpendix  B,  x 
lacrimale.     See  Lacrimal  bone 
linguae.     See  Hyoid  bone 
longum.     See  Bone,  long 
lunatum,  202.     See  also  Semilunar  bone 
magnum,  205 

morphology  of.  Appendix  F,  xxiv 

ossification  of,  207 
metacarpalia.     See  Bones,  metacarpal 
metatarsalia.     See  Bones,  metatarsal 
multangulum  majus.     See  Trapezium 

minus.     See  Trapezoid  bone 
nasale.     See  Nasal  bone 

naviculare  manus.       See   Scaphoid   bone  of 
hand 

pedis.     See  Navicular  bone  of  foot 
occipitale.     See  Occipital  bone 
odontoideum.  Appendix  B,  vi 
orbiculare,  756 
j)alatinum.     See  Palate  bone 
parietale.     See  Parietal  bone 
penis,  1172 

pisiforme.     See  Pisiform  bone 
planum.     See  Bone,  flat 

of  ethmoid,  128 

relation  of,  to  orbit,  149 
variations  in.  Appendix  B,  ix 
pubis,  217.     Sec  also  Pubis 
radiale,  Appendix  F,  xxiv 
sacrum.     See  Sacrum 
sesamoidea.     See  Bones,  sesamoid 
sj)henoidale.     See  Sphenoid  bone 
subcapitulum.  Appendix  B,  xi 
sustentaculi,  Appendix  B,  xiii 
suturarum.     See  Bones,  sutu.ral 
tarsi.     See  Bones,  tarsal 
temporale.     See  Temporal  bone 
tibiale,  Appendix  F,  xxiv 
trigonum.  Appendix  B,  xii,  xiii ;  Appendix  F, 
xxiv 


1392 


INDEX. 


Os  or  ossa,  triquetrum,  203.    See  also  Cuneiform 
bone  of  hand 

ulnare,  Appendix  F,  xxiv 

Vesaleanum,  251,  Apjjendix  B,  xiii 

zygomaticuui,  140.     See  echo  Malar  bone 
Osseous  labyrinth,  759 
Ossicles,  ejjipteric,  133 

of  Kerkring,  112 
Ossicula  auditus,  754 
articulations  of,  756 
deA^eloi^ment  of,  757 
ligaments  of,  757 
movements  of,  758 
Ossification,  72 

of  larpigeal  cartilages,  961 

of  special  bones.     See  under  the  several  bones 
Osteoblasts,  73 
Osteoclasts,  74 
Osteology,  3,  69 

descrij^tive  terms  of,  70 
Ostium  abdominale  tuba;  uterinae,  1185 

pharyngeum  tubas  auditivae,  753,  754 

primum  of  heart,  930 

secundum  of  heart,  930 

tympanicum  tubse  auditivaa,  753 

uterinum  tubse,  1186 
Otic  ganglion,  685,  707 
development  of,  699 

vesicle,  769 
Otoconia,  763 
Ovarian  artery,  843.     See  also  Artery 

fimbria,  1184,  1186 

fossa,  1182 

ligament,  1184,  1190 

plexus,  714 

vein,  894 

abnormalities  of,  955 
morphology  of,  944 
Ovarium.     See  Ovary 
Ovary,  1182 

bursa  of,  1189 

connexions  of,  1183 

corpora  albicantia  of,  1184 

corpora  lutea  of,  1184 

descent  of,  1184 

development  of,  1204 

egg-tubes  of,  1184 

Graafian  follicles  of,  1184,  1204 

hilum  of,  1182 

ligament  of,  1184,  1190 

me.sovarium  of,  1182,  1184,  1189 

nerves  of,  1185 

ova  of,  1184.     See  also  Ovum 

poles  of,  1182 

position  of,  1182 

primitive  follicles  of,  1204 

stroma  of,  1184 

structure  of,  1184 

surgical  anatomy  of,  1283,  1284 

suspensory  ligament  of,  1183 

vessels  of,  1185 
Ovules  of  Naboth,  1191 
Ovum,  7,  10 

alecitlial,  11 

centrolecithal,  11 

eutolecitha],  11 

fertilisation  of,  16 

maturation  of,  12 

oligolecithal,  11 

in  ovary,  1184,  1204 

primitive,  1204 

relation  of,  to  decidua,  53 


Ovum,  segmentation  of,  17 
special  characters  of,  12 
telolecithal,  11 

Pacchionian  bodies,  602 
depressions,  108,  166 
Pacinian  corpuscles,  775 
Pad,  incisive,  998,  1000 

suctorial,  394,  399,  997 
Palatal  process,  136,  159,  171 
Palate,  998 

arches  of,  999,  1000,  1034 
bone,  138 

relation  of,  to  nasal  fossae,  170 
to  orbit,  149 
to  zygomatic  fossa,  155 
cleft,  137,  1013 

surgical  anatomy  of,  1240 
development  of,  40,  1013 
glands  of,  998,  999 
hard,  159,  176,  998 

surgical  anatomy  of,  1245 
incisive  pad  of,  998,  1000 
mucous  membrane  of,  999 
muscles  of,  412 

development  of,  441 
nerves  of,  1000 
pillars  of,  999,  1000,  1034 
raphe  of,  998 
ruga}  of,  998,  999 
soft,  998 

level  of,  1289 
taste-buds  of,  770 
tuberosity  of,  139, 
uvula  of,  999 
vessels  of,  1000 
Palatine  arches,  999,  1000,  1034 
aponeurosis,  999 

arteries,  809,  812.     See  also  Arteries 
canal,  accessory,  139,  161 

superior  openings  of,  157 
anterior,  136,  161,  172 
posterior,  135,  136,  161 
foramen,  greater  posterior,  161 
surgical  anatomy  of,  1246 
lesser  j^osterior,  139,  161 
fossa,  anterior,  136 
glands,  998,  999 
nerves,  683,  1000 
suture,  median,  161 

transverse,  161 
vein,  880 
Palato-ethmoidal  suture,  149 
Palato-glossus  muscle,  409 
action  of,  413 
nerve-supply  of,  413 
Palato-maxillary  canal,  135 
index.  Appendix  D,  xviii 
Palato-pharyngeus  muscle,  411 
action  of,  413 
nerve-supply  of,  413 
Palatum.     See  Palate 

durum.     See  Palate,  hard 
molle.     See  Palate,  soft 
Pallium.     See  Cerebral  cortex 
Palm,  surgical  anatomy  of,  1301 
Palmar  arcli,  deep,  836 

aljnormalities  of,  952 
morjjhology  of,  943 
surgical  anatomy  of,  1301 
superficial,  836 

abnormalities  of,  952 


INDEX. 


1393 


Palmar  arch,  superficial,  morphology  of,  943 
surgical  anatomy  of,  1301 
fascia,  338 

ligaments  of  carpal  joints,  285 
of  carpo-metacarpal  joints,  287 
of  metacarpo-phalangeal  joints,  288 
Palmaris  brevis  muscle,  336 
longus  muscle,  339 
action  of,  352 
nerve-supjily  of,  351 
Palpebrte.     See  Eyelids 
Palpebral  arteries,  816 
fissure,  738 
ligaments,  739 

surgical  anatomy  of,  1239 
nerves,  682 
veins,  740 
Pampiniform  plexus,  894,  1162 
Pancreas,  1124 
accessorium,  1128 
development  of,  1129 
duct  of,  1127 

termination  of,  1068,  1070 
accessory,  1128 
lesser,  1128 
lymphatics  of,  1129 
nerves  of,  1129 
omental  tuberosity  of,  1127 
peritoneal  relations  of,  1127 
processus  uncinatus  of,  1126 
structure  of,  1128 
surgical  anatomy  of,  1276,  1289 
variations  in,  1128 
vessels  of,  1128 
Pancreatic  artery,  844.     See  also  Arteries 

veins,  904 
Pancreatico-duodenal  arteries.     See  Arteries 

vein,  903 
Panniculus  adiposus,  318 

carnosus,  318,  395 
Papilla  or  Papillae,  bile,  1070,  1120 
conicee.     See  Filiform  pajDillee 
corii.     See  Papillte  of  skin 
dentis,  1026 

duodeni.     See  Papilla,  bile 
fungiformes.     See  Fungiform  papillae 
lacrimales,  738,  740 
lenticulares,  1003 
linguales.     See  Papillae  of  tongue 
mammae.     See  Nipple 
of  nail,  775 
nervi  optici,  731 
jiili,  777 
renalis,  1137 
of  skin,  773 

of  tongue,  1003.     See  also  Tongue 
of  tooth,  1025,  1026 
vallatae.     See  Circumvallate  papillae 
Paracentral  lobule,  562 
Parachordal  cartilages.  Appendix  E,  xxi 
Paradidymis,  1160 

origin  of,  1199 
Paraduodenal  fossa,  1069 
Paraflocculus,  509 
Parallel  sulcus,  567 

topography  of,  1224,  1225 
Paramastoid  process.  Appendix  B,  ix 
Paramedial  sulcus,  561 
Parametrium,  1191 
Parapophysis,  Appendix  C,  xiv 
Parapyramidal  fissure,  508 
Pararectal  fossa,  1090,  1101 

93 


Parasinoidal   sinuses,    603.      See  also   Lacunae 

laterales  of  longitudinal  sinus 
Parasternal  line,  1253 
Parathyroid  glands,  1218 
Para-urethral  duct,  1158,  1196 
Paravesical  fossa,  1101,  1155 
Paraxial  mesoderm,  26 
Parenchyma  testis,  1161 
Paries  carotica,  750 
jugularis,  749 
labyrintliica,  752 
mastoidea,  749 
membranacea,  750 
tegmentalis,  749 
Parietal  artery,  810 
bone,  106 

ossification  of,  108 
relation  of,  to  sutures,  157,  158 
variations  in.  Appendix  B,  viii 
eminence,  107,  152 

topography  of,  12-24 
foramen,  107,  157,  166 

abnormality  of.  Appendix  B,  viii 
gyri,  563.     See  also  Gyri 
lobe,  562 
Parieto-mastoid  suture,  151 
Parieto-occipital  arterv,  821 
fissure,  558,  559,  565 

topography  of,  1223,  1225 
Parieto-temporal  artery,  818 
Paroccipital  ^^I'ocess,  Appendix  B,  vi,  ix 
Paroophoron,  1187,  1199 
Parotid  artery,  of  posterior  auricular,  808 
of  superficial  temporal,  809 
duct,  1011 

surgical  anatomy  of,  1238 
fascia,  395,  1010 
gland,  1009 
accessory,  1011 
development  of,  1013 
duct  of,  1011 

surgical  anatomy  of,  1238 
nerves  of,  1011 
relation  of,  to  external  auditory  meatus, 

1230 
socia  of,  1011 
surgical  anatomy  of,  1238 
vessels  of,  1011 
lymphatic  glands,  910 
recess,  1010 
Parovarium,  1187,  1199 

Pars  abdominalis.     See  (Esophagus,  abdominal 
v'  portion  of 

et  pelvina  s.  sympathici.     See  Sympathetic 
system,  lumbar  and  sacral 
alaris  musculi  nasalis.      See  Muscle,  dilator 

naris 
analis  recti.     See  Anal  canal 
basilaris  ossis  occipitalis.     See  Occipital  bone, 

basilar  part  of 
basilaris  pontis.      See  Pons  Varolii,  ventral 

portion  of 
calcaneo-cuboidea.     See  Ligament,  calcaneo- 
cuboid, internal 
calcaneo-navicularis.    See  Ligament,  calcaneo- 

scaplioid,  external 
cavernosa.     See  Urethra,  spongy  portion  of 
centralis  of  lateral  ventricle,  574 
cephalica    et    cervicalis    s.    sympathici.     See 

Sympathetic  system,  cervical 
cervicalis.    See  Oesophagus,  cervical  portion  of 
ciliaris  retinae,  729,  731 


1394 


INDEX. 


Pars  ciliaris  retiiiiie,  development  of,  742 
convoliita.     See  Kidney,  labyrintli  of 
dorsalis    pontis.     See    Pons    Varolii,    dorsal 

portion  of 
flaccida  niembranjie  tynipani,  750 
frontalis    capsulas    interna.      See    Capsule, 
internal,  anterior  limb  of 
operculi,  556 
intermedia  of  Wrisberg,  522 
development  of,  699 
origin  of,  524 

relation  of,  to  chorda  tympani,  687 
to  geniculate  ganglion,  686 
to  vestibular  nerve,  689 
iridica  retiuaj,  730,  731 

development  of,  742 
lacrimalis.     See  Muscle,  tensor  tarsi 
laryngea.     See  Pharynx,  laryngeal 
mamillaris  hyjaothalami,  542 
membranacea.     See  Urethra,  membranous 
septi,  791 

abnormalities  of,  947 
nasalis.     See  Naso-jiharynx 
occipitalis    capsuliB    internfe.     See   Capsule, 

internal,  posterior  limb  of 
optica  hypothalami,  542 

retinae,  731 
oralis.     See  Pharynx,  oral 
orbitalis,  561 
j^arietalis  operculi,  556 
prima    nervi    facialis.     See    Nerve,    facial, 

radicular  part  of 
prostatica.     See  Urethra,  jjrostatic 
secunda    nervi    facialis.     See    Nejve,  facial, 

emergent  part  of 
temporalis  operculi,  556 
tensa  membranee  tymj)ani,  750 
thoracalis.        See      CEsophagus,         thoracic 
portion  of 
s.  sympathici.     See  Sympathetic  system, 
thoracic 
transversa.     See  Muscle,  dejjressor  alee  nasi 
triangularis,  561 
Patella,  229 

articular  surface  of,  297 
ligaments  of,  298 

relation  of,  to  fascia  lata,  355,  371 

to  quadriceps  (extensor)  femoris,  359 
topograj^hy  of,  1307 
topograjjhy  of,  1307 
Patellar  plexus,  647 

Pathetic  nerve,  677.     See  also  Nerve,  trochlear 
Pecten  ossis  ])i\\As      See  Pubic  crest 
Pectineal  line,  226 
Pectineus  muscle,  361 
action  of,  370,  371 
nerve-supjjly  of,  370 
Pectiniform  septum  of  penis,  1172 
Pectoral  artery,  829 
fascia,  322 

girdle.  Appendix  F,  xxv 
lymphatic  glands,  914 
region,  fascite  of,  322 

muscles  of,  323 
ridge,  190 
Pectoralis  major  muscle,  323 
action  of,  327,  331,  419 
nerve-su]>p]y  of,  327 
minimus,  325 
ininor  muscle,  325 

action  of,  327,  331,  419 
nerve-supply  of,  327 


Pedicles  of  A^ertebraj,  77 
cervical,  78,  80 
lumbar,  83 
thoracic,  81 
Peduncles     of     cerebellum,      510.      See     also 
Cerebellum 
of  cerebrum,  532 
of  corjjora  mammillaria,  548 
olivary,  495 
of  pineal  body,  547 

development  of,  594 
Pedun cuius  cerebri,  532 
Pelvic  colon,  1085,  1086 
toj^ograjDhy  of,  1274 
diajjhragm,  438 
fascite,  434,  1045 
girdle,  212 

morphology  of,  Apjjendix  F,  xxv 
mesocolon,  1086,  1100 
plexus,  714 
Pelvis,  219,  1045 
articulations  of,  289 
axis  of,  221 
brim  of,  221,  1045 
cavity  of,  1046 
diameters  of,  221,  223 
false,  219 
fascise  of,  433 
growth  of,  222 
inlet  of,  220 

sexual  differences  in,  222 
ligaments  of,  289 
lymphatics  of,  918 
major,  219 

mechanism  and  movements  of,  293,  370,  393 
minor,  219 
muscles  of,  438 
outlet  of,  221 

sexual  differences  in,  222 
peritoneum  of,  1100 
position  of,  221 
renalis,  1141 

development  of,  1199,  1202 
sexual  differences  in,  221,  222 
true,  219,  220 
Penis,  1170 

artery  of,  854,  1172 
bone  of,  1172 
bulbus  urethras  of,  1171 
corona  glandis  of,  1170 
corpora  cavernosa  of,  1170 

structure  of,  1172 
corpus  sjiongiosum  of,  1170 

structure  of,  1172 
crura  of,  1171 

development  of,  1200,  1206 
dorsal  vein  of,  897 
fascia  of,  1172 
glans  of,  1170 

development  of,  1206 
meatus  urinarius  of,  1170 
nerves  of,  1172 
pmeputial  glands  of,  1171 
prejjuce  of,  1171 
septum  of,  1172 
structure  of,  1172 
suspensory  ligament  of,  1172 
tunica  albuginea  of,  1172 
vessels  of,  854,  1172 
Perforated  space.     See  Locus  perforatus 
Perforating  arteries.     See  Arteries 
cutaneous  nerve,  657 


INDEX. 


1395 


Pericardiac  nerve,  695 
Pericardiaco-itlirenic  artery,  825 
Pericardial  area,  23,  925 

arteries,  of  aorta,  839 

of  intej'iial  mammary,  826 
Pericardium,  793 

development  of,  925 

great  oblique  sijius  of,  795 
transverse  sinus  of,  794 

paracentesis  of,  1264 

sinuses  of,  795 

structure  of,  795 

vestigial  fold  of,  784,  795 
Perichondrium,  74 
Pericranium,  1222 
Perilympha,  762 
Perilymphatic  space,  762,  770 
Perimysium  externum,  317 

internum,  317 
Perineal  arteries,  854,  117U 

body,  1194 

fascia  of  Colles,  1277 

fold,  45 

ligament,  transverse,  293 

nerves,  659.     See  also  Nerves 
Perineum,  1194 

central  point  of,  1277 

fasciai  of,  430 

muscles  of,  431 

rectal  triangle  of,  1277 

surgical  anatomy  of,  1277 

triangular  ligament  of,  292 

urogenital  triangle  of,  1277 
Periosteum,  71 

relation  of,  to  ossification,  73 

alveolare,  1016,  1025 
development  of,  1027 

alveolo -dental.     See  Periosteum  alveolare 
Perirenal  arteries,  842 
Peritoneal  cavity,  1267 

subdivisions  of,  1267 
Peritoneum,  1048,  1097 

development  of,  1105 

duodenal  fossae  of,  1068 

duodeno-jejunal  fossa  of,  1069,  1272 

femoral  fossa  of,  1098 

folds  of,  1049.     See  also  Mesentery,  Mesocolon, 
Omentum 

foramen  of  Winslow  of,  1049,  1102 

great  sac  of,  1049,  1097 

inguinal  fossse  of,  1098 

intersigmoid  fossa  of,  1086 
surgical  anatomy  of,  1274 

ligaments  of,  1050,  1099,  1154,  1189 
surgical  anatomy  of,  1284 

mesenterico-mesocolic  fold  of,  1069 

mesenteries   of,  1050.     See   also    Mesentery, 
Mesocolon 

omenta  of,  1049.     See  also  Omentum 

paraduodenal  fossa  of,  1068,  1069 

pararectal  fossa  of,  1090,  1101 

paravesical  fossa  of,  1101,  1155 

parietal,  1097 

j)elvic,  1100 

pouch  ^f  Douglas  of,  1090,  1101,  1189 
surgical  anatomy  of,  1283,  1284 

processus  vaginalis  of,  1167,  1190 

recto-vesical  pouch  of,  1090,  1100,  1155 
surgical  anatomy  of,  1282 

relation  of,  to  bladder,  1153 
to  csecum,  1076 
to  colon,  1083,  1084,  1085 


Peritoneum,  relation   of,  to  duodenum,  1067 
1068,  1069 
to  kidney,  1135 
to  liver,  1115 
to  pancreas,  1127 
to  rectum,  1089 
to  spleen,  1212 
to  stomacli,  1057 
to  uterus,  1189 
small  sac  of,  1049,  1097,  1102,  1107 
surgical  anatomy  of,  1267 
utero-vesical  pouch  of,  1101,  1189 
visceral,  1097 
Perivascular  lymph -spaces,  905 
Permanent  teeth,  1014,  1015,  1016 
Peronseo-calcaneus  muscle,  380 

externus  muscle,  376 
Peronreo-cuboideus  muscle,  376 
Peronseus  accessorius  muscle,  376 
brevis  muscle,  375 

action  of,  384 
digiti  quinti  muscle,  376 
longus  muscle,  375 

action  of,  384 
tertius  muscle,  375 
action  of,  384 
Peroneal  artery,  865.     See  also  Artery 
nerve,  648,  650 
spine,  244 
tubercle,  1311 
Pes  anserinus,  687 
hippocampi,  577 
Petit,  canal  of,  736 
triangle  of,  320,  424 

surgical  anatomy  of,  1285 
Petro-basilar  fissure,  117 
Petro-mastoid  suture,  1233 
Petro-occipital  fissure,  163 
Petrosal  artery,  811 

nerve,  great  deep,  687,  707 
small  deep,  689,  707 
superficial,  external,  687 
large,  686 
small,  689 
process,  123 

sinus,  inferior,  876,  887 
superior,  886 
Petro-squamous  fissure,  118 
suture,  113,  114 

surgical  anatomy  of,  1233 
Petro-tympanic  fissure,  750 
Petrous  ganglion,  689,  700,  701 
Peyer's  patches,  1062,  1064,  1073,  1074 
Phaenozygous  crania,  158,  Appendix  D,  xvii 
Phalangeal  process  of  lamina  reticularis,  767 
Phalanges  of  foot,  251 
of  hand,  210 
of  rods  of  Corti,  767 
Pliaryngeal  artery,  ascending,  808,  1037 
development  of,  933 
nerves,  1037 

of  Meckel's  ganglion,  683 
of  ninth  cranial  nerve,  690 
of  sympathetic,  707 
of  vagus,  692 
plexus,  690,  692,  707 
tubercle.  111,  163,  166 
veins,  876 
Pharyngo-glossus,  1242 
Pharyngotomy,  1218 
Pharynx,  993,  1029 
aponeurosis  of,  1037 


1396 


INDEX. 


Pharynx,  bursa  of,  1033 
cavity  of,  1031 
development  of,  34,  1037 
Eustachian  cusliion  of,  1033 

orifice  of,  1033 
glands  of,  1037 
isthmus  of,  998,  1032,  1034 
laryngeal,  1032,  1036 
lateral  recesses  of,  1031,  1033,  1034 

development  of,  1038 
levator  ciishion  of,  1034 
lymphatics  of,  1037 

surgical  anatomy  of,  1246 
muscles  of,  410 
action  of,  413 
development  of,  441 
nerve-supj)ly  of,  413 
nasal,  1032 

naso-pharyngeal  groove  of,  1034 
nerves  of,  1037 
oiDenings  of,  1032 
oral,  1032,  1034 

palatine  arch  of,  j)osterior,  1034 
pharyngo-epiglottic  fold  of,  963,  1002,  1036 
relations  of,  1031 
salpingo-palatine  fold  of,  1033 
salpingo-pharyngeal  fold  of,  1033 
sinus  jjyriformis  of,  1036 
tonsillaris  of,  1034,  1035 
develoj^ment  of,  1038 
structure  of,  1037 
supratonsillar  fossa  of,  1034,  1035,  1036 

development  of,  1038 
tonsil  of,  palatine,  1034,  1035 

pharyngeal,  1033,  1037 
vault  of,  1033 
vessels  of,  1037 
Philtrum,  39,  996,  1013 
Phrenic  artery,  inferior,  839 
variability  of,  949 
superior,  825 
nerve,  621 

surgical  anatomy  of,  1251 
vein,  893 
Phrenico-colic  ligament,  1083,  1104 
Phrenico-pleural  fascia,  982 
Phylogeny,  1 
Pia  mater,  603 

choroid  plexuses  of,  575,  604,  605 
encephali,  603 

ligamentum  denticulatum  of,  605 
linea  splendens  of,  605 
spinalis,  453,  605 
tela  choroidea  of,  604 
velum  interpositum  of,  604 
Pigmentary  layer  of  otitic  vesicle,  742 
Pillars  of  Corti,  766 

of  fauces  (anterior  and  posterior),  999,  1034 

surgical  anatomy  of,  1244 
of  fornix,  548,  550,  566,  572 
of  superficial  inguinal  ring,  423 
Pilus.     See  Hair 
Pineal  body,  531,  547 
development  of,  594 
eye,  547 
Pinna,  743 

development  of,  43,  66 
Piriform  fascia,  434 
muscle,  366 

action  of,  370,  371 

Piriformis  muscle,  366 

action  of,  370,  393 


Piriformis  muscle,  nerve-supply  of,  370 
Pisi-cuneiform  articulation,  286 
Pisiform  bone,  203 

morpliology  of.  Appendix  F,  xxv 
ossification  of,  207 
surgical  anatomy  of,  1299 
Pisi-metacarpal  ligament,  286,  340 
Pisi-unciform  ligament,  286,  340 
Pit,  auditory,  66,  769 

nasal,  703 

olfactory,  38 

rectal,  1093 
of  stomach,  96,  102 
Pituitary  artery,  815 

body,  549 

development  of,  42 

fossa,  121,  170 ;  Appendix  E,  xxi 
Placenta,  52 

foetal,  55,  59 

matenial,  56,  58,  59 

separation  of,  59 

uterina.     See  Placenta,  maternal 
Placental  area,  24,  48,  52,  54 
Plane,  coronal,  5 

frontal,  5 

mesial,  4 

of  segmentation,  17 
Plantar  arch,  866 

morphology  of,  943 
surgical  anatomy  of,  1312 

artery,  external,  866 
internal,  865 

fascia,  372 

ligaments,  311 

nerves,  654 
Plantaris  muscle,  377 

action  of,  384 
Planum     nuchale.        See     Nuchal     plane     of 
occipital  bone 

occipitale.     See  Occipital  i:)lane 

•popliteum.     See  Popliteal  surface  of  femur 

sternale,  95 

temporale,  107 
Platyhieric  sacrum,  Appendix  D,  xx 
Platyknemia,  Appendix  B,  xii 
Platyknemic  index,  ApjDendix  D,  xx 
Platymeria,  Appendix  B,  xii 
Platymeric  index.  Appendix  D,  xx 
Platypellic  pelvis,  Aj^pendix  D,  xix 
Platyrhine  skulls,  717  ;  Appendix  D,  xviii 
Platysma  muscle,  395 

action  of,  399 
Pleura,  976,  977 

blood-vessels  of,  874,  973 

cervicalis,  977 

costalis,  977,  978 

diaphragmatica,  977,  978 

lines  of  reflexion  of,  978,  979,  1258 

lymphatics  of,  983 

mediastinalis,  977,  978,  1260 

paracentesis  of,  1260 

parietalis,  977 

pericardiaca,  978 

phrenico-pleural  fascia  of,  982 

pulmonalis.     See  Visceral  pleura 

relation  of,  to  oesophagus,  1040 

relation  of,  to  twelfth  rib,  1259,  1290 

sinus  costo-mediastinalis  of,  988 
phrenico-costalis  of,  986 

stomata  of,  983 

structvire  of,  983 

surgical  anatomy  of,  1258 


INDEX. 


1397 


Pleura,  visceral,  977,  982 
Pleural  cavities,  976 

veins,  874 
Plexus  or  Plexuses,  annularis,  727 
aorticus,  710,  711,  714 
aorticus  abdomiiuilis,  711 
aorticus  thoracalis,  710 
of  Auerbach  in  stomach,  1060 

in  intestines,  1073 
basilaris,  885 
brachialis,  616,  617,  622 

communications  of,  623 

comjjosition  of,  623 

infraclavicular  branches  of,  625 

inner  cord  of,  623,  625 

morphology  of,  662,  663 

outer  cord  of,  623,  625 

position  of,  622 

posterior  cord  of,  623,  625 

primary  cords  of,  623 

secondary  cords  of,  624 

supraclavicular  branches  of,  624 

surgical  anatomy  of,  1252 

variations  in,  673 
cardiac,  deep,  693,  694,  708,  712,  793 

superficial,  693,  707,  712,  793 
cardiacus.  See  P.,  cardiac,  superficial  and  deep 
caroticus  communis.     See  P.,  carotid 

externus.     See  P.,  carotid,  external 
carotid,  707,  712 

external,  707,  712 
cavernosus  concharum,  722 
cavernosus  of  cervical  sympathetic,  707,  712 

clitoridis,  715 

penis,  714 
cervicalis,  610,  616,  617 

ascending  branches  of,  617 

communications  of,  617,  620 

cutaneous  branches  of,  617 

descending  branches  of,  617 

external  branches  of,  617,  619 

internal  branches  of,  617,  619 

morphology  of,  622 

muscular  branches  of,  617,  619,  621 

posterior,  610,  612 
morphology  of,  614 

surgical  anatomy  of,  1251 
chorioideus  ventriculi  lateralis.  See  P. ,  choroid 
quarti.     See  P.,  choroid 
tertii.     See  P.,  choroid 
choroid,  of  fourth  ventricle,  512 
development  of,  529 

of  lateral  ventricle,  575,  604 
of  descending  horn  of,  578 
development  of,  596 

of  third  ventricle,  550,  604 
coccygeus,  658 
coeliacus,  712,  713 
coronarius  cordis  anterior,  694 

posterior,  694 
leferentialis.     See  P.,  spermatic 
dentalis  inferior.     *S'ee  Nerve,  dental,  inferior 

superior.       See   Nerve,   dental,    anterior, 
middle,  and  posterior 
diaphragmatic,  622,  713 
fundamental,  of  cornea,  727 
gulte,  695,  1040 
hiemorrhoidal,  714,  1096 

external  venous,  1096 

internal  venous,  1096 
hepaticus,  713 
hypogastric,  712,  714 


Plexus  or  Plexuses,  infra-orbital,  682,  688 
lienalis.     See  Splenic  plexus 
of  limbs,  composition  of,  663 
of  limbs,  development  of,  662 

distribution  of  nerves  of,  663,  672 

morjjhology  of,  662 

significance  of,  674 

trunks  of,  663 

variations  in,  673 
lumbalis.     See  Lum))ar  plexus 
lumbo-sacralis,  610,  639 

connexions  of,  with  sympathetic,  639 

constitution  of,  639 

subdivisions  of,  639 

variations  in,  673 
of  Meissner,  1060,  1073 
mesenteric,  inferior,  714 

superior,  713 
myeutericus.     See  P.  of  Auerbach 
obturator,  644,  646 
oesophageal,  691,  695,  1040 
ovarian,  714 

pampiniforniis,  894,  1162 
patellar,  647 
pelvic,  712,  714 
pharyngeus,  690,  707,  712 
pharyngeus  venosus,  876,  1037 
post-vertebral  venous,  887 
prostatic  venous,  1173,  1279 
prostatico-vesical  venous,  896 
prostaticus,  714 
pterygoid  venous,  880 
pudendalis,  639,  655 

branches  of,  655 

morphology  of,  660 

position  and  constitution  of,  655 
pulmonalis,  691 

anterior,  693,  694 

posterior,  691,  694,  710 
renal,  710,  713 
sacral,  639,  647    . 

anterior  branches  of,  648 

articular  branches  of,  648,  649,  650 

communications  of,  with  sympathetic,  647 

muscular  Ijranches  of,  648 

position  and  constitution  of,  647 

terminal  branches  of,  650 
sciatic,  639,  647 
solar,  710,  712 
spermatic,  714 
spinal  venous,  887,  888 
splenic,  713,  1213 
subclavius,  708,  712 
subepithelial,  of  cornea,  727 
submucosus.     See  P.  of  Meissner 
subjjleural  arterial,  825 
subsartorial,  644 
supra  renal  is,  713 
symjaathici,  712 
thyroid,  708,  712 
tonsillaris,  689,  690,  1036 
tympanicus,  689,  707 
uterine,  714 

venous,  896 
utero-vaginalis,  1192,  1195 
vaginalis,  714 
venosus,  896 
vertebralis,  712,  718 
vesicalis,  714,  1157,  1195 

venosus  inferior,  896 
superior,  896 
Plica  or  Plicaj,  alares.     See  Alar  ligaments 


1398 


INDEX. 


Plica    or    Plicte,    aiiipulUf.      See    Ampulla    of 
Fallopian  tube 
aiyepiglottica.      See    Aryteno-epiglottideau 

folds 
axillaris  anterior  et  posterior.     See  Folds  of 

axilla 
circulares  (Kerkringi).     See  Valvulte  conni- 

ventes 
glosso-ejiiglottica  lateralis.      See  Glosso-epi- 

glottidean  folds 
glosso-epiglottica  niediaiui.      See  Friiinuluui 

of  epiglottis 
ileo-caicalis.     See  Ileo-ctvcal  fold 
inguinalis,  1168 
lacriinalis,  741 
longitudinalis  duodeni,  1070 
recto- Lite j'ina.     See  Recto-uterine  fold 
salpingo-palatina.    See  Saljiingo-palatine  fold 
salpingo-jjliarvngea.  See Salpingo-pliaryngeal 

fold 
semilunaris  coli,  1075 
semilunaris  conjunctivte,  738 
sublingualis,  1005 
synovialis  patellaris,  302 
triangularis  of  tonsil,  1036 
tubarite,  1186 
uretericse,  1151 
urogenit^lis,  1204 

ventricularis.    See  Larynx,  vocal  cord  of,  false 
vesicalis  transversa,  1156 
vocalis.     See  Larynx,  vocal  cord  of,  true 
Plicse  fimbriatse  of  tongue,  1005 

palmatte,  1188 
Pneumogastric  nerve,  690.    See  also  Nerve,  vagus 
Pogonion,  Appendix  D,  xvi 
Point,  alveolar,  Appendix  D,  xvi 
jugal,  Apjjendix  D,  xvi 
occipital,  171 ;  Appendix  D,  xvi 
subnasal.  Appendix  D,  xvi 
supra-auricular.  Appendix  D,  xvi 
Sylvian,  555 
Polar  bodies,  13,  15 

field,  9 
Poles  of  cerebrum,  554 
of  eyeball,  724 
formative,  11 
of  lens,  737 
nutritive,  11 
Polymasty,  1208 
Polymorphic  cells,  585,  586 
Polypbyodont  dentition,  1029 
Polythely,  1208 
Pomum  Adami,  958,  972 

surface  anatomy  of,  1248 
Pons  hepatis,  1111,  1114 
Varolii,  486 

acustic  area  of,  488 

central  tegmental  tract  of,  502 

corpus  trapezoides  of,  501,  520 

cortico-pontine  fibres  of,  501,  540,  583,  591 

development  of,  477,  480,  528 

eminentia  teres  of,  488 

fillet-fibres  of,  502,  504 

fovea  superior  of,  488 

gray  matter  of,  500 

internal  structure  of,  499 

locus  cocruleus  of,  488 

mesencephalic  root  of  fiftli  nerve  in,  504 

nuclei  of,  502,  504,  505,  539 

origin  of  nerves  from,  486,  514 

position  and  connexions  of,  475,  486 

posterior  longitudinal  bundle  in,  502,  504 


Pons  Varolii,  pyramidal  tract  in,  499 
raphe  of,  502 
restiform  body  in,  502 
reticular  formation  of,  499,  502 
spinal  root  of  fifth  nerve  in,  502 
substantia  ferruginea  of,  488,  504 
sulcus  basilaris  of,  486 
tegmental  part  of,  499,  501 
transverse  fibres  of,  499,  500 
veins  of,  883 
ventral  portion  of,  499 
Ponticulus,  745 
Pontine  flexure  of  brain,  479 
Poples.     See  Popliteal  space 
Popliteal  artery,  863.     See  also  Artery 
fascia,  356 
groove,  227 
line,  233 

lymphatic  glands,  916 
nerve,  external,  650.     See  also  Nerve 

internal,  652.     See  also  Nerve 
space,  surgical  anatomy  of,  1305 
surface,  226 
vein,  897,  898 

abnormality  of,  955 
Popliteus  fascia,  378 
muscle,  378 
action  of,  371 
minor,  378 
Pore,  gustatory,  711 
Porta  hepatis,  1115 
Portal  canals,  1120 
fissure,  1113,  1115 
system,  783 

vein,  901,  1120.     See  also  Vena  portas 
Portio  supra  vaginalis  cervicis  uteri,  1188 

vaginalis  cervicis  uteri,  1188 
Poms  opticus,  731 
sudoriferus,  778 
Post-anal  gut,  45 
Post-auditory  j)rocess,  120,  121 
Post-auricular  point,  1224 
Post-branchial  bodies,  36 
Post-central  anastomosis,  940 
arteries,  838 
gyri,  563 
line,  1225 
Post-coronal  depression,  153,  158 
Post-costal  anastomoses,  940 
Post-glenoid  tubercle,  113 
Post-neural  anastomoses,  940 
Post-parietal  gyrus,  563,  564 
Post-pharyngeal  lymphatic  glands,  911 
Post-sphenoid  bone,  126 
Post-transverse  anastomoses,  840 
Post-vertebral  venous  plexus,  887 
Pouch  of  Douglas,  1090,  1100 
relation  of,  to  uterus,  1189 
surgical  anatomy  of,  1283,  1284 
duodenal,  1070 
of  Prussak,  758 
of  Rathke,  42 
recto-genital,  1090,  1100 
recto-vesical,  1090,  1100,  1155 

surgical  anatomy  of,  1282 
utero-vesical,  1101,  1189 
Poupart,  ligament  of,  429 

surl'ace  anatomy  of,  1305 
line,  1047 
plane,  1047 
Prai-basi-occipital  bone.  Appendix  B,  viii 
Prsecentral  sulcus,  560,  561 


INDEX. 


1399 


Proeceiitral  sulcus,  surface  anatomy  of,  1225 

Praecordial  area,  1262 

Prsecuneus,  563 

Prie -inter-parietal  bone.  Appendix  13,  viii 

Prtelaminar  arteries,  838 

PriBOccipital  notch,  562 

Praejjutium  clitoridis,  1196,  1197 

penis,  1171 
Pre-aortic  lymphatic  glands,  922 
Pre-auricular  lymphatic  gland,  1238 

point,  1224 
Precentral  line,  1225 

Prechordal  portion  of  skull,  Appendix  E,  xxi 
Precoracoid,  ApjDendix  F,  xxv 
Precostal  anastomoses,  940 
Prehallux,  Appendix  F,  xxv 
Pre-interparietal  bones.  Appendix  B,  viii 
Prelaminar  anastomoses,  940 
Prelaryngeal  lymphatic  glands,  911 
Premaxilla;,  137,  1013 
Premaxillary  suture,  137 
Premolar  teeth,  1015,  1018 
Preneural  anastomoses,  940 
Prepatellar  bursa,  1307 
Prepollex,  Ajjpendix  F,  xxv 
Prepuce,  1171,  1197 
Preputial  glands,  1171 
Presphenoid  bone,  126  ;  Appendix  E,  xxi 
Presternum,  94 
Pretracheal  glands,  911 
Prevertebral  arteries,  809 

fascia,  395 

muscles,  413 
Prickle -cells,  773 
Primitive  alimentary  canal,  32,  1104 

aortie,  61,  62,  925,  926 
branches  of,  933 
morphology  of,  939,  942 

cerebral  vesicles,  476,  481 

groove,  20,  66 

heart,  928 

streak,  19,  21 

vascular  system,  60 
Primordial  bones.  Appendix  E,  xx 
Princeps  cervicis  artery,  808 

hallucis  artery,  869 

pollicis  artery,  833 
absence  of,  952 
Prismata  adamantina,  1023 
Pro-amnion,  23 
Pro-amniotic  area,  23 
Pro-atlas,  Appendix  B,  ix 
Process  or  Processes  ;  Processus 

accessorius  vertebrarum,  84 

acromion,  183,  186 

alaris  oss.  ethmoidalis,  127 

alveolaris  maxillae,  132,  136 
absorption  of,  181 

angularis  of  frontal  bone,  103,  105,  147 
surface  anatomy  of,  1224,  1237 

anterior  mallei.     See  Malleus,  755 

articularis,  77 
of  cervical  vertebrae,  78 
of  dorsal  vertebrte,  81 
of  lumbar  vertebrae,  84 
of  sacrum,  85,  86 

axial,  of  neuroblast,  22 

basilar,  108,  110,  159 

capitular,  of  vertebra,  Appendix  C,  xiv 

caudal,  43 

caudatus  hepatis.     See  Caudate  lobe 

ciliares,  729 


Process  or  Pi'ocesses,  clinoideus  anterior,  123 

clinoideus  medius,  122 

jjosterior,  122,  169 
cochleariformis,  116,  750 

surgical  anatomy  of,  1232 
condyloideus  mandibuke.    Sec  Condyle  of  jaw 
coracoideus,  185 

morjihology  of,  Ap2)endix  F,  xxv 

ossification  of,  187 

surface  anatomy  of,  1292 
coronoideus  mandibular,  143,  156 
surface  anatomy  of,  1237 

ulnsB,  194 

surface  anatomy  of,  1297 
epicondylic,  of  humerus,  191 

surface  anatomy  of,  1296 
ethmoidalis  of  inferior  turbinate  bone,  130 
facial,  of  parotid,  1010,  1011 
falciformis  of  sacro-sciatic  ligament,  292 
frontalis  maxillte,  133,  135 
of  zygomatic  bone,  140 
fronto-nasal,  38 
fronto-sphenoidalis.     See  Process,  frontal,  of 

zygomatic  bone 
funicular,  of  peritoneum,  1266 
globular,  39,  68 
hamular,  of  sphenoid,  125 

surgical  anatomy  of,  1246 

of  lacrimal,  131 
intermaxillaris,  41 
intrajugularis,  110 
jugular,  of  occipital  bone,  110,  159 
lacrimalis    conchae    nasalis    inferioris.      See 
Lacrimal   process  of    inferior    tur- 
binate 
lateralis  mallei.  See  Malleus,  processus  brevis  of 

nasalis,  93 

tali,  239 

tuberis  calcanei,  243 
lenticularis  incudis,  756 
malar,  of  maxilla,  135 
mammillares  vertebrarum,  84 
marginalis  of  zygomatic  bone,  140 
mastoideus,  115,  752.  See  also  Mastoid  process 
maxillaris  concha;  nasalis  inferioris.     See  P., 

maxillary,  of  inferior  turbinated 
maxillary,  of  inferior  turbinate  bone,  130 

of  mandibular  arch,  36,  38,  39,  41 
first  aj^jjearance  of,  66,  67 

of  palate  bone,  139 
medialis  tuberis  calcanei,  243 
muscular,  of  vertebrte,  76 
muscularis,  960,  971 
nasal,  of  frontal  bone,  104 

lateral,  39 

median,  39 

of  maxilla,  135 
odontoid,  80 

ossification  of,  93 
olecranon,  194 

surface  anatomy  of,  1296 
orbitalis  ossis  palatini,  139 

of  zygomatic  bone,  141 
palatal,  136 

palatinus.     See  P.,  palatal 
paramastoideus,  Appendix  B,  ix 
paroccipital,  Appendix  B,  iv 
petrosal,  123 
phalangeal,  of  lamina  reticularis,  767 

of  rods  of  Corti,  767 
post-auditory,  120 
pterygoideus,  125,  161 


1400 


INDEX. 


Process  or  Processes,  j^terygo-spinous,  125 
pyramidalis  ossis  palatini.      See  Tuberosity 

of  palate  bone 
reticularis,  457 
sphenoidalis  oss.  palatini,  140 

septi  cartilaginei,  718 
spinosus  veitebrarum  cervicalium,  78 
lunibaliiim,  83 
sacri,  85 

serial  lioniology  of,  Appendix  C,  xiv 
surface  anatomy  of,  1253,  1284 
thoracalium,  81 
styloid,  of  fibula,  234 
styloideus  ossis  metacarj)alis  iii,  209 
temporalis,  37,  116 
ossification  of,  120 
relation     of,     to     jugular     foramen, 

164 
root  of,  165 
radii,  199 

surface  anatomy  of,  1298 
ulnse,  197 
supracondyloideus.     See  Epicondylic  process 

surface  anatomy  of,  1298 
temporal,  of  zygomatic  bone,  140 
of  Tomes,  1028 

transversus  vertebrarum  cervicalium,  78 
lumbalium,  83 
sacri,  85 

serial  homology  of.  Appendix  C,  xiv 
surface  anatomy  of,  1251 
tboracalium,  81 
trochlearis,  244 

tubarius  of  pterygoid  process,  754 
tubercular,  of  vertebrae.  Appendix  C,  xiv 
turbinated,  of  ethmoid,  128 

surgical  anatomy  of,  1239 
unciform,  of  unciform  bone,  205 
uncinatus  ossis  ethmoidalis,  129 

pancreatis,  1126,  1128 
vaginalis  ossis  sphenoidalis,  125 
peritonei,  1167,  1190 

surgical  anatomy  of,  1266 
of  temporal  bone,  114,  154 
vermiformis.     See  Vermiform  appendix 
vocalis,  961,  971 
xiphoideus,  94,  96 
zygomaticus  ossis  frontalis,  104 
maxillae,  135 
temi^oralis,  113,  154 
Proctodjeum,  45,  68,  1105 
Profunda  artery  of  ulnar,  835 
brachii  inferior  artery,  831 

superior  artery,  831 
cervicis  artery,  826,  941 
clitoridis  artery,  854 
femoris  artery,  860 

abnormalities  of,  953 
penis  artery,  854,  1173 
Prognathous  skulls.  Appendix  D,  xviii 
Projection  fibres  of  cerebrum,  588,  591 
Prominentia  canalis  facialis,  752 
laryngea.     See  Pomum  Adami 
spiralis,  765 
styloidea,  750 
Promoutorium  cochleae,  1232 
sacri,  86 

surgical  anatomy  of,  1290 
tyrapani,  752 
Pronation,  movement  of,  283,  352 
Pronator  quadratus  muscle,  343 
action  of,  352 


Pronator  radii  teres  muscle,  338 

action  of,  352 
Pronephros,  1201 
Pronucleus,  female,  13,  16 

male,  16 
Pro-otic  j)art  of  temporal  bone,  119 
Prophase,  10,  13 
Prosencephalon,  476,  478,  481 
Prostate,  1159,  1173 
apex  of,  1174,  1278 
base  of,  1173,  1278 
capsule  of,  1174 
development  of,  1205 
ducts  of,  1175 
glands  of,  1175,  1179 
lateral  lobes  of,  1174 
middle  lobe  of,  1174 
nerves  of,  1176 
structure  of,  1175 
surgical  anatomy  of,  1278 
vessels  of,  1176 
Prostatectomy,  1279 
Prostatic  plexus,  714,  1173,  1279 
urethra,  1177 

development  of,  1203 
utricle,  1178,  1199 
Prostatico-vesical  venous  plexus,  896 
Prosthion,  Appendix  D,  xvi 
Protoplasm,  8 

Protoplasmic  process  of  Deiters,  445 
Protovertebral  somites,  26,  30,  31 
Protuberantia  mentalis,  142 
occipitalis  externa,  108,  158 
interna,  109 
Prussak,  pouch  of,  758 
Psalterium,  572,  589 
Psoas  magnus  muscle,  359 
actions  of,  370,  371 
parvus,  360 

actions  of,  370,  371 
Pterion,  151 ;  Appendix  D,  xvi 

surface  anatomy  of,  1224 
Pteriotic  part  of  temporal  bone,  120 
Pterygoid  artery,  812 
fossa,  125 
muscles,  402 
actions  of,  404 
nerves,  683 
notch,  126 
plate,  external,  125 

internal,  125 
plexus,  venous,  880 
px'ocess,  125,  161 
ridge.     See  Crest,  infratemporal 
tubercle,  125 
vein,  880 
Pterygo-maxillary  fissure,  155 
Pterygo-2jalatine  artery,  812 
canal,  126 
nerve,  683 
sulcus,  126 
vein,  880 
Pterygo-spinous  ligament,  269,  395 

process,  125 
Pubic  arch,  221 

artery  of  deep  epigastric,  857 

of  obturator,  852 
crest,  217 

sexual  difference  of,  222 
surface  anatomy  of,  1306 
ligaments,  292 
lymjjhatic  glands,  916 


INDEX. 


1401 


Pubic  portion  of  fascia  lata,  354 
region,  1047 
spine,  217 

surface  anatomy  of,  1306 
vein,  900 
Pubis,  212,  217 

morphology  of,  Aj^pendix  F,  xxv 
Pubo-capsular  ligament,  295 
Pubo-cavernosus  muscle,  432 
Pubo-coccygeus  muscle,  438,  1095 
Pubo-femoral  ligament,  295,  296 
Pubo-prostatic  ligaments,  436,  1156 
Pubo-rectalis  muscle,  438 
Pudendal  plexus,  639,  655 
branches  of,  655 
nerve,  inferior,  657 
Pudendum  muliebre,  1195 
Pudic  artery,  accessory,  953 

external,  deep,  860,  1170 

superficial,  859,  1170 
internal,  853 
surgical  anatomy  of,  1278,  1303 
nerve,  658 
veins,  896,  901 
Pulmo.     See  Lung 
Pulmonary  artery,  795,  989,  991 
abnormalities  of,  947 
development  of,  930,  933 
morphology  of,  942 
topography  of,  1264 
nerves,  691,  709,  989 
orifice,  789,  790 

surface  anatomy  of,  1262 
plexus,  691 

anterior,  693,  694 
posterior,  691,  694,  710 
valve,  790 

vascular  system,  783,  870 
veins,  870,  989,  992 
develojoment  of,  938 
niorjahology  of,  945 
orifices  of,  784,  788 
Pulp  cavity  of  spleen,  1213 
of  tooth,  1016,  1025,  1027 
Pulpa  dentis.     See  Pulp  of  tooth 
Pulpa  lienis.     See  Pulp  of  spleen 
Pulvinar  thalami,  531,  544,  552 
Puncta  lacrimalia,  740 

surgical  anatomy  of,  1238 
Pupilla,  730 
dilator  of,  731 
sphincter  of,  731 
Pupillary  border,  730 
membrane,  730,  742 
Purkinje,  cells  of,  512,  514 

fibres  of,  791 
Purple,  visual,  732 
Putamen,  580 

Pyloric  antrum,  1051,  1052,  1055 
artery,  845,  1060 

morphology  of,  942 
canal,  1052,  1055 
ligaments,  1058 

portion  of  stomach,  1050,  1051,  1052,  1055 
sphincter,  1056,  1058 
valve,  1056 
vein,  903,  1060 

morphology  of,  945 
Pylorus,  993,  1051,  1056 

surgical  anatomy  of,  1270,  1288,  1290 
Pyramid  of  cerebellum,  507,  508 
of  medulla  oblongata,  483,  528 


Pyramid   of   medulla    oblongata,    decussation 
of,  482,  483,  490 
renal,  1138 

tract,  591 

of  tympanic  cavity,  749 

of  vestibule,  759 
Pyramidal  bone.     See  Cuneiform  bone 

cells,  585 

lobe  of  thyroid,  1216,  1217 

nucleus,  490 

Ijrocess  of  palate  bone,  139 

tract,  591 
Pyramidalis  abdominis  muscle,  426 

nasi  muscle,  397 
Pyramis.     See  Pyramid 
Pyrenin,  9 

Quadrangular  lobule,  507 
Quadrate  lobe  of  liver,  1113 

lobule,  563 
Quadratus  femoris  muscle,  367 
action  of,  370,  371 
lumborum  muscle,  430 
Quadriceps  (extensor)  femoris  muscle,  357 

action  of,  370,  371 
Quadrigeminal  bodies,  531.     See  also  Corpora 
quadrigemina 

Racemose  glands,  1007 
Radial  artery,  831.     See  also  Artery 
fossa,  192 
nerve,  634 

surface  anatomy  of,  1301 
vein,  891.     See  also  Vein 
Radiale,  os.  Appendix  F,  xxiv 
Radialis  indicis  artery,  833.     See  also  Artery 
Radiatio,  Radiation — 
auditory,  583,  591,  593 
corporis  callosi,  571,  588 

pars  occipitalis  of.     See  Forceps  major 
striati,  581 
occipito-thalamica.     See  Optic  radiation 
optic,  553,  583,  591 
thalamica,  543,  545 
Radicular  cells,  464 

veins  of  medulla  oblongata,  883 
Radii  lentis,  737 
Radio-carj^al  joint,  283 
movements  at,  284 
surgical  anatomy  of,  1298 
synovial  membrane  of,  284 
Radio-humeral  index.  Appendix  D,  xx 
Radio-ulnar  joint,  inferior,  282 

superior,  281 
Radius,  198 

architecture  of,  Appendix  A,  iii 
connexions  of,  200 
homology  of,  Appendix  F,  xxiv 
movements  of,  on  ulna,  283 
ossification  of,  200 
surgical  anatomy  of,    1297,  1298 
variations  in,  Aj^pendix  B,  xi 
Radix  anterior  nervorum  spinalium,  443 
arcus  vertebrse.     See  Pedicles  of  vertebrae 
brevis  ganglii  ciliaris.     See  Ciliary  ganglion, 

short  root  of 
cochlearis  nervi  acustici,  688,  699 
dentis,  1015 
descendens  mesencephalica  n.  trigemini,  504, 

524,  526,  540 
lateralis  tractus  optici,  532,  552 
linguae,  1000 


1402 


INDEX. 


Radix    longa    ganglii    ciliaris.       See    Ciliary 
ganglion,  long  root  of 
medialis  tractus  optici,  532,  552 
mesenteric     See  Mesentery,  root  of 
nasi,  717 

nervi  facialis.     See  Nerve,  facial,  root  of 
penis,  1171 
jjili,  776 

liosterior  nervorum  spinaliiim,  443 
pulmonis.     See  Lung,  root  of 
sympathica  ganglii  ciliaris,  681 

submaxillaris,  685 
unguis,  775 
Ramus,  Rami  (arteriarum) — 

acetabuli.     See  Acetabular  braiicli  of  internal 

circumflex  artery 
acromialis.       See  Acromio  -  thoracic   artery  ; 
Suprascaj)ular  artery,  acromial  branch 
of 
ad    pontem.      See   Basilar    artery,   pontine 

branches  of 
anterior  A.  thyreoidete  superioris,  805 
ascendens  A.  circumflexse  femoris  lateralis,  861 
A.  transversfB  colli.     See  Artery,  cervical, 
superficial 
auriculares  anteriores,  809 
auricularis  arterite  occipitalis,  808 

posterioris,  808 
bronchiales.     See  Bronchial  arteries 
calcanei  laterales.     See  Artery,  calcaneal,  ex- 
ternal 
medialis.     See  A.,  calcaneal,  internal 
carotico-tympanicus.      See  A.,  tympanic,  of 

internal  carotid 
carpeus  dorsalis  A.  radialis.     See  A.,  carpal, 
posterior  radial 
dorsalis  A.  ulnaris.    See  A.,  carpal,  posterior 

ulnar 
volaris  A.  radialis.    See  A. ,  carpal,  anterior 

radial 
volaris  A.  ulnaris.    See  A,  carpal,  anterior 
ulnar 
circumflexus  A.  coronarise  sinistrai,  800 
cochlese  A.  auditivse  internee,  769 
communicans  A.  tibialis  ^Josterioris.     See  A., 

communicating,  posterior 
communicans   A.    peroneai.        See   A.,    com- 
municating, peroneal 
cricothyreoideus.     See  A.,  cricothyroid 
cutanei  anteriores  (pectorales  et  abdominis), 

838 
deltoideus,  829 

descendens  anterior  A.    coronarise   sinistrse, 
800 
A.  occipitalis.     See  A.  jjrinceps  cervicis 
A.  circumflexEB  femoris  lateralis,  861 
A.  transversjo    colli.      See   A.,    scapular, 

posterior 
posterior  A.  coronariie  sinistrte,  800 
dexter  A.  hepatica;,  845 
dorsalis  A.  costo-cervicalis,  826 
A.  liuguie,  805 
A.  lumbalium,  841 
duodenales  A.  gastroduodenalis,  845 
epiploici  A.  gastroej)iploicai  dextne,  845 
fibularis.     See  A.,  fibular,  superior 
frontalis  A.  temporalis  superficialis,  810 
glandulares  A.  maxillaris  externae.     See  A., 
submaxillary 
A.  thyreoidea?  inferioris,  823 
hyoideus  A.  thyroidete  superioris,  804 
hyoideus  A.  lingualis,  805 


Ramus,  iliacus  A.  iliolumbalis,  850 

intercostales  A.  mammarife  internas.     See  A., 

intercostal,  anterior 
intestini  tenuis,  846,  1073 
mammarii    externi    A.  thoracalis    lateralis, 

829 
mammarii  A.  mammariae  interna;,  826 
mammarii      laterales      A.      intercostalium, 
837 
mediales  A.  intercostalium,  837 
mastoideus  A.  occij)italis,  808 

A.  auricularis  posterioris,  808 
mediastinales  aortae,  825,  839 
meningeus  accessorius.      See  A.,  meningeal, 
small 
A.  occipitalis,  807 
A.  vertebralis,  819 
mylohyoideus,  812 

obturatorius  A.  epigastricas  inferioris,  857 
occiijitalis  A.  auricularis  posterioris,  808 
cesojjhagei  aortae.     See  Arteries,  oesophageal 
A.      gastricte     sinistrse.        See      Arteries, 
oesophageal,  of  coronary 
ovarii  A.  uterinae,  843 

pancreatici  A.  lienalis.      See  Arteries,  pan- 
creatic, of  splenic 
A.  pancreaticoduodenalis  superioris,  845 
parotidei  A.  temporalis  superficialis,  809 
parietalis      A.      temporalis       superficialis, 

810 
pectorales  A.  thoracoacromialis.    See  Arteries, 

pectoral,  of  acromio-thoracic 
perforans  A.   tibialis     posterioris.      See   A,, 
peroneal,  anterior 
A.  mammariae  in  teniae,  826 
A.  metacarpalium  volarium.     See  A.,  per- 
forating, inferior,  of  hand 
A.  metatarsalium  plantarium.    S'ee  A.,  per- 
forating, anterior,  of  foot  ' 
pericardiaci  aortae,  839 
petrosus  superficialis  A.  maxillaris  interna;, 

811 
pharyngei  A.  pharyngeae  ascendentis,  809 
jDosterior  A.  thyreoideae  superioris,  805 
A.  obturatoriae,  852 
A.  intercostalium,  837 
j)terygoidei  A.  maxillaris  internae,  814 
pubicus  A.  epigastrica;  inferioris.       See  A., 

jDubic,  of  deep  ep>igastric 
l^ubicus  A.  obturatoriae,  852 
sapheuus.     See  Anastomotica  magna,  super- 
ficial branch  of 
sinister  A.  hepaticae,  845 
spinalis  A.  intercostalium,  838 
A.  vertebralium,  818 
A.  intercostalis  sujiremae,  826 
A.  lumbalium,  841 
A.  iliolumbalis,  850 
A.  sacralis  lateralis,  850 
stapedius  A.  stylomastoideae,  808 
sternomastoideus   A.    thyreoidea;  superioris, 

805 
suprarenales  superiores,  839 
tonsillares  A.  maxillaris  externce.      See  A., 

tonsillar,  of  facial 
tracheales  A.  thyreoidea;  inferioris,  823 
tubarius  A.  uterinum,  1186 
vestibulares  A.  auditivae  internae,  769 
volaris    profundus.      See    A.,    profunda,    of 

ulnar 
volaris    superficialis.       See    A.,     superficial 
volar 


INDEX. 


1403 


Eamus     anterior     asceiideiis     fissura^     cerebri 
lateralis,  556 
anterior  liorizontalis  fissurai  cerebri  lateralis, 

556 
posterior  fissurai  cerebri  lateralis,  656 
Ramus  lironcliialis  eparterialis.     See  Ejjarterial 
Imjuchus 
])r(jnchialis  hyperarterialis.     See  Hypart(!rial 
bronchus 
Rami  communicantes,  gray,  615,  616 
cervical,  706,  708 
development  of,  715 
functions  of,  705 
lumbar,  711 
of  plexus,  brachial,  623 
cervical,  617,  620 
lumbo-sacral,  639 
pudendal,  655 
sacral,  647 
of  thoracic  nerves,  636,  637,  638 
Rami  communicantes,  white,  609,  615,  616 
cervical,  706 
development  of,  662,  715 
lumbar  part  of,  711 
of  lumbo-sacral  plexus,  640 
of  pelvic  plexus,  712,  713,  714 
of  pudendal  ^^lexus,  655 
of  sacral  plexus,  647,  704 
of  solar  plexus,  712,  713,  714 
of  thoracic  symj)athetic,  709,  710 
thoracico-lumbar,  704 
Ramus,  rami  (nervorum) — 

alveolares  superiores  anteriores,  682 

posteriores,  681 
alveolaris  superior  medius.  682 
anastomotici  cum  nervo  faciali,  684 

hyj)Oglosso,  685 
anastomoticus  cum  chorda  tympani,  686 
nervo  auriculo-temporali,  686 
N.  facialis   cum   nervo   glosso-pharyngeo, 

687 
N.  vagi  cum  nervo  glosso-pharyngeo,  687 
cum  nervo  laryngeo  inferiore,  692 
ulnari,  628 
ranio  auriculari  nervi  vagi,  690 
peroneeus.        See     Nervus     communicans 
fibularis 
anterior  nervi  obturatorii,  644 
anterior  nervorum  sjainalium.    See  N.,  spinal, 
anterior  primary  division  of 
rami  cutanei   lateralis   (pectoralis   et   ab- 
dominalis),  636,  637,  638 
anteriores   N.  thoracalium.      See   N.,  inter- 
costal 
nervorum  cervicalium,  617 

lumbalium,  sacralium,  coccygeorum,  639 
auricularis  N.  vagi,  692 
buccales  N.  facialis,  688 
calcanei  laterales,  653 

mediales.     See  N.,  calcanean,  internal 
cardiaci  inferiores  N.  vagi,  692 

superiores  N.  vagi,  692 
cceliaci  N.  vagi,  693 
colli     N.     facialis.        See     Inframandibular 

nerve 
communicans  nervorum  spinalium,  609 
communicantes  ganglii    submaxillaris    cum 

nervo  linguali,  685 
cutanei  anteriores  nervi  femoralis,  646 

cruris  mediales,  646 
cutaneus  anterior  (pectoralis  et  abdominalis), 
636 


Ramus     cutaneus    anterior    nervi    ilio-liypo- 
gastrici.      See   N.,  ilio-hypogastric, 
hyijogastric  branch  of 
lateralis   (i)ectoralis   et  abd(nninalis),  636, 
637,  638 
neivi    ilio-hypogastrici.      See    N.,    ilio- 
hypogastric, iliac  branch  of 
nisrvorum  thoracalium.    See  N.,  thoracic, 
posterior  primary  divisions  of,  external 
cutaneous  branch  of 
medialis  nervorum   thoracalium.     See  N., 
tlioracic,  ixjsterior  primary  divisions  of, 
internal  cutaneous  branch  of 
nervi  obturatorii,  644 

palmaris   nervi   ulnaris.       See    N.,    ulnar, 
(palmar  cutaneous  branch) 
dentales  inferiores,  685 

superiores,  682 
descendens  N.  hypoglossi,  697 
digastricus  N.  facialis,  687 
dorsalis   manus   nervi   ulnaris.       See  Ulnar 

N.  (dorsal  cutaneous  branch) 
externus   nervi   accessorii.      See   N.,   spinal, 
accessory,  spinal  part  of 
laryngei  superioris,  692 
frontalis  nervi  ophthalmici,  679 
gastrici  N.  vagi,  693 
hepatici  N.  vagi,  693 
inferior  nervi  oculomotorii,  677 
inferiores  nervi  cutanei  colli,  618 
infrapatellaris.       See    N.,    long    saphenous, 

jjatellar  branch  of 
internus    nervi    accessorii.      See    N.,   spinal 
accessory,  medullary  ^lortion  of 
laryngei  superioris,  692 
isthmi  faucium,  685 
labiales  inferiores  N.  mentalis,  685 

sujieriores  N.  maxillaris,  682 
laryngo-pliaryngei,  707 

lateralis    ramorum    posteriorum    nervorum 
cervicalium.   See  N.,  spinal, posterior 
primary     divisions     of,      external 
branches  of 
N.      lumbalium.      See     N.,     lumbar, 
posterior  primary  division   of,  ex- 
ternal branch  of 
nervorum  sacralium  et  coccygei.     See  N., 
sacral,    posterior      primary     divi- 
sion of,  external  brancli  of 
lienales  nervi  vagi,  693 
linguales  N.  glossopharyngei,  690 
N.  hypoglossi,  697 
N.  lingualis,  685 
marginalis   mandibulae.       See   Supramandi- 

bular  nerve 
mediales    ramorum    posteriorum    N.    cervi- 
calium. See  N .,  spinal,  posterior  prim  - 
ary  division  of,  internal  branch  of 
medialis   ramorum  posteriorum  N.   lumba- 
lium. See  N. ,  lumbar,  jjosterior  prim- 
ary division  of,  internal  branch  of 
nervorum  sacralium  et  coccygei.      See  N. 
sacralis,  posterior  primary  division 
of,  internal  branch  of 
membranre  tympani  N.  auriculo-temporalis, 

684 
meningeus  nervi  vagi,  692 

nervorum  spinalium,  609 
mentales  nervi  mentalis,  685 
musculares  nervi  axillaris,  632 
femoralis,  645 
ilio-hypogastrici,  642 


1-404 


INDEX. 


Rami  musculares  iiervi  ilio-iuguinalis,  643 
iscliiadici,  648 
luediani,  628 
musculo-cutanei,  627 
perouaii,  650 
profundi,  651 
superficialis,  650 
i-adialis,  633 
tibialis,  652 
iiliiaris,  631 
nei'vorum  thoracaliuni,  636,  637,  638 
plexus  lumbalis,  642 
nasalea  exterui  N.  naso-ciliaris,  680 
interni  N.  naso-ciliaris,  680 
laterales  N.  naso-ciliaris,  680 
niediales  N.  naso-ciliaris,  680 
nasalis  externus  N.  naso-ciliaris,  680 
occipitalis  N.  auricularis  posterioris,  687 
CESophagei  N.  vagi,  693,  695 
orbitales  ganglii  spheno-palatini,  683 
palmaris   nervi   mediani.     See   N.,  median, 

palmar  cutaneous  branch  of 
palpebrales  inferiores  nervi  niaxillaris,  682 
palpebralis  inferior nerviinfra-trochlearis, 680 

superior  nervi  infra -trochlearis,  680 
parotide!  nervi  auriculo-temporalis,  684 
pericardiacus  nervi  phrenici,  622 
perineales  nervi  cutanei  fenioris  posterioris,657 
pharyngei  nervi  glosso-pliaryngei,  690 

nervi  vagi,  692 
phrenico-abdoniinales  nervi  plirenici,  692 
posterior  nervi  obturatorii,  644 

nervorum     spinalium.       See     N.,    s]3inal, 
posterior  primary  division  of 
posteriores  nervorum  cervicalium,  610 

lumbalium,  sacralium,  coccygeorum,  613 
thoracalium,  613 
profundus  nervi  plantaris  lateralis,  655 

radialis.     See  N.,  interosseous,  posterior 
ulnaris,  631 
pulmonalis  partis  tlioracalis  sympatliici,  710 
renales  N.  vagi,  693 
renalis  nervi  splanchnici  minoris,  710 
stylohyoideus,  687 
stylopharyngeus,  690 
submaxillares  ganglii  submaxillaris,  685 
super ficialis  N.  plantaris  lateralis,  654 
nervi  radialis.     See  N.,  radial 
N.  ulnaris,  630 
superior  N.  oculomotorii,  677 
superiores  nervi  cutanei  colli,  618 
temporales  N.  facialis,  687 

superficiales  N.  auriculo-temporalis,  684 
thyreohyoideus  N.  hypoglossi,  697 
tonsillares  N.  glossopharyngei,  690 
tracheales  nervi  recurrentis  N.  vagi,  693 
tubsb  plexus  tymi^anici,  689 
ulnaris  nervi  cutanei   antibracliii    medialis. 
See  N.,  internal  cutaneous  (posterior 
branch) 
volaris   nervi   cutanei  antibrachii  medialia. 
See  N.,  internal  cutaneous  (posterior 
branch) 
zygomatici  N.  facialis,  688 
zygomatico-facialis,  681 
zygomati co-temporal  is,  681 
Ramus  o.ssis  ischii  inferior,  216 
superior,  216 
rnandibulaj,  143,  155 

surgical  anatomy  of,  1237 
pubis  inferior,  218 
superior,  217 


Ranine  artery,  805 
vein,  876,  1006 

surgical  anatomy  of,  1244 
Raphe  medullaj,  489,  528 
palati,  998 
pharyngis,  410 
pontis  Varolii,  502 
scroti,  1169 
'  of  tongue,  1002 
Rathke,  pouch  of,  42,  1033 
Rauber,  cells  of,  18 
Receptaculum  chyli,  907,  956 
Recess  or  Recessus,  cochlearis,  759 

duodenojejunalis.     See  Fossa  duodeno-jejunal 

ellipticus  vestibuli,  759 

epitympanicus,  748 

ileoctecalis.     See  Fossa  ileocaecal 

infundibuli,  551 

intersigmoideus,  1086 

labyrinth!,  769 

lateral,  of  jjharynx,  1033 

lateralis  fosste  rhomboideee.     See  Ventricle, 

fourth,  lateral  recess  of 
naso-palatinus,  720 
opticus,  551,  595 
parotid,  1010 

pharyngeus  (Rosenmulleri),  1033 
pinealis,  551,  594 
piriformis,  1036 
sacciformis      articulationis      radio  -  ulnaris 

distalis,  282 
sphaericus  vestibuli,  759 
spheno-ethmoidalis,  173,  720 
sujDra-pinealis,  551 
utriculi,  762 
Recesses  of  Troltsch,  758 
Rectal  examination,  1281,  1283 
fascia,  1091 
lymphatic  glands,  920 
triangle  of  perinoium,  1277 
Recto-coccygeus  muscle,  1093 
Recto-genital  folds,  1101 

pouch,  1090,  1100,  1101 
Recto-uterine  fold,  1189 

muscle,  1189 
Recto- vaginal  fold,  1189 
Recto-vesical  fascia,  436 
pouch,  1090,  1100,  1155 
surgical  anatomy  of,  1282 
Rectum,  993,  1074,  1085,  1087 
ampulla  of,  1089,  1091 
anal  orifice  of,  1074,  1091 
curvatures  of,  1088,  1281 
develoijment  of,  45 
nerves  of,  1095 
pars  analis  of,  1091 
peritoneal  relations  of,  1089 
pits  of,  1093 
sphincter  of,  1095 
structure  of,  1092 
surgical  anatomy  of,  1281 
valves  of,  1089,  1093 
variations  in,  1097 
vessels  of,  1095 
Rectus  abdominis  muscle,  427 
capitis  anticus  major  muscle,  414 
minor  muscle,  415 
lateralis  muscle,  393,  415 
posticus  major  muscle,  392 
minor  muscle,  392 
femoris  muscle,  357 
action  of,  370 


INDEX. 


1405 


Eectus  muscles  of  orbit,  external,  400 
inferior,  400 
internal,  400 
superior,  400 
actions  of,  401 
Red  marrow,  72 

nucleus,  535,  536,  546 
Regiones  abdominis,  1047.     See  also  Aljdomen 
Reicliert,  cartilage  of,  146 
Reid,  base  line  of,  1227 
Reil,  island  of,  556,  567 
Reissner,  membrane  of,  765 
Ren.     See  Kidney 
Renal  artery,  842.     See  also  Artery- 
fascia,  1132 

impression  on  liver,  1113 
plexus,  710,  713 
vein,  893.     See  also  Vein 
Rejiroduction  of  cells,  9 
Reproductive  cells,  10 
organs,  female,  1181 
male,  1159 
Reserve  germs  of  teetli,  1027 
Respiration,  movements  of,  419 
muscles  of,  415,  419 
organs  of,  957 
Respiratory  system,  957 
Restiform  body,  485,  489 
development  of,  528 
structure  of,  502,  510 
Rete  testis,  1161,  1204 

venosum  dorsalis  manus,  890 
pedis,  900 
vertebrarum,  887 
Reticular  formation,  457,  460,  490,  498 
structure  of,  499,  502 
process,  457 
Retina,  725,  731 

bacillary  layer  of,  732,  734 
bipolar  cells  of,  732,  733 
blind  spot  of,  732 
blood-vessels  of,  735 
cone-granules  of,  733 
cones  of,  734,  743 
development  of,  699,  742 
fovea  centralis  of,  731,  734 
ganglionic  layer  of,  732 
granule  layer  of,  732,  733 
horizontal  cells  of,  732 
macula  lutea  of,  731,  734 
membran?e  limitantes  of,  734 
molecular  layer  of,  732,  733 
morj^liology  of,  703 
nervous  lamina  of,  731 
nuclear  layer  of,  732,  733 
optic  cup  of,  731 

disc  of,  731 
ora  serrata  of,  731,  735 
pars  ciliaris  of,  729,  731,  735,  742 
iridica  of,  730,  731,  735,  742 
optica  of,  731 
physiological,  731 
relation  of  optic  fibres  to,  552 
rod -granules  of,  733 
rods  of,  734,  743 
spongioblasts  of,  732,  742 
stratum  opticum  of,  732 

pigmenti  of,  731,  732,  734 
structure  of,  732 
sustentacular  fibres  of,  732,  734 
visual  purple  of,  732,  734 
Retinacula,  295 


Retinacula  cutis,  772 
Retinal  layer  of  optic  vesicle,  742 
Retrahens  aurem  muscle,  396,  399 
Retro-cajcal  fossae,  1081 
Retro-colic  fossae,  1081 
Retro-pharyngeal  space,  931,  1037 
Retzius,  cavum  of     See  Retzius,  space  of 
space  of,  437,  1278 
stria3  of,  1024 
Rhineiicephalon,  568,  584 

development  of,  698 
Rhinion,  Apjiendix  D,  xvi 
Rhodopsin,  732,  734 
Rhombencephalon,  476,  481 

development  of,  526 
Rhombic  lip,  527 
Rhomboid  impression,  182 

ligament,  274,  275 
Rhomboidal  sinus,  22 
Rhomboideus  major  muscle,  322 
minor  muscle,  322 
actions  of,  327 
Ribs,  97 

architectiire  of.  Appendix  A,  i 

bicipital.  Appendix  B,  viii 

cartilages  of,  100,  271 

cervical,  81,  92,  A2:)pendix  B,  vii.  Appendix 

C,  xiv 
eleventh,  100 
false,  97 
first,  99 
floating,  97 
lumbar,  92,  Appendix  B,  vii.  Appendix  C, 

xiv 
movements  of,  272,  419 
ossification  of,  100 
second,  99 

surface  anatomy  of,  1255 
tenth,  100 
true,  97 
twelfth,  100 

surface  anatomy  of,  1285,  1290 
variations  in.  Appendix  B,  vii 
vertebral,  97 
vertebro-chondral,  97 
vertebro-sternal,  97 
Ridge,  basal,  of  tooth,  1017 

epicondylic.     See  Epicondylic  line 
genital,  1204 
interosseous,  of  fibula,  236 

of  tibia,  232 
intertrochanteric,  224 
mylohyoid,  143 
oblique,  of  clavicle,  183 
pectoral,  190 

pterygoid.     See  Crest,  infratemporal 
superciliary,  103,  147,  180 
surface  anatomy  of,  1237 
supraorbital,  103 
temporal,  104,  107,  153 
trapezoid,  183 
Wolffian,  46,  66,  662 
Riedel's  lobe  of  liver,  1117 
Rima  glottidis,  966,  971 

surface  anatomy  of,  1249 
oris,  995 

palpebrarum,  738 
pudendi,  1195 

vestibuli.     See  Glottis  spuria,  966 
Ring,  abdominal.     See  Inguinal  rings 
crural.     See  Femoral  ring 
tympanic,  120,  748 


1406 


INDEX. 


Riolan,  muscle  of,  739 
Risorius  muscle,  398,  399 
Rivinus,  ducts  of,  1013 

notch  of,  750,  1232 
Rods  of  Corti,  766 

head -plate  of,  766 
phalangeal  processes  of,  767 

retinal,  734,  743 
Rod-bipolars  of  retina,  732 
Rod-graiiules  of  retina,  733 
Rolandic  angle,  558 

fissure,  558.     See  also  Fissure 
Rolando,  funiculus  of,  485,  491 

substantia  gelatinosa  of,  456,  461,  468,  502 

tubercle  of,  485,  491 
Roof-nucleus,  510,  511,  521 
Root  of  lung,  989 

surface  anatomy  of,  1260,  1290 
Root-membrane  of  teeth,  1016,  1025 
Roots  of  aortic  arch,  928,  932 

of  nerves,  608 
Rosenmiiller,  fossas  of,  754,  1033,  1034 
surgical  anatomy  of,  1246 

organ  of,  1187 
Rosenthal,  canalis  spiralis  of,  761 
Rostrum  of  corpus  callosum,  571 

ossis  sphenoidalis,  123 
Rotation,  movement  of,  259 
Rotator  humeri  muscle,  332 
Rotatores  dorsi  muscles,  392,  393 
Round  ligament  of  liver,  903,  935, 
of  uterus,  1190 

surgical  anatomj^  of,  1284 
Rubro-spinal  tract,  537 
Rudimentum  j^rocessus  vaginalis,  1168 
Ruffini,  endings  of,  775 
Rugae  of  hard  palate,  998,  999 

of  scrotum,  1170 

of  stomach,  1059 

vaginales,  1195 
Running,  movements  of,  385 
Ruysch,  membrane  of,  728 

Sac,  lacrimal,  740,  741,  743 
develo^iment  of,  40 
surgical  anatomy  of,  1239 
omental,  1102 
tooth,  1027,  1028 
Sacculi,  laryngeal,  967 

Sacculus  of  membranous  labyrinth,  759,  762, 
763 
development  of,  769 
ductus  endolymphaticus  of,  763,  769 
reuniens  of,  763,  770 
utriculo-saccularis  of,  763 
macula  acustica  of,  763 
sinus  utricularis  of,  763 
Saccus  lacrimal  is.     See  Sac,  lacrimal 
endolymphaticus,  763 
reuniens,  929 
Sacral  arteries,  lateral,  850,  943 
middle,  841,  942,  949,  1095 
canal,  87 
crest,  85 
ganglia,  711 
index,  Apjiendix  D,  xix 
lymphatic  glands,  921 
nerves,  607 
notcli,  84 
plexus,  639,  647 

anterior  branches  of,  648 
articular  branches  of,  648,  649,  650 


Sacral  plexus,  communications  of,  with  sym- 
patlietic,  647 
muscular  branches  of,  648 
position  and  constitution  of,  647 
symj^athetic,  711 
terminal  branches  of,  650 
promontory,  86,  220 
veins,  895,  896 
Sacro-coccygeal  joint,  264 

nerves,  614,  658 
Sacro-genital  fold,  1156 
Sacro-iliac  joint,  290 

surface  anatomy  of,  1302 
ligaments,  290 
Sacro-sciatic  foramina,  220,  291 
ligaments,  291,  292 
notch,  216,  221 
Sacro-vertebral  angle,  88,  222 
Sacrum,  84,  219,  221,  222 
ossification  of,  94 
promontory  of,  86,  220 

level  of,  1290 
serial  homology  of,  Aj^pendix  C,  xiv 
variations  in,  Appendix  B,  vi 
Sagittal  fontanelle,  Apjoendix  B,  viii 
plane,  5 

sulcus,  105,  108,  109 
suture,  107,  157,  158,  181 
Saliva,  995 

Salivary  glands,  994,  995,  1009 
development  of,  1013 
structure  of,  1008 
nucleus,  524 
Salpingo-palatine  fold,  754,  1033 
Salpingo-pharyngeal  fascia,  754 
fold,  754,  1033 
muscle,  411 
Santorini,  cartilages  of,  961,  962 
fissures  of,  745,  748 
tubercle  of,  964 
Saphenous  artery,  862,  953 
nerve,  long,  646 

surface  anatomy  of,  1308,  1310,  1312 
short,  653 

surface  anatomy  of,  1312 
opening,  354 

surface  anatomy  of,  1306 
veins,  900.     See  also  Vein 
Sarcolemma,  317 
Sartorius  muscle,  356 

action  of,  371,  393 
Scala  tympani,  761 

vestibuli,  761 
Scalene  tubercle,  99 
Scalenus  anticus  muscle,  413 
medius  muscle,  414 
posticus  muscle,  414 

actions  of  these,  419 
Scalp,  1222 

arteries  of,  1222 
lympliatics  of,  1223 
muscles  of,  395,  399 
surgical  anatomy  of,  1222 
veins  of,  879 
Scapha  auriculae,  744 
Scai)ho- cuboid  joint,  311 
Scapho-cuneiform  joint,  312 
Scajjlioid  bone  of  foot,  245 
ossification  of,  249 
surface  anatomy  of,  1311 
of  liand,  202 

ossification  of,  207 


INDEX. 


1407 


Scaphoid  bone  of  hand,  surface  anatomy  of,  1298 
variations  in,  Ajjpendix  B,  xi 

fossa,  125,  161 
Scapula,  183 

architecture  of,  Appendix  A,  ii 

connexions  of,  187 

homology  of,  Ap^iendix  F,  xxv 

ligaments  of,  275 

movements  of,  327 

ossification  of,  187 

surface  anatomy  of,  1289,  1290,  1292 

variations  in.  Appendix  B,  x 
Scapular  arteries,  dorsal,  829 
posterior,  824 
subscapular,  829 
transverse,  825 

index,  Ajjpendix  D,  xix 

line,  1253 

notch,  185 
Scapulo-clavicular  joint,  274 
Scapus  pili.     See  Shaft  of  hair,  776 
Scarjja,  fascia  of,  1278 

foramina  of,  136,  161 

ganglion  of,  768 
Schindylesis,  256 
Schlemm,  canal  of,  725 
Schneiderian  membrane,  722 
Schreger,  lines  of,  1024 
Schultze,  comma  tract  of,  466 
Sciatic  artery,  854.     See  also  Artery 

foramen,  greater,  220,  292 
lesser,  220,  292 

nerve,  great,  647,  648.     See  also  Nerve 
small,  656,  665.     See  also  Nerve 

notch,  greater,  213,  216 
lesser,  216 

plexus,  639,  647 

veins,  895 
Sclera,  725 

canal  of  Schlemm  of,  725 

development  of,  743 

foramina  of,  725 

lamina  cribrosa  of,  725 
fusca  of,  725 

sinus  venosus  of,  725 

spatium  perichorioideale  of,  725,  728 

suprascleral  sj^ace  of,  725 
Scleratogenous  layer,  30,  72,  90 
Sclero -cornea,  725 
Sclerotic  coat,  725 
Scrotal  arteries,  854 
Scrotum,  1159,  1169 

develoj)ment  of,  1207 

septum  of,  431,  1170 
Sebaceous  glands,  777,  778 
Sebum  cutaneum,  777 
Secondary  bones.  Appendix  E,  xx 

tympanic  membrane,  752 
Sectiones  cerebelli,  509 

corporum  quadrageminorum,  533 

medullee  oblongatse,  489 
spinalis,  456,  458 

jiontis,  499 

telencephali,  579,  580,  581,  582,  584 
Segmental  arteries,  932,  933,  939 
anastomoses  of,  939 
somatic,  933,  939 
splanchnic,  933,  939,  942 

tvpe,  2 

veins,  838,  943 
Segmentation  cavitv,  18 

of  head,  183 


Segmentation  nucleus,  17 
of  ovum,  17,  65 
jilanes  of,  17 
Sella  turcica,  121,  168 
Semicanalis  m.  tensoris  tympani,  116,  750 

tubaj  auditivae,  116,  750 
Semicircular  canals,  759,  760,  764 
ampullae  of,  760,  764 
crista  acustica  of,  764 
crus  commune  of,  760 
cupola  terminalis  of,  764 
development  of,  769 
external,  760,  1235 
membranous,  759,  764 
osseous,  759,  760 
jjosterior,  760 
superior,  760 
Semilunar  bone,  202 

homodynamy  of,  Ajipendix  F,  xxiv 
ossification  of,  207 
variation  in.  Appendix  B,  xi 
cartilage,  external,  301 
internal,  301 

surgical  anatomy  of,  1307,  1308 
fascia.     See  Bicipital  fascia 
ganglion,  710,  712 
space  of  Traube,  1271 
Semimembranosus  muscle,  369 
action  of,  370 
surface  anatomy  of,  1305 
Seminal  vesicles,  1159,  1162,  1164 
development  of,  1199,  1205 
structure  of,  1166 
vessels  of,  1167 
Seminiferous  tubules,  1120,  1161 
Semispinalis  muscle,  391 
capitis  muscle,  389 
colli  muscle,  391,  392 
dorsi  muscle,  391,  392 
Semitendinosus  muscle,  369 
action  of,  371 
surface  anatomy  of,  1305 
Sense  organs,  717 
Septal  artery  of  nose,  807 
Septo-marginal  tract,  468 
Septula  testis,  1161 

Septum  or  Septa,  of  aortic  bulb,  930,  947 
atriorum.     See  Sei^tum  of  auricles 
of  auricles,  786,  787,  788 

development  of,  930,  947 
canalis  musculo-tubarii.     See   Process,  coch- 

leariform 
cartilagineum  nasi,  717 
corporum  cavernosoruni.     See  Septum,  pec- 

tiniform 
crural.     See  Femoral  septum 
glandis  j^enis,  1172 
intermedium  of  heart,  929 
intermuscular,  of  arm,  332 
of  foot,  1312 
of  leg,  371 
of  thigh,  354,  1304 
intermusculare  femoris  laterale,  354 
mediale,  354 
fibuhe  anterius,  371 

posterius,  371 
humeri  laterale,  332 
mediale,  332 
linguae,  1005 
lucidum,  573,  597 
membranaceum  ventriculorum,  791 
musculare  ventriculorum,  791 


1408 


INDEX. 


Septum  or  Septa,  nasi,  150,  159,  172,  175,  720 
cartilage  of,  717 
developineut  of,  41 
surgical  anatomy  of,  1239 
orbitale,  739 

pectiniforni,  of  jienis,  1172 
pellucidum.     See  Septum  lueidum 
posticum  of  arachnoid,  602,  606 
prinium,  930 
scroti,  431,  1170 
secundum,  930 
sinuum  frontal ium,  Appendix  A,  i 

sphenoidalium.  Appendix  A,  ii 
spurium  of  auricles,  931 
of  tongue,  1005 
transversum,  926,  1122 

of  semicircular  canals,  764 
tubfe.     See  Coclilearifurm  j^rocess 
of  uterus,  1192 
of  vagina,  1195 
ventriculorum,  789,  791 
development  of,  929,  947 
Serial  homology,  3 

of  vertebric.  Appendix  C,  xiii 
Serous  glands,  1008 
Serratus  anterior  muscle,  326 
action  of,  327,  419 
surgical  anatomy  of,  1255 
magnus  muscle.     See  Serratus  anterior 
posterior  inferior  muscle,  387,  392,  393 
superior  muscle,  386,  392 
actions  of,  393,  419 
Sesamoid  bones  of  llexor  hallucis  brevis,  382 
patella,  229,  359 

of  short  muscles  of  thuml),  212,  288,  344 
cartilages  of  larynx,  960 
of  no.se,  717 
Sexual  eminence,  1200,  1206 
Sheath,  axillary,  828 
carotid,  395,  802 
crural.     See  Femoral  sheath 
dentinal,  1024,  1028 
digital,  of  fingers,  338 

surgical  anatomy  of,  1301,  1302 
of  toes,  373 
femoral,  356,  421,  859 
medullary,  444,  465 
mitochondrial,  15 
primitive,  444 
of  prostate,  1279 
of  rectus  mu.scle,  422,  425,  427 
synovial,  at  wrist,  337,  338 
surgical  anatomy  of,  1301 
Shin,  232 
Short  Vjone.s,  70 
Shoulder,  fasci;e  of,  327 
muscles  of,  327 

surgical  anatomy  of,  1291 
Shoulder-blade,  183 
girdle,  187,  254 

movements  of,  327,  410 
joint,  276 

bursa?  connected  with,  278 
movements  at,  278,  331,  335 
nerves  of,  625,  632 
Shrapnell,  membrane  of,  750,  1232 
Sigmoid  artery,  848,  1075 
cavity,  great,  194,  195 
small,  195 

of  radius.     See  Ulnar  notch 
flexure,  993,  1074,  1084 
mesocolon,  1086 


Sigmoid  notch,  143 

veins,  904 
Sinus  aortiie.     See  Sinus  of  Valsalva! 
arcuatus,  35,  37,  1013 
of  Arlt,  741 
basilar,  881 
cavernosus,  886 
circularis,  885 
coronarius,  784,  787,  870 

abnormalities  of,  954 

development  of,  931,  932 

luorishology  of,  944 
.  costo-mediastinalis,  988 
dune  matris,  883 
epididymidis,  1160 
ethmoidalis.     See  Ethmoidal  cells 
frontalis,  104.     See  also  Frontal  sinus 

surgical  anatomy  of,  1235 
intercavernosus  anterior,  885 

posterior,  885 
lactiferi,  1208 
laryngeal,  967 
lateral,  886 

abnormalities  of,  954 

morphology  of,  944 

surgical  anatomy  of,  1225,  1229, 1234,  1235 
longitudinal,  great.     See  Sinus,  longitudinal, 
superior 

inferior,  599,  884 
abnormalities  of,  954 

superior,  599,  884 

surgical  anatomy  of,  1229 
of  Maier,  740 

niaxillaris  (Highmori),  136.  See  also  Maxillary 
sinus 

surgical  anatomy  of,  1240 
oblique,  of  pericardium,  795 
occipitalis,  886,  954 
of  palate  bone,  172 
parasinoidalis,  1229 
petrosus  inferior,  876,  887 

superior,  599,  886 
phrenico-costalis,  986 
pocularis,  1164,  1205 
of  jjortal  vein,  903 
pyriformis,  965,  1036 
rectales,  1095 

rectus.     See  Straight  sinus 
renalis,  1130,  1137 
rhomboidalis,  22 

sagittalis  inferior.     See  Sinus,  longitudinal, 
inferior 

superior.    See  Sinus,  longitudinal,  superior 
sphenoidalis,  121 

extent  of.  Appendix  A,  ii. 

opening  into,  123 

relation  of,  to  nasal  fossse,  172 
to  orbit,  150 
spheno-j)arietalis,  886,  954 
squamo-petrosal,  954 
straight,  599,  885 
superior  of  utricle,  762 
tarsi,  243 

tonsillaris,  1034,  1035,  1038 
transversus  duraj  matris.     See  Sinus,  lateral 

pericardii,  794 
tympani,  752 

urogenital  is.     See  Canal,  urogenital 
utricularis,  763 
of  Valsalva,  797 
venosus,  927,  929,  930 

scleras,  725  ■  '■ 


INDEX. 


1409 


Sinuses,  lympli,  906 

venous,  of  cranium,  880 
Skein,  chromatin,  10 
Skeletal  muscles,  317 
Skeleton,  69 

appendicular,  69,  70 

morphology  of.  Appendix  F,  xxiii 

axial,  69,  70 

development  of,  24,  35,  36,  40,  41,  47 

splanchnic,  69 
Skin,  772 

appendages  of,  775 

corium  of,  773 

development  of,  778 

of  embryo,  68 

epidermis  of,  773,  778 

papillse  of,  773 

pigment  of,  774 

retinacula  of,  772 

tactile  corpuscles  of,  774,  775 
discs  of,  774 
Skull,  age  differences  in,  181 

akrocephalic,  Aj)pendix  D,  xvii 

bones  of,  103 

brachycephalic.  Appendix  D,  xvii 

brachyfacial.  Appendix  D,  xvii 

brachyuranic,  Aj^pendix  D,  xviii 

breadth  of,  Ajjpendix  D,  xv 
cajaacity  of,  Appendix  D,  xv 
chamaecephalic,  Aj)2)endix  D,  xvii 
chordal,  Apjiendix  E,  xxi 
coronal  sections  of,  173 
cryptozygous,  158,  Appendix  D,  xvii 
dermic,  Aj)pendix  E,  xxii 
development  of,  Appendix  E,  xx 
dolicho-cephalic.  Appendix  D,  xv 
dolicho-facial.  Appendix  D,  xvii 
dolicho-uranic.  Appendix  D,  xviii 
fixed  points  of,  Appendix  D,  xvi 
height  of,  170,  177,  Appendix  D,  xvii 

female,  180 
hypsicephalic.  Appendix  D,  xvii 
indices  of.  Appendix  D 
interior  of,  166 

length  of,  170,  Appendix  D,  xv 
leptoiarosopic.  Appendix  D,  xvii 
leptorhine.  Appendix  D,  xviii 
ligaments  of,  266,  267 

macrodont,  1029.     See  also  Skull,  megadont 
measurements  of,  Ajjpendix  D 
megacephalic.  Appendix  D,  xv 
megadont.  Appendix  D,  xviii 
megaseme,  Appendix  D,  xviii 
mesaticephalic.  Appendix  D,  xv 
mesial  sagittal  section  of,  170 
mesocephalic.  Appendix  D,  xv 
mesodont,  1029,  Appendix  D,  xviii 
mesognathous.  Appendix  D,  xviii 
mesorhine.  Appendix  D,  xviii 
mesoseme.  Appendix  D,  xviii 
mesuranic.  Appendix  D,  xviii 
metopic,  158,  Appendix  B,  viii 
metriocephalic.  Appendix  D,  xvii 
microcephalic.  Appendix  D,  xv 
microdont,  1029,  Appendix  D,  xviii 
microseme.  Appendix  D,  xviii 
morphology  of,' Appendix  E 
norma  basalis  of,  159 
frontalis  of,  146 

lateralis  of,  151 
occipitalis  of,  157 

verticalis  of,  158 

94 


Skull,  orthocephalic.  Appendix  D,  xvii 
orthognathous.  Appendix  D,  xviii 
phajnozygous,  158,  Appendix  D,  xvii 
platyrhine.  Appendix  D,  xviii 
prechordal,  Ap2)endix  E,  xxi 
primordial.  Appendix  E,  xxii 
prognathous.  Appendix  D,  xviii 
in  section,  166 
sexual  differences  in,  180 
surgical  anatomy  of,  1223 
tapeinocephalic.  Appendix  D,  xvii 
trabecular  portion  of.  Appendix  E 
ujjper  aspect  of  base  of,  166 
vertebral  portion  of.  Appendix  E 
vertebrate  theory  of.  Appendix  E 
as  a  whole,  146 
Smegma  embryonum,  779 

l^rseputii,  1171 
Socia  parotidis,  1011 
Solar  plexus,  712 
Soleus  muscle,  378 
action  of,  384 

surgical  anatomy  of,  1309,  1310 
Solitary  glands,  1062,  1063,  1073,  1075 
Somaesthetic  area,  593 
Somatic  mesoderm,  25,  50 

segmental  arteries,  938,  939 
Somatopleure,  26 
Somites,  mesodermic,  26,  30,  31,  66 

protovertebral,  26,  30,  31,  66 
Space  of  Burns,  879 
epidural,  598,  600 
intercostal,  101 
interpeduncular,  475,  478 
interpleural,  977,  982 
mediastinal,  977,  982 
of  Nuel,  767 

retropharyngeal,  1031,  1037 
semilunar,  of  Traube,  1271 
subarachnoid,  597,  601,  1227 
cisternae  of,  602 

communications  of,  with  ventricles,  601 
fluid  of,  601,  603 

ligamenta  denticulata  of,  602,  605 
septum  posticum  of,  602,  606 
spinal,  602 

trabecular  tissue  of,  601 
subdural,  597,  600 

surgical  anatomy  of,  1291 
Spaces  of  Fontana,  727 

interglobular,  of  dentine,  1024 
lymphatic,  904 
perivascular,  905 
Spatia  anguli  iridis,  727 

intercostalia.     See  Space,  intercostal 
interglobularia.     See  Spaces,  interglobular 
perichorioidealia,  725,  728 
j)erilymphaticum  auris  interna,  762 
zonularia,  735 
Sperm  cells,  13,  1204 
Spermatic  artery,  842,  1162 
abnormalities  of,  949 
morphology  of,  942 
cord,  1162,  1168 

surgical  anatomy  of,  1265 
fascia,  428 
plexus,  714 
vein,  894 

abnormalities  of,  955 
development  of,  938 
morphology  of,  944,  945 
surgical  anatomy  of,  1280 


1410 


INDEX. 


Spermatids,  13,  15 
Spermatocyte,  13,  15 
of  first  order,  13,  15 
of  second  order,  13,  15 
Spermatogonia,  13,  15 
Spermatozoa,  7,  13,  15,  1061 
Spheno-ethmoidal  recess,  172 
Sphenoid  bone,  121 

architecture  of,  Api:)endix  A,  ii 
connexions  of,  126 
ossification  of,  126 
variations  in,  Appendix  B,  ix 
Sphenoidal  angle  of  parietal  bone,  108,  153 
crest  of  sphenoid  bone,  123 
fissure,  149.     See  also  Fissure  sphenoidal 
process  of  palate,  140 
sinus.    Appendix    A,    ii.       See    also    Sinus 

sphenoidalis 
spine,  123 
turbinals,  127,  170 
Spheno-mandibular  ligament,  37,  268 
Spheno-maxillary  fissure,  149.    See  also  Fissure 

fossa,  156 
Spheno-palatine  artery,  813 
foramen,  139,  156,  172 
ganglion,  682,  699 
nerves,  681 
notch,  139 
vein,  880 
Spheno-parietal  sinus,  886,  954 

suture,  151 
Spheno-petrous  fissure,  162,  163 
Spheno-squamous  suture,  155,  159 
Spheno-vomerine  canal.  Appendix  B,  x 
Spheno-zygomatic  suture,  149 
Sphere,  attraction,  9,  10,  11 
Sphincter  ani  externus,  431,  1095 
action  of,  433 
internus,  1093,  1095 
pupillae,  731 
pyloric,  1056,  1058 
recti,  1095 
vaginae,  432 
vesicae,  1157 
Spigelian  lobe  of  liver,  1112 
Spina  or  Spine,  alar  of  sphenoid,  123,  154,  165 
angularis.     See  Spine,  alar 
bifida,  91 
ethmoidalis,  123 
frontalis,  104 

genialis.     See  Spina  mentalis 
helicis,  745 

iliaca  anterior  inferior,  213 
superior,  212,  222 
posterior  inferior,  213,  222 

superior,  213,  222 
surface  anatomy  of,  1302,  1305 
ischiadica,  216 

sexual  differences  of,  221 
surface  anatomy  of,  1303 
mentalis,  143 
nasal.     See  Spina  frontalis 
nasalis  anterior,  136,  150,  1237 

posterior,  138,  159 
palatine.     See  Spina  nasalis  posterior 
peroneal,  244 

variations  in,  Appendix  B,  xiii 
pubic,  217,  1306 
scapula;,  185 
sphenoidal,  123 
suprameatal,  114,  1230,  1233 
of  tibia,  231 


Spina   or   Spine,   trochlearis  of  frontal  bone, 
105,  147 
tympanica  major,  748 
minor,  748 
Spinal  accessory  nerve,  695.     See  also  Nerve 
arteries  of  ilio-lumbar,  850 
of  intercostals,  838 
of  lateral  sacral,  850 
of  vertebral,  818,  819 
canal,  76,  87,  88 
column,  75,  88 
cord,  443,  452 

anterior  root-zone  of,  609 

basis  bundle  of,  anterior,  470,  473 

lateral,  468,  470,  473 
Cauda  equina  of,  454,  609 
cell-columns  of,  461 

intermedio-lateral,  461,  463 
posterior,  461,  463 
ventral,  461 
central  canal  of,  456,  459,  460,  473,  484 
cervical  enlargement  of,  454,  457,  1298 
Clarke's   vesicular    column   of,   464,   468, 

■     469 
columns  of,  antero-lateral,  455 
anterior,  455,  459,  470,  473,  483 
of  Burdach  of,  455,  466,  473,  484,  491 
of  Goll  of,  455,  466,  473,  484,  491 
grey,  456,  457,  460,  461 
lateral,  455,  459,  468,  473,  484 
of  nerve-cells  of,  461,  462 
posterior,  455,  459,  466,  468,  473,  484 
white,  455,  459 
commissure  of,  anterior  white,  456,  470, 
473 
grey,  456 
anterior,  456 
posterior,  456,  457,  471 
conus  medullaris  of,  452,  458,  459 
cornua  of,  456 

anterior,  456,  457,  460,  461,  469,  490, 

515 
lateral,  456,  457,  460,  461 
posterior,  456,  457,  460,  461,  468,  491, 
492,  499 
development  of,  471 
dorsal  nucleus  of,  464 
enlargements  of,  454,  457 

surgical  anatomy  of,  1289,  1290 
fasciculus  solitarius  in,  518 
filum  terminale  of,  452,  459 
fissures  of,  454 

antero-median,  455,  460,  473 
postero-median,  455,  460,  473 
formatio  reticularis  of,  457,  460 
funiculus  cuneatus  of,  455,  466,  473 

gracilis  of,  455,  466,  473 
grey  matter  of,  456,  457,  460,  461 
internal  strvicture  of,  456 
intersegmental  association  fibres  of,  468, 470 
length  of,  452 

ligamenta  denticulata  of,  453,  602 
longitudinal  commissural  fibres  of,  468, 470 
lower  limit  of,  in  child,  1290 
lumbar  enlargement  of,  454,  457,  1290 
marginal  tract  of  Lriwentlial  of,  521 
membranes  of,  453,  597,  599,  601,  605 
nerve-cells  of,  445,  461 
nerve-fibres  of,  444,  465,  466,  468 
neuroglia  of,  461,  465 

origin  of  nerves  from,  443,  453,  455,  515, 
516,  608 


INDEX. 


1411 


Spinal   cord,   posterior   paramedian  sulcus  of, 
455,  460 
postero-lateral  sulcus  of,  455 
regional  dilferences  in,  457,  460 
regions  of,  454 
relation  of,  to  vertebrae,  452 
segments  of,  454 
sensory  and  motor  distribution  of  various 

segments  of  1291 
septa  of,  453,  455,  459,  460,  465,  473 
substantia  gelatinosa  of,  456,  457,  461,  468, 

525 
sulci  of,  454 

surgical  anatomy  of,  1290 
theca  of,  453 

tract  of  Burdacli  of,  466,  473,  484,  491 
comma,  466 

descending  septo-marginal,  468 
direct  cerebellar,  464,  468,  473 
of  Goll,  466,  473,  484,  491 
of  Gowers,  468,  473 
of  Lissauer,  468 

pyramidal,  crossed,  468,  469,  473 
direct,  470,  473 
trigeminal  root-iibres  in,  526 
veins  of,  888 

white  matter  of,  459,  460,  465 
foramen  of  cervical  vertebrae,  78 
of  lumbar  vertebrae,  83 
of  thoracic  vertebrte,  81 
ganglia,  443,  608,  661 
nerves,  443,  607 
venous  plexus,  anterior,  887 
posterior,  887 
Spinalis  dorsi  muscle,  381 
Spindle,  achromatic,  10,  13 
Spine,  75,  88.     See  also  Vertebral  column 
Spines  of  various  bones.     See  Spina 
Spino-glenoid  ligament,  275 
Spino-thalamic  tract,  468,  494 
Siainous  process  of  cervical  vertebrae,  78,  80 
of  lumbar  vertebrae,  83 
of  thoracic  vertebrae,  81 
of  sacrum,  85 

homology  of  spinous  j) recesses.  Appendix 

surgical  anatomy  of  spinous  processes,  1284 
Spiral  fasciculi  of  cochlear  nerve,  768 

ganglion,  768 

line  of  femur,  224,  226 

tubules,  1139 
Splanchnic  ganglion,  710 

mesoderm,  25,  50 

nerve,  710 

segmental  arteries,  939,  942 

skeleton,  69 
Splanchnology,  3 
Splanchnopleure,  26 
Spleen,  1210 

accessory,  1212 

development  of,  1213 

hilum  of,  1211 

Malpighian  corpuscles  of,  1213 

nerves  of,  1212 

notches  and  tissures  of,  1212 

peritoneal  relations  of,  1212 

pulp  of,  1213 

structure  of,  1213 

surgical  anatomy  of,  1288 

sustentaculum  of,  1083 

trabeculae  of,  1213 
Splenial  centre  of  mandible,  145 


Splenic  artery,  844,  1212,  1213.  See  also  Ailery 

flexure  of  colon,  1074,  1083 

surgical  anatomy  of,  1274,  1288,  1290 

lymphatic  glands,  918 

plexus,  713 

vein,  901,  904,  1213 
Sjjlenium  cor])oris  callosi,  571 
Splenius  capitis  muscle,  387 
action  of,  392 

colli  muscle,  387 
action  of,  392 
Spongioblasts,  22,  471,  661,  732,  742 
Spongioplasm,  8 
Spongy  bone,  71 
Spot,  germinal,  10,  11 
Spur  of  malleus,  755 
Squama  occipitalis,  108 

temporalis,  112 
Squamo-jietrosal  sinus,  944,  954 
Squamosal  bone,  Appendix  E,  xxi 
Squamoso-mastoid  suture,  113 
Squamous  suture,  151 
Stalk,  allantoic,  51,  65 

body,  33,  50,  65 

optic,  478,  698,  703,  741,  742 

of  thalamic  radiation,  545 
Stajjedial  artery,  757 
Stapedius  muscle,  757 
Stapes,  756 

annular  ligament  of,  752 

development  of,  757 

ligaments  of,  757 

movemeiits  of,  758 

surgical  anatomy  of,  1232 
Stellate  ligament,  269 
Stenson,  canals  of,  998 

duct  of,  995,  1011 

foramen  of,  136,  137,  161 
Stephanion,  152,  158 ;  Appendix  D,  xvi 
Sternal  angle,  95 

articulations,  272 

bar,  91 

furrow,  1253 

line  of  i:)leural  reflexion,  979,  980. 

lines,  1253 

lymphatic  glands,  924 

nerve,  617,  619,  622 

veins,  874 
Sternalis  muscle,  325 
Sternebrae,  95 
Sterno-clavicular  joint,  27S,  275 

movements  at,  327 
Sterno-clavicularis  muscle,  326 
Sterno-cleido-mastoid  muscle,  405 
action  of,  393,  419 
surgical  anatomy  of,  1249 
Sterno-hyoid  muscle,  406 

action  of,  410 
Sterno-mastoid  artery  of  occipital,  807 

of  superior  thyroid,  805 
Sterno-mastoid    muscle.       See    Sterno  -  cleido- 

mastoid 
Sterno-pericardial  ligaments,  793 
Sterno-thyreoid  muscle,  406 

action  of,  410 
Sternum,  94 

architecture  of.  Appendix  A, 

movements  of,  272 

ossification  of,  96 

surgical  anatomy  of,  1255 

variations  in.  Appendix  B,  vii 
Stigmata  of  capillaries,  780 


1412 


INDEX. 


Stilling,  canal  of,  736 
Stomach,  993,  1050 
aretB  gastricte  of,  1059 
arteries  of,  1060 
bed  of,  1053 
capacity  of,  1053 
cardiac  orifice  of,  1051,  1055 

surgical  anatomy  of,  1271,  1287,  1290 
portion  of,  1055 
of  child,  1057 

curvatures  of,  1051,  1052,  1055 
development  of,  1105 
in  female,  1057 
form  of,  1051,  1052 
foveoliB  of,  1059 
fundus  of,  1051,  1052,  1055 

surgical  anatomy  of,  1271,  1290 
gastro-phrenic  ligament  of,  1057 
glands  of,  1059 
great  curvature  of,  1055 

surgical  anatomy  of,  1271,  1290 
hour-glass,  1058 
lesser  curvature  of,  1055 

surgical  anatomy  of,  1271,  1290 
lymphatics  of,  918,  1060 
mucous  membrane  of,  1059 
muscular  coat  of,  1058 
peritoneal  relations  of,  1057 
pit  of,  96,  102 
plicee  villosae  of,  1059 
position  of,  1051,  1052 
pyloric  antrum  of,  1051,  1052,  1055 
canal  of,  1052,  1055 
ligaments  of,  1058 
orifice  of,  1051,  1058 

surface  anatomy  of,  1271 
portion  of,  1055 

surgical  anatomy  of,  1228,  1290 
sphincter  of,  1056,  1058 
valve  of,  1056 
relations  of,  1053 
rugae  of,  1059 
serous  coat  of,  1058 
«ize  of,  1053 
structure  of,  1058 
submucous  coat  of,  1059 
surfaces  of,  1051,  1054 
surgical  anatomy  of,  1271,  1286 
uncovered  area  of,  1057 
veins  of,  1060 
Stomach-bed,  1053 
Stomach-chamber,  1053 
Stomata  of  capillaries,  780 
Stoniatodajum,  34,  38,  66,  1105 
Straight  sinus,  885 
Strand -cells,  465 

Stratum  bacillare  retinas,  732,  734 
cinereum  colliculi  superioris,  534 

ce rebel]  i,  509 
circulare  membranas  tympani,  751 

musculare  ventriculi,  1058 
compactum,  57,  58 
comeum  epidermis,  773 

unguis,  776 
cutaneum  membranse  tympani,  751 
disjunctuin,  774 
filamentoHum,  774 
germinativum  epidermis,  773 

unguis,  776 
granulosum  cerebelli,  513 

ovarii,  1185 
griseum  coUicuH  superioris,  534 


Stratum  griseum  centrale  pedunculi  cerebri,  533 
interolivare,  496 
lemnisci,  534 

longitudinale  musculare  ventriculi,  1058 
lucidum,  774 
mucosum  epidermis,  773,  774 

membrante  tympani,  751 
opticum,  534,  732 
pigmenti  retinae,  731,  732,  734 
radiatum  membranse  tympani,  751 
spongiosum,  57,  58 
zonale  cerebri,  585 

sectionum  corporum  quadrigeminorum,  534 
thalamencephali,  545 
Streak,  primitive,  19,  21,  65 
Stria  or  Striae  acusticae,  481,  497,  521 
of  Gennari,  585 
longitudinalis  lateralis,  571 

medialis,  571 
medullaris  thalami,  548 

fossae  rhomboideae.     See  Striae  acusticae 
olfactorii    lobi    intermedia.       See    Olfactory 
tract,  middle  root,  570 
lateralis.      See    Olfactory   tract,   lateral 

root,  570 
medialis.      See   Olfactory    tract,  mesial 
root,  570 
of  Retzius,  1024 

terminalis.     See  Taenia  semicircularis 
transversae  corporis  callosi,  571 
vascularis  auris  internee,  765 
Striate  arteries,  817 

veins,  882 
Stripe  of  Hensen,  767 
Stroma  iridis,  730 
ovarii,  1184 
vitreum,  736 
Stylo-auricularis  muscle,  746 
Styloid  process  of  fibula,  234 
of  metacarpal  bone,  209 

variations  in.  Appendix  B,  xi 
of  radius,  200 

surgical  anatomy  of,  1298 
of  temporal  bone,  116,  154,  156,  164 
development  of,  37 
ossification  of,  120 
of  ulna,  197 

surface,  anatomy  of,  1298 
Stylo-glossus  muscle,  409,  410 
Stylo-hyals,  37,  120,  146 
Stylo-hyoid  ligament,  37,  146,  269 
muscle,  407 
action  of,  410 
Stylo-mandibular  ligament,  269,  395,  1010 
Stylo-mastoid  artery,  808 

foramen,  116,  164 
Stylo-pharyngeus  muscle,  411,  413 
Subacromial  bursa,  278 
Subanconeus  muscle,  335 
Subarachnoid  fluid,  601,  603 
space,  597,  601 

surgical  anatomy  of,  1227 
Subarcuate  fossa,  119,  121 
Subcallosal  gyrus,  571,  573,  597 
Subclavian  artery,  821,  822 

abnormalities  of,  947,  948,  951 
branches  of,  823 
develoj^ment  of,  933,  934 
morphology  of,  941,  942 
surgical  anatomy  of,  1252,  1255 
groove,  99 
loop,  708 


INDEX. 


1413 


Subclavian  lymphatic  tnink,  908 
plexus,  708 
vein,  936,  938 

abnonnalities  of,  955 
luorpliology  of,  944,  946 
surgical  anatomy  of,  1252 
Subclavius  muscle,  325 

action  of,  326 
Subcoracoid  centre,  188 ;  Appendix  F,  xxv 
Subcostal  angle,  102 
artery,  838 
groove,  98 
line,  1047 
muscles,  416,  419 
plane,  1047 
Subcrureus,  359 
Subdeltoid  bursa,  278 
Subdural  s^jace,  597,  600 

surgical  anatomy  of,  1291 
Sublingual  arterv,  805 
glaAid,  805,  1012 

develojiment  of,  1013 
surgical  anatomy  of,  1244 
region,  997 
Submalleolar  apophysis,  Appendix  B,  xiii 
Submaxillary  artery,  806 
fossa,  143 

ganglion,  685,  687,  707 
gland,  995, 1011 

develojiment  of,  1013 
duct  of,  997,  1012 
surgical  anatomy  of,  1249 
lymphatic  glands,  911,  1250 
Submental  artery,  806 

triangle,  1248 
Subnasal  point,  Appendix  B,  xvi 
Suboccipital  nerve,  611,  614 

triangle,  391 
Subpleural  jilexus,  825 
Subpubic  ligament,  292 
Subscapular  artery,  829 
of  suprascapular,  825 
bursa,  278 
fossa,  187 

lymphatic  glands,  914 
nerve,  long,  635 
lower,  635 
short,  635 
Subscai)ularis  muscle,  331 
action  of,  331 
minor  muscle,  331 
Substantia  adamantina,  1023 
corticalis  lentis,  734 
lympho-glandulae,  906 
sectionum  telencephali,  584 
cerebelli,  512 
eburnea,  1024 
ferruginea,  488,  504 
gelatinosa  Rolandi,  456,  461,  468,  485,  490, 

491,  502,  525,  528 
grisea  centralis  medullse,  456 
lentis,  736 

medullaris  lympho-glandulse,  906 
nigra,  533,  548,  581 
propria  cornete,  726 
Subthalamic  tegmental  region,  542,  546 
Suctorial  pad,  399,  407,  997 
Sudoriferous  glands,  778 
Sulcus  or  Sulci 
alar,  717 

alveolo-glossal,  1244 
anthelicis  transversus,  745 


Sulcus  or  Sulci,  arteriie  occipitalis,  115 

temporalis  mediae,  113 

vertebralis,  79 
auris  anterior,  744 
basilaris  of  pons,  486 

bicipitalis  lateralis.      See  Furrow,  bicipital, 
external 

medialis.    See  Furrow,  bicipital,  internal 
calcanei,  243 
callosal,  568 

caroticus.     See  Groove,  carotid 
centralis  cerebri  (Rolandi),  558 

insulpe,  568 
cerebelli,  506,  529 
cerebri,  554 

development  of,  596 
chiasmatis.     See  Optic  groove 
cinguli.     See  Fissure,  calloso-marginal 
circularis  Reilii,  556,  567 
of  cord,  454,  455,  460 
coronarius  cordis,  783 
corporis  callosi.     See  S.  callosal 
costse,  98 
cruris  helicis,  745 
diagonalis,  560,  561 
ethmoidalis  ossis  nasalis,  132 
fimbrio-dentate,  569 
frontal,  of  frontal  bone,  105 

surface  anatomy  of,  1225 
frontalis  inferior,  560 

superior,  560 

surface  anatomy  of,  1225 
fronto-marginalis,  560,  561 
hamuli  pterygoidei,  125 
horizontalis  cerebelli,  506 
hypothalamicus  Monroi.     See  S.  of  Monro 
intermedins    posterior    medulla?   oblongatae. 

See  Paramedian  grooA^e,  455 
intraparietalis,  563 

intertubercularis  humeri.  See  Groove,  bicipital 
lacrimalis  maxillse,  135 

ossis  lacrimalis,  131 
lateral,  of  parietal  bone,  108 
lateralis  niesencephali,  533 

posterior  medullse  oblongatae,  482 
spinalis,  455 
limiting,  of  Reil,  556 
longitudinalis  of  heart,  784 
lunatus  occipitalis,  567 
malleolaris,  233,  237,  748 
medianus  posterior  medullfe  spinalis,  455 
of  Monro,  551,  594 

musculi  iiexoris  hallucis  longi  calcanei,  244 
tali,  241 

peronsei  calcanei,  244 
ossis  cuboidei,  247 
mylo-hyoideus,  143 
nervi  oculo-motorii,  533 

petrosi  superficialis  majoris,  118 
minoris,  118 

radialis.     See  Groove,  musculo-sjiiral 

ulnaris,  191 
obturatorius,  218 
occipitalis  lateralis,  564,  566 

transversus,  563,  564,  566 
occipito-temporal,  566,  567 
oculo-nasal,  39 
olfactorius,  562 
orbitalis,  562 
parallel,  567 

surface  anatomy  of,  1224,  1225 
paramedians,  560,  561 


1414 


INDEX. 


Sulcus  or  Sulci,  of  parietal  lobe,  563 
perouaei,  237 

petrosus  inferior  ossis  occipitalis.  111 
temporalis,  116 
sui:)erior,  116 
post-central,  563,  564 

surface  anatomy  of,  1225 
post-limbic,  563 
prascentralis,  560,  561,  564 
surface  anatomy  of,  1225 
primarius,  530 
promontorii,  752 
pterygo-palatinus,  126 
rostrales,  561 

sagittalis  ossis  frontalis.     See  S.,  frontal 
occipitalis,  109 
parietalis,  108 
sclerae,  724 
sigmoideus,  116 
spiralis  externus  cochleEe,  765 

internus  cochleae,  765 
subclavise,  99 

subclavius  pulmonis,  985,  987  ■ 
subparietalis.     See  S.,  post-limbic 
tali,  240 

temporalis  inferior,  567 
medius,  567 
superior,  567 
terminalis  atrii  dextri  (His),  786,  787 
significance  of,  932 
linguee,  1000,  1014 
transversus  ossis  occii^italis,  109 

parietalis.     See  Groove  for  lateral  sinus 
tubae  auditivae,  124,  163 
tympanicus,  748,  750 
vallecula;,  506,  507 
Superciliary  ridge,  103,  147 
sexual  differences  of,  180 
surface  anatomy  of,  1237 
Superficialis  volse  artery,  832 
Supination,  movement  of,  283,  352 
Supinator  radii  brevis  muscle,  349 
action  of,  352 
longus.     See  Brachio-radialis 
Supracallosal  gyrus,  569,  571 
Supraclavicular  nerves,  624 
Suprahyoid  artery,  805 

lymphatic  glands,  911,  1218 
muscles,  406,  410 
Supramandibular  nerve,  688 
Supramarginal  gyrus,  563,  564 
surface  anatomy  of,  1224 
triangle,  1225 
Supramastoid  crest,  113,  152 
Suprameatal  spine,  114,  1230,  1233 

triangle,  114,  154 
Supranasal  bone,  Appendix  B,  viii 
Supraoccipital  bone,  113 

development  of.  Appendix  E,  xxi 
Supraorbital  artery,  816,  1224 
foramen,  103,  147 
margin,  104,  147 
nerve,  679 
notch,  103,  147 

surface  anatomy  of,  1224 
ridge,  103 
vein,  879 
Suprarenal  artery,  842,  942 
capsule,  1213 

development  of,  715,  1216 
in  foetus,  1215 
nerves  of,  1215 


Suprarenal  capsule,  structure  of,  1215 
surgical  anatomy  of,  1286,  1290 
vessels  of,  1215 
impression  of  liver,  1111 
plexus,  713 
vein,  893 

abnormalities  of,  955 
development  of,  938 
morphology  of,  944,  945 
Suprascapular  artery,  825 
ligament,  275 
nerve,  624,  625,  673 
notch,  184 
region,  1284 
vein,  879 
Suprascleral  lymjphatic  space,  725 
Supraspinatus  muscle,  329 

action  of,  331 
Supraspinous  artery,  825 
fossa,  185 
ligament,  264 
Suprasternal  artery,  825 
notch,  95 
region,  1253 
Supratonsillar  fossa,  1034,  1035,  1036,  1038 
Supratrochlear  foramen.  Appendix  B,  xi 
lymphatic  glands,  914 
nerve,  679 
Sural  arteries,  863,  864 

nerve,  650,  657 
Surface  and  surgical  anatomy,  1222 
of  abdomen,  1264 
of  abdominal  wall,  1264 
of  abdominal  cavity,  1267 
of  ankle,  1310 
of  arm,  1295 
of  axilla,  1293 
of  back,  1284 
of  buttock,  1302 
of  cranium,  1222 
of  ear,  1229 
of  elbow,  1296 
of  face,  1236 
of  female  pelvis,  1282 
of  foot,  1310 
of  forearm,  1298 
of  hand,  1298 
of  head,  1222 
of  heart,  1262 
of  knee,  1307 
of  leg,  1308 
of  lungs,  1255 
of  neck,  1246 
of  perineum,  1277 
of  popliteal  space,  1305 
of  shoulder,  1291 
of  thigh,  1303,  1305 
of  thorax,  1253 
Surgical  neck  of  humerus,  190 
Suspensory  ligament  of  clitoris,  1197 
of  lens,  736 
of  ovary,  1183 
of  penis,  1172 
muscle  of  duodenum,  1070 
Sustentacular  cells,  13 
Sustentaculum  lienis,  1083 
tali,  244 

architecture  of.  Appendix  A,  v 
surface  anatomy  of,  1311 
variation  in.  Appendix  B,  xiii 
Sutural  bones,  133 
Suture,  Sutura,  255,  256 


INDEX. 


1415 


Suture,  Sutura,  coronalis,  108,  151,  158 

synostosis  of,  181 
dentata,  256 

develoiameut  of,  260 
frontalis,  147 
fronto-malar,    1224.     See  also  Sutura    zygo- 

matico-fron  talis 
fronto-maxillaris,  147 
fronto-squamosal,  119,  133 
harmonia,  256 

infraorbitalis,  Appendix  B,  ix 
intermaxillaris,  136,  150 
internasalis,  obliteration  of,  Appendix  B,  x 
lambdoid,  108,  109,  151,  157,  158 

surgical  anatomy  of,  1223,  1225 
linibosa,  256 
malo-maxillary.       See    Sutura    zygomatico- 

niaxillaris 
masto-squamosal,  113,  114 
metopic,  106 
naso-frontal,  147 
notlia,  256 

occipito-mastoid,  151,  165 
orbito-maxillary  frontal,  Appendix  B,  ix 
palatina  mediana,  161 

transversa,  161 
parieto-mastoidea,  151 
petro-squamous,  113,  114  ;  Appendix  B,  x 

surgical  anatomy  of,  1233 
premaxillary,  137 
saggital,  107,  157,  158,  181 
serrata,  256 
spheno-parietalis,  151 
spheno-squamosa,  155,  159 
spheno-zygomatica ,  149 
squamosa,  151,  256 
squamosa-mastoidea,  113,  114 
vera,  256 

zygoniatico-frontalis,  147 
zygoraatico-maxillaris,  147,  150,  155 
Swallowing,  movements  in,  413 
Sweat  glands,  778 

develoi3ment  of,  779 

ducts  of,  778 

glomerulus  of,  778 

orifice  of,  778 
Sylvian  aqueduct,  476,  478,  481,  531,  533,  542, 
551 
fissure,  553,  555,  562 

development  of,  556,  557 

surgical  anatomy  of,  1224,  1225 
fossa,  556,  596 
line,  1225 

point,  555,  1224,  1225 
vein,  882 
Symmetry,  4 
Sympathetic  system,  443,  703 

cervical,  706,  715,  1251 

commissural  cords  of,  703,  705,  706,  710,  711 

development  of,  715 

functions  of,  704 

ganglia  of,  704.     See  also  Ganglia 

gangliated  cord  of,  704,  705,  709,  710 

general  structure  of,  704 

lumbar,  710 

morj^hology  of,  716 

nerve-fibres  of,  704 

plexuses  of,  712 

rami  communicantes  of,  704,  705.     See  also 
Kami 

sacral,  711 

thoracic,  708 


Symphysis  of  jaw,  141 
ossis  pubis,  217,  292 
sacro-coccygea,  264 
Synarthrosis,  255,  257 
Synchondrosis,  255,  256,  260 
cranii,  256 
epiphyseos,  266 
neuro-central,  92 

petro-occipitalis.     See  Petro-jugular,  256 
spheno-occipitalis,  256 
sternalis,  272 
Syndesmosis   tibio-fibularis.     See  Joint,  tibio- 
fibular, inferior 
Synovia,  256,  260 
Synovial  bursae,  258 
fat-pads,  258,  281,  295 

membranes  of  joints  of  lower  limb,  293  to  315 
of  pelvis,  290 
of  thorax,  270,  271,  272 
of  upper  limb,  273  to  288 
of  temporo-mandibular  joint,  268 
sheaths  at  wrist,  337 
Systema  lymphaticum,  904 
nervorum  centrale,  443 
periphericum,  607 
sympathicum,  703 
Systematic  anatomy,  3 
Systemic  circulation,  783,  870 

Table   of  relations   of  structures   to  vertebral 

spines,  1289 
Tactile  corpuscles,  774,  775 

discs,  774 
Taenia  coli,  1061,  1074,  1087 

fimbriae.     See  Taenia  hippocampi 

fornicis,  572 

hippocamjji,  572 

pontis,  548 

semicircularis,  544,  574,  576,  582 

thalami,  544,  547,  594 
Tail,  45,  66 

fold,  27,  33,  49 

gut,  45 
Talo-calcaneal  joint,  308,  315 
Talo-calcaneo-navicular  joint,  309 
Talo-fibular  ligaments,  307 
Talo-scaphoid  joint,  309,  315,  1312 
Talo-tibial  ligaments,  307 
Talus,  238 

Tangential  fibres  of  cortex,  585 
Tapeinocephalic  skulls,  Appendix  D,  xvii 
Tapetum,  571,  576,  588,  591 

cellulosum,  729 

of  chorioid,  729 

fibrosum,  729 
Tarsal  arches  of  eyelids,  740 

artery,  869 

cartilages,  1239 

glands,  739 

ligaments  of  eyelid,  739,  741 
Tarsale,  os.  Appendix  F,  xxiv 
Tarso-meta tarsal  joints,  313 

surgical  anatomy  of,  1311 
Tarsus,  238,  248 

architecture  of.  Appendix  A,  v 
ossification  of,  249 
transverse  articulation  of,  311 
variations  in.  Appendix  B,  xiii 

palpebrae,  738 
Taste  buds,  770,  1004 

nerves  of,  771 

organs,  770 


1416 


INDEX. 


Tectorial  membrane,  766,  767 
Teeth,  995,  1014,  1242 

alveoli  of,  1016,  1027,  1028 

apical  foramen  of,  1015 

arrangement  of,  in  jaws,  1021 

auditory,  766 

basal  ridge  of,  1017 

bicuspid,  1015,  1018 

canine,  1015,  1017,  1023 

cementum  of,  1014,  1023,  1025,  1027 

cingulum  of,  1017 

contact  surface  of,  1016 

cro^^^l  of,  1015 

cusps  of,  1015,  1017,  1021 

deciduous,  1015,  1022,  1027 

dental  index  of,  1029 
lamina  of,  1026 

dentine  of,  1014,  1023,  1024,  1025,  1026,  1028 

dermal,  1025 

development  of,  1025 

enamel  of,  1014,  1023,  1025,  1026,  1028 

eruption  of,  1022,  1025,  1027,  1028 

eye,  1017 

fangs  of,  1015 

follicles  of,  1027,  1028 

germs  of,  1027 

grinding  surfaces  of,  1016 

gubernaculum  of,  1028 

incisor,  1015,  1017,  1022 

lingual  cusp  of,  1017 

milk,  1014,  1015,  1022,  1027,  1242 

molar,  1015,  1019,  1022,  1027 

morphology  of,  1029 

multicuspidate,  1019 

Nasmytli's  membrane  of,  1024 

nerves  of,  dental  anterior,  682 
inferior,  685 
middle,  682 
posterior,  681 

papilla  of,  1025,  1026 

permanent,  1014,  1015,  1016,  1027,  1242 

premolar,  1015,  1018 

pulp  of,  1016,  1023,  1025,  1027 
cavity  of,  1016,  1027 

relative  sizes  of,  1080 

reserve  germs  of,  1027 

root  membrane  of,  1015,  1016,  1027 

roots  of,  1016,  1025,  1027 

structure  of,  1015,  1023 

tartar  of,  1016 

temporary,  1014,  1022,  1027 

tubercles  of,  1015 

variations  of,  1022 

wisdom,  1015,  1019 
Tegmen  tympani,  118,  169,  749,  752 
surgical  anatomy  of,  1232 

ventriculi  quarti.   See  Ventricle,  fourth,  roof  of 
Tegmental  region,  subthalamic,  542,  546 
Tegmentum,  532,  535,  542,  546,  550 
Tela  chorioidea  ventriculi  quarti,  604 
tertii.     See  Velum  interpositum 

submucosa  intestini,  1061 
peritonei,  1097 
ventriculi,  1059 

subserosa,  1045 
Telencephalon,  478,  481,  553,  594 
Telolecithal  ova,  11 
Telophase,  10 
Temporal  area,  125 

artery,  deep,  anterior,  812 
posterior,  812 
middle,  809 


Temporal  artery  of  j)osterior  cerebral,  821 
of  retina,  735 

superficial,  809.     See  also  Artery 
bone,  112,  153,  159 

architecture  of.  Appendix  A,  ii 
connexions  of,  119 

mastoid  antrum  of,  752.     See  also  Antnim 
ossification  of,  119 

petromastoid  part  of,  112,  115,  159 
squamous  part  of,  112,  120,  159 
tympanic  part  of,  112,  114,  119,  159 
variations  in,  Appendix  B,  ix 
canal,  141,  153 
crest,  104,  107,  151 

surface  anatomy  of,  1224,  1237 
fascia,  394 
fossa,  107,  153 
gyri,  567.     See  also  Gvri 
line,  104,  107,  146,  15-1,  153 
lobe,  567,  588 

surgical  anatomy  of,  1225 
muscle,  402,  404 
nerve  of  auriculo-temporal,  684 
deep,  683 
of  facial,  687 
of  orbital,  1224 
of  superior  maxillary,  681 
plane,  107 
process,  140 
ridge,  104,  152,  153 
sulci,  567 
veins,  879,  880 
Temporo-maxillary  arch,  Appendix  B,  x 
joint,  267 

surgical  anatomy  of,  1230 
vein,  876,  880.     See  also  Vein 
Temporo-pontine  tract,  540,  583,  591 
Tendo  calcaneus  (Achillis),  377 
surgical  anatomy  of,  1310 
Tendon,  conjoint,  425,  426 

surgical  anatomy  of,  1266 
Tenon,  capsule  of,  399,  724 
Tensor  fasciae  femoris.     See  T.  fascise  latse 
latse  femoris  muscle,  365 
action  of,  370,  371,  393 
surgical  anatomy  of,  1303,  1306 
palati  muscle,  412.     See  also  Muscle 
tarsi  muscle,  397,  399,  741 
tympani  muscle,  757,  1232 
Tentorium  cerebelli,  475,  599,  1225. 
Teres  major  muscle,  330 
minor  muscle,  329 
actions  of,  331 
Testicular  artery,  843 
Testis,  1159 

coni  vasculosi  of,  1162,  1204 
descent  of,  1167 
development  of,  1204 
digital  fossa  of,  1160 
epididymis  of,  1160 
gubernaculum  of,  1168 
hydatids  of,  1160,  1199,  1205 
lobes  of,  1161 
mediastinum  of,  1161 
mesentery  of,  1167 
nerves  of,  1162 
paradidymis  of,  1160,  1199 
processus  vaginalis  of,  1167 
rete  of,  1161,  1204 
seminiferous  tubules  of,  1161,  1204 
septula  of,  1161 
structure  of,  1161 


INDEX. 


1417 


Testis,  tubuli  recti  of,  1161,  1204 
tunica  albuginea  of,  1161,  1204 
vaginalis  of,  1160,  1167 
vasculosa  of,  1161 
undescended,  1168 
vas  deferens  of,  1159,  1162 

develoi^ment  of,  1199,  1202,  1204 
vasa  efferentia  of,  1162,  1204 
vessels  of,  1162 
Thalamencephalon,  478,  481 
Thalamic  radiation,  543,  545 
Thalamo-cortical  fibres,  591,  593 
Thalamo-striate  fibres,  581,  583 
Thalamus,  optic,  542 

anterior  nucleus  of,  545 

tubercle  of,  544 
bundle  of  Vicq  d'Azyr  of,  545 
central  nucleus  of,  545 
connexions  of,  with  basal  ganglia,  545 
with  cerebral  cortex,  543,  545 
with  hippocampus,  572 
with  optic  tract,  545,  552 
development  of,  478,  480,  594 
external  geniculate  body  of,  544.     See  also 

Corpora  geniculata 
external  medullary  lamina  of,  543 
fillet  fibres  of,  539 
grey  matter  of,  544 
internal  medullary  lamina  of,  545 
lateral  nucleus  of,  545 
mesial  nucleus  of,  545 
nucleus  arcuatus  of,  545 
position  and  connexions  of,  476, 542, 544, 575 
pulvinar  of,  531,  544,  552 
radiation  of,  543,  545 
stratum  zonale  of,  544,  545,  552 
stria  medullaris  of,  544,  548 
surfaces  of,  543,  544,  550 
taenia  of,  544,  547,  594 
Thebesius,  valve  of,  787,  788,  871,  932 
Theca  of  cord,  453 

folliculi,  1185 
Thigh  bone,  223 

Third  ventricle,  550.     See  also  Ventricle 
Thoracic  arteries,  828,  829 
aorta,  797,  798 
duct,  904,  906,  1040 
abnormalities  of,  956 
surgical  anatomy  of,  1252,  1289 
ganglia,  706,  708,  712 
nerves,  613.     See  also  Nerve 
vertebrse,  76,  81 
Thorax,  101 

aortic  area  of,  1262 
apertures  of,  101,  102 
cavity  of,  976 
in  foetus,  102 
joints  of,  269 
lines  of,  1253 
lymphatics  of,  923 
mediastiniim  of,  976 
mitral  area  of,  1262 
muscles  of,  415,  419 
praecordial  area  of,  1262 
pulmonary  area  of,  1262 
regions  of,  1253 
sexual  differences  in,  102 
sternal  furrow  of,  1253 
surgical  anatomy  of,  1253 
tricuspid  area  of,  1262 
walls  of,  101 
Thumb,  movements  of,  353 


Thumb,  muscles  of,  343,  350 
Thymus  gland,  1218 
development  of,  1220 
structure  of,  1220 
Thyreo-hyal,  146 

Thyreo-hyoid  arch,  36,  37,  441,  702 
bar,  146 

membrane,  962,  1218 
muscle,  406 
action  of,  410 
Thyro-ary-epiglottidean  muscle,  968 

action  of,  971 
Thyro-arytenoid  ligaments,  963 
muscle,  968,  969 
action  of,  971 
Thyro-epiglottidean  ligament,  964 

muscle,  970 
Thyro-glossal  duct,  37,  1014,  1217 

surgical  anatomy  of,  1242 
Thyroid  artery,  inferior,  823.     See  also  Avteij 
superior,  804.     See  also  Artery 
axis  artery,  823.     See  also  Axis 
body,  1216 

accessory,  1217 
development  of,  1217 
isthmus  of,  1216,  1217 

surgical  anatomy  of,  1249 
lateral  lobes  of,  1216,  1217 
levator  of,  1217 
pyramidal  lobe  of,  1216,  1217 
structure  of,  1217 
variations  in,  1217 
cartilage,  958,  992 
develoj)ment  of,  37,  992 
ossification  of,  961 
foramen.     See  Obturator  foramen 
rudiments,  1217 
veins,  875,  876.     See  also  Vein 
Thyroidea  ima  artery,  801.     See  also  Artery 
Tibia,  230 

architecture  of.  Appendix  A,  v 
connexions  of,  233 
homology  of,  Ajjpendix  F,  xxiii 
ossification  of,  234 
surgical  anatomy  of,  1308 
variations  in.  Appendix  B,  xii 
Tibial  artery,  anterior,  867.     See  also  Artery 
posterior,  865.     See  also  Artery 
recurrent,  868.     See  also  Artery 
lymphatic  gland,  916 
nerve,  647,  648.     See  also  Nerve 
anterior,  650,  651 
communicating,  653 
posterior,  652 
recurrent,  650 
Tibiale,  os,  Apjjendix  F,  xxiv 
Tibialis  anterior  muscle,  373 
action  of,  384 
surface  anatomy  of,  1312 
anticus  muscle.     See  T.  anterior 
posterior  miTScle,  379 
action  of,  384 

surface  anatomy  of,  1311,  1312 
posticus  muscle.     See  T.  posterior 
Tibio-fascialis  anticus  muscle,  374 
Tibio-femoral  index,  Ap^jendix  D,  xx 
Tibio-fibular  joint,  inferior,  304 
movements  at,  383 
superior,  304 
ligament,  interosseous,  305 
transverse,  305 
Tibio-navicular  ligament,  307 


1418 


INDEX. 


Toes,  digital  sheaths  of,  373 

movements  of,  384 
Tomes,  tibrils  of,  1024,  1028 

processes  of,  1028 
Tongue,  995,  1000 

ajjical  glands  of,  1006 

arteries  of,  1006 

development  of,  35,  37,  1013 

finibri;«  of,  770 

folia  of,  1004 

foramen  cajcum  of,  1000,  1014,  1217,  1242 

freuum  of,  997,  1005 

surgical  anatomy  of,  1244 

glands  of,  1006 

lingual  duct  of,  1217 

tonsils.     See  Tongue,  lymphoid  follicles  of 

lymphatics  of,  1244 

lymphoid  follicles  of,  1001,  1242 

mucous  membrane  of,  1001,  1006 

muscles  of,  408,  409,  441,  701,  1005 
surgical  anatomy  of,  1243 

nerves  of,  1006 

oral  part  of,  1002,  1242 

papillaj  of,  770,  1002,  1003 

pharyngeal  part  of,  1001,  1242 

plicaj  fimbriatiB  of,  1005 

raphe  of,  1002 

sejitum  of,  1005 

structure  of,  1005 

sulcus  terminalis  of,  1000,  1014 

surgical  anatomy  of,  1242 

taste-buds  of,  770,  1004 

thyro-glossal  duct  of,  37,  1014 

surgical  anatomy  of,  1217,  1242 

veins  of,  1006 
Tonsil  or  Tonsilla,  cerebelli,  507 

of  Eustachian  tube,  754 

intestinal,  1064 

lingual     See  Tongue,  lymphoid  follicles  of 

palatina,  995,  1034,  1035 
develojjnient  of,  1037 
lymphatics  of,  1036 
nerves  of,  1036 
plica  triangularis  of,  1036 
surgical  anatomy  of,  1244 
vessels  of,  1036 

pharyngea,  1033,  1037 
surgical  anatomy  of,  1246 
Tonsillar  arteries,  806, 1006, 1036.  See  also  Artery 

plexus,  698,  1036 
Tonsillitic  nerve,  690,  1036 
Tooth-band,  1026 
Topographical  anatomy,  4 
Torcular  Herophili,  109,  884 
Torus  tuberis.     See  Eustachian  cushion 
Touch,  organs  of,  772 
Trabeculfe  carnese  cordis,  790 

corporum  cavemosorum,  1179 

cranii.  Appendix  E,  xxi 

lienis,  1213 
Trachea,  972 

bifurcation  of,  1260,  1289 

cartilaginous  rings  of,  973,  975,  991 

development  of,  35,  38,  992 

fibro-elastic  membrane  of,  975 

mucous  glands  of,  975 
membrane  of,  975 

muscle  of,  975 

relations  of,  974 

structure  of,  975 

surface  and  surgical  anatomy  of,  1249,  1289 
Tracheal  arteries,  823 


Tracheal  cartilages,  962 
Trachelo-mastoid  muscle,  389 

action  of,  393 
Tracheotomy,  1249 

Tracts  or  Tractus,  of  basis-bundle,  470.    See  also 
Basis  bundle 
Burdach,  466,  473.     See  also  Spinal  cord 
callosal,  crossed,  546 
central  tegmental,  of  pons,  502 
cerebello-olivary,  496,  497,  510 
comma,  466 

of  corpus  trapezoides,  501 
cortico-pontine,  501,  540,  583,  591 
direct  cerebellar,  464,  468,  473,  484,  485,  496, 
510 

sensory,  468 

sensory  cerebellar,  521 
of  fillet.     See  Fillet 
fronto-pontine,  540,  583,  591 
of  GoU,  466,  473.     See  also  Spinal  cord 
of  Gowers,  469,  473,  484,  498,  511 
of  Lissauer,  468 
marginal,  of  Lowenthal,  521 
myelinisation  of,  473 
olfactorius,  569,  596 

lateral  root  of,  570 

mesial  root  of,  570,  573 

structure  of,  587 
opticus,  475,  532,  675,  698 

cerebral  connexions  of,  552 

commissural  fibres  of,  552 

efferent  fibres  of,  552 

lateral  root  of,  532,  552 

mesial  root  of,  532,  552 
posterior    longitudinal.      See    Longitudinal 

bundle 
pyramidal,  591 

in  cerebral  heruispheres,  591 

crossed,  468,  469,  473,  483,  490,  591 

direct,  470,  473,  483,  490,  591 

in  internal  capsule,  583 

in  medulla,  489,  490 

in  pons,  499 
rubro-spinal,  537 
septo-marginal  descending,  468 
solitarius.     See  Fasciculus  solitarius 
spinalis  nervi  trigemini,  525 
spino-thalamic,  468,  494- 
spiralis  foraminosus,  761,  762 
temporo-pontine,  583,  591 
Tragicus  muscle,  746 
Tragus,  744 

Transpyloric  plane,  1267 
Transversalis  abdominis  muscle,  425 
cervicis  muscle,  389 
fascia,  420,  1044 
Transverse  artery  of  basilar,  820 

cervical  artery,  823 

facial  artery,  809 
carpal  articulation,  285 
fissure  of  brain,  604 
humeral  ligament,  277 
intermetacarpal  ligament,  287 
ligament  of  acetabulum,  294 

of  knee,  302 

tibio-tibular,  305 
metacarpal  ligaments,  288,  338 
metatarsal  ligament,  314,  373 
perineal  ligament,  293 
processes  of  vertebra,  cervical,  78,  79,  80 
lumbar,  83 
sacral,  85 


INDEX. 


1419 


Transverse  processes  of  vertebrte,  thoracic,  81,  82 

tarsal  articulation,  311 

vesical  fold,  1156 
Transversus  abdominis.     See  Transversalis 

auriculaj  muscle,  746 

lingUiB,  409,  1005 

perinei  profundus  muscle,  433 
superticialis  muscle,  431 

thoracis  muscle.     See  Triangularis  sterni 

vagin;e  muscle,  433 
Trapezium,  204,  207,  253  ;  Appendix  F,  xxix 

surgical  anatomy  of,  1299 
Trapezius  muscle,  319,  327 

surgical  anatomy  of,  1285 
Trapezoid  bone,  204,  207  ;  Appendix  F,  xxv 

ligament,  274,  275 

ridge  of  clavicle,  183 
Traube,  semilunar  space  of,  1271 
Triangle  of  auscultation,  320 

carotid,  1250,  1251 

digastric,  1249 

epigastric,  1255 

of  Hesselbach,  429,  1266 

of  Macewen.     See  Suprameatal  triangle 

of  Petit,  320,  424 

surgical  anatomy  of,  1285 

rectal,  of  perineum,  1277 

submental,  1248 

sviboccijjital,  391 

supraniarginal,  1225 

suprameatal,  154 

urogenital,  1277 
Triangles  of  neck,  1249.     See  also  Neck 
Triangular  fascia,  424 

tibro-cartilage,  282,  283 

ligaments  of  perineum,  292,  434 
Triangularis  sterni  muscle,  416,  419 
Triceps  brachii  muscle,  331,  335 
surgical  anatomy  of,  1295 

surse  muscle,  376 
Tricusi^id  area,  1262 

orifice,  787,  789 

surface  anatomy  of,  1162,  1290 

valve,  789 
Trigeminal  nerve,  678.     See  also  Nerve 
Trigona  fibrosa,  789 
Trigonum  acustici,  488 

collaterale.     See  Trigone  of  lateral  ventricle 

habenulse,  544,  547,  594 

hypoglossi,  488,  516,  527 

of  lateral  ventricle,  576 

lumbale.     See  Triangle  of  Petit 

olfactorium,  570 

vagi,  488,  517,  527 

vesica},  1151,  1203 
Trochanter  major,  225,  1302 

minor,  225,  1302 

tertius,  226  ;  Appendix  B,  xii 
Trochlea,  192 

fern  oris,  228 

humeri,  192 

of  sujjerior  oblique  muscle,  400 

tali,  238 
Trochlear  fossa,  105,  147 

nerve,  540,  677 

spine,  105 

surface,  188 
Trolard,  anastomotic  vein  of,  883 
Troltsch,  recesses  of,  758 
Trunci  lumbales,  908 

Truncus  corporis  callosi.     See  Corpus  callosum, 
body  of 


Truncus  costo-cervicalis.      See  Artery,   inter- 
costal, superior 

intestinalis,  908 
jugularis  lymphaticus,  908 

lumbo-sacralis.     See  Lumbo-sacral  cord 

subclavius,  908 

sympathicus.      See  Sympathetic   gangliated 
cords 

thyreo-cervicalis.     See  Thyroid  axis  artery 
Trunks  of  brachial  ])lexus,  623,  663 

of  sacral  plexus,  648,  664 
Tuba  auditiva.     See  Eustachian  tube 

uterina.     See  Fallopian  tube 
Tubal  artery,  843 
Tube,  Eustacliian,  750,  753 

Falloijian,  1181,  1185 

neural,  21,  471.     See  also  Neural  tube 
Tuber  calcanei,  243 

cinereum,  475,  478,  548,  550,  595 

frontale.     See  Frontal  eminence 

ischiadicum,  216 

maxillare,  134,  155 

mentale,  142 

omentale  hepatis,  1113 
pancreatis,  1127 

parietale.     See  Parietal  eminence 

valvulae,  507,  508 

vermis  cerebelli,  507 
Tubercula  dentis.     See  Cusps  of  teeth 
Tubercular  point  of  hip,  1302 

process  of  vertebra.  Appendix  C,  xiv 
Tuberculum  or  Tubercle,  accessory,  84 

acusticum,  519,  520 

adductor,  226,  229 

surgical  anatomy  of,  1308 

amygdaloid,  576 

anterius  atlantis,  79 
helicis,  43 
thalami,  544 
vertebrarum  cervicalium,  78 

anthelicis,  43 

antitragicum,  43 

of  astragalus,  241 

of  atlas,  79 

auriculae  Darwinii,  744,  745 

caroticum,  1252 

cinereum,  485 

conoid,  of  clavicle,  183 

costse.     See  Tubercle  of  Rib 

of  cuboid,  247 

cuneate,  485,  492 

cuneiform,  964 

deltoid,  of  clavicle,  182 

dental,  1015 

dorsal,  of  radius,  1298 

epiglottidis.     See  Cushion  of  epiglottis 

of  femur,  224 

genital,  45,  66 

impar,  35,  1013 

intercondyloideum  laterale,  231 
mediale,  231 

intermedium  helicis,  43 

intervenosum,  788 

jugulare,  110 

labial,  996 

lobulare,  43 

of  Lower,  788 

majus  humeri,  188 

mental,  142 

of  fiftli  metacarpal  bone,  210,  1299 

minus  humeri,  189 

obturatorium  anterius,  218 


1420 


INDEX. 


Tuberculum   or   Tubercle,    obturatorium   pos- 
terius,  218 
olfactory,  670 
of  OS  calcis,  243 
ossis  naviciilaris   manus.      See   Tubercle    of 

scaphoid  bone  of  hand 
papillare  hepatis,  1112 
peroneal,  1311 
pharyngeal,  111,  163,  166 
posterius  atlantis,  79 

vertebraruni  cervicaliuni,  78 
post-glen  old,  113;  Appendix  B,  ix 
pterygoid,  125,  161 
pubicum.     See  Spine  of  pubis 
for  tlie  quadratus,  224 
of  rib,  97,  99,  100 
Rolandi,  485,  491 
of  Santorini,  964 
scaleni,  99 

of  scapKoid  bone  of  hand,  202 
surgical  anatomy  of,  1298 

of  foot,  245 

surgical  anatomy  of,  1311 
sellse,  122 
supratragicum,  744 
of  thalamus,  544 
of  tibia,  232 
tragicum,  43 
vertebrarterial,  1252 
of  zygoma,  113 
Tuberositas  or  Tuberosity,  bicipital,  199 
coracoidea  claviculae.     See  Conoid  tubercle 
costalis  claviculse.     See  Rhomboid  impression 
deltoidea  humeri.     See  Deltoid  eminence 
of  femur.     See  Epicondyle  of  femur 
of  fifth  metatarsal,  251 
of  humerus,  188,  189,  1292 
iliaca,  214 

infra-glenoidalis,  185 
of  ischium,  216,  221,  222 

surgical  anatomy  of,  1302 
malar,  140 

of  maxilla,  134,  136,  155 
of  navicular  bone,  245 
omentale.     See  Omental  tuberosity 
of  OS  calcis,  244 
ossis  cuboidei,  247 

metatarsalis  V.,  251 

navicularis  pedis.  See  Tubercle  of  scaphoid 
of  palate  bone,  139 
of  radius,  199 
of  scai:)hoid  of  foot,  245 

of  hand,  202 
supra-glenoidalis,  185 
of  tibia,  232 

surgical  anatomy  of,  1308 
ulnae,  194 
Tubes,  bronchial,  in  lung,  989 

dentinal,  1024,  1028 
Tubular  glands,  1007 
Tubides  of  kidney,  1139,  1199,  1202 
of  parovarium,  1187 
Wolffian,  1201 
Tubuli  recti  testis,  1161,  1204 
renales,  1139,  1199,  1202 
seminiferi  contorti,  1161,  1204 

recti,  1161 
Tunica  albuginea,  1161,  1204 

of  corpus  cavemosum,  1172 
conjunctiva  bulbi,  739 

palpebrarum,  739 
dartos,  1170 


Tunica  externa  or  adventitia  of  arteries,  781 
of  lymphatics,  905 
of  veins,  782 
interna  or  intima  of  arteries,  781 
of  lymphatics,  905 
of  veins,  782 
media  of  arteries,  781 
of  lymphatics,  905 
of  veins,  782 
mucosa  lingute,  1006 
tubte  auditivee,  754 
tympanica,  758 
serosa,  1048 

vaginalis  propria  testis,  1160,  1167 
vasculosi  oculi,  725,  727 
Tunnel  of  Corti,  766 
Turbinals,  sphenoidal,  127 
Turbinate  processes  of  ethmoid,  128,  150 
174,  1239 
bone,  inferior,  130,  150,  175 

surgical  anatomy  of,  1239 
crest,  inferior,  135,  138 
superior,  136 
Tympanic  antrum,  752 
arteries.     See  Artery 
attic,  1232,  1233 
canaliculus,  117 
cavity,  748  ;  Appendix  A,  ii 
atrium  of,  748 
blood-vessels  of,  758 
development  of,  43,  44 
menibrana  tympani  secundaria  of,  752 
mucous  membrane  of,  758 
muscles  of,  757 
nerves  of,  758 

orifice  of  Eustachian  tube  in,  750 
promontory  of,  752 
pyramid  of,  749 
recessus  epitympanicus  of,  748- 
sinus  of,  752 
tegmen  of,  749,  752 
groove,  748,  750 
membrane,  43,  750 
folds  of,  1231 
paracentesis  of,  1232 
triangular  cone  of,  1232 
surgical  anatomy  of,  1231 
nerve,  689,  702,  758 
ossicles,  754 

part  of  temporal  bone,  112,  113,  114,  156,  164 
ossification  of,  119 
sexual  difference  in,  181 
plate.        See    Tympanic    part    of   temporal 
bone 
fibrous,  748 
plexus,  689,  707 
ring,  44,  120,  748 
Tymjmno-hyal,  37,  120 
Tympano-mastoid  fissure,  114 
Tympanum,    748 ;  Appendix  A,  ii.      See   also 
Tympanic  cavity 
development  of,  43,  44 
walls  of,  749,  750,  1232,  1233 

Ulna,  194 

architecture  of.  Appendix  A,  iii 

connexions  of,  197 

homology  of,  Api^cndix  F,  xxiv 

ossification  of,  197 

surgical  anatomy  of,  1297,  1298 

variations  in,  A^ipendix  B,  xi 
Ulnar  artery,  834.     See  also  Artery 


Index. 


1421 


Ulnar  furrow,  197 

nerve,  629.     See  also  Nerve 

notch,  200 

veins,  891.     See  also  Vein 
Ulnare,  os,  Ajipendix  F,  xxiv 
Umbilical  arteries,  51,  848 

cord,  51,  52 

fissure,  ill4 

fossa,  1114 

notch,  1114 

orifice,  27 

region,  1047,  1267 

vein,  51,  63,  935 

vesicle,  48 

zone,  1047 
Umbilicus,  68,  1264,  1290 
Umbo  membran<B  tympani,  751 
Unciform  bone,  205 

surface  anatomy  of,  1299 
variation  in,  Apjjendix  B,  xiii 
Uncinate  process  of  ethmoicj,  129 

of  i^ancreas,  1126,  1128 
Uncus  gyri  hipj)ocampi,  568,  584 
Ungual  phalanges  of  fingers,  211,  252 

of  toes,  252 
Ungues,  775 
Urachus,  51,  1198,  1146,  1156 

surgical  anatomy  of,  1203 
Ureter,  1130, 1141,  1276 

development  of,  1199,  1202 

in  female,  1143 

orifice  of,  1142,  1151 

pelvic  portion  of,  1142 

structure  of,  1143 

surgical  anatomy  of,  1276,  1283,  1284,  1286, 
1290 

variations  in,  1144 
Ureteral  artery  of  renal,  842 

of  spermatic,  843 
Urethra,  1130,  1157,  1159 

crista  of,  female,  1158 
male,  1178 

development  of,  1200,  1203,  1206 

external  orifice  of,  1158,  1170,  1180 
surface  anatomy  of,  1282 

female,  1157,  1282 

fossa  navicularis  of,  1180 

glands  of,  1158,  1177,  1180 

internal  orifice  of,  1145,  1146 

lacunae  of,  1158,  1180 

male,  1177,  1278 

membranous,  1177,  1179,  1203 
surgical  anatomy  of,  1278 

muliebris.     See  Urethra,  female 

prostatic,  1177,  1178,  1203 

septum  of,  1206 

spongy  portion  of,  1177,  1179,  1203 

structure  of,  1158,  1180 

surgical  anatomy  of,  1278 

virilis.     See  Urethra,  male 
Urinary  organs,  1130 
Urogenital  canal,  1200 

cleft,  1195,  1200,  1207 

fissure,  1200 

organs,  develoj)ment  of,  1198 

space,  1200 

system,  1130 

triangle  of  perineum,  1277 
Uterine  artery,  852.     See  also  Artery 
of  ovarian,  843,  1192 

decidua,  53,  54,  56,  57 

glands,  1191 


Uterine  plexus,  714 

veins,  896 

venous  jjlexuses,  896 
Utero-sacral  ligaments,  1189 
Utero-vesical  fold,  1189 

pouch,  1101,  1189 
Uterus,  1182,  1187 

anteflexed,  1190 

anteverted,  1190 

arbor  vitai  of,  1188,  1191 

broad  ligaments  of,  1101,  1189 
surgical  anatomy  of,  1284 

cavity  of,  1188 

cervical  ganglion  of,  1192 

cervix  of,  1188 

connexions  of,  1189 

development  of,  1199,  1205 

at  different  ages,  1191 

external  os  of,  1188 

fundus  of,  1187,  1284 

glands  of,  1191 

horns  of,  1192 

internal  os  of,  1188 

masculinus,  1179 

in  menstruation,  1192 

nerves  of,  1192 

periodic  changes  in,  1192 

peritoneal  relations  of,  1189 

position  of,  1190 

pregnant,  53,  56,  1192 

relations  of,  1190 

retroverted,  1190 

round  ligament  of,  1190,  1284 

septum  of,  1192 

structure  of,  1191 

surgical  anatomy  of,  1284 

variations  in,  1192 

vessels  of,  1192 
Utricle,  759,  762 

macula  acustica  of,  762,  763 

recessus  of,  762 

sinus  superior  of,  763 
Utri cuius.     See  Utricle 

prostaticus,  1169,  1179,  1199,  1205 
Uvula  vermis  cerebelli,  507,  508 

palatina,  999 

vesicae,  1151 

Vagina,  1182,  1192 

bulbs  of,  1283 

carina  urethralis  of,  1195 

carunculae  of,  1193,  1197 

columns  of,  1195 

development  of,  1199,  1200,  1205 

digital  exploration  of,  1199,  1200,  1205 

fornix  of,  1193,  1283 

hymen  of,  1193,  1196,  1205 

introitus  of,  1283 

mucous  membrane  of,  1195 

muscular  coat  of,  1195 

nerves  of,  1195 

orifice  of,  1196 

relations  of,  1193 

rugae  of,  1196 

septum  of,  1195 

structure  of,  1195 

variations  in,  1195 

vessels  of,  1195 

vestibule  of,  1196 
Vagina  mucosa  intertubercularis  musculi  bi- 
cipitis  brachii,  333 

musculi  recti  abdominis.    See  Sheath  of  rectus 


1422 


INDEX. 


Vagina  nervi  optici,  725 

processus  styloidei.     See  Vaginal  process  of 

temporal  bone 

tendinis  musculi  extensoris  carpi  ulnaris,  337 

digiti  quinti,  337 

liallucis  longi,  379 

pollicis  longi,  337 

flexoris  liallucis  longi,  379 

pollicis  longi,  342 
peronffii  longi  plantaris,  375 
tibialis  anterioris,  374 
posterioris,  379 
tendinum  digitalis.     See  Sheath,  digital,  of 
fingers 
pedis.     See  Slieatli,  digital,  of  toes 
Vaginai  tendinum  musculi  extensoris  digitorum 
pedis  longi,  374 
flexoris  digitorum  pedis  longi,  379 
musculorum  abductoris  longi  et  extensoris 
brevis  pollicis,  337 
extensoris  digitorum  communis  et  ex- 
tensoris indicis,  337 
extensorum  carpi  radialium,  337 
flexorum  communium,  337 
peronseorum  communis,  372 
Vaginal  artery,  851,  1195 
of  liver,  1120 
ligaments,  378 
plexus,  714 
process  of  temporal  bone,  114,  164 

sphenoid  bone,  125,  158 
veins,  896 

venous  plexuses,  896 
Vagus  nerve,  690.     See  also  Nerve 
Vallecida  cerebelli,  506 
epiglottica,  963 
of  larynx,  963 
Sylvii,  555 
of  tongue,  1002 
Vallum  of  circumvallate  papillee,  1004 

unguis,  775 
Valve  or  Valves,  anal,  1093,  1095 
aortic,  791,  932 
of  Beraud,  741 
of  Eustachius,  787,  788,  892 

deA'elopment  of,  932 
of  Hasner,  741 
of  Houston,  1093 

ileo-csecal,  1076,   1077.     See  also  lleo-csecal 
valve 
surface  anatomy  of,  1273 
of  Kohlrausch,  1093 
of  Krause,  741 
of  lymphatic  vessels,  905 
mitral,  790 
pulmonary,  790,  932 
pyloric,  1056 
rectal,  1089,  1093 
of  Thebe.sius,  787,  788,  871,  932 
tricuspid,  789 
of  veins,  782 
venous,  of  heart,  931 
of  Vieussens,  486,  511,  529 
Valvula  or  Valvulte,  bicuspidalis.     See  Valve, 
mitral 
coli.     See  Valve,  ileo-csecal 
conniventes,  1062,  1070,  1073,  1074 
fossaj  navicularis,  1180 
processus  vermiformis,  1080 
pylori,  1056 

semilunares    A.    pulmonalis.       See    Valves, 
pulmonary 


Valvula  or  Valvulae,  sinus  coronarii.    See  Valve 
of  Thebesius 
venae  cavee  inferioris.  See  Valve  of  Eustachius 
semilunares  aortoe.     See  Valves,  aortic 
Vas  afferens  renis,  1140 
deferens,  1159,  1162 
ampulla  of,  1164,  1166 
development  of,  1199,  1204 
structure  of,  1166 
surgical  anatomy  of,  1280 
efferens  renis,  1140 
prominens,  765 
spirale,  766 
Vasa  aberrantia,  838,  946,  952 
auris  internee,  769 
brevia,  904,  1060 
efferentia  testis,  1162,  1199,  1204 
intestini  tenuis,  1073 
sanguinea  retinse,  735 
vasorum,  783 
Vascular  area,  61 
system,  780 

abnormalities  of,  946 
blood,  780 
development  of,  925 
divisions  of,  783 
lymph,  780,  904 
morphology  of,  938 
primitive,  60 
Vastus  externus.     See  V.  lateralis 
intermedins  muscle,  359.     See  also  Muscle 
internus.     See  V.  medialis 
lateralis  muscle,  358.     See  also  Muscle 
medialis  muscle,  358,     See  also  Muscle 
Vater,  ampulla  of,  1120 
Vein  or  Veins  ;  Vena  or  Venae,  780,  870 
abnormalities  of,  954 
advehentes,  935 
allantoic,  62,  934 
anal,  1096 

anastomotic,  posterior,  883 
anastomotica  magna,  883 
angularis,  879 

anonymae  dextra  et  sinistra.     See  V.,  inno- 
minate 
appendicular,  903 
aquaeductus  vestibuli,  769 
arciformes  renis,  1140 
auditivae  internae,  769 
auriculares  anteriores,  746 

posteriores,  878 
axillaris,  888 

abnormality  of,  946 
develoj^ment  of,  938 
surface  anatomy  of,  1292 
azygos  major,  872 

abnormality  of,  954 
development  of,  936,  937 
morphology  of,  945 
surface  anatomy  of,  1289 
minor  inferior,  872 

aljnormalities  of,  954 
development  of,  936,  937 
morphology  of,  944,  945 
superior,  872 

abnormalities  of,  954 
development  of,  936 
morphology  of,  945 
basalis  (Rosenthal!),  883 
basilica,  891 

abnormalities  of,  955 
development  of,  938 


Index. 


1423 


Vein  or  Veins — continued 
basilica,  morphology  of,  946 

surface  anatomy  of,  1295,  1296 
basis  vertebi'ie,  887 
of  bones,  75 
brachiales,  889 
brachio-cephalic,  873 
of  brain,  881 

broncliiales  anteriores,  873,  989 
posterior,  873,  989 

morphology  of,  944,  945 
buccal,  880 

canaliculi  cochlepe,  769 
canalis  pterygoidese.     See  Vein,  vidian 
capillary,  780 
cardiac,  anterior,  871 
great,  871 
inferior,  871 
middle,  871 
small,  871 
smallest,  871 
cardinal,  935,  936 

morphology  of,  944 
cava  inferior,  870,  892 
abnormality  of,  955 
development  of,  936,  937 
fossa  of,  1111,  1115 
morjohology  of,  944 
orifice  of,  784,  787 
surface  anatomy  of,  1277 
superior,  870,  871 
abnormality  of,  954 
development  of,  936 
morphology  of,  944 
orifice  of,  784,  787 
surface  anatomy  of,  1264 
centralis  retinae,  735 
cepbalica,  891 

abnormality  of,  955 
development  of,  938 
morphology  of,  946 
surface  anatomy  of,  1296 
cerebelli,  883 
cerebri,  882 
anterior,  883 
deep,  882 
inferior,  882 

magna.     See  V.  of  Galen 
superficialis,  882 
superior,  882 
cervical,  transverse,  879 
cervicalis  profunda  anterior,  875 

posterior,  875 
chorioidea,  882 
ciliares,  731 
circumflexa  ilium  profunda,  899 

superficialis,  901 
colica  dextra,  903 
media,  903 
sinistra,  904 
comites,  871,  946,  955 
conjunctivales,  740 
cordis.     See  V.  cardiac 
coronaria  ventriculi,  903,  1060 
coronary,  left,  871 

right,  871 
of  corpus  striatum,  574,  882 
of  cranium,  880,  883 
cystica,  903 

deep,  of  trunk  and  limbs,  874 
dental,  inferior,  880 
supei'ior,  880 


Vein  or  Veins — continued 
development  of,  62,  934 
digitales  pedis,  900 

morphology  of,  946 

nianus,  889 
diploicaj,  880 

frontalis,  881 

occipitalis,  881 

temporalis,  881 
dorsalis  clitoridis,  897 

linguaa,  1006 

penis,  897,  1173 
duodenales,  1070 
elastic  layer  of,  782 
emissary,  884,  886 
endothelium  of,  782 
epigastric,  deep,  900 
epigastrica  inferior.     See  V.,  epigastric,  deep 

superficialis,  901 

superior,  874 
facialis  anterior,  876 

surface  anatomy  of,  1237 

communis,  876 

surface  anatomy  of,  1251 

posterior.     See  V.  temporo-maxillary 

profunda,  877 
femoralis,  897,  898 

morphology  of,  946 

superficialis,  900 
of  forearm,  superficial,  890 
frontalis,  879 
of  Galen,  604,  882 
gastricaj,  904,  1060 
gastro-epiploicse,  903,  904,  1060 
glutaeae  inferiores,  895 

superiores,  895 
hsemorrhoidales  inferiores,  896,  1096 
ha^morrhoidalis  (media),  896,  945,  1096 

superior,  904,  945,  1096 
of  head  and  neck,  875 
of  heart,  787,  788,  793,  871 

morjjhology  of,  945 
hemiazygos.     See  V.  azygos  minor  inferior 

accessoria.     See  V.  azygos  minor  superior 
hepaticee,  892,  1120 

abnormality  of,  955 

development  of,  935 

interlobular,  893,  1120 

morphology  of,  945 

sublobular,  893,  1121 
hypogastrica.     See  V.,  iliac,  internal 
ileo-csecal,  903 
ileo-colic,  903 

iliac,  internal,  895,  936,  937 
morphology  of,  944,  946 
iliaca  communis,  895 

abnormalities  of,  955 
development  of,  936,  937 
morphology  of,  944 
surface  anatomy  of,  1277 

externa,  897,  899 
ilio-lumbalis,  895 
infraorbital,  880 
innominate,  873 

left,  874 

development  of,  936 
morjjhology  of,  944 

right,  874 

development  of,  936 
intercostal,  anterior,  873 

left  superior,  873,  904 
development  of,  936,  937 


1424 


INDEX. 


Vein  or  Y ei'os,— -continued 

intercostal,  left  superior,  morpliology  of,  944, 
945 
posterior,  873,  875 
first  left,  874 
first  right,  874 
right  superior,  873 
morphology  of,  945 
intercostales,  873 
intercostalis   suprema.      See   V.,   intercostal, 

posterioi",  first 
interdigital,  of  foot,  900  . 

of  hand,  890 
interlobares  renis,  1140 
interlobulares  renis,  1140 

hepatis,  1120 
interosseous,  of  hand,  890 
interventricular,  inferior,  871 
intestinales,  903,  1073 
jugular,  posterior  external,  877 

primitive,  935,  936,  937 
jugularis  anterior,  879 
abnormalities  of,  954 
externa,  877 

abnormalities  of,  954 
development  of,  936 
surgical  anatomy  of,  1252 
interna,  875 

abnormalities  of,  954 
bulb  of,  876 
development  of,  936 
morphology  of,  944 
surgical  anatomy  of,  1251 
labialis,  877 
of  large  intestine,  1075 
lienalis,  904.     See  V.  splenic 
lingualis,  876 
of  liver,  1129,  1121 
of  lower  limb,  897 

abnormalities  of,  955 
deep,  897 

development  of,  938 
morphology  of,  946 
superficial,  897,  900 
development  of,  938 
lumbales.     See  V.,  lumbar 
lumbar,  894 

abnormalities  of,  955 
ascending,  872,  894 
development  of,  937 
morphology  of,  945 
magna  Galeni,  604,  881 
mammaria  interna,  874 
marginal,  of  heart,  871 
massetericee,  880 
maxillaris  interna,  880 

morjihology  of,  945 
median,  of  bulb,  883 
cephalic,  890 

abnormalities  of,  955 
surgical  anatomy  of,  1297 
of  forearm.     See  V.  mediana  antibrachii 
mediana  antibrachii,  890 
abnormalities  of,  955 
development  of,  938 
surgical  anatomy  of,  1297 
basilica,  891 

surgical  anatomy  of,  1297 
mediastinales,  874 
of  medulla  oblongata,  883 
meningeal,  880,  881 
mesenterica  inferior,  901,  904 


Vein  or  Veins — continued 

mesenterica  inferior,  morphology  of,  945 
superior,  901,  903 
morphology  of,  945 
metacarpeie  dorsales,  890 
of  mid-brain,  883 
minimaj  cordis,  787,  788,  871 
morphology  of,  943 
muscle-fibres  of,  782 
musculo-phrenic,  874 
nasales,  880 
nerves  of,  783 

obliqua  atrii  sinistri  (Marshall!),  785,  871 
obturatorise,  895 
occipitalis,  876,  879 
CESophagese,  1042 
ophthalmica  inferior,  879 

superior,  879 
of  orbit,  879 
ovarian,  894 

abnormality  of,  955 
morjjhology  of,  944 
ovarica.    See  V.,  ovarian 
palatina  posterior,  880 
palpebral,  740 
pancreaticBe,  904 

pancreatico-duodenales,  903,  1070 
parotidese,  1011 
pharyngess,  876 
phrenicse,  893 
poplitete,  897,  898 

abnormalities  of,  955 
portse,  901,  1120 
branches  of,  903 
capillaries  of,  902 
development  of,  935 
morphology  of,  945 
sinus  of,  903 

surgical  anatomy  of,  1290 
profunda  clitoridis,  897 
femoris,  899 
penis,  897 
pterygoid,  880 

of  pterygo-maxillary  region,  879 
pterygo-palatine,  880 
pubic,  900 
pudic,  internal,  896 

superficial,  901 
pulmonales,  870,  989,  992 
development  of,  938 
morphology  of,  945 
orifices  of,  784,  788 
pyloric,  903,  1060 

morphology  of,  945 
radiales,  891 

abnormalities  of,  955 
development  of,  938 
morphology  of,  946 
radicular,  of  bidb,  883 
ranine,  876,  1006 

surgical  anatomy  of,  1244 
of  rectum  and  anus,  1096 
renales,  893 

abnormalities  of,  955 
development  of,  938 
morjihology  of,  944,  945 
revehentes,  935 
sacrales,  895,  896 
saphena  magna.     See  V,  saphenous,  internal 

parva.     See  V.,  sajihenous,  external 
saphenous,  extca-nal,  900,  901 
abnormalities  of,  955 


INDEX. 


1425 


Vein  or  Veins — continued 

saphenous,  external,  development  of,  938 
moriDhology  of,  946 

internal,  900 

abnormalities  of,  955 
development  of,  938 
morj)hology  ot!,  946 

long.     See  V.,  saphenous,  internal 

short.     See  V.,  saphenous,  external 

surgical  anatomy  of,  1306,  1308,  1310,  1312 
of  scalp,  879 

surgical  anatomy  of,  1222 
sciatic,  895 
of  scrotum,  1170 
segmental,  838,  943 
sigmoideae,  904 
spermatici\;,  894 

abnormalities  of,  955 

development  of,  938 

morphology  of,  944,  945 

surgical  anatomy  of,  1280 
spheno-jmlatine,  880 
spinales,  887 

longitudinales  anteriores,  887 
posteriores,  887 
of  spinal  cord,  888 
splenic,  901,  904,  1212 
sternal,  874 
of  stomach,  1060 
striate,  inferior,  882 
structure  of,  782 
subclavia,  877 

abnormalities  of,  955 

development  of,  936,  938 

morphology  of,  944,  946 

surgical  anatomy  of,  1252 
superlicial,  of  trunk  and  limbs,  870 
supra-orbitalis,  879 
suprarenales,  893 

abnormalities  of,  955 

development  of,  938 

moriJhology  of,  944,  945 
suprascapular,  879 
Sylvian,  882 
temj)orales  profundte,  880 

suiDerficiales,  879 
temporo-maxillary,  876,  880 

abnormalities  of,  954 

morphology  of,  944 
terminalis.     See  Vein  of  corpus  striatum 
testicularis,  1162 
thyreoideas  inferiores,  875,  1217 
mor2)hology  of,  945 
surgical  anatomy  of,  1249 

superiores,  876,  945,  1217,  1218 
thyroid,  middle,  876,  945,  1217 
tibiales  anteriores,  898 

posteriores,  898 
tonsillares,  1036 

transversee  colli.     See  V.,  transverse  cervical 
transverse  cervical,  879 
tunica  externa  of,  782 

intima  of,  782 

media  of,  782 
tympanica?,  758 
ulnares,  891 

develojiment  of,  938 

morphology  of,  946 
umbilicalis,  51,  63,  935 
of  uptj^er  limb,  888 

abnormalities  of,  955 
deep  branches  of,  888 

95 


Vein  or  Veins — continued 

of  upi:)er  limb,  develoiiment  of,  938 
morjjhology  of,  946 
superficial  branches  of,  889 
abnormalities  of,  955 
uterime,  896 
vaginal,  896 
valves  of,  782 
of  vertebrae,  887 
vertebralis,  875 
vesical,  1157 
vessels  of,  782 
vestibulares,  769 
Vidian,  880 
visceral,  871 

morphology  of,  945 
vitelline,  62,  926,  934 
vorticosa3,  725,  728 
Velum  interpositum,  550,  604 

medullare  anterius  cerebelli.     See  V.,  medul- 
lary, superior 
posterius    cerebelli.      See    V.,    medullary, 
inferior 
medullary,  inferior,  508,  511,  530 

superior,  476,  486,  611,  529 
pendulum  palati,  998 
Venous  arch,  dorsal,  of  foot,  900,  946 
of  hand,  890 
transverse,  of  foot,  900 
sinuses  of  cranium,  880,  883,  954 
valves  of  heart,  931 
Ventricles,  cerebral,  development  of,  478,  595 
fifth,  573 
fourth,  475,  487 

acustic  area  of,  488,  520,  527 
area  postrema  of,  488 
calamus  scrij)torius  of,  488 
choroid  plexuses  of,  512,  529,  604 
eminentia  teres  of,  488,  524,  527 
floor  of,  482,  487,  499,  527 
foramen  of  Majendie  of,  512,  601 
fovea  inferior  of,  488,  527 

superior  of,  488,  527 
funiculus  separans  of,  488 
lateral  recesses  of,  487,  512,  601 
ligula  of,  512 

locus  coeruleus  of,  488,  527 
obex  of,  512 
plica  choroidea  of,  529 
roof  of,  487,  511,  529 
striae  acusticte  of,  488,  497,  521 
substantia  ferruginea  of,  488 
trigonum  acustici  of,  488 
hypoglossi  of,  488,  516,  527 
vagi  of,  488,  517,  527 
lateral,  476,  573 

amygdaloid  tubercle  of,  576 

body  of,  573,  574 

bulb  of,  576 

calcar  avis  of,  576 

choroid  plexus  of,  575,  576,  578,  604 

development  of,  596 

eminentia  collateralis  of,  560,  576,  578 

ependyma  of,  573,  578 

fimbria  of,  568,  572,  577 

floor  of,  574,  576 

foramina  of,  573,  594 

hijjpocampus  major  of,  576 

horns  of,  573,  574,  576 

surgical  anatomy  of,  1224 
nuclei  of,  574,  575,  576,  579,  580 
pars  centralis  of,  574 


1426 


INDEX. 


Ventricles,  cerebral,  lateral,  shape  of,  573 

taenia  semieircularis  of,  574,  576,  582 
trigonum  of,  576 
third,  476,  550 

choroid  plexus  of,  604 

floor  of,  550 

foramina  of,  551 

grey  commissure  of,  544,  550,  594 

infundibulum  of,  548,  551 

development  of,  595 
recessus  opticus  of,  551,  595 
pinealis  of,  551,  594 
suprapinealis  of,  551 
roof  of,  550,  595 
sulcus  of  Monro  of,  551,  594 
.    walls  of,  550 
of  heart,  783,  788 
development  of,  929 
left,  790 
muscle  of,  792 
right,  789 
septum  of,  789,  791 
abnormality  of,  947 
development  of,  927 
of  larynx,  967 
of  nose,  719 
of  Verga,  572 
Ventriculus.     See  Stomach 

cordis.     See  Ventricles  of  heart 
cerebri.     See  Ventricles,  cerebral 
laryngis  (Morgagnii),  967 
terminalis  of  cord,  459 
Verga,  ventricle  of,  572 
Vermiform  appendix,  993,  1074,  1079 
in  animals,  1080 
development  of,  1078 
at  different  ages,  1080 
lymphoid  nodules  of,  1081 
mesentery  of,  1080,  1105 
position  of,  1079 
structure  of,  1080 
surgical  anatomy  of,  1273 
valve  of,  1080 
vessels  of,  1081 
Vermis  cerebelli,  506,  507 
Vernix  caseosa,  779 
Vertebra  or  Vertebrae,  75 
anticlinal,  89 

architecture  of,  Appendix  A,  i 
cervicales,  78,  79 
coccygese,  76,  87 

ossification  of,  94 
common  characters  of,  76 
dorsal,  81,  82 
epiphyses  of,  92 
false,  76,  84 
fixed,  76,  84 

fulcralis.  Appendix  B,  vi 
lumbales  or  lumbar,  83,  84 
movable,  76,  78 
ossification  of,  92 
prominens,  80 

pseudo-sacral.  Appendix  C,  xv 
relation  of,  to  cord,  452 

important  structures  to  spines  of,  1289 
to  spinal  iierves,  608 
sacrales,  84,  85 

ossification  of,  94 
serial  homology  of,  Ajipendix  C,  xiv 
thoracales.     See  V.,  dorsal 
true,  76,  78 
typical,  76 


Vertebra  or  Vertebrae,  variations  in.  Appen- 
dix B,  vi 
veins  of,  887 
Vertebral  aponeurosis,  319,  385 
arterial  tubercle,  1252 
artery,  818.     See  also  Artery 
border  of  scapula,  183 
bow,  91 
column,  75,  88 

articulation  of,  with  cranium,  266 
cartilaginous,  91 
curves  of,  88 
length  of,  90 
ligaments  of,  266 
membranous,  30,  91 
movements  of,  264,  392 
surgical  anatomy  of,  1291 
variations  in.  Appendix  B,  vi 
as  a  whole,  88 
foramen,  76 
formula,  76 

line  of  pleural  reflexion,  980 
plexus,  708 
vein,  875 
Vertebrarterial  foramen,  76,  77,  78 

serial  homology  of.  Appendix  G,  xiv  _ 
variation  in,  Appendix  B,  vi 
Vertebrate  theory  of  skull.  Appendix  E,  xxii 
Vertebro-chondral  ribs,  97 
Vertebro-sternal  ribs,  97 
Vertical  plate  of  ethmoid,  127,  172 

of  palate  bone,  138 
Verumontanum,  1178 
Vesalius,  foramen  of,  124,  168 
Vesica  urinaria.     See  Bladder,  urinary 
Vesica  fellea.     See  Gall-bladder 
Vesical  arteries,  851,  852.     See  also  Artery 
inferior,  851,  1157,  1166 
middle,  851 
of  obturator,  852 
superior,  851,  1157,  1166 
plexus  of  nerves,  714,  1157 
venous,  inferior,  896,  945 
superior,  896,  945 
Vesicle,  auditory,  703 
blastodermic,  18,  19,  58 
cerebral,  22,  66,  476,  481 
chorionic,  52 
germinal,  11 
optic,  478,  480,  741 
otic,  769 

recessus  labyrinthi  of,  769 
umbilical,  48 
Vesico-vaginal  artery,  1195 
Vesicula  seminalis,  1159,  1162,  1164 
development  of,  1199,  1205 
structure  of,  1166 
vessels  of,  1167 
Vestibular  ganglion,  689,  699 

nerve,  689,  768 
Vestibule  or  vestibulum,  aortic,  791 
aqueduct  of,  119,  759 
of  labyrinth,  759 
aqueduct  of,  759 
crista  of,  759 
development  of,  769 
fenestra  ovalis  of,  752,  759 
fissura  of,  760 
macula  cribrosa  of,  759 
pyramid  of,  759 
recessus  cochlearis  of,  759 
ellipticus  of,  759 


6ex. 


1427 


Vestibule  or  vestibulum,  of  labyrinth,  recessus 
spbericiis  of,  759 

laryngis,  965 

nasi,  719 

oris,  995 

vaginte,  1196 
bulb  of,  1182,  1198 
glands  of,  1197 
Vestigial  fold,  784,  795 
Vibrissse,  719 
Vicq  d'Azyr,  band  of,  585 

fasciculus  of,  545,  548,  572 
Vidian  artery  of  internal  carotid,  815 
of  internal  maxillary,  812 

canal,  126,  162 

nerve,  682,  707 

vein,  880 
Vieussens,  annulus  of,  787 

ansa  of,  708 

limbus  of,  930 

valve  of,  486 
Villi,  arachnoidal,  884 

chorionic,  52,  54,  55,  58 

intestinales,  1062,  1073 
Vincula  accessoria  tendinuni,  341 
Visceral    arches,   35,   36,   701  ;    Appendix   E, 
xxii 

clefts,  35,  43,  66,  67,  701 

veins,  871,  945 
Visual  area,  593 

purple,  732 
Vitelline  body,  11 

cavity,  26 

duct,  1073,  1105 

membrane,  11 

veins,  62,  926,  934 
Vitello-intestinal  duct,  33,  48,  51,  1105 
Vitellus,  10 

Vitreous  body,  725,  735 
composition  of,  736 
development  of,  742 
fossa  patellaris  of,  735 
hyaloid  canal  of,  736,  742 
membrane  of,  735 
Vocal  cords,  964,  965.     See  also  Larynx 
Voice,  organs  of,  957 
Volaris  profunda  artery,  835 

suf)erficialis  artery,  832 
Vomer,  131,  132,  172 

architecture  of,  ApjDendix  A,  ii 

connexions  of,  132 

ossification  of,  132 

variations  in,  Aj^pendix  B,  x 
Vomerine  cartilage,  718 
Vulva,  1195 

anterior  commissure  of,  1195 

bulbus  vestibuli  of,  1198 

clitoris  of,  1197 

development  of,  1206 

fossa  navicularis  of,  1196 

frenulum  clitoridis  of,  1196 

labia  majora  of,  1195,  1182,  1207 
minora  of,  1182,  1195 

mons  veneris  of,  1195 

nerves  of,  1195 

posterior  commissure  of,  1195 

prseputium  clitoridis  of,  1196 

surgical  anatomy  of,  1282 

urogenital  space  of,  1195,  1200,  1207 

vessels  of,  1195 

vestibular  glands  of,  1197 

vestibule  of,  1196 


Walking,  movements  of,  384 
Wallerian  degeneration,  466 
Wharton,  duct  of,  997,  1012 
surgical  anatomy  of,  1244 
jelly  of,  51 
White  line  of  anus,  1095 

of  pelvis,  434,  438 
White  matter,  development  of,  471 
of  cerebellum,  509,  514 
of  cerebral  hemispheres,  554,  588 
cerebrosjjinal,  443 
of  cord,  459,  465 
of  medulla,  489 
Willis,  circle  of,  821 
Wind-pipe,  972 
Wing,  of  splienoid,  orbital,  123 

temj)oral,  123 
Winslow,  foramen  of,  1049,  1097,  1102,  1107 

surgical  anatomy  of,  1272 
Wirsung,  duct  of,  1127 
Wisdom  teeth,  1015,  1019 
Wolffian  body,  32,  1201 
duct,  1198,  1200,  1204 
glomeruli,  1201 
ridge,  46,  66,  662 
tubules,  1201 
Womb,  1182,  1187 

Wormian  bones,-  10,  133  ;  Appendix  B,  viii 
Wrisberg,  ganglion  of,  693 
pars  intermedia  of,  522,  524,  686,  687,  689, 
699 
Wrist,  annular  ligaments  of,  337 
arterial  arches  of,  835 
bones  of,  201 
movements  at,  352 
synovial  sheaths  at,  337,  338 

Xiphisternal  joint,  272 

surface  anatomy  of,  1255,  1267,  1290 
Xiphoid  cartilage,  94,  96 

Y-ligament  of  Bigelow,  295 
Yellow  marrow,  71 
Yolk,  10 

formative,  10 

nutritive,  10 

sac,  28,  48,  60,  65 

Zahnleiste.     See  Dental  lamina 
Zinn,  zonule  of,  735 
Zona  arcuata,  766 

fasciculata  glan dulse  suprarenalis,  1215 

glomerulosa  glandulae  suprarenalis,  1215 

orbicularis,  295 

pectinata,  766 

pellucida,  11 

reticularis  glandulse  suprarenalis,  1215 

striata,  11 
Zones  of  abdomen,  1047 
Zonula  ciliaris,  735 
Zonule  of  Zinn,  735 
Zygapophyses,  77  ;  Appendix  C,  xiv 
Zygoma,  113 
Zygomatic  arch,  154,  162 

surface  anatomy  of,  1222,  1237 

bone,  140.     See  also  Malar  bone 

fossa,  154 

lymphatic  glands,  909 

process,  113 
Zygomatico-orbital  artery,  810 
Zygomaticus  major  muscle,  397 

minor  muscle,  397 
actions  of,  397 


.^ 


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